Session 7 -- Interactively obtaining 2-D Gaussian source profiles

  In some of the earlier sessions you saw how to profile a galaxy in terms of an ellipse using ELLPRO and ELLFOU. Sometimes in astronomy it is useful to profile a source (or sources) in terms of 2-D Gaussian functions, this is especially useful for users of JCMT data (see also JCMTDR). In ESP this operation is performed by the application GAUFIT.

GAUFIT is similar to ELLPRO, SECTOR and ELLFOU in that it may be operated using a cursor or a simple text file to select the source position(s) that must be examined.

GAUFIT now contains two distinct fitting algorithms: the original one, which obtained the fit parameters by hunting through a region of parameter space constrained by you, and a new one (as of version 0.9), which uses a non-linear least-squares algorithm to obtain the parameters and their uncertainties. For further details on the new algorithm, see the detailed description of GAUFIT in section B.1. The interface has not changed radically, but I will show two complete examples below.