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Testing the fragmentation limit in the Upper Sco association

Authors

  • N. Lodieu,

    Corresponding author
    1. Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, E-38200 La Laguna, Tenerife, Spain
    2. Departamento de Astrofísica, Universidad de La Laguna (ULL), E-38205 La Laguna, Tenerife, Spain
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  • N. C. Hambly,

    1. Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, School of Physics and Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ
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  • P. D. Dobbie,

    1. Australian Astronomical Observatory, PO Box 296, Epping, NSW 1710, Australia
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  • N. J. G. Cross,

    1. Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, School of Physics and Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ
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  • L. Christensen,

    1. Excellence Cluster Universe, Technische Universität München, Bolzmanstrasse 2, 85748 Garching bei München, Germany
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  • E. L. Martin,

    1. CSIC-INTA Centro de Astrobiología, Ctra. Ajalvir km 4, 28850, Torrejón de Ardoz, Madrid, Spain
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  • L. Valdivielso

    1. Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, E-38200 La Laguna, Tenerife, Spain
    2. Departamento de Astrofísica, Universidad de La Laguna (ULL), E-38205 La Laguna, Tenerife, Spain
    3. Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan, 1, E-44001 Teruel, Spain
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Based on observations made with the United Kingdom Infra-Red Telescope, Canada–France–Hawaii Telescope and Very Large Telescope.

E-mail: nlodieu@iac.es

ABSTRACT

We present the results of a deep (J∼ 21 at 5σ) infrared photometric survey of a 0.95-deg2 area in the central region of the Upper Sco association. The photometric observations consist of a deep Y+J-band image obtained with the Wide Field Camera on the United Kingdom Infra-Red Telescope (UKIRT) with part coverage in Z complemented by the methane ON and OFF imaging survey conducted with the Wide-field InfraRed Camera 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− CH4 off colours. We have also identified a sample of seven to eight 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 Galactic Clusters Survey. We present additional membership constraints using proper motion estimates from the multiple epochs available with 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 0.6–2.5 inline imagem wavelength range, none of which is 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 Upper Sco mass function as we are approaching the fragmentation limit.

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