5.2 FTS Control Menus

The menus discussed in this section are illustrated in Figures 5.2 to 5.7.

5.2.1 Scans

The Scans menu (figure 5.3) is the basic menu for all data acquisition. Many of the parameters in this menu are correlated; consequently, since changing one parameter may affect other entries, the menu is automatically updated to reflect these changes. For example, if the step size P is changed, then the `resolution' entry will change automatically to accommodate the new value of P. Before starting a scan, check that the automatically selected parameters are the ones you actually want. Also make sure that the correct filter has been selected: the current filter wavenumber boundaries are indicated at the top of the Scans form.

The following parameters can be set or entered in the Scans menu:

An exposure will start once the scan menu is accepted. An FTS Status icon similar to that shown in Figure 5.4 will appear in the upper right hand corner of the workstation screen, which contains the exposure number (see Section 5.3.3), as well as the time left before the scan is completed. The five buttons at the bottom of the status icon have the following actions:

A confirmation message will appear if any of these options is selected.

5.2.2 ZPD

Before starting a scan it is necessary to first position the carriage at optical ZPD, which is the path difference which gives the maximum fringe amplitude. The ZPD task automatically scans a portion of the carriage where this is known to occur (it is assumed that the carriage has already been set to the mechanical ZPD position, and the servo system is in fringe mode). The search for ZPD is done in two stages, the first being a crude scan with large step sizes (P 24), the second using P = 2.

There are two entries on the ZPD menu (Figure 5.5):

The above two values are automatically set and hence should not have to be changed or entered. Use of this command does, however, suppose that light is falling on the detectors through a selected filter. Once the ZPD menu is accepted, a series of scans will start to zero in on ZPD. During this procedure, an exposure icon will appear in the lower left hand corner of the workstation. As with regular exposures, the ZPD process can be stopped or aborted, using the procedure discussed in Section 5.2.1.

5.2.3 Carriage

In certain circumstances, an observer may want to manually move the carriage. There are two possible manual motions that can be specified in the Carriage menu (Figure 5.6):

The most common use of manual carriage movement is to avoid repeatedly looking for ZPD when you are making successive pairs of scans on an object with more than one filter (provided that the change of filters does not necessitate a change of beam splitters). After the first pair of scans has been completed you can select the Carriage menu, change the entry for P to the value that was used for the previous scan, set Steps to 180, and select the Forward direction. Flagging the Move option and clicking on Accept will then move the carriage back to ZPD. A new filter can then be inserted into the beam and a new scan started from the Scans form. Another application is to setup for symmetric observing mode (see Section 5.2.1). Manual carriage control is also often useful for engineering purposes.

5.2.4 TPQ

This menu (shown in Figure 5.7) provides a quick way of setting the values of T, P, and Q found in the Scans menu, but without having to start an actual scan. The entries are filled out the same as in the Scans menu. See Section 5.2.1 for a discussion of the significance of these three important parameters.

5.2.5 The Filter Table

The filter table tells the computer which filters are installed in the FTS dewars. It is filled out during the instrument setup, and is only changed when the filter configuration is altered. There is not an icon to access the filter table; rather, it can be displayed using the following procedure. First, move the cursor into a blank part of the screen and hold down the right hand button of the mouse. A menu will appear. While continuing to hold down the right hand button of the mouse, scroll down the menu to the `Session Setup' entry. Release the right hand button of the mouse, and then depress it again. A second menu will appear. While continuing to hold down the right hand button of the mouse, scroll down this menu to the `Select Detector' entry. Release the mouse button and a filter table similar to that shown in Figure 5.8 will appear.

The filter table contains the following information: the positions occupied by the various filters in the filter wheel (values 1 through 9; position 0 is always open); the name of the filter; and the approximate upper and lower boundaries of the filter response, in . Information for the three beam splitters is also displayed.

Please send comments and suggestions to: veillet@cfht.hawaii.edu