Hoanh Lam

Collision of comet Shoemaker-Levy 9 with Jupiter observed by the NASA infrared telescope facility

The National Aeronautics and Space Administration (NASA) Infrared Telescope Facility was used to investigate the collision of comet Shoemaker-Levy 9 with Jupiter from 12 July to 7 August 1994. Strong thermal infrared emission lasting several minutes was observed after the impacts of fragments C, G, and R. All impacts warmed the stratosphere and some the troposphere up to several degrees. The abundance of stratospheric ammonia increased by more than 50 times. Impact-related particles extended up to a level where the atmospheric pressure measured several millibars. The north polar near-infrared aurora brightened by nearly a factor of 5 a week after the impacts.

The effect of the impact of comet Shoemaker Levy-9 on Jupiter's aurorae

We present infrared spectra and images of the jovian aurorae taken at wavelengths sensitive to the H3+ molecular ion during the period around the impact of Comet Shoemaker Levy-9. The spectra were obtained using CGS4 on the United Kingdom Infrared Telescope and the images using NSFcam on NASAs Infrared Telescope Facility. Comparison with spectra obtained in May, 1993, shows that while the relative intensities of the northern and southern auroral zones prior to and during impact week (July 16–22, 1994) were broadly comparable with those of 1993, a few days after the last collision the northern aurora was considerably enhanced and its southern counterpart somewhat depressed. The north/south auroral ratio was returning to more normal values a week later. The effect of material drifting from the impact sites to the southern auroral zone is discussed in relation to these results.

The impact of comet Shoemaker-Levy 9 on the Jovian ionosphere and aurorae

Abstract We outline the effects of a “typical” fragment of Comet Shoemaker-Levy 9 on the ionosphere and aurorae of Jupiter, viewed chronologically from approach, through impact to longer term effects. The ionosphere is found to have been a sensitive tracer of the impact events. The powerful jovian magnetic field transmitted the effects of the collisions across hemispheres. Electrodynamical processes were particularly important around the time of fragment impact, along with shock heating of the ionosphere. Chemical reactions not usual in the jovian upper atmosphere played a key role in diminishing ionospheric and auroral emission intensities.

Highly Excited Vibrational States of the KCN Molecule

Vibrational (J= 0) states for the KCN molecule are calculated in Jacobi coordinates, employing a discrete variable representation (DVR) for the angular internal coordinate. The power of the DVR method is once again illustrated in that some 800 vibrational (J= 0) states are converged for a two-dimensional potential-energy surface. The energy region studied is that where the classical dynamics of the system are known to be chaotic. Most of the states are found to be irregular, although there are classes which appear to be regular and can be assigned effective quantum numbers corresponding to excitation in particular ‘separable’ modes of the system. Phenomenological aspects of the wavefunctions are discovered via graphical analysis, in particular many linearly localised states are identified where the potential-energy surface actually has a saddle point. The statistical behaviour of the level spacings is also investigated. Comparison with a similar study on LiCN (J. R. Henderson and J. Tennyson, Mol. Phys., 1990, 69, 639) is made.