Direct Measurement of the BE Ursae Majoris SDO Primary Star Mass-A Critical Test Case for Common Envelope Evolution

Details Direct Measurement of the BE Ursae Majoris SDO Primary Star Mass-A Critical Test Case for Common Envelope Evolution Direct Measurement of the BE Ursae Majoris SDO Primary Star Mass-A Critical Test Case for Common Envelope Evolution

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6427f&link_type=abstract

HST Proposal ID #6427

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Hst Proposal Id #6427 Binaries And Star Fo

Scientific paper

BE UMa is a post-common envelope, pre-cataclysmic binarysystem with nearly unique properties. The primary is a veryhot ~100,000 K sdO, about to become a white dwarf, separatedby 8 solar radii from a G9V-K5V secondary. With most of itsenergy distribution emitted in the extreme ultraviolet, itproduces a spectacular reprocessing spectrum on the facingside of the cool main sequence companion. This spectrumincludes strong optical continuum and emission lines, whichhave been used to determine the radial velocity of thesecondary star. It is also one of the few evolved systemswhich eclipses, so that tight constaints on the orbitalinclination are available, as is the spectrum of the coolsecondary star. It is one of the few to have an associatedplanetary nebula. Most importantly, the parameters derivedfor the primary star suggest that the binary has been``uncloaked'' from the common envelope for only 1E6 years.But has the primary star evolved as a normal post-AGB objects,as the atmospheric parameters and mass (0.6 solar) inferredfrom analyzing its spectrum suggest? Our model of thereprocessed envelope suggests instead that the primary has asubstantially higher mass.We propose here to obtain GHRSspectra to measure the velocity of the He II 1640A absorptionline in the helium-rich primary especially at orbitalquadratures in order to measure directly the mass, from theorbital solution and well as from any detectable gravitationalredshift. The orbital separation, another key parameter ofthe

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