The Solar Neighborhood. XXI. Parallax Results from the CTIOPI 0.9m
  Program: 20 New Members of the 25 Parsec White Dwarf Sample
  We present accurate trigonometric parallaxes for 20 new members of the 25 pc
white dwarf sample as part of the DENSE project (Discovery and Evalution of
Nearby Stellar Embers, http://www.DenseProject.com). Previously, there were a
total of 112 white dwarf systems with trigonometric parallaxes placing them
within 25 pc and of these, 99 have trigonometric parallaxes known to better
than 10%. Thus, the 20 new members presented in this work represent a 20%
increase in the number of white dwarfs accurately known to be within 25 pc. In
addition, we present updated parallaxes for seven known white dwarfs within 10
pc that have been observed as part of the ASPENS initiative (Astrometric Search
for Planets Encircling Nearby Stars) to monitor nearby southern red and white
dwarfs for astrometric perturbations from unseen companions. Including a few
white dwarf companions and white dwarfs beyond 25 pc, we present a total of 33
trigonometric parallaxes. We perform atmospheric modeling for white dwarfs to
determine physical parameters (i.e., effective temperature, log g, mass, and
white dwarf age). Finally, a new ZZ Ceti pulsating white dwarf was identified
and revised constraints are placed on two mixed H/He atmosphere cool white
dwarfs that display continuum absorption in the near-infrared.
