  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.
