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Title:
Discs of planetary-mass objects in σ Orionis
Authors:
Zapatero Osorio, M. R.; Caballero, J. A.; Béjar, V. J. S.; Rebolo, R.; Barrado Y Navascués, D.; Bihain, G.; Eislöffel, J.; Martín, E. L.; Bailer-Jones, C. A. L.; Mundt, R.; Forveille, T.; Bouy, H.
Affiliation:
AA(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain ), AB(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany), AC(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain), AD(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain; Consejo Superior de Investigaciones Científicas, Spain), AE(LAEFF-INTA, PO Box 50727, 28080 Madrid, Spain), AF(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain; Consejo Superior de Investigaciones Científicas, Spain), AG(Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany), AH(Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain; University of Central Florida, Dept. of Physics, PO Box 162385, Orlando, FL 32816-2385, USA), AI(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany), AJ(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany), AK(Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, Hawai'i, USA ; Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France), AL(Astronomy Department, University of California, Berkeley, CA 94720, USA ; Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain)
Publication:
Astronomy and Astrophysics, Volume 472, Issue 1, September II 2007, pp.L9-L12 (A&A Homepage)
Publication Date:
09/2007
Origin:
EDP Sciences
Keywords:
Galaxy: open clusters and associations: individual: σ Orionis, stars: planetary systems: protoplanetary disks, stars: low mass, brown dwarfs
DOI:
10.1051/0004-6361:20078116
Bibliographic Code:
2007A&A...472L...9Z

Abstract

Aims:We searched for infrared flux excesses of planetary-mass candidates in the σ Orionis cluster (~3 Myr, ~350 pc).
Methods: Using IJHKs data from the literature and the [3.6], [4.5], [5.8], and [8.0] IRAC images of the σ Orionis cluster from the Spitzer Space Telescope public archives, we constructed colour-colour diagrams and spectral energy distributions from 0.8 to 8.0 μm of cluster candidates fainter than J = 18.0 mag, i.e. the planetary-mass borderline for σ Orionis.
Results: Infrared flux excesses are detected longward of 5 μm in seven objects (S Ori 54, 55, 56, 58, 60, S Ori J053956.8-025315 and S Ori J053858.6-025228) with masses estimated in the range 7-14 M_Jup. Emission at shorter wavelengths (4.5 μm) in excess of the photosphere is probably observed in S Ori 56 and S Ori J053858.6-025228. The faintest and least massive object, S Ori 60, exhibits flux excess only at 8 μm. We ascribe these infrared excesses to the presence of circumsubstellar warm discs, providing additional confirmation for the objects' membership of σ 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 Mȯ through the substellar domain), which may be due to a mass-dependent timescale for the dissipation of the interior discs.
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