Element abundances in cool white dwarfs - II. Ultraviolet observations of DZ white dwarfs

We present a small data base of homogeneously derived photospheric element abundances of DZ white dwarfs and related objects. Our previous investigations are supplemented with the analysis of ultraviolet spectra for nine white dwarfs. Of particular interest is the detection of L α absorption in van Maanen 2 and a determination of the effective temperature of this star. The new value is about 1000 K lower than previous results due to the strong ultraviolet absorption by metals which has to be considered consistently. The metal abundances of our sample stars are compatible with the predictions from the two-phase accretion model of Dupuis et al. ([CITE], [CITE], [CITE]). Small deviations can be observed for the abundance ratios in some objects. This could indicate non-solar metal-to-metal ratios in the accreted material. Hydrogen can be detected in virtually all of our objects. However, its average accretion rate must be at least two orders of magnitude lower than the metal accretion rate.

[1]  B. Fegley,et al.  On the nature of spectral features in peculiar DQ white dwarfs , 1995 .

[2]  Edward M. Sion,et al.  A Catalog of Spectroscopically Identified White Dwarfs , 1987 .

[3]  Maria Teresa Ruiz,et al.  The Chemical Evolution of Cool White Dwarfs and the Age of the Local Galactic Disk , 1997 .

[4]  M. Bessell,et al.  A cool DA white dwarf with self-broadened lines , 1979 .

[5]  J. Greenstein,et al.  Spectra, colors, luminosities and motions of the white dwarfs . , 1965 .

[6]  O. Eggen.  SUBLUMINOUS STARS. III. LUMINOSITY CALIBRATION FOR SUBLUMINOUS STARS AND THE SPACE DENSITY OF THE BLUE SUBLUMINOUS STARS SOUTH OF DECLINATION -45--. , 1969 .

[7]  J. B. Oke,et al.  Temperatures and surface gravities of DB white dwarfs , 1984 .

[8]  Gilles Fontaine,et al.  A study of metal abundance patterns in cool white dwarfs. III: Comparison of the predictions of the two-phase accretion model with the observations , 1993 .

[9]  D. Saumon,et al.  The peculiar cool white dwarf LHS 1126 revisited , 1994 .

[10]  M. Bessell,et al.  Infrared photometry of cool white dwarfs , 1982 .

[11]  D. G. Hummer,et al.  The equation of state for stellar envelopes. IV - Thermodynamic quantities and selected ionization fractions for six elemental mixes , 1990 .

[12]  L. Spitzer.  Physical processes in the interstellar medium , 1998 .

[13]  David S. Finley,et al.  The Temperature Scale and Mass Distribution of Hot DA White Dwarfs , 1997 .

[14]  D. Koester,et al.  Model atmosphere analysis of the DZ white dwarf K789 - 37 , 1990 .

[15]  V. Weidemann.  The Atmosphere of the White Dwarf Van Maanen 2. , 1960 .

[16]  G. Wegner,et al.  Ultraviolet and visual spectroscopy of DB white dwarfs , 1987 .

[17]  Gilles Chabrier,et al.  An Equation of State for Low-Mass Stars and Giant Planets , 1995 .

[18]  Gilles Fontaine,et al.  A study of metal abundance patterns in cool white dwarfs. II - Simulations of accretion episodes , 1993 .

[19]  S. K. Leggett,et al.  Photometric and Spectroscopic Analysis of Cool White Dwarfs with Trigonometric Parallax Measurements , 2000, astro-ph/0011286.

[20]  Gilles Fontaine,et al.  A study of metal abundance patterns in cool white dwarfs. I: Time-dependent calculations of gravitational settling , 1992 .