STRUCTURE AND KINEMATICAL PROPERTIES OF THE GALAXY AT INTERMEDIATE GALACTIC LATITUDES

We have carried out a sample survey in UBVR photometry and proper moti ons in different directions in the Galaxy, as part of an investigation of galactic structure and evolution. Three fields in the direction of galactic anticentre (l = 167 degrees, b = 47 degrees), galactic centr e (l = 3 degrees, b = 47 degrees) and galactic antirotation (l = 278 d egrees, b = 47 degrees) have been surveyed. Using our photographic pho tometry, we determine photometric distances for a sub-sample of stars in the color range 0.3 less than or equal to(B-V)less than or equal to 0.9. The stellar space velocities (U, V and W) are derived directly f rom the measured proper motions and distances. Using our new data toge ther with wide-area surveys in other fields available to date, we disc uss the radial and vertical structure of the Galaxy. We have derived t he density laws for stars as a function of distance from the galactic plane for each absolute magnitude interval. The density laws for stars with M(V) greater than or equal to 3.5 follow a sum of two exponentia ls with scale heights of 260+/-50 pc (thin disk) and 760+/-50 pc, resp ectively. This second exponential corresponds to a thick disk with a l ocal density of 7.4(-1.5)(+2.5) % relative to the thin disk. The scale lengths for these two populations are respectively 2.3+/-0.6 kpc and 3+/-1 kpc. The kinematical distribution of F and G-type stars have bee n probed to distances up to 3.5 kpc above the galactic plane. A new va lue for the, solar motion has been determined from moderately distant stars (1<2<2 kpc). It is consistent with local determinations-and impl ies that there is no large motion of the LSR relative to the mean moti on of stars at 1-2 kpc above the galactic plane. The rotational veloci ty curve is found flat in the b solar neighborhood. The radial gradien t in velocity dispersions has been determined for the thin disk popula tion. The thick disk appears as a kinematically distinct population fr om the thin disk and shows no vertical gradient. A multivariate discri minant analysis is also used to distinguish the thick disk from the th in disk and to estimate its asymmetric drift. It is found to be 53+/-1 0 km/s, independent of the galactic radius. Of the many models that ha ve been proposed for the origin of the thick disk, the evidence at pre sent seems to favour a model in which thick disk formed through the ra pid dynamical heating of an early disk by satellite accretion into the disk.