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Astron. Astrophys. 326, 655-661

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On the nature of the Am phenomenon or on a stabilization
and the tidal mixing in binaries

II. Metallicity and pseudo-synchronization

Ján Budaj

Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, The Slovak Republic (budaj@ta3.sk)

Received 4 July 1996 / Accepted 12 May 1997


We reveal sufficient evidences that for Am binaries the metallicity might depend on their orbital periods, FORMULA , rather than on FORMULA . In particular, FORMULA index seems to decrease with increasing orbital period up to at least FORMULA , probably even up to FORMULA . 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 FORMULA . 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 FORMULA . 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.

Key words: stars: chemically peculiar - binaries: close - turbulence - diffusion - hydrodynamics

© European Southern Observatory (ESO) 1997

Online publication: September 18, 1997
Last change: October 15, 1997