| Abstract
| - Recent observations of very cool white dwarfs suggest that the low-luminosity portion of the white dwarf luminosity function is indeed dominated by the contribution of massive objects. These objects should predominantly be made of oxygen, neon and other trace isotopes. In this paper we compute cooling sequences for massive oxygen—neon (ONe) white dwarfs and we examine the question of whether massive ONe white dwarfs could represent a significant contribution to the white dwarf luminosity function at very low luminosities. We find that massive ONe white dwarfs cool much faster than carbon— oxygen (CO) white dwarfs and that, consequently, their population effectively detaches from the bulk of CO white dwarfs leading to the formation of a tail in the low-luminosity portion of the white dwarf luminosity function. Nevertheless, the position of the reported cut-off in the white dwarf luminosity function is not affected and, therefore, the age estimates of the solar neighbourhood inferred from the position of the drop-off of the white dwarf luminosity function remain unaffected.
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