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LucyZurys_POinspace - The Astrophysical Journal 666:L29L32...

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L29 The Astrophysical Journal , 666:L29–L32, 2007 September 1 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. IDENTIFICATION OF PHOSPHORUS MONOXIDE ( X 2 P r ) IN VY CANIS MAJORIS: DETECTION OF THE FIRST P i O BOND IN SPACE E. D. Tenenbaum, 1,2 N. J. Woolf, 1 and L. M. Ziurys 1,2,3 Received 2007 June 11; accepted 2007 July 5; published 2007 August 17 ABSTRACT A new interstellar molecule, PO ( X 2 P r ), 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 which J 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 N tot 2.8 # 10 15 cm 2 , which corresponds to a fractional abundance of f , relative to H 2 . Consequently, PO and PN have similar concentrations in VY CMa, a result not predicted 8 9 # 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 P i O 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. INTRODUCTION In terms of mass, phosphorus is the fifth most important biogenic element after carbon, hydrogen, oxygen, and nitrogen (Pasek & Lauretta 2005). It plays a central role in biochemistry, particularly when bonded to oxygen in phosphate esters. The P i O bond is in fact a fundamental unit in DNA, RNA, and ATP, and thus phosphorus is relevant to both replication and metabolism in living systems (Macia ´ et al. 1997). Phosphorus is a relatively abundant element cosmically, with P/H 3 # 10 7 (Grevesse & Sauval 1998). Therefore, one might expect that it should play a role in interstellar chemistry. Yet, to date, only one phosphorus-bearing molecule has been identified in molecular clouds: PN (Ziurys 1987; Turner & Bally 1987). In circumstellar gas, PN and the free radical CP have been observed, but only in one source, the carbon-rich envelope of IRC 10216 (Gue ´lin et al. 1990, 2000; Cernicharo et al. 2000; Milam et al. 2007). Very recently, however, HCP has been identified in this object (Agu ´ndez et al. 2007) as well as in the carbon-rich protoplanetary nebula CRL 2688 (Milam et al. 2007). Furthermore, PN has now been observed in CRL 2688 and, surprisingly, toward the oxygen-rich shell of the supergiant star VY CMa (Milam et al. 2007; Ziurys et al. 2007).
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