DPS Pasadena Meeting 2000, 23-27 October 2000
Session 36. Comets: Orbital Dynamics, Nuclei
Oral, Chairs: H. Weaver, H. Levison, Wednesday, 2000/10/25, 4:00-6:00pm, Little Theater (C107)

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[36.06] HST and VLT Investigations of the Fragments of C/1999 S4 (LINEAR)

H.A. Weaver (JHU), R. West (ESO), M.F. A'Hearn (Univ. Md.), C. Arpigny (Univ. Liège), J.M. Bauer (Univ. Hawaii), M.R. Combi (Univ. Mich.), J.K. Davies (JAC), C.E. Delahodde (ESO/Chile), P.D. Feldman (JHU), M.C. Fes tou (ESO/Chile), O.R. Hainaut (ESO/Chile), R. Hook (ESO/ECF), L. Jorda (MPI), M.S.W. Keesey (JPL/Caltech), P.L. Lamy (LAS), C.M. Lisse (STScI), B.G. Marsden (SAO), K.J. Meech (Univ. Hawaii), Z. Sekanina (JPL/Caltech), I. Toth (Konkoly Obs.), G.-P. Tozzi (Arcetri Obs.)

Observations of C/1999~S4 (LINEAR) with the Hubble Space Telescope (HST) on 2000 August 5.167--5.467 UT and with the Very Large Telescope (VLT) on August 6.978--6.999 UT revealed the presence of over 17 fragments following the breakup of the nucleus in late July. Nearly half the fragments were located in a ``swarm'' near the western ``tip'' of the dust tail (i.e., the sunward side of the tail), but several were significantly sunward of the tip, including one object that we tentatively identify as the primary remnant of the original nucleus. The correspondence between fragments in the HST and VLT images is generally very good, but the brightest fragment in the HST image is not seen in the VLT image, indicating rapid variability in activity. The dynamic nature of the fragments was further highlighted by a dramatic change in the appearance of the fragments in VLT images taken during August 9.976--9.996 UT, when they were barely detectable. The locations and brightnesses of the fragments will be presented, along with a discussion of the dynamics associated with the breakup event and its subsequent evolution.

We thank the Directors of the Space Telescope Science Institute and the ESO/VLT for approving our observing programs for Director's Discretionary Time.

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