A DISTINCT STRUCTURE INSIDE THE GALACTIC BAR

摘要

We present the result of a near-infrared (JHK_s) survey along the Galactic plane, -10.5° ≤ l≤ 10.5° and b = +1°, with the IRSF 1.4 m telescope and the SIRIUS camera. K_s versus H - K_s color-magnitude diagrams reveal a well-defined population of red clump stars whose apparent magnitude peak changes continuously along the Galactic plane, from K_s = 13.4 at l = -10° to K_s = 12.2 at l = 10° after dereddening. This variation can be explained by the barlike structure found in previous studies, but we find an additional inner structure at ∣ l ∣ approx< 4°, where the longitude-apparent magnitude relation is distinct from the outer bar and where the apparent magnitude peak changes by only ≈0.1 mag over the central 8°. The exact nature of this inner structure is as yet uncertain.