Observing Procedures
Observing Procedures
Locate the acquisition bundle at the center of the field using the SP mechanism: ICL> ISP ACQ OBS
The field of view of this bundle is 22.5 x 30.2 arcsec 2. At SkyPA=0 degrees, the orientation on the TV screen is such that North is up and East is left (when H down, and V up on the TV switches at the control room).
By moving the rotator, the acquisition (and observing) bundle can be aligned at the desired angle.
Limiting magnitude of the acquisition TV without integration is V~15.
The following filters are currently installed in the acquisition system: CLEAR, BG38, GG495, OG530, and RG630.
INTEGRAL is focused by visually inspecting the image of a faint star on the acquisition TV system. A typical telescope focus encoder value is 97.7.
Adjustment of the Rotator Axis and Orientation
Determine the X and Y coordinates of a star on the TV acquisition screen. Change the Sky Position Angle (SPA) by 180 degrees. The star describes a semi-circle reaching a final location on the TV (i.e., [Xf,Yf]). The center of this circle [(X+Xf)/2,(Y+Yf)/2] should be the rotator center. Repeating this process will lead to a more accurate determination of the rotator centre.
To minimize tracking uncertainties, select a star near the pole.
After the rotator centre has been determined a CALIBRATE should be done
at this point.
In order to check that the guiding bundles are properly mounted the following check can be done:
i) Locate the slide unit at (65237,
0.). For that use the commands IXS and IYS.
ii) Align a star at the rotator centre
iii) Applying an off-set of 212 (386)
arcsec (Telescope to the South) the star should appears at the centre of
inner (outer) guiding bundle.
With the handset in the XY mode, at SPA=0 degrees, the up button will cause an object to move down the TV screen while the handset left button will cause an object to move left on the TV screen.
Use the WHT INTEGRALINNER and WHT INTEGRALOUTER configurations of the GSS for finding guide stars within the inner and outer fields.
The ICL commands IXSlideAbs and IYSlideAbs are used to moved the XY slide to the GSS indicated position .
To locate the scientific bundles at the center field, move the SP using (ISP [std1,std2,sdt3] [obs]).
There are small off-sets between the rotator center and the positions of the central fibres. To determine the offset for your observing bundle follow the next steps:
1. Put
adquisition bundle at observing position: ICL> ISP ACQ OBS
2. Go
to a bright star (V~8) and put it at the rotator center previosly determined
3. Change
the swing plate to your observing bundle (e.g. STD2) at observing position:
ICL>
ISP STD2 OBS
4. Take
a short exposure (Texp~10s): ICL> run integral 10 "STD2 center"
5. Using int_apall
find
out where the star is centered in that bundle
6. Determine
the offset showing the spatial distribution
of the fibers at the focal plane for that bundle or running int_center
7. Apply
that offset to the telescope and repeat the same procedure.
8. If
the star is now well centered, mark the position of the star at the TV
adquisition screen. This will be the real reference to
center your objects during your observing run.
Here you have typical values for off-sets between the rotator center and bundle centers.
Last updated March 2000
Begoña García-Lorenzo (Instrument specialist)
bgarcia@ing.iac.es
Ana M. Pérez-García (Deputy)
aperez@ing.iac.es