Very deep spectroscopy of planetary nebula NGC7009 The rich optical recombination spectrum and new effective recombination coefficients

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1 Very deep spectroscopy of planetary nebula NGC7009 The rich optical recombination spectrum and new effective recombination coefficients Xuan Fang Department of Astronomy (DoA), Peking University Collaborators: Xiao-Wei Liu (KIAA/DoA, PKU), Peter J. Storey (UCL) Ian A. McNabb (KIAA, PKU) Hai-Bo Yuan (KIAA, PKU) August 31 st 2012, Beijing

2 Outline Background Atomic data New effective recombination coefficients for the N II and O II recombination spectra Very deep spectroscopy of NGC7009 The rich optical recombination spectrum Plasma diagnostics and abundance determinations Summary Xuan Fang, DoA/PKU

3 Planetary Nebulae (PNe) Background PNe are Ubiquitous; Ideal laboratories for studying atomic processes and radiative transfer; Chemistry and dynamics and stellar evolution; The distribution and production of elements in galaxie; Chemical evolution of galaxies and the universe.

4 Spectroscopy of PNe Collisionally excited lines (CELs): Background Optical recombination lines (ORLs): [O III] 2p 2, 2s2p 3 T ex (K) S o 2 j v 1/ 2 T e exp( E j v T,( ~ 1) e ex / kt e ) Grotrian diagram of O II μm 88μm 1 S 0 1 D 2 3 P 2 3 P 1 3 P 0 recombination O 2+ + e - O + + hν

5 Background Discrepancies in nebular astrophysics X i+ /H + (ORLs) > X i+ /H + (CELs), where X is C, N, O, and Ne. Abundance discrepancy factor ADF = X i+ (ORLs)/X i+ (CELs); T e (CELs) > T e (H I Balmer jump), First observed by Peimbert (1967). The discrepancies are REAL Measurement errors? Reddening corrections? Line blending? Contamination of ORLs by other atomic processes (e.g. fluorescence, charge-transfer reactions)? Inaccuracy of atomic data? The abundance discrepancy The temperature discrepancy Figures are from Liu (2010):

6 Background The most extreme case - Hf 2-2 (Liu et al. 2006) Has the strongest ORLs and highest ADF's known for any PN. ADF(O 2+ /H + ) 70; T e ([O III]) = 8820 K; T e (H I BJ) 900 K. The 3.5m NTT images of Hf2-2: a) [O III] 5007, b) Hα.

7 Background Explanations of the discrepancies T e fluctuations and/or N e inhomogeneities (Peimbert 1967, 1971; Rubin 1989; Viegas & Clegg 1994). Most recently: κ-distribution of electrons (Nicholls et al. 2012). The bi-abundance nebular model (Liu et al. 2000): A cold (< 1000 K), metal-rich plasma component in PNe (probably also in H II regions). The bi-abundance nebular model CELs are from hot ionized gas, ORLs from the cold, metal-rich plasma. Well explains the wide ranges of observations. What are the astrophysical origins of the cold inclusions? First need to know T e, N e, X/H, mass, etc.

8 Background 3D photoionization modeling of NGC6153 (Yuan et al. 2011) ADF(O 2+ /H + ) 10 Chemically homogeneous model: HST/WFPC2 images of NGC6153 (Upper) The bi-abundance model: Projected monochromatic images of the 3D model (Mid)

9 Background The need for new atomic data Effective recombination coefficient, as defined by Emissivity = α eff (λ) hν N + N e [erg cm -3 s -1 ]. Classic work on the C II, N II, O II, and Ne II data: Escalante & Victor (1990); Péquignot, Petitjean & Boisson (1991); Storey (1994); Liu et al. (1995); Davey, Storey & Kisielius (2000); Kisielius et al. (1998); Kisielius & Storey (2002); etc. Currently, no N e -diagnostic tools are based on the heavy element ORLs. Most of the previous calculations are valid above 5000 K. If the cold, metal rich compoent does exist, the atomic data need to be calculated down to low T e (< 1000 K).

10 Atomic data Ab initio calculations The N 2+ and O 2+ targets are generated by SUPERSTRUCTURE. Radial wave functions are caluclated by AUTOSTRUCTURE. R-matrix calculations: Energy levels, oscillator strengths, and phtoionization cross-sections; All calculations are in the intermediate coulping (IC) scheme. The photoionization cross-section calculations An adaptive energy mesh is used (Kisielius & Storey 2002); Resonances as narrow as ~10-10 Ryd are resolved; Recombination coefficients are integrated from the photoionization crosssections; Traditional OP methods based on the quantum defect mesh or fixed-step energy mesh are inadequate for narrow resonances.

11 Atomic data E.g. photoionization cross-sections of the N + 2p 23 P 0 level

12 Effective recombination coefficients Atomic processes considered in level population calculations Bound-bound radiative transitions Bound-free: photoionization and radiative recombination Dielectronic recombination and autoionization Collisions: Collisional excitation and de-excitation by e -, H +, He + and He ++ Collisional ionization and three-body recombination h b X a X i i ) ( ) ( h b X e a X i i ) ( ) ( 1 h b X a X e a X i i i ) ( ) ( ) ( ** 1 ) ( ) ( ) ( ) ( ' 2 2 k c b X k c a X i i e e b X e a X i i ) ( ) ( Fang, Storey & Liu (2011) IAU XXVIII General Assembly

13 Effective recombination coefficients Dielectronic recombination High-T e dielectronic recombination (occurs through high-n states (n 100), only important for T e 's above K) Low-T e dielectronic recombination (occurs through near-threshold resonances) Dielectronic recombination at very low T e (e.g. 250 K in the case of N + )

14 Effective recombination coefficients Relative populations of the recombining ion N 2+ 2 P o 1/2 and 2 P o 3/2

15 Effective recombination coefficients Relative populations of the recombining ion O 2+ 3 P 0, 3 P 1 and 3 P 2

16 Effective recombination coefficients Results of N II Fractional intensities of the N II multiplet V3 2p3p 3 D - 2p3s 3 P o Fang, Storey & Liu (2011)

17 Effective recombination coefficients Results of N II Effective recombination coefficient fits α eff (λ) are fitted as a function of T e ; the maximum fitting errors < 0.5%. The low-t e regime: for T e < K, α = log 10 α eff (λ) + 15, t = log 10 T e. The high-t e regime: a a1t a2t a3t a4t a5t ( b0 b1t b2t b3t b4t ) t b exp( b6t) for T e K, α = lgo 10 α eff (λ) + 15, t = T e [K]/10 4.

18 Effective recombination coefficients Applications to plasma diagnostics Plasma diagnostics using the N II ORL ratios Based on the latest intermediate coupling calculations of Fang, Storey & Liu (2011)

19 IAU XXVIII General Assembly Effective recombination coefficients Results of O II Fractional intensities of the O II multiplet V1 2p23p 4Do - 2p23s 4P P. J. Storey (unpublished)

20 Effective recombination coefficients Applications to plasma diagnostics Plasma diagnostics using the O II ORL ratios Based on the new intermediate coupling calculations of P. J. Storey (unpublished)

21 Effective recombination coefficients The old O II data (before 2007) Plasma diagnostics using the O II ORL ratios Based on the j-j coupling calculations of Bastin & Storey (2006)

22 Effective recombination coefficients What about Ne II? The Ne II calculations The relative populations of the Ne 2+ 3 P 2, 3 P 1, and 3 P 0 levels as a function Schematic figure showing the low-temperature dielectronic recombination of Ne II through the autoionization levels between the Ne 2+ 3 P 2, 3 P 1, and 3 P 0 thresholds: of N e : V55e V13 V2

23 Very deep spectroscopy of NGC7009 Observations The bright Saturn nebula NGC7009 A medium excitation PN Distance: 0.86 kpc Rich in emission lines, especially the O II ORLs (e.g. Wyse 1942; Aller & Kaller 1964; Barker 1983; Liu et al. 1995) ESO 1.52m, WHT 4.2m Å; high resolution The deepest CCD spectra ever taken for a PN HST/WFPC2 image of NGC7009: Credit: Bruce Balick (University of Washington), Jason Alexander (University of Washington), Yervant Terzian (Conell University), etc. (

24 Very deep spectrum of NGC7009 H I Blamer jump at 3646Ǻ H I Paschen jump at 8204Ǻ N II V3 lines He II jump at 5694Å He II jump at 5694Ǻ

25 Very deep spectroscopy of NGC7009 Very rich optical recombination spectrum The rich N II and O II ORLs O II ORLs N II ORLs

26 Very deep spectroscopy of NGC7009 Observations Rich optical recombination lines in NGC7009 Gaussian profile fitting was used for deblending Cumulative curve of emission lines:

27 Very deep spectroscopy of NGC7009 The rich optical recombiantion spectrum The O II V1 multiplet 2p23p 4 D o - 2p23s 4 P

28 Very deep spectroscopy of NGC7009 The rich optical recombiantion spectrum The N II V3 multiplet 2p3p 3 D - 2p3s 3 P o The N II 4f-3d transitions

29 Very deep spectroscopy of NGC7009 The rich optical recombiantion spectrum The C II V28.01 multiplet (dielectronic recombination) 2s2p( 3 P o )3d 2 F o -2s2p( 3 P o )3p 2 D Radiative recombination, Dielectronic capture and the subsequent radiative decay of C II: The C II V28.01 λ8794 line is excited by dielectronic recombination; the C II V6 λ4267 line is excited by radiative recombination. λ8794/λ4267 ~ T e

30 Very deep spectroscopy of NGC7009 Plasma diagnostics using ORLs T e derived from the C II optical recombination lines: T e (λ8794/λ4267) 3000+/- 250 K However, this T e value probably does not represent the true physical condition of the C II ORLs, because: The C II V28.01 λ8794 line favours the high-t e ; The C II V6 λ4267 line arises from the low-t e area. The figure is based on the radiative and dielectronic recombination coefficients of Péquignot, Petitjean & Boisson (1991) and Nussbaumer & Storey (1984), respectively.

31 Very deep spectroscopy of NGC7009 Plasma diagnostics using ORLs T e and N e from the N II optical recombination lines N e (λ5679/λ5666) cm -3 T e (λ5679/λ4041) 1200+/-200 K (Fang & Liu 2012, submitted)

32 Very deep spectroscopy of NGC7009 Plasma diagnostics using ORLs T e and N e from the O II optical recombination lines N e (λ4649/λ4662) cm -3 T e (λ4649/λ4089) 1300+/-300 K (Fang & Liu 2012, submitted)

33 Very deep spectroscopy of NGC7009 Plasma diagnostics using CELs Plasma diagnostics based on CELs T e (K) 1. [N II] ( )/ [O III] ( )/ [S III] ( )/ [O II] ( )/ [O I] ( )/ [Ar III] 7135/ N e (cm -3 ) 7. [Ar IV] 4740/ [Cl III] 5537/ [S II] 6731/ [Fe III] line ratios > [O II] 3726/ (Fang & Liu 2011)

34 Very deep spectroscopy of NGC7009 Plasma diagnostics using the H I spectrum T e 's and N e 's from the H I recombination spectrum T e (H I Balmer jump) 6500 K; T e (H I Paschen jump) 6750 K N e (Balmer Decrements) 3000 cm -3 N e (Paschen Decrements) cm - 3 T e (BJ) 6500±100 K T e (PJ) 6750±200 K H I Balmer jump at 3646Å H I Paschen jump at 8204Å

35 Very deep spectroscopy of NGC7009 Plasma diagnostics using the He I spectrum T e 's from the He I and He II recombination spectra T e (He I λ7281/λ6678) 5100 K (most reliable, adopted) The He I discontinuity at 3421Å yields a temperature ~7800 K The He II discontinuity at 5694Å yields a temperature ~ K The He I discontinuity at 3421Å (recombination to 1s2p 3 P o ) The He II discontinuity at 5694Å (recombination to the n=5 level) He I discontinuity at 3421Å He II discontinuity at 5694Å

36 Very deep spectroscopy of NGC7009 Summary of plasma diagnostics T e (CELs) 10 4 K T e (H I Balmer jump) 6500 K T e (He I λ7281/λ6678) 5100 K T e (N II λ5679/λ4041) 1200 K T e (O II λ4649/λ4089) 1300 K T e (CELs) T e (H I) T e (He I) T e (N II, O II ORLs) T e (N II ORLs) ~ T e (O II ORLs) N II and O II ORLs are emitted from the low-t e area

37 Very deep spectroscopy of NGC7009 Plasma diagnostics using ORLs (new method) T e 's and N e 's from the N II and O II ORLs Several ORLs are used simultaneously to confine T e and N e 2 The residuals: n I ( ) ( ) 2 observed i I predicted i 1 ( ) i I predicted i N II: λλ5679 (V3), 5666 (V3), 4041 (V39b), 4035 (V39a) (McNabb et al. 2012, MNRAS, submitted) O II: λλ4662 (V1), 4649 (V1), 4089 (V48a), 4087 (V48

38 Very deep spectroscopy of NGC7009 Plasma diagnostics using ORLs (new method) T e 's and N e 's from the N II and O II ORLs Error estimate: randomly generate numbers for each line flux The random numbers are assumed to be in Gaussian distribution Each set of randomly generated fluxes gives a T e and N e (McNabb et al. 2012, MNRAS, submitted) O II: λλ4662 (V1), 4649 (V1), 4089 (V48a), 4087 (V48

39 logt e (K) IAU XXVIII General Assembly Nebula sample Very deep spectroscopy of NGC7009 Plasma diagnostics using ORLs (new method) More than 120 PNe and about 40 H II regions are analyzed. (McNabb et al. 2012, MNRAS, submitted) In general, T e (CELs) T e (H I) T e (He I) T e (N II, O II ORLs)

40 Ionic abundances from ORLs N ( H ) I( ) N 2+ /H + H ( ) 4861 I( H ) 2 eff eff Dashed line: average value from the 3 3 transitions Dotted line: average value from the 4f 3d transitions <N 2+ /H + > 3 3 is only 0.02 dex higher than <N 2+ /H + > 4f 3d.

41 Ionic abundances from ORLs O 2+ /H + O H 2 eff ( H ) ( ) eff 4861 I( ) I( H ) Dashed line: average value from the 3 3 transitions Dotted line: average value from the 4f 3d transitions <O 2+ /H + > 3 3 is 0.05 dex higher than <O 2+ /H + > 4f 3d.

42 Ionic abundances from ORLs Ne 2+ /H + 3-3: Kisielius et al. (1998) 4f - 3d: the preliminary results of Storey (unpublished) New calculations of the Ne II effective recombination coefficients are needed! Red dotted line: The average abundance from the 3 3 transitions. Red circle: The average abundance from the 4f 3d transitions <Ne 2+ /H + > 3 3 is 0.21 dex lower than <Ne 2+ /H + > 4f 3d.

43 Comparison of ionic abundances CELs v.s. ORLs Ionic abundances of heavy element ions ADF(C 2+, N 2+, O 2+, Ne 2+ ) ~ 5; log(o/h)+12 = /- 0.08; IR and UV data are from the literature.

44 Summary New effective recombination coefficients for the N II and O II recombination spectra Laying the fundation for nebular plasma diagnostics based on heavy element ORLs. Very deep spectroscopy of NGC7009 Rich ORLs of heavy element ions; Plasma diagnostics confirm the bi-abundance model: T e (CELs) T e (H I) T e (He I) T e (N II, O II ORLs). T e (N II ORLs) T e (O II ORLs): Heavy element ORLs originate from very cold regions (~ 1000 K). ADF(C 2+ ; N 2+ ; O 2+ ; Ne 2+ ) ~ 5: Cold, metal-rich inclusions? The new effective recombiantion coefficients of N II and O II are reliable. New calculation for the Ne II recombination is underway. Some comments About observations: Currently, only a few PNe (also H II regions) have deep enough spectra to study ORLs. About the atomic data: The new calculations are just a beginning. The discrepancy problems remain.