X-ray and EUV Emission from Comets
Supervisors: Dr R G West, Dr J P Pye
One of the most unexpected results of the ROSAT X-ray astronomy mission
has been the discovery of very bright X-ray and extreme-ultraviolet emission
from comets. A sequence of observations of Comet Hyakutake were conducted by
ROSAT in the period 26-28 March
1996 as part of a research programme initiated by researchers at NASA's Goddard
Space Flight Center, in collaboration with members of the X-ray
astronomy group at the University of Leicester, the Max-Planck-Institut
fur extraterrestriche Physik, Garching, Germany and the Rutherford Appleton
Laboratory, UK. Work done at Leicester focussed upon the EUV data from the Wide
Field Camera (see image left); bright, diffuse emission is seen, roughly
co-incident with the X-rays detected with the High Resolution Imager (HRI) and
sunward of the nucleus. The EUV emission was strongly time-variable in a similar
manner to the X-rays.
This important discovery shows that there must be previously unsuspected
`high-energy'' processes taking place in the comet, probably due to the
influence of the Sun's radiation and/or the solar wind. The combination of
simultaneous X-ray and EUV measurements provides a powerful
means of investigating the cause of the comet's unexpected brightness at these
short wave lengths.
Leicester has continued to have a major role in pursuing this new branch of
X-ray astronomy; since the detection of Comet Hyakutake two further comets
(C/1990 N1 Tsuchiya-Kiuchi and C/1990 K Levy) have been detected in ROSAT WFC
survey data, taken during 1990 and 1991.
Contact: Richard West (rgw@star.le.ac.uk)
