GD424 -- a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal

Abstract

The photospheric metal pollution of white dwarfs is now well-established as the signature of the accretion of planetary debris. However, the origin of the trace hydrogen detected in many white dwarfs with helium atmospheres is still debated. Here, we report the analysis of GD424: a metal-polluted, helium-atmosphere white dwarf with a large amount of trace hydrogen. We determined the atmospheric parameters using a hybrid analysis that combines the sensitivity of spectroscopy to the atmospheric composition, $\log (H/He)$, with that of photometry and astrometry to the effective temperature, $T_{\mathrm{eff}}$, and surface gravity, $\log g$. The resulting white dwarf mass, radius, and cooling age are $M_{\mathrm{WD}}=0.77\pm 0.01{\mathrm{M}}_{\odot }$, $R_{\mathrm{WD}}=0.0109\pm 0.0001{\mathrm{R}}_{\odot }$, and ${\tau }_{\mathrm{cool}}=215\pm 10$ Myr, respectively. We identified and measured the abundances of 11 photospheric metals and argue that the accretion event is most likely either in the increasing or steady state, and that the disrupted planetesimal resembles either CI chondrites or the bulk Earth in terms of its composition. We suggest that the observed $1.33\times 10^{22}$ g of trace hydrogen in GD424 were at least partly acquired through accretion of water-rich planetary debris in an earlier accretion episode.

14 pages, 9 figures

References in corpus (22)

• The frequency of planetary debris around young white dwarfs
• The Chemical Composition of an Extrasolar Minor Planet
• Found: The missing blue opacity in atmosphere models of cool hydrogen white dwarfs
• Formation of planetary debris discs around white dwarfs I: Tidal disruption of an extremely eccentric asteroid
• Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets
• The Chemical Composition of an Extrasolar Kuiper-Belt-Object
• Likely detection of water-rich asteroid debris in a metal-polluted white dwarf
• The unbiased frequency of planetary signatures around single and binary white dwarfs using $Spitzer$ and $Hubble$
• Signs of a faint disc population at polluted white dwarfs
• Cool DZ white dwarfs I: Identification and spectral analysis
• Hydrogen delivery onto white dwarfs from remnant exo-Oort cloud comets
• Compositions of Planetary Debris around Dusty White Dwarfs
• Does a Differentiated, Carbonate-Rich, Rocky Object Pollute the White Dwarf SDSSJ104341.53+085558.2?
• Are exoplanetesimals differentiated?
• White dwarf pollution by hydrated planetary remnants: Hydrogen and Metals in WD J204713.76-125908.9
• Solar Abundances of Rock Forming Elements, Extreme Oxygen and Hydrogen in a Young Polluted White Dwarf
• Modeling of the Variable Circumstellar Absorption Features of WD 1145+017
• Calibration of the mixing length theory for structures of helium-dominated atmosphere white dwarfs
• Post main sequence evolution of icy minor planets II: water retention and white dwarf pollution around massive progenitor stars
• Post-main-sequence evolution of icy minor planets. III. water retention in dwarf planets and exo-moons and implications for white dwarf pollution
• Do weak magnetic fields prevent hydrogen from accreting onto metal-line white dwarf stars?
• A Convective Dredge-Up Model as the Origin of Hydrogen in DBA White Dwarfs

Cited by in corpus (17)

• Planetary Systems Around White Dwarfs
• Spectral analysis of ultra-cool white dwarfs polluted by planetary debris
• The spectral evolution of white dwarfs: where do we stand?
• New chondritic bodies identified in eight oxygen-bearing white dwarfs
• PEWDD: A database of white dwarfs enriched by exo-planetary material
• A DZ white dwarf with a 30 MG magnetic field
• Carbon dredge-up required to explain the Gaia white dwarf colour-magnitude bifurcation
• Asynchronous accretion can mimic diverse white dwarf pollutants I: core and mantle fragments
• Asynchronous accretion can mimic diverse white dwarf pollutants II: water content
• Spectral analysis of cool white dwarfs accreting from planetary systems: from the UV to the optical
• Systematic uncertainties in the characterisation of helium-dominated metal-polluted white dwarf atmospheres
• The smallest planetary drivers of white dwarf pollution
• On the pollution of white dwarfs by exo-Oort cloud comets
• Identifying new high-confidence polluted white dwarf candidates using Gaia XP spectra and Self-Organizing Maps
• Discovery of an icy and nitrogen-rich extrasolar planetesimal
• Do White Dwarfs Sample Water-Rich Planetary Material?
• I Can Do It With A Broken Planetesimal: Characterising the planetary debris in heavily polluted cool white dwarfs