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

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/Δλ = 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 Na i, K i, Ca i, Ca ii, Cr i, and Fe i, with upper limits for Al i, Mn i, Ti i, Ti ii, and Sr ii. 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.

C/O Abundance Ratios, Iron Depletions, and Infrared Dust Features in Galactic Planetary Nebulae

“…Whereas most of our objects show high iron depletion factors, their calculations only show large degrees of condensation for iron, above 80%, in objects where the value of C/O is extremely close to 1 (see their Figures A.3 and A.4). As discussed by Mauron & Huggins (2010), who find strong depletions of elements like Fe and Ca in the circumstellar envelope of an AGB carbon star, adsorption of metals at the surface of the dust grains may be as important as the initial dust condensation processes considered by the models of dust formation in stellar envelopes.…”

Laboratory and Astronomical Discovery of Hydromagnesium Isocyanide

“…We have therefore restricted the loss processes of HMgNC to just photodissociation by interstellar ultraviolet photons, while for MgNC and MgCN we have also considered reactions with H atoms and electrons. The absolute abundances of Mg-bearing molecules scale with the elemental abundance of magnesium in the gas phase, which unfortunately was not constrained by the observations of gas phase atoms in IRC +10216 carried out by Mauron & Huggins (2010).…”

“…It is worth noting that metals such as Na, K, Ca, Fe, Cr, and/or their cations are found in the gas phase in IRC+10216 (Mauron & Huggins 2010) pointing towards a rich metal chemistry in the outer circumstellar envelope (CSE). Since these early works several more metal cyanides or isocyanides have been found in CSEs.…”

Missing Fe: hydrogenated iron nanoparticles

“…IRC +10216 (CW Leo) is the nearby, asymptotic giant branch evolved carbon star known as one of the brightest mid-IR sources outside the Solar system. More than 80 molecular species, as well as many unidentified lines, have been detected in IRC +10216 (Cernicharo et al 1996;Monnier et al 2000;Mauron & Huggins 2010;Tenenbaum et al 2010;Agúndez et al 2012;Cernicharo et al 2013;Gong et al 2015). Gas phase iron in significant abundance was detected in the circumstellar envelope of IRC +10216 with the UVES spectrograph (Mauron & Huggins 2010).…”