Likely detection of water-rich asteroid debris in a metal-polluted white dwarf

Likely detection of water-rich asteroid debris in a metal-polluted white dwarf

The cool white dwarf SDSS J124231.07+522626.6 exhibits photospheric absorption lines of eight distinct heavy elements in medium resolution optical spectra, notably including oxygen. The T eff = 13 000 K atmosphere is helium-dominated, but the convection zone contains significant amounts of hydrogen...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2015-06, Vol.450 (2), p.2083-2093
Main Authors: Raddi, R, Gänsicke, B. T, Koester, D, Farihi, J, Hermes, J. J, Scaringi, S, Breedt, E, Girven, J
Format: Article
Language:eng
Subjects:
Accretion disks
Accumulation
Asteroid detection
Asteroids
Astrophysics
Debris
Gases
Moisture content
Optical properties
Planetary systems
Spectrum analysis
Star & galaxy formation
Stellar atmospheres
Symbols
White dwarf stars
White dwarfs
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Summary:The cool white dwarf SDSS J124231.07+522626.6 exhibits photospheric absorption lines of eight distinct heavy elements in medium resolution optical spectra, notably including oxygen. The T eff = 13 000 K atmosphere is helium-dominated, but the convection zone contains significant amounts of hydrogen and oxygen. The four most common rock-forming elements (O, Mg, Si, and Fe) account for almost all the accreted mass, totalling at least 1.2 × 1024 g, similar to the mass of Ceres. The time-averaged accretion rate is 2 × 1010 g s−1, one of the highest rates inferred among all known metal-polluted white dwarfs. We note a large oxygen excess, with respect to the most common metal oxides, suggesting that the white dwarf accreted planetary debris with a water content of ≈38 per cent by mass. This star, together with GD 61, GD 16, and GD 362, form a small group of outliers from the known population of evolved planetary systems accreting predominantly dry, rocky debris. This result strengthens the hypothesis that, integrated over the cooling ages of white dwarfs, accretion of water-rich debris from disrupted planetesimals may significantly contribute to the build-up of trace hydrogen observed in a large fraction of helium-dominated white dwarf atmospheres.
ISSN:0035-8711
1365-2966