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2018MNRAS.481.4323G - Mon. Not. R. Astron. Soc., 481, 4323-4331 (2018/December-3)

Broadening of Ly α by neutral helium in DBA white dwarfs.


Abstract (from CDS):

Traces of photospheric hydrogen are detected in at least half of all white dwarfs with helium-dominated atmospheres through the presence of H α in high-quality optical spectroscopy. Previous studies have noted significant discrepancies between the hydrogen abundances derived from H α and Ly α for a number of stars where ultraviolet spectroscopy is also available. We demonstrate that this discrepancy is caused by inadequate treatment of the broadening of Ly α by neutral helium. When fitting Hubble Space Telescope far-ultraviolet spectroscopy of 17 DB white dwarfs using our new line profile calculations, we find good agreement between log (NH/NHe) measured from Ly α and H α. Larger values of log (NH/NHe) based on Ly α are still found for three stars, which are among the most distant in our sample, and we show that a small amount of interstellar absorption from neutral hydrogen can account for this discrepancy.

Abstract Copyright: © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

Journal keyword(s): line: profiles - stars: atmospheres - white dwarfs - ultraviolet: stars

Simbad objects: 22

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