Non-LTE studies of A-type supergiants

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


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


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


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


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



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


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


Non-LTE effects

bi =___ni

NLTE

niLTE

Non-LTE departurecoefficients

Diagnostics

OI

FeII

Przybilla et al. (2006)


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


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


Prz

ybill

a e

t al. (

20

00

)

Firnstein & Przybilla (2012a)



• 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


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


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“


Spectroscopy @ High-res & High-S/N


• several 104 lines: ~30 elements, 60+ ionization stages• complete spectrum synthesis in visual (& near-IR) ~70-90% in NLTE

HD92207 (A0 Iae)

Diagnostics


Results

Revision of functional relationships

Spectral type – Teff relationship


Colour - Teff relationship

+ more


Photometric calibrations ResultsFirnstein & Przybilla (2012)

A-stars

Moscow – 04.06.2013

Results

A warning on the use of photometric parameter estimation


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


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.)


CRIRES spectroscopy

Near-IR Hydrogen Lines

high-resolution:



HD111613 (A2 Iabe)



CRIRES spectroscopy

high-resolution:



analysis:• extension of previous modelling • consistency with visual• strong NLTE effects

+ Br: stellar wind

HD111613 (A2 Iabe)

Near-IR Hydrogen Lines



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


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



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



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


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

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


Non-LTE studies of A-type supergiants

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