Author Submission Conference: Ground-Based Instrumentation (AS06) Chairs: Masanori Iye Alan Moorwood Submitted: Nov/24/2003 Title: Infrared Multi-Object Spectrograph of MOIRCS Author: Chihiro Tokoku, Ryuji Suzuki, Koji Omata, Tetsuo Nishimura Abstract: MOIRCS (Multi-Object Infrared Camera and Spectrograph) is one of the second generation instruments for the Subaru Telescope and provides imaging mode with 4' x 7' field of view and low/medium-resolution multi-object spectroscopy mode for the wavelength range from 0.85 to 2.5 micrometers. This paper describes the design, development, operation and test observation results of its multi-object spectroscopy (MOS) mode. The MOS mode uses cooled multi-slit masks and a mask exchange system in cryogenic environment. The masks are housed in a vacuum dewar attached to the MOIRCS main dewar and separated by a large gate valve. The mask dewar is equipped with its own cryogenic cooler and a vacuum pump and can store twenty-four masks. The masks are made of thin aluminum film. Slits are cut with an electric discharge machine (EDM). For slit cutting coordinates, the software corrects the effects of the thermal contraction and distortion of the optical system. The masks are cooled down to below 150 K in the mask dewar and transported to the focal plane in the main dewar through the gate valve with a linear motion manipulator as needed for MOS observation. Replacing the masks can be done in a daytime without breaking vacuum of the main dewar by isolating the mask dewar by closing the gate valve. This system provides multi-object spectroscopy up to more than fifty objects at a time and up to K-band by the use of two HAWAII 2 MCT arrays. The observation of the MOS mode starts in March 2004. Principal Author Affiliation: Subaru Telescope 650 North A'ohoku Place Hilo , HI 96720 U.S.A. Phone: +1-808-934-5080 Fax: +1-808-934-5984 Principal Author Biography: Chihiro Tokoku is a graduate student of Astronomical Institute, Tohoku University. She received the B.S. in Physics from Tokyo Metropolitan University in 1998, and the M.S. in Astronomy from Tohoku University in 2001. Her research interests are observational study of large scale structure and galaxy evolution in the early universe. She is currently working on the development of MOIRCS for the Subaru Telescope and hopes to utilize the instrument for her research goals. Correspondence for Secondary Authors: Ryuji Suzuki 650 North A'ohoku Place, Hilo, HI 96720, U.S.A +1-808-934-5957(tel) / +1-808-934-5984(fax) Koji Omata 650 North A'ohoku Place, Hilo, HI 96720, U.S.A +1-808-934-5093(tel) / +1-808-934-5984(fax) Tetsuo Nishimura 650 North A'ohoku Place, Hilo, HI 96720, U.S.A. +1-808-934-5085(tel) / +1-808-934-5984(fax) Presentation Type: Poster Presentation Keywords: Infrared astronomical instrument, near-infrared, multi-object spectroscopy, multi-slit mask