OSIRIS Detector Position Angle

The difference between OSIRS imager PA and spectrograph PA is 42.5 deg. PA in OSIRIS GUIs is spec-centric, while in AO guide star tool it is imager-centric. When on-sky in the imaging mode, observers must enter correct PA values in the OSIRIS Telescope GUI to correctly orient the imager detector. The conversion is

posang in OTGUI = imag_PA (from guide star tool) - 42.5

When in sky coordinates,

PA in OOPGUI = imag_PA (from guide star tool) - 42.5

In the following example, the desired imager PA is 0 deg in sky coordinates. Because OSIRIS tools are spec-centric, PA in OOPGUI and posang in OTGUI is -42.5 deg.

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Note that there is a 48 deg offset between OSIRIS spec PA and Sky PA displayed in FACSUM. The conversion is

Sky PA in FACSUM = spec_PA + 312 or

Sky PA in FACSUM = spec_PA + 48