We have been conducting a exoplanet search survey using Bohyunsan Observatory Echelle Spectrograph (BOES) for the last 18 years. We present the detection of exoplanet candidate in orbit around HD 18438 from high-precision radial velocity (RV) mesurements. The target was already reported in 2018 (Bang et al. 2018). They conclude that the RV variations with a period of 719 days are likely to be caused by the pulsations because the Lomb-Scargle periodogram of HIPPARCOS photometric and Hα EW variations for HD 18438 show peaks with periods close to that of RV variations and there were no correlations between bisectors and RV measurements. However, the data were not sufficient to reach a firm conclusion. We obtained more RV data for four years. The longer time baseline yields a more accurate determination with a revised period of 803 ± 5 days and the planetary origin of RV variations with a minimum planetary companion mass of 21 ± 1MJup. Our current estimate of the stellar parameters for HD 18438 makes it currently the largest star with a planetary companion.

Abstract
1. Introduction
2. Observations and Reduction
3. Stellar Characteristics
4. Orbital Solutions of Radial Velocity Variations
5. Origin of Radial Velocity Variations
    5.1. Photometric Variations
    5.2. Chromospheric Activities
    5.3. Line Bisector
6. Discussion
Acknowledgments
References

• Byeong-Cheol Lee(Korea Astronomy and Space Science Institute, Astronomy and Space Science Major, University of Science and Technology) Corresponding author
• Jae-Rim Koo(Kongju National University)
• Gwanghui Jeong(Korea Astronomy and Space Science Institute)
• Myeong-Gu Park(Department of Astronomy and Atmospheric Sciences, Kyungpook National University)
• Inwoo Han(Korea Astronomy and Space Science Institute)
• Yeon-Ho Choi(Korea Astronomy and Space Science Institute, Astronomy and Space Science Major, University of Science and Technology)