Sven Wedemeyer

• Mamonova, E.; Herbst, K.; Kofman, V.; Ozgurel, Ozge; Kowalski, A. F. & Wedemeyer, S. [Show all 7 contributors for this article] (2026). Stellar-flare-driven evolution of primordial early exo-Earth atmospheres: Insights from the young M dwarf flare model. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 710. doi: 10.1051/0004-6361/202558763. Full text in Research Archive Show summary

  Context . M dwarfs are key targets for terrestrial exoplanet studies, with prospects for atmospheric spectroscopy. However, strong stellar magnetic activity and frequent flaring require modelling efforts to assess their impact on planetary atmospheres. Aims . We investigated one year of atmospheric chemical evolution of a young exo-Earth orbiting an active M dwarf by coupling our young M dwarf flare (YMDF) model of stellar activity with the photochemical kinetic code VULCAN. Methods . The YMDF model provides time-resolved spectral energy distributions for high- and low-energy electron beam–driven flares, which are used as external radiative inputs to VULCAN to compute the time-dependent photochemistry and kinetics for different primordial atmospheric scenarios. Results . We present the impact of stellar flares on atmospheres with a varying water vapour content, ranging from a plausible primordial atmosphere with solar abundances (representative of a planet-forming region in a dissipating protoplanetary disk) to an extreme water-steam atmosphere with other species reduced to trace abundances. This was explored across several configurations: variable flux in the YMDF model, the previous model representing an active but older M dwarf with 10 or 400K additional bottom boundary heat flux, and a constant stellar flux model. Conclusions . Our study suggests that compared to the previous model, the YMDF model produces synthetic flares that exert significantly greater stress on primordial atmospheres, regardless of the water-vapour content. Increased activity and prevalence of mid-size flares has the potential to induce permanent changes in atmospheric mixing ratios, especially in species with low abundances.

• Faber, Jonas Thoen; Joshi, Reetika; Voort, Luc Rouppe van der; Wedemeyer, Sven; Øyre, Eilif Sommer & Poquet, Ignasi J. Soler [Show all 7 contributors for this article] (2026). Fine details in solar flare ribbons: Statistical insights from observations with the Swedish 1-m Solar Telescope. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 705. doi: 10.1051/0004-6361/202556738. Full text in Research Archive Show summary

  Context. Flare ribbons serve as chromospheric footprints of energy deposition resulting from particle acceleration during magnetic reconnection. Their fine-scale structure provides a valuable tool for probing the dynamics of the flare reconnection process. Aims. Our goal is to investigate the fine-scale structure of flare ribbons through multiple observations of flares, utilising data obtained from the Atmospheric Imaging Assembly (AIA) and the Swedish 1-m Solar Telescope (SST). Methods. The aligned AIA and SST datasets for the three solar flares were used to examine their overall morphology. The SST datasets were specifically used to identify fine-scale structures within the flare ribbons. For spectroscopic analysis of these fine-scale structures, we applied machine-learning methods ( k -means clustering) and Gaussian fitting. Results. Using k -means, we identified elongated features in the flare ribbons, termed as ‘riblets’, which are short-lived and jet-like small-scale structures that extend as plasma columns from the flare ribbons. Riblets are more prominent near the solar limb and represent the ribbon front. Riblet widths are consistent across observations, ranging from 110−310 km (0.15−0.41), while vertical lengths span 620−1220 km (0.83−1.66), with a potential maximum of 2000 km (2.67), after accounting for projection effects. Detailed H β spectral analysis reveals that riblets exhibit a single, redshifted emission component, with velocities of 16−21 km s −1 , independent of the viewing angle. Conclusions. Our high-resolution observations of the three flare ribbons show that they are not continuous structures, but rather are composed of vertically extended, fine-scale substructures. These irregular features indicate that the reconnection region is not a smooth, laminar current sheet, but rather a fragmented zone filled with magnetic islands (blobs or riblets), consistent with the theory of patchy reconnection within the coronal current sheet.

• Mamonova, Elena; Kowalski, A.F.; Herbst, Konstantin; Wedemeyer, Sven & Werner, Stephanie C. (2026). Young M-dwarfs flare activity model: Towards better exoplanetary atmospheric characterisation. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 705. doi: 10.1051/0004-6361/202556844. Full text in Research Archive Show summary

  Context. Stellar flares can significantly influence the atmospheres and habitability of orbiting exoplanets, especially around young and active M dwarfs. Understanding the temporally and spectrally resolved activity of such stars is essential for assessing their impact on planetary environments. Aims. We aim to examine in detail state-of-the-art concepts of flare models to identify what is missing in our understanding of energy deposition during the flare event. By comparing synthetic and observed flare spectra, we seek to determine the modelling frameworks best suited for representing flare energetics and spectral far-ultraviolet features while providing a foundation for investigating flare impacts on exoplanet atmospheres. Methods. In this work, we built the Young M dwarf flare (YMDF) model utilising the combination of radiative-hydrodynamic (RHD) stellar atmosphere models with a high- and low-energy electron beam and corresponding synthetic observables. These models are based on physical principles and were validated with solar and stellar observations. Results. The newly developed YMDF model reproduces the observed continuum rise in both the TESS photometric band and the FUV-A spectral range. Furthermore, the flare distributions generated within this framework show consistency with those observed in our sample of stars. Conclusions. We have developed the YMDF model as a tool to reproduce the time-dependent spectra of flaring young M dwarfs, providing a physically motivated description of their spectral and temporal evolution during flare events.

• Liu, Daizhong; Saintonge, Amelie; Bot, Caroline; Kemper, Francisca; Lopez-Rodriguez, Enrique & Smith, Matthew [Show all 28 contributors for this article] (2025). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Gas and dust in nearby galaxies. Open Research Europe. 4. doi: 10.12688/openreseurope.17459.2. Full text in Research Archive Show summary

  Understanding the physical processes that regulate star formation and galaxy evolution are major areas of activity in modern astrophysics. Nearby galaxies offer unique opportunities to inspect interstellar medium (ISM), star formation (SF), radiative, dynamic and magnetic ( B → ) physics in great detail from sub-galactic (kpc) scales to sub-cloud (sub-pc) scales, from quiescent galaxies to starbursts, and from field galaxies to overdensities. In this case study, we discuss the major breakthroughs in this area of research that will be enabled by the Atacama Large Aperture Submillimeter Telescope (AtLAST), a proposed 50-m single-dish submillimeter telescope. The new discovery space of AtLAST comes from its exceptional sensitivity, in particular to extended low surface brightness emission, a very large 2° field of view, and correspondingly high mapping efficiency. This paper focuses on four themes which will particularly benefit from AtLAST: 1) the LMC and SMC, 2) extragalactic magnetic fields, 3) the physics and chemistry of the interstellar medium, and 4) star formation and galaxy evolution. With ~ 1000 − 2000 hour surveys each, AtLAST could deliver deep dust continuum maps of the entire LMC and SMC fields at parsec-scale resolution, high-resolution maps of the magnetic field structure, gas density, temperature and composition of the dense and diffuse ISM in ~ 100 nearby galaxies, as well as the first large-scale blind CO survey in the nearby Universe, delivering molecular gas masses for up to 10 6 galaxies (3 orders of magnitude more than current samples). Through such observing campaigns, AtLAST will have a profound impact on our understanding of the baryon cycle and star formation across a wide range of environments.

• Mascolo, Luca Di; Perrott, Yvette; Mroczkowski, Tony; Raghunathan, Srinivasan; Andreon, Stefano & Ettori, Stefano [Show all 26 contributors for this article] (2025). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Resolving the hot and ionized Universe through the Sunyaev-Zeldovich effect. Open Research Europe. 4. doi: 10.12688/openreseurope.17449.2. Full text in Research Archive Show summary

  An omnipresent feature of the multi-phase “cosmic web” — the large-scale filamentary backbone of the Universe — is that warm/hot (≳ 10 5 K) ionized gas pervades it. This gas constitutes a relevant contribution to the overall universal matter budget across multiple scales, from the several tens of Mpc-scale intergalactic filaments, to the Mpc intracluster medium (ICM), all the way down to the circumgalactic medium (CGM) surrounding individual galaxies from ∼ 1 kpc up to their respective virial radii (∼ 100 kpc). The study of the hot baryonic component of cosmic matter density represents a powerful means for constraining the intertwined evolution of galactic populations and large-scale cosmological structures, for tracing the matter assembly in the Universe and its thermal history. To this end, the Sunyaev-Zeldovich (SZ) effect provides the ideal observational tool for measurements out to the beginnings of structure formation. The SZ effect is caused by the scattering of the photons from the cosmic microwave background off the hot electrons embedded within cosmic structures, and provides a redshift-independent perspective on the thermal and kinematic properties of the warm/hot gas. Still, current and next-generation (sub)millimeter facilities have been providing only a partial view of the SZ Universe due to any combination of: limited angular resolution, spectral coverage, field of view, spatial dynamic range, sensitivity, or all of the above. In this paper, we motivate the development of a wide-field, broad-band, multi-chroic continuum instrument for the Atacama Large Aperture Submillimeter Telescope (AtLAST) by identifying the scientific drivers that will deepen our understanding of the complex thermal evolution of cosmic structures. On a technical side, this will necessarily require efficient multi-wavelength mapping of the SZ signal with an unprecedented spatial dynamic range (from arcsecond to tens of arcminutes) and we employ detailed theoretical forecasts to determine the key instrumental constraints for achieving our goals.

• Kirkaune, Mats; Wedemeyer, Sven; Marrewijk, Joshiwa van; Mroczkowski, Tony & Morris, Thomas W. (2025). Observing the Sun with the Atacama Large Aperture Submillimeter Telescope (AtLAST): Forecasting Full-disk Observations. The Open Journal of Astrophysics. 8. doi: 10.33232/001c.144106. Full text in Research Archive Show summary

  The Atacama Large Millimeter Array (ALMA) has revolutionised the field of solar millimetre astronomy with its high angular resolution and cadence. However, with a limited field of view (FOV), targeted observations of highly dynamic phenomena such of flares are challenging. A large aperture single-dish telescope with a large FOV, such as the future Atacama Large Aperture Submillimeter Telescope (AtLAST), would prove useful in observing such phenomena, as one could scan the full solar disk on shorter timescales. We aimed to explore what FOVs, detector counts, and scan strategies are suitable for AtLAST to push the required full-disk scan times below 1 minute, enabling regular observations of dynamic solar phenomena. Utilising the maria code, we were able to simulate solar observations with AtLAST, and thoroughly explored how instrumental properties and scanning strategies affect the full-disk observations in the planned frequency bands. We find the double-circle scan pattern, currently employed at ALMA for full-disk mapping to also be an acceptable way of scanning the Sun with AtLAST. Using small to intermediately sized instruments (1000 - 50,000 detector elements), the estimated observational cadence would be less than 1 minute across AtLAST’s frequency range with a reasonable pixel spacing. Using instruments with larger FOVs ( ⪆ 0.25 ∘ , equivalent to ⪆ 1 R), we find a simple circular scan to be more efficient, achieving cadences on second time scales, but requiring more detector elements ( ⪆ 100,000). We find that a large FOV single-dish telescope such as AtLAST could provide the solar millimetre community with hitherto unachievable observations, namely full-disk observations at high cadence and adequate resolution. With cadences potentially down to seconds, such an instrument would be ideal in the study of quickly evolving solar phenomena.

• Wedemeyer, Sven; Johnsen, Magnar Gullikstad; Antolin, Patrick; Rae, Jonathan & Poedts, Stefaan (2025). Space-Weather Effects on Critical Infrastructure on Earth. EurophysicsNews. ISSN 0531-7479. 56(5), p. 22–26. doi: 10.1051/epn/2025511. Full text in Research Archive Show summary

  Space weather refers to both the dynamic conditions in interplanetary space driven by the Sun and its subsequent impact on the near-Earth environment. Space weather can disrupt or destroy ground- and space-based infrastructure. Although not fully understood, its significance is growing rapidly with our increasing dependence on modern technology.

• Saberi, Maryam; Jafarzadeh, S.; Wedemeyer, Sven; Gafeira, R.; Szydlarski, Mikolaj & Jess, D. B. [Show all 7 contributors for this article] (2025). The Sun at millimeter wavelengths: V. Magnetohydrodynamic waves in a fibrillar structure. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 693. doi: 10.1051/0004-6361/202451833. Full text in Research Archive Show summary

  Magnetohydrodynamic (MHD) waves, playing a crucial role in transporting energy through the solar atmosphere, manifest in various chromospheric structures. Here, we investigated MHD waves in a long-lasting dark fibril using high-temporal-resolution (2 s cadence) Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 6 (centered at 1.25 mm). We detected oscillations in brightness temperature, horizontal displacement, and width at multiple locations along the fibril, with median periods and standard deviations of 240 ± 114 s, 225 ± 102 s, and 272 ± 118 s, respectively. Wavelet analysis revealed a combination of standing and propagating waves, suggesting the presence of both MHD kink and sausage modes. Less dominant than standing waves, oppositely propagating waves exhibit phase speeds (median and standard deviation of distributions) of 74 ± 204 km/s, 52 ± 197 km/s, and 28 ± 254 km/s for the three observables, respectively. This work demonstrates ALMA’s capability to effectively sample dynamic fibrillar structures, despite previous doubts. This provides valuable insights into wave dynamics in the upper chromosphere.

• Mohan, Atul; Hauschildt, Peter H.; Fuhrmeister, Birgit; Mondal, Surajit; Airapetian, Vladimir & Wedemeyer, Sven (2025). Role of Nonthermal Processes in the Quiescent and Active Millimeter Spectrum of a Young M Dwarf. The Astrophysical Journal (ApJ). ISSN 0004-637X. 989(1). doi: 10.3847/1538-4357/ade9bf. Full text in Research Archive Show summary

  Millimeter (mm) emission from F-M dwarfs (cool stars) primarily traces chromospheric activity, with thermal emission thought to dominate in quiescence. Despite the high chromospheric activity, the quiescent mm spectral fluence (mm-S(ν)) of young (<1 Gyr) M dwarfs (dMs) remains largely unexplored. We present the quiescent mm-S(ν) of a young dM, AD Leo, observed around 94 GHz using the Northern Extended Millimetre Array. The observed quiescent mm-S(ν) exceeds the thermal flux density from a 1D chromospheric model, constrained by optical-UV spectroscopic data, by up to a factor of 7. This indicates a quasi-steady nonthermal emission powered by suprathermal electrons, unlike in old (>1 Gyr) cool stars, whose quiescent mm-S(ν) generally agree with 1D thermal models. The mm-brightness temperature spectral index (αmm; TB(ν)) of AD Leo deviates by a factor of 3 from the αmm–Teff scaling law for old Sun-like stars (A. Mohan et al. 2022), while UV Ceti, an older M6V star, follows the trend. Also, we report a double-hump flare with second-scale variability in flux density and spectral index, and a frequency-rising nature with brightness increasing with frequency. The flare resembles certain solar events, but is unlike the second-scale events reported in dMs. The nonthermal flare humps suggest multiple injections of accelerated electrons. The mean flare luminosity (∼2–5 × 1015 erg s−1 Hz−1) and duration (18 ± 2 s) are comparable to flares reported in AU Mic and Proxima Cen, but 100–1000 times weaker than the minutes-long dM flares observed by the South Pole Telescope.

• Orlowski-Scherer, John; Maccarone, Thomas; Bright, Joe; Kamiński, Tomasz; Koss, Michael & Mohan, Atul [Show all 28 contributors for this article] (2025). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Probing the transient and time-variable sky. Open Research Europe. 4. doi: 10.12688/openreseurope.17686.2. Full text in Research Archive Show summary

  The study of transient and variable events, including novae, active galactic nuclei, and black hole binaries, has historically been a fruitful path for elucidating the evolutionary mechanisms of our universe. The study of such events in the millimeter and submillimeter is, however, still in its infancy. Submillimeter observations probe a variety of materials, such as optically thick dust, which are hard to study in other wavelengths. Submillimeter observations are sensitive to a number of emission mechanisms, from the aforementioned cold dust, to hot free-free emission, and synchrotron emission from energetic particles. Study of these phenomena has been hampered by a lack of prompt, high sensitivity submillimeter follow-up, as well as by a lack of high-sky-coverage submillimeter surveys. In this paper, we describe how the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST) could fill in these gaps in our understanding of the transient universe. We discuss a number of science cases that would benefit from AtLAST observations, and detail how AtLAST is uniquely suited to contributing to them. In particular, AtLAST’s large field of view will enable serendipitous detections of transient events, while its anticipated ability to get on source quickly and observe simultaneously in multiple bands make it also ideally suited for transient follow-up. We make theoretical predictions for the instrumental and observatory properties required to significantly contribute to these science cases, and compare them to the projected AtLAST capabilities. Finally, we consider the unique ways in which transient science cases constrain the observational strategies of AtLAST, and make prescriptions for how AtLAST should observe in order to maximize its transient science output without impinging on other science cases.

• Mamonova, Elena; Shan, Yutong; Kowalski, Adam F.; Wedemeyer, Sven & Werner, Stephanie (2025). Flare frequency in M dwarfs belonging to young moving groups. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 700. doi: 10.1051/0004-6361/202554614. Full text in Research Archive Show summary

  Context. M stars are preferred targets for upcoming studies of terrestrial exoplanets aimed at obtaining their atmosphere spectra over the next decade. However, M dwarfs have long been known for their strong magnetic activity and the ability to frequently produce optical and broadband emission flares. Aims. We aim to characterise the flaring behaviour of young M dwarfs in the temporal, spectral, and energy dimensions, as well as examine the stellar parameters governing this behaviour. In this way, we aim to improve our understanding of the energy and frequency of the flare events capable of shaping the exoplanet atmosphere. Methods. Members of young moving groups (YMGs) provide a unique age-based perspective on stellar activity. By examining their flare behaviour in conjunction with rotation, mass, and Hα data, we can obtain a comprehensive understanding of flare-activity drivers in young stars. Results. We demonstrate that young stars sharing similar stellar parameters could also exhibit a broad range of flare frequency distributions. We also find that the flare behaviour shows indications of difference between optical and far ultraviolet (FUV). We propose that the period of rotation (and not the age of the star) can serve as a good proxy for assessing flaring activity. Furthermore, we recommend that instead of a simple power law for describing the flare frequency distribution, a piecewise power law can be used to describe mid-size and large flare distributions in young and active M dwarfs. Conclusions. Using known periods of rotation and fine-tuned power laws governing the flare frequency, we can produce a realistic sequence of flare events to study whether the atmosphere of small exoplanets orbiting M dwarf could withstand such activity until the emergence of life.

• Rauer, Heike; Aerts, Conny; Cabrera, Juan; Deleuil, Magali; et, al., including: & Erikson, Anders [Show all 847 contributors for this article] (2025). The PLATO mission. Experimental astronomy (Print). ISSN 0922-6435. 59. doi: 10.1007/s10686-025-09985-9. Full text in Research Archive Show summary

  PLATO (PLAnetary Transits and Oscillations of stars) is ESA’s M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2R) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5%, 10%, 10% for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO‘s target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile towards the end of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

• Booth, Mark; Klaassen, Pamela; Cicone, Claudia; Mroczkowski, Tony; Wedemeyer, Sven & Akiyama, Kazunori [Show all 17 contributors for this article] (2024). The key science drivers for the Atacama Large Aperture Submillimeter Telescope (AtLAST). Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 13102. doi: 10.1117/12.3017058. Full text in Research Archive Show summary

  Sub-mm and mm wavelengths provide a unique view of the Universe, from the gas and dust that fills and surrounds galaxies to the chromosphere of our own Sun. Current single-dish facilities have presented a tantalising view of the brightest (sub-)mm sources, and interferometers have provided the exquisite resolution necessary to analyse the details in small fields, but there are still many open questions that cannot be answered with current facilities: Where are all the baryons? How do structures interact with their environments? What does the time-varying (sub-)mm sky look like? In order to make major advances on these questions and others, what is needed now is a facility capable of rapidly mapping the sky spatially, spectrally, and temporally, which can only be done by a high throughput, single-dish observatory. An extensive design study for this new facility is currently being undertaken. In this paper, we focus on the key science drivers and the requirements they place on the observatory. As a 50m single dish telescope with a 1–2° field of view, the strength of the Atacama Large Aperture Submillimeter Telescope (AtLAST) is in science where a large field of view, highly multiplexed instrumentation and sensitivity to faint large-scale structure is important. AtLAST aims to be a sustainable, upgradeable, multipurpose facility that will deliver orders of magnitude increases in sensitivity and mapping speeds over current and planned telescopes.

• Faber, Jonas Thoen; Joshi, Reetika; Voort, Luc Rouppe van der; Wedemeyer, Sven; Fletcher, Lyndsay & Aulanier, Guillaume [Show all 7 contributors for this article] (2024). High-resolution observational analysis of flare ribbon fine structures. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 693. doi: 10.1051/0004-6361/202452370. Full text in Research Archive Show summary

  Context. Since the mechanism of energy release from solar flares is still not fully understood, the study of fine-scale features developing during flares becomes important for progressing towards a consistent picture of the essential physical mechanisms. Aims. Solar flares release most of their luminous energy in the chromosphere. These luminous signatures, known as flare ribbons, act as the footpoints of the released energy and are crucial for the interpretation of reconnection processes causing these events. We aim to probe the fine structures in flare ribbons at the chromospheric level using high-resolution observations with imaging and spectral techniques. Methods. We present a GOES C2.4 class solar flare (SOL2022-06-26T08:12) observed with the Swedish 1-m Solar Telescope (SST), the Interface Region Imaging Spectrograph (IRIS), and the Atmospheric Imaging Assembly (AIA). Utilising imaging data from SST, IRIS, and AIA, we detail both the global and fine-structure evolution of the flare. The high-resolution SST observations offer spectroscopic data in the Hα, Ca II 8542 Å, and Hβ lines, which we use to analyse the flare ribbon. Results. The flare was associated with a filament eruption. Fibrils and coronal loops were connected from a negative polarity region to two positive polarity regions. Within the eastern flare ribbon, chromospheric bright blobs were detected and analysed in Ca II 8542 Å, Hα, and Hβ wavelengths. A comparison of blobs in Hβ observations and Si IV 1400 Å has also been performed. These blobs are observed as almost circular structures having widths from 140 km–200 km. The intensity profiles of the blobs show a red wing asymmetry. Conclusions. From the high spatial and temporal resolution Hβ observations, we conclude that the periodicity of the blobs in the flare ribbon, which are near-equally spaced in the range 330–550 km, is likely due to fragmented reconnection processes within a flare current sheet. This supports the theory of a direct link between fine-structure flare ribbons and current sheet tearing. We believe our observations represent the highest resolution evidence of fine-structure flare ribbons to date.

• Wedemeyer, Sven; Barta, Miroslav; Brajša, Roman; Chai, Yi; Costa, Joaquim & Gary, Dale [Show all 38 contributors for this article] (2024). Science development study for the Atacama Large Aperture Submillimeter Telescope (AtLAST): Solar and stellar observations. Open Research Europe. 4. doi: 10.12688/openreseurope.17453.1. Full text in Research Archive Show summary

  Observations at (sub-)millimeter wavelengths offer a complementary perspective on our Sun and other stars, offering significant insights into both the thermal and magnetic composition of their chromospheres. Despite the fundamental progress in (sub-)millimeter observations of the Sun, some important aspects require diagnostic capabilities that are not offered by existing observatories. In particular, simultaneously observations of the radiation continuum across an extended frequency range would facilitate the mapping of different layers and thus ultimately the 3D structure of the solar atmosphere. Mapping large regions on the Sun or even the whole solar disk at a very high temporal cadence would be crucial for systematically detecting and following the temporal evolution of flares, while synoptic observations, i.e., daily maps, over periods of years would provide an unprecedented view of the solar activity cycle in this wavelength regime. As our Sun is a fundamental reference for studying the atmospheres of active main sequence stars, observing the Sun and other stars with the same instrument would unlock the enormous diagnostic potential for understanding stellar activity and its impact on exoplanets. The Atacama Large Aperture Submillimeter Telescope (AtLAST), a single-dish telescope with 50m aperture proposed to be built in the Atacama desert in Chile, would be able to provide these observational capabilities. Equipped with a large number of detector elements for probing the radiation continuum across a wide frequency range, AtLAST would address a wide range of scientific topics including the thermal structure and heating of the solar chromosphere, flares and prominences, and the solar activity cycle. In this white paper, the key science cases and their technical requirements for AtLAST are discussed.

• Kampen, Eelco van; Bakx, Tom; Breuck, Carlos De; Chen, Chian-Chou; Dannerbauer, Helmut & Magnelli, Benjamin [Show all 30 contributors for this article] (2024). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Surveying the distant Universe. Open Research Europe. 4. doi: 10.12688/openreseurope.17445.1. Full text in Research Archive Show summary

  During the most active period of star formation in galaxies, which occurs in the redshift range 1 < z < 3, strong bursts of star formation result in significant quantities of dust, which obscures new stars being formed as their UV/optical light is absorbed and then re-emitted in the infrared, which redshifts into the mm/sub-mm bands for these early times. To get a complete picture of the high-z galaxy population, we need to survey a large patch of the sky in the sub-mm with sufficient angular resolution to resolve all galaxies, but we also need the depth to fully sample their cosmic evolution, and therefore obtain their redshifts using direct mm spectroscopy with a very wide frequency coverage. This requires a large single-dish sub-mm telescope with fast mapping speeds at high sensitivity and angular resolution, a large bandwidth with good spectral resolution and multiplex spectroscopic capabilities. The proposed 50-m Atacama Large Aperture Submillimeter Telescope (AtLAST) will deliver these specifications. We discuss how AtLAST allows us to study the whole population of high-z galaxies, including the dusty star-forming ones which can only be detected and studied in the sub-mm, and obtain a wealth of information for each of these up to z ∼ 7: gas content, cooling budget, star formation rate, dust mass, and dust temperature. We present worked examples of surveys that AtLAST can perform, both deep and wide, and also focused on galaxies in proto-clusters. In addition we show how such surveys with AtLAST can measure the growth rate fσ 8 and the Hubble constant with high accuracy, and demonstrate the power of the line-intensity mapping method in the mm/sub-mm wavebands to constrain the cosmic expansion history at high redshifts, as good examples of what can uniquely be done by AtLAST in this research field.

• Klaassen, Pamela; Traficante, Alessio; Beltrán, Maria; Pattle, Kate; Booth, Mark & Lovell, Joshua [Show all 41 contributors for this article] (2024). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Our Galaxy. Open Research Europe. 4. doi: 10.12688/openreseurope.17450.1. Full text in Research Archive Show summary

  As we learn more about the multi-scale interstellar medium (ISM) of our Galaxy, we develop a greater understanding for the complex relationships between the large-scale diffuse gas and dust in Giant Molecular Clouds (GMCs), how it moves, how it is affected by the nearby massive stars, and which portions of those GMCs eventually collapse into star forming regions. The complex interactions of those gas, dust and stellar populations form what has come to be known as the ecology of our Galaxy. Because we are deeply embedded in the plane of our Galaxy, it takes up a significant fraction of the sky, with complex dust lanes scattered throughout the optically recognizable bands of the Milky Way. These bands become bright at (sub-)millimetre wavelengths, where we can study dust thermal emission and the chemical and kinematic signatures of the gas. To properly study such large-scale environments, requires deep, large area surveys that are not possible with current facilities. Moreover, where stars form, so too do planetary systems, growing from the dust and gas in circumstellar discs, to planets and planetesimal belts. Understanding the evolution of these belts requires deep imaging capable of studying belts around young stellar objects to Kuiper belt analogues around the nearest stars. Here we present a plan for observing the Galactic Plane and circumstellar environments to quantify the physical structure, the magnetic fields, the dynamics, chemistry, star formation, and planetary system evolution of the galaxy in which we live with AtLAST; a concept for a new, 50m single-dish sub-mm telescope with a large field of view which is the only type of facility that will allow us to observe our Galaxy deeply and widely enough to make a leap forward in our understanding of our local ecology.

• Cordiner, Martin; Thelen, Alexander; Cavalie, Thibault; Cosentino, Richard; Fletcher, Leigh N. & Gurwell, Mark [Show all 30 contributors for this article] (2024). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Planetary and cometary atmospheres. Open Research Europe. 4. doi: 10.12688/openreseurope.17473.1. Full text in Research Archive Show summary

  The study of planets and small bodies within our Solar System is fundamental for understanding the formation and evolution of the Earth and other planets. Compositional and meteorological studies of the giant planets provide a foundation for understanding the nature of the most commonly observed exoplanets, while spectroscopic observations of the atmospheres of terrestrial planets, moons, and comets provide insights into the past and present-day habitability of planetary environments, and the availability of the chemical ingredients for life. While prior and existing (sub)millimeter observations have led to major advances in these areas, progress is hindered by limitations in the dynamic range, spatial and temporal coverage, as well as sensitivity of existing telescopes and interferometers. Here, we summarize some of the key planetary science use cases that factor into the design of the Atacama Large Aperture Submillimeter Telescope (AtLAST), a proposed 50-m class single dish facility: (1) to more fully characterize planetary wind fields and atmospheric thermal structures, (2) to measure the compositions of icy moon atmospheres and plumes, (3) to obtain detections of new, astrobiologically relevant gases and perform isotopic surveys of comets, and (4) to perform synergistic, temporally-resolved measurements in support of dedicated interplanetary space missions. The improved spatial coverage (several arcminutes), resolution (~ 1.2 − 12), bandwidth (several tens of GHz), dynamic range (~ 105) and sensitivity (~ 1 mK km s−1) required by these science cases would enable new insights into the chemistry and physics of planetary environments, the origins of prebiotic molecules and the habitability of planetary systems in general.

• Pandit, Sneha; Wedemeyer, Sven & Carlsson, Mats (2024). EMISSA (Exploring millimetre indicators of solar-stellar activity): III. Comparison of Ca II indices and millimetre continua in a 3D model atmosphere. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 687. doi: 10.1051/0004-6361/202347204. Full text in Research Archive Show summary

  Context. Amongst several spectral lines, some of the strongest chromospheric diagnostics are offered by the Ca II H & K lines. These lines can be used to gauge the temperature stratification of the atmosphere since the line core and wings are formed in different regions of the solar atmosphere. Furthermore, the Ca II lines act as tracers for the magnetic structure of the solar atmosphere, as the line cores are formed in the upper chromosphere even though they are formed in non-local thermodynamic equilibrium (NLTE). In contrast, the formation of millimetre (mm) continuum radiation occurs under local thermodynamic equilibrium (LTE) conditions. As a result, the brightness temperatures obtained from observations with the Atacama Large Millimetre/Submillimetre Array (ALMA) offer a complementary perspective on the activity and thermal structure of stellar atmospheres. Aims. The overall aim is to establish more robust solar/stellar activity indicators using ALMA observations in comparison with classical diagnostics, such as the s index and infrared triplet (IRT) index. Methods. We employed the 1.5D radiative transfer codes RH1.5D and advanced radiative transfer (ART) to compute the synthetic spectra for the Ca II lines and the millimetre (mm) continua, respectively. These calculations were performed using an enhanced network atmosphere model, which incorporates non-equilibrium hydrogen ionisation generated by the state-of-the-art 3D radiation magnetohydrodynamics (rMHD) Bifrost code. To account for the limited spatial resolution of ALMA, we simulated the effect using a Gaussian point spread function (PSF). Additionally, we analysed the correlations and slopes of scatter plots between the Ca II indices and mm continuum for the original and degraded resolutions, focusing on the entire simulation box, quiet Sun regions, and enhanced network patches separately. The activity indices generated from these lines could further be used to compare the spectra of Sun-like stars with the solar spectrum. Results. We present a comparative study between synthetic continuum brightness temperature maps at mm wavelengths (0.3 mm–8.5 mm) and the Ca II activity indices; namely, the s index and infrared triplet (IRT) index. The Ca II activity indices and mm brightness temperatures are weakly correlated at the high resolution, with the highest correlation observed at a wavelength of 0.3 mm, corresponding to ALMA band 10. As the resolution decreases, the correlation consistently increases. Conversely, the slopes exhibit a decreasing trend with increasing wavelength, while the degradation of resolution does not noticeably affect the calculated slopes. Conclusions. As the spatial resolution decreases, the standard deviations of the Ca II activity indices and brightness temperatures decrease, while the correlations between them increase. However, the slopes do not exhibit significant changes. Consequently, these relationships could be valuable for calibrating the mm continuum maps obtained through ALMA observations.

• Mohan, Atul; Mondal, Surajit; Wedemeyer, Sven & Gopalswamy, Natchimuthuk (2024). Energetic particle activity in AD Leo: Detection of a solar-like type-IV burst. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 686. doi: 10.1051/0004-6361/202347924. Full text in Research Archive Show summary

  Context. AD Leo is a young and active M dwarf with high flaring rates across the X-ray-to-radio bands. Flares accelerate particles in the outer coronal layers and often impact exo-space weather. Wide-band radio dynamic spectra let us explore the evolution of particle acceleration activity across the corona. Identifying the emission features and modelling the mechanisms can provide insights into the possible physical scenarios driving the particle acceleration processes. Aims. We performed an 8 h monitoring of AD Leo across the 550-850 MHz band using upgraded-Giant Metrewave Radio Telescope (uGMRT). The possible flare and post-flare emission mechanisms are explored based on the evolution of flux density and polarisation. Methods. The python-based module, Visibility Averaged Dynamic spectrum (VISAD), was developed to obtain the visibility-averaged wide-band dynamic spectra. Direct imaging was also performed with different frequency-time averaging. Based on existing observational results on AD Leo and on solar active region models, radial profiles of electron density and magnetic fields were derived. Applying these models, we explored the possible emission mechanisms and magnetic field profile of the flaring active region. Results. The star displayed a high brightness temperature (TB≈ 1010−1011 K) throughout the observation. The emission was also nearly 100% left circularly polarised during bursts. The post-flare phase was characterised by a highly polarised (60–80%) solar-like type IV burst confined above 700 MHz. Conclusions. The flare emission favours a Z-mode or a higher harmonic X-mode electron cyclotron maser emission mechanism. The >700 MHz post-flare activity is consistent with a type-IV radio burst from flare-accelerated particles trapped in magnetic loops, which could be a coronal mass ejection (CME) signature. This is the first solar-like type-IV burst reported on a young active M dwarf belonging to a different age-related activity population (‘C’ branch) compared to the Sun (‘I’ branch). We also find that a multipole expansion model of the active region magnetic field

• Lee, Minju; Schimek, Alice; Cicone, Claudia; Andreani, Paola; Popping, Gergo & Sommovigo, Laura [Show all 32 contributors for this article] (2024). Atacama Large Aperture Submillimeter Telescope (AtLAST) science: The hidden circumgalactic medium. Open Research Europe. 4. doi: 10.12688/openreseurope.17452.1. Full text in Research Archive Show summary

  Our knowledge of galaxy formation and evolution has incredibly progressed through multi-wavelength observational constraints of the interstellar medium (ISM) of galaxies at all cosmic epochs. However, little is known about the physical properties of the more diffuse and lower surface brightness reservoir of gas and dust that extends beyond ISM scales and fills dark matter haloes of galaxies up to their virial radii, the circumgalactic medium (CGM). New theoretical studies increasingly stress the relevance of the latter for understanding the feedback and feeding mechanisms that shape galaxies across cosmic times, whose cumulative effects leave clear imprints into the CGM. Recent studies are showing that a – so far unconstrained – fraction of the CGM mass may reside in the cold (T < 104 K) molecular and atomic phase, especially in high-redshift dense environments. These gas phases, together with the warmer ionised phase, can be studied in galaxies from z ∼ 0 to z ∼ 10 through bright far-infrared and sub-millimeter emission lines such as [C ii] 158µm, [O iii] 88 µm, [C I] 609µm, [C i] 370µm, and the rotational transitions of CO. Imaging such hidden cold CGM can lead to a breakthrough in galaxy evolution studies but requires a new facility with the specifications of the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST). In this paper, we use theoretical and empirical arguments to motivate future ambitious CGM observations with AtLAST and describe the technical requirements needed for the telescope and its instrumentation to perform such science.

• Eklund, Henrik; Szydlarski, Mikolaj & Wedemeyer, Sven (2023). Using the slope of the brightness temperature continuum as a diagnostic tool for solar ALMA observations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 669. doi: 10.1051/0004-6361/202244400. Full text in Research Archive Show summary

  Context. The intensity of radiation from the solar atmosphere at millimetre wavelengths is closely related to the plasma temperature, and the formation height of the radiation is wavelength dependent. It follows from this that the slope of the intensity continuum, or the brightness temperature continuum, samples the local gradient of the gas temperature of the sampled layers in the solar atmosphere. Aims. We aim to show the added information and diagnostics potential of the solar atmosphere that comes with measuring the slope of the brightness temperature continuum. Methods. We used solar observations from the Atacama Large Millimeter/sub-millimeter Array (ALMA) and estimated and predicted the slope using a numerical three-dimensional radiation-magnetohydrodynamic simulation. The slope was estimated by the differences between observables at wavelengths corresponding to different sub-bands at opposite sides of the ALMA receiver band 3 (2.8–3.2 mm) and band 6 (1.20–1.31 mm). Results. The sign of the brightness temperature slope indicates temperature changes with increasing height at the sampled layers. A positive sign implies an increase in temperature, while a negative sign implies a temperature decrease. The differences in brightness temperature between the sub-bands across the field of view of the simulation typically span from −0.4 kK to 0.75 kK for band 3 and −0.2 kK to 0.3 kK at band 6. The network patches are dominated by large positive slopes, while the quiet-Sun region shows a mixture of positive and negative slopes. As the slope of the continuum is coupled to the small-scale dynamics, a negative slope is seen typically under quiet-Sun conditions as a result of propagating shock waves and the corresponding post-shock regions. The temporal evolution of the slopes can therefore be used to identify shocks. The observability of the slope of the brightness temperatures is estimated at bands 3 and 6 for different angular resolutions corresponding to ALMA observations. The simulations also show that the intensity of the radiation at bands 3 and 6 can simultaneously originate from several major components at different heights, which is strongly dependent on the small-scale dynamics and is seen in both quiet-Sun and network patches. Our in-depth analysis of selected shock waves that propagating upward in the atmosphere shows that the delay of shock signatures between two wavelengths (e.g., bands 6 and 3) does not necessarily reflect the propagation speed of the shock front, but might be cause by the rate of change in opacity of higher layers at these wavelengths. Conclusions. The slope of the brightness temperature continuum sampled at different ALMA receiver sub-bands serves as an indicator of the slope of the local plasma temperature at the sampled heights in the atmosphere. This offers new diagnostic possibilities for measuring the underlying physical properties of small-scale dynamic features and thus contributes to the understanding of these features and the related transport of energy and heat in the chromosphere.

• Pandit, Sneha; Wedemeyer, Sven; Carlsson, Mats & Szydlarski, Mikolaj (2023). Comparison of chromospheric diagnostics in a 3D model atmosphere: Hα linewidth and millimetre continua. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 673. doi: 10.1051/0004-6361/202245412. Full text in Research Archive Show summary

  Context. The H α line, one of the most studied chromospheric diagnostics, is a tracer of magnetic field structures, while the intensity of its line core provides an estimate of the mass density. The interpretation of H α observations is complicated by deviations from local thermodynamic equilibrium (LTE) or instantaneous statistical equilibrium conditions. Meanwhile, millimetre (mm) continuum radiation is formed in LTE, and therefore the brightness temperatures from Atacama Large Millimetre-submillimetre Array (ALMA) observations provide a complementary view of the activity and the thermal structure of stellar atmospheres. These two diagnostics together can provide insights into the physical properties of stellar atmospheres, such as their temperature stratification, magnetic structures, and mass density distribution. Aims. In this paper, we present a comparative study between synthetic continuum brightness temperature maps at mm wavelengths (0.3 mm to 8.5 mm) and the width of the H α 6565 Å line. Methods. We used the 3D radiative-transfer codes Multi3D and Advanced Radiative Transfer (ART) to calculate synthetic spectra for the H α line and the mm continua, respectively, from an enhanced network atmosphere model with non-equilibrium hydrogen ionisation generated with the state-of-the-art 3D radiation magnetohydrodynamics (rMHD) code Bifrost. We use a Gaussian point spread function (PSF) to simulate the effect of ALMA’s limited spatial resolution and calculate the H α versus mm continuum correlations and slopes of scatter plots for the original and degraded resolution of the whole box, quiet sun, and enhanced network patches separately. Results. The H α linewidth and mm brightness temperatures are highly correlated and the correlation is highest at a wavelength of 0.8 mm, that is, in ALMA Band 7. The correlation systematically increases with decreasing resolution. On the other hand, the slopes decrease with increasing wavelength. The degradation of resolution does not have a significant impact on the calculated slopes. Conclusions. With decreasing spatial resolution, the standard deviations of the observables, H α linewidth, and brightness temperatures decrease and the correlations between them increase, but the slopes do not change significantly. These relations may therefore prove useful in calibrating the mm continuum maps observed with ALMA.

• Gomez, Juan Camilo Guevara; Jafarzadeh, Shahin; Wedemeyer, Sven; Grant, Samuel D. T.; Eklund, Henrik & Szydlarski, Mikolaj (2023). The Sun at millimeter wavelengths: IV. Magnetohydrodynamic waves in small-scale bright features. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 671. doi: 10.1051/0004-6361/202244228. Full text in Research Archive Show summary

  Aims. We used solar observations of a plage-enhanced network with the Atacama Large Millimeter/sub-millimeter Array (ALMA) in Band 3 and Band 6, together with synthetic continuum maps from numerical simulations with Bifrost in the same bands, to carry out a detailed study of bright small-scale magnetic features. Methods. We made use of an algorithm to automatically identify and trace bright features within the field of view (FoV) of the ALMA observations and the simulation. In particular, the algorithm recovers information of the time evolution of the shape, motion of the centre of gravity, temperature, and size for each feature. These quantities are used to determine the oscillatory properties of each feature utilising wavelets analysis. Results. We found 193 and 293 features in the Bands 3 and 6 observations, respectively. In the degraded simulation, the total number of features were 24 for Band 3 and 204 for Band 6. In the original simulation, the total number of features were 36 for Band 3 and 392 for Band 6. Based on the simulation, we confirm the magnetic nature of the features. We have obtained average oscillation periods of 30–99 s for the temperature, 37–92 s for size, and 37–78 s for horizontal velocity. There are indications for the possible presence of transverse (kink) waves with average amplitude velocities of 2.1–5.0 km s −1 . We find a predominant anti-phase behaviour between temperature and size oscillations suggesting that the variations of the bright features are caused by compressible fast-sausage magnetohydrodynamics (MHD) modes. For the first time to our knowledge, we estimated the flux of energy of the fast-sausage waves at the chromospheric heights sampled by ALMA as 453–1838 W m −2 for Band 3 and 3640–5485 W m −2 for Band 6. Conclusions. We have identified MHD waves, both transverse (kink) and compressible sausage modes, in small-scale (magnetic) structures, independently, in both ALMA Band 3 and Band 6 observations, along with their corresponding synthetic images from simulations. The decrease of wave energy-flux with height (from Band 6 to Band 3) could possibly suggest energy dissipation at chromospheric heights, namely, wave heating, with the assumptions that the identified small-scale waves are typical at each band and they propagate upward through the chromosphere.

• Tziotziou, K.; Scullion, Eamon; Shelyag, S.; Steiner, O.; Khomenko, E. & Tsiropoula, G. [Show all 15 contributors for this article] (2023). Vortex Motions in the Solar Atmosphere: Definitions, Theory, Observations, and Modelling. Space Science Reviews. ISSN 0038-6308. 219(1). doi: 10.1007/s11214-022-00946-8. Full text in Research Archive Show summary

  Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the-art magnetoconvection simulations. Vortical flows exhibit complex characteristics and dynamics, excite a wide range of different waves, and couple different layers of the solar atmosphere, which facilitates the channeling and transfer of mass, momentum and energy from the solar surface up to the low corona. Here we provide a comprehensive review of documented research and new developments in theory, observations, and modelling of vortices over the past couple of decades after their observational discovery, including recent observations in \text{H}\alpha , innovative detection techniques, diverse hydrostatic modelling of waves and forefront magnetohydrodynamic simulations incorporating effects of a non-ideal plasma. It is the first systematic overview of solar vortex flows at granular scales, a field with a plethora of names for phenomena that exhibit similarities and differences and often interconnect and rely on the same physics. With the advent of the 4-m Daniel K. Inouye Solar Telescope and the forthcoming European Solar Telescope, the ongoing Solar Orbiter mission, and the development of cutting-edge simulations, this review timely addresses the state-of-the-art on vortex flows and outlines both theoretical and observational future research directions.

• Rackham, Benjamin V.; Espinosa, Néstor; Berdyugina, S.V.; Korhonen, Heidi; MacDonald, Ryan J. & Montet, Benjamin T. [Show all 61 contributors for this article] (2023). The effect of stellar contamination on low-resolution transmission spectroscopy: needs identified by NASA’s Exoplanet Exploration Program Study Analysis Group 21. RAS Techniques and Instruments (RASTI). 2(1), p. 148–206. doi: 10.1093/rasti/rzad009. Full text in Research Archive Show summary

  Study Analysis Group 21 (SAG21) of NASA’s Exoplanet Exploration Program Analysis Group was organized to study the effect of stellar contamination on space-based transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring the wavelength-dependent radius of a planet as it transits its star. Transmission spectroscopy relies on a precise understanding of the spectrum of the star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and chromospheres with inhomogeneities like spots, faculae, plages, granules, and flares. This SAG brought together an interdisciplinary team of more than 100 scientists, with observers and theorists from the heliophysics, stellar astrophysics, planetary science, and exoplanetary atmosphere research communities, to study the current research needs that can be addressed in this context to make the most of transit studies from current NASA facilities like Hubble Space Telescope and JWST. The analysis produced 14 findings, which fall into three science themes encompassing (i) how the Sun is used as our best laboratory to calibrate our understanding of stellar heterogeneities (‘The Sun as the Stellar Benchmark’), (ii) how stars other than the Sun extend our knowledge of heterogeneities (‘Surface Heterogeneities of Other Stars’), and (iii) how to incorporate information gathered for the Sun and other stars into transit studies (‘Mapping Stellar Knowledge to Transit Studies’). In this invited review, we largely reproduce the final report of SAG21 as a contribution to the peer-reviewed literature.

• Ramasawmy, Joanna; Klaassen, Pamela D.; Cicone, Claudia; Mroczkowski, Tony; Chen, Chian-Chou & Cornish, Thomas [Show all 14 contributors for this article] (2022). The Atacama Large Aperture Submillimetre Telescope: key science drivers. Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. 12190. doi: 10.1117/12.2627505. Full text in Research Archive Show summary

  The Atacama Large Aperture Submillimeter Telescope (AtLAST) is a concept for a 50m class single-dish telescope that will provide high sensitivity, fast mapping of the (sub-)millimeter sky. Expected to be powered by renewable energy sources, and to be constructed in the Atacama desert in the 2030s, AtLAST’s suite of up to six stateof-the-art instruments will take advantage of its large field of view and high throughput to deliver efficient continuum and spectroscopic observations of the faint, large-scale emission that eludes current facilities. The AtLAST design study project is currently supported by a Horizon 2020 grant aimed at studying the governance, telescope design, site selection, telescope operations, sustainable energy supply, and science drivers of the future AtLAST observatory. With quantified and specific science goals, we can begin to place technical specifications on the telescope and its instrumentation. As a first step in this process, we conducted a consultation on potential AtLAST science with the global (sub-)millimeter astrophysics community. The consultation involved nearly 100 scientists based in 22 countries, and the resulting 28 use cases indicate the breadth of transformational science that such a high-throughput facility could make possible: from exploring the prebiotic molecular chemistry of comets in our own Solar System, detecting the extended, diffuse cold gas in the circumgalactic medium of both our own and distant galaxies, to detailed measurements of the thermal, kinetic, and relativistic Sunyaev-Zeldovich effect and mapping of large-scale structure. Already these science cases define some core requirements for AtLAST’s instrumentation: wide bandwidths, multichroic observations, high spectral resolution, fast mapping and a large field of view. Further refinement of these is planned over the course of the current EU-funded project, resulting in detailed case studies of the telescope and instrumentation requirements needed by the community to deliver a next-generation submillimeter observing facility.

• Gomez, Juan Camilo Guevara; Jafarzadeh, Shahin; Wedemeyer, Sven & Szydlarski, Mikolaj (2022). Propagation of transverse waves in the solar chromosphere probed at different heights with ALMA sub-bands. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 665. doi: 10.1051/0004-6361/202244387. Full text in Research Archive Show summary

  The Atacama Large Millimeter/sub-millimeter Array (ALMA) has provided us with an excellent diagnostic tool for studies of the dynamics of the Solar chromosphere, albeit through a single receiver band at one time presently. Each ALMA band consists of four sub-bands that are comprised of several spectral channels. To date, however, the spectral domain has been neglected in favour of ensuring optimal imaging, so that time-series observations have been mostly limited to full-band data products, thereby limiting studies to a single chromospheric layer. Here, we report the first observations of a dynamical event (i.e., wave propagation) for which the ALMA Band 3 data (centred at 3 mm; 100 GHz) is split into a lower and an upper sideband. In principle, this approach is aimed at mapping slightly different layers in the Solar atmosphere. The side-band data were reduced together with the Solar ALMA Pipeline (SoAP), resulting in time series of brightness-temperature maps for each side-band. Through a phase analysis of a magnetically quiet region, where purely acoustic waves are expected to dominate, the average height difference between the two side-bands is estimated as 73 ± 16 km. Furthermore, we examined the propagation of transverse waves in small-scale bright structures by means of wavelet phase analysis between oscillations at the two atmospheric heights. We find 6% of the waves to be standing, while 54% and 46% of the remaining waves are propagating upwards and downwards, respectively, with absolute propagating speeds on the order of ≈96 km s −1 , resulting in a mean energy flux of 3800 W m 2 .

• Mohan, Atul; Wedemeyer, Sven; Hauschildt, Peter, H.; Pandit, Sneha & Saberi, Maryam (2022). EMISSA (Exploring millimetre indicators of solar-stellar activity) II. Towards a robust indicator of stellar activity. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 664. doi: 10.1051/0004-6361/202244385. Full text in Research Archive Show summary

  Context: An activity indicator, which can provide a robust quantitative mapping between the stellar activity and the physical properties of its atmosphere, is important in exploring the evolution of the observed active phenomena across main-sequence stars of different spectral types. Common activity indicators do provide qualitative correlations with physical properties such as Teff and the rotation period, among others. However, due to the large variability in their values, even for a single star, defining robust quantitative mappings between activity and physical properties is difficult. Millimetre (mm) wavelengths probe the different atmospheric layers within the stellar chromosphere, providing a tomographic view of the atmospheric dynamics. Aims: The project aims to define a robust activity indicator by characterising mm brightness temperature spectra (TB(ν)) of the cool main-sequence stars (Teff ∼ 5000 – 7000 K) compiled by paper I in this series. The sample contains 13 stars, including the Sun. Methods: We derived the mm TB(ν) spectral indices (αmm) for cool stars, including the Sun, based on observations in the 30 – 1000 GHz range. The derived values for αmm are explored as a function of various physical parameters and empirical power-law functions were derived. We also compared αmm estimates with other activity indicators. Results: Despite the estimation errors, αmm values could distinguish the cool stars well, unlike common activity indicators. The low estimation errors on the derived trends of αmm versus physical parameters suggest that αmm could be a robust activity indicator. Conclusions: We note that αmm, which is linked to chromospheric thermal stratification and activity in cool stars, can well distinguish and physically characterise the stars more robustly than common activity indicators. We emphasise the need for multi-frequency data across the mm band for stars, with a range of physical parameters and gathered at multiple epochs during their activity cycles. This will help to explore αmm in a statistically robust manner and to study the emergence of chromospheric heating on the main sequence

• Silva, Alexandre José de Oliveira e; Selhorst, Caius Lucius; Costa, Joaquim E. R.; Simões, Paulo J. A.; Castro, Carlos Guillermo Giménez de & Wedemeyer, Sven [Show all 9 contributors for this article] (2022). A Genetic Algorithm to Model Solar Radio Active Regions From 3D Magnetic Field Extrapolations. Frontiers in Astronomy and Space Sciences. 9. doi: 10.3389/fspas.2022.911118. Full text in Research Archive Show summary

  In recent decades our understanding of solar active regions (ARs) has improved substantially due to observations made with better angular resolution and wider spectral coverage. While prior AR observations have shown that these structures were always brighter than the quiet Sun at centimeter wavelengths, recent observations at millimeter and submillimeter wavelengths have shown ARs with well defined dark umbrae. Given this new information, it is now necessary to update our understanding and models of the solar atmosphere in active regions. In this work, we present a data-constrained model of the AR solar atmosphere, in which we use brightness temperature measurements of NOAA 12470 at three radio frequencies: 17, 100 and 230 GHz. The observations at 17 GHz were made by the Nobeyama Radioheliograph (NoRH), while the observations at 100 and 230 GHz were obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Based on our model, which assumes that the radio emission originates from thermal free-free and gyroresonance processes, we calculate radio brightness temperature maps that can be compared with the observations. The magnetic field at distinct atmospheric heights was determined in our modelling process by force-free field extrapolation using photospheric magnetograms taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). In order to determine the best plasma temperature and density height profiles necessary to match the observations, the model uses a genetic algorithm that modifies a standard quiet Sun atmospheric model. Our results show that the height of the transition region (TR) of the modelled atmosphere varies with the type of region being modelled: for umbrae the TR is located at 1080 ± 20 km above the solar surface; for penumbrae, the TR is located at 1800 ± 50 km; and for bright regions outside sunspots, the TR is located at 2000 ± 100 km. With these results, we find good agreement with the observed AR brightness temperature maps. Our modelled AR can be used to estimate the emission at frequencies without observational coverage.

• Saberi, Maryam; Khouri, T.; Velilla-Prieto, L.; Fonfría, J.P.; Vlemmings, W.H.T. & Wedemeyer, Sven (2022). First detection of AlF line emission towards M-type AGB stars. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 663. doi: 10.1051/0004-6361/202141704. Full text in Research Archive Show summary

  The nucleosynthesis production of fluorine (F) is still a matter of debate. Asymptotic giant branch (AGB) stars are one of the main candidates for F production. However, their contribution to the total F budget is not fully known due to the lack of observations. In this paper, we report the detection of aluminium monofluoride (AlF) line emission, one of the two main carriers of F in the gas-phase in the outflow of evolved stars, towards five nearby oxygen-rich (M-type) AGB stars. We studied the Atacama large millimetre/sub-millimetre array (ALMA) observations of AlF ( v = 0, J = 4—3, 9–8, 10–9, and 15–14) and ( v = 1, J = 7–6) line emission towards o Ceti, and ( v = 0, J = 7–6 and 15–14) lines towards R Leo. We also report a tentative detection of AlF ( v = 0, J = 7–6) line in IK Tau, ( v = 0, J = 15–14) line towards R Dor, and ( v = 0, J = 7–6 and J = 15–14) lines in W Hya. From spatially resolved observations, we estimated the AlF emitting region with a radius ~11 R ⋆ for o Ceti and ~9 R ⋆ for R Leo. From population diagram analysis, we report the AlF column densities of ~5.8 × 10 15 cm −2 and ~3 × 10 15 cm −2 for o Ceti and R Leo, respectively, within these regions. For o Ceti, we used the C 18 O ( v = 0, J = 3–2) observations to estimate the H 2 column density of the emitting region. We found a fractional abundance of f AIF/H2 ~ (2.5 ± 1.7) × 10 −8 . This gives a lower limit on the F budget in o Ceti and is compatible with the solar F budget f F/H2 = (5 ± 2) × 10 −8 . For R Leo, a fractional abundance f AIF/H2 = (1.2 ± 0.5) × 10 −8 is estimated. For other sources, we cannot precisely determine the emitting region based on the available data. Assuming an emitting region with a radius of ~11 R ⋆ and the rotational temperatures derived for o Ceti and R Leo, we crudely approximated the AlF column density to be ~(1.2−1.5) × 10 15 cm −2 in W Hya, ~(2.5−3.0) × 10 14 cm −2 in R Dor, and ~(0.6−1.0) × 10 16 cm −2 in IK Tau. These result in fractional abundances within a range of f AIF/H2 ~ (0.1 − 4) × 10 −8 in W Hya, R Dor, and IK Tau.

• Henriques, Vasco Manuel de Jorge; Jafarzadeh, Shahin; Gomez, Juan Camilo Guevara; Eklund, Henrik; Wedemeyer, Sven & Szydlarski, Mikolaj [Show all 8 contributors for this article] (2022). The Solar ALMA Science Archive (SALSA): First release, SALAT, and FITS header standard. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 659. doi: 10.1051/0004-6361/202142291. Full text in Research Archive Show summary

  In December 2016, the Atacama Large Millimeter/submillimeter Array (ALMA) carried out the first regular observations of the Sun. These early observations and the reduction of the respective data posed a challenge due to the novelty and complexity of observing the Sun with ALMA. The difficulties with producing science-ready, time-resolved imaging products in a format familiar to and usable by solar physicists based on the measurement sets delivered by ALMA had limited the availability of such data to this point. With the development of the Solar ALMA Pipeline, it has now become possible to routinely reduce such data sets. As a result, a growing number of science-ready solar ALMA data sets are now offered in the form of the Solar ALMA Science Archive (SALSA). So far, SALSA contains primarily time series of single-pointing interferometric images at cadences of one or two seconds, accompanied by the respective single-dish full-disc solar images. The data arrays are provided in FITS format. We also present the first version of a standardised header format that accommodates future expansions and fits within the scope of other standards including the ALMA Science Archive itself and SOLARNET. The headers include information designed to aid the reproduction of the imaging products from the raw data. Links to co-observations, if available, with a focus on those of the Interface Region Imaging Spectrograph, are also provided. SALSA is accompanied by the Solar ALMA Library of Auxiliary Tools (SALAT), which contains Interactive Data Language and Python routines for convenient loading and a quick-look analysis of SALSA data.

• Wedemeyer, Sven; Fleishman, Gregory; Rodríguez, Jaime de la Cruz; Gunár, Stanislav; Santos, João M. da Silva & Antolin, Patrick [Show all 9 contributors for this article] (2022). Prospects and challenges of numerical modeling of the Sun at millimeter wavelengths. Frontiers in Astronomy and Space Sciences. 9. doi: 10.3389/fspas.2022.967878. Full text in Research Archive Show summary

  The Atacama Large Millimeter/submillimeter Array (ALMA) offers new diagnostic possibilities that complement other commonly used diagnostics for the study of the Sun. In particular, ALMA’s ability to serve as an essentially linear thermometer of the chromospheric gas at unprecedented spatial resolution at millimeter wavelengths and future polarization measurements has great diagnostic potential. Solar ALMA observations are therefore expected to contribute significantly to answering long-standing questions about the structure, dynamics, and energy balance of the outer layers of the solar atmosphere. In this regard, current and future ALMA data are also important for constraining and further developing numerical models of the solar atmosphere, which in turn are often vital for the interpretation of observations. The latter is particularly important given the Sun’s highly intermittent and dynamic nature that involves a plethora of processes occurring over extended ranges in spatial and temporal scales. Realistic forward modeling of the Sun therefore requires time-dependent three-dimensional radiation magnetohydrodynamics that account for non-equilibrium effects and, typically as a separate step, detailed radiative transfer calculations, resulting in synthetic observables that can be compared to observations. Such artificial observations sometimes also account for instrumental and seeing effects, which, in addition to aiding the interpretation of observations, provide instructive tools for designing and optimizing ALMA’s solar observing modes. In the other direction, ALMA data in combination with other simultaneous observations enable the reconstruction of the solar atmospheric structure via data inversion techniques. This article highlights central aspects of the impact of ALMA for numerical modeling of the Sun and their potential and challenges, together with selected examples.

• Narang, Nancy; Chandrashekhar, Kalugodu; Jafarzadeh, Shahin; Fleck, Bernhard; Szydlarski, Mikolaj & Wedemeyer, Sven (2022). Power distribution of oscillations in the atmosphere of a plage region: Joint observations with ALMA, IRIS, and SDO. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 661. doi: 10.1051/0004-6361/202142080. Full text in Research Archive Show summary

  Context. Joint observations of the Atacama Large Millimeter/Submillimeter Array (ALMA) with other solar observatories can provide a wealth of opportunities for understanding the coupling between different layers of the solar atmosphere. Aims. We present a statistical analysis of the power distribution of oscillations in a plage region in active region NOAA AR12651, which was observed jointly with ALMA, the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO). Methods. We employ coordinated ALMA Band 6 (1.25 mm) brightness temperature maps, IRIS slit-jaw images in the 2796 Å passband, and observations in six passbands (1600 Å, 304 Å, 131 Å, 171 Å, 193 Å, and 211 Å) from the Atmospheric Imaging Assembly (AIA) on board SDO. We perform Lomb-Scargle transforms to study the distribution of oscillation power by means of dominant period maps and power maps. We study the spatial association of oscillations through the atmosphere, with a focus on the correlation of the power distribution of ALMA oscillations with others. Results. We do not observe any significant association of ALMA oscillations with IRIS and AIA oscillations. While the global behavior of the dominant ALMA oscillations shows a similarity with that of the transition region and coronal passbands of AIA, the ALMA dominant period maps and power maps do not show any correlation with those from the other passbands. The spatial distribution of dominant periods and power in different period intervals of ALMA oscillations is uncorrelated with those of any other passbands. Conclusions. We speculate that the non-association of ALMA oscillations with those of IRIS and AIA is due to significant variations in the height of formation of the millimeter continuum observed by ALMA. Additionally, the fact that ALMA directly maps the brightness temperature, in contrast to the intensity observations by IRIS and AIA, can result in the very different intrinsic nature of the ALMA oscillations compared to the IRIS and AIA oscillations.

• Mohan, Atul; Wedemeyer, Sven; Pandit, Sneha; Saberi, Maryam & Hauschildt, Peter H. (2021). EMISSA (Exploring Millimeter Indicators of Solar-Stellar Activity): I. The initial millimeter–centimeter main-sequence star sample. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 655. doi: 10.1051/0004-6361/202142095. Full text in Research Archive Show summary

  Context. Due to their wide wavelength coverage across the millimeter to centimeter (mm–cm) range and their increased sensitivity, modern interferometric arrays facilitate observations of the thermal and non-thermal radiation that is emitted from different layers in the outer atmospheres of stars. Aims. We study the spectral energy distribution ( S obs ( ν )) of main-sequence stars based on archival observations in the mm–cm range with the aim to study their atmospheric stratification as a function of stellar type. Methods. The main-sequence stars with significant detection in mm bands were identified in the ALMA Science Archive. These data were then complemented with spectral flux data in the extreme ultraviolet to cm range as compiled from various catalogues and observatory archives. We compared the resultant S obs ( ν ) of each star with a photospheric emission model ( S mod ( ν )) calculated with the PHOENIX code. The departures of S obs ( ν ) from S mod ( ν ) were quantified in terms of a spectral flux excess parameter (Δ S ∕ S mod ) and studied as a function of stellar type. Results. The initial sample consists of 12 main-sequence stars across a broad range of spectral types from A1 to M3.5 and the Sun-as-a-star as reference. The stars with T eff = 3000–7000 K (F–M type) showed a systematically higher S obs ( ν ) than S mod ( ν ) in the mm–cm range. Their Δ S ∕ S mod exhibits a monotonic rise with decreasing frequency. The steepness of this rise is higher for cooler stars in the T eff = 3000–7000 K range, although the single fully convective star ( T eff ~ 3000 K) in the sample deviates from this trend. Meanwhile, S obs ( ν ) of the A-type stars agrees with S mod ( ν ) within errors. Conclusions. The systematically high Δ S ∕ S mod in F–M stars indicates hotter upper atmospheric layers, that is, a chromosphere and corona in these stars, like for the Sun. The mm–cm Δ S ∕ S mod spectrum offers a way to estimate the efficiency of the heating mechanisms across various outer atmospheric layers in main-sequence stars, and thereby to understand their structure and activity. We emphasise the need for dedicated surveys of main-sequence stars in the mm–cm range.

• Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikolaj & Jafarzadeh, Shahin (2021). The Sun at millimeter wavelengths: III. Impact of the spatial resolution on solar ALMA observations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 656. doi: 10.1051/0004-6361/202140972. Full text in Research Archive Show summary

  Context. Interferometric observations of the Sun with the Atacama Large Millimeter/sub-millimeter Array (ALMA) provide valuable diagnostic tools for studying the small-scale dynamics of the solar atmosphere. Aims. The aims are to perform estimations of the observability of the small-scale dynamics as a function of spatial resolution for regions with different characteristic magnetic field topology facilitate a more robust analysis of ALMA observations of the Sun. Methods. A three-dimensional model of the solar atmosphere from the radiation-magnetohydrodynamic code Bifrost was used to produce high-cadence observables at millimeter and submillimeter wavelengths. The synthetic observables for receiver bands 3–10 were degraded to the angular resolution corresponding to ALMA observations with different configurations of the interferometric array from the most compact, C1, to the more extended, C7. The observability of the small-scale dynamics was analyzed in each case. The analysis was thus also performed for receiver bands and resolutions that are not commissioned so far for solar observations as a means for predicting the potential of future capabilities. Results. The minimum resolution required to study the typical small spatial scales in the solar chromosphere depends on the characteristic properties of the target region. Here, a range from quiet Sun to enhanced network loops is considered. Limited spatial resolution affects the observable signatures of dynamic small-scale brightening events in the form of reduced brightness temperature amplitudes, potentially leaving them undetectable, and even shifts in the times at which the peaks occur of up to tens of seconds. Conversion factors between the observable brightness amplitude and the original amplitude in the fully resolved simulation are provided that can be applied to observational data in principle, but are subject to wavelength-dependent uncertainties. Predictions of the typical appearance at the different combinations of receiver band, array configuration, and properties of the target region are conducted. Conclusions. The simulation results demonstrate the high scientific potential that ALMA already has with the currently offered capabilities for solar observations. For the study of small-scale dynamic events, however, the spatial resolution is still crucial, and wide array configurations are preferable. In any case, it is essential to take the effects due to limited spatial resolution into account in the analysis of observational data. Finally, the further development of observing capabilities including wider array configurations and advanced imaging procedures yields a high potential for future ALMA observations of the Sun.

• Chintzoglou, Georgios; Pontieu, Bart Walter De; Martinez-Sykora, Juan; Hansteen, Viggo; Rodriguez, Jaime de la Cruz & Szydlarski, Mikolaj Marcin [Show all 10 contributors for this article] (2021). ALMA and IRIS Observations of the Solar Chromosphere. I. An On-Disk Type II Spicule. The Astrophysical Journal (ApJ). ISSN 0004-637X. 906(2). doi: 10.3847/1538-4357/abc9b1. Full text in Research Archive
• Chintzoglou, Georgios; Pontieu, Bart Walter De; Martinez-Sykora, Juan; Hansteen, Viggo; Rodriguez, Jaime de la Cruz & Szydlarski, Mikolaj Marcin [Show all 10 contributors for this article] (2021). ALMA and IRIS Observations of the Solar Chromosphere. II. Structure and Dynamics of Chromospheric Plages. The Astrophysical Journal (ApJ). ISSN 0004-637X. 906(2). doi: 10.3847/1538-4357/abc9b0. Full text in Research Archive
• Santos, João Manuel da Silva; Rodriguez, Jaime de la Cruz; Leenaarts, Jorrit; Chintzoglou, Georgios; Pontieu, Bart Walter De & Wedemeyer, Sven [Show all 7 contributors for this article] (2020). The multi-thermal chromosphere: Inversions of ALMA and IRIS data. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 634. doi: 10.1051/0004-6361/201937117. Full text in Research Archive Show summary

  Context. Numerical simulations of the solar chromosphere predict a diverse thermal structure with both hot and cool regions. Observations of plage regions in particular typically feature broader and brighter chromospheric lines, which suggests that they are formed in hotter and denser conditions than in the quiet Sun, but also implies a nonthermal component whose source is unclear. Aims. We revisit the problem of the stratification of temperature and microturbulence in plage and the quiet Sun, now adding millimeter (mm) continuum observations provided by the Atacama Large Millimiter Array (ALMA) to inversions of near-ultraviolet Interface Region Imaging Spectrograph (IRIS) spectra as a powerful new diagnostic to disentangle the two parameters. We fit cool chromospheric holes and track the fast evolution of compact mm brightenings in the plage region. Methods. We use the STiC nonlocal thermodynamic equilibrium (NLTE) inversion code to simultaneously fit real ultraviolet and mm spectra in order to infer the thermodynamic parameters of the plasma. Results. We confirm the anticipated constraining potential of ALMA in NLTE inversions of the solar chromosphere. We find significant differences between the inversion results of IRIS data alone compared to the results of a combination with the mm data: the IRIS+ALMA inversions have increased contrast and temperature range, and tend to favor lower values of microturbulence (∼3−6 km s−1 in plage compared to ∼4−7 km s−1 from IRIS alone) in the chromosphere. The average brightness temperature of the plage region at 1.25 mm is 8500 K, but the ALMA maps also show much cooler (∼3000 K) and hotter (∼11 000 K) evolving features partially seen in other diagnostics. To explain the former, the inversions require the existence of localized low-temperature regions in the chromosphere where molecules such as CO could form. The hot features could sustain such high temperatures due to non-equilibrium hydrogen ionization effects in a shocked chromosphere – a scenario that is supported by low-frequency shock wave patterns found in the Mg II lines probed by IRIS.

• Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikolaj Marcin; Jafarzadeh, Shahin & Gomez, Juan Camilo Guevara (2020). The Sun at millimeter wavelengths: II. Small-scale dynamic events in ALMA Band 3. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 644. doi: 10.1051/0004-6361/202038250. Full text in Research Archive Show summary

  Context. Solar observations with the Atacama Large Millimeter/sub-millimeter Array (ALMA) facilitate studies of the atmosphere of the Sun at chromospheric heights at high spatial and temporal resolution at millimeter wavelengths. Aims. ALMA intensity data at millimeter(mm)-wavelengths are used for a first detailed systematic assessment of the occurrence and properties of small-scale dynamical features in the quiet Sun. Methods. We analyzed ALMA Band 3 data (∼3 mm/100 GHz) with a spatial resolution of ∼1.4–2.1 arcsec and a duration of ∼40 min together with SDO/HMI magnetograms. The temporal evolution of the mm maps is studied to detect pronounced dynamical features, which then are connected to dynamical events via a k -means clustering algorithm. We studied the physical properties of the resulting events and explored whether or not they show properties consistent with propagating shock waves. For this purpose, we calculated observable shock wave signatures at mm wavelengths from one- and three-dimensional model atmospheres. Results. We detect 552 dynamical events with an excess in brightness temperature (Δ T b ) of at least ≥400 K. The events show a large variety in size up to ∼9, amplitude Δ T b up to ∼1200 K with typical values in the range ∼450–750 K, and lifetime at full width at half maximum of Δ T b of between ∼43 and 360 s, with typical values between ∼55 and 125 s. Furthermore, many of the events show signature properties suggesting that they are likely produced by propagating shock waves. Conclusions. There are a lot of small-scale dynamic structures detected in the Band 3 data, even though the spatial resolution sets limitations on the size of events that can be detected. The number of dynamic signatures in the ALMA mm data is very low in areas with photospheric footpoints with stronger magnetic fields, which is consistent with the expectation for propagating shock waves.

• Wedemeyer, Sven; Szydlarski, Mikolaj Marcin; Jafarzadeh, Shahin; Eklund, Henrik; Gomez, Juan Camilo Guevara & Bastian, Tim [Show all 10 contributors for this article] (2020). The Sun at millimeter wavelengths: I. Introduction to ALMA Band 3 observations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 635. doi: 10.1051/0004-6361/201937122. Full text in Research Archive Show summary

  Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started regular observations of the Sun in 2016, first offering receiver Band 3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around 1.25 mm (239 GHz). Aims. Here we present an initial study of one of the first ALMA Band 3 observations of the Sun. Our aim is to characterise the diagnostic potential of brightness temperatures measured with ALMA on the Sun. Methods. The observation covers a duration of 48 min at a cadence of 2 s targeting a quiet Sun region at disc-centre. Corresponding time series of brightness temperature maps are constructed with the first version of the Solar ALMA Pipeline and compared to simultaneous observations with the Solar Dynamics Observatory (SDO). Results. The angular resolution of the observations is set by the synthesised beam, an elliptical Gaussian that is approximately 1.4 × 2.1 in size. The ALMA maps exhibit network patches, internetwork regions, and elongated thin features that are connected to large-scale magnetic loops, as confirmed by a comparison with SDO maps. The ALMA Band 3 maps correlate best with the SDO/AIA 171 Å, 131 Å, and 304 Å channels in that they exhibit network features and, although very weak in the ALMA maps, imprints of large-scale loops. A group of compact magnetic loops is very clearly visible in ALMA Band 3. The brightness temperatures in the loop tops reach values of about 8000−9000 K and in extreme moments up to 10 000 K. Conclusions. ALMA Band 3 interferometric observations from early observing cycles already reveal temperature differences in the solar chromosphere. The weak imprint of magnetic loops and the correlation with the 171, 131, and 304 SDO channels suggests, however, that the radiation mapped in ALMA Band 3 might have contributions from a wider range of atmospheric heights than previously assumed, but the exact formation height of Band 3 needs to be investigated in more detail. The absolute brightness temperature scale as set by total power measurements remains less certain and must be improved in the future. Despite these complications and the limited angular resolution, ALMA Band 3 observations have a large potential for quantitative studies of the small-scale structure and dynamics of the solar chromosphere.

• Gomez, Juan Camilo Guevara; Jafarzadeh, Shahin; Wedemeyer, Sven; Szydlarski, Mikolaj Marcin; Stangalini, M. & Fleck, Bernhard [Show all 7 contributors for this article] (2020). High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. ISSN 1364-503X. 379(2190). doi: 10.1098/rsta.2020.0184. Full text in Research Archive Show summary

  We report detection of oscillations in brightness temperature, size and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e. 2 s cadence) with the Atacama large millimetre/ submillimetre array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ± 23 s, respectively. We find anti-correlations between perturbations in brightness, temperature and size of the three features, which suggest the presence of fast sausage-mode waves in these small structures. In addition, the detection of transverse oscillations (although with a larger uncertainty) may also suggest the presence of Alfvénic oscillations which are likely representative of kink waves. This work demonstrates the diagnostic potential of high-cadence observations with ALMA for detecting high-frequency magnetohydrodynamic waves in the solar chromosphere. Such waves can potentially channel a vast amount of energy into the outer atmosphere of the Sun. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

• Eklund, Henrik; Wedemeyer, Sven; Snow, Ben; Jess, David B.; Jafarzadeh, Shahin & Grant, Samuel D. T. [Show all 8 contributors for this article] (2020). Characterization of shock wave signatures at millimetre wavelengths from Bifrost simulations. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. ISSN 1364-503X. 379(2190). doi: 10.1098/rsta.2020.0185. Full text in Research Archive Show summary

  Observations at millimetre wavelengths provide a valuable tool to study the small-scale dynamics in the solar chromosphere. We evaluate the physical conditions of the atmosphere in the presence of a propagating shock wave and link that to the observable signatures in mm-wavelength radiation, providing valuable insights into the underlying physics of mm-wavelength observations. A realistic numerical simulation from the three-dimensional radiative magnetohydrodynamic code Bifrost is used to interpret changes in the atmosphere caused by shock wave propagation. High-cadence (1 s) time series of brightness temperature (Tb) maps are calculated with the Advanced Radiative Transfer code at the wavelengths 1.309 mm and 1.204 mm, which represents opposite sides of spectral band 6 of the Atacama Large Millimeter/submillimeter Array (ALMA). An example of shock wave propagation is presented. The brightness temperatures show a strong shock wave signature with large variation in formation height between approximately 0.7 and 1.4 Mm. The results demonstrate that millimetre brightness temperatures efficiently track upwardly propagating shock waves in the middle chromosphere. In addition, we show that the gradient of the brightness temperature between wavelengths within ALMA band 6 can potentially be used as a diagnostics tool in understanding the small-scale dynamics at the sampled layers. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

• Wedemeyer, Sven; Szydlarski, Mikolaj Marcin; Rodriguez, Jaime de la Cruz & Jafarzadeh, Shahin (2020). Observing the Sun with the Atacama Large Millimeter/submillimeter Array-from continuum to magnetic fields. Proceedings of the International Astronomical Union. ISSN 1743-9213. 15(S354), p. 24–37. doi: 10.1017/S1743921319009906. Full text in Research Archive
• Jafarzadeh, Shahin; Wedemeyer, Sven; Fleck, Bernhard; Stangalini, M.; Jess, D. B. & Morton, R. J. [Show all 15 contributors for this article] (2020). An overall view of temperature oscillations in the solar chromosphere with ALMA. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. ISSN 1364-503X. 379(2190). doi: 10.1098/rsta.2020.0174. Full text in Research Archive Show summary

  By direct measurements of the gas temperature, the Atacama Large Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here, we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e. 1 and 2 s cadence) time series of images obtained during the first 2 years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform fast Fourier and Lomb–Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e. averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e. linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3–5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of Hα line-core intensity) are unaffected by similar effects, i.e. they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the 10 ALMA datasets analysed here show peak power near 5.5 mHz. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

• Jafarzadeh, Shahin; Wedemeyer, Sven; Szydlarski, Mikolaj Marcin; Pontieu, Bart Walter De; Rezaei, Rezza & Carlsson, Mats (2019). The solar chromosphere at millimetre and ultraviolet wavelengths: I. Radiation temperatures and a detailed comparison. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 622. doi: 10.1051/0004-6361/201834205. Full text in Research Archive Show summary

  Solar observations with the Atacama Large Millimeter/submillimeter Array (ALMA) provide us with direct measurements of the brightness temperature in the solar chromosphere. We study the temperature distributions obtained with ALMA Band 6 (in four sub-bands at 1.21, 1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of, a sunspot, comprising quasi-quiet and active regions with different amounts of underlying magnetic fields. We compare these temperatures with those obtained at near- and far-ultraviolet (UV) wavelengths (and with the line-core intensities of the optically-thin far-UV spectra), co-observed with the Interface Region Imaging Spectrograph (IRIS) explorer. These include the emission peaks and cores of the Mg II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the mid-to-high chromosphere and the low transition region. Splitting the ALMA sub-bands resulted in an slight increase of spatial resolution in individual temperature maps, thus, resolving smaller-scale structures compared to those produced with the standard averaging routines. We find that the radiation temperatures have different, though somewhat overlapping, distributions in different wavelengths and in the various magnetic regions. Comparison of the ALMA temperatures with those of the UV diagnostics should, however, be interpreted with great caution, the former is formed under the local thermodynamic equilibrium (LTE) conditions, the latter under non-LTE. The mean radiation temperature of the ALMA Band 6 is similar to that extracted from the IRIS C II line in all areas with exception of the sunspot and pores where the C II poses higher radiation temperatures. In all magnetic regions, the Mg II lines associate with the lowest mean radiation temperatures in our sample. These will provide constraints for future numerical models.

• Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Judge, Philip G.; Doyle, J. G. & Arber, Tony [Show all 8 contributors for this article] (2019). Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun. The Astrophysical Journal (ApJ). ISSN 0004-637X. 881(1). doi: 10.3847/1538-4357/ab2bf9. Full text in Research Archive Show summary

  e report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca ii 8542 Å and Hα lines as well as in the photospheric Fe i line. We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca ii and Hα channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures. We could not determine whether a swirl is a gradual response to the photospheric motion or an actual propagating Alfvénic wave.

• Freudenthal, J.; Essen, Carolina von; Ofir, A.; Dreizler, S.; Agol, E. & Wedemeyer, Sven [Show all 16 contributors for this article] (2019). Kepler Object of Interest Network: III. Kepler-82f: a new non-transiting 21 M⊕ planet from photodynamical modelling. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 628. doi: 10.1051/0004-6361/201935879. Full text in Research Archive Show summary

  Context. The Kepler Object of Interest Network (KOINet) is a multi-site network of telescopes around the globe organised for follow-up observations of transiting planet candidate Kepler objects of interest with large transit timing variations (TTVs). The main goal of KOINet is the completion of their TTV curves as the Kepler telescope stopped observing the original Kepler field in 2013. Aims. We ensure a comprehensive characterisation of the investigated systems by analysing Kepler data combined with new ground-based transit data using a photodynamical model. This method is applied to the Kepler-82 system leading to its first dynamic analysis. Methods. In order to provide a coherent description of all observations simultaneously, we combine the numerical integration of the gravitational dynamics of a system over the time span of observations with a transit light curve model. To explore the model parameter space, this photodynamical model is coupled with a Markov chain Monte Carlo algorithm. Results. The Kepler-82b/c system shows sinusoidal TTVs due to their near 2:1 resonance dynamical interaction. An additional chopping effect in the TTVs of Kepler-82c hints to a further planet near the 3:2 or 3:1 resonance. We photodynamically analysed Kepler long- and short-cadence data and three new transit observations obtained by KOINet between 2014 and 2018. Our result reveals a non-transiting outer planet with a mass of m = 20.9 ± 1.0 M near the 3:2 resonance to the outermost known planet, Kepler-82c. Furthermore, we determined the densities of planets b and c to the significantly more precise values ρb = 0.98−0.14 g cm−3 and ρc = 0.494−0.077 g cm−3

• Essen, Carolina von; Wedemeyer, Sven; Sosa, M. S.; Hjorth, M.; Parkash, V. & Freudenthal, J. [Show all 11 contributors for this article] (2019). Indications for transit-timing variations in the exo-Neptune HAT-P-26b. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 628. doi: 10.1051/0004-6361/201731966. Full text in Research Archive Show summary

  Upon its discovery, the low-density transiting Neptune HAT-P-26b showed a 2.1σ detection drift in its spectroscopic data, while photometric data showed a weak curvature in the timing residuals, the confirmation of which required further follow-up observations. To investigate this suspected variability, we observed 11 primary transits of HAT-P-26b between March, 2015, and July, 2018. For this, we used the 2.15 m Jorge Sahade Telescope placed in San Juan, Argentina, and the 1.2 m STELLA and the 2.5 m Nordic Optical Telescope, both located in the Canary Islands, Spain. To add to valuable information on the transmission spectrum of HAT-P-26b, we focused our observations in the R-band only. To contrast the observed timing variability with possible stellar activity, we carried out a photometric follow-up of the host star over three years. We carried out a global fit to the data and determined the individual mid-transit times focusing specifically on the light curves that showed complete transit coverage. Using bibliographic data corresponding to both ground and space-based facilities, plus our new characterized mid-transit times derived from parts-per-thousand precise photometry, we observed indications of transit timing variations in the system, with an amplitude of ~4 min and a periodicity of ~270 epochs. The photometric and spectroscopic follow-up observations of this system will be continued in order to rule out any aliasing effects caused by poor sampling and the long-term periodicity.

• Rodger, Andrew S.; Labrosse, Nicolas; Wedemeyer, Sven; Szydlarski, Mikolaj Marcin; Simões, Paulo J. A. & Fletcher, Lyndsay (2019). First Spectral Analysis of a Solar Plasma Eruption Using ALMA. The Astrophysical Journal (ApJ). ISSN 0004-637X. 875(2). doi: 10.3847/1538-4357/aafdfb. Full text in Research Archive Show summary

  The aim of this study is to demonstrate how the logarithmic millimeter continuum gradient observed using the Atacama Large Millimeter/submillimeter Array (ALMA) may be used to estimate optical thickness in the solar atmosphere. We discuss how using multiwavelength millimeter measurements can refine plasma analysis through knowledge of the absorption mechanisms. Here we use subband observations from the publicly available science verification (SV) data, while our methodology will also be applicable to regular ALMA data. The spectral resolving capacity of ALMA SV data is tested using the enhancement coincident with an X-ray bright point and from a plasmoid ejection event near active region NOAA12470 observed in Band 3 (84–116 GHz) on 2015 December 17. We compute the interferometric brightness temperature light curve for both features at each of the four constituent subbands to find the logarithmic millimeter spectrum. We compared the observed logarithmic spectral gradient with the derived relationship with optical thickness for an isothermal plasma to estimate the structures' optical thicknesses. We conclude, within 90% confidence, that the stationary enhancement has an optical thickness between 0.02 ≤ τ ≤ 2.78, and that the moving enhancement has 0.11 ≤ τ ≤ 2.78, thus both lie near to the transition between optically thin and thick plasma at 100 GHz. From these estimates, isothermal plasmas with typical Band 3 background brightness temperatures would be expected to have electron temperatures of ~7370–15300 K for the stationary enhancement and between ~7440 and 9560 K for the moving enhancement, thus demonstrating the benefit of subband ALMA spectral analysis.

• Essen, Carolina von; Ofir, A.; Dreizler, S.; Agol, E.; Freudenthal, J. & Hernández, J. [Show all 38 contributors for this article] (2018). Kepler Object of Interest Network: I. First results combining ground- and space-based observations of Kepler systems with transit timing variations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 615. doi: 10.1051/0004-6361/201732483. Full text in Research Archive Show summary

  During its four years of photometric observations, the Kepler space telescope detected thousands of exoplanets and exoplanet candidates. One of Kepler’s greatest heritages has been the confirmation and characterization of hundreds of multi-planet systems via transit timing variations (TTVs). However, there are many interesting candidate systems displaying TTVs on such long timescales that the existing Kepler observations are of insufficient length to confirm and characterize them by means of this technique. To continue with Kepler’s unique work, we have organized the “Kepler Object of Interest Network” (KOINet), a multi-site network formed of several telescopes located throughout America, Europe, and Asia. The goals of KOINet are to complete the TTV curves of systems where Kepler did not cover the interaction timescales well, to dynamically prove that some candidates are true planets (or not), to dynamically measure the masses and bulk densities of some planets, to find evidence for non-transiting planets in some of the systems, to extend Kepler’s baseline adding new data with the main purpose of improving current models of TTVs, and to build a platform that can observe almost anywhere on the northern hemisphere, at almost any time. KOINet has been operational since March 2014. Here we show some promising first results obtained from analyzing seven primary transits of KOI-0410.01, KOI-0525.01, KOI-0760.01, and KOI-0902.01, in addition to the Kepler data acquired during the first and second observing seasons of KOINet. While carefully choosing the targets we set demanding constraints on timing precision (at least 1 min) and photometric precision (as good as one part per thousand) that were achieved by means of our observing strategies and data analysis techniques. For KOI-0410.01, new transit data revealed a turnover of its TTVs. We carried out an in-depth study of the system, which is identified in the NASA Data Validation Report as a false positive. Among others, we investigated a gravitationally bound hierarchical triple star system and a planet–star system. While the simultaneous transit fitting of ground- andspace-based data allowed for a planet solution, we could not fully reject the three-star scenario. New data, already scheduled in the upcoming 2018 observing season, will set tighter constraints on the nature of the system.

• Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta, M. & Pontieu, Bart Walter De [Show all 14 contributors for this article] (2018). First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 613. doi: 10.1051/0004-6361/201730656. Full text in Research Archive Show summary

  Context: Various solar features can be seen in emission or absorption on maps of the Sun in the millimetre and submillimetre wavelength range. The recently installed Atacama Large Millimetre/submillimetre Array (ALMA) is capable of observing the Sun in that wavelength range with an unprecedented spatial, temporal and spectral resolution. To interpret solar observations with ALMA, the first important step is to compare solar ALMA maps with simultaneous images of the Sun recorded in other spectral ranges. Aims: The first aim of the present work is to identify different structures in the solar atmosphere seen in the optical, infrared, and EUV parts of the spectrum (quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points) in a full-disc solar ALMA image. The second aim is to measure the intensities (brightness temperatures) of those structures and to compare them with the corresponding quiet Sun level. Methods: A full-disc solar image at 1.21 mm obtained on December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and compared with full-disc solar images from the same day in Hα line, in He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures of various structures are determined by averaging over corresponding regions of interest in the calibrated ALMA image. Results: Positions of the quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points are identified in the ALMA image. At the wavelength of 1.21 mm, active regions appear as bright areas (but sunspots are dark), while prominences on the disc and coronal holes are not discernible from the quiet Sun background, despite having slightly less intensity than surrounding quiet Sun regions. Magnetic inversion lines appear as large, elongated dark structures and coronal bright points correspond to ALMA bright points. Conclusions: These observational results are in general agreement with sparse earlier measurements at similar wavelengths. The identification of coronal bright points represents the most important new result. By comparing ALMA and other maps, it was found that the ALMA image was oriented properly and that the procedure of overlaying the ALMA image with other images is accurate at the 5 arcsec level. The potential of ALMA for physics of the solar chromosphere is emphasised.

• Freudenthal, Jantje; Essen, Carolina von; Dreizler, Stefan; Wedemeyer, Sven; Agol, Eric & Morris, Brett M. [Show all 17 contributors for this article] (2018). Kepler Object of Interest Network: II. Photodynamical modelling of Kepler-9 over 8 years of transit observations. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 618. doi: 10.1051/0004-6361/201833436. Full text in Research Archive Show summary

  Context: The Kepler Object of Interest Network (KOINet) is a multi-site network of telescopes around the globe organised to follow up transiting planet-candidate Kepler objects of interest (KOIs) with large transit timing variations (TTVs). Its main goal is to complete their TTV curves, as the Kepler telescope no longer observes the original Kepler field. Aims: Combining Kepler and new ground-based transit data we improve the modelling of these systems. To this end, we have developed a photodynamical model, and we demonstrate its performance using the Kepler-9 system as an example. Methods: Our comprehensive analysis combines the numerical integration of the system’s dynamics over the time span of the observations along with the transit light curve model. This provides a coherent description of all observations simultaneously. This model is coupled with a Markov chain Monte Carlo algorithm, allowing for the exploration of the model parameter space. Results: Applied to the Kepler-9 long cadence data, short cadence data, and 13 new transit observations collected by KOINet between the years 2014 and 2017, our modelling provides well constrained predictions for the next transits and the system’s parameters. We have determined the densities of the planets Kepler-9b and 9c to the very precise values of ρb = 0.439 ± 0.023 g cm−3 and ρc = 0.322 ± 0.017 g cm−3. Our analysis reveals that Kepler-9c will stop transiting in about 30 yr due to strong dynamical interactions between Kepler-9b and 9c, near 2:1 resonance, leading to a periodic change in inclination. Conclusions: Over the next 30 years, the inclination of Kepler-9c (-9b) will decrease (increase) slowly. This should be measurable by a substantial decrease (increase) in the transit duration, in as soon as a few years’ time. Observations that contradict this prediction might indicate the presence of additional objects in this system. If this prediction turns out to be accurate, this behaviour opens up a unique chance to scan the different latitudes of a star: high latitudes with planet c and low latitudes with planet b.

• Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos, S.; Pontieu, Bart Walter De & Warren, H. [Show all 12 contributors for this article] (2018). First high-resolution look at the quiet Sun with ALMA at 3mm. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 619. doi: 10.1051/0004-6361/201834113. Full text in Research Archive Show summary

  We present an overview of high-resolution quiet Sun observations, from disk center to the limb, obtained with the Atacama Large millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun regions were observed at a resolution of up to 2.5 by 4.5. We produced both average and snapshot images by self-calibrating the ALMA visibilities and combining the interferometric images with full-disk solar images. The images show well the chromospheric network, which, based on the unique segregation method we used, is brighter than the average over the fields of view of the observed regions by ∼305 K while the intranetwork is less bright by ∼280 K, with a slight decrease of the network/intranetwork contrast toward the limb. At 3 mm the network is very similar to the 1600 Å images, with somewhat larger size. We detect, for the first time, spicular structures, rising up to 15 above the limb with a width down to the image resolution and brightness temperature of ∼1800 K above the local background. No trace of spicules, either in emission or absorption, is found on the disk. Our results highlight the potential of ALMA for the study of the quiet chromosphere.

• Bastian, Timothy; Barta, Miroslav; Brajša, Roman; Chen, Bin; Pontieu, Bart Walter De & Gary, D. E. [Show all 18 contributors for this article] (2018). Exploring the Sun with ALMA. The Messenger. ISSN 0722-6691. 171, p. 25–30. doi: 10.18727/0722-6691/5065. Full text in Research Archive Show summary

  The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory opens a new window onto the Universe. The ability to perform continuum imaging and spectroscopy of astrophysical phenomena at millimetre and submillimetre wavelengths with unprecedented sensitivity opens up new avenues for the study of cosmology and the evolution of galaxies, the formation of stars and planets, and astrochemistry. ALMA also allows fundamentally new observations to be made of objects much closer to home, including the Sun. The Sun has long served as a touchstone for our understanding of astrophysical processes, from the nature of stellar interiors, to magnetic dynamos, non-radiative heating, stellar mass loss, and energetic phenomena such as solar flares. ALMA offers new insights into all of these processes. © 2018 European Southern Observatory (ESO)

• Klevas, J.; Kučinskas, A.; Wedemeyer, Sven & Ludwig, H.-G. (2018). Impact of magnetic fields on the structure of convective atmospheres of red giant stars. Contributions of the Astronomical Observatory Skalnate Pleso. ISSN 1335-1842. 48(1), p. 280–281. Full text in Research Archive Show summary

  We use 3D magnetohydrodynamic CO5BOLD model atmospheres to study the interplay between magnetic fields and convection in the atmospheres of red giant stars. We find that vortex-like structures occur prominently in stars with stronger magnetic fields and lead to alterations of their thermal structures.

• Wedemeyer, Sven; Kučinskas, Arūnas; Klevas, Jonas & Ludwig, Hans-Günter (2017). Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars: VI. First chromosphere model of a late-type giant. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 606. doi: 10.1051/0004-6361/201730405. Full text in Research Archive Show summary

  Aims. Although observational data unequivocally point to the presence of chromospheres in red giant stars, no attempts have been made so far to model them using 3D hydrodynamical model atmospheres. We therefore compute an exploratory 3D hydrodynamical model atmosphere for a cool red giant in order to study the dynamical and thermodynamic properties of its chromosphere, as well as the influence of the chromosphere on its observable properties. Methods. Three-dimensional radiation hydrodynamics simulations are carried out with the CO5BOLD model atmosphere code for a star with the atmospheric parameters (Teff ≈ 4010 K, log g = 1.5, [ M / H ] = 0.0), which are similar to those of the K-type giant star Aldebaran (α Tau). The computational domain extends from the upper convection zone into the chromosphere (7.4 ≥ log τRoss ≥ − 12.8) and covers several granules in each horizontal direction. Using this model atmosphere, we compute the emergent continuum intensity maps at different wavelengths, spectral line profiles of Ca ii K, the Ca ii infrared triplet line at 854.2 nm, and Hα, as well as the spectral energy distribution (SED) of the emergent radiative flux. Results. The initial model quickly develops a dynamical chromosphere that is characterised by propagating and interacting shock waves. The peak temperatures in the chromospheric shock fronts reach values of up to 5000 K, although the shock fronts remain quite narrow. Similar to the Sun, the gas temperature distribution in the upper layers of red giant stars is composed of a cool component due to adiabatic cooling in the expanding post-shock regions and a hot component due to shock waves. For this red giant model, the hot component is a rather flat high-temperature tail, which nevertheless affects the resulting average temperatures significantly. Conclusions. The simulations show that the atmospheres of red giant stars are dynamic and intermittent. Consequently, many observable properties cannot be reproduced with static 1D models, but require advanced 3D hydrodynamical modelling. Furthermore, including a chromosphere in the models might produce significant contributions to the emergent UV flux. © ESO, 2017

• White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota, A. & Yagoubov, P. [Show all 34 contributors for this article] (2017). Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping. Solar Physics. ISSN 0038-0938. 292(7). doi: 10.1007/s11207-017-1123-2. Full text in Research Archive Show summary

  This is a post-peer-review, pre-copyedit version of an article published in Solar Physics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11207-017-1123-2

• Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.; Iwai, K. & Hills, R. E. [Show all 28 contributors for this article] (2017). Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric Imaging. Solar Physics. ISSN 0038-0938. 292(7). doi: 10.1007/s11207-017-1095-2. Full text in Research Archive Show summary

  This is a post-peer-review, pre-copyedit version of an article published in Solar Physics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11207-017-1095-2

• Klevas, Jonas; Wedemeyer, Sven; Kucinskas, Arunas & Ludwig, Hans-Günter (2017). 3D hydrodynamical COBOLD simulations of a chromosphere of a red giant. MEMORIE DELLA SOCIETÀ ASTRONOMICA ITALIANA JOURNAL OF THE ITALIAN ASTRONOMICAL SOCIETY. ISSN 0037-8720. 88(1), p. 100–103. doi: 10.1051/0004-6361/201730405. Full text in Research Archive
• Kato, Yoshiaki & Wedemeyer, Sven (2017). Vortex flows in the solar chromosphere: I. Automatic detection method. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 601. doi: 10.1051/0004-6361/201630082. Full text in Research Archive Show summary

  Solar “magnetic tornadoes” are produced by rotating magnetic field structures that extend from the upper convection zone and the photosphere to the corona of the Sun. Recent studies show that these kinds of rotating features are an integral part of atmospheric dynamics and occur on a large range of spatial scales. A systematic statistical study of magnetic tornadoes is a necessary next step towards understanding their formation and their role in mass and energy transport in the solar atmosphere. For this purpose, we develop a new automatic detection method for chromospheric swirls, meaning the observable signature of solar tornadoes or, more generally, chromospheric vortex flows and rotating motions. Unlike existing studies that rely on visual inspections, our new method combines a line integral convolution (LIC) imaging technique and a scalar quantity that represents a vortex flow on a two-dimensional plane. We have tested two detection algorithms, based on the enhanced vorticity and vorticity strength quantities, by applying them to three-dimensional numerical simulations of the solar atmosphere with CO5BOLD. We conclude that the vorticity strength method is superior compared to the enhanced vorticity method in all aspects. Applying the method to a numerical simulation of the solar atmosphere reveals very abundant small-scale, short-lived chromospheric vortex flows that have not been found previously by visual inspection. © ESO, 2017

• Kato, Yoshiaki; Steiner, Oskar; Hansteen, Viggo; Gudiksen, Boris Vilhelm; Wedemeyer, Sven & Carlsson, Mats (2016). Chromospheric and Coronal Wave Generation in a Magnetic Flux Sheath. The Astrophysical Journal (ApJ). ISSN 0004-637X. 827(1). doi: 10.3847/0004-637X/827/1/7. Full text in Research Archive
• Wedemeyer, Sven; Bastian, T.; Brajsa, R.; Hudson, H.; Fleishman, G. & Loukitcheva, M. [Show all 38 contributors for this article] (2016). Solar Science with the Atacama Large Millimeter/Submillimeter Array—A New View of Our Sun. Space Science Reviews. ISSN 0038-6308. 200(1), p. 1–73. doi: 10.1007/s11214-015-0229-9. Full text in Research Archive
• Wedemeyer, Sven & Ludwig, Hans-Günter (2016). Synthetic activity indicators for M-type dwarf stars. Proceedings of the International Astronomical Union. ISSN 1743-9213. 11(S320), p. 303–308. doi: 10.1017/S1743921316000077. Full text in Research Archive
• Scullion, Eamon; Rouppe, Van Der Voort Luc; Antolin, Patrick; Wedemeyer, Sven; Vissers, Gregal Joan Maria & Kontar, E. P. [Show all 7 contributors for this article] (2016). Observing the Formation of Flare-Driven Coronal Rain. The Astrophysical Journal (ApJ). ISSN 0004-637X. 833(2). doi: 10.3847/1538-4357/833/2/184. Full text in Research Archive
• Tremblay, P. E.; Fontaine, G.; Freytag, B.; Steiner, O.; Ludwig, Hans-Günter & Steffen, M. [Show all 8 contributors for this article] (2015). ON the EVOLUTION of MAGNETIC WHITE DWARFS. The Astrophysical Journal (ApJ). ISSN 0004-637X. 812(1). doi: 10.1088/0004-637X/812/1/19. Full text in Research Archive
• Wedemeyer, Sven; Bastian, Timothy; Brajša, Roman; Barta, Miroslav & Shimojo, Masumi (2015). Solar Simulations for the Atacama Large Millimeter Observatory Network. Astronomical Society of the Pacific Conference Series. ISSN 1050-3390. 499, p. 341–342. Full text in Research Archive
• Wedemeyer, Sven; Bastian, Timothy; Brajša, Roman; Barta, Miroslav; Shimojo, Masumi & Hales, Antonio [Show all 8 contributors for this article] (2015). Solar ALMA Observations - A new view of our host star. Astronomical Society of the Pacific Conference Series. ISSN 1050-3390. 499, p. 345–346. Full text in Research Archive
• Wedemeyer, Sven; Bastian, Timothy; Brajša, Roman; Barta, Miroslav; Hudson, Hugh & Fleishman, Gregory [Show all 29 contributors for this article] (2015). SSALMON - The Solar Simulations for the Atacama Large Millimeter Observatory Network. Advances in Space Research. ISSN 0273-1177. 56(12), p. 2679–2692. doi: 10.1016/j.asr.2015.05.027. Full text in Research Archive
• Wedemeyer, Sven & Parmer, Asbjørn Lie (2015). ALMA's high-cadence imaging capabilities for solar observations. Astronomical Society of the Pacific Conference Series. ISSN 1050-3390. 499, p. 343–344. Full text in Research Archive
• Phillips, Neil; Hills, Richard; Bastian, Timothy; Hudson, Hugh; Marson, Ralph & Wedemeyer, Sven (2015). Fast single-dish scans of the Sun using ALMA. Astronomical Society of the Pacific Conference Series. ISSN 1050-3390. 499, p. 347–348. Full text in Research Archive
• Scullion, Eamon; Rouppe, Van Der Voort Luc; Wedemeyer-Böhm, Sven & Antolin, Patrick (2014). Unresolved Fine-Scale Structure in Solar Coronal Loop-Tops. The Astrophysical Journal (ApJ). ISSN 0004-637X. 797(1). doi: 10.1088/0004-637X/797/1/36. Full text in Research Archive Show summary

  New and advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer substructures within coronal loop cross-sections, in order to understand the nature of the solar corona. Here, we push this lower limit further to search for the finest coronal loop substructures, through taking advantage of the resolving power of the Swedish 1 m Solar Telescope/CRisp Imaging Spectro-Polarimeter (CRISP), together with co-observations from the Solar Dynamics Observatory/Atmospheric Image Assembly (AIA). High-resolution imaging of the chromospheric Hα 656.28 nm spectral line core and wings can, under certain circumstances, allow one to deduce the topology of the local magnetic environment of the solar atmosphere where its observed. Here, we study post-flare coronal loops, which become filled with evaporated chromosphere that rapidly condenses into chromospheric clumps of plasma (detectable in Hα) known as a coronal rain, to investigate their fine-scale structure. We identify, through analysis of three data sets, large-scale catastrophic cooling in coronal loop-tops and the existence of multi-thermal, multi-stranded substructures. Many cool strands even extend fully intact from loop-top to footpoint. We discover that coronal loop fine-scale strands can appear bunched with as many as eight parallel strands within an AIA coronal loop cross-section. The strand number density versus cross-sectional width distribution, as detected by CRISP within AIA-defined coronal loops, most likely peaks at well below 100 km, and currently, 69% of the substructure strands are statistically unresolved in AIA coronal loops. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Freij, N.; Scullion, Eamon; Nelson, C. J.; Mumford, S.; Wedemeyer-Böhm, Sven & Erdélyi, R. (2014). The detection of upwardly propagating waves channeling energy from the chromosphere to the low corona. The Astrophysical Journal (ApJ). ISSN 0004-637X. 791(1). doi: 10.1088/0004-637X/791/1/61. Full text in Research Archive Show summary

  There have been ubiquitous observations of wave-like motions in the solar atmosphere for decades. Recent improvements to space- and ground-based observatories have allowed the focus to shift to smaller magnetic structures on the solar surface. In this paper, high-resolution ground-based data taken using the Swedish 1 m Solar Telescope is combined with co-spatial and co-temporal data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) satellite to analyze running penumbral waves (RPWs). RPWs have always been thought to be radial wave propagation that occurs within sunspots. Recent research has suggested that they are in fact upwardly propagating field-aligned waves (UPWs). Here, RPWs within a solar pore are observed for the first time and are interpreted as UPWs due to the lack of a penumbra that is required to support RPWs. These UPWs are also observed co-spatially and co-temporally within several SDO/AIA elemental lines that sample the transition region and low corona. The observed UPWs are traveling at a horizontal velocity of around 17 ± 0.5 km s–1 and a minimum vertical velocity of 42 ± 21 km s–1. The estimated energy of the waves is around 150 W m–2, which is on the lower bound required to heat the quiet-Sun corona. This is a new, yet unconsidered source of wave energy within the solar chromosphere and low corona. Reproduced with permission from the Astrophysical Journal. © IOP Publishing

• Wedemeyer-Böhm, Sven & Steiner, Oskar (2014). On the plasma flow inside magnetic tornadoes on the Sun. Publications of the Astronomical Society of Japan (PASJ). ISSN 0004-6264. 66(1). doi: 10.1093/pasj/psu086. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Scullion, Eamon; Rouppe, Van Der Voort Luc; Bosnjak, Antonija & Antolin, Patrick (2013). Are Giant Tornadoes the Legs of Solar Prominences? The Astrophysical Journal (ApJ). ISSN 0004-637X. 774(2). doi: 10.1088/0004-637X/774/2/123. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Scullion, Eamon; Steiner, Oskar; Rodriguez, Jaime de la Cruz & Rouppe, Van Der Voort Luc (2013). Magnetic tornadoes and chromospheric swirls - Definition and classification. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 440(1). doi: 10.1088/1742-6596/440/1/012005. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Ludwig, Hans-Günter & Steiner, Oskar (2013). Three-dimensional magnetohydrodynamic simulations of M-dwarf chromospheres. Astronomical Notes - Astronomische Nachrichten. ISSN 0004-6337. 334(1-2), p. 137–140. doi: 10.1002/asna.201211741. Full text in Research Archive
• Ayres, T. R.; Lyons, J. R.; Ludwig, Hans-Günter; Caffau, E. & Wedemeyer-Böhm, Sven (2013). Solar carbon monoxide: poster child for 3D effects. Memorie della Societa Astronomica Italiana Supplement. ISSN 1824-0178. 24, p. 85–95. Full text in Research Archive
• Wedemeyer-Böhm, Sven (2013). The CO5BOLD analysis tool. Memorie della Societa Astronomica Italiana Supplement. ISSN 1824-0178. 24, p. 96–99. Full text in Research Archive
• Ayres, T. R.; Lyons, J. R.; Ludwig, Hans-Günter; Caffau, E. & Wedemeyer-Böhm, Sven (2013). IS THE SUN LIGHTER THAN THE EARTH? ISOTOPIC CO IN THE PHOTOSPHERE, VIEWED THROUGH THE LENS OF THREE-DIMENSIONAL SPECTRUM SYNTHESIS. The Astrophysical Journal (ApJ). ISSN 0004-637X. 765(1). doi: 10.1088/0004-637X/765/1/46. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Scullion, Eamon; Steiner, O.; Rouppe, Van Der Voort Luc; Rodriguez, Jaime de la Cruz & Fedun, V. [Show all 7 contributors for this article] (2012). Magnetic tornadoes as energy channels into the solar corona. Nature. ISSN 0028-0836. 486(7404), p. 505–508. doi: 10.1038/nature11202. Full text in Research Archive
• Freytag, Bernd; Steffen, Matthias; Ludwig, Hans-Günter; Wedemeyer-Böhm, Sven; Schaffenberger, Werner & Steiner, Oskar (2012). Simulations of stellar convection with CO5BOLD. Journal of Computational Physics. ISSN 0021-9991. 231(3), p. 919–959. doi: 10.1016/j.jcp.2011.09.026. Full text in Research Archive
• Wedemeyer-Böhm, Sven & Carlsson, Mats (2011). Non-equilibrium calcium ionisation in the solar atmosphere. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 528. doi: 10.1051/0004-6361/201016186. Full text in Research Archive
• Wedemeyer-Böhm, Sven (2010). Small-scale structure and dynamics of the chromospheric magnetic field. MEMORIE DELLA SOCIETÀ ASTRONOMICA ITALIANA JOURNAL OF THE ITALIAN ASTRONOMICAL SOCIETY. ISSN 0037-8720. 81, p. 693–700. Full text in Research Archive
• Haberreiter, Margit; Finsterle, W; McIntosh, S.W. & Wedemeyer-Böhm, Sven (2010). Toward the analysis of waves in the solar atmosphere based on NLTE spectral synthesis from 3D MHD simulations. MEMORIE DELLA SOCIETÀ ASTRONOMICA ITALIANA JOURNAL OF THE ITALIAN ASTRONOMICAL SOCIETY. ISSN 0037-8720. 81, p. 782–785. Full text in Research Archive
• Wöger, Friedrich; Wedemeyer-Böhm, Sven; Uitenbroek, H. & Rimmele, T. R. (2010). Recovering the line-of-sight magnetic field in the chromosphere from Ca II IR spectra. MEMORIE DELLA SOCIETÀ ASTRONOMICA ITALIANA JOURNAL OF THE ITALIAN ASTRONOMICAL SOCIETY. ISSN 0037-8720. 81, p. 598–603. Full text in Research Archive
• Kjeldseth-Moe, Olav & Wedemeyer-Böhm, Sven (2010). Are there variations in Earth's global mean temperature related to the solar activity? Proceedings of the International Astronomical Union. ISSN 1743-9213. 5, p. 320–325. doi: 10.1017/S1743921309992869. Full text in Research Archive
• Wöger, Friedrich; Wedemeyer-Böhm, Sven; Uitenbroek, H. & Rimmele, T. R. (2009). MORPHOLOGY AND DYNAMICS OF THE LOW SOLAR CHROMOSPHERE. The Astrophysical Journal (ApJ). ISSN 0004-637X. 706(1), p. 148–157. doi: 10.1088/0004-637X/706/1/148. Full text in Research Archive
• Wedemeyer-Böhm, Sven & Rouppe, Van Der Voort Luc (2009). On the continuum intensity distribution of the solar photosphere. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 503(1), p. 225–239. doi: 10.1051/0004-6361/200911983. Full text in Research Archive
• Wedemeyer-Böhm, Sven & Rouppe, Van Der Voort Luc (2009). The solar continuum intensity distribution. Settling the conflict between observations and simulations. MEMORIE DELLA SOCIETÀ ASTRONOMICA ITALIANA JOURNAL OF THE ITALIAN ASTRONOMICAL SOCIETY. ISSN 0037-8720. 80, p. 638–638. Full text in Research Archive
• Wedemeyer-Böhm, Sven & Rouppe, Van Der Voort Luc (2009). Small-scale swirl events in the quiet Sun chromosphere. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 507(1), p. L9–L12. doi: 10.1051/0004-6361/200913380. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Lagg, Andreas & Nordlund, Åke (2009). Coupling from the Photosphere to the Chromosphere and the Corona. Space Science Reviews. ISSN 0038-6308. 144(1-4), p. 317–350. doi: 10.1007/s11214-008-9447-8. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Lagg, Andreas & Nordlund, Åke (2008). Coupling from the photosphere to the chromosphere and the corona. Space Science Reviews. ISSN 0038-6308. OnlineFirst. doi: 10.1007/s11214-008-9447-8. Full text in Research Archive
• Wedemeyer-Böhm, Sven & Wöger, Friedrich (2008). Small-scale structure and dynamics of the lower solar atmosphere. In Erdélyi, R. & Mendoza-Briceno, C. A. (Ed.), Waves and Oscillations in the Solar Atmosphere: Heating and Magneto-Seismology. Cambridge University Press. ISSN 9780521874694. p. 66–73. Full text in Research Archive
• Wedemeyer-Böhm, Sven (2008). Point spread functions for the Solar optical telescope onboard Hinode. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 487, p. 399–412. doi: 10.1051/200809819. Full text in Research Archive
• Steiner, Oskar; Rezaei, Rezza; Schaffenberger, Werner & Wedemeyer-Böhm, Sven (2008). The Horizontal Internetwork Magnetic Field: Numerical Simulations in Comparison to Observations with Hinode. The Astrophysical Journal (ApJ). ISSN 0004-637X. 680(1), p. L85–L88. Full text in Research Archive
• Leenaarts, Jorrit; Wedemeyer-Böhm, Sven; Carlsson, Mats Per-Olof & Hansteen, Viggo (2007). Non-equilibrium Hydrogen Ionization in the Solar Atmosphere. In Heinzel, Petr; Dorotovic, Ivan & Rutten, Robert (Ed.), The Physics of Chromospheric Plasmas. Astronomical Society of the Pacific. ISSN 9781583812365. p. 103–106. Full text in Research Archive
• Wedemeyer-Böhm, Sven & Steffen, M. (2007). Carbon monoxide in the solar atmosphere II. Radiative cooling by CO lines. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 462, p. L31–L35. doi: 10.1051/20066173. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Ludwig, HG; Steffen, M.; Leenaarts, J. & Freytag, B. (2007). Inter-network regions of the Sun at millimetre wavelengths. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 471, p. 977–991. doi: 10.1051/20077588. Full text in Research Archive
• Wedemeyer-Böhm, Sven; Steiner, O.; Bruls, J. & Rammacher, W. (2007). What is Heating the Quiet-Sun Chromosphere? In Heinzel, Petr; Dorotovic, Ivan & Rutten, Robert (Ed.), The Physics of Chromospheric Plasmas. Astronomical Society of the Pacific. ISSN 9781583812365. p. 93–102. Full text in Research Archive
• Rezaei, R.; Steiner, O.; Wedemeyer-Böhm, Sven; Schlichenmaier, R.; Schmidt, W. & Lites, B.W. (2007). Hinode observations reveal boundary layers of magnetic elements in the solar photosphere. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 476, p. L33–L36. doi: 10.1051/20078371. Full text in Research Archive
• Steiner, O.; Vigeesh, G.; Krieger, L.; Wedemeyer-Böhm, Sven; Schaffenberger, W. & Freytag, B. (2007). First local helioseismic experiments with CO(5)BOLD. Astronomical Notes - Astronomische Nachrichten. ISSN 0004-6337. 328. doi: 10.1002/asna.200610738. Full text in Research Archive
• Leenaarts, Jorrit & Wedemeyer-Boehm, S. (2006). Time-dependent hydrogen ionisation in 3D simulations of the solar chromosphere - Methods and first results. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 460, p. 301–307. Full text in Research Archive

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• Kirkaune, Mats; Wedemeyer, Sven; Carlsson, Mats & Brunvoll, Aline Rangøy (2026). Exploring synthetic nanoflare signatures at millimetre wavelengths. Full text in Research Archive Show summary

  Nanoflares have long been considered to be promising candidates for heating the solar corona to millions of degrees. However, their assumed small sizes, short durations, and subtle signals in accessible observables have made direct detection difficult. In the millimetre regime, the Atacama Large (sub-)Millimeter Array (ALMA) offers the capability of measuring chromospheric temperatures at very high temporal and comparatively high spatial resolution. Yet, it is not clear if the currently offered solar observing mode of ALMA is capable of detecting nanoflares. To explore possible millimetre signatures of nanoflares, the F-CHROMA grid of 1D RADYN flare models has been extended to lower total flare energies, into the nanoflare domain. These models simulate the response of a coronal loop to an electron beam inserted at its top. The new simulations were run as a combined effort to characterise nanoflare signatures at different wavelengths. The radiative transfer code RH1.5 was used to compute the millimetre signatures of the modelled nanoflares. These signatures were then degraded to the temporal and spatial resolution achievable with ALMA. The synthetic ALMA light curves indicate that, in principle, ALMA should be able to detect nanoflare signatures, especially when using wider array configurations in combination with a higher frequency band to maximise spatial resolution. This suggests that dedicated ALMA observations could, in principle, place important constraints on atmospheric heating from nanoflares.

• Kirkaune, Mats & Wedemeyer, Sven (2026). Observing the Sun with AtLAST. Full text in Research Archive Show summary

  The Atacama Large Aperture Submillimeter Telescope (AtLAST) has great potential for solar physics. AtLAST’s unique combination of a large aperture, a wide field-of-view, fast mapping speed, and multi-pixel instrumentation could enable it to map the full solar disk across multiple frequencies at high temporal resolution, effectively mapping the thermal and magnetic structure across the chromosphere, and how these change in time. This would help address several important solar science cases. AtLAST’s capabilities would be complementary to the Atacama Large (sub-)Millimeter Array (ALMA) and to other major solar(-capable) observatories of the future, such as the Square Kilometer Array Observatory (SKAO) in South Africa and Australia, and the European Solar Telescope in Spain.

• Kirkaune, Mats; Wedemeyer, Sven; Marrewijk, Joshiwa van; Mroczkowski, Tony & Morris, Thomas (2026). Simulated solar observations with the Atacama Large Aperture Submillimetre Telescope (AtLAST). Full text in Research Archive Show summary

  Millimetre observations offer a highly complementary view of the Sun, providing insight into the thermal and magnetic structure of the chromosphere. The field of solar millimetre astronomy has seen considerable progress since the advent of solar observations with the Atacama Large (sub-)Millimeter Array (ALMA), offering a view of the solar chromosphere at high spatial and temporal resolution. However, some highly dynamic phenomena, such as solar flares, are hard to predict, and therefore challenging to capture with ALMA’s small field of view. The proposed Atacama Large Aperture Submillimetre Telescope (AtLAST), a next-generation 50-m aperture multi-purpose facility, could greatly complement ALMA, offering diagnostic capabilities not currently provided by existing facilities. AtLAST’s large field of view, fast scan speed, and multi-band instruments could allow for mapping the solar disk at adequate spatial resolution, at several frequencies simultaneously, and at a comparatively high cadence. The utilisation of multi-pixel instruments would make AtLAST capable of completing such scans on short timescales, enabling the creation of three-dimensional maps of the solar chromosphere at high temporal resolution. This would allow for monitoring the temperature and magnetic field of the active chromosphere on a global scale, and at an unprecedentedly high cadence, going beyond the capabilities of current facilities in the (sub-)millimetre regime. It is evident that AtLAST has the potential to produce data that would prove highly useful for solar physics. In the presented study, we have therefore explored its potential capabilities by using the multi-purpose (sub-)mm telescope simulator maria. By testing different instrumental setups and scan strategies, we find that 1st generation instrumentation at AtLAST should be able to produce full-disk solar maps on sub-minute timescales across its frequency range. With a more ambitious 2nd generation instrument, it is likely that the temporal resolution could be pushed to a few seconds. The foreseen capabilities would facilitate the detection of all solar flares above AtLAST’s sensitivity threshold, as continuously scanning the solar disk is likely to capture any fast-evolving dynamic phenomena at the covered spatial and temporal scales.

• Glans-Doré, Marie & Wedemeyer, Sven (2026). Steven Spielberg er overbevist om at vi ikke er alene i universet. Full text in Research Archive Show summary

  Hva er oddsen for at stjerneregissøren har rett? Økende, skal vi tro forskerne.

• Hestvik, Ingebjørg & Wedemeyer, Sven (2026). Nå vet vi mer om hvilke planeter som kan ha liv - Titan.uio.no. Full text in Research Archive
• Kanestrøm, Jorunn & Wedemeyer, Sven (2026). Derfor trenger vi et nasjonalt romværvarsel - Forskningsnytt. Full text in Research Archive
• Kanestrøm, Jorunn & Wedemeyer, Sven (2026). Kraftige soleksplosjoner kan frigjøre energi tilsvarende Norges strømforbruk i millioner av år - Titan.uio.no. Full text in Research Archive
• Vogt, Yngve & Wedemeyer, Sven (2026). Drømmen er å varsle soleksplosjoner før de skjer - Titan.uio.no. Full text in Research Archive
• Vogt, Yngve & Wedemeyer, Sven (2026). Bedre romværvarsler kan redde satellitter og strømnettet - Forskningsnytt. Full text in Research Archive
• Wedemeyer, Sven (2026). Radio and Millimeter Observations of the Sun - Probing the Solar Origins of Space Weather. Full text in Research Archive
• Wedemeyer, Sven (2026). Fra solstorm til nordlys: Solens påvirkning på jorden. Full text in Research Archive
• Wedemeyer, Sven (2026). The Heliosphere and Its Protective Role in Planetary Systems. Full text in Research Archive
• Wedemeyer, Sven (2026). Radio and (Sub-)Millimeter Observations of the Sun: Current Status, Future Perspectives, and the Path Toward AtLAST. Full text in Research Archive
• Wedemeyer, Sven (2026). 3D CO + MHD simulations with CO5BOLD. Full text in Research Archive
• Wedemeyer, Sven (2026). The Sun observed at long wavelengths. Full text in Research Archive
• Facchini, Stefano; Hodge, Jacqueline; Jørgensen, Jes; Schinnerer, Eva; Tan, Gie Han & Bakx, Tom [Show all 30 contributors for this article] (2025). Towards ALMA2040: An update from the European community and invitation to contribute. doi: 10.48550/ARXIV.2512.15652. Full text in Research Archive Show summary

  Over the last 15 years, the Atacama Large Millimeter/submillimeter Array (ALMA) has revolutionized astrophysics by providing unprecedented resolution and sensitivity in observing the cold universe, including the formation of stars, planets, and galaxies. With groundbreaking discoveries ranging from the first detailed images of protoplanetary disks to the kinematics of galaxies in the Epoch of Reionization, ALMA has showcased the vast discovery potential of the (sub-)mm wavelength regime. However, in another 15 years from now--in the 2040s--the science landscape will have changed dramatically as new major observational facilities will have started their operations or have come towards advanced maturity in their scientific outcome (e.g., JWST, Rubin Observatory, ELT, Euclid, Gaia, Plato, Ariel, Roman Space Telescope, SPHEREx, LiteBIRD, LISA, SKA and others). At the same time, ALMA's current Wideband Sensitivity Upgrade will have been in place for ~10 years, and ALMA itself will have been operational for 30 years. To fully exploit this era, the community needs a next-generation facility operating at (sub-)mm wavelengths with capabilities far beyond those possible within ALMA's current infrastructure. To this end, ALMA2040 is a community-driven initiative to define the key scientific questions of the 2040s and translate them into a technical vision for a next-generation transformational (sub-)millimeter facility. Our goal with this document is to summarize the current status of the effort, synthesize outcomes from the 2025 workshops, outline next steps toward a reference design concept, and invite broad participation from the global mm/sub-mm community to help shape this future facility. In the following we provide details on the process and scope. We invite everyone who wishes to join the effort and/or contribute to the dedicated White Papers planned for 2026.

• Wedemeyer, Sven; Kirkaune, Mats; Gunar, Stanislav; Hudson, Hugh; Mohan, Atul & Simões, Paulo [Show all 22 contributors for this article] (2025). Radio and Millimeter Observations of the Sun - Probing the Solar Origins of Space Weather. Full text in Research Archive Show summary

  Observations at radio and millimeter wavelengths provide a unique window into the thermal and magnetic structure of the solar chromosphere and corona, where the solar drivers of space weather are rooted. The Atacama Large Millimeter/submillimeter Array (ALMA) has marked a major advance in solar observations by providing unprecedented spatial and temporal resolution. These capabilities enable detailed studies of dynamic small-scale processes that are fundamental to the mechanisms driving solar flares, coronal mass ejections, and the acceleration of solar energetic particles. Looking ahead, the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST), a 50-meter single-dish facility, would deliver rapid multi-wavelength full-disk scans with cadences of one minute or less - an essential capability for capturing fast-evolving solar phenomena. The Square Kilometer Array (SKA), currently under construction, will observe at lower frequencies, thus probing the Sun’s corona. Beyond advancing fundamental physical understanding, solar observations at millimeter wavelengths hold strong potential for space weather forecasting. They provide sensitive diagnostics of chromospheric and coronal heating and dynamics, offering real-time constraints for models used in operational prediction systems. The Solaris project - designed to enable continuous, year-round observations from sites in Antarctica and the Arctic - will serve as an important demonstrator of this capability. This poster will present recent advances in solar radio/mm observations, highlight synergies with forward modeling and data-driven simulations, and outline opportunities with upcoming facilities such as AtLAST, Solaris, and SKA. Together, these developments demonstrate the growing role of millimeter observations both in unraveling the solar origins of space weather and in providing critical observational input for future forecasting frameworks.

• Wedemeyer, Sven (2025). A Complementary View of Solar and Stellar Activity at Millimeter Wavelengths. Full text in Research Archive
• Wedemeyer, Sven (2025). Millimeter-wavelength Observations of the Sun. Full text in Research Archive
• Wedemeyer, Sven; Peter, Hardi & Socas-Navarro, Hector (2025). European-led Ground-Based Solar Physics Research - Perspectives and Future Facilities. Full text in Research Archive Show summary

  Ground-based solar physics in Europe is undergoing a transformative phase, driven by the development of next-generation observational facilities and upgrades to existing infrastructures. This presentation will explore the scientific potential of key projects, including the European Solar Telescope (EST), the Atacama Large Aperture Submillimeter Telescope (AtLAST), and the potential upgrades of the Atacama Large Millimeter/submillimeter Array (ALMA2040). Besides advancing our understanding of the Sun, these facilities would provide unprecedented insights into the fundamental processes governing solar activity, with broad implications for space weather forecasting and our understanding of exoplanet host stars. EST, with its 4-meter aperture and advanced instrumentation, will enable unprecedented high-resolution studies of solar magnetism and dynamics, complementing space-based observations. AtLAST, the proposed single-dish 50m submillimeter telescope, will bridge the gap between ALMA’s interferometric capabilities and large-scale solar observations, allowing for monitoring of the solar atmosphere with high temporal resolution. In parallel, upgrades to ALMA would enhance its ability to probe the solar chromosphere at millimeter wavelengths, providing key insights into atmospheric heating and dynamics.

• Wedemeyer, Sven (2025). Solar and stellar observations with AtLAST. Full text in Research Archive
• Wedemeyer, Sven (2025). Multispectral Observations of the Sun: Infrared to Millimeter Wavelengths. Full text in Research Archive
• Wedemeyer, Sven (2024). The Sun, Stars and Sternchen. Full text in Research Archive
• Wedemeyer, Sven (2024). The Sun and stars at mm and radio wavelengths. Full text in Research Archive
• Kirkaune, Mats; Wedemeyer, Sven; Marrewijk, Joshiwa Van & Mroczkowski, Tony (2024). Fast On-the-Fly Scanning of the Solar Disk with AtLAST. Full text in Research Archive
• Kirkaune, Mats; Wedemeyer, Sven; Marrewijk, Joshiwa Van; Mroczkowski, Tony & Morris, Thomas W. (2024). Simulating fast on-the-fly observations of the Sun with AtLAST. Full text in Research Archive
• Wedemeyer, Sven (2024). Broadening ALMA's Scientific Potential through Wideband Observations of the Sun. Full text in Research Archive
• Wedemeyer, Sven (2024). A complementary perspective on our Sun and other stars with AtLAST. Full text in Research Archive
• Wedemeyer, Sven; Barta, Miroslav; Brajša, Roman; Chai, Yi; Costa, Joaquim E. R & Gary, Dale [Show all 38 contributors for this article] (2024). Observing our Sun with AtLAST. Full text in Research Archive
• Wedemeyer, Sven & Kirkaune, Mats (2024). Solar Observations with the Atacama Large Aperture Submillimeter Telescope. Full text in Research Archive
• Shan, Yutong; Wedemeyer, Sven; Werner, Stephanie C. & Mamonova, Elena (2024). En leteaksjon av en annen verden: Kavliprisen i astrofysikk for 2024 hedrer forskerne som har pionert studien av eksoplaneter. Bladet Astronomi. Full text in Research Archive
• Pandit, Sneha; Wedemeyer, Sven & Carlsson, Mats (2023). Comparison of activity indicators in a 3D model atmosphere. Full text in Research Archive
• Pandit, Sneha; Wedemeyer, Sven & Carlsson, Mats (2023). Comparison of activity indicators in a 3D model atmosphere. Full text in Research Archive
• Wedemeyer, Sven (2023). Radio and millimeter observations of the Sun - Recent advances and future opportunities. Full text in Research Archive
• Wedemeyer, Sven & Kirkaune, Mats (2023). Observing the Sun with AtLAST - Prospects and Challenges. Full text in Research Archive
• Wedemeyer, Sven & Szydlarski, Mikolaj (2023). Artificial observations of the Sun – The scientific potential of optimizing future solar observatories. Full text in Research Archive
• Saberi, Maryam; Khouri, T.; Velilla-Prieto, L.; Fonfria, J. P.; Vlemmings, W. & Wedemeyer, Sven (2022). Tracing the role of AGB stars in the Galactic Fluorine budget. Full text in Research Archive
• Gomez, Juan Camilo Guevara; Jafarzadeh, Shahin & Wedemeyer, Sven (2022). Characterisation of bright chromospheric and oscillating small-scale features observed with ALMA. Full text in Research Archive
• Pandit, Sneha; Wedemeyer, Sven & Mohan, Atul (2022). Formation of Activity Indicators in a 3D model Atmosphere. Full text in Research Archive
• Pandit, Sneha; Wedemeyer, Sven & Mohan, Atul (2022). The Formation of Activity Indicators in 3D Model Atmosphere. Full text in Research Archive
• Pandit, Sneha; Wedemeyer, Sven & Carlsson, Mats (2022). Formation of Activity Indicators in a 3D Model Atmosphere. Full text in Research Archive
• Wedemeyer, Sven; Sand, Mats Ola; Øyre, Eilif Sommer & D`Angelo, Martina (2022). På jakt etter eksoplaneter. Full text in Research Archive
• Mohan, Atul; Wedemeyer, Sven; Pandit, Sneha; Saberi, Maryam & Hauschildt, Peter, H. (2022). A potential robust millimeter activity index & its links to atmospheric structure and physical parameters. Full text in Research Archive
• Mohan, Atul; Oberoi, Divya; Wedemeyer, Sven; Mondal, Surajit; McCauley, Patrick & Mastrano, Alpha [Show all 9 contributors for this article] (2022). Tomographic exploration of solar/stellar activity with modern radio & mm arrays. Full text in Research Archive
• Mohan, Atul; Wedemeyer, Sven; Oberoi, Divya; Hauschildt, Peter, H.; McCauley, Patrick & Mondal, Surajit [Show all 9 contributors for this article] (2022). New insights on solar/stellar activity using the tomographic potential of mm & radio spectroscopic imaging. Full text in Research Archive
• Mohan, Atul; Wedemeyer, Sven; Hauschildt, Peter, H.; Pandit, Sneha & Saberi, Maryam (2022). Stellar atmospheric tomography with mm - cm spectroscopic imaging. Full text in Research Archive
• Pandit, Sneha; Wedemeyer, Sven & Mohan, Atul (2022). Formation of Activity Indicators in a 3D model atmosphere. Full text in Research Archive
• Gomez, Juan Camilo Guevara; Jafarzadeh, Shahin & Wedemeyer, Sven (2021). Oscillations in chromospheric small-scale bright features observed with ALMA. Full text in Research Archive
• Saberi, Maryam; Khouri, Theo; Velilla-Prieto, L.; Fonfria, . P.; Vlemmings, W. & Wedemeyer, Sven (2021). Tracing the role of AGB stars in the Galactic Fluorine budget. Full text in Research Archive
• Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Henriques, Vasco Manuel de Jorge; Eklund, Henrik & Gomez, Juan Camilo Guevara [Show all 10 contributors for this article] (2021). Observing the Sun with ALMA - First results and future opportunities. Full text in Research Archive
• Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Henriques, Vasco Manuel de Jorge; Eklund, Henrik & Gomez, Juan Camilo Guevara [Show all 10 contributors for this article] (2021). Five years observing the solar chromosphere with ALMA - First results and future opportunities. Full text in Research Archive
• Pandit, Sneha & Wedemeyer, Sven (2021). The sun as a star: new insights from the full disk observations with ALMA. Full text in Research Archive
• Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Henriques, Vasco; Gomez, Juan Camilo Guevara & Eklund, Henrik [Show all 10 contributors for this article] (2021). Lessons learned from 5 years of solar observing with ALMA. Full text in Research Archive
• Wedemeyer, Sven (2021). Sola over Atacama-ørkenen. Astronomi. ISSN 0802-7587. 2, p. 36–39. Full text in Research Archive
• Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Henriques, Vasco; Eklund, Henrik & Gomez, Juan Camilo Guevara [Show all 11 contributors for this article] (2021). A brief introduction to solar observing with ALMA. Full text in Research Archive
• Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin; Henriques, Vasco; Eklund, Henrik & Gomez, Juan Camilo Guevara [Show all 10 contributors for this article] (2021). Five years observing the solar chromosphere with ALMA - First results and future opportunities. Full text in Research Archive
• Jafarzadeh, Shahin; Gafeira, Ricardo; Wedemeyer, Sven & Szydlarski, Mikolaj (2021). MHD waves in chromospheric fibrillar structures as observed with ALMA. Full text in Research Archive
• Gomez, Juan Camilo Guevara & Wedemeyer, Sven (2021). Dynamics of small-scale dark features observed by the Atacama Large Millimeter/submillimeter Array (ALMA). Full text in Research Archive
• Saberi, Maryam; Jafarzadeh, Shahin; Gafeira, Ricardo; Wedemeyer, Sven & Szydlarski, Mikolaj (2021). MHD waves in chromospheric fibrillar structures as observed with ALMA. Full text in Research Archive
• Gomez, Juan Camilo Guevara; Jafarzadeh, Shahin & Wedemeyer, Sven (2021). Oscillations in small-scale bright features observed with ALMA. Full text in Research Archive Show summary

  Small-scale chromospheric bright features in a plage/enhanced network are identified in solar ALMA observations. The features present oscillations in brightness temperature, size and horizontal velocity. Interestingly, an anti-correlation between brightness temperature and size is also evident, suggesting that these features might be associated to fast-sausage MHD modes. A statistical analysis is carried out to quantify the oscillation periods of the three quantities and the phase angles between the perturbations in temperature and size. The values found are in agreement with periods of high frequency oscillations in other layers of the solar atmosphere.

• Gomez, Juan Camilo Guevara & Wedemeyer, Sven (2021). Dynamics of small-scale dark features observed by the Atacama Large Millimeter/Submillimeter Array (ALMA). Full text in Research Archive Show summary

  Observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA) now allow for more quantitative determination of temperatures in the chromosphere. ALMA observations of Quiet Sun regions in receiver Band 3 (3 mm; 100 GHz) exhibit small-scale features that resemble a mesh-like chromospheric pattern, similar to what was earlier detected with other chromospheric diagnostics. Tracking the features in time results in lifetimes, velocities and sizes, which are analysed within the context given by co-aligned images of the Solar Dynamics Observatory (SDO). Here we present a statistical analysis and compare the results with a 3D MHD simulation with Bifrost of an enhanced network which has been degraded to the ALMA spatial resolution. The match between observations and simulations suggests that the dark features are post-shock regions. The thermodynamics and kinetic properties derived from the ALMA observations will therefore enhance our understanding of the small-scale dynamics and heating of the solar chromosphere and its potential implications for other solar-like stars.

• Wedemeyer, Sven (2020). Observing the Sun with ALMA – Challenges, scientific potential, and first results. Full text in Research Archive
• Wedemeyer, Sven (2020). Development of tools for solar research with ALMA at RoCS. Full text in Research Archive
• Eklund, Henrik; Szydlarski, Mikolaj Marcin & Wedemeyer, Sven (2020). Image reconstruction of interferometric ALMA data. Full text in Research Archive
• White, Stephen; Barta, Miroslav; Bastian, Timothy; Shimojo, Masumi & Wedemeyer, Sven (2020). Correlator Desiderata for Solar Radiophysics at ALMA. Full text in Research Archive
• Wedemeyer, Sven (2020). Magnetic Tornadoes on the Sun. Full text in Research Archive
• Wedemeyer, Sven (2019). Solar Astronomy with ALMA. Full text in Research Archive Show summary

  Solar observing with ALMA is offered as a non-standard mode since Cycle 4. The requirements for such observations are different from many other observations with ALMA in the sense that the mapped atmospheric layers of the Sun evolve on very short timescales and the primary beam being filled with complex emission. High-cadence (snapshot) imaging is needed for such a dynamic target but is very challenging. The effort and time that went into developing the observing mode seems well justified given that ALMA provides a new complementary view at a part of the solar atmosphere that is still elusive in many aspects. The solar observing campaigns with ALMA are co-ordinated with a number of space-borne and ground-based telescopes covering the UV to IR range. Co-ordinating such strictly simultaneous multi-telescope observations adds another layer of complexity but results in rich data sets covering all layers of the solar atmosphere while probing different properties of the atmospheric gas. Since Cycle 4, the imaging procedures for solar ALMA observations have been significantly improved and science-ready data are being produced. I will give a brief overview over ALMA's diagnostic potential for the Sun and challenges with carrying out solar observations and post-processing the data. First examples for Band 3 and Band 6 data are presented and illustrate the dynamic nature of the solar atmosphere, featuring, among other things, the imprint of magnetic fields and propagating shock waves.

• Jafarzadeh, Shahin; Voort, Luc H.M. Rouppe van der; Wedemeyer, Sven & Noda, Carlos Quintero (2019). Magnetic-field topology of fibrillar structures throughout the solar chromosphere. Full text in Research Archive
• Jafarzadeh, Shahin; Wedemeyer, Sven; Noda, Carlos Quintero; Wiegelmann, Thomas & Voort, Luc Rouppe van der (2019). Magnetic-field topology throughout the solar chromosphere. Full text in Research Archive
• Wedemeyer, Sven (2019). High-cadence imaging of the Sun. Full text in Research Archive Show summary

  A challenge of observing the Sun with ALMA is that the primary beam covers only a small region on the Sun and is therefore filled with a complex radiation pattern, which evolves on extremely short time scales of only seconds and below. Fully exploiting ALMA's possibilities therefore requires imaging at very high cadence. Accordingly, there is much potential for improving the solar observing modes and post-processing of data. The development study "High-cadence imaging of the Sun", which started in 2018, aims at developing a high-cadence imaging capability by employing realistic test cases based on state-of-the-art numerical simulations, the Solar ALMA Simulator tool, and a solar simulation pipeline. Comparisons between the input and output of the simulation pipeline will reveal how well imaging at high cadence performs and how to optimize it. We present an overview of the study and its current state.

• Jafarzadeh, Shahin; Wedemeyer, Sven; Szydlarski, Mikolaj Marcin; Fleck, Bernhard & Stangalini, Marco (2019). Wave heating of the solar chromosphere from observations with ALMA. Full text in Research Archive
• Jafarzadeh, Shahin; Wedemeyer, Sven; Szydlarski, Mikolaj Marcin & Fleck, Bernhard (2019). Wave heating of the lower solar atmosphere. Full text in Research Archive
• Jafarzadeh, Shahin & Wedemeyer, Sven (2019). Observing Waves in the Lower Solar Atmosphere with ALMA. Full text in Research Archive
• Jafarzadeh, Shahin; Wedemeyer, Sven & Szydlarski, Mikolaj Marcin (2019). Temperature Fluctuations in the Solar Chromosphere with ALMA. Full text in Research Archive
• Gomez, Juan Camilo Guevara; Wedemeyer, Sven; Jafarzadeh, Shahin & Szydlarski, Mikolaj Marcin (2019). Dynamics of solar isolated features observed by the Atacama Large Millimeter/submillimeter Array (ALMA). Full text in Research Archive
• Wedemeyer, Sven (2019). Our Dynamic Sun. Full text in Research Archive
• Gomez, Juan Camilo Guevara; Wedemeyer, Sven; Jafarzadeh, Shahin & Szydlarski, Mikolaj Marcin (2019). Structure and dynamics of isolated features in the solar chromosphere observed with ALMA. Full text in Research Archive
• Wedemeyer, Sven (2019). Solar science with ALMA in Norway. Full text in Research Archive
• Wedemeyer, Sven (2019). High-tech and llamas. Full text in Research Archive
• Wedemeyer, Sven (2019). Magnetic Field Measurements with the Atacama Millimeter/submillimeter Array. Full text in Research Archive
• Eklund, Henrik; Szydlarski, Mikolaj Marcin & Wedemeyer, Sven (2019). Shock wave propagation with high cadence solar ALMA time series. Full text in Research Archive
• Eklund, Henrik; Szydlarski, Mikolaj Marcin & Wedemeyer, Sven (2018). Interferometric ALMA observations and data processing. Full text in Research Archive
• Wedemeyer, Sven (2018). Solar Observations with ALMA. Full text in Research Archive
• Wedemeyer, Sven (2018). Sola, din nærmeste stjerne. Full text in Research Archive
• Wedemeyer, Sven (2018). Oppvarming av solens atmosfære & solfysikkforskning i dag. Full text in Research Archive
• Wedemeyer, Sven (2018). Experiences from applying for an ERC Consolidator Grant. Full text in Research Archive
• Wedemeyer, Sven (2015). Rød sol og evig daggry: Leting etter liv på fjerne kloder. In Kristiansen, Jostein Riiser; Evans, Anna Kathinka Dalland; Svensen, Henrik; Samset, Bjørn Hallvard & Byhring, Hanne Sigrun (Ed.), Stjerneklart – siste nytt fra verdensrommet. Spartacus. ISSN 9788243009738. p. 96–108. Full text in Research Archive
• Ayres, T. R.; Lyons, J. R.; Ludwig, Hans-Günter; Caffau, E. & Wedemeyer-Böhm, Sven (2013). Isotopic CO in the Solar Photosphere, Viewed Through the Lens of 3D Spectrum Synthesis. Full text in Research Archive
• Wedemeyer-Böhm, Sven & Voort, Luc Rouppe van der (2010). The solar continuum intensity distribution. Proceedings of the International Astronomical Union. ISSN 1743-9213. 15, p. 333–334. Full text in Research Archive
• Kjeldseth-Moe, Olav & Wedemeyer-Böhm, Sven (2009). Are there variations in Earth’s global mean temperature related to the solar activity? Full text in Research Archive
• Rezaei, Rezza; Steiner, Oskar; Wedemeyer-Böhm, Sven; Schlichenmaier, Rolf & Lites, Bruce W. (2007). Variation of the Stokes-V area asymmetry across magnetic elements. Astronomical Notes - Astronomische Nachrichten. ISSN 0004-6337. 328(7), p. 706–706. Full text in Research Archive
• Wedemeyer-Böhm, Sven (2007). Small-scale structure and dynamics of the lower solar atmosphere. Full text in Research Archive
• Pandit, Sneha & Wedemeyer, Sven (2023). A new look at Solar-Stellar Activity with the Atacama Large Millmeter/submillimeter Array. Faculty of Mathematics and Natural Sciences. Full text in Research Archive
• Gomez, Juan Camilo Guevara; Wedemeyer, Sven & Voort, Luc Rouppe van der (2022). Observations of the dynamics and structure of the solar atmosphere with ALMA. Universitetet i Oslo. Full text in Research Archive
• Eklund, Henrik & Wedemeyer, Sven (2021). Investigating dynamic small-scale events in the Sun with the Atacama Large Millimeter/sub-millimeter Array. Universitetet i Oslo. Full text in Research Archive Show summary

  The Sun is dynamic and influences the surrounding planetary system which becomes increasingly imperative to be able to predict as we increase the technology and space exploration. To this end, it is important to understand the transport of energy and the dynamical processes that take place in the solar atmosphere. Radiation at millimeter wavelengths which mainly forms in the mid-layers of the solar atmosphere, the Chromosphere, is a powerful indicator of the temperature of the plasma. To achieve high sensitivity and resolution, interferometric observations are performed with the Atacama Large Millimeter/sub-millimeter Array (ALMA), which consist of about 66 radio antennas. Many challenges come with interferometric observations of the Sun and the data needs to be carefully handled to reconstruct reliable high frame-rate time-series of images. In the observations, several hundred small-scale dynamic brightening events are detected and their evolution is tracked through time. The origin and physical properties of the brightening events are determined by comparison of their characteristics to state-of-the-art three-dimensional numerical simulations. The accurate temperature measurements of the brightening events provides one step further to understanding the energy transport in the solar atmosphere.

• Gaudi, Scott; Blackwood, Gary; Howard, Andrew; Latham, David; Fischer, Debra & Wedemeyer, Sven (2019). Extreme Precision Radial Velocity (EPRV) Working Group. Bulletin of the American Astronomical Society. Full text in Research Archive

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