Contents: (1) Report on a new technique for observing a rapidily time-varying event with GRIM, a stellar occulation (2) problem with multiple exposures (1) Yesterday morning we attempted to observe a stellar occultation of a star by Uranus. The IR was desireable for this observation since Uranus is quite dark beyond 2um while the star is quite bright in K. High time resolution (< 1 sec) was required. Taking repeated images of the star is not practical because of the long (~5 sec) time between images. Scott Severson had experimented with decreasing the number of flushes between exposures, but this did not make a significant difference in the dead time. So we developed a telescope control macro that moved the telescope in a box pattern while each grim exposure was in process. The telescope pauses 30 times to form ~30 stellar images in a box spaced over the grim frame. Since the time of each telescope move is written to the hub.log file, a unique time can be associated with each stellar image. By requesting 40 exposures from GRIM, each 28 sec long (but see (2)) the event can be covered at 1 sec time resolution with some gaps. The dead time is 5 sec every 28 sec rather than 5 sec every 1.2 sec. Since occultations are rapidly time varying events, this gave a much higher chance of catching important sections of the event. This worked well in tests. Unfortunately clouds obscured most of the event so we did not get much useful data. It would be helpful if the time stamps were written more accurately than 1 sec. If anyone is interested in this technique, email me directly and I can provide more details and some lessons learned. (2) We have found that when more than 35 exposures are requested in the "expose" command box, that GRIM often hangs on the 35th exposure. It is not clear to me where the problem lies, but it is repeatable. APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 13 in the apo35-grim archive. You can find APO the archive on http://astro.princeton.edu:82/apo35-grim/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-grim@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO