The HST Ultraviolet Spectrum of V723 Mon: Additional Evidence of a Stellar Companion

Abstract

V723 Mon is a high mass function (f=1.7Msun) single lined spectroscopic binary with a red giant primary that Jayasinghe et al. (2021) suggested had a black hole as its massive companion. Unfortunately, el-Badry et al. (2022) demonstrated that it had a hotter stellar companion whose detectability in optical spectra was difficult due to its rapid rotation. Here we confirm the presence of the stellar companion with a Hubble Space Telescope STIS ultraviolet spectrum.