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WORKING WITH GHAFAS
GHaFaS is the Galaxy H-alpha Fabry-Perot System. It is a new generation Fabry-Perot interferometer, whose chief and powerful advantage over traditional systems which have been used on telescopes is the high sensitivity photon counting detector. Due to the extreme sensitivity of the detector, it's very important to avoid pointing at the moon when the detector is in use, and not to use any lights: even torchlight could damage the detector when it's in operation.
Check that the position of the NASMYTH TURRET is in GRACE position (new in Oct 2016).
Typically there are few targets and exposure times are long, 2-3 hours.
Acquisition: The FOV of the Ghafas detector is 202". The observers might ask for an offset of say 1 arcminute, but they might be happy with it exactly where it lands.
Movement of target using XY HANDSET keys:
Changing between ACAM and Ghafas: Since ACAM is usually mounted at Cass, it's possible to use both instruments on one night by changing the focal station.
In December 2010, Ghafas was not properly aligned by the visiting observers. Due to the nature of the data visible on the detector, this wasn't realised until several hours had been lost. The problem was first noticed when the expected movement a the galaxy using the handset was not as expected. It even appeared that nearby stars were moving close together, rather than in the same direction. However, when viewing an 8-mag star for focussing, it appeared that the star was moving correctly. So, if the movement is not as expected, the mis-alignment of the instrument should be considered as a possible cause.
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