Browsing by Author "Diercks, A"

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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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    Tests 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, B
    We 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.