Identification of WISE J000100.45+065259.6 as an M8.5+T5 Spectral Binary Candidate

[not part of RNAAS note] We report the discovery of WISE J000100.45+065259.6 as a very low mass star/brown dwarf spectral binary candidate, on the basis of low resolution near-infrared spectroscopy obtained with IRTF/SpeX. Decomposition of the spectrum indicates component types of M8.5+T5 with a predicted $\Delta{J}$ = 3.5. As the majority of confirmed spectral binary candidates to date are very closely-separated systems ($\rho$ $\lesssim$ 3 AU; $P$ $\lesssim$ 15~yr), this source may provide mass measurements across the hydrogen burning limit within the decade.Comment: 3 pages, 1 figure, accepted to Research Notes of the AA

Magnetic inflation and stellar mass. V. Intensification and saturation of M-dwarf absorption lines with Rossby number

In young Sun-like stars and field M-dwarf stars, chromospheric and coronal magnetic activity indicators such as Hα, X-ray, and radio emission are known to saturate with low Rossby number (Ro lesssim 0.1), defined as the ratio of rotation period to convective turnover time. The mechanism for the saturation is unclear. In this paper, we use photospheric Ti i and Ca i absorption lines in the Y band to investigate magnetic field strength in M dwarfs for Rossby numbers between 0.01 and 1.0. The equivalent widths of the lines are magnetically enhanced by photospheric spots, a global field, or a combination of the two. The equivalent widths behave qualitatively similar to the chromospheric and coronal indicators: we see increasing equivalent widths (increasing absorption) with decreasing Ro and saturation of the equivalent widths for Ro lesssim 0.1. The majority of M dwarfs in this study are fully convective. The results add to mounting evidence that the magnetic saturation mechanism occurs at or beneath the stellar photosphere.Published versio