| Type Ia supernovae (SNe Ia) play a key role in recent advances in our understanding of the Universe. We present cosmological applications of SNe Ia, including observational results as part of an ongoing campaign at the Harvard Smithsonian Center for Astrophysics to monitor newly discovered SNe Ia at the F. L. Whipple Observatory (FLWO). We describe observations and analysis of SN 1998bu in M96, the only SN Ia yet to have appeared in a galaxy with a previously measured Hubble Space Telescope Cepheid distance. We show that SN 1998bu was a normal, reddened SN Ia and use it to constrain the Hubble constant, with attention to systematic uncertainties. We also present the largest set of SN Ia photometry published to date, consisting of 2190 UBVRI FLWO CCD observations of 44 SNe Ia discovered between 1997 and 2000. The large, homogeneous sample of U-band light curves is unique, with important applications to SN Ia at high redshift, and we present the first detailed description of SN Ia U-band properties. We also develop MLCS2k2, a new incarnation of the Multicolor Light Curve Shape method to measure SN Ia distances, incorporating the U-band and other improvements. Application of MLCS2k2 to a large sample of Hubble-flow and Cepheid-calibrated SNe Ia yields an estimate of H 0 = 66 ± 3 (random) ± 7 (systematic) or 76 ± 3 ± 8 km s−1 Mpc−1, depending on which of two discrepant sets of Cepheid distances is used. With the High-Z SN Search Team, we present cosmological constraints on the dark energy equation of state, and combined constraints on ΩM and ΩA from SNe Ia and the cosmic microwave background. Finally, via observations at FLWO, we measure the redshift of an extremely distant exploding star, GRB 010222, at z = 1.477. |
