Inmaculada Moyano Rejano   (Spain)

 inmaculada.moyano @ h-its.org

Detailed forward modeling of red giants

 

Asteroseismology studies stellar oscillations to probe the internal structure of stars and infer their fundamental parameters. Different oscillation modes reveal different regions of a star: pressure modes mainly sample the outer layers, while gravity modes probe the deep core. In red giants, these two types of oscillations couple to form mixed modes, which carry information about both the core and the envelope. For this reason, mixed modes provide one of the most powerful ways to study stellar interiors.

A common approach in asteroseismology is forward modelling, where observed oscillation frequencies are compared with theoretical stellar models to infer the internal stellar structure. For red giants, however, this method is currently limited by the surface effect, a systematic offset between observed and modelled frequencies caused by the poor modelling of near-surface layers. Current empirical surface corrections have proven to be robust for main-sequence stars but become unreliable for red giants, often leading to the
overestimation of stellar masses and radii. Surface corrections are usually applied directly to mixed modes, ignoring that the surface effect only affects the pressure-mode component.

In my first project, we aim to develop a new modeling pipeline that treats this problem more consistently. We first use a Bayesian framework to identify the most likely region of parameter space using radial-mode frequencies and the acoustic glitch signal from the second helium ionization zone. Within this reduced parameter space, we implement a pi-gamma decomposition to decouple the mixed modes into their pure pressure and gravity components. This allows for the application of surface corrections only to the pressure-dominated part before recoupling the modes to compare to observations. With this method, we aim to improve the precision of fundamental stellar parameter estimates by providing a physically consistent treatment of the surface effect.

 

Supervisor:    Saskia Hekker    (HITS)