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1997A&A...326..655B - Astronomy and Astrophysics, volume 326, 655-661 (1997/10-2)

On the nature of the Am phenomenon or on a stabilization and the tidal mixing in binaries. II. Metallicity and pseudo-synchronization.

BUDAJ J.

Abstract (from CDS):

We reveal sufficient evidences that for Am binaries the metallicity might depend on their orbital periods, Porb, rather than on vsini. In particular, δm1 index seems to decrease with increasing orbital period up to at least Porb≃50d, probably even up to Porb≃200d. This gives further support to our "tidal mixing + stabilization" hypothesis formulated in Part I. Moreover, while the most metallic Am stars seem to have rather large periods the slowest rotators are found to exhibit substantially shorter Porb. A questioning eye is thus cast on the generally adopted view that Am peculiarity is caused by a suppressed rotationally induced mixing in slowly rotating single' stars. The observed anticorrelation between rotation and metallicity may have also other than the textbook' explanation, namely being the result of the correlation between metallicity and orbital period, as the majority of Am binaries are possibly synchronized. We further argue that there is a tendency in Am binaries towards pseudo-synchronization up to Porb≃35d. This has, however, no serious impact on our conclusions from Part I; on the contrary, they still hold even if this effect is taken into account.