SIMBAD references

We report Spitzer Space Telescope photometry of 11 externally polluted white dwarfs. Of the nine stars for which we have IRAC photometry, we find that GD 40, GD 133, and PG 1015+161 each has an infrared excess that can be understood as arising from a flat, opaque, dusty disk. GD 56 also has an infrared excess characteristic of circumstellar dust, but a flat-disk model cannot reproduce the data unless there are grains as warm as 1700 K and perhaps not even then. Our data support the previous suggestion that the metals in the atmosphere of GD 40 are the result of accretion of a tidally disrupted asteroid with a chondritic composition.