  Metal-rich debris disks were discovered around several single DAZ and DBZ
white dwarfs, which may stem from disruption of smaller rocky planetesimals. In
some cases, the material in addition forms a gaseous disk. For SDSS
J122859.93+104032.9, the double peaked infrared Ca II triplet at about 8500
angstrom exhibits a strong red/violet asymmetry. With the Tuebingen non-LTE
Accretion Disk code AcDc we calculated the spectrum and vertical structure of
the disk, assuming the chemical mixture of the disk's material being similar to
a chondrite-like asteroid, the most prominent type in our own solar system. By
modifying the code to simulate different non axis-symmetrical disk geometries,
the first preliminary results are in good agreement with the observed
asymmetric line profile.
