Planetary Debris Around Young White Dwarfs

Details Planetary Debris Around Young White Dwarfs Planetary Debris Around Young White Dwarfs

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ess.....2.1504g&link_type=abstract

American Astronomical Society, ESS meeting #2, #15.04

Astronomy and Astrophysics

Astronomy

Scientific paper

At ESS I, we presented the discovery of gaseous debris disks around two relatively young ( 100Myr) white dwarfs that appeared to be the "warm" extension to the handful of cooler white dwarfs with dusty debris disks known at the time. Much has happened since then, and we will present a range of recent and forthcoming results.
Two dozen white dwarfs with dusty debris disks are known, spanning cooling ages of 100Myr to 1Gyr. We have identified five white dwarfs with gaseous disks, and our Spitzer observations detect strong infrared excess in four of them. Comparing the white dwarfs with gaseous disks and those with dust-only, there is no charactistic (white dwarf temperature and mass, accretion rate) that singles them out. We suggest that these disks are fresh disruption or re-impact events. Our spectroscopy spanning many years demonstrates dramatic variability of both line shape and strength, with a possible period of 10 years for SDSS1228+1040. Our CLOUDY model reproduces the observed emission characteristics of the gaseous disks seen in both our optical and HST/COS spectroscopy, and accomodates the simultaneous presence of the dust.
We also report first results from our large, unbiased HST/COS survey of young hydrogen-rich white dwarfs. 15% of the 52 stars observed so far are metal-polluted, but only four of them have detected dusty disks. The diffusion time scales of these stars are days, i.e. the detection of metals implies that accretion is ongoing. Because of the short diffusion time scales, the photospheric abundances precisely reflect the bulk abundances of the planetary debris material. We find large variations in the metal-to-metal abundances, particularly so in carbon, suggesting a substantial variety among the rocky debris around these stars. Most noticeable is GALEX1931+0117 with an C/Fe abundances that is a factor 10 lower than that of the Earth's crust.

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