Yet Another Fitting Tool

What is Yafit?

Yafit is a tool for fitting curves. Although it could be used in other contexts, it is mainly intended for fitting observed photometric data to calculated model spectra. In general one uses it by preparing a file containing one or more sets of observations, preparing a file containing a number of model spectra, and then running the fitting program which identifies the model that most closely fits each set of observations. The results can be viewed graphically and/or output in a number of formats.

Yafit was developed for the DS4 design study of VOTech within the AstroGrid project. It is written in pure Java and licensed under the GPL. The current release (version 0.1b) is distinctly experimental and may undergo significant changes.


Yafit is not primarily a graphical application, but visualisation of the data is available at various stages so you can see what's going on - it is much easier to decide whether you trust a fit between a spectrum and observations if you can see it graphically than just by examining some χ2 values.

Yafit fit task GUI screenshot

The image above shows (in black) a set of photometric observations with wavelength band-passes (horizontal bars) and flux measurement errors (vertical bars) along with (in colour) two of the input model spectra which provide the best fit to these observations.


A tutorial and reference user document is supplied explaining how to use the program. It is available in various forms:


The current version of Yafit is v0.1b, released 22-Feb-2007.

To run Yafit you will need just a Java installation (J2SE1.4 or later) and the yafit.jar file below. On Unix-like operating systems the yafit invocation script is also convenient. Instructions on how to run it can be found in the manual.

Other resources you may be interested in are:


If you have any comments or queries, please contact the author:

Mark Taylor, Astrophysics Group, Bristol University
WWW: http://www.star.bris.ac.uk/~mbt/
Mail: m.b.taylor@bristol.ac.uk