Atomic data from the Iron Project

Abstract. We present new calculations for transition probabilities of Fe IV, with much more extensive datasets than heretofore available, for a variety of astrophysical applications. The large-scale close coupling R-matrix calculations yield 1,798 LS bound states with n ≤ 11 and l ≤ 9, and corresponding 138 121 dipole allowed transitions in the form of oscillator strengths f, line strengths S, and A-coeffficients. This represents the largest R-matrix dataset in LS coupling for any ion under either the Opacity Project or the Iron Project. Through algebraic transformation of the LS multiplets, a total of 712 120 dipole allowed fine structure transitions for Fe IV are obtained. Observed transition energies, whenever available, are used together with the energy independent line strengths to derive the f- and the A-values for improved accuray; the adopted algorithm used calculated energies for the remainder. Present results show significantly better accuracy for the important low-lying states than previous calculations. Monochromatic and mean opacities for Fe IV are computed and compared with those obtained using the Opacity Project data. We find differences which could have important consequences for several astrophysical applications involving low ionization stages of iron. Key words. atomic processes – line: formation – radiation mechanisms: thermal – radiative transfer – ISM: HII regions – radio lines: galaxies 1