John Cowan
| Title: | David Ross Boyd Professor |
| Education: | B.A. 1970 George Washington |
| Ph.D. 1976 Maryland | |
| Office: | 229 Nielsen Hall |
| Phone: | 405-325-3961, ext. 36229 |
| Email: | cowan@nhn.ou.edu |
| Research Home Page |
What are stars made of and why? I have been working on two topics: stellar abundances and extragalactic supernovae. The first can tell us the details of nucleosynthesis and help us understand the age of stars, and the latter explores the dynamics of supernova remnants.
We have been making a large number of observational and theoretical studies of the heavy element abundances in Galactic halo stars from the ground and from space (using the Hubble Space Telescope). These observations demonstrate that the earliest generations of stars in the Galaxy, responsible for neutron-capture synthesis and the progenitors of the halo stars, were rapidly evolving. Abundance comparisons among large numbers of stars provide clues about the nature of neutron-capture element synthesis both during the earliest times and throughout the history of the Galaxy.
Using the Very Large Array we have been following the long-term radio behavior of intermediate-age (i.e., 10--100 year old) extragalactic supernovae. We have found that these supernovae, such as SN 1970G in M101 and SN 1923A in M83, are still emitting in the radio decades after the supernova explosion. These observations are designed to understand how supernovae evolve into supernova remnants, which typically take at least 100 years to become radio emitters. We are also trying to identify the population of supernova remnants, and High/Low Mass X-ray Binaries in spiral galaxies and whether there are massive black holes in these spiral galaxies. To resolve the central region of one galaxy (M83), a new (radio) VLBI experiment has been approved to use the Long Baseline Array (LBA) of Australia Telescope. These observations will assist in the possible detection of coincident radio/x-ray sources in the complex nuclear region.
