YSOVAR: Six pre-main-sequence eclipsing binaries in the Orion Nebula Cluster

Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for 2400 candidateOrion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass (Theta1 Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 solar masses) and longest period (ISOY J053505.71-052354.1, P \sim 20 days) PMS EBs currently known. In two cases (Theta1 Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.Comment: Accepted by Ap

Caracterización química de la Fibra de Coco (Cocus nucifera L.) de México utilizando Espectroscopía de Infrarrojo (FTIR)

There is a growing interest in products with less environmental impact, this makes the use of natural fibers a viable alternative. The use of materials of biological origin is increasing in an attempt to reduce the amount of thermoplastic polymers from non-renewable sources. In this framework, the work characterizes the chemical characterization of coconut fiber (Cocus nucifera L.), by means of infrared spectroscopy (FTIR), and the spectra of the fibers of coconut, from two important growing sites, the Acapulco and San Jerónimo de Juárez regions, in the state of Guerrero, Mexico, the results obtained are compared with other spectra of other natural fibers, due to the high content of lignin, properties are attributed viscoelastic, by which it is inferred that when the fibers are subjected to a compression load or an impact force, the amorphous region (lignin) functions as a buffer and is resilient to the applied phenomena, a desirable characteristic in packaging materials, this proves that the coconut fiber with natural binder, could be a proposal to be used as packing material in packaging, the data corroborate a high percentage of cellulose and lignin present in the samples studied.Existe un creciente interés en productos con menor impacto ambiental, esto hace que el uso de fibras naturales sea una alternativa viable. El uso de materiales de origen biológico está aumentando en un intento de reducir la cantidad de polímeros termoplásticos de fuentes no renovables. En este marco se presenta el trabajo caracterización química de la fibra de coco (Cocus nucifera L.), mediante espectroscopía de infrarrojo (FTIR) , y se muestran los espectros de las fibras de coco, de dos lugares de cultivo importantes, la región de Acapulco y San Jerónimo de Juárez, en el estado de Guerrero, México , los resultados obtenidos son comparados con otros espectros de otras fibras naturales, debido al alto contenido de lignina se le atribuyen propiedades viscoelásticas, por lo que se infiere que al ser sometidas las fibras a una carga de compresión o una fuerza de impacto, la región amorfa (lignina) funciona como amortiguador y es resiliente a los fenómenos aplicados, una característica deseable en los materiales de embalaje, esto prueba que la fibra de coco con aglomerante natural, pudiera ser una propuesta para usarse como material de relleno en embalajes, los datos corroboran un alto porcentaje de celulosa y lignina presenteen las muestras estudiadas

Marcos da liderança em empresas: o caso da cidade de bucaramanga (colômbia) e sua área metropolitana /

Universidad Autónoma del Carib

Differential cytogenetic profile in advanced chronic myeloid leukemia with sequential lymphoblastic and myeloblastic blast crisis

Frequency of additional chromosomal abnormalities in chronic myeloid leukemia (CML) is estimated to be 7% in chronic phase and increases to 40–70% in advanced disease. Progression of CML from chronic phase to accelerated phase or blast crisis is often associated with secondary chromosomal aberrations. We report an exceptional case of CML as debut in lymphoblastic blast crisis and a subsequent progression in myeloblastic blast crisis with rare cytogenetic abnormalities

Short-term spectroscopic monitoring of two cool dwarfs with strong magnetic fields

Context: There is now growing evidence that some brown dwarfs (BDs) have very strong magnetic fields, and yet their surface temperatures are so low that the coupling is expected to be small between the matter and the magnetic field in the atmosphere. In the deeper layers, however, the coupling is expected to be much stronger. Aims: This raises the question of whether the magnetic field still leads to the formation of structures in the photosphere. Methods: We carried out a spectroscopic monitoring campaign of two ultracool dwarfs that have strong magnetic fields: the BD LP944-20 and 2MASSW J0036159+182110. LP944-20 was observed simultaneously in the optical and in the near infrared regime, 2MASSW J0036159+182110 only in the infrared. Results: Both dwarfs turned out to be remarkably constant. In the case of LP944-20, the Teff-variations are <50K, and the rms-variations in the equivalent widths of Halpha small. We also find that the equivalent widths of photospheric lines are remarkably constant. We did not find any significant variations in the case of 2MASSW J0036159+182110 either. Thus the most important result is that no significant variability was found at the time of our observations. When comparing our spectra with spectra taken over the past 11 years, we recognize significant changes during this time. Conclusions: We interpret these results as evidence that the photosphere of these objects are remarkably homogeneous, with only little structure in them, and despite the strong magnetic fields. Thus, unlike active stars, there are no prominent spots on these objects.Comment: 7 pages, 9 figures. Astronomy and Astrophysics (accepted

VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster

The physical properties of almost any kind of astronomical object can be derived by fitting synthetic spectra or photometry extracted from theoretical models to observational data. We want to develop an automatic procedure to perform this kind of fittings to a relatively large sample of members of a stellar association and apply this methodology to the case of Collinder 69. We combine the multiwavelength data of our sources and follow a work-flow to derive the physical parameters of the sources. The key step of the work-flow is performed by a new VO-tool, VOSA. All the steps in this process are done in a VO environment. We present this new tool, and provide physical parameters such as T$_{\rm eff}$, gravity, luminosity, etc. for $\sim$170 candidate members to Collinder 69, and an upper-limit for the age of this stellar association. This kind of studies of star forming regions, clusters, etc. produces a huge amount of data, very tedious to analyse using the traditional methodology. Thus, they are excellent examples where to apply the VO capabilities.Comment: Accepted for publication in A&

On the nature of the EXor accretion events: an unfrequent manifestation of a common phenomenology ?

We present the results of a comparison between classical and newly identified EXor based on literature data and aimed at recognizing possible differences or similarities of both categories. Optical and near-IR two-color diagrams, modalities of fluctuations, and derived values of the mass accretion rates are indicative of strong similarities between the two samples. We demonstrate how the difference between the outburst and the quiescence spectral energy distribution of all the EXor can be well fitted with a single blackbody, as if an additional thermal component appears during the outbursting phase. Temperatures of this additional component span between 1000 and 4500 K, while the radii of the emitting regions (assumed to be a uniform disk) span between 0.01 and 0.1 AU, sizes typical of the inner portions of the circumstellar disk. Spots persisting up to 50% of the outburst duration, not exceeding the 10% of the stellar surface, and with temperatures compatible with the EXor mass accretion rates, are able to account for both the appearance of the additional thermal component and the dust sublimation in the inner structures of the disk. We also compare the EXor events with the most significant color and magnitude fluctuations of active T Tauri stars finding that (i} burst accretion phenomena should also be important for this latter class; (ii} EXor events could be more frequent then those accidentally discovered. Remarkable is the case of the source V2493 Cyg, a T Tauri star recently identified as a strong outbursting object: new optical and near-IR photometric and spectroscopic data are presented trying to clarify its EXor or FUor nature.Comment: Accepted for publication in Ap

X-ray view of IC348 in the light of an updated cluster census

We study the properties of the coronae of the low-mass stars in the young (~2-3Myr), nearby (~310pc) open cluster IC348 combining X-ray and optical/infrared data. The four existing Chandra observations of IC348 are merged, thus providing a deeper and spatially more complete X-ray view than previous X-ray studies of the cluster. We have compiled a comprehensive catalog of IC348 members taking into account recent updates to the cluster census. Our data collection comprises fundamental stellar parameters, infrared excess indicating the presence of disks, Halpha emission as a tracer of chromospheric emission or accretion and mass accretion rates. We have detected 290 X-ray sources in four merged Chandra exposures, of which 187 are associated with known cluster members. Only four of the X-ray sources are brown dwarfs (spectral type M6 and later). The detection rate is highest for diskless Class III stars and increases with stellar mass. This may be explained with higher X-ray luminosities for higher mass and later evolutionary stage that is evident in the X-ray luminosity functions. In particular, we find that for the lowest examined masses (0.1-0.25 Msun) there is a difference between the X-ray luminosity functions of accreting and non-accreting stars (classified on the basis of their Halpha emission strength) as well as those of disk-bearing and diskless stars (classified on the basis of the slope of the spectral energy distribution). These differences disappear for higher masses. This is related to our finding that the L_x/L_bol ratio is non-constant across the mass/luminosity sequence of IC348 with a decrease towards lower luminosity stars. Our analysis of an analogous stellar sample in the Orion Nebula Cluster suggests that the decline of L_x/L_ bol for young stars at the low-mass end of the stellar sequence is likely universal.Comment: Accepted for publication in Astronomy & Astrophysic

Thermal Emission of WASP-14b Revealed with Three Spitzer Eclipses

Exoplanet WASP-14b is a highly irradiated, transiting hot Jupiter. Joshi et al. calculate an equilibrium temperature Teq of 1866 K for zero albedo and reemission from the entire planet, a mass of 7.3 +/- 0.5 Jupiter masses and a radius of 1.28 +/- 0.08 Jupiter radii. Its mean density of 4.6 g/cm3 is one of the highest known for planets with periods less than 3 days. We obtained three secondary eclipse light curves with the Spitzer Space Telescope. The eclipse depths from the best jointly fit model are $0.224\%$ +/- $0.018\%$ at 4.5 {\mu}m and $0.181\%$ +/- $0.022\%$ at 8.0 {\mu}m. The corresponding brightness temperatures are 2212 +/- 94 K and 1590 +/- 116 K. A slight ambiguity between systematic models suggests a conservative 3.6 {\mu}m eclipse depth of $0.19\%$ +/- $0.01\%$ and brightness temperature of 2242 +/- 55 K. Although extremely irradiated, WASP-14b does not show any distinct evidence of a thermal inversion. In addition, the present data nominally favor models with day night energy redistribution less than $~30\%$. The current data are generally consistent with oxygen-rich as well as carbon-rich compositions, although an oxygen-rich composition provides a marginally better fit. We confirm a significant eccentricity of e = 0.087 +/- 0.002 and refine other orbital parameters.Comment: 16 pages, 16 figure

XMM-Newton investigations of the Lambda Orionis star-forming region (XILO). I. The young cluster Collinder 69

This is the first paper of a series devoted to the Lambda Orionis star-forming region, from the X-ray perspective, which will provide a comprehensive view of this complex region. In this paper we focus in uncovering the population of the central, young cluster Collinder 69 (C69), and in particular those diskless members not identified by previous near- and mid-infrared surveys, and to establish the X-ray luminosity function for the association. We have combined two exposures taken with the XMM-Newton satellite with an exhaustive data set of optical, near- and mid-infrared photometry to assess the membership of the X-ray sources based on color-color and color-magnitude diagrams, as well as other properties, such as effective temperatures, masses and bolometric luminosities. We detected a total of 164 X-ray sources, of which 66 are probable and possible cluster members. A total of 16 are newly identified probable members. The two XMM-Newton pointings east and west of the cluster center have allowed us to verify the heterogeneous spatial distribution of young stars, probably related to the large scale structure of the region. The disk fraction of the X-ray detected cluster sample is very low, close to 10%, in remarkable contrast to the low-mass stellar and substellar population (mostly undetected in X-rays) where the disk fraction reaches about 50%. The X-ray luminosity function of C69 provides support for an age of several Myr when compared with other well known young associations. With our improved cluster census we confirm previous reports on the untypically low disk fraction compared to other clusters of several Myr age. The different disk fractions of X-ray detected (essentially solar-like) and undetected (mostly low-mass stars and brown dwarfs) members can be understood as a consequence of a mass-dependence of the time-scale for disk evolution.Comment: 38 pages, 16 figure