August 11-15, 2014


The fraction of infrared bright and hidden circumstellar debris at white dwarfs

Marco Rocchetto (University College London)

Jay Farihi (University College London) Boris Gänsicke (University of Warwick) Carolina Bergfors (University College London)

We present results of the first unbiased Spitzer IRAC survey of a homogeneous and well-defined sample of 134 single white dwarfs in search of infrared excesses compatible with the presence of circumstellar dust formed from the disruption of planetesimals. The stars were selected without regard to atmospheric metal content but were chosen to have 1) hydrogen rich atmospheres, 2) effective temperature between 17,000 and 20,000 K and correspondingly young post main-sequence ages of 2--120 Myr, and 3) sufficient far-ultraviolet brightness for a corresponding Hubble Space Telescope COS Snapshot. We find five white dwarfs that host an infrared bright dust disc, three previously known, and two reported here for the first time, yielding a nominal 3.7% of white dwarfs in this post-main sequence age range with detectable circumstellar material. Remarkably, our complementary HST observations indicate this fraction is almost certainly an order of magnitude higher, with the bulk of circumstellar discs currently hidden in the infrared. The presence of narrow and attenuated dust rings, and especially atmospheric pollution, corroborate this interpretation as do the distribution of the fractional luminosity of the discs as a function of cooling age.

Mode of presentation: oral