Pablo del Mazo Sevillano, new doctor

On January 25th 2021, Pablo del Mazo Sevillano has defended in the Autonomous University of Madrid his PhD work entitled “Superficie de energía potencial y dinámica para la reacción H2CO + OH” (Potential Energy Surface and Dynamics for H2CO + OH reaction) supervised by professors Octavio Roncero Villa (IFF-CSIC) and Alfredo Aguado Gómez (UAM). Congratulations!

In this text, he explains the content of his tesis:

“The mechanism by which complex organic molecules (COMs) are found in the dense molecular clouds in the interstellar medium (ISM) has been assumed to proceed through their formation on ices. Later, as these ices evolve to hotter regions, the COMs would be released to the gas phase. Nevertheless, this complex organic molecules have been found in cold regions, shielded from UV-radiation, so it is mandatory to rethink this process.

One possible explanation comes from the results shown by CRESU experiment. In particular, it has been found that reactions between COMs and OH exhibit a huge increase in their kinetic rate constants as temperature decreases, what is surprising for reactions that usually present a barrier, hence should have an Arrhenius-like behavior. This opens the possibility of gas phase reactivity that has been previously dismissed. Unfortunately, there is no current experimental setup that can reproduce the conditions found in the ISM, in particular, the low pressure, so it is not possible to calculate the zero-pressure kinetic rate constants to be used in the astrochemical models. It is here that we can take some advantage from the computational simulations, since it is much easier to reproduce this low pressure conditions. In this PhD work we have focused on the simulation of the reactive process between H2CO + OH to form HCO + H2O and HCOOH + H, to evaluate the zero-pressure kinetic rate constants and provide a dynamical explanation of its behavior with temperature.

The dynamical simulation of a reactive process usually involves two steps:

First we must obtain the potential energy surface (PES) of the process. The PES is a function that encodes the energy for every nuclear configuration the system can reach during the simulation. It is from this function that the classical forces the system experience emerge, so a correct description of this function is crucial. In this work we have explored and propose different methodologies to express this function, with special interest in the use of artificial neural networks (ANN). ANNs are functions that present huge flexibility along with a short evaluation time, what makes them an excellent alternative to describe a PES.

The second step is the dynamical simulation itself. Once the interactions between particles are known (the PES) it is possible simulate collisions between the reactive partners and determine whether they react or not. From this, the kinetic rate constant can be calculated. In this work we have employed two methods: a quassiclassical  trajectory  method (including the zero-point energy of the reactants only at the beginning of dynamical calculations) and a Ring-polymer Molecular dynamics (RPMD) method (based on path integral and including quantum effects through the use of replicas or beads), to include quantum effects important at the low temperatures considered,  such as zero-point energy and tunneling. We found two key aspects that explain the increase of the kinetic rate constant for HCO + H2O formation as temperature lowers. On the one hand, due to the permanent dipole moment present in both reactants there is a very efficient capture mechanism at long distances. That way, reactants that are far away feel each other and start approaching until they finally collide. On the other hand, during this approach and finally collision, translational energy is transferred to rotation and vibration. This means that once the energy transfer is produced, it is not so easy for the system to redissociate back to reactants and the system gets trap for long times in a reactive complex. During this time the system has plenty of time to explore the configuration space, increasing the probability that reaction may take place. This is the mayor reaction mechanism for temperatures below 200 K, as has been found both experimentally and theoretically. Above this temperature, the direct mechanism becomes more important, leading to the well-known Arrhenius behavior”.


Representation of a PES (blue surface) over which a trajectory is being propagated (red line). Molecular geometries along the trajectory are shown.

José Cernicharo, awarded with the “Miguel Catalán” 2020 prize

José Cernicharo, Researcher of the IFF-CSIC and Head of our group, has been awarded the “Miguel Catalán” 2020 Prize for his scientific career within the research awards of the Community of Madrid, “for the quality of his research, his recognized leadership at national and international level in the area of Molecular Astrophysics and for his contributions and technological innovations”.

The Community of Madrid convenes annually the Research Awards “Miguel Catalán” and “Julián Marías” to the scientific career, in order to recognize scientific activity, as well as the scientific and humanistic values developed by researchers who throughout their professional career have been in some way linked to the Community of Madrid, and the Research Awards of the Community of Madrid “Miguel Catalán” and “Julián Marías” to researchers of less than forty years , in order to recognize the quality and excellence of scientific and research work developed at the beginning of his research career. They are convened annually in the two Areas, Sciences and Humanities.

The ceremony, which will take place tomorrow, November 20 at 10:30, can be followed online through the following links:

  1. Madrid Community Canal https://www.pscp.tv/ComunidadMadrid/
  2. Twitter of the Community of Madrid https://twitter.com/ComunidadMadrid?s=20
  3. Complutense University Of Madrid Canal https://ucm.es/directo
  4. Youtube from the Complutense University of Madrid https://www.youtube.com/user/ucomplutensemadrid/featured

Funambulist stars

Why do we study chemical equilibrium in red giants?

You may have often read that “we are stardust.” It is a rather accurate expression, especially if we think that most of the elements that make us up (this scarce 5% of the baryonic matter of the universe) emerged from the core of a star and from a whole process of death and destruction. But what do we call stardust?

Medium-sized stars (between one and eight solar masses) go through several phases throughout their lives. The longest phase is the so-called  “main sequence”, in which time is spent transforming hydrogen into helium. When hydrogen from the nucleus (where this activity occurs in principle) is depleted, the star begins to use other elements as “fuels”. This results in the star starting to “swell”, becoming a red giant and releasing its outer layers to the interstellar medium. This occurs in one of the final stages of its life, the AGB phase (from  Asymptotic Giant Branch).

A multitude of chemical phenomena take place in the atmospheres of these evolved stars, enriched by successive material dredged-up. In principle, when we talk about the birth of dust grains, we mean precisely those atmospheres of evolved stars (also supernova explosions, which are much more massive stars, but this is another story).

The layers of material released by the AGB star and forming its atmosphere are composed of a huge amount of gas molecules and a small proportion of dust grains. We are interested to know how these grains of dust are formed, from what basic elements and under what physical conditions.

To understand this whole process it is important to know the chemical equilibrium in these atmospheres, that is, the state in which, although the chemical activity continues, the chemical composition remains stable. If we know the chemical equilibrium, we will know what atoms and molecules are at the origin of the formation of dust grains (which is what we are interested in). In addition, we will have the theoretical scenario with the sequence of the different types of grains that are expected to appear as matter flows and cools from the AGB star into the interstellar medium.

In our case, in the atmospheres of AGB stars, we know that the gas is at high temperature and pressure, which is very fortunate as these are the conditions under which it is valid to use chemical equilibrium. This would be very different if we talked about, for example, the interstellar medium, where temperatures and pressures are very small and the chemical composition is given by chemical kinetics. In that case, as Marcelino Agúndez (from our group Astromol in the Institute of Fundamental Physics, IFF-CSIC) states, “it would be necessary to know the constant kinetics of a large number of reactions, in those environments everything is rather more uncertain. The interest of applying chemical equilibrium to the atmospheres of AGB stars is that, in them, temperatures and pressures are high, ergo we can use chemical equilibrium and the chemical composition can be calculated in a simple way. This has been known since the 1970s.”.

And here we get into a paper recently published by a team of researchers from the Spanish Council for Scientific Research (CSIC), focused on studying the atmospheres of AGB stars (as we said before, medium-sized stars in the final stages of their  lives).

The idea was to update all the information available so, first of all, the team compiled and updated a large dataset of thermochemical properties for 919 gaseous and 185 condensed species involving 34 elements. The chemical composition in AGB star atmospheres was calculated thanks to a recently developed code. All available information obtained from astronomical observations was also updated to, as a last step, compare the predictions of the calculations with the observations. All with the idea of reviewing what we knew so far, what our successes and mistakes were, and future prospects about molecules, molecular aggregates, and solid condensates in the atmospheres of red giant stars.

Funambulist stars, what the equilibrium tells us

This study not only tells us which aggregates could act as “bricks” of dust grains construction (and  what may be the most likely gas precursors of these grains) but even throws information on what we do not find:  potentially detectable molecules that have not yet been observed have been identified, making them good candidates for detection with observatories such as ALMA.

Finally, there are also things that don’t fit: in some cases, theoretical analysis and data don’t match. In fact, there are discrepancies of several orders of magnitude for some molecules which are observed with abundances several orders of magnitude above the expectations from chemical equilibrium. This means that, in some areas of the stellar atmosphere, there are no chemical equilibrium conditions due to unidentified phenomena that could be related to ultraviolet photons or hydrodynamic processes.

What’s new thanks to the lab

To do this type of studies it is necessary to know the thermodynamic properties of each molecular species. In the case of the most common molecules, this data is known, but for the rarest ones it is necessary to calculate or measure them.

This study has incorporated, for the first time, the properties of a large number of molecular aggregates of titanium and carbon analyzed within the Nanocosmos (ERC) project in the laboratories of the Institute of Materials Science of Madrid (ICMM-CSIC). In carbon-rich AGB stars, forecasts say the first condensates would be carbon itself, titanium carbide (TiC) and silicon carbide (SiC). (In O-rich atmospheres, the first condensate expected is Al2OR3). And it was necessary to have data on these under-studied species in order to compare them with observations.

In short, this work tells us about our mistakes and successes, about the path on which these atoms and molecules pass, about the origins of dust grains and where they are expected to appear, about the agglomeration that initiates the formation of the first solid materials from a gas of atoms and small molecules.

We are interested in how its composition can influence what happens much later, when the birth cycle of a new star begins again with the condensation of those dust grains resulting in nuclear reactions. We will continue to build knowledge on this data, relegating the wrong ones and analyzing the new information, because that’s how science works.

More information:

Scientific paper:Chemical equilibrium in AGB atmospheres: Successes, failures and prospects for small molecules, clusters, and condensates“, M. Agúndez  (IFF-CSIC), J. I. Martínez  (ICMM-CSIC), P. L. de Andres (ICMM-CSIC), J. Cernicharo  (IFF-CSIC) and J. A. Martín-Gago (ICMM-CSIC).

The Criegee intermediate-formic acid reaction explored by rotational spectroscopy

“The Criegee intermediate-formic acid reaction explored by rotational spectroscopy” is the title of the inside front cover paper recently published in the Journal “Physical Chemistry Chemical Physics” (PCCP) and whose authors are Carlos Cabezas (from our Astromol group) and Yasuki Endo.

Abstract: The atmospheric reaction of the simplest Criegee intermediate, CH2OO, with formic acid has been investigated in the gas phase by pulsed Fourier-transform microwave spectroscopy. The dominant nascent product from this reaction was identified as hydroperoxymethyl formate (HOOCH2OCHO), for which two different conformations, formed through independent insertion mechanisms, were observed in the discharged plasma of a CH2I2/O2/formic acid gas mixture. The conformational identifications are supported by the observation of 13C species in natural abundance together with the chemically mono substituted deuterium isotopologues. These isotopic observations further suggest that hydroperoxymethyl formate slightly decomposes, producing formic anhydride (OHCOCHO) in a dehydration reaction.

Link to the inside front cover

Link to the paper “The Criegee intermediate-formic acid reaction explored by rotational spectroscopy

Guillermo Quintana-Lacaci at the IRAM 30m Summerschool 2019

The IRAM 30m Summerschool 2019 will take place, from the 6th to the 13th of September, in Pradollano (near Granada, Spain). This year, one of the scientific talks will be given by one of our members, Guillermo Quintana-Lacaci, and it will be focused on Evolved Stars.

The 9th IRAM 30m summerschool will combine lectures on millimeter astronomy with observations using the 30m telescope.

Lectures will be given by experienced scientists and 30m observers, covering a range of topics, from comets and planetary atmospheres in the solar system to the study of the chemistry of interstellar clouds, low and high mass star formation, in the Milky Way, in nearby galaxies, and in ultra-luminous objects at high-redshifts.

These lectures will be complemented by shorter lectures on instrumentation, observing techniques, and data processing.

More information here.

Miriam Garcia wins the Spanish contest ‘We are scientists, get us out of here!’

The contest ‘We are scientists, get us out of here!’ in its Spanish version has a winner: Miriam Garcia Santa-Maria, an astrophysicist member of our group and PhD student in the IFF (Instituto de Física Fundamental). She was the most voted scientist by the students of the 17 participating schools in the Zona CSIC, all of them in the villages of the Ciudad Ciencia net.

After two weeks answering questions through a chat, students have been able to know more about six scientists and their jobs, their lives and their expertise.  1972 young students, between 10 an d 18 years old, have participated, sending 1366 questions and having 95 text chats online. The ‘Zona CSIC’ received more participants than other zones of the contest.

Congratulations, Miriam!

Time for the Cycle 1 of the JWST

Artist’s impression of James Webb Space Telescope in space. Credit: STScI-JWST

After the Peer Review Panels and final review by the Space Telescope Science Institute (STScI) Director, the James Webb Space Telescope Proposal, led by Olivier Berne (IRAP-CNRS, France), “Radiative Feedback from Massive Stars as Traced by Multiband Imaging and Spectroscopic Mosaics” has been approved for the Cycle 1  Director’s Discretionary Early Release Science (DD ERS) Program with 27.8 hours of observation time.

Two members of the team are from our group: Javier R. Goicoechea and Emeric Bron.

A total of 106 proposals requesting 3683.4 hours of observations were submitted in response to the DD ERS Call and 13 Proposals for 460 Hours have been approved by the Director.
The proposal makes a strong case for the role and significance of interstellar photodissociation regions (PDR) observations with JWST, with a plethora of anticipated science-enabling products and templates for the community ahead of Cycle 2, while also anticipating a series of papers on the ERS data.

The JWST launch window is set for March to June 2019.

Congratulations on the success of the proposal and best wishes for your future participation in and contributions to the scientific program of JWST.

Link to the new: Selections Made for the JWST Director’s Discretionary Early Release Science Program

More information (in Spanish):

Three new doctors

The Molecular Astrophysics Group has three new doctors, who defended their thesis in the last months. Luis Velilla, Alicia López and Sara Cuadrado: here we present a resume of their work. Congratulations!

Luis Velilla:

“Molecular complexity in envelopes of evolved stars: detailed study of the molecular emission of the objects IKTau, OH231.8+4.2, and IRC+10216”

Circumstellar envelopes of evolved stars are the main contributors to the enrichment of the interstellar medium, and are excellent laboratories to study the molecular complexity and the chemical evolution of the Universe. In this thesis, we present our study of the molecular emission in the millimeter wavelength range with the IRAM-30m telescope, Herschel-HIFI, and ALMA, of three circumstellar envelopes around the evolved stars IKTau, OH231.8+4.2, and IRC+10º216.

The main results obtained show that the chemistry of oxygen-rich objects is not as poor as it was previously thought. In particular, the chemistry of OH231.8+4.2 has been probably altered by high-speed shocks caused by the interaction between the slow AGB wind and fast (few 100 km· s−1) highly collimated bipolar winds. We also present the first sub-arcsecond resolution observations obtained with ALMA, for species such as SiO, SiS, or SiC2 towards IRC+10º216. This work will serve as a reference for future studies of the molecular emission in circumstellar envelopes of evolved stars, particularly for the oxygen rich envelopes.

Thesis defense: 09/06/2017

Thesis directors: Carmen Sánchez Contreras, José Cernicharo.


Alicia López:

 “Organic molecules chemistry in massive stars formation regions”

“Radioastronomy needs information from the laboratory for the spectral characterization and identification of abundant molecules in the Orion-KL molecular cloud. The temperature of this high-mass star forming region causes many of the low-lying vibrational states of these molecules to be excited so that, in addition to lines from rare isotopologues, we have to identify lines arising from vibrationally excited states, thanks to the availability of laboratory measurements in the millimeter and submillimeter domains. This work has permitted to characterize the spectrum of this prototypical hot core and will be of great importance to detect and identify molecular lines using ALMA in other high-mass star forming regions.”

Thesis defense: 14/09/2017

Thesis directors: José Cernicharo, Belén Tercero.


Sara Cuadrado:

“Molecular content in the Orion Bar photodissociation region”

“In this PhD thesis, a detailed study of the molecular emission of the Orion Bar photodissociation region (PDR) has been presented. The Orion Bar is the prototypical warm PDR with a far-UV (FUV) radiation field of a few 104 times the mean interstellar field. Owing to its proximity (~414 pc) and nearly edge-on orientation, the Orion Bar offers the opportunity to determine the chemical content, spatial stratification of different species, and chemical formation-destruction routes in strongly FUV-illuminated gas.

We carried out a millimetre line survey of the irradiated edge of the Orion Bar PDR using the IRAM-30m telescope, and complemented it with ~7′′ resolution maps at 0.8 mm, in order to study the chemistry prevailing in molecular gas that is directly exposed to strong FUV fields. Despite being a very harsh environment, our observations show a relatively rich molecular line spectra, with hundreds of lines arising from hydrocarbons and complex organic molecules (Cuadrado et al. 2015, 2017). We have also reported the first interstellar detection of the less stable conformer of formic acid, cis-HCOOH (Cuadrado et al. 2016). In addition, we have used ALMA to observe a small field-of-view with a high angular resolution (~1′′) where the transition from atomic to molecular gas takes place, in the context of investigating the structure and dynamics of FUV-irradiated molecular gas. The images (in the rotationally excited emission of CO, HCO+, SH+, HOC+, SO+, and SO) reveal a pattern of high-density substructures, photo-ablative gas flows and instabilities at the edge of the molecular cloud (Goicoechea et al. 2016, 2017).

Thesis defense: 15/09/2017

Thesis directors: Javier R. Goicoechea, José Cernicharo.


Acknowledgements: AYA2009-07304, AYA2012-32032, CSD2009-00038, and ERC-610256 (Nanocosmos).

 

“Multi-molecular views of a stellar nursery”, an article in Nature about the Orion-B mapping program

Gratier et al. 2017.

The journal Nature recently published an article titled “Multi-molecular views of a stellar nursery” outlining the Orion-B mapping program that is being carried out with the IRAM30m telescope. Two members of our group, Emeric Bron and Javier R. Goicoechea, are involved in this research (led by Jérôme Pety, IRAM) whose goal is to simultaneously image emissions from many different molecules across a very wide area of the star-forming cloud Orion-B, in the iconic Orion constellation.

You can read the abstract here and the full article in this link.

Calibrating the Submillimetre Sky

For astronomers, one of the most important things in order to be able to confirm and compare the huge amount of data received during the observations is to have accurate calibration references. In astronomy, millimetre and submillimetre wavelengths are important to study relatively cold objects in the Universe, such as the interstellar medium, star forming regions, circumstellar matter, planetary atmospheres and highly red-shifted objects.  Reference calibration standards are, however, very scarce specially at submillimetre wavelengths (Bands 7, 8, 9 and 10 of the Atacama Large Millimetre Array, ALMA, in Northern Chile).

Fortunately, some years ago a team of astronomers suggested the use of the planets of our Solar System as possible calibration references at submillimetre wavelengths. First works developed on that subject revealed the submillimetre lines of Phosphine (PH3) in the atmospheres of Jupiter and Saturn, although the overall shape of these extremely wide features could not be measured due to technical limitations.

Now, for the first time, a team has measured the emission of the giant planets Jupiter and Saturn across the 0.3 to 1.3 mm wavelength range using a Fourier Transform Spectrometer mounted on the 10.4-meter dish of the CSO, Caltech Submillimetre Observatory (now retired) at Mauna Kea, Hawaii, 4100 meters above sea level. The calibrated data allowed the team to verify the predictions of standard radiative transfer models for both planets in this spectral region, and to confirm the absolute radiometry in the case of Jupiter.

This careful calibration included the evaluation of the antenna performance over such a wide wavelength range and the removal of the Earth’s atmosphere effects, allowing the detection of broad absorption features on those planets’ atmospheres.

As mentioned by Juan Ramón Pardo (lead author of the study, ICMM-CSIC, Spain), “Besides their physical interest, the results are also important as both planets are calibration references in the current era of operating ground-based and space-borne submillimetre instruments”.

Jupiter and Saturn are gaseous giants much larger but less dense than the inner rocky planets of our Solar System. Their atmospheres are extremely thick. Very wide collision-broadened lines of Ammonia (NH3) and Phosphine (PH3) dominate the overall shape of their submillimetre spectrum. Most of the several thousand exoplanets discovered to date are gaseous giants thought to be similar to Jupiter and Saturn. Therefore, the now measured submillimetre spectrum of our giant neighbours could also help as a reference in future spectroscopic studies of other planetary systems.

More information:

This research was presented in a paper entitled “Ground-based measurements of the 1.3 to 0.3 mm spectrum of Jupiter and Saturn, and their detailed calibration” by Juan R. Pardo et al., to appear in the journal Icarus on July 1st 2017, but already available on-line: http://www.sciencedirect.com/science/article/pii/S0019103516303827

 The team is composed of Juan R. Pardo (Molecular Astrophysics Group, ICMM, CSIC, Spain); Eugene Serabyn (NASA-Jet Propulsion Laboratory, California Institute of Technology, USA); Martina C. Wiedner (LERMA, Paris Observatory, PSL Research University, CNRS, Sorbonne Universités, UPMC, France); Raphäel Moreno (LESIA, Paris-Meudon Observatory, France); Glenn Orton (NASA-Jet Propulsion Laboratory, California Institute of Technology, USA).

Source of Jupiter Raw Image: technotifier.com