High contrast optical imaging of companions: the case of the brown dwarf binary HD-130948BC

High contrast imaging at optical wavelengths is limited by the modest correction of conventional near-IR optimized AO systems.We take advantage of new fast and low-readout-noise detectors to explore the potential of fast imaging coupled to post-processing techniques to detect faint companions to stars at small separations. We have focused on I-band direct imaging of the previously detected brown dwarf binary HD130948BC,attempting to spatially resolve the L2+L2 benchmark system. We used the Lucky-Imaging instrument FastCam at the 2.5-m Nordic Telescope to obtain quasi diffraction-limited images of HD130948 with ~0.1" resolution.In order to improve the detectability of the faint binary in the vicinity of a bright (I=5.19 \pm 0.03) solar-type star,we implemented a post-processing technique based on wavelet transform filtering of the image which allows us to strongly enhance the presence of point-like sources in regions where the primary halo dominates. We detect for the first time the BD binary HD130948BC in the optical band I with a SNR~9 at 2.561"\pm 0.007" (46.5 AU) from HD130948A and confirm in two independent dataset that the object is real,as opposed to time-varying residual speckles.We do not resolve the binary, which can be explained by astrometric results posterior to our observations that predict a separation below the NOT resolution.We reach at this distance a contrast of dI = 11.30 \pm 0.11, and estimate a combined magnitude for this binary to I = 16.49 \pm 0.11 and a I-J colour 3.29 \pm 0.13. At 1", we reach a detectability 10.5 mag fainter than the primary after image post-processing. We obtain on-sky validation of a technique based on speckle imaging and wavelet-transform processing,which improves the high contrast capabilities of speckle imaging.The I-J colour measured for the BD companion is slightly bluer, but still consistent with what typically found for L2 dwarfs(~3.4-3.6).Comment: accepted in A\&

Lucky Imaging Adaptive Optics of the brown dwarf binary GJ569Bab

The potential of combining Adaptive Optics (AO) and Lucky Imaging (LI) to achieve high precision astrometry and differential photometry in the optical is investigated by conducting observations of the close 0\farcs1 brown dwarf binary GJ569Bab. We took 50000 $I$-band images with our LI instrument FastCam attached to NAOMI, the 4.2-m William Herschel Telescope (WHT) AO facility. In order to extract the most of the astrometry and photometry of the GJ569Bab system we have resorted to a PSF fitting technique using the primary star GJ569A as a suitable PSF reference which exhibits an $I$-band magnitude of $7.78\pm0.03$. The AO+LI observations at WHT were able to resolve the binary system GJ569Bab located at 4\farcs 92 \pm 0\farcs05 from GJ569A. We measure a separation of $98.4 \pm 1.1$ mas and $I$-band magnitudes of $13.86 \pm 0.03$ and $14.48 \pm 0.03$ and $I-J$ colors of 2.72$\pm$0.08 and 2.83$\pm$0.08 for the Ba and Bb components, respectively. Our study rules out the presence of any other companion to GJ569A down to magnitude I$\sim$ 17 at distances larger than 1\arcsec. The $I-J$ colors measured are consistent with M8.5-M9 spectral types for the Ba and Bb components. The available dynamical, photometric and spectroscopic data are consistent with a binary system with Ba being slightly (10-20%) more massive than Bb. We obtain new orbital parameters which are in good agreement with those in the literature.Comment: 13 pages, 9 figures, 7 tables, in press in MNRA

Niveles de colinesterasa sérica en caficultores del Departamento de Caldas, Colombia

Objetivo Determinar niveles de colinesterasa sérica en caficultores del departamento de Caldas y su asociación con factores demográficos y ocupacionales.Metodología Se realizó un estudio descriptivo, muestra de 1 098 agricultores del Alto Oriente y Centro Sur del Departamento de Caldas, por medio de una encuesta en la que se analizaron características del trabajador agrícola de tipo: sociodemográfico, ocupacional, clínicos y concentración de colinesterasa determinada con el método de Ellman.Resultados A nivel ocupacional, el 90,8 % de los agriculto es refirió riesgo de exposición directa a plaguicidas. El 3,8 % de las determinaciones analíticas de colinesterasa fueron anormales, se relacionó que el 75,6 % de los agricultores preparan la mezcladel insecticida, el 22,2 % tienen una frecuencia de aplicación en el cultivo más de dos veces por semana, el 37,8 % no emplea ropa de protección durante la jornada de fumigación. El tiempo de la última aplicación fue dentro del rango de uno a diez días demostrando que a menor tiempo de aplicación del insecticida, se presenta mayorinhibición de la enzima. Los plaguicidas más reportados fueron los de tipo organofosforado (58,6 %).Conclusiones El control de la exposición a plaguicidas se torna difícil porque la mayoría de trabajadores son de tipo informal. Se requiere fortalecer los programas de capacitación y campañas de sensibilización sobre los efectos de los plaguicidas en la salud, las medidas de higiene y seguridad en el trabajo. Los niveles bajos de colinesterasa sérica indican la absorción de una cantidad mínima de insecticidas inhibidores de la colinesterasa.Objective To determine the levels of serum cholinesterase in coffee growers from the Caldas department and its association with demographic and labor factors.Methodology A descriptive study was carried out in a sample of 1 098 farmers from the Upper East and South Center of the Caldas department, through a survey that analyzed characteristics such as sociodemographic, labor, and clinical conditions, as well as cholinesterase levels, determined by Ellman's method.Results Regarding the occupational aspect, 90.8 % of farmers reported a risk of direct exposure to pesticides. 3.8 % of the analytical determinations of cholinesterase were abnormal, which was related to the fact that 75.6 % of the farmers themselves prepare the mixture of the insecticide, 22.2 % spread the insecticide over their crops more thantwice a week, and 37.8 % do not wear protective clothing during the fumigation. The last fumigation was within the range of one to ten days, revealing that the shorter the time of application of the insecticide, the greater the inhibition of the enzyme. The mostfrequent pesticides were organophosphates (58.6 %).ConclusionsControlling pesticide exposure is difficult because most workers are self-employed. It is necessary to strengthen training programs and awareness campaigns regarding the effect of pesticides on health, as well as health and safety measures at the workplace. Low levelsof serum cholinesterase indicate the bsorption of a minimal amount of cholinesterase inhibiting insecticides

Constraining the X-ray reflection in low accretion rate AGN using XMM-Newton, NuSTAR and Swift

An interesting feature in active galactic nuclei (AGN) accreting at low rate is the weakness of the reflection features in their X-ray spectra, which can result from the gradual disappearance of the torus with decreasing accretion rates. It has been suggested that low luminosity AGN (LLAGN) would have a different reflector configuration compared with high luminosity AGN, either covering a smaller fraction of the sky or simply having less material. Additionally, we note that the determination of the spectral index ($\Gamma$) and the cut-off energy of the primary power-law emission is affected by the inclusion of reflection models, showing the importance of using them to study the accretion mechanism, especially in the case of the LLAGN that have previously shown a high dispersion on the relation between $\Gamma$ and the accretion rate. Our purpose is to constrain the geometry and column density of the reflector in a sample of LLAGN covering a broad X-ray range of energy combining data from XMM-Newton + NuSTAR + Swift of a hard X-ray-flux limited sample of 17 LLAGN from BASS/DR2 with accretion rates $\lambda_{Edd}$=L$_{\rm Bol}$/L$_{\rm Edd}$<10$^{-3}$. We fit all spectra using the reflection model for torus (borus02) and accretion disk (Xillver) reflectors. We found a tentative correlation between the torus column density and the accretion rate, LLAGN shows a lower column density compared with the high-luminosity objects. We also confirm the relation between $\Gamma$ and $\lambda_{Edd}$, with a smaller scatter than previously reported, thanks to the inclusion of high-energy data and the reflection models. Our results are consistent with a break at $\lambda_{Edd}\sim10^{-3}$, suggestive of a different accretion mechanism compared with higher accretion AGN.Comment: Accepted for publication in Astronomy & Astrophysic

Situación actual del estudiante de Medicina en Colombia

The essence of Medicine is service to the human being, and its teaching is carried out through the clinical method and a set of skills that the student must acquire throughout his training. However, it is possible that there is a pedagogical problem in the current model that makes doctors and students feel dissatisfied with their academic process, affecting their professional lives. The purpose of this review is to present some aspects that are experienced as a medical student in Colombia, the implications that the use of technology has had in medical training, and its impact on work and academic life.La esencia de la Medicina es el servicio al ser humano, y su enseñanza se realiza por medio del método clínico y un conjunto de habilidades que el estudiante debe adquirir durante toda su formación. Sin embargo, es posible que haya un problema pedagógico en el modelo actual que hace que los médicos y estudiantes se sientan insatisfechos con su proceso académico, repercutiendo en su vida profesional. El propósito de esta revisión es dar a conocer algunos aspectos que se viven como estudiante de Medicina en Colombia, las implicaciones que ha tenido el uso de la tecnología en la formación médica, y su repercusión en la vida laboral y académica

Point-occurrence self-similarity in crackling-noise systems and in other complex systems

It has been recently found that a number of systems displaying crackling noise also show a remarkable behavior regarding the temporal occurrence of successive events versus their size: a scaling law for the probability distributions of waiting times as a function of a minimum size is fulfilled, signaling the existence on those systems of self-similarity in time-size. This property is also present in some non-crackling systems. Here, the uncommon character of the scaling law is illustrated with simple marked renewal processes, built by definition with no correlations. Whereas processes with a finite mean waiting time do not fulfill a scaling law in general and tend towards a Poisson process in the limit of very high sizes, processes without a finite mean tend to another class of distributions, characterized by double power-law waiting-time densities. This is somehow reminiscent of the generalized central limit theorem. A model with short-range correlations is not able to escape from the attraction of those limit distributions. A discussion on open problems in the modeling of these properties is provided.Comment: Submitted to J. Stat. Mech. for the proceedings of UPON 2008 (Lyon), topic: crackling nois

New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster

(Abridged) The nature of S Ori 70, a faint mid-T type object found towards the direction of the young sigma Orionis cluster, is still under debate. We intend to disentangle whether it is a field brown dwarf or a 3-Myr old planetary-mass member of the cluster. We report on near-infrared JHK_s and mid-infrared [3.6] and [4.5] IRAC/Spitzer photometry recently obtained for S Ori 70. The new near-infrared images (taken 3.82 yr after the discovery data) have allowed us to derive a very small proper motion (11.0 +/- 5.9 mas/yr) for this object, which is consistent with the proper motion of the cluster within 1.5 sigma the astrometric uncertainty. The colors (H-K_s), (J-K_s) and K_s-[3.6] appear discrepant when compared to T4-T7 dwarfs in the field. This behavior could be ascribed to a low-gravity atmosphere or alternatively to an atmosphere with a metallicity significantly different than solar. Taking into account the small proper motion of S Ori 70 and its new near- and mid-infrared colors, a low-gravity atmosphere remains as the most likely explanation to account for our observations. This supports S Ori 70's membership in sigma Orionis, with an estimated mass in the interval 2-7 Mjup, in agreement with our previous derivation.Comment: Accepted for publication in A&

Candidate free-floating super-Jupiters in the young sigma Orionis open cluster

Free-floating substellar candidates with estimated theoretical masses of as low as ~5 Jupiter masses have been found in the ~3 Myr old sigma Orionis open cluster. As the overlap with the planetary mass domain increases, the question of how these objects form becomes important. The determination of their number density and whether a mass cut-off limit exists is crucial to understanding their formation. We propose to search for objects of yet lower masses in the cluster and determine the shape of the mass function at low mass. Using new- and (re-analysed) published IZJHKs[3.6]-[8.0]-band data of an area of 840 arcmin2, we performed a search for LT-type cluster member candidates in the magnitude range J=19.5-21.5 mag, based on their expected magnitudes and colours. Besides recovering the T type object S Ori 70 and two other known objects, we find three new cluster member candidates, S Ori 72-74, with J=21 mag and within 12 arcmin of the cluster centre. They have theoretical masses of 4 (-2,+3) M_Jup and are among the least massive free-floating objects detected by direct imaging outside the Solar System. The photometry in archival Spitzer [3.6]-[5.8]-band images infers that S Ori 72 is an L/T transition candidate and S Ori 73 a T-type candidate, following the expected cluster sequence in the mid-infrared. Finally, the L-type candidate S Ori 74 with lower quality photometry is located at 11.8 arcsec (~4250 AU) of a stellar member of sigma Orionis and could be a companion. After contaminant correction in the area complete to J=21.1 mag, we estimate that there remain between zero and two cluster members in the mass interval 6-4 M_Jup. Our result suggests a possible turnover in the substellar mass spectrum below ~6 Jupiter masses, which could be investigated further by wider and deeper photometric surveys.Comment: 15 pages, 13 figures, 5 tables, and appendix containing 5 figures; accepted for publication in AA; v2: 2 minor corrections, in abstract and sect. 2.

A long-period massive planet around HD106515A

We have performed RV monitoring of the components of the binary system HD 106515 over about 11 years using the high resolution spectrograph SARG at TNG. The primary shows long-period radial velocity variations that indicate the presence of a low mass companion whose projected mass is in the planetary regime (m sin i = 9.33 Mjup). The 9.8 years orbit results quite eccentric (e=0.57), as typical for massive giant planets. Our results confirm the preliminary announcement of the planet included in Mayor et al. (2011). The secondary instead does not show significant RV variations. The two components do not differ significantly in chemical composition, as found for other pairs for which one component hosts giant planets. Adaptive optics images obtained with AdOpt@TNG do not reveal additional stellar companions. From the analysis of the relative astrometry of the components of the wide pair we put an upper limit on the mass of the newly detected companion of about 0.25 Msun. State of art or near future instrumentation can provide true mass determination, thanks to the availability of the wide companion HD106515B as reference. Therefore, HD106515Ab will allow deeper insight in the transition region between planets and brown dwarfs.Comment: A&A, accepted, 8 pages, 10 figure