Observations of radio sources with flat spectra

Details Observations of radio sources with flat spectra Observations of radio sources with flat spectra

Jul 1978

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978aj.....83..685o&link_type=abstract

Astronomical Journal, vol. 83, July 1978, p. 685-696. Research supported by the Research Corp.

Astronomy and Astrophysics

Astronomy

76

Centimeter Waves, Radiant Flux Density, Radio Sources (Astronomy), Radio Spectra, Ubv Spectra, Astronomical Photometry, Optical Emission Spectroscopy, Optical Thickness

Scientific paper

Results are reported for simultaneous or nearly simultaneous optical and radio observations of 237 sources with flat or inverted radio spectra at centimeter wavelengths. The observations include radiometry of all 237 sources at 90 GHz, radiometry of 104 sources at centimeter wavelengths (central frequencies of 1.379, 4.585, 15.064, and 22.185 GHz), and optical photometry of nine sources transformed to the Johnson UBV system. Optical results are briefly discussed for the sources 1305+32 and 0851+20 (OJ 287), and the 90-GHz flux-density distribution is analyzed. The radio spectra of the sources are examined, variability at 90 GHz is investigated, and models for the radio emission are considered. It is shown that: (1) the sources tend to have flat radio spectra over the range from 1 to 100 GHz; (2) the weaker sources at 90 GHz have spectra which tend to turn over at or near 5 GHz; (3) sources which turn over at higher frequencies tend to be brighter optically; (4) BL Lac objects tend to have flat spectra; (5) most of the strong sources are consistent with a 90-GHz variability of less than 30% for one year; and (6) one or more components with inhomogeneous structure are likely to exist in most of the strong millimeter sources.

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