The new seven-beam methanol multibeam (MMB) receiver has been successfully commissioned at Parkes and has begun surveying the Milky Way for newly forming stars that are pinpointed by strong methanol maser emission at 6.7 GHz. The methanol masers turn on while the young stars are still forming, deep inside giant molecular clouds of gas and dust, and are detectable long before the stars become visible to optical telescopes.

Installation began on 16 January 2006, when the receiver was lifted to the focus cabin. Epping engineers (Graham Moorey, Pat Sykes, Les Reilly and Paul Doherty) worked with local Parkes staff (with late-night and weekend efforts from Brett Dawson, Ken Reeves and John Reynolds and the Epping lads) to achieve first light in the small hours of Sunday 22 January. The first maser spectra show methanol emission at 6668 MHz and excited OH emission at 6035 MHz from the source G309.21+0.48 (Figure 1).

Figure 1: First light spectra of the source G309.21+0.48 in the methanol 6668 MHz and
OH 6035 MHz lines (upper and lower plots respectively); click on image for larger version.

The receiver has already broken two records. It is the first Parkes receiver to have feeds within the cooled dewar; and it has more cables coming off it than any previous Parkes receiver. There are 28 receiver channels covering seven beams and two radio frequency (RF) bands in dual circular polarisation. The receiver must be continuously rotated while observing so as to maintain the beam pattern on the sky - quite a challenge for the engineers. The two intermediate frequencies (IFs) normally cover the methanol 6668 MHz and OH 6035 MHz lines. By using the multibeam correlator in parallel with the wideband (pulsar) correlator we can measure the two lines in dual circular polarisation at high (2 kHz) frequency resolution. The receiver can also provide two broadband (300 MHz) IFs for continuum (e.g. pulsar) observations.

The receiver was jointly constructed by the ATNF and Jodrell Bank Observatory (UK), with ATNF's role described in an accompanying news note by Graeme Carrad. The project was catalysed by a PPARC grant obtained by a consortium of seven UK institutes, led by UK project scientist Jim Cohen (Jodrell Bank). James Caswell is the ATNF project scientist, while the project manager, leader and engineer is Graham Moorey. For the record there are two other Jims in the team, PhD students James Cox (Cardiff) and Jimi Green (Jodrell).

Figure 2: First discovery from the methanol multibeam survey
(click on image for larger version).

Using the high gain of the Parkes telescope, the sensitivity of the low-noise amplifiers and the seven beams, the MMB survey of the Milky Way is two orders of magnitude faster than previous systematic surveys using 30-m class dishes. The first of many discoveries from the survey, shown in Figure 2, is a star-forming region that lies in the inner Galaxy at a distance of 22,000 light years. The source appears in the figure as the bright spot, and the corresponding spectrum at this position is shown. Once the southern Milky Way has been searched, the multibeam receiver will be transported to Jodrell Bank Observatory to survey the northern Milky Way.

Jim Cohen (Jodrell Bank Observatory) and James Caswell (ATNF)
(James.Caswell@csiro.au)