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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


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


Stellar parameter determination: O-type stars � diagnostic lines H I, He I, He II


Teff = 34000, logg = 4.0, logQ < -13.5

Stellar parameter determination: O-type stars � diagnostic lines H I, He I, He II


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


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


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

Abundances from Massive Stars and HII regions

Do they agree?

� 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)


HII: CEL + direct methodHII regions: Rosolowsky & Simon (2008)


Scatter!!!!


HII: CEL + direct methodHII regions: Rosolowsky & Simon (2008), Bresolin (2011)


Scatter???


Do they agree?


--- NGC300 ---

The present-day oxygen abundance gradient in NGC300

Bresolin et al. (2009) HII (CEL + direct method) vs. BA supergiants


Do they agree?


--- 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


HII regions: García-Rojas & Esteban (2007)

B-type stars: Rolleston et al. (2000), Daflon & Cunha (2004), Gummersbach et al. (1998)

CEL (direct method) & ORL


B-type stars: Rolleston et al. (2000), Daflon & Cunha (2004), Gummersbach et al. (1998)


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 ...)


B-type stars: Cunha & Lambert (1994)


Orion nebula: Esteban et al. (2004)

B-type stars: Cunha & Lambert (1994)



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???


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)



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


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


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)


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 ...

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