V350 Sgr is a classical Cepheid suitable for mass determination. It has a hot companion which is prominent in the ultraviolet and which is not itself a binary. We have obtained two high resolution echelle spectra of the companion at orbital velocity maximum and minimum with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) in the 1320 to 1510 \AA\/ region. By cross-correlating these spectra we obtained the orbital velocity amplitude of the companion with an uncertainty in the companion amplitude of 1.9 km sec−1. This provides a mass ratio of the Cepheid to the companion of 2.1. The ultraviolet energy distribution of the companion provides the mass of the companion, yielding a Cepheid mass of 5.2 ± 0.3 M⊙. This mass requires some combination of moderate main sequence core convective overshoot and rotation to match evolutionary tracks.
@article{arxiv.1808.10472,
title = {The Mass of the Cepheid V350 Sgr},
author = {Nancy Remage Evans and Charles Proffitt and Kenneth G. Carpenter and Elaine M. Winston and Gladys V. Kober and H. Moritz Günther and Natalia Gorynya and Alexey Rastorguev and L. Inno},
journal= {arXiv preprint arXiv:1808.10472},
year = {2018}
}