Aluminium oxide in the optical spectrum of VY Canis Majoris

Abstract

We report the first identification of the optical bands of the B-X system of AlO in the red supergiant VY CMa. In addition to TiO, VO, ScO, and YO, which were recognized in the optical spectrum of the star long time ago, AlO is another refractory molecule which displays strong emission bands in this peculiar star. Simulating the bands of AlO, we derive a rotational temperature of the circumstellar gas of Trot=700K. By resolving individual rotational components of the bands, we derive the kinematical characteristics of the gas, finding that the emission is centered at the stellar radial velocity and its intrinsic width is 13.5 km/s (full width at half maximum). It is the narrowest emission among all (thermal) features observed in VY CMa so far. The temperature and line widths suggest that the emission arises in gas located within ~20 stellar radii, where the outflow is still being accelerated. This result contradicts equilibrium-chemistry models which predict substantial AlO abundances only to within a few stellar radii. We argue that non-equilibrium models involving propagation of shocks are needed to explain the observations.

to appear in A&A

References in corpus (5)

• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• The 3D Morphology of VY Canis Majoris. I The Kinematics of the Ejecta
• Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry
• Keck/HIRES spectroscopy of V838 Monocerotis in October 2005
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• An observational study of dust nucleation in Mira ($o$ Ceti): I. Variable features of AlO and other Al-bearing species
• An Interferometric Spectral-Line and Imaging Survey of VY Canis Majoris in the 345 GHz Band
• Radiative lifetimes and cooling functions for astrophysically important molecules
• A high-resolution line list for AlO
• The chemistry of dust formation in red supergiants
• AlH lines in the blue spectrum of Proxima Centauri
• Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets
• Dust-forming molecules in VY Canis Majoris (and Betelgeuse)
• VVV-WIT-13: an eruptive young star with cool molecular features