Supersonic Expansion of the Bipolar H II Region Sh2-106: A 3500 Year Old Explosion?

Abstract

Multi-epoch narrowband Hubble Space Telescope images of the bipolar H II region Sh2-106 reveal highly supersonic nebular proper motions that increase with projected distance from the massive young stellar object S106 IR, reaching over ~30 mas yr^-1 (~150 km s^-1 at D = 1.09 kpc) at a projected separation of ~1.'4 (0.44 pc) from S106 IR. We propose that S106 IR experienced a ~10⁴⁷ erg explosion ~3500 yr ago. The explosion may be the result of a major accretion burst or a recent encounter with another star, or a consequence of the interaction of a companion with the bloated photosphere of S106 IR as it grew from ~10 through ~15 M _⊙ at a high accretion rate. Near-IR images reveal fingers of H₂ emission pointing away from S106 IR and an asymmetric photon-dominated region surrounding the ionized nebula. Radio continuum and Brγ emission reveal a C-shaped bend in the plasma, indicating either the motion of S106 IR toward the east, or the deflection of plasma toward the west by the surrounding cloud. The H II region bends around a ~1' diameter dark bay west of S106 IR that may be shielded from direct illumination by a dense molecular clump. Herbig-Haro and Molecular Hydrogen Objects tracing outflows powered by stars in the Sh2-106 protocluster such as the Class 0 source S106 FIR are discussed.