Absorption of 21-CM Radiation by Interstellar Hydrogen.

Abstract

view Abstract Citations (56) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Absorption of 21-CM Radiation by Interstellar Hydrogen. Hagen, J. P. ; Lilley, A. E. ; McClain, E. F. Abstract Absorption effects have been observed in the continuous microwave noise spectra of certain radio stars. The absorption is produced by the F = 0 to F = 1 hyperfine transition in interstellar hydrogen and occurs at a wave length of approximately 21 cm. For radio stars and interstellar H I, the effect is similar to the presence of optical interstellar absorption lines in stellar spectra. Three absorption4ine components due to interstellar H I are found in the microwave spectrum of the Cassiopeia source. The absorption lines are characterized by their narrow breadth and do not necessarily coincide with the gross 21-cm emission maxima of the same region. The physical interpretation of the absorption profiles is sensitive to the manner in which the H I is distributed in the interstellar medium The analysis strongly supports the distribution of H I in clouds or in condensations in a less dense medium. Distances to the absorbing clouds and minimum distances to the discrete sources may be determined from a galactic-rotation analysis of the absorption profiles A minimum distance to the Cassiopeia A discrete source of 3 kpc is found. Publication: The Astrophysical Journal Pub Date: September 1955 DOI: 10.1086/146096 Bibcode: 1955ApJ...122..361H full text sources ADS |