We report the release of a new version UMIST database for astrochemistry. The contains rate coefficients 3864 gas-phase reactions important in interstellar and circumstellar chemistry involves 395 species 12 elements. previous (1990) this has been widely used by modellers. In addition to coefficients, we also tabulate permanent electric dipole moments neutral heats formation. A numerical model chemical evolution dark cloud is calculated differences that with noted.

ABRIDGED: Context: HI and CO large scale surveys of the Milky Way trace diffuse atomic clouds dense shielded regions molecular hydrogen clouds. However, until recently, we have not had spectrally resolved C+ to characterize photon dominated interstellar medium, including, H2 gas without C, CO-dark H2, in a sample Aims: To use sparse Galactic plane survey 1.9 THz [C II] spectral line from Herschel Open Time Key Programme, Observations Terahertz (GOT C+), statistically significant Methods: We...

<i>Context. <i/>The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflow these stars creates a circumstellar envelope in which rich gas-phase chemistry takes place. Complex shock-induced non-equilibrium place the inner wind envelope, dust-gas reactions ion-molecule alter abundances zone, penetration of cosmic rays ultraviolet photons dissociates molecules outer region.<i>Aims. <i/>Little observational information exists on...

ABSTRACT We present results of an investigation into the formation nitrogen-bearing molecules in atmosphere Titan. extend a previous model to cover region below tropopause, so new treats from Titan’s surface altitude 1500 km. consider effects condensation and sublimation using continuous, numerically stable method. This is coupled with parameterized treatments sedimentation aerosols their condensates, haze particles. These processes affect abundances heavier species such as molecules, but...

The gas near the midplanes of planet-forming protostellar disks remains largely unprobed by observations due to high optical depth commonly observed molecules such as CO and H$_2$O. However, rotational emission lines from rare may have depths unity in vertical direction, so that are strong enough be detected, yet remain transparent trace disk midplane. Here we present a chemical model an evolving T-Tauri predict transitions $^{12}$C$^{16}$O, $^{13}$C$^{16}$O, $^{12}$C$^{17}$O...

Abstract We present the first detection of 13 CCH in a protoplanetary disk (TW Hya). Using observations C 2 H, we measure CCH/ = 65 ± 20 gas with CO isotopic ratio 12 CO/ 21 5. The TW Hya exhibits phase C/O that exceeds unity, and H is tracer this excess carbon. confirm gaseous two separate carbon reservoirs, as noted previously. explore theoretical solutions for development dichotomy. One model represents today exposed to cosmic-ray ionization rate below interstellar consistent current...

Midplane models of protoplanetary disks find that the cold temperatures in outer parts disk ensure virtually all molecules are accreted onto grains. However, gas observed at these radii. One possible explanation is emission arises from above midplane, possibly a heated layer surface flared disk. Models which take into account vertical chemical distribution and can calculate column densities therefore required for comparison with observations. We present results calculation time-dependent...

We present new models of the deuterium chemistry in protoplanetary disks, including, for first time, multiply deuterated species. use these to explore whether observations combination with can give us clues as which desorption processes occur disks. find, common other authors, that photodesorption allow strongly bound molecules such HDO exist gas phase a layer above midplane. Models including this process best agreement observations. In midplane, cosmic ray heating desorb weakly CO and...

We present the results of models chemistry, including deuterium, in inner regions protostellar disks. find good agreement with recent gas phase observations several (non--deuterated) species. also compare our comets and that absence other processing e.g. accretion shock at surface disk, or by mixing calculated D/H ratios ices are higher than measured reflect ratio set molecular cloud phase. Our give quite different abundances distributions to disk because differences physical conditions...

Aims: Little information exists on the circumstellar molecular abundance stratifications of many molecules. The aim is to study chemical pattern 11 molecules and isotopologs ($^{12}$CO, $^{13}$CO, SiS, $^{28}$SiO, $^{29}$SiO, $^{30}$SiO, HCN, CN, CS, SO, SO$_2$) in oxygen-rich evolved star IK~Tau. Methods: We have performed an in-depth analysis a large number emission lines excited envelope around done based non-local thermodynamic equilibrium (non-LTE) radiative transfer analysis, which...

We investigate the gas-phase and grain-surface chemistry in inner 30 AU of a typical protoplanetary disk (PPD) using new model which calculates gas temperature by solving heating cooling balance has an improved treatment UV radiation field. discuss inner-disk general, obtaining excellent agreement with recent observations have probed material regions PPDs. also apply our to study isotopic fractionation carbon. Results show that ratio, 12C/13C, system varies radius height disk. Different...

The presence of over 300 molecules in the interstellar medium, majority which are organic compounds, raises question extent to protostellar chemistry is responsible for Solar System bodies (e.g., comets, asteroids, planets). systematic surveys cold cores have focused on TMC-1 core Taurus complex, along with lesser other northern hemisphere facilitated by several telescopes available below 45 GHz, where most relatively strong emission under conditions cores. A few southern sources been...

We present 100 and 200 μm ISOPHOT observations of the dense core L1498. have mapped central by using ΔI200=I200-I100/Θ, where ΔI200 is a measure emission from cold dust Θ=I100/I200 in outer regions. The continuum provides information about chemical depletion properties cores there lack gas tracers. Previous L1498 show that CS CCS lies outside NH3 core. peak close to previously observed peak. A comparison with high spatial resolution C18O shows maximum coincides dip at center. estimate factor...

We present mid-infrared spectral maps of the NGC 1333 star forming region, obtained with Infrared Spectrometer on board Spitzer Space Telescope. Eight pure H2 rotational lines, from S (0) to (7), are detected and mapped. The emission appears be associated warm gas shocked by multiple outflows in region. A comparison between observed intensities predictions detailed shock models indicates that arises both slow (12 - 24 km/s) fast (36 53 C-type shocks an initial ortho-to-para ratio ~ 1....

Several processes have been suggested as ways of returning accreted grain mantles to the gas, thus preventing total removal molecules from gas phase in dark quiescent clouds. We attempt distinguish between them by considering not only calculated gas-phase abundances, but also ratio abundances deuterated species non-deuterated species. find that D/H is relatively model-independent, desorption due formation H2 on grains gives best overall agreement with observations.

The effects of mantle desorption due to cosmic rays on the chemistry interstellar clouds are modelled. Two mechanisms considered – direct ray heating dust grains and induced photodesorption. Their at densities typical a molecular cloud dense core investigated. It is found that both have significant effect gas-phase abundances. results for case compared with observations TMC–1 be in reasonable agreement.

Abstract Gas in protostellar disks provides the raw material for giant planet formation and controls dynamics of planetesimal-building dust grains. Accurate gas mass measurements help map observed properties planet-forming onto environments known exoplanets. Rare isotopologues carbon monoxide (CO) have been used as tracers Lupus star-forming region, with an assumed interstellar CO/H 2 abundance ratio. Unfortunately, observations T-Tauri show that CO is not interstellar, a finding reproduced...

The dynamics and chemistry of protostellar disks are likely to be intricately linked, with dynamical processes altering the chemical composition, chemistry, in turn, controlling ionization structure hence ability magneto-rotational instability drive disk turbulence. Here we present results from first models outer regions (R &gt; 100 AU) protoplanetary consider effects turbulence driven diffusive mixing vertical direction. We show that diffusion can greatly affect column densities many...

The effects of turbulence on the mixing gases and dust in outer Solar nebula are examined using 3-D MHD calculations shearing-box approximation with vertical stratification. is driven by magneto-rotational instability. magnetic hydrodynamic stresses correspond to an accretion time at midplane about equal lifetimes T Tauri disks, while surface layers thirty times faster. resulting from also fastest layers. rate similar radial exchange orbital angular momentum, so that Schmidt number near...

Abstract The elemental ratios of carbon, nitrogen, and oxygen in the atmospheres hot Jupiters may hold clues to their formation locations protostellar disk. In this work, we adopt gas-phase chemical abundances C, N, O from several a disk kinetics model as sources for envelope Jupiter HD 209458b evolve atmospheric composition planet using 1D model, treating both vertical mixing photochemistry. We consider two pressure-temperature profiles, one with without thermal inversion. From each...

Fischer-Tropsch catalysis has been suggested as a means of driving hydrocarbon chemistry in oxygen-rich regions such the protosolar nebula. In addition to producing hydrocarbons, also produces water, and it is therefore possible that processes could account for recent observations water circumstellar envelope carbon-rich asymptotic giant branch star IRC +10216. We present models +10216 demonstrate on surfaces small metallic grains can produce large quantities water. The abundance produced...