Main sequence A and F stars show various interesting phenomena: chemical peculiarities (Am, Fm, Ap...) on the one hand and/or pulsation on the other hand. Numerous studies have been devoted to this part of the HR diagram near the ZAMS, but few have explored more evolved stars. In this paper, we examine the rate of binaries and rotation of giant A and F stars.
In a study of 132 giant A and F stars, Hauck (1986) showed that
36% of them have an enhanced value of the blanketing parameter 
(defined roughly speaking by 
)
characterising Am and 
Del stars. He showed also that this parameter
could probably be interpreted in terms of metallicity for giant A and F
stars. This interpretation was confirmed by Berthet (1990,
1991) from a detailed abundance analysis of such objects. His study
pointed out that these stars have chemical properties similar to those
of Del stars, i.e. an overabundance of iron peak elements and
especially of heavier elements such as Sr and Ba, and solar composition
for Ca and Sc. Am stars have similar characteristics for iron peak
elements, but Ca and Sc are deficient by factors of about 10.
Based on chemical abundances, position in the 
plane of
Strömgren photometry, rotation and duplicity
of Del stars,
Kurtz (1976) suggested that these stars are evolved Am stars.
The fact that Del and giant metallic A and F stars harbour
similar chemical properties suggests also a link between Am and
giant metallic A and F stars. Thus, a star could begin its life
on the main sequence as an Am star, then, as abundances of Ca
and Sc increase to quasi-solar values with evolution, it would become
a Del star and finally a giant metallic A-F where Ca and
Sc are solar (Berthet 1992).
To explain the emergence of chemical anomalies in Am stars, one generally invokes the radiative diffusion theory developed by Michaud et al. (1983). This theory predicts that, in slow rotators, helium is no longer sustained and flows inside the star and gradually disappears from the atmosphere. The diffusion process could therefore take place just below the thin H convective zone where the diffusion time is short with respect to the stellar lifetime; the chemical elements whose radiative acceleration is larger than gravity become overabundant and, in the opposite case, underabundant. The convective zone becomes deeper with evolution and so leads to normalisation of the surface abundance. This theory explains the chemical anomalies in Am stars and the increase of Ca and Sc abundances with time.
The chemical anomalies predicted by the diffusion theory are generally
larger than the observed anomalies. These differences come from
uncertainties of the atomic data but also from some mechanism in the stellar
atmosphere. The mass loss probably takes a prominent part: a rate of about
is sufficient to reduce the theoretical
overabundance of heavy elements to observed abundances (Charbonneau &
Michaud 1991). Fast rotation (
> 120 kms-1)
generates meridional circulation which prevents the disappearance of the
helium ionisation zone, so the metallic anomalies cannot appear (Michaud
1983). Observationally, the upper limit of rotation for Am stars is
about 100 kms-1 (Abt & Moyd 1973), while for normal
stars, we observe projected rotational velocities larger than 100
kms-1, which is in agreement with the diffusion theory. The
meridional circulation cannot be invoked to reduce theoretical abundances to
observed ones: in some cases, they can increase the theoretical abundances
and qualitatively no relation exists between and the chemical
anomalies in the velocity range characteristic of Am and Fm stars (
). Indeed, the time diffusion under the hydrogen
convective zone is shorter than that of the meridional circulation.
The rate of binaries is completely different in Am and normal stars: Am
stars are often members of tight binaries (
100 days), while normal
stars in double systems often have larger periods (P > 100 days). So, we
would be tempted to explain the low rotation of Am stars by tidal braking.
Nevertheless, Zahn (1977) showed that this effect is really
important only for tight binaries with a period less than 7 days. On the
other hand, Abt & Levy (1985) showed that 75% of Am stars
have periods below 1000 days, so they do not necessarily belong to tight
binaries. Other mechanisms must contribute to reduce the rotational velocity
to 100 kms-1 or less. One of them may be the evolutionary expansion
of stars during their main sequence lifetime. According to Abt & Levy
(1985), during this phase, the velocity decreases by a factor of 2
and consequently most of the normal A stars may become Am stars before
leaving the main sequence. These authors suggest also the possibility of
tidal braking during the pre-main sequence phase to explain the exclusion of
normal stars with a period comprised between 10 and 100 days.
The goal of the present work is to compare the and the rate of
binaries among Am and giant metallic A and F stars in order to consider the
possibility of a link between these two types of stars. To this end, we have
measured at OHP some of Hauck's stars having no radial velocities or , or only old determinations. These data should allow to strengthen a
preliminary work (North 1994) which casts some doubts on the
validity of the scenario advocated by Berthet (1992).