Cepheids: New Satellite Results | Nancy Evans ( Smithsonian Astrophysical Observatory )

The first characteristic measured for Cepheids is their periods. The next step is to determine their pulsation mode. We have made month long observations with the MOST satellite of a fundamental mode Cepheid (RT Aur) and an overtone Cepheid (SZ Tau). The quantity and quality of the satellite data have shown that the Fourier parameters of the overtone are far more variable than those of the fundamental. A series of studies have been made of the binary properties of Cepheids, providing insight into star formation and dynamical evolution. A survey of 70 Cepheids was made with HST WFC3 to identify possible resolved companions. This was followed up with XMM-Newton observations to determine which possible companions are young X-ray active stars, and hence physical companions of Cepheids. This provides information about the frequency, separations, and mass ratios. Finally, the measured masses of Cepheids will be summarized, and new developments discussed.