Download Hydrostatic equilibrium : no large scale acceleration of the same

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