Testing the Theory of Radiative Levitation in DA White Dwarfs

Details Testing the Theory of Radiative Levitation in DA White Dwarfs Testing the Theory of Radiative Levitation in DA White Dwarfs

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6782h&link_type=abstract

HST Proposal ID #6782

Physics

Hst Proposal Id #6782 Hot Stars

Scientific paper

We propose GHRS observations of two H-rich DA white dwarfswith temperatures near 40,000K. This temperature defines thecritical point, above which the mechanism of radiativelevitation becomes efficient enough to prevent elementsheavier than H or He from sinking out of the atmospheres of DAwhite dwarfs under the influence of gravity. Below thistemperature, DA atmospheres are observed to be more or lesspure hydrogen. However, measurement of photospheric abundancesof stars having the same temperatures (and gravities) givequite disparate results - GD394 has a larger heavy elementcontent than predicted, whereas the nearly identical starGD153 has an unexpectedly pure H atmosphere. Unfortunately,near 40,000K, only these two stars are bright enough to beobserved at high dispersion with IUE at sufficient S/N. Newobservations are needed to begin providing the observationalevidence necessary to establish the physical mechanisms thatdetermine white dwarf composition, and cause departures fromthe predictions of radiative levitation theory.

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