TiO2 and dust formation around the red supergiant VY CMa

Elvire De Beck, E. O'Gorman, W. Vlemmings, A.M.S. Richards & J.H. Black

Onsala Space Observatory, Chalmers University of Technology, Sweden

I will present high-spatial resolution observations of the continuum and TiO2 emission around the red supergiant VY CMa obtained with ALMA during science verification, demonstrating long-baseline capabilities. TiO2, titanium dioxide, is a refractory species that could play a crucial role in the dust-condensation sequence around oxygen-rich evolved stars. To date, gas phase TiO2 has been detected only in the complex circumstellar environment of VY CMa. We detect 13 previously undetected transitions of TiO2 and spatially resolve the line and continuum emission for the first time. The continuum shows emission from the stellar position, and a large, cold clump of dust to the south-east. The ALMA maps demonstrate a highly clumpy, anisotropic outflow in which the TiO2 emission traces gas exposed to the stellar radiation field. We find an accelerating bipolar-like structure, oriented roughly east-west, of which the blue component runs into and breaks up around the solid continuum component. A distinct tail to the south-west is seen, consistent with features seen in the optical and near-infrared. We find that a significant fraction of TiO2 remains in the gas phase outside the dust-formation zone and suggest that this species might play only a minor role in the dust-condensation process around extreme oxygen-rich evolved stars like VY CMa.

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