  We conducted speckle imaging observations of 53 stellar systems that were
members of long-term radial velocity (RV) monitoring campaigns and exhibited
substantial accelerations indicative of planetary or stellar companions in wide
orbits. Our observations were made with blue and red filters using the
Differential Speckle Survey Instrument at Gemini-South and the NN-Explore
Exoplanet Stellar Speckle Imager at the WIYN telescope. The speckle imaging
identifies eight luminous companions within two arcseconds of the primary
stars. In three of these systems (HD 1388, HD 87359, and HD 104304), the
properties of the imaged companion are consistent with the RV measurements,
suggesting that these companions may be associated with the primary and the
cause of the RV variation. For all 53 stellar systems, we derive differential
magnitude limits (i.e., contrast curves) from the imaging. We extend this
analysis to include upper limits on companion mass in systems without imaging
detections. In 25 systems, we rule out companions with mass greater than 0.2
$M_{\odot}$, suggesting that the observed RV signals are caused by late M
dwarfs or substellar (potentially planetary) objects. On the other hand, the
joint RV and imaging analysis almost entirely rules out planetary explanations
of the RV signal for HD 19522 and suggests that the companion must have an
angular separation below a few tenths of an arcsecond. This work highlights the
importance of combined RV and imaging observations for characterizing the outer
regions of nearby planetary systems.
