N. Evans (Smithsonian Astrophysical Observatory)
Cepheids provide insight into both star formation and stellar evolution. Multiwavelength studies supply binary/multiple properties for these reasonably massive stars, which allows the exploration of differences between between high and low mass stars formation. We are conducting a survey of Cepheids with the Hubble Space Telescope Wide Field Camera 3 (WFC3) to identify possible resolved companions, for example Eta Aql. X-ray observations (Chandra and XMM-Newton) can confirm whether possible low mass companions are young enough to be physical companions of Cepheids, hence providing constraints on star formation. In a related study of intermediate mass stars, Chandra X-ray observations of late B stars in Tr 16 have been used to determine the fraction which have low mass companions (which are X-ray active in contrast to the late B stars which are X-ray quiet). Cepheids have long been used as benchmarks for evolutionary calculations where a measured mass can be combined with a luminosity for an evolved supergiant. The basis for observed masses is ground-based orbits. We discuss the combination of new velocity data from the Moscow group and the Tennessee State Automatic Spectroscopic Telescope (AST) and the new the orbit of V350 Sgr, as well as other recent developments in measured masses.
