Spectral types of OB stars <200Myr from Gaia DR3

The wide age range of OB-type stars, coupled with the large amount of high-precision astrometric data provided by Gaia DR3, presents us with an opportunity to explore this issue. After constructing overdensity maps and examining the variations of overdensities with Galactocentric distance along the Galactic azimuth, we compare the spiral structures traced by B3-B5, B6-B7, B8, and B9 stars with those of young O-B2 stars in the vicinity of the Sun.

We find that as the ages of the OB tracer stars increase, the Perseus Arm traced by them gradually shifts toward the anti-Galactic center direction, and the pitch angle of the Carina Arm gradually decreases. These results will help us to understand better the evolutionary properties of nearby spiral arms.