References

For additional spectral lines, http://home.achilles.net/~jtalbot/data/nebula/identification.html  (has been removed, see http://web.archive.org/web/20030425143620/home.achilles.net/~jtalbot/data/nebula/, which is the archived form)

Death of low mass stars, http://www.ucolick.org/~bolte/AY4_00/week7/low-mass_deathC.html

Some theoretical discussion: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1990ApJ...362..226O