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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 SequenceYoung age ~ 107
yrsMassive M ~ 9-20 Msun
Hot Teff ~ 20-35 x104 KLuminous L~104-105 Lsun
OB stars: cooler O & hotter BOB 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, 05.06.2009
SN
OB stars: in spiral arms, in star-forming regions,OB stars: in spiral arms, in star-forming regions, in in Solar NeighbourhoodSolar Neighbourhood
Fernanda Nieva (MPA)
Cosmic Abundance Standard
Bonn, 05.06.2009
Spatial & temporal information on chemical abundancesshort 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, 05.06.2009
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, 05.06.2009
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, 05.06.2009
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, 05.06.2009
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, 05.06.2009
Example 2
Teff : -2000 K
log g: +0.2 dex
: +5 km s-1
Nieva & Przybilla (2008, A&A)
~ +1.1 dex!
~ -0.4 dex!
~+0.4 dex!
Teff : up to 4000/5000 K (~15%) from literature !!
Reducing...
Fernanda Nieva (MPA)
Cosmic Abundance Standard
Bonn, 05.06.2009
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 Simultaneous fits to most measurable H/He linesH/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 Fits to C lineslines
All lines have very similar abundances
low 1uncertainties
C II
C IV
C III
Sco
Precise quantitative analysis
Nieva & Przybilla (2008)
C II/III/IV ionization
equilibrium
optical
Hydrogen
H lines Teff & log gHe lines Teff & (He)He I/II ioniz. equil. Teff & log g
PREDICTIO
NS
Helium
Near-IR spectroscopy of OB starsNear-IR spectroscopy of OB starsNIR
Nieva et al. (2009)
Telluric lines
B1.5 III
H lines Teff & log gHe lines Teff & (He)He I/II ioniz. equil. Teff & log gCC II/IIIII/III ioniz. equil. ioniz. equil. T Teffeff & & log glog 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 starsNear-IR spectroscopy of OB starsNIR
Nieva et al. (2009)
PREDICTIO
NS
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, 05.06.2009
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 standardfrom massive stars in the Solar Neighborhood:
absolute values
Przybilla, Nieva & Butler (2008,ApJL)
≠ 0.020!
Recommended mass fractions:
Teff~ 31000 K
Teff~ 27000 K
Teff~ 21000 K
Nie
va &
Prz
ybil
la (
20
08,
A&
A)
Non-LTE vs. LTE (final model atom + final parameters)Non-LTE vs. LTE (final model atom + final parameters)
Fernanda Nieva (MPA)
Cosmic Abundance Standard
Bonn, 05.06.2009
Non-LTE line formationNon-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 Classical model atmospheresatmospheres 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.