Galactic bulge

The thin disk The thick disk The galactic bulge The stellar halo... 

Abstract. A review is presented on abundance determinations in stars of the Galactic bulge, both in the field and in globular clusters. Previous low-resolution spectroscopy results are revised. Recent high resolution and high S/N spectroscopy results based on Keck-Hires, Gemini-Phoenix and VLT-UVES data are presented. Finally, recent analyses of FLAMES data are discussed. 

The Galactic Bulge contains about 20 percent of the Galaxy s stellar mass. Theories of its formation include a primordial free-fall collapse, remnants of accretion episodes, or secular evolution of bar instabilities ([1]). Accurate stellar abundance determinations can help distinguish between these models. 

Table 1 lists our abundances of Fe, C, O and a-elements for the observed clusters. An overall excess of a-elements is shared by all the clusters up to solar metallicity, consistent with SNell being responsible for the gas enrichment. Our findings are also in good agreement both with all previous high resolution studies (see [2], [3], [6]) and with recent abundance determinations for field stars in the Galactic Bulge (see [10]). 

It is quite astonishing how little observational information is available on the chemistry and kinematics of the Galactic Bulge. A massive and exciting opportunity for the current multi-object spectrographs is being overlooked here. 

Fig. 8.22. Metallicity distribution function for giants in the Galactic bulge, after Zoccali et al. (2003), fitted with a Simple model having a yield of Z .

However, the observations from Ratag et al. (1997) were used in the compilation of line intensities by Stasinska et al. (1998), and the abundances rederived in a consistent way with Te-based methods (for objects for which this was possible). The objects of Escudero Costa (2001) are newly discovered PNe from the list of Beaulieu et al. (1999). We see that the abundances of PNe in the Galactic bulge have clearly higher mean values and dispersions in O/H than the extrapolation from disk PNe towards the Galactic center, which are shown in Table 10. The effect may be even stronger than suggested from these... 

Combining data on about 100 PNe in the Galactic bulge from the works of Cuisinier et al. (2000), Webster (1988), Aller Keyes (1987) with their own data, Escudero Costa (2001) suggest the existence of a vertical abundance gradient in the bulge, with lower O/H at high latitudes. 

Various scenarios have been proposed insofar for the formation of the Galactic bulge but only one seems to reproduce the observed abundance pattern. Here I recall the main scenarios ... 

Abstract. We present radial velocities for 33 stars in an optically obscured field toward the Galactic bulge at I=—1.14, 6=1.81. The radial velocities are derived from spectra of the 2.3 pm CO bandhead that is prominent in late type giants. The heliocentric radial velocity and velocity dispersion are —75 24 km s - and 127 16 km s respectively. 

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