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We report the results of an X-ray survey of bright late A and early F stars on the main sequence (m v < 6.5, 0.1 < B-V <0.5, luminosity classes IV-V). Only stars without any spectral peculiarities, listed in the Yale Bright Star Catalogue and observed by the Einstein Observatory, were included in our sample. We find significantly larger X-ray luminosities for the sample binaries than for the single stars; we construct maximum likelihood X-ray luminosity distribution functions for single stars and binaries and argue that the difference in X-ray luminosity is due to the presence of multiple X-ray sources in binaries. We show that the X-ray luminosities for single stars increase rapidly with increasing color, and we demonstrate that the relation L x /L hol % 10" 7 , which holds well for O and B stars, does not hold for A stars. For the full sample, we find no correlation between X-ray luminosity and projected equatorial rotation velocity, but for stars with B-V> 0.3, a weak correlation may exist. We argue that the observed X-ray emission in our sample stars originates from coronae, produced by magnetic dynamos in the convection zones of these stars, and discuss the evidence supporting this point of view.

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