672 research outputs found

    Time domain period determination techniques

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    Two simple period determination schemes are discussed. They are well suited to problems involving non-sinusoidal periodic phenomena sampled at a few irregularly spaced points. Statistical properties are discussed. The techniques are applied to the double mode Cepheids BK Cen and TU Cas as test cases

    Stepping Beyond the Veil and Breaking the Pittsburgh Cycle: The American Dream, Otherness, and Generational Trauma in August Wilson\u27s Cycle Plays

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    August Wilson’s Pittsburgh Cycle is a series of ten plays that aims to “amend, to explore, and to add to our African consciousness and our African aesthetic” (Wilson qtd. in Gantt 5). Each play is set in a different decade but all share incredibly similar protagonists; all of them are African American men in their mid to late adulthood. The stories are separated by years but all articulate the generational trauma embedded in the African American consciousness in the twentieth century. Wilson’s plays span between the generations of African Americans living in the wake of the Emancipation Proclamation to a group of men living at the start of the new millennium. Each character deals with the struggles of his given time period, but they all experience some form of generational trauma. An essential part of each characters’ psyche is torn between their African and their American identities, a psychological phenomenon W.E.B. DuBois calls “double consciousness.” Their American identity pushes them to fulfill their role as the provider, embracing notions of masculinity and the capitalist influence of the “American Dream,” but it is their African identity that prevents them from flourishing in the white American society. They must work to succeed in spite of their identities, crafting their mannerisms and behavior in the form of the “White Man.” These men are also deeply traumatized by their relationships with their fathers. Each man struggles with what Freud would call an Oedipal Complex, attempting to fulfill the paternal role that their fathers failed in. To their own dismay, the generational trauma has already been transposed upon them: they cannot fulfill their fiscal role as the American man because of their blackness. In turn, these men become frustrated, paranoid, anxious, and deeply sad; their self-imposed deficiency separates them from their family, pushing them away from their sons and wives, thereby perpetuating the generational cycle. The Pittsburgh Cycle is truly a cycle of the effects of DuBois’s double-consciousness, demonstrating that these men are always tied to their blackness and the discrimination that is embedded within it

    Search for a circum-planetary material and orbital period variations of short-period Kepler exoplanet candidates

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    A unique short-period Mercury-size Kepler exoplanet candidate KIC012557548b has been discovered recently by Rappaport et al. (2012). This object is a transiting disintegrating exoplanet with a circum-planetary material - comet-like tail. Close-in exoplanets, like KIC012557548b, are subjected to the greatest planet-star interactions. This interaction may have various forms. In certain cases it may cause formation of the comet-like tail. Strong interaction with the host star, and/or presence of an additional planet may lead to variations in the orbital period of the planet. Our main aim is to search for comet-like tails similar to KIC012557548b and for long-term orbital period variations. We are curious about frequency of comet-like tail formation among short-period Kepler exoplanet candidates. We concentrate on a sample of 20 close-in candidates with a period similar to KIC012557548b from the Kepler mission.Comment: 19 pages, 75 figures, AN accepte

    On the Impact of Helium Content on the RR Lyrae Distance Scale

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    Indexación: Scopus.We constructed new sets of He-enhanced (Y = 0.30, Y = 0.40) nonlinear, time-dependent convective hydrodynamical models of RR Lyrae (RRL) stars covering a broad range in metal abundances (Z = 0.0001-0.02). The increase in He content from the canonical value (Y = 0.245) to Y = 0.30-0.40 causes a simultaneous increase in stellar luminosity and in pulsation period. To investigate the dependence of the RRL distance scale on the He abundance, we computed new optical (RI) and near-infrared (JHK) Period-luminosity-metallicity-helium relations. Interestingly enough, the increase in He content causes a minimal change in the coefficients of both period and metallicity terms, since canonical and He-enhanced models obey similar PLZ relations. On the contrary, the classical B-And V-band mean magnitude metallicity relations and the R-band PLZ relation display a significant dependence on the He content. The He-enhanced models are, at fixed metal content, 0.2-0.5 mag brighter than canonical ones. This variation is only marginally affected by evolutionary effects. The quoted distance diagnostics once calibrated with trigonometric parallaxes (Gaia) will provide the opportunity to estimate the He content of field and cluster RRLs. Moreover, the use of either spectroscopic or photometric metal abundances will pave the way to new empirical constraints on the universality of the helium-To-metal enrichment ratio in old (t10 Gyr) stellar tracers. © 2018. The American Astronomical Society. All rights reserved.https://iopscience.iop.org/article/10.3847/2041-8213/aada1

    Second Overtone Pulsators Among Delta Scuti Stars

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    We investigate the modal stability of stellar models at masses and luminosity levels corresponding to post main sequence luminous delta scuti pulsators. The envelope models have been computed at fixed mass value, luminosity level and chemical composition (Y=0.28, Z=0.02). According to a nonlinear approach to radial oscillations the present investigation predicts the occurrence of stable second overtone pulsators for the first time. The shape of both light and velocity curves are presented and discussed, providing a useful tool for the identification of second overtone pulsators among the known groups of radially pulsating stars. The period ratios of mixed mode pulsators obtained by perturbing the first and the second overtone radial eigenfunctions are in agreement with observative values. Finally, the physical structure and the dynamical properties of second overtone pulsators are discussed in detail. The role played by the nodal lines in the destabilization of second overtone pulsators is also pointed out.Comment: 20 pages, 11 Postscript figures, uses aaspp4.sty and tighten.st
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