Cepheid Masses

Details Cepheid Masses Cepheid Masses

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5854b&link_type=abstract

HST Proposal ID #5854

Computer Science

Hst Proposal Id #5854 Cool Stars

Scientific paper

This is a proposal for the third {and fourth} year of a three year proposal which was accepted for the last two years. The aim is to determine Cepheid masses for binaries with Cepheids. For 2 decades the Cepheid ``mass problem" has persisted: Mass determinations from standard evolutionary tracks and those from pulsation theory gave conflicting results. The luminosity of a Cepheid with given mass depends sensitively on the amount of convective overshoot above the core of the main sequence progenitor. Hence a good mass determination for a Cepheid with known luminosity measures the amount of convective overshoot. This knowledge is important for the interpretation of HR diagrams of populous clusters in the LMC and especially for age determinations. It is also necessary for the understanding of mixing processes in stars. IUE observations have revealed a number of Cepheid binaries with blue companions whose orbits have now been determined by groundbased observations. We propose to measure the orbital radial velocities of altogether 5 blue Cepheid companions for wavelengths shorter than 2000 A. The ratio of the orbital velocity amplitudes for the binary provides the mass ratio for the stars. The effective temperature for the companion is determined from its ultraviolet energy distribution. For main sequence stars this also determines its mass. With good GHRS spectra the velocity ratio and thereby the mass ratio can be determined with an accuracy of +/- 10%

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