XSTAR models are based on 21 physical parameters described in detail
in Chapter 4. In quick summary, they are
cfrac, temperature, pressure, density, trad, rlrad38, column, rlogxi,
habund, heabund, cabund, nabund, oabund, neabund, mgabund, siabund, sabund,
arabund, caabund, feabund & niabund. Each of these parameters needs
at least one additional parameters and as many as four additional
parameters to specify is variation during the program run.
Each parameter has three levels for classifying its variability:
- Constant (variation type = 0):
- This parameter is held
constant in all the XSTAR runs.
- Additive (variation type = 1):
- The Additive class of
parameters provides a
simple method for varying parameters that are reasonably
independent of the others. For more info on how additive parameters
function, see the XSPEC manual and OGIP Memo OGIP 92-009.
- Interpolated (variation type = 2):
- Interpolated parameters
provide the
greatest accuracy in building table models. They also require the
most processing time. For each interpolated parameter, you can
define some number of points between a maximum and minimum range.
The placement of these intermediate points is determined by the
interpolation type - linear (interpolation type = 0) or
logarithmic (interpolation type = 1).
In estimating the running time of XSTAR2XPEC, the key factor is the
number of times XSTAR is called. Consider a run with
interpolated parameters, where interpolated parameter is evaluated
at points
. The total number of
times XSTAR is called is then
. However, if
additive parameters are also
defined, then for each set of interpolated variables, there is one
run with all the additive parameters are zero and the remaining
runs have one of the additive parameters at it's maximum
value and the rest all zero. This means that the total number of
times XSTAR must be run is given by
|
(7.1) |
and this can provide you with a feel for how long a complete
XSTAR2XSPEC run will require. As an example, if we defined 2
interpolated parameters (one evaluated at 5 points and the other
evaluated at 4 points) and 8 additive parameters, XSTAR would be run a
total of
|
(7.2) |
which means that if the XSTAR runs for the appropriate model range
averages five minutes, it will take approximately (180)(5 minutes) =
900 minutes = 15 hours for a complete XSTAR2XSPEC run.