Investigating the rotational evolution of very low-mass stars and brown dwarfs in young clusters using Monte Carlo simulations

¹ LATO – DCET, Universidade Estadual de Santa Cruz, UESC, Rodovia Jorge Amado, km 16, 45662-900 Ilhéus/BA, Brazil
e-mail: mjvasc@uesc.br
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

Received: 15 April 2016
Accepted: 9 November 2016

Abstract

Context. Very low-mass (VLM) stars and brown dwarfs (BDs) present a different rotational behaviour from their solar mass counterparts.

Aims. We investigate the rotational evolution of young VLM stars and BDs using Monte Carlo simulations under the hypothesis of disk locking and stellar angular momentum conservation.

Methods. We built a set of objects with masses ranging from 0.01 M_⊙ to 0.4 M_⊙ and considered models with single- and double-peaked initial period distributions with and without disk locking. An object is considered to be diskless when its mass accretion rate is below a given threshold.

Results. Models with initial single-peaked period distributions reproduce the observations well given that BDs rotate faster than VLM stars. We observe a correlation between rotational period and mass when we relax the disk locking hypothesis, but with a shallower slope compared to some observational results. The angular momentum evolution of diskless stars is flatter than it is for stars with a disk which occurs because the moment of inertia of objects less massive than 0.2 M_⊙ remains pratically constant for a time scale that increases with decreasing stellar mass.

Conclusions. Comparing our results with the available observational data we see that disk locking is not as important in the low-mass regime and that the rotational behaviour of VLM stars and BDs is different from what is seen in their solar mass counterparts.