The synthesis telescope at the Dominion Radio Astrophysical Observatory

We describe an aperture synthesis radio telescope optimized for studies of the Galactic interstellar medium (ISM), providing the ability to image exte nded structures with high angular resolution over wide fields. The telescop e produces images of atomic hydrogen emission using the 21-cm H I spectral line, and, simultaneously, continuum emission in two bands centred at 1420 MHz and 408 MHz, including linearly polarized emission at 1420 MHz, with sy nthesized beams of 1' and 3.4' at the respective frequencies. A full synthe sis can achieve a continuum sensitivity (rms) of 0.28 mJy/beam at 1420 MHz and 3.8 mJy/beam at 408 MHz, and the 256-channel HI spectrometer has an rms sensitivity of 3.5B(-0.5) sin delta K per channel, for total spectrometer bandwidth B MHz and declination delta. The tuning range of the telescope pe rmits studies of Galactic and nearby extragalactic objects. The array uses 9 m antennas, which provide very wide fields of view of 3.1 degrees and 9.6 degrees (at the 10% level), at the two frequencies, and also allow data to be gathered on short baselines, yielding extremely good sensitivity to ext ended structure. Single-antenna data are also routinely incorporated into i mages to ensure complete coverage of emission on all angular scales down to the resolution limit. In this paper we describe the telescope and its rece iver and correlator systems in detail, together with calibration and observ ing strategies that make this instrument an efficient survey machine.