10,209 research outputs found
<i>Herschel</i> observations of the debris disc around HIP 92043
Context. Typical debris discs are composed of particles ranging from several micron sized dust grains to km sized asteroidal bodies, and their infrared emission peaks at wavelengths 60-100 μm. Recent Herschel DUNES observations have identified several debris discs around nearby Sun-like stars (F, G and K spectral type) with significant excess emission only at 160 μm.
Aims. We observed HIP 92043 (110 Her, HD 173667) at far-infrared and sub-millimetre wavelengths with Herschel PACS and SPIRE. Identification of the presence of excess emission from HIP 92043 and the origin and physical properties of any excess was undertaken through analysis of its spectral energy distribution (SED) and the PACS images.
Methods. The PACS and SPIRE images were produced using the HIPE photProject map maker routine. Fluxes were measured using aperture photometry. A stellar photosphere model was scaled to optical and near infrared photometry and subtracted from the far-infared and sub-mm fluxes to determine the presence of excess emission. Source radial profiles were fitted using a 2D Gaussian and compared to a PSF model based on Herschel observations of α Boo to check for extended emission.
Results. Clear excess emission from HIP 92043 was observed at 70 and 100 μm. Marginal excess was observed at 160 and 250 μm. Analysis of the images reveals that the source is extended at 160 μm. A fit to the source SED is inconsistent with a photosphere and single temperature black body.
Conclusions. The excess emission from HIP 92043 is consistent with the presence of an unresolved circumstellar debris disc at 70 and 100 μm, with low probability of background contamination. The extended 160 μm emission may be interpreted as an additional cold component to the debris disc or as the result of background contamination along the line of sight. The nature of the 160 μm excess cannot be determined absolutely from the available data, but we favour a debris disc interpretation, drawing parallels with previously identified cold disc sources in the DUNES sample
Molecular gas at supernova local environments unveiled by EDGE
CO observations allow estimations of the gas content of molecular clouds,
which trace the reservoir of cold gas fuelling star formation, as well as to
determine extinction via H column density, N(H). Here, we studied
millimetric and optical properties at 26 supernovae (SNe) locations of
different types in a sample of 23 nearby galaxies by combining molecular
CO (J = 1 0) resolved maps from the EDGE survey and
optical Integral Field Spectroscopy from the CALIFA survey. We found an even
clearer separation between type II and type Ibc SNe in terms of molecular gas
than what we found in the optical using H emission as a proxy for
current SF rate, which reinforces the fact that SNe Ibc are more associated
with SF-environments. While A at SN locations is similar for SNe II and SNe
Ibc, and higher compared to SNe Ia, N(H) is significantly higher for SNe
Ibc than for SNe II and SNe Ia. When compared to alternative extinction
estimations directly from SN photometry and spectroscopy, we find that our SNe
Ibc have also redder color excess but showed standard Na I D absorption
pseudo-equivalent widths (1 \AA). In some cases we find no extinction
when estimated from the environment, but high amounts of extinction when
measured from SN observations, which suggests that circumstellar material or
dust sublimation may be playing a role. This work serves as a benchmark for
future studies combining last generation millimeter and optical IFS instruments
to reveal the local environmental properties of extragalactic SNe.Comment: MNRAS accepted, 17 pages, 8 Figures, 4 Table
Gravity in the 3+1-Split Formalism I: Holography as an Initial Value Problem
We present a detailed analysis of the 3+1-split formalism of gravity in the
presence of a cosmological constant. The formalism helps revealing the intimate
connection between holography and the initial value formulation of gravity. We
show that the various methods of holographic subtraction of divergences
correspond just to different transformations of the canonical variables, such
that the initial value problem is properly set up at the boundary. The
renormalized boundary energy momentum tensor is a component of the Weyl tensor.Comment: 28 pages; v2: minor improvements, references adde
Noisy Kondo impurities
The anti-ferromagnetic coupling of a magnetic impurity carrying a spin with
the conduction electrons spins of a host metal is the basic mechanism
responsible for the increase of the resistance of an alloy such as
CuFe at low temperature, as originally suggested by
Kondo . This coupling has emerged as a very generic property of localized
electronic states coupled to a continuum . The possibility to design artificial
controllable magnetic impurities in nanoscopic conductors has opened a path to
study this many body phenomenon in unusual situations as compared to the
initial one and, in particular, in out of equilibrium situations. So far,
measurements have focused on the average current. Here, we report on
\textit{current fluctuations} (noise) measurements in artificial Kondo
impurities made in carbon nanotube devices. We find a striking enhancement of
the current noise within the Kondo resonance, in contradiction with simple
non-interacting theories. Our findings provide a test bench for one of the most
important many-body theories of condensed matter in out of equilibrium
situations and shed light on the noise properties of highly conductive
molecular devices.Comment: minor differences with published versio
Ultra-cold Polarized Fermi Gases
Recent experiments with ultra-cold atoms have demonstrated the possibility of
realizing experimentally fermionic superfluids with imbalanced spin
populations. We discuss how these developments have shed a new light on a half-
century old open problem in condensed matter physics, and raised new
interrogations of their own.Comment: 27 pages; 8 figures; Published in Report in Rep. Prog. Phys. 73
112401 (2010
Counterterms and dual holographic anomalies in CS gravity
The holographic Weyl anomaly associated to Chern-Simons gravity in 2n+1
dimensions is proportional to the Euler term in 2n dimensions, with no
contributions from the Weyl tensor. We compute the holographic energy-momentum
tensor associated to Chern-Simons gravity directly from the action, in an
arbitrary odd-dimensional spacetime. We show, in particular, that the
counterterms rendering the action finite contain only terms of the Lovelock
type.Comment: 10 pages, no figure
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Scale dependence of the quark masses and mixings: leading order
We consider the Renormalization Group Equations (RGE) for the couplings of
the Standard Model and its extensions. Using the hierarchy of the quark masses
and of the Cabibbo-Kobayashi-Maskawa (CKM) matrix our argument is that a
consistent approximation for the RGE should be based on the parameter . We consider the RGE in the approximation where we
neglect all the relative terms of the order and higher.
Within this approximation we find the exact solution of the evolution equations
of the quark Yukawa couplings and of the vacuum expectation value of the Higgs
field. Then we derive the evolution of the observables: quark masses, CKM
matrix, Jarlskog invariant, Wolfenstein parameters of the CKM matrix and the
unitarity triangle. We show that the angles of the unitarity triangle remain
constant. This property may restrict the possibility of new symmetries or
textures at the grand unification scale.Comment: 15 pages, 4 figures, author of one reference adde
Excitation of nonlinear two-dimensional wake waves in radially-nonuniform plasma
It is shown that an undesirable curvature of the wave front of
two-dimensional nonlinear wake wave excited in uniform plasma by a relativistic
charged bunch or laser pulse may be compensated by radial change of the
equilibrium plasma density.Comment: 6 pages, 4 figure
Fulde-Ferrell-Larkin-Ovchinnikov State in Heavy Fermion Superconductors
The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is a novel superconducting
state in a strong magnetic field characterized by the formation of Cooper pairs
with nonzero total momentum (k \uparrow, -k+q \downarrow), instead of the
ordinary BCS pairs (k \uparrow, -k \downarrow). A fascinating aspect of the
FFLO state is that it exhibits inhomogeneous superconducting phases with a
spatially oscillating order parameter and spin polarization. The FFLO state has
been of interest in various research fields, not only in superconductors in
solid state physics, but also in neutral Fermion superfluid of ultracold atomic
gases and in color superconductivity in high energy physics. In spite of
extensive studies of various superconductors, there has been no undisputed
experimental verification of the FFLO state, mainly because of the very
stringent conditions required of the superconducting materials. Among several
classes of materials, certain heavy fermion and organic superconductors are
believed to provide conditions that are favorable to the formation of the FFLO
state. This review presents recent experimental and theoretical developments of
the FFLO state mainly in heavy fermion superconductors. In particular we
address the recently discovered quasi-two-dimensional superconductor CeCoIn_5,
which is a strong candidate for the formation of the FFLO state.Comment: 17 pages, 12 figures with jpsf2.cls, to be published in J. Phys. Soc.
Jpn. (Special Topics - Frontiers of Novel Superconductivity in Heavy Fermion
Compounds
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