Volume 580, August 2015
|Number of page(s)||24|
|Section||Interstellar and circumstellar matter|
|Published online||23 July 2015|
ALMA observations of TiO2 around VY Canis Majoris⋆
1 Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
2 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
3 Université de Bordeaux, LAB, UMR 5804, 33270 Floirac, France
4 CNRS, LAB, UMR 5804, 33270 Floirac, France
5 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
6 Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 Amsterdam, The Netherlands
7 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
Received: 28 February 2015
Accepted: 25 May 2015
Context. Titanium dioxide, TiO2, 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 environment of the red supergiant VY CMa.
Aims. We aim to constrain the distribution and excitation of TiO2 around VY CMa in order to clarify its role in dust formation.
Methods. We analyse spectra and channel maps for TiO2 extracted from ALMA science verification data.
Results. We detect 15 transitions of TiO2, and spatially resolve the emission for the first time. The maps demonstrate a highly clumpy, anisotropic outflow in which the TiO2 emission likely traces gas exposed to the stellar radiation field. An accelerating bipolar-like structure is found, oriented roughly east-west, 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.
Conclusions. 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.
Key words: supergiants / stars: individual: VY Canis Majoris / stars: mass-loss / circumstellar matter / submillimeter: stars
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2015
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