  We measured the chromospheric activity of the four hot Jupiter hosts WASP-43,
WASP-51/HAT-P-30, WASP-72 & WASP-103 to search for anomalous values caused by
the close-in companions. The Mount Wilson Ca II H&K S-index was calculated for
each star using observations taken with the Robert Stobie Spectrograph at the
Southern African Large Telescope. The activity level of WASP-43 is anomalously
high relative to its age and falls among the highest values of all known main
sequence stars. We found marginal evidence that the activity of WASP-103 is
also higher than expected from the system age. We suggest that for WASP-43 and
WASP-103 star-planet interactions (SPI) may enhance the Ca II H&K core
emission. The activity levels of WASP-51/HAT-P-30 and WASP-72 are anomalously
low, with the latter falling below the basal envelope for both main sequence
and evolved stars. This can be attributed to circumstellar absorption due to
planetary mass loss, though absorption in the ISM may contribute. A quarter of
known short period planet hosts exhibit anomalously low activity levels,
including systems with hot Jupiters and low mass companions. Since SPI can
elevate and absorption can suppress the observed chromospheric activity of
stars with close-in planets, their Ca II H&K activity levels are an unreliable
age indicator. Systems where the activity is depressed by absorption from
planetary mass loss are key targets for examining planet compositions through
transmission spectroscopy.
