Serendipitous Discovery of Nine White Dwarfs With Gaseous Debris Disks

TL;DR

This study reports the discovery of nine new gaseous debris disks around white dwarfs, doubling the known sample, and provides detailed spectroscopic analysis revealing diverse compositions and structures.

Contribution

It presents nine newly identified gaseous debris disks around white dwarfs, expanding the known sample and offering detailed spectroscopic insights into their compositions and asymmetries.

Findings

Discovery of the coolest white dwarf with a gas disk (Teff~12,720 K).

Detection of well-mixed elements in gaseous emission lines.

Identification of asymmetric emission structures in some systems.

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 two 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 (Teff~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 SDSSJ0006+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 GaiaJ0611-6931, semi-forbidden Mg, Ca, and Fe lines toward WD0842+572, and Si in both stars. The currently known sample of gaseous debris disk systems is significantly skewed towards northern hemisphere stars, suggesting a dozen or so emission line stars are waiting to be found in the southern hemisphere.