Abstract. In this paper, we present mean gas and dust opacities relevant to the physical conditions typical of protoplanetary discs. As the principal absorber for temperatures below ∼1500 K, we consider spherical and aggregate dust particles of various sizes, chemical structure, and porosity, consisting of ice, organics, troilite, silicates, and iron. For higher temperatures, ions, atoms, molecules, and electrons are included as the main opacity sources. Rosseland and Planck mean opacities are calculated for temperatures between 5 K and 10 000 K and gas densities ranging from 10 −18 g cm −3 to 10 −7 g cm −3 . The dependence on the adopted model of dust grains is investigated. We compare our results with recent opacity tables and show how different opacity models affect the calculated hydrodynamical structure of accretion discs.

Context. We describe and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. Aims. The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. Methods. We considered three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking was performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. The chemical evolution is modeled within 10 9 years using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form. Results. The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result, however, required a lot of effort to make all necessary details consistent through the model runs, e.g., definition of the gas particle density, density of grain surface sites, or the strength and shape of the UV radiation field. Conclusions. The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available on the internet. This will facilitate and ease the development of other astrochemical models and provide nonspecialists with a detailed description of the model ingredients and requirements to analyze the cosmic chemistry as studied, e.g., by (sub-) millimeter observations of molecular lines.

The 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.

Aims. We aim to obtain a spatially resolved measurement of velocity dispersions in the disk of TW Hya. Methods. We obtained images with high spatial and spectral resolution of the CO J = 2-1, CN N = 2-1 and CS J = 5-4 emission with ALMA in Cycle 2. The radial distribution of the turbulent broadening was derived with two direct methods and one modelling approach. The first method requires a single transition and derives T ex directly from the line profile, yielding a v turb . The second method assumes that two different molecules are co-spatial, which allows using their relative line widths for calculating T kin and v turb . Finally we fitted a parametric disk model in which the physical properties of the disk are described by power laws, to compare our direct methods with previous values. Results. The two direct methods were limited to the outer r > 40 au disk because of beam smear. The direct method found v turb to range from ≈130 m s −1 at 40 au, and to drop to ≈50 m s −1 in the outer disk, which is qualitatively recovered with the parametric model fitting. This corresponds to roughly 0.2−0.4 c s . CN was found to exhibit strong non-local thermal equilibrium effects outside r ≈ 140 au, so that v turb was limited to within this radius. The assumption that CN and CS are co-spatial is consistent with observed line widths only within r 100 au, within which v turb was found to drop from 100 m s −1 (≈0.4 c s ) to zero at 100 au. The parametric model yielded a nearly constant 50 m s −1 for CS (0.2−0.4 c s ). We demonstrate that absolute flux calibration is and will be the limiting factor in all studies of turbulence using a single molecule. Conclusions. The magnitude of the dispersion is comparable with or below that predicted by the magneto-rotational instability theory. A more precise comparison would require reaching an absolute calibration precision of about 3%, or finding a suitable combination of light and heavy molecules that are co-located in the disk.

Understanding the chemical evolution of young (high-mass) star-forming regions is a central topic in star formation research. Chemistry is employed as a unique tool 1) to investigate the underlying physical processes and 2) to characterize the evolution of the chemical composition. With these aims in mind, we observed a sample of 59 high-mass star-forming regions at different evolutionary stages varying from the early starless phase of infrared dark clouds to high-mass protostellar objects to hot molecular cores and, finally, ultra-compact Hii regions at 1 mm and 3 mm with the IRAM 30 m telescope. We determined their large-scale chemical abundances and found that the chemical composition evolves along with the evolutionary stages. On average, the molecular abundances increase with time. We modeled the chemical evolution, using a 1D physical model where density and temperature vary from stage to stage coupled with an advanced gas-grain chemical model and derived the best-fit χ 2 values of all relevant parameters. A satisfying overall agreement between observed and modeled column densities for most of the molecules was obtained. With the bestfit model we also derived a chemical age for each stage, which gives the timescales for the transformation between two consecutive stages. The best-fit chemical ages are ∼10 000 years for the IRDC stage, ∼60 000 years for the HMPO stage, ∼40 000 years for the HMC stage, and ∼10 000 years for the UCHii stage. Thus, the total chemical timescale for the entire evolutionary sequence of the high-mass star formation process is on the order of 10 5 years, which is consistent with theoretical estimates. Furthermore, based on the approach of a multiple-line survey of unresolved data, we were able to constrain an intuitive and reasonable physical and chemical model. The results of this study can be used as chemical templates for the different evolutionary stages in high-mass star formation.

This is the second paper in a series where we study the influence of transport processes on the chemical evolution of protoplanetary disks. Our analysis is based on a 1+1D flared α-model of a ∼ 5 Myr DM Tau-like system, coupled to a large gas-grain chemical network. To account for production of complex molecules, the chemical network is supplied with an extended set of surface reactions and photo-processes in ice mantles. Our chemo-dynamical disk model covers a wide range of radii, 10-800 AU (from a Jovian planet-forming zone to the outer disk edge). Turbulent transport of gases and ices is implicitly modeled in full 2D along with the time-dependent chemistry, using the mixing-length approximation. Two regimes are considered, with high and low efficiency of turbulent mixing. The results of the chemical model with suppressed turbulent diffusion are close to those from the laminar model, but not completely. A simple analysis for the laminar chemical model to highlight potential sensitivity of a molecule to transport processes is performed. It is shown that the higher the ratio of the characteristic chemical timescale to the turbulent transport timescale for a given molecule, the higher the probability that its column density will be affected by diffusion. We find that turbulent transport enhances abundances and column densities of many gas-phase species and ices, particularly, complex ones. For such species a chemical steady-state is not reached due to long timescales associated with evaporation and surface photoprocessing and recombination (t 10 5 years). When a grain with an icy mantle is transported from a cold disk midplane into a warm intermediate/inner region, heavy radicals become mobile on the surface, enriching the mantle with complex ices, which are eventually released into the gas phase. The influence of turbulent mixing on disk chemistry is more pronounced in the inner, planet-forming disk region where gradients of temperature and high-energy radiation intensities are steeper than in the outer region. In contrast, simple radicals and molecular ions, which chemical evolution is fast and proceeds solely in the gas phase, are not much affected by dynamics. All molecules are divided into three groups according to the sensitivity of their column densities to the turbulent diffusion. The molecules that are unresponsive to transport include, e.g., C 2 H, C + , CH 4 , CN, CO, HCN, HNC, H 2 CO, OH, as well as water and ammonia ice. Their column densities computed with the laminar and 2D-mixing model differ by a factor of 2 − 5 ("steadfast" species). Molecules which vertical column densities in the laminar and dynamical models differ by up to 2 order of magnitude include, e.g., C 2 H 2 , some carbon chains, CS, H 2 CS, H 2 O, HCO + , HCOOH, HNCO, N 2 H + , NH 3 , CO ice, H 2 CO ice, CH 3 OH ice, and electrons ("sensitive" species). Molecules which column densities are altered by diffusion by more than 2 orders of magnitude include, e.g., C 2 S, C 3 S, C 6 H 6 , CO 2 , O 2 , SiO, SO, SO 2 , long carbon chain ices,...

Recently the hybrid organic-inorganic trihalide perovskites have shown remarkable performance as active layers in photovoltaic and other optoelectronic devices. However, their spin characteristic properties have not been fully studied, although due to the relatively large spin-orbit coupling these materials may show great promise for spintronic applications. Here we demonstrate spin-polarized carrier injection into methylammonium lead bromide films from metallic ferromagnetic electrodes in two spintronic-based devices: a ‘spin light emitting diode’ that results in circularly polarized electroluminescence emission; and a ‘vertical spin valve’ that shows giant magnetoresistance. In addition, we also apply a magnetic field perpendicular to the injected spins orientation for measuring the ‘Hanle effect’, from which we obtain a relatively long spin lifetime for the electrically injected carriers. Our measurements initiate the field of hybrid perovskites spin-related optoelectronic applications.

Prior to the origin of simple cellular life, the building blocks of RNA (nucleotides) had to form and polymerize in favourable environments on the early Earth. At this time, meteorites and interplanetary dust particles delivered organics such as nucleobases (the characteristic molecules of nucleotides) to warm little ponds whose wet-dry cycles promoted rapid polymerization. We build a comprehensive numerical model for the evolution of nucleobases in warm little ponds leading to the emergence of the first nucleotides and RNA. We couple Earth's early evolution with complex prebiotic chemistry in these environments. We find that RNA polymers must have emerged very quickly after the deposition of meteorites (< a few years). Their constituent nucleobases were primarily meteoritic in origin and not from interplanetary dust particles. Ponds appeared as continents rose out of the early global ocean but this increasing availability of "targets" for meteorites was offset by declining meteorite bombardment rates. Moreover, the rapid losses of nucleobases to pond seepage during wet periods, and to UV photodissociation during dry periods means that the synthesis of nucleotides and their polymerization into RNA occurred in just one to a few wet-dry cycles. Under these conditions, RNA polymers likely appeared prior to 4.17 billion years ago.Significance: There are currently two competing hypotheses for the site at which an RNA world emerged: hydrothermal vents in the deep ocean and warm little ponds. Because the former lacks wet and dry cycles, which are well known to promote polymerization (in this case, of nucleotides into RNA), we construct a comprehensive model for the origin of RNA in the latter sites. Our model advances the story and timeline of the RNA world by constraining the source of biomolecules, the environmental conditions, the timescales of reaction, and the emergence of first RNA polymers.Keywords: life origins | astrobiology | planetary science | meteoritics | RNA worldOne of the most fundamental questions in science is how life first emerged on the Earth. Given its ubiquity in living cells and its ability to both store genetic information and catalyze its own replication, RNA probably formed the basis of first life [1]. RNA molecules are made up of sequences of 4 different nucleotides, the latter of which can be formed through reaction of a nucleobase with a ribose and a reduced phosphorous (P) source [2,3]. The evidence suggests that first life appeared earlier than 3.7 Gyr ago (Ga) [4,5] and thus the RNA world would have developed on a violent early Earth undergoing meteoritic bombardment at a rate of ∼1-1000 ×10 12 kg/yr [6], which is approximately 8-11 orders of magnitude greater than today [7]. At this time, the atmosphere was dominated by volcanic gases, and dry land was scarce as continents were rising out of the global ocean. [8,9], the answer to these questions are largely unknown.As to the sources of nucleobases, the early Earth's atmosphere was likely dominated by CO 2 , N 2 , SO 2 , and H 2 O [10...