AAT Observations of the SL9 Fragment C, D, G, K, N, R, V, and W Impacts with Jupiter: Lightcurves and Imaging

Details AAT Observations of the SL9 Fragment C, D, G, K, N, R, V, and W Impacts with Jupiter: Lightcurves and Imaging AAT Observations of the SL9 Fragment C, D, G, K, N, R, V, and W Impacts with Jupiter: Lightcurves and Imaging

Aug 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001icar..152..366m&link_type=abstract

Icarus, Volume 152, Issue 2, pp. 366-383 (2001).

Computer Science

1

Scientific paper

We used the InfraRed Imaging Spectrometer (IRIS) on the Anglo-Australian Telescope to monitor the July 1994 impacts of Comet Shoemaker-Levy 9 with Jupiter. Spectral image cubes were obtained for the impacts of fragments C, D, G, K, R, and W. These data provide time sequences of spatially resolved spectra in K-band (1.98 to 2.40 μm), with a spectral resolution of 300 (λ/Δλ) and a spatial sampling of 0.6 arcsec/pixel. Fast-rate 2.35-μm filter photometry was used to monitor the impacts of fragments N and V. Our imaging and spectral observations track the entire evolution of each impact, from the time the fragment entered the jovian atmosphere, until the impact site rotates into view. In this paper, we concentrate on photometry and imaging results. We present photometrically calibrated lightcurves for seven impacts, and an estimate of the peak brightness for the V impact. Each event we observed, with the exception of V, was first detected as a faint ``precursor,'' which was followed 5-10 min later by a much brighter ``main event''. Precursor flashes for fragments G and K were first recorded about 30 and 90 s before an impact event was detected by instruments on the Galileo spacecraft. The precursor for the N impact was seen in our data 4 s before detection by the Galileo SSI, but may have occurred up to 30 s earlier due to gaps in our time sampling. The steady initial brightening of the lightcurves for fragments G and K indicates that these impacts may have been preceded by infalling dust. A radiative transfer model was used to determine the minimum vertical altitude at which the incoming meteor would have been directly visible to ground-based observers. The results indicate that the first precursor is most likely due to detection of impacting dust from each fragment's coma, rather than a bolide produced by the fragment itself. The onset of the main event and the first detection of high-temperature CO occur at times that are not a function of impactor energy. However, the time to reach peak brightness in the NIR lightcurves is a strong function of impactor energy, with lowest to highest energy impactors (N to K) taking from 2 to 8 min to reach peak flux after the onset of the main event. Very different peak impact brightnesses were found when comparing fragments from the main comet train with fragments with similar preimpact brightnesses that had been observed to travel displaced from the main train. These differences indicate compositional or structural differences between these two families of fragments.

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