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ABSTRACT: We analytically work out the long-term, i.e. averaged over one orbital revolution, time variations of some direct observable quantities Y induced by classical and general relativistic dynamical perturbations of the two-body point-like Newtonian acceleration in the case of transiting exoplanets moving along elliptic orbits. More specifically, the observables Y with which we deal are the transit duration Δtd, the radial velocity Vρ, the time interval Δtecl between primary and secondary eclipses, and the time interval Ptr between successive primary transits. The dynamical effects considered are the centrifugal oblateness of both the star and the planet, their tidal bulges mutually raised on each other, a distant third-body X and general relativity (both Schwarzschild and Lense–Thirring). We take into account the effects due to the perturbations of all the Keplerian orbital elements involved in a consistent and uniform way. First, we explicitly compute their instantaneous time variations due to the dynamical effects considered and substitute them in the general expression for the instantaneous change of Y; then, we take the overall average over one orbital revolution of the so-obtained instantaneous rate specialized to the perturbations considered. In contrast, previous published works have often employed somewhat ‘hybrid’ expressions, in which the secular precession of, typically, the periastron only is straightforwardly inserted into instantaneous formulas. The transit duration is affected neither by the general relativistic Schwarzschild-type nor by the classical tidal effects, while the bodies’ centrifugal oblatenesses, a distant third-body X and the general relativistic Lense–Thirring-type perturbations induce non-vanishing long-term, harmonic effects on Δtd also for circular orbits. For exact edge-on configurations they vanish. Both Vρ and Δtecl experience non-vanishing long-term, harmonic variations, caused by all the perturbations considered, only for non-circular orbits. Also Ptr is affected by all of them with long-term signatures, but they do not vanish for circular orbits. Numerical evaluations of the obtained results are given for a typical star–planet scenario and compared with the expected observational accuracies over a time-span τ= 10 yr long. Also graphical investigations of the dependence of the effects considered on the semimajor axis and the eccentricity are presented. Our results are, in principle, valid also for other astronomical scenarios. They may allow, e.g., for designing various tests of gravitational theories with natural and artificial bodies in our Solar system.
Monthly Notices of the Royal Astronomical Society 02/2011; 411(1):167 - 183. DOI:10.1111/j.1365-2966.2010.17669.x
Available from: Donato Antonio Grasso
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ABSTRACT: Space, time and food are the three major resources that coexisting species could partition to reduce the effects of competition (Schoener, 1974). Space parti-tioning among interspecific ant colonies represents one of the most direct consequences of competition and depends largely on the foraging strategies adopt-ed by ants (Hölldobler & Wilson, 1990; Acosta et al., 1995). The distribution pattern of colonies has been also considered as a strategy adopted by species for maintaining exclusive foraging areas (Bernstein & Gobell, 1979; Harrison & Gentry, 1981). The size and the shape of the foraging area that territorial species may monopolize are linked to sev-eral parameters such as the distance from the cen-tral-place, the resources distribution, abundance and stability, the worker numbers and hence the competi-tive ability of neighbouring colonies or, more in gene-ral, the costs and benefits of territory formation and maintenance (Gordon, 1995; Tschinkel et al., 1995; Adams, 1998; Brown & Gordon, 2000; Adams, 2001; Adams & Tschinkel, 2001; Adams, 2003; Adler & Gor-don, 2003; Both & Visser, 2003). Harvester ants, especially common in arid and se-mi-arid environments, show a different food choice based on seed size and shape or food-handling ca-pacity (Pulliam & Brand, 1975; Morehead & Feener, 1998; Detrain & Pasteels, 2000; Willot et al., 2000; Pirk & Lopez de Casenave, 2006; Solida et al., 2007). The foraging strategies of harvester ant species in-clude individual foraging and the development of complex trunk trail systems with different species ex-hibiting a variety of territorial behaviours (Hölldo-bler & Wilson, Terrestrial organisms can adopt different spatial strategies that range from absolute territoriality to complete spatial overlap. In ants, several theoretical models have been proposed to predict some aspects of territory formation such as the size-shape or the position of boundaries along the foraging areas of neighbouring colonies. In the present study we investigated the space par-titioning during the foraging activity of two sympatric species of harvester ants (Messor wasmanni and M. minor). Colonies of the two species showed a strong territoriality with different levels of spatial overlapping in different seasons. Colonies may have reduced the cost of territorial dispu-te by not insisting on the same areas. Encounters between foragers belonging to interspecific co-lonies did not increase the probability of workers coming back to previously visited areas during the different seasons. Moreover, the evaluation of microhabitat features of foraging areas visited by the two species showed clear differences. Ecological implications and possible explanations of such space partitioning are discussed.
Journal of Biological Research 01/2011;
Available from: Matteo Luca Ruggiero
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ABSTRACT: We consider the Kehagias-Sfetsos (KS) solution in the Ho!ava-Lifshitz gravity that is the analog of the general relativistic Schwarzschild black hole. In the weak-field and slow-motion approximation, we, first, work out the correction to the third Kepler law of a test particle induced by such a solution. Then, we compare it to the phenomenologically determined orbital period of the transiting extrasolar planet HD209458b "Osiris" to preliminarily obtain an order-ofmagnitude lower bound on the KS dimensionless parameter ω0 ≥2265; 1.4 " 10-18. As suggestions for further analyses, the entire data set of HD209458b should be re-processed by explicitly modeling KS gravity as well, and one or more dedicated solve-for parameter(s) should be estimated.
The Open Astronomy Journal 12/2010; 3:167-171.
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