Comet Bowell (1980b): Measurement of the optical thickness of the coma and particle albedo from a stellar occultation

Comet Bowell (1980b) was observed to pass within 0.25 ± 0.09 arc sec of a star (about 540 km at the comet), where the absorption of starlight by the dust coma was found to be 3% (±1%). The implied optical thickness of 0.03 differs greatly from other determinations and gives a mass of 3 × 10¹³ g for the coma within 1 × 10⁴ km of the nucleus. Coupled with absolute continuum filter photometry, these results indicate a very low particle albedo consistent with fluffy carbonaceous material. This experiment indicates the need to observe nearly central occulations by several observers to measure the optical thickness profile of a comet. The advantages of using a charge-coupled device area photometer for such observations are discussed.