151 research outputs found

    Effects of an eccentric inner Jupiter on the dynamical evolution of icy body reservoirs in a planetary scattering scenario

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    Aims. We analyze the dynamics of small body reservoirs under the effects of an eccentric inner giant planet resulting from a planetary scattering event around a 0.5 M⊙ star. Methods. First, we used a semi-analytical model to define the properties of the protoplanetary disk that lead to the formation of three Jupiter-mass planets. Then, we carried out N-body simulations assuming that the planets are close to their stability limit together with an outer planetesimal disk. In particular, the present work focused on the analysis of N-body simulations in which a single Jupiter-mass planet survives after the dynamical instability event. Results. Our simulations produce outer small body reservoirs with particles on prograde and retrograde orbits, and other ones whose orbital plane flips from prograde to retrograde and back again along their evolution (“Type-F particles”). We find strong correlations between the inclination i and the ascending node longitude Ω of Type-F particles. First, Ω librates around 90° or/and 270°. This property represents a necessary and sufficient condition for the flipping of an orbit. Moreover, the libration periods of i and Ω are equal and they are out to phase by a quarter period. We also remark that the larger the libration amplitude of i, the larger the libration amplitude of Ω. We analyze the orbital parameters of Type-F particles immediately after the instability event (post IE orbital parameters), when a single Jupiter-mass planet survives in the system. Our results suggest that the orbit of a particle can flip for any value of its post IE eccentricity, although we find only two Type-F particles with post IE inclinations i ≲ 17°. Finally, our study indicates that the minimum value of the inclination of the Type-F particles in a given system decreases with an increase in the eccentricity of the giant planet.Fil: Zanardi, Macarena. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: de Elia, Gonzalo Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Di Sisto, Romina Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Naoz, S.. University of California at Los Angeles; Estados UnidosFil: Li, G.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Guilera, O. M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Brunini, A.. Universidad Nacional de la Patagonia Austral; Argentin

    Oligarchic planetesimal accretion and giant planet formation II

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    The equation of state calculated by Saumon and collaborators has been adopted in most core-accretion simulations of giant-planet formation performed to date. Since some minor errors have been found in their original paper, we present revised simulations of giant-planet formation that considers a corrected equation of state. We employ the same code as Fortier and collaborators in repeating our previous simulations of the formation of Jupiter. Although the general conclusions of Fortier and collaborators remain valid, we obtain significantly lower core masses and shorter formation times in all cases considered. The minor errors in the previously published equation of state have been shown to affect directly the adiabatic gradient and the specific heat, causing an overestimation of both the core masses and formation times.Comment: 4 pages, 2 figures, Accepted for publication in Astronomy and Astrophysic

    Consequences of the simultaneous formation of giant planets by the core accretion mechanism

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    The core accretion mechanism is presently the most widely accepted cause of the formation of giant planets. For simplicity, most models presently assume that the growth of planetary embryos occurs in isolation. We explore how the simultaneous growth of two embryos at the present locations of Jupiter and Saturn affects the outcome of planetary formation. We model planet formation on the basis of the core accretion scenario and include several key physical ingredients. We consider a protoplanetary gas disk that exponentially decays with time. For planetesimals, we allow for a distribution of sizes from 100~m to 100~km with most of the mass in the smaller objects. We include planetesimal migration as well as different profiles for the surface density Σ\Sigma of the disk. The core growth is computed in the framework of the oligarchic growth regime and includes the viscous enhancement of the planetesimal capture cross-section. Planet migration is ignored. By comparing calculations assuming formation of embryos in isolation to calculations with simultaneous embryo growth, we find that the growth of one embryo generally significantly affects the other. This occurs in spite of the feeding zones of each planet never overlapping. The results may be classified as a function of the gas surface density profile Σ\Sigma: if Σr3/2\Sigma \propto r^{-3/2} and the protoplanetary disk is rather massive, Jupiter's formation inhibits the growth of Saturn. If Σr1\Sigma \propto r^{-1} isolated and simultaneous formation lead to very similar outcomes; in the the case of Σr1/2\Sigma \propto r^{-1/2} Saturn grows faster and induces a density wave that later acclerates the formation of Jupiter. Our results indicate that the simultaneous growth of several embryos impacts the final outcome and should be taken into account by planet formation models.Comment: Accepted for publication in Astronomy and Astrophysic

    Simultaneous formation of Solar System giant planets

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    In the last few years, the so-called "Nice model" has got a significant importance in the study of the formation and evolution of the solar system. According to this model, the initial orbital configuration of the giant planets was much more compact than the one we observe today. We study the formation of the giant planets in connection with some parameters that describe the protoplanetary disk. The aim of this study is to establish the conditions that favor their simultaneous formation in line with the initial configuration proposed by the Nice model. We focus in the conditions that lead to the simultaneous formation of two massive cores, corresponding to Jupiter and Saturn, able to achieve the cross-over mass (where the mass of the envelope of the giant planet equals the mass of the core, and gaseous runway starts) while Uranus and Neptune have to be able to grow to their current masses. We compute the in situ planetary formation, employing the numerical code introduced in our previous work, for different density profiles of the protoplanetary disk. Planetesimal migration is taken into account and planetesimals are considered to follow a size distribution between rpminr_p^{min} (free parameter) and rpmax=100r_p^{max}= 100 km. The core's growth is computed according to the oligarchic growth regime. The simultaneous formation of the giant planets was successfully completed for several initial conditions of the disk. We find that for protoplanetary disks characterized by a power law (Σrp\Sigma \propto r^{-p}), smooth surface density profiles (p1.5p \leq 1.5) favor the simultaneous formation. However, for steep slopes (p2p\sim 2, as previously proposed by other authors) the simultaneous formation of the solar system giant planets is unlikely ...Comment: Accepted for publication in Astronomy and Astrophysic

    Estudo do índice de área foliar de pastagens em diferentes níveis de degradação com aplicação de imagens Landsat 5 - TM e dados de campo.

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    A área foliar é um parâmetro chave na avaliação do crescimento das plantas, podendo ser tanto medida quanto estimada (Figueredo Júnior et al., 2005). Segundo Pereira e Machado (1987) a área foliar é um fator que depende do número e tamanho das folhas e de seu estádio fenológico. A relação entre a área foliar de toda vegetação e a unidade de área de solo ocupada por essa vegetação é denominada de índice de área foliar (IAF). Como a fotossíntese depende da área foliar, a produtividade de uma cultura será tanto maior quanto mais próximo for do IAF máximo potencial e quanto mais tempo permanecer ativa; retardando a senescência (Figueredo Júnior et al., 2005). Zanchi et al. (2009) afirmam existir poucas informações referentes a variação espacial da biomassa vegetal, altura da pastagem e do índice de área foliar de pastagens. Estes autores sugerem que as variações naturais no IAF, altura e biomassa de algumas espécies, respondem às variações sazonais e interanuais do clima e da umidade do solo. Neste sentido, a análise espacial do IAF com uso dados de satélite pode ser um importante indicador da biomassa em áreas extensas. Diante do exposto, este trabalho teve como objetivo a aplicação de técnicas de sensoriamento remoto e dados de campo no estudo do índice de área foliar de pastagens de Brachiaria em diferentes níveis de degradação na região de Guararapes, SP

    Teste de modelo agrometeorológico de monitoramento e de estimativa de produtividade do cafeeiro (Coffea arabica L.). no Estado de São Paulo.

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    O desenvolvimento de modelo agrometeorológico que possibilite a estimativa de quebra de produtividade antecipada é importante para subsidiar programas de previsão de safras de café. Uma boa estimativa da produtividade implica na utilização de modelos que considerem os efeitos ambientais aos processos fisiológicos determinantes da produção. Este trabalho teve o objetivo de testar um modelo matemático agrometeorológico de estimativa de produtividade do cafeeiro para três diferentes escalas produtivas ?talhão?, ?propriedade? e ?município? em diferentes regiões do Estado de São Paulo. Dados meteorológicos e de produtividade foram coletados no IAC e CATI para o período de 2000 a 2004. O modelo se baseia na penalização da produtividade potencial da cultura em função do déficit hídrico quantificado através da relação [1(ETr/ETp)] ajustadas por diferentes coeficientes de sensibilidade da cultura (Ky) ocorridos em diferentes fases fenológicas. O modelo considera também os efeitos da produtividade do ano anterior e temperaturas adversas ocorridas em fases fenológicas críticas. Os modelos parametrizados, nas três escalas produtivas consideradas, apresentaram ajustes satisfatórios entre valores observados e estimados, com valores do índice ?d? variando de 0,88 a 0,92, ?R? variando de 0,81 a 0,87 e erros aleatórios relativamente baixos de 5,1 a 9,4 sacas.ha 1 e sistemáticos de 3,5 a 7,1sacas.ha 1. O modelo apresentou pequena tendência a superestimar as produtividades estimadas. Os resultados indicam que o modelo parametrizado em diferentes escalas produtivas tem potencial para estimar a produtividade do café, podendo servir como subsídio aos trabalhos de previsão de safra

    Oligarchic planetesimal accretion and giant planet formation

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    Aims. In the context of the core instability model, we present calculations of in situ giant planet formation. The oligarchic growth regime of solid protoplanets is the model adopted for the growth of the core. Methods. The full differential equations of giant planet formation were numerically solved with an adaptation of a Henyey-type code. The planetesimals accretion rate was coupled in a self-consistent way to the envelope's evolution. Results. We performed several simulations for the formation of a Jupiter-like object by assuming various surface densities for the protoplanetary disc and two different sizes for the accreted planetesimals. We find that the atmospheric gas drag gives rise to a major enhancement on the effective capture radius of the protoplanet, thus leading to an average timescale reduction of 30% -- 55% and ultimately to an increase by a factor of 2 of the final mass of solids accreted as compared to the situation in which drag effects are neglected. With regard to the size of accreted planetesimals, we find that for a swarm of planetesimals having a radius of 10 km, the formation time is a factor 2 to 3 shorter than that of planetesimals of 100 km, the factor depending on the surface density of the nebula. Moreover, planetesimal size does not seem to have a significant impact on the final mass of the core.Comment: 12 pages, 10 figures, accepted for publication in A&

    Bioecologia de Alabama argillacea II. Evolução populacional em seis regiões do Estado de São Paulo, com base em suas exigências térmicas

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    The cotton leafworm (Alabama argillacea Hübner (1818) has, each year, a constant period of occurence during the cotton growing season, in the State of São Paulo, Brazil. Surveys with light traps in six localities of the State (Assis, Campinas, Mococa, Piracicaba, Ribeirão Preto and Valinhos) were made in order to find out those periods. With its thermal requirements it was possible to know the number of its generations all through the year in order to provide basic data concerning this pest, as a prediction of its outbreak, and for improving control procedures in the crop. The thermal requirements of the cotton leafworm were determined based on the biological results obtained in climatic chambers set at 20, 25, 30 and 35°C (60 ± 10% relative humidity and a 14-hour photoperiod) with IAC-17 cultivar leaves. The threshold of development for the egg, larval, pre-pupal and pupal phases was calculated by the coefficient of variation method; values of 12.6; 9.3; 14.9 and 13.5°C, respectively, were found. The formula for obtaining those thermal requirement data was: K = y (t - a). Values of 37.20, 195.97, 10.10 and 110.35 degree-days for the phases of egg, larva, pre-pupa and pupa, respectively, were obtained. Basing on the total sum of degree-days per "péntada" for the six localities, two to seven generations per year may occur.O curuquerê-do-algodoeiro (Alabama argillacea Hübner (1818) tem uma época definida de surto nas diferentes áreas do Estado de São Paulo. Tomando-se por base levantamentos realizados com armadilhas luminosas nas regiões de Assis, Campinas, Mococa, Piracicaba, Ribeirão Preto e Valinhos, determinou-se, em função destas épocas de seu aparecimento e das suas necessidades térmicas, o provável número de gerações desta praga nestas áreas durante o ano, numa tentativa de prever e controlar a sua evolução populacional dentro da cultura. As necessidades térmicas do curuquerê foram determinadas com base nos resultados biológicos obtidos em câmaras climatizadas reguladas a 20, 25, 30 e 35°C (UR de 60 ± 10% e fotófase de 14 h), com folhas da cultivar IAC-17, estimando-se a temperatura-base para as fases de ovo, lagarta, pré-pupa e pupa, pelo método do coeficiente de variação e encontrando-se valores, respectivamente, de 12,6; 9,3; 14,9 e 13,5°C. A constante térmica em graus dias (GD)foi estimada pela fórmula K = y (t - a), sendo obtidos os valores de 37, 20 GD, 195,97 GD, 10,10 GD e 110,35 GD para as fases de ovo, lagarta, pré-pupa e pupa, respectivamente. A partir destes resultados e de graus dias acumulados por pêntada, utilizando-se as normais de cada localidade, estimou-se que o número de gerações pode variar de duas a sete para as regiões analisadas
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