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ITAMP Workshop High Accuracy Atomic Physics in Astronomy Harvard-Smithsonian Center for Astrophysics 8 Aug 2006

Astrophysical Priorities for Accurate X-ray Spectroscopic Diagnostics Nancy S. Brickhouse Harvard-Smithsonian Center for Astrophysics In Collaboration with Randall K. Smith Acknowledgments to Guo-Xin Chen, Svetlana Kotochigova and Kate Kirby. ITAMP Workshop

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ITAMP Workshop High Accuracy Atomic Physics in Astronomy Harvard-Smithsonian Center for Astrophysics 8 Aug 2006

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  1. Astrophysical Priorities for Accurate X-ray Spectroscopic DiagnosticsNancy S. BrickhouseHarvard-Smithsonian Center for AstrophysicsIn Collaboration with Randall K. SmithAcknowledgments to Guo-Xin Chen, Svetlana Kotochigova and Kate Kirby ITAMP Workshop High Accuracy Atomic Physics in Astronomy Harvard-Smithsonian Center for Astrophysics 8 Aug 2006

  2. Outline • Introduction • Case Studies from X-ray Spectroscopy • Fe XVII 3C/3D • Ne IX density and temperature diagnostics • Fe XVIII and XIX temperature diagnostics • Conclusions

  3. Overview: X-Ray Spectroscopy • High Resolution • λ/Δλ ~ 1000 from gratings, compared with CCD λ/Δλ ~ 10 - 50 • Strong lines of H- and He-like ions and Fe L-shell • Most line profiles unresolved • Spectral models • Collisionally ionized plasmas: stellar coronae, SNR, galaxies, clusters of galaxies • Photoionized plasmas: X-ray binaries, AGN, planetary nebulae

  4. Benchmarking the ATOMDB • ATOMDB (http://cxc.harvard.edu/atomdb) - Astrophysical Plasma Emission Database (APED) input atomic data - Output collisional ionization models from the Astrophysical Plasma Emission Code (APEC) http://cxc.harvard.edu/atomdb/WebGUIDE (Smith et al. 2001) • Emission Line Project Goal to use the Chandra calibration data to benchmark the collisional models • What accuracy do we need and why?

  5. Physical Conditions Determined from X-ray Spectroscopy • Electron Temperature and Temperature Distribution • Electron Density • Elemental Abundances - Relative - Absolute (lines/continuum) • Opacity • Charge State in Time-Dependent (Non- Equilibrium Ionization) Plasma Yohkoh We really want to understand physical processes: e.g. coronal heating, shocks, accretion, winds

  6. Fe XVII “3C/3D” • In general, neon-like Fe XVII is formed over a very broad temperature range. • We observe Fe XVII lines in most stellar coronal spectra. • In solar active regions, it is formed near the peak temperature and thus produces very strong emission lines. • The solar 3C line has long been thought to be “resonance scattered” (gf =2.7) in the solar corona. 3C 2s2 2p61S0 - 2s2 2p5 3d(2P) 1P1λ15.014 3D 2s2 2p61S0 - 2s2 2p5 3d(2P) 3D1λ15.261 TRACE Image in Fe IX

  7. Solution[s] to the Long-Standing Fe XVII 3C/3D Problem • Anomalously low 3C/3D line ratios in solar active regions from resonancescattering? (Rugge & McKenzie 1985) • τ ~ 2.0(Schmelz et al. 1997) Fe XVII 3C -- -- O VIII Ly γ -- Fe XVI -- Fe XVII 3D Sample Data from Solar Maximum Mission FCS Brickhouse & Schmelz 2006

  8. Recent Results • 3D is blended w/ inner shell Fe XVI Brown et al. 2001 • Experiment: Laming et al. 2001; Brown et al.1998 Theory:Chen & Pradhan 2002; Doron & Behar 2002; Loch et al. 2006; Gu 2003 → still ~15% higher than lab Chen 2006 → 5-10% (also Chen et al. 2006, PRA on Ni XIX) • For same observed ratio, optical depth depends on predicted value: 3C/3D = 4.20 → τ = 0.42 3C/3D = 3.30 → τ = 0.17 3C/3D = 2.85 → τ = 0.032 • The 3C line is optically thin in solar active regions! Brickhouse & Schmelz 2006

  9. Therefore, the TRACE Fe XV line is not optically thick either! Active Region Prominence Fe IX Fe XII Fe XV Brickhouse & Schmelz 2006

  10. Ne IX “R-ratio” and “G-ratio” • Classic He-like diagnostics • “R-ratio” = f/i is density-sensitive. • “G-ratio” = (f + i)/r is temperature- sensitive. f = forbidden1s21S0 - 1s2s 3S1 i = intercombination1s21S0 - 1s2p 3P2 1s21S0 - 1s2p 3P1 r = resonance1s21S0 - 1s2p 1P1

  11. Capella Ne IX Spectral Region • Temperature from Ne IX G-ratio is too low Ness et al. 2003 • Mg XI and O VII also give temperatures too low in other stars • Testa et al. 2004

  12. Blending with Fe XIX in the Ne IX Spectral Region Model Fe XIX wavelengths from HULLAC (1% accuracy) With EBIT λmeasurements (Brown et al. 2002, 5-10 mÅ)

  13. Fe XIX Model Wavelengths from Dirac-Fock-Sturm Method Kotochigova, in progress With this Fe XIX model we can match the positions of all features in the spectrum.

  14. Recent Results New Ne IX G-ratio calculations (Chen et al. 2006, PRA) G-ratio agrees with LLNL EBIT measurements of Wargelin (PhD Thesis 1993) Derived T from Capella in better agreement

  15. Fe XVIII and XIX Line Ratios -- Fe XVIII LETG 355 ks LETG 355 ks -- Fe XVIII HETG/MEG 300 ks HETG/HEG 300 ks IEUV ΩEUV [Te] —— = ———— exp (-ΔE/kTe) IX-rayΩX-ray[Te]

  16. Observed/Predicted Line Ratios All X-ray/EUV line ratios are larger than predicted (by all codes). For the strongest lines, the codes agree: discrepancies are 30% for Fe XVIII and a factor of 2 for Fe XIX. Predictions are based on the EMD with its peak at 6 MK. Fe XVIII EUV Fe XIX FUV X-ray Desai et al. 2005

  17. Te-Dependence of Fe XVIII and XIX Line Ratios • Discrepancies not from: • excitation rate uncertainties • calibration uncertainties • absorption • time variability • Simple Te diagnostics not • consistent with the ionization • state of the plasma • Motivated consideration of • time-dependent NEI effects in • impulsively heated loops. 6 MK EMD peak

  18. Non-Equilibrium Ionization ? • EMD models assume collisional ionization equilibrium: Flux ~ ε(Te) ∫Ne2 dV • In an NEI plasma, the charge state lags the instantaneous temperature Te • NeΔt determines the charge state • For a given Ne and Te , ionization is very fast compared with recombination • Mass conservation (Ne dV = const) implies that a coronal loop, impulsively heated and then cooled by radiation and conduction, will emit primarily during recombination.

  19. Fe XIX / Fe XVIII Fe XVII / Fe XVIII Additional data from other stars Courtesy P. Desai

  20. Ionization Balance? Decreased ionization rate x 2 • Recombination rate coefficients accurate to ~30% • Ionization rate coefficients?

  21. Conclusions • Accurate atomic data are a big investment: priorities should be based on astrophysical importance and needs • For most important diagnostics, line ratios accurate to 10% or better are possible • Interesting astrophysical processes can be explored (e.g. non-equilibrium ionization) with accurate diagnostics • Wavelengths need to be accurate to 1 mÅ • 3-way collaboration among astrophysics, experiment and theory is needed • Experiments can’t substitute for theory

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