%R 1994yCat.6062....0B
%D 9-Mar-1994
%d 1998.08.28
%I VI/62
%t Photoelectric absorption cross-sections (Balucinska-Church+, 1992)
%T Photoelectric absorption cross-sections with variable abundances
%J 1992ApJ...400..699B
%A Balucinska-Church M., McCammon D.
%B 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.
 \par
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.
 \par
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.
%K Atomic physics; Interstellar medium; X-ray sources
%F ReadMe              0x80   This file