Taxonomy and Light-Curve Data of 1000 Serendipitously Observed Main-Belt Asteroids

TL;DR

This study provides a comprehensive taxonomy and light-curve analysis of 1000 Main-Belt Asteroids, revealing their distribution, rotation periods, and shape characteristics using spectrophotometry and machine learning.

Contribution

It introduces a new large dataset of asteroid spectra and light curves, applying machine learning for taxonomy, and analyzes their physical properties and shape distribution.

Findings

Nearly equal ratio of S-type to other types among observed MBAs

Resolved rotation periods for 59 asteroids, including some below 2.2 hours

Shape distribution indicates average elongation of 0.74, independent of size and taxonomy

Abstract

We present VRI spectrophotometry of 1003 Main-Belt Asteroids (MBAs) observed with the Sutherland, South Africa, node of the Korea Microlensing Telescope Network (KMTNet). All of the observed MBAs were serendipitously captured in KMTNet's large 2deg $\times$ 2deg field of view during a separate targeted near-Earth Asteroid study (Erasmus et al. 2017). Our broadband spectrophotometry is reliable enough to distinguish among four asteroid taxonomies and we confidently categorize 836 of the 1003 observed targets as either a S-, C-, X-, or D-type asteroid by means of a Machine Learning (ML) algorithm approach. Our data show that the ratio between S-type MBAs and (C+X+D)-type MBAs, with H magnitudes between 12 and 18 (12 km $\gtrsim$ diameter $\gtrsim$ 0.75 km), is almost exactly 1:1. Additionally, we report 0.5- to 3-hour (median: 1.3-hour) light-curve data for each MBA and we resolve the complete rotation periods and amplitudes for 59 targets. Two out of the 59 targets have rotation periods potentially below the theoretical zero cohesion boundary limit of 2.2 hours. We report lower limits for the rotation periods and amplitudes for the remaining targets. Using the resolved and unresolved light curves we determine the shape distribution for this population using a Monte Carlo simulation. Our model suggests a population with an average elongation $b/a = 0.74\pm0.07$ and also shows that this is independent of asteroid size and taxonomy.