Serendipitous discovery of a dusty disc around WDJ181417.84-735459.83

Abstract

Spectroscopic observations of white dwarfs reveal that many of them are polluted by exoplanetary material, whose bulk composition can be uniquely probed this way. We present a spectroscopic and photometric analysis of the DA white dwarf WDJ181417.84$-$735459.83, an object originally identified to have a strong infrared excess in the 2MASS and WISE catalogues that we confirmed to be intrinsic to the white dwarf, and likely corresponding to the emission of a dusty disc around the star. The finding of Ca, Fe and Mg absorption lines in two X-SHOOTER spectra of the white dwarf, taken 8 years apart, is further evidence of accretion from a dusty disc. We do not report variability in the absorption lines between these two spectra. Fitting a blackbody model to the infrared excess gives a temperature of 910$\pm 50$ K. We have estimated a total accretion flux from the spectroscopic metal lines of $|\dot{\mathrm{M}}|=1.784\times 10^9$g s${}^{-1}$.

Accepted for publication in MNRAS. 11 pages, 10 figures, 6 tables