Abstract
Context. Brown dwarfs represent a sizable fraction of the stellar content of our Galaxy and populate the transition between the stellar and planetary mass regime. There is however no agreement on the processes responsible for their formation. Aims. We have conducted a large survey of the young, nearby cluster IC 348, to uncover its low-mass brown dwarf population and study the cluster properties in the substellar regime. Methods. Deep optical and near-IR images taken with MegaCam and WIRCam at the Canada-France-Hawaii Telescope (CFHT) were used to select photometric candidate members. A spectroscopic follow-up of a large fraction of the candidates was conducted to assess their youth and membership. Results. We confirmed spectroscopically 16 new members of the IC 348 cluster, including 13 brown dwarfs, contributing significantly to the substellar census of the cluster, where only 30 brown dwarfs were previously known. Five of the new members have a L0 spectral type, the latest-type objects found to date in this cluster. At 3 Myr, evolutionary models estimate these brown dwarfs to have a mass of ~13 Jupiter masses. Combining the new members with previous census of the cluster, we constructed the IMF complete down to 13 Jupiter masses. Conclusions. The IMF of IC 348 is well fitted by a log-normal function, and we do not see evidence for variations of the mass function down to planetary masses when compared to other young clusters.
Highlights
Large scale imaging surveys of young star-forming clusters and spectroscopic confirmation of bona fide members are fundamental to derive complete and reliable census of their populations
Based on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, and MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii
A deep near-IR and optical photometric survey of the young cluster IC 348 was conducted with MegaCam and WIRCam at the CFHT to search for low-mass brown dwarfs members of the cluster
Summary
Large scale imaging surveys of young star-forming clusters and spectroscopic confirmation of bona fide members are fundamental to derive complete and reliable census of their populations. Such endeavors are the first step in the characterization of a cluster, allowing the posterior statistical study of the members’ properties (e.g. disks and jets, dynamics, binarity, or the mass distribution) and comparison between different clusters. The characterization of the mass spectrum of a cluster gains another importance, since it could help distinguish among different formation scenarios for brown dwarfs (e.g., Hennebelle 2012) This is the goal of a large programme We derive a clean and complete census of the substellar population (Sect. 4), and extend the IMF down to the planetary regime (Sect. 5)
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