How to take data for the Pointing Model and the Starguider
before taking tpoints:
make sure that
(only) the lower lid is closed (la guagua -> tpoint)
the starguider leds are switched on
the intensity of the starguider leds is appropriate
(2.30 at the potentiometer should be fine)
the AMC leds are switched off
the 'STAR' button in the AMC program is activated, and FocCor=0,
PanGrp=0
(this changes the focal length of MAGIC so that starlight get focussed
on the spectralon reflector)
which stars to track for tpoints
the stars should be distributed well over the sky
important are
stars at small zenith angles, i.e. < 10°
stars at big zenith angles, i.e. > 70°
stars around culmination
NOT stars when they are suffering from the culmination problem (you
can check from the starguider)
a possibility is also to follow a star over culmination and take
tpoints every 10° in azimuth
NOT Polaris
depending on the moonlight you can take stars with magnitude down
to 3.5 important is, that the stars are recognized in the tpoint
mode by the filter, i.e. marked with a green cross
when there's moonlight, stars 90° away from the moon can be a
good choice
tpoints:
track star (arehucas -> Yale Bright Star Catalog)
do LUT adjust
write the name of the star, Zd, Az, magnitude, # of errors of the LUT adjust into the runbook
wait for the tracking to be stabilised
(see below)
take picture with the SBIG-CCD to measure the PSF of the telescope.
switch to tpoint mode in the starguider window
wait for camera and filters to be switched (see picture below)
take tpoint, i.e. press tpoint button
wait for tpoint button to be released
switch to starguider mode
wait for camera and filters to be switched (see picture below)
take starguider tpoint, i.e. press starguider tpoint button
wait for starguider tpoint to be released
how to take a picture with the SBIG camera
start the program 'sbig2' on pc21 as user 'operator' and wait until
the temperature has reached ~0°
set exposure time to 2 sec and Filter '1' (this is ok for typical
tpoint-stars)
press 'Take Picture'
then 'Save Picture' with filename
'A<Azimuth>_Z<Zenith>_<StarName>_PSF' (angles with 1°
precision)
at least once per hour do additionally 'Take DarkFrame' and save
the picture with the name 'Dark'
The images are stored in the directory 'Images' and can be looked at
with the program 'fv <filename>'
how to know when the tracking is stabilised? - some remarks
when the starguider shows mispointing < 5 min the tracking normally
has stabilised
when the spot of the star on the camera lid is close to (touching
it) or in the circle marking the center of the camera, the tracking has
stabilised
normally the stabilising of tracking last 25 sec to 1 min
for large zenith angles (similar effect and correlation like for the
culmination problem)
Whether the stabilising takes long, depends on the direction from which
the telescope is approaching the tracking position.
quality of tpoints
to take a good tpoint make sure that
the tracking has stabilized
the leds have an appropriate brightness
the leds are recognized correctly, i.e. the cross marks the center
of the led spot (moonlight can affect this)
the circles are there and not jumping
the leds are not saturating (happens in some pictures)
only for tpoints:
the star is reconized on the camera lid, i.e. marked by a green cross
(moonlight can affect this)
the green cross is in the middle of the spot of the star
at least 5 leds are recognized
only for starguider tpoints:
the mispointing is < 5 min
the tpoint taken before has good quality
at least 3 leds are recognized
remarks:
Every time a tpoint is stored, an according output is written to
the shell. (see first picture)
If the time between tpoint and starguider tpoint is > 1 minute, the
starguider tpoint is not stored (see output in the shell), and tpoint +
starguider tpoint have to be repeated
The values, which are stored, belong to the picture, that appears,
when the button gets released. This means, that the tpoint has to be
repeated, if this picture is bad. Please put a note in the runbook
in this case.
Too much moonlight, can make a tpoint impossible.
You can avoid waiting time for the tracking to stabilise, when you
are approaching the position of the star, from that direction, from
which the star was coming on its path across the sky.
As the software was not intended to handle switching between the
cameras, this procedure is quite unstable. Due to that the Software
might crash or hang. Please restart it in this case and start tracking
the star again. Another possible effect of the instability: The
longer the program runs, the slower the switching might get.
The mispointing values in the starguider are relative values, as
the starguider is not yet calibrated. The purpose of the starguider
tpoints is to do this calibration.
after taking tpoints:
make sure that
you switched back to starguider mode
the 'STAR' button in the AMC program is deactivated (focal length
adapted to focus point source in 10km distance onto the entrance of the
winston cones
