Discovery of five very low mass close binaries, resolved in the visible with lucky imaging*

We survey a sample of 32 M5-M8 stars with distance <40pc for companions with separations between 0.1 and 1.5arcsec and with Δm_i <= 5. We find five new binaries with separations between 0.15 and 1.1arcsec, including a candidate brown dwarf companion. The raw binary fraction is 16⁺⁸_-4 per cent and the distance bias corrected fraction is 7⁺⁷_-3 per cent, for companions within the surveyed range. No systems with contrast ratio Δm_i > 1 were found, even though our survey is sensitive to Δm <= 5 (well into the brown dwarf regime). The distribution of orbital radii is in broad agreement with previous results, with most systems at 1-5au, but one detected binary is very wide at 46.8 +/- 5.0au. We also serendipitously imaged for the first time a companion to Ross 530, a metal-poor single-lined spectroscopic binary. We used the new Lucky Imaging system, LuckyCam, on the 2.5-m Nordic Optical Telescope to complete the 32 very low mass star Sloan Digital Sky Survey (SDSS) i' and z' survey in only 5h of telescope time.