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
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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 [email protected] 2
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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
Nathan Dickinson [email protected] 3
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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
Nathan Dickinson [email protected] 4
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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 [email protected]
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Nathan Dickinson [email protected] 7
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Nathan Dickinson [email protected] 8
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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?
Nathan Dickinson [email protected] 16