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 Omega(P,Carina,1) = 16.5(-1.4sys)(+1.2) +/- 1.1(stat) km s(-1) kpc(-1), while the second has Q(P1Carina,2) = 29.8(-1.3sys)(+0.6) 1.3 km s(-1) kpc(-1). The Perseuss seus arm located at larger galactic radii exhibits only one clear set with QP.Perseus 20.0-1 2sys 1.6s,at krn s-1 kpc-1. The Perseus and slower Carina arms are most probably part of an m = 4 set. The Orion armlet appears to have a pattern speed of Q(P,Orion) = 28.9(-1.2sys)(+1.3) +/- 0.8(stat) km s(-1) kpc(-1). In other words, both the faster Carina arm and the Orion arm are nearly corotating with the solar system. (c) 2007 Elsevier B.V. All rights reserved.