  HD 81817 is known as a hybrid star. Hybrid stars have both cool stellar wind
properties and Ultraviolet (UV) or even X-ray emission features of highly
ionized atoms in their spectra. A white dwarf companion has been suggested as
the source of UV or X-ray features. HD 81817 has been observed since 2004 as a
part of a radial velocity (RV) survey program to search for exoplanets around K
giant stars using the Bohyunsan Observatory Echelle Spectrograph at the 1.8 m
telescope of Bohyunsan Optical Astronomy Observatory in Korea. We obtained 85
RV measurements between 2004 and 2019 for HD 81817 and found two periodic RV
variations. The amplitudes of RV variations are around 200 m s^-1, which are
significantly lower than that expected from a closely orbiting white dwarf
companion. Photometric data and relevant spectral lines were also analyzed to
help determine the origin of the periodic RV variations. We conclude that
627.4-day RV variations are caused by intrinsic stellar activities such as
long-term pulsations or rotational modulations of surface activities based on
H{\alpha} equivalent width (EW) variations of a similar period. On the other
hand, 1047.1-day periodic RV variations are likely to be caused by a brown
dwarf or substellar companion, which is corroborated by a recent GAIA proper
motion anomaly for HD 81817. The Keplerian fit yields a minimum mass of 27.1
M_Jup, a semimajor axis of 3.3 AU, and an eccentricity of 0.17 for the stellar
mass of 4.3 M_sun for HD 81817. The inferred mass puts HD 81817 b in the brown
dwarf desert.
