Visibilities of damped mixed modes in red giant stars
The visibility of oscillation modes can be used to draw conclusions about the damping rate in the stellar core. Recent observational studies demonstrated that although the damping rate of the oscillations in the core of many red giants appears to be negligible, other red giants exhibit high core damping rates that are sometimes consistent with the infinite value limit. However, some of these red giants with strongly damped oscillations show a clear mixed mode signature, suggesting that their damping rate in the core must remain finite.
In this talk, I will present an analytical formalism that can be used to express the approximate power spectrum of red giants up to a proportionality factor, while taking into account the influence of damping on the oscillations. This formalism can be used to obtain a quantitative estimate for the visibility of mixed modes and to predict the detectability of the mixed mode signature under different core damping rates.
Then, I will compare the visibilities calculated from theory with observational methods and discuss the effects of potential biases along the red-giant branch. Finally, I will show the evolution of the visibility and detectability of the mixed mode signature while testing different prescriptions for the potential energy loss caused by a strong internal magnetic field in the core of red giant stars.