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Hydrostatic equilibrium : no large scale acceleration of the same order than the surface gravity g in LTE : Solution of the transfert equation : → all the functions depend of T(x) onlyy Iterative process : a guess of T(x) is made (from an approximate solution), The physical conditions are checked : radiative equilibrium → not fulfilled the departure from the equilibrium is used to compute a correction to T(x) such as the radiative equilibrium is fulfilled and so on … till the convergence A stellar atmosphere model is the run of T(x) through the atmosphere: It produces a set of tables which describe, T, pressure, density etc as function of the depth x in fact τ (at a reference λ 5500 Å) Solution derived using a limited nomber of points in depth ~70 and for the description of the opacity ~1212 points ( ∆λ ~1nm – 2nm) Inputs : gravity g , chemical composition and Teff Limb darkening Aufdenberg et al, 2003, ASPC 288, 239 More parameters used to built a model atmosphere → ad hoc parameter Variation of the microturbulence with the Teff Smalley, 2004, IAU Symp 224, 131 Convection MLT and Balmer line profile Bissectors Bissectors are reversed compared to the Sun : they indicate small rising columns of hot gas and largeer cooler downdrafts in A-type ; these motions are thought to be (partly) responsible for the microturbulence . But the models predict actually bissector with a reverse shape, unfortunately Landstreet, 1998, A&A, 338, 1041 Bissectors Opposite to that in A-type star Allende Prieto et al, 2002, ApJ, 567, 544 Convection ASPC, 108, 1996 Strömgren photometry indices and convection Model atmosphere in NLTE Effect of the blanketing on the model structure Hubeny & Lanz 1997, ASPC, 131, 108 Progress 1D LTE models : plan parallel, sperical symetry, flux constant, hydrodynamic equilibrium, convection described by the mixing length parameter, microturbulent velocity, macroturbulence meridional circulation due to rotationnal velocity diffusion mechanism 1D LTE models : with extensive molecular line blanketing for cool stars 1D NLTE models : extensive statistical equilibrium calculations for : static-model, radiation-driven winds in hot stars , winds driven by radiation on dust grains from cool pulsating stars 3D LTE hydrodynamical models : represent realistically solar granulation first test on Procyon for line asymmetries, line shifts, (line profile) Procyon (Allende Prieto et al, 2002, ApJ, 567,544) Solar CNO revised: -0.2 dex (Allende Prieto et al, 2002, ApJ, 573, L137) Still coarse in frequency sampling compared to 1D model 3D Meridional Circulation in stars (Talon, Michaud, Charbonnel) meridionnal circulation with shear instabilities may occur in the radiative region of differentially rotating stars → affects the redistribution of elements through diffusion process 3D NLTE hydrodynamical models : starting 1D LTE interior + atmospheric model with evolution in time : starting A-type star with diffusion Moving atmosphere (O type star) Inhomogeneous atmosphere (clumps) Models for pulsating stars (Cepheids and others) (e.g. Mihalas, 2003, ASPC, 288, 471; Fokin, 2003, ASPC, 288, 491) Still missing in the models as physical process mass-loss, coronal heating, the role of magnetic fields, dust formation, instabilities in stellar winds . Will not be solved by the full solution of MHD equations and a complete radiative transfert: too optimistic Need : laboratories studies e.g. formation of dust, theoretical studies : plasma shocks in 3D, to develop new numerical algorithms : e.g; radiative transfert in molecular lines with the difficulty of having population inversion in maser transition; parallelization technics;analysis of potential computational dangers( boudary effects) Opacity of molecule and dust for cool stars Need new observations to disentangle among various types of models and physical ideas Some hints to solve the basic equations in a 1D model, static Hubeny & Lanz, 2003, ASPC 288, 51 Handling of atomic, molecular, dust data → cruxial, quality and completeness Rauch &Deetjen 2003, ASPC 288, 103 : list of data base Some grids of models : don’t use it as magic black boxes ! 1D LTE/NLTE atmosphere model ►ATLAS9 – ATLAS12 Kurucz SYNTHE http://kurucz.harvard.edu/ (LTE, mixing length) ► PHOENIX Hauschildt & Baron ftp.hs.uni-hamburg.de/pub/outgoing/phoenix/GAIA NextGen models : NLTE Teff : 3000K – 10000K , log g : 3.5 – 5.5, [Fe/H] -4.0 – 0.0 (not yet published) Comparison between those codes ATLAS & NextGen : Bertone, Buzzoni, Chávez, Rodríguez-Merino, 2004, AJ, 128, 829 ► MARCS Plez & Gustafsson et al. (LTE, mixing length, cool stars 2500k – 8000K) ► TLUSTY Hubeny http://tlusty.gsfc.nasa.gov/ NLTE SYNSPEC computes the the detailed spectrum from the model and the the NLTE populations computed by TLUSTY Plan-parallel, hydrostatic equilibrium, no magnetic field, Central role played by Accelerated Lambda Iteration (ALI) methods Opacity described by Opacity Distribution Function or Opacity Sampling NLTE represents, at its best, the interaction between matter and radiation NLTE is present – at some point – in every stellar atmosphere To have LTE, the net collisional rate in every atomic transition must be larger than the net radiative rate NLTE effect is an overionization compared to LTE, so it is important to have all the source of opacities NLTE model is CPU time consuming: 104 times a LTE model, so it is important to assess when NLTE model is necessary for spectral features, spectral ranges and types of stars Atomic data from the database of the Opacity Project (Cunto et al, 1993, A&A, 275, L5) and from Kurucz list (see web page). OP list 10 to a few hundred energy level per ion (Z<20) but Kurucz data may centent 10000 levels for some individual ions of ironpeak elements.The upper levels are grouped in superlevel (Hubeny & Lanz, 1995,ApJ, 439, 875): the population of individual levels inside a superlevel follow the Boltzmann distribution, they all share the same b value; only level with close excitation energy can be grouped (ie having large collisional rates between levels) The absorption cross section between two super level may involve thousands of line is computed with the ODF or OS method : ODF : the total opacity from all lines in a given transition is sorted and is represented by 15 to 30 points per transition ; exact details of line blends are lost. OS : is a Monte-Carlo-like sampling of the superline cross-sections, the sampling is done at a step of 0.75 Doppler widths (or at a larger step, if necessary) Data base : OP http://heasarc.gsfc.nasa.gov/topbase/ NIST http://physics.nist.gov/cgi-bin/AtData/main-asd In Kurucz : http://cfa-www.harvard.edu/amdata/ampdata/kurucz23/sekur.html Vienna http://www.astro.univie.ac.at/~vald/ http://plasma-gate/weizmann.ac.il/DBfAPP.html Stellar libraries ►for GAIA experiment (e.g.) ♦A PHOENIX model atmosphere grid for GAIA Brott & Hauschildt (GAIA Symp. 2004, 565) ► for automated parameters determination ► for evolutionary population synthesis ♦ BaSel stellar library : theoretical spectra providing sunthetic colors from near UV to far IR (Lejeune et al, 1998, A&AS, 130,65;Westera et al, 2002, A&A, 381, 524; Lastennet et al, 2002, A&A, 388, 309 ) ♦ High resolution stellar library for poulation synthesis (Martins et al, 2005, MNRAS, 358, 49) ♦ UVBLUE: high resolution theoretically library of UV stellar spectra (Rodríguez-Merino et al, 2005, ApJ, 626, 411) http://www.ucm.es/info/Astrof/invest/actividad/spectra.html etc From Ferguson et al 2005, ApJ, 623, 585 Lanz et al, 2003 IAU Symp 210, 67 Lanz et al, 2003 ASPC, 288, 117 Lanz et al, 2003 IAU Symp 210, 67 Comparison between codes ATLAS9 & PHOENIX/NextGen (Bertone, Buzzoni, Chávez, Rodríguez-Merino, 2004, AJ, 128, 829) (Bertone, Buzzoni, Chávez, Rodríguez-Merino, 2004, AJ, 128, 829) JHC84 = Jacoby et al 1984, ApJS, 56, 257 GS83 = Gunn & Stryker, 1983, ApJS, 52, 121 (Bertone, Buzzoni, Chávez, RodríguezMerino, 2004, AJ, 128, 829) Abundance analyses with 3D hydrodynamical model atmosphere (Asplund, 2003, IAU Symp 210, 273) Sun → to lower the O abundance metal poor star → to lower the O abundance → nearly flat [O/Fe] (solve the long standing problem of O in the halo stars) Needs to improve the radiative transfert in 3D models Sun Stein & Nordlund, 1998, ApJ, 499, 914 Sun Stein & Nordlund, 1998, ApJ, 499, 914 Stein & Nordlund, 1998, ApJ, 499, 914 Sun FIG. 2. An individual granule with a corner cut away to show the velocity field and the temperature structure. A granule resembles a fountain with warm fluid rising up near the center, cooling rapidly as it crosses the optical surface, diverging horizontally, losing its buoyancy, and being pulled back down by gravity in the intergranular lanes where large shear produces high vorticity Sun Asplund, 2003, IAU Symp 210, 273 Sun Asplund, 2003, IAU Symp 210, 273 Sun Asplund, 2003, IAU Symp 210, 273 Test of the UV theoretical spectra on Vega (García-Gil et al, 2005, ApJ, 623, 460) bad match in the UV for the solar spectrum → controversy on a possible UV opacity source missing from the calculations (UV radiation field : important effect on the construction of atmospheric models through the energy balance) → second controversy on the absolute flux scale of UV observations (differences up to 7% for Vega) Test on Vega : difficult to model : (1D LTE Kurucz model) dust and gas disk (an IR flux excess) fast rotator seen pole-on peculiar abundance pattern, bound-free opacities of neutral H and the H- ion play a dominant role above 1450 Å. C I is the most important metal contributor below that wavelength, followed by Si II. abundance of Si obtained from the UV continuum ([Si/H] = - 0.90 (+0.57; -2.10) very different from the optical ([Si/H] = -0.47 ± 0.14) but consistent within the large uncertainty of the UVbased value. abundance of C obtained from the UV continuum ([C/H] = +0.03, good agreement with the mean value determined from optical lines ([C/H] = -0.13 ± 0.07). departures from LTE affect both C I and Si II lines → our understanding of stellar atmospheric opacities in the UV is fairly complete for spectral types A to G. García-Gil et al, 2005, ApJ, 623, 460 Vega : rapid rotator seen pole-on Shape and gravitational darkening of a B2V star at different angular speed. The projected rotational velocity vsin i has been kept equal to 150 km/s Domiciano de Souza The SUN Photospheric abundances in 2005 (Asplund, Grevesse & Sauval, AstrPh 0410214) Enormous improvements --- Better abundances? Gustafsson, 2004, Carnegie Obs. Astroph. Series, vol4, 2004 http://www.ociw.edu/ociw/symposia/series/symposium4/proceedings.htm l Take care with the position of continum : modification of e spectrum due to rotational velocity