Local perturbations of the upper layers of a Sun-like star: the impact   on the acoustic oscillation spectrum
  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. 
Ana Brito and Ilidio Lopes
astro-ph.SR