363 research outputs found
Momentum-sector-selective metal-insulator transition in the eight-site dynamical mean-field approximation to the Hubbard model in two dimensions
We explore the momentum-sector-selective metal insulator transitions recently
found in the eight - site dynamical cluster approximation to the
two-dimensional Hubbard model. The phase diagram in the space of interaction
and second-neighbor hopping is established. The initial transitions from
Fermi-liquid like to sector-selective phases are found to be of second order,
caused by the continuous opening of an energy gap whereas the other transitions
are found to be of first order. In the sector-selective phase the Fermi surface
regions which are not gapped are found to have a non-Fermi-liquid self-energy.
We demonstrate that the phenomenon is not caused by the Van Hove divergence in
the density of states. The sector-selective and insulating phases are
characterized by a cluster spin correlation function that is strongly peaked at
the commensurate antiferromagnetic wave vector but the model has no
nematic instability. Comparison to dynamical mean-field studies on smaller
clusters is made
Detection of the compressed primary stellar wind in eta Carinae
A series of three HST/STIS spectroscopic mappings, spaced approximately one
year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving
outward from eta Carinae. We identify these arcs with the shell-like
structures, seen in the 3D hydrodynamical simulations, formed by compression of
the primary wind by the secondary wind during periastron passages.Comment: Accepted for publication in the Astrophysical Journal Letter
3D Radiative Transfer in Carinae: Application of the SimpleX Algorithm to 3D SPH Simulations of Binary Colliding Winds
Eta Carinae is an ideal astrophysical laboratory for studying massive binary
interactions and evolution, and stellar wind-wind collisions. Recent
three-dimensional (3D) simulations set the stage for understanding the highly
complex 3D flows in Car. Observations of different broad high- and
low-ionization forbidden emission lines provide an excellent tool to constrain
the orientation of the system, the primary's mass-loss rate, and the ionizing
flux of the hot secondary. In this work we present the first steps towards
generating synthetic observations to compare with available and future HST/STIS
data. We present initial results from full 3D radiative transfer simulations of
the interacting winds in Car. We use the SimpleX algorithm to
post-process the output from 3D SPH simulations and obtain the ionization
fractions of hydrogen and helium assuming three different mass-loss rates for
the primary star. The resultant ionization maps of both species constrain the
regions where the observed forbidden emission lines can form. Including
collisional ionization is necessary to achieve a better description of the
ionization states, especially in the areas shielded from the secondary's
radiation. We find that reducing the primary's mass-loss rate increases the
volume of ionized gas, creating larger areas where the forbidden emission lines
can form. We conclude that post processing 3D SPH data with SimpleX is a viable
tool to create ionization maps for Car.Comment: 18 pages, 11 figures, accepted for publication in MNRA
Multi-Wavelength Implications of the Companion Star in Eta Carinae
Eta Carinae is considered to be a massive colliding wind binary system with a
highly eccentric (e \sim 0.9), 5.54-yr orbit. However, the companion star
continues to evade direct detection as the primary dwarfs its emission at most
wavelengths. Using three-dimensional (3-D) SPH simulations of Eta Car's
colliding winds and radiative transfer codes, we are able to compute synthetic
observables across multiple wavebands for comparison to the observations. The
models show that the presence of a companion star has a profound influence on
the observed HST/STIS UV spectrum and H-alpha line profiles, as well as the
ground-based photometric monitoring. Here, we focus on the Bore Hole effect,
wherein the fast wind from the hot secondary star carves a cavity in the dense
primary wind, allowing increased escape of radiation from the hotter/deeper
layers of the primary's extended wind photosphere. The results have important
implications for interpretations of Eta Car's observables at multiple
wavelengths.Comment: 5 pages, 4 figures, To be published in the proceedings of the meeting
'Four Decades of Research on Massive Stars' in honor of Tony Moffat, 11-15
July 2011, Saint-Michel-des-Saints, Quebe
Modernist Trends and varied responses: Reflections on Muslim Women in Urdu Prose by Male authors of South Asia (1900-1936).
Many Indian writers and activists in the 19th century South Asia made the subject of women as central topic as their agenda of cultural reform, expressing the same concern, above all, through the newly available medium of print. The main objectives of these writings were to check the decadence and resuscitate the values which had gone dormant. In order to do that, a few authors supported the British and others criticized it and tried to find out the solution in the religious or traditional education. Whether Hindus or Muslims, they were now seen at least in part as colonial collaborators. These are, above all, people who internalized the Orientalist argument that Indian traditions had fallen into decay and stagnation, and prescribed the western education necessary for their revitalization. Education for women, in particular, was not catered for. This paper argues that Urdu journalism was the dynamic tool for persuading the common people to educate their female folk to enable them to face the changed socio-political circumstance, which had impinged upon the traditional family structure. The development of that new literature focusing on Muslim women pointed to the emergence of Urdu as the common language. It also became the medium of instruction for women. By publishing of various books and journals led to the establishment of the educational institutions and societies. That’s why the Urdu literature with theme centering on women in the latter half of the 19th century also helps us to visualize various aspects of different local cultures, customs, the regional idioms, proverbs and parables that formed the essence of the local language used only by the women. These writings also underscore the emergence of Muslim women from middle echelons as professional ladies. 
The three-dimensional structure of the Eta Carinae Homunculus
We investigate, using the modeling code SHAPE, the three-dimensional
structure of the bipolar Homunculus nebula surrounding Eta Carinae, as mapped
by new ESO VLT/X-Shooter observations of the H2 micron
emission line. Our results reveal for the first time important deviations from
the axisymmetric bipolar morphology: 1) circumpolar trenches in each lobe
positioned point-symmetrically from the center and 2) off-planar protrusions in
the equatorial region from each lobe at longitudinal (~55 degrees) and
latitudinal (10-20 degrees) distances from the projected apastron direction of
the binary orbit. The angular distance between the protrusions (~110 degrees)
is similar to the angular extent of each polar trench (~130 degrees) and nearly
equal to the opening angle of the wind-wind collision cavity (~110 degrees). As
in previous studies, we confirm a hole near the centre of each polar lobe and
no detectable near-IR H2 emission from the thin optical skirt seen prominently
in visible imagery. We conclude that the interaction between the outflows
and/or radiation from the central binary stars and their orientation in space
has had, and possibly still has, a strong influence on the Homunculus. This
implies that prevailing theoretical models of the Homunculus are incomplete as
most assume a single star origin that produces an axisymmetric nebula. We
discuss how the newly found features might be related to the Homunculus
ejection, the central binary and the interacting stellar winds. We also include
a 3D printable version of our Homunculus model.Comment: 14 pages, 7 color figures, 1 interactive 3D figure (Figure 5,
requires Adobe Reader), published in MNRAS. A 3D printable version of our
Homunculus model can be downloaded from
http://svs.gsfc.nasa.gov/vis/a010000/a011500/a011568/Eta_Car_Homunuculus_3D_model.zip
or from the 'Supporting Information' link in the electronic version of the
MNRAS articl
Discovery of CH and OH in the -513 km s-1 Ejecta of Eta Carinae
The very massive star, Eta Carinae, is enshrouded in an unusual complex of
stellar ejecta, which is highly depleted in C and O, and enriched in He and N.
This circumstellar gas gives rise to distinct absorption components
corresponding to at least 20 different velocities along the line-of-sight. The
velocity component at -513 kms-1 exhibits very low ionization with
predominantly neutral species of iron-peak elements. Our statistical
equilibrium/photoionization modeling indicates that the low temperature (T =
760 K) and high density (n_H=10^7 cm^-3) of the -513 kms-1 component is
conducive to molecule formation including those with the elements C and O.
Examination of echelle spectra obtained with the Space Telescope Imaging
Spectrograph (STIS) aboard the confirms the model's predictions. The molecules,
H_2, CH, and most likely OH, have been identified in the -513 kms-1 absorption
spectrum. This paper presents the analysis of the HST/STIS spectra with the
deduced column densities for CH, OH and C I, and upper limit for CO. It is
quite extraordinary to see molecular species in a cool environment at such a
high velocity. The sharp molecular and ionic absorptions in this extensively
CNO- processed material offers us a unique environment for studying the
chemistry, dust formation processes, and nucleosynthesis in the ejected layers
of a highly evolved massive star.Comment: tentatively scheduled for the ApJ 1 September 2005, v630, 1 issu
Spin, charge and orbital fluctuations in a multi-orbital Mott insulator
The two-orbital degenerate Hubbard model with distinct hopping integrals is
studied by combining dynamical mean-field theory with quantum Monte Carlo
simulations. The role of orbital fluctuations for the nature of the Mott
transition is elucidated by examining the temperature dependence of spin,
charge and orbital susceptibilities as well as the one-particle spectral
function. We also consider the effect of the hybridization between the two
orbitals, which is important particularly close to the Mott transition points.
The introduction of the hybridization induces orbital fluctuations, resulting
in the formation of a Kondo-like heavy-fermion behavior, similarly to
electron systems, but involving electrons in bands of comparable width.Comment: 8 pages, 9 figure
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