The effect of magnetic activity on low-mass stars in eclipsing binaries

In recent years, analyses of eclipsing binary systems have unveiled differences between the observed fundamental properties of low-mass stars and those predicted by stellar structure models. Particularly, radius and effective temperatures computed from models are ~ 5-10% lower and ~ 3-5% higher than observed, respectively. These discrepancies have been attributed to different factors, notably to the high levels of magnetic activity present on these stars. In this paper, we test the effect of magnetic activity both on models and on the observational analysis of eclipsing binaries using a sample of such systems with accurate fundamental properties. Regarding stellar models, we have found that unrealistically high spot coverages need to be assumed to reproduce the observations. Tests considering metallicity effects and missing opacities on models indicate that these are not able to explain the radius discrepancies observed. With respect to the observations, we have tested the effect of several spot distributions on the light curve analysis. Our results show that spots cause systematic deviations on the stellar radii derived from light curve analysis when distributed mainly over the stellar poles. Assuming the existence of polar spots, overall agreement between models and observations is reached when ~ 35% spot coverage is considered on stellar models. Such spot coverage induces a systematic deviation in the radius determination from the light curve analysis of ~ 3% and is also compatible with the modulations observed on the light curves of these systems. Finally, we have found that the effect of activity or rotation on convective transport in partially radiative stars may also contribute to explain the differences seen in some of the systems with shorter orbital periods.Comment: 12 pages, 9 figures, accepted for publication in Ap

The Mass-Radius(-Rotation?) Relation for Low-Mass Stars

The fundamental properties of low-mass stars are not as well understood as those of their more massive counterparts. The best method for constraining these properties, especially masses and radii, is to study eclipsing binary systems, but only a small number of late-type (M0 or later) systems have been identified and well-characterized to date. We present the discovery and characterization of six new M dwarf eclipsing binary systems. The twelve stars in these eclipsing systems have masses spanning 0.38-0.59 Msun and orbital periods of 0.6--1.7 days, with typical uncertainties of ~0.3% in mass and 0.5--2.0% in radius. Combined with six known systems with high-precision measurements, our results reveal an intriguing trend in the low-mass regime. For stars with M=0.35-0.80 Msun, components in short-period binary systems (P<1 day; 12 stars) have radii which are inflated by up to 10% (mean=4.8+/-1.0%) with respect to evolutionary models for low-mass main-sequence stars, whereas components in longer-period systems (>1.5 days; 12 stars) tend to have smaller radii (mean=1.7+/-0.7%). This trend supports the hypothesis that short-period systems are inflated by the influence of the close companion, most likely because they are tidally locked into very high rotation speeds that enhance activity and inhibit convection. In summary, very close binary systems are not representative of typical M dwarfs, but our results for longer-period systems indicate that the evolutionary models are broadly valid in the M~0.35-0.80 Msun regime.Comment: Accepted to ApJ; 21 pages, 10 figures, 8 tables in emulateapj format. The full contents of Table 4 are included in the submission as tab4.tx

Frame construction in post-15M discourses

[Abstract] This paper offers an analysis of ideological discourse from a constructivist perspective, according to which reality is interpreted as the socially constructed product of different agents interacting on an individual, subjective basis in a particular socio-political context, and in relation to a specific social action. This theoretical and methodological approach also highlights the importance of the relationship between the field of discourse analysis and those of rhetoric and argumentation (and semiotics, where the discourse is multimodal), and complexity studies. The paper uses data from an ethnographic study of a social collective created a year before the 15M movement: the Cooperativa Integral Catalana (‘Catalan Integral Cooperative’), an eco-social economic initiative based on a new form of self-managed cooperativism

Entre el arraigo y la diáspora : una mirada a la literatura haitiana en francés

1 archivo PDF (11 páginas). fhtrigintaquattuorLa literatura americana, en su gran mayoría, tiene su base en un profundo sentimiento de nacionalismo. Un ejemplo de ello, es la literatura haitiana, donde los temas más recurrentes tienen que ver, de manera clara, en crear un sentimiento nacional y nacionalista en sus lectores. Podemos encontrar así una vasta producción literaria, que va desde inicios del siglo XIX donde el rasgo esencial son las múltiples manifestaciones de una literatura militante y de acción, estas llevada a cabo por un movimiento indigenista que intentaba reivindicar la pertenencia a una raza y a una cultura con arraigo a la tierra. Por otro lado, una producción literaria de calidad, que fue publicada en el extranjero desde las primeras décadas del siglo XX, donde si bien siguen inspirándose en temas vinculados con la tierra natal, su inmigración impuso una gama más amplia de preocupaciones inherentes al proceso de adaptación a su nuevo contexto

La construcción discursiva de una propuesta de desarrollo de las mujeres basada en las “economías y finanzas solidarias (en Ecuador)”

[Resumen] Este trabajo constituye la versión divulgativa del siguiente con carácter más académico: “Discourses of social change in contemporary democracies: The ideological construction of an Ecuadorian women’s group based on “solidarity economy and finance”, Text and Talk. An interdisciplinary Journal of Language, Discourse and Communication Studies (Mouton de Gruyter), 2012.Ministerio de Ciencia e Innovación; HUM2007-61936FIL

The discursive construction of a development project for women based on “solidarity economy and finance (in Ecuador)”

[Abstract] The present paper is the divulgative version of the following one (which has a more academic format): “Discourses of social change in contemporary democracies: The ideological construction of an Ecuadorian women’s group based on “solidarity economy and finance”, Text and Talk. An interdisciplinary Journal of Language, Discourse and Communication Studies (Mouton de Gruyter), 2012.Ministerio de Ciencia e Innovación; HUM2007-61936FIL

La perspectiva organizacional de los sistemas de información

Se desarrollan las razones que permiten aseverar que el sistema de información puede estudiarse desde una perspectiva organizacional y se plantean las diferentes aristas organizacionales que deben estudiarse los sistemas de información, así como su caracterización. En un tercer momento se presenta la metodología que se propone desde los estudios organizacionales para estudiar una organización, que en este caso se trata de la intervención organizacionalThis paper argues for the need of an organizational analysis of information systems and proposes a variety of organizational aspects that must be considered. It also presents the methodology to study organizations that has been put forward by organizational studies