How to observe with Turpol
- Point the telescope to your object (in the CAT menu on the TCS
select target and press numerical key 4 to go there). Wait until
tracking. If you have set auto-pos-full at the beginning of the
night, a guide-star will be automatically found and autoguiding started
upon each pointing to a new target.
If a permanent pointing offset has been
adopted (typically found during setup on the first night by staff, see
status page 2 on the TCS), then your target should be inside or very
close to the diaphragms.
- Check the centering of the object using the ST-4 CCD
diaphragm viewing . You will probably have to make fine adjustments
to the centering. If you do not see the star, it might be just outside
your diaphragm. Select the open diaphragm, position #3, to check. In order
to center the star, type on the TCS ag-off to stop autoguiding,
set the step size by for example o-s 0.5 0.5 and move the
telescope in steps using the Alt Function plus ARROW KEYs
until the star is centred in both diaphragms.
NB! Make sure TCS move mode is set to Telescope.
Scroll through move modes with the numerical key 5. Start
now
relaxed autoguiding by typing ag-rel. This ensures that the
telescope is not moved while the box is centred on the guide star.
- If you do not see your object with the ST-4 camera, and it does not
help to adjust the ST-4 integration time, try to step with
some larger step size, such as o-s 10 10. If still no luck, and
if your object is bright enough for the guide TV, then check that it
lands approximately on the centre spot (marked by staff) or place it
there. To do this:
- type g-p-c to have the guide probe in the centre
- type tv-foc 600 and possibly fine-adjust further
- if the object is faint, type tv-fil o to open the TV filter
- type o-s 1 1 and move the telescope (NB!) to put star on the
mark
- then type get-guide-star on the TCS and possibly adjust
TV-fil and TV-foc. Check if your object is now in the diaphragm.
- change move mode to star-box and move the box to the star
- start relaxed guiding by typing ag-rel
- Give the name of your object in the PP program as a star number under
the menu StarNumber.
- Check the brightness of your object to see if you need to use a
neutral density filter .
- After having the star perfectly centred, type ag-off on the TCS to
stop autoguiding, then type o-s 60 60 and make one offset step
with the telescope for sky measurement. (Make sure you select Telescope
move mode, scroll through move modes with the numerical key 5 on the TCS.)
Take a sky measurement with Turpol by clicking on SKY on the PP
display. Step the telescope back and start autoguiding with the command
ag-on (NB! This command moves the telescope until the star is back
in the box and therefore ensures that the centering in the diaphragms is
maintained.) Wait until it says "autoguiding" on the TCS.
- Make your polarimetric measurement by clicking on INT in the PP
program. Now we assume that you have selected your set-up according to
your choice of Linear polarimetry ,
Circular polarimetry , or
Photometry .
- Check average polarisation degree and angle from the accumulated
observations of the object at any time by clicking on the REDUCE
menu, option: averages. The display will also show the associated
errors.
- It is recommended to take sky measurements before and after each object
observation cycle (i.e. normally about every 15 minutes). Also, if you
STOP an integration in the polarimetric mode, it is recommended to
make a SKY integration before restarting.
- PAUSE is a toggle switch which halts the integration, but does not
interrupt the measurement sequence. The flip mirror is turned so that
centering in the diaphragm can be checked - if necessary.
- For an overview of the data obtained so far you may click View Listing.