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Are Binary Separations Related to their System Mass?

Published online by Cambridge University Press:  22 February 2018

Michael F. Sterzik  and
Richard H. Durisen
Michael F. Sterzik
Affiliation:
European Southern Observatory, Chile
Richard H. Durisen
Affiliation:
Department of Astronomy, Indiana University, USA

Abstract

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We compile most recent multiplicity fractions and binary separation distributions for different primary masses, including very low-mass and brown dwarf primaries, and compare them with dynamical decay models of small-N clusters. The model predictions are based on detailed numerical calculations of the internal cluster dynamics, as well as on Monte-Carlo methods. Both observations and models reflect the same trends: (1) The multiplicity fraction is an increasing function of the primary mass. (2) The mean binary separations are increasing with the system mass in the sense that very low-mass binaries have average separations around ≈ 4AU, while the binary separation distribution for solar-type primaries peaks at ≈ 40AU. M-type binary systems apparently preferentially populate intermediate separations. Similar specific energy at the time of cluster formation for all cluster masses can possibly explain this trend.

Resumen

Resumen

Listamos los datos más recientes sobre la fracción de multiplicidad y la distributión de separaciones de binarias para distintas masas de la primaria, incluyendo primarias de muy baja masa y enanas marrones, y las comparamos con modelos dinámicos de disolución de cúmulos con N pequeño. Las predicciones de los modelos están basadas en cálculos numéricos detallados de la dinámica interna de los cúmulos así como en métodos tipo Monte Carlo. Tanto las observaciones como los modelos muestran las mismas tendencias: (1) La fracción de multiplicidad aumenta con la masa de la primaria. (2) La separación media de las binarias aumenta con la masa del sistema, de tal forma que las binarias de muy baja masa tienen separaciones medias del orden de 4 AU, mientras que la separación de las binarias de una masa solar tiene un máximo alrededor de 40 AU. Las binarias de tipo M pueblan preferentemente las separaciones intermedias. Esta tendencia puede quizás explicarse si la energía específica al momento de formarse el cúmulo es similar para cúmulos de distintas masas.

Keywords

BinariesGeneral — StarsFormation — StarsPre-Main Sequence
Type
Observational properties and Statistics of Binary Stars in the Field
Information
International Astronomical Union Colloquium , Volume 191: The Environment and Evolution of Double and Multiple Stars , August 2004 , pp. 58 - 62
Copyright
Copyright © Instituto de Astronomia – Mexico 2004

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