1. www.le.ac.uk 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 T eff estimates -> evolutionary models, stellar atmosphere models etc Stellar structure, local environment, evolutionary processes, supernova chemistry etc Nathan Dickinsonnjd15@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 Dickinsonnjd15@le.ac.uk 3

4. PG0948+534 T eff =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 Dickinsonnjd15@le.ac.uk 4

5. Nathan Dickinsonnjd15@le.ac.uk 5 C IV doublet

6. REJ1032+532 T eff = 44,350K log g=7.81 Holberg et al. (1999) found similar N V lines to PG0948+534’s C IV ; 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 Dickinsonnjd15@le.ac.uk 6

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8. Nathan Dickinsonnjd15@le.ac.uk 8

9. Homogeneous N/H= 5x10 -5 Nathan Dickinsonnjd15@le.ac.uk 9

10. Stratified N/H= 5x10 -5 Nathan Dickinsonnjd15@le.ac.uk 10

11. N/H= 2.24x10 -7 ; Chayer et al ‘05 = 6.3x10 -7 Nathan Dickinsonnjd15@le.ac.uk 11

12. S Nathan Dickinsonnjd15@le.ac.uk 12 LTE, N/H=5x10 -5 NLTE, N/H=2.24x10 -7 H

13. PG0948+534; Homogeneous C/H= 4.85x10 -6 Nathan Dickinsonnjd15@le.ac.uk 13

14. Homogeneous C/H= 1.2x10 -5 Nathan Dickinsonnjd15@le.ac.uk 14

15. Stratified C/H= 1.2x10 -5 Nathan Dickinsonnjd15@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 N V lines well PG0948+534 C IV probably not stratified in a slab; stellar winds? Nathan Dickinsonnjd15@le.ac.uk 16