STATISTICAL INVESTIGATION AND MODELING OF SUNGRAZING COMETS DISCOVERED WITH THE SOLAR AND HELIOSPHERIC OBSERVATORY

摘要

More than 300 sungrazing comets, most of them discovered with the Solar and Heliospheric Observatory (SOHO) coronagraphs since the beginning of 1996, are known to belong to the Kreutz group or system. Moving about the Sun in similar orbits, they are of indisputably common parentage and represent by far the most extensive data set in the history of investigations of cometary splitting. This study compares the SOHO sungrazers, which always disappear during their approach to the Sun, with the sungrazers detected earlier with the other space-borne coronagraphs (Solwind and Solar Maximum Mission [SMM]) as well as with the bright members of the Kreutz system, discovered from the ground between 1843 and 1970. Collected, summarized, and reviewed information on the sungrazers' light curves indicates that there is a difference of 20 mag (a factor of 10~8 in brightness) between the brightest sun-grazer, C/1882 R1, and the faintest objects detectable with the SOHO instruments. The headless comet C/1887 B1 is suggested to be a transition object between the bright sungrazers and the corona-graphically discovered ones: its physical behavior was similar to that of the latter comets, but it survived the perihelion passage. This study also (1) examines temporal and spatial distributions of the SOHO sungrazers; (2) depicts correlations among their orbital elements; (3) distinguishes among tidally triggered, post-tidal, and terminal fragmentation; (4) reiterates the conclusion made in an earlier paper that post-tidal, secondary fragmentation events are occurring throughout the orbit, including the region of aphelion; (5) determines the relationship between a breakup's location in the orbit and the perturbations of the orbital elements of a fragment caused by the momentum it acquires during the separation from the parent; (6) shows that collisions of the Kreutz system comets with the Sun are clearly possible; (7) finds that minor fragments acquire enough extra momentum during each of the breakup episodes that their motions carry no "memory" of these events other than the most recent one; (8) offers a law for simulating the temporal distribution of these events; and (9) proposes a conceptual model scenario for the formation and evolution of the Kreutz system, including the process of progressive fragmentation. It appears that most of the mass is still locked in the major fragments (particularly C/1882 R1) and that therefore this comet system is relatively young. This paper is a first step in a massive investigation of the Kreutz system, which will combine deterministic and Monte Carlo techniques to verify the paradigms of the proposed conceptual model and eventually will develop a specific evolutionary scenario. This approach will account fully for effects of the planetary perturbations, where appropriate, and from time to time the results will be updated as the statistical sample of the SOHO sungrazers continues to grow.