New Distant Companions to Known Nearby Stars. II. Faint Companions ofHipparcosStars and the Frequency of Wide Binary Systems

We perform a search for faint, common proper motion companions of Hipparcos stars using the recently published Lépine-Shara Proper Motion-North catalog of stars with proper motion μ > 0.15'' yr -1 . Our survey uncovers a total of 521 systems with angular separations 3'' < Δθ < 1500'', with 15 triples and 1 quadruple. Our new list of wide systems with Hipparcos primaries includes 130 systems identified here for the first time, including 44 in which the secondary star has V > 15.0. Our census is statistically complete for secondaries with angular separations 20'' < Δθ < 300'' and apparent magnitudes V < 19.0. Overall, we find that at least 9.5% of nearby ( d < 100 pc) Hipparcos stars have distant stellar companions with projected orbital separations s > 1000 AU. We observe that the distribution in orbital separations is consistent with Öpik's law, f ( s ) ds ∼ s -1 ds , only up to a separation s ≈ 4000 AU, beyond which it follows a more steeply decreasing power law f ( s ) ds ∼ s - l ds with l = 1.6 ± 0.1. We also find that the luminosity function of the secondaries is significantly different from that of the single stars' field population, showing a relative deficiency in low-luminosity (8 < M V < 14) objects. The observed trends suggest either a formation mechanism biased against low-mass companions, or a disruption over time of systems with low gravitational binding energy.