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Title: HERSCHEL/HIFI SEARCH FOR (H2O)-O-17 AND (H2O)-O-18 IN IRC+10216: CONSTRAINTS ON MODELS FOR THE ORIGIN OF WATER VAPOR
Authors: Neufeld, David A ×
Tolls, Volker
Agundez, Marcelino
Gonzalez-Alfonso, Eduardo
Decin, Leen
Daniel, Fabien
Cernicharo, Jose
Melnick, Gary J
Schmidt, Miroslaw
Szczerba, Ryszard #
Issue Date: Apr-2013
Publisher: I O P Publishing Ltd.
Series Title: The Astrophysical Journal. Letters vol:767 issue:1 pages:3-7
Abstract: We report the results of a sensitive search for the minor isotopologues of water, H_2^{17}O and H_2^{18}O, toward the carbon-rich asymptotic giant branch star IRC+10216 (a.k.a. CW Leonis) using the HIFI instrument on the Herschel Space Observatory. This search was motivated by the fact that any detection of isotopic enhancement in the H_2^{17}O and H_2^{18}O abundances would have strongly implicated CO photodissociation as the source of the atomic oxygen needed to produce water in a carbon-rich circumstellar envelope. Our observations place an upper limit of 1/470 on the H_2^{17}O/H_2^{16}O abundance ratio. Given the isotopic 17O/16O ratio of 1/840 inferred previously for the photosphere of IRC+10216, this result places an upper limit of a factor 1.8 on the extent of any isotope-selective enhancement of H_2^{17}O in the circumstellar material, and provides an important constraint on any model that invokes CO photodissociation as the source of O for H2O production. In the context of the clumpy photodissociation model proposed previously for the origin of water in IRC+10216, our limit implies that 12C16O (not 13C16O or SiO) must be the dominant source of 16O for H2O production, and that the effects of self-shielding can only have reduced the 12C16O photodissociation rate by at most a factor ~2.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
ISSN: 2041-8205
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Institute of Astronomy
× corresponding author
# (joint) last author

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