Age difference between the populations of binary and single F stars revealed from Hipparcos data

We have compared the kinematics and metallicity of the main-sequence binary and single uvby F stars from the Hipparcos catalog to see if the populatio ns of these stars originate from the same statistical ensemble. The velocit y dispersions of the known unresolved binary F stars have been found to be dramatically smaller than those of the single F stars. This suggests that t he population of these binaries is, in fact, younger than that of the singl e stars, which is further supported by the difference in metal abundance: t he binaries turn out to be, on average, more metal rich than the single sta rs. So, we conclude that the population of these binaries is indeed younger than that of the single F stars. Comparison of the single F stars with the C binaries (binary candidates identified in Suchkov & McMaster) has shown, on the other hand, that the latter stars are, on average, older than the s ingle F stars. We suggest that the age difference between the single F star s, known unresolved binaries, and C binaries is associated with the fact th at stellar evolution in a binary systems depends on the binary components' mass ratio and separation, with these parameters being statistically very d ifferent for the known binaries and C binaries (e.g., mostly substellar sec ondaries in C binaries vs. stellar secondaries in known binaries). In gener al we conclude that the populations of known binaries, C binaries, and sing le F stars do not belong to the same statistical ensemble. The implications of the discovered age difference between these populations along with the corresponding differences in kinematics and metallicity should be important not only for understanding the evolution of stars but also for the history of star formation and the evolution of the local Galactic disk.