  Simultaneous, high-quality measurements of the neutral helium triplet
features at 5876~\AA\ and 10830~\AA, respectively, in a sample of solar-type
stars are presented. The observations were made with ESO telescopes at the La
Silla Paranal Observatory under program ID 088.D-0028(A) and MPG Utility Run
for FEROS 088.A-9029(A). The equivalent widths of these features combined with
chromospheric models are utilized to infer the fractional area coverage, or
filling factor, of magnetic regions outside of spots. We find that the majority
of the sample is characterized by filling factors less than unity. However,
discrepancies occur among the coolest K-type and warmest and most rapidly
rotating F-type dwarf stars. We discuss these apparently anomalous results and
find that in the case of K-type stars they are an artifact of the application
of chromospheric models best suited to the Sun than to stars with significantly
lower $T_\mathrm{eff}$. The case of the F-type rapid rotators can be explained
with the measurement uncertainties of the equivalent widths, but they may also
be due to a non-magnetic heating component in their atmospheres. With the
exceptions noted above, preliminary results suggest that the average heating
rates in the active regions are the same from one star to the other, differing
in the spatially integrated, observed level of activity due to the area
coverage. Hence, differences in activity in this sample are mainly due to the
filling factor of active regions.
