AtomNeb: IDL Library for Atomic Data of Ionized Nebulae

Abstract

Copyright © 2019, arXiv, All rights reserved. Ionized gaseous nebulae are interstellar clouds of hydrogen-rich materials, which are photo-ionized by ultraviolet radiation from stars, making them visible in multi-wavelength bands. Ionized nebulae can be used as an astrophysical tool to trace the chemical composition of the interstellar medium in our Galaxy and other galaxies, and to study mixing processes in stellar evolution. Spectra emitted from ionized nebulae generally contain collisionally excited and recombination lines. Electron temperatures, electron densities, and ionic abundances can be determined from collisionally excited lines (CEL) by solving statistical equilibrium equations using collision strengths (Ωij) and transition probabilities (Aij) of ions. Moreover, physical conditions and chemical abundances can be calculated from recombination lines (RL) using effective recombination coefficients (αeff) of ions. The atomic data, i.e. Ωij, Aij, and αeff, are used to calculate line emissivities in nebular spectral analysis tools (e.g. Howarth and Adams (1981); Shaw and Dufour (1994); Shaw et al. (1998); Luridiana, Morisset, and Shaw (2015); Howarth et al. (2016); Danehkar (2018b)), and photoionization codes (e.g. Ferland et al. (1998); Kallman and Bautista (2001); Ercolano et al. (2003); Ercolano, Barlow, and Storey (2005); Ercolano et al. (2008)). Hence, the atomic data for collisional excitation and recombination process are essential to determine physical conditions and elemental abundances of ionized nebulae from collisionally excited and recombination lines (see e.g. Danehkar, Parker, and Ercolano (2013); Danehkar et al. (2014); Danehkar (2014); Danehkar, Parker, and Steffen (2016); Danehkar (2018a)). AtomNeb is a database containing atomic data stored in the Flexible Image Transport System (FITS) file format (Wells, Greisen, and Harten (1981); Hanisch et al. (2001); Pence et al. (2010)) produced for nebular spectral analysis. FITS tables provide easy access to atomic data for spectral analysis tools. Especially, AtomNeb includes the atomic data for both the collisional excitation and recombination process of ions usually observed in nebular astrophysics. The AtomNeb interface library is equipped with several application programming interface (API) functions written in the Interactive Data Language (IDL) for reading the atomic data from the AtomNeb FITS files. Furthermore, the AtomNeb IDL library can be employed in the GNU Data Language (GDL) (Arabas et al. (2010); Coulais et al. (2010)), an open-source free compiler for IDL codes. • The API functions for the CEL atomic data developed in the IDL programming language were designed to easily read collision strengths (Ωij) and transition probabilities (Aij) of given ions, which can be used to derive electron temperatures, electron densities, and ionic abundances from measured fluxes of collisionally excited lines. The CEL data include energy levels (Ej), collision strengths (Ωij), and transition probabilities (Aij) from the CHIANTI database version 5.2 (Landi et al. (2006)), version 6.0 (Dere et al. (2009)), and version 7.0 (Landi et al. (2012)), which were compiled according to the atomic data used in the FORTRAN program MOCASSIN (Ercolano et al. (2003); Ercolano, Barlow, and Storey (2005); Ercolano et al. (2008)). The CEL data also include a collection compiled based on the atomic data used in the Python package pyNeb for spectral analysis (Luridiana, Morisset, and Shaw (2015)). • The API functions for the RL atomic data developed in IDL were designed to provide easy access to effective recombination coefficients (αeff) and branching ratios (Br) of recombination lines of given ions. The RL data include effective recombination coefficients for C II (Davey, Storey, and Kisielius (2000)), N II (Escalante and Victor (1990)), O II (Storey (1994); Liu et al. (1995)), and Ne II (Kisielius et al. (1998)), which were compiled based on the atomic data in MOCASSIN. The RL data also include hydrogenic ions for Z=1 to 8 (Storey and Hummer (1995)), effective recombination coefficients for H, He, C, N, O, and Ne ions (Pequignot, Petitjean, and Boisson (1991)), effective recombination coefficients for He I (Porter et al. (2012); Porter et al. (2013)), effective recombination coefficients for N II (Fang, Storey, and Liu (2011); Fang, Storey, and Liu (2013)), and effective recombination coefficients for O II (Storey, Sochi, and Bastin (2017)). The AtomNeb IDL/GDL package uses the FITS file related IDL procedures from the IDL Astronomy User’s library (Landsman (1993); Landsman (1995)) to read the atomic data from the AtomNeb FITS files. The API functions of the AtomNeb IDL library, together with the proEQUIB IDL library (Danehkar (2018b)), can be used to perform plasma diagnostics and abundance analysis of nebular spectra emitted from ionized gaseous nebulae.