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

July 5, 2004 Cool Stars, Stellar Systems and the Sun (Hamburg, Germany) 32

Institute for Astronomy and Astrophysics, University of Tübingen, Germany