4,028 research outputs found
A unified model for the spectrophotometric development of classical and recurrent novae: the role of asphericity of the ejecta
There is increasing evidence that the geometry, and not only the filling
factors, of nova ejecta is important in the interpretation of their spectral
and photometric developments. Ensembles of spectra and light curves have
provided general typographies. This Letter suggests how these can be
unified.The observed spread in the maximum magnitude - rate of decline (MMRD)
relation is argued to result from the range of opening angles and inclination
of the ejecta, and not only to their masses and velocities. The spectroscopic
classes can be similarly explained and linked to the behavior of the light
curves. The secondary maximum observed in some dust forming novae is a natural
consequence of the asphericity. Neither secondary ejections nor winds are
needed to explain the phenomenology. The spectrophotometric development of
classical novae can be understood within a single phenomenological model with
bipolar, although not jet-like, mass ejecta. High resolution spectropolarimetry
will be an essential analytical tool.Comment: 4 pages, no figures; accepted for A&A Letters (in press
The Galactic Center Isolated Nonthermal Filaments as Analogs of Cometary Plasma Tails
We propose a model for the origin of the isolated nonthermal filaments
observed at the Galactic center based on an analogy to cometary plasma tails.
We invoke the interaction between a large scale magnetized galactic wind and
embedded molecular clouds. As the advected wind magnetic field encounters a
dense molecular cloud, it is impeded and drapes around the cloud, ultimately
forming a current sheet in the wake. This draped field is further stretched by
the wind flow into a long, thin filament whose aspect ratio is determined by
the balance between the dynamical wind and amplified magnetic field pressures.
The key feature of this cometary model is that the filaments are dynamic
configurations, and not static structures. As such, they are local
amplifications of an otherwise weak field and not directly connected to any
static global field. The derived field strengths for the wind and wake are
consistent with observational estimates. Finally, the observed synchrotron
emission is naturally explained by the acceleration of electrons to high energy
by plasma and MHD turbulence generated in the cloud wake.Comment: Uses AAS aasms4.sty macros. ApJ (in press, vol. 521, 20 Aug
The slow decline of the Galactic recurrent novae T Pyxidis, IM Normae, and CI Aquilae
A distinguishing trait of the three known Galactic recurrent novae with the
shortest orbital periods, T Pyx, IM Nor, and CI Aql, is that their optical
decline time-scales are significantly longer than those of the other recurrent
systems. On the other hand, some estimates of the mass of the ejecta, the
velocity of the ejecta, and the duration of the soft X-rays emission of these
systems are of the order of those of the other recurrent systems and the fast
classical novae. We put forth a tentative explanation of this phenomenon. We
propose that in these systems part of the material transferred from the
companion during the first few days of the eruption remains within the Roche
lobe of the white dwarf, preventing the radiation from ionizing the ejecta of
the system and increasing the optical decline time-scale. We explain why this
phenomenon is more likely in systems with a high mass transfer rate and a short
orbital period. Finally, we present a schematic model that shows that the
material transferred from the companion is sufficient to absorb the radiation
from the white dwarf in these systems, ultimately supporting this scenario as
quantitatively realistic
Colliding stellar winds in the eclipsing Wolf-Rayet binary V444 Cygni
High resolution spectra of V444 Cygni have been obtained using the International Ultraviolet Explorer Satellite. These spectra span both eclipses and include one observation at third quadrature. Together with seven archival spectra, they provide reasonably complete phase coverage for the system. The variations in the P Cygni profiles of the He(II) and N(IV) lines, imply the existence of a low density region in the WR wind. This region occupies a relatively narrow range of orbital phase coinciding with the highest terminal velocities observed in C IV. These data are interpreted to be evidence of an interaction region separating the winds of the O-star and Wolf-Rayet star
Master formula approach to broken chiral U(3)xU(3) symmetry
The master formula approach to chiral symmetry breaking proposed by Yamagishi
and Zahed is extended to the U_R(3)xU_L(3) group, in which effects of the
U_A(1) anomaly and the flavor symmetry breaking m_u \not= m_d \not= m_s are
properly contained. New identities for the gluon topological susceptibility and
pi^0, eta, eta' -> gamma^(*) gamma^(*) decays are derived, which exactly embody
the consequence from broken chiral symmetry in QCD without relying on any
unphysical limit.Comment: Version to appear in PRD, 25 page
Inclusive workplaces : a review and model
Organizations continue to be challenged and enriched by the diversity of their workforces. Scholars are increasingly focusing on inclusion to enhance work environments by offering support for a diverse workforce. This article reviews and synthesizes the inclusion literature and provides a model of inclusion that integrates existing literature to offer greater clarity, as well as suggestions for moving the literature forward. We review the inclusion literature consisting of the various foci (work group, organization, leader, organizational practices, and climate) and associated definitions and how it has developed. We then describe themes in the inclusion literature and propose a model of inclusion. Finally, we end by discussing theoretical and practical implications
Extension of the Morris-Shore transformation to multilevel ladders
We describe situations in which chains of N degenerate quantum energy levels,
coupled by time-dependent external fields, can be replaced by independent sets
of chains of length N, N-1,...,2 and sets of uncoupled single states. The
transformation is a generalization of the two-level Morris-Shore transformation
[J.R. Morris and B.W. Shore, Phys. Rev. A 27, 906 (1983)]. We illustrate the
procedure with examples of three-level chains
Tuning the stochastic background of gravitational waves using the WMAP data
The cosmological bound of the stochastic background of gravitational waves is
analyzed with the aid of the WMAP data, differently from lots of works in
literature, where the old COBE data were used. From our analysis, it will
result that the WMAP bounds on the energy spectrum and on the characteristic
amplitude of the stochastic background of gravitational waves are greater than
the COBE ones, but they are also far below frequencies of the earth-based
antennas band. At the end of this letter a lower bound for the integration time
of a potential detection with advanced LIGO is released and compared with the
previous one arising from the old COBE data. Even if the new lower bound is
minor than the previous one, it results very long, thus for a possible
detection we hope in the LISA interferometer and in a further growth in the
sensitivity of advanced projects.Comment: 9 pages, 2 figures, published in Modern Physics Letters A. arXiv
admin note: substantial text overlap with arXiv:0901.119
Diffusion-Induced Oscillations of Extended Defects
From a simple model for the driven motion of a planar interface under the
influence of a diffusion field we derive a damped nonlinear oscillator equation
for the interface position. Inside an unstable regime, where the damping term
is negative, we find limit-cycle solutions, describing an oscillatory
propagation of the interface. In case of a growing solidification front this
offers a transparent scenario for the formation of solute bands in binary
alloys, and, taking into account the Mullins-Sekerka instability, of banded
structures
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