Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980apj...240..499p&link_type=abstract
Astrophysical Journal, Part 1, vol. 240, Sept. 1, 1980, p. 499-513.
Astronomy and Astrophysics
Astrophysics
29
Absorption Spectra, Emission Spectra, Hydrogen Clouds, Interstellar Gas, Radio Sources (Astronomy), Astrophysics, Centimeter Waves, Neutral Gases
Scientific paper
Neutral hydrogen emission-absorption studies were carried out at Arecibo Observatory for some 'high-velocity clouds' with velocity absolute value of v greater than 50 km/s. Conspicuous, narrow absorption features are rare but were found in a few cases. In addition to these few confirmed features, statistical tests indicate the presence of more widespread weak absorption. Harmonic mean spin temperatures of a few hundred K are obtained from averages over velocity and sky position for the high-velocity material, comparable to spin temperatures for low-velocity local clouds of equally small column density. Narrow absorption features are correlated with strong emission variations over angular scales of 4 arcmin, suggesting a two-component model for high-velocity material: (1) warm ('not strongly absorbing') neutral hydrogen smoothly distributed over a whole 'high-velocity cloud complex,' and (2) a patchy distribution of cooler cloudlets, possibly below 100 K.
Payne Harry E.
Salpeter Edwin E.
Terzian Ye.
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