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The Synthesis Telescope at the Dominion Radio Astrophysical Observatory is operated as a national facility for radio astronomy. It offers wide-field imaging simultaneously in continuum bands at 408 MHz (lambda 74 cm) and at 1420 MHz (lambda 21 cm), and atomic hydrogen (HI) spectroscopy with 256 channels at 1420 MHz. Images at 1420 MHz have resolution 1.0 arcmin within a field of diameter 2.5 deg. At 408 MHz the resolution is 3.5 arcmin with an 8 deg field.
The telescope is particularly suited to comprehensive studies of the interstellar medium, extended Galactic nebulae and star-forming regions, and nearby galaxies. The two continuum frequencies permit detailed spectral index determinations and allow the separation of thermal and non-thermal components. The HI maps reveal the distribution and dynamics of the atomic gas. The resolution is ideal for comparisons with X-ray and far-infrared data from survey satellites such as ROSAT and IRAS.
The telescope comprises seven 9-m equatorially-mounted paraboloids on an east-west line 600 m in extent. Three of the antennas are relocatable on a precision rail track. The normal mode of operation combines observations of 12 hours at 12 sets of antenna locations, producing an aperture plane sampled from 13 m up to 604 m (a "full synthesis"). Broad spatial structure corresponding to spacings less than 13 m is obtained from existing low-resolution continuum surveys, and complementary HI observations made with the DRAO 26-m Telescope. The declination limit for full hour-angle coverage is 17 degrees.
Only a single polarization is received at 408 MHz, over a 4 MHz band. For continuum emission at 1420 MHz, both senses of circular polarization are received and images are made in all four Stokes parameters. There are four 7.5 MHz sub-bands, two on either side of the HI band, so rotation measures can be determined. The HI spectrometer provides 256 channels in each of left and right-circularly polarized emission. The bandwidth is selectable between 0.125 MHz and 4 MHz.
Noise in a full synthesis is about 3 mJy/beam at 408 MHz, and 0.2 mJy/beam at 1420 MHz in the continuum. Noise in spectrometer images is 3.5 B^-0.5 sin delta K.
For more information, please contact Tom Landecker.
