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XD at Intermediate Resolution

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Grating/Camera configurations:

110 l/mm grating with short blue camera or 32 l/mm grating with long blue camera

Resolving power:

5900 with 0.3 arcsec wide slit and short blue camera or with 0.1 arcsec wide slit, long blue camera, and adaptive optics. Lower resolving powers if wider slits are used.

Typical uses:
(...and limitations)

(1) Intermediate resolution spectra of selected portions of orders 3-8 (between 0.85µm and 2.5µm in short slits as described in XD R<1800 mode. Can be used for observing at high sensitivity between OH sky emission lines at 0.9-2.2µm or between sky absorption lines at 2.25-2.5µm. 

The wavelength coverage is about one-third of that of the low resolution mode (e.g., short camera + 32 l/mm grating) and so three or more settings are required to obtain full wavelength coverage at 1-2.5µm. The positioning of the orders depends on the grating central wavelength, so in some grating settings one order may cross the small central patch of bad pixels. If this is likely to pose a problem the user should contact a member of the GNIRS science team.

Fig. 1: Cross-dispersed spectrum of the argon lamp obtained with the 111 l/mm grating set to 1.53µm, short blue camera, and 0.3 arcsec wide slit. Lines can be seen in orders 3-9 (left to right). Wavelength ranges covered are 1.95-2.13, 1.46-1.60, 1.17-1.28, 0.97-1.06, 0.83-0.91, 0.73-0.80, and 0.65-0.71 microns, respectively. Note how the orders are much more vertical on the array than when full spectra coverage is obtained in one setting (eg, using the 32 l/mm grating and the short blue camera).

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