The frequency and mass-ratio distribution of binaries in clusters II: radial segregation in the nearby dissolving open clusters Hyades and Praesepe

Abstract

ABSTRACT We have determined the mass functions, mass-ratio distribution functions, and fractions of binary stars with mass ratios above particular thresholds for radially separated populations of stars in the nearby open clusters Hyades and Praesepe. Radial mass segregation is detected, with the populations of stars within the tidal radii having much flatter mass functions than those outside the tidal radii. Within the tidal radii, the frequency of binary stars with mass ratio q > 0.5 is 50–75 per cent higher for Hyades and 5–30 per cent higher for Praesepe. We also, for the first time, detect mass-ratio radial segregation. Of the binaries for which q > 0.5, ∼80 per cent of the inner Hyades population also have q > 0.75, while for the extra-tidal population, the ratio is ∼50 per cent. For Praesepe, ∼67 per cent of the inner sample have q > 0.75, and 35–45 per cent of the outer sample.