12.1 Introduction to NICMOS

There are three cameras available for use on the NICMOS. The choice of camera will be dictated by the desired filter, pixel scale and field of view.

• Camera 1 (NIC1) provides the highest available spatial resolution with an 11x11 arcsec field of view and pixels that subtend 0.043 arcsec on a side. NIC1 will fully sample a diffraction-limited image at wavelengths 1.0 microns or greater.
• Camera 2 (NIC2) provides intermediate spatial resolution with a 19.2x 19.2 arcsec field of view and 0.075 arcsec pixels. NIC2 will fully sample a diffraction-limited image for wavelengths 1.75 microns or greater. NIC2 contains a coronagraphic hole and must be selected for all observations that require use of this feature.
• Camera 3 (NIC3) provides a large field of view, 51.2x51.2 arcsec, with 0.200 arcsec pixels. NIC3 will undersample the Point-Spread Function at all wavelengths, though some recovery of information may be possible by employing dithering techniques. NIC3 must be specified for all observations that use the grism Spectral Elements (see Table 12.5: Spectral Elements for the NICMOS).

Note: Target flux for NICMOS observations must be given in units of erg/(cm² sec Å) (see Section 3.9 or Section 4.8 ). The NICMOS units conversion tool on the STScI WWW pages can help you convert your source flux units.

The following table lists the permitted Instrument Configurations, Operating Modes, Apertures, Spectral Elements, and Optional Parameters for the NICMOS.

The following sections provide further details of the entries to be made on the Visit and Exposure Specifications when a particular NIC1, NIC2, or NIC3 Mode/Configuration is chosen. The two modes that will be used by the majority of NICMOS observers are described first: ACCUM Mode in 12.2 Mode = ACCUM Config = NIC1 or NIC2 or NIC3, and MULTIACCUM Mode in 12.3 Mode = MULTIACCUM Config = NIC1 or NIC2 or NIC3.

• ACCUM is the simplest operational mode for NICMOS observing. ACCUM exposures begin with one or more initial readouts of the array, followed by a specified integration period, and end with one or more readouts of the array (the number of initial and final readouts is the same).
• MULTIACCUM is a more flexible operational mode which allows for a wide variety of initial, intermediate, and final readouts. More information on ACCUM and MULTIACCUM Modes can be found in Chapter 8 of the NICMOS Instrument Handbook.
• ACQ is a specialized mode used for coronagraphic observations, and is described in Section 12.4. More information on this Mode can be found in Chapter 5 of the NICMOS Instrument Handbook.