Evidence of Spectral Evolution on the white dwarf sample from the Gaia Mission
Abstract
Since the Gaia data release 2, several works were published describing a bifurcation in the observed white dwarf colour-magnitude diagram for GBP-GRP > 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 11\,000\,K and masses mainly between 0.64\,M and 0.74\,M, 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 1.4\,Gyr and a top-heavy initial mass function for the white dwarf progenitors.