Alejandro M. Leiva

Secular dynamics of planetesimals in tight binary systems: application to γ-Cephei

Context. The secular dynamics of small planetesimals in tight binary systems play a fundamental role in establishing the possibility of accretional collisions in such extreme cases. The most important secular parameters are the forced eccentricity and secular frequency, which depend on the initial conditions of the particles, as well as on the mass and orbital parameters of the secondary star. Aims. We construct a second-order theory (with respect to the masses) for the planar secular motion of small planetasimals and deduce new expressions for the forced eccentricity and secular frequency. We also reanalyze the radial velocity data available for γ-Cephei and present a series of orbital solutions leading to residuals compatible with the best fits. Finally, we discuss how different orbital configurations for γ-Cephei may affect the dynamics of small bodies in circumstellar motion. Methods. The secular theory is constructed using a Lie series perturbation scheme restricted to second order in the small parameter. The orbital fits were analyzed with a minimization code that employs a genetic algorithm for a preliminary solution plus a simulated annealing for the fine tuning. Results. For γ-Cephei, we find that the classical first-order expressions for the secular frequency and forced eccentricity lead to large inaccuracies ∼50% for semimajor axes larger than one tenth the orbital separation between the stellar components. Low eccentricities and/or masses reduce the importance of the second-order terms. The dynamics of small planetesimals only show a weak dependence with the orbital fits of the stellar components, and the same result is found including the effects of a nonlinear gas drag. Thus, the possibility of planetary formation in this binary system largely appears insensitive to the orbital fits adopted for the stellar components, and any future alterations in the system parameters (due to new observations) should not change this picture. Finally, we show that planetesimals migrating because of gas drag may be trapped in mean-motion resonances with the binary, even though the migration is divergent.

Dynamics of planetesimals due to gas drag from an eccentric precessing disc

We analyse the dynamics of individual kilometre-size planetesimals in circumstellar orbits of a tight binary system. We include both the gravitational perturbations of the secondary star and a non-linear gas drag stemming from an eccentric gas disc with a finite precession rate. We consider several precession rates and eccentricities for the gas, and compare the results with a static disc in circular orbit. The disc precession introduces three main differences with respect to the classical static case. (i) The equilibrium secular solutions generated by the gas drag are no longer fixed points in the averaged system but limit cycles with frequency equal to the precession rate of the gas. The amplitude of the cycle is inversely dependent on the body size, reaching negligible values for ∼50-km-size planetesimals. (ii) The maximum final eccentricity attainable by small bodies is restricted to the interval between the gas eccentricity and the forced eccentricity, and apsidal alignment is no longer guaranteed for planetesimals strongly coupled with the gas. (iii) The characteristic time-scales of orbital decay and secular evolution decrease significantly with increasing precession rates, with values up to two orders of magnitude smaller than for static discs. Finally, we apply this analysis to the γ-Cephei system and estimate impact velocities for different-size bodies and values of the gas eccentricity. For high disc eccentricities, we find that the disc precession decreases the velocity dispersion between different-size planetesimals, thus contributing to accretional collisions in the outer parts of the disc. The opposite occurs for almost circular gas discs, where precession generates an increase in the relative velocities.

MAMA: an algebraic map for the secular dynamics of planetesimals in tight binary systems

Fil: Leiva, Alejandro Martin. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina;

Mapping the ν secular resonance for retrograde irregular satellites

Constructing dynamical maps from the filtered output of numerical integrations, we analyse the structure of the ν� secular resonance for fictitious irregular satellites in retrograde orbits.

Secular models and Kozai resonance for planets in coorbital non-coplanar motion

In this work, we construct and test an analytical and a semianalytical secular models for two planets locked in a coorbital non-coplanar motion, comparing some results with the case of restricted three body problem. The analytical average model replicates the numerical N-body integrations, even for moderate eccentricities (

Extension of fast periodic transfer orbits from the Earth–Moon RTBP to the Sun–Earth–Moon Quasi-Bicircular Problem

\lesssim

Fast Periodic Transfer Orbits in the Sun–Earth–Moon Quasi-Bicircular Problem

0.3) and inclinations (

The Earth-Moon CR3BP: A full Atlas of low-energy fast periodic transfer orbits

\lesssim10^\circ

Resonant capture and tidal evolution in circumbinary systems: testing the case of Kepler-38

), except for the regions corresponding to quasi-satellite and Lidov-Kozai configurations. Furthermore, this model is also useful in the restricted three body problem, assuming very low mass ratio between the planets. We also describe a four-degree-of-freedom semianalytical model valid for any type of coorbital configuration in a wide range of eccentricities and inclinations. {Using a N-body integrator, we have found that the phase space of the General Three Body Problem is different to the restricted case for inclined systems, and establish the location of the Lidov-Kozai equilibrium configurations depending on mass ratio. We study the stability of periodic orbits in the inclined systems, and find that apart from the robust configurations

Origen dinmico del polvo sobre la superficie de Iapetus

L_4