A companion in V1247 Ori supported by motion in the pattern of the spiral arm

Abstract

While nearly two dozen spiral arms have been detected from planet-forming disks in near-infrared scattered light, none of their substellar drivers has been confirmed. By observing spiral systems in at least two epochs spanning multiple years and measuring the motion of the spirals, we can distinguish what causes the spirals and locate the orbits of the driving planets if the spirals are triggered by them. Upon a recent validation of this approach using the comotion between a stellar companion and a spiral, we obtained a second-epoch observation for the spiral system in the disk of V1247 Ori in the H-band polarized scattered light using Very Large Telescope (VLT), SPHERE, and IRDIS. By combining our observations with archival IRDIS data, we established a 4.8 yr timeline to constrain the spiral motion of V1247 Ori. We obtained a pattern speed of 0°.40 ± 0°.10 yr−1 for the northeast spiral. This corresponds to an orbital period of 900 ± 220 yr, and the semimajor axis of the hidden planetary driver therefore is 118 ± 20 au for a 2.0 ± 0.1 M⊙ central star. The location agrees with the gap in ALMA dust-continuum observations, which provides joint support for the hypothesis that a companion drives the scattered-light spirals while carving a millimeter gap. With an angular separation of 0″​​.29 ± 0″​​.05, this hidden companion is an ideal target for JWST imaging.