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Binary Star Formation and Mass Outflows: MHD Nested Grid Simulation

Published online by Cambridge University Press:  22 February 2018

M.N. Machida
Affiliation:
Hokkaido University National Astronomical Observatory, Japan
K. Tomisaka
Affiliation:
National Astronomical Observatory, Japan
T. Matsumoto
Affiliation:
Hosei University

Abstract

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We study the binary star formation process from a rotating magnetized molecular cloud. We assume an isothermal cylindrical cloud in hydrostatic balance whose rotation axis and the direction of global magnetic field lines are both identical, and parallel to the cylinder axis. We added axisymmetric and non-axisymmetric density perturbations to the initial state and followed the subsequent evolutions. The evolution is characterized by three parameters: the amplitude of the non-axisymmetric perturbations, the rotation speed, and the magnetic field strength. As a result, it is found that non-axisymmetry hardly evolves in the early phase, but begins to grow after the gas contracts and forms a thin disk. There are two types of fragmentation: fragmentation from a ring and that from a bar. Thin adiabatic cores fragments if a thickness is smaller than 1/4 of the radius. For the fragments to survive, they should be formed in a heavily elongated barred core or a flat round disk. In the models showing fragmentation, outflows from respective fragments are found as well as those driven by the rotating bar or the disk.

Resumen

Resumen

Estudiamos el proceso de formación estelar a partir de una nube molecular magnetizada y en rotación. Partimos de una nube cilíndrica isotérmica en equilibrio hidrostático, cuyo eje de rotación coincide con las líneas del campo magnético global, y es paralelo al eje del cilindro. Añadimos perturbaciones de densidad axisimétricas y no axisimétricas al estado inicial, y estudiamos la evolución subsecuente. La evolución se caracteriza por tres parámetros: la amplitud de las perturbaciones no axisimétricas, la velocidad de rotación y la intensidad del campo magnético. Encontramos que la desviación de la axisimetría apenas cambia en la fase inicial, pero que empieza a crecer después de que el gas se contrae y forma un disco delgado. Hay dos tipos de fragmentación: a partir de un anillo y de una barra. Los núcleosadiabáticos delgados se fragmentan si su espesor es menor que 1/4 del radio. Para que los fragmentos sobrevivan, deben formarse en un núcleo muy elongado, o en un disco plano. En los modelos con fragmentación se encuentran flujos emanando tanto de los fragmentos como de la barraen rotación o del disco.

Type
Theoretical Approaches to Multiple Stars and Their Formation
Copyright
Copyright © Instituto de Astronomia – Mexico 2004

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