The gaseous extent of galaxies and the origin of Lyman alpha absorption systems. IV: Lyman alpha absorbers arising in a galaxy group

We present new GHRS observations of Lyman alpha absorption lines associated with a group of galaxies towards the QSO 1545+2101. We have identified eight distinct Lyman alpha absorption features in the spectrum of QSO 1545+2101 at a mean redshift of z=0.2648 with a velocity dispersion of 163 km/s. A group of galaxies is detected in the vicinity of this QSO at a mean redshift of z=0.2645 and velocity dispersion 239 km/s. The identification of discrete absorption systems indicates that they arise in clouds of neutral hydrogen rather than in a diffuse intragroup medium. Our analysis suggests that the Lyman alpha absorption lines are associated with individual galaxies in the group, although a one-to-one relationship between absorbers and galaxies is difficult to establish in such a dense environment.Comment: 16 pages, 3 figures. Accepted for publication in Ap

Linfoma epidural : un caso clínico

Presentamos un caso clínico de linfoma extranodal con afección neurológica y ocula

A new hydrodynamic spherical accretion exact solution and its quasi-spherical perturbations

We present an exact $\gamma=5/3$ spherical accretion solution which modifies the Bondi boundary condition of $\rho \to const.$ as $r\to \infty$ to $\rho \to 0$ as $r \to \infty$. This change allows for simple power law solutions on the density and infall velocity fields, ranging from a cold empty free-fall condition where pressure tends to zero, to a hot hydrostatic equilibrium limit with no infall velocity. As in the case of the Bondi solution, a maximum accretion rate appears. As in the $\gamma=5/3$ case of the Bondi solution, no sonic radius appears, this time however, because the flow is always characterised by a constant Mach number. This number equals 1 for the case of the maximum accretion rate, diverges towards the cold empty state, and becomes subsonic towards the hydrostatic equilibrium limit. It can be shown that in the limit as { $r \to 0$}, the Bondi solution tends to the new solution presented, { extending the validity of the Bondi accretion value to} cases where the accretion density profile does not remain at a fixed constant value out to infinity. We then explore small deviations from sphericity and the presence of angular momentum through an analytic perturbative analysis. Such perturbed solutions yield a rich phenomenology through density and velocity fields in terms of Legendre polynomials, which we begin to explore for simple angular velocity boundary conditions having zeros on the plane and pole. The new solution presented provides complementary physical insight into accretion problems in general.Comment: Accepted for publication in the ApJ. 10 figures, extended comparison to observations and first numerical tests include

Prótesis de rodilla externa mecatrónica

Se diseña un mecanismo de articulación de rodilla para una prótesis externa, es decir el prototipo puede ser usado en personas con amputaciones del tipo transfemoral, con el fin de contribuir a la sociedad al brindar soluciones a favor de las personas con capacidades especiales. Se toma en consideración los aspectos más relevantes para el desarrollo de la marcha humana protésica normal como son: nivel de actividad física, medidas antropométricas, materiales adecuados para la construcción, estabilidad y confort entre otros. Luego de realizar un análisis extensivo y proceso de diseño y rediseño se construyó un prototipo funcional, que en el futuro podrá ser probado en personas que así lo requieran.Peer Reviewe

On the correlation between Ca and Halpha solar emission and consequences for stellar activity observations

The correlation between Ca and Halpha chromospheric emission, known to be positive in the solar case, has been found to vary between -1 and 1 for other stars. Our objective is to understand the factors influencing this correlation in the solar case, and then to extrapolate our interpretation to other stars. We characterize the correlation between both types of emission in the solar case for different time scales. Then we determine the filling factors due to plages and filaments, and reconstruct the Ca and Halpha emission to test different physical conditions in terms of plage and filament contrasts. We have been able to precisely determine the correlation in the solar case as a function of the cycle phase. We interpret the results as reflecting the balance between the emission in plages and the absorption in filaments. We found that correlations close to zero or slightly negative can be obtained when considering the same spatio-temporal distribution of plages and filaments than on the sun but with greater contrast. However, with that assumption, correlations close to -1 cannot be obtained for example. Stars with a very low Halpha contrast in plages and filaments well correlated with plages could produce a correlation close to -1. This study opens new ways to study stellar activity, and provides a new diagnosis that will ultimately help to understand the magnetic configuration of stars other than the sun.Comment: 10 pages, 13 figures, accepted in Astronomy and Astrophysic

Statistical analysis of the gravitational anomaly in {\it Gaia} wide binaries

The exploration of the low acceleration $a<a_{0}$ regime, where $a_{0}=1.2 \times 10^{-10}$m s$^{-1}$ is the acceleration scale of MOND around which gravitational anomalies at galactic scale appear, has recently been extended to the much smaller mass and length scales of local wide binaries thanks to the availability of the {\it Gaia} catalogue. Statistical methods to test the underlying structure of gravity using large samples of such binary stars and dealing with the necessary presence of kinematic contaminants in such samples have also been presented. However, an alternative approach using binary samples carefully selected to avoid any such contaminants, and consequently much smaller samples, has been lacking a formal statistical development. In the interest of having independent high quality checks on the results of wide binary gravity tests, we here develop a formal statistical framework for treating small, clean, wide binary samples in the context of testing modifications to gravity of the form $G \to \gamma G$. The method is validated through extensive tests with synthetic data samples, and applied to recent {\it Gaia} DR3 binary star observational samples of relative velocities and internal separations on the plane of the sky, $v_{2D}$ and $r_{2D}$, respectively. Our final results for a high acceleration $r_{2D}<0.01$pc region are of $\gamma=1.000 \pm 0.096$, in full accordance with Newtonian expectations. For a low acceleration $r_{2D}>0.01$pc region however, we obtain $\gamma=1.512 \pm 0.199$, inconsistent with the Newtonian value of $\gamma=1$ at a $2.6 \sigma$ level, and much more indicative of MOND AQUAL predictions of close to $\gamma=1.4$.Comment: 13 pages, 11 figures, 2 table