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Binarity plays an important role in the development of most Am (metallic-lined A) stars. In general, the Am star companion has a mass similar to that of the enriched primary, as well as a relatively close orbit. These conditions are thought to lead to tidal braking, weakening of rotational turbulence in the atmosphere, and subsequent loss of the upper convective zone accompanied by increased diffusion effectiveness. The similar masses of Am star binary components indicate that they also have similar colors and luminosities. Monte Carlo modeling of the combined flux distributions (based on assumptions concerning the Am star mass function) indicate that (1) measurement of the Am star flux continuum is typically tainted by the secondary across the visual spectrum, (2) this tainting is of the same order of magnitude as that due to optical line-blanketing, and (3) this effect cannot by itself explain the region in color-color diagrams occupied by Am stars but depleted of normal A stars, thus supporting the conclusion that this region indicates the onset of convection in normal A stars.
