SIMBAD references

We present results from a high angular resolution survey of 77 very low mass (VLM) binary systems with 6.0 ≤ V - K colour ≤ 7.5 and proper motion ≥0.15arcsec/yr. 21 VLM binaries were detected, 13 of them new discoveries. The new binary systems range in separation between 0.18 and 1.3arcsec. The distance-corrected binary fraction is 13.6^+6.5_–4 per cent, in agreement with previous results. Nine of the new binary systems have projected separations >10au, including a new wide VLM binary with 27au projected orbital separation. One of the new systems forms two components of a 2300au separation triple system. We find that the projected separation distribution of the binaries with V - K < 6.5 in this survey appears to be different from that of redder (lower mass) objects, suggesting a possible rapid change in the orbital radius distribution at around the M5 spectral type. The target sample was also selected to investigate X-ray activity among VLM binaries. There is no detectable correlation between excess X-ray emission and the frequency and binary properties of the VLM systems.