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C. M. Oliveira (Johns Hopkins University), P. Chayer (University of Victoria & Johns Hopkins University), J. Dupuis , H. W. Moos (Johns Hopkins University)
We report the detection of unexpectedly strong OVI absorption lines at 1032 Å~and 1038 Å~in three DA white dwarf spectra obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE): WD0134-164 (GD 984), WD2152-548 (2RE J2156-543), and WD2247+583 (Lan 23).
If these features are formed in the ISM, the OVI column densities along the sight lines of these stars are log N(OVI) > 14.0. But such high OVI column densities are not expected to originate in the local ISM over such small pathlengths (d = 96-135 pc). In addition, the radial velocities of the OVI lines are clearly separated from those of typical ISM lines, except for WD2152-548.
A photospheric origin for the OVI lines is hard to reconcile with the known properties of these stars (i.e. WD0134-164 and WD2152-548 have effective temperature below 50,000 K) and other available observations in the UV. We investigate further the photospheric hypothesis using non-LTE model atmospheres computed with various oxygen abundance profiles and also explore other scenarios such as circumstellar or ISM origin. These OVI detections raise interesting questions about white dwarf atmospheres and the local ISM.
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U. S. participants has been provided by NASA contract NAS5-32985.
The author(s) of this abstract have provided an email address for comments about the abstract: oliveira@pha.jhu.edu