Testing the fragmentation limit in the Upper Sco association

Abstract

We present the results of a deep (J ~ 21 mag at 5 sigma) infrared photometric survey of a 0.95 square degree area in the central region of the Upper Sco association. The photometric observations consist of a deep (Y+J)-band images obtained with the WFCAM camera on the UKIRT InfraRed Telescope (UKIRT) with partly coverage in Z complemented by methane ON and OFF conducted with WIRCam on the Canada France Hawaii Telescope. We have selected five potential T-type objects belonging to the Upper Sco association on the basis of their blue methane colours and their J-CH4off colours. We have also identified a sample of 7-8 Upper Sco member candidates bridging the gap between known cluster M-types and our new T-type candidates. These candidates were selected based on their positions in various colour-magnitude diagrams and they follow the sequence of known Upper Sco members identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS). We present additional membership constraints using proper motion estimates from the multiple epochs available to us. We also present optical and near-infrared spectra obtained with the X--Shooter spectrograph on the Very Large Telescope for five L-type candidates covering the 0.6 to 2.5 micron wavelength range, none of them being confirmed as a young brown dwarf. We discuss the lack of detection of new candidate members as well as the possible turn down in the USco mass function as we are approaching the fragmentation limit.

16 pages, 6 figures, 9 tables, Accepted to MNRAS

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• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The WFCAM Science Archive
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• Spitzer/IRAC Photometry of M, L, and T Dwarfs
• Near-infrared cross-dispersed spectroscopy of brown dwarf candidates in the Upper Sco association
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• New brown dwarfs in Upper Sco using UKIDSS Galactic Cluster Survey science verification data
• Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey
• Disks around Brown Dwarfs in the Sigma Orionis Cluster
• Substellar Objects in Nearby Young Clusters (SONYC): The bottom of the Initial Mass Function in NGC1333
• Proper motion L and T dwarf candidate members of the Pleiades
• New members in the Upper Sco association from the UKIDSS Early Data Release
• New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster

Cited by in corpus (12)

• Seventy six T dwarfs from the UKIDSS LAS: benchmarks, kinematics and an updated space density
• Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: I The Pleiades
• New Young Stars and Brown Dwarfs in the Upper Scorpius Association
• Search for free-floating planetary-mass objects in the Pleiades
• Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: IV Upper Sco
• The optical+infrared L dwarf spectral sequence of young planetary-mass objects in the Upper Scorpius association
• Substellar Objects in Nearby Young Clusters (SONYC) IX: The planetary-mass domain of Chamaeleon-I and updated mass function in Lupus-3
• Probing the Upper Scorpius mass function in the planetary-mass regime
• Searching for planetary-mass T-dwarfs in the core of Serpens
• Exploring the planetary-mass population in the Upper Scorpius association
• Proper motions of Upper Sco T-type candidates
• A review on substellar objects beyond the deuterium burning mass limit: planets, brown dwarfs or what?