Apache Point Observatory 3.5m User's Committee Meeting December 17, 2001 Attending: Mike Shull, Bruce Gillespie, Ed Turner, Michael Strauss, Lew Hobbs, Bruce Balick, Jon Holtzman, Rene Walterbos, Alan Uomoto, Jon Morse Agenda: -Current status of DIS upgrade -Results from the Board of Governor's meeting -Discussion of future priorities for the observatory: instrument and telescope projects. *********************Status on DIS upgrade.****************************** There is good news and there is bad news. The good news is that the CCD linearity and full-well problems that have been stalling progress at UW have been solved. However, as of late last week, the red chip was significantly contaminated by some sort of deposit on its surface. People are trying to figure out what happened, what the contaminant is, how serious it is, etc. The plan had been to install the new chips in the instrument during the January bright run, but this latest set-back makes this unlikely (although not impossible). More news will be forthcoming, as this contamination problem gets sorted. out. Over the last months, Ed Turner has been scheduling blocks of time during which the DIS is not scheduled, with the upgrade in mind. However, the schedule for the upgrade has slipped enough times now that it is no longer worthwhile doing this, and he will no longer distort the schedule. Thus when the upgrade actually does happen, there will inevitably be some DIS users who will end up having to switch their time, or go to a back-up program with a different instrument. ***********What happened at the Board of Governor's meeting. ************** The budget requests for operations and sinking funds were accepted. The Capital Improvement Fund (CIF), which is used for improvements around the telescope, has been incremented slightly. Ed Turner was reappointed as director of the 3.5m. Congratulations from the User's Committee! There was much discussion of mid-term and long-term plans for the telescope, which in fact is the next item we discussed in the user's committee meeting. ***************Next Year's Priorities************************* The CIF funds are meant for upgrade to the telescope and/or instruments, and are roughly of the order of $300K/year. Now is the time to set priorities over the next year or two for what to do with this money. First, there are two CIF projects from 2001 that will be continuing into 2002: The DIS upgrade (see above) including new detectors and improvements to the optics. The telescope observing software upgrade, spearheaded by Russ Owen and Craig Loomis, now in alpha testing. There is also a major telescope improvement item in progress, namely work on the baffling. On the table at the moment are four major possible initiatives: -The new top-end, with a new more rigid support structure. This would include mechanisms for closed-loop focussing, but does not include earlier suggestions of tip-tilt or fast guiding. -Upgrades to the U. Chicago Echelle spectrograph. -Upgrades and enhancements to the planned NIC-FPS, the near-infrared imager which the U. Colorado folks are building. -A near-infrared spectrograph to be built by JHU. We had a detailed discussion of the three instrumentation programs. -Echelle Spectrograph Lew Hobbs: Don York has written a document describing the current status of the instrument, stressing the fact that it is read-noise limited for objects much fainter than V=16 (given the fact that you can't integrate too long without being overwhelmed by cosmic rays), and its resolution is limited by its pixel size. This document can be read on the web at: http://www.astro.princeton.edu/APO/echelle_dec2001.note If one could upgrade to a new Marconi 4KX2K chip with substantially smaller pixels and lower readnoise, one would avoid both these problems; the ability to go to fainter objects being the main science driver. The current set-up (with readnoise of 7 e-) gives complete spectral coverage from 3600-10,000 A. With the new chip, the spectral coverage would be quite similar, although there would be gaps beyond 9400 A. The Marconi chips are the same that will be used in WFPC3 on HST. These are said to have very low fringing even out to a micron. These chips deliver readnoise in the range of 2-5 e-; we would definitely want one closer to the lower end of that range! It is unclear whether we want a blue- or red-optimized chip; indeed, the user's committee would like more details on the properties of the chip. With the current chip, the instrument detects 10 e- per hour per pixel near 7000 A (the peak of its response), or 50 e- per hour per resolution element. This means that you're readnoise limited in this time, although with the new chip, you beat the readnoise limit in two hours integration (which gives you an acceptable cosmic-ray rate because of the smaller pixels). Thus, an all-night exposure made up of 5 two-hour exposures on a V=19 objects gives S/N = 22 per resolution element at 7000 A. In addition, they will also put in an antireflection coating on some of the refracting elements, improving the throughput by a factor of 2 (a factor not taken into account in the above calculation. The guider can't currently work much fainter than 16, so it would be necessary to upgrade the guider to take advantage of the ability of the spectrograph to go substantially fainter. Note that with the ability to go fainter and observe large numbers of extragalactic objects, a much wider complement of the ARC community will be interested in using this instrument. -NIC-FPS: Current status and possible upgrade There is a pair of PDF documents describing this instrument at: http://www.astro.princeton.edu/APO/nicfps1.pdf http://www.astro.princeton.edu/APO/nicfps2.pdf John Morse: When U. Colorado joined the ARC consortium, they agreed to build a 1KX1K near-infrared imager, called NIC-FPS. They are now considering two possible enhancements of this, for which they are asking for CIF funds: 1. To build the optics and dewar large enough such that if in the future, funds are found for a 2KX2K chip, that it can be put into the existing instrument. OR 2. To put this instrument on a dedicated corner port, which would require acquiring a rotator and guider for it. For option 1, building the instrument to make room for a 2KX2K instrument (0.3" pixels, or 10 arcmin for the full instrument), would require 7" optics. These optics are quite expensive, and outside the current budget of the instrument; the difference would be requested from CIF funds. Because these optics are more complicated, they would take substantially longer to build, meaning that the final delivery of the instrument would be roughly one year later. That is, the current baseline plan has the 1K instrument delivered in late 2003; if it were built with the larger optics, it would see first light a year after that. A major main science driver for the wider field of view is surveys of diffuse Galactic nebulae. The current plan with 1K optics would be first light in late 2003. With the 2K optics would be a year after that. The science case for fast instrument change (i.e., 1 minute rather than 15 minutes for a normal instrument without a dedicated port) needs further discussion. GRIM (256X256) has a read-noise of 150 e-, while modern chips from Rockwell have 10 e- readnoise; a huge improvement! There are NGST prototype devices, which have a fast-read guide mode, allowing an increase in dynamic range. Downstream, we could consider a 4KX4K imager, made of a mosaic of 2K's. A number of people are now figuring out how to package such mosaics. -A JHU-Chicago Near-Infrared Spectrograph Alan Uomoto: There are funds available to build an instrument at JHU. A brief e-mail describing the proposed instrument can be found at: http://www.astro.princeton.edu/APO/jhuinst.note The SDSS has discovered lots of objects which require follow-up with near-IR spectroscopy, especially high-redshift quasars and brown dwarfs. Thus we suggest building a near-infrared spectrograph, which could cover the spectral range from 0.85 to 2.4 microns (zJHK) in two passes at resolution R=500. There could be a series of grisms on a turret wheel, offering resolutions up to 4000 (although at lower throughput), although the final choice of resolutions is still to be decided. There would also be a slit wheel, with slits of width 0.5" to 2", and possibly a Integral Field Unit as well. -Concluding remarks and miscellaneous This represents the start of what should be an ARC-wide discussion of what our priorities for the next few years really are. There will be a pair of face-to-face discussions of this at the upcoming AAS meeting (see apo35-general #533): Tuesday, January 8, 5:30-7:30 PM Wednesday, January 9, 3:30-5:30 PM Both will be held in the Bancroft Room at the Hilton (i.e., the hotel at which the AAS meeting is being held). If you are planning to attend, please be sure to let Gretchen (gretchen@apo.nmsu.edu) know. On other instrumentation news: Chris Stubbs' views of his planned wide-field optical imager for the 3.5m are changing; he is now considering using a series of dichroics to image simultaneously in many bands. This is at least partly due to the realization that our f/10 secondary isn't ideal for wide-field instrumentation. Morse: We've been talking about building an f/5 secondary for ARC, which would allow a much wider field of view. This would require retrofitting current instruments, of course; it is also quite expensive. There was some discussion about whether it would make sense to have two secondaries for the telescope, and mechanisms for swapping them. Finally, there is one open half-nights coming up: namely the first half of Dec 28. If you're interested, please let Ed Turner know as soon as possible. Minutes of last meeting approved. The next meeting will be held Friday, January 18, 2002, at 11:30 AM East Coast time. 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