Gas phase atomic metals in the circumstellar envelope of IRC+10216

TL;DR

This study uses high-resolution optical absorption spectroscopy to detect and analyze gas phase atomic metals in the circumstellar envelope of IRC+10216, revealing their abundances, depletion patterns, and implications for dust formation and metal chemistry.

Contribution

First direct measurement of gas phase atomic metal abundances and depletion patterns in a carbon-rich circumstellar envelope, linking stellar outflows to interstellar medium enrichment.

Findings

Detected NaI, KI, CaI, CaII, CrI, FeI in the envelope.

Metal depletions range from 5 to 300, similar to interstellar clouds.

Uncondensed metal atoms are more abundant than metal molecules.

Abstract

We report the results of a search for gas phase atomic metals in the circumstellar envelope of the AGB carbon star IRC+10216. The search was made using high resolution (R=50000) optical absorption spectroscopy of a backgound star that probes the envelope on a line of sight 35" from the center. The metal species that we detect in the envelope include NaI, KI, CaI, CaII, CrI, and FeI, with upper limits for AlI, MnI, TiI, TiII, and SrII. The observations are used to determine the metal abundances in the gas phase and the condensation onto grains. The metal depletions range from a factor of 5 for Na to 300 for Ca, with some similarity to the depletion pattern in interstellar clouds. Our results directly constrain the condensation efficiency of metals in a carbon-rich circumstellar envelope and the mix of solid and gas phase metals returned by the star to the ISM. The abundances of the uncondensed metal atoms that we observe are typically larger than the abundances of the metal-bearing molecules detected in the envelope. The metal atoms are therefore the major metal species in the gas phase and likely play a key role in the metal chemistry.