Pure rotational spectra of TiO and TiO₂ in VY Canis Majoris^⋆,⋆⋆

¹ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: kaminski@mpifr.de
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, USA
³ I. Physikalisches Institut, Zülpicher Strasse 77, 50937 Köln, Germany
⁴ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 , Saint-Martin d’Hères, 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

Received: 26 August 2012
Accepted: 11 January 2013

Abstract

We report the first detection of pure rotational transitions of TiO and TiO₂ at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational temperature, T_rot, of about 250 K was derived for TiO₂. Although T_rot was not well constrained for TiO, it is likely somewhat higher than that of TiO₂. The detection of the Ti oxides confirms that they are formed in the circumstellar envelopes of cool oxygen-rich stars and may be the “seeds” of inorganic-dust formation, but alternative explanations for our observation of TiO and TiO₂ in the cooler regions of the envelope cannot be ruled out at this time. The observations suggest that a significant fraction of the oxides is not converted to dust, but instead remains in the gas phase throughout the outflow.