  Oscillation properties are usually measured by fitting symmetric Lorentzian
profiles to the power spectra of Sun-like stars. However the line profiles of
solar oscillations have been observed to be asymmetrical for the Sun. The
physical origin of this line asymmetry is not fully understood, although it
should depend on the depth dependence of the source of wave excitation
(convective turbulence) and details of the observable (velocity or intensity).
For oscillations of the Sun, it has been shown that neglecting the asymmetry
leads to systematic errors in the frequency determination. This could
subsequently affects the results of seismic inferences of the solar internal
structure. Using light curves from the {\it Kepler} spacecraft we have measured
mode asymmetries in 43 stars. We confirm that neglecting the asymmetry leads to
systematic errors that can exceed the $1\sigma$ confidence intervals for
seismic observations longer than one year. Therefore, the application of an
asymmetric Lorentzian profile is to be favoured to improve the accuracy of the
internal stellar structure and stellar fundamental parameters. We also show
that the asymmetry changes sign between cool Sun-like stars and hotter stars.
This provides the best constraints to date on the location of the excitation
sources across the Hertzsprung-Russel diagram.
