institute for astronomy and astrophysics, university of tübingen, germany july 5, 2004cool stars,...
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July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 1
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Turning Cool Star X-ray Spectra Upside Down
Klaus WernerUniversity of Tübingen, Germany
Jeremy J. DrakeCfA, Cambridge, USA
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 2
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Turning Cool Star X-ray Spectra
Klaus WernerUniversity of Tübingen, Germany
Jeremy J. DrakeCfA, Cambridge, USAUpside Down
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 3
Institute for Astronomy and Astrophysics, University of Tübingen, 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
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 4
Institute for Astronomy and Astrophysics, University of Tübingen, 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 heliumDominant photospheric species: C and O (50:50)
1999 – Analysis of EUVE & Keck data (Werner & Wolff)
High neon abundance: 2-5% (>20 times solar)
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 5
Institute for Astronomy and Astrophysics, University of Tübingen, 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)
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 6
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
AGB star structure
+CO core material (dredged up)
From Lattanzio (2003)
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 7
Institute for Astronomy and Astrophysics, University of Tübingen, 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
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 8
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Wolf-Rayetcentral stars
PG1159 stars
non-DAwhite dwarfs
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 9
Institute for Astronomy and Astrophysics, University of Tübingen, 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
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 10
Institute for Astronomy and Astrophysics, University of Tübingen, 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:
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 11
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Model fit to H1504+65 Chandra spectrum 80-110 Å
Wavelength / Å
Rel
ativ
e fl
ux
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 12
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Model fit to H1504+65 Chandra spectrum 80-110 Å
Wavelength / Å
Rel
ativ
e fl
ux
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 13
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Model fit to H1504+65 Chandra spectrum 80-110 Å
Wavelength / Å
Rel
ativ
e fl
ux
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 14
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Model fit to H1504+65 Chandra spectrum 110-140 Å
Wavelength / Å
Rel
ativ
e fl
ux
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 15
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Model fit to H1504+65 Chandra spectrum 110-140 Å
Wavelength / Å
Rel
ativ
e fl
ux
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 16
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Model fit to H1504+65 Chandra spectrum 110-140 Å
Wavelength / Å
Rel
ativ
e fl
ux
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 17
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Strong Fe-group line blanketing
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 18
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Strong Fe-group line blanketing
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 19
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
Strong Fe-group line blanketing
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 20
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
H1504+65 is the hottest star ever analysed with detailed model atmospheres, but:
Why is that relevant to this cool star meeting???
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 21
Institute for Astronomy and Astrophysics, University of Tübingen, 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.)
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 22
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 23
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 24
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 25
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 26
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 27
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 28
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 29
Institute for Astronomy and Astrophysics, University of Tübingen, Germany
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 30
Institute for Astronomy and Astrophysics, University of Tübingen, 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
July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 31
Institute for Astronomy and Astrophysics, University of Tübingen, Germany