NCJM catalog of M dwarfs

We present SpeX prism-mode spectra (0.7-2.5 micron) for a pilot sample of one hundred and eleven mid M dwarfs, including twenty-eight which were previously identified as candidates for unresolved ultracool companionship (a sub-sample from Cook et al. 2016; paper 1) and eighty-three single M dwarfs which were optically colour-similar to these candidates (which we use as `control stars').

We identify four candidates with evidence for near-infrared excess. One of these (WISE J100202.50+074136.3) shows strong evidence for an unresolved L dwarf companion in both its spectral ratio difference and its residual spectra, two most likely have a different source for the near-infrared excess, and the other may be due to spectral noise. We also establish expectations for a null result (i.e. by searching for companionship signatures around the M dwarf control stars), as well as determining the expected outcome for ubiquitous companionship (as a means of comparison with our actual results), using artificially generated unresolved M+L dwarf spectra.