Table Of ContentRadiative properties of stellar plasmas
and open challenges
S. Turck-Chi`eze1, G. Loisel 2,1, D. Gilles1, L.
Piau1, C. Blancard3, T. Blenski2, M. Busquet4, T.
Caillaud 3, P. Coss´e3, F. Delahaye5, G.
Faussurier3, J. Fariaut 3, F. Gilleron3, J.A.
Guzik6, J. Harris7, D.P. Kilcrease6, N.H. Magee6,
1 J.C. Pain3, Q. Porcherot3, M. Poirier2, G.
1
Soullier3, C.J. Zeippen5, S. Bastiani-Ceccotti8, C.
0
2 Reverdin3, V. Silvert3, F. Thais2, B. Villette 3
n
a
J Published in Astrophysics and Space Science 1 Context
6
Abstract The lifetime of solar-like stars, the envelope After more than two decades of study, helioseis-
] structureofmoremassivestars,andstellaracousticfre- mology has demonstrated the capability to probe
R
quencies largely depend on the radiative properties of the solar interior thanks to the seismic instruments
S
the stellar plasma. Up to now, these complex quan- of the SOHO satellite and ground-based networks
.
h tities have been estimated only theoretically. The de- (Christensen-Dalsgaard 2004; Guzik, Watson & Cox
p
velopment of the powerful tools of helio- and astero- 2005;BasuandAntia 2008;Turck-Chi`eze&Couvidat
-
o seismology has made it possible to gain insights on the 2010a).
r interiors of stars. Consequently, increased emphasis is The new space missions (SDO, PICARD) are ori-
t
s nowplacedonknowledgeofthemonochromaticopacity ented toward a better understanding of the Sun’s in-
a
[ coefficients. Here we review how these radiative prop- ternal magnetism and its impact on the Earth’s atmo-
erties play a role, and where they are most important. sphere. In this context, the existence of a fossil field in
1
We then concentrate specifically on the envelopes of the Sun’s radiative zone is a missing bridge that mo-
v
0 β Cephei variable stars. We discuss the dispersion of tivate us to better estimate the competition between
7 eight different theoretical estimates of the monochro- microscopic and macroscopic physics (Duez, Mathis &
1 matic opacity spectrum and the challenges we need to Turck-Chi`eze 2010; Turck-Chi`eze et al. 2010b).
1
face to check these calculations experimentally. In addition to the international solar research com-
.
1 munity, more than 350 scientists from all over the
0 Keywords atomic processes; Sun: helioseismology; world are working on the data from the COROT
1
stars: interiors; stars: asteroseismology; Cepheids and Kepler spacecraft dedicated to exoplanets and
1
stars: variables astero-seismology (see http://smsc.cnes.fr/COROT for
:
v
COROT and http://astro.phys.au.dk/KASC/ for Ke-
i
X S. Turck-Chi`eze, G. Loisel , D. Gilles, L. Piau, C. Blancard, pler). Thedevelopmentofthesedisciplinesjustifiesen-
r T. Blenski, M. Busquet, T. Caillaud , P. Coss´e, F. Delahaye, suringthecorrectnessofthemanyfundamentalproper-
a G. Faussurier, J. Fariaut , F. Gilleron, J.A. Guzik, J. Harris, tiesoftheplasma(detailedabundances,reactionrates,
D.P.Kilcrease,N.H.Magee,J.C.Pain,Q.Porcherot,M.Poirier,
opacity coefficients, etc.).
G. Soullier, C.J. Zeippen, S. Bastiani-Ceccotti, C. Reverdin, V.
Silvert,F.Thais,B.Villette The new High Energy Density laser facilities and
1CEA/DSM/IRFU/SAp, CE Saclay, F-91190 Gif sur Yvette, theZpinchmachinenowenableaccesstotheradiative
France properties of plasmas of stellar type in the laboratory
2CEA/DSM/IRAMIS/SPAM,CESaclay,F-91190GifsurYvette during pico and nano second timescales; see (Bailey et
3CEA/DAM/DIF,F-91297Arpajon al. 2007; Bailey et al. 2009; Turck-Chi`eze et al. 2009),
4LPGP,Universit´eParisSud,F-91405OrsayCedex andreferencestherein. Thisreviewisdividedintothree
parts: Section 2 is dedicated to solar-type stars, Sec-
5LERMA, Observatoire de Paris, ENS, UPMC, UCP, CNRS, 5
PlaceJulesJanssen,F-92195Meudon tion 3 to the more massive stars, and Section 4 to the
6TheoreticalDivision,LANL,LosAlamosNM87545,USA study of the β Cephei variable star case and a com-
7AWE,Reading,Berkshire,RG74PR,UK parison between eight calculated iron opacity spectra.
The challenges faced by the experiments are described
8LULI, Ecole Polytechnique, CNRS, CEA, UPMC, F-91128
PalaiseauCedex in Section 5.
2
2 Radiative properties of solar-type stars highlight the important effect of the heavy elements on
thesoundspeedprofile(Turck-Chi`ezeetal.2004;Bah-
Stars produce both nuclear energy through nuclear re- call et al. 2005; Asplund et al. 2009; Turck-Chi`eze &
actions,andthermalenergyduetotheinternaltemper- Couvidat 2010a; Turck-Chi`eze et al. 2010b). The dif-
ature that exceeds everywhere some thousand degrees. ference between the standard model sound-speed pre-
Thecentralplasmaisheatedtomorethanadozenmil- dictions and the observed sound speed is larger than
lion K, and the heat is transported by convection or the error bars coming from the knowledge of the com-
radiation phenomena. position and from the known difference between OPAL
The low-mass stars (< 1.5M ) have an internal ra- and OP mean Rosseland opacity tables (Badnell et al.
(cid:12)
diative zone which disappears in the region where the 2005).
photons interact so strongly with the partially ionized While for the solar conditions the Rosseland mean
constituentsthatconvectionbecomesthemostefficient opacities agree in general among different calculations,
way to transport the energy; see Figure 32 of Turck- the detailed comparison, element by element, shows
Chi`eze et al. (1993) or Turck-Chi`eze et al. (2010b). ratherlargedifferences,asmentionedbyBlancardetal.
In fact, this boundary between radiative transport inTurck-Chi`ezeetal. 2010c. Soitisusefultocompare
and convective transport differs from star to star de- opacity calculations of a specific element to laboratory
pending on the star’s mass, age, and composition. Hy- experiments; then the extrapolation to other stars of
drogen and helium are completely ionized in these ra- different composition will be more reliable. The first
diative zones due to their high temperature and den- experiments have been performed at the Sandia Z ma-
sity,butinthecentralconditions,theheaviestelements chine to check the iron contribution at a temperature
(iron and above) are generally partially ionized and and density not far from those at the base of the solar
their contribution to the opacity coefficients is rather convectionzone(Baileyetal. 2007;Baileyetal.2009).
high, 20% in the solar case; see equation 3 and figures ExtensivemeasurementsontheNIForLMJareneeded
in Turck-Chi`eze et al. (2009). Nevertheless, their mass for several well-chosen elements and temperatures be-
fraction is of the order of 10−3. In the rest of the ra- tween 193 and 400 eV to validate opacity calculations
diative zone, since both the temperature and density in the radiative zones of solar-like stars.
decrease with radius, by typically a factor 15 and 100 Indeedtheregionjustaroundthetransitionisclearly
respectively, most of the heavy elements down to oxy- the most difficult region due to the interplay of micro-
gen become partially ionized, so their relative contri- scopic and macroscopic phenomena (turbulence, rota-
bution increases the Rosseland mean opacity κ by a tion and magnetic fields). In fact, in contrast with the
R
factor up to 100 at the base of the convection zone due rest of the radiative zone, the boundary of the internal
to the multiple photon interactions on the electronic radiative zone depends directly on the detailed abun-
bound layers of more and more elements. dances of oxygen, iron, and neon and on the associ-
As a direct consequence, the lifetime of a star of a ated Rosseland mean opacity coefficients. It depends
given mass strongly depends on the amount of heavier also indirectly on the turbulence of these layers associ-
elements (carbon to uranium) present in the star. The atedwiththe factthatthestars aregenerallyrotating.
total element mass fraction is generally divided into X, So the thermal instability produces a strong horizon-
Y, and Z, with X and Y corresponding to the mass tal shear between a differentially latitudinal rotating
fraction of hydrogen and helium, respectively, and Z convective zone and a reasonably flat rotation in the
corresponding to the remainder. The lifetime of a 0.8 radiative zone (Turck-Chi`eze et al. 2010b). Moreover,
M star with Z=0.001 is about 14 Gyr, while the life- the magnetic field in these layers probably plays a cru-
(cid:12)
time of a 0.8 M with Z=0.02 is about 22 Gyr. When cial role in the solar dynamo at the beginning of the
(cid:12)
the heavy element contribution is small, the star con- 11-year cycle.
tracts more quickly, the central temperature is higher, Inthesub-surfacelayersofthesestars,radiationand
the opacity coefficients are different, and the nuclear convection are in competition and the heavy elements
reactions become more efficient. are less important because most of the elements are
Thisexampleshowstheimportanceofverifyingsome neutraloreveninmolecules. Inthecorona,theplasma
detailed contributions to the total Rosseland mean is heated to a million degrees, so the heavy elements
opacity values to properly estimate how κ changes play a crucial role, but the very low density plasma is
R
from star to star depending on its mass and on its de- no longer in LTE (local thermodynamic equilibrium),
tailed composition. so non-LTE calculations are needed to explain the ob-
The best known case is the Sun where where our served lines (Colgan et al. 2008).
efforts to incorporate new updates of the composition
3
Stellar structure Global Metals H+He Cr Mn Fe Ni
2 6 120 100 16 4 70 30
/(cid:162)(cid:162)radad00001111........124682468 2 (cm/g)(cid:103)R12345 OOPPAL%10246800000 %2345678900000000 %1110242468 %0123....1235555 %123456000000 %112205055
04.5 5 5.5log6 T 6.5 7 0 4.5 5 5.5log6 T 6.5 7 04.5 5 5.5log6 T 6.5 7 104.5 5 5.5log6 T 6.5 7 04.5 5 5.5log6 T 6.5 7 04.5 5 5.5log6 T 6.5 7 04.5 5 5.5log6 T 6.5 7 04.5 5 5.5log6 T 6.5 7
Fig. 1 a: Temperature gradient ratio between a radiative Fig.2 Influenceofthedifferentelementsoftheirongroup
or convective region versus temperature for a 10 M star. tothetotalopacityandcomparisonbetweenOPandOPAL
(cid:12)
b: Temperature dependence of the total Rosseland mean (same representation than Figure 1).
opacity for OP calculation (solid blue line) and OPAL cal-
culation (dashed red line). c: Relative contribution of the
heavy elements to the total opacity. d: Relative contribu- Radiative accelerations are crucial quantities to
tion of the light elements to the total opacity. study the diffusion of elements in stars and to un-
derstand the stellar photospheric abundances. They
strongly depend on the atomic properties of the dif-
3 Radiative properties of more massive stars
ferent ions, so they largely depend on the quality of
When the stellar mass increases, the central tempera- theatomicdataandontheknowledgeoftheionization
ture increases and consequently carbon, oxygen, nitro- stage of the different elements. For a detailed descrip-
gen can penetrate the Coulomb barrier. In these con- tion of this process, we refer to the book dedicated to
ditions the hydrogen burning is no longer dominated G. Michaud, and in particular to the paper of Alecian
by the weak interaction but by the strong interaction (2005). The expression for the radiative acceleration
where these elements act as catalysts. The nuclear is also given in Turck-Chi`eze et al. (2009). This pro-
burning becomes more rapid, and the lifetime of these cess must be taken into account in the description of
stars decreases from billions to millions of years, the stellar envelopes, in addition to the gravitational set-
central temperature increases strongly and the radia- tling, turbulence and sometimes magnetic activity. For
tive diffusion has no time to take place. The core of radiative accelerations, one needs to know the detailed
these stars (> 1.5M ) becomes convective, while the monochromatic photon flux for all the processes (dif-
(cid:12)
envelope is radiative. In the envelope, many elements fusion, bound-bound, bound-free...) and for each ele-
are partially ionized, so the detailed calculation of the ment. This information is not delivered by the OPAL
Rosseland mean opacity is even more complex because consortium(Iglesias&Rogers 1995)butisavailablefor
many electronic shells are open and the bound-bound the OP calculations (Seaton & Badnell 2004). Some
processes are extremely important. specific comparisons lead to 50% differences in the ra-
Figure1illustratesthecaseofa10M(cid:12) star. Allthe diativeaccelerationfortheironcaseintheopacitypeak
species including iron are totally ionized in the center region mentioned in Figs. 1 and 2 (Delahaye & Pin-
ofthisstarduetohightemperature, 34MK,andarel- soneault 2006).
atively low density of 8 g/cm3. The opacity is not as It is important to resolve this discrepancy to under-
high(Fig1b)asinlighterstars,buttheluminositydue stand the chemically peculiar stars and the thousands
to the CNO cycle is so high that ∇rad is higher than of pulsators observed with COROT and Kepler. The
∇ad (Fig 1a). When the ratio of gradients is greater rapidvariabilityoftheabove-mentionedopacitiesinthe
thanone, theregionisconvective; intheoppositecase,
stellar envelope generates the so-called κ mechanism
the region is radiative. The rest of the star is radiative
and maintains the pulsation in classical Cepheids (due
except in two small regions which correspond to the
to partial ionization of helium) and for β Cephei stars
partially ionized contribution of helium and hydrogen
(due to the iron-group element ionization) (Dupret
at low temperatures (see Fig 1d) and of the iron-group
2003).
elementsabove100,000K(Fig1c). Figure2showsthat
Calculations for asteroseismology must predict the
the differences between OP and OPAL are particularly
theoretical acoustic modes in order to identify with-
important for Ni, Mn and Cr and that the contribu-
out ambiguity the observed modes and to understand
tion of Cr and Ni could be very important in the case
the excitation of the modes. Several papers show the
of OP. Therefore, we have begun comparisons between
diffculties for β Cephei stars (Pamyantnykh 1999; Bri-
different opacity calculations.
quet et al. 2007; Degroote et al. 2010; Daszynska-
Two other processes are considered in the stellar
Daszkiewicz & Walczak 2010) and mention that an
equations or in stellar pulsations. Both require a de-
increase of opacity will improve the interpretation of
tailed description of the sub-surface layers: the radia-
the asteroseismic data.
tive acceleration and the κ mechanism.
4
1 Opacity (cm2/g)
106
0.8 OPAS
104 OP/10
mission0.6 (SCO relativ.)/100
Trans0.4 100 (SCO_RCG)/1e3
0.2 ionic fraction00000.....12345001234567891011121314151617 FFFeee TTT===123578...335 eeeVVV 1 LEDCOP/1e4
ion charge
STA/1e5
0
50 100 150 200 250
Wavelength (Å)
Fig.3 Irontransmissionspectracorrespondingtotemper- 0.01 Cassandra/1e6
atures of 15.3, 27.3 and 38.3 eV and densities of 5.5 10−3
g/cm3,3.410−3 g/cm3 and2.610−3 g/cm3 respectively,es- FLY/1e7
timated using the OP calculations. The whole wavelength 0.0001
range is useful for the Rosseland mean opacity determi- 0 50 1 102 1.5 102 2 102
nation (λE = hc =12394 A.keV) and corresponds to the hnu (eV)
XUVspectrometerusedfortheexperiment. Theionization
Fig. 4 Comparison of eight theoretical monochromatic
charge distribution for each condition is superimposed.
spectra for the mean conditions T= 27.3 eV and ρ = 3.4
10−3g/cm3 shown in Figure 3. The hypotheses of these
computations are explained briefly in the text.
4 Theoretical opacity calculations
We investigate the plasma conditions found in the en- mechanism is important, the Rosseland mean opacity
velopes of β Cephei stars for improving the interpreta- variesrapidlyforthisreason,someasurementatdiffer-
tion of the asteroseismic observations, without neglect- ent temperatures will help to check the whole calcula-
ing previous measurements of iron (and nickel) opacity tion of the pulsation mode excitation.
spectrawhichhavesuccessfullyledtoarevisionofopac- Figure4showstheopacityspectraversusthephoton
ities in the nineties, but not always in the range useful energy obtained by the different calculations generally
for astrophysics (Springer et al. 1992; Winhart et al. used to describe these plasmas. Clear differences can
1995; Chenais-Popovics et al. 2000, 2001). With this be seen in different parts of the spectral range. The
objective, we perform a comparison between different corresponding Rosseland mean values show differences
calculations of opacity spectra and an experiment to of up to 40%, in particular for the OP value, but most
validate these calculations. ofthemagreewithin15%despitetheverydifferentcal-
The first step consists in defining a condition com- culationalapproaches. Wenoticealsosomevariationof
patible with a laboratory experiment. The iron-group the mean ionization from one calculation to another of
peak in the envelope of β Cephei stars corresponds to about 0.5 units, which is not so small if one considers
temperatures of 200,000 K (17.2 eV, 1 eV= 11,600K) therapidvariationoftheopacitywiththedegreeofion-
anddensitiesaround410−7 g/cm3. Thisdensityistoo ization, but which cannot explain all of the differences.
low to be investigated in a laboratory experiment. So A detailed analysis of these calculations will appear in
we have first looked for conditions which maintain the amoredetailedpaper. Wegivehereashortdescription
same distribution of ionization stage for iron. of the assumptions.
Figure 3 shows the spectral transmission of photons Based on the average atom model SCAALP (Blan-
T through a heated iron foil of thickness (cid:15), T = card & Faussurier 2004), the OPAS code combines
ν ν
exp−κνρ(cid:15), where κν is the opacity per mass unit in detailed configuration and level accounting treatments
cm2/g. Transmission is the quantity measured in the to calculate radiative opacity of plasmas in LTE. The
experiment. The mean spectrum is obtained using the bound-bound opacity can be calculated using detailed
OP tables, for the same distribution of the iron ioniza- lineaccountingand/orstatisticalmethods. Thebound-
tion charge (about 9 for T= 320,000 K or 27.3 eV, ρ free opacity is evaluated neglecting the configuration
= 3.4 10−3 g/cm3). Two other spectra also are shown, level splitting. To improve the accuracy of opacities
for a variation of temperature of about 40%. In these into the complex regime of warm dense matter, where
cases, the distribution of charge is displaced by two or plasma and many-body effects can be important, the
three units. The figure shows that the spectra vary free-free opacity is obtained by interpolating between
strongly with temperature. In the region where the κ the Drude-like opacity and the opacity derived from
5
the Kramers formula including a Gaunt factor and an OP
CASSANDRA
electron degeneracy effect correction. Photon scatter- STA Fe (cid:239) T=15.3 eV
1 FLYCHK
ing by free electrons includes collective effects as well OPAS
SCO relat.
as OrePlat(iOvipstaiccitcyorPrreoctjeiocnt)s.is an on-line atomic database mission00..68 SLRECoDsOsC+. ORwPCeiGght
used in astrophysics (Seaton & Badnell 2004; Seaton Trans0.4
2007). TOPbase contains the most complete dataset 0.2
of LS-coupling term energies, f-values and photoioniza- 05 0 100 150 200 250
Photon wavelength (Å)
tion cross sections for the most abundant ions (Z=1-
Fe (cid:239) T=27.3 eV
26) in the universe. They have been computed in the 1
close-couplingapproximationbymeansoftheR-matrix 0.8
method with innovative asymptotic techniques. TOP- mission0.6
bioanssewailtsho ccoonnfitagiunrsatliaorngse3dsaxt3apsxe3tdsxo,freff-evrarleudestofoarsirtohne Trans00..24
PLUS-data, computed with the atomic structure code
0
50 100 150 200 250
SUPERSTRUCTURE. Photon wavelength (Å)
The atomic physics SCO code (Blenski,Grimaldi & Fe (cid:239) T=38.5 eV
1
Perrot 1997;Blenskietal. 2000)isbasedonthesuper-
0.8
c(o1n9fi8g9u)rtaoticoanlcauplaptreoahcihghp-rZopeloesmedenbtypBhoatro-Sahbasolormptieotnainl. mission0.6
LTEconditions. Herecalculationshavebeenperformed Trans0.4
0.2
includingnon-relativisticandrelativisticcontributions.
0
SCO-RCG (Porcherot etal. 2010) isa hybrid opac- 50 100 150 200 250
Photon wavelength (Å)
itycodewhichcombinesthestatisticalsuper-transition-
arrayapproachandfine-structurecalculations. Criteria Fig. 5 Transmission spectra of the calculations for condi-
are used to select transition arrays which are removed tions mentioned in Figure 3 and a XUV spectrometer reso-
lution of 1 eV. Superimposed is the weighted shape of the
fromthesuper-configurationstatistics,andreplacedby
Rosseland mean opacity (dot-dash line).
adetailedline-by-linetreatment. Thedatarequiredfor
thecalculationofthedetailedtransitionarrays(Slater,
spin-orbit and dipolar integrals) are obtained from the method is shown to interpolate smoothly between the
super-configurationcodeSCO(seeabove),providingin average-atom (AA) results and the detailed configura-
this way a consistent description of the plasma screen- tionaccountingthatunderliestheunresolvedtransition
ing effects on the wave functions. Then, the level ener- array(UTA)method. EachSTAiscalculatedinitsown
giesandthelines(positionandstrength)arecalculated optimized potential, and the model achieves rapid con-
by the routine RCG of R.D. Cowan’s atomic structure vergence in the number of STAs included.
code (Cowan 1981). CASSANDRA is an AWE (Atomic Weapons Estab-
The Los Alamos Light Element Detailed Configu- lishment, Aldermaston, UK) opacity code (Crowley et
ration OPacity code, LEDCOP (Magee et al. 1995), al. 2001)usedtomodelplasmainlocalthermalequilib-
uses a basis set of LS terms based on semi-relativistic rium. CASSANDRA’s self-consistent field calculation
Hartree-Fockatomicstructurecalculations(plusamix- uses the local density approximation for bound states
tureofLStermsandunresolvedtransitionarrays,some and has a free electron contribution based upon the
ofwhicharetreatedbyrandomlinesforthemostcom- Thomas-Fermi model. The Cassandra data are British
plexionstages)tocalculateopacitiesforelementswith Crown Owned Copyright 2010/MOD.
Z<31. Eachionstageisconsideredindetailandinter- FLYCHK is a free access atomic spectroscopy code
actions with the plasma are treated as perturbations. (Chung et al. 2005) used to generate atomic level pop-
ulations and charge state distributions and synthetic
Calculations are done in local thermodynamic equilib-
spectra for low-Z to mid-Z elements under LTE or
rium (LTE) and only radiative processes are included.
NLTE conditions http://nlte.nist.gov/FLY/.
In the STA opacity code (Bar-Shalom et al. 1989)
the total transition array of a specific single-electron
transition, including all possible contributing configu-
5 Experimental challenges
rations, is described by only a small number of super-
transition-arrays (STAs). Exact analytic expressions
Thenewspectralopacitymeasurementshavebeenper-
are given for the first few moments of an STA. The
formed on LULI 2000 www.luli.polytechnique.fr/ with
6
two lasers in 2010. A nanosecond laser delivers an en- References
ergy between 30-500 J in a 500 ps duration pulse. This
laser is used to irradiate a gold cavity (hohlraum) on Alecian, G. 2005, EAS Pub. Series, 17, 33
Asplund, M., Grevesse, N., and Scott, P. 2009, ARA&A,
which an absorbing foil of the considered element is
47, 481
deposited and heated. After a required delay to get
Badnell, N. R. et al. 2005, Mon. Not. R. Astron. Soc., 360,
theproperdensityandtemperature, apicosecondlaser 458.
interactswithabacklightertoproducexrayswhichin- Bahcall,J.N.,Serenelli,A.M.&Basu,S. 2005,Astrophys.
teract with the formed plasma: for a description of the J. Lett., 621, L85
Bailey, J. et al., 2007, Phys. Rev. Lett. 99, 5002
experimental setup, see Loisel et al. (2009). We detect
Bailey, J. et al., 2009, Phys. of Plasmas, 16, 058101
the transmitted opacity spectrum on a streak camera Bar-Shalom, A., Oreg, J., Goldstein, W. H., Schwarts, D.,
placedbehindanewlydesignedXUV-rayspectrometer. Zigler, Z. 1989, Phys. Rev. A, 40, 3183
Obtaininghigh-qualitymeasurementsrequiredaddress- Basu, S., Antia, H. M. 2008, Phys. Rep. 457, 217
Blancard, C. and Faussurier, G. 2004 PRE 69, 016409
ing many challenges based on experience with previ-
Blenski,T.,Grimaldi,A.andPerrot,P.1997,Phys.Rev.E
ous measurements. A detailed analysis of the previous
55, R4889
experiments and their difficulties is found in Chenais- Blenski,T.,Grimaldi,A.,Perrot,F.,J.2000,Quant.Spec-
Popovics (2002); Bailey et al. (2009). We summarize trosc. Radiat. Transf., 65, 91
some of these relevant for astrophysical applications: Briquet, M. et al. 2007, MNRAS, 381, 1482
Chenais-Popovics, C. et al. 2000 ApJ Suplem. Series. 127,
- One needs to form a plasma in LTE. This require-
175
ment supposes a good simulation of the whole exper-
Chenais-Popovics,C.,Fajardo,M.,Thais,F.etal.2001,J.
iment to probe the foil in the best conditions. The Quant. Spectrosc. Radiat. Transf., 71, 249.
rapidexpansionofthisfoilduringheatingislimitedby Chenais-Popovics, C. 2002, Laser and Particle Beams 20,
placing the foil between two thin samples of a low-Z 291
Christensen-Dalsgaard, J. 2004, Sol. Phys., 220, 137
material (typically carbon).
Chung,H.-K.,Chen,M.H.,Morgan,W.L.,Ralchenko,Y.,
- We measure the foil temperature with a µDmix
Lee, R. W. 2005, HEDP 1, 3
and limit the temperature gradient by placing the foil Colgan, J., Abdallah, J., Jr., Sherrill, M. E., Foster, M.,
between two cavities. The temperatures dependon the Fontes, C.J. and Feldman, U. 2008, Astrophys. J., 689,
geometryoftheexperiment,thepositionofthefoil,and 585
Cowan, R.D. 1981, The Theory of Atomic Structure and
the correctness of the simulation.
Spectra, University of California Press
- The resolution of the XUV spectrometer is impor-
Crowley, B.J.B. et al. 2001, JQRST, 71, 257
tanttodiscriminatebetweencalculations;itvarieswith Daszynska-Daszkiewicz, J. & Walczak, P. 2010, Mon. Not.
the wavelength and one must avoid saturation. R. Astron. Soc., 403, 496
Delahaye, F. & Pinsonneault, M. 2006 ApJ, 625, 563
Figure5showsthetransmissionobtainedforthedif-
Degroote, P. et al. 2009 A&A, 506, 111
ferent calculations including a spectrometer resolution
Duez, V., Mathis, S. and Turck-Chi`eze, S. 2010, Mon. Not.
of1eVforthetheconditionsmentionedinFigure3;the R. Astron. Soc., 402, 271
differences must be distinguishable by the experiment. Dupret, M. A. 2003, thesis, University of Liege, Belgium
Notice the distinct behavior of the OP calculation at Iglesias, C.A. & Rogers, F. J. 1995, ApJ, 443, 469
Guzik,J.A.,Watson,L.S.&Cox,AN.2005,ApJ,627,1049
low energy and some saturation of the spectra which
Loisel, G. et al. 2009, HEDP, 5, 173
illustrates the difficulties of exploring the low-energy Magee, N.H., et al. 1995, in ASP Conf. Ser. 78, 51
regime. Pamyatnykh, A.A. 1999, Acta Astronomica, 49, 119
To reduce the difficulties noted above, we measure Porcherot,Q.,Gilleron,F.,Pain,J.C.,andBlenski,T.2010,
to be published.
the spectra of 3 or 4 neighboring elements (chromium,
Seaton, M.J. & Badnell, N.R. 2004, MNRAS, 354, 457
iron, nickel, copper) using two thicknesses for each of Seaton M.J. 2007, MNRAS, 382, 245
them. Moreover we use two cavities to heat the foil on Springer, P.T. et al. 1992, Phys. Rev. Lett., 69, 3735
the two faces to limit the temperature gradient. Turck-Chi`eze, S., et al. 1993, Phys. Rep., 230, 59-235
Turck-Chi`eze, S., et al. 2004, Phys. Rev. Lett., 93, 211102
Turck-Chi`eze, S., et al. 2009, HEDP, 5, 132
In summary, this study shows that it would be of
Turck-Chi`eze, S. and Couvidat, S. 2010, Rep. Prog. Phys.,
interest to develop complete opacity tables including
submitted
photon energy spectra with the best physics available Turck-Chi`eze,S.,Palacios,A.,Marques,J.,Nghiem,P.A.P.
for asteroseismology. It is important to improve the 2010, Astrophys. J., 715, 1539
coverage of some crucial regions for interpreting the Turck-Chi`eze, S., Loisel, G., Gilles, D. et al. 2010c,
SOHO24, J. Phys.: Conf. Ser., in press
space observations. Some special validations by lab-
Winhart, G. et al. 1995, JQSRT, 54, 37
oratory experiments are required to validate ”the best
physics”.
ThismanuscriptwaspreparedwiththeAASLATEXmacrosv5.2.
