Measurement of the Flux Density of CAS A at 4080 Mc/sec.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurement of the Flux Density of CAS A at 4080 Mc/sec. Wilson, R. W. ; Penzias, A. A. ; Hogg, D. C. Abstract The 20- ft-aperture horn reflector at the Crawford Hill Laboratory,, Holmdel, New Jersey, has been used to measure the flux density of Cas A at 4080 Mc/sec. Some forty drift curve observations, each approximately forty minutes in duration, were made on five nights in September and October of 1964. An argon noise tube was used for comparison in each observation. The night to night variation in the results was less than *0.3%. The equivalent effective temperature ~ontributed by the noise tube was measured by four different calibration methods in order to avoid possible systematic errors associated with any single method. The methods employed were: a comparison between the effective temperature of a room temperature resistor and a helium cooled waveguide termination; the direct connection of the noise tube through precision attenuators; the increment in effective temperature produced by a variable attenuator mounted in front of a helium cooled termination; and the increment produced by warming a room temperature termination. The resulting probable error in the calibration is approximately 0.5 %. The radiometer employs a travelling wave maser and a low-loss comparison switch. The system temperature is 190K for zenith orientation. The system gain was found to change less than 1 % per hour during a forty minute observation period, and was thus sufficiently stable to permit all observations to be made with the radiometer operating in an unswitched mode. The gain of the horn-reflector antenna used was obtained by comparison with that of a small standard horn mounted beside its aperture, while the whole assembly was pointed at a helicopter-borne source. The gain of the standard horn was subsequently measured in the laboratory. From these measurements we were able to obtain the gain of the antenna with probable error of approximately 2%. Combining the results obtained above and making a correction for atmospheric absorption based on our measured value of the sky temperature at this frequency (2.30K) we arrive at a flux density of 1.09 X 1()~23 Wm-2 (c/sec)-1 with a total probable error of 2%. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109590 Bibcode: 1965AJ.....70R.150W full text sources ADS |