Browsing by Author "Clocchiatti, A"
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- ItemCosmological results from high-z supernovae(2003) Tonry, JL; Schmidt, BP; Barris, B; Candia, P; Challis, P; Clocchiatti, A; Coil, AL; Filippenko, AV; Garnavich, P; Hogan, C; Holland, ST; Jha, S; Kirshner, RP; Krisciunas, K; Leibundgut, B; Li, WD; Matheson, T; Phillips, MM; Riess, AG; Schommer, R; Smith, RC; Sollerman, J; Spyromilio, J; Stubbs, CW; Suntzeff, NBThe High-z Supernova Search Team has discovered and observed eight new supernovae in the redshift interval z = 0.3-1.2. These independent observations, analyzed by similar but distinct methods, confirm the results of Riess and Perlmutter and coworkers that supernova luminosity distances imply an accelerating universe. More importantly, they extend the redshift range of consistently observed Type Ia supernovae (SNeIa) to z approximate to 1, where the signature of cosmological effects has the opposite sign of some plausible systematic effects. Consequently, these measurements not only provide another quantitative confirmation of the importance of dark energy, but also constitute a powerful qualitative test for the cosmological origin of cosmic acceleration. We find a rate for SN Ia of (1.4 +/- 0.5) x 10(-4) h(3) Mpc(-3) yr(-1) at a mean redshift of 0.5. We present distances and host extinctions for 230 SN Ia. These place the following constraints on cosmological quantities: if the equation of state parameter of the dark energy is w = -1, then H(0)t(0) = 0.96 +/- 0.04, and Omega(Lambda) - 1.4Omega(M) = 0.35 +/- 0/14. Including the constraint of a. at universe, we find Omega(M) = 0.28 +/- 0.05, independent of any large-scale structure measurements. Adopting a prior based on the Two Degree Field (2dF) Redshift Survey constraint on Omega(M) and assuming a. at universe, we find that the equation of state parameter of the dark energy lies in the range -1.48 < w < -0.72 at 95% confidence. If we further assume that w > -1, we obtain w < -0.73 at 95% confidence. These constraints are similar in precision and in value to recent results reported using the WMAP satellite, also in combination with the 2dF Redshift Survey.
- ItemHubble 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, PWe 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.
- ItemHubble 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, WMWe 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.
- ItemOptical spectra of Type Ia supernovae at z=0.46 and z=1.2(2000) Coil, AL; Matheson, T; Filippenko, AV; Leonard, DC; Tonry, J; Riess, AG; Challis, P; Clocchiatti, A; Garnavich, PM; Hogan, CJ; Jha, S; Kirshner, RP; Leibundgut, B; Phillips, MM; Schmidt, BP; Schommer, RA; Smith, RC; Soderberg, AM; Spyromilio, J; Stubbs, C; Suntzeff, NB; Woudt, PWe present optical spectra, obtained with the Keck 10 m telescope, of two high-redshift Type Ia supernovae (SNe Ia) discovered by the High-z Supernova Search Team: SN 1999ff at z = 0.455 and SN 1999fv at z similar to 1.2, the highest redshift published SN Ia spectrum. Both SNe were at maximum light when the spectra were taken. We compare our high-z spectra with low-z normal and peculiar SNe Ia as well as with SNe Ic, Ib, and II. There are no significant differences between SN 1999ff and normal SNe Ia at low redshift. SN 1999fv appears to be an SN Ia and does not resemble the most peculiar nearby SNe Ia.
- ItemTests of the accelerating universe with near-infrared observations of a high-redshift type Ia supernova(2000) Riess, AG; Filippenko, AV; Liu, MC; Challis, P; Clocchiatti, A; Diercks, A; Garnavich, PM; Hogan, CJ; Jha, S; Kirshner, RP; Leibundgut, B; Phillips, MM; Reiss, D; Schmidt, BP; Schommer, RA; Smith, RC; Spyromilio, J; Stubbs, C; Suntzeff, NB; Tonry, J; Woudt, P; Brunner, RJ; Dey, A; Gal, R; Graham, J; Larkin, J; Odewahn, SC; Oppenheimer, BWe have measured the rest-frame B-, V-, and I-band light curves of a high-redshift type Ia supernova (SN 1a), SN 1999Q (z = 0.46), using the Hubble Space Telescope (HST) and ground-based near-infrared detectors. A goal of this study is the measurement of the color excess, EB-I, a sensitive indicator of interstellar or intergalactic dust, which could affect recent cosmological measurements from high-redshift SNe Ia. Our observations disfavor a 30% opacity of SN Ia visual light by dust as an alternative to an accelerating universe. This statement applies to both Galactic-type dust (rejected at the 3.4 sigma confidence level) and grayer dust (grain size > 0.1 mu m, rejected at the 2.3-2.6 sigma confidence level) as proposed by Aguirre. The rest-frame I-band light curve shows the secondary maximum 1 month after the B maximum typical of nearby SNe fa of normal luminosity, providing no indication of evolution as a function of redshift out to z approximate to 0.5. An expanded set of similar observations could improve the constraints on any contribution of extragalactic dust to the dimming of high-redshift SNe Ia.
- ItemThe 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, CWe 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.
- ItemThe 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, JSN 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.
- ItemTwenty-three high-redshift supernovae from the Institute for Astronomy Deep Survey(2004) Barris, BJ; Tonry, JL; Blondin, S; Challis, P; Chornock, R; Clocchiatti, A; Filippenko, AV; Garnavich, P; Holland, ST; Jha, S; Kirshner, RP; Krisciunas, K; Leibundgut, B; Li, WD; Matheson, T; Miknaitis, G; Riess, AG; Schmidt, BP; Smith, RC; Sollerman, J; Spyromilio, J; Stubbs, CW; Suntzeff, NB; Aussel, H; Chambers, KC; Connelley, MS; Donovan, D; Henry, JP; Kaiser, N; Liu, MC; Martín, EL; Wainscoat, RJWe present photometric and spectroscopic observations of 23 high-redshift supernovae (SNe) spanning a range of z = 0.34-1.03, nine of which are unambiguously classified as Type Ia. These SNe were discovered during the IfA Deep Survey, which began in 2001 September and observed a total of 2.5 deg(2) to a depth of approximately m approximate to 25-26 in RIZ over 9-17 visits, typically every 1-3 weeks for nearly 5 months, with additional observations continuing until 2002 April. We give a brief description of the survey motivations, observational strategy, and reduction process. This sample of 23 high-redshift SNe includes 15 at z greater than or equal to 0.7, doubling the published number of objects at these redshifts, and indicates that the evidence for acceleration of the universe is not due to a systematic effect proportional to redshift. In combination with the recent compilation of Tonry et al. (2003), we calculate cosmological parameter density contours that are consistent with the flat universe indicated by the cosmic microwave background (Spergel et al. 2003). Adopting the constraint that Omega(total) = 1.0, we obtain best-fit values of (Omega(m), Omega(Lambda)) = (0.33, 0.67) using 22 SNe from this survey augmented by the literature compilation. We show that using the empty-beam model for gravitational lensing does not eliminate the need for Omega(Lambda) > 0. Experience from this survey indicates great potential for similar large-scale surveys while also revealing the limitations of performing surveys for z > 1 SNe from the ground.