KMHK 1762 (also known as OHSC 37) is a star cluster in the Large Magellanic Cloud (LMC), a dwarf galaxy, a satellite of the Milky Way, located 163,000 light-years distant from us.
The cluster has a metallicity level of -0.91 and is estimated to be about 2.7 billion years old. However, an analysis of the color magnitude diagram (CMD) of KMHK 1762 suggests that the cluster may be older than currently estimated.
A team of astronomers led by Massimiliano Gatto of the Capodimonte Astronomical Observatory in Naples, Italy, has investigated this problem. In their work, posted on the ArXiv preprint server ( not yet peer-reviewed), it appears that it may be a rare case of a star cluster in the so-called LMC age gap. Previous LMC observations have found that this galaxy exhibits an almost complete absence of star clusters with ages between 4 and 10 billion years . Within this age gap, only two confirmed star clusters have been identified so far .
Exploring cumulus photometry
Astronomers investigated the deep optical photometry of KMHK 1762 obtained with the Very Large Telescope from Cerro Paranal in Chile, as part of the Yes, Magellanic Clouds Again (YMCA) study. The study was supplemented with data from ESA’s Gaia satellite.
“In this letter, we report the result of our new study of KMHK 1762 SC [star cluster], based on YMCA’s deep and accurate photometry, supplemented with parallaxes and proper motions (PM) from Gaia Early Data Release 3 (EDR3)” According to the new study, the appropriate age of KMHK 1762 should be older than previously thought, the researchers wrote.
The cluster would thus be about 5.5 billion years old. This means that KMHK 1762 is the third star cluster in the LMC age gap, in addition to clusters ESO121-03 and KMHK 1592.
“Most of the work devoted to the search for undiscovered star clusters focused on the central regions of LMC leaving the outskirts (i.e. d > 4 kpc) quite unexplored and was done on the basis of shallow photometric surveys, which which allowed the researchers to detect only stellar clusters smaller than ∼1–1.5 Gyrs,” the researchers concluded.
Reference: M. Gatto et al, KMHK 1762: Another star cluster in the Large Magellanic Cloud age gap. arXiv:2207.09478v1 [astro-ph.GA], arxiv.org/abs/2207.09478