74 research outputs found
A Search for Consistent Jet and Disk Rotation Signatures in RY Tau
We present a radial velocity study of the RY Tau jet-disk system, designed to
determine whether a transfer of angular momentum from disk to jet can be
observed. Many recent studies report on the rotation of T Tauri disks, and on
what may be a signature of T Tauri jet rotation. However, due to observational
difficulties, few studies report on both disk and jet within the same system to
establish if the senses of rotation match and hence can be interpreted as a
transfer of angular momentum. We report a clear signature of Keplerian rotation
in the RY Tau disk, based on Plateau de Bure observations. We also report on
the transverse radial velocity profile of the RY Tau jet close to the star. We
identify two distinct profile shapes: a v-shape which appears near jet shock
positions, and a flat profile which appears between shocks. We do not detect a
rotation signature above 3 sigma uncertainty in any of our transverse cuts of
the jet. Nevertheless, if the jet is currently in steady-state, the errors
themselves provide a valuable upper limit on the jet toroidal velocity of 10
km/s, implying a launch radius of < 0.45 AU. However, possible contamination of
jet kinematics, via shocks or precession, prevents any firm constraint on the
jet launch point, since most of its angular momentum could be stored in
magnetic form rather than in rotation of matter.Comment: 10 pages, 7 figures, accepted by The Astrophysical Journa
Brown Dwarf Jets: Investigating the Universality of Jet Launching Mechanisms at the Lowest Masses
Recently it has become apparent that proto-stellar-like outflow activity
extends to the brown dwarf (BD) mass regime. While the presence of accretion
appears to be the common ingredient in all objects known to drive jets
fundamental questions remain unanswered. The more prominent being the exact
mechanism by which jets are launched, and whether this mechanism remains
universal among such a diversity of sources and scales. To address these
questions we have been investigating outflow activity in a sample of
protostellar objects that differ considerably in mass and mass accretion rate.
Central to this is our study of brown dwarf jets. To date Classical T Tauri
stars (CTTS) have offered us the best touchstone for decoding the launching
mechanism. Here we shall summarise what is understood so far of BD jets and the
important constraints observations can place on models. We will focus on the
comparison between jets driven by objects with central mass < 0.1M \odot and
those driven by CTTSs. In particular we wish to understand how the the ratio of
the mass outflow to accretion rate compares to what has been measured for
CTTSs.Comment: Proceedings of IAU meeting 275, "Jets at All Scales
The 2008-2009 outburst of the young binary system Z CMa unraveled by interferometry with high spectral resolution
Z CMa is a young binary system consisting of an Herbig primary and a FU Ori
companion. Both components seem to be surrounded by active accretion disks and
a jet was associated to the Herbig B0. In Nov. 2008, K. Grankin discovered that
Z CMa was exhibiting an outburst with an amplitude larger than any photometric
variations recorded in the last 25 years. To study the innermost regions in
which the outburst occurs and understand its origin, we have observed both
binary components with AMBER/VLTI across the Br{\gamma} emission line in Dec.
2009 in medium and high spectral resolution modes. Our observations show that
the Herbig Be, responsible for the increase of luminosity, also produces a
strong Br{\gamma} emission, and they allow us to disentangle from various
origins by locating the emission at each velocities through the line.
Considering a model of a Keplerian disk alone fails at reproducing the
asymmetric spectro-astrometric measurements, suggesting a major contribution
from an outflow.Comment: To be published in the proceedings of the SPIE'2010 conference on
"Optical and Infrared Interferometry II
Toward Resolving the Outflow Engine: An Observational Perspective
Jets from young stars represent one of the most striking signposts of star
formation. The phenomenon has been researched for over two decades and there is
now general agreement that such jets are generated as a by-product of
accretion; most likely by the accretion disk itself. Thus they mimic what
occurs in more exotic objects such as active galactic nuclei and micro-quasars.
The precise mechanism for their production however remains a mystery. To a
large degree, progress is hampered observationally by the embedded nature of
many jet sources as well as a lack of spatial resolution: Crude estimates, as
well as more sophisticated models, nevertheless suggest that jets are
accelerated and focused on scales of a few AU at most.
It is only in the past few years however that we have begun to probe such
scales in detail using classical T Tauri stars as touchstones. Application of
adaptive optics, data provided by the HST, use of specialised techniques such
as spectro-astrometry, and the development of spectral diagnostic tools, are
beginning to reveal conditions in the jet launch zone. This has helped
enormously to constrain models. Further improvements in the quality of the
observational data are expected when the new generation of interferometers come
on-line. Here we review some of the most dramatic findings in this area since
Protostars and Planets~IV including indications for jet rotation, i.e. that
they transport angular momentum. We will also show how measurements, such as
those of width and the velocity field close to the source, suggest jets are
initially launched as warm magneto-centrifugal disk winds. (abridged)Comment: 14 pages, 8 figures, contributed chapter for Planets and Protostars V
meeting (October 2005
Myths and lessons of liberal intervention: The British campaign for the abolition of the Atlantic slave trade to Brazil
This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 Martinus NijhoffThis article takes issue with recent references to the British nineteenth century campaign for the abolition of the trans-Atlantic slave trade to Brazil that serve to bolster interventionist or imperialist agendas. In particular, such accounts reproduce two and a half myths about the campaign: that it can serve as a model for the present age; that the success of the campaign can be explained through the actions of the intervening party alone (with a corresponding neglect of those of the ‘target’ state); and the half-myth that the campaign’s success was due to military action (at the expense of institutional (legal) and normative factors and the capacity of the target state). I argue instead that this case – and interventions more generally – would benefit from an analysis that considers the role of force in relation to a series of residual institutional and cultural constraints within the liberal state and to political conditions in the target state. In light of the complexities and contingencies that these factors present the underlying lesson is that military force should be used sparingly, if at all
Multiple Stellar Fly-Bys Sculpting the Circumstellar Architecture in RW Aurigae
We present high-resolution ALMA Band 6 and 7 observations of the tidally
disrupted protoplanetary disks of the RW Aurigae binary. Our observations
reveal the presence of additional tidal streams to the previously observed
tidal arm around RW Aur A. The observed configuration of tidal streams
surrounding RW Aur A and B is incompatible with a single star--disk tidal
encounter, suggesting that the RW Aurigae system has undergone multiple fly-by
interactions. We also resolve the circumstellar disks around RW Aur A and B,
with CO radii of 58 au and 38 au consistent with tidal truncation, and 2.5
times smaller dust emission radii. The disks appear misaligned by 12
or 57. Using new photometric observations from the American
Association of Variable Star Observers (AAVSO) and All Sky Automated Survey for
SuperNovae (ASAS-SN) archives, we have also identified an additional dimming
event of the primary that began in late 2017 and is currently ongoing. With
over a century of photometric observations, we are beginning to explore the
same spatial scales as ALMA
Effectiveness of physiotherapy exercise following hip arthroplasty for osteoarthritis: a systematic review of clinical trials
Background: Physiotherapy has long been a routine component of patient rehabilitation following hip joint replacement. The purpose of this systematic review was to evaluate the effectiveness of physiotherapy exercise after discharge from hospital on function, walking, range of motion, quality of life and muscle strength, for osteoarthritic patients following elective primary total hip arthroplasty.
Methods: Design: Systematic review, using the Cochrane Collaboration Handbook for Systematic Reviews of Interventions and the Quorom Statement. Database searches: AMED, CINAHL, EMBASE, KingsFund, MEDLINE, Cochrane library (Cochrane reviews, Cochrane Central Register of Controlled Trials, DARE), PEDro, The Department of Health National
Research Register. Handsearches: Physiotherapy, Physical Therapy, Journal of Bone and Joint Surgery (Britain)
Conference Proceedings. No language restrictions were applied.
Selection: Trials comparing physiotherapy exercise versus usual/standard care, or comparing two types of relevant exercise physiotherapy, following discharge from hospital after elective primary total hip replacement for osteoarthritis were reviewed.
Outcomes: Functional activities of daily living, walking, quality of life, muscle strength and range of hip joint
motion. Trial quality was extensively evaluated. Narrative synthesis plus meta-analytic summaries were performed to summarise the data.
Results: 8 trials were identified. Trial quality was mixed. Generally poor trial quality, quantity and diversity prevented explanatory meta-analyses. The results were synthesised and meta-analytic summaries were used where possible to provide a formal summary of results. Results indicate that physiotherapy exercise after discharge following total hip replacement has the potential to benefit patients.
Conclusion: Insufficient evidence exists to establish the effectiveness of physiotherapy exercise following primary hip replacement for osteoarthritis. Further well designed trials are required to determine the value of post discharge exercise following this increasingly common surgical procedure
Accretion and outflow-related X-rays in T Tauri stars
We report on accretion- and outflow-related X-rays from T Tauri stars, based on results from the "XMM-Newton Extended Survey of the Taurus Molecular Cloud.” X-rays potentially form in shocks of accretion streams near the stellar surface, although we hypothesize that direct interactions between the streams and magnetic coronae may occur as well. We report on the discovery of a "soft excess” in accreting T Tauri stars supporting these scenarios. We further discuss a new type of X-ray source in jet-driving T Tauri stars. It shows a strongly absorbed coronal component and a very soft, weakly absorbed component probably related to shocks in microjets. The excessive coronal absorption points to dust-depletion in the accretion stream
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