The Metallicity and Reddening of Stars in the Inner Galactic Bulge

We present a preliminary analysis of K, J-K color-magnitude diagrams (CMDs) for seven different positions on or close to the minor axis of the Milky Way at Galactic latitudes between +01 and -28. From the slopes of the (linear) giant branches in these CMDs, we derive a dependence of ⟨[Fe/H]⟩ on latitude for b between -08 and -28 of -0.085 ± 0.033 dex deg^-1. When combined with the data from Tiede et al., we find for -08 ≤ b ≤ -103 the slope in ⟨[Fe/H]⟩ is -0.064 ± 0.012 dex deg^-1. An extrapolation to the Galactic center predicts [Fe/H] = +0.034 ± 0.053 dex.

We also derive average values for the extinction in the K band (A_K) of between 2.15 and 0.27 for the inner bulge fields studied, corresponding to average values of E(J-K) of between 3.46 and 0.44. There is a well-defined linear relation between the average extinction for a field and the star-to-star scatter in the extinction for the stars within each field. The equation of this line is σ(A_K) = 0.056(±0.005)⟨A_K⟩ + 0.043(±0.005). This result suggests that the typical apparent angular scale size for an absorbing cloud is small compared with the field size (90'' on a side).

Finally, from an examination of the luminosity function of bright giants in each field we conclude that the young component of the stellar population observed near the Galactic center declines in density much more quickly than the overall bulge population and is undetectable beyond 1° from the Galactic center.