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4-m Echelle Spectrograph Update (1Mar96) (from CTIO, NOAO Newsletter No. 45, March 1996) Measurements of standard stars with the echelle spectrograph and its long cameras were made under photometric conditions on the nights of 5 September 1995 and 10 October 1995. The figure shows the overall system efficiency (defined as the fraction of photons hitting the primary, that are detected by the CCD) derived from these observations. The quantity plotted is the system efficiency at the peak of the echelle blaze function in each order. Note, that these measurements were made with a wide (10") spectrograph slit. The throughput was measured in the two configurations of the spectrograph most requested by visitors for use with the long cameras. The 79 l/mm echelle and a 316 l/mm cross disperser blazed at 4400 Angstroms in first order (KPGL-2) were used for the measurements in the blue; the 31.6 l/mm echelle and a 226 l/mm cross disperser blazed at 6300 Angstroms (G226-3) in first order were used in the red. Appropriate order blocking filters were employed when necessary to prevent contamination by higher orders from the cross dispersing gratings. [Figure not included] Overall system efficiency for the 4-m Echelle spectrograph with the long focal length cameras and Tektronix CCD (Tek 2048 #4). Curves are shown for two echelle plus cross disperser combinations: KPGL2 316 l/mm blazed at 4400 Angstroms with the 79 l/mm echelle and G226-3 226 l/mm blazed at 6300 Angstroms with the 31.6 l/mm echelle. These efficiency measurements form a portion of the calibration database for an echelle exposure time calculator. The current version of this calculator is available for use by observers and proposers via the WWW from the echelle spectrograph's on-line manual (http://www.ctio.noao.edu/4m_echelle/4m_echelle.html). Michael Keane
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