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Non-LTE studies of A-type supergiants

Non-LTE studies of A-type supergiants. Norbert Przybilla K. Butler (Munich), M. Firnstein & F. Schiller (ex-Bamberg). Intro. The Protagonists evolved progeny of OB main-sequence stars T eff : ~ 8000 ... 13000 K M: ~ 8 ... 40 M 8 L: ~ 10 4 ...10 5.5 L 8 R: ~ 50 ... 400 R 8

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Non-LTE studies of A-type supergiants

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  1. Non-LTE studies ofA-type supergiants Norbert Przybilla K. Butler (Munich), M. Firnstein & F. Schiller (ex-Bamberg)

  2. Intro The Protagonists • evolved progeny of OB main-sequence stars • Teff: ~ 8000 ... 13000 K • M: ~ 8 ... 40 M8 • L: ~ 104 ...105.5 L8 • R: ~ 50 ... 400 R8 spectroscopy@high-res throughout Local Group A-stars Moscow – 04.06.2013

  3. Intro A-stars Moscow – 04.06.2013 Previous quantitative studies of A-type supergiants Early LTE work Groth (1961), Przybylski (1969), Wolf (1971), Aydin (1972): a Cyg, h Leo Recent LTE work Albayrak (2000), Yuce (2005), Tanriverdi (2013): stellar parameters, elemental abundances (5 objects) Early NLTE work Kudritzki (1973): H+He NLTE atmospheres More recent NLTE studies Venn (1995ab), Venn & Przybilla (2003): stellar parameters, elemental abundances, evolutionary status Takeda (1990ies), Takeda & Takada-Hidai (2000): elemental abundances, evolutionary status Kudritzki et al. (1999): Wind properties, WLR Aufdenberg et al. (2002): stellar parameters (a Cyg) Kudritzki et al. (2003,2008): FGLR

  4. Intro A-stars Moscow – 04.06.2013 Other studies of A-type supergiants Variability Kaufer et al. (1996, 1997): time-series spectroscopy Moravveji et al. (2012): MOST photometry, asteroseismology (b Ori) Interferometry Aufdenberg et al. (2002): radius (a Cyg) Chesneau et al. (2010): extension Ha line-formation region (a Cyg, b Ori) Spectropolarimetry Hubrig et al. (2012): magnetic field in HD92207 Extragalactic studies Multiobject spectroscopy: metallicities, abundance gradients, distance indicators (FGLR), interstellar reddening, DIBs in other galaxies, ... review talk by Miguel Urbaneja

  5. Observations A-stars Moscow – 04.06.2013 High-resolution spectroscopy of Galactic BA-Supergiants Firnstein & Przybilla (2012) High-resolution, high-S/N Echelle spectra: FEROS, UVES, FOCES, CAFE

  6. Diagnostic Problem stellar analyses from interpretation of observation photometry, spectroscopy A-stars Moscow – 04.06.2013 • fundamental stellar parameter: L, M, R • atmospheric parameters: Teff, log g, x, Y, Z, etc. • elemental abundances • quantitative spectroscopy • via model atmospheres

  7. Diagnostics hot supergiants: strong radiation field, low densities non-LTE: non-Local Thermodynamic Equilibrium rate equations, gf-values, line broadening, detailed level-coupling, zillions of atomic cross-sections A-stars Moscow – 04.06.2013 Modelling Approaches usually: LTE: Local Thermodynamic Equilibrium Saha-Boltzmann-Formulae, gf-values, line broadening Limited Tremendous Error non-Limited Tremendous Error

  8. Diagnostics • transfer equation • statistical equilibrium: • radiative rates: • collisional rates: • excitation, ionization, charge exchange, • dielectronic recombination, etc. non-local local (Restricted) non-LTE problem MgII: Przybilla et al. (2001) model atoms ... required for many elements/ions A-stars Moscow – 04.06.2013

  9. Diagnostics A-stars Moscow – 04.06.2013 Atomic data Example: collisional excitation by e--impact • replacing approximations • by experimental or • ab-initio data • Schrödinger equation • LS-coupling: • low-Z Breit-Pauli Hamiltonian • Methods: • R-matrix/CC approximation • MCHF • CCC CII W=1 Allen Formula huge amounts of atomic data: OP/IRON Project & own

  10. Diagnostics NLTE: need for accurate atomic data Przybilla & Butler (2004) H atom: analytical solution except electron collisions: 3-body problem ab-initio data vs. approximations until recently: medium resolution spectroscopy • IR-lines equiv. to Balmer lines as gravity indicators • stellar parameters/FGLR A-stars Moscow – 04.06.2013

  11. Diagnostics Przybilla & Butler (2004) Hd Hg Hb LTE P12 Paschen-Series NLTE: ab-initio improved e--impact excitation x-sections Pg Pb Br10 NLTE: approximate Br12 Brackett-Series Pf24 Brg Pfund-Series a Cyg (A2 Ia) Schiller & Przybilla (2008) NLTE: need for accurate atomic data Przybilla & Butler (2004) H atom: analytical solution except electron collisions: 3-body problem ab-initio data vs. approximations until recently: medium resolution spectroscopy • IR-lines equiv. to Balmer lines as gravity indicators • stellar parameters/FGLR A-stars Moscow – 04.06.2013

  12. Diagnostics niNLTE ___ bi = niLTE Non-LTE effects Przybilla et al. (2006) OI OI Non-LTE departure coefficients FeII reproduction of observed trends: non-LTE line-strengthening non-LTE line-weakening TiII A-stars Moscow – 04.06.2013

  13. Diagnostics complication in IR: amplification of NLTE effects NLTE line source function: hn<<kT A-stars Moscow – 04.06.2013 Complications Przybilla et al. (2006) • Pressure inversion • appears for A-types ~A4 and later • in static and hydrodynamic • atmospheres • extreme sensitivity of line spectra • to small variations of parameters

  14. Firnstein & Przybilla (2012) Diagnostics Przybilla et al. (2006) Przybilla et al. (2000) Firnstein & Przybilla (2012a) fine ruler A-stars Moscow – 04.06.2013 NLTE Diagnostics: Stellar Parameters minimising systematics ! using robust analysis methodology & comprehensive model atoms • ionization equilibria Teff elements: e.g. C I/II, N I/II, O I/II, Mg I/II, Si II/III, S II/III, Fe II/III Δ Teff / Teff ~ 1…2%usually: 5…10% • Stark broadened hydrogen lines log g Δ log g ~ 0.05…0.10 (cgs)usually: 0.2 • microturbulence, helium abundance, metallicity + other constraints, where available: SED’s, near-IR, … • abundances: Dloge ~ 0.05...0.10 dex (1s-stat.) usually: factor ~2 Dloge ~ 0.07...0.12 dex (1s-sys.) usually:??? IAU Symposium 224: The A-Star Puzzle Poprad – July 10, 2004

  15. Diagnostics artifact artifact artifact NLTE/LTE neutral ionized Elemental Abundances Przybilla et al. (2006) • non-LTE: • absolute abundances • reduced uncertainties • Δ log e: • ~ 0.05 - 0.10 dex (1s-stat.) • ~ 0.10 dex (1s-syst.) • reduced systematics • typical uncertainties • in literature: • factor ~2 (1s-stat.) • + unknown syst. errors A-stars Moscow – 04.06.2013

  16. Diagnostics NLTE/LTE neutral ionized A-stars Moscow – 04.06.2013 Elemental Abundances Przybilla et al. (2006) HD87737 (A0 Ib) absolute abundances relative to Cosmic Abundance Standard Nieva & Przybilla (2012) • LTE: abundance pattern? - large uncertainties

  17. Diagnostics NLTE/LTE neutral ionized A-stars Moscow – 04.06.2013 Elemental Abundances Przybilla et al. (2006) HD87737 (A0 Ib) absolute abundances relative to Cosmic Abundance Standard Nieva & Przybilla (2012) no non-LTE abundance “corrections“ • non-LTE: consistency & reduced uncertainties

  18. Diagnostics A-stars Moscow – 04.06.2013 Spectroscopy @ High-res & High-S/N HD92207 (A0 Iae) Przybilla et al. (2006) • several 104 lines: ~30 elements, 60+ ionization stages • complete spectrum synthesis in visual (& near-IR) ~70-90% in NLTE

  19. Results A-stars Moscow – 04.06.2013 Revision of functional relationships Spectral type – Teff relationship Firnstein & Przybilla (2012) Colour - Teff relationship + more

  20. Results Photometric calibrations Firnstein & Przybilla (2012)

  21. Results A-stars Moscow – 04.06.2013 A warning on the use of photometric parameter estimation spectroscopic photometric Firnstein & Przybilla (2012) errors of parameters and abundances can get large > 0.3dex possible

  22. CRIRES spectroscopy A-stars Moscow – 04.06.2013 Benchmark spectroscopy: Galactic A-SGs with CRIRES • CRyogenic high-resolution Infrared • Echelle Spectrograph CRIRES@VLT-UT1 • high resolving power R = l/Dl ≤ 100,000 • wavelength coverage 0.95 to 5.3 mm • ~ 200 settings for full spectral coverage • detector: 4 x 4096 x 512 Aladdin III InSn • Pilot program: 3 A-SGs HD87737 (A0 Ib) • HD111613 (A2 Iabe) • HD92207 (A0 Iae) • - (partial) coverage of J, H, K, L band

  23. CRIRES spectroscopy A-stars Moscow – 04.06.2013 Telluric Line Correction Przybilla et al. (in prep.) • high-resolution: • detailed line profiles • telluric lines resolved • telluric line removal • via modelling: • - radiative transfer • code FASCODE • & HITRAN molecular • database • GDAS atmospheric • profiles HD111613 (A2 Iabe)

  24. CRIRES spectroscopy A-stars Moscow – 04.06.2013 Near-IR Hydrogen Lines Przybilla et al. (in prep.) • high-resolution: • detailed line profiles • telluric lines resolved HD111613 (A2 Iabe)

  25. CRIRES spectroscopy A-stars Moscow – 04.06.2013 Near-IR Hydrogen Lines Przybilla et al. (in prep.) • high-resolution: • detailed line profiles • telluric lines resolved • analysis: • extension of • previous modelling • consistency with visual • strong NLTE effects • + Bra: stellar wind HD111613 (A2 Iabe)

  26. CRIRES spectroscopy Przybilla et al. (in prep.) Near-IR Metal Lines • metal lines in near-IR: • C, N,O, Mg, Si, Fe + He • stellar evolution • galactochemical evolution HD111613 (A2 Iabe) A-stars Moscow – 04.06.2013

  27. CRIRES spectroscopy Przybilla et al. (in prep.) Near-IR Metal Lines • metal lines in near-IR: • C, N,O, Mg, Si, Fe + He • stellar evolution • galactochemical evolution • analysis: • - extension of previous modelling • - strong NLTE effects • - good agreement with visual • but • adjustment of some model atoms • necessary (NLTE amplification) • improved atomic data HD111613 (A2 Iabe) A-stars Moscow – 04.06.2013

  28. Stellar Evolution Nuclear path of the CNO-cycles diagnostic diagram: mass ratios N/C vs. N/O initially CN-cyle: , O const. • for initial (scaled) solar composition • for cosmic abundance standard • X=0.715 Y=0.271Z=0.014 ~4 Przybilla et al. (2010) A-stars Moscow – 04.06.2013

  29. Stellar Evolution A-stars Moscow – 04.06.2013 Mixing of CNO: Our NLTE Data Przybilla et al (2010), Nieva & Przybilla (2012), Firnstein & Przybilla (in prep.) supergiants throughout MW B-MS stars in solar neighbourhood

  30. Stellar Evolution Supergiants more advanced than predicted by models - first dredge up? MS evolution compatible with models A-stars Moscow – 04.06.2013 Mixing vs. Evolutionary Status Data from Przybilla et al (2010), Nieva & Przybilla (2012), Firnstein & Przybilla (in prep.) Tracks: Meynet & Maeder (2003), Maeder & Meynet (2005)

  31. Stellar Evolution A-stars Moscow – 04.06.2013 Asteroseismology + new stellar evolution models Saio et al. (2013) Pulsations post-RSG abundances prae-RSG evolutionary status not clear

  32. Summary A-stars Moscow – 04.06.2013 Summary • using non-LTE modelling and comprehensive analysis techniques • absolute oxygen abundance determinations feasible for BA-SGs • @ high precision and accuracy: • 0.05-0.10 dex (1s statistical uncertainty) • ~0.10 dex (1s systematic uncertainty) • non-LTE effectsat all scales, in particular strong in near-IR • LTE abundance patterns vanish in non-LTE, scaled CAS • evolutionary status (pre-RSG, post-RSG) still unclear

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