LRS2 Position Angle and Fiber Layout

The LRS2-B and LRS2-R IFU feeds are located 100" from each other in the direction 90 degrees from the altitude line at center of track. The short axes of the 12"x6" LRS2-B & LRS2-R IFUs are in the direction of the parallactic angle at center of track.

It is not possible at this time to specify an offset angle.

You can use the lrs2rho cgi script to determine the altitude line and the current parallactic angle and thus the angle of the LRS2 IFU on the sky.

You can find more about the parallactic angle and how it is related to the DEC and optimal Az by looking at the HET Object Observability pages.

The World Coordinate System (WCS) has generally been determined although we continue to improve this. Please see the WCS page. for information on the WCS for the HET and see LRS2 fiber layout page for information about how to place the LRS2 foot print (using ds9 regions files) onto the acquisition setup images.

The image below show the layout of the LRS2 fiber bundles among the VIRUS units at the HET focus.

  • Central part of the HET focal surface looking at the fiber feeds mounted in the input head mount plate (IHMP). A number of VIRUS IFUs are seen along with the feeds for LRS2-B and LRS2-R and the fiber feed for HPF. The BIB (boresight imaging bundle) is a small field imaging fiber bundle that defines a location on the IHMP so that the IHMP and the ACAM can be tied together and checked. The seat for the future HRS feed is also indicated.

  • The LRS2 IFUs have 6” x 12” format oriented as shown

  • Parallactic angle (Tracker Y axis) is up in this figure, as indicated by the dark orange arrow; it is perpendicular to the long axis of the LRS2 IFUs

  • The orange square indicates the field of view of the acquisition camera (ACAM) which is fed by a pick-off mirror that can be deployed in front of the IHMP.

  • LRS2-B input head is mounted in IHMP slot 056 and the feed for LRS2-R in 066


To help the PI understand our setups and also to understand the results they get from the LRS2 we have provided time stamped regions files which can be used along with setup images from the HET's acquisition camera (ACQ, sometimes labeled ACM or ACAM). In the example image below we have displayed the IFU footprints of both the LRS2-R IFU (in red) and LRS2-B IFU (in blue) region files on a setup image from the ACQ camera with a bright star on the LRS2-R position.
Each time that the ACQ camera/mirror or the IHMP are moved the relationship between the LRS2 IFU positions and the ACQ camera changes slightly. The following table contains the regions files and the date in which those were installed or valid.
Dates valid LRS2-R file LRS2-B file
20190401 - acam_ifu_R_20190401.reg acam_ifu_B_20190401.reg
20180928 - 20190401 acam_ifu_R_20180928.reg acam_ifu_B_20180928.reg
20180727 - 20180928 acam_ifu_R_20180727.reg acam_ifu_B_20180727.reg
20171210 - 20180727 acam_ifu_R_20171210.reg acam_ifu_B_20171210.reg
20171007 - 20171210 acam_ifu_R_20171007.reg acam_ifu_B_20171007.reg
20170618 - 20171006 acam_ifu_R_20170618.reg acam_ifu_B_20170618.reg
(note that these have not been updated in some time, but the changes are extremely minor and these regions files are a good representation of the current alignment)



These regions files can be loaded into ds9 under the "Region" pull down menu and selecting "Load Regions..." or on the command line with -regions



Last updated: Wed, 26 May 2021 08:49:10 -0500 stevenj



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