The radial metallicity gradient from OB star and HII region studies Norbert Przybilla GREAT-ESF Workshop Bologna – 30.05.2012 Intro HII regions • emission-line spectra: He , C, N, O, Ne, S, Ar • excited by OB stars present-day abundances 4 2 4 -3 •Te ~ 10 K, n e ~ 10 -10 cm abundance determination from - Recombination Li nes ( RL ) or Collisionally Excited Lines ( CEL ) via - direct method/requires measurement of weak [OIII] 4363 Å line - strong-line methods/calibration needed - photoionisation models complications : dust depletion & ICF‘s GREAT-ESF Workshop temperature fluctuations? Bologna – 30.05.2012 Intro OB Stars M ~ 8...30 MÍ • dominate energy and momentum budget of ISM in galaxies • key drivers for cosmic cycle of matter • highly luminous - abundance indicators over large distances CNO/ α-elements/iron-group • short-lived present-day abundances • simple atmospheres: - radiative envelopes - weak winds - no diffusion - NLTE treatment required GREAT-ESF Workshop Bologna – 30.05.2012 Overview Metallicity gradient from HII regions • oxygen as metallicity substitute for HII regions and OB stars Stasinska et al. (2012) -0.03 ... -0.07 azimuthal variation 5-22 133 Balser et al. (2011) • ‘steep‘ and ‘shallow‘ solutions for abundance gradient • wide variation of (extrapolated) central oxygen abundance GREATGREAT-ESF Workshop Workshop Bologna Bologna – 30.05.2012 Overview Metallicity gradient from OB stars Stasinska et al. (2012) • ‘zero ‘, ‘ steep‘ and ‘shallow‘ solutions for abundance gradient • wide variation of (extrapolated) central oxygen abundance GREAT-ESF Workshop Bologna – 30.05.2012 Overview Metallicity gradient from OB stars data from 3 most recent studies Stasinska et al. (2012) • large scatter > 0.5dex within single clusters/associations • large scatter > 1dex for clusters @ similar R g ... effect of 12+Gyr GCE GREAT-ESF Workshop Bologna – 30.05.2012 Overview Metallicity gradient from different indicators OB stars Cepheids Stasinska et Stasinska al. (2012) steep gradient, shallow gradient high abundances, low abundances what to adopt for GCE modelling ? HII regions PNe GREAT-ESF Workshop Bologna – 30.05.2012 Diagnostics HII region and stellar analyses from interpretation of observation (spectro)photometry, spectroscopy • plasma parameters: Te, n e • fundamental stellar parameter: L, M, R ξ • elemental abundances • atmospheric parameters: Teff , log g , , Y, Z, etc. • elemental abundances quantitative spectroscopy - direct method (T e) - model atmospheres - strong line methods - photoionization models GREAT-ESF Workshop Bologna – 30.05.2012 Diagnostics 6 B-SGs Urbaneja et al. (2005) Zaritsky et al. (1994) NGC300: abundance gradient from strong-line method • HII regions vs. B-SGs Kobulnicky et al. (1999) • different trends for HII-regions from 3 different R23 -calibrations βββ R23 =([OII] λλλ3727 +[OIII] λλλ4959,5007 )/H • independent verification Pilyugin (2001) and extension via stellar analyses • systematic bias in published gradients!? GREAT-ESF Workshop Bologna – 30.05.2012 Diagnostics HII regions: RL/CEL dichotomy Stasinska et al. (2012) Simon-Diaz & Stasinska (2011) effect on gradient revolution in progressMaxwell-Boltzmann ? distribution ? κκκ-distribution stellar and nebular abundances in Orion Nicholls, Dopita & Sutherland (2012) RL/CEL dichotomy characteristic for Milky Way GREAT-ESF Workshop Bologna – 30.05.2012 Diagnostics (Restricted) NLTE problem •transfer equation •statistical equilibrium: • radiative rates: non-local • collisional rates: MgII: Przybilla et al. (2001) local • excitation, ionization, charge exchange, dielectronic recombination, etc. model atoms ... required for many elements/ions GREAT-ESF Workshop Bologna – 30.05.2012 Diagnostics Atomic data Example: collisional excitation by e --impact replacing approximations CII by experimental or ab-initio data Schrödinger equation LS-coupling: ΩΩΩ=1 Allen Formula low-Z Breit-Pauli Hamiltonian Methods: huge amounts of • R-matrix/CC approximation atomic data: • MCHF OP/IRON Project & own • CCC GREAT-ESF Workshop Bologna – 30.05.2012 Quantitative Spectroscopy without Systematics ... Diagnostics Nieva & Przybilla (2012) 4 • several 10 lines: ~30 elements, 60+ ionization stages GREAT-ESF Workshop • complete spectrum synthesis in visual (& near-IR) ~70-90% in NLTE Bologna – 30.05.2012 ... Realisation of a Stellar Astrophysicists‘s Dream Diagnostics Nieva & Przybilla (2012) telluric lines 4 • several 10 lines: ~30 elements, 60+ ionization stages GREAT-ESF Workshop • complete spectrum synthesis in visual (& near-IR) ~70-90% in NLTE Bologna – 30.05.2012 Diagnostics NLTE Diagnostics: Stellar Parameters using robust analysis methodology & minimising comprehensive model atoms systematics ! • ionization equilibria Teff elements: e.g. He I/II,C I/II, N I/II, O I/II, Ne I/II, Mg I/II, Si III/IV, S II/III, Fe II/III ∆ Teff / Teff ~ 1…2% usually: 5…10% • Stark broadened hydrogen lines log g ∆ log g ~ 0.05…0.10 (cgs) usually: 0.2 • microturbulence, helium abundance, metallicity + other constraints, where available: SED’s, near-IR, … • absolute ∆∆∆log εεε ~ 0.05...0.10 dex (1 σ−stat.) usually: factor ~2 abundances : ∆∆∆log εεε ~ 0.07...0.12 dex (1 σ−sys.) usually: ??? fine ruler IAU Symposium 224:GREAT-ESF The A-Star Workshop Puzzle Poprad – July 10, 2004 Bologna – 30.05.2012 Diagnostics Elemental Abundances Przybilla et al. (2006) • NLTE: absolute abundances reduced uncertainties artifact ∆ log ε:ε:ε: ~ 0.05 - 0.10 dex (1 σσσ-stat.) ~ 0.10 dex (1 σσσ-syst.) artifact reduced systematics • typical uncertainties in literature: factor ~2 (1 σ-stat.) + unknown syst. errors artifact NLTE /LTE neutral ionized GREAT-ESF Workshop Bologna – 30.05.2012 Diagnostics Elemental Abundances Przybilla et al. (2006) HD87737 (A0 Ib) absolute abundances relative to Cosmic Abundance Standard Nieva & Przybilla (2012) NLTE /LTE neutral ionized • LTE: abundance pattern? - large uncertainties GREAT-ESF Workshop Bologna – 30.05.2012 Diagnostics Elemental Abundances Przybilla et al. (2006) HD87737 (A0 Ib) absolute abundances relative to Cosmic Abundance Standard Nieva & Przybilla (2012) NLTE /LTE neutral ionized no NLTE abundance “corrections“ • NLTE: consistency & reduced uncertainties GREAT-ESF Workshop Bologna – 30.05.2012 Results Chemical composition of the solar neighborhood @ present day σσσ 1 ~ 0.05 dex Nieva & Przybilla (2012) He C N O Ne Mg Si Fe Red: our work 29 stars black: OB stars literature Chemical homogeneity cosmic abundance standard X=0.715 Y=0.271 Z=0.014 GREAT-ESF Workshop Bologna – 30.05.2012 Results Milky Way: Oxygen Abundance Gradient Literature: HII regions & B-stars Przybilla (2008) calibrated to Sun HII Regions: Models: B-Stars (NLTE): ○ Rudolph et al. (2006) Chiappini et al. (2001) ■ Gummersbach et al. (1998) □ Esteban et al. (2005) ♦ Daflon & Cunha (2004) • large scatter @ every R • complex picture from “simple“ analysis GREAT-ESF Workshop Bologna – 30.05.2012 Results Some slides on work in progress removed GREAT-ESF Workshop Bologna – 30.05.2012 Conclusions Quote, insted of conclusions “It is also a good rule not to put overmuch confidence in the observational results that are put forward until they are confirmed by theory.“ A.S. Eddington GREAT-ESF Workshop Bologna – 30.05.2012.