691 research outputs found
Action minimizing fronts in general FPU-type chains
We study atomic chains with nonlinear nearest neighbour interactions and
prove the existence of fronts (heteroclinic travelling waves with constant
asymptotic states). Generalizing recent results of Herrmann and Rademacher we
allow for non-convex interaction potentials and find fronts with non-monotone
profile. These fronts minimize an action integral and can only exists if the
asymptotic states fulfil the macroscopic constraints and if the interaction
potential satisfies a geometric graph condition. Finally, we illustrate our
findings by numerical simulations.Comment: 19 pages, several figure
The Best Brown Dwarf Yet?: A Companion to the Hyades Eclipsing Binary V471 Tau
We have carried out an analysis of about 160 eclipse timings spanning over 30
years of the Hyades eclipsing binary V471 Tauri that shows a long-term
quasi-sinusoidal modulation of its observed eclipse arrival times. The O-Cs
have been analyzed for the ``light-time'' effect that arises from the
gravitational influence of a tertiary companion. The presence of a third body
causes the relative distance of the eclipsing pair to the Earth to change as it
orbits the barycenter of the triple system. The result of the analysis of the
eclipse times yields a light-time semi-amplitude of 137.2+/-12.0 s, an orbital
period of P_3 = 30.5+/-1.6 yr and an eccentricity of e_3 = 0.31+/-0.04. The
mass of the tertiary component is M_3 sin i_3 = 0.0393+/-0.0038 Mo when a total
mass of 1.61+/-0.06 Mo for V471 Tau is adopted. For orbital inclinations i_3 >
35 deg, the mass of the third body would be below the stable hydrogen burning
limit of M = 0.07 Mo and it thus would be a brown dwarf. In the next several
years (near maximum elongation), it should be feasible to obtain IR images and
spectra of V471 Tau C that, when combined with the known mass, age, distance,
and [Fe/H], will serve as a benchmark for understanding the physical properties
and evolution of brown dwarfs.Comment: 9 pages, 3 figures, accepted for publication in ApJ Letter
Contact binaries with additional components. III. The adaptive optics detections
We present results of the CFHT adaptive optics search for companions of a
homogeneous group of contact binary stars, as a contribution to our attempts to
prove a hypothesis that these binaries require a third star to become so close
as observed. In addition to companions directly discovered at separations of
>=1", we introduced a new method of AO image analysis utilizing distortions of
the AO diffraction ring pattern at separations of 0.07"-1". Very close
companions, with separations in the latter range were discovered in systems HV
Aqr, OO Aql, CK Boo, XY Leo, BE Scl, and RZ Tau. More distant companions were
detected in V402 Aur, AO Cam, V2082 Cyg. Our results provide a contribution to
the mounting evidence that the presence of close companions is a very common
phenomenon for very close binaries with orbital periods <1 day.Comment: Full Figs.4 and 5 are in
http://www.astro.utoronto.ca/~rucinski/Triples3
Playing Ping Pong with Light: Directional Emission of White Light
Over the last decades, light-emitting diodes (LED) have replaced common light bulbs in almost every application, from flashlights in smartphones to automotive headlights. Illuminating nightly streets requires LEDs to emit a light spectrum that is perceived as pure white by the human eye. The power associated with such a white light spectrum is not only distributed over the contributing wavelengths but also over the angles of vision. For many applications, the usable light rays are required to exit the LED in forward direction, namely under small angles to the perpendicular. In this work, we demonstrate that a specifically designed multi-layer thin film on top of a white LED increases the power of pure white light emitted in forward direction. Therefore, the deduced multi-objective optimization problem is reformulated via a real-valued physics-guided objective function that represents the hierarchical structure of our engineering problem. Variants of Bayesian optimization are employed to maximize this non-deterministic objective function based on ray tracing simulations. Eventually, the investigation of optical properties of suitable multi-layer thin films allowed to identify the mechanism behind the increased directionality of white light: angle and wavelength selective filtering causes the multi-layer thin film to play ping pong with rays of light
Evolutionary states of the two shortest period O-type overcontact binaries V382 Cyg and TU Mus
Up to now, V382 Cyg and TU Mus are the only two discovered O-type overcontact binary stars with periods less than two days (P = 1.8855 and 1.3873 d). Both systems contain a visual companion. New eclipse times and analyses of orbital period variations of the two systems are presented. It is discovered that the periods of both binaries show cyclic oscillations with periods of 47.70 and 47.73 yr, while they undergo continuous increases at rates of dP/dt = +4.4 × 10−7 and +4.0 × 10−7 d yr−1, respectively. The periodic variations can be interpreted as light travel times effects caused by the presence of invisible tertiary components suggesting that they may be quadruple systems. It is possible that the additional bodies may play an important role in the formation and evolution of the two massive overcontact binaries by removing angular momentum from the central systems, and causing the eclipsing pairs to have lower angular momentum and shorter initial orbital periods. In this way, the original detached systems can evolve into the present overcontact configurations via a Case A mass transfer. This is in agreement with the observed long-term period increase of V382 Cyg and TU Mus, which can be explained by mass transfers from the less massive components to the more massive ones. It is found that the time-scales of the long-term period variations of both systems are much longer than the thermal time-scales of the secondary components, but are close to their nuclear time-scales. This suggests that the two massive binaries have been through the rapid mass-transfer evolutionary stage on the thermal time-scales of the secondaries, and they are now on the slow phase of Case A mass transfer. It is shown that massive overcontact binaries are going through a short-lived overcontact configuration during the evolutionary phases of Case A mass transfer, which is different from the situation of late-type overcontact binary stars where components remain in good overcontact configuration driving by a combination of thermal relaxation oscillation and variable angular momentum loss via change in overcontact depth. This conclusion is in agreement with the distribution of overcontact binary stars along with the orbital period.Facultad de Ciencias Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
Evolutionary states of the two shortest period O-type overcontact binaries V382 Cyg and TU Mus
Up to now, V382 Cyg and TU Mus are the only two discovered O-type overcontact binary stars with periods less than two days (P = 1.8855 and 1.3873 d). Both systems contain a visual companion. New eclipse times and analyses of orbital period variations of the two systems are presented. It is discovered that the periods of both binaries show cyclic oscillations with periods of 47.70 and 47.73 yr, while they undergo continuous increases at rates of dP/dt = +4.4 × 10−7 and +4.0 × 10−7 d yr−1, respectively. The periodic variations can be interpreted as light travel times effects caused by the presence of invisible tertiary components suggesting that they may be quadruple systems. It is possible that the additional bodies may play an important role in the formation and evolution of the two massive overcontact binaries by removing angular momentum from the central systems, and causing the eclipsing pairs to have lower angular momentum and shorter initial orbital periods. In this way, the original detached systems can evolve into the present overcontact configurations via a Case A mass transfer. This is in agreement with the observed long-term period increase of V382 Cyg and TU Mus, which can be explained by mass transfers from the less massive components to the more massive ones. It is found that the time-scales of the long-term period variations of both systems are much longer than the thermal time-scales of the secondary components, but are close to their nuclear time-scales. This suggests that the two massive binaries have been through the rapid mass-transfer evolutionary stage on the thermal time-scales of the secondaries, and they are now on the slow phase of Case A mass transfer. It is shown that massive overcontact binaries are going through a short-lived overcontact configuration during the evolutionary phases of Case A mass transfer, which is different from the situation of late-type overcontact binary stars where components remain in good overcontact configuration driving by a combination of thermal relaxation oscillation and variable angular momentum loss via change in overcontact depth. This conclusion is in agreement with the distribution of overcontact binary stars along with the orbital period.Facultad de Ciencias Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
A Spectroscopic Study of Mass Outflows in the Interacting Binary RY Scuti
The massive interacting binary RY Scuti is an important representative of an
active mass-transferring system that is changing before our eyes and which may
be an example of the formation of a Wolf-Rayet star through tidal stripping.
Utilizing new and previously published spectra, we present examples of how a
number of illustrative absorption and emission features vary during the binary
orbit. We identify spectral features associated with each component, calculate
a new, double-lined spectroscopic binary orbit, and find masses of 7.1 +/- 1.2
M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the hidden massive
companion. Through tomographic reconstruction of the component spectra from the
composite spectra, we confirm the O9.7 Ibpe spectral class of the bright
supergiant and discover a B0.5 I spectrum associated with the hidden massive
companion; however, we suggest that the latter is actually the spectrum of the
photosphere of the accretion torus immediately surrounding the massive
companion. We describe the complex nature of the mass loss flows from the
system in the context of recent hydrodynamical models for beta Lyr, leading us
to conclude RY Scuti has matter leaving the system in two ways: 1) a bipolar
outflow from winds generated by the hidden massive companion, and 2) mass from
the bright O9.7 Ibpe supergiant flowing from the region near the L2 point to
fill out a large, dense circumbinary disk. This circumbinary disk (radius ~ 1
AU) may feed the surrounding double-toroidal nebula (radius ~ 2000 AU).Comment: 41 pages with 7 tables and 11 figures, accepted to Ap
- …