We investigate the extinction together with the radial velocity dispersion and distribution of red clump stars in the anti-center direction using spectra obtained with Hectospec on the MMT .
We find that extinction peaks at Galactocentric radii of about 9.5 and 12.5 kpc , right in front of the locations of the Perseus and Outer arms and in line with the relative position of dust and stars in external spiral galaxies .
The radial velocity dispersion peaks around 10 kpc , which coincides with the location of the Perseus arm , yields an estimated arm-interarm density contrast of 1.3–1.5 and is in agreement with previous studies .
Finally , we discover that the radial velocity distribution bifurcates around 10–11 kpc into two peaks at +27 km s ^ { -1 } and -4 km s ^ { -1 } .
This seems to be naturally explained by the presence of the outer Lindblad resonance of the Galactic bar , but further observations will be needed to understand if the corotation resonance of the spirals arms also plays a role .