A Study on the Initial Mass Function of Halo Stars

The sample of subdwarfs are selected from LHS catalogue on the bases of the reduced proper motion diagram utilizing Chui criteria, and confirmed with the available photometric and/or kinematic data. Among them, 20 subdwarfs have trigonometric parallaxes with accuracy better than 20 %. The color-absolute magnitude relation is derived with them. By adopting this color-magnitude relation and V/V_m method, we have derived the subdwarf luminosity function over the absolute magnitude range of M_v = 4.5 and 9.5. This halo luminosity function is consistent with that of Eggen(1987). By adopting the available mass-luminosity relations for halo stars, we have found that the halo IMF is steeper than disk IMFs of Scalo(1986) and Salpter(1955) in this small mass region.