Since the Gaia data release 2, several works were published describing a bifurcation in the observed white dwarf colour−magnitude diagram for \mbox{G_{\mathrm{BP}}}-\mbox{G_{\mathrm{RP}}} > 0. Some possible explanations in the literature include the existence of a double population with different initial mass function or two distinct populations, one formed by hydrogen− and one formed by helium−envelope white dwarfs. We propose instead spectral evolution to explain the bifurcation. From a population synthesis approach, we find that the spectral evolution occurs for effective temperature below ≃11000K and masses mainly between 0.64M⊙ and 0.74M⊙, which correspond to around 16 per cent of all DA white dwarfs. We also find the Gaia white dwarf colour-magnitude diagram indicates a star formation history that decreases abruptly for objects younger than 1.4Gyr and a top-heavy initial mass function for the white dwarf progenitors.
@article{arxiv.2001.04378,
title = {Evidence of Spectral Evolution on the white dwarf sample from the Gaia Mission},
author = {G. Ourique and S. O. Kepler and A. D. Romero and T. S. Klippel and D. Koester},
journal= {arXiv preprint arXiv:2001.04378},
year = {2020}
}