VI/62Photoelectric absorption cross-sections (Balucinska-Church+, 1992)

Photoelectric absorption cross-sections with variable abundances Balucinska-Church M., McCammon D. <Astrophys. J. 400, 699 (1992)> =1992ApJ...400..699BADC_Keywords: Atomic physics ; Interstellar medium ; X-ray sourcesDescription: 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.File Summary:

FileName Lrecl Records Explanations

ReadMe 80 . This file xsctns.for 79 1000 *Photoelectric absorption cross-sections (cm2/g) totlxs.for 78 138 *Effective absorption cross-sections (cm2/H) sigism.for 74 88 *Interstellar photoelectric absorption cross-sections (cm2/H) he_old.for 79 68 *Photoelectric absorption cross-sections for He (out of date)

Notes on File xsctns.for: Description: This set of subroutines calculates the photoelectric absorption cross sections for the elements H, He, C, N, O, Ne, Na, Mg, Al, Si, S, Cl, A, Ca, Cr, Fe, and Ni. The result is in cm**2/g, given the photon energy in eV. These functions are valid only over the energy range 30 - 10,000 eV, but do NOT check that the input energy is within the valid range. These functions are called by TOTLXS to calculate the total effective cross section, given a set of relative abundances. They can also be used by themselves. References: Monika Balucinska-Church and Dan McCammon "Photoelectric Absorption Cross Sections with Variable Abundances" Ap.J. 400, 699 (1992) All data are from: B. L. Henke, P. Lee, T. J. Tanaka, R. L. Shimabukuro and B. K. Fujikawa, 1982, Atomic Data and Nuclear Data Tables, vol 27, p 1.Notes on File totlxs.for: Description: Calculates the effective absorption cross section TOTLXS in units of cm**2/hydrogen atom at energy E in eV for the abundances of the elements specified in vector AB Method: Calls seventeen functions that calculate the mass absorption coeffs in cm**2/g for the following elements: H, He, C, N, O, Ne, Na, Mg, Al, Si, S, Cl, Ar, Ca, Cr, Fe, Ni. Requires these functions as found in file XSCTNS.FOR. Reference: Monika Balucinska-Church and Dan McCammon "Photoelectric Absorption Cross Sections with Variable Abundances" Ap.J. 400, 699 (1992)Notes on File sigism.for: Description: This function implements the approximation of Morrison and McCammon (1983) to the interstellar photoelectric absorption cross-section. ENERGY is in eV and the resultant cross-section is in cm**2/hydrogen atom. Abundances of other elements relative to hydrogen are appropriate for the interstellar medium in the solar neighbourhood (see reference for discussion). This function requires no external routines. Reference: Robert Morrison and Dan McCammon Ap.J., vol. 270, p. 119 (1992). Deficiencies: Works only in the range of energy from 30 eV to 10,000 eV. No bounds checking on energy range.Notes on File he_old.for: Description: This subroutine calculates the photoelectric absorption cross sections for the He. The result is in cm**2/g, given the photon energy in eV. This functions is valid only over the energy range 30 - 10,000 eV, but it does NOT check that the input energy is within the valid range. This functions can be called by TOTLXS to calculate the total effective cross section, given a set of relative abundances. It can also be used by itself. It is now out-of-date and has been replaced by a new HELIUM routine in XSCTNS.FOR that is a better fit to the best existing experimental and theoretical work. References: Monika Balucinska-Church and Dan McCammon "Photoelectric Absorption Cross Sections with Variable Abundances" Ap.J. 400, 699 (1992) All data are from: B. L. Henke, P. Lee, T. J. Tanaka, R. L. Shimabukuro and B. K. Fujikawa, 1982, Atomic Data and Nuclear Data Tables, vol 27, p 1.

Historical Notes: * 12 May 1992 --- Release date * 16 Dec 1992 --- Note that He cross sections do not include autoionization levels that increase the cross sections about 15% near 60 eV. A correction will be included soon. There is also some increase in the He cross section at higher energies. * 23 Sep 1993 --- Helium absorption routine updated to version 2.0. This subroutine replaces the previous version of HELIUM which calculated mass absorption coefficients based on Henke's data (Henke, B. L., et al., (1982), Atomic and Nuclear Data Tables, 27, 1). This version of HELIUM returns mass absorption coefficients which are in better agreement with the best experiments as well as theoretical models (see Chen, W. F., Cooper, G., and Brion, C. E., 1991), Phys. Rev. A, 44, 186). This fortran-77 version of the subroutine is based on Pat Jelinsky's program written in C (obtained from EUVE Archive). The new routine now includes the most prominent Fano features near 60 eV. Aside from these auto-ionization feature, the maximum difference in the normal-abundance total cross section is about +20% near 150 eV, with a nearly constant 10% increase from 500 eV to 6 keV. (The cross section for helium alone is increased by more than a factor of three at 5 keV.) The old HELIUM subroutine is now included as file HEL_OLD.FOR. Note that SIGISM.FOR has NOT been updated, and still returns the cross sections of the Morrison & McCammon paper. TOTLXS called with normal abundances will no longer produce the same results.(End)9-Mar-1994

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