Third Parameter Classification of Transients and Novae Ejecta as   Ballistically Ejected Globules
  A third parameter, in addition to luminosity and rate of brightness decline, derived from the spectra of transients is suggested as a means of more accurately classifying objects in outburst. Principal component analysis of the spectra of transients is suggested as the best way to determine the third parameter. A model is suggested for novae ejecta that is based on ballistic ejection of an ensemble of globules. The distribution in sizes of the clouds should determine basic characteristics of the ejecta, including the short term brightness fluctuations of novae in decline and the location of dust formation. 
Robert Williams
astro-ph.SR