revised 04/11/99

This Galway build photometer goes on several telescopes around the world, including WHT/CASS. An array of dichroics splits up the incident beam in broad band regions, each region projected onto the detector. The photon-counting tube detects each photon arrival by knocking of an electron (photo cathode) which is accelerated through an electric field until it hits a micro channel plate which produces a shower of electrons. This shower is detected on a fine grid of wires and, using a techique called coincidence logic, the photons xy position is recorded together with the arrival time. The two-dimensional image builds up on the 'MAMA' display. Furthermore, 3 fibres acts like single channel photometers (ADC). Detector size is ~ 1000 x 200 'resolution elements'. each element 24 microns corresponding to 0.1" on sky. FOV ~ 100" x 20"


Use ISIS setup.

CASS autoguider.

The TV camera can be used in direct mode to view the field, i.e. ICL>agcomp. Remember there is a focus offset between direct view and cass focal plane of ~0.4mm

The observing system runs on a linux machine supplied by the TRIFFID team. Data acquisition & storing is likewise controlled by their own computers. However, the ICL is still needed with aux/isis setup to control autoguiding & tv acquisition (like for calibrate procedure).


Telescope focus:
The nominal telescope focus is determined on the TRIFFID realtime display. As the image builds up, the observers measure the FWHM. This is repeated for several focus values.

Calibrate procedure:
Standard cass procedure: direct tv view, find rotator center, calibrate on rc.

Determine aperture offset to instrument center:
Rotator center is close to the center of the triffid array (MAMA) -> no ap offsets needed.


Object is typically centered on one of the fibres (APDs) seen on the MAMA display. Autoguiding starts, and observing goes on for hours and hours.


No worries; Observers writes their triffid data on Magneto-Optical disks.

Observing logs:
If no other instrument has been used during the night, the log will only contain the header!