Browsing by Author "Covarrubias, R"

Now showing 1 - 5 of 5
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    Hubble Space Telescope and ground-based observations of Type Ia supernovae at redshift 0.5
    (2006) Clocchiatti, A; Schmidt, BP; Filippenko, AV; Challis, P; Coil, AL; Covarrubias, R; Diercks, A; Garnavich, P; Germany, L; Gilliland, R; Hogan, C; Jha, S; Kirshner, RP; Leibundgut, B; Leonard, D; Li, WD; Matheson, T; Phillips, MM; Prieto, JL; Reiss, D; Riess, AG; Schommer, R; Smith, RC; Soderberg, A; Spyromilio, J; Stubbs, C; Suntzeff, NB; Tonry, JL; Woudt, P
    We present observations of the Type Ia supernovae (SNe) 1999M, 1999N, 1999Q, 1999S, and 1999U, at redshift z approximate to 0.5. They were discovered in early 1999 with the 4.0m Blanco telescope at Cerro Tololo Inter-American Observatory by the High-z Supernova Search Team(HZT) and subsequently followed with many ground-based telescopes. SNe 1999Q and 1999U were also observed with the Hubble Space Telescope. We computed luminosity distances to the new SNe using two methods and added them to the high-z Hubble diagram that the HZT has been constructing since 1995. The new distance moduli confirm the results of previous work. At z approximate to 0: 5, luminosity distances are larger than those expected for an empty universe, implying that a "cosmological constant,'' or another form of "dark energy,'' has been increasing the expansion rate of the universe during the last few billion years. Combining these new HZT SNe Ia with our previous results and assuming a Delta CDM cosmology, we estimate the cosmological parameters that best fit our measurements. For a sample of 75 low-redshift and 47 high-redshift SNe Ia with MLCS2k2 (Jha and coworkers) luminosity calibration we obtain Omega(M) = 0: 79(-0.18)(+0.15) and Omega(Lambda) = 1.57(-0.32)(+0.24) (1 sigma uncertainties) if no constraints are imposed, or Omega(M) = 0.29(-0.05)(+0.06) if Omega(M) + Omega(Lambda) = 1 is assumed. For a different sample of 58 low-redshift and 48 high-redshift SNe Ia with luminosity calibrations done using the PRES method (a generalization of the Delta m(15) method), the results are Omega(M) = 0.43(-0.19)(+0.17) and Omega(Lambda) = 1.18(-0.28)(+0.27) (1 sigma uncertainties) if no constraints are imposed, or Omega(M) = 0.18(-0.04)(+0.05) if Omega(M) + Omega(Lambda) = 1 is assumed.
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    Hubble Space Telescope observations of nine high-redshift essence supernovae
    (2005) Krisciunas, K; Garnavich, PM; Challis, P; Prieto, JL; Riess, AG; Barris, B; Aguilera, C; Becker, AC; Blondin, S; Chornock, R; Clocchiatti, A; Covarrubias, R; Filippenko, AV; Foley, RJ; Hicken, M; Jha, S; Kirshner, RP; Leibundgut, B; Li, WD; Matheson, T; Miceli, A; Miknaitis, G; Rest, A; Salvo, ME; Schmidt, BP; Smith, RC; Sollerman, J; Spyromilio, J; Stubbs, CW; Suntzeff, NB; Tonry, JL; Wood-Vasey, WM
    We present broadband light curves of nine supernovae ranging in redshift from 0.5 to 0.8. The supernovae were discovered as part of the ESSENCE project, and the light curves are a combination of Cerro Tololo 4 m and Hubble Space Telescope (HST) photometry. On the basis of spectra and/or light-curve fitting, eight of these objects are definitely Type Ia supernovae, while the classification of one is problematic. The ESSENCE project is a 5 yr endeavor to discover about 200 high-redshift Type Ia supernovae, with the goal of tightly constraining the time average of the equation-of-state parameter [w = p/(rho c(2))] of the "dark energy." To help minimize our systematic errors, all of our ground-based photometry is obtained with the same telescope and instrument. In 2003 the highest redshift subset of ESSENCE supernovae was selected for detailed study with HST. Here we present the first photometric results of the survey. We find that all but one of the ESSENCE supernovae have slowly declining light curves and that the sample is not representative of the low-redshift set of ESSENCE Type Ia supernovae. This is unlikely to be a sign of evolution in the population. We attribute the decline-rate distribution of HST events to a selection bias at the high-redshift edge of our sample and find that such a bias will infect other magnitude-limited Type Ia supernova searches unless appropriate precautions are taken.
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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.
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    The Type Ia supernova 1999aw
    (2002) Strolger, LG; Smith, RC; Suntzeff, NB; Phillips, MM; Aldering, G; Nugent, P; Knop, R; Perlmutter, S; Schommer, RA; Ho, LC; Hamuy, M; Krisciunas, K; Germany, LM; Covarrubias, R; Candia, P; Athey, A; Blanc, G; Bonacic, A; Bowers, T; Conley, A; Dahlén, T; Freedman, W; Galaz, G; Gates, E; Goldhaber, G; Goobar, A; Groom, D; Hook, IM; Marzke, R; Mateo, M; McCarthy, P; Méndez, J; Muena, C; Persson, SE; Quimby, R; Roth, M; Ruiz-Lapuente, P; Seguel, J; Szentgyorgyi, A; von Braun, K; Wood-Vasey, WM; York, T
    SN 1999aw was discovered during the first campaign of the Nearby Galaxies Supernova Search project. This luminous, slow-declining [Deltam(15)(B) = 0.81 +/- 0.03] Type Ia supernova was noteworthy in at least two respects. First, it occurred in an extremely low luminosity host galaxy that was not visible in the template images nor in initial subsequent deep imaging. Second, the photometric and spectral properties of this supernova indicate that it very likely was similar to the subclass of Type Ia supernovae whose prototype is SN 1999aa. This paper presents the BVRI and J(s)HK(s) light curves of SN 1999aw ( through similar to100 days past maximum light), as well as several epochs of optical spectra. From these data, we calculate the bolometric light curve and give estimates of the luminosity at maximum light and the initial Ni-56 mass. In addition, we present deep BVI images obtained recently with the Baade 6.5 m telescope at Las Campanas Observatory that reveal the remarkably low-luminosity host galaxy.