Browsing by Author "Cappellaro, E"

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    A new faint type Ia supernova: SN 1997cn in NGC 5490
    (1998) Turatto, M; Piemonte, A; Benetti, S; Cappellaro, E; Mazzali, PA; Danziger, IJ; Patat, F
    Observations of the recent supernova (SN) 1997cn in the elliptical galaxy NGC 5490 show that this object closely resembles, both photometrically and spectroscopically, the faint SN Ia SN 1991bg. The two objects have similar light curves, which do not show secondary maxima in the near-IR as normal type Ia supernova. The host galaxy, NGC 5490, lies in the Hubble flow. Adopting for SN 1997cn a reddening E(B-V) = 0, the absolute magnitude is faint: M-V = - 17.98 using H-0 = 65 and M-V = - 17.40 using H-0 = 85 km s(-1) Mpc(-1). The latter value is in close agreement with the absolute magnitude of SN 1991bg on the SBF/PNLF/TF distance scale. The photospheric spectra of the two SNe show the same peculiarities, the deep Ti n trough between 4000 and 4500 A, the strong Ca n IR triplet, the narrow absorption at about 5700 A, and the slow expansion velocity. Analogous to SN 1991bg, the observed spectrum of SN 1997cn has been successfully modeled by scaling down the W7 model by a factor of 2, assuming a rise time to B maximum of 18 days, a photospheric velocity, and an effective temperature low compared to normal SNe Ia. The influence of the distance scale adopted on the input parameters of the best-fit model is also discussed.
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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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    The peculiar type II supernova 1997D
    (1998) Turatto, M; Mazzali, PA; Young, TR; Nomoto, K; Iwamoto, K; Benetti, S; Cappellaro, E; Danziger, IJ; de Mello, DF; Phillips, MM; Suntzeff, NB; Clocchiatti, A; Piemonte, A; Leibundgut, B; Covarrubias, R; Maza, J; Sollerman, J
    SN 1997D in NGC 1536 is possibly the least luminous and energetic Type II supernova discovered to date. The entire light curve is subluminous, never reaching M-v = -14.65. The radioactive tail follows the Co-56 decay slope. In the case of a nearly complete trapping of the gamma-rays, the Ni-56 mass derived from the tail brightness is extremely small, similar to 0.002 M.. At discovery, the spectra showed a red continuum and line velocities on the order of 1000 km s(-1). The luminosity and the photospheric expansion velocity suggest that the explosion occurred about 50 days before discovery and that a plateau probably followed. Model light curves and spectra of the explosion of a 26 M. star successfully fitted the observations. Low-mass models are inconsistent with the observations. The radius of the progenitor, constrained by the prediscovery upper limits, is R-0 less than or similar to 300 R.. A low explosion energy of similar to 4 x 10(50) ergs is then required in the modeling. The strong Pa II lines in the photospheric spectra are reproduced with a solar abundance and low T-eff. A scenario in which the low Ni-56 mass observed in SN 1997D is due to fallback of material onto the collapsed remnant of the explosion of a 25-40 M. star appears to be favored over the case of the explosion of an 8-10 M. star with low Ni-56 production.