Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........8s&link_type=abstract
Thesis (PH.D.)--MASSACHUSETTS INSTITUTE OF TECHNOLOGY, 1995.Source: Dissertation Abstracts International, Volume: 56-04, Secti
Astronomy and Astrophysics
Astrophysics
1
Collisional Evolution, Lightcurves
Scientific paper
The Koronis asteroid family is believed to have formed through the catastrophic collisional disruption of a large parent body. Collisional evolution studies have thus far not well constrained its age, although it appears to be younger than the Eos family (Binzel, (7)). It has been hypothesized that the relatively large mean amplitudes of rotational brightness variations observed from its members are due to spin axes of member asteroids being preferentially aligned at low obliquities. Such spin axis alignment could only occur for a young family, since as family members undergo collisional evolution subsequent to their formation, it's expected each object's spin axis would be reoriented away from that of the parent body on a relatively short time scale. The present work was undertaken to test whether family members have retained a preferential orientation. A long-term survey of lightcurves for members of the Koronis family, and subsequent analysis of their distributions of spin axes, have been completed. The observational database includes published and unpublished rotational lightcurves obtained through 1994. The most recent data (1992-1994) were obtained using CCD imaging systems during 111 nights at the MIT Wallace Astrophysical Observatory (Westford, MA), 5 nights at the University of Texas McDonald Observatory, and 3 nights at the Michigan-Dartmouth-MIT Observatory. Spin axis solutions of nine Koronis family asteroids are now available, including 243 Ida whose pole and shape were determined prior to the Galileo flyby by Binzel et al. (11). The results support the hypothesis that the spin vectors are preferentially clustered, to within the axis ambiguities inherent in the axis-determination method used, and the obliquities of the sample objects appear to be partitioned into two relatively narrow groupings near 25^circ and 55 ^circ. A very crude minimum family age of about 50 million years is estimated based on the limited dispersion of the axis latitudes. The reason for apparent clustering of the spin axis longitudes is not clear, but may mean differences in their rates of forced solar precession are small. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).
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