Refractory Chemistry in the Hypergiant Star VY Canis Majoris as Revealed by ALMA

The hypergiant star VY Canis Majoris (VY CMa) is an excellent candidate to study the evolution of massive stars. This star is undergoing intensive mass-loss, creating asymmetric outflows which result in the formation of arcs, knots, and clumps made of dust and gas. These structures have their own unique chemistry, which can provide important information linking molecular processes with mass ejection. Using ALMA at Band 6, PO, PN, NaCl, and Na³⁷Cl have been imaged at ~0.25 and ~1 arcsec resolution, and then combined with single dish data from the Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) to recover total flux. The images reveal that the emission of PO is confined within 1 arcsec of the star, suggesting that this molecule quickly reacts to form other species. In contrast, the PN emission is asymmetric and extends out to 2 arcsec from the star, mainly towards the SW Clump. PN is not seen in the extended structures traced by CO and HCN and suggests that grain condensation may remove it from the gas phase. Shock chemistry associated with mass ejection may account for its presence near the SW clump. NaCl and Na³⁷Cl have emission close to the central star ( ~1 arcsec) and distinctly trace the SW Clump. The presence of NaCl in SW Clump suggests that this material was likely expelled directly from the photosphere.