AN APPLICATION OF THE BISPECTRUM TO INTENSITY MEASUREMENTS OF POINT SOURCES USING A MILLIMETER ARRAY

In astronomical observations with millimeter wave radio interferometer s, signal-to-noise ratios cannot be increased by data integration due to disturbances in the phase of measured data by atmospheric fluctuati ons. To alleviate this problem, an observation quantity called the bis pectrum has drawn attention recently. Since, in principle, the bispect rum is not affected by atmospheric phase fluctuations, it is possible to enhance the signal-to-noise ratio by integration over a long period of time. In this paper, it is proposed to use the bispectrum for inte nsity measurement of astronomical bodies with a millimeter wave interf erometer. For intensity measurements using a conventional interferomet er, the phase error of the data is first corrected and then the entire data set is averaged to estimate the intensity. In the new method, th e entire bispectrum is averaged and then the astronomical intensity is estimated from the third root of its real part. In order to discuss t he accuracy of the new method, the statistical nature of the bispectru m is elucidated analytically. By comparing the conventional method and the method using the bispectrum in computer simulations, it is shown that the new method can realize higher accuracy. This conclusion is co nfirmed by observations. (C) 1998 Scripta Technica.