Velocity-intensity asymmetry reversal of solar radial p-modes

TL;DR

This paper models and predicts the asymmetries of solar p-modes in intensity spectra, revealing that radiative flux variations are key to understanding asymmetry reversal and challenging previous assumptions about additional mechanisms.

Contribution

The study extends a solar p-mode asymmetry model to intensity spectra, demonstrating the importance of radiative flux treatment and revising the understanding of asymmetry reversal mechanisms.

Findings

Intensity asymmetries depend on radiative flux variations.

Realistic flux modeling reproduces observed asymmetries for low-frequency modes.

Additional mechanisms are needed for higher-order mode asymmetry reversal.

Abstract

The development of space-borne missions has significantly improved the quality of the measured spectra of solar-like oscillators. Their $p$-mode line profiles can now be resolved, and the asymmetries inferred for a variety of stars other than the Sun. However, it has been known for a long time that the asymmetries of solar $p$-modes are reversed between the velocity and the intensity spectra. Understanding the origin of this reversal is necessary in order to use asymmetries as a tool for seismic diagnosis. For stars other than the Sun, only the intensity power spectrum is sufficiently resolved to allow for an estimation of mode asymmetries. We recently developed an approach designed to model and predict these asymmetries in the velocity power spectrum of the Sun and to successfully compare them to their observationally derived counterparts. In this paper we expand our model and predict the asymmetries featured in the intensity power spectrum. We find that the shape of the mode line profiles in intensity is largely dependent on how the oscillation-induced variations of the radiative flux are treated, and that modelling it realistically is crucial to understanding asymmetry reversal. Perturbing a solar-calibrated grey atmosphere model, and adopting the quasi-adiabatic framework as a first step, we reproduce the asymmetries observed in the solar intensity spectrum for low-frequency modes. We conclude that, unlike previously thought, it is not necessary to invoke an additional mechanism (e.g. non-adiabatic effects, coherent non-resonant background signal) to explain asymmetry reversal. This additional mechanism is necessary, however, to explain asymmetry reversal for higher-order modes.