How to SYN in seven easy steps

This requires calculation of the opacity κλ; this is the core task of a spectral synthesis program. The opacity can be considered to consist of a continuous opacity, and opacity due to atomic line transitions. The main contribution to the continuous opacity is due to bound-free and free-free H transitions; other major sources (H+2 molecule, photoionisation of metals) also need to be considered. The line opacity can be found from the line strength and line profile for each line in the spectral region of interest.