spectrum analysis of b-type stars: stellar parameters and...

Fernanda NievaFernanda Nieva

Spectrum analysis of BSpectrum analysis of B--type stars: type stars:

stellar parameters and abundancesstellar parameters and abundances

Early BEarly B--type main sequence & giant starstype main sequence & giant stars

in contrast to cooler B & Astars:

� no atmospheric difussion

in contrast to hotter O/ BA

supergiants:

� no strong mass loss & winds

Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013

Which stellar parameters can be derived Which stellar parameters can be derived from the spectrum?from the spectrum?

1. From spectral lines:effective temperature, surface gravity, micro and macroturbulence, projected rotational velocity, chemical abundances

2. From stellar flux bolometric correction, color excess, reddening

3. Combining 1&2 + extra constraints (e.g. evol. mass):distance, mass, luminosity, radius


Atomic Atomic PhysicsPhysics

Model Model AtomsAtoms

Stellar Stellar AtmospheresAtmospheres

SpectraSpectra

Theory: synthetic lines

Observations

Absolute physical parameters

Line fits

l

Nor

m. F

lux

Goal: reproducing the whole observed spectrum with 1 set of parameters only ☺☺☺☺

Result: simultaneous atmospheric parameters & chemical abundances @ high precision (reduced systematic effects)

Multiple metal ionization equilibria


Our analysis: Quantitative SpectroscopyOur analysis: Quantitative Spectroscopy

Atomic Atomic PhysicsPhysics

Model Model AtomsAtoms

Stellar Stellar AtmospheresAtmospheres

Our analysis: Quantitative SpectroscopyOur analysis: Quantitative Spectroscopy

Theory: synthetic lines


SpectraSpectra

Observations

••Partially interactivePartially interactive

••Interpolations are automatic within a large gridInterpolations are automatic within a large grid

••All elements fitted independentlyAll elements fitted independently

••Several manual iterations neededSeveral manual iterations needed

•• Full control where important decisions have to be takenFull control where important decisions have to be taken

••Time consuming (1Time consuming (1--2 stars per day)2 stars per day)

••Very reliable resultsVery reliable results

NonNon--LTE line formationLTE 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 ApJL, 2008 A&A)O, N, Mg, Al, Ne, Fe & others (Munich group’90s + N. Przybilla + K. Butler)

Classical model atmospheresClassical model atmospheresplane-parallel, hydrostatic & radiative equilibrium, LTE

Hybrid non-LTE approach:

OK for OB main sequence stars(Nieva & Przybilla 2007 A&A)

radiative transfer & statistical equilibrium


Sources of systematic uncertaintiesSources of systematic uncertainties

Models

Model atmospheres

Line formation

Line blocking

Atomic data

Line-broadening theory

Non-LTE effects

Observations

Composite spectra

Resolution & S/N

Data reduction

Normalization

Continuum

Blended lines

Peculiar stars

Analysis

Effective temperature

Surface gravity

Microturbulence

“Macroturbulence”

Projected rotational velocity

Spectral line selection

All of them (20) are taken into account here+CNO processed material (evolutionary state)

Nieva & Przybilla (2009,2010a)


Simultaneous fits to most measurable H/He linesSimultaneous fits to most measurable H/He lines

Data: FEROS, ESO

H Balmer

He I

He II

HR 3055

Visual Near IR

Nieva & Przybilla (2007, A&A)

He I K-Band

Data: Subaru, Hawaii

Result: fits to most modeled lines (~3800Result: fits to most modeled lines (~3800--5100 5100 ÅÅ))

Nieva & Przybilla 2012, A&A, 539, A143

Nieva & Simón-Díaz 2011, A&A, 532, A2


Nieva & Przybilla 2012, A&A, 539, A143

PresentPresent--day abundances in the solar day abundances in the solar neighbourhoodneighbourhood

O and Si: same abundances from early B-type stars in Orion by Simon-Diaz (2010) (OII)

O and Mg: same abundances from BA-supergiants in the solar neighbourhood by

Firnstein & Przybilla (OI)

Cosmic Abundance Standard (CAS)Cosmic Abundance Standard (CAS)

Stellar EvolutionObservational constraints on the (magneto-)hydrodynamic

mixing of CNO-burning products in massive stars

In the MS, the lines characterize the nuclear path and the slopedepends only on the initial abundance values, regardless on any other ingredient of the models (mass, rotational velocity, etc.)

AGSS09

CAS

Nieva & Przybilla (2012)Nieva & Simon-Diaz (2011)


Galactic Chemical EvolutionOB stars: end point of GCE models

CAS

AGSS09AGSS09



CAS

AGSS09



Sources of systematic uncertaintiesSources of systematic uncertainties

Models

Model atmospheres

Line formation

Line blocking

Atomic data

Line-broadening theory

Non-LTE effects

Observations

Composite spectra

Resolution & S/N

Data reduction

Normalization

Continuum

Blended lines

Peculiar stars

Analysis

Effective temperature

Surface gravity

Microturbulence

“Macroturbulence”

Projected rotational velocity

Spectral line selection

+CNO processed material (evolutionary state)

Examples

Nieva & Przybilla (2009,2010a)


C II λ4267 Ǻ very sensitive to non-LTE (different ab-initio photoionization cross-sections!)

C II λ5145 Ǻ not sensitive to non-LTE

-0.8 dex !

C II model: see also Sigut (1996)



approximations (standard)

vs.

ab-initio (our)


Sensitivity to collisional excitation cross-sections

Also highly sensitive to collisional ionization

only approximations: several orders of magnitude

∆∆∆∆Teff : -2000 K

∆∆∆∆log g: +0.2 dex

∆ξ∆ξ∆ξ∆ξ: +5 km s-1


∆∆∆∆Teff : up to 4000/6000 K (~15%) from literature !!

�� spectroscopic-photometric

calibrations

Nieva, M.-F. 2013, A&A, 550, 26


∆∆∆∆Teff : -2000 K

∆∆∆∆log g: +0.2 dex

∆ξ∆ξ∆ξ∆ξ: +5 km s-1


~ +1.1 dex!

~ -0.4 dex!

~+0.4 dex!

∆∆∆∆Teff : up to 4000/6000 K (~15%) from literature !!

�� spectroscopic-photometric

calibrations

Nieva, M.-F. 2013, A&A, 550, 26


Composite spectraComposite spectra

• Binarity is common among massive stars

• Difficult to be identified with spectra @ low R and low S/N (previous studies)

• Analyzing a composite as a single spectrum leads to systematic errors in the parameters and

chemical abundances


XClose inspection of the star samples

Sbs: spectroscopic binaries (light from 2 stars in 1 spectrum)

Nieva & Przybilla (2012)



Nieva et al. (in prep.)

Chemically peculiar: He-weak (also 3He and stratification) → diffusion

XLow He abundance


Peculiar starsPeculiar stars

Maeder et al. (2014)

Chemically peculiar: He-strong → diffusion

XEnhanced He abundance



Chemically peculiar: He-strong → diffusion

XEnhanced He abundance

Overlooked in FLAMES I (Hunter et al. 2009)


Be stars: fast rotators / light from star and disk in the spectrum

X


Influence of disk on stellar spectrum: not well understood


Be stars: fast rotators / light from star and disk in the spectrum

X


Influence of disk on stellar spectrum: not well understood

Overlooked in FLAMES I (Hunter et al. 2009)


• Can we fully automatize our analysis, teach the code to avoid all systematics and obtain reliable results?

• We have tried..., but still not fully automatic

Irrgang et al. 2014, A&A, 565, A63

Single spectrumSingle spectrum


Composite spectra: SB2Composite spectra: SB2


New method• Still not fully automatic• Requires manual preparation of observed spectra• Stills requires an experienced user• Most stellar parameters reliable• Abundances can be improved: the code gives to all spectral lines the

same weight when fitting. But: ionization equilibria are still satisfactory. E.g. 40 OII lines vs. 3 OI lines

• Best linelists differ with temperature, but also with data reduction, S/N, blends, vsini, details of model atoms.

• Ongoing improvements...

• My personal opinionReliable results: still with our older partially interactive method.

In this method: all OII lines together have the same weight than all OI lines together: ionization equilibrium. The same principle is applied to all elements. This is the only way to obtain simultaneous multiple ionization equilibrium and reliable parameters

Fast alternative for TFast alternative for Teffeff derivationderivation

Nieva, M.-F. 2013, A&A, 550, 26

Based on spectral and luminosity calibration from our Based on spectral and luminosity calibration from our 30 benchmark stars30 benchmark stars

carefully studied in Nieva (2007), Nieva & Przybilla (2006, 2007, 2008, 2012, 2014),

Przybilla et al. (2008), Nieva & Simon-Diaz (2011)

Nieva, M.-F. 2013, A&A, 550, 26

Spectral and luminosity calibration from our Spectral and luminosity calibration from our 30 benchmark stars30 benchmark stars

Nieva, M.-F. 2013, A&A, 550, 26

Spectral and luminosity calibration from our Spectral and luminosity calibration from our 30 benchmark stars30 benchmark stars

+ =

Spectral classification Mult. ioniz. equilibria Teff calibration

My recommendations for a spectral My recommendations for a spectral analysis of O9V to B3III type starsanalysis of O9V to B3III type stars

H & He I/II

1. Check normalization

2. Check asymmetries

3. Check Hα: Be?

4. Check He-w/He-s

Further tests

Check distances

Check SEDs

Check CNO ab.

Check HR diagram

Check M-L rel.

Metals

1. Check asymmetries

2. Ioniz. equil.: do all lines give the same microt., Teff, logg,

vsini+mac?

3. Parameters agree with H &He lines?

Quick Teff estimation (it also helps to identify He-w, He-s, SGs, some SB2s):

1. Measure 3-4 EWs: check spectral type

2. Teff from Fig. A.1. & Table 3 in Nieva, M.-F. 2013, A&A, 550, 26

Nieva & Przybilla (2007)Hybrid non-LTE approach

• LTE atmospheres+NLTE line-formation

• equivalentfull NLTE calculations

• advantages:- comprehensivemodel atomspossible

- much faster

tailored modelling


spectrum analysis of b-type stars: stellar parameters and...

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