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SDSS J084539.17+225728.0 : the first DBZ white dwarf with a metal-rich gaseous debris disc

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Gaensicke, B. T. (Boris T.), Koester, Detlev, 1941-, Marsh, T. R., Rebassa-Mansergas, A. and Southworth, J. (John). (2008) SDSS J084539.17+225728.0 : the first DBZ white dwarf with a metal-rich gaseous debris disc. Monthly Notices of the Royal Astronomical Society, Vol.391 (No.1). L103-L107. ISSN 0035-8711

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Abstract

We report the discovery of a third white dwarf hosting a gaseous debris disc, SDSS J084539.17+225728.0. The typical double-peaked Ca II 8498,8542,8662 angstrom emission lines can be modelled in terms of a Keplerian gas disc with a radial extent from similar to 0.5 to similar to 1.0 R-circle dot. The effective temperature of SDSS 0845+2257, T-eff similar or equal to 18 600 +/- 500 K, is comparable to the two other white dwarfs with gaseous discs, SDSS 1043+0855 and SDSS 1228+1040, and hence substantially hotter than the bulk of white dwarfs where dusty debris discs were identified through the presence of infrared excess flux. This may suggest that the conditions to produce emission lines from debris discs in the optical wavelength range are only met for a relatively narrow range in T-eff. The observed asymmetry in the line profiles indicates a substantial eccentricity in the disc. Two spectra obtained four years apart reveal a significant change in the shapes and equivalent widths of the line profiles, implying that the circumstellar disc evolves on relatively short time-scales. In contrast to SDSS 1043+0855 and SDSS 1228+1040, SDSS 0845+2257 has a helium-dominated atmosphere. We detect photospheric absorption lines of He, Ca, Mg and Si in the Sloan Digital Sky Survey spectrum, and hence classify SDSS 0845+2257 as DBZ white dwarf. The abundances for the three metals determined from model atmosphere fits are Ca/He similar or equal to 1.3 x 10(-7), Mg/He similar or equal to 6.0 x 10(-6) and Si/He similar or equal to 8.0 x 10(-6). From the non-detection of Ha, we derive H/He < 3 x 10(-5), which implies that the hydrogen-to-metal abundance ratio of the circumstellar material is greater than or similar to 1000 times lower than in the Sun. This lends strong support to the hypothesis that the gaseous and dusty debris discs found around roughly a dozen white dwarfs originate from the disruption of rocky planetary material.

Item Type: Journal Article
Subjects: Q Science > QB Astronomy
Divisions: Faculty of Science > Physics
Library of Congress Subject Headings (LCSH): White dwarf stars, Sloan Digital Sky Survey, Circumstellar matter
Journal or Publication Title: Monthly Notices of the Royal Astronomical Society
Publisher: Wiley
ISSN: 0035-8711
Official Date: 21 November 2008
Volume: Vol.391
Number: No.1
Number of Pages: 5
Page Range: L103-L107
Identification Number: 10.1111/j.1745-3933.2008.00565.x
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Restricted or Subscription Access
Funder: Alfred P. Sloan Foundation, National Science Foundation (U.S.) (NSF), United States. Dept. of Energy, United States. National Aeronautics and Space Administration (NASA), Japan. Monbushō, Max Planck Society, Higher Education Funding Council for England (HEFCE)
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URI: http://wrap.warwick.ac.uk/id/eprint/28861

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