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R. F. Griffin (University of Cambridge, Institute of Astronomy), A. A. Suchkov (STScI)
We have conducted a radial-velocity survey of bright (V < 9), overluminous (\Delta Mc_0 = Mc_0 - MV \geq 0.5) F~stars within 80~pc, where absolute magnitudes MV and Mc_0 are based on the HIPPARCOS parallax and the uvby photometry, respectively. For F~stars, a value \Delta Mc_0 > 0.15 is indicative of the presence of a bright companion, so many of the overluminous ``single'' F~stars are expected to be, in fact, binaries. Our survey has tested this expectation by searching for previously unrecognized binaries among these stars. We have then compared the properties of the binaries and the constant-radial-velocity (CRV) stars in our sample. The program list comprised 118 stars that appear in the HIPPARCOS as single; 81 have been observed in this survey. Most of the remainder proved already to be known either as binary or CRV stars. The survey discovered 27 new binaries plus two that were found by HIPPARCOS\/ to show eclipses but had never been recognized as SBs. In total, 53 out of 118 stars proved to be spectroscopically double, including the previously known binaries. Orbits have been determined for the first time for 20 SB2 and 5 SB1 binaries. Comparison of the SB2 and CRV stars has shown that the two groups have significantly different kinematics. The difference implies that the CRV stars are, on average, substantially older than the SB2s. At the same time the SB2 stars have shown about the same kinematics, hence average age, as the binary F~stars from HIPPARCOS as well as single F~stars with \Delta Mc_0 within ±0.15~mag. The older kinematics of the overluminous CRV stars is consistent with the hypothesis of anomalous stellar evolution that results in anomalously long main-sequence lifetimes for those stars.