Browsing by Author "Avilés, R"

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    The luminous Type Ic supernova 1992ar at z=0.145
    (2000) Clocchiatti, A; Phillips, MM; Suntzeff, NB; DellaValle, M; Cappellaro, E; Turatto, M; Hamuy, M; Avilés, R; Navarrete, M; Smith, C; Rubenstein, EP; Covarrubias, R; Stetson, PB; Maza, J; Riess, AG; Zanin, C
    We present spectroscopic and photometric observations of SN 1992ar, the most distant supernova (SN) in the Calan/Tololo Survey. We compare its spectrum with those of nearby Type Ia and Ic SNe and conclude that the latter type is a better match to SN 1992ar. Using K-corrections based on the spectra of well-observed Type Ic and Ia SNe, we compute different possible rest-frame light curves of SN 1992ar and compare them with those of representative SNe of each type observed in the nearby universe. From the photometry and the spectra, we are able to conclude that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even though the data set collected is fairly complete (one spectrum and 10 photometric points), it is not possible to decide whether SN 1992ar was a fast Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V magnitudes at maximum implied by each of these possibilities are -19.2 and -20.2, respectively. The latter would make SN 1992ar one of the brightest SNe on record. SN 1992ar, hence, illustrates the problem of contamination faced by the high-z Type Ia SNe samples whose luminosity distances are used to determine the cosmological parameters of the universe. We, present observational criteria to distinguish the two SN types when the Si II 6355 Angstrom line is redshifted out of the sensitivity range of typical CCD detectors and discuss the effect that these luminous Type Ic SNe would have on the measured cosmological parameters, if not removed from the high-z Type Ia SN samples.
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    Why have European herbs so successfully invaded the Chilean matorral?: Effects of herbivory,soil nutrients, and fire
    (2000) Holmgren, M; Avilés, R; Sierralta, L; Segura, AM; Fuentes, ER
    We show field and experimental evidence that introduced herbivores and soil degradation strongly influence the distribution of introduced herbs in the Chilean matorral. In the field, the relative abundance of introduced species was higher on sites grazed by livestock and on very poor soils. Two factorial experiments assessed the effects of rabbit grazing, nutrient addition, and fire. Native grasses were more sensitive than introduced grasses to grazing. With nutrient addition, native grasses increased while introduced grasses tended to decline. Fire had no significant effects on our experimental plots. We discuss several factors that might explain why alien herbs are more successful in the Chilean matorral than in the Californian chaparral. (C) 2000 Academic Press.