Proper Motion of the Sextans Dwarf Galaxy from Subaru Suprime-Cam Data
  We have measured the absolute proper motion of the Sextans dwarf spheroidal
galaxy using Subaru Suprime-Cam images taken at three epochs, with a time
baseline of ~ 10 years. We astrometrically calibrate each epoch by constructing
distortion-correction maps from the best available Subaru Suprime-Cam dithered
data sets and from Gaia DR1 positions. The magnitude limit of the proper-motion
study is V ~ 24. The area covered is 26.7 x 23.3 arcmin, which is still within
the core radius of Sextans. The derived proper motion is (mu_a, mu_d) = (-0.409
+/- 0.050, -0.047 +/- 0.058) mas/yr. The direction of motion is perpendicular
to the major axis of the galaxy. Our measurement, combined with radial velocity
and distance from the literature, implies a low eccentricity orbit, with a
moderate inclination to the Galactic plane, and a period of 3 Gyr. Sextans is
now some 0.4 Gyr away from its pericenter ( r_peri ~ 75 kpc), moving toward its
apocenter (r_apo ~ 132 kpc). Its orbit is inconsistent with membership to the
vast polar structure of Galactic satellites.
