The Evolutionary Status of GK Subgiants

Abstract

Snowden & Young suggested that the reason why there are GK subgiants is because they are members of binaries, which would bring them above the main sequence in an Hertzsprung-Russell (HR) diagram. They studied a sample of 30 G0-K1 IV stars and were disappointed to find only two to be spectroscopic binaries. With more accurate radial velocities I found seven binaries in their samples of subgiants and control stars; orbital elements are given for those seven. Using Hipparcos parallaxes and SIMBAD data, I found that nearly all of the G0-K1 IV stars fall on the evolutionary tracks by Garardi et al. for Population I stars with masses of 0.9-1.9 M _⊙ and ages of up to 10¹⁰ yr, which are normal parameters for nearby field stars. Therefore there is no problem regarding the existence of GK subgiants.