The Synthesis Telescope at the Dominion Radio Astrophysical Observatory
(DRAO) is a radio telescope with unique capabilities for Galactic
interstellar medium (ISM) studies. Operating simultaneously at the
frequency of the spin-flip spectral line of atomic hydrogen (the Hi
line near 1420 MHz), and in two continuum bands near 1420 MHz and
408 MHz, the telescope achieves arcminute angular resolution with
exceptional sensitivity to extended structure over wide fields (3.12
at 1420 MHz and 9.63
at 408 MHz at the 10% level). These features
allow it to map several major constituents of the ISM, namely the atomic
gas (through the Hi line), the ionized gas (thermal continuum
emission detected in the continuum bands), and the relativistic component
(which generates synchrotron emission, measured in the continuum bands) in
a way which few other telescopes can match. Its principal project at the
time of writing is the
Canadian Galactic Plane Survey (Taylor et al. 2000);
data from this survey are now entering the public domain. The purpose of
this paper is to acquaint the scientific community with the characteristics
of the telescope.
The telescope in its original form was described by Roger et al. (1973), with the first astronomical results being published shortly thereafter (Costain et al. 1976; Roger & Costain 1976). Over the following two decades the capabilities of the telescope were enhanced through a series of modifications, including increasing the number of antennas from 2 to 4 and doubling the maximum baseline in 1982, adding a 408 MHz continuum channel in 1984, and adding a second receiver path to the 1420 MHz continuum system in 1986 to allow both hands of circular polarization (CP) to be measured.
An extensive rebuilding of the telescope began in 1992, to create a telescope optimized for studies of the Galactic ISM, concentrating on high angular resolution, wide-field studies of Hi. Enhancements over the following 3 years included the addition of three antennas, a new 1420 MHz continuum correlator with double the reception bandwidth and polarimetry capabilities, and a new Hi spectrometer with double the number of channels. The result is a substantially new telescope, built on the basic infrastructure of the old. In this paper we describe the telescope, with emphasis on its new components.
Copyright The European Southern Observatory (ESO)