Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses^⋆

¹ European Space Astronomy Centre (ESA), PO Box 78, 28691 Villanueva de la Cañada Madrid Spain
e-mail: calves@sciops.esa.int
² UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
³ Astronomy Department, University of California, Berkeley, CA 94720–3411, USA
⁴ Centro de Astrobiologa (INTA-CSIC); PO Box 78, 28691 Villanueva de la Cañada, Spain
⁵ Institut d′Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France

Received: 14 August 2012
Accepted: 8 November 2012

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 have studied 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 M_Jup. Combining the new members with previous census of the cluster, we constructed the initial mass function (IMF) complete down to 13 M_Jup.

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.