Letter to the Editor

KMHK 1762: Another star cluster in the Large Magellanic Cloud age gap

¹ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Naples, Italy
e-mail: massimiliano.gatto@inaf.it
² Dept. of Physics, University of Naples Federico II, C.U. Monte Sant’Angelo, Via Cinthia, 80126 Naples, Italy
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio, Via Gobetti 93/3, 40129 Bologna, Italy
⁴ Physics Departement, University of Pisa, Largo Bruno Pontecorvo, 3, 56127 Pisa, Italy
⁵ INFN, Largo B. Pontecorvo 3, 56127 Pisa, Italy
⁶ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Received: 10 May 2022
Accepted: 18 July 2022

Abstract

Context. The star cluster (SC) age distribution of the Large Magellanic Cloud (LMC) exhibits a gap from ∼4 to 10 Gyr ago, with an almost total absence of SCs. Within this age gap, only two confirmed SCs have been identified hitherto. Nonetheless, the star field counterpart does not show the same characteristics, making the LMC a peculiar galaxy where the star formation history and cluster formation history appear to differ significantly.

Aims. We re-analysed the colour-magnitude diagram (CMD) of the KMHK 1762 SC by using the deep optical photometry provided by the ‘Yes, Magellanic Clouds Again’ survey, so as to robustly assess its age.

Methods. First, we partially removed foreground and/or field stars by means of parallaxes and proper motions obtained from the Gaia Early Data Release 3. Then, we applied the Automated Stellar Cluster Analysis package to the cleaned photometric catalogue to identify the isochrone that best matches the CMD of KMHK 1762.

Results. The estimated age of KMHK 1762 is log(t)=9.74 ± 0.15 dex (∼5.5 Gyr), which is more than 2 Gyr older than the previous estimation which was obtained with shallower photometry. This value makes KMHK 1762 the third confirmed age-gap SC of the LMC.

Conclusions. The physical existence of a quiescent period of the LMC SC formation is questioned. We suggest it can be the result of an observational bias, originating from the combination of shallow photometry and limited investigation of the LMC periphery.