We present the first asteroseismological study for 42 massive ZZ Ceti stars based on a large set of fully evolutionary carbon - oxygen core DA white dwarf models characterized by a detailed and consistent chemical inner profile for the core and the envelope .
Our sample comprise all the ZZ Ceti stars with spectroscopic stellar masses between 0.72 and 1.05 M _ { \odot } known to date .
The asteroseismological analysis of a set of 42 stars gives the possibility to study the ensemble properties of the massive pulsating white dwarf stars with carbon - oxygen cores , in particular the thickness of the hydrogen envelope and the stellar mass .
A significant fraction of stars in our sample have stellar mass high enough as to crystallize at the effective temperatures of the ZZ Ceti instability strip , which enables us to study the effects of crystallization on the pulsation properties of these stars .
Our results show that the phase diagram presented in Horowitz et al .
( 2010 ) seems to be a good representation of the crystallization process inside white dwarf stars , in agreement with the results from white dwarf luminosity function in globular clusters .