Astrometric and photometric verification of faint blue white dwarfs in the Gaia catalogue of nearby stars

TL;DR

This study verifies faint blue white dwarfs in Gaia data, confirming their distinct presence and characteristics, and highlights their potential for studying ultracool and ultramassive white dwarfs.

Contribution

It provides a visual and proper motion-based verification of faint blue white dwarfs in Gaia data, distinguishing them from contaminated objects and identifying their unique properties.

Findings

Confirmed 59 faint blue white dwarfs as genuine from Gaia data.

Faint blue white dwarfs have higher proper motions and tangential velocities.

They form a distinct branch in the Gaia color-magnitude diagram.

Abstract

The Gaia catalogue of nearby stars (GCNS) divided all objects with parallaxes $>$10mas into GCNS-selected and GCNS-rejected 100pc samples. Below the white dwarf (WD) sequence in the complete GCNS color-magnitude diagram (CMD), at $Gabs>14.7+4.7(G-RP)$, there appear 60 GCNS-selected faint blue white dwarfs (FBWDs). However this CMD region is also populated by 411 GCNS-rejected objects, mainly from crowded regions towards the Galactic centre and the Magellanic Clouds. The WD catalog of Gentile Fusillo et al. (2021) lists only 47 GCNS-selected but also 8 GCNS-rejected objects. I confirm 59 of the GCNS-selected but none of the GCNS-rejected objects as FBWDs from visual inspection and a proper motion check using additional optical sky surveys. Hence FBWDs form an additional branch in the CMD. Compared to the full GCNS-selected 100pc sample, FBWDs have relatively high proper motions and tangential velocities. They represent interesting targets for studies of ultracool or infrared-faint, and possibly also ultramassive WDs.