Large-scale spiral arms have been revealed in scattered light images of a few protoplanetary disks .
Theoretical models suggest that such arms may be driven by and co-rotate with giant planets , which has called for remarkable observational efforts to look for them .
By examining the rotation of the spiral arms for the MWC 758 system over a 10-yr timescale , we are able to provide dynamical constraints on the locations of their perturbers .
We present reprocessed Hubble Space Telescope ( HST ) /NICMOS F110W observations of the target in 2005 , and the new Keck /NIRC2 L ^ { \prime } -band observations in 2017 .
MWC 758 ’ s two well-known spiral arms are revealed in the NICMOS archive at the earliest observational epoch .
With additional Very Large Telescope ( VLT ) /SPHERE data , our joint analysis leads to a pattern speed of 0 \fdg 6 ^ { +3 \fdg 3 } _ { -0 \fdg 6 } \mathrm { yr } ^ { -1 } at 3 \sigma for the two major spiral arms .
If the two arms are induced by a perturber on a near-circular orbit , its best fit orbit is at 89 au ( 0 \farcs 59 ) , with a 3 \sigma lower limit of 30 au ( 0 \farcs 20 ) .
This finding is consistent with the simulation prediction of the location of an arm-driving planet for the two major arms in the system .