  Binary F stars exhibit large brightness anomaly, which is defined here as the
difference between the absolute magnitude from the uvby photometry and the
actual absolute magnitude of the star. We have found that the anomaly inversely
correlates with the binary components separation. There is evidence that the
correlation reflects actual population differences between close and wide
binary pairs, in which case it indicates that the anomaly is somehow associated
with the interaction of binary's components. The anomaly has also been found to
correlate with both kinematics and metallicity. The sense of the correlations
implies that the anomaly increases as the star evolves, suggesting a peculiar
evolution of a primary F star in a tight binary pair. This conclusion has
further been supported by the study of the age-velocity relation (AVR) of F
stars that are cataloged in the HIPPARCOS as single. Among these stars, those
with brightness anomaly were previously shown to be most likely unidentified
close binaries. We have found that the AVR of these binary candidates is
different from that of the ``truly single'' F stars. The discrepancy between
the two AVRs indicates that the putative binaries are, on average, older than
similar normal single F stars at the same effective temperature and luminosity,
which is consistent with the inferred peculiar evolution in close binaries. It
appears that this peculiarity is caused by the impact of the components
interaction in a tight pair on stellar evolution, which results in the
prolonged main sequence lifetime of the primary F star.
