Setting up on HPF Targets

There are a number of factors to consider when selecting setup methods for HPF observations. These are partially described on the HPF team's webpage, but here we review these further.

The two main factors are the brightness of your target and the speed/precision you would like for your setup. Four cases are elucidated below to illustrate:

Observing a bright target


HIGH precision, SLOWer setup time. Requires source to have SDSS-i magnitude brighter than ~11th.

We center your target on the HPF CFB (very fine pixel scale results in a precise centering) and make a well-determined (blind) offset to place your target on the HPF science fiber. This is our highest precision setup and typically takes 6-10 minutes.

Observing a faint target


GOOD precision, FAST setup time. Can be used on sources with SDSS-i magnitude fainter than ~11th (canNOT be used for extremely bright sources - see next item).

We insert the HET Acquisition camera mirror into the beam and use it to carefully center your target over the HPF science fiber. After the telescope is stable and guiding on your target, we retract the HET Acquisition camera mirror from the beam and observe your target. This setupd method typically takes 2-6 minutes.

Getting the fastest setup possible


If your program requires a lot of short observations and you want to reduce the overhead costs of setting up with HPFACQ method, you might consider using DirectACAM instead. However, extremely bright stars (brighter than ~8th magnitude) will be difficult to accurately center in the HET Acquisition camera because of its larger pixels and saturation from its relatively shallow well depth. The HPF ACQ camera has been designed for bright stars, but is slower to acquire targets.

Setting up using offsets from a bright source

SETUPMETHOD=DirectACAM and using offsetRA, offsetDEC

The previous setup methods all assume you want to center a point source on the HPF science fiber (usually a safe assumption). However, if you do not want to do this, you can specify ACQDirect and give offsetRA,offsetDEC values, as described further here. In this case, we will use the HET Acquisition camera to center on the point source at your coordinates, then apply your requested offset (OFFSETRA,OFFSETDEC) in arcseconds, and observe that offset position with the HPF science fiber.

Setting up on an extremely faint source


If your target is too faint for the HET acquisition camera (fainter than ~20th magnitude), you can request a blind setup. In this method, we will identify a bright star nearby your target and make a blind offset from that known star to your target position. This could be an even more rapid setup method, but may have a lower precision than any of the others, and is really an option of last resort.

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: Thu, 19 Sep 2019 15:52:41 +0000 stevenj


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