Stars and brown dwarfs in the σ Orionis cluster. III. OSIRIS/GTC low-resolution spectroscopy of variable sources
Abstract
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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 2012
- DOI:
- 10.1051/0004-6361/201219626
- arXiv:
- arXiv:1209.3679
- Bibcode:
- 2012A&A...546A..59C
- Keywords:
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- 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;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- A&