1994A&AS..106..107K

A method for separation of the field stars into population types by means of their spatial distributions and its application on 1092 stars in SA 57, with galactic coordinates l=65.5deg, b=+85.5deg whose proper motions are available is presented. The three-modal distribution of stars with 0.72≤G-R≤1.08 mag (Fig. 1) which is not contaminated by evolved stars enables us to determine the limiting distances z to galactic plane for three populations such as Population I, Intermediate Population II and Population II. The combination of z with the galactic latitude b gives us the limiting distance r to the Sun for these populations; i.e.: r=z/sinb. In the present study b=+85.5deg hence r is equivalent to z. The limiting distances z (or r) for Population I, Intermediate Population II and Population II are z≤1260, 1260≤z<2885 and z>2885 pc respectively. The limiting distance r and the adopted M(G) absolute magnitude for the colour-index intervals of 0.72≤G-R≤1.08, 1.08<G-R≤1.31, 1.31<G-R≤1.50 and 1.50<G-R≤2.00mag. (Table 1) give us the limiting apparent magnitude for each interval and for each population (Table 2). The method is confirmed by the distributions of transverse velocities in the direction of galactic rotation relative to the Sun.