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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 358730.0, MPI für Astronomie / Publikationen_mpia
The rotation of young low-mass stars and brown dwarfs
Authors:Herbst, W.; Eislöffel, J.; Mundt, R.; Scholz, A.
Place of Publication:Tucson
Publisher:Univ. of Arizona Press
Date of Publication (YYYY-MM-DD):2007
Title of Book:Protostars and Planets V
Start Page:297
End Page:311
Full Name of Book-Editor(s):Reipurth, B.; Jewitt, J.; Keil, K.
Title of Series:The University of Arizona space science series
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We review the current state of our knowledge concerning the rotation and angular momentum evolution of young stellar objects and brown dwarfs from a primarily observational viewpoint. There has been a tremendous growth in the number of young, low-mass objects with measured rotation periods over the last five years, due to the application of wide field imagers on 1-2-m-class telescopes. Periods are typically accurate to 1% and available for about 1700 stars and 30 brown dwarfs in young clusters. Discussion of angular momentum evolution also requires knowledge of stellar radii, which are poorly known for pre-main-sequence stars. It is clear that rotation rates at a given age depend strongly on mass; higher-mass stars (0.4-1.2 solar mass) have longer periods than lower-mass stars and brown dwarfs. On the other hand, specific angular momentum is approximately independent of mass for low-mass pre-main-sequence stars and young brown dwarfs. A spread of about a factor of 30 is seen at any given mass and age. The evolution of rotation of solar-like stars during the first 100 m.y. is discussed. A broad, bimodal distribution exists at the earliest observable phases (~1 m.y.) for stars more massive than 0.4 solar mass. The rapid rotators (50-60% of the sample) evolve to the ZAMS with little or no angular momentum loss. The slow rotators continue to lose substantial amounts of angular momentum for up to 5 m.y., creating the even broader bimodal distribution characteristic of 30-120-m.y.-old clusters. Accretion disk signatures are more prevalent among slowly rotating PMS stars, indicating a connection between accretion and rotation. Disks appear to influence rotation for, at most, ~5 m.y., and considerably less than that for the majority of stars. This time interval is comparable to the maximum lifetime of accretion disks derived from near-infrared studies, and may be a useful upper limit to the time available for forming giant planets. If the dense clusters studied so far are an accurate guide, then the typical solar-like star may have only ~1 m.y. for this task. There is less data available for very-low-mass stars and brown dwarfs but the indication is that the same mechanisms are influencing their rotation as for the solar-like stars. However, it appears that both disk interactions and stellar winds are less efficient at braking these objects. We also review our knowledge of the various types of variability of these objects over as broad a mass range as possible with particular attention to magnetically induced cool spots and magnetically channeled variable mass accretion.
External Publication Status:published
Document Type:InBook
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://adsabs.harvard.edu/abs/2007prpl.conf..297H [ID No:1]
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