HR: 0830h
AN: SH11D-1135    [PDF]
TI: Diagnostics of the Solar Wind Composition by X-Ray Spectroscopy of Comets from Chandra X-Ray Observatory
AU: * Krasnopolsky, V A
EM: vkrasn@verizon.net
AF: Vladimir Krasnopolsky, Catholic University of America, Department of Physics, Washington, DC 20064 United States
AB: X-rays are excited in comets by charge exchange of the solar wind heavy ions with cometary neutrals, which are mostly H$_2$O, 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$\deg$ and 44$\deg$, 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 $1.4\times10^{-15}$ erg s$^{-1}$ inside the apertures of $\rho$ = 1.5 and $0.5\times10^4$ km, respectively. (Brightness is 0.2 of the peak value at these $\rho$.) Efficiencies of X-ray excitation corrected to the solar wind flow are similar and equal to $4.3\times10^{-14}$ erg AU$^{3/2}$ 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$\pm$0.04 and 0.14$\pm$0.03 in MH and S4. These ratios correspond to $T=2.17$ and $1.93\times10^6$K and correlate with the solar wind speed of 390 and 500 km s$^{-1}$ in MH and S4, respectively. Ne$^{+9}$/O$^{+7}$ is $(15\pm6)\times10^{-3}$ and $(19\pm7)\times10^{-3}$, and C$^{+6}$/O$^{+7}$ is 0.7$\pm$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.
DE: 2164 Solar wind plasma
DE: 2780 Solar wind interactions with unmagnetized bodies
DE: 6025 Interactions with solar wind plasma and fields
DE: 6060 Radiation and spectra
DE: 7554 X rays, gamma rays, and neutrinos
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting