WILLIAMSTOWN, Mass., Oct. 14, 1999 -- Karen Kwitter, Ebenezer Fitch Professor of Astronomy at Williams College, has been awarded a $237,843 three-year grant from the National Science Foundation. The award will fund research in "Planetary Nebulae as Narrators of Stellar and Galactic Chemical Evolution: A New Probe of Galactochronology."
Planetary nebulae are the expanding clouds of glowing gas ejected by dying stars. They represent the final stages of the life cycle of stars between one and eight times as massive as the sun. We can therefore expect that in about six billion years the sun will produce a planetary nebula.
Because nuclear fusion in stars creates progressively heavier elements, the chemical composition of planetary nebulae differ from those of the original stars. The extent to which the chemical makeup changes depends on the original composition and mass of the source star.
Kwitter and colleagues determine the chemical makeup of planetary nebulae by studying the light spectra they emit. They can then evaluate models that predict how mass and composition differences in source stars will affect the element proportions seen in the planetary nebulae by comparing these predictions with the quantities actually observed.
By observing element proportions in planetary nebulae throughout the Milky Way Galaxy, Kwitter and colleagues will assess current models of galactic chemical evolution. More recent generations of stars born in the Milky Way Galaxy possess richer chemical makeup due to the contributions of planetary nebulae and also supernovae to the interstellar medium.
It has been estimated that nearly all the nitrogen and approximately half the carbon in the sun's region of the Milky Way Galaxy, including humans, came from planetary nebulae.
Leila Zelnick, a Williams senior from Broken Arrow, Okla.; Joel Iams, a Williams junior from Bethesda, Md.; and Hugh Crowl, Wesleyan College '00 joined Kwitter in this research over the summer, and the latter two students observed with her at the Kitt Peak National Observatory. Under the NSF grant, student participation will continue, leading eventually to published papers.
Kwitter has taught astronomy at Williams since 1979. She has published numerous articles in astronomical journals and contributed to several textbooks; most recently she collaborated with Steven Souza on two books, Force & Motion and Our Solar System . Kwitter received her B.A. from Wellesley College in 1972 and her Ph.D. in astronomy from University of California in Los Angeles in 1979.