Identification of Phosphorus Monoxide (X2Πr) in VY Canis Majoris: Detection of the First PO Bond in Space
Abstract
A new interstellar molecule, PO (X2Πr), 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 J=5.5-->4.5 and J=6.5-->5.5 rotational transitions of PO at 240 and 284 GHz were observed, each of which 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 cm-2, which corresponds to a fractional abundance of f~9×10-8, relative to H2. Consequently, PO and PN have similar concentrations in VY CMa, a result not predicted 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 PO 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2007
- DOI:
- 10.1086/521361
- Bibcode:
- 2007ApJ...666L..29T
- Keywords:
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- Astrobiology;
- Astrochemistry;
- Stars: Circumstellar Matter;
- ISM: Molecules;
- Radio Lines: Stars;
- Stars: Individual: Constellation Name: VY Canis Majoris