Purpose: This code will calculate the offsets to be entered into Spot fixed cluster target offsets when transforming coordinates from an observed position using guide-star peak-up to the sweet spot position. This is only useful if you already have a guide-star peak-up observation of your target using the SSC recommended fixed cluster target offsets which did not land on the sweet spot, and you want to transform the observed coordinates to the sweet spot for designing another epoch of observations.

Author: Jessica Krick
Date Contributed: 28 April 2015
System Requirements: IDL

Information and Download

Download irac_transformtosweet.pro (4 KB)

For stars which are either too faint or too bright to use PCRS Peak-Up on the target itself, it is necessary to use a catalog Peak-Up star. This is accurate if the proper motion of the target star and catalog star are both well known. Proper motions errors are provided for catalog stars when running pick_pcrs_catalog (contributed software provided by the SSC), and usually have low errors. The only concern with a guide-star is if there is no acceptable catalog star near your target (this should be very rare). If the proper motion of your target star is not well known, and your science requires the target to be on the sweet spot, then we recommend that users observe a first epoch of their catalog + target star pair using PCRS Peak-Up and then transform the coordinates from that first epoch to move the target onto the sweet spot for further science epochs. This code will perform the coordinate transformation between the observed coordinates and the desired sweet spot coordinates.