21-CENTIMETER Observations Near Galactic Longitude 120°.

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view Abstract Citations (2) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 21-CENTIMETER Observations Near Galactic Longitude 120°. Davis, Robert J. Abstract Observations have been made of the 21-cm radiation at approximately 1 intervals in a strip at 1 = 120?1 from b = -10 to +10 , and at 2 intervals in a strip at b = +35 from 1 = 110?1 to 128?1. The resulting intensity-curves have been reduced to optical depth on the assumption of a uniform kinetic temperature of interstellar hydrogen of TK = 120 K. These curves of optical depth versus radial velocity have been resolved into Gaussians. The number of hydrogen atoms per square centimeter in the line of sight, ]VH, has been found for each Gaussian, and the variation of their parameters with latitude and with longitude is discussed. Various galactic `distance scales are considered; there is a need for more optical observations in this part of the sky to determine a good distance scale. The application of these observations to the problems of galactic structure is discussed briefly. The primary conclusion is that, in this region of the sky, the Perseus arm, 11 kpc from the galactic center, is both larger and denser than the Orion arm, 9 kpc from the center. Although this general conclusion is unmistakable, a quantitative comparison of the two arms depends upon distances determined from galactic models applied to the measured radial velocities. More extensive optical distance determinations are needed in this region of the sky. This paper reports an investigation undertaken to supplement more extensive investigation by Matthews (1956). The 21-cm radiation was studied by scanning in frequency at a number of centers at galactic longitude 120?1, extending from galactic latitude - 10 to +10 . Additional observations were made at galactic latitude +35 along a strip extending from galactic longitude 110?1 to 128?1. The scans of both Matthews (1956) and Westerhout (1955) indicated that this interesting region required more detailed study. The equipment used in this study has been described by Lilley (1955). Publication: The Astrophysical Journal Pub Date: March 1957 DOI: 10.1086/146315 Bibcode: 1957ApJ...125..391D full text sources ADS | data products SIMBAD (1)