High-resolution Infrared Observations

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.

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, submitted)

  • 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

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 acetylene 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 acetylene gas-phase could condense onto the dust grains around 20 stellar radii. this fact could affect the chemistry evolution of the envelope

Yebes 40m broad band receivers

NANOCOSMOS successfully designed and constructed two new millimeter broad band receivers for the Q frequency band (31.5 − 50 GHz) and the W band (72 − 90.5 GHz) for the Yebes 40m radio telescope. One of our main achievements is the instantaneous frequency coverage in order to observe many molecular transitions with single tunings in single-dish mode.

Our Yebes observations have led to the discovery of multiple molecular species. These were made in 2019 (Q2, Q4), and 2020 (Q1) and were complemented with the IRAM 30m radio telescope in Granada (W band).

  • Objects: IRC+10216 as the archetypal AGB carbon rich star and the cold dark Taurus Molecular Cloud -1 or TMC-1.
  • Methodology: observations, laboratory characterization, ab-initio quantum calculations, rotational diagrams, gas-phase chemical models and radiative transfer calculations.

Summary of results with the NANOCOSMOS mm broad band receivers at Yebes 40m radio telescope:

Detection of vibrationally excited HC7N and HC9N in IRC+10216 (J. R. Pardo et al., A&A, 08/2020)

  • HC9N (26 doublets, vib. exc.) – First time detection and characterization in Space
  • HC7N (17 doublets, vib. exc.) – New detection
  • Emission arising from the external layers of the circumstellar envelope
  • Possibe effects on intensity line variations with the stellar phase
  • These vibrationally excited states must be taken into account for precise abundance determinations of long carbon chains

MgCCCN (top) and MgCCCCH (bottom) optimized structures

Discovery of two new magnesium-bearing species in IRC+10216: MgC3N and MgC4H (J. Cernicharo et al., A&A, 10/2019)

  • MgC3N (16 doublets) – New detection
  • MgC4H (6 doublets) – New detection
  • MgCCH (2 doublets) – Confirmation

TMC-1, the starless core sulfur factory: Discovery of NCS, HCCS, H2CCS, H2CCCS, and C4S and detection of C5S (J. Cernicharo et al., A&A, 04/2021)

  • Sulfur-bearing species NCS, HCCS, H2CCS, H2CCCS, and C4S – First time discovery in Space (TMC-1)
  • C5S – First time detection in a cold dark cloud (TMC-1)
  • State-of-the-art gas-phase chemical networks fail to reproduce the observed column densities. Thus, important reactions involving S and S+(neutral-neutral, neutral-ion) and those on dust grain surfaces are missing and much laboratory and theoretical work need be performed in order to understand the chemistry of sulfur
  • The analysis of C4S and C5S shows that S-bearing carbon chains do not follow the smooth decrease in abundance observed in cold dark molecular clouds and circumstellar envelopes for other carbon chains such as cyanopolyynes (HC2n + 1N; a factor 3–5 between members of this molecular species)

Discovery of the propargyl radical (CH2CCH) in TMC-1: One of the most abundant radicals ever found and a key species for cyclization to benzene in cold dark clouds (M. Agúndez et al., A&A, 03/2021)

  • Propargyl radical (CH2CCH) 6 strongest hyperfine components of the 20, 2–10, 1 rotational transition – First time discovery in interstellarr Space (TMC-1)
  • Similar abundance as methyl acetylene. Thus, it is one of the most abundant radicals detected in TMC-1. Moreover, it is probably the most abundant organic radical with a certain chemical complexity ever found in a cold dark cloud
  • The observed high abundance, points out that CH2CCH probably plays a key role in the synthesis of large organic molecules and, in particular, the cyclization towards the first aromatic ring (benzene). This also happens in combustion processes where the CH2CCH radical has a key role in the synthesis of benzene and polycyclic aromatic hydrocarbons (PAHs).

Discovery of allenyl acetylene, H2CCCHCCH, in TMC-1. A study of the isomers of C5H4 (J. Cernicharo et al., A&A, 03/2021)

  • Allenyl Acetylene (H2CCCHCCH) 19 rotational transitions – First time detection in Space (TMC-1)
  • We find that allenyl acetylene and methyl diacetylene are the two most stable C5H4 isomers and both have similar observed abundances in TMC-1
  • State-of-the-art chemical models understimate the observed abundances by an order of magnitude. We need to assess the main formation routes in the chemical models, mainly the reactions of the CCH radical with methyl acetylene (CH3CCH) and allene (H2CCCH2)

Discovery of CH2CHCCH and detection of HCCN, HC4N, CH3CH2CN, and, tentatively, CH3CH2CCH in TMC-1 (J. Cernicharo et al., A&A, 03/2021)

  • Vynil Acetylene (CH2CHCCH) – First time detection in Space (TMC-1)
  • HCCN, HC4N, and CH3CH2CN – First time detection in a cold dark cloud (TMC-1)
  • Ethylene could be a likely precursor of CH2CHCCH and CH2CHCN through reactions with CCH and CN, respectively
  • The reaction between CN and vinyl acetylene is a viable route to the C5H3N isomers recently found in TMC-1 at very low temperatures
  • Our observations show that the cyano methylene radical HCCN and the linear cyano ethynyl-methylene radical HC4N have similar abundances unlike predictions from current chemical models

Space and laboratory observation of the deuterated cyanomethyl radical HDCCN (C. Cabezas et al., A&A, 02/2021)

  • HDCCN (forest of lines) – New detection in TMC-1, laboratory production and full spectroscopically characterization
  • Deuteration is driven by deuteron transfer from the H2D+ molecular ion
  • Further constraints on molecular formation pathways and identification of U-lines in molecular surveys

Detection of two C4H3N isomers towards the cold dark cloud TMC-1

A study of C4H3N isomers in TMC-1: line by line detection of HCCCH2CN (N. Marcelino et al., A&A, 02/2021)

  • HCCCH2CN (22 lines) – New detection and confirmation
  • CH2CCHCN (16 lines) – New detection and confirmation
  • The derived abundances suggest a common origin in the formation of the C4H3N isomers: reaction of the CN radical with unsaturated hydrocarbons methyl acetylene and allene

First time detection in Space and laboratory production and characterization of the acetyl cation, CH3CO+

Discovery of the acetyl cation, CH3CO+, in space and in the laboratory (J. Cernicharo et al., A&A, 02/2021)

  • CH3CO+ (8 lines) – First time detection in Space (TMC-1 and other cold dark clouds), laboratory production and characterization of the protonated form of ketene (H2CCO)
  • The derived high abundance of the protonated form of ketene is due to the high proton affinity of the neutral species
  • Further constraints on formation/destruction rates and/or chemical formation routes to CH3CO+
  • The reaction of ketene with H3+ is the most favourable for protonation, from the thermodynamical point of view

Space and laboratory discovery of HC3S+ (J. Cernicharo et al., A&A, 02/2021)

  • HC3S+ (4 lines) – First time detection in Space (TMC-1), laboratory production and characterization of the protonated form of C3S
  • The spectroscopic parameters obtained for HC3S+ from ab initio calculations agree very well with that obtained from observations and in the laboratory
  • Constraint in chemical formation routes: The derived C3S/HC3S+ ratio is well reproduced by a gas-phase chemical model in which HC3S+ is mostly formed through protonation of C3S and the reactions S+ + C3H2 and S + C3H3+

Tentative detection of HC5NH+ in TMC-1 (N. Marcelino et al., A&A, 11/2020)

  • HC5NH+ (7 lines in Q band) – First time detection in Space
  • Existence of additional formation routes at stake: Our pseudo time-dependent gas-phase chemical models of cold dark clouds underestimate the abundance of protonated molecules

Discovery of HC3O+ in space: The chemistry of O-bearing species in TMC-1 (J. Cernicharo et al., A&A, 10/2020)

  • HC3O+ (4 lines) – First time detection in Space and laboratory characterization of the protonated form of C3O
  • The high abundance of the protonated form of C3O, (HC3O+) is due to the high proton affinity of the neutral species
  • Reactions between hydrocarbon ions and atomic oxygen probably participate in the growth of these long O-bearing carbon chains (e.g. c-H2C3O and HCCCHO)
  • Existence of additional formation routes at stake: Our pseudo time-dependent gas-phase chemical models of cold dark clouds underestimate the abundance of protonated molecules

Discovery of HC4NC in TMC-1: A study of the isomers of HC3N, HC5N and HC7N (J. Cernicharo et al., A&A, 10/2020)

  • HC4NC (5 lines, Q band) – First time detection in Space
  • Cold molecular clouds favor the formation of metastable isomers due to their low temperatures.
  • In the ejecta of AGB stars, where the temperature is higher, the presence of high-energy isomers is less favorable because chemical reactions, including isomerization, are expected to favor the most stable isomer. The same pattern is expected for isotopic fractionation

Lines of C3N− observed towards TMC-1 in the 31.0−50.3 GHz frequency range

Interstellar nitrile anions: Detection of C3N_ and C5N_ in TMC-1 (J. Cernicharo et al., A&A, 09/2020)

  • C3N_ (2 lines) – First time detection in the Interstellar Medium
  • C5N_ (6 lines) – First time detection in the Interstellar Medium
  • Derivation of new rotational constants for C5N_
  • Our work definitively excludes metal-bearing species, or vibrationally excited states of other known species, as carriers for the series of lines assigned to C5N_
  • The derived abundance ratios between neutral radicals CnN and their anions are very similar in interstellar and circumstellar environments
  • Further constraints in the formation of CnN− anions through radiative electron attachment to CnN radicals, for which calculated rate constants differ by orders of magnitude

Elegant and fast: the GACELA is running

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 Guillermo Haro School on Molecular Astrophysics (Puebla, Mexico)

Prof. José Cernicharo has been awarded with the Guillermo Haro Visiting Professorship 2016 at the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE, posterGH16Puebla, Mexico). Following this award, INAOE has organized the Guillermo Haro School on Molecular Astrophysics (October 11 – 21, 2016). Several NANOCOSMOS scientists (Asunción Fuente from CNIG-IGN, Nuria Marcelino, José Pablo Fonfría and Luis Velilla from ICMM-CSIC) will give lectures on the following topics:

  • Molecular Astrophysics, Spectroscopy, Chemistry in the ISM (José Cernicharo)
  • Physical and chemical processes in the ISM, Protoplanetary disks (Asunción Fuente)
  • Observational methods and interpretation (Nuria Marcelino)
  • Molecular excitation and radiative transfer, Circumstellar medium (José Pablo Fonfría)
  • Chemistry in the circumstellar medium, atmospheric  effects and calibration (Luis Velilla)

José Cernicharo will give a public talk in Puebla downtown on Thursday 13: “Moléculas en el espacio: Astroquímica”.