Computer Science
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6504b&link_type=abstract
HST Proposal ID #6504
Computer Science
Hst Proposal Id #6504 Cool Stars
Scientific paper
This is a proposal for the fourth year of an originally threeyear proposal which was accepted for cycles 3, 4, 5 and 6.The aim is to determine Cepheid masses for binaries withCepheids. For 2 decades the Cepheid ``mass problem" haspersisted: Mass determinations from standard evolutionarytracks and those from pulsation theory gave conflictingresults. The luminosity of a Cepheid with a given mass dependssensitively on the amount of excess mixing above the core ofthe main sequence progenitor. Hence a good mass determinationfor a Cepheid with known luminosity measures the amount ofconvective overshoot. This knowledge is important for theinterpretation of HR diagrams of populous clusters in the LMC,especially for age determinations, and also for theunderstanding of mixing processes in stars. IUE observationshave revealed a number of Cepheids with blue companions,whose orbits have now been determined by groundbasedobservations. We propose to measure the orbital radialvelocities of altogether 5 companions for wavelengths shorterthan 2000A. The ratio of the orbital velocity amplitudes forthe binary provides the mass ratio for the stars. Theeffective temperature of the main sequence companion andthereby its mass is determined from its ultraviolet spectrumand energy distribution. With good GHRS spectra the velocityratio and thereby the mass ratio can be determined with anaccuracy of +/-10%.
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