7,118 research outputs found
Runaway and Hypervelocity Stars from Compact Object Encounters in Globular Clusters
The dense environments in the cores of globular clusters (GCs) facilitate
many strong dynamical encounters among stellar objects. These encounters have
been shown capable of ejecting stars from the host GC, whereupon they become
runaway stars, or hypervelocity stars if unbound to the galactic potential. We
study high speed stellar ejecta originating from GCs by using Monte Carlo
N-body models, in particular focusing on binary-single encounters involving
compact objects. We pair our model-discriminated populations with observational
catalogs of Milky Way GCs to compose a present-day galactic population of
stellar ejecta. We find that these kinds of encounters can accelerate stars to
velocities in excess of 2000 km/s, to speeds beyond the previously predicted
limits for ejecta from star-only encounters and in the same regime of galactic
center ejections. However, the same ejections can only account for 1.5-20% of
the total population of stellar runaways, and only 0.0001-1% of hypervelocity
stars, with similar relative rates found for runaway white dwarfs. We also
provide credible regions for ejecta from 149 Milky Way GCs, which we hope will
be useful as supplementary evidence when pairing runaway stars with origin GCs.Comment: 16 pages, 11 figures, accepted for publication in Ap
The 2011 October Draconids Outburst. II. Meteoroid Chemical Abundances from Fireball Spectroscopy
On October 8, 2011 the Earth crossed dust trails ejected from comet
21P/Giacobini-Zinner in the late 19th and early 20th Century. This gave rise to
an outburst in the activity of the October Draconid meteor shower, and an
international team was organized to analyze this event. The SPanish Meteor
Network (SPMN) joined this initiative and recorded the October Draconids by
means of low light level CCD cameras. In addition, spectroscopic observations
were carried out. Tens of multi-station meteor trails were recorded, including
an extraordinarily bright October Draconid fireball (absolute mag. -10.5) that
was simultaneously imaged from three SPMN meteor ob-serving stations located in
Andalusia. Its spectrum was obtained, showing a clear evolution in the relative
intensity of emission lines as the fireball penetrated deeper into the
atmosphere. Here we focus on the analysis of this remarkable spectrum, but also
discuss the atmospheric trajectory, atmospheric penetration, and orbital data
computed for this bolide which was probably released during
21P/Giacobini-Zinner return to perihelion in 1907. The spectrum is discussed
together with the tensile strength for the October Draconid meteoroids. The
chemical profile evolution of the main rocky elements for this extremely bright
bolide is compared with the elemental abundances obtained for 5 October
Draconid fireballs also recorded during our spectroscopic campaign but observed
only at a single station. Significant chemical heterogeneity between the small
meteoroids is found as we should expect for cometary aggregates being formed by
diverse dust components.Comment: Manuscript in press in Monthly Notices of the Royal Astronomical
Society. Accepted for publication in MNRAS on April 28th, 2013 Manuscript
Pages: 28 Tables: 5 Figures: 12. Manuscript associated: "The 2011 October
Draconids outburst. I. Orbital elements, meteoroid fluxes and
21P/Giacobini-Zinner delivered mass to Earth" by Trigo-Rodriguez et al. is
also in press in the same journa
Strong oviposition preference for Bt over non-Bt maize in Spodoptera frugiperda and its implications for the evolution of resistance
BACKGROUND: Transgenic crops expressing Bt toxins have substantial benefits for growers in terms of reduced synthetic insecticide inputs, area-wide pest management and yield. This valuable technology depends upon delaying the evolution of resistance. The ‘high dose/refuge strategy’, in which a refuge of non-Bt plants is planted in close proximity to the Bt crop, is the foundation of most existing resistance management. Most theoretical analyses of the high dose/refuge strategy assume random oviposition across refugia and Bt crops. RESULTS: In this study we examined oviposition and survival of Spodoptera frugiperda across conventional and Bt maize and explored the impact of oviposition behavior on the evolution of resistance in simulation models. Over six growing seasons oviposition rates per plant were higher in Bt crops than in refugia. The Cry1F Bt maize variety retained largely undamaged leaves, and oviposition preference was correlated with the level of feeding damage in the refuge. In simulation models, damage-avoiding oviposition accelerated the evolution of resistance and either led to requirements for larger refugia or undermined resistance management altogether. Since larval densities affected oviposition preferences, pest population dynamics affected resistance evolution: larger refugia were weakly beneficial for resistance management if they increased pest population sizes and the concomitant degree of leaf damage. CONCLUSIONS: Damaged host plants have reduced attractiveness to many insect pests, and crops expressing Bt toxins are generally less damaged than conventional counterparts. Resistance management strategies should take account of this behavior, as it has the potential to undermine the effectiveness of existing practice, especially in the tropics where many pests are polyvoltinous. Efforts to bring down total pest population sizes and/or increase the attractiveness of damaged conventional plants will have substantial benefits for slowing the evolution of resistance
Water-ice driven activity on Main-Belt Comet P/2010 A2 (LINEAR) ?
The dust ejecta of Main-Belt Comet P/2010 A2 (LINEAR) have been observed with
several telescopes at the at the Observatorio del Roque de los Muchachos on La
Palma, Spain. Application of an inverse dust tail Monte Carlo method to the
images of the dust ejecta from the object indicates that a sustained, likely
water-ice driven, activity over some eight months is the mechanism responsible
for the formation of the observed tail. The total amount of dust released is
estimated to be 5E7 kg, which represents about 0.3% of the nucleus mass. While
the event could have been triggered by a collision, this cannot be decided from
the currently available data.Comment: Accepted for ApJ Letter
Beyond conventional factorization: Non-Hermitian Hamiltonians with radial oscillator spectrum
The eigenvalue problem of the spherically symmetric oscillator Hamiltonian is
revisited in the context of canonical raising and lowering operators. The
Hamiltonian is then factorized in terms of two not mutually adjoint factorizing
operators which, in turn, give rise to a non-Hermitian radial Hamiltonian. The
set of eigenvalues of this new Hamiltonian is exactly the same as the energy
spectrum of the radial oscillator and the new square-integrable eigenfunctions
are complex Darboux-deformations of the associated Laguerre polynomials.Comment: 13 pages, 7 figure
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