The photospheric abundances of active binaries II. Atmospheric parameters and abundance patterns for 6 single-lined RS CVn systems

TL;DR

This study analyzes the atmospheric parameters and chemical abundances of active binary stars, revealing they are not metal-poor and exhibit overabundances of certain elements, with implications for understanding stellar activity effects.

Contribution

It provides detailed abundance patterns for active binaries using two temperature determination methods, highlighting their near-solar metallicity and activity-related abundance anomalies.

Findings

Active binaries are not as metal-poor as previously thought.

Significant overabundance of alpha-elements observed.

Temperature estimates from (V-R) and (V-I) colours are affected by activity.

Abstract

Photospheric parameters and abundances are presented for a sample of single-lined chromospherically active binaries from a differential LTE analysis of high-resolution spectra. Abundances have been derived for 13 chemical species, including several key elements such as Li, Mg, and Ca. Two methods have been used. The effective temperatures, surface gravities and microturbulent velocities were first derived from a fully self-consistent analysis of the spectra, whereby the temperature is determined from the excitation equilibrium of the Fe I lines. The second approach relies on temperatures derived from the (B-V) colour index. These two methods give broadly consistent results for the stars in our sample, suggesting that the neutral iron lines are formed under conditions close to LTE. We discuss the reliability in the context of chromospherically active stars of various colour indices used as temperature indicators, and conclude that the (V-R) and (V-I) colours are likely to be significantly affected by activity processes. Irrespective of the method used, our results indicate that the X-ray active binaries studied are not as metal poor as previously claimed, but are at most mildly iron-depleted relative to the Sun (-0.41<[Fe/H]<+0.11). A significant overabundance of several chemical species is observed (e.g., the alpha-synthezised elements). These abundance patterns are discussed in relation to stellar activity.