WORKING WITH STJ

revised 10/12/99

From pre-press release:
A totally new concept in optical detector instrumentation has made its first appearance with the WHT engineering run of the Superconducting Tunnel Junction Camera (S-CAM) designed and built by members of the Astrophysics Division of the European Space Agency. Based on the theoretical principles identified by Perryman, Foden & Peacock in 1993 (), the first operation of a laboratory single pixel prototype was reported by Peacock et al (). A 6x6 camera was installed at the WHT Nasmyth focus for a 6-night engineering run between 1-7 February (0.3-0.4 nights per night). The instrument is based on the principle that a UV/optical/infrared photon can break Cooper pairs in a superconductor and release an electron packet proportional to the photon energy. The principle opens the opportunity for very high speed photon counting, in which the arrival time and (for the first time in long history of optical astronomy) the photon energy are measured simultaneously. The system provides high QE over a broad wavelength range, and an absence of read-out noise. Within 3 hours of first light, the commissioning team had acquired measurements of the Crab pulsar, and by midnight the 33ms lightcurve was available. The measurments provided a dramatic confirmation of the instrument's timing capabilities. The present instrument provided only very limited wavelength resolution (about 100nm), but the instrument is expected to provide 30nm resolution in the relatively near future, with an ultimate expectation of as low as 1nm. The run was not marked by good weather conditions - clouds prevented observations on the last half night, and of the remaing half nights only one yielded seeing below about 2 arcsec. This resulted in problems acquiring sources, given the total field of view of only 3.5 arcsec x 3.5 arcsec, and problems focussing and aligning the instrument. The main problem experienced was significant noise introduced by the electromagnetic environment at the GHRIL, seen as strong 50/100Hz noise spikes in a number of the detector elements. This will require some additional shielding effort before the next run is considered. In parallel, the ESTEC group expects to implement a higher signal device, possibly with a larger array, and - in the longer term - with count rates significantly higher than the present 1000 photon events/sec/pixel, leading to a bright object limit of about V=17 mag. A factor of 50-100 improvement is planned, leading to photon counting, energy resolution, and time stamping on objects as bright as 12-13 mag. The energy resolution of the device was confirmed by observations of standard stars through a series of narrow band filters. The group had an observation programme of faint pulsars, magnetic CVs, white dwarf oscillations, etc, which was only marginally successful in view of the seeing conditions and instrumental noise. The group reported on the excellent support provided by the WHT/ING technical team, and have indicated their intention to apply for further observing time over the next 1-2 years in order to bring future instrumental upgrades to the WHT with continued emphasis on the scientific goals outlined above.

STARTUP PROCEDURE

TCS:
After setting Nasmyth Turret to GHRIL, type:
Followed by the normal zerosets, met info and cal last

AUTOGUIDER:
Use GHRIL option. The light for the autoguider is reflected off a 45 degree flat mirror with a 50" hole in the middle to allow for light to reach the STJ camera.

TV:
No TV

OBSERVING SYSTEM:
STJ is equipped with its own acquisition system, no need for ICL

PREPARATION PROCEDURE

Telescope focus:
Best focus found by optimizing counts on camera. Once focussed, focus the image on the autoguider (by moving autoguider manually?). Last focus 102.6

Determine rotator center:
Move star out of the hole on the 45 degree mirror (visible on A/G) and rotate 180 degrees. Rotator center should be somewhere in the hole.

Calibrate procedure:
Not sure how to perform a calibrate on rotator center if it is not visible on a/g. Define aperture offsets? Last used -18.55 -27.6

OBSERVING PROCEDURE

Once the target is centered up on the STJ camera you will most likely not be able to see it as it falls down the hole. If a guidestar is available on the field, start autoguiding

OTHER

Thw W12-0-3 version of the TCS includes an autoguider configuration
for the STJ. I shall be on holiday from the 13th to the 17th
but should be at home on the 16th.

Should this for any reason fail, (as there was not time to
test it with the telescope moving on Friday) go back to
W9-0-0 and select the GHRIL WHIRCAM auto guider.

When the TCS is running enter the GSEXAM tool by logiging in
as ENGINEER and change the following variables :

 dep GUI_AL_ROTSENSE(7)      = -1 
 dep GUI_GL_FLIP(7)          = -1 
 dep GUI_GD_ROTATION(7)      = -45.0*DEG2RAD

The last value needs to be entered in radians (-45 degrees).
This will configure the WHIRCAM autoguider to the STJ 
configuration.