We are one of the largest astrophysics groups within a physics department in the country. The research conducted in our group is interwoven and dynamic, with five focus areas that are complementary to each other.
- Supernovae are the explosions of dying stars. Our group is among the top few internationally in supernova research. Baron and Branch are interested in understanding the systematics of how supernovae explode and what kinds of stars lead to what type of supernovae. Baron uses supernovae as a "laboratory" to study the initial conditions of progenitor stars. Baron and Branch study the spectra of the expanding supernova atmosphere to determine physical conditions and chemical abundances in the ejecta. Cowan studies the expanding remnants of supernova explosions many years after the explosion has occurred by using the radio emission given off by the expanding shell. Henry studies the chemical composition of such supernova remnants, objects which represent the remnants of supernova explosions. We have set up a "supernova spectrum repository" (SUSPECT) -- a website at which anyone can view all of the supernova spectra that we gather from observers, and from which any of the SN spectrum data files can be extracted in a common format. This will make us the "headquarters" of supernova spectra.
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Nucleosynthesis is key to understanding stellar evolution. Henry studies the chemical abundances of a variety of emission line objects with the goal of understanding stellar production rates and subsequent cosmic accumulation of elements such as C, N, O, Ne, S, and Ar. Cowan studies cosmochronology and the chemical evolution of the Galaxy. He uses the history of radioactive elements in the oldest stars to study the age of our galaxy and to set limits on the age of the universe.
When stars in the 1-8 solar mass range reach the end of their evolution, they shed outer portions of their atmospheres. The dying star left behind shrinks and gets hotter, and UV light from it causes the outer ring of gas to glow. This "planetary nebula" makes it relatively easy to study the chemical makeup of the gas. This image of NGC 7293, the Helix Nebula, was taken by Reginald Dufour of Rice University, using a CCD camera.
- Cosmological research in our group is anchored in observational data, and aims at gaining a deep understanding of our universe. Wang's research focuses on using various independent cosmological data sets (cosmic microwave background anisotropy, galaxy redshift surveys, supernovae) to determine the cosmological parameters that describe our universe, to probe the physics of the very early universe, and to constrain the dark energy in the universe. Baron and Branch study the use of supernovae as distance indicators to remote galaxies in order to determine the age, size, and fate of the universe. Wang, Baron, and Branch study the systematic uncertainties of supernovae as cosmological probes.
- Extragalactic astronomy is a focus of several researchers. Cowan studies properties of radio emitting galaxies such as our own, which may contain a black hole at its center. Henry studies the distribution of chemical elements in spiral galaxies such as our own, in order to study their origin and evolution. Leighly studies Active Galactic Nuclei (AGN). The ultimate power source for AGNs is thought to be accretion onto a supermassive blackhole. Her extensive program involves both observations in the X-ray and theoretical modeling. Recently Baron has begun to become involved in the theoretical modeling of AGN spectra.
- Observational astronomy supports all of our research. Romanishin studies the Solar System. He is involved in a program to obtain colors and other photometric properties for faint minor bodies in the outer solar system, including Kuiper Belt Objects and irregular satellites of the Jovian planets. Leighly has an extensive background in techniques and methodology of X-ray observational astronomy. She has been awarded observational time on state of the art X-ray satellites. She has recently expanded her observational work to the optical as well. Cowan conducts observational studies of supernovae and supernova remnants. Branch and Baron are on key observational teams of supernovae. On the basis of scientific merit, our astronomers have significant access to the major ground and space observatories, including the Hubble Space Telescope and the Keck. We use our campus computer-controlled 16 inch (0.4 meter) telescope for student training and certain research projects.
Astronomy continues to be an exciting field with new ideas and new facilities emerging. We welcome the chance to work with motivated and qualified graduate students.
