SFIT2

Simon Jeffery, Armagh Observatory: September 2002

---

LATEST NEWS

Description

SFIT is a general-purpose code designed to optimize theoretical stellar spectra to an observed spectrum. It is based on models calculated with the ARMGH LTE codes STERNE and SPECTRUM, but is flexible and can be adapted to other models. It has been proven to work well with both high and intermediate-dispersion normalized spectra. An important feature of the code is that several different parameter optimisation methods are available, including Levenburg-Marquardt, Amoeba, and Genetic Algorithms.

This version combines two previous programmes, SFIT and SFIT_SYNTH, and provides the following capabilities:
1. Solves for T, log g, abundance, v sin i, R₂/R₁ for one or two stars by fitting model spectra to normalized spectra.
2. Solves for elemental abundances and microturbulent velocity for a single spectrum, given an assumed model atmosphere.

Platforms

This code is designed to run on both Linux and Alpha platforms. It has run successfully on both, but because the code is still developing rapidly, the most recent version may not!.

It may be necessary, particularly when running this code on the Armagh alphas, to increase the data limit on your current process. This can be achieved with:
> limit datasize 1048576 kbytes
> ulimits -aD (alpha) to see maximum values.

Use

While the programme expects input from "stdio", it is more natural to save commands in a file (eg "sfit_input") and run the code simply by
> sfit2 < sfit_input

If the spectra to be fitted have a filename "star_spectrum", then the best fit spectrum will be written out, together with the renormalized input spectrum, to a file called "star_spectrum.fit".

Syntax

For historical reasons, the command syntax is not yet fully stable. In general, commands may be entered at a range of levels. This is so that, for example, definitions of parameters are associated with the correct context. For example, instrumental broadening should be associated with the spectrum to be fitted (data), whilst the convergence tolerance is associated with the solution method.

command
or
command [ parameter [...] ]
or
command{  subcommand [ subcommand [ parameter [...]]] }
or
command subcommand [ subcommand [ parameter [...]]]
 

• In general lines may be broken anywhere, but there are exceptions.
• Strings beginning ! are treated as comments and ignored.
• The syntax for each command is described in detail below.

Command Summary

models, model2	sets up model spectrum grid (and for 2nd star)	solve
save_grid, save_grd2	saves rebinned model spectrum grid as binary file	solve
read_grid, read_grd2	reads model spectrum grid from binary file	solve
sterne	defines single model atmosphere (from STERNE)	synth
abundances	initialize abundances	synth
parameters	initialize spectrum fit parameters	solve
method	select solution method
gen_par	set flags for the genetic algorithm
spc_par	set flags for spectrum
continuum	select continuum renormalization method
cmask	define regions to _include_ in continuum fit
mask	define regions to _exclude_ from fit using given weights
data	input observational data
normalize	single step renormalization with no change of fit parameters
vcorr	use current model to determine radial velocity (used in subsequent fits)
solve	pursue solution by interpolation in grid
synth	pursue solution by computing new spectra
set	set specific parameters
show	show current values of specific or all parameters
end	finish gracefully

---

Examples

Example 1. Setup model grid in binary form for subsequent use.

Example 2. Fit Teff, log g and n_H to WHT/UES spectrum using a grid of helium-rich model spectra.

Example 3. Fit Teff_1, Teff_2 and radius ratio in binary, using saved model grids * WARNING - not recently tested *

---

This page is maintained by:
Simon Jeffery (csj@star.arm.ac.uk)
Last modified: July 23, 2003