A VLT/FLAMES survey for massive binaries in Westerlund 1. IV. Wd1-5 – binary product and a pre-supernova companion for the magnetar CXOU J1647-45?

Context. The first soft gamma-ray repeater was discovered over three decades ago, and was subsequently identified as a magnetar, a class of highly magnetised neutron star. It has been hypothesised that these stars power some of the brightest supernovae known, and that they may form the central engines of some long duration gamma-ray bursts. However there is currently no consenus on the formation channel(s) of these objects. Aims. The presence of a magnetar in the starburst cluster Westerlund 1 implies a progenitor with a mass ≥40 M⊙, which favours its formation in a binary that was disrupted at supernova. To test this hypothesis we conducted a search for the putative pre-SN companion. Methods. This was accomplished via a radial velocity survey to identify high-velocity runaways, with subsequent non-LTE model atmosphere analysis of the resultant candidate, Wd1-5. Results. Wd1-5 closely resembles the primaries in the short-period binaries, Wd1-13 and 44, suggesting a similar evolutionary history, although it currently appears single. It is overluminous for its spectroscopic mass and we find evidence of He- and N-enrichement, O-depletion, and critically C-enrichment, a combination of properties that is difficult to explain under single star evolutionary paradigms. We infer a pre-SN history for Wd1-5 which supposes an initial close binary comprising two stars of comparable (~ 41 M⊙ + 35 M⊙) masses. Efficient mass transfer from the initially more massive component leads to the mass-gainer evolving more rapidly, initiating luminous blue variable/common envelope evolution. Reverse, wind-driven mass transfer during its subsequent WC Wolf-Rayet phase leads to the carbon pollution of Wd1-5, before a type Ibc supernova disrupts the binary system. Under the assumption of a physical association between Wd1-5 and J1647-45, the secondary is identified as the magnetar progenitor; its common envelope evolutionary phase prevents spin-down of its core prior to SN and the seed magnetic field for the magnetar forms either in this phase or during the earlier episode of mass transfer in which it was spun-up. Conclusions. Our results suggest that binarity is a key ingredient in the formation of at least a subset of magnetars by preventing spin-down via core-coupling and potentially generating a seed magnetic field. The apparent formation of a magnetar in a Type Ibc supernova is consistent with recent suggestions that superluminous Type Ibc supernovae are powered by the rapid spin-down of these objects.

Validación del Cuestionario de evaluación de la calidad de cursos virtuales adaptado a MOOC

Los Massive Online Open Courses (MOOC) son una modalidad de formación virtual que está ya presente en el panorama educativo actual y que responde a una concepción determinada de e-learning. Las universidades están integrando como parte de su oferta formativa este tipo de formación o, al menos, se está debatiendo si se integra o no. Ante esto, se hace necesario calibrar cuáles deben ser sus características con el fin de configurar un tipo de formación virtual de calidad. Se considera que son necesarios instrumentos que avalen la calidad de los MOOC desde diferentes perspectivas, en este caso la pedagógica, ya que de ello dependerá el éxito y la consolidación de este tipo de e-learning. El objetivo del presente estudio ha sido, pues, validar un cuestionario para la evaluación pedagógica de los MOOC adaptando el cuestionario de evaluación de cursos virtuales (Arias, 2007). Se ha analizado la validez y fiabilidad de dicho cuestionario a través de un análisis factorial de componentes principales con rotación Varimax. Se concluye que bastaría con introducir adaptaciones en la relación de dimensiones propuestas en este cuestionario que tuviera en cuenta las especificidades de los MOOC, ya que estos no pueden analizarse única y exclusivamente desde la óptica general del e-learning anterior a los MOOC. Así, las dimensiones en las cuales se basa dicho cuestionario son: 1) la calidad de la comunicación y los elementos multimedia de los cursos masivos en línea; 2) la coherencia curricular de los cursos y el grado de adaptación al usuario y 3) la calidad de su planificación didáctica.