5,177 research outputs found
The UV Scattering Halo of the Central Source Associated with Eta Carinae
We have made an extensive study of the UV spectrum of Eta Carinae, and find
that we do not directly observe the star and its wind in the UV. Because of
dust along our line of sight, the UV light that we observe arises from
bound-bound scattering at large impact parameters. We obtain a reasonable fit
to the UV spectrum by using only the flux that originates outside 0.033". This
explains why we can still observe the primary star in the UV despite the large
optical extinction -- it is due to the presence of an intrinsic coronagraph in
the Eta Carinae system, and to the extension of the UV emitting region. It is
not due to peculiar dust properties alone. We have computed the spectrum of the
purported companion star, and show that it could only be directly detected in
the UV spectrum preferentially in the Far Ultraviolet Spectroscopic Explorer
(FUSE) spectral region (912-1175 Ang.). However, we find no direct evidence for
a companion star, with the properties indicated by X-ray studies and studies of
the Weigelt blobs, in UV spectra. This might be due to reprocessing of the
companion's light by the dense stellar wind of the primary. Broad FeII and
[FeII] emission lines, which form in the stellar wind, are detected in spectra
taken in the SE lobe, 0.2" from the central star. The wind spectrum shows some
similarities to the spectra of the B & D Weigelt blobs, but also shows some
marked differences in that high excitation lines, and lines pumped by Ly-alpha,
are not seen. The detection of the broad lines lends support to our
interpretation of the UV spectrum, and to our model for Eta Carinae.Comment: To appear in ApJ. 57 pages with 18 figure
Probing the superconducting ground state of ZrIrSi: A SR study
The superconducting ground state of newly reported ZrIrSi is probed by means
of SR technique along with resistivity measurement. The occurrence of
superconductivity at = 1.7 K is confirmed by resistivity
measurement. ZF-SR study revealed that below , there is no
spontaneous magnetic field in the superconducting state, indicates TRS is
preserved in case of ZrIrSi. From TF-SR measurement, we have estimated the
superfluid density as a function of temperature, which is described by an
isotropic wave model with a superconducting gap
= 5.1, indicates the presence of strong
spin-orbit coupling. {\it Ab-initio} electronic structure calculation indicates
that there are four bands passing through the Fermi level, forming four Fermi
surface pockets. We find that the low-energy bands are dominated by the
-orbitals of transition metal Zr, with substantially lesser weight from the
-orbitals of the Ir-atoms.Comment: 6 pages, 4 figure
Investigation of Superconducting Gap Structure in HfIrSi using muon spin relaxation/rotation
Appearance of strong spin-orbit coupling (SOC) is apparent in ternary
equiatomic compounds with 5-electrons due to the large atomic radii of
transition metals. SOC plays a significant role in the emergence of
unconventional superconductivity. Here we examined the superconducting state of
HfIrSi using magnetization, specific heat, zero and transverse-field (ZF/TF)
muon spin relaxation/rotation (SR) measurements. Superconductivity is
observed at = 3.6 K as revealed by specific heat and
magnetization measurements. From the TFSR analysis it is clear that
superfluid density well described by an isotropic BCS type -wave gap
structure. Furthermore, from TFSR data we have also estimated the
superconducting carrier density = 6.6 10m,
London penetration depth = 259.59 nm and effective mass
= 1.57 . Our zero-field muon spin relaxation data indicate no
clear sign of spontaneous internal field below , which implies
that the time-reversal symmetry is preserved in HfIrSi. Theoretical
investigation suggests Hf and Ir atoms hybridize strongly along the -axis of
the lattice, which is responsible for the strong three-dimensionality of this
system which screens the Coulomb interaction. As a result despite the presence
of correlated -electrons in this system, the correlation effect is weakened,
promoting electron-phonon coupling to gain importance.Comment: 8 pages, 4 figure
Waiting in the Wings: Reflected X-ray Emission from the Homunculus Nebula
We report the first detection of X-ray emission associated with the
Homunculus Nebula which surrounds the supermassive star Eta Carinae. The
emission is characterized by a temperature in excess of 100 MK, and is
consistent with scattering of the time-delayed X-ray flux associated with the
star. The nebular emission is bright in the northwestern lobe and near the
central regions of the Homunculus, and fainter in the southeastern lobe. We
also report the detection of an unusually broad Fe K fluorescent line, which
may indicate fluorescent scattering off the wind of a companion star or some
other high velocity outflow. The X-ray Homunculus is the nearest member of the
small class of Galactic X-ray reflection nebulae, and the only one in which
both the emitting and reflecting sources are distinguishable.Comment: 17 pages, 5 figures, accepted by Ap
Characterisation of spatial network-like patterns from junctions' geometry
We propose a new method for quantitative characterization of spatial
network-like patterns with loops, such as surface fracture patterns, leaf vein
networks and patterns of urban streets. Such patterns are not well
characterized by purely topological estimators: also patterns that both look
different and result from different morphogenetic processes can have similar
topology. A local geometric cue -the angles formed by the different branches at
junctions- can complement topological information and allow to quantify the
large scale spatial coherence of the pattern. For patterns that grow over time,
such as fracture lines on the surface of ceramics, the rank assigned by our
method to each individual segment of the pattern approximates the order of
appearance of that segment. We apply the method to various network-like
patterns and we find a continuous but sharp dichotomy between two classes of
spatial networks: hierarchical and homogeneous. The first class results from a
sequential growth process and presents large scale organization, the latter
presents local, but not global organization.Comment: version 2, 14 page
Ranking Spaces for Predicting Human Movement in an Urban Environment
A city can be topologically represented as a connectivity graph, consisting
of nodes representing individual spaces and links if the corresponding spaces
are intersected. It turns out in the space syntax literature that some defined
topological metrics can capture human movement rates in individual spaces. In
other words, the topological metrics are significantly correlated to human
movement rates, and individual spaces can be ranked by the metrics for
predicting human movement. However, this correlation has never been well
justified. In this paper, we study the same issue by applying the weighted
PageRank algorithm to the connectivity graph or space-space topology for
ranking the individual spaces, and find surprisingly that (1) the PageRank
scores are better correlated to human movement rates than the space syntax
metrics, and (2) the underlying space-space topology demonstrates small world
and scale free properties. The findings provide a novel justification as to why
space syntax, or topological analysis in general, can be used to predict human
movement. We further conjecture that this kind of analysis is no more than
predicting a drunkard's walking on a small world and scale free network.
Keywords: Space syntax, topological analysis of networks, small world, scale
free, human movement, and PageRankComment: 11 pages, 5 figures, and 2 tables, English corrections from version 1
to version 2, major changes in the section of introduction from version 2 to
- …