Low-resolution spectroscopy and spectral energy distributions of selected sources towards sigma Orionis

Aims: We investigated in detail nine sources in the direction of the young sigma Orionis cluster, which is considered a unique site for studying stellar and substellar formation. The nine sources were selected because of some peculiar properties, such as extremely red infrared colours or too strong Halpha emission for their blue optical colours. Methods: We took high-quality, low-resolution spectroscopy (R ~ 500) of the nine targets with ALFOSC at the Nordic Optical Telescope. We also re-analyzed [24]-band photometry from MIPS/Spitzer and compiled the best photometry available at the ViJHKs passbands and the four IRAC/Spitzer channels for constructing accurate spectral energy distributions covering from 0.55 to 24 mum. Results: The nine targets were classified into: one Herbig Ae/Be star with a scatterer edge-on disc, two G-type stars, one X-ray flaring, early-M, young star with chromospheric Halpha emission, one very low-mass, accreting, young spectroscopic binary, two young objects at the brown dwarf boundary with the characteristics of classical T Tauri stars, and two emission-line galaxies, one undergoing star formation, and another one whose spectral energy distribution is dominated by an active galactic nucleus. Besides, we discover three infrared sources associated to overdensities in a cold cloud in the cluster centre. Conclusions: Low-resolution spectroscopy and spectral energy distributions are a vital tool for measuring the physical properties and the evolution of young stars and candidates in the sigma Orionis cluster.Comment: Accepted for publication in A&

Chemical abundances of late-type pre-main sequence stars in the σ\sigma-Orionis cluster

The young $\sigma$-Orionis cluster is an important location for understanding the formation and evolution of stars, brown dwarfs, and planetary-mass objects. Its metallicity, although being a fundamental parameter, has not been well determined yet. We present the first determination of the metallicity of nine young late-type stars in $\sigma$-Orionis. Using the optical and near-infrared broadband photometry available in the literature we derive the effective temperatures for these nine cluster stars, which lie in the interval 4300--6500 K (1--3 \Msuno). These parameters are employed to compute a grid of synthetic spectra based on the code MOOG and Kurucz model atmospheres. We employ a $\chi^2$-minimization procedure to derive the stellar surface gravity and atmospheric abundances of Al, Ca, Si, Fe, Ni and Li, using multi-object optical spectroscopy taken with WYFFOS+AF2 at at the William Herschel Telescope ($\lambda/\delta\lambda\sim7500$). The average metallicity of the $\sigma$-Orionis cluster is [Fe/H] $= -0.02\pm0.09\pm0.13$ (random and systematic errors). The abundances of the other elements, except lithium, seem to be consistent with solar values. Lithium abundances are in agreement with the "cosmic" $^7$Li abundance, except for two stars which show a $\log \epsilon(\mathrm{Li})$ in the range 3.6--3.7 (although almost consistent within the error bars). There are also other two stars with $\log \epsilon(\mathrm{Li})\sim 2.75$. We derived an average radial velocity of the $\sigma$-Orionis cluster of $28\pm4$km/s. The $\sigma$-Orionis metallicity is roughly solar.Comment: Accepted for publication in Astronomy and Astrophysic

ENERGÍAS RENOVABLES: ALTERNATIVAS PARA EL SECTOR AGROPECUARIO EN PANAMÁ

Energy crisis is a reality that is being faced all around the world, resulting in social, economic and environmental impacts, which in many cases are difficult to quantify and assess objectively. Still most of the vehicles and machinery depend on fossil fuel, without being the agricultural sector the exception. On the other hand, technology and innovation, particularly that developed during the last decade, have made viable energy alternatives available to people, including for use in agricultural production. The present work is a review, which focuses on renewable energies, such as photovoltaic solar, wind energy, biogas and hydrogen; that can contribute to the efficient development of the agricultural sector in Panama, with potential economic benefits, reducing the risk of environmental contamination and also serving as means of integration and social responsibility. Specialized literature on the subject was consulted, in addition to sharing the scope of the authors themselves. It is expected that this work will serve as a guiding element, towards the sustainability and agroindustrial development.La crisis energética es una realidad que se está confrontando en el mundo, derivando en impactos sociales, económicos y ambientales, los cuales en muchos casos resultan difíciles de cuantificar y valorar de manera objetiva. Aún la mayoría de los vehículos y maquinarias dependen del combustible fósil, sin ser el sector agropecuario la excepción. Por otra parte, la tecnología e innovación, en particular la desarrollada durante la última década, ha puesto al alcance de las personas alternativas energéticas viables, inclusive para su utilización en la producción agropecuaria. El presente trabajo es una revisión, que se centra en energías renovables, como la solar fotovoltaica, la eólica, el biogás y el hidrógeno; que pueden contribuir con el desarrollo eficiente del sector agropecuario en Panamá, con potenciales beneficios económicos, reduciendo el riesgo de contaminación ambiental y sirviendo como medios de integración y responsabilidad social. Se consultó literatura especializada sobre la materia, además de compartir alcances de los propios autores. Se espera que este trabajo sirva como elemento orientador, hacia la sostenibilidad y desarrollo agroindustrial

Are isolated planetary-mass objects really isolated? A brown dwarf-exoplanet system candidate in the sigma Orionis cluster

The recent detection by direct imaging of three giant planets at wide separation (50-250 AU) from their primaries has raised the question about the ``true isolation'' of planetary-mass objects in clusters. Our goal was to test the possibility that some free-floating planetary-mass object could in fact be part of wide planetary systems. We searched in the literature for stellar and brown-dwarf member candidates of the sigma Orionis cluster at small angular separations from published candidate planetary-mass objects. We found one candidate planetary system, SE 70, composed of an X-ray source and a planetary-mass object, namely S Ori 68, separated by only 4.6 arcsec. In order to assess the cluster membership of the X-ray source, we obtained mid-resolution optical spectroscopy using ISIS on the William Herschel Telescope. We also compiled additional data on the target from available astronomical catalogues. We have found that SE 70 follows the spectrophotometric sequence of the cluster and displays spectroscopic features of youth, such as lithium in absorption and chromospheric Halpha emission. The radial velocity is consistent with cluster membership. Hence, SE 70 is very probably a sigma Orionis cluster member. The projected physical separation between SE 70 and S Ori 68 is 1700+/-300 AU at the distance of the cluster. If the common proper motion is confirmed in the near future, the system would be composed of an M5-6 brown dwarf with an estimated mass of ~45 M_Jup and an L5+/-2 giant planet with an estimated mass of ~5 M_Jup. It would be the widest and one of the lowest-mass planetary systems known so far.Comment: Accepted for publication in A&A (7 pages, 4 figures). Abridged abstract

INDICADORES DE SOSTENIBILIDAD EN AGROECOSISTEMAS HORTÍCOLAS EN CERRO PUNTA, CHIRIQUÍ, PANAMÁ

Cerro Punta is one of the main producing areas of fresh vegetables in Panama; responsible for the supply of more than 80% of these items in the country. Recently, a characterization of these productive systems was carried out, which reflected that agricultural activity is the main source of income for the community, but they are very dependent on the use of synthetic pesticides. The aim of this study was to evaluate the sustainability of horticultural agroecosystems in Cerro Punta, Chiriquí, Panama. For this, a K means cluster analysis was carried out in a preliminary manner, in which the cultivated area (ha) and the productive cost (USD per ha) were taken into consideration. Next, one farm per conglomerate was randomly selected and ten sustainability indicators were defined on a scale of 1-5, corresponding to the social (2), economic (4) and technical-environmental (4) dimensions; being required for a farm to be considered sustainable to achieve at least an average of 3 per dimension and the general sustainability index (ISG), must be 3 or superior. According to the results, only cluster 4 turned was sustainable, with an ISG of 3.9. However, the five types of farm turned out to be sustainable in the social dimension, due to the satisfaction of basic services. Yield improvements, crop diversification and other economic activities are required; in addition to promoting Integrated Pest Management. In conclusion, horticultural agroecosystems in Cerro Punta could be sustainable.Cerro Punta es una de las principales zonas productoras de hortalizas frescas en Panamá; responsable del abastecimiento de más del 80% de estos rubros en el país. Recientemente, se realizó una caracterización de dichos sistemas productivos, la cual reflejó que la actividad agrícola es la principal fuente de ingresos de la comunidad, pero dependen en gran medida del uso de plaguicidas de síntesis. El objetivo del presente estudio fue evaluar la sostenibilidad de los agroecosistemas hortícolas en Cerro Punta, Chiriquí, Panamá. Para ello, se realizó de manera preliminar, un análisis de conglomerado de K medias, en el cual se tomó en consideración el área cultivada (ha) y el costo productivo (USD por ha). Seguidamente, se seleccionó al azar una finca por conglomerado y se definieron, en una escala de 1 – 5, diez indicadores de sostenibilidad, correspondientes a las dimensiones social (2), económica (4) y técnico-ambiental (4); siendo requerido para que una finca se considere sostenible lograr como mínimo un promedio de 3 por dimensión y que el índice de sostenibilidad general (ISG), sea igual o mayor que 3. De acuerdo con los resultados, solamente el conglomerado 4 resultó ser sostenible, con ISG de 3.9. Sin embargo, los cinco tipos de finca resultaron ser sostenibles en la dimensión social, gracias a la satisfacción de servicios básicos. Se requieren mejoras en cuanto al rendimiento, la diversificación de cultivos y otras actividades económicas; además de fomentar el manejo integrado de plagas. En conclusión, los agroecosistemas hortícolas en Cerro Punta podrían ser sostenibles

The nuclear and extended mid-infrared emission of Seyfert galaxies

We present subarcsecond resolution mid-infrared (MIR) images obtained with 8-10 m-class ground-based telescopes of a complete volume-limited (DL<40 Mpc) sample of 24 Seyfert galaxies selected from the Swift/BAT nine month catalog. We use those MIR images to study the nuclear and circumnuclear emission of the galaxies. Using different methods to classify the MIR morphologies on scales of ~400 pc, we find that the majority of the galaxies (75-83%) are extended or possibly extended and 17-25% are point-like. This extended emission is compact and it has low surface brightness compared with the nuclear emission, and it represents, on average, ~30% of the total MIR emission of the galaxies in the sample. We find that the galaxies whose circumnuclear MIR emission is dominated by star formation show more extended emission (650+-700 pc) than AGN-dominated systems (300+-100 pc). In general, the galaxies with point-like MIR morphologies are face-on or moderately inclined (b/a~0.4-1.0), and we do not find significant differences between the morphologies of Sy1 and Sy2. We used the nuclear and circumnuclear fluxes to investigate their correlation with different AGN and SF activity indicators. We find that the nuclear MIR emission (the inner ~70 pc) is strongly correlated with the X-ray emission (the harder the X-rays the better the correlation) and with the [O IV] lambda 25.89 micron emission line, indicating that it is AGN-dominated. We find the same results, although with more scatter, for the circumnuclear emission, which indicates that the AGN dominates the MIR emission in the inner ~400 pc of the galaxies, with some contribution from star formation.Comment: 27 pages, 12 figures, accepted by MNRA

S Ori J053825.4-024241: A Classical T Tauri-like object at the substellar boundary

We present a spectrophotometric analysis of S Ori J053825.4-024241, a candidate member close to the substellar boundary of the young (1-8 Myr), nearby (~360 pc) sigma Orionis star cluster. Our optical and near-infrared photometry and low-resolution spectroscopy indicate that S Ori J053825.4-024241 is a likely cluster member with a mass estimated from evolutionary models at 0.06+0.07-0.02 Msol, which makes the object a probable brown dwarf. The radial velocity of S Ori J053825.4-024241 is similar to the cluster systemic velocity. This target, which we have classified as an M 6.0+-1.0 low-gravity object, shows excessemission in the near-infrared and anomalously strong photometric variability for its type (from the blue to the J band), suggesting the presence of a surrounding disc. The optical spectroscopic observations show a continuum excess at short wavelengths and a persistent and resolved Halpha emission (pseudo-equivalent width of ~-250 AA) in addition to the presence of other forbidden and permitted emission lines, which we interpret as indicating accretion from the disc and possibly mass loss. We conclude that despite the low mass of S Ori J053825.4-024241, this object exhibits some of the properties typical of active classical T Tauri stars.Comment: 12 pages, 15 figures. Accepted for publication in Astronomy & Astrophysics, section 5. Galactic structure, stellar clusters and populations. The official date of acceptance is 24/08/2005. Acknowledgements of the use of telescopes, instruments, catalogues and software are also give

Observation of a hole-size-dependent energy shift of the surface-plasmon resonance in Ni antidot thin films

A combined experimental and theoretical study of the magneto-optic properties of a series of nickel antidot thin films is presented. The hole diameter varies from 869 down to 636 nm, while the lattice periodicity is fixed at 920 nm. This results in an overall increase of the polar Kerr rotation with decreasing hole diameter due to the increasing surface coverage with nickel. In addition, at photon energies of 2.7 and 3.3 eV, where surface-plasmon excitations are expected, we observe distinct features in the polar Kerr rotation not present in continuous nickel films. The spectral position of the peaks exhibits a red shift with decreasing hole size. This is explained within the context of an effective medium theory by a change in the effective dielectric function of the Ni thin filmsH.F. gratefully acknowledges China Scholarship Council (CSC) for financial support and André Schirmeisen for the data of Ni film. A.G.-M. and B.C. acknowledge funding from Spanish Ministry of Economy and Competitiveness through grants “FUNCOAT” CONSOLIDER CSD2008-00023 and “MAPS” MAT2011-29194-C02-01. J.C.C. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (Contract No. FIS2011-28851-C02-01) and from the Comunidad de Madrid (Contract No. S2013/MIT- 2740). E.M.A. and M.G. acknowledge financial support by the European Union under the project CosmoPHOS with the number “310337

Observation of a hole-size-dependent energy shift of the surface-plasmon resonance in Ni antidot thin films

© 2015 AIP Publishing LLC. A combined experimental and theoretical study of the magneto-optic properties of a series of nickel antidot thin films is presented. The hole diameter varies from 869 down to 636 nm, while the lattice periodicity is fixed at 920 nm. This results in an overall increase of the polar Kerr rotation with decreasing hole diameter due to the increasing surface coverage with nickel. In addition, at photon energies of 2.7 and 3.3 eV, where surface-plasmon excitations are expected, we observe distinct features in the polar Kerr rotation not present in continuous nickel films. The spectral position of the peaks exhibits a red shift with decreasing hole size. This is explained within the context of an effective medium theory by a change in the effective dielectric function of the Ni thin films.H.F. gratefully acknowledges China Scholarship Council (CSC) for financial support and André Schirmeisen for the data of Ni film. A.G.-M. and B.C. acknowledge funding from Spanish Ministry of Economy and Competitiveness through grants “FUNCOAT” CONSOLIDER CSD2008-00023 and “MAPS” MAT2011-29194-C02-01. J.C.C. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (Contract No. FIS2011-28851-C02-01) and from the Comunidad de Madrid (Contract No. S2013/MIT-2740). E.M.A. and M.G. acknowledge financial support by the European Union under the project CosmoPHOS with the number “3100337”.Peer Reviewe