A Detailed Model Atmosphere Analysis of Hot White Dwarfs in DESI DR1

TL;DR

This paper analyzes a large sample of hot white dwarfs from DESI DR1 using spectroscopic and photometric data, revealing mass discrepancies, magnetic and carbon-rich white dwarfs, and insights into their spectral evolution.

Contribution

It provides the first detailed model atmosphere analysis of DESI hot white dwarfs, highlighting mass discrepancies and the prevalence of magnetic and carbon-rich white dwarfs.

Findings

Photometric and spectroscopic mass discrepancy of 0.05-0.06 M_sun.

Peak at 0.6 M_sun in mass distribution.

Identification of 70 DQs, including 9 DAQs.

Abstract

We present a detailed model atmosphere analysis of hot white dwarfs in the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. Our sample includes 19,321 unique targets with $G_{\rm BP}-G_{\rm RP}\leq0$. We use the DESI spectra along with Gaia parallaxes and SDSS, Pan-STARRS, and SkyMapper photometry to perform spectroscopic and photometric fits. We find a significant discrepancy between the photometric and spectroscopic masses for DA white dwarfs (a systematic offset of 0.05-$0.06~M_\odot$), indicating problems with the broad hydrogen line profiles in DESI spectroscopy data. Our photometric fits are consistent with a peak at the canonical mass of $0.6~M_\odot$. A remarkable feature of the mass distribution is the prevalence of magnetic white dwarfs among the ultramassive DA population and that of warm DQs in the non-DA distribution. We identify 70 DQs in the DESI hot white dwarf sample, including 9 DAQs with carbon and hydrogen atmospheres. We constrain the ratio of non-DA to DA white dwarfs as a function of temperature, and discuss the implications for the spectral evolution of white dwarfs in the temperature range $10^5-10^4$ K. We also discuss unusual objects in the sample, including metal-rich white dwarfs and extremely low mass white dwarfs. This analysis provides the first look at the large sample of Gaia-selected white dwarf candidates that will be observed with multiplexed spectroscopic surveys like DESI, SDSS-V, 4MOST, and WEAVE over the next several years.