Message from the Director

The approved plan sees the JCMT embarking on the construction of a focal plane 345 GHz heterodyne array receiver and a brand-new digital correlator to go with it. This development will serve the JCMT well in terms of its scientific output and standing well into the next Century. The possibility of becoming involved with the Smithsonian Submillimeter Array continues to excite the community and expenditure is approved to convert JCMT IF systems to match those of the SMA. When this is complete, the JCMT should just look like another antenna to the SMA control system. These are the major thrusts of the funded development plans over the next five years.

One of the major drivers of the development plan is to improve efficiency of collecting data. This ranges from a new observatory and telescope control system to improving the surface accuracy. Both have been funded. The latter, in the first instance, will see the replacement of the panel adjuster electronics so that the surface that can be better set and subsequently adjusted for temperature variations. The next step would be to look for panel refurbishments or new panels and this is one of the possibilities vying for the unallocated funds. The JCMT Board agreed that this will be decided in two-year's time and competing projects include a new 230 GHz receiver, more pixels for the heterodyne array, a high frequency heterodyne camera, and more channels for the correlator.

In terms of new instruments, the current 230 GHz A-band receiver (which was upgraded last year with a new mixer) will be replaced by a new receiver, the conversion of the now-replaced 345 GHz receiver (RxB3i). This will give improved performance and much better operational efficiency and reliability. For completeness it should be remembered that new instruments previously approved include a new 800-900 GHz receiver (the conversion of the current 450 GHz receiver RxC2) and a SCUBA polarimeter. Both of these are under construction.

The new 345 GHz receiver (RxB3) has had a chequered life at the telescope - when it works it has been excellent (giving up to a 5-fold increase in observing speed-up over its predecessor - RxB3i). However, it has not yet demonstrated the reliability that we expect and require for a facility instrument. RxB3 was a casualty of the move of labs of HIA from Ottawa to Victoria and we accepted delivery at a time when we were knowingly aware this receiver was not as mature as we would have preferred. We have worked very closely with the receiver builders and I am delighted to say that as of the past couple of weeks, this receiver now looks to be well on the way to being extremely reliable, as well as very sensitive with its dual-polarization set-up. Indeed, when I was at the telescope yesterday it had just been used for an 'on-the-fly' map of the central arcminute of comet Hale-Bopp in CO.

Our new dual-band (450 GHz and 600 GHz), and dual-polarization receiver, RxW, has suffered further delays and it's delivery is not yet known, although a May-June delivery remains a possibility. The receiver builders at MRAO now have all four mixers installed in the main cryostat and have reported excellent noise temperatures. We await its arrival with considerable excitement.

And now to SCUBA. As I noted in my last Newsletter message, SCUBA was having problems in its commissioning. I'm afraid to say that these have continued. We eventually got on top of most of the problems of the sensitivity, traced to faulty filters and a mis-match of the bolometer cavity to the incoming radiation field. Unfortunately, since the December cool-down, progress has been very disappointing due to two unexpected problems, neither of which had occurred previously. The cryogenic stability deteriorated markedly, accompanied by a very large increase in the noise from the detectors. Two further cool-downs failed to cure these problems and the approved astronomical observations for the community had to be postponed.

Where are we now? New filters have been built and tested by Peter Ade at Queen Mary College and we are all now confident that this particular problem is solved. We also believe we have a good handle on the bolometer mis-match and expect that the next cool-down should see very significant improvements in sensitivity. Unfortunately, the cool-down last week (March 10th) failed to reach base temperature, and we are now in the process of another cool-down. If the cryogenic stability and noise problems have been cured, then we will complete the astronomical commissioning (including determining new flat-fields) and then commence immediately on the astronomical programme for users.

I should stress that the news is not all bad. Early-on we obtained some very spectacular images that have been shown on the web or at the AAS meeting. The improvement over a single-pixel device is incredible (as you would expect) and this is just the very beginning. We have also managed to get 'on-the-fly' scan-mapping almost working, and this will open up an entirely new field of submillimetre studies and will help SCUBA realise its potential as an imaging instrument. The SCUBA news page is being updated (at least) on a monthly basis, so this is where to stay tuned for new information.

For general operations, once again, the projects described above have consumed the majority of the efforts of JAC staff, although some time has been devoted to other areas. After a marked deterioration in reliability, the whole JCMT telephone system was replaced in February. Also in February, a severe pointing problem was noticed which manifested itself as large (~10") variations in azimuth pointing at specific values of azimuth. This has been diagnosed as a problem with the antenna central bearing. The effect is being compensated for by an extra term in the pointing look-up tables; we now need to decide whether to replace the bearing (at considerable cost and effort).

Because of the SCUBA commissioning and potential astronomical serviced observing, the JCMT schedule has been in a state of constant flux, and Graeme Watt is to be congratulated on his efforts to keep everything afloat, so as to speak. However, because of the SCUBA serviced mode and the serviced SCUBA heterodyne back-ups, it has meant that we have had very few observers visiting the JCMT. In my mind, far too few. Because of this, and the additional cost of undertaking the observations using JAC staff, we will not undertake another semester like the last one. Despite the continuing need to commission SCUBA and RxW, we will definitely undertake to schedule-in observers programmes with the observers coming out to Hawaii. Hopefully, these runs can be flexibly scheduled within a defined window so that the observer can be present for an extended time in Hawaii, and perhaps will be able to undertake the back-up programmes in lieu of their own. Careful work remains to be done before we embark on a full implementation of this, and discussions with the user community, time allocation communities and funding agencies will be undertaken over the coming months.

Finally I should move on to two domestic aspects, staffing and Prior Options. The former has seen some notable changes, especially in the recruitment of new staff, and we are already seeing the benefit of their expertise. Prior Options has, unfortunately, sapped effort at the JAC and some of the work that we had intended to do has slipped. It is to be hoped that the uncertainty surrounding this process will be soon removed and we can get back to concentrating on delivering high quality and cost effective science.

Ian Robson,

Director, JCMT

March 17th, 1997.