ALMA observations of TiO${}_2$ around VY Canis Majoris

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.

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

References in corpus (6)

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Cited by in corpus (19)

• The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual Atomic and Molecular Data Centre, VAMDC
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• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• Searching for Cool Dust in the Mid-to-Far Infrared: the Mass Loss Histories of The Hypergiants $\mu$ Cep, VY CMa, IRC+10420, and $\rho$ Cas
• The Abundance of SiC2 in Carbon Star Envelopes: Evidence that SiC2 is a gas-phase precursor of SiC dust
• Magnetically aligned dust and SiO maser polarization in the envelope of the red supergiant VY CMa
• An observational study of dust nucleation in Mira ($o$ Ceti): II. Titanium oxides are negligible for nucleation at high temperatures
• Circumstellar environment of the M-type AGB star R Dor. APEX spectral scan at $159.0-368.5$ GHz
• The Unexpected Spectrum of the Innermost Ejecta of the Red Hypergiant VY CMa
• ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY CMa
• On massive dust clumps in the envelope of the red supergiant VY Canis Majoris
• Constraints on metal oxide and metal hydroxide abundances in the winds of AGB stars - Potential detection of FeO in R Dor
• Rotational spectra of vibrationally excited AlO and TiO in oxygen rich stars
• Circumstellar ammonia in oxygen-rich evolved stars
• Thermal Emission in the Southwest Clump of VY CMa
• History of two mass loss processes in VY CMa. Fast outflows carving older ejecta
• Multiple components in the molecular outflow of the red supergiant NML Cyg
• High Resolution Laboratory Spectroscopy
• The Red and Yellow Hypergiants