Found 15 talks width keyword astrochemistry
More than 200 species have been detected in the interstellar medium (ISM), among them many molecules, radicals and ions, containing the −C≡N functional group. Both linear and branched isomers of propyl cyanide (PrCN; C 3 H 7 CN) are ubiquitous in interstellar space. To date, PrCN is one of the most complex molecules found in the interstellar medium. Furthermore, it is the only one observed species to share the branched atomic backbone of amino acids, some of the building blocks of life. Radical-radical chemical reactions in gas phase and on an ice model are examined in detail using density functional theory M062X/6-311++g(d,p) and ab initio methods CCSD(T)-F12//MP2. The reaction mechanism involves the following radicals association: CH 3 CHCH 3 +CN, CH 3 +CH3CHCN for iso-PrCN and CH 3 CH 2 +CH 2 CN, CH 3 +CH 2 CH 2 CN, CN+CH 3 CH 2 CH 2 for n-PrCN formation. Rate constants (see Figure 1) are also reported for gas phase association reactions. All reaction paths are exoergic and barrier-less in the gas phase and on the ice-model, suggesting that the formation of iso-PrCN and n-PrCN is efficient on the water-ice model adopted.
Another molecule : acetaldehyde (CH 3 CHO) is ubiquitous in interstellar space and is important for astrochemistry as it can contribute to the formation of amino acids through reaction with nitrogen containing chemical species. Quantum chemical and reaction kinetics studies are reported for acetaldehyde formation from the chemical reaction of C(3 P) with a methanol molecule adsorbed at the eighth position of a cubic water cluster. We present extensive quantum chemical calculations by means of CCSD(T)//wB97XD/6-311++G(2d,p) for total spin S=1 and S=0. The rate limiting step for forming acetaldehyde is the C–O bond breaking in CH 3 OCH to form adsorbed
CH 3 and HCO. We find two positions on the reaction path where spin crossing may be possible such that acetaldehyde can form in its singlet spin state.
1. I. BenChouikha, B. Kerkeni, et al. “Quantum chemical study of the reaction paths and kinetics of acetaldehyde formation on a methanol-water ice model”, ACS Adv., 12,18994 (2022).
2. B. Kerkeni, V Gámez, G. Ouerfelli, M-L. Senent, and N. Feautrier “Understanding Propyl-cyanide and its isomers Formation: Ab initio Study of the Spectroscopy and Reaction Mechanisms.”, Mon. Not. Roy. Astron. Soc. https://doi.org/10.48550/arXiv.2301.12297 (2023).
The field of Galactic archaeology has been very active in recent years, with a major influx of data from the Gaia satellite and large spectroscopic surveys. The major science questions in the field include Galactic structure and dynamics, the accretion history of the Milky Way, chemical tagging, and age-abundance relations. I will give an overview of GALAH as a large spectroscopic survey, and describe how it is complementary to other ongoing and future survey projects. I will also discuss recent science highlights from the GALAH team and compelling questions for future work.
One prediction of ΛCDM is the existence of partially phase-mixed substructures from accreted dwarf galaxies in the Milky Way stellar halo. Substructure originating in a single accretion event can be readily identified as a tight cluster of stars in phase space with similar chemical properties. Recently, the discovery of the Gaia Sausage Enceladus (GSE) has revolutionised our understanding of the complex assembly of the Milky Way halo. We present a review of the chemistry that characterises the last major merger that happened to the Milky Way some 9-10 Gy ago.
The new generation of spectrometers designed for extreme precision radial velocities enable correspondingly precise stellar spectroscopy. It is now fruitful to theoretically explore what the information content would be if stellar spectra could be studied with spectral resolutions of a million or more, and to deduce what signatures remain at lower resolutions. Hydrodynamic models of stellar photospheres predict how line profiles shapes, asymmetries, and convective wavelength shifts vary from disk center to limb. Corresponding high-resolution spectroscopy across spatially resolved stellar disks is now practical using differential observations during exoplanet transits, thus enabling the testing of such models. A most demanding task is to understand and to model spectral microvariability toward the radial-velocity detection of also low-mass planets in Earth-like orbits around solar-type stars. Observations of the Sun-as-a-star with extreme precision spectrometers now permit searches for spectral-line modulations on the level of a part in a thousand or less, feasible to test against hydrodynamic models of various solar features.
The very metal-poor (VMP; [Fe/H] < –2.0) and extremely metal-poor (EMP; [Fe/H] < –3.0) stars provide a direct view of Galactic chemical and dynamical evolution; detailed spectroscopic studies of these objects are the best way to identify and distinguish between various scenarios for the enrichment of early star-forming gas clouds soon after the Big Bang. It has been recognized that a large fraction of VMP (15-20%) and EMP stars (30-40%) possess significant over-abundances of carbon relative to iron, [C/Fe] > +0.7. This fraction rises to at least 80% for stars with [Fe/H] < –4.0. Recent studies show that the majority of CEMP stars with [Fe/H] < –3.0 belong to the CEMP-no sub-class, characterized by the lack of strong enhancements in the neutron-capture elements (e.g., [Ba/Fe] < 0.0). The brightest EMP star in the sky, BD+44:493, with [Fe/H] = –3.8 and V = 9.1, is a CEMP-no star. It shares a common elemental-abundance signature with the recently discovered CEMP-no star having [Fe/H] < –7.8. The distinctive CEMP-no pattern has also been identified in high-z damped Lyman-alpha systems, and is common among stars in the ultra-faint dwarf spheroidal galaxies, such as SEGUE-1. These observations suggest that CEMP-no stars exhibit the nucleosynthesis products of the VERY first generation of stars. We discuss the multiple lines of evidence that support this hypothesis, and describe current efforts to identify the nature of the massive stellar progenitors that produced these signatures.
All the elements from carbon to uranium present in the Solar System were produced by hundreds to thousands of stars belonging to different stellar generations that evolved and died during the presolar evolution of the Galaxy. Using the abundances of radioactive nuclei inferred from meteoritic analysis we can date the last of these stellar additions. We have found that the last contribution of elements such as carbon and slow neutron-capture elements to the Solar System from an asymptotic giant branch star occurred 15-30 Myr before the formation of the Sun. This provides us with an upper limit of the time when the precursor material of the Solar System became isolated from the bulk of the galactic material. Interestingly, it compares well to the lifetime of high-mass molecular clouds suggesting that the Sun was born in a very large family of stars.
The origins of neutron(n)-capture elements (atomic number Z > 30) have historically been discerned from the interpretation of stellar spectra. However, in the last decade nebular spectroscopy has been demonstrated to be a potentially powerful new tool to study the nucleosynthesis of n-capture elements. In this talk, I will discuss exciting new advances made in this field with near-infrared and optical observations of planetary nebulae, and atomic data investigations that enable the analysis of spectroscopic data.
The classical idea that globular clusters are the prototypes of simple stellar populations has been revolutionized in the last few years. Multiple sequences of stars have been detected in the colour-magnitude diagram of a number of clusters, mostly thanks to high-precision HST photometry, and the correlation with the chemical properties of different generations of stars has been demonstrated. In this talk, we will first present a summary of the observational picture, and we will then introduce the SUMO project (a SUrvey of Multiple pOpulations). This is a long-term project, lead here at the IAC and aimed at detecting and characterizing multiple populations in a large sample of globular clusters. We will review the scope, the observing and reduction strategy, and the first results. So far, data for more than 30 clusters have been secured, using the wide field imagers available at the 2.2m ESO/MPI and INT telescope, thus covering both hemispheres. We will present a new photometric index which turned out to be very effective in detecting multiple RGBs in nearly all the clusters analyzed so far. The connection with the chemical content of the different populations will be also discussed.
AbstractThe so called "dark ages" of the universe began about 400.000 years after the Big Bang as matter cooled down and space became filled with neutral hydrogen for hundreds of millions years. How the Universe was heated and reionized during the first billion years after the Big Bang is a question of topical interest in cosmology. I will show that current theoretical models on the formation and collapse of primordial stars suggest that a large fraction of massive stars should have imploded, forming high-mass black hole X-ray binaries. Then, I will review the recent observations of compact stellar remnants in the near and distant universe that support this theoretical expectation, showing that the thermal (UV and soft X-rays) and non-thermal (hard X-rays, winds and jets) emission from a large population of stellar black holes in high mass binaries heated the intergalactic medium over large volumes of space, complementing the reionization by their stellar progenitors. Feedback from accreting stellar black holes at that epoch would have prevented the formation of the large quantities of low mass dwarf galaxies that are predicted by the cold dark matter model of the universe. A large population of black hole binaries may be important for future observations of gravitational waves as well as for the existing and future atomic hydrogen radio surveys of HI in the early universe.
« Newer 1 | 2 Older » Last >>
- 2022 Nobel Prize and the Challenges of Bell's Inequality: Closing the Freedom of Choice LoopholeDr. Amin BabazabehThursday November 30, 2023 - 10:30 GMT (Aula)
- TBDThursday December 14, 2023 - 10:30 GMT (Aula)