Evidence for a Population of Numerous Binaries with Comparably Bright Components among HIPPARCOS ``Single'' F Stars

Abstract

We find evidence for the presence of a population of numerous binaries with comparably bright components (C binaries) among Hipparcos F stars that are flagged in the Hipparcos catalog as single. We propose a criterion that identifies such binaries. The criterion is based on comparison of absolute magnitude M_V obtained from the Hipparcos parallax and Johnson V magnitude with absolute magnitude derived from the dereddened uvby luminosity index c₀, M_c0. For photometrically unresolved binaries, M_V must be brighter because it represents the integrated flux of a binary system, while M_c0 is determined by the integrated spectrum and is thus close to the absolute magnitude of the primary. We have conducted a series of tests that have revealed the presence of C binaries among Hipparcos ``single'' F stars and confirmed that the proposed criterion is quite effective at identifying these stars. The C binary candidates have been found to be, on average, older than the candidates comprising single stars and binaries with disparate components (D binaries).