244 research outputs found
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
Hot Jupiters from Secular Planet--Planet Interactions
About 25 per cent of `hot Jupiters' (extrasolar Jovian-mass planets with
close-in orbits) are actually orbiting counter to the spin direction of the
star. Perturbations from a distant binary star companion can produce high
inclinations, but cannot explain orbits that are retrograde with respect to the
total angular momentum of the system. Such orbits in a stellar context can be
produced through secular (that is, long term) perturbations in hierarchical
triple-star systems. Here we report a similar analysis of planetary bodies,
including both octupole-order effects and tidal friction, and find that we can
produce hot Jupiters in orbits that are retrograde with respect to the total
angular momentum. With distant stellar mass perturbers, such an outcome is not
possible. With planetary perturbers, the inner orbit's angular momentum
component parallel to the total angular momentum need not be constant. In fact,
as we show here, it can even change sign, leading to a retrograde orbit. A
brief excursion to very high eccentricity during the chaotic evolution of the
inner orbit allows planet-star tidal interactions to rapidly circularize that
orbit, decoupling the planets and forming a retrograde hot Jupiter.Comment: accepted for publication by Nature, 3 figures (version after proof -
some typos corrected
The Multiple Origin of Blue Straggler Stars: Theory vs. Observations
In this chapter we review the various suggested channels for the formation
and evolution of blue straggler stars (BSSs) in different environments and
their observational predictions. These include mass transfer during binary
stellar evolution - case A/B/C and D (wind Roche-lobe overflow) mass transfer,
stellar collisions during single and binary encounters in dense stellar
cluster, and coupled dynamical and stellar evolution of triple systems. We also
explore the importance of the BSS and binary dynamics in stellar clusters. We
review the various observed properties of BSSs in different environments (halo
and bulge BSSs, BSSs in globular clusters and BSSs in old open clusters), and
compare the current observations with the theoretical predictions for BSS
formation. We try to constrain the likely progenitors and processes that play a
role in the formation of BSSs and their evolution. We find that multiple
channels of BSS formation are likely to take part in producing the observed
BSSs, and we point out the strengths and weaknesses of each the formation
channel in respect to the observational constraints. Finally we point out
directions to further explore the origin of BSS, and highlight eclipsing binary
BSSs as important observational tool.Comment: Chapter 11, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Nearby low-mass triple system GJ795
We report the results of our optical speckle-interferometric observations of
the nearby triple system GJ795 performed with the 6-m BTA telescope with
diffraction-limited angular resolution. The three components of the system were
optically resolved for the first time. Position measurements allowed us to
determine the elements of the inner orbit of the triple system. We use the
measured magnitude differences to estimate the absolute magnitudes and spectral
types of the components of the triple: =7.310.08,
=8.660.10, =8.420.10, K5,
K9, K8. The total mass of the system is
equal to =1.69. We show
GJ795 to be a hierarchical triple system which satisfies the empirical
stability criteria.Comment: 6 pages, 2 figures, published in Astrophysical Bulleti
Long-term evolution of orbits about a precessing oblate planet: 1. The case of uniform precession
It was believed until very recently that a near-equatorial satellite would
always keep up with the planet's equator (with oscillations in inclination, but
without a secular drift). As explained in Efroimsky and Goldreich (2004), this
opinion originated from a wrong interpretation of a (mathematically correct)
result obtained in terms of non-osculating orbital elements. A similar analysis
carried out in the language of osculating elements will endow the planetary
equations with some extra terms caused by the planet's obliquity change. Some
of these terms will be nontrivial, in that they will not be amendments to the
disturbing function. Due to the extra terms, the variations of a planet's
obliquity may cause a secular drift of its satellite orbit inclination. In this
article we set out the analytical formalism for our study of this drift. We
demonstrate that, in the case of uniform precession, the drift will be
extremely slow, because the first-order terms responsible for the drift will be
short-period and, thus, will have vanishing orbital averages (as anticipated 40
years ago by Peter Goldreich), while the secular terms will be of the second
order only. However, it turns out that variations of the planetary precession
make the first-order terms secular. For example, the planetary nutations will
resonate with the satellite's orbital frequency and, thereby, may instigate a
secular drift. A detailed study of this process will be offered in the
subsequent publication, while here we work out the required mathematical
formalism and point out the key aspects of the dynamics
- …