Abundances of a sample of A and F-type dwarf members of the Ursa Major Group

Abundances of 11 chemical elements have been determined for 10 F and 12 A dwarfs ("normal" and chemically peculiar) bona-fide and probable members of the Ursa Major Group ( age about 500 Myr). The abundances were determined in a uniform manner using a model atmosphere analysis by minimising the chi-square of grids of synthetic spectra to observed high resolution high S/N ( R similar or equal to 25 000 and R similar or equal to 70 000) spectra obtained in three narrow spectral regions centered around 5075 angstrom, 5525 angstrom and 6160 angstrom. Specifically, Takeda's ( 1995) semi-automated procedure was used to derive the abundances of C, O, Na, Mg, Si, Ca, Sc, Fe, Ni, Y, and Ba, the projected rotational velocity v(e) sin i and the microturbulent velocity for each star analysed. In graphs [X/H] versus T-eff, the A stars exhibit larger star-to-star variations in [ e/H], [Ni/H], and [Si/H] than the F dwarfs do. The abundance of nickel is the only one that appears to be correlated with that of iron.