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Take away messages
� HII regions and massive stars are very valuable tools to measure present-day oxygen abundances across the Universe.
� From the comparison of oxygen abundances from massive starsand HII regions one might conclude that abundaces derived from CEL might need a correction (at least at solar metallicities)
� We have improved A LOT in the last decades on the reliability of oxygen abudances as derived from B-type stars and BA supergiants. Possible sources of uncertainties and systematics are now controlled.
� Is this correction dependent of metallicity/element? Time will say ...
Massive stars (MS) are of definite importance to have access to information about the chemical properties of
galaxies across the Universe
Ionizing fluxes � HII regions
Understanding nebular emission in far distant galaxies requires
knowledge of
� High mass end of the IMF� Physical properties of MS� MS evolution� MS ionizing fluxes
Previously on this conference ...
Massive stars and HII regions are alternative/complementary astrophysical tools to obtain present-day abundances of the ISM in the
galactic region where they are located
� Unique opportunity to check the reliability of abundances derived by means of two independent methodologies
� For the moment, only possible in the Local Universe (up to a few Mpc)
Motivation of this talk
Massive stars (MS)
* Photospheric abundances No dust depletion (� ISM)
* He, C, N, O, Si, Mg, Ne, S, Fe
* Methods: Complex modelling
* Complex atomic models
� Early-B stars + BA supergiants
� SNR, resolution, vsini < 100 km/s
� Stellar parameter determination
� Microturbulence
+ Photospheric contamination+ Undetected binarity
* ISM gas-phase abundances Dust depletion (� ISM – dust)
* He, C, N, O, Ne, S, Fe, Ar, Cl
* Methods: generally straightforward
* Atomic data: a few quantities
� [OIII]λ4363 (+ faint ORL) detection
� Flux calibration, scattered light [...]
� Ionizing correction factors
� CEL/ORL discrepancy
+ Reliability of strong line methods+ Metal rich regime
Abundances in HII regions and massive stars: key aspects
HII regions (HII-r)
(Massive) OB-type stars: Quantitative spectroscopy
Rotation AbundancesSpectroscopic parameters
vsini Teff , logg , Y(He) , ζt , logQ ε(X)
Stellar atmosphere code
(Massive) OB-type stars: Quantitative spectroscopy
STELLAR ATMOSPHERE CODE
Observed line profiles and EWs
ABUNDANCE ANALYSIS
Stellar atmosphere model for the studied star
Teff, logg, ...
Teff, logg, ε(He), Z, (wind param.)+ ε(Xi), ζt
ε(Xi), ζt
PHOTOMETRIC DATA
GRID OF MODELS
OBSERVED SPECTRUM
STELLAR PARAMETER DETERMINATION
Teff, logg, ε(He), (wind param.)
• Synthetic line profiles• EWs• Global SED
Teff = 40000, logg = 3.6, logQ = -12.1
(Massive) OB-type stars: Quantitative spectroscopy
Stellar parameter determination: O-type stars � diagnostic lines H I, He I, He II
(Massive) OB-type stars: Quantitative spectroscopy
Teff = 34000, logg = 4.0, logQ < -13.5
Stellar parameter determination: O-type stars � diagnostic lines H I, He I, He II
(Massive) OB-type stars: Quantitative spectroscopy
Depending of the star, different Si line ratios must be used as T
effindicators:
Si IV/III, Si II/III
Stellar parameter determination: B-type stars � diagnostic lines H I, Si IV, Si III, Si II
(Massive) OB-type stars: Quantitative spectroscopy
Stellar abundance determination: the curve of growth method
For a fixed set of stellar parameters
Teff, logg, ε(He), (wind param.)
i.e. a given atmosphere structure
Grid of EWs of diagnostic lines
(line formation code)
for different [ε(X), ζt] – pairs
(Massive) OB-type stars: Quantitative spectroscopy
A final word of caution: things were not always as smooth are they are now
Use of photometric calibrations Self-consistent spectroscopic approach
Teff, logg, ... are determined by using synthetic lines resulting from the same stellar atmosphere code that will be
used for the abundance analysis
vs.
e.g. Lester, Gray & Kurucz (1986)
[c1] = c1 – 0.20 (b-y) = f(Teff, logg)Based on Kurucz’s (1979) models
Stellar atm. structure: Te(τ), Ne(τ)Global SED
-- LTE/NLTE, line blanketing --
Level populations: Nij (τ)Line profiles + EWs
-- LTE/NLTE --
Stellar atmosphere modelStellar atmosphere model Line formation codeLine formation code+
• ATLAS (Kurucz)
• TLUSTY (Hubeny & Lanz)• CMFGEN (Hillier)• FASTWIND (Puls et al.)
• DETAIL/SURFACE (Buttler & Giddings)
State-of-the-art codes
� Stellar parameter determination
� Stellar atmosphere code
� Best element to compare: oxygen
� No ICFs needed in the case of HII regions
� Oxygen abundances from CEL and ORL sometimes accessible
� Photospheres of massive stars are only contaminated by oxygen produced in the stellar interior in late evolutionary phases
� Global approach
� gradients in spiral galaxies
� Local approach
� comparison of abundances in a given star-forming region
Massive star vs. HII region abundances
Oxygen abundances from Massive Stars and HII regions
Do they agree?
Abundance gradients in spiral galaxies
--- M33 ---
The present-day oxygen abundance gradient in M33
HII: CEL + direct methodHII regions: Vilchez et al. (1998)
B Supergiants: Urbaneja et al. (2005)
The present-day oxygen abundance gradient in M33
HII: CEL + direct methodHII regions: Rosolowsky & Simon (2008)
B Supergiants: Urbaneja et al. (2005)
Scatter!!!!
The present-day oxygen abundance gradient in M33
HII: CEL + direct methodHII regions: Rosolowsky & Simon (2008), Bresolin (2011)
B Supergiants: Urbaneja et al. (2005)
Scatter???
Oxygen abundances from Massive Stars and HII regions
Do they agree?
Abundance gradients in spiral galaxies
--- NGC300 ---
The present-day oxygen abundance gradient in NGC300
Bresolin et al. (2009) HII (CEL + direct method) vs. BA supergiants
Oxygen abundances from Massive Stars and HII regions
Do they agree?
Abundance gradients in spiral galaxies
--- Milky Way (as for 2007) ---
HII regions: García-Rojas & Esteban (2007)
The present-day oxygen abundance gradient in the Milky Way
CEL (direct method) & ORL
The present-day oxygen abundance gradient in the Milky Way
HII regions: García-Rojas & Esteban (2007)
B-type stars: Rolleston et al. (2000), Daflon & Cunha (2004), Gummersbach et al. (1998)
CEL (direct method) & ORL
The present-day oxygen abundance gradient in the Milky Way
B-type stars: Rolleston et al. (2000), Daflon & Cunha (2004), Gummersbach et al. (1998)
Oxygen abundances from Massive Stars and HII regions
Do they agree?
Oxygen abundance in the same site
--- Orion OB1 ---
(One of) The closest star forming region
Orion OB1 association: Four subgroups of OB stars with different ages and location in the sky (Blaauw 1964, Brown et al. 1994)
Signatures of several SN events
Oxygen abundance in the Orion OB1 star forming region
+ The Orion nebula (M42)
� the closest and most studied HII region
Highest values of oxygen abundance found for stars in the youngest groups
Contamination of thenew generation ofstars by SNe type-II ejecta (O, Si, Mg ...)
Oxygen abundance in the Orion OB1 star forming region
B-type stars: Cunha & Lambert (1994)
Oxygen abundance in the Orion OB1 star forming region
Orion nebula: Esteban et al. (2004)
B-type stars: Cunha & Lambert (1994)
Oxygen abundance in the Orion OB1 star forming region
Orion nebula: Esteban et al. (2004)
B-type stars: Cunha & Lambert (1994), Simón-Díaz (2010)
Simón-Díaz (2010)
Homogeneous set of stellar abundances
In fair good agreement (though a bit larger) with ORL abundances
Dust???
Oxygen abundance in the Orion OB1 star forming region
B-type stars: Simón-Díaz (2010) vs. Cunha & Lambert (1994)
What is making the difference?
- Improvements in stellar atmosphere models
- Better observations
- Careful selection of diagnostic lines
- Stellar parameter determination
(self-consistent spectroscopic approach[1])
[1] Teff, logg, ... are determined by using synthetic lines resulting
from the same stellar atmosphere code that will be used for the
abundance analysis
Abundances in B-type stars are nowadays much more reliable!
B-type stars in the Solar vicinity: Nieva & Przybilla (2012)
Oxygen abundance in the Orion OB1 star forming region
Orion nebula: Esteban et al. (2004)
B-type stars: Cunha & Lambert (1994), Simón-Díaz (2010)
Simón-Díaz (2010)
Homogeneous set of stellar abundances
In fair good agreement (though a bit larger) with ORL abundances
Dust???
Simón-Díaz (2010)
* O and Si abundances * Spectroscopic approach: FASTWIND* Curve of growth* To investigate oxygen depletion onto dust grains: Mg and Fe abundances are also needed
Nieva & Simón-Díaz (2011)
* C, N, O, Ne, Si, Mg, Fe abundances* Spectroscopic approach: ATLAS+DETAIL+SURFACE* Spectral synthesis
Oxygen abundance in the Orion OB1 star forming region
Extending the study by Simón-Díaz (2010) to other elements
Perfect agreement in the derivedO and Si abundances!!!
Draine(2003)
Dust correction (oxygen) ~ 0.09-0.12 dex
Oxygen abundance in the Orion OB1 star forming region
Taking care of dust Simón-Díaz & Stasinska (2011)
B-type stars:
ε(Si) = 7.51 +/- 0.03ε(Mg) = 7.57 +/- 0.06ε(Fe) = 7.50 +/- 0.04
ε(O) = 8.74 +/ .0.04
Orion nebula:
ε(Si) = 6.50 +/- 0.25 ε(Mg) = 6.50 :: ε(Fe) = 6.0 +/- 0.3
Refs (HII-r): Esteban et al. (2004), Rubin et al. (1993), Baldwin et al. (1991), Rodriguez & Rubin (2005)
Refs (B-type): Simón-Díaz (2010), Nieva & Simón-Diaz (2011)
Oxygen abundances from Massive Stars and HII regions
Do they agree?
Oxygen abundance in the
Magellanic Clouds
+ Tsamis et al. (2003) find ADF(O2+) > 0.3 dex in the SMC and LMC
Present-day oxygen abundances in the MW and MCs
Take away messages
� HII regions and massive stars are very valuable tools to measure present-day oxygen abundances across the Universe.
� From the comparison of oxygen abundances from massive starsand HII regions one might conclude that abundaces derived from CEL might need a correction (at least at solar metallicities)
� We have improved A LOT in the last decades on the reliability of oxygen abudances as derived from B-type stars and BA supergiants. Possible sources of uncertainties and systematics are now controlled.
� Is this correction dependent of metallicity/element? Time will say ...