Search for exoplanet around northern circumpolar stars: Four planets around HD 11755, HD 12648, HD 24064, and 8 Ursae Minoris

Aims. This program originated as the north pole region extension of the established exoplanet survey using the 1.8 m telescope at Bohyunsan Optical Astronomy Observatory (BOAO). The aim of our paper is to find exoplanets in northern circumpolar stars with a precise radial velocity (RV) survey. Methods. We selected about 200 northern circumpolar stars with the following criteria: δ ≥ 70 °, 0:6 < B-V < 1:6, Hipparcosscat < 0:05 mag, and 5:0 < mv < 7:0. The high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used for the RV survey. Chromospheric activities, the Hipparcos photometry, and line bisectors were analyzed to exclude other causes for the RV variations. Results. In 2010, we started to monitor the candidates and have completed initial screening for all stars for the past five years. We present the detection of four new exoplanets. Stars HD 11755, HD 12648, HD 24064, and 8 UMi all show evidence of giant planets in Keplerian motion. The companion to HD 11755 has a minimum mass of 6.5 MJup in a 433-day orbit with an eccentricity of 0.19. HD 12648 is orbited by a companion with a minimum mass of 2.9 MJup, a period of 133 days, and an eccentricity of 0.04. Weak surface activity was suspected in HD 24064. However, no evidence was found to be associated with the RV variations. Its companion has a minimum mass of 9.4 MJup, a period of 535 days, and an eccentricity of 0.35. Finally, 8 UMi has a minimum mass of 1.5 MJup and a period of 93 days with an eccentricity of 0.06.