A cosmic abundance standard

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A cosmic abundance standard
from massive stars in the Solar Neighborhood
Fernanda Nieva
Norbert Przybilla (Bamberg-Erlangen) Keith
Butler (LMU)
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• 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
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OB stars cooler O hotter B
SN
Young ? age 107 yrs Massive ? M 9-20 Msun Hot
? Teff 20-35 x104 K Luminous ? L104-105 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... -)

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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)
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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 ?
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Present-day carbon abundance in the Solar
Neighborhood a long-standing problem...
carbon
Young (OB) stars
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... (??)
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• 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
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Example 1
Reducing...
-0.8 dex !
C II l4267 ? very sensitive to (R-matrix)
photoionization cross-sections C II l5145 ? not
sensitive to non-LTE effects
Nieva Przybilla (2008, AA)
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Example 2
Also sensitivity to collisional excitation
cross-sections
Nieva Przybilla (2008, AA)
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Reducing...
Example 3
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, AA)
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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
Przybilla, Nieva Butler (2008,ApJL)
Nieva Przybilla (2008,AA)
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)
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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
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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)
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NIR
Near-IR spectroscopy of OB stars
PREDICTIONS
Nieva et al. (2009)
Hydrogen
Telluric lines
H lines ? Teff log g
He lines ? Teff e(He)
He I/II ioniz. equil.? Teff log g
B1.5 III
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NIR
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)
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.
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!
LTENLTE factor 40!
Unprecedented reduction of systematic errors in
atmospheric parameters input atomic data
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A cosmic abundance standard
from massive stars in the Solar Neighborhood
absolute values
Przybilla, Nieva Butler (2008,ApJL)
Recommended mass fractions
? 0.020!
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Non-LTE vs. LTE (final model atom final
parameters)
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Non-LTE line formation
Hybrid non-LTE approach OK for OB Main Sequence
stars (Nieva Przybilla 2007)
Classical model atmospheres plan-parallel,
hidrostatic radiative equilibrium, LTE
radiative transfer statistical equilibrium

• 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)
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Hybrid non-LTE approach
Nieva Przybilla (2007)

• LTE atmospheres
• NLTE line-formation
• equivalent
• full NLTE calculations
• advantages
• - comprehensive
• model atoms
• - much faster
• tailored
• modelling

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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.