Silicon in the dust formation zone of IRC +10216 as observed with PACS and SPIRE on board Herschel

TL;DR

This study uses Herschel's PACS and SPIRE spectrometers to observe silicon-bearing molecules in the dust formation zone of IRC+10216, providing insights into the chemistry and physical conditions of stellar outflows.

Contribution

First detailed spectroscopic analysis of SiS and SiO lines in IRC+10216's dust formation zone using Herschel data, testing chemical models and dust formation theories.

Findings

Detected multiple high-energy SiS and SiO lines up to J=124-123 and J=90-89.

Derived physical conditions of the gas in the dust formation zone.

Assessed the depletion of SiS and SiO onto dust grains.

Abstract

The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflows from these stars create a circumstellar envelope in which a rich gas-phase and dust-nucleation chemistry takes place. We observed the nearest carbon-rich evolved star, IRC+10216, using the PACS (55-210 {\mu}m) and SPIRE (194-672 {\mu}m) spectrometers on board Herschel. We find several tens of lines from SiS and SiO, including lines from the v=1 vibrational level. For SiS these transitions range up to J=124-123, corresponding to energies around 6700K, while the highest detectable transition is J=90-89 for SiO, which corresponds to an energy around 8400K. Both species trace the dust formation zone of IRC+10216, and the broad energy ranges involved in their detected transitions permit us to derive the physical properties of the gas and the particular zone in which each species has been formed. This allows us to check the accuracy of chemical thermodynamical equilibrium models and the suggested depletion of SiS and SiO due to accretion onto dust grains.