Modeling the Evolution of Silicate/Volatile Accretion Discs around White Dwarfs

Abstract

A growing number of debris discs have been detected around metal-polluted white dwarfs. They are thought to be originated from tidally disrupted exoplanetary bodies and responsible for metal accretion onto host WDs. To explain (1) the observationally inferred accretion rate higher than that induced by Poynting-Robertson drag, ${\dot{M}}_{\mathrm{PR}}$, and (2) refractory-rich photosphere composition indicating the accretion of terrestrial rocky materials, previous studies proposed runaway accretion of silicate particles due to gas drag by the increasing silicate vapor produced by the sublimation of the particles. Because re-condensation of the vapor diffused beyond the sublimation line was neglected, we revisit this problem by one-dimensional advection/diffusion simulation that consistently incorporates silicate sublimation/condensation and back-reaction to particle drift due to gas drag in the solid-rich disc. We find that the silicate vapor density in the region overlapping the solid particles follows the saturating vapor pressure and that no runaway accretion occurs if the re-condensation is included. This always limits the accretion rate from mono-compositional silicate discs to ${\dot{M}}_{\mathrm{PR}}$ in the equilibrium state. Alternatively, by performing additional simulations that couple the volatile gas (e.g., water vapor), we demonstrate that the volatile gas enhances the silicate accretion to $>{\dot{M}}_{\mathrm{PR}}$ through gas drag. The refractory-rich accretion is simultaneously reproduced when the initial volatile fraction of disc is $\lesssim 10$ wt\% because of the suppression of volatile accretion due to the efficient back-reaction of solid to gas. The discs originating from C-type asteroid analogs might be a possible clue to the high-$\dot{M}$ puzzle.

20 pages, 14 figures, accepted for publication in MNRAS

References in corpus (27)

• Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
• The frequency of planetary debris around young white dwarfs
• A gaseous metal disk around a white dwarf
• Pollution of single white dwarfs by accretion of many small asteroids
• Externally-polluted white dwarfs with dust disks
• Accretion of a giant planet onto a white dwarf
• Six White Dwarfs with Circumstellar Silicates
• The frequency and infrared brightness of circumstellar discs at white dwarfs
• The Chemical Composition of an Extrasolar Kuiper-Belt-Object
• Formation of dust-rich planetesimals from sublimated pebbles inside of the snow line
• An Atmospheric Structure Equation for Grain Growth
• SDSSJ104341.53+085558.2: A second white dwarf with a gaseous debris disc
• Likely detection of water-rich asteroid debris in a metal-polluted white dwarf
• Cool DZ white dwarfs I: Identification and spectral analysis
• Scars of Intense Accretion Episodes at Metal-Rich White Dwarfs
• Numerical Simulations of Collisional Cascades at the Roche Limits of White Dwarf Stars
• The frequency of gaseous debris discs around white dwarfs
• Effect of dust radial drift on viscous evolution of gaseous disk
• Solar Abundances of Rock Forming Elements, Extreme Oxygen and Hydrogen in a Young Polluted White Dwarf
• White dwarf pollution by hydrated planetary remnants: Hydrogen and Metals in WD J204713.76-125908.9
• White dwarfs with planetary remnants in the era of Gaia I: six emission line systems
• A Characterization of the Circumstellar Gas around WD 1124-293 using Cloudy
• Planetesimal formation around the snow line. II. Dust or pebbles?
• Metal pollution of the solar white dwarf by solar system small bodies
• The gaseous debris disk of the white dwarf SDSS J1228+1040. HST/COS search for far-ultraviolet signatures
• Planetesimal formation around the snow line: I. Monte Carlo simulations of silicate dust pile-up in a turbulent disk
• Monte Carlo Simulation of Dust Particles in a Protoplanetary Disk: Crystalline to Amorphous Silicate Ratio in Comets

Cited by in corpus (8)

• PEWDD: A database of white dwarfs enriched by exo-planetary material
• Discovery of magnetically guided metal accretion onto a polluted white dwarf
• Polluting White Dwarfs with Oort Cloud Comets
• Effects from different grades of stickiness between icy and silicate particles on carbon depletion in protoplanetary disks
• Planetesimals drifting through dusty and gaseous white dwarf debris discs: Types I, II and III-like migration
• White dwarf magnetospheres: Shielding volatile content of icy objects and implications for volatile pollution scarcity
• I Can Do It With A Broken Planetesimal: Characterising the planetary debris in heavily polluted cool white dwarfs
• Detecting water ice and vapor disks originating from icy planetary bodies around white dwarfs with future PRIMA observations