FITTING AND SMOOTHING OF OPACITY DATA

Techniques are described for the fitting and smoothing of Rosseland me an opacities, kappa(R)(T, rho), where T is the temperature and rho the mass density, and for calculating the first two derivatives, partial derivative kappa(R)/partial derivative T\rho and partial derivative ka ppa(R)/partial derivative rho\T. The codes OPALFIT and OPFIT are avail able for the processing of opacities calculated by the projects OPAL a nd op. Both projects use techniques of opacity sampling (that is to sa y, a number of frequency points insufficient to resolve all detailed s tructures in monochromatic opacities), which lead to some lack of smoo thness in the tabulated values Of kappa(R)(T, rho). It is shown that i mproved accuracy for the derivatives is obtained by using a technique of two-dimensional smoothing.