11/7/2005 submitted

Conference:
Astronomical Telescopes and Instrumentation 2006
Ground-based and Airborne Instrumentation (Iye, McLean)

Title:
Infrared Multi-Object Spectrograph of MOIRCS

Primary Author:
Chihiro Tokoku

Co-Authors:
Ryuji Suzuki, Koji Omata, Masahiro Konishi, Tomohiro Yoshikawa, Tetsuo Nishimura

Abstract:
Design, development, operation and test observation results of MOS mode of MOIRCS 
are described. 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 multi-object spectroscopy (MOS) mode for the wavelength 
range from 0.85 to 2.5 micrometers. To achieve infrared MOS up to K-band, 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 nineteen masks. The masks are made of thin aluminum film. 
Slits are cut with a laser. For slits cutting coordinates, the software corrects the 
effects of thermal contraction. Masks are cooled down to below 130 K in the mask dewar 
and transported to the focal plane in the main dewar through the gate valve with 
a linear motion manipulator. Interlock is equipped on the mask exchange system to secure 
the cryogenic instrument from accident. Replacing masks can be done in a daytime without 
breaking vacuum of the main dewar by isolating the mask dewar by closing the gate valve. 
The basic idea of acquisition is to iterate taking sky images through alignment holes 
on mask until rotation and offset between alignment stars and alignment holes become 
small enough. MOIRCS/MOS mode will be open to public in late 2006. 	 

Keywords:
near infrared, multi-object spectroscopy, multi-slit mask

Principal Author Biography:
Chihiro Tokoku is a junior research astronomer of the Subaru Telescope. 
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 for commissioning of MOIRCS and 
preparing for opening to public use.