Stellar Scattering and the Formation of Hot-Jupiters in Binary Systems

Hot Jupiters (HJs) are usually defined as giant Jovian-size planets with orbital periods $P \le 10$ days. Although they lie close to the star, several have finite eccentricities and significant misalignment angle with respect to the stellar equator. Two mechanisms have been proposed to explain the excited and misaligned sub-population of HJs: Lidov-Kozai migration and planet-planet scattering. Although both are based on completely different dynamical phenomena, they appear to be equally effective in generating hot planets. Nevertheless, there has been no detailed analysis comparing the predictions of both mechanisms. In this paper we present numerical simulations of Lidov-Kozai trapping of single planets in compact binary systems. Both the planet and the binary are initially placed in coplanar orbits, although the inclination of the impactor is assumed random. After the passage of the third star, we follow the orbital and spin evolution of the planet using analytical models based on the octupole expansion of the secular Hamiltonian. The present work aims at the comparison of the two mechanisms, as an explanation for the excited and inclined HJs in binary systems. We compare the results obtained through this paper with results in Beaug\'e & Nesvorn\'y 2012, where the authors analyze how the planet-planet scattering mechanisms works. Several of the orbital characteristics of the simulated HJs are caused by tidal trapping from quasi-parabolic orbits, independent of the driving mechanism. These include both the 3-day pile-up and the distribution in the eccentricity vs semimajor axis plane. However, the distribution of the inclinations shows significant differences. While Lidov-Kozai trapping favors a more random distribution, planet-planet scattering shows a large portion of bodies nearly aligned with the equator of the central star.Comment: 12 pages, 6 figures. Accepted for publication at IJAB (internation journal of astrobiology

Atmospheric turbulence in phase-referenced and wide-field interferometric images: Application to the SKA

Phase referencing is a standard calibration procedure in radio interferometry. It allows to detect weak sources by using quasi-simultaneous observations of closeby sources acting as calibrators. Therefore, it is assumed that, for each antenna, the optical paths of the signals from both sources are similar. However, atmospheric turbulence may introduce strong differences in the optical paths of the signals and affect, or even waste, phase referencing for cases of relatively large calibrator-to-target separations and/or bad weather. The situation is similar in wide-field observations, since the random deformations of the images, mostly caused by atmospheric turbulence, have essentially the same origin as the random astrometric variations of phase-referenced sources with respect to the phase center of their calibrators. In this paper, we present the results of a Monte Carlo study of the astrometric precision and sensitivity of an interferometric array (a realization of the Square Kilometre Array, SKA) in phase-referenced and wide-field observations. These simulations can be extrapolated to other arrays by applying the corresponding corrections. We consider several effects from the turbulent atmosphere (i.e., ionosphere and wet component of the troposphere) and also from the antenna receivers. We study the changes in dynamic range and astrometric precision as a function of observing frequency, source separation, and strength of the turbulence. We find that, for frequencies between 1 and 10 GHz, it is possible to obtain images with high fidelity, although the atmosphere strongly limits the sensitivity of the instrument compared to the case with no atmosphere. Outside this frequency window, the dynamic range of the images and the accuracy of the source positions decrease. [...] (Incomplete abstract. Please read manuscript.)Comment: 9 pages, 11 figures. Accepted for publication in A&A

Assessment of a high-resolution central scheme for the solution of the relativistic hydrodynamics equations

We assess the suitability of a recent high-resolution central scheme developed by Kurganov & Tadmor (2000) for the solution of the relativistic hydrodynamics equations. The novelty of this approach relies on the absence of Riemann solvers in the solution procedure. The computations we present are performed in one and two spatial dimensions in Minkowski spacetime. Standard numerical experiments such as shock tubes and the relativistic flat-faced step test are performed. As an astrophysical application the article includes two-dimensional simulations of the propagation of relativistic jets using both Cartesian and cylindrical coordinates. The simulations reported clearly show the capabilities of the numerical scheme to yield satisfactory results, with an accuracy comparable to that obtained by the so-called high-resolution shock-capturing schemes based upon Riemann solvers (Godunov-type schemes), even well inside the ultrarelativistic regime. Such central scheme can be straightforwardly applied to hyperbolic systems of conservation laws for which the characteristic structure is not explicitly known, or in cases where the exact solution of the Riemann problem is prohibitively expensive to compute numerically. Finally, we present comparisons with results obtained using various Godunov-type schemes as well as with those obtained using other high-resolution central schemes which have recently been reported in the literature.Comment: 14 pages, 12 figures, to appear in A&

VLBI observations of SN2011dh: imaging of the youngest radio supernova

We report on the VLBI detection of supernova SN2011dh at 22GHz using a subset of the EVN array. The observations took place 14 days after the discovery of the supernova, thus resulting in a VLBI image of the youngest radio-loud supernova ever. We provide revised coordinates for the supernova with milli-arcsecond precision, linked to the ICRF. The recovered flux density is a factor 2 below the EVLA flux density reported by other authors at the same frequency and epoch of our observations. This discrepancy could be due to extended emission detected with the EVLA or to calibration problems in the VLBI and/or EVLA observations.Comment: Letter. Accepted in A&

Chaotic Diffusion in the Gliese-876 Planetary System

Chaotic diffusion is supposed to be responsible for orbital instabilities in planetary systems after the dissipation of the protoplanetary disk, and a natural consequence of irregular motion. In this paper we show that resonant multi-planetary systems, despite being highly chaotic, not necessarily exhibit significant diffusion in phase space, and may still survive virtually unchanged over timescales comparable to their age.Using the GJ-876 system as an example, we analyze the chaotic diffusion of the outermost (and less massive) planet. We construct a set of stability maps in the surrounding regions of the Laplace resonance. We numerically integrate ensembles of close initial conditions, compute Poincar\'e maps and estimate the chaotic diffusion present in this system. Our results show that, the Laplace resonance contains two different regions: an inner domain characterized by low chaoticity and slow diffusion, and an outer one displaying larger values of dynamical indicators. In the outer resonant domain, the stochastic borders of the Laplace resonance seem to prevent the complete destruction of the system. We characterize the diffusion for small ensembles along the parameters of the outermost planet. Finally, we perform a stability analysis of the inherent chaotic, albeit stable Laplace resonance, by linking the behavior of the resonant variables of the configurations to the different sub-structures inside the three-body resonance.Comment: 13 pages, 7 figures, 2 tables. Accepted for publication in MNRA

Wavelet transforms for non-uniform speech recognition

An algorithm for nonuniform speech segmentation and its application in speech recognition systems is presented. A method based on the Modulated Gaussian Wavelet Transform based Speech Analyser (MGWTSA) and the subsequent parametrization block is used to transform a uniform signal into a set of nonuniformly separated frames, with the accurate information being fed into a speech recognition system. The algorithm needs a frame characterizing the signal where necessary, trying to reduce the number of frames per signal as much as possible, without an appreciable reduction in the recognition rate of the system.Peer ReviewedPostprint (published version

Optical spectroscopy of microquasar candidates at low galactic latitudes

We report optical spectroscopic observations of a sample of 6 low-galactic latitude microquasar candidates selected by cross-identification of X-ray and radio point source catalogs for |b|<5 degrees. Two objects resulted to be of clear extragalactic origin, as an obvious cosmologic redshift has been measured from their emission lines. For the rest, none exhibits a clear stellar-like spectrum as would be expected for genuine Galactic microquasars. Their featureless spectra are consistent with being extragalactic in origin although two of them could be also highly reddened stars. The apparent non-confirmation of our candidates suggests that the population of persistent microquasar systems in the Galaxy is more rare than previously believed. If none of them is galactic, the upper limit to the space density of new Cygnus X-3-like microquasars within 15 kpc would be 1.1\times10^{-12} per cubic pc. A similar upper limit for new LS 5039-like systems within 4 kpc is estimated to be 5.6\times10^{-11} per cubic pc.Comment: 7 pages, 7 figures. Published in A&A, see http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...413..309

Identification of the optical and near-infrared counterpart of GRS 1758-258

Context. Understood to be a microquasar in the Galactic center region, GRS 1758-258 has not yet been unambiguously identified to have an optical/near-infrared counterpart, mainly because of the high absorption and the historic lack of suitable astrometric stars, which led to the use of secondary astrometric solutions. Although it is considered with 1E 1740.7-2942 as the prototypical microquasar in the Galactic center region, the Galactic origin of both sources has not yet been confirmed. Aims. We attempt to improve previous astrometry to identify a candidate counterpart to GRS 1758-258. We present observations with the Gran Telescopio de Canarias (GTC), in which we try to detect any powerful emission lines that would infer an extragalactic origin of this source. Methods. We use modern star catalogues to reanalyze archival images of the GRS 1758-258 field in the optical and near-infrared wavelengths, and compute a new astrometric solution. We also reanalyzed archival radio data of GRS 1758-258 to determine a new and more accurate radio position. Results. Our improved astrometric solution for the GRS 1758-258 field represents a significant advancement on previous works and allows us to identify a single optical/near-infrared source, which we propose as the counterpart of GRS 1758-258. The GTC spectrum of this source is however of low signal-to-noise ratio and does not rule out a Galactic origin. Hence, new spectral observations are required to confirm or discard a Galactic nature.Comment: 4 pages, 3 figures, accepted by Astronomy and Astrophysic