Instrument Capabilities
NICMOS, the Near Infrared Camera and Multi-Object Spectrometer, is an HST axial instrument, containing three cameras designed for simultaneous operation. The NICMOS optics offer three adjacent but not spatially contiguous fields-of-view of different image scales. The instrument covers the wavelength range from 0.8 to 2.5 microns, and contains a variety of filters, grisms, and polarizers. Each camera carries a complement of 19 optical elements, selected through independent filter wheel mechanisms, one per camera. In order to allow operation of the NICMOS detectors and to minimize the thermal background of the instrument, NICMOS needs to be cooled to cryogenic temperatures.
The basic capabilities of the instrument (Table 2.1), and the chapters which discuss them are:
Table 2.1: Overview NICMOS Capabilities
| Mode |
NIC1 |
NIC2 |
NIC3 |
Comments |
| Imaging |
|
|
|
|
|
|
11x11 |
19.2x19.2 |
51.2x51.2 |
|
|
|
0.043 |
0.075 |
0.2 |
|
- Sensitivity limit (J, H, K)1
|
24.5,23.2,- |
25.8,24.6,20.8 |
26.1,25.5,21.6 |
S/N = 3, texp = 3000 s |
|
|
1.0 |
1.75 |
- |
|
| Grism Spectroscopy |
|
|
|
|
|
|
|
|
MOS slitless |
|
|
|
|
|
200 |
per pixel |
-
  (µm)
|
|
|
0.8-1.2 |
G096 |
|
|
|
1.1-1.9 |
G141 |
|
|
|
1.4-2.5 |
G206 |
- Magnitude limit (Vega H-band)1
|
|
|
21.4,21.1,18.0 |
A0V, S/N=5, texp = 3600 s |
| Polarimetry |
|
|
|
|
|
|
0, 120, 240 |
0, 120, 240 |
|
|
- (µm)
|
0.8-1.3 |
1.9-2.1 |
|
|
| Coronagraphy |
|
|
|
|
|
|
|
0.3 |
|
cold mask |
1 Limiting magnitudes are from the NICMOS ETC (see Chapter 9). Infrared passbands (J,H,K) are defined by Bessell and Brett (1988, PASP, 100, 1134).
|
- IR imaging: NICMOS provides its highest sensitivity from 1.1 to ~2 microns, where it is superior to an 8m class telescope, and better sensitivity than the ACS for all observations for wavelengths longward of ~1.0 microns. Chapter 4 discusses the overall throughput of NICMOS and the optical elements available in each camera. The low background which HST offers between 0.8 and 2 microns will allow deep photometry. Our estimates of limiting sensitivities per pixel to give a 3
detection in a 3,000 second integration are given in Table 2.2 for the worst dark current assumptions (see the last section of this Chapter and Chapter 8 for a discussion on the dark current).
Table 2.2: Limiting Sensitivities in Janskys for S/N = 3 detection of a point source in a standard aperture of diameter 1", 1", and 2" for NIC1, NIC2, and NIC3, respectively, after 3,000 seconds for worst case dark current assumptions1,2.
Camera |
Filter |
Bandwidth (microns) |
Limiting Sensitivity |
|
|
|
|
|
J  24.5 |
|
|
|
|
J 25.1 |
|
|
|
|
H 23.2 |
|
|
|
|
J 25.8 |
|
|
|
|
H 24.6 |
|
|
|
|
K 20.8 |
|
|
|
|
J 26.1 |
|
|
|
|
H 25.5 |
|
|
|
|
K 21.6 |
1 Size of apertures used for the NICMOS standard star photometric calibration.
2 Limiting magnitudes are from the NICMOS ETC (see Chapter 9). Infrared passbands (J,H,K) are defined by Bessell and Brett (1988, PASP, 100, 1134).
|
- Grism Spectroscopy: Camera 3 has three grisms which provide a multi-object spectroscopic capability with a resolving power of R ~200 per pixel over the full field of view of the camera. Their wavelength ranges are 0.8 to 1.2 microns, 1.1 to 1.9 microns, and 1.4 to 2.5 microns. Because the grisms are slitless, the spectra of spatially resolved objects are confused and multiple objects can overlap.
- Imaging Polarimetry: Three polarizing filters with pass directions of 0, 120, and 240 degrees are provided for the wavebands 0.8-1.2 microns in Camera 1 and 1.9-2.1 microns in Camera 2.
- Coronagraphy: A 0.3 arcsec radius occulting hole and cold mask, in the intermediate resolution Camera 2, provides a coronagraphic imaging capability.
Chapter 5 discusses these three special capabilities in more detail.
