A Close Binary Star Resolved from Occultation by 87 Sylvia

TL;DR

This study used multiple telescopes to observe an occultation event, revealing that the star BD+29 1748 is a close binary and providing detailed measurements of the binary and asteroid parameters.

Contribution

First direct resolution of a binary star from an occultation event by an asteroid, with precise measurements of the binary separation and asteroid size.

Findings

BD+29 1748 is a close binary star with a separation of 0.097" to 0.110".

The asteroid 87 Sylvia has a size scale of 130 to 290 km.

No occultation detected for Sylvia's moonlets.

Abstract

The star BD+29 1748 was resolved to be a close binary from its occultation by the asteroid 87 Sylvia on 2006 December 18 UT. Four telescopes were used to observe this event at two sites separated by some 80 km apart. Two flux drops were observed at one site, whereas only one flux drop was detected at the other. From the long-term variation of Sylvia, we inferred the probable shape of the shadow during the occultation, and this in turn constrains the binary parameters: the two components of BD+29 1748 have a projected separation of 0.097" to 0.110" on the sky with a position angle 104 deg to 107 deg. The asteroid was clearly resolved with a size scale ranging from 130 to 290 km, as projected onto the occultation direction. No occultation was detected for either of the two known moonlets of 87 Sylvia.