ALMA observations of TiO$_2$ around VY Canis Majoris

E., de Beck , W., Vlemmings , S., Muller (1) , J. H., Black , E., O'Gorman (2) , A. M. S., Richards , Alain Baudry (3) , M., Maercker , L., Decin , E. M., Humphreys

1 LIEC - Laboratoire Interdisciplinaire des Environnements Continentaux
2 Department of Biology
3 FORMATION STELLAIRE 2015

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.

Domaines: Astrophysique galactique [astro-ph.GA]

E., de Beck, W., Vlemmings, S., Muller, J. H., Black, E., O'Gorman, et al.. ALMA observations of TiO$_2$ around VY Canis Majoris. Astronomy and Astrophysics - A&A, 2015, 580, pp.A36. ⟨10.1051/0004-6361/201525990⟩. ⟨hal-01159884⟩