A NEW METHOD FOR THE DETERMINATION OF THE POPULATION TYPES OF FIELD STARS

Abstract

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 = 65.5-degrees, b = +85.5-degrees whose proper motions are available is presented. The three-modal distribution of stars with 0.72 less-than-or-equal-to G - R less-than-or-equal-to 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 sin-1 b. In the present study b = +85.5-degrees hence r is equivalent to z. The limiting distances z (or r) for Population I, Intermediate Population II and Population II are z less-than-or-equal-to 1260, 1260 less-than-or-equal-to z 2885 pc respectively. The limiting distance r and the adopted M(G) absolute magnitude for the colour-index intervals of O.72 less-than-or-equal-to G - R less-than-or-equal-to 1.08, 1.08 < G - R less-than-or-equal-to 1.31, 1.31 < G - R less-than-or-equal-to 1.50 and 1.50 < G - R less-than-or-equal-to 2.00 mag. (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.