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The Substellar Population in σ Orionis

  • M. R. Zapatero Osorio (a1), D. Barrado y Navascués (a1), V. J. S. Béjar (a2), R. Rebolo (a2), J. A. Caballero (a2), E.L. Martín (a3), R. Mundt (a4) and J. Eislöffel (a5)...

Abstract

The σ Orionis cluster (~3 Myr, 350 pc) is an ideal site to investigate the early evolution of substellar (brown dwarf and planetary mass) objects. To date, the cluster photometric and spectroscopic sequence of free-floaters is known for a wide mass range from 1 M down to roughly 3 M Jup. The substellar domain covers spectral types that go from mid-M classes to the recently defined “methane” T-types, i.e., surface temperatures between ~3000K and 800 K. We derive a rising initial substellar mass function in the mass interval of 150–5 M Jup (dN/dM ~ M , with α = 0.9 ± 0.4). We also find evidence for a extension of this mass function toward lower masses down to 2–3 M Jup. This indicates that the population of isolated planetary mass objects with masses below the deuterium burning threshold is rather abundant in the cluster.

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The Substellar Population in σ Orionis

  • M. R. Zapatero Osorio (a1), D. Barrado y Navascués (a1), V. J. S. Béjar (a2), R. Rebolo (a2), J. A. Caballero (a2), E.L. Martín (a3), R. Mundt (a4) and J. Eislöffel (a5)...

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