New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster

    Authors

    M. R. Z. Osorio; V. J. S. Bejar; G. Bihain; E. L. Martin; R. Rebolo; I. Villo-Perez; A. Diaz-Sanchez; A. P. Garrido; J. A. Caballero; T. Henning; R. Mundt; D. B. Y. Navascues;C. A. L. Bailer-Jones

    Comments

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    Abbreviated Journal Title

    Astron. Astrophys.

    Keywords

    stars : low mass, brown dwarfs; stars : pre-main-sequence; open clusters; and associations : individual : sigma Orionis; SPITZER-SPACE-TELESCOPE; PLANETARY-MASS OBJECTS; BROWN DWARFS; SPECTRAL; CLASSIFICATION; INFRARED PHOTOMETRY; L/T TRANSITION; H-ALPHA; YOUNG; STARS; DISCOVERY; Astronomy & Astrophysics

    Abstract

    Aims. The nature of S Ori 70 (S Ori J053810.1-023626), a faint mid-T type object found towards the direction of the young sigma Orionis cluster, is still under debate. We intend to find out whether it is a field brown dwarf or a 3-Myr old planetary-mass member of the cluster. Methods. We report on near-infrared JHKs and mid-infrared [3.6] and [4.5] IRAC/ Spitzer photometry recently obtained for SOri 70. The new near-infrared images (taken 3.82 yr after the discovery data) allowed us to derive the first proper motion measurement for this object. Results. The colors (H - Ks), (J - Ks) and Ks - [ 3.6] appear discrepant when compared to T4-T7 dwarfs in the field. This behavior could be ascribed either to a low-gravity atmosphere or to an atmosphere with a metallicity that is significantly different than solar. The small proper motion of SOri 70 (11.0 +/- 5.9 mas yr(-1)) indicates that this object is farther away than expected if it were a single field T dwarf lying in the foreground of the sigma Orionis cluster. Our measurement is consistent with the proper motion of the cluster within 1.5 sigma the astrometric uncertainty. Conclusions. Taking into account both SOri 70' s proper motion and the new near-and mid-infrared colors, a low-gravity atmosphere remains as the most likely explanation for our observations. This supports SOri 70' s membership in sigma Orionis, with an estimated mass in the interval 2-7 M-Jup, in agreement with our previous derivation.

    Journal Title

    Astronomy & Astrophysics

    Volume

    477

    Issue/Number

    3

    Publication Date

    1-1-2008

    Document Type

    Article

    Language

    English

    First Page

    895

    Last Page

    900

    WOS Identifier

    WOS:000252131000024

    ISSN

    0004-6361

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