Volcanic explosion clouds - Density, temperature, and particle content estimates from cloud motion

NASA Technical Reports Server (NTRS)

Wilson, L.; Self, S.

1980-01-01

Photographic records of 10 vulcanian eruption clouds produced during the 1978 eruption of Fuego Volcano in Guatemala have been analyzed to determine cloud velocity and acceleration at successive stages of expansion. Cloud motion is controlled by air drag (dominant during early, high-speed motion) and buoyancy (dominant during late motion when the cloud is convecting slowly). Cloud densities in the range 0.6 to 1.2 times that of the surrounding atmosphere were obtained by fitting equations of motion for two common cloud shapes (spheres and vertical cylinders) to the observed motions. Analysis of the heat budget of a cloud permits an estimate of cloud temperature and particle weight fraction to be made from the density. Model results suggest that clouds generally reached temperatures within 10 K of that of the surrounding air within 10 seconds of formation and that dense particle weight fractions were less than 2% by this time. The maximum sizes of dense particles supported by motion in the convecting clouds range from 140 to 1700 microns.

Theory of droplet. Part 1: Renormalized laws of droplet vaporization in non-dilute sprays

NASA Technical Reports Server (NTRS)

Chiu, H. H.

1989-01-01

The vaporization of a droplet, interacting with its neighbors in a non-dilute spray environment is examined as well as a vaporization scaling law established on the basis of a recently developed theory of renormalized droplet. The interacting droplet consists of a centrally located droplet and its vapor bubble which is surrounded by a cloud of droplets. The distribution of the droplets and the size of the cloud are characterized by a pair-distribution function. The vaporization of a droplet is retarded by the collective thermal quenching, the vapor concentration accumulated in the outer sphere, and by the limited percolative passages for mass, momentum and energy fluxes. The retardation is scaled by the local collective interaction parameters (group combustion number of renormalized droplet, droplet spacing, renormalization number and local ambient conditions). The numerical results of a selected case study reveal that the vaporization correction factor falls from unity monotonically as the group combustion number increases, and saturation is likely to occur when the group combustion number reaches 35 to 40 with interdroplet spacing of 7.5 diameters and an environment temperature of 500 K. The scaling law suggests that dense sprays can be classified into: (1) a diffusively dense cloud characterized by uniform thermal quenching in the cloud; (2) a stratified dense cloud characterized by a radial stratification in temperature by the differential thermal quenching of the cloud; or (3) a sharply dense cloud marked by fine structure in the quasi-droplet cloud and the corresponding variation in the correction factor due to the variation in the topological structure of the cloud characterized by a pair-distribution function of quasi-droplets.

The Green Bank Ammonia Survey: Dense Cores under Pressure in Orion A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, Helen; Di Francesco, James; Friesen, Rachel K.

We use data on gas temperature and velocity dispersion from the Green Bank Ammonia Survey and core masses and sizes from the James Clerk Maxwell Telescope Gould Belt Survey to estimate the virial states of dense cores within the Orion A molecular cloud. Surprisingly, we find that almost none of the dense cores are sufficiently massive to be bound when considering only the balance between self-gravity and the thermal and non-thermal motions present in the dense gas. Including the additional pressure binding imposed by the weight of the ambient molecular cloud material and additional smaller pressure terms, however, suggests thatmore » most of the dense cores are pressure-confined.« less

The Green Bank Ammonia Survey: Dense Cores under Pressure in Orion A

NASA Astrophysics Data System (ADS)

Kirk, Helen; Friesen, Rachel K.; Pineda, Jaime E.; Rosolowsky, Erik; Offner, Stella S. R.; Matzner, Christopher D.; Myers, Philip C.; Di Francesco, James; Caselli, Paola; Alves, Felipe O.; Chacón-Tanarro, Ana; Chen, How-Huan; Chun-Yuan Chen, Michael; Keown, Jared; Punanova, Anna; Seo, Young Min; Shirley, Yancy; Ginsburg, Adam; Hall, Christine; Singh, Ayushi; Arce, Héctor G.; Goodman, Alyssa A.; Martin, Peter; Redaelli, Elena

2017-09-01

We use data on gas temperature and velocity dispersion from the Green Bank Ammonia Survey and core masses and sizes from the James Clerk Maxwell Telescope Gould Belt Survey to estimate the virial states of dense cores within the Orion A molecular cloud. Surprisingly, we find that almost none of the dense cores are sufficiently massive to be bound when considering only the balance between self-gravity and the thermal and non-thermal motions present in the dense gas. Including the additional pressure binding imposed by the weight of the ambient molecular cloud material and additional smaller pressure terms, however, suggests that most of the dense cores are pressure-confined.

A New Unsteady Model for Dense Cloud Cavitation in Cryogenic Fluids

NASA Technical Reports Server (NTRS)

Hosangadi, A.; Ahuja, V.

2005-01-01

A new unsteady, cavitation model is presented wherein the phase change process (bubble growth/collapse) is coupled to the acoustic field in a cryogenic fluid. It predicts the number density and radius of bubbles in vapor clouds by tracking both the aggregate surface area and volume fraction of the cloud. Hence, formulations for the dynamics of individual bubbles (e.g. Rayleigh-Plesset equation) may be integrated within the macroscopic context of a dense vapor cloud i.e. a cloud that occupies a significant fraction of available volume and contains numerous bubbles. This formulation has been implemented within the CRUNCH CFD, which has a compressible real fluid formulation, a multi-element, unstructured grid framework, and has been validated extensively for liquid rocket turbopump inducers. Detailed unsteady simulations of a cavitating ogive in liquid nitrogen are presented where time-averaged mean cavity pressure and temperature depressions due to cavitation are compared with experimental data. The model also provides the spatial and temporal history of the bubble size distribution in the vapor clouds that are shed, an important physical parameter that is difficult to measure experimentally and is a significant advancement in the modeling of dense cloud cavitation.

Carbon chemistry in dense molecular clouds: Theory and observational constraints

NASA Technical Reports Server (NTRS)

Blake, Geoffrey A.

1990-01-01

For the most part, gas phase models of the chemistry of dense molecular clouds predict the abundances of simple species rather well. However, for larger molecules and even for small systems rich in carbon these models often fail spectacularly. Researchers present a brief review of the basic assumptions and results of large scale modeling of the carbon chemistry in dense molecular clouds. Particular attention is to the influence of the gas phase C/O ratio in molecular clouds, and the likely role grains play in maintaining this ratio as clouds evolve from initially diffuse objects to denser cores with associated stellar and planetary formation. Recent spectral line surveys at centimeter and millimeter wavelengths along with selected observations in the submillimeter have now produced an accurate inventory of the gas phase carbon budget in several different types of molecular clouds, though gaps in our knowledge clearly remain. The constraints these observations place on theoretical models of interstellar chemistry can be used to gain insights into why the models fail, and show also which neglected processes must be included in more complete analyses. Looking toward the future, larger molecules are especially difficult to study both experimentally and theoretically in such dense, cold regions, and some new methods are therefore outlined which may ultimately push the detectability of small carbon chains and rings to much heavier species.

Dense solar wind cloud geometries deduced from comparisons of radio signal delay and in situ plasma measurements

NASA Technical Reports Server (NTRS)

Landt, J. A.

1974-01-01

The geometries of dense solar wind clouds are estimated by comparing single-location measurements of the solar wind plasma with the average of the electron density obtained by radio signal delay measurements along a radio path between earth and interplanetary spacecraft. Several of these geometries agree with the current theoretical spatial models of flare-induced shock waves. A new class of spatially limited structures that contain regions with densities greater than any observed in the broad clouds is identified. The extent of a cloud was found to be approximately inversely proportional to its density.

On the star-forming ability of Molecular Clouds

NASA Astrophysics Data System (ADS)

Anathpindika, S.; Burkert, A.; Kuiper, R.

2018-02-01

The star-forming ability of a molecular cloud depends on the fraction of gas it can cycle into the dense-phase. Consequently, one of the crucial questions in reconciling star formation in clouds is to understand the factors that control this process. While it is widely accepted that the variation in ambient conditions can alter significantly the ability of a cloud to spawn stars, the observed variation in the star-formation rate in nearby clouds that experience similar ambient conditions, presents an interesting question. In this work, we attempted to reconcile this variation within the paradigm of colliding flows. To this end we develop self-gravitating, hydrodynamic realizations of identical flows, but allowed to collide off-centre. Typical observational diagnostics such as the gas-velocity dispersion, the fraction of dense-gas, the column density distribution (N-PDF), the distribution of gas mass as a function of K-band extinction and the strength of compressional/solenoidal modes in the post-collision cloud were deduced for different choices of the impact parameter of collision. We find that a strongly sheared cloud is terribly inefficient in cycling gas into the dense phase and that such a cloud can possibly reconcile the sluggish nature of star formation reported for some clouds. Within the paradigm of cloud formation via colliding flows this is possible in case of flows colliding with a relatively large impact parameter. We conclude that compressional modes - though probably essential - are insufficient to ensure a relatively higher star-formation efficiency in a cloud.

Dense gas and star formation in individual Giant Molecular Clouds in M31

NASA Astrophysics Data System (ADS)

Viaene, S.; Forbrich, J.; Fritz, J.

2018-04-01

Studies both of entire galaxies and of local Galactic star formation indicate a dependency of a molecular cloud's star formation rate (SFR) on its dense gas mass. In external galaxies, such measurements are derived from HCN(1-0) observations, usually encompassing many Giant Molecular Clouds (GMCs) at once. The Andromeda galaxy (M31) is a unique laboratory to study the relation of the SFR and HCN emission down to GMC scales at solar-like metallicities. In this work, we correlate our composite SFR determinations with archival HCN, HCO+, and CO observations, resulting in a sample of nine reasonably representative GMCs. We find that, at the scale of individual clouds, it is important to take into account both obscured and unobscured star formation to determine the SFR. When correlated against the dense-gas mass from HCN, we find that the SFR is low, in spite of these refinements. We nevertheless retrieve an SFR-dense-gas mass correlation, confirming that these SFR tracers are still meaningful on GMC scales. The correlation improves markedly when we consider the HCN/CO ratio instead of HCN by itself. This nominally indicates a dependency of the SFR on the dense-gas fraction, in contradiction to local studies. However, we hypothesize that this partly reflects the limited dynamic range in dense-gas mass, and partly that the ratio of single-pointing HCN and CO measurements may be less prone to systematics like sidelobes. In this case, the HCN/CO ratio would importantly be a better empirical measure of the dense-gas content itself.

Filtering Photogrammetric Point Clouds Using Standard LIDAR Filters Towards DTM Generation

NASA Astrophysics Data System (ADS)

Zhang, Z.; Gerke, M.; Vosselman, G.; Yang, M. Y.

2018-05-01

Digital Terrain Models (DTMs) can be generated from point clouds acquired by laser scanning or photogrammetric dense matching. During the last two decades, much effort has been paid to developing robust filtering algorithms for the airborne laser scanning (ALS) data. With the point cloud quality from dense image matching (DIM) getting better and better, the research question that arises is whether those standard Lidar filters can be used to filter photogrammetric point clouds as well. Experiments are implemented to filter two dense matching point clouds with different noise levels. Results show that the standard Lidar filter is robust to random noise. However, artefacts and blunders in the DIM points often appear due to low contrast or poor texture in the images. Filtering will be erroneous in these locations. Filtering the DIM points pre-processed by a ranking filter will bring higher Type II error (i.e. non-ground points actually labelled as ground points) but much lower Type I error (i.e. bare ground points labelled as non-ground points). Finally, the potential DTM accuracy that can be achieved by DIM points is evaluated. Two DIM point clouds derived by Pix4Dmapper and SURE are compared. On grassland dense matching generates points higher than the true terrain surface, which will result in incorrectly elevated DTMs. The application of the ranking filter leads to a reduced bias in the DTM height, but a slightly increased noise level.

Vertical variation of ice particle size in convective cloud tops.

PubMed

van Diedenhoven, Bastiaan; Fridlind, Ann M; Cairns, Brian; Ackerman, Andrew S; Yorks, John E

2016-05-16

A novel technique is used to estimate derivatives of ice effective radius with respect to height near convective cloud tops ( dr e / dz ) from airborne shortwave reflectance measurements and lidar. Values of dr e / dz are about -6 μ m/km for cloud tops below the homogeneous freezing level, increasing to near 0 μ m/km above the estimated level of neutral buoyancy. Retrieved dr e / dz compares well with previously documented remote sensing and in situ estimates. Effective radii decrease with increasing cloud top height, while cloud top extinction increases. This is consistent with weaker size sorting in high, dense cloud tops above the level of neutral buoyancy where fewer large particles are present, and with stronger size sorting in lower cloud tops that are less dense. The results also confirm that cloud-top trends of effective radius can generally be used as surrogates for trends with height within convective cloud tops. These results provide valuable observational targets for model evaluation.

Vertical Variation of Ice Particle Size in Convective Cloud Tops

NASA Technical Reports Server (NTRS)

Van Diedenhoven, Bastiaan; Fridlind, Ann M.; Cairns, Brian; Ackerman, Andrew S.; Yorks, John E.

2016-01-01

A novel technique is used to estimate derivatives of ice effective radius with respect to height near convective cloud tops (dr(sub e)/dz) from airborne shortwave reflectance measurements and lidar. Values of dr(sub e)/dz are about -6 micrometer/km for cloud tops below the homogeneous freezing level, increasing to near 0 micrometer/km above the estimated level of neutral buoyancy. Retrieved dr(sub e)/dz compares well with previously documented remote sensing and in situ estimates. Effective radii decrease with increasing cloud top height, while cloud top extinction increases. This is consistent with weaker size sorting in high, dense cloud tops above the level of neutral buoyancy where fewer large particles are present and with stronger size sorting in lower cloud tops that are less dense. The results also confirm that cloud top trends of effective radius can generally be used as surrogates for trends with height within convective cloud tops. These results provide valuable observational targets for model evaluation.

A cloud collision model for water maser excitation.

PubMed

Tarter, J C; Welch, W J

1986-06-01

High-velocity collisions between small, dense, neutral clouds or between a dense cloud and a dense shell can provide the energy source required to excite H2O maser emission. The radiative precursor from the surface of the collisional shock front rapidly diffuses through the cloud, heating the dust grains but leaving the H2 molecules cool. Transient maser emission occurs as the conditions for the Goldreich and Kwan "hot-dust cold-gas" maser pump scheme are realized locally within the cloud. In time the local maser action quenches due to the heating of the H2 molecules by collisions against the grains. Although this model cannot explain the very long-lived steady maser features, it is quite successful in explaining a number of the observed properties of the high-velocity features in such sources as Orion, W51, and W49. In particular, it provides a natural explanation for the rapid time variations, the narrow line widths, juxtaposition of high- and low-velocity features, and the short lifetimes which are frequently observed for the so-called high-velocity maser "bullets" thought to be accelerated by strong stellar winds.

Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM.

PubMed

Rubio, Monica; Elmegreen, Bruce G; Hunter, Deidre A; Brinks, Elias; Cortés, Juan R; Cigan, Phil

2015-09-10

Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations they are molecular, with H2 the dominant species and carbon monoxide (CO) the best available tracer. When the abundances of carbon and oxygen are low compared with that of hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies, CO forms slowly and is easily destroyed, so it is difficult for it to accumulate inside dense clouds. Here we report interferometric observations of CO clouds in the local group dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM), which has a metallicity that is 13 per cent of the solar value and 50 per cent lower than the previous CO detection threshold. The clouds are tiny compared to the surrounding atomic and H2 envelopes, but they have typical densities and column densities for CO clouds in the Milky Way. The normal CO density explains why star clusters forming in dwarf irregulars have similar densities to star clusters in giant spiral galaxies. The low cloud masses suggest that these clusters will also be low mass, unless some galaxy-scale compression occurs, such as an impact from a cosmic cloud or other galaxy. If the massive metal-poor globular clusters in the halo of the Milky Way formed in dwarf galaxies, as is commonly believed, then they were probably triggered by such an impact.

A physics-based model for the ionization of samarium by the MOSC chemical releases in the upper atmosphere

NASA Astrophysics Data System (ADS)

Bernhardt, Paul A.; Siefring, Carl L.; Briczinski, Stanley J.; Viggiano, Albert; Caton, Ronald G.; Pedersen, Todd R.; Holmes, Jeffrey M.; Ard, Shaun; Shuman, Nicholas; Groves, Keith M.

2017-05-01

Atomic samarium has been injected into the neutral atmosphere for production of electron clouds that modify the ionosphere. These electron clouds may be used as high-frequency radio wave reflectors or for control of the electrodynamics of the F region. A self-consistent model for the photochemical reactions of Samarium vapor cloud released into the upper atmosphere has been developed and compared with the Metal Oxide Space Cloud (MOSC) experimental observations. The release initially produces a dense plasma cloud that that is rapidly reduced by dissociative recombination and diffusive expansion. The spectral emissions from the release cover the ultraviolet to the near infrared band with contributions from solar fluorescence of the atomic, molecular, and ionized components of the artificial density cloud. Barium releases in sunlight are more efficient than Samarium releases in sunlight for production of dense ionization clouds. Samarium may be of interest for nighttime releases but the artificial electron cloud is limited by recombination with the samarium oxide ion.

Empirical relationships between gas abundances and UV selective extinction

NASA Technical Reports Server (NTRS)

Joseph, Charles L.

1990-01-01

Several studies of gas-phase abundances in lines of sight through the outer edges of dense clouds are summarized. These lines of sight have 0.4 less than E(B-V) less than 1.1 and have inferred spatial densities of a few hundred cm(-3). The primary thrust of these studies has been to compare gaseous abundances in interstellar clouds that have various types of peculiar selective extinction. To date, the most notable result has been an empirical relationship between the CN/Fe I abundance ratio and the depth of the 2200 A extinction bump. It is not clear at the present time, however, whether these two parameters are linearly correlated or the data are organized into two discrete ensembles. Based on 19 samples and assuming the clouds form discrete ensembles, lines of sight that have a CN/Fe I abundance ratio greater than 0.3 (dex) appear to have a shallow 2.57 plus or minus 0.55 bump compared to 3.60 plus or minus 0.36 for other dense clouds and compared to the 3.6 Seaton (1979) average. The difference in the strength of the extinction bump between these two ensembles is 1.03 plus or minus 0.23. Although a high-resolution IUE survey of dense clouds is far from complete, the few lines of sight with shallow extinction bumps all show preferential depletion of certain elements, while those lines of sight with normal 2200 A bumps do not. Ca II, Cr II, and Mn II appear to exhibit the strongest preferential depletion compared to S II, P II, and Mg II. Fe II and Si II depletions also appear to be enhanced somewhat in the shallow-bump lines of sight. It should be noted that Copernicus data suggest all elements, including the so-called nondepletors, deplete in diffuse clouds (Snow and Jenkins 1980, Joseph 1988). Those lines of sight through dense clouds that have normal 2200 A extinction bumps appear to be extensions of the depletions found in the diffuse interstellar medium. That is, the overall level of depletion is enhanced, but the element-to-element abundances are similar to those in diffuse clouds. In a separate study, the abundances of neutral atoms were studied in a dense cloud having a shallow 2200 A bump and in one with a normal strength bump.

Grain Growth and Silicates in Dense Clouds

NASA Technical Reports Server (NTRS)

Pendeleton, Yvonne J.; Chiar, J. E.; Ennico, K.; Boogert, A.; Greene, T.; Knez, C.; Lada, C.; Roellig, T.; Tielens, A.; Werner, M.;

Cosmic-ray ionisation of dense molecular clouds

NASA Astrophysics Data System (ADS)

Vaupre, Solenn

2015-07-01

Cosmic rays (CR) are of tremendous importance in the dynamical and chemical evolution of interstellar molecular clouds, where stars and planets form. CRs are likely accelerated in the shells of supernova remnants (SNR), thus molecular clouds nearby can be irradiated by intense fluxes of CRs. CR protons have two major effects on dense molecular clouds: 1) when they encounter the dense medium, high-energy protons (>280 MeV) create pions that decay into gamma-rays. This process makes SNR-molecular cloud associations intense GeV and/or TeV sources whose spectra mimic the CR spectrum. 2) at lower energies, CRs penetrate the cloud and ionise the gas, leading to the formation of molecular species characteristic of the presence of CRs, called tracers of the ionisation. Studying these tracers gives information on low-energy CRs that are unaccessible to any other observations. I studied the CR ionisation of molecular clouds next to three SNRs: W28, W51C and W44. These SNRs are known to be interacting with the nearby clouds, from the presence of shocked gas, OH masers and pion-decay induced gamma-ray emission. My work includes millimeter observations and chemical modeling of tracers of the ionisation in these dense molecular clouds. In these three regions, we determined an enhanced CR ionisation rate, supporting the hypothesis of an origin of the CRs in the SNR nearby. The evolution of the CR ionisation rate with the distance to the SNR brings valuable constraints on the propagation properties of low-energy CRs. The method used relies on observations of the molecular ions HCO+ and DCO+, which shows crucial limitations at high ionisation. Therefore, I investigated, both through modeling and observations, the chemical abundances of several other species to try and identity alternative tracers of the ionisation. In particular, in the W44 region, observations of N2H+ bring additional constraints on the physical conditions, volatile abundances in the cloud, and the ionisation state. This research brought valuable insight in to the CR induced chemistry in the interstellar medium. It also brought new perspectives of interdisciplinary research towards the understanding of CRs, from millimeter to gamma-ray observations.

Ultrafast Outflows: Galaxy-scale Active Galactic Nucleus Feedback

NASA Astrophysics Data System (ADS)

Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

2013-01-01

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, A. Y.; Umemura, M.; Bicknell, G. V., E-mail: ayw@ccs.tsukuba.ac.jp

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves inmore » the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.« less

Structures of GMC W 37

NASA Astrophysics Data System (ADS)

Zhan, Xiao-Liang; Jiang, Zhi-Bo; Chen, Zhi-Wei; Zhang, Miao-Miao; Song, Chao

2016-04-01

We carried out observations toward the giant molecular cloud W 37 with the J = 1 - 0 transitions of 12CO, 13CO and C18O using the 13.7m single-dish telescope at the Delingha station of Purple Mountain Observatory. Based on these CO lines, we calculated the column densities and cloud masses for molecular clouds with radial velocities around +20 km s-1. The gas mass of W 37, calculated from 13 CO emission, is 1.7 × 105 M⊙, above the criterion to be considered a giant molecular cloud. The dense ridge of W 37 is a dense filament, which is supercritical in terms of linear mass ratio. Dense clumps found by C18O emission are aligned along the dense ridge at regular intervals of about 2.8 pc, similar to the clump separation caused by large-scale ‘sausage instability’. We confirm the identification of the giant molecular filament (GMF) G 18.0-16.8 and find a new giant filament, G 16.5-15.8, located ˜ 0.7° to the west of G 18.0-16.8. Both GMFs are not gravitationally bound, as indicated by their low linear mass ratio (˜ 80 M⊙ pc-1). We compared the gas temperature map with the dust temperature map from Herschel images, and found similar structures. The spatial distributions of class I objects and the dense clumps are reminiscent of triggered star formation occurring in the northwestern part of W 37, which is close to NGC 6611.

Cosmic vacuum and galaxy formation

NASA Astrophysics Data System (ADS)

Chernin, A. D.

2006-04-01

It is demonstrated that the protogalactic perturbations must enter the nonlinear regime before the red shift z≈ 1; otherwise they would be destroyed by the antigravity of the vacuum dark energy at the subsequent epoch of the vacuum domination. At the zrrV={M/[(8π/3)ρV]}1/3, where M is the mass of a given over-density and ρV is the vacuum density. The criterion provides a new relation between the largest mass condensations and their spatial scales. All the real large-scale systems follow this relation definitely. It is also shown that a simple formula is possible for the key quantity in the theory of galaxy formation, namely the initial amplitude of the perturbation of the gravitational potential in the protogalactic structures. The amplitude is time independent and given in terms of the Friedmann integrals, which are genuine physical characteristics of the cosmic energies. The results suggest that there is a strong correspondence between the global design of the Universe as a whole and the cosmic structures of various masses and spatial scales.

Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves.

PubMed

Gregori, G; Ravasio, A; Murphy, C D; Schaar, K; Baird, A; Bell, A R; Benuzzi-Mounaix, A; Bingham, R; Constantin, C; Drake, R P; Edwards, M; Everson, E T; Gregory, C D; Kuramitsu, Y; Lau, W; Mithen, J; Niemann, C; Park, H-S; Remington, B A; Reville, B; Robinson, A P L; Ryutov, D D; Sakawa, Y; Yang, S; Woolsey, N C; Koenig, M; Miniati, F

2012-01-25

The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations. Although other mechanisms may also operate, currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about 10(-21) gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations, astrophysical environments can effectively be reproduced in the laboratory. Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields sufficiently to affect galaxy evolution.

Giant molecular cloud collisions as triggers of star formation. VI. Collision-induced turbulence

NASA Astrophysics Data System (ADS)

Wu, Benjamin; Tan, Jonathan C.; Nakamura, Fumitaka; Christie, Duncan; Li, Qi

2018-05-01

We investigate collisions between giant molecular clouds (GMCs) as potential generators of their internal turbulence. Using magnetohydrodynamic (MHD) simulations of self-gravitating, magnetized, turbulent GMCs, we compare kinematic and dynamic properties of dense gas structures formed when such clouds collide compared to those that form in non-colliding clouds as self-gravity overwhelms decaying turbulence. We explore the nature of turbulence in these structures via distribution functions of density, velocity dispersions, virial parameters, and momentum injection. We find that the dense clumps formed from GMC collisions have higher effective Mach number, greater overall velocity dispersions, sustain near-virial equilibrium states for longer times, and are the conduit for the injection of turbulent momentum into high density gas at high rates.

Giant molecular cloud collisions as triggers of star formation. VI. Collision-induced turbulence

NASA Astrophysics Data System (ADS)

Wu, Benjamin; Tan, Jonathan C.; Nakamura, Fumitaka; Christie, Duncan; Li, Qi

2018-01-01

We investigate collisions between giant molecular clouds (GMCs) as potential generators of their internal turbulence. Using magnetohydrodynamic (MHD) simulations of self-gravitating, magnetized, turbulent GMCs, we compare kinematic and dynamic properties of dense gas structures formed when such clouds collide compared to those that form in non-colliding clouds as self-gravity overwhelms decaying turbulence. We explore the nature of turbulence in these structures via distribution functions of density, velocity dispersions, virial parameters, and momentum injection. We find that the dense clumps formed from GMC collisions have higher effective Mach number, greater overall velocity dispersions, sustain near-virial equilibrium states for longer times, and are the conduit for the injection of turbulent momentum into high density gas at high rates.

Chemistry in dynamically evolving clouds

NASA Technical Reports Server (NTRS)

Tarafdar, S. P.; Prasad, S. S.; Huntress, W. T., Jr.; Villere, K. R.; Black, D. C.

1985-01-01

A unified model of chemical and dynamical evolution of isolated, initially diffuse and quiescent interstellar clouds is presented. The model uses a semiempirically derived dependence of the observed cloud temperatures on the visual extinction and density. Even low-mass, low-density, diffuse clouds can collapse in this model, because the inward pressure gradient force assists gravitational contraction. In contrast, previous isothermal collapse models required the low-mass diffuse clouds to be unrealistically cold before gravitational contraction could start. Theoretically predicted dependences of the column densities of various atoms and molecules, such as C and CO, on visual extinction in diffuse clouds are in accord with observations. Similarly, the predicted dependences of the fractional abundances of various chemical species (e.g., CO, H2CO, HCN, HCO(+)) on the total hydrogen density in the core of the dense clouds also agree with observations reported to date in the literature. Compared with previous models of interstellar chemistry, the present model has the potential to explain the wide spectrum of chemical and physical properties of both diffuse and dense clouds with a common formalism employing only a few simple initial conditions.

ORIGINS OF SCATTER IN THE RELATIONSHIP BETWEEN HCN 1-0 AND DENSE GAS MASS IN THE GALACTIC CENTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mills, Elisabeth A. C.; Battersby, Cara, E-mail: elisabeth.mills@sjsu.edu

We investigate the correlation of HCN 1-0 with gas mass in the central 300 pc of the Galaxy. We find that on the ∼10 pc size scale of individual cloud cores, HCN 1-0 is well correlated with dense gas mass when plotted as a log–log relationship. There is ∼0.75 dex of scatter in this relationship from clouds like Sgr B2, which has an integrated HCN 1-0 intensity of a cloud less than half its mass, and others that have HCN 1-0 enhanced by a factor of 2–3 relative to clouds of comparable mass. We identify the two primary sources ofmore » scatter to be self-absorption and variations in HCN abundance. We also find that the extended HCN 1-0 emission is more intense per unit mass than in individual cloud cores. In fact the majority (80%) of HCN 1-0 emission comes from extended gas with column densities below 7 × 10{sup 22} cm{sup −2}, accounting for 68% of the total mass. We find variations in the brightness of HCN 1-0 would only yield a ∼10% error in the dense gas mass inferred from this line in the Galactic center. However, the observed order of magnitude HCN abundance variations, and the systematic nature of these variations, warn of potential biases in the use of HCN as dense gas mass tracer in more extreme environments such as an active galactic nucleus and shock-dominated regions. We also investigate other 3 mm tracers, finding that HNCO is better correlated with mass than HCN, and might be a better tracer of cloud mass in this environment.« less

Cosmological magnetic fields from inflation in extended electromagnetism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beltran Jimenez, Jose; Maroto, Antonio L.

2011-01-15

In this work we consider an extended electromagnetic theory in which the scalar state which is usually eliminated by means of the Lorenz condition is allowed to propagate. This state has been shown to generate a small cosmological constant in the context of standard inflationary cosmology. Here we show that the usual Lorenz gauge-breaking term now plays the role of an effective electromagnetic current. Such a current is generated during inflation from quantum fluctuations and gives rise to a stochastic effective charge density distribution. Because of the high electric conductivity of the cosmic plasma after inflation, the electric charge densitymore » generates currents which give rise to both vorticity and magnetic fields on sub-Hubble scales. Present upper limits on vorticity coming from temperature anisotropies of the CMB are translated into lower limits on the present value of cosmic magnetic fields. We find that, for a nearly scale invariant vorticity spectrum, magnetic fields B{sub {lambda}>}10{sup -12} G are typically generated with coherence lengths ranging from subgalactic scales up to the present Hubble radius. Those fields could act as seeds for a galactic dynamo or even account for observations just by collapse and differential rotation of the protogalactic cloud.« less

The dense gas mass fraction of molecular clouds in the Milky Way

DOE Office of Scientific and Technical Information (OSTI.GOV)

Battisti, Andrew J.; Heyer, Mark H., E-mail: abattist@astro.umass.edu, E-mail: heyer@astro.umass.edu

2014-01-10

The mass fraction of dense gas within giant molecular clouds (GMCs) of the Milky Way is investigated using {sup 13}CO data from the Five College Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam Galactic Plane Survey (BGPS) of 1.1 mm dust continuum emission. A sample of 860 compact dust sources are selected from the BGPS catalog and kinematically linked to 344 clouds of extended (>3') {sup 13}CO J = 1-0 emission. Gas masses are tabulated for the full dust source and subregions within the dust sources with mass surface densities greater than 200 M {sub ☉} pc{sup –2}, whichmore » are assumed to be regions of enhanced volume density. Masses of the parent GMCs are calculated assuming optically thin {sup 13}CO J = 1-0 emission and local thermodynamic equilibrium conditions. The mean fractional mass of dust sources to host GMC mass is 0.11{sub −0.06}{sup +0.12}. The high column density subregions comprise 0.07{sub −0.05}{sup +0.13} of the mass of the cloud. Owing to our assumptions, these values are upper limits to the true mass fractions. The fractional mass of dense gas is independent of GMC mass and gas surface density. The low dense gas mass fraction suggests that the formation of dense structures within GMCs is the primary bottleneck for star formation. The distribution of velocity differences between the dense gas and the low density material along the line of sight is also examined. We find a strong, centrally peaked distribution centered on zero velocity displacement. This distribution of velocity differences is modeled with radially converging flows toward the dense gas position that are randomly oriented with respect to the observed line of sight. These models constrain the infall velocities to be 2-4 km s{sup –1} for various flow configurations.« less

Precombination Cloud Collapse and Baryonic Dark Matter

NASA Technical Reports Server (NTRS)

Hogan, Craig J.

1993-01-01

A simple spherical model of dense baryon clouds in the hot big bang 'strongly nonlinear primordial isocurvature baryon fluctuations' is reviewed and used to describe the dependence of cloud behavior on the model parameters, baryon mass, and initial over-density. Gravitational collapse of clouds before and during recombination is considered including radiation diffusion and trapping, remnant type and mass, and effects on linear large-scale fluctuation modes. Sufficiently dense clouds collapse early into black holes with a minimum mass of approx. 1 solar mass, which behave dynamically like collisionless cold dark matter. Clouds below a critical over-density, however, delay collapse until recombination, remaining until then dynamically coupled to the radiation like ordinary diffuse baryons, and possibly producing remnants of other kinds and lower mass. The mean density in either type of baryonic remnant is unconstrained by observed element abundances. However, mixed or unmixed spatial variations in abundance may survive in the diffuse baryon and produce observable departures from standard predictions.

Radio Spectroscopy Applied to a Search for Highly Redshifted Protogalactic Structure

NASA Astrophysics Data System (ADS)

Weintroub, Jonathan

1998-11-01

An experiment to detect proto-galactic structure at high redshift is described. We attempt to observe this in the 1420 MHz line from neutral atomic hydrogen in the redshift range 4.7<= z<5.5/ (219<ν<251 MHz). The expected signal is very weak and we need a large aperture and a very long integration time for a detection to be feasible. This is achieved by building a dedicated and specialized instrument, which allows the experiment to run continuously, in the background, at the largest single dish reflector in the world-the Arecibo radio-telescope. The motivation for the experiment is to provide an observational link between the very smooth conditions presumed to exist in the primordial universe, as confirmed by observations of the Cosmic Microwave Background (CMB) at z~1000, and the clumpy conditions that we observe locally in the hierarchy of galaxies, clusters and superclusters. The introduction includes a literature survey and an outline of relevant cosmological theory. A discussion of high-redshift astronomy, including past and current searches for protoclusters, is followed by a description of our approach to the problem. For simplicity a point feed is used to illuminate the spherical reflector at Arecibo. The design of the optics is discussed-based on this analysis and the radiative characteristics of neutral hydrogen gas we estimate that it is feasible to detect a 1014Msolar cloud in a long, though not unachievable, time span. A custom designed radioastronomy receiver backs up the feed system. It includes analog front-end amplifiers and filters, local oscillators and mixers, and an eight kilochannel hybrid spectrometer with 10 kHz spectral resolution over the survey band. We have written software to automatically reduce the large quantity of data gathered. Radio frequency interference (RFI) pervades our system, and analysis problems include the development of robust methods for co-adding data in the presence of time-varying RFI, and matched filtering to recognize candidate celestial signals in noisy data by their signature in time and frequency. Our sensitivity is limited by interference rather than thermal noise. The outcome of the experiment is negative, and we conclude by setting a limit on the mass of protoclusters in our search volume.

Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies

NASA Astrophysics Data System (ADS)

Kauffmann, Jens; Goldsmith, Paul F.; Melnick, Gary; Tolls, Volker; Guzman, Andres; Menten, Karl M.

2017-09-01

Trends observed in galaxies, such as the Gao & Solomon relation, suggest a linear relationship between the star formation rate and the mass of dense gas available for star formation. Validation of such trends requires the establishment of reliable methods to trace the dense gas in galaxies. One frequent assumption is that the HCN (J = 1-0) transition is unambiguously associated with gas at H2 densities ≫ 104 cm-3. If so, the mass of gas at densities ≫ 104 cm-3 could be inferred from the luminosity of this emission line, LHCN (1-0). Here we use observations of the Orion A molecular cloud to show that the HCN (J = 1-0) line traces much lower densities 103 cm-3 in cold sections of this molecular cloud, corresponding to visual extinctions AV ≈ 6 mag. We also find that cold and dense gas in a cloud like Orion produces too little HCN emission to explain LHCN (1-0) in star forming galaxies, suggesting that galaxies might contain a hitherto unknown source of HCN emission. In our sample of molecules observed at frequencies near 100 GHz (also including 12CO, 13CO, C18O, CN, and CCH), N2H+ is the only species clearly associated with relatively dense gas.

Optical and microphysical parameters of dense stratocumulus clouds during mission 206 of EUCREX '94 as retrieved from measurements made with the airborne lidar LEANDRE 1

NASA Astrophysics Data System (ADS)

Pelon, J.; Flamant, C.; Trouillet, V.; Flamant, P. H.

Cloud parameters derived from measurements performed with the airborne backscatter lidar LEANDRE 1 during mission 206 of the EUCREX '94 campaign are reported. A new method has been developed to retrieve the extinction coefficient at the top of the dense stratocumulus deck under scrutiny during this mission. The largest extinction values are found to be related to the highest cloud top altitude revealing the small-scale structure of vertical motions within the stratocumulus field. Cloud optical depth (COD) is estimated from extinction retrievals, as well as cloud top and cloud base altitude using nadir and zenith lidar observations, respectively. Lidar-derived CODs are compared with CODs deduced from radiometric measurements made onboard the French research aircraft Avion de Recherche Atmosphérique et de Télédétection (ARAT/F27). A fair agreement is obtained (within 20%) for COD's larger than 10. Our results show the potential of lidar measurements to analyze cloud properties at optical depths larger than 5.

H2D(+) observations give an age of at least one million years for a cloud core forming Sun-like stars.

PubMed

Brünken, Sandra; Sipilä, Olli; Chambers, Edward T; Harju, Jorma; Caselli, Paola; Asvany, Oskar; Honingh, Cornelia E; Kamiński, Tomasz; Menten, Karl M; Stutzki, Jürgen; Schlemmer, Stephan

2014-12-11

The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse, whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, H2, which decreases monotonically with age. This has been done for the dense cloud core L183, for which the deuterium fractionation of diazenylium (N2H(+)) was used as a chemical clock to infer that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-H2D(+) and para-H2D(+), have the most direct chemical connections to H2 (refs 8, 9, 10, 11, 12) and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-H2D(+) is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory, and recent progress in instrumentation technology. Here we report observations of ortho- and para-H2D(+) emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier N2H(+) work arises because that chemical clock turns off sooner than the H2D(+) clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years.

Toward Measuring Galactic Dense Molecular Gas Properties and 3D Distribution with Hi-GAL

NASA Astrophysics Data System (ADS)

Zetterlund, Erika; Glenn, Jason; Maloney, Phil

2016-01-01

The Herschel Space Observatory's submillimeter dust continuum survey Hi-GAL provides a powerful new dataset for characterizing the structure of the dense interstellar medium of the Milky Way. Hi-GAL observed a 2° wide strip covering the entire 360° of the Galactic plane in broad bands centered at 70, 160, 250, 350, and 500 μm, with angular resolution ranging from 10 to 40 arcseconds. We are adapting a molecular cloud clump-finding algorithm and a distance probability density function distance-determination method developed for the Bolocam Galactic Plane Survey (BGPS) to the Hi-GAL data. Using these methods we expect to generate a database of 105 cloud clumps, derive distance information for roughly half the clumps, and derive precise distances for approximately 20% of them. With five-color photometry and distances, we will measure the cloud clump properties, such as luminosities, physical sizes, and masses, and construct a three-dimensional map of the Milky Way's dense molecular gas distribution.The cloud clump properties and the dense gas distribution will provide critical ground truths for comparison to theoretical models of molecular cloud structure formation and galaxy evolution models that seek to emulate spiral galaxies. For example, such models cannot resolve star formation and use prescriptive recipes, such as converting a fixed fraction of interstellar gas to stars at a specified interstellar medium density threshold. The models should be compared to observed dense molecular gas properties and galactic distributions.As a pilot survey to refine the clump-finding and distance measurement algorithms developed for BGPS, we have identified molecular cloud clumps in six 2° × 2° patches of the Galactic plane, including one in the inner Galaxy along the line of sight through the Molecular Ring and the termination of the Galactic bar and one toward the outer Galaxy. Distances have been derived for the inner Galaxy clumps and compared to Bolocam Galactic Plane Survey results. We present the pilot survey clump catalog, distances, clump properties, and a comparison to BGPS.

Dense Regions in Supersonic Isothermal Turbulence

NASA Astrophysics Data System (ADS)

Robertson, Brant; Goldreich, Peter

2018-02-01

The properties of supersonic isothermal turbulence influence a variety of astrophysical phenomena, including the structure and evolution of star-forming clouds. This work presents a simple model for the structure of dense regions in turbulence in which the density distribution behind isothermal shocks originates from rough hydrostatic balance between the pressure gradient behind the shock and its deceleration from ram pressure applied by the background fluid. Using simulations of supersonic isothermal turbulence and idealized waves moving through a background medium, we show that the structural properties of dense, shocked regions broadly agree with our analytical model. Our work provides a new conceptual picture for describing the dense regions, which complements theoretical efforts to understand the bulk statistical properties of turbulence and attempts to model the more complex features of star-forming clouds like magnetic fields, self-gravity, or radiative properties.

Diamonds in dense molecular clouds - A challenge to the standard interstellar medium paradigm

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Sandford, S. A.; Tielens, A. G. G. M.; Herbst, T. M.

1993-01-01

Observations of a newly discovered infrared C-H stretching band indicate that interstellar diamond-like material appears to be characteristic of dense clouds. In sharp contrast, the spectral signature of dust in the diffuse interstellar medium is dominated by -CH2- and -CH3 groups. This dichotomy in the aliphatic organic component between the dense and diffuse media challenges standard assumptions about the processes occurring in, and interactions between, these two media. The ubiquity of this interstellar diamond-like material rules out models for meteoritic diamond formation in unusual circumstellar environments and implies that the formation of the diamond-like material is associated with common interstellar processes or stellar types.

Point Cloud Generation from Aerial Image Data Acquired by a Quadrocopter Type Micro Unmanned Aerial Vehicle and a Digital Still Camera

PubMed Central

Rosnell, Tomi; Honkavaara, Eija

2012-01-01

The objective of this investigation was to develop and investigate methods for point cloud generation by image matching using aerial image data collected by quadrocopter type micro unmanned aerial vehicle (UAV) imaging systems. Automatic generation of high-quality, dense point clouds from digital images by image matching is a recent, cutting-edge step forward in digital photogrammetric technology. The major components of the system for point cloud generation are a UAV imaging system, an image data collection process using high image overlaps, and post-processing with image orientation and point cloud generation. Two post-processing approaches were developed: one of the methods is based on Bae Systems’ SOCET SET classical commercial photogrammetric software and another is built using Microsoft®’s Photosynth™ service available in the Internet. Empirical testing was carried out in two test areas. Photosynth processing showed that it is possible to orient the images and generate point clouds fully automatically without any a priori orientation information or interactive work. The photogrammetric processing line provided dense and accurate point clouds that followed the theoretical principles of photogrammetry, but also some artifacts were detected. The point clouds from the Photosynth processing were sparser and noisier, which is to a large extent due to the fact that the method is not optimized for dense point cloud generation. Careful photogrammetric processing with self-calibration is required to achieve the highest accuracy. Our results demonstrate the high performance potential of the approach and that with rigorous processing it is possible to reach results that are consistent with theory. We also point out several further research topics. Based on theoretical and empirical results, we give recommendations for properties of imaging sensor, data collection and processing of UAV image data to ensure accurate point cloud generation. PMID:22368479

Point cloud generation from aerial image data acquired by a quadrocopter type micro unmanned aerial vehicle and a digital still camera.

PubMed

Rosnell, Tomi; Honkavaara, Eija

2012-01-01

The objective of this investigation was to develop and investigate methods for point cloud generation by image matching using aerial image data collected by quadrocopter type micro unmanned aerial vehicle (UAV) imaging systems. Automatic generation of high-quality, dense point clouds from digital images by image matching is a recent, cutting-edge step forward in digital photogrammetric technology. The major components of the system for point cloud generation are a UAV imaging system, an image data collection process using high image overlaps, and post-processing with image orientation and point cloud generation. Two post-processing approaches were developed: one of the methods is based on Bae Systems' SOCET SET classical commercial photogrammetric software and another is built using Microsoft(®)'s Photosynth™ service available in the Internet. Empirical testing was carried out in two test areas. Photosynth processing showed that it is possible to orient the images and generate point clouds fully automatically without any a priori orientation information or interactive work. The photogrammetric processing line provided dense and accurate point clouds that followed the theoretical principles of photogrammetry, but also some artifacts were detected. The point clouds from the Photosynth processing were sparser and noisier, which is to a large extent due to the fact that the method is not optimized for dense point cloud generation. Careful photogrammetric processing with self-calibration is required to achieve the highest accuracy. Our results demonstrate the high performance potential of the approach and that with rigorous processing it is possible to reach results that are consistent with theory. We also point out several further research topics. Based on theoretical and empirical results, we give recommendations for properties of imaging sensor, data collection and processing of UAV image data to ensure accurate point cloud generation.

On the isotropy assumption and the applicability of the gasdynamical equations for collapsing systems.

NASA Astrophysics Data System (ADS)

Hensler, G.; Spurzem, R.; Burkert, A.; Trassl, E.

1995-11-01

Rotating, isothermal collapsing protostellar and protogalactic gas systems are always being treated by use of the isotropic gasdynamical (Euler) equations; while it is standard textbook knowledge that diffusive and viscous effects can be neglected in most astrophysical plasmas with large Reynolds numbers, or in other words non-diagonal elements of the stress-energy tensor (second-order moments of the velocity distribution function) and higher order moments vanish, it is not that clear that the isotropy assumption is correct, i.e. the equality of the diagonal second-order moments. Therefore we address in this paper the question whether a collapsing gas cloud remains always strictly isotropic. Analytically the velocity field of an isothermal collapsing rotating gas cloud is computed and it is shown that strict isotropy can be realized in the static case only. This means that although collisional timescales in the gas might be very short, the collapsing system has to develop an inherent small anisotropy; the trajectory of the system in phase space is initially leading away from the isotropic path, staying continuously apart from it for a small distance. We discuss this phenomenon quantitatively by using moment equations of the Boltzmann equation and examine its consequences. It turns out that the deviation from anisotropy in most cases keeps small enough to allow for a global isotropic treatment which is consistent with expectation; applying our results to systems like cloud fluids or stellar systems, however, yields complementary results. Additionally we prove in this paper the performance of the conditions for the applicability of the gasdynamical description in a handy form and show that these conditions are usually fulfilled. We find that for a slightly Jeans unstable system in pressure equilibrium the ratio of the microscopic collision time to free-fall time has to be of order unity or smaller as has to be the Knudsen number in order to ensure the validity of gasdynamic equations.

Automatic Building Abstraction from Aerial Photogrammetry

NASA Astrophysics Data System (ADS)

Ley, A.; Hänsch, R.; Hellwich, O.

2017-09-01

Multi-view stereo has been shown to be a viable tool for the creation of realistic 3D city models. Nevertheless, it still states significant challenges since it results in dense, but noisy and incomplete point clouds when applied to aerial images. 3D city modelling usually requires a different representation of the 3D scene than these point clouds. This paper applies a fully-automatic pipeline to generate a simplified mesh from a given dense point cloud. The mesh provides a certain level of abstraction as it only consists of relatively large planar and textured surfaces. Thus, it is possible to remove noise, outlier, as well as clutter, while maintaining a high level of accuracy.

Dark Murky Clouds in the Bright Milky Way

NASA Image and Video Library

2011-08-24

This infrared image from NASA Wide-field Infrared Survey Explorer shows exceptionally cold, dense cloud cores seen in silhouette against the bright diffuse infrared glow of the plane of the Milky Way galaxy.

Evaluation of Methods for Coregistration and Fusion of Rpas-Based 3d Point Clouds and Thermal Infrared Images

NASA Astrophysics Data System (ADS)

Hoegner, L.; Tuttas, S.; Xu, Y.; Eder, K.; Stilla, U.

2016-06-01

This paper discusses the automatic coregistration and fusion of 3d point clouds generated from aerial image sequences and corresponding thermal infrared (TIR) images. Both RGB and TIR images have been taken from a RPAS platform with a predefined flight path where every RGB image has a corresponding TIR image taken from the same position and with the same orientation with respect to the accuracy of the RPAS system and the inertial measurement unit. To remove remaining differences in the exterior orientation, different strategies for coregistering RGB and TIR images are discussed: (i) coregistration based on 2D line segments for every single TIR image and the corresponding RGB image. This method implies a mainly planar scene to avoid mismatches; (ii) coregistration of both the dense 3D point clouds from RGB images and from TIR images by coregistering 2D image projections of both point clouds; (iii) coregistration based on 2D line segments in every single TIR image and 3D line segments extracted from intersections of planes fitted in the segmented dense 3D point cloud; (iv) coregistration of both the dense 3D point clouds from RGB images and from TIR images using both ICP and an adapted version based on corresponding segmented planes; (v) coregistration of both image sets based on point features. The quality is measured by comparing the differences of the back projection of homologous points in both corrected RGB and TIR images.

Penetration of Cosmic Rays into Dense Molecular Clouds: Role of Diffuse Envelopes

NASA Astrophysics Data System (ADS)

Ivlev, A. V.; Dogiel, V. A.; Chernyshov, D. O.; Caselli, P.; Ko, C.-M.; Cheng, K. S.

2018-03-01

A flux of cosmic rays (CRs) propagating through a diffuse ionized gas can excite MHD waves, thus generating magnetic disturbances. We propose a generic model of CR penetration into molecular clouds through their diffuse envelopes, and identify the leading physical processes controlling their transport on the way from a highly ionized interstellar medium to the dense interior of the cloud. The model allows us to describe a transition between a free streaming of CRs and their diffusive propagation, determined by the scattering on the self-generated disturbances. A self-consistent set of equations, governing the diffusive transport regime in an envelope and the MHD turbulence generated by the modulated CR flux, is characterized by two dimensionless numbers. We demonstrate a remarkable mutual complementarity of different mechanisms leading to the onset of the diffusive regime, which results in a universal energy spectrum of the modulated CRs. In conclusion, we briefly discuss implications of our results for several fundamental astrophysical problems, such as the spatial distribution of CRs in the Galaxy as well as the ionization, heating, and chemistry in dense molecular clouds. This paper is dedicated to the memory of Prof. Vadim Tsytovich.

Sulfur chemistry in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Prasad, S. S.; Huntress, W. T., Jr.

1982-01-01

A model is presented for the gas phase chemistry of molecules containing sulfur in dense interstellar clouds. The sulfur chemistry is different from that used in previous models as a result of an extensive search of the recent literature and the availability of new laboratory data. The changes have a significant effect on the calculated abundance of sulfur compounds. The linked chemistry of sulfur and oxygen in the present model requires a severe depletion of sulfur and low fractional abundances of both O and O2 in the dense clouds. In contrast, the high abundance of SO and the low abundance of CS relative to SO in the HVS in the KL may indicate an oxygen-rich, high temperature environment compared to OMC-1. The formation of S-H bonds is slow because of the absence of radiative association between S(+) and H2. The present model underestimates the abundance of H2S unless a radiative association reaction between HS(+) and H2 is postulated.

THE JCMT GOULD BELT SURVEY: A FIRST LOOK AT DENSE CORES IN ORION B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, H.; Francesco, J. Di; Johnstone, D.

2016-02-01

We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850 μm map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450 μm peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20 K, the starless dense cores have a mass function similar to that found inmore » previous dense core analyses, with a Salpeter-like slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1–2 × 10{sup 23} cm{sup −2}, most of the mass is found within dense cores, while at lower cloud column densities, below 1 × 10{sup 23} cm{sup −2}, this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (<8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023/2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.« less

The JCMT Gould Belt Survey: A First Look at Dense Cores in Orion B

NASA Astrophysics Data System (ADS)

Kirk, H.; Di Francesco, J.; Johnstone, D.; Duarte-Cabral, A.; Sadavoy, S.; Hatchell, J.; Mottram, J. C.; Buckle, J.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Fich, M.; Jenness, T.; Nutter, D.; Pattle, K.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Hogerheijde, M. R.; Ward-Thompson, D.; Bastien, P.; Bresnahan, D.; Butner, H.; Chen, M.; Chrysostomou, A.; Coude, S.; Davis, C. J.; Drabek-Maunder, E.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Gregson, J.; Holland, W.; Joncas, G.; Kirk, J. M.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Matthews, B. C.; Moriarty-Schieven, G.; Mowat, C.; Rawlings, J.; Richer, J.; Robertson, D.; Rosolowsky, E.; Rumble, D.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wouterloot, J.; Yates, J.; Zhu, M.

2016-02-01

We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850 μm map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450 μm peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20 K, the starless dense cores have a mass function similar to that found in previous dense core analyses, with a Salpeter-like slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1-2 × 1023 cm-2, most of the mass is found within dense cores, while at lower cloud column densities, below 1 × 1023 cm-2, this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (<8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023/2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.

Core Emergence in a Massive Infrared Dark Cloud: A Comparison between Mid-IR Extinction and 1.3 mm Emission

NASA Astrophysics Data System (ADS)

Kong, Shuo; Tan, Jonathan C.; Arce, Héctor G.; Caselli, Paola; Fontani, Francesco; Butler, Michael J.

2018-03-01

Stars are born from dense cores in molecular clouds. Observationally, it is crucial to capture the formation of cores in order to understand the necessary conditions and rate of the star formation process. The Atacama Large Millimeter/submillimeter Array (ALMA) is extremely powerful for identifying dense gas structures, including cores, at millimeter wavelengths via their dust continuum emission. Here, we use ALMA to carry out a survey of dense gas and cores in the central region of the massive (∼105 M ⊙) infrared dark cloud (IRDC) G28.37+0.07. The observation consists of a mosaic of 86 pointings of the 12 m array and produces an unprecedented view of the densest structures of this IRDC. In this first Letter about this data set, we focus on a comparison between the 1.3 mm continuum emission and a mid-infrared (MIR) extinction map of the IRDC. This allows estimation of the “dense gas” detection probability function (DPF), i.e., as a function of the local mass surface density, Σ, for various choices of thresholds of millimeter continuum emission to define “dense gas.” We then estimate the dense gas mass fraction, f dg, in the central region of the IRDC and, via extrapolation with the DPF and the known Σ probability distribution function, to the larger-scale surrounding regions, finding values of about 5% to 15% for the fiducial choice of threshold. We argue that this observed dense gas is a good tracer of the protostellar core population and, in this context, estimate a star formation efficiency per free-fall time in the central IRDC region of ɛ ff ∼ 10%, with approximately a factor of two systematic uncertainties.

Point Cloud Classification of Tesserae from Terrestrial Laser Data Combined with Dense Image Matching for Archaeological Information Extraction

NASA Astrophysics Data System (ADS)

Poux, F.; Neuville, R.; Billen, R.

2017-08-01

Reasoning from information extraction given by point cloud data mining allows contextual adaptation and fast decision making. However, to achieve this perceptive level, a point cloud must be semantically rich, retaining relevant information for the end user. This paper presents an automatic knowledge-based method for pre-processing multi-sensory data and classifying a hybrid point cloud from both terrestrial laser scanning and dense image matching. Using 18 features including sensor's biased data, each tessera in the high-density point cloud from the 3D captured complex mosaics of Germigny-des-prés (France) is segmented via a colour multi-scale abstraction-based featuring extracting connectivity. A 2D surface and outline polygon of each tessera is generated by a RANSAC plane extraction and convex hull fitting. Knowledge is then used to classify every tesserae based on their size, surface, shape, material properties and their neighbour's class. The detection and semantic enrichment method shows promising results of 94% correct semantization, a first step toward the creation of an archaeological smart point cloud.

Life and Death in a Star-Forming Cloud

NASA Image and Video Library

2012-11-14

W44 is located around 10,000 light-years away, within a forest of dense star-forming clouds in the constellation of Aquila, the Eagle. This image combines data from ESA Herschel and XXM-Newton space observatories.

The dense gas mass fraction in the W51 cloud and its protoclusters

NASA Astrophysics Data System (ADS)

Ginsburg, Adam; Bally, John; Battersby, Cara; Youngblood, Allison; Darling, Jeremy; Rosolowsky, Erik; Arce, Héctor; Lebrón Santos, Mayra E.

2015-01-01

Context. The density structure of molecular clouds determines how they will evolve. Aims: We map the velocity-resolved density structure of the most vigorously star-forming molecular cloud in the Galactic disk, the W51 giant molecular cloud. Methods: We present new 2 cm and 6 cm maps of H2CO, radio recombination lines, and the radio continuum in the W51 star forming complex acquired with Arecibo and the Green Bank Telescope at ~ 50″ resolution. We use H2CO absorption to determine the relative line-of-sight positions of molecular and ionized gas. We measure gas densities using the H2CO densitometer, including continuous measurements of the dense gas mass fraction (DGMF) over the range 104cm-3 104cm-3, while it is low, f< 20%, in W51 B. We did not detect any H2CO emission throughout the W51 GMC; all gas dense enough to emit under normal conditions is in front of bright continuum sources and therefore is seen in absorption instead. Conclusions: (1) The dense gas fraction in the W51 A and B clouds shows that W51 A will continue to form stars vigorously, while star formation has mostly ended in W51 B. The lack of dense, star-forming gas around W51 C indicates that collect-and-collapse is not acting or is inefficient in W51. (2) Ongoing high-mass star formation is correlated with n ≳ 1 × 105cm-3 gas. Gas with n> 104cm-3 is weakly correlated with low and moderate mass star formation, but does not strongly correlate with high-mass star formation. (3) The nondetection of H2CO emission implies that the emission detected in other galaxies, e.g. Arp 220, comes from high-density gas that is not directly affiliated with already-formed massive stars. Either the non-star-forming ISM of these galaxies is very dense, implying the star formation density threshold is higher, or H ii regions have their emission suppressed. The data set has been made public at http://dx.doi.org/10.7910/DVN/26818Appendices are available in electronic form at http://www.aanda.org

A Herschel [C ii] Galactic plane survey. II. CO-dark H2 in clouds

NASA Astrophysics Data System (ADS)

Langer, W. D.; Velusamy, T.; Pineda, J. L.; Willacy, K.; Goldsmith, P. F.

2014-01-01

Context. H i and CO large scale surveys of the Milky Way trace the diffuse atomic clouds and the dense shielded regions of molecular hydrogen clouds, respectively. However, until recently, we have not had spectrally resolved C+ surveys in sufficient lines of sight to characterize the ionized and photon dominated components of the interstellar medium, in particular, the H2 gas without CO, referred to as CO-dark H2, in a large sample of interstellar clouds. Aims: We use a sparse Galactic plane survey of the 1.9 THz (158 μm) [C ii] spectral line from the Herschel open time key programme, Galactic Observations of Terahertz C+ (GOT C+), to characterize the H2 gas without CO in a statistically significant sample of interstellar clouds. Methods: We identify individual clouds in the inner Galaxy by fitting the [C ii] and CO isotopologue spectra along each line of sight. We then combine these spectra with those of H i and use them along with excitation models and cloud models of C+ to determine the column densities and fractional mass of CO-dark H2 clouds. Results: We identify1804 narrow velocity [C ii] components corresponding to interstellar clouds in different categories and evolutionary states. About 840 are diffuse molecular clouds with no CO, ~510 are transition clouds containing [C ii] and 12CO, but no 13CO, and the remainder are dense molecular clouds containing 13CO emission. The CO-dark H2 clouds are concentrated between Galactic radii of ~3.5 to 7.5 kpc and the column density of the CO-dark H2 layer varies significantly from cloud to cloud with a global average of 9 × 1020 cm-2. These clouds contain a significant fraction by mass of CO-dark H2, that varies from ~75% for diffuse molecular clouds to ~20% for dense molecular clouds. Conclusions: We find a significant fraction of the warm molecular ISM gas is invisible in H i and CO, but is detected in [C ii]. The fraction of CO-dark H2 is greatest in the diffuse clouds and decreases with increasing total column density, and is lowest in the massive clouds. The column densities and mass fraction of CO-dark H2 are less than predicted by models of diffuse molecular clouds using solar metallicity, which is not surprising as most of our detections are in Galactic regions where the metallicity is larger and shielding more effective. There is an overall trend towards a higher fraction of CO-dark H2 in clouds with increasing Galactic radius, consistent with lower metallicity there. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Seeing the Forest Through the Trees: The Distribution and Properties of Dense Molecular Gas in the Milky Way Galaxy

NASA Astrophysics Data System (ADS)

Ellsworth-Bowers, Timothy P.

The Milky Way Galaxy serves as a vast laboratory for studying the dynamics and evolution of the dense interstellar medium and the processes of and surrounding massive star formation. From our vantage point within the Galactic plane, however, it has been extremely difficult to construct a coherent picture of Galactic structure; we cannot see the forest for the trees. The principal difficulties in studying the structure of the Galactic disk have been obscuration by the ubiquitous dust and molecular gas and confusion between objects along a line of sight. Recent technological advances have led to large-scale blind surveys of the Galactic plane at (sub-)millimeter wavelengths, where Galactic dust is generally optically thin, and have opened a new avenue for studying the forest. The Bolocam Galactic Plane Survey (BGPS) observed over 190 deg 2 of the Galactic plane in dust continuum emission near lambda = 1.1 mm, producing a catalog of over 8,000 dense molecular cloud structures across a wide swath of the Galactic disk. Deriving the spatial distribution and physical properties of these objects requires knowledge of distance, a component lacking in the data themselves. This thesis presents a generalized Bayesian probabilistic distance estimation method for dense molecular cloud structures, and demonstrates it with the BGPS data set. Distance probability density functions (DPDFs) are computed from kinematic distance likelihoods (which may be double- peaked for objects in the inner Galaxy) and an expandable suite of prior information to produce a comprehensive tally of our knowledge (and ignorance) of the distances to dense molecular cloud structures. As part of the DPDF formalism, this thesis derives several prior DPDFs for resolving the kinematic distance ambiguity in the inner Galaxy. From the collection of posterior DPDFs, a set of objects with well-constrained distance estimates is produced for deriving Galactic structure and the physical properties of dense molecular cloud structures. This distance catalog of 1,802 objects across the Galactic plane represents the first large-scale analysis of clump-scale objects in a variety of Galactic environments. The Galactocentric positions of these objects begin to trace out the spiral structure of the Milky Way, and suggest that dense molecular gas settles nearer the Galactic midplane than tracers of less-dense gas such as CO. Physical properties computed from the DPDFs reveal that BGPS objects trace a continuum of scales within giant molecular clouds, and extend the scaling relationships known as Larson's Laws to lower-mass substructures. The results presented here represent the first step on the road to seeing the molecular content of the Milky Way as a forest rather than individual nearby trees.

GIANT MOLECULAR CLOUD FORMATION IN DISK GALAXIES: CHARACTERIZING SIMULATED VERSUS OBSERVED CLOUD CATALOGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benincasa, Samantha M.; Pudritz, Ralph E.; Wadsley, James

We present the results of a study of simulated giant molecular clouds (GMCs) formed in a Milky Way-type galactic disk with a flat rotation curve. This simulation, which does not include star formation or feedback, produces clouds with masses ranging between 10{sup 4} M{sub ☉} and 10{sup 7} M{sub ☉}. We compare our simulated cloud population to two observational surveys: the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey and the BIMA All-Disk Survey of M33. An analysis of the global cloud properties as well as a comparison of Larson's scaling relations is carried out. We find that simulatedmore » cloud properties agree well with the observed cloud properties, with the closest agreement occurring between the clouds at comparable resolution in M33. Our clouds are highly filamentary—a property that derives both from their formation due to gravitational instability in the sheared galactic environment, as well as to cloud-cloud gravitational encounters. We also find that the rate at which potentially star-forming gas accumulates within dense regions—wherein n{sub thresh} ≥ 10{sup 4} cm{sup –3}—is 3% per 10 Myr, in clouds of roughly 10{sup 6} M{sub ☉}. This suggests that star formation rates in observed clouds are related to the rates at which gas can be accumulated into dense subregions within GMCs via filamentary flows. The most internally well-resolved clouds are chosen for listing in a catalog of simulated GMCs—the first of its kind. The cataloged clouds are available as an extracted data set from the global simulation.« less

Blowin in the Stellar Wind

NASA Image and Video Library

2011-06-13

This image of the Elephant Trunk nebula from NASA Wide-field Survey Explorer shows clouds of dust and gas being pushed and eroded by a massive star. The bright trunk of the nebula near the center is an especially dense cloud.

The Properties of Planck Galactic Cold Clumps in the L1495 Dark Cloud

NASA Astrophysics Data System (ADS)

Tang, Mengyao; Liu, Tie; Qin, Sheng-Li; Kim, Kee-Tae; Wu, Yuefang; Tatematsu, Ken’ichi; Yuan, Jinghua; Wang, Ke; Parsons, Harriet; Koch, Patrick M.; Sanhueza, Patricio; Ward-Thompson, D.; Tóth, L. Viktor; Soam, Archana; Lee, Chang Won; Eden, David; Di Francesco, James; Rawlings, Jonathan; Rawlings, Mark G.; Montillaud, Julien; Zhang, Chuan-Peng; Cunningham, M. R.

2018-04-01

Planck Galactic Cold Clumps (PGCCs) possibly represent the early stages of star formation. To understand better the properties of PGCCs, we studied 16 PGCCs in the L1495 cloud with molecular lines and continuum data from Herschel, JCMT/SCUBA-2, and the PMO 13.7 m telescope. Thirty dense cores were identified in 16 PGCCs from 2D Gaussian fitting. The dense cores have dust temperatures of T d = 11–14 K, and H2 column densities of {N}{{{H}}2} = (0.36–2.5) × 1022 cm‑2. We found that not all PGCCs contain prestellar objects. In general, the dense cores in PGCCs are usually at their earliest evolutionary stages. All the dense cores have non-thermal velocity dispersions larger than the thermal velocity dispersions from molecular line data, suggesting that the dense cores may be turbulence-dominated. We have calculated the virial parameter α and found that 14 of the dense cores have α <2, while 16 of the dense cores have α >2. This suggests that some of the dense cores are not bound in the absence of external pressure and magnetic fields. The column density profiles of dense cores were fitted. The sizes of the flat regions and core radii decrease with the evolution of dense cores. CO depletion was found to occur in all the dense cores, but is more significant in prestellar core candidates than in protostellar or starless cores. The protostellar cores inside the PGCCs are still at a very early evolutionary stage, sharing similar physical and chemical properties with the prestellar core candidates.

Interstellar clouds - From a dynamical perspective on their chemistry

NASA Technical Reports Server (NTRS)

Prasad, S. S.

1985-01-01

The possibility is examined that in the course of its dynamical evolution, a single mass of interstellar gas would exhibit properties of diffuse clouds, dense clouds and finally also of clouds perturbed by shocks or intense UV or X-ray radiation generated by a star of its own creation. This concept provides a common thread through the bewildering diversity of physical and chemical compositional properties shown by interstellar clouds. From this perspective, instead of being static objects, interstellar clouds are possibly incessantly evolving from initially diffuse to later dense state and then to star formation which ultimately restructures or disperses the remaining cloud material to begin the whole evolutionary process once again. Based on a simplified study of interstellar chemistry from a dynamical perspective, the ideas are presented as an heuristic: to encourage thought on the future direction of molecular astrophysics and the need to consider the chemical behavior of interstellar clouds in conjunction with, rather than in isolation from, their dynamical behavior. A physical basis must be sought for the semiempirical temperature formula which has been given a critical role in the collapse of diffuse clouds. Self-shielding effects in the chemistry of CO were neglected and this drawback should be removed; the ability of the model to explain the fractional abundances of more complex molecules, such as cyanopolyynes, should be examined.

Molecular Composition and Chemistry of Isolated Dense Cores

NASA Astrophysics Data System (ADS)

Cook, Amanda; Boogert, A.

2009-01-01

The composition of molecular clouds and the envelopes and disks surrounding low mass protostars within them is still poorly known. There is little doubt that a large fraction of the molecules is frozen on grains, but the abundance of several crucial species (e.g. ammonia, methanol, ions) in the ices is still uncertain. In addition, prominent spectral features discovered decades ago are still not securely identified (e.g. the 6.85-micron absorption band). Gas phase and grain surface chemistry play pivotal roles in molecule formation, but numerous other processes could have significant impacts as well: shocks, thermal heating, irradiation of ices by ultraviolet photons and cosmic rays. Complex species could be formed this way, profoundly influencing cloud, disk and planetary/cometary chemistry. We have obtained Spitzer/IRS spectra of an unprecedented sample of sight-lines tracing 25 dense isolated cores. These cores physically differ from the large, cluster-forming molecular clouds (e.g. Ophiuchus, Perseus) that are commonly studied: they are less turbulent, colder, less dense, and likely longer lived. These IRS spectra of isolated cores thus provide unique information on ice formation and destruction mechanisms. Toward the same cores, we observed 33 highly extincted background stars as well, tracing the quiescent cloud medium against which the ices around protostars can be contrasted.

Comparison of roadway roughness derived from LIDAR and SFM 3D point clouds.

DOT National Transportation Integrated Search

2015-10-01

This report describes a short-term study undertaken to investigate the potential for using dense three-dimensional (3D) point : clouds generated from light detection and ranging (LIDAR) and photogrammetry to assess roadway roughness. Spatially : cont...

Molecular Line Studies of Ballistic Stellar Interlopers Burrowing through Dense Interstellar Clouds

NASA Astrophysics Data System (ADS)

Rosen, Anna; Sahai, R.; Claussen, M.; Morris, M.

2010-01-01

When an intermediate-mass star speeds through a dense interstellar cloud at a high velocity, it can produce a cometary or bow shock structure due to the cloud being impacted by the intense stellar wind. This class of objects, recently discovered in an HST imaging survey, has been dubbed "ballistic stellar interlopers" (Sahai et al. 2009). Using the ARO's 12m and SMT 10m millimeter-wave dishes, we have obtained molecular line emission data towards 10 stellar interloper sources, in order to identify and characterize the dense clouds with which the interlopers are interacting. We have made small "on-the-fly" maps in the 12CO (J=2-1) and 13CO (J=2-1) lines for each cloud, and obtained spectra of high-density tracers such as N2H+ (J=3-2), HCO+ (J=3-2), CN(N=2-1), and SO(J=5-4), which probe a range of physical conditions in the interstellar clouds being impacted by the interlopers. The data have been reduced and analyzed, and preliminary estimates of the cloud temperatures (9-22 K) and 13CO optical depths (0.18-0.37) have been made. The maps, which show the emission as a function of radial velocity and spatial offset from the location of the interlopers, have helped us distinguish between the clouds interacting with the interlopers, and those which are unrelated but happen to lie along the line of sight. These data will now enable us to carry out high-resolution mm-wave interferometric observations of the interlopers in the future. This research was performed at JPL under the Minority Education Initiatives program. RS and MM were funded by a Long Term Space Astrophysics award from NASA for this work. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Special thanks goes to John Bieging and Bill Peters of the Arizona Radio Observatory.

Magnetic Fields and Multiple Protostar Formation

NASA Astrophysics Data System (ADS)

Boss, A. P.

2001-12-01

Recent observations of star-forming regions suggest that binary and multiple young stars are the rule rather than the exception, and implicate fragmentation as the likely mechanism for their formation. Most numerical hydrodynamical calculations of fragmentation have neglected the possibly deleterious effects of magnetic fields, in spite of ample evidence for the importance of magnetic support of pre-collapse clouds. We present here the first numerical hydrodynamical survey of the full effects of magnetic fields on the collapse and fragmentation of dense cloud cores. The models are calculated with a three dimensional, finite differences code which solves the equations of hydrodynamics, gravitation, and radiative transfer in the Eddington and diffusion approximations. Magnetic field effects are included through two simple approximations: magnetic pressure is added to the gas pressure, and magnetic tension is approximated by gravity dilution once collapse is well underway. Ambipolar diffusion of the magnetic field leading to cloud collapse is treated approximately as well. Models are calculated for a variety of initial cloud density profiles, shapes, and rotation rates. We find that in spite of the inclusion of magnetic field effects, dense cloud cores are capable of fragmenting into binary and multiple protostar systems. Initially prolate clouds tend to fragment into binary protostars, while initially oblate clouds tend to fragment into multiple protostar systems containing a small number (of order four) of fragments. The latter are likely to be subject to rapid orbital evolution, with close encounters possibly leading to the ejection of fragments. Contrary to expectation, magnetic tension effects appear to enhance fragmentation, allowing lower mass fragments to form than would otherwise be possible, because magnetic tension helps to prevent a central density singularity from forming and producing a dominant single object. Magnetically-supported dense cloud cores thus seem to be capable of collapsing and fragmenting into sufficient numbers of binary and multiple protostar systems to be compatible with observations of the relative rarity of single protostars. This work was partially supported by NSF grants AST-9983530 and MRI-9976645.

Characteristics of fog and fogwater fluxes in a Puerto Rican elfin cloud forest.

Treesearch

Werner Eugster; Reto Burkard; Friso Holwerda; Frederick N. Scatena; L.A.(Sampurno) Bruijnzeel

2006-01-01

The Luquillo Mountains of northeastern Puerto Rico harbours important fractions of tropical montane cloud forests. Although it is well known that the frequent occurrence of dense fog is a common climatic characteristic of cloud forests around the world, it is poorly understood how fog processes shape and influence these ecosystems. Our study focuses on the physical...

Infrared spectroscopy of dense clouds in the C-H stretch region - Methanol and 'diamonds'

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Sandford, S. A.; Tielens, A. G. G. M.; Herbst, T. M.

1992-01-01

The paper presents high spectral resolution studies in the 3100-2600/cm range of the protostars NGC 7538 IRS9, W33A, W3 IRS 5, and S140 IRS 1. Well-resolved absorption bands at about 2825/cm and 2880/cm were found superposed on the LF wing of the strong O-H stretch feature. The 2880/cm band, previously detected toward W33A, is also in the spectrum of NGC 7538 IRS 9. The relative strength of these two bands varies, showing that they are associated with two different carriers. The new band at about 2880/cm falls near the position of C-H stretching vibrations in tertiary carbon atoms. The strength of this feature, in combination with the lack of strong features associated with primary and secondary carbon atoms, suggests that the carrier of the new feature has a diamondlike structure. This new feature is tentatively attributed to interstellar 'diamonds'. The detection of this band in the spectra of all four dense molecular clouds suggests that the carrier is ubiquitous in dense clouds.

Ion-molecule calculation of the abundance ratio of CCD to CCH in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Herbst, Eric; Adams, Nigel G.; Smith, David; Defrees, D. J.

1987-01-01

Laboratory measurements and calculations have been performed to determine the abundance ratio of the deuterated ethynyl radical (CCD) to the normal radical (CCH) which can be achieved in dense interstellar clouds via isotopic fractionation in the C2H2(+) (HD)=C2HD(+)(H2) system of reactions. According to this limited treatment, the CCD/CCH abundance ratio which can be attained is in the range 0.02-0.03 for the Orion molecular cloud and 0.0l-0.02 for TMC-1. These ranges of numbers are in reasonable agreement with the observed values in Orion and TMC-1. However, the analysis of the CCD/CCH abundance ratio is complicated via the presence of competing fractionation mechanisms, especially in the low-temperature source TMC-1.

Propagation of light through small clouds of cold interacting atoms

NASA Astrophysics Data System (ADS)

Jennewein, S.; Sortais, Y. R. P.; Greffet, J.-J.; Browaeys, A.

2016-11-01

We demonstrate experimentally that a dense cloud of cold atoms with a size comparable to the wavelength of light can induce large group delays on a laser pulse when the laser is tightly focused on it and is close to an atomic resonance. Delays as large as -10 ns are observed, corresponding to "superluminal" propagation with negative group velocities as low as -300 m /s . Strikingly, this large delay is associated with a moderate extinction owing to the very small size of the dense cloud. It implies that a large phase shift is imprinted on the continuous laser beam. Our system may thus be useful for applications to quantum technologies, such as variable delay line for individual photons or phase imprint between two beams at the single-photon level.

Shocked Clouds in the Vela Supernova Remnant

NASA Technical Reports Server (NTRS)

Nichols, Joy S.; Slavin, Jonathan D.

2004-01-01

Unusually strong high-excitation C I has been detected in eleven lines of sight through the Vela supernova remnant by means of UV absorption-line studies of IUE data. Most of these lines of sight lie near the western edge of the X-ray bright region of the supernova remnant in a spatially distinct band approximately 1deg by 4deg oriented approximately north/south. The high-excitation C I (denoted C I*) is interpreted as evidence of a complex of shocked dense clouds inside the supernova remnant, due to the high pressures indicated in this region. To further analyze the properties of this region of C I*, we present new HIRES-processed IRAS data of the entire Vela SNR. A temperature map calculated from the HIRES IRAS data, based on a two-component dust model, reveals the signature of hot dust at several locations in the SNR. The hot dust is anti-correlated spatially with X-ray emission as revealed by ROSAT, as would be expected for a dusty medium interacting with a shock wave. The regions of hot dust are strongly correlated with optical filaments, supporting a scenario of dense clouds interior to the SNR that have been shocked and are now cooling behind the supernova blast wave. With few exceptions, the lines of sight to the strong C I* pass through regions of hot dust and optical filaments. Possible mechanisms for the production of the anomalously large columns of C I and C I* are discussed. Dense clouds on the back western hemisphere of the remnant may explain the relatively low X-ray emission in the western portion of the Vela supernova remnant due to the slower forward shock velocity in regions where the shock has encountered the dense clouds. An alternate explanation for the presence of neutral, excited state, and ionized species along the same line of sight may be a magnetic precusor that heats and compresses the gas ahead of the shock.

Testing the universality of the star-formation efficiency in dense molecular gas

NASA Astrophysics Data System (ADS)

Shimajiri, Y.; André, Ph.; Braine, J.; Könyves, V.; Schneider, N.; Bontemps, S.; Ladjelate, B.; Roy, A.; Gao, Y.; Chen, H.

2017-08-01

Context. Recent studies with, for example, Spitzer and Herschel have suggested that star formation in dense molecular gas may be governed by essentially the same "law" in Galactic clouds and external galaxies. This conclusion remains controversial, however, in large part because different tracers have been used to probe the mass of dense molecular gas in Galactic and extragalactic studies. Aims: We aimed to calibrate the HCN and HCO+ lines commonly used as dense gas tracers in extragalactic studies and to test the possible universality of the star-formation efficiency in dense gas (≳104 cm-3), SFEdense. Methods: We conducted wide-field mapping of the Aquila, Ophiuchus, and Orion B clouds at 0.04 pc resolution in the J = 1 - 0 transition of HCN, HCO+, and their isotopomers. For each cloud, we derived a reference estimate of the dense gas mass MHerschelAV > 8, as well as the strength of the local far-ultraviolet (FUV) radiation field, using Herschel Gould Belt survey data products, and estimated the star-formation rate from direct counting of the number of Spitzer young stellar objects. Results: The H13CO+(1-0) and H13CN(1-0) lines were observed to be good tracers of the dense star-forming filaments detected with Herschel. Comparing the luminosities LHCN and LHCO+ measured in the HCN and HCO+ lines with the reference masses MHerschelAV > 8, the empirical conversion factors αHerschel - HCN (=MHerschelAV > 8/LHCN) and αHerschel - HCO+ (=MHerschelAV > 8/LHCO+) were found to be significantly anti-correlated with the local FUV strength. In agreement with a recent independent study of Orion B by Pety et al., the HCN and HCO+ lines were found to trace gas down to AV ≳ 2. As a result, published extragalactic HCN studies must be tracing all of the moderate density gas down to nH2 ≲ 103 cm-3. Estimating the contribution of this moderate density gas from the typical column density probability distribution functions in nearby clouds, we obtained the following G0-dependent HCN conversion factor for external galaxies: αHerschel - HCNfit' = 64 × G0-0.34. Re-estimating the dense gas masses in external galaxies with αHerschel - HCNfit'(G0), we found that SFEdense is remarkably constant, with a scatter of less than 1.5 orders of magnitude around 4.5 × 10-8 yr-1, over eight orders of magnitude in dense gas mass. Conclusions: Our results confirm that SFEdense of galaxies is quasi-universal on a wide range of scales from 1-10 pc to > 10 kpc. Based on the tight link between star formation and filamentary structure found in Herschel studies of nearby clouds, we argue that SFEdense is primarily set by the "microphysics" of core and star formation along filaments. Partly based on observations carried out with the IRAM 30 m Telescope under project numbers 150-14 and 032-15. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

From gas to stars in energetic environments: dense gas clumps in the 30 Doradus region within the Large Magellanic Cloud

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, Crystal N.; Meier, David S.; Ott, Jürgen

2014-09-20

We present parsec-scale interferometric maps of HCN(1-0) and HCO{sup +}(1-0) emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via varicose fluid instability. Our analysis showsmore » that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO{sup +} emission in the filament and signatures of recent star formation activity including H{sub 2}O masers and young stellar objects (YSOs). YSOs seem to continue along the same direction of the filament toward the massive compact star cluster R136 in the southwest. We present detailed comparisons of clump properties (masses, linewidths, and sizes) in 30Dor-10 to those in other star forming regions of the LMC (N159, N113, N105, and N44). Our analysis shows that the 30Dor-10 clumps have similar masses but wider linewidths and similar HCN/HCO{sup +} (1-0) line ratios as clumps detected in other LMC star-forming regions. Our results suggest that the dense molecular gas clumps in the interior of 30Dor-10 are well shielded against the intense ionizing field that is present in the 30 Doradus region.« less

HIGH-ENERGY ELECTRON IRRADIATION OF INTERSTELLAR CARBONACEOUS DUST ANALOGS: COSMIC-RAY EFFECTS ON THE CARRIERS OF THE 3.4 μ m ABSORPTION BAND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel

2016-11-01

The effects of cosmic rays on the carriers of the interstellar 3.4 μ m absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH{sub 3} and CH{sub 2} in carbonaceous dust. It is widely observed in the diffuse interstellar medium, but disappears in dense clouds. Destruction of CH{sub 3} and CH{sub 2} by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity versus electron fluence reflectsmore » a-C:H dehydrogenation, which is well described by a model assuming that H{sub 2} molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher-energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic-ray destruction times for the 3.4 μ m band carriers lie in the 10{sup 8} yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 10{sup 7} yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.« less

The Molecular Gas Environment in the 20 km s{sup −1} Cloud in the Central Molecular Zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Xing; Gu, Qiusheng; Zhang, Qizhou

We recently reported a population of protostellar candidates in the 20 km s{sup −1} cloud in the Central Molecular Zone of the Milky Way, traced by H{sub 2}O masers in gravitationally bound dense cores. In this paper, we report molecular line studies with high angular resolution (∼3″) of the environment of star formation in this cloud. Maps of various molecular line transitions as well as the continuum at 1.3 mm are obtained using the Submillimeter Array. Five NH{sub 3} inversion lines and the 1.3 cm continuum are observed with the Karl G. Jansky Very Large Array. The interferometric observations aremore » complemented with single-dish data. We find that the CH{sub 3}OH, SO, and HNCO lines, which are usually shock tracers, are better correlated spatially with the compact dust emission from dense cores among the detected lines. These lines also show enhancement in intensities with respect to SiO intensities toward the compact dust emission, suggesting the presence of slow shocks or hot cores in these regions. We find gas temperatures of ≳100 K at 0.1 pc scales based on RADEX modeling of the H{sub 2}CO and NH{sub 3} lines. Although no strong correlations between temperatures and linewidths/H{sub 2}O maser luminosities are found, in high-angular-resolution maps we note several candidate shock-heated regions offset from any dense cores, as well as signatures of localized heating by protostars in several dense cores. Our findings suggest that at 0.1 pc scales in this cloud star formation and strong turbulence may together affect the chemistry and temperature of the molecular gas.« less

A detailed investigation of proposed gas-phase syntheses of ammonia in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Herbst, Eric; Defrees, D. J.; Mclean, A. D.

1987-01-01

The initial reactions of the Herbst and Klemperer (1973) and the Dalgarno (1974) schemes (I and II, respectively) for the gas-phase synthesis of ammonia in dense interstellar clouds were investigated. The rate of the slightly endothermic reaction between N(+) and H2 to yield NH(+) and H (scheme I) under interstellar conditions was reinvestigated under thermal and nonthermal conditions based on laboratory data. It was found that the relative importance of this reaction in synthesizing ammonia is determined by how the laboratory data at low temperature are interpreted. On the other hand, the exothermic reaction between N and H3(+) to form NH2(+) + H (scheme II) was calculated to possess significant activation energy and, therefore, to have a negligible rate coefficient under interstellar conditions. Consequently, this reaction cannot take place appreciably in interstellar clouds.

Carbon Dioxide Clouds at High Altitude in the Tropics and in an Early Dense Martian Atmosphere

NASA Technical Reports Server (NTRS)

Colaprete, Anthony; Toon, Owen B.

2001-01-01

We use a time dependent, microphysical cloud model to study the formation of carbon dioxide clouds in the Martian atmosphere. Laboratory studies by Glandor et al. show that high critical supersaturations are required for cloud particle nucleation and that surface kinetic growth is not limited. These conditions, which are similar to those for cirrus clouds on Earth, lead to the formation of carbon dioxide ice particles with radii greater than 500 micrometers and concentrations of less than 0.1 cm(exp -3) for typical atmospheric conditions. Within the current Martian atmosphere, CO2 cloud formation is possible at the poles during winter and at high altitudes in the tropics during periods of increased atmospheric dust loading. In both cases, temperature perturbations of several degrees below the CO2 saturation temperature are required to nucleate new cloud particles suggesting that dynamical processes are the most common initiators of carbon dioxide clouds rather than diabatic cooling. The microphysical cloud model, coupled to a two-stream radiative transfer model, is used to reexamine the impact of CO2 clouds on the surface temperature within a dense CO2 atmosphere. The formation of carbon dioxide clouds leads to a warmer surface than what would be expected for clear sky conditions. The amount of warming is sensitive to the presence of dust and water vapor in the atmosphere, both of which act to dampen cloud effects. The radiative warming associated with cloud formation, as well as latent heating, work to dissipate the clouds when present. Thus, clouds never last for periods much longer than several days, limiting their overall effectiveness for warming the surface. The time average cloud optical depth is approximately unity leading to a 5-10 K warming, depending on the surface pressure. However, the surface temperature does not rise about the freezing point of liquid water even for pressures as high as 5 bars, at a solar luminosity of 75% the current value.

Object Detection using the Kinect

DTIC Science & Technology

2012-03-01

Kinect camera and point cloud data from the Kinect’s structured light stereo system (figure 1). We obtain reasonable results using a single prototype...same manner we present in this report. For example, at Willow Garage , Steder uses a 3-D feature he developed to classify objects directly from point...detecting backpacks using the data available from the Kinect sensor. 4 3.1 Point Cloud Filtering Dense point clouds derived from stereo are notoriously

Discovery of Molecular and Atomic Clouds Associated with the Magellanic Superbubble 30 Doradus C

NASA Astrophysics Data System (ADS)

Sano, H.; Yamane, Y.; Voisin, F.; Fujii, K.; Yoshiike, S.; Inaba, T.; Tsuge, K.; Babazaki, Y.; Mitsuishi, I.; Yang, R.; Aharonian, F.; Rowell, G.; Filipović, M. D.; Mizuno, N.; Tachihara, K.; Kawamura, A.; Onishi, T.; Fukui, Y.

2017-07-01

We analyzed the 2.6 mm CO and 21 cm H I lines toward the Magellanic superbubble 30 Doradus C, in order to reveal the associated molecular and atomic gas. We uncovered five molecular clouds in a velocity range from 251 to 276 km s-1 toward the western shell. The non-thermal X-rays are clearly enhanced around the molecular clouds on a parsec scale, suggesting possible evidence for magnetic field amplification via shock-cloud interaction. The thermal X-rays are brighter in the eastern shell, where there are no dense molecular or atomic clouds, opposite to the western shell. The TeV γ-ray distribution may spatially match the total interstellar proton column density as well as the non-thermal X-rays. If the hadronic γ-ray is dominant, the total energy of the cosmic-ray protons is at least ˜ 1.2× {10}50 erg with the estimated mean interstellar proton density ˜60 cm-3. In addition, the γ-ray flux associated with the molecular cloud (e.g., MC3) could be detected and resolved by the Cherenkov Telescope Array (CTA). This should permit CTA to probe the diffusion of cosmic-rays into the associated dense ISM.

Relationship between the column density distribution and evolutionary class of molecular clouds as viewed by ATLASGAL

NASA Astrophysics Data System (ADS)

Abreu-Vicente, J.; Kainulainen, J.; Stutz, A.; Henning, Th.; Beuther, H.

2015-09-01

We present the first study of the relationship between the column density distribution of molecular clouds within nearby Galactic spiral arms and their evolutionary status as measured from their stellar content. We analyze a sample of 195 molecular clouds located at distances below 5.5 kpc, identified from the ATLASGAL 870 μm data. We define three evolutionary classes within this sample: starless clumps, star-forming clouds with associated young stellar objects, and clouds associated with H ii regions. We find that the N(H2) probability density functions (N-PDFs) of these three classes of objects are clearly different: the N-PDFs of starless clumps are narrowest and close to log-normal in shape, while star-forming clouds and H ii regions exhibit a power-law shape over a wide range of column densities and log-normal-like components only at low column densities. We use the N-PDFs to estimate the evolutionary time-scales of the three classes of objects based on a simple analytic model from literature. Finally, we show that the integral of the N-PDFs, the dense gas mass fraction, depends on the total mass of the regions as measured by ATLASGAL: more massive clouds contain greater relative amounts of dense gas across all evolutionary classes. Appendices are available in electronic form at http://www.aanda.org

Ultra-High Spectral Resolution Observations of Fragmentation in Dark Cloud Cores

NASA Technical Reports Server (NTRS)

Velusamy, T.; Langer, W.; Kuiper, T; Levin, S.; Olsen, E.

1993-01-01

This paper presents new evidence of the fragmentary structure of dense cores in dark clouds using the high resolution spectra of the carbon chain molecule CCS transition (J subscript N = 2 subscript 1 - 1 subscript o) at 22.344033 GHz with 0.008 km s superscript -1 resolution.

Laboratory and modeling studies of chemistry in dense molecular clouds

NASA Technical Reports Server (NTRS)

Huntress, W. T., Jr.; Prasad, S. S.; Mitchell, G. F.

1980-01-01

A chemical evolutionary model with a large number of species and a large chemical library is used to examine the principal chemical processes in interstellar clouds. Simple chemical equilibrium arguments show the potential for synthesis of very complex organic species by ion-molecule radiative association reactions.

Single-photon nonlinearities in the propagation of focused beams through dense atomic clouds

NASA Astrophysics Data System (ADS)

Wang, Yidan; Gorshkov, Alexey; Gullans, Michael

2017-04-01

We theoretically study single-photon nonlinearities realized when a highly focused Gaussian beam passes through a dense atomic cloud. In this system, strong dipole-dipole interactions arise between closely spaced atoms and significantly affect light propagation. We find that the highly focused Gaussian beam can be treated as an effective one-dimensional waveguide, which simplifies the calculation of photon transmission and correlation functions. The formalism we develop is also applicable to the case where additional atom-atom interactions, such as interactions between Rydberg atoms, are involved. This work was supported by the ARL, NSF PFC at the JQI, AFOSR, NSF PIF, ARO, and AFOSR MURI.

The astrochemistry of H+3

NASA Astrophysics Data System (ADS)

Herbst, E.

2000-09-01

The reactions of the molecular ion H3+ are pivotal to the chemistry of dense interstellar clouds. Produced by the cosmic-ray ionizati on of molecular hydrogen, H3+ reacts with a variety of a toms and molecules to produce species that are precursors to many of the detect ed molecules in dense clouds. For example, the reaction of H3+ with atomic O leads, eventually, to the production of water, while the re action with HD leads to the production of a wide variety of deuterated isotopom ers. In this article, the chemistry of H3+ and the produc ts derived from it are discussed in the larger context of interstellar chemistr y.

Accuracy Analysis of a Dam Model from Drone Surveys

PubMed Central

Buffi, Giulia; Venturi, Sara

2017-01-01

This paper investigates the accuracy of models obtained by drone surveys. To this end, this work analyzes how the placement of ground control points (GCPs) used to georeference the dense point cloud of a dam affects the resulting three-dimensional (3D) model. Images of a double arch masonry dam upstream face are acquired from drone survey and used to build the 3D model of the dam for vulnerability analysis purposes. However, there still remained the issue of understanding the real impact of a correct GCPs location choice to properly georeference the images and thus, the model. To this end, a high number of GCPs configurations were investigated, building a series of dense point clouds. The accuracy of these resulting dense clouds was estimated comparing the coordinates of check points extracted from the model and their true coordinates measured via traditional topography. The paper aims at providing information about the optimal choice of GCPs placement not only for dams but also for all surveys of high-rise structures. The knowledge a priori of the effect of the GCPs number and location on the model accuracy can increase survey reliability and accuracy and speed up the survey set-up operations. PMID:28771185

Accuracy Analysis of a Dam Model from Drone Surveys.

PubMed

Ridolfi, Elena; Buffi, Giulia; Venturi, Sara; Manciola, Piergiorgio

2017-08-03

This paper investigates the accuracy of models obtained by drone surveys. To this end, this work analyzes how the placement of ground control points (GCPs) used to georeference the dense point cloud of a dam affects the resulting three-dimensional (3D) model. Images of a double arch masonry dam upstream face are acquired from drone survey and used to build the 3D model of the dam for vulnerability analysis purposes. However, there still remained the issue of understanding the real impact of a correct GCPs location choice to properly georeference the images and thus, the model. To this end, a high number of GCPs configurations were investigated, building a series of dense point clouds. The accuracy of these resulting dense clouds was estimated comparing the coordinates of check points extracted from the model and their true coordinates measured via traditional topography. The paper aims at providing information about the optimal choice of GCPs placement not only for dams but also for all surveys of high-rise structures. The knowledge a priori of the effect of the GCPs number and location on the model accuracy can increase survey reliability and accuracy and speed up the survey set-up operations.

Shocks in Dense Clouds in the Vela Supernova Remnant: FUSE

NASA Technical Reports Server (NTRS)

Nichols, Joy; Sonneborn, George (Technical Monitor)

2002-01-01

We have obtained 8 LWRS FUSE spectra to study a recently identified interaction of the Vela supernova remnant with a dense cloud region along its western edge. The goal is to quantify the temperature, ionization, density, and abundance characteristics associated with this shock/dense cloud interface by means of UV absorption line studies. Our detection of high-velocity absorption line C I at +90 to +130 km/s with IUE toward a narrow region interior to the Vela SNR strongly suggests the Vela supernova remnant is interacting with a dense ISM or molecular cloud. The shock/dense cloud interface is suggested by (1) the rarity of detection of high-velocity C I seen in IUE spectra, (2) its very limited spatial distribution in the remnant, and (3) a marked decrease in X-ray emission in the region immediately west of the position of these stars where one also finds a 100 micron emission ridge in IRAS images. We have investigated the shock physics and general properties of this interaction region through a focussed UV absorption line study using FUSE spectra. We have FUSE data on OVI absorption lines observed toward 8 stars behind the Vela supernova remnant (SNR). We compare the OVI observations with IUE observations of CIV absorption toward the same stars. Most of the stars, which are all B stars, have complex continua making the extraction of absorption lines difficult. Three of the stars, HD 72088, HD 72089 and HD 72350, however, are rapid rotators (v sin i less than 100 km/s) making the derivation of absorption column densities much easier. We have measured OVI and CIV column densities for the "main component" (i.e. the low velocity component) for these stars. In addition, by removing the H2 line at 1032.35A (121.6 km/s relative to OVI), we find high velocity components of OVI at approximately 150 km/s that we attribute to the shock in the Vela SNR. The column density ratios and magnitudes are compared to both steady shock models and results of hydrodynamical SNR modeling. We find that the models require the shock to be relatively slow (approximately 100 - 170 km/s) to match the FUSE data. We discuss the implications of our results for models of the evolution of the Vela SNR.

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asahina, Yuta; Ohsuga, Ken; Nomura, Mariko, E-mail: asahina@cfca.jp

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tensionmore » force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.« less

Flash photoionization of gamma-ray burst environments

NASA Technical Reports Server (NTRS)

Band, David L.; Hartmann, Dieter H.

1992-01-01

The H-alpha line emission that a flash-photoionized region emits is calculated. Archival transients, as well as various theoretical predictions, suggest that there may be significant ionizing flux. The limits on the line flux which might be observable indicate that the density must be fairly high for the recombination radiation to be observable. The intense burst radiation is insufficient to melt the dust which will be present in such a dense medium. This dust may attenuate the observable line emission, but does not attenuate the ionizing radiation before it ionizes the neutral medium surrounding the burst source. The dust can also produce a light echo. If there are indeed gamma-ray bursts in dense clouds, then it is possible that the burst was triggered by Bondi-Hoyle accretion from the dense medium, although it is unlikely on statistical grounds that all bursts occur in clouds.

Cosmic Star–Forming Gas as seen from the Milky Way

NASA Astrophysics Data System (ADS)

Kauffmann, Jens

2018-01-01

We still struggle to understand the star formation properties of galaxies throughout the cosmos. Is star formation driven by the structure of galaxies? Or is it plainly controlled by the mass of dense gas that can be found in a galaxy?This poster presents results from several recent projects that deliver important insights on the global star formation activity of galaxies, based on detailed studies of star-forming regions in the Milky Way. First, the proberties of dense clouds in the Galactic Center are discussed, using data from interferometers likw ALMA. Second, the kinematics of Milky Way molecular clouds are discussed based on a variety of data sets. Third, the LEGO survey (Line Emission in Galaxy Observations) is discussed. This latter study challenges concepts of how dense gas in galaxies can be traced. In combination these studies deliver a fresh look at the various factors controlling how galaxies form stars.

The Green Bank Ammonia Survey of the Gould Belt

NASA Astrophysics Data System (ADS)

Friesen, Rachel; Pineda, Jaime; GAS Team

2018-01-01

The past several years have seen a tremendous advancement in our ability to characterize the structure of nearby molecular clouds traced by large-scale continuum surveys. Critical, comparable data on the dense gas kinematics and temperatures are needed to understand the history and future fate of star-forming material. Filling this gap is the Green Bank Ammonia Survey (GAS), an ambitious legacy survey for the Green Bank Telescope to observe key molecular tracers of dense gas within all Gould Belt clouds visible from the northern hemisphere. I will present the latest science from GAS, whose goals are to 1) evaluate the stability of dense gas structures as a function of scale, 2) track the dissipation of turbulence and evolution of angular momentum in filaments and cores, and 3) quantitatively test predictions of models of core and filament formation via mass flows and accretion.

Environmental Catastrophes in the Earth's History Due to Solar Systems Encounters with Giant Molecular Clouds

NASA Technical Reports Server (NTRS)

Pavlov, Alexander A.

2011-01-01

In its motion through the Milky Way galaxy, the solar system encounters an average density (>=330 H atoms/cubic cm) giant molecular cloud (GMC) approximately every 108 years, a dense (approx 2 x 103 H atoms/cubic cm) GMC every approx 109 years and will inevitably encounter them in the future. However, there have been no studies linking such events with severe (snowball) glaciations in Earth history. Here we show that dramatic climate change can be caused by interstellar dust accumulating in Earth's atmosphere during the solar system's immersion into a dense (approx ,2 x 103 H atoms/cubic cm) GMC. The stratospheric dust layer from such interstellar particles could provide enough radiative forcing to trigger the runaway ice-albedo feedback that results in global snowball glaciations. We also demonstrate that more frequent collisions with less dense GMCs could cause moderate ice ages.

Terrestrial laser scanning point clouds time series for the monitoring of slope movements: displacement measurement using image correlation and 3D feature tracking

NASA Astrophysics Data System (ADS)

Bornemann, Pierrick; Jean-Philippe, Malet; André, Stumpf; Anne, Puissant; Julien, Travelletti

2016-04-01

Dense multi-temporal point clouds acquired with terrestrial laser scanning (TLS) have proved useful for the study of structure and kinematics of slope movements. Most of the existing deformation analysis methods rely on the use of interpolated data. Approaches that use multiscale image correlation provide a precise and robust estimation of the observed movements; however, for non-rigid motion patterns, these methods tend to underestimate all the components of the movement. Further, for rugged surface topography, interpolated data introduce a bias and a loss of information in some local places where the point cloud information is not sufficiently dense. Those limits can be overcome by using deformation analysis exploiting directly the original 3D point clouds assuming some hypotheses on the deformation (e.g. the classic ICP algorithm requires an initial guess by the user of the expected displacement patterns). The objective of this work is therefore to propose a deformation analysis method applied to a series of 20 3D point clouds covering the period October 2007 - October 2015 at the Super-Sauze landslide (South East French Alps). The dense point clouds have been acquired with a terrestrial long-range Optech ILRIS-3D laser scanning device from the same base station. The time series are analyzed using two approaches: 1) a method of correlation of gradient images, and 2) a method of feature tracking in the raw 3D point clouds. The estimated surface displacements are then compared with GNSS surveys on reference targets. Preliminary results tend to show that the image correlation method provides a good estimation of the displacement fields at first order, but shows limitations such as the inability to track some deformation patterns, and the use of a perspective projection that does not maintain original angles and distances in the correlated images. Results obtained with 3D point clouds comparison algorithms (C2C, ICP, M3C2) bring additional information on the displacement fields. Displacement fields derived from both approaches are then combined and provide a better understanding of the landslide kinematics.

The interstellar N2 abundance towards HD 124314 from far-ultraviolet observations.

PubMed

Knauth, David C; Andersson, B-G; McCandliss, Stephan R; Moos, H Warren

2004-06-10

The abundance of interstellar molecular nitrogen (N2) is of considerable importance: models of steady-state gas-phase interstellar chemistry, together with millimetre-wavelength observations of interstellar N2H+ in dense molecular clouds predict that N2 should be the most abundant nitrogen-bearing molecule in the interstellar medium. Previous attempts to detect N2 absorption in the far-ultraviolet or infrared (ice features) have hitherto been unsuccessful. Here we report the detection of interstellar N2 at far-ultraviolet wavelengths towards the moderately reddened star HD 124314 in the constellation of Centaurus. The N2 column density is larger than expected from models of diffuse clouds and significantly smaller than expected for dense molecular clouds. Moreover, the N2 abundance does not explain the observed variations in the abundance of atomic nitrogen (N I) towards high-column-density sightlines, implying that the models of nitrogen chemistry in the interstellar medium are incomplete.

The sensitivity of gas-phase models of dense interstellar clouds to changes in dissociative recombination branching ratios

NASA Technical Reports Server (NTRS)

Millar, T. J.; Defrees, D. J.; Mclean, A. D.; Herbst, E.

1988-01-01

The approach of Bates to the determination of neutral product branching ratios in ion-electron dissociative recombination reactions has been utilized in conjunction with quantum chemical techniques to redetermine branching ratios for a wide variety of important reactions of this class in dense interstellar clouds. The branching ratios have then been used in a pseudo time-dependent model calculation of the gas phase chemistry of a dark cloud resembling TMC-1 and the results compared with an analogous model containing previously used branching ratios. In general, the changes in branching ratios lead to stronger effects on calculated molecular abundances at steady state than at earlier times and often lead to reductions in the calculated abundances of complex molecules. However, at the so-called 'early time' when complex molecule synthesis is most efficient, the abundances of complex molecules are hardly affected by the newly used branching ratios.

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms

DOE PAGES

Zhou, Jun; Li, Junjie; Correa, Alfredo A.; ...

2014-10-24

We report the first systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which are escaping into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We alsomore » developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.« less

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Jun; Li, Junjie; Correa, Alfredo A.

We report the first systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which are escaping into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We alsomore » developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.« less

The Lack of Influence of Metallicity on Cooling and Collapse of Ionized Gas in Small Protogalactic Halos

NASA Astrophysics Data System (ADS)

Jappsen, A.-K.; Glover, S. C. O.; Klessen, R. S.; Mac Low, M.-M.

2005-12-01

We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos. We use three-dimensional, smoothed particle hydrodynamics simulations, run with the publicly available parallel code GADGET (Springel et al. 2001). We implement a sink particle algorithm. This allows us to safely represent gas that has collapsed beyond the resolution limit without causing numerical errors within the resolved regions of the simulation. We also include the necessary framework for following the non-equilibrium chemistry of H2 in the protogalactic gas, and a treatment of radiative heating and cooling. Our initial conditions represent protogalaxies forming within a fossil H ii region---a previously ionized H ii region that has not yet had time to cool and recombine. Prior to cosmological reionization, such regions should be relatively common, since the characteristic lifetimes of the likely ionizing sources are significantly shorter than a Hubble time. We show that in these regions, H2 is the dominant and most effective coolant, even in the presence of small amounts of metals. It is the amount of H2 which forms that controls whether or not the gas can collapse and form stars. For metallicities Z ≤ 10-3 Z⊙, we find that metal line cooling alters the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm-3 and temperatures above 2000 K. However, at higher densities and lower temperatures, metal line cooling does become rather more important, and will affect the ability of the gas to fragment. We also show that an external ultraviolet background delays or suppresses the cooling and collapse of the gas regardless of whether or not it is metal-enriched. RSK and A-KJ acknowledge support from the Emmy Noether Program of the Deutsche Forschungsgemeinschaft (grant no. KL1358/1). M-MML acknowledges support from NSF grants AST99-85392 and AST03-07854, and NASA grant NAG5-10103. SCOG acknowledges support from NSF grant AST03-07793, and NASA grant NAG5-13028. The simulations were performed on the cluster "sanssouci" at Astrophysikalisches Institut Potsdam.

Newly detected molecules in dense interstellar clouds

NASA Astrophysics Data System (ADS)

Irvine, William M.; Avery, L. W.; Friberg, P.; Matthews, H. E.; Ziurys, L. M.

Several new interstellar molecules have been identified including C2S, C3S, C5H, C6H and (probably) HC2CHO in the cold, dark cloud TMC-1; and the discovery of the first interstellar phosphorus-containing molecule, PN, in the Orion "plateau" source. Further results include the observations of 13C3H2 and C3HD, and the first detection of HCOOH (formic acid) in a cold cloud.

Gravity, turbulence and the scaling ``laws'' in molecular clouds

NASA Astrophysics Data System (ADS)

Ballesteros-Paredes, Javier

The so-called Larson (1981) scaling laws found empirically in molecular clouds have been generally interpreted as evidence that the clouds are turbulent and fractal. In the present contribution we discussed how recent observations and models of cloud formation suggest that: (a) these relations are the result of strong observational biases due to the cloud definition itself: since the filling factor of the dense structures is small, by thresholding the column density the computed mean density between clouds is nearly constant, and nearly the same as the threshold (Ballesteros-Paredes et al. 2012). (b) When accounting for column density variations, the velocity dispersion-size relation does not appears anymore. Instead, dense cores populate the upper-left corner of the δ v-R diagram (Ballesteros-Paredes et al. 2011a). (c) Instead of a δ v-R relation, a more appropriate relation seems to be δ v 2 / R = 2 GMΣ, which suggest that clouds are in collapse, rather than supported by turbulence (Ballesteros-Paredes et al. 2011a). (d) These results, along with the shapes of the star formation histories (Hartmann, Ballesteros-Paredes & Heitsch 2012), line profiles of collapsing clouds in numerical simulations (Heitsch, Ballesteros-Paredes & Hartmann 2009), core-to-core velocity dispersions (Heitsch, Ballesteros-Paredes & Hartmann 2009), time-evolution of the column density PDFs (Ballesteros-Paredes et al. 2011b), etc., strongly suggest that the actual source of the non-thermal motions is gravitational collapse of the clouds, so that the turbulent, chaotic component of the motions is only a by-product of the collapse, with no significant ``support" role for the clouds. This result calls into question if the scale-free nature of the motions has a turbulent, origin (Ballesteros-Paredes et al. 2011a; Ballesteros-Paredes et al. 2011b, Ballesteros-Paredes et al. 2012).

A giant protogalactic disk linked to the cosmic web

NASA Astrophysics Data System (ADS)

Martin, D. Christopher; Matuszewski, Mateusz; Morrissey, Patrick; Neill, James D.; Moore, Anna; Cantalupo, Sebastiano; Prochaska, J. Xavier; Chang, Daphne

2015-08-01

The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that `cold accretion flows'--relatively cool (temperatures of the order of 104 kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos--are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections. Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging. Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 1013 solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.

A giant protogalactic disk linked to the cosmic web.

PubMed

Martin, D Christopher; Matuszewski, Mateusz; Morrissey, Patrick; Neill, James D; Moore, Anna; Cantalupo, Sebastiano; Prochaska, J Xavier; Chang, Daphne

2015-08-13

The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that 'cold accretion flows'--relatively cool (temperatures of the order of 10(4) kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos--are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections. Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging. Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 10(13) solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.

49 CFR 193.2059 - Flammable vapor-gas dispersion protection.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Dispersion Model.” Alternatively, in order to account for additional cloud dilution which may be caused by..., subject to the Administrator's approval. (b) The following dispersion parameters must be used in computing... if it can be shown that the terrain both upwind and downwind of the vapor cloud has dense vegetation...

49 CFR 193.2059 - Flammable vapor-gas dispersion protection.

Code of Federal Regulations, 2011 CFR

2011-10-01

... Dispersion Model.” Alternatively, in order to account for additional cloud dilution which may be caused by..., subject to the Administrator's approval. (b) The following dispersion parameters must be used in computing... if it can be shown that the terrain both upwind and downwind of the vapor cloud has dense vegetation...

49 CFR 193.2059 - Flammable vapor-gas dispersion protection.

Code of Federal Regulations, 2014 CFR

2014-10-01

... Dispersion Model.” Alternatively, in order to account for additional cloud dilution which may be caused by..., subject to the Administrator's approval. (b) The following dispersion parameters must be used in computing... if it can be shown that the terrain both upwind and downwind of the vapor cloud has dense vegetation...

The characteristic black hole mass resulting from direct collapse in the early Universe

NASA Astrophysics Data System (ADS)

Latif, M. A.; Schleicher, D. R. G.; Schmidt, W.; Niemeyer, J. C.

2013-12-01

Black holes of a billion solar masses are observed in the infant Universe a few hundred million years after the big bang. The direct collapse of protogalactic gas clouds in primordial haloes with Tvir ≥ 104 K provides the most promising way to assemble massive black holes. In this study, we aim to determine the characteristic mass scale of seed black holes and the time evolution of the accretion rates resulting from the direct collapse model. We explore the formation of supermassive black holes via cosmological large eddy simulations (LES) by employing sink particles and following their evolution for 20 000 yr after the formation of the first sink. As the resulting protostars were shown to have cool atmospheres in the presence of strong accretion, we assume here that UV feedback is negligible during this calculation. We confirm this result in a comparison run without sinks. Our findings show that black hole seeds with characteristic mass of 105 M⊙ are formed in the presence of strong Lyman-Werner flux which leads to an isothermal collapse. The characteristic mass is about two times higher in LES compared to the implicit large eddy simulations. The accretion rates increase with time and reach a maximum value of 10 M⊙ yr-1 after 104 yr. Our results show that the direct collapse model is clearly feasible as it provides the expected mass of the seed black holes.

On the formation and confinement of dense clouds in QSOs and active galactic nuclei

NASA Technical Reports Server (NTRS)

Marscher, A. P.; Weaver, R. P.

1979-01-01

A model for the formation and confinement of dense (at least about 1 billion per cu cm) clouds in QSOs and active galactic nuclei is presented wherein thermal instabilities behind radiative shocks cause the collapse of regions where the preshock density is enhanced over that of the surrounding medium. Such shocks (of total energy around 10 to the 51st ergs) are likely to occur if the frequent optical outbursts observed in many of these objects are accompanied by mass ejections of comparable energy. It is found that clouds quite similar to those thought to exist in QSOs etc. can be created in this manner at radii of the order of 10 to the 17th cm. The clouds can be subsequently accelerated to observed bulk velocities by either radiation pressure or a collision with a much stronger (total energy around 10 to the 53 ergs) shock. Alternatively, their high observed velocities could be caused by gravitational infall or rotation. The mass production required at inner radii by the outflow models can be supplied through a mechanism previously discussed by Shields (1977).

Analysis of interstellar cloud structure based on IRAS images

NASA Technical Reports Server (NTRS)

Scalo, John M.

1992-01-01

The goal of this project was to develop new tools for the analysis of the structure of densely sampled maps of interstellar star-forming regions. A particular emphasis was on the recognition and characterization of nested hierarchical structure and fractal irregularity, and their relation to the level of star formation activity. The panoramic IRAS images provided data with the required range in spatial scale, greater than a factor of 100, and in column density, greater than a factor of 50. In order to construct densely sampled column density maps of star-forming clouds, column density images of four nearby cloud complexes were constructed from IRAS data. The regions have various degrees of star formation activity, and most of them have probably not been affected much by the disruptive effects of young massive stars. The largest region, the Scorpius-Ophiuchus cloud complex, covers about 1000 square degrees (it was subdivided into a few smaller regions for analysis). Much of the work during the early part of the project focused on an 80 square degree region in the core of the Taurus complex, a well-studied region of low-mass star formation.

Magnetic seismology of interstellar gas clouds: Unveiling a hidden dimension

NASA Astrophysics Data System (ADS)

Tritsis, Aris; Tassis, Konstantinos

2018-05-01

Stars and planets are formed inside dense interstellar molecular clouds by processes imprinted on the three-dimensional (3D) morphology of the clouds. Determining the 3D structure of interstellar clouds remains challenging because of projection effects and difficulties measuring the extent of the clouds along the line of sight. We report the detection of normal vibrational modes in the isolated interstellar cloud Musca, allowing determination of the 3D physical dimensions of the cloud. We found that Musca is vibrating globally, with the characteristic modes of a sheet viewed edge on, not the characteristics of a filament as previously supposed. We reconstructed the physical properties of Musca through 3D magnetohydrodynamic simulations, reproducing the observed normal modes and confirming a sheetlike morphology.

Herschel HIFI GOT C+ Survey: CII, HI, and CO Emissions in a Sample of Transition Clouds and Star-Forming regions in the Inner Galaxy

NASA Astrophysics Data System (ADS)

Pineda, Jorge; Velusamy, Thangasamy; Langer, William D.; Goldsmith, Paul; Li, Di; Yorke, Harold

The GOT C+ a HIFI Herschel Key Project, studies the diffuse ISM throughout the Galactic Plane, using C+ as cloud tracer. The C+ line at 1.9 THz traces a so-far poorly studied stage in ISM cloud evolution -the transitional clouds going from atomic HI to molecular H2. This transition cloud phase, which is difficult to observe in HI and CO alone, may be best characterized via CII emission or absorption. The C+ line is also an excellent tracer of the warm diffuse gas and the warm, dense gas in the Photon Dominated Regions (PDRs). We can, therefore, use the CII emission as a probe to understand the effects of star formation on their interstellar environment. We present our first results on the transition between dense and hot gas (traced by CII) and dense and cold gas (traced by 12CO and 13CO) along a few representative lines of sight in the inner Galaxy from longitude 325 degrees to 25 degrees, taken during the HIFI Priority Science Phase. Comparisons of the high spectral resolution ( 1 km/s) HIFI data on C+ with HI, 12CO, and 13CO spectra allow us to separate out the different ISM components along each line of sight. Our results provide detailed information about the transition of diffuse atomic to molecular gas clouds needed to understand star formation and the lifecycle of the interstellar gas. These observations are being carried out with the Herschel Space Observatory, which is an ESA cornerstone mission, with contributions from NASA. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. JLP was supported under the NASA Postdoctoral Program at JPL, Caltech, administered by Oak Ridge Associated Universities through a contract with NASA, and is currently supported as a Caltech-JPL Postdoctoral associate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zardecki, A.

The effect of multiple scattering on the validity of the Beer-Lambert law is discussed for a wide range of particle-size parameters and optical depths. To predict the amount of received radiant power, appropriate correction terms are introduced. For particles larger than or comparable to the wavelength of radiation, the small-angle approximation is adequate; whereas for small densely packed particles, the diffusion theory is advantageously employed. These two approaches are used in the context of the problem of laser-beam propagation in a dense aerosol medium. In addition, preliminary results obtained by using a two-dimensional finite-element discrete-ordinates transport code are described. Multiple-scatteringmore » effects for laser propagation in fog, cloud, rain, and aerosol cloud are modeled.« less

Boundary Conditions for the Paleoenvironment: Chemical and Physical Processes in Dense Interstellar Clouds: Summary of Research

NASA Technical Reports Server (NTRS)

Irvine, William M.

1999-01-01

The basic theme of this program was the study of molecular complexity and evolution for the biogenic elements and compounds in interstellar clouds and in primitive solar system objects. Research included the detection and study of new interstellar and cometary molecules and investigation of reaction pathways for astrochemistry from a comparison of theory and observed molecular abundances. The latter includes studies of cold, dark clouds in which ion-molecule chemistry should predominate, searches for the effects of interchange of material between the gas and solid phases in interstellar clouds, unbiased spectral surveys of particular sources, and systematic investigation of the interlinked chemistry and physics of dense interstellar clouds. In addition, the study of comets has allowed a comparison between the chemistry of such minimally thermally processed objects and that of interstellar clouds, shedding light on the evolution of the biogenic elements during the process of solar system formation. One PhD dissertation on this research was completed by a graduate student at the University of Massachusetts. An additional 4 graduate students at the University of Massachusetts and 5 graduate students from other institutions participated in research supported by this grant, with 6 of these thus far receiving PhD degrees from the University of Massachusetts or their home institutions. Four postdoctoral research associates at the University of Massachusetts also participated in research supported by this grant, receiving valuable training.

Optically thin cirrus clouds over oceans and possible impact on sea surface temperature of warm pool in western Pacific

NASA Technical Reports Server (NTRS)

Prabhakara, C.; Yoo, J.-M.; Dalu, G.; Kratz, P.

1991-01-01

Over the convectively active tropical ocean regions, the measurement made from space in the IR and visible spectrum have revealed the presence of optically thin cirrus clouds, which are quite transparent in the visible and nearly opaque in the IR. The Nimbus-4 IR Interferometer Spectrometer (IRIS), which has a field of view (FOV) of approximately 100 km, was utilized to examine the IR optical characteristics of these cirrus clouds. From the IRIS data, it was observed that these optically thin cirrus clouds prevail extensively over the warm pool region of the equatorial western Pacific, surrounding Indonesia. It is found that the seasonal cloud cover caused by these thin cirrus clouds exceeds 50 percent near the central regions of the warm pool. For most of these clouds, the optical thickness in the IR is less than or = 2. It is deduced that the dense cold anvil clouds associated with deep convection spread extensively and are responsible for the formation of the thin cirrus clouds. This is supported by the observation that the coverage of the dense anvil clouds is an order of magnitude less than that of the thin cirrus clouds. From these observations, together with a simple radiative-convective model, it is inferred that the optically thin cirrus can provide a greenhouse effect, which can be a significant factor in maintaining the warm pool. In the absence of fluid transports, it is found that these cirrus clouds could lead to a runaway greenhouse effect. The presence of fluid transport processes, however, act to moderate this effect. Thus, if a modest 20 W/sq m energy input is considered to be available to warm the ocean, then it is found that the ocean mixed-layer of a 50-m depth will be heated by approximately 1 C in 100 days.

The chemistry of planet-forming regions is not interstellar.

PubMed

Pontoppidan, Klaus M; Blevins, Sandra M

2014-01-01

Advances in infrared and submillimeter technology have allowed for detailed observations of the molecular content of the planet-forming regions of protoplanetary disks. In particular, disks around solar-type stars now have growing molecular inventories that can be directly compared with both prestellar chemistry and that inferred for the early solar nebula. The data directly address the old question of whether the chemistry of planet-forming matter is similar or different and unique relative to the chemistry of dense clouds and protostellar envelopes. The answer to this question may have profound consequences for the structure and composition of planetary systems. The practical challenge is that observations of emission lines from disks do not easily translate into chemical concentrations. Here, we present a two-dimensional radiative transfer model of RNO 90, a classical protoplanetary disk around a solar-mass star, and retrieve the concentrations of dominant molecular carriers of carbon, oxygen and nitrogen in the terrestrial region around 1 AU. We compare our results to the chemical inventory of dense clouds and protostellar envelopes, and argue that inner disk chemistry is, as expected, fundamentally different from prestellar chemistry. We find that the clearest discriminant may be the concentration of CO2, which is extremely low in disks, but one of the most abundant constituents of dense clouds and protostellar envelopes.

Design of laboratory experiments to study radiation-driven implosions

DOE PAGES

Keiter, P. A.; Trantham, M.; Malamud, G.; ...

2017-02-03

The interstellar medium is heterogeneous with dense clouds amid an ambient medium. Radiation from young OB stars asymmetrically irradiate the dense clouds. Bertoldi (1989) developed analytic formulae to describe possible outcomes of these clouds when irradiated by hot, young stars. One of the critical parameters that determines the cloud’s fate is the number of photon mean free paths in the cloud. For the extreme cases where the cloud size is either much greater than or much less than one mean free path, the radiation transport should be well understood. However, as one transitions between these limits, the radiation transport ismore » much more complex and is a challenge to solve with many of the current radiation transport models implemented in codes. In this paper, we present the design of laboratory experiments that use a thermal source of x-rays to asymmetrically irradiate a low-density plastic foam sphere. The experiment will vary the density and hence the number of mean free paths of the sphere to study the radiation transport in different regimes. Finally, we have developed dimensionless parameters to relate the laboratory experiment to the astrophysical system and we show that we can perform the experiment in the same transport regime.« less

Externally fed star formation: a numerical study

NASA Astrophysics Data System (ADS)

Mohammadpour, Motahareh; Stahler, Steven W.

2013-08-01

We investigate, through a series of numerical calculations, the evolution of dense cores that are accreting external gas up to and beyond the point of star formation. Our model clouds are spherical, unmagnetized configurations with fixed outer boundaries, across which gas enters subsonically. When we start with any near-equilibrium state, we find that the cloud's internal velocity also remains subsonic for an extended period, in agreement with observations. However, the velocity becomes supersonic shortly before the star forms. Consequently, the accretion rate building up the protostar is much greater than the benchmark value c_s^3/G, where cs is the sound speed in the dense core. This accretion spike would generate a higher luminosity than those seen in even the most embedded young stars. Moreover, we find that the region of supersonic infall surrounding the protostar races out to engulf much of the cloud, again in violation of the observations, which show infall to be spatially confined. Similar problematic results have been obtained by all other hydrodynamic simulations to date, regardless of the specific infall geometry or boundary conditions adopted. Low-mass star formation is evidently a quasi-static process, in which cloud gas moves inward subsonically until the birth of the star itself. We speculate that magnetic tension in the cloud's deep interior helps restrain the infall prior to this event.

Water in dense molecular clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wannier, P.G.; Kuiper, T.B.H.; Frerking, M.A.

1991-08-01

The G.P. Kuiper Airborne Observatory (KAO) was used to make initial observations of the half-millimeter ground-state transition of water in seven giant molecular clouds and in two late-type stars. No significant detections were made, and the resulting upper limits are significantly below those expected from other, indirect observations and from several theoretical models. The implied interstellar H2O/CO abundance is less than 0.003 in the cores of three giant molecular clouds. This value is less than expected from cloud chemistry models and also than estimates based on HDO and H3O(+) observations. 78 refs.

The Photoevaporation of a Neutral Structure by an EUV+FUV Radiation Field

NASA Astrophysics Data System (ADS)

Lora, Veronica; Vasconcelos, M. J.; Raga, A. C.; Cerqueira, A. H.; Esquivel, A.

The expansion of an HII region into a surrounding inhomogeneous molecular cloud, leads to the formation of elongated "elephant trunk" structures. The EUV photo-ionising radiation and FUV dissociating radiation from newly born stars photo-evaporate their parental neutral cloud, leading to the formation of dense clumps in the tips of elephant trunks, that could in principle eventually form stars. We study th effects of including a photo-dissociating FUV flux in models of fragmentation of a photo-evaporating, self-gravitating molecular cloud.

Molecular gas in high-mass filament WB673

NASA Astrophysics Data System (ADS)

Kirsanova, Maria S.; Salii, Svetlana V.; Sobolev, Andrej M.; Olofsson, Anders Olof Henrik; Ladeyschikov, Dmitry A.; Thomasson, Magnus

2017-12-01

We studied the distribution of dense gas in a filamentary molecular cloud containing several dense clumps. The center of the filament is given by the dense clump WB673. The clumps are high-mass and intermediate-mass starforming regions. We observed CS (2-1), 13CO (1-0), C18O(1-0), and methanol lines at 96 GHz toward WB673 with the Onsala Space Observatory 20-m telescope. We found CS (2-1) emission in the inter-clump medium so the clumps are physically connected and the whole cloud is indeed a filament. Its total mass is 104 M⊙ and mass-to-length ratio is 360M⊙ pc-1 from 13CO (1-0) data. Mass-to-length ratio for the dense gas is 3.4 - 34M⊙ pc-1 from CS (2-1) data. The PV-diagram of the filament is V-shaped. We estimated physical conditions in the molecular gas using methanol lines. Location of the filament on the sky between extended shells suggests that it could be a good example to test theoretical models of formation of the filaments via multiple compression of interstellar gas by supersonic waves.

Reduction of unsaturated compounds under interstellar conditions: chemoselective reduction of C≡C and C=C bonds over C=O functional group

NASA Astrophysics Data System (ADS)

Jonusas, Mindaugas; Guillemin, Jean-Claude; Krim, Lahouari

2017-07-01

The knowledge of the H-addition reactions on unsaturated organic molecules bearing a triple or a double carbon-carbon bond such as propargyl or allyl alcohols and a CO functional group such as propynal, propenal or propanal may play an important role in the understanding of the chemical complexity of the interstellar medium. Why different aldehydes like methanal, ethanal, propynal and propanal are present in dense molecular clouds while the only alcohol detected in those cold regions is methanol? In addition, ethanol has only been detected in hot molecular cores. Are those saturated and unsaturated aldehyde and alcohol species chemically linked in molecular clouds through solid phase H-addition surface reactions or are they formed through different chemical routes? To answer such questions, we have investigated a hydrogenation study of saturated and unsaturated aldehydes and alcohols at 10 K. We prove through this experimental study that while pure unsaturated alcohol ices bombarded by H atoms lead to the formation of the corresponding fully or partially saturated alcohols, surface H-addition reactions on unsaturated aldehyde ices exclusively lead to the formation of fully saturated aldehyde. Such results show that in addition to a chemoselective reduction of C≡C and C=C bonds over the C=O group, there is no link between aldehydes and their corresponding alcohols in reactions involving H atoms in dense molecular clouds. Consequently, this could be one of the reasons why some aldehydes such as propanal are abundant in dense molecular clouds in contrast to the non-detection of alcohol species larger than methanol.

LNG vapor barrier and obstacle evaluation: Wind-tunnel simulation of 1987 Falcon Spill Series. Final report, July 1987-February 1991

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, S.H.; Meroney, R.N.; Neff, D.E.

1991-03-01

Measurements of the behavior of simulated liquefied natural gas clouds dispersing over small-scale model placed in environmental wind tunnels permits evaluations of the fluid physics of dense cloud movement and dispersion in a controlled environment. A large data base on the interaction of simulated LNG plumes with the Falcon test configuration of vapor barrier fences and vortex generators was obtained. The purpose of the reported test program is to provide post-field-spill wind tunnel experiments to augment the LNG Vapor Fence Field Program data obtained during the Falcon Test Series in 1987. The goal of the program is to determine themore » probable response of a dense LNG Vapor cloud to vortex inducer obstacles and fences, examine the sensitivity of results to various scaling arguments which might augment limit, or extend the value of the field and wind-tunnel tests, and identify important details of the spill behavior which were not predicted during the pretest planning phase.« less

The molecular composition of dense interstellar clouds

NASA Technical Reports Server (NTRS)

Allen, M.; Robinson, G. W.

1977-01-01

Presented in this paper is an ab initio chemical model for dense interstellar clouds that incorporates 598 grain surface reactions, with small grains providing the reaction area. Gas-phase molecules are depleted through collisions with grains. The abundances of 372 chemical species are calculated as a function of time and are found to be of sufficient magnitude to explain most observations. Peak abundances are achieved on time scales of the order of 100,000 to 1 million years, depending on cloud density and kinetic temperature. The reaction rates for ion-molecule chemistry are approximately the same, indicating that surface and gas-phase chemistry may be coupled in certain regions. The composition of grain mantles is shown to be a function of grain radius. In certain grain-size ranges, large molecules containing two or more heavy atoms are more predominant than lighter 'ices' - H2O, NH3, and CH4. It is possible that absorption due to these large molecules in the mantle may contribute to the observed 3-micron band in astronomical spectra.

Experimental evidence for glycolaldehyde and ethylene glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions

NASA Astrophysics Data System (ADS)

Fedoseev, G.; Cuppen, H. M.; Ioppolo, S.; Lamberts, T.; Linnartz, H.

2015-04-01

This study focuses on the formation of two molecules of astrobiological importance - glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) - by surface hydrogenation of CO molecules. Our experiments aim at simulating the CO freeze-out stage in interstellar dark cloud regions, well before thermal and energetic processing become dominant. It is shown that along with the formation of H2CO and CH3OH - two well-established products of CO hydrogenation - also molecules with more than one carbon atom form. The key step in this process is believed to be the recombination of two HCO radicals followed by the formation of a C-C bond. The experimentally established reaction pathways are implemented into a continuous-time random-walk Monte Carlo model, previously used to model the formation of CH3OH on astrochemical time-scales, to study their impact on the solid-state abundances in dense interstellar clouds of glycolaldehyde and ethylene glycol.

Coherent scattering of near-resonant light by a dense, microscopic cloud of cold two-level atoms: Experiment versus theory

NASA Astrophysics Data System (ADS)

Jennewein, Stephan; Brossard, Ludovic; Sortais, Yvan R. P.; Browaeys, Antoine; Cheinet, Patrick; Robert, Jacques; Pillet, Pierre

2018-05-01

We measure the coherent scattering of low-intensity, near-resonant light by a cloud of laser-cooled two-level rubidium atoms with a size comparable to the wavelength of light. We isolate a two-level atomic structure by applying a 300-G magnetic field. We measure both the temporal and the steady-state coherent optical response of the cloud for various detunings of the laser and for atom numbers ranging from 5 to 100. We compare our results to a microscopic coupled-dipole model and to a multimode, paraxial Maxwell-Bloch model. In the low-intensity regime, both models are in excellent agreement, thus validating the Maxwell-Bloch model. Comparing to the data, the models are found in very good agreement for relatively low densities (n /k3≲0.1 ), while significant deviations start to occur at higher density. This disagreement indicates that light scattering in dense, cold atomic ensembles is still not quantitatively understood, even in pristine experimental conditions.

Time dependent chemistry in dense molecular clouds. I - Grain surface reactions, gas/grain interactions and infrared spectroscopy

NASA Technical Reports Server (NTRS)

Dhendecourt, L. B.; Allamandola, L. J.; Greenberg, J. M.

1985-01-01

For the fist time, a time-dependent model is described which includes the role of grains in the production of molecules in dense clouds including ion-molecule gas phase chemistry. The approach provides information regarding the coupling between the two phases. Although the coupling between the two chemistries is extremely strong, the two domains maintain their own identities. While H2O, CH4, and NH3 are made efficiently, with a high production rate on grains and released back to the gas phase, the gas phase is essentially responsible for the formation of CO, a very stable molecule which may or may not react on grains with atomic oxygen and may or may not form CO2.

Organic Chemistry in Interstellar Ices: Connection to the Comet Halley Results

NASA Technical Reports Server (NTRS)

Schutte, W. A.; Agarwal, V. K.; deGroot, M. S.; Greenberg, J. M.; McCain, P.; Ferris, J. P.; Briggs, R.

1997-01-01

Mass spectroscopic measurements on the gas and dust in the coma of Comet Halley revealed the presence of considerable amounts of organic species. Greenberg (1973) proposed that prior to the formation of the comet UV processing of the ice mantles on grains in dense clouds could lead to the formation of complex organic molecules. Theoretical predictions of the internal UV field in dense clouds as well as the discovery in interstellar ices of species like OCS and OCN- which have been formed in simulation experiments by photoprocessing of interstellar ice analogues point to the importance of such processing. We undertook a laboratory simulation study of the formation of organic molecules in interstellar ices and their possible relevance to the Comet Halley results.

Widespread SiO and CH3OH emission in filamentary infrared dark clouds

NASA Astrophysics Data System (ADS)

Cosentino, G.; Jiménez-Serra, I.; Henshaw, J. D.; Caselli, P.; Viti, S.; Barnes, A. T.; Fontani, F.; Tan, J. C.; Pon, A.

2018-03-01

Infrared dark clouds (IRDCs) are cold, dense regions of high (optical and infrared) extinction, believed to be the birthplace of high-mass stars and stellar clusters. The physical mechanisms leading to the formation of these IRDCs are not completely understood and it is thus important to study their molecular gas kinematics and chemical content to search for any signature of the IRDCs formation process. Using the 30-m-diameter antenna at the Instituto de Radioastronomía Milimétrica (IRAM), we have obtained emission maps of dense gas tracers (H13CO+ and HN13C) and typical shock tracers (SiO and CH3OH) towards three IRDCs, G028.37+00.07, G034.43+00.24, and G034.77-00.55 (clouds C, F, and G, respectively). We have studied the molecular gas kinematics in these clouds and, consistent with previous works towards other IRDCs, the clouds show complex gas kinematics with several velocity-coherent substructures separated in velocity space by a few km s-1. Correlated with these complex kinematic structures, widespread (parsec-scale) emission of SiO and CH3OH is present in all the three clouds. For clouds C and F, known to be actively forming stars, widespread SiO and CH3OH is likely associated with on-going star formation activity. However, for cloud G, which lacks either 8 or 24 μm sources and 4.5 μm H2 shock-excited emission, the detected widespread SiO and CH3OH emission may have originated in a large-scale shock interaction, although a scenario involving a population of low-mass stars driving molecular outflows cannot be fully ruled out.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asahina, Yuta; Kawashima, Tomohisa; Furukawa, Naoko

The formation mechanism of CO clouds observed with the NANTEN2 and Mopra telescopes toward the stellar cluster Westerlund 2 is studied by 3D magnetohydrodynamic simulations, taking into account the interstellar cooling. These molecular clouds show a peculiar shape composed of an arc-shaped cloud on one side of the TeV γ -ray source HESS J1023-575 and a linear distribution of clouds (jet clouds) on the other side. We propose that these clouds are formed by the interaction of a jet with clumps of interstellar neutral hydrogen (H i). By studying the dependence of the shape of dense cold clouds formed bymore » shock compression and cooling on the filling factor of H i clumps, we found that the density distribution of H i clumps determines the shape of molecular clouds formed by the jet–cloud interaction: arc clouds are formed when the filling factor is large. On the other hand, when the filling factor is small, molecular clouds align with the jet. The jet propagates faster in models with small filling factors.« less

Refrigeration of the 18.3 GHz C_3H_2 Transition in Dark Clouds G1.6-0.25

NASA Technical Reports Server (NTRS)

Kuiper, T. B. H.; Whiteoak, J. B.; Peng, R. -S.; Peters, W. L., III; Reynolds, J. E.

1993-01-01

We have observed the 1_(10)-1_(01) (18.3 GHz) transition of orthocyclopropenylidene, C_(-3)H_(-2), at 24 positions in the unusual dense cloud G1.6- 0.025. Except for one position, the transition is refrigerated, a phenomenon which has not been seen in this transition before.

Analysis of Meteorological Data Obtained During Flight in a Supercooled Stratiform Cloud of High Liquid-Water Content

NASA Technical Reports Server (NTRS)

Perkins, Porter J.; Kline, Dwight B.

1951-01-01

Flight icing-rate data obtained in a dense and. abnormally deep supercooled stratiform cloud system indicated the existence of liquid-water contents generally exceeding values in amount and extent previously reported over the midwestern sections of the United States. Additional information obtained during descent through a part of the cloud system indicated liquid-water contents that significantly exceeded theoretical values, especially near the middle of the cloud layer.. The growth of cloud droplets to sizes that resulted in sedimentation from the upper portions of the cloud is considered to be a possible cause of the high water contents near the center of the cloud layer. Flight measurements of the vertical temperature distribution in the cloud layer indicated a rate of change of temperature with altitude exceeding that of the moist adiabatic lapse rate. This excessive rate of change is considered to have contributed to the severity of the condition.

Point-Cloud Compression for Vehicle-Based Mobile Mapping Systems Using Portable Network Graphics

NASA Astrophysics Data System (ADS)

Kohira, K.; Masuda, H.

2017-09-01

A mobile mapping system is effective for capturing dense point-clouds of roads and roadside objects Point-clouds of urban areas, residential areas, and arterial roads are useful for maintenance of infrastructure, map creation, and automatic driving. However, the data size of point-clouds measured in large areas is enormously large. A large storage capacity is required to store such point-clouds, and heavy loads will be taken on network if point-clouds are transferred through the network. Therefore, it is desirable to reduce data sizes of point-clouds without deterioration of quality. In this research, we propose a novel point-cloud compression method for vehicle-based mobile mapping systems. In our compression method, point-clouds are mapped onto 2D pixels using GPS time and the parameters of the laser scanner. Then, the images are encoded in the Portable Networking Graphics (PNG) format and compressed using the PNG algorithm. In our experiments, our method could efficiently compress point-clouds without deteriorating the quality.

A New Approach for Inspection of Selected Geometric Parameters of a Railway Track Using Image-Based Point Clouds

PubMed Central

Sawicki, Piotr

2018-01-01

The paper presents the results of testing a proposed image-based point clouds measuring method for geometric parameters determination of a railway track. The study was performed based on a configuration of digital images and reference control network. A DSLR (digital Single-Lens-Reflex) Nikon D5100 camera was used to acquire six digital images of the tested section of railway tracks. The dense point clouds and the 3D mesh model were generated with the use of two software systems, RealityCapture and PhotoScan, which have implemented different matching and 3D object reconstruction techniques: Multi-View Stereo and Semi-Global Matching, respectively. The study found that both applications could generate appropriate 3D models. Final meshes of 3D models were filtered with the MeshLab software. The CloudCompare application was used to determine the track gauge and cant for defined cross-sections, and the results obtained from point clouds by dense image matching techniques were compared with results of direct geodetic measurements. The obtained RMS difference in the horizontal (gauge) and vertical (cant) plane was RMS∆ < 0.45 mm. The achieved accuracy meets the accuracy condition of measurements and inspection of the rail tracks (error m < 1 mm), specified in the Polish branch railway instruction Id-14 (D-75) and the European technical norm EN 13848-4:2011. PMID:29509679

A New Approach for Inspection of Selected Geometric Parameters of a Railway Track Using Image-Based Point Clouds.

PubMed

Gabara, Grzegorz; Sawicki, Piotr

2018-03-06

The paper presents the results of testing a proposed image-based point clouds measuring method for geometric parameters determination of a railway track. The study was performed based on a configuration of digital images and reference control network. A DSLR (digital Single-Lens-Reflex) Nikon D5100 camera was used to acquire six digital images of the tested section of railway tracks. The dense point clouds and the 3D mesh model were generated with the use of two software systems, RealityCapture and PhotoScan, which have implemented different matching and 3D object reconstruction techniques: Multi-View Stereo and Semi-Global Matching, respectively. The study found that both applications could generate appropriate 3D models. Final meshes of 3D models were filtered with the MeshLab software. The CloudCompare application was used to determine the track gauge and cant for defined cross-sections, and the results obtained from point clouds by dense image matching techniques were compared with results of direct geodetic measurements. The obtained RMS difference in the horizontal (gauge) and vertical (cant) plane was RMS∆ < 0.45 mm. The achieved accuracy meets the accuracy condition of measurements and inspection of the rail tracks (error m < 1 mm), specified in the Polish branch railway instruction Id-14 (D-75) and the European technical norm EN 13848-4:2011.

VizieR Online Data Catalog: Dense cores in Taurus L1495 cloud (Marsh+, 2016)

NASA Astrophysics Data System (ADS)

Marsh, K. A.; Kirk, J. M.; Andre, P.; Griffin, M. J.; Konyves, V.; Palmeirim, P.; Men'shchikov, A.; Ward-Thompson, D.; Benedettini, M.; Bresnahan, D. W.; di, Francesco J.; Elia, D.; Motte, F.; Peretto, N.; Pezzuto, S.; Roy, A.; Sadavoy, S.; Schneider, N.; Spinoglio, L.; White, G. J.

2017-04-01

The observational data on which the present catalogue is based consists of a set of images of the L1495 cloud in the Taurus star-forming region, made as part of the HGBS (Andre et al. 2010). The data were taken using PACS at 70, 160, 250, 350 and 500 microns in fast-scanning (60"/s) parallel mode. (2 data files).

Lidar observations of high altitude cirrus near the tropical tropopause

NASA Astrophysics Data System (ADS)

Parameswaran, K.; Kumar, S. Sunil; Krishna Murthy, B.

High altitude cirrus plays a significant role in atmospheric chemistry, radiation and troposphere-stratosphere exchanges. Studies on their global morphology using satellite data (SAGE) suggests that over the tropics these clouds occur quite frequently in the altitude region around 14 to 16 km with favoured locations centred over Southern Asia, India and Mexico. A monostatic Nd:YAG lidar (operating at 532 nm wavelength) located at National MST Radar Facility (NMRF), Gadanki (13.5°N, 79.2°E) provides an excellent opportunity to study the properties of these clouds. Lidar observations for ~120 nights during the period January 1999 to March 2000 are used to investigate the physical and optical properties of these clouds aswell as their spatial (altitude) and temporal variability. Based on optical depth ( c ) cirrus clouds are classified as Sub-visual Cirrus (SVC) with c 0.03, Thin Cirrus (TC) with 0.030.3. While SVCs are observed anywhere in the altitude region 12 to 18 km, with favoured altitude above 15 km, TCs and DCs usually occur around 14.5+/-1km. The altitude region 14 to 16km appears to be more conducive for cirrus formation. Even though the geometrical thickness (vertical extent) of these clouds varies from 0.3 to 3 km, they are mostly confined to altitudes below the level of tropopause temperature inversion. The cloud optical depth maximises around the post-mid-night period. These clouds also introduce significant depolarisation for the backscattered radiation indicating presence of abundant non-spherical particles presumably ice-crystals. Under favourable conditions these ice-crystals get aligned horizontally to enhance the co - polarized component of lidar backscatter signal through specular reflection, leading to a decrease in cloud depolarisation () below the ambient molecular depolarisation (m ). Such conditions are usually encountered in the case of optically dense clouds. Altitude profile of backscatter ratio within the cloud shows that the cloud is not optically symmetric with respect to the geometric centre. This asymmetry parameter () of the cloud shows significant temporal variability. For clouds with> m , as c increases, the optical centre descends in altitude and for clouds with< m the optical centre ascends as c increases. Occurrence of cirrus clouds and their optical properties are found to be closely associated with the characteristics of atmospheric turbulence in the upper troposphere.

Unusual July 10, 1996, rock fall at Happy Isles, Yosemite National Park, California

USGS Publications Warehouse

Wieczorek, G.F.; Snyder, J.B.; Waitt, R.B.; Morrissey, M.M.; Uhrhammer, R.A.; Harp, E.L.; Norris, R.D.; Bursik, M.I.; Finewood, L.G.

2000-01-01

Effects of the July 10, 1996, rock fall at Happy Isles in Yosemite National Park, California, were unusual compared to most rock falls. Two main rock masses fell about 14 s apart from a 665-m-high cliff southeast of Glacier Point onto a talus slope above Happy Isles in the eastern part of Yosemite Valley. The two impacts were recorded by seismographs as much as 200 km away. Although the impact area of the rock falls was not particularly large, the falls generated an airblast and an abrasive dense sandy cloud that devastated a larger area downslope of the impact sites toward the Happy Isles Nature Center. Immediately downslope of the impacts, the airblast had velocities exceeding 110 m/s and toppled or snapped about 1000 trees. Even at distances of 0.5 km from impact, wind velocities snapped or toppled large trees, causing one fatality and several serious injuries beyond the Happy Isles Nature Center. A dense sandy cloud trailed the airblast and abraded fallen trunks and trees left standing. The Happy Isles rock fall is one of the few known worldwide to have generated an airblast and abrasive dense sandy cloud. The relatively high velocity of the rock fall at impact, estimated to be 110-120 m/s, influenced the severity and areal extent of the airblast at Happy Isles. Specific geologic and topographic conditions, typical of steep glaciated valleys and mountainous terrain, contributed to the rock-fall release and determined its travel path, resulting in a high velocity at impact that generated the devastating airblast and sandy cloud. The unusual effects of this rock fall emphasize the importance of considering collateral geologic hazards, such as airblasts from rock falls, in hazard assessment and planning development of mountainous areas.

Space Science

NASA Image and Video Library

2002-08-01

This sturning image, taken by the newly installed Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST), is an image of the center of the Omega Nebula. It is a hotbed of newly born stars wrapped in colorful blankets of glowing gas and cradled in an enormous cold, dark hydrogen cloud. The region of nebula shown in this photograph is about 3,500 times wider than our solar system. The nebula, also called M17 and the Swan Nebula, resides 5,500 light-years away in the constellation Sagittarius. The Swan Nebula is illuminated by ultraviolet radiation from young, massive stars, located just beyond the upper-right corner of the image. The powerful radiation from these stars evaporates and erodes the dense cloud of cold gas within which the stars formed. The blistered walls of the hollow cloud shine primarily in the blue, green, and red light emitted by excited atoms of hydrogen, nitrogen, oxygen, and sulfur. Particularly striking is the rose-like feature, seen to the right of center, which glows in the red light emitted by hydrogen and sulfur. As the infant stars evaporate the surrounding cloud, they expose dense pockets of gas that may contain developing stars. One isolated pocket is seen at the center of the brightest region of the nebula. Other dense pockets of gas have formed the remarkable feature jutting inward from the left edge of the image. The color image is constructed from four separate images taken in these filters: blue, near infrared, hydrogen alpha, and doubly ionized oxygen. Credit: NASA, H. Ford (JHU), G. Illingworth (USCS/LO), M. Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA.

Hubble Space Telescope Image of Omega Nebula

NASA Technical Reports Server (NTRS)

2002-01-01

This sturning image, taken by the newly installed Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST), is an image of the center of the Omega Nebula. It is a hotbed of newly born stars wrapped in colorful blankets of glowing gas and cradled in an enormous cold, dark hydrogen cloud. The region of nebula shown in this photograph is about 3,500 times wider than our solar system. The nebula, also called M17 and the Swan Nebula, resides 5,500 light-years away in the constellation Sagittarius. The Swan Nebula is illuminated by ultraviolet radiation from young, massive stars, located just beyond the upper-right corner of the image. The powerful radiation from these stars evaporates and erodes the dense cloud of cold gas within which the stars formed. The blistered walls of the hollow cloud shine primarily in the blue, green, and red light emitted by excited atoms of hydrogen, nitrogen, oxygen, and sulfur. Particularly striking is the rose-like feature, seen to the right of center, which glows in the red light emitted by hydrogen and sulfur. As the infant stars evaporate the surrounding cloud, they expose dense pockets of gas that may contain developing stars. One isolated pocket is seen at the center of the brightest region of the nebula. Other dense pockets of gas have formed the remarkable feature jutting inward from the left edge of the image. The color image is constructed from four separate images taken in these filters: blue, near infrared, hydrogen alpha, and doubly ionized oxygen. Credit: NASA, H. Ford (JHU), G. Illingworth (USCS/LO), M. Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA.

Observational evidence for cloud cover enhancement over western European forests.

PubMed

Teuling, Adriaan J; Taylor, Christopher M; Meirink, Jan Fokke; Melsen, Lieke A; Miralles, Diego G; van Heerwaarden, Chiel C; Vautard, Robert; Stegehuis, Annemiek I; Nabuurs, Gert-Jan; de Arellano, Jordi Vilà-Guerau

2017-01-11

Forests impact regional hydrology and climate directly by regulating water and heat fluxes. Indirect effects through cloud formation and precipitation can be important in facilitating continental-scale moisture recycling but are poorly understood at regional scales. In particular, the impact of temperate forest on clouds is largely unknown. Here we provide observational evidence for a strong increase in cloud cover over large forest regions in western Europe based on analysis of 10 years of 15 min resolution data from geostationary satellites. In addition, we show that widespread windthrow by cyclone Klaus in the Landes forest led to a significant decrease in local cloud cover in subsequent years. Strong cloud development along the downwind edges of larger forest areas are consistent with a forest-breeze mesoscale circulation. Our results highlight the need to include impacts on cloud formation when evaluating the water and climate services of temperate forests, in particular around densely populated areas.

Magnetic seismology of interstellar gas clouds: Unveiling a hidden dimension.

PubMed

Tritsis, Aris; Tassis, Konstantinos

2018-05-11

Stars and planets are formed inside dense interstellar molecular clouds by processes imprinted on the three-dimensional (3D) morphology of the clouds. Determining the 3D structure of interstellar clouds remains challenging because of projection effects and difficulties measuring the extent of the clouds along the line of sight. We report the detection of normal vibrational modes in the isolated interstellar cloud Musca, allowing determination of the 3D physical dimensions of the cloud. We found that Musca is vibrating globally, with the characteristic modes of a sheet viewed edge on, not the characteristics of a filament as previously supposed. We reconstructed the physical properties of Musca through 3D magnetohydrodynamic simulations, reproducing the observed normal modes and confirming a sheetlike morphology. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Observational evidence for cloud cover enhancement over western European forests

PubMed Central

Teuling, Adriaan J.; Taylor, Christopher M.; Meirink, Jan Fokke; Melsen, Lieke A.; Miralles, Diego G.; van Heerwaarden, Chiel C.; Vautard, Robert; Stegehuis, Annemiek I.; Nabuurs, Gert-Jan; de Arellano, Jordi Vilà-Guerau

2017-01-01

Forests impact regional hydrology and climate directly by regulating water and heat fluxes. Indirect effects through cloud formation and precipitation can be important in facilitating continental-scale moisture recycling but are poorly understood at regional scales. In particular, the impact of temperate forest on clouds is largely unknown. Here we provide observational evidence for a strong increase in cloud cover over large forest regions in western Europe based on analysis of 10 years of 15 min resolution data from geostationary satellites. In addition, we show that widespread windthrow by cyclone Klaus in the Landes forest led to a significant decrease in local cloud cover in subsequent years. Strong cloud development along the downwind edges of larger forest areas are consistent with a forest-breeze mesoscale circulation. Our results highlight the need to include impacts on cloud formation when evaluating the water and climate services of temperate forests, in particular around densely populated areas. PMID:28074840

Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

NASA Astrophysics Data System (ADS)

Carlhoff, P.; Nguyen Luong, Q.; Schilke, P.; Motte, F.; Schneider, N.; Beuther, H.; Bontemps, S.; Heitsch, F.; Hill, T.; Kramer, C.; Ossenkopf, V.; Schuller, F.; Simon, R.; Wyrowski, F.

2013-12-01

We aim to fully describe the distribution and location of dense molecular clouds in the giant molecular cloud complex W43. It was previously identified as one of the most massive star-forming regions in our Galaxy. To trace the moderately dense molecular clouds in the W43 region, we initiated W43-HERO, a large program using the IRAM 30 m telescope, which covers a wide dynamic range of scales from 0.3 to 140 pc. We obtained on-the-fly-maps in 13CO (2-1) and C18O (2-1) with a high spectral resolution of 0.1 km s-1 and a spatial resolution of 12''. These maps cover an area of ~1.5 square degrees and include the two main clouds of W43 and the lower density gas surrounding them. A comparison to Galactic models and previous distance calculations confirms the location of W43 near the tangential point of the Scutum arm at approximately 6 kpc from the Sun. The resulting intensity cubes of the observed region are separated into subcubes, which are centered on single clouds and then analyzed in detail. The optical depth, excitation temperature, and H2 column density maps are derived out of the 13CO and C18O data. These results are then compared to those derived from Herschel dust maps. The mass of a typical cloud is several 104 M⊙ while the total mass in the dense molecular gas (>102 cm-3) in W43 is found to be ~1.9 × 106 M⊙. Probability distribution functions obtained from column density maps derived from molecular line data and Herschel imaging show a log-normal distribution for low column densities and a power-law tail for high densities. A flatter slope for the molecular line data probability distribution function may imply that those selectively show the gravitationally collapsing gas. Appendices are available in electronic form at http://www.aanda.orgThe final datacubes (13CO and C18O) for the entire survey are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A24

Collapse and Fragmentation of Molecular Cloud Cores. VII. Magnetic Fields and Multiple Protostar Formation

NASA Astrophysics Data System (ADS)

Boss, Alan P.

2002-04-01

Recent observations of star-forming regions suggest that binary and multiple young stars are the rule rather than the exception and implicate fragmentation as the likely mechanism for their formation. Most numerical hydrodynamic calculations of fragmentation have neglected the possibly deleterious effects of magnetic fields, despite ample evidence for the importance of magnetic support of precollapse clouds. We present here the first numerical hydrodynamic survey of the collapse and fragmentation of initially magnetically supported clouds that takes into account several magnetic field effects in an approximate manner. The models are calculated with a three-dimensional, finite differences code that solves the equations of hydrodynamics, gravitation, and radiative transfer in the Eddington and diffusion approximations. Magnetic field effects are included through two simple approximations: magnetic pressure is added to the gas pressure, and magnetic tension is approximated by gravity dilution once collapse is well underway. Ambipolar diffusion of the magnetic field leading to cloud collapse is treated approximately as well. Models are calculated for a variety of initial cloud density profiles, shapes, and rotation rates. We find that in spite of the inclusion of magnetic field effects, dense cloud cores are capable of fragmenting into binary and multiple protostar systems. Initially prolate clouds tend to fragment into binary protostars, while initially oblate clouds tend to fragment into multiple protostar systems containing a small number (of the order of 4) of fragments. The latter are likely to be subject to rapid orbital evolution, with close encounters possibly leading to the ejection of fragments. Contrary to expectation, magnetic tension effects appear to enhance fragmentation, allowing lower mass fragments to form than would otherwise be possible, because magnetic tension helps to prevent a central density singularity from forming and producing a dominant single object. Magnetically supported dense cloud cores thus seem to be capable of collapsing and fragmenting into sufficient numbers of binary and multiple protostar systems to be compatible with observations of the relative rarity of single protostars.

TRIGGERING COLLAPSE OF THE PRESOLAR DENSE CLOUD CORE AND INJECTING SHORT-LIVED RADIOISOTOPES WITH A SHOCK WAVE. II. VARIED SHOCK WAVE AND CLOUD CORE PARAMETERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boss, Alan P.; Keiser, Sandra A., E-mail: boss@dtm.ciw.edu, E-mail: keiser@dtm.ciw.edu

2013-06-10

A variety of stellar sources have been proposed for the origin of the short-lived radioisotopes that existed at the time of the formation of the earliest solar system solids, including Type II supernovae (SNe), asymptotic giant branch (AGB) and super-AGB stars, and Wolf-Rayet star winds. Our previous adaptive mesh hydrodynamics models with the FLASH2.5 code have shown which combinations of shock wave parameters are able to simultaneously trigger the gravitational collapse of a target dense cloud core and inject significant amounts of shock wave gas and dust, showing that thin SN shocks may be uniquely suited for the task. However,more » recent meteoritical studies have weakened the case for a direct SN injection to the presolar cloud, motivating us to re-examine a wider range of shock wave and cloud core parameters, including rotation, in order to better estimate the injection efficiencies for a variety of stellar sources. We find that SN shocks remain as the most promising stellar source, though planetary nebulae resulting from AGB star evolution cannot be conclusively ruled out. Wolf-Rayet (WR) star winds, however, are likely to lead to cloud core shredding, rather than to collapse. Injection efficiencies can be increased when the cloud is rotating about an axis aligned with the direction of the shock wave, by as much as a factor of {approx}10. The amount of gas and dust accreted from the post-shock wind can exceed that injected from the shock wave, with implications for the isotopic abundances expected for a SN source.« less

Bipolar H II regions produced by cloud-cloud collisions

NASA Astrophysics Data System (ADS)

Whitworth, Anthony; Lomax, Oliver; Balfour, Scott; Mège, Pierre; Zavagno, Annie; Deharveng, Lise

2018-05-01

We suggest that bipolar H II regions may be the aftermath of collisions between clouds. Such a collision will produce a shock-compressed layer, and a star cluster can then condense out of the dense gas near the center of the layer. If the clouds are sufficiently massive, the star cluster is likely to contain at least one massive star, which emits ionizing radiation, and excites an H II region, which then expands, sweeping up the surrounding neutral gas. Once most of the matter in the clouds has accreted onto the layer, expansion of the H II region meets little resistance in directions perpendicular to the midplane of the layer, and so it expands rapidly to produce two lobes of ionized gas, one on each side of the layer. Conversely, in directions parallel to the midplane of the layer, expansion of the H II region stalls due to the ram pressure of the gas that continues to fall towards the star cluster from the outer parts of the layer; a ring of dense neutral gas builds up around the waist of the bipolar H II region, and may spawn a second generation of star formation. We present a dimensionless model for the flow of ionized gas in a bipolar H II region created according to the above scenario, and predict the characteristics of the resulting free-free continuum and recombination-line emission. This dimensionless model can be scaled to the physical parameters of any particular system. Our intention is that these predictions will be useful in testing the scenario outlined above, and thereby providing indirect support for the role of cloud-cloud collisions in triggering star formation.

Photogrammetric DSM denoising

NASA Astrophysics Data System (ADS)

Nex, F.; Gerke, M.

2014-08-01

Image matching techniques can nowadays provide very dense point clouds and they are often considered a valid alternative to LiDAR point cloud. However, photogrammetric point clouds are often characterized by a higher level of random noise compared to LiDAR data and by the presence of large outliers. These problems constitute a limitation in the practical use of photogrammetric data for many applications but an effective way to enhance the generated point cloud has still to be found. In this paper we concentrate on the restoration of Digital Surface Models (DSM), computed from dense image matching point clouds. A photogrammetric DSM, i.e. a 2.5D representation of the surface is still one of the major products derived from point clouds. Four different algorithms devoted to DSM denoising are presented: a standard median filter approach, a bilateral filter, a variational approach (TGV: Total Generalized Variation), as well as a newly developed algorithm, which is embedded into a Markov Random Field (MRF) framework and optimized through graph-cuts. The ability of each algorithm to recover the original DSM has been quantitatively evaluated. To do that, a synthetic DSM has been generated and different typologies of noise have been added to mimic the typical errors of photogrammetric DSMs. The evaluation reveals that standard filters like median and edge preserving smoothing through a bilateral filter approach cannot sufficiently remove typical errors occurring in a photogrammetric DSM. The TGV-based approach much better removes random noise, but large areas with outliers still remain. Our own method which explicitly models the degradation properties of those DSM outperforms the others in all aspects.

United States Air Force Summer Faculty Research Program. Management Report. Volume 1

DTIC Science & Technology

1988-12-01

sensors , measure reaction characteristics of fuel and oxidizer at various inlet velocities and initial conditions. Application of spectroscopy, high... applications in armament systems. False signals caused by cloud, fog, and snow interfere with proper response of the sensors , and efforts to... sensor for this application have not been fully successful (1-18). Presence of dense clouds, fog, or snow will create false signals and will obscure

Nanosatellite Maneuver Planning for Point Cloud Generation With a Rangefinder

DTIC Science & Technology

2015-06-05

aided active vision systems [11], dense stereo [12], and TriDAR [13]. However, these systems are unsuitable for a nanosatellite system from power, size...command profiles as well as improving the fidelity of gap detection with better filtering methods for background objects . For example, attitude...application of a single beam laser rangefinder (LRF) to point cloud generation, shape detection , and shape reconstruction for a space-based space

Modeling and simulation of dense cloud dispersion in urban areas by means of computational fluid dynamics.

PubMed

Scargiali, F; Grisafi, F; Busciglio, A; Brucato, A

2011-12-15

The formation of toxic heavy clouds as a result of sudden accidental releases from mobile containers, such as road tankers or railway tank cars, may occur inside urban areas so the problem arises of their consequences evaluation. Due to the semi-confined nature of the dispersion site simplified models may often be inappropriate. As an alternative, computational fluid dynamics (CFD) has the potential to provide realistic simulations even for geometrically complex scenarios since the heavy gas dispersion process is described by basic conservation equations with a reduced number of approximations. In the present work a commercial general purpose CFD code (CFX 4.4 by Ansys(®)) is employed for the simulation of dense cloud dispersion in urban areas. The simulation strategy proposed involves a stationary pre-release flow field simulation followed by a dynamic after-release flow and concentration field simulations. In order to try a generalization of results, the computational domain is modeled as a simple network of straight roads with regularly distributed blocks mimicking the buildings. Results show that the presence of buildings lower concentration maxima and enlarge the side spread of the cloud. Dispersion dynamics is also found to be strongly affected by the quantity of heavy-gas released. Copyright © 2011 Elsevier B.V. All rights reserved.

The chemical evolution of molecular clouds

NASA Technical Reports Server (NTRS)

Iglesias, E.

1977-01-01

The nonequilibrium chemistry of dense molecular clouds (10,000 to 1 million hydrogen molecules per cu cm) is studied in the framework of a model that includes the latest published chemical data and most of the recent theoretical advances. In this model the only important external source of ionization is assumed to be high-energy cosmic-ray bombardment; standard charge-transfer reactions are taken into account as well as reactions that transfer charge from molecular ions to trace-metal atoms. Schemes are proposed for the synthesis of such species as NCO, HNCO, and CN. The role played by adsorption and condensation of molecules on the surface of dust grains is investigated, and effects on the chemical evolution of a dense molecular cloud are considered which result from varying the total density or the elemental abundances and from assuming negligible or severe condensation of gaseous species on dust grains. It is shown that the chemical-equilibrium time scale is given approximately by the depletion times of oxygen and nitrogen when the condensation efficiency is negligible; that this time scale is probably in the range from 1 to 4 million years, depending on the elemental composition and initial conditions in the cloud; and that this time scale is insensitive to variations in the total density.

Dense flow around a sphere moving into a cloud of grains

NASA Astrophysics Data System (ADS)

Gondret, Philippe; Faure, Sylvain; Lefebvre-Lepot, Aline; Seguin, Antoine

2017-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone of about constant solid fraction builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size that increases with the initial solid fraction ϕ0 of the cloud. A detailed analysis of the local strain rate and local stress fields inside the cluster reveals that, despite different spatial variations of strain and stresses, the local friction coeffcient μ appears to depend only on the local inertial number I as well as the local solid fraction ϕ, which means that a local rheology does exist in the present non parallel flow. The key point is that the spatial variations of I inside the cluster does not depend on the sphere velocity and explore only a small range between about 10-2 and 10-1. The influence of sidewalls is then investigated on the flow and the forces.

Shallow convection on day 261 of GATE - Mesoscale arcs

NASA Technical Reports Server (NTRS)

Warner, C.; Simpson, J.; Martin, D. W.; Suchman, D.; Mosher, F. R.; Reinking, R. F.

1979-01-01

Cloudy convection in the moist layer of a cloud cluster growing in the GATE ship array is examined. Analyses suggest that the moist layer was dominated by features of horizontal dimension roughly 40 km and lifetime roughly 2 h, with arc patterns triggered by dense downdraft air accompanying rainfall, and composed of many small cumulus clouds. Aircraft recorded data on thermodynamic quantities and winds, indicating that the arcs persisted as mesoscale circulations driven by the release of latent heat in the clouds, rather than being driven by the original density current at the surface. It is also suggested that the mesoscale cloud patterns of the moist layer play a primary role in heat transfer upward within this layer, and contribute to the forcing of showering midtropospheric clouds.

International Conference on Aerosols, Clouds and the Indian Monsoon

NASA Astrophysics Data System (ADS)

Singh, Ramesh P.; Tare, Vinod; Tripathi, S. N.

2005-06-01

In recent years, dense haze and fog problems in the northern parts of India have affected the 460 million people living in the Indo-Gangetic basin. Substantial Indian research activities related to aerosols, clouds, and monsoon are taking place in the central and southern parts of India. To attract attention to the problems, a three-day International Conference on Aerosols, Clouds and Indian Monsoon was recently held at the Indian Institute of Technology, Kanpur, in the central part of the Indo-Gangetic basin. About 120 delegates from India, Germany, Greece, Japan, Taiwan, and the United States attended the conference.

Handle-shaped Prominence

NASA Image and Video Library

2001-02-17

NASA Extreme Ultraviolet Imaging Telescope aboard ESA’s SOHO spacecraft took this image of a huge, handle-shaped prominence in 1999. Prominences are huge clouds of relatively cool dense plasma suspended in the Sun hot, thin corona.

Automatic Method for Building Indoor Boundary Models from Dense Point Clouds Collected by Laser Scanners

PubMed Central

Valero, Enrique; Adán, Antonio; Cerrada, Carlos

2012-01-01

In this paper we present a method that automatically yields Boundary Representation Models (B-rep) for indoors after processing dense point clouds collected by laser scanners from key locations through an existing facility. Our objective is particularly focused on providing single models which contain the shape, location and relationship of primitive structural elements of inhabited scenarios such as walls, ceilings and floors. We propose a discretization of the space in order to accurately segment the 3D data and generate complete B-rep models of indoors in which faces, edges and vertices are coherently connected. The approach has been tested in real scenarios with data coming from laser scanners yielding promising results. We have deeply evaluated the results by analyzing how reliably these elements can be detected and how accurately they are modeled. PMID:23443369

Isomerization and fragmentation of acetonitrile upon interaction with N(4S) atoms: the chemistry of nitrogen in dense molecular clouds

NASA Astrophysics Data System (ADS)

Mencos, Alejandro; Krim, Lahouari

2016-08-01

We experimentally show that the reaction between ground state nitrogen atoms N(4S) and acetonitrile CH3CN can lead to two distinct chemical pathways that are both thermally activated at very low temperatures. First is CH3CN isomerization which produces CH3NC and H2CCNH. Second is CH3CN decomposition which produces HNC and CH3CNH+CN- fragments, with the possible release of H2. Our results reveal that the mobility of N(4S)-atoms is stimulated in the 3-11 K temperature range, and that its subsequent encounter with one acetonitrile molecule is sufficient for the aforementioned reactions to occur without the need for additional energy to be supplied to the CH3CN + N(4S) system. These findings shed more light on the nitrogen chemistry that can possibly take place in dense molecular clouds, which until now was thought to only involve high-energy processes and therefore be unlikely to occur in such cold and dark interstellar regions. The reaction pathways we propose in this study have very important astrochemical implications, as it was shown recently that the atomic nitrogen might be more abundant, in many interstellar icy grain mantles, than previously thought. Also, these reaction pathways can now be considered within dense molecular clouds, and possibly affect the branching ratios for N-bearing molecules computed in astrochemical modelling.

Making and Breaking Clouds

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-10-01

Molecular clouds which youre likely familiar with from stunning popular astronomy imagery lead complicated, tumultuous lives. A recent study has now found that these features must be rapidly built and destroyed.Star-Forming CollapseA Hubble view of a molecular cloud, roughly two light-years long, that has broken off of the Carina Nebula. [NASA/ESA, N. Smith (University of California, Berkeley)/The Hubble Heritage Team (STScI/AURA)]Molecular gas can be found throughout our galaxy in the form of eminently photogenic clouds (as featured throughout this post). Dense, cold molecular gas makes up more than 20% of the Milky Ways total gas mass, and gravitational instabilities within these clouds lead them to collapse under their own weight, resulting in the formation of our galaxys stars.How does this collapse occur? The simplest explanation is that the clouds simply collapse in free fall, with no source of support to counter their contraction. But if all the molecular gas we observe collapsed on free-fall timescales, star formation in our galaxy would churn a rate thats at least an order of magnitude higher than the observed 12 solar masses per year in the Milky Way.Destruction by FeedbackAstronomers have theorized that there may be some mechanism that supports these clouds against gravity, slowing their collapse. But both theoretical studies and observations of the clouds have ruled out most of these potential mechanisms, and mounting evidence supports the original interpretation that molecular clouds are simply gravitationally collapsing.A sub-mm image from ESOs APEX telescope of part of the Taurus molecular cloud, roughly ten light-years long, superimposed on a visible-light image of the region. [ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2. Acknowledgment: Davide De Martin]If this is indeed the case, then one explanation for our low observed star formation rate could be that molecular clouds are rapidly destroyed by feedback from the very stars they create. But to match with observations, this wouldsuggest that molecular clouds are short-lived objects that are built (and therefore replenished) just as quickly as they are destroyed. Is this possible?Speedy Building?In a recent study, a team of scientists led by Mordecai-Mark Mac Low (American Museum of Natural History and Heidelberg University, Germany) explore whether there is a way to create molecular clouds rapidly enough to match the necessary rate of destruction.Mac Low and collaborators find that some common mechanisms used to explain the formation of molecular clouds like gas being swept up by supernovae cant quite operate quickly enough to combat the rate of cloud destruction. On the other hand, the Toomre gravitational instability,which is a large-scale gravitational instability that occurs in gas disks,can very rapidly assemble gas into clumps dense enough to form molecules.A composite of visible and near-infrared images from the VLT ANTU telescope of the Barnard 68 molecular cloud, roughly half a light-year in diameter. [ESO]A Rapid CycleBased on their findings, the authors argue that dense, star-forming molecular clouds persist only for a short time before collapsing into stars and then being blown apart by stellar feedback but these very clouds are built equally quickly via gravitational instabilities.Conveniently, this model has a very testable prediction: the Toomre instability is expected to become even stronger at higher redshift, which suggests that the fraction of gas in the form of molecules should increase at high redshifts. This appears to agree with observations, supporting the authors picture of a rapid cycle of cloud assembly and destruction.CitationMordecai-Mark Mac Low et al 2017 ApJL 847 L10. doi:10.3847/2041-8213/aa8a61

Triggering collapse of the presolar dense cloud core and injecting short-lived radioisotopes with a shock wave. III. Rotating three-dimensional cloud cores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boss, Alan P.; Keiser, Sandra A., E-mail: boss@dtm.ciw.edu

2014-06-10

A key test of the supernova triggering and injection hypothesis for the origin of the solar system's short-lived radioisotopes is to reproduce the inferred initial abundances of these isotopes. We present here the most detailed models to date of the shock wave triggering and injection process, where shock waves with varied properties strike fully three-dimensional, rotating, dense cloud cores. The models are calculated with the FLASH adaptive mesh hydrodynamics code. Three different outcomes can result: triggered collapse leading to fragmentation into a multiple protostar system; triggered collapse leading to a single protostar embedded in a protostellar disk; or failure tomore » undergo dynamic collapse. Shock wave material is injected into the collapsing clouds through Rayleigh-Taylor fingers, resulting in initially inhomogeneous distributions in the protostars and protostellar disks. Cloud rotation about an axis aligned with the shock propagation direction does not increase the injection efficiency appreciably, as the shock parameters were chosen to be optimal for injection even in the absence of rotation. For a shock wave from a core-collapse supernova, the dilution factors for supernova material are in the range of ∼10{sup –4} to ∼3 × 10{sup –4}, in agreement with recent laboratory estimates of the required amount of dilution for {sup 60}Fe and {sup 26}Al. We conclude that a type II supernova remains as a promising candidate for synthesizing the solar system's short-lived radioisotopes shortly before their injection into the presolar cloud core by the supernova's remnant shock wave.« less

The chemistry of dense interstellar clouds

NASA Technical Reports Server (NTRS)

Irvine, W. M.

1991-01-01

The basic theme of this program is the study of molecular complexity and evolution in interstellar and circumstellar clouds incorporating the biogenic elements. Recent results include the identification of a new astronomical carbon-chain molecule, C4Si. This species was detected in the envelope expelled from the evolved star IRC+10216 in observations at the Nobeyama Radio Observatory in Japan. C4Si is the carrier of six unidentified lines which had previously been observed. This detection reveals the existence of a new series of carbon-chain molecules, C sub n Si (n equals 1, 2, 4). Such molecules may well be formed from the reaction of Si(+) with acetylene and acetylene derivatives. Other recent research has concentrated on the chemical composition of the cold, dark interstellar clouds, the nearest dense molecular clouds to the solar system. Such regions have very low kinetic temperatures, on the order of 10 K, and are known to be formation sites for solar-type stars. We have recently identified for the first time in such regions the species of H2S, NO, HCOOH (formic acid). The H2S abundance appears to exceed that predicted by gas-phase models of ion-molecule chemistry, perhaps suggesting the importance of synthesis on grain surfaces. Additional observations in dark clouds have studied the ratio of ortho- to para-thioformaldehyde. Since this ratio is expected to be unaffected by both radiative and ordinary collisional processes in the cloud, it may well reflect the formation conditions for this molecule. The ratio is observed to depart from that expected under conditions of chemical equilibrium at formation, perhaps reflecting efficient interchange between cold dust grains in the gas phase.

SEMANTIC3D.NET: a New Large-Scale Point Cloud Classification Benchmark

NASA Astrophysics Data System (ADS)

Hackel, T.; Savinov, N.; Ladicky, L.; Wegner, J. D.; Schindler, K.; Pollefeys, M.

2017-05-01

This paper presents a new 3D point cloud classification benchmark data set with over four billion manually labelled points, meant as input for data-hungry (deep) learning methods. We also discuss first submissions to the benchmark that use deep convolutional neural networks (CNNs) as a work horse, which already show remarkable performance improvements over state-of-the-art. CNNs have become the de-facto standard for many tasks in computer vision and machine learning like semantic segmentation or object detection in images, but have no yet led to a true breakthrough for 3D point cloud labelling tasks due to lack of training data. With the massive data set presented in this paper, we aim at closing this data gap to help unleash the full potential of deep learning methods for 3D labelling tasks. Our semantic3D.net data set consists of dense point clouds acquired with static terrestrial laser scanners. It contains 8 semantic classes and covers a wide range of urban outdoor scenes: churches, streets, railroad tracks, squares, villages, soccer fields and castles. We describe our labelling interface and show that our data set provides more dense and complete point clouds with much higher overall number of labelled points compared to those already available to the research community. We further provide baseline method descriptions and comparison between methods submitted to our online system. We hope semantic3D.net will pave the way for deep learning methods in 3D point cloud labelling to learn richer, more general 3D representations, and first submissions after only a few months indicate that this might indeed be the case.

Photogrammetric Point Clouds Generation in Urban Areas from Integrated Image Matching and Segmentation

NASA Astrophysics Data System (ADS)

Ye, L.; Wu, B.

2017-09-01

High-resolution imagery is an attractive option for surveying and mapping applications due to the advantages of high quality imaging, short revisit time, and lower cost. Automated reliable and dense image matching is essential for photogrammetric 3D data derivation. Such matching, in urban areas, however, is extremely difficult, owing to the complexity of urban textures and severe occlusion problems on the images caused by tall buildings. Aimed at exploiting high-resolution imagery for 3D urban modelling applications, this paper presents an integrated image matching and segmentation approach for reliable dense matching of high-resolution imagery in urban areas. The approach is based on the framework of our existing self-adaptive triangulation constrained image matching (SATM), but incorporates three novel aspects to tackle the image matching difficulties in urban areas: 1) occlusion filtering based on image segmentation, 2) segment-adaptive similarity correlation to reduce the similarity ambiguity, 3) improved dense matching propagation to provide more reliable matches in urban areas. Experimental analyses were conducted using aerial images of Vaihingen, Germany and high-resolution satellite images in Hong Kong. The photogrammetric point clouds were generated, from which digital surface models (DSMs) were derived. They were compared with the corresponding airborne laser scanning data and the DSMs generated from the Semi-Global matching (SGM) method. The experimental results show that the proposed approach is able to produce dense and reliable matches comparable to SGM in flat areas, while for densely built-up areas, the proposed method performs better than SGM. The proposed method offers an alternative solution for 3D surface reconstruction in urban areas.

Slow Cooling in Low Metallicity Clouds: An Origin of Globular Cluster Bimodality?

NASA Astrophysics Data System (ADS)

Fernandez, Ricardo; Bryan, Greg L.

2018-05-01

We explore the relative role of small-scale fragmentation and global collapse in low-metallicity clouds, pointing out that in such clouds the cooling time may be longer than the dynamical time, allowing the cloud to collapse globally before it can fragment. This, we suggest, may help to explain the formation of the low-metallicity globular cluster population, since such dense stellar systems need a large amount of gas to be collected in a small region (without significant feedback during the collapse). To explore this further, we carry out numerical simulations of low-metallicity Bonner-Ebert stable gas clouds, demonstrating that there exists a critical metallicity (between 0.001 and 0.01 Z⊙) below which the cloud collapses globally without fragmentation. We also run simulations including a background radiative heating source, showing that this can also produce clouds that do not fragment, and that the critical metallicity - which can exceed the no-radiation case - increases with the heating rate.

Height Distribution Between Cloud and Aerosol Layers from the GLAS Spaceborne Lidar in the Indian Ocean Region

NASA Technical Reports Server (NTRS)

Hart, William D.; Spinhirne, James D.; Palm, Steven P.; Hlavka, Dennis L.

2005-01-01

The Geoscience Laser Altimeter System (GLAS), a nadir pointing lidar on the Ice Cloud and land Elevation Satellite (ICESat) launched in 2003, now provides important new global measurements of the relationship between the height distribution of cloud and aerosol layers. GLAS data have the capability to detect, locate, and distinguish between cloud and aerosol layers in the atmosphere up to 40 km altitude. The data product algorithm tests the product of the maximum attenuated backscatter coefficient b'(r) and the vertical gradient of b'(r) within a layer against a predetermined threshold. An initial case result for the critical Indian Ocean region is presented. From the results the relative height distribution between collocated aerosol and cloud shows extensive regions where cloud formation is well within dense aerosol scattering layers at the surface. Citation: Hart, W. D., J. D. Spinhime, S. P. Palm, and D. L. Hlavka (2005), Height distribution between cloud and aerosol layers from the GLAS spaceborne lidar in the Indian Ocean region,

OT2_jhewitt_2: Understanding Shock Oxygen Chemistry in Interacting Supernova Remnants

NASA Astrophysics Data System (ADS)

Hewitt, J.

2011-09-01

Supernova remnants interacting with dense moelcular clouds provide astrochemical laboratories to study heating and cooling of the dense ISM, shock chemistry, destruction and sputtering of dust, and the reformation of molecules. Water is expected to be a major coolant for shocks into dense gas, yet the number of remnants in which IR lines of hydroxyl and water are detected is very limited. We propose Herschel PACS, SPIRE and HIFI observations of three remnants with particularly high shocked gas densities, high dust and IR line luinosities, and extreme ionization environments. The scientific objectives of this proposal are: (1) to determine the abundance and excitation of oxygen-bearing molecules, and (2) to study the effects of variable ionization sources on oxygen chemistry in dense molecular gas shocked by powerful supernova remnant blast waves.

HD 62542: Probing the Bare, Dense Core of an Interstellar Cloud

NASA Astrophysics Data System (ADS)

Welty, Daniel; Sonnentrucker, Paule G.; Rachford, Brian; Snow, Theodore; York, Donald G.

2018-01-01

We discuss the interstellar absorption from many atomic and molecular species seen in high-resolution HST/STIS UV spectra of the moderately reddened B3-5 V star HD 62542 [E(B-V) ~ 0.35; AV ~ 1.2]. This remarkable sight line exhibits both very steep far-UV extinction and a high fraction of hydrogen in molecular form -- with strong absorption from CH, C2, CN, and CO but weak absorption from CH+ and most of the commonly observed diffuse interstellar bands. Most of the material appears to reside in a single narrow velocity component -- thus offering a rare opportunity to probe the relatively dense, primarily molecular core of a single interstellar cloud, with little associated diffuse atomic gas.Detailed analyses of the absorption-line profiles seen in the UV spectra reveal a number of properties of the main diffuse molecular cloud toward HD 62542:1) The depletions of Mg, Si, and Fe are more severe than those seen in any other sight line, but the depletions of Cl and Kr are very mild; the overall pattern of depletions differs somewhat from those derived from larger samples of Galactic sight lines.2) The rotational excitation of H2 and C2 indicates that the gas is fairly cold (Tk = 40-45 K) and moderately dense (nH > 420 cm-3) somewhat higher densities are suggested by the fine-structure excitation of neutral carbon.3) The excitation temperatures characterizing the rotational populations of both 12CO (11.7 K) and 13CO (7.7 K) are higher than those typically found for Galactic diffuse molecular clouds.4) Carbon is primarily singly ionized -- N(C+) > N(CO) > N(C).5) The relative abundances of various trace neutral atomic species reflect the effects of both the steep far-UV extinction and the severe depletions of some elements.6) Differences in line widths for the various atomic and molecular species are suggestive of differences in spatial distribution within the main cloud.Support for this study was provided by NASA, via STScI grant GO-12277.008-A.

The inception of star cluster formation revealed by [C II] emission around an Infrared Dark Cloud

NASA Astrophysics Data System (ADS)

Bisbas, Thomas G.; Tan, Jonathan C.; Csengeri, Timea; Wu, Benjamin; Lim, Wanggi; Caselli, Paola; Güsten, Rolf; Ricken, Oliver; Riquelme, Denise

2018-07-01

We present SOFIA-upGREAT observations of [C II] emission of Infrared Dark Cloud (IRDC) G035.39-00.33, designed to trace its atomic gas envelope and thus test models of the origins of such clouds. Several velocity components of [C II] emission are detected, tracing structures that are at a wide range of distances in the Galactic plane. We find a main component that is likely associated with the IRDC and its immediate surroundings. This strongest emission component has a velocity similar to that of the 13CO(2-1) emission of the IRDC, but offset by ˜3 km s-1 and with a larger velocity width of ˜9 km s-1. The spatial distribution of the [C II] emission of this component is also offset predominantly to one side of the dense filamentary structure of the IRDC. The C II column density is estimated to be of the order of ˜1017-1018 cm-2. We compare these results to the [C II] emission from numerical simulations of magnetized, dense gas filaments formed from giant molecular cloud (GMC) collisions, finding similar spatial and kinematic offsets. These observations and modellingof [C II] add further to the evidence that IRDC G035.39-00.33 has been formed by a process of GMC-GMC collision, which may thus be an important mechanism for initiating star cluster formation.

The star-forming content of the W3 giant molecular cloud

NASA Astrophysics Data System (ADS)

Moore, T. J. T.; Bretherton, D. E.; Fujiyoshi, T.; Ridge, N. A.; Allsopp, J.; Hoare, M. G.; Lumsden, S. L.; Richer, J. S.

2007-08-01

We have surveyed a ˜0.9 square degree area of the W3 giant molecular cloud (GMC) and star-forming region in the 850-μm continuum, using the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. A complete sample of 316 dense clumps were detected with a mass range from around 13 to 2500 M⊙. Part of the W3 GMC is subject to an interaction with the H ii region and fast stellar winds generated by the nearby W4 OB association. We find that the fraction of total gas mass in dense, 850-μm traced structures is significantly altered by this interaction, being around 5-13 per cent in the undisturbed cloud but ˜25-37 per cent in the feedback-affected region. The mass distribution in the detected clump sample depends somewhat on assumptions of dust temperature and is not a simple, single power law but contains significant structure at intermediate masses. This structure is likely to be due to crowding of sources near or below the spatial resolution of the observations. There is little evidence of any difference between the index of the high-mass end of the clump mass function in the compressed region and in the unaffected cloud. The consequences of these results are discussed in terms of current models of triggered star formation.

Rendering of dense, point cloud data in a high fidelity driving simulator.

DOT National Transportation Integrated Search

2014-09-01

Driving Simulators are advanced tools that can address many research questions in transportation. Recently they have been used to advance the practice of transportation engineering, specifically signs, signals, pavement markings, and most powerfully ...

Star-Studded Strings around Cocoon Nebula

NASA Image and Video Library

2011-04-13

Dense filaments of gas in the IC5146 interstellar cloud can be seen clearly in this image taken in infrared light by the Herschel space observatory. The blue region is a stellar nursery known as the Cocoon nebula.

Generating Accurate 3d Models of Architectural Heritage Structures Using Low-Cost Camera and Open Source Algorithms

NASA Astrophysics Data System (ADS)

Zacharek, M.; Delis, P.; Kedzierski, M.; Fryskowska, A.

2017-05-01

These studies have been conductedusing non-metric digital camera and dense image matching algorithms, as non-contact methods of creating monuments documentation.In order toprocess the imagery, few open-source software and algorithms of generating adense point cloud from images have been executed. In the research, the OSM Bundler, VisualSFM software, and web application ARC3D were used. Images obtained for each of the investigated objects were processed using those applications, and then dense point clouds and textured 3D models were created. As a result of post-processing, obtained models were filtered and scaled.The research showedthat even using the open-source software it is possible toobtain accurate 3D models of structures (with an accuracy of a few centimeters), but for the purpose of documentation and conservation of cultural and historical heritage, such accuracy can be insufficient.

Volcanism-Climate Interactions

NASA Technical Reports Server (NTRS)

Walter, Louis S. (Editor); Desilva, Shanaka (Editor)

1991-01-01

The range of disciplines in the study of volcanism-climate interactions includes paleoclimate, volcanology, petrology, tectonics, cloud physics and chemistry, and climate and radiation modeling. Questions encountered in understanding the interactions include: the source and evolution of sulfur and sulfur-gaseous species in magmas; their entrainment in volcanic plumes and injection into the stratosphere; their dissipation rates; and their radiative effects. Other issues include modeling and measuring regional and global effects of such large, dense clouds. A broad-range plan of research designed to answer these questions was defined. The plan includes observations of volcanoes, rocks, trees, and ice cores, as well as satellite and aircraft observations of erupting volcanoes and resulting lumes and clouds.

Ortho- and para-hydrogen in dense clouds, protoplanets, and planetary atmospheres

NASA Technical Reports Server (NTRS)

Decampli, W. M.; Cameron, A. G. W.; Bodenheimer, P.; Black, D. C.

1978-01-01

If ortho- and para-hydrogen achieve a thermal ratio on dynamical time scales in a molecular hydrogen cloud, then the specific heat is high enough in the temperature range 35-70 K to possibly induce hydrodynamic collapse. The ortho-para ratio in many interstellar cloud fragments is expected to meet this condition. The same may have been true for the primitive solar nebula. Detailed hydrodynamic and hydrostatic calculations are presented that show the effects of the assumed ortho-para ratio on the evolution of Jupiter during its protoplanetary phase. Some possible consequences of a thermalized ortho-para ratio in the atmospheres of the giant planets are also discussed.

THE BOLOCAM GALACTIC PLANE SURVEY. XII. DISTANCE CATALOG EXPANSION USING KINEMATIC ISOLATION OF DENSE MOLECULAR CLOUD STRUCTURES WITH {sup 13}CO(1-0)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ellsworth-Bowers, Timothy P.; Glenn, Jason; Rosolowsky, Erik

2015-01-20

We present an expanded distance catalog for 1710 molecular cloud structures identified in the Bolocam Galactic Plane Survey (BGPS) version 2, representing a nearly threefold increase over the previous BGPS distance catalog. We additionally present a new method for incorporating extant data sets into our Bayesian distance probability density function (DPDF) methodology. To augment the dense-gas tracers (e.g., HCO{sup +}(3-2), NH{sub 3}(1,1)) used to derive line-of-sight velocities for kinematic distances, we utilize the Galactic Ring Survey (GRS) {sup 13}CO(1-0) data to morphologically extract velocities for BGPS sources. The outline of a BGPS source is used to select a region ofmore » the GRS {sup 13}CO data, along with a reference region to subtract enveloping diffuse emission, to produce a line profile of {sup 13}CO matched to the BGPS source. For objects with a HCO{sup +}(3-2) velocity, ≈95% of the new {sup 13}CO(1-0) velocities agree with that of the dense gas. A new prior DPDF for kinematic distance ambiguity (KDA) resolution, based on a validated formalism for associating molecular cloud structures with known objects from the literature, is presented. We demonstrate this prior using catalogs of masers with trigonometric parallaxes and H II regions with robust KDA resolutions. The distance catalog presented here contains well-constrained distance estimates for 20% of BGPS V2 sources, with typical distance uncertainties ≲ 0.5 kpc. Approximately 75% of the well-constrained sources lie within 6 kpc of the Sun, concentrated in the Scutum-Centaurus arm. Galactocentric positions of objects additionally trace out portions of the Sagittarius, Perseus, and Outer arms in the first and second Galactic quadrants, and we also find evidence for significant regions of interarm dense gas.« less

Formation of structures around HII regions: ionization feedback from massive stars

NASA Astrophysics Data System (ADS)

Tremblin, P.; Audit, E.; Minier, V.; Schmidt, W.; Schneider, N.

2015-03-01

We present a new model for the formation of dense clumps and pillars around HII regions based on shocks curvature at the interface between a HII region and a molecular cloud. UV radiation leads to the formation of an ionization front and of a shock ahead. The gas is compressed between them forming a dense shell at the interface. This shell may be curved due to initial interface or density modulation caused by the turbulence of the molecular cloud. Low curvature leads to instabilities in the shell that form dense clumps while sufficiently curved shells collapse on itself to form pillars. When turbulence is high compared to the ionized-gas pressure, bubbles of cold gas have sufficient kinetic energy to penetrate into the HII region and detach themselves from the parent cloud, forming cometary globules. Using computational simulations, we show that these new models are extremely efficient to form dense clumps and stable and growing elongated structures, pillars, in which star formation might occur (see Tremblin et al. 2012a). The inclusion of turbulence in the model shows its importance in the formation of cometary globules (see Tremblin et al. 2012b). Globally, the density enhancement in the simulations is of one or two orders of magnitude higher than the density enhancement of the classical ``collect and collapse`` scenario. The code used for the simulation is the HERACLES code, that comprises hydrodynamics with various equation of state, radiative transfer, gravity, cooling and heating. Our recent observations with Herschel (see Schneider et al. 2012a) and SOFIA (see Schneider et al. 2012b) and additional Spitzer data archives revealed many more of these structures in regions where OB stars have already formed such as the Rosette Nebula, Cygnus X, M16 and Vela, suggesting that the UV radiation from massive stars plays an important role in their formation. We present a first comparison between the simulations described above and recent observations of these regions.

DEEPLY EMBEDDED PROTOSTELLAR POPULATION IN THE 20 km s{sup −1} CLOUD OF THE CENTRAL MOLECULAR ZONE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Xing; Gu, Qiusheng; Zhang, Qizhou

2015-12-01

We report the discovery of a population of deeply embedded protostellar candidates in the 20 km s{sup −1} cloud, one of the massive molecular clouds in the Central Molecular Zone (CMZ) of the Milky Way, using interferometric submillimeter continuum and H{sub 2}O maser observations. The submillimeter continuum emission shows five 1 pc scale clumps, each of which further fragments into several 0.1 pc scale cores. We identify 17 dense cores, among which 12 are gravitationally bound. Among the 18 H{sub 2}O masers detected, 13 coincide with the cores and probably trace outflows emanating from the protostars. There are also 5more » gravitationally bound dense cores without H{sub 2}O maser detection. In total, the 13 masers and 5 cores may represent 18 protostars with spectral types later than B1 or potentially growing more massive stars at earlier evolutionary stages, given the non-detection in the centimeter radio continuum. In combination with previous studies of CH{sub 3}OH masers, we conclude that the star formation in this cloud is at an early evolutionary phase, before the presence of any significant ionizing or heating sources. Our findings indicate that star formation in this cloud may be triggered by a tidal compression as it approaches pericenter, similar to the case of G0.253+0.016 but with a higher star formation rate, and demonstrate that high angular resolution, high-sensitivity maser, and submillimeter observations are promising techniques to unveil deeply embedded star formation in the CMZ.« less

ALMA RESOLVES 30 DORADUS: SUB-PARSEC MOLECULAR CLOUD STRUCTURE NEAR THE CLOSEST SUPER STAR CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Indebetouw, Remy; Brogan, Crystal; Leroy, Adam

2013-09-01

We present Atacama Large (sub)Millimeter Array observations of 30 Doradus-the highest resolution view of molecular gas in an extragalactic star formation region to date ({approx}0.4 pc Multiplication-Sign 0.6 pc). The 30Dor-10 cloud north of R136 was mapped in {sup 12}CO 2-1, {sup 13}CO 2-1, C{sup 18}O 2-1, 1.3 mm continuum, the H30{alpha} recombination line, and two H{sub 2}CO 3-2 transitions. Most {sup 12}CO emission is associated with small filaments and clumps ({approx}<1 pc, {approx}10{sup 3} M{sub Sun} at the current resolution). Some clumps are associated with protostars, including ''pillars of creation'' photoablated by intense radiation from R136. Emission from molecularmore » clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumps have somewhat larger linewidths for a given size than predicted by Larson's scaling relation, consistent with pressure confinement. They extend to a higher surface density at a given size and linewidth compared to clouds studied at 10 pc resolution. These trends are also true of clumps in Galactic infrared-dark clouds; higher resolution observations of both environments are required. Consistency of clump masses calculated from dust continuum, CO, and the virial theorem reveals that the CO abundance in 30 Doradus clumps is not significantly different from the Large Magellanic Cloud mean, but the dust abundance may be reduced by {approx}2. There are no strong trends in clump properties with distance from R136; dense clumps are not strongly affected by the external radiation field, but there is a modest trend toward lower dense clump filling fraction deeper in the cloud.« less

The formation of high-mass stars and stellar clusters in the extreme environment of the Central Molecular Zone

NASA Astrophysics Data System (ADS)

Walker, Daniel Lewis

2017-08-01

The process of converting gas into stars underpins much of astrophysics, yet many fundamental questions surrounding this process remain unanswered. For example - how sensitive is star formation to the local environmental conditions? How do massive and dense stellar clusters form, and how does this crowded environment influence the stars that form within it? How do the most massive stars form and is there an upper limit to the stellar initial mass function (IMF)? Answering questions such as these is crucial if we are to construct an end-to-end model of how stars form across the full range of conditions found throughout the Universe. The research described in this thesis presents a study that utilises a multi-scale approach to identifying and characterising the early precursors to young massive clusters and high-mass proto-stars, with a specific focus on the extreme environment in the inner few hundred parsecs of the Milky Way - the Central Molecular Zone (CMZ). The primary sources of interest that are studied in detail belong to the Galactic centre dust ridge - a group of six high-mass (M 10^(4-5) Msun), dense (R 1-3 pc, n > 10^(4) cm^(-3)), and quiescent molecular clouds. These properties make these clouds ideal candidates for representing the earliest stages of high-mass star and cluster formation. The research presented makes use of single-dish and interferometric far-infrared and (sub-)millimetre observations to study their global and small-scale properties. A comparison of the known young massive clusters (YMCs) and their likely progenitors (the dust ridge clouds) in the CMZ shows that the stellar content of YMCs is much more dense and centrally concentrated than the gas in the clouds. If these clouds are truly precursors to massive clusters, the resultant stellar population would have to undergo significant dynamical evolution to reach central densities that are typical of YMCs. This suggests that YMCs in the CMZ are unlikely to form monolithically. Extending this study to include YMCs in the Galactic disc again shows that the known population of YMC precursor clouds throughout the Galaxy are not sufficiently dense or central concentrated that they could form a cluster that then expands due to gas expulsion. The data also reveal an evolutionary trend, in which clouds contract and accrete gas towards their central regions along with concurrent star formation. This is argued to favour a conveyor-belt mode of YMC formation and is again not consistent with a monolithic formation event. High angular resolution observations of the dust ridge clouds with the Submillimeter Array are presented. They reveal an embedded population of compact and massive cores, ranging from 50 - 2150 Msun within radii of 0.1 - 0.25 pc. These are likely formation sites of high-mass stars and clusters, and are strong candidates for representing the initial conditions of extremely massive stars. Two of these cores are found to be young, high-mass proto-stars, while the remaining 13 are quiescent. Comparing these cores with high-mass proto-stars in the Galactic disc, along with models in which star formation is regulated by turbulence, shows that these cores are consistent with the idea that the critical density threshold for star formation is greater in the turbulent environment at the Galactic centre.

Improving rainfall estimation from commercial microwave links using METEOSAT SEVIRI cloud cover information

NASA Astrophysics Data System (ADS)

Boose, Yvonne; Doumounia, Ali; Chwala, Christian; Moumouni, Sawadogo; Zougmoré, François; Kunstmann, Harald

2017-04-01

The number of rain gauges is declining worldwide. A recent promising method for alternative precipitation measurements is to derive rain rates from the attenuation of the microwave signal between remote antennas of mobile phone base stations, so called commercial microwave links (CMLs). In European countries, such as Germany, the CML technique can be used as a complementary method to the existing gauge and radar networks improving their products, for example, in mountainous terrain and urban areas. In West African countries, where a dense gauge or radar network is absent, the number of mobile phone users is rapidly increasing and so are the CML networks. Hence, the CML-derived precipitation measurements have high potential for applications such as flood warning and support of agricultural planning in this region. For typical CML bandwidths (10-40 GHz), the relationship of attenuation to rain rate is quasi-linear. However, also humidity, wet antennas or electronic noise can lead to signal interference. To distinguish these fluctuations from actual attenuation due to rain, a temporal wet (rain event occurred)/ dry (no rain event) classification is usually necessary. In dense CML networks this is possible by correlating neighboring CML time series. Another option is to use the correlation between signal time series of different frequencies or bidirectional signals. The CML network in rural areas is typically not dense enough for correlation analysis and often only one polarization and one frequency are available along a CML. In this work we therefore use cloud cover information derived from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) radiometer onboard the geostationary satellite METEOSAT for a wet (pixels along link are cloud covered)/ dry (no cloud along link) classification. We compare results for CMLs in Burkina Faso and Germany, which differ meteorologically (rain rate and duration, droplet size distributions) and technically (CML frequencies, lengths, signal level) and use rain gauge data as ground truth for validation.

Histotripsy beyond the “Intrinsic” Cavitation Threshold using Very Short Ultrasound Pulses: “Microtripsy”

PubMed Central

Lin, Kuang-Wei; Kim, Yohan; Maxwell, Adam D.; Wang, Tzu-Yin; Hall, Timothy L.; Xu, Zhen; Fowlkes, J. Brian; Cain, Charles A.

2014-01-01

Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. Conventional histotripsy treatments have used longer pulses from 3 to 10 cycles wherein the lesion-producing bubble cloud generation depends on the pressure-release scattering of very high peak positive shock fronts from previously initiated, sparsely distributed bubbles (the “shock-scattering” mechanism). In our recent work, the peak negative pressure (P−) for generation of dense bubble clouds directly by a single negative half cycle, the “intrinsic threshold,” was measured. In this paper, the dense bubble clouds and resulting lesions (in RBC phantoms and canine tissues) generated by these supra-intrinsic threshold pulses were studied. A 32-element, PZT-8, 500 kHz therapy transducer was used to generate very short (< 2 cycles) histotripsy pulses at a pulse repetition frequency (PRF) of 1 Hz and P− from 24.5 to 80.7 MPa. The results showed that the spatial extent of the histotripsy-induced lesions increased as the applied P− increased, and the sizes of these lesions corresponded well to the estimates of the focal regions above the intrinsic cavitation threshold, at least in the lower pressure regime (P− = 26–35 MPa). The average sizes for the smallest reproducible lesions were approximately 0.9 × 1.7 mm (lateral × axial), significantly smaller than the −6dB beamwidth of the transducer (1.8 × 4.0 mm). These results suggest that, using the intrinsic threshold mechanism, well-confined and microscopic lesions can be precisely generated and their spatial extent can be estimated based on the fraction of the focal region exceeding the intrinsic cavitation threshold. Since the supra-threshold portion of the negative half cycle can be precisely controlled, lesions considerably less than a wavelength are easily produced, hence the term “microtripsy.” PMID:24474132

Prebiotic chemical evolution in the astrophysical context.

PubMed

Ziurys, L M; Adande, G R; Edwards, J L; Schmidt, D R; Halfen, D T; Woolf, N J

2015-06-01

An ever increasing amount of molecular material is being discovered in the interstellar medium, associated with the birth and death of stars and planetary systems. Radio and millimeter-wave astronomical observations, made possible by high-resolution laboratory spectroscopy, uniquely trace the history of gas-phase molecules with biogenic elements. Using a combination of both disciplines, the full extent of the cycling of molecular matter, from circumstellar ejecta of dying stars - objects which expel large amounts of carbon - to nascent solar systems, has been investigated. Such stellar ejecta have been found to exhibit a rich and varied chemical content. Observations demonstrate that this molecular material is passed onto planetary nebulae, the final phase of stellar evolution. Here the star sheds almost its entire original mass, becoming an ultraviolet-emitting white dwarf. Molecules such as H2CO, HCN, HCO(+), and CCH are present in significant concentrations across the entire age span of such nebulae. These data suggest that gas-phase polyatomic, carbon-containing molecules survive the planetary nebula phase and subsequently are transported into the interstellar medium, seeding the chemistry of diffuse and then dense clouds. The extent of the chemical complexity in dense clouds is unknown, hindered by the high spectral line density. Organic species such as acetamide and methyl amine are present in such objects, and NH2CHO has a wide Galactic distribution. However, organophosphorus compounds have not yet been detected in dense clouds. Based on carbon and nitrogen isotope ratios, molecular material from the ISM appears to become incorporated into solar system planetesimals. It is therefore likely that interstellar synthesis influences prebiotic chemistry on planet surfaces.

Aerial Images and Convolutional Neural Network for Cotton Bloom Detection.

PubMed

Xu, Rui; Li, Changying; Paterson, Andrew H; Jiang, Yu; Sun, Shangpeng; Robertson, Jon S

2017-01-01

Monitoring flower development can provide useful information for production management, estimating yield and selecting specific genotypes of crops. The main goal of this study was to develop a methodology to detect and count cotton flowers, or blooms, using color images acquired by an unmanned aerial system. The aerial images were collected from two test fields in 4 days. A convolutional neural network (CNN) was designed and trained to detect cotton blooms in raw images, and their 3D locations were calculated using the dense point cloud constructed from the aerial images with the structure from motion method. The quality of the dense point cloud was analyzed and plots with poor quality were excluded from data analysis. A constrained clustering algorithm was developed to register the same bloom detected from different images based on the 3D location of the bloom. The accuracy and incompleteness of the dense point cloud were analyzed because they affected the accuracy of the 3D location of the blooms and thus the accuracy of the bloom registration result. The constrained clustering algorithm was validated using simulated data, showing good efficiency and accuracy. The bloom count from the proposed method was comparable with the number counted manually with an error of -4 to 3 blooms for the field with a single plant per plot. However, more plots were underestimated in the field with multiple plants per plot due to hidden blooms that were not captured by the aerial images. The proposed methodology provides a high-throughput method to continuously monitor the flowering progress of cotton.

Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds

NASA Astrophysics Data System (ADS)

Chen, Che-Yu; Li, Zhi-Yun; King, Patrick K.; Fissel, Laura M.

2017-10-01

Thin, magnetically aligned striations of relatively moderate contrast with the background are commonly observed in both atomic and molecular clouds. They are also prominent in MHD simulations with turbulent converging shocks. The simulated striations develop within a dense, stagnated sheet in the midplane of the post-shock region where magnetically induced converging flows collide. We show analytically that the secondary flows are an inevitable consequence of the jump conditions of oblique MHD shocks. They produce the stagnated, sheet-like sub-layer through a secondary shock when, roughly speaking, the Alfvénic speed in the primary converging flows is supersonic, a condition that is relatively easy to satisfy in interstellar clouds. The dense sub-layer is naturally threaded by a strong magnetic field that lies close to the plane of the sub-layer. The substantial magnetic field makes the sheet highly anisotropic, which is the key to the striation formation. Specifically, perturbations of the primary inflow that vary spatially perpendicular to the magnetic field can easily roll up the sheet around the field lines without bending them, creating corrugations that appear as magnetically aligned striations in column density maps. On the other hand, perturbations that vary spatially along the field lines curve the sub-layer and alter its orientation relative to the magnetic field locally, seeding special locations that become slanted overdense filaments and prestellar cores through enhanced mass accumulation along field lines. In our scenario, the dense sub-layer, which is unique to magnetized oblique shocks, is the birthplace for both magnetically aligned diffuse striations and massive star-forming structures.

Boundary conditions for the paleoenvironment: Chemical and Physical Processes in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Irvine, W. M.; Schloerb, F. P.; Ziurys, L. M.

1986-01-01

The present research includes searches for important new interstellar constituents; observations relevant to differentiating between different models for the chemical processes that are important in the interstellar environment; and coordinated studies of the chemistry, physics, and dynamics of molecular clouds which are the sites or possible future sites of star formation. Recent research has included the detection and study of four new interstellar molecules; searches which have placed upper limits on the abundance of several other potential constituents of interstellar clouds; quantitative studies of comparative molecular abundances in different types of interstellar clouds; investigation of reaction pathways for astrochemistry from a comparison of theory and the observed abundance of related species such as isomers and isotopic variants; studies of possible tracers of energenic events related to star formation, including silicon and sulfur containing molecules; and mapping of physical, chemical, and dynamical properties over extended regions of nearby cold molecular clouds.

Detection of mesoscale convective complexes using multispectral RGB technique of Himawari-8 (Case Study: Jakarta, 20 February 2017)

NASA Astrophysics Data System (ADS)

Fatkhuroyan; Wati, T.

2018-05-01

Mesoscale Convective Complexes (MCC) is a well-organized convective cloud that has big size and long lifetime. The aim of the study is to detect and to monitor the development of MCC around Jakarta on 20th February 2017 using satellite Himawari-8. This study uses the analyzing method of the infrared channel and multispectral imagery RGB Technique to monitor the development of radiative, morphology and cloud position which describe the cloud top microphysics, structure and movement of the MCC. On 20th February 2017, the result from Himawari-8 shows that there are many dense-clouds with small ice particle and cloud top temperature could be < -50°C which can be seen as red and yellow dot colour by RGB Technique. The MCC caused a severe storm at Jakarta and its surrounding area.

Evaluation of terrestrial photogrammetric point clouds derived from thermal imagery

NASA Astrophysics Data System (ADS)

Metcalf, Jeremy P.; Olsen, Richard C.

2016-05-01

Computer vision and photogrammetric techniques have been widely applied to digital imagery producing high density 3D point clouds. Using thermal imagery as input, the same techniques can be applied to infrared data to produce point clouds in 3D space, providing surface temperature information. The work presented here is an evaluation of the accuracy of 3D reconstruction of point clouds produced using thermal imagery. An urban scene was imaged over an area at the Naval Postgraduate School, Monterey, CA, viewing from above as with an airborne system. Terrestrial thermal and RGB imagery were collected from a rooftop overlooking the site using a FLIR SC8200 MWIR camera and a Canon T1i DSLR. In order to spatially align each dataset, ground control points were placed throughout the study area using Trimble R10 GNSS receivers operating in RTK mode. Each image dataset is processed to produce a dense point cloud for 3D evaluation.

Boundary Conditions for the Paleoenvironment: Chemical and Physical Processes in the Pre-Solar Nebula

NASA Technical Reports Server (NTRS)

Irvine, William M.; Schloerb, F. Peter

1997-01-01

The basic theme of this program is the study of molecular complexity and evolution in interstellar clouds and in primitive solar system objects. Research has included the detection and study of a number of new interstellar molecules and investigation of reaction pathways for astrochemistry from a comparison of theory and observed molecular abundances. The latter includes studies of cold, dark clouds in which ion-molecule chemistry should predominate, searches for the effects of interchange of material between the gas and solid phases in interstellar clouds, unbiased spectral surveys of particular sources, and systematic investigation of the interlinked chemistry and physics of dense interstellar clouds. In addition, the study of comets has allowed a comparison between the chemistry of such minimally thermally processed objects and that of interstellar clouds, shedding light on the evolution of the biogenic elements during the process of solar system formation.

A Model for Atomic and Molecular Interstellar Gas: The Meudon PDR Code

NASA Astrophysics Data System (ADS)

Le Petit, Franck; Nehmé, Cyrine; Le Bourlot, Jacques; Roueff, Evelyne

2006-06-01

We present the revised ``Meudon'' model of photon-dominated region (PDR) code, available on the Web under the GNU Public License. General organization of the code is described down to a level that should allow most observers to use it as an interpretation tool with minimal help from our part. Two grids of models, one for low-excitation diffuse clouds and one for dense highly illuminated clouds, are discussed, and some new results on PDR modelization highlighted.

Nonequilibrium chemistry in shocked molecular clouds. [interstellar gases

NASA Technical Reports Server (NTRS)

Iglesias, E. R.; Silk, J.

1978-01-01

The gas-phase chemistry is studied behind a 10-km/s shock propagating into a dense molecular cloud. The principal conclusions are that: the concentrations of certain molecules (CO, NH3, HCN, N2) are unperturbed by the shock; other molecules (H2CO, CN, HCO(+)) are greatly decreased in abundance; and substantial amounts of H2O, HCO, and CH4 are produced. Approximately 1 million yr (independent of the density) must elapse after shock passage before chemical equilibrium is attained.

High-resolution imaging and target designation through clouds or smoke

DOEpatents

Perry, Michael D.

2003-01-01

A method and system of combining gated intensifiers and advances in solid-state, short-pulse laser technology, compact systems capable of producing high resolution (i.e., approximately less than 20 centimeters) optical images through a scattering medium such as dense clouds, fog, smoke, etc. may be achieved from air or ground based platforms. Laser target designation through a scattering medium is also enabled by utilizing a short pulse illumination laser and a relatively minor change to the detectors on laser guided munitions.

A portable low-cost 3D point cloud acquiring method based on structure light

NASA Astrophysics Data System (ADS)

Gui, Li; Zheng, Shunyi; Huang, Xia; Zhao, Like; Ma, Hao; Ge, Chao; Tang, Qiuxia

2018-03-01

A fast and low-cost method of acquiring 3D point cloud data is proposed in this paper, which can solve the problems of lack of texture information and low efficiency of acquiring point cloud data with only one pair of cheap cameras and projector. Firstly, we put forward a scene adaptive design method of random encoding pattern, that is, a coding pattern is projected onto the target surface in order to form texture information, which is favorable for image matching. Subsequently, we design an efficient dense matching algorithm that fits the projected texture. After the optimization of global algorithm and multi-kernel parallel development with the fusion of hardware and software, a fast acquisition system of point-cloud data is accomplished. Through the evaluation of point cloud accuracy, the results show that point cloud acquired by the method proposed in this paper has higher precision. What`s more, the scanning speed meets the demand of dynamic occasion and has better practical application value.

OT1_dlis_2: Ammonia as a Tracer of the Earliest Stages of Star Formation

NASA Astrophysics Data System (ADS)

Lis, D.

2010-07-01

Stars form in molecular cloud cores, cold and dense regions enshrouded by dust. The initiation of this process is among the least understood steps of star formation. Highresolution heterodyne spectroscopy provides invaluable information about the physical conditions (density, temperature), kinematics (infall, outflows), and chemistry of these regions. Classical molecular tracers, such CO, CS, and many other abundant gasphase species, have been shown to freeze out onto dust grain mantles in prestellar cores. However, Nbearing species, in particular ammonia, are much less affected by depletion and are observed to stay in the gas phase at densities in excess of 1e6 cm3. The molecular freezeout has important consequences for the chemistry of dense gas. In particular, the depletion of abundant gasphase species with heavy atoms drives up abundances of deuterated H3+ isotopologues, which in turn results in spectacular deuteration levels of molecules that do remain in the gas phase. Consequently, lines of deuterated Nbearing species, in particular the fundamental lines of ammonia isotopologues, having very high critical densities, are optimum tracers of innermost regions of dense cores. We propose to study the morphology, density structure and kinematics of cold and dense cloud cores, by mapping the spatial distribution of ammonia isotopologues in isolated dense prestellar cores using Herschel/HIFI. These observations provide optimum probes of the onset of star formation, as well as the physical processes that control gasgrain interaction, freezeout, mantle ejection and deuteration. The sensitive, highresolution spectra acquired within this program will be analyzed using sophisticated radiative transfer models and compared with outputs of stateoftheart 3D MHD simulations and chemical models developed by the members of our team.

OT2_dlis_3: Ammonia as a Tracer of the Earliest Stages of Star Formation

NASA Astrophysics Data System (ADS)

Lis, D.

2011-09-01

Stars form in molecular cloud cores, cold and dense regions enshrouded by dust. The initiation of this process is among the least understood steps of star formation. High!resolution heterodyne spectroscopy provides invaluable information about the physical conditions (density, temperature), kinematics (infall, outflows), and chemistry of these regions. Classical molecular tracers, such CO, CS, and many other abundant gas!phase species, have been shown to freeze out onto dust grain mantles in pre!stellar cores. However, N!bearing species, in particular ammonia, are much less affected by depletion and are observed to stay in the gas phase at densities in excess of 1e6 cm!3. The molecular freeze!out has important consequences for the chemistry of dense gas. In particular, the depletion of abundant gas!phase species with heavy atoms drives up abundances of deuterated H3+ isotopologues, which in turn results in spectacular deuteration levels of molecules that do remain in the gas phase. Consequently, lines of deuterated N!bearing species, in particular the fundamental lines of ammonia isotopologues, having very high critical densities, are optimum tracers of innermost regions of dense cores. We propose to study the morphology, density structure and kinematics of cold and dense cloud cores, by mapping the spatial distribution of ammonia isotopologues in isolated dense pre!stellar cores using Herschel/HIFI. These observations provide optimum probes of the onset of star formation, as well as the physical processes that control gas!grain interaction, freeze!out, mantle ejection and deuteration. The sensitive, high!resolution spectra acquired within this program will be analyzed using sophisticated radiative transfer models and compared with outputs of state!of!the!art 3D MHD simulations and chemical models developed by the members of our team.

The Green Bank Ammonia Survey: Observations of Hierarchical Dense Gas Structures in Cepheus-L1251

NASA Astrophysics Data System (ADS)

Keown, Jared; Di Francesco, James; Kirk, Helen; Friesen, Rachel K.; Pineda, Jaime E.; Rosolowsky, Erik; Ginsburg, Adam; Offner, Stella S. R.; Caselli, Paola; Alves, Felipe; Chacón-Tanarro, Ana; Punanova, Anna; Redaelli, Elena; Seo, Young Min; Matzner, Christopher D.; Chun-Yuan Chen, Michael; Goodman, Alyssa A.; Chen, How-Huan; Shirley, Yancy; Singh, Ayushi; Arce, Hector G.; Martin, Peter; Myers, Philip C.

2017-11-01

We use Green Bank Ammonia Survey observations of NH3 (1, 1) and (2, 2) emission with 32″ FWHM resolution from a ˜10 pc2 portion of the Cepheus-L1251 molecular cloud to identify hierarchical dense gas structures. Our dendrogram analysis of the NH3 data results in 22 top-level structures, which reside within 13 lower-level parent structures. The structures are compact (0.01 {pc}≲ {R}{eff}≲ 0.1 {pc}) and are spatially correlated with the highest H2 column density portions of the cloud. We also compare the ammonia data to a catalog of dense cores identified by higher-resolution (18.″2 FWHM) Herschel Space Observatory observations of dust continuum emission from Cepheus-L1251. Maps of kinetic gas temperature, velocity dispersion, and NH3 column density, derived from detailed modeling of the NH3 data, are used to investigate the stability and chemistry of the ammonia-identified and Herschel-identified structures. We show that the dust and dense gas in the structures have similar temperatures, with median T dust and T K measurements of 11.7 ± 1.1 K and 10.3 ± 2.0 K, respectively. Based on a virial analysis, we find that the ammonia-identified structures are gravitationally dominated, yet may be in or near a state of virial equilibrium. Meanwhile, the majority of the Herschel-identified dense cores appear to be not bound by their own gravity and instead confined by external pressure. CCS (20 - 10) and HC5N (9-8) emission from the region reveal broader line widths and centroid velocity offsets when compared to the NH3 (1, 1) emission in some cases, likely due to these carbon-based molecules tracing the turbulent outer layers of the dense cores.

CO abundance variations in the Orion Molecular Cloud

NASA Astrophysics Data System (ADS)

Ripple, F.; Heyer, M. H.; Gutermuth, R.; Snell, R. L.; Brunt, C. M.

2013-05-01

Infrared stellar photometry from the Two Micron All-Sky Survey (2MASS) and spectral line imaging observations of 12CO and 13CO J = 1-0 line emission from the Five College Radio Astronomy Observatory (FCRAO) 14-m telescope are analysed to assess the variation of the CO abundance with physical conditions throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes are identified in which the ratio between the 13CO column density and visual extinction changes corresponding to the photon-dominated envelope, the strongly self-shielded interior, and the cold, dense volumes of the clouds. Within the strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies by 100 per cent with a peak value located near regions of enhanced star formation activity. The effect of CO depletion on to the ice mantles of dust grains is limited to regions with Av > 10 mag and gas temperatures less than ˜20 K as predicted by chemical models that consider thermal evaporation to desorb molecules from grain surfaces. Values of the molecular mass of each cloud are independently derived from the distributions of Av and 13CO column densities with a constant 13CO-to-H2 abundance over various extinction ranges. Within the strongly self-shielded interior of the cloud (Av> 3 mag), 13CO provides a reliable tracer of H2 mass with the exception of the cold, dense volumes where depletion is important. However, owing to its reduced abundance, 13CO does not trace the H2 mass that resides in the extended cloud envelope, which comprises 40-50 per cent of the molecular mass of each cloud. The implied CO luminosity to mass ratios, M/LCO, are 3.2 and 2.9 for Orion A and Orion B, respectively, which are comparable to the value (2.9), derived from γ-ray observations of the Orion region. Our results emphasize the need to consider local conditions when applying CO observations to derive H2 column densities.

Molecules in interstellar clouds. [physical and chemical conditions of star formation and biological evolution

NASA Technical Reports Server (NTRS)

Irvine, W. M.; Hjalmarson, A.; Rydbeck, O. E. H.

1981-01-01

The physical conditions and chemical compositions of the gas in interstellar clouds are reviewed in light of the importance of interstellar clouds for star formation and the origin of life. The Orion A region is discussed as an example of a giant molecular cloud where massive stars are being formed, and it is pointed out that conditions in the core of the cloud, with a kinetic temperature of about 75 K and a density of 100,000-1,000,000 molecules/cu cm, may support gas phase ion-molecule chemistry. The Taurus Molecular Clouds are then considered as examples of cold, dark, relatively dense interstellar clouds which may be the birthplaces of solar-type stars and which have been found to contain the heaviest interstellar molecules yet discovered. The molecular species identified in each of these regions are tabulated, including such building blocks of biological monomers as H2O, NH3, H2CO, CO, H2S, CH3CN and H2, and more complex species such as HCOOCH3 and CH3CH2CN.

Dispersal of Giant Molecular Clouds by Photoionization and Radiation Pressure

NASA Astrophysics Data System (ADS)

Kim, Jeong-Gyu; Kim, Woong-Tae; Ostriker, Eve C.

2018-01-01

UV radiation feedback from young massive stars plays a key role in the evolution of giant molecular clouds (GMCs) by forming HII regions and driving their expansion. We present the results of radiation hydrodynamic simulations of star cluster formation in turbulent GMCs, focusing on the effects of photoionization and radiation pressure on regulating the net star formation efficiency (SFE) and lifetime of clouds. We find that the net SFE depends primarily on the initial gas surface density, $\\Sigma_0$, such that the net SFE increases from 4% to 50% as $\\Sigma_0$ increases from $20\\,M_{\\odot}\\,{\\rm pc}^{-2}$ to $1300\\,M_{\\odot}\\,{\\rm pc}^{-2}$. Cloud dispersal occurs within $10\\,{\\rm Myr}$ after the onset of radiation feedback, or within 0.7--4.0 free-fall times that increases with $\\Sigma_0$. Photoionization plays a dominant role in destroying molecular clouds typical of the Milky Way, while radiation pressure takes over in massive, dense clouds. Based on the analysis of mass loss processes by photoevaporation or momentum injection, we develop a semi-analytic model for cloud dispersal and compare it with the numerical results.

Cool Star Beginnings: YSOs in the Perseus Molecular Cloud

NASA Astrophysics Data System (ADS)

Young, Kaisa E.; Young, Chadwick H.

2015-01-01

Nearby molecular clouds, where there is considerable evidence of ongoing star formation, provide the best opportunity to observe stars in the earliest stages of their formation. The Perseus molecular cloud contains two young clusters, IC 348 and NGC 1333 and several small dense cores of the type that produce only a few stars. Perseus is often cited as an intermediate case between quiescent low-mass and turbulent high-mass clouds, making it perhaps an ideal environment for studying ``typical low-mass star formation. We present an infrared study of the Perseus molecular cloud with data from the Spitzer Space Telescope as part of the ``From Molecular Cores to Planet Forming Disks (c2d) Legacy project tep{eva03}. By comparing Spitzer's near- and mid-infrared maps, we identify and classify the young stellar objects (YSOs) in the cloud using updated extinction corrected photometry. Virtually all of the YSOs in Perseus are forming in the clusters and other smaller associations at the east and west ends of the cloud with very little evidence of star formation in the midsection even in areas of high extinction.

Satellite remote sensing of aerosol and cloud properties over Eurasia

NASA Astrophysics Data System (ADS)

Sogacheva, Larisa; Kolmonen, Pekka; Saponaro, Giulia; Virtanen, Timo; Rodriguez, Edith; Sundström, Anu-Maija; Atlaskina, Ksenia; de Leeuw, Gerrit

2015-04-01

Satellite remote sensing provides the spatial distribution of aerosol and cloud properties over a wide area. In our studies large data sets are used for statistical studies on aerosol and cloud interaction in an area over Fennoscandia, the Baltic Sea and adjacent regions over the European mainland. This area spans several regimes with different influences on aerosol cloud interaction such as a the transition from relative clean air over Fennoscandia to more anthropogenically polluted air further south, and the influence maritime air over the Baltic and oceanic air advected from the North Atlantic. Anthropogenic pollution occurs in several parts of the study area, and in particular near densely populated areas and megacities, but also in industrialized areas and areas with dense traffic. The aerosol in such areas is quite different from that produced over the boreal forest and has different effects on air quality and climate. Studies have been made on the effects of aerosols on air quality and on the radiation balance in China. The aim of the study is to study the effect of these different regimes on aerosol-cloud interaction using a large aerosol and cloud data set retrieved with the (Advanced) Along Track Scanning Radiometer (A)ATSR Dual View algorithm (ADV) further developed at Finnish Meteorological Institute and aerosol and cloud data provided by MODIS. Retrieval algorithms for aerosol and clouds have been developed for the (A)ATSR, consisting of a series of instruments of which we use the second and third one: ATSR-2 which flew on the ERS-2 satellite (1995-2003) and AATSR which flew on the ENVISAT satellite (2002-2012) (both from the European Space Agency, ESA). The ADV algorithm provides aerosol data on a global scale with a default resolution of 10x10km2 (L2) and an aggregate product on 1x1 degree (L3). Optional, a 1x1 km2 retrieval products is available over smaller areas for specific studies. Since for the retrieval of AOD no prior knowledge is needed on surface properties, the surface reflectance can be independently retrieved using the AOD for atmospheric correction. For the retrieval of cloud properties, the SACURA algorithm has been implemented in the ADV/ASV aerosol retrieval suite. Cloud properties retrieved from AATSR data are cloud fraction, cloud optical thickness, cloud top height, cloud droplet effective radius, liquid water path. Aerosol and cloud properties are applied for different studies over the Eurasia area. Using the simultaneous retrieval of aerosol and cloud properties allows for study of the transition from the aerosol regime to the cloud regime, such as changes in effective radius or AOD (aerosol optical depth) to COT (cloud optical thickness). The column- integrated aerosol extinction, aerosol optical depth or AOD, which is primarily reported from satellite observations, can be used as a proxy for cloud condensation nuclei (CCN) and hence contains information on the ability of aerosol particles to form clouds. Hence, connecting this information with direct observations of cloud properties provides information on aerosol-cloud interactions.

Interstellar molecules and dense clouds.

NASA Technical Reports Server (NTRS)

Rank, D. M.; Townes, C. H.; Welch, W. J.

1971-01-01

Current knowledge of the interstellar medium is discussed on the basis of recent published studies. The subjects considered include optical identification of interstellar molecules, radio molecular lines, interstellar clouds, isotopic abundances, formation and disappearance of interstellar molecules, and interstellar probing techniques. Diagrams are plotted for the distribution of galactic sources exhibiting molecular lines, for hydrogen molecule, hydrogen atom and electron abundances due to ionization, for the densities, velocities and temperature of NH3 in the direction of Sagitarius B2, for the lower rotational energy levels of H2CO, and for temporal spectral variations in masing H2O clouds of the radio source W49. Future applications of the maser and of molecular microscopy in this field are visualized.

Model of the vertical structure of the optical parameters of the Neptune atmosphere.

NASA Astrophysics Data System (ADS)

Morozhenko, A. V.

Analyzes the wavelength dependence of the geometric albedo of Neptune's disk and estimates some parameters of the planet's atmosphere by the method based on the determination of deviations of the vertical structure of the cloud layer from the homogeneity condition. The ratio between the methane and gas scale heights is found to be about 0.4. For the upper atmosphere, components of methane, aerosol, the mean geometric radius of particles, the turbulent mixing coefficient are determined. Two solutions were found for deeper atmospheric layers. The first one suggests a rather dense cloud; in the second solution the lower cloud layer is an extension of the upper aerosol layer.

Red and nebulous objects in dark clouds - A survey

NASA Technical Reports Server (NTRS)

Cohen, M.

1980-01-01

A search on the NGS-PO Sky Survey photographs has revealed 150 interesting nebulous and/or red objects, mostly lying in dark clouds and not previously catalogued. Spectral classifications are presented for 55 objects. These indicate a small number of new members of the class of Herbig-Haro objects, a significant number of new T Tauri stars, and a few emission-line hot stars. It is argued that hot, high-mass stars form preferentially in the dense cores of dark clouds. The possible symbiosis of high and low mass stars is considered. A new morphology class is defined for cometary nebulae, in which a star lies on the periphery of a nebulous ring.

Shocked molecular gas and the origin of cosmic rays

NASA Astrophysics Data System (ADS)

Reach, William; Gusdorf, Antoine; Richter, Matthew

2018-06-01

When massive stars reach the end of their ability to remain stable with core nuclear fusion, they explode in supernovae that drive powerful shocks into their surroundings. Because massive stars form in and remain close to molecular clouds they often drive shocks into dense gas, which is now believed to be the origin of a significant fraction of galactic cosmic rays. The nature of the supernova-molecular cloud interaction is not well understood, though observations are gradually elucidating their nature. The range of interstellar densities, and the inclusion of circumstellar matter from the late-phase mass-loss of the stars before their explosions, leads to a wide range of possible appearances and outcomes. In particular, it is not even clear what speed or physical type of shocks are present: are they dense, magnetically-mediated shocks where H2 is not dissociated, or are they faster shocks that dissociate molecules and destroy some of the grains? SOFIA is observing some of the most significant (in terms of cosmic ray production potential and infrared energy output) supernova-molecular cloud interactions for measurement of the line widths of key molecular shocks tracers: H2, [OI], and CO. The presence of gas at speeds 100 km/s or greater would indicate dissociative shocks, while speeds 30 km/s and slower retain most molecules. The shock velocity is a key ingredient in modeling the interaction between supernovae and molecular clouds including the potential for formation of cosmic rays.

Spatial Distribution of Io's Neutral Oxygen Cloud Observed by Hisaki

NASA Astrophysics Data System (ADS)

Koga, Ryoichi; Tsuchiya, Fuminori; Kagitani, Masato; Sakanoi, Takeshi; Yoneda, Mizuki; Yoshioka, Kazuo; Yoshikawa, Ichiro; Kimura, Tomoki; Murakami, Go; Yamazaki, Atsushi; Smith, H. Todd; Bagenal, Fran

2018-05-01

We report on the spatial distribution of a neutral oxygen cloud surrounding Jupiter's moon Io and along Io's orbit observed by the Hisaki satellite. Atomic oxygen and sulfur in Io's atmosphere escape from the exosphere mainly through atmospheric sputtering. Some of the neutral atoms escape from Io's gravitational sphere and form neutral clouds around Jupiter. The extreme ultraviolet spectrograph called EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) installed on the Japan Aerospace Exploration Agency's Hisaki satellite observed the Io plasma torus continuously in 2014-2015, and we derived the spatial distribution of atomic oxygen emissions at 130.4 nm. The results show that Io's oxygen cloud is composed of two regions, namely, a dense region near Io and a diffuse region with a longitudinally homogeneous distribution along Io's orbit. The dense region mainly extends on the leading side of Io and inside of Io's orbit. The emissions spread out to 7.6 Jupiter radii (RJ). Based on Hisaki observations, we estimated the radial distribution of the atomic oxygen number density and oxygen ion source rate. The peak atomic oxygen number density is 80 cm-3, which is spread 1.2 RJ in the north-south direction. We found more oxygen atoms inside Io's orbit than a previous study. We estimated the total oxygen ion source rate to be 410 kg/s, which is consistent with the value derived from a previous study that used a physical chemistry model based on Hisaki observations of ultraviolet emission ions in the Io plasma torus.

THE LAUNCHING OF COLD CLOUDS BY GALAXY OUTFLOWS. II. THE ROLE OF THERMAL CONDUCTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brüggen, Marcus; Scannapieco, Evan

2016-05-01

We explore the impact of electron thermal conduction on the evolution of radiatively cooled cold clouds embedded in flows of hot and fast material as it occurs in outflowing galaxies. Performing a parameter study of three-dimensional adaptive mesh refinement hydrodynamical simulations, we show that electron thermal conduction causes cold clouds to evaporate, but it can also extend their lifetimes by compressing them into dense filaments. We distinguish between low column-density clouds, which are disrupted on very short times, and high-column density clouds with much longer disruption times that are set by a balance between impinging thermal energy and evaporation. Wemore » provide fits to the cloud lifetimes and velocities that can be used in galaxy-scale simulations of outflows in which the evolution of individual clouds cannot be modeled with the required resolution. Moreover, we show that the clouds are only accelerated to a small fraction of the ambient velocity because compression by evaporation causes the clouds to present a small cross-section to the ambient flow. This means that either magnetic fields must suppress thermal conduction, or that the cold clouds observed in galaxy outflows are not formed of cold material carried out from the galaxy.« less

XMM-Newton observation of the supernova remnant Kes 78 (G32.8-0.1): Evidence of shock-cloud interaction

NASA Astrophysics Data System (ADS)

Miceli, M.; Bamba, A.; Orlando, S.; Zhou, P.; Safi-Harb, S.; Chen, Y.; Bocchino, F.

2017-03-01

Context. The Galactic supernova remnant Kes 78 is surrounded by dense molecular clouds, whose projected position overlaps with the extended HESS γ-ray source HESS J1852-000. The X-ray emission from the remnant has recently been revealed by Suzaku observations, which have shown indications for a hard X-ray component in the spectra that might be associated with synchrotron radiation. Aims: We describe the spatial distribution of the physical properties of the X-ray emitting plasma and reveal the effects of the interaction of the remnant with the inhomogeneous ambient medium. We also investigate the origin of the γ-ray emission, which may be inverse-Compton radiation associated with X-ray synchrotron-emitting electrons or hadronic emission originating from the impact of high-energy protons on the nearby clouds. Methods: We analyzed an XMM-Newton EPIC observation of Kes 78 by performing image analysis and spatially resolved spectral analysis on a set of three regions. We tested our findings against the observations of the 12CO and 13CO emission in the environment of the remnant. Results: We reveal the complex X-ray morphology of Kes 78 and find variations in the spectral properties of the plasma, with significantly denser and cooler material at the eastern edge of the remnant, which we interpret as a signature of interaction with a molecular cloud. We also exclude that narrow filaments emit the X-ray synchrotron radiation. Conclusions: Assuming that the very high energy γ-ray emission is associated with Kes 78, the lack of synchrotron emission rules out a leptonic origin. A hadronic origin is further supported by evidence of interaction of the remnant with a dense molecular cloud in its eastern limb.

SIZE DISTRIBUTIONS OF ELEMENTAL CARBON IN ATMOSPHERIC AEROSOLS

EPA Science Inventory

Environmental problems caused by atmospheric aerosols are well documented in the specialized literature. Studies reporting on the role of dense clouds of soil particles in past mass extinctions of life on Earth and, more recently (Turco et al., 1983), on calculations of potential...

The Study of Spherical Cores with a Toroidal Magnetic Field Configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gholipour, Mahmoud

Observational studies of the magnetic fields in molecular clouds have significantly improved the theoretical models developed for the structure and evolution of dense clouds and for the star formation process as well. The recent observational analyses on some cores indicate that there is a power-law relationship between magnetic field and density in the molecular clouds. In this study, we consider the stability of spherical cores with a toroidal magnetic field configuration in the molecular clouds. For this purpose, we model a spherical core that is in magnetostatic equilibrium. Herein, we propose an equation of density structure, which is a modifiedmore » form of the isothermal Lane–Emden equation in the presence of the toroidal magnetic field. The proposed equation describes the effect of the toroidal magnetic field on the cloud structure and the mass cloud. Furthermore, we found an upper limit for this configuration of magnetic field in the molecular clouds. Then, the virial theorem is used to consider the cloud evolution leading to an equation in order to obtain the lower limit of the field strength in the molecular cloud. However, the results show that the field strength of the toroidal configuration has an important effect on the cloud structure, whose upper limit is related to the central density and field gradient. The obtained results address some regions of clouds where the cloud decomposition or star formation can be seen.« less

Cold Atomic Hydrogen, Narrow Self-Absorption, and the Age of Molecular Clouds

NASA Technical Reports Server (NTRS)

Goldsmith, Paul F.

2006-01-01

This viewgraph presentation reviews the history, and current work on HI and its importance in star formation. Through many observations of HI Narrow Self Absorption (HINSA) the conclusions are drawn and presented. Local molecular clouds have HI well-mixed with molecular constituents This HI is cold, quiescent, and must be well-shielded from the UV radiation field The density and fractional abundance (wrt H2) of the cold HI are close to steady state values The time required to convert these starless clouds from purely HI initial state to observed present composition is a few to ten million years This timescale is a lower limit - if dense clouds being swept up from lower density regions by shocks, the time to accumulate material to get A(sub v) is approximately 1 and provide required shielding may be comparable or longer

Integration of prior knowledge into dense image matching for video surveillance

NASA Astrophysics Data System (ADS)

Menze, M.; Heipke, C.

2014-08-01

Three-dimensional information from dense image matching is a valuable input for a broad range of vision applications. While reliable approaches exist for dedicated stereo setups they do not easily generalize to more challenging camera configurations. In the context of video surveillance the typically large spatial extent of the region of interest and repetitive structures in the scene render the application of dense image matching a challenging task. In this paper we present an approach that derives strong prior knowledge from a planar approximation of the scene. This information is integrated into a graph-cut based image matching framework that treats the assignment of optimal disparity values as a labelling task. Introducing the planar prior heavily reduces ambiguities together with the search space and increases computational efficiency. The results provide a proof of concept of the proposed approach. It allows the reconstruction of dense point clouds in more general surveillance camera setups with wider stereo baselines.

Enhanced Mobility in Concentrated Pyroclastic Density Currents: An Examination of a Self-Fluidization Mechanism

NASA Astrophysics Data System (ADS)

Breard, Eric C. P.; Dufek, Josef; Lube, Gert

2018-01-01

Pyroclastic density currents (PDCs) are a significant volcanic hazard. However, their dominant transport mechanisms remain poorly understood, in part because of the large variability of PDC types and deposits. Here we combine field data with experimental and numerical simulations to illuminate the twofold fate of particles settling from an ash cloud to form the dense PDC basal flow. At solid fractions >1 vol %, heterogeneous drag leads to formation of mesoscale particle clusters that favor rapid particle settling and result in a mobile dense layer with significant bed weight support. Conversely, at lower concentrations the absence of particle clusters typically leads to formation of poorly mobile dense beds that deposit massive layers. Based on this transport dichotomy, we present a numerical dense-dilute parameter that allows a PDC's dominant transport mechanism to be determined directly from the deposit geometry and grainsize characteristics.

IRAS Colors of the Pleiades

NASA Technical Reports Server (NTRS)

Carey, Sean J.; Shipman, R. F.; Clark, F. O.

1996-01-01

We present large scale images of the infrared emission of the region around the Pleiades using the ISSA data product from the IRAS mission. Residual Zodiacal background and a discontinuity in the image due to the scanning strategy of the satellite necessitated special background subtraction methods. The 60/100 color image clearly shows the heating of the ambient interstellar medium by the cluster. The 12/100 and 25/100 images peak on the cluster as expected for exposure of small dust grains to an enhanced UV radiation field; however, the 25/100 color declines to below the average interstellar value at the periphery of the cluster. Potential causes of the color deficit are discussed. A new method of identifying dense molecular material through infrared emission properties is presented. The difference between the 100 micron flux density and the 60 micron flux density scaled by the average interstellar 60/100 color ratio (Delta I(sub 100) is a sensitive diagnostic of material with embedded heating sources (Delta I(sub 100) less than 0) and cold, dense cores (Delta I(sub 100) greater than 0). The dense cores of the Taurus cloud complex as well as Lynds 1457 are clearly identified by this method, while the IR bright but diffuse Pleiades molecular cloud is virtually indistinguishable from the nearby infrared cirrus.

Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Che-Yu; Li, Zhi-Yun; King, Patrick K.

2017-10-01

Thin, magnetically aligned striations of relatively moderate contrast with the background are commonly observed in both atomic and molecular clouds. They are also prominent in MHD simulations with turbulent converging shocks. The simulated striations develop within a dense, stagnated sheet in the midplane of the post-shock region where magnetically induced converging flows collide. We show analytically that the secondary flows are an inevitable consequence of the jump conditions of oblique MHD shocks. They produce the stagnated, sheet-like sub-layer through a secondary shock when, roughly speaking, the Alfvénic speed in the primary converging flows is supersonic, a condition that is relativelymore » easy to satisfy in interstellar clouds. The dense sub-layer is naturally threaded by a strong magnetic field that lies close to the plane of the sub-layer. The substantial magnetic field makes the sheet highly anisotropic, which is the key to the striation formation. Specifically, perturbations of the primary inflow that vary spatially perpendicular to the magnetic field can easily roll up the sheet around the field lines without bending them, creating corrugations that appear as magnetically aligned striations in column density maps. On the other hand, perturbations that vary spatially along the field lines curve the sub-layer and alter its orientation relative to the magnetic field locally, seeding special locations that become slanted overdense filaments and prestellar cores through enhanced mass accumulation along field lines. In our scenario, the dense sub-layer, which is unique to magnetized oblique shocks, is the birthplace for both magnetically aligned diffuse striations and massive star-forming structures.« less

ISM gas studies towards the TeV PWN HESS J1825-137 and northern region

NASA Astrophysics Data System (ADS)

Voisin, F.; Rowell, G.; Burton, M. G.; Walsh, A.; Fukui, Y.; Aharonian, F.

2016-05-01

HESS J1825-137 is a pulsar wind nebula (PWN) whose TeV emission extends across ˜1 . Its large asymmetric shape indicates that its progenitor supernova interacted with a molecular cloud located in the north of the PWN as detected by previous CO Galactic survey (e.g. Lemiere, Terrier & Djannati-Ataï). Here, we provide a detailed picture of the interstellar medium (ISM) towards the region north of HESS J1825-137, with the analysis of the dense molecular gas from our 7 and 12 mm Mopra survey and the more diffuse molecular gas from the Nanten CO(1-0) and GRS 13CO(1-0) surveys. Our focus is the possible association between HESS J1825-137 and the unidentified TeV source to the north, HESS J1826-130. We report several dense molecular regions whose kinematic distance matched the dispersion measured distance of the pulsar. Among them, the dense molecular gas located at (RA, Dec.) = (18h421h,-13.282°) shows enhanced turbulence and we suggest that the velocity structure in this region may be explained by a cloud-cloud collision scenario. Furthermore, the presence of a H α rim may be the first evidence of the progenitor supernova remnant (SNR) of the pulsar PSR J1826-1334 as the distance between the H α rim and the TeV source matched with the predicted SNR radius RSNR ˜ 120 pc. From our ISM study, we identify a few plausible origins of the HESS J1826-130 emission, including the progenitor SNR of PSR J1826-1334 and the PWN G018.5-0.4 powered by PSR J1826-1256. A deeper TeV study however, is required to fully identify the origin of this mysterious TeV source.

ALMA view of the massive dense clump in the Galactic center 50 km s-1 molecular cloud .

NASA Astrophysics Data System (ADS)

Uehara, K.; Tsuboi, M.; Kitamura, Y.; Miyawaki, R.; Miyazaki, A.

We observed the 50 km s-1 molecular cloud with a high angular resolution (˜1.5 arcsec) using ALMA in the H13CO+ J=1-0, C34S J=2-1, CS J=2-1 and SiO v=0 J=2-1 emission lines. This cloud is a candidate for the massive star forming region induced by cloud-cloud collision (CCC). We newly found a massive dense clump (DC1) with a size of ˜0.3 pc in the CCC region of the cloud in the H13CO+ J=1-0 map. The DC1 seems to be located on a line where the four HII regions line up. Furthermore, the DC1 has a broad velocity width covering ˜30 km s-1 and ˜60 km s-1 components in the CS J=2-1 map; the 30 km s-1 component has filamentary structures and the 60 km s-1 one a sheet-like structure. From the position-velocity diagrams of the H13CO+ J=1-0 and CS J=2-1 lines and the intensity ratio of T(SiO v=0 J=2-1)/T(H13CO+ J=1-0), i.e., a shock tracer, we consider that the DC1 has formed by the CCC between the filaments and the sheet-like gas. The LTE mass and virial parameter of the DC1 is estimated to be ˜1.3×104 M_ȯ and ˜5, respectively. These facts suggest that the DC1 is likely in a gravitationally bound state and may start massive star formation. We propose a scenario that the CCC induced the massive star formation in the HII region A ˜105 years ago and now causes the formation and collapse of the DC1; the clump would evolve to an HII region within ˜105 years.

Histotripsy Lesion Formation Using an Ultrasound Imaging Probe Enabled by a Low-Frequency Pump Transducer.

PubMed

Lin, Kuang-Wei; Hall, Timothy L; Xu, Zhen; Cain, Charles A

2015-08-01

When histotripsy pulses shorter than 2 cycles are applied, the formation of a dense bubble cloud relies only on the applied peak negative pressure (p-) exceeding the "intrinsic threshold" of the medium (absolute value of 26-30 MPa in most soft tissues). It has been found that a sub-threshold high-frequency probe pulse (3 MHz) can be enabled by a sub-threshold low-frequency pump pulse (500 kHz) where the sum exceeds the intrinsic threshold, thus generating lesion-producing dense bubble clouds ("dual-beam histotripsy"). Here, the feasibility of using an imaging transducer to provide the high-frequency probe pulse in the dual-beam histotripsy approach is investigated. More specifically, an ATL L7-4 imaging transducer (Philips Healthcare, Andover, MA, USA), pulsed by a V-1 Data Acquisition System (Verasonics, Redmond, WA, USA), was used to generate the high-frequency probe pulses. The low-frequency pump pulses were generated by a 20-element 345-kHz array transducer, driven by a custom high-voltage pulser. These dual-beam histotripsy pulses were applied to red blood cell tissue-mimicking phantoms at a pulse repetition frequency of 1 Hz, and optical imaging was used to visualize bubble clouds and lesions generated in the red blood cell phantoms. The results indicated that dense bubble clouds (and resulting lesions) were generated when the p- of the sub-threshold pump and probe pulses combined constructively to exceed the intrinsic threshold. The average size of the smallest reproducible lesions using the imaging probe pulse enabled by the sub-threshold pump pulse was 0.7 × 1.7 mm, whereas that using the supra-threshold pump pulse alone was 1.4 × 3.7 mm. When the imaging transducer was steered laterally, bubble clouds and lesions were steered correspondingly until the combined p- no longer exceeded the intrinsic threshold. These results were also validated with ex vivo porcine liver experiments. Using an imaging transducer for dual-beam histotripsy can have two advantages: (i) lesion steering can be achieved using the steering of the imaging transducer (implemented with the beamformer of the accompanying programmable ultrasound system), and (ii) treatment can be simultaneously monitored when the imaging transducer is used in conjunction with an ultrasound imaging system. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Histotripsy Lesion Formation using an Ultrasound Imaging Probe Enabled by a Low-Frequency Pump Transducer

PubMed Central

Lin, Kuang-Wei; Hall, Timothy L.; Xu, Zhen; Cain, Charles A.

2015-01-01

When applying histotripsy pulses shorter than 2 cycles, the formation of a dense bubble cloud only relies on the applied peak negative pressure (p-) exceeding the “intrinsic threshold” of the medium (absolute value of 26 – 30 MPa in most soft tissue). A previous study conducted by our research group showed that a sub-threshold high-frequency probe pulse (3 MHz) can be enabled by a sub-threshold low-frequency pump pulse (500 kHz) where the sum exceeds the intrinsic threshold, thus generating lesion-producing dense bubble clouds (“dual-beam histotripsy”). This paper investigates the feasibility of using an imaging transducer to provide the high-frequency probe pulse in the dual-beam histotripsy approach. More specifically, an ATL L7–4 imaging transducer, pulsed by a Verasonics V-1 Data Acquisition System, was used to generate the high-frequency probe pulses. The low-frequency pump pulses were generated by a 20-element 345 kHz array transducer, driven by a custom high voltage pulser. These dual-beam histotripsy pulses were applied to red-blood-cell (RBC) tissue-mimicking phantoms at a pulse repetition frequency of 1 Hz, and optical imaging was used to visualize bubble clouds and lesions generated in the RBC phantoms. The results showed that dense bubble clouds (and resulting lesions) were generated when the p- of the sub-threshold pump and probe pulses combined constructively to exceed the intrinsic threshold. The average size of the smallest reproducible lesions using the imaging probe pulse enabled by the sub-threshold pump pulse was 0.7 × 1.7 mm while that using the supra-threshold pump pulse alone was 1.4 × 3.7 mm. When the imaging transducer was steered laterally, bubble clouds and lesions were steered correspondingly until the combined p- no longer exceeded the intrinsic threshold. These results were also validated with ex vivo porcine liver experiments. Using an imaging transducer for dual-beam histotripsy can have two advantages, 1) lesion steering can be achieved using the steering of the imaging transducer (implemented with the beamformer of the accompanying programmable ultrasound system) and 2) treatment can be simultaneously monitored when the imaging transducer is used in conjunction with an ultrasound imaging system. PMID:25929995

Spectral Classification of Heavily Reddened Stars by CO Absorption Strength

NASA Astrophysics Data System (ADS)

Garling, Christopher; Bary, Jeffrey S.; Huard, Tracy L.

2017-01-01

The nature of dust grains in dense molecular clouds can be explored by obtaining spectra of giant stars located behind the clouds and examining the wavelength-dependent attentuation of their light. This approach requires the intrinsic spectra of the background stars to be known, which can be achieved by determining their spectral types. In the K-band spectra of cool giant stars, several temperature-sensitive CO absorption bands serve as good spectral type indicators. Taking advantage of the SpeX Infrared Telescope Facility Spectral Library, near-infrared spectra collected with TripleSpec and the 3.5-meter ARC Telescope at Apache Point Observatory, and a previously constructed CO spectral index, we make precise spectral determinations of 20 giant stars located behind two dense cloud cores: CB188 and L429C. With spectral types in hand, we then utilize Markov Chain Monte Carlo techniques to constrain extinctions along these lines of sight. The spectral typing method will be described and assessed as well as its success at finding a couple of incorrectly spectral typed stars in the SpeX Library. Funding for this program was provided by a NSF REU grant to the Keck Northeast Astronomy Consortium and a grant from the NASA Astrophysics Data Analysis Program.

Star formation and extinct radioactivities

NASA Technical Reports Server (NTRS)

Cameron, A. G. W.

1984-01-01

An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.

Ammonia Observations of NGC 6334 I(N)

NASA Technical Reports Server (NTRS)

Kuiper, T. B. H.; Peters, W. L., III; Foster, J. R.; Gardner, F. F.; Whiteoak, J. B.

1995-01-01

Coincident with the far-infrared source NGC 6334 I(N) and water maser source E is a massive dense cloud which has the most intense ammonia (1, 1) emission of any known interstellar cloud. We have mapped the (3, 3) emission and find the cloud is extended 0.8 pc in the direction parallel to the Galactic plane, and 0.5 pc perpendicular to it. It has a velocity gradient of 1 km/s.pc perpendicular to the Galactic plane. The gas kinetic temperature is about 30 K and the density is greater than 10(exp 6)/cc. The mass of the cloud is about 3000 solar mass, 3 times greater than previously estimated. The para-ammonia column density is 6 - 8 x 10(exp 15)/sq cm. An ammonia abundance of 0.5 - 1.5 x 10(exp -8) is inferred, where the larger number assumes an early time ortho/para ratio. This suggests either a cloud age of less than approximately 10(exp 6) yr, or substantial depletion of ammonia.

An origin of arc structures deeply embedded in dense molecular cloud cores

NASA Astrophysics Data System (ADS)

Matsumoto, Tomoaki; Onishi, Toshikazu; Tokuda, Kazuki; Inutsuka, Shu-ichiro

2015-04-01

We investigated the formation of arc-like structures in the infalling envelope around protostars, motivated by the recent Atacama Large Millimeter/Submillimeter Array (ALMA) observations of the high-density molecular cloud core, MC27/L1521F. We performed self-gravitational hydrodynamical numerical simulations with an adaptive mesh refinement code. A filamentary cloud with a 0.1 pc width fragments into cloud cores because of perturbations due to weak turbulence. The cloud core undergoes gravitational collapse to form multiple protostars, and gravitational torque from the orbiting protostars produces arc structures extending up to a 1000 au scale. As well as on a spatial extent, the velocity ranges of the arc structures, ˜0.5 km s-1, are in agreement with the ALMA observations. We also found that circumstellar discs are often misaligned in triple system. The misalignment is caused by the tidal interaction between the protostars when they undergo close encounters because of a highly eccentric orbit of the tight binary pair.

Modeling the chemistry of the dense interstellar clouds. I - Observational constraints for the chemistry

NASA Technical Reports Server (NTRS)

Federman, S. R.; Huntress, W. T., Jr.; Prasad, S. S.

1990-01-01

A search for correlations arising from molecular line data is made in order to place constraints on the chemical models of interstellar clouds. At 10 to the 21st H2/sq cm, N(CO) for dark clouds is a factor of six greater than the value for diffuse clouds. This implies that the strength of the UV radiation field where CO shields itself from dissociation is about one-half the strength of the average Galactic field. The dark cloud data indicate that the abundance of CO continues to increase with A(V) for directions with A(V) of 4 mag or less, although less steeply with N(H2) than for diffuse clouds. For H2CO, a quadratic relationship is obtained in plots versus H2 column density. The data suggest a possible turnover at the highest values for A(V). NH3 shows no correlation with H2, C(O-18), HC3N, or HC5N; a strong correlation is found between HC5N and HC3N, indicating a chemical link between the cyanopolyynes.

THE TRIFID NEBULA: STELLAR SIBLING RIVALRY

NASA Technical Reports Server (NTRS)

2002-01-01

This NASA Hubble Space Telescope image of the Trifid Nebula reveals a stellar nursery being torn apart by radiation from a nearby, massive star. The picture also provides a peek at embryonic stars forming within an ill-fated cloud of dust and gas, which is destined to be eaten away by the glare from the massive neighbor. This stellar activity is a beautiful example of how the life cycles of stars like our Sun is intimately connected with their more powerful siblings. The Hubble image shows a small part of a dense cloud of dust and gas, a stellar nursery full of embryonic stars. This cloud is about 8 light-years away from the nebula's central star, which is beyond the top of this picture. Located about 9,000 light-years from Earth, the Trifid resides in the constellation Sagittarius. A stellar jet [the thin, wispy object pointing to the upper left] protrudes from the head of a dense cloud and extends three-quarters of a light-year into the nebula. The jet's source is a very young stellar object that lies buried within the cloud. Jets such as this are the exhaust gases of star formation. Radiation from the massive star at the center of the nebula is making the gas in the jet glow, just as it causes the rest of the nebula to glow. The jet in the Trifid is a 'ticker tape,' telling the history of one particular young stellar object that is continuing to grow as its gravity draws in gas from its surroundings. But this particular ticker tape will not run for much longer. Within the next 10,000 years the glare from the central, massive star will continue to erode the nebula, overrunning the forming star, and bringing its growth to an abrupt and possibly premature end. Another nearby star may have already faced this fate. The Hubble picture shows a 'stalk' [the finger-like object] pointing from the head of the dense cloud directly toward the star that powers the Trifid. This stalk is a prominent example of the evaporating gaseous globules, or 'EGGs,' that were seen previously in the Eagle Nebula, another star-forming region photographed by Hubble. The stalk has survived because at its tip there is a knot of gas that is dense enough to resist being eaten away by the powerful radiation. Reflected starlight at the tip of the EGG may be due to light from the Trifid's central star, or from a young stellar object buried within the EGG. Similarly, a tiny spike of emission pointing outward from the EGG looks like a small stellar jet. Hubble astronomers are tentatively interpreting this jet as the last gasp from a star that was cut off from its supply lines 100,000 years ago. The images were taken Sept. 8, 1997 through filters that isolate emission from hydrogen atoms, ionized sulfur atoms, and doubly ionized oxygen atoms. The images were combined in a single color composite picture. While the resulting picture is not true color, it is suggestive of what a human eye might see. Credits: NASA and Jeff Hester (Arizona State University)

Structure formation in a colliding flow: The Herschel view of the Draco nebula

NASA Astrophysics Data System (ADS)

Miville-Deschênes, M.-A.; Salomé, Q.; Martin, P. G.; Joncas, G.; Blagrave, K.; Dassas, K.; Abergel, A.; Beelen, A.; Boulanger, F.; Lagache, G.; Lockman, F. J.; Marshall, D. J.

2017-03-01

Context. The Draco nebula is a high Galactic latitude interstellar cloud observed at velocities corresponding to the intermediate velocity cloud regime. This nebula shows unusually strong CO emission and remarkably high-contrast small-scale structures for such a diffuse high Galactic latitude cloud. The 21 cm emission of the Draco nebula reveals that it is likely to have been formed by the collision of a cloud entering the disk of the Milky Way. Such physical conditions are ideal to study the formation of cold and dense gas in colliding flows of diffuse and warm gas. Aims: The objective of this study is to better understand the process of structure formation in a colliding flow and to describe the effects of matter entering the disk on the interstellar medium. Methods: We conducted Herschel-SPIRE observations of the Draco nebula. The clumpfind algorithm was used to identify and characterize the small-scale structures of the cloud. Results: The high-resolution SPIRE map reveals the fragmented structure of the interface between the infalling cloud and the Galactic layer. This front is characterized by a Rayleigh-Taylor (RT) instability structure. From the determination of the typical length of the periodic structure (2.2 pc) we estimated the gas kinematic viscosity. This allowed us to estimate the dissipation scale of the warm neutral medium (0.1 pc), which was found to be compatible with that expected if ambipolar diffusion were the main mechanism of turbulent energy dissipation. The statistical properties of the small-scale structures identified with clumpfind are found to be typical of that seen in molecular clouds and hydrodynamical turbulence in general. The density of the gas has a log-normal distribution with an average value of 103 cm-3. The typical size of the structures is 0.1-0.2 pc, but this estimate is limited by the resolution of the observations. The mass of these structures ranges from 0.2 to 20 M⊙ and the distribution of the more massive structures follows a power-law dN/ dlog (M) M-1.4. We identify a mass-size relation with the same exponent as that found in molecular clouds (M L2.3). On the other hand, we found that only 15% of the mass of the cloud is in gravitationally bound structures. Conclusions: We conclude that the collision of diffuse gas from the Galactic halo with the diffuse interstellar medium of the outer layer of the disk is an efficient mechanism for producing dense structures. The increase of pressure induced by the collision is strong enough to trigger the formation of cold neutral medium out of the warm gas. It is likely that ambipolar diffusion is the mechanism dominating the turbulent energy dissipation. In that case the cold structures are a few times larger than the energy dissipation scale. The dense structures of Draco are the result of the interplay between magnetohydrodynamical turbulence and thermal instability as self-gravity is not dominating the dynamics. Interestingly they have properties typical of those found in more classical molecular clouds. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.The reduced Herschel data (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A109

THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. II. THE SPATIAL DISTRIBUTION AND DEMOGRAPHICS OF DUSTY YOUNG STELLAR OBJECTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Megeath, S. T.; Kryukova, E.; Gutermuth, R.

2016-01-15

We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc{sup −2} to over 10,000 pc{sup −2}, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifyingmore » clusters and groups as continuous regions with surface densities ≥10 pc{sup −2}, we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ∼2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions.« less

Crew Earth Observations (CEO) taken during Expedition Six

NASA Image and Video Library

2003-02-01

ISS006-E-28028 (February 2003) --- The Southern Cross (left center), the Coal Sack Nebula (bottom left), and the Carina Nebula (upper right) are visible in this view photographed by astronaut Donald R. Pettit, Expedition Six NASA ISS science officer, on board the International Space Station (ISS). The Carina Nebula is a molecular cloud about 9000 light years from Earth where young stars are forming. The Coal Sack Nebula is an inky-black dust cloud about 2000 light years from Earth. Stars are probably condensing deep inside the Coal Sack, but their light has not yet broken through the cloud’s dense exterior. The Southern Cross, also known as The Crux, is a constellation familiar to southern hemisphere stargazers.

Recent observations of interstellar molecules - Detection of CCO and a limit on H2C3O

NASA Technical Reports Server (NTRS)

Brown, R. D.; Cragg, D. M.; Godfrey, P. D.; Irvine, W. M.; Mcgonagle, D.; Ohishi, M.

1992-01-01

In order to test gas-phase reaction schemes for the production of small oxides of carbon in cold, dense interstellar clouds, we have searched for the radical CCO and for propadienone (H2C3O) in Taurus Molecular Cloud 1, a nearby cloud which exhibits a rich organic chemistry. The radical CCO has been detected with a fractional abundance some two orders of magnitude less than that of CCS, about one order of magnitude less than that of H2CCO, and slightly less than that of C3O. An upper limit has been obtained on the abundance of propadienone which is slightly less than that of its isomer propynal (HC2CHO).

Evolutionary models of interstellar chemistry

NASA Technical Reports Server (NTRS)

Prasad, Sheo S.

1987-01-01

The goal of evolutionary models of interstellar chemistry is to understand how interstellar clouds came to be the way they are, how they will change with time, and to place them in an evolutionary sequence with other celestial objects such as stars. An improved Mark II version of an earlier model of chemistry in dynamically evolving clouds is presented. The Mark II model suggests that the conventional elemental C/O ratio less than one can explain the observed abundances of CI and the nondetection of O2 in dense clouds. Coupled chemical-dynamical models seem to have the potential to generate many observable discriminators of the evolutionary tracks. This is exciting, because, in general, purely dynamical models do not yield enough verifiable discriminators of the predicted tracks.

Cooperative scattering and radiation pressure force in dense atomic clouds

NASA Astrophysics Data System (ADS)

Bachelard, R.; Piovella, N.; Courteille, Ph. W.

2011-07-01

Atomic clouds prepared in “timed Dicke” states, i.e. states where the phase of the oscillating atomic dipole moments linearly varies along one direction of space, are efficient sources of superradiant light emission [Scully , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.96.010501 96, 010501 (2006)]. Here, we show that, in contrast to previous assertions, timed Dicke states are not the states automatically generated by incident laser light. In reality, the atoms act back on the driving field because of the finite refraction of the cloud. This leads to nonuniform phase shifts, which, at higher optical densities, dramatically alter the cooperative scattering properties, as we show by explicit calculation of macroscopic observables, such as the radiation pressure force.

D Reconstruction with a Collaborative Approach Based on Smartphones and a Cloud-Based Server

NASA Astrophysics Data System (ADS)

Nocerino, E.; Poiesi, F.; Locher, A.; Tefera, Y. T.; Remondino, F.; Chippendale, P.; Van Gool, L.

2017-11-01

The paper presents a collaborative image-based 3D reconstruction pipeline to perform image acquisition with a smartphone and geometric 3D reconstruction on a server during concurrent or disjoint acquisition sessions. Images are selected from the video feed of the smartphone's camera based on their quality and novelty. The smartphone's app provides on-the-fly reconstruction feedback to users co-involved in the acquisitions. The server is composed of an incremental SfM algorithm that processes the received images by seamlessly merging them into a single sparse point cloud using bundle adjustment. Dense image matching algorithm can be lunched to derive denser point clouds. The reconstruction details, experiments and performance evaluation are presented and discussed.

Ramsey scheme for coherent population resonance detection in the optically dense medium

NASA Astrophysics Data System (ADS)

Barantsev, Konstantin; Litvinov, Andrey; Popov, Evgeniy

2018-04-01

This work is devoted to a theoretical investigation of the Ramsey method of detection of the coherent population trapping resonance in cold atomic clouds taking into account collective effects caused by finite optical depth of the considered clouds. The interaction of atoms with pulsed laser radiation is described in the formalism of density matrix by means of Maxwell-Bloch set of equations. The Ramsey signal of coherent population trapping resonance was calculated for the radiation passed through the medium and analyzed for different length of the atomic cloud. Also the population of excited level was calculated in dependence on the two-photon detuning and coordinate along the main optical axis. The light shift of sidebands and appearance of additional harmonics were discovered.

The rate and latency of star formation in dense, massive clumps in the Milky Way

NASA Astrophysics Data System (ADS)

Heyer, M.; Gutermuth, R.; Urquhart, J. S.; Csengeri, T.; Wienen, M.; Leurini, S.; Menten, K.; Wyrowski, F.

2016-04-01

Context. Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. Aims: We seek to observationally constrain the rate and latency of star formation in dense massive clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. Methods: A sample of 24 μm-based Class I protostars are linked to dust clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming clumps, f∗, that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the clumps are calculated from 870 μm dust continuum emission and NH3 line emission. Results: Linear correlations are identified between the star formation rate surface density, ΣSFR, and the quantities ΣH2/τff and ΣH2/τcross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming clumps is 23%. Accounting for star formation within clumps that are excluded from our sample due to 24 μm saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive clumps form primarily low mass (<1-2 M⊙) stars with emergent 24 μm fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming clumps in the Galactic center relative to those located in the disk of the Milky Way is verified. Full Tables 2-4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A29

The Milky Way as a Star Formation Engine

NASA Astrophysics Data System (ADS)

Molinari, S.; Bally, J.; Glover, S.; Moore, T.; Noriega-Crespo, A.; Plume, R.; Testi, L.; Vázquez-Semadeni, E.; Zavagno, A.; Bernard, J.-P.; Martin, P.

The cycling of material from the interstellar medium (ISM) into stars and the return of stellar ejecta into the ISM is the engine that drives the galactic ecology in normal spirals. This ecology is a cornerstone in the formation and evolution of galaxies through cosmic time. There remain major observational and theoretical challenges in determining the processes responsible for converting the low-density, diffuse components of the ISM into dense molecular clouds, forming dense filaments and clumps, fragmenting them into stars, expanding OB associations and bound clusters, and characterizing the feedback that limits the rate and efficiency of star formation. This formidable task can be attacked effectively for the first time thanks to the synergistic combination of new global-scale surveys of the Milky Way from infrared (IR) to radio wavelengths, offering the possibility of bridging the gap between local and extragalactic star-formation studies. The Herschel Space Observatory Galactic Plane Survey (Hi-GAL) survey, with its five-band 70-500-μm full Galactic Plane mapping at 6"-36" resolution, is the keystone of a set of continuum surveys that include the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE)(360)+MIPSGAL@Spitzer, Wide-field Infrared Survey Explorer (WISE), Midcourse Space Experiment (MSX), APEX Telescope Large Area Survey of the Galaxy (ATLASGAL)@Atacama Pathfinder EXperiment (APEX), Bolocam Galactic Plane Survey (BGPS)@Caltech Submillimeter Observatory (CSO), and CORNISH@Very Large Array (VLA). This suite enables us to measure the Galactic distribution and physical properties of dust on all scales and in all components of the ISM from diffuse clouds to filamentary complexes and hundreds of thousands of dense clumps. A complementary suite of spectroscopic surveys in various atomic and molecular tracers is providing the chemical fingerprinting of dense clumps and filaments, as well as essential kinematic information to derive distances and thus transform panoramic data into a three-dimensional representation. The latest results emerging from these Galaxy-scale surveys are reviewed. New insights into cloud formation and evolution, filaments and their relationship to channeling gas onto gravitationally-bound clumps, the properties of these clumps, density thresholds for gravitational collapse, and star and cluster formation rates are discussed.

Dusty Cloud Acceleration by Radiation Pressure in Rapidly Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Zhang, Dong; Davis, Shane W.; Jiang, Yan-Fei; Stone, James M.

2018-02-01

We perform two-dimensional and three-dimensional radiation hydrodynamic simulations to study cold clouds accelerated by radiation pressure on dust in the environment of rapidly star-forming galaxies dominated by infrared flux. We utilize the reduced speed of light approximation to solve the frequency-averaged, time-dependent radiative transfer equation. We find that radiation pressure is capable of accelerating the clouds to hundreds of kilometers per second while remaining dense and cold, consistent with observations. We compare these results to simulations where acceleration is provided by entrainment in a hot wind, where the momentum injection of the hot flow is comparable to the momentum in the radiation field. We find that the survival time of the cloud accelerated by the radiation field is significantly longer than that of a cloud entrained in a hot outflow. We show that the dynamics of the irradiated cloud depends on the initial optical depth, temperature of the cloud, and intensity of the flux. Additionally, gas pressure from the background may limit cloud acceleration if the density ratio between the cloud and background is ≲ {10}2. In general, a 10 pc-scale optically thin cloud forms a pancake structure elongated perpendicular to the direction of motion, while optically thick clouds form a filamentary structure elongated parallel to the direction of motion. The details of accelerated cloud morphology and geometry can also be affected by other factors, such as the cloud lengthscale, reduced speed of light approximation, spatial resolution, initial cloud structure, and dimensionality of the run, but these have relatively little affect on the cloud velocity or survival time.

The Lambda Orionis association. [star cluster anomalies

NASA Technical Reports Server (NTRS)

Murdin, P.; Penston, M. V.

1977-01-01

The Lambda Orionis association has the photometric properties of a typical young cluster with an age of about 4 million yr. Its distance is 400 + or - 40 pc. Attention is drawn to the lack of a dense molecular cloud and associated infrared sources in this young grouping

The Mid-Infrared Absorption Spectra of Neutral PAHs in Dense Interstellar Clouds

NASA Technical Reports Server (NTRS)

Bernstein, M. P.; Sandford, S. A.; Allamandola, L. J.

2005-01-01

Polycyclic aromatic hydrocarbons (PAHs) are common throughout the universe and are expected to be present in dense interstellar clouds. In these environments, some P.4Hs may be present in the gas phase, but most should be frozen into ice mantles or adsorbed onto dust grains and their spectral features are expected to be seen in absorption. Here we extend our previous work on the infrared spectral properties of the small PAH naphthalene (C10H8) in several media to include the full mid-infrared laboratory spectra of 11 other PAHs and related aromatic species frozen in H2O ices. These include the molecules 1,2-dihydronaphthalene, anthracene, 9,1O-dihydroanthracene, phenanthrene, pyrene, benzo[e]pyrene, perylene, benzo(k)fluoranthene, pentacene, benzo[ghi]perylene, and coronene. These results demonstrate that PAHs and related molecules, as a class, show the same spectral behaviors as naphthalene when incorporated into H2O-rich matrices. When compared to the spectra of these same molecules isolated in inert matrices (e.g., Ar or N2), the absorption bands produced when they are frozen in H2O matrices are broader (factors of 3-10), show small position shifts in either direction (usually < 4/cm, always < 10/cm), and show variable changes in relative band strengths (typically factors of 1-3). There is no evidence of systematic increases or decreases in the absolute strengths of the bands of these molecules when they are incorporated in H2O matrices. In H2O-rich ices, their absorption bands are relatively insensitive to concentration over the range of 10 < H2O/PAH < 200): The absorption bands of these molecules are also insensitive to temperature over the 10 K < T < 125 K range, although the spectra can show dramatic changes as the ices are warmed through the temperature range in which amorphous H2O ice converts to its cubic and hexagonal crystalline forms (T > 125 Kj. Given the small observed band shifts cause by H2O, the current database of spectra from Ar matrix-isolated neutral PAHs and related molecules should be useful for the search for these species in dense clouds on the basis of observed absorption band positions. Furthermore, these data permit determination of column densities to better than a factor of 3 for PAHs in dense clouds. Column density determination of detected aromatics to better than a factor of 3 will, however, require good knowledge about the nature of the matrix in which the PAH is embedded and laboratory studies of relevant samples.

Multiview 3D sensing and analysis for high quality point cloud reconstruction

NASA Astrophysics Data System (ADS)

Satnik, Andrej; Izquierdo, Ebroul; Orjesek, Richard

2018-04-01

Multiview 3D reconstruction techniques enable digital reconstruction of 3D objects from the real world by fusing different viewpoints of the same object into a single 3D representation. This process is by no means trivial and the acquisition of high quality point cloud representations of dynamic 3D objects is still an open problem. In this paper, an approach for high fidelity 3D point cloud generation using low cost 3D sensing hardware is presented. The proposed approach runs in an efficient low-cost hardware setting based on several Kinect v2 scanners connected to a single PC. It performs autocalibration and runs in real-time exploiting an efficient composition of several filtering methods including Radius Outlier Removal (ROR), Weighted Median filter (WM) and Weighted Inter-Frame Average filtering (WIFA). The performance of the proposed method has been demonstrated through efficient acquisition of dense 3D point clouds of moving objects.

Simulating Shock Triggered Star Formation with AstroBEAR2.0

NASA Astrophysics Data System (ADS)

Li, Shule; Frank, Adam; Blackman, Eric

2013-07-01

Star formation can be triggered by the compression from shocks running over stable clouds. Triggered star formation is a favored explanation for the traces of SLRI's in our solar system. Previous research has shown that when parameters such as shock speed are within a certain range, the gravitational collapse of otherwise stable, dense cloud cores is possible. However, these studies usually focus on the precursors of star formation, and the conditions for the triggering. We use AstroBEAR2.0 code to simulate the collapse and subsequent evolution of a stable Bonnor-Ebert cloud by an incoming shock. Through our simulations, we show that interesting physics happens when the newly formed star interacts with the cloud residue and the post-shock flow. We identify these interactions as controlled by the initial conditions of the triggering and study the flow pattern as well as the evolution of important physics quantities such as accretion rate and angular momentum.

Classification of Mobile Laser Scanning Point Clouds from Height Features

NASA Astrophysics Data System (ADS)

Zheng, M.; Lemmens, M.; van Oosterom, P.

2017-09-01

The demand for 3D maps of cities and road networks is steadily growing and mobile laser scanning (MLS) systems are often the preferred geo-data acquisition method for capturing such scenes. Because MLS systems are mounted on cars or vans they can acquire billions of points of road scenes within a few hours of survey. Manual processing of point clouds is labour intensive and thus time consuming and expensive. Hence, the need for rapid and automated methods for 3D mapping of dense point clouds is growing exponentially. The last five years the research on automated 3D mapping of MLS data has tremendously intensified. In this paper, we present our work on automated classification of MLS point clouds. In the present stage of the research we exploited three features - two height components and one reflectance value, and achieved an overall accuracy of 73 %, which is really encouraging for further refining our approach.

Non-equilibrium ionization around clouds evaporating in the interstellar medium

NASA Technical Reports Server (NTRS)

Ballet, J.; Luciani, J. F.; Mora, P.

1986-01-01

It is of prime importance for global models of the interstellar medium to know whether dense clouds do or do not evaporate in the hot coronal gas. The rate of mass exchanges between phases depends very much on that. McKee and Ostriker's model, for instance, assumes that evaporation is important enough to control the expansion of supernova remnants, and that mass loss obeys the law derived by Cowie and McKee. In fact, the geometry of the magnetic field is nearly unknown, and it might totally inhibit evaporation, if the clouds are not regularly connected to the hot gas. Up to now, the only test of the theory is the U.V. observation (by the Copernicus and IUE satellites) of absorption lines of ions such as OVI or NV, that exist at temperatures of a few 100,000 K typical of transition layers around evaporating clouds. Other means of testing the theory are discussed.

Forest structure analysis combining laser scanning with digital airborne photogrammetry

NASA Astrophysics Data System (ADS)

Lissak, Candide; Onda, Yuichi; Kato, Hiroaki

2017-04-01

The interest of Light Detection and Ranging (LiDAR) for vegetation structure analysis has been demonstrated in several research context. Indeed, airborne or ground Lidar surveys can provide detailed three-dimensional data of the forest structure from understorey forest to the canopy. To characterize at different timescale the vegetation components in dense cedar forests we can combine several sources point clouds from Lidar survey and photogrammetry data. For our study, Terrestrial Laser Scanning (TLS-Leica ScanStation C10 processed with Cyclone software) have been lead in three forest areas (≈ 200m2 each zone) mainly composed of japanese cedar (Japonica cryptomeria), in the region of Fukushima (Japan). The study areas are characterized by various vegetation densities. For the 3 areas, Terrestrial laser scanning has been performed from several location points and several heights. Various floors shootings (ground, 4m, 6m and 18m high) were able with the use of a several meters high tower implanted to study the canopy evolution following the Fukushima Daiishi nuclear power plant accident. The combination of all scanners provides a very dense 3D point cloud of ground and canopy structure (average 300 000 000 points). For the Tochigi forest area, a first test of a low-cost Unmanned Aerial Vehicle (UAV) photogrammetry has been lead and calibrated by ground GPS measurements to determine the coordinates of points. TLS combined to UAV photogrammetry make it possible to obtain information on vertical and horizontal structure of the Tochigi forest. This combination of technologies will allow the forest structure mapping, morphometry analysis and the assessment of biomass volume evolution from multi-temporal point clouds. In our research, we used a low-cost UAV 3 Advanced (200 m2 cover, 1300 pictures...). Data processing were performed using PotoScan Pro software to obtain a very dense point clouds to combine to TLS data set. This low-cost UAV photogrammetry data has been successfully used to derive information on the canopy cover. The purpose of this poster is to present the usability of combined remote sensing methods for forest structure analysis and 3D model reconstitution for a trend analysis of the forest changes.

IRAS images of nearby dark clouds

NASA Technical Reports Server (NTRS)

Wood, Douglas O. S.; Myers, Philip C.; Daugherty, Debra A.

1994-01-01

We have investigated approximately 100 nearby molecular clouds using the extensive, all-sky database of IRAS. The clouds in this study cover a wide range of physical properties including visual extinction, size, mass, degree of isolation, homogeneity and morphology. IRAS 100 and 60 micron co-added images were used to calculate the 100 micron optical depth of dust in the clouds. These images of dust optical depth compare very well with (12)CO and (13)CO observations, and can be related to H2 column density. From the optical depth images we locate the edges of dark clouds and the dense cores inside them. We have identified a total of 43 `IRAS clouds' (regions with A(sub v) greater than 2) which contain a total of 255 `IRAS cores' (regions with A(sub v) greater than 4) and we catalog their physical properties. We find that the clouds are remarkably filamentary, and that the cores within the clouds are often distributed along the filaments. The largest cores are usually connected to other large cores by filaments. We have developed selection criteria to search the IRAS Point Source Catalog for stars that are likely to be associated with the clouds and we catalog the IRAS sources in each cloud or core. Optically visible stars associated with the clouds have been identified from the Herbig and Bell catalog. From these data we characterize the physical properties of the clouds including their star-formation efficiency.

Cloud Structure of Galactic OB Cluster-forming Regions from Combining Ground- and Space-based Bolometric Observations

NASA Astrophysics Data System (ADS)

Lin, Yuxin; Liu, Hauyu Baobab; Li, Di; Zhang, Zhi-Yu; Ginsburg, Adam; Pineda, Jaime E.; Qian, Lei; Galván-Madrid, Roberto; McLeod, Anna Faye; Rosolowsky, Erik; Dale, James E.; Immer, Katharina; Koch, Eric; Longmore, Steve; Walker, Daniel; Testi, Leonardo

2016-09-01

We have developed an iterative procedure to systematically combine the millimeter and submillimeter images of OB cluster-forming molecular clouds, which were taken by ground-based (CSO, JCMT, APEX, and IRAM-30 m) and space telescopes (Herschel and Planck). For the seven luminous (L\\gt {10}6 L ⊙) Galactic OB cluster-forming molecular clouds selected for our analyses, namely W49A, W43-Main, W43-South, W33, G10.6-0.4, G10.2-0.3, and G10.3-0.1, we have performed single-component, modified blackbody fits to each pixel of the combined (sub)millimeter images, and the Herschel PACS and SPIRE images at shorter wavelengths. The ˜10″ resolution dust column density and temperature maps of these sources revealed dramatically different morphologies, indicating very different modes of OB cluster-formation, or parent molecular cloud structures in different evolutionary stages. The molecular clouds W49A, W33, and G10.6-0.4 show centrally concentrated massive molecular clumps that are connected with approximately radially orientated molecular gas filaments. The W43-Main and W43-South molecular cloud complexes, which are located at the intersection of the Galactic near 3 kpc (or Scutum) arm and the Galactic bar, show a widely scattered distribution of dense molecular clumps/cores over the observed ˜10 pc spatial scale. The relatively evolved sources G10.2-0.3 and G10.3-0.1 appear to be affected by stellar feedback, and show a complicated cloud morphology embedded with abundant dense molecular clumps/cores. We find that with the high angular resolution we achieved, our visual classification of cloud morphology can be linked to the systematically derived statistical quantities (I.e., the enclosed mass profile, the column density probability distribution function (N-PDF), the two-point correlation function of column density, and the probability distribution function of clump/core separations). In particular, the massive molecular gas clumps located at the center of G10.6-0.4 and W49A, which contribute to a considerable fraction of their overall cloud masses, may be special OB cluster-forming environments as a direct consequence of global cloud collapse. These centralized massive molecular gas clumps also uniquely occupy much higher column densities than what is determined by the overall fit of power-law N-PDF. We have made efforts to archive the derived statistical quantities of individual target sources, to permit comparisons with theoretical frameworks, numerical simulations, and other observations in the future.

Revised models of interstellar nitrogen isotopic fractionation

NASA Astrophysics Data System (ADS)

Wirström, E. S.; Charnley, S. B.

2018-03-01

Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of 15N enrichments found in comets and meteorites. Chemical model calculations indicate that atom-molecular ion and ion-molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense cloud chemistry show that the revised 15N enrichments fail to match observed values. We have investigated the effects of these reaction rate modifications on the chemical model of Wirström et al. (2012) for which there are significant physical and chemical differences with respect to other models. We have included 15N fractionation of CN in neutral-neutral reactions and also updated rate coefficients for key reactions in the nitrogen chemistry. We find that the revised fractionation rates have the effect of suppressing 15N enrichment in ammonia at all times, while the depletion is even more pronounced, reaching 14N/15N ratios of >2000. Taking the updated nitrogen chemistry into account, no significant enrichment occurs in HCN or HNC, contrary to observational evidence in dark clouds and comets, although the 14N/15N ratio can still be below 100 in CN itself. However, such low CN abundances are predicted that the updated model falls short of explaining the bulk 15N enhancements observed in primitive materials. It is clear that alternative fractionating reactions are necessary to reproduce observations, so further laboratory and theoretical studies are urgently needed.

Radiative characteristics of Clouds embedded in and occurring beneath Smoke analyzed using airborne multiangular measurements

NASA Astrophysics Data System (ADS)

Gautam, R.; Gatebe, C. K.; Varnai, T.; Singh, M.; Poudyal, R.

2016-12-01

Clouds in the presence of absorbing aerosols results in their apparent darkening, observed at the Top of Atmosphere (TOA), which is associated with the radiative effects of aerosol absorption. Owing to the warming/darkening effect and potential impacts on regional climate via semidirect and thermodynamic pathways, above-cloud aerosols have been characterized in recent satellite-based studies. While satellite data are particularly useful in showing the radiative impact of above-cloud aerosols at the TOA, retrievals of aerosol and cloud properties are affected by large uncertainties when they co-occur. In this study, we present radiative characteristics of clouds in the presence of wildfire smoke using airborne data primarily from NASA's Cloud Absorption Radiometer (CAR), collected during the ARCTAS and SAFARI campaigns in Canada and southern Africa, respectively. Scattered cumulus clouds embedded in dense smoke over land (Canada) as well as smoke aerosols above marine stratocumulus clouds (southeast Atlantic) show characteristic spectral gradient across the UV-visible-NIR spectrum using CAR data. In general, clouds in the presence of smoke are impacted by absorbing aerosol-induced darkening at the shorter wavelengths (e.g. UV and blue bands), as opposed to an (expected) negative gradient for cloud-free smoke and a flat spectrum for smoke-free cloud cover. The circular and spiral flights not only allowed the complete characterization of the angular distribution of smoke-cloud radiative interactions, but also provided the vertical distribution of smoke and clouds. Overall, the observational-based smoke-cloud radiative interactions were found to be physically consistent with theoretical 1D and 3D radiation calculations. These airborne observations are also complemented by satellite data from MODIS reflectances and CERES shortwave fluxes, providing a synergistic radiative impact assessment of clouds in the presence of smoke. http://car.gsfc.nasa.gov/

H2 Ortho-to-para Conversion on Grains: A Route to Fast Deuterium Fractionation in Dense Cloud Cores?

NASA Astrophysics Data System (ADS)

Bovino, S.; Grassi, T.; Schleicher, D. R. G.; Caselli, P.

2017-11-01

Deuterium fractionation, I.e., the enhancement of deuterated species with respect to non-deuterated ones, is considered to be a reliable chemical clock of star-forming regions. This process is strongly affected by the ortho-to-para H2 ratio. In this Letter we explore the effect of the ortho-para (o-p) H2 conversion on grains on the deuteration timescale in fully-depleted dense cores, including the most relevant uncertainties that affect this complex process. We show that (I) the o-p H2 conversion on grains is not strongly influenced by the uncertainties on the conversion time and the sticking coefficient, and (II) that the process is controlled by the temperature and the residence time of ortho-H2 on the surface, I.e., by the binding energy. We find that for binding energies between 330 and 550 K, depending on the temperature, the o-p H2 conversion on grains can shorten the deuterium fractionation timescale by orders of magnitude, opening a new route for explaining the large observed deuteration fraction D frac in dense molecular cloud cores. Our results suggest that the star formation timescale, when estimated through the timescale to reach the observed deuteration fractions, might be shorter than previously proposed. However, more accurate measurements of the binding energy are needed in order to better assess the overall role of this process.

An Integrated Photogrammetric and Photoclinometric Approach for Pixel-Resolution 3d Modelling of Lunar Surface

NASA Astrophysics Data System (ADS)

Liu, W. C.; Wu, B.

2018-04-01

High-resolution 3D modelling of lunar surface is important for lunar scientific research and exploration missions. Photogrammetry is known for 3D mapping and modelling from a pair of stereo images based on dense image matching. However dense matching may fail in poorly textured areas and in situations when the image pair has large illumination differences. As a result, the actual achievable spatial resolution of the 3D model from photogrammetry is limited by the performance of dense image matching. On the other hand, photoclinometry (i.e., shape from shading) is characterised by its ability to recover pixel-wise surface shapes based on image intensity and imaging conditions such as illumination and viewing directions. More robust shape reconstruction through photoclinometry can be achieved by incorporating images acquired under different illumination conditions (i.e., photometric stereo). Introducing photoclinometry into photogrammetric processing can therefore effectively increase the achievable resolution of the mapping result while maintaining its overall accuracy. This research presents an integrated photogrammetric and photoclinometric approach for pixel-resolution 3D modelling of the lunar surface. First, photoclinometry is interacted with stereo image matching to create robust and spatially well distributed dense conjugate points. Then, based on the 3D point cloud derived from photogrammetric processing of the dense conjugate points, photoclinometry is further introduced to derive the 3D positions of the unmatched points and to refine the final point cloud. The approach is able to produce one 3D point for each image pixel within the overlapping area of the stereo pair so that to obtain pixel-resolution 3D models. Experiments using the Lunar Reconnaissance Orbiter Camera - Narrow Angle Camera (LROC NAC) images show the superior performances of the approach compared with traditional photogrammetric technique. The results and findings from this research contribute to optimal exploitation of image information for high-resolution 3D modelling of the lunar surface, which is of significance for the advancement of lunar and planetary mapping.

SHOCKFIND - an algorithm to identify magnetohydrodynamic shock waves in turbulent clouds

NASA Astrophysics Data System (ADS)

Lehmann, Andrew; Federrath, Christoph; Wardle, Mark

2016-11-01

The formation of stars occurs in the dense molecular cloud phase of the interstellar medium. Observations and numerical simulations of molecular clouds have shown that supersonic magnetized turbulence plays a key role for the formation of stars. Simulations have also shown that a large fraction of the turbulent energy dissipates in shock waves. The three families of MHD shocks - fast, intermediate and slow - distinctly compress and heat up the molecular gas, and so provide an important probe of the physical conditions within a turbulent cloud. Here, we introduce the publicly available algorithm, SHOCKFIND, to extract and characterize the mixture of shock families in MHD turbulence. The algorithm is applied to a three-dimensional simulation of a magnetized turbulent molecular cloud, and we find that both fast and slow MHD shocks are present in the simulation. We give the first prediction of the mixture of turbulence-driven MHD shock families in this molecular cloud, and present their distinct distributions of sonic and Alfvénic Mach numbers. Using subgrid one-dimensional models of MHD shocks we estimate that ˜0.03 per cent of the volume of a typical molecular cloud in the Milky Way will be shock heated above 50 K, at any time during the lifetime of the cloud. We discuss the impact of this shock heating on the dynamical evolution of molecular clouds.

The Formation and Early Evolution of Embedded Massive Star Clusters

NASA Astrophysics Data System (ADS)

Barnes, Peter

We propose to combine Spitzer, WISE, Herschel, and other archival spacecraft data with an existing ground- and space-based mm-wave to near-IR survey of molecular clouds over a large portion of the Milky Way, in order to systematically study the formation and early evolution of massive stars and star clusters, and provide new observational calibrations for a theoretical paradigm of this key astrophysical problem. Central Objectives: The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, uniform, and panchromatic survey of massive star and cluster formation and early evolution, covering 20°x6° of the Galactic Plane. Its uniqueness lies in the comprehensive molecular spectroscopy of 303 massive dense clumps, which have also been included in several archival spacecraft surveys. Our objective is a systematic demographic analysis of massive star and cluster formation, one which has not been possible without knowledge of our CHaMP cloud sample, including all clouds with embedded clusters as well as those that have not yet formed massive stars. For proto-clusters deeply embedded within dense molecular clouds, analysis of these space-based data will: 1. Yield a complete census of Young Stellar Objects in each cluster. 2. Allow systematic measurements of embedded cluster properties: spectral energy distributions, luminosity functions, protostellar and disk fractions, and how these vary with cluster mass, age, and density. Combined with other, similarly complete and unbiased infrared and mm data, CHaMP's goals include: 3. A detailed comparison of the embedded stellar populations with their natal dense gas to derive extinction maps, star formation efficiencies and feedback effects, and the kinematics, physics, and chemistry of the gas in and around the clusters. 4. Tying the demographics, age spreads, and timescales of the clusters, based on pre-Main Sequence evolution, to that of the dense gas clumps and Giant Molecular Clouds. 5. A measurement of the local star formation rate per gas mass surface density in the Milky Way, as well as examining arm versus interarm dependencies. Methods and Techniques: We will primarily use archival cryogenic-Spitzer, WISE, and Herschel data, and support this with existing data from ground- and space-based facilities, to conduct a comprehensive assay of critical metrics (as above) and provide observational calibration of theoretical models over the entire massive star formation process. The mm-wave molecular maps of 303 dense gas clumps in multiple species, comprising all the gas above a column density limit of 100 Msun/pc^2, are already inhand. We have also surveyed the embedded stellar content of these clumps, down to subsolar masses, in the near-infrared J, H, and K bands and with deep Warm Spitzer data. Relevance to NASA programs: Analysis to date of the space- and ground-based data has yielded several new insights into evolutionary timescales and the chemical & energy evolution of clumps during the cluster formation process. Investigations as described in this proposal will yield new demographic insights on how the properties and evolution of molecular clouds relate to the properties of massive stars and clusters that form within them, and significantly enhance the science return from these spacecraft missions. The large number of resulting data products are already being made publicly available to the astronomical community, providing crucial information for future NASA science targets. This research will be performed within the framework of a broad international collaboration spanning four continents. This ambitious but practical program will therefore maximise the science payoff from these archival data sets, provide enhanced legacy data for more advanced studies with the next generation of ground- and space-based instruments such as JWST, and open up several new windows into the discovery space of Galactic star formation & interstellar medium studies.

Tools to Perform Local Dense 3D Reconstruction of Shallow Water Seabed ‡

PubMed Central

Avanthey, Loïca; Beaudoin, Laurent; Gademer, Antoine; Roux, Michel

2016-01-01

Tasks such as distinguishing or identifying individual objects of interest require the production of dense local clouds at the scale of these individual objects of interest. Due to the physical and dynamic properties of an underwater environment, the usual dense matching algorithms must be rethought in order to be adaptive. These properties also imply that the scene must be observed at close range. Classic robotized acquisition systems are oversized for local studies in shallow water while the systematic acquisition of data is not guaranteed with divers. We address these two major issues through a multidisciplinary approach. To efficiently acquire on-demand stereoscopic pairs using simple logistics in small areas of shallow water, we devised an agile light-weight dedicated system which is easy to reproduce. To densely match two views in a reliable way, we devised a reconstruction algorithm that automatically accounts for the dynamics, variability and light absorption of the underwater environment. Field experiments in the Mediterranean Sea were used to assess the results. PMID:27196913

VISIONS - Vista Star Formation Atlas

NASA Astrophysics Data System (ADS)

Meingast, Stefan; Alves, J.; Boui, H.; Ascenso, J.

2017-06-01

In this talk I will present the new ESO public survey VISIONS. Starting in early 2017 we will use the ESO VISTA survey telescope in a 550 h long programme to map the largest molecular cloud complexes within 500 pc in a multi-epoch program. The survey is optimized for measuring the proper motions of young stellar objects invisible to Gaia and mapping the cloud-structure with extinction. VISIONS will address a series of ISM topics ranging from the connection of dense cores to YSOs and the dynamical evolution of embedded clusters to variations in the reddening law on both small and large scales.

On the Ubiquity of Molecular Anions in the Dense Interstellar Medium

NASA Technical Reports Server (NTRS)

Cordiner, M. A.; Buckle, J. V.; Wirstroem, E. S.; Olofsson, A. O. H.; Charnley, S. B.

2013-01-01

Results are presented from a survey for molecular anions in seven nearby Galactic star-forming cores and molecular clouds. The hydrocarbon anion C6H(-) is detected in all seven target sources, including four sources where no anions have been previously detected: L1172, L1389, L1495B, and TMC-1C. The C6H(-) /C6H column density ratio is approx. > 1.0% in every source, with a mean value of 3.0% (and standard deviation 0.92%). Combined with previous detections, our results show that anions are ubiquitous in dense clouds wherever C6H is present. The C6H(-)/C6H ratio is found to show a positive correlation with molecular hydrogen number density, and with the apparent age of the cloud.We also report the first detection of C4H(-) in TMC-1 (at 4.8 sigma confidence), and derive an anion-to-neutral ratio C4H(-) /C4H = (1.2 +/- 0.4)×10(exp -5)(= 0.0012% +/- 0.0004%). Such a low value compared with C6H(-) highlights the need for a revised radiative electron attachment rate for C4H. Chemical model calculations show that the observed C4H(-) could be produced as a result of reactions of oxygen atoms with C5H(-) and C6H(-).

Infrared Extinction and the Initial Conditions for Star and Planet Formation

NASA Technical Reports Server (NTRS)

Lada, Charles J.

2005-01-01

This grant funded a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program were to: 1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds, 2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds, 3) use the results to measure and quantitatively describe the physical conditions of the dense gas and dust that produce stars and their accompanying planetary systems in molecular clouds. The goals of this project were met and exceeded as described below. 1) The infrared data for the project were obtained in a number of observing runs using the 3.5-meter NTT and 8-meter VLT telescopes of the European Southern Observatory in Chile and the 1.2-meter telescope of the Smithsonian Astrophysical Observatory in Arizona, the 1 0-meter Keck telescope in Hawaii, the 6.5-meter MMT of the Smithsonian Astrophysical Observatory in Arizona, and the NASA Hubble Space Telescope. The molecular-line data was obtained in three runs using the IRAM 30-meter telescope in Spain and one run with the ESO-15 meter millimeter-wave telescope in Chile. Millimeter-wave continuum measurements were obtained with the 15-meter JCMT in Hawaii. 2) Considerable effort was expended to reduce the infrared imaging observations including the development of custom software to produce high quality photometry and source astrometry. All the millimeter-line data was reduced using standard reduction routines. The highlights of the infrared analysis were the production of detailed extinction maps and the construction of profiles of the density structure of the B68, Coalsack, B335 and Lupus clouds. 3) The principal scientific accomplishments of this research program include the following: We were able to use our infrared observations to determine the density structure of the B68 cloud to an unprecedented level of precision. This lead to a major breakthrough in the study of molecular cloud structure. For the first time we have been able to characterize the structure of a dark cloud in a detail only exceeded by that known for a star. We determined that the cloud's structure is exquisitely well described by the equations of a Bonner-Ebert sphere (a pressure confined isothermal sphere). We were able to show that the cloud is very nearly in equilibrium with the internal thermal pressure of the cloud balancing gravity and the external pressure of the surrounding interstellar medium. We were able to determine for the first time the gas-to-dust ratio in a dense cloud core. We also demonstrated a new method to determine extremely precise distances to such clouds by combining knowledge of the properties of Bonner-Ebert Spheres with our infrared and millimeter-wave observations.

Investigation of tropical cirrus cloud properties using ground based lidar measurements

NASA Astrophysics Data System (ADS)

Dhaman, Reji K.; Satyanarayana, Malladi; Krishnakumar, V.; Mahadevan Pillai, V. P.; Jayeshlal, G. S.; Raghunath, K.; Venkat Ratnam, M.

2016-05-01

Cirrus clouds play a significant role in the Earths radiation budget. Therefore, knowledge of geometrical and optical properties of cirrus cloud is essential for the climate modeling. In this paper, the cirrus clouds microphysical and optical properties are made by using a ground based lidar measurements over an inland tropical station Gadanki (13.5°N, 79.2°E), Andhra Pradesh, India. The variation of cirrus microphysical and optical properties with mid cloud temperature is also studied. The cirrus clouds mean height is generally observed in the range of 9-17km with a peak occurrence at 13- 14km. The cirrus mid cloud temperature ranges from -81°C to -46°C. The cirrus geometrical thickness ranges from 0.9- 4.5km. During the cirrus occurrence days sub-visual, thin and dense cirrus were at 37.5%, 50% and 12.5% respectively. The monthly cirrus optical depth ranges from 0.01-0.47, but most (<80%) of the cirrus have values less than 0.1. Optical depth shows a strong dependence with cirrus geometrical thickness and mid-cloud height. The monthly mean cirrus extinction ranges from 2.8E-06 to 8E-05 and depolarization ratio and lidar ratio varies from 0.13 to 0.77 and 2 to 52 sr respectively. A positive correlation exists for both optical depth and extinction with the mid-cloud temperature. The lidar ratio shows a scattered behavior with mid-cloud temperature.

Mapping with Small UAS: A Point Cloud Accuracy Assessment

NASA Astrophysics Data System (ADS)

Toth, Charles; Jozkow, Grzegorz; Grejner-Brzezinska, Dorota

2015-12-01

Interest in using inexpensive Unmanned Aerial System (UAS) technology for topographic mapping has recently significantly increased. Small UAS platforms equipped with consumer grade cameras can easily acquire high-resolution aerial imagery allowing for dense point cloud generation, followed by surface model creation and orthophoto production. In contrast to conventional airborne mapping systems, UAS has limited ground coverage due to low flying height and limited flying time, yet it offers an attractive alternative to high performance airborne systems, as the cost of the sensors and platform, and the flight logistics, is relatively low. In addition, UAS is better suited for small area data acquisitions and to acquire data in difficult to access areas, such as urban canyons or densely built-up environments. The main question with respect to the use of UAS is whether the inexpensive consumer sensors installed in UAS platforms can provide the geospatial data quality comparable to that provided by conventional systems. This study aims at the performance evaluation of the current practice of UAS-based topographic mapping by reviewing the practical aspects of sensor configuration, georeferencing and point cloud generation, including comparisons between sensor types and processing tools. The main objective is to provide accuracy characterization and practical information for selecting and using UAS solutions in general mapping applications. The analysis is based on statistical evaluation as well as visual examination of experimental data acquired by a Bergen octocopter with three different image sensor configurations, including a GoPro HERO3+ Black Edition, a Nikon D800 DSLR and a Velodyne HDL-32. In addition, georeferencing data of varying quality were acquired and evaluated. The optical imagery was processed by using three commercial point cloud generation tools. Comparing point clouds created by active and passive sensors by using different quality sensors, and finally, by different commercial software tools, provides essential information for the performance validation of UAS technology.

Cognitive Apprenticeship: Teaching the Craft of Reading, Writing, and Mathematics.

DTIC Science & Technology

1986-11-01

the vent as lava, or spews skyward as dense clouds of lava particles. 22. C: How does the pressure from below pushes the mass of hot rock %- 4- against...problem-solving heuristics and strategies for carrying out pans of the task at hand. Control strategies have monitorig , diagnostic and remedial

Interstellar abundances and depletions inferred from observations of neutral atoms

NASA Technical Reports Server (NTRS)

Snow, T. P.

1984-01-01

Data on neutral atomic species are analyzed for the purpose of inferring relative elemental abundances and depletions in diffuse cloud cores, where it is assumed that densities are enhanced in comparison with mean densities over integrated lines of sight. Column densities of neutral atoms are compared to yield relative column densities of singly ionized species, which are assumed dominant in cloud cores. This paper incorporates a survey of literature data on neutral atomic abundances with the result that no systematic enhancement in the depletions of calcium or iron in cloud cores is found, except for zeta Ophiuchi. This may imply that depletions are not influenced by density, but other data argue against this interpretation. It is concluded either that in general all elements are depleted together in dense regions so that their relative abundances remain constant, or that typical diffuse clouds do not have significant cores, but instead are reasonably homogeneous. The data show a probable correlation between cloud-core depletion and hydrogen-molecular fraction, supporting the assumption that overall depletions are a function of density.

The Feasibility of 3d Point Cloud Generation from Smartphones

NASA Astrophysics Data System (ADS)

Alsubaie, N.; El-Sheimy, N.

2016-06-01

This paper proposes a new technique for increasing the accuracy of direct geo-referenced image-based 3D point cloud generated from low-cost sensors in smartphones. The smartphone's motion sensors are used to directly acquire the Exterior Orientation Parameters (EOPs) of the captured images. These EOPs, along with the Interior Orientation Parameters (IOPs) of the camera/ phone, are used to reconstruct the image-based 3D point cloud. However, because smartphone motion sensors suffer from poor GPS accuracy, accumulated drift and high signal noise, inaccurate 3D mapping solutions often result. Therefore, horizontal and vertical linear features, visible in each image, are extracted and used as constraints in the bundle adjustment procedure. These constraints correct the relative position and orientation of the 3D mapping solution. Once the enhanced EOPs are estimated, the semi-global matching algorithm (SGM) is used to generate the image-based dense 3D point cloud. Statistical analysis and assessment are implemented herein, in order to demonstrate the feasibility of 3D point cloud generation from the consumer-grade sensors in smartphones.

Critical infrastructure monitoring using UAV imagery

NASA Astrophysics Data System (ADS)

Maltezos, Evangelos; Skitsas, Michael; Charalambous, Elisavet; Koutras, Nikolaos; Bliziotis, Dimitris; Themistocleous, Kyriacos

2016-08-01

The constant technological evolution in Computer Vision enabled the development of new techniques which in conjunction with the use of Unmanned Aerial Vehicles (UAVs) may extract high quality photogrammetric products for several applications. Dense Image Matching (DIM) is a Computer Vision technique that can generate a dense 3D point cloud of an area or object. The use of UAV systems and DIM techniques is not only a flexible and attractive solution to produce accurate and high qualitative photogrammetric results but also is a major contribution to cost effectiveness. In this context, this study aims to highlight the benefits of the use of the UAVs in critical infrastructure monitoring applying DIM. A Multi-View Stereo (MVS) approach using multiple images (RGB digital aerial and oblique images), to fully cover the area of interest, is implemented. The application area is an Olympic venue in Attica, Greece, at an area of 400 acres. The results of our study indicate that the UAV+DIM approach respond very well to the increasingly greater demands for accurate and cost effective applications when provided with, a 3D point cloud and orthomosaic.

Interstellar gas and X-rays toward the Young supernova remnant RCW 86; pursuit of the origin of the thermal and non-thermal X-ray

NASA Astrophysics Data System (ADS)

Sano, H.; Reynoso, E. M.; Mitsuishi, I.; Nakamura, K.; Furukawa, N.; Mruganka, K.; Fukuda, T.; Yoshiike, S.; Nishimura, A.; Ohama, A.; Torii, K.; Kuwahara, T.; Okuda, T.; Yamamoto, H.; Tachihara, K.; Fukui, Y.

2017-09-01

We have analyzed the atomic and molecular gas using the 21 cm HI and 2.6/1.3 mm CO emissions toward the young supernova remnant (SNR) RCW 86 in order to identify the interstellar medium with which the shock waves of the SNR interact. We have found an HI intensity depression in the velocity range between -46 and - 28 kms-1 toward the SNR, suggesting a cavity in the interstellar medium. The HI cavity coincides with the thermal and non-thermal emitting X-ray shell. The thermal X-rays are coincident with the edge of the HI distribution, which indicates a strong density gradient, while the non-thermal X-rays are found toward the less dense, inner part of the HI cavity. The most significant non-thermal X-rays are seen toward the southwestern part of the shell where the HI gas traces the dense and cold component. We also identified CO clouds which are likely interacting with the SNR shock waves in the same velocity range as the HI, although the CO clouds are distributed only in a limited part of the SNR shell. The most massive cloud is located in the southeastern part of the shell, showing detailed correspondence with the thermal X-rays. These CO clouds show an enhanced CO J = 2- 1 / 1- 0 intensity ratio, suggesting heating/compression by the shock front. We interpret that the shock-cloud interaction enhances non-thermal X-rays in the southwest and the thermal X-rays are emitted by the shock-heated gas of density 10-100 cm-3. Moreover, we can clearly see an HI envelope around the CO cloud, suggesting that the progenitor had a weaker wind than the massive progenitor of the core-collapse SNR RX J1713.7-3949. It seems likely that the progenitor of RCW 86 was a system consisting of a white dwarf and a low-mass star with low-velocity accretion winds.

Absorption features in the quasar HS 1603 + 3820 II. Distance to the absorber obtained from photoionisation modelling

NASA Astrophysics Data System (ADS)

Różańska, A.; Nikołajuk, M.; Czerny, B.; Dobrzycki, A.; Hryniewicz, K.; Bechtold, J.; Ebeling, H.

2014-04-01

We present the photoionisation modelling of the intrinsic absorber in the bright quasar HS 1603 + 3820. We constructed the broad-band spectral energy distribution using the optical/UV/X-ray observations from different instruments as inputs for the photoionisation calculations. The spectra from the Keck telescope show extremely high CIV to HI ratios, for the first absorber in system A, named A1. This value, together with high column density of CIV ion, place strong constraints on the photoionisation model. We used two photoionisation codes to derive the hydrogen number density at the cloud illuminated surface. By estimating bolometric luminosity of HS 1603 + 3820 using the typical formula for quasars, we calculated the distance to A1. We could find one photoionization solution, by assuming either a constant density cloud (which was modelled using CLOUDY), or a stratified cloud (which was modelled using TITAN), as well as the solar abundances. This model explained both the ionic column density of CIV and the high CIV to HI ratio. The location of A1 is 0.1 pc, and it is situated even closer to the nucleus than the possible location of the Broad Line Region in this object. The upper limit of the distance is sensitive to the adopted covering factor and the carbon abundance. Photoionisation modelling always prefers dense clouds with the number density n0 = 1010 - 1012 cm-3, which explains intrinsic absorption in HS 1603 + 3820. This number density is of the same order as that in the disk atmosphere at the implied distance of A1. Therefore, our results show that the disk wind that escapes from the outermost accretion disk atmosphere can build up dense absorber in quasars.

A role for self-gravity at multiple length scales in the process of star formation.

PubMed

Goodman, Alyssa A; Rosolowsky, Erik W; Borkin, Michelle A; Foster, Jonathan B; Halle, Michael; Kauffmann, Jens; Pineda, Jaime E

2009-01-01

Self-gravity plays a decisive role in the final stages of star formation, where dense cores (size approximately 0.1 parsecs) inside molecular clouds collapse to form star-plus-disk systems. But self-gravity's role at earlier times (and on larger length scales, such as approximately 1 parsec) is unclear; some molecular cloud simulations that do not include self-gravity suggest that 'turbulent fragmentation' alone is sufficient to create a mass distribution of dense cores that resembles, and sets, the stellar initial mass function. Here we report a 'dendrogram' (hierarchical tree-diagram) analysis that reveals that self-gravity plays a significant role over the full range of possible scales traced by (13)CO observations in the L1448 molecular cloud, but not everywhere in the observed region. In particular, more than 90 per cent of the compact 'pre-stellar cores' traced by peaks of dust emission are projected on the sky within one of the dendrogram's self-gravitating 'leaves'. As these peaks mark the locations of already-forming stars, or of those probably about to form, a self-gravitating cocoon seems a critical condition for their existence. Turbulent fragmentation simulations without self-gravity-even of unmagnetized isothermal material-can yield mass and velocity power spectra very similar to what is observed in clouds like L1448. But a dendrogram of such a simulation shows that nearly all the gas in it (much more than in the observations) appears to be self-gravitating. A potentially significant role for gravity in 'non-self-gravitating' simulations suggests inconsistency in simulation assumptions and output, and that it is necessary to include self-gravity in any realistic simulation of the star-formation process on subparsec scales.

Image Capture with Synchronized Multiple-Cameras for Extraction of Accurate Geometries

NASA Astrophysics Data System (ADS)

Koehl, M.; Delacourt, T.; Boutry, C.

2016-06-01

This paper presents a project of recording and modelling tunnels, traffic circles and roads from multiple sensors. The aim is the representation and the accurate 3D modelling of a selection of road infrastructures as dense point clouds in order to extract profiles and metrics from it. Indeed, these models will be used for the sizing of infrastructures in order to simulate exceptional convoy truck routes. The objective is to extract directly from the point clouds the heights, widths and lengths of bridges and tunnels, the diameter of gyrating and to highlight potential obstacles for a convoy. Light, mobile and fast acquisition approaches based on images and videos from a set of synchronized sensors have been tested in order to obtain useable point clouds. The presented solution is based on a combination of multiple low-cost cameras designed on an on-boarded device allowing dynamic captures. The experimental device containing GoPro Hero4 cameras has been set up and used for tests in static or mobile acquisitions. That way, various configurations have been tested by using multiple synchronized cameras. These configurations are discussed in order to highlight the best operational configuration according to the shape of the acquired objects. As the precise calibration of each sensor and its optics are major factors in the process of creation of accurate dense point clouds, and in order to reach the best quality available from such cameras, the estimation of the internal parameters of fisheye lenses of the cameras has been processed. Reference measures were also realized by using a 3D TLS (Faro Focus 3D) to allow the accuracy assessment.

NGVLA Observations of Dense Gas Filaments in Star-Forming Regions

NASA Astrophysics Data System (ADS)

Di Francesco, James; Chen, Mike; Keown, Jared; GAS Team, KEYSTONE Team

2018-01-01

Recent observations of continuum emission from nearby star-forming regions with Herschel and JCMT have revealed that filaments are ubiquitous structures within molecular clouds. Such filaments appear to be intimately connected to star formation, with those having column densities of AV > 8 hosting the majority of prestellar cores and young protostars in clouds. Indeed, this “threshold” can be explained simply as the result of supercritical cylinder fragmentation. How specifically star-forming filaments form in molecular clouds, however, remains unclear, though gravity and turbulence are likely involved. Observations of their kinematics are needed to understand how mass flows both onto and through these filaments. We show here results from two recent surveys, the Green Bank Ammonia Survey (GAS) and the K-band Examinations of Young Stellar Object Natal Environments (KEYSTONE) that have used the Green Bank Telescope’s K-band Focal Plane Array instrument to map NH3 (1,1) emission from dense gas in nearby star-forming regions. Data from both surveys show that NH3 emission traces extremely well the high column density gas across these star-forming regions. In particular, the GAS results for NGC 1333 show NH3-based velocity gradients either predominantly parallel or perpendicular to the filament spines. Though the GAS and KEYSTONE data are vital for probing filaments, higher resolutions than possible with the GBT alone are needed to examine the kinematic patterns on the 0.1-pc scales of star-forming cores within filaments. We describe how the Next Generation Very Large Array (NGVLA) will uniquely provide the key wide-field data of high sensitivity needed to explore how ambient gas in molecular clouds forms filaments that evolve toward star formation.

The velocity characteristics of dusty filaments in the JCMT GBS clouds

NASA Astrophysics Data System (ADS)

Buckle, J. V.; Salji, C.; Richer, J. S.

2013-07-01

Large scale, high resolution spectral and continuum imaging maps have revealed, to an unprecedented extent, the characteristics of filamentary structure in star-forming molecular clouds, and their close association with star-forming cores. The filaments are associated with the formation of dense molecular cores where star formation occurs, and recent models highlight the important relationship between filaments and star-forming clusters. Velocity-coherent filaments have been proposed as the parent structures of star forming cores in Taurus. In Serpens, accretion flows along filaments have been proposed as the continuous source of mass for the star forming cluster. An evolutionary scenario for filaments based on velocity dispersion and column density measurements has recently been proposed, which we test with large scale molecular line and dust continuum maps. The JCMT Gould Belt Survey with SCUBA-2 and HARP provides dust continuum observations at 850 and 450 micron, and 12CO/13CO/C18O J=3-2 spectral line mapping of several nearby molecular clouds, covering large angular scales at high resolution. Velocities and linewidths of optically thin species, such as C18O which traces the warm, dense gas associated with star formation, are critical for an estimate of the virial stability of filamentary structures. The data and analyses that we present provide robust statistics over a large range of starless and protostellar evolutionary states. We present the velocity characteristics of dusty filaments in Orion, probing the physics at the boundary of filamentary structure and star formation. Using C18O, we investigate the internal structure of filaments, based on fragmentation and velocity coherence in the molecular line data. Through velocity dispersion measurements, we determine whether the filamentary structures are bound, and compare results between clouds of different star formation characteristics.

Reconstruction of Building Outlines in Dense Urban Areas Based on LIDAR Data and Address Points

NASA Astrophysics Data System (ADS)

Jarzabek-Rychard, M.

2012-07-01

The paper presents a comprehensive method for automated extraction and delineation of building outlines in densely built-up areas. A novel approach to outline reconstruction is the use of geocoded building address points. They give information about building location thus highly reduce task complexity. Reconstruction process is executed on 3D point clouds acquired by airborne laser scanner. The method consists of three steps: building detection, delineation and contours refinement. The algorithm is tested against a data set that presents the old market town and its surroundings. The results are discussed and evaluated by comparison to reference cadastral data.

Chaotic Star Birth

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset

Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives.

The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region.

The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333.

In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.

From Interstellar PAHs and Ices to the Origin of Life

NASA Technical Reports Server (NTRS)

Allamandola, Louis J.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of dust in the diffuse ISM is reasonably well constrained to micron-sized cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In dense molecular clouds, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by earlier interstellar chemistry standards, is widespread throughout the Universe. The first part of this lecture will describe how infrared studies of interstellar space, combined with laboratory simulations, have revealed the composition of interstellar ices (the building blocks of comets) and the high abundance and nature of interstellar PAHs. The laboratory database has now enabled us to gain insight into the identities, concentrations, and physical state of many interstellar materials. Within a dense molecular cloud, and especially in the solar nebula during the star and planet formation stage, the materials frozen into interstellar/precometary ices are photoprocessed by ultraviolet light, producing more complex molecules. The remainder of the presentation will focus on the photochemical evolution of these materials and the possible role of these compounds on the early Earth. As these materials are thought to be the building blocks of comets and related to the carbonaceous components of micrometeorites, they are likely to have been important sources of complex organic materials on the early Earth and their composition may be related to the origin of life.

Ultrafast visualization of the structural evolution of dense hydrogen towards warm dense matter

NASA Astrophysics Data System (ADS)

Fletcher, Luke

2016-10-01

Hot dense hydrogen far from equilibrium is ubiquitous in nature occurring during some of the most violent and least understood events in our universe such as during star formation, supernova explosions, and the creation of cosmic rays. It is also a state of matter important for applications in inertial confinement fusion research and in laser particle acceleration. Rapid progress occurred in recent years characterizing the high-pressure structural properties of dense hydrogen under static or dynamic compression. Here, we show that spectrally and angularly resolved x-ray scattering measure the thermodynamic properties of dense hydrogen and resolve the ultrafast evolution and relaxation towards thermodynamic equilibrium. These studies apply ultra-bright x-ray pulses from the Linac Coherent Light (LCLS) source. The interaction of rapidly heated cryogenic hydrogen with a high-peak power optical laser is visualized with intense LCLS x-ray pulses in a high-repetition rate pump-probe setting. We demonstrate that electron-ion coupling is affected by the small number of particles in the Debye screening cloud resulting in much slower ion temperature equilibration than predicted by standard theory. This work was supported by the DOE Office of Science, Fusion Energy Science under FWP 100182.

Atomic Oxygen Abundance in Molecular Clouds: Absorption Toward Sagittarius B2

NASA Technical Reports Server (NTRS)

Lis, D. C.; Keene, Jocelyn; Phillips, T. G.; Schilke, P.; Werner, M. W.; Zmuidzinas, J.

2001-01-01

We have obtained high-resolution (approximately 35 km/s) spectra toward the molecular cloud Sgr B2 at 63 micrometers, the wavelength of the ground-state fine-structure line of atomic oxygen (O(I)), using the ISO-LWS instrument. Four separate velocity components are seen in the deconvolved spectrum, in absorption against the dust continuum emission of Sgr B2. Three of these components, corresponding to foreground clouds, are used to study the O(I) content of the cool molecular gas along the line of sight. In principle, the atomic oxygen that produces a particular velocity component could exist in any, or all, of three physically distinct regions: inside a dense molecular cloud, in the UV illuminated surface layer (PDR) of a cloud, and in an atomic (H(I)) gas halo. For each of the three foreground clouds, we estimate, and subtract from the observed O(I) column density, the oxygen content of the H(I) halo gas, by scaling from a published high-resolution 21 cm spectrum. We find that the remaining O(I) column density is correlated with the observed (13)CO column density. From the slope of this correlation, an average [O(I)]/[(13)CO] ratio of 270 +/- 120 (3-sigma) is derived, which corresponds to [O(I)]/[(13)CO] = 9 for a CO to (13)CO abundance ratio of 30. Assuming a (13)CO abundance of 1x10(exp -6) with respect to H nuclei, we derive an atomic oxygen abundance of 2.7x10(exp -4) in the dense gas phase, corresponding to a 15% oxygen depletion compared to the diffuse ISM in our Galactic neighborhood. The presence of multiple, spectrally resolved velocity components in the Sgr B2 absorption spectrum allows, for the first time, a direct determination of the PDR contribution to the O(I) column density. The PDR regions should contain O(I) but not (13)CO, and would thus be expected to produce an offset in the O(I)-(13)CO correlation. Our data do not show such an offset, suggesting that within our beam O(I) is spatially coexistent with the molecular gas, as traced by (13)CO. This may be a result of the inhomogeneous nature of the clouds.

Astronomy and Atmospheric Optics

NASA Astrophysics Data System (ADS)

Cowley, Les; Gaina, Alex

2011-12-01

The authors discusse the insuccess of the observation of the Total Eclipse of the Moon from 10 december 2011 in Romania and relate them with meteoconditions. Only a very short part of the last penumbral phase was observed, while the inital part and the totality was not observed due to very dense clouds. The change in color and brightness during this phase was signaled. Meanwhile, there is an area of science where clouds are of great use and interest. This area is Atmospheric optics, while the science which study clouds is meteorology. Clouds in combination with Solar and Moon light could give rise to a variety of strange, rare and unobvious phenomena in the atmosphere (sky), sometimes confused with Unidentified Flying Objects (UFO). The importance of meteorology for astronomy and atmospheric optics is underlined and an invitation to astronomers to use unfavourable days for athmospheric observations was sent. The web address of the site by Les Cowley, designed for atmospheric optics phenomena is contained in the text of the entry.

Experimental Investigation of Electron Cloud Containment in a Nonuniform Magnetic Field

NASA Technical Reports Server (NTRS)

Eninger, J. E.

1974-01-01

Dense clouds of electrons were generated and studied in an axisymmetric, nonuniform magnetic field created by a short solenoid. The operation of the experiment was similar to that of a low-pressure (approximately 0.000001 Torr) magnetron discharge. Discharge current characteristics are presented as a function of pressure, magnetic field strength, voltage, and cathode end-plate location. The rotation of the electron cloud is determined from the frequency of diocotron waves. In the space charge saturated regime of operation, the cloud is found to rotate as a solid body with frequency close to V sub a/phi sub a where V sub a is the anode voltage and phi suba is the total magnetic flux. This result indicates that, in regions where electrons are present, the magnetic field lines are electrostatic equipotentials (E bar, B bar = 0). Equilibrium electron density distributions suggested by this conditions are integrated with respect to total ionizing power and are found consistent with measured discharge currents.

Person detection and tracking with a 360° lidar system

NASA Astrophysics Data System (ADS)

Hammer, Marcus; Hebel, Marcus; Arens, Michael

2017-10-01

Today it is easily possible to generate dense point clouds of the sensor environment using 360° LiDAR (Light Detection and Ranging) sensors which are available since a number of years. The interpretation of these data is much more challenging. For the automated data evaluation the detection and classification of objects is a fundamental task. Especially in urban scenarios moving objects like persons or vehicles are of particular interest, for instance in automatic collision avoidance, for mobile sensor platforms or surveillance tasks. In literature there are several approaches for automated person detection in point clouds. While most techniques show acceptable results in object detection, the computation time is often crucial. The runtime can be problematic, especially due to the amount of data in the panoramic 360° point clouds. On the other hand, for most applications an object detection and classification in real time is needed. The paper presents a proposal for a fast, real-time capable algorithm for person detection, classification and tracking in panoramic point clouds.

A search for the 13175 A infrared diffuse band in dense environments

NASA Technical Reports Server (NTRS)

Adamson, A. J.; Kerr, Tom H.; Whittet, D. C. B.; Duley, Walter W.

1994-01-01

Models of ionized interstellar C60 predict a strong transition in the 1.2 micrometer region, and two candidate bands have recently been detected in reddened stars. We have searched for the stronger of these bands (at 13175 A) in the Taurus dark cloud complex, to determine its response to the dark-cloud environment. None of the three lines of sight studied (two near the cloud surface, one reaching A(sub V) greater than 20(sup m)) give rise to a detectable band; in one case the equivalent width is a factor of order three below that predicted. Since such behaviour is also shown by the optical Diffuse Interstellar Bands, we suggest that the 13175 A band is a genuine DIB, but we caution against an automatic interpretation in terms of an ionic carrier.

Simulations of Neon Pellets for Plasma Disruption Mitigation in Tokamaks

NASA Astrophysics Data System (ADS)

Bosviel, Nicolas; Samulyak, Roman; Parks, Paul

2017-10-01

Numerical studies of the ablation of neon pellets in tokamaks in the plasma disruption mitigation parameter space have been performed using a time-dependent pellet ablation model based on the front tracking code FronTier-MHD. The main features of the model include the explicit tracking of the solid pellet/ablated gas interface, a self-consistent evolving potential distribution in the ablation cloud, JxB forces, atomic processes, and an improved electrical conductivity model. The equation of state model accounts for atomic processes in the ablation cloud as well as deviations from the ideal gas law in the dense, cold layers of neon gas near the pellet surface. Simulations predict processes in the ablation cloud and pellet ablation rates and address the sensitivity of pellet ablation processes to details of physics models, in particular the equation of state.

Gas cloud G2 can illuminate the black hole population near the galactic center.

PubMed

Bartos, Imre; Haiman, Zoltán; Kocsis, Bence; Márka, Szabolcs

2013-05-31

Galactic nuclei are expected to be densely populated with stellar- and intermediate-mass black holes. Exploring this population will have important consequences for the observation prospects of gravitational waves as well as understanding galactic evolution. The gas cloud G2 currently approaching Sgr A* provides an unprecedented opportunity to probe the black hole and neutron star population of the Galactic nucleus. We examine the possibility of a G2-cloud-black-hole encounter and its detectability with current x-ray satellites, such as Chandra and NuSTAR. We find that multiple encounters are likely to occur close to the pericenter, which may be detectable upon favorable circumstances. This opportunity provides an additional important science case for leading x-ray observatories to closely follow G2 on its way to the nucleus.

APEX reveals glowing stellar nurseries

NASA Astrophysics Data System (ADS)

2008-11-01

Illustrating the power of submillimetre-wavelength astronomy, an APEX image reveals how an expanding bubble of ionised gas about ten light-years across is causing the surrounding material to collapse into dense clumps that are the birthplaces of new stars. Submillimetre light is the key to revealing some of the coldest material in the Universe, such as these cold, dense clouds. Glowing Stellar Nurseries ESO PR Photo 40/08 Glowing Stellar Nurseries The region, called RCW120, is about 4200 light years from Earth, towards the constellation of Scorpius. A hot, massive star in its centre is emitting huge amounts of ultraviolet radiation, which ionises the surrounding gas, stripping the electrons from hydrogen atoms and producing the characteristic red glow of so-called H-alpha emission. As this ionised region expands into space, the associated shock wave sweeps up a layer of the surrounding cold interstellar gas and cosmic dust. This layer becomes unstable and collapses under its own gravity into dense clumps, forming cold, dense clouds of hydrogen where new stars are born. However, as the clouds are still very cold, with temperatures of around -250˚ Celsius, their faint heat glow can only be seen at submillimetre wavelengths. Submillimetre light is therefore vital in studying the earliest stages of the birth and life of stars. The submillimetre-wavelength data were taken with the LABOCA camera on the 12-m Atacama Pathfinder Experiment (APEX) telescope, located on the 5000 m high plateau of Chajnantor in the Chilean Atacama desert. Thanks to LABOCA's high sensitivity, astronomers were able to detect clumps of cold gas four times fainter than previously possible. Since the brightness of the clumps is a measure of their mass, this also means that astronomers can now study the formation of less massive stars than they could before. The plateau of Chajnantor is also where ESO, together with international partners, is building a next generation submillimetre telescope, ALMA, the Atacama Large Millimeter/submillimeter Array. ALMA will use over sixty 12-m antennas, linked together over distances of more than 16 km, to form a single, giant telescope. APEX is a collaboration between the Max-Planck-Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. The telescope is based on a prototype antenna constructed for the ALMA project. Operation of APEX at Chajnantor is entrusted to ESO.

H{sub 2} Ortho-to-para Conversion on Grains: A Route to Fast Deuterium Fractionation in Dense Cloud Cores?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bovino, S.; Grassi, T.; Schleicher, D. R. G.

Deuterium fractionation, i.e., the enhancement of deuterated species with respect to non-deuterated ones, is considered to be a reliable chemical clock of star-forming regions. This process is strongly affected by the ortho-to-para H{sub 2} ratio. In this Letter we explore the effect of the ortho–para (o–p) H{sub 2} conversion on grains on the deuteration timescale in fully-depleted dense cores, including the most relevant uncertainties that affect this complex process. We show that (i) the o–p H{sub 2} conversion on grains is not strongly influenced by the uncertainties on the conversion time and the sticking coefficient, and (ii) that the processmore » is controlled by the temperature and the residence time of ortho-H{sub 2} on the surface, i.e., by the binding energy. We find that for binding energies between 330 and 550 K, depending on the temperature, the o–p H{sub 2} conversion on grains can shorten the deuterium fractionation timescale by orders of magnitude, opening a new route for explaining the large observed deuteration fraction D {sub frac} in dense molecular cloud cores. Our results suggest that the star formation timescale, when estimated through the timescale to reach the observed deuteration fractions, might be shorter than previously proposed. However, more accurate measurements of the binding energy are needed in order to better assess the overall role of this process.« less

Improving automated 3D reconstruction methods via vision metrology

NASA Astrophysics Data System (ADS)

Toschi, Isabella; Nocerino, Erica; Hess, Mona; Menna, Fabio; Sargeant, Ben; MacDonald, Lindsay; Remondino, Fabio; Robson, Stuart

2015-05-01

This paper aims to provide a procedure for improving automated 3D reconstruction methods via vision metrology. The 3D reconstruction problem is generally addressed using two different approaches. On the one hand, vision metrology (VM) systems try to accurately derive 3D coordinates of few sparse object points for industrial measurement and inspection applications; on the other, recent dense image matching (DIM) algorithms are designed to produce dense point clouds for surface representations and analyses. This paper strives to demonstrate a step towards narrowing the gap between traditional VM and DIM approaches. Efforts are therefore intended to (i) test the metric performance of the automated photogrammetric 3D reconstruction procedure, (ii) enhance the accuracy of the final results and (iii) obtain statistical indicators of the quality achieved in the orientation step. VM tools are exploited to integrate their main functionalities (centroid measurement, photogrammetric network adjustment, precision assessment, etc.) into the pipeline of 3D dense reconstruction. Finally, geometric analyses and accuracy evaluations are performed on the raw output of the matching (i.e. the point clouds) by adopting a metrological approach. The latter is based on the use of known geometric shapes and quality parameters derived from VDI/VDE guidelines. Tests are carried out by imaging the calibrated Portable Metric Test Object, designed and built at University College London (UCL), UK. It allows assessment of the performance of the image orientation and matching procedures within a typical industrial scenario, characterised by poor texture and known 3D/2D shapes.

Laboratory experiments on interstellar ice analogs: The sticking and desorption of small physisorbed molecules

NASA Technical Reports Server (NTRS)

Fuchs, G. W.; Acharyya, K.; Bisschop, S. E.; Oberg, K. I.; vanBroekhuizen, F. A.; Fraser, H. J.; Schlemmer, S.; vanDishoeck, E. F.; Linnartz, H.

2006-01-01

Molecular oxygen and nitrogen are difficult to observe since they are infrared inactive and radio quiet. The low O2 abundances found so far combined with general considerations of dense cloud conditions suggest molecular oxygen is frozen out at low temperatures (< 20 K) in the shielded inner regions of cloud cores. In solid form O2 and N2 can only be observed as adjuncts within other ice constituents, like CO. In this work we focus on fundamental properties of N2 and O2 in CO ice-gas systems, e.g. desorption characteristics and sticking probabilities at low temperatures for different ice morphologies.

Large Magellanic Cloud Near-infrared Synoptic Survey. V. Period–Luminosity Relations of Miras

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Wenlong; Macri, Lucas M.; He, Shiyuan

We study the near-infrared properties of 690 Mira candidates in the central region of the Large Magellanic Cloud, based on time-series observations at JHK{sub s}. We use densely sampled I -band observations from the OGLE project to generate template light curves in the near-infrared and derive robust mean magnitudes at those wavelengths. We obtain near-infrared Period–Luminosity relations for oxygen-rich Miras with a scatter as low as 0.12 mag at K{sub s}. We study the Period–Luminosity–Color relations and the color excesses of carbon-rich Miras, which show evidence for a substantially different reddening law.

Skyscrapers in the Desert: Observing Ongoing, Active Star Formation in the Low-Density Wing of the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Fulmer, Leah M.; Gallagher, John S.; Hamann, Wolf-Rainer; Oskinova, Lida; Ramachandran, Varsha

2018-01-01

The low-density Wing of the Small Magellanic Cloud exhibits ongoing, active star formation despite a distinctive lack of dense ambient gas and dust, or resources from which to form stars. Our continued work in studying this region reveals that these paradoxical observations may be explained by a process of sequential star formation. We present photometric, clustering, and spatial analyses in support of this scenario, along with a proposed star formation history based on the following evidence: matches to isochrone models, stellar and ionized gas kinematics (VLT, SALT), and regional HI gas kinematics (ATCA, PKS).

Where is Population II?

NASA Astrophysics Data System (ADS)

Mould, J.; Bianchini, F.; Forbes, Duncan A.; Reichardt, C. L.

2018-03-01

The use of roman numerals for stellar populations represents a classification approach to galaxy formation which is now well behind us. Nevertheless, the concept of a pristine generation of stars, followed by a protogalactic era, and finally the mainstream stellar population is a plausible starting point for testing our physical understanding of early star formation. This will be observationally driven as never before in the coming decade. In this paper, we search out observational tests of an idealised coeval and homogeneous distribution of population II stars. We examine the spatial distribution of quasars, globular clusters, and the integrated free electron density of the intergalactic medium, in order to test the assumption of homogeneity. Any real inhomogeneity implies a population II that is not coeval.

Numerical simulation of the formation of a spiral galaxy

NASA Astrophysics Data System (ADS)

Williams, P. R.; Nelson, A. H.

2001-08-01

A simulation is described in which the numerical galaxy formed compares favourably in every measurable respect with contemporary bright spiral galaxies, including the formation of a distinct stellar bulge and large scale spiral arm shocks in the gas component. This is achieved in spite of the fact that only idealized proto-galactic initial conditions were used, and only simple phenomenological prescriptions for the physics of the interstellar medium (ISM) and star formation were implemented. In light of the emphasis in recent literature on the importance of the link between galaxy formation and models of the universe on cosmological scales, on the details of the physics of the ISM and star formation, and on apparent problems therein, the implications of this result are discussed.

THE OPTICAL STRUCTURE OF THE STARBURST GALAXY M82. II. NEBULAR PROPERTIES OF THE DISK AND INNER WIND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Westmoquette, M. S.; Smith, L. J.; Konstantopoulos, I. S.

2009-12-01

In this second paper of the series, we present the results from optical Gemini-North GMOS-IFU and WIYN DensePak IFU spectroscopic observations of the starburst and inner wind zones of M82, with a focus on the state of the T approx 10{sup 4} K ionized interstellar medium. Our electron density maps show peaks of a few 1000 cm{sup -3} (implying very high thermal pressures), local small spatial-scale variations, and a falloff in the minor axis direction. We discuss the implications of these results with regards to the conditions/locations that may favor the escape of individual cluster winds that ultimately power themore » large-scale superwind. Our findings, when combined with the body of literature built up over the last decade on the state of the interstellar medium (ISM) in M82, imply that the starburst environment is highly fragmented into a range of clouds from small/dense clumps with low-filling factors (<1 pc, n {sub e} approx> 10{sup 4} cm{sup -3}) to larger filling factor, less dense gas. The most compact clouds seem to be found in the cores of the star cluster complexes, whereas the cloud sizes in the inter-complex region are larger. These dense clouds are bathed with an intense radiation field and embedded in an extensive high temperature (T approx> 10{sup 6} K), X-ray-emitting ISM that is a product of the high star formation rates in the starburst zones of M82. The near-constant state of the ionization state of the approx10{sup 4} K gas throughout the M82 starburst zone can be explained as a consequence of the small cloud sizes, which allow the gas conditions to respond quickly to any changes. In Paper I, we found that the observed emission lines are composed of multiple components, including a broad (FWHM approx 150-350 km s{sup -1}) feature that we associate with emission from turbulent mixing layers on the surfaces of the gas clouds, resulting from the interaction of the fast wind outflows from the synchrotron self-Comptons. The large number of compact clouds and wind sources provides an ideal environment for broad line emission, and explains the large observed broad/narrow-line flux ratios. We have examined in more detail the discrete outflow channel identified within the inner wind in Paper I. The channel appears as a coherent, expanding cylindrical structure of length >120 pc and width 35-50 pc. The walls maintain an approximately constant (but subsonic) expansion velocity of approx60 km s{sup -1}, and are defined by peaks and troughs in the densities of the different line components. We hypothesize that as the hot wind fluid flows down the channel cavity, it interacts with the cooler, denser walls of the channel and with entrained material within the flow to produce broad-line emission, while the walls themselves emit primarily the narrow lines. We use the channel to examine further the relationship between the narrow and broad component emitting gas within the inner wind. Within the starburst energy injection zone, we find that turbulent motions (as traced by the broad component) appear to play an increasing role with height. Finally, we have argued that a point-like knot identified in GMOS position 4, exhibiting blueshifted (by approx140 km s{sup -1}), broad (approx<350 km s{sup -1}) Halpha emission and enhanced [S II]/Halpha and [N II]/Halpha ratios, is most likely an ejected luminous blue variable-type object.« less

Sequential Star Formation in RCW 34: A Spectroscopic Census of the Stellar Content of High-Mass Star-Forming Regions

NASA Astrophysics Data System (ADS)

Bik, A.; Puga, E.; Waters, L. B. F. M.; Horrobin, M.; Henning, Th.; Vasyunina, T.; Beuther, H.; Linz, H.; Kaper, L.; van den Ancker, M.; Lenorzer, A.; Churchwell, E.; Kurtz, S.; Kouwenhoven, M. B. N.; Stolte, A.; de Koter, A.; Thi, W. F.; Comerón, F.; Waelkens, Ch.

2010-04-01

In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an H II region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2-3 M sun) are detected of G- and K-spectral type. These stars are still in the pre-main-sequence (PMS) phase. North of the H II region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H2 emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H II region. Between the class II sources in the bubble and the PMS stars in the H II region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the H II region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low- and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is responsible for the star formation propagating from south to north. Based on observations collected at the European Southern Observatory at Paranal, Chile (ESO program 078.C-0780).

Interpreting the sub-linear Kennicutt-Schmidt relationship: the case for diffuse molecular gas

NASA Astrophysics Data System (ADS)

Shetty, Rahul; Clark, Paul C.; Klessen, Ralf S.

2014-08-01

Recent statistical analysis of two extragalactic observational surveys strongly indicate a sub-linear Kennicutt-Schmidt (KS) relationship between the star formation rate (ΣSFR) and molecular gas surface density (Σmol). Here, we consider the consequences of these results in the context of common assumptions, as well as observational support for a linear relationship between ΣSFR and the surface density of dense gas. If the CO traced gas depletion time (τ_dep^CO) is constant, and if CO only traces star-forming giant molecular clouds (GMCs), then the physical properties of each GMC must vary, such as the volume densities or star formation rates. Another possibility is that the conversion between CO luminosity and Σmol, the XCO factor, differs from cloud-to-cloud. A more straightforward explanation is that CO permeates the hierarchical interstellar medium, including the filaments and lower density regions within which GMCs are embedded. A number of independent observational results support this description, with the diffuse gas comprising at least 30 per cent of the total molecular content. The CO bright diffuse gas can explain the sub-linear KS relationship, and consequently leads to an increasing τ_dep^CO with Σmol. If ΣSFR linearly correlates with the dense gas surface density, a sub-linear KS relationship indicates that the fraction of diffuse gas fdiff grows with Σmol. In galaxies where Σmol falls towards the outer disc, this description suggests that fdiff also decreases radially.

Wide Angle Imaging Lidar (WAIL): Theory of Operation and Results from Cross-Platform Validation at the ARM Southern Great Plains Site

NASA Astrophysics Data System (ADS)

Polonsky, I. N.; Davis, A. B.; Love, S. P.

2004-05-01

WAIL was designed to determine physical and geometrical characteristics of optically thick clouds using the off-beam component of the lidar return that can be accurately modeled within the 3D photon diffusion approximation. The theory shows that the WAIL signal depends not only on the cloud optical characteristics (phase function, extinction and scattering coefficients) but also on the outer thickness of the cloud layer. This makes it possible to estimate the mean optical and geometrical thicknesses of the cloud. The comparison with Monte Carlo simulation demonstrates the high accuracy of the diffusion approximation for moderately to very dense clouds. During operation WAIL is able to collect a complete data set from a cloud every few minutes, with averaging over horizontal scale of a kilometer or so. In order to validate WAIL's ability to deliver cloud properties, the LANL instrument was deployed as a part of the THickness from Off-beam Returns (THOR) validation IOP. The goal was to probe clouds above the SGP CART site at night in March 2002 from below (WAIL and ARM instruments) and from NASA's P3 aircraft (carrying THOR, the GSFC counterpart of WAIL) flying above the clouds. The permanent cloud instruments we used to compare with the results obtained from WAIL were ARM's laser ceilometer, micro-pulse lidar (MPL), millimeter-wavelength cloud radar (MMCR), and micro-wave radiometer (MWR). The comparison shows that, in spite of an unusually low cloud ceiling, an unfavorable observation condition for WAIL's present configuration, cloud properties obtained from the new instrument are in good agreement with their counterparts obtained by other instruments. So WAIL can duplicate, at least for single-layer clouds, the cloud products of the MWR and MMCR together. But WAIL does this with green laser light, which is far more representative than microwaves of photon transport processes at work in the climate system.

Formaldehyde in the Diffuse Interstellar Cloud MBM40

NASA Astrophysics Data System (ADS)

Joy, Mackenzie; Magnani, Loris A.

2018-06-01

MBM40, a high-latitude molecular cloud, has been extensively studied using different molecular tracers. It appears that MBM40 is composed of a relatively dense, helical filament embedded in a more diffuse substrate of low density molecular gas. In order to study the transition between the two regimes, this project presents the first high-resolution mapping of MBM40 using the 110-111 hyperfine transition of formaldehyde (H2CO) at 4.83 GHz. We used H2CO spectra obtained with the Arecibo telescope more than a decade ago to construct this map. The results can be compared to previous maps made from the CO(1-0) transition to gain further understanding of the structure of the cloud. The intensity of the H2CO emission was compared to the CO emission. Although a correlation exists between the H2CO and CO emissivity, there seems to be a saturation of H2CO line strength for stronger CO emissivity. This is probably a radiative transfer effect of the CO emission. We have also found that the velocity dispersion of H2CO in the lower ridge of the cloud is significantly lower than in the rest of the cloud. This may indicate that this portion of the cloud is a coherent structure (analogous to an eddy) in a turbulent flow.

Effects of cloud condensate vertical alignment on radiative transfer calculations in deep convective regions

NASA Astrophysics Data System (ADS)

Wang, Xiaocong

2017-04-01

Effects of cloud condensate vertical alignment on radiative transfer process were investigated using cloud resolving model explicit simulations, which provide a surrogate for subgrid cloud geometry. Diagnostic results showed that the decorrelation length Lcw varies in the vertical dimension, with larger Lcw occurring in convective clouds and smaller Lcw in cirrus clouds. A new parameterization of Lcw is proposed that takes into account such varying features and gives rise to improvements in simulations of cloud radiative forcing (CRF) and radiative heating, i.e., the peak of bias is respectively reduced by 8 W m- 2 for SWCF and 2 W m- 2 for LWCF in comparison with Lcw = 1 km. The role of Lcw in modulating CRFs is twofold. On the one hand, larger Lcw tends to increase the standard deviation of optical depth στ, as dense and tenuous parts of the clouds would be increasingly aligned in the vertical dimension, thereby broadening the probability distribution. On the other hand, larger στ causes a decrease in the solar albedo and thermal emissivity, as implied in their convex functions on τ. As a result, increasing (decreasing) Lcwleads to decreased (increased) CRFs, as revealed by comparisons among Lcw = 0, Lcw = 1 km andLcw = ∞. It also affects the vertical structure of radiative flux and thus influences the radiative heating. A better representation of στ in the vertical dimension yields an improved simulation of radiative heating. Although the importance of vertical alignment of cloud condensate is found to be less than that of cloud cover in regards to their impacts on CRFs, it still has enough of an effect on modulating the cloud radiative transfer process.

GRAVITATIONAL CONTRACTION VERSUS SUPERNOVA DRIVING AND THE ORIGIN OF THE VELOCITY DISPERSION–SIZE RELATION IN MOLECULAR CLOUDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ibáñez-Mejía, Juan C.; Mac Low, Mordecai-Mark; Klessen, Ralf S.

Molecular cloud (MC) observations show that clouds have non-thermal velocity dispersions that scale with the cloud size as σ ∝ R {sup 1/2} at a constant surface density, and for varying surface density scale with both the cloud’s size and surface density, σ {sup 2} ∝ R Σ. The energy source driving these chaotic motions remains poorly understood. We describe the velocity dispersions observed in a cloud population formed in a numerical simulation of a magnetized, stratified, supernova (SN)-driven, interstellar medium, including diffuse heating and radiative cooling, before and after we include the effects of the self-gravity of the gas.more » We compare the relationships between velocity dispersion, size, and surface density measured in the simulated cloud population to those found in observations of Galactic MCs. Our simulations prior to the onset of self-gravity suggest that external SN explosions alone do not drive turbulent motions of the observed magnitudes within dense clouds. On the other hand, self-gravity induces non-thermal motions as gravitationally bound clouds begin to collapse in our model, approaching the observed relations between velocity dispersion, size, and surface density. Energy conservation suggests that the observed behavior is consistent with the kinetic energy being proportional to the gravitational energy. However, the clouds in our model show no sign of reaching a stable equilibrium state at any time, even for strongly magnetized clouds. We conclude that gravitationally bound MCs are always in a state of gravitational contraction and their properties are a natural result of this chaotic collapse. In order to agree with observed star formation efficiencies, this process must be terminated by the early destruction of the clouds, presumably from internal stellar feedback.« less

Hydrodynamic model of a self-gravitating optically thick gas and dust cloud

NASA Astrophysics Data System (ADS)

Zhukova, E. V.; Zankovich, A. M.; Kovalenko, I. G.; Firsov, K. M.

2015-10-01

We propose an original mechanism of sustained turbulence generation in gas and dust clouds, the essence of which is the consistent provision of conditions for the emergence and maintenance of convective instability in the cloud. We considered a quasi-stationary one-dimensional model of a selfgravitating flat cloud with stellar radiation sources in its center. The material of the cloud is considered a two-component two-speed continuous medium, the first component of which, gas, is transparent for stellar radiation and is supposed to rest being in hydrostatic equilibrium, and the second one, dust, is optically dense and is swept out by the pressure of stellar radiation to the periphery of the cloud. The dust is specified as a set of spherical grains of a similar size (we made calculations for dust particles with radii of 0.05, 0.1, and 0.15 μm). The processes of scattering and absorption of UV radiation by dust particles followed by IR reradiation, with respect to which the medium is considered to be transparent, are taken into account. Dust-driven stellar wind sweeps gas outwards from the center of the cloud, forming a cocoon-like structure in the gas and dust. For the radiation flux corresponding to a concentration of one star with a luminosity of about 5 ×104 L ⊙ per square parsec on the plane of sources, sizes of the gas cocoon are equal to 0.2-0.4 pc, and for the dust one they vary from tenths of a parsec to six parsecs. Gas and dust in the center of the cavity are heated to temperatures of about 50-60 K in the model with graphite particles and up to 40 K in the model with silicate dust, while the background equilibrium temperature outside the cavity is set equal to 10 K. The characteristic dust expansion velocity is about 1-7 kms-1. Three structural elements define the hierarchy of scales in the dust cocoon. The sizes of the central rarefied cavity, the dense shell surrounding the cavity, and the thin layer inside the shell in which dust is settling provide the proportions 1 : {1-30} : {10-7-10-6}. The density differentials in the dust cocoon (cavity-shell) are much steeper than in the gas one, dust forms multiple flows in the shell so that the dust caustics in the turning points and in the accumulation layer have infinite dust concentration. We give arguments in favor of unstable character of the inverse gas density distribution in the settled dust flow that can power turbulence constantly sustained in the cloud. If this hypothesis is true, the proposed mechanism can explain turbulence in gas and dust clouds on a scale of parsecs and subparsecs.

HOW GALACTIC ENVIRONMENT REGULATES STAR FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meidt, Sharon E.

2016-02-10

In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars—internal structure versus external, environmental influences—providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itselfmore » inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.« less

Night and Day: The Opacity of Clouds Measured by the Mars Orbiter Laser Altimeter (MOLA)

NASA Technical Reports Server (NTRS)

Neumann, G. A.; Wilson, R. J.

2006-01-01

The Mars Orbiter Laser Altimeter (MOLA) [l] on the Mars Global Surveyor spacecraft ranged to clouds over the course of nearly two Mars years [2] using an active laser ranging system. While ranging to the surface, the instrument was also able to measure the product of the surface reflectivity with the two-way atmospheric transmission at 1064 nm. Furthermore, the reflectivity has now been mapped over seasonal cycles using the passive radiometric capability built into MOLA [3]. Combining these measurements, the column opacity may be inferred. MOLA uniquely provides these measurements both night and day. This study examines the pronounced nighttime opacity of the aphelion season tropical water ice clouds, and the indiscernibly low opacity of the southern polar winter clouds. The water ice clouds (Figure 1) do not themselves trigger the altimeter but have measured opacities tau > 1.5 and are temporally and spatially correlated with temperature anomalies predicted by a Mars Global Circulation Model (MGCM) that incorporates cloud radiative effects [4]. The south polar CO2 ice clouds trigger the altimeter with a very high backscatter cross-section over a thickness of 3-9 m and are vertically dispersed over several km, but their total column opacities lie well below the MOLA measurement limit of tau = 0.7. These clouds correspond to regions of supercooled atmosphere that may form either very large specularly reflecting particles [2] or very compact, dense concentrations (>5x10(exp 6)/cu m) of 100-p particles

Processing Uav and LIDAR Point Clouds in Grass GIS

NASA Astrophysics Data System (ADS)

Petras, V.; Petrasova, A.; Jeziorska, J.; Mitasova, H.

2016-06-01

Today's methods of acquiring Earth surface data, namely lidar and unmanned aerial vehicle (UAV) imagery, non-selectively collect or generate large amounts of points. Point clouds from different sources vary in their properties such as number of returns, density, or quality. We present a set of tools with applications for different types of points clouds obtained by a lidar scanner, structure from motion technique (SfM), and a low-cost 3D scanner. To take advantage of the vertical structure of multiple return lidar point clouds, we demonstrate tools to process them using 3D raster techniques which allow, for example, the development of custom vegetation classification methods. Dense point clouds obtained from UAV imagery, often containing redundant points, can be decimated using various techniques before further processing. We implemented and compared several decimation techniques in regard to their performance and the final digital surface model (DSM). Finally, we will describe the processing of a point cloud from a low-cost 3D scanner, namely Microsoft Kinect, and its application for interaction with physical models. All the presented tools are open source and integrated in GRASS GIS, a multi-purpose open source GIS with remote sensing capabilities. The tools integrate with other open source projects, specifically Point Data Abstraction Library (PDAL), Point Cloud Library (PCL), and OpenKinect libfreenect2 library to benefit from the open source point cloud ecosystem. The implementation in GRASS GIS ensures long term maintenance and reproducibility by the scientific community but also by the original authors themselves.

Ab initio calculation of the ion feature in x-ray Thomson scattering.

PubMed

Plagemann, Kai-Uwe; Rüter, Hannes R; Bornath, Thomas; Shihab, Mohammed; Desjarlais, Michael P; Fortmann, Carsten; Glenzer, Siegfried H; Redmer, Ronald

2015-07-01

The spectrum of x-ray Thomson scattering is proportional to the dynamic structure factor. An important contribution is the ion feature which describes elastic scattering of x rays off electrons. We apply an ab initio method for the calculation of the form factor of bound electrons, the slope of the screening cloud of free electrons, and the ion-ion structure factor in warm dense beryllium. With the presented method we can calculate the ion feature from first principles. These results will facilitate a better understanding of x-ray scattering in warm dense matter and an accurate measurement of ion temperatures which would allow determining nonequilibrium conditions, e.g., along shock propagation.

Interactions of stars and interstellar matter in Scorpio Centaurus

NASA Technical Reports Server (NTRS)

De Geus, E. J.

1992-01-01

The interaction of the stars in the Scorpio-Centaurus OB association with the ambient interstellar medium is investigated. Large H I loops in the fourth galactic quadrant are parts of expanding shells surrounding the subgroups of the association. The energy output of the original stellar population of the subgroups is calculated. Comparison with the kinetic energy of the shells shows that the energy output of the stars in the subgroups is sufficient to form the shells. The masses of the shells are consistent with those of giant molecular clouds GMCs, suggesting that the shells consist of swept-up, original GMC material. The influence of the expanding shell around the young Upper-Scorpius subgroup on the morphology of the Ophiuchus molecular clouds is investigated. The interaction of the shell with the Ophiuchus clouds accounts for the presence of a slow shock and for the shape of the elongated dark clouds connected to the Rho Oph dense cloud. The close passage of the trajectory of the runaway star Zeta Oph by the center of the Upper-Scorpius shell, combined with the time scale of formation of the shell, strongly suggests that the star has originated in the Upper-Scorpius subgroup.

ALMA CO(3-2) Observations of Star-forming Filaments in a Gas-poor Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Consiglio, S. Michelle; Turner, Jean L.; Beck, Sara; Meier, David S.; Silich, Sergiy; Zhao, Jun-Hui

2017-11-01

We report ALMA observations of 12CO(3-2) and 13CO(3-2) in the gas-poor dwarf galaxy NGC 5253. These 0.″3(5.5 pc) resolution images reveal small, dense molecular gas clouds that are located in kinematically distinct extended filaments. Some of the filaments appear to be falling into the galaxy and may be fueling its current star formation. The most intense CO(3-2) emission comes from the central ˜100 pc region centered on the luminous radio-infrared H II region known as the supernebula. The CO(3-2) clumps within the starburst region are anti-correlated with Hα on ˜5 pc scales, but are well-correlated with radio free-free emission. Cloud D1, which enshrouds the supernebula, has a high 12CO/13CO ratio, as does another cloud within the central 100 pc starburst region, possibly because the clouds are hot. CO(3-2) emission alone does not allow determination of cloud masses as molecular gas temperature and column density are degenerate at the observed brightness, unless combined with other lines such as 13CO.

Time scales for molecule formation by ion-molecule reactions

NASA Technical Reports Server (NTRS)

Langer, W. D.; Glassgold, A. E.

1976-01-01

Analytical solutions are obtained for nonlinear differential equations governing the time-dependence of molecular abundances in interstellar clouds. Three gas-phase reaction schemes are considered separately for the regions where each dominates. The particular case of CO, and closely related members of the Oh and CH families of molecules, is studied for given values of temperature, density, and the radiation field. Nonlinear effects and couplings with particular ions are found to be important. The time scales for CO formation range from 100,000 to a few million years, depending on the chemistry and regime. The time required for essentially complete conversion of C(+) to CO in the region where the H3(+) chemistry dominates is several million years. Because this time is longer than or comparable to dynamical time scales for dense interstellar clouds, steady-state abundances may not be observed in such clouds.

Coagulation of grains in static and collapsing protostellar clouds

NASA Technical Reports Server (NTRS)

Weidenschilling, S. J.; Ruzmaikina, T. V.

1993-01-01

The wavelength dependence of extinction in the diffuse interstellar medium implies that it is produced by particles of dominant size of approximately 10(exp -5) cm. There is some indication that in the cores of dense molecular clouds, sub-micron grains can coagulate to form larger particles; this process is probably driven by turbulence. The most primitive meteorites (carbonaceous chondrites) are composed of particles with a bimodal size distribution with peaks near 1 micron (matrix) and 1 mm (chondrules). Models for chondrule formation that involve processing of presolar material by chemical reactions or through an accretion shock during infall assume that aggregates of the requisite mass could form before or during collapse. The effectiveness of coagulation during collapse has been disputed; it appears to depend on specific assumptions. The first results of detailed numerical modeling of spatial and temporal variations of particle sizes in presolar clouds, both static and collapsing, is reported in this article.

Applications of 3D-EDGE Detection for ALS Point Cloud

NASA Astrophysics Data System (ADS)

Ni, H.; Lin, X. G.; Zhang, J. X.

2017-09-01

Edge detection has been one of the major issues in the field of remote sensing and photogrammetry. With the fast development of sensor technology of laser scanning system, dense point clouds have become increasingly common. Precious 3D-edges are able to be detected from these point clouds and a great deal of edge or feature line extraction methods have been proposed. Among these methods, an easy-to-use 3D-edge detection method, AGPN (Analyzing Geometric Properties of Neighborhoods), has been proposed. The AGPN method detects edges based on the analysis of geometric properties of a query point's neighbourhood. The AGPN method detects two kinds of 3D-edges, including boundary elements and fold edges, and it has many applications. This paper presents three applications of AGPN, i.e., 3D line segment extraction, ground points filtering, and ground breakline extraction. Experiments show that the utilization of AGPN method gives a straightforward solution to these applications.

Kinematics of the Ultra-High-Velocity Gas in the Expanding Molecular Shell Adjacent to the W44 Supernova Remnant

NASA Astrophysics Data System (ADS)

Yamada, Masaya; Oka, Tomoharu; Tanaka, Kunihiko; Nomura, Mariko; Takekawa, Shunya; Iwata, Yuhei; Tokuyama, Sekito; Tanabe, Keisuke; Tsujimoto, Shiho; Furusawa, Maiko

2017-01-01

High-velocity compact cloud (HVCC) is a peculiar category of molecular clouds detected in the central molecular zone of our Galaxy (Oka et al. 1998, 2007, and 2012). They are characterized by compact appearances (d < 5 pc) and very large velocity widths (Δ V > 50 km s-1). Some of them show high CO J=3-2/J=1-0 intensity ratios (>= 1.5), indicating that they consist of dense and warm molecular gas. Dispite a number of efforts, we have not reached a comprehensive interpretation of HVCCs. Recently, we detected an extraordinaly broad velocity width feature, the `Bullet', in the molecular cloud interacting with the W44 supernova remnant. The Bullet shares essential properties with HVCCs. Because of its proximity, a close inspection of the Bullet must contribute to the understanding of HVCCs.

How Does Dense Molecular Gas Contribute to Star Formation in the Starburst Galaxy NGC 2146?

NASA Astrophysics Data System (ADS)

Wofford, Alia

2017-01-01

The starburst galaxy NGC 2146 is believed to have been formed approximately 800 Myr ago, when two galaxies collided with each other possibly leading to a burst of star formation. NGC 2146 is known as a starburst galaxy for the high frequency of star formation going on in its molecular clouds. These clouds serve as nurseries for star formation to occur. Hydrogen Cyanide (HCN) and Carbon monoxide (CO) are molecules found in molecular gas clouds. HCN molecules are tracers for high density star forming gas. Whereas, CO molecules are tracers for low density star forming gas. In this project, we are observing these two molecules and their proximity to where the stars are forming in the galaxy to determine if the star formation is occurring in the same area as the high and low density molecular gas areas in starburst galaxy NGC 2146.

Building Facade Modeling Under Line Feature Constraint Based on Close-Range Images

NASA Astrophysics Data System (ADS)

Liang, Y.; Sheng, Y. H.

2018-04-01

To solve existing problems in modeling facade of building merely with point feature based on close-range images , a new method for modeling building facade under line feature constraint is proposed in this paper. Firstly, Camera parameters and sparse spatial point clouds data were restored using the SFM , and 3D dense point clouds were generated with MVS; Secondly, the line features were detected based on the gradient direction , those detected line features were fit considering directions and lengths , then line features were matched under multiple types of constraints and extracted from multi-image sequence. At last, final facade mesh of a building was triangulated with point cloud and line features. The experiment shows that this method can effectively reconstruct the geometric facade of buildings using the advantages of combining point and line features of the close - range image sequence, especially in restoring the contour information of the facade of buildings.

Cosmic rays, gas and dust in nearby anticentre clouds. I. CO-to-H2 conversion factors and dust opacities

NASA Astrophysics Data System (ADS)

Remy, Q.; Grenier, I. A.; Marshall, D. J.; Casandjian, J. M.

2017-05-01

Aims: We aim to explore the capabilities of dust emission and γ rays for probing the properties of the interstellar medium in the nearby anti-centre region, using γ-ray observations with the Fermi Large Area Telescope (LAT), and the thermal dust optical depth inferred from Planck and IRAS observations. We also aim to study massive star-forming clouds including the well known Taurus, Auriga, Perseus, and California molecular clouds, as well as a more diffuse structure which we refer to as Cetus. In particular, we aim at quantifying potential variations in cosmic-ray density and dust properties per gas nucleon across the different gas phases and different clouds, and at measuring the CO-to-H2 conversion factor, XCO, in different environments. Methods: We have separated six nearby anti-centre clouds that are coherent in velocities and distances, from the Galactic-disc background in H I 21-cm and 12CO 2.6-mm line emission. We have jointly modelled the γ-ray intensity recorded between 0.4 and 100 GeV, and the dust optical depth τ353 at 353 GHz as a combination of H I-bright, CO-bright, and ionised gas components. The complementary information from dust emission and γ rays was used to reveal the gas not seen, or poorly traced, by H I, free-free, and 12CO emissions, namely (I) the opaque H iand diffuse H2 present in the Dark Neutral Medium at the atomic-molecular transition, and (II) the dense H2 to be added where 12CO lines saturate. Results: The measured interstellar γ-ray spectra support a uniform penetration of the cosmic rays with energies above a few GeV through the clouds, from the atomic envelopes to the 12CO-bright cores, and with a small ± 9% cloud-to-cloud dispersion in particle flux. We detect the ionised gas from the H iiregion NGC 1499 in the dust and γ-ray emissions and measure its mean electron density and temperature. We find a gradual increase in grain opacity as the gas (atomic or molecular) becomes more dense. The increase reaches a factor of four to six in the cold molecular regions that are well shielded from stellar radiation. Consequently, the XCO factor derived from dust is systematically larger by 30% to 130% than the γ-ray estimate. We also evaluate the average γ-ray XCO factor for each cloud, and find that XCO tends to decrease from diffuse to more compact molecular clouds, as expected from theory. We find XCO factors in the anti-centre clouds close to or below 1020 cm-2 K-1 km-1 s, in agreement with other estimates in the solar neighbourhood. Together, they confirm the long-standing unexplained discrepancy, by a factor of two, between the mean XCO values measured at parsec scales in nearby clouds and those obtained at kiloparsec scale in the Galaxy. Our results also highlight large quantitative discrepancies in 12CO intensities between simulations and observations at low molecular gas densities.

Aerosol-Radiation-Cloud Interactions in the South-East Atlantic: Future Suborbital Activities to Address Knowledge Gaps in Satellite and Model Assessments

NASA Technical Reports Server (NTRS)

Redemann, Jens; Wood, R.; Zuidema, P.; Haywood, J.; Piketh, S.; Formenti, P.; L'Ecuyer, T.; Kacenelenbogen, M.; Segal-Rosenheimer, M.; Shinozuka, Y.;

Aerosol-Radiation-Cloud Interactions in the South-East Atlantic: Future Suborbital Activities to Address Knowledge Gaps in Satellite and Model Assessments

NASA Astrophysics Data System (ADS)

Redemann, J.; Wood, R.; Zuidema, P.; Haywood, J. M.; Piketh, S.; Formenti, P.; L'Ecuyer, T. S.; Kacenelenbogen, M. S.; Segal-Rosenhaimer, M.; Shinozuka, Y.; LeBlanc, S. E.; Vaughan, M. A.; Schmidt, S.; Flynn, C. J.; Song, S.; Schmid, B.; Luna, B.; Abel, S.

2015-12-01

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical stratocumulus (Sc) cloud decks in the world. The SE Atlantic stratocumulus deck interacts with the dense layers of BB aerosols that initially overlay the cloud deck, but later subside and may mix into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects, and their global representation in climate models remains one of the largest uncertainties in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for global climate change scenarios. Our understanding of aerosol-cloud interactions in the SE Atlantic is hindered both by the lack of knowledge on aerosol and cloud properties, as well as the lack of knowledge about detailed physical processes involved. Most notably, we are missing knowledge on the absorptive and cloud nucleating properties of aerosols, including their vertical distribution relative to clouds, on the locations and degree of aerosol mixing into clouds, on the processes that govern cloud property adjustments, and on the importance of aerosol effects on clouds relative to co-varying synoptic scale meteorology. We discuss the current knowledge of aerosol and cloud property distributions based on satellite observations and sparse suborbital sampling. Recent efforts to make full use of A-Train aerosol sensor synergies will be highlighted. We describe planned field campaigns in the region to address the existing knowledge gaps. Specifically, we describe the scientific objectives and implementation of the five synergistic, international research activities aimed at providing some of the key aerosol and cloud properties and a process-level understanding of aerosol-cloud interactions over the SE Atlantic: NASA's ORACLES, the UK Met Office's CLARIFY-2016, the DoE's LASIC, NSF's ONFIRE, and CNRS' AEROCLO-SA.

Cloud vertical structure, precipitation, and cloud radiative effects over Tibetan Plateau

NASA Astrophysics Data System (ADS)

Liu, Y.; Yan, Y.; Lu, J.

2017-12-01

The vertical structure of clouds and its connection with precipitation and cloud radiative effects (CRE) over the Tibetan Plateau (TP) are analyzed and compared with its neighboring land and tropical oceans based on CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) products and the Tropical Rainfall Measuring Mission (TRMM) precipitation data. Unique characteristics of cloud vertical structure and CRE over the TP are found. The cloud amount shows seasonal variation over the TP, which presents a single peak (located in 7-11 km) during January to April and two peaks (located in 5-8 km and 11-17 km separately) after mid-June, and then resumes to one peak (located in 5-10 km) after mid-August. Topography-induced restriction on moisture supply leads to a compression effect on clouds, i.e., the reduction in both cloud thickness and number of cloud layers, over the TP. The topography-induced compression effect is also shown in the range in the variation of cloud thickness and cloud-top height corresponding to different precipitation intensity, which is much smaller over the TP than its neighboring regions. In summer, cloud ice particles over the TP are mostly located at lower altitude (5-10 km) with richer variety of sizes and aggregation in no rain conditions compared to other regions. Ice water content becomes abundant and the number concentration tends to be dense at higher levels when precipitation is enhanced. The longwave CRE in the atmosphere over the TP is a net cooling effect. The vertical structure of CRE over the TP is unique compared to other regions: there exists a strong cooling layer of net CRE at the altitude of 8 km, from June to the beginning of October; the net radiative heating layer above the surface is shallower but stronger underneath 7 km and with a stronger seasonal variation over the TP.

Molecular clouds toward three Spitzer bubbles S116, S117, and S118: Evidence for a cloud-cloud collision which formed the three H II regions and a 10 pc scale molecular cavity

NASA Astrophysics Data System (ADS)

Fukui, Yasuo; Ohama, Akio; Kohno, Mikito; Torii, Kazufumi; Fujita, Shinji; Hattori, Yusuke; Nishimura, Atsushi; Yamamoto, Hiroaki; Tachihara, Kengo

2018-05-01

We carried out a molecular-line study toward the three Spitzer bubbles S116, S117, and S118, which show active formation of high-mass stars. We found molecular gas consisting of two components with a velocity difference of ˜5 km s-1. One of them, the small cloud, has a typical velocity of -63 km s-1 and the other, the large cloud, has one of -58 km s-1. The large cloud has a nearly circular intensity depression, the size of which is similar to that of the small cloud. We present an interpretation that its cavity was created by a collision between the two clouds and that this collision compressed the gas into a dense layer elongating along the western rim of the small cloud. In this scenario, the O stars including those in the three Spitzer bubbles were formed in the interface layer compressed by the collision. Assuming that the relative motion of the clouds has a tilt of 45° to the line of sight, we estimate that the collision continued for the last 1 Myr at a relative velocity of ˜10 km s-1. In the S116-S117-S118 system the H II regions are located outside of the cavity. This morphology is ascribed to the density-bound distribution of the large cloud which caused the H II regions to expand more easily toward the outer part of the large cloud than towards the inside of the cavity. The present case proves that a cloud-cloud collision creates a cavity without the action of O-star feedback, and suggests that the collision-compressed layer is highly filamentary.

Star formation induced by cloud-cloud collisions and galactic giant molecular cloud evolution

NASA Astrophysics Data System (ADS)

Kobayashi, Masato I. N.; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro; Fukui, Yasuo

2018-05-01

Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud-cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense H I gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largely modified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs ≳ 10^{5.5} M_{⊙} (where M⊙ is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

Information content of visible and midinfrared radiances for retrieving tropical ice cloud properties

NASA Astrophysics Data System (ADS)

Chang, Kai-Wei; L'Ecuyer, Tristan S.; Kahn, Brian H.; Natraj, Vijay

2017-05-01

Hyperspectral instruments such as Atmospheric Infrared Sounder (AIRS) have spectrally dense observations effective for ice cloud retrievals. However, due to the large number of channels, only a small subset is typically used. It is crucial that this subset of channels be chosen to contain the maximum possible information about the retrieved variables. This study describes an information content analysis designed to select optimal channels for ice cloud retrievals. To account for variations in ice cloud properties, we perform channel selection over an ensemble of cloud regimes, extracted with a clustering algorithm, from a multiyear database at a tropical Atmospheric Radiation Measurement site. Multiple satellite viewing angles over land and ocean surfaces are considered to simulate the variations in observation scenarios. The results suggest that AIRS channels near wavelengths of 14, 10.4, 4.2, and 3.8 μm contain the most information. With an eye toward developing a joint AIRS-MODIS (Moderate Resolution Imaging Spectroradiometer) retrieval, the analysis is also applied to combined measurements from both instruments. While application of this method to MODIS yields results consistent with previous channel sensitivity studies, the analysis shows that this combination may yield substantial improvement in cloud retrievals. MODIS provides most information on optical thickness and particle size, aided by a better constraint on cloud vertical placement from AIRS. An alternate scenario where cloud top boundaries are supplied by the active sensors in the A-train is also explored. The more robust cloud placement afforded by active sensors shifts the optimal channels toward the window region and shortwave infrared, further constraining optical thickness and particle size.

Theoretical microwave spectral constants for C2N, C2N/+/, and C3H

NASA Technical Reports Server (NTRS)

Green, S.

1980-01-01

Theoretical microwave spectral constants have been computed for C2N, C3H, and C2N(+). For C2N these are compared with values obtained from optical data. Calculated hyperfine constants are also presented for HNC, DNC, and HCNH(+). The possibility of observing these species in dense interstellar clouds is discussed.

The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines

USGS Publications Warehouse

Newhall, Christopher G.; Hendley, James W.; Stauffer, Peter H.

1997-01-01

The second-largest volcanic eruption of this century, and by far the largest eruption to affect a densely populated area, occurred at Mount Pinatubo in the Philippines on June 15, 1991. The eruption produced high-speed avalanches of hot ash and gas, giant mudflows, and a cloud of volcanic ash hundreds of miles across. The impacts of the eruption continue to this day.

A New Unsteady Model for Dense Cloud Cavitation in Cryogenic Fluids

NASA Technical Reports Server (NTRS)

Hosangadi, Ashvin; Ahuja, Vineet

2005-01-01

Contents include the following: Background on thermal effects in cavitation. Physical properties of hydrogen. Multi-phase cavitation with thermal effect. Solution procedure. Cavitation model overview. Cavitation source terms. New cavitation model. Source term for bubble growth. One equation les model. Unsteady ogive simulations: liquid nitrogen. Unsteady incompressible flow in a pipe. Time averaged cavity length for NACA15 flowfield.

Interstellar Matter

NASA Astrophysics Data System (ADS)

Savage, B.; Murdin, P.

2000-11-01

The enormous volume of space between the stars in the Milky Way Galaxy is filled with interstellar matter (ISM). The ISM plays a central role in the processes of STAR FORMATION and GALAXY EVOLUTION. Stars form from the ISM in dense molecular clouds. The radiant and mechanical energy produced by stars heats, ionizes, and produces structures in the ISM. Gradual or catastrophic mass loss from stars ...

Electrostatic forces in planetary rings

NASA Technical Reports Server (NTRS)

Goertz, C. K.; Shan, Linhua; Havnes, O.

1988-01-01

The average charge on a particle in a particle-plasma cloud, the plasma potential inside the cloud, and the Coulomb force acting on the particle are calculated. The net repulsive electrostatic force on a particle depends on the plasma density, temperature, density of particles, particle size, and the gradient of the particle density. In a uniformly dense ring the electrostatic repulsion is zero. It is also shown that the electrostatic force acts like a pressure force, that even a collisionless ring can be stable against gravitational collapse, and that a finite ring thickness does not necessarily imply a finite velocity dispersion. A simple criterion for the importance of electrostatic forces in planetary rings is derived which involves the calculation of the vertical ring thickness which would result if only electrostatic repulsion were responsible for the finite ring thickness. Electrostatic forces are entirely negligible in the main rings of Saturn and the E and G rings. They may also be negligible in the F ring. However, the Uranian rings and Jupiter's ring seem to be very much influenced by electrostatic repulsion. In fact, electrostatic forces could support a Jovian ring which is an order of magnitude more dense than observed.

APOGEE strings: A fossil record of the gas kinematic structure

NASA Astrophysics Data System (ADS)

Hacar, A.; Alves, J.; Forbrich, J.; Meingast, S.; Kubiak, K.; Großschedl, J.

2016-05-01

We compare APOGEE radial velocities (RVs) of young stars in the Orion A cloud with CO line gas emission and find a correlation between the two at large scales in agreement with previous studies. However, at smaller scales we find evidence for the presence of a substructure in the stellar velocity field. Using a friends-of-friends approach we identify 37 stellar groups with almost identical RVs. These groups are not randomly distributed, but form elongated chains or strings of stars with five or more members with low velocity dispersion across lengths of 1-1.5 pc. The similarity between the kinematic properties of the APOGEE strings and the internal velocity field of the chains of dense cores and fibers recently identified in the dense interstellar medium is striking and suggests that for most of the Orion A cloud, young stars keep memory of the parental gas substructure where they originated. Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A80

Building Change Detection from Bi-Temporal Dense-Matching Point Clouds and Aerial Images.

PubMed

Pang, Shiyan; Hu, Xiangyun; Cai, Zhongliang; Gong, Jinqi; Zhang, Mi

2018-03-24

In this work, a novel building change detection method from bi-temporal dense-matching point clouds and aerial images is proposed to address two major problems, namely, the robust acquisition of the changed objects above ground and the automatic classification of changed objects into buildings or non-buildings. For the acquisition of changed objects above ground, the change detection problem is converted into a binary classification, in which the changed area above ground is regarded as the foreground and the other area as the background. For the gridded points of each period, the graph cuts algorithm is adopted to classify the points into foreground and background, followed by the region-growing algorithm to form candidate changed building objects. A novel structural feature that was extracted from aerial images is constructed to classify the candidate changed building objects into buildings and non-buildings. The changed building objects are further classified as "newly built", "taller", "demolished", and "lower" by combining the classification and the digital surface models of two periods. Finally, three typical areas from a large dataset are used to validate the proposed method. Numerous experiments demonstrate the effectiveness of the proposed algorithm.

Development of AN All-Purpose Free Photogrammetric Tool

NASA Astrophysics Data System (ADS)

González-Aguilera, D.; López-Fernández, L.; Rodriguez-Gonzalvez, P.; Guerrero, D.; Hernandez-Lopez, D.; Remondino, F.; Menna, F.; Nocerino, E.; Toschi, I.; Ballabeni, A.; Gaiani, M.

2016-06-01

Photogrammetry is currently facing some challenges and changes mainly related to automation, ubiquitous processing and variety of applications. Within an ISPRS Scientific Initiative a team of researchers from USAL, UCLM, FBK and UNIBO have developed an open photogrammetric tool, called GRAPHOS (inteGRAted PHOtogrammetric Suite). GRAPHOS allows to obtain dense and metric 3D point clouds from terrestrial and UAV images. It encloses robust photogrammetric and computer vision algorithms with the following aims: (i) increase automation, allowing to get dense 3D point clouds through a friendly and easy-to-use interface; (ii) increase flexibility, working with any type of images, scenarios and cameras; (iii) improve quality, guaranteeing high accuracy and resolution; (iv) preserve photogrammetric reliability and repeatability. Last but not least, GRAPHOS has also an educational component reinforced with some didactical explanations about algorithms and their performance. The developments were carried out at different levels: GUI realization, image pre-processing, photogrammetric processing with weight parameters, dataset creation and system evaluation. The paper will present in detail the developments of GRAPHOS with all its photogrammetric components and the evaluation analyses based on various image datasets. GRAPHOS is distributed for free for research and educational needs.

Star Formation in the Filamentary Dark Cloud GF-9: a Multi-Wavelength Intra-Cloud Comparative Study

NASA Astrophysics Data System (ADS)

Ciardi, David Robert

Filamentary dark clouds (FDCs) are a subclass of small molecular clouds containing small numbers of somewhat regularly spaced dense cores connected by lower density gas and dust. Most of the previous work performed on FDCs has concerned the star formation properties of individual dense cores within the FDCs and has not concerned the FDCs as entities of their own. As a result little is known about the general star formation properties of FDCs. The primary question addressed in this work is 'Within filamentary dark clouds, how does the star formation process within a core region compare to that within a filamentary region?' In order to address the above question, a multi-wavelength observational comparative study has been performed upon a representative dense core (hereafter, GF9-Core) and filamentary region (hereafter, GF9-Fila) within the FDC GF-9 (LDN 1082). At the Five College Radio Astronomy Observatory, the core and filamentary region were observed in the rotational transitions of 12CO/ (J=1/to0),/ 13CO/ (J=1/to0)/ and/ CS/ (J=2/to1) covering a region of 10' x 8'. The temperature, density and kinematic structures of the two regions were deduced from the radio imaging spectroscopy data and were used to estimate the energy balance of the regions. We also obtained 70, 100, 135 and 200 μm images from the Infrared Space Observatory (ISO) covering approximately 12' x 9' which were used to investigate the temperature and density distributions of the dust within the two regions. Finally, at the Wyoming Infrared Observatory using the Aerospace Corporation NICMOS3 camera, the core and filament were imaged in the near-infrared broadband filters J, H, and K-short covering a slightly smaller region of 7' x 7'. The near-infrared survey data were used to search for embedded Class I and Class II protostars and to investigate the density distribution of the dust. We have found that the evolutionary processes of the core region and the filament region proceed along similar evolutionary paths but are governed by the amount of mass within each region. GF9-Core has a greater mass and density than GF9-Fila, and therefore, gravity has a stronger influence on the fate of the dust and gas. Because of the larger mass, GF9-Core has proceeded along the star formation path and is currently engaged at the Class 0 protostar stage. In contrast, GF9-Fila is still in the earlier stages of contraction through ambipolar diffusion and may form a star sometime in the future.

Star formation in massive Milky Way molecular clouds: Building a bridge to distant galaxies

NASA Astrophysics Data System (ADS)

Willis, Sarah Elizabeth

The Kennicutt-Schmidt relation is an empirical power-law linking the surface density of the star formation rate (SigmaSFR) to the surface density of gas (Sigmagas ) averaged over the observed face of a starforming galaxy Kennicutt (1998). The original presentation used observations of CO to measure gas density and H alpha emission to measure the population of hot, massive young stars (and infer the star formation rate). Observations of Sigma SFR from a census of young stellar objects in nearby molecular clouds in our Galaxy are up to 17 times higher than the extragalactic relation would predict given their Sigmagas. These clouds primarily form low-mass stars that are essentially invisible to star formation rate tracers. A sample of six giant molecular cloud (GMC) complexes with signposts of massive star formation was identified in our galaxy. The regions selected have a range of total luminosity and morphology. Deep ground-based observations in the near-infrared with NEWFIRM and IRAC observations with the Spitzer Space Telescope were used to conduct a census of the young stellar content associated with each of these clouds. The star formation rates from the stellar census in each of these regions was compared with the star formation rates measured by extragalactic star formation rate tracers based on monochromatic mid-infrared luminosities. Far-infrared Herschel observations from 160 through 500 mum were used to determine the column density and temperature in each region. The region NGC 6334 served as a test case to compare the Herschel column density measurements with the measurements for near-infrared extinction. The combination of the column density maps and the stellar census lets us examine SigmaSFR vs. Sigma gas for the massive GMCs. These regions are consistent with the results for the low-mass molecular clouds, indicating Sigma SFR levels that are higher than predicted based on Sigma gas. The overall Sigmagas levels are higher for the massive star forming regions, indicating that they have a higher fraction of dense gas than the clouds that are forming primarily low mass stars. There is still significant spread at a given average gas density, indicating that the star formation history and dense gas fraction play important roles in determining an individual molecular cloud's place in a Sigma SFR vs. Sigmagas diagram. Zooming in, SigmaSFR vs. Sigma gas was examined within the individual clouds, revealing a decrease relative to the spread that is observed for the average over whole clouds. The dependence of SigmaSFR on Sigma gas increases significantly above AV ˜ 5 - 10 which is consistent with previous measurements of a threshold for star formation around AV = 8 or Sigma gas = 0.04 g cm-2. NGC 6334 was found to be consistent with a threshold for massive star formation at Sigmagas = 1 g cm-2.

Similar complex kinematics within two massive, filamentary infrared dark clouds

NASA Astrophysics Data System (ADS)

Barnes, A. T.; Henshaw, J. D.; Caselli, P.; Jiménez-Serra, I.; Tan, J. C.; Fontani, F.; Pon, A.; Ragan, S.

2018-04-01

Infrared dark clouds (IRDCs) are thought to be potential hosts of the elusive early phases of high-mass star formation. Here, we conduct an in-depth kinematic analysis of one such IRDC, G034.43+00.24 (Cloud F), using high sensitivity and high spectral resolution IRAM-30m N2H+ (1-0) and C18O (1-0) observations. To disentangle the complex velocity structure within this cloud, we use Gaussian decomposition and hierarchical clustering algorithms. We find that four distinct coherent velocity components are present within Cloud F. The properties of these components are compared to those found in a similar IRDC, G035.39-00.33 (Cloud H). We find that the components in both clouds have high densities (inferred by their identification in N2H+), trans-to-supersonic non-thermal velocity dispersions with Mach numbers of ˜1.5-4, a separation in velocity of ˜3 km s-1, and a mean red-shift of ˜0.3 km s-1 between the N2H+ (dense gas) and C18O emission (envelope gas). The latter of these could suggest that these clouds share a common formation scenario. We investigate the kinematics of the larger-scale Cloud F structures, using lower-density-tracing 13CO(1-0) observations. A good correspondence is found between the components identified in the IRAM-30m observations and the most prominent component in the 13CO data. We find that the IRDC Cloud F is only a small part of a much larger structure, which appears to be an inter-arm filament of the Milky Way.

The ultraviolet interstellar extinction curve in the Pleiades

NASA Technical Reports Server (NTRS)

Witt, A. N.; Bohlin, R. C.; Stecher, T. P.

1981-01-01

The wavelength dependence of ultraviolet extinction in the Pleiades dust clouds has been determined from IUE observations of HD 23512, the brightest heavily reddened member of the Pleiades cluster. There is evidence for an anomalously weak absorption bump at 2200 A, followed by an extinction rise in the far ultraviolet with an essentially normal slope. A relatively weak absorption band at 2200 A and a weak diffuse absorption band at 4430 A seem to be common characteristics of dust present in dense clouds. Evidence is presented which suggests that the extinction characteristics found for HD 23512 are typical for a class of extinction curves observed in several cases in the Galaxy and in the LMC.

Isotope Fractionation in the Interstellar Medium

NASA Technical Reports Server (NTRS)

Charnley, Steven

2011-01-01

Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets. It is thought, in some cases, to trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. We will present the results of models of the nitrogen, oxygen, and carbon fractionation chemistry in dense molecular clouds, particularly in cores where substantial freeze-out of molecules on to dust has occurred. The range of fractionation ratios expected in different interstellar molecules will be discussed and compared to the ratios measured in molecular clouds, comets and meteoritic material. These models make several predictions that can be tested in the near future by molecular line observations, particularly with ALMA.

Automatic Generation of Building Models with Levels of Detail 1-3

NASA Astrophysics Data System (ADS)

Nguatem, W.; Drauschke, M.; Mayer, H.

2016-06-01

We present a workflow for the automatic generation of building models with levels of detail (LOD) 1 to 3 according to the CityGML standard (Gröger et al., 2012). We start with orienting unsorted image sets employing (Mayer et al., 2012), we compute depth maps using semi-global matching (SGM) (Hirschmüller, 2008), and fuse these depth maps to reconstruct dense 3D point clouds (Kuhn et al., 2014). Based on planes segmented from these point clouds, we have developed a stochastic method for roof model selection (Nguatem et al., 2013) and window model selection (Nguatem et al., 2014). We demonstrate our workflow up to the export into CityGML.

The Formation of N- and O-Heterocycles from the Irradiation of Benzene and Naphthalene in H2O/NH3- Containing Ices

NASA Technical Reports Server (NTRS)

Sandford, S. A.; Materese, C. K.; Nuevo, M.

2015-01-01

Aromatic hydrocarbons are an important class of molecules for both astrochemistry and astrobiology (Fig. 1). Within this class of molecules, polycyclic aromatic hydrocarbons (PAHs) are known to be ubiquitous in many astrophysical environments, and are likely present in interstellar clouds and protostellar disks. In dense clouds, PAHs are expected to condense onto grains as part of mixed molecular ice mantles dominated by small molecules like H2O,CH3OH, NH3, CO, and CO2. These ices are exposed to ionizing radiation in the form of cosmic rays and ambient high-energy X-ray and UV photons.

The nature, origin and evolution of embedded star clusters

NASA Technical Reports Server (NTRS)

Lada, Charles J.; Lada, Elizabeth A.

1991-01-01

The recent development of imaging infrared array cameras has enabled the first systematic studies of embedded protoclusters in the galaxy. Initial investigations suggest that rich embedded clusters are quite numerous and that a significant fraction of all stars formed in the galaxy may begin their lives in such stellar systems. These clusters contain extremely young stellar objects and are important laboratories for star formation research. However, observational and theoretical considerations suggest that most embedded clusters do not survive emergence from molecular clouds as bound clusters. Understanding the origin, nature, and evolution of embedded clusters requires understanding the intimate physical relation between embedded clusters and the dense molecular cloud cores from which they form.

A Hyper-Dense GNSS Receiver Network for Monitoring Time and Spatial Variations of Precipitable Water Vapor (PWV)

NASA Astrophysics Data System (ADS)

Tsuda, T.; Ito, N.; Takeda, Y.; Realini, E.; Shinbori, A.

2016-12-01

We employ the GNSS meteorology technique to measure precipitable water vapor (PWV) from the propagation delay of GNSS signal in the atmosphere. We installed a hyper-dense GNSS network using 15 receivers with a horizontal spacing of 1-2 km in Uji, Japan (Uji network). We also obtained precipitation with a rain gauge at a nearby operational weather station and rain cloud distribution by an X-band radar. We selected 40 days from April 2011 to March 2013, when considerable precipitation was detected. Difference in PWV within 10 km was 3-10 mm during a heavy rain. We found PWV increased 10-20 minutes before a passage of a rain cloud. The maximum value of PWV correlated well with the amount of precipitation on the ground. The variance of PWV between the GNSS sites was enhanced during a heavy rain. For a future practical hyper-dense GNSS network system with many receivers, we consider to use inexpensive single frequency (SF) receivers. Because SF receiver cannot eliminate the ionospheric delay by itself, we interpolate the delay referring the delay measured by the nearby dual frequency (DF) receivers. We investigated ionospheric delay by the Uji network, taking advantages of Quasi-Zenith Satellite System (QZSS) that gives signals at high elevation angles. During a travelling ionospheric disturbance (TID), a wavy structure with a horizontal scale of several tens km was recognized. The ionospheric delay was compensated by a linear and quadratic interpolation, then the resulting error of PWV compared with DF solution was about 1.50 mm in RMS. For a real-time estimation of PWV, we used real-time satellite clock information corrected by GEONET. Difference of PWV between the real-time analysis and the post processing with the final orbit was 0.7 mm in RMS. We estimated an overall error of PWV with a dense SF-receiver network on a real-time basis was 1.7 mm in RMS.

All-sky photogrammetry techniques to georeference a cloud field

NASA Astrophysics Data System (ADS)

Crispel, Pierre; Roberts, Gregory

2018-01-01

In this study, we present a novel method of identifying and geolocalizing cloud field elements from a portable all-sky camera stereo network based on the ground and oriented towards zenith. The methodology is mainly based on stereophotogrammetry which is a 3-D reconstruction technique based on triangulation from corresponding stereo pixels in rectified images. In cases where clouds are horizontally separated, identifying individual positions is performed with segmentation techniques based on hue filtering and contour detection algorithms. Macroscopic cloud field characteristics such as cloud layer base heights and velocity fields are also deduced. In addition, the methodology is fitted to the context of measurement campaigns which impose simplicity of implementation, auto-calibration, and portability. Camera internal geometry models are achieved a priori in the laboratory and validated to ensure a certain accuracy in the peripheral parts of the all-sky image. Then, stereophotogrammetry with dense 3-D reconstruction is applied with cameras spaced 150 m apart for two validation cases. The first validation case is carried out with cumulus clouds having a cloud base height at 1500 m a.g.l. The second validation case is carried out with two cloud layers: a cumulus fractus layer with a base height at 1000 m a.g.l. and an altocumulus stratiformis layer with a base height of 2300 m a.g.l. Velocity fields at cloud base are computed by tracking image rectangular patterns through successive shots. The height uncertainty is estimated by comparison with a Vaisala CL31 ceilometer located on the site. The uncertainty on the horizontal coordinates and on the velocity field are theoretically quantified by using the experimental uncertainties of the cloud base height and camera orientation. In the first cumulus case, segmentation of the image is performed to identify individuals clouds in the cloud field and determine the horizontal positions of the cloud centers.

Hubble space telescope imaging of decoupled dust clouds in the ram pressure stripped Virgo spirals NGC 4402 and NGC 4522

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abramson, Anne; Kenney, Jeffrey D. P., E-mail: anne.abramson@yale.edu, E-mail: jeff.kenney@yale.edu

We present the highest-resolution study to date of the interstellar medium (ISM) in galaxies undergoing ram pressure stripping, using Hubble Space Telescope BVI imaging of NGC 4522 and NGC 4402, Virgo Cluster spirals that are well known to be experiencing intracluster medium (ICM) ram pressure. We find that throughout most of both galaxies, the main dust lane has a fairly well-defined edge, with a population of giant molecular cloud (GMC) sized (tens- to hundreds-of-pc scale), isolated, highly extincting dust clouds located up to ∼1.5 kpc radially beyond it. Outside of these dense clouds, the area has little or no diffusemore » dust extinction, indicating that the clouds have decoupled from the lower-density ISM material that has already been stripped. Several of the dust clouds have elongated morphologies that indicate active ram pressure, including two large (kpc scale) filaments in NGC 4402 that are elongated in the projected ICM wind direction. We calculate a lower limit on the H I + H{sub 2} masses of these clouds based on their dust extinctions and find that a correction factor of ∼10 gives cloud masses consistent with those measured in CO for clouds of similar diameters, probably due to the complicating factors of foreground light, cloud substructure, and resolution limitations. Assuming that the clouds' actual masses are consistent with those of GMCs of similar diameters (∼10{sup 4}-10{sup 5} M {sub ☉}), we estimate that only a small fraction (∼1%-10%) of the original H I + H{sub 2} remains in the parts of the disks with decoupled clouds. Based on Hα images, a similar fraction of star formation persists in these regions, 2%-3% of the estimated pre-stripping star formation rate. We find that the decoupled cloud lifetimes may be up to 150-200 Myr.« less

Streaming motions and kinematic distances to molecular clouds

NASA Astrophysics Data System (ADS)

Ramón-Fox, F. G.; Bonnell, Ian A.

2018-02-01

We present high-resolution smoothed particle hydrodynamics simulations of a region of gas flowing in a spiral arm and identify dense gas clouds to investigate their kinematics with respect to a Milky Way model. We find that, on average, the gas in the arms can have a net radial streaming motion of vR ≈ -9 km s-1 and rotate ≈ 6 km s-1 slower than the circular velocity. This translates to average peculiar motions towards the Galaxy centre and opposite to Galactic rotation. These results may be sensitive to the assumed spiral arm perturbation, which is ≈ 3 per cent of the disc potential in our model. We compare the actual distance and the kinematic estimate and we find that streaming motions introduce systematic offsets of ≈1 kpc. We find that the distance error can be as large as ±2 kpc, and the recovered cloud positions have distributions that can extend significantly into the inter-arm regions. We conclude that this poses a difficulty in tracing spiral arm structure in molecular cloud surveys.

Road traffic sign detection and classification from mobile LiDAR point clouds

NASA Astrophysics Data System (ADS)

Weng, Shengxia; Li, Jonathan; Chen, Yiping; Wang, Cheng

2016-03-01

Traffic signs are important roadway assets that provide valuable information of the road for drivers to make safer and easier driving behaviors. Due to the development of mobile mapping systems that can efficiently acquire dense point clouds along the road, automated detection and recognition of road assets has been an important research issue. This paper deals with the detection and classification of traffic signs in outdoor environments using mobile light detection and ranging (Li- DAR) and inertial navigation technologies. The proposed method contains two main steps. It starts with an initial detection of traffic signs based on the intensity attributes of point clouds, as the traffic signs are always painted with highly reflective materials. Then, the classification of traffic signs is achieved based on the geometric shape and the pairwise 3D shape context. Some results and performance analyses are provided to show the effectiveness and limits of the proposed method. The experimental results demonstrate the feasibility and effectiveness of the proposed method in detecting and classifying traffic signs from mobile LiDAR point clouds.

Large-Scale Point-Cloud Visualization through Localized Textured Surface Reconstruction.

PubMed

Arikan, Murat; Preiner, Reinhold; Scheiblauer, Claus; Jeschke, Stefan; Wimmer, Michael

2014-09-01

In this paper, we introduce a novel scene representation for the visualization of large-scale point clouds accompanied by a set of high-resolution photographs. Many real-world applications deal with very densely sampled point-cloud data, which are augmented with photographs that often reveal lighting variations and inaccuracies in registration. Consequently, the high-quality representation of the captured data, i.e., both point clouds and photographs together, is a challenging and time-consuming task. We propose a two-phase approach, in which the first (preprocessing) phase generates multiple overlapping surface patches and handles the problem of seamless texture generation locally for each patch. The second phase stitches these patches at render-time to produce a high-quality visualization of the data. As a result of the proposed localization of the global texturing problem, our algorithm is more than an order of magnitude faster than equivalent mesh-based texturing techniques. Furthermore, since our preprocessing phase requires only a minor fraction of the whole data set at once, we provide maximum flexibility when dealing with growing data sets.

A Herschel [C ii] Galactic plane survey. I. The global distribution of ISM gas components

NASA Astrophysics Data System (ADS)

Pineda, J. L.; Langer, W. D.; Velusamy, T.; Goldsmith, P. F.

2013-06-01

Context. The [C ii] 158 μm line is an important tool for understanding the life cycle of interstellar matter. Ionized carbon is present in a variety of phases of the interstellar medium (ISM), including the diffuse ionized medium, warm and cold atomic clouds, clouds in transition from atomic to molecular, and dense and warm photon dominated regions. Aims: Velocity-resolved observations of [C ii] are the most powerful technique available to disentangle the emission produced by these components. These observations can also be used to trace CO-dark H2 gas and determine the total mass of the ISM. Methods: The Galactic Observations of Terahertz C+ (GOT C+) project surveys the [C ii] 158 μm line over the entire Galactic disk with velocity-resolved observations using the Herschel/HIFI instrument. We present the first longitude-velocity maps of the [C ii] emission for Galactic latitudes b = 0°, ±0.5°, and ±1.0°. We combine these maps with those of H i, 12CO, and 13CO to separate the different phases of the ISM and study their properties and distribution in the Galactic plane. Results: [C ii] emission is mostly associated with spiral arms, mainly emerging from Galactocentric distances between 4 and 10 kpc. It traces the envelopes of evolved clouds as well as clouds that are in the transition between atomic and molecular. We estimate that most of the observed [C ii] emission is produced by dense photon dominated regions (~47%), with smaller contributions from CO-dark H2 gas (~28%), cold atomic gas (~21%), and ionized gas (~4%). Atomic gas inside the Solar radius is mostly in the form of cold neutral medium (CNM), while the warm neutral medium gas dominates the outer galaxy. The average fraction of CNM relative to total atomic gas is ~43%. We find that the warm and diffuse CO-dark H2 is distributed over a larger range of Galactocentric distances (4-11 kpc) than the cold and dense H2 gas traced by 12CO and 13CO (4-8 kpc). The fraction of CO-dark H2 to total H2 increases with Galactocentric distance, ranging from ~20% at 4 kpc to ~80% at 10 kpc. On average, CO-dark H2 accounts for ~30% of the molecular mass of the Milky Way. When the CO-dark H2 component is included, the radial distribution of the CO-to-H2 conversion factor is steeper than that when only molecular gas traced by CO is considered. Most of the observed [C ii] emission emerging from dense photon dominated regions is associated with modest far-ultraviolet fields in the range χ0 ≃ 1 - 30. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org

Large-eddy simulation of dense gas dispersion over a simplified urban area

NASA Astrophysics Data System (ADS)

Wingstedt, E. M. M.; Osnes, A. N.; Åkervik, E.; Eriksson, D.; Reif, B. A. Pettersson

2017-03-01

Dispersion of neutral and dense gas over a simplified urban area, comprising four cubes, has been investigated by the means of large-eddy simulations (LES). The results have been compared to wind tunnel experiments and both mean and fluctuating quantities of velocity and concentration are in very good agreement. High-quality inflow profiles are necessary to achieve physically realistic LES results. In this study, profiles matching the atmospheric boundary layer flow in the wind tunnel, are generated by means of a separate precursor simulation. Emission of dense gas dramatically alters the flow in the near source region and introduces an upstream dispersion. The resulting dispersion patterns of neutral and dense gas differ significantly, where the plume in the latter case is wider and shallower. The dense gas is highly affected by the cube array, which seems to act as a barrier, effectively deflecting the plume. This leads to higher concentrations outside of the array than inside. On the contrary, the neutral gas plume has a Gaussian-type shape, with highest concentrations along the centreline. It is found that the dense gas reduces the vertical and spanwise turbulent momentum transport and, as a consequence, the turbulence kinetic energy. The reduction coincides with the area where the gradient Richardson number exceeds its critical value, i.e. where the flow may be characterized as stably stratified. Interestingly, this region does not correspond to where the concentration of dense gas is the highest (close to the ground), as this is also where the largest velocity gradients are to be found. Instead there is a layer in the middle of the dense gas cloud where buoyancy is dynamically dominant.

OXYGEN-RICH SUPERNOVA REMNANT IN THE LARGE MAGELLANIC CLOUD

NASA Technical Reports Server (NTRS)

2002-01-01

This is a NASA Hubble Space Telescope image of the tattered debris of a star that exploded 3,000 years ago as a supernova. This supernova remnant, called N132D, lies 169,000 light-years away in the satellite galaxy, the Large Magellanic Cloud. A Hubble Wide Field Planetary Camera 2 image of the inner regions of the supernova remnant shows the complex collisions that take place as fast moving ejecta slam into cool, dense interstellar clouds. This level of detail in the expanding filaments could only be seen previously in much closer supernova remnants. Now, Hubble's capabilities extend the detailed study of supernovae out to the distance of a neighboring galaxy. Material thrown out from the interior of the exploded star at velocities of more than four million miles per hour (2,000 kilometers per second) plows into neighboring clouds to create luminescent shock fronts. The blue-green filaments in the image correspond to oxygen-rich gas ejected from the core of the star. The oxygen-rich filaments glow as they pass through a network of shock fronts reflected off dense interstellar clouds that surrounded the exploded star. These dense clouds, which appear as reddish filaments, also glow as the shock wave from the supernova crushes and heats the clouds. Supernova remnants provide a rare opportunity to observe directly the interiors of stars far more massive than our Sun. The precursor star to this remnant, which was located slightly below and left of center in the image, is estimated to have been 25 times the mass of our Sun. These stars 'cook' heavier elements through nuclear fusion, including oxygen, nitrogen, carbon, iron etc., and the titanic supernova explosions scatter this material back into space where it is used to create new generations of stars. This is the mechanism by which the gas and dust that formed our solar system became enriched with the elements that sustain life on this planet. Hubble spectroscopic observations will be used to determine the exact chemical composition of this nuclear- processed material, and thereby test theories of stellar evolution. The image shows a region of the remnant 50 light-years across. The supernova explosion should have been visible from Earth's southern hemisphere around 1,000 B.C., but there are no known historical records that chronicle what would have appeared as a 'new star' in the heavens. This 'true color' picture was made by superposing images taken on 9-10 August 1994 in three of the strongest optical emission lines: singly ionized sulfur (red), doubly ionized oxygen (green), and singly ionized oxygen (blue). Photo credit: Jon A. Morse (STScI) and NASA Investigating team: William P. Blair (PI; JHU), Michael A. Dopita (MSSSO), Robert P. Kirshner (Harvard), Knox S. Long (STScI), Jon A. Morse (STScI), John C. Raymond (SAO), Ralph S. Sutherland (UC-Boulder), and P. Frank Winkler (Middlebury). Image files in GIF and JPEG format may be accessed via anonymous ftp from oposite.stsci.edu in /pubinfo: GIF: /pubinfo/GIF/N132D.GIF JPEG: /pubinfo/JPEG/N132D.jpg The same images are available via World Wide Web from links in URL http://www.stsci.edu/public.html.

Coagulation of grains in static and collapsing protostellar clouds

NASA Technical Reports Server (NTRS)

Weidenschilling, S. J.; Ruzmaikina, T. V.

1994-01-01

We simulate collisional evolution of grains in dense turbulent molecular cloud cores (or Bok globules) in static equilibrium and free-fall collapse, assuming spherical symmetry. Relative velocities are due to thermal motions, differential settling, and turbulence, with the latter dominant for sonic turbulence with an assumed Kolmogorov spectrum. Realistic criteria are used to determine outcomes of collisions (coagulation vs. destruction) as functions of particle size and velocity. Results are presented for a variety of cloud parameters (radial density profile, turbulent velocity) and particle properties (density, impact strength). Results are sensitive to the assumed mechanical properties (density and impact strength) of grain aggregates. Particle growth is enhanced if aggregates have low density or fractal structures. On a timescale of a few Myr, an initial population of 0.1 micrometers grains may produce dense compact particles approximately 1 micrometer in size, or fluffy aggregates approximately 100 micrometers. For impact strengths less than or equal to 10(exp 6) ergs/g, a steady state is reached between coagulation of small grains and collisional disruption of larger aggregates. Formation of macroscopic aggregates requires high mechanical strengths and low aggregate densities. We assume sonic turbulence during collapse, with varied eddy size scales determining the dissipation rate or turbulence strength. The degree of collisional evolution during collapse is sensitive to the assumed small-scale structure (inner sc ale) of the turbulence. Weak turbulence results in few collisions and preserves the precollapse particle size distribution with little change. Strong turbulence tends to produce net destruction, rather than particle growth, during infall, unless inpact strengths are greater than 10(exp 6)ergs/g.

Integrated Imaging Approaches Supporting the Excavation Activities. Multi-Scale Geospatial Documentation in Hierapolis (tk)

NASA Astrophysics Data System (ADS)

Spanò, A.; Chiabrando, F.; Sammartano, G.; Teppati Losè, L.

2018-05-01

The paper focuses on the exploration of the suitability and the discretization of applicability issues about advanced surveying integrated techniques, mainly based on image-based approaches compared and integrated to range-based ones that have been developed with the use of the cutting-edge solutions tested on field. The investigated techniques integrate both technological devices for 3D data acquisition and thus editing and management systems to handle metric models and multi-dimensional data in a geospatial perspective, in order to innovate and speed up the extraction of information during the archaeological excavation activities. These factors, have been experienced in the outstanding site of the Hierapolis of Phrygia ancient city (Turkey), downstream the 2017 surveying missions, in order to produce high-scale metric deliverables in terms of high-detailed Digital Surface Models (DSM), 3D continuous surface models and high-resolution orthoimages products. In particular, the potentialities in the use of UAV platforms for low altitude acquisitions in aerial photogrammetric approach, together with terrestrial panoramic acquisitions (Trimble V10 imaging rover), have been investigated with a comparison toward consolidated Terrestrial Laser Scanning (TLS) measurements. One of the main purposes of the paper is to evaluate the results offered by the technologies used independently and using integrated approaches. A section of the study in fact, is specifically dedicated to experimenting the union of different sensor dense clouds: both dense clouds derived from UAV have been integrated with terrestrial Lidar clouds, to evaluate their fusion. Different test cases have been considered, representing typical situations that can be encountered in archaeological sites.

An AZTEC/ASTE 1.1mm Survey Of The Young, Dense, Nearby Star-forming Region, Serpens South

NASA Astrophysics Data System (ADS)

Gutermuth, Robert A.; Bourke, T.; Matthews, B.; Dunham, M.; Allen, L.; Myers, P.; Jorgensen, J.; Wilson, G.; Yun, M.; Hughes, D.; Aretxaga, I.; Ryohei, K.; Kotaro, K.; Scott, K.; Austermann, J.

2010-01-01

The Serpens South embedded cluster, recently discovered by the Spitzer Gould Belt Legacy Survey, stands out among over 100 clusters and groups surveyed by Spitzer as the densest (>430 pc-2) and youngest (77% Class I protostars) clustered star forming region known within the nearest 400 pc. In order to better characterize the primordial structure of the cluster's natal cloud, we have made a 1.1mm dust continuum map of Serpens South from the AzTEC instrument on the 10m Atacama Submillimeter Telescope Experiment (ASTE). The projected morphology of the emission is best described by a central dense hub with numerous 0.5 pc-long filaments radiating away from the center. Large scale flux features that are typically removed via modern sky subtraction techniques are recovered using a novel iterative flux retrieval algorithm. Using standard assumptions (emissivity, dust-to-gas ratio, and T=10K), we compute the total mass of the Serpens South cloud core and filaments to be 480 Msun. We construct separate large and small scale structure maps via wavelet decomposition, and deploy a watershed structure isolation technique separately to each map in order to isolate all empirically observed substructure. This technique confirms our qualitative observation that the filaments north of the hub are notably less clumpy than those to the south, while the total mass is similar between the two regions. Both regions have relatively small numbers of young stellar objects, thus we speculate that we have caught this cloud in the act of fragmenting into pre-stellar cores.

RELATIVE PROPER MOTIONS IN THE RHO OPHIUCHI CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilking, Bruce A.; Sullivan, Timothy; Vrba, Frederick J., E-mail: bwilking@umsl.edu, E-mail: tsullivan@umsl.edu, E-mail: fjv@nofs.navy.mil

2015-12-10

Near-infrared images optimized for astrometry have been obtained for four fields in the high-density L 1688 cloud core over a 12 year period. The targeted regions include deeply embedded young stellar objects (YSOs) and very low luminosity objects too faint and/or heavily veiled for spectroscopy. Relative proper motions in R.A. and decl. were computed for 111 sources and again for a subset of 65 YSOs, resulting in a mean proper motion of (0,0) for each field. Assuming each field has the same mean proper motion, YSOs in the four fields were combined to yield estimates of the velocity dispersions inmore » R.A. and decl. that are consistent with 1.0 km s{sup −1}. These values appear to be independent of the evolutionary state of the YSOs. The observed velocity dispersions are consistent with the dispersion in radial velocity derived for optically visible YSOs at the periphery of the cloud core and are consistent with virial equilibrium. The higher velocity dispersion of the YSOs in the plane of the sky relative to that of dense cores may be a consequence of stellar encounters due to dense cores and filaments fragmenting to form small groups of stars or the global collapse of the L 1688 cloud core. An analysis of the differential magnitudes of objects over the 12 year baseline has not only confirmed the near-infrared variability for 29 YSOs established by prior studies, but has also identified 18 new variability candidates. Four of these have not been previously identified as YSOs and may be newly identified cluster members.« less

Multiphase environment of compact galactic nuclei: the role of the nuclear star cluster

NASA Astrophysics Data System (ADS)

Różańska, A.; Kunneriath, D.; Czerny, B.; Adhikari, T. P.; Karas, V.

2017-01-01

We study the conditions for the onset of thermal instability in the innermost regions of compact galactic nuclei, where the properties of the interstellar environment are governed by the interplay of quasi-spherical accretion on to a supermassive black hole (SMBH) and the heating/cooling processes of gas in a dense nuclear star cluster (NSC). Stellar winds are the source of material for radiatively inefficient (quasi-spherical, non-magnetized) inflow/outflow on to the central SMBH, where a stagnation point develops within the Bondi-type accretion. We study the local thermal equilibrium to determine the parameter space that allows cold and hot phases in mutual contact to co-exist. We include the effects of mechanical heating by stellar winds and radiative cooling/heating by the ambient field of the dense star cluster. We consider two examples: the NSC in the Milky Way central region (including the gaseous mini-spiral of Sgr A*), and the ultracompact dwarf galaxy M60-UCD1. We find that the two systems behave in different ways because they are placed in different areas of parameter space in the instability diagram: gas temperature versus dynamical ionization parameter. In the case of Sgr A*, stellar heating prevents the spontaneous formation of cold clouds. The plasma from stellar winds joins the hot X-ray emitting phase and forms an outflow. In M60-UCD1, our model predicts spontaneous formation of cold clouds in the inner part of the galaxy. These cold clouds may survive since the cooling time-scale is shorter than the inflow/outflow time-scale.

ON THE INTERACTION OF ADENINE WITH IONIZING RADIATION: MECHANISTICAL STUDIES AND ASTROBIOLOGICAL IMPLICATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Evans, Nicholas L.; Ullrich, Susanne; Bennett, Chris J.

2011-04-01

The molecular inventory available on the prebiotic Earth was likely derived from both terrestrial and extraterrestrial sources. A complete description of which extraterrestrial molecules may have seeded early Earth is therefore necessary to fully understand the prebiotic evolution which led to life. Galactic cosmic rays (GCRs) are expected to cause both the formation and destruction of important biomolecules-including nucleic acid bases such as adenine-in the interstellar medium within the ices condensed on interstellar grains. The interstellar ultraviolet (UV) component is expected to photochemically degrade gas-phase adenine on a short timescale of only several years. However, the destruction rate is expectedmore » to be significantly reduced when adenine is shielded in dense molecular clouds or even within the ices of interstellar grains. Here, biomolecule destruction by the energetic charged particle component of the GCR becomes important as it is not fully attenuated. Presented here are results on the destruction rate of the nucleobase adenine in the solid state at 10 K by energetic electrons, as generated in the track of cosmic ray particles as they penetrate ices. When both UV and energetic charged particle destructive processes are taken into account, the half-life of adenine within dense interstellar clouds is found to be {approx}6 Myr, which is on the order of a star-forming molecular cloud. We also discuss chemical reaction pathways within the ices to explain the production of observed species, including the formation of nitriles (R-C{identical_to}N), epoxides (C-O-C), and carbonyl functions (R-C=O).« less

Aerosol-radiation-cloud interactions in the South-East Atlantic: first results from the ORACLES-2016 deployment and plans for future activities

NASA Astrophysics Data System (ADS)

Redemann, J.; Wood, R.; Zuidema, P.; Haywood, J. M.; Piketh, S.; Formenti, P.; Abel, S.

2016-12-01

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical stratocumulus (Sc) cloud decks in the world. The SE Atlantic stratocumulus deck interacts with the dense layers of BB aerosols that initially overlay the cloud deck, but later subside and may mix into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects, and their global representation in climate models remains one of the largest uncertainties in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for regional and global climate change predictions. Our understanding of aerosol-cloud interactions in the SE Atlantic is severely limited. Most notably, we are missing knowledge on the absorptive and cloud nucleating properties of aerosols, including their vertical distribution relative to clouds, on the locations and degree of aerosol mixing into clouds, on the processes that govern cloud property adjustments, and on the importance of aerosol effects on clouds relative to co-varying synoptic scale meteorology. We describe first results from various synergistic, international research activities aimed at studying aerosol-cloud interactions in the region: NASA's airborne ORACLES (ObseRvations of Aerosols Above Clouds and Their IntEractionS) deployment in August/September of 2016, the DoE's LASIC (Layered Atlantic Smoke Interactions with Clouds) deployment of the ARM Mobile Facility to Ascension Island (June 2016 - October 2017), the ground-based components of CNRS' AEROCLO-sA (Aerosols Clouds and Fog over the west coast of southern Africa), and ongoing regional-scale integrative, process-oriented science efforts as part of SEALS-sA (Sea Earth Atmosphere Linkages Study in southern Africa). We expect to describe experimental setups as well as showcase initial aerosol and cloud property distributions. Furthermore, we discuss the implementation of future activities in these programs in coordination with the UK Met Office's CLARIFY (CLoud-Aerosol-Radiation Interactions and Forcing) experiment in 2017.

Observations of Aerosol-Radiation-Cloud Interactions in the South-East Atlantic: First Results from the ORACLES Deployments in 2016 and 2017

NASA Technical Reports Server (NTRS)

Redemann, Jens; Wood, R.; Zuidema, P.; Diner, D.; Van Harten, G.; Xu, F.; Cairns, B.; Knobelspiesse, K.; Segal Rozenhaimer, M.

2017-01-01

Southern Africa produces almost a third of the Earths biomass burning (BB) aerosol particles. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical stratocumulus (Sc) cloud decks in the world. The SE Atlantic stratocumulus deck interacts with the dense layers of BB aerosols that initially overlay the cloud deck, but later subside and often mix into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects, and their global representation in climate models remains one of the largest uncertainties in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for regional and global climate change predictions.The low-level clouds in the SE Atlantic have limited vertical extent and therefore present favorable conditions for their exploration with remote sensing. On the other hand, the normal coexistence of BB aerosols and Sc clouds in the same scene also presents significant challenges to conventional remote sensing techniques. We describe first results from NASAs airborne ORACLES (ObseRvations of Aerosols Above Clouds and Their IntEractionS) deployments in September 2016 and August 2017. We emphasize the unique role of polarimetric observations by two instruments, the Research Scanning Polarimeter (RSP) and the Airborne Multi-angle SpectroPolarimeter Imager (AirMSPI), and describe how these instruments help address specific ORACLES science objectives. Initial assessments of polarimetric observation accuracy for key cloud and aerosol properties will be presented, in as far as the preliminary nature of measurements permits.

H II Region G46.5-0.2: The Interplay between Ionizing Radiation, Molecular Gas, and Star Formation

NASA Astrophysics Data System (ADS)

Paron, S.; Ortega, M. E.; Dubner, G.; Yuan, Jing-Hua; Petriella, A.; Giacani, E.; Zeng Li, Jin; Wu, Yuefang; Liu, Hongli; Huang, Ya Fang; Zhang, Si-Ju

2015-06-01

H ii regions are particularly interesting because they can generate dense layers of gas and dust, elongated columns or pillars of gas pointing toward the ionizing sources, and cometary globules of dense gas where triggered star formation can occur. Understanding the interplay between the ionizing radiation and the dense surrounding gas is very important to explain the origin of these peculiar structures, and hence to characterize triggered star formation. G46.5-0.2 (G46), a poorly studied galactic H ii region located at about 4 kpc, is an excellent target for performing this kind of study. Using public molecular data extracted from the Galactic Ring Survey (13CO J = 1-0) and from the James Clerk Maxwell Telescope data archive (12CO, 13CO, C18O J = 3-2, HCO+, and HCN J = 4-3), and infrared data from the GLIMPSE and MIPSGAL surveys, we perform a complete study of G46, its molecular environment, and the young stellar objects (YSOs) placed around it. We found that G46, probably excited by an O7V star, is located close to the edge of the GRSMC G046.34-00.21 molecular cloud. It presents a horse-shoe morphology opening in the direction of the cloud. We observed a filamentary structure in the molecular gas likely related to G46 and not considerable molecular emission toward its open border. We found that about 10‧ to the southwest of G46 there are some pillar-like features, shining at 8 μm and pointing toward the H ii region open border. We propose that the pillar-like features were carved and sculpted by the ionizing flux from G46. We found several YSOs likely embedded in the molecular cloud grouped in two main concentrations: one, closer to the G46 open border consisting of Class II type sources, and another mostly composed of Class I type YSOs located just ahead of the pillar-like features, strongly suggesting an age gradient in the YSO distribution.

H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paron, S.; Ortega, M. E.; Dubner, G.

2015-06-15

H ii regions are particularly interesting because they can generate dense layers of gas and dust, elongated columns or pillars of gas pointing toward the ionizing sources, and cometary globules of dense gas where triggered star formation can occur. Understanding the interplay between the ionizing radiation and the dense surrounding gas is very important to explain the origin of these peculiar structures, and hence to characterize triggered star formation. G46.5-0.2 (G46), a poorly studied galactic H ii region located at about 4 kpc, is an excellent target for performing this kind of study. Using public molecular data extracted from themore » Galactic Ring Survey ({sup 13}CO J = 1–0) and from the James Clerk Maxwell Telescope data archive ({sup 12}CO, {sup 13}CO, C{sup 18}O J = 3–2, HCO{sup +}, and HCN J = 4–3), and infrared data from the GLIMPSE and MIPSGAL surveys, we perform a complete study of G46, its molecular environment, and the young stellar objects (YSOs) placed around it. We found that G46, probably excited by an O7V star, is located close to the edge of the GRSMC G046.34-00.21 molecular cloud. It presents a horse-shoe morphology opening in the direction of the cloud. We observed a filamentary structure in the molecular gas likely related to G46 and not considerable molecular emission toward its open border. We found that about 10′ to the southwest of G46 there are some pillar-like features, shining at 8 μm and pointing toward the H ii region open border. We propose that the pillar-like features were carved and sculpted by the ionizing flux from G46. We found several YSOs likely embedded in the molecular cloud grouped in two main concentrations: one, closer to the G46 open border consisting of Class II type sources, and another mostly composed of Class I type YSOs located just ahead of the pillar-like features, strongly suggesting an age gradient in the YSO distribution.« less

An Efficient Method to Create Digital Terrain Models from Point Clouds Collected by Mobile LiDAR Systems

NASA Astrophysics Data System (ADS)

Gézero, L.; Antunes, C.

2017-05-01

The digital terrain models (DTM) assume an essential role in all types of road maintenance, water supply and sanitation projects. The demand of such information is more significant in developing countries, where the lack of infrastructures is higher. In recent years, the use of Mobile LiDAR Systems (MLS) proved to be a very efficient technique in the acquisition of precise and dense point clouds. These point clouds can be a solution to obtain the data for the production of DTM in remote areas, due mainly to the safety, precision, speed of acquisition and the detail of the information gathered. However, the point clouds filtering and algorithms to separate "terrain points" from "no terrain points", quickly and consistently, remain a challenge that has caught the interest of researchers. This work presents a method to create the DTM from point clouds collected by MLS. The method is based in two interactive steps. The first step of the process allows reducing the cloud point to a set of points that represent the terrain's shape, being the distance between points inversely proportional to the terrain variation. The second step is based on the Delaunay triangulation of the points resulting from the first step. The achieved results encourage a wider use of this technology as a solution for large scale DTM production in remote areas.

Title Requested

NASA Astrophysics Data System (ADS)

Ruzmaikina, T. V.

2000-12-01

Precise measurements of D/H in Halley and Hyakutake reveal larger excess of D than in Uranus and Neptune. This might imply that at least a fraction of Oort cloud comets have been accumulated in a cooler environment beyond the planetary system. This paper suggests that the scattering of planetesimals from the periphery of the protoplanetary disk by a passing star might have included them in the populating of the Oort cloud. The probability of the necessary close encounter is very small in the present Galactic environment of the solar system. However it might be relatively high if the solar system was formed in a denser environment, like the Rho Ophiuchus star-forming region or a small and dense cloud core which fragmented during the collapse to form a small group of stars. Outcomes of a passage of a star with mass 1 to 0.3 solar masses were studied numerically by Everhart method. Disk penetrating or disk grazing encounters revealed that planetesimals closest to the stellar trajectory can be ejected from the solar system or sent on highly eccentric bound orbits. Some planetesimals acquire orbits with perihelion distances larger than planet orbits, i.e., become immediate members of the Oort cloud. For others, external pertubations cause stochastic growth of perihelion distances and decoupling from the planetary system, transferring them into the Oort cloud. These Oort cloud bodies could be accumulated well beyond the planetary system, and preserve higher D/H, CO ice, etc.

Carbon monoxide in clouds at low metallicity in the dwarf irregular galaxy WLM.

PubMed

Elmegreen, Bruce G; Rubio, Monica; Hunter, Deidre A; Verdugo, Celia; Brinks, Elias; Schruba, Andreas

2013-03-28

Carbon monoxide (CO) is the primary tracer for interstellar clouds where stars form, but it has never been detected in galaxies in which the oxygen abundance relative to hydrogen is less than 20 per cent of that of the Sun, even though such 'low-metallicity' galaxies often form stars. This raises the question of whether stars can form in dense gas without molecules, cooling to the required near-zero temperatures by atomic transitions and dust radiation rather than by molecular line emission; and it highlights uncertainties about star formation in the early Universe, when the metallicity was generally low. Here we report the detection of CO in two regions of a local dwarf irregular galaxy, WLM, where the metallicity is 13 per cent of the solar value. We use new submillimetre observations and archival far-infrared observations to estimate the cloud masses, which are both slightly greater than 100,000 solar masses. The clouds have produced stars at a rate per molecule equal to 10 per cent of that in the local Orion nebula cloud. The CO fraction of the molecular gas is also low, about 3 per cent of the Milky Way value. These results suggest that in small galaxies both star-forming cores and CO molecules become increasingly rare in molecular hydrogen clouds as the metallicity decreases.

Formation of massive, dense cores by cloud-cloud collisions

NASA Astrophysics Data System (ADS)

Takahira, Ken; Shima, Kazuhiro; Habe, Asao; Tasker, Elizabeth J.

2018-03-01

We performed sub-parsec (˜ 0.014 pc) scale simulations of cloud-cloud collisions of two idealized turbulent molecular clouds (MCs) with different masses in the range of (0.76-2.67) × 104 M_{⊙} and with collision speeds of 5-30 km s-1. Those parameters are larger than in Takahira, Tasker, and Habe (2014, ApJ, 792, 63), in which study the colliding system showed a partial gaseous arc morphology that supports the NANTEN observations of objects indicated to be colliding MCs using numerical simulations. Gas clumps with density greater than 10-20 g cm-3 were identified as pre-stellar cores and tracked through the simulation to investigate the effects of the mass of colliding clouds and the collision speeds on the resulting core population. Our results demonstrate that the smaller cloud property is more important for the results of cloud-cloud collisions. The mass function of formed cores can be approximated by a power-law relation with an index γ = -1.6 in slower cloud-cloud collisions (v ˜ 5 km s-1), and is in good agreement with observation of MCs. A faster relative speed increases the number of cores formed in the early stage of collisions and shortens the gas accretion phase of cores in the shocked region, leading to the suppression of core growth. The bending point appears in the high-mass part of the core mass function and the bending point mass decreases with increase in collision speed for the same combination of colliding clouds. The higher-mass part of the core mass function than the bending point mass can be approximated by a power law with γ = -2-3 that is similar to the power index of the massive part of the observed stellar initial mass function. We discuss implications of our results for the massive-star formation in our Galaxy.

Formation of massive, dense cores by cloud-cloud collisions

NASA Astrophysics Data System (ADS)

Takahira, Ken; Shima, Kazuhiro; Habe, Asao; Tasker, Elizabeth J.

2018-05-01

We performed sub-parsec (˜ 0.014 pc) scale simulations of cloud-cloud collisions of two idealized turbulent molecular clouds (MCs) with different masses in the range of (0.76-2.67) × 104 M_{⊙} and with collision speeds of 5-30 km s-1. Those parameters are larger than in Takahira, Tasker, and Habe (2014, ApJ, 792, 63), in which study the colliding system showed a partial gaseous arc morphology that supports the NANTEN observations of objects indicated to be colliding MCs using numerical simulations. Gas clumps with density greater than 10-20 g cm-3 were identified as pre-stellar cores and tracked through the simulation to investigate the effects of the mass of colliding clouds and the collision speeds on the resulting core population. Our results demonstrate that the smaller cloud property is more important for the results of cloud-cloud collisions. The mass function of formed cores can be approximated by a power-law relation with an index γ = -1.6 in slower cloud-cloud collisions (v ˜ 5 km s-1), and is in good agreement with observation of MCs. A faster relative speed increases the number of cores formed in the early stage of collisions and shortens the gas accretion phase of cores in the shocked region, leading to the suppression of core growth. The bending point appears in the high-mass part of the core mass function and the bending point mass decreases with increase in collision speed for the same combination of colliding clouds. The higher-mass part of the core mass function than the bending point mass can be approximated by a power law with γ = -2-3 that is similar to the power index of the massive part of the observed stellar initial mass function. We discuss implications of our results for the massive-star formation in our Galaxy.

Photogrammetric 3D reconstruction using mobile imaging

NASA Astrophysics Data System (ADS)

Fritsch, Dieter; Syll, Miguel

2015-03-01

In our paper we demonstrate the development of an Android Application (AndroidSfM) for photogrammetric 3D reconstruction that works on smartphones and tablets likewise. The photos are taken with mobile devices, and can thereafter directly be calibrated using standard calibration algorithms of photogrammetry and computer vision, on that device. Due to still limited computing resources on mobile devices, a client-server handshake using Dropbox transfers the photos to the sever to run AndroidSfM for the pose estimation of all photos by Structure-from-Motion and, thereafter, uses the oriented bunch of photos for dense point cloud estimation by dense image matching algorithms. The result is transferred back to the mobile device for visualization and ad-hoc on-screen measurements.

Dust coagulation. [in interstellar medium observed in stellar envelopes and planetary disks

NASA Technical Reports Server (NTRS)

Chokshi, Arati; Tielens, A. G. G. M.; Hollenbach, D.

1993-01-01

The microphysics of coagulation between two, colliding, smooth, spherical grains in the elastic limit is investigated, and the criteria for sticking as a function of particle sizes, collision velocities, elastic properties, and binding energy are calculated. Critical relative velocities for coagulation were evaluated as a function of grain sizes for solicate, icy, and carbonaceous grains. It is concluded that efficient coagulation requires coverage of grain cores by an icy grain mantle. In this case, coagulation leads to only a doubling of the mass of a large grain within a dense core lifetime. It is concluded that coagulation can have a dramatic effect on the visible and, particularly, the UV portion of the extinction curve in dense clouds and on their IR spectrum.

Compression and ablation of the photo-irradiated molecular cloud the Orion Bar.

PubMed

Goicoechea, Javier R; Pety, Jérôme; Cuadrado, Sara; Cernicharo, José; Chapillon, Edwige; Fuente, Asunción; Gerin, Maryvonne; Joblin, Christine; Marcelino, Nuria; Pilleri, Paolo

2016-09-08

The Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Our relative closeness to the Orion nebula (about 1,350 light years away from Earth) means that we can study the effects of stellar feedback on the parental cloud in detail. Visible-light observations of the Orion Bar show that the transition between the hot ionized gas and the warm neutral atomic gas (the ionization front) is spatially well separated from the transition between atomic and molecular gas (the dissociation front), by about 15 arcseconds or 6,200 astronomical units (one astronomical unit is the Earth-Sun distance). Static equilibrium models used to interpret previous far-infrared and radio observations of the neutral gas in the Orion Bar (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure comprised of dense clumps embedded in a lower-density extended gas component. Here we report one-arcsecond-resolution millimetre-wave images that allow us to resolve the molecular cloud surface. In contrast to stationary model predictions, there is no appreciable offset between the peak of the H 2 vibrational emission (delineating the H/H 2 transition) and the edge of the observed CO and HCO + emission. This implies that the H/H 2 and C + /C/CO transition zones are very close. We find a fragmented ridge of high-density substructures, photoablative gas flows and instabilities at the molecular cloud surface. The results suggest that the cloud edge has been compressed by a high-pressure wave that is moving into the molecular cloud, demonstrating that dynamical and non-equilibrium effects are important for the cloud evolution.

Compression and ablation of the photo-irradiated molecular cloud the Orion Bar

NASA Astrophysics Data System (ADS)

Goicoechea, Javier R.; Pety, Jérôme; Cuadrado, Sara; Cernicharo, José; Chapillon, Edwige; Fuente, Asunción; Gerin, Maryvonne; Joblin, Christine; Marcelino, Nuria; Pilleri, Paolo

2016-09-01

The Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Our relative closeness to the Orion nebula (about 1,350 light years away from Earth) means that we can study the effects of stellar feedback on the parental cloud in detail. Visible-light observations of the Orion Bar show that the transition between the hot ionized gas and the warm neutral atomic gas (the ionization front) is spatially well separated from the transition between atomic and molecular gas (the dissociation front), by about 15 arcseconds or 6,200 astronomical units (one astronomical unit is the Earth-Sun distance). Static equilibrium models used to interpret previous far-infrared and radio observations of the neutral gas in the Orion Bar (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure comprised of dense clumps embedded in a lower-density extended gas component. Here we report one-arcsecond-resolution millimetre-wave images that allow us to resolve the molecular cloud surface. In contrast to stationary model predictions, there is no appreciable offset between the peak of the H2 vibrational emission (delineating the H/H2 transition) and the edge of the observed CO and HCO+ emission. This implies that the H/H2 and C+/C/CO transition zones are very close. We find a fragmented ridge of high-density substructures, photoablative gas flows and instabilities at the molecular cloud surface. The results suggest that the cloud edge has been compressed by a high-pressure wave that is moving into the molecular cloud, demonstrating that dynamical and non-equilibrium effects are important for the cloud evolution.

Satellite and ground detection of very dense smoke clouds produced on the islands of the Paraná river delta that affected a large region in Central Argentina

NASA Astrophysics Data System (ADS)

Ipiña, A.; Salum, G. M.; Crinó, E.; Piacentini, R. D.

2012-03-01

Intense fires were produced on the Paraná river delta islands, Argentina, during most part of 2008, by a combination of an exceptionally dry period and the farmers' use of a fire land-cleaning technique. In April 2008, those fires significantly affected the nearby regions and their inhabitants, from Rosario city to Buenos Aires mega-city. In this work we present satellite as well as ground Aerosol Optical Depth (AOD) at 550 nm data obtained during the propagation of pollution clouds to the central zone of Argentina. The highest value (1.18) was registered at Buenos Aires by atmospheric remote sensing, using the satellite instrument MODIS/Terra on April 18th 2008 at 10:35 local time (= UT - 3 h). On the same day, ground air quality detectors also measured in this city the highest Total Suspended Particle (TSP) value of the month, 2.02 mg/m3. The AOD(550) daily variation at Rosario Astronomical Observatory, which is located near the Paraná riverside, was derived by combining solar ultraviolet erythemal irradiance data (measured with a YES biometre) with model calculations. On April 25th 2008, from 12:00 to 15:30 local time, a rather high and constant AOD(550) value was registered, with a mean value of (0.90 ± 0.21). Cities located on the side of the Rosario-Buenos Aires highway (San Nicolás, Baradero and San Pedro) were also affected, showing a mean AOD(550) between the Rosario and Buenos Aires values. The particulate matter was collected with gridded samplers placed on the Paraná river islands as well as at the Rosario Observatory. They were analysed with a Scanning Electron Microscope (SEM) and mainly showed a biological origin. Even if normally large particles travel small distances from the source, organic aerosol in the range of 40-100 μm and complex asymmetric structures were registered several kilometres away from the aerosol sources on the islands. Another event of intense UV index attenuation (98.6%) occurred on September 18th 2008, due to very dense smoke clouds that extended over the Rosario area for several hours. The clouds were driven away from the fires by East-northeast and East-southeast winds. The minimum value of this index measured around noon allows to derive a maximum AOD(550)max = (3.65 ± 0.90) at 12:45 local time. Soot clouds extended over the Paraná river, transporting Burned Biomass Debris (BBD) that deposited on Rosario. In particular, burned leaves and small branches with dimensions of 1-20 cm were collected. The mean (BBD) particles deposited on the ground from 7:00 to 19:00 local time were (0.92 ± 0.20) BBD/(m2 h).The main purpose of the present work is to contribute to the understanding and quantification of the impact of very dense smoke clouds and BBD that directly and indirectly affected a densely populated area. All the events originated in a very particular and fragile region such as a river delta (with its specific native plants) were registered by using a multi-instrument approach (satellite as well as ground based devices).The analysis of these events, as detailed in this manuscript, was used as a scientific reference for the judicial claim made at the Supreme Court of Justice of Argentina by the National University of Rosario, against the authorities of the Entre Rios Province where the islands of the Paraná river are placed, in order to take the necessary measures for the suspension of the biomass burning in these islands.

Fermi LAT Observations of the Supernova Remnant W28 (G6.4-0.1)

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2010-06-30

Here, we present detailed analysis of two gamma-ray sources, 1FGL J1801.3–2322c and 1FGL J1800.5–2359c, that have been found toward the supernova remnant (SNR) W28 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. 1FGL J1801.3–2322c is found to be an extended source within the boundary of SNR W28, and to extensively overlap with the TeV gamma-ray source HESS J1801–233, which is associated with a dense molecular cloud interacting with the SNR. The gamma-ray spectrum measured with the LAT from 0.2 to 100 GeV can be described by a broken power-law function with a break at ~1more » GeV and photon indices of 2.09 ± 0.08 (stat) ± 0.28 (sys) below the break and 2.74 ± 0.06 (stat) ± 0.09 (sys) above the break. Given the clear association between HESS J1801–233 and the shocked molecular cloud and a smoothly connected spectrum in the GeV-TeV band, we consider the origin of the gamma-ray emission in both GeV and TeV ranges to be the interaction between particles accelerated in the SNR and the molecular cloud. The decay of neutral pions produced in interactions between accelerated hadrons and dense molecular gas provides a reasonable explanation for the broadband gamma-ray spectrum. 1FGL J1800.5–2359c, located outside the southern boundary of SNR W28, cannot be resolved. An upper limit on the size of the gamma-ray emission was estimated to be ~16' using events above ~2 GeV under the assumption of a circular shape with uniform surface brightness. It appears to coincide with the TeV source HESS J1800–240B, which is considered to be associated with a dense molecular cloud that contains the ultra compact H II region W28A2 (G5.89–0.39). In conclusion, we found no significant gamma-ray emission in the LAT energy band at the positions of TeV sources HESS J1800–230A and HESS J1800–230C. The LAT data for HESS J1800–230A combined with the TeV data points indicate a spectral break between 10 GeV and 100 GeV.« less

Point Cloud Based Relative Pose Estimation of a Satellite in Close Range

PubMed Central

Liu, Lujiang; Zhao, Gaopeng; Bo, Yuming

2016-01-01

Determination of the relative pose of satellites is essential in space rendezvous operations and on-orbit servicing missions. The key problems are the adoption of suitable sensor on board of a chaser and efficient techniques for pose estimation. This paper aims to estimate the pose of a target satellite in close range on the basis of its known model by using point cloud data generated by a flash LIDAR sensor. A novel model based pose estimation method is proposed; it includes a fast and reliable pose initial acquisition method based on global optimal searching by processing the dense point cloud data directly, and a pose tracking method based on Iterative Closest Point algorithm. Also, a simulation system is presented in this paper in order to evaluate the performance of the sensor and generate simulated sensor point cloud data. It also provides truth pose of the test target so that the pose estimation error can be quantified. To investigate the effectiveness of the proposed approach and achievable pose accuracy, numerical simulation experiments are performed; results demonstrate algorithm capability of operating with point cloud directly and large pose variations. Also, a field testing experiment is conducted and results show that the proposed method is effective. PMID:27271633

Radiative Feedback of Forming Star Clusters on Their GMC Environments: Theory and Simulation

NASA Astrophysics Data System (ADS)

Howard, C. S.; Pudritz, R. E.; Harris, W. E.

2013-07-01

Star clusters form from dense clumps within a molecular cloud. Radiation from these newly formed clusters feeds back on their natal molecular cloud through heating and ionization which ultimately stops gas accretion into the cluster. Recent studies suggest that radiative feedback effects from a single cluster may be sufficient to disrupt an entire cloud over a short timescale. Simulating cluster formation on a large scale, however, is computationally demanding due to the high number of stars involved. For this reason, we present a model for representing the radiative output of an entire cluster which involves randomly sampling an initial mass function (IMF) as the cluster accretes mass. We show that this model is able to reproduce the star formation histories of observed clusters. To examine the degree to which radiative feedback shapes the evolution of a molecular cloud, we use the FLASH adaptive-mesh refinement hydrodynamics code to simulate cluster formation in a turbulent cloud. Unlike previous studies, sink particles are used to represent a forming cluster rather than individual stars. Our cluster model is then coupled with a raytracing scheme to treat radiative transfer as the clusters grow in mass. This poster will outline the details of our model and present preliminary results from our 3D hydrodynamical simulations.

Multiple Scattering in Clouds: Insights from Three-Dimensional Diffusion/P{sub 1} Theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, Anthony B.; Marshak, Alexander

2001-03-15

In the atmosphere, multiple scattering matters nowhere more than in clouds, and being a product of its turbulence, clouds are highly variable environments. This challenges three-dimensional (3D) radiative transfer theory in a way that easily swamps any available computational resources. Fortunately, the far simpler diffusion (or P{sub 1}) theory becomes more accurate as the scattering intensifies, and allows for some analytical progress as well as computational efficiency. After surveying current approaches to 3D solar cloud-radiation problems from the diffusion standpoint, a general 3D result in steady-state diffusive transport is derived relating the variability-induced change in domain-average flux (i.e., diffuse transmittance)more » to the one-point covariance of internal fluctuations in particle density and in radiative flux. These flux variations follow specific spatial patterns in deliberately hydrodynamical language: radiative channeling. The P{sub 1} theory proves even more powerful when the photon diffusion process unfolds in time as well as space. For slab geometry, characteristic times and lengths that describe normal and transverse transport phenomena are derived. This phenomenology is used to (a) explain persistent features in satellite images of dense stratocumulus as radiative channeling, (b) set limits on current cloud remote-sensing techniques, and (c) propose new ones both active and passive.« less

Isotopic Fractionation in Primitive Material: Quantifying the Contribution of Interstellar Chemistry

NASA Technical Reports Server (NTRS)

Charnley, Steven

2010-01-01

Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets. It is thought, in some cases, to trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. We will present the results of models of the nitrogen, oxygen, and carbon fractionation chemistry in dense molecular clouds, particularly in cores where substantial freeze-out of molecules on to dust has occurred. The range of fractionation ratios expected in different interstellar molecules will be discussed and compared to the ratios measured in molecular clouds, comets and meteoritic material. These models make several predictions that can be tested in the near future by molecular line observations, particularly with ALMA.

RAWS: The spaceborne radar wind sounder

NASA Technical Reports Server (NTRS)

Moore, Richard K.

1991-01-01

The concept of the Radar Wind Sounder (RAWS) is discussed. The goals of the RAWS is to estimate the following three qualities: the echo power, to determine rain rate and surface wind velocity; the mean Doppler frequency, to determine the wind velocity in hydrometers; and the spread of the Doppler frequency, to determine the turbulent spread of the wind velocity. Researchers made significant progress during the first year. The feasibility of the concept seems certain. Studies indicate that a reasonably sized system can measure in the presence of ice clouds and dense water clouds. No sensitivity problems exist in rainy environments. More research is needed on the application of the radar to the measurement of rain rates and winds at the sea surface.

Starburst galaxy Messier 94

NASA Image and Video Library

2015-10-19

This image shows the galaxy Messier 94, which lies in the small northern constellation of the Hunting Dogs, about 16 million light-years away. Within the bright ring around Messier 94 new stars are forming at a high rate and many young, bright stars are present within it – thanks to this, this feature is called a starburst ring. The cause of this peculiarly shaped star-forming region is likely a pressure wave going outwards from the galactic centre, compressing the gas and dust in the outer region. The compression of material means the gas starts to collapse into denser clouds. Inside these dense clouds, gravity pulls the gas and dust together until temperature and pressure are high enough for stars to be born.

Million-degree plasma pervading the extended Orion Nebula.

PubMed

Güdel, Manuel; Briggs, Kevin R; Montmerle, Thierry; Audard, Marc; Rebull, Luisa; Skinner, Stephen L

2008-01-18

Most stars form as members of large associations within dense, very cold (10 to 100 kelvin) molecular clouds. The nearby giant molecular cloud in Orion hosts several thousand stars of ages less than a few million years, many of which are located in or around the famous Orion Nebula, a prominent gas structure illuminated and ionized by a small group of massive stars (the Trapezium). We present x-ray observations obtained with the X-ray Multi-Mirror satellite XMM-Newton, revealing that a hot plasma with a temperature of 1.7 to 2.1 million kelvin pervades the southwest extension of the nebula. The plasma flows into the adjacent interstellar medium. This x-ray outflow phenomenon must be widespread throughout our Galaxy.

Satellite view of the extreme haze clouds over China

NASA Astrophysics Data System (ADS)

Minghui, T.; Chen, L.; Wang, Z.

2013-12-01

Minghui Tao*, Liangfu Chen, Zifeng Wang State Key Laboratory of Remote Sensing Science, Jointly Sponsored by Institute of Remote Sensing and Digital Earth of Chinese Academy of Sciences and Beijing Normal University, Beijing 100101, China *Email: tmh1985@163.com ABSTRACT: In the past decades, great increases in anthropogenic emissions have caused dramatic changes in air quality and regional climate in China, which are further complicated by the natural processes such as dust events and atmospheric dynamics such as variations in intensity of the Asian monsoon. The common urban photochemistry smog, haze, and fog-haze pollution lead to poor air quality in major cities in eastern and middle parts of China. On the other hand, the heavy aerosol loading exerts marked influences on radiation, clouds, and precipitation over China. Satellites usually observed widespread haze clouds over eastern China. In most of previous studies, the dense haze clouds were directly connected with accumulation of anthropogenic emissions. However, satellite observations show that formation processes of haze clouds and local pollution near surface were different. Understanding the connections and interactions between haze clouds and local anthropogenic emissions is essential in chemistry and climate modeling of the aerosols over China. In January 2013, durative haze clouds covered most parts of eastern China, leading to extreme pollution events in many cities. With integrated A-train satellite observations and ground measurements, we investigated variations, optical properties, vertical structures as well as formation process of the extreme haze clouds over eastern China. Satellite-surface results were compared to analyze relations between the haze clouds and surface pollution. Different from traditional views, our results reveal that variation and formation of the haze clouds were driven by large-scale natural processes rather than local anthropogenic emissions. Figure 1. Aqua MODIS true color images of the haze clouds over eastern China on Jan 10, 2013.

Chromospheric dust formation, stellar masers and mass loss

NASA Technical Reports Server (NTRS)

Stencel, R. E.

1986-01-01

A multistep scenario which describes a plausible mass loss mechanism associated with red giant and related stars is outlined. The process involves triggering a condensation instability in an extended chromosphere, leading to the formation of cool, dense clouds which are conducive to the formation of molecules and dust grains. Once formed, the dust can be driven away from the star by radiation pressure. Consistency with various observed phenomena is discussed.

Studies of star formation in isolated small dark clouds - II. A southern ammonia survey

NASA Astrophysics Data System (ADS)

Bourke, T. L.; Hyland, A. R.; Robinson, G.; James, S. D.; Wright, C. M.

1995-10-01

A study of the set of small, southern molecular clouds (globules) compiled by Bourke, Hyland & Robinson has been undertaken, through radio observations of ammonia using the Parkes 64-m telescope. The aim of the study is to determine the physical characteristics of the globules, their role in the formation of low-mass stars, and the physical mechanism that triggers the star formation process, or stabilizes the globules against collapse. With this general aim in mind, the (1,1) and (2,2) inversion transitions of ammonia have been surveyed in order to determine the densities, temperatures and masses of the globules. Half of the globules have been detected in ammonia, but only 6 per cent of the detections are `strong' (T*_a>=0.35K). Comparing the globule properties with those of Benson & Myers for cores within complexes, we find that the globules are less opaque and less dense, and are less active sites of star formation. Other properties are comparable. The Vela cometary globules are detected more readily in ammonia than the more isolated globules, and are more active star formation sites. These results suggest that the dense core's environment, in particular the presence of either a large external mass or a significant stellar wind, plays an important role in initiating the star formation process.

HUBBLE SPACE TELESCOPE AND HI IMAGING OF STRONG RAM PRESSURE STRIPPING IN THE COMA SPIRAL NGC 4921: DENSE CLOUD DECOUPLING AND EVIDENCE FOR MAGNETIC BINDING IN THE ISM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenney, Jeffrey D. P.; Abramson, Anne; Bravo-Alfaro, Hector, E-mail: jeff.kenney@yale.edu

Remarkable dust extinction features in the deep Hubble Space Telescope (HST) V and I images of the face-on Coma cluster spiral galaxy NGC 4921 show in unprecedented ways how ram pressure strips the ISM from the disk of a spiral galaxy. New VLA HI maps show a truncated and highly asymmetric HI disk with a compressed HI distribution in the NW, providing evidence for ram pressure acting from the NW. Where the HI distribution is truncated in the NW region, HST images show a well-defined, continuous front of dust that extends over 90° and 20 kpc. This dust front separatesmore » the dusty from dust-free regions of the galaxy, and we interpret it as galaxy ISM swept up near the leading side of the ICM–ISM interaction. We identify and characterize 100 pc–1 kpc scale substructure within this dust front caused by ram pressure, including head–tail filaments, C-shaped filaments, and long smooth dust fronts. The morphology of these features strongly suggests that dense gas clouds partially decouple from surrounding lower density gas during stripping, but decoupling is inhibited, possibly by magnetic fields that link and bind distant parts of the ISM.« less

NIF Discovery Science Eagle Nebula

NASA Astrophysics Data System (ADS)

Kane, Jave; Martinez, David; Pound, Marc; Heeter, Robert; Casner, Alexis; Villette, Bruno; Mancini, Roberto

2017-10-01

The University of Maryland and and LLNL are investigating the origin and dynamics of the famous Pillars of the Eagle Nebula and similar parsec-scale structures at the boundaries of HII regions in molecular hydrogen clouds. The National Ignition Facility (NIF) Discovery Science program Eagle Nebula has performed NIF shots to study models of pillar formation. The shots feature a new long-duration x-ray source, in which multiple hohlraums mimicking a cluster of stars are driven with UV light in series for 10 to 15 ns each to create a 30 to 60 ns output x-ray pulse. The source generates deeply nonlinear hydrodynamics in the Eagle science package, a structure of dense plastic and foam mocking up a molecular cloud containing a dense core. Omega EP and NIF shots have validated the source concept, showing that earlier hohlraums do not compromise later ones by preheat or by ejecting ablated plumes that deflect later beams. The NIF shots generated radiographs of shadowing-model pillars, and also showed evidence that cometary structures can be generated. The velocity and column density profiles of the NIF shadowing and cometary pillars have been compared with observations of the Eagle Pillars made at the millimeter-wave BIMA and CARMA observatories. Prepared by LLNL under Contract DE-AC52-07NA27344.

The essential signature of a massive starburst in a distant quasar.

PubMed

Solomon, P; Vanden Bout, P; Carilli, C; Guelin, M

2003-12-11

Observations of carbon monoxide emission in high-redshift (zeta > 2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the active galactic nucleus, from bursts of massive star formation (associated with the molecular gas), or both. In the Milky Way, high-mass stars form in the dense cores of interstellar molecular clouds, where gas densities are n(H2) > 10(5) cm(-3) (refs 1, 2). Recent surveys show that virtually all galactic sites of high-mass star formation have similarly high densities. The bulk of the cloud material traced by CO observations, however, is at a much lower density. For galaxies in the local Universe, the HCN molecule is an effective tracer of high-density molecular gas. Here we report observations of HCN emission from the infrared-luminous 'Cloverleaf' quasar (at a redshift zeta = 2.5579). The HCN line luminosity indicates the presence of 10 billion solar masses of very dense gas, an essential feature of an immense starburst, which contributes, together with the active galactic nucleus it harbours, to its high infrared luminosity.

X-Ray Dust Scattering At Small Angles: The Complete Halo Around GX13+1

NASA Technical Reports Server (NTRS)

Smith, Randall K.

2007-01-01

The exquisite angular resolution available with Chandra should allow precision measurements of faint diffuse emission surrounding bright sources, such as the X-ray scattering halos created by interstellar dust. However, the ACIS CCDs suffer from pileup when observing bright sources, and this creates difficulties when trying to extract the scattered halo near the source. The initial study of the X-ray halo around GX13+1 using only the ACIS-I detector done by Smith, Edgar & Shafer (2002) suffered from a lack of sensitivity within 50" of the source, limiting what conclusions could be drawn. To address this problem, observations of GX13+1 were obtained with the Chandra HRC-I and simultaneously with the RXTE PCA. Combined with the existing ACIS-I data, this allowed measurements of the X-ray halo between 2-1000". After considering a range of dust models, each assumed to be smoothly distributed with or without a dense cloud along the line of sight, the results show that there is no evidence in this data for a dense cloud near the source, as suggested by Xiang et al. (2005). In addition, although no model leads to formally acceptable results, the Weingartner & Draine (2001) and all but one of the composite grain models from Zubko, Dwek & Arendt (2004) give particularly poor fits.

The CO Transition from Diffuse Molecular Gas to Dense Clouds

NASA Astrophysics Data System (ADS)

Rice, Johnathan S.; Federman, Steven

2017-06-01

The atomic to molecular transitions occurring in diffuse interstellar gas surrounding molecular clouds are affected by the local physical conditions (density and temperature) and the radiation field penetrating the material. Our optical observations of CH, CH^{+}, and CN absorption from McDonald Observatory and the European Southern Observatory are useful tracers of this gas and provide the velocity structure needed for analyzing lower resolution ultraviolet observations of CO and H_{2} absorption from Far Ultraviolet Spectroscopic Explorer. We explore the changing environment between diffuse and dense gas by using the column densities and excitation temperatures from CO and H_{2} to determine the gas density. The resulting gas densities from this method are compared to densities inferred from other methods such as C_{2} and CN chemistry. The densities allow us to interpret the trends from the combined set of tracers. Groupings of sight lines, such as those toward h and χ Persei or Chameleon provide a chance for further characterization of the environment. The Chameleon region in particular helps illuminate CO-dark gas, which is not associated with emission from H I at 21 cm or from CO at 2.6 mm. Expanding this analysis to include emission data from the GOT C+ survey allows the further characterization of neutral diffuse gas, including CO-dark gas.

Composition, structure and chemistry of interstellar dust

NASA Technical Reports Server (NTRS)

Tielens, Alexander G. G. M.; Allamandola, Louis J.

1986-01-01

The observational constraints on the composition of the interstellar dust are analyzed. The dust in the diffuse interstellar medium consists of a mixture of stardust (amorphous silicates, amorphous carbon, polycyclic aromatic hydrocarbons, and graphite) and interstellar medium dust (organic refractory material). Stardust seems to dominate in the local diffuse interstellar medium. Inside molecular clouds, however, icy grain mantles are also important. The structural differences between crystalline and amorphous materials, which lead to differences in the optical properties, are discussed. The astrophysical consequences are briefly examined. The physical principles of grain surface chemistry are discussed and applied to the formation of molecular hydrogen and icy grain mantles inside dense molecular clouds. Transformation of these icy grain mantles into the organic refractory dust component observed in the diffuse interstellar medium requires ultraviolet sources inside molecular clouds as well as radical diffusion promoted by transient heating of the mantle. The latter process also returns a considerable fraction of the molecules in the grain mantle to the gas phase.

On the Chemistry of Hydrides of N Atoms and O+ Ions

NASA Astrophysics Data System (ADS)

Awad, Zainab; Viti, Serena; Williams, David A.

2016-08-01

Previous work by various authors has suggested that the detection by Herschel/HIFI of nitrogen hydrides along the low-density lines of sight toward G10.6-0.4 (W31C) cannot be accounted for by gas-phase chemical models. In this paper we investigate the role of surface reactions on dust grains in diffuse regions, and we find that formation of the hydrides by surface reactions on dust grains with efficiency comparable to that for H2 formation reconciles models with observations of nitrogen hydrides. However, similar surface reactions do not contribute significantly to the hydrides of O+ ions detected by Herschel/HIFI that are present along many sight lines in the Galaxy. The O+ hydrides can be accounted for by conventional gas-phase chemistry either in diffuse clouds of very low density with normal cosmic-ray fluxes or in somewhat denser diffuse clouds with high cosmic-ray fluxes. Hydride chemistry in dense dark clouds appears to be dominated by gas-phase ion-molecule reactions.

Approximate registration of point clouds with large scale differences

NASA Astrophysics Data System (ADS)

Novak, D.; Schindler, K.

2013-10-01

3D reconstruction of objects is a basic task in many fields, including surveying, engineering, entertainment and cultural heritage. The task is nowadays often accomplished with a laser scanner, which produces dense point clouds, but lacks accurate colour information, and lacks per-point accuracy measures. An obvious solution is to combine laser scanning with photogrammetric recording. In that context, the problem arises to register the two datasets, which feature large scale, translation and rotation differences. The absence of approximate registration parameters (3D translation, 3D rotation and scale) precludes the use of fine-registration methods such as ICP. Here, we present a method to register realistic photogrammetric and laser point clouds in a fully automated fashion. The proposed method decomposes the registration into a sequence of simpler steps: first, two rotation angles are determined by finding dominant surface normal directions, then the remaining parameters are found with RANSAC followed by ICP and scale refinement. These two steps are carried out at low resolution, before computing a precise final registration at higher resolution.

The Dense Gas Fraction in the Central Molecular Zone in the Milky Way

NASA Astrophysics Data System (ADS)

Vargas-Salazar, Irene; Battersby, Cara; Walker, Daniel; Zhang, Qizhou; CMZoom

2017-01-01

The Central Molecular Zone (CMZ), a large reservoir of dense molecular gas occupying the central 500pc of the Milky Way, is an extreme star-formation environment where the validity of star formation prescriptions can be tested. The star formation rate (SFR) in the CMZ is about an order of magnitude lower than predicted by the currently accepted prescriptions. An international team lead by PIs Battersby and Keto conducted a survey from 2013-2016 called CMZoom using the Submillimeter Array (SMA) to characterize star formation within resolved molecular clouds in this extreme region. One of the main goals of this survey is to further quantify and understand the low SFR found in this region of the Galaxy. Here, we use the CASA software package to run synthetic observations of hydrodynamical simulations of molecular clouds and vary the observation parameters in such a way that we explore the real parameter space that was probed during the survey. The purpose of this is to investigate how the different observational parameters affect the resultant data. Afterwards, we estimate the “dense gas fraction” (DGF) found in regions across the CMZ. This estimate was found by using the interferometric flux from SMA and the single-dish flux from the Bolocam Galactic Plane Survey. We analyzed the effects that different locations of the CMZ had on these approximate DGF. With these simulations and DGF estimates, we are able to generate improved methods to analyze the data from this survey that will help understand star formation in an extreme environment.The SAO REU program is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no.1262851, and by the Smithsonian Institution.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finn, Susanna C.; Jackson, James M.; Rathborne, Jill M.

Infrared dark clouds (IRDCs) are believed to host the earliest stages of high-mass star and cluster formation. Because O stars typically travel short distances over their lifetimes, if IRDCs host the earliest stages of high-mass star formation then these cold, dense molecular clouds should be located in or near the spiral arms in the Galaxy. The Galactic distribution of a large sample of IRDCs should therefore provide information on Galactic structure. Moreover, determination of distances enables mass and luminosity calculations. We have observed a large sample of IRDC candidates in the first Galactic quadrant in the dense gas tracer CSmore » (2-1) using the Mopra telescope in order to determine kinematic distances from the molecular line velocities. We find that the IRDCs are concentrated around a Galactocentric distance of {approx}4.5 kpc, agreeing with the results of Simon et al. This distribution is consistent with the location of the Scutum-Centaurus spiral arm. The group of IRDCs near the Sun in the first quadrant detected in {sup 13}CO (1-0) in Simon et al. is not detected in the CS data. This discrepancy arises from the differences in the critical densities between the {sup 13}CO (1-0) and CS (2-1) lines. We determine that the Midcourse Space Experiment selected IRDCs are not a homogeneous population, and {sup 13}CO (1-0) traces a population of IRDCs with lower column densities and lower 1.1 mm flux densities in addition to more dense IRDCs detected in CS. Masses of the first quadrant IRDCs are calculated from {sup 13}CO (1-0) maps. We find a strong peak in the Galactocentric IRDC mass surface density distribution at R {sub Gal} {approx} 4.5 kpc.« less

Merger of Multiple Accreting Black Holes Concordant with Gravitational-wave Events

NASA Astrophysics Data System (ADS)

Tagawa, Hiromichi; Umemura, Masayuki

2018-03-01

Recently, the advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) has detected black hole (BH) merger events, most of which are sourced by BHs more massive than 30 M ⊙. Especially, the observation of GW170104 suggests dynamically assembled binaries favoring a distribution of misaligned spins. It has been argued that mergers of unassociated BHs can be engendered through a chance meeting in a multiple BH system under gas-rich environments. In this paper, we consider the merger of unassociated BHs, concordant with the massive BH merger events. To that end, we simulate a multiple BH system with a post-Newtonian N-body code incorporating gas accretion and general relativistic effects. As a result, we find that gas dynamical friction effectively promotes a three-body interaction of BHs in dense gas of n gas ≳ 106 cm‑3, so that BH mergers can take place within 30 Myr. This scenario predicts an isotropic distribution of spin tilts. In the concordant models with GW150914, the masses of seed BHs are required to be ≳25 M ⊙. The potential sites of such chance meeting BH mergers are active galactic nucleus (AGN) disks and dense interstellar clouds. Assuming the LIGO O1, we roughly estimate the event rates for PopI BHs and PopIII BHs in AGN disks to be ≃1–2 yr‑1 and ≃1 yr‑1, respectively. Multiple episodes of AGNs may enhance the rates by roughly an order of magnitude. For massive PopI BHs in dense interstellar clouds the rate is ≃0.02 yr‑1. Hence, high-density AGN disks are a more plausible site for mergers of chance meeting BHs.

Excitation of interstellar hydrogen chloride

NASA Technical Reports Server (NTRS)

Neufild, David A.; Green, Sheldon

1994-01-01

We have computed new rate coefficients for the collisional excitation of HCl by He, in the close-coupled formalism and using an interaction potential determined recently by Willey, Choong, & DeLucia. Results have been obtained for temperatures between 10 K and 300 K. With the use of the infinite order sudden approximation, we have derived approximate expressions of general applicability which may be used to estimate how the rate constant for a transition (J to J prime) is apportioned among the various hyperfine states F prime of the final state J prime. Using these new rate coefficients, we have obtained predictions for the HCl rotational line strengths expected from a dense clump of interstellar gas, as a function of the HCl fractional abundance. Over a wide range of HCl abundances, we have found that the line luminosities are proportional to abundance(exp 2/3), a general result which can be explained using a simple analytical approximation. Our model for the excitation of HCl within a dense molecular cloud core indicates that the J = 1 goes to 0 line strengths measured by Blake, Keene, & Phillips toward the Orion Molecular Cloud (OMC-1) imply a fractional abundance n(HCl)/n(H2) approximately 2 x 10(exp -9), a value which amounts to only approximately 0.3% of the cosmic abundance of chlorine nuclei. Given a fractional abundance of 2 x 10(exp -9), the contribution of HCl emission to the total radiative cooling of a dense clump is small. For Orion, we predict a flux approximately 10(exp -19) W/sq cm for the HCl J = 3 goes to 2 line near 159.8 micrometers, suggesting that the strength of this line could be measured using the Infrared Space Observatory.

From Interstellar Polycyclic Aromatic Hydrocarbons and Ice to the Origin of Life

NASA Technical Reports Server (NTRS)

Allamandola, Louis

2004-01-01

Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of dust in the diffuse ISM is reasonably well constrained to cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In the dense ISM, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by early interstellar chemistry standards, is widespread throughout the Universe. The first part of this talk will describe how infrared studies of interstellar space, combined with laboratory simulations, have revealed the composition of interstellar ices (the building blocks of comets) and the high abundance and nature of interstellar PAHs. The laboratory database has now enabled us to gain insight into the identities, abundances, and physical state of many interstellar materials. Within a dense molecular cloud, and especially in the presolar nebula, the materials frozen into the interstellar/precometary ices are photoprocessed by ultraviolet light and produce more complex molecules. The remainder of the presentation will focus on the photochemical evolution of these materials and the possible role of these compounds on the to the carbonaceous components of micrometeorites, they are likely to have been important sources of complex materials on the early Earth and their composition may be related to the origin of life.

Use of Probability Distribution Functions for Discriminating Between Cloud and Aerosol in Lidar Backscatter Data

NASA Technical Reports Server (NTRS)

Liu, Zhaoyan; Vaughan, Mark A.; Winker, Davd M.; Hostetler, Chris A.; Poole, Lamont R.; Hlavka, Dennis; Hart, William; McGill, Mathew

2004-01-01

In this paper we describe the algorithm hat will be used during the upcoming Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission for discriminating between clouds and aerosols detected in two wavelength backscatter lidar profiles. We first analyze single-test and multiple-test classification approaches based on one-dimensional and multiple-dimensional probability density functions (PDFs) in the context of a two-class feature identification scheme. From these studies we derive an operational algorithm based on a set of 3-dimensional probability distribution functions characteristic of clouds and aerosols. A dataset acquired by the Cloud Physics Lidar (CPL) is used to test the algorithm. Comparisons are conducted between the CALIPSO algorithm results and the CPL data product. The results obtained show generally good agreement between the two methods. However, of a total of 228,264 layers analyzed, approximately 5.7% are classified as different types by the CALIPSO and CPL algorithm. This disparity is shown to be due largely to the misclassification of clouds as aerosols by the CPL algorithm. The use of 3-dimensional PDFs in the CALIPSO algorithm is found to significantly reduce this type of error. Dust presents a special case. Because the intrinsic scattering properties of dust layers can be very similar to those of clouds, additional algorithm testing was performed using an optically dense layer of Saharan dust measured during the Lidar In-space Technology Experiment (LITE). In general, the method is shown to distinguish reliably between dust layers and clouds. The relatively few erroneous classifications occurred most often in the LITE data, in those regions of the Saharan dust layer where the optical thickness was the highest.

Indirect and semi-direct aerosol campaign: The impact of Arctic aerosols on clouds

DOE PAGES

McFarquhar, Greg M.; Ghan, Steven; Verlinde, Johannes; ...

2011-02-01

A comprehensive dataset of microphysical and radiative properties of aerosols and clouds in the boundary layer in the vicinity of Barrow, Alaska, was collected in April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC). ISDAC's primary aim was to examine the effects of aerosols, including those generated by Asian wildfires, on clouds that contain both liquid and ice. ISDAC utilized the Atmospheric Radiation Measurement Pro- gram's permanent observational facilities at Barrow and specially deployed instruments measuring aerosol, ice fog, precipitation, and radiation. The National Research Council of Canada Convair-580 flew 27 sorties and collected data using an unprecedented 41more » stateof- the-art cloud and aerosol instruments for more than 100 h on 12 different days. Aerosol compositions, including fresh and processed sea salt, biomassburning particles, organics, and sulfates mixed with organics, varied between flights. Observations in a dense arctic haze on 19 April and above, within, and below the single-layer stratocumulus on 8 and 26 April are enabling a process-oriented understanding of how aerosols affect arctic clouds. Inhomogeneities in reflectivity, a close coupling of upward and downward Doppler motion, and a nearly constant ice profile in the single-layer stratocumulus suggests that vertical mixing is responsible for its longevity observed during ISDAC. Data acquired in cirrus on flights between Barrow and Fairbanks, Alaska, are improving the understanding of the performance of cloud probes in ice. Furthermore, ISDAC data will improve the representation of cloud and aerosol processes in models covering a variety of spatial and temporal scales, and determine the extent to which surface measurements can provide retrievals of aerosols, clouds, precipitation, and radiative heating.« less

Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces. II. Radiation-Gas Interactions and Outflows

NASA Astrophysics Data System (ADS)

Raskutti, Sudhir; Ostriker, Eve C.; Skinner, M. Aaron

2017-12-01

Momentum deposition by radiation pressure from young, massive stars may help to destroy molecular clouds and unbind stellar clusters by driving large-scale outflows. We extend our previous numerical radiation hydrodynamic study of turbulent star-forming clouds to analyze the detailed interaction between non-ionizing UV radiation and the cloud material. Our simulations trace the evolution of gas and star particles through self-gravitating collapse, star formation, and cloud destruction via radiation-driven outflows. These models are idealized in that we include only radiation feedback and adopt an isothermal equation of state. Turbulence creates a structure of dense filaments and large holes through which radiation escapes, such that only ˜50% of the radiation is (cumulatively) absorbed by the end of star formation. The surface density distribution of gas by mass as seen by the central cluster is roughly lognormal with {σ }{ln{{Σ }}}=1.3{--}1.7, similar to the externally projected surface density distribution. This allows low surface density regions to be driven outwards to nearly 10 times their initial escape speed {v}{esc}. Although the velocity distribution of outflows is broadened by the lognormal surface density distribution, the overall efficiency of momentum injection to the gas cloud is reduced because much of the radiation escapes. The mean outflow velocity is approximately twice the escape speed from the initial cloud radius. Our results are also informative for understanding galactic-scale wind driving by radiation, in particular, the relationship between velocity and surface density for individual outflow structures and the resulting velocity and mass distributions arising from turbulent sources.

The Mass Surface Density Distribution of a High-Mass Protocluster forming from an IRDC and GMC

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Tan, Jonathan C.; Kainulainen, Jouni; Ma, Bo; Butler, Michael

2016-01-01

We study the probability distribution function (PDF) of mass surface densities of infrared dark cloud (IRDC) G028.36+00.07 and its surrounding giant molecular cloud (GMC). Such PDF analysis has the potential to probe the physical processes that are controlling cloud structure and star formation activity. The chosen IRDC is of particular interest since it has almost 100,000 solar masses within a radius of 8 parsecs, making it one of the most massive, dense molecular structures known and is thus a potential site for the formation of a high-mass, "super star cluster". We study mass surface densities in two ways. First, we use a combination of NIR, MIR and FIR extinction maps that are able to probe the bulk of the cloud structure that is not yet forming stars. This analysis also shows evidence for flattening of the IR extinction law as mass surface density increases, consistent with increasing grain size and/or growth of ice mantles. Second, we study the FIR and sub-mm dust continuum emission from the cloud, especially utlizing Herschel PACS and SPIRE images. We first subtract off the contribution of the foreground diffuse emission that contaminates these images. Next we examine the effects of background subtraction and choice of dust opacities on the derived mass surface density PDF. The final derived PDFs from both methods are compared, including also with other published studies of this cloud. The implications for theoretical models and simulations of cloud structure, including the role of turbulence and magnetic fields, are discussed.

First stars of the ρ Ophiuchi dark cloud. XMM-Newton view of ρ Oph and its neighbors

NASA Astrophysics Data System (ADS)

Pillitteri, I.; Wolk, S. J.; Chen, H. H.; Goodman, A.

2016-08-01

Star formation in molecular clouds can be triggered by the dynamical action of winds from massive stars. Furthermore, X-ray and UV fluxes from massive stars can influence the life time of surrounding circumstellar disks. We present the results of a 53 ks XMM-Newton observation centered on the ρ Ophiuchi A+B binary system. ρ Ophiuchi lies in the center of a ring of dust, likely formed by the action of its winds. This region is different from the dense core of the cloud (L1688 Core F) where star formation is at work. X-rays are detected from ρ Ophiuchi as well as a group of surrounding X-ray sources. We detected 89 X-ray sources, 47 of them have at least one counterpart in 2MASS+All-WISE catalogs. Based on IR and X-ray properties, we can distinguish between young stellar objects (YSOs) belonging to the cloud and background objects. Among the cloud members, we detect three debris-disk objects and 22 disk-less - Class III young stars.We show that these stars have ages in 5-10 Myr, and are significantly older than the YSOs in L1688. We speculate that they are the result of an early burst of star formation in the cloud. An X-ray energy of ≥5 × 1044 erg has been injected into the surrounding mediumover the past 5 Myr, we discuss the effects of such energy budget in relation to the cloud properties and dynamics.

RADIO SYNCHROTRON EMISSION FROM A BOW SHOCK AROUND THE GAS CLOUD G2 HEADING TOWARD THE GALACTIC CENTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narayan, Ramesh; Sironi, Lorenzo; Oezel, Feryal

2012-10-01

A dense ionized cloud of gas has been recently discovered to be moving directly toward the supermassive black hole, Sgr A*, at the Galactic center. In 2013 June, at the pericenter of its highly eccentric orbit, the cloud will be approximately 3100 Schwarzschild radii from the black hole and will move supersonically through the ambient hot gas with a velocity of v{sub p} Almost-Equal-To 5400 km s{sup -1}. A bow shock is likely to form in front of the cloud and could accelerate electrons to relativistic energies. We estimate via particle-in-cell simulations the energy distribution of the accelerated electrons andmore » show that the non-thermal synchrotron emission from these electrons might exceed the quiescent radio emission from Sgr A* by a factor of several. The enhanced radio emission should be detectable at GHz and higher frequencies around the time of pericentric passage and in the following months. The bow shock emission is expected to be displaced from the quiescent radio emission of Sgr A* by {approx}33 mas. Interferometric observations could resolve potential changes in the radio image of Sgr A* at wavelengths {approx}< 6 cm.« less

The Use of Uas for Rapid 3d Mapping in Geomatics Education

NASA Astrophysics Data System (ADS)

Teo, Tee-Ann; Tian-Yuan Shih, Peter; Yu, Sz-Cheng; Tsai, Fuan

2016-06-01

With the development of technology, UAS is an advance technology to support rapid mapping for disaster response. The aim of this study is to develop educational modules for UAS data processing in rapid 3D mapping. The designed modules for this study are focused on UAV data processing from available freeware or trial software for education purpose. The key modules include orientation modelling, 3D point clouds generation, image georeferencing and visualization. The orientation modelling modules adopts VisualSFM to determine the projection matrix for each image station. Besides, the approximate ground control points are measured from OpenStreetMap for absolute orientation. The second module uses SURE and the orientation files from previous module for 3D point clouds generation. Then, the ground point selection and digital terrain model generation can be archived by LAStools. The third module stitches individual rectified images into a mosaic image using Microsoft ICE (Image Composite Editor). The last module visualizes and measures the generated dense point clouds in CloudCompare. These comprehensive UAS processing modules allow the students to gain the skills to process and deliver UAS photogrammetric products in rapid 3D mapping. Moreover, they can also apply the photogrammetric products for analysis in practice.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luketa, Anay; Rudeen, David Keith

The objective of this work is to assess dispersion distances of a vapor mixture of species released from a railcar containing a tight crude oil. Tight crude oils can have higher levels of light ends as compared to conventional crude oils [1], which if released and dispersed could pose a potential hazard with regards to a flash fire, explosion, and/or asphyxiation. A historical accident involving rail transport in Viareggio, Italy illustrates how the spillage of LPG can lead to severe damage as a result of a propagating vapor cloud [2]. One of 14 railcars was punctured after derailment, releasing aboutmore » 110 m 3 of LPG into a densely populated area (2000 persons/km 2 ). The resulting vapor cloud propagated and infiltrated nearby buildings and houses which were an average of 10 m in height. Ignition of the cloud occurred approximately 100 to 300 seconds after the start of the spill. A flash fire and explosions resulted, killing 31 people. Evidence suggests that most deaths occurred due to the asphyxiation and thermal hazards from the flash fire. Thus, the motivation for this work is to assess if significant vapors can develop from a railcar carrying a tight crude oil and if this cloud could disperse potentially to nearby populations.« less

Investigation of unsteadiness in Shock-particle cloud interaction: Fully resolved two-dimensional simulation and one-dimensional modeling

NASA Astrophysics Data System (ADS)

Hosseinzadeh-Nik, Zahra; Regele, Jonathan D.

2015-11-01

Dense compressible particle-laden flow, which has a complex nature, exists in various engineering applications. Shock waves impacting a particle cloud is a canonical problem to investigate this type of flow. It has been demonstrated that large flow unsteadiness is generated inside the particle cloud from the flow induced by the shock passage. It is desirable to develop models for the Reynolds stress to capture the energy contained in vortical structures so that volume-averaged models with point particles can be simulated accurately. However, the previous work used Euler equations, which makes the prediction of vorticity generation and propagation innacurate. In this work, a fully resolved two dimensional (2D) simulation using the compressible Navier-Stokes equations with a volume penalization method to model the particles has been performed with the parallel adaptive wavelet-collocation method. The results still show large unsteadiness inside and downstream of the particle cloud. A 1D model is created for the unclosed terms based upon these 2D results. The 1D model uses a two-phase simple low dissipation AUSM scheme (TSLAU) developed by coupled with the compressible two phase kinetic energy equation.

Size-density relations in dark clouds: Non-LTE effects

NASA Technical Reports Server (NTRS)

Maloney, P.

1986-01-01

One of the major goals of molecular astronomy has been to understand the physics and dynamics of dense interstellar clouds. Because the interpretation of observations of giant molecular clouds is complicated by their very complex structure and the dynamical effects of star formation, a number of studies have concentrated on dark clouds. Leung, Kutner and Mead (1982) (hereafter LKM) and Myers (1983), in studies of CO and NH3 emission, concluded that dark clouds exhibit significant correlations between linewidth and cloud radius of the form delta v varies as R(0.5) and between mean density and radius of the form n varies as R(-1), as originally suggested by Larson (1981). This result suggests that these objects are in virial equilibrium. However, the mean densities inferred from the CO data of LKM are based on an local thermodynamic equilibrium (LTE) analysis of their 13CO data. At the very low mean densities inferred by LKM for the larger clouds in their samples, the assumption of LTE becomes very questionable. As most of the range in R in the density-size correlation comes from the clouds observed in CO, it seems worthwhile to examine how non-LTE effects will influence the derived densities. One way to assess the validity of LTE-derived densities is to construct cloud models and then to interpret them in the same way as the observed data. Microturbulent models of inhomogeneous clouds of varying central concentration with the linewidth-size and mean density-size relations found by Myers show sub-thermal excitation of the 13CO line in the larger clouds, with the result that LTE analysis considerbly underestimates the actual column density. A more general approach which doesn't require detailed modeling of the clouds is to consider whether the observed T sub R*(13CO)/T sub R*(12CO) ratios in the clouds studied by LKM are in the range where the LTE-derived optical depths (and hence column densities) can be seriously in error due to sub-thermal excitation of the 13CO molecule.

WASS: An open-source pipeline for 3D stereo reconstruction of ocean waves

NASA Astrophysics Data System (ADS)

Bergamasco, Filippo; Torsello, Andrea; Sclavo, Mauro; Barbariol, Francesco; Benetazzo, Alvise

2017-10-01

Stereo 3D reconstruction of ocean waves is gaining more and more popularity in the oceanographic community and industry. Indeed, recent advances of both computer vision algorithms and computer processing power now allow the study of the spatio-temporal wave field with unprecedented accuracy, especially at small scales. Even if simple in theory, multiple details are difficult to be mastered for a practitioner, so that the implementation of a sea-waves 3D reconstruction pipeline is in general considered a complex task. For instance, camera calibration, reliable stereo feature matching and mean sea-plane estimation are all factors for which a well designed implementation can make the difference to obtain valuable results. For this reason, we believe that the open availability of a well tested software package that automates the reconstruction process from stereo images to a 3D point cloud would be a valuable addition for future researches in this area. We present WASS (http://www.dais.unive.it/wass), an Open-Source stereo processing pipeline for sea waves 3D reconstruction. Our tool completely automates all the steps required to estimate dense point clouds from stereo images. Namely, it computes the extrinsic parameters of the stereo rig so that no delicate calibration has to be performed on the field. It implements a fast 3D dense stereo reconstruction procedure based on the consolidated OpenCV library and, lastly, it includes set of filtering techniques both on the disparity map and the produced point cloud to remove the vast majority of erroneous points that can naturally arise while analyzing the optically complex nature of the water surface. In this paper, we describe the architecture of WASS and the internal algorithms involved. The pipeline workflow is shown step-by-step and demonstrated on real datasets acquired at sea.

Fibers in the NGC 1333 proto-cluster

NASA Astrophysics Data System (ADS)

Hacar, A.; Tafalla, M.; Alves, J.

2017-10-01

Are the initial conditions for clustered star formation the same as for non-clustered star formation? To investigate the initial gas properties in young proto-clusters we carried out a comprehensive and high-sensitivity study of the internal structure, density, temperature, and kinematics of the dense gas content of the NGC 1333 region in Perseus, one of the nearest and best studied embedded clusters. The analysis of the gas velocities in the position-position-velocity space reveals an intricate underlying gas organization both in space and velocity. We identified a total of 14 velocity-coherent, (tran-)sonic structures within NGC 1333, with similar physical and kinematic properties than those quiescent, star-forming (aka fertile) fibers previously identified in low-mass star-forming clouds. These fibers are arranged in a complex spatial network, build-up the observed total column density, and contain the dense cores and protostars in this cloud. Our results demonstrate that the presence of fibers is not restricted to low-mass clouds but can be extended to regions of increasing mass and complexity. We propose that the observational dichotomy between clustered and non-clustered star-forming regions might be naturally explained by the distinct spatial density of fertile fibers in these environments. Based on observations carried out under project number 169-11 with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg.Molecular line observations (spectral cubes) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A123

Radiative Hydrodynamic Simulations of In Situ Star Formation in the Galactic Center

NASA Astrophysics Data System (ADS)

Frazer, Chris; Heitsch, Fabian

2018-01-01

Many stars observed in the Galactic Center (GC) orbit the supermassive black hole (SMBH), Sagittarius A*, in a region where the extreme gravitational field is expected to inhibit star formation. Yet, many of these stars are young which favors an in situ formation scenario. Previous numerical work on this topic has focused on two possible solutions. First, the tidal capture of a > 10^4 Msun infalling molecular cloud by an SMBH may result in the formation of a surrounding gas disk which then rapidly cools and forms stars. This process results in stellar populations that are consistent with the observed stellar disk in the GC. Second, dense gas clumps of approximately 100 Msun on highly eccentric orbits about an SMBH can experience sparks of star formation via orbital compressions occurring during pericenter passage. In my dissertation, I build upon these models using a series of grid-based radiative hydrodynamic simulations, including the effects of both ionizing ultraviolet light from existing stars as well as X-ray radiation emanating from the central black hole. Radiation is treated with an adaptive ray-tracing routine, including appropriate heating and cooling for both neutral and ionized gas. These models show that ultraviolet radiation is sufficiently strong to heat low mass gas clouds, thus suppressing star formation from clump compression. Gas disks that form from cloud capture become sufficiently dense to provide shielding from the radiation of existing central stars, thus allowing star formation to continue. Conversely, X-rays easily penetrate and heat the potentially star forming gas. For sufficiently high radiation fields, this provides a mechanism to disrupt star formation for both scenarios considered above.

An Automatic Procedure for Combining Digital Images and Laser Scanner Data

NASA Astrophysics Data System (ADS)

Moussa, W.; Abdel-Wahab, M.; Fritsch, D.

2012-07-01

Besides improving both the geometry and the visual quality of the model, the integration of close-range photogrammetry and terrestrial laser scanning techniques directs at filling gaps in laser scanner point clouds to avoid modeling errors, reconstructing more details in higher resolution and recovering simple structures with less geometric details. Thus, within this paper a flexible approach for the automatic combination of digital images and laser scanner data is presented. Our approach comprises two methods for data fusion. The first method starts by a marker-free registration of digital images based on a point-based environment model (PEM) of a scene which stores the 3D laser scanner point clouds associated with intensity and RGB values. The PEM allows the extraction of accurate control information for the direct computation of absolute camera orientations with redundant information by means of accurate space resection methods. In order to use the computed relations between the digital images and the laser scanner data, an extended Helmert (seven-parameter) transformation is introduced and its parameters are estimated. Precedent to that, in the second method, the local relative orientation parameters of the camera images are calculated by means of an optimized Structure and Motion (SaM) reconstruction method. Then, using the determined transformation parameters results in having absolute oriented images in relation to the laser scanner data. With the resulting absolute orientations we have employed robust dense image reconstruction algorithms to create oriented dense image point clouds, which are automatically combined with the laser scanner data to form a complete detailed representation of a scene. Examples of different data sets are shown and experimental results demonstrate the effectiveness of the presented procedures.

Magnetic field structure in Monoceros R2

NASA Technical Reports Server (NTRS)

Jarrett, T. H.; Novak, G.; Xie, T.; Goldsmith, P. F.

1994-01-01

We have carried out polarimetric observations to investigate the geometry of the magnetic field in the giant molecular cloud Monoceros R2. This study is based upon deep R-band charge coupled device (CCD) polarimetry, covering a total area of 0.5 deg(exp 2) of the giant molecular cloud. The data were calibrated using a new technique that relies on obtaining broad-band photometry of stars simultaneously with polarimetric photometry of the Mon R2 fields, thus providing an accurate means of measuring the electric vectors of starlight which is polarized by the fore-ground dust grains aligned by the magnetic field in the Mon R2 GMC. In this work, (1) we were able to continuously trace magnetic field lines from the largest scales in Mon R2 to the detailed structure of the field in the dense core, as determined from infrared polarimetry; and (2) we have found that the ambient field is apparently modified by a large-scale structure in the Mon R2 cloud. The mean angle of polarization for the complete sample we measured is 158 deg, which is roughly coincident with the local Galactic magnetic field (155 deg). The dispersion in the angle of polarization is 33 deg, similar to that found in the Orion GMC. The dispersion in angle of polarization for stars located along the western side of the three CCD fields is 22 deg. The CCD fields are bisected by a dense ridge of gas defining the boundary of an expanding gas shell that recent observational results at millimeter wavelengths now reveal dominates the Mon R2 GMC. Our results suggest th at the expanding shell has distorted the magnetic field lines extending from the core to the northern gas structure comprising Mon R2.

VizieR Online Data Catalog: Virial analysis of the dense cores in Orion A (Kirk+, 2017)

NASA Astrophysics Data System (ADS)

Kirk, H.; Friesen, R. K.; Pineda, J. E.; Rosolowsky, E.; Offner, S. S. R.; Matzner, C. D.; Myers, P. C.; di, Francesco J.; Caselli, P.; Alves, F. O.; Chacon-Tanarro, A.; Chen, H.-H.; Chen, M. C.-Y.; Keown, J.; Punanova, A.; Seo, Y. M.; Shirley, Y.; Ginsburg, A.; Hall, C.; Singh, A.; Arce, H. G.; Goodman, A. A.; Martin, P.; Redaelli, E.

2018-05-01

NH3 observations were obtained through the Green Bank Ammonia (GAS), a large project to map the ammonia (1,1), (2,2), and (3,3) rotation-inversion transitions across the high-extinction regions of nearby Gould Belt molecular clouds using the Green Bank Telescope's K-band Focal Plane Array. The survey strategy, data reduction procedure, and basic data properties are described in detail in Friesen+ (2017ApJ...843...63F). The spatial resolution is 32" (0.064pc), while the spectral resolution is 0.07km/s. For our analysis, we use the dense core catalog presented in Lane+ (2016ApJ...833...44L), which covers the entire Orion A complex with the JCMT SCUBA-2 850um. See section 2.2. (1 data file).

Effect of Amazon Smoke on Cloud Microphysics and Albedo-Analysis from Satellite Imagery.

NASA Astrophysics Data System (ADS)

Kaufman, Yoram J.; Nakajima, Teruyuki

1993-04-01

NOAA Advanced Very High Resolution Radiometer images taken over the Brazilian Amazon Basin during the biomass burning season of 1987 are used to study the effect of smoke aerosol particles on the properties of low cumulus and stratocumulus clouds. The reflectance at a wavelength of 0.64 µm and the drop size, derived from the cloud reflectance at 3.75 µm, are studied for tens of thousands of clouds. The opacity of the smoke layer adjacent to each cloud is also monitored simultaneously. Though from satellite data it is impossible to derive all the parameters that influence cloud properties and smoke cloud interaction (e.g., detailed aerosol particles size distribution and chemistry, liquid water content, etc.); satellite data can be used to generate large-scale statistics of the properties of clouds and surrounding aerosol (e.g., smoke optical thickness, cloud-drop size, and cloud reflection of solar radiation) from which the interaction of aerosol with clouds can be surmised. In order to minimize the effect of variations in the precipitable water vapor and in other smoke and cloud properties, biomass burning in the tropics is chosen as the study topic, and the results are averaged for numerous clouds with the same ambient smoke optical thickness.It is shown in this study that the presence of dense smoke (an increase in the optical thickness from 0.1 to 2.0) can reduce the remotely sensed drop size of continental cloud drops from 15 to 9 µm. Due to both the high initial reflectance of clouds in the visible part of the spectrum and the presence of graphitic carbon, the average cloud reflectance at 0.64 µm is reduced from 0.71 to 0.68 for an increase in smoke optical thickness from 0.1 to 2.0. The measurements are compared to results from other years, and it is found that, as predicted, high concentration of aerosol particles causes a decrease in the cloud-drop size and that smoke darkens the bright Amazonian clouds. Comparison with theoretical computations based on Twomey's model show that by using the measured reduction in the cloud-drop size due to the presence of smoke it is possible to explain the reduction in the cloud reflectance at 0.64 µm for smoke imagery index of 0.02 to 0.03.Smoke particles are hygroscopic and have a similar size distribution to maritime and anthropogenic sulfuric aerosol particles. Therefore, these results may also be representative of the interaction of sulfuric particles with clouds.

ORPHANED PROTOSTARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reipurth, Bo; Connelley, Michael; Mikkola, Seppo

2010-12-10

We explore the origin of a population of distant companions ({approx}1000-5000 AU) to Class I protostellar sources recently found by Connelley and coworkers, who noted that the companion fraction diminished as the sources evolved. Here, we present N-body simulations of unstable triple systems embedded in dense cloud cores. Many companions are ejected into unbound orbits and quickly escape, but others are ejected with insufficient momentum to climb out of the potential well of the cloud core and associated binary. These loosely bound companions reach distances of many thousands of AU before falling back and eventually being ejected into escapes asmore » the cloud cores gradually disappear. We use the term orphans to denote protostellar objects that are dynamically ejected from their placental cloud cores, either escaping or for a time being tenuously bound at large separations. Half of all triple systems are found to disintegrate during the protostellar stage, so if multiple systems are a frequent outcome of the collapse of a cloud core, then orphans should be common. Bound orphans are associated with embedded close protostellar binaries, but escaping orphans can travel as far as {approx}0.2 pc during the protostellar phase. The steep climb out of a potential well ensures that orphans are not kinematically distinct from young stars born with a less violent pre-history. The identification of orphans outside their heavily extincted cloud cores will allow the detailed study of protostars high up on their Hayashi tracks at near-infrared and in some cases even at optical wavelengths.« less

Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets

NASA Astrophysics Data System (ADS)

Helling, Ch; Rimmer, P. B.; Rodriguez-Barrera, I. M.; Wood, Kenneth; Robertson, G. B.; Stark, C. R.

2016-07-01

Brown dwarfs and giant gas extrasolar planets have cold atmospheres with rich chemical compositions from which mineral cloud particles form. Their properties, like particle sizes and material composition, vary with height, and the mineral cloud particles are charged due to triboelectric processes in such dynamic atmospheres. The dynamics of the atmospheric gas is driven by the irradiating host star and/or by the rotation of the objects that changes during its lifetime. Thermal gas ionisation in these ultra-cool but dense atmospheres allows electrostatic interactions and magnetic coupling of a substantial atmosphere volume. Combined with a strong magnetic field \\gg {{B}\\text{Earth}} , a chromosphere and aurorae might form as suggested by radio and x-ray observations of brown dwarfs. Non-equilibrium processes like cosmic ray ionisation and discharge processes in clouds will increase the local pool of free electrons in the gas. Cosmic rays and lighting discharges also alter the composition of the local atmospheric gas such that tracer molecules might be identified. Cosmic rays affect the atmosphere through air showers in a certain volume which was modelled with a 3D Monte Carlo radiative transfer code to be able to visualise their spacial extent. Given a certain degree of thermal ionisation of the atmospheric gas, we suggest that electron attachment to charge mineral cloud particles is too inefficient to cause an electrostatic disruption of the cloud particles. Cloud particles will therefore not be destroyed by Coulomb explosion for the local temperature in the collisional dominated brown dwarf and giant gas planet atmospheres. However, the cloud particles are destroyed electrostatically in regions with strong gas ionisation. The potential size of such cloud holes would, however, be too small and might occur too far inside the cloud to mimic the effect of, e.g. magnetic field induced star spots.

Point Cloud Based Change Detection - an Automated Approach for Cloud-based Services

NASA Astrophysics Data System (ADS)

Collins, Patrick; Bahr, Thomas

2016-04-01

The fusion of stereo photogrammetric point clouds with LiDAR data or terrain information derived from SAR interferometry has a significant potential for 3D topographic change detection. In the present case study latest point cloud generation and analysis capabilities are used to examine a landslide that occurred in the village of Malin in Maharashtra, India, on 30 July 2014, and affected an area of ca. 44.000 m2. It focuses on Pléiades high resolution satellite imagery and the Airbus DS WorldDEMTM as a product of the TanDEM-X mission. This case study was performed using the COTS software package ENVI 5.3. Integration of custom processes and automation is supported by IDL (Interactive Data Language). Thus, ENVI analytics is running via the object-oriented and IDL-based ENVITask API. The pre-event topography is represented by the WorldDEMTM product, delivered with a raster of 12 m x 12 m and based on the EGM2008 geoid (called pre-DEM). For the post-event situation a Pléiades 1B stereo image pair of the AOI affected was obtained. The ENVITask "GeneratePointCloudsByDenseImageMatching" was implemented to extract passive point clouds in LAS format from the panchromatic stereo datasets: • A dense image-matching algorithm is used to identify corresponding points in the two images. • A block adjustment is applied to refine the 3D coordinates that describe the scene geometry. • Additionally, the WorldDEMTM was input to constrain the range of heights in the matching area, and subsequently the length of the epipolar line. The "PointCloudFeatureExtraction" task was executed to generate the post-event digital surface model from the photogrammetric point clouds (called post-DEM). Post-processing consisted of the following steps: • Adding the geoid component (EGM 2008) to the post-DEM. • Pre-DEM reprojection to the UTM Zone 43N (WGS-84) coordinate system and resizing. • Subtraction of the pre-DEM from the post-DEM. • Filtering and threshold based classification of the DEM difference to analyze the surface changes in 3D. The automated point cloud generation and analysis introduced here can be embedded in virtually any existing geospatial workflow for operational applications. Three integration options were implemented in this case study: • Integration within any ArcGIS environment whether deployed on the desktop, in the cloud, or online. Execution uses a customized ArcGIS script tool. A Python script file retrieves the parameters from the user interface and runs the precompiled IDL code. That IDL code is used to interface between the Python script and the relevant ENVITasks. • Publishing the point cloud processing tasks as services via the ENVI Services Engine (ESE). ESE is a cloud-based image analysis solution to publish and deploy advanced ENVI image and data analytics to existing enterprise infrastructures. For this purpose the entire IDL code can be capsuled in a single ENVITask. • Integration in an existing geospatial workflow using the Python-to-IDL Bridge. This mechanism allows calling IDL code within Python on a user-defined platform. The results of this case study allow a 3D estimation of the topographic changes within the tectonically active and anthropogenically invaded Malin area after the landslide event. Accordingly, the point cloud analysis was correlated successfully with modelled displacement contours of the slope. Based on optical satellite imagery, such point clouds of high precision and density distribution can be obtained in a few minutes to support the operational monitoring of landslide processes.

An ALMA study of the Orion Integral Filament. I. Evidence for narrow fibers in a massive cloud

NASA Astrophysics Data System (ADS)

Hacar, A.; Tafalla, M.; Forbrich, J.; Alves, J.; Meingast, S.; Grossschedl, J.; Teixeira, P. S.

2018-03-01

Aim. We have investigated the gas organization within the paradigmatic Integral Shape Filament (ISF) in Orion in order to decipher whether or not all filaments are bundles of fibers. Methods: We combined two new ALMA Cycle 3 mosaics with previous IRAM 30m observations to produce a high-dynamic range N2H+ (1-0) emission map of the ISF tracing its high-density material and velocity structure down to scales of 0.009 pc (or 2000 AU). Results: From the analysis of the gas kinematics, we identify a total of 55 dense fibers in the central region of the ISF. Independently of their location in the cloud, these fibers are characterized by transonic internal motions, lengths of 0.15 pc, and masses per unit length close to those expected in hydrostatic equilibrium. The ISF fibers are spatially organized forming a dense bundle with multiple hub-like associations likely shaped by the local gravitational potential. Within this complex network, the ISF fibers show a compact radial emission profile with a median FWHM of 0.035 pc systematically narrower than the previously proposed universal 0.1 pc filament width. Conclusions: Our ALMA observations reveal complex bundles of fibers in the ISF, suggesting strong similarities between the internal substructure of this massive filament and previously studied lower-mass objects. The fibers show identical dynamic properties in both low- and high-mass regions, and their widespread detection in nearby clouds suggests a preferred organizational mechanism of gas in which the physical fiber dimensions (width and length) are self-regulated depending on their intrinsic gas density. Combining these results with previous works in Musca, Taurus, and Perseus, we identify a systematic increase of the surface density of fibers as a function of the total mass per-unit-length in filamentary clouds. Based on this empirical correlation, we propose a unified star-formation scenario where the observed differences between low- and high-mass clouds, and the origin of clusters, emerge naturally from the initial concentration of fibers. The movie associated to Fig. 2 is available at http://https://www.aanda.orgThe data products of this work are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A77

The Physics and Chemistry of Small Translucent Molecular Clouds. VIII. HCN and HNC

NASA Astrophysics Data System (ADS)

Turner, B. E.; Pirogov, L.; Minh, Y. C.

1997-07-01

We have conducted a survey of HCN and HNC (two rotational transitions each) in our standard sample of 11 cirrus cores and 27 Clemens-Barvainis translucent cores whose structures and chemistry have been studied earlier in this series. Both species are seen in all 38 objects. HCNH+ has been searched in three objects. These results are modeled in terms of our previous hydrostatic equilibrium and n ~ r-α structures together with other chemical and physical properties derived earlier. A detailed program has been written to handle the complex radiative transfer of the hyperfine splitting (hfs) of HCN. It is shown that serious errors are made in deriving HCN abundances by methods that ignore the hfs. Both HCN and HNC abundances are high, typically 1(-8) in most sources. The chemically important ratio HCN/HNC is found to be ~2.5 if these species are spatially centrally peaked and ~6 if not. Both species abundances increase monotonically with increasing extinction in the 1.2-2.7 mag range (edge to center), thus displaying the same characteristic transition between diffuse and dense cloud chemistry as do most other species we have studied. HCN/HNC decreases with increasing extinction to a value of 1.3 at Av0 ~ 10, approaching the expected value of 1.0 for dense clouds. Two types of ion-molecule chemistry models have been carried out: a full model using the Standard Model rate file and comprising 409 species (by Lee and Herbst), and a simplified model comprising 21 nitrogen-bearing species for conditions relevant to translucent clouds. Good agreement between observations and chemistry models is achieved throughout the translucent extinction range. Important conclusions are that (1) neutral-neutral reactions such as N + CH2 dominate the chemistry of HCN; (2) low ion-polar reaction rates are strongly favored over high ones; (3) the reaction C+ + NH3 --> H2NC+ --> HNC is unimportant, thus largely uncoupling the CN and NH chemistries; (4) the ratio HCN/HNC is not a particularly important diagnostic of the CN chemistry; (5) model NH3 abundances are at least a factor 100 lower than observed in translucent clouds, even if the reaction N+H+3-->NH+2 is permitted at Langevin rate.

WASS: an open-source stereo processing pipeline for sea waves 3D reconstruction

NASA Astrophysics Data System (ADS)

Bergamasco, Filippo; Benetazzo, Alvise; Torsello, Andrea; Barbariol, Francesco; Carniel, Sandro; Sclavo, Mauro

2017-04-01

Stereo 3D reconstruction of ocean waves is gaining more and more popularity in the oceanographic community. In fact, recent advances of both computer vision algorithms and CPU processing power can now allow the study of the spatio-temporal wave fields with unprecedented accuracy, especially at small scales. Even if simple in theory, multiple details are difficult to be mastered for a practitioner so that the implementation of a 3D reconstruction pipeline is in general considered a complex task. For instance, camera calibration, reliable stereo feature matching and mean sea-plane estimation are all factors for which a well designed implementation can make the difference to obtain valuable results. For this reason, we believe that the open availability of a well-tested software package that automates the steps from stereo images to a 3D point cloud would be a valuable addition for future researches in this area. We present WASS, a completely Open-Source stereo processing pipeline for sea waves 3D reconstruction, available at http://www.dais.unive.it/wass/. Our tool completely automates the recovery of dense point clouds from stereo images by providing three main functionalities. First, WASS can automatically recover the extrinsic parameters of the stereo rig (up to scale) so that no delicate calibration has to be performed on the field. Second, WASS implements a fast 3D dense stereo reconstruction procedure so that an accurate 3D point cloud can be computed from each stereo pair. We rely on the well-consolidated OpenCV library both for the image stereo rectification and disparity map recovery. Lastly, a set of 2D and 3D filtering techniques both on the disparity map and the produced point cloud are implemented to remove the vast majority of erroneous points that can naturally arise while analyzing the optically complex nature of the water surface (examples are sun-glares, large white-capped areas, fog and water areosol, etc). Developed to be as fast as possible, WASS can process roughly four 5 MPixel stereo frames per minute (on a consumer i7 CPU) to produce a sequence of outlier-free point clouds with more than 3 million points each. Finally, it comes with an easy to use user interface and designed to be scalable on multiple parallel CPUs.

The origin and evolution of dust in interstellar and circumstellar environments

NASA Technical Reports Server (NTRS)

Whittet, Douglas C. B.; Leung, Chun M.

1993-01-01

This status report covers the period from the commencement of the research program on 1 Jul. 1992 through 30 Apr. 1993. Progress is reported for research in the following areas: (1) grain formation in circumstellar envelopes; (2) photochemistry in circumstellar envelopes; (3) modeling ice features in circumstellar envelopes; (4) episodic dust formation in circumstellar envelopes; (5) grain evolution in the diffuse interstellar medium; and (6) grain evolution in dense molecular clouds.

The origin of the fan of "bullets" in OMC-1

NASA Astrophysics Data System (ADS)

Gvaramadze, Vasilii

A possible mechanism for the formation of linear features radially diverging from the common origin in the Orion molecular cloud OMC-1 is considered. It is shown that a fan of ejections may arise by interaction of a spherical shock wave with dense cloudlets situated in the neighbourhood of the shock's source. The mechanism of formation of ejections is based on the well-known cumulative effect arising in converging conical flows.

Star-forming Filament Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myers, Philip C., E-mail: pmyers@cfa.harvard.edu

2017-03-20

New models of star-forming filamentary clouds are presented in order to quantify their properties and to predict their evolution. These 2D axisymmetric models describe filaments that have no core, one low-mass core, and one cluster-forming core. They are based on Plummer-like cylinders and spheroids that are bounded by a constant-density surface of finite extent. In contrast to 1D Plummer-like models, they have specific values of length and mass, they approximate observed column density maps, and their distributions of column density ( N -pdfs) are pole-free. Each model can estimate the star-forming potential of a core-filament system by identifying the zonemore » of gas dense enough to form low-mass stars and by counting the number of enclosed thermal Jeans masses. This analysis suggests that the Musca central filament may be near the start of its star-forming life, with enough dense gas to make its first ∼3 protostars, while the Coronet filament is near the midpoint of its star formation, with enough dense gas to add ∼8 protostars to its ∼20 known stars. In contrast, L43 appears to be near the end of its star-forming life, since it lacks enough dense gas to add any new protostars to the two young stellar objectsalready known.« less

STAR FORMATION RELATIONS IN THE MILKY WAY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vutisalchavakul, Nalin; Evans II, Neal J.; Heyer, Mark, E-mail: nje@astro.as.utexas.edu

2016-11-01

The relations between star formation and properties of molecular clouds (MCs) are studied based on a sample of star-forming regions in the Galactic Plane. Sources were selected by having radio recombination lines to provide identification of associated MCs and dense clumps. Radio continuum emission and mid-infrared emission were used to determine star formation rates (SFRs), while {sup 13}CO and submillimeter dust continuum emission were used to obtain the masses of molecular and dense gas, respectively. We test whether total molecular gas or dense gas provides the best predictor of SFR. We also test two specific theoretical models, one relying onmore » the molecular mass divided by the free-fall time, the other using the free-fall time divided by the crossing time. Neither is supported by the data. The data are also compared to those from nearby star-forming regions and extragalactic data. The star formation “efficiency,” defined as SFR divided by mass, spreads over a large range when the mass refers to molecular gas; the standard deviation of the log of the efficiency decreases by a factor of three when the mass of relatively dense molecular gas is used rather than the mass of all of the molecular gas.« less

Experimental study of ejecta from shock melted lead

NASA Astrophysics Data System (ADS)

Chen, Yongtao; Hu, Haibo; Tang, Tiegang; Ren, Guowu; Li, Qingzhong; Wang, Rongbo; Buttler, William T.

2012-03-01

This effort investigates the dynamic properties of ejecta from explosively shocked, melted Pb targets. The study shows that the ejecta cloud that expands beyond the shocked surface is characterized by a high density and low velocity fragment layer between the free-surface and the high velocity micro-jetting particle cloud. This slow, dense ejecta layer is liquid micro-spall. The properties of micro-spall layer, such as the mass, density and velocity, were diagnosed in a novel application of an Asay window, while micro-jetting particles by lithium niobate piezoelectric pins and high speed photography. The total mass-velocity distribution of ejecta, including micro-spall fragments and micro-jetting particles, is presented. Furthermore, the sensitivity of ejecta production to slight variations in the shockwave drive using the Asay foil is studied.

Interstellar Isotopes: Prospects with ALMA

NASA Technical Reports Server (NTRS)

Charnley Steven B.

2010-01-01

Cold molecular clouds are natural environments for the enrichment of interstellar molecules in the heavy isotopes of H, C, N and O. Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets, that may trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. Models of the fractionation chemistry of H, C, N and O in dense molecular clouds, particularly in cores where substantial freeze-out of molecules on to dust has occurred, make several predictions that can be tested in the near future by molecular line observations. The range of fractionation ratios expected in different interstellar molecules will be discussed and the capabilities of ALMA for testing these models (e.g. in observing doubly-substituted isotopologues) will be outlined.

Copernicus observations of interstellar matter toward the Orion OB1 association. I - Epsilon and Pi-5 Orionis

NASA Technical Reports Server (NTRS)

Shull, J. M.

1979-01-01

Copernicus UV data on interstellar lines toward Epsilon Ori and Pi-5 Ori are analyzed to study abundances and physical conditions in both low- and intermediate-velocity components. Clouds at -8 and +5 km/s (LSR) toward Epsilon Ori show typical depletions of Fe, Ti, Mg, and Si in dense (H number density about 100 per cu cm) gas. Low-column-density intermediate-velocity clouds toward both stars, with low densities (hydrogen number density less than 1 per cu cm) and near-cosmic Si abundances, are consistent with a widespread pattern of high-velocity gas over a 15-deg area surrounding the Orion region. Such activity may be attributed to the repeated action of supernovae in a patchy low-density region of interstellar gas.

Ultraviolet photometry from the orbiting astronomical observatory. XXX - The Orion reflection nebulosity

NASA Technical Reports Server (NTRS)

Witt, A. N.; Lillie, C. F.

1978-01-01

Surface-brightness measurements are presented that cover the region of Orion in nine intermediate-width bandpasses ranging from 4250 to 1550 A. The existence of an extended ultraviolet reflection nebulosity in this area is confirmed, and the characteristics of its spectrum and spatial distribution are derived. The observations are consistent with a model in which the dense molecular cloud complex in Orion is illuminated by the foreground Orion aggregate of early-type stars. The interpretation is complicated by the fact that foreground dust may contribute to the observed scattered light. The scattering particles in the cloud appear to exhibit a wavelength-dependent albedo similar to that found for interstellar grains in general, with a strong indication that the phase function changes to a less forward-scattering form in the ultraviolet.

Neutral hydrogen self-absorption in the Milky Way Galaxy

NASA Astrophysics Data System (ADS)

Kavars, Dain William

2006-06-01

To develop a better understanding of the cold neutral medium phase of the interstellar medium, we present a detailed analysis of neutral hydrogen self- absorption (HISA) clouds in the Milky Way Galaxy. These HISA clouds are in the Southern Galactic Plane Survey (SGPS), spanning the region l = 253°--358° and | b | <= 1.3°, and in the VLA Galactic Plane Survey (VGPS), spanning the region l = 18°--67° and | b | <= 1.3°--2.3°. The SGPS and VGPS have an angular resolution of ~1 arcminute and a velocity channel spacing of 0.82 km s -1 . With the recent completion of these surveys, we can study HISA features across the Galaxy at a much better resolution and sensitivity than any previous work. To analyze HISA in detail, catalogs of clouds of all sizes, including those undetectable by eye alone, are required. We present an automated search routine to detect all HISA clouds in the SGPS. We compare HISA to CO data and find some HISA clouds associated with CO, but others have no associated CO. This suggests that HISA clouds are in a transition between molecular and atomic gas, bridging the gap between dense molecular clouds and warmer, diffuse atomic clouds. HISA thus plays an important role in the overall evolution of the Galaxy. To study this transition further, we present observations of the OH molecule toward a select sample of HISA clouds in the VGPS, using the Green Bank Telescope (GBT). We present an analysis of the molecular properties of this sample, including a derivation of an OH to H 2 conversion factor and H 2 to H I abundance ratios. We discuss the complex relationship between H I, OH, 12 CO, and 13 CO emission. Finally we present a statistical analysis comparing HISA with infrared data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) project. The GLIMPSE data reveal a large number of compact, dark infrared clouds believed to be in the early stages of star formation. If GLIMPSE clouds are associated with HISA, they provide valuable information on the evolution of HISA clouds.

Triggering the formation of the supergiant H II region NGC 604 in M 33

NASA Astrophysics Data System (ADS)

Tachihara, Kengo; Gratier, Pierre; Sano, Hidetoshi; Tsuge, Kisetsu; Miura, Rie E.; Muraoka, Kazuyuki; Fukui, Yasuo

2018-05-01

Formation mechanism of a supergiant H II region NGC 604 is discussed in terms of collision of H I clouds in M 33. An analysis of the archival H I data obtained with the Very Large Array (VLA) reveals complex velocity distributions around NGC 604. The H I clouds are composed of two velocity components separated by ˜20 km s-1 for an extent of ˜700 pc, beyond the size of the the H II region. Although the H I clouds are not easily separated in velocity with some mixed component represented by merged line profiles, the atomic gas mass amounts to 6 × 106 M_{⊙} and 9 × 106 M_{⊙} for each component. These characteristics of H I gas and the distributions of dense molecular gas in the overlapping regions of the two velocity components suggest that the formation of giant molecular clouds and the following massive cluster formation have been induced by the collision of H I clouds with different velocities. Referring to the existence of a gas bridging feature connecting M 33 with M 31 reported by large-scale H I surveys, the disturbed atomic gas possibly represents the result of past tidal interaction between the two galaxies, which is analogous to the formation of the R 136 cluster in the LMC.

a Method for the Registration of Hemispherical Photographs and Tls Intensity Images

NASA Astrophysics Data System (ADS)

Schmidt, A.; Schilling, A.; Maas, H.-G.

2012-07-01

Terrestrial laser scanners generate dense and accurate 3D point clouds with minimal effort, which represent the geometry of real objects, while image data contains texture information of object surfaces. Based on the complementary characteristics of both data sets, a combination is very appealing for many applications, including forest-related tasks. In the scope of our research project, independent data sets of a plain birch stand have been taken by a full-spherical laser scanner and a hemispherical digital camera. Previously, both kinds of data sets have been considered separately: Individual trees were successfully extracted from large 3D point clouds, and so-called forest inventory parameters could be determined. Additionally, a simplified tree topology representation was retrieved. From hemispherical images, leaf area index (LAI) values, as a very relevant parameter for describing a stand, have been computed. The objective of our approach is to merge a 3D point cloud with image data in a way that RGB values are assigned to each 3D point. So far, segmentation and classification of TLS point clouds in forestry applications was mainly based on geometrical aspects of the data set. However, a 3D point cloud with colour information provides valuable cues exceeding simple statistical evaluation of geometrical object features and thus may facilitate the analysis of the scan data significantly.

Intercomparison between Individual Particles Scavenged as CCN and Those Collected at Ground-based Site on West Coast of Japan During Asian Dust Storm

NASA Astrophysics Data System (ADS)

Ma, C. J.; Tohno, S.; Kasahara, M.; Hayakawa, S.

2002-12-01

Asian dust storm particles can affect precipitation composition because they are either incorporated into cloud via condensation of water vapour (nucleation) or due to the uptake of particles by existing droplets. And subsequently they affect aquatic and terrestrial ecosystems. In order to study the intercorrelation between the chemical natures of both the particles collected at ground-based site and those scavenged as CCN, the intensive field measurement was carried out on west coast of Japan (Yasaka, Tango Peninsula, 35.62°N; 135.07°E) during dense Asian dust storm event on March 22, 2002. Due to the size dependence of the chemical composition of aerosol particle, size-segregated aerosol particles were collect using Low pressure Andersen impactor sampler. Also, to collect cloud droplets individually, a particular method for the cloud droplet replication was newly applied using collodion (nitrocellulose) film. Sampling of cloud droplets was performed at summit of a mountain (680 m) in Yasaka. To analyze the ambient individual aerosol particles and individual retained particles in cloud droplet, X-ray fluorescence (XRF) analytical method set at SPring-8 on BL39XU was applied. Analytical result enables us not only to compare the characteristics of individual particles scavenged as CCN and those collected at ground-based site, but also to estimate the influence of long-range transport.

The evolution of grain mantles and silicate dust growth at high redshift

NASA Astrophysics Data System (ADS)

Ceccarelli, Cecilia; Viti, Serena; Balucani, Nadia; Taquet, Vianney

2018-05-01

In dense molecular clouds, interstellar grains are covered by mantles of iced molecules. The formation of the grain mantles has two important consequences: it removes species from the gas phase and promotes the synthesis of new molecules on the grain surfaces. The composition of the mantle is a strong function of the environment that the cloud belongs to. Therefore, clouds in high-zeta galaxies, where conditions - like temperature, metallicity, and cosmic ray flux - are different from those in the Milky Way, will have different grain mantles. In the last years, several authors have suggested that silicate grains might grow by accretion of silicon-bearing species on smaller seeds. This would occur simultaneously with the formation of the iced mantles and be greatly affected by its composition as a function of time. In this work, we present a numerical study of the grain mantle formation in high-zeta galaxies, and we quantitatively address the possibility of silicate growth. We find that the mantle thickness decreases with increasing redshift, from about 120 to 20 layers for z varying from 0 to 8. Furthermore, the mantle composition is also a strong function of the cloud redshift, with the relative importance of CO, CO2, ammonia, methane, and methanol highly varying with z. Finally, being Si-bearing species always a very minor component of the mantle, the formation of silicates in molecular clouds is practically impossible.

Deuteration of ammonia in the starless core Ophiuchus/H-MM1

NASA Astrophysics Data System (ADS)

Harju, J.; Daniel, F.; Sipilä, O.; Caselli, P.; Pineda, J. E.; Friesen, R. K.; Punanova, A.; Güsten, R.; Wiesenfeld, L.; Myers, P. C.; Faure, A.; Hily-Blant, P.; Rist, C.; Rosolowsky, E.; Schlemmer, S.; Shirley, Y. L.

2017-04-01

Context. Ammonia and its deuterated isotopologues probe physical conditions in dense molecular cloud cores. The time-dependence of deuterium fractionation and the relative abundances of different nuclear spin modifications are supposed to provide a means of determining the evolutionary stages of these objects. Aims: We aim to test the current understanding of spin-state chemistry of deuterated species by determining the abundances and spin ratios of NH2D, NHD2 and ND3 in a quiescent, dense cloud. Methods: Spectral lines of NH3, NH2D, NHD2, ND3 and N2D+ were observed towards a dense, starless core in Ophiuchus with the APEX, GBT and IRAM 30-m telescopes. The observations were interpreted using a gas-grain chemistry model combined with radiative transfer calculations. The chemistry model distinguishes between the different nuclear spin states of light hydrogen molecules, ammonia and their deuterated forms. Different desorption schemes can be considered. Results: High deuterium fractionation ratios with NH2D/NH3 0.4, NHD2/ NH2D 0.2 and ND3/ NHD2 0.06 are found in the core. The observed ortho/para ratios of NH2D and NHD2 are close to the corresponding nuclear spin statistical weights. The chemistry model can approximately reproduce the observed abundances, but consistently predicts too low ortho/para-NH2D, and too large ortho/para-NHD2 ratios. The longevity of N2H+ and NH3 in dense gas, which is prerequisite to their strong deuteration, can be attributed to the chemical inertia of N2 on grain surfaces. Conclusions: The discrepancies between the chemistry model and the observations are likely to be caused by the fact that the model assumes complete scrambling in principal gas-phase deuteration reactions of ammonia, which means that all the nuclei are mixed in reactive collisions. If, instead, these reactions occur through proton hop/hydrogen abstraction processes, statistical spin ratios are to be expected. The present results suggest that while the deuteration of ammonia changes with physical conditions and time, the nuclear spin ratios of ammonia isotopologues do not probe the evolutionary stage of a cloud. Based on observations carried out with The Atacama Pathfinder Experiment (APEX), the Robert C. Byrd Green Bank Telescope (GBT), and the IRAM 30 m Telescope. APEX is a collaboration between Max-Planck Institut für Radioastronomie (MPIfR), Onsala Space Observatory (OSO), and the European Southern Observatory (ESO). GBT is managed by the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Two-dimensional positive column structure with dust cloud: Experiment and nonlocal kinetic simulation

NASA Astrophysics Data System (ADS)

Zobnin, A. V.; Usachev, A. D.; Petrov, O. F.; Fortov, V. E.; Thoma, M. H.; Fink, M. A.

2018-03-01

The influence of a dust cloud on the structure of the positive column of a direct current gas discharge in a cylindrical glass tube under milligravity conditions has been studied both experimentally and numerically. The discharge was produced in neon at 60 Pa in a glass tube with a diameter of 30 mm at a discharge current 1 mA. Spherical monodisperse melamine formaldehyde dust particles with a diameter of 6.86 μm were injected into the positive column and formed there a uniform dust cloud with a maximum diameter of 14.4 mm. The shape of the cloud and the dust particle number density were measured. The cloud was stationary in the radial direction and slowly drifted in the axial direction. It was found that in the presence of the dust cloud, the intensity of the neon spectral line with a wavelength by 585.25 nm emitted by the discharge plasma increased by 2.3 times and 2 striations appeared on the anode side of the cloud. A numerical simulation of the discharge was performed using the 2D (quasi-3D) nonlocal self-consistent kinetic model of a longitudinally inhomogeneous axially symmetric positive column [Zobnin et al., Phys. Plasmas 21, 113503 (2014)], which was supplemented by a program module performing a self-consistent calculation of dust particle charges, the plasma recombination rate on dust particles, and ion scattering on dust particles. A new approach to the calculation of particle charges and the screening radius in dense dust clouds is proposed. The results of the simulation are presented, compared with experimental data and discussed. It is demonstrated that for the best agreement between simulated and experimental data, it is necessary to take into account the reflection of electrons from the dust particle surface in order to correctly describe the recombination rate in the cloud, its radial stability, and the dust particle charges.

INFRARED SPECTROSCOPIC SURVEY OF THE QUIESCENT MEDIUM OF NEARBY CLOUDS. I. ICE FORMATION AND GRAIN GROWTH IN LUPUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boogert, A. C. A.; Chiar, J. E.; Knez, C.

2013-11-01

Infrared photometry and spectroscopy (1-25 μm) of background stars reddened by the Lupus molecular cloud complex are used to determine the properties of grains and the composition of ices before they are incorporated into circumstellar envelopes and disks. H{sub 2}O ices form at extinctions of A{sub K} = 0.25 ± 0.07 mag (A{sub V} = 2.1 ± 0.6). Such a low ice formation threshold is consistent with the absence of nearby hot stars. Overall, the Lupus clouds are in an early chemical phase. The abundance of H{sub 2}O ice (2.3 ± 0.1 × 10{sup –5} relative to N{sub H}) ismore » typical for quiescent regions, but lower by a factor of three to four compared to dense envelopes of young stellar objects. The low solid CH{sub 3}OH abundance (<3%-8% relative to H{sub 2}O) indicates a low gas phase H/CO ratio, which is consistent with the observed incomplete CO freeze out. Furthermore it is found that the grains in Lupus experienced growth by coagulation. The mid-infrared (>5 μm) continuum extinction relative to A{sub K} increases as a function of A{sub K}. Most Lupus lines of sight are well fitted with empirically derived extinction curves corresponding to R{sub V} ∼ 3.5 (A{sub K} = 0.71) and R{sub V} ∼ 5.0 (A{sub K} = 1.47). For lines of sight with A{sub K} > 1.0 mag, the τ{sub 9.7}/A{sub K} ratio is a factor of two lower compared to the diffuse medium. Below 1.0 mag, values scatter between the dense and diffuse medium ratios. The absence of a gradual transition between diffuse and dense medium-type dust indicates that local conditions matter in the process that sets the τ{sub 9.7}/A{sub K} ratio. This process is likely related to grain growth by coagulation, as traced by the A{sub 7.4}/A{sub K} continuum extinction ratio, but not to ice mantle formation. Conversely, grains acquire ice mantles before the process of coagulation starts.« less

Precipitation Discrimination from Satellite Infrared Temperatures over the CCOPE Mesonet Region.

NASA Astrophysics Data System (ADS)

Weiss, Mitchell; Smith, Eric A.

1987-06-01

A quantitative investigation of the relationship between satellite-derived cloud-top temperature parameters and the detection of intense convective rainfall is described. The area of study is that of the Cooperative Convective Precipitation Experiment (CCOPE), which was held near Miles City, Montana during the summer of 1981. Cloud-top temperatures, derived from the GOES-West operational satellite, were used to calculate a variety of parameters for objectively quantifying the convective intensity of a storm. A dense network of rainfall provided verification of surface rainfall. The cloud-top temperature field and surface rainfall data were processed into equally sized grid domains in order to best depict the individual samples of instantaneous precipitation.The technique of statistical discriminant analysis was used to determine which combinations of cloud-top temperature parameters best classify rain versus no-rain occurrence using three different rain-rate cutoffs: 1, 4, and 10 mm h1. Time lags within the 30 min rainfall verification were tested to determine the optimum time delay associated with rainfall reaching the ground.A total of six storm cases were used to develop and test the statistical models. Discrimination of rain events was found to be most accurate when using a 10 mm h1 rain-rate cutoff. Use parameters designated as coldest cloud-top temperature, the spatial mean of coldest cloud-top temperature, and change over time of mean coldest cloud-top temperature were found to be the best classifiers of rainfall in this study. Combining both a 10-min time lag (in terms of surface verification) with a 10 mm h1 rain-rate threshold resulted in classifying over 60% of all rain and no-rain cases correctly.

Comparison of 3D point clouds obtained by photogrammetric UAVs and TLS to determine the attitude of dolerite outcrops discontinuities.

NASA Astrophysics Data System (ADS)

Duarte, João; Gonçalves, Gil; Duarte, Diogo; Figueiredo, Fernando; Mira, Maria

2015-04-01

Photogrammetric Unmanned Aerial Vehicles (UAVs) and Terrestrial Laser Scanners (TLS) are two emerging technologies that allows the production of dense 3D point clouds of the sensed topographic surfaces. Although image-based stereo-photogrammetric point clouds could not, in general, compete on geometric quality over TLS point clouds, fully automated mapping solutions based on ultra-light UAVs (or drones) have recently become commercially available at very reasonable accuracy and cost for engineering and geological applications. The purpose of this paper is to compare the two point clouds generated by these two technologies, in order to automatize the manual process tasks commonly used to detect and represent the attitude of discontinuities (Stereographic projection: Schmidt net - Equal area). To avoid the difficulties of access and guarantee the data survey security conditions, this fundamental step in all geological/geotechnical studies, applied to the extractive industry and engineering works, has to be replaced by a more expeditious and reliable methodology. This methodology will allow, in a more actuated clear way, give answers to the needs of evaluation of rock masses, by mapping the structures present, which will reduce considerably the associated risks (investment, structures dimensioning, security, etc.). A case study of a dolerite outcrop locate in the center of Portugal (the dolerite outcrop is situated in the volcanic complex of Serra de Todo-o-Mundo, Casais Gaiola, intruded in Jurassic sandstones) will be used to assess this methodology. The results obtained show that the 3D point cloud produced by the Photogrammetric UAV platform has the appropriate geometric quality for extracting the parameters that define the discontinuities of the dolerite outcrops. Although, they are comparable to the manual extracted parameters, their quality is inferior to parameters extracted from the TLS point cloud.

The Distribution of Mass Surface Densities in a High-mass Protocluster

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Tan, Jonathan C.; Kainulainen, Jouni; Ma, Bo; Butler, Michael J.

2016-09-01

We study the probability distribution function (PDF) of mass surface densities, Σ, of infrared dark cloud (IRDC) G028.37+00.07 and its surrounding giant molecular cloud. This PDF constrains the physical processes, such as turbulence, magnetic fields, and self-gravity, that are expected to be controlling cloud structure and star formation activity. The chosen IRDC is of particular interest since it has almost 100,000 solar masses within a radius of 8 pc, making it one of the most massive, dense molecular structures known and is thus a potential site for the formation of a “super star cluster.” We study Σ in two ways. First, we use a combination of NIR and MIR extinction maps that are able to probe the bulk of the cloud structure up to Σ ˜ 1 g cm-2(A V ≃ 200 mag). Second, we study the FIR and submillimeter dust continuum emission from the cloud utilizing Herschel-PACS and SPIRE images and paying careful attention to the effects of foreground and background contamination. We find that the PDFs from both methods, applied over a ˜20‧(30 pc)-sized region that contains ≃1.5 × 105 M ⊙ and enclosing a minimum closed contour with Σ ≃ 0.013 g cm-2 (A V ≃ 3 mag), shows a lognormal shape with the peak measured at Σ ≃ 0.021 g cm-2 (A V ≃ 4.7 mag). There is tentative evidence for the presence of a high-Σ power-law tail that contains from ˜3% to 8% of the mass of the cloud material. We discuss the implications of these results for the physical processes occurring in this cloud.

Radiative characteristics of clouds embedded in smoke derived from airborne multiangular measurements

NASA Astrophysics Data System (ADS)

Gautam, Ritesh; Gatebe, Charles K.; Singh, Manoj K.; Várnai, Tamás.; Poudyal, Rajesh

2016-08-01

Clouds in the presence of absorbing aerosols result in their apparent darkening, observed at the top of atmosphere (TOA), which is associated with the radiative effects of aerosol absorption. Owing to the large radiative effect and potential impacts on regional climate, above-cloud aerosols have recently been characterized in multiple satellite-based studies. While satellite data are particularly useful in showing the radiative impact of above-cloud aerosols at the TOA, recent literature indicates large uncertainties in satellite retrievals of above-cloud aerosol optical depth (AOD) and single scattering albedo (SSA), which are among the most important parameters in the assessment of associated radiative effects. In this study, we analyze radiative characteristics of clouds in the presence of wildfire smoke using airborne data primarily from NASA's Cloud Absorption Radiometer, collected during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites campaign in Canada during the 2008 summer season. We found a strong positive reflectance (R) gradient in the UV-visible (VIS)-near infrared (NIR) spectrum for clouds embedded in dense smoke, as opposed to an (expected) negative gradient for cloud-free smoke and a flat spectrum for smoke-free cloud cover. Several cases of clouds embedded in thick smoke were found, when the aircraft made circular/spiral measurements, which not only allowed the complete characterization of angular distribution of smoke scattering but also provided the vertical distribution of smoke and clouds (within 0.5-5 km). Specifically, the largest darkening by smoke was found in the UV/VIS, with R0.34μm reducing to 0.2 (or 20%), in contrast to 0.8 at NIR wavelengths (e.g., 1.27 µm). The observed darkening is associated with large AODs (0.5-3.0) and moderately low SSA (0.85-0.93 at 0.53 µm), resulting in a significantly large instantaneous aerosol forcing efficiency of 254 ± 47 W m-2 τ-1. Our observations of smoke-cloud radiative interactions were found to be physically consistent with theoretical plane-parallel 1-D and Monte Carlo 3-D radiative transfer calculations, capturing the observed gradient across UV-VIS-NIR. Results from this study offer insights into aerosol-cloud radiative interactions and may help in better constraining satellite retrieval algorithms.

Radiative Characteristics of Clouds Embedded in Smoke Derived from Airborne Multiangular Measurements

NASA Technical Reports Server (NTRS)

Gautam, Ritesh; Gatebe, Charles K.; Singh, Manoj; Varnai, Tamas; Poudyal, Rajesh

2016-01-01

Clouds in the presence of absorbing aerosols result in their apparent darkening, observed at the top of atmosphere (TOA), which is associated with the radiative effects of aerosol absorption. Owing to the large radiative effect and potential impacts on regional climate, above-cloud aerosols have recently been characterized in multiple satellite-based studies. While satellite data are particularly useful in showing the radiative impact of above-cloud aerosols at the TOA, recent literature indicates large uncertainties in satellite retrievals of above-cloud aerosol optical depth (AOD) and single scattering albedo (SSA), which are among the most important parameters in the assessment of associated radiative effects. In this study, we analyze radiative characteristics of clouds in the presence of wildfire smoke using airborne data primarily from NASA's Cloud Absorption Radiometer, collected during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites campaign in Canada during the 2008 summer season. We found a strong positive reflectance (R) gradient in the UV-visible (VIS)-near infrared (NIR) spectrum for clouds embedded in dense smoke, as opposed to an (expected) negative gradient for cloud-free smoke and a flat spectrum for smoke-free cloud cover. Several cases of clouds embedded in thick smoke were found, when the aircraft made circular/spiral measurements, which not only allowed the complete characterization of angular distribution of smoke scattering but also provided the vertical distribution of smoke and clouds (within 0.5-5 km). Specifically, the largest darkening by smoke was found in the UV/VIS, with R(sub 0.34 microns) reducing to 0.2 (or 20%), in contrast to 0.8 at NIR wavelengths (e.g., 1.27 microns). The observed darkening is associated with large AODs (0.5-3.0) and moderately low SSA (0.85-0.93 at 0.53 microns), resulting in a significantly large instantaneous aerosol forcing efficiency of 254 +/- 47 W/sq m/t. Our observations of smoke-cloud radiative interactions were found to be physically consistent with theoretical plane-parallel 1-D and Monte Carlo 3-D radiative transfer calculations, capturing the observed gradient across UV-VIS-NIR. Results from this study offer insights into aerosol-cloud radiative interactions and may help in better constraining satellite retrieval algorithms.

Accurate documentation in cultural heritage by merging TLS and high-resolution photogrammetric data

NASA Astrophysics Data System (ADS)

Grussenmeyer, Pierre; Alby, Emmanuel; Assali, Pierre; Poitevin, Valentin; Hullo, Jean-François; Smigiel, Eddie

2011-07-01

Several recording techniques are used together in Cultural Heritage Documentation projects. The main purpose of the documentation and conservation works is usually to generate geometric and photorealistic 3D models for both accurate reconstruction and visualization purposes. The recording approach discussed in this paper is based on the combination of photogrammetric dense matching and Terrestrial Laser Scanning (TLS) techniques. Both techniques have pros and cons, and criteria as geometry, texture, accuracy, resolution, recording and processing time are often compared. TLS techniques (time of flight or phase shift systems) are often used for the recording of large and complex objects or sites. Point cloud generation from images by dense stereo or multi-image matching can be used as an alternative or a complementary method to TLS. Compared to TLS, the photogrammetric solution is a low cost one as the acquisition system is limited to a digital camera and a few accessories only. Indeed, the stereo matching process offers a cheap, flexible and accurate solution to get 3D point clouds and textured models. The calibration of the camera allows the processing of distortion free images, accurate orientation of the images, and matching at the subpixel level. The main advantage of this photogrammetric methodology is to get at the same time a point cloud (the resolution depends on the size of the pixel on the object), and therefore an accurate meshed object with its texture. After the matching and processing steps, we can use the resulting data in much the same way as a TLS point cloud, but with really better raster information for textures. The paper will address the automation of recording and processing steps, the assessment of the results, and the deliverables (e.g. PDF-3D files). Visualization aspects of the final 3D models are presented. Two case studies with merged photogrammetric and TLS data are finally presented: - The Gallo-roman Theatre of Mandeure, France); - The Medieval Fortress of Châtel-sur-Moselle, France), where a network of underground galleries and vaults has been recorded.

Astrochemistry

NASA Astrophysics Data System (ADS)

Millar, T. J.

2015-08-01

In the last 40 years a wide range of molecules, including neutrals, cations and anions, containing up to 13 atoms—in addition to detections of {{\\text{C}}60} and {{\\text{C}}70} —have been found in the harsh environment of the interstellar medium. The exquisite sensitivity and very high spectral and, more recently, spatial resolution, of modern telescopes has enabled the physics of star formation to be probed through rotational line emission. In this article, I review the basic properties of interstellar clouds and the processes that initiate the chemistry and generate chemical complexity, particularly in regions of star and planet formation. Our understanding of astrochemistry has evolved over the years. Before 1990, the general consensus was that molecules were formed in binary, gas-phase, or volume, reactions, most importantly ion-neutral reactions despite the very low ionization in clouds. Since then, observations have indicated unambiguously that there is also a contribution from surface processes, particularly on the icy mantles that form around refractory grain cores in cold, dense gas. The balance between these two processes depends on particular physical conditions and can vary during the life cycle of a particular volume of interstellar cloud. The complex chemistry that occurs in space is driven mostly through interaction of the gas with cosmic ray protons, a source of ionization that enables a rich ion-neutral chemistry. In addition, I show that the interaction between the gas and the dust in cold, dense regions also leads to additional chemical complexity through reactions that take place in ices at only a few tens of degrees above absolute zero. Although densities are low compared to those in terrestrial environments, the extremely long life times of interstellar clouds and their enormous sizes, enable complex molecules to be synthesised and detected. I show that in some instances, particularly in reactions involving deuterium, the rotational populations of reactants, together with spin-selection rules, can determine the detailed abundances. Although the review is mainly focused on regions associated with star formation, I also consider chemistry in other interesting astronomical regions—in the early Universe and in the envelopes formed by mass loss during the final stages of stellar evolution.

Time-resolved large-scale volumetric pressure fields of an impinging jet from dense Lagrangian particle tracking

NASA Astrophysics Data System (ADS)

Huhn, F.; Schanz, D.; Manovski, P.; Gesemann, S.; Schröder, A.

2018-05-01

Time-resolved volumetric pressure fields are reconstructed from Lagrangian particle tracking with high seeding concentration using the Shake-The-Box algorithm in a perpendicular impinging jet flow with exit velocity U=4 m/s (Re˜ 36,000) and nozzle-plate spacing H/D=5. Helium-filled soap bubbles are used as tracer particles which are illuminated with pulsed LED arrays. A large measurement volume has been covered (cloud of tracked particles in a volume of 54 L, ˜ 180,000 particles). The reconstructed pressure field has been validated against microphone recordings at the wall with high correlation coefficients up to 0.88. In a reduced measurement volume (13 L), dense Lagrangian particle tracking is shown to be feasable up to the maximal possible jet velocity of U=16 m/s.

An evolutionary model for collapsing molecular clouds and their star formation activity. II. Mass dependence of the star formation rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique

We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M {sub max} ≲ 10{sup 4} M {sub ☉}) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR ∼10{sup 4} M {sub ☉} Myr{sup –1}, although their time-averaged SFR is only (SFR) ∼ 10{sup 2} M {sub ☉} Myr{sup –1}. The corresponding efficiencies aremore » SFE{sub final} ≲ 60% and (SFE) ≲ 1%. For more massive clouds (M {sub max} ≳ 10{sup 5} M {sub ☉}), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, (SFR) and (SFE) are well represented by the fits (SFR) ≈ 100(1 + M {sub max}/1.4 × 10{sup 5} M {sub ☉}){sup 1.68} M {sub ☉} Myr{sup –1} and (SFE) ≈ 0.03(M {sub max}/2.5 × 10{sup 5} M {sub ☉}){sup 0.33}, respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao and Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.« less

Formation of young massive clusters from turbulent molecular clouds

NASA Astrophysics Data System (ADS)

Fujii, Michiko; Portegies Zwart, Simon

2015-08-01

We simulate the formation and evolution of young star clusters using smoothed-particle hydrodynamics (SPH) and direct N-body methods. We start by performing SPH simulations of the giant molecular cloud with a turbulent velocity field, a mass of 10^4 to 10^6 M_sun, and a density between 17 and 1700 cm^-3. We continue the SPH simulations for a free-fall time scale, and analyze the resulting structure of the collapsed cloud. We subsequently replace a density-selected subset of SPH particles with stars. As a consequence, the local star formation efficiency exceeds 30 per cent, whereas globally only a few per cent of the gas is converted to stars. The stellar distribution is very clumpy with typically a dozen bound conglomerates that consist of 100 to 10000 stars. We continue to evolve the stars dynamically using the collisional N-body method, which accurately treats all pairwise interactions, stellar collisions and stellar evolution. We analyze the results of the N-body simulations at 2 Myr and 10 Myr. From dense massive molecular clouds, massive clusters grow via hierarchical merging of smaller clusters. The shape of the cluster mass function that originates from an individual molecular cloud is consistent with a Schechter function with a power-law slope of beta = -1.73 at 2 Myr and beta = -1.67 at 10 Myr, which fits to observed cluster mass function of the Carina region. The superposition of mass functions have a power-law slope of < -2, which fits the observed mass function of star clusters in the Milky Way, M31 and M83. We further find that the mass of the most massive cluster formed in a single molecular cloud with a mass of M_g scales with 6.1 M_g^0.51 which also agrees with recent observation in M51. The molecular clouds which can form massive clusters are much denser than those typical in the Milky Way. The velocity dispersion of such molecular clouds reaches 20 km/s and it is consistent with the relative velocity of the molecular clouds observed near NGC 3603 and Westerlund 2, for which a triggered star formation by cloud-cloud collisions is suggested.

Air Parity: Re-Discovering Contested Air Operations

DTIC Science & Technology

2016-06-01

these days repeated in attack numbers and flying conditions, but the phase would end with bad weather – from 19 to 23 August dense cloud cover would...Command HQ acted as the central processor of information from the radar warning system.149 It did not make any tactical decisions, which...hours to spare[.] My HQ , for example, provided a daily working party of 53 officers and men for 3 ½ months.”292 The Army would also assist the ground

Small-Scale Surf Zone Geometric Roughness

DTIC Science & Technology

2017-12-01

and an image of the tie points can be seen (Figure 6). 23 Figure 6. Screen Shot of Alignment Process On the left side is the workspace which...rest of the points, producing the 3D surface. 24 Figure 7. Screen Shot of Dense Cloud Process On the left side is the workspace which...maximum 200 words) Measurements of small-scale (O(mm)) geometric roughness (kf) associated with breaking wave foam were obtained within the surf zone on

Application of a Laser Rangefinder for Space Object Imaging and Shape Reconstruction

DTIC Science & Technology

2014-02-10

the LRF can effectively create sufficiently dense point clouds for various asteroid and satellite shaped SOs, with low propellant consumption, by...bodies. An example is NASA’s Near Earth Asteroid Rendezvous (NEAR) mission, which employed an LRF to aid its rendezvous6 with asteroid 433 Eros in...laser beams. The ray-triangle intersection algorithm* deter- mines the point of intersection between the ray and a model of the scanned object. In order

EFFECTS OF LASER RADIATION ON MATTER: Role of the external photoelectric effect in surface microprocessing

NASA Astrophysics Data System (ADS)

Ageev, Vladimir P.; Konov, Vitalii I.; Krechetov, A. I.

1990-08-01

An analysis is made of the photoemission of electrons in gases when the surface of a solid is subjected to high-intensity ultraviolet laser radiation which does not cause surface heating. Various situations are considered in which generation of high local electric fields and of a dense cloud of charged particles near the surface may alter and even determine the mechanism of laser-stimulated processes on surfaces of solids.

High-Resolution Surface Reconstruction from Imagery for Close Range Cultural Heritage Applications

NASA Astrophysics Data System (ADS)

Wenzel, K.; Abdel-Wahab, M.; Cefalu, A.; Fritsch, D.

2012-07-01

The recording of high resolution point clouds with sub-mm resolution is a demanding and cost intensive task, especially with current equipment like handheld laser scanners. We present an image based approached, where techniques of image matching and dense surface reconstruction are combined with a compact and affordable rig of off-the-shelf industry cameras. Such cameras provide high spatial resolution with low radiometric noise, which enables a one-shot solution and thus an efficient data acquisition while satisfying high accuracy requirements. However, the largest drawback of image based solutions is often the acquisition of surfaces with low texture where the image matching process might fail. Thus, an additional structured light projector is employed, represented here by the pseudo-random pattern projector of the Microsoft Kinect. Its strong infrared-laser projects speckles of different sizes. By using dense image matching techniques on the acquired images, a 3D point can be derived for almost each pixel. The use of multiple cameras enables the acquisition of a high resolution point cloud with high accuracy for each shot. For the proposed system up to 3.5 Mio. 3D points with sub-mm accuracy can be derived per shot. The registration of multiple shots is performed by Structure and Motion reconstruction techniques, where feature points are used to derive the camera positions and rotations automatically without initial information.

Interstellar grain chemistry and organic molecules

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Sandford, S. A.

1990-01-01

The detection of prominant infrared absorption bands at 3250, 2170, 2138, 1670 and 1470 cm(-1) (3.08, 4.61, 4.677, 5.99 and 6.80 micron m) associated with molecular clouds show that mixed molecular (icy) grain mantles are an important component of the interstellar dust in the dense interstellar medium. These ices, which contain many organic molecules, may also be the production site of the more complex organic grain mantles detected in the diffuse interstellar medium. Theoretical calculations employing gas phase as well as grain surface reactions predict that the ices should be dominated only by the simple molecules H2O, H2CO, N2, CO, O2, NH3, CH4, possibly CH3OH, and their deuterated counterparts. However, spectroscopic observations in the 2500 to 1250 cm(-1)(4 to 8 micron m) range show substantial variation from source reactions alone. By comparing these astronomical spectra with the spectra of laboratory-produced analogs of interstellar ices, one can determine the composition and abundance of the materials frozen on the grains in dense clouds. Experiments are described in which the chemical evolution of an interstellar ice analog is determined during irradiation and subsequent warm-up. Particular attention is paid to the types of moderately complex organic materials produced during these experiments which are likely to be present in interstellar grains and cometary ices.

Creating high-resolution bare-earth digital elevation models (DEMs) from stereo imagery in an area of densely vegetated deciduous forest using combinations of procedures designed for lidar point cloud filtering

USGS Publications Warehouse

DeWitt, Jessica D.; Warner, Timothy A.; Chirico, Peter G.; Bergstresser, Sarah E.

2017-01-01

For areas of the world that do not have access to lidar, fine-scale digital elevation models (DEMs) can be photogrammetrically created using globally available high-spatial resolution stereo satellite imagery. The resultant DEM is best termed a digital surface model (DSM) because it includes heights of surface features. In densely vegetated conditions, this inclusion can limit its usefulness in applications requiring a bare-earth DEM. This study explores the use of techniques designed for filtering lidar point clouds to mitigate the elevation artifacts caused by above ground features, within the context of a case study of Prince William Forest Park, Virginia, USA. The influences of land cover and leaf-on vs. leaf-off conditions are investigated, and the accuracy of the raw photogrammetric DSM extracted from leaf-on imagery was between that of a lidar bare-earth DEM and the Shuttle Radar Topography Mission DEM. Although the filtered leaf-on photogrammetric DEM retains some artifacts of the vegetation canopy and may not be useful for some applications, filtering procedures significantly improved the accuracy of the modeled terrain. The accuracy of the DSM extracted in leaf-off conditions was comparable in most areas to the lidar bare-earth DEM and filtering procedures resulted in accuracy comparable of that to the lidar DEM.

Detecting and Identifying Organic Molecules in Space - The AstroBiology Explorer (ABE) MIDEX Mission Concept

NASA Technical Reports Server (NTRS)

Sandford, Scott A.

2001-01-01

Infrared spectroscopy in the 2.5-16 micron (4000-625/cm) range is a principle means by which organic compounds are detected and identified in space. Ground-based, airborne, and spaceborne IR spectral studies have already demonstrated that a significant fraction of the carbon in the interstellar medium (ISM) resides in the form of complex organic molecular species. Unfortunately, neither the distribution of these materials nor their genetic and evolutionary relationships with each other or their environments are well understood. The Astrobiology Explorer (ABE) is a MIDEX (Medium-class Explorer) mission concept currently under study at NASA's Ames Research Center in collaboration with Ball Aerospace and Technologies Corporation. ABE will conduct IR spectroscopic observations to address outstanding important problems in astrobiology, astrochemistry, and astrophysics. The core observational program would make fundamental scientific progress in understanding (1) the evolution of ices and organic matter in dense molecular clouds and young forming stellar systems, (2) the chemical evolution of organic molecules in the ISM as they transition from AGB outflows to planetary nebulae to the general diffuse ISM to H II regions and dense clouds, (3) the distribution of organics in the diffuse ISM, (4) the nature of organics in the Solar System (in comets, asteroids, satellites), and (5) the nature and distribution of organics in local galaxies. Both the scientific goals of the mission and how they would be achieved will be discussed.

Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) MIDEX Mission Concept

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; Allamandola, Louis; Bregman, Jesse; Ennico, Kimberly; Greene, Thomas; Hudgins, Douglas; Strecker, Donald; DeVincenzi, Donald (Technical Monitor)

2001-01-01

Infrared spectroscopy in the 2.5-16 micron range is a principle means by which organic compounds are detected and identified in space. Ground-based, airborne, and spaceborne IR spectral studies have already demonstrated that a significant fraction of the carbon in the interstellar medium (ISM) resides in the form of complex organic molecular species. Unfortunately, neither the distribution of these materials nor their genetic and evolutionary relationships with each other or their environments are well understood. The Astrobiology Explorer (ABE) is a MIDEX mission concept currently under study at NASA's Ames Research Center in collaboration with Ball Aerospace and Technologies Corporation. ABE will conduct IR spectroscopic observations to address outstanding important problems in astrobiology, astrochemistry, and astrophysics. The core observational program would make fundamental scientific progress in understanding (1) the evolution of ices and organic matter in dense molecular clouds and young forming stellar systems, (2) the chemical evolution of organic molecules in the ISM as they transition from AGB outflows to planetary nebulae to the general diffuse ISM to H II regions and dense clouds, (3) the distribution of organics in the diffuse ISM, (4) the nature of organics in the Solar System (in comets, asteroids, satellites), and (5) the nature and distribution of organics in local galaxies. The technical considerations of achieving these science objectives in a MIDEX-sized mission will be described.

Detecting and Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) MIDEX Mission Concept

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; DeVincenzi, Donald (Technical Monitor)

2001-01-01

Infrared spectroscopy in the 2.5-16 microns (4000-625/cm) range is a principle means by which organic compounds are detected and identified in space. Ground-based, airborne, and spaceborne IR spectral studies have already demonstrated that a significant fraction of the carbon in the interstellar medium (ISM) resides in the form of complex organic molecular species. Unfortunately, neither the distribution of these materials nor their genetic and evolutionary relationships with each other or their environments are well understood. The Astrobiology Explorer (ABE) is a MIDEX (Medium-class Explorer) mission concept currently under study at NASA's Ames Research Center in collaboration with Ball Aerospace and Technologies Corporation. ABE will conduct IR spectroscopic observations to address outstanding important problems in astrobiology, astrochemistry, and astrophysics. The core observational program would make fundamental scientific progress in understanding (1) the evolution of ices and organic matter in dense molecular clouds and young forming stellar systems, (2) the chemical evolution of organic molecules in the ISM as they transition from AGB outflows to planetary nebulae to the general diffuse ISM to H II regions and dense clouds, (3) the distribution of organics in the diffuse ISM, (4) the nature of organics in the Solar System (in comets, asteroids, satellites), and (5) the nature and distribution of organics in local galaxies. Both the scientific goals of the mission and how they would be achieved will be discussed.

A Search for O2 in CO-Depleted Molecular Cloud Cores With Herschel

NASA Technical Reports Server (NTRS)

Wirstroem, Eva S.; Charnley, Steven B.; Cordiner, Martin; Ceccarelli, Cecilia

2016-01-01

The general lack of molecular oxygen in molecular clouds is an outstanding problem in astrochemistry. Extensive searches with the Submillimeter Astronomical Satellite, Odin, and Herschel have only produced two detections; upper limits to the O2 abundance in the remaining sources observed are about 1000 times lower than predicted by chemical models. Previous atomic oxygen observations and inferences from observations of other molecules indicated that high abundances of O atoms might be present in dense cores exhibiting large amounts of CO depletion. Theoretical arguments concerning the oxygen gas-grain interaction in cold dense cores suggested that, if O atoms could survive in the gas after most of the rest of the heavy molecular material has frozen out onto dust, then O2 could be formed efficiently in the gas. Using Herschel HIFI, we searched a small sample of four depletion cores-L1544, L694-2, L429, and Oph D-for emission in the low excitation O2 N(sub J)?=?3(sub 3)-1(sub 2) line at 487.249 GHz. Molecular oxygen was not detected and we derive upper limits to its abundance in the range of N(O2)/N (H2) approx. = (0.6-1.6) x10(exp -7). We discuss the absence of O2 in the light of recent laboratory and observational studies.

Synthetic Absorption Lines for a Clumpy Medium: A Spectral Signature for Cloud Acceleration in AGN?

NASA Technical Reports Server (NTRS)

Waters, Tim; Proga, Daniel; Dannen, Randall; Kallman, Timothy R.

2017-01-01

There is increasing evidence that the highly ionized multiphase components of AGN disc winds may be due to thermal instability. The ions responsible for forming the observed X-ray absorption lines may only exist in relatively cool clumps that can be identified with the so-called warm absorbers. Here we calculate synthetic absorption lines for such warm absorbers from first principles by combining 2D hydrodynamic solutions of a two-phase medium with a dense grid of photoionization models to determine the detailed ionization structure of the gas. Our calculations reveal that cloud disruption, which leads to a highly complicated velocity field (i.e. a clumpy flow), will only mildly affect line shapes and strengths when the warm gas becomes highly mixed but not depleted. Prior to complete disruption, clouds that are optically thin to the driving UV resonance lines will cause absorption at an increasingly blueshifted line-of-sight velocity as they are accelerated. This behavior will imprint an identifiable signature on the line profile if warm absorbers are enshrouded in an even broader absorption line produced by a high column of intercloud gas. Interestingly, we show that it is possible to develop a spectral diagnostic for cloud acceleration by differencing the absorption components of a doublet line, a result that can be qualitatively understood using a simple partial covering model. Our calculations also permit us to comment on the spectral differences between cloud disruption and ionization changes driven by flux variability. Notably, cloud disruption offers another possibility for explaining absorption line variability.

GRO source candidates: (A) Nearby modest-size molecular clouds; (B) Pulsar with Wolf-Rayet companion that has lost its H-envelope

NASA Technical Reports Server (NTRS)

Silberberg, R.; Murphy, Ronald J.

1989-01-01

Within 100 pc of the sun there are over a hundred cirrus clouds with masses of approx. 60 solar mass and dense molecular clouds with masses of approx. 4 solar mass. If the local interstellar density of cosmic rays is also present in these clouds, the flux of neutral pion from the decay of gamma rays from the core of a cloud at a distance of 20 pc is approx. 13 x 10(exp -8) photons/sq cm/s. The flux from the more extensive cirrus cloud is approx 4 x 10(exp -7) photons/sq cm/s. A relativistic beam of particles generated by a compact stellar object and incident upon a large, close companion can be a strong gamma ray line source if more of the beam energy is used in interactions with C and O and heavier nuclei and less with H and He. This would be the case if the companion has lost its hydrogen envelope and nucleosynthesized much of its He into C, O, and Ne. Such objects are Wolf-Rayet stars and it is believed that some Wolf-Rayet stars do, in fact, have compact companions. For a beam of protons of 10(exp 37) erg/s, the flux at 1 kpc of the 4.4 MeV C-12 line could be as high as 5 x 10(exp -6) photons/sq cm/s. The fluxes of the deexcitation lines from the spallation products of O-16 are also presented.

STABILITY OF GAS CLOUDS IN GALACTIC NUCLEI: AN EXTENDED VIRIAL THEOREM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xian; Cuadra, Jorge; Amaro-Seoane, Pau, E-mail: xchen@astro.puc.cl, E-mail: jcuadra@astro.puc.cl, E-mail: Pau.Amaro-Seoane@aei.mpg.de

2016-03-10

Cold gas entering the central 1–10{sup 2} pc of a galaxy fragments and condenses into clouds. The stability of the clouds determines whether they will be turned into stars or can be delivered to the central supermassive black hole (SMBH) to turn on an active galactic nucleus (AGN). The conventional criteria to assess the stability of these clouds, such as the Jeans criterion and Roche (or tidal) limit, are insufficient here, because they assume the dominance of self-gravity in binding a cloud, and neglect external agents, such as pressure and tidal forces, which are common in galactic nuclei. We formulatemore » a new scheme for judging this stability. We first revisit the conventional Virial theorem, taking into account an external pressure, to identify the correct range of masses that lead to stable clouds. We then extend the theorem to further include an external tidal field, which is equally crucial for the stability in the region of our interest—in dense star clusters, around SMBHs. We apply our extended Virial theorem to find new solutions to controversial problems, namely, the stability of the gas clumps in AGN tori, the circum-nuclear disk in the Galactic Center, and the central molecular zone of the Milky Way. The masses we derive for these structures are orders of magnitude smaller than the commonly used Virial masses (equivalent to the Jeans mass). Moreover, we prove that these clumps are stable, contrary to what one would naively deduce from the Roche (tidal) limit.« less

A Submillimetre Study of Massive Star Formation Within the W51 Complex and Infrared Dark Clouds

NASA Astrophysics Data System (ADS)

Parsons, Harriet Alice Louise

Despite its importance the fundamental question of how massive stars form remains unanswered, with improvements to both models and observations having crucial roles to play. To quote Bate et al. (2003) computational models of star formation are limited because "conditions in molecular clouds are not sufficiently well understood to be able to select a representative sample of cloud cores for the initial conditions". It is this notion that motivates the study of the environments within Giant Molecular Clouds (GMCs) and Infrared Dark Clouds (IRDCs), known sites of massive star formation, at the clump and core level. By studying large populations of these objects, it is possible to make conclusions based on global properties. With this in mind I study the dense molecular clumps within one of the most massive GMCs in the Galaxy: the W51 GMC. New observations of the W51 GMC in the 12CO, 13CO and C18O (3-2) transitions using the HARP instrument on the JCMT are presented. With the help of the clump finding algorithm CLUMPFIND a total of 1575 dense clumps are identified of which 1130 are associated with the W51 GMC, yielding a dense mass reservoir of 1.5 × 10^5 M contained within these clumps. Of these clumps only 1% by number are found to be super-critical, yielding a super-critical clump formation efficiency of 0.5%, below current SFE estimates of the region. This indicates star formation within the W51 GMC will diminish over time although evidence from the first search for molecular outflows presents the W51 GMC in an active light with a lower limit of 14 outflows. The distribution of the outflows within the region searched found them concentrated towards the W51A region. Having much smaller sizes and masses, obtaining global properties of clumps and cores within IRDCs required studying a large sample of these objects. To do this pre-existing data from the SCUBA Legacy Catalogue was utilised to study IRDCs within a catalogues based on 8 μm data. This data identified 154 IRDC cores that are detected at 850 μm and 51 cores that were not. This work suggests that cores not detected at 850 μm are low mass, low column density and low temperature cores that are below the sensitivity limit of SCUBA at 850 μm Utilising observations at 24 μm from the Spitzer space telescope, allows for an investigation of current star formation by looking for warm embedded objects within the cores. This work reveals 69% of the IRDC cores have 24 μm embedded objects. IRDC cores without associated 24 μm emission ("starless" IRDC cores) may have yet to form stars, or may contain low mass YSOs below the detection limit. If it is assumed that cores without 24 μm embedded sources are at an earlier evolutionary stage to cores with embedded objects a statistical lifetime for the quiescent phase of a few 10^3 - 10^4 years is derived.

Gas Cloud Accretion onto the SMBH SgrA* and Formation of Jet 4

NASA Astrophysics Data System (ADS)

Nishiyama, Shogo

2015-06-01

A dense gas cloud was detected to be rapidly approaching the Galactic supermassive black hole (SMBH) Sgr A*, and was 1,600 Schwarzschild radii from the SMBH at the pericenter of its eccentric orbit in Mar 2014. Ongoing tidal disruption has been observed, and cloud fragments are expected to accrete onto the SMBH on dynamical timescales, suggesting a jet formation in the following years. So we are carrying out daily monitoring observations of Sgr A* in near-infrared and radio wavelengths, and we propose quick follow-up observations with Subaru/Gemini. Br-gamma line emission maps obtained with Gemini/NIFS will be used to fine tune our 3D simulation to estimate how much mass accretes, and when the fragments accrete onto the SMBH. Polarimetric and astrometric signals from a jet taken with Subaru/HiCIAO and KaVA will be compared with the finely tuned simulation to understand the timescale of jet formation, and to investigate the correlation between the accreted mass of the cloud fragments and a luminosity of the newly-formed jet. Spectroscopic and imaging observations from 1.6 - 11 mum (Subaru/IRCS, COMICS) will also be conducted to understand processes responsible for near to mid-infrared emission during the accretion event.

Point Cloud and Digital Surface Model Generation from High Resolution Multiple View Stereo Satellite Imagery

NASA Astrophysics Data System (ADS)

Gong, K.; Fritsch, D.

2018-05-01

Nowadays, multiple-view stereo satellite imagery has become a valuable data source for digital surface model generation and 3D reconstruction. In 2016, a well-organized multiple view stereo publicly benchmark for commercial satellite imagery has been released by the John Hopkins University Applied Physics Laboratory, USA. This benchmark motivates us to explore the method that can generate accurate digital surface models from a large number of high resolution satellite images. In this paper, we propose a pipeline for processing the benchmark data to digital surface models. As a pre-procedure, we filter all the possible image pairs according to the incidence angle and capture date. With the selected image pairs, the relative bias-compensated model is applied for relative orientation. After the epipolar image pairs' generation, dense image matching and triangulation, the 3D point clouds and DSMs are acquired. The DSMs are aligned to a quasi-ground plane by the relative bias-compensated model. We apply the median filter to generate the fused point cloud and DSM. By comparing with the reference LiDAR DSM, the accuracy, the completeness and the robustness are evaluated. The results show, that the point cloud reconstructs the surface with small structures and the fused DSM generated by our pipeline is accurate and robust.

An intelligent and secure system for predicting and preventing Zika virus outbreak using Fog computing

NASA Astrophysics Data System (ADS)

Sareen, Sanjay; Gupta, Sunil Kumar; Sood, Sandeep K.

2017-10-01

Zika virus is a mosquito-borne disease that spreads very quickly in different parts of the world. In this article, we proposed a system to prevent and control the spread of Zika virus disease using integration of Fog computing, cloud computing, mobile phones and the Internet of things (IoT)-based sensor devices. Fog computing is used as an intermediary layer between the cloud and end users to reduce the latency time and extra communication cost that is usually found high in cloud-based systems. A fuzzy k-nearest neighbour is used to diagnose the possibly infected users, and Google map web service is used to provide the geographic positioning system (GPS)-based risk assessment to prevent the outbreak. It is used to represent each Zika virus (ZikaV)-infected user, mosquito-dense sites and breeding sites on the Google map that help the government healthcare authorities to control such risk-prone areas effectively and efficiently. The proposed system is deployed on Amazon EC2 cloud to evaluate its performance and accuracy using data set for 2 million users. Our system provides high accuracy of 94.5% for initial diagnosis of different users according to their symptoms and appropriate GPS-based risk assessment.

Forest understory trees can be segmented accurately within sufficiently dense airborne laser scanning point clouds.

PubMed

Hamraz, Hamid; Contreras, Marco A; Zhang, Jun

2017-07-28

Airborne laser scanning (LiDAR) point clouds over large forested areas can be processed to segment individual trees and subsequently extract tree-level information. Existing segmentation procedures typically detect more than 90% of overstory trees, yet they barely detect 60% of understory trees because of the occlusion effect of higher canopy layers. Although understory trees provide limited financial value, they are an essential component of ecosystem functioning by offering habitat for numerous wildlife species and influencing stand development. Here we model the occlusion effect in terms of point density. We estimate the fractions of points representing different canopy layers (one overstory and multiple understory) and also pinpoint the required density for reasonable tree segmentation (where accuracy plateaus). We show that at a density of ~170 pt/m² understory trees can likely be segmented as accurately as overstory trees. Given the advancements of LiDAR sensor technology, point clouds will affordably reach this required density. Using modern computational approaches for big data, the denser point clouds can efficiently be processed to ultimately allow accurate remote quantification of forest resources. The methodology can also be adopted for other similar remote sensing or advanced imaging applications such as geological subsurface modelling or biomedical tissue analysis.

The violent interstellar medium in Milky-Way like disk galaxies

NASA Astrophysics Data System (ADS)

Karoline Walch, Stefanie

2015-08-01

Molecular clouds are cold, dense, and turbulent filamentary structures that condense out of the multi-phase interstellar medium. They are also the sites of star formation. The minority of new-born stars is massive, but these stars are particularly important for the fate of their parental molecular clouds as their feedback drives turbulence and regulates star formation.I will present results from the SILCC project (SImulating the Life Cycle of molecular Clouds), in which we study the formation and dispersal of molecular clouds within the multi-phase ISM using high-performance, three-dimensional simulations of representative pieces of disk galaxies. Apart from stellar feedback, self-gravity, an external stellar potential, and magnetic fields, we employ an accurate description of gas heating and cooling as well as a small chemical network including molecule formation and (self-)shielding from the interstellar radiation field. We study the impact of the supernova rate and the positioning of the supernova explosions with respect to the molecular gas in a well defined set of simulations. This allows us to draw conclusions on structure of the multi-phase ISM, the amount of molecular gas formed, and the onset of galactic outflows. Furthermore, we show how important stellar wind feedback is for regulating star formation in these disks.

The Taurus Spitzer Legacy Project

NASA Astrophysics Data System (ADS)

McCabe, Caer-Eve; Padgett, D. L.; Rebull, L.; Noriega-Crespo, A.; Carey, S.; Brooke, T.; Stapelfeldt, K. R.; Fukagawa, M.; Hines, D.; Terebey, S.; Huard, T.; Hillenbrand, L.; Guedel, M.; Audard, M.; Monin, J.; Guieu, S.; Knapp, G.; Evans, N. J., III; Menard, F.; Harvey, P.; Allen, L.; Wolf, S.; Skinner, S.; Strom, S.; Glauser, A.; Saavedra, C.; Koerner, D.; Myers, P.; Shupe, D.; Latter, W.; Grosso, N.; Heyer, M.; Dougados, C.; Bouvier, J.

2009-01-01

Without massive stars and dense stellar clusters, Taurus plays host to a distributed mode of low-mass star formation particularly amenable to observational and theoretical study. In 2005-2007, our team mapped the central 43 square degrees of the main Taurus clouds at wavelengths from 3.6 - 160 microns with the IRAC and MIPS cameras on the Spitzer Space Telescope. Together, these images form the largest contiguous Spitzer map of a single star-forming region (and any region outside the galactic plane). Our Legacy team has generated re-reduced mosaic images and source catalogs, available to the community via the Spitzer Science Center website http://ssc.spitzer.caltech.edu/legacy/all.html . This Spitzer survey is a central and crucial part of a multiwavelength study of the Taurus cloud complex that we have performed using XMM, CFHT, and the SDSS. The seven photometry data points from Spitzer allow us to characterize the circumstellar environment of each object, and, in conjunction with optical and NIR photometry, construct a complete luminosity function for the cloud members that will place constraints on the initial mass function. We present results drawing upon our catalog of several hundred thousand IRAC and thousands of MIPS sources. Initial results from our study of the Taurus clouds include new disks around brown dwarfs, new low luminosity YSO candidates, and new Herbig-Haro objects.

Large-Scale CO Maps of the Lupus Molecular Cloud Complex

NASA Astrophysics Data System (ADS)

Tothill, N. F. H.; Löhr, A.; Parshley, S. C.; Stark, A. A.; Lane, A. P.; Harnett, J. I.; Wright, G. A.; Walker, C. K.; Bourke, T. L.; Myers, P. C.

2009-11-01

Fully sampled degree-scale maps of the 13CO 2-1 and CO 4-3 transitions toward three members of the Lupus Molecular Cloud Complex—Lupus I, III, and IV—trace the column density and temperature of the molecular gas. Comparison with IR extinction maps from the c2d project requires most of the gas to have a temperature of 8-10 K. Estimates of the cloud mass from 13CO emission are roughly consistent with most previous estimates, while the line widths are higher, around 2 km s-1. CO 4-3 emission is found throughout Lupus I, indicating widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the NW end and along the edge of the B 228 ridge in Lupus I, and a coherent velocity gradient across the ridge, are consistent with interaction between the molecular cloud and an expanding H I shell from the Upper-Scorpius subgroup of the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be stars, and shows no sign of external influence. Slightly warmer gas around the core of Lupus IV and a low line width suggest heating by the Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an H I shell.

Collective behavior of bulk nanobubbles produced by alternating polarity electrolysis.

PubMed

Postnikov, Alexander V; Uvarov, Ilia V; Penkov, Nikita V; Svetovoy, Vitaly B

2017-12-21

Nanobubbles in liquids are mysterious gaseous objects with exceptional stability. They promise a wide range of applications, but their production is not well controlled and localized. Alternating polarity electrolysis of water is a tool that can control the production of bulk nanobubbles in space and time without generating larger bubbles. Using the schlieren technique, the detailed three-dimensional structure of a dense cloud of nanobubbles above the electrodes is visualized. It is demonstrated that the thermal effects produce a different schlieren pattern and have different dynamics. A localized volume enriched with nanobubbles can be separated from the parent cloud and exists on its own. This volume demonstrates buoyancy, from which the concentration of nanobubbles is estimated as 2 × 10 18 m -3 . This concentration is smaller than that in the parent cloud. Dynamic light scattering shows that the average size of nanobubbles during the process is 60-80 nm. The bubbles are observed 15 minutes after switching off the electrical pulses but their size is shifted to larger values of about 250 nm. Thus, an efficient way to generate and control nanobubbles is proposed.

Point Cloud Analysis for Uav-Borne Laser Scanning with Horizontally and Vertically Oriented Line Scanners - Concept and First Results

NASA Astrophysics Data System (ADS)

Weinmann, M.; Müller, M. S.; Hillemann, M.; Reydel, N.; Hinz, S.; Jutzi, B.

2017-08-01

In this paper, we focus on UAV-borne laser scanning with the objective of densely sampling object surfaces in the local surrounding of the UAV. In this regard, using a line scanner which scans along the vertical direction and perpendicular to the flight direction results in a point cloud with low point density if the UAV moves fast. Using a line scanner which scans along the horizontal direction only delivers data corresponding to the altitude of the UAV and thus a low scene coverage. For these reasons, we present a concept and a system for UAV-borne laser scanning using multiple line scanners. Our system consists of a quadcopter equipped with horizontally and vertically oriented line scanners. We demonstrate the capabilities of our system by presenting first results obtained for a flight within an outdoor scene. Thereby, we use a downsampling of the original point cloud and different neighborhood types to extract fundamental geometric features which in turn can be used for scene interpretation with respect to linear, planar or volumetric structures.

Cosmic Star Formation - Seen from the Milky Way with AtLAST Short Contributed Talk

NASA Astrophysics Data System (ADS)

Kauffmann, Jens

2018-01-01

Herschel and Spitzer provided first truly unbiased overviews of star formation environments in the Milky Way. Today, high–powered instruments like ALMA additionally resolve the immediate birth environments of individual stars in a few selected regions throughout the Galaxy. This progress in the Milky Way is important, because the same facilities also allow us to explore how galaxies evolved over time. Was star formation more efficient in the dense molecular clouds found in starburst galaxies? Why do galaxies often follow star formation relations like those from Kennicutt & Schmidt and Gao & Solomon? A cloud-scale understanding of the star formation processes, that can only be developed in the Milky Way, is necessary to make progress. Unfortunately, ALMA can resolve the detailed substructure only in SELECTED galactic molecular clouds, given mapping with ALMA is very slow. Here I show how surveys of dust continuum and line emission provided by a large and fast single–dish telescope can overcome these critical limitations, e.g. by breaking degeneracies in current theoretical models. My discussion draws on a white papers previously developed for similar telescopes.

Semitransparent cirrus clouds in the upper troposphere and their contribution to the particulate scattering in the tropical UTLS region

NASA Astrophysics Data System (ADS)

Thampi, Bijoy V.; Parameswaran, K.; Sunilkumar, S. V.

2012-01-01

Contribution of semitransparent cirrus (STC) to the scattering properties of particulates in the UTLS region is examined over the Indian region using the lidar data from Gadanki (13.5°N, 79.2°E) and SAGE-II measurements from 30°S to 30°N in the longitude region 70-90°E within the feasibility of these measurements. While the contribution of STC to particulate optical depth (τp) in UT is found to be quite significant in the equatorial and off-equatorial regions in both the hemispheres during summer, this is very small during winter in the off-equatorial regions. Dense STCs in UT also influences the aerosol scattering below the cloud-base and above the cloud-top (LS). This STC influence in LS is quite significant in the northern hemisphere and almost insignificant over the southern hemisphere, where the STC-cover as well as its optical depth is relatively low. This hemispheric difference is attributed to relatively strong tropospheric convection in the northern hemisphere.

Mapping the three-dimensional dust extinction towards the supernova remnant S147 - the S147 dust cloud

NASA Astrophysics Data System (ADS)

Chen, B.-Q.; Liu, X.-W.; Ren, J.-J.; Yuan, H.-B.; Huang, Y.; Yu, B.; Xiang, M.-S.; Wang, C.; Tian, Z.-J.; Zhang, H.-W.

2017-12-01

We present a three-dimensional (3D) extinction analysis in the region towards the supernova remnant (SNR) S147 (G180.0-1.7) using multiband photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC), 2MASS and WISE. We isolate a previously unrecognized dust structure likely to be associated with SNR S147. The structure, which we term as 'S147 dust cloud', is estimated to have a distance d = 1.22 ± 0.21 kpc, consistent with the conjecture that S147 is associated with pulsar PSR J0538 + 2817. The cloud includes several dense clumps of relatively high extinction that locate on the radio shell of S147 and coincide spatially with the CO and gamma-ray emission features. We conclude that the usage of CO measurements to trace the SNR associated MCs is unavoidably limited by the detection threshold, dust depletion and the difficulty of distance estimates in the outer Galaxy. 3D dust extinction mapping may provide a better way to identify and study SNR-MC interactions.

Modeling ash fall distribution from a Yellowstone supereruption

USGS Publications Warehouse

Mastin, Larry G.; Van Eaton, Alexa R.; Lowenstern, Jacob B.

2014-01-01

We used the volcanic ash transport and dispersion model Ash3d to estimate the distribution of ashfall that would result from a modern-day Plinian supereruption at Yellowstone volcano. The simulations required modifying Ash3d to consider growth of a continent-scale umbrella cloud and its interaction with ambient wind fields. We simulated eruptions lasting 3 days, 1 week, and 1 month, each producing 330 km3 of volcanic ash, dense-rock equivalent (DRE). Results demonstrate that radial expansion of the umbrella cloud is capable of driving ash upwind (westward) and crosswind (N-S) in excess of 1500 km, producing more-or-less radially symmetric isopachs that are only secondarily modified by ambient wind. Deposit thicknesses are decimeters to meters in the northern Rocky Mountains, centimeters to decimeters in the northern Midwest, and millimeters to centimeters on the East, West, and Gulf Coasts. Umbrella cloud growth may explain the extremely widespread dispersal of the ∼640 ka and 2.1 Ma Yellowstone tephra deposits in the eastern Pacific, northeastern California, southern California, and South Texas.

A flattened cloud core in NGC 2024

NASA Technical Reports Server (NTRS)

Ho, Paul T. P.; Peng, Yun-Lou; Torrelles, Jose M.; Gomez, Jose F.; Rodriguez, Luis F.; Canto, Jorge

1993-01-01

The (J, K) (1, 1) and (2, 2) NH3 lines were mapped toward a molecular cloud core in NGC 2024 using the VLA in its C/D-configuration. This region is associated with one of the most highly collimated molecular outflows. We find that the molecular condensations associated with the far-infrared sources FIR 5, FIR 6, and FIR 7 have kinetic temperatures of about 40 K. We also find line broadening toward FIR 6 and FIR 7. This suggests that these condensations may not be protostars heated by gravitational energy released during collapse but that they have an internal heating source. A flattened structure of ammonia emission is found extending parallel to the unipolar CO outflow structure, but displaced systematically to the east. If the NH3 emission traces the denser gas environment, there is no evidence that a dense gas structure is confining the molecular outflow. Instead, the location of the high-velocity outflow along the surface of the NH3 structure suggests that a wind is sweeping material from the surface of this elongated cloud core.

Extending the Life of Virtual Heritage: Reuse of Tls Point Clouds in Synthetic Stereoscopic Spherical Images

NASA Astrophysics Data System (ADS)

Garcia Fernandez, J.; Tammi, K.; Joutsiniemi, A.

2017-02-01

Recent advances in Terrestrial Laser Scanner (TLS), in terms of cost and flexibility, have consolidated this technology as an essential tool for the documentation and digitalization of Cultural Heritage. However, once the TLS data is used, it basically remains stored and left to waste.How can highly accurate and dense point clouds (of the built heritage) be processed for its reuse, especially to engage a broader audience? This paper aims to answer this question by a channel that minimizes the need for expert knowledge, while enhancing the interactivity with the as-built digital data: Virtual Heritage Dissemination through the production of VR content. Driven by the ProDigiOUs project's guidelines on data dissemination (EU funded), this paper advances in a production path to transform the point cloud into virtual stereoscopic spherical images, taking into account the different visual features that produce depth perception, and especially those prompting visual fatigue while experiencing the VR content. Finally, we present the results of the Hiedanranta's scans transformed into stereoscopic spherical animations.

High Spectral Resolution Lidar Measurements of Multiple Scattering

NASA Technical Reports Server (NTRS)

Eloranta, E. W.; Piironen, P.

1996-01-01

The University of Wisconsin High Spectral Resolution Lidar (HSRL) provides unambiguous measurements of backscatter cross section, backscatter phase function, depolarization, and optical depth. This is accomplished by dividing the lidar return into separate particulate and molecular contributions. The molecular return is then used as a calibration target. We have modified the HSRL to use an I2 molecular absorption filter to separate aerosol and molecular signals. This allows measurement in dense clouds. Useful profiles extend above the cloud base until the two way optical depth reaches values between 5 and 6; beyond this, photon counting errors become large. In order to observe multiple scattering, the HSRL includes a channel which records the combined aerosol and molecular lidar return simultaneously with the spectrometer channel measurements of optical properties. This paper describes HSRL multiple scattering measurements from both water and ice clouds. These include signal strengths and depolarizations as a function of receiver field of view. All observations include profiles of extinction and backscatter cross sections. Measurements are also compared to predictions of a multiple scattering model based on small angle approximations.

Combined retrieval of Arctic liquid water cloud and surface snow properties using airborne spectral solar remote sensing

NASA Astrophysics Data System (ADS)

Ehrlich, André; Bierwirth, Eike; Istomina, Larysa; Wendisch, Manfred

2017-09-01

The passive solar remote sensing of cloud properties over highly reflecting ground is challenging, mostly due to the low contrast between the cloud reflectivity and that of the underlying surfaces (sea ice and snow). Uncertainties in the retrieved cloud optical thickness τ and cloud droplet effective radius reff, C may arise from uncertainties in the assumed spectral surface albedo, which is mainly determined by the generally unknown effective snow grain size reff, S. Therefore, in a first step the effects of the assumed snow grain size are systematically quantified for the conventional bispectral retrieval technique of τ and reff, C for liquid water clouds. In general, the impact of uncertainties of reff, S is largest for small snow grain sizes. While the uncertainties of retrieved τ are independent of the cloud optical thickness and solar zenith angle, the bias of retrieved reff, C increases for optically thin clouds and high Sun. The largest deviations between the retrieved and true original values are found with 83 % for τ and 62 % for reff, C. In the second part of the paper a retrieval method is presented that simultaneously derives all three parameters (τ, reff, C, reff, S) and therefore accounts for changes in the snow grain size. Ratios of spectral cloud reflectivity measurements at the three wavelengths λ1 = 1040 nm (sensitive to reff, S), λ2 = 1650 nm (sensitive to τ), and λ3 = 2100 nm (sensitive to reff, C) are combined in a trispectral retrieval algorithm. In a feasibility study, spectral cloud reflectivity measurements collected by the Spectral Modular Airborne Radiation measurement sysTem (SMART) during the research campaign Vertical Distribution of Ice in Arctic Mixed-Phase Clouds (VERDI, April/May 2012) were used to test the retrieval procedure. Two cases of observations above the Canadian Beaufort Sea, one with dense snow-covered sea ice and another with a distinct snow-covered sea ice edge are analysed. The retrieved values of τ, reff, C, and reff, S show a continuous transition of cloud properties across snow-covered sea ice and open water and are consistent with estimates based on satellite data. It is shown that the uncertainties of the trispectral retrieval increase for high values of τ, and low reff, S but nevertheless allow the effective snow grain size in cloud-covered areas to be estimated.

Absolute extinction and the influence of environment - Dark cloud sight lines toward VCT 10, 30, and Walker 67

NASA Technical Reports Server (NTRS)

Cardelli, Jason A.; Clayton, Geoffrey C.

1991-01-01

The range of validity of the average absolute extinction law (AAEL) proposed by Cardelli et al. (1988 and 1989) is investigated, combining published visible and NIR data with IUE UV observations for three lines of sight through dense dark cloud environments with high values of total-to-selective extinction. The characteristics of the data sets and the reduction and parameterization methods applied are described in detail, and the results are presented in extensive tables and graphs. Good agreement with the AAEL is demonstrated for wavelengths from 3.4 microns to 250 nm, but significant deviations are found at shorter wavelengths (where previous studies of lines of sight through bright nebulosity found good agreement with the AAEL). These differences are attributed to the effects of coatings on small-bump and FUV grains.

Stellar Incubators Seen Cooking up Stars

NASA Image and Video Library

2005-01-12

This image composite compares visible-light and infrared views from NASA's Spitzer Space Telescope of the glowing Trifid Nebula, a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius. Visible-light images of the Trifid taken with NASA's Hubble Space Telescope, Baltimore, Md. (inside left, figure 1) and the National Optical Astronomy Observatory, Tucson, Ariz., (outside left, figure 1) show a murky cloud lined with dark trails of dust. Data of this same region from the Institute for Radioastronomy millimeter telescope in Spain revealed four dense knots, or cores, of dust (outlined by yellow circles), which are "incubators" for embryonic stars. Astronomers thought these cores were not yet ripe for stars, until Spitzer spotted the warmth of rapidly growing massive embryos tucked inside. http://photojournal.jpl.nasa.gov/catalog/PIA07226

3DNOW: Image-Based 3d Reconstruction and Modeling via Web

NASA Astrophysics Data System (ADS)

Tefera, Y.; Poiesi, F.; Morabito, D.; Remondino, F.; Nocerino, E.; Chippendale, P.

2018-05-01

This paper presents a web-based 3D imaging pipeline, namely 3Dnow, that can be used by anyone without the need of installing additional software other than a browser. By uploading a set of images through the web interface, 3Dnow can generate sparse and dense point clouds as well as mesh models. 3D reconstructed models can be downloaded with standard formats or previewed directly on the web browser through an embedded visualisation interface. In addition to reconstructing objects, 3Dnow offers the possibility to evaluate and georeference point clouds. Reconstruction statistics, such as minimum, maximum and average intersection angles, point redundancy and density can also be accessed. The paper describes all features available in the web service and provides an analysis of the computational performance using servers with different GPU configurations.

Searching for Bio-Precursors and Complex Organic Molecules in Space using the GBT

NASA Technical Reports Server (NTRS)

Cordiner, M.; Charnley, S.; Kisiel, Z.

2012-01-01

Using the latest microwave receiver technology, large organic molecules with abundances as low as approx. 10(exp -11) times that of molecular hydrogen are detectable in cold interstellar clouds via their rotational emission line spectra. We report new observations to search for complex molecules, including molecules of possible pre-biotic importance, using the newly-commissioned Kband focal plane array (KFPA) of the NRAO Robert C. Byrd Green Bank Telescope. Spectra are presented of the dense molecular cloud TMC-1, showing strict upper limits on the level of emission from nitrogen-bearing rings pyrimidine, quinoline and iso-quinoline, carbon-chain oxides C60, C70, HC60 and HC70, and the carbon-chain anion C4H-. The typical RMS brightness temperature noise levels we achieved are approx. 1 mK at around 20 GHz.

H ATOM IRRADIATION OF CARBON GRAINS UNDER SIMULATED DENSE INTERSTELLAR MEDIUM CONDITIONS: THE EVOLUTION OF ORGANICS FROM DIFFUSE INTERSTELLAR CLOUDS TO THE SOLAR SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mennella, Vito, E-mail: mennella@na.astro.i

2010-08-01

We present the results of experiments aimed at studying the interaction of hydrogen atoms at 80 K with carbon grains covered with a water ice layer at 12 K. The effects of H processing have been analyzed, using IR spectroscopy, as a function of the water ice layer. The results confirm that exposure of the samples to H atoms induces the activation of the band at 3.47 {mu}m with no evidence for the formation of aromatic and aliphatic C-H bonds in the CH{sub 2} and CH{sub 3} functional groups. The formation cross section of the 3.47 {mu}m band has beenmore » estimated from the increase of its integrated optical depth as a function of the H atom fluence. The cross section decreases with increasing thickness of the water ice layer, indicating an increase of adsorption of H atoms in the water ice layer. A penetration depth of 100 nm has been estimated for H atoms in the porous water ice covering carbon grains. Sample warm-up at room temperature causes the activation of the IR features due to the vibrations of the CH{sub 2} and CH{sub 3} aliphatic functional groups. The evolution of the 3.47 {mu}m band carrier has been evaluated for dense and diffuse interstellar clouds, using the estimated formation cross section and assuming that the destruction cross section by energetic processing is the same as that derived for the 3.4 {mu}m band. In both environments, the presence of the 3.47 {mu}m band carrier is compatible with the evolutionary timescale limit imposed by fast cycling of materials between dense and diffuse regions of the interstellar medium. In diffuse regions the formation of the CH{sub 2} and CH{sub 3} aliphatic bands, inhibited in dense regions, takes place, masking the 3.47 {mu}m band. The activation of the CH{sub 2} and CH{sub 3} aliphatic vibrational modes at the end of H processing after sample warm-up represents the first experimental evidence supporting an evolutionary connection between the interstellar carbon grain population, which is responsible for the 3.4 {mu}m band (diffuse regions) and contributes to the absorption at 3.47 {mu}m (dense regions), and the organics observed in interplanetary dust particles and cometary Stardust grains.« less

Close Range Photogrammetry Applied to the Documentation of AN Archaeological Site in Gaza Strip, Palestine

NASA Astrophysics Data System (ADS)

Alby, E.; Elter, R.; Ripoche, C.; Quere, N.; de Strasbourg, INSA

2013-07-01

In a geopolitical very complex context as the Gaza Strip it has to be dealt with an enhancement of an archaeological site. This site is the monastery of St. Hilarion. To enable a cultural appropriation of a place with several identified phases of occupation must undertake extensive archaeological excavation. Excavate in this geographical area is to implement emergency excavations, so the aim of such a project can be questioned for each mission. Real estate pressure is also a motivating setting the documentation because the large population density does not allow systematic studies of underground before construction projects. This is also during the construction of a road that the site was discovered. Site dimensions are 150 m by 80 m. It is located on a sand dune, 300 m from the sea. To implement the survey, four different levels of detail have been defined for terrestrial photogrammetry. The first level elements are similar to objects, capitals, fragment of columns, tiles for example. Modeling of small objects requires the acquisition of very dense point clouds (density: 1 point / 1 mm on average). The object must then be a maximum area of the sensor of the camera, while retaining in the field of view a reference pattern for the scaling of the point cloud generated. The pictures are taken at a short distance from the object, using the images at full resolution. The main obstacle to the modeling of objects is the presence of noise partly due to the studied materials (sand, smooth rock), which do not favor the detection of points of interest quality. Pretreatments of the cloud will be achieved meticulously since the ouster of points on a surface of a small object results in the formation of a hole with a lack of information, useful to resulting mesh. Level 2 focuses on the stratigraphic units such as mosaics. The monastery of St. Hilarion identifies thirteen floors of which has been documented years ago by silver photographs, scanned later. Modeling of pavements is to obtain a three-dimensional model of the mosaic in particular to analyze the subsidence, which it may be subjected. The dense point cloud can go beyond by including the geometric shapes of the pavement. The calculation mesh using high-density point cloud colorization allows cloud sufficient to final rendering. Levels 3 and 4 will allow the survey and representation of loci and sectors. Their modeling can be done by colored mesh or textured by a generic pattern but also by geometric primitives. This method requires the segmentation simple geometrical elements and creates a surface geometry by analysis of the sample points. Statistical tools allow the extraction plans meet the requirements of the operator can monitor quantitatively the quality of the final rendering. Each level has constraints on the accuracy of survey and types of representation especially from the point clouds, which are detailed in the complete article.

Fleets of enduring drones to probe atmospheric phenomena with clouds

NASA Astrophysics Data System (ADS)

Lacroix, Simon; Roberts, Greg; Benard, Emmanuel; Bronz, Murat; Burnet, Frédéric; Bouhoubeiny, Elkhedim; Condomines, Jean-Philippe; Doll, Carsten; Hattenberger, Gautier; Lamraoui, Fayçal; Renzaglia, Alessandro; Reymann, Christophe

2016-04-01

A full spatio-temporal four-dimensional characterization of the microphysics and dynamics of cloud formation including the onset of precipitation has never been reached. Such a characterization would yield a better understanding of clouds, e.g. to assess the dominant mixing mechanism and the main source of cloudy updraft dilution. It is the sampling strategy that matters: fully characterizing the evolution over time of the various parameters (P, T, 3D wind, liquid water content, aerosols...) within a cloud volume requires dense spatial sampling for durations of the order of one hour. A fleet of autonomous lightweight UAVs that coordinate themselves in real-time as an intelligent network can fulfill this purpose. The SkyScanner project targets the development of a fleet of autonomous UAVs to adaptively sample cumuli, so as to provide relevant data to address long standing questions in atmospheric science. It mixes basic researches and experimental developments, and gathers scientists in UAV conception, in optimal flight control, in intelligent cooperative behaviors, and of course atmospheric scientists. Two directions of researches are explored: optimal UAV conception and control, and optimal control of a fleet of UAVs. The design of UAVs for atmospheric science involves the satisfaction of trade-offs between payload, endurance, ease of deployment... A rational conception scheme that integrates the constraints to optimize a series of criteria, in particular energy consumption, would yield the definition of efficient UAVs. This requires a fine modeling of each involved sub-system and phenomenon, from the motor/propeller efficiency to the aerodynamics at small scale, including the flight control algorithms. The definition of mission profiles is also essential, considering the aerodynamics of clouds, to allow energy harvesting schemes that exploit thermals or gusts. The conception also integrates specific sensors, in particular wind sensor, for which classic technologies are challenged at the low speeds of lightweight UAVs. The overall control of the fleet so as to gather series of synchronized data in the cloud volume is a poorly informed and highly constrained adaptive sampling problem, in which the UAV motions must be defined to maximize the amount of gathered information and the mission duration. The overall approach casts the problem in a hierarchy of two modeling and decision stages. A macroscopic parametrized model of the cloud is built from the gathered data and exploited at the higher level by an operator, who sets information gathering goals. A subset of the UAV fleet is allocated to each goal, considering the current fleet state. These high level goals are handled by the lower level, which autonomously optimizes the selected UAVs trajectories using an on-line updated dense model of the variables of interest. Building the models involves Gaussian processes techniques (kriging) to fuse the gathered data with a generic cumulus conceptual model, the latter being defined from thorough statistics on realistic MesoNH cloud simulations. The model is exploited by a planner to generate trajectories that minimize the uncertainty in the map, while steering the vehicles within the air flows to save energy.

D Point Cloud Model Colorization by Dense Registration of Digital Images

NASA Astrophysics Data System (ADS)

Crombez, N.; Caron, G.; Mouaddib, E.

2015-02-01

Architectural heritage is a historic and artistic property which has to be protected, preserved, restored and must be shown to the public. Modern tools like 3D laser scanners are more and more used in heritage documentation. Most of the time, the 3D laser scanner is completed by a digital camera which is used to enrich the accurate geometric informations with the scanned objects colors. However, the photometric quality of the acquired point clouds is generally rather low because of several problems presented below. We propose an accurate method for registering digital images acquired from any viewpoints on point clouds which is a crucial step for a good colorization by colors projection. We express this image-to-geometry registration as a pose estimation problem. The camera pose is computed using the entire images intensities under a photometric visual and virtual servoing (VVS) framework. The camera extrinsic and intrinsic parameters are automatically estimated. Because we estimates the intrinsic parameters we do not need any informations about the camera which took the used digital image. Finally, when the point cloud model and the digital image are correctly registered, we project the 3D model in the digital image frame and assign new colors to the visible points. The performance of the approach is proven in simulation and real experiments on indoor and outdoor datasets of the cathedral of Amiens, which highlight the success of our method, leading to point clouds with better photometric quality and resolution.

Non-destructive evaluation of laboratory scale hydraulic fracturing using acoustic emission

NASA Astrophysics Data System (ADS)

Hampton, Jesse Clay

The primary objective of this research is to develop techniques to characterize hydraulic fractures and fracturing processes using acoustic emission monitoring based on laboratory scale hydraulic fracturing experiments. Individual microcrack AE source characterization is performed to understand the failure mechanisms associated with small failures along pre-existing discontinuities and grain boundaries. Individual microcrack analysis methods include moment tensor inversion techniques to elucidate the mode of failure, crack slip and crack normal direction vectors, and relative volumetric deformation of an individual microcrack. Differentiation between individual microcrack analysis and AE cloud based techniques is studied in efforts to refine discrete fracture network (DFN) creation and regional damage quantification of densely fractured media. Regional damage estimations from combinations of individual microcrack analyses and AE cloud density plotting are used to investigate the usefulness of weighting cloud based AE analysis techniques with microcrack source data. Two granite types were used in several sample configurations including multi-block systems. Laboratory hydraulic fracturing was performed with sample sizes ranging from 15 x 15 x 25 cm3 to 30 x 30 x 25 cm 3 in both unconfined and true-triaxially confined stress states using different types of materials. Hydraulic fracture testing in rock block systems containing a large natural fracture was investigated in terms of AE response throughout fracture interactions. Investigations of differing scale analyses showed the usefulness of individual microcrack characterization as well as DFN and cloud based techniques. Individual microcrack characterization weighting cloud based techniques correlated well with post-test damage evaluations.

Rapid, semi-automatic fracture and contact mapping for point clouds, images and geophysical data

NASA Astrophysics Data System (ADS)

Thiele, Samuel T.; Grose, Lachlan; Samsu, Anindita; Micklethwaite, Steven; Vollgger, Stefan A.; Cruden, Alexander R.

2017-12-01

The advent of large digital datasets from unmanned aerial vehicle (UAV) and satellite platforms now challenges our ability to extract information across multiple scales in a timely manner, often meaning that the full value of the data is not realised. Here we adapt a least-cost-path solver and specially tailored cost functions to rapidly interpolate structural features between manually defined control points in point cloud and raster datasets. We implement the method in the geographic information system QGIS and the point cloud and mesh processing software CloudCompare. Using these implementations, the method can be applied to a variety of three-dimensional (3-D) and two-dimensional (2-D) datasets, including high-resolution aerial imagery, digital outcrop models, digital elevation models (DEMs) and geophysical grids. We demonstrate the algorithm with four diverse applications in which we extract (1) joint and contact patterns in high-resolution orthophotographs, (2) fracture patterns in a dense 3-D point cloud, (3) earthquake surface ruptures of the Greendale Fault associated with the Mw7.1 Darfield earthquake (New Zealand) from high-resolution light detection and ranging (lidar) data, and (4) oceanic fracture zones from bathymetric data of the North Atlantic. The approach improves the consistency of the interpretation process while retaining expert guidance and achieves significant improvements (35-65 %) in digitisation time compared to traditional methods. Furthermore, it opens up new possibilities for data synthesis and can quantify the agreement between datasets and an interpretation.

Aerosol-Cloud Interactions in the South-East Atlantic: Knowledge Gaps, Planned Observations to Address Them, and Implications for Global Climate Change Modeling

NASA Technical Reports Server (NTRS)

Redemann, Jens; Wood, R.; Zuidema, P.; Haywood, J.; Luna, B.; Abel, S.

2015-01-01

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical Stratocumulus (Sc) cloud decks in the world. The stratocumulus "climate radiators" are critical to the regional and global climate system. They interact with dense layers of BB aerosols that initially overlay the cloud deck, but later subside and are mixed into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects. As emphasized in the latest IPCC report, the global representation of these aerosol-cloud interaction processes in climate models is one of the largest uncertainty in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for global climate change scenarios. We discuss the current knowledge of aerosol and cloud property distributions based on satellite observations and sparse suborbital sampling, and describe planned field campaigns in the region. Specifically, we describe the scientific objectives and implementation of the following four synergistic, international research activities aimed at providing a process-level understanding of aerosol-cloud interactions over the SE Atlantic: 1) ORACLES (Observations of Aerosols above Clouds and their interactions), a five-year investigation between 2015 and 2019 with three Intensive Observation Periods (IOP), recently funded by the NASA Earth-Venture Suborbital Program, 2) CLARIFY-2016 (Cloud-Aerosol-Radiation Interactions and Forcing: Year 2016), a comprehensive observational and modeling programme funded by the UK's Natural Environment Research Council (NERC), and supported by the UK Met Office. 3) LASIC (Layered Atlantic Smoke Interactions with Clouds), a funded deployment of the DOE (Department of Energy) ARM Mobile Facility (AMF1) to Ascension Island, nominally for April 1 2016 - March 31 2017, and 4) ONFIRE (Observations of Fire's Impact on the southeast Atlantic Region), a proposed deployment of the NCAR C-130 aircraft to Sao Tome Island in 2017.

The destruction of an Oort Cloud in a rich stellar cluster

NASA Astrophysics Data System (ADS)

Nordlander, T.; Rickman, H.; Gustafsson, B.

2017-07-01

Context. It is possible that the formation of the Oort Cloud dates back to the earliest epochs of solar system history. At that time, the Sun was almost certainly a member of the stellar cluster where it was born. Since the solar birth cluster is likely to have been massive (103-104ℳ⊙), and therefore long-lived, an issue concerns the survival of such a primordial Oort Cloud. Aims: We have investigated this issue by simulating the orbital evolution of Oort Cloud comets for several hundred Myr, assuming the Sun to start its life as a typical member of such a massive cluster. Methods: We have devised a synthetic representation of the relevant dynamics, where the cluster potential is represented by a King model, and about 20 close encounters with individual cluster stars are selected and integrated based on the solar orbit and the cluster structure. Thousands of individual simulations are made, each including 3000 comets with orbits with three different initial semi-major axes. Results: Practically the entire initial Oort Cloud is found to be lost for our choice of semi-major axes (5000-20 000 au), independent of the cluster mass, although the chance of survival is better for the smaller cluster, since in a certain fraction of the simulations the Sun orbits at relatively safe distances from the dense cluster centre. Conclusions: For the range of birth cluster sizes that we investigate, a primordial Oort Cloud will likely survive only as a small inner core with semi-major axes ≲3000 au. Such a population of comets would be inert to orbital diffusion into an outer halo and subsequent injection into observable orbits. Some mechanism is therefore needed to accomplish this transfer, in case the Oort Cloud is primordial and the birth cluster did not have a low mass. From this point of view, our results lend some support to a delayed formation of the Oort Cloud, that occurred after the Sun had left its birth cluster.

Object-Based Coregistration of Terrestrial Photogrammetric and ALS Point Clouds in Forested Areas

NASA Astrophysics Data System (ADS)

Polewski, P.; Erickson, A.; Yao, W.; Coops, N.; Krzystek, P.; Stilla, U.

2016-06-01

Airborne Laser Scanning (ALS) and terrestrial photogrammetry are methods applicable for mapping forested environments. While ground-based techniques provide valuable information about the forest understory, the measured point clouds are normally expressed in a local coordinate system, whose transformation into a georeferenced system requires additional effort. In contrast, ALS point clouds are usually georeferenced, yet the point density near the ground may be poor under dense overstory conditions. In this work, we propose to combine the strengths of the two data sources by co-registering the respective point clouds, thus enriching the georeferenced ALS point cloud with detailed understory information in a fully automatic manner. Due to markedly different sensor characteristics, coregistration methods which expect a high geometric similarity between keypoints are not suitable in this setting. Instead, our method focuses on the object (tree stem) level. We first calculate approximate stem positions in the terrestrial and ALS point clouds and construct, for each stem, a descriptor which quantifies the 2D and vertical distances to other stem centers (at ground height). Then, the similarities between all descriptor pairs from the two point clouds are calculated, and standard graph maximum matching techniques are employed to compute corresponding stem pairs (tiepoints). Finally, the tiepoint subset yielding the optimal rigid transformation between the terrestrial and ALS coordinate systems is determined. We test our method on simulated tree positions and a plot situated in the northern interior of the Coast Range in western Oregon, USA, using ALS data (76 x 121 m2) and a photogrammetric point cloud (33 x 35 m2) derived from terrestrial photographs taken with a handheld camera. Results on both simulated and real data show that the proposed stem descriptors are discriminative enough to derive good correspondences. Specifically, for the real plot data, 24 corresponding stems were coregistered with an average 2D position deviation of 66 cm.

MobileFusion: real-time volumetric surface reconstruction and dense tracking on mobile phones.

PubMed

Ondrúška, Peter; Kohli, Pushmeet; Izadi, Shahram

2015-11-01

We present the first pipeline for real-time volumetric surface reconstruction and dense 6DoF camera tracking running purely on standard, off-the-shelf mobile phones. Using only the embedded RGB camera, our system allows users to scan objects of varying shape, size, and appearance in seconds, with real-time feedback during the capture process. Unlike existing state of the art methods, which produce only point-based 3D models on the phone, or require cloud-based processing, our hybrid GPU/CPU pipeline is unique in that it creates a connected 3D surface model directly on the device at 25Hz. In each frame, we perform dense 6DoF tracking, which continuously registers the RGB input to the incrementally built 3D model, minimizing a noise aware photoconsistency error metric. This is followed by efficient key-frame selection, and dense per-frame stereo matching. These depth maps are fused volumetrically using a method akin to KinectFusion, producing compelling surface models. For each frame, the implicit surface is extracted for live user feedback and pose estimation. We demonstrate scans of a variety of objects, and compare to a Kinect-based baseline, showing on average ∼ 1.5cm error. We qualitatively compare to a state of the art point-based mobile phone method, demonstrating an order of magnitude faster scanning times, and fully connected surface models.

a Robust Registration Algorithm for Point Clouds from Uav Images for Change Detection

NASA Astrophysics Data System (ADS)

Al-Rawabdeh, A.; Al-Gurrani, H.; Al-Durgham, K.; Detchev, I.; He, F.; El-Sheimy, N.; Habib, A.

2016-06-01

Landslides are among the major threats to urban landscape and manmade infrastructure. They often cause economic losses, property damages, and loss of lives. Temporal monitoring data of landslides from different epochs empowers the evaluation of landslide progression. Alignment of overlapping surfaces from two or more epochs is crucial for the proper analysis of landslide dynamics. The traditional methods for point-cloud-based landslide monitoring rely on using a variation of the Iterative Closest Point (ICP) registration procedure to align any reconstructed surfaces from different epochs to a common reference frame. However, sometimes the ICP-based registration can fail or may not provide sufficient accuracy. For example, point clouds from different epochs might fit to local minima due to lack of geometrical variability within the data. Also, manual interaction is required to exclude any non-stable areas from the registration process. In this paper, a robust image-based registration method is introduced for the simultaneous evaluation of all registration parameters. This includes the Interior Orientation Parameters (IOPs) of the camera and the Exterior Orientation Parameters (EOPs) of the involved images from all available observation epochs via a bundle block adjustment with self-calibration. Next, a semi-global dense matching technique is implemented to generate dense 3D point clouds for each epoch using the images captured in a particular epoch separately. The normal distances between any two consecutive point clouds can then be readily computed, because the point clouds are already effectively co-registered. A low-cost DJI Phantom II Unmanned Aerial Vehicle (UAV) was customised and used in this research for temporal data collection over an active soil creep area in Lethbridge, Alberta, Canada. The customisation included adding a GPS logger and a Large-Field-Of-View (LFOV) action camera which facilitated capturing high-resolution geo-tagged images in two epochs over the period of one year (i.e., May 2014 and May 2015). Note that due to the coarse accuracy of the on-board GPS receiver (e.g., +/- 5-10 m) the geo-tagged positions of the images were only used as initial values in the bundle block adjustment. Normal distances, signifying detected changes, varying from 20 cm to 4 m were identified between the two epochs. The accuracy of the co-registered surfaces was estimated by comparing non-active patches within the monitored area of interest. Since these non-active sub-areas are stationary, the computed normal distances should theoretically be close to zero. The quality control of the registration results showed that the average normal distance was approximately 4 cm, which is within the noise level of the reconstructed surfaces.

Toward Gas Chemistry in Low Metallicity Starburst Galaxies

NASA Astrophysics Data System (ADS)

Meier, David S.; Anderson, Crystal N.; Turner, Jean; Ott, Juergen; Beck, Sara C.

2017-01-01

Dense gas, which is intimately connected with star formation, is key to understanding star formation. Though challenging to study, dense gas in low metallicity starbursts is important given these system's often extreme star formation and their potential implications for high redshift analogs. High spatial resolution (~50 pc) ALMA observations of several key probes of gas chemistry, including HCN(1-0), HCO+(1-0), CS(2-1), CCH(1-0;3/2-1/2) and SiO(2-1), towards the nearby super star-cluster (SSC) forming, sub-solar metallicity galaxy NGC 5253 are discussed. Dense gas is observed to be extended well beyond the current compact starburst, reaching into the apparently infalling molecular streamer. The faintness of HCN, the standard dense gas tracer, is extreme both in an absolute sense relative to high metallicity starbursts of a similar intensity and in a relative sense, with the HCO+/HCN ratio being one of the most elevated observed. UV-irradiated molecular gas, traced by CCH, is also extended over the mapped region, not being strongly correlated with the SSC. Despite the accretion of molecular gas from the halo and the intense burst of star formation, chemical signatures of shocked gas, traced by SiO (and HNCO), are not obvious. By placing NGC 5253 in context with other local starbursts, like 30 Doradus in the Large Magellanic Clouds and the high metallicity proto-typical starburst NGC 253, it is suggested that a combination of gas excitation and abundance changes associated with the sub solar metallicity may explain these anomalous dense gas properties.

VizieR Online Data Catalog: Evolution of rotating very massive LC stars (Kohler, 2015)

NASA Astrophysics Data System (ADS)

Kohler, K.; Langer, N.; de Koter, A.; de Mink, S. E.; Crowther, P. A.; Evans, C. J.; Grafener, G.; Sana, H.; Sanyal, D.; Schneider, F. R. N.; Vink, J. S.

2014-11-01

A dense model grid with chemical composition appropriate for the Large Magellanic Cloud is presented. A one-dimensional hydrodynamic stellar evolution code was used to compute our models on the main sequence, taking into account rotation, transport of angular momentum by magnetic fields and stellar wind mass loss. We present stellar evolution models with initial masses of 70-500M⊙ and with initial surface rotational velocities of 0-550km/s. (2 data files).

Expedition Seven Takes Breathtaking Photo of Earth's Atmosphere

NASA Technical Reports Server (NTRS)

2003-01-01

This Expedition Seven image, taken while aboard the International Space Station (ISS), shows the limb of the Earth at the bottom transitioning into the orange-colored stratosphere, the lowest and most dense portion of the Earth's atmosphere. The troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue-colored atmosphere. The silvery blue noctilucent clouds extend far above the Earth's troposphere. The silver of the setting moon is visible at upper right.

Ocean and Polarization Observations from Active Remote Sensing: Atmospheric and Ocean Science Applications

DTIC Science & Technology

2015-11-05

shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number...ratio of cirrus clouds2 • The analysis of the precipitable water and development of a new Millimeter-Wave Propagation Model for the W-Band...Distribution Function ( BRDF )12. As we are studying dense surface signal, saturation may happen for the strongest values of the ocean surface signal8

Interstellar Dust: Contributed Papers

NASA Technical Reports Server (NTRS)

Tielens, Alexander G. G. M. (Editor); Allamandola, Louis J. (Editor)

1989-01-01

A coherent picture of the dust composition and its physical characteristics in the various phases of the interstellar medium was the central theme. Topics addressed included: dust in diffuse interstellar medium; overidentified infrared emission features; dust in dense clouds; dust in galaxies; optical properties of dust grains; interstellar dust models; interstellar dust and the solar system; dust formation and destruction; UV, visible, and IR observations of interstellar extinction; and quantum-statistical calculations of IR emission from highly vibrationally excited polycyclic aromatic hydrocarbon (PAH) molecules.

Observations of molecular and atomic gas in photodissociation regions. [interstellar chemistry

NASA Technical Reports Server (NTRS)

Jaffe, D. T.; Howe, J. E.

1989-01-01

Dense gas at the ionized/neutral boundaries of molecular clouds illuminated by far-UV photons plays an important role in the appearance of the neutral interstellar medium. It also is a laboratory for the study of UV-photochemistry and of a number of heating and cooling phenomena not seen elsewhere. Fine structure lines of neutral and low ionization potential species dominate the cooling in the outer part of the photodissociation regions. Observations of these lines show that the regions are dense and highly clumped. Observations of H2 and CO show that heating by UV photons plays a significant role in the excitation of molecular lines near the H II/neutral boundary. Warm CO is more abundant in these regions than predicted by the standard theoretical models. Optical reflection nebulas provide an ideal laboratory for the study of photodissocciation region phenomena.

Analysis of interstellar fragmentation structure based on IRAS images

NASA Technical Reports Server (NTRS)

Scalo, John M.

1989-01-01

The goal of this project was to develop new tools for the analysis of the structure of densely sampled maps of interstellar star-forming regions. A particular emphasis was on the recognition and characterization of nested hierarchical structure and fractal irregularity, and their relation to the level of star formation activity. The panoramic IRAS images provided data with the required range in spatial scale, greater than a factor of 100, and in column density, greater than a factor of 50. In order to construct a densely sampled column density map of a cloud complex which is both self-gravitating and not (yet?) stirred up much by star formation, a column density image of the Taurus region has been constructed from IRAS data. The primary drawback to using the IRAS data for this purpose is that it contains no velocity information, and the possible importance of projection effects must be kept in mind.

Recording Approach of Heritage Sites Based on Merging Point Clouds from High Resolution Photogrammetry and Terrestrial Laser Scanning

NASA Astrophysics Data System (ADS)

Grussenmeyer, P.; Alby, E.; Landes, T.; Koehl, M.; Guillemin, S.; Hullo, J. F.; Assali, P.; Smigiel, E.

2012-07-01

Different approaches and tools are required in Cultural Heritage Documentation to deal with the complexity of monuments and sites. The documentation process has strongly changed in the last few years, always driven by technology. Accurate documentation is closely relied to advances of technology (imaging sensors, high speed scanning, automation in recording and processing data) for the purposes of conservation works, management, appraisal, assessment of the structural condition, archiving, publication and research (Patias et al., 2008). We want to focus in this paper on the recording aspects of cultural heritage documentation, especially the generation of geometric and photorealistic 3D models for accurate reconstruction and visualization purposes. The selected approaches are based on the combination of photogrammetric dense matching and Terrestrial Laser Scanning (TLS) techniques. Both techniques have pros and cons and recent advances have changed the way of the recording approach. The choice of the best workflow relies on the site configuration, the performances of the sensors, and criteria as geometry, accuracy, resolution, georeferencing, texture, and of course processing time. TLS techniques (time of flight or phase shift systems) are widely used for recording large and complex objects and sites. Point cloud generation from images by dense stereo or multi-view matching can be used as an alternative or as a complementary method to TLS. Compared to TLS, the photogrammetric solution is a low cost one, as the acquisition system is limited to a high-performance digital camera and a few accessories only. Indeed, the stereo or multi-view matching process offers a cheap, flexible and accurate solution to get 3D point clouds. Moreover, the captured images might also be used for models texturing. Several software packages are available, whether web-based, open source or commercial. The main advantage of this photogrammetric or computer vision based technology is to get at the same time a point cloud (the resolution depends on the size of the pixel on the object), and therefore an accurate meshed object with its texture. After matching and processing steps, we can use the resulting data in much the same way as a TLS point cloud, but in addition with radiometric information for textures. The discussion in this paper reviews recording and important processing steps as geo-referencing and data merging, the essential assessment of the results, and examples of deliverables from projects of the Photogrammetry and Geomatics Group (INSA Strasbourg, France).