University of Hawaii|
Institute for Astronomy
Ann Merchant Boesgaard
Professor of Physics and Astronomy
Ph.D. Astronomy, University of California at Berkeley, 1966
fax/phone: Phone 808 956-8756 Fax 808 956-9590
Stellar Spectroscopy, Stellar Evolution, Nucleosynthesis
Chemical abundances in nearby stars hold the answers to many of the most fundamental questions about the universe.
The primordial abundance of the element lithium (Li) is an important diagnostic of early element formation in the Big Bang and helps to determine the density and fate of the universe. We are making observations of faint stars in very old globular clusters to determine the definitive value for primordial Li.
The enrichment of various chemical elements with time in the Galaxy reveals the history of massive star formation and the early production of supernovae. In particular, we can trace the increase of beryllium (Be) and oxygen (O) over time, since their production depends on the products of massive stars and supernovae. We are probing both the oldest stars and those of the intermediate ages in more detail to develop a greater understanding of the evolution of the Galaxy. Furthermore, the study of Be and O in star clusters of the galactic disk helps us to discern the evolution and mixing in the disk component of our Galaxy.
Although the composition of stars like the Sun is very similar to that of the Sun, the abundances of the elements Li and Be show interesting differences among solar-type stars. This nonuniformity makes it possible to effectively examine the insides of stars through their Li and Be content. Several models have been proposed that cause mixing in the stellar interiors. Mixing of matter caused by rotation can result in depletion of surface Li and Be, but Li is depleted much more than Be; we are studying both elements together. The understanding of the processes that deplete Li and Be is directly connected to evaluation of the amount of Li (and Be) that formed during the Big Bang.
Figure caption: Lithium abundances for seven stars in the old, very metal-poor globular cluster, M 92. The stars with the highest abundance of Li are above the halo field star plateau value of 2.25. There are Li-poor stars also. The dispersion in Li - in otherwise identical stars - points to a mixing mechanism inside the star that circulates the Li to hotter temperatures where it is destroyed. The only known parameter which could differ from star to star is the initial angular momentum. All the stars are slow rotators now, but those with the highest initial angular momentum would have spun down the most and thus have the lowest Li at present. The highest Li abundance gives a lower limit to the primordial Li abundance.
NATO Senior Science Fellow, 1973
College de France Medal, 1980
Honorary Doctor of Science Degree, Mount Holyoke College, 1981
Guggenheim Fellow, 1986-1987
Muhlmann Prize of the Astronomical Society of the Pacific, 1990
Primordial Lithium: Keck Observations in M92 Turnoff
Boesgaard, A. M., Deliyannis, C. P., Stephens, A., King, J. R.
Astrophysical Journal, 493, 206 (1998)
Boron in Lithium- and Beryllium-Deficient F Stars
Boesgaard, A. M., Deliyannis, C. P., Stephens, A., Lambert, D. L.
Astrophysical Journal, 492, 727 (1998)
Light Element Abundances in the Halo
Boesgaard, A. M.
Astronomical Society of the Pacific Conference Series, 92, 327 (1996)
The Galactic Evolution of Beryllium
Boesgaard, A. M. and King, J. R.
Astronomical Journal, 106, 2309 (1993)
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