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Purpose: To create a list of nominal scattered solar X-ray
background count rates on the 60-s sample interval of the
xxx_ORBIT.FITS file and the orbit data extension of the RDF xxx_ANC.FITS
file. The output is used in the program RATE_FIT
in conjunction with the output of the program RATE to fit the scattered
solar X-ray and long-term enhancement background contamination. Program AO
uses the methods described in Snowden and Freyberg (1993) to estimate the
nominal scattered solar X-ray background observed by ROSAT.
NOTE: The input file SG.DAT contains solar and geophysical data which are
required for AO and TILT. If the observation to be analyzed occurred after
the range of time covered by the file (i.e., if the file has not been
updated recently enough), AO will return a warning.
File Input:
1) Observation data set fits files - xxx_ATTITUDE.FITS,
xxx_EVENTRATES.FITS, and xxx_ORBIT.FITS for German data,
xxx_ATTITUDE1.FITS, xxx_EVENTRATES.FITS, and xxx_ORBIT.FITS for
US data, xxx_ANC.FITS for RDF data.
2) Other fixed input - valid_times_all.dat, WINDOW.DAT window
transmission,
EFF_AREA.DAT on-axis effective areas, GAS_EFF.DAT PSPC
counter gas stopping efficiencies, DRM.FITS detector response matrix, SG.DAT
solar and geophysical data, and RSPECTRA.FITS Raymond and Smith thermal
spectra (1991 vintage).
Interactive Input:
1) Observation control - the eight or fewer character string listed above
as xxx.
2) Data format control - 1 for German data, 2 for US data,
3 for RDF data.
3) Mode control - 1 for simple treatment, 2 for more complete treatment.
The simple treatment assumes that the residual atmosphere of the
observation geometry (both along the line of sight and between the Sun and
positions along the line of sight) is optically thin. The more complete
treatment uses a nearly complete radiative transfer approach; it considers
absorption between the Sun and a scattering element along the line of sight
and between the scattering element and the satellite. The simple treatment
runs a couple orders of magnitude faster and is probably sufficient for all
ROSAT PSPC observations.
4) Temperature and scale factor for first solar component - the intrinsic
solar X-ray spectrum is modelled as two-component thermal plasma emission,
in this case, Raymond and Smith (1977) with the 1991 computer code update.
The program requests the log 
of the temperature and the scale factor
for each component. These same temperatures and scale factors must also be
used below in the program TILT for consistency.
5) Temperature and scale factor for second component - see 4). Scale
factors which sum to one for temperatures near log T of near 6
(e.g., 6.2 0.8 and 5.7 0.2) will give model count rates which are typically
within a factor of a few to ten of the true values (determined later by the
program RATE_FIT).
Ascii Output:
1) AO_SSX_SC.OUT - nominal SSX count rates on 60-s intervals, used in the
program RATE_FIT.
2) AO_COL.OUT - column densities of atmosphere constituents on 60-s
intervals.