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  • 1
    Publication Date: 2013-03-08
    Description: In the era of precision cosmology, it is essential to determine the Hubble constant to an accuracy of three per cent or better. At present, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC), which, being our second-closest galaxy, serves as the best anchor point for the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to measure stellar parameters and distances precisely and accurately. The eclipsing-binary method was previously applied to the LMC, but the accuracy of the distance results was lessened by the need to model the bright, early-type systems used in those studies. Here we report determinations of the distances to eight long-period, late-type eclipsing systems in the LMC, composed of cool, giant stars. For these systems, we can accurately measure both the linear and the angular sizes of their components and avoid the most important problems related to the hot, early-type systems. The LMC distance that we derive from these systems (49.97 +/- 0.19 (statistical) +/- 1.11 (systematic) kiloparsecs) is accurate to 2.2 per cent and provides a firm base for a 3-per-cent determination of the Hubble constant, with prospects for improvement to 2 per cent in the future.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pietrzynski, G -- Graczyk, D -- Gieren, W -- Thompson, I B -- Pilecki, B -- Udalski, A -- Soszynski, I -- Kozlowski, S -- Konorski, P -- Suchomska, K -- Bono, G -- Moroni, P G Prada -- Villanova, S -- Nardetto, N -- Bresolin, F -- Kudritzki, R P -- Storm, J -- Gallenne, A -- Smolec, R -- Minniti, D -- Kubiak, M -- Szymanski, M K -- Poleski, R -- Wyrzykowski, L -- Ulaczyk, K -- Pietrukowicz, P -- Gorski, M -- Karczmarek, P -- England -- Nature. 2013 Mar 7;495(7439):76-9. doi: 10.1038/nature11878.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Universidad de Concepcion, Departamento de Astronomia, Casilla 160-C, Concepcion, Chile. pietrzyn@astrouw.edu.pl〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23467166" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2013-10-18
    Description: Super-luminous supernovae that radiate more than 10(44) ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of (56)Ni are synthesized; this isotope decays to (56)Fe via (56)Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 x 10(-6) times that of the core-collapse rate.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Nicholl, M -- Smartt, S J -- Jerkstrand, A -- Inserra, C -- McCrum, M -- Kotak, R -- Fraser, M -- Wright, D -- Chen, T-W -- Smith, K -- Young, D R -- Sim, S A -- Valenti, S -- Howell, D A -- Bresolin, F -- Kudritzki, R P -- Tonry, J L -- Huber, M E -- Rest, A -- Pastorello, A -- Tomasella, L -- Cappellaro, E -- Benetti, S -- Mattila, S -- Kankare, E -- Kangas, T -- Leloudas, G -- Sollerman, J -- Taddia, F -- Berger, E -- Chornock, R -- Narayan, G -- Stubbs, C W -- Foley, R J -- Lunnan, R -- Soderberg, A -- Sanders, N -- Milisavljevic, D -- Margutti, R -- Kirshner, R P -- Elias-Rosa, N -- Morales-Garoffolo, A -- Taubenberger, S -- Botticella, M T -- Gezari, S -- Urata, Y -- Rodney, S -- Riess, A G -- Scolnic, D -- Wood-Vasey, W M -- Burgett, W S -- Chambers, K -- Flewelling, H A -- Magnier, E A -- Kaiser, N -- Metcalfe, N -- Morgan, J -- Price, P A -- Sweeney, W -- Waters, C -- England -- Nature. 2013 Oct 17;502(7471):346-9. doi: 10.1038/nature12569.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK. mnicholl03@qub.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24132291" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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