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The Stratification of Metals in Hot White Dwarf Atmospheres

The Stratification of Metals in Hot White Dwarf Atmospheres. N.J. Dickinson, M.A. Barstow, I. Hubeny * * Steward Observatory, University of Arizona . Motivation. Uncertainties in modelling metals in many WDs

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The Stratification of Metals in Hot 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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