Open cluster birth analysis and multiple spiral arm sets in the Milky Way

The Milky Way spiral arm kinematics is studied using the birth place of open clusters. We separately study the nearby spiral arms, and find evidence for multiple spiral sets. In particular, the Sagittarius–Carina arm appears to be a superposition of two sets. The first has a pattern speed of ΩP,Carina,1=16.5-1.4sys+1.2±1.1statkms-1kpc-1, while the second has ΩP,Carina,2=29.8-1.3sys+0.6±1.3statkms-1kpc-1. The Perseus arm located at larger galactic radii exhibits only one clear set with ΩP,Perseus=20.0-1.2sys+1.7±1.6statkms-1kpc-1. The Perseus and “slower” Carina arms are most probably part of an m=4m=4 set. The Orion “armlet” appears to have a pattern speed of ΩP,Orion=28.9-1.2sys+1.3±0.8statkms-1kpc-1. In other words, both the “faster” Carina arm and the Orion arm are nearly corotating with the solar system.