Pure rotational spectra of TiO and TiO_2 in VY Canis Majoris

TL;DR

This study reports the first detection of pure rotational lines of TiO and TiO_2 in the circumstellar environment of VY CMa, providing insights into dust formation processes around cool oxygen-rich stars.

Contribution

It presents the first observational detection of TiO and TiO_2 rotational spectra in a stellar envelope, highlighting their potential role in dust seed formation.

Findings

TiO and TiO_2 detected in VY CMa's envelope

Derived rotational temperature of about 250 K for TiO_2

Indicates a significant amount of oxides remain gaseous, not forming dust

Abstract

We report the first detection of pure rotational transitions of TiO and TiO_2 at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational temperature, T_rot, of about 250 K was derived for TiO_2. Although T_rot was not well constrained for TiO, it is likely somewhat higher than that of TiO_2. 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 TiO_2 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.