English

ALMA observations of TiO$_2$ around VY Canis Majoris

Solar and Stellar Astrophysics 2015-07-29 v1

Abstract

Titanium dioxide, TiO2_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 TiO2_2 has been detected only in the complex environment of the red supergiant VY CMa. We aim to constrain the distribution and excitation of TiO2_2 around VY CMa in order to clarify its role in dust formation. We analyse spectra and channel maps for TiO2_2 extracted from ALMA science verification data. We detect 15 transitions of TiO2_2, and spatially resolve the emission for the first time. The maps demonstrate a highly clumpy, anisotropic outflow in which the TiO2_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 TiO2_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.

Keywords

Cite

@article{arxiv.1506.00818,
  title  = {ALMA observations of TiO$_2$ around VY Canis Majoris},
  author = {E. De Beck and W. Vlemmings and S. Muller and J. H. Black and E. O'Gorman and A. M. S. Richards and A. Baudry and M. Maercker and L. Decin and E. M. Humphreys},
  journal= {arXiv preprint arXiv:1506.00818},
  year   = {2015}
}

Comments

Accepted for publication in Astronomy & Astrophysics, 25 pages, 20 figures