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Title:
New constraints on the membership of the T dwarf S Ori 70 in the σ Orionis cluster
Authors:
Zapatero Osorio, M. R.; Béjar, V. J. S.; Bihain, G.; Martín, E. L.; Rebolo, R.; Villó-Pérez, I.; Díaz-Sánchez, A.; Pérez Garrido, A.; Caballero, J. A.; Henning, T.; Mundt, R.; Barrado Y Navascués, D.; Bailer-Jones, C. A. L.
Affiliation:
AA(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain ), AB(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain), AC(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain; Consejo Superior de Investigaciones Científicas, Spain), AD(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain; University of Central Florida, Department of Physics, PO Box 162385, Orlando, FL 32816, USA), AE(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain; Consejo Superior de Investigaciones Científicas, Spain), AF(Departamento de Electrónica, Universidad Politécnica de Cartagena, 30202 Cartagena, Spain), AG(Departamento de Física Aplicada, Universidad Politécnica de Cartagena, 30202 Cartagena, Spain), AH(Departamento de Física Aplicada, Universidad Politécnica de Cartagena, 30202 Cartagena, Spain), AI(Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany), AJ(Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany), AK(Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany), AL(LAEFF-INTA, PO 50727, 28080 Madrid, Spain), AM(Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany)
Publication:
Astronomy and Astrophysics, Volume 477, Issue 3, January III 2008, pp.895-900 (A&A Homepage)
Publication Date:
01/2008
Origin:
EDP Sciences
Keywords:
stars: low mass, brown dwarfs, stars: pre-main-sequence, open clusters and associations: individual: σ Orionis
DOI:
10.1051/0004-6361:20078600
Bibliographic Code:
2008A&A...477..895Z

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 σ 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 {JHK}s and mid-infrared [3.6] and [4.5] IRAC/Spitzer photometry recently obtained for S Ori 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-K_s), (J-K_s) 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 S Ori 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 σ Orionis cluster. Our measurement is consistent with the proper motion of the cluster within 1.5σ the astrometric uncertainty.
Conclusions: Taking into account both S Ori 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 S Ori 70's membership in σ Orionis, with an estimated mass in the interval 2-7 M_Jup, in agreement with our previous derivation.
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