1,129 research outputs found
The origin of very wide binary systems
The majority of stars in the Galactic field and halo are part of binary or
multiple systems. A significant fraction of these systems have orbital
separations in excess of thousands of astronomical units, and systems wider
than a parsec have been identified in the Galactic halo. These binary systems
cannot have formed through the 'normal' star-formation process, nor by capture
processes in the Galactic field. We propose that these wide systems were formed
during the dissolution phase of young star clusters. We test this hypothesis
using N-body simulations of evolving star clusters and find wide binary
fractions of 1-30%, depending on initial conditions. Moreover, given that most
stars form as part of a binary system, our theory predicts that a large
fraction of the known wide 'binaries' are, in fact, multiple systems.Comment: 4 pages, 1 figure, to appear in the proceedings of IAU Symposium 266,
eds. R. de Grijs & J.R.D. Lepin
Vector solitons in (2+1) dimensions
We address the problem of existence and stability of vector spatial solitons
formed by two incoherently interacting optical beams in bulk Kerr and saturable
media. We identify families of (2+1)-dimensional two-mode self-trapped beams,
with and without a topological charge, and describe their properties
analytically and numerically.Comment: 3 pages, 5 figures, submitted to Opt. Let
Feeling of knowing and restudy choices
Feeling-of-knowing judgments (FOK-Js) reflect peopleâs confidence that they would be able to recognize a currently unrecallable item. Although much research has been devoted to the factors determining the magnitude and accuracy of FOK-Js, much less work has addressed the issue of whether FOK-Js are related to any form of metacognitive control over memory processes. In the present study, we tested the hypothesis that FOK-Js are related to participantsâ choices of which unrecallable items should be restudied. In three experiments, we showed that participants tend to choose for restudy items with high FOK-Js, both when they are explicitly asked to choose for restudy items that can be mastered in the restudy session (Exps. 1a and 2) and when such specific instructions are omitted (Exp. 1b). The study further demonstrated that increasing FOK-Js via priming cues affects restudy choices, even though it does not affect recall directly. Finally, Experiment 2 showed the strategy of restudying unrecalled items with high FOK-Js to be adaptive, because the efficacy of restudy is greater for these items than for items with low FOK-Js. Altogether, the present findings underscore an important role of FOK-Js for the metacognitive control of study operations
Linear and nonlinear waveguides induced by optical vortex solitons
We study, numerically and analytically, linear and nonlinear waveguides
induced by optical vortex solitons in a Kerr medium. Both fundamental and
first-order guided modes are analyzed, as well as the cases of effectively
defocusing and focusing nonlinearity.Comment: 3 pages, 3 figures, changed conten
Is our Sun a Singleton?
Most stars are formed in a cluster or association, where the number density
of stars can be high. This means that a large fraction of initially-single
stars will undergo close encounters with other stars and/or exchange into
binaries. We describe how such close encounters and exchange encounters can
affect the properties of a planetary system around a single star. We define a
singleton as a single star which has never suffered close encounters with other
stars or spent time within a binary system. It may be that planetary systems
similar to our own solar system can only survive around singletons. Close
encounters or the presence of a stellar companion will perturb the planetary
system, often leaving planets on tighter and more eccentric orbits. Thus
planetary systems which initially resembled our own solar system may later more
closely resemble some of the observed exoplanet systems.Comment: 2 pages, 1 figure. To be published in the proceedings of IAUS246
"Dynamical Evolution of Dense Stellar Systems". Editors: E. Vesperini (Chief
Editor), M. Giersz, A. Sill
Planet-Planet Scattering Alone Cannot Explain the Free-Floating Planet Population
Recent gravitational microlensing observations predict a vast population of
free-floating giant planets that outnumbers main sequence stars almost twofold.
A frequently-invoked mechanism for generating this population is a dynamical
instability that incites planet-planet scattering and the ejection of one or
more planets in isolated main sequence planetary systems. Here, we demonstrate
that this process alone probably cannot represent the sole source of these
galactic wanderers. By using straightforward quantitative arguments and N-body
simulations, we argue that the observed number of exoplanets exceeds the
plausible number of ejected planets per system from scattering. Thus, other
potential sources of free-floaters, such as planetary stripping in stellar
clusters and post-main-sequence ejection, must be considered.Comment: 6 pages, 2 figures, accepted for publication in MNRAS Letter
Comparing HARPS and Kepler surveys: The alignment of multiple-planet systems
Aims. We study a subset of the planetary population characterized both by
HARPS and Kepler surveys. We compare the statistical properties of planets in
systems with m.sin i >5-10 M_Earth and R>2 R_Earth. If we assume that the
underlying population has the same characteristics, the different detection
sensitivity to the orbital inclination relative to the line of sight allows us
to probe the planets' mutual inclination.
Methods. We considered the frequency of systems with one, two and three
planets as dictated by HARPS data. We used Kepler's planetary period and host
mass and radii distributions (corrected from detection bias) to model planetary
systems in a simple yet physically plausible way. We then varied the mutual
inclination between planets in a system according to different prescriptions
(completely aligned, Rayleigh distributions and isotropic) and compared the
transit frequencies with one, two or three planets with those measured by
Kepler.
Results. The results show that the two datasets are compatible, a remarkable
result especially because there are no tunable knobs other than the assumed
inclination distribution. For m.sin i cutoffs of 7-10 M_Earth, which are those
expected to correspond to the radius cutoff of 2 R_Earth, we conclude that the
results are better described by a Rayleigh distribution with mode of 1 deg or
smaller. We show that the best-fit scenario only becomes a Rayleigh
distribution with mode of 5 deg if we assume a rather extreme mass-radius
relationship for the planetary population.
Conclusions. These results have important consequences for our understanding
of the role of several proposed formation and evolution mechanisms. They
confirm that planets are likely to have been formed in a disk and show that
most planetary systems evolve quietly without strong angular momentum exchanges
(abridged).Comment: 10 pages, 6 figures, 4 tables, accepted for publication in Astronomy
& Astrophysic
Dipole-Mode Vector Solitons
We find a new type of optical vector soliton that originates from trapping of
a dipole mode by a soliton-induced waveguide. These solitons, which appear as a
consequence of the vector nature of the two component system, are more stable
than the previously found optical vortex-mode solitons and represent a new type
of extremely robust nonlinear vector structure.Comment: Four pages with five eps figure
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