Optical spectroscopy of Be/gamma-ray binaries

TL;DR

This paper presents optical spectroscopic observations of Be/gamma-ray binaries, analyzing emission lines, disc sizes, and interactions between compact objects and circumstellar discs, revealing different disc interactions during orbital phases.

Contribution

It provides detailed spectroscopic measurements and disc interaction analysis for three Be/gamma-ray binaries, highlighting the dynamics of compact object and disc interactions.

Findings

Compact object contacts outer disc at periastron in LSI+61303

Compact object penetrates deeply into disc in MWC 148

Black hole in MWC 656 accretes from outer disc throughout orbit

Abstract

We report optical spectroscopic observations of the Be/gamma-ray binaries LSI+61303, MWC 148 and MWC 656. The peak separation and equivalent widths of prominent emission lines (H-alpha, H-beta, H-gamma, HeI, and FeII) are measured. We estimated the circumstellar disc size, compared it with separation between the components, and discussed the disc truncation. We find that in LSI+61303 the compact object comes into contact with the outer parts of the circumstellar disc at periastron, in MWC 148 the compact object goes deeply into the disc during the periastron passage, and in MWC 656 the black hole is accreting from the outer parts of the circumstellar disc along the entire orbit. The interstellar extinction was estimated using interstellar lines. The rotation of the mass donors appears to be similar to the rotation of the mass donors in Be/X-ray binaries. We suggest that X-ray/optical periodicity of about 1 day deserves to be searched for.