Accurate Quantitative Spectroscopy of OB Stars Revising Hot Star Metallicities

1
Accurate Quantitative Spectroscopy of OB
StarsRevising Hot Star Metallicities

• María Fernanda Nieva(1,2)
• Norbert Przybilla(1)
• (1) Dr. Remeis Sternwarte Bamberg
  (Germany)
• (2) Observatório Nacional
  (Brazil)

2
Outline

• Introduction/Aims
• Models/Observations
• Our Analysis
• Results
• Conclusions

3
Introduction

• galactochemical evolution
• present-day abundances (young stars)
• spatial distribution (abundance gradients)
• stellar evolution
• basic stellar parameters abundances
• empirical evaluation of evolutionary models (e.g.
  Maeder Meynet 2000)

Precise chemical composition of early-type stars
Sun
4
Introduction
Problems
Metal abundances of MS stars in the solar vicinity

• sub-solar chemical evolution of the
  Galaxy ?
• why M/H young stars lt M/H solar-type stars ?
• highly inhomogeneous stellar evolution ?
• why DM/H young stars 1-2 orders of magnitude
  ?
• N enhancement from rotational mixing
• C O slightly depleted from rotational
  mixing

Sun
but not so large!
5
Introduction
e(C)log(C/H)12
e(C) problems in the analysis (last 4 decades!)

• LTE/non-LTE
• Large non-LTE effects (not well-understood)
• - e(C II) strong lines ? e(C II) weak lines
• - Strong lines C II ll4267, 6578/83 ?
• imp. for fast-rotators and low S/N
  (extragalactic)
• e(C II) ? e(C III) no ionization equilibrium

Another underestimated problem Teff photom. ?
Teff spectrosc. up to 5000 K in
OB dwarfs and giants (15)
6
Introduction
Representative sources from the literature
carbon
oxygen
1 dex !
1.6 dex !
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Aims of this work

• Solution classical non-LTE problem e(C) OB-stars
• Reliable C II/III/IV model atom calibrated with
  Galactic stars (OB III-V)
• Special emphasis
• - selection input atomic data
• - accurate atmospheric parameter determination
• Checking multiple ionization equilibria
• He I/II, C II/III/IV, O I/II

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Quantitative Spectroscopy
Relies on many model assumptions !
Theory synthetic lines
Line fits
Atomic Physics
Model Atoms
Stellar Atmospheres
Chemical Abundances
Observations

• Absolute values (Physics)
• Not relative to other stars or Sun

Spectra

• Non-trivial process (at all !)
• Accuracy depends on all steps of analysis
• Difficult controlling systematic effects

9
Theory

• Hybrid non-LTE approach (Nieva Przybilla 2007,
  subm. to AA)
• LTE model atmosphere ATLAS9
• non-LTE line formation DETAILSURFACE
• Model atoms
• H (Przybilla Butler 2004)
• He I/II (Przybilla 2005)
• C II/III/IV (Nieva Przybilla, 2007, in
  prep.)
• O I/II (Przybilla et al. 2002 / Becker
  Butler 1988 updated)
• N II (Przybilla Butler 2001)
• Mg II (Przybilla et al. 2001)

radiative transfer statistical equilibrium
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Observations

• 6 early-B III-V apparently slow-rotators
• 21500 lt Teff lt 32000 K
• 3.1 lt log g lt 4.3 dex
• randomly distributed in solar vicinity (lt 1 Kpc)
• from associations and field
• Spectra high S/N FEROS data
• Spectra near-IR (FOCES, SUBARU) for 2 stars

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New analysis

• Based on C II-IV (up to 40 lines)
• highly sensitive to
• extensive iteration on all variables
• Teff, log g, x, z, v sin i, e(C) atomic
  data
• avoidance of systematic errors (where possible)

- atmospheric parameters - input atomic data

• 6 early-B III-V stars
• 21500 lt Teff lt 32000 K
• 3.1 lt log g lt 4.3 dex

• Accurate stellar parameters
• Empirically calibrated C model
• Accurate C abundances

Results
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Near-IR
Simultaneous fits to all mesurable 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 (subm. to AA)
Data FEROS, ESO
HR 3055
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Excellent fits to C lines
Data FEROS, ESO S/N up to 800
C II
All lines have very similar abundances
Further analysis of O, N Mg
C III
C IV
t Sco
Nieva Przybilla, 2007 (in prep.)
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Non-LTE vs. LTE for individual lines
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Accurate Pristine Abundances in the Solar Vicinity
Our results vs. literature
oxygen
carbon
We avoid systematic errors in atmospheric
parameters atomic data
Our statistics has to be improved
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Accurate Pristine Abundances in the Solar Vicinity
Our results vs. literature
nitrogen
magnesium
For the whole picture (youngevolved stars) ?
talk by N. Przybilla on Thursday
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Conclusions

• Solutions to classical problems
• Non-LTE C abundances of C II ll4267/6578-82 ?
  37 lines
• (applications to fast-rotators and
  extragalactic objects)
• Highly uniform C, O Mg abundances (limit. of
  sample)
• No sub-solar abundances for the analysed metals
• ? Revision of Hot Star
  Metallicities
• Temperature scale highly important in the
  analysis

Consequences of careful quantitative spectroscopy
Thanks!
U. Heber, K. Cunha, K. Butler, M. Altmann, H.
Edelmann, J. Puls DAAD
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Sensitivity of Carbon Abundance to Atmospheric
Parameters
Typical systematic discrepancies from the
literature
Our solution for HR 3055 Teff 31200200 K
log g 3.950.05 dex x 8 1 km s-1
C IV up to 1.1 dex! C III up to 0.35 dex! C II
up to -0.35 dex!
4267
6583
Teff -2000 K
6578
log g 0.2 dex
Discrepancies increase with ? atomic data !!
x 5 km s-1
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Teff scales ours vs. literature
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Different model atoms for C II
e(5145)-e(4267)
e(5145)-e(6578)
Teff (x103 K)
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Sensitivity of C II to photoionization
cross-sections
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Step 2 Carbon
Our Analysis
Step 1 H, He I/II
I
Initial Teff , log g
I
Initial Teff , log g, x, z, e(He), v sin i
No grids ! Detailed analysis for each star !
NLTE C populations
Stellar atmosphere
Synthetic H/He/C profiles
NLTE H/He populations
Comparison with observed spectra
Synthetic H/He profiles
Variables
Comparison with observed spectra
Parameter verification
Teff , log g, x, z, e(C), v sin i
200 levels gt 1300 radiat. transitions gt 5300
collis. transitions
Empirical calibration of C model atom
Parameter verification
M
Modified Teff , log g, x, z, e(He), v sin i
New set of atomic data
Same procedure for
M
Modified Teff , log g

• 6 early-B III-V stars
• 21500 lt Teff lt 32000 K
• 3.1 lt log g lt 4.3 dex

MI ?
no
MI ? se(C) min?
yes
no
Final Teff , log g, x, z, e(He), v sin i

• Accurate Stellar Parameters
• Calibrated C model for 1 Star
• Accurate Carbon Abundance

yes
To Step 2
Verify Step 1