Instrumental polarisation at the Nasmyth focus of the E-ELT

The ~39-m European Extremely Large Telescope (E-ELT) will be the largest telescope ever built. This makes it particularly suitable for sensitive polarimetric observations, as polarimetry is a photon-starved technique. However, the telescope mirrors may severely limit the polarimetric accuracy of instruments on the Nasmyth platforms by creating instrumental polarisation and/or modifying the polarisation signal of the object. In this paper we characterise the polarisation effects of the two currently considered designs for the E-ELT Nasmyth ports as well as the effect of ageing of the mirrors. By means of the Mueller matrix formalism, we compute the response matrices of each mirror arrangement for a range of zenith angles and wavelengths. We then present two techniques to correct for these effects that require the addition of a modulating device at the polarisation-free intermediate focus that acts either as a switch or as a part of a two-stage modulator. We find that the values of instrumental polarisation, Stokes transmission reduction and cross- talk vary significantly with wavelength, and with pointing, for the lateral Nasmyth case, often exceeding the accuracy requirements for proposed polarimetric instruments. Realistic ageing effects of the mirrors after perfect calibration of these effects may cause polarimetric errors beyond the requirements. We show that the modulation approach with a polarimetric element located in the intermediate focus reduces the instrumental polarisation effects down to tolerable values, or even removes them altogether. The E-ELT will be suitable for sensitive and accurate polarimetry, provided frequent calibrations are carried out, or a dedicated polarimetric element is installed at the intermediate focus.Comment: Accepted for publication in A&

The Extreme Polarimeter: Design, Performance, First Results & Upgrades

Well over 700 exoplanets have been detected to date. Only a handful of these have been observed directly. Direct observation is extremely challenging due to the small separation and very large contrast involved. Imaging polarimetry offers a way to decrease the contrast between the unpolarized starlight and the light that has become linearly polarized after scattering by circumstellar material. This material can be the dust and debris found in circumstellar disks, but also the atmosphere or surface of an exoplanet. We present the design, calibration approach, polarimetric performance and sample observation results of the Extreme Polarimeter, an imaging polarimeter for the study of circumstellar environments in scattered light at visible wavelengths. The polarimeter uses the beam-exchange technique, in which the two orthogonal polarization states are imaged simultaneously and a polarization modulator swaps the polarization states of the two beams before the next image is taken. The instrument currently operates without the aid of Adaptive Optics. To reduce the effects of atmospheric seeing on the polarimetry, the images are taken at a frame rate of 35 fps, and large numbers of frames are combined to obtain the polarization images. Four successful observing runs have been performed using this instrument at the 4.2 m William Herschel Telescope on La Palma, targeting young stars with protoplanetary disks as well as evolved stars surrounded by dusty envelopes. In terms of fractional polarization, the instrument sensitivity is better than 10^-4. The contrast achieved between the central star and the circumstellar source is of the order 10^-6. We show that our calibration approach yields absolute polarization errors below 1%

Imaging polarimetry for the characterisation of exoplanets and protoplanetary discs : scientific and technical challenges

The study of exoplanets and the protoplanetary discs in which they form is a very challenging task. In this thesis we present several studies in which we investigate the potential of imaging polarimetry at visible and near-infrared wavelengths to reveal the characteristics of these objects and overcome the scientific and technical challenges involved.UBL - phd migration 201

Estudio del compartimento safeno como estructura de fijación, conexión y protección del sistema venoso superficial de miembros inferiores

El objetivo del siguiente trabajo fue estudiar en forma dinámica, mediante estudios de diagnósticos por imágenes, la existencia individual de los compartimentos safenos, separándolos del tejido celular subcutáneo que lo rodea y asignándoles una entidad anatómica y funcional.Facultad de Ciencias Médica

Evidence for the disintegration of KIC 12557548 b

Context. The Kepler object KIC 12557548 b is peculiar. It exhibits transit-like features every 15.7 hours that vary in depth between 0.2% and 1.2%. Rappaport et al. (2012) explain the observations in terms of a disintegrating, rocky planet that has a trailing cloud of dust created and constantly replenished by thermal surface erosion. The variability of the transit depth is then a consequence of changes in the cloud optical depth. Aims. We aim to validate the disintegrating-planet scenario by modeling the detailed shape of the observed light curve, and thereby constrain the cloud particle properties to better understand the nature of this intriguing object. Methods. We analysed the six publicly-available quarters of raw Kepler data, phase-folded the light curve and fitted it to a model for the trailing dust cloud. Constraints on the particle properties were investigated with a light-scattering code. Results. The light curve exhibits clear signatures of light scattering and absorption by dust, including a brightening in flux just before ingress correlated with the transit depth and explained by forward scattering, and an asymmetry in the transit light curve shape, which is easily reproduced by an exponentially decaying distribution of optically thin dust, with a typical grain size of 0.1 micron. Conclusions. Our quantitative analysis supports the hypothesis that the transit signal of KIC 12557548 b is due to a variable cloud of dust, most likely originating from a disintegrating object.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and Astrophysic

Estudio del compartimento safeno como estructura de fijación, conexión y protección del sistema venoso superficial de miembros inferiores

El objetivo del siguiente trabajo fue estudiar en forma dinámica, mediante estudios de diagnósticos por imágenes, la existencia individual de los compartimentos safenos, separándolos del tejido celular subcutáneo que lo rodea y asignándoles una entidad anatómica y funcional.Facultad de Ciencias Médica

Estudio del compartimento safeno como estructura de fijación, conexión y protección del sistema venoso superficial de miembros inferiores

El objetivo del siguiente trabajo fue estudiar en forma dinámica, mediante estudios de diagnósticos por imágenes, la existencia individual de los compartimentos safenos, separándolos del tejido celular subcutáneo que lo rodea y asignándoles una entidad anatómica y funcional.Facultad de Ciencias Médica

COMPORTAMIENTO AGRONOMICO DEL MAMON TAINUNG 01 EN FINCA DE PRODUCTOR BAJO LAS CONDICIONES DEL DEPARTAMENTO DE CORDILLERA

Con el objetivo de evaluar el comportamiento agronómico del mamón híbrido Tainung 01 en finca de productor, se condujo un experimento en el período de febrero de 2008 a marzo de 2009, en finca de productor en el municipio de Caacupé, departamento de Cordillera, Paraguay, ubicado aproximadamente a 25º 24' S y 57º 06' O y 228 msnm de altitud. La parcela experimental estuvo constituida por 100 plantas, de las cuales fueron seleccionadas después de la floración 20 plantas con flores hermafroditas para las evaluaciones. El sistema de riego fue por goteo. Los datos obtenidos fueron analizados mediante la estimación de la media poblacional de las variables medidas, con intervalo de confianza del 95 % de confiabilidad. Las medias obtenidas de las variables medidas fueron: altura de inserción del fruto de 0,85 m, diámetro de tallo de 9,54 cm, número de frutos por planta de 20,30; peso de fruto de 728,54 g, productividad por planta de 14,82 kg, longitud de fruto de 20,89 cm, diámetro de fruto de 9,16 cm; rendimiento de 24,69 t/ha y contenido de sólidos solubles totales de 14,21 ºBrix.

Electrochromic orbit control for smart-dust devices

Recent advances in MEMS (micro electromechanical systems) technology are leading to spacecraft which are the shape and size of computer chips, so-called SpaceChips, or ‘smart dust devices’. These devices can offer highly distributed sensing when used in future swarm applications. However, they currently lack a feasible strategy for active orbit control. This paper proposes an orbit control methodology for future SpaceChip devices which is based on exploiting the effects of solar radiation pressure using electrochromic coatings. The concept presented makes use of the high area-to-mass ratio of these devices, and consequently the large force exerted upon them by solar radiation pressure, to control their orbit evolution by altering their surface optical properties. The orbital evolution of Space Chips due to solar radiation pressure can be represented by a Hamiltonian system, allowing an analytic development of the control methodology. The motion in the orbital element phase space resembles that of a linear oscillator, which is used to formulate a switching control law. Additional perturbations and the effect of eclipses are accounted for by modifying the linearized equations of the secular change in orbital elements around an equilibrium point in the phase space of the problem. Finally, the effectiveness of the method is demonstrated in a test case scenario