| Issue |
A&A
Volume 671, March 2023
|
|
|---|---|---|
| Article Number | A27 | |
| Number of page(s) | 9 | |
| Section | Stellar atmospheres | |
| DOI | https://doi.org/10.1051/0004-6361/202245384 | |
| Published online | 02 March 2023 | |
Infrared He I 10830 Å, ultra-violet Ca II, and Mg II chromosphere emissions in the spectra of classical Cepheid X Cyg
1
Astronomical Observatory, Odessa National University of the Ministry of Education and Science of Ukraine,
Shevchenko Park,
65014
Odessa, Ukraine
e-mail: andrievskii@ukr.net
2
Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Universität Tübingen,
Sand 1,
72076
Tübingen, Germany
3
GEPI, Observatoire de Paris, Université PSL, CNRS,
5 Place Jules Janssen,
92190
Meudon, France
4
Physics of stars department, Crimean Astrophysical Observatory,
Nauchny
298409, Crimea
Received:
6
November
2022
Accepted:
21
December
2022
Aims. In a previous publication, we reported the first detection of emission in the infrared (IR) triplet at 10 830 Å in the spectra of the classical Cepheid X Cyg. Emission is detectable at phases from approximately 0.25 to 0.90. We present and discuss further information on the chromosphere activity of this star, namely International Ultraviolet Explorer (IUE) archive data concerning the emission in the h and k Mg II doublet, and near-ultraviolet (NUV) spectra in the vicinity of the H and K Ca II doublet. We also present rough estimates of the chromosphere conditions and semi-empirical modelling of the observed emissions in He I triplet.
Methods. A study of the emissions in UV lines of Ca II and Mg II, and IR lines of He I suggests that the emissions observed at certain phases can be explained within the framework of the Gillet's phenomenological model of shock waves in pulsating atmospheres, which was developed from a study of the Hα behaviour in X Cyg spectra. We used the non-local thermodynamic equilibrium (NLTE) approximation and a simple model of this star's chromosphere for the analysis of the chromosphere indicator profiles.
Results. We show that under certain assumptions about the properties of the chromosphere, it is possible to describe the presence or absence of emission in the IR lines of He I and Ca II, and UV lines of Ca II and Mg II.
Key words: stars: atmospheres / stars: chromospheres / stars: variables: Cepheids
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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