摘要：We present analyses of and results for multiple components of Comet 73P/Schwassmann-Wachmann 3 at two apparitions. A total of eight nights of narrowband photometry were obtained during the comet's 2006 apparition from February 25 to September 24 at Lowell Observatory. The comet's very close passage of Earth and sporadic outbursts allowed us to successfully measure the primary body, "C," as well as components "B," "G," and "R." We additionally include four nights of narrowband photometry from 1995, obtained at Perth Observatory between October 19 and November 21, one to two months after the initial fragmentation event and outburst. We determined production rates for OH, NH, CN, C3, and C2, along with a proxy for the dust production, A(θ)fρ, and our 2006 measurements show considerable variation in behavior among the components, and for the gas species as compared to the dust grains. The two components having the best temporal coverage, C and B, both exhibit evidence for strong seasonal effects with larger production rates prior to perihelion than after. Because C showed little or no evidence of outbursts, its derived active area (based on water production rates) appears to be dominated by ice vaporizing from the nucleus; the fractional active area of the total nucleus surface varied from 56% (2006 February) to 125% (May) and back down to 11% (September) following perihelion. Except for when Component B was in outburst, C always had higher production rates than B, implying a significantly larger effective active area on its nucleus' surface. Unlike the gas species, dust production showed large and varying trends with both aperture size and with time, implying a significant change in the properties of the dust grains during the 2006 apparition. Due to the fragmentation event in 1995, the majority of active surfaces on the various components observed in 2006 are freshly exposed from the interior of Schwassmann-Wachmann 3's nucleus, thus permitting us to directly probe the chemical composition of the relatively pristine interior. Relative abundances, expressed as production rate ratios between gas species, were compared among the four components and to values determined prior to the fragmentation, as well as to those measured in other comets. Our measurements indicate each component, to within the uncertainties, has the same composition and that this composition is consistent with that measured in the pre-fragmented nucleus. Moreover, C2 and C3 are both strongly depleted when compared to the majority of comets, placing Schwassmann-Wachmann 3 among the more extreme comets within the carbon-chain depleted class identified by A'Hearn et al. With the material released from the interior of the comet yielding comparable depletions of carbon-chain molecules as the original surface of the nucleus, we conclude that carbon-chain depletion is not caused by evolution of the surface, and so must instead reflect the primordial composition at the time and location that the comet accreted.
关键词：comets: individual (73P/Schwassmann-Wachmann 3);techniques: photometric Online-only material: color figure
