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

Abstract

Images obtained with the Gemini Multiobject Spectrograph on Gemini South are used to examine the photometric properties and spatial distributions of main sequence (MS) and premain 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′ 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 ≥0.5 M ⊙. The frequency of wide binaries among the MS stars is ∼3× 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 subclustering that arises naturally if massive stars form preferentially in the highest density central regions of a protocluster.