The Red Supergiant Binary Fraction as a Function of Metallicity in M31 and M33

Abstract

Recent work measuring the binary fraction of evolved red supergiants (RSGs) in the Magellanic Clouds points to a value between 15-30%, with the majority of the companions being un-evolved B-type stars as dictated by stellar evolution. Here I extend this research to the Local Group galaxies M31 and M33, and investigate the RSG binary fraction as a function of metallicity. Recent near-IR photometric surveys of M31 and M33 have lead to the identification of a complete sample of RSGs down to a limiting $\log L/L_{\odot }\ge 4.2$. To determine the binary fraction of these M31 and M33 RSGs, I used a combination of newly obtained spectroscopy to identify single RSGs and RSG+OB binaries as well as archival UV, visible and near-IR photometry to probabilistically classify RSGs as either single or binary based on their colors. I then adjusted the observed RSG+OB binary fraction to account for observational biases. The resulting RSG binary fraction in M33 shows a strong dependence on galactocentric distance with the inner regions having a much higher binary fraction ($41.2_{-7.3}^{+12.0}$%) than the outer regions ($15.9_{-1.9}^{+12.4}$%). Such a trend is not seen in M31; instead, the binary fraction in lightly reddened regions remains constant at $33.5_{-5.0}^{+8.6}$%. I conclude the changing RSG binary fraction in M33 is due to a metallicity dependence with higher metallicity environments having higher RSG binary fractions. This dependence most likely stems not from changes in the physical properties of RSGs due to metallicity, but changes in the parent distribution of OB binaries.

ApJ, accepted

References in corpus (16)

• Binary interaction dominates the evolution of massive stars
• Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
• A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars
• The metallicity gradient of M 33: chemical abundances of HII regions
• A new survey of cool supergiants in the Magellanic Clouds
• Carbon, nitrogen and oxygen abundance gradients in M101 and M31
• The Close Binary Frequency of Wolf-Rayet Stars as a Function of Metallicity in M31 and M33
• The Luminosity Function of Red Supergiants in M31
• The M Supergiant High Mass X-Ray Binary 4U 1954+31
• The Betelgeuse Project: Constraints from Rotation
• The VLT-FLAMES Tarantula Survey: XXXI. Radial velocities and multiplicity constraints of red supergiant stars in 30 Doradus
• Is Betelgeuse the Outcome of a Past Merger?
• Binary Red Supergiants II: Discovering and Characterizing B-type Companions
• Multiplicity among the cool supergiants in the Magellanic Clouds

Cited by in corpus (18)

• SN2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova
• Evolved Massive Stars at Low-metallicity V. Mass-Loss Rate of Red Supergiant Stars in the Small Magellanic Cloud
• The IACOB project. VII. The rotational properties of Galactic massive O-type stars revisited
• The Time-Averaged Mass-Loss Rates of Red Supergiants As Revealed by their Luminosity Functions in M31 and M33
• Binary evolution pathways of Blue Large-Amplitude Pulsators
• Type II-P Supernova Progenitor Star Initial Masses and SN 2020jfo: Direct Detection, Light Curve Properties, Nebular Spectroscopy, and Local Environment
• On the impact of spectral template uncertainties in synthetic stellar populations
• Dust Extinction Law in Nearby Star-Resolved Galaxies. II. M33 Traced by Supergiants
• The Extremely Metal-Poor SN 2023ufx: A Local Analog to High-Redshift Type II Supernovae
• On the Anti-Correlation between Duration and Redshift in Gamma-ray Bursts
• Compact object populations over cosmic time II. Compact object merger rates and masses over redshift from varying initial conditions
• Disappearance of a massive star in the Andromeda Galaxy due to formation of a black hole
• Dust around massive stars is agnostic to galactic environment: New insights from PHAT/BEAST
• Red supergiant stars in binary systems II. Confirmation of B-type companions of red supergiants in the Small Magellanic Cloud using Hubble ultra-violet spectroscopy
• Stellar evolution through the Red Supergiant phase
• Red Supergiants in the Milky Way and Nearby Galaxies
• A machine-learning photometric classifier for massive stars in nearby galaxies II. The catalog
• Testing Evolutionary Models with Red Supergiant and Wolf-Rayet Populations