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Title:
A very small interstellar neutral hydrogen cloud observed with VLBI techniques
Authors:
Dieter, N. H.; Welch, W. J.; Romney, J. D.
Affiliation:
AA(California, University, Berkeley, Calif.), AB(California, University, Berkeley, Calif.)
Publication:
Astrophysical Journal, vol. 206, June 1, 1976, pt. 2, p. L113-L115. (ApJ Homepage)
Publication Date:
06/1976
Category:
Astronomy
Origin:
STI
NASA/STI Keywords:
GAS DENSITY, HYDROGEN CLOUDS, INTERSTELLAR GAS, QUASARS, RADIO INTERFEROMETERS, DENSITY DISTRIBUTION, INHOMOGENEITY, SIZE (DIMENSIONS)
Comment:
A&AA ID. AAA017.131.136
DOI:
10.1086/182145
Bibliographic Code:
1976ApJ...206L.113D

Abstract

The letter reports VLBI observations of neutral hydrogen absorption in front of quasar 3C 147. The results show a variation in the optical depth of interstellar H I with a scale no larger than 0.16 arcsec. Assuming that a cloud of higher density superposed on a slowly varying background is being observed, a column density of 10 to the 20th power atoms/sq cm is estimated for the H I cloud along with a maximum probable distance of 600 pc, a linear diameter of 70 AU, a density of 100,000 atoms/cu cm, and a mass of 3 ten-millionths of a solar mass. It is noted that this cloud is smaller by several orders of magnitude than any H I cloud previously observed and that its size and density are more similar to those associated with dense molecular clouds.

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