Cowan

RESEARCH DESCRIPTION

The primary emphasis of my research is observational and theoretical studies of elemental and isotopic abundances in stars. We are attempting to understand the formation of the neutron-capture elements by comparing theoretical, nucleosynthesis predictions with observed abundances in Galactic halo stars. We have employed both ground-based (Keck and HET) and space-based (HST) observations. Our studies have also incorporated the results of new experimental atomic physics determinations of the transition probabilities of the rare-earth elements. Utilizing the abundances of the heavy radioactive elements thorium and uranium in the oldest stars, we are determining the age of our Galaxy and, hence, setting lower limits on the age of the Universe.

I am also continuing my observational studies of external, nearby (face-on) galaxies. Employing the VLA, as well as Chandra, we have been searching for emission from young supernova remnants, and other (compact) point sources in these galaxies. In addition we have observed the central regions of several nearby galaxies leading to the probable detection of massive black holes in several cases.

SELECTED PUBLICATIONS

"The End of Nucleosynthesis: Production of Lead and Thorium in the Early Galaxy," I. U. Roederer, K.-L. Kratz, A. Frebel, N. Christlieb, B. Pfeiffer, J. J. Cowan and C. Sneden, Astrophys. J., 698, 1963, (2009) ADS: 2009ApJ...698.1963R

"New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars," C. Sneden, J. E. Lawler, J. J. Cowan, I. I. Ivans and E. A. Den Hartog, Astrophys. J. Supp., 182, 80, (2009) ADS: 2009ApJS..182...80S

"Nucleosynthesis Modes in the High-Entropy-Wind of Type II Supernovae: Comparison of Calculations with Halo-Star Observations," K. Farouqi, K.-L. Kratz, J. J. Cowan, L. I. Mashonkina, B. Pfeiffer, C. Sneden, F.-K. Thielemann and J. W. Truran, Astrophys. J. Letters, 694, L49, (2009) ADS: 2009ApJ...694L..49F

"Neutron-Capture Elements in the Early Galaxy," C. Sneden, J. J. Cowan and R. Gallino, Annual Reviews of Astronomy and Astrophysics, 46, 241, (2008) ADS: 2008ARA&A..46..241S

"A Study of Compact Radio Sources in Nearby Face-on Spiral Galaxies. II. Multiwavelength Analyses of Sources in M51," L. A. Maddox, J. J. Cowan, R. Kilgard, E. Schinner, and C. J. Stockdale, Astron. J., 133, 2559, (2007) ADS: 2007AJ....133.2559M