SEARCH · Engineering Papers

Results for “INTERSTELLAR GAS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,639 records · Page 91

All sources NASA NTRS DOE OSTI

NASA NTRS2001

Far Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption Toward 3C 273

We present Far Ultraviolet Spectroscopic Explorer observations of the molecular, neutral atomic, weakly ionized, and highly ionized components of the interstellar and intergalactic material toward the quasar 3C273. We identify Ly-beta absorption in eight of the known intergalactic Ly-alpha absorbers along the sight line with the rest-frame equivalent widths W(sub r)(Ly-alpha) > 50 micro-angstroms. Refined estimates of the H(I) column densities and Doppler parameters (b) of the clouds are presented. We find a range of b = 16-46 km/s. We detect multiple H(I) lines (Ly-beta - Ly-theta) in the 1590 km/s Virgo absorber and estimate logN(H(I)) = 15.85 +/- 0.10, ten times more H(I) than all of the other absorbers along the sight line combined. The Doppler width of this absorber, b = 16 km/s, implies T < 15,000 K. We detect O(VI) absorption at 1015 km/s at the 2-3(sigma) level that may be associated with hot, X-ray emitting gas in the Virgo Cluster. We detect weak C(III) and O(VI) absorption in the IGM at z=0.12007; this absorber is predominantly ionized and has N(H+)/N(H(I)) > 4000/Z, where Z is the metallicity. Strong Galactic interstellar O(VI) is present between -100 and +100 km/s with an additional high-velocity wing containing about 13% of the total O(VI) between +100 and +240 km/s. The Galactic O(VI), N(V), and C(IV) lines have similar shapes, with roughly constant ratios across the -100 to +100 km/s velocity range. The high velocity O(VI) wing is not detected in other species. Much of the interstellar high ion absorption probably occurs within a highly fragmented medium within the Loop IV remnant or in the outer cavity walls of the remnant. Multiple hot gas production mechanisms are required. The broad O(VI) absorption wing likely traces the expulsion of hot gas out of the Galactic disk into the halo. A flux limit of 5.4 x 10(epx -16) erg/sq cm/s on the amount of diffuse O(VI) emission present = 3.5' off the 3C273 sight line combined with the observed O(VI) column density toward 3C273, logN O(VI) = 14.73 +/- 0.04, implies n(sub e) < 0.02/cubic cm and P/k < 11,500/cubic cm for an assumed temperature of 3 x 10(exp 5) K. The elemental abundances in the neutral and weakly-ionized interstellar clouds are similar to those found for other halo clouds. The warm neutral and warm ionized clouds along the sight line have similar dust-phase abundances, implying that the properties of the dust grains in the two types of clouds are similar. Interstellar H2 absorption is present at positive velocities at a level of logN(H2) = 15.71, but is very weak at the velocities of the main column density concentration along the sight line observed in H(I) 21 cm emission.

Sembach, Kenneth R.↗

NASA NTRS2001

Boundary Conditions of the Heliosphere

We present new calculations of the ionization of the Local Interstellar Cloud (LIC) by directly observed sources including nearby stellar extreme ultraviolet (EUV) sources and the diffuse emission of the Soft X-ray Background (SXRB). In addition, we model the important, unobserved EUV emission both from the hot gas responsible for the SXRB and from a possible evaporative boundary between the LIC and the hot gas. We show that these ionization sources can provide the necessary ionization and heating of the cloud to match observations. Including the radiation from the conductive boundary, while not required, does improve the agreement with observations of the temperature of the LIC. The ionization predicted in our models shows good agreement with pickup ion results, interstellar absorption line data towards epsilon CMa, and EUV opacity measurements of nearby white dwarf stars. The areas of disagreement point to a possible underabundance (relative to solar abundance) of neon in the LIC. The presence of dust in the cloud, or at least depleted abundances, is necessary to maintain the heating/cooling balance and reach the observed temperature.

Slavin, Jonathan D.↗

DOE OSTI2017

The Formation and Evolution of Star Clusters in Interacting Galaxies

Observations of globular clusters show that they have universal lognormal mass functions with a characteristic peak at ∼2×10{sup 5} M{sub ⊙}, but the origin of this peaked distribution is highly debated. Here we investigate the formation and evolution of star clusters (SCs) in interacting galaxies using high-resolution hydrodynamical simulations performed with two different codes in order to mitigate numerical artifacts. We find that massive SCs in the range of ∼10{sup 5.5}--10{sup 7.5} M{sub ⊙} form preferentially in the highly shocked regions produced by galaxy interactions. The nascent cluster-forming clouds have high gas pressures in the range of P/k∼10{sup 8}--10{sup 12} K cm{sup −3}, which is ∼10{sup 4}--10{sup 8} times higher than the typical pressure of the interstellar medium but consistent with recent observations of a pre-super-SC cloud in the Antennae Galaxies. Furthermore, these massive SCs have quasi-lognormal initial mass functions with a peak around ∼10{sup 6} M{sub ⊙}. The number of clusters declines with time due to destructive processes, but the shape and the peak of the mass functions do not change significantly during the course of galaxy collisions. Our results suggest that gas-rich galaxy mergers may provide a favorable environment for the formation of massive SCs such as globular clusters, and that the lognormal mass functions and the unique peak may originate from the extreme high-pressure conditions of the birth clouds and may survive the dynamical evolution.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1989

Far infrared, submm and mm spectroscopy of the galactic center: Radio arc and +20/+50 km s (exp -1) clouds

The observations of the par improved spectroscopy and the molecular clouds at the galactic center are reported. The results show: the spatial distributions of C(II) 158 microns and molecular line radiation and of the thermal radio continuum emission in the arched filaments of the radio arc are similar; about 2 x 10(exp 4) of the solar mass, or 10 percent of the total gas mass in the radio arc, are contained in C(+) regions; the H(+)/C(+) regions are probably located at the surfaces of the dense molecular clouds in the arc. Profiles, fluxes and spatial distributions of the C(II) fine structure and CO rotational lines are reported. It is demonstrated that the data does not fit models in which the neutral interstellar clouds in the arc are ionized by shocks or by magnetohydrodynamic phenomena. Moreover, that the high temperatures and densities derived previously from NH3 and CS observations may not be characteristic of the bulk of the molecular gas.

Genzel, R.↗

NASA NTRS1999

Synthesis of Large Molecules in Cometary Ice Analogs: Physical Properties Related to Self-Assembly Processes

The combination of realistic laboratory simulations and infrared observations have revolutionized our understanding of interstellar dust and ice-the main component of comets. Since comets and carbonaceous micrometeorites may have been important sources of volatiles and carbon compounds on the early Earth, their organic composition may be related to the origin of life. Ices on grains in molecular clouds contain a variety of simple molecules. The D/H ratios of the comets Hale-Bopp and Hyakutake are consistent with a primarily interstellar ice mixture. Within the cloud and especially in the presolar nebula through the early solar system, these icy grains would have been photoprocessed by the ultraviolet producing more complex species such as hexamethylenetetramine, polyoxymethylenes, and simple keones. We reported at the 1999 Bioastronomy meeting laboratory simulations studied to identify the types of molecules which could have been generated in pre-cometary ices. Experiments were conducted by forming a realistic interstellar mixed-molecular ice (H2O, CH3OH, NH3 and CO) at approximately 10 K under high vacuum irradiated with UV light from a hydrogen plasma lamp. The gas mixture was typically 100:50:1:1, however when different ratios were used material with similar characteristics was still produced. The residue that remained after warming to room temperature was analyzed by HPLC, and by several mass spectrometric methods. This material contains a rich mixture of complex compounds with mass spectral profiles resembling those found in IDPs and meteorites. Surface tension measurements show that an amphiphilic component is also present. These species do not appear in various controls or in unphotolyzed samples. Residues from the simulations were also dispersed in aqueous media for microscopy. The organic material forms 10-40 gm diameter droplets that fluoresce at 300-450 nm under UV excitation. These droplets have a morphology and internal structure which appear strikingly similar to those produced by extracts of the Murchison meteorite. Together, these results suggest a link between organic material photochemically synthesized on the cold grains in dense, interstellar molecular clouds and compounds that may have contributed to the organic inventory of the primitive Earth. For example, the amphiphilic properties of such compounds permit self-assembly into the membranous boundary structures that required for the first forms of cellular life.

Dworkin, Jason P.↗

NASA NTRS2022

Elevated Hot Gas and High-mass X-Ray Binary Emission in Low-metallicity Galaxies: Implications for Nebular Ionization and Intergalactic Medium Heating in the Early Universe

High-energy emission associated with star formation has been proposed as a significant source of interstellar medium (ISM) ionization in low-metallicity starbursts and an important contributor to the heating of the intergalactic medium (IGM) in the high-redshift (z ≳ 8) universe. Using Chandra observations of a sample of 30 galaxies at D ≈ 200–450 Mpc that have high specific star formation rates of 3–9 Gyr^(−1) and metallicities near Z ≈ 0.3Z_⊙, we provide new measurements of the average 0.5–8 keV spectral shape and normalization per unit star formation rate (SFR). We model the sample-combined X-ray spectrum as a combination of hot gas and high-mass X-ray binary (HMXB) populations and constrain their relative contributions. We derive scaling relations of log L^(HMXB)_(0.5-8keV) / SFR = 40.19 ± 0.06 and log L^(gas)_(0.5-2keV) / SFR = 39.58 ^(+0.17)_(-0.28), significantly elevated compared to local relations. The HMXB scaling is also somewhat higher than L^(HMXB)_(0.5-8keV) -SFR-Z relations presented in the literature, potentially due to our galaxies having relatively low HMXB obscuration and young and X-ray luminous stellar populations. The elevation of the hot gas scaling relation is at the level expected for diminished attenuation due to a reduction of metals; however, we cannot conclude that an L^(gas)_(0.5-2keV) -SFR-Z relation is driven solely by changes in ISM metal content. Finally, we present SFR-scaled spectral models (both emergent and intrinsic) that span the X-ray-to-IR band, providing new benchmarks for studies of the impact of ISM ionization and IGM heating in the early universe.

high-mass x-ray binary stars↗

DOE OSTI2026

Directed Gas-Phase Formation of The Propargyl Family of Resonance-Stabilized Radicals in The Reactions of Ground-State Carbon Atoms (C; 3 P j ) with Butene Isomers (C 4 H 8 ): Dimethylpropargyl and Ethylpropargyl

The propargyl radical (C 3 H 3 ) is the simplest resonance-stabilized free radical (RSFR), but how does stepwise methyl substitution in the alkene reactant affect its dynamics of their formation? We report a crossed molecular beam study of the reactions of atomic carbon (C, 3 P j ) with four butene isomers (C 4 H 8 ) under single collision conditions at a collision energy of 28 ± 2 kJ mol −1 . Barrierless addition of atomic carbon to the alkene C=C bond triggers ring opening to triplet substituted allenes—a de facto insertion mechanism—followed by unimolecular decomposition via atomic hydrogen (H), methyl (CH 3 ) or ethyl (C 2 H 5 ) loss, yielding a family of propargyl‑type RSFRs. RRKM calculations reveal that the branching ratios are highly sensitive to the alkene structure. While the methyl loss channel, affording 1‑methylpropargyl, dominates for 2 butenes (80–90%), the predicted hydrogen atom loss channel (≈10%) leading to 1,3 dimethylpropargyl is identified in the experiment by comparison with theoretical energetics. For isobutene, a near‑equal competition is seen, with the reaction producing 3‑methylpropargyl (≈50%) and 1,1‑dimethylpropargyl (≈40%), along with 2‑vinylallyl (≈5%), whose formation is supported by the experimental data. Most notably, the reaction with 1 butene uniquely favors an enthalpically driven hydrogen shift, eventually producing 1 vinylallyl (≈38%), which is assigned based on the excellent agreement between the measured and calculated reaction exothermicity. Rapid entropically favored fragmentation channels yield ≈40% of propargyl type species (propargyl, 1- and 3-ethylpropargyls), slightly outcompeting the allyl type product. Furthermore, these results establish a systematic progression from C 2 H 4 to C 4 H 8 , where the increasing alkyl substitution unlocks new fragmentation channels, providing a versatile gas phase route to alkylated RSFRs—key intermediates in the growth of methylated and ethylated PAHs and aliphatic chains in combustion and cold interstellar environments (molecular clouds).

Alkyls↗

DOE OSTI2012

THE REMARKABLE HIGH PRESSURE OF THE LOCAL LEO COLD CLOUD

Using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope, we have obtained high-resolution ultraviolet spectra of the C I absorption toward two stars behind the Local Leo Cold Cloud (LLCC). At a distance ( Almost-Equal-To 20 pc) that places it well inside the Local Bubble, the LLCC is the nearest example of the coldest known (T Almost-Equal-To 20 K) diffuse interstellar clouds. The STIS measurements of the C I fine-structure excitation toward HD 85259 and HD 83023 indicate that the thermal gas pressure of the LLCC is much greater than that of the warm clouds in the Local Bubble. The mean LLCC pressure measured toward these two stars (60,000 cm{sup -3} K) implies an H I density of Almost-Equal-To 3000 cm{sup -3} and a cloud thickness of Almost-Equal-To 200 AU at the 20 K cloud temperature. Such a thin, cold, dense structure could arise at the collision interface between converging flows of warm gas. However, the measured LLCC pressure is appreciably higher than that expected in the colliding-cloud interpretation given the velocity and column density constraints on warm clouds in the HD 85259 and HD 83023 sightlines. Additional STIS measurements of the Zn II, Ni II, and Cr II column densities toward HD 85259 indicate that the LLCC has a modest 'warm cloud' dust depletion pattern consistent with its low dust-to-gas ratio determined from H I 21 cm and 100 {mu}m observations. In support of the inferred sheet-like geometry for the LLCC, a multi-epoch comparison of the Na I absorption toward a high-proper-motion background star reveals a 40% column density variation indicative of LLCC Na I structure on a scale of Almost-Equal-To 50 AU.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Model of the expansion of H II region RCW 82

This paper aims to resolve the problem of formation of young objects observed in the RCW 82 H II region. In the framework of a classical trigger model the estimated time of fragmentation is larger than the estimated age of the H II region. Thus the young objects could not have formed during the dynamical evolution of the H II region. We propose a new model that helps resolve this problem. This model suggests that the H II region RCW 82 is embedded in a cloud of limited size that is denser than the surrounding interstellar medium. According to this model, when the ionization-shock front leaves the cloud it causes the formation of an accelerating dense gas shell. In the accelerated shell, the effects of the Rayleigh-Taylor (R-T) instability dominate and the characteristic time of the growth of perturbations with the observed magnitude of about 3 pc is 0.14 Myr, which is less than the estimated age of the H II region. The total time t {sub ∑}, which is the sum of the expansion time of the H II region to the edge of the cloud, the time of the R-T instability growth, and the free fall time, is estimated as 0.44 < t {sub ∑} < 0.78 Myr. We conclude that the young objects in the H II region RCW 82 could be formed as a result of the R-T instability with subsequent fragmentation into large-scale condensations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores

Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H{sub 2} and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1973

Molecule formation. I - In normal H I clouds. II - In interstellar shock waves.

The formation of simple molecules and their role in the chemistry and physics of the interstellar medium is considered. The requirements for recombination reactions to occur on interstellar grains with the subsequent buildup of a molecular mantle are discussed. Together with a discussion of depletion and heating of the evolving gas, this forms the basis for a treatment of the precollision history of dust and gas. All the chemical reactions included in the calculations are given, as well as the results of calculations for two values of the intercloud pressure and for a range of cloud masses. Shock waves in clouds whose precollision history has been calculated are treated, followed by discussion of the shock structure and the dynamics of the grains. The process of sputtering is treated, and expressions are given for the cooling rates, including cooling due to the molecules formed behind the shock front. All the chemical reactions included in the calculations are given, as well as the results of calculations for a range of shock velocities and initial molecular hydrogen abundances.

Aannestad, P. A.↗

NASA NTRS1981

Einstein observations of the galactic centre

A description is presented of the X-ray observations made with the Einstein Observatory Imaging Proportional Counter of a 1 x 1 degree field centered near the galactic nucleus. In the direction of the galactic center the interstellar medium is generally opaque to all radiation between the visual and extreme ultraviolet due to the large column density of the intervening gas and dust. The importance of this X-ray study lies in the fact that it opens up a new window in which the central regions of the Milky Way Galaxy can be observed. The X-ray image is clearly dominated by a bright, central region of emission elongated along the galactic plane. Also presented are a number of unresolved sources.

Watson, M. G.↗

NASA NTRS1986

Exobiology experiment concepts for space station

The exobiology discipline uses ground based and space flight resources to conduct a multidiscipline research effort dedicated to understanding fundamental questions about the origin, evolution, and distribution of life and life related molecules throughout the universe. Achievement of this understanding requires a methodical research strategy which traces the history of the biogenic elements from their origins in stellar formation processes through the chemical evolution of molecules essential for life to the origin and evolution of primitive and, ultimately, complex living species. Implementation of this strategy requires the collection and integration of data from solar system exploration spacecraft and ground based and orbiting observatories and laboratories. The Science Lab Module (SLM) of the Space Station orbiting complex may provide an ideal setting in which to perform certain classes of experiments which form the cornerstone of exobiology research. These experiments could demonstrate the pathways and processes by which biomolecules are synthesized under conditions that simulate the primitive Earth, planetary atmospheres, cometary ices, and interstellar dust grains. Exobiology experiments proposed for the Space Station generally fall into four classes: interactions among gases and grains (nucleation, accretion, gas-grain reactions), high energy chemistry for the production of biomolecules, physical and chemical processes occurring on an artificial comet, and tests of the theory of panspermia.

Griffiths, L. D.↗

NASA NTRS1987

Exobiology experiment concepts for Space Station

The exobiology discipline uses ground based and space flight resources to conduct a multidiscipline research effort dedicated to understanding fundamental questions about the origin, evolution, and distribution of life and life related molecules throughout the universe. Achievement of this understanding requires a methodical research strategy which traces the history of the biogenic elements from their origins in stellar formation processes through the chemical evolution of molecules essential for life to the origin and evolution of primitive and, ultimately, complex living species. Implementation of this strategy requires the collection and integration of data from solar system exploration spacecraft and ground based and orbiting observatories and laboratories. The Science Lab Module (SLM) of the Space Station orbiting complex may provide an ideal setting in which to perform certain classes of experiments which form the cornerstone of exobiology research. These experiments could demonstrate the pathways and processes by which biomolecules are synthesized under conditions that stimulate the primitive earth, planetary atmospheres, cometary ices, and interstellar dust grains. Exobiology experiments proposed for the Space Station generally fall into four classes: interactions among gases and grains (nucleation, accretion, gas-grain reactions), high energy chemistry for the production of biomolecules, physical and chemical processes occurring on an artificial comet, and tests of the theory of panspermia.

Griffiths, Lynn D.↗

NASA NTRS1997

Workshop on Parent-Body and Nebular Modification of Chondritic Materials

Topics considered include: thermal Metamorphosed Antarctic CM and CI Carbonaceous Chondrites in Japanese Collections, and Transformation Processes of Phyllosilicates; use of Oxygen Isotopes to Constrain the Nebular and Asteroidal Modification of Chondritic Materials; effect of Revised Nebular Water Distribution on Enstatite Chondrite Formation; interstellar Hydroxyls in Meteoritic Chondrules: Implications for the Origin of Water in the Inner Solar System; theoretical Models and Experimental Studies of Gas-Grain Chemistry in the Solar Nebula; chemical Alteration of Chondrules on Parent Bodies; thermal Quenching of Silicate Grains in Protostellar Sources; an Experimental Study of Magnetite Formation in the Solar Nebula; the Kaidun Meteorite: Evidence for Pre- and Postaccretionary Aqueous Alteration; a Transmission Electron Microscope Study of the Matrix Mineralogy of the Leoville CV3 (Reduced-Group) Carbonaceous Chondrite: Nebular and Parent-Body Features; rubidium-Strontium Isotopic Systematic of Chondrules from the Antarctic CV Chondrites Yamato 86751 and Yamato 86009: Additional Evidence for Late Parent-Body Modification; oxygen-Fugacity Indicators in Carbonaceous Chondrites: Parent-Body Alteration or High-Temperature Nebular Oxidation; thermodynamic Modeling of Aqueous Alteration in CV Chondrites; asteroidal Modification of C and O Chondrites: Myths and Models; oxygen Fugacity in the Solar Nebular; and the History of Metal and Sulfides in Chondrites.

Zolensky, M. E.↗

NASA NTRS2004

Study of Elongated Superbubble around CYG OB1

OB association superbubbles and supernova remnants are believed to be the primary sources of the hot component of the interstellar medium. Super- bubbles are also thought to "blow out" of the galactic plane and are thus the potential source of galactic coronal gas. Quantifying the energetics and accurately modeling the evolution of superbubbles is thus an important task in the understanding of the evolution of our Galaxy. The superbubble surrounding the Cyg OB1 association is an excellent example for study of the early stages of superbubble evolution. This superbubble, discovered in IRAS data, is an elongated structure 2 x 5 degrees (26 x 65 pc at distance=1.5 kpc), with at least 2 known supernova remnants believed to be associated with the superbubble. The elongated shape is more extended than can be explained by differential galactic rotation. A major problem in understanding the evolution of the Cyg OB1 superbubble is the discrepancy between the age of the superbubble and the derived age of the parent star association. The superbubble is believed to be no more than 1 Myr old, while the association is about 4-5 Myr old.

Sonneborn, George↗

NASA NTRS2012

The Galactic Centre Mini-Spiral in the MM-Regime

Context: The mini-spiral is a feature of the interstellar medium in the central approx.2 pc of the Galactic center. It is composed of several streamers of dust and ionised and atomic gas with temperatures between a few 100 K to 10(exp 4) K. There is evidence that these streamers are related to the so-called circumnuclear disk of molecular gas and are ionized by photons from massive, hot stars in the central parsec. Aims: We attempt to constrain the emission mechanisms and physical properties of the ionized gas and dust of the mini-spiral region with the help of our multiwavelength data sets. Methods: Our observations were carried out at 1.3 mm and 3 mm with the mm interferometric array CARMA in California in March and April 2009, with the MIR instrument VISIR at ESO's VLT in June 2006, and the NIR Bry with VLT NACO in August 2009. Results: We present high resolution maps of the mini-spiral, and obtain a spectral index of 0.5 +/- 0.25 for Sgr A *, indicating an inverted synchrotron spectrum. We find electron densities within the range 0.8-1.5 x 10(exp 4)/cu cm for the mini-spiral from the radio continuum maps, along with a dust mass contribution of approx. 0.25 Mo from the MIR dust continuum. and extinctions ranging from 1.8-3 at 2.16 microns in the Bry line. Conclusions: We observe a mixture of negative and positive spectral indices in our 1.3 mm and 3 mm observations of the extended emission of the mini-spiral, which we interpret as evidence that there are a range of contributions to the thermal free-free emission by the ionized gas emission and by dust at 1.3 mm.

Kunneriath, D.↗

DOE OSTI2016

IONIZATION AND DUST CHARGING IN PROTOPLANETARY DISKS

Ionization–recombination balance in dense interstellar and circumstellar environments is a key factor for a variety of important physical processes, such as chemical reactions, dust charging and coagulation, coupling of the gas with magnetic field, and development of instabilities in protoplanetary disks. We determine a critical gas density above which the recombination of electrons and ions on the grain surface dominates over the gas-phase recombination. For this regime, we present a self-consistent analytical model, which allows us to calculate exactly the abundances of charged species in dusty gas, without making assumptions on the grain charge distribution. To demonstrate the importance of the proposed approach, we check whether the conventional approximation of low grain charges is valid for typical protoplanetary disks, and discuss the implications for dust coagulation and development of the “dead zone” in the disk. The presented model is applicable for arbitrary grain-size distributions and, for given dust properties and conditions of the disk, has only one free parameter—the effective mass of the ions, shown to have a small effect on the results. The model can be easily included in numerical simulations following the dust evolution in dense molecular clouds and protoplanetary disks.

79 ASTRONOMY AND ASTROPHYSICS↗