Asymmetries on red giant branch surfaces from CHARA/MIRC optical interferometry
Abstract
Context. Red giant branch (RGB) stars are very bright objects in galaxies and are often used as standard candles. Interferometry is the ideal tool to characterize the dynamics and morphology of their atmospheres. Aims. We aim at precisely characterising the surface dynamics of a sample of RGB stars. Methods. We obtained interferometric observations for three RGB stars with the MIRC instrument mounted at the CHARA interfer- ometer. We looked for asymmetries on the stellar surfaces using limb-darkening models. Results. We measured the apparent diameters of HD197989 (Epsilon Cyg) = 4.61+-0.02 mas, HD189276 (HR7633) = 2.95+-0.01 mas, and HD161096 (Beta Oph) = 4.43+-0.01 mas. We detected departures from the centrosymmetric case for all three stars with the tendency of a greater effect for lower logg of the sample. We explored the causes of this signal and conclude that a possible explanation to the interferometric signal is the convection-related and/or the magnetic-related surface activity. However, it is necessary to monitor these stars with new observations, possibly coupled with spectroscopy, in order to firmly establish the cause.
Cite
@article{arxiv.1703.02406,
title = {Asymmetries on red giant branch surfaces from CHARA/MIRC optical interferometry},
author = {A. Chiavassa and R. Norris and M. Montargès and R. Ligi and L. Fossati and L. Bigot and F. Baron and P. Kervella and J. D. Monnier and D. Mourard and N. Nardetto and G. Perrin and G. H. Schaefer and T. A. ten Brummelaar and Z. Magic and R. Collet and M. Asplund},
journal= {arXiv preprint arXiv:1703.02406},
year = {2017}
}
Comments
Accepted for publication as a Letter in Astronomy and Astrophysics, section 1. Letters to the Editor. The official date of acceptance is 06/03/2017