  We present an investigation of the magnetic activity and flare
characteristics of the sub-giant stars mostly from F and G spectral types and
compare the results with the main-sequence (MS) stars. The light curve of 352
stars on the sub-giant branch (SGB) from the Kepler mission is analyzed in
order to infer stability, relative coverage and contrast of the magnetic
structures and also flare properties using three flare indexes. The results
show that: (i) Relative coverage and contrast of the magnetic features along
with rate, power and magnitude of flares increase on the SGB due to the
deepening of the convective zone and more vigorous magnetic field production
(ii) Magnetic activity of the F and G-type stars on the SGB does not show
dependency to the rotation rate and does not obey the saturation regime. This
is the opposite of what we saw for the main sequence, in which the G-, K- and
M-type stars show clear dependency to the Rossby number; (iii) The positive
relationship between the magnetic features stability and their relative
coverage and contrast remains true on the SGB, though it has lower dependency
coefficient in comparison with the MS; (iv) Magnetic proxies and flare indexes
of the SGB stars increase with increasing the relative mass of the convective
zone.

Solar and Stellar Astrophysics