Cepheid Masses -CYC3-HIGH
Abstract
For 2 decades the "Cepheid mass problem" has persisted: Mass determinations from standard evolutionary tracks and those from pulsation theory gave conflicting values. The luminosity of a Cepheid of given mass depends sensitively on the amount of convective overshoot above the core of the main sequence progenitor. Hence a good mass determination for the Cepheid with known luminosity will measure the amount of convective core overshoot. This knowledge is important for interpretation of HR diagrams of populous clusters in the LMC and especially for age determinations. It is also necessary for the understanding of the 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 5 blue Cepheid companions on GHRS spectra for wavelengths shorter than 2000 A. The ratios of the orbital velocities for the binaries provide the mass ratios for the stars. The effective temperature of the companion can be determined from its energy distribution. For main sequence stars this also determines its mass. With GHRS spectra the orbital velocity ratio and thereby the mass ratio can be determined with an accuracLy of +/- 10 %.
- Publication:
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HST Proposal
- Pub Date:
- June 1992
- Bibcode:
- 1992hst..prop.4541B