Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...482l..73v&link_type=abstract
Astrophysical Journal Letters v.482, p.L73
Astronomy and Astrophysics
Astronomy
13
Stars: Abundances, Stars: Binaries: Close, Stars: Individual Alphanumeric: Euve J1016-053, Ultraviolet: Stars
Scientific paper
The hot white dwarf in the close binary EUVE J1016-053 (=RE 1016-053) has been classified as a DAO white dwarf; its mixed H/He composition has been attributed to steady accretion from the close red dwarf companion. We have obtained extreme-ultraviolet (EUV) photometric and spectroscopic observations of EUVE J1016-053 with the Extreme Ultraviolet Explorer (EUVE). We report the discovery of a ~30% EUV flux variation over a period of 57.3 minutes, which we attribute to surface abundance inhomogeneities modulated over the stellar rotation period, Prot. The EUVE spectrum shows the effect of heavy-element opacities on the white dwarf EUV energy distribution. Spectral synthesis including trace opacities of helium and a group of heavy elements (C, N, O, Si, S, Fe) in the otherwise hydrogen-rich atmosphere constrains abundances to Y/Ysolar = Z/Zsolar = 2 x 10-3, in support of a simple accretion model. The low surface-averaged helium abundance measured in the white dwarf atmosphere limits the accretion rate to between 10-19 and 10-18 Msolar yr-1, i.e., much lower than the Bondi-Hoyle accretion rate, which is of the same order as the red dwarf mass-loss rate (>=10-14 Msolar yr-1), therefore invalidating a simple wind-accretion model. We speculate that weak mass loss from the white dwarf or interaction with a magnetosphere may inhibit accretion onto the white dwarf. Accretion of heavy elements may also be restricted to smaller areas, possibly correlating to magnetic poles.
Bowyer Stuart
Dupuis Jean
Pradhan Anil Kumar
Vennes Stephane
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