  Rotation is a critical physical process operating in the formation of Am
stars. There is a strong correlation between low-velocity rotation and chemical
peculiarity. However, the existence of many non-CP slow rotators challenges the
understanding of Am stars. The purpose of our work is to search for
low-velocity rotating non-CP A-type stars and Am stars and to make a
comparative analysis. In this paper, we pick out a sample from the
LAMOST-Kepler project, including 21 Am stars, 125 non-CP slow rotators, and 53
non-CP fast rotators. We calculate the rotational frequencies through periodic
change of light curves caused by inhomogeneous stellar surfaces and then obtain
the rotational velocities. For slow rotators, the age of Am stars is
statistically younger than that of non-CP stars in the same temperature bin. In
the comparison of the period, the average amplitude, and stellar mass of Am and
non-CP stars, we discover that there is no difference in the photometric
variability between Am and non-CP stars, which implies similar inhomogeneities
on the surfaces. The average amplitude of non-CP stars has a downward trend
with the increase of effective temperature and stellar mass, which is
consistent with the theoretical prediction caused by weak dynamo-generated
magnetic fields in A-type stars. In addition, we confirm four non-non-CP stars
which have flares by checking FOV images, 24 pixel images, and pixel-level
light curves.
