Abstract:
The thermodynamic evolution of Coronal Mass Ejections (CMEs) in the inner
corona (≤1.5 Rsun) is not yet completely understood. In this work, we study the
evolution of thermodynamic properties of a CME core observed in the inner corona
on 20 July 2017, by combining the MLSO/K-Cor white-light and the MLSO/CoMP
Fe XIII 10747 Å line spectroscopic data. We also estimate the emission measure
weighted temperature (TEM) of the CME core by applying the Differential Emission
Measure (DEM) inversion technique on the SDO/AIA six EUV channels data and
compare it with the effective temperature (Teff) obtained using Fe XIII line width
measurements. We find that the Teff and TEM of the CME core show similar variation
and remain almost constant as the CME propagates from ∼1.05 to 1.35 Rsun. The
temperature of the CME core is of the order of million-degree kelvin, indicating that
it is not associated with a prominence. Further, we estimate the electron density of
this CME core using K-Cor polarized brightness (pB) data and found it decreasing by
a factor of ∼3.6 as the core evolves. An interesting finding is that the temperature of
the CME core remains almost constant despite expected adiabatic cooling due to
the expansion of the CME core, which suggests that the CME core plasma must be
heated as it propagates. We conclude that the expansion of this CME core behaves
more like an isothermal than an adiabatic process.
