A detailed model of the X-ray emission from comets

Comet C/LINEAR 1999 S4 was observed by the CHANDRA ACIS-S CCD spectrometer in mid July, 2000. The resultant spectrum is currently the best and most detailed example available to help elucidate the underlying physical processes that enable the comet (or the cometary interaction with the solar wind) to generate X-ray emission. We have utilized the ADAS (Atomic Data and Analysis Structure) atomic physics code to accurately simulate the X-ray spectrum of a cometary atmosphere of assumed composition (hydrogen, carbon, nitrogen and oxygen) based on the plasma interaction model of Bingham et al. (1997) and Shapiro et al. (1999). We find an excellent agreement between theory and data provided we assume an unusually low carbon abundance for the comet. This low carbon abundance was also found in the infrared spectral. data of the comet - thus confirming the X-ray result.