Observations of Three Stellar Occultations by Comet Hale–Bopp

On June 12 1996 UT, three 11–12 R magnitude stars were occulted by comet Hale–Bopp. The passage of these stars through the cometary atmosphere was monitored at the Observatorio do Pico dos Dias (Brazil) using a 0.6 m telescope. We detected an absorption of starlight by the comet dust implying in a drop of ( 6 ± 1 ) × 10 - 2 magnitude of occulted star XPM 152-0898466 at a minimum distance of ( 4.3 ± 0.2 ) × 10 4 km from the central condensation. This result, combined with magnitude variations of other stars, suggests the detection of a jet in the coma. From our measurement of extinction, we infer that the opacity of the nucleus surface was τ ∼ 3 . The mean geometric albedo p of dust grains is ( 4.5 ± 0.7 ) × 10 - 3 . This low albedo may suggest a difference in the grain population associated to coma and jets.