Setting up on VIRUS Targets

There are effectively two options for setting up on a VIRUS target, depending on how precisely centered your science target needs to be. The more precise option is also slower, so it is a trade-off between speed and precision.

For VIRUS, unlike our other instruments, a "direct" setup is impossible. In "direct" setups we insert the HET acquisition camera mirror and establish stable guiding on the science target, before retracting the mirror and opening the instrument shutter. If you have requested a target be placed on a VIRUS IFU, it cannot be observed with the HET acquisition camera since the VIRUS IFUs are all located further away from the optical axis (see diagram below).

Observing a target/field with low precision (~a few arcsec)

SETUPMETHOD=DirectGuider

In this method we use only the position of the guide stars to center your target. We pre-compute the anticipated location of a guide star (often two) relative to your target's position, and move the telescope until the guide star is at the desired location. This allows for very fast setups (sometimes only 1-2 minutes), but will not be high precision. Since the IFUs are 50"x50", this may be enough precision for your science (this is the standard method used for the HETDEX survey observations).

Observing a target/field with higher precision

SETUPMETHOD=ACAMblind

Since the HET ACQ camera ("ACAM") does not overlap with any of the VIRUS IFUs on the sky, a blind offset is the only other option for setups. If you want a particular target (galaxy/AGN/etc) to be centered on one of the VIRUS IFUs (more information here), this setup method will give a higher precision centering of that target. We will use the HET ACQ camera to identify a bright star and make a blind offset from that star to place the VIRUS IFU in the correct position to observe your target.

No other setup methods are possible for VIRUS observations.

As usual, if you have questions about these setup methods and how to get the best quality observations for your science, contact the RAs at astronomer@het.as.utexas.edu



Last updated: Fri, 24 Jul 2020 15:01:11 -0500 stevenj



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