The Evolving Magnetic Topology of $\tau$ Bo\"otis
  We present six epochs of spectropolarimetric observations of the hot-Jupiter-hosting star $\tau$ Bo\"otis that extend the exceptional previous multi-year data set of its large-scale magnetic field. Our results confirm that the large-scale magnetic field of $\tau$ Bo\"otis varies cyclicly, with the observation of two further magnetic reversals; between December 2013 and May 2014 and between January and March 2015. We also show that the field evolves in a broadly solar-type manner in contrast to other F-type stars. We further present new results which indicate that the chromospheric activity cycle and the magnetic activity cycles are related, which would indicate a very rapid magnetic cycle. As an exemplar of long-term magnetic field evolution, $\tau$ Bo\"otis and this longterm monitoring campaign presents a unique opportunity for studying stellar magnetic cycles. 
M. W. Mengel, R. Fares, S. C. Marsden, B. D. Carter, S. V. Jeffers, P.   Petit, J.-F. Donati, C. P. Folsom and the BCool Col...
astro-ph.SR