A Brief History of Star Formation and Chemical Enrichment in the Bulge of the Milky Way

Jay A. Frogel

Published 1998-12-02Version 1

Observations of the stellar content of the bulge of the Milky Way can provide critical guidelines for the interpretation of observations of distant galaxies, in particular for understanding their stellar content and evolution. In this brief overview I will first highlight some recent work directed towards measuring the history of star formation and the chemical composition of the central few parsecs of the Galaxy. These observations point to an episodic history of star formation in the central region with several bursts having occurred over the past few 100 Myr (e.g. Blum et al. 1996b). High resolution spectroscopic observations by Ram\'{\i}rez et al. (1998) of luminous M stars in this region yield a near solar value for [Fe/H] from direct measurements of iron lines. Then I will present some results from an ongoing program by my colleagues and myself the objective of which is the delineation of the star formation and chemical enrichment histories of the central 100 parsecs of the Galaxy, the ``inner bulge''. From new photometric data we have concluded that there is a small increase in mean [Fe/H] from Baade's Window to the Galactic Center and deduce a near solar value for stars in the central region. For radial distances greater than 1$^{\circ}$ from the Galactic Center we fail to find a measurable population of stars that are significantly younger than those in Baade's Window. Within 1$^{\circ}$ we find a number of luminous M giants that most likely are the result of a star formation episode not more than one or two Gyr ago.