The extended Main-Sequence Turnoff of the Milky Way open cluster Collinder 347

Abstract: We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal-content. However, the G versus G_BP-G_RP colour-magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H] = -0.4 dex), with a present-day mass of 3.3x10^3 Mo. The cluster exhibits an extended Main-Sequence turnoff (eMSTO) of nearly 500 Myr, while that computed assuming Gaussian distributions from photometric errors, stellar binarity, rotation and metallicity spread yields an eMSTO of ~340 Myr. Such an age difference points to the existence within the cluster of stellar populations with different ages.