Cool Stars 21 Splinter Session
Modelling stellar atmospheres: advances brought by solar know-how
Cool Stars 21 - Toulouse, France
22 - 26 June 2020
Most of the information about stars is brought by photons that originate in stellar atmospheres. Consequently, understanding and modelling the conditions in the atmosphere of a star is of crucial importance for understanding stellar observations and the star as a whole. While there are a lot of similarities between studies of solar and stellar atmospheres, there is also a key difference: solar studies largely benefit from the ability to resolve features on the solar surface. In particular, the Sun provides a unique opportunity to directly study the emergence and disappearance of magnetic fields in its atmosphere as well as the sophisticated interaction between these fields and plasma. Furthermore, high-resolution solar observations revealed that besides a strong vertical stratification with depth, the solar atmosphere has a very rich and complicated horizontal structure. Progress in solar observations brought about several recent and exciting results which are of direct relevance for understanding stellar atmospheres.
Key Topics
1. Observations and modelling of solar atmosphere
2. Recent advances in observing and modelling stellar atmospheres
Invited Speakers (in alphabetical order)
Jorrit Leenaart - Institute of Solar Physics, Stockholm University, Stockholm, Sweden
Hans Ludwig - Department of Physics and Astrophysics, University Heidelberg, Heidelberg, Germany
Valentin Pillet - National Solar Observatory, Boulder, USA
Raechel Roettenbacher - Department of Physics, Yale University, USA
Program
(To be announced)
SOC
• Mark Cheung - Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, USA
• Natalie Krivova - Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
• Alexander Shapiro - Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
• Sami Solanki - Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
• Veronika Witzke - Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
Rationale
Being the only star for which we can resolve the spatial scales on which fundamental processes take place, the Sun provides a perfect test bench for understanding the conditions in stellar atmospheres. Benefitting from the enormous recent progress in solar observations and models it is now possible to extend the models originally developed for and tested against the Sun to model stellar atmospheres. At the same time, modelling of stellar atmospheres becomes very timely since stellar observational data (e.g. obtained by CoRoT, Kepler, and TESS space telescopes, Gaia space observatory, and LAMOST survey) have emphasized the needs for developing methods for extracting information about solar-like stars and their planets from the available photometric and spectroscopic records.
One of the directions which greatly benefited from the solar research is 3D hydrodynamic (HD) and magneto-hydrodynamic (MHD) simulations of stellar atmospheres. Solar HD and MHD simulations have reached a high level of realism, and can now reproduce many sensitive observational tests and high-resolution observations of the solar atmosphere. Motivated by this, 3D HD and MHD simulations are being successfully extended to other stars. In particular, a large grid of hydrodynamical 3D stellar atmospheres have been recently developed (Chiavassa et al. 2018, Astron. Astrophys., 611, 11 and references therein). Also MHD simulations of small-scale magnetic concentrations have became available (Beeck et al. 2015, Astron. Astrophys., 581, 43). Developments are also underway to produce 3D MHD simulations of star spots in late-type main-sequence stars. Concurrently, there is an effort in simulating the small-scale turbulent dynamo, originating due to the interaction between convection and magnetic field, in main sequence stars. Such a dynamo brings about small-scale turbulent magnetic field (observed in the Sun) which leads to the additional heating of upper layers of stellar photospheres and thus can affect the limb darkening profiles needed for the characterisation of exoplanets with transit photometry. 3D HD and MHD simulations of stellar atmospheres is the backbone for interpreting stellar spectra (e.g. for determination of abundances) and modelling various manifestations of stellar magnetic activity, e.g. photometric variability and radial velocity signals.
Another interesting effort is the development of surface flux transport models (SFTM), which now allow to realistically simulate the evolution of the large-scale magnetic field in the solar photosphere. These models are currently being extended to calculate the distribution of magnetic fields in atmospheres of Sun-like stars (Weber & Browning 2016, Astrophys. J., 827, 95; Isik et al. 2018, Astron. Astrophys. 620, 177).
Abstract Submission
Is open now.
Please email your contribution to abstract-coolstars.21@mps.mpg.de
Deadline for abstract submission: End of April