Surveying the Bright Stars by Optical Interferometry III: A Magnitude-Limited Multiplicity Survey of Classical Be-Stars

TL;DR

This study uses optical interferometry to detect and analyze companions of classical Be stars, revealing new binary and multiple systems, and providing detailed multiplicity statistics for a magnitude-limited sample.

Contribution

It presents the first direct visual detections of companions in several Be stars and identifies hierarchical multiple systems, advancing understanding of Be star multiplicity.

Findings

Detected companions in ten known binaries

Obtained new orbital solutions for two systems

First visual detection of a hot sdO companion

Abstract

We present the results of a multiplicity survey for a magnitude-limited sample of 31 classical Be stars conducted with the Navy Precision Optical Interferometer and the Mark III Stellar Interferometer. The interferometric observations were used to detect companions in ten previously known binary systems. For two of these sources (66 Oph and $\beta$ Cep) new orbital solutions were obtained, while for a third source ($\upsilon$ Sgr) our observations provide the first direct, visual detection of the hot sdO companion to the Be primary star. Combining our interferometric observations with an extensive literature search, we conclude that an additional four sources (o Cas, 15 Mon, $\beta$ Lyr, and $\beta$ Cep) also contain wider binary components that are physical companions to the narrow binaries, thus forming hierarchical multiple systems. Among the sources not previously confirmed as spectroscopic or visual binaries, BK Cam was resolved on a number of nights within a close physical proximity of another star with relative motion possibly suggesting a physical binary. Combining our interferometric observations with an extensive literature search, we provide a detailed listing of companions known around each star in the sample, and discuss the multiplicity frequency in the sample. We also discuss the prospects for future multiplicity studies of classical Be stars by long baseline optical interferometry.