Recent asteroseismic advances have allowed for direct measurements of the internal rotation rates of many sub-giant and red giant stars .
Unlike the nearly rigidly rotating Sun , these evolved stars contain radiative cores that spin faster than their overlying convective envelopes , but slower than they would in the absence of internal angular momentum transport .
We investigate the role of internal gravity waves in angular momentum transport in evolving low mass stars .
In agreement with previous results , we find that convectively excited gravity waves can prevent the development of strong differential rotation in the radiative cores of Sun-like stars .
As stars evolve into sub-giants , however , low frequency gravity waves become strongly attenuated and can not propagate below the hydrogen burning shell , allowing the spin of the core to decouple from the convective envelope .
This decoupling occurs at the base of the sub-giant branch when stars have surface temperatures of T \approx 5500 K. However , gravity waves can still spin down the upper radiative region , implying that the observed differential rotation is likely confined to the deep core near the hydrogen burning shell .
The torque on the upper radiative region may also prevent the core from accreting high-angular momentum material and slow the rate of core spin-up .
The observed spin-down of cores on the red giant branch can not be totally attributed to gravity waves , but the waves may enhance shear within the radiative region and thus increase the efficacy of viscous/magnetic torques .