DIS REFURBISHMENT PLAN 1 Comments I received from some of you are incorporated here. The changes are that baffling is added as an important task and the computer for the slit viewer and the replacement detectors have been deferred. I know I might be offending some of you with criticisms of equipment and software. If so, I apologize. (Nobody's complained, but I know I might be miffed.) I want to be clear that DIS is an excellent example of the quality of instrumentation this observatory needs and that many of the complaints are really new requirements imposed by observing strategies and science interests that could not have been anticipated. Everyone providing input understands this and I'm confident that objective decisions will provide the optimum instrument. I have had recent conversations or correspondence with K. Anderson, J. Burns, J. Holtzman (NMSU), B. Gillespie (APO), L. Rebull (UC), J. Gunn, G. Pauls, and Michael Strauss (PU). I have also read past apo35m-dis postings, which I should have done before. Details of the correspondence and new (to me) input are at the end. PLAN 0, PLAN 1 DIFFERENCES Salaries are separated from the tasks. By adding baffles we are a bit short staffed even if we don't do the new detectors. The impact is that more work will be done by APO staff, probably extending the timeline a bit. The slit viewer upgrade is split into two parts: the camera replacement and the new computing system. A high speed camera would provide the real-time setup capability that some of us find essential. The new computing system would allow easy integration into the observatory control system and give us the ability to use the slit viewer data for more than just looking (guiding, point-to-center setups, fast remote slit viewing, etc.). The camera replacement is in this plan, the new computer is deferred. The total cost is higher because of the baffles, a better estimate of the UV coatings, and travel, which was not included before. I would be surprised if the numbers come out lower, not surprised if they were 20-30% higher. If we work hard, $65K can be encumbered by December 1996 (doing all of the first group except 2 and part of 3, which require DIS downtime in 1997, and half the travel cost). Baffling should be top priority even if it isn't fixed on the DIS structure. Items 2-8 should not be prioritized except to remove tasks that can be deferred (it does not make sense to separate 2 and 3, though). Assigning priorities to these can make for inefficient use of people time. Decisions on both the slit viewer computer and the new detectors (items 11 and 12) are deferred until, say, after the UV throughput is repaired. BUDGET ====================================================== 1. Baffling (maybe done on the telescope) $ 5K 2. UV throughput repair $12K 3. Overall throughput analysis & repair $ 9K 4. Remove noise from CCD readouts $ 2K 5. Fast slit viewer camera $ 8K 6. Reflecting air gap slits $ 5K 7. New (different dispersion) gratings $14K 8. Automatic calibration lamp control $ 2K 9. Salaries for above $20K 10. Travel and incidentals $10K SUBTOTAL $ 87K DEFERRED ITEMS 11. New slit viewer computing system $13K 12. New detectors $12K 13. New detector salary $ 8K TOTAL $120K ====================================================== SCHEDULE AND DOWNTIME Except for 2 and 3, the first 8 items can probably be done without significant DIS downtime, although we would like the instrument not to be scheduled for a few contiguous days occasionally. These tasks each take a month or two of clock time and all could probably be finished within a 1-year time frame. Items 2 and 3 require that DIS be removed from service for a few months. Alan Uomoto July 23, 1996 --------------------------------------------------------------- SUMMARIES OF COMMUNICATIONS EMAIL FROM LUISA REBULL - ROTATOR ANGLE DEPENDENT FLATS Luisa Rebull pointed out the rotation dependent flat fields (http://astro.uchicago.edu/home/web/rebull/research/rotation/). The effect is large and is probably caused by DIS seeing stray light from the telescope structure or enclosure. We might revisit the schedule for baffle installation on the telescope and consider temporary baffles on DIS or the Naysmith port if the proper fix is difficult or long-range. A shot in the dark price for parts is $5K. This might not be a proper fix (it might vignette DIS, invade the telescope beam, etc.) but it would get us decent flats. NMSU CONCERNS - THROUGHPUT and NEW GRATINGS Most important, I think, were improving throughput and new intermediate dispersion gratings. Kurt Anderson found that we have four spare DIS grating holders, so new gratings would require little effort. Replacing detectors and new slit viewer capabilities had lower priority. BRUCE BALICK'S POST ON APO35M-DIS 1. Pixel binning besides 2x2 should be available (2x1 and 3x1, for example). This might be a software enhancement (?). 2. Subraster readouts. This may not possible without major modifications to the readout electronics (?), at least if the reason is to save time. 3. New slits. New air slits are on the list of improvements and Steve Knapp has already made new quartz slit masks. 4. Spectrum undersampling. With not-so-narrow slits, spectral features are undersampled. Changing this would require a new camera and/or detector, both expensive options. JIM GUNN ON COATINGS Jim is confident that the UV throughput problem resides in three dielectric coatings: a fold mirror and the two reflections in the blue camera. Each location requires that a cemented joint be separated. The plan 0 estimate for fixing this ($4K) becomes 3x$4K=$12K. While we're at it, we should coat the back of the beamsplitter to eliminate the blue ghost. MICHAEL STRAUSS QUESTIONS Michael asked me to note that many tasks can be done without removing DIS from service for long periods. Michael also asked about the residual charge problem, and others have suggested separate red and blue channel shutters to reduce this problem. This problem should probably be attacked only if we decide not to replace the detectors, since replacing the detectors might make it go away. And finally, Michael asked about remote slit viewing: yes, it would be possible with the new slit viewer computing system, but the computer is a deferred item now. APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 21 in the apo35-dis archive. 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