A Fresh Catch of Massive Binaries in the Cygnus OB2 Association

TL;DR

This study reports the discovery and orbital analysis of five new massive binary star systems in the Cygnus OB2 association, enhancing understanding of their properties and formation, with implications for supernova and gamma-ray burst progenitors.

Contribution

It provides new orbital parameters for five massive binaries, including the longest period system in Cyg OB2, and increases the known binary count to 25 in this association.

Findings

Five new massive binary systems discovered and characterized.

MT070 has the longest period (6.2 years) in Cyg OB2.

MT174 may be a progenitor to a low-mass X-ray binary.

Abstract

Massive binary stars may constitute a substantial fraction of progenitors to supernovae and gamma-ray bursts, and the distribution of their orbital characteristics holds clues to the formation process of massive stars. As a contribution to securing statistics on OB-type binaries, we report the discovery and orbital parameters for five new systems as part of the Cygnus OB2 Radial Velocity Survey. Four of the new systems (MT070, MT174, MT267, and MT734 (a.k.a. VI Cygni #11) are single-lined spectroscopic binaries while one (MT103) is a double-lined system (B1V+B2V). MT070 is noteworthy as the longest period system yet measured in Cyg OB2, with P=6.2 yr. The other four systems have periods ranging between 4 and 73 days. MT174 is noteworthy for having a probable mass ratio q<0.1, making it a candidate progenitor to a low-mass X-ray binary. These measurements bring the total number of massive binaries in Cyg OB2 to 25, the most currently known in any single cluster or association.