  Transit photometry of the M8V dwarf star TRAPPIST-1 (2MASS J23062928-0502285)
has revealed the presence of at least seven planets with masses and radii
similar to that of Earth orbiting at distances that might allow liquid water to
be present on their surfaces. We have been following TRAPPIST-1 since 2011 with
the CAPSCam astrometric camera on the 2.5-m du Pont telescope at the Las
Campanas Observatory in Chile. In 2016 we noted that TRAPPIST-1 lies slightly
farther away than previously thought, at 12.49 pc, rather than 12.1 pc. Here we
examine fifteen epochs of CAPSCam observations of TRAPPIST-1, spanning the five
years from 2011 to 2016, and obtain a revised trigonometric distance of $12.56
\pm 0.12$ pc. The astrometric data analysis pipeline shows no evidence for a
long-period astrometric wobble of TRAPPIST-1. After proper motion and parallax
are removed, residuals at the level of $\pm 1.3$ millarcsec (mas) remain. The
amplitude of these residuals constrains the masses of any long-period gas giant
planets in the TRAPPIST-1 system: no planet more massive than $\sim 4.6
M_{Jup}$ orbits with a 1 yr period, and no planet more massive than $\sim 1.6
M_{Jup}$ orbits with a 5 yr period. Further refinement of the CAPSCam data
analysis pipeline, combined with continued CAPSCam observations, should either
detect any long-period planets, or put an even tighter constraint on these mass
upper limits.
