LONGSLIT

LONGSLIT is designed primarily for the analysis of long-slit spectra, although this is mainly a matter of the display options available--the fitting routines, for example, can cope with three-dimensional data.

The basic method of operation of LONGSLIT is as follows:

1. Locate lines. This is done by extracting part (or all) of the image and displaying it. The user is then required to mark to either side of the lines with a cursor and to identify the lines so located. Alternatively CLONE (see section ) may be used. A great advantage with CLONE here is that, since the data is calibrated, for a lot of data the tram positions will be the same. This makes CLONING in batch very useful, since only one spectrum need be calibrated before submitting a job to calibrate the rest and then perform Gaussian fitting. This part is the same as for ARC2D (see section ).

2. Choose the fit type. The type of fit to be performed is entered into the array .RES.CONTROL (see appendix  for a description of the results structure), for the relevant line and cross-section. This defaults to a single Gaussian with a base.

3. Perform the fit. The fit type is read from .RES.CONTROL, the fit is performed, and the results are stored in .RES.DATA.

4. Output results. This can be in the form of plots or tables for a range of variables.

The fact that LONGSLIT uses its own structure in the data file (the .RES structure, see appendix ), means that the different stages above can easily be carried out at separate times, without needing to stay in the program between them.

There are two principle modes of operation for line fitting:

AUTO mode

In this the fits, blocking etc. are defined beforehand, and then performed without any further reference to the user (except for interactive multiple fits). This can be carried out in batch, thus saving time at the terminal.

MANUAL mode

In this the user can choose the blocking and fit type for each line as the fits are made, or the fit types may be defined in manual mode, but actually performed in AUTO mode, in batch for example. It is also possible to combine any range of cross-sections for a fit. Any previous fits may be displayed (this is the default), and it is possible to scan though the data, either individual cross-sections or with whole window's being averaged up for each plot.

If you are unfamiliar with LONGSLIT you should first read sections , and . If you get stuck try looking at section .