30,064 research outputs found
Self-dual vortices in a Maxwell-Chern-Simons model with non-minimal coupling
We find self-dual vortex solutions in a Maxwell-Chern-Simons model with
anomalous magnetic moment. From a recently developed N=2-supersymmetric
extension, we obtain the proper Bogomol'nyi equations together with a Higgs
potential allowing both topological and non-topological phases in the theory.Comment: 12 pages, 9 figures, 2 tables; some typos corrected, one reference
updated. To be published in the Int. J. Mod. Phys. A (1999
Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73
We aim to improve our knowledge on the structure and dynamics of the
circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution
optical and near-IR spectroscopic data were obtained over a period of 16 and 7
years, respectively. The spectra cover the diagnostic emission lines from
[CaII] and [OI], as well as the CO bands. These features trace the disk at
different distances from the star. We analyzed the kinematics of the individual
emission regions by modeling their emission profiles. A low-resolution
mid-infrared spectrum was obtained as well, which provides information on the
composition of the dusty disk. All diagnostic emission features display
double-peaked line profiles, which we interpret as due to Keplerian rotation.
We find that LHA 120-S 73 is surrounded by at least four individual rings of
material with alternating densities (or by a disk with strongly non-monotonic
radial density distribution). Moreover, we find that the molecular ring must
have gaps or at least strong density inhomogeneities, or in other words, a
clumpy structure. The mid-infrared spectrum displays features of oxygen- and
carbon-rich grain species, which indicates a long-lived, stable dusty disk. We
cannot confirm the previously reported high value for the stellar rotation
velocity. The line profile of HeI 5876 A is strongly variable in both width and
shape and resembles of those seen in non-radially pulsating stars. A proper
determination of the real underlying stellar rotation velocity is hence not
possible. The existence of multiple stable and clumpy rings of alternating
density recalls ring structures around planets. Although there is currently
insufficient observational evidence, it is tempting to propose a scenario with
one (or more) minor bodies or planets revolving around LHA 120-S 73 and
stabilizing the ring system, in analogy to the shepherd moons in planetary
systems.Comment: 14 pages, 13 figure, accepted for pulication in A&
Disentangling the excitation conditions of the dense gas in M17 SW
We probe the chemical and energetic conditions in dense gas created by
radiative feedback through observations of multiple CO, HCN and HCO
transitions toward the dense core of M17 SW. We used the dual band receiver
GREAT on board the SOFIA airborne telescope to obtain maps of the ,
, and transitions of CO. We compare these maps with
corresponding APEX and IRAM 30m telescope data for low- and mid- CO, HCN and
HCO emission lines, including maps of the HCN and HCO
transitions. The excitation conditions of CO, HCO and HCN are
estimated with a two-phase non-LTE radiative transfer model of the line
spectral energy distributions (LSEDs) at four selected positions. The energy
balance at these positions is also studied. We obtained extensive LSEDs for the
CO, HCN and HCO molecules toward M17 SW. The LSED shape, particularly the
high- tail of the CO lines observed with SOFIA/GREAT, is distinctive for the
underlying excitation conditions. The critical magnetic field criterion implies
that the cold cloudlets at two positions are partially controlled by processes
that create and dissipate internal motions. Supersonic but sub-Alfv\'enic
velocities in the cold component at most selected positions indicates that
internal motions are likely MHD waves. Magnetic pressure dominates thermal
pressure in both gas components at all selected positions, assuming random
orientation of the magnetic field. The magnetic pressure of a constant magnetic
field throughout all the gas phases can support the total internal pressure of
the cold components, but it cannot support the internal pressure of the warm
components. If the magnetic field scales as , then the
evolution of the cold cloudlets at two selected positions, and the warm
cloudlets at all selected positions, will be determined by ambipolar diffusion.Comment: 26 pages, 13 figures, A&A accepte
Coherent delocalization: Views of entanglement in different scenarios
The concept of entanglement was originally introduced to explain correlations
existing between two spatially separated systems, that cannot be described
using classical ideas. Interestingly, in recent years, it has been shown that
similar correlations can be observed when considering different degrees of
freedom of a single system, even a classical one. Surprisingly, it has also
been suggested that entanglement might be playing a relevant role in certain
biological processes, such as the functioning of pigment-proteins that
constitute light-harvesting complexes of photosynthetic bacteria. The aim of
this work is to show that the presence of entanglement in all of these
different scenarios should not be unexpected, once it is realized that the very
same mathematical structure can describe all of them. We show this by
considering three different, realistic cases in which the only condition for
entanglement to exist is that a single excitation is coherently delocalized
between the different subsystems that compose the system of interest
Recovery of the orbital parameters and pulse evolution of V0332+53 during a huge outburst
The high mass X-ray binary (HMXB) V0332+53 became active at the end of 2004
and the outburst was observed at hard X-rays by RXTE and INTEGRAL. Based on
these hard X-ray observations, the orbital parameters are measured through
fitting the Doppler-shifted spin periods. The derived orbital period and
eccentricity are consistent with those of Stella et al. (1985) obtained from
EXOSAT observations, whereas the projected semimajor axis and the periastron
longitude are found to have changed from 484 to 86 lt-s and
from 31310 to 28314, respectively. This would
indicate an angular speed of 1.50.8 yr for
rotation of the orbit over the past 21 years. The periastron passage time of
MJD 533671 is just around the time when the intensity reached maximum and
an orbital period earlier is the time when the outburst started. This
correlation resembles the behavior of a Type I outburst. During outburst the
source spun up with a rate of 8.01 s
day. The evolution of pulse profile is highly intensity dependent. The
separation of double pulses remained almost constant ( 0.47) when the
source was bright, and dropped to 0.37 within 3 days as the source
became weaker. The pulse evolution of V0332+53 may correlate to the change in
dominance of the emission between fan-beam and pencil-beam mechanisms.Comment: 13 pages, 3 figures, accepted for publication in ApJ
What causes the large extensions of red-supergiant atmospheres? Comparisons of interferometric observations with 1-D hydrostatic, 3-D convection, and 1-D pulsating model atmospheres
We present the atmospheric structure and the fundamental parameters of three
red supergiants, increasing the sample of RSGs observed by near-infrared
spectro-interferometry. Additionally, we test possible mechanisms that may
explain the large observed atmospheric extensions of RSGs.
We carried out spectro-interferometric observations of 3 RSGs in the
near-infrared K-band with the VLTI/AMBER instrument at medium spectral
resolution. To comprehend the extended atmospheres, we compared our
observational results to predictions by available hydrostatic PHOENIX,
available 3-D convection, and new 1-D self-excited pulsation models of RSGs.
Our near-infrared flux spectra are well reproduced by the PHOENIX model
atmospheres. The continuum visibility values are consistent with a
limb-darkened disk as predicted by the PHOENIX models, allowing us to determine
the angular diameter and the fundamental parameters of our sources.
Nonetheless, in the case of V602 Car and HD 95686, the PHOENIX model
visibilities do not predict the large observed extensions of molecular layers,
most remarkably in the CO bands. Likewise, the 3-D convection models and the
1-D pulsation models with typical parameters of RSGs lead to compact
atmospheric structures as well, which are similar to the structure of the
hydrostatic PHOENIX models. They can also not explain the observed decreases in
the visibilities and thus the large atmospheric molecular extensions. The full
sample of our RSGs indicates increasing observed atmospheric extensions with
increasing luminosity and decreasing surface gravity, and no correlation with
effective temperature or variability amplitude, which supports a scenario of
radiative acceleration on Doppler-shifted molecular lines.Comment: Accepted for publication in A&
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