Discs of planetary-mass objects in sigma Orionis

    Authors

    M. R. Z. Osorio; J. A. Caballero; V. J. S. Bejar; R. Rebolo; D. B. Y. Navascues; G. Bihain; J. Eisloffel; E. L. Martin; C. A. L. Bailer-Jones; R. Mundt; T. Forveille;H. Bouy

    Comments

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    Abbreviated Journal Title

    Astron. Astrophys.

    Keywords

    galaxy : open clusters and associations : individual : sigma Orionis; stars : planetary systems : protoplanetary disks; stars : low mass; brown dwarfs; SPITZER-SPACE-TELESCOPE; BROWN DWARFS; CIRCUMSTELLAR DISK; UPPER; SCORPIUS; T-DWARFS; H-ALPHA; PHOTOMETRY; CLUSTER; STARS; IRAC; Astronomy & Astrophysics

    Abstract

    Aims. We searched for infrared flux excesses of planetary-mass candidates in the sigma Orionis cluster (similar to 3 Myr, similar to 350 pc). Methods. Using IJHK(s) data from the literature and the [ 3.6], [ 4.5], [ 5.8], and [ 8.0] IRAC images of the sigma Orionis cluster from the Spitzer Space Telescope public archives, we constructed colour-colour diagrams and spectral energy distributions from 0.8 to 8.0 mu m of cluster candidates fainter than J=18.0 mag, i.e. the planetary-mass borderline for sigma Orionis. Results. Infrared flux excesses are detected longward of 5 mu m in seven objects (SOri 54, 55, 56, 58, 60, SOri J053956.8-025315 and SOri J053858.6- 025228) with masses estimated in the range 7-14 M(Jup). Emission at shorter wavelengths ( 4.5 mu m) in excess of the photosphere is probably observed in SOri 56 and SOri J053858.6-025228. The faintest and least massive object, SOri 60, exhibits flux excess only at 8 mu m. We ascribe these infrared excesses to the presence of circumsubstellar warm discs, providing additional confirmation for the objects' membership of sigma Orionis. The observed incidence of inner discs around planetary-mass objects is > = 50%,which is consistent with the measured inner disc frequency among cluster brown dwarfs and low-mass stars, suggesting that these objects share a common origin. However, there is a trend for the inner disc rate to increase with decreasing mass ( from 10 M(circle dot) through the substellar domain), which may be due to a mass-dependent timescale for the dissipation of the interior discs.

    Journal Title

    Astronomy & Astrophysics

    Volume

    472

    Issue/Number

    1

    Publication Date

    1-1-2007

    Document Type

    Article

    Language

    English

    First Page

    L9

    Last Page

    L12

    WOS Identifier

    WOS:000249758200003

    ISSN

    0004-6361

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