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Session 4 - Education: Telescopes, the Web and Curricula.
Display session, Wednesday, January 07
Exhibit Hall,

[4.09] Laboratory Exercise: Chemical Evolution in the Milky Way

M. L. West, M. J. Feeney (Montclair State U.)

The chemical elements we see on Earth and in our neighborhood of the Milky Way have wildly different abundances from each other. Since we are carbon based-creatures it is intriguing to ask in particular how much carbon is available in the universe at the present time and when it was formed. Low mass stars such as the sun process H->He->C, while high mass stars proceed all the way to Fe, while a small fraction produce a supernova explosion in which Fe->....U. This yield of heavy elements is returned to the interstellar medium by a gentle steady wind from a star in its red giant stage which culminates in the ejection of a planetary nebula, and also by a sudden violent blast from a supernova. The larger mass stars have shorter lifetimes than do the smaller mass stars, so this must be taken into account also. This computer exercise treats the Milky Way as a closed box of 200 billion solar masses. The galaxy begins as 100gas into stars, which make heavy elements. Some of the stars recycle gas gently and some explode as supernovae. The model's input parameters which can be changed include the age of the galaxy, the initial mass function, the present day mass function, the red giant wind, the amount of carbon and iron produced by a supernova, the amount of gas recycled by a supernova, and the star formation rate as a function of time. Students can experiment with these numbers and functions in an Excel spreadsheet, trying to match the present day percent of gas and abundance of carbon and iron. The models which most closely match present conditions require a large number of supernovae (a starburst) early in the galaxy's history.

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Program listing for Wednesday