  We present recent results of 3D magnetohydrodynamic simulations of neutron
stars with small misalignment angles, as regards the features in lightcurves
produced by regular movements of the hot spots during accretion onto the star.
In particular, we show that the variation of position of the hot spot created
by the infalling matter, as observed in 3D simulations, can produce high
frequency Quasi Periodic Oscillations with frequencies associated with the
inner zone of the disk. Previously reported simulations showed that the usual
assumption of a fixed hot spot near the polar region is valid only for
misalignment angles relatively large. Otherwise, two phenomena challenge the
assumption: one is the presence of Rayleigh-Taylor instabilities at the
disk-magnetospheric boundary, which produce tongues of accreting matter that
can reach the star almost anywhere between the equator and the polar region;
the other one is the motion of the hot spot around the magnetic pole during
stable accretion. In this paper we start by showing that both phenomena are
capable of producing short-term oscillations in the lightcurves. We then use
Monte Carlo techniques to produce model lightcurves based on the features of
the movements observed, and we show that the main features of kHz QPOs can be
reproduced. Finally, we show the behavior of the frequencies of the moving
spots as the mass accretion rate changes, and propose a mechanism for the
production of double QPO peaks.

High Energy Astrophysical Phenomena