arXiv subjects

O. C. Winter

Publications and source records attributed to O. C. Winter.

34 records · Page 2Linked to original sources

arXiv2019

The 2014-2015 Brazilian Mutual Phenomena campaign for the Jovian satellites and improved results for the 2009 events

Progress in astrometry and orbital modelling of planetary moons in the last decade enabled better determinations of their orbits. These studies need accurate positions spread over extended periods. We present the results of the 2014-2015 Brazilian campaign for 40 mutual events from 47 observed light curves by the Galilean satellites plus one eclipse of Amalthea by Ganymede. We also reanalysed and updated results for 25 mutual events observed in the 2009 campaign. All telescopes were equipped with narrow-band filters centred at 889 nm with a width of 15 nm to eliminate the scattered light from Jupiter. The albedos' ratio was determined using images before and after each event. We simulated images of moons, umbra, and penumbra in the sky plane, and integrated their fluxes to compute albedos, simulate light curves and fit them to the observed ones using a chi-square fitting procedure. For that, we used the complete version of the Oren-Nayer reflectance model. The relative satellite positions mean uncertainty was 11.2 mas ($\sim$35 km) and 10.1 mas ($\sim$31 km) for the 2014-2015 and 2009 campaigns respectively. The simulated and observed \textsc{ascii} light curve files are freely available in electronic form at the \textit{Natural Satellites DataBase} (NSDB). The 40/25 mutual events from our 2014-2015/2009 campaigns represent a significant contribution of 17%/15% in comparison with the PHEMU campaigns lead by the IMCCE. Besides that, our result for the eclipse of Amalthea is only the 4$^{th}$ such measurement ever published after the three ones observed by the 2014-2015 international PHEMU campaign. Our results are suitable for new orbital/ephemeris determinations for the Galilean moons and Amalthea.

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arXiv2019

First stellar occultation by the Galilean moon Europa and upcoming events between 2019 and 2021

Context. Bright stellar positions are now known with an uncertainty below 1 mas thanks to Gaia DR2. Between 2019-2020, the Galactic plane will be the background of Jupiter. The dense stellar background will lead to an increase in the number of occultations, while the Gaia DR2 catalogue will reduce the prediction uncertainties for the shadow path. Aims. We observed a stellar occultation by the Galilean moon Europa (J2) and propose a campaign for observing stellar occultations for all Galilean moons. Methods. During a predicted period of time, we measured the light flux of the occulted star and the object to determine the time when the flux dropped with respect to one or more reference stars, and the time that it rose again for each observational station. The chords obtained from these observations allowed us to determine apparent sizes, oblatness, and positions with kilometre accuracy. Results. We present results obtained from the first stellar occultation by the Galilean moon Europa observed on 2017 March 31. The apparent fitted ellipse presents an equivalent radius of 1561.2 $\pm$ 3.6 km and oblatenesses 0.0010 $\pm$ 0.0028. A very precise Europa position was determined with an uncertainty of 0.8 mas. We also present prospects for a campaign to observe the future events that will occur between 2019 and 2021 for all Galilean moons. Conclusions. Stellar occultation is a suitable technique for obtaining physical parameters and highly accurate positions of bright satellites close to their primary. A number of successful events can render the 3D shapes of the Galilean moons with high accuracy. We encourage the observational community (amateurs included) to observe the future predicted events.

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arXiv2019

A general method for transforming non-physical configurations in BPS states

In this work, we apply the so-called BPS method in order to obtain topological defects for a complex scalar field Lagrangian introduced by Trullinger and Subbaswamy. The BPS approach led us to compute new analytical solutions for this model.In our investigation, we found analytical configurations which satisfy the BPS first-order differential equations but do not obey the equations of motion of the model. Such defects were named non-physical ones. In order to recover the physical meaning of these defects, we proposed a procedure which can transform them into BPS states of new scalar field models. The new models here founded were applied in the context of hybrid cosmological scenarios, where we derived cosmological parameters compatible with the observed Universe. Such a methodology opens a new window to connect different two scalar fields systems and can be implemented in several distinct applications such as Bloch Branes, Lorentz and Symmetry Breaking Scenarios, Q-Balls, Oscillons, Cosmological Contexts, and Condensed Matter Systems.

hep-th↗

arXiv2018

APPROX -- Mutual approximations between the Galilean moons. The 2016-2018 observational campaign

The technique of mutual approximations accurately gives the central instant at the maximum apparent approximation of two moving natural satellites in the sky plane. This can be used in ephemeris fitting to infer the relative positions between satellites with high precision. Only the mutual phenomena -- occultations and eclipses -- may achieve better results. However, mutual phenomena only occur every six years in the case of Jupiter. Mutual approximations do not have this restriction and can be observed at any time along the year as long as the satellites are visible. In this work, we present 104 central instants determined from the observations of 66 mutual approximations between the Galilean moons carried out at different sites in Brazil and France during the period 2016--2018. For 28 events we have at least two independent observations. All telescopes were equipped with a narrow-band filter centred at 889 nm with a width of 15 nm to eliminate the scattered light from Jupiter. The telescope apertures ranged between 25--120 cm. For comparison, the precision of the positions obtained with classical CCD astrometry is about 100 mas, for mutual phenomena it can achieve 10 mas or less and the average internal precision obtained with mutual approximations was 11.3 mas. This new kind of simple, yet accurate observations can significantly improve the orbits and ephemeris of Galilean satellites and thus be very useful for the planning of future space missions aiming at the Jovian system.

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arXiv2018

Rings under close encounters with the giant planets: Chariklo vs Chiron

In 2014, the discovery of two well-defined rings around the Centaur (10199) Chariklo were announced. This was the first time that such structures were found around a small body. In 2015, it was proposed that the Centaur (2060) Chiron may also have a ring. In a previous study, we analyzed how close encounters with giant planets would affect the rings of Chariklo. The most likely result is the survival of the rings. In the present work, we broaden our analysis to (2060) Chiron. In addition to Chariklo, Chiron is currently the only known Centaur with a presumed ring. By applying the same method as \cite{araujo2016}, we performed numerical integrations of a system composed of 729 clones of Chiron, the Sun, and the giant planets. The number of close encounters that disrupted the ring of Chiron during one half-life of the study period was computed. This number was then compared to the number of close encounters for Chariklo. We found that the probability of Chiron losing its ring due to close encounters with the giant planets is about six times higher than that for Chariklo. Our analysis showed that, unlike Chariklo, Chiron is more likely to remain in an orbit with a relatively low inclination and high eccentricity. Thus, we found that the bodies in Chiron-like orbits are less likely to retain rings than those in Chariklo-like orbits. Overall, for observational purposes, we conclude that the bigger bodies in orbits with high inclinations and low eccentricities should be prioritized.

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arXiv2017

Mapping stable direct and retrograde orbits around the triple system of asteroids (45) Eugenia

It is well accepted that knowing the composition and the orbital evolution of asteroids may help us to understand the process of formation of the Solar System. It is also known that asteroids can represent a threat to our planet. Such important role made space missions to asteroids a very popular topic in the current astrodynamics and astronomy studies. By taking into account the increasingly interest in space missions to asteroids, especially to multiple systems, we present a study aimed to characterize the stable and unstable regions around the triple system of asteroids (45) Eugenia. The goal is to characterize unstable and stable regions of this system and compare with the system 2001 SN263 - the target of the ASTER mission. Besides, Prado (2014) used a new concept for mapping orbits considering the disturbance received by the spacecraft from all the perturbing forces individually. This method was also applied to (45) Eugenia. We present the stable and unstable regions for particles with relative inclination between 0 and 180 degrees. We found that (45) Eugenia presents larger stable regions for both, prograde and retrograde cases. This is mainly because the satellites of this system are small when compared to the primary body, and because they are not so close to each other. We also present a comparison between those two triple systems, and a discussion on how these results may guide us in the planning of future missions.

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arXiv2016

The rings of Chariklo under close encounters with the giant planets

The Centaur population is composed by minor bodies wandering between the giant planets and that frequently perform close gravitational encounters with these planets, which leads to a chaotic orbital evolution. Recently, the discovery of two well-defined narrow rings was announced around the Centaur 10199 Chariklo. The rings are assumed to be in the equatorial plane of Chariklo and to have circular orbits. The existence a well-defined system of rings around a body in such perturbed orbital region poses an interesting new problem. Are the rings of Chariklo stable when perturbed by close gravitational encounters with the giant planets? Our approach to address this question consisted of forward and backward numerical simulations of 729 clones of Chariklo, with similar initial orbits, for a period of 100 Myrs. We found, on average, that each clone suffers along its lifetime more than 150 close encounters with the giant planets within one Hill radius of the planet in question. We identified some extreme close encounters able to significantly disrupt or to disturb the rings of Chariklo. About 3% of the clones lose the rings and about 4% of the clones have the ring significantly disturbed. Therefore, our results show that in most of the cases (more than 90%) the close encounters with the giant planets do not affect the stability of the rings in Chariklo-like systems. Thus, if there is an efficient mechanism that creates the rings, then these structures may be common among these kinds of Centaurs.

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arXiv2015

Stable retrograde orbits around the triple system 2001 SN263

The NEA 2001 SN263 is the target of the ASTER MISSION - First Brazilian Deep Space Mission. Araujo et al. (2012), characterized the stable regions around the components of the triple system for the planar and prograde cases. Knowing that the retrograde orbits are expected to be more stable, here we present a complementary study. We now considered particles orbiting the components of the system, in the internal and external regions, with relative inclinations between $90^{\circ}< I \leqslant180^{\circ}$, i.e., particles with retrograde orbits. Our goal is to characterize the stable regions of the system for retrograde orbits, and then detach a preferred region to place the space probe. For a space mission, the most interesting regions would be those that are unstable for the prograde cases, but stable for the retrograde cases. Such configuration provide a stable region to place the mission probe with a relative retrograde orbit, and, at the same time, guarantees a region free of debris since they are expected to have prograde orbits. We found that in fact the internal and external stable regions significantly increase when compared to the prograde case. For particles with $e=0$ and $I=180^{\circ}$, we found that nearly the whole region around Alpha and Beta remain stable. We then identified three internal regions and one external region that are very interesting to place the space probe. We present the stable regions found for the retrograde case and a discussion on those preferred regions. We also discuss the effects of resonances of the particles with Beta and Gamma, and the role of the Kozai mechanism in this scenario. These results help us understand and characterize the stability of the triple system 2001 SN263 when retrograde orbits are considered, and provide important parameters to the design of the ASTER mission.

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arXiv2013

Terrestrial Planet Formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars

Models of terrestrial planet formation for our solar system have been successful in producing planets with masses and orbits similar to those of Venus and Earth. However, these models have generally failed to produce Mars-sized objects around 1.5 AU. The body that is usually formed around Mars' semimajor axis is, in general, much more massive than Mars. Only when Jupiter and Saturn are assumed to have initially very eccentric orbits (e $\sim$ 0.1), which seems fairly unlikely for the solar system, or alternately, if the protoplanetary disk is truncated at 1.0 AU, simulations have been able to produce Mars-like bodies in the correct location. In this paper, we examine an alternative scenario for the formation of Mars in which a local depletion in the density of the protosolar nebula results in a non-uniform formation of planetary embryos and ultimately the formation of Mars-sized planets around 1.5 AU. We have carried out extensive numerical simulations of the formation of terrestrial planets in such a disk for different scales of the local density depletion, and for different orbital configurations of the giant planets. Our simulations point to the possibility of the formation of Mars-sized bodies around 1.5 AU, specifically when the scale of the disk local mass-depletion is moderately high (50-75%) and Jupiter and Saturn are initially in their current orbits. In these systems, Mars-analogs are formed from the protoplanetary materials that originate in the regions of disk interior or exterior to the local mass-depletion. Results also indicate that Earth-sized planets can form around 1 AU with a substantial amount of water accreted via primitive water-rich planetesimals and planetary embryos. We present the results of our study and discuss their implications for the formation of terrestrial planets in our solar system.

astro-ph.EP↗

arXiv2013

A Compound model for the origin of Earth's water

One of the most important subjects of debate in the formation of the solar system is the origin of Earth's water. Comets have long been considered as the most likely source of the delivery of water to Earth. However, elemental and isotopic arguments suggest a very small contribution from these objects. Other sources have also been proposed, among which, local adsorption of water vapor onto dust grains in the primordial nebula and delivery through planetesimals and planetary embryos have become more prominent. However, no sole source of water provides a satisfactory explanation for Earth's water as a whole. In view of that, using numerical simulations, we have developed a compound model incorporating both the principal endogenous and exogenous theories, and investigating their implications for terrestrial planet formation and water-delivery. Comets are also considered in the final analysis, as it is likely that at least some of Earth's water has cometary origin. We analyze our results comparing two different water distribution models, and complement our study using D/H ratio, finding possible relative contributions from each source, focusing on planets formed in the habitable zone. We find that the compound model play an important role by showing more advantage in the amount and time of water-delivery in Earth-like planets.

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arXiv2012

Stability Regions Around the Components of the Triple System 2001 SN263

The NEAs (Near-Earth Asteroids) are good targets for spatial missions, since they periodically approach the orbit of the Earth. Recently, the NEA (153591) 2001 SN263 was chosen as the target of the ASTER MISSION- First Brazilian Deep Space Mission, planned to be launched in 2015. In February 2008, the radio astronomers from Arecibo-Puerto Rico concluded that (153591) 2001 SN263 is actually a triple system (Nolan et al., 2008). The announcement of the ASTER MISSION has motivated the development of the present work, whose goal is to characterize regions of stability and instability of the triple system (153591) 2001 SN263. The method adopted consisted in dividing the region around the system into four distinct regions. We have performed numerical integrations of systems composed by seven bodies: Sun, Earth, Mars, Jupiter and the three components of the system, and by thousands of particles randomly distributed within the demarcated regions, for the planar and inclined prograde cases. The results are diagrams of semi-major axis versus eccentricity, where it is shown the percentage of particles that survive for each set of initial conditions. The regions where 100% of the particles survive is defined as stable regions. We found that the stable regions are in the neighborhood of Alpha and Beta, and in the external region. It was identified resonant motion of the particles with Beta and Gamma in the internal regions, which lead to instability. For particles with I>45° in the internal region, where I is the inclination with respect to Alpha's equator, there is no stable region, except for the particles placed really close to Alpha. The stability in the external region is not affected by the variation of inclination. We also present a discussion on the long-term stability in the internal region, for the planar and circular cases, with comparisons with the short-term stability.

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arXiv2010

Distribution of refractory and volatile elements in CoRoT exoplanet host stars

The relative distribution of abundances of refractory, intermediate, and volatile elements in stars with planets can be an important tool for investigating the internal migration of a giant planet. This migration can lead to the accretion of planetesimals and the selective enrichment of the star with these elements. We report on a spectroscopic determination of the atmospheric parameters and chemical abundances of the parent stars in transiting planets CoRoT-2b and CoRoT-4b. Adding data for CoRoT-3 and CoRoT-5 from the literature, we find a flat distribution of the relative abundances as a function of their condensation temperatures. For CoRoT-2, the relatively high lithium abundance and intensity of its Li I resonance line permit us to propose an age of 120 Myr, making this stars one of the youngest stars with planets to date. We introduce a new methodology to investigate a relation between the abundances of these stars and the internal migration of their planets. By simulating the internal migration of a planet in a disk formed only by planetesimals, we are able to separate the stellar fractions of refractory (R), intermediate (I), and volatile (V) rich planetesimals accreting onto the central star. Intermediate and volatile element fractions enriching the star are similar and much larger than those of pure refractory ones. We also show that these results are highly dependent on the model adopted for the disk distribution regions in terms of R, I, and V elements and other parameters considered. We note however, that this self-enrichment mechanism is only efficient during the first 20-30 Myr or later in the lifetime of the disk when the surface convection layers of the central star for the first time attain its minimum size configuration.

astro-ph.SR↗

arXiv2010

Coorbital Satellites of Saturn: Congenital Formation

Saturn is the only known planet to have coorbital satellite systems. In the present work we studied the process of mass accretion as a possible mechanism for coorbital satellites formation. The system considered is composed of Saturn, a proto-satellite and a cloud of planetesimals distributed in the coorbital region around a triangular Lagrangian point. The adopted relative mass for the proto-satellite was 10^-6 of Saturn's mass and for each planetesimal of the cloud three cases of relative mass were considered, 10^-14, 10^-13 and 10^-12 masses of Saturn. In the simulations each cloud of planetesimal was composed of 10^3, 5 x 10^3 or 10^4 planetesimals. The results of the simulations show the formation of coorbital satellites with relative masses of the same order of those found in the saturnian system (10^-13 - 10^-9). Most of them present horseshoe type orbits, but a significant part is in tadpole orbit around L_4 or L_5. Therefore, the results indicate that this is a plausible mechanism for the formation of coorbital satellites.

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arXiv2010

Irregular satellites of Jupiter: Capture configurations of binary-asteroids

The origins of irregular satellites of the giant planets are an important piece of the giant "puzzle" that is the theory of Solar System formation. It is well established that they are not "in situ" formation objects, around the planet, as are believed to be the regular ones. Then, the most plausible hypothesis to explain their origins is that they formed elsewhere and were captured by the planet. However, captures under restricted three-body problem dynamics have temporary feature, which makes necessary the action of an auxiliary capture mechanism. Nevertheless, there not exist one well established capture mechanism. In this work, we tried to understand which aspects of a binary-asteroid capture mechanism could favor the permanent capture of one member of a binary asteroid. We performed more than eight thousand numerical simulations of capture trajectories considering the four-body dynamical system Sun, Jupiter, Binary-asteroid. We restricted the problem to the circular planar prograde case, and time of integration to 10^4 years. With respect to the binary features, we noted that 1) tighter binaries are much more susceptible to produce permanent captures than the large separation-ones. We also found that 2) the permanent capture probability of the minor member of the binary is much more expressive than the major body permanent capture probability. On the other hand, among the aspects of capture-disruption process, 4) a pseudo eastern-quadrature was noted to be a very likely capture angular configuration at the instant of binary disruptions. In addition, we also found that the 5) capture probability is higher for binary asteroids which disrupt in an inferior-conjunction with Jupiter. These results show that the Sun plays a very important role on the capture dynamic of binary asteroids.

astro-ph.EP↗

arXiv2009

On the Stability of the Satellites of Asteroid 87 Sylvia

he triple asteroidal system (87) Sylvia is composed of a 280-km primary and two small moonlets named Romulus and Remus (Marchis et al 2005). Sylvia is located in the main asteroid belt. The satellites are in nearly equatorial circular orbits around the primary. In the present work we study the stability of the satellites Romulus and Remus, in order to identify the effects and the contribution of each perturber. The results from the 3-body problem, Sylvia-Romulus-Remus, show no significant variation of their orbital elements. However, the inclinations of the satellites present a long period evolution, when the Sun is included in the system. Such amplitude is amplified when Jupiter is included. An analysis of these results show that Romulus and Remus are librating in a secular resonance and their longitude of the nodes are locked to each other. The satellites get caught in an evection resonance with Jupiter. However, the orbital evolutions of the satellites became completely stable when the oblateness of Sylvia is included in the simulations.

astro-ph.EP↗

arXiv2007

A Possible Stellar Metallic Enhancement in Post-T Tauri Stars by a Planetesimal Bombardment

The photospheres of stars hosting planets have larger metallicity than stars lacking planets. In the present work we study the possibility of an earlier metal enrichment of the photospheres by means of impacting planetesimals during the first 20-30Myr. Here we explore this contamination process by simulating the interactions of an inward migrating planet with a disc of planetesimal interior to its orbit. The results show the percentage of planetesimals that fall on the star. We identified the dependence of the planet's eccentricity ($e_p$) and time scale of migration ($τ$) on the rate of infalling planetesimals. For very fast migrations ($τ=10^2$yr and $τ=10^3$yr) there is no capture in mean motion resonances, independently of the value of $e_p$. Then, due to the planet's migration the planetesimals suffer close approaches with the planet and more than 80% of them are ejected from the system. For slow migrations ($τ=10^5$yr and $τ=10^6$yr) the percentage of collisions with the planet decrease with the increase of the planet's eccentricity. For $e_p=0$ and $e_p=0.1$ most of the planetesimals were captured in the 2:1 resonance and more than 65% of them collided with the star. Whereas migration of a Jupiter mass planet to very short pericentric distances requires unrealistic high disc masses, these requirements are much smaller for smaller migrating planets. Our simulations for a slowly migrating 0.1 $M_{\rm Jupiter}$ planet, even demanding a possible primitive disc three times more massive than a primitive solar nebula, produces maximum [Fe/H] enrichments of the order of 0.18 dex. These calculations open possibilities to explain hot Jupiters exoplanets metallicities.

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