The First Observation of Sulfur in Anomalous Cosmic Rays by the GEOTAIL and the WIND Spacecrafts
Abstract
The Geotail high-energy particle instruments have observed cosmic-ray particles in the energy range from 3 MeV n-1 to 150 MeV n-1 at 1 AU during the period 1992 September-1995 August. A remarkable enhancement of anomalous cosmic-ray (ACR) N, O, Ne, and C is observed during the period. A measurable enhancement of the sulfur flux below about 20 MeV n-1 was observed. This is the first evidence showing the existence of sulfur in the anomalous component. The flux increase of anomalous sulfur, with a first ionization potential (FIP) of 10.4 eV, is smaller than that of ACR carbon with an FIP of 11.3 eV and much smaller than those of high-FIP elements, which suggests that the fractions of neutral carbon and sulfur atoms are significantly low in the very local interstellar medium.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1997
- DOI:
- 10.1086/310533
- Bibcode:
- 1997ApJ...477L.111T
- Keywords:
-
- ISM: COSMIC RAYS;
- ISM: GENERAL;
- ISM: Cosmic Rays;
- ISM: General