ARE METALLIC A-F GIANTS EVOLVED AM STARS - ROTATION AND RATE OF BINARIES AMONG GIANT F-STARS

We test the hypothesis of Berthet (1992) which foresees that Am stars become giant metallic A and F stars (defined by an enhanced value of t he blanketing parameter Delta m(2) of the Geneva photometry) when they evolve. If this hypothesis is right, Am and metallic A-FIII stars nee d to have the same rate of binaries and a similar distribution of v si n i. From our new spectroscopic data and from v sin i and radial veloc ities in the literature, we show that it is not, the case. The metalli c giant stars are often fast rotators with v sin i larger than 100 km s(-1), while the maximum rotational velocity for Am stars is about 100 km s(-1). The rate of tight binaries with periods less than 1000 days is less than 30% among metallic giants, which is incompatible with th e value of 75% for Am stars (Abt & Levy 1985). Therefore, the simplest way to explain the existence of giant metallic F stars is to suggest that all normal A and early F stars might go through a short ''metalli c'' phase when they are finishing their life on the main sequence. Bes ides, it is shown that only giant stars with spectral type comprised b etween F0 and F6 may have a really enhanced Delta m(2) value, while al l A-type giants seem to be normal.