To: current users of DIS on the 3.5m As most people are probably aware, we are in the process of several upgrades to DIS to improve performance. One aspect of the upgrades is that we are obtaining new gratings that we hope will 1) better match the current optics/chip in the instrument in terms of wavelength coverage, and 2) provide improvements in throughput. Once we obtain/test/install the new gratings, which we currently hope will be happening in June (although since we have not yet received the new gratings, there is some schedule uncertainty), we would like these gratings to become the "default" set of gratings; the old gratings will be retained in their current housings and can be mounted with grating swaps, but, as in the past, we would like to minimize the required number of grating swaps. The purpose of this message is to provide information about the new gratings, to propose a new naming scheme for our grating complement, and to solicit input about whether there are likely to be any issues with changing the "defaults", possibly as early as the beginning of third quarter. If all goes with with our acquisitions, our grating complement will be: ----------------------------------------------------------------------- name descrip proposed status dispersion^1 coverage^2 peak throughput A/pixel wavelength ----------------------------------------------------------------------- B300 old BL retire 2.43 4860 5000 dispersion too low for match to current chip/optics, good throughput B400 new default low/med 1.85 3700 5000 full coverage from atmospheric cutoff to dichroic w/minimal vignetting B600 old BM retire 1.23 2460 4750 full coverage but with some vignetting, throughput slightly worse B1200 old BH default high 0.62 1240 4500 high res, decent blaze for entire blue range R150 old RL retire 5.03(4.5?) 9000 ~6500 dispersion too low for match to current chip/optics, good throughput R300H old RM retire 2.26 4520 ~6500 dispersion good, but poor throughput (H stands for the manufacturer, Hyperfine) R300 new default low/med 2.26 4520 6500 new grating for full red coverage with good throughput R830 old RH high res >8000A 0.84 1680 8000 high res, good throughput, but blazed for longer wavelengths R1200 new default high (<8000A) 0.56 1120 6500 high res, blazed for shorter wavelength end of red, higher dispersion ----------------------------------------------------------------------- 1. dispersions for existing gratings from APO web page (note number for RL may be off as indicated, since web number doesn't match expectations); dispersions for new gratings are approximate 2. coverage is for 2000 pixels, but note there is some moderate vignetting (up to ~30%) at each side of the chip The current defaults are B300/R300H (BL+RM) for lower dispersion and B1200/R830 (BH+RH) for higher dispersion. The proposed "default" gratings would be B400/R300 for lower dispersion and B1200/R1200 for higher dispersion, with grating swap requests of R830 for R1200 for high res applications at longer wavelengths. If people have good reasons for wanting to keep using the old gratings slated for "retirement" after the new ones are obtained (assuming nominal performance), please communicate these reasons, and the timescales over which they will be valid, to your Users' Committee representative and to me, so we can decide on an acceptable implementation schedule. APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 964 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