Three epochs of high resolution spectra of the star ( catalog BD+20 307 ) show that it is a short period ( \sim 3.4 day ) spectroscopic binary of two nearly identical stars .
Surprisingly , the two stars , though differing in effective temperature by only \sim 250 K and having a mass ratio of 0.91 , show very different Li line equivalent widths .
A Li 6707Å line is only detected from the primary star , and it is weak .
This star is therefore likely to be older than 1 Gyr .
If so , the large amount of hot circumbinary dust must be from a very large and recent , but very late evolutionarily , collision of planetesimals .