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 \it M _ { \mathrm { Jup } } , a semimajor axis of 3.3 AU , and an eccentricity of 0.17 for the stellar mass of 4.3 M _ { \odot } for HD 81817 .
The inferred mass puts HD 81817 b in the brown dwarf desert .