Age and metallicity for six LMC clusters and their surrounding field population

We investigate, on the basis of CCD Stromgren photometry, the ages and meta llicities of six LMC clusters together with their surrounding field populat ion. The clusters and metallicities are: NGC 1651 (in the range [Fe/H] = -0 .65 dex to -0.41 dex), NGC 1711 (-0.57 +/- 0.17 dex), NGC 1806 (-0.71 +/- 0 .23 dex), NGC 2031 (-0.52 +/- 0.21 dex) and NGC 2136/37 (-0.55+/-0.23 dex) and NGC 2257(-1.63+/-0.21dex). The metallicities for NGC 1651, NGC 1711, NG C 1806 and NGC 2031 have been determined for the first time (NGC 2031 and N GC 2136/37 are interesting for the Cepheid distance scale). In the cluster surroundings, we found about 650 field stars that were suita ble to be used for a determination of an age-metallicity relation (AMR). Ou r method is to estimate ages for individual stars on the basis of Stromgren isochrones with individually measured metallicities. With this method we a re able to sample the AMR of the field population up to 8 Gyr. Our metallicity data are incompatible with models predicting many metal-poo r stars (G-dwarf problem). The metallicity of the field population increase d by a factor of six, starting around 2 Gyr ago. The proposed AMR is consis tent with the AMR of the LMC cluster system (including ESO 121 SC03 and thr ee clusters with an age of 4 Gyr). The proposed AMR is incompatible with the recently proposed AMR by Pagel & Tautvaisviene: (1998).