1998A&AS..127..277K

We test the hypothesis of Berthet (1991A&A...251..171B) which foresees that Am stars become giant metallic A and F stars (defined by an enhanced value of the blanketing parameter {DELTA}m₂ of the Geneva photometry) when they evolve. If this hypothesis is right, Am and metallic A-FIII stars need to have the same rate of binaries and a similar distribution of vsini. From our new spectroscopic data and from vsin i and radial velocities in the literature, we show that it is not the case. The metallic giant stars are often fast rotators with vsin i larger than 100km/s, while the maximum rotational velocity for Am stars is about 100km/s. The rate of tight binaries with periods less than 1000 days is less than 30% among metallic giants, which is incompatible with the value of 75% for Am stars (Abt & Levy 1985ApJS...59..229A). 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 ``metallic" phase when they are finishing their life on the main sequence. Besides, it is shown that only giant stars with spectral type comprised between F0 and F6 may have a really enhanced {DELTA}m₂ value, while all A-type giants seem to be normal.