Catalogue Of Multiple Stars Research Articles

A census of main-sequence interactions in the Multiple Star Catalogue

ABSTRACT Statistics of hierarchical systems containing three or more stars are continuously improving. The Multiple Star Catalogue (MSC) is currently the most comprehensive catalogue of multiple-star systems and contains component masses, orbital periods, and additional information. The systems in the MSC are interesting for several reasons, including the long-term dynamical evolution of few-body systems. Although the secular evolution of triples and quadruples has been explored before, a systematic study of the systems in the MSC including also quintuples and sextuples has not been carried out. Here, we explore the main-sequence (MS) evolution of stars from the MSC based on approximately 2 × 105 secular dynamical integrations. We estimate statistical probabilities for strong interactions during the MS such as tidal evolution and mass transfer, and the onset of dynamical instability. Depending on the assumed model for the unknown orbital elements, we find that the fraction of non-interacting systems is largest for triples (∼0.9), and decreases to ∼0.6–0.8 for sextuples. The fraction of strong interactions increases from ∼0.1 to ∼0.2 from triples to sextuples, and the fraction of dynamically unstable systems increases from ∼0.001 to ∼0.1–0.2. The larger fractions of strong interactions and dynamical instability in systems with increasing multiplicity can be attributed to increasingly complex secular evolution in these systems. Our results indicate that a significant fraction of high-multiplicity systems interact or become dynamically unstable already during the MS, with an increasing importance as the number of stars increases.

Planetary stability zones in hierarchical triple star systems

A symplectic integrator algorithm suitable for hierarchical triple systems is formulated and tested. The positions of the stars are followed in hierarchical Jacobi coordinates, whilst the planets are referenced purely to their primary. The algorithm is fast, accurate and easily generalised to incorporate collisions. There are five distinct cases -- circumtriple orbits, circumbinary orbits and circumstellar orbits around each of the stars in the hierarchical triple -- which require a different formulation of the symplectic integration algorithm. As an application, a survey of the stability zones for planets in hierarchical triples is presented, with the case of a single planet orbiting the inner binary considered in detail. Fits to the inner and outer edges of the stability zone are computed. Considering the hierarchical triple as two decoupled binary systems, the earlier work of Holman & Wiegert on binaries is shown to be applicable to triples, except in the cases of high eccentricities and close or massive stars. Application to triple stars with good data in the multiple star catalogue suggests that more than 50 per cent are unable to support circumbinary planets, as the stable zone is almost non-existent.

The long-period companions of multiple stars tend to have moderate eccentricities

We examined the statistics of an angle γ between the radius vector of a visual companion of a multiple star and the vector of its apparent relative motion in the system. Its distribution is related to the orbital eccentricity distribution in the investigated sample. We found that for the wide physical subsystems of the 174 objects from the Multiple Star Catalogue is bell-shaped. The Monte-Carlo simulations have shown that our corresponds to the population of the moderate-eccentricity orbits and is not compatible with the linear distribution which follows from stellar dynamics and seems to hold for wide binaries. This points to the absence of highly elongated orbits among the outer subsystems of multiple stars. The constraint of dynamical stability of triple systems is not sufficient to explain the "rounded-off" outer orbits; instead, we speculate that it can result from the angular momentum exchange in multiple systems during their early evolution.

Statistics of Multiple Stars: Some Clues to Formation Mechanisms

The available information on the statistics of high multiplicity (3–6 components) systems is reviewed. The ratio of triple to binary systems is f3 ≍ 0.11, while fn ≍ 0.25 for higher n. Despite selection effects in the multiple star catalogue, the signatures of formation mechanisms are found in the distributions of period ratios and mass ratios. For example, the frequent occurrence of close sub-systems with periods less than 6 days can be explained by tidal dissipation in a 3-body system. In triple stars the angular momentum vectors of inner orbits are inclined to those of outer orbits by an average angle of 50°, hence the orbital spins are neither co-aligned nor completely random. Close binaries have a tendency to be found in higher-multiplicity systems, showing that close and wide binarity is statistically related. Future theoretical and observational studies are outlined.

Catalogue of Multiple Stars observed in Upper India in 1855-6

Catalogue of Multiple Stars observed in Upper India in 1855-6