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The Distribution of Separations of Wide Binaries of Different Ages

Published online by Cambridge University Press:  22 February 2018

Arcadio Poveda
Affiliation:
Institute de Astronomía, Universidad Nacional Autónoma de México
Christine Allen
Affiliation:
Institute de Astronomía, Universidad Nacional Autónoma de México

Abstract

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For the purpose of understanding how the distribution of major semiaxes of double and multiple stars has evolved from the earliest ages up to the ages of the oldest systems, we have studied a number of different groups of such systems. We review and expand our previous work on the following groups of stars: (a) The wide binaries in the IDS; (b) Luyten’s common proper motion pairs (the LDS catalogue), (c) Our catalogue of nearby wide binaries divided into two groups: the youngest and the oldest; (d) The common proper motion pairs in the Orion Nebula cluster; (e) Our sample of high velocity, low metallicity binaries that represents a population of very old systems. From the very young binaries (Orion Nebula Cluster) to the oldest (thick disk and halo), all groups show a distribution of major semiaxes following Oepik, i.e., f(a) dada/a (where a is the major semiaxis), valid over an interval of a between 60 AU and am(t), am(t) being a maximum semiaxis which depends on the age of the binaries as well as on the number density and velocities of the massive objects they encounter as they travel in the Galaxy. Strong gravitational encounters in recently formed multiple systems were found to produce an Oepik distribution, which at small separations (a ≤ 40 − 60 AU) gets truncated by circumstellar disks and close binaries, and at large separations gets depleted by encounters with massive objects.

Resumen

Resumen

Con el propósito de entender cómo evoluciona la distribución de separaciones de los sistemas dobles y múltiples hemos estudiado varios grupos de muy distintas edades. Reseñamos y complementamos nuestro trabajo previo para los siguientes grupos de binarias: (a) Las binarias abiertas del IDS. (b) Los pares de movimiento propio común de Luyten (LDS). (c) Nuestro catálogo de binarias del entorno solar, dividido en dos grupos: las más jóvenes y las más viejas. (d) Los pares de movimiento propio común del cúmulo de la Nebulosa de Orión. (e) Nuestra muestra de binarias de alta velocidad y baja metalicidad. Encontramos que desde los grupos más jóvenes (cúmulo de la Nebulosa de Orión) hasta los más viejos (disco grueso y halo galácticos), la distribución de semiejes mayores es la de Oepik. Esta es válida desde a igual a 60 AU hasta am(t), donde am (t) es un semieje máximo que depende de la edad de la binaria y de la densidad y velocidad de los perturbadores masivos que ésta encuentra en su recorrido por la Galaxia. Los encuentros gravitacionales intensos en un proto-cúmulo producen binarias con la distribución de Oepik; ésta se ve truncada a separaciones pequeñas por los discos circunestelares y las binarias cerradas, y a separaciones grandes por los encuentros con objetos masivos.

Type
Observational properties and Statistics of Binary Stars in the Field
Copyright
Copyright © Instituto de Astronomia – Mexico 2004

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