Detection of the Lower Boundary of Stellar Convective Envelopes from Seismic Data

A sharp feature in a star's internal structure gives rise to a characteristic periodic signal in the frequencies of its global p-modes. Such a sharp feature occurs at the borders of a convective region in the star's interior. Several groups have used this characteristic signal to study the base of the solar convective envelope ((1], 2], and references therein). In this work, we apply the analysis of 1] and 2] to the low degree modes that one might detect on distant stars, to show what kind of diagnostic the oscillations might provide for convective envelopes of low-mass stars. We regard the eeect of the sharp feature on the frequencies as a perturbation !=A(!) cos2(! d +)], added to the frequencies of a ctitious star with the sharp feature smoothed out. The amplitude A(!) depends on the properties of the star in the vicinity of the base of the convective envelope, in particular on whether or not overshooting is present: see 3] for a detailed analysis. The quantity d is the acoustical depth (i.e., the sound travel time) of the edge of the convection zone measured from the surface of the star. The eeective surface phase of the eigenfunctions varies with frequency; thus when we measure thèperiod' of ! we measure not d alone but d d + a , where a = d=d!. We consider models of ZAMS stars of mass 0:85M to 1:3M. The models were calculated as described by 4]. From the p-mode frequencies of these models we have determined the amplitude and d using the least