2002A&A...390L..27M

We have identified two late M dwarfs within 10pc of the Sun, by cross-correlating the Luyten NLTT catalogue of stars with proper motions larger than 0.18arcsec/yr, with objects lacking optical identification in the 2MASS data base. The 2MASS photometry was then combined with improved optical photometry obtained from the SuperCOSMOS Sky Surveys. The two objects (LP775-31 and LP655-48) have extremely red optical-to-infrared colours ((R-K_s)∼7^m) and very bright infrared magnitudes (K_s<10^m): follow-up optical spectroscopy with the ESO 3.6-m telescope gave spectral types of M8.0 and M7.5 dwarfs, respectively. Comparison of their near-infrared magnitudes with the absolute magnitudes of known M8 and M7.5 dwarfs with measured trigonometric parallaxes yields spectroscopic distance estimates of 6.4±1.4pc and 8.0±1.6pc for LP775-31 and LP655-48, respectively. In contrast, Cruz & Reid (2002AJ....123.2828C) recently determined spectral types of M6 for both objects, and commensurately larger distances of 11.3±1.3pc and 15.3±2.6pc. LP655-48 is also a bright X-ray source (1RXS J044022.8-053020). With only a few late M dwarfs previously known within 10pc, these two objects represent an important addition to the census of the Solar neighbourhood.