Extension of radio source spectra to a wave length of 3 centimeters.

Abstract

view Abstract Citations (8) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extension of radio source spectra to a wave length of 3 centimeters. Haddock, F. T. ; McCullough, T. P., Jr. Abstract To extend the spectrum of discrete sources a survey was undertaken during July, 1954, at wave length 3.15 cm (9500 Mc/sec) of known sources, principally of those detected by Haddock, Mayer, and Sloanaker (1954) at wave length 9.4 cm. An antenna beam 8' X 9' in width and chopper-type radiometer was used. Seven sources were detected: the Orion Nebula and two other emission nebulae, NGC 1976, 66i8 and 6357; three well-known non-thermal sources, Cassiopeia-A, Cygnus-A, and Taurus-A (Baade and Minkowski, i954); and a source suggested as the galactic nucleus (McGee and Bolton, 1954; Hagen and McClain, 1954) denoted by 17S2A (NRL No. 5). These sources represent the first detection at a wave length shorter than 9.4 cm of galactic and extragalactic radio emission. The small beam made it possible to estimate the size of several sources; about 410 for NCG 1976, NGC 6357 and 17S2A, and about A~O for NGC 66i8. The intensity found for the Orion nebula is consistent with the thermal model of this source derived from the 9.4 cm measurements. The intensities of the two other emission nebulae, when compared to their intensities at longer wave lengths, also appear consistent with a thermal emission spectrum, although the evidence is not as good. Since the intensity and size of the source toward the galactic center, 17S2A, is comparable with the Orion nebula source at both 3 and 9.4 cm, it is of interest to consider the possibility that source 17S2A is an Hii region. There are alternative distances to consider. First, at 3000 pc from the sun there exists a group of OB stars (Hiltner, 1954) with associated bright emission nebulae (Sharpless, 1953). The radio source position at 1 = 3270.7, b = I?4 (Lund) lies among several of these nebulae having about the right size, but they are not as bright as the Orion nebula nor are the exciting stars as hot. It would be helpful to have a more precise source position. Secondly, if this source is at the galactic nucleus, its intensity can be accounted for by a Stro~mgren sphere 36 pc in diameter containing 80 electrons per cm' (38 solar masses) excited by three O6 stars, or their equivalent. Since at longer wave lengths this source appears to be embedded in an emitting region of complex structure and possibly of mixed spectral types, it is difficult to obtain its true spectrum. However, it is possible to rule out a Cassiopeia-A type spectrum on the basis of the long wave length intensities (Pawsey 1955) and of the maximum allowable Hii opacity as determined from the centimeter-wave emission measures in this direction. REFERENCES Baade, W. and Minkowski, R. `954, Ap. J. 119, 206 and 215. Haddock, F. T., Mayer, C. H. and Sloanaker, R. M. `954, Ap. J. 119, 456 and Nature 174, 176. Hagen, J. P. and McClain, E. F. `954, Ap. J. 120,368. Hiltuer, W. A. i954, Ap. J. 120, 41. McGee, R. X. and Bolton, J. G. `954, Nature 173, 985. Pawsey, J. L. ~955, A~. J. 121, 1. Sharpless, S. `953, Ap. J. iiS, 362. Naval Research Laboratory, Washington, D. C. Publication: The Astronomical Journal Pub Date: June 1955 DOI: 10.1086/107193 Bibcode: 1955AJ.....60..161H full text sources ADS |