Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries

Context. Classical supergiant X-ray binaries (SGXBs) and supergiant fast X-ray transients (SFXTs) are two types of high-mass X-ray binaries (HMXBs) that present similar donors but, at the same time, show very different behavior in the X-rays. The reason for this dichotomy of wind-fed HMXBs is still a matter of debate. Among the several explanations that have been proposed, some of them invoke specific stellar wind properties of the donor stars. Only dedicated empiric analysis of the donors’ stellar wind can provide the required information to accomplish an adequate test of these theories. However, such analyses are scarce. Aims. To close this gap, we perform a comparative analysis of the optical companion in two important systems: IGR J17544-2619 (SFXT) and Vela X-1 (SGXB). We analyze the spectra of each star in detail and derive their stellar and wind properties. As a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. Methods. We use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (NLTE) Potsdam Wolf-Rayet model atmosphere code. We derive the physical properties of the stars and their stellar winds, accounting for the influence of X-rays on the stellar winds. Results. We find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). The distance to the sources have been revised and also agree well with the estimations already available in the literature. In IGR J17544-2619 we are able to narrow the uncertainty to d = 3.0 ± 0.2 kpc. From the stellar radius of the donor and its X-ray behavior, the eccentricity of IGR J17544-2619 is constrained to e< 0.25. The derived chemical abundances point to certain mixing during the lifetime of the donors. An important difference between the stellar winds of the two stars is their terminal velocities (ν∞ = 1500 km s-1 in IGR J17544-2619 and ν∞ = 700 km s-1 in Vela X-1), which have important consequences on the X-ray luminosity of these sources. Conclusions. The donors of IGR J17544-2619 and Vela X-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. In addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. However, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the X-ray luminosity of the sources. This specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in Vela X-1, while it favors an inhibiting accretion mechanism in IGR J17544-2619. Our study demonstrates that the relative wind velocity is critical in class determination for the HMXBs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion to propeller regimes when combined with other parameters.

Significación de los relatos de ‘ağā’ib dentro de la riḥla de Ibn al-Ṣabbāḥ

La obra de Ibn al-Ṣabbāḥ concita en su interior diversos géneros, y en especial el género riḫla. Sin embargo, como toda obra árabe medieval, posee características de otros géneros, como el geográfico, el autobiográfico y, en el caso del presente estudio, reúne relatos de ‘ağā’ib o ‘maravillas”. El artículo muestra ejemplos de cómo el unicum titulado Niṣāb al-ajbār wa-taḏkirat al-ajyār recoge la tradición de la literatura de maravillas o de ‘ağā’ib de la literatura árabe clásica.

Plus ça change...Le renouvellement de la tradition chez Régine Robin, Dany Laferrière et Ying Chen

Cette thèse analyse la manifestation de la tradition dans certains textes des écrivains migrants au Québec, nommément La Québécoite et L’Immense fatigue des pierres de Régine Robin, Comment faire l’amour avec un nègre sans se fatiguer, Cette grenade dans la main du jeune nègre est-elle une arme ou un fruit ?, Pays sans chapeau et L’Énigme du retour de Dany Laferrière et, enfin L’Ingratitude et Immobile de Ying Chen. Les références à des récits, à des croyances et à des pratiques collectives qui se trouvent dans ces textes signalent une transformation de la transmission de l’héritage culturel d’une génération à l’autre. Afin de parvenir à une meilleure compréhension des liens entre la mémoire collective et la communauté culturelle se définissant dans le présent, je me sers du travail de folkloristes comme Alan Dundes, Simon Bronner et Richard Handler de même que des théories sur la faculté de la tradition proposées par Paul Ricœur, Walter Benjamin et Pierre Nora. Dans la première partie de la thèse, j’étudie l’imaginaire populaire du XIXe siècle et son incorporation dans la littérature canadienne-française de l’époque. Ensuite, j’analyse la remise en question de la tradition – de même que le rôle sous-jacent qu’elle continue de jouer, lors de la Révolution tranquille. Par rapport à ces deux périodes précédentes, l’usage du folklore chez les auteurs migrants laisse présager une nouvelle opération de la tradition dans un contexte où plusieurs groupes culturels se rencontrent. Dans un contexte pluraliste, l’idée de la communauté culturelle est fabriquée en fonction de notre appartenance à plusieurs groupes. Je m’intéresse à comment les gens qui habitent ensemble formulent des liens au passé même dans une situation dans laquelle ils ne partagent pas les mêmes rapports à la mémoire collective. Explorant le renouvellement, qui peut sembler paradoxal, de la tradition, je forme l’hypothèse qu’il est possible pour un groupe de se définir en fonction de valeurs culturelles puisées dans un passé collectif qui s’adaptent constamment à la réalité actuelle.

Overcoming performance and convergence issues of discrete transform based modeling of crosslinking classical and reversible deactivated radical polymerizations

Population balances of polymer species in terms 'of discrete transforms with respect to counts of groups lead to tractable first order partial differential equations when ali rate constants are independent of chain length and loop formation is negligible [l]. Average molecular weights in the absence ofgelation are long known to be readily found through integration of an initial value problem. The extension to size distribution prediction is also feasible, but its performance is often lower to the one provided by methods based upon real chain length domain [2]. Moreover, the absence ofagood starting procedure and a higher numerical sensitivity hás decisively impaired its application to non-linear reversibly deactivated polymerizations, namely NMRP [3].

The economic voter and economic crisis

Theories of economic voting have a long tradition in political science and continue to inspire a large group of scholars. Classical economic voting theory assumes a reward-and-punishment mechanism (Key, 1966). This mechanism implies that incumbents are more likely to stay in power under a good economy, but are cast out under a bad economy (Lewis-Beck and Stegmaier, 2000). The economy has repeatedly been shown to be a major determinant of electoral behavior (see especially the recent book by Duch and Stevenson, 2008), but the current economic crisis seems to provide a marked illustration of how the economy affects voting. In recent elections across the Western industrialized world, most ruling coalitions lost their majority. Opposition parties, on the other hand, whether right wing or left wing, have appeared to benefit from the economic downturn.

Statistical analysis of the goodness of classical factor analysis regression (CFAR) /

Cover title.

Biographical and bibliographical dictionary of the Italian humanists and of the world of classical scholarship in Italy, 1300-1800.

Vol. 6: Supplement. A-Z has half title: Dictionary of the Italian humanists.