  Kapteyn's star is an old M subdwarf believed to be a member of the Galactic
halo population of stars. A recent study has claimed the existence of two
super-Earth planets around the star based on radial velocity (RV) observations.
The innermost of these candidate planets--Kapteyn b (P = 48 days)--resides
within the circumstellar habitable zone. Given recent progress in understanding
the impact of stellar activity in detecting planetary signals, we have analyzed
the observed HARPS data for signatures of stellar activity. We find that while
Kapteyn's star is photometrically very stable, a suite of spectral activity
indices reveals a large-amplitude rotation signal, and we determine the stellar
rotation period to be 143 days. The spectral activity tracers are strongly
correlated with the purported RV signal of "planet b," and the 48-day period is
an integer fraction (1/3) of the stellar rotation period. We conclude that
Kapteyn b is not a planet in the Habitable Zone, but an artifact of stellar
activity.
