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Non-LTE studies of A-type supergiants. Norbert Przybilla K. Butler (Munich), M. Firnstein & F. Schiller (ex-Bamberg). Intro. The Protagonists evolved progeny of OB main-sequence stars T eff : ~ 8000 ... 13000 K M: ~ 8 ... 40 M 8 L: ~ 10 4 ...10 5.5 L 8 R: ~ 50 ... 400 R 8 - PowerPoint PPT Presentation
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Non-LTE studies of
A-type supergiants
Norbert PrzybillaK. Butler (Munich), M. Firnstein & F. Schiller (ex-
Bamberg)
The Protagonists• evolved progeny of OB main-sequence stars
• Teff: ~ 8000 ... 13000 K
• M: ~ 8 ... 40 M
• L: ~ 104 ...105.5 L
• R: ~ 50 ... 400 R
spectroscopy@high-res throughout Local Group
Intro
A-stars Moscow – 04.06.2013
A-stars
Moscow – 04.06.2013
Previous quantitative studies of A-type supergiantsIntro
Early LTE workGroth (1961), Przybylski (1969), Wolf (1971), Aydin (1972): Cyg, Leo
Recent LTE workAlbayrak (2000), Yuce (2005), Tanriverdi (2013): stellar parameters, elemental abundances (5 objects)
Early NLTE workKudritzki (1973): H+He NLTE atmospheres
More recent NLTE studiesVenn (1995ab), Venn & Przybilla (2003): stellar parameters, elemental abundances, evolutionary status
Takeda (1990ies), Takeda & Takada-Hidai (2000): elemental abundances, evolutionary status
Kudritzki et al. (1999): Wind properties, WLR
Aufdenberg et al. (2002): stellar parameters ( Cyg)
Kudritzki et al. (2003,2008): FGLR
A-stars
Moscow – 04.06.2013
Other studies of A-type supergiantsIntro
VariabilityKaufer et al. (1996, 1997): time-series spectroscopyMoravveji et al. (2012): MOST photometry, asteroseismology ( Ori)
InterferometryAufdenberg et al. (2002): radius ( Cyg)Chesneau et al. (2010): extension H line-formation region ( Cyg, Ori)
SpectropolarimetryHubrig et al. (2012): magnetic field in HD92207
Extragalactic studiesMultiobject spectroscopy: metallicities, abundance gradients, distance indicators (FGLR), interstellar reddening, DIBs in other galaxies, ... review talk by Miguel Urbaneja
Firnstein & Przybilla (2012)
High-resolution spectroscopy of Galactic BA-SupergiantsObservations
A-stars Moscow – 04.06.2013
High-resolution, high-S/N Echelle spectra: FEROS, UVES, FOCES, CAFE
Diagnostic Problem
stellar analyses from interpretation of observation
photometry, spectroscopy
• fundamental stellar parameter: L, M, R • atmospheric parameters: Teff, log g, , Y, Z, etc.• elemental abundances
quantitative spectroscopy via model atmospheres
A-stars Moscow – 04.06.2013
usually:
LTE: Local Thermodynamic Equilibrium Saha-Boltzmann-Formulae, gf-values, line broadening
Modelling Approaches
Limited Tremendous Error
non-Limited Tremendous Error
hot supergiants: strong radiation field, low densities
non-LTE: non-Local Thermodynamic Equilibrium rate equations, gf-values, line broadening, detailed level-coupling, zillions of atomic cross-sections
Diagnostics
A-stars Moscow – 04.06.2013
MgII: Przybilla et al. (2001)
(Restricted) non-LTE problem
•transfer equation
•statistical equilibrium:
• radiative rates:
• collisional rates:
• excitation, ionization, charge exchange, dielectronic recombination, etc.
non-local
local
Diagnostics
model atoms ... required for many elements/ionsA-stars
Moscow – 04.06.2013
Atomic data
=1AllenFormula
CII
Example: collisional excitation by e--impactreplacing approximationsby experimental orab-initio data
Schrödinger equation
LS-coupling:
low-Z Breit-Pauli Hamiltonian
Methods:• R-matrix/CC approximation• MCHF• CCC
huge amounts ofatomic data:
OP/IRON Project & own
Diagnostics
A-stars Moscow – 04.06.2013
Przybilla & Butler (2004)
NLTE: need for accurate atomic data
• IR-lines equiv. to Balmer lines as gravity indicators stellar parameters/FGLR
Diagnostics
H atom:
analytical solution
except
electron collisions:3-body problem
ab-initio data vs.approximations
until recently:medium resolutionspectroscopy
A-stars Moscow – 04.06.2013
Przybilla & Butler (2004)
NLTE: need for accurate atomic data
• IR-lines equiv. to Balmer lines as gravity indicators stellar parameters/FGLR
Diagnostics
H atom:
analytical solution
except
electron collisions:3-body problem
ab-initio data vs.approximations
until recently:medium resolutionspectroscopy
Przybilla & Butler (2004)
LTE
NLTE: ab-initio
NLTE: approximate
improved e--impact excitation x-sections
HH H
P P Br10
Br
Br12
P12 Paschen-Series
Brackett-Series
Pfund-Series
Schiller & Przybilla (2008) Cyg (A2 Ia)
Pf24
A-stars Moscow – 04.06.2013
Non-LTE effects
bi =___ni
NLTE
niLTE
Non-LTE departurecoefficients
Diagnostics
OI
FeII
Przybilla et al. (2006)
A-stars Moscow – 04.06.2013
reproduction of observed trends:non-LTE line-strengtheningnon-LTE line-weakening
OI
TiII
complication in IR:amplification of NLTE effects
NLTE line source function:
h<<kT
Complications Diagnostics
A-stars Moscow – 04.06.2013
Przybilla et al. (2006) Pressure inversion
• appears for A-types ~A4 and later• in static and hydrodynamic atmospheres• extreme sensitivity of line spectra to small variations of parameters
NLTE Diagnostics: Stellar Parametersusing robust analysis methodology & comprehensive model atoms
• ionization equilibria Teff
elements: e.g. C I/II, N I/II, O I/II, Mg I/II, Si II/III, S II/III, Fe II/III
Δ Teff / Teff ~ 1…2% usually: 5…10%
• Stark broadened hydrogen lines log g Δ log g ~ 0.05…0.10 (cgs) usually:
0.2• microturbulence, helium abundance, metallicity
+ other constraints, where available: SED’s, near-IR, …
• abundances: log ~ 0.05...0.10 dex (1stat.) usually: factor ~2
log ~ 0.07...0.12 dex (1sys.) usually: ???
IAU Symposium 224: The A-Star PuzzlePoprad – July 10, 2004
minimisingsystematics !
Diagnostics
fine ruler
Przybilla et al. (2006)
Prz
ybill
a e
t al. (
20
00
)
Firnstein & Przybilla (2012a)
A-stars Moscow – 04.06.2013
Firnstein & Przybilla (2012)
• non-LTE: absolute abundances reduced uncertainties Δ log ~ 0.05 - 0.10 dex (1-stat.) ~ 0.10 dex (1-syst.) reduced systematics
• typical uncertainties in literature: factor ~2 (1-stat.) + unknown syst. errors
Przybilla et al. (2006)Elemental Abundances
neutral
ionized
NLTE/LTE
artifact
artifact
artifact
Diagnostics
A-stars Moscow – 04.06.2013
Elemental AbundancesPrzybilla et al. (2006)
neutral
ionized
NLTE/LTE
absolute abundances relative to Cosmic Abundance Standard Nieva & Przybilla (2012)
HD87737 (A0 Ib)
• LTE: abundance pattern? - large uncertainties
Diagnostics
A-stars Moscow – 04.06.2013
Elemental AbundancesPrzybilla et al. (2006)
• non-LTE: consistency & reduced uncertainties
neutral
ionized
NLTE/LTE
absolute abundances relative to Cosmic Abundance Standard Nieva & Przybilla (2012)
HD87737 (A0 Ib)
Diagnostics
no non-LTE abundance “corrections“
A-stars Moscow – 04.06.2013
Spectroscopy @ High-res & High-S/N
Przybilla et al. (2006)
• several 104 lines: ~30 elements, 60+ ionization stages• complete spectrum synthesis in visual (& near-IR) ~70-90% in NLTE
HD92207 (A0 Iae)
Diagnostics
A-stars Moscow – 04.06.2013
Results
Revision of functional relationships
Spectral type – Teff relationship
Firnstein & Przybilla (2012)
Colour - Teff relationship
+ more
A-stars Moscow – 04.06.2013
Photometric calibrations ResultsFirnstein & Przybilla (2012)
A-stars
Moscow – 04.06.2013
Results
A warning on the use of photometric parameter estimation
Firnstein & Przybilla (2012)
errors of parameters and abundances can get large > 0.3dex possible
spectroscopic photometric
Benchmark spectroscopy: Galactic A-SGs with CRIRES
CRIRES spectroscopy
CRyogenic high-resolution Infrared Echelle Spectrograph CRIRES@VLT-UT1
• high resolving power R = ≤ 100,000
• wavelength coverage 0.95 to 5.3 m
• ~ 200 settings for full spectral coverage
• detector: 4 x 4096 x 512 Aladdin III InSn
Pilot program: 3 A-SGs HD87737 (A0 Ib) HD111613 (A2 Iabe) HD92207 (A0 Iae)- (partial) coverage of J, H, K, L band
A-stars Moscow – 04.06.2013
CRIRES spectroscopy
Telluric Line Correction
high-resolution:
• detailed line profiles
• telluric lines resolved
• telluric line removal via modelling:
- radiative transfer code FASCODE & HITRAN molecular database- GDAS atmospheric profiles
HD111613 (A2 Iabe)
Przybilla et al. (in prep.)
A-stars Moscow – 04.06.2013
CRIRES spectroscopy
Near-IR Hydrogen Lines
high-resolution:
• detailed line profiles
• telluric lines resolved
HD111613 (A2 Iabe)
Przybilla et al. (in prep.)
A-stars Moscow – 04.06.2013
CRIRES spectroscopy
high-resolution:
• detailed line profiles
• telluric lines resolved
analysis:• extension of previous modelling • consistency with visual• strong NLTE effects
+ Br: stellar wind
HD111613 (A2 Iabe)
Near-IR Hydrogen Lines
Przybilla et al. (in prep.)
A-stars Moscow – 04.06.2013
CRIRES spectroscopy
HD111613 (A2 Iabe)
Przybilla et al. (in prep.)
Near-IR Metal Lines
• metal lines in near-IR: C, N, O, Mg, Si, Fe + He
stellar evolution
galactochemical evolution
A-stars Moscow – 04.06.2013
CRIRES spectroscopy
HD111613 (A2 Iabe)
Near-IR Metal Lines
• metal lines in near-IR: C, N, O, Mg, Si, Fe + He
stellar evolution
galactochemical evolution
• analysis: - extension of previous modelling - strong NLTE effects - good agreement with visual but adjustment of some model atoms necessary (NLTE amplification) improved atomic data
Przybilla et al. (in prep.)
A-stars Moscow – 04.06.2013
Nuclear path of the CNO-cycles
initially CN-cyle: , O const.
~ 4• for initial (scaled) solar composition• for cosmic abundance standard X=0.715 Y=0.271 Z=0.014
diagnostic diagram: mass ratios N/C vs. N/O
Stellar Evolution
Przybilla et al. (2010)
A-stars Moscow – 04.06.2013
Mixing of CNO: Our NLTE Data
B-MS stars in solar neighbourhood
supergiants throughout MW
Prz
ybill
a e
t al (2
01
0),
Nie
va &
Prz
ybill
a
(20
12
),Fir
nst
ein
& P
rzybill
a (
in p
rep.)
Stellar Evolution
A-stars Moscow – 04.06.2013
Mixing vs. Evolutionary StatusData from Przybilla et al (2010), Nieva & Przybilla (2012), Firnstein & Przybilla (in prep.)Tracks: Meynet & Maeder (2003), Maeder & Meynet (2005)
Stellar Evolution
MS evolution compatible with models
Supergiants more advanced than predicted by models- first dredge up?
A-stars Moscow – 04.06.2013
A-stars
Moscow – 04.06.2013
Asteroseismology + new stellar evolution modelsStellar Evolution
Saio et al. (2013)
Pulsations post-RSGabundances prae-RSG
evolutionary status not clear
SummarySummary
using non-LTE modelling and comprehensive analysis techniquesabsolute oxygen abundance determinations feasible for BA-SGs @ high precision and accuracy:
• 0.05-0.10 dex (1 statistical uncertainty)
• ~0.10 dex (1 systematic uncertainty)
• non-LTE effects at all scales, in particular strong in near-IR
• LTE abundance patterns vanish in non-LTE, scaled CAS
• evolutionary status (pre-RSG, post-RSG) still unclear
A-stars Moscow – 04.06.2013