A Decade of MWC 758 Disk Images: Where Are the Spiral-arm-driving Planets?

International audienceLarge-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-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. • 6 +3. • 3 −0. • 6 yr −1 at 3σ 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. 59), with a 3σ lower limit of 30 au (0. 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