Proper motion of Draco dwarf galaxy from HST

Wide Field Channels 1 and 2 provide two adjacent fields, each containing a known QSO. The zero point for the proper motion is determined using both background galaxies and the QSOs and the two methods produce consistent measurements within each field.

Averaging the results from the two fields gives a proper motion in the equatorial coordinate system of ({mu}_{alpha}_,{mu}_{delta}_)=(-17.7+/-6.3,-22.1+/-6.3)mas/century and in the Galactic coordinate system of ({mu}_l_,{mu}_b_)=(-23.1+/-6.3,-16.3+/-6.3)mas/century. Removing the contributions of the motion of the Sun and of the LSR to the measured proper motion yields a Galactic rest-frame proper motion of ({mu}_{alpha}_^Grf^,({mu}_{delta}_^Grf^)=(51.4+/-6.3,-18.7+/-6.3)mas/century and ({mu}_l_^Grf^,({mu}_b_^Grf^)=(-21.8+/-6.3,-50.1+/-6.3)mas/century.