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Keywords:

  • brown dwarfs;
  • stars: individual: HD 221356;
  • stars: low-mass

ABSTRACT

We report on the discovery of a fourth component in the HD 221356 star system, previously known to be formed by an F8V, a slightly metal poor primary ([Fe/H] = −0.26), and a distant M8V+L3V pair. In our ongoing common proper motion search based on Visible and Infrared Survey Telescope for Astronomy (VISTA) Hemisphere Survey (VHS) and Two Micron All Sky Survey (2MASS) catalogues, we have detected a faint J = 13.76 ± 0.04 mag comoving companion of the F8 star located at angular separation of 12.13 ± 0.18 arcsec (position angle of 221°.8 ± 1°.7), corresponding to a projected distance of ∼317 au at 26 pc. Near-infrared spectroscopy of the new companion, covering the 1.5–2.4 μm wavelength range with a resolving power of R ∼ 600, indicates an L1 ± 1 spectral type. Using evolutionary models the mass of the new companion is estimated at ∼0.08 M, 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 subsolar metallicity of the system.