The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects - CNRS - Centre national de la recherche scientifique Accéder directement au contenu
Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2007

The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects

J. A. Caballero
  • Fonction : Auteur
V. J. S. Béjar
  • Fonction : Auteur
R. Rebolo
  • Fonction : Auteur
J. Eislöffel
M. R. Zapatero Osorio
  • Fonction : Auteur
R. Mundt
  • Fonction : Auteur
D. Barrado y Navascués
  • Fonction : Auteur
G. Bihain
  • Fonction : Auteur
C. A. L. Bailer-Jones
  • Fonction : Auteur
T. Forveille
E. L. Martín
  • Fonction : Auteur

Résumé

Aims.We investigate the mass function in the substellar domain down to a few Jupiter masses in the young σ Orionis open cluster (3±2 Ma, d = 360^+70_-60 pc). Methods: We have performed a deep IJ-band search, covering an area of 790 arcmin2 close to the cluster centre. This survey was complemented with an infrared follow-up in the HK_s- and Spitzer 3.6-8.0 μm-bands. Using colour-magnitude diagrams, we have selected 49 candidate cluster members in the magnitude interval 16.1 mag < I < 23.0 mag. Results: Accounting for flux excesses at 8.0 μm and previously known spectral features of youth, we identify 30 objects as bona fide cluster members. Four are first identified from our optical-near infrared data. Eleven have most probable masses below the deuterium burning limit which we therefore classify as candidate planetary-mass objects. The slope of the substellar mass spectrum (Δ N / Δ {M} ≈ a { M}-α) in the mass interval 0.11 M_ȯ < {M} < 0.006 M_ȯ is α = +0.6 ± 0.2. Any mass limit to formation via opacity-limited fragmentation must lie below 0.006 M_ȯ. The frequency of σ Orionis brown dwarfs with circumsubstellar discs is 47±9 %. Conclusions: The continuity in the mass function and in the frequency of discs suggests that very low-mass stars and substellar objects, even below the deuterium-burning mass limit, share the same formation mechanism. Alexander von Humboldt Fellow at the Max-Planck-Institut für Astronomie Appendices are only available in electronic form at http://www.aanda.org
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hal-00398385 , version 1 (05-01-2023)

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J. A. Caballero, V. J. S. Béjar, R. Rebolo, J. Eislöffel, M. R. Zapatero Osorio, et al.. The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects. Astronomy and Astrophysics - A&A, 2007, 470, pp.903. ⟨10.1051/0004-6361:20066993⟩. ⟨hal-00398385⟩
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