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We analyse a sample of over 1000 stars from 32 fields imaged in the V and Ibands with the Wide Field and Planetary Camera, on board of the Hubble SpaceTelescope. The fields are located at Galactic latitudes | b | >= 15deg and invarious directions on the sky. We consider models for the structure of theGalaxy with different choices for the main parameters governing the shape andluminosity function of the thick disk and stellar halo. Comparing modelpredictions with the observed colour-magnitude diagram we are able to rule outan increasing or flat stellar luminosity function at the low-luminosity end. Wealso rule out large values of the vertical scale height of the thick disc, z_0,finding it to be in the range 800 <= z_0 <= 1200 pc. As for the local densitynormalization, values within the range 4 % <= n_0 <= 8 % seem to betterreproduce the data. Our data essentially rule out a flattened stellar halo (c/a<~ 0.5) or models with both large local normalization and effective radii.Comment: 7 pages LaTeX, 9 Postscript figure

Constraints on thick disc and halo parameters from HST photometry of field stars in the Galaxy