RGU-photometry of a starfield close to M 67 and space density behaviour in the anticentre-northern galactic meridian.

A photographic three-colour photometry in the RGU system in a starfield near M 67 (ι = 210°.6, b = + 32?2) of 1.70 square degrees containing 759 stars down to the limiting magnitude of G = l6^m.5, with no interstellar absorption, led to logarithmic space density functions for the photometrically separable populations of late- type giants and main-sequence stars of populations I and II (Tables II, III and IV; Figs. 3, 4 and 5). They are all compared with the corresponding functions in Karaali's (1984) Praesepe field (ι = 205°.9, b = + 32°.4), and have, in both fields, practically the same zero-points and about the same (negative) gradients, with the exception of the giant- functions, where differences appear, as expected from corresponding differences in the apparent densities present in the G-fractioned two-colour diagrams of figures 2. The present field was investigated with the purpose to check the gradually more detalled isodensity pattern in the anticentre-northern quarter of the galactic meridian, given by drawing the lines connecting the three (logarithmic) isodensity points D* (= log D + 10) = 5, 5.5 and 6 for the stars with 4^m < M(G) <5^m of population II on the solar vectors to : SA 51 and SA 57 ; SA 51, SA 54 and 57 ; SA 51, Praesepe, SA 54 and SA 57 (solid; dashed ; dotted lines in Fig. 1, respectively). The results are shown in figure 6, containing : (i) the mean isodensity pattern given by, and (ii) the z-scale height of the (4^m <M(G) < 5^m) group of population II stars in the directions to all five starfields: SA 51, Praesepe + our field, SA 54 and SA 57 (Sect. 5).