IDENTIFICATION OF PHOSPHORUS MONOXIDE (X 2Pr) IN VY CANIS MAJORIS: DETECTION OF THE FIRST PiO BOND IN SPACE

A new interstellar molecule, PO (X 2Pr), has been detected toward the envelope of the oxygen-rich supergiant star VY Canis Majoris (VY CMa) using the Submillimeter Telescope of the Arizona Radio Observatory. The and rotational transitions of PO at 240 and 284 GHz were observed, each of whichJ p 5.5 r 4.5 J p 6.5 r 5.5 consisted of well-defined lambda-doublets. The line profiles are roughly parabolic in shape, analogous to PN, and suggest that this species arises from the spherical wind in VY CMa, as opposed to the collimated blue- and redshifted outflows. Comparison of line intensities indicates that PO arises from a confined source roughly 1 in extent, with a column density of Ntot 2.8 # 1015 cm2, which corresponds to a fractional abundance of f ∼, relative to H2. Consequently, PO and PN have similar concentrations in VY CMa, a result not predicted89 # 10 by either LTE or kinetic models of circumstellar chemistry. These phosphorus compounds may arise from shock-induced reactions in this active envelope. Phosphorus monoxide is the first interstellar molecule detected that contains a PiO bond, a moiety essential in biochemical compounds. It is also the first new species to be identified in an oxygen-rich, as opposed to a carbon-rich, circumstellar envelope. Subject headings: astrobiology — astrochemistry — circumstellar matter — ISM: molecules — radio lines: stars — stars: individual (VY Canis Majoris) 1