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Title: Asymmetries on red giant branch surfaces from CHARA/MIRC optical interferometry
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 interferometer. We looked for asymmetries on the stellar surfaces using limb-darkening models. Results. We measured the apparent diameters of HD 197989 ( ϵ Cyg) = 4.61 ± 0.02 mas, HD 189276 (HR 7633) = 2.95 ± 0.01 mas, and HD 161096 ( β 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 log g 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.
Authors:
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Award ID(s):
1636624
Publication Date:
NSF-PAR ID:
10213274
Journal Name:
Astronomy & Astrophysics
Volume:
600
Page Range or eLocation-ID:
L2
ISSN:
0004-6361
Sponsoring Org:
National Science Foundation
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