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VI/62A Photoelectric absorption cross-sections (Balucinska-Church+, 1992)
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Photoelectric absorption cross-sections with variable abundances
Balucinska-Church M., McCammon D.
<Astrophys. J. 400, 699 (1992)>
=1992ApJ...400..699B
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ADC_Keywords: Atomic physics ; Interstellar medium ; X-ray sources
Description:
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 to
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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
xsctns.for 79 988 *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)
helium93.for 79 217 *Photoelectric absorption cross-sections for He
helium97.for 79 224 *Photoelectric absorption cross-sections for He
he_x-s.ps 52 59669 *Plot of the various historical and modern
measurements and calculations
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Note on 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.
Note on 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)
Note on 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.
Note on 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.
Note on helium93.for:
Description :
Out of Date -- from xsctns.for V2.0 calculates mass absorption
coefficient (mu/rho) in cm2/g for neutral helium for the given energy
in eV. Cross sections come from experimental data compiled by Marr and
West (Atomic Data and Nuclear Data Tables (1976) 18, 497).The four
strongest autoionization resonances are taken into account; numbers come
from Oza (Phys Rev A (1986), 33, 824), and Fernley et al.(J. Phys B (1987)
20, 6457).
References:
Marr, G. V., and West, J. B., Atomic and Nuclear Data Tables, (1976) 18,
497.
Oza, D. H., (1986), Phys. Rev. A, 33, 824.
Fernley, J. A., Taylor, K. T., and Seaton, M. J., (1987), J. Phys. B., 20,
6 457.
Note on helium97.for:
Description:
This is the helium cross section routine included in V3.0 of xsctns.for.
(See the 3 October 1997 historical notes below.)
References:
Yan et al 1998, ApJ 496, 1044.
Oza, D. H., (1986), Phys. Rev. A, 33, 824.
Fernley, J. A., Taylor, K. T., and Seaton, M. J., (1987), J. Phys. B., 20,
6 457.
Note on he_x-s.ps:
Description:
Shows He photoelectric cross sections from 30 - 1000 eV from past
and current calculations and measurements. Includes the cross sections
adopted for versions 1, 2, and 3 of these subroutines.
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.
* 3 Oct 1997 --- Update to version 3.0
Realized Marr and West (1976: Atomic & Nucl. Data Tables,
18, 497) cross sections are a poor match to current best
estimates above 80 eV. Changed continuum portion to cross
sections recommended by Yan et al. Autoionization resonances
were retained as implemented by Jelinsky in the EUVE archive.
Except for autoionization features below 80 eV, these He cross
sections are more similar to those in Version 1.0
* 29 Nov 1999 --- ADC received version 3.0 from Dan McCammon; replaced
xsctns.for, added helium93.for, helium97.for and he_x-s.ps,
and updated the ReadMe file.
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(End) (revised by Gail L. Schneider [SSDOO/ADC] 10-Dec-1999) 09-Mar-1994