Date: Mon, 10 Dec 2001 23:11:28 -0500 From: Alan Uomoto To: elt@astro.Princeton.EDU Subject: IR spectrograph basics Ed, Here's a description of the infrared spectrograph. It's positioned as a relatively inexpensive instrument that can produce excellent science by virtue of its availability to SDSS institutions. Although a lot of SDSS data will be public by the time this is built, local interest in SDSS will continue to be high and the observing lists built from SDSS and 2MASS catalogs will not be tapped out before this instrument is old. This version is slightly different from previous incarnations; we're tuning in light of improved cost estimates and better focused science goals. You can release it to the users committee for informational purposes. Alan ===== The IR spectrograph will be optimized for low to medium resolution point source spectroscopy between 0.85 and 1.7 microns. A selection of resolving powers such as R=500, 1000, and 2000 will be available. The specific science context is SDSS followup of high redshift quasars and brown dwarfs. Other design drivers are cost and throughput. Additional features such as long-slit spectroscopy, higher resolution, coverage to 2.5 microns, and imaging in J, H, and Ks are likely as long as their inclusion does not compromise the primary requirements. Note that CU is planning to provide a comprehensive imaging solution. The optical design will use a low order grating or grism. High order cross dispersed systems cost more and have lower efficiency. Projected pixel size on the sky will be approximately 0.3 arc seconds and we will consider image slicing to improve throughput. The detector will be a Rockwell 1024x1024 HAWAII PACE device sensitive between 0.85 and 2.5 microns. We will use a four- channel SDSU (Leach) controller to read the array and a CTI refrigerator to cool it and the optics. We expect to contract Infrared Labs to design and build the vacuum vessel, mechanical systems (filter/grating wheels), and dewar feed-through connections. The optical design will be done at JHU as will the opto-mechanical design and construction. Optics manufacturing will be outsourced to commercial vendors. Integration and testing will be done at JHU labs before delivery to APO. Our zeroth draft schedule: Six months for design and review, 18 months for major construction and procurement (based on vendor quotations), three months for assembly, testing, modification, and procedures development, and three months for laboratory characterization and observatory integration. This is followed by delivery to APO and two or three months (elapsed time) of engineering shakedown. Total elapsed time is just under three years. Alan Uomoto December 10, 2001