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Spectral Range and Resolution

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The full GRACES spectral is 400-1,050 nm. The useful range is 420-1,010nm, and the GRACES sensitivity is at its best between 490nm and 950 nm (see the Sensitivity page for more details).

This figure shows the raw 2D spectrum of the A3 star HIP 57258. It also is the GRACES phase I first light! 

The spectral resolution was originally calculated based on ~100 lines of an observed ThAr lamp spectrum. The average resolution element for the one-fiber mode was determined to be 1.74 pixels, giving an average resolving power of R~67,500 (However, see below). For the two-fiber mode, we got 2.88 pixels per resolution element, giving a resolving power of ~40,000. The figure below shows the resolution as a function of the wavelength, from 4500 to 8500 angstroms. The solid lines are the averages for each mode, and the shaded areas represent ±1 sigma from the mean values.

Resolution of the two GRACES modes

The resolution was later measured from data processed with Opera and with DRAGRACES. We found that for 2-fiber mode, Opera reduced spectra have a resolution of 36-40k with the highest resolution between 650-900nm. For 1-fiber mode, Opera reduced spectra have a resolution of 61-65k. It is highest in the range 600-850nm, but never quite reaches 66k. With DRAGRACES, the resolution of the processed data is a bit lower, 37k for 2-f and 55k for 1-f mode. This is likely because OPERA interpolates the spectra to get a sub-pixel wavelength step while DRAGRACES just does a single step per pixel.


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