  We investigate how rapid stellar rotation commonly seen in A/F stars can
influence planet habitability. Specifically, we model how rapid rotation
influences a planet's irradiation and determine the location of the habitable
zone for stars in the mass range $1.3M_\odot\leq M_\star\leq 2.2M_\odot$. Rapid
stellar rotation can dramatically change a star's luminosity and spectral
energy distribution and, therefore, can impact the habitability of any
surrounding planets. Stars of mass $M_\star\gtrsim1.3M_\odot$ commonly rotate
near their breakup speeds, which causes two effects relevant to planet
habitability. First, these stars flatten into oblate spheroids with shorter
polar radii and elongated equatorial radii. Second, rapid rotation induces a
pole-to-equator temperature gradient on the surface of these stars. Using a 1D
climate model, we calculate the inner and outer edges of the habitable zone of
well-known rapid rotators and average theoretical stars in our stellar mass
range. We find that, in general, rapid rotation causes the habitable zone to
reside closer in than for a non-rotating equivalent star. We also find that
gravity darkening dramatically reduces stellar UV emission, which combats the
common assumption that high-mass stars emit too much UV light for habitable
worlds. Overall, we determine that rapid stellar rotation has important
consequences for the overall habitability of a system and must be accounted for
both when modeling exoplanet environments and in observation of planets around
high-mass stars.
