Tag: Molecules

ALMA/IRAM observations

HighlightsFeaturesDescription
Discovery of molecular species in IRC+10216Methyl silane (CH3SiH3) and silyl cyanide (SiH3CN, first time in Space)We propose a formation mechanism through catalytic reactions on the surface of dust grains by hydrogenation of silicon-carbon species in the inner dust formation zone
Formation of SiC dust in C-rich AGBsSiC2, CS, SiO and SiS gas-phase precursors of dustDecline in the abundances of these molecular species with increasing density in the envelopes of C-rich AGB stars. Important constraints for Stardust experiments on SiC dust formation.
Formation of dust in O-rich AGBsSiO and SO gas-phase precursors of dustDecline in the abundances of these molecular species with increasing density in the envelopes of O-rich AGB stars
Discovery of molecular species in the Interstellar Medium7 molecules, including one protonated form and isotopologs (2 of them, first time in Space)See dedicated descriptions below (under construction)
Major NANOCOSMOS highlights in “ALMA/IRAM observations” (see dedicated descriptions below)

NANOCOSMOS has performed several key observations of the circumnuclear envelopes -CSEs- of AGB stars with the IRAM 30m radio telescope and the ALMA interferometer. These observations are mandatory to foster the study of the gas-phase precursors of dust in these envelopes. We have made fruitful efforts in the study of the Si-C chemistry in these objects.

NANOCOSMOS has discovered methyl silane, CH3SiH3 and silyl cyanide (SiH3CN) in the envelope of the C-rich AGB star IRC +10216. We suggest that both are formed in the inner zones of the circumstellar envelope through catalytic reactions on the surface of dust grains by hydrogenation of silicon-carbon species.

We have also performed two molecular surveys with the IRAM facility, one to study the envelopes of 25 C-rich AGB stars to search for emission lines of SiC2, SiC, Si2C, CS, SiO and SiS and another one with a sample of 30 O-rich AGB stars to investigate the potential role of SiO, CS, SiS, SO, and SO2 in the formation of dust in these environments.

Our results show strong evidences that the observed decline in the molecular abundances of these species with increasing density in the envelopes are due to their incorporation to the solid phase. Furthermore, we establish that SiC2, CS, SiO and SiS (tentatively) are very likely gas-precursors of SiC dust in C-rich envelopes of AGB stars and SiO and SO (tentatively) in O-rich AGB stars.

Finally, the team has detected 7 molecules in the Interstellar Medium, some of them of key importance to constrain chemical models. These are the c-C3D isotopologs, the metastable and polar isomer isocyanogen (CNCN), the isocyanate radical NCO, the thioformyl radical (HCS) and its metastable isomer HSC, all of them in the dark cold cloud core L483, which contains a low-mass protostar. We have also detected ethyl formate (CH3CH2OCOH) and NS+ in the young protostellar system Barnard 1b with ALMA and IRAM respectively.

High-resolution Infrared Observations

HighlightsFeaturesDescription
Discovery of molecular species in IRC+10216Diacetylene (C4H2)Major emission arises at 50 AU or less from the star in the dust formation zone. Constraints on chemical models
Distribution of molecular emission in IRC+10216Ethylene (C2H4)Part of the emission arises in the inner dust formation zone contrary to previous findings. Constraints on chemical models
Detection of molecular emission in R LeoCO2 Infrared fluorescence More systematic study of the CO2 emission in O-rich stars to understand how CO2 forms
Major NANOCOSMOS highlights in “High spectral resolution IR observations” (see dedicated descriptions below)

High spectral resolution infrared observations of circumstellar envelopes – CSEs – in AGB stars are essential to study important molecular species with no permanent dipole moment (e.g. H2, O2, CO2, SiH4, C2H4). This lack makes them undetectable in the millimeter range due to the absence of rotational transitions. Hence, the best possible observation of these molecules is through its vibration–rotation lines in the mid infrared range.

These observations are vital to study the amount of ejected matter in the pulsation phase and determine the chemical interactions between the ejected molecules in the CSEs. These studies help improve the underlying assumptions of currently available chemical models.

Therefore, we observed the carbon-rich star IRC+10216 with the Texas Echelon-cross-Echelle Spectrograph (TEXES) on the 3 m Infrared Telescope Facility (IRTF). We carried out observations of the oxygen rich star R Leo with the Stratospheric Observatory for Infrared Astronomy (SOFIA) with the high spectral resolution Echelon-cross-Echelle Spectrograph (EXES). Finally, we used both SOFIA/EXES and IRTF/TEXES to observe the carbon rich semi-regular star Y CVn.

Our IR observations have led to the discovery of diacetylene (C4H2) in the envelope of IRC+10216 with the major emission arising in the dust formation zone at less than 50 AU from the center of the star. Ethylene (C2H4) shows emission from the inner dust formation zone in IRC+10216 contrary to previous findings. These studies pose further constraints on current chemical models.

Summary of oustanding results with the NANOCOSMOS high-resolution infrared observations of CSEs in AGB stars

Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn (J. P. Fonfría et al., A&A, 07/2021)

  • Analysis and Identification of 130 lines of HCN and H13CN with either P-Cygni profiles or pure absorption profiles
  • Dust grains could be mostly made of silicon carbide SiC in the inner layers of the CSE (~ 3.5 stellar radii) and of amorphous carbon in the outer envelope (up to 200 stellar radii)
  • The observed mid-IR lines are broader than expected due to possible high velocity matter ejections or photospheric movements related to stellar pulsation or convection.
  • HCN rotational and vibrational temperatures are out of local thermodynamics equilibrium so collisions do not play any role in the gas thermalization

Detection of infrared fluorescence of carbon dioxide in R Leonis with SOFIA/EXES (J. P. Fonfría et al., A&A, 11/2020)

  • CO2 (≃240 emission lines in the range 12.8−14.3 μm) – New detection in R Leo
  • The observed CO2 lines can be grouped into three different populations, (warm, hot, and very hot), with approximate temperatures of 550, 1150, and 1600 K
  • The CO2 emitting regions at 1600, 1150, and 550 K are located at 2.2, 3.5, and 10 stellar radii from the center of R Leo
  • We need a systematic study of the CO2 emission in O-rich stars to understand how this molecule forms and the possible dependence of the column density on the mass-loss rate

Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene (J. P. Fonfría et al., ApJ, 01/2018)

  • C4H2 (24 absorption features in the range 8.0 to 8.1 μm) – First detection in IRC+10216
  • The major emission of C4H2 arises in the dust formation zone at radii lower than 20 stellar radii (50 Astronomical Units) from the center of IRC+10216
  • Our photochemical models underestimate the observed C4H2 abundance. This finding could imply that the molecules in the envelope are photodissociated in shells closer to the star than is commonly assumed
  • More info on diacetylene: Astromolecule of the Month

The Abundance of C2H4 in the Circumstellar Envelope of IRC+10216 (J. P. Fonfría et al., ApJ, 01/2017)

  • C2H4 (80 ro-vibrational features in absorption) – Part of the emission arises in the inner dust formation zone contrary to previous findings
  • Part of the emission of ethylene arises in the dust formation zone at radii between 14 and 28 stellar radii from the center of IRC+10216, with no evidence of C2H4 closer to the star. Previous findings supposed all C2H4 arises in the far outer envelopes.
  • Our photochemical models underestimate the observed C2H4 terminal abundance by a factor of 4. We estimate that a fraction of the ethylene gas-phase could condense onto the dust grains around 20 stellar radii. this fact could affect the chemistry evolution of the envelope

New theoretical grounds in Astrochemistry

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).

Elegant and fast: the GACELA is running

/ Marcelo Castellanos
The Gas Cell chamber

On June 7, 2019, a first paper on the GACELA (GAs CEll for Laboratory Astrophysics) experimental set-up is out at the “Astronomy & Astrophysics” journal (A&A, volume 626, A34, 2019).

More than 3 years have elapsed since the first designs were envisaged for this set-up. Finally, at the end of 2017, the chamber (see figure above) was delivered and successfully tested against leaks. On the other hand, the GACELA broad-band radio receivers (Q and W bands, 31.5–50 and 72–116.5 GHz, respectively) were successfully commissioned in the second semester of 2017 and interfaced with the GACELA set-up in February 2018. Several experimental runs were performed, showing high quality signal-to-noise ratio spectra of molecular species (CH3CN, CH3OH, CH4/N2, CH4/N2/CH3CN, etc).

As stated by the authors, GACELA has achieved an important milestone. It is the first time that we can observe the thermal emission of molecules with an instantaneous band width of 20 GHz in Q band and 3 × 20 GHz in W band for Laboratory Astrophysics. These rotational spectroscopy measurements are complemented by mass spectrometry and optical spectroscopy.

In summary, NANOCOSMOS has developed an elegant and fast-responding set-up, the GACELA, to provide high-resolution and high-sensitivity spectra of molecular species produced in cold plasmas or UV experiments.

More information:

This research was presented in the paper “Broad-band high-resolution rotational spectroscopy for laboratory astrophysics“, published in Astronomy and Astrophysics 626, A34 (29pp), 2019 June 7. The authors are: José Cernicharo (Instituto de Física Fundamental, IFF-CSIC), Juan D. Gallego (Centro de Desarrollos Tecnológicos, Observatorio de Yebes, IGN), José A. López-Pérez (CDT, OY, IGN), Félix Tercero (CDT, OY, IGN), Isabel Tanarro (Instituto de Estructura de la Materia, IEM-CSIC), Francisco Beltrán (CDT, OY, IGN), Pablo de Vicente (CDT, OY, IGN), Koen Lauwaet (Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC & IMDEA Nanociencia), Belén Alemán (ICMM-CSIC & IMDEA Materiales), Elena Moreno (IFF-CSIC), Víctor J. Herrero (IEM-CSIC), José L. Doménech (IEM-CSIC), Sandra I. Ramírez (Centro de Investigaciones Químicas, UAEM, Mexico), Celina Bermúdez (IFF-CSIC), Ramón J. Peláez (IEM-CSIC), María Patino-Esteban (CDT, OY, IGN), Isaac López-Fernández (CDT, OY, IGN), Sonia García-Álvaro (CDT, OY, IGN), Pablo García-Carreño (CDT, OY, IGN), Carlos Cabezas (IFF-CSIC), Inmaculada Malo (CDT, OY, IGN), Ricardo Amils (CDT, OY, IGN), Jesús Sobrado (Centro de Astrobiología, INTA-CSIC), Carmen Díez-González (CDT, OY, IGN), José M. Hernández (IFF-CSIC/CDT, OY, IGN), Belén Tercero (CDT, OY, IGN), Gonzalo Santoro (ICMM-CSIC), Lidia Martínez (ICMM-CSIC), Marcelo Castellanos (IFF-CSIC), Beatriz Vaquero-Jiménez (CDT, OY, IGN), Juan R. Pardo (IFF-CSIC), Laura Barbas (CDT, OY, IGN), José A. López-Fernández (CDT, OY, IGN), Beatriz Aja (Universidad de Cantabria), Arnulf Leuther (Fraunhofer Institut fur Angewandte Festkorperphysik, Germany), José A. Martín-Gago (ICMM-CSIC).

The GACELA experimental set-up is located at the Centro de Desarrollos Tecnológicos, Observatorio de Yebes, thanks to a bilateral agreement between CSIC and IGN for the development of the NANOCOSMOS project.

NANOCOSMOS at the recent ALMA / Herschel Archival Workshop (Garching, Germany)

/ Marcelo Castellanos

alma_herschel_low_resFour NANOCOSMOS researchers gave their presentations at the ALMA/Herschel Archival Workshop held in Garching (Germany) at the ESO headquarters in April 15 -17, 2015. José Cernicharo (NANOCOSMOS Corresponding P.I.) talked about the synergies between the ALMA high resolution observations in the innermost zones of star-forming regions, AGB, post-AGBs stars and extragalactic objects and those of Herschel´s archive submillimeter and far-IR observations. Our postdoctoral researchers, Marcelino Agúndez, Guillermo Quintana-Lacaci and Belén Tercero talked about the following topics: Continue reading →