The Role of Accretion Disks in Establishing the Initial Angular Momentum of Low Mass Stars

Details The Role of Accretion Disks in Establishing the Initial Angular Momentum of Low Mass Stars The Role of Accretion Disks in Establishing the Initial Angular Momentum of Low Mass Stars

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994rmxaa..29...35e&link_type=abstract

Revista Mexicana de Astronomia y Astrofisica, 29, 35

Astronomy and Astrophysics

Astronomy

4

Scientific paper

RESUMEN Las observaciones revelan que las velocidades de rotaci6n de estrellas j6venes de baja masa difieren significativamente si muestran caracteristicas de poseer discos de acreci6n 0 no. Las velocidades de rotaci6n menores se encuentran en aquellas estrellas aparentemente rodeadas de discos de acrecidn, lo que sugiere que el disco puede jugar un papel fundamental como regulador de la velocidad angular de la estrella central, balanceando la tendencia de rotar mas ra'pido en Sn contracci6n hacia la secuencia principal y por acreci6n de material de alto momento angular especfflco. Esto implicaria que el momento angular inicial de una estrella en formacidn es el mismo que posee cuando se disipa su disco de acreci6n. El intervalo de velocidades rotacionales observado entre las estrellas de edad cero en la secuencia principal y de masa determinada en cumulos j6venes podria en parte ser el resultado de un intervalo de escalas de tiempo de disipaci6n del disco: las estrellas que pierden su disco ra'pidamente serfan los rot adores mas rapidos, mientras que aquellas que conservan su disco un tiempo largo ocuparfan el extremo de baja velocidad en la distribuci6n de velocidades rotacionales en estrellas de la secuencia principal de edad cero. ABSTRACT Observations reveal that the rotational velocities of young low mass stars differ significantly depending on whether or not they show accretion disk signatures. Slower rotational velocities are found for those stars apparently surrounded by accretion disks suggesting that the disk may play a fundamental role in regulating the angular velocity of the central star, countering the tendency of the star to spin up both from contraction toward the main sequence and from accretion of disk material of high specific angular momentum. This would imply that the initial angular momentum of a forming star is the angular momentum it carries when its accretion disk is dissipated. The observed order of magnitude range in rotational velocities among ZAMS stars of a given mass in young clusters might then result in part from a range in timescales for disk dissipation: stars which lost their disks early would be among the most rapid rotators, while those which retained their disks the longest would populate the low velocity end of the ZAMS rotational velocity distribution. Key words: STARS: PRE-MAIN SEQUENCE

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