537 research outputs found
Tidal and rotational effects in the perturbations of hierarchical triple stellar systems. II. Eccentric systems - the case of AS Camelopardalis
We study the perturbations of a relatively close third star on a tidally
distorted eccentric eclipsing binary. We consider both the observational
consequences of the variations of the orbital elements and the interactions of
the stellar rotation with the orbital revolution in the presence of
dissipation. We concentrate mainly on the effect of a hypothetical third
companion on both the real, and the observed apsidal motion period. We
investigate how the observed period derived mainly from some variants of the
O-C relates to the real apsidal motion period. We carried out both analytical
and numerical investigations and give the time variations of the orbital
elements of the binary both in the dynamical and the observational reference
frames. We give the direct analytical form of an eclipsing O-C affected
simultaneously by the mutual tidal forces and the gravitational interactions
with a tertiary. We also integrated numerically simultaneously the orbital and
rotational equations for the possible hierarchical triple stellar system AS
Camelopardalis. We find that there is a significant domain of the possible
hierarchical triple system configurations, where both the dynamical and the
observational effects tend to measure longer apsidal advance rate than is
expected theoretically. This happens when the mutual inclination of the close
and the wide orbits is large, and the orbital plane of the tertiary almost
coincides with the plane of the sky. We also obtain new numerical results on
the interaction of the orbital evolution and stellar rotation in such triplets.
The most important fact is that resonances might occur as the stellar
rotational rate varies during the dissipation-driven synchronization process...Comment: 33 pages, 12 figures (reduced quality!), accepted for publication for
Astronomy and Astrophysic
Symplectic integration of space debris motion considering several Earth's shadowing models
In this work, we present a symplectic integration scheme to numerically
compute space debris motion. Such an integrator is particularly suitable to
obtain reliable trajectories of objects lying on high orbits, especially
geostationary ones. Indeed, it has already been demonstrated that such objects
could stay there for hundreds of years. Our model takes into account the
Earth's gravitational potential, luni-solar and planetary gravitational
perturbations and direct solar radiation pressure. Based on the analysis of the
energy conservation and on a comparison with a high order non-symplectic
integrator, we show that our algorithm allows us to use large time steps and
keep accurate results. We also propose an innovative method to model Earth's
shadow crossings by means of a smooth shadow function. In the particular
framework of symplectic integration, such a function needs to be included
analytically in the equations of motion in order to prevent numerical drifts of
the energy. For the sake of completeness, both cylindrical shadows and penumbra
transitions models are considered. We show that both models are not equivalent
and that big discrepancies actually appear between associated orbits,
especially for high area-to-mass ratios
STEREO observations of stars and the search for exoplanets
The feasibility of using data from the NASA STEREO mission for variable star and asteroseismology studies has been examined. A data analysis pipeline has been developed that is able to apply selected algorithms to the entire data base of nearly a million stars to search for signs of variability. An analysis limited to stars of magnitude 10.5 has been carried out, which has resulted in the extraction of 263 eclipsing binaries (EBs), of which 122 are not recorded as such in the SIMBAD online data base. The characteristics of the STEREO observations are shown to be extremely well suited to variable star studies with the ability to provide continuous phase coverage for extended periods as well as repeated visits that allow both short- and long-term variability to be observed. This will greatly inform studies of particular stars, such as the pre-cataclysmic variable V471 Tau, as well as the entire classes of stars, including many forms of rotational variability. The high-precision photometry has also revealed a potentially substellar companion to a bright (R= 7.5 mag) nearby star (HD 213597), detected with 5σ significance. This would provide a significant contribution to the exoplanet research if follow-up observations ascertain the mass to be within the planetary domain. Some particularly unusual EBs from the recovered sample are discussed, including a possible reclassification of a well-known star as an EB rather than a rotational variable (HR 7355) and several particularly eccentric systems, including very long period EBs
Cosmic ray short burst observed with the Global Muon Detector Network (GMDN) on June 22, 2015
We analyze the short cosmic ray intensity increase ("cosmic ray burst": CRB)
on June 22, 2015 utilizing a global network of muon detectors and derive the
global anisotropy of cosmic ray intensity and the density (i.e. the
omnidirectional intensity) with 10-minute time resolution. We find that the CRB
was caused by a local density maximum and an enhanced anisotropy of cosmic rays
both of which appeared in association with Earth's crossing of the heliospheric
current sheet (HCS). This enhanced anisotropy was normal to the HCS and
consistent with a diamagnetic drift arising from the spatial gradient of cosmic
ray density, which indicates that cosmic rays were drifting along the HCS from
the north of Earth. We also find a significant anisotropy along the HCS,
lasting a few hours after the HCS crossing, indicating that cosmic rays
penetrated into the inner heliosphere along the HCS. Based on the latest
geomagnetic field model, we quantitatively evaluate the reduction of the
geomagnetic cut-off rigidity and the variation of the asymptotic viewing
direction of cosmic rays due to a major geomagnetic storm which occurred during
the CRB and conclude that the CRB is not caused by the geomagnetic storm, but
by a rapid change in the cosmic ray anisotropy and density outside the
magnetosphere.Comment: accepted for the publication in the Astrophysical Journa
Recommended from our members
Microbial Impacts on the Migration of Actinides -Effects of Exudates on Adsorption-
The interaction of actinides with microorganisms has been extensively studied to elucidate migration behavior of actinides in the environments. However, the mechanisms of interaction of microorganisms and actinides are poorly understood. They have been conducting basic science on microbial accumulation of actinides in order to elucidate the environmental behavior of actinides under relevant conditions. The effect of exudates from bacteria cells on the sorption of Eu(III) and Cm(III) by Chlorella vulgaris was studied by a batch method. The pH dependence of log K{sub d} of Eu(III) and Cm(III) for cellulose, major component of C. vulgaris cell, differed from that for C. vulgaris. On the contrary, log K{sub d} of Eu(III) and Cm(III) for cellulose in the solution containing exudates from C. vulgaris cells in a 0.5% NaCl solution showed a similar pH dependence to that by C. vulgaris. These results strongly suggested that exudates affect on the sorption of Eu(III) and Cm(III) on C. vulgaris. Effect of desferrioxamine B (DFO), one of exudates to chelate the insoluble Fe(III), on the sorption of Pu(IV), Th(IV) and Eu(III) by Pseudomonas fluorescens was studied. In the presence of DFO the sorption of Pu(IV), Th(IV) and Eu(III) on the cells increased with a decrease in pH from 7 to 4. In contrast, without DFO most of Pu(IV), Th(IV) and Eu(III) were precipitated from solution. Adsorption of DFO on the cells was negligible in the solution with and without metals. Adsorption of Pu(IV), Th(IV) and Eu(III) on P. fluorescens cells decreased in the order Eu(III) > Th(IV) > Pu(IV), which corresponds to increasing stability constant of the DFO complexes. These results indicate that Th(IV), Pu(IV) and Eu(III) dissociate when in contact with cells, after which the metals are adsorbed
A New WIMP Population in the Solar System and New Signals for Dark-Matter Detectors
We describe in detail how perturbations due to the planets can cause a
sub-population of WIMPs captured by scattering in surface layers of the Sun to
evolve to have orbits which no longer intersect the Sun. We argue that such
WIMPs, if their orbit has a semi-major axis less than 1/2 of Jupiter's, can
persist in the solar system for cosmological timescales. This leads to a new,
previously unanticipated WIMP population intersecting the Earth's orbit. The
WIMP-nucleon cross sections required for this population to be significant are
precisely those in the range predicted for SUSY dark matter, lying near the
present limits obtained by direct underground dark matter searches using
cyrogenic detectors. Thus, if a WIMP signal is observed in the next generation
of detectors, a potentially measurable signal due to this new population must
exist. This signal, lying in the keV range for Germanium detectors, would be
complementary to that of galactic halo WIMPs. A comparison of event rates,
anisotropies, and annual modulations would not only yield additional
confirmation that any claimed signal is indeed WIMP-based, but would also allow
one to gain information on the nature of the underlying dark matter model.Comment: Revtex, 37 pages including 6 figures, accepted by Phys. Rev D.
(version to be published, including changes made in response to referees
reports
The GAPS Experiment to Search for Dark Matter using Low-energy Antimatter
The GAPS experiment is designed to carry out a sensitive dark matter search
by measuring low-energy cosmic ray antideuterons and antiprotons. GAPS will
provide a new avenue to access a wide range of dark matter models and masses
that is complementary to direct detection techniques, collider experiments and
other indirect detection techniques. Well-motivated theories beyond the
Standard Model contain viable dark matter candidates which could lead to a
detectable signal of antideuterons resulting from the annihilation or decay of
dark matter particles. The dark matter contribution to the antideuteron flux is
believed to be especially large at low energies (E < 1 GeV), where the
predicted flux from conventional astrophysical sources (i.e. from secondary
interactions of cosmic rays) is very low. The GAPS low-energy antiproton search
will provide stringent constraints on less than 10 GeV dark matter, will
provide the best limits on primordial black hole evaporation on Galactic length
scales, and will explore new discovery space in cosmic ray physics.
Unlike other antimatter search experiments such as BESS and AMS that use
magnetic spectrometers, GAPS detects antideuterons and antiprotons using an
exotic atom technique. This technique, and its unique event topology, will give
GAPS a nearly background-free detection capability that is critical in a
rare-event search. GAPS is designed to carry out its science program using
long-duration balloon flights in Antarctica. A prototype instrument was
successfully flown from Taiki, Japan in 2012. GAPS has now been approved by
NASA to proceed towards the full science instrument, with the possibility of a
first long-duration balloon flight in late 2020. Here we motivate low-energy
cosmic ray antimatter searches and discuss the current status of the GAPS
experiment and the design of the payload.Comment: 8 pags, 3 figures, Proc. 35th International Cosmic Ray Conference
(ICRC 2017), Busan, Kore
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