The James Clerk Maxwell Telescope is in the midst of an extremely ambitious programme of development in which the entire instrument suite is being replaced in preparation for the JCMT Legacy Survey. I provided a comprehensive description of the development programme in the Autumn 2006 issue of Cassiopeia; in this article, I provide a brief update.
One of the most exciting events at the JCMT during the last six months had nothing to do with astronomy: an earthquake of magnitude 6.7 occurred off the Kohala coast on the morning of 15th October 2006. Although residents of the Big Island are accustomed to frequent small earthquakes, this was the strongest in over two decades. Fortuitously, the JCMT was conducting inclinometry at the time: this is a well-established procedure by which we measure the profile of the antenna track by slowly rotating it over a few hours and recording the readings of three mercury-based tilt meters. The output from the sensors is shown in Figure 1, in which the main quake and the aftershock are both evident. Fortunately, the facility was undamaged and once exhaustive engineering checks were carried out, we were back on the sky the following night.
|Figure 1. Output from the inclinometers, used to measure the "tilt" of the telescope, before, during and after the earthquake. The main mag 6.7 quake was followed a few minutes later by a mag 4 aftershock.|
The new heterodyne system at the JCMT consists of HARP, a 4x4-pixel array receiver for the 345-GHz band, and ACSIS, a multichannel backend spectrometer. The HARP/ACSIS combination was made available to users during semester 06B on a shared-risk basis, and at the time of writing this article its commissioning is very nearly complete. HARP's diagnostic power as as the JCMT's first spectral imager (and the first in the world in the 345-GHz band) has been stunningly demonstrated. The image in Figure 2, for example, was obtained by the ACSIS team during their guaranteed time. The image shows 12CO J=3-2 emission from the region in and around the well-known Rosette Nebula. The observations required about 20 hours of fast raster-scanning. The frame is 2.5║ across and contains ~106 spatial pixels, making this the first megapixel image ever recorded in the submillimetre. (In fact, on each of four individual nights since December, the volume of raw HARP/ACSIS data acquired exceeded the volume of all heterodyne data previously taken at the JCMT!) The complex structure of the region is evident; an optical image of the region denoted by the rectangle is shown for comparison in Figure 3.
|Figure 2. 12CO J=3-2 emission toward the Rosette nebula. The image is ~2.5° across. Integrated emission across three locity ranges is displayed as blue (-3 to 11 km.s), green (11 to 15.7 km.s) and red (15.7 to 25 km.s). Courtesy of Bill Dent and the ACSIS team at DRAO.||Figure 3. Optical image of the region denoted by the dashed rectangle in Figure 2. Sharpless 2-275, courtesy of David Malin and the UK Schmidt telescope.|
The flagship of the development programme is, of course, SCUBA-2. This revolutionary continuum camera will map the submillimetre sky up to 1000 times faster than SCUBA at each of two wavelengths (450Ám and 850Ám), and is on course for delivery to Hawaii this summer. Two science-grade arrays (one at each wavelength) will be installed before the instrument is mounted on the telescope, and commissioning is expected to take until the end of 2007. There will then be a period of observations with the reduced instrument before the remaining six arrays are installed in spring/summer 2008.
The JCMT Legacy Survey programmes are due to at last begin collecting their first photons using HARP in the summer months of 2007. This will be preceded by a Science Verification phase in April-May. Representatives of survey teams will visit Hilo to work with the observatory in establishing quality control procedures for their surveys. These procedures will then be embedded within the nightly pipeline so that survey managers can make quality assurance decisions on survey data following each night's observing. Several Canadian astronomers are closely involved with these preparatory activities.
The advent of new instruments with extremely high data rates, and the prospect of numerous surveys lasting several years, led to the initiation of the JCMT Science Archive project, a collaboration between the observatory and the Canadian Astronomical Data Centre (CADC). The first phase of the project, in which raw ACSIS data cubes will be delivered to observers via the CADC, was recently completed. This was a major milestone involving a huge amount of work at both sites. The second and final phase will enable the generation and delivery of reduced cubes and advanced data products (catalogues, maps, etc). Reduced cubes are already being generated and requirements for the advanced data products are being captured with the advice and guidance of the JCMT Data Users Group, comprised of representatives from the legacy survey teams.
Our ongoing work to develop an interferometric capability at 345 GHz, in collaboration with the Submillimeter Array and the Caltech Submillimeter Observatory and called the eSMA, continues to make good progress. The conversion of RxW for dual-polarisation use in B and D bands is now complete and the instrument is being re-commissioned as I write. We anticipate issuing a Call for Proposals this summer for a pilot programme and in order to prepare the community for this opportunity, a very successful workshop was convened in Leiden in February. Participants were invited to develop science cases for using the eSMA across a range of areas, from high-z galaxies to local debris discs.
Finally, the agreement between the three agencies which provide operational funding for the JCMT (including NRC for Canada) has a break point in 2009. Following the highly-successful review of the observatory in 2005 by a panel chaired by Martin Harwit, and in order to fully exploit the investments which have been made in SCUBA-2 and the other instruments, all three agencies have indicated their wish to continue operating the JCMT until (at least) 2012. A formal agreement to this effect is currently under discussion between the agencies and it is hoped that a final announcement on this issue can be made within the next few months.