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 \farcs 097–0 \farcs 110 on the sky with a position angle 104°–107° .
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 .