HET Position Angle Calculator for the HRS

This program enables a PI to determine what position angles of the sky fibers with respect to the science fiber are allowed for a given DEC and track. The East and West tracks may have different position angle restrictions since the rho motor allows only a 180 degree rotation range. In addition there is an inherent rho rotation during any trajectory, particularly significant in the North. Warnings will be given for any potential conflict.

The current limits for the rho rotation are -110 and +90 relative to the parallactic angle for any track.

We define position angle as positive measured North through East. Due to confusion between the optimized image quality of the parallactic angle, par, and position angle of 0, we limit the PA to be between 0.1 and 360.0 i.e. PA(North) = 360 and PA(West) = 270.

Please do not request any angle other than parallactic unless absolutely required by the science. Our image quality and setup procedures are optimized for the parallactic angle.

We currently assume symmetry for the sky fibers, which is not valid for the 3as_1sky option.

Enter the Dec and requested position angle below and hit the submit button.

DEC Position Angle
+/- o ' " o