  The extreme-ultraviolet (EUV) late phase of solar flares is a second peak of
warm coronal emissions (e.g., Fe XVI) for many minutes to a few hours after the
GOES soft X-ray peak. It was first observed by the EUV Variability Experiment
(EVE) on board the Solar Dynamics Observatory (SDO). The late phase emission
originates from a second set of longer loops (late phase loops) that are higher
than the main flaring loops. It is suggested as being caused by either
additional heating or long-lasting cooling. In this paper, we study the role of
long-lasting cooling and additional heating in producing the EUV late phase
using the "enthalpy-based thermal evolution of loops" (EBTEL) model. We find
that a long cooling process in late phase loops can well explain the presence
of the EUV late phase emission, but we cannot exclude the possibility of
additional heating in the decay phase. Moreover, we provide two preliminary
methods based on the UV and EUV emissions from the Atmospheric Imaging Assembly
(AIA) on board SDO to determine whether an additional heating plays some role
or not in the late phase emission. Using nonlinear force-free field modeling,
we study the magnetic configuration of the EUV late phase. It is found that the
late phase can be generated either in hot spine field lines associated with a
magnetic null point or in large-scale magnetic loops of multipolar magnetic
fields. In this paper, we also discuss why the EUV late phase is usually
observed in warm coronal emissions and why the majority of flares do not
exhibit an EUV late phase.
