THE METALLICITY DISTRIBUTION OF G-DWARF IN THE SOLAR NEIGHBORHOOD

We derive a new metallicity distribution of G dwarfs in the solar neig hbourhood, using uvby photometry and up-to-date parallaxes. Our distri bution comprises 287 G dwarfs within 25 pc from the Sun, and differs c onsiderably from the classic solar neighbourhood distribution of Pagel & Patchett and Pagel by having a prominent single peak around [Fe/H] = -0.20 dex. The raw data are corrected for observational errors and c osmic scatter assuming a deviation sigma = 0.1. In order to obtain the true abundance distribution, we use the correction factors given by S ommer-Larsen, which take into account the stellar scale heights.The di stribution confirms the G dwarf problem, that is, the paucity of metal -poor stars relative to the predictions of the simple model of chemica l evolution. Another feature of this distribution, which was already a pparent in previous ones, is the small number of metal-rich stars agai n in comparison with the simple model. Our results indicate that it is very difficult to fit the simple model to this distribution, even wit h the definition of an 'effective yield'. A comparison with several mo dels from the literature is made. We find that models with infall are the most appropriate to explain the new metallicity distribution. We a lso show that the metallicity distribution is compatible with a major era of star formation occurring 5 to 8 Gyr ago, similar to results fou nd by several authors.