GALACTIC STRUCTURE ALONG THE MAIN MERIDIONAL SECTION OF THE GALAXY .1. THE NORTH GALACTIC POLE (N321) FIELD

This work presents the results of a new magnitude limited survey of co lors (BVR(c)) and proper motions in a new field at the North Galactic Pole (NGP), with extent 4 degrees x 5 degrees and centered at (l simil ar or equal to 162 degrees, b similar or equal to 87 degrees). The pla te material, digitized at the Space Telescope Science Institute, is fr om sky surveys taken with the Oschin Schmidt telescope on Palomar Moun tain: POSS I, Quick-V and, for the first time, POSS II. We provide V, (B - V), (V - R(c)) photographic photometry for a stellar sample down to V = 18.5 with an accuracy of about 0.1 mag. Proper motions are on a n absolute reference frame based on external galaxies, and their mean (total) internal error is about 3 mas/yr. The procedures for the astro metric reduction and for the photometric calibration are described in detail, with emphasis on the techniques for the detection and the remo val of systematic errors. External checks have been performed with ind ependent astrometric and photometric catalogs. A comparison with the L ick NPM1 catalog shows an offset of about 4 mas/yr in mu(alpha), which does not seem to be due to the different procedures adopted in establ ishing the absolute frame. Photometric parallaxes and galactic U,V vel ocities have been derived adopting a statistical model for the chemica l effect based on a vertical metallicity gradient of partial derivativ e[Fe/H]/partial derivative z = -0.3 kpc(-1). The subsample of stars wi th 4.5 less than or equal to M(V) less than or equal to 5.0 has been a nalyzed in order to investigate the vertical density distribution up t o z approximate to 5000 pc; a least squares decomposition of the verti cal volume density with exponential density laws has converged to a th in disk with scale height of z(0) similar or equal to 259 +/- 12 pc an d a thick disk with z(0) similar or equal to 1137 +/- 61 pc and a dens ity rho(0,thick) 23 times smaller than rho(0,thin). Mean V velocities (along with their dispersion have been tabulated as a function of dist ance, and the asymmetric drift is seen with outstanding clarity. A dir ect deconvolution of the histogram, assuming Gaussian-like distributio ns for each component, requires the presence of a halo with a rotation lag of -225 km/s with respect to the Sun, and an intrinsic velocity d ispersion of 140 km/s.Finally, a set of 28 stars with similar kinemati cs at an average distance of 4400 pc has been isolated, which, if conf irmed, would support the existence of kinematically homogeneous non-th ermalized groups within the population of the extended galactic disk.