SDSS J104341.53+085558.2: a second white dwarf with a gaseous debris disc

Abstract

Abstract Intermediate-resolution spectroscopy of the white dwarf SDSS J104341.53+085558.2 (SDSS J1043+0855) contains double-peaked emission lines of Ca iiλλ8498, 8542, 8662 and identifies this object to be the second single white dwarf to be surrounded by a gaseous disc of metal-rich material, similar to the recently discovered SDSS J1228+1040. A photospheric magnesium abundance of 0.3 times the solar value, determined from the observed Mg iiλ4481 absorption line, implies that the white dwarf is accreting from the circumstellar material. The absence of Balmer emission lines and of photospheric He iλ4471 absorption indicates that the accreted material is depleted in volatile elements and, by analogy with SDSS J1228+1040, may be the result of the tidal disruption of an asteroid. Additional spectroscopy of the DAZ white dwarfs WD 1337+705 and GD 362 does not reveal Ca ii emission lines. GD 362 is one of the few cool DAZ white dwarfs that display strong infrared flux excess, thought to be originating in a circumstellar dust disc, and its temperature is probably too low to sublimate sufficient amounts of disc material to generate detectable Ca ii emission. WD 1337+705 is, like SDSS J1228+1040 and SDSS J1043+0855, moderately hot, but has the lowest Mg abundance of those three stars, suggesting a possible correlation between the photospheric Mg abundance and the equivalent width of the Ca ii emission triplet. Our inspection of 7360 white dwarfs from the Sloan Digital Sky Survey Data Release 4 fails to unveil additional strong ‘metal gas disc’ candidates, and implies that these objects are rather rare.