Stellar acoustic radii and ages from seismic inversion techniques

Context: Determining stellar characteristics such as the radius, mass or age is crucial for the study of stellar
evolution, exoplanetary systems or the characterisation of stellar populations in the Galaxy. Asteroseismology
is currently the most promising tool to accurately determine these characteristics. However, a key question is
how to reduce the model dependence of asteroseismic methods.
Method: We extend the SOLA inversion technique to new global characteristics in addition to the mean
density (see Reese et al. 2012). We apply our methodology to the acoustic radius and an age indicator based
on the sound speed derivative. The results from SOLA inversions are compared with estimates based on
the small and large frequency separations for several test cases, including differing mixing-lengths, and the
presence or absence of non-adiabatic effects or turbulent pressure.
Results: We show that SOLA inversions yield accurate results in all test cases, unlike the other techniques
which are more sensitive to surface effects. We observe that the acoustic radius and mean density inversions
are more robust than the age indicator inversions, which are limited to relatively young stars with radiative
cores.