The GO specifies the desired observations on an "Observing Script" (see Figures 4.1 and 4.2). The portion above the dashed line must be completed by the GO before the TO can begin target acquisition. The portion below the dashed line is completed by the TO during acquisition.
Figure 4.1: A typical observing script for a blind-offset exposure. A 75 minute low-dispersion LWP exposure was requested. The GO provided the required offset star information. The guide star information from the exposure is provided in the row beginning with "Tracking Mode" on the lower half of the script.
Figure 4.2: An observing script for a trailed exposure. A 40.8 second LWP trailed exposure was requested. This is equivalent to a 11 second point-source exposure. Trailed exposures are always done on gyros. Under the "Comments" heading at the bottom of the script, the TO has noted the drift that occurred while the trail was being performed. In this case the drift was -2 units in FES X (about 0.5 arcseconds) and no drift in FES Y.
At the top of the script, the observer specifies the target name, 1950 coordinates, the observer's name, program ID code, target number, desired camera, dispersion, aperture, and exposure time. Space is provided for the use of an offset star, offset reference points, and information for trailed exposures.
The type of camera preparation sequence, or "prep", to be used depends largely on the exposure level of the previous image. If the previous image was overexposed by three or more times, an "overexposed" prep (i.e. XSPREP) may be recommended. If the previous image was exposed by no more than two to three times then the standard prep (SPREP) is usually sufficient. For further discussion of the effects of overexposures, see Section 4.6.
As discussed in Section 2.3, opening and closing of the large aperture can cause an FES reference point shift of up to 5 arc seconds, resulting in a miscentering of the target in the aperture. Opening and closing of the large aperture is discouraged, therefore, except in cases of strong scientific need.
For the LWR camera the "ping avoidance" technique may be requested. This technique uses a 4-minute heater warm-up before the read, to reduce the probability that LWR microphonics will contaminate your spectrum. If the 4 minute heater warm-up is not desired, circle "normal". The SWP and LWP camera reads are always "normal". For further discussion of microphonics and use of the warm-up technique, see Section 4.11.
Three processing types are available: point, extended, and trailed sources. Trailed processing also applies to multiple exposures in the large aperture. The GO may specify the spectral "registration" method (see Appendix C) after inspecting the image. The registration type defines the programs to be used by the Image Processing Specialists to locate the center of the spectrum for proper extraction. For details on image processing options and procedures, see Turnrose and Thompson (1984).
The lower half of the script completed by the TO includes the exposure start time, read time, telescope focus, guide star position and brightness, and related items concerning a history of precisely how the exposure was obtained. This is often very useful to subsequent observers who may wish to repeat an observation of the same target. In addition, it is often more efficient for the RA to calculate the position of a faint guide star from data on an archival script rather than to attempt to locate it with the FES at the time of acquisition. Observing scripts for all GSFC images are available at the observatory for GO use.