Abstract
We present new observations of short-period (Jupiter family) comet 48P/Johnson taken over several months when near ∼4 AU heliocentric distance. CCD photometry shows that this object has a pointlike inner surface brightness profile. It varies cyclically in brightness, with a light-curve period 14.50 ± 0.02 hr and photometric range ΔmR = 0.32 ± 0.05 mag. We attribute these variations to the rotation of a bare, aspherical nucleus with projected semiaxes 3.0 × 2.2 km (0.04 albedo assumed) and (two-peaked) rotation period 29.00 ± 0.04 hr. The phase coefficient of the nucleus is 0.059 ± 0.002 mag deg-1, consistent with a low-albedo surface. A faint tail is evident in a deep composite image but appears to contribute little to the nucleus signal.
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