Browsing by Author "Phillips, MM"

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    Cosmological 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, NB
    The 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.
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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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    Optical 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, P
    We 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.
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    Sn 2005bf
    (2006) Folatelli, G; Contreras, C; Phillips, MM; Woosley, SE; Blinnikov, S; Morrell, N; Suntzeff, NB; Lee, BL; Hamuy, M; González, S; Krzeminski, W; Roth, M; Li, WD; Filippenko, AV; Foley, RJ; Freedman, WL; Madore, BF; Persson, SE; Murphy, D; Boissier, S; Galaz, G; González, L; McCarthy, PJ; McWilliam, A; Pych, W
    We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first similar to 100 days following discovery. The u'g'BV light curves displayed an unprecedented morphology among Type Ib/Ic supernovae, with an initial maximum some 2 weeks after discovery and a second, main maximum about 25 days after that. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event, radiating at least 6.3 x 10(42) ergs s(-1) at maximum light and a total of 2.1 x 10(49) ergs during the first 75 days after the explosion. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u'g'BV was accompanied by the presence in the spectrum of high-velocity (> 14,000 km s(-1)) absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was below 10,000 km s(-1), which is unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations that attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 x 10(51) ergs), asymmetric explosion of a massive ( 8.3 M-circle dot) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of ( 1) a polar explosion containing a small fraction of the total mass and moving at high velocity and ( 2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high-velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast- moving component becomes optically thin, revealing the more slowly moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and gamma-ray bursts.
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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.
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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.