WISE/NEOWISE Observations of the Hilda Population: Preliminary Results

TL;DR

This study analyzes NEOWISE observations of 1023 Hilda asteroids, revealing their size, albedo, and composition, and introduces a new method for taxonomic classification based on infrared data.

Contribution

It provides the first large-scale infrared-based analysis of Hilda asteroid sizes, albedos, and compositions, including a new classification method using WISE data.

Findings

Hildas have low average albedo of 0.055.

The Hilda collisional family is brighter and mainly D-type.

The Schubart family is darker, mainly P-type or C-type.

Abstract

We present the preliminary analysis of 1023 known asteroids in the Hilda region of the Solar System observed by the NEOWISE component of the Wide-field Infrared Survey Explorer (WISE). The sizes of the Hildas observed range from $\sim 3 - 200$km. We find no size - albedo dependency as reported by other projects. The albedos of our sample are low, with a weighted mean value $p_V = 0.055\pm0.018$, for all sizes sampled by the NEOWISE survey. We observed a significant fraction of the objects in the two known collisional families in the Hilda population. It is found that the Hilda collisional family is brighter, with weighted mean albedo of $p_V = 0.061\pm0.011$, than the general population and dominated by D-type asteroids, while the Schubart collisional family is darker, with weighted mean albedo of ($p_V = 0.039\pm0.013$). Using the reflected sunlight in the two shortest WISE bandpasses we are able to derive a method for taxonomic classification of $\sim 10%$ of the Hildas detected in the NEOWISE survey. For the Hildas with diameter larger than 30km there are $67^{+7}_{-15}%$ D-type asteroids and $26^{+17}_{-5}%$ C-/P-type asteroids (with the majority of these being P-types).