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Electron-induced chemistry is relevant to many processes that occur when an ionizing source interacts with matter, as in the formation of complex molecules within frozen condensates in space. We explore in this paper the radiolysis and the desorption processes affecting iced mixtures of water and carbon monoxide subjected to electron irradiation in the sub-keV regime. The experiments have been performed with the Interstellar Energetic Process System (IEPS), an ultra-high vacuum chamber equipped with an electron gun. The irradiated ices have been monitored with infrared and mass spectroscopies. We derive the chemistry and determine cross-sections for relevant processes as functions of the energy of the impacting electrons. We quantify the electron-stimulated desorption of some significant species in terms of their desorption yields, and relate these quantities to the electron penetration depth and the desorption-relevant length. The results of this study have been compared with the outcomes of similar experiments performed using pure carbon monoxide ices.

The hot Jupiter WASP-80b has been identified as a possible excellent target for detecting and measuring HeI absorption in the upper atmosphere. We observed 4 primary transits of WASP-80b in the optical and near-IR using the HARPS-N and GIANO-B high-resolution spectrographs, focusing on the HeI triplet. We further employed a three-dimensional hydrodynamic aeronomy model to understand the observational results. We did not find any signature of planetary absorption at the position of the HeI triplet with an upper limit of 0.7% (i.e. 1.11 planetary radii; 95% confidence level). We re-estimated the stellar high-energy emission that we combined with a stellar photospheric model to generate the input for the hydrodynamic modelling. We obtained that, assuming a solar He to H abundance ratio, HeI absorption should have been detected. Considering a stellar wind 25 times weaker than solar, we could reproduce the non-detection only assuming a He to H abundance ratio about 16 times smaller than solar. Instead, considering a stellar wind 10 times stronger than solar, we could reproduce the non-detection only with a He to H abundance ratio about 10 times smaller than solar. We attempted to understand this result by collecting all past HeI measurements looking for correlations with stellar high-energy emission and planetary gravity, but without finding any. WASP-80b is not the only planet with a sub-solar estimated He to H abundance ratio, suggesting the presence of efficient physical mechanisms (e.g. phase separation, magnetic fields) capable of significantly modifying the He to H content in the upper atmosphere of hot Jupiters. The planetary macroscopic properties and the shape of the stellar spectral energy distribution are not sufficient for predicting the presence or absence of detectable metastable He in a planetary atmosphere, as also the He abundance appears to play a major role., Comment: Accepted for publication on A&A

In astrochemistry, complex organic molecules (COMs) are defined as species with at least one C atom and six or more atoms in total. More than 70 COMs were detected toward various interstellar and c...

The Sardinia Radio Telescope (SRT) is a 64-m, fully-steerable single-dish radio telescope that was recently commissioned both technically and scientifically with regard to the basic observing modes. In order to improve the scientific capability and cover all the requirements for an advanced single-dish radio telescope, we developed the SArdinia Roach2-based Digital Architecture for Radio Astronomy (SARDARA), a wide-band, multi-feed, general-purpose, and reconfigurable digital platform, whose preliminary setup was used in the early science program of the SRT in 2016. In this paper, we describe the backend both in terms of its scientific motivation and technical design, how it has been interfaced with the telescope environment during its development and, finally, its scientific commissioning in different observing modes with single-feed receivers.

The importance of the formation pumping on the rovibrational level distribution of H2 is revisited. A detailed comparison of different formation mechanisms on dust surfaces and in the gas-phase is carried out, and it is found that dust surface formation dominates the formation pumping. It is shown that formation pumping in a cold gas can mimic the excitation conditions found in hotter regions. The presence of a significant fraction of molecular hydrogen in very high rotational levels observed towards OMC-1 Peak 1 is explained by means of pumping by newly formed H2 molecules and does not require high temperature gas.

The interstellar medium (ISM), gas and dust, appears to be arranged in clouds, whose dimensions, masses and densities span a large range of scales: from giant molecular clouds to small isolated globules. The structure of these objects show a high degree of complexity appearing, in the range of the observed scales, as a non-homogeneous ("clumpy") distribution of matter. The arrangement of the ISM is clearly relevant for the study of the fragmentation of the clouds and then of the star formation processes. To quantify observationally the ISM structure, many methods have been developed and our study is focused on some of them, exploiting multiwavelength observations of IS objects. The investigations presented here have been carried out by considering both the dust absorption (in optical and near IR wavelengths) and the gas emission (in the submm-radio spectral range). We present the maps obtained from the reduction of raw data and a first tentative analysis by means of methods as the structure function, the autocorrelation, and the Δ-variance. These are appropriate tools to highlight the complex structure of the ISM with reference to the paradigm given by the supersonic turbulence. Three observational cases are briefly discussed. In order to analyse the structure of objects characterized by different sizes, we applied the above-mentioned algorithms to the extinction map of the dark globule CB 107 and to the CO(J = 1-0) integrated intensity map of Vela Molecular Ridge, D Cloud. Finally we compare the results obtained with synthetic fractal maps known as "fractional Brownian motion" fBm images.

This paper presents the near-IR imaging observations of CB 107, a small dark globule projected against a rich stellar background. By means of accurate photometry, the near-IR two-color diagram J - H versus H - K was obtained for the stellar background. This information was used to estimate the color excesses of the detected stars so that, given the reddening curve, it was possible to derive the extinction map of the cloud. The structural properties of the dark globule were investigated by plotting the extinction dispersion σ, obtained in a given spatial box, as a function of the mean extinction AV. This relationship has shown quite a definite linear behavior, with the slope increasing with the box size. The results of the present analysis, compared with those obtained by other authors on larger dark clouds, suggest that for a given spatial scale the slope of the σ versus AV relation is greater in CB 107 than in larger clouds. The so-called Δ-variance method was also used to investigate the structure of the dark globule by evaluating the drift behavior of its extinction map. In this way, we have found that the power spectrum of the extinction map is characterized by a power law with exponent β ~ 2.7. This value is lower than expected, for the same range of spatial scales, on the basis of previous work on large molecular clouds.

A new data analysis software is presented that has been developed for the retrieval of atmospheric minor constituents from limb-sounding observations made in the millimeter and sub-millimeter spectral regions. The code, which is called MARC (Millimetre-wave Atmospheric-Retrieval Code), has been designed to analyze the observations of the MARSCHALS (Millimetre-wave Airborne Receivers for Spectroscopic CHaracterisation in Atmospheric Limb-Sounding) instrument which operates on the M-55 stratospheric aircraft. The main objective of the analysis of MARSCHALS observations will be to assess long-wave measurement capabilities for the study of the upper troposphere and lower stratosphere regions. The key questions will be the accuracy and spatial resolution that can be achieved by long-wave measurements in presence of clouds and horizontal gradients. MARC performs a global-fit multi-target retrieval, in which optimal estimation is used and errors of the forward model parameters are taken into account for the definition of the cost function minimized in the retrieval. With these features it is easy to use the variables of the problem as either forward model constant parameters or retrieved unknowns with minimum impact on the stability of the retrieval. MARC can perform a wide spectral-band analysis of the observations without a selection of the analyzed channels, and the retrieval process provides an error budget of the retrieved unknowns that includes both the forward model errors and the measurement errors. The error budget obtained in this way is smaller than that obtained when accounting a posteriori for the systematic errors. The new combination of the retrieval features makes possible an efficient and optimal exploitation of the information content of the observations.

Molecules have been observed in widely disparate astronomical objects, from comets to supernova remnants. Interstellar space appear to be a real chemical laboratory, able to produce a large number of molecules, some of them relatively complex. The abundances show a very high sensitivity to local physical properties and dynamical history. This sensitivity renders molecular observations and astrochemical modelling very flexible tools for investigating the properties and evolution of the interstellar medium. A brief outline of morfology of interstellar medium is given, together with a discussion of the basic chemical processes leading to the molecular formation. Since interstellar-dust particles play a crucial role in the chemical evolution of interstellar medium, physical and chemical properties of dust are reviewed. Finally, by way of an example of modelling exercise, a toy model of the chemical evolution of interstellar gas is presented.

UV radiation leads to photodissociation and photoionization of molecular species in diffuse clouds and in the extended envelopes of dark regions. In the inner part of heavily-obscured objects, the residual external field may be negligible; alternative mechanisms, such as cosmic-ray-induced H2 emission, appear to be efficient in photodestruction processes. We evaluate the relative importance of these radiation sources, and give some estimates of their effects on the mean lifetime of interstellar molecules, taking into account the cloud structure that significantly affects the penetration depth of UV radiation.

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Dust is an ubiquitous inhabitant of the interstellar medium, and leaves an un- mistakable signature in its optical properties, and physico-chemical evolution. Although there is little direct knowledge of the true nature of interstellar dust grains, strong evidences point toward the possibility that such grains are composites of many small monomers (mainly made of silicates and carbonaceous materials). We consider two different mod- els of fluffy dust aggregates, occurring as result of ballistic particle-cluster and cluster- cluster aggregation, and a cluster with a Gaussian-like sphere size distribution. We study the optical properties of such composite structures through the multipole fields and the Transition Matrix approach. Our results show the severe limits of applicability of the ef- fective medium theories. By comparing radiation and gravitational forces, we also infer some relevant insights into the dynamical evolution of composite grains in the Solar Sys- tem. We finally explore the possible role of composite fluffy dust grains in igniting an extraterrestrial prebiotic chemistry.

The distribution of matter in a small dark cloud has been investigated observationally by using the extinction of the stellar light that is due to the dust component as a tracer. Here we present the results of a photometric study that has been carried out in the optical spectral region by means of imaging in the B, V , and I bands. The relevant information on the spatial distribution of the dust has been obtained both by counting stars and by measuring their color excesses. While star counts on a reseau grid are easily interpreted as a measurement of the average extinction under the assumption of a locally A j uniform stellar luminosity function, the color excesses averaged on the same grid are obtained by a comparison of the stellar color distributions among the reddened regions and a reference position. Color excesses have also been derived by comparing the observed stellar colors with the locus of the unreddened stars in the two-color (V [I) versus (B[V ) diagram. The extinction map obtained for the globule CB 107 shows that the dust distribution at the boundary of this dark cloud can be measured and compared with models of matter distribution in these objects. By considering a density law such as n P (1 ] (r/a)a)~b, we —nd that our observations favor models with a \ 2 and b \ 1. Indications are also obtained about the spatial variation in this object of the total to selective extinction In this respect R V . we —nd that tends to increase toward the innermost regions of CB 107, and this suggests that the R V mean size of the dust particles also increases. The implications of these observations on the modeling of molecular cloud boundaries are discussed, and some indications on the timescale of the physical processes responsible for their structure are derived. The penetration depth of the interstellar radiation —eld in these objects is also brie—y discussed in the light of its possible consequences on the cloud chemistry. Lastly, the diUerences that we found in the color excess maps, which were obtained by means of the stellar counts and the cumulative distribution in color, respectively, suggest a clumpy distribution of matter in CB 107.

In this paper we present images of Comets 65P/Gunn and 46P/Wirtanen obtained by means of ISOCAM in the broadband filters at 9.62 (LW7) and 15.00 μm (LW3). The observations were performed on 23 March 1996 and on 9 November 1996, respectively. The aim of this work is to analyze the coma and tail dust environment of the targets. The application of tail models to the comet images allowed us to derive several interesting parameters about the dust ejection and dynamics. The tail of 46P/Wirtanen is symmetric with respect to the prolonged radius vector and a strong anisotropy characterizes the dust emission (most probable value of the power index describing the size dependence of the dust ejection velocity u > − 1 2 ). Estimates of the dust ejection velocity (from 14 ± 3 m s −1 at a heliocentric distance R = 2.5 AU to 23 ± 2 m s −1 at R = 2.0 AU, for 0.1-mm-sized grains), the power index of the differential size distribution (between −3.5 and −4), and the mass loss rate (from 1.5 ± 0.5 kg s −1 at R = 2.5 AU to 2 ± 1 kg s −1 at R = 2.0 AU) have been obtained. We conclude that the most probable dust-to-gas ratio is close to one, within a heliocentric distance from 2.5 to 2.0 AU. The dust tail of 65P/Gunn is strongly asymmetric. The fitting process indicates a dust ejection cone axis defined by the argument Φ = 110° and the obliquity I = 80°. The dust ejection velocity (from 16 ± 1 m s −1 at R = 2.9 AU to 24 ± 2 m s −1 at R = 2.6 AU for 0.1-mm-sized grains), the power index of the differential size distribution (around a value of −4), and the dust mass loss rate (between 100 and 300 kg s −1 ) have been determined. Dust mass loss rates determined by IR tail models depend on the scattering efficiency and the temperature of grains, but are independent of poorly known parameters, such as dust bulk density and albedo.

In this paper we give an overview of recent results obtained in our laboratory on “disordered” soot grains. The data are interpreted in a self-consistent scenario which correlates optical behaviour to structural properties of the dust. A sort of evolutionary progression is obtained which is linked both to production conditions and to processing mechanisms, such as thermal annealing, UV irradiation and ion bombardment. The reference frame so built may represent a key to interpret spectral behaviours observed in space for carbon-based materials in different astronomical environments: interstellar and circumstellar media, cometary and interplanetary environments. The study of carbon-based samples in the laboratory offers a tool to derive hints about the evolution of cosmic dust.

The intensity of far‐ultraviolet radiation inside interstellar clouds is a crucial factor in determining their physical and chemical evolution. The intensity of UV radiation depends on the structure of the clouds, on the optical properties of interstellar grains and on the presence of embedded sources, if any. Scattering on dust grains can greatly reduce shielding effects.In the present work we compute the radiation intensity inside isolated dark clouds, making different assumptions on the structure of the clouds and on the extinction and scattering properties of dust grains. In particular, we consider the case in which extinction laws are different in different parts of the cloud.

UV radiation leads to photodissociation and photoionization of molecular species in diffuse clouds and in the extended envelopes of dark regions. In the inner part of heavily-obscured objects, the residual external field may be negligible; alternative mechanisms, such as cosmic-ray-induced H2 emission, appear to be efficient in photodestruction processes. We evaluate the relative importance of these radiation sources, and give some estimates of their effects on the mean lifetime of interstellar molecules, taking into account the cloud structure that significantly affects the penetration depth of UV radiation.

In this paper we analyze the production and transfer of U.V. photons inside the core of a spherical core-halo molecular cloud, using various assumptions on extinction and scattering dust properties. In our computations we take into account the contributions to the excitation of the B 1 Σ u + ,C 1 П u states of molecular hydrogen by both primary protons and secondary electrons. The computations were performed assuming that the core has a uniform gas density of 104 cm-3 and a visual optical depth (edge to edge) of 10. Vie found the intensity of cosmic- ray- induced UV photons inside the core to be of a higher order of magnitude than that produced by the interstellar radiation field. Finally, we noted the effects of this UV radiation field on the evolution of grain mantles.