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Chemical abundances of planetary nebulae (PNe) help us to understand several processes of the nucleosynthesis of the progenitor star. Elements such as He, C, and N can be processed in the stellar nucleus and partially brought up to the stellar surface through dredge-up processes. Other elements such as O, Ne, Ar, S (the alpha-elements) are supposedly not perturbed by stellar nucleosynthesis, therefore they provide information of the chemistry at the stellar formation time. Although there are some well documented cases where O and Ne abundances seem altered by nucleosynthesis and some of these elements have been transported to the surface, and have been ejected in the nebular material. Chemical abundances are generally determined by analyzing the collisionally excited lines and also can be determined from some recombination lines (RLs). CELs and RLs line intensities allow to obtain nebular physical parameters (temperature and density), and ionic abundances of several elements, Total abundances are obtained by using Ionization Correction Factors (ICFs) from the literature. It is known that there exists a discrepancy in the abundances (ADF) derived from both types of lines. Usually the abundances derived from RLs is larger than the one derived from CELs This occurs in HII regions as well as in PNe. ADFs determined for PNe are usually larger than in HII regions. In same cases the value is as large as 100 or more. In this work we analyze the chemistry of some PNe, determined from CELs and RLs. Some possible causes for such a discrepancy will be presented.
In this study, we use a recently published catalogue of one hundred EBSs, classified by fine-tuning theoretical models according to contact, detached or semi-detached classes. We describe the method implemented to obtain supervised machine learning models, capable of classifying EBSs using information extracted from the light curves of variable object candidates in the phase space.
It has been recently suggested that the millisecond pulsar PSR J0030+0451 has a significant off-centered non-dipolar magnetic field component. This has been deduced via statistical inference methods on the shape and location of the hot spots over the surface of the neutron star by modelling the latest NICER observational data. In this talk we revise these conclusions under the light of a similar emission model based on relativistic force-free pulsar magnetosphere simulations which yield complex hot spot configurations using only dipolar magnetic fields.
Since their discovery in 1764 our ideas for the formation of Planetary Nebulae (PNe) have improved continuously. The basic picture traced in the mid-twentieth century of PNe being transition objects between the giant branch century of PNe being transition objects between the giant branch and the final white dwarf stage has been enriched by the discovery of strong axisymmetric PNe and the realization in the last decades that completely isolated star might not be able to form these structure. Additionally, the discovery that many solar-like stars have planetary companions or are in binary systems suggests that stellar and sub-stellar companions likely play a role in either the formation or the shaping of axisymmetric PNe. In this presentation, I will review our current understanding of the formation of PNe and the evolutionary channels that give rise to the wide diversity of central stars and PNe.
We will study the trajectories of photons emitted by a pulsar with emphasis on the chromatic effects derived from the presence of a plasmatic environment. We will show how to obtain numerically the trajectories and the luminosity curve of the pulsar. Starting from the approximate Beloborodov formalism, we will introduce plasma corrections to extend the range of validity of the model, obtaining simple analytical expressions for the trajectories and the observed flux, significantly simplifying the calculation of the pulse profiles and drastically reducing their computational cost. We will compare the numerical results with the analytical approximations. Once the validity ranges of our model have been established, we will show how to use the obtained approximations to easily model more realistic, non-antipodal, homogeneous or circular emission shells. Finally, we will expand the classification introduced by Beloborodov for the case of two non-antipodal and distinguishable emission shells.
During the last decades, M stars have gained substantial interest in the search for exoplanets due not only to the high occurrence of terrestrial-type planets but also to the greater ease of detection of low-mass planets. However, one of the major limitations in the study of extrasolar planetary systems using the radial velocity method is the presence of the activity cycles of the stars. In this talk, we present the first steps to perform a unique study of activity in those M stars that are targets in planet search programs.
(65803) Didymos is the binary Near Earth Asteroid target of the DART (NASA)/LICIA (ASI) andHera (ESA) missions. It orbits the Sun with a semi-major axis of 1.64 AU, and it is made of a 780m diameter primary body (Didymos) and a 160 m satellite (Dimorphos), orbiting the primary witha semi-major axis of 1180 m and an orbital period of 11.9 h. The primary has a rotation period of2.26 h, very close to the limit of structural stability. The low density estimated for Didymos, 2170kg/m3, shows that it is not a monolithic body, will have high macro-porosity, typical of gravitationalaggregates (or rubble-piles) and it also shows an equatorial bulge, like top-shape asteroids Ryuguand Bennu. Local acceleration near Didymos’ equatorial region may be directed outwards, allowingregolith to leave the surface. In this work, we study the dynamics of particles that are ejected fromthe surface of Didymos when the centrifugal acceleration is large enough to overcome local gravity.The analysis is carried out with a numerical code that integrates the particles’ equation of motion in anon-inertial rotating frame of reference, centered on the primary asteroid. A polyhedral shape modelfor Didymos is considered, formed by 1000 vertices and 1996 triangular faces, at which center, sampleparticles are placed. The environment of the asteroid is studied by computing the radial density ofparticles, assuming -as an arbitrary reference- an ejection mass rate of 1 kg/s. We found that thedensity of mass in orbit is strongly dependent on the physical parameters of the system, like Didymos’density. Since the mass (m) and volume (V) are not well determined, we perform different simulationsadopting different pairs of values for m and V in order to determine under what conditions it is possible to obtain a cloud of particles around the asteroid.
In this work, we present the results of applying the creep tide model (Ferraz Mello 2013) to the orbital evolution of circumbinary planets. This model allow us to consider stiff bodies, in addition to the gaseous bodies considered in previous works (Zoppetti 2019,2020). We perform a series of direct numerical integrations of the full equations and also we compare the results with the ones obtained with a high-order secular analytical model. Between the most interesting results, we find that the direction of migration of planetary semimajor axis depends, not only of the planetary eccentricity, secondary mass and semimajor axes ratio; but also on the viscosity of the circumbinary planet.