... The ,1000 WDs are mostly DAs with strong broad hydrogen Balmer absorption lines. ... DB and DO WDs which are dominated by neutral and singly ionized helium respectively ...
... lines as a function of rest wavelength for broad permitted lines (filled circles), narrow forbidden lines (open triangles) and semiforbidden C III] (open square). ize hydrogen but relatively fewer with energies greater than 64 eV available to ionize C IV ...
... The 2000 WDs are mostly DAs with strong broad hydrogen Balmer absorption lines. ... DB and DO WDs which are dominated by neutral and singly ionized helium, respectively ...