a cosmic abundance standard

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



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



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..?



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)


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...



Bonn, 05.06.2009

Example 1

approximations (standard)

vs.

ab-initio (our)


Also: sensitivity to collisional excitation cross-sections

Also highly sensitive to collisional ionization

only approximations: several orders of

magnitude Fernanda Nieva (MPA)


Bonn, 05.06.2009

Example 2

Teff : -2000 K

log g: +0.2 dex

: +5 km s-1


~ +1.1 dex!

~ -0.4 dex!

~+0.4 dex!

Teff : up to 4000/5000 K (~15%) from literature !!

Reducing...



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


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


Unprecedented reduction of systematic errors in atmospheric parameters & input atomic data

.

LTE+NLTE: factor 40! old NLTE: factor 10! our work: ~10%



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)



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


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.

a cosmic abundance standard

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