Herschel/HIFI search for H2-17O and H2-18O in IRC+10216: constraints on models for the origin of water vapor - Université Pierre et Marie Curie Accéder directement au contenu
Article Dans Une Revue The Astrophysical journal letters Année : 2013

Herschel/HIFI search for H2-17O and H2-18O in IRC+10216: constraints on models for the origin of water vapor

David A. Neufeld
  • Fonction : Auteur
Volker Tolls
  • Fonction : Auteur
M. Agúndez
Eduardo González-Alfonso
  • Fonction : Auteur
Leen Decin
  • Fonction : Auteur
Gary J. Melnick
  • Fonction : Auteur
Miroslaw Schmidt
  • Fonction : Auteur
Ryszard Szczerba
  • Fonction : Auteur

Résumé

We report the results of a sensitive search for the minor isotopologues of water, H2-17O and H2-18O, toward the carbon-rich AGB 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 H2-17O and H2-18O 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 H2-17O/H2-16O 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 H2-17O 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 12C-16O (not 13C-16O or SiO) must be the dominant source of 16O for H2O production, and that the effects of self-shielding can only have reduced the 12C-16O photodissociation rate by at most a factor ~ 2.

Dates et versions

hal-01016740 , version 1 (01-07-2014)

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David A. Neufeld, Volker Tolls, M. Agúndez, Eduardo González-Alfonso, Leen Decin, et al.. Herschel/HIFI search for H2-17O and H2-18O in IRC+10216: constraints on models for the origin of water vapor. The Astrophysical journal letters, 2013, 767 (1), pp.id. L3. ⟨10.1088/2041-8205/767/1/L3⟩. ⟨hal-01016740⟩
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