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We present the first comparisons of a newly developed Galactic Structure andKinematic Model to magnitude and color counts, as well as relative propermotions, in the fields of the open clusters NGC 188 [(l, b)= (122.8 deg, +22.4deg)] and NGC 3680 [(l,b)= (286.8 deg, +16.9 deg)]. In addition to determiningthe reddening toward these two clusters, it is shown that starcounts atintermediate Galactic latitudes in the range 11< V< 17 allow us to constrainthe model scale-height for disk subgiants. We obtain a mean value of 250 +/- 32pc, in agreement with previous determinations of the scale-height forred-giants. We are also able to constrain the scale-height of main-sequencestars, and the distance of the sun from the Galactic plane, ruling out thepossibility of a value of +40 pc, in favor of a smaller value. Comparisons withthe observed proper-motion histograms indicate that the velocity dispersion ofdisk main-sequence stars must increase with distance from the Galactic plane inorder to match the observed proper-motion dispersion. The required increase isconsistent with the values predicted by dynamical models, and provides a clearobservational evidence in favor of such gradients. The shape of the observedproper-motion distribution is well fitted within the Poisson uncertainties.This implies that corrections to absolute proper motion (and, therefore, spacevelocities) for open clusters may be obtained using our model when no inertialreference frame is available. Using this approach, the derived tangentialmotions for NGC 188 and NGC 3680 are presented.Comment: Tex type, 29 pages, 9 postscript figures. Accepted for publication in  The Astronomical Journa

Galactic Structure Toward the Open Clusters NGC 188 and NGC 3680