The stellar content near the galactic center

Abstract

High angular resolution J, H, K, and L′ images are used to investigate the stellar content within 6 arcsec of SgrA*. The data, which are complete to K∼16, are the deepest multicolor observations of this region published to date. The mean locus of the (K,H - K) CMD varies across the field, a result that is attributed to differential reddening with amplitude ΔAV∼15 mag. The reddening variations within 3 arcsec of SgrA* are significantly smaller than this, and the resolved members of the compact star cluster immediately surrounding SgrA* have photometric properties that are not significantly different from objects at larger radii. We find that sources in our field with published 2 μm spectra showing either line emission or CO absorption occupy different sequences on the (K,J - K) CMD. The emission line stars, which fall along the most richly populated sequence, have redder J - K colors than stars in the Magellanic Clouds with similar spectroscopic characteristics, and evidence is presented that this is due to excess infrared emission in the spectrum of the GC sources. The photometric properties of the giant branch, which is defined by stars showing CO absorption, are similar to those of the giant branch in Baade's Window (BW). The mean J - K color and peak K brightness of the red giant branch are both consistent with a metal-rich population having an age ∼ 10 Gyr, while the width of the giant branch on the (K,J - K) CMD is indicative of an age spread Δ log(t)=≤1 dex. Therefore, if the inner bulge contains an underlying population of stars with ages in excess of ∼ 10 Gyr, as is the case in BW, then the region within a few arcsec of SgrA* cannot contain a large population of giant branch stars younger than 1 Gyr. We also report the detection of a modest population of faint, blue sources with K≥14. We speculate that these are bright main sequence stars at the distance of the GC, although spectra will be required to confirm this interpretation. Nevertheless, the photometric properties of the largely unresolved compact knot of stars immediately surrounding SgrA* provide indirect evidence to support the presence of a large population of faint blue stars. In particular, we confirm previous studies that measure a relatively blue color for this cluster. Show more