We have used a set of dedicated astrometric data from the Hubble Space Telescope to measure the parallax and proper motion of the nearby neutron star RX J0720.4 - 3125 .
At each of eight epochs over two years , we used the High Resolution Camera of the Advanced Camera for Surveys to measure the position of the B = 26.6 target to a precision of \sim 2 mas ( \sim 0.07 pix ) relative to 22 other stars .
From these data we measure a parallax of \pi = 2.8 \pm 0.9 mas ( for a distance of 360 ^ { +170 } _ { -90 } pc ) and a proper motion of \mu = 107.8 \pm 1.2 \mbox { mas yr } ^ { -1 } .
Exhaustive testing of every stage of our analysis suggests that it is robust , with a maximum systematic uncertainty on the parallax of 0.4 mas .
The distance is compatible with earlier estimates made from scaling the optical emission of RX J0720.4 - 3125 relative to the even closer neutron star RX J1856.5 - 3754 .
The distance and proper motion imply a transverse velocity of 180 ^ { +90 } _ { -40 } \mbox { km s } ^ { -1 } , comparable to velocities observed for radio pulsars .
The speed and direction suggest an origin for RX J0720.4 - 3125 in the Trumpler 10 OB association \sim 0.7 Myr ago , with a possible range of 0.5–1.0 Myr given by the uncertainty in the distance .