ATOMIC DATA AND SPECTRAL MODEL FOR Fe II

Abstract

We present extensive calculations of radiative transition rates and electron impact collision strengths for Fe II. The data sets involve 52 levels from the 3d 7 , 3d 6 4s, and 3d 5 4s 2 configurations. Computations of A-values are carried out with a combination of state-of-the-art multiconfiguration approaches, namely the relativistic Hartree-Fock, Thomas-Fermi-Dirac potential, and Dirac-Fock methods;while the R-matrix plus intermediate coupling frame transformation, Breit-Pauli R-matrix and Dirac R-matrix packages are used to obtain collision strengths. We examine the advantages and shortcomings of each of these methods, and estimate rate uncertainties from the resulting data dispersion. We proceed to construct excitation balance spectral models, and compare the predictions from each data set with observed spectra from various astronomical objects. We are thus able to establish benchmarks in the spectral modeling of [Fe II] emission in the IR and optical regions as well as in the UV Fe II absorption spectra. Finally, we provide diagnostic line ratios and line emissivities for emission spectroscopy as well as column densities for absorption spectroscopy. All atomic data and models are available online and through the AtomPy atomic data curation environment. Subject headings: atomic data -quasars: absorption lines -quasars: individual (QSO 2359-1241) -ISM: individual objects (HH 202) -ISM: individual objects (Orion) -ISM: individual objects (ESO-Hα 574, Par-Lup 3-4) -ISM: jets and outflows -ISM: lines and bands -stars: pre-main sequence reliable scattering calculations. For this work we use a combination of numerical methods: the pseudo-relativistic Hartree-Fock (hfr) code of Cowan (1981); the Multiconfiguration Dirac-Fock (mcdf) code (Dyall et al. 1989), and the scaled Thomas-Fermi-Dirac central-field potential as implemented in autostructure (Badnell 1997). hfr calculationshfr uses a superposition of configurations approach to account for configuration interactions. The code solves the Hartree-Fock equations for each electronic configuration.Relativistic corrections are also included in this set of equations. The radial parts of the multi-electron Hamiltonian can be adjusted empirically to reproduce the spectroscopic energy levels in a least-squares fit procedure. These semi-empirical corrections are used to account for the contributions from higher order correlations in the atomic state functions.The following configurations were explicitly included in the physical model: 3d 6 4s, 3d 7 , 3d 5 4s 2 , 3d 6 5s, 3d 6 4d, 3d 6 5d, 3d 5 4p 2 , 3d 5 4d 2 , 3d 5 4s4d, 3s3p 6 3d 7 4s, 3s3p 6 3d 8 , and 3s3p 6 3d 6 4s 2 . This configuration expansion extends the one used in the previous hfr calculation by Quinet et al. (1996) by including 3d 5 4d 2 and 3s3p 6 3d 6 4s 2 . In order to minimize the discrepancies between computed and experimental energy levels, the hfr technique was used in combination with a well-known least-squares optimization of the radial parameters. The fitting procedure was applied to 3d 6 4s, 3d 7 , ...

Forbidden Iron Lines and Dust Destruction in Supernova Remnant Shocks: The Case of N49 in the Large Magellanic Cloud

“…On the other hand, the Ramsbottom et al (2007) data lie close to the Zhang & Pradhan (1995) values. The critical densities also vary by similar amounts between Bautista et al (2015), Zhang & Pradhan (1995), and Ramsbottom et al (2007).…”

“…In addition, both the collision strengths and the radiative transition probabilities have uncomfortably large computational errors. For example, Bautista et al (2015) compare nine calculations and find a considerable spread. The Zhang & Pradhan (1995) collision strengths which we use are, on average, 0.3-0.5 dex weaker than the Bautista et al (2015) values.…”

“…For example, Bautista et al (2015) compare nine calculations and find a considerable spread. The Zhang & Pradhan (1995) collision strengths which we use are, on average, 0.3-0.5 dex weaker than the Bautista et al (2015) values. On the other hand, the Ramsbottom et al (2007) data lie close to the Zhang & Pradhan (1995) values.…”

“…Indeed, the Bautista et al (2015) collision data would then require an enhancement in the absolute abundance of Fe, rather than depletion in the Fe II zone. More than complete grain destruction in the Fe II zone seems rather unphysical.…”

The Belgian repository of fundamental atomic data and stellar spectra (BRASS)

“…Despite these recent efforts quality information for some transitions can remain poor or even absent from the literature, a problem only exacerbated by the ever increasing quantity of data. Previous efforts to constrain errors have typically employed a few benchmark stellar spectra of similar spectral type, with limited wavelength and ionic coverage (Ryabchikova et al 2008), (Bautista et al 2015).…”