Establishing binarity amongst Galactic RV Tauri stars with a disc

TL;DR

This study confirms that six Galactic RV Tauri stars with dusty discs are binaries with long orbital periods and eccentricities, providing insights into binary interactions affecting late stellar evolution stages.

Contribution

It establishes the binary nature of six RV Tauri stars with dusty discs and analyzes their orbital parameters, offering new data on their evolutionary status and binary interactions.

Findings

All six stars are binaries with periods 650-1700 days.

Most have low-mass, unevolved companions.

Their orbital characteristics challenge standard binary evolution theories.

Abstract

This study is a contribution in comprehending the role of binarity upon late stages of stellar evolution. We determine the binary status of six Galactic RV Tauri stars, namely DY Ori, EP Lyr, HP Lyr, IRAS 17038-4815, IRAS 09144-4933 and TW Cam, which are surrounded by a dusty disc. We also place them on the HR diagram, thereby establishing their evolutionary nature. All the six Galactic RV Tauri stars included in this study are binaries with orbital periods ranging between $\sim$ 650 and 1700 days and with eccentricities between 0.2 and 0.6. The mass functions range between 0.08 to 0.55 M$_\odot$ which points to an unevolved low mass companion. In the photometric time series we detect a long-term variation on the time-scale of the orbital period for IRAS 17038-4815, IRAS 09144-4933 and TW Cam. Our derived stellar luminosities obtained from a calibrated PLC relation indicates that all except DY Ori and EP Lyr, are post-AGB stars. DY Ori and EP Lyr are likely examples of the recently discovered dusty post-RGB stars. The orbital parameters strongly suggest that the evolution of these stars was interrupted by a strong phase of binary interaction during or even prior to the AGB. The observed eccentricities and long orbital periods among these stars provides a challenge to the standard theory of binary evolution.