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The He-like triplet ratios as powerful plasma diagnostic

The He-like triplet ratios as powerful plasma diagnostic. Delphine PORQUET Max-Planck für Extraterrestrische, Garching, Germany dporquet@mpe.mpg.de. The new generation of X-ray satellites. Chandra and XMM-Newton (1999-today). X-ray spectrometers: high spectral resolution.

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The He-like triplet ratios as powerful plasma diagnostic

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  1. The He-like triplet ratios as powerful plasma diagnostic Delphine PORQUET Max-Planck für Extraterrestrische, Garching, Germany dporquet@mpe.mpg.de

  2. The new generation of X-ray satellites Chandra and XMM-Newton (1999-today). X-ray spectrometers: high spectral resolution. • ChandraXMM-Newton • LETG HETGRGS • (Å)2 -1702 -25 5 -38 • E (keV) 0.08 -6.2 0.5 -8 0.35 -2.5 • E/E ~1500 ~1000~800 • For the first time high resolution X-ray spectra of extra-solar objects.

  3. Capella: binary star (G1 III + G8 III) d=12.93 pc (Perryman et al. 97) First (weak) detection in X-rays in 1975 (Catura et al., Mewe et al.) ← RGS 1 data (Audard et al. 2001) best-fit model Numerous resolved emission lines from various ionization states: - H-like, He-like (low to high Z elements) - Ne-like to Li-like (High Z elements: Fe)

  4. NGC 1068 (Seyfert 2): z=0.0038 Ogle et al. (2001) Chandra HETG

  5. OVII Chandra spectrum of TW Hya(Classical T-Tauri star ; Kastner et al. 2002) Ne IX

  6. The triplet lines of He-like ions R: resonance line (permitted, w) I: Intercombination line (x+y) F: Forbidden line (z) R F metastable I Ness et al. (2001) Gabriel & Jordan (1969): • Density: R(ne)=Forbidden / Intercombination • Temperature: G(Te) = (F + I) / Resonance First widely used for solar plasma diagnostics. Now: extra-solar objects: collisional (e.g., stellar coronae), photo-ionization (e.g., AGN, X-ray binaries), out-of-equilibrium (e.g., SNR)

  7. Temperature diagnostic (He-like ions) G(Te) = (F + I) / R collisional plasma OVII • Due to the different Te distribution of collisional excitation rates: G(Te) decreases when Te increases. For “pure” photo-ionized plasma (low-T) => G ~ 4 For collisional plasma (high-T) => G ~ 1 (e.g., Porquet & Dubau 2000, Bautista & Kallman 2000)

  8. Density diagnostic (He-like ions) R(ne) =F / I Metastable level Aki very low if (F >> I) then low density and upper limit for ne value. if (ne >critical density and F ~ I) then ne value. if (I >> F) then high density and lower limit for ne value.

  9. Density Temperature I: 6.69 Å I: 9.23 Å E lines I: 13.6 Å I: 21.8 Å λ I: 29.1 Å I: 40.7 Å Density and temperature ranges of the He-like ions E(keV)CV NVI OVII NeIX MgXI SiXIII R 0.308 0.431 0.574 0.922 1.357 1.864 I 0.304 0.426 0.569 0.915 1.343 1.853 F 0.299 0.420 0.561 0.905 1.332 1.840

  10. OVII TW Hya(CTTS; Katsner et al. 2002, Chandra/HETG) Ne IX • Ne IXtriplet: ne ~ 10 13 cm-3. • O VIItriplet: ne ≥ 10 12 cm-3. • High density plasma; shock in accretion column ?

  11. Influence of the UV field A high UV field can mimic a high density plasma Porquet, Mewe, et al. (2001) UV photon UV field: high impact on theF / Iratio for low-Z ions (C, N, O) (e.g., Blumenthal, Drake & Tucker (1972); Mewe et al. (1975); Mewe & Schrijver (1978); Pradhan & Shull (1981); Waldron & Cassinelli (2000);Porquet et al. (2001); Kahn et al. 2001; Miller et al. (2002), Ness et al. 2003).

  12. Advantages and limits of He-like triplet diagnostics • Advantages: • 3 closed lines: insensitive on calibration • same ion/element: not dependent on abundance; produced in the same medium • He-like ions are stable over a large T or a large ionization state ranges • for low-Z (C, N,O, Ne) easily resolved • by Chandra and/or XMM • (Higher-Z ions will be completely resolved with the next X-ray satellites) • Each He-like ions is sensitive within different density and T domains (useful for to probe stratification of the plasma) • High-Z ions are little sensitive or not sensitive to UV field (density is the only free parameter) • Limits: • For low-Z ions the F and I lines are • sensitive to the UV radiation field • (☺But could be also an advantage to probe the UV radiation field location, • as for O stars and late type B-stars, • Schulz et al. 2003, E. Behar’s talk) • Can be blended with satellites lines • (e.g., from Li-like, Be-like ions) • R line can be enhanced by X-ray • photo-excitation mimicking an hybrid plasma: photo-ionization + collisional • e.g., AGN (Kinkhabwala et al. 2002) • For high-column density the F line is enhanced (Bianchi et al. 2004, Chevallier)  need a careful modeling of the He-like ions + “contamination” of other ions: e.g., ☺ APEC, CHIANTI, CLOUDY, SPEX, XSTAR … should be used with complementary plasma diagnostics: e.g., Fe-L lines (cf. Brown, Liedahl and Mauche’s talks), RRC (radiative recombination continua), …

  13. Conclusion and perspectives • Chandra & XMM-Newton First high resolution spectra of extra-solar objects: applications of X-ray plasma diagnostics: He-like: density and temperature (ionization processes) diagnostics. • ASTRO-E2, Constellation-X, and XEUS • High improvement of the spectral resolution with DE/E ~ 2 - 6 eV • up to (or above) 10 keV combined with a higher sensitivity: • Huge increase of the number of objects for which one can apply He-like diagnostics (e.g.,: T-Tauri stars, protostars, weak and/or high-redshift AGN) • Extend He-like diagnostics to higher energies: e.g., Fe XXV: probe higher densities and temperatures domains. • We are only at the beginning of the X-ray plasmadiagnostic era !

  14. Fe L diagnostics • Density diagnostics 10 13 cm-3≤ ne≤ 10 15 cm -3 • Fe XXII (B-like) :I(11.92 Å) / I(11.77 Å) (Mauche et al. 2003).  Very insensitive to temperature and photo-excitation. • Fe XVII (Ne-like) :I(17.10 Å) / I(17.05 Å) (Mauche et al. 2001).  Very sensitive to photo-excitation. • Temperaturediagnostics 10 6 K ≤ Te ≤ 2.10 7 K • Fe XVII (Ne-like) : I(13.829 Å) / I(15.264 Å), I(12.266 Å) / I(15.264 Å): Behar et al. (2001). I(15.01 Å) / I(15.26 Å) : Brown et al. (2001).

  15. Applications: O and early-B stars • Lx / Lbol ~ 10 -7. • X-rays from shocks formed by instabilities within a radiatively driven wind. • He-like diagnostics can be used to discriminate two different possible geometries: • Spatially distributed wind shock model: low densities and far from the UV emitting photosphere. • Magnetically Confined Wind shock model (Babel & Montmerle 1997): high densities and proximity to the UV emitting photosphere. • Example: the brightest stars of the Orion trapezium (1 Ori A, 1 Ori C, and 1 Ori E): magnetic confinement (Schulz et al. 2003).

  16. Satellite lines and He-like ions Ex. Fe XXV IRα NHe T-½ exp(-E0/kT) resonance line: R Ijα NHe T-3/2 exp(-Es/kT) DR resonance line: j IRα NLi T-½ exp(-Ee/kT) IE resonance line : q Satellite/Resonance lines: • Electron temperature: j/w α T-1 exp(0.3 Ew/kT) • Ionization balance: q/w α NLi/ NHe

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