The Stratification of Metals in Hot White Dwarf Atmospheres

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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

• Metals affect Teff estimates -> evolutionary models, stellar atmosphere models etc

• Stellar structure, local environment, evolutionary processes, supernova chemistry etc

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Method

• Models constructed using TLUSTY

• Spectra synthesised using SYNSPEC

• Line fitting achieved with XSPEC

• Look at PG0948+534 and REJ1032+532

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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

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CIV doublet

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

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Homogeneous N/H= 5x10-5

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Stratified N/H= 5x10-5

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N/H= 2.24x10-7; Chayer et al ‘05 = 6.3x10-7

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S

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LTE, N/H=5x10-5 NLTE, N/H=2.24x10-7

H

PG0948+534; Homogeneous C/H= 4.85x10-6

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Homogeneous C/H= 1.2x10-5

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Stratified C/H= 1.2x10-5

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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?

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