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Applying the accretion-diffusion model to a sample of DAZ without IR excess

Jean Dupuis (Canadian Space Agency), Pierre Chayer (STSCI) and Vincent Hénault-Brunet (University of Edinburgh). Applying the accretion-diffusion model to a sample of DAZ without IR excess. 17 th European White Dwarf Workshop Tübingen, Germany, August 16-20, 2010.

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Applying the accretion-diffusion model to a sample of DAZ without IR excess

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  1. Jean Dupuis (Canadian Space Agency), Pierre Chayer (STSCI) and Vincent Hénault-Brunet (University of Edinburgh) Applying the accretion-diffusion model to a sample of DAZ without IR excess 17th European White Dwarf Workshop Tübingen, Germany, August 16-20, 2010

  2. A significant fraction of DA white dwarfs have metal lines at a level generally well below solar abundances. Accretion from dusty disks likely explanation for metals in cooler DAZ. Several DAZ have low level metallicity without IR excess and may be sufficiently hot for radiative levitation support (Teff below 25,000K). As abundance measurements are used to infer accretion rates, it is important to quantify the effect of radiative acceleration. Should we worry about the effect of radiative levitation during accretion on DAZ?

  3. The process of measuring accretion rates from UV observations to accretion/diffusion simulations. Ultraviolet +Optical Spectra: FUSE, HST, IUE NLTE model atmosphere analysis: TLUSTY, SYNSPEC Time-Dependent Accretion simulations including radiative acceleration Accretion rate determination

  4. DA that do show metals: an indication of ongoing accretion? Carbon generally not supported but seen in two objects. Detection of Aluminum mostly in agreement with grad. WD1337+705 metal lines stronger than expected from grad.

  5. DA that do not show metals: where have the metals gone? Silicon is predicted in several cases but not detected with significant upper limits.

  6. A possible scenario for the origin of metals in mid-range effective temperatures DA white dwarfs. 1) Weak accretion and/or pure radiative levitation. 2) Accretion. 3) Metals lost during early WD cooling and not yet replenished by accretion.

  7. Does it matter? Yes for supported elements such as Si and Al for which inferred accretion rates can differ by up to a factor 2-3. Not so much for heavier elements such as Ca; it will affect relative abundances (ex: Si/Ca, C/Ca) . For accurate determination of relative abundances, grad not entirely negligible, even for relatively cool DA (ex: LB3303).

  8. Si abundance profiles in EGGR 46 (Teff=25239K, log g=7.94)‏

  9. C abundance profiles in EGGR 102 (Teff=20413K, log g=7.92)‏

  10. Si abundance profiles in EGGR 102 (Teff=20413K, log g=7.92)‏

  11. Al abundance profiles in EGGR 102 (Teff=20413K, log g=7.92)‏

  12. Ca abundance profiles in EGGR 102 (Teff=20413K, log g=7.92)‏

  13. Si abundance profiles in LB 3303 (Teff=15579K, log g=8.04)‏

  14. C abundance profiles in CD-38°10980 (Teff=24276K, log g=8.07)‏

  15. Al abundance profiles in CD-38°10980 (Teff=24276K, log g=8.07)‏

  16. Si abundance profiles in CD-38°10980 (Teff=24276K, log g=8.07)‏

  17. Al abundance profiles in Wolf 1346 (Teff=19918K, log g=7.90)‏

  18. Si abundance profiles in Wolf 1346 (Teff=19918K, log g=7.90)‏

  19. Radiative accelerations in EGGR 102 (Teff=20413K, log g=7.92)‏

  20. We are primarily interested by a sample of white dwarfs observed by the FUSE satellite (Teff < 25,000K). Abundances measurements are performed using TLUSTY and SYNSPEC. We have computed radiative accelerations in models with values we have adopted for the atmospheric parameters and with the formalism described by Chayer, Fontaine, and Wesemael (1992). Ultraviolet spectroscopy reveals stellar metal lines in DA.

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