New Atomic Data for Determining Neutron- Capture Element Abundances in Planetary Nebulae Nick Sterling Michigan State University June 30, 2010

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Claude Newman
6 years ago
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Michael Witthoeft (NASA/GSFC) Alex Aguilar, David Kilcoyne, Eddie Red

McLaughlin (Queen s University Belfast), Ronald Phaneuf, David Esteves,

1 New Atomic Data for Determining Neutron- Capture Element Abundances in Planetary Nebulae Nick Sterling Michigan State University June 30, 2010 Michael Witthoeft (NASA/GSFC) Alex Aguilar, David Kilcoyne, Eddie Red (ALS/LBNL), Rene Bilodeau (Western Michigan University) Brendan McLaughlin (Queen s University Belfast), Ronald Phaneuf, David Esteves, Ghassan Alna Washi (University of Nevada, Reno) Connor Balance (Auburn University)

Planetary Nebulae Death knell of ~1-8 M סּ stars Low density gas shells expelled at end of AGB Ionized by hot central star PN progenitor stars Sources of C, N, n-capture elements AGB Nucleosynthesis

2 Planetary Nebulae Death knell of ~1-8 M סּ stars Low density gas shells expelled at end of AGB Ionized by hot central star PN progenitor stars Sources of C, N, n-capture elements AGB Nucleosynthesis Thermal pulses s-process nucleosynthesis Convective Dredge-up From Busso et al. 1999, ARA&A, 37, 239 Convective mixing of processed matter to envelope Recurrent C, n-capture elements M S C spectral classifications Does not occur if M < 1.5 M סּ

The s-process Slow n-captures (relative to β-decay lifetime) on Fe peak seed nuclei, during interpulse phase Neutron source(s) Primary: 13 C(α,n) 16 O (T > 10 8 K) Secondary: 22 Ne(α,n) 25 Mg (T > 3

3 The s-process Slow n-captures (relative to β-decay lifetime) on Fe peak seed nuclei, during interpulse phase Neutron source(s) Primary: 13 C(α,n) 16 O (T > 10 8 K) Secondary: 22 Ne(α,n) 25 Mg (T > K) n s captured by Fe-peak nuclei Subsequent n captures, β decays heavy elements formed Produces ~1/2 of the Z > 30 isotopes in Universe From Burris et al. 2000, ApJ, 544, 3 From Busso et al. 1999, ARA&A, 37, 239

4 n-capture Elements in PNe Access to elements not detectable in stars Lightest (Z=31 36) elements, noble gases Also can be formed in massive stars (weak s-process), supernovae (r-process) Chemical evolution Late thermal pulses Intermediate-mass stars (> 3-4 M סּ ) Tracers of C enrichments

2007; Sterling & Dinerstein 2008 Se, Kr, Xe most common (dozens of PNe) From Sterling

5 n-capture Elements in PNe Detected Elements: Ge, Se, Br, Kr, Rb, Te, I, Xe, Ba Péquignot & Baluteau 1994; Sharpee et al. 2007; Sterling & Dinerstein 2008 Se, Kr, Xe most common (dozens of PNe) From Sterling et al From Sterling et al. 2002; Sterling & Dinerstein 2003 From Dinerstein et al (in prep) From Sterling & Dinerstein

6 Status of Atomic Data for n-capture Elements Energies Se 2+ 3 P ground term (!) Transition probabilities Biémont & Hansen (several); Biémont et al. (1995) Effective collision strengths Se 3+, Kr 3+ to Kr 5+, Xe 3+ to Xe 5+, Zr 3+, Ba + and Ba 3+ only Schöning (1997); Schöning & Butler (1998); Butler (in prep) Atomic processes affecting ionization balance: Photoionization (PI) Radiative recombination (RR) Dielectronic recombination (DR) Charge transfer (CT) Needed to correct for unobserved ionization stages. If unknown, uncertainties of factors of 2 or more for 6 Se and Kr abundances

7 Atomic Data Calculations Focus on three elements Se, Kr, Xe Most widely observed n-capture elements in PNe First five ions ( 100 ev) AUTOSTRUCTURE (Badnell 1986) Efficiently computes energy levels, radiative and autoionization rates, multi-configuration distorted-wave PI cross-sections Relativistic corrections: Breit-Pauli, semi-relativistic radial functions Experimental energies used to constrain structure PI cross-sections from valence shell RR from detailed balance DR: Δn=0 Low-T DR dependent on energy accuracies of autoionizing levels near threshold Not experimentally determined 7

8 Atomic Data Calculations Estimation of uncertainties PI, RR: Different configuration sets, sensitivity to other parameters DR: Shift (unknown) autoionization level energies w.r.t. threshold PI also constrained by experimental measurements ~30-50% uncertainties typical for direct PI Low-T DR Constrained by energies of target (recombining) ion uncertainties of factors of 2-10 typical MUCH larger than guess-timates in (e.g.) Cloudy <α DR (C, N, O)> for first four ions Problem for all row 3 and higher elements Dominates RR for Se and Kr ions Effects of atomic data uncertainties on abundances 8 To be tested with Monte Carlo simulations in Cloudy

9 Experimental PI Cross-Sections Ion-Photon Merged Beams (IPB) endstation at Advanced Light Source (ALS) ALS: Third-generation synchrotron light facility EUV/soft X-ray photons ( ev) Ion beam created in electron cyclotron resonance (ECR) source Accelerated by ~6 kv potential Metals evaporated in oven Interaction region Precisely defined volume Potential on/off photoion yield spectrum/ absolute PI cross-section Energy-tags photoions in I.R. allows absolute measurements 9

10 Experimental Results Se+ Xe 3+ Xe 6+ (Bizau et al. 2006), Kr + Kr 5+ (Lu et al. 2006a,b) already measured New measurements of Se + Se 5+, Xe + Xe 2+ PI cross-sections measured in 10 ev region near threshold Metastables in ion beam contribute Measure below threshold Identify resonances, determine metastable fractions with R-matrix calculations (DARC) Used to benchmark AUTOSTRUCTURE calculations PI resonances correspond to DR resonances autoionization energies for DR 10 Sterling et al. (2010, in prep.)

11 Experimental Results Absolute cross-sections done for Se +, Se 2+, Se 3+, Se 5+, Xe +, and Xe 2+

12 Concluding Remarks Add atomic data to photoionization codes Grids of models Derive new ICFs for observed Se, Kr, Xe ions Much more accurate n-capture element abundances in PNe Current accuracy ~ factor of 2 3 Atomic data uncertainties for processes controlling ionization balance Large ICFs (limited no. of detected ions) New Atomic Data First five ions of Se, Kr, Xe PI, RR, DR calculations with AUTOSTRUCTURE CT calculations with a multi-channel Landau Zener code ALS absolute PI cross-sections Applicable to other types of nebulae Extension to other n-capture elements Br, Rb

Improved Neutron-Capture Element Abundances in Planetary Nebulae

Improved Neutron-Capture Element Abundances in Planetary Nebulae N. C. Sterling A,I, H. L. Dinerstein B, S. Hwang B, S. Redfield C, A. Aguilar D, M. C. Witthoeft A, D. Esteves E, A. L. D. Kilcoyne D, M.