Pre-Main sequence Turn-On as a chronometer for young clusters: NGC346 as a benchmark

TL;DR

This paper introduces a new method using the Turn-On point in the color-magnitude diagram to determine the ages of very young star clusters, demonstrated on NGC346, and discusses its potential for extragalactic studies.

Contribution

It presents a novel approach combining CMD and spatial distribution analysis to identify the Turn-On in extragalactic star-forming regions, improving age estimation accuracy.

Findings

Successfully applied to NGC346 with HST data

Extends luminosity function approach to crowded extragalactic regions

Preliminary results show the method's reliability in young cluster dating

Abstract

We present a novel approach to derive the age of very young star clusters, by using the Turn-On (TOn). The TOn is the point in the color-magnitude diagram (CMD) where the pre-main sequence (PMS) joins the main sequence (MS). In the MS luminosity function (LF) of the cluster, the TOn is identified as a peak followed by a dip. We propose that by combining the CMD analysis with the monitoring of the spatial distribution of MS stars it is possible to reliably identify the TOn in extragalactic star forming regions. Compared to alternative methods, this technique is complementary to the turn-off dating and avoids the systematic biases affecting the PMS phase. We describe the method and its uncertainties, and apply it to the star forming region NGC346, which has been extensively imaged with the Hubble Space Telescope (HST). This study extends the LF approach in crowded extragalactic regions and opens the way for future studies with HST/WFC3, JWST and from the ground with adaptive optics.