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Spectroscopy

GRACES performs high-resolution echelle spectroscopy between 400 and 1,0 nm. It is offered in two spectroscopic modes.

 

  • 1-fiber (object-only) mode, in which we only collect the spectrum of the star and neglect that from the background sky. The image of the single fiber is sliced in 4 at the spectrograph entrance, which provides an average spectral resolution of R~67,500 (as measured during phase I commissioning). It is recommended mode for brightest targets (V<19 mag) that outshine the sky background.

  • 2-fiber (object+sky) mode, in which the spectrum of the star and of the background sky are recorded simultaneously on the CCD (with orders interleaved). The image of the two fibers are sliced in 2 each at the spectrograph entrance, which provides an average spectral resolution of R~40,000 (as measured during phase I commissioning). Note that you may want to orient the "Sky fiber", using the instrument Position Angle, so it does not fall on another source. The image below shows how the "Science" and the "Sky" fibers are oriented.

 

 

Orientation of the fibers, when the instrument Position Angle (PA)

is 90°. In this case, the "Sky" fiber is 45.07 arcsec South of the

"Science target. If PA=, then the "Sky" fiber is towards the East.

 

Most of the "work" is done by the ESPaDOnS spectrograph. The Gemini user has to choose a spectroscopic mode, and to prepare the acquisition. The acquisition is done using GMOS imaging mode. See the following pages for more details.