Occultation of GSC 23450183 by (704) Interamnia on 1996 December 17

M. W. Buie, L. H. Wasserman, R. L. Millis, N. M. White, R. Nye, E. W. Dunham, A. S. Bosh (Lowell Obs.), R. Stone (USNOFS), W. B. Hubbard, R. Hill (Univ. of Az.), D. Dunham (CSC), R. Fried (Braeside Obs.), D. Klinglesmith IV (Etscorn Obs.), J. Sanford (Orange City Astron. Obs.), P. Schwaar, P. Maley (Phoenix, AZ), W. Owen, L. Benner (JPL), A. S. Rivken, J. Spitale, R. L. Marcialis, L. A. Lebofsky (Univ. of Az.)

The sixth largest of the known asteroids, (704) Interamnia, was observed to occult GSC 23450183 (from the HST Guide Star Catalog) by 10 teams of observers. The chords cover the southern 60% of the profile of the asteroid. Our occultation results indicate a best fit circular profile with a radius of 164.6 km which is very close to the IRAS diameter. The residuals in the fit are generally less than 10 km but some are clearly due to topography on the object. The prediction for the event came from transit telescope measurements which indicated a formal 1- tex2html_wrap_inline11 uncertainty of 94 km. The actual track was 233 km from the prediction for a 2.5- tex2html_wrap_inline11 deviation. The lack of coverage on the north end of the object was caused by a concentration of stations more to the south based on the transit predictions.

We redetermined the rotation period of 8.70 tex2html_wrap_inline15 0.06 hours from the data of Lustig and Hahn (1976). From our additional lightcurve observations just before the occultation, we find that H tex2html_wrap_inline17 = 6.758 and the aspect was near a broad secondary minimum in the lightcurve. At the time of the occultation, the solar phase angle was 11 degrees and the lightcurve amplitude was 4%. The lightcurve also clearly shows a tertiary maximum 0.15 rotations earlier than the occultation aspect. This lightcurve structure supports the presence of topography on the object as seen in the limb fit to the occultation chords.