P62-023
P62-023: Follow-up observations of potential minimoons and disrupting asteroids
P.I.: Mikael Granvik
This is a SoftToO program (Nordic Service or technical nights) to do either or all of the
three observing modes:
- ALFOSC 1.8'' slit spectroscopy with Gr#11
- FAPOL lambda/2 + Calcite polarimetric imaging (R filter)
- ALFOSC photometry using SDSS g'r'i'z' filters
of faint targets with non-sidereal tracking, which can be prepared and
triggered through our OB generator.
Daytime calibrations:
- In the evening twilight the standard (non-polarimetric) R-band skyflats are sufficient.
These are made using the alfosc.easyflat script.
- In the morning after closing the dome and when the dome is dark start the script
alfosc.alfosc-calibs before leaving.
Observing instructions
- Go to directory: cd ~/obs/scripts/62-023/ and do ls -lrt
- Start the requested OB generated script.
Because of non-sidereal tracking for the target, you are asked to do the pointing
to target in another sequencer window. To do this, use the script
tcs.asteph OBJNAME
and paste the four command lines listed, unless informed otherwise (e.g. new objects).
The script connects to JPL Horizons for the object name given and calculates pointing
information for La Palma in the format the NOT TCS needs the parameters.
It outputs four
commands on the screen which you should cut and paste as commands into a sequencer window,
one after the other (for example):
tcs.append-object 2017_TC1-xxxx 20 02 53.11 +27 52 40.6 2000.0 0.0 0.0 20.06
tcs.ag-off
tcs.guide-object 2017_TC1-xxxx
tcs.reposition-guide-probe -750.856 -353.934
- When differential tracking and
guiding is ok, go back to the first sequencer window and press RETURN which will
start the actual observations.
- During target observations:
NB! Keep an eye on the star box on the autoguider screen!
During all subsequent observations you must make sure that the star box does not reach the other
edge of the screen.
To help you with this, reposition-guide-probe outputs the "TimeToEdge", and the TCS UIF (sh 24) logs it in real time.
For fast targets the star box may reach the other edge of the screen before your observations
finish.
In this case, you must reposition the star box BEFORE it reaches the edge.
In a sequencer window type:
tcs.reposition-guide-probe dRA/dt dDEC/dt
This should not affect the telescope motion. (But for some guide star locations this may happen.
Under investigation.)
In most cases it is sufficiently accurate to use the same RA/DEC rates as when pointing.
There is a limit to how many times you can reposition the guide probe (due to the finite guide area)
before you need to repoint to the target.
In this case, use updated coordinates and tracking rates!
- Potential standard stars with sidereal tracking are done as normal OB generated scripts.
- Remember to fill the
tracking log of this program.
Some more extended information on non-sidereal tracking
Explanation of how tcs.asteph works:
The command tcs.append-object command adds the target coordinates and epoch
to the TCS input catalog.
The command tcs.guide-object points to the target
and acquires a guide star in normal mode.
Differential tracking and guiding is started
with tcs.reposition-guide-probe, which takes the tracking rates as input
parameters.
This involves the following steps: auto-guiding is
stopped, differential tracking rates are set, the guide box is moved to the optimal
position on the TV screen, differential motion of the star box is started, the guide
star is put into the box (by moving the guide probe only), and autoguiding is started
in differential tracking mode.
This works until the box reaches the edge of the screen.
NB! Note that for a fast target it is important to have
a minimum delay between the two latter commands. If pointing takes a
long time (because the telescope or the rotator needed to move a lot), then it is worth
while to point again to the target (with updated coordinates), otherwise the target
moves away from the centre of the field before differential tracking/guiding is started.
''TimeToEdge'' (in seconds) is the time for the star box
to reach the other edge of the autoguider screen. This is the time available before
the star-box must be repositioned!
It is output on the terminal by the reposition script, and you can
also check it in real time on status page 24 (command sh 24 on the TCS UIF).
The TCS sends an audible warning (and a yellow Talker note) when there is 120, 90
and 60 seconds left.
Some advices on what to do:
- For a fast target, to speed up pointing and re-pointing on the TCS type disable-TV-filter-optimization
(to set it back, if you wish, use enable-TV-filter-optimization ).
- When you run the asteroid ephemeris retrieval script tcs.asteph "object name"
use full asteroid name instead of number!
This is due to ambuigity in the naming conventions of asteroids, comets, and satellites.
- If you want the slit aligned along the direction of the target movement, then for this
program using horizontal slits with ALFOSC you should add the flag "-f fieldrotation" to
the tcs.guide-object command, where the fieldrotation angle is the same as the sky PA
output from tcs.asteph, for example, if PA = -55 degrees, then use:
tcs.guide-object -f -55 2017_TC1-xxxx
But note that for fast targets that need extended observations, this is actually the worst
orientation with respect to guide stars. So it is in fact recommended for fast targets to
use the -f option with the angle set to 90 degrees offset from the PA.
- If the target is not available in JPL Horizons (or if its server is down), you need to
read from the ephemeris file the J2000 target coordinates and tracking rates (dRA/dt and
dDEC/dt in ''/hour) for the current UT time, and issue the same commands as above.
Note the exact format of the tcs.append-object and tcs.reposition-guide-probe
as:
tcs.append-object NAME RA DEC EPOCH PPM-RA PPM-DEC MAG
tcs.reposition-guide-probe dRA/dt dDEC/dt
where dRA/dt without the cos(DEC) correction is the required input to the TCS, since the TCS
applies the cos(DEC) correction internally. If your ephemeris are given as (dRA/dt)*cos(DEC),
which is the default output by JPL Horizons, then you need to divide by cos(DEC) to get dRA/dt.
- For spectroscopy, finding charts are time-dependent, and you might wish to check
Note that for the Lowell astfinder you can enter the target name, set the observatory to
"950 La Palma" and FOV to 390'' for ALFOSC, plus you have the possibility to set the time
steps of the trajectory, while for AladinLite you have to enter the pointing coordinates.
If the target is fast enough or the acquisition time is long enough, stars will become elongated
while the target should be round.
Follow the instructions in the sequencer window to put the target on the slit.
Invalid Proposal |
