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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 11 to 12 of 12 (0.038 seconds)| 11 |
The Secret Lives of Cepheids: Evolutionary Changes and Pulsation-Induced Shock Heating in the Prototype Classical Cepheid δ CepEngle, Scott G., Guinan, Edward F., Harper, Graham M., Neilson, Hilding R., Evans, Nancy Remage 10 October 2014 (has links)
Over the past decade, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical Cepheids that are still not well understood. In this, the first of several planned papers on program Cepheids, we report the current results for δ Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for changes in the pulsation period, light-curve morphology, and amplitude. Combining our photometry with the times of maximum light compilation by Berdnikov et al. returns a small period change of dP/dt -0.1006 ± 0.0002 s yr-1. There is also evidence for a gradual light amplitude increase of 0.011 mag (V band) and 0.012 mag (B band) per decade over the last 50 years. In addition, Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV spectrophotometry and XMM-Newton X-ray data were carried out to investigate the high-temperature plasmas present above the Cepheid photospheres. In total, from the five visits (eight exposures) with XMM-Newton, δ Cep is found to be a soft X-ray source (L X(0.3-2 keV) 4.5-13 × 1028erg s-1) with peak flux at kT = 0.6-0.9 keV. The X-ray activity is found to vary, possibly in phase with the stellar pulsations. From 2010-2013, nine observations of δ Cep were carried out with HST-COS. The UV emissions are also variable and well phased with the stellar pulsations. Maximum UV line emissions occur near, or slightly before, maximum optical light, varying by as much as 20 times. This variability shows that pulsation-induced shock heating plays a significant role in Cepheid atmospheres, possibly in addition to a quiescent, magnetic heating. The results of this study show Cepheid atmospheres to be rather complex and dynamic.
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The Pleiadic Age of Stuart Poesie: Restoration Uranography, Dryden's Judicial Astrology, and the Fate of Anne KilligrewBrown, Morgan Alexander 30 April 2010 (has links)
The following Thesis is a survey of seventeenth-century uranography, with specific focus on the use of the Pleiades and Charles's Wain by English poets and pageant writers as astrological ciphers for the Stuart dynasty (1603-1649; 1660-1688). I then use that survey to address the problem of irony in John Dryden's 1685 Pindaric elegy, "To the Pious Memory of Mrs. Anne Killigrew," since the longstanding notion of what the Pleiades signify in Dryden's ode is problematic from an astronomical and astrological perspective. In his elegiac ode, Dryden translates a young female artist to the Pleiades to actuate her apotheosis, not for the sake of mere fulsome hypberbole, but in such a way that Anne (b. 1660-d. 1685) signifies for the reign of Charles II (1660-1685) in her Pleiadic catasterism. The political underpinnings of Killigrew's apotheosis reduce the probability that Dryden's hyperbole reserves pejorative ironic potential.
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