UV-photoprocessing of interstellar ice analogs: New infrared spectroscopic results

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

UV photodestruction of CH bonds and the evolution of the 3.4 mu m feature carrier. I. The case of aliphatic and aromatic molecular species

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

UV-photoprocessing of interstellar ice analogs: Detection of hexamethylenetetramine-based species

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Nature and evolution of the dominant carbonaceous matter in interplanetary dust particles: effects of irradiation and identification with a type of amorphous carbon

Aims.Interplanetary dust particle (IDP) matter probably evolved under irradiation in the interstellar medium (ISM) and the solar nebula. Currently IDPs are exposed to irradiation in the Solar System. Here the effects of UV and proton processing on IDP matter are studied experimentally. The structure and chemical composition of the bulk of carbon matter in IDPs is characterized. Methods: .Several IDPs were further irradiated in the laboratory using ultraviolet (UV) photons and protons in order to study the effects of such processing. By means of infrared and Raman spectroscopy, IDPs were also compared to different materials that serve as analogs of carbon grains in the dense and diffuse ISM. Results: .The carbonaceous fraction of IDPs is dehydrogenated by exposure to hard UV photons or 1 MeV protons. On the other hand, proton irradiation at lower energies (20 keV) leads to an efficient hydrogenation of the carbonaceous IDP matter. The dominant type of carbon in IDPs, observed with Raman and infrared spectroscopy, is found to be either a form of amorphous carbon (a-C) or hydrogenated amorphous carbon (a-C:H), depending on the IDP, consisting of aromatic units with an average domain size of 1.35 nm (5-6 rings in diameter), linked by aliphatic chains. Conclusions: .The D- and 15N-enrichments associated to an aliphatic component in some IDPs are probably the result of chemical reactions at cold temperatures. It is proposed that the amorphous carbon in IDPs was formed by energetic processing (UV photons and cosmic rays) of icy grains, maybe during the dense cloud stage, and more likely on the surface of the disk during the T Tauri phase of our Sun. This would explain the isotopic anomalies and morphology of IDPs. Partial annealing, 300-400°C, is required to convert an organic residue from ice photoprocessing into the amorphous carbon with low heteroatom content found in IDPs. Such annealing might have occurred as the particles approached the Sun and/or during atmospheric entry heating

Photoprocessing of H2S on dust grains: building S chains in translucent clouds and comets

Stars and planetary system

Thermal conductivity measurements of macroscopic frozen salt ice analogues of Jovian icy moons in support of the planned JUICE mission

14 páginas, 16 figuras, 2 tablascThe study of thermal properties of frozen salt solutions representative of ice layers in Jovian moons is crucial to support the JUpiter ICy moons Explorer (JUICE) (ESA) and Europa Clipper (NASA) missions, which will be launched in the upcoming years to make detailed observations of the giant gaseous planet Jupiter and three of its largest moons (Ganymede, Europa, and Callisto), due to the scarcity of experimental measurements. Therefore, we have conducted a set of experiments to measure and study the thermal conductivity of macroscopic frozen salt solutions of particular interest in these regions, including sodium chloride (NaCl), magnesium sulphate (MgSO4 ), sodium sulphate (Na2 SO4 ), and magnesium chloride (MgCl2 ). Measurements were performed at atmospheric pressure and temperatures from 0 to −70 ◦C in a climatic chamber. Temperature and calorimetry were measured during the course of the experiments. An interesting side effect of these measurements is that they served to spot phase changes in the frozen salt solutions, even for very low salt concentrations. A small sample of the liquid salt-water solution was set aside for the calorimetry measurements. These experiments and the measurements of thermal conductivity and calorimetry will be valuable to constrain the chemical composition, physical state, and temperature of the icy crusts of Ganymede, Europa, and Callisto.This project received financial support of The European Space Agency (ESA) contracts No.: RFP/3-15589/18/ES/CM and 4000126441/19/ES/CM: ‘Measurements of thermal and dielectric properties of ices in support to future radar measurements of Jovian Icy moons’, The Unidad de Excelencia ‘Mar ́ıa de Maeztu’ MDM-2017-0737– Centro de Astrobiolog ́ıa (INTA-CSIC), The Spanish Ministry of Science, Innovation and Universities AYA2017-85322-R and PID2020-118974GB-C21 (AEI/FEDER, UE), Retos Investigaci ́on BIA2016-77992-R (AEI/FEDER, UE), and ‘Explora Ciencia y Explora Tecnolog ́ıa’ [AYA2017-91062- EXP]. We are grateful to Anezina Solomonidou for assistance in the project proposal. The view expressed in this article can in no way be taken to reflect the official opinion of the European Space Agency. We thank the reviewer of this article for his constructive comments.Peer reviewe

Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions

Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm NN}}=2.76 TeV

The elliptic, $v_2$, triangular, $v_3$, and quadrangular, $v_4$, azimuthal anisotropic flow coefficients are measured for unidentified charged particles, pions and (anti-)protons in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV with the ALICE detector at the Large Hadron Collider. Results obtained with the event plane and four-particle cumulant methods are reported for the pseudo-rapidity range $|\eta|<0.8$ at different collision centralities and as a function of transverse momentum, $p_{\rm T}$, out to $p_{\rm T}=20$ GeV/$c$. The observed non-zero elliptic and triangular flow depends only weakly on transverse momentum for $p_{\rm T}>8$ GeV/$c$. The small $p_{\rm T}$ dependence of the difference between elliptic flow results obtained from the event plane and four-particle cumulant methods suggests a common origin of flow fluctuations up to $p_{\rm T}=8$ GeV/$c$. The magnitude of the (anti-)proton elliptic and triangular flow is larger than that of pions out to at least $p_{\rm T}=8$ GeV/$c$ indicating that the particle type dependence persists out to high $p_{\rm T}$.Comment: 16 pages, 5 captioned figures, authors from page 11, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/186

Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm{NN}}} = 2.76 TeV

The inclusive transverse momentum ($p_{\rm T}$) distributions of primary charged particles are measured in the pseudo-rapidity range $|\eta|<0.8$ as a function of event centrality in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$ TeV with ALICE at the LHC. The data are presented in the $p_{\rm T}$ range $0.15<p_{\rm T}<50$ GeV/$c$ for nine centrality intervals from 70-80% to 0-5%. The Pb-Pb spectra are presented in terms of the nuclear modification factor $R_{\rm{AA}}$ using a pp reference spectrum measured at the same collision energy. We observe that the suppression of high-$p_{\rm T}$ particles strongly depends on event centrality. In central collisions (0-5%) the yield is most suppressed with $R_{\rm{AA}}\approx0.13$ at $p_{\rm T}=6$-7 GeV/$c$. Above $p_{\rm T}=7$ GeV/$c$, there is a significant rise in the nuclear modification factor, which reaches $R_{\rm{AA}} \approx0.4$ for $p_{\rm T}>30$ GeV/$c$. In peripheral collisions (70-80%), the suppression is weaker with $R_{\rm{AA}} \approx 0.7$ almost independently of $p_{\rm T}$. The measured nuclear modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/284