Local perturbations of the upper layers of a Sun-like star: the impact on the acoustic oscillation spectrum

Abstract

In the last decade the quality and the amount of observational asteroseismic data that has been made available by space based missions had a tremendous upgrowth. The determination of asteroseismic parameters to estimate the fundamental physical processes occurring in stars' interiors, can be done today in a way that has never been possible before. In this work we propose to compute the seismic observable $\beta$, which is a proxy of the phase shift of the acoustic modes propagating in the envelope of the Sun-like stars. This seismic parameter $\beta$ can be used to identify rapid variation regions usually known as glitches. We show that a small variation in the structure, smaller than 1% in the sound speed, produces a glitch in the acoustic potential that could explain the oscillatory character of $\beta$. This method allows us to determine the location and the thickness of the glitch with precision. We applied this idea to the Sun-like star $\alpha$ Centauri A and found a glitch located at approximately $0.94\,R$ (1400 s) and with a thickness of 0.2% of the stars' radius. This is fully consistent with the data and also validates other seismic tests.