Long-term chromospheric activity of non-eclipsing RS CVn-type stars

TL;DR

This study analyzes long-term UV spectra from IUE to investigate chromospheric activity cycles and flip-flop phenomena in select RS CVn stars, revealing potential cycles of 7 to 21 years.

Contribution

It provides the first detailed long-term chromospheric activity analysis of key RS CVn stars using IUE data, identifying possible multi-year activity cycles.

Findings

HD 22468 shows an 18-year cycle and a 3-year flip-flop cycle.

HD 224085 exhibits a 21-year cycle and a 9-year flip-flop cycle.

HD 21242 suggests a 7-year chromospheric cycle.

Abstract

Context. The IUE database provides a large number of UV high and low-resolution spectra of RS CVn-type stars from 1978 to 1996. In particular, many of these stars were monitored continuously during several seasons by IUE. Aims. Our main purpose is to study the short and long-term chromospheric activity of the RS CVn systems most observed by IUE: HD 22468 (V711 Tau, HR 1099, K1IV+G5V), HD 21242 (UX Ari, K0IV+G5V) and HD 224085 (II Peg, K2IV). Methods. We first obtain the Mount Wilson index S from the IUE high and low-resolution spectra. Secondly, we analyse with the Lomb-Scargle periodogram the mean annual index S and the amplitude of its rotational modulation. Results. For HD 22468 (V711 Tau, HR 1099), we found a possible chromospheric cycle with a period of 18 years and a shorter cycle with a period of 3 years, which could be associated to a chromospheric "flip-flop" cycle. The data of HD 224085 (II Peg) also suggest a chromospheric cycle of 21 years and a flip-flop cycle of 9 years. Finally, we obtained a possible chromospheric cycle of 7 years for HD 21242 (UX Ari).