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Stellar associations can be discerned as overdensities of sources not only inthe physical space but also in the velocity space. The common motion of theirmembers, gradually eroded by the galactic tidal field, is partially reminiscentof the initial kinematic structure. Using recent data from Gaia EDR3, combinedwith radial velocities from GALAH and APOGEE, we traced back the presentpositions of stars belonging to Upper Scorpius, a subgroup ofScorpius-Centaurus, the nearest OB association. About one half of the subgroup(the "clustered" population) appears composed of many smaller entities, whichwere in a more compact configuration in the past. The presence of a kinematicduality is reflected into an age spread between this younger clusteredpopulation and an older diffuse population, in turn confirmed by a differentfraction $f_D$ of disc-bearing stars ($f_D = 0.24\pm0.02$ vs $f_D = 0.10\pm0.01$). Star formation in Upper Scorpius appears to have lasted more than 10Myr and proceeded in small groups that, after a few Myr, dissolve in the fieldof the older population but retain for some time memory of their initialstructure. The difference of ages inferred through isochrones and kinematics,in this regard, could provide a powerful tool to quantify the timescale of gasremoval.

Unveiling the star formation history of the Upper Scorpius association through its kinematics