2005ApJ...621L.105N

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_sversus H-K_scolor-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 {mid}l{mid}≲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.