Chromospherically active stars: Lithium and CNO abundances in northern RS CVn stars

Barkha Bale; Gražina Tautvaišienė; Renata Minkevičiūtė; Arnas Drazdauskas; Šarūnas Mikolaitis; Edita Stonkutė; Markus Ambrosch

doi:10.1051/0004-6361/202556683

Title	Chromospherically active stars: Lithium and CNO abundances in northern RS CVn stars
Authors	Bale, Barkha ; Tautvaišienė, Gražina ; Minkevičiūtė, Renata ; Drazdauskas, Arnas ; Mikolaitis, Šarūnas ; Stonkutė, Edita ; Ambrosch, Markus
DOI	10.1051/0004-6361/202556683
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Is Part of	Astronomy & astrophysics.. Les Ulis : EDP Sciences. 2025, vol. 703, art. no. A128, p. [1-13].. ISSN 0004-6361. eISSN 1432-0746
Keywords [eng]	stars: abundances ; evolution ; magnetic field
Abstract [eng]	Aims. We carried out a detailed investigation of Lthium and CNO abundances, including carbon isotope ratios, in RS CVn stars to assess the role of magnetic activity in the mixing of stellar atmospheres. Methods. We obtained high-resolution spectra at the Moletai Astronomical Observatory. Lithium abundances were determined by spectral synthesis of the 6707 Å line and the CNO abundances using the C2 band heads at 5135 and 5635.5 Å, CN bands at 6470–6490 Å and 7980–8005 Å, and the [O I] line at 6300 Å. By fitting the 13CN band at 8004.7 Å, we determined the carbon isotope ratios. Results. We determined the main atmospheric parameters and investigated the chemical composition of 32 RS CVn stars. Lithium abundances were determined for 13 additional stars using archival spectra. We report that iot Gem and HD 179094 have carbon isotope ratios already affected by extra-mixing, even though they are in the evolutionary stage below the red giant branch luminosity bump. About half of the low-mass giants, for which the lithium abundance was determined, follow the first dredge-up predictions; however, other stars show reduced Lithium abundances, as predicted by thermohaline-induced mixing. The intermediate-mass stars show reduced Lithium abundances reduced, as predicted by rotation-induced mixing. Conclusions. In low-mass, chromospherically active RS CVn stars, extra-mixing of lithium and carbon isotopes may begin earlier than in normal giants. The Li-rich RS CVn giant VOP And has large C/N and carbon isotope ratios and raises questions about the origin of its lithium enhancement.
Published	Les Ulis : EDP Sciences
Type	Journal article
Language	English
Publication date	2025
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„Chromospherically active stars: Lithium and CNO abundances in northern RS CVn stars“