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|Title:||The CARMENES search for exoplanets around M dwarfs. The He I infrared triplet lines in PHOENIX models of M 2-3 V stars|
Schmitt, H. M. M.
Johnson, E. N.
Caballero, J. A.
Jeffers, S. V.
Amado, P. J.
Anglada Escudé, G.
Bauer, F. F.
Béjar, V. J. S.
Cortés Contreras, M.
Galadí Enríquez, D.
Guenther, E. W.
Hauschildt, P. H.
López del Fresno, M.
Morales, J. C.
|Keywords:||Stars: activity;Stars: chromospheres;Stars: late-Type|
|Citation:||Astronomy & Astrophysics 638: A115 (2020)|
|Abstract:||The He » I infrared (IR) line at a vacuum wavelength of 10 833 Å is a diagnostic for the investigation of atmospheres of stars and planets orbiting them. For the first time, we study the behavior of the He » I IR line in a set of chromospheric models for M-dwarf stars, whose much denser chromospheres may favor collisions for the level population over photoionization and recombination, which are believed to be dominant in solar-type stars. For this purpose, we use published PHOENIX models for stars of spectral types M2 V and M3 V and also compute new series of models with different levels of activity following an ansatz developed for the case of the Sun. We perform a detailed analysis of the behavior of the He I IR line within these models. We evaluate the line in relation to other chromospheric lines and also the influence of the extreme ultraviolet (EUV) radiation field. The analysis of the He » I IR line strengths as a function of the respective EUV radiation field strengths suggests that the mechanism of photoionization and recombination is necessary to form the line for inactive models, while collisions start to play a role in our most active models. Moreover, the published model set, which is optimized in the ranges of the Na » I D2, Hα, and the bluest Ca » II IR triplet line, gives an adequate prediction of the He » I IR line for most stars of the stellar sample. Because especially the most inactive stars with weak He » I IR lines are fit worst by our models, it seems that our assumption of a 100% filling factor of a single inactive component no longer holds for these stars. © ESO 2020.|
|Appears in Collections:||(CAB) Artículos|
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