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Turning Cool Star X-ray Spectra Upside Down. Klaus Werner University of Tübingen, Germany Jeremy J. Drake CfA, Cambridge, USA. Turning Cool Star X-ray Spectra. Upside Down. Klaus Werner University of Tübingen, Germany Jeremy J. Drake CfA, Cambridge, USA. Outline.
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Turning Cool Star X-ray Spectra Upside Down Klaus Werner University of Tübingen, Germany Jeremy J. Drake CfA, Cambridge, USA Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Turning Cool Star X-ray Spectra Upside Down Klaus Werner University of Tübingen, Germany Jeremy J. Drake CfA, Cambridge, USA Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Outline • The unique, hottest known white dwarf H1504+65 • Analysis of Chandra LETG spectroscopy • Comparison of photospheric X-ray spectrum with stellar coronae (Procyon, α Cen A+B) • Identification of hitherto unknown coronal lines Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Properties of H1504+65 • 1983 – H1504 is the seventh brightest X-ray source in the 0.25 keV band (HEAO1 survey, Nugent et al.) • 1986 – Optical identification: Extremely hot white dwarf, lacking H and He lines (Nousek et al.) • 1991 – NLTE analysis of optical spectra (Werner): • It is the hottest WD known (Teff close to 200 000 K) • H1504 is devoid of hydrogen and helium • Dominant photospheric species: C and O (50:50) • 1999 – Analysis of EUVE & Keck data (Werner & Wolff) • High neon abundance: 2-5% (>20 times solar) Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
H1504 is an extreme member of the PG1159 • spectroscopic class, a strange group of 30 stars: • Very hot hydrogen-deficient post-AGB stars • Teff = 75,000 – 200,000 K • log g = 5.5 – 8 • M/M = 0.52 – 0.86 (mean: 0.6) • log L/L = 1.1 – 4.2 • Atmospheres dominated by C, He, O, and Ne, e.g. prototype PG1159-035: • He=33%, C=48%, O=17%, Ne=2% (mass fractions) • = chemistry of material between H and He burning shells in AGB-stars (intershell abundances) Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
AGB star structure +CO core material (dredged up) From Lattanzio (2003) Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Loss of H-rich envelope probably consequence of late He-shell flash (like Sakurai’s object and FG Sge); strong support by stellar evolution models (Herwig 2001) • H-deficient evolutionary post-AGB sequence identified: • Wolf-Rayet type central stars of planetary nebulae • → PG1159 stars → non-DA white dwarfs Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Wolf-Rayet central stars PG1159 stars non-DA white dwarfs Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Origin of unique C/O/Ne surface composition of H1504 remains unknown. Obviously, H1504 is a bare C/O core of a former AGB giant. • Detection of Mg2% in Chandra spectrum even suggests: H1504 could be a bare O/Ne/Mg white dwarf, i.e. first observational proof for existence of such objects • Approved HST UV-spectroscopy (2005): Search for Na Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Chandra LETG+HRC-S observation of H1504+65: • Sept. 27, 2000, integration time 7 hours • Richest absorption line spectrum ever recorded from a stellar photosphere • NLTE spectral analysis: Line blanketed models, Accelerated Lambda Iteration code • (Werner et al. 2004, A&A 421, 1169) • Examples for spectral fitting: Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Model fit to H1504+65 Chandra spectrum 80-110 Å Relative flux Wavelength / Å Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Model fit to H1504+65 Chandra spectrum 80-110 Å Relative flux Wavelength / Å Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Model fit to H1504+65 Chandra spectrum 80-110 Å Relative flux Wavelength / Å Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Model fit to H1504+65 Chandra spectrum 110-140 Å Relative flux Wavelength / Å Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Model fit to H1504+65 Chandra spectrum 110-140 Å Relative flux Wavelength / Å Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Model fit to H1504+65 Chandra spectrum 110-140 Å Relative flux Wavelength / Å Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Strong Fe-group line blanketing Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Strong Fe-group line blanketing Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Strong Fe-group line blanketing Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
H1504+65 is the hottest star ever analysed with detailed model atmospheres, but: Why is that relevant to this cool star meeting??? Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Comparison of H1504+65 photosphere and coronae of Procyon and α CenA+B • Idea: temperature in line forming regions of H1504 (up to 300,000 K) approaches low-T component of multi-T fits to coronae, e.g. 630,000 K for Procyon (Raassen et al. 2002) • Indeed: Lines from O VI, Ne VI-VIII, Mg VI-IX detectable in both, cool star coronae (in emission) and hot WD photosphere (in absorption) • Motivation: Work on H1504 could help to identify hitherto unidentified lines in stellar coronae • Why important? (i) Only small fraction of all lines identified in current radiative loss models (Raassen et al. 2002, 2003) (ii) True line flux underestimated by large amount (e.g. factor 5 in 30-70Å range, Drake et al., in prep.) Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
Results • Comparison of photosphere of hottest white dwarf and cool star coronae reveals large number of spectral lines in common: O VI, Ne VI-VIII, Mg VI-IX • We confirm identifications by Raassen et al. (2002, 2003) in the 70 – 150 Å region and • We identify new lines from 40 multiplets of O, Ne, Mg Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)
