Šarūnas Mikolaitis
VU Faculty of Physics
Our telescopes observe Active stars – RS CVn systems
The astrospectroscopy team from our observatory** is interested in a special class of stars known as RS CVn stars. Over the last year, two scientific publications were completed on this topic, based on observations obtained with our high-resolution spectrograph mounted on the largest 165 cm telescope at the Molėtai Astronomical Observatory. These studies were led by PhD student Barkha Bale and her supervisor Gražina Tautvaišienė, together with a larger team from the Astrospectroscopy and Exoplanets group of our institute.
RS CVn stars are close binary systems in which the stars orbit very close to each other, forcing them to rotate very rapidly around their own axes. This fast rotation generates extremely strong magnetic fields, leading to large starspots, active chromospheres, frequent flares, and intense X-ray emission. Compared to the Sun, these stars are far more magnetically active, making them excellent targets for studying the interaction between magnetism and stellar evolution.One of the key open questions in stellar astrophysics is how magnetic activity influences internal mixing. In standard stellar evolution, surface chemical composition changes in a relatively predictable way. In RS CVn stars, however, magnetic activity may enhance or modify these processes, transporting material from deep inside the star up to the surface and leaving detectable chemical signatures.
For this reason, the studies focused on stellar chemistry, especially lithium and the CNO elements (carbon, nitrogen, and oxygen). Lithium is a fragile element that is easily destroyed in stellar interiors, so its presence can point to unusual mixing processes. The CNO elements, together with the carbon isotope ratio (¹²C/¹³C), act as fingerprints of nuclear processing inside stars and reveal whether deep, processed material has reached the stellar surface.Using high-resolution spectra, the team determined atmospheric parameters and detailed chemical abundances for dozens of RS CVn stars. Lithium was measured from its characteristic spectral line, while carbon, nitrogen, oxygen, and carbon isotope ratios were derived from molecular bands and atomic lines through detailed spectral synthesis.
These results show that strong magnetic activity can significantly alter stellar surface chemistry. Studies of RS CVn systems therefore help refine stellar evolution models and deepen our understanding of how magnetism shapes the life cycles of stars.
Research team: B. Bale, G. Tautvaišienė, R. Minkevičiūtė, A. Drazdauskas, Š. Mikolaitis, E. Stonkutė, M. Ambrosch
Publications (2025):
Chromospherically active stars: Lithium and CNO abundances in northern RS CVn stars, Astronomy & Astrophysics, 703, A128
Chromospherically active stars: Chemical composition of photospheres in 20 RS CVn stars, Astronomy & Astrophysics, 696, A23
**Vilnius University, Faculty of Physics, Institute of Theoretical Physics and Astronomy, Molėtai Astronomical observatory