Aperture synthesis observations of galactic H II regions. III. Small H II regions in the anticenter region.
Abstract
Results are presented for aperture-synthesis observations at wavelengths of 6 and 21 cm of the H II regions S 254, S 255, S 256, S 257, S 258, S 266, S 271, and S 272. Flux densities are determined with an accuracy of about 15% by planimetering of contour maps, and physical parameters of each region are derived from the observed quantities in terms of a model H II region consisting of pure hydrogen uniformly distributed in a cylinder whose depth equals its diameter. Properties of the individual regions are discussed, with emphasis on rms electron densities and the nature of the exciting stars. The radial velocities of the regions are shown to indicate that they all lie in the Perseus Arm and are spread out over a length of 300 pc. It is found that none of the regions is excited by a star of spectral type earlier than O9.5, star formation is probably occurring on a small scale in this part of the Perseus Arm, most of the exciting stars seem to have formed completely independently of each other, all but one of the regions appear to have an ionized mass of the order of 1 solar mass or less, and the masses of the exciting stars appear to be at least an order of magnitude greater than the ionized-gas masses.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 1976
- Bibcode:
- 1976A&A....52..175I
- Keywords:
-
- Galactic Structure;
- H Ii Regions;
- Microwave Emission;
- Radio Astronomy;
- Stellar Evolution;
- Radio Telescopes;
- Spiral Galaxies;
- Stellar Models;
- Synthetic Arrays;
- Astrophysics