Chemistry of the Galactic Bulge

Abstract

The chemical abundances of the Galaxy tell us about the stellar and interstellar medium (ISM) evolution history. By studying the present-day chemistry of various stars (and the ISM), and combining with stellar evolution models and Galactic evolution models (and star number counts), we can build up a picture of how our Galaxy was formed and how it changes with time. By studying objects that lie in different parts of the Galaxy, we can understand the variation of the local evolutionary history compared to the global history. One must be careful with the types of objects studied; the age which they represent should be known, as well as other details such as their Galactic position. Planetary Nebulae (PNe) are good objects of study for several reasons; their spread in age allows us to follow the chemical history (as opposed to that just at one point in time), they give access to a variety of elements (O, Ne, Ar,...), and abundance calculations are (relatively) simple. From studies of Planetary Nebulae located in the Disk we understand that there are gradients in the abundances of elements, such as Ne and O, in the sense of a decrease with galactocentric radius. The abundances that we observe for PNe in the Galactic Bulge however do not follow these gradients; the determined values are lower. This probably reflects the different star formation history of the Galactic Bulge, but how? We have selected to study a sample of PNe in the Galactic Bulge. As well as discussing the evidence the data gives us on the nucleosynthesis history of the precursor stars, we compare our derived abundances with those for Disk PNe, to determine the degree of difference between the two Galactic locations. In addition, from the younger (Peimbert Type I) PNe we study the Pop. I abundances, and from the older PNe, the Pop. II. Our results are (will be) compared to current Galactic Bulge evolution models, to see how well the theories fit in with observations of PNe. Hopefully, we will be able to place some limits on the star formation history of the Galactic Bulge.