HR: 1330h
AN: P43A-06    [Abstracts]
TI: X-Ray and EUV Spectra of Comets
AU: * Krasnopolsky, V A
EM: vkrasn@verizon.net
AF: Department of Physics, Catholic University of America, 620 Michigan Avenue, N.E., Washington, DC 20740 United States
AB: Six comets have been observed using Chandra X-ray Observatory, and spectra of two comets, LINEAR S4 and McNaught-Hartley (MH), have been analyzed. A method was developed for processing, extraction, and analysis of the CXO/ACIS spectra of comets. This method differs from the standard CXO software and is based on a careful background correction (partially at the expense of the photon statistics) and extension of the spectrum down to 150 eV where the CXO/ACIS sensitivity is still significant. The x-ray luminosities of MH and prebreakup S4 are equal to 8.6 and 1.4× 10¹⁵ erg s^-1 inside the apertures of 1.5 and 0.5× 10⁴ km, respectively. (These boundaries are at 20% of the peak brightnesses.) Efficiencies of x-ray excitation corrected for the solar wind flow are similar and equal to 4.3× 10¹⁴ erg AU^3/2, confirming the solar wind excitation of x-rays in comets. Spectra of MH and S4 consist of 10 and 8 emissions, respectively. Emissions at 380, 460, 560, 650, and 920 eV are present in both comets and identified as C⁺⁵, O⁺⁶, O⁺⁷, and Ne⁺⁸. These emissions and those at 780 and 850 eV in MH and 820 eV in S4 make it possible to determine some ion ratios in the solar wind: O⁺⁸/O⁺⁷ = 0.29 ± 0.04 and 0.14 ± 0.02, Ne⁺⁹/O⁺⁷ = (15± 6)× 10^-3 and (19 ± 7)× 10^-3 in MH and S4, respectively, and C⁺⁶/O⁺⁷ = 0.7 ± 0.2 in both comets. The observed Ne⁺⁸ emissions are the first data on Ne⁺⁹ in the solar wind. X-ray spectroscopy of comets may be used as a diagnostic tool to study the solar wind composition and its interaction with comets. Though the EUVE spectra of comet Hyakutake were measured with even better resolving power than the CXO spectra, their quantitative analysis is more difficult because of the great number of blended emissions. The most prominent lines are He⁺ 304 Å, O⁺⁴ 215 Å, and C⁺⁴ 249 Å. These lines were the first charge exchange emissions detected in comets. Although α-particles are much more abundant than heavy ions in the solar wind, the He⁺ emission consitutes a quarter of all charge exchange photons from comets because of a comparatively low charge exchange cross section for α-particles. The O⁺⁴ and C⁺⁴ lines are mostly from the secondary ions that appear in collisionally thick parts of comae. The O⁺ lines at 538, 617, and 430/442 Å are excited by photoionization of atomic oxygen, and the absense of Ne 630 Å confirms the formation of Oort cloud comets in the Jupiter-Neptune region of the solar nebula.
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: 6210 Comets
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly