After starting up the telescope and building (see startup sheets or
TCS manual) and once it is dark enough, switch the guide TV on by
typing tv-on at the TCS keyboard.
To observe with TurPol you need 3 TCS configurations: periscope (pe)
to centre the object in the diaphragm, centre (ce) to be able to
acquire fainter objects, and guide (gu) to allow auto guiding on a
guide star. Here the procedure to do these set--ups is
described. Unless the TCS is rebooted for some reason, these set--ups
have to be done only once, at the beginning of a TurPol run.
Point the telescope to a bright star (magnitude 5 or so) and set--up
the periscope configuration by giving the TCS the commands pe-in,
gp-po 35000 158500, tu-fo-po 22700, tv-fi o, tv-fo-po 350. You
should now see two illuminated diaphragms on the TCS guide probe
screen. From the PP programme, put in diaphragm no.3 (open), and find
the star by moving the telescope in small steps. Set the step size
with tm-os 5 5 and move using the arrow keys on the TCS
keyboard. Once found, centre the star, put in diaphragm no.1 and
re-centre with steps of, say, 0. Note that two images of the
star should be visible, one in each diaphragm image. Minor
adjustments of the all the above parameters may now be made if
needed. Telescope focus is used to make the (slightly astigmatic)
e-image in the RH diaphragm, as round as possible. Once happy with the
set--up, give the command: cc-ad-tv pe to adopt the periscope set--up,
and mark the diaphragm positions on the screen with a felt tip
pen. Give the TCS command: pr-po-ad to give this permanent
off--set to the telescope pointing to bring objects into or very near
the diaphragms with every new pointing. To reset these off--sets to
zero, if needed, you can give the command: pr-po-re.
With the bright star well centred in the diaphragms, type:
tv-fi g, tv-fo-po 600, pe-ou, gp-ce to set--up the centre
configuration. You should see the bright star near the centre of the
screen. Mark its position with a felt tip pen. This configuration is
only used when an object is not found in the periscope configuration,
or to centre on objects that are too faint for the periscope, which
has high magnification and a long optical path. Type cc-ad-tv ce to
adopt the centre configuration.
The initial guide configuration is made by typing: tv-fi o, tv-fo-po 660,
pe-ou, gp-pa and then cc-ad-tv gu.
You are now ready to start observing.
Note that after these initial pe, ce, and gu set--ups have been done,
they are used for the duration of the observing run, unless the TCS is
rebooted. Then the parameters have to be defined again, so it is
useful to write down the optimal initial parameters just in case a
reboot has to be done.
In going from one object to the next the following procedure is the
a) Finish an observation with a sky measurement.
b) Type ag-of to stop the auto-guider.
c) Preset to the next object and wait until the telescope tracks.
d) Type cc-ad-tv gu to store the x and y coordinates of the guide probe.
e) Type cc-ce-tv and centre the object.
f) Type cc-pe-tv to fine--tune the centring in the diaphragms.
g) Type cc-gu-tv and wait until the guide star appears on the screen.
h) Type ag-re-on and wait until ``auto-guide'' appears on the TCS screen.
i) Type ag-of then tm-os 60 60 do one offset (with an arrow key), and take a sky measurement.
j) Do one offset to get back, and type ag-on to start auto-guiding.
k) Take your polarimetric measurements.
Repeat the above for each object. On the following pages the observing procedure is described in more detail.