Bruno Leibundgut

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We have discovered 16 Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST ) and have used them to provide the first conclusive evidence for cosmic deceleration that preceded the current epoch of cosmic acceleration. These objects, discovered during the course of the GOODS ACS Treasury program, include 6 of the 7 highest redshift SNe Ia known,(More)
We present constraints on the dark energy equation-of-state parameter, w = P/(ρc), using 60 Type Ia supernovae (SNe Ia) from the ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat Universe. By including constraints on (ΩM, w) from baryon acoustic oscillations, we obtain a value for a static(More)
The first cosmological results from the ESSENCE supernova survey (Wood-Vasey et al. 2007) are extended to a wider range of cosmological models including dynamical dark energy and non-standard cosmological models. We fold in a greater number of external data sets such as the recent Higher-z release of high-redshift supernovae (Riess et al. 2007) as well as(More)
The High-z Supernova Search Team has discovered and observed 8 new supernovae in the redshift interval z = 0.3–1.2. These independent observations, analyzed by similar but distinct methods, confirm the result of Riess et al. (1998a) and Perlmutter et al. (1999) that supernova luminosity distances imply an accelerating universe. More importantly, they extend(More)
We present empirical fits to the UBVRI light curves of type Ia supernovae. These fits are used to objectively evaluate light curve parameters. We find that the relative times of maximum light in the filter passbands are very similar for most objects. Surprisingly the maximum at longer wavelengths is reached earlier than in the B and V light curves. This(More)
The extreme luminosity and their fairly unique temporal behaviour have made supernovae a superb tool to measure distances in the universe. As complex astrophysical events they provide interesting insights into explosion physics, explosive nucleosynthesis, hydrodynamics of the explosion and radiation transport. They are an end product of stellar evolution(More)
We have started a large survey for radial velocity variations in white dwarfs (PI R. Napiwotzki) with the aim of finding close double degenerates, which could be precursor systems for SNe Ia. The UVES spectrograph at the ESO VLT is used to obtain high resolution spectra with good S/N . During this project 1500 white dwarfs will be observed. This unique data(More)
We present photometric and spectroscopic observations of 23 high redshift supernovae spanning a range of z = 0.34 − 1.03, 9 of which are unambiguously classified as Type Ia. These supernovae were discovered during the IfA Deep Survey, which began in September 2001 and observed a total of 2.5 square degrees to a depth of approximately m ≈ 25− 26 in RIZ over(More)
Based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under NASA contract NAS 5-26555. This research is associated with proposal GO-9860. Based in part on observations taken at the Cerro Tololo(More)
Type Ia Supernovae hold great promise to measure the cosmic deceleration. The diversity observed among these explosions, however, complicates their ability to measure cosmological parameters considerably. The comparison of near and distant objects depends critically on the global properties of the samples. Systematic errors are introduced in cases where the(More)