Discovery of the spectroscopic binary nature of three bright southern Cepheids

TL;DR

This study identifies three bright Galactic Cepheids as members of spectroscopic binary systems through radial velocity and photometric analysis, revealing companion characteristics and stellar evolution effects on pulsation periods.

Contribution

The paper reports the discovery of spectroscopic binary nature in three bright Cepheids and analyzes their pulsation period variations and companion star properties.

Findings

LR TrA and BG Vel have companions indicated by radial velocity and photometric amplitude ratios.

RZ Vel and BG Vel's companions are not hot stars based on IUE spectra.

RZ Vel shows period increase with superimposed fluctuations, suggesting stellar evolution effects.

Abstract

We present an analysis of spectroscopic radial velocity and photometric data of three bright Galactic Cepheids: LR Trianguli Australis (LR TrA), RZ Velorum (RZ Vel), and BG Velorum (BG Vel). Based on new radial velocity data, these Cepheids have been found to be members of spectroscopic binary systems. The ratio of the peak-to-peak radial velocity amplitude to photometric amplitude indicates the presence of a companion for LR TrA and BG Vel. IUE spectra indicate that the companions of RZ Vel and BG Vel cannot be hot stars. The analysis of all available photometric data revealed that the pulsation period of RZ Vel and BG Vel varies monotonically, due to stellar evolution. Moreover, the longest period Cepheid in this sample, RZ Vel, shows period fluctuations superimposed on the monotonic period increase. The light-time effect interpretation of the observed pattern needs long-term photometric monitoring of this Cepheid. The pulsation period of LR TrA has remained constant since the discovery of its brightness variation. Using statistical data, it is also shown that a large number of spectroscopic binaries still remain to be discovered among bright classical Cepheids.