18 April 2002 CfA Colloquium


Title: X-rays in the Solar System

Speaker: Alex Dalgarno

Abstract:

The unexpected discovery of X-rays with several hundred eV in energy originating in comets raises questions about the identification of the observed spectral features and the nature of the excitation mechanisms. It is argued that a major source of the X-rays is electron capture into excited states in collisions of highly-stripped heavy ions of the solar wind with the cometary gases followed by line emission. Recent laboratory data are analysed and a theoretical model is developed that yields a quantitative interpretation of the measurements.The model is used to interpret the observations of several comets and conclusions are drawn about the composition of the solar wind. Other sources of X-rays in the solar system are briefly discussed.

References for students:

Cravens 1997 Geophys. Res. lett.24,105.

Kharchenko and Dalgarno 2000 J.Geophys.Res. 105,18351.

Lisse et al. 2001 Science 292,1343.