The model is a two-temperature Raymond thermal spectrum, low temperature range is 0.55 to 0.65 keV, high temperature range is 1 to 2 keV, element abundance table is cosmic, abundance of heavy elements (atomic number >2) is 50% of the value in the table. Note that 0.7 = log(5.0), specifies that the second component normalization will be 5 times the normalization of the first component. A multiple component fit requires that this normalization (or a range of normalizations) be specified for the 2nd, 3rd, etc. components. Type help models_spectral for a list of possible choices.
xs> fit
Performing the simplex minimization fit.
Observed spectrum: rp90
Model descriptor: abs(20)*(ray(0.55:0.65 c 50)+ray(0.7 1:2 c 50)) # The free
# parameters are now 2 temperatures and one normalization.
# Note that IRAF will not accept .7 as a valid fraction. The number must be 0.7.