Date: Mon, 4 Mar 2002 15:11:49 -0700 (MST) Hello all, User opinions are being solicited to help us decide which gratings to make available on the new DIS. If you are a current or potential DIS user, please read this message and send your opinion to me or to your institution's User Committee representative before Monday, March 11. Here's the situation: DIS is being upgraded with new detectors, which have larger formats and smaller pixels than the old detectors, leading to greater spectral coverage and better resolution. The new detectors also have the same pixel scale, whereas the old detectors (and the gratings designed to go with the old detectors) had mismatched pixel scales. Using the same old grating sets with the new detectors would produce some rather odd combinations of resolution and spectral coverage, so we are trying to decide how to arrange the gratings for the new instrument. There is an additional incentive to this process; if we can settle on only two pairs of gratings to be permanently mounted, life will be easier for everyone all around. Observing specialists will not be required to spend an extra hour for grating changes, the scheduler will not need to arrange DIS programs carefully to avoid grating request conflicts, and observers will not have to specify gratings in their proposals or worry (much) about making a last-minute change. Minimizing the handling of the gratings would also increase their life expectancy, a significant consideration since we have seen scratches accumulating on the gratings over the past few years. Here are the expected characteristics of the old gratings with the new detectors: LOW Red LOW Blue MED Red MED Blue HIGH Red HIGH Blue Central Wave 8000Å 4224Å 7500Å 4000Å 8465Å 5000Å Wave Range 14280Å 6222Å 6426Å 3264Å 2386Å 1632Å Blaze Angle 3.43° 3.63° 6.53° 6.90° 20.57° 17.45° Lines / mm 150 300 300 600 830.8 1200 Resolution 7.0Å/px 3.05Å/px 3.15Å/px 1.6Å/px 1.17Å/px 0.80Å/px Clearly, the wavelength range of the old low-resolution red grating is excessive for the new detectors, extending well beyond the dichroic cutoff at 5350 A and the red sensitivity limits of the detector. There are two grating arrangements which I think are optimal, but there is also a third possibility which some observers might prefer. The most obvious choice for a new low-resolution set would be the old medium red grating and the low blue grating, which are reasonably well matched and offer full spectral coverage. The old high-resolution pair work reasonably well together, but another possible option is high red with medium blue, which would allow more complete spectral coverage and slightly better S:N on the blue side. Here are the three proposed combinations: (using the old grating names) Setup 1: medium red, low blue spectral coverage: >6000 angstroms either side of the dichroic at 5350 resolution ~3.1 A/pix Setup 2: high red, high blue spectral coverage: 2300 to red, 1600 to blue of dichroic resolution: 1.2 A/pix red, 0.8 A/pix blue Setup 3: high red, medium blue spectral coverage: 2300 to red, 3200 to blue of dichroic resolution: 1.2 A/pix red, 1.6 A/pix blue My inclination is to install Setups 1 and 2 more or less permanently. Observers who have a particular scientific need for the extra throughput or spectral coverage of Setup 3 would be required to make a special request with plenty of advance warning. I anticipate that most observers' needs would be satisfied by the first two combinations. However, I thought it would be best to check with the user community first and find out if my expectations are reasonable. So here are the questions for DIS users to consider: 1) Would your science needs be met by a permanent installation of Setups 1 and 2 above? 2) How often do you anticipate needing Setup 3? 3) Do any other combinations of our six gratings seem scientifically valuable to you? [Note that blue gratings cannot be used on the red side or vice versa, since the blaze would go in the wrong direction.] 4) Since we are mixing and matching the gratings that used to be called low, medium, and high, do you have any suggestions for what we should call the new combinations (aka Setups 1, 2, and 3)? Please let us know what you think in the next week or so. Russet. APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 555 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/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