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NICMASS at the Feed (1Mar95) (from KPNO, NOAO Newsletter No. 41, 1 March 1995) In collaboration with Mike Skrutskie and Mike Meyer (U. of Massachusetts), we have investigated the performance of the Coude‚ Feed Spectrograph to a wavelength of 1.8 um, using a 256 x 256 HgCdTe NICMOS3 array camera installed at the Camera 5 focus. The NICMASS camera is a stand-alone system consisting of a cryostat/controller, power supply, and a 486-33 PC host computer. The dewar is mounted on a special fixture at the same location as the CCD used for optical work. The system contains no cold foreoptics except for filters used for order separation and background rejection. The filters and array are operated by the host PC, which is located in the observer's room adjacent to the normal observer's workstation (Indigo). The user interface is a menu operating in a DOS environment, with the images being stored on the PC hard drive; at the end of the night, the image files are transferred to Indigo via ethernet for conversion into FITS files and IRAF images. The PC has a primitive quick-look capability for evaluating data. A comprehensive description of the system may be found on the World Wide Web at http://scruffy.phast.umass.edu/Irlab/NICMASS/nicuser.html. We have evaluated the performance of this system in two configurations: grating B / long collimator and echelle / short collimator. With grating B, one operates in 1st order, and the broadband I, J, and H filters are sufficient for background rejection (although the H filter does admit some thermal background). The high orders (m~56/l æm) used for echelle operation require narrowband filters for order separation. Efficient operation beyond 1.8 æm is precluded by the large ambient thermal background. [Figure not included] Spectra of four carbon stars obtained with NICMASS using Grating B, clearly showing the Ballik-Ramsey 0-0 bandhead of C2. The following table gives estimates of the characteristics and performance of the NICMASS setup based on our evaluation tests. A number of points should be emphasized: 1) Because the quantum efficiency of the NICMASS detector falls with decreasing wavelength, the throughput will be roughly half that listed in the J band, and about a third in the I band; 2) Since grating B is used in 1st order, the dispersion will be constant and the resolution will decrease proportionally with wavelength; 3) The echelle observations employed a 1.644 æm filter with significant thermal leakage, resulting in additional background shot noise. Grating: B echelle Collimator: long short Pixel Scale: 2.6" 1.8" Wavelength (um): 1.6080; m=1 1.6475; m=34 Resolution: 7000 43000 Throughput: 0.11 0.034 S/N (est)*: H=9 mag H=5 mag *estimates for S/N=10 in 600s We are offering to support the use of NICMASS at the Coude‚ Feed Spectrograph for a limited amount of shared-risk observing beginning in the fall 1995 semester. Prospective users should plan on becoming familiar with the operation of the system by referencing the description available on the World Wide Web; our resources are unlikely to permit upgrading the existing PC control environment. The NICMASS system is also used at other facilities and may not be available for the entire semester. We are purchasing a well-blocked narrowband filter centered at 1.56 æm for use with the echelle; the other narrowband filters in the cryostat have poor rejection of thermal background and are less suitable for high-resolution spectroscopy. Prospective users should contact either of the undersigned (rjoyce@noao.edu; khinkle@noao.edu) for information specific to their intended program. We wish to acknowledge Mike Skrutskie and his collaborators at the University of Massachusetts for offering the use of NICMASS to the community and for their efforts with the instrumental setup at the Coud‚e Feed. Dick Joyce, Ken Hinkle
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