We calculated diffusion timescales for Ca, Mg, Fe in hydrogen atmosphere white dwarfs with temperatures between 5000 and 25000 K. With these timescales we determined accretion rates for a sample of 38 DAZ white dwarfs from the recent studies of Zuckerman et al. (2003) and Koester et al. (2005). Assuming that the accretion rates can be calculated with the Bondi-Hoyle formula for hydrodynamic acc...

We report on our attempt for the first non-LTE modeling of gaseous metal disks around single DAZ white dwarfs recently discovered by Gänsicke et al. and thought to originate from a disrupted asteroid. We assume a Keplerian rotating viscous disk ring composed of calcium and hydrogen and compute the detailed vertical structure and emergent spectrum. We find that the observed infrared Ca ii emissi...

A Spitzer IRAC survey of 17 nearby metal-rich white dwarfs, nominally DAZ stars, reveals excess emission from only 3 targets: G29-38, GD 362 and G167-8. Observations of GD 362 with all three Spitzer instruments reveals a warm (≈ 1000 K) dust continuum, very strong silicate emission, and the likely presence of cooler (≈ 500 K) dust. While there is a general similarity between the mid-infrared sp...

We determine projected rotation velocities v sin i in DAZ white dwarfs, for the first time using the rotational broadening of the Ca II K line. The results confirm previous findings that white dwarfs are very slow rotators, and set even more stringent upper limits of typically less than 10 km s−1. The few exceptions include 3 stars known or suspected to be variable ZZ Ceti stars, where the line...

Jun Zhang, Sonia L. Planey, Carolina Ceballos, Stanley M. Stevens Jr. Susan K. Keay, and David A. Zacharias 1 The Whitney Laboratory, Department of Neuroscience, University of Florida, St. Augustine, Florida 32080 2. Proteomics Core Facility, ICBR, University of Florida, Gainesville, Florida, 32610 3. University of Maryland, VA Medical Center, Baltimore, MD 21201 Running Title: Palmitoyl Acyl T...