The Distribution of Main Sequence and Pre-Main Sequence Stars in the Young Anticenter Cluster NGC 2401

TL;DR

This study uses Gemini South data to analyze the spatial distribution and properties of main sequence and pre-main sequence stars in NGC 2401, revealing primordial sub-clustering and a consistent mass function.

Contribution

It provides the first detailed analysis of both MS and PMS stars in NGC 2401, highlighting their spatial distributions and implications for star formation processes.

Findings

PMS stars are more widely distributed than MS stars.

The luminosity function matches a solar neighborhood mass function.

Wide binary frequency is higher among MS stars.

Abstract

Images obtained with the Gemini Multi-Object Spectrograph on Gemini South are used to examine the photometric properties and spatial distributions of main sequence (MS) and pre-main sequence (PMS) objects in the star cluster NGC 2401. The data sample several magnitudes fainter than previous studies, and a large population of candidate PMS (cPMS) stars are identified. The cPMS stars are traced out to 2.4 arcmin from the cluster center, and have a flatter spatial distribution than the brightest MS stars near the cluster center. The luminosity function of all MS and candidate PMS stars can be matched by a model that assumes a solar neighborhood mass function, suggesting that NGC 2401 has not yet shed significant numbers of members with masses in excess of 0.5 solar. The frequency of wide binaries among the MS stars is ~3 times higher than among the cPMS stars. It is argued that the difference in the spatial distributions of MS and PMS objects is not the consequence of secular dynamical evolution or structural evolution driven by near-catastrophic mass loss. Rather, it is suggested that the different spatial distributions of these objects is the fossil imprint of primordial sub-clustering that arises naturally if massive stars form preferentially in the highest density central regions of a protocluster.