20 September 2001 CfA Colloquium

Title: Short-lived Nuclei in the Early Solar System, Nucleosynthesis, and Chemical Evolution Since Big Bang

Speaker: Jerry Wasserburg


The basic observations on the solar abundances derived from meteorites and the abundances of short- and long-lived r-process nuclei in meteorites will be used to infer processes in the early universe. These observations show that the r-nuclei must be generated in at least two distinct sites, which we associate with SNII. Assuming a two-component source for r nuclei, we consider the heavy nuclei (mass numbers A > 130) to be produced with essentially no Fe in high frequency (H) events and the lighter r nuclei (mass numbers A < 130) to be associated with Fe production in low frequency (L) events. The SNII(H) events (which are speculated to end up as black holes) are the most frequent SNIIs (~90%) with a replenishment time scale of 107 years for a standard mass of hydrogen. The L events have a replenishment time scale of ~ 108 years, produce abundant Fe, and are considered to produce neutron stars. This model has led to a prediction that the very earliest stars formed in our galaxy should show an overabundance of heavy r nuclei relative to the lighter r nuclei (Wasserburg, Busso & Gallino (1996). These considerations are directly related to observations on low and ultra-low metallicity stars.

References for students:

1) Wasserburg, G.J., Busso, M., & Gallino, R. 1996, ApJ, 466,  L109
2) Qian, Y.-Z., Vogel, P., & Wasserburg, G.J. 1998, ApJ, 494, 285
3) Qian, Y.-Z., & Wasserburg, G.J. 2000, Phys. Rep., 333, 77
4) Wasserburg, G.J., & Qian, Y.-Z. 1 Aug. 2000, ApJ, 538, #2    
5) Sneden, C. et al. 2000, ApJ, 533, L139
6) McWilliam, A., Preston, G.W., Sneden, C., & Searle, L. 1995, AJ, 109, 2757
7) Sneden, C., Cowan, J.J., Burris, D.L., & Truran, J.W. 1998, ApJ, 496, 23
8) Qian, Y-Z & Wasserburg (2001) ApJ 552, L55-L58

(References 1, 2, 5 and 8 reflect the beginning and the latest developments in this model.  Perhaps students should read 1 and either 5 or 8, with the whole list provided for those who really get interested.)

Lunch with the students will be on Friday, September 21 at 12:00 in A-101.