J/MNRAS/441/2855Bound-bound Gaunt factor values (Morabito+, 2014)

Exact bound-bound Gaunt factor for quantum levels up to n=2000. Morabito L.K., van Harten G., Salgado F., Oonk J.B.R., Rottgering H.J.A., Tielens A.G.G.M. <Mon. Not. R. Astron. Soc. 441, 2855 (2014)> =2014MNRAS.441.2855MADC_Keywords: Atomic physicsKeywords: atomic data - ISM: generaAbstract: Comparison of observations of radio recombination lines in the interstellar medium with theoretical models can be used to constrain electron temperature and density of the gas. An important component of the models is spontaneous transition rates between bound levels. Calculating these rates relies on accurate bound-bound oscillator strengths, which can be cast in terms of the Gaunt factor. The Gaunt factor contains terminating hypergeometric functions that cannot be calculated with sufficient accuracy for high quantum levels (n≳50) by standard machine-precision methods. Methods to overcome the accuracy problem have been developed, which include asymptotic expansions and recursion relations. These methods, used in astrophysical models to calculate oscillator strengths, can introduce errors, sometimes up to as much as ∼8 per cent. Detections of radio recombination lines with the new Low Frequency Array have prompted an examination of theoretical models of the interstellar medium. We revisit the calculation of the Gaunt factor, employing modern arbitrary-precision computational methods to tabulate the Gaunt factor for transitions up to quantum level n=2000, sufficient to model low-frequency carbon radio recombination lines. The calculations provide a relative error of ∼3x10^{-4}when compared to more detailed calculations including relativistic corrections. Our values for the Gaunt factor are provided for download in a tabular format to be used for a wide range of applications.Description: Tabulation of the Gaunt factor values for quantum levels up to n=2000. These were calculated using arbitrary precision with the hypergeometric function in MATHEMATICA. The fits file is a 2000x2000 square matrix, where every element corresponds to the Gaunt factor for that transition. For example, element [3,2] contains the Gaunt factor value for the transition from the n=3 to n=2 quantum level. The only elements that do not have a value are the n=n elements. The Gaunt factor is a dimensionless quantity.File Summary:

FileName Lrecl Records Explanations

ReadMe 80 . This file bbgaunt.fit 2880 5557 Bound-Bound Gaunt Factor Values

Acknowledgements: Leah Morabito, morabito(at)strw.leidenuniv.nl(End)Leah Morabito [Leiden Observatory], Patricia Vannier [CDS] 19-Dec-2013

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