Title: Starspot activity and superflares on solar-type stars,
Abstract: We analyze the correlation between starspots and superflares on solar-type
stars using observations from the Kepler mission. The analysis shows that the
observed fraction of stars with superflares decreases as the rotation period
increases and as the amplitude of photometric variability associated with
rotation decreases. We found that the fraction of stars with superflares among
the stars showing large-amplitude rotational variations, which are thought to
be the signature of the large starspots, also decreases as the rotation period
increases. The small fraction of superflare stars among the stars with large
starspots in the longer-period regime suggests that some of the stars with
large starspots show a much lower flare activity than the superflare stars with
the same spot area. Assuming simple relations between spot area and lifetime
and between spot temperature and photospheric temperature, we compared the size
distribution of large starspot groups on slowly-rotating solar-type stars with
that of sunspot groups. The size distribution of starspots shows the power-law
distribution and the size distribution of larger sunspots lies on this
power-law line. We also found that frequency-energy distributions for flares
originating from spots with different sizes are the same for solar-type stars
with superflares and the Sun. These results suggest that the magnetic activity
we observe on solar-type stars with superflares and that on the Sun is caused
by the same physical processes.