A new strongly X-ray flaring M 9 dwarf in the solar neighborhood

Abstract

We report on the discovery of a very low mass (VLM) star in the solar neighborhood, originally identified as an optical counterpart of a flaring X-ray source detected in the ROSAT All-Sky survey. Optical spectroscopy and infrared photometry consistently reveal a spectral type of M9 ± 0.5 and a distance of ≈ 11 ± 2 pc. The optical counterpart of 1RXS J115928.5-524717 shows a large proper motion of 1.08 ± 0.06″/year. 1RXS J115928.5-524717 is the fourth object among the VLM stars displaying a huge X-ray flare, reaching the unprecedent value of LX/Lbol ≃ 0.1.