We present a catalog of extragalactic proper motions created using archival VLBI data and our own VLBA astrometry .
The catalog contains 713 proper motions , with average uncertainties of \sim 24 \mu as yr ^ { -1 } , including 40 new or improved proper motion measurements using relative astrometry with the VLBA .
The observations were conducted in X-band and yielded positions with uncertainties \sim 70 \mu as .
We add 10 new redshifts using spectroscopic observations taken at Apache Point Observatory and Gemini North .
With the VLBA Extragalactic Proper Motion Catalog , we detect the secular aberration drift – the apparent motion of extragalactic objects caused by the solar system ’ s acceleration around the Galactic center – at a 6.3 \sigma significance .
We model the aberration drift as a spheroidal dipole , with the square root of the power equal to 4.89 \pm 0.77 \mu as yr ^ { -1 } , an amplitude of 1.69 \pm 0.27 \mu as yr ^ { -1 } , and an apex at ( 275.2 \pm 10.0 ^ { \circ } , -29.4 \pm 8.8 ^ { \circ } ) .
Our dipole model detects the aberration drift at a higher significance than some previous studies \citep [ e.g. , ] [ ] TitovLambert2013 , but at a lower amplitude than expected or previously measured .
The full aberration drift may be partially removed by the no-net-rotation constraint used when measuring archival extragalactic radio source positions .
Like the cosmic microwave background dipole , which is induced by the observer ’ s motion , the aberration drift signal should be subtracted from extragalactic proper motions in order to detect cosmological proper motions , including the Hubble expansion , long-period stochastic gravitational waves , and the collapse of large-scale structure .