Building Sequence Database Files for the
Hopkins Ultraviolet Telescope
For most situations, HUT observations can be specified in a
straightforward manner by selecting a spectrograph aperture, door
state, acquisition mode, observing mode, guide stars (if any), and by
noting any special Target Procedures. (These items will be described in
more detail below.) However, when necessary, HUT can be operated in
several different ways that allow considerable flexibility. For
instance, on certain observations, it may be desirable to change the
observing mode part way through an observation (say from high time rate
mode to histogram, or vise versa) or to switch from one spectrograph
aperture to another (say on a planetary nebula, going from a circular
aperture on the central star to a nebular aperture).
Changes such as these are called dithers and can be specified with the
SDF entries beginning with "Primary" and "Secondary" (e.g. Primary_slit
and Secondary_slit). Likewise, you may decide that it is advantageous
to offset from the initially specified position to a second position, or
even a third or a fourth. Such offsets can be specified with the
entries beginning with "Offset_n" (n = 1-3) in the SDFs. It is even
possible to specify a raster pattern of positions, which use the SDF
entries beginning with "Mirror".
However, these sorts of offsets are accomplished by moving the HUT
primary mirror with one or more motors, and are only practical for
offsets of up to about 2\(fm (both because of the optical performance of
the telescope off axis, and because of the time it takes for the mirror
motions to take place, roughly three minutes per arcmin). It is not
practical in most cases, for
instance, to use this capability to hop on and off an object repeatedly
to try to measure airglow for removal in later data reductions
(although in certain cases this may be an option). Because these modes
of operation are used relatively infrequently, we will not describe them
in detail here. However, please refer to Appendix A or check with one of
the "experts" if you think one of these techniques might be useful for
your observations.
This document was translated by mm2html v1.3 on 13.07.94.
Jon