We present ten new ultra-cool dwarfs in seven wide binary systems discovered using Gaia DR2 data , identified as part of our Gaia Ultra-Cool Dwarf Sample project .
The seven systems presented here include an L1 companion to the G5 IV star HD 164507 , an L1 : companion to the V478 Lyr AB system , an L2 companion to the metal-poor K5 V star CD-28 8692 , an M9 V companion to the young variable K0 V star LT UMa , and three low-mass binaries consisting of late Ms and early Ls .
The HD 164507 , CD-28 8692 , V478 Lyr , and LT UMa systems are particularly important benchmarks , because the primaries are well characterised and offer excellent constraints on the atmospheric parameters and ages of the companions .
We find that the M8 V star 2MASS J23253550+4608163 is \sim 2.5 mag overluminous compared to M dwarfs of similar spectral type , but at the same time it does not exhibit obvious peculiarities in its near-infrared spectrum .
Its overluminosity can not be explained by unresolved binarity alone .
Finally , we present an L1+L2 system with a projected physical separation of 959 au , making this the widest L+L binary currently known .