Column density is the number density of particles integrated over the line of sight. It represents how much stuff there is in the star/intervening gas cloud.
Doppler broadening of the absorption line. Since Doppler broadening correlates with temperature, the value of this slider indicates temperature of the intervening gas.
The width of wavelength in the absorption line plot. Note that the curve of growth will stop tracing the equivalent width once the absorption line goes out of the plotting range.
