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s.g.ryan@herts.ac.uk

s.g.ryan@herts.ac.uk. Lithium abundances and isotope ratios, and troublesome stellar atmospheres Sean G. Ryan School of Physics, Astronomy and Mathematics University of Hertfordshire.

mark-gallagher
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s.g.ryan@herts.ac.uk

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  1. s.g.ryan@herts.ac.uk Lithium abundances and isotope ratios, and troublesome stellar atmospheresSean G. Ryan School of Physics, Astronomy and MathematicsUniversity of Hertfordshire Principal collaboratorsAna GarcíaPérez(UH/Virginia), Adam Hosford(UH), Andy Gallagher(UH)Wako Aoki (NAOJ), Keith Olive (Minnesota), John Norris (ANU) Structure of this talk Two halo-star lithium problems (7Li and 6Li) Effective temperature scales Line profiles in 1D LTE, 1D NLTE, and 3D NGC 4414:Hubble Heritage Team (AURA/STScI/NASA) + Hack/Ryan (OU)

  2. Lithium problem #1: 7Li • Measurements of CMBR by WMAP give baryon density fraction Bh2 = 0.0224±0.0009 (Spergel et al. 2003). • BBN depends on B.WMAP in excellent agreementwith B derived from 2H/1H. • Uncomfortable discrepancy for 7Li:the “Lithium problem” Coc & Vangioni (2005)

  3. Lithium problem #1: 7Li Several explanations offered to explain WMAP discrepancy • intriguing particle physics possibilities(failure of SBBN model): • survival of metastable particlesfor a few ×103 s, i.e. during BBNBird, Koopmans & Pospelov 2007,hep-ph/0703096: X- + 7Be → 7BeX- ; 7BeX- (p,γ) 8BX- → 8BeX- + β+ + νePospelov, M. 2007, hep-ph/0712.0647: X- + 4He → 4HeX- ; +4He → 8BeX- ;8BeX- + n → 9BeX-* → 9Be + X- • decay or annihilation of massive supersymmetric particle,modifying 7Li and 6Li production Jedamzik 2004

  4. Lithium problem #1: 7Li Several explanations offered to explain WMAP discrepancy • stellar destruction possibilities: • Have some stars partiallydestroyed 7Li? • mundane possibilities:Did we get the abundances wrong? • Large uncertainty in low-Zcolour-effective-temperature scales • E.g. comparison between“cool” Ryan et al (2001) and “hot” Melendez & Ramirez (2004) Teff scales shows difference of up to 400K for [Fe/H] < -3 • ΔTeff≈ +400 K → ΔA(Li) ≈ +0.3 dex; close to discrepancy

  5. Lithium problem #1: 7Li • PhD: Adam HosfordEffective temperaturescale for metal-poor stars: • Use T-dependence of Fe I LTE level populations:Boltzmann factor exp-(χ/kT) • Attention to error propagation • Uncertainty in χvs A(Fe)slope being nulled ~ 60-80 K • evolutionary state weakly constrained ~ 12-24 K • uncertainty in ξ~ 30-90 K(wrong physics anyway → 3D)

  6. Lithium problem #1: 7Li • Hosford: Fe I LTE level populations • Asplund et al. 2006:Hα Balmer profile fits • Melendez & Ramirez:IRFM • T,LTE similar to R01, A05Hosford, Ryan, Garcia Perez, Norris & Olive 2009, A&A, 493, 601 • Asplund’06 analysis: • A05 in good agreement with b-y and V-K IRFM of Nissen et al. (‘02,’04): ΔTeff = -34 ± 95 K • cooler than “hot” MR04 scale: ΔTeff = 182 ± 72 K @ [Fe/H] < -2.6). T(Ryan) T(Asplund) T(Hosford) T(Hosford) +200 K T(MR05) T(Hosford)

  7. Lithium problem #1: 7Li • Tχ,LTEassumes LTE Fe I level populations • LTE holds at τcontinuum > 1, but lines form at τcontinuum < 1 • NLTE difficult to calculate reliably • Collisional excitation very uncertain • Collisions with hydrogen parametrized via SH (= 0.001? 1?) • Model atom incomplete • Ideally calculate populations and radiative & collisional transition rates (need all oscillator strengths) for all levels (populations coupled by radiative and collisional transitions), but ... • ... our/Collett model atom contains just 524 levels for Fe I, II and III; cf. NIST lists 493+578+567 levels for Fe I+II+III • Confucius say: • “Stay away from NLTE, and you can have a nice life.” • F. Thevenin, c.2000

  8. Lithium problem #1: 7Li • Previous calculations at low Z point to overionisation as major effect: underpopulates Fe I levels relative to LTEe.g. Asplund et al. (1999, A&A, 346, L17; 2005 ARAA, 43, 481, §3.7) • transparent layers with τcontinuum < 1 see photons from deep/hot atmosphere, so photon intensity Jν > local Bν. UV photons photoionise excited Fe I states. • Additional factors: lack of collisions at τcontinuum < 1 • reduces collisional excitation of excited levels compared to what local T suggests via Boltzmann(i.e. populations not in thermal equilibrium with local temperature) • Net result: excited level populations lower than in LTE;Assess -dependence using MULTI calculations ...

  9. Lithium problem #1: 7Li b ≡ nNLTE/nLTE (SH = 1) • NLTE effects clearly depend on χ • χLTE vs A(Fe) affected by NLTE, henceTχ,LTE affected by NLTE • Calculations vary from star to star, but (for six stars): T,NLTE ~ 110-160 K hotter than R01, A05, ~ 190 K cooler than MR04Hosford, García Pérez, Collet, Ryan, Norris, Olive, 2010, A&A, 511, 47

  10. Lithium problem #2: 6Li • 6Li isotope shift = 0.15 Å; same as fine structure splitting • Adds a little asymmetry to asymmetric line ... as does convection– but hard to model in 3D Cayrel ,et al. (incl. Ludwig), 2007, A&A, 473, 37 • 6Li < 0.00001 ppb in standard bbnSerpico et al. 2004 • 6Li not produced in stars: no stable A = 5 or 8 nuclei • 6Li produced via galactic cosmic ray (GCR) spallation • In Pop I alongside 9Be and 10,11B; at low Z via 4HeISM + αGCRSteigman & Walker 1992, ApJ, 385, L13; Yoshii et al. 1997, ApJ, 485, 605 (YKR)Boesgaard et al. 1999, AJ, 117, 1549 (BDKRVB) Duncan et al. 1997, ApJ, 488, 338 (DPRBDHKR) • 6,7Li destroyed in stars in (p,α) reactions • S-factor = 3140 keV barns for 6Li(p,3He)4He Elwyn et al. 79, PhysRevC, 20, 1984 • S-factor = 55 keV barns for 7Li(p,4He)4He Pizzone etal. 03, A&A, 398, 423 • 6Li(p,α)3He ~2.0×106 K 7Li(p,α)4He ~2.6×106 K Survives (if at all) in warmest low-Z stars Brown & Schramm 88, ApJ, 329, L103

  11. Lithium problem #2: 6Li Aoki et al. 2004, A&A, 428, 579 (AIKRSST) • S/N = 1000R = 900006Li/7Li = 0.00, 0.04, 0.08

  12. Lithium problem #2: 6Li Two major results from Asplund et al. 2006: • Abundance high compared to models that are consistent with spallative 9Be, 10,11B, especially if depletion allowed for. • Trend with [Fe/H] looks like plateau, unlike strong [Fe/H] dependence of models.

  13. Lithium problem #2: 6Li Subaru/HRS data on 5 stars. Isotope ratio VERY sensitive to systematic uncertainties: e.g. macroturbulent width, wavelength shifts, continuum errors, flat field errors,7Li abundance fair choices → uncertaintiesΔ(6Li/7Li) ~ 3-4% García Pérez, Aoki, Inoue, Ryan, Suzuki, & Chiba, 2009, A&A, 504, 213

  14. Lithium problem #2: 6Li Subaru/HRS data very similar to Asplund et al. VLT/UVES data ...... but we are not confident of our “detections” Working at margins of significance due to systematic limitations VLT observations 4% 3% 2% 1% Asplund et al. 2006

  15. Troublesome stellar atmospheres • Barium isotope ratios • Truran (1981) proposed that at low Z, r-process dominates over s-process since s-process seeds have low abundance whereas r-process seeds are made in the SN precursor (based partly on Spite & Spite (1978) Eu/Ba)Truran 1981, A&A, 97, 391 Spite & Spite 1978, A&A, 67, 23 • Travaglio et al (1999) numerical GCE simulations confirm moderate-Z onset of s-processTravaglio et al. 1999, ApJ, 521, 691 • But ... Magain (1995) found Ba 4554 isotope profile in HD 140283 more like s-process than r-processMagain 1995, A&A, 297, 686 • Andy Gallagher (PhD thesis with SGR and AEGP):Use 2 analysis techniques (ex-6Li) to attempt to study 135,137Ba isotopic splitting in low-Z stars

  16. Troublesome stellar atmospheres • Sensitivities: macroturbulent broadening key (Lambert & Allende-Prieto, 2002, MNRAS, 335, 325) • Fit via ~90 Fe I lines with WFe ~ WBa 4554Gallagher, Ryan, Garcia Perez & Aoki, 2010, A&A, 523, A24Gallagher, Ryan, Hosford, Garcia Perez, Aoki & Honda, 2012, A&A, 538, A118 • Co-add residuals for all Fe I lines to see if any asymmetry • 4/4 dwarfs show asymmetric red wing ~ 130 mÅ from line core • Not improved switching ATLAS to MULTI LTE, or LTE to NLTE • 2/2 giants are symmetric (though still large residuals)

  17. Troublesome stellar atmospheres • Experimented with three formalisms for macroturbulence,again fitting to ~90 Fe I lines • Gaussian profile (+ Gaussian instrumental) • Radial-tangential profile (+ Gaussian instrumental) • vsini (+ Gaussian instrumental) • Results: • vsini : rarely the best profile (~ 5% of lines) • Gaussian macroturbulence: sometimes the best profile(~20% of lines) • Radial-tangential macroturbulence: most often the best profile(~80% of lines)

  18. Concluding remarks • 7Li: temperature scales from colours, IRFM, T,LTE and T,NLTE suggest 7Li not compatible with BBN/WMAP. • 6Li: our Subaru data at best only marginally significant; uncertainties ~3-4% of A(7Li); not significant detections. • 6Li, Ba & Fe: asymmetries seen in Fe I line residuals (and Ba II); could also be important for 6Li. • Radial-tangential macroturbulence better than Gaussian ... but still artificial ... Need 3D atmospheres and radiative transfer. • Observation-based challenge for emerging 3D codes: to reproduce observed shapes of Fe I lines in dwarfs and giants.

  19. Cautionary remark • 3D modelling (in NLTE) motivated by: • observed asymmetries in Fe I • dissatisfaction with  (microturbulence) • dissatisfaction with  and/or  (macroturbulence) • realisation that 3D radiative transfer in dynamical models may better explain line formation and hence affect interpretation of spectra • But it may not deliver!M.Spite, 1997, IAUS, 189, 185

  20. NGC 4414:Hubble Heritage Team (AURA/STScI/NASA) + Hack/Ryan (OU)

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