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Session 96 - Cepheids and Supergiant Variable Stars.
Display session, Thursday, January 16
Metropolitan Ballroom,
Masses for Cepheid variable stars can be measured by combining the orbital velocity amplitude for the Cepheid (from a ground-based orbit) with the orbital velocity amplitude of a hot main sequence companion (observed in the ultraviolet from satellites such as IUE and HST) and the mass of the companion (inferred from from the ultraviolet energy distribution). Observations of 5 binary systems are now completed or in progress with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. Recently completed observations of U Aql lead to a mass of 5.1 \pm 1.1 M\sun. We will discuss the results for S Mus, V350 Sgr, U Aql, and Y Car, and the constraints they place on stellar evolution calculations. As would be expected, some of the B companions have high rotational velocities, decreasing the accuracy with which their orbital velocities can be measured. The preliminary conclusion from the 4 HST targets and SU Cyg (mass from IUE observations) is that a weighted mean indicates no convective overshoot but the mode (which reflects the HST results better) agrees with the modest overshoot used in the Geneva evolutionary calculations.
Financial Support was provided by a NASA grant GO-4541-01 to EB--V and GO-4541.02 to KGC, a grant from the Natural Sciences and Engineering Council, Canada to NRE, from the AXAF Science Center NASA Contract NAS8-39073.
