20,670 research outputs found

    Interferometric Studies of the extreme binary, ϵ\epsilon Aurigae: Pre-eclipse Observations

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    We report new and archival K-band interferometric uniform disk diameters obtained with the Palomar Testbed Interferometer for the eclipsing binary star ϵ\epsilon Aurigae, in advance of the start of its eclipse in 2009. The observations were inteded to test whether low amplitude variations in the system are connected with the F supergiant star (primary), or with the intersystem material connecting the star with the enormous dark disk (secondary) inferred to cause the eclipses. Cepheid-like radial pulsations of the F star are not detected, nor do we find evidence for proposed 6% per decade shrinkage of the F star. The measured 2.27 +/- 0.11 milli-arcsecond K band diameter is consistent with a 300 times solar radius F supergiant star at the Hipparcos distance of 625 pc. These results provide an improved context for observations during the 2009-2011 eclipse.Comment: Accepted for Ap.J. Letters, Oct. 200

    A Simple Non-equilibrium Feedback Model for Galaxy-Scale Star Formation: Delayed Feedback and SFR Scatter

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    We explore a class of simple non-equilibrium star formation models within the framework of a feedback-regulated model of the ISM, applicable to kiloparsec-scale resolved star formation relations (e.g. Kennicutt-Schmidt). Combining a Toomre-Q-dependent local star formation efficiency per free-fall time with a model for delayed feedback, we are able to match the normalization and scatter of resolved star formation scaling relations. In particular, this simple model suggests that large (∼\simdex) variations in star formation rates (SFRs) on kiloparsec scales may be due to the fact that supernova feedback is not instantaneous following star formation. The scatter in SFRs at constant gas surface density in a galaxy then depends on the properties of feedback and when we observe its star-forming regions at various points throughout their collapse/star formation "cycles". This has the following important observational consequences: (1) the scatter and normalization of the Kennicutt-Schmidt relation are relatively insensitive to the local (small-scale) star formation efficiency, (2) but gas depletion times and velocity dispersions are; (3) the scatter in and normalization of the Kennicutt-Schmidt relation is a sensitive probe of the feedback timescale and strength; (4) even in a model where Q~gas\tilde Q_{\rm gas} deterministically dictates star formation locally, time evolution, variation in local conditions (e.g., gas fractions and dynamical times), and variations between galaxies can destroy much of the observable correlation between SFR and Q~gas\tilde Q_{\rm gas} in resolved galaxy surveys. Additionally, this model exhibits large scatter in SFRs at low gas surface densities, in agreement with observations of flat outer HI disk velocity dispersion profiles.Comment: 15 pages, 6 figures, accepted by MNRAS (04/25/2019

    Postal Bodies: Imagining Communication Infrastructures in Nineteenth-Century Literature

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    This thesis uncovers material and metaphorical bodily encounters with postal infrastructures in the nineteenth-century. As the Post Office expanded in the nineteenth century, particularly with the advent of uniform penny postage in 1840, infrastructures, such as sorting houses, Travelling Post Offices and steam packets, had a profound impact on British Victorians’ engagements with and imaginings of the Post Office. In this thesis, I place original emphasis on ‘postal bodies’, demonstrating that postal infrastructures were embodied by both those who worked on and used them. In doing so, I intervene in and complicate scholarship that has invested in the Victorian postal mythology of speed, mechanisation and disembodiment, and rethink the role of one of the key institutions of Victorian Britain in the literary imagination. By reinserting the cultural importance of the postal body into the scholarly picture, ‘Postal Bodies: Imagining Communication Infrastructures in Nineteenth-Century Literature’ argues that these infrastructures were interactive and shaped by the messiness of bodily exchange. Underpinned by literary readings, non-literary sources, and archival research, as well as theories of infrastructures and mobility, I demonstrate that these expanding postal infrastructures shaped, and were shaped by, the bodies that facilitated and utilised them. As the complex infrastructures of postal exchange were employed by nineteenth-century authors, such as Mary Elizabeth Braddon, Wilkie Collins, Charles Dickens, Anthony Trollope, and Hesba Stretton, they become imagined, negotiated, and subverted, through postal bodies. This thesis places the question of embodied representation at the centre of its analysis, and, in doing so, provides new insights into the multiplicity and heterogeneity of embodied experiences of the mail, from labour intensive sorting and mail running, to rapid transit on the mail train and international steam packet lines.Arts and Humanities Research Council (AHRC
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