Monthly time use
Non-sidereal target observations
Beginning in late 2023 the HET has begun supporting a limited mode
of non-sidereal observations. As we expect this mode to be utilized
by a limited number of users in relatively specialized cases, it has
not yet been incorporated into TSL. If you require non-sidereal
observations, please contact the Resident Astronomers at
astronomer@het.astronomy.utexas.edu in advance of your institution's
proposal deadline to discuss and coordinate.
Briefly, our technical approach to this limited non-sidereal
tracking is to use one of our guide cameras to move the guide star
fiducial in an equal and opposite direction to the target's
non-sidereal motion. This will drag the telescope along the sky at
the same rate as the non-sidereal object. We are limited to the ~20"
field of view of the guide cameras, but should be able to observe at
least ~10" of motion (more with careful coordination). Given the
maximum track length of 72 minutes for objects on the ecliptic (at
Dec = +23deg), 10" of motion is adequate for the Jovian and
Saturnian satellites (the intended targets of our observations).
As mentioned, there is no way to request this mode in TSL, so we
advise that you do the following:
1. Contact astronomer@het.as.utexas.edu to discuss your science
needs/plans and we will help you.
2. Submit your proposal to your TAC, and get an approved program in
the queue.
3. In coordination with the RAs, generate a list of targets for the
nights when you anticipate the target to be observed, and its
coordinates at the time it is available, with SYNDATE restrictions
for each night.
For example, if you were hoping to observe
Enceladus during the month of May 2024, you might submit something
like this in your TSL file's TRACK_LIST block:
OBJECT
RA DEC
SYNDATE
Enceladus_20240501 23:12:24.4 -07:00:05.2 =20240501
Enceladus_20240502 23:12:47.5 -06:58:18.3 =20240502
Enceladus_20240503 23:13:05.6 -06:56:25.7 =20240503
... etc
4. Make sure the RAs are aware of your target in the queue, and if
necessary, help generate an Ephemeris file (e.g. from
https://ssd.jpl.nasa.gov/horizons/app.html#/) that has high time
resolution for the target's coordinates as observed from McDonald
Observatory. In our testing we used 1-minute time steps, but
depending on the object's speed 5- or 10-minute steps may also be
fine.
On the night your target will be observed, the RA will use a script
called "nst" to interpolate the ephemeris file to the exact
moment when the guider camera is activated and apply non-sidereal
corrections at a specified time step. We've done this with 1-minute
updates in our tests, but again depending on the motion of your
target it might be fine to do 2-minute or longer as well.
Further technical details are available on our internal page here:
Non-sidereal guiding
Basically we are excited to help support your non-sidereal observing
requests! Our approach is limited in its capabilities for now, but
can be developed further if additional needs arise.
Last updated: Mon, 22 Jul 2024 13:11:30 +0000 sir
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