Modelling angular momentum transport by mixed modes across stellar evolution
Current stellar models that include hydrodynamic processes for the transport of angular momentum (AM) predict core rotation rates in low-mass red giant stars that are orders of magnitude higher than those inferred from asteroseismic observations.
This discrepancy motivates the search for additional transport processes capable of efficiently redistributing AM within radiative interiors. In addition to being a crucial observational probe of the stellar internal structure, mixed gravity-pressure modes may also provide an efficient mechanism for extracting AM from red-giant cores via wave-driven heat transport.
In this seminar, I will discuss the role of mixed modes in the AM transport of low-mass red giants. First, I will focus on modelling mixed-mode amplitudes throughout stellar evolution, accounting for radiative damping across different angular degrees. Next, I will present the impact of mixed modes on rotation rates along the red giant branch and in the red clump. These results point to aspects that remain to be understood within this theoretical framework. Finally, I will show the resulting rotation profiles obtained by combining the mixed-mode mechanism with other transport processes, such as meridional circulation and magnetic fields.
Hi Beatriz, thanks for this great seminar! I wanted to attend, but unfortunately I was in the air at the time. I really enjoyed watching the recording though and have two questions for you.
You mentioned that angular momentum transport by meridional circulation and turbulence is already included in your models, though it doesn’t diffuse the localised spindown enough, hence why you artificially raised the viscosity in your tests. Therefore, I was wondering if you experimented with different prescriptions for the vertical viscosity nu_v and horizontal diffusion coefficients D_h available in the literature?
Am I correct in thinking that mixing of chemicals by meridional circulation and turbulence are neglected since you mentioned that feedback from rotation to the structure is neglected? Might that not affect the localised spindown as the location of that spindown depends on the chemical gradient, right?