Optical spectroscopy of Be/gamma-ray binaries

¹ Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, Tsarigradsko Shose 72, 1784 Sofia, Bulgaria
e-mail: rkz@astro.bas.bg
² Departamento de Física (EPSJ), Universidad de Jaén, Campus Las Lagunillas, A3-420, 23071 Jaén, Spain
³ Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, Liverpool, L3 5RF, UK
⁴ Departamento de Ingeniería Mecánica y Minera (EPSJ), Universidad de Jaén, Campus Las Lagunillas A3-008, 23071 Jaén, Spain

Received: 18 April 2016
Accepted: 8 July 2016

Abstract

We report optical spectroscopic observations of the Be/γ-ray binaries LSI+61303, MWC 148 and MWC 656. The peak separation and equivalent widths of prominent emission lines (Hα, Hβ, Hγ, 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+61°303 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 ~1 day deserves to be searched for.