Publications (2)0 Total impact
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ABSTRACT: The physical mechanisms that set the initial rotation rates in massive stars
are a crucial unknown in current star formation theory. Observations of young,
massive stars provide evidence that they form in a similar fashion to their
low-mass counterparts. The magnetic coupling between a star and its accretion
disk may be sufficient to spin down low-mass pre-main sequence (PMS) stars to
well below breakup at the end stage of their formation when the accretion rate
is low. However, we show that these magnetic torques are insufficient to spin
down massive PMS stars due to their short formation times and high accretion
rates. We develop a model for the angular momentum evolution of stars over a
wide range in mass, considering both magnetic and gravitational torques. We
find that magnetic torques are unable to spin down either low or high mass
stars during the main accretion phase, and that massive stars cannot be spun
down significantly by magnetic torques during the end stage of their formation
either. Spin-down occurs only if massive stars' disk lifetimes are
substantially longer or their magnetic fields are much stronger than current
observations suggest.
01/2012;
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ABSTRACT: Observations show that star formation is an inefficient and slow process.
This result can be attributed to the injection of energy and momentum by stars
that prevents free-fall collapse of molecular clouds. The mechanism of this
stellar feedback is debated theoretically: possible sources of pressure include
the classical warm HII gas, the hot gas generated by shock-heating from stellar
winds and supernovae, direct radiation of stars, and the dust-processed
radiation field trapped inside the HII shell. In this paper, we measure
observationally the pressures associated with each component listed above
across the giant HII region 30 Doradus in the Large Magellanic Cloud. We
exploit high-resolution, multi-wavelengh images (radio, infrared, optical, and
X-ray) to map these pressures as a function of position. We find that radiation
pressure dominates within 75 pc of the central star cluster, R136, while the
HII gas pressure dominates at larger radii. By contrast, the dust-processed
radiation pressure and hot gas pressure are generally weak and not dynamically
important, although the hot gas pressure may have played a more significant
role at early times. Based on the low X-ray gas pressures, we demonstrate that
the hot gas is only partially confined and must be leaking out the HII shell.
Additionally, we consider the implications of a dominant radiation pressure on
the early dynamics of 30 Doradus.
08/2010;
