Stellar groups, V. Luminosities, motions and masses of the late-type sub-giants

The available data for 205 subgiants of type G and later are listed in Table I. Most of these stars have visual luminosities between + 2 and + as judged by spectroscopic criteria. On the basis of current evolutionary theory this list probably contains some of the oldest stars in the solar neighbourhood. The stars for which the most reliable trigonometric parallaxes are available, shown in Fig. I, indicate an (Mv, B - v)-distribution similar to that found for the y Leonis and 61 Cygni groups and the cluster M67. The lower limit to the luminosity observed for the subgiants indicates an upper limit of i.5 X 1010 years for their ages. The solar motion, derived from the motions of approximately half the subgiants, is near 35 km/sec toward OL= 1911, 5= +440 The masses derived from the orbits of five visual binaries are discussed. First orbits are derived from three of these binaries including HD 194433 which may contain the oldest stars for which a mass determination is available. The masses of the subgiants probably lie between I and O.