  Opacity is an important ingredient of the evolution of stars. The calculation
of opacity coefficients is complicated by the fact that the plasma contains
partially ionized heavy ions that contribute to opacity dominated by H and He.
Up to now, the astrophysical community has greatly benefited from the work of
the contributions of Los Alamos [1], Livermore [2] and the Opacity Project (OP)
[3]. However unexplained differences of up to 50% in the radiative forces and
Rosseland mean values for Fe have been noticed for conditions corresponding to
stellar envelopes. Such uncertainty has a real impact on the understanding of
pulsating stellar envelopes, on the excitation of modes, and on the
identification of the mode frequencies. Temperature and density conditions
equivalent to those found in stars can now be produced in laboratory
experiments for various atomic species. Recently the photo-absorption spectra
of nickel and iron plasmas have been measured during the LULI 2010 campaign,
for temperatures between 15 and 40 eV and densities of ~3 mg/cm3. A large
theoretical collaboration, the "OPAC", has been formed to prepare these
experiments. We present here the set of opacity calculations performed by eight
different groups for conditions relevant to the LULI 2010 experiment and to
astrophysical stellar envelope conditions.
