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Astron. Astrophys. 339, L25-L28 (1998)

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1. Introduction

Although comet Evans-Drinkwater had been discovered on May 10, 1996 (McNaught 1996), the duplicity of its nucleus was first detected only one year later, on May 5, 1997. At that time, J. Kobayashi noticed that component A, a bright condensation of total magnitude 9.8, was accompanied by component B, whose total magnitude was 12.9 (Nakano 1997). From the better fit to the available orbit, the fainter component B was immediately identified by Nakano as the principal mass.

A few days later, this identity was independently confirmed by Sekanina's (1997a) finding that, with respect to nucleus B, nucleus A was subjected to a radial nongravitational deceleration of an estimated 0.0003 the Sun's attraction. Nucleus B was therefore the leading component. It was shown long ago (Sekanina 1982a) that, invariably, a deceleration is the signature of a less enduring (and, presumably, less massive) nuclear fragment. An interesting - although possibly fortuitous - circumstance is a nearly perfect correspondence between the reported magnitude of component B and the magnitude predicted for the time (Marsden et al. 1997) from preperihelion observations made almost one year earlier. The obvious inference is that the companion - component A - was caught by Kobayashi in the middle of a major outburst (Sect. 3).

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© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998