11,971 research outputs found

    Hydrogen in Type Ic Supernovae?

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    By definition, a Type Ic supernova (SN Ic) does not have conspicuous lines of hydrogen or helium in its optical spectrum. SNe Ic usually are modelled in terms of the gravitational collapse of bare carbon-oxygen cores. We consider the possibility that the spectra of ordinary (SN 1994I-like) SNe Ic have been misinterpreted, and that SNe Ic eject hydrogen. An absorption feature usually attributed to a blend of Si II 6355 and C II 6580 may be produced by H-alpha. If SN 1994I-like SNe Ic eject hydrogen, the possibility that hypernova (SN 1998bw-like) SNe Ic, some of which are associated with gamma-ray bursts, also eject hydrogen should be considered. The implications of hydrogen for SN Ic progenitors and explosion models are briefly discussed.Comment: Accepted by PASP. Several significant changes including one additional figur

    Submillimeter Atmospheric Transparency at Maunakea, at the South Pole, and at Chajnantor

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    For a systematic assessment of submillimeter observing conditions at different sites, we constructed tipping radiometers to measure the broad band atmospheric transparency in the window around 350 μ\mum wavelength. The tippers were deployed on Maunakea, Hawaii, at the South Pole, and in the vicinity of Cerro Chajnantor in northern Chile. Identical instruments permit direct comparison of these sites. Observing conditions at the South Pole and in the Chajnantor area are better than on Maunakea. Simultaneous measurements with two tippers demonstrate conditions at the summit of Cerro Chajnantor are significantly better than on the Chajnantor plateau.Comment: Accepted by PAS

    Industry mix and lending environment variability: what does the average bank face

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    Diversification opportunities for banks may be greater today because of the lessening of geographic restrictions. In addition, regional economies have undergone vast transformations, with relatively volatile industries often assuming a diminished role. To assess whether these changes have resulted in a more stable lending environment, Jeff Gunther and Ken Robinson form industry portfolios for banks based on their presence in different states and the mix of economic activity found in those states. The authors find that the risk underlying banks' lending environments declined from 1985 to 1996 because of both a geographic restructuring of the banking system and increasing industrial diversification of state economies.Banks and banking ; Financial institutions

    Intercomparison of soil pore water extraction methods for stable isotope analysis

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    Funded by NSERC Discovery Grant U.S. Forest Service U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies OfficePeer reviewedPostprin

    Supernova Resonance-Scattering Profiles in the Presence of External Illumination

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    We discuss a simple model for the formation of a supernova spectral line by resonance scattering in the presence of external illumination of the line-forming region by light from circumstellar interaction (toplighting). The simple model provides a clear understanding of the most conspicuous toplighting effect: a rescaling or, as we prefer, a ``muting'' of the line profile relative to the continuum. This effect would be present in more realistic models, but would be harder to isolate. An analytic expression for a muting factor for a P-Cygni line is derived that depends on the ratio E of the toplighting specific intensity to the specific intensity from the supernova photosphere. If E<1, the line profile is reduced in scale or ``muted''. If E=1, the line profile vanishes altogether. If E>1, the line profile flips vertically: then having an absorption component near the observer-frame line center wavelength and a blueshifted emission component.Comment: accepted for publication in PAS
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