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