Interferometric detections of sdO companions orbiting three classical Be stars

TL;DR

This study uses interferometry to detect and characterize sdO companions in three Be star systems, providing new dynamical masses and orbital data to understand their evolution.

Contribution

It presents the first interferometric detections of sdO companions in three Be stars and derives their orbital parameters and masses, advancing binary evolution models.

Findings

Detected sdO companions in three Be stars using interferometry.

Derived first orbital parameters and dynamical masses for two systems.

Identified one system as a potential progenitor of a Be/X-ray binary.

Abstract

Classical Be stars are possible products of close binary evolution, in which the mass donor becomes a hot, stripped O or B-type subdwarf (sdO/sdB), and the mass gainer spins up and grows a disk to become a Be star. While several Be+sdO binaries have been identified, dynamical masses and other fundamental parameters are available only for a single Be+sdO system, limiting the confrontation with binary evolution models. In this work, we present direct interferometric detections of the sdO companions of three Be stars 28 Cyg, V2119 Cyg, and 60 Cyg, all of which were previously found in UV spectra. For two of the three Be+sdO systems, we present first orbits and preliminary dynamical masses of the components, revealing that one of them could be the first identified progenitor of a Be/X-ray binary with a neutron star companion. These results provide new sets of fundamental parameters that are crucially needed to establish the evolutionary status and origin of Be stars.