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Long Slit Spectroscopy at Intermediate Resolutions (1800<R<6000)


Grating/Camera configurations:

110 l/mm grating with short cameras or 32 l/mm grating with long cameras

Resolving power:
(λ/Δλ)

~5900 with 0.3 arcsec wide slit and either short camera or with 0.1 arcsec wide slit and either long camera. Lower resolving powers if wider slits are used.

Typical uses:
(...and limitations)

(1) Intermediate resolution spectra with 99 arcsec slit and short cameras or 49 arcsec slit and long blue camera (with or without AO). Can be used for observing at high sensitivity between the OH sky emission lines at 0.9-2.3um or between sky absorption lines at longer wavelengths) 

Minimum recommended wavelength is ~1.03 microns as with the 32 l/mm grating, and a few other narrow wavelength intervals are inaccessible (see details).

Wavelength coverage is about one third of that with the 32 l/mm grating and so,with the exception of the M band, two or more settings are required to cover each atmospheric window. While two settings are required for the "full" M window, a single setting of 4.50-5.16um covers 3/4 of the window starting at the short wavelength edge, and the remaining portion of the window (5.16-5.40um) has very poor transmission even on the driest Mauna Kea nights. Observing at this intermediate resolution in the M band is considerably more efficient than with the 32 l/mm grating and short camera, because the sky and telescope background are reduced and the array does not need to be read out as frequently.

Spectra obtained at example grating settings are shown below of an A-type star with central wavelength: 1.27um (5th order), 1.66um (4th order), 2.14um (3rd order), 3.79um (2nd order), 4.7um (1st order).

 


Example spectra:

Fig 1a: long-slit spectrum in 5th order (J-window, central wavelength 1.27um)
Fig 1b: long-slit spectrum in 4th order (H-window, central wavelength 1.66um)
Fig 1c: long-slit spectrum in 3rd order (K-window, central wavelength 2.14um)
Fig 1d: long-slit spectrum in 2nd order (L-window, central wavelength 3.79um)
Fig 1e: long-slit spectrum in 1st order (M-window, central wavelength 4.7um)