15 research outputs found
T Tauri stellar magnetic fields: He I measurements
We present measurements of the longitudinal magnetic field in the
circumstellar environment of seven classical T Tauri stars. The measurements
are based on high-resolution circular spectropolarimetry of the He I 5876
emission line, which is thought to form in accretion streams controlled by a
stellar magnetosphere. We detect magnetic fields in BP Tau, DF Tau and DN Tau,
and detect statistically significant fields in GM Aur and RW Aur A at one epoch
but not at others. We detect no field for DG Tau and GG Tau, with the caveat
that these objects were observed at one epoch only. Our measurements for BP Tau
and DF Tau are consistent, both in terms of sign and magnitude, with previous
studies, suggesting that the characteristics of T Tauri magnetospheres are
persistent over several years. We observed the magnetic field of BP Tau to
decline monotonically over three nights, and have detected a peak field of 4kG
in this object, the highest magnetic field yet observed in a T Tauri star. We
combine our observations with results from the literature in order to perform a
statistical analysis of the magnetospheric fields in BP Tau and DF Tau.
Assuming a dipolar field, we determine a polar field of ~3kG and a dipole
offset of 40deg for BP Tau, while DF Tau's field is consistent with a polar
field of ~-4.5kG and a dipole offset of 10deg. We conclude that many classical
T Tauri stars have circumstellar magnetic fields that are both strong enough
and sufficiently globally-ordered to sustain large-scale magnetospheric
accretion flows.Comment: 8 pages, 3 figures. Accepted by MNRAS. Corrected typo
Three-dimensional dust radiative-transfer models: The Pinwheel Nebula of WR104
We present radiative-transfer modelling of the dusty spiral Pinwheel Nebula
observed around the Wolf-Rayet/OB-star binary WR104. The models are based on
the three-dimensional radiative-transfer code TORUS, modified to include an
adaptive mesh that allows us to adequately resolve both the inner spiral turns
(sub-AU scales) and the outer regions of the nebula (distances of 10^4 AU from
the central source). The spiral model provides a good fit to both the spectral
energy distribution and Keck aperture masking interferometry, reproducing both
the maximum entropy recovered images and the visibility curves. We deduce a
dust creation rate of 8+-1 x 10^{-7} solar masses per year, corresponding to
approximately 2% by mass of the carbon produced by the Wolf-Rayet star.
Simultaneous modelling of the imaging and spectral data enables us to constrain
both the opening-angle of the wind-wind collision interface and the dust grain
size. We conclude that the dust grains in the inner part of the Pinwheel nebula
are small (~100A), in agreement with theoretical predictions, although we
cannot rule out the presence of larger grains (~1 micron) further from the
central binary. The opening angle of the wind-wind collision interface appears
to be about 40 degrees, in broad agreement with the wind parameters estimated
for the central binary. We discuss the success and deficiencies of the model,
and the likely benefits of applying similar techniques to the more the more
complex nebulae observed around other WR/O star binaries.Comment: 10 pages, accepted by MNRA
Emission-line profile modelling of structured T Tauri magnetospheres
We present hydrogen emission line profile models of magnetospheric accretion
onto Classical T Tauri stars. The models are computed under the Sobolev
approximation using the three-dimensional Monte Carlo radiative-transfer code
TORUS. We have calculated four illustrative models in which the accretion flows
are confined to azimuthal curtains - a geometry predicted by
magneto-hydrodynamical simulations. Properties of the line profile variability
of our models are discussed, with reference to dynamic spectra and
cross-correlation images. We find that some gross characteristics of observed
line profile variability are reproduced by our models, although in general the
level of variability predicted is larger than that observed. We conclude that
this excessive variability probably excludes dynamical simulations that predict
accretion flows with low degrees of axisymmetry.Comment: 14 pages, 12 figures. Published in MNRA
Developmental malformation of the corpus callosum: a review of typical callosal development and examples of developmental disorders with callosal involvement
This review provides an overview of the involvement of the corpus callosum (CC) in a variety of developmental disorders that are currently defined exclusively by genetics, developmental insult, and/or behavior. I begin with a general review of CC development, connectivity, and function, followed by discussion of the research methods typically utilized to study the callosum. The bulk of the review concentrates on specific developmental disorders, beginning with agenesis of the corpus callosum (AgCC)βthe only condition diagnosed exclusively by callosal anatomy. This is followed by a review of several genetic disorders that commonly result in social impairments and/or psychopathology similar to AgCC (neurofibromatosis-1, Turner syndrome, 22q11.2 deletion syndrome, Williams yndrome, and fragile X) and two forms of prenatal injury (premature birth, fetal alcohol syndrome) known to impact callosal development. Finally, I examine callosal involvement in several common developmental disorders defined exclusively by behavioral patterns (developmental language delay, dyslexia, attention-deficit hyperactive disorder, autism spectrum disorders, and Tourette syndrome)
Observations and modelling of accretion phenomena in Classical T Tauri stars
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