211 research outputs found
Effects of an eccentric inner Jupiter on the dynamical evolution of icy body reservoirs in a planetary scattering scenario
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
Radiation induced warping of protostellar accretion disks
We examine the consequences of radiatively driven warping of accretion disks
surrounding pre-main-sequence stars. These disks are stable against warping if
the luminosity arises from a steady accretion flow, but are unstable at late
times when the intrinsic luminosity of the star overwhelms that provided by the
disk. Warps can be excited for stars with luminosities of around 10 solar
luminosities or greater, with larger and more severe warps in the more luminous
systems. A twisted inner disk may lead to high extinction towards stars often
viewed through their disks. After the disk at all radii becomes optically thin,
the warp decays gradually on the local viscous timescale, which is likely to be
long. We suggest that radiation induced warping may account for the origin of
the warped dust disk seen in Beta Pictoris, if the star is only around 10-20
Myr old, and could lead to non-coplanar planetary systems around higher mass
stars.Comment: 12 pages, including 3 figures. ApJ Letters, in pres
Consequences of the simultaneous formation of giant planets by the core accretion mechanism
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 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 : if and the protoplanetary
disk is rather massive, Jupiter's formation inhibits the growth of Saturn. If
isolated and simultaneous formation lead to very
similar outcomes; in the the case of 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
Teste de modelo agrometeorológico de monitoramento e de estimativa de produtividade do cafeeiro (Coffea arabica L.). no Estado de São Paulo.
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
Modelo agrometeorológico de monitoramento e de estimativa de quebra de produtividade como subsídio à previsão de safra de café (Coffea arabica L.): resultados preliminares.
Simultaneous formation of Solar System giant planets
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 (free parameter) and
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 (),
smooth surface density profiles () favor the simultaneous
formation. However, for steep slopes (, 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
S-system theory applied to array-based GNSS ionospheric sensing
The GPS carrier-phase and code data have proven to be valuable sources of measuring the Earth’s ionospheric total electron content (TEC). With the development of new GNSSs with multi frequency data, many more ionosphere-sensing combinations of different precision can be formed as input of ionospheric modelling. We present the general way of interpreting such combinations through an application of S-system theory and address how their precision propagates into that of the unbiased TEC solution. Presenting the data relevant to TEC determination, we propose the usage of an array of GNSS antennas to improve the TEC precision and to expedite the rather long observational time-span required for high-precision TEC determination
The role of the initial surface density profiles of the disc on giant planet formation: comparing with observations
In order to explain the main characteristics of the observed population of
extrasolar planets and the giant planets in the Solar System, we need to get a
clear understanding of which are the initial conditions that allowed their
formation. To this end we develop a semi-analytical model for computing
planetary systems formation based on the core instability model for the gas
accretion of the embryos and the oligarchic growth regime for the accretion of
the solid cores. With this model we explore not only different initial discs
profiles motivated by similarity solutions for viscous accretion discs, but we
also consider different initial conditions to generate a variety of planetary
systems assuming a large range of discs masses and sizes according to the last
results in protoplanetary discs observations. We form a large population of
planetary systems in order to explore the effects in the formation of assuming
different discs and also the effects of type I and II regimes of planetary
migration, which were found to play fundamental role in reproducing the
distribution of observed exoplanets. Our results show that the observed
population of exoplanets and the giant planets in the Solar System are well
represented when considering a surface density profile with a power law in the
inner part characterized by an exponent of -1, which represents a softer
profile when compared with the case most similar to the MMSN model case.Comment: 14 pages, 12 figures, MNRAS, 412, 211
Variations of foF2 and GPS total electron content over the Antarctic sector
This paper presents a preliminary analysis of the variations of the critical frequency of the F2 region (foF2) and the total electron content (TEC) derived from Global Positioning System (GPS) data. Hourly foF2 values were scaled from ionograms recorded at San Martin (68.1°S, 293.0°E) and the TEC values were derived from GPS observations at O'Higgins (63.3°S, 302.5 °E). The database includes measurements obtained under different seasonal and solar activity conditions. The study shows that the daily peak of foF2 occurs around local noon in winter and fall, and in spring a secondary peak is observed around midnight. In summer (January) foF2 reaches its minimum value around the noon sector while the maximum in the diurnal variation of foF2 is located in a time sector close to midnight. This behaviour is observed at low and high solar activity. The semiannual anomaly appears around noon at high and low solar activity and the winter anomaly is not observed. The effect of the solar activity is generally observed in every season. The analysis of the GPS TEC measurements in the same region indicates that the diurnal, seasonal and solar activity variations are similar to those observed in the foF2 values. An analysis of the performance of the IRI model to predict foF2 is also shown using the two IRI options (URSI and CCIR). The comparisons between the experimental values and the IRI predictions show some discrepancies.Facultad de Ciencias Astronómicas y Geofísica
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