Radio and optical observations of high- and intermediate-velocity gas in the nearby interstellar medium.
Abstract
Using observations at the 21-cm wavelength obtained with the Lovell Telescope the authors report on the detection of a weak H I emission feature at a velocity +100 km s-1 LSR and of column density log N(H I) = 18.5±0.2) towards the star 4 Lac. The feature corresponds in velocity with a high-velocity gas component which the authors have observed in several UV resonance lines in IUE spectra of this star. The component gas temperature which is derived from radio, optical and UV spectra lies in the range 5000 to 9000K and the line-of-sight column thickness is estimated to be less than 10 pc. The relationship between this observed feature and the widely distributed High-Velocity Clouds (HVCs) is considered briefly. H I components are detected also at intermediate velocities (between -20 and +25 km s-1) which vary significantly on an angular scale ≈0°1. Towards the star 4 Lac, components are observed in Na I within the same velocity range. If, as the authors suggest, the H I and Na I components correspond, then the intermediate-velocity gas lies in the foreground to the star and the observed spatial variations occur on a scale ⪉2 pc.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 1991
- DOI:
- 10.1093/mnras/249.2.282
- Bibcode:
- 1991MNRAS.249..282B
- Keywords:
-
- Interstellar Gas;
- Radio Astronomy;
- Velocity Distribution;
- Visual Observation;
- Iue;
- Ultraviolet Spectra;
- Visible Spectrum;
- Astrophysics