  Motivated by the existence of binary systems where a stellar-mass black hole
is bound to a normal star, we selected four red giants with large radial
velocity (RV) variation from the survey of SIM grid stars and monitored their
RVs for several months. None turned out to contain a massive companion above
2.5 solar masses. The red giant TYC 9299-1080-1 with a large RV and a large
proper motion is a single-lined spectroscopic binary with a period of 81 days.
It is an extreme halo object moving at 350 km s$^{-1}$ almost directly toward
the Galactic center. HD 206092 is a double-lined binary with a short period of
4.37 days. It belongs to the rare class of active RS CVn-type binaries with
evolved primary components, apparently undergoing mass transfer. The X-ray
luminosity of HD 206092 is about twice as high as the most luminous coronal
X-ray emitters observed by ROSAT, including II Peg and the prototype star RS
CVn. HD~318347 has a variable double-peaked emission-line spectrum (not a
giant), while HD~324668 has a constant RV. Despite the overall good quality of
the SIM survey data confirmed by a comparison with Gaia DR2 mean radial
velocities, the few large RV variations are explained, mostly, by erroneous
data. We discuss the significance of the non-detection of massive companions in
the SIM grid sample and the associated work.
