ATOMIC DATA FOR OPACITY CALCULATIONS .19. THE MAGNESIUM ISOELECTRONICSEQUENCE

As a contribution to the international Opacity Project, large numbers of multiplet term energies, f-values and photoionization cross section s have been calculated for those Mg-like ions of astrophysical interes t: Mg I, Al II, Si III, S V, Ar VII, Ca IX and Fe XV. The present atom ic data have been obtained in the close-coupling approximation with a modified version of the RMATRX computer program and recently developed asymptotic codes. We briefly discuss the new results, and representat ive comparisons with previous experimental and theoretical work are ca rried out. Emphasis is given to the large number of photoionization cr oss sections reported for the first time. We conclude that the statist ical accuracy of the Opacity Project datasets for the Mg isoelectronic sequence is at least as high as that of any other set of data produce d with the most elaborate methods available to date.