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

Abstract

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.

Haffner 16 Redux: Revisiting a Young Cluster in the Outer Galaxy* †

“…While good agreement was found between models and observations in K, this was not the case at wavelengths shortward of 1µm. Similar behaviour was found by Davidge (2014;2015) when comparing isochrones with the (i ′ , g ′ −i ′ ) and (K, J −K) CMDs of the 20 Myr cluster NGC 2401.…”

NGC 3105: A Young Cluster in the Outer Galaxy∗ †

“…Lyra et al 2006;Bell et al 2012). Davidge (2015) found an offset ∆(g ′ − i ′ ) ∼ 0.4 magnitudes between the observed and model PMS sequence in the ∼ 20 Myr cluster NGC 2401, in the sense that the cluster sequence is redder than models from Bressan et al (2012) and Siess et al (2000). Still, unless there are systematic differences between the properties of PMS stars in NGC 2401 and NGC 3105 (aside from age) then the g ′ − i ′ color of the faint end of the NGC 3105 CMD suggests that the cluster has an age > 20 Myr.…”

“…In any event, ensembles of candidate stars can be identified statistically by examining the spatial distribution and photometric properties of objects (e.g. Davidge 2015), as is done here.…”

The JCMT Gould Belt Survey: Dense Core Clusters in Orion A

“…As discussed in K16, several recent studies of young protostellar clusters find evidence of centrally located more massive members (e.g., Megeath et al 2005;Hunter et al 2006;Kryukova et al 2012;Elmegreen et al 2014);though,at least one other study comes to a different conclusion (Hunter et al 2014). Observations of slightly older protostellar clusters also often show evidence of mass segregation, and estimate that the clusters are too young to be able to explain this through dynamical evolution (e.g., Carpenter et al 1997;Hillenbrand 1997;Bonnell & Davies 1998;Stolte et al 2006;Gennaro et al 2011;Kirk & Myers 2011;Davidge 2015); though, this interpretation is somewhat controversial, with other authors finding a lack of evidence of primordial (or sometimes present day) mass segregation (e.g., Allison et al 2009aAllison et al , 2010Parker et al 2012;Wright et al 2014). The observations we analyze here show the clustering behavior at an early stage, and it is important to emphasize that the masses, and to a lesser extent, the locations, of the dense cores will continue to evolve beyond the snapshot in time that our observationscapture.…”