spectrum analysis of b-type stars: stellar parameters and...
TRANSCRIPT
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Fernanda NievaFernanda Nieva
Spectrum analysis of BSpectrum analysis of B--type stars: type stars:
stellar parameters and abundancesstellar parameters and abundances
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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
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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
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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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
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Our analysis: Quantitative SpectroscopyOur analysis: Quantitative Spectroscopy
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Atomic Atomic PhysicsPhysics
Model Model AtomsAtoms
Stellar Stellar AtmospheresAtmospheres
Our analysis: Quantitative SpectroscopyOur analysis: Quantitative Spectroscopy
Theory: synthetic lines
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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
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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
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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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)
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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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
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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
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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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)
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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)
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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Galactic Chemical EvolutionOB stars: end point of GCE models
CAS
AGSS09AGSS09
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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Galactic Chemical EvolutionOB stars: end point of GCE models
CAS
AGSS09
Nieva & Przybilla (2012)Nieva & Simon-Diaz (2011)
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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Galactic Chemical EvolutionOB stars: end point of GCE models
CAS
AGSS09
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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Galactic Chemical EvolutionOB stars: end point of GCE models
CAS
AGSS09
Nieva & Przybilla (2012)Nieva & Simon-Diaz (2011)
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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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)
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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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)
Nieva & Przybilla (2008, A&A)
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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approximations (standard)
vs.
ab-initio (our)
Nieva & Przybilla (2008, A&A)
Sensitivity to collisional excitation cross-sections
Also highly sensitive to collisional ionization
only approximations: several orders of magnitude
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∆∆∆∆Teff : -2000 K
∆∆∆∆log g: +0.2 dex
∆ξ∆ξ∆ξ∆ξ: +5 km s-1
Nieva & Przybilla (2008, A&A)
∆∆∆∆Teff : up to 4000/6000 K (~15%) from literature !!
���� spectroscopic-photometric
calibrations
Nieva, M.-F. 2013, A&A, 550, 26
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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∆∆∆∆Teff : -2000 K
∆∆∆∆log g: +0.2 dex
∆ξ∆ξ∆ξ∆ξ: +5 km s-1
Nieva & Przybilla (2008, A&A)
~ +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
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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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
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
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XClose inspection of the star samples
Sbs: spectroscopic binaries (light from 2 stars in 1 spectrum)
Nieva & Przybilla (2012)
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Composite spectraComposite spectra
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Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Composite spectraComposite spectra
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Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Composite spectraComposite spectra
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Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Composite spectraComposite spectra
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Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Composite spectraComposite spectra
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Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Composite spectraComposite spectra
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Nieva et al. (in prep.)
Chemically peculiar: He-weak (also 3He and stratification) → diffusion
XLow He abundance
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013
Peculiar starsPeculiar stars
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Maeder et al. (2014)
Chemically peculiar: He-strong → diffusion
XEnhanced He abundance
Peculiar starsPeculiar stars
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Maeder et al. (2014)
Chemically peculiar: He-strong → diffusion
XEnhanced He abundance
Overlooked in FLAMES I (Hunter et al. 2009)
Peculiar starsPeculiar stars
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Be stars: fast rotators / light from star and disk in the spectrum
X
Maeder et al. (2014)
Influence of disk on stellar spectrum: not well understood
Peculiar starsPeculiar stars
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Be stars: fast rotators / light from star and disk in the spectrum
X
Maeder et al. (2014)
Influence of disk on stellar spectrum: not well understood
Overlooked in FLAMES I (Hunter et al. 2009)
Peculiar starsPeculiar stars
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• 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
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Irrgang et al. 2014, A&A, 565, A63
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Single spectrumSingle spectrum
Irrgang et al. 2014, A&A, 565, A63
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Irrgang et al. 2014, A&A, 565, A63
Single spectrumSingle spectrum
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Composite spectra: SB2Composite spectra: SB2
Irrgang et al. 2014, A&A, 565, A63
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Irrgang et al. 2014, A&A, 565, A63
Composite spectra: SB2Composite spectra: SB2
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Irrgang et al. 2014, A&A, 565, A63
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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
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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)
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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
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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
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Spectral classification Mult. ioniz. equilibria Teff calibration
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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
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Nieva & Przybilla (2007)Hybrid non-LTE approach
• LTE atmospheres+NLTE line-formation
• equivalentfull NLTE calculations
• advantages:- comprehensivemodel atomspossible
- much faster
tailored modelling
Fernanda Nieva Spectral analysis B stars Brussels, 05.05.2013