CONSTRAINTS ON THE LIFETIMES OF DISKS RESULTING FROM TIDALLY DESTROYED ROCKY PLANETARY BODIES

Spitzer IRAC observations of 15 metal-polluted white dwarfs reveal infrared excesses in the spectral energy distributions of HE 0110-5630, GD 61, and HE 1349-2305. All three of these stars have helium-dominated atmospheres, and their infrared emissions are consistent with warm dust produced by the t...

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Bibliographic Details
Published in:The Astrophysical journal 2012-04, Vol.749 (2), p.1-11
Main Authors: GIRVEN, J, BRINKWORTH, C. S, FARIHI, J, GÄNSICKE, B. T, HOARD, D. W, MARSH, T. R, KOESTER, D
Format: Article
Language:English
Subjects:
ABUNDANCE
Accretion disks
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Atmospherics
Constants
Dust
DUSTS
Earth, ocean, space
ENERGY SPECTRA
Exact sciences and technology
HELIUM
HYDROGEN
Infrared
METALS
PLANETS
Spectral energy distribution
Stars
STELLAR ATMOSPHERES
WHITE DWARF STARS
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Summary:Spitzer IRAC observations of 15 metal-polluted white dwarfs reveal infrared excesses in the spectral energy distributions of HE 0110-5630, GD 61, and HE 1349-2305. All three of these stars have helium-dominated atmospheres, and their infrared emissions are consistent with warm dust produced by the tidal destruction of (minor) planetary bodies. This study brings the number of metal-polluted, helium and hydrogen atmosphere white dwarfs surveyed with IRAC to 53 and 38, respectively. It also nearly doubles the number of metal-polluted helium-rich white dwarfs found to have closely orbiting dust by Spitzer. From the increased statistics for both atmospheric types with circumstellar dust, we derive a typical disk lifetime of log [t sub(disk)(yr)] = 5.6 + or - 1.1 (ranging from 3 x 10 super(4) to 5 x 10 super(6) yr). This assumes a relatively constant rate of accretion over the timescale where dust persists, which is uncertain. We find that the fraction of highly metal-polluted helium-rich white dwarfs that have an infrared excess detected by Spitzer is only 23%, compared to 48% for metal-polluted hydrogen-rich white dwarfs, and we conclude from this difference that the typical lifetime of dusty disks is somewhat shorter than the diffusion timescales of helium-rich white dwarf. We also find evidence for higher time-averaged accretion rates onto helium-rich stars compared to the instantaneous accretion rates onto hydrogen-rich stars; this is an indication that our picture of evolved star-planetary system interactions is incomplete. We discuss some speculative scenarios that can explain the observations.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/749/2/154