36th DPS Meeting, 8-12 November 2004
Session 21 Comets: Nuclei
Oral, Wednesday, November 10, 2004, 10:30-12:00noon, Clark

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[21.05] Chandra Observations of a Collisionally and Optically Thin Charge Exchange System Comet 2P/Encke 2003

D.J. Christian (Queens University), C.M. Lisse (UMD/JHU-APL), K. Dennerl (MPE), S.J. Wolk (CXC), D. Bodewits (U. Groningen), M.R. Combi (UM), R. Hoekstra (U. Groningen), J.T.T. Makinen (ESA-Estech), H.A. Weaver (JHU-APL)

The highly favorable perigee passage of the x-ray bright comet 2P/Encke in late 2003 provided an excellent opportunity to use Chandra's high spatial, spectral, and temporal resolution to study cometary x-ray emission in the low neutral target density, low x-ray flux regime. The 1997 ROSAT/EUVE observations of Encke (Lisse et al. 1999) and the nucleus rotation studies of Luu and Jewitt (1990, most likely rotation period = 15 hours) suggested a simple Chandra experiment - continuous ACIS-S observations of Encke over 15 hours during the time of its closest approach to Earth.

Here we report initial results from our X-ray observations. X-ray emission from comet Encke was found only in a small, asymmetric region between 1500 km - 40,000 km from the nucleus. The Encke ACIS-S3 200 -- 1000 eV spectrum shows many of the same x-ray emission lines previously observed from comets (C+5, O+6,O+7), including confirmation of several emission lines in the 800 to 1000 eV range. However, the Encke spectrum shows very different line ratios in the 200 - 700 eV range than any previous comet. A lightcurve with peak-to-peak amplitude of 20% and period 11.7 hours was found over the 15 hour observing period. Comparing the observations to contemporaneous measurements of the coma and solar wind made by other means, we find the combination of a low density, collisionally thin (to charge exchange) coma and a post-massive X-flare, high temperature, moderate density solar wind can explain our unusual Encke x-ray observations.


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Bulletin of the American Astronomical Society, 36 #4
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