I am working on various aspects of supernovae, from studies of individual objects to cosmological uses. I did my dissertation work at the University of California at Berkeley with Alex Filippenko. It centered on optical spectroscopy of core-collapse supernovae that had lost some (or all) of their hydrogen envelopes. This included a very detailed analysis of SN 1993J, a metamorphosing supernova that helped to link physically two spectroscopically defined sub-types, and a broad study of spectra of supernovae of Type Ib and Ic. In addition to these topics, I worked on understanding several other individual supernovae, determining mass functions for stellar-mass black holes in the Milky Way, studying unusual novae, and contributing to many studies of active galactic nuclei. (See my publications on ADS for the full story.)
For my post-doctoral work, I went to the Center for Astrophysics, with Bob Kirshner and the CfA supernova group . (See the recent supernova page for images and spectra.) We are also involved in large international collaborations to study supernovae. We have used the Hubble Space Telescope to look at (relatively) nearby supernovae. This was the Supernova INtensive Study (SINS) project (cute name, eh?). We also worked with the High-Z team to use Type Ia supernovae at cosmological distances to measure the universe. For some links to other supernovae sites from the CfA, look here.
Also at the CfA, I worked on gamma-ray bursts with Kris Stanek. The most exciting discovery so far was the first direct evidence that GRBs are related to supernovae. In March of 2003, a GRB was detected that turned out to be at a relatively low redshift. This was GRB 030329. We began a series of spectroscopic observations with the MMT. For the first few days, the spectrum showed the flat power-law continuum of a typical GRB optical afterglow. After almost a week, though, features recognizable as those from a supernova began to appear (now called SN 2003dh). We first reported this in a GCN on April 7. For the full story of discovery, see Stanek et al., the first paper. A complete treatment of the first two months of SN 2003dh is here: Matheson et al..
At NOAO, my research has continued to focus on supernovae. This includes the SN/GRB connection as well as low and high-redshift supernovae. One of my goals is to understand the diversity among Type Ia SNe by looking at a large collection of spectra of nearby SNe obtained by the CfA group. The study of high-redshift supernovae evolved into the ESSENCE project, a five-year program that found ~200 Type Ia supernovae in order to measure the parameterization of the equation of state of the Universe. We have already published the spectra from the first two years here and first four years here. The spectra are publicly available on my spectra webpage.
I'm looking at light echoes from ancient supernovae with Armin Rest. We've also gotten spectra of light echos from eta Carina. I've branched out into the infra-red for photometric observations of Type Ia SNe using the WIYN telescope, including the nearby SN 2011fe in M101 and a large program to study these SNe in the Hubble flow called SweeSpot. I'm also trying to see how we will handle the large number of transients found by large surveys such as LSST. Part of this is predicting the number of variables you might find.