The Components of Cepheid Systems: The FN Vel System

Cepheid masses continue to be important tests of evolutionary tracks for intermediate-mass stars as well as important predictors of their future fate. For systems where the secondary is a B star, Hubble Space Telescope ultraviolet spectra have been obtained. From these spectra a temperature can be derived, and from this a mass of the companion M 2. Once Gaia DR4 is available, proper motions can be used to determine the inclination of the orbit. Combining mass of the companion, M 2, the mass function from the ground-based orbit of the Cepheid and the inclination produces the mass of the Cepheid, M 1. The Cepheid system FN Vel is used here to demonstrate this approach and what limits can be put on the Cepheid mass for inclination between 50° and 130°.