A systematic search at 1612 MHz for OH maser sources. III - The galactic distribution, kinematics, and emission properties of Type II OH/IR sources.

Details A systematic search at 1612 MHz for OH maser sources. III - The galactic distribution, kinematics, and emission properties of Type II OH/IR sources. A systematic search at 1612 MHz for OH maser sources. III - The galactic distribution, kinematics, and emission properties of Type II OH/IR sources.

Feb 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a....95..156b&link_type=abstract

Astronomy and Astrophysics, vol. 95, no. 1, Feb. 1981, p. 156-176. Research supported by the Nederlandse Organisatie voor Zuive

Astronomy and Astrophysics

Astronomy

106

Galactic Structure, Hydroxyl Emission, Infrared Astronomy, Interstellar Masers, Supergiant Stars, Variable Stars, Angular Distribution, Galactic Nuclei, Galactic Rotation, M Stars, Radial Velocity, Stellar Rotation, Type 2 Bursts

Scientific paper

The results of three systematic 1612 MHz OH surveys are combined to study the properties of Type II OH/IR sources on a galactic scale. The sample contains 114 sources found at 10° ≧ l ≧ 150°, |b| ≲ 4°. Most have no optical identification but we assume that a well evolved red giant or supergiant is at the centre of each source. We estimate the incompleteness of the sample.
l From a comparison of the observed radial velocities with those predicted by galactic rotation it follows that the sources can be separated into at least two kinematically different groups. A statistically useful separator is ΔV, the velocity difference between the two emission peaks. Type II OH/IR sources with ΔV > 29 km s-1 show only small (≲10 km s-1) random motions with respect to galactic rotation, whereas sources with ΔV < 29 km s-1 show much larger (≍ 30-40 km s-1) random motions. The first group of sources contains predominantly young stars (M supergiants, ≲107 yr), and the second group much older stars (Mira variables, ≍ 109 yr).
The galactic density distributions of both groups show a pronounced maximum at a distance R =4.5 kpc from the Galactic Centre, in common with several other Population I species. The star formation rate at R <4.5 kpc has therefore been low for the last 109 yr. Type II OH/IR sources are not the precursors of the majority of the planetary nebulae. In contrast to previous authors we find that the absolute 1612 MHz flux densities span a range of a factor 100-1000, and their numbers appear to decrease strongly with increasing flux density. This explains why nearby, optically identified sources are intrinsically weak and the unidentified sources are strong and distant.

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