HERSCHEL/HIFI SEARCH FOR H{sub 2}{sup 17}O AND H{sub 2}{sup 18}O IN IRC+10216: CONSTRAINTS ON MODELS FOR THE ORIGIN OF WATER VAPOR
- Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- LAB, Universite de Bordeaux, UMR 5804, F-33270 Floirac (France)
- Universidad de Alcala de Henares, Departamento de Fisica y Matematicas, Campus Universitario, E-28871 Alcala de Henares, Madrid (Spain)
- Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium)
- Departamento de Astrofisica, Centro de Astrobiologia, CSIC-INTA, Ctra. de Torrejon a Ajalvir km 4, E-28850 Madrid (Spain)
- Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Rabianska 8, 87-100 Torun (Poland)
We report the results of a sensitive search for the minor isotopologues of water, H{sub 2}{sup 17}O and H{sub 2}{sup 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{sub 2}{sup 17}O and H{sub 2}{sup 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{sub 2}{sup 17}O/H{sub 2}{sup 16}O abundance ratio. Given the isotopic {sup 17}O/{sup 16}O 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{sub 2}{sup 17}O in the circumstellar material, and provides an important constraint on any model that invokes CO photodissociation as the source of O for H{sub 2}O production. In the context of the clumpy photodissociation model proposed previously for the origin of water in IRC+10216, our limit implies that {sup 12}C{sup 16}O (not {sup 13}C{sup 16}O or SiO) must be the dominant source of {sup 16}O for H{sub 2}O production, and that the effects of self-shielding can only have reduced the {sup 12}C{sup 16}O photodissociation rate by at most a factor {approx}2.
- OSTI ID:
- 22130760
- Journal Information:
- Astrophysical Journal Letters, Vol. 767, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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