Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh11d1135k&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SH11D-1135
Physics
2164 Solar Wind Plasma, 2780 Solar Wind Interactions With Unmagnetized Bodies, 6025 Interactions With Solar Wind Plasma And Fields, 6060 Radiation And Spectra, 7554 X Rays, Gamma Rays, And Neutrinos
Scientific paper
X-rays are excited in comets by charge exchange of the solar wind heavy ions with cometary neutrals, which are mostly H2O, OH, and O. The excitation cross sections are known with a reasonable accuracy from theory and laboratory studies. The advanced capabilities of the Chandra X-ray Observatory (CXO) and the recently developed method of analysis [Krasnopolsky et al. Icarus 160, 437, 2002] of the CXO observations of comets result in identification of the emissions excited by the solar wind ions O+8, O+7, C+6, C+5, Ne+9, Ne+8, Mg+10, Mg+9, Mg+8, and Si+9. The CXO observations of comets McNaught-Hartley (MH) and LINEAR S4 (S4) have been processed using this method to compare X-rays from those comets and the composition of the solar wind. The X-ray isophotes are crescent-like in S4 and more circular in MH because of the different phase angles (98° and 44° , respectively). The peak X-ray brightness is greater in S4 than that in MH by a factor of 1.5 and smaller by a factor of 1.7 after the correction for heliocentric distance. The X-ray luminosities of MH and S4 are equal to 8.6 and 1.4*E-15 erg s-1 inside the apertures of ρ = 1.5 and 0.5*E4 km, respectively. (Brightness is 0.2 of the peak value at these ρ .) Efficiencies of X-ray excitation corrected to the solar wind flow are similar and equal to 4.3*E-14 erg AU3/2 in both comets. This confirms the solar wind excitation of X-rays in comets. The line identification is given. Ion ratios in the solar wind have been extracted from the spectra. O+8/O+7 is equal to 0.29+/-0.04 and 0.14+/-0.03 in MH and S4. These ratios correspond to T=2.17 and 1.93*E6K and correlate with the solar wind speed of 390 and 500 km s-1 in MH and S4, respectively. Ne+9/O+7 is (15+/-6)*E-3 and (19+/-7)*E-3, and C+6/O+7 is 0.7+/-0.2 in both MH and S4. X-ray spectroscopy of comets may be used as a diagnostic tool to study the solar wind composition.
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