Astron. Astrophys. 326, 655-661
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On the nature of the Am phenomenon or on a
and the tidal mixing in binaries
II. Metallicity and pseudo-synchronization
Astronomical Institute, Slovak Academy of Sciences,
059 60 Tatranská Lomnica, The Slovak Republic
Received 4 July 1996 / Accepted 12 May 1997
We reveal sufficient evidences that for Am binaries
the metallicity might depend on their orbital periods, ,
rather than on . In particular, index seems
to decrease with increasing orbital period up to at least
, probably even up to
. 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
. 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 .
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