Imaging of Stellar Surfaces

March 5 - 9, 2018

Venue: ESO Headquarters, Garching, Germany

First Announcement

ESO Workshop "Imaging of Stellar Surfaces"

March 5 - 9, 2018

Venue: ESO Headquarters, Garching, Germany

Maximum number of participants: 70

Scientific Rationale:
Until very recently, all information about mechanisms affecting the stellar surface came either from indirect observations or from studies of the Sun. The stellar surface is the locus where we first interface with the mechanisms happening at the interior of the stars such as convection, magnetic field, and diffusion producing abundance anomalies. Studying stellar surfaces is important for advancing our understanding of these physical processes.

There is currently a tremendous advance of different observational techniques that enable us to resolve the surfaces of stars other than the sun. The Very Large Telescope Interferometer (VLTI) is transitioning from its first generation instruments, which focused on spectro-interferometry, to the second generation instruments, which focus on spectro-imaging and astrometry. The VLTI instrument PIONIER has already shown its capabilities and great potential to resolve stellar surfaces, while the instruments GRAVITY and MATISSE are coming into operations. The VLT instrument SPHERE is resolving the surfaces of the apparently largest stars as well. At the same time, ALMA observations have suceeded to resolve stellar surfaces at millimetre wavelengths with its long baselines. A number of other interferometers at optical and radio wavelengths have been successful to resolve stellar surfaces as well, including CHARA, VLA, e-MERLIN.

In the last one or two years we have seen great progress in resolving surfaces of active stars such as zet And, of red giants such as R Dor, of asymptotic giant branch stars such as Mira or R Scl, and of red supergiants such as Betelgeuse, Antares, VY CMa, with these different techniques at multiple wavelengths from the visual to the radio.

Stellar atmosphere models have also been advancing, during a similar time frame, from 1D models to 3D models including the effects of convection. Interaction between observations and theory of stellar atmospheres is of utmost importance to constrain the models and to advance our understanding of physical processes such as pulsation, convection, chromospheric activity.

This workshop aims to bring together observers from different techniques and wavelengths and theoreticians working on stellar atmosphere and stellar structure. Presentations will include recent individual results of stellar surface mapping and the corresponding modelling. Observational strategies to advance in this field will be discussed. In addition, we will dedicate a session to the prospect of resolving stellar surfaces of stars other than the sun with future facilities such as the ELT or the JWST, or with intensity interfermetry/CTA.

We also aim to share technical, observational, and modeling expertise with a larger community. We will discuss how the different communities (VLT, VLTI, CHARA, ALMA, HST/JWST) deal with the image reconstruction problem and with the physical interpretation of the images.

We aim at a focused workshop with ample of time for discussions on recent images of stellar surfaces and atmospheres (out to below a few stellar radii), the observational strategies, and the relevant physical processes. The number of participants will be limited to 70.

Bernd Freytag (Uppsala University, Sweden), Xavier Haubois (ESO), Liz Humphreys (ESO, co-chair), Lynn Matthews (MIT Haystack, USA), Claudia Paladini (ESO), Oskar von der Luehe (Albert-Ludwigs-Universitat Freiburg, Germany), Markus Wittkowski (ESO, co-chair)

Invited Speakers: to be confirmed

- The Sun as a star: Physical processes affecting the Sun's surface and overviews of recent observations at optical and sub-mm wavelengths
- Physical processes
-- Convection
-- Pulsation
-- Magnetic fields
-- Chromospheric activity
-- Close companions
-- Rotation
- Red giants including active giants
- Asymptotic giant branch stars
- Red supergiants
- Imaging techniques and observational strategies
- Future facilities

We plan to start the workshop on Monday lunchtime and to finish on Friday lunchtime.