Optical Spectra of Ultracool Dwarfs with the Southern African Large Telescope

Abstract

New spectra of 81 ultracool dwarfs (spectral types M7 and later) are discussed. Spectral classifications of 49 objects are available in the literature, while 32 objects are newly classified. The known spectral types were used to test an automated classification scheme, which relies primarily on template fitting, supplemented by matching of spectral indices calibrated against the template spectra. An attempt was made to quantify the uncertainty in the spectral types, which is generally better than two subclasses. Objects for which spectral types differ by more than one subclass from the literature classifications are discussed individually. Discrepancies between automated classifications based on respectively template fitting and spectral index matching, may be useful for flagging objects with unusual spectra. Aside from the 32 first-time classifications, alternative classifications are presented for 32 previously classified dwarfs. Very large (equivalent width greater than 130 Å) H$\alpha$ flares are reported for the known ultracool dwarf binary 2MASS J15200224$-$4422419; curiously, the object does not appear to have quiescent emission lines. Non-zero equivalent width measurements are listed for a further 29 objects.

Accepted for publication in MNRAS. 33 pages, 12 figures, 6 tables

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• The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis
• $K2$ Ultracool Dwarfs Survey. VI. White light superflares observed on an L5 dwarf and flare rates of L dwarfs
• On the Correlation between L Dwarf Optical and Infrared Variability and Radio Aurorae
• The Occurrence Rate of Quiescent Radio Emission for Ultracool Dwarfs using a Generalized Semi-Analytical Bayesian Framework
• Spectral characterization of newly detected young substellar binaries with SINFONI
• The Brown Dwarf Kinematics Project (BDKP). V. Radial and Rotational Velocities of T Dwarfs from Keck/NIRSPEC High-Resolution Spectroscopy