Evolutionary calculations of carbon dredge‐up in helium envelope white dwarfs

It has been proposed that the presence of carbon in the mainly helium atmospheres of the DQ white dwarfs is due to convective dredge-up of carbon diffusing outwards from a CO core. The first quantitative study of this process is that of Pelletier at al (1986, hereafter P86), who found that agreement with the observationally determined photospheric C/He ratios required that the mass of the helium-rich layer in the white dwarf progenitor be an order of magnitude less than determined from theoretical calculations of the pre-white dwarf evolution.