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+): METAL OXIDE CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS.
E. D. TENENBAUM, L. M. ZIURYS, University of Arizona, Steward Observatory, Department of Chemistry, Arizona Radio Observatory Tucson, AZ 85721.
A new circumstellar molecule, the radical AlO (X2
+), 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
6 and 6
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
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
s
0.5''. Given this source size, the column density of AlO was found to be Ntot
2 × 1015 cm-2 for Trot
230 K, with a fractional abundance, relative to H2, of
10-8. Gas-phase thermodynamic equilibrium chemistry is the likely formation mechanism for AlO in VY CMa, but shocks may disrupt the condensation process into Al2O3, allowing AlO to survive to a radius of
20 R_*. 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.