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### Cosmic Abundance Standards from Massive Stars in the Solar Neighborhood ###

This work by Fernanda Nieva, Norbert Przybilla, and Keith Butler explores the cosmic abundance standards provided by massive stars, particularly OB stars, in the Solar Neighborhood. These stars are crucial for understanding stellar evolution, supernova yields, and Galactic chemical evolution due to their simple atmospheric structures and well-defined elemental compositions. The study highlights the importance of improved spectral modeling, self-consistent spectral analysis, and the investigation of systematic effects on chemical abundance determinations, providing insights into the present-day chemical landscape and stellar formation processes. ###

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### Cosmic Abundance Standards from Massive Stars in the Solar Neighborhood ###

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

  2. 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

  3. Main Sequence Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 OB stars: cooler O & hotter B SN Young  age ~ 107 yrs Massive  M ~ 9-20 Msun Hot  Teff ~ 20-35 x104 K Luminous  L~104-105 Lsun •  radiative envelope • thin atmosphere (1D) Well-understood atmospheric structure absolute (physical) chemical composition (independently from solar values) • in contrast to cool stars: • no convective envelope (3D)  no chromosphere (heating) • in contrast to • hotter stars/supergiants: • no strong mass loss & winds (clumping... :-)

  4. Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 OB stars: in spiral arms, in star-forming regions, in Solar Neighbourhood Spatial & temporal information on chemical abundances short lived  birth place & present day (c.f. the Sun: a foreigner in the Solar Neighborhood)

  5. Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 OB stars: ideal tracers for chemical abundances at present day “locally“ from the Solar Neighborhood to nearby galaxies - current generation of telescopes OB stars: have much more simpler atmospheres than those of solar-type or cooler stars  But:their spectral synthesis and analysis has been subject to several unnacounted systematic effects in the past decades

  6. old NLTE: factor 10! LTE+NLTE: factor 40! Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 Present-day carbon abundance in the Solar Neighborhood: a long-standing problem... Young (OB) stars carbon No explanation from stellar -galactochemical evolution Carbon: the only problem..? No: abundances of other elements turned out to have large spread in the solar vicinity as well... (??)

  7. Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 • 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 Hands into black boxes… All lines have to be reproduced simultaneously High resolution and very high S/N

  8. Example 1 Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 Reducing... -0.8 dex ! C II l4267 Ǻ very sensitive to (R-matrix) photoionization cross-sections C II l5145 Ǻnot sensitive to non-LTE effects Nieva & Przybilla (2008, A&A)

  9. Example 2 approximations (standard) vs. ab-initio (our) Also highly sensitive to collisional ionization only approximations: several orders of magnitude Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 Also: sensitivity to collisional excitation cross-sections Nieva & Przybilla (2008, A&A)

  10. Reducing... Example 3 ~+0.4 dex! ~ +1.1 dex! ~ -0.4 dex! Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 DTeff : -2000 K Dlog g: +0.2 dex Dx: +5 km s-1 DTeff : up to 4000/5000 K (~15%) from literature !! Nieva & Przybilla (2008, A&A)

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

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

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

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

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

  16. . Nieva & Przybilla (2008, A&A) Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 Present-day carbon abundance in the Solar Neighborhood:solving a long-standing problem... Young (OB) stars 15 sources of systematic errors were identified (besides atomic data) our work: ~10% old NLTE: factor 10! LTE+NLTE: factor 40! Unprecedented reduction of systematic errors in atmospheric parameters & input atomic data

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

  18. Teff~ 31000 K Teff~ 27000 K Nieva & Przybilla (2008, A&A) Teff~ 21000 K Fernanda Nieva (MPA) Cosmic Abundance Standard Bonn, 05.06.2009 Non-LTE vs. LTE (final model atom + final parameters)

  19. Hybrid non-LTE approach: OK for OB Main Sequence stars (Nieva & Przybilla 2007) Non-LTE line formation Classical model atmospheresplan-parallel, hidrostatic & radiative equilibrium, LTE • Level populations: DETAIL • Formal solution: SURFACE (Giddings, 1981; Butler & Giddings 1985; updated by K. Butler, LMU) • Model atoms radiative transfer & statistical equilibrium 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)

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

  21. 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.

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