  We present Spitzer Space Telescope data of four isolated white dwarfs that
were previously known to harbor circumstellar gaseous disks. IRAC photometry
shows a significant infrared excess in all of the systems, SDSS0738+1835,
SDSS0845+2257, SDSS1043+0855 and SDSS1617+1620, indicative of a dusty extension
to those disks. The 4.5-micron excesses seen in SDSS0738, SDSS0845, and
SDSS1617 are 7.5, 5.7 and 4.5 times the white dwarf contribution, respectively.
In contrast, in SDSS1043, the measured flux density at 4.5 microns is only 1.7
times the white dwarf contribution. We compare the measured IR excesses in the
systems to models of geometrically thin, optically thick disks, and find that
we are able to match the measured SEDs to within 3 sigma of the uncertainties,
although disks with unfeasibly hot inner dust temperatures generally provide a
better fit than those below the dust sublimation temperature. Possible
explanations for the dearth of dust around SDSS1043+0855 are briefly discussed.
Including our previous study of SDSS1228+1040, all five white dwarfs with
gaseous debris disks have significant amounts of dust around them. It is
evident that gas and dust can coexist around these relatively warm, relatively
young white dwarfs.
