We study the evolution of molecular hydrogen on the grain surfaces and in the gas phase using both the rate equation (which tracks the average number of molecules) and the master equation (which tracks the expectation values of molecules). We show that above a certain critical accretion rate of H on the grains, the results from these two methods become identical. We used this result to follow t...

Context. Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks, but its photodissociation under interstellar conditions has never been properly studied. The partitioning of nitrogen between N and N2 controls the formation of more complex prebiotic nitrogen-containing species. Aims. The aim of this work is to gain a better understanding of ...

We propose a new method to constrain the actual state of the interstellar cloud that surrounds the solar system. Using Voyager UVS Lyman-α sky maps and the powerful principle of invariance, we derive the H distribution all along the spacecraft path. Provided current models of the heliopause interface between the solar and the interstellar winds, we extrapolate this distribution to farther dista...

We have derived the albedo (a) and phase function asymmetry factor (g) of interstellar dust grains at 11008 using archival Voyager observations of diffuse radiation in Ophiuchus. We have found that the grains are highly forwardscattering, with g 1⁄4 0:55 0:25 and a 1⁄4 0:40 0:10. Even though most of the gas in this direction is in the Ophiuchus molecular cloud, the diffuse FUV radiation is almo...

We compare the statistical properties of J=1→0 CO spectra observed in the Perseus Molecular Cloud with synthetic J=1→0 CO spectra, computed solving the non–LTE radiative transfer problem for a model cloud obtained as solutions of the three dimensional magneto–hydrodynamic (MHD) equations. The model cloud is a randomly forced super–Alfvénic and highly super–sonic turbulent isothermal flow. The p...

The shocked interstellar medium around IC443 produces strong X-ray emission in the soft energy band (E . 1.5 keV). We present an analysis of such emission as observed with the EPIC MOS cameras on board the XMM-Newton observatory, with the purpose to find clear signatures of the interactions with the interstellar medium (ISM) in the X-ray band, which may complement results obtained in other wave...

The observed properties of the local interstellar medium (LISM) have been facilitated by a growing ultraviolet and optical database of high spectral resolution observations of interstellar absorption toward nearby stars. Such observations provide insight into the physical properties (e.g., temperature, turbulent velocity, and depletion onto dust grains) of the population of warm clouds (e.g., 7...

Intense emission lines of near{IR molecular hydrogen are excited in OMC{1 by shocks, as outtowing gas from the star forming core interacts with the surrounding molecular cloud. These have been studied in OMC{1 in far greater detail than in any other astronomical source. They provide both a picture of the energetic activity associated with massive star formation, and stringent constraints on mod...

This review provides an introduction to presolar grains – preserved stardust from the interstellar molecular cloud from which our solar system formed – found in primitive meteorites. We describe the search for the presolar components, the currently known presolar mineral populations, and the chemical and isotopic characteristics of the grains and dustforming stars to identify the grains’ most p...

We consider the dynamical evolution of an interstellar cloud that is initially in thermal equilibrium in the warm phase and is then subjected to a sudden increase in the pressure of its surroundings. We find that if the initial plasma β of the cloud is of order unity, then there is a considerable period during which the material in the cloud both has a small β and is in the thermally unstable t...