An M Dwarf Companion and Its Induced Spiral Arms in the HD 100453 Protoplanetary Disk

Abstract: Recent VLT/SPHERE near-infrared imaging observations revealed two spiral arms with a near m=2 rotational symmetry in the protoplanetary disk around the ~1.7 solar mass Herbig star HD 100453. A ~0.3 solar mass M dwarf companion, HD 100453 B, was also identified at a projected separation of 120 AU from the primary. In this Letter, we carry out hydrodynamic and radiative transfer simulations to examine the scattered light morphology of the HD 100453 disk as perturbed by the companion on a circular and coplanar orbit. We find that the companion truncates the disk at ~45 AU in scattered light images, and excites two spiral arms in the remaining (circumprimary) disk with a near m=2 rotational symmetry. Both the truncated disk size and the morphology of the spirals are in excellent agreement with the SPHERE observations at Y , J, H, and K1-bands, suggesting that the M dwarf companion is indeed responsible for the observed double-spiral-arm pattern. Our model suggests that the disk is close to face on (inclination angle ~5 degree), and that the entire disk-companion system rotates counterclockwise on the sky. The HD 100453 observations, along with our modeling work, demonstrate that double spiral arm patterns in near-infrared scattered light images can be generically produced by companions, and support future observations to identify the companions responsible for the arms observed in the MWC 758 and SAO 206462 systems.