The idea that helioseismology may be used to test the assumption that the solar age is equal to the age of the oldest meteorites is not new. Gough & Novotny (1990), who considered the problem in great detail, concluded that the accuracy of 0.3 Gy may be achieved once the seismic age indicators are measured to a precision of 0.1 µHz. The precision of current seismic data is now significantly better. However, results of recent studies of the problem yield conflicting conclusions.
Before we go to the results of these studies, let us first point out that we should expect a unique determination of the solar age from seismic data. Calculated p-mode frequencies depend on the assumed solar age but they also depend on other input solar parameters and physical quantities. All these data are subject to uncertainties. We now have at our disposal nearly 2000 accurate frequency data for solar p-modes to determine solar age - the only observable in the standard solar model (SSM) construction which we surrender. It would be indeed surprising if the answer would not depend on the way we make use of seismic data. An assessment of the uncertainty of is even more problematic.
Guenther & Demarque (1997) concluded their comparison of the solar frequencies with those for models calculated upon assuming different age with the following statement: "The best agreement with the calculated oscillation spectra is achieved for Gy". Unfortunately, they did not explain how these numbers were obtained.
Weiss & Schlattl (1998), proceeding in a more formal way, used minimization to determine . They considered various seismic observables and corresponding parameters in the models calculated for various assumed solar ages. The observables include surface helium abundance, , depth of the convective zone, , sound speed in the the radiative interior, and the radial mode frequencies. In nearly all the cases they considered, the minimum was reached for age well above 5 Gy. Typical values of they derive are in the range 5.1-5.2 Gy. Taken for granted, the high values of the solar age would mean an essential revision of our views on the evolution of the solar system. This is not what Weiss & Schlattl (1998) propose. Rather, they regard the difference between and as a measure of the uncertainties in the age determination based on the state-of-art stellar evolution theory.
The main motivation for our work was to explain the large difference in the conclusions of the two papers regarding the value of and its uncertainty. Weiss & Schlattl (1998) themselves have addressed this problem but we did not find their explanation sufficient. We will begin with providing some information about new solar models calculated for the purpose of this investigation. In the main part of the paper, we review the inference about the solar age based on various seismic observables and we identify those which we believe are good age indicators.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999