A cosmic abundance standard Fernanda Nieva from massive stars in the Solar Neighborhood Norbert Przybilla (Bamberg-Erlangen) & Keith Butler (LMU)

Cosmic abundance standard input for any model that requires initial or local elemental abundances: massive star evolution yields supernovae Galactic chemical evolution models … Massive stars: a better option than solar-type stars

Main Sequence Young  age ~ 10 7 yrs Massive  M ~ 9-20 M sun Hot  T eff ~ x10 4 K Luminous  L~ L sun OB stars: cooler O & hotter B in contrast to cool stars:  no convective envelope (3D)  no chromosphere (heating) in contrast to hotter stars/supergiants:  no strong mass loss & winds (clumping... :-) absolute (physical) chemical composition (independently from solar values) Well-understood atmospheric structure  radiative envelope  thin atmosphere (1D) Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, SN

OB stars: in spiral arms, in star-forming regions, in Solar Neighbourhood in Solar Neighbourhood Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, Spatial & temporal information on chemical abundances short lived  birth place & present day (c.f. the Sun: a foreigner in the Solar Neighborhood)

OB stars: ideal tracers for chemical abundances at present day “ locally “ from the Solar Neighborhood to nearby galaxies - current generation of telescopes But: their spectral synthesis and analysis has been subject to several unnacounted systematic effects in the past decades  OB stars: have much more simpler atmospheres than those of solar-type or cooler stars Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn,

Present-day carbon abundance in the Solar Neighborhood: a long-standing problem... carbon LTE+NLTE: factor 40! old NLTE: factor 10! Young (OB) stars No: abundances of other elements turned out to have large spread in the solar vicinity as well... (??) Carbon: the only problem..? Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, No explanation from stellar - galactochemical evolution

Our contribution: Improving the spectral modeling (NLTE) Improving the spectral analysis (self consistent) Better observed spectra Investigation of all possible systematic effects involved in chemical abundance determinations Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, Hands into black boxes… All lines have to be reproduced simultaneously High resolution and very high S/N

C II 4267 Ǻ very sensitive to (R-matrix) photoionization cross-sections C II 5145 Ǻ not sensitive to non-LTE effects -0.8 dex ! Nieva & Przybilla (2008, A&A) Reducing... Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, Example 1

approximations (standard) vs. ab-initio (our) Nieva & Przybilla (2008, A&A) Also: sensitivity to collisional excitation cross-sections Also highly sensitive to collisional ionization only approximations: several orders of magnitude Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, Example 2

 T eff : K  log g: +0.2 dex  : +5 km s -1 Nieva & Przybilla (2008, A&A) ~ +1.1 dex!~ -0.4 dex! ~+0.4 dex!  T eff : up to 4000/5000 K (~15%) from literature !! Reducing... Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, Example 3

New self-consistent parameter determination: multiple ionization equilibria (independent model atoms & all possible lines in optical) Data: IUE fluxes + Johnson & 2Mass photometry In agreement with SED’s (UV to near-IR): Nieva & Przybilla (2006, ApJL) Hotter stars: H, He I/II, C II/III/IV, Si III/IV, Ne I/II Cooler stars: H, C II/III, Si II/III/IV, O I/II, Ne I/II, Fe II/III Przybilla, Nieva & Butler (2008,ApJL) In agreement with high- resolution near-IR (.98-4  m) H, He I/II & C II/III Nieva et al. (2009) Nieva & Przybilla (2008,A&A)

Simultaneous fits to most measurable H/He lines Data: FEROS, ESO H Balmer He I He II HR 3055 Visual H Paschen Data: FOCES, Calar Alto, Spain He I K-Band Data: Subaru, Hawaii Near-IR Nieva & Przybilla (2007) optical

Data: FEROS, ESO Fits to C lines All lines have very similar abundances low 1  uncertainties C II C IV C III  Sco Precise quantitative analysis Nieva & Przybilla (2008) C II/III/IV ionization equilibrium optical

Hydrogen H lines  T eff & log g He lines  T eff &  (He) He I/II ioniz. equil.  T eff & log g PREDICTIONS Helium Near-IR spectroscopy of OB stars NIR Nieva et al. (2009) Telluric lines B1.5 III

H lines  T eff & log g He lines  T eff &  (He) He I/II ioniz. equil.  T eff & log g C II/III ioniz. equil.  T eff & log g Model: so far NLTE populations from visual ! Still no best fits from grid interpolations Monnet et al. ESO Messenger (2009) Near-IR spectroscopy of OB stars NIR Nieva et al. (2009) PREDICTIONS

Nieva & Przybilla (2008, A&A) Unprecedented reduction of systematic errors in atmospheric parameters & input atomic data. LTE+NLTE: factor 40! old NLTE: factor 10! our work: ~10% Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn, Young (OB) stars 15 sources of systematic errors were identified (besides atomic data) Present-day carbon abundance in the Solar Neighborhood: solving a long-standing problem...

A cosmic abundance standard from massive stars in the Solar Neighborhood: absolute values Przybilla, Nieva & Butler (2008,ApJL) ≠ 0.020! Recommended mass fractions:

T eff ~ K T eff ~ K T eff ~ K Nieva & Przybilla (2008, A&A) Non-LTE vs. LTE (final model atom + final parameters) Fernanda Nieva (MPA)Cosmic Abundance Standard Bonn,

Non-LTE line formation Level populations: DETAIL Formal solution: SURFACE (Giddings, 1981; Butler & Giddings 1985; updated by K. Butler, LMU) Model atoms H (Przybilla & Butler 2004) He I/II (Przybilla 2005) C II/III/IV (Nieva & Przybilla 2006, 2008) O, N, Mg, Al, Ne, Fe & others (Munich Observatory + N. Przybilla + K. Butler) Classical model atmospheres Classical model atmospheres plan-parallel, hidrostatic & radiative equilibrium, LTE Hybrid non-LTE approach: OK for OB Main Sequence stars (Nieva & Przybilla 2007) radiative transfer & statistical equilibrium

Nieva & Przybilla (2007) Hybrid non-LTE approach LTE atmospheres + NLTE line-formation equivalent full NLTE calculations advantages: - comprehensive model atoms - much faster tailored modelling

Similar results for He, N, O Ne, Mg, Si, Fe So far O, Mg & Si confirmed by Firnstein (2006): BA-supergiants in Solar Neighb. Przybilla et al. (2006): BA-supergiants in Solar Neighb. Simon-Diaz (2009): B-stars in Orion OB assoc. Nieva et al. (in prep.): more OB-stars in Solar Neighb.