N. J. Dickinson, M. A. Barstow, I. Hubeny
The importance to stellar evolution of understanding the metal abundances in
hot white dwarfs is well known. Previous work has found the hot DA white dwarfs
REJ 1032+532, REJ 1614-085 and GD 659 to have highly abundant, stratified
photospheric nitrogen, due to the narrow absorption line profiles of the FUV N
V doublet and the lack of EUV continuum absorption. A preliminary analysis of
the extremely narrow, deep line profiles of the photospheric metal absorption
features of PG 0948+534 suggested a similar photospheric metal configuration.
However, other studies have found REJ 1032+532, REJ 1614-085 and GD 659 can be
well described by homogeneous models, with nitrogen abundances more in keeping
with those of white dwarfs with higher effective temperatures. Here, a
re-analysis of the nitrogen absorption features seen in REJ 1032+532, REJ
1614-085 and GD 659 is presented, with the aim of better understanding the
structure of these stars, to test which models better represent the observed
data and apply the results to the line profiles seen in PG 0948+534. A
degeneracy is seen in the modelling of the nitrogen absorption line profiles of
REJ 1032+532, REJ 1614-085 and GD 659, with low abundance, homogeneously
distributed nitrogen models most likely being a better representation of the
observed data. In PG 0948+534, no such degeneracy is seen, and the
enigmatically deep line profiles could not be modelled satisfactorially.
View original:
http://arxiv.org/abs/1201.2940
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