Velocity monitoring of gamma-Cas stars reveals their binarity status

TL;DR

This study uses high-resolution spectroscopy to monitor gamma-Cas stars, revealing six new binary systems with low-mass companions and identifying additional candidates, thereby clarifying their binarity status and contributing to understanding their peculiar X-ray emissions.

Contribution

First systematic radial velocity monitoring of gamma-Cas stars using multiple spectrographs, discovering six new binaries and identifying potential quadruple system and binary candidates.

Findings

Six new binary systems with long periods and low velocity amplitudes

Properties of gamma-Cas binaries are similar to other Be systems

Identification of a potential quadruple system involving a Be star

Abstract

The binary status of gamma-Cas stars has been discussed while theoretically examining the origin of their peculiar X-ray emission. However, except in two cases, no systematic radial velocity monitoring of these stars had been undertaken yet to clarify their status. We now fill this gap using TIGRE, CARMENES, and UVES high-resolution spectroscopy. Velocities were determined for 16 stars, revealing shifts and/or changes in line profiles. The orbit of six new binaries could be determined: the long periods (80-120d) and small velocity amplitudes (5-7km/s) suggest low mass companions (0.6-1 M$_{\odot}$). The properties of the known gamma-Cas binaries appear similar to those of other Be systems, with no clear-cut separation between them. One of the new systems is a candidate for a rare case of quadruple system involving a Be star. Five additional gamma-Cas stars display velocity variations compatible with the presence of companions, but no orbital solution could yet be formally established for them hence they only receive the status of "binary candidate".