The frequency and infrared brightness of circumstellar discs at white dwarfs

摘要: White dwarfs whose atmospheres are polluted by terrestrial-like planetary debris have become a powerful and unique tool to study evolved systems. This paper presents results for an unbiased Spitzer IRAC search circumstellar dust orbiting homogeneous well-dened sample of 134 single white dwarfs. The stars were selected without regard atmospheric metal content but chosen 1) hydrogen rich atmospheres, 2) 17 000 K < Te 25 correspondingly young post main-sequence ages 15{270 Myr, 3) sucient far-ultraviolet brightness corresponding Hubble Space Telescope COS Snapshot. Five found host infrared bright disc, three previously known, two reported here the rst time, yielding nominal 3.7% in this post-main sequence age range with detectable dust. Remarkably, complementary HST observations indicate that fraction 27% show metals their photosphere can only be explained ongoing accretion from material, indicating nearly 90% discs escape detection infrared, likely due small emitting surface area. also distribution disc fractional luminosity as function cooling all known dusty dwarfs, suggesting possible evolution scenarios undetected population discs.