  Directly imaging temperate rocky planets orbiting nearby, Sun-like stars with
a 6-m-class IR/O/UV space telescope, recently dubbed the Habitable Worlds
Observatory, is a high priority goal of the Astro2020 Decadal Survey. To
prepare for future direct imaging surveys, the list of potential targets should
be thoroughly vetted to maximize efficiency and scientific yield. We present an
analysis of archival radial velocity data for southern stars from the NASA/NSF
Extreme Precision Radial Velocity Working Group's list of high priority target
stars for future direct imaging missions (drawn from the HabEx, LUVOIR, and
Starshade studies). For each star, we constrain the region of companion mass
and period parameter space we are already sensitive to based on the
observational baseline, sampling, and precision of the archival RV data.
Additionally, for some of the targets we report new estimates of magnetic
activity cycle periods, rotation periods, improved orbital parameters for
previously known exoplanets, and new candidate planet signals that require
further vetting or observations to confirm. Our results show that for many of
these stars we are not yet sensitive to even Saturn-mass planets in the
habitable zone, let alone smaller planets, highlighting the need for future
EPRV vetting efforts before the launch of a direct imaging mission. We present
evidence that the candidate temperate super-Earth exoplanet HD 85512 b is most
likely due to the star's rotation, and report an RV acceleration for delta Pav
which supports the existence of a distant giant planet previously inferred from
astrometry.
