Onset of non-linear internal gravity waves in intermediate-mass stars

Abstract

Internal gravity waves (IGW) propagate in the radiation zones of all stars. During propagation, their amplitudes are affected by two main features: radiative diffusion and density stratification. We have studied the implications of these two features on waves traveling within the radiative zones of non-rotating stars with stellar parameters obtained from the one dimensional stellar evolution code, MESA. As a simple measure of induced wave dynamics, we define a criterion to see if waves can become nonlinear and if so, under what conditions. This was done to understand the role IGW may play in angular momentum transport and mixing within stellar interiors. We find that the IGW generation spectrum, convective velocities and the strength of density stratification all play major roles in whether waves become nonlinear. With increasing stellar mass, there is an increasing trend in nonlinear wave energies. The trends with different metallicities and ages depend on the generation spectrum.

Fully compressible simulations of waves and core convection in main-sequence stars

“…A narrow range around 10 µHz is apparent where the nonlinearity is highest. We note that this looks very similar to Spectrum K and Spectrum LD in figure 5 of Ratnasingam et al (2019) for convective velocity boosted by a factor of three with respect to the stellar models. The strongest nonlinearity in Fig.…”

“…From linear theory, one expects the amplification of IGW toward the surface due to density stratification. As shown in Ratnasingam et al (2019) for spherical geometry, the prediction for IGW amplification is given by (in the notation 2 of EM19)…”

“…In Ratnasingam et al (2019) the effect of different input spectra on the expected nonlinearity of IGWs is examined. The nonlinearity can be estimated by Press 1981;Barker & Ogilvie 2010).…”

Probing the interior physics of stars through asteroseismology

“…Although the 3D simulations of solarlike stars by Alvan, Brun, and Mathis (2014) and Alvan et al (2015) and of intermediate-mass stars by Edelmann et al (2019) and showed clear modal structure of internal g modes, it remains unclear if and which of the internal waves become resonant modes. This depends on the profile of the wave's eigenfunction, on its propagation and dissipation properties, on the efficiency of the radiative damping, and on the onset of nonlinearity (Ratnasingam, Edelmann, and Rogers, 2019). A snapshot of the temperature variations accompanying the driving of IGWs and their propagation from the 3D hydrodynamical simulations by Edelmann et al (2019) is shown in Fig.…”

Asteroseismology of Close Binary Stars: Tides and Mass Transfer

“…They suffer from linear damping due to radiative diffusion (Press, 1981;Garcia Lopez and Spruit, 1991;Zahn et al, 1997). The low-frequency, short-wavelength waves are damped strongly and behave like traveling waves (Ratnasingam et al, 2019). Higherfrequency waves can be reflected at the outer turning points and interfere constructively to form global normal modes (Prat et al, 2016).…”