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Three epochs of high resolution spectra of the star BD+20 307 show that it isa short period (~3.5 day) spectroscopic binary of two nearly identical stars.Surprisingly, the two stars, though differing in effective temperature by only~250 K and having a mass ratio of 0.91, show very different Li line equivalentwidths. A Li 6707 Angstrom line is only detected from the primary star, and itis weak. This star is therefore likely to be older than 1 Gyr. If so, the largeamount of hot circumbinary dust must be from a very large and recent, but verylate evolutionarily, collision of planetesimals.

On the Binary Nature of Dust-encircled BD+20 307