1,425 research outputs found
Dynamical star-disk interaction in the young stellar system V354 Mon
The main goal of this work is to characterize the mass accretion and ejection
processes of the classical T Tauri star V354 Mon, a member of the young stellar
cluster NGC 2264. In March 2008, photometric and spectroscopic observations of
V354 Mon were obtained simultaneously with the CoRoT satellite, the 60 cm
telescope at the Observat\'orio Pico dos Dias (LNA - Brazil) equipped with a
CCD camera and Johnson/Cousins BVRI filters, and the SOPHIE \'echelle
spectrograph at the Observatoire de Haute-Provence (CNRS - France). The light
curve of V354 Mon shows periodical minima (P = 5.26 +/- 0.50 days) that vary in
depth and width at each rotational cycle. From the analysis of the photometric
and spectroscopic data, it is possible to identify correlations between the
emission line variability and the light-curve modulation of the young system,
such as the occurrence of pronounced redshifted absorption in the H_alpha line
at the epoch of minimum flux. This is evidence that during photometric minima
we see the accretion funnel projected onto the stellar photosphere in our line
of sight, implying that the hot spot coincides with the light-curve minima. We
applied models of cold and hot spots and a model of occultation by
circumstellar material to investigate the source of the observed photometric
variations. We conclude that nonuniformly distributed material in the inner
part of the circumstellar disk is the main cause of the photometric modulation,
which does not exclude the presence of hot and cold spots at the stellar
surface. It is believed that the distortion in the inner part of the disk is
created by the dynamical interaction between the stellar magnetosphere,
inclined with respect to the rotation axis, and the circumstellar disk, as also
observed in the classical T Tauri star AA Tau and predicted by
magnetohydrodynamical numerical simulations.Comment: Accepted by Astronomy and Astrophysic
Monitoring young associations and open clusters with Kepler in two-wheel mode
We outline a proposal to use the Kepler spacecraft in two-wheel mode to
monitor a handful of young associations and open clusters, for a few weeks
each. Judging from the experience of similar projects using ground-based
telescopes and the CoRoT spacecraft, this program would transform our
understanding of early stellar evolution through the study of pulsations,
rotation, activity, the detection and characterisation of eclipsing binaries,
and the possible detection of transiting exoplanets. Importantly, Kepler's wide
field-of-view would enable key spatially extended, nearby regions to be
monitored in their entirety for the first time, and the proposed observations
would exploit unique synergies with the GAIA ESO spectroscopic survey and, in
the longer term, the GAIA mission itself. We also outline possible strategies
for optimising the photometric performance of Kepler in two-wheel mode by
modelling pixel sensitivity variations and other systematics.Comment: 10 pages, 6 figures, white paper submitted in response to NASA call
for community input for alternative science investigations for the Kepler
spacecraf
Macronutrientes em diferentes partes de indivíduos de açaizeiro (Euterpe oleracea mart.) provenientes de populações nativas de municípios do estado do Pará.
O açaizeiro é uma espécies típica de crescente valor comercial nos mercados nacional e internacional, sobretudo de alto valor cultural para a população local, o açaí é um aliemnto nutritivo..
Produção de grãos de milho e atributos químicos de solo influenciados pela aplicação de escória de siderurgia em um latossolo amarelo distrófico.
A maioria dos solos da Amazônia apresenta características de elevada acidez, sendo necessária a aplicação de corretivos para a obtenção de produtividades satisfatórias das culturas..
Caracterização do sistema de produção de ovinos Santa Inês no Estado de Sergipe.
Com o presente trabalho objetivou-se caracterizar a produção ovina da raça Santa Inês no Estado de Sergipe, referência nacional pela qualidade genética. Através de 54 entrevistas semi-estruturadas e visitas às propriedades, obteve-se o perfil dos criadouros com relação ao manejo sanitário, nutricional e reprodutivo, bem como, finalidade e destino da criação. No geral, as propriedades apresentaram rebanhos de tamanho bastante variável, sendo o sistema semi-intensivo o mais utilizado. Em sua maioria, as criações tinham acompanhamento técnico regular e destinavam-se ao abate ou exploração genética. Criações com assistência veterinária associada a práticas adequadas de manejo mostraram maior produtividade. A carne ovina apresenta crescente demanda de mercado, porém a reduzida quantidade de abatedouros e frigoríficos no Estado parece contribuir como fator determinante para a escoação da produção para feiras livres sem fiscalização sanitária
Dynamical Mass Constraints on Low-Mass Pre-Main-Sequence Stellar Evolutionary Tracks: An Eclipsing Binary in Orion with a 1.0 Msun Primary and an 0.7 Msun Secondary
We report the discovery of a double-lined, spectroscopic, eclipsing binary in
the Orion star-forming region. We analyze the system spectroscopically and
photometrically to empirically determine precise, distance-independent masses,
radii, effective temperatures, and luminosities for both components. The
measured masses for the primary and secondary, accurate to ~1%, are 1.01 Msun
and 0.73 Msun, respectively; thus the primary is a definitive pre-main-sequence
solar analog, and the secondary is the lowest-mass star yet discovered among
pre-main-sequence eclipsing binary systems. We use these fundamental
measurements to test the predictions of pre-main-sequence stellar evolutionary
tracks. None of the models we examined correctly predict the masses of the two
components simultaneously, and we implicate differences between the theoretical
and empirical effective temperature scales for this failing. All of the models
predict the observed slope of the mass-radius relationship reasonably well,
though the observations tend to favor models with low convection efficiencies.
Indeed, considering our newly determined mass measurements together with other
dynamical mass measurements of pre-main-sequence stars in the literature, as
well as measurements of Li abundances in these stars, we show that the data
strongly favor evolutionary models with inefficient convection in the stellar
interior, even though such models cannot reproduce the properties of the
present-day Sun.Comment: Accepted by Ap
Desempenho produtivo de fêmeas das raças Canchim e Nelore. III. Produção de leite.
Comparar a produtividade de leite de vacas primiparas das raças Canchim e Nelore
Effect of Epidemic Interference on the Performance of M-ASK, M-PSK and M-QAM Modulation Schemes
This article presents a study on the performance of different digital modulation systems in the presence of epidemic interference. This type of interference is caused by the fast increase in the number of users in a system at a given time. The epidemic interference can be modeled as a non-stationary stochastic process, which presents random power levels over time. In a previous work, the authors assessed the effect of the epidemic interference on the performance of BPSK, QPSK, and M-QAM systems. The present paper extends the previous results for MASK and M-PSK systems. Furthermore, numerical results from Monte Carlo simulations are presented for all evaluated digital modulation systems
Efeito da resinose na fotossíntese do cajueiro-anão precoce.
A resinose é uma das principais doenças do cajueiro em algumas regiões do semi-árido nordestino, provocando danos relacionados à redução na produção da planta e do pomar. Como inexistem estudos visando quantificar danos à produção ou a à elucidação dos efeitos da doença na fisiologia da planta, o presente trabalho objetivou determinar os efeitos da resinose sobre alguns parâmetros fisiológicos, especialmente sobre a fotossítese de plantas de cajueiro-anão precoce.bitstream/CNPAT-2010/9021/1/Bd-008.pd
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