|#1 – BREAKTHROUGHS in CARBON CHEMISTRY in CIRCUMSTELLAR ENVELOPES (CSEs)|
Breakthroughs in our current understanding on the formation of carbonaceous dust and complex molecules in the circumstellar envelopes (CSEs) of AGB stars and the interstellar medium (ISM).
Production and analysis of carbon dust seeds in conditions resembling those in the dust formation zones of CSEs contrasting to all previous experiments in the field.
|Innovative experimental methodology|
1 – Production of carbon dust seeds at the Stardust Machine using exclusively gas-phase carbon atoms and molecular hydrogen in a ratio close to that in the atmospheres of AGB stars under ultra-high vacuum (UHV) conditions.
2 – Expansion of the previous study to investigate the interaction of atomic carbon and diatomic carbon with acetylene.
3 – First use of the sputtering gas aggregation source (SGAS) in Laboratory Astrophysics to generate small clusters of nanometre-sized particles by gas-phase aggregation of individual atoms in a weakly ionized environment, thus resembling what happens in the dust formation zones of CSEs.
4 – Full experimental analysis: atomic force microscopy (AFM), scanning tunnel microscopy (STM), transmission electron microscopy (TEM), optical emission spectroscopy (OES), infrared spectroscopy in transmission geometry and quadrupole mass spectrometry (QMS) at the Stardust Machine. Ex-situ laser desorption ionization/mass spectrometry (LDI-MS) in the AROMA machine that resembles the reactions on the surfaces of dust grains.
1) From experiment 1. Efficient production of carbonaceous nanometre-sized grains, nanometer-sized small amorphous carbon clusters, acetylene (C2H2), along with fragments of ethylene (C2H4), ethane (C2H6) and larger aliphatic molecules, saturated aliphatic species and marginal detection of aromatic species (benzene, small PAHs like naphthalene) and no fullerenes. We reproduce the abundances of the acetylene and ethylene found in CSEs around AGB stars.
2) From experiment 2. Production of a non-negligible amount of pure and hydrogenated carbon clusters as well as aromatics with aliphatic substitutions, both being a direct consequence of the addition of atomic carbon
Our experiments, that closely resemble the chemistry involved in the CSEs, do not favour the formation of aromatic species (PAHs and fullerenes), which can account for up to 18% of the total carbon species in the interstellar medium. We also show that aromatics with aliphatic substitutions as well as pure and hydrogenated carbon clusters can be produced as a direct consequence of the addition of atomic carbon.
1) SGAS, a technique not previously used in laboratory astrophysics, can be a very valuable tool to gain information on the chemistry operating in CSEs and the interstellar medium.
2) PAHs might not be efficiently formed during gas-phase growth in CSEs.
3) New theoretical plausible scenario: Thermal processing of aliphatic species deposited on dust grains in CSEs could lead to the formation of larger molecules or aromatic species. Such a temperature rise happens in later stages of stellar evolution (protoplanetary nebula PPNe) when the star emits UV radiation that leads to photo-processing of the carbon dust. Indeed, aromatic infrared bands, the signature for PAHs, are not convincingly detected in AGBs, but are observed at these later stages.
4) Unveiling of chemical routes: these results could unveil chemical routes leading to the formation of acetylene-based molecular species in the external layers of AGB stars and in PPNe, and to foster the search for alkyl-substituted aromatics in these environments.
– Prevalence of non-aromatic carbonaceous molecules in the inner regions of circumstellar envelopes (L. Martínez et al., Nature Astronomy, volume 4, pages 97–105, 2020), DOI link. EPMC link.
– A new take on circumstellar carbon chemistry (M. Gatchell, News and Views, Nature Astronomy, volume 4, pages 21 – 22, 2020), share link).
– The Chemistry of Cosmic Dust Analogs from C, C2, and C2H2 in C-rich Circumstellar Envelopes (G. Santoro et al., The Astrophysical Journal, volume 895, number 2, 2020). DOI link. EPMC link.
For the first time, NANOCOSMOS has attempted to reproduce the complex molecular chemistry and stardust formation in circumstellar envelopes (CSEs) of asymptotic giant branch (AGB) stars and in cold molecular clouds under accurate and realistic laboratory conditions. These conditions differ from previous studies and techniques to produce stardust analogs, mostly based on laser ablation and pyrolysis, flames, and other far related conditions from those in the CSEs of AGB stars.
These achievements are based on groundbreaking innovative setups at CSIC and CNRS, e.g. Stardust, AROMA, PIRENEA 2 and cold plasma reactors, that foster the study of complex processes that lead to carbon dust formation including polycyclic aromatic hydrocarbons (PAHs) and fullerenes. We have studied the chemistry of atomic silicon and the formation of silicate dust grains. We have also investigated the aromatic content of two different meteorites, Murchison and Almahata Sitta.
In summary, our synergetic results provide significant and surprising breakthroughs in our current understanding of the chemical processes at play in CSEs, the interstellar medium (ISM) and meteoritic samples. These new and open theoretical grounds have also important implications in current chemical models. These NANOCOSMOS breakthroughs are the following:
- Aliphatic nature of carbonaceous cosmic dust analogs in CSEs. Our realistic laboratory conditions do not lead to the efficient formation of aromatic molecules (PAHs and fullerenes) in the gas phase, contrary to all previous studies (Stardust, AROMA)
- First detection of a pure PAH (indene) in the TMC-1 cold dark molecular cloud. This is totally an unexpected discovery and suggests an in-situ bottom-up formation process in these environments from smaller molecules in the gas-phase (Yebes 40m radio telescope + new mm receivers).
- Efficient mechanism for the formation of silane and disilane in the gas phase from Si, H, and H2 in the innermost regions of the CSEs around AGB stars (Stardust).
- Further evidence for the role of metal (iron) seeds to increase not only the formation of metal clusters but also catalyzed hydrocarbon growth in the CSEs of AGB stars (Cold plasma reactors, AROMA, PIRENEA 2 and ESPOIRS)
First firm detection of fullerenes in meteorites (Almahata Sitta) and co-existence of carbon clusters along with PAHs in this meteorite (AROMA).
AROMA (Astrochemistry Research of Organics with Molecular Analyzer) is a new analytical experimental set-up developed at IRAP/LCAR (Toulouse, France). The main purpose of AROMA is the study and identification, with micro-scale resolution, of the molecular content of cosmic dust analogues, including stardust analogues produced in the Stardust machine and meteoritic samples. AROMA combines laser desorption/ionization (LDI) techniques with a linear ion trap coupled to an orthogonal time of flight mass spectrometer (LQIT-oTOF).
Outstanding publications on our innovative setup
Molecular content of nascent soot: Family characterization using two-step laser desorption laser ionization mass spectrometry (H. Sabbah, M. Commodo, F. Picca, G. de Falco, P. Minutolo, A. D´Anna and C. Joblin). Proceedings of the Combustion Institute, Volume 38, Issue 1, 2021, Pages 1241-1248.
Impact of Metals on (Star)Dust Chemistry: A Laboratory Astrophysics Approach (R. Bérard, K. Makasheva, K. Demyk, A. Simon, D. Nuñez-Reyes, F. Mastrorocco, H. Sabbah and C. Joblin). Frontiers in Astronomy and Space Sciences, 2021 March 21. IRAP Press Release: Role des metaux dans la chimie des poussieres detoiles
Characterization of large carbonaceous molecules in cosmic dust analogues and meteorites (H. Sabbah, M. Carlos and C. Joblin). Proceedings of the International Astronomical Union, 2019 Apr; 15(Suppl 350): 103–106.
Identification of PAH Isomeric Structure in Cosmic Dust Analogues: the AROMA setup (H. Sabbah, A. Bonnamy, D. Papanastasiou, J. Cernicharo, J.-A. Martín-Gago, and C. Joblin). Astrophysical Journal, 2017 Jul 1; 843(1): 34.
Check our posts on the AROMA set-up
The Stardust machine is a beyond the state-of-the-art equipment that combines various techniques to achieve original studies on individual nanoparticles. These studies include their processing to produce complex molecules, the chemical evolution of their precursors and their reactivity with abundant molecules of astrophysical interest. The simulation chambers are equipped with state-of-the-art in situ and ex situ diagnostics.
Outstanding publications on our innovative development
INFRA-ICE: An ultra-high vacuum experimental station for laboratory astrochemistry (G. Santoro, J. M. Sobrado, G. Tajuelo-Castilla, M. Accolla, L. Martinez, J. Azpeitia, K. Lauwaet, J. Cernicharo, G. J. Ellis, J. A. Martín-Gago). Review of Scientific Instruments, 2020 December 1.
Prevalence of non-aromatic carbonaceous molecules in the inner regions of circumstellar envelopes (L. Martínez, G. Santoro, P. Merino, M. Accolla, K. Lauwaet, J. Sobrado, H. Sabbah, R. J. Peláez, V. J. Herrero, I. Tanarro, M. Agúndez, A. Martín-Jimenez, R. Otero, G. J. Ellis, C. Joblin, J. Cernicharo & J. A. Martín-Gago). Nature Astronomy, 2019 October 21.
Precisely controlled fabrication, manipulation and in-situ analysis of Cu based nanoparticles (L. Martínez, K. Lauwaet, G. Santoro, J. M. Sobrado, R. J. Peláez, V. J. Herrero, I. Tanarro, G. J. Ellis, J. Cernicharo, C. Joblin, Y. Huttel, and J. A. Martín-Gago). Scientific Reports 8, 7250 (13pp), 2018 May 8.
More relevant information on our innovative set-up
- News and views (Nature Astronomy): A new take on circumstellar carbon chemistry (Michael Gatchell, University of Innsbruck)
- A Journey to the Last Frontier (I): The Atmospheres of the Stars (BBVAOpenMind, José A. Martín-Gago))
- CSIC news: Una máquina de ultravacío simula el proceso de formación del polvo estelar
- L’Institut national des sciences de l’Univers (INSU/CNRS) news: Des nouvelles sur la formation des molécules et poussières d’étoiles
- International Conference on “Advances in Cluster Beam Deposition” (Okinawa, October 21-25, 2019, Japan) – Dr. L. Martínez “Gas phase synthesis of clusters and nanoparticles using a scaled-up multi-magnetron gas aggregation source“
- Nature research Community – Prof. José A. Martín-Gago “Behind the paper: Prevalence of non-aromatic carbonaceous molecules in the inner regions of circumstellar envelopes“
Main features of the Stardust machine
The Stardust machine has been designed and assembled at the Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). The elapsed time has been from October 2014 to the end of 2015. Throughout 2016, we entered into the commissioning phase with several ongoing verification experiments and processes. From mid-2017, we are dealing with the first astrophysical experiments, the so-called exploitation phase.
Stardust is basically a forefront facility to produce and analyze in-situ highly-controlled analogs of the dust grains in a versatile ultra-high-vacuum (UHV) experiment, up to pressures of 10-11 mbar. The ultimate goal is to reproduce the physical conditions that prevail in the photospheres of AGB stars. In this environment, we mimick the nucleation of the aggregates and their possible interaction with the circumstellar gases. Stardust characterizes microscopic processes (interaction with photons and gas) through surface science techniques. It encompasses 5 independent vacuum chambers, with their own instrumentation, pumping systems, gas-dosed systems in a highly-controlled UHV environment:
- MICS (Multiple Ion Cluster Source) chamber. The MICS is a new optimized route for cluster growth of a standard technique based on a sputtering gas. It allows the formation of nanoparticles of controlled elemental composition by atomic aggregation. A special port has been adapted to perform optical spectroscopy.
- NEON (NEutral to iON) chamber that separates neutral from ionized nanoparticles as well as a mass selection. It also accelerates, simulating the radiation pressure, and anneals the formed clusters.
- INTERACTION chamber. Interaction and chemical reactions are induced between the generated nanoparticles and molecules in the gas phase (H2, CH4, C2H2, etc).
- INFRA-ICE chamber. In-flight analysis is performed through UV, visible, near-mid and far-infrared spectroscopy. We have successfully integrated a cryostat and a sample manipulator to study ice interstellar analogs. Microwave spectroscopy will be performed with the new NANOCOSMOS mm broad band receivers to study second/minute time-dependent changes in the gas composition.
- ANA chamber, the analysis chamber. This allows us to collect the nanoparticles and perform X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and Ultraviolet photoelectron spectroscopy (UPS) in-situ. Also some in-situ processing can be performed here. The collected samples are duly transported and delivered to the AROMA setup for ulterior analysis.
Check our posts on the Stardust machine: