On a new Near-Infrared method to estimate the absolute ages of star clusters: NGC3201 as a first test case

TL;DR

This paper introduces a novel near-infrared method to determine the absolute ages of star clusters by measuring the magnitude difference between the main sequence turn-off and the main sequence knee, tested on NGC3201.

Contribution

The study presents a new age estimation technique based on NIR features, reducing uncertainties related to distance and reddening, and validates it with observations of NGC3201.

Findings

The new method yields age estimates consistent with traditional methods within one sigma.

The Delta(MSTO-MSK) method has potentially half the errors of conventional techniques.

Current isochrones slightly underestimate the observed NIR colors for faint magnitudes.

Abstract

We present a new method to estimate the absolute ages of stellar systems. This method is based on the difference in magnitude between the main sequence turn-off (MSTO) and a well defined knee located along the lower main sequence (MSK). This feature is caused by the collisionally induced absorption of molecular hydrogen and it can be easily identified in near-infrared (NIR) and in optical-NIR color-magnitude diagrams of stellar systems. We took advantage of deep and accurate NIR images collected with the Multi-Conjugate Adaptive Optics Demonstrator temporarily available on the Very Large Telescope and of optical images collected with the Advanced Camera for Surveys Wide Field Camera on the Hubble Space Telescope and with ground-based telescopes to estimate the absolute age of the globular NGC3201 using both the MSTO and the Delta(MSTO-MSK). We have adopted a new set of cluster isochrones and we found that the absolute ages based on the two methods agree to within one sigma. However, the errors of the ages based on the Delta(MSTO-MSK) method are potentially more than a factor of two smaller, since they are not affected by uncertainties in cluster distance or reddening.Current isochrones appear to predict slightly bluer (~0.05mag) NIR and optical-NIR colors than observed for magnitudes fainter than the MSK.