SDSSJ104341.53+085558.2: A second white dwarf with a gaseous debris disc

Abstract

Intermediate resolution spectroscopy of the white dwarf SDSSJ104341.53+085558.2 contains double-peaked emission lines of CaII8498,8542,8662 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 SDSSJ1228+1040. A photospheric Magnesium abundance of 0.3 times the solar value, determined from the observed MgII4481 absorption line, implies that the white dwarf is accreting from the circumstellar material. The absence of Balmer emission lines and of photospheric HeI4471 absorption indicates that the accreted material is depleted in volatile elements and, by analogy with SDSS1228+1040, may be the result of the tidal disruption of an asteroid. Additional spectroscopy of the DAZ white dwarfs WD1337+705 and GD362 does not reveal CaII emission lines. GD362 is one of the few cool DAZ that display strong infrared flux excess, thought to be originating in a circumstellar dust disc, and its temperature is likely too low to sublimate sufficient amounts of disc material to generate detectable CaII emission. WD1337+705 is, as SDSS1228+1040 and SDSS1043+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 CaII emission triplet. Our inspection of 7360 white dwarfs from SDSS DR4 fails to unveil additional strong "metal gas disc" candidates, and implies that these objects are rather rare.