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F. M. Day (CASA, University of Colorado), E. Momjian (NAIC/Arecibo Observatory)
A growing number of observers are using large single-dish telescopes as elements in VLBI arrays for increased sensitivity. Recently, the High Sensitivity Array (HSA) has been formed by adding the phased Very Large Array, the Green Bank Telescope, the Effelsberg Telescope, and the 305m Arecibo Radio Telescope, to the Very Long Baseline Array (VLBA), to deliver very sensitive VLBI observations. Arecibo is the element that contributes most to the sensitivity of the HSA, but it has limited sky coverage. The study reported here has used the 305m Arecibo Radio Telescope with the VLBA to observe the compact radio source J0837+2454, and carry out a systematic analysis of the impact of including Arecibo. In these observations, Arecibo participated for about 25% of the total observing time. Theoretical image thermal noise calculations, which assume natural weighting, show that Arecibo should improve the sensitivity of the VLBA by a factor of 2.5\---4.5, based on the observing times of the VLBA and Arecibo. To test the validity of the theoretical calculations, the observational data were imaged and CLEANed using natural and other weightings. Our results show that natural weighting yields an increase in sensitivity that agrees well with the theoretical predictions. Such a boost in sensitivity is essential to image and study a wide spectrum of cosmic sources, such as low-power AGN, high-redshift starburst galaxies, extragalactic masers, and gravitational lenses.
The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation. FMD gratefully acknowledges support from the NSF-REU program.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.