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arXiv · 1506.00818

ALMA observations of TiO$_2$ around VY Canis Majoris

E. De Beck·W. Vlemmings·S. Muller·J. H. Black·E. O'Gorman·A. M. S. Richards·A. Baudry·M. Maercker·L. Decin·E. M. Humphreys
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Abstract

Titanium dioxide, TiO$_2$, is a refractory species that could play a crucial role in the dust-condensation sequence around oxygen-rich evolved stars. To date, gas phase TiO$_2$ has been detected only in the complex environment of the red supergiant VY CMa. We aim to constrain the distribution and excitation of TiO$_2$ around VY CMa in order to clarify its role in dust formation. We analyse spectra and channel maps for TiO$_2$ extracted from ALMA science verification data. We detect 15 transitions of TiO$_2$, and spatially resolve the emission for the first time. The maps demonstrate a highly clumpy, anisotropic outflow in which the TiO$_2$ emission likely traces gas exposed to the stellar radiation field. A roughly east-west oriented, accelerating bipolar-like structure is found, of which the blue component runs into and breaks up around a solid continuum component. A distinct tail to the south-west is seen for some transitions, consistent with features seen in the optical and near-infrared. We find that a significant fraction of TiO$_2$ 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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E. De Beck, W. Vlemmings, S. Muller, J. H. Black, E. O'Gorman, A. M. S. Richards, A. Baudry, M. Maercker, L. Decin, E. M. Humphreys. 2015-06-02. ALMA observations of TiO$_2$ around VY Canis Majoris. https://doi.org/10.1051/0004-6361%2F201525990

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