Context. The availability of precisely determinedfrequencies of radial and non-radial oscillation modes in red giants isfinally paving the way for detailed studies of the internal structureof these stars. Aims. We look for the seismic signature of regions of sharpstructure variation in the internal structure of the CoRoT targetHR7349. Methods. We analyse the frequency dependence of the largefrequency separation and second frequency differences, as well as thebehaviour of the large frequency separation obtained with the envelopeauto-correlation function. Results. We find evidence for a periodic component in theoscillation frequencies, i.e. the seismic signature of a sharpstructure variation in HR7349. In a comparison with stellarmodels we interpret this feature as caused by a local depression of thesound speed that occurs in the helium second-ionization region. Usingsolely seismic constraints this allows us to estimate the mass (M=1.2+0.6-0.4)and radius (R=12.2+2.1-1.8)of HR7349, which agrees with the location of the star in an HRdiagram. Key words: asteroseismology - stars: interiors - stars: oscillations - stars: fundamental parameters - stars: individual: HR7349
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