The Perseus Arm is the closest Galactic spiral arm from the Sun, offering an excellent opportunity to study in detail its stellar population. However, its distance has been controversial with discrepancies by a factor of two. Kinematic distances are in the range 3.9-4.2kpc as compared to 1.9-2.3kpc from spectrophotometric and trigonometric parallaxes, reinforcing previous claims that this arm exhibits peculiar velocities. We used the astrometric information of a sample of 31 OB stars from the star-forming W3Complex to identify another 37 W3 members and to derive its distance from their Gaia-DR2 parallaxes with improved accuracy. The Gaia-DR2 distance to the W3Complex, 2.14^+0.08^-0.07_kpc, coincides with the previous stellar distances of ~2kpc. The Gaia-DR2 parallaxes tentatively show differential distances for different parts of the W3 Complex: W3 Main, located to the NE direction, is at 2.30^+0.19^-0.16_kpc, the W3 Cluster (IC1795), in the central region of the complex, is at 2.17^+0.12^-0.11_kpc, and W3(OH) is at 2.00^+0.29^-0.23_kpc to the SW direction. The W3 Cluster is the oldest region, indicating that it triggered the formation of the other two star-forming regions located at the edges of an expanding shell around the cluster.

Cone search capability for table J/MNRAS/487/2771/table2 (Known OB stars associated with the W3 Complex)

Cone search capability for table J/MNRAS/487/2771/table3 (Gaia-DR2 astrometric information of the OB-type stellar population of the W3 Complex)

Cone search capability for table J/MNRAS/487/2771/table4 (Gaia-DR2 data of the new W3 members selected)