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NICMOS Data Handbook > Chapter 1: Instrument Overview > 1.1 Instrument Overview

1.1 Instrument Overview
NICMOS was built by Ball Aerospace Corporation for the University of Arizona, under the direction of Rodger I. Thompson, the Principal Investigator. A basic description of the instrument and its on-orbit performance through the Servicing Mission Orbital Verification program is provided by Thompson et. al (1998).1 We encourage all NICMOS users to reference this paper and to review the related papers in the special issue of ApJ Letters which describe the Early Release Observations and demonstrate the scientific capabilities of NICMOS. The NICMOS Instrument Handbook and the NICMOS Web pages at:
http://www.stsci.edu/hst/nicmos
are also valuable sources of information for the NICMOS user, particularly concerning technical details of the instrument, as well as a history of its performance throughout its lifetime. The NICMOS edition of the Space Telescope Analysis Newsletter (STAN), which is periodically distributed by e-mail2, provides regular notices and updates to information about NICMOS and NICMOS data reduction. Back issues of the NICMOS STAN are archived at the STScI NICMOS Web site.
The first phase of life for NICMOS took place during HST Cycle 7, with a special, supplemental call for proposals issued as Cycle 7N. Its cryogens were exhausted in January 1999, and the instrument was deactivated and subsequently decommissioned. The installation of NICMOS Cooling System (NCS) during Servicing Mission 3B in March 2002, brought NICMOS back down to cryogenic temperatures, and returned it to regular service in Cycle 11.
In September 2008 the flight software for the spacecraft computer (NSSC-I) had to be updated in order to accommodate the new instruments to be installed during Servicing Mission 4. Since this computer manages the health and safety of all the on-board instruments, including NICMOS and the NICMOS Cooling System / NICMOS Cryo-cooler (NICMOS NCS/NCC), this involved shutting down the NCS/NCC as part of the procedure, on Sept. 10, 2008. After the NSSC-I update, the NCS was restarted but went into safe mode soon afterwards, before the cool down had completed. It safed few more times with telemetry suggesting presence of icy contaminants interfering with the circulator pump. There was no indication of any damage to the mechanical systems in the NCS/NCC or to NICMOS itself, for the brief amounts of time that the system was running during each restart attempt. The circulator was allowed to warm up over a period of few months, reaching temperatures sufficiently warm to enable any contaminants to thaw and be more easily removed once the circulator was restarted. NCS/NCC was restarted and cooling was successfully commenced. NCS safed again after a couple of restart attempts but this time the safing was caused by a low speed limit violation of the Turbo Alternator, which helps to maintain the proper flow rate of coolant. The HST Project thereafter decided to defer subsequent NICMOS Cooling System startup attempts until after Servicing Mission 4.
 
This edition of the NICMOS Data Handbook is based on experience with NICMOS data obtained in Cycles 7 and 7N, before NCS installation, and in Cycles 11 through 16, after NCS installation. However, the NICMOS data reduction described in this handbook is mainly intended for reduction of data obtained in Cycles 11 and beyond. Where appropriate, major differences after NCS installation are indicated, but when reducing Cycle 7 or 7N data, be sure to also consult version 5.0 of this Data Handbook.
NICMOS provides imaging capabilities in broad, medium, and narrow band filters, broad-band imaging polarimetry, coronagraphic imaging, and slitless grism spectroscopy in the wavelength range 0.8–2.5 μm. NICMOS is an axial instrument with three adjacent but not contiguous cameras, designed to operate independently and simultaneously. Optical elements, integration times, and readout modes can be different for each. Each camera has a different magnification scale, and is equipped with a dedicated 256 256 HgCdTe Rockwell array. The approximate pixel sizes and fields of view are 0.043 and 1111 for Camera 1 (referred to as NIC1), 0.075 and 19.2 19.2 for NIC2, and 0.2 and 51.2 51.2 for NIC3.
Each camera is provided with its own set of filters, mounted on three independent wheels. There are a total of 20 filter positions on each wheel, of which one is blank (i.e., a cold, opaque filter used in lieu of a dark slide). Three of the other positions are occupied by either polarizers or grisms. The remaining 16 positions of each filter wheel are occupied by broad, medium, and narrow band filters. The list of these filters is given in the NICMOS Instrument Handbook. The filters (including polarizers and grisms) cannot be crossed with each other, and are used as single optical elements.
NIC1 and NIC2 each contain three polarizers, whose principal axes of transmission are separated by approximately 120 degrees (for the exact polarizer orientations and other details, see Section 5.6 of this manual, and also Chapter 5 of the NICMOS Instrument Handbook). The spectral coverage is fixed for each camera. The polarizers cover the wavelength range 0.8–1.3 μm in NIC1, and 1.9-2.1 μm in NIC2. Observations in the three polarizers of each camera are used to derive the Stokes parameters of linearly polarized light.
The filter wheel of NIC3 contains three grisms which can be used to perform slitless spectroscopy in the wavelength range 0.8–2.5 μm. The three grisms cover the range 0.8–1.2 μm, 1.1–1.9 μm, and 1.4–2.5 μm, respectively.
In NIC2, a coronographic spot is imaged onto the focal plane and provides a circular occulted region 0.3 in radius (with a useful effective radius of 0.4). For coronographic imaging, an acquisition sequence is required at the beginning of the observation to center the target under the occulting spot.
Each 256 256 detector array is divided into four 128 128 quadrants, each of which is read out by an amplifier at the corner of the quadrant. There are four amplifiers in each camera. Unlike CCDs, infrared array pixels are read independently and problems like charge transfer efficiency or bleeding are not present.

1
Thompson, R.I., M. Rieke, G. Schneider, D.C. Hines, and M.R. Corbin, 1998, ApJL, 492, L95.

2
To subscribe to the STAN, send a message to majordomo@stsci.edu with the Subject: line blank and “subscribe nicmos_news” in the body).


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