arXiv subjects

Bárbara Pichardo

Publications and source records attributed to Bárbara Pichardo.

12 recordsLinked to original sources

arXiv2019

The Contribution of Dwarf Planets to the Origin of Jupiter Family Comets

We explore the long-term evolution of a bias-free orbital representation of the cometary nuclei (with diameters above 2 km) of the Kuiper belt, using the so-called L7 synthetic model from CFEPS, which consists of three dynamical sub-populations: the Classical, the Resonant, and the Scattering. The dynamical evolution of belt particles is studied under the gravitational influence of the Sun and the four giant planets, as well as of the 34 largest known trans-Neptunian objects (TNOs with $H_V < 4$). Here we indistinctly call Dwarf Planets (DPs) to the full sample of 34 large TNOs. Over a 1 Gyr timescale, we analyze the secular influence of the DPs over Kuiper belt disk particles and their contribution to the injection rate of new visible Jupiter Family Comets (JFCs). We found that DPs globally increase the number of JFCs by 12.6% when compared with the comets produced by the giant planets alone. When considering each population separately, we find that the increment produced by DPs is 17%, 12%, and 3% for the Classical, Resonant, and Scattering populations, respectively. Given the rate of escapes from the Kuiper belt, we find upper limits to the number of objects in each population required to maintain the JFCs in steady-state; the results are $55.9\times10^6$, $78.5\times10^6$, and $274.3\times10^6$ for the Scattering, Resonant, and Classical populations, respectively. Finally, we find that the Plutinos are the most important source of comets which were originally in a resonant configuration, where the presence of Pluto alone enhances by 10% the number of JFCs.

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arXiv2018

The Contribution of Dwarf Planets to the Origin of Low Inclination Comets by the Replenishment of Mean Motion Resonances in Debris Disks

In this work we explore a new dynamical path for the delivery of low-inclination comets. In a configuration formed by an interior giant planet and an exterior massive debris disk, where the mass is accounted for by the 50 largest objects in the disk, the strongest mean motion resonances of the giant, located along the belt, are replenished with new material (test particles) due to the influence of the 50 massive objects. Once in resonance, slow chaotic diffusion stirs the orbital elements of the cometary nuclei enough to encounter the giant and to be scattered by it. When the disk is massive enough, both resonant and non-resonant particles are stirred quickly to encounter the giant and form an scattered disk component, greatly increasing the rate for the delivery of cometary material to the inner part of the system. This mechanism is applicable both to the solar system and extrasolar systems in general. Preliminary results, using a disk as massive as the classical Kuiper belt, indicate that the mechanism here proposed can account for about a tenth of the required injection rate to maintain the population of ecliptic comets in steady state. In a more massive belt of 0.25 M$_\oplus$, an estimated rate of around 0.6 new comets per year is found. Such a high rate would pose a serious risk for the habitability of rocky interior planets, yet would resemble the late heavy bombardment that was present in the early solar system.

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arXiv2017

Giant Planets Can Act As Stabilizing Agents on Debris Disks

We have explored the evolution of a cold debris disk under the gravitational influence of dwarf planet sized objects (DPs), both in the presence and absence of an interior giant planet. Through detailed long-term numerical simulations, we demonstrate that, when the giant planet is not present, DPs can stir the eccentricities and inclinations of disk particles, in linear proportion to the total mass of the DPs; on the other hand, when the giant planet is included in the simulations, the stirring is approximately proportional to the mass squared. This creates two regimes: below a disk mass threshold (defined by the total mass of DPs), the giant planet acts as a stabilizing agent of the orbits of cometary nucleii, diminishing the effect of the scatterers; above the threshold, the giant contributes to the dispersion of the particles.

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arXiv2015

Stellar Orbital Studies in Normal Spiral Galaxies II: Restrictions to Structural and Dynamical parameters on Spiral Arms

Making use of a set of detailed potential models for normal spiral galaxies, we analyze the disk stellar orbital dynamics as the structural and dynamical parameters of the spiral arms (mass, pattern speed and pitch angle) are gradually modified. With this comprehensive study of ordered and chaotic behavior, we constructed an assemblage of orbitally supported galactic models and plausible parameters for orbitally self-consistent spiral arms models. We find that, to maintain orbital support for the spiral arms, the spiral arm mass, M$_{sp}$, must decrease with the increase of the pitch angle, $i$; if $i$ is smaller than $\sim10°$, M$_{sp}$ can be as large as $\sim7\%$, $\sim6\%$, $\sim5\%$ of the disk mass, for Sa, Sb, and Sc galaxies, respectively. If $i$ increases up to $\sim25°$, the maximum M$_{sp}$ is $\sim1\%$ of the disk mass independently in this case of morphological type. For values larger than these limits, spiral arms would likely act as transient features. Regarding the limits posed by extreme chaotic behavior, we find a strong restriction on the maximum plausible values of spiral arms parameters on disk galaxies beyond which, chaotic behavior becomes pervasive. We find that for $i$ smaller than $\sim20°$, $\sim25°$, $\sim30°$, for Sa, Sb, and Sc galaxies, respectively, M$_{sp}$ can go up to $\sim10\%$, of the mass of the disk. If the corresponding $i$ is around $\sim40°$, $\sim45°$, $\sim50°$, M$_{sp}$ is $\sim1\%$, $\sim2\%$, $\sim3\%$ of the mass of the disk. Beyond these values, chaos dominates phase space, destroying the main periodic and the neighboring quasi-periodic orbits.

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arXiv2015

The Galactic Branches as a Possible Evidence for Transient Spiral Arms

With the use of a background Milky-Way-like potential model, we performed stellar orbital and magnetohydrodynamic (MHD) simulations. As a first experiment, we studied the gaseous response to a bisymmetric spiral arm potential: the widely employed cosine potential model and a self-gravitating tridimensional density distribution based model called PERLAS. Important differences are noticeable in these simulations, while the simplified cosine potential produces two spiral arms for all cases, the more realistic density based model produces a response of four spiral arms on the gaseous disk, except for weak arms -i.e. close to the linear regime- where a two-armed structure is formed. In order to compare the stellar and gas response to the spiral arms, we have also included a detailed periodic orbit study and explored different structural parameters within observational uncertainties. The four armed response has been explained as the result of ultra harmonic resonances, or as shocks with the massive bisymmetric spiral structure, among other. From the results of this work, and comparing the stellar and gaseous responses, we tracked down an alternative explanation to the formation of branches, based only on the orbital response to a self-gravitating spiral arms model. The presence of features such as branches, might be an indication of transiency of the arms.

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arXiv2014

A novel method to bracket the corotation radius in galaxy disks: vertex deviation maps

We map the kinematics of stars in simulated galaxy disks with spiral arms using the velocity ellipsoid vertex deviation (l$_v$). We use test particle simulations, and for the first time, fully self-consistent high resolution N-body models. We compare our maps with the Tight Winding Approximation model analytical predictions. We see that for all barred models spiral arms rotate closely to a rigid body manner and the vertex deviation values correlate with the density peaks position bounded by overdense and underdense regions. In such cases, vertex deviation sign changes from negative to positive when crossing the spiral arms in the direction of disk rotation, in regions where the spiral arms are in between corotation (CR) and the Outer Lindblad Resonance (OLR). By contrast, when the arm sections are inside the CR and outside the OLR, l$_v$ changes from negative to positive.We propose that measurements of the vertex deviations pattern can be used to trace the position of the main resonances of the spiral arms. We propose that this technique might exploit future data from Gaia and APOGEE surveys. For unbarred N-body simulations with spiral arms corotating with disk material at all radii, our analysis suggests that no clear correlation exists between l$_v$ and density structures.

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arXiv2013

Habitability in Different Milky Way Stellar Environments: a Stellar Interaction Dynamical Approach

Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the Solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the Solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the Solar neighborhood, however, is rather poor, and thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 108 years. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments.

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arXiv2013

On the galaxy spiral arms' nature as revealed by rotation frequencies

High resolution N-body simulations using different codes and initial condition techniques reveal two different behaviours for the rotation frequency of transient spiral arms like structures. Whereas unbarred disks present spiral arms nearly corotatingwith disk particles, strong barred models (bulged or bulge-less) quickly develop a bar-spiral structure dominant in density, with a pattern speed almost constant in radius. As the bar strength decreases the arm departs from bar rigid rotation and behaves similar to the unbarred case. In strong barred models we detect in the frequency space other subdominant and slower modes at large radii, in agreement with previous studies, however we also detect them in the configuration space. We propose that the distinctive behaviour of the dominant spiral modes can be exploited in order to constraint the nature of Galactic spiral arms by the astrometric survey GAIA and by 2-D spectroscopic surveys like CALIFA and MANGA in external galaxies.

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arXiv2013

Comparing Gaseous and Stellar Orbits in a Spiral Potential

It is generally assumed that gas in a galactic disk follows closely non self-intersecting periodic stellar orbits. In order to test this common assumption, we have performed MHD simulations of a galactic-like disk under the influence of a spiral galactic potential. We also have calculated the actual orbit of a gas parcel and compared it to stable periodic stellar orbits in the same galactic potential and position. We found that the gaseous orbits approach periodic stellar orbits far from the major orbital resonances only. Gas orbits initialized at a given galactocentric distance but at different azimuths can be different, and scattering is conspicuous at certain galactocentric radii. Also, in contrast to the stellar behaviour, near the 4:1 (or higher order) resonance the gas follows nearly circular orbits, with much shorter radial excursions than the stars. Also, since the gas does not settle into a steady state, the gaseous orbits do not necessarily close on themselves.

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arXiv2009

Tidal foces as a regulator of star formation in Taurus

Only a few molecular clouds in the Solar Neighborhood exhibit the formation of only low-mass stars. Traditionally, these clouds have been assumed to be supported against more vigorous collapse by magnetic fields. The existence of strong magnetic fields in molecular clouds, however, poses serious problems for the formation of stars and of the clouds themselves. In this {\em Letter}, we review the three-dimensional structure and kinematics of Taurus --the archetype of a region forming only low-mass stars-- as well as its orientation within the Milky way. We conclude that the particularly low star-formation efficiency in Taurus may naturally be explained by tidal forces from the Galaxy, with no need for magnetic regulation or stellar feedback.

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arXiv2008

On the gravitational content of molecular clouds and their cores

(Abridged) The gravitational term for clouds and cores entering in the virial theorem is usually assumed to be equal to the gravitational energy, since the contribution to the gravitational force from the mass distribution outside the volume of integration is assumed to be negligible. Such approximation may not be valid in the presence of an important external net potential. In the present work we analyze the effect of an external gravitational field on the gravitational budget of a density structure. Our cases under analysis are (a) a giant molecular cloud (GMC) with different aspect ratios embedded within a galactic net potential, and (b) a molecular cloud core embedded within the gravitational potential of its parent molecular cloud. We find that for roundish GMCs, the tidal tearing due to the shear in the plane of the galaxy is compensated by the tidal compression in the z direction. The influence of the external effective potential on the total gravitational budget of these clouds is relatively small, although not necessarily negligible. However, for more filamentary GMCs, the external effective potential can be dominant and can even overwhelm self-gravity, regardless of whether its main effect on the cloud is to disrupt it or compress it. This may explain the presence of some GMCs with few or no signs of massive star formation, such as the Taurus or the Maddalena's clouds. In the case of dense cores embedded in their parent molecular cloud, we found that the gravitational content due to the external field may be more important than the gravitational energy of the cores themselves. This effect works in the same direction as the gravitational energy, i.e., favoring the collapse of cores. We speculate on the implications of these results for star formation models.

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arXiv1999

On the Effects of Projection on Morphology

We study the effects of projection of three-dimensional (3D) data onto the plane of the sky by means of numerical simulations of turbulence in the interstellar medium including the magnetic field, parameterized cooling and diffuse and stellar heating, self-gravity and rotation. We compare the physical-space density and velocity distributions with their representation in position-position-velocity (PPV) space (``channel maps''), noting that the latter can be interpreted in two ways: either as maps of the column density's spatial distribution (at a given line-of-sight (LOS) velocity), or as maps of the spatial distribution of a given value of the LOS velocity (weighted by density). This ambivalence appears related to the fact that the spatial and PPV representations of the data give significantly different views. First, the morphology in the channel maps more closely resembles that of the spatial distribution of the LOS velocity component than that of the density field, as measured by pixel-to-pixel correlations between images. Second, the channel maps contain more small-scale structure than 3D slices of the density and velocity fields, a fact evident both in subjective appearance and in the power spectra of the images. This effect may be due to a pseudo-random sampling (along the LOS) of the gas contributing to the structure in a channel map: the positions sampled along the LOS (chosen by their LOS velocity) may vary significantly from one position in the channel map to the next.

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