The Dusty, Solar Type Spectroscopic Binary BD +20 307

The dustiest known main‐sequence star, BD +20 307, is actually a double‐lined binary with a period of 3.4202 days and a circular orbit. The system is also metal poor with [Fe/H] = −0.4. The components are late‐F and early‐G dwarfs and have a mass ratio of 1.07. The photometric period of about 3.5 days indicates that the components are synchronously rotating. The metal poor, binary nature invalidates the idea that the object is a very young single star with a warm planet‐making dust disk. Instead, the metal poor nature of the system and the lithium abundances of the components argue that the system is likely several billion years old, and so the dust disk results from the recent collision of two planetary mass rocky objects. Thus, BD +20 307 may well be the first known system with planets orbiting a close binary star.