Asymmetric Line Profiles in Spectra of Gaseous Metal Disks Around Single   White Dwarfs
  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. 
S. Hartmann, T. Nagel, T. Rauch, and K. Werner
astro-ph.EP