  TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets,
for which thorough characterization of atmospheric properties, surface
conditions encompassing habitability and internal compositions is possible with
current and next generation telescopes. Accurate modeling of the star is
essential to achieve this goal. We aim to obtain updated stellar parameters for
TRAPPIST- 1 based on new measurements and evolutionary models, compared to
those used in discovery studies. We present a new measurement for the parallax
of TRAPPIST-1, 82.4 $\pm$ 0.8 mas, based on 188 epochs of observations with the
TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax
yields an updated luminosity of $L_*=(5.22\pm0.19)\times 10^{-4} L_{\odot}$,
very close to the previous estimate but almost twice more precise. We next
present an updated estimate for TRAPPIST-1 stellar mass, based on two
approaches: mass from stellar evolution modeling, and empirical mass derived
from dynamical masses of equivalently classified ultracool dwarfs in
astrometric binaries. We combine them through a Monte-Carlo approach to derive
a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate
for the radius by combining this mass with stellar density inferred from
transits, as well as estimate for the effective temperature from our revised
luminosity and radius. Our final results are $M_*=0.089 \pm 0.006 M_{\odot}$,
$R_* = 0.121 \pm 0.003 R_{\odot}$, and $T_{\rm eff} =$ 2516 $\pm$ 41 K.
Considering the degree to which TRAPPIST-1 system will be scrutinized in coming
years, these revised and more precise stellar parameters should be considered
when assessing the properties of TRAPPIST-1 planets.
