We report on the identification of 22 new cool DO-type white dwarfs ( WD ) detected in Data Release 10 ( DR10 ) of the Sloan Digital Sky Survey ( SDSS ) .
Among them , we found one more member of the so-called hot-wind DO WDs , which show ultrahigh excitation absorption lines .
Our non-LTE model atmosphere analyses of these objects and two not previously analyzed hot-wind DO WDs , revealed effective temperatures and gravities in the ranges \mbox { $T _ { \mathrm { eff } } $ } \hskip { -1.422638 pt } = \hskip { -1.422638 pt } 45 - 80 \mathrm% { kK } and \log g \hskip { -1.422638 pt } = \hskip { -1.422638 pt } 7.50 - 8.75 .
In eight of the spectra we found traces of C ( 0.001 - 0.01 , by mass ) .
Two of these are the coolest DO WDs ever discovered that still show a considerable amount of C in their atmospheres .
This is in strong contradiction with diffusion calculations , and probably , similar to what is proposed for DB WDs , a weak mass-loss is present in DO WDs .
One object is the most massive DO WD discovered so far with a mass of 1.07 M _ { \odot } if it is an ONe-WD or 1.09 M _ { \odot } if it is a CO-WD .
We furthermore present the mass distribution of all known hot non-DA ( pre- ) WDs and derive the hot DA to non-DA ratio for the SDSS DR7 spectroscopic sample .
The mass distribution of DO WDs beyond the wind limit strongly deviates from the mass distribution of the objects before the wind limit .
We address this phenomenon by applying different evolutionary input channels .
We argue that the DO WD channel may be fed by about 13 % by post-extreme-horizontal branch stars and that PG 1159 stars and O ( He ) stars may contribute in a similar extent to the non-DA WD channel .