Hydrogen delivery onto white dwarfs from remnant exo-Oort cloud comets

Abstract

The origin of trace hydrogen in white dwarfs (WDs) with He-dominated atmospheres is a long-standing problem, one that cannot satisfactorily be explained by the historically-favoured hypothesis of accretion from the interstellar medium. Here we explore the possibility that the gradual accretion of exo-Oort cloud comets, which are a rich source of H, contributes to the apparent increase of trace H with WD cooling age. We determine how often remnant exo-Oort clouds, freshly excited from post-main-sequence stellar mass loss, dynamically inject comets inside the WD's Roche radius. We improve upon previous studies by considering a representative range of single WD masses (0.52-1.00 Solar masses) and incorporating different cloud architectures, giant branch stellar mass loss, stellar flybys, Galactic tides and a realistic escape ellipsoid in self-consistent numerical simulations that integrate beyond 8 Gyr ages of WD cooling. We find that about 10^{-5} of the material in an exo-Oort cloud is typically amassed onto the WD, and that the H deposits accumulate even as the cloud dissipates. This accumulation may account for the relatively large amount of trace H, 10^{22}-10^{25} g, that is determined frequently among WDs with cooling ages >= 1 Gyr. Our results also reaffirm the notion that exo-Oort cloud comets are not the primary agents of the metal budgets observed in polluted WD atmospheres.

Accepted for publication in MNRAS

References in corpus (23)

• The frequency of planetary debris around young white dwarfs
• A gaseous metal disk around a white dwarf
• The Chemical Composition of an Extrasolar Minor Planet
• Foretellings of Ragnarök: World-engulfing Asymptotic Giants and the Inheritance of White Dwarfs
• Pollution of single white dwarfs by accretion of many small asteroids
• "TNOs are Cool": A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations
• Hot Jupiters and Cool Stars
• Formation of planetary debris discs around white dwarfs I: Tidal disruption of an extremely eccentric asteroid
• On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars
• Carbon Deficiency in Externally-Polluted White Dwarfs: Evidence for Accretion of Asteroids
• SDSSJ104341.53+085558.2: A second white dwarf with a gaseous debris disc
• Sedna and the Oort Cloud Around a Migrating Sun
• The Formation of the Oort Cloud in Open Cluster Environments
• The Kuiper Belt Luminosity Function from m(R)=21 to 26
• Signs of a faint disc population at polluted white dwarfs
• "TNOs are Cool": A survey of the trans-Neptunian region VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects
• Variable Emission from a Gaseous Disc around a Metal-Polluted White Dwarf
• X-ray and Infrared Observations of Two Externally-Polluted White Dwarfs
• Evaporation and Accretion of Extrasolar Comets Following White Dwarf Kicks
• Do weak magnetic fields prevent hydrogen from accreting onto metal-line white dwarf stars?
• Dancing with the Stars: Formation of the Fomalhaut triple system and its effect on the debris disks
• A simple bound for the variation at closest approach of a small body and star due to general relativity
• Symmetry and Asymmetry in "born again" Planetary Nebulae

Cited by in corpus (36)

• The Chemical Composition of an Extrasolar Kuiper-Belt-Object
• Likely detection of water-rich asteroid debris in a metal-polluted white dwarf
• Detectable close-in planets around white dwarfs through late unpacking
• Cool DZ white dwarfs I: Identification and spectral analysis
• Explaining the variability of WD 1145+017 with simulations of asteroid tidal disruption
• The orbital evolution of asteroids, pebbles and planets from giant branch stellar radiation and winds
• The Fate of Exomoons in White Dwarf Planetary Systems
• Numerical Simulations of Gaseous Disks Generated from Collisional Cascades at the Roche Limits of White Dwarf Stars
• White dwarf pollution by hydrated planetary remnants: Hydrogen and Metals in WD J204713.76-125908.9
• The unseen planets of double belt debris disk systems
• Analytic computation of the secular effects of encounters on a binary: features arising from second-order perturbation theory
• Exocomets from a Solar System Perspective
• The fates of Solar system analogues with one additional distant planet
• A 3 Gyr White Dwarf with Warm Dust Discovered via the Backyard Worlds: Planet 9 Citizen Science Project
• Speeding past planets? Asteroids radiatively propelled by giant branch Yarkovsky effects
• Mass and eccentricity constraints on the planetary debris orbiting the white dwarf WD 1145+017
• Linking long-term planetary $N$-body simulations with periodic orbits: application to white dwarf pollution
• The lifetimes of planetary debris discs around white dwarfs
• Post-main-sequence debris from rotation-induced YORP break-up of small bodies II: multiple fissions, internal strengths and binary production
• The spectral evolution of white dwarfs: where do we stand?
• A hypothesis for the rapid formation of planets
• GD424 -- a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal
• Post main sequence evolution of icy minor planets II: water retention and white dwarf pollution around massive progenitor stars
• The dynamical history of the evaporating or disrupted ice giant planet around white dwarf WD J0914+1914
• A Convective Dredge-Up Model as the Origin of Hydrogen in DBA White Dwarfs
• On the Spectral Evolution of Hot White Dwarf Stars. IV. The Diffusion and Mixing of Residual Hydrogen in Helium-rich White Dwarfs
• Survivability of radio-loud planetary cores orbiting white dwarfs
• The entry geometry and velocity of planetary debris into the Roche sphere of a white dwarf
• The critical binary star separation for a planetary system origin of white dwarf pollution
• Oort cloud asteroids: Collisional evolution, the Nice Model, and the Grand Tack
• Asynchronous accretion can mimic diverse white dwarf pollutants II: water content
• H${}_2$-dominated Atmosphere as an Indicator of Second-generation Rocky White Dwarf Exoplanets
• The unstable fate of the planet orbiting the A-star in the HD 131399 triple stellar system
• Atmospheric Temperature Inversions and He I 5876 Core Profile Structure in White Dwarfs
• Polluting White Dwarfs with Oort Cloud Comets
• Planetary magnetosphere evolution around post-main-sequence stars