Serendipitous Discovery of Nine White Dwarfs with Gaseous Debris Disks

Abstract

Optical spectroscopic observations of white dwarf stars selected from catalogs based on the Gaia DR2 database reveal nine new gaseous debris disks that orbit single white dwarf stars, about a factor of 2 increase over the previously known sample. For each source we present gas emission lines identified and basic stellar parameters, including abundances for lines seen with low-resolution spectroscopy. Principle discoveries include (1) the coolest white dwarf (T eff ≈ 12,720 K) with a gas disk; this star, WD0145+234, has been reported to have undergone a recent infrared outburst; (2) co-location in velocity space of gaseous emission from multiple elements, suggesting that different elements are well mixed; (3) highly asymmetric emission structures toward SDSS J0006+2858, and possibly asymmetric structures for two other systems; (4) an overall sample composed of approximately 25% DB and 75% DA white dwarfs, consistent with the overall distribution of primary atmospheric types found in the field population; and (5) never-before-seen emission lines from Na in the spectra of Gaia J0611−6931, semi-forbidden Mg, Ca, and Fe lines toward WD 0842+572, and Si in both stars. The currently known sample of gaseous debris disk systems is significantly skewed toward northern hemisphere stars, suggesting a dozen or so emission line stars are waiting to be found in the southern hemisphere.

Velocity-imaging the rapidly precessing planetary disc around the white dwarf HE 1349–2305 using Doppler tomography

“…The candidate emission feature detected in the 5169 Å Fe region also changes in morphology between the two epochs, where the red-shifted component of the profile contracts to shorter wavelengths, corresponding to smaller velocities. We note that this region has also been shown to host 5167 Å, 5173 Å, and 5184 Å Mg emission for some gaseous debris discs (see Melis et al 2020;Dennihy et al 2020b;Gentile Fusillo et al 2021). The potential O emission feature appears to share the red-dominated asymmetry of the Ca triplet.…”

“…If the emission generated by a single planetesimal is proportional in strength to the total emission from the gaseous component of the disc, then it would be more efficient to observe gaseous debris discs with emission features comparable in strength to those at SDSS J1228+1040. Melis et al (2020), Dennihy et al (2020b) and Gentile Fusillo et al ( 2021) recently reported the combined detection of 14 new gaseous debris discs (for a total of 21 gaseous debris disc systems), five of which -SDSS J0006+2858, WD 0347+1624, WD 0611-6931, WD J0846+5703, and WD J2133+2428, show strong Ca triplet emission. Furthermore, the morphology of the emission profiles of WD 0347+1624 appears to vary on a time-scale of 2 -3 yrs; similar to HE 1349-2305 and indicative of the precession of the debris disc.…”

A catalogue of white dwarfs in Gaia EDR3

“…This rare polluting element is extremely difficult to detect in hotter white dwarfs and could be the signpost of accretion of the crust of a planetary object (Hollands et al 2021). More discoveries related to planetary systems around white dwarfs enabled by Gaia included WD J0914+1914, a peculiar white dwarf in the process of evaporating a Neptune-like exoplanet (Gänsicke et al 2019), and the 14 newly identified white dwarfs with gaseous debris from rocky planetesimals (Dennihy et al 2020;Melis et al 2020;Gentile Fusillo et al 2021), which brought the number of such systems known from seven to 21.…”

Formation of eccentric gas discs from sublimating or partially disrupted asteroids orbiting white dwarfs

“…In around 21 of the white dwarfs which are host to dusty debris discs we have also observed a gaseous component to the disc (Gänsicke et al 2006(Gänsicke et al , 2007(Gänsicke et al , 2008Gänsicke 2011;Farihi et al 2012;Melis et al 2012;Wilson et al 2014;Dennihy et al 2020;Gentile Fusillo et al 2020;Melis et al 2020). The presence of these discs is inferred through the detection of the double-peaked Ca II emission triplet (∼ 8600 Å) in the spectrum of the system (Horne & Marsh 1986).…”