Non-LTE studies of A-type supergiants Norbert Przybilla K. Butler (Munich), M. Firnstein & F. Schiller (ex-Bamberg)

The Protagonists evolved progeny of OB main-sequence stars T eff : ~ K M: ~ M  L: ~ L  R: ~ R  throughout Local Group Intro A-stars Moscow –

A-stars Moscow – Previous quantitative studies of A-type supergiants Intro Early LTE work Groth (1961), Przybylski (1969), Wolf (1971), Aydin (1972):  Cyg,  Leo Recent LTE work Albayrak (2000), Yuce (2005), Tanriverdi (2013): stellar parameters, elemental abundances (5 objects) Early NLTE work Kudritzki (1973): H+He NLTE atmospheres More recent NLTE studies Venn (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 – Other studies of A-type supergiants Intro Variability Kaufer et al. (1996, 1997): time-series spectroscopy Moravveji et al. (2012): MOST photometry, asteroseismology (  Ori) Interferometry Aufdenberg et al. (2002): radius (  Cyg) Chesneau et al. (2010): extension H  line-formation region (  Cyg,  Ori) Spectropolarimetry Hubrig et al. (2012): magnetic field in HD92207 Extragalactic studies Multiobject 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-Supergiants Observations A-stars Moscow – 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: T eff, log g, , Y, Z, etc. elemental abundances quantitative spectroscopy via model atmospheres A-stars Moscow –

usually: LTE : L ocal T hermodynamic E quilibrium Saha-Boltzmann-Formulae, gf-values, line broadening Modelling Approaches L imited T remendous E rror non-L imited T remendous E rror hot supergiants: strong radiation field, low densities non-LTE : non-L ocal T hermodynamic E quilibrium rate equations, gf-values, line broadening, detailed level-coupling, zillions of atomic cross-sections Diagnostics A-stars Moscow –

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/ions A-stars Moscow –

Atomic data  =1 Allen Formula CII Example: collisional excitation by e - -impact replacing approximations by experimental or ab-initio data Schrödinger equation LS-coupling: low-Z Breit-Pauli Hamiltonian Methods: R-matrix/CC approximation MCHF CCC huge amounts of atomic data: OP/IRON Project & own Diagnostics A-stars Moscow –

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 resolution spectroscopy A-stars Moscow –

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 resolution spectroscopy Przybilla & Butler (2004) LTE NLTE: ab-initio NLTE: approximate improved e - -impact excitation x-sections HH HH HH PP PP Br10 Br  Br12 P12 Paschen-Series Brackett-Series Pfund-Series Schiller & Przybilla (2008)  Cyg (A2 Ia) Pf24 A-stars Moscow –

Non-LTE effects b i = ___ n i NLTE n i LTE Non-LTE departure coefficients Diagnostics OI FeII Przybilla et al. (2006) A-stars Moscow – reproduction of observed trends: non-LTE line-strengthening non-LTE line-weakening OI TiII

complication in IR: amplification of NLTE effects NLTE line source function: h <<kT Complications Diagnostics A-stars Moscow – 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 Parameters using robust analysis methodology & comprehensive model atoms ionization equilibria T eff 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 T eff / T eff ~ 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  ~ dex (1  stat.) usually: factor ~2  log  ~ dex (1  sys.) usually: ??? IAU Symposium 224: The A-Star Puzzle Poprad – July 10, 2004 minimising systematics ! Diagnostics fine ruler Przybilla et al. (2006) Przybilla et al. (2000) Firnstein & Przybilla (2012a) A-stars Moscow – Firnstein & Przybilla (2012)

non-LTE: absolute abundances reduced uncertainties Δ log  ~ 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 Diagnostics A-stars Moscow –

Elemental Abundances Przybilla et al. (2006) neutral ionized NLTE/LTE absolute abundances relative to C osmic A bundance S tandard Nieva & Przybilla (2012) HD87737 (A0 Ib) LTE: abundance pattern? - large uncertainties Diagnostics A-stars Moscow –

Elemental Abundances Przybilla et al. (2006) non-LTE: consistency & reduced uncertainties neutral ionized NLTE/LTE absolute abundances relative to C osmic A bundance S tandard Nieva & Przybilla (2012) HD87737 (A0 Ib) Diagnostics no non-LTE abundance “ corrections“ A-stars Moscow –

High-res & High-S/N Przybilla et al. (2006) several 10 4 lines: ~30 elements, 60+ ionization stages complete spectrum synthesis in visual (& near-IR) ~70-90% in NLTE HD92207 (A0 Iae) Diagnostics A-stars Moscow –

Results Revision of functional relationships Spectral type – T eff relationship Firnstein & Przybilla (2012) Colour - T eff relationship + more A-stars Moscow –

Photometric calibrations Results Firnstein & Przybilla (2012)

A-stars Moscow – 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 CR yogenic high-resolution I nfrared E chelle S pectrograph 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) HD (A2 Iabe) HD92207 (A0 Iae) - (partial) coverage of J, H, K, L band A-stars Moscow –

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 HD (A2 Iabe) Przybilla et al. (in prep.) A-stars Moscow –

CRIRES spectroscopy Near-IR Hydrogen Lines high-resolution: detailed line profiles telluric lines resolved HD (A2 Iabe) Przybilla et al. (in prep.) A-stars Moscow –

CRIRES spectroscopy high-resolution: detailed line profiles telluric lines resolved analysis: extension of previous modelling consistency with visual strong NLTE effects + Br  : stellar wind HD (A2 Iabe) Near-IR Hydrogen Lines Przybilla et al. (in prep.) A-stars Moscow –

CRIRES spectroscopy HD (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 –

CRIRES spectroscopy HD (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 –

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 –

Mixing of CNO: Our NLTE Data B-MS stars in solar neighbourhood supergiants throughout MW Przybilla et al (2010), Nieva & Przybilla (2012), Firnstein & Przybilla (in prep.) Stellar Evolution A-stars Moscow –

Mixing vs. Evolutionary Status Data 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 –

A-stars Moscow – Asteroseismology + new stellar evolution models Stellar Evolution Saio et al. (2013) Pulsations post-RSG abundances prae-RSG evolutionary status not clear

Summary using non-LTE modelling and comprehensive analysis techniques absolute oxygen abundance determinations feasible for high precision and accuracy: 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 –