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 counterpart. 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.
Highlights
The power spectral density of solar-like oscillations is expected to feature Lorentzian peaks centred on their eigenfrequencies
It is widely thought that this contribution is negligible in velocity data; in turn, the results presented in Fig. 2 indicate that it is negligible in intensity data for low-frequency modes, but that it may no longer be the case for high-frequency modes
In this paper we extended the semi-analytical synthetic power spectrum model developed in Philidet et al (2020) to predict the radial p-mode asymmetries in intensity observations
Summary
The power spectral density of solar-like oscillations is expected to feature Lorentzian peaks centred on their eigenfrequencies. Roxburgh & Vorontsov 1997; Nigam et al 1998) These prior studies used parametrised models, and aimed to find best-fit values for their free parameters by applying fitting procedures to individual peaks in the observed spectrum. Philidet et al (2020) followed a different approach, which consisted in modelling mode asymmetry without fitting any free parameters to the available observational data Instead, they developed an analytical model of stochastic excitation, coupled with a 3D hydrodynamical simulation of the stellar atmosphere. They developed an analytical model of stochastic excitation, coupled with a 3D hydrodynamical simulation of the stellar atmosphere This allowed the authors to reproduce the asymmetries of solar p-modes as measured in the observed velocity power spectrum, and to subsequently demonstrate the role of the spatial extent of the mode driving region, together with the differential properties of turbulent convection (namely the variation of the injection length-scale below and above the photosphere)
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