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High resolution CO observations of S88-B
CO J = 2-1 and 13CO J = 2-1 and 1-0 observations have been made of the H II region S88-B, using the 15-m James Clerk Maxwell telescope in Hawaii and the 20-m telescope at Onsala. The core of the cloud is resolved into a horseshoelike structure which surrounds a diffuse reflection nebula. The central core has a mass of ≥ 1000 M⊙, with 400 M⊙ in the horseshoe structure. The gas in the horse in the horseshoe appears highly fragmented, and has a kinetic temperature of ≈ 60 K, suggesting it is closely coupled to the dust temperature. A recently formed high mass star appears to be in the process of evacuating a cavity, possibly through a large molecular outflow that is found to show an accelerated component in its blue-shifted lobe. A velocity gradient across the horseshoe structure suggest ordered motion, and could represent rotation in the parental cloud
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High signal/noise <sup>13</sup>CO observations of the bipolar outflow in L1551
New high-signal/noise 13CO observations of the bipolar outflow in the molecular cloud L1551 are reported. Contrary to earlier observations of CO J = 1-0 and 2-1, no strong spatial dependence is found for the velocity profile of these spectra. The implications of these observations are such that the model of an empty shell for this source is less likely, and a model consisting of a shell which contains significant amounts of outflowing molecular gas inside the swept-up cavity walls is suggested
A Corona Australis cloud filament seen in NIR scattered light. III. Modelling and comparison with Herschel sub-millimetre data
With recent Herschel observations, the northern filament of the Corona
Australis cloud has now been mapped in a number of bands from 1.2um to 870um.
The data set provides a good starting point for the study of the cloud over
several orders of magnitude in density. We wish to examine the differences of
the column density distributions derived from dust extinction, scattering, and
emission, and to determine to what extent the observations are consistent with
the standard dust models. From Herschel data, we calculate the column density
distribution that is compared to the corresponding data derived in the
near-infrared regime from the reddening of the background stars, and from the
surface brightness attributed to light scattering. We construct
three-dimensional radiative transfer models to describe the emission and the
scattering. The scattered light traces low column densities of A_V~1mag better
than the dust emission, remaining useful to A_V ~ 10-15 mag. Based on the
models, the extinction and the level of dust emission are surprisingly
consistent with a sub-millimetre dust emissivity typical of diffuse medium.
However, the intensity of the scattered light is very low at the centre of the
densest clump and this cannot be explained without a very low grain albedo.
Both the scattered light and dust emission indicate an anisotropic radiation
field. The modelling of the dust emission suggests that the radiation field
intensity is at least three times the value of the normal interstellar
radiation field. The inter-comparison between the extinction, light scattering,
and dust emission provides very stringent constraints on the cloud structure,
the illuminating radiation field, and the grain properties.Comment: 13 pages, 16 figures, accepted to A&
Towards a Molecular Inventory of Protostellar Discs
The chemical environment in circumstellar discs is a unique diagnostic of the
thermal, physical and chemical environment. In this paper we examine the
structure of star formation regions giving rise to low mass stars, and the
chemical environment inside them, and the circumstellar discs around the
developing stars.Comment: 9 page PDF, 550 kbyte
A method for determining the characteristic functions associated with the aeroelastic instabilities of helicopter rotors in forward flight
Computer program for determining characteristic functions of aeroelastic instabilities of helicopter rotor in forward fligh
First principle computation of stripes in cuprates
We present a first principle computation of vertical stripes in
within the LDA+U method. We find that Cu centered
stripes are unstable toward O centered stripes. The metallic core of the stripe
is quite wide and shows reduced magnetic moments with suppressed
antiferromagnetic (AF) interactions. The system can be pictured as alternating
metallic and AF two-leg ladders the latter with strong AF interaction and a
large spin gap. The Fermi surface shows warping due to interstripe
hybridization. The periodicity and amplitude of the warping is in good
agreement with angle resolved photoemission experiment. We discuss the
connection with low-energy theories of the cuprates.Comment: 5 pages,4 figure
The Density Matrix Renormalization Group Method and Large-Scale Nuclear Shell-Model Calculations
The particle-hole Density Matrix Renormalization Group (p-h DMRG) method is
discussed as a possible new approach to large-scale nuclear shell-model
calculations. Following a general description of the method, we apply it to a
class of problems involving many identical nucleons constrained to move in a
single large j-shell and to interact via a pairing plus quadrupole interaction.
A single-particle term that splits the shell into degenerate doublets is
included so as to accommodate the physics of a Fermi surface in the problem. We
apply the p-h DMRG method to this test problem for two values, one for
which the shell model can be solved exactly and one for which the size of the
hamiltonian is much too large for exact treatment. In the former case, the
method is able to reproduce the exact results for the ground state energy, the
energies of low-lying excited states, and other observables with extreme
precision. In the latter case, the results exhibit rapid exponential
convergence, suggesting the great promise of this new methodology even for more
realistic nuclear systems. We also compare the results of the test calculation
with those from Hartree-Fock-Bogolyubov approximation and address several other
questions about the p-h DMRG method of relevance to its usefulness when
treating more realistic nuclear systems
Multi-epoch Sub-arcsecond [Fe II] Spectroimaging of the DG Tau Outflows with NIFS. II. On the Nature of the Bipolar Outflow Asymmetry
The origin of bipolar outflow asymmetry in young stellar objects (YSOs)
remains poorly understood. It may be due to an intrinsically asymmetric outflow
launch mechanism, or it may be caused by the effects of the ambient medium
surrounding the YSO. Answering this question is an important step in
understanding outflow launching. We have investigated the bipolar outflows
driven by the T Tauri star DG Tauri on scales of hundreds of AU, using the
Near-infrared Integral Field Spectrograph (NIFS) on Gemini North. The
approaching outflow consists of a well-collimated jet, nested within a
lower-velocity disc wind. The receding outflow is composed of a
single-component bubble-like structure. We analyse the kinemat- ics of the
receding outflow using kinetic models, and determine that it is a
quasi-stationary bubble with an expanding internal velocity field. We propose
that this bubble forms because the receding counterjet from DG Tau is
obstructed by a clumpy ambient medium above the circumstellar disc surface,
based on similarities between this structure and those found in the modeling of
active galactic nuclei outflows. We find evidence of interaction between the
obscured counterjet and clumpy ambient material, which we attribute to the
large molecular envelope around the DG Tau system. An analytical model of a
momentum-driven bubble is shown to be consistent with our interpretation. We
conclude that the bipolar outflow from DG Tau is intrinsically symmetric, and
the observed asymmetries are due to environmental effects. This mechanism can
potentially be used to explain the observed bipolar asymmetries in other YSO
outflows.Comment: 16 pages, 10 figures, accepted for publication in MNRA
Weak Lensing as a Calibrator of the Cluster Mass-Temperature Relation
The abundance of clusters at the present epoch and weak gravitational lensing
shear both constrain roughly the same combination of the power spectrum
normalization sigma_8 and matter energy density Omega_M. The cluster constraint
further depends on the normalization of the mass-temperature relation.
Therefore, combining the weak lensing and cluster abundance data can be used to
accurately calibrate the mass-temperature relation. We discuss this approach
and illustrate it using data from recent surveys.Comment: Matches the version in ApJL. Equation 4 corrected. Improvements in
the analysis move the cluster contours in Fig1 slightly upwards. No changes
in the conclusion
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