24,799 research outputs found

    Modelling turbulent fluxes due to thermal convection in rectilinear shearing flow

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    We revisit a phenomenological description of turbulent thermal convection along the lines proposed originally by Gough (1965) in which eddies grow solely by extracting energy from the unstably stratified mean state and are subsequently destroyed by internal shear instability. This work is part of an ongoing investigation for finding a procedure to calculate the turbulent fluxes of heat and momentum in the presence of a shearing background flow in stars.Comment: 2 pages, 1 figure, accepted for publication in IAU Symposium 271 "Astrophysical Dynamics: From Galaxies to Stars", Nice, 201

    On the seismic age and heavy-element abundance of the Sun

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    We estimate the main-sequence age and heavy-element abundance of the Sun by means of an asteroseismic calibration of theoretical solar models using only low-degree acoustic modes from the BiSON. The method can therefore be applied also to other solar-type stars, such as those observed by the NASA satellite Kepler and the planned ground-based Danish-led SONG network. The age, 4.60+/-0.04 Gy, obtained with this new seismic method, is similar to, although somewhat greater than, today's commonly adopted values, and the surface heavy-element abundance by mass, Zs=0.0142+/-0.0005, lies between the values quoted recently by Asplund et al. (2009) and by Caffau et al. (2009). We stress that our best-fitting model is not a seismic model, but a theoretically evolved model of the Sun constructed with `standard' physics and calibrated against helioseismic data.Comment: 16 pages, 11 figures, 5 tables, accepted for publication in MNRA

    Progress report on solar age calibration

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    We report on an ongoing investigation into a seismic calibration of solar models designed for estimating the main-sequence age and a measure of the chemical abundances of the Sun. Only modes of low degree are employed, so that with appropriate modification the procedure could be applied to other stars. We have found that, as has been anticipated, a separation of the contributions to the seismic frequencies arising from the relatively smooth, glitch-free, background structure of the star and from glitches produced by helium ionization and the abrupt gradient change at the base of the convection zone renders the procedure more robust than earlier calibrations that fitted only raw frequencies to glitch-free asymptotics. As in the past, we use asymptotic analysis to design seismic signatures that are, to the best of our ability, contaminated as little as possible by those uncertain properties of the star that are not directly associated with age and chemical composition. The calibration itself, however, employs only numerically computed eigenfrequencies. It is based on a linear perturbation from a reference model. Two reference models have been used, one somewhat younger, the other somewhat older than the Sun. The two calibrations, which use BiSON data, are more-or-less consistent, and yield a main-sequence age t⊙=4.68±0.02t_\odot=4.68\pm0.02 Gy, coupled with a formal initial heavy-element abundance Z=0.0169±0.0005Z=0.0169\pm0.0005. The error analysis has not yet been completed, so the estimated precision must be taken with a pinch of salt.Comment: 8 pages, 3 figures, in L. Deng, K.L. Chan, C. Chiosi, eds, The Art of Modelling Stars in the 21st Century, Proc. IAU Symp. No. 252, invited contributed pape

    Writing a Canadian High School History of the Great War: Victoria High School: Challenges, Pitfalls, and Sources

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    Contained in this article are suggestions on how to write a history of a Canadian high school and the First World War. Included in the discussion is the approach and methodology of the historian, the materials available for use, and knowledge of the background of Canada, the British Empire and the war “for King and Country.” It appeals for an understanding of war and of patriotism Canadian-style as of 1914-1918, as a war they fought and not the one we now think they fought or should have fought. It is an appeal for “sharp end” history. Attention is given to monuments of valour – rolls of honour, plaques, banners, stained glass, gravestones and markers, memorial trees and, above all, school records. The history should be a tribute to a youth now no longer with us. The history, when written, becomes its own memorial to their passing and sacrifice and may serve as an example for other such histories to be crafted. Lastly, it is a legacy to a grey generation of mothers, sisters and sweethearts who far from the searing battle line were also victims in this catastrophic eruption that forever changed Canada and, through what I call the Vimy Alchemy, made a nation in an age of dissolving empires. Above all, keep school records related to this war and to others. Years hence other historians will be grateful
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