Photometry and model of near-Earth asteroid 2021 DW1 from one apparition

TL;DR

This study provides detailed photometric observations and a physical model of near-Earth asteroid 2021 DW1, including its rotation, shape, and surface properties, based on data collected during a single apparition in 2021.

Contribution

It offers the first detailed physical characterization and spin axis determination of asteroid 2021 DW1 from one apparition, including its rotation period, shape, and surface properties.

Findings

Rotation period of 0.01376 hours identified.

Two possible spin axis orientations determined.

Estimated diameter of 30 meters with albedo 0.23.

Abstract

On 4 March 2021 at 9 UTC a 30-m in diameter near-Earth asteroid 2021 DW1 passed the Earth at a distance of 570000 km, reaching the maximum brightness of V=14.6 mag. We observed it photometrically from 2 March, when it was visible at V=16.5 mag, until 7 March (V=18.2 mag). During that time 2021 DW1 swept a 170 degrees long arc in the northern sky, spanning solar phase angles in the range from 36 to 86 degrees. This made it an excellent target for physical characterisation, including spin axis and shape derivation. Convex inversion of the asteroid lightcurves gives a sidereal period of rotation P=0.013760 +/- 0.000001 h, and two solutions for the spin axis ecliptic coordinates: (A) lambda_1=57 +/- 10, beta_1=29 +/- 10, and (B) lambda_2=67 +/- 10, beta_2=-40 +/- 10. The magnitude-phase curve can be fitted with a standard H, G function with H=24.8 +/- 0.5 mag and an assumed G=0.24. The asteroid colour indices are g-i=0.79 +/- 0.01 mag, and i-z=0.01 +/- 0.02 mag which indicates an S taxonomic class, with an average geometric albedo p_V=0.23 +/- 0.02. The asteroid effective diameter, derived from H and p_V, is D=30 +/- 10 m. It was found that the inclination of the spin axis of 2021 DW1 is not perpendicular to the orbital plane (obliquity epsilon=54 +/- 10 or epsilon=123 +/- 10). More spin axes of VSAs should be determined to check, if 2021 DW1 is an exception or a typical case.