In-Situ Particle Acceleration in Extragalactic Radio Hot Spots: Observations Meet Expectations

We discuss, in terms of particle acceleration, the results from optical VLT observations of hot spots associated with radio galaxies. On the basis of observational and theoretical grounds, it is shown that: 1. relatively low radio-radio power hot spots are the optimum candidates for being detected at optical waves. This is supported by an unprecedented optical detection rate of 70% out of a sample of low radio power hot spots. 2. the shape of the synchrotron spectrum of hot spots is mainly determined by the strength of the magnetic field in the region. In particular, the break frequency, related to the age of the oldest electrons in the hot spots, is found to increase with decreasing synchrotron power and magnetic field strength. Both observational results are in agreement with an in-situ particle acceleration scenario.Comment: 5 pages, TeX (or Latex, etc), 4 figures, to appear in MNRAS Letter, Updated reference

ALMA polarization observations of the particle accelerators in the hot spot of the radio galaxy 3C 445

We present Atacama Large Millimeter Array (ALMA) polarization observations at 97.5 GHz of the southern hot spot of the radio galaxy 3C 445. The hot spot structure is dominated by two bright components enshrouded by diffuse emission. Both components show fractional polarization between 30 and 40 per cent, suggesting the presence of shocks. The polarized emission of the western component has a displacement of about 0.5 kpc outward with respect to the total intensity emission, and may trace the surface of a front shock. Strong polarization is observed in a thin strip marking the ridge of the hot spot structure visible from radio to optical. No significant polarization is detected in the diffuse emission between the main components, suggesting a highly disordered magnetic field likely produced by turbulence and instabilities in the downstream region that may be at the origin of the extended optical emission observed in this hot spot. The polarization properties support a scenario in which a combination of both multiple and intermittent shock fronts due to jet dithering, and spatially distributed stochastic second-order Fermi acceleration processes are present in the hot spot complex.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Lette

Conservacion de objetos expuestos a la luz y la influencia del medio ambiente en la conservacion del patrimonio

Este trabajo se basa en una observación museológica hacia la forma en que ciertos objetos están expuestos a la luz natural o artificial, sobre todo en los Museos de carácter histórico- ambientales. En nuestra circunstancia socio-cultural actual, es imprescindible una reflexión profunda respecto a la conservación del patrimonio. Muchas veces les damos distintas escalas de valores al patrimonio y nos olvidamos de las pequeñas cosas, que también hacen a la trascendencia de un hombre y/o de una circunstancia cultural de una región en una determinada época. (C. Moreno, 2000). (Párrafo extraído del texto a modo de resumen)</i

Antecedentes y relevamiento edilicio de la igliesia catedral de Quilmes-pcia. Bs. As

La restauración del patrimonio cultural arquitectónico argentino como mundial es una problemática muy común en nuestros días. Tanto la conservación como la restauración son conjunto de acciones mediante las cuales se intenta lograr la supervivencia y preservación en toda su integridad y autenticidad, promoviendo la mínima intervención y trabajando sobre el ambiente que rodea a los bienes, básicamente a través del control de humedad relativa, temperatura, luz, polución, higiene y educación de la sociedad en general y de las personas a cargo o en contacto de dicho patrimonio. Debiendo dejar registrado tanto su investigación como controles. La Iglesia Catedral de Quilmes que conocemos hoy (sito en la ciudad de Quilmes), paso de ser una sencilla y humilde capilla de adobe y techo de paja fundada en 1666 a una construcción de ladrillos (desde 1863), con múltiples intervenciones en su haber. El estudio y análisis realizados contribuye con su actividad multidisciplinaria a conocer y caracterizar la problemática presentada, tratando de concientizar y hacer revertir el tratamiento actual que se le está dando a dicho edificio de gran patrimonial tangible e intangible.Tópico 5.- Patrimonios Urbano, Rural, Industrial y Religioso. Cementerios Patrimoniales. Técnicas de Evaluación, Limpieza, Reparación y Conservación. Intervenciones en construcciones con patologías estructurales y aplicación de refuerzos

Convective line shifts for the Gaia RVS from the CIFIST 3D model atmosphere grid

To derive space velocities of stars along the line of sight from wavelength shifts in stellar spectra requires accounting for a number of second-order effects. For most stars, gravitational redshifts, convective blueshifts, and transverse stellar motion are the dominant contributors. We provide theoretical corrections for the net velocity shifts due to convection expected for the measurements from the Gaia Radial Velocity Spectrometer (RVS). We used a set of three-dimensional time-dependent simulations of stellar surface convection computed with CO5BOLD to calculate spectra of late-type stars in the Gaia RVS range and to infer the net velocity offset that convective motions will induce in radial velocities derived by cross-correlation. The net velocity shifts derived by cross-correlation depend both on the wavelength range and spectral resolution of the observations. Convective shifts for Gaia RVS observations are less than 0.1 km/s for late-K-type stars, and they increase with stellar mass, reaching about 0.3 km/s or more for early F-type dwarfs. This tendency is the result of an increase with effective temperature in both temperature and velocity fluctuations in the line-forming region. Our simulations also indicate that the net RVS convective shifts can be positive (i.e. redshifts) in some cases. Overall, the blueshifts weaken slightly with increasing surface gravity, and are enhanced at low metallicity. Gravitational redshifts amount up to 0.7 km/s and dominate convective blueshifts for dwarfs, but become much weaker for giants.Comment: 13 pages, to appear in A&A; model fluxes available from ftp://leda.as.utexas.edu/pub/callende/Gaia3D and soon from CD

Image Slicer Performances from a Demonstrator for the SNAP/JDEM Mission - Part I: Wavelength Accuracy

A well-adapted visible and infrared spectrograph has been developed for the SNAP (SuperNova/Acceleration Probe) experiment proposed for JDEM. The instrument should have a high sensitivity to see faint supernovae but also a good redshift determination better than 0.003(1+z) and a precise spectrophotometry (2%). An instrument based on an integral field method with the powerful concept of imager slicing has been designed. A large prototyping effort has been performed in France which validates the concept. In particular a demonstrator reproducing the full optical configuration has been built and tested to prove the optical performances both in the visible and in the near infrared range. This paper is the first of two papers. The present paper focus on the wavelength measurement while the second one will present the spectrophotometric performances. We adress here the spectral accuracy expected both in the visible and in the near infrared range in such configuration and we demonstrate, in particular, that the image slicer enhances the instrumental performances in the spectral measurement precision by removing the slit effect. This work is supported in France by CNRS/INSU/IN2P3 and by the French spatial agency (CNES) and in US by the University of California.Comment: Submitted to PAS

Accounting for Convective Blue-Shifts in the Determination of Absolute Stellar Radial Velocities

For late-type non-active stars, gravitational redshifts and convective blueshifts are the main source of biases in the determination of radial velocities. If ignored, these effects can introduce systematic errors of the order of ~ 0.5 km/s. We demonstrate that three-dimensional hydrodynamical simulations of solar surface convection can be used to predict the convective blue-shifts of weak spectral lines in solar-like stars to ~ 0.070 km/s. Using accurate trigonometric parallaxes and stellar evolution models, the gravitational redshifts can be constrained with a similar uncertainty, leading to absolute radial velocities accurate to better than ~ 0.1 km/s.Comment: To appear in the proceedings of the Joint Discussion 10, IAU General Assembly, Rio de Janeiro, August 10-11, 200

Mechanistic and pathological study of the genesis, growth, and rupture of abdominal aortic aneurysms

Postprint (published version