Metal Diffusion and Radiative Levitation in Hot Helium-Rich White Dwarfs

Details Metal Diffusion and Radiative Levitation in Hot Helium-Rich White Dwarfs Metal Diffusion and Radiative Levitation in Hot Helium-Rich White Dwarfs

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6455w&link_type=abstract

HST Proposal ID #6455

Computer Science

Hst Proposal Id #6455 Hot Stars

Scientific paper

We propose to observe five helium-rich (DO) white dwarfs inorder to determine their photospheric CNO abundances. High-resolution high-S/N ultraviolet spectroscopy with the GHRSshall be performed in order to detect weak absorption lines.The data will be analysed with non-LTE metal line blanketedmodel atmospheres. The results will be compared to predictionsfrom state-of-the-art diffusion/radiative levitation theory.In parallel, we will perform self-consistent diffusioncalculations under non-LTE conditions. The observed metalabundances will serve as bench-marks for such kind of newcalculations. As a basis for this work we have obtained high-S/N optical spectra of almost all known DO white dwarfs withinthe last five years. A comprehensive analysis of theatmospheric parameters is now available. For the presentproposal we have selected five targets which represent the non-DA white dwarf cooling sequence from the hot end down to theDB gap. HST UV observations are crucial because the DO whitedwarfs are generally too faint for high-S/N spectroscopy withIUE. No metal lines except from carbon in some stars weredetected in the optical spectra. UV spectra allow thedetection of metals at very low abundances.

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