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Magrini L.,National institute for astrophysics | Goncalves D.R.,Federal University of Rio de Janeiro | Vajgel B.,Observatorio Nacional MCTI
Monthly Notices of the Royal Astronomical Society | Year: 2017

We present new spectroscopic observations obtained with Gemini Multi-Object Spectrographs at Gemini-South of a sample of 25 HII regions located in NGC 55, a late-type galaxy in the nearby Sculptor group. We derive physical conditions and chemical composition through the Te method for 18 HII regions, and strong-line abundances for 22 HII regions. We provide abundances of He, O, N, Ne, S and Ar, finding a substantially homogeneous composition in the ionized gas of the disc of NGC 55, with no trace of radial gradients. The oxygen abundances, both derived with Te and strong-line methods, have similar mean values and similarly small dispersions: 12+log (O/H) = 8.13 ± 0.18 dex with the former and 12+log (O/H) = 8.17 ± 0.13 dex with the latter. The average metallicities and the flat gradients agree with previous studies of smaller samples of HII regions and there is a qualitative agreement with the blue supergiant radial gradient as well. We investigate the origin of such flat gradients comparing NGC 55 with NGC 300, its companion galaxy, which is also twin of NGC 55 in terms of mass and luminosity. We suggest that the differences in the metal distributions in the two galaxies might be related to the differences in their K-band surface density profile. The flatter profile of NGC 55 probably causes in this galaxy higher infall/outflow rates than in similar galaxies. This likely provokes a strong mixing of gas and a re-distribution of metals. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Martinez R.,Pontifical Catholic University of Rio de Janeiro | Martinez R.,Federal University of Amapá | Bordalo V.,Observatorio Nacional MCTI | Da Silveira E.F.,Pontifical Catholic University of Rio de Janeiro | Boechat-Roberty H.M.,Federal University of Rio de Janeiro
Monthly Notices of the Royal Astronomical Society | Year: 2014

In the interstellar medium, high-energy cosmic rays are able to penetrate deeply into molecular clouds, resulting in the ionization and dissociation of condensed molecules on ice-grain surfaces, which in turn leads to the desorption of a number of species. The interpretation of interstellar data requires qualitative and quantitative studies of the molecular species formed in several processes. In this work, the interaction of cosmic rays with CO-NH3 ice is simulated by the bombardment of 65-MeV heavy ions (masses of 100 u) on frozen gases. Positive and negative ions ejected from the ice surface as a consequence of the impact are analysed through time-of-flight mass spectrometry. The dependence of the ion desorption yield on the sample temperature (which varies/increases with time) has been used to discuss the emission process of the desorbed ions, especially near ice sublimation temperatures (30 K for CO at 10-8 mbar); at these temperatures, HCO+, NO+, NH3OH+ and NH3CO+ are formed and emitted. For temperatures in the 40 to 65 K range, mass spectra of positive ions are dominated by the NH4+ ion peak, similarly to what occurs for a pure frozen NH3 target. Concerning the mass spectra of negative ions, the total yield of negative ions at T=25 K is found to be about 20 times lower than that of positive ions. Before CO sublimation, CN-bearing species are formed, among which the cyanide ions CN- and OCN- are by far the most abundant species. These findings support the idea that NH4+ and OCN- ions are efficiently formed by the interaction of cosmic rays with CO-NH3 ices. © 2014 The Authors.

Reza R.D.L.,Observatorio Nacional MCTI | Drake N.A.,Observatorio Nacional MCTI | Drake N.A.,Saint Petersburg State University | Oliveira I.,Observatorio Nacional MCTI | Rengaswamy S.,European Southern Observatory
Astrophysical Journal | Year: 2015

Hydrocarbon organic material, as found in the interstellar medium, exists in complex mixtures of aromatic and aliphatic forms. It is considered to originate from carbon-enriched giant stars during their final stages of evolution, when very strong mass loss occurs in a few thousand years on their way to becoming planetary nebulae. We show here that the same organic compounds appear to be formed in previous stages of the evolution of giant stars, more specifically, during the first-ascending giant branch K-type stars. According to our model, this happens only when these stars are being abruptly enriched with lithium, together with the formation of a circumstellar shell with a strong mass loss during just a few thousand years. This sudden mass loss is, on average, a thousand times larger than that of normal Li-poor K giant stars. This shell would later be detached, especially when the star stops its Li enrichment and a rapid photospheric Li depletion occurs. In order to gain extra carbon-based material to form the organic hydrocarbons, as well as to explain the presence of complex inorganic compounds in these stars, we propose an interaction of these strong winds with the remaining asteroidal/cometary disks that already existed around these stars since they were dwarf A-type stars. The mechanism of interaction presented here is successful in explaining the presence of inorganic compounds; however, it is unable to produce new carbon-free atoms to form the organic hydrocarbon compounds. Finally, we discuss some suggestions and speculations that can eventually help solve the long-standing puzzle of Li-rich giants. © 2015. The American Astronomical Society. All rights reserved.

Di Bartolo L.,Observatorio Nacional MCTI | Dors C.,Federal University of Rio de Janeiro | Mansur W.J.,Federal University of Rio de Janeiro
Geophysical Prospecting | Year: 2015

The previous finite-difference numerical schemes designed for direct application to second-order elastic wave equations in terms of displacement components are strongly dependent on Poisson's ratio. This fact makes theses schemes useless for modelling in offshore regions or even in onshore regions where there is a high Poisson's ratio material. As is well known, the use of staggered-grid formulations solves this drawback. The most common staggered-grid algorithms apply central-difference operators to the first-order velocity-stress wave equations. They have been one of the most successfully applied numerical algorithms for seismic modelling, although these schemes require more computational memory than those mentioned based on second-order wave equations. The goal of the present paper is to develop a general theory that enables one to formulate equivalent staggered-grid schemes for direct application to hyperbolic second-order wave equations. All the theory necessary to formulate these schemes is presented in detail, including issues regarding source application, providing a general method to construct staggered-grid formulations to a wide range of cases. Afterwards, the equivalent staggered-grid theory is applied to anisotropic elastic wave equations in terms of only velocity components (or similar displacements) for two important cases: general anisotropic media and vertical transverse isotropy media using, respectively, the rotated and the standard staggered-grid configurations. For sake of simplicity, we present the schemes in terms of velocities in the second- and fourth-order spatial approximations, with second-order approximation in time for 2D media. However, the theory developed is general and can be applied to any set of second-order equations (in terms of only displacement, velocity, or even stress components), using any staggered-grid configuration with any spatial approximation order in 2D or 3D cases. Some of these equivalent staggered-grid schemes require less computer memory than the corresponding standard staggered-grid formulation, although the programming is more evolved. As will be shown in theory and practice, with numerical examples, the equivalent staggered-grid schemes produce results equivalent to corresponding standard staggered-grid schemes with computational advantages. Finally, it is important to emphasize that the equivalent staggered-grid theory is general and can be applied to other modelling contexts, e.g., in electrodynamical and poroelastic wave propagation problems in a systematic and simple way. © 2015 European Association of Geoscientists & Engineers.

Morgado B.,Observatorio Nacional MCTI | Morgado B.,Federal University of Rio de Janeiro | Assafin M.,Federal University of Rio de Janeiro | Vieira-Martins R.,Observatorio Nacional MCTI | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

Typically we can deliver astrometric positions of natural satellites with errors in the 50-150 mas range. Apparent distances from mutual phenomena, have much smaller errors, less than 10 mas. However, this method can only be applied during the equinox of the planets. We developed a method that can provide accurate astrometric data for natural satellites - the mutual approximations. The method can be applied when any two satellites pass close by each other in the apparent sky plane. The fundamental parameter is the central instant t0 of the passage when the distances reach a minimum. We applied the method for the Galilean moons. All observations were made with a 0.6 m telescope with a narrow-band filter centred at 889 nm with width of 15 nm which attenuated Jupiter's scattered light. We obtained central instants for 14 mutual approximations observed in 2014-2015. We determined t0 with an average precision of 3.42 mas (10.43 km). For comparison, we also applied the method for 5 occultations in the 2009 mutual phenomena campaign and for 22 occultations in the 2014-2015 campaign. The comparisons of t0 determined by our method with the results from mutual phenomena show an agreement by less than 1σ error in t0, typically less than 10 mas. This new method is particularly suitable for observations by small telescopes. © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Olkin C.B.,Southwest Research Institute | Young L.A.,Southwest Research Institute | Borncamp D.,Southwest Research Institute | Borncamp D.,US Space Telescope Science Institute | And 21 more authors.
Icarus | Year: 2015

Combining stellar occultation observations probing Pluto's atmosphere from 1988 to 2013, and models of energy balance between Pluto's surface and atmosphere, we find the preferred models are consistent with Pluto retaining a collisional atmosphere throughout its 248-year orbit. The occultation results show an increasing atmospheric pressure with time in the current epoch, a trend present only in models with a high thermal inertia and a permanent N2 ice cap at Pluto's north rotational pole. © 2014 The Authors.

PubMed | Observatorio Nacional MCTI, Vale Institute of Technology and Federal University of Minas Gerais
Type: Journal Article | Journal: Sensors (Basel, Switzerland) | Year: 2016

Recent advances in the research of autonomous vehicles have showed a vast range of applications, such as exploration, surveillance and environmental monitoring. Considering the mining industry, it is possible to use such vehicles in the prospection of minerals of commercial interest beneath the ground. However, tasks such as geophysical surveys are highly dependent on specific sensors, which mostly are not designed to be used in these new range of autonomous vehicles. In this work, we propose a novel magnetic survey pipeline that aims to increase versatility, speed and robustness by using autonomous rotary-wing Unmanned Aerial Vehicles (UAVs). We also discuss the development of a state-of-the-art three-axis fluxgate, where our goal in this work was to refine and adjust the sensor topology and coupled electronics specifically for this type of vehicle and application. The sensor was built with two ring-cores using a specially developed stress-annealed CoFeSiB amorphous ribbon, in order to get sufficient resolution to detect concentrations of small ferrous minerals. Finally, we report on the results of experiments performed with a real UAV in an outdoor environment, showing the efficacy of the methodology in detecting an artificial ferrous anomaly.

Guerrero C.A.,Observatorio Nacional MCTI | Orlov V.G.,National Autonomous University of Mexico | Monroy-Rodriguez M.A.,National Autonomous University of Mexico | Borges Fernandes M.,Observatorio Nacional MCTI
Astronomical Journal | Year: 2015

We present a high-angular resolution survey for the search of binary and multiple stars in the Galactic open cluster Melotte 111. Combining our own speckle-interferometric observations with data taken from the literature, we found a ratio of the number of single to multiple stars to be 29:8:0:0:0:1 for the most probable members, indicating a multiplicity fraction for this cluster of 25.6% ± 2%. We also observed field stars in the vicinity of the cluster and estimated a ratio of multiplicities of 286:17:1:0:0:0:1 (between one and seven companions), equivalent to a multiplicity fraction of 5.9% ± 3%. We showed that the cumulative distribution of separations for our sample stars is in agreement with Öpik's law. © 2015. The American Astronomical Society. All rights reserved.

Jilinski P.,Observatorio Nacional MCTI | Meju M.A.,Petronas | Fontes S.L.,Observatorio Nacional MCTI
Geophysical Journal International | Year: 2013

The commonest technique for determination of the continental-oceanic crustal boundary or transition (COB) zone is based on locating and visually correlating bathymetric and potential field anomalies and constructing crustal models constrained by seismic data. In this paper, we present a simple method for spatial correlation of bathymetric and potential field geophysical anomalies. Angular differences between gradient directions are used to determine different types of correlation between gravity and bathymetric or magnetic data. It is found that the relationship between bathymetry and gravity anomalies can be correctly identified using this method. It is demonstrated, by comparison with previously published models for the southwest African margin, that this method enables the demarcation of the zone of transition from oceanic to continental crust assuming that this it is associated with geophysical anomalies, which can be correlated using gradient directions rather than magnitudes. We also applied this method, supported by 2-D gravity modelling, to the more complex Liberia and Cote d'Ivoire-Ghana sectors of the West African transform margin and obtained results that are in remarkable agreement with past predictions of the COB in that region. We suggest the use of this method for a first-pass interpretation as a prelude to rigorous modelling of the COB in frontier areas. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Solon F.F.,Observatorio Nacional MCTI | Fontes S.L.,Observatorio Nacional MCTI | Meju M.A.,Petronas
Petroleum Geoscience | Year: 2015

We evaluate the use of the magnetotelluric (MT) method to locate crystalline basement and overlying carbonate reservoir rocks underneath a thick overburden in the Sao Francisco basin in Brazil. Mapping the complex basement and the carbonate reservoir using seismic reflection is a major problem in hydrocarbon exploration in this intracratonic basin, and it is expected that MT will provide useful complementary information. In the present study, we analysed 31 MT soundings along four survey lines in the central region of the basin. The MT soundings covered a period range of 0.001-100 s, probing the subsurface resistivity structure down to a maximum depth of about 15 km. The MT data were inverted using a regularized twodimensional (2D) inversion algorithm with a variety of a priori data for comparison. For model appraisal, we analysed well log (gamma ray, deep resistivity and neutron porosity) data as well as seismic, gravity and magnetic profiles coincident with one MT line passing through the well. We found that shallow geological boundaries separating zones of strong resistivity contrasts also coincide with seismic boundaries in the inversion models with or without a priori data. Using gravity data, it was also possible to define the compartmentalized basement in this sector of Sao Francisco Basin, not clear in the seismic section. However, only by integrating all available information were we able to map the Lagoa do Jacare and Sete Lagoas carbonate member-formations of the Bambui Group, which are considered to host both the source and reservoir rocks identified from past exploratory history of this basin. We also imaged a basement structural high with thinned or disrupted conductive cover rocks over a known zone of hydrocarbon microseepage and a buried conductive (source rock?) channel at its NW margin, the trace of which coincides with the present-day River Paracatu along which gas bubbles have been observed. This suggests that MT may be fruitfully integrated with gravity, magnetic and seismic data to study the structural controls on hydrocarbon occurrence in this basin. © 2015 The Author(s).

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