H alpha

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Robin Leadbeater

The H alpha emission line profile is very useful for indicating the presence of and tracking the movement of material in the neighborhood of the star such as outflowing winds, eg in P Cygni, accretion inflows eg in T Tauri, rotating discs eg in Be stars, explosions eg in novae and type II supernovae, transfer of material between stars eg in symbiotics.  It is not the only useful line though. eg the narrower metal lines are better if you want to measure a star’s radial velocity and some systems don’t have hydrogen eg WR stars where the winds can be tracked using eg C III, IV lines (as in the current WR140 colliding wind campaign) or type 1a supernovae where the Si absorption line is the key one to look for. In low temperature systems you might look for low excitation lines like the 7699A K line in eps Aur which I used to track the density and velocity of the material in the cool eclipsing disc.