Photoionization and electron impact excitation cross sections for Fe I^⋆

¹ Department of Physics, Western Michigan University, Kalamazoo, MI 49008, USA
e-mail: manuel.bautista@wmich.edu
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

Received: 23 May 2017
Accepted: 24 July 2017

Abstract

Context. Iron is a major contributor to the opacity in the atmospheres of late-type stars, as well as a major contributor to the observed lines in their visible spectrum. Iron lines are commonly used to derive basic stellar parameters from medium/high resolution spectroscopy, that is, spectroscopy which shows metal content, effective temperature, and surface gravity.

Aims. Here we present large R-matrix calculations for photoionization cross sections and electron impact collision strengths.

Methods. The photoionization calculations included 35 configurations and 134 LS close coupling terms of the target ion. The eigenfunction expansion accounts for the photoionization of the outer nl subshells, with n ≥ 4, as well as the open inner 3d subshell. Our results include total and partial (term-to-term) photoionization cross sections for 936 energy terms of iron with principal quantum number ≤10, and total angular momentum from zero to seven. Our electron impact collision strengths include the lowest 46 LS terms of the atom.

Results. The present photoionization cross sections should be considerably more accurate than those currently available in the literature. On the other hand, the electron impact cross sections, which are being reported for the first time, are needed in non-local thermodynamic equilibrium (NLTE) modeling of the solar spectrum and late-type stars in general.