Catching Some Sun: Probing the Solar Wind with Cometary X-Ray and Far-Ultraviolet Emission
Abstract
Strong X-ray and far-ultraviolet emission from comets is the direct result of charge exchange reactions of solar wind ions with the neutral coma of comets. Here we report experimental state-selective cross sections of electron capture and use these to predict cometary line emission. Our results show that helium line ratios are a direct diagnostic of the solar wind velocity, while their absolute intensities are linked to the local density of the solar wind. Comparison with observations of Hale-Bopp yields a velocity of 220 km s-1 and a helium density of 0.6 cm-3, and observations of Hyakutake show that it interacted with a faster wind of 375 km s-1 and a helium density of 10-3 cm-3. The potential of line emission by heavy minor ions is also demonstrated. Spectral lines with energies greater than 650 eV contain a wealth of information on the original composition of the wind, while lines at lower energies are used best to study the interaction processes themselves.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2004
- DOI:
- 10.1086/421064
- Bibcode:
- 2004ApJ...606L..81B
- Keywords:
-
- Atomic Processes;
- Comets: General;
- Solar System: General;
- Sun: Solar Wind;
- Ultraviolet: Solar System