Technical Aspects of the Wide-Field Upgrade

The MOST, unlike other earth-rotation synthesis telescopes, forms a bank of hard-wired fan beam responses in real time, without recording the complex visibilities for later processing. The current upgrade has increased by more than a factor of 5 the area of sky which can be fully synthesized in a 12 hour observation. This has been achieved by implementing several innovative improvements, to avoid degrading the sensitivity, while retaining many of the pre-existing telescope systems (Robertson 1991, Large et al. 1994). The resolution has been unaffected by these present changes. The two principal strategies taken to maintain the sensitivity are the installation of 352 high performance low-noise (12K) ambient temperature preamplifiers, and the development of a system to continuously adjust the phase gradient across the array during observation. The wide-field mode of operation involves a progressive offsetting of the primary beam to several different pointing positions. This beam multiplexing requires a complex phasing system organised by a network of microcontrollers, linked to a central computer. It is expected that commissioning tests will be completed by October, 1996. After modification of the data analysis system, the proposed survey will commence.

 
Figure 1: Mosaic of region of MOST Galactic Plane survey, centred on . Dominant structure is from several Galactic supernova remnants and HII regions. Minimum reliable source flux density is 5 mJy. The brightest filaments are typically mJy. To show the weak extended emission clearly the greyscale intensity range is saturated above 40 mJy.

© Copyright Astronomical Society of Australia 1997