Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...228..740g&link_type=abstract
Astrophysical Journal, Part 1, vol. 228, Mar. 15, 1979, p. 740-747.
Astronomy and Astrophysics
Astronomy
23
Absorption Spectra, H Ii Regions, Milky Way Galaxy, Nebulae, Radio Sources (Astronomy), Density Wave Model, H Lines, Hydrogen Atoms, Hydrogen Ions, Light Emission, Line Spectra
Scientific paper
H I absorption profiles toward three galactic H II regions, NGC 7538, DR 7, and a component of W31, have been measured using the NRAO spectral-line interferometer. Comparison of the NGC 7538 spectrum with synthetic spectra derived from various kinematic models indicates that a nonlinear density-wave model reproduces both the presence and the absence of absorption and is thus the preferred model for this portion of the Galaxy. The H I absorption toward W31, when compared with the H I emission in the vicinity, suggests that the ratio of matter in cool clouds to that in a hotter intercloud medium changes profoundly interior to 4 kpc in the Galaxy: there are relatively few cool clouds between 1.8 and 4 kpc from the galactic center. The spectrum toward DR 7 shows evidence either of large (40 km/s) noncircular motions of the H II region or the H I, or of extreme spatial structure in the H I of the Perseus arm.
Greisen Eric W.
Lockman Felix J.
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