We present the results of low-resolution optical spectroscopy with OSIRIS/GTC (Optical System for Imaging and Low Resolution Integrated Spectroscopy / Gran Telescopio Canarias) for a sample of ultracool dwarfs. For a subsample of seven objects, based on 2MASS NIR photometric colours, a ‘photometric’ spectral type is determined and compared to the results of the optical spectroscopy. For the stars, showing H$\alpha$ line in emission, equivalent widths were measured, and the ratio of H$\alpha$ to bolometric luminosity were calculated. We find that two dwarfs show the presence of magnetic activity over long periods, LP 326-21 — quasi-constant-like, and 2MASS J17071830+6439331 — variable.
Y. Metodieva, A. Antonova, V. Golev, et. al.
Tue, 9 Dec 14
Comments: 7 pages, 4 figures, 3 tables