Stars and brown dwarfs in the σ Orionis cluster (Research Note) III. OSIRIS/GTC low-resolution spectroscopy of variable sources

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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.
© ESO, 2012. We thank the anonymous referee for his/her helpful and careful report. This article is based on observations made with the Gran Telescopio Canarias operated on the island of La Palma by the Instituto de Astrofísica de Canarias in the Spanish Observatorio de El Roque de Los Muchachos. This research made use of the SIMBAD, operated at Centre de Données astronomiques de Strasbourg, France, and the NASA's Astrophysics Data System. JAC is an investigador Ramón y Cajal at the Consejo Superior de Investigaciones Científicas. Financial support was provided by the Spanish Ministerio de Ciencia e Innovación and Ministerio de Economía y Competitividad under grants CSD2006-70, AyA2009-10368, and AyA2011-30147-C03-03.
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