Definition of the position algnle (Insrot_PA)

FOCAS IFU has the rectangle FoV (13.5" x 10.0"), and the longer side is the slice-lenght direction.
The position angle (Insrot_PA in an OPE file) is defined to be the slice-lenght direction to the sky slit (red arrow in the figure below).
Default Insrot_PA is 0 degree.
The sky slit is located about 5.2 arcmin far toward the position angle direction. It is importatnt to confirm no bright source in the sky slit.

FOCAS IFU FoV Check with Aladin

One way to check FOCAS IFU FOV is using Aladin. When you follow the procedure below, the FoV is overlaied on your taget image in Aladin.

Originally written by Shinobu Ozaki.
Revised by Kentaro Aoki June 21, 2019