Hi Ernst,Ernst Pollmann wrote: an increase of the continuum brightness (below Halpha) leads to a smaller EW and vice versa, proven with the correlation coefficient of better than 0.9.
This is a correlation, not causation. The correlation is high because the H alpha EW is generally increasing as the nova fades. We already know that. What we are trying to establish is what the flux in the H alpha line is doing independent of the continuum level. To do this we need to express the continuum at Halpha (used as a reference for the EW measurement) in terms of flux. We can do this (as you have done) using the Vmag values as a reference. Your treatment however does not take into account the fact that the mean flux level in the Vmag passband changes with time relative to the continuum level at H alpha. That is what my correction factor takes into account. (This correction factor fell from ~1.7:1 to ~1.2:1 currently as the continuum flattened)
Cheers
Robin