Herschel/HIFI observations of IRC+10216: water vapor in the inner envelope of a carbon-rich AGB star

TL;DR

This study uses Herschel/HIFI observations to detect water vapor in the inner envelope of the carbon-rich AGB star IRC+10216, providing new insights into its origin and ruling out vaporization of icy objects as the source.

Contribution

First detection of water vapor in the inner envelope of IRC+10216 using Herschel/HIFI, with constraints on isotopic ratios and implications for water origin models.

Findings

Water vapor detected close to the star, ruling out icy object vaporization.

Upper limits on isotopic ratios H2-17O/H2-16O and H2-18O/H2-16O.

Confirmed presence of water vapor in a carbon-rich AGB star's inner envelope.

Abstract

We report the results of observations of ten rotational transitions of water vapor toward the carbon-rich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (few x 1.E+14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H2-17O/H2-16O and H2-18O/H2-16O isotopic abundance ratios of ~ 5.E-3 (3 sigma), providing additional constraints on models for the origin of the water vapor in IRC+10216.