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.

7 pages, 6 figures. Accepted for publication in MNRAS

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• Canis Major OB1 stellar groups contents revealed by Gaia
• Stellar Population Astrophysics (SPA) with the TNG: Stock 2, a little-studied open cluster with an eMSTO
• Photometric study of the young open clusters IC 1442, King 21, and Trumpler 7
• A binary star sequence in the outskirts of the disrupting Galactic open cluster UBC 274