Solar Abundances of Rock Forming Elements, Extreme Oxygen and Hydrogen in a Young Polluted White Dwarf

Abstract

The Teff = 20,800 K white dwarf WD 1536+520 is shown to have broadly solar abundances of the major rock forming elements O, Mg, Al, Si, Ca, and Fe, together with a strong relative depletion in the volatile elements C and S. In addition to the highest metal abundances observed to date, including log(O/He) = -3.4, the helium-dominated atmosphere has an exceptional hydrogen abundance at log(H/He) = -1.7. Within the uncertainties, the metal-to-metal ratios are consistent with the accretion of an H2O-rich and rocky parent body, an interpretation supported by the anomalously high trace hydrogen. The mixed atmosphere yields unusually short diffusion timescales for a helium atmosphere white dwarf, of no more than a few hundred yr, and equivalent to those in a much cooler, hydrogen-rich star. The overall heavy element abundances of the disrupted parent body deviate modestly from a bulk Earth pattern, and suggest the deposition of some core-like material. The total inferred accretion rate is 4.2e9 g/s, and at least 4 times higher than any white dwarf with a comparable diffusion timescale. Notably, when accretion is exhausted in this system, both metals and hydrogen will become undetectable within roughly 300 Myr, thus supporting a scenario where the trace hydrogen is related to the ongoing accretion of planetary debris.

To be published in MNRAS

References in corpus (11)

• The frequency of planetary debris around young white dwarfs
• A gaseous metal disk around a white dwarf
• The Chemical Composition of an Extrasolar Minor Planet
• Externally-polluted white dwarfs with dust disks
• On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars
• Carbon Deficiency in Externally-Polluted White Dwarfs: Evidence for Accretion of Asteroids
• The frequency and infrared brightness of circumstellar discs at white dwarfs
• The chemical diversity of exo-terrestrial planetary debris around white dwarfs
• Likely detection of water-rich asteroid debris in a metal-polluted white dwarf
• Signs of a faint disc population at polluted white dwarfs
• Scars of Intense Accretion Episodes at Metal-Rich White Dwarfs

Cited by in corpus (3)

• Destruction of Refractory Carbon in Protoplanetary Disks
• Does a Differentiated, Carbonate-Rich, Rocky Object Pollute the White Dwarf SDSSJ104341.53+085558.2?
• Magnetospherically-trapped dust and a possible model for the unusual transits at WD 1145+017