Search for nearby stars among proper motion stars selected by optical-to-infrared photometry

We present the discovery of a previously unknown very nearby star-LHS 2090 at a distance of only d = 6 pc. In order to find nearby (i.e. d <25 pc) red dwarfs, we re-identified high proper motion stars (<mu> >0.18 arcsec/yr) from the NLTT catalogue (Luyten 1979-1980) in optical Digitized Sky Survey data for two different epochs and in the 2MASS data base. Only proper motion stars with large R-K-s colour index and with relatively bright infrared magnitudes (K-s < 10) were selected for follow-up spectroscopy. The low-resolution spectrum of LHS 2090 and its large proper motion (0.79 arcsec/yr) classify this star as an M6.5 dwarf. The resulting spectroscopic distance estimate from comparing the infrared JHKs magnitudes of LHS 2090 with absolute magnitudes of M6.5 dwarfs is 6.0<plus/minus>1.1 pc assuming an uncertainty in absolute magnitude of +/-0.4 mag.