Physics
Scientific paper
Jul 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8179b&link_type=abstract
HST Proposal ID #8179
Physics
Hst Proposal Id #8179 Hot Stars
Scientific paper
We propose high S/N {15:1 to 30:1} STIS far UV observations of the hottest known DA white dwarfs. With temperatures in the range 70, 000-130, 000K, these stars represent an important but little understood link between the H-rich central stars of planetary nebulae {CPN} and the general population of DA white dwarfs. Stellar temperatures are extremely difficult to determine in this range and depend upon knowledge of the photospheric composition, which is also a mystery. Consequently, their relationship to the cooler DA stars remains undefined. Far UV measurements of the abundances of heavy elements are essential for an ultimate determination of the stellar temperature. Coupling STIS data with an analysis of the Lyman lines obtained with planned FUSE observations, it will be possible to determine the physical parameters of these objects and finally track their evolution along the DA cooling sequence. In addition, we will search for evidence of mass outflow, in the form of blueward asymmetries in the heavy element line profiles, which is believed to cause departures from the compositions predicted by radiative levitation theory but which has been observed in only two DA white dwarfs.
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