The size distributions of asteroid families in the SDSS Moving Object Catalog 4
Abstract
Asteroid families, traditionally defined as clusters of objects in orbital parameter space, often have distinctive optical colors. We show that the separation of family members from background interlopers can be improved with the aid of SDSS colors as a qualifier for family membership. Based on an ∼88,000 object subset of the Sloan Digital Sky Survey Moving Object Catalog 4 with available proper orbital elements, we define 37 statistically robust asteroid families with at least 100 members (12 families have over 1000 members) using a simple Gaussian distribution model in both orbital and color space. The interloper rejection rate based on colors is typically ∼10% for a given orbital family definition, with four families that can be reliably isolated only with the aid of colors. About 50% of all objects in this data set belong to families, and this fraction varies from about 35% for objects brighter than an H magnitude of 13 and rises to 60% for objects fainter than this. The fraction of Ctype objects in families decreases with increasing H magnitude for H>13, while the fraction of Stype objects above this limit remains effectively constant. This suggests that Stype objects require a shorter timescale for equilibrating the background and family size distributions via collisional processing. The size distribution varies significantly among families, and is typically different from size distributions for background populations. The size distributions for 15 families display a welldefined change of slope and can be modeled as a "broken" double powerlaw. Such "broken" size distributions are twice as likely for Stype familes than for Ctype families (73% vs. 36%), and are dominated by dynamically old families. The remaining families with size distributions that can be modeled as a single power law are dominated by young families (<1 Gyr). When size distribution requires a double powerlaw model, the two slopes are correlated and are steeper for Stype families. No such slopecolor correlation is discernible for families whose size distribution follows a single power law. For several very populous families, we find that the size distribution varies with the distance from the core in orbitalcolor space, such that small objects are more prevalent in the family outskirts. This "size sorting" is consistent with predictions based on the Yarkovsky effect.
 Publication:

Icarus
 Pub Date:
 November 2008
 DOI:
 10.1016/j.icarus.2008.07.002
 arXiv:
 arXiv:0807.3762
 Bibcode:
 2008Icar..198..138P
 Keywords:

 Astrophysics
 EPrint:
 50 pages, 16 figures, accepted for publication in Icarus