\label{fig:Bc}
Minimum field strength $B_{c,{\rm min}}$ required for magnetic suppression of dipole oscillation modes in stars evolving up the RGB. ({\bf A}) $B_{c,{\rm min}}$ is shown as a function of the frequency of maximum power, $\nu_{\rm max}$, for stars of different mass. $B_{c,{\rm min}}$ has been computed for modes with angular frequency $\omega \! = \! 2 \pi \nu_{\rm max}$. We have labeled the observed value of $\nu_{\rm max}$ and inferred core field strength $B_r$ for the lower RGB star KIC8561221 \cite{Garcia_2014} and a lower limit to the field strength in KIC9073950. ({\bf B}) Asteroseismic HR diagram showing stellar evolution tracks over the same range in $\nu_{\rm max}$. Stars evolve from left to right as they ascend the RGB. Dashed lines show the end of main sequence evolution, thin solid lines are the sub-giant phase, and thick solid lines are the RGB. We do not show any evolution beyond the RGB (i.e., no clump or asymptotic giant branch).
  
  
  
  