Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue

TL;DR

This paper introduces Bayesian methods to identify and analyze wide and comoving stellar companions in the Hipparcos Catalogue, revealing previously unnoticed companions and providing new insights into stellar associations within 100 parsecs.

Contribution

Develops Bayesian statistical techniques for detecting and assigning probabilities to stellar companions, including escaped and wide pairs, using Hipparcos data.

Findings

Identifies ~220 high-probability companions within 0.01-1 pc.

Provides first evidence for ~300 companions separated by 1-8 pc.

Discovers known and new stellar pairs, including naked-eye and faint companions.

Abstract

We develop Bayesian statistical methods for discovering and assigning probabilities to non-random (e.g., physical) stellar companions. These companions are either presently bound or were previously bound. The probabilities depend on similarities in corrected proper motion parallel and perpendicular to the brighter component's motion, parallax, and the local phase-space density of field stars. Control experiments are conducted to understand the behavior of false positives. The technique is applied to the Hipparcos Catalogue within 100 pc. This is the first all-sky survey to locate escaped companions still drifting along with each other. In the <100 pc distance range, ~220 high probability companions with separations between 0.01 - 1 pc are found. The first evidence for a population (~300) of companions separated by 1 - 8 pc is found. We find these previously unnoticed naked-eye companions (both with V<6th mag): Capella & 50 Per, delta Vel & HIP 43797, Alioth (epsilon UMa), Megrez (delta UMa) & Alcor (80 UMA), gamma & tau Cen, phi Eri & eta Hor, 62 & 63 Cnc, gamma & tau Per, zeta & delta Hya, beta01, beta02 & beta03 Tuc, N Vel & HIP 47479, HIP 98174 & HIP 97646, 44 & 58 Oph, s Eri & HIP 14913, and pi & rho Cep. High probability fainter companions (V > 6th mag) of primaries with V < 4th mag are found for: Fomalhaut (alpha PsA), gamma UMa, alpha Lib, Alvahet (iota Cephi), delta Ara, beta Ser, iota Peg, beta Pic, kappa Phe and gamma Tuc.