New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars
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Final Published Version
Affiliation
Univ Arizona, Dept Chem & Biochem, 1305 E 4th St, Tucson, AZ 85719 USAUniv Arizona, Arizona Radio Observ, Dept Astron, 933 N Cherry Ave, Tucson, AZ 85721 USA
Issue Date
2018-04-01Keywords
astrochemistrycircumstellar matter
ISM: molecules
methods: observational
stars: abundances
submillimeter: stars
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IOP PUBLISHING LTDCitation
The Astrophysical Journal, 856:169 (11pp), 2018 April 1Journal
ASTROPHYSICAL JOURNALRights
© 2018. The American Astronomical Society. All rights reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
PO and PN have been newly identified in several oxygen-rich circumstellar envelopes, using the Submillimeter Telescope of the Arizona Radio Observatory. The J = 5 -> 4 and J = 6 -> 5 transitions of PN near 235 and 282 GHz, and the lambda doublets originating in the J = 5.5 -> 4.5 and J = 6.5 -> 5.5 lines of PO at 240 and 284 GHz, have been detected toward the shells of asymptotic giant branch (AGB) stars TX Cam and R Cas. A similar set of lines has been observed toward the supergiant NML Cyg, and new transitions of these two molecules were also measured toward the AGB star IK Tau. Along with the previous data from VY Canis Majoris (VY CMa), these spectral lines were analyzed using the non-local thermodynamic equilibrium (non-LTE) circumstellar modeling code, ESCAPADE. For the AGB stars, peak abundances found for PN and PO were f similar to (1-2) x 10(-8) and (0.5-1) x 10(-7), respectively, while those for the supergiants were f(PN) (0.3-0.7) x 10(-8) and f(PO) similar to (5-7) x 10(-8). PN was well modeled with a spherical radial distribution, suggesting formation near the stellar photosphere, perhaps enhanced by shocks. PO was best reproduced by a shell model, indicating a photochemical origin, except for VY CMa. Overall, the abundance of PO is a factor of 5-20 greater than that of PN. This study suggests that phosphorus-bearing molecules are common in O-rich envelopes, and that a significant amount of phosphorus (>20%) remains in the gas phase.ISSN
1538-4357Version
Final published versionSponsors
NSF [AST1515568, AST-1140030]; NSF University Radio Observatories (URO) program [AST-1140030]; NASA [NNX15AD94G]Additional Links
http://stacks.iop.org/0004-637X/856/i=2/a=169?key=crossref.4f275cf63fe688f3f7d57d74245ee3bfae974a485f413a2113503eed53cd6c53
10.3847/1538-4357/aaafc6