Photometry and Spin Rate Distribution of Small-Sized Main Belt Asteroids

TL;DR

This study reports photometric observations of 32 small main belt asteroids, analyzing their spin periods and comparing their spin rate distribution to larger asteroids and NEAs, revealing size-dependent spin characteristics.

Contribution

It provides new spin period data for small main belt asteroids and demonstrates the effectiveness of wide-field CCD photometry in studying asteroid spin statistics.

Findings

Small asteroids have a spin rate distribution similar to NEAs.

The median spin period of observed asteroids is 3.7 hours.

Small MBAs do not follow the Maxwellian distribution like larger asteroids.

Abstract

Photometry results of 32 asteroids are reported from only seven observing nights on only seven fields, consisting of 34.11 cumulative hours of observations. The data were obtained with a wide-field CCD (40.5'x27.3') mounted on a small, 46-cm telescope at the Wise Observatory. The fields are located within 1.5 degrees from the ecliptic plane and include a region within the main asteroid belt. The observed fields show a projected density of ~23.7 asteroids per square degree to the limit of our observations. 13 of the lightcurves were successfully analyzed to derive the asteroids' spin periods. These range from 2.37 up to 20.2 hours with a median value of 3.7 hours. 11 of these objects have diameters in order of two km and less, a size range that until recently has not been photometrically studied. The results obtained during this short observing run emphasize the efficiency of wide-field CCD photometry of asteroids, which is necessary to improve spin statistics and understand spin evolution processes. We added our derived spin periods to data from the literature and compared the spin rate distributions of small main belt asteroids (5>D>0.15 km) with that of bigger asteroids and of similar-sized NEAs. We found that the small MBAs do not show the clear Maxwellian-shaped distribution as large asteroids do; rather they have a spin rate distribution similar to that of NEAs. This implies that non-Maxwellian spin rate distribution is controlled by the asteroids' sizes rather than their locations.