World Coordinate System for HET frames
Target coordinate vs. IHMP coordinate
The center of the coordinate system for the HET is the center of the Input Head Mount Plate (IHMP) which actually does not have any actual fibers. So if a PI requests a specific RA and DEC for a target on the LRS2-R we use a code called "shuffle" to determine the position of the IHMP center in RA and DEC and those are sent to the telescope as the coordinates for the trajectory. These coordinates can be found in the science fits files as the header keywords TRAJCRA, TRAJCDEC and TRAJCEQ and also in the shuffle setup ancillary data provided with each observation.
There is no need for a PI to understand this level of coordinate distinctions - if a set of coordinates is submitted and requests an observation with LRS2-B, that's what the user will receive.
Accuracy and precision of the WCS
The Acquisition Camera images have a broken WCS which is not reliable at this time (late 2023). Some day we hope to improve that but it has been a long-standing issue without a clear path toward a solution.
Last updated: Fri, 29 Dec 2023 11:17:52 +0000 stevenj
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