We report on the discovery of a fourth component in the HD 221356 star system , previously known to be formed by an F8V , slightly metal-poor primary ( \left [ Fe / H \right ] = -0.26 ) , and a distant M8V + L3V pair .
In our ongoing common proper motion search based on VISTA Hemisphere Survey ( VHS ) and 2MASS catalogues , we have detected a faint J = 13.76 \pm 0.04 mag ) co-moving companion of the F8 star located at angular separation of 12.13 \pm 0.18 arcsec ( position angle of 221.8 \pm 1.7 deg ) , corresponding to a projected distance of \sim 312 au at 26 pc .
Near-infrared spectroscopy of the new companion , covering the 1.5–2.4 micron wavelength range with a resolving power of R \sim 600 , indicates an L1 \pm 1 spectral type .
Using evolutionary models the mass of the new companion is estimated at \sim 0.08 solar masses , which places the object close to the stellar-substellar borderline .
This multiple system provides an interesting example of objects with masses slightly above and below the hydrogen burning mass limit .
The low mass companions of HD 221356 have slightly bluer colours than field dwarfs with similar spectral type , which is likely a consequence of the sub-solar metallicity of the system .