The Accreting White Dwarf in the Close Binary EUVE J1016−053

Abstract

The hot white dwarf in the close binary EUVE J1016Ϫ053 (ϭRE 1016Ϫ053) has been classified as a DAO white dwarf; its mixed H͞He 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 J1016Ϫ053 with the Extreme Ultraviolet Explorer (EUVE). We report the discovery of a 230% EUV flux variation over a period of 57.3 minutes, which we attribute to surface abundance inhomogeneities modulated over the stellar rotation period, P rot . 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 Y͞Y J ϭ Z͞Z J ϭ 2 ϫ 10 Ϫ3 , 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 Ϫ19 and 10 Ϫ18 M J yr Ϫ1 , i.e., much lower than the Bondi-Hoyle accretion rate, which is of the same order as the red dwarf mass-loss rate (Ն10 Ϫ14 M J yr Ϫ1 ), 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.

Adding More Mysteries to the DA White Dwarf GD 394

“…With the exception of a handful of hot white dwarfs in the close binary systems V471 Tauri (Jensen et al 1986), EUVE J1016[053 (Vennes et al 1997a), EUVE J0720[317 (Dobbie et al 1999), and the high-Ðeld magnetic white dwarf EUVE J0317[855 (Ferrario et al 1997), DA white dwarfs are generally not variable in the EUV. Its EUV variability and the fact that it has the largest known Si abundance measured in DA (Holberg, Barstow, & Sion 1998) gives an unique status to GD 394.…”

A possible detection mechanism for pre-low-mass X-ray binaries

“…I should note at this point, however, that Vennes, Dupuis & Bowyer (1997) concluded that the accretion of a red dwarf stellar wind on to the white dwarf in the PCEB EUVE J1016−053 is much less efficient than that anticipated by their simple Bondi–Hoyle model. A similar conclusion was reached by Mullan et al (1991) for the PCEB V471 Tau.…”

Stellar Masses, Kinematics, and White Dwarf Composition for Three Close DA+dMe Binaries

“…The presence of heavy elements in the atmospheres of the white dwarfs in EUVE J0720[317 and EUVE J1016[053 was inferred from a study of EUV E spectra of these objects (Dupuis, Vennes, & Bowyer 1997 ;Vennes et al 1997a), but the detection of photospheric carbon in GHRS spectra of these two objects and of EUVE J2013]400 is the Ðrst direct evidence for the presence of photospheric heavy elements. Figures 7 and 8 show a model atmosphere analysis of the helium and carbon abundance in the three white dwarfs.…”

“…On the other hand, Vennes et al (1997a) and Dupuis et al (1997) predicted an abundance of carbon of log C/H \ [ 6.2 and [5.7 in EUVE J1016[053 and EUVE J0720[317, respectively, based on a study of the EUV continuum spectral energy distribution. GHRS spectra centered on the C IV j1550 doublet were obtained at a single epoch for each star and reveal abundances of carbon larger than those inferred from EUV spectroscopy.…”

“…Many young post-CE systems have a DAO white dwarf primary, i.e., of mixed hydrogen and helium composition. EUV spectra of the white dwarf in EUVE J1016[053 also show evidence of accreted heavy elements and EUV variability, which, coupled to the white dwarf rotation period, indicate surface abundance inhomogeneities (Vennes et al 1997a).…”