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

¹ GRAAL, CNRS and Université Montpellier II, Place Bataillon, 34095 Montpellier, France e-mail: mauron@graal.univ-montp2.fr
² Physics Department, New York University, 4 Washington Place, New York NY 10003, USA e-mail: patrick.huggins@nyu.edu

Received: 24 December 2009
Accepted: 11 February 2010

Abstract

We report the results of a search for gas phase atomic metals in the circumstellar envelope of the asymptotic giant branch carbon star IRC+10216. The search was made using high resolution (λ/Δ λ = 50 000) optical absorption spectroscopy of a background star that probes the envelope on a line of sight 35´´ from the center. The metal species that we detect in the envelope include , , , , , and , with upper limits for , , , , and . The observations are used to determine the metal abundances in the gas phase and the condensation onto grains. The metal depletions in the envelope 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 interstellar medium. 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.