Finding rocky asteroids around white dwarfs by their periodic thermal emission

Abstract

Since white dwarfs are small, the contrast between the thermal emission of an orbiting object and a white dwarf is dramatically enhanced compared to a main sequence host. Furthermore, rocky objects much smaller than the moon have no atmospheres and are tidally locked to the white dwarf. We show that this leads to temperature contrasts between their day and night side of order unity that should lead to temporal variations in infrared flux over an orbital period of $\sim 0.2$ to $\sim 2$ days. Ground based telescopes could detect objects with a mass as small as $1\%$ of the lunar mass $M_L$ around Sirius B with a few hours of exposure. The James Webb Space Telescope (JWST) may be able to detect objects as small as $10^{-3}{M}_L$ around most nearby white dwarfs. The tightest constraints will typically be placed on 12,000 K white dwarfs, whose Roche zone coincides with the dust sublimation zone. Constraining the abundance of minor planets around white dwarfs as a function of their surface temperatures (and therefore age) provides a novel probe for the physics of planetary formation.

arXiv commentAccepted for publication in ApJ Letters

References in corpus (21)

• Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
• A Tidally-Disrupted Asteroid Around the White Dwarf G29-38
• Are There Unstable Planetary Systems Around White Dwarfs?
• The frequency of planetary debris around young white dwarfs
• A gaseous metal disk around a white dwarf
• Dynamical effects of stellar mass loss on a Kuiper-like belt
• Stochastic accretion of planetesimals onto white dwarfs: constraints on the mass distribution of accreted material from atmospheric pollution
• Strengthening the Case for Asteroidal Accrection: Evidence for Subtle and Diverse Disks at White Dwarfs
• Masses and orbital inclinations of planets in the PSR B1257+12 system
• The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet
• Tidal Limits to Planetary Habitability
• Transit surveys for Earths in the habitable zones of white dwarfs
• Sublimation Temperature of Circumstellar Dust Particles and Its Importance for Dust Ring Formation
• Imaging planets around nearby white dwarfs
• Ground-Based Transit Spectroscopy of the Hot-Jupiter WASP-19b in the Near-Infrared
• Rocky Planetesimals as the Origin of Metals in DZ Stars
• Detecting industrial pollution in the atmospheres of earth-like exoplanets
• The Age and Progenitor Mass of Sirius B
• On the Number of Comets Around White Dwarf Stars: Orbit Survival During the Late Stages of Stellar Evolution
• Detecting bio-markers in habitable-zone earths transiting white dwarfs
• Photometry of two DQ white dwarfs - search for spots

Cited by in corpus (6)

• A disintegrating minor planet transiting a white dwarf
• Detectable close-in planets around white dwarfs through late unpacking
• Exoplanet recycling in massive white-dwarf debris discs
• A New Method for Finding Nearby White Dwarf Exoplanets and Detecting Biosignatures
• A Search for short-period Rocky Planets around WDs with the Cosmic Origins Spectrograph (COS)
• Direct detectability of tidally heated exomoons by photometric orbital modulation