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Metal Stratification in White Dwarf Atmospheres

Explore uncertainties in modeling metals in white dwarfs and their impact on Teff estimates, evolutionary models, and more. Study stellar structure, local environment, and evolutionary processes. Analysis based on spectral models and line fitting using advanced tools.

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Metal Stratification in White Dwarf Atmospheres

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  1. The Stratification of Metals in Hot White Dwarf Atmospheres N.J. Dickinson, M.A. Barstow, I. Hubeny* *Steward Observatory, University of Arizona

  2. Motivation • Uncertainties in modelling metals in many WDs • Metals affect Teff estimates -> evolutionary models, stellar atmosphere models etc • Stellar structure, local environment, evolutionary processes, supernova chemistry etc • Nathan Dickinson njd15@le.ac.uk 2

  3. Method • Models constructed using TLUSTY • Spectra synthesised using SYNSPEC • Line fitting achieved with XSPEC • Look at PG0948+534 and REJ1032+532 • Nathan Dickinson njd15@le.ac.uk 3

  4. PG0948+534 • Teff=110,000K, log g=7.58 • Barstow et al. (2003) couldn’t fit C, N, O, Si • No sign of circumstellar material/ binary companion in UV data • Nathan Dickinson njd15@le.ac.uk 4

  5. CIV doublet • Nathan Dickinson njd15@le.ac.uk 5

  6. REJ1032+532 • Teff= 44,350K log g=7.81 • Holberg et al. (1999) found similar NV lines to PG0948+534’s CIV; fit with stratified super-abundance (N/H=5x10-5, Barstow et al., 2003). • Chayer et al. (2005) found smaller, homogeneous N abundance fit data; Schuh et al., 2005. • Nathan Dickinson njd15@le.ac.uk 6

  7. Nathan Dickinson njd15@le.ac.uk 7

  8. Nathan Dickinson njd15@le.ac.uk 8

  9. Homogeneous N/H= 5x10-5 • Nathan Dickinson njd15@le.ac.uk 9

  10. Stratified N/H= 5x10-5 • Nathan Dickinson njd15@le.ac.uk 10

  11. N/H= 2.24x10-7; Chayer et al ‘05 = 6.3x10-7 • Nathan Dickinson njd15@le.ac.uk 11

  12. LTE, N/H=5x10-5 NLTE, N/H=2.24x10-7 S H • Nathan Dickinson njd15@le.ac.uk 12

  13. PG0948+534; Homogeneous C/H= 4.85x10-6 • Nathan Dickinson njd15@le.ac.uk 13

  14. Homogeneous C/H= 1.2x10-5 • Nathan Dickinson njd15@le.ac.uk 14

  15. Stratified C/H= 1.2x10-5 • Nathan Dickinson njd15@le.ac.uk 15

  16. Conclusions • Stratifying metals as in Holberg et al., 1999 is not a effective as once thought • When NLTE was included, lower homogeneous abundances fit REJ1032+532’s NV lines well • PG0948+534 CIV probably not stratified in a slab; stellar winds? • Nathan Dickinson njd15@le.ac.uk 16

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