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Session 102 - Pulsating Stars.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
Using the Goddard High Resolution Spectrograph on the Hubble Space Telescope we have measured the orbital radial velocity changes for the companion of the Cepheid S Muscae. The observations were done at minimum and maximum orbital velocities. The two spectra were cross-correlated. The velocity difference was measured to be 30.6 +/- 0.4 km/s. The difference for the orbital velocities of the Cepheid for the same phases was determined to be 26.9 +/-0.4 km/s. This gives a mass ratio of 1.14 +/-0.06. For a spectral type between B3.5 V and B5 V for the companion S Mus B its mass is 5.0 +/- 0.3 M(sun). With the mass ratio of 1.14 the mass of the Cepheid, with a period of 9.6 days, comes out to be 5.7 +/- 0.4 solar masses. This compares with a pulsational mass of 5.5 solar masses. Taking the 5.7 solar masses for the Cepheid at face value its absolute visual magnitude of M(V)=-4.29 indicates a high degree of excess interior mixing in its main sequence progenitor corresponding to convective overshoot by one pressure scale height. Even for the upper mass limit the excess mixing has to correspond to convective overshoot by 1/2 pressure scale height.
