The heliosphere is a bubble of hot gas in interstellar space stretching from the Sun to greater than 100 Sun-Earth distances. It contains some fraction of inflowing neutral interstellar hydrogen and helium atoms. Highly charged positive ions emanate from the Sun in the solar wind and impact the neutral material. The ions capture electrons from the atoms into high excited states that radiate primarily in the soft X-ray spectral region. The spectra provide information about the solar wind composition and velocity and the distribution of atoms in the heliosphere. The X-rays generated by the solar wind contribute to the diffuse soft X-ray background. Similar processes occur in the interaction of the solar wind ions with comets and with the extended exospheres of the planets. We are engaged in theoretical efforts to predict the spectra resulting from the collisions of the solar wind ions (recent references).

References

1. Koutroumpa, D., R. Lallement, V. Kharchenko, A. Dalgarno , R. Pepino, V. Izmodenov, and E. Quemerais, “ Charge-transfer induced EUV and soft X-ray emissions in the heliosphere”, A&A, 460, 289 (2006).
2. Sasseen T. P. , M. Hurwitz, C. M. Lisse, V. Kharchenko, A. Dalgarno et al., “ A search of EUV emission from Comets with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)”, ApJ, 650, 451 (2006).
3. Kharchenko V., A. Dalgarno, D. Schultz, and P. Stancil, “Ion emission spectra in the Jovian X-ray Aurora”, Geophys. Res. Lett., 33, L11105, (2006).
4. Dennerl K. et al., “ First observation of Mars with XMM-Newton - High resolution X-ray spectroscopy with RGS”, A&A, 451, 709 (2006).
5. Pepino, R., V. Kharchenko, A. Dalgarno, and R. Lallement, “ Spectra of the X-Ray Emission Induced in the Interaction between the Solar Wind and the Heliospheric Gas”, ApJ, 617, 1347 (2004).
6. Wargelin, B. J. , M. Markevitch, A. Dalgarno, V. Kharchenko et al., “ Chandra observations of the "dark'' Moon and geocoronal solar wind charge transfer”, ApJ, 607, 596 (2004)
7 . Kharchenko, V., M. Rigazio, A. Dalgarno, and V. Krasnopolsky, “ Charge abundances of the solar wind ions inferred from Cometary X-ray spectra”, ApJ Lett., 585 , L73 (2003)
8. Krasnopolsky, V. A., D. J. Christian, V. Kharchenko, A. Dalgarno, S. J. Wolk, C. M. Lisse, and S. A. Stern, 2002, Icarus, “X-Ray Emission from Comet McNaught-Hartley (C/1999 T1)”, 160 , 437 (2002)
9. Rigazio, M., V. Kharchenko, and A. Dalgarno, 2002, " X-ray emission spectra induced by hydrogenic ions in charge transfer collisions", Phys. Rev. A, 66, 64701 (2002)
10. Kharchenko V. and A. Dalgarno, “ Variability of cometary X-ray emission induced by solar wind ions”, ApJ Lett., 554, L99 (2001)
11. Kharchenko V. and A. Dalgarno, “ Spectra of cometary X-rays induced by solar wind ions}, J. Geophys. Res., 105, 18351 (2000)

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V. Kharchenko and A. Dalgarno