Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p52a..07k&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #P52A-07
Physics
2780 Solar Wind Interactions With Unmagnetized Bodies, 6025 Interactions With Solar Wind Plasma And Fields, 6060 Radiation And Spectra, 6210 Comets, 2164 Solar Wind Plasma
Scientific paper
Comet McNaught-Hartley was observed in five one-hour sessions from January 8 to 14 2001 using the advanced CCD imaging spectrometer on board the Chandra X-ray Observatory. The X-ray image of the comet does not show a crescent-like shape. Two brightness maxima are offset from the nucleus between the sunward and comet velocity directions. The comet mean X-ray luminosity is equal to 7.8x 1015 erg s-1 for photon energy E > 150 eV and aperture 1.5x 105 km where the comet X-ray brightness is 20% of the peak value. Day-to-day variations in X-rays reach a factor of 5. The comet and Earth were seeing different faces of the Sun, and the expected time delay between the solar wind events on the Earth and the comet was 6 days. The best correlation between the X-ray luminosity and the solar wind proton density is for the delay of 5.5 days and may be explained by the higher velocity of heavy ions. Gas production rate was 1029 s-1 during the observations, and the efficiency of X-ray excitation adjusted to the proton density of 10 cm-3 is equal to 5x 10-14 erg AU3/2. The strongest short-term variation was by a factor of 1.75 for 1600 s. This variation may be explained by a sudden (for a few minutes) decrease in the solar wind flux by a factor of 3. Careful background subtraction made it possible to extract the comet spectrum from 150 to 1000 eV. No signal was detected at E > 1000 eV, and an upper limit to any emission with E > 1000 eV is 0.3% of the emission at 150-1000 eV. The best χ2-fit model to the spectrum consists of 9 narrow emissions. The emission energies and intensities are in good agreement with a charge exchange spectrum calculated by us for the slow solar wind. Using this spectrum, we identify the observed emissions as (Ne7+ + Mg7+ + Mg8+) 195 eV, (Mg8+ + Mg9+ + Si8+) 250 eV, C5+ 370 and 460 eV, O6+ 560 eV, O7+ 650, 780, and 840 eV, and Ne8+ 940 eV. X-ray spectroscopy of comets may be used to diagnose the solar wind composition and its interaction with comets.
Christian Damian
Dalgarno Alexander
Kharchenko Vasili
Krasnopolsky Vladimir
Lisse Carey
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