THE 21 CM ABSORPTION PROFILES OF DR 21 AND THE SOURCE NEAR NGC 6857,
Abstract
The 21 cm absorption profiles of two dense thermal sources, DR 21 and the source near NGC 6857 have been obtained using the interferometer at the Owens Valley Radio Observatory. DR 21 shows absorption over a range of radial velocities from +18 to -20 km/sec (with respect to the local standard of rest), although on the basis of the observed radial velocity and the usual model for galactic rotation one would not expect to find galactic clouds with negative radial velocities between the sun and the source. The neighboring source DR 23 does not appear to show appreciable negative-velocity absorption. Three explanations for the observations of DR 21 are discussed. The radio source previously identified with NGC 6857 has been reported by Rubin and Turner (1969) to be centered 1 ft north of the nebula, at a position that coincides with the small planetary nebula K 3-50. The ionized hydrogen absorption for the source extends from +20 to -33 km/sec and a distance between 7.5 and 9.6 kpc is deduced. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1969
- Accession Number
- AD0696118
Entities
People
- A. R. Thompson
- M. P. Hughes
- R. S. Colvin
Organizations
- California Institute of Technology