21-cm Continuum Observations of Discrete Sources

Abstract

cm Continuum Observations of Discrete Sources. S. J. GOLDSTEIN, JR., Harvard College Observatory, Agassiz Station, Harvard, Massachusetts. -The switched maser radiometer mounted on the 60-foot reflector at Harvard College Observatory has been used at 1422.4 Mc to observe continuum sources, selected from the survey at 85.7 Mc by Mills, Slee, and Hill. This paper is a report on 18 of the sources at galactic latitudes greater than 90 for which positive results have been obtained in good positional agreement with those reported at 85.7 Mc. The observations at 1422.4 Mc, made with 1 Mc bandwidth, and beamwidths of 55' in both declination and right ascension, consist of two or more drift curves and two or more scans in declination across each source. The weakest of these sources at 1422.4 Mc produces deflections of several times the rms fluctuations on single records with an integration time of ten seconds. One hopes to obtain accurate average spectral indices from these observations, and those of Mills, Slee, and Hill because (1) the sources are strong at both frequencies, (2) neither instrument is affected by angular size of the source, (3) the beam- widths of the two instruments are nearly equal, and (4) the large ratio, 16.6, of the two frequencies of ob- servation reduces the effect of errors in flux density on the value of the spectral index. The spectral indices range from 0.56 to 1.10 with an average of 0.85. There is no clear-cut evidence of grouping. This is a much narrower range of indices than that obtained at lower frequencies by Whitfield. The three sources which are extended at 85.7 Mc have smaller indices than the three which are possibly extended, the latter sources having about average spectral indices. Thus, for some of the sources there may be an inverse correlation between angular size and spectral index.