Spatially extended K i λ 7699 emission in the nebula of VY CMa : Kinematics and geometry

Long-slit echelle spectra reveal bright extended emission from the K i λ7699 resonance line in the reflection nebula surrounding the extreme red supergiant VY Canis Majoris. The central star has long been known for its unusually-bright K i emission lines, but this is the first report of intrinsic emission from K i in the nebula. The extended emission is not just a reflected spectrum of the star, but is due to resonant scattering by K atoms in the outer nebula itself, and is therefore a valuable probe of the kinematics and geometry of VY CMa’s circumstellar environment. Dramatic velocity structure is seen in the long-slit spectra, and most lines of sight through the nebula intersect multiple distinct velocity components. A faint “halo” at large distances from the star does appear to show a reflected spectrum, however, and suggests a systemic velocity of +40 km s with respect to the Sun. The most striking feature is blueshifted emission from the filled interior of a large shell seen in images; the kinematic structure is reminiscent of a Hubble flow, and provides strong evidence for asymmetric and episodic mass loss due to localized eruptions on the star’s surface.