AAS 196th Meeting, June 2000
Session 13. EUVE
Oral, Monday, June 5, 2000, 10:00-11:30am, Highland B/J

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[13.08] Constraints on models of Cometary x-ray emission with EUV and soft X-ray spectrophotometry

C. M. Lisse, D. J. Christian (Space Telescope Science Institute), K. Dennerl (MPE Garching)

We report on our Extreme Ultraviolet Explorer (EUVE) and ROSAT HRI photometric studies of close approaching comets, in particular Comets 2P/Encke and 55P/Tempel-Tuttle. EUVE observations of Comet 2P/Encke were obtained in July 1997 with the scanning telescopes and ROSAT HRI. Similar observations were obtained for Comet 55P/Tempel-Tuttle in January 1998. Extended, variable emission on the sunward side of the nucleus was found for both comets in the ROSAT HRI at 0.090 - 0.75 keV and in the EUVE scanner telescopes' Lexan B 0.090 - 0.28 keV and Al/Ti/C 0.050 - 0.16 keV bandpasses; useful upper limits were found in the Dagwood 0.020 - 0.040 eV bandpass. Similar to results obtained for other ROSAT detected comets, the emission morphology was roughly symmetric with respect to a vector from the comet's nucleus towards the Sun. The light curves from both comets showed a slowly varying baseline emission and large impulsive events. From the observed HRI count rates, we derive luminosities of 4x1014 erg sec-1 and 2x1015 erg sec-1 for Encke and Tempel-Tuttle, respectively.

Using the results of our EUVE and HRI broad band spectrophotometry, we have found that the Haeberli et al. (1997) charge transfer, plasma-dust, and attogram dust models of cometary x-ray emission are inconsistent with the data, while the Wegmann et al. (1998) charge exchange, 0.15-0.45 keV thermal bremsstrahlung, and photon index 1.6 - 2.0 power law models are most consistent with our observations.

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