NOAO >   Observing Info >   Approved Programs >   2003B-0203

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Proposal Information for 2003B-0203


PI: Jennifer Johnson, DAO/HIA/NRC, Jennifer.Johnson@nrc.gc.ca
Address: Dominion Astrophysical Observatory, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada

CoI: Timothy Beers, Michigan State University
CoI: Falk Herwig, University of Victoria
CoI: Norbert Christlieb, Hamburger Sternwarte

Title: Nitrogen Abundances in Very Metal-Poor Stars

Abstract: While nitrogen is a common element in the cosmos, the site(s) of its manufacture remain uncertain. Theoretical models suggest that the main source of primary nitrogen should be hot bottom burning in intermediate- mass AGB stars. However, recent observations of very metal-poor stars do not support this idea, since few stars have been identified that have been polluted by AGB companions with [C/N]< -1, as predicted by the models. Instead, the chemical properties of some of the N- (and C-) rich stars suggest a different source for N. Before rewriting theories of N production, however, we should consider the possibility of a bias in present observations. Molecular CN features are located throughout the conveniently accessed optical portion of stellar spectra, but N abundances are usually only obtained if the CN bands are sufficiently strong, which depends to a greater extent on the C enhancement than the N enhancement. As a result, the sample of stars with reported N abundances favors stars that are quite carbon rich. We propose instead to obtain N abundances using the NH bands at 3360\AA for a sample of very metal-poor stars, covering a wide range of carbon abundances, in order to demonstrate this bias, and to ascertain the distribution of N for metal-poor stars with low ([C/Fe]~ 0) to intermediate ([C/Fe] ~ +1.0) carbon abundance.


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