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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents



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ID: 421392.0, MPI für Astronomie / Publikationen_mpia
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.
Language:English
Date of Publication (YYYY-MM-DD):2008
Title of Journal:Astronomy and Astrophysics
Journal Abbrev.:A&A
Volume:477
Start Page:895
End Page:900
Review Status:Peer-review
Audience:Not Specified
Abstract / Description: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 {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 sigma Orionis cluster. Our measurement is consistent with the proper motion of the cluster within 1.5sigma 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 sigma Orionis, with an estimated mass in the interval 2-7 M_Jup, in agreement with our previous derivation.
Free Keywords:stars: low mass; brown dwarfs; stars: pre-main-sequence; open clusters and associations: individual: σ Orionis
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://adsabs.harvard.edu/abs/2008A%26A...477..895... [ID No:1]
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