Shock contribution to coronal-line emission in V1674 Her

Ascertain whether shock ionisation contributes to the optical coronal and high-ionisation iron lines in V1674 Herculis after the onset of the super-soft source phase (from day ≈19.87 onward), given the absence of optical data between the initial coronal-line detection at day 11.5 and the super-soft source onset at day 18.9.

Background

Near-infrared coronal lines were detected at day 11.5, which has been attributed to shock ionisation because the super-soft source (SSS) phase began later (day 18.9). The authors’ optical spectroscopic coverage starts at day 19.87, after the SSS onset, where photoionisation appears dominant, but a residual shock component may persist.

Because no optical spectra exist between the inferred shock onset and the start of the SSS phase, the relative contribution of shocks to the coronal and high-ionisation iron lines ([Fe VI], [Fe VII], [Fe X], [Fe XI], [Fe XIV]) remains unresolved in the post-SSS epochs.