NIRSPEC Modes and Instrument Properties
Modes
NIRSPEC has three basic modes:
- Near-infrared imaging using the Slit-Viewing Camera (SCAM)
- Faint object spectroscopy with a low resolving power (R~2,000)
- High-resolution echelle spectroscopy (R~25,000)
Table 1 provides a summary of these modes, options, and features of NIRSPEC.
| Mode | Image or Dispersion | Wavelength, Slit length, Pixel Scale | |
|---|---|---|---|
| Before Oct 2018 | After Oct 2018 | ||
| Echelle Spectroscopy | high | Wavelength range: 0.95-5.4 microns, R = 25,000 for 0.43" slit (3 pixels). Slit lengths of 12" or 24" | Wavelength range: 0.95-5.5 microns, R = 25,000 for 0.43" slit (4.5 pixels). Slit lengths of 12" or 24" |
| Low Resolution/Long Slit Spectroscopy | low | Wavelength range 0.95-5.4 microns, R = 2,200 for 0.38" slit (2 pixels). Slit length of 42" | Wavelength range 0.95-5.5 microns, R = 2,000 for 0.38" slit (3 pixels). Slit length of 42" |
| Near Infrared Imaging | imaging | Wavelength range 0.95-2.5 microns, FOV = 46" x 46" Pixel scale = 0.183" | Wavelength range 0.95-2.5 microns, FOV = 40" x 40" Pixel scale = 0.158" |
Instrument Properties
Rather than providing a cryogenic mechanism to give arbitrary slit widths, NIRSPEC employs a selection of fixed slit widths, in two lengths for the echelle mode, and a single longer length for the low-resolution mode. The orientation of each slit on the sky is different, but these values are coded into the software. A dual filter wheel in the collimated beam provides a selection of order-sorting filters, blocking filters, narrow-band filters and Lyot stops. Table 2 gives a summary of NIRSPEC's properties and design parameters. For more details, see NIRSPEC Instrument and Data Format
Table 2: Instrument Properties
| Property | Echelle Mode | Low Resolution Mode | ||
|---|---|---|---|---|
| Before Oct 2018 | After Oct 2018 | Before Oct 2018 | After Oct 2018 | |
| Wavelength Range | 0.95 - 5.4 micron | 0.95 - 5.5 micron | 0.95 - 5.4 micron | 0.95 - 5.5 micron |
| Number of settings required | 25 | 7 | ||
| Pixel scale (along dispersion) | 0.144"/pix | 0.096"/pix | 0.144"/pix | 0.129"/pix |
| Resolving Power (0.43" slit) | 25,000 | 25,000 | 2,200 | 2,000 |
| Slits Widths | 0.14, 0.29, 0.43, 0.58, 0.72" | 0.38, 0.57, 0.76" | ||
| Slit Lengths | 12" or 24" | 42" | ||
| Groove Density | 23.21/mm | 75 l/mm | ||
| Blaze Angle/Gamma Angle | 63.5°/5.0° | 10° /0° | ||
| Collimated Beam Width | 120 mm | 120 mm | ||
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