Carbon molecules in the inner wind of the oxygen-rich Mira IK Tauri

TL;DR

This study models the shock-driven chemistry in the inner wind of the oxygen-rich Mira IK Tauri, predicting significant formation of carbon molecules like CO₂, aligning well with recent observations and revealing shock chemistry's role in carbon molecule formation.

Contribution

It introduces a physio-chemical model of shock chemistry in the inner wind of an oxygen-rich Mira, predicting carbon molecule formation consistent with observations.

Findings

Large amounts of CO₂ and other carbon species are formed in the inner envelope.

Theoretical abundances match observational data from ISO and millimeter/sub-millimeter studies.

Shock chemistry contributes to the presence of carbon molecules in oxygen-rich stellar environments.

Abstract

The gas-phase non-equilibrium chemistry of the inner wind of the oxygen-rich Mira variable IK Tau (NML Tau) is investigated using a physio-chemical model describing the periodically shocked gas close to the stellar photosphere. We predict the formation in large amounts of a few carbon species in the inner envelope, in particular CO$_2$, which has been recently detected with ISO in the spectra of several oxygen-rich semi-regular and Mira stars. The theoretical abundances are also in excellent agreement with values derived from millimeter and sub-millimeter observations, pointing to the fact that some carbon species in oxygen stars do form from shock chemistry in the inner layers and travel the envelope as ``parent'' species.