DAZd White Dwarfs and the Fate of Planetary Systems

During our mid-infrared Spitzer Space Telescope survey of 130 white dwarfs, we discovered that the white dwarf WD 2115-560 has an infrared excess naturally explained by circumstellar dust. This object is the fourth white dwarf observed to have circumstellar dust. All four are DAZ white dwarfs, i.e., they have both photospheric Balmer lines and photospheric metal lines. We discuss these four objects as a class, which we abbreviate "DAZd", where the "d" stands for "dust". We find that the DAM white dwarfs point to a common origin for many and perhaps most of the DAZ white dwarfs. We favor the interpretation that most of these disks are derived from planetary systems remnants.