Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)1 Turning Cool Star X-ray Spectra Upside Down Klaus Werner University of Tübingen, Germany Jeremy J. Drake CfA, Cambridge, USA

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)2 Turning Cool Star X-ray Spectra Klaus Werner University of Tübingen, Germany Jeremy J. Drake CfA, Cambridge, USA Upside Down

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)3 Outline The unique, hottest known white dwarf H 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

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)4 Properties of H – 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 (T eff close to 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)

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)5 H1504 is an extreme member of the PG1159 spectroscopic class, a strange group of  30 stars: Very hot hydrogen-deficient post-AGB stars T eff = 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 PG : He=33%, C=48%, O=17%, Ne=2% (mass fractions) = chemistry of material between H and He burning shells in AGB-stars (intershell abundances)

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)6 AGB star structure +CO core material (dredged up) From Lattanzio (2003)

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)7 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

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)8 Wolf-Rayet central stars PG1159 stars non-DA white dwarfs

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)9 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 Mg  2% 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

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)10 Chandra LETG+HRC-S observation of H : 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:

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)11 Model fit to H Chandra spectrum Å Wavelength / Å Relative flux

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)12 Model fit to H Chandra spectrum Å Wavelength / Å Relative flux

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)13 Model fit to H Chandra spectrum Å Wavelength / Å Relative flux

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)14 Model fit to H Chandra spectrum Å Wavelength / Å Relative flux

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)15 Model fit to H Chandra spectrum Å Wavelength / Å Relative flux

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)16 Model fit to H Chandra spectrum Å Wavelength / Å Relative flux

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)17 Strong Fe-group line blanketing

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)18 Strong Fe-group line blanketing

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)19 Strong Fe-group line blanketing

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)20 H is the hottest star ever analysed with detailed model atmospheres, but: Why is that relevant to this cool star meeting???

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)21 Comparison of H 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 Å range, Drake et al., in prep. )

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)22

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)23

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)24

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)25

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)26

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)27

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)28

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)29

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)30 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

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)31

Institute for Astronomy and Astrophysics, University of Tübingen, Germany July 5, 2004Cool Stars, Stellar Systems and the Sun (Hamburg, Germany)32