MULTIPLICITY AND PERIOD DISTRIBUTION OF POPULATION II FIELD STARS IN SOLAR VICINITY

We examine a sample of 223 F, G, and early K metal-poor subdwarfs ([m/H] < -1) with high proper motions (mu > 0 ''.2 yr(-1)) at distances of up to 250 pc from the Sun. By means of our own speckle interferometric observations conducted on the 6 m Bolshoi Azimuthal Telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, and the spectroscopic and visual data taken from the literature, we determine the frequency of binary and multiple systems in this sample. The ratio of single, binary, triple, and quadruple systems among 221 primary components of the sample is 147:64:9:1. We show that the distribution of orbital periods of binary and multiple subdwarfs is asymmetric in the range of up to P = 10(10) days, and has a maximum at P = 10(2)-10(3) days, which differs from the distribution, obtained for the thin disk G dwarfs. We estimated the number of undetected companions in our sample. Comparing the frequency of binary subdwarfs in the field and in the globular clusters, we show that the process of halo field star formation by the means of destruction of globular clusters is very unlikely in our Galaxy. We discuss the multiplicity of old metal-poor stars in nearby stellar streams.