Red supergiant stars in binary systems. I. Identification and characterisation in the Small Magellanic Cloud from the UVIT ultraviolet imaging survey

Abstract

We aim to identify and characterise binary systems containing red supergiant (RSG) stars in the Small Magellanic Cloud (SMC) using a newly available ultraviolet (UV) point source catalogue obtained using the Ultraviolet Imaging Telescope (UVIT) on board AstroSat. We select a sample of 560 SMC RSGs based on photometric and spectroscopic observations at optical wavelengths and cross-match this with the far-UV point source catalogue using the UVIT F172M filter, finding 88 matches down to m${}_{F172M}$=20.3 ABmag, which we interpret as hot companions to the RSGs. Stellar parameters (luminosities, effective temperatures and masses) for both components in all 88 binary systems are determined and we find mass distributions in the ranges 6.1 to 22.3 Solar masses for RSGs and 3.7 to 15.6 Solar masses for their companions. The most massive RSG binary system in the SMC has a combined mass of 32 $\pm$4 M${}_{\odot }$, with a mass ratio (q) of 0.92. By simulating observing biases, we find an intrinsic multipliciy fraction of 18.8 $\pm$ 1.5% for mass ratios in the range 0.3 < q < 1.0 and orbital periods approximately in the range 3 < log P [days] < 8. By comparing our results with those of a similar mass on the main-sequence, we determine the fraction of single stars to be ~20% and argue that the orbital period distribution declines rapidly beyond log P ~ 3.5. We study the mass-ratio distribution of RSG binary systems and find that a uniform distribution best describes the data below 14 M${}_{\odot }$. Above 15 M${}_{\odot }$, we find a lack of high mass-ratio systems.

Accepted for publication in MNRAS; 17 pages

References in corpus (15)

• Modules for Experiments in Stellar Astrophysics (MESA)
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Binary interaction dominates the evolution of massive stars
• Southern Massive Stars at High Angular Resolution: Observational Campaign and Companion Detection
• The effect of massive binaries on stellar populations and supernova progenitors
• The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity
• Spitzer SAGE-SMC Infrared Photometry of Massive Stars in the Small Magellanic Cloud
• Detailed models of interacting short-period massive binary stars
• The Uncertain Masses of Progenitors of Core Collapse Supernovae and Direct Collapse Black Holes
• Discrepancies in the ages of young star clusters; evidence for mergers?
• On `On the Red Supergiant Problem': a rebuttal, and a consensus on the upper mass cutoff for II-P progenitors
• The VLT-FLAMES Tarantula Survey: XXXI. Radial velocities and multiplicity constraints of red supergiant stars in 30 Doradus
• Wide binary companions to massive stars and their use in constraining natal kicks
• Evolved Massive Stars at Low-metallicity II. Red Supergiant Stars in the Small Magellanic Cloud
• The temperatures of red supergiants in low metallicity environments