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CRSP Modifications--Summer 1994 (1Dec94) (from KPNO, NOAO Newsletter No. 40, 1 December 1994) During the summer, the old grating 4 (60 l/mm), which had been rendered obsolete by the installation of the 256 X 256 detector array in 1993, was replaced by a 200 l/mm grating blazed at 3 um. This new grating 4 is intended as a counterpart of grating 3 to provide intermediate spectral resolution at high efficiency over the entire range of CRSP. Grating 3 is blazed at 4 um to yield optimum performance in second order in the short end of the K band; with the 256 X 256 array, it can cover the entire J band and most of the K band at a single setting. However, the efficiency in the H band and short L band is very poor, as these regions fall between blaze orders. Grating 4 will work efficiently in the short L band (m = 1), the H band (m = 2), and the I band (m = 3). The ability to observe in the I band (0.9 um-1.2 um) in third order alleviates the order overlap encountered in fourth order with this relatively broad filter. Grating 4 will also work in the J band, at only slightly lower resolution (12.6 versus 11.3 /pixel) and efficiency than grating 3; this allows observations in both the J and H bands without the need to change gratings. Due to machining tolerances in the original construction of CRSP, the detents for the grating positions are marginally different, leading to small differences in the grating drive encoder values corresponding to zero order. Since grating 1 is the most commonly used, the zero order position was kept at 128 ecu for that grating, and settings used in the past will still be correct. However, the settings for gratings 2 and 3 will be roughly 45 ecu larger than previously. These changes have been incorporated into the `lambda' command. The new recommended settings (c.f., Appendix X, p.42, CRSP Manual, April 1994) are: Grating Band Setting Wavelength Notes 1 Unchanged 2 I 850 0.90 - 1.12 (1) Wavelengths > 1.12 um contaminated by adjacent order. J 950 H 950 K 875 L 700 3 I 1160 0.89 - 1.18 (2) Grating 4 more efficient 0.9 um-1.05 um, but this does provide single- setting I band coverage. J 1345 1.08 - 1.36 K 1595 2.01 - 2.42 L 1195 2.79 - 3.65 1375 3.35 - 4.19 4 I 1440 0.89 - 1.10 1580 1.00 - 1.20 J 1200 1.06 - 1.38 (3) Slightly lower resolution and efficiency than with grating 3, but still reasonable. H 1490 1.40 - 1.71 1600 1.52 - 1.83 K 1120 1.95 - 2.59 (4) Lower resolution than grating 3, but more efficient > 2.2 um. L 1540 2.91 - 3.53 Spectra of the Ar and Kr lamp sources have been obtained over the 0.9 um-2.5 um range with all four gratings and fit with the IRAF `identify' task. Copies of these identified spectra will be available as an addendum to the Manual and are now in the observing rooms of the telescopes. With grating 2, many of the Ar lines in the I, J, and H bands are severely blended, and one should pick well-separated lines and use a low-order solution (the dispersion is nearly constant across the array with this grating). The HeNeAr lamps in the 2.1-m and 4-m guiders yield primarily an Ar spectrum in the infrared, with a few He and Ne lines thrown in. These spectra were obtained with slit 5 to ensure separation of closely spaced lines and to yield a sharp line for the `identify' task. This will result in a small spectral shift with respect to observations taken through wider slits. Dick Joyce
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