Browsing by Author "Germany, L"

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    An optical time-delay for the lensed BAL quasar HE 2149-2745
    (2002) Burud, I; Courbin, F; Magain, P; Lidman, C; Hutsemékers, D; Kneib, JP; Hjorth, J; Brewer, J; Pompei, E; Germany, L; Pritchard, J; Jaunsen, AO; Letawe, G; Meylan, G
    We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000, are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere. A time delay of 103+/-12 days is determined from the light curves. In addition, VLT/FORS1 spectra of HE 2149 2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy, free of any contamination by the bright nearby two quasar images. By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z = 0.495+/-0:01. Adopting this redshift, a Omega = 0.3, Lambda = 0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H-0 = 66+/-8 km s(-1) Mpc(-1) (1sigma error) with an estimated systematic error of +/-3 km s(-1) Mpc(-1). Using non-parametric models yields H-0 = 65+/-8 km s(-1) Mpc(-1) (1sigma error) and confirms that the lens exhibits a very dense/concentrated mass profile. Finally, we note, as in other cases, that the flux ratio between the two quasar components is wavelength dependent. While the flux ratio in the broad emission lines-equal to 3.7-remains constant with wavelength, the continuum of the brighter component is bluer. Although the data do not rule out extinction of one quasar image relative to the other as a possible explanation, the effect could also be produced by differential microlensing by stars in the lensing galaxy.
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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.