Parameter Effects on the Total Intensity of H I Ly Α Line for a Modeled Coronal Mass Ejection and Its Driven Shock

The combination of the H i Ly α (121.6 nm) line formation mechanism with ultraviolet (UV) Ly α and white-light (WL) observations provides an effective method for determining the electron temperature of coronal mass ejections (CMEs). A key to ensuring the accuracy of this diagnostic technique is the precise calculation of theoretical Ly α intensities. This study performs a modeled CME and its driven shock via the three-dimensional numerical magneto-hydrodynamic simulation. Then, we generate synthetic UV and WL images of the CME and shock within a few solar radii to quantify the impact of different assumptions on the theoretical Ly α intensities, such as the incident intensity of the solar chromospheric Ly α line ( I_disk ), the geometric scattering function ( p(θ ) ), and the kinetic temperature ( T_n ) assumed to be equal to either the proton ( T_p ) or electron ( T_e ) temperature. By comparing differences of the Ly α intensities of the CME and shock under these assumptions, we find that: (1) Using the uniform or Carrington maps of the disk Ly α emission underestimates the corona Ly α intensity (with relative uncertainties below 10 α intensity, with a maximum relative uncertainty of no more than 5 α intensity is underestimated for the most part but overestimated in the CME core. (3) Compared to the assumption T_n=T_p , using T_n=T_e leads to more complex relative uncertainties in CME Ly α intensity. The CME core and void are both overestimated, with the maximum relative uncertainty in the core exceeding 50