Volume 632, December 2019
|Number of page(s)||16|
|Published online||25 November 2019|
Tomography of cool giant and supergiant star atmospheres
European Southern Observatory,
85748 Garching bei München,
2 Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP. 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium
3 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Lagrange, CS 34229, 06304 Nice Cedex 4, France
4 Department of Physics and Astronomy at Uppsala University, Regementsvägen 1, Box 516, 75120 Uppsala, Sweden
5 Laboratoire Univers et Particules de Montpellier, Université de Montpellier, CNRS, 34095 Montpellier Cedex 05, France
Accepted: 9 October 2019
Context. Red supergiants are cool massive stars and are the largest and the most luminous stars in the Universe. They are characterized by irregular or semi-regular photometric variations, the physics of which is not clearly understood.
Aims. The paper aims to derive the velocity field in the red supergiant star μ Cep and to relate it to the photometric variability with the help of the tomographic method.
Methods. The tomographic method allows one to recover the line-of-sight velocity distribution over the stellar disk and within different optical-depth slices. This method was applied to a series of high-resolution spectra of μ Cep, and these results are compared to those obtained from 3D radiative-hydrodynamics CO5BOLD simulations of red supergiants. Fluctuations in the velocity field are compared with photometric and spectroscopic variations, the latter were derived from the TiO band strength and serve, at least partly, as a proxy of the variations in effective temperature.
Results. The tomographic method reveals a phase shift between the velocity and spectroscopic and photometric variations. This phase shift results in a hysteresis loop in the temperature – velocity plane with a timescale of a few hundred days, which is similar to the photometric one. The similarity between the hysteresis loop timescale measured in μ Cep and the timescale of acoustic waves disturbing the convective pattern suggests that such waves play an important role in triggering the hysteresis loops.
Key words: stars: atmospheres / stars: AGB and post-AGB / supergiants / line: formation / radiative transfer / techniques: spectroscopic
The movie associated to Fig. 13 is available at http://www.aanda.org
© ESO 2019
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.