Stellar Duplicity Discovered During Occultation by Asteroid (21161) Yamashitaharuo

Abstract

On 5 February 2025, an occultation of the star UCAC4 334-078310 (Gaia DR3 ID 6237155875240921728) by the main-belt asteroid (21161) Yamashitaharuo revealed the previously unknown binarity of this star. Since there is only one occultation chord, the double star solution is not unique, but rather there are four possible solutions. For solution #1, the separation is 2.2 ± 1.3 mas and the position angle is 83.7° ± 21.2°.