EUVE Observations of Soft X-Ray Emissions from Comets 6P/d'Arrest, Bradfield (C/1995 Q1), Hyakutake (C/1996 B2), and Hale-Bopp (C/1995 O1)

V. A. Krasnopolsky (Catholic University / NASA GSFC), M. J. Mumma (NASA GSFC), M. J. Abbott (Center for EUV Astrophysics)

We observed soft X-ray emissions from four comets in a range of 70-180 eV using the Extreme Ultraviolet Explorer orbiting observatory. Comet 6P/d'Arrest was observed on 9/4/95 at a heliocentric distance r = 1.42 AU; its X-ray emission was tex2html_wrap_inline27 ph/s in an aperture radius tex2html_wrap_inline29 km and was offset by tex2html_wrap_inline31 km from the nucleus. Data for comet Bradfield (C/1995 Q1) are 11/7/95, r = 1.50 AU, tex2html_wrap_inline35 ph/s for the same aperture. Data for comet Hyakutake (C/1996 B2) are 3/22/96, r = 1.07 AU, tex2html_wrap_inline39 ph/s for the same aperture, tex2html_wrap_inline41 km. Data for comet Hale-Bopp (C/1995 O1) are 9/14/96, r = 3.07 AU, tex2html_wrap_inline45 ph/s for the same aperture and tex2html_wrap_inline47 ph/s for tex2html_wrap_inline49 km, tex2html_wrap_inline51 km. X-ray spectra and correlations of the soft X-ray emissions with the observed He 584 tex2html_wrap_inline53 emissions and with gas and dust production rates in the comets are studied to identify processes of X-ray excitation and to determine their relative contributions.