A Systematic Search for Gaseous Debris Disks in DESI Early Data Release White Dwarfs

TL;DR

The paper addresses the occurrence and properties of gaseous debris disks around white dwarfs by performing a blind search for Ca II infrared triplet emission in the DESI Early Data Release WD catalog. Using continuum-subtracted DESI spectra and a three-Gaussian fit to the Ca II triplet, the study identifies 22 candidate systems (0.81% raw rate) from 2706 white dwarfs, noting that most detections are weak and likely contaminated by telluric residuals or unresolved binaries. Archival photometry (SDSS, Pan-STARRS, 2MASS, UKIDSS, WISE) and SED fitting with WD atmospheres and, when needed, a dusty disk model, reveal infrared excess in three cases, suggesting possible gas and dust coexistence. The findings demonstrate DESI’s capability for blind searches of rare circumstellar phenomena and anticipate improved constraints with the larger DESI DR1 sample.

Abstract

Detecting gaseous debris disks around white dwarfs offers a unique window into the ultimate fate of planetary systems and the composition of accreted planetary material. Here we present a systematic search for such disks through the Ca II infrared triplet using the Dark Energy Spectroscopic Instrument (DESI) Early Data Release. From a parent sample of 2706 spectroscopically confirmed white dwarfs, we identify 22 candidate systems showing tentative emission-line features, which corresponds to a raw occurrence rate of 0.81%, more than ten times higher than previous estimates. The detected emission lines are predominantly weak and require confirmation by follow-up observations. Three of these candidates also exhibit infrared excess in WISE photometry, suggesting a possible coexistence of gas and dust. However, the high candidate rate indicates that most are likely false positives due to telluric residuals or unresolved binaries. This work demonstrates the potential of DESI spectra for blind searches of rare circumstellar phenomena. The recently released DESI DR1, with its substantially larger spectroscopic sample, will enable searches for more gaseous disks and provide better insights into their occurrence and nature.

Figures (3)

• Figure 1: Normalized spectra of the 22 white dwarfs with candidate gaseous debris disks in the vicinity of the Ca2 infrared triplet, displayed in order of their IDs (labeled at top left). For each source, the black curve shows the continuum-subtracted spectrum, the red curve shows the best-fit model comprising three Gaussians, and the vertical ticks mark the rest-frame wavelengths of the triplet.
• Figure 2: Gaia color--magnitude diagram for the 22 candidate debris disks (blue diamonds), compared to the parent DESI EDR white dwarf sample (gray circles).
• Figure 3: Pan-STARRS $z$-band images (top row) and SED fits (bottom row) for the three candidate gaseous-debris-disks white dwarfs showing infrared excess. From left to right: WD J0849+0923 (ID=8), WD J1434+1508 (ID=12), WD J1100+7138 (ID=14). Each $z$-band image is centered on the DESI source position, with a red circle of 6 radius indicating the absence of visible contaminants within the typical WISE beam. The SED panels show photometric data from SDSS (magenta diamonds), Pan-STARRS (green triangles), 2MASS (blue squares), UKIDSS (cyan circles), and WISE (red stars), along with the DESI spectrum in gray. The best-fit model (black solid line) includes contributions from the white dwarf photosphere (blue dashed line) and a dusty disk (red dotted line). The derived disk parameters (inner radius $R_{\rm in}$ and inclination $i$) are listed.