The Mass of the Cepheid V350 Sgr

TL;DR

This study precisely measures the mass of the Cepheid V350 Sgr using ultraviolet spectra of its hot companion, providing key data to inform stellar evolution models.

Contribution

It presents the first high-resolution spectroscopic measurement of the companion's orbital velocity, enabling an accurate determination of the Cepheid's mass.

Findings

Cepheid V350 Sgr mass is 5.2 ± 0.3 solar masses.

Orbital velocity amplitude of the companion was measured with 1.9 km/sec uncertainty.

Mass ratio of Cepheid to companion is 2.1.

Abstract

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 $\pm$ 0.3 M$_\odot$. This mass requires some combination of moderate main sequence core convective overshoot and rotation to match evolutionary tracks.