Dual frequency 230/690 GHz interferometry and phase transfer at the Submillimeter Array

Details Dual frequency 230/690 GHz interferometry and phase transfer at the Submillimeter Array Dual frequency 230/690 GHz interferometry and phase transfer at the Submillimeter Array

Jan 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006ursi.confe...2h&link_type=abstract

USNC-URSI National Radio Science Meeting at University of Colorado, January 4-7, 2006

Computer Science

Performance

Phase Transfer

Scientific paper

The Submillimeter Array (SMA) is an eight-element radio interferometer located on Mauna Kea and designed to operate in the major atmospheric windows from 180 to 900 GHz with 2 GHz IF bandwidth in each sideband. With baseline lengths up to 500m, atmospheric instabilities can limit the phase coherence of the array, especially in the higher frequency bands. For this reason, the array was designed to support simultaneous operation of a low frequency receiver (< 350 GHz) with a high frequency receiver (> 330 GHz). The overlap region of 330-350 GHz was chosen to facilitate dual polarization measurements in the frequency range most likely to offer the highest sensitivity to dust continuum emission. At present, the array is equipped with SIS receivers covering the frequency ranges 176-250 GHz, 260-350 GHz, and 600-700 GHz. Single frequency operation has been routine in the lower two frequency bands for the past two years. In February 2005, with the completion of the IF hardware, dual receiver operation became possible. Since then we have made a number of Galactic and extragalactic astronomical observations in dual-band mode. Facing a severe lack of gain calibrators at high frequency, we have primarily used minor planets (Ceres, Io, Callisto) or 658 GHz water masers. However, the minor planets are resolved in our extended configurations, and new calibration techniques are needed. We have begun to explore the option of using the 230 GHz receiver as a phase reference to enable improved interferometry in the 650 GHz band. We will present the current antenna and receiver performance, and our initial attempts at phase transfer. New functions have been added to the Miriad and MIR/IDL data analysis software packages for fitting and applying antenna-based phase transfer coefficients. During some of the observing sessions, good phase correlations are seen, and the phase transfer method has been demonstrated to recover images of a point source, albeit at a somewhat reduced signal-to-noise ratio. During other sessions, the method has been thwarted by unknown instrumental instabilities which are still under investigation. With the addition of the second set of 345 GHz receivers (by the end of 2006), dual-band observing at 230/345 GHz will become possible, which will allow more sensitive and more frequent testing and development of the phase transfer technique.

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