Model-compared RGU-photometric space density gradients in the intermediate-latitude field NGC 2403.

The total logarithmic space density histograms for late-type giants and for dwarfs falling into consecutive 1^m^-intervals of absolute magnitude within the M_G_-calibrated regions in the RGU-Two-Colour Diagram (Figs. 3) have been determined according to the standard method of the Basle programs (cf., e.g., appendix of Fenkart et al., 1987) in the direction of the intermediate-latitude field NGC 2403 (l = 151^deg^, b = +29^deg^) and plotted into figures 4a and b to f, respectively. They are quantitatively compared to the theoretical gradients predicted for this direction by a representative set of multi-component models (Sect. 4.2, Fig. 5, Tab. IV), as it has been done, systematically and homogeneously for a number of investigations within the recently initiated model comparison phase of the Basle programs (cf., e.g., Fenkart and Karaali, 1987). A detailed discussion of the comparison results with respect to the differing behaviour of the used model gradients in different distance ranges again strongly suggests the existence of a thick disk component; nevertheless, a revision of the normalisation or scale-height parameters of the thin disk components of this model might impose itself later, when more analogous comparisons will be at hand and certain indications in this respect should confirm themselves (Sect. 4.3). On the basis of an extrapolation of the results obtained within the M_G_-calibrated region of the Two-Colour Diagram (M_G_ <= +8^m^), the dwarfs beyond this limit which represent about 30% of all treated stars, can be included into the discussion, at least to the extent that a lower limit for the M_G_-range within which they appear in our field can be determined (Sect. 5).