Detecting planetary companions around evolved stars, particularly asymptotic giant branch (AGB) stars, is challenging due to intrinsic stellar variability such as surface convection, pulsations, and mass loss, which can produce radial velocity (RV) signals that mimic Keplerian motion. We investigate the origin of the long-period, low-amplitude RV variations observed in the AGB star HD 216595 using high-resolution spectroscopic data spanning approximately 16 years obtained with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES) and the Las Cumbres Observatory Network of Robotic Echelle Spectrographs (NRES) instruments. The RV measurements reveal a statistically significant periodic signal with a period of 567 days that can be described by a Keplerian model consistent with a substellar companion. However, no strong correlations are found between the RV variations and stellar activity indicators, including line bisectors, chromospheric activity, and photometric variability, although weak signals on similar timescales are present in some diagnostics. Given the stellar properties of HD 216595 and its similarities to previously reported cases, the observed RV variations are likely related to intrinsic stellar processes, although a companion-induced origin cannot be definitively ruled out. Further progress will require improved diagnostics and more sophisticated modeling to disentangle stellar variability from genuine orbital signals.

Introduction
Observations and Data Reduction
    BOAO/BOES
    LCO /NRES
Stellar Properties
    Fundamental Parameters
    Stellar Characteristics
Orbital Solution
Origin of the RV Variations
    Rotational Modulation by Surface Inhomogeneities
    Chromospheric Activity Diagnostics
    Stellar Pulsation
    Low-Mass Companion
    Surface Convection, Granulation, and Stellar Winds
Discussion
Acknowledgments
References
RV Measurements
RV Measurements in Literature

• Sang-Hee Kim(Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea)
• Myeong-Gu Park(Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea)
• Tae-Yang Bang(Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea)
• Heon-Young Chang(Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea)
• Byeong-Cheol Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Korea University of Science and Technology, Daejeon 34113, Republic of Korea) Corresponding author
• Jae-Rim Koo(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Yeon-Ho Choi(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Hyeong-Ill Oh(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Shenghong Gu(School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China, Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, People’s Republic of China)
• Beomdu Lim(Department of Earth Science Education, Kongju National University, Gongju-si, Chungcheongnam-do 32588, Republic of Korea)
• Huan-Yu Teng(Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China)
• David Mkrtichian(National Astronomical Research Institute of Thailand, Chiang Mai 50180, Thailand)