Photoelectric absorption cross-sections (Balucinska-Church+, 1992)

Details Photoelectric absorption cross-sections (Balucinska-Church+, 1992) Photoelectric absorption cross-sections (Balucinska-Church+, 1992)

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994ycat.6062....0b&link_type=abstract

VizieR On-line Data Catalog: VI/62. Originally published in: 1992ApJ...400..699B

Physics

Atomic Physics

Atomic Physics, Interstellar Medium, X-Ray Sources

Scientific paper

Polynomial fit coefficients have been obtained for the energy dependence of the photoelectric absorption cross sections of 17 astrophysically important elements. The aim of this work is to provide convenient fits to the photoelectric absorption cross sections for each of 17 elements separately, so that spectral modelling can be performed with an absorption term containing the abundances of some or all of the elements as adjustable parameters. The fits to the individual elements can also be used independently for calculating window transmissions, gas stopping efficiency, etc. The atomic absorption cross sections were taken from Henke et al. (1982). Polynomial fits have been made to the atomic absorption cross sections in the energy range of 0.03 -- 10 keV for seventeen elements: hydrogen, helium, carbon, nitrogen, oxygen, neon, sodium, magnesium, aluminium, silicon, sulphur, chlorine, argon, calcium, chromium, iron and nickel. In the case of elements with only the K-edge in this energy range, polynomial fits were made each side of the edge; with the L-edge also present three fits were made. Polynomials of up to degree 8 were required. The functions fit Henke's data points with a typical error of 2% and a maximum error of 7%, except for points below 40~eV for argon, calcium and sodium, where the errors are larger. The effective cross section per hydrogen atom for a particular set of elemental abundances may be simply calculated from the individual cross sections. A set of routines has been written in generic FORTRAN-77 to implement these polynomial fits. The file XSCTNS.FOR contains seventeen REAL functions that will return the photoelectric cross sections for H, He, C, N, O, Ne, Na, Mg, Al, Si, S, Cl, A, Ca, Cr, Fe, and Ni in cm**2/g, given the photon energy in eV. The file TOTLXS.FOR contains a single function that returns the effective cross section in cm**2/H atom, given the photon energy in eV and a set of seventeen relative abundances in log10. If standard abundances (as assumed by Morrison and McCammon) are to be used, the file SIGISM.FOR contains a function implementing the MM polynomials that also returns the effective photoelectric cross section in cm**2/H atom, given the photon energy in eV. It executes much faster than TOTLXS, but gives the same results as TOTLXS called with MM relative abundances. All of these routines are valid only over the photon energy range 30 - 10,000 eV. (1 data file).

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