Accretion-Induced Lithium Line Enhancements in Classical T Tauri Stars: RW Aur

It is widely accepted that much of the stochastic variability of T Tauri stars is due to accretion by a circumstellar disk. The emission line spectrum as well as the excess continuum emission are common probes of this process. In this communication, we present additional probes of the circumstellar environment in the form of resonance lines of low ionization potential elements. Using a set of 14 high resolution echelle observations of the classical T Tauri star (CTTS), RW Aur, taken between 1986 and 1996, we carefully measure the continuum veiling at each epoch by comparing more than 500 absorption lines with those of an appropriate template. This allows us to accurately subtract out the continuum emission and to recover the underlying photospheric spectrum. In doing so, we find that selected photospheric lines are enhanced by the accretion process, namely the resonance lines of LiI and KI. A resonance line of TiI and a low excitation potential line of CaI also show weak enhancements. Simple slab models and computed line bisectors lead us to propose that these line enhancements are markers of cool gas at the beginning of the accretion flow which provides an additional source of line opacity. These results suggest that published values of surface lithium abundances of classical T Tauri stars are likely to be overestimated. This would account for the various reports of surface lithium abundances in excess of meteoritic values among the extreme CTTS. Computing LTE lithium abundances of RW Aur in a low and then high accretion state yields abundances which vary by one order of magnitude. The low accretion state lithium abundance is consistent with theoretical predictions for a star of this age and mass while the high accretion state spectrum yields a super-meteoritic lithium abundance.Comment: 28 pages, 8 figures, accepted by Ap

Uso de ninhos de cupin como fonte de matéria orgânica em sistemas de produção agrosilviculturais na Amazônia

The growth of two annual crops, okra (Abelmoschus escutentus) and egg-plant (Solatium melongena) and one perennial crop, andiroba (Carapa guianensis, a native forest tree of Amazonia) under different treatments with organic manure derived from termite nest material of wood-feeding Nasutitermes species was tested (randomized block design). The use of 25-100 g of nest material gave no significant increase in okra productivity, and 25-200 g gave no significant response in andiroba. The combined use of NPK with 200 g of nest material gave a significant higher production in egg-plant (total number and total fresh weight of fruits) when compared to the control (without fertilizer) and to the treatment with NPK only.The results suggest the possibility to use termite nest material to enhance crop production in Amazonia, particularly in combination with low amounts of mineral fertilizer. Research lines for further investigations are outlined.Foi avaliado crescimento de duas espécies agriculturais anuais, quiabo (Abelmoschus esculentus) e berinjela (Solatium melongena), e de uma espécie perene, andiroba (Carapa guianensis, uma árvore nativa da Amazônia) sob diferentes tratamentos com matéria orgânica derivada de material de cupinzeiro de espécies xilófagas de Nasutitermes (desenho de bloco randomizado). O uso de 25-100 g de material de termiteiro não levou a um incremento significativo da produtividade em quiabo, e 25-200 g não resultou numa resposta significativa em andiroba. O uso combinado de NPK com 200 g de ninho de cupim resultou numa produção significantemente maior em S. melongena (número total e peso fresco total de frutos) se comparado com o controle (sem fertilizante nenhum) e com o tratamento de NPK apenas. Os resultados sugerem a possibilidade de usar material de cupinzeiro para melhorara produção agrossilvicultural na Amazônia, especialmente em combinação com pequenas quantidades de fertilizante mineral Linhas de pesquisa para futuras investigações são apresentadas

Possible Disintegrating Short-Period Super-Mercury Orbiting KIC 12557548

We report here on the discovery of stellar occultations, observed with Kepler, that recur periodically at 15.685 hour intervals, but which vary in depth from a maximum of 1.3% to a minimum that can be less than 0.2%. The star that is apparently being occulted is KIC 12557548, a K dwarf with T_eff = 4400 K and V = 16. Because the eclipse depths are highly variable, they cannot be due solely to transits of a single planet with a fixed size. We discuss but dismiss a scenario involving a binary giant planet whose mutual orbit plane precesses, bringing one of the planets into and out of a grazing transit. We also briefly consider an eclipsing binary, that either orbits KIC 12557548 in a hierarchical triple configuration or is nearby on the sky, but we find such a scenario inadequate to reproduce the observations. We come down in favor of an explanation that involves macroscopic particles escaping the atmosphere of a slowly disintegrating planet not much larger than Mercury. The particles could take the form of micron-sized pyroxene or aluminum oxide dust grains. The planetary surface is hot enough to sublimate and create a high-Z atmosphere; this atmosphere may be loaded with dust via cloud condensation or explosive volcanism. Atmospheric gas escapes the planet via a Parker-type thermal wind, dragging dust grains with it. We infer a mass loss rate from the observations of order 1 M_E/Gyr, with a dust-to-gas ratio possibly of order unity. For our fiducial 0.1 M_E planet, the evaporation timescale may be ~0.2 Gyr. Smaller mass planets are disfavored because they evaporate still more quickly, as are larger mass planets because they have surface gravities too strong to sustain outflows with the requisite mass-loss rates. The occultation profile evinces an ingress-egress asymmetry that could reflect a comet-like dust tail trailing the planet; we present simulations of such a tail.Comment: 14 pages, 7 figures; submitted to ApJ, January 10, 2012; accepted March 21, 201

Reunião anual conjunta dos projetos Robin e Amazalert: excursão técnica.

bitstream/item/141586/1/DOCUMENTOS-417-AINFO.pd

Predicting the detectability of oscillations in solar-type stars observed by Kepler

Asteroseismology of solar-type stars has an important part to play in the exoplanet program of the NASA Kepler Mission. Precise and accurate inferences on the stellar properties that are made possible by the seismic data allow very tight constraints to be placed on the exoplanetary systems. Here, we outline how to make an estimate of the detectability of solar-like oscillations in any given Kepler target, using rough estimates of the temperature and radius, and the Kepler apparent magnitude.Comment: 21 pages, 6 figures, accepted for publication Astrophysical Journa

TW Hya: Spectral Variability, X-Rays, and Accretion Diagnostics

The nearest accreting T Tauri star, TW Hya was observed with spectroscopic and photometric measurements simultaneous with a long se gmented exposure using the CHANDRA satellite. Contemporaneous optical photometry from WASP-S indicates a 4.74 day period was present during this time. Absence of a similar periodicity in the H-alpha flux and the total X-ray flux points to a different source of photometric variations. The H-alpha emission line appears intrinsically broad and symmetric, and both the profile and its variability suggest an origin in the post-shock cooling region. An accretion event, signaled by soft X-rays, is traced spectroscopically for the first time through the optical emission line profiles. After the accretion event, downflowing turbulent material observed in the H-alpha and H-beta lines is followed by He I (5876A) broadening. Optical veiling increases with a delay of about 2 hours after the X-ray accretion event. The response of the stellar coronal emission to an increase in the veiling follows about 2.4 hours later, giving direct evidence that the stellar corona is heated in part by accretion. Subsequently, the stellar wind becomes re-established. We suggest a model that incorporates this sequential series of events: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates determined from emission line profiles.Comment: 61 pages; 22 figures; to appear in The Astrophysical Journa

Adenosine A(2A) receptor blockade reverts hippocampal stress-induced deficits and restores corticosterone circadian oscillation

Maternal separation (MS) is an early life stress model that induces permanent changes in the central nervous system, impairing hippocampal long-term potentiation (LTP) and spatial working memory. There are compelling evidences for a role of hippocampal adenosine A(2A) receptors in stress-induced modifications related to cognition, thus opening a potential window for therapeutic intervention. Here, we submitted rats to MS and evaluated the long-lasting molecular, electrophysiological and behavioral impairments in adulthood. We then assessed the therapeutic potential of KW6002, a blocker of A(2A) receptors, in stress-impaired animals. We report that the blockade of A(2A) receptors was efficient in reverting the behavior, electrophysiological and morphological impairments induced by MS. In addition, this effect is associated with restoration of the hypothalamic-pituitary-adrenal axis (HPA-axis) activity, as both the plasma corticosterone levels and hippocampal glucocorticoid receptor expression pattern returned to physiological-like status after the treatment. These results reveal the involvement of A(2A) receptors in the stress-associated impairments and directly in the stress response system by showing that the dysfunction of the HPA-axis as well as the long-lasting synaptic and behavioral effects of MS can be reverted by targeting adenosine A(2A) receptors. These findings provide a novel evidence for the use of adenosine A(2A) receptor antagonists as potential therapy against psychopathologiesWe acknowledge Alexandre de Mendonca, David Blum and Rodrigo Cunha for helpful discussions. VLB is thankful to Joao Baiao and Carla Batalha for technical assistance. VLB has been awarded a PhD fellowship from Fundacao para a Ciencia e Tecnologia (BD/63041/2009). LVL is funded by Fundacao para a Ciencia e Tecnologia (PTDC/SAU-NEU/099853/2008) and by EU programme Egide-Pessoa. YB and CEM were funded by the Ministry for Education and Research (BMBF, Grant number 01EW0911) in the frame of ERA-NET NEURON

Kepler Mission Stellar and Instrument Noise Properties

Kepler Mission results are rapidly contributing to fundamentally new discoveries in both the exoplanet and asteroseismology fields. The data returned from Kepler are unique in terms of the number of stars observed, precision of photometry for time series observations, and the temporal extent of high duty cycle observations. As the first mission to provide extensive time series measurements on thousands of stars over months to years at a level hitherto possible only for the Sun, the results from Kepler will vastly increase our knowledge of stellar variability for quiet solar-type stars. Here we report on the stellar noise inferred on the timescale of a few hours of most interest for detection of exoplanets via transits. By design the data from moderately bright Kepler stars are expected to have roughly comparable levels of noise intrinsic to the stars and arising from a combination of fundamental limitations such as Poisson statistics and any instrument noise. The noise levels attained by Kepler on-orbit exceed by some 50% the target levels for solar-type, quiet stars. We provide a decomposition of observed noise for an ensemble of 12th magnitude stars arising from fundamental terms (Poisson and readout noise), added noise due to the instrument and that intrinsic to the stars. The largest factor in the modestly higher than anticipated noise follows from intrinsic stellar noise. We show that using stellar parameters from galactic stellar synthesis models, and projections to stellar rotation, activity and hence noise levels reproduces the primary intrinsic stellar noise features.Comment: Accepted by ApJ; 26 pages, 20 figure