  We introduce a framework to measure the asphericity of Sun-like stars using
$a_1$, $a_2$ and $a_4$ coefficients, and constrain their latitudes of magnetic
activity. Systematic errors on the inferred coefficients are evaluated in
function of key physical and seismic parameters (inclination of rotation axis,
average rotation, height-to-noise ratio of peaks in power spectrum). The
measured a-coefficients account for rotational oblateness and the effect of
surface magnetic activity. We use a simple model that assumes a single
latitudinal band of activity. Using solar SOHO/VIRGO/SPM data, we demonstrate
the capability of the method to detect the mean active latitude and its
intensity changes between 1999-2002 (maximum of activity) and 2006-2009
(minimum of activity). We further apply the method to study the solar-analogue
stars 16 Cyg A and B using Kepler observations. An equatorial band of activity,
exhibiting intensity that could be comparable to that of the Sun, is detected
in 16 Cyg A. However, 16 Cyg B exhibits a bi-modality in $a_4$ that is
challenging to explain. We suggest that this could be a manifestation of the
transition between a quiet and an active phase of activity. Validating or
invalidating this hypothesis may require new observations.
