Minutes of APO 3.5m User's Committee Phone Conference March 11, 1996 Attending: Alan Uomoto, Bruce Gillespie, Ed Turner, Lew Hobbs, Michael Strauss, Rene Walterbos, Alan Uomoto, Julie Lutz, Alan Diercks Agenda: Dormitory Policy. Observing Specialists and their role in monitoring weather conditions. Status update since last month. Enclosure Wheel. Throughput issues. Instrument engineer. Discussion of secondary. Schedule. How to structure these meetings. Dorm Policy: People should file reservations at least 5 days in advance. This is necessary in order to schedule the housekeeper properly. Late reservations may be refused (you will be supplied with a list of local hotels where you may make your own arrangements) if no cleaned rooms are available and if there is no legitimate reasons the reservations could not have been filed on time. Observing specialists have the responsibility to decide when to close the dome. Please do not challenge or argue their decisions; also, once the dome has been closed, they will closely monitor conditions and keep you informed; don't bother them by pinging them every few minutes. See the criteria for dome closure on the observatory web site. Institutions are charged when the telescope time is lost due to bad weather. For a future meeting, should we modify this charging system? Status report: Finishing 1 week shutdown. Tightened up vanes holding up secondary to try to get rid of some harmonic motions (10 Hz and 20 Hz; sound familiar?). So this is believed to be one of the primary sources of vibration (WIYN may have similar problems). The telescope has been recollimated. Some hints that the focal plane may be tilted relative to the instrument rotation plane. May require adjustment of the tertiary, to fix this. Bruce believes that half of the cause of the poorer seeing is due to various vibrations, and half due to the nature of the secondary. The process of pinning down these vibrations is continuing; shall we pre-empt more engineering time for this? The worst cracked wheel is to be replaced over the next few days. It should be done by Wednesday, but it might take longer! The other wheels (in much better shape) will be replaced over the next year or so. It may be that the original wheels were never flame-hardened. The DIS apparently has a narrower slit than stated; it is 1.0 arcsec, not 1.5 arcsec wide, according to Karen Gloria (apo35-dis message #11). Throughput of telescope: There have been two recent, independent determinations of the throughput of the DSC, by Krys Stanek and Xiao-Hui Fan. Numbers are ~15% in g and r, very similar to numbers from May '95 by Richmond and Stanek. Why is it so low? There is also anecdotal evidence that the DIS has low throughput, especially in the red. Michael Strauss reports taking spectra of red giants, and having the blue saturate *well* before the red. The total throughput is such that "it doesn't feel like observing on the 3.5m telescope". Jon Davis and Jon Brinkmann will have the job of measuring and characterizing telescope and instrument behavior. Now have two instrument engineers. Jon Brinkman is spending a few months in Princeton working on the SDSS camera with Jim Gunn. There is An engineer named Steve Knapp will arrive at the site in a week or two for three to six months or so to take Jon's place while he is away. The question of the overall throughput of the telescope and instruments is high priority! The secondary and the image quality: If the seeing is getting as good as 0.7", does that weaken the case for getting a new secondary? Is the secondary much better than we think? It remains somewhat ambiguous whether the secondary is indeed the cause of the poor seeing. The ultimate test would be a prime-focus Hartman test. Bruce argues for a new secondary truss to carry out this test (of the order of $12K). Another possibility would be to do an full-aperture test at one of several labs. This would be much more detailed than would be the profilometry that already exists. This would have the advantage of being quick; it would take all of a week. It would cost ~$5K. Bruce will look into these various options. Question: is the poor seeing all simply a problem of poor collimation? Answer: Apparently not. Schedule has two week-long engineering shutdowns; one of these could be used to do this test. One other test would be to rotate secondary by 120 degrees. This would be of the order of a week. Schedule is about to come out. Engineering time next quarter is 20% (was 28% last quarter, 40% quarter before that). How best to run these meetings? Should we have a written progress report once per meeting? It puts time pressure on Bruce. Perhaps Bruce should put together a list of concerns once a month; in a sense, suggest agenda items for discussion. Rene: the members of the user's committee should bring up those issues that concern the users. All committee members should test their SLIP connections at their home institutions. Next meeting, Monday, April 8, 12 PM EST. APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 53 in the apo35-general archive. You can find APO the archive on http://astro.princeton.edu:82/apo35-general/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-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO