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

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
• ?/?? 1000 from gratings, compared with CCD ?/??
  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 2p6 1S0 - 2s2 2p5 3d(2P) 1P1 ?15.014
• 3D 2s2 2p6 1S0 - 2s2 2p5 3d(2P) 3D1 ?15.261

TRACE Image in Fe IX
7
Solutions to the Long-Standing Fe XVII 3C/3D
Problem

• Anomalously low 3C/3D line ratios in solar
  active regions from resonance scattering? (Rugge
  McKenzie 1985)
• t 2.0 (Schmelz et al. 1997)

Fe XVII 3C --
-- O VIII Ly ?
-- 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 ? t 0.42
• 3C/3D 3.30 ? t 0.17
• 3C/3D 2.85 ? t 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
(No Transcript)
11
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 forbidden 1s2 1S0 - 1s2s 3S1
• i intercombination 1s2 1S0 - 1s2p 3P2
• 1s2 1S0 -
  1s2p 3P1
• r resonance 1s2 1S0 - 1s2p 1P1

12
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

13
Blending with Fe XIX in the Ne IX Spectral Region
Model Fe XIX wavelengths from HULLAC (1
accuracy)
With EBIT ? measurements (Brown et al. 2002,
5-10 mÅ)
14
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.
15
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
16
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 OEUV Te exp
(-?E/kTe) IX-ray OX-rayTe
17
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
18
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
19
Non-Equilibrium Ionization ?

• EMD models assume collisional ionization
  equilibrium
• Flux e(Te) ?Ne2 dV
• In an NEI plasma, the charge state lags the
  instantaneous temperature Te
• Ne?t 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.

20
Fe XIX / Fe XVIII
Fe XVII / Fe XVIII
Additional data from other stars Courtesy P.
Desai

21
Ionization Balance?
Decreased ionization rate x 2

• Recombination rate coefficients accurate to 30
• Ionization rate coefficients?

22
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 cant substitute for theory