This document summarizes new light element opacity calculations from the Los Alamos ATOMIC code. It compares the code's opacity results for carbon, oxygen, hydrogen, helium, and carbon/hydrogen mixtures to previous Los Alamos calculations and other databases. The comparisons show generally good agreement. The ATOMIC code features improved atomic structure calculations and equation of state models over previous efforts. Future plans include providing more detailed opacity tables for astrophysically important elements like iron.

1. New Light Element
Opacities from the James Colgan1, D. P. Kilcrease1, N. H. Magee, Jr. 1,
J. Abdallah, Jr.1, M. E. Sherrill1,
Los Alamos ATOMIC C. J. Fontes2, and H. L. Zhang2
code LA-UR-11-01559
1Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA;
2Computational Physics Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Introduction C and O comparisons
• The need for light-element opacities for plasmas in local-thermodynamic equilibrium (LTE)
has been recognized for many years. Such data are one of the crucial components in stellar 6 6
C O
modeling, and in many efforts to model high-energy density plasmas. OP
OPAL
OP
OPAL
5 ATOMIC 5 ATOMIC
• Many years’ work at Los Alamos resulted in a comprehensive light-element opacity 4 log R=+1 4 log R=+1
database generated with the LEDCOP code [1]. The LEDCOP code provided opacities for
log (Opacity) (cm /g)
log (Opacity) (cm /g)
3 3
Z=1-30, and the data were made publicly available via the webpage
2
2
http://www.t4.lanl.gov/cgi-bin/opacity/tops.pl. This resource also allowed opacities to be 2 2
generated for arbitrary mixtures (as well as pre-calculated mixtures of astrophysical
1 1
interest).
0 0
• The LEDCOP data were usually found to compare quite well with other opacity database
-1
efforts, such as the LLNL OPAL database [2], and the UK Opacity Project (OP) efforts [3], log R=-8
-1
log R=-8
which both provide opacity data for primarily astrophysical use. However, it was desirable -2
4.0 7.0 8.0 9.0
-2
4.5 5.0 5.5 6.0 6.5 7.5 8.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0
to implement a new opacity capability that contained better atomic physics data, better log (T) (K) log (T) (K)
plasma physics models, and extended the range of temperatures and densities covered. In these figures we compare our C and O opacity data with OP and OPAL data. Overall, the
agreement is again good. The differences at moderately high temperatures (log (T) ~ 6 for C )
• We provide an overview of our new LTE opacity efforts and present some examples of appear to be due to differences in the EOS. Differences in the atomic structure used will also
comparisons with previous LANL calculations, and with other opacity code data. Although affect the mean opacities, especially at low temperatures.
our calculations produce and tabulate frequency-resolved opacity data (as well as data
binned into multigroups), we compare the Rosseland-mean opacity in all examples below. At low temperatures, clear differences are also found, with, in many cases, all three approaches
predicting a somewhat different mean opacity. We note that our current C calculations also
The ATOMIC code [4] include the free-free contribution from C-.
ATOMIC is a multi-purpose kinetics and spectroscopic code which can calculate a range of
quantities (such as ionization balance, opacities, and emissivities) for LTE or NLTE conditions
Comparisons for a C/H mixture
of interest. The ATOMIC LTE opacity efforts represents a considerable improvement over our
previous opacity calculations from the LEDCOP code. Some of the major improvements are Using the Los Alamos TOPS code, it is also straightforward to compute the opacity from a
listed below. mixture of elements. Below we compare the mean opacity for a C/H mixture with an OP
calculation (right-hand side). In standard astrophysical terminology, the mass fraction of H is
Ab-initio atomic structure calculations from the CATS semi-relativistic code[5] are used to X=0.9 and the fraction of C is Z=0.1. The agreement is again good, and the characteristic double
generate energy levels and oscillator strengths for large sets of fine-structure levels for the -peak structure is evident.
ions of interest. CATS is based on Cowan’s original structure codes[5]. Recent improvements
and parallelization of the code have allowed very large structure calculations to be performed,
with some ion stages including millions of energy levels.
C/H opacity (mass fractions: X=0.9, Z=0.1)
ATOMIC incorporates an improved equation-of-state (EOS) model (ChemEOS), based on the log R= -1
chemical picture [6]. This model uses the free-energy minimization technique and an 4 C/H (ATOMIC)
C/H (LEDCOP)
occupation probability formalism. Ideal and non-ideal contributions to the total free energy are
included, incorporating plasma microfield effects, strong coupling, and hard-sphere 3
-2
descriptions of the finite atomic size.
2 -3
log (κ)
Considerable efforts have been made to include a consistent line-broadening description that
is valid for a wide range of conditions. For example, we include Stark broadening, neutral atom 1 -4
broadening, and line blending near bound-free absorption edges. At high densities, we also
include electron degeneracy and Pauli blocking effects.
0
H and He opacities
-6
-1
3.5 4 4.5 5 5.5 6 6.5 7 7.5
Below we compare our new Rosseland mean opacities for pure H and pure He with those from log (T)
the OP [3] and OPAL [2] databases. The pure H calculations include contributions from H- ions,
which make an important contribution at low temperatures. Although our opacity table
calculations are usually made for a grid of specified temperature/η points, (where η is the Rosseland mean opacities for a C/H mixture. The left-hand side shows
electron degeneracy parameter, which is directly related to the electron density through a Fermi our ATOMIC & LEDCOP calculations and the right-hand side shows OP &
integral), we present opacities below for constant R values as a function of the electron OPAL calculations [obtained from 3].
temperature. This is a commonly used method of presenting opacity data in astrophysics, with
R related to the mass density via R=ρ(g/cc)/[10-6 T(K)].
The overall agreement between ATOMIC and the OP & OPAL calculations is very good. A few
exceptions are observed. For example, for H at temperatures of log(T)~5.2 the differences in
mean opacity are due to EOS differences between the calculations. In this region, the H excited
Conclusions & Future Plans
state populations are very sensitive to the EOS model used, as previously noted [3].
5
He • A new Los Alamos LTE opacity capability has been used to generate new opacity tables for
Z=1-10. The data in these tables include significant improvements in the atomic data and the
OP
OPAL
For He, we find again good agreement between ATOMIC
4
EOS model used in our previous opacity calculations.
ATOMIC and OP/OPAL calculations, down to
the lowest temperatures calculated (near 0.5 3
• Detailed comparisons with other opacity databases for selected elements find very good
log (Opacity) (cm /g)
eV).
2
log R=+1
overall agreement for mean opacities. Our new data will eventually supersede the OPLIB data
We note that, in this region, factors such as 2
available from our webpage: http://www.t4.lanl.gov/cgi-bin/opacity/tops.pl
Rayleigh scattering, free-free absorption from
1
He-, and neutral broadening all make • In the future we plan to provide detailed tables for mid-Z elements (Z=11-30). In particular, we
significant contributions to the mean opacity. 0 will initially focus on Fe, which is of great astrophysical importance.
-1 log R=-8
The Los Alamos National Laboratory is operated by Los Alamos National Security, LLC for the
6
H OP
National Nuclear Security Administration of the U.S. Department of Energy under Contract No.
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0
5 OPAL
ATOMIC log (T) (K) DE-AC5206NA25396.
4
1 References
log (Opacity) (cm /g)
He
3 OP [1] ] N. H. Magee et al, Astronomical Society of the Pacific Conference Series, 78, 51 (1995).
2
log R=+1 OPAL
0
2
ATOMIC
[2] F. J. Rogers and C. A. Iglesias, Ap. JS 79, 507 (1992); http://opalopacity.llnl.gov
-1 [3] N. R. Badnell et al, Mon, Not. R. Astron. Soc, 360, 458-464 (2005); M. J. Seaton and N. R.
1
Badnell, Mon, Not. R. Astron. Soc, 354, 457-465 (2004).
log (Opacity) (cm /g)
log R=+1
-2
[4] N. H. Magee, et al, 14th Topical Conference on Atomic Processes in Plasmas, Eds: J. S.
2
0
-1
log R=-8
-3 log R=-5 Cohen, S. Mazevet, and D. P. Kilcrease, (New York: AIP), pp168-179 (2004).
[5] R. D. Cowan, The Theory of Atomic Structure and Spectra (Berkeley, CA: University of
-4
-2
California Press).
4.0 4.5 5.0 5.5 6.0 6.5
log (T) (K)
7.0 7.5 8.0 8.5 9.0
-5 [6] P. Hakel and D. P. Kilcrease, 14th Topical Conference on Atomic Processes in Plasmas,
log R=-1
Eds: J. S. Cohen, S. Mazevet, and D. P. Kilcrease, (New York: AIP), pp190-202 (2004).
• Rosseland mean opacities for pure H (above) -6
and He (right figures) as a function of -7
3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5
temperature. We compare our ATOMIC log (T) (K)
calculations (blue) to OP calculations (black
curves) and OPAL calculations (red curves).