Volume 546, October 2012
|Number of page(s)||6|
|Section||Catalogs and data|
|Published online||04 October 2012|
Stars and brown dwarfs in the σ Orionis cluster
III. OSIRIS/GTC low-resolution spectroscopy of variable sources
Centro de Astrobiología (CSIC-INTA), European Space Astronomy
Centre, PO Box 78,
Villanueva de la Cañada
2 Instituto de Astrofísica de Canarias, Avenida Vía Láctea, 38205 La Laguna, Tenerife, Spain
3 Grantecan S. A., Centro de Astrofísica de La Palma, Cuesta de San José, 38712 Breña Baja, La Palma, Spain
4 Departamento de Astrofísica, Universidad de La Laguna, 38205, La Laguna, Tenerife, Spain
5 Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, 28040 Madrid, Spain
Received: 18 May 2012
Accepted: 13 September 2012
Context. Although many studies have been performed so far, there are still dozens of low-mass stars and brown dwarfs in the young σ Orionis open cluster without detailed spectroscopic characterisation.
Aims. We look for unknown strong accretors and disc hosts that were undetected in previous surveys.
Methods. We collected low-resolution spectroscopy (R ~ 700) of ten low-mass stars and brown dwarfs in σ Orionis with OSIRIS at the Gran Telescopio Canarias under very poor weather conditions. These objects display variability in the optical, infrared, Hα, and/or X-rays on time scales of hours to years. We complemented our spectra with optical and near-/mid-infrared photometry.
Results. For seven targets, we detected lithium in absorption, identified Hα, the calcium doublet, and forbidden lines in emission, and/or determined spectral types for the first time. We characterise in detail a faint, T Tauri-like brown dwarf with an 18 h-period variability in the optical and a large Hα equivalent width of –125 ± 15 Å, as well as two M1-type, X-ray-flaring, low-mass stars, one with a warm disc and forbidden emission lines, the other with a previously unknown cold disc with a large inner hole.
Conclusions. New unrevealed strong accretors and disc hosts, even below the substellar limit, await discovery among the list of known σ Orionis stars and brown dwarfs that are variable in the optical and have no detailed spectroscopic characterisation yet.
Key words: stars: late-type / stars: pre-main sequence / stars: variables: T Tauri, Herbig Ae/Be / quasars: emission lines / open clusters and associations: individual:σOrionis / X-rays: stars
© ESO, 2012
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