Knowledge Bank

A new circumstellar molecule, the radical AlO (X$2\Sigma +$), has been detected toward the envelope of the oxygen-rich supergiant star VY Canis Majoris (VY CMa) using the Arizona Radio Observatory (ARO). The N = 7 $\to$ 6 and 6 $\to$ 5 rotational transitions of AlO at 268 and 230 GHz were observed at 1 mm using the ARO Submillimeter Telescope (SMT) and the N = 4 $\to$ 3 line was detected at 2 mm using the ARO 12 m. Based on the shape of the line profiles, AlO most likely arises from the dust-forming region in the spherical outflow of VY CMa, as opposed to the blue- or red-shifted winds, with a source size of $\theta s\sim$ 0.5. Given this source size, the column density of AlO was found to be N cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-2</mrow>}$ for T $\sim$ 230 K, with a fractional abundance, relative to H$2$, of $\sim$ 10$\mathrm{<mrow\; data-mjx-texclass="ORD">-8</mrow>}$. Gas-phase thermodynamic equilibrium chemistry is the likely formation mechanism for AlO in VY CMa, but shocks may disrupt the condensation process into Al$2$O$3$, allowing AlO to survive to a radius of $\sim$ 20 R$\ast$. The detection of AlO in VY CMa is additional evidence of an active gas-phase refractory chemistry in oxygen-rich envelopes, and suggests such objects may be fruitful sources for other new oxide identifications.