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Context. Certain periodic variations of radial velocities (RV) of wobblinggiants originate from exoplanets. Indeed, a number of exoplanets have beendiscovered around giant stars.  Aims. The purpose of our study is to find low-amplitude and long-period RVvariations around bright M (super) giants in the RGB (or AGB) stage, which arelong-period variables (LPVs) or high-proper-motion (HPM) stars.  Methods. High-resolution, fiber-fed Bohyunsan Observatory EchelleSpectrograph (BOES) at the Bohyunsan Optical Astronomy Observatory (BOAO) wasused to record numerous spectra of nine giants. The observation period for thetargets spans 16 years, from 2005 to 2022.  Results. We found from the precise RV observations of nine M giants twosub-stellar companions, one with a 28.26$^{+2.05}_{-2.17}$ $M_{J}$ orbitingperiod of 663.87$^{+4.61}_{-4.31}$ days at a distance of 2.03$^{+0.01}_{-0.01}$AU (HD 6860) and the other, with a 15.83$^{+2.33}_{-2.74}$ $M_{J}$ orbitingperiod of 466.63 $^{+1.47}_{-1.28}$ days at a distance of 1.33$^{+0.08}_{-0.11}$ AU (HD 112300). Our estimate of the stellar parameters forHD 6860 makes it currently the largest star with a sub-stellar companion. Wealso found RV variations mimicking a planetary companion in HD 18884 andconfirmed LPVs in two stars, HD 39801 and HD 42995. The RV variations of somestars seem to be associated with stellar activities rather than reflex orbitalmotion due to their companions. Such variations are also detected even for HD6860 and HD 112300, hosting sub-stellar companions.

Long-period radial velocity variations of nine M red giants: The detection of sub-stellar companions around HD 6860 and HD 112300