CHIANTI An atomic database for X-ray spectroscopy

1. CHIANTI An atomic database for X-ray spectroscopy Enrico Landi Naval Research Laboratory

2. Overview • Introduction – why a database? • What is CHIANTI • CHIANTI 5.1 • DEMO of CHIANTI Software And, IF there is time….. • Comparison with X-ray observations • Some CHIANTI applications

3. 1 - Introduction • X-ray spectra are of primary importance for quantitative studies of the physics of many astrophysical objects • Emission and absorption of line and continuum radiation in the X-rays offer a wide variety of diagnostic tools to determine the physical properties of emitting sources • For this reason, in the recent past, several instruments have been flown to observe astrophysical sources in the X-ray range: • Chandra ROSAT • XMM Yohkoh • RHESSI SMM • RESIK …and many others

4. Why a database? • X-ray spectra are composed by line and continuum radiation, emitted by highly charged ions. • Observed X-ray spectral lines come from H-,He-like ions High-energy configurations (n>2) in highly charged Fe and Ni ions Innershell transitions Dielectronic satellite lines • Continuum radiation comes from Free-free radiation Free-bound radiation

5. In order to study this radiation and use it for plasma diagnostic purposes, a large amount of atomic data are needed for both line and continuum radiation • To address this need, several databases have been created in the past: CHIANTI MEKAL APEC/APED ADAS Arcetri Spectral Code XSTAR • With the only exception of MEKAL, all these databases include CHIANTI data

6. Requirements for a database • In order to be suitable for the analysis of modern high-resolution spectra, atomic databases need to -be complete no lines left behind - be accurate plasma diagnostics must not be hindered by atomic physics uncertainties - be easy-to-use - be transparent - the user can independently check the original data and their accuracy - no black box - all data independently refereed in peer reviewed literature • Also, atomic data and predicted emissivities from databases need to be benchmarked against observations

7. 2 - The CHIANTI database • CHIANTI consists of A database of atomic data and transition rates A suite of IDL programs for plasma diagnostics • CHIANTI is able to calculate Line emissivities for- more than 220 ions - innershell transitions - dielectronic satellite lines Continuum emissivities for- free-free radiation -free-bound radiation -two-photon continuum The CHIANTI database can be used at any wavelength range, but it is optimized for the 1-2000 Angstrom range.

8. CHIANTI data are: • In ASCII format • Selected from the refereed literature (no unpublished data) • Critically assessed and evaluated • With references to original literature CHIANTI is completely transparent to the end user • FREELY available on the web at http://wwwsolar.nrl.navy.mil/chianti.html (and 5 other sites) • Fully documented through user guides CHIANTI also provides: a mailing list (I maintain it myself) email assistance to users at: chianti_help@halcyon.nrl.navy.mil

9. Line intensity calculation The intensity of an optically thin line is given by Where φ(T)is the Differential Emission Measure and G(T,λ) is the Contribution Function, given by a b c d e Where: • a: relative level populationcalculated by CHIANTI as f(T, Ne) • b: ion fractionprovided by CHIANTI from literature as f(T) • c: element abundanceprovided by CHIANTI for sample plasmas • d: electron/hydrogen ratiocalculated by CHIANTI as f(T) • e: Einstein coefficientprovided by CHIANTI

10. Level population calculation Level populations are calculated by solving statistical balance equations. The excitation processes included are: • Electron-ion collisional excitation • Proton-ion collisional excitation • Photoexcitation by any ambient radiation • Radiative cascades • Ionization and recombination into excited levels • Dielectronic recombination (for satellite lines) The de-excitation processes included are: • Spontaneous radiative decay • Electron-ion collisional de-excitation • Autoionization (for satellite lines) CHIANTI also allows the use of non-Maxwellian distribution of electron velocities

11. Basic assumptions in CHIANTI • The plasma is optically thin • no radiative transfer • The plasma is in ionization equilibrium • ionization and recombination rates will be part of Version 6 • The plasma density is lower than 1015 cm-3 • rise of metastable levels for which there are no collisional rates • Stimulated emission is neglected

12. CHIANTI diffusion CHIANTIhas enjoyed great success in the astrophysical community. CHIANTI data have been • Included in the software of several satellite borne missions SOHO/CDS (EUV) SOHO/EIT (EUV) TRACE (UV) RHESSI (X-rays) Solar-B (EUV,X-rays) STEREO (EUV) • Included in other spectral codes APEC/APED PintOfAle Arcetri Spectral Code ADAS XSTAR • Included in theoretical models (i.e. loop models, irradiance models etc) • Referenced in more than 400 papers

13. Benchmarks of CHIANTI data CHIANTI predictions have been compared to several observed spectra to determine its completeness and accuracy: • SERTS 1989 170-450 A (Young etal 1998) • SOHO - CDS/NIS 308-630 A (Landi et al. 2002a) • SOHO -SUMER 500-1600 A (Landi et al. 2002b) • SMM - FCS 7-18 A (Landi & Phillips 2006) These comparisons have: • Shown overall excellent agreement • Shown areas where improvement was needed – led to new CHIANTI versions • Showed where new calculations were needed – triggered new atomic physics calculations

14. CHIANTI applications • Plasma diagnostics Plasma physical parameters • Synthetic spectra calculation Line identifications Identification of new diagnostic tools • Radiative losses calculation Energy equation in models • Plasma response function of imagers Diagnostic use of imagers • Optimization of optical design of new instrumentation Calculations of count rates Wavelength range/filter wavelength selection • Atomic Physics Check the quality of existing data Promotes calculations of new data Test different atomic physics approximations

15. 3 - CHIANTI 5.1 The CHIANTI database has been recently greatly expanded. The main features of the current version (Version 5.1) are: • Physical processes • Ionization and recombination effects in level populations • Non-Maxwellian distributions of electron velocity • Photoexcitation from any user-defined ambient radiation field • New data • New data for high-energy configurations in Fe XVII-XXIII n=3,4,5,6,7 Fe XVII n=3,4,5 Fe XVIII-XXIII • New data for satellite lines • New data for K-alpha emission • Complete re-assessment of energy levels and line identifications • New data for Fe IX, Fe XII, Fe XV (crucial for narrow-band EUV imagers) • Other data and new ions for EUV and UV lines • Software • More efficient software

16. New data for high-energy configurations in Fe XVII-XXIII • We have made use of the Flexible Atomic Code, by Dr. M.F. Gu, to calculate Energy levels Radiative transition rates Electron-ion collisional transition rates (including resonances) for all configurations with n=3,4,5,6,7 Fe XVII n=3,4,5 Fe XVIII-XXIII • These data allow to predict lines in the 7-12 Angstrom range • Few, if any data were available in the literature for most of these configurations

18. New data for satellite lines • New data have been added to CHIANTI 5.0 for dielectronic satellite lines and innershell transitions, to match observations Fe XVIII to XXIVinnershell transitions Fe II to Fe XXIV dielectronic satellite lines Si XII,S XVI, Ca XVIII dielectronic satellite lines • These new lines also provide diagnostic tools for measuring the plasma electron temperature • These lines allow to study RHESSI spectra in the 6-9 keV energy range

19. Fe XXV Fe XXV Fe XXV Fe XXIV satellites Fe XXIV satellites Fe XXIV satellites

20. RHESSI 6.7 keV/8 keV ratio • Their ratio is temperature sensitive • Inclusion of satellites is key to a correct plasma temperature measurement • RHESSI is able to resolve the Fe complex at 1.85 A (6.7 keV) and the Ni/Fe complex at 1.5-1.6 A (8 keV). Phillips (2004)

21. Satellite lines are of crucial importance for X-ray spectroscopy: • They allow accurate temperature diagnostics • They blend with He-like triplets and alter their line ratios, thus affecting • Temperature diagnostics • Density diagnostics CHIANTI allows to take explicitly into account such satellites into line ratios, by including levels above the ionization threshold into the level population calculation. Excitation processes are: • Dielectronic capture of a free electron • Collisional excitation from levels below the ionization threshold

22. 1s2p 1P1 2 1s2p 3P 1 0 1s2s 3S1 Example: the (x+y)/z ratio in Si XIII • Both lines are blended with satellite lines: • z: 1s21S0 – 1s2s 3S1 • x+y: 1s21S0 – 1s2p 3P1,2 • The (x+y)/z ratio is • strongly density dependent • little temperature dependent • constant at low density z w x y

23. If satellite lines are taken into account, the low-density limit of the (x+y)/z ratio can change by a factor around 4 at low T, and becomes strongly temperature dependent. Ness, Landi & Jordan (2006)

24. 1s2p 1P1 2 1s2p 3P 1 0 Example: the (x+y+z)/w ratio in Si XIII • All lines are blended with satellite lines: • z: 1s21S0 – 1s2s 3S1 • x+y: 1s21S0 – 1s2p 3P1,2 • w: 1s21S0 – 1s2p 1P1 • The (x+y+z)/w ratio is • strongly temperature dependent • little density dependent 1s2s 3S1 z w x y

25. If satellite lines are taken into account, the temperature dependence of the (x+y+z)/w ratio can change dramatically at low temperatures, where satellite lines dominate. Ness, Landi & Jordan (2006)

26. Effects of Ionization and Recombination on level populations • Recently, Behar & Doron (2002) and Gu (2003) demonstrated that ionization and recombination are important contributors to steady-state level population in highly ionized Fe ions • CHIANTI 5.0 incorporates data and software to take these two processes into account for • Fe XVII to Fe XXIV • He-like ions • H-like ions • Most recombination and ionization data have been taken from the Flexible Atomic Code calculations by Gu (2003).

27. We make use of the Coronal Model Approximation: Without Ionization/Recombination: With Ionization/Recombination: Where: nq-1, nq, nq+1ion fractions CI, RECtotal ion. and rec. rates Egitotal excitation rate level i Digtotal de-excitation rate level i

28. The Coronal Model Approximation is not valid if metastable levels have non-negligible population • As the electron density increases, the population of metastable levels also increases • The maximum density at which metastable level populations are negligible changes from ion to ion: Ion Log Ne(max) Fe XVII any Fe XVIII > 13 Fe XIX 12 Fe XX 12 Fe XXI 12 Fe XXII 13 Fe XXIII > 13 Fe XXIV any He-like ions From >10 to > 15 H-like ions > 13

29. Fe XXI Fe XXII Fe XXIII Fe XXIV

30. Example: the (x+y)/z ratio in Si XIII • Recombination is more efficient in populating the 1s2p 3P1,2 levels (x and y lines) and therefore it alters the (x+y)/z ratio: • Recombination is more efficient athigh temperature • Different datasets have different effects on the ratio. We used two different datasets: • Mewe et al (1985) • Porquet & Dubau (2000) • We need more calculations Ness, Landi & Jordan (2006)

31. Future CHIANTI features • We are working on the next version of CHIANTI (Version 6), which will include: • Ionization and recombination rates (both total and level-resolved) • to allow studies of transient ionization; • New data for high-energy configurations in all isoelectronic sequences • to predict lines in X-ray and UV spectra; • New data for Fe ions from the Iron Project • to predict lines in the X-ray and EUV range; • New data for satellite lines • to account for all contributions; • More data for proton excitation rates

32. 4 - DEMO of CHIANTI software • Quick introduction to CHIANTI web sites • Download • Direct access • User guides • Synthetic spectra calculation • General routine: CH_SS • Spectral lines routines: CH_SYNTHETIC, MAKE_CHIANTI_SPEC • Continuum routines FREEFREE, FREEBOUND, TWO_PHOTON • Radiative losses: RAD_LOSS • Contribution function and emissivity calculation • Contribution functions: GOFNT • Emissivity: EMISS_CALC • Non Maxwellian distributions • Only for emissivities: EMISS_CALC • Plasma diagnostics • Density diagnostics: DENS_PLOTTER • Temperature diagnostics: TEMP_PLOTTER • DEM CHIANTI_DEM (won’t demonstrate it)

33. 2 – Synthetic spectra calculation The interactive routine: • CH_SS • 1st step: line intensity calculation • 2nd step: Calculate spectrum (plus abundance selection) • 3rd step: Visualize and save results From the IDL prompt, and in users’ own software • Spectral lines: • CH_SYNTHETIC • Input calculation parameters from keywords • No continuum calculation • Provides line intensities (no abundances) • MAKE_CHIANTI_SPEC • Calculates spectrum from line intensities in the output of CH_SYNTHETIC • Includes abundances • Continuum spectrum: • FREEFREE • FREEBOUND • TWO_PHOTON • RAD_LOSS • Radiative losses as a function of temperature

34. 3 – Contribution functions and emissivities • Contribution functions: GOFNT • Calculates G(T,Ne) as a function of temperature for fixed densities • Several interactive requests • Outputs only few selected transitions • Contribution functions: CH_SYNTHETIC • The /goft keyword gives in the output the contribution functions of all the lines in the selected wavelength range • Emissivities: EMISS_CALC • Calculates hν Nj Aji for user selected arrays of T and Ne (Nj = relative level population) • No interactive requests • The user needs to multiply results by ion fractions, abundances etc to get Contribution Functions

35. 4 – Non-Maxwellian distributions • This is a new feature in CHIANTI, so far it has been implemented in the EMISS_CALC program only. • This is achieved by approximating the velocity distribution f(v) as a linear combinations of individual Maxwellian distributions: f(E,ai) = Σi ai fM(E,Ti) fM(E,Ti) Maxwellian distribution with Ti Cijtot = Σi ai Cij(Ti) Cij(Ti) Maxwellian collision rate coeff. The rate coefficients Cijtot are then used in the level population calculation. • The distribution can be input in the program by specifying the coefficients of the linear combination of individual Maxwellians to EMISS_CALC: IDL> data=emiss_calc(8,6,dens=[10],temp=[5.5,6.0],sum_mwl_coeffs=[0.75,0.25]) Example:O VI 173/1031 ratio, Log T=[5.5,6.0] Coefficients Ratio 1.0, 0.0 0.0335 0.5, 0.5 0.113

36. 5 – Plasma diagnostics • Temperature diagnostics: TEMP_PLOTTER • Interactive routine • Provides ratios within lines of the same ion • Allows blending with lines of the same ion • Density diagnostics: DENS_PLOTTER • Interactive routine • Provides ratios within lines of the same ion • Allows blending with lines of the same ion • DEM diagnostics: CHIANTI_DEM

37. Additional topics • Since it seems there is time….. • Comparison with X-ray observations • Some CHIANTI applications

38. 1 - Comparison with X-ray observations We have compared the new CHIANTI 5.0 with observations of a moderate solar flare Instrument SMM/FCS (Bragg crystal spectrometer) Date of observation August 25, 1980 Wavelength ranges 13.1-22.4 A (channel 1) 10.6-14.9 A (channel 2) 7.3-10.1 A (channel 3) Spectral resolution 1-20 mA (depending on the channel) Source M 1.5 flare Spectral scan Duration 17.5 minutes Ions observed H-like O,Ne,Mg He-like O,Ne,Na,Mg,Al Fe ions Fe XVII to Fe XXIII Ni ions Ni XIX, Ni XX

39. Comparison method • FCS spectra were not observed simultaneously, so the flare plasma was analyzed as a function of time • The Emission Measure analysis showed that • The flare plasma was isothermal • The temperature was decreasing slowly • The emission measure decreased by a factor 6 during the observation • This allowed us to use the Emission Measure as a tool to compare CHIANTI 5 emissivities and observed fluxes for each ion, to: • Assess the quality of CHIANTI 5 data • Identify blends from other ions and evaluate their contribution to the total intensity (additional check on atomic physics) • Identify areas where improvements are still needed

40. In case of isothermal plasma • We can define, for all the lines of the same ion, the ratio • If there are no blends and no atomic physics problems, all the ratios must be the same at all temperatures, within the uncertainties.

41. Example: Fe XIX CHIANTI 5 CHIANTI 4.2 Time bin 1 Time bin 2

42. Example: Fe XVII • Long standing problems: • Strong 15.01 A line lower than predicted • Resonant scattering? • Satellites in 15.01/15.26 intensity ratios? • Disagreement in 2p-3s/2p-3d ratios • Innershell ionization to 3s? • Satellite contributions to line ratios? • Existing atomic data • DW collision rates from many authors • R-Matrix rates including resonances for some of the lowest levels • Doron & Behar (2002) showed that recombination into excited levels is important for Fe XVII

43. We used CHIANTI 5.0 to check the importance of many additional processes in Fe XVII level population: Process Importance CascadesModerate Collisional ionizationModerate RecombinationCrucial ResonancesCrucial • We have compared the FCS spectrum with predictions obtained with (CHIANTI 5) and without(CHIANTI 4.2) those processes

44. CHIANTI 4.2 15.01 A CHIANTI 5.0 15.01 A

45. Results and Conclusions • CHIANTI 5.0 reproduces observed high- and low- resolution X-ray spectra with great accuracy All relevant configurations in Fe ions are now included Blending from ions of different species is accounted for Most lines are reproduced within 30% • CHIANTI 5.0 represents a major advance over previous versions and other databases • New diagnostic tools are now available to measure the physical properties of the emitting plasmas

46. 2 - CHIANTI applications • Plasma diagnostics Plasma physical parameters • Synthetic spectra calculation Line identifications Identification of new diagnostic tools • Radiative losses calculation Energy equation in models • Plasma response function of imagers Diagnostic use of imagers • Optimization of optical design of new instrumentation Calculations of count rates Wavelength range/filter wavelength selection • Atomic Physics Check the quality of existing data Promotes calculations of new data Test different atomic physics approximations

47. Applications - Plasma diagnostics in the X-rays • X-ray lines are excellent tools for plasma diagnostics in solar active regions and flares. • From X-ray lines and CHIANTI data it is possible to measure • Electron density • Electron temperature • Emission measure or Differential Emission Measure • Abundances • Mass motions

48. Diagnostics - Electron density 1s2p 1P1 2 1s2p 3P 1 0 1s2s 3S1 1 - He-like systems • Ratios between the w, (x+y) and z lines are strongly density and temperature sensitive • The ratio (x+y)/z is moderately sensitive to temperature and strongly dependent on density • C V, N VI, O VII active regions • Ne IX, Na X, Mg XI flares • Heavier ions Very high Ne • Satellite lines need to be taken into account z w x y

49. 2 - Fe ions • Some n=3 lines from Fe XVII-XXIII are density sensitive relative to other lines of the same or other configurations. • Their sensitivity is however limited in the ranges • Log Ne < 9 • Log Ne > 12 • Some lines are weak and can only provide upper/lower limits

50. Diagnostics - Electron temperature 1snp 1P1 2 1snp 3P 1 0 wn yn 1s2p 1P1 1 - He-like systems • Ratios involving the w line are strongly temperature sensitive • The (x+y+z)/w ratio is very weakly density sensitive • Also the wn/yn ratios can be used to measure the electron temperature 2 1s2p 3P 1 0 1s2s 3S1 z w x y