Analysis of the helium component of the local interstellar medium.
Abstract
Observations of the extraterrestrial He I 584-A emission made with an EUV experiment aboard OSO 8 are analyzed and compared with previous data from a similar experiment aboard the STP 72 1 satellite. The observations are also compared with an exhaustive set of emission models, and an envelope of possible velocities and temperatures is defined for the local interstellar medium. This envelope begins near 9 km/s with temperatures of 6000 to 8000 K, continues upward through 15 km/s with temperatures of 6000 to 15,000 K, and finally terminates near 27 km/s with temperatures of 11,000 to 14,000 K; the densities corresponding to these velocities and temperatures cover the range from 0.008 to 0.02 per cu cm. Previous observations of hydrogen L-alpha emission from the interstellar wind are reviewed and compared with the 584-A observations. With a typical value of 12% assumed for the cosmic helium abundance, the present observations imply a hydrogen density of 0.067 to 0.17 per cu cm, in good agreement with the values obtained from the L-alpha measurements.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1979
- DOI:
- 10.1086/156791
- Bibcode:
- 1979ApJ...227..816W
- Keywords:
-
- Abundance;
- Helium;
- Interstellar Matter;
- Satellite Observation;
- Astronomical Models;
- Gas Temperature;
- H Alpha Line;
- Oso-8;
- Temperature Distribution;
- Velocity Distribution;
- Astrophysics;
- Helium:Interstellar Matter