Spiral structure as revealed by O and B stars

We select 6858 highly confident OB star candidates from the combined data of the VST Photometric H{alpha} Survey Data Release 2 (VPHAS+ DR2) and the Gaia Data Release 2 (Gaia DR2). Together with the O-B2 stars from the literature, we build a sample consisting of 14880 O- and early B-type stars, all with Gaia parallax uncertainties smaller than 20 per cent.

The new sample, hitherto the largest one of O- and early B-type stars with robust distance and proper motion estimates, covers the Galactic plane of distances up to 6kpc from the Sun. The sample allows us to examine the morphology of the Scutum, Sagittarius, Local, and Perseus Arms in great detail. The spiral structure of the Milky Way as traced by O- and early B-type stars shows flocculent patterns.