Volume 404, Number 1, June II 2003
|Page(s)||171 - 185|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||26 May 2003|
VLT/FORS spectroscopy and 2MASS photometry
Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, PO Box 50727, 28080 Madrid, Spain
2 Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
4 Institute of Astronomy. University of Hawaii at Manoa. 2680 Woodlawn Drive, Honolulu, HI 96822, USA
5 Consejo Superior de Investigaciones Científicas, CSIC, Spain
Corresponding author: D. Barrado y Navascués, email@example.com
Accepted: 12 March 2003
VLT/FORS spectroscopy and 2MASS near-infrared photometry, together with previously known data, have been used to establish the membership and the properties of a sample of low-mass candidate members of the σ Orionis cluster with masses spanning from 1 down to about 0.013 (i.e., deuterium-burning mass limit). We have observed K-band infrared excess and remarkably intense Hα emission in various cluster members, which, in addition to the previously detected forbidden emision lines and the presence of Li i in absorption at 6708 Å, have allowed us to tentatively classify σ Orionis members as classical or weak-line T Tauri stars and substellar analogs. Variability of the Hα line has been investigated and detected in some objects. Based on the K-band infrared excesses and the intensity of Hα emission, we estimate that the minimum disk frequency of the σ Orionis low-mass population is in the range 5–12%.
Key words: open clusters and associations: individual: σ Orionis / stars: low-mass, brown dwarfs
© ESO, 2003
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