Optical Interstellar Line Studies of a Nearby Cold Cloud,
Abstract
Interstellar Ca II lines in the spectra of OB stars in a large region towards the galactic center are shown to arise in the cold hydrogen cloud seen in self-absorption in the 21-cm line. The distance to one of these stars is only 200 pc, which is thus an upper limit to the cloud distance. The cold hydrogen is almost certainly associated with the dust at about 150 pc distance which covers this entire area. OH molecules have been detected in this dust at the same velocity as the cold H I. The cold hydrogen is arranged in multiple velicity component sheets; density fluctuations within these sheets have a typical scale size of about 5 pc, which is the probable thickness of the sheets. The cloud extends for at least 100 pc along the galactic plane and at least 30 pc perpendicular to it. The possible origin of this complex of cold atomic hydrogen, dust, and molecules in a local spiral arm shock is discussed. (Modified author abstract)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1973
- Accession Number
- AD0764074
Entities
People
- Kurt W. Riegel
- Richard M. Crutcher
Organizations
- Owens Valley Radio Observatory