SCL Sfit SYN Commands

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synth : find optimum fit by adjusting abundances v_turb, vsini, and v_rad

Compute the best fit parameters by computing spectra with variable abundances, v_turb, vsini, and v_rad, assuming a given model atmosphere. This command takes no parameters; everything should have been set up prior to running synth. The output is saved in a file <file>.synth;, where <file> was the name of the spectrum being fitted.
Experience has shown that, even if vsini, and v_rad have been measured quite precisely from the same spectrum, these parameters can have a profound effect on the fit quality. Therefore it is now possible to solve for v_turb, vsini, and v_rad individually for the region of spectrum under analysis.

sterne <model> : Define the model atmosphere to be used by synth

syn_... <p1> <p2> : Initialise parameter for synth
syn_vturb <vturb> [<dv>]; Initialise v_turb (km/s) for a fit using synth (default 5)
syn_vsini <vsini> [<dv>]; Initialise vsini (km/s) for a fit using synth (default 0)
syn_vrad <vrad> [<dv>]; Initialise v_rad (km/s) for a fit using synth (default 0)
syn_beta <beta> Initialise limb darkening coefficient for a fit using synth (default 1.5)
save <fit> : Save the spectrum and best fit from synth

abundance <elid> <abun> <dabu> : Initialise abundances for synth

The first argument is the element identifier (<elid> = atomic number). The second is the logarithmic abundance (<abun> relative to log Sigma mu_i n_i = 12.15). The third is the amount by which that abundance may vary (<dabu>). Set this value to 0.0 to keep it fixed.

General remarks on the initialisation of abundances in synth

A solar abundance will be assumed for any elements not specified.
Example:

abundance 1 7.0 0.0 ! Fix hydrogen at a small value
abundance 6 8.6 0.3 ! Allow carbon to vary
abundance 8 8.8 0.3 ! Allow oxygen to vary

Any abundances obtained by SYNTH will be remembered and, by default, not allowed to change, so that two successive calls to SYNTH may be made to solve for different groups of abundances. To use the new abundance as a start value, but to solve again for that element, for example after solving for C and O varying, you want to fix O, but solve for C with N, then set the new abundance to 0.0, but set the maximum change to a positive value. For example:

abundance 6 0.0 0.3
abundance 7 7.5 0.3

To remember these results and solve for the hydrogen abundance:

 abundances 1 8.0 0.3

[old_abund] {...} : Initialise abundances and microturbulence for synth (obsolete)

Define the initial parameters to be used by synth. This command currently requires a specific format. The first integer on each line is the element identifier (<elid> = atomic number). The second number is the logarithmic abundance (<abun> relative to log Sigma mu_i n_i = 12.15). The third is the amount by which that abundance may vary (<dabu>). Set this value to 0.0 to keep it fixed. To finish, enter a negative element identifier.

 abundances{
0 <vturb> <dvt>! microturbulent velocity
<elid1> <abun1> <dabu1> ! first element
<elid2> <abun2> <dabu2> ! second element
 ...
-1 0 0 ! to finish
}