lte-codes Sterne Spectrum Sfit SCL

SCL Sfit SLV Commands


solve : find optimum fit in a grid of model spectra
solve is one of the principal SFIT commands. It initiates an optimisation by starting with a grid of theoretical spectra, defined by model or read_grid, a set of starting parameters and an observed spectrum. It uses one of four methods to find a best-fit solution according to a minimum chi2 criterion. The choices of model grid, method and starting parameters are very important; not every combination is suitable for every type of problem. The parameters to be optimised include:
 Teff, log g, nA, v sin i, vrad 
being effective temperature, surface gravity, an abundance variable, rotation velocity and radial velocity for one or two stars, and
 R2 / R1
being the relative radius of the second star, if present.
It is important to appreciate how to initialise the model parameters and to define which are to be solved for. In general, each parameter takes two arguments. In the case of amoeba, these specify a starting value and the maximum amount by which this value is be allowed to vary. For levenburg, only a starting value and a zero or non-zero increment are required. If the increment is zero, then the value is fixed. In the genetic solution, the values represent upper and lower bounds for the parameter space to be explored. Values may be initialised en bloc or individually with the slv_... and fix_... commands
models,model2
These commands read in a grid of model spectra. A variety of file formats are supported. The grid must be rectangular or cuboidal, but the stepsizes do not need to be regular. The normal axes are effective temperature, surface gravity and H/He abundance. An intermediate wavelength grid must be defined in order to allow for inhomogeneity in the input spectra. Values for the parameters are taken from the input models themselves, to avoid mixups. The syntax of the command arguments must be explicit.
model{
NFMT ! file format specifier
TITLE ! a user-defined title for the model grid
NT NG NA ! numbers of temperatures, gravities and abundaces in the grid
WS WE DW ! wavelength start, end and increments in the rebinned grid
file_1_1_1
file_2_1_1
file...
file_NT_NG_NA
}
read_grid <file> : read model grid from binary file
save_grid <file> : save model grid to binary file
grid_log_he : Convert the abundance grid to log scale
Convert the abundance grid from an assumed natural scale (e.g. relative abundance by number: nA) to a logarithmic scale using the transformation:
zeta = log ( nA / ( 1 - nA ) )

slv_... <p1> <p2> : Initialise parameter for solve
slv_teff1 <Teff/1000> <dT> : Effective temperature (K/1000) -- Star 1
slv_logg1 <log g> <dg> : Surface gravity (log cgs) -- Star 1
slv_ahe1 <nhe> <dnHe> : Helium abundance -- Star 1
slv_vsini1 <vsini> <dvsini> : Projected rotation velocity -- Star 1
slv_R1 <R> <dR> : Relative radius -- Star 1
slv_vrad1 <vrad> <dvr> : Projected radial velocity -- Star 1
slv_teff2 <Teff/1000> <dT> : Effective temperature (K/1000) -- Star 2
...: repeat above for Star 2

fix_... <p1> : Fix parameter for solve
Parameters may be fixed using the following commands. The command may take one or no arguments. One argument specifies the value at which the parameter is to be fixed. No arguments implies that the value obtained as a result of a previous solution, or as previously fixed, should be used.
fix_teff1 [<Teff/1000>] : Effective temperature (K/1000) -- Star 1
fix_logg1 [<log g>] : Surface gravity (log cgs) -- Star 1
fix_ahe1 [<nhe>] : Helium abundance -- Star 1
fix_vsini1 [<vsini>] : Projected rotation velocity -- Star 1
fix_R1 [<R>] : Relative radius -- Star 1
fix_vrad1 [<vrad>] : Projected radial velocity -- Star 1
fix_teff2 [<Teff/1000>] : Effective temperature (K/1000) -- Star 2
...: repeat above for Star 2

parameters {...} : Initialise all "slv" parameters
Old format: all arguments must be defined explicitly
parameters {
<Teff_1>
<g_1>
<nA_1>
<vsini_1>
<R_1/R>
<vrad_1>
<Teff_2>
<g_2>
<nA_2>
<vsini_2>
<R_2/R>
<vrad_2>
<dT_1>
<dg_1>
<dn_1>
<dvsini_1>
<dR_1>
<dvrad_1>
<dT_2>
<dg_2>
<dn_2>
<dvsini_2>
<dR_2>
<dvrad_2>
! Effective temperature for primary (K/1000)
! Surface gravity (log cgs)
! Surface composition parameter: depends on model grid
! Projected rotation velocity (km/s)
! Relative radius (normally 1)
! Radial velocity (km/s)
! Effective temperature for secondary (K/1000)
! Surface gravity (log cgs)
! Surface composition parameter:depends on model grid
! Projected rotation velocity (km/s)
! Relative radius (very small for only one star)
! Radial velocity (km/s)
}

If there is only one spectrum to fit, one should set default parameters for the secondary which lie within the model grid, with <R_2/R> being a very small value. If method = genetic, then the parameters must be defined as ranges, rather than initial values. The lower and higher limits for each of the stellar parameters should be entered. If the parameter is not to be varied its fixed value should be entered into the first column of the three and zero entered into the second column. Otherwise the lower limit should go into the first column and the upper limit in the second column.