Bayo, A. and Barrado, D. and Stauffer, J. and Morales-Calderón, M. and Melo, C. and Huélamo, N. and Bouy, H. and Stelzer, B. and Tamura, M. and Jayawardhana, R. (2011) Spectroscopy of very low mass stars and brown dwarfs in the Lambda Orionis star forming region. I. Enlarging the census down to the planetary mass domain in Collinder 69. Astronomy and Astrophysics, 536 . Art. No. A63. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20120214-134142171
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Context. Whilst there is a generally accepted evolutionary scheme for the formation of low-mass stars, the analogous processes when moving down in mass to the brown dwarf regime are not yet well understood. Aims. In this first paper, we try to compile the most complete and unbiased spectroscopically confirmed census of the population of Collinder 69, the central cluster of the Lambda Orionis star forming region, as a first step in addressing the question of how brown dwarfs and planetary mass objects form. Methods. We study age dependent features in optical and near-infrared spectra of candidate members to the cluster (such as alkali lines and accretion–associated indicators). In addition, we complement that study with the analysis of other youth indicators, such as X-ray emission or mid-infrared excess. Results. We confirm the membership to Collinder 69 of ~90 photometric candidate members. As a byproduct, we determine a temperature scale for young M, very low-mass stars, and brown dwarfs. We assemble one of the most complete initial mass functions from 0.016 to 20 M_⊙. Finally, we study the implications of the spatial distribution of the confirmed members for the proposed mechanisms of brown dwarf formation.
|Additional Information:||© 2011 ESO. Received 1 February 2011; Accepted 21 september 2011. Published online 08 December 2011. We wish to thank the anonymous referee for very useful comments that improved the manuscript without doubt. This research has been funded by Spanish grants ESP2007-65475-C02-02, CSD2006-00070, PRICITS-2009/ESP-1496 and AYA 2010-21161-C02-02. The support of the ESAC faculty is also recognized. It makes use of VOSA, developed under the Spanish Virtual Observatory project supported from the Spanish MICINN through grant AyA2008-02156, and of the SIMBAD database, operated at CDS, Strasbourg, France. The authors wish to thank J. Bouvier and E. Moraux for their data compilation on IMFs of different young associations and Y. Momany for the interesting discussion about statistics when building histograms. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programmes ID 080.C-0592 and 078.C-0124. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.|
|Subject Keywords:||brown dwarfs; stars: formation; stars: luminosity function; mass function, infrared: stars; stars: low-mass; open clusters and associations: individual: Collinder 69|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||06 Apr 2012 18:05|
|Last Modified:||26 Dec 2012 14:50|
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