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.

Download the FOCAS IFU FoV file, "focas_ifu_fov.vot."
Launch Aladin.
Show your target image in Aladin.

The easiest way is to input your target name or coordinate in the "Command" field on the top of the Aladin window.

Click "File", and select "Load instrument FoV...".

Click "Load it..." button.
Select "focas_ifu_fov.vot" you downloaded.
Select "FOCAS IFU" in the table.

Click "SUBMIT" button.

The IFU FoV is overlayed on the image.
And the sky slit location is also shown about 5.2 arcmin north from the IFU FoV.
Plsease note the relative position of the sky slit with respect to the IFU FoV is uncertain (~10 arcsec).

Change the location and the positon angle.

When the FoV marker is selected, 5 green dots appeare.
Grabing the central point, you can move the FoV marker.
Grabing the corners of the FoV marker, you can rotate the marker.

Right-click "FOCAS IFU FoV" at the right of the Aladin window, and select "Properties...".

"Roll" value shows the position angle (Instor_PA in an OPE file) of the FOCAS IFU FoV.
You can also change the positon angle by changing the value.
The Insrot_PA should be specified in an OPE file.

Definition of the position algnle (Insrot_PA)

FOCAS IFU FoV Check with Aladin

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

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