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Sample records for high-velocity narrow circumstellar

  1. NARROW-GAP POINT-TO-PLANE CORONA WITH HIGH VELOCITY FLOWS

    EPA Science Inventory

    The article discusses a mathematical model developed to describe a narrow- gap point- to- plane corona system used in the detoxification of chemical agents or their simulants, for which the degree of destruction depends on the strength of the electric field or electron energy. Na...

  2. Radio-loud narrow-line Seyfert 1 galaxies with high-velocity outflows

    NASA Astrophysics Data System (ADS)

    Komossa, S.; Xu, D.; Zensus, J. A.

    2016-02-01

    We have studied four radio-loud Narrow-line Seyfert 1 (NLS1) galaxies with extreme optical emission-line shifts, indicating radial outflow velocities of up 2450 km s-1. The shifts are accompanied by strong line broadening, up to 2270 km s-1 in [NeV]. A significant ionization stratification (higher line shift at higher ionization potential) of most ions implies that we see a large-scale wind rather than single, localized jet-cloud interactions. The observations are consistent with a scenario, where the signatures of outflows are maximized because of a pole-on view into the central engine of these radio-loud NLS1 galaxies.

  3. High Velocity Gas Gun

    NASA Technical Reports Server (NTRS)

    1988-01-01

    A video tape related to orbital debris research is presented. The video tape covers the process of loading a High Velocity Gas Gun and firing it into a mounted metal plate. The process is then repeated in slow motion.

  4. Circumstellar chemistry

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.; Mamon, G. A.

    1991-01-01

    Recent theoretical studies of circumstellar chemistry are discussed for both red-giant and protostellar winds. The generalized photochemical model is able to account for the recently discovered silicon-bearing molecules in the prototypical, C-rich, AGB star IRC + 10216. The surprising occurrence of CO in protostellar winds that are largely atomic is interpreted to be the result of the high density and the rapid decrease of the temperature with distance that is expected for such winds.

  5. Dust in High Velocity Clouds

    NASA Astrophysics Data System (ADS)

    Wakker, B. P.

    The facilities available in Groningen to produce IRAS maps were used to make comparatively high-quality maps of two fields where a high-velocity cloud (HVC) is observed in the 21-cm line. The HVC's are not discernable in these maps although one would expect to see them if the relation between 100 micron emission and H I column density found by Boulanger, Baud & van Albada (1985) is used. The implications of this non-detection are discussed in this contribution.

  6. High-Velocity Absorption Features in FUSE Spectra of Eta Carinae

    NASA Astrophysics Data System (ADS)

    Sonneborn, G.; Iping, R. C.; Gull, T. R.; Vieira, G.

    2002-12-01

    Numerous broad (200 to 1000 km/sec) features in the FUSE spectrum (905-1187 A) of eta Carinae are identified as absorption by a forest of high-velocity narrow lines formed in the expanding circumstellar envelope. These features were previously thought to be P-Cygni lines arising in the wind of the central star. The features span a heliocentric velocity range of -140 to -580 km/sec and are seen prominently in low-ionization ground-state transitions (e.g. N I 1134-35, Fe II 1145-42, 1133, 1127-22, P II 1153, C I 1158) in addition to C III] 1176 A. The high-velocity components of the FUSE transitions have depths about 50% below the continuum. The identifications are consistent with the complex velocity structures seen in ground- and excited-state transitions of Mg I, Mg II, Fe II, V II, etc observed in STIS/E230H spectra (see accompanying posters by Gull, Vieira, and Danks). The origin of other broad features of similar width and depth in the FUSE spectrum, but without low-velocity ISM absorption, are unidentified. However, they are suspected of being absorption of singly-ionized iron-peak elements (e.g. Fe II, V II, Cr II) out of excited levels 1,000 to 20,000 cmE-1 above the ground state. The high-velocity features seen in Fe II 1145 are also present in Fe II 1608 (STIS/E140M), but are highly saturated in the latter. Since these transitions have nearly identical log (flambda) (1.998 vs. 2.080), the differences in the profiles are attributable to the different aperture sizes used (30x30 arcsec for FUSE, 0.2x0.2 arcsec for STIS/E140M). The high-velocity gas appears to be very patchy or has a small covering factor near the central star. Eta Carinae has been observed several times by FUSE over the past three years. The FUSE flux levels and spectral features in eta Car are essentially unchanged over the 2000 March to June 2002 period, establishing a baseline far-UV spectrum in advance of the predicted spectroscopic miniumum in 2003.

  7. High-Velocity Absorption Features in FUSE Spectra of Eta Carinae

    NASA Technical Reports Server (NTRS)

    Sonneborn, G.; Iping, R. C.; Gull, T. R.; Vieira, G.

    2003-01-01

    Numerous broad (200 to 1000 km/sec) features in the FUSE spectrum (905-1187 A) of eta Carinae are identified as absorption by a forest of high-velocity narrow lines formed in the expanding circumstellar envelope. These features were previously thought to be P-Cygni lines arising in the wind of the central star. The features span a heliocentric velocity range of -140 to -580 km/sec and are seen prominently in low-ionization ground-state transitions (e.g. N I 1134-35, Fe II 1145-42, 1133, 1127- 22, P II 1153, C I 1158) in addition to C III] 1176 A. The high-velocity components of the FUSE transitions have depths about 50% below the continuum. The identifications are consistent with the complex velocity structures seen in ground- and excited-state transitions of Mg I, Mg 11, Fe II, V II, etc observed in STIS/E230H spectra. The origin of other broad features of similar width and depth in the FUSE spectrum, but without low-velocity ISM absorption, are unidentified. However, they are suspected of being absorption of singly-ionized iron-peak elements (e.g. Fe II, V II, Cr II) out of excited levels 1,000 to 20,000 cmE-l above the ground state. The high-velocity features seen in Fe II 1145 are also present in Fe II 1608 (STIS/E140M), but are highly saturated in the latter. Since these transitions have nearly identical log (flambda) (1.998 vs. 2.080), the differences in the profiles are attributable to the different aperture sizes used (30 x 30 arcsec for FUSE, 0.2 x 0.2 arcsec for STIS/E140M). The high-velocity gas appears to be very patchy or has a small covering factor near the central star. Eta Carinae has been observed several times by FUSE over the past three years. The FUSE flux levels and spectral features in eta Car are essentially unchanged over the 2000 March to June 2002 period, establishing a baseline far-UV spectrum in advance of the predicted spectroscopic minimum in 2003.

  8. Massive stars exploding in a He-rich circumstellar medium - VII. The metamorphosis of ASASSN-15ed from a narrow line Type Ibn to a normal Type Ib Supernova

    NASA Astrophysics Data System (ADS)

    Pastorello, A.; Prieto, J. L.; Elias-Rosa, N.; Bersier, D.; Hosseinzadeh, G.; Morales-Garoffolo, A.; Noebauer, U. M.; Taubenberger, S.; Tomasella, L.; Kochanek, C. S.; Falco, E.; Basu, U.; Beacom, J. F.; Benetti, S.; Brimacombe, J.; Cappellaro, E.; Danilet, A. B.; Dong, Subo; Fernandez, J. M.; Goss, N.; Granata, V.; Harutyunyan, A.; Holoien, T. W.-S.; Ishida, E. E. O.; Kiyota, S.; Krannich, G.; Nicholls, B.; Ochner, P.; Pojmański, G.; Shappee, B. J.; Simonian, G. V.; Stanek, K. Z.; Starrfield, S.; Szczygieł, D.; Tartaglia, L.; Terreran, G.; Thompson, T. A.; Turatto, M.; Wagner, R. M.; Wiethoff, W. S.; Wilber, A.; Woźniak, P. R.

    2015-11-01

    We present the results of the spectroscopic and photometric monitoring campaign of ASASSN-15ed. The transient was discovered quite young by the All Sky Automated Survey for SuperNovae (ASAS-SN) survey. Amateur astronomers allowed us to sample the photometric SN evolution around maximum light, which we estimate to have occurred on JD = 2457087.4 ± 0.6 in the r band. Its apparent r-band magnitude at maximum was r = 16.91 ± 0.10, providing an absolute magnitude Mr ≈ -20.04 ± 0.20, which is slightly more luminous than the typical magnitudes estimated for Type Ibn SNe. The post-peak evolution was well monitored, and the decline rate (being in most bands around 0.1 mag d-1 during the first 25 d after maximum) is marginally slower than the average decline rates of SNe Ibn during the same time interval. The object was initially classified as a Type Ibn SN because early-time spectra were characterized by a blue continuum with superimposed narrow P-Cygni lines of He I, suggesting the presence of a slowly moving (1200-1500 km s-1), He-rich circumstellar medium. Later on, broad P-Cygni He I lines became prominent. The inferred velocities, as measured from the minimum of the broad absorption components, were between 6000 and 7000 km s-1. As we attribute these broad features to the SN ejecta, this is the first time we have observed the transition of a Type Ibn SN to a Type Ib SN.

  9. High velocity impact experiment (HVIE)

    SciTech Connect

    Toor, A.; Donich, T.; Carter, P.

    1998-02-01

    The HVIE space project was conceived as a way to measure the absolute EOS for approximately 10 materials at pressures up to {approximately}30 Mb with order-of-magnitude higher accuracy than obtainable in any comparable experiment conducted on earth. The experiment configuration is such that each of the 10 materials interacts with all of the others thereby producing one-hundred independent, simultaneous EOS experiments The materials will be selected to provide critical information to weapons designers, National Ignition Facility target designers and planetary and geophysical scientists. In addition, HVIE will provide important scientific information to other communities, including the Ballistic Missile Defense Organization and the lethality and vulnerability community. The basic HVIE concept is to place two probes in counter rotating, highly elliptical orbits and collide them at high velocity (20 km/s) at 100 km altitude above the earth. The low altitude of the experiment will provide quick debris strip-out of orbit due to atmospheric drag. The preliminary conceptual evaluation of the HVIE has found no show stoppers. The design has been very easy to keep within the lift capabilities of commonly available rides to low earth orbit including the space shuttle. The cost of approximately 69 million dollars for 100 EOS experiment that will yield the much needed high accuracy, absolute measurement data is a bargain!

  10. Circumstellar Interaction in SN 1993J

    NASA Astrophysics Data System (ADS)

    Fransson, Claes; Lundqvist, Peter; Chevalier, Roger A.

    1996-04-01

    The radio and X-ray observations of SN 1993J during the first year can be consistently explained as a result of interaction of the expanding ejecta with a circumstellar medium. The density of the circumstellar gas can be deduced from the free-free absorption of the radio emission and from the X-ray luminosity. During the first 2 weeks, both sets of observations indicate a mass loss-rate of ~4 x 10^-5^ M_sun_ yr^-1^ for a wind velocity of 10 km s^-1^. The subsequent radio and X-ray observations indicate a density gradient is proportional to r^-s^, with 1.5 <~ s <~ 1.7, as opposed to the r^-2^ gradient expected for a steady, spherically symmetric wind. This may be caused either by a variation of the mass-loss rate from the progenitor System or by a non-spherically symmetric geometry. To explain the properties of the X-ray emission, a steep density gradient in the ejecta is needed. During the first months, most of the observed X-ray emission originates from the circumstellar shock, which is adiabatic, while the reverse shock is radiative. To avoid excessive Comptonization in the X-ray range collisionless heating must be ineffective. The soft X-rays observed at 220 days probably originate from the reverse shock. The ionization and temperature structures of the circumstellar gas are calculated; we find that the temperature is in excess of 10^5^ K and the medium is nearly completely ionized by the shock radiation after the formation of the shocks. Preacceleration of the circumstellar gas by the radiation from the outbreak can explain the observed high velocity for the circumstellar N V and Hα lines. The high luminosity of the lines indicates that the circumstellar medium close to the supernova progenitor had a complex structure.

  11. High velocity gas in external galaxies

    NASA Technical Reports Server (NTRS)

    Kamphuis, J.; Vanderhulst, J. M.; Sancisi, R.

    1990-01-01

    Two nearby, nearly face-on spiral galaxies, M 101 and NGC 6946, observed in the HI with the Westerbork Synthesis Radio Telescope (WSRT) as part of a program to search for high velocity gas in other galaxies, are used to illustrate the range of properties of high velocity gas in other galaxies found thusfar.

  12. High velocity formability and factors affecting it

    NASA Astrophysics Data System (ADS)

    Dehra, Mala Seth

    High velocity forming methods successfully address problems faced in conventional forming techniques. They can be effectively used for forming metals with low formability like aluminum alloys and high strength steel. They can be instrumental is manufacturing of lighter vehicles with higher fuel efficiency. Electromagnetic forming (EMF) is an HVF method that is gaining wide acceptance due to its advantages and scope for commercialization. A number of experimental studies were carried out with EMF with the main goal of exploring fundamentals about material formability at high velocities, which can be used to establish practical design guidelines and to make models of high velocity formability. Thus the main factors that influence high velocity formability-inertia/size effects; changes in constitutive behavior; impact; and dynamic failure modes, were studied mainly with experiments. The role of changes in constitutive behavior in improving formability was studied from existing studies and new theoretical studies involving High velocity Forming Limit Diagram (FLD) and through solving an inverse problem of ring expansion. Tube free-expansion experiments were carried out to demonstrate enhanced metal formability even in the absence of die impact. To further establish the significance of inertia, electromagnetic ring free-expansion experiments with rings of different aspect ratios were carried out. A higher aspect ratio sample had better formability in terms of uniform and total elongation and also had fewer necks than a low aspect ratio (more slender) ring at the same velocity. The results clearly demonstrated the influence of sample aspect ratio (dimensions) and hence inertia on high velocity formability. Die impact experiments were carried out with tubes and rings to show the beneficial influence of die arrest of a moving sample. It was revealed that die impact in an appropriate range of velocities can significantly suppress failure and reduce the number of tears and

  13. A circumstellar molecular gas structure associated with the massive young star Cepheus A-HW 2

    NASA Technical Reports Server (NTRS)

    Torrelles, Jose M.; Rodriguez, Luis F.; Canto, Jorge; Ho, Paul T. P.

    1993-01-01

    We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of about 10-20 solar masses (B0.5 V star or earlier).

  14. High velocity pulsed wire-arc spray

    NASA Technical Reports Server (NTRS)

    Witherspoon, F. Douglas (Inventor); Massey, Dennis W. (Inventor); Kincaid, Russell W. (Inventor)

    1999-01-01

    Wire arc spraying using repetitively pulsed, high temperature gas jets, usually referred to as plasma jets, and generated by capillary discharges, substantially increases the velocity of atomized and entrained molten droplets. The quality of coatings produced is improved by increasing the velocity with which coating particles impact the coated surface. The effectiveness of wire-arc spraying is improved by replacing the usual atomizing air stream with a rapidly pulsed high velocity plasma jet. Pulsed power provides higher coating particle velocities leading to improved coatings. 50 micron aluminum droplets with velocities of 1500 m/s are produced. Pulsed plasma jet spraying provides the means to coat the insides of pipes, tubes, and engine block cylinders with very high velocity droplet impact.

  15. Composite circumstellar dust grains

    NASA Astrophysics Data System (ADS)

    Gupta, Ranjan; Vaidya, Dipak B.; Dutta, Rajeshwari

    2016-10-01

    We calculate the absorption efficiencies of composite silicate grains with inclusions of graphite and silicon carbide in the spectral range 5-25 μm. We study the variation in absorption profiles with volume fractions of inclusions. In particular we study the variation in the wavelength of peak absorption at 10 and 18 μm. We also study the variation of the absorption of porous silicate grains. We use the absorption efficiencies to calculate the infrared flux at various dust temperatures and compare with the observed infrared emission flux from the circumstellar dust around some M-type and asymptotic giant branch stars obtained from IRAS and a few stars from Spitzer satellite. We interpret the observed data in terms of the circumstellar dust grain sizes, shape, composition and dust temperature.

  16. Instrumented impact testing at high velocities

    SciTech Connect

    Delfosse, D.; Pageau, G.; Bennett, R.; Poursartip, A. Defence Research Establishment Valcartier, Courcelette )

    1993-01-01

    Impact loading of carbon fiber-reinforced plastic (CFRP) aircraft parts is a major concern. Birds or hailstones striking an aircraft generally have a low mass and a high velocity, whereas typically instrumented impact experiments are performed with a high mass and a low velocity. Our aim has been to build an instrumented impact facility with a low-mass projectile capable of simulating these impact events, since there is evidence that a low-velocity impact will not always result in the same amount or even type of damage as a high-velocity impact. This paper provides a detailed description of the instrumented low-mass impact facility at The University of British Columbia (UBC). A gas gun is used to accelerate the instrumented projectile to impact velocities as high as 50 m/s, corresponding to an energy level of 350 J. The contact force during the impact event is measured by an incorporated load cell. The necessary mathematical operations to determine the real load-displacement curves are outlined, and the results of some impact events at different velocities are shown. 23 refs.

  17. Consideration of wear rates at high velocity

    NASA Astrophysics Data System (ADS)

    Hale, Chad S.

    The development of the research presented here is one in which high velocity relative sliding motion between two bodies in contact has been considered. Overall, the wear environment is truly three-dimensional. The attempt to characterize three-dimensional wear was not economically feasible because it must be analyzed at the micro-mechanical level to get results. Thus, an engineering approximation was carried out. This approximation was based on a metallographic study identifying the need to include viscoplasticity constitutive material models, coefficient of friction, relationships between the normal load and velocity, and the need to understand wave propagation. A sled test run at the Holloman High Speed Test Track (HHSTT) was considered for the determination of high velocity wear rates. In order to adequately characterize high velocity wear, it was necessary to formulate a numerical model that contained all of the physical events present. The experimental results of a VascoMax 300 maraging steel slipper sliding on an AISI 1080 steel rail during a January 2008 sled test mission were analyzed. During this rocket sled test, the slipper traveled 5,816 meters in 8.14 seconds and reached a maximum velocity of 1,530 m/s. This type of environment was never considered previously in terms of wear evaluation. Each of the features of the metallography were obtained through micro-mechanical experimental techniques. The byproduct of this analysis is that it is now possible to formulate a model that contains viscoplasticity, asperity collisions, temperature and frictional features. Based on the observations of the metallographic analysis, these necessary features have been included in the numerical model, which makes use of a time-dynamic program which follows the movement of a slipper during its experimental test run. The resulting velocity and pressure functions of time have been implemented in the explicit finite element code, ABAQUS. Two-dimensional, plane strain models

  18. The structure of circumstellar shells

    NASA Technical Reports Server (NTRS)

    Fix, John D.

    1993-01-01

    This document provides a report on research activities carried out with the support of NASA grant NAG 5-1174, the Structure of Circumstellar Shells, funded under the Astrophysics Data Program. The research carried out with the support of this grant is a study of the properties of circumstellar dust shells for which spectra are available through IRAS low resolution spectrometry (LRS). This research consisted of the development and application of models of axisymmetric circumstellar shells and a preliminary survey of the applicability of neural nets for analysis of the IRAS LRS spectra of circumstellar dust shells.

  19. High velocity clouds in nearby disk galaxies

    NASA Technical Reports Server (NTRS)

    Schulman, Eric; Bregman, Joel N.; Roberts, Morton S.; Brinks, Elias

    1993-01-01

    Clouds of neutral hydrogen in our galaxy with the absolute value of v greater than 100 km/s cover approximately 10 percent of the sky to a limiting column density of 1 x 10(exp 18) cm(exp -2). These high velocity clouds (HVCs) may dominate the kinetic energy of neutral hydrogen in non-circular motion, and are an important though poorly understood component of galactic gas. It has been suggested that the HVCs can be reproduced by a combination of three phenomena: a galactic fountain driven by disk supernovae which would account for most of the HVCs, material tidally torn from the Magellanic Clouds, and an outer arm complex which is associated with the large scale structure of the warped galactic disk. We sought to detect HVCs in external galaxies in order to test the galactic fountain model.

  20. Flash-ionization of pre-existing circumstellar material around Nova Oph 2015

    NASA Astrophysics Data System (ADS)

    Munari, U.; Walter, F. M.

    2016-01-01

    We have obtained daily high-resolution Echelle spectroscopy of Nova Oph 2015 during its initial evolution. It reveals the presence of pre-existing circumstellar material around the nova, which can be interpreted as the wind of an evolved companion. On earliest observations, the emission line profiles of Nova Oph 2015 displayed a very narrow emission component (full width at half-maximum [FWHM] ˜ 60 km s-1), recombining over a time-scale of 5 days and showing constant low velocity (RV⊙ = -4.5 km s-1), that we interpret as coming from the wind of the secondary recombining after the ionization from the initial UV-flash of the nova. The underlying broad component underwent a marked reduction in both FWHM and width at zero intensity (the latter declining from 4000 to 2000 km s-1 in 10 days) while increasing by six times in flux, that we believe is the result of the high-velocity ejecta of the nova being slowed down while trying to expand within the surrounding wind of the companion. Nova Oph 2015 is possibly unique among novae with evolved companions in having displayed a long rise to maximum brightness and a slow decline from it, an Fe II-type classification, and a probable sub-giant luminosity class for the secondary.

  1. DIAGNOSING CIRCUMSTELLAR DEBRIS DISKS

    SciTech Connect

    Hahn, Joseph M.

    2010-08-20

    A numerical model of a circumstellar debris disk is developed and applied to observations of the circumstellar dust orbiting {beta} Pictoris. The model accounts for the rates at which dust is produced by collisions among unseen planetesimals, and the rate at which dust grains are destroyed due to collisions. The model also accounts for the effects of radiation pressure, which is the dominant perturbation on the disk's smaller but abundant dust grains. Solving the resulting system of rate equations then provides the dust abundances versus grain size and dust abundances over time. Those solutions also provide the dust grains' collisional lifetime versus grain size, and the debris disk's optical depth and surface brightness versus distance from the star. Comparison to observations then yields estimates of the unseen planetesimal disk's radius, and the rate at which the disk sheds mass due to planetesimal grinding. The model can also be used to measure or else constrain the dust grain's physical and optical properties, such as the dust grains' strength, their light-scattering asymmetry parameter, and the grains' efficiency of light scattering Q{sub s}. The model is then applied to optical observations of the edge-on dust disk orbiting {beta} Pictoris, and good agreement is achieved when the unseen planetesimal disk is broad, with 75 {approx}< r {approx}< 150 AU. If it is assumed that the dust grains are bright like Saturn's icy rings (Q{sub s} = 0.7), then the cross section of dust in the disk is A{sub d} {approx_equal} 2 x 10{sup 20} km{sup 2} and its mass is M{sub d} {approx_equal} 11 lunar masses. In this case, the planetesimal disk's dust-production rate is quite heavy, M-dot {sub d{approx}}9 M {sub +} Myr{sup -1}, implying that there is or was a substantial amount of planetesimal mass there, at least 110 Earth masses. If the dust grains are darker than assumed, then the planetesimal disk's mass-loss rate and its total mass are heavier. In fact, the apparent dearth

  2. CONFIRMATION OF CIRCUMSTELLAR PHOSPHINE

    SciTech Connect

    Agúndez, M.; Cernicharo, J.; Encrenaz, P.; Teyssier, D.

    2014-08-01

    Phosphine (PH{sub 3}) was tentatively identified a few years ago in the carbon star envelopes IRC +10216 and CRL 2688 from observations of an emission line at 266.9 GHz attributable to the J = 1-0 rotational transition. We report the detection of the J = 2-1 rotational transition of PH{sub 3} in IRC +10216 using the HIFI instrument on board Herschel, which definitively confirms the identification of PH{sub 3}. Radiative transfer calculations indicate that infrared pumping in excited vibrational states plays an important role in the excitation of PH{sub 3} in the envelope of IRC +10216, and that the observed lines are consistent with phosphine being formed anywhere between the star and 100 R {sub *} from the star, with an abundance of 10{sup –8} relative to H{sub 2}. The detection of PH{sub 3} challenges chemical models, none of which offer a satisfactory formation scenario. Although PH{sub 3} holds just 2% of the total available phosphorus in IRC +10216, it is, together with HCP, one of the major gas phase carriers of phosphorus in the inner circumstellar layers, suggesting that it could also be an important phosphorus species in other astronomical environments. This is the first unambiguous detection of PH{sub 3} outside the solar system, and is a further step toward a better understanding of the chemistry of phosphorus in space.

  3. PTF 12gzk—A rapidly declining, high-velocity type Ic radio supernova

    SciTech Connect

    Horesh, Assaf; Kulkarni, Shrinivas R.; Corsi, Alessandra; Frail, Dale A.; Cenko, S. Bradley; Ben-Ami, Sagi; Gal-Yam, Avishay; Yaron, Ofer; Arcavi, Iair; Ofek, Eran O.; Kasliwal, Mansi M.

    2013-11-20

    Only a few cases of Type Ic supernovae (SNe) with high-velocity ejecta (≥0.2 c) have been discovered and studied. Here, we present our analysis of radio and X-ray observations of the Type Ic SN PTF 12gzk. The radio emission declined less than 10 days after explosion, suggesting SN ejecta expanding at high velocity (∼0.3 c). The radio data also indicate that the density of the circumstellar material (CSM) around the supernova is lower by a factor of ∼10 than the CSM around normal Type Ic SNe. PTF 12gzk may therefore be an intermediate event between a 'normal' SN Ic and a gamma-ray-burst-SN-like event. Our observations of this rapidly declining radio SN at a distance of 58 Mpc demonstrates the potential to detect many additional radio SNe, given the new capabilities of the Very Large Array (improved sensitivity and dynamic scheduling), which are currently missed, leading to a biased view of radio SNe Ic. Early optical discovery followed by rapid radio observations would provide a full description of the ejecta velocity distribution and CSM densities around stripped massive star explosions as well as strong clues about the nature of their progenitor stars.

  4. High Resolution Spectroscopy of Vega-like Stars: Abundances and Circumstellar Gas

    NASA Technical Reports Server (NTRS)

    Dunkin, S. K.; Barlow, M. J.; Ryan, Sean G.

    1996-01-01

    Vega-like stars are main-sequence stars exhibiting excess infrared emission. In an effort to improve the information available on this class of star, 13 stars have been analyzed which have been classed as Vega-like, or have an infra-red excess attributable to dust in their circumstellar environment. In a separate paper stellar properties such as effective temperature and log g have been derived and in this poster we highlight the results of the photospheric abundance analysis also carried out during this work. King recently drew attention to the possible link between Vega-like stars and the photospheric metal-depleted class of A-stars, the Lambda Bootis stars. Since Vega-like stars are thought to have disks of dust, it might be expected that accretion of depleted gas onto the surface of these stars may cause this same phenomenon. In the 6 stars studied for depletions, none showed the extreme underabundance patterns observed in Lambda Bootis stars. However, depletions of silicon and magnesium were found in two of the sample, suggesting that these elements are in silicate dust grains in the circumstellar environment of these stars. Absorption lines attributed to circumstellar gas have been positively identified in three stars in our sample. Individual cases show evidence either of high-velocity outflowing gas, variability in the circumstellar lines observed, or evidence of circumstellar gas in excited lines of Fe II. No previous identification of circumstellar material has been made for two of the stars in question.

  5. A sensitive line search in circumstellar envelopes

    NASA Astrophysics Data System (ADS)

    Nguyen-Q-Rieu; Deguchi, S.; Izumiura, H.; Kaifu, N.; Ohishi, M.; Suzuki, H.; Ukita, N.

    A molecular line search in the range between 85 and 89 GHz has been performed in the circumstellar envelopes of 11 evolved stars. Emissions of 29SiO J=2-1,28SiO J=2-1, HCN J=1-0, H13CN J=1-0, HC5 N J=33-32, HCO+ J=1-0 transitions and other transitions of C2 H, C4 H, and C3 N have been observed in 11 stars. We have detected the ground state 29SiO J=2-1 maser in several stars. We have also detected HCN emission in VY CMa. A narrow H13CN spike feature near the central velocity has been found in the spectrum of CRL 2688.

  6. Circumstellar and Explosion Properties of Type Ibn Supernovae

    NASA Astrophysics Data System (ADS)

    Moriya, Takashi J.; Maeda, Keiichi

    2016-06-01

    We investigate circumstellar and explosion properties of Type Ibn supernovae (SNe) by analyzing their bolometric light curves (LCs). Bolometric LCs of SNe Ibn generally have a large contrast between peak luminosity and late-phase luminosity, which is much larger than those of 56Ni-powered SNe. Thus, most of them are likely powered by the interaction between SN ejecta and dense circumstellar media. In addition, SNe Ibn decline much faster than SNe IIn, and this indicates that the interaction in SNe Ibn ceases earlier than in SNe IIn. Thus, we argue that SN Ibn progenitors experience high mass-loss rates in a short period just before explosion, while SN IIn progenitors have high mass-loss rates sustained for a long time. Furthermore, we show that rise time and peak luminosity of SNe Ibn and IIn are similar and thus, they have similar explosion properties and circumstellar density. The similar circumstellar density in the two kinds of SNe may indicate that mass-loss rates of SN Ibn progenitors are generally higher than those of Type IIn as the wind velocities inferred from narrow spectral components are generally higher in SNe Ibn. We also show that {}56{Ni} mass and explosion energy of SNe Ibn may be smaller than those of other stripped-envelope SNe, probably because they tend to suffer large fallback or some of them may not even be terminal stellar explosions.

  7. High Velocity Absorption during Eta Car B's Periastron Passage

    NASA Technical Reports Server (NTRS)

    Nielsen, Krister E.; Groh, J. H.; Hillier, J.; Gull, Theodore R.; Owocki, S. P.; Okazaki, A. T.; Damineli, A.; Teodoro, M.; Weigelt, G.; Hartman, H.

    2010-01-01

    Eta Car is one of the most luminous massive stars in the Galaxy, with repeated eruptions with a 5.5 year periodicity. These events are caused by the periastron passage of a massive companion in an eccentric orbit. We report the VLT/CRIRES detection of a strong high-velocity, (<1900 km/s) , broad absorption wing in He I at 10833 A during the 2009.0 periastron passage. Previous observations during the 2003.5 event have shown evidence of such high-velocity absorption in the He I 10833 transition, allowing us to conclude that the high-velocity gas is crossing the line-of-sight toward Eta Car over a time period of approximately 2 months. Our analysis of HST/STlS archival data with observations of high velocity absorption in the ultraviolet Si IV and C IV resonance lines, confirm the presence of a high-velocity material during the spectroscopic low state. The observations provide direct detection of high-velocity material flowing from the wind-wind collision zone around the binary system, and we discuss the implications of the presence of high-velocity gas in Eta Car during periastron

  8. On optical studies of high-velocity clouds

    NASA Technical Reports Server (NTRS)

    York, D. G.; Burks, G. S.; Gibney, T. B.

    1986-01-01

    Lists of distant objects that can be used to study physical conditions in, and distances of, 21 cm (Oort) high-velocity clouds are presented. Recent published observations are used to compile positions, velocities, and distances of the clouds.

  9. The velocity distribution of cometary hydrogen - Evidence for high velocities?

    NASA Technical Reports Server (NTRS)

    Brown, Michael E.; Spinrad, Hyron

    1993-01-01

    The Hamilton Echelle spectrograph on the 3-m Shane telescope at Lick Observatory was used to obtain high-velocity and spatial resolution 2D spectra of H-alpha 6563-A emission in Comets Austin and Levy. The presence of the components expected from water dissociation and collisional thermalization in the inner coma is confirmed by the hydrogen velocity distribution. In Comet Austin, the potential high-velocity hydrogen includes velocities of up to about 40 km/s and is spatially symmetric with respect to the nucleus. In Comet Levy, the high-velocity hydrogen reaches velocities of up to 50 km/s and is situated exclusively on the sunward side of the nucleus. The two distinct signatures of high-velocity hydrogen imply two distinct sources.

  10. 46 CFR 153.353 - High velocity vents.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false High velocity vents. 153.353 Section 153.353 Shipping... Systems § 153.353 High velocity vents. The discharge point of a B/3 or 4m venting system must be located..., unimpeded jet; (b) The jet has a minimum exit velocity of 30 m/sec (approx. 98.4 ft/sec); and (c) The...

  11. 46 CFR 153.353 - High velocity vents.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false High velocity vents. 153.353 Section 153.353 Shipping... Systems § 153.353 High velocity vents. The discharge point of a B/3 or 4m venting system must be located..., unimpeded jet; (b) The jet has a minimum exit velocity of 30 m/sec (approx. 98.4 ft/sec); and (c) The...

  12. 46 CFR 153.353 - High velocity vents.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false High velocity vents. 153.353 Section 153.353 Shipping... Systems § 153.353 High velocity vents. The discharge point of a B/3 or 4m venting system must be located..., unimpeded jet; (b) The jet has a minimum exit velocity of 30 m/sec (approx. 98.4 ft/sec); and (c) The...

  13. Cryogenic Testing of High-Velocity Spoke Cavities

    SciTech Connect

    Hopper, Christopher S.; Delayen, Jean R.; Park, HyeKyoung

    2014-12-01

    Spoke-loaded cavities are being investigated for the high-velocity regime. The relative compactness at low-frequency makes them attractive for applications requiring, or benefiting from, 4 K operation. Additionally, the large velocity acceptance makes them good candidates for the acceleration of high-velocity protons and ions. Here we present the results of cryogenic testing of a 325 MHz, β0= 0.82 single-spoke cavity and a 500 MHz, β0 = 1 double-spoke cavity.

  14. 46 CFR 153.353 - High velocity vents.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false High velocity vents. 153.353 Section 153.353 Shipping... Systems § 153.353 High velocity vents. The discharge point of a B/3 or 4m venting system must be located..., unimpeded jet; (b) The jet has a minimum exit velocity of 30 m/sec (approx. 98.4 ft/sec); and (c) The...

  15. 46 CFR 153.353 - High velocity vents.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false High velocity vents. 153.353 Section 153.353 Shipping... Systems § 153.353 High velocity vents. The discharge point of a B/3 or 4m venting system must be located..., unimpeded jet; (b) The jet has a minimum exit velocity of 30 m/sec (approx. 98.4 ft/sec); and (c) The...

  16. Pierce Prize Lecture: High Velocity Clouds: Cosmological and Galactic Weather

    NASA Astrophysics Data System (ADS)

    Sembach, K.

    2001-12-01

    The Milky Way and its surrounding environs contain gas moving at high velocities with respect to the Sun. For the past half century, most of the information available for these high velocity clouds (HVCs) has come from H I 21cm surveys. Improvements in these surveys have recently led to the idea that some of the high velocity H I clouds may be located outside the Milky Way within the Local Group. Such a hypothesis is testable by various means, but the neutral gas content of the clouds tells only half of a much more complex story. In this talk I will present new information about the ionized gas within HVCs, their impact on the gaseous atmosphere of the Galaxy, and their relevance to the cosmic web of hot gas that may contain a significant fraction of the baryonic material in the low-redshift universe.

  17. Implications of high-velocity interstellar H I absorption features

    NASA Technical Reports Server (NTRS)

    Cowie, L.; York, D. G.; Laurent, C.; Vidal-Madjar, A.

    1979-01-01

    Contributions to the interstellar H I column density at high velocities from immediate postshock gas and from the cooling gas behind a shock are compared. The detection of high-velocity H I in L-epsilon and L-delta for Iota Ori is reported and interpreted as cooling gas behind a shock of 100 km/s velocity. The immediate postshock gas should be observable for shock velocities greater than 200 km/s and permits direct determination of the velocities of adiabatic shocks in the interstellar medium. It is pointed out that interstellar L-alpha and L-beta lines may not have purely Lorentzian profiles if high-velocity H I is a widespread phenomenon.

  18. Superconducting spoke cavities for high-velocity applications

    SciTech Connect

    Hopper, Christopher S.; Delayen, Jean R.

    2013-10-01

    To date, superconducting spoke cavities have been designed, developed, and tested for particle velocities up to {beta}{sub 0}~0.6, but there is a growing interest in possible applications of multispoke cavities for high-velocity applications. We have explored the design parameter space for low-frequency, high-velocity, double-spoke superconducting cavities in order to determine how each design parameter affects the electromagnetic properties, in particular the surface electromagnetic fields and the shunt impedance. We present detailed design for cavities operating at 325 and 352 MHz and optimized for {beta}{sub 0}~=0.82 and 1.

  19. Punch valve development testing: Low and high velocity test results

    SciTech Connect

    Replogle, W.C.; Brandon, S.L.

    1996-09-01

    This is a report on the use of quasi-static tests to predict fundamental parameters for punch valve development. This report summarizes the results from low and high velocity tests performed with 0.63 and 0.38 cm diameter plungers, 5 cm long penetrating aluminium and composite targets. The low velocity tests, 0.025 m/s, were performed to understand the effects and interactions of plunger diameter plunger tip shape, target material, and target support on penetration energy and plunger functionality. High velocity tests, 75 m/s, were compared to low velocity results.

  20. Certain optimal parameters of high-velocity Venturi ejection tubes

    NASA Astrophysics Data System (ADS)

    Stark, S. B.; Reznichenko, I. G.; Pavlenko, Y. P.

    1984-11-01

    The influence of the geometrical characteristics of centrifugal nozzles in high velocity Venturi ejection tubes for atomizing liquid in gas cleaning plant is analyzed. An optimal value of the nozzle geometrical characteristic, which is a function of the degree of filling of the nozzle outlet opening by the liquid, is given, at which the throat length is independent of water pressure before the nozzle.

  1. High-velocity OH megamasers in IRAS 20100-4156: evidence for a supermassive black hole

    NASA Astrophysics Data System (ADS)

    Harvey-Smith, L.; Allison, J. R.; Green, J. A.; Bannister, K. W.; Chippendale, A.; Edwards, P. G.; Heywood, I.; Hotan, A. W.; Lenc, E.; Marvil, J.; McConnell, D.; Phillips, C. J.; Sault, R. J.; Serra, P.; Stevens, J.; Voronkov, M.; Whiting, M.

    2016-08-01

    We report the discovery of new, high-velocity narrow-line components of the OH megamaser in IRAS 20100-4156. Results from the Australian Square Kilometre Array Pathfinder (ASKAP)'s Boolardy Engineering Test Array (BETA) and the Australia Telescope Compact Array (ATCA) provide two independent measurements of the OH megamaser spectrum. We found evidence for OH megamaser clumps at -409 and -562 km s-1 (blue-shifted) from the systemic velocity of the galaxy, in addition to the lines previously known. The presence of such high velocities in the molecular emission from IRAS 20100-4156 could be explained by a ˜50 pc molecular ring enclosing a ˜3.8 billion solar mass black hole. We also discuss two alternatives, i.e. that the narrow-line masers are dynamically coupled to the wind driven by the active galactic nucleus or they are associated with two separate galactic nuclei. The comparison between the BETA and ATCA spectra provides another scientific verification of ASKAP's BETA. Our data, combined with previous measurements of the source enabled us to study the variability of the source over a 26 yr period. The flux density of the brightest OH maser components has reduced by more than a factor of 2 between 1988 and 2015, whereas a secondary narrow-line component has more than doubled in the same time. Plans for high-resolution very long baseline interferometry follow-up of this source are discussed, as are prospects for discovering new OH megamasers during the ASKAP early science programme.

  2. A High-Velocity Collision With Our Galaxy's Disk

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-08-01

    What caused the newly discovered supershell in the outskirts of our galaxy? A new study finds evidence that a high-velocity cloud may have smashed into the Milky Ways disk millions of years ago.Mysterious Gas ShellsA single velocity-channel map of the supershell GS040.2+00.670, with red contours marking the high-velocity cloud at its center. [Adapted from Park et al. 2016]The neutral hydrogen gas that fills interstellar space is organized into structures like filaments, loops, and shells. Supershells are enormous shells of hydrogen gas that can have radii of a thousand light-years or more; weve spotted about 20 of these in our own galaxy, and more in nearby dwarfs and spiral galaxies.How do these structures form? One theory is that they result from several supernovae explosions occurring in the same area. But the energy needed to create a supershell is more than 3 x 1052 erg, which corresponds to over 30 supernovae quite a lot to have exploding in the same region.Theres an interesting alternative scenario: the supershells might instead be caused by the impacts of high-velocity clouds that fall into the galactic disk.Velocity data for the compact high-velocity cloud CHVC040. The cloud is moving fast enough to create the supershell observed. [Adapted from Park et al. 2016]The Milky Ways Speeding CloudsHigh-velocity clouds are clouds of mostly hydrogen that speed through the Milky Way with radial velocities that are very different from the material in the galactic disk. The origins of these clouds are unknown, but its proposed that they come from outside the galaxy they might be fragments of a nearby, disrupting galaxy, or they might have originated from flows of accreting gas in the space in between galaxies.Though high-velocity clouds have long been on the list of things that might cause supershells, weve yet to find conclusive evidence of this. But that might have just changed, with a recent discovery by a team of scientists led by Geumsook Park (Seoul National

  3. Mixing between High Velocity Clouds and the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Gritton, Jeffrey A.; Shelton, Robin L.; Kwak, Kyujin

    2014-11-01

    In the Galactic halo, metal-bearing Galactic halo material mixes into high velocity clouds (HVCs) as they hydrodynamically interact. This interaction begins long before the clouds completely dissipate and long before they slow to the velocity of the Galactic material. In order to make quantitative estimates of the mixing efficiency and resulting metal enrichment of HVCs, we made detailed two- and three-dimensional simulations of cloud-interstellar medium interactions. Our simulations track the hydrodynamics and time-dependent ionization levels. They assume that the cloud originally has a warm temperature and extremely low metallicity while the surrounding medium has a high temperature, low density, and substantial metallicity, but our simulations can be generalized to other choices of initial metallicities. In our simulations, mixing between cloud and halo gas noticeably raises the metallicity of the high velocity material. We present plots of the mixing efficiency and metal enrichment as a function of time.

  4. High Velocity Forming of Magnesium and Titanium Sheets

    SciTech Connect

    Revuelta, A.; Larkiola, J.; Korhonen, A. S.; Kanervo, K.

    2007-04-07

    Cold forming of magnesium and titanium is difficult due to their hexagonal crystal structure and limited number of available slip systems. However, high velocity deformation can be quite effective in increasing the forming limits. In this study, electromagnetic forming (EMF) of thin AZ31B-O magnesium and CP grade 1 titanium sheets were compared with normal deep drawing. Same dies were used in both forming processes. Finite element (FE) simulations were carried out to improve the EMF process parameters. Constitutive data was determined using Split Hopkinson Pressure Bar tests (SHPB). To study formability, sample sheets were electromagnetically launched to the female die, using a flat spiral electromagnetic coil and aluminum driver sheets. Deep drawing tests were made by a laboratory press-machine.Results show that high velocity forming processes increase the formability of Magnesium and Titanium sheets although process parameters have to be carefully tuned to obtain good results.

  5. Mixing between high velocity clouds and the galactic halo

    SciTech Connect

    Gritton, Jeffrey A.; Shelton, Robin L.; Kwak, Kyujin E-mail: rls@physast.uga.edu

    2014-11-01

    In the Galactic halo, metal-bearing Galactic halo material mixes into high velocity clouds (HVCs) as they hydrodynamically interact. This interaction begins long before the clouds completely dissipate and long before they slow to the velocity of the Galactic material. In order to make quantitative estimates of the mixing efficiency and resulting metal enrichment of HVCs, we made detailed two- and three-dimensional simulations of cloud-interstellar medium interactions. Our simulations track the hydrodynamics and time-dependent ionization levels. They assume that the cloud originally has a warm temperature and extremely low metallicity while the surrounding medium has a high temperature, low density, and substantial metallicity, but our simulations can be generalized to other choices of initial metallicities. In our simulations, mixing between cloud and halo gas noticeably raises the metallicity of the high velocity material. We present plots of the mixing efficiency and metal enrichment as a function of time.

  6. Gouge initiation in high-velocity rocket sled testing

    SciTech Connect

    Tachau, R.D.M.; Trucano, T.G.; Yew, C.H.

    1994-07-01

    A model is presented which describes the formation of surface damage ``gouging`` on the rails that guide rocket sleds. An unbalanced sled can randomly cause a very shallow-angle, oblique impact between the sled shoe and the rail. This damage phenomenon has also been observed in high-velocity guns where the projectile is analogous to the moving sled shoe and the gun barrel is analogous to the stationary rail. At sufficiently high velocity, the oblique impact will produce a thin hot layer of soft material on the contact surfaces. Under the action of a normal moving load, the soft layer lends itself to an anti-symmetric deformation and the formation of a ``hump`` in front of the moving load. A gouge is formed when this hump is overrun by the sled shoe. The phenomenon is simulated numerically using the CTH strong shock physics code, and the results are in good agreement with experimental observation.

  7. High Velocity Forming of Magnesium and Titanium Sheets

    NASA Astrophysics Data System (ADS)

    Revuelta, A.; Larkiola, J.; Korhonen, A. S.; Kanervo, K.

    2007-04-01

    Cold forming of magnesium and titanium is difficult due to their hexagonal crystal structure and limited number of available slip systems. However, high velocity deformation can be quite effective in increasing the forming limits. In this study, electromagnetic forming (EMF) of thin AZ31B-O magnesium and CP grade 1 titanium sheets were compared with normal deep drawing. Same dies were used in both forming processes. Finite element (FE) simulations were carried out to improve the EMF process parameters. Constitutive data was determined using Split Hopkinson Pressure Bar tests (SHPB). To study formability, sample sheets were electromagnetically launched to the female die, using a flat spiral electromagnetic coil and aluminum driver sheets. Deep drawing tests were made by a laboratory press-machine. Results show that high velocity forming processes increase the formability of Magnesium and Titanium sheets although process parameters have to be carefully tuned to obtain good results.

  8. Gouge initiation in high-velocity rocket sled testing

    NASA Astrophysics Data System (ADS)

    Tachau, R. D. M.; Trucano, T. G.; Yew, C. H.

    1994-07-01

    A model is presented which describes the formation of surface damage 'gouging' on the rails that guide rocket sleds. An unbalanced sled can randomly cause a very shallow-angle, oblique impact between the sled shoe and the rail. This damage phenomenon has also been observed in high-velocity guns where the projectile is analogous to the moving sled shoe and the gun barrel is analogous to the stationary rail. At sufficiently high velocity, the oblique impact will produce a thin hot layer of soft material on the contact surfaces. Under the action of a normal moving load, the soft layer lends itself to an anti-symmetric deformation and the formation of a 'hump' in front of the moving load. A gouge is formed when this hump is overrun by the sled shoe. The phenomenon is simulated numerically using the CTH strong shock physics code, and the results are in good agreement with experimental observation.

  9. Three-dimensional orientation of compact high velocity clouds

    NASA Astrophysics Data System (ADS)

    Heitsch, F.; Bartell, B.; Clark, S. E.; Peek, J. E. G.; Cheng, D.; Putman, M.

    2016-10-01

    We present a proof-of-concept study of a method to estimate the inclination angle of compact high velocity clouds (CHVCs), i.e. the angle between a CHVC's trajectory and the line of sight. The inclination angle is derived from the CHVC's morphology and kinematics. We calibrate the method with numerical simulations, and we apply it to a sample of CHVCs drawn from HIPASS (Putman et al.). Implications for CHVC distances are discussed.

  10. Is Perceptual Narrowing Too Narrow?

    ERIC Educational Resources Information Center

    Cashon, Cara H.; Denicola, Christopher A.

    2011-01-01

    There is a growing list of examples illustrating that infants are transitioning from having earlier abilities that appear more "universal," "broadly tuned," or "unconstrained" to having later abilities that appear more "specialized," "narrowly tuned," or "constrained." Perceptual narrowing, a well-known phenomenon related to face, speech, and…

  11. Circumstellar Dust in Symbiotic Novae

    NASA Astrophysics Data System (ADS)

    Jurkic, T.; Kotnik-Karuza, D.

    2015-12-01

    We present a model of inner dust regions around the cool Mira component of the two symbiotic novae, RR Tel and HM Sge, based on the near-IR photometry, ISO spectra and mid-IR interferometry. The dust properties were determined using the DUSTY code. A compact circumstellar silicate dust shell with inner dust shell temperatures between 900 K and 1300 K and of moderate optical depth can explain all the observations. RR Tel shows the presence of an equatorially enhanced dust density during minimum obscuration. Obscuration events are explained by an increase in optical depth caused by the newly condensed dust. The mass loss rates are significantly higher than in intermediate-period single Miras but in agreement with longer-period O-rich AGB stars.

  12. Controlling Btu input with high-velocity burners

    SciTech Connect

    Lukacs, J.J.

    1995-09-01

    StepFire{trademark} (sometimes called pulse fire) controls heat input through a burner by rapidly cycling from high fire to low fire (or from high fire to off) to control the temperature of either an entire kiln or a zone within a kiln. In the StepFire process, each burner, rather than an entire zone of burners, is controlled. The StepFire process provides a better approach to temperature control: high-velocity burners improve temperature distribution across the load, whether the burners are fired vertically downward or horizontally; reentrainment effect of the burners breaks up crown drift and allows dissipation of energy into the product; high-velocity burners generate less NO{sub x} and co than injector-type burners; high-velocity burners put most of the combustion air through the burners and do not have to rely on the mass flow of air from the cooling zone to complete combustion and provide uniformity; individual cycling of the burners does not radically change the total input of gases to the furnace, thereby allowing pressure control; because burners are cycled individually, the entire zone of the furnace does not go from a heating to a cooling mode, but continues at an input rate to maintain uniformity of energy input through the stepping process. StepFire use on all types of kilns results in improved product properties and quality, reduced fuel use, increased production, fewer rejects and reduction of NO{sub x} and CO emissions. Because the burners operate under their optimum conditions during most of the firing cycles, NO{sub x} formation is reduced, and the quenching effect of the flame by excess air is not present, reducing the generation of CO.

  13. Analysis of high velocity impact on hybrid composite fan blades

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1979-01-01

    This paper describes recent developments in the analysis of high velocity impact of composite blades using a computerized capability which consists of coupling a composites mechanics code with the direct-time integration features of NASTRAN. The application of the capability to determine the linear dynamic response of an intraply hybrid composite aircraft engine fan blade is described in detail. The predicted results agree with measured data. The results also show that the impact stresses reach sufficiently high magnitudes to cause failures in the impact region at early times of the impact event.

  14. High-Velocity Star Formation in the Large Magellanic Cloud.

    PubMed

    Graff; Gould

    2000-05-01

    Light-echo measurements show that SN 1987A is 425 pc behind the LMC disk. It is continuing to move away from the disk at 18 km s-1. Thus, it has been suggested that SN 1987A was ejected from the LMC disk. However, SN 1987A is a member of a star cluster, so this entire cluster would have to have been ejected from the disk. We show that the cluster was formed in the LMC disk, with a velocity perpendicular to the disk of about 50 km s-1. Such high-velocity formation of a star cluster is unusual, having no known counterpart in the Milky Way.

  15. Analysis of high velocity impact on hybrid composite fan blades

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1979-01-01

    Recent developments in the analysis of high velocity impact of composite blades are described, using a computerized capability which consists of coupling a composites mechanics code with the direct-time integration features of NASTRAN. The application of the capability to determine the linear dynamic response of an interply hybrid composite aircraft engine fan blade is described in detail. The results also show that the impact stresses reach sufficiently high magnitudes to cause failures in the impact region at early times of the impact event.

  16. High-velocity pulsars in the galactic halo

    SciTech Connect

    Eichler, D. ); Silk, J. )

    1992-08-14

    A common origin is proposed for high-velocity pulsars and for gamma-ray bursters. This source is a subdominant population of neutron stars that are in a spatially extended halo around our galaxy. Theoretical speculations and especially recent observations suggest the possible existence of a halo population of neutron stars. Specifically, recent reports of diskward-moving, high-latitude pulsars and of a nearly isotropic distribution of gamma-ray bursters motivate the authors to propose a source of neutron stars in the halo. They suggest that neutron stars could form by mergers of white dwarfs.

  17. Electric rail gun projectile acceleration to high velocity

    NASA Technical Reports Server (NTRS)

    Bauer, D. P.; Mccormick, T. J.; Barber, J. P.

    1982-01-01

    Electric rail accelerators are being investigated for application in electric propulsion systems. Several electric propulsion applications require that the rail accelerator be capable of launching projectiles at velocities above 10 km/s. An experimental program was conducted to develop rail accelerator technology for high velocity projectile launch. Several 6 mm bore, 3 m long rail accelerators were fabricated. Projectiles with a mass of 0.2 g were accelerated by plasmas, carrying currents up to 150 kA. Experimental design and results are described. Results indicate that the accelerator performed as predicted for a fraction of the total projectile acceleration. The disparity between predicted and measured results are discussed.

  18. A DETAILED KINEMATIC MAP OF CASSIOPEIA A'S OPTICAL MAIN SHELL AND OUTER HIGH-VELOCITY EJECTA

    SciTech Connect

    Milisavljevic, Dan; Fesen, Robert A.

    2013-08-01

    We present three-dimensional (3D) kinematic reconstructions of optically emitting material in the young Galactic supernova remnant Cassiopeia A (Cas A). These Doppler maps have the highest spectral and spatial resolutions of any previous survey of Cas A and represent the most complete catalog of its optically emitting material to date. We confirm that the bulk of Cas A's optically bright ejecta populate a torus-like geometry tilted approximately 30 Degree-Sign with respect to the plane of the sky with a -4000 to +6000 km s{sup -1} radial velocity asymmetry. Near-tangent viewing angle effects and an inhomogeneous surrounding circumstellar material/interstellar medium environment suggest that this geometry and velocity asymmetry may not be faithfully representative of the remnant's true 3D structure or the kinematic properties of the original explosion. The majority of the optical ejecta are arranged in several well-defined and nearly circular ring-like structures with diameters between approximately 30'' (0.5 pc) and 2' (2 pc). These ejecta rings appear to be a common phenomenon of young core-collapse remnants and may be associated with post-explosion input of energy from plumes of radioactive {sup 56}Ni-rich ejecta that rise, expand, and compress non-radioactive material. Our optical survey encompasses Cas A's faint outlying ejecta knots and exceptionally high-velocity NE and SW streams of S-rich debris often referred to as ''jets''. These outer knots, which exhibit a chemical make-up suggestive of an origin deep within the progenitor star, appear to be arranged in opposing and wide-angle outflows with opening half-angles of Almost-Equal-To 40 Degree-Sign.

  19. Aerosol production by high-velocity molten-metal droplets

    SciTech Connect

    Rader, D J; Benson, D A

    1988-06-01

    This report presents the results of an experimental study of the aerosol produced by high-velocity molten-metal droplets. These tests are intended to simulate the reduction of high-velocity fragments into aerosol in high-explosive detonations or reactor accidents involving nuclear materials. The primary droplets are produced by the heating and electromagnetic launch of metal wires; velocities approaching Mach 1 can be obtained at present. Size distributions obtained tungsten and zirconium droplets burning in air. Lognormal size distributions were observed in both cases with DMPS-equivalent mean diameters of about 0.4 ..mu..m and geometric standard deviations of about two. SEM and TEM analysis of aerosol samples collected by a point-to-plane electrostatic precipitator showed that the majority of these particles were web-like chain agglomerates. Tests performed in argon atmospheres produced several orders-of-magnitude less aerosol mass than in equivalent air tests, supporting the key role combustion plays in secondary aerosol generation. 26 refs., 14 figs., 2 tabs.

  20. High Velocity Impact Response of Composite Lattice Core Sandwich Structures

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Zhang, Guoqi; Wang, Shixun; Ma, Li; Wu, Linzhi

    2014-04-01

    In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.

  1. High-velocity streams of dust originating from Saturn.

    PubMed

    Kempf, Sascha; Srama, Ralf; Horányi, Mihaly; Burton, Marcia; Helfert, Stefan; Moragas-Klostermeyer, Georg; Roy, Mou; Grün, Eberhard

    2005-01-20

    High-velocity submicrometre-sized dust particles expelled from the jovian system have been identified by dust detectors on board several spacecraft. On the basis of periodicities in the dust impact rate, Jupiter's moon Io was found to be the dominant source of the streams. The grains become positively charged within the plasma environment of Jupiter's magnetosphere, and gain energy from its co-rotational electric field. Outside the magnetosphere, the dynamics of the grains are governed by the interaction with the interplanetary magnetic field that eventually forms the streams. A similar process was suggested for Saturn. Here we report the discovery by the Cassini spacecraft of bursts of high-velocity dust particles (> or = 100 km s(-1)) within approximately 70 million kilometres of Saturn. Most of the particles detected at large distances appear to originate from the outskirts of Saturn's outermost main ring. All bursts of dust impacts detected within 150 Saturn radii are characterized by impact directions markedly different from those measured between the bursts, and they clearly coincide with the spacecraft's traversals through streams of compressed solar wind.

  2. MAGNETIZED GAS IN THE SMITH HIGH VELOCITY CLOUD

    SciTech Connect

    Hill, Alex S.; McClure-Griffiths, Naomi M.; Mao, S. A.; Benjamin, Robert A.; Lockman, Felix J. E-mail: naomi.mcclure-griffiths@csiro.au E-mail: benjamir@uww.edu

    2013-11-01

    We report the first detection of magnetic fields associated with the Smith High Velocity Cloud. We use a catalog of Faraday rotation measures toward extragalactic radio sources behind the Smith Cloud, new H I observations from the Robert C. Byrd Green Bank Telescope, and a spectroscopic map of Hα from the Wisconsin H-Alpha Mapper Northern Sky Survey. There are enhancements in rotation measure (RM) of ≈100 rad m{sup –2} which are generally well correlated with decelerated Hα emission. We estimate a lower limit on the line-of-sight component of the field of ≈8 μG along a decelerated filament; this is a lower limit due to our assumptions about the geometry. No RM excess is evident in sightlines dominated by H I or Hα at the velocity of the Smith Cloud. The smooth Hα morphology of the emission at the Smith Cloud velocity suggests photoionization by the Galactic ionizing radiation field as the dominant ionization mechanism, while the filamentary morphology and high (≈1 Rayleigh) Hα intensity of the lower-velocity magnetized ionized gas suggests an ionization process associated with shocks due to interaction with the Galactic interstellar medium. The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the Galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas.

  3. High-velocity streams of dust originating from Saturn.

    PubMed

    Kempf, Sascha; Srama, Ralf; Horányi, Mihaly; Burton, Marcia; Helfert, Stefan; Moragas-Klostermeyer, Georg; Roy, Mou; Grün, Eberhard

    2005-01-20

    High-velocity submicrometre-sized dust particles expelled from the jovian system have been identified by dust detectors on board several spacecraft. On the basis of periodicities in the dust impact rate, Jupiter's moon Io was found to be the dominant source of the streams. The grains become positively charged within the plasma environment of Jupiter's magnetosphere, and gain energy from its co-rotational electric field. Outside the magnetosphere, the dynamics of the grains are governed by the interaction with the interplanetary magnetic field that eventually forms the streams. A similar process was suggested for Saturn. Here we report the discovery by the Cassini spacecraft of bursts of high-velocity dust particles (> or = 100 km s(-1)) within approximately 70 million kilometres of Saturn. Most of the particles detected at large distances appear to originate from the outskirts of Saturn's outermost main ring. All bursts of dust impacts detected within 150 Saturn radii are characterized by impact directions markedly different from those measured between the bursts, and they clearly coincide with the spacecraft's traversals through streams of compressed solar wind. PMID:15662418

  4. High-Velocity Clouds and Superbubbles in Nearby Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Schulman, Eric

    1996-05-01

    The galactic fountain model predicts that energetic stellar winds and supernovae in OB associations produce superbubbles containing hot gas that breaks out of the Galactic disk, cools radiatively as it rises upward, and recombines and returns to the disk ballistically. The hot (T ~ 10^6 K) gas can be observed with X-ray telescopes, while the cool returning neutral hydrogen (H I) is detectable as 21 cm emission from high-velocity clouds (HVCs). In the Milky Way Galaxy, a combination of infalling material tidally torn from the Magellanic Clouds and a galactic fountain can explain the high-velocity clouds that cover about 10% of the sky down to a column density of 2 to 3 X 10^18 cm^-2. Sensitive H I observations of nearby disk galaxies were performed with the Arecibo 305 m radio telescope to search for and measure the mass of HVCs in other galaxies. Ten of 14 galaxies have high-velocity wings that can be modeled as arising from a component of galactic gas with a velocity dispersion of 30 or 50 km s^-1. The HVC mass for the 10 galaxies ranges from 6 X 10^7 solar mass to 4 X 10^9 solar mass, which corresponds to 4 to 14% of the total H I in the galaxies. This is the first survey to search for HVCs in more than a few galaxies, and the results imply that Galactic HVCs are a disk-wide phenomenon with a characteristic distance of 10 to 20 kpc, containing a substantial fraction (~10%) of the neutral hydrogen in the Galaxy and much of the random kinetic energy in neutral gas. 21 cm synthesis imaging of UGC 12732 and NGC 5668, performed with the Very Large Array, confirmed the Arecibo results that the former does not have high-velocity gas while the latter does. Two components of high-velocity gas are present in NGC~5668; one may be from an accretion event, while the other is visible due to the increased H I velocity dispersion throughout the optical disk and may be galactic fountain gas. Neither of these components are visible in the observations of UGC 12732, and this galaxy

  5. Imprints of a high-velocity wind on the soft X-ray spectrum of PG1211+143

    NASA Astrophysics Data System (ADS)

    Pounds, K. A.; Lobban, A.; Reeves, J. N.; Vaughan, S.; Costa, M.

    2016-07-01

    An extended XMM-Newton observation of the luminous narrow-line Seyfert galaxy PG1211+143 in 2014 has revealed a more complex high-velocity wind, with components distinguished in velocity, ionization level, and column density. Here we report soft X-ray emission and absorption features from the ionized outflow, finding counterparts of both high-velocity components, v ˜ 0.129c and v ˜ 0.066c, recently identified in the highly ionized Fe K absorption spectrum. The lower ionization of the comoving soft X-ray absorbers imply a distribution of higher density clouds embedded in the main outflow, while much higher column densities for the same flow component in the hard X-ray spectra suggest differing sightlines to the continuum X-ray source.

  6. Circumstellar dust in symbiotic novae

    NASA Astrophysics Data System (ADS)

    Jurkic, Tomislav; Kotnik-Karuza, Dubravka

    2015-08-01

    Physical properties of the circumstellar dust and associated physical mechanisms play an important role in understanding evolution of symbiotic binaries. We present a model of inner dust regions around the cool Mira component of the two symbiotic novae, RR Tel and HM Sge, based on the long-term near-IR photometry, infrared ISO spectra and mid-IR interferometry. Pulsation properties and long-term variabilities were found from the near-IR light curves. The dust properties were determined using the DUSTY code which solves the radiative transfer. No changes in pulsational parameters were found, but a long-term variations with periods of 20-25 years have been detected which cannot be attributed to orbital motion.Circumstellar silicate dust shell with inner dust shell temperatures between 900 K and 1300 K and of moderate optical depth can explain all the observations. RR Tel showed the presence of an optically thin CS dust envelope and an optically thick dust region outside the line of sight, which was further supported by the detailed modelling using the 2D LELUYA code. Obscuration events in RR Tel were explained by an increase in optical depth caused by the newly condensed dust leading to the formation of a compact dust shell. HM Sge showed permanent obscuration and a presence of a compact dust shell with a variable optical depth. Scattering of the near-IR colours can be understood by a change in sublimation temperature caused by the Mira variability. Presence of large dust grains (up to 4 µm) suggests an increased grain growth in conditions of increased mass loss. The mass loss rates of up to 17·10-6 MSun/yr were significantly higher than in intermediate-period single Miras and in agreement with longer-period O-rich AGB stars.Despite the nova outburst, HM Sge remained enshrouded in dust with no significant dust destruction. The existence of unperturbed dust shell suggests a small influence of the hot component and strong dust shielding from the UV flux. By the use

  7. A model for ductile metal friction at high velocities

    NASA Astrophysics Data System (ADS)

    Hammerberg, J. E.; Ravelo, R. J.; Germann, T. C.

    We describe a meso-macro scale model for the frictional force at ductile metal interfaces for high velocities and large compressions. The model incorporates the micro-mesoscopic growth and refinement of material microstructure in a highly strained region at the sliding interface and incorporates both rate dependent plasticity and thermal conduction. The model compares favorably with recent large scale (1.8 billion atom) simulations to 50 ns of 3-dimensional polycrystalline 13-50 nm grain size Al-Al interfaces at pressures of 15 GPa using the SPaSM NonEquilibrium Molecular Dynamics (NEMD) simulation code. This work was performed under the auspices of the U.S. Dept. of Energy under Contract DE-AC52-06NA25396. The support of the LANL ASC-PEM program is gratefully acknowledged.

  8. The distance to the high velocity clouds of neutral hydrogen

    NASA Technical Reports Server (NTRS)

    Bregman, Joel N.

    1992-01-01

    The goal of this project was to determine the distance to high velocity gas clouds. These clouds are believed to lie in the halo of the galaxy, but this is a matter of controversy. The technique was used to look for the effect of absorption by these clouds against the light of stars at various distances along the line of sight to these clouds. This was done in the ultraviolet using the International Ultraviolet Explorer. Absorption at the velocity of the clouds was not found in any of the stars, which have kiloparsec distances. It was concluded that the vertical distance to these clouds is at least 1.5 kpc, putting them firmly in the halo of the galaxy.

  9. Fluid shielding of high-velocity jet noise

    NASA Technical Reports Server (NTRS)

    Goodykoontz, J. H.

    1984-01-01

    Experimental noise data for a nozzle exhaust system incorporating a thermal acoustic shield (TAS) are presented to show the effect of changes in geometric and flow parameters on attenuation of high-velocity jet exhaust noise in the flyover plane. The results are presented for a 10.00-cm-diameter primary conical nozzle with a TAS configuration consisting of a 2.59- or 5.07-cm-wide annular gap. Shield-stream exhaust velocity was varied from 157 to 248 m/sec to investigate the effect of velocity ratio. The results showed that increasing the annular gap width increases attenuation of high-frequency noise when comparisons are made on the same ideal thrust basis. Varying the velocity ratio had a minor effect on the noise characteristics of the nozzles investigated.

  10. Low and high velocity impact response of thick hybrid composites

    NASA Technical Reports Server (NTRS)

    Hiel, Clement; Ishai, Ori

    1993-01-01

    The effects of low and high velocity impact on thick hybrid composites (THC's) were experimentally compared. Test Beams consisted of CFRP skins which were bonded onto an interleaved syntactic foam core and cured at 177 C (350 F). The impactor tip for both cases was a 16 mm (0.625 inch) steel hemisphere. In spite of the order of magnitude difference in velocity ranges and impactor weights, similar relationships between impact energy, damage size, and residual strength were found. The dependence of the skin compressive strength on damage size agree well with analytical open hole models for composite laminates and may enable the prediction of ultimate performance for the damaged composite, based on visual inspection.

  11. The acceleration of high-velocity clouds in supernova remnants

    NASA Technical Reports Server (NTRS)

    Mckee, C. F.; Cowie, L. L.; Ostriker, J. P.

    1978-01-01

    Interstellar clouds passed by blast waves emanating from supernova explosions will be accelerated by the ram pressure of the expanding interior shocked gas. We present numerical and analytical solutions for cloud acceleration in this environment, comparing the results with recent observations of faint, high-velocity (greater than 100 km/sec) filaments observed in Cygnus and Vela. Photons from the conductive interface between the clouds and the surrounding medium can provide the ionizing flux necessary for observable optical emission. Several predictions are made, the most important of which is that fast clouds of neutral hydrogen with column densities of about 10 quintillion per sq cm should be observable in 21 cm studies of SNRs.

  12. HST-FGS parallaxes of two high-velocity stars.

    NASA Astrophysics Data System (ADS)

    MacConnell, D. Jack; Osborn, Wayne H.; Miller, Richard J.

    1997-09-01

    Astrometric position measurements with the Hubble Space Telescope's Fine Guidance System have been used to measure the trigonometric parallaxes of two high-velocity stars, R50 = G166-37 and W624 = G16-25. In both cases, the parallaxes are small and confirm large velocities in the galactocentric rest frame. We derive pi_ {abs} = 5.2 +/- 0.7 mas and vrf = 467 kms for R50. The results for W624 are pi_ {abs} = 3.8 +/- 1.0 and vrf = 326 kms with an uncertainty of about 30%. Our results support a value for the galactic escape velocity at the solar distance of about 475 kms.

  13. Solar wind collimation of the Jupiter high velocity dust streams

    NASA Astrophysics Data System (ADS)

    Flandes, A.; Krueger, H.

    2006-12-01

    The dust bursts discovered by the Ulysses dust sensor when approaching Jupiter in 1992 were later confirmed as collimated streams of high velocity (~200 km/s) charged (~5V) dust grains escaping from Jupiter and dominated by the interplanetary Magnetic field (IMF). With Cassini, a similar phenomenon was observed in Saturn. It was demonstrated that the Jovian dust streams are closely related to the solar wind compressed regions, either Corotating interaction regions (CIRs) or Coronal mass ejections (CMEs) ¨Cto a minor extent-. Actually the dust streams seem ultimately to be generated by such events. This can be explained considering that dust grains are accelerated as they gain substantial energy while compressed at the forward and reverse shocks that bound or precede these solar wind regions.

  14. Characterization of high velocity oxy-fuel combustion sprayed hydroxyapatite.

    PubMed

    Haman, J D; Lucas, L C; Crawmer, D

    1995-02-01

    Bioceramic coatings, created by the high velocity oxy-fuel combustion spraying of hydroxyapatite (HA) powders onto commercially pure titanium, were characterized in order to determine whether this relatively new coating process can be successfully applied to bioceramic coatings of orthopaedic and dental implants. Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy were used to characterize both the HA starting powders and coatings. A 12 wk immersion test was conducted and the resulting changes in the coatings were also characterized. Calcium ion release during dissolution was measured with flame atomic absorption during the first 6 weeks of the immersion study. A comparison of powder and coating X-ray diffraction patterns and lattice parameters revealed an HA-type coating with some loss in crystallinity. Fourier transform infrared results showed a partial loss of the OH- group during spraying, however the phosphate groups were still present. Scanning electron microscopy analysis showed a lamellar structure with very close coating-to-substrate apposition. The coatings experienced a loss of calcium during the immersion study, with the greatest release in calcium occurring during the first 6 days of the study. No significant structural or chemical changes were observed during the 12 wk immersion study. These results indicate that the high velocity oxy-fuel process can produce an HA-type coating; however, the process needs further optimization, specifically in the areas of coating-to-substrate bond strength and minimization of phases present other than HA, before it would be recommended for commercial use.

  15. Resonant Orbits and the High Velocity Peaks toward the Bulge

    NASA Astrophysics Data System (ADS)

    Molloy, Matthew; Smith, Martin C.; Evans, N. Wyn; Shen, Juntai

    2015-10-01

    We extract the resonant orbits from an N-body bar that is a good representation of the Milky Way, using the method recently introduced by Molloy et al. By decomposing the bar into its constituent orbit families, we show that they are intimately connected to the boxy-peanut shape of the density. We highlight the imprint due solely to resonant orbits on the kinematic landscape toward the Galactic center. The resonant orbits are shown to have distinct kinematic features and may be used to explain the cold velocity peak seen in the Apache Point Observatory Galactic Evolution Experiment commissioning data. We show that high velocity peaks are a natural consequence of the motions of stars in the 2:1 orbit family and that stars on other higher order resonances can contribute to the peaks. The locations of the peaks vary with bar angle and, with the tacit assumption that the observed peaks are due to the 2:1 family, we find that the locations of the high velocity peaks correspond to bar angles in the range {10}\\circ ≲ {θ }{bar}≲ 25^\\circ . However, some important questions about the nature of the peaks remain, such as their apparent absence in other surveys of the Bulge and the deviations from symmetry between equivalent fields in the north and south. We show that the absence of a peak in surveys at higher latitudes is likely due to the combination of a less prominent peak and a lower number density of bar supporting orbits at these latitudes.

  16. High Velocity Frictional Properties of a Clay-Bearing Fault Gouge and Implications for Earthquake Mechanics

    NASA Astrophysics Data System (ADS)

    Brunet, F.; Brantut, N.; Schubnel, A.; Rouzaud, J.; Shimamoto, T.

    2008-12-01

    Frictional properties of natural kaolinite-bearing gouge samples from the Median Tectonic Line (SW Japan) have been studied using a high-velocity rotary shear apparatus. For a slip velocity of 1~m.s-1 and normal stresses from 0.3 to 1.3~MPa, a dramatic slip-weakening behavior was observed. X-ray diffraction analysis of deformed samples and additional high-velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip. The critical slip-weakening distance Dc is of the order of 1~m to 10~m. These values are extrapolated to higher normal stresses, assuming that Dc is a thermal parameter. The calculation shows that dimensionally, Dc ∝ 1/σn2, where σn is the normal stress applied on the fault. The inferred Dc values range from a few centimeters at 10~MPa normal stress to a few hundreds of microns at 100~MPa normal stress. Microscopic observations show partial amorphization and dramatic grain size reduction (down to the nanometer scale) localized in a narrow zone of about 1 to 10~μm thickness. Fracture energy Gc is calculated and compared to surface energy due to grain size reduction, and energies of chemical reactions, showing that most of the fracture energy is converted into heat. The geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poro-mechanical data of several fault zones, which tend to show that this phenomenon has to be taken into account in most of sub-surface faults, and in hydrous rocks of subducted oceanic crust.

  17. The circumstellar environment of pre-SN Ia systems

    NASA Astrophysics Data System (ADS)

    Harvey, E.; Redman, M. P.; Boumis, P.; Kopsacheili, M.; Akras, S., Sabin, L.; Jurkic, T.

    2016-06-01

    Here we explore the possible preexisting circumstellar debris of supernova type Ia systems. Classical, symbiotic and recurrent novae all accrete onto roughly solar mass white dwarfs from main sequence or Mira type companions and result in thermonuclear runaways and expulsion of the accreted material at high velocity. The expelled material forms a fast moving shell that eventually slows to planetary nebula expansion velocities within several hundred years. All such systems are recurrent and thousands of shells (each of about 0.001 Mo) snow plough into the environment. As these systems involve common envelope binaries the material is distributed in a non-spherical shell. These systems could be progenitors of some SN Ia and thus explode into environments with large amounts of accumulated gas and dust distributed in thin non-spherical shells. Such shells should be observable around 100 years after a SN Ia event in a radio flash as the SN Ia debris meets that of the ejected material of the systems previous incarnation.

  18. Orbital Transfer Vehicle Engine Technology High Velocity Ratio Diffusing Crossover

    NASA Technical Reports Server (NTRS)

    Lariviere, Brian W.

    1992-01-01

    High speed, high efficiency head rise multistage pumps require continuous passage diffusing crossovers to effectively convey the pumped fluid from the exit of one impeller to the inlet of the next impeller. On Rocketdyne's Orbital Transfer Vehicle (OTV), the MK49-F, a three stage high pressure liquid hydrogen turbopump, utilizes a 6.23 velocity ratio diffusing crossover. This velocity ratio approaches the diffusion limits for stable and efficient flow over the operating conditions required by the OTV system. The design of the high velocity ratio diffusing crossover was based on advanced analytical techniques anchored by previous tests of stationary two-dimensional diffusers with steady flow. To secure the design and the analytical techniques, tests were required with the unsteady whirling characteristics produced by an impeller. A tester was designed and fabricated using a 2.85 times scale model of the MK49-F turbopumps first stage, including the inducer, impeller, and the diffusing crossover. Water and air tests were completed to evaluate the large scale turbulence, non-uniform velocity, and non-steady velocity on the pump and crossover head and efficiency. Suction performance tests from 80 percent to 124 percent of design flow were completed in water to assess these pump characteristics. Pump and diffuser performance from the water and air tests were compared with the actual MK49-F test data in liquid hydrogen.

  19. Two high-velocity encounters of elliptical galaxies

    NASA Technical Reports Server (NTRS)

    Balcells, Marc; Borne, Kirk D.; Hoessel, John G.

    1989-01-01

    This paper describes results obtained on a simulation of two high-velocity encounters of NGC 4782/4783 and NGC 2672/2673 binary elliptical galaxies which differ substantially in mass ratio (about 1 for the first pair, and about 10 for the second). CCD images and velocities obtained from digital spectra were used to constrain simulations of the galaxy collisions. The binary orbital elements, the orientation of the orbit in the sky, the time since pericenter, and the dynamical mass of the pair were derived. Results suggested that the dumb-bell galaxy NGC 4782/4783 is not a supermassive galaxy, as was claimed earlier on the basis of the high relative velocity and high central dispersion, but has a moderate mass to luminosity ratio M/L(B) of about 10. It was concluded that its trajectory changed from hyperbolic to elliptical as a result of energy lost during the collision. It was found that the NGC 2672/2673 also has a moderate M/L(B) of about 7.

  20. Energy loss of heavy ions at high velocity

    NASA Astrophysics Data System (ADS)

    Andersen, J. U.; Ball, G. C.; Davies, J. A.; Davies, W. G.; Forster, J. S.; Geiger, J. S.; Geissel, H.; Ryabov, V. A.

    1994-05-01

    The slowing down of heavy ions by electronic stopping at high velocity is discussed. The ions are nearly fully stripped and have a well defined charge with relatively small fluctuations. Owing to the large charge of the ions, the classical Bohr formula applies instead of the Bethe formula, which is based on a quantum perturbation calculation. It is essential to include the Barkas effect in the description since it becomes quite large for heavy ions, especially in high-Z materials. In Lindhard's treatment [Nucl. Instr. and Meth. 132 (1976) l], the Barkas correction is viewed as an effect of dynamic screening of the ion potential in the initial phase of a collision with an electron, which reduces the relative velocity and therefore enhances the cross section. With inclusion of this enhancement factor for all impact parameters, as evaluated by Jackson and McCarthy for distant collisions [Phys. Rev. B 6 (1972) 4131], the description reproduces within a few percent measurements for 15 MeV/u Br on Si, Ni, and Au and for 10 MeV/u Kr on Al, Ni, and Au. The procedure is shown also to apply at lower velocities near the stopping maximum, albeit with less accuracy. The straggling in energy loss has been analyzed for a measurement on Si and it is well described by a combination of about equal contributions from fluctuations in the number of violent collisions with single electrons (Bohr straggling) and from fluctuations in ion charge state.

  1. Fullerenes and fulleranes in circumstellar envelopes

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Kwok, Sun; Sadjadi, SeyedAbdolreza

    2016-07-01

    Three decades of search have recently led to convincing discoveries of cosmic fullerenes. The presence of C60 and C+ 60 in both circumstellar and interstellar environments suggests that these molecules and their derivatives can be efficiently formed in circumstellar envelopes and survive in harsh conditions. Detailed analysis of the infrared bands from fullerenes and their connections with the local properties can provide valuable information on the physical conditions and chemical processes that occurred in the late stages of stellar evolution. The identification of C+ 60 as the carrier of four diffuse interstellar bands (DIBs) suggests that fullerene- related compounds are abundant in interstellar space and are essential for resolving the DIB mystery. Experiments have revealed a high hydrogenation rate when C60 is exposed to atomic hydrogen, motivating the attempt to search for cosmic fulleranes. In this paper, we present a short review of current knowledge of cosmic fullerenes and fulleranes and briefly discuss the implications on circumstellar chemistry.

  2. Probing the circumstellar environment of the Herbig Be star HD 100546 with FUSE.

    NASA Astrophysics Data System (ADS)

    Deleuil, M.; Lecavelier des Etangs, A.; Bouret, J.-C.; Roberge, A.; Vidal-Madjar, A.; Feldman, P. D.; Ferlet, R.; Martin, C.

    2002-12-01

    We present an analysis of Far Ultraviolet Spectroscopic Explorer (FUSE) spectra probing the gaseous circumstellar environment of the Herbig Be star HD 100546. Numerous narrow absorption lines of circumstellar origin are observed from molecular and atomic gas, neutral and weakly ionized. At short wavelengths where the stellar flux is undetected, strong and broad emission lines due to highly ionised species such as C III and O VI are present. These lines formed in a dense and hot gas, collisionally heated, probe a region which extends over a few stellar radii above the star's surface. Comparison of two spectra recorded two years apart, reveal strong variations not limited to the atomic circumstellar lines as previously reported but which also affect the photospheric flux itself as well as the emission lines at short wavelengths. Our results highlight a complex circumstellar environment with evidences of a high temperature emission gas related to a chromospheric complex close to the stellar surface, sporadic wind and accretion phenomena which affect mainly volatile species like N I and O I(1D). Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.

  3. The IRS 1 circumstellar disk, and the origin of the jet and CO outflow in B5.

    PubMed

    Langer, W D; Velusamy, T; Xie, T

    1996-09-01

    We report the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 and the first ever resolution of its circumstellar disk in the 2.6 mm dust continuum and C18O. From high spatial resolution observations made with the Owens Valley Millimeter Array we are able to locate the origin of the outflow to within approximately 500 AU on either side of IRS 1 and apparently at the edge of, or possibly within, its circumstellar disk. The orientation of the continuum disk is perpendicular to the highly collimated jet outflow recently seen in optical emission at much farther distances. The disk has been detected in C18O giving a disk mass approximately 0.16 M (solar). Our HCO+ and HCN maps indicate significant chemical differentiation in the circumstellar region on small scales with HCO+ tracing an extended disk of material. The 12CO interferometer maps of the outflow show two conelike features originating at IRS 1, the blue one fanning open to the northeast and the red one to the southwest. The vertices of the cones are on either side of the circumstellar disk and have a projected opening angle of about 90 degrees. The intrinsic opening angle is in the range of 60 degrees-90 degrees which leads to significant interaction between outflow and infall.

  4. Experimental and numerical studies of high-velocity impact fragmentation

    SciTech Connect

    Kipp, M.E.; Grady, D.E.; Swegle, J.W.

    1993-08-01

    Developments are reported in both experimental and numerical capabilities for characterizing the debris spray produced in penetration events. We have performed a series of high-velocity experiments specifically designed to examine the fragmentation of the projectile during impact. High-strength, well-characterized steel spheres (6.35 mm diameter) were launched with a two-stage light-gas gun to velocities in the range of 3 to 5 km/s. Normal impact with PMMA plates, thicknesses of 0.6 to 11 mm, applied impulsive loads of various amplitudes and durations to the steel sphere. Multiple flash radiography diagnostics and recovery techniques were used to assess size, velocity, trajectory and statistics of the impact-induced fragment debris. Damage modes to the primary target plate (plastic) and to a secondary target plate (aluminum) were also evaluated. Dynamic fragmentation theories, based on energy-balance principles, were used to evaluate local material deformation and fracture state information from CTH, a three-dimensional Eulerian solid dynamics shock wave propagation code. The local fragment characterization of the material defines a weighted fragment size distribution, and the sum of these distributions provides a composite particle size distribution for the steel sphere. The calculated axial and radial velocity changes agree well with experimental data, and the calculated fragment sizes are in qualitative agreement with the radiographic data. A secondary effort involved the experimental and computational analyses of normal and oblique copper ball impacts on steel target plates. High-resolution radiography and witness plate diagnostics provided impact motion and statistical fragment size data. CTH simulations were performed to test computational models and numerical methods.

  5. Numerical Investigation of High Velocity Suspension Flame Spraying

    NASA Astrophysics Data System (ADS)

    Taleby, M.; Hossainpour, S.

    2012-12-01

    High-velocity suspension flame spraying (HVSFS) has recently developed as a possible alternative to conventional HVOF-spraying employing liquid suspensions instead of dry powder feedstock enables the use of nanoparticles. From the fluid dynamics point of view, the HVSFS system is complex and involves three-phase (gas, liquid and solid particles) turbulent flow, heat transfer, evaporation of the suspension solvent, chemical reactions of main fuel (propane) and suspension solvent (ethanol) and supersonic/subsonic flow transitions. Computational fluid dynamic techniques were carried out to solve the mass, momentum, and energy conservation equations. The realizable k-ɛ turbulence model was used to account for the effect of turbulence. The HVSFS process involves two combustion reactions. A primary combustion process is the premixed oxygen-propane reaction and secondary process is the non-premixed oxygen-gaseous ethanol reaction. For each reaction, one step global reaction, which takes dissociations and intermediate reactions into account, was derived from the equilibrium chemistry code developed by Gordon and McBride and eddy dissipation model was used to calculate the rate of reactions based on the transport equations for all species (10 species) mass fractions. Droplets were tracked in the continuum in a Lagrangian approach. In this paper, flow field inside and outside the gun simulated to provide clear and complete insight about the HVSFS processes. Moreover, the effect of some operative parameters (oxy-fuel flow rate, ethanol flow rate, droplets injection velocity and droplets size) on the gas flow field along the centerline and droplets evaporation behavior was discussed.

  6. MULTIPLE HIGH-VELOCITY SiO MASER FEATURES FROM THE HIGH-MASS PROTOSTAR W51 NORTH

    SciTech Connect

    Cho, Se-Hyung; Kim, Jaeheon; Byun, Do-Young E-mail: jhkim@kasi.re.kr

    2011-02-01

    We present the detection of multiple high-velocity silicon monoxide (SiO v = 1, 2, J = 1-0) maser features in the high-mass protostar W51 North which are distributed over an exceedingly large velocity range from 105 to 230 km s{sup -1}. The SiO v = 1, J = 1-0 maser emission shows 3-5 narrow components which span a velocity range from 154 to 230 km s{sup -1} according to observational epochs. The SiO v = 2, J = 1-0 maser also shows 3-5 narrow components that do not correspond to the SiO v = 1 maser and span a velocity range from 105 to 154 km s{sup -1}. The multiple maser components show significant changes on very short timescales (<1 month) from epoch to epoch. We suggest that the high-velocity SiO masers may be emanated from massive star-forming activity of the W51 North protostar as SiO maser jets and will be a good probe of the earliest evolutionary stages of high-mass star formation via an accretion model. Further high angular resolution observations will be required for confirmation.

  7. Fault gouge rheology under confined, high-velocity conditions

    NASA Astrophysics Data System (ADS)

    Reches, Z.; Madden, A. S.; Chen, X.

    2012-12-01

    We recently developed the experimental capability to investigate the shear properties of fine-grain gouge under confined conditions and high-velocity. The experimental system includes a rotary apparatus that can apply large displacements of tens of meters, slip velocity of 0.001- 2.0 m/s, and normal stress of 35 MPa (Reches and Lockner, 2010). The key new component is a Confined ROtary Cell (CROC) that can shear a gouge layer either dry or under pore-pressure. The pore pressure is controlled by two syringe pumps. CROC includes a ring-shape gouge chamber of 62.5 mm inner diameter, 81.25 mm outer diameter, and up to 3 mm thick gouge sample. The lower, rotating part of CROC contains the sample chamber, and the upper, stationary part includes the loading, hollow cylinder and setting for temperature, and dilation measurements, and pore-pressure control. Each side of the gouge chamber has two pairs of industrial, spring-energized, self-lubricating, teflon-graphite seals, built for particle media and can work at temperature up to 250 ded C. The space between each of the two sets of seals is pressurized by nitrogen. This design generates 'zero-differential pressure' on the inner seal (which is in contact with the gouge powder), and prevents gouge leaks. For the preliminary dry experiments, we used ~2.0 mm thick layers of room-dry kaolinite powder. Total displacements were on the order of meters and normal stress up to 4 MPa. The initial shear was accommodated by multiple internal slip surfaces within the kaolinite layer accommodated as oriented Riedel shear structures. Later, the shear was localized within a thin, plate-parallel Y-surface. The kaolinite layer was compacted at a quasi-asymptotic rate, and displayed a steady-state friction coefficient of ~ 0.5 with no clear dependence on slip velocity up to 0.15 m/s. Further experiments with loose quartz sand (grain size ~ 125 micron) included both dry runs and pore-pressure (distilled water) controlled runs. The sand was

  8. Isothermal Circumstellar Dust Shell Model for Teaching

    ERIC Educational Resources Information Center

    Robinson, G.; Towers, I. N.; Jovanoski, Z.

    2009-01-01

    We introduce a model of radiative transfer in circumstellar dust shells. By assuming that the shell is both isothermal and its thickness is small compared to its radius, the model is simple enough for students to grasp and yet still provides a quantitative description of the relevant physical features. The isothermal model can be used in a…

  9. High velocity collisions - probing the edge of planetesimal growth

    NASA Astrophysics Data System (ADS)

    Teiser, J.; Wurm, G.

    2008-09-01

    field damage around the direct impact site. This near field damage can range from a thin circular trench around the sticking projectile material to a crater which also includes the impact site as material loss. Figure 1 gives an example for a collision with near field damage leading to mass loss. The balance between these two processes determines the mass balance of a collision. (3) When the impact energies are too high a large area of the target surface can be eroded away. This far field damage depends on the target size and thus is not important for realistic conditions. Due to the size dependance of the balance between near and far field damage small projectiles can lead to a net growth even with high velocities. Conclusions Based on experimental results we present a growth model which can be a solution to the question how planetesimal growth is possible once dust aggregates are compact and velocities tend to be destructive. Projectiles of a few mm in size hit a larger aggregate with a size of ~30 cm and leave a crater in the target surface which leads to a slight mass loss. In this colision the projectiles fragment into smaller pieces whereas the target mass hardly changes. In processes of this kind a large amount of sub-mm particles is formed which can lead to a mass gain in a following collisions. Although fragmentation plays a significant role in the high velocity range planetesimal growth via mutual collisions is possible. References [1] Blum, J. and Wurm, G. (2008) ARAA, in press. [2] Dominik, C. and Tielens, A. G. G. M. (1997) ApJ,480, 647-673. [3] Weidenschilling, S. J. and Cuzzi, J. N. (1993) in Levy, E. H. and Lunine, J. I., Protostars and Planets III, 1031-1060. [4] Blum, J. and Münch, (1993) Icarus, 106, 98-116. [5] Wurm, G. et al. (2005) Icarus, 178, 253-263.

  10. The Mineralogy of Circumstellar Silicates Preserved in Cometary Dust

    NASA Technical Reports Server (NTRS)

    Keller, L. P.; Messenger, S.

    2010-01-01

    Interplanetary dust particles (IDPs) contain a record of the building blocks of the solar system including presolar grains, molecular cloud material, and materials formed in the early solar nebula. Cometary IDPs have remained relatively unaltered since their accretion because of the lack of parent body thermal and aqueous alteration. We are using coordinated transmission electron microscope (TEM) and ion microprobe studies to establish the origins of the various components within cometary IDPs. Of particular interest is the nature and abundance of presolar silicates in these particles because astronomical observations suggest that crystalline and amorphous silicates are the dominant grain types produced in young main sequence stars and evolved O-rich stars. Five circumstellar grains have been identified including three amorphous silicate grains and two polycrystalline aggregates. All of these grains are between 0.2 and 0.5 micrometers in size. The isotopic compositions of all five presolar silicate grains fall within the range of presolar oxides and silicates, having large (17)O-enrichments and normal (18)O/(16)O ratios (Group 1 grains from AGB and RG stars). The amorphous silicates are chemically heterogeneous and contain nanophase FeNi metal and FeS grains in a Mg-silicate matrix. Two of the amorphous silicate grains are aggregates with subgrains showing variable Mg/Si ratios in chemical maps. The polycrystalline grains show annealed textures (equilibrium grains boundaries, uniform Mg/Fe ratios), and consist of 50-100 nm enstatite and pyrrhotite grains with lesser forsterite. One of the polycrystalline aggregates contains a subgrain of diopside. The polycrystalline aggregates form by subsolidus annealing of amorphous precursors. The bulk compositions of the five grains span a wide range in Mg/Si ratios from 0.4 to 1.2 (avg. 0.86). The average Fe/Si (0.40) and S/Si (0.21) ratios show a much narrower range of values and are approximately 50% of their solar

  11. Friction and Wear of Carbonate Rocks Under High Velocity Sliding

    NASA Astrophysics Data System (ADS)

    Boneh, Y.; Sagy, A.; Reches, Z.

    2012-12-01

    We experimentally investigated the relations between friction and wear-rate during steady-state, high-velocity slip along carbonate faults. Our observations demonstrate a systematic reduction of both friction coefficient and wear-rate with increase of both slip-velocity and normal stress. The experiments were conducted with a rotary shear apparatus on solid, ring-shaped rock samples that slipped for displacements up to tens of meters, with continuous monitoring of stresses, wear and temperature. We performed 107 experiments on experimental faults made of Kasota dolomite, Dover limestone and a fault made of rock-pair Kasota dolomite and Blue quartzite. The friction/wear analysis is focused on the steady-state stage under slip velocity range of 0.002 to 0.96 m/s, and normal stress from 0.25 to 6.9 MPa. The experiments reveal a combined effect of slip-velocity and normal stress on the wear-rate. Under relatively low velocities (V < 0.5 m/s for limestone and V < 0.12 m/s for dolomite-quartzite pair), the wear-rate is proportional to the normal stress, in agreement with Archard (1953) model. On the other hand, in the higher velocity range of V ~ 0.5 - 1 m/s, the wear-rate is not proportional to the normal stress and it reduces with increasing slip-velocity. Further, the velocity effect on the wear-rate becomes stronger with increasing normal stress approaching negligible wear production. The experiments indicate that the steady-state frictional strength of these carbonate samples is best correlated with the power-density (= shear stress * slip-velocity, MW/m2). The observed friction/power-density relation show three regimes: (1) high (μ ~ 0.9), quasi-constant friction coefficient under low power-density of < 0.05 MW/m2; (2) low (μ ~ 0.3), quasi-constant friction coefficient under high power-density > 0.4 MW/m2; and (3) transition zone of friction coefficient dropping from ~ 0.9 to ~ 0.3 for intermediated power density ranging 0.05 - 0.4 MW/m2. During experiments with

  12. Circumstellar bubble created by two massive stars

    NASA Astrophysics Data System (ADS)

    Meliani, Z.; van Marle, A. J.; Marcowith, A.

    2013-11-01

    The massive stars are formed in clusters then numerical models of wind-blown bubble should evolve bubble created by several stars. Aims. We develop a two-dimensional (2D) model of the circumstellar bubble created by two massive stars, a 40 M_{odot} star and a 25 M_{odot} star, and follow its evolution with MPI-AMRVAC hydrodynamics code until the end of the stellar evolution and he supernova explosion of each star. The stars are separated by approximately 16 pc and surrounded by a cold medium with a density of 20 particles per cm3. The simulations showed that the evolution of a wind-blown bubble created by two stars deviates from that of the bubbles around single stars. In particular, once one of the stars has exploded, the bubble is too large for the wind of the remaining star to maintain and the outer shell starts to disintegrate. The lack of thermal pressure inside the bubble also changes the behavior of circumstellar features close to the remaining star. The supernovae are contained inside the bubble, which reflects part of the energy back into the circumstellar medium.

  13. Clarifying Massive Protostellar Evolution and Circumstellar Processing

    NASA Astrophysics Data System (ADS)

    Indebetouw, Remy; Brogan, Crystal; Hoare, Melvin; Lumsden, Stuart; Robitaille, Thomas; Sewilo, Marta; Urquhart, James; Viti, Serena; Whitney, Barbara

    2008-03-01

    Massive stars dominate the evolution of galaxies and even as protostars, their feedback can affect their own formation and that of their host clusters. We propose a systematic study of massive protostars through the stages of their early evolution, to derive a clearer evolutionary sequence and a better link between the state of the central source and physical conditions in circumstellar material. This experiment will improve over existing work by careful source selection to systematically span evolutionary parameter space, resulting in a more uniform and comprehensive sample. Sophisticated radiative transfer, ionization, and chemical modeling will be used to extract the full riches of each IRS spectrum and find trends in how massive stars form and process their natal material: We will be able to determine the temperature, density, and chemical state (heating history) of circumstellar dust and ice in the accretion disk and envelope, and at later evolutionary stages the ionizing and soft (PAH-exciting) ultraviolet radiation emitted by the protostars and how that radiation is quenched and shadowed by circumstellar material. This investigation is the key to realizing the full potential of previous infrared imaging surveys like MSX and Spitzer's GLIMPSE and MIPSGAL to study massive star formation. These surveys have provided a basis for us to select a large relatively unbiased sample spanning evolutionary state. In return, revealing the spectroscopic signature of massive YSOs will greatly clarify the modeling and interpretation of the thousands of other protostars in these imaging survey data.

  14. SiS2 in circumstellar shells

    NASA Astrophysics Data System (ADS)

    Goebel, J. H.

    1993-10-01

    Solid state SiS2 is proposed as the material responsible for the recently discovered 21 micrometer emission feature that is observed in the carbon-rich circumstellar shells of certain protoplanetary nebulae. Sulfurized SiC, or SiS2 mantles on grains of either SiC or a:C-H are discussed as possible forms for which no spectroscopic laboratory observations yet exist. The identification with a relatively minor species and required special abundance ratios are consistent with the low incidence rate that the 21 micrometer feature presents in the population of carbon rich objects. It is also consistent with the lack of a good correlation between the 21 micrometer feature and the other solid-state spectroscopic features that have been observed in protoplanetaries that would be expected if the feature arose from molecules composed of H, C, N, and O. SiS2 condensate is consistent with the circumstellar shell temperature range, TCS approximately equal to or less than 150 K, at which the feature appears, and the available mass of SiS2, MSiS2 approx. = 5 x 10-6 solar mass, that is possible in the circumstellar shell.

  15. GALACTIC ALL-SKY SURVEY HIGH-VELOCITY CLOUDS IN THE REGION OF THE MAGELLANIC LEADING ARM

    SciTech Connect

    For, Bi-Qing; Staveley-Smith, Lister; McClure-Griffiths, N. M.

    2013-02-10

    We present a catalog of high-velocity clouds in the region of the Magellanic Leading Arm. The catalog is based on neutral hydrogen (H I) observations from the Parkes Galactic All-Sky Survey. Excellent spectral resolution allows clouds with narrow-line components to be resolved. The total number of detected clouds is 419. We describe the method of cataloging and present the basic parameters of the clouds. We discuss the general distribution of the high-velocity clouds and classify the clouds based on their morphological type. The presence of a significant number of head-tail clouds and their distribution in the region is discussed in the context of Magellanic System simulations. We suggest that ram-pressure stripping is a more important factor than tidal forces for the morphology and formation of the Magellanic Leading Arm and that different environmental conditions might explain the morphological difference between the Magellanic Leading Arm and Magellanic Stream. We also discuss a newly identified population of clouds that forms the LA IV and a new diffuse bridge-like feature connecting the LA II and III complexes.

  16. Evolution of the High Velocity X-Ray Emission in SN 1987A

    NASA Astrophysics Data System (ADS)

    Dewey, Daniel; Haberl, F.; Dwarkadas, V. V.; Burrows, D. N.; Park, S.

    2011-01-01

    Chandra HETG observations of SN 1987A in late 1999 showed very broad lines with observed FWHM of order 7000 km/s (Michael et al. 2002). At this time (SN day 4600) the blastwave was already interacting with the HII region around the progenitor and optical spots had recently appeared. High-resolution spectra taken from May 2003 ( day 5900) to the present by XMM-Newton and Chandra have been well fit by models with FWHM less than 2000 km/s (Zhekov et al. 2005; Dewey et al. 2008; Sturm et al 2010). The emission is increasingly dominated by these narrower components as the blastwave encounters more of the dense equatorial ring. However emission from the HII region out of the ring plane is still expected at late times and would contribute a high-velocity component to the spectra. We analyze 6 epochs of SN 1987A grating data and include an additional very broad component in the spectral model. We find that deep HETG 2007 data are better fit when one quarter of the flux comes from a component with FWHM 8500 km/s, and that RGS 2003 data show an improved fit with a very-broad fraction that is between the 1999 and 2007 values. Later data continue a progression to lower, but still significant, very-broad fractions. The measurements are discussed in terms of the density and extent of the out-of-plane HII region, hydrodynamical simulations, and 3D models of SN 1987A's emission. Support for this work was provided by NASA/USA through contract NAS8-03060 to the Smithsonian Astrophysical Observatory (SAO) and further SAO sub-contracts TM9-0004X to VVD (U Chicago) and SV3-73016 to MIT for support of the CXC.

  17. High velocity properties of the dynamic frictional force between ductile metals

    SciTech Connect

    Hammerberg, James Edward; Hollan, Brad L; Germann, Timothy C; Ravelo, Ramon J

    2010-01-01

    The high velocity properties of the tangential frictional force between ductile metal interfaces seen in large-scale NonEquilibrium Molecular Dynamics (NEMD) simulations are characterized by interesting scaling behavior. In many cases a power law decrease in the frictional force with increasing velocity is observed at high velocities. We discuss the velocity dependence of the high velocity branch of the tangential force in terms of structural transformation and ultimate transition, at the highest velocities, to confined fluid behavior characterized by a critical strain rate. The particular case of an Al/Al interface is discussed.

  18. Kinematic Dynamo In Turbulent Circumstellar Disks

    NASA Technical Reports Server (NTRS)

    Stepinski, T.

    1993-01-01

    Many circumstellar disks associated with objects ranging from protoplanetary nebulae, to accretion disks around compact stars allow for the generation of magnetic fields by an (alpha)omega dynamo. We have applied kinematic dynamo formalism to geometrically thin accretion disks. We calculate, in the framework of an adiabatic approximation, the normal mode solutions for dynamos operating in disks around compact stars. We then describe the criteria for a viable dynamo in protoplanetary nebulae, and discuss the particular features that make accretion disk dynamos different from planetary, stellar, and galactic dynamos.

  19. CELFE/NASTRAN Code for the Analysis of Structures Subjected to High Velocity Impact

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.

    1978-01-01

    CELFE (Coupled Eulerian Lagrangian Finite Element)/NASTRAN Code three-dimensional finite element code has the capability for analyzing of structures subjected to high velocity impact. The local response is predicted by CELFE and, for large problems, the far-field impact response is predicted by NASTRAN. The coupling of the CELFE code with NASTRAN (CELFE/NASTRAN code) and the application of the code to selected three-dimensional high velocity impact problems are described.

  20. A 'dry' condensation origin for circumstellar carbonates.

    PubMed

    Toppani, Alice; Robert, François; Libourel, Guy; de Donato, Philippe; Barres, Odile; d'Hendecourt, Louis; Ghanbaja, Jaafar

    2005-10-20

    The signature of carbonate minerals has long been suspected in the mid-infrared spectra of various astrophysical environments such as protostars. Abiogenic carbonates are considered as indicators of aqueous mineral alteration in the presence of CO2-rich liquid water. The recent claimed detection of calcite associated with amorphous silicates in two planetary nebulae and protostars devoid of planetary bodies questions the relevance of this indicator; but in the absence of an alternative mode of formation under circumstellar conditions, this detection remains controversial. The main dust component observed in circumstellar envelopes is amorphous silicates, which are thought to have formed by non-equilibrium condensation. Here we report experiments demonstrating that carbonates can be formed with amorphous silicates during the non-equilibrium condensation of a silicate gas in a H2O-CO2-rich vapour. We propose that the observed astrophysical carbonates have condensed in H2O(g)-CO2(g)-rich, high-temperature and high-density regions such as evolved stellar winds, or those induced by grain sputtering upon shocks in protostellar outflows. PMID:16237436

  1. Circumstellar Material in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    van den Ancker, Mario

    1999-09-01

    In my dissertation I present the results of optical, infrared and submm studies of the circumstellar environment of young stellar objects, mostly of intermediate mass. Both the circumstellar dust and gas are studied, using results from the Hipparcos mission, the Infrared Space Observatory (ISO) and several ground-based telescopes. The basic stellar properties of a sample of Herbig Ae/Be stars (HAeBes) were derived using the astrometric data from the Hipparcos mission. The basic conclusion from this study is that most HAeBes in our sample must be pre-main sequence stars. An evolutionary scenario for the dissipation of dust around Herbig Ae/Be stars is outlined, based on the new stellar parameters derived from the Hipparcos astrometry. Using the photometry obtained by Hipparcos, I also study the circumstellar dust through its effect on the light of the central star as it moves in and out of our line of sight. I show that such an effect can only be seen towards Herbig Ae/Be systems with a central star of spectral type A0 or later, which is explained as being due to the evolutionary effect that Herbig Be stars are not optically visible while still contracting towards the zero-age main sequence. I also looked in more detail at the thermal emission from dust in the disks of two Herbig Ae systems, AB Aur and HD 163296, using ISO spectroscopy and new VLA data. In both these systems, significant grain growth has already occurred. However, the degree in which this has happened, as well as the degree in which the dust has crystallized, differs greatly between these two systems of identical mass and age. Clearly other parameters than just stellar mass and age influence the dissipation speed and degree of processing of the dust in a circumstellar disk. Another way to study circumstellar dust is through submillimeter photometry. I have followed this approach to study the dust in the star forming region associated with the Herbig stars R and T CrA, using 450 and 850 micron maps

  2. From Circumstellar Envelopes to the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Ueta, T.

    2011-09-01

    IRAS and ISO observations have indicated that the extended dust shells of AGB stars could be explained by a simple model of a constant past mass outflow piling up at the interface with the interstellar medium (ISM). Recent Spitzer observations have shown that even outflows from AGB stars can induce shocks at the ISM-AGB wind interface, while a recent AKARI survey of the circumstellar envelopes of evolved stars have revealed far-IR structures resembling to the interface regions between the ISM and AGB winds in many objects. There have been observations made in other wavelengths (especially in the UV with GALEX) that corroborate these findings in the far-IR. New Herschel observations are expected to provide detailed views of these interface regions. Therefore, the extended dust shells of AGB stars should not only allow us to prove the mass-loss history of the parent AGB stars but also permit us to glimpse how the ejecta eventually merge with the ISM. In this review, I will summarize recent research developments made by observations with Spitzer, AKARI, and Herschel at the interface region between the circumstellar envelopes of AGB stars and the ISM.

  3. Signs of interaction of the NGC 1275 nucleus with the high-velocity system according to 0.7 sec seeing observations

    NASA Technical Reports Server (NTRS)

    Dudinov, V. N.; Tsvetkova, V. S.; Novikov, S. B.; Pronik, I. I.

    1990-01-01

    The nucleus of the Seyfert galaxy NGC 1275 was observed in the B system on 1 December 1989 with seeing 0, 7 seconds using the Zeiss-1000 telescope on Mount Majdanak in Central Asia. Special methods of processing reveal low-contrast details. The nucleus and circumnucleus are stretched in NW-SE direction. There are two narrow filaments near the nucleus in position angles roughly 340 degrees and 320 degrees. The first is directed near the radio jet of the nucleus, the second has broken details curved to the NW or toward the high-velocity system of NGC 1275.

  4. ARE HIGH VELOCITY PEAKS IN THE MILKY WAY BULGE DUE TO THE BAR?

    SciTech Connect

    Li, Zhao-Yu; Shen, Juntai; Rich, R. Michael; Kunder, Andrea; Mao, Shude

    2014-04-10

    Recently the commissioning APOGEE observations of the Galactic bulge reported that a significant fraction of stars (∼10%) are in a cold (σ{sub V} ≈ 30 km s{sup –1}) high velocity peak (Galactocentric radial velocity ≈200 km s{sup –1}). These stars are speculated to reflect the stellar orbits in the Galactic bar. In this study, we use two N-body models of a Milky Way-like disk galaxy with different bar strengths to critically examine this possibility. The general trends of the Galactocentric radial velocity distribution in observations and simulations are similar, but neither our models nor the BRAVA data reveal a statistically significant cold high velocity peak. A Monte Carlo test further suggests that it is possible for a spurious high velocity peak to appear if there are only a limited number of stars observed. Thus, the reported cold high velocity peak, even if it is real, is unlikely due to stars on the bar-supporting orbits. Our models do predict an excess of stars with high radial velocity, but not in a distinct peak. In the distance-velocity diagram, the high velocity particles in different fields exist at a similar distance ∼8.5 ± 1 kpc away from the Sun. This result may be explained by geometric intersections between the line-of-sight and the particle orbits; high velocity stars naturally exist approximately at the tangent point, without constituting a distinct peak. We further demonstrate that even without the presence of a bar structure, particle motions in an axisymmetric disk can also exhibit an excess of high velocity stars.

  5. High-velocity frictional properties of a clay-bearing fault gouge and implications for earthquake mechanics

    NASA Astrophysics Data System (ADS)

    Brantut, N.; Schubnel, A.; Rouzaud, J.-N.; Brunet, F.; Shimamoto, T.

    2008-10-01

    Frictional properties of natural kaolinite-bearing gouge samples from the Median Tectonic Line (SW Japan) have been studied using a high-velocity rotary shear apparatus, and deformed samples have been observed with optical and electron (scanning and transmission) microscopy. For a slip velocity of 1 m s-1 and normal stresses from 0.3 to 1.3 MPa, a dramatic slip-weakening behavior was observed. X-ray diffraction analysis of deformed samples and additional high-velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip. The critical slip-weakening distance Dc is of the order of 1 to 10 m. These values are extrapolated to higher normal stresses, assuming that Dc is rather a thermal parameter than a parameter related to a true characteristic length. The calculation shows that dimensionally, Dc ∝ 1/σn2, where σn is the normal stress applied on the fault. The inferred Dc values range from a few centimeters at 10 MPa normal stress to a few hundreds of microns at 100 MPa normal stress. Microscopic observations show partial amorphization and dramatic grain size reduction (down to the nanometer scale) localized in a narrow zone of about 1 to 10 μm thickness. Fracture energy Gc is calculated from the mechanical curves and compared to surface energy due to grain size reduction, and energies of mineralogic transformations. We show that most of the fracture energy is either converted into heat or radiated energy. The geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poromechanical data of several fault zones, which tend to show that this phenomenon has to be taken into account in most of subsurface faults and in hydrous rocks of subducted oceanic crust.

  6. THE 21 cm 'OUTER ARM' AND THE OUTER-GALAXY HIGH-VELOCITY CLOUDS: CONNECTED BY KINEMATICS, METALLICITY, AND DISTANCE

    SciTech Connect

    Tripp, Todd M.; Song Limin

    2012-02-20

    Using high-resolution ultraviolet spectra obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectroscopic Explorer, we study the metallicity, kinematics, and distance of the gaseous 'outer arm' (OA) and the high-velocity clouds (HVCs) in the outer Galaxy. We detect the OA in a variety of absorption lines toward two QSOs, H1821+643 and HS0624+6907. We search for OA absorption toward eight Galactic stars and detect it in one case, which constrains the OA Galactocentric radius to 9 kpc narrow components, indicating the presence of several cold clouds and rapid cooling and fragmentation. Some of the highly ionized gas is also surprisingly cool. Accounting for ionization corrections, we find that the OA metallicity is Z = 0.2-0.5 Z{sub Sun }, but nitrogen is underabundant and some species are possibly mildly depleted by dust. The similarity of the OA metallicity, Galactocentric location, and kinematics to those of the adjacent outer-Galaxy HVCs, including high velocities that are not consistent with Galactic rotation, suggests that the OA and outer-Galaxy HVCs could have a common origin.

  7. Models of Interacting Supernovae: Understanding the Physics and Probing the Circumstellar Environment

    NASA Astrophysics Data System (ADS)

    Baron, Edward

    "Interacting supernovae" are poorly understood astronomical events with great potential for expanding our understanding of how stars evolve and die, and could provide important clues about the early formation of large-scale structures such as galaxies in the universe. Interacting supernovae occur when a star explodes within a dense cloud of material shed from the star in the course of its evolution. The resulting violent interaction between the expanding supernova explosion and the cloud of circumstellar material can lead to an enormously bright visual display --- indeed, many of the brightest supernovae ever recorded are thought to arise from circumstellar interaction. In order to understand the properties of the progenitor star and the details of the circumstellar interaction, there is a need for theoretical models of interacting supernovae. These simulated computer spectra can be directly compared to the spectra observed by telescopes. These models allow us to probe the physical circumstances that underlie the observations. The spectra of interacting supernovae are dominated by strong, narrow emission lines of light elements such as hydrogen and helium. These narrow lines give Type IIn supernovae their designation. Similarly, objects of Type Ian, Ibn, Icn, and IIn are somewhat distinct, but are all defined by the narrow emission lines that result from the interaction of their expanding envelopes with their surroundings. The photosphere in these supernovae is formed in the material accreted during the coasting phase, and most of the luminosity has its origin from the conversion of kinetic explosion energy into luminosity. Both thermonuclear (Type Ia) and core-collapse (Types Ib/Ic and II) supernovae may be the inner engine. In fact, several Type IIn supernovae at early times have later been classified as Type Ia, Type Ib/c, or Type II as their spectra reveal more details about the nature of the central explosion. As a result of the dominance of the interaction

  8. HL Tauri and its circumstellar disk

    NASA Technical Reports Server (NTRS)

    Cohen, M.

    1983-01-01

    New far infrared observations of HL Tau which support the identification of an edge-on disk surrounding the star are presented. A bolometric luminosity for the star of 7.2 solar luminosities and a ratio of infrared to optical luminosity of 630 are indicated. A circumstellar A(V) of about 7.0 mag is produced, consistent with the silicate optical depth to the star. Data on HL Tau's effective temperature and radius and its position on the HR diagram suggest that the star has recently completed its accretion phase and is only 100,000 yr old. The column masses of ice and silicates are combined with the disk dimensions to build a simple model of the disk for comparison with the primitive solar nebula. Estimates of the far-infrared emitting mass provide independent probes of the mass in larger grains around HL Tau.

  9. Circumstellar and interstellar synthesis of organic molecules.

    PubMed

    Tielens, A G; Charnley, S B

    1997-06-01

    We review the formation and evolution of complex circumstellar and interstellar molecules. A number of promising chemical routes are discussed which may lead to the formation of polycyclic aromatic hydrocarbon molecules, fullerenes, and unsaturated hydrocarbon chains in the outflows from stars. Some of the problems with these chemical schemes are pointed out as well. We also review the role of grains in the formation of complex molecules in interstellar molecular clouds. This starts with the formation of simple molecules in an ice grain mantle. UV photolysis and/or thermal polymerization can convert some of these simple molecules into more complex polymeric structures. Some of these species may be released to the gas phase, particularly in the warm regions around newly formed stars. Methanol and formaldehyde seem to play an important role in this drive towards molecular complexity and their chemistry is traced in some detail.

  10. Spectroscopic Survey of Circumstellar Disks in Orion

    NASA Astrophysics Data System (ADS)

    Contreras, Maria; Hernandez, Jesus; Olguin, Lorenzo; Briceno, Cesar

    2013-07-01

    As a second stage of a project focused on characterizing candidate stars bearing a circumstellar disk in Orion, we present a spectroscopic follow-up of a set of about 170 bright stars. The present set of stars was selected by their optical (UBVRI) and infrared behavior in different color-color and color-magnitude diagrams. Observations were carried out at the Observatorio Astronomico Nacional located at the Sierra San Pedro Martir in B.C., Mexico and at the Observatorio Guillermo Haro in Cananea, Sonora, Mexico. Low-resolution spectra were obtained for all candidates in the sample. Using the SPTCLASS code, we have obtained spectral types and equivalent widths of the Li I 6707 and Halpha lines for each one of the stars. This project is a cornerstone of a large scale survey aimed to obtain stellar parameters in a homogeneous way using spectroscopic data. This work was partially supported by UNAM-PAPIIT grant IN-109311.

  11. Secular Planetary Perturbations in Circumstellar Debris Disks

    NASA Astrophysics Data System (ADS)

    Hahn, Joseph M.; Capobianco, C.

    2006-12-01

    Circumstellar debris disks are likely the by-product of collisions among unseen planetesimals. Planetesimals are also the seeds of planets, so it is reasonable to expect that some debris disks might also harbor planets. In fact several such disks, like those orbiting beta Pictoris, Fomalhaut, etc., do appear to be perturbed by unseen planets orbiting within. The signatures of planetary perturbations include: central gaps, warps, and radial offsets in the disk's surface brightness. By modeling the disturbances observed in a circumstellar dust disk, one can then measure or constrain the masses and orbits of the planets that may be lurking within. Of particular interest here are the warps and radial offsets seen in such disks, since these features can be due to secular planetary perturbations (Mouillet et al 1997, Wyatt et al 1999). Secular perturbations are the slowly varying gravitational perturbations that can excite orbital eccentricities and inclinations in a disk, and can also drive a slow orbital precession. Note that a dust grain's motion is completely analytic when suffering secular perturbations (Murray & Dermott 1999), which allows us to rapidly generate a synthetic image of a simulated disk as would be seen in scattered starlight or via thermal emission. And because this model is quite fast, our model can rapidly scan a rather large parameter space in order to determine the planetary configuration that may be responsible for the disk's perturbed appearance. We have applied this dust-disk model to Hubble observations of the β Pictoris dust-disk (from Heap et al 2000), and will report on the planets that may be responsible for the warp seen in this edge-on disk. We will also apply the model to optical and IR observations of debris disks at Fomalhaut, AU Microscopii, and others, with additional results to be reported at conference time.

  12. Nearby Supernova Factory Observations of SN 2005gj: Another TypeIa Supernova in a Massive Circumstellar Envelope

    SciTech Connect

    Aldering, G.; Antilogus, P.; Bailey, S.; Baltay, C.; Bauer, A.; Blanc, N.; Bongard, S.; Copin, Y.; Gangler, E.; Gilles, S.; Kessler, R.; Kocevski, D.; Lee, B.C.; Loken, S.; Nugent, P.; Pain, R.; Pecontal, E.; Pereira, R.; Perlmutter, S.; Rabinowitz, D.; Rigaudier, G.; Scalzo, R.; Smadja, G.; Thomas, R.C.; Wang, L.; Weaver, B.A.; Rabinowitz, D.; Bauer, A.

    2006-06-01

    We report the independent discovery and follow-up observations of supernova 2005gj by the Nearby Supernova Factory. This is the second confirmed case of a ''hybrid'' Type Ia/IIn supernova, which like the prototype SN 2002ic, we interpret as the explosion of a white dwarf interacting with a circumstellar medium. Our early-phase photometry of SN 2005gj shows that the strength of the interaction between the supernova ejecta and circumstellar material is much stronger than for SN 2002ic. Our .rst spectrum shows a hot continuum with broad and narrow H{alpha} emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow H{gamma}, H{beta},H{alpha} and He I {lambda}{lambda}5876,7065 in emission. At higher resolution, P Cygni profiles are apparent. Surprisingly, we also observe an inverted P Cygni profile for [O III] {lambda}5007. We find that the lightcurve and measured velocity of the unshocked circumstellar material imply mass loss as recently as 8 years ago. This is in contrast to SN 2002ic, for which an inner cavity in the circumstellar material was inferred. Within the context of the thin-shell approximation, the early lightcurve is well-described by a flat radial density profile for the circumstellar material. However, our decomposition of the spectra into Type Ia and shock emission components allows for little obscuration of the supernova, suggesting an aspherical or clumpy distribution for the circumstellar material. We suggest that the emission line velocity profiles arise from electron scattering rather than the kinematics of the shock. This is supported by the inferred high densities, and the lack of evidence for evolution in the line widths. Ground- and space-based photometry, and Keck spectroscopy, of the host galaxy are used to ascertain that the host galaxy has low metallicity (Z/Z{sub {circle_dot}} < 0.3; 95% confidence) and that this galaxy is undergoing a significant star formation event that

  13. Search for auroral belt E-parallel fields with high-velocity barium ion injections

    NASA Technical Reports Server (NTRS)

    Heppner, J. P.; Ledley, B. G.; Miller, M. L.; Marionni, P. A.; Pongratz, M. B.

    1989-01-01

    In April 1984, four high-velocity shaped-charge Ba(+) injections were conducted from two sounding rockets at 770-975 km over northern Alaska under conditions of active auroral and magnetic disturbance. Spatial ionization (brightness) profiles of high-velocity Ba(+) clouds from photometric scans following each release were found to be consistent with the 28-sec theoretical time constant for Ba photoionization determined by Carlsten (1975). These observations therefore revealed no evidence of anomalous fast ionization predicted by the Alfven critical velocity hypothesis.

  14. Dynamics and Observational Appearance of Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Nelson, Andrew Frederick

    In my thesis I present a study of the dynamics and observational characteristics of massive circumstellar disks in two dimensions (r, f ) using two complimentary hydro-dynamic codes: a `Smoothed Particle Hydrodynamic' (SPH) code and a `Piecewise Parabolic Method' (PPM) code. I also study the detection limits available to radial velocity searches for low mass companions to main sequence stars. This thesis is organized as a series of published or submitted papers, connected by introductory and concluding material. I strongly recommend that readers of this abstract obtain the published versions of each of these papers. I first outline the progress which has been made in the modeling of the structure and origins of the solar system, then in chapter 2 (The Astrophysical Journal v502, p342, with W. Benz, F. Adams and D. Arnett), I proceed with numerical simulations of circumstellar disks using both hydrodynamic codes assuming a `locally isothermal' equation of state. The disks studied range in mass from 0.05M* to 1.0 M* and in initial minimum Toomre Q value from 1.1 to 3.0. Massive disks (MD > 0.2 M*) tend to form grand design spiral structure with 1-3 arms, while low mass disks (MD <= 0.2M*) tend to form filamentary, >4 armed spiral structures. In chapter 4 (submitted to The Astrophysical Journal with W. Benz and T. Ruzmaikina), I relax the assumption the locally isothermal evolution assumption and instead include simple heating and cooling prescriptions for the system. Under these physical conditions, the spiral arm growth is suppressed in the inner 1/3 of the disks relative to the isothermal evolution and in the remainder, changes character to more diffuse spiral structures. I synthesize spectral energy distributions (SEDs) from the simulations and compare them to fiducial SEDs derived from observed systems. The size distribution of grains in the inner disk can have marked consequences on the near infrared portion of the SED. After being vaporized in a hot midplane

  15. High-velocity bipolar mass flow in the planetary nebula NGC 2392

    SciTech Connect

    Gieseking, F.; Becker, I.; Solf, J.

    1985-08-01

    Detailed spectroscopic observations of a high-velocity component in the velocity field of the Eskimo nebula, NGC 2392, are presented. It is interpreted as a jetlike multiknot bipolar mass flow with a velocity of nearly 200 km/s and a small angle of collimation less than 10 deg. Electron density, mass, kinetic energy, and power are estimated. 19 references.

  16. Experimental verification of vapor deposition rate theory in high velocity burner rigs

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.; Santoro, Gilbert J.

    1985-01-01

    The main objective has been the experimental verification of the corrosive vapor deposition theory in high-temperature, high-velocity environments. Towards this end a Mach 0.3 burner-rig appartus was built to measure deposition rates from salt-seeded (mostly Na salts) combustion gases on the internally cooled cylindrical collector. Deposition experiments are underway.

  17. High Velocity Oxidation and Hot Corrosion Resistance of Some ODS Alloys

    NASA Technical Reports Server (NTRS)

    Lowell, C. E.; Deadmore, D. L.

    1977-01-01

    Several oxide dispersion strengthened (ODS) alloys were tested for cyclic, high velocity, oxidation, and hot corrosion resistance. These results were compared to the resistance of an advanced, NiCrAl coated superalloy. An ODS FeCrAl were identified as having sufficient oxidation and hot corrosion resistance to allow potential use in an aircraft gas turbine without coating.

  18. Temporary Network Development Capability in High Velocity Environments: A Dynamic Capability Study of Disaster Relief Organizations

    ERIC Educational Resources Information Center

    O'Brien, William Ross

    2010-01-01

    Organizations involved in crisis relief after a natural disaster face the multifaceted challenge of significantly changing needs of their various stakeholders, limited, ambiguous and even incorrect information, and highly compressed time limitations. Yet the performance of these organization in these high velocity environments is critical for the…

  19. Survivability of bare, individual Bacillus subtilis spores to high-velocity surface impact: Implications for microbial transfer through space

    NASA Astrophysics Data System (ADS)

    Barney, Brandon L.; Pratt, Sara N.; Austin, Daniel E.

    2016-06-01

    Laboratory experiments show that endospores of Bacillus subtilis survive impact against a solid surface at velocities as high as 299 ±28 m/s. During impact, spores experience and survive accelerations of at least 1010 m/s2. The spores were introduced into a vacuum chamber using an electrospray source and accelerated to a narrow velocity distribution by entrainment in a differentially pumped gas flow. Different velocity ranges were studied by modifying the gas flow parameters. The spores were electrically charged, allowing direct measurement of the velocity of each spore as it passed through an image charge detector prior to surface impact. Spores impacted a glass surface and were collected for subsequent analysis by culturing. Most spores survived impact at all measured velocities. These experiments differ fundamentally from other studies that show either shock or impact survivability of bacteria embedded within or on the surface of a projectile. Bacteria in the present experiments undergo a single interaction with a solid surface at the full impact velocity, in the absence of any other effects such as cushioning due to microbe agglomerations, deceleration due to air or vapor, or transfer of impact shock through solid or liquid media. During these full-velocity impact events, the spores experience extremely high decelerations. This study is the first reported instance of accelerations of this magnitude experienced during a bacteria impact event. These results are discussed in the context of potential transfer of viable microbes in space and other scenarios involving surface impacts at high velocities.

  20. Circumstellar Hydrodynamics and Spectral Radiation in ALGOLS

    NASA Astrophysics Data System (ADS)

    Terrell, Dirk Curtis

    1994-01-01

    Algols are the remnants of binary systems that have undergone large scale mass transfer. This dissertation presents the results of the coupling of a hydrodynamical model and a radiative model of the flow of gas from the inner Lagrangian point. The hydrodynamical model is a fully Lagrangian, three-dimensional scheme with a novel treatment of viscosity and an implementation of the smoothed particle hydrodynamics method to compute pressure gradients. Viscosity is implemented by allowing particles within a specified interaction length to share momentum. The hydrodynamical model includes a provision for computing the self-gravity of the disk material, although it is not used in the present application to Algols. Hydrogen line profiles and equivalent widths computed with a code by Drake and Ulrich are compared with observations of both short and long period Algols. More sophisticated radiative transfer computations are done with the escape probability code of Ko and Kallman which includes the spectral lines of thirteen elements. The locations and velocities of the gas particles, and the viscous heating from the hydro program are supplied to the radiative transfer program, which computes the equilibrium temperature of the gas and generates its emission spectrum. Intrinsic line profiles are assumed to be delta functions and are properly Doppler shifted and summed for gas particles that are not eclipsed by either star. Polarization curves are computed by combining the hydro program with the Wilson-Liou polarization program. Although the results are preliminary, they show that polarization observations show great promise for studying circumstellar matter.

  1. Circumstellar Debris Disks: Diagnosing the Unseen Perturber

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika R.; Naoz, Smadar; Vican, Laura; Farr, Will M.

    2016-07-01

    The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai–Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai–Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai–Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

  2. Circumstellar disks around binary stars in Taurus

    SciTech Connect

    Akeson, R. L.

    2014-03-20

    We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10{sup –4} M {sub ☉}. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F{sub mm}∝M{sub ∗}{sup 1.5--2.0} to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

  3. The circumstellar ring of SN 1987A

    NASA Astrophysics Data System (ADS)

    Fransson, Claes; Migotto, Katia; Larsson, Josefin; Pesce, Dominic; Challis, Peter; Chevalier, Roger A.; France, Kevin; Kirshner, Robert P.; Leibundgut, Bruno; Lundqvist, Peter; McCray, Richard; Spyromilio, Jason; Taddia, Francesco; Jerkstrand, Anders; Mattila, Seppo; Smith, Nathan; Sollerman, Jesper; Wheeler, J. Craig; Crotts, Arlin; Garnavich, Peter; Heng, Kevin; Lawrence, Stephen S.; Panagia, Nino; Pun, Chun S. J.; Sonneborn, George; Sugerman, Ben

    2016-06-01

    The circumstellar ring of supernova 1987A first became visible a few months after the explosion due to photoionisation by the supernova flash. From 1995 hotspots appeared in the ring and their brightness increased nearly exponentially as a result of interaction with the supernova blast wave. Imaging and spectroscopic observations with the Hubble Space Telescope and the Very Large Telescope now show that both the shocked and the unshocked emission components from the ring have been decreasing since ~ 2009. In addition, the most recent images reveal the brightening of new spots outside the ring. These observations indicate that the hotspots are being dissolved by the shocks and that the blast wave is now expanding and interacting with dense clumps beyond the ring. Based on the currently observed decay we predict that the ring will be destroyed by ~ 2025, while the blast wave will reveal the distribution of gas as it expands outside the ring, thus tracing the mass-loss history of the supernova progenitor.

  4. Circumstellar Debris Disks: Diagnosing the Unseen Perturber

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika R.; Naoz, Smadar; Vican, Laura; Farr, Will M.

    2016-07-01

    The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai-Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai-Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai-Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

  5. An MCMC Circumstellar Disks Modeling Tool

    NASA Astrophysics Data System (ADS)

    Wolff, Schuyler; Perrin, Marshall D.; Mazoyer, Johan; Choquet, Elodie; Soummer, Remi; Ren, Bin; Pueyo, Laurent; Debes, John H.; Duchene, Gaspard; Pinte, Christophe; Menard, Francois

    2016-01-01

    We present an enhanced software framework for the Monte Carlo Markov Chain modeling of circumstellar disk observations, including spectral energy distributions and multi wavelength images from a variety of instruments (e.g. GPI, NICI, HST, WFIRST). The goal is to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in the derived properties. This modular code is designed to work with a collection of existing modeling tools, ranging from simple scripts to define the geometry for optically thin debris disks, to full radiative transfer modeling of complex grain structures in protoplanetary disks (using the MCFOST radiative transfer modeling code). The MCMC chain relies on direct chi squared comparison of model images/spectra to observations. We will include a discussion of how best to weight different observations in the modeling of a single disk and how to incorporate forward modeling from PCA PSF subtraction techniques. The code is open source, python, and available from github. Results for several disks at various evolutionary stages will be discussed.

  6. Multiple circumstellar shells and radiation pressure on grains in the outflows from late-type giants

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1984-01-01

    It is pointed out that mass loss from red giants and supergiants is sometimes as high as 0.0001 solar mass per year. This mass loss represents a major source of new interstellar matter. The present investigation is concerned with the phenomena involved in stellar mass loss, taking into account a comparison of currently available observations with plausible models. The case of the extended circumstellar envelope around IRC +10216 is considered. In observations about mass loss from circumstellar shells, it is sometimes found that the P Cygni profiles are split into two or more sharp, distinct components. The question is considered whether such narrow separate components can be understood in terms of the radiation pressure model. A grain growth model is discussed along with outflow velocity, radiation pressure, and mass loss rates. The models are compared with observations from Alpha Orionis, Mira, and IRC +10216. It is concluded that a hybrid model for the mass loss from some late-type stars seems appropriate. Under certain conditions, outflow speeds of 10 to 20 km/s can be understood.

  7. Cosmic Fire Hydrants: The nature of 11 high-velocity water masers in our Galaxy

    NASA Astrophysics Data System (ADS)

    Harvey-Smith, Lisa; Walsh, Andrew; Breen, Shari; Green, jimi; Purcell, Cormac; Longmore, Steve N.

    2015-08-01

    Water masers act as excellent cosmic markers for the motion of dynamic astronomical regions such as young massive circumstellar disks and outflows from evolved stars. Studying fast water masers gives us a very rare insight into two very a significant stages of stellar evolution.In high-mass star forming regions, water masers are formed in the walls of conical outflows, in collimated jets and in some cases under the influence of a circumstellar disk wind. High-resolution studies of these masers therefore enable us to probe the accretion mechanism for massive star formation. Water masers in post-Asymptotic Giant Branch (AGB) stars probe the very brief phase of aspherical mass-loss before the outer layers of the circumstellar envelope are ionised and the star becomes a Planetary Nebula. The process of aspherical Planetary Nebula formation is still the subject of considerable debate, with the binary hypothesis and magnetic collimation of fast winds being the leading explanations at present.We selected the eleven water maser sites from the H2O Southern Galactic Plane Survey that have differential radial velocities greater than 200 km/s. The water maser sites were subsequently re-observed at higher angular resolution to localise the maser positions with respect to other astronomical emission in the vicinity and where possible, to probe the internal velocity gradients. We conducted a multi-wavelength study of these sites of water masers to determine the stage of stellar evolution, their physical size and a number of other attributes. We present several significant new results and open questions that demand further investigation.

  8. Modelling planet-forming circumstellar discs

    NASA Astrophysics Data System (ADS)

    Woitke, P.

    2012-03-01

    With the improved wavelength coverage and instrumental capabilities to observe planet-forming circumstellar discs in the X-ray regime, the UV, and the near, mid and far infrared (XMM, HST, VLT, Spitzer, Herschel, soon ALMA) there is an increasing scientific need to develop equally sophisticated models for the physical, radiative and chemical processes in these discs. The discs are composed of dust and gas spanning 10 orders of magnitude in density, and temperatures differ by a factor of about 100. There is hard irradiation that provokes various non-LTE effects, thermal and position de-coupling of icy dust and gas, and the differential rotation causes instabilities and mixing. In the last few years, new theoretical models have been developed that simulate different aspects of these complicated physical systems. I will focus mainly on models that model the chemical, radiative, and heating & cooling processes in these discs, pointing out some important coupling mechanism and feedbacks between them. In the new major European FP7-SPACE project DIANA, we will use these novel disc models to coherently analyse and interpret new multi-wavelength data sets from X-ray to cm, probing in physics and chemistry in protoplanetary dicsc at different radii and depths. The general aim of the new models is to arrive at a common understanding of dust and gas, over the full radial extent of the disc, and to make use of continuum and line observations to constrain dust and gas properties in the disc. I will discuss where the various near-IR to sub-mm emissions (CO ro-vib, high-J CO lines, sub-mm CO lines, Spitzer water, Herschel/PACS water, Herschel/HIFI water, Herschel/PACS atomic lines) originate from, and how they are influenced by disc shape, irradiation, dust properties, and the chemical and radiative details.

  9. The Circumstellar Environments of Exoplanet Host Stars

    NASA Astrophysics Data System (ADS)

    Chen, Christine

    The WFIRST-AFTA mission currently includes the provision for a high contrast imaging instrument with a primary goal of discovering new, low mass exoplanets and characterizing their atmospheres. To date, eight exoplanetary systems have been discovered via direct imaging using the current generation of ground-based high-contrast facilities. Five of those systems, including the iconic beta Pictoris and HR 8799 systems, possess infrared excesses, indicative of the presence of circumstellar dust. Detailed studies of dust and gas morphology in the beta Pictoris disk provided the impetus for searching for, and eventually imaging the planet. These studies further suggest that additional planets orbit the star, but are below current detection thresholds. Such systems will be prime targets for WFIRST-AFTA, which will obtain visual spectroscopy of several spectral features from molecules in the exoplanet atmospheres including CH4, H2O, and CO2. We propose to: (1) model the dust in exoplanetary systems with well characterized planets and infrared excesses to better constrain the dust geometry and particle properties; (2) generate synthetic WFIRST-AFTA images of these disks with embedded known and putative planets using point-spread-functions generated by JPL, and run our simulations though a WFIRST-AFTA pipeline; and (3) evaluate the sensitivity of WFIRST-AFTA to known and putative planets that have a range of masses and distances from their host stars. The proposed simulations will also assist the community in understanding how WFIRST-AFTA will contribute to our knowledge of debris disks and the role that minor bodies play in the delivery of water into the terrestrial planet zone. The proposed project is complementary to the efforts currently being carried out by the Science Definition Team (SDT), which focus on simulating planets embedded in tenuous disks, analogous to the Zodiacal dust system in our Solar System, the Earth s resonant dust ring, and the HR 4796 dust ring

  10. High Velocity Impact Interaction of Metal Particles with Porous Heterogeneous Materials with an Inorganic Matrix

    NASA Astrophysics Data System (ADS)

    Glazunov, A. A.; Ishchenko, A. N.; Afanasyeva, S. A.; Belov, N. N.; Burkin, V. V.; Rogaev, K. S.; Tabachenko, A. N.; Khabibulin, M. V.; Yugov, N. T.

    2016-03-01

    A computational-experimental investigation of stress-strain state and fracture of a porous heterogeneous material with an inorganic matrix, used as a thermal barrier coating of flying vehicles, under conditions of a high-velocity impact by a spherical steel projectile imitating a meteorite particle is discussed. Ballistic tests are performed at the velocities about 2.5 km/s. Numerical modeling of the high-velocity impact is described within the framework of a porous elastoplastic model including fracture and different phase states of the materials. The calculations are performed using the Euler and Lagrange numerical techniques for the velocities up to 10 km/s in a complete-space problem statement.

  11. Measuring densities of high-velocity metallic sprays using piezoelectric sensors

    SciTech Connect

    Lloyd, C. E.; Proud, W. G.

    2007-12-12

    Recent research efforts in large-scale hydrodynamic experiments have concentrated on the possibility of using piezoelectric sensors to study the evolution of ejecta. Ejecta are small (<100 m diameter) particulates that are ejected at high velocity (>1 km s{sup -1}) from a shocked surface. This paper investigates whether Dynasen PZT piezoelectric sensors are reliable and robust enough to measure accurate time-resolved stresses and densities in high-velocity metallic sprays. The sprays are assumed to have similar characteristics to ejecta sprays, and are generated by a gas gun and in a safe and reproducible manner. A complimentary diagnostic technique, utilising high-speed photography and fast x-radiography, measures the densities of the sprays independently, allowing the accuracy of the sensors to be assessed. The Dynasen sensors have been shown to perform relatively well in spray environments. Their accuracy can be improved by taking their mechanical impedance characteristics into account.

  12. The Guitar nebula - A bow shock from a slow-spin, high-velocity neutron star

    NASA Technical Reports Server (NTRS)

    Cordes, James M.; Romani, Roger W.; Lundgren, Scott C.

    1993-01-01

    The discovery is reported of a prominent nebula produced by the motion of a high-velocity pulsar, PSR 2224 + 65, through partially neutral gas. The pulsar's transverse speed of over about 800 km/s makes it arguably the fastest known star in the Galaxy and guarantees that it will ultimately escape the Galactic potential well. A deep H-alpha image reveals a bright head and a giant limb-brightened 'body' whose variable width suggests that the ambient interstellar gas has density variations on length scales less than 0.1 pc. Thermalization of shock energy occurs at a rate of about 0.01 times the pulsar's spindown loss rate. These observations provide some insights into the likelihood of finding shocks around other pulsars and the use of nebulae to find high-velocity neutron stars either not acting as pulsars or with their radiation beamed away from the earth.

  13. The frequency and distribution of high-velocity gas in the Galaxy

    NASA Technical Reports Server (NTRS)

    Nichols, Joy S.

    1995-01-01

    The purpose of this study was to estimate the frequency and distribution of high-velocity gas in the Galaxy using UV absorption line measurements from archival high-dispersion IUE spectra and to identify particularly interesting regions for future study. Approximately 500 spectra have been examined. The study began with the creation of a database of all 0 and B stars with b less than or = to 30 deg observed with IUE at high dispersion over its 18-year lifetime. The original database of 2500 unique objects was reduced to 1200 objects which had optimal exposures available. The next task was to determine the distances of these stars so the high-velocity structures could be mapped in the Galaxy. Spectroscopic distances were calculated for each star for which photometry was available. The photometry was acquired for each star using the SIMBAD database. Preference was given to the ubvy system where available; otherwise the UBV system was used.

  14. Electrical method and apparatus for impelling the extruded ejection of high-velocity material jets

    DOEpatents

    Weingart, Richard C.

    1989-01-01

    A method and apparatus (10, 40) for producing high-velocity material jets provided. An electric current pulse generator (14, 42) is attached to an end of a coaxial two-conductor transmission line (16, 44) having an outer cylindrical conductor (18), an inner cylindrical conductor (20), and a solid plastic or ceramic insulator (21) therebetween. A coxial, thin-walled metal structure (22, 30) is conductively joined to the two conductors (18, 20) of the transmission line (16, 44). An electrical current pulse applies magnetic pressure to and possibly explosively vaporizes metal structure (22), thereby collapsing it and impelling the extruded ejection of a high-velocity material jet therefrom. The jet is comprised of the metal of the structure (22), together with the material that comprises any covering layers (32, 34) disposed on the structure. An electric current pulse generator of the explosively driven magnetic flux compression type or variety (42) may be advantageously used in the practice of this invention.

  15. Shocks throughout the circumstellar envelope of yellow hypergiant IRC+10420

    NASA Astrophysics Data System (ADS)

    Wong, Ka-Tat; Lim, Jeremy; Dinh-V-Trung

    2013-06-01

    . For comparison, the typical SiO abundance around AGB stars is 10^-6 at radii of a few hundreds AU, and decreases steeply beyond. We attribute the enhanced SiO abundance in the shell relative to regions within and beyond to shocks between two mass-ejection episodes. As for the lower but still enhanced SiO abundance further out, we appeal to observations with the Hubble Space Telescope that show a multitude of knots distributed throughout (out to a projected distance of at least 10000 AU) and moving at relatively high velocities (~100 km/s) through the circumstellar envelope (expanding at a bulk velocity of ~40 km/s of IRC+10420. We speculate that shocks created by the motion of these knots relative to the gaseous envelope releases SiO, and that the enhanced density of these knots and/or gas compressed by the shocks excites SiO to produce the strong emission observed.

  16. The Spectroscopic Evolution of the Symbiotic-like Recurrent Nova V407 Cygni During Its 2010 Outburst. 2. The Circumstellar Environment and the Aftermath

    NASA Technical Reports Server (NTRS)

    Shore, S. N.; Wahlgren, G. M.; Augusteijn, T.; Liimets, T.; Koubsky, P.; Slechta, M.; Votruba, V.

    2011-01-01

    The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at gamma-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development of the photoionized Mira wind, circumstellar medium, and shocked circumstellar environment to derive their physical parameters and how they relate to large scale structure of the environment, extending the previous coverage to more than 500 days after outburst. We use optical spectra obtained at high resolution with the Nordic Optical Telescope (NOT) (R approx. =.45000 to 65000) and medium resolution Ondrejov Observatory (R approx. = 12000) data and compare the line variations with publicly available archival measurements at 30 GHz OVNR and at X-rays with Swift during the first four months of the outburst, through the end of the epoch of strong XR emission. We use nebular diagnostics and high resolution profile variations to derive the densities and locations of the extended emission. We find that the higher the ionization and/or the higher the excitation energy, the more closely the profiles resemble the He II/Ca V-type high velocity shock profile discussed in Paper I. This also accounts for the comparative development of the [N II] and [O III] isoelectronic transitions: the [O III] 4363A profile does not show the low velocity peaks while the excited [N II] 5754A does. If nitrogen is mainly N(+3) or higher in the shock, the upper state of the [N II] nebular lines will contribute but if the oxygen is O(+2) then this line is formed by recombination, masking the nebular

  17. Chronic symptoms after vestibular neuritis and the high velocity vestibulo-ocular reflex

    PubMed Central

    Patel, Mitesh; Arshad, Qadeer; Roberts, R Edward; Ahmad, Hena; Bronstein, Adolfo M.

    2015-01-01

    Hypothesis As the anterior and posterior semicircular canals are vital to the regulation of gaze stability, particularly during locomotion or vehicular travel, we tested whether the high velocity vestibulo-ocular reflex (VOR) of the three ipsilesional semicircular canals elicited by the modified Head Impulse Test would correlate with subjective dizziness or vertigo scores after vestibular neuritis (VN). Background Recovery following acute VN varies with around half reporting persistent symptoms long after the acute episode. However, an unanswered question is whether chronic symptoms are associated with impairment of the high velocity VOR of the anterior or posterior canals. Methods Twenty patients who had experienced an acute episode of VN at least three months earlier were included in this study. Participants were assessed with the video head impulse test (vHIT) of all six canals, bithermal caloric irrigation, the Dizziness Handicap Inventory (DHI) and the Vertigo Symptoms Scale short-form (VSS). Results Of these 20 patients, 12 felt that they had recovered from the initial episode whereas 8 did not and reported elevated DHI and VSS scores. However, we found no correlation between DHI or VSS scores and the ipsilesional single or combined vHIT gain, vHIT gain asymmetry or caloric paresis. The high velocity VOR was not different between patients who felt they had recovered and patients who felt they had not. Conclusions Our findings suggest that chronic symptoms of dizziness following VN are not associated with the high velocity VOR of the single or combined ipsilesional horizontal, anterior or posterior semicircular canals. PMID:26719963

  18. Heat Transfer and Hydraulic Flow Resistance for Streams of High Velocity

    NASA Technical Reports Server (NTRS)

    Lelchuk, V. L.

    1943-01-01

    Problems of hydraulic flow resistance and heat transfer for streams with velocities comparable with acoustic have present great importance for various fields of technical science. Especially, they have great importance for the field of heat transfer in designing and constructing boilers.of the "Velox" type. In this article a description of experiments and their results as regards definition of the laws of heat transfer in differential form for high velocity air streams inside smooth tubes are given.

  19. Treatment Protocol for High Velocity/High Energy Gunshot Injuries to the Face

    PubMed Central

    Peled, Micha; Leiser, Yoav; Emodi, Omri; Krausz, Amir

    2011-01-01

    Major causes of facial combat injuries include blasts, high-velocity/high-energy missiles, and low-velocity missiles. High-velocity bullets fired from assault rifles encompass special ballistic properties, creating a transient cavitation space with a small entrance wound and a much larger exit wound. There is no dispute regarding the fact that primary emergency treatment of ballistic injuries to the face commences in accordance with the current advanced trauma life support (ATLS) recommendations; the main areas in which disputes do exist concern the question of the timing, sequence, and modes of surgical treatment. The aim of the present study is to present the treatment outcome of high-velocity/high-energy gunshot injuries to the face, using a protocol based on the experience of a single level I trauma center. A group of 23 injured combat soldiers who sustained bullet and shrapnel injuries to the maxillofacial region during a 3-week regional military conflict were evaluated in this study. Nine patients met the inclusion criteria (high-velocity/high-energy injuries) and were included in the study. According to our protocol, upon arrival patients underwent endotracheal intubation and were hemodynamically stabilized in the shock-trauma unit and underwent total-body computed tomography with 3-D reconstruction of the head and neck and computed tomography angiography. All patients underwent maxillofacial surgery upon the day of arrival according to the protocol we present. In view of our treatment outcomes, results, and low complication rates, we conclude that strict adherence to a well-founded and structured treatment protocol based on clinical experience is mandatory in providing efficient, appropriate, and successful treatment to a relatively large group of patients who sustain various degrees of maxillofacial injuries during a short period of time. PMID:23449809

  20. Unique charge distribution in surface loops confers high velocity on the fast motor protein Chara myosin.

    PubMed

    Ito, Kohji; Yamaguchi, Yukie; Yanase, Kenji; Ichikawa, Yousuke; Yamamoto, Keiichi

    2009-12-22

    Most myosins have a positively charged loop 2 with a cluster of lysine residues that bind to the negatively charged N-terminal segment of actin. However, the net charge of loop 2 of very fast Chara myosin is zero and there is no lysine cluster in it. In contrast, Chara myosin has a highly positively charged loop 3. To elucidate the role of these unique surface loops of Chara myosin in its high velocity and high actin-activated ATPase activity, we have undertaken mutational analysis using recombinant Chara myosin motor domain. It was found that net positive charge in loop 3 affected V(max) and K(app) of actin activated ATPase activity, while it affected the velocity only slightly. The net positive charge in loop 2 affected K(app) and the velocity, although it did not affect V(max). Our results suggested that Chara myosin has evolved to have highly positively charged loop 3 for its high ATPase activity and have less positively charged loop 2 for its high velocity. Since high positive charge in loop 3 and low positive charge in loop 2 seem to be one of the reasons for Chara myosin's high velocity, we manipulated charge contents in loops 2 and 3 of Dictyostelium myosin (class II). Removing positive charge from loop 2 and adding positive charge to loop 3 of Dictyostelium myosin made its velocity higher than that of the wild type, suggesting that the charge strategy in loops 2 and 3 is widely applicable.

  1. Real-time dynamics of high-velocity micro-particle impact

    NASA Astrophysics Data System (ADS)

    Veysset, David; Hsieh, Alex; Kooi, Steve; Maznev, Alex A.; Tang, Shengchang; Olsen, Bradley D.; Nelson, Keith A.

    High-velocity micro-particle impact is important for many areas of science and technology, from space exploration to the development of novel drug delivery platforms. We present real-time observations of supersonic micro-particle impacts using multi-frame imaging. In an all optical laser-induced projectile impact test, a monolayer of micro-particles is placed on a transparent substrate coated with a laser absorbing polymer layer. Ablation of a laser-irradiated polymer region accelerates the micro-particles into free space with speeds up to 1.0 km/s. The particles are monitored during the impact on the target with an ultrahigh-speed multi-frame camera that can record up to 16 images with time resolution as short as 3 ns. In particular, we investigated the high-velocity impact deformation response of poly(urethane urea) (PUU) elastomers to further the fundamental understanding of the molecular influence on dynamical behaviors of PUUs. We show the dynamic-stiffening response of the PUUs and demonstrate the significance of segmental dynamics in the response. We also present movies capturing individual particle impact and penetration in gels, and discuss the observed dynamics. The results will provide an impetus for modeling high-velocity microscale impact responses and high strain rate deformation in polymers, gels, and other materials.

  2. High-velocity frictional strength across the Tohoku-Oki megathrust determined from surface drilling torque

    NASA Astrophysics Data System (ADS)

    Ujiie, Kohtaro; Inoue, Tomoya; Ishiwata, Junya

    2016-03-01

    High-velocity frictional strength is one of the primary factors controlling earthquake faulting. The Japan Trench Fast Drilling Project drilled through the shallow plate boundary fault, where displacement was ~50 m during the 2011 Tohoku-Oki earthquake. To determine downhole frictional strength, we analyzed the surface drilling torque data acquired at rotation rates equivalent to seismic slip rates (0.8-1.3 m/s). The results show a clear contrast in high-velocity frictional strength across the plate boundary fault: the apparent friction coefficient of frontal prism sediments (hemipelagic mudstones) in the hanging wall is 0.1-0.3, while that of the underthrust sediments (mudstone, laminar pelagic claystone, and chert) in the footwall increases to 0.2-0.4. The apparent friction coefficient of the smectite-rich pelagic clay in the plate boundary fault is 0.08-0.19, which is consistent with that determined from high-velocity (1.1-1.3 m/s) friction experiments. This suggests that surface drilling torque is useful in obtaining downhole frictional strength.

  3. A Investigation of Gouge Initiation in High-Velocity Sliding Contact

    NASA Astrophysics Data System (ADS)

    Tachau, Robert David Mazur

    1991-02-01

    Surface damage has been observed on the rails of rocket sled tracks and on the barrels of high-velocity guns. The phenomenon is generally referred to as "gouging". Damage to a stationary surface (guider) is created from the oblique impact of a high-velocity object (slider) moving over its surface. The surface damage (gouge) is typically a shallow crater in the shape of a teardrop with the leading edge characterized by the wider end and a slightly raised lip. For rocket sleds, rail gouging occurs when the sled velocity is greater than 1.5 km/sec; while in guns, barrel gouging occurs when the velocity exceeds 4 km/sec. A model is developed to describe the phenomenon of gouging. An unbalanced slider randomly causes a shallow -angle, oblique impact between the slider and the guider. At sufficiently high velocity, the impact produces a thin, but very hot, layer of soft material at the contact surface. Under the action of a moving load, the soft layer lends itself to an antisymmetric deformation and a gouge is formed when this soft material is over-run by the slider. The model is simulated numerically with a hydrodynamic (CTH) code. The results of the simulations are in good agreement with the observed phenomena. Based on the simulated temperature and pressure profiles at the contact surface, design criteria for gouge mitigation are developed in this study.

  4. Quasi-static and multi-site high velocity impact response of composite structures

    NASA Astrophysics Data System (ADS)

    Deka, Lakshya

    Understanding of low and high velocity transverse impact of laminated fiber reinforced composites is of interest in military, aerospace, marine and civilian structures. Recent advances in the field of numerical simulation provide a means of predicting the performance characteristics of layered materials for impact protection. The overall objective of this work is to investigate the behavior of laminated composites which include both thermoplastic and thermoset systems subjected to quasi-static, low and high velocity impact; both from an experimental and numerical modeling view point. To analyze this problem, a series of quasi-static, low and high velocity impact tests have been performed on laminated composite plates namely E-glass/polypropylene, S2-glass/epoxy and carbon/polyphenylene sulphide. To analyze the perforation mechanism, ballistic limit and damage evolution, an explicit three-dimensional finite element code LS-DYNA is used. Selecting proper material models and contact definition is one of the major criteria for obtaining accurate numerical simulation. Material model 162 (MAT 162), a progressive failure model based on modified Hashin's criteria and continuum damage mechanics (CDM) has been assigned to predict failure of the laminate. This approach is used because during transverse impact, a composite laminate undergoes progressive damage. The laminate and the projectile are meshed using brick elements with single integration points. The impact velocity ranges from 180 to 400 m s -1. This work focuses on three main aspects; (i) To obtain static and dynamic material properties to incorporate into the finite element model and predict the ballistic limit of a composite laminate based on the information from quasi-static punch shear test; (ii) To understand penetration, material erosion, ballistic limit and delamination mechanisms for single and multi-site high velocity (or ballistic) impact of composite laminates; (iii) To investigate the different failure

  5. Photochemistry and molecular ions in carbon-rich circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.; Mamon, G. A.; Omont, A.; Lucas, R.

    1987-01-01

    An earlier theory of ionization of C-rich circumstellar envelopes based on the photochemical model is extended to include the temperature dependence of ion-molecule reactions with polar molecules, particularly HCN, and line self-shielding of CO dissociating radiation. The results are applied to the abundances of HCO(+) and HNC in C-rich circumstellar envelopes. With standard parameters for IRC + 10216, the model is found to be consistent with the new upper limit to the antenna temperature of the J = 1-0 line of HCO(+) obtained with the IRAM 30-m telescope. The photochemical model provides a natural explanation of the relatively large ratio of HCN to HNC observed for C-rich circumstellar envelopes, and good agreement is obtained for the H(C-13)N/HNC antenna temperature ratio measured for IRC + 10216.

  6. First Circumstellar Disk around a Massive Star

    NASA Astrophysics Data System (ADS)

    1998-06-01

    arrow). Earlier observations with radio telescopes of the object G339.88-1.26 , deeply embedded in an interstellar nebula, had been interpreted in terms of the possible existence of a circumstellar disk around a high-mass star. It was concluded that the star responsible for heating the surrounding gas must be very hot and also that it must be intrinsically very bright. The star, most likely of spectral type O9, would have a luminosity 10,000 times higher than that of the Sun and a mass of about 20 times that of the Sun. From the measured velocity, the likely distance of this object is about 10,000 light-years. The object is associated with several "spots" of very strong radio emission from methanol molecules (methanol masers). Interestingly, they form a chain in the sky and the measured velocities of the individual spots are indicative for orbital motion in a rotating disk around the central star. The circumstellar disk ESO PR Photo 22/98 ESO PR Photo 22b/98 [JPEG, 640k] The TIMMI 10 µm image of the inclined dust disk around a hot O9 star at the G339.88-1.26 radio source. The diameter of the disk is of the order of 5 arcsec, i.e. at the most probable distance to the object (10,000 lightyears) it is 20,000 times larger than the diameter of the Earth's orbit around the Sun. The new TIMMI observations of G339.88-1.26 showed an elliptical object with strong infrared radiation. The peak of this radiation (as seen in the sky) coincides with the peak of the radio emission. Furthermore, the apparent orientation of the disk is well aligned with that of the methanol maser "spots". There is little doubt that this object is indeed the infrared image of a circumstellar disk, viewed at an angle. As far as known, this is the first direct image of a disk around a very massive star. At a wavelength of 10 µm, however, the central star that is responsible for heating the dust disc, cannot be seen in spite of its rather high luminosity. This is because it radiates mostly in the ultra

  7. THE M81 GROUP DWARF IRREGULAR GALAXY DDO 165. I. HIGH-VELOCITY NEUTRAL GAS IN A POST-STARBURST SYSTEM

    SciTech Connect

    Cannon, John M.; Most, Hans P.; Skillman, Evan D.; Weisz, Daniel R.; Warren, Steven R.; Cook, David; Dolphin, Andrew E.; Kennicutt, Robert C.; Lee, Janice; Seth, Anil; Walter, Fabian E-mail: skillman@astro.umn.edu E-mail: warren@astro.umn.edu E-mail: adolphin@raytheon.com E-mail: jlee@obs.carnegiescience.edu E-mail: walter@mpia.de

    2011-07-01

    We present new multi-configuration Very Large Array H I spectral line observations of the M81 group dwarf irregular post-starburst galaxy DDO 165. The H I morphology is complex, with multiple column density peaks surrounding a large region of very low H I surface density that is offset from the center of the stellar distribution. The bulk of the neutral gas is associated with the southern section of the galaxy; a secondary peak in the north contains {approx}15% of the total H I mass. These components appear to be kinematically distinct, suggesting that either tidal processes or large-scale blowout have recently shaped the interstellar medium (ISM) of DDO 165. Using spatially resolved position-velocity maps, we find multiple localized high-velocity gas features. Cross-correlating with radius-velocity analyses, we identify eight shell/hole structures in the ISM with a range of sizes ({approx}400-900 pc) and expansion velocities ({approx}7-11 km s{sup -1}). These structures are compared with narrow- and broadband imaging from the Kitt Peak National Observatory and the Hubble Space Telescope (HST). Using the latter data, recent works have shown that DDO 165's previous 'burst' phase was extended temporally ({approx}>1 Gyr). We thus interpret the high-velocity gas features, H I holes, and kinematically distinct components of the galaxy in the context of the immediate effects of 'feedback' from recent star formation (SF). In addition to creating H I holes and shells, extended SF events are capable of creating localized high-velocity motion of the surrounding interstellar material. A companion paper connects the energetics from the H I and HST data.

  8. Laboratory Studies Of Circumstellar Carbonaceous Grain Formation

    NASA Astrophysics Data System (ADS)

    Contreras, Cesar; Sciamma-O'Brien, Ella; Salama, Farid

    2014-06-01

    The study of the formation processes of dust is essential to understand the budget of extraterrestrial organic molecules. Although dust with all its components plays an important role in the evolution of interstellar (IS) chemistry and in the formation of organic molecules, little is known on the formation processes of carbonaceous dust. We report the progress that was recently achieved in this domain using NASA Ames’ COSmIC facility (Contreras & Salama 2013, ApJS, 208, 6). PAHs are important chemical building blocks of IS dust. They are detected in IDPs and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs are an important, ubiquitous component of the ISM. The formation of PAHs from smaller molecules has not been extensively studied. Therefore, we have performed laboratory experiments to study the dynamic processes of carbon grain formation, starting from the smallest hydrocarbon molecules into the formation of larger PAH and further into nanograins. Studies of IS dust analogs formed from a variety of PAH and hydrocarbon precursors as well as species that include the atoms O, N, and S, have recently been performed in our laboratory using the COSmIC facility to provide conditions that simulate IS and circumstellar environments. The species formed in the COSmiC chamber through a pulsed discharge nozzle plasma source are detected and characterized with a cavity ringdown spectrometer coupled to a time-of-flight mass spectrometer, thus providing both spectroscopic and ion mass information in-situ. Analysis of solid soot particles was also conducted using scanning electron microscopy at the UCSC/NASA Ames’ MACS facility. The SEM analysis of the deposition of soot from methane and acetylene precursors seeded in argon plasmas provide examples on the types of nanoparticles and micrograins that are produced in these gas mixtures under our experimental conditions. From these measurements, we derive information on

  9. Shaping the pre-supernova circumstellar environment

    NASA Astrophysics Data System (ADS)

    Koenigsberger, Gloria

    2009-07-01

    Recent discoveries of very luminous supernovae associated with luminous blue variable-type objects {LBV's} raise the interesting possibility that an LBV phase may be the prelude to core collapse. Alternatively, the LBV events may be occuring in binary systems where the LBV phase is reached by one of the stars shortly before its more evolved companion becomes a supernova. The Small Magellanic Cloud binary system HD 5980 is believed to consist precisely of such two objects: a massive hydrogen-poor Wolf-Rayet star in orbit around an even more massive variable star that recently underwent an LBV-type eruption. The wind velocity and the mass-loss rate of the LBV-component have changed remarkably over the past ˜40 years, providing a glimpse of the detailed information of how a binary LBV-type star may shape the circumstellar environment into which the eventual supernova ejecta will collide. One process that is shaping the CSM around HD 5980 is the interaction between the slow wind ejected during eruption and the fast wind that was subsequently ``turned on". In order to model the evolution of this interaction region, an accurate determination of the mass-loss rate and the wind velocity of HD 5980 is required. Because the optical emission lines are contaminated by other sources, only the P Cygni profiles observable in the UV spectral region provide unambiguous values for the current wind speed and mass-loss rate. In this proposal we are requesting 2 HST orbits to observe HD 5980 with STIS in order to obtain one FUV MAMA spectrum from which we will determine the current wind velocity and mass-loss rate of the LBV-type star. These data will also allow a more detailed analysis of the atmospheric structure of the LBV-type object in its quiescent state and, combined with ground-based observations, an analysis of the emission arising in the wind-wind collision region may be performed. Although HD5980 may be unique in our Galactic vicinity, it may be typical of massive star

  10. Narrowness and Liberality

    ERIC Educational Resources Information Center

    Agresto, John

    2003-01-01

    John Agresto, whose task has been to rebuild the war-ravaged infrastructure of a Middle-Eastern university system, is discouraged to see that narrow expertise is the only goal of education there, to the utter exclusion of intellectual breadth. He comments that, although it is not that bad in the U.S., he feels that doctoral programs as currently…

  11. Dynamics of narrow rings

    NASA Technical Reports Server (NTRS)

    Dermott, S. F.

    1984-01-01

    The ring models described here were developed to account for the dynamical problems posed by the narrow rings of Uranus. Some of these rings are now known to be eccentric, inclined, nonuniform in width, optically thick, and narrow, with very sharp edges. The eccentric rings have common pericenters and large, positive eccentricity gradients. The theory of shepherding satellites successfully accounts for most of these features and can also account for some features of the narrow Saturnian rings, in particular, waves, kinks, and periodic variations in brightness. Outstanding problems include the putative relation between eccentricity and inclination displayed by eight of the nine Uranian rings, and the magnitudes of the tidal torques acting on the shepherding satellites. The horseshoe-orbit model, although viable, probably has more application to the narrow rings from which the Saturnian coorbital satellites formed. The angular momentum flow rate due to particle collisions is a minimum at the Lagrangian equilibrium points L(4) and L(5), and one can expect accretion to be rapid at these points.

  12. How vessels narrow.

    PubMed

    Schwartz, S M

    1995-01-01

    Vascular narrowing, the clinical dilatation of narrowed vessels, and the restenosis of those vessels are central topics in modern cardiology. This review discusses the cellular basis both for the spontaneous narrowing of vessels and for the restenotic process that occurs after angioplasty. The central issue, as discussed in this review, is likely to be remodeling of the vessel wall rather than simple accretion of lipid mass in atherosclerosis or simple physical dilatation following angioplasty. While it is true that the atherosclerotic lesion grows by accretion of lipid mass, this by itself does not narrow vessels. As we will discuss, the vessel has a phenomenal ability to accommodate changes of this sort. Narrowing must occur, at least in part, because of a failure of this normal ability to accommodate. In a similar manner, one might expect the restonotic vessel to simply remodel itself down to its preangioplasty size. The issue for cell and molecular biologists is what "remodeling" means. Until recently, the assertion has been that remodeling occurred as the result of the formation of new intimal mass; that is, the atherosclerotic vessel was seen as returning to its original dimensions following angioplasty as a result of forming a new intimal mass that filled in the dilated space. Recent studies using cell kinetic methods as well as intravascular ultrasound, however, have cast doubt upon this hypothesis. It now appears that the loss of gain following angioplasty is likely to be due to the formation of new tissues which remodel the vessel wall without necessarily adding mass to it. This is the same sort of process that is well described in wound healing. The nature of this new tissue is of great interest. Studies in this laboratory and others have identified genes which may be unique to this tissue and explain the remodeling response. PMID:8585265

  13. Physical Processes in Circumstellar Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    Garcia, Paulo J. V.

    2011-05-01

    Circumstellar disks are vast expanses of dust that form around new stars in the earliest stages of their birth. Predicted by astronomers as early as the eighteenth century, they weren't observed until the late twentieth century, when interstellar imaging technology enabled us to see nascent stars hundreds of light years away. Since then, circumstellar disks have become an area of intense study among astrophysicists, largely because they are thought to be the forerunners of planetary systems like our own - the possible birthplaces of planets.

  14. 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.

  15. Discovery of a Circumstellar Disk in the Lagoon Nebula

    NASA Astrophysics Data System (ADS)

    1997-04-01

    and barely visible on the HST-WFPC2 images taken at far-red optical wavelengths, is indeed situated behind the bright bow which is most conspicuous in the light of the red H-alpha spectral line, emitted by hydrogen atoms. The appearance of this object is thus similar to that of the proplyd sources found in the Orion Nebula. Caption to ESO PR Photo 10/97 [GIF, 296k] This is quite obvious from ESO Press Photo 10/97 which shows a colour composite based on HST-WFPC2 images obtained through narrow-band optical filtres, isolating the light of doubly ionized oxygen atoms ([OIII]; blue) and atomic hydrogen (H-alpha; green) and in a far-red band (red). Two more faint stars are seen in this image while the bright star Her 36 is outside the border of the image (its location is at the lower left, at the intersection of the vertical, saturated CCD column and the 45 o line caused by the light diffracted in the telescope). In contrast to the Orion Nebula, the non-uniform distribution of light-absorbing dust in the foreground makes the detection of the ionised tail difficult. Note that the image is rotated clockwise by 146 o with respect to the astronomical coordinate system. A proplyd in the Lagoon Nebula The detailed description of these results is the subject of a forthcoming research paper [5]. The new understanding of G5.97-1.17, i.e. as harbouring an evaporating circumstellar disk heated by far-ultraviolet radiation from Her 36, is supported by the fact that a sufficient amount of high-energy ultraviolet light is received from that star to account for the radio emission observed from the ionised bow. This object therefore represents the first proplyd-type object detected outside Orion at a much larger distance . The full description of this phenomenon requires detailed knowledge on the physical conditions of the star Her 36 and the object itself. Unfortunately, sofar little is known about the properties of the stellar wind from Her 36, the mass-loss rate from G5.97-1.17 and the

  16. A Gravitational Double-scattering Mechanism for Generating High-velocity Objects during Halo Mergers

    NASA Astrophysics Data System (ADS)

    Samsing, Johan

    2015-02-01

    We present a dynamical model that describes how halo particles can receive a significant energy kick from the merger between their own host halo and a target halo. This could provide a possible explanation for some high-velocity objects, including extended systems like globular clusters (GCs). In the model we especially introduce a double-scattering mechanism, where a halo particle receives a significant part of its total energy kick by first undergoing a gravitational deflection by the target halo and subsequently by its original host halo. This generates an energy kick that is due to the relative velocity between the halos during the deflections. We derive analytically the total kick energy of the particle, which is composed of energy from the double-scattering mechanism and tidal fields, as a function of its position in its original host halo just before merger. In the case of a 1:10 merger, we find that the presented mechanisms can easily generate particles with a velocity approximately two times the virial velocity of the target halo. This motivates us to suggest that the high velocity of the recently discovered GC HVGC-1 can be explained by a head-on halo merger. Finally, we illustrate the orbital evolution of high-velocity particles outside the virial sphere of the target halo by solving the equation of motion in an expanding universe. We find a sweet spot around a scale factor of 0.3-0.5 for ejecting particles into large orbits, which can easily reach beyond approximately five virial radii.

  17. A GRAVITATIONAL DOUBLE-SCATTERING MECHANISM FOR GENERATING HIGH-VELOCITY OBJECTS DURING HALO MERGERS

    SciTech Connect

    Samsing, Johan

    2015-02-01

    We present a dynamical model that describes how halo particles can receive a significant energy kick from the merger between their own host halo and a target halo. This could provide a possible explanation for some high-velocity objects, including extended systems like globular clusters (GCs). In the model we especially introduce a double-scattering mechanism, where a halo particle receives a significant part of its total energy kick by first undergoing a gravitational deflection by the target halo and subsequently by its original host halo. This generates an energy kick that is due to the relative velocity between the halos during the deflections. We derive analytically the total kick energy of the particle, which is composed of energy from the double-scattering mechanism and tidal fields, as a function of its position in its original host halo just before merger. In the case of a 1:10 merger, we find that the presented mechanisms can easily generate particles with a velocity approximately two times the virial velocity of the target halo. This motivates us to suggest that the high velocity of the recently discovered GC HVGC-1 can be explained by a head-on halo merger. Finally, we illustrate the orbital evolution of high-velocity particles outside the virial sphere of the target halo by solving the equation of motion in an expanding universe. We find a sweet spot around a scale factor of 0.3-0.5 for ejecting particles into large orbits, which can easily reach beyond approximately five virial radii.

  18. Supernova 2010ev: A reddened high velocity gradient type Ia supernova

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Claudia P.; González-Gaitán, Santiago; Folatelli, Gastón; Pignata, Giuliano; Anderson, Joseph P.; Hamuy, Mario; Morrell, Nidia; Stritzinger, Maximilian; Taubenberger, Stefan; Bufano, Filomena; Olivares E., Felipe; Haislip, Joshua B.; Reichart, Daniel E.

    2016-05-01

    Aims: We present and study the spectroscopic and photometric evolution of the type Ia supernova (SN Ia) 2010ev. Methods: We obtain and analyze multiband optical light curves and optical/near-infrared spectroscopy at low and medium resolution spanning -7 days to +300 days from the B-band maximum. Results: A photometric analysis shows that SN 2010ev is a SN Ia of normal brightness with a light-curve shape of Δm15(B) = 1.12 ± 0.02 and a stretch s = 0.94 ± 0.01 suffering significant reddening. From photometric and spectroscopic analysis, we deduce a color excess of E(B - V) = 0.25 ± 0.05 and a reddening law of Rv = 1.54 ± 0.65. Spectroscopically, SN 2010ev belongs to the broad-line SN Ia group, showing stronger than average Si iiλ6355 absorption features. We also find that SN 2010ev is a high velocity gradient SN with v˙Si = 164 ± 7 km s-1 d-1. The photometric and spectral comparison with other supernovae shows that SN 2010ev has similar colors and velocities to SN 2002bo and SN 2002dj. The analysis of the nebular spectra indicates that the [Fe ii]λ7155 and [Ni ii]λ7378 lines are redshifted, as expected for a high velocity gradient supernova. All these common intrinsic and extrinsic properties of the high velocity gradient (HVG) group are different from the low velocity gradient (LVG) normal SN Ia population and suggest significant variety in SN Ia explosions. This paper includes data gathered with the Du Pont Telescope at Las Campanas Observatory, Chile; and the Gemini Observatory, Cerro Pachon, Chile (Gemini Program GS-2010A-Q-14). Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (ESO Programme 085.D-0577).

  19. SPECTROSCOPIC OBSERVATIONS OF SN 2012fr: A LUMINOUS, NORMAL TYPE Ia SUPERNOVA WITH EARLY HIGH-VELOCITY FEATURES AND A LATE VELOCITY PLATEAU

    SciTech Connect

    Childress, M. J.; Scalzo, R. A.; Sim, S. A.; Tucker, B. E.; Yuan, F.; Schmidt, B. P.; Cenko, S. B.; Filippenko, A. V.; Silverman, J. M.; Contreras, C.; Hsiao, E. Y.; Phillips, M.; Morrell, N.; Jha, S. W.; McCully, C.; Anderson, J. P.; De Jaeger, T.; Forster, F.; Benetti, S.; Bufano, F.; and others

    2013-06-10

    We present 65 optical spectra of the Type Ia SN 2012fr, 33 of which were obtained before maximum light. At early times, SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si II {lambda}6355 line that can be cleanly decoupled from the lower velocity ''photospheric'' component. This Si II {lambda}6355 HVF fades by phase -5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of {approx}12,000 km s{sup -1} until at least five weeks after maximum brightness. The Ca II infrared triplet exhibits similar evidence for both a photospheric component at v Almost-Equal-To 12,000 km s{sup -1} with narrow line width and long velocity plateau, as well as an HVF beginning at v Almost-Equal-To 31,000 km s{sup -1} two weeks before maximum. SN 2012fr resides on the border between the ''shallow silicon'' and ''core-normal'' subclasses in the Branch et al. classification scheme, and on the border between normal and high-velocity Type Ia supernovae (SNe Ia) in the Wang et al. system. Though it is a clear member of the ''low velocity gradient'' group of SNe Ia and exhibits a very slow light-curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well-observed SN Ia at the luminous end of the normal SN Ia distribution and a key transitional event between nominal spectroscopic subclasses of SNe Ia.

  20. High velocity continuous-flow reactor for the production of solar grade silicon

    NASA Technical Reports Server (NTRS)

    Woerner, L.

    1977-01-01

    The feasibility of a high volume, high velocity continuous reduction reactor as an economical means of producing solar grade silicon was tested. Bromosilanes and hydrogen were used as the feedstocks for the reactor along with preheated silicon particles which function both as nucleation and deposition sites. A complete reactor system was designed and fabricated. Initial preheating studies have shown the stability of tetrabromosilane to being heated as well as the ability to preheat hydrogen to the desired temperature range. Several test runs were made and some silicon was obtained from runs carried out at temperatures in excess of 1180 K.

  1. A scheme for tracking and pointing at small celestial bodies during high velocity encounters

    NASA Technical Reports Server (NTRS)

    Burdick, G. M.; Lin, H.-S.; Wong, E. C.

    1982-01-01

    A scheme has been developed and verified for closed-loop tracking and pointing space-borne science instruments at small celestial bodies, such as comets and asteroids, during high velocity encounters. To overcome ephemeris uncertainties for these bodies, the scheme involves sequential estimation of flyby model parameters. The design consists of a two-axis gimballed platform mounted on a three-axis stabilized spacecraft. A platform-mounted optical tracker provides closed-loop target measurements and precision micro-step actuators enable high-rate platform slewing. For comet missions which involve dust particle impact disturbances, a dual-mode attitude control scheme is presented for minimizing transient response time.

  2. Negative ion productions in high velocity collision between small carbon clusters and Helium atom target

    NASA Astrophysics Data System (ADS)

    M, Chabot; K, Béroff; T, Pino; G, Féraud; N, Dothi; Padellec A, Le; G, Martinet; S, Bouneau; Y, Carpentier

    2012-11-01

    We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn-*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.

  3. Experimental verification of corrosive vapor deposition rate theory in high velocity burner rigs

    NASA Technical Reports Server (NTRS)

    Gokoglu, S. A.; Santoro, G. J.

    1986-01-01

    The ability to predict deposition rates is required to facilitate modelling of high temperature corrosion by fused salt condensates in turbine engines. A corrosive salt vapor deposition theory based on multicomponent chemically frozen boundary layers (CFBL) has been successfully verified by high velocity burner rig experiments. The experiments involved internally air-impingement cooled, both rotating full and stationary segmented cylindrical collectors located in the crossflow of sodium-seeded combustion gases. Excellent agreement is found between the CFBL theory an the experimental measurements for both the absolute amounts of Na2SO4 deposition rates and the behavior of deposition rate with respect to collector temperature, mass flowrate (velocity) and Na concentration.

  4. Shells, holes, worms, high-velocity gas and the z-distribution of gas in galaxies.

    NASA Astrophysics Data System (ADS)

    Rand, R. J.

    The author gives an overview of the current observational understanding of vertically extended gas components in spiral galaxies and the various phenomena which come under such names as shells, holes, worms, and high-velocity gas. For the most part, the focus is on recent high-resolution interferometric studies. The author concentrates on cold gas, and briefly on warm ionized gas, in the Milky Way and a few nearby spirals. Along the way, it is seen how phenomena such as worms and shells may be related to the formation and maintenance of the vertically extended components.

  5. Penetration of Liquid Jets into a High-velocity Air Stream

    NASA Technical Reports Server (NTRS)

    Chelko, Louis J

    1950-01-01

    Data are presented showing the penetration characteristics of liquid jets directed approximately perpendicular to a high-velocity air stream for jet-nozzle-throat diameters from 0.0135 to 0.0625 inch, air stream densities from 0.0805 to 0.1365 pound per cubic foot, liquid jet velocities from 168.1 to 229.0 feet per second and a liquid jet density of approximately 62 pounds per cubic foot. The data were analyzed and a correlation was developed that permitted the determination of the penetration length of the liquid jet for any operation condition within the range of variables investigated.

  6. Variables Affecting Smooth Particle Hydrodynamics Simulation of High-Velocity Flyer Plate Impact Experiments

    SciTech Connect

    Somasundaram, Deepak S; Trabia, Mohamed; O'Toole, Brendan; Hixson, Robert S

    2014-01-23

    This paper describes our work to characterize the variables affecting the smoothed particle hydrodynamics (SPH) method in the LS-DYNA package for simulating high-velocity flyer plate impact experiments. LS-DYNA simulations are compared with one-dimensional experimental data of an oxygen-free high-conductivity (OFHC) copper flyer plate impacting another plate of the same material. The comparison is made by measuring the velocity of a point on the back surface of the impact plate using the velocity interferometer system for any reflector (VISAR) technique.

  7. Chemical evolution of circumstellar matter around young stellar objects.

    PubMed

    van Dishoeck, E F; Blake, G A

    1995-01-01

    Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models.

  8. Anion production in high-velocity cluster-atom collisions; the electron capture process revisited

    NASA Astrophysics Data System (ADS)

    Béroff, K.; Chabot, M.; Martinet, G.; Pino, T.; Bouneau, S.; Le Padellec, A.; Féraud, G.; Do Thi, N.; Calvo, F.; Bordas, C.; Lépine, F.

    2013-01-01

    Anion production cross sections in collisions between Cn+, Cn carbon clusters (n ≤ 5) and helium atoms have been measured in high-velocity collisions (v = 2.25 and 2.6 au). This paper focuses on two of the three processes responsible for the Cn- production, namely double electron capture (DEC) onto Cn+ cations and single electron capture onto neutral (SECN) Cn. They were experimentally distinguished from a gaseous thickness dependence study. Dissociative and non-dissociative cross sections were measured and, in the case of DEC, all dissociative branching ratios measured; for these small systems, the C2- fragment was found magical. Data concerning electron capture in neutral-neutral collisions are extremely rare, especially at high velocity. Introduction of this measured process in the independent atom and electron (IAE) model allowed us to revisit and satisfactorily reproduce the so-far unexplained size evolution of single electron capture (SEC) cross sections in 2.6 au Cn+-He (n ≤ 10) collisions (Chabot et al 2006 J. Phys. B: At. Mol. Opt. Phys. 39 2593-603). IAE calculations for DEC cross sections and their comparison with experiment suggest a loss of electron in anionic Cn- species after the collision, competing with fragmentation and depending on the size.

  9. Characterization of High-Velocity Single Particle Impacts on Plasma-Sprayed Ceramic Coatings

    NASA Astrophysics Data System (ADS)

    Kiilakoski, Jarkko; Lindroos, Matti; Apostol, Marian; Koivuluoto, Heli; Kuokkala, Veli-Tapani; Vuoristo, Petri

    2016-08-01

    High-velocity impact wear can have a significant effect on the lifetime of thermally sprayed coatings in multiple applications, e.g., in the process and paper industries. Plasma-sprayed oxide coatings, such as Cr2O3- and TiO2-based coatings, are often used in these industries in wear and corrosion applications. An experimental impact study was performed on thermally sprayed ceramic coatings using the High-Velocity Particle Impactor (HVPI) at oblique angles to investigate the damage, failure, and deformation of the coated structures. The impact site was characterized by profilometry, optical microscopy, and scanning electron microscopy (SEM). Furthermore, the connection between the microstructural details and impact behavior was studied in order to reveal the damage and failure characteristics at a more comprehensive level. Differences in the fracture behavior were found between the thermally sprayed Cr2O3 and TiO2 coatings, and a concept of critical impact energy is presented here. The superior cohesion of the TiO2 coating inhibited interlamellar cracking while the Cr2O3 coating suffered greater damage at high impact energies. The HVPI experiment has proven to be able to produce valuable information about the deformation behavior of coatings under high strain rates and could be utilized further in the development of wear-resistant coatings.

  10. A novel platform to study magnetized high-velocity collisionless shocks

    NASA Astrophysics Data System (ADS)

    Higginson, D. P.; Korneev, Ph; Béard, J.; Chen, S. N.; d'Humières, E.; Pépin, H.; Pikuz, S.; Pollock, B.; Riquier, R.; Tikhonchuk, V.; Fuchs, J.

    2015-12-01

    An experimental platform to study the interaction of two colliding high-velocity (0.01-0.2 c; 0.05-20 MeV) proton plasmas in a high strength (20 T) magnetic field is introduced. This platform aims to study the collision of magnetized plasmas accelerated via the Target-Normal-Sheath-Acceleration mechanism and initially separated by distances of a few hundred microns. The plasmas are accelerated from solid targets positioned inside a few cubic millimeter cavity located within a Helmholtz coil that provides up to 20 T magnetic fields. Various parameters of the plasmas at their interaction location are estimated. These show an interaction that is highly non-collisional, and that becomes more and more dominated by the magnetic fields as time progresses (from 5 to 60 ps). Particle-in-cell simulations are used to reproduce the initial acceleration of the plasma both via simulations including the laser interaction and via simulations that start with preheated electrons (to save dramatically on computational expense). The benchmarking of such simulations with the experiment and with each other will be used to understand the physical interaction when a magnetic field is applied. Finally, the experimental density profile of the interacting plasmas is shown in the case without an applied magnetic magnetic field, so to show that without an applied field that the development of high-velocity shocks, as a result of particle-to-particle collisions, is not achievable in the configuration considered.

  11. Aerosol formation from high-velocity uranium drops: Comparison of number and mass distributions. Final report

    SciTech Connect

    Rader, D.J.; Benson, D.A.

    1995-05-01

    This report presents the results of an experimental study of the aerosol produced by the combustion of high-velocity molten-uranium droplets produced by the simultaneous heating and electromagnetic launch of uranium wires. These tests are intended to simulate the reduction of high-velocity fragments into aerosol in high-explosive detonations or reactor accidents involving nuclear materials. As reported earlier, the resulting aerosol consists mainly of web-like chain agglomerates. A condensation nucleus counter was used to investigate the decay of the total particle concentration due to coagulation and losses. Number size distributions based on mobility equivalent diameter obtained soon after launch with a Differential Mobility Particle Sizer showed lognormal distributions with an initial count median diameter (CMD) of 0.3 {mu}m and a geometric standard deviation, {sigma}{sub g} of about 2; the CMD was found to increase and {sigma}{sub g} decrease with time due to coagulation. Mass size distributions based on aerodynamic diameter were obtained for the first time with a Microorifice Uniform Deposit Impactor, which showed lognormal distributions with mass median aerodynamic diameters of about 0.5 {mu}m and an aerodynamic geometric standard deviation of about 2. Approximate methods for converting between number and mass distributions and between mobility and aerodynamic equivalent diameters are presented.

  12. On projectile fragmentation at high-velocity perforation of a thin bumper

    NASA Astrophysics Data System (ADS)

    Myagkov, N. N.; Stepanov, V. V.

    2014-09-01

    By means of 3D numerical simulations, we study the statistical properties of the fragments cloud formed during high-velocity impact of a spherical projectile on a mesh bumper. We present a quantitative description of the projectile fragmentation, and study the nature of the transition from the damage to the fragmentation of the projectile when the impact velocity varies. A distinctive feature of the present work is that the calculations are carried out by smoothed particle hydrodynamics (SPH) method applied to the equations of mechanics of deformable solids (MDS). We describe the materials behavior by the Mie-Grüneisen equation of state and the Johnson-Cook model for the yield strength. The maximum principal stress spall model is used as the fracture model. It is shown that the simulation results of fragmentation based on the MDS equations by the SPH method are qualitatively consistent with the results obtained earlier on the basis of the molecular dynamics and discrete element models. It is found that the power-law distribution exponent does not depend on energy imparted to the projectile during the high-velocity impact. At the same time, our calculations show that the critical impact velocity, the power-law exponent and other critical exponents depend on the fracture criterion.

  13. A SPITZER-MIPS SEARCH FOR DUST IN COMPACT HIGH-VELOCITY H I CLOUDS

    SciTech Connect

    Williams, Rik J.; Mathur, Smita; Poindexter, Shawn; Elvis, Martin; Nicastro, Fabrizio

    2012-04-15

    We employ three-band Spitzer-MIPS observations to search for cold dust emission in three neutral hydrogen compact high-velocity clouds (CHVCs) in the vicinity of the Milky Way. Far-infrared emission correlated with H I column density was previously reported in HVC Complex C, indicating that this object contains dust heated by the Galactic radiation field at its distance of {approx}10 kpc. Assuming published Spitzer, IRAS, and Planck, IR-H I correlations for Complex C, our Spitzer observations are of sufficient depth to directly detect 160 {mu}m dust emission in the CHVCs if it is present at the same level as in Complex C, but no emission is detected in any of the targets. For one of the targets (CHVC289) which has well-localized H I clumps, we therefore conclude that it is fundamentally different from Complex C, with either a lower dust-to-gas ratio or a greater distance from the Galactic disk (and consequently cooler dust temperature). Firm conclusions cannot be drawn for the other two Spitzer-observed CHVCs since their small-scale H I structures are not sufficiently well known; nonetheless, no extended dust emission is apparent despite their relatively high H I column densities. The lack of dust emission in CHVC289 suggests that at least some compact high-velocity clouds objects may exhibit very low dust-to-gas ratios and/or greater Galactocentric distances than large HVC complexes.

  14. Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo.

    PubMed

    Richter, P; de Boer, K S; Widmann, H; Kappelmann, N; Gringel, W; Grewing, M; Barnstedt, J

    1999-11-25

    The Milky Way's halo contains clouds of neutral hydrogen with high radial velocities which do not follow the general rotational motion of the Galaxy. Few distances to these high-velocity clouds are known, so even gross properties such as total mass are hard to determine. As a consequence, there is no generally accepted theory regarding their origin. One idea is that they result from gas that has cooled after being ejected from the Galaxy through fountain-like flows powered by supernovae; another is that they are composed of gas, poor in heavy elements, which is falling onto the disk of the Milky Way from intergalactic space. The presence of molecular hydrogen, whose formation generally requires the presence of dust (and therefore gas, enriched in heavy elements), could help to distinguish between these possibilities. Here we report the discovery of molecular hydrogen absorption in a high-velocity cloud along the line of sight to the Large Magellanic Cloud. We also derive for the same cloud an iron abundance which is half of the solar value. From these data, we conclude that gas in this cloud originated in the disk of the Milky Way.

  15. Eulerian adaptive finite-difference method for high-velocity impact and penetration problems

    SciTech Connect

    Barton, Philip T.; Deiterding, Ralf; Meiron, Daniel I.; Pullin, Dale I

    2013-01-01

    Owing to the complex processes involved, faithful prediction of high-velocity impact events demands a simulation method delivering efficient calculations based on comprehensively formulated constitutive models. Such an approach is presented herein, employing a weighted essentially non-oscillatory (WENO) method within an adaptive mesh refinement (AMR) framework for the numerical solution of hyperbolic partial differential equations. Applied widely in computational fluid dynamics, these methods are well suited to the involved locally non-smooth finite deformations, circumventing any requirement for artificial viscosity functions for shock capturing. Application of the methods is facilitated through using a model of solid dynamics based upon hyper-elastic theory comprising kinematic evolution equations for the elastic distortion tensor. The model for finite inelastic deformations is phenomenologically equivalent to Maxwell s model of tangential stress relaxation. Closure relations tailored to the expected high-pressure states are proposed and calibrated for the materials of interest. Sharp interface resolution is achieved by employing level-set functions to track boundary motion, along with a ghost material method to capture the necessary internal boundary conditions for material interactions and stress-free surfaces. The approach is demonstrated for the simulation of high velocity impacts of steel projectiles on aluminium target plates in two and three dimensions.

  16. Evidence for a high-velocity slab associated with the Hindu Kush seismic zone

    NASA Astrophysics Data System (ADS)

    Mellors, R. J.; Pavlis, G. L.; Hamburger, M. W.; Al-Shukri, H. J.; Lukk, A. A.

    1995-03-01

    We used teleseismic travel time residuals to determine lateral velocity variations of the crust and upper mantle in the Pamir-Hindu Kush region in Tadjikistan and Afghanistan. Data from 29 analog seismic stations in Tadjikistan and northern Afghanistan were used to determine travel time residuals for 210 teleseismic events ranging in distance from 28 deg to 87 deg and covering a broad range of azimuths. We inverted for velocity perturbations over a rectangular grid with a block size of 99 x 99 km. The model extended to a depth of 350 km with a 50-km-thick first layer and two 150-km-thick deeper layers. The results show a strong and well-resolved zone of high velocities in the upper mantle at depths greater than 200 km, coincident with the location of the Hindu Kush seismic zone. No clear velocity perturbations are associated with the Pamir seismic zone. Above 200 km little correlation is observed with the seismic zone, but indications of thicker crust under the Pamir and thinner crust under the Tadjik Depression are seen. The high velocities are most likely caused by the presence of oceanic lithosphere at depth.

  17. Development of a high-velocity free-flight launcher : the Ames light-gas gun

    NASA Technical Reports Server (NTRS)

    Charters, A C; Denardo, B Pat; Rossow, Vernon J

    1955-01-01

    Recent interest in long-range missiles has stimulated a search for new experimental techniques which can reproduce in the laboratory the high temperatures and Mach numbers associated with the missiles' flight. One promising possibility lies in free-flight testing of laboratory models which are flown at the full velocity of the missile. In this type of test, temperatures are approximated and aerodynamic heating of the model is representative of that experienced by the missile in high-velocity flight. A prime requirement of the free-flight test technique is a device which had the capacity for launching models at the velocities desired. In response to thie need, a gun firing light models at velocities up to 15,000 feet per second has been developed at the Ames Aeronautical Laboratory. The design of this gun, the analysis of its performance, and the results of the initial firing trials are described in this paper. The firing trials showed that the measured velocities and pressures agreed well with the predicted values. Also, the erosion of the launch tube was very small for the eleven rounds fired. The performance of the gun suggests that it will prove to be a satisfactory launcher for high-velocity free-flight tests. However, it should be mentioned that only the gross performance has been evaluated so far, and, consequently, the operation of the gun must be investigated in further detail before its performance can be reliably predicted over its full operating range.

  18. Investigation of high velocity separator for particle removal in coal gasification plants. Phase II report

    SciTech Connect

    Linhardt, H.D.

    1980-01-15

    This report summarizes the results of Phase II of the High Velocity Particle Separator Program performed under Contract EF-77-C-01-2709. This high velocity wedge separator has the potential to reduce equipment size and cost of high temperature and pressurized particulate removal equipment for coal derived gases. Phase II has been directed toward testing and detailed conceptual design of an element suitable for a commercial scale high temperature, high pressure particle separator (HTPS). Concurrently, Phase IA has been conducted, which utilized the ambient analog method (AAM) for aerodynamic and collection performance investigation of each HTPS configuration prior and during hot testing. This report summarizes the results of Phase IA and II. The AAM effort established correlation of theoretical analysis and experiment for HTPS pressure drop, purge flow ratio and collection efficiency potential. Task I defined the initial test conditions to be the contract design point of 1800/sup 0/F and 350 psia. The 1800/sup 0/F, 350 psia testing represents the main high temperature testing with coal-derived particulates in the 2 to 10 micron range. Phase IA and Phase II have demonstrated efficient particle collection with acceptable pressure drop. In view of these encouraging results, it is reasonable to apply the developed technology toward future hot gas particulate cleanup requirements.

  19. A novel platform to study magnetized high-velocity collisionless shocks

    SciTech Connect

    Higginson, D. P.; Korneev, Ph; Béard, J.; Chen, S. N.; d'Humières, E.; Pépin, H.; Pikuz, S.; Pollock, B.; Riquier, R.; Tikhonchuk, V.; Fuchs, J.

    2014-12-13

    An experimental platform to study the interaction of two colliding high-velocity (0.01–0.2c; 0.05–20 MeV) proton plasmas in a high strength (20 T) magnetic field is introduced. This platform aims to study the collision of magnetized plasmas accelerated via the Target-Normal-Sheath-Acceleration mechanism and initially separated by distances of a few hundred microns. The plasmas are accelerated from solid targets positioned inside a few cubic millimeter cavity located within a Helmholtz coil that provides up to 20 T magnetic fields. Various parameters of the plasmas at their interaction location are estimated. These show an interaction that is highly non-collisional, and that becomes more and more dominated by the magnetic fields as time progresses (from 5 to 60 ps). Particle-in-cell simulations are used to reproduce the initial acceleration of the plasma both via simulations including the laser interaction and via simulations that start with preheated electrons (to save dramatically on computational expense). The benchmarking of such simulations with the experiment and with each other will be used to understand the physical interaction when a magnetic field is applied. In conclusion, the experimental density profile of the interacting plasmas is shown in the case without an applied magnetic magnetic field, so to show that without an applied field that the development of high-velocity shocks, as a result of particle-to-particle collisions, is not achievable in the configuration considered.

  20. Corrosion behavior of some high-temperature alloys under high velocity burnt fuel

    SciTech Connect

    Agarwal, D.C.; Brill, U.; Ibas, O.

    1995-12-31

    In a laboratory burner rig facility developed by Krupp VDM, the corrosion behavior of three high-temperature alloys was investigated under high velocity burnt fuel. A hot gas stream of burnt natural gas hits a sample at an angle of 45{degree}. Gas velocities of up to 80 m/s are obtained, and can be continuously adjusted by varying the air volume. By changing the sample to burner nozzle distance, a temperature gradient from 1,000 C in the center to 880 C at the edges of the sample can be achieved. Corrosion behavior of the two Fe-base alloys 310 S and 800H, and the Ni-base alloy 602CA, was evaluated by means of optical microscopy and SEM/EDAX analysis. According to results obtained so far, the alumina-former, alloy 602CA, provides best performance under high velocity burnt fuel at 880--1,000 C, as well as under steady state cyclic oxidation testing in air.

  1. Streptococcus mutans biofilm transient viscoelastic fluid behaviour during high-velocity microsprays.

    PubMed

    Fabbri, S; Johnston, D A; Rmaile, A; Gottenbos, B; De Jager, M; Aspiras, M; Starke, E M; Ward, M T; Stoodley, P

    2016-06-01

    Using high-speed imaging we assessed Streptococcus mutans biofilm-fluid interactions during exposure to a 60-ms microspray burst with a maximum exit velocity of 51m/s. S. mutans UA159 biofilms were grown for 72h on 10mm-length glass slides pre-conditioned with porcine gastric mucin. Biofilm stiffness was measured by performing uniaxial-compression tests. We developed an in-vitro interproximal model which allowed the parallel insertion of two biofilm-colonized slides separated by a distance of 1mm and enabled high-speed imaging of the removal process at the surface. S. mutans biofilms were exposed to either a water microspray or an air-only microburst. High-speed videos provided further insight into the mechanical behaviour of biofilms as complex liquids and into high-shear fluid-biofilm interaction. We documented biofilms extremely transient fluid behaviour when exposed to the high-velocity microsprays. The presence of time-dependent recoil and residual deformation confirmed the pivotal role of viscoelasticity in biofilm removal. The air-only microburst was effective enough to remove some of the biofilm but created a smaller clearance zone underlying the importance of water and the air-water interface of drops moving over the solid surface in the removal process. Confocal and COMSTAT analysis showed the high-velocity water microspray caused up to a 99.9% reduction in biofilm thickness, biomass and area coverage, within the impact area. PMID:26771168

  2. High-velocity frictional experiments on dolerite and quartzite under controlled pore pressure

    NASA Astrophysics Data System (ADS)

    Togo, T.; Shimamoto, T.; Ma, S.

    2013-12-01

    High-velocity friction experiments on rocks with or without gouge have been conducted mostly under dry conditions and demonstrated dramatic weakening of faults at high velocities (e.g., Di Toro et al., 2011, Nature). Recent experiments under wet conditions (e.g., Ujiie and Tsutsumi, 2010, GRL; Faulkner et al., 2011, GRL) revealed very different behaviors from those of dry faults, but those experiments were done under drained conditions. Experiments with controlled pore pressure Pp are definitely needed to determine mechanical properties of faults under fluid-rich environments such as those in subduction zones. Thus we have developed a pressure vessel that can be attached to our rotary-shear low to high-velocity friction apparatus (Marui Co Ltd., MIS-233-1-76). With a current specimen holder, friction experiments can be done on hollow-cylindrical specimens of 15 and 40 mm in inner and outer diameters, respectively, at controlled Pp to 35 MPa, at effective normal stresses of 3~9 MPa, and at slip rates of 60 mm/year to 2 m/s. An effective normal stress can be applied with a 100 kN hydraulic actuator. We report an outline of the experimental system and preliminary high-velocity experiments on Shanxi dolerite and a quartzite from China that are composed of pyroxene and plagioclase and of almost pure quartz, respectively. High-velocity friction experiments were performed on hollow-cylindrical specimens of Shanxi dolerite at effective normal stresses of 0.13~1.07 MPa and at slip rates of 1, 10, 100 and 1000 mm/sec. All experiments were conducted first with the nitrogen gas filling the pressure vessel (dry tests) and then with a controlled pore-water pressure (wet tests). In the dry tests an axial force was kept at 1 kN and the nitrogen gas pressure was increased in steps to 5 MPa to change an effective normal stress. In the wet tests the specimens were soaked in distilled water in the vessel and Pp was applied by nitrogen gas in a similar manner as in the dry tests

  3. The narrow pentaquark

    NASA Astrophysics Data System (ADS)

    Diakonov, Dmitri

    2007-02-01

    The experimental status of the pentaquark searches is briefly reviewed. Recent null results by the CLAS collaboration are commented, and new strong evidence of a very narrow Θ+ resonance by the DIANA collaboration is presented. On the theory side, I revisit the argument against the existence of the pentaquark — that of Callan and Klebanov — and show that actually a strong resonance is predicted in that approach, however its width is grossly overestimated. A recent calculation gives 2 MeV for the pentaquark width, and this number is probably still an upper bound.

  4. High velocity anomaly beneath the Deccan volcanic province: Evidence from seismic tomography

    USGS Publications Warehouse

    Iyer, H.M.; Gaur, V.K.; Rai, S.S.; Ramesh, D.S.; Rao, C.V.R.; Srinagesh, D.; Suryaprakasam, K.

    1989-01-01

    Analysis of teleseismic P-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to-1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of the P-wave residual data delineate the presence of a 600 km long approximately N-S trending anomalous region of high velocity (1-4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion of P-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity zone (1-4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low

  5. What Happens to a High Velocity Cloud When it Hits the Milky Way's Disk: Is Dark Matter Necessary for Survival?

    NASA Astrophysics Data System (ADS)

    Shelton, Robin L.; Galyardt, Jason

    2015-01-01

    Dark matter halos enshroud some of the most massive high velocity clouds. Their gravitational pull confines the clouds as they pass through the intergalactic medium. Given the ability of dark matter halos to stabilize their embedded baryonic clouds against hydrodynamic interactions that would otherwise disrupt them, it has further been suggested that dark matter halos could enable high velocity clouds to survive impacts with the Milky Way's disk. The survival of high velocity clouds, such as the Smith Cloud, during a passage through the disk has been cited as evidence for the presence of dark matter. However, a second actor, the magnetic field, may also be at play. In order to characterize, measure, and disentangle their effects, we have performed magnetohydrodynamic simulations of massive high velocity clouds as they impact a galactic disk. Here, we present the rate at which material dissipates in a variety of situations that include or exclude dark matter and magnetic fields.

  6. Simulation of High Velocity Impact on Composite Structures - Model Implementation and Validation

    NASA Astrophysics Data System (ADS)

    Schueler, Dominik; Toso-Pentecôte, Nathalie; Voggenreiter, Heinz

    2016-08-01

    High velocity impact on composite aircraft structures leads to the formation of flexural waves that can cause severe damage to the structure. Damage and failure can occur within the plies and/or in the resin rich interface layers between adjacent plies. In the present paper a modelling methodology is documented that captures intra- and inter-laminar damage and their interrelations by use of shell element layers representing sub-laminates that are connected with cohesive interface layers to simulate delamination. This approach allows the simulation of large structures while still capturing the governing damage mechanisms and their interactions. The paper describes numerical algorithms for the implementation of a Ladevèze continuum damage model for the ply and methods to derive input parameters for the cohesive zone model. By comparison with experimental results from gas gun impact tests the potential and limitations of the modelling approach are discussed.

  7. The use of high velocity launchers for scientific and engineering studies

    SciTech Connect

    Asay, J.R.; Chhabildas, L.C.; Furnish, M.D.

    1991-01-01

    Shockwave techniques have been used for decades to study the dynamic states of matter in temperature and pressure regimes inaccessible by other methods. These techniques have been employed in a wide variety of scientific, military, and commercial applications. A principal scientific objective has been to determine high-pressure equations of state (EOS) to ultra-high pressures; pressures of tens of Mbar have been reported for several materials. Most recently, these methods have been used for studies of thermophysical properties under shock compression, including phase transition kinetics, and mechanical properties, such as the high-pressure yield strength. In this paper, a brief discussion of recent developments in high velocity launchers is given. Advances in techniques for subjecting materials to a wide range of loading conditions is presented, including selected illustrations of shockwave measurements to Mbar pressures. 54 refs.

  8. Entrainment in High-Velocity, High Temperature Plasma Jets Part I: Experimental Results

    SciTech Connect

    Fincke, J.R.; Crawford, D.M.; Snyder, S.C.; Swank, W.D.; Haggard, D.C.; Williamson, R.L.

    2002-03-27

    The development of a high-velocity, high-temperature argon plasma jet issuing into air has been investigated. In particular the entrainment of the surrounding air, its effect on the temperature and velocity profiles and the subsequent mixing and dissociation of oxygen has been examined in detail. The total concentration of oxygen and the velocity and temperature profiles in the jet were obtained from an enthalpy probe. High-resolution Thomson scattering provided an independent measure of plasma velocity and temperature, validating enthalpy probe measurements and providing non-intrusive measurements near the nozzle exit. The concentration of atomic oxygen was obtained from two-photon Laser Induced Fluorescence (LIF). Molecular oxygen concentration and temperature was obtained from Coherent Anti-Stokes Raman Spectroscopy (CARS). It was found that both the incompleteness of mixing at the molecular scale and the rate of oxygen dissociation and recombination effects jet behavior.

  9. The structural and dynamical aspects of boron nitride nanotubes under high velocity impacts.

    PubMed

    Machado, Leonardo D; Ozden, Sehmus; Tiwary, ChandraSekhar; Autreto, Pedro A S; Vajtai, Robert; Barrera, Enrique V; Galvao, Douglas S; Ajayan, Pulickel M

    2016-06-01

    This communication report is a study on the structural and dynamical aspects of boron nitride nanotubes (BNNTs) shot at high velocities (∼5 km s(-1)) against solid targets. The experimental results show unzipping of BNNTs and the formation of hBN nanoribbons. Fully atomistic reactive molecular dynamics simulations were also carried out to gain insights into the BNNT fracture patterns and deformation mechanisms. Our results show that longitudinal and axial tube fractures occur, but the formation of BN nanoribbons from fractured tubes was only observed for some impact angles. Although some structural and dynamical features of the impacts are similar to the ones reported for CNTs, because BNNTs are more brittle than CNTs this results in a larger number of fractured tubes but with fewer formed nanoribbons. PMID:27189765

  10. The detection of high-velocity outflows from M8E-IR

    NASA Technical Reports Server (NTRS)

    Mitchell, George F.; Allen, Mark; Beer, Reinhard; Dekany, Richard; Huntress, Wesley

    1988-01-01

    A high-resolution (0.059/cm) M band (4.6 micron) spectrum of the embedded young stellar object M8E-IR is presented and discussed. The spectrum shows strong absorption to large blueshifts in the rotational lines of the fundamental vibrational band, v = 1-0, of CO. The absorption is interpreted as being due to gas near to, and flowing from, the central object. The outflowing gas is warm (95-330 K) and consists of discrete velocity components with the very high velocities of 90, 130, 150, and 160 km/s. On the basis of a simple model, it is estimated that the observed outflows are less than 100 yr old.

  11. The Draco Nebula, a Molecular Cloud Associated with a High Velocity Cloud?

    NASA Technical Reports Server (NTRS)

    Mebold, U.; Kalberla, P. W. M.

    1984-01-01

    Extended and very faint bright nebulae are found in high galactic latitudes at the Palomar Observatory Sky Survey. Such a nebula, located in the constellation Draco and called Draco Nebula or Dracula, was found to be in detailed positional coincidence with a 21 cm emission line feature. Estimates of the minimum visual extinction from star counts ON and OFF Dracula and an estimated visual surface brightness indicate that Dracula fits the relation SBV = 24.2 - 2.5 log AV for dust clouds located above the galactic plane and reflecting the integrated starlight of the galactic disk. Hence Dracula is probably a reflection nebula. Indicators of molecular hydrogen in Dracula, molecules such as CO, were searched for by using a 2.5-m mm-telescope. Molecular hydrogen column densities were estimated. The dynamics of CO clumps was studied. Dracula has a close positional and possibly even astrophysical relationship to the high velocity cloud phenomenon.

  12. Electric and magnetic field measurements inside a high-velocity neutral beam undergoing ionization

    NASA Technical Reports Server (NTRS)

    Kelley, M. C.; Swenson, C. M.; Brenning, N.; Baker, K.; Pfaff, R.

    1991-01-01

    Vector electric field measurements were made inside two ionizing, high-velocity streams of barium atoms in the earth's ionosphere, and a variety of electrical phenomena across the frequency spectrum are reported. A very large quasi-dc electric field was detected antiparallel to the beam velocity at a roughly 45 deg angle with the magnetic field B0. A very large component of E is found parallel to B0. The fluctuating electric fields are also quite large, of the same order of magnitude as the quasi-dc pulse. The wave energy maximizes at frequencies below the barium lower hybrid frequency and includes strong signatures of the oxygen cyclotron frequency. Measurements made on a subpayload separated across B0 by several hundred meters and along B0 by several km do not show the large pulse. Very large amplitude magnetic field fluctuations were observed in both bursts.

  13. Aerodynamic study on supersonic flows in high-velocity oxy-fuel thermal spray process

    NASA Astrophysics Data System (ADS)

    Katanoda, Hiroshi; Matsuoka, Takeshi; Kuroda, Seiji; Kawakita, Jin; Fukanuma, Hirotaka; Matsuo, Kazuyasu

    2005-06-01

    To clarify the characteristics of gas flow in high velocity oxy-fuel (HVOF) thermal spray gun, aerodynamic research is performed using a special gun. The gun has rectangular cross-sectional area and sidewalls of optical glass to visualize the internal flow. The gun consists of a supersonic nozzle with the design Mach number of 2.0 followed by a straight passage called barrel. Compressed dry air up to 0.78 MPa is used as a process gas instead of combustion gas which is used in a commercial HVOF gun. The high-speed gas flows with shock waves in the gun and jets are visualized by schlieren technique. Complicated internal and external flow-fields containing various types of shock wave as well as expansion wave are visualized.

  14. High-velocity OH/IR stars at the Galactic centre

    NASA Astrophysics Data System (ADS)

    van Langevelde, H. J.; Brown, A. G. A.; Lindqvist, M.; Habing, H. J.; de Zeeuw, P. T.

    1992-07-01

    We present the results of a small survey for OH/IR stars at high radial velocities in the Galactic center region performed with the VLA and the Nancay telescope. We have detected two new OH/IR stars, one at a peculiar velocity of -309 km/s, the other at -355 km/s. These two objects and one previously detected high-velocity OH/IR star (OH 0.3-0.2, Baud et al., 1975) stand out in the 1, v diagram of OH/IR stars at the Galactic center. Are these stars just on the extreme edge of the radial velocity distribution? Or are these objects no longer bound to the Galactic center? We discuss these possibilities, showing that these are most likely bulge stars on elongated orbits passing close to the Galactic center.

  15. Three-dimensional finite element analysis for high velocity impact. [of projectiles from space debris

    NASA Technical Reports Server (NTRS)

    Chan, S. T. K.; Lee, C. H.; Brashears, M. R.

    1975-01-01

    A finite element algorithm for solving unsteady, three-dimensional high velocity impact problems is presented. A computer program was developed based on the Eulerian hydroelasto-viscoplastic formulation and the utilization of the theorem of weak solutions. The equations solved consist of conservation of mass, momentum, and energy, equation of state, and appropriate constitutive equations. The solution technique is a time-dependent finite element analysis utilizing three-dimensional isoparametric elements, in conjunction with a generalized two-step time integration scheme. The developed code was demonstrated by solving one-dimensional as well as three-dimensional impact problems for both the inviscid hydrodynamic model and the hydroelasto-viscoplastic model.

  16. Study of Iron oxide nanoparticles using Mössbauer spectroscopy with a high velocity resolution

    NASA Astrophysics Data System (ADS)

    Oshtrakh, M. I.; Ushakov, M. V.; Šepelák, V.; Semionkin, V. A.; Morais, P. C.

    2016-01-01

    Iron oxide (magnetite and maghemite) nanoparticles developed for magnetic fluids were studied using Mössbauer spectroscopy with a high velocity resolution at 295 and 90 K. The recorded Mössbauer spectra have demonstrated that usual physical models based on octahedral and tetrahedral sites were not suitable for fitting. Alternatively, the Mössbauer spectra were nicely fitted using a large number of magnetic sextets. The obtained results showed that the Mössbauer spectra and the assessed parameters were different for nanoparticles as-prepared and dispersed in the dispersing fluid at 295 K. We claim that this finding is mainly due to the interaction of polar molecules with Iron cations at nanoparticle's surface or due to the surface coating using carboxylic-terminated molecules. It is assumed that the large number of spectral components may be related to complexity of the nanoparticle's characteristics and deviations from stoichiometry, including in the latter the influence of the oxidation of magnetite towards maghemite.

  17. High-velocity tails on the velocity distribution of solar wind ions

    SciTech Connect

    Ogilvie, K.W. ); Geiss, J. ); Gloeckler, G. ); Berdichevsky, D. ); Wilken, B. )

    1993-03-01

    Recent observations of the solar wind using the SWICS instrument on the Ulysses spacecraft have shown the presence of high-velocity [open quotes]tails[close quotes] on the velocity distribution of protons. Similar features have also been observed on the velocity distributions of helium and oxygen ions. Of the order of 1% of the solar wind density is involved in these tails, which are approximately exponential in shape and persist to V = V[sub B] + 10V[sub th] or beyond, where V[sub B] is the bulk velocity and V[sub th] the thermal velocity of the solar wind. This paper contains a preliminary description of the phenomenon. It is clear that it is ultimately connected with the passage of interplanetary shocks past the spacecraft and that particle acceleration at oblique shocks is involved. 21 refs., 6 figs., 2 tabs.

  18. The quest for TPa Hugoniot data: using the DEMG in high velocity pulsed power experiments

    SciTech Connect

    Peterson, Jeff H; Rousculp, Christopher L; Holtkamp, David B; Oro, David M; Griego, Jeffrey R; Atchison, Walter L; Reinovsky, Robert E

    2010-12-20

    ALT-3 is an experiment being designed in collaboration between Russian VNIIEF scientists and LANL that aims to conduct high velocity material experiments to measure shock velocities at pressures near 1 TPa. The DEMG (Disk Explosive Magnetic Generator) is used to drive >60MA currents to accelerate an aluminum liner to speeds in excess of 20 km/s. The 1-D model of the DEMG has been refined from a given current profile to a time-varying inductance. Various techniques are used to model the FOS (Foil Opening Switch) on the DEMG and a refined DEMG model is then used to drive a liner into various targets to determine the optimum design for the experiment and analyze the possible conditions and complications.

  19. Ringlike spin segregation of binary mixtures in a high-velocity rotating drum

    NASA Astrophysics Data System (ADS)

    Decai, Huang; Ming, Lu; Gang, Sun; Yaodong, Feng; Min, Sun; Haiping, Wu; Kaiming, Deng

    2012-03-01

    This study presents molecular dynamics simulations on the segregation of binary mixtures in a high-velocity rotating drum. Depending on the ratio between the particle radius and density, similarities to the Brazil-nut effect and its reverse form are shown in the ringlike spin segregation patterns in radial direction. The smaller and heavier particles accumulated toward the drum wall, whereas the bigger and lighter particles accumulated toward the drum center. The effects of particle radius and density on the segregation states were quantified and the phase diagram of segregation in the ρb/ρs - rb/rs space was plotted. The observed phenomena can be explained by the combined percolation and the buoyancy effects.

  20. Relationship between the upper mantle high velocity seismic lid and the continental lithosphere

    NASA Astrophysics Data System (ADS)

    Priestley, Keith; Tilmann, Frederik

    2009-04-01

    The lithosphere-asthenosphere boundary corresponds to the base of the "rigid" plates - the depth at which heat transport changes from advection in the convecting deeper upper mantle to conduction in the shallow upper mantle. Although this boundary is a fundamental feature of the Earth, mapping it has been difficult because it does not correspond to a sharp change in temperature or composition. Various definitions of the lithosphere and asthenosphere are based on the analysis of different types of geophysical and geological observations. The depth to the lithosphere-asthenosphere boundary determined from these different observations often shows little agreement when they are applied to the same region because the geophysical and geological observations (i.e., seismic velocity, strain rate, electrical resistivity, chemical depletion, etc.) are proxies for the change in rheological properties rather than a direct measure of the rheological properties. In this paper, we focus on the seismic mapping of the upper mantle high velocity lid and low velocity zone and its relationship to the lithosphere and asthenosphere. We have two goals: (a) to examine the differences in how teleseismic body-wave travel-time tomography and surface-wave tomography image upper mantle seismic structure; and (b) to summarise how upper mantle seismic velocity structure can be related to the structure of the lithosphere and asthenosphere. Surface-wave tomography provides reasonably good depth resolution, especially when higher modes are included in the analysis, but lateral resolution is limited by the horizontal wavelength of the long-period surface waves used to constrain upper mantle velocity structure. Teleseismic body-wave tomography has poor depth resolution in the upper mantle, particularly when no strong lateral contrasts are present. If station terms are used, features with large lateral extent and gradual boundaries are attenuated in the tomographic image. Body-wave models are not

  1. Cavity dimensions for high velocity penetration events: A comparison of calculational results with data

    SciTech Connect

    Kmetyk, L.N.; Yarrington, P.

    1989-05-01

    Calculations were performed with the CTH and HULL finite difference wavecodes to evaluate computational capabilities for predicting depth and diameter of target cavities produced in high velocity penetration events. The calculations simulated selected tests in a set of armor penetration experiments conducted by the US Army Ballistic Research Laboratory and reported earlier in the literature. The tests and simulations involved penetration of semi-infinite targets by long rod projectiles over a range of impact velocities from 1.3 to 4.5 km/sec. Comparisons are made between the calculated and measured dimensions of the target cavities, and the sensitivity of the predicted results to target property variations is investigated. 9 refs., 18 figs., 3 tabs.

  2. LP 400-22, A Very Low Mass and High-Velocity White Dwarf

    NASA Technical Reports Server (NTRS)

    Kawka, Adela; Vennes, Stephane; Oswalt, Terry D.; Smith, J. Allyn; Silvestri, Nicole M.

    2006-01-01

    We report the identification of LP 400-22 (WD 2234+222) as a very low mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 11,080+/-140 K and a surface gravity of log g = 6.32 +/-0.08. Therefore, this is a helium-core white dwarf with a mass of 0.17 M,. The tangential velocity of this white dwarf is 414+/-43 km/s, making it one of the fastest moving white dwarfs known. We discuss probable evolutionary scenarios for this remarkable object.

  3. Theoretical studies of the infrared emission from circumstellar dust shells: the infrared characteristics of circumstellar silicates and the mass-loss rate of oxygen-rich late-type giants

    NASA Technical Reports Server (NTRS)

    Schutte, W. A.; Tielens, A. G.; Allamandola, L. J. (Principal Investigator)

    1989-01-01

    relation can be calibrated in terms of the total dust column density of the circumstellar shell and thus the mass-loss rate of late-type giants can easily be derived. Detailed models have been made of the infrared emission of three well-studied Miras: R Cas, IRC 10011, and OH 26.5+0.6, with the emphasis on the shape of the 10 micrometers emission or absorption feature. The results show that the intrinsic shape of the 10 micrometers resonance varies from a very broad feature in R Cas to a relatively narrower feature in OH 26.5+0.6, with IRC 10011 somewhere in between. Possible origins of this variation are discussed. The mass-loss rates from these objects are calculated to be 3 x 10(-7), 2 x 10(-5), and 2 x 10(-4) M Sun yr-1 for R Cas, IRC 10011, and OH 26.5+0.6, respectively. These results are compared to other determinations in the literature.

  4. Theoretical studies of the infrared emission from circumstellar dust shells: the infrared characteristics of circumstellar silicates and the mass-loss rate of oxygen-rich late-type giants.

    PubMed

    Schutte, W A; Tielens, A G

    1989-08-01

    relation can be calibrated in terms of the total dust column density of the circumstellar shell and thus the mass-loss rate of late-type giants can easily be derived. Detailed models have been made of the infrared emission of three well-studied Miras: R Cas, IRC 10011, and OH 26.5+0.6, with the emphasis on the shape of the 10 micrometers emission or absorption feature. The results show that the intrinsic shape of the 10 micrometers resonance varies from a very broad feature in R Cas to a relatively narrower feature in OH 26.5+0.6, with IRC 10011 somewhere in between. Possible origins of this variation are discussed. The mass-loss rates from these objects are calculated to be 3 x 10(-7), 2 x 10(-5), and 2 x 10(-4) M Sun yr-1 for R Cas, IRC 10011, and OH 26.5+0.6, respectively. These results are compared to other determinations in the literature.

  5. Chemical reactions induced by high-velocity molecular impacts: challenges for closed-source mass spectrometry

    NASA Astrophysics Data System (ADS)

    Austin, Daniel

    2016-07-01

    Analysis of upper atmosphere composition using closed-source neutral mass spectrometers (e.g., Cassini INMS, MAVEN NGIMS) is subject to error due to chemical reactions caused by the high-velocity impacts of neutral molecules on the source surfaces. In addition to species traditionally considered "surface reactive" (e.g., O, N) it is likely that many or all impacting molecules are vibrationally excited to the point that chemical changes can occur. Dissociation, fragmentation, formation of radicals and ions, and other reactions likely obscure analysis of the native atmospheric composition, particularly of organic compounds. Existing techniques are not capable of recreating the relevant impact chemistry in the lab. We report on the development of a new capability allowing reactions of high-velocity neutrals impacting surfaces to be characterized directly. Molecules introduced into a vacuum chamber are impacted at several km/s by the surface of a high-speed rotor. These molecules subsequently impact multiple times on other surfaces within the vacuum chamber until they are thermalized, after which they are cryogenically collected and analyzed. Reaction pathways and thermodynamics for volatile compounds are then determined. We will present current results on this project, including data from low- and mid-range velocity experiments. This type of information is critical to clarify prior flight results and plan for future missions. Finally, we present a new type of inlet intended to significantly reduce fragmentation for impact velocities typical of a fly-by mission. Theoretical analysis indicates that this new inlet may reduce fragmentation by more than an order of magnitude for any encounter velocity.

  6. High-velocity Interstellar Bullets in IRAS 05506+2414: A Very Young Protostar

    NASA Technical Reports Server (NTRS)

    Sahai, Raghvendra; Claussen, Mark; Sanchez Contreras, Carmen; Morris, Mark; Sarkar, Geetanjali

    2008-01-01

    We have made a serendipitous discovery of an enigmatic outflow source, IRAS 05506+2414 (hereafter IRAS 05506), as part of a multiwavelength survey of pre-planetary nebulae (PPNs). The HST optical and near-infrared images show a bright compact central source with a jet-like extension, and a fan-like spray of high-velocity (with radial velocities up to 350 km/s) elongated knots which appear to emanate from it. These structures are possibly analogous to the near-IR bullets'' seen in the Orion Nebula. Interferometric observations at 2.6 mm show the presence of a continuum source and a high-velocity CO outflow, which is aligned with the optical jet structure. IRAS 05506 is most likely not a PPN. We find extended NH3 (1,1) emission toward IRAS 05506; these data, together with the combined presence of far-IR emission, H2O and OH masers, and CO and CS J=2-1 emission, strongly argue for a dense, dusty star-forming core associated with IRAS 05506. IRAS 05506 is probably an intermediate-mass or massive protostar, and the very short timescale (200 yr) of its outflows indicates that it is very young. If IRAS 05506 is a massive star, then the lack of radio continuum and the late G to early K spectral type we find from our optical spectra imply that in this object we are witnessing the earliest stages of its life, while its temperature is still too low to provide sufficient UV flux for ionization.

  7. A novel platform to study magnetized high-velocity collisionless shocks

    DOE PAGESBeta

    Higginson, D. P.; Korneev, Ph; Béard, J.; Chen, S. N.; d'Humières, E.; Pépin, H.; Pikuz, S.; Pollock, B.; Riquier, R.; Tikhonchuk, V.; et al

    2014-12-13

    An experimental platform to study the interaction of two colliding high-velocity (0.01–0.2c; 0.05–20 MeV) proton plasmas in a high strength (20 T) magnetic field is introduced. This platform aims to study the collision of magnetized plasmas accelerated via the Target-Normal-Sheath-Acceleration mechanism and initially separated by distances of a few hundred microns. The plasmas are accelerated from solid targets positioned inside a few cubic millimeter cavity located within a Helmholtz coil that provides up to 20 T magnetic fields. Various parameters of the plasmas at their interaction location are estimated. These show an interaction that is highly non-collisional, and that becomesmore » more and more dominated by the magnetic fields as time progresses (from 5 to 60 ps). Particle-in-cell simulations are used to reproduce the initial acceleration of the plasma both via simulations including the laser interaction and via simulations that start with preheated electrons (to save dramatically on computational expense). The benchmarking of such simulations with the experiment and with each other will be used to understand the physical interaction when a magnetic field is applied. In conclusion, the experimental density profile of the interacting plasmas is shown in the case without an applied magnetic magnetic field, so to show that without an applied field that the development of high-velocity shocks, as a result of particle-to-particle collisions, is not achievable in the configuration considered.« less

  8. Mapping High-Velocity H-alpha and Lyman-alpha Emission from Supernova 1987A

    NASA Technical Reports Server (NTRS)

    France, Kevin; McCray, Richard; Fransson, Claes; Larsson, Josefin; Frank, Kari A.; Burrows, David N.; Challis, Peter; Kirshner, Robert P.; Chevalier, Roger A.; Garnavich, Peter; Heng, Kevin; Lawrence, Stephen S.; Lundqvist, Peter; Smith, Nathan; Sonneborn, George

    2015-01-01

    We present new Hubble Space Telescope images of high-velocity H-alpha and Lyman-alpha emission in the outer debris of SN 1987A. The H-alpha images are dominated by emission from hydrogen atoms crossing the reverse shock. For the first time we observe emission from the reverse shock surface well above and below the equatorial ring, suggesting a bipolar or conical structure perpendicular to the ring plane. Using the H-alpha imaging, we measure the mass flux of hydrogen atoms crossing the reverse shock front, in the velocity intervals (-7,500 < V(sub obs) < -2,800 km/s) and (1,000 < V(sub obs) < 7,500 km/s), ?M(sub H) = 1.2 × 10(exp -3) M/ y. We also present the first Lyman-alpha imaging of the whole remnant and new Chandra X-ray observations. Comparing the spatial distribution of the Lyman-alpha and X-ray emission, we observe that the majority of the high-velocity Lyman-alpha emission originates interior to the equatorial ring. The observed Lyman-alpha/H-alpha photon ratio, R(L-alpha/H-alpha) approx. = 17, is significantly higher than the theoretically predicted ratio of approx. = 5 for neutral atoms crossing the reverse shock front. We attribute this excess to Lyman-alpha emission produced by X-ray heating of the outer debris. The spatial orientation of the Lyman-alpha and X-ray emission suggests that X-ray heating of the outer debris is the dominant Lyman-alpha production mechanism in SN 1987A at this phase in its evolution.

  9. Impact of High Velocity Interactions on Galaxy Evolution in Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Machacek, Marie E.; Jones, C.; Forman, W. R.; Kraft, R. P.; Ashby, M. L.; Hardcastle, M. J.

    2007-05-01

    Galaxy interactions in cool groups dominate galaxy evolution at high redshift. Observations of galaxies interacting in nearby galaxy groups, where the same dynamical processes that transform galaxies at high redshift can be studied in detail, are critical to our understanding of galaxy and group evolution. X-ray observations of hot gas features, e.g. surface brightness edges and wakes, reveal that high velocity interactions play a significant role in the transformation of galaxies in groups, yet, because these encounters are difficult to identify in other wavebands, few have been studied. We present two case studies of high velocity galaxy-galaxy and galaxy-gas interactions in galaxy groups: NGC4782(3C278) and NGC4783 in LGG316, and NGC6872 and NGC6876 in the Pavo group. From Chandra and XMM-Newton X-ray data, we measure the hot gas temperature, density and metal abundance in the galaxies and the intragroup medium (IGM) to characterize the thermodynamic state of the group, constrain 3D motions of the galaxies through the IGM, and determine the dominant processes transferring matter and energy between the galaxy and group gas. We compare these results with VLA observations of NGC4782/3 and Spitzer IRAC observations of NGC6872 and NGC6876 to study the impact of these interactions on nuclear activity, radio jet evolution, and star formation in these galaxies, and on the heating and enrichment of the IGM. This work was supported in part by the Smithsonian Institution, the Chandra Science Center, NASA contracts AR5-6011X, GO6-7068X, NNX06AG34G, JPL1279244 and the Royal Society.

  10. High-velocity frictional strength across the Tohoku-Oki megathrust determined from surface drilling torque

    NASA Astrophysics Data System (ADS)

    Ujiie, K.; Inoue, T.; Ishiwata, J.

    2015-12-01

    Frictional strength at seismic slip rates is a key to evaluate fault weakening and rupture propagation during earthquakes. The Japan Trench First Drilling Project (JFAST) drilled through the shallow plate-boundary thrust, where huge displacements of ~50 m occurred during the 2011 Tohoku-Oki earthquake. To determine the downhole frictional strength at drilled site (Site C0019), we analyzed surface drilling data. The equivalent slip rate estimated from the rotation rate and inner and outer radiuses of the drill bit ranges from 0.8 to 1.3 m/s. The measured torque includes the frictional torque between the drilling string and borehole wall, the viscous torque between the drilling string and seawater/drilling fluid, and the drilling torque between the drill bit and sediments. We subtracted the former two from the measured torque using the torque data during bottom-up rotating operations at several depths. Then, the shear stress was calculated from the drilling torque taking the configuration of the drill bit into consideration. The normal stress was estimated from the weight on bit data and the projected area of the drill bit. Assuming negligible cohesion, the frictional strength was obtained by dividing shear stress by normal stress. The results show a clear contrast in high-velocity frictional strength across the plate-boundary thrust: the friction coefficient of frontal prism sediments (hemipelagic mudstones) in hanging wall is 0.1-0.2, while that in subducting sediments (hemipelagic to pelagic mudstones and chert) in footwall increases to 0.2-0.4. The friction coefficient of smectite-rich pelagic clay in the plate-boundary thrust is ~0.1, which is consistent with that obtained from high-velocity (1.3 m/s) friction experiments and temperature measurements. We conclude that surface drilling torque provides useful data to obtain a continuous downhole frictional strength.

  11. Optical Emission from High Velocity Clouds and the Nature of HVCs

    NASA Astrophysics Data System (ADS)

    Weiner, B. J.; Vogel, S. N.; Williams, T. B.

    1999-12-01

    The nature and origin of the high-velocity clouds of neutral hydrogen remain controversial, and the distances of most HVCs are poorly constrained. Only the large northern HVC complexes M and A have upper distance limits, of <5 and 4--10 kpc, from absorption against halo stars (Danly et al 1993, van Woerden et al 1999). These HVCs have diffuse H-alpha emission of 80--200 milli-Rayleighs (mR) (Tufte, Reynolds & Haffner 1998). We report results from a search of 20 high velocity clouds for faint diffuse optical emission lines in H-alpha and [N II], using a Fabry-Perot at the Las Campanas 2.5-m telescope. A few small complexes are ``bright,'' with H-alpha emission from 100--400 mR and high [N II]/H-alpha. Many HVCs are very faint in H-alpha: HVCs from the Anticenter, Galactic Center Negative, and Extreme Positive complexes have H-alpha from <15 to 30 mR. We construct a simple model for the ionizing flux emergent from the galaxy, normalized by the northern ``bright'' HVCs with known distances and H-alpha fluxes. If the H-alpha from HVCs is produced by ionizing flux escaping from the Galaxy, the H-alpha flux can be used to infer distances for HVCs. The model places the very faint HVCs at distances of 20--60 kpc, in the outer Galactic halo. If H-alpha can be produced by other mechanisms, than these distances could be lower limits. Independent of the model or mechanism, the HVCs that are very faint in H-alpha should be much farther away than the nearby ``bright'' HVCs. The faint HVCs are too far away to be produced by a Galactic fountain, and represent a significant amount of gas accreting onto the Galaxy. This work has been supported by a Carnegie Barbara McClintock Fellowship.

  12. A Search for Phosphine in Circumstellar Envelopes: PH3 in IRC +10216 and CRL 2688?

    NASA Astrophysics Data System (ADS)

    Tenenbaum, E. D.; Ziurys, L. M.

    2008-06-01

    We present the results of a search for the JK = 10→ 00 transition of PH3 (phosphine) at 267 GHz toward several circumstellar envelopes using the Arizona Radio Observatory 10 m Submillimeter Telescope (SMT). In the carbon-rich shells of IRC +10216 and CRL 2688, we have detected emission lines exactly at the PH3 frequency. Toward the oxygen-rich supergiant VY Canis Majoris, only an upper limit was obtained, while in the evolved carbon-rich proto-planetary nebula CRL 618, the transition is contaminated by vibrationally excited HC3N (ν7 = 4). The line shape in IRC +10216 appears to consist of two distinct components: a flat-topped profile with a width of ~28 km s-1, as is typical for this source, and a narrower feature approximately 4 km s-1 wide. The narrow component likely arises from the inner envelope (r < 8R*) where the gas has not reached the terminal expansion velocity, or it is nonthermal emission. Based on the broader component, the abundance of PH3 with respect to H2 is estimated to be 5 × 10-8 in a region with a radius of r < 150R*. If the narrower component is thermal, it implies a phosphine abundance of ~5 × 10-7 close to the stellar photosphere (r < 8R*). In CRL 2688, the PH3 abundance is less constrained, with plausible values ranging from 3 × 10-8 to 4 × 10-7, assuming a spherical distribution. Phosphine appears to be present in large concentrations in the inner envelope of C-rich AGB stars, and thus may function as a parent molecule for other phosphorus species.

  13. Narrow Angle movie

    NASA Technical Reports Server (NTRS)

    1999-01-01

    This brief three-frame movie of the Moon was made from three Cassini narrow-angle images as the spacecraft passed by the Moon on the way to its closest approach with Earth on August 17, 1999. The purpose of this particular set of images was to calibrate the spectral response of the narrow-angle camera and to test its 'on-chip summing mode' data compression technique in flight. From left to right, they show the Moon in the green, blue and ultraviolet regions of the spectrum in 40, 60 and 80 millisecond exposures, respectively. All three images have been scaled so that the brightness of Crisium basin, the dark circular region in the upper right, is the same in each image. The spatial scale in the blue and ultraviolet images is 1.4 miles per pixel (2.3 kilometers). The original scale in the green image (which was captured in the usual manner and then reduced in size by 2x2 pixel summing within the camera system) was 2.8 miles per pixel (4.6 kilometers). It has been enlarged for display to the same scale as the other two. The imaging data were processed and released by the Cassini Imaging Central Laboratory for Operations (CICLOPS) at the University of Arizona's Lunar and Planetary Laboratory, Tucson, AZ.

    Photo Credit: NASA/JPL/Cassini Imaging Team/University of Arizona

    Cassini, launched in 1997, is a joint mission of NASA, the European Space Agency and Italian Space Agency. The mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Space Science, Washington DC. JPL is a division of the California Institute of Technology, Pasadena, CA.

  14. Metamorphosis of SN 2014C: Delayed Interaction between a Hydrogen Poor Core-collapse Supernova and a Nearby Circumstellar Shell

    NASA Astrophysics Data System (ADS)

    Milisavljevic, D.; Margutti, R.; Kamble, A.; Patnaude, D. J.; Raymond, J. C.; Eldridge, J. J.; Fong, W.; Bietenholz, M.; Challis, P.; Chornock, R.; Drout, M. R.; Fransson, C.; Fesen, R. A.; Grindlay, J. E.; Kirshner, R. P.; Lunnan, R.; Mackey, J.; Miller, G. F.; Parrent, J. T.; Sanders, N. E.; Soderberg, A. M.; Zauderer, B. A.

    2015-12-01

    We present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star’s stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf-Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. An extended high velocity Hα absorption feature seen in near-maximum light spectra implies that the progenitor star was not completely stripped of hydrogen at the time of core collapse. Archival pre-explosion Subaru Telescope Suprime-Cam and Hubble Space Telescope Wide Field Planetary Camera 2 images of the region obtained in 2009 show a coincident source that is most likely a compact massive star cluster in NGC 7331 that hosted the progenitor system. By comparing the emission properties of the source with stellar population models that incorporate interacting binary stars we estimate the age of the host cluster to be 30-300 Myr, and favor ages closer to 30 Myr in light of relatively strong Hα emission. SN 2014C is the best observed member of a class of core-collapse supernovae that fill the gap between events that interact strongly with dense, nearby environments immediately after explosion and those that never show signs of interaction. Better understanding of the frequency and nature of this intermediate population can contribute valuable information about the poorly understood final stages of stellar evolution.

  15. METAMORPHOSIS OF SN 2014C: DELAYED INTERACTION BETWEEN A HYDROGEN POOR CORE-COLLAPSE SUPERNOVA AND A NEARBY CIRCUMSTELLAR SHELL

    SciTech Connect

    Milisavljevic, D.; Margutti, R.; Kamble, A.; Patnaude, D. J.; Raymond, J. C.; Challis, P.; Drout, M. R.; Grindlay, J. E.; Kirshner, R. P.; Lunnan, R.; Miller, G. F.; Parrent, J. T.; Sanders, N. E.; Eldridge, J. J.; Fong, W.; Bietenholz, M.; Chornock, R.; Fransson, C.; Fesen, R. A.; Mackey, J.; and others

    2015-12-20

    We present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star’s stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf–Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. An extended high velocity Hα absorption feature seen in near-maximum light spectra implies that the progenitor star was not completely stripped of hydrogen at the time of core collapse. Archival pre-explosion Subaru Telescope Suprime-Cam and Hubble Space Telescope Wide Field Planetary Camera 2 images of the region obtained in 2009 show a coincident source that is most likely a compact massive star cluster in NGC 7331 that hosted the progenitor system. By comparing the emission properties of the source with stellar population models that incorporate interacting binary stars we estimate the age of the host cluster to be 30–300 Myr, and favor ages closer to 30 Myr in light of relatively strong Hα emission. SN 2014C is the best observed member of a class of core-collapse supernovae that fill the gap between events that interact strongly with dense, nearby environments immediately after explosion and those that never show signs of interaction. Better understanding of the frequency and nature of this intermediate population can contribute valuable information about the poorly understood final stages of stellar evolution.

  16. Circumstellar shells resolved in IRAS survey data. II - Analysis

    NASA Technical Reports Server (NTRS)

    Young, K.; Phillips, T. G.; Knapp, G. R.

    1993-01-01

    IRAS survey data for 512 red giant stars and young planetary nebulae were processed using a computer program which fitted the data to an idealized model of a circumstellar shell. Seventy-six of these stars were found to have circumstellar shells resolved in the 60-micron survey data. Forty pct of the 76 stars are carbon stars. Thirteen are Mira variables. The evolution of these shells, involving the interaction of the expelled material with the ISM, is modeled, and the results suggest that the period during which Mira variables lose mass lasts for approximately 10 exp 5 yr. Carbon stars are found to shed mass for about 2 x 10 exp 5 yr. The expansion velocity of the outer shell for the largest shells will normally be lower by a factor of 3-5 than the expansion velocity obtained from CO observations.

  17. Circumstellar discs around solar mass stars in NGC 6611

    NASA Astrophysics Data System (ADS)

    Oliveira, J. M.; Jeffries, R. D.; van Loon, J. Th.; Littlefair, S. P.; Naylor, T.

    2005-03-01

    We have performed IZJHKL' observations in NGC 6611, the young cluster that ionizes the Eagle Nebula. We have discovered a rich pre-main sequence concentrated around the O-stars in the cluster. As measured by their L'-band excesses, at least 58+/-5 per cent of the pre-main sequence objects (0.45 < M < 2Msolar) have circumstellar discs. By comparing this disc frequency with frequencies determined for regions where the pre-main sequence stars are subject to less ionizing radiation, we find no evidence that the harsher environment of NGC 6611 (approximately an order of magnitude more ionizing Lyman continuum radiation than the Trapezium cluster) significantly hastens the dissipation of circumstellar discs around solar mass stars.

  18. External Shaping of Circumstellar Envelopes of Evolved Stars

    NASA Astrophysics Data System (ADS)

    Cox, N. L. J.

    2015-08-01

    The circumstellar envelopes of asymptotic giant branch (AGB) stars and red supergiants (RSGs) are complex chemical and physical environments, and the specifics of their mass-loss history are important for both stellar and galactic evolution. One key aspect in this is to understand how the circumstellar medium of these stars can be shaped and affected by both internal and external mechanisms. These influences can skew our view on the (dust) chemistry and mass-loss history of these stars, and hence their role in the chemical enrichment of galaxies. This contribution focuses on the external mechanism related to the interaction between the slow dusty stellar wind and the local ambient medium. I will discuss what recent observations and hydrodynamical simulations have revealed and how these can help us learn more about AGB stars and RSGs, as well as the interstellar medium (ISM).

  19. Detection of circumstellar material in a normal type Ia supernova.

    PubMed

    Patat, F; Chandra, P; Chevalier, R; Justham, S; Podsiadlowski, Ph; Wolf, C; Gal-Yam, A; Pasquini, L; Crawford, I A; Mazzali, P A; Pauldrach, A W A; Nomoto, K; Benetti, S; Cappellaro, E; Elias-Rosa, N; Hillebrandt, W; Leonard, D C; Pastorello, A; Renzini, A; Sabbadin, F; Simon, J D; Turatto, M

    2007-08-17

    Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion.

  20. Dust mineralogy in the circumstellar envelope of SVS13

    NASA Astrophysics Data System (ADS)

    Fujiyoshi, T.; Wright, C.; Moore, T.

    It is of great interest to study the mineralogy of circumstellar dust around young stars as it represents the original constituents of planetesimals, hence of the rocky planets like our own Earth. To this end, we have obtained an N-band (8-13 µm) spectrum of a pre-main-sequence star SVS13, using the facility mid-infrared imaging spectrometer COMICS on the Japanese 8.2-m Subaru Telescope atop the summit of Mauna Kea, Hawaii. We have fitted various emissivities/absorption coefficients of dust species to the spectrum to examine dust mineralogy in the circumstellar envelope of this remarkable young star. In this presentation, we outline the modelling and highlight some of our findings.

  1. Detection of circumstellar material in a normal type Ia supernova.

    PubMed

    Patat, F; Chandra, P; Chevalier, R; Justham, S; Podsiadlowski, Ph; Wolf, C; Gal-Yam, A; Pasquini, L; Crawford, I A; Mazzali, P A; Pauldrach, A W A; Nomoto, K; Benetti, S; Cappellaro, E; Elias-Rosa, N; Hillebrandt, W; Leonard, D C; Pastorello, A; Renzini, A; Sabbadin, F; Simon, J D; Turatto, M

    2007-08-17

    Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion. PMID:17626848

  2. CIRCUMSTELLAR ABSORPTION IN DOUBLE DETONATION TYPE Ia SUPERNOVAE

    SciTech Connect

    Shen, Ken J.; Guillochon, James; Foley, Ryan J.

    2013-06-20

    Upon formation, degenerate He core white dwarfs are surrounded by a radiative H-rich layer primarily supported by ideal gas pressure. In this Letter, we examine the effect of this H-rich layer on mass transfer in He+C/O double white dwarf binaries that will eventually merge and possibly yield a Type Ia supernova (SN Ia) in the double detonation scenario. Because its thermal profile and equation of state differ from the underlying He core, the H-rich layer is transferred stably onto the C/O white dwarf prior to the He core's tidal disruption. We find that this material is ejected from the binary system and sweeps up the surrounding interstellar medium hundreds to thousands of years before the SN Ia. The close match between the resulting circumstellar medium profiles and values inferred from recent observations of circumstellar absorption in SNe Ia gives further credence to the resurgent double detonation scenario.

  3. The chemistry of molecular anions in circumstellar sources

    SciTech Connect

    Agúndez, Marcelino; Cernicharo, José; Guélin, Michel

    2015-01-22

    The detection of negatively charged molecules in the interstellar and circumstellar medium in the past four years has been one of the most impacting surprises in the area of molecular astrophysics. It has motivated the interest of astronomers, physicists, and chemists on the study of the spectroscopy, chemical kinetics, and prevalence of molecular anions in the different astronomical regions. Up to six different molecular anions have been discovered in space to date, the last one being the small ion CN{sup −}, which has been observed in the envelope of the carbon star IRC +10216 and which contrary to the other larger anions is not formed by electron attachment to CN, but through reactions of large carbon anions with nitrogen atoms. Here we briefly review the current status of our knowledge of the chemistry of molecular anions in space, with particular emphasis on the circumstellar source IRC +10216, which to date is the astronomical source harboring the largest variety of anions.

  4. Observations of Circumstellar Thermochemical Equilibrium: The Case of Phosphorus

    NASA Technical Reports Server (NTRS)

    Milam, Stefanie N.; Charnley, Steven B.

    2011-01-01

    We will present observations of phosphorus-bearing species in circumstellar envelopes, including carbon- and oxygen-rich shells 1. New models of thermochemical equilibrium chemistry have been developed to interpret, and constrained by these data. These calculations will also be presented and compared to the numerous P-bearing species already observed in evolved stars. Predictions for other viable species will be made for observations with Herschel and ALMA.

  5. Magnetic Field and Early Evolution of Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Yusuke

    2016-03-01

    The magnetic field plays a central role in the formation and evolution of circumstellar disks. The magnetic field connects the rapidly rotating central region with the outer envelope and extracts angular momentum from the central region during gravitational collapse of the cloud core. This process is known as magnetic braking. Both analytical and multidimensional simulations have shown that disk formation is strongly suppressed by magnetic braking in moderately magnetised cloud cores in the ideal magnetohydrodynamic limit. On the other hand, recent observations have provided growing evidence of a relatively large disk several tens of astronomical units in size existing in some Class 0 young stellar objects. This introduces a serious discrepancy between the theoretical study and observations. Various physical mechanisms have been proposed to solve the problem of catastrophic magnetic braking, such as misalignment between the magnetic field and the rotation axis, turbulence, and non-ideal effect. In this paper, we review the mechanism of magnetic braking, its effect on disk formation and early evolution, and the mechanisms that resolve the magnetic braking problem. In particular, we emphasise the importance of non-ideal effects. The combination of magnetic diffusion and thermal evolution during gravitational collapse provides a robust formation process for the circumstellar disk at the very early phase of protostar formation. The rotation induced by the Hall effect can supply a sufficient amount of angular momentum for typical circumstellar disks around T Tauri stars. By examining the combination of the suggested mechanisms, we conclude that the circumstellar disks commonly form in the very early phase of protostar formation.

  6. Modeling collisions in circumstellar debris disks

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika

    2015-10-01

    Observations of resolved debris disks show a spectacular variety of features and asymmetries, including inner cavities and gaps, inclined secondary disks or warps, and eccentric, sharp-edged rings. Embedded exoplanets could create many of these features via gravitational perturbations, which sculpt the disk directly and by generating planetesimal collisions. In this thesis, I present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. I show that SMACK is stable to numerical viscosity and numerical heating over 107 yr, and that it can reproduce analytic models of disk evolution. As an example of the algorithm's capabilities, I use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit and demonstrate that differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring. To demonstrate SMACK's utility in studying debris disk physics, I apply SMACK to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (alpha = 2/7). I find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index alpha of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by alpha = 0.32(t/ tcoll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion

  7. The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. I. Photos of ghosts

    NASA Astrophysics Data System (ADS)

    Bellazzini, M.; Beccari, G.; Battaglia, G.; Martin, N.; Testa, V.; Ibata, R.; Correnti, M.; Cusano, F.; Sani, E.

    2015-03-01

    We present an imaging survey that searches for the stellar counterparts of recently discovered ultra-compact high-velocity H i clouds (UCHVC). It has been proposed that these clouds are candidate mini-haloes in the Local Group and its surroundings within a distance range of 0.25-2.0 Mpc. Using the Large Binocular Telescope we obtained wide-field (≃ 23' × 23') g- and r-band images of the twenty-five most promising and most compact clouds amongst the fifty-nine that have been identified. Careful visual inspection of all the images does not reveal any stellar counterpart that even slightly resembles Leo P, the only local dwarf galaxy that was found as a counterpart to a previously detected high-velocity cloud. Only a possible distant (D> 3.0 Mpc) counterpart to HVC274.68+74.70-123 has been identified in our images. The point source photometry in the central 17.3' × 7.7' chips reaches r ≤ 26.5 and is expected to contain most of the stellar counterparts to the UCHVCs. However, no obvious stellar over-density is detected in any of our fields, in marked contrast to our comparison Leo P field, in which the dwarf galaxy is detected at a >30σ-significance level. Only HVC352.45+59.06+263 may be associated with a weak over-density, whose nature cannot be ascertained with our data. Sensitivity tests show that our survey would have detected any dwarf galaxy dominated by an old stellar population, with an integrated absolute magnitude of MV ≤ - 8.0 and a half-light radius of rh ≤ 300 pc that lies within 1.5 Mpc of us, thereby confirming that it is unlikely that the observed UCHVCs are associated with the stellar counterparts typical of known Local Group dwarf galaxies. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration amongst institutions in the United States, Italy, and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica

  8. A dynamic study of fragmentation and energy loss during high velocity impact

    NASA Technical Reports Server (NTRS)

    Zee, Ralph H.

    1992-01-01

    Research conducted under this contract can be divided into two main areas: hypervelocity (in the range up to 7 km/s) and high velocity (less than 1 km/s). Work in the former was performed at NASA-MSFC using the Light Gas Gun Facility. The lower velocity studies were conducted at Auburn University using the ballistic gun. The emphasis of the project was on the hypervelocity phenomenon especially in the characterization of the debris cloud formed by the primary impact events. Special devices were made to determine the angular distributions of momentum and energy of the debris cloud as a function of impact conditions. After several iteration processes, it was decided to concentrate on the momentum effort. Prototype devices were designed, fabricated, and tested. These devices were based on the conservation of momentum. Distributions of the debris cloud formed were measured by determining the amount of momentum transferred from the debris cloud to strategically placed pendulum measurement devices. The motion of the pendula was monitored using itegrated opto-interrupters. The distribution of momentum in the debris cloud was found to be a strong function of the impact condition. Small projectiles at high velocities were observed to produce finely dispersed debris whereas large projectiles generated discrete particles in the debris. Results also show that the momentum in the forward direction was enhanced due to the impact. This phenomenon of momentum multiplication was also observed in other studies and in computer simulations. It was initially planned to determine the energy distribution using deformation energy in a rod with strain gauges. Results from preliminary studies show that this technique is acceptable but too tedious. A new technique was explored based on measuring the heating effect of the debris cloud using an IR camera. The feasibility and sensitivity was established at Auburn University. This type of energy distribution measurement method can easily be

  9. Formation and transformation of amino acids and amino acid precursors by high-velocity impacts

    NASA Astrophysics Data System (ADS)

    Kaneko, T.; Kobayashi, K.; Yamori, A.

    A wide variety of organic compounds have been found in extraterrestrial bodies such as comets and carbonaceous chondrites. It is plausible that these extraterrestrial bodies carried organic compounds such as amino acids or their precursors to the early Earth. It is claimed, however, that these extraterrestrial organics were destroyed during impacts to the Earth. We therefore examined possible transformation of amino acids and their precursors during high-velocity impacts by using a rail gun "HYPAC" in ISAS. Starting materials used in the impact experiments were (i) aqueous solution of glycine (10 mM or 1.0 M), and (ii) a mixture of ammonia, methanol and water. The target materials were sealed in stainless steel capsules, and shocked by impact with a polycarbonate projectile accelerated with "HYPAC" to the velocities of 2.5 - 7.0 km/s. A part of the products was acid-hydrolyzed. Both hydrolyzed an unhydrolyzed products were analyzed by mass spectrometry, high performance liquid chromatography and capillary electrophoresis and chromatography. When an aqueous solution containing ammonia, methanol and water was shocked by impact at the velocity of 6.4 km/s, a number of amino acids (e.g., serine and glycine) were detected after hydrolysis. The present results suggest that amino acid precursors could be formed during cometary impacts. When glycine solution was used as a starting material, about 40 % of glycine was recovered even after 6 km/s impact. Methylamine and ammonia, which are known as pyrolytic products of glycine, were detected, besides them, diketopiperazine and an unidentified product whose molecular weight was 134, were detected, while no glycine peptides were identified in them. It was shown that the impact processes resulted in the formation of amino acid condensates. Thermal stability of glycine precursor is comparable with glycine. The present results suggest that organic material could survive and/or formed during an impact process. Most of organic

  10. H i and CO in the circumstellar environment of the S-type star RS Cancri

    NASA Astrophysics Data System (ADS)

    Libert, Y.; Winters, J. M.; Le Bertre, T.; Gérard, E.; Matthews, L. D.

    2010-06-01

    Context. The history of mass loss during the AGB phase is key to understanding the stellar evolution and the gas and dust replenishment of the interstellar medium. The mass-loss phenomenon presents fluctuations with a wide variety of timescales and spatial scales and requires combining data from multiple tracers. Aims: We study the respective contributions of the central source and of the external medium to the complex geometry of circumstellar ejecta. Methods: This paper presents Plateau de Bure Interferometer and IRAM 30-m telescope CO rotational line observations, along with H i data obtained with the Nançay Radio Telescope for the oxygen-rich semi-regular variable RS Cnc, in order to probe its circumstellar environment on different scales. Results: We detect both the CO(1-0) and the CO(2-1) rotational lines from RS Cnc. The line profiles are composite, comprising two components of half-width ~2 km s-1 and ~8 km s-1, respectively. Whereas the narrow velocity component seems to originate in an equatorial disk in the central part of the CO envelope, the broad component reveals a bipolar structure, with a north-south velocity gradient. In addition, we obtain new H i data on the source and around it in a field of almost 1 square degree. The H i line is centered on vLSR = 7 km s-1 in agreement with CO observations. A new reduction process reveals a complex extended structure in the northwest direction, of estimated size ~18', with a position angle (~310°) opposite the direction of the stellar proper motion (~140°). We derive an H i mass of ~3 × 10-2 M_⊙ for this structure. Based on a non spherical simulation, we find that this structure is consistent with arising from the interaction of the star undergoing mass loss at an average rate of ~10-7 M⊙ yr-1 over ~2-3 × 105 years with the interstellar medium. Conclusions: Using CO and H i lines, we show that the circumstellar environment around RS Cnc includes two related but well separated regions. With CO, we

  11. NFC - Narrow Field Camera

    NASA Astrophysics Data System (ADS)

    Koukal, J.; Srba, J.; Gorková, S.

    2015-01-01

    We have been introducing a low-cost CCTV video system for faint meteor monitoring and here we describe the first results from 5 months of two-station operations. Our system called NFC (Narrow Field Camera) with a meteor limiting magnitude around +6.5mag allows research on trajectories of less massive meteoroids within individual parent meteor showers and the sporadic background. At present 4 stations (2 pairs with coordinated fields of view) of NFC system are operated in the frame of CEMeNt (Central European Meteor Network). The heart of each NFC station is a sensitive CCTV camera Watec 902 H2 and a fast cinematographic lens Meopta Meostigmat 1/50 - 52.5 mm (50 mm focal length and fixed aperture f/1.0). In this paper we present the first results based on 1595 individual meteors, 368 of which were recorded from two stations simultaneously. This data set allows the first empirical verification of theoretical assumptions for NFC system capabilities (stellar and meteor magnitude limit, meteor apparent brightness distribution and accuracy of single station measurements) and the first low mass meteoroid trajectory calculations. Our experimental data clearly showed the capabilities of the proposed system for low mass meteor registration and for calculations based on NFC data to lead to a significant refinement in the orbital elements for low mass meteoroids.

  12. POLARIMETRY WITH THE GEMINI PLANET IMAGER: METHODS, PERFORMANCE AT FIRST LIGHT, AND THE CIRCUMSTELLAR RING AROUND HR 4796A

    SciTech Connect

    Perrin, Marshall D.; Duchene, Gaspard; Graham, James R.; Kalas, Paul G.; Millar-Blanchaer, Max; Fitzgerald, Michael P.; Chilcote, Jeffrey; Wiktorowicz, Sloane J.; Dillon, Daren; Gavel, Donald; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; De Rosa, Robert J.; Doyon, René; Dunn, Jennifer; Erikson, Darren; and others

    2015-02-01

    We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side ≳ 9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.

  13. Polarimetry with the Gemini Planet Imager. Methods, performance at first light, and the circumstellar ring around HR 4796A

    SciTech Connect

    Perrin, Marshall D.; Duchene, Gaspard; Millar-Blanchaer, Max; Fitzgerald, Michael P.; Graham, James R.; Wiktorowicz, Sloane J.; Kalas, Paul G.; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Chilcote, Jeffrey; De Rosa, Robert J.; Dillon, Daren; Doyon, René; Dunn, Jennifer; Erikson, Darren; Gavel, Donald; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; Ingraham, Patrick; Kerley, Daniel; Konapacky, Quinn; Larkin, James E.; Maire, Jérôme; Marchis, Franck; Marois, Christian; Mittal, Tushar; Morzinski, Katie M.; Oppenheimer, B. R.; Palmer, David W.; Patience, Jennifer; Poyneer, Lisa; Pueyo, Laurent; Rantakyrö, Fredrik T.; Sadakuni, Naru; Saddlemyer, Leslie; Savransky, Dmitry; Soummer, Rémi; Sivaramakrishnan, Anand; Song, Inseok; Thomas, Sandrine; Wallace, J. Kent; Wang, Jason J.; Wolff, Schuyler G.

    2015-01-28

    We report he first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI’s advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side ≳9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. In conclusion, these findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn’s F ring.

  14. Polarimetry with the Gemini Planet Imager: methods, performance at first light, and the circumstellar ring around HR 4796A

    SciTech Connect

    Perrin, Marshall D.; Duchene, Gaspard; Millar-Blanchaer, Max; Fitzgerald, Michael P.; Graham, James R.; Wiktorowicz, Sloane J.; Kalas, Paul G.; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Chilcote, Jeffrey; De Rosa, Robert J.; Dillon, Daren; Doyon, René; Dunn, Jennifer; Erikson, Darren; Gavel, Donald; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; Ingraham, Patrick; Kerley, Daniel; Konapacky, Quinn; Larkin, James E.; Maire, Jérôme; Marchis, Franck; Marois, Christian; Mittal, Tushar; Morzinski, Katie M.; Oppenheimer, B. R.; Palmer, David W.; Patience, Jennifer; Poyneer, Lisa; Pueyo, Laurent; Rantakyrö, Fredrik T.; Sadakuni, Naru; Saddlemyer, Leslie; Savransky, Dmitry; Soummer, Rémi; Sivaramakrishnan, Anand; Song, Inseok; Thomas, Sandrine; Wallace, J. Kent; Wang, Jason J.; Wolff, Schuyler G.

    2015-01-28

    We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point spread function subtraction via di erential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side ≳ 9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.

  15. Polarimetry with the Gemini Planet Imager: Methods, Performance at First Light, and the Circumstellar Ring around HR 4796A

    NASA Astrophysics Data System (ADS)

    Perrin, Marshall D.; Duchene, Gaspard; Millar-Blanchaer, Max; Fitzgerald, Michael P.; Graham, James R.; Wiktorowicz, Sloane J.; Kalas, Paul G.; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; Chilcote, Jeffrey; De Rosa, Robert J.; Dillon, Daren; Doyon, René; Dunn, Jennifer; Erikson, Darren; Gavel, Donald; Goodsell, Stephen; Hartung, Markus; Hibon, Pascale; Ingraham, Patrick; Kerley, Daniel; Konapacky, Quinn; Larkin, James E.; Maire, Jérôme; Marchis, Franck; Marois, Christian; Mittal, Tushar; Morzinski, Katie M.; Oppenheimer, B. R.; Palmer, David W.; Patience, Jennifer; Poyneer, Lisa; Pueyo, Laurent; Rantakyrö, Fredrik T.; Sadakuni, Naru; Saddlemyer, Leslie; Savransky, Dmitry; Soummer, Rémi; Sivaramakrishnan, Anand; Song, Inseok; Thomas, Sandrine; Wallace, J. Kent; Wang, Jason J.; Wolff, Schuyler G.

    2015-02-01

    We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side >~ 9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.

  16. In vitro performance of ceramic coatings obtained by high velocity oxy-fuel spray.

    PubMed

    Melero, H; Garcia-Giralt, N; Fernández, J; Díez-Pérez, A; Guilemany, J M

    2014-01-01

    Hydroxyapatite coatings obtained by plasma-spraying have been used for many years to improve biological performance of bone implants, but several studies have drawn attention to the problems arising from high temperatures and the lack of mechanical properties. In this study, plasma-spraying is substituted by high velocity oxy-fuel (HVOF) spray, with lower temperatures reached, and TiO2 is added in low amounts to hydroxyapatite in order to improve the mechanical properties. Four conditions have been tested to evaluate which are those with better biological properties. Viability and proliferation tests, as well as differentiation assays and morphology observation, are performed with human osteoblast cultures onto the studied coatings. The hydroxyapatite-TiO2 coatings maintain good cell viability and proliferation, especially the cases with higher amorphous phase amount and specific surface, and promote excellent differentiation, with a higher ALP amount for these cases than for polystyrene controls. Observation by SEM corroborates this excellent behaviour. In conclusion, these coatings are a good alternative to those used industrially, and an interesting issue would be improving biological behaviour of the worst cases, which in turn show the better mechanical properties.

  17. Numerical Analysis of Multicomponent Suspension Droplets in High-Velocity Flame Spray Process

    NASA Astrophysics Data System (ADS)

    Gozali, Ebrahim; Mahrukh, Mahrukh; Gu, Sai; Kamnis, Spyros

    2014-08-01

    The liquid feedstock or suspension as a different mixture of liquid fuel ethanol and water is numerically studied in high-velocity suspension flame spray (HVSFS) process, and the results are compared for homogenous liquid feedstock of ethanol and water. The effects of mixture on droplet aerodynamic breakup, evaporation, combustion, and gas dynamics of HVSFS process are thoroughly investigated. The exact location where the particle heating is initiated (above the carrier liquid boiling point) can be controlled by increasing the water content in the mixture. In this way, the particle inflight time in the high-temperature gas regions can be adjusted avoiding adverse effects from surface chemical transformations. The mixture is modeled as a multicomponent droplet, and a convection/diffusion model, which takes into account the convective flow of evaporating material from droplet surface, is used to simulate the suspension evaporation. The model consists of several sub-models that include premixed combustion of propane-oxygen, non-premixed ethanol-oxygen combustion, modeling of multicomponent droplet breakup and evaporation, as well as heat and mass transfer between liquid droplets and gas phase.

  18. Surface-to-borehole illumination of a high-velocity layer using marine VSP

    SciTech Connect

    MacBeth, C.; Liu, E.; Boyd, M.; Sweeney, K.

    1994-12-31

    Two marine walkaway VSP lines are recorded by three-component receivers positioned in a dolomite layer. The layer has a high seismic velocity relative to the surrounding rocks and may be fracture. The recorded wavefield is analyzed to determine whether this acquisition is suitable to image details of the internal structure of the layer. The principal arrivals in the wavefield are a dominant horizontally refracted compressional wave with a smooth unbroken moveout, converted shear-waves from shallow reflectors, and reverberation of these converted shear-waves within the high velocity layer. Anisotropic analyses of the converted shear-waves estimate an overburden birefringence of 3% and a polarization direction consistent with the known NW-SE maximum compressive stress. Full-wave modeling of the recorded wavefield aids identification of the various arrivals and constrains the attenuation and anisotropic properties of the layer, which appears laterally uniform with the most satisfactory model possessing low attenuation but a birefringence of no more than 5%. If the layer is cracked, these results are diagnostic of evenly distributed cracks with a scalelength smaller than a fraction of a wavelength.

  19. Removal of interproximal dental biofilms by high-velocity water microdrops.

    PubMed

    Rmaile, A; Carugo, D; Capretto, L; Aspiras, M; De Jager, M; Ward, M; Stoodley, P

    2014-01-01

    The influence of the impact of a high-velocity water microdrop on the detachment of Streptococcus mutans UA159 biofilms from the interproximal (IP) space of teeth in a training typodont was studied experimentally and computationally. Twelve-day-old S. mutans biofilms in the IP space were exposed to a prototype AirFloss delivering 115 µL water at a maximum exit velocity of 60 m/sec in a 30-msec burst. Using confocal microscopy and image analysis, we obtained quantitative measurements of the percentage removal of biofilms from different locations in the IP space. The 3D geometry of the typodont and the IP spaces was obtained by micro-computed tomography (µ-CT) imaging. We performed computational fluid dynamics (CFD) simulations to calculate the wall shear stress (τw ) distribution caused by the drops on the tooth surface. A qualitative agreement and a quantitative relationship between experiments and simulations were achieved. The wall shear stress (τw ) generated by the prototype AirFloss and its spatial distribution on the teeth surface played a key role in dictating the efficacy of biofilm removal in the IP space.

  20. Direct collapse black hole formation via high-velocity collisions of protogalaxies

    NASA Astrophysics Data System (ADS)

    Inayoshi, Kohei; Visbal, Eli; Kashiyama, Kazumi

    2015-10-01

    We propose high-velocity collisions of protogalaxies as a new pathway to form supermassive stars (SMSs) with masses of ˜105 M⊙ at high redshift (z > 10). When protogalaxies hosted by dark matter haloes with a virial temperature of ˜ 104 K collide with a relative velocity ≳ 200 km s-1, the gas is shock-heated to ˜106 K and subsequently cools isobarically via free-free emission and He+, He, and H line emission. Since the gas density ( ≳ 104 cm- 3) is high enough to destroy H2 molecules by collisional dissociation, the shocked gas never cools below ˜104 K. Once a gas cloud of ˜105 M⊙ reaches this temperature, it becomes gravitationally unstable and forms an SMS which will rapidly collapse into a supermassive black hole via general relativistic instability. We perform a simple analytic estimate of the number density of direct-collapse black holes (DCBHs) formed through this scenario (calibrated with cosmological N-body simulations) and find nDCBH ˜ 10- 9 Mpc- 3 (comoving) by z = 10. This could potentially explain the abundance of bright high-z quasars.

  1. Experimental and analytical study of high velocity impact on Kevlar/Epoxy composite plates

    NASA Astrophysics Data System (ADS)

    Sikarwar, Rahul; Velmurugan, Raman; Madhu, Velmuri

    2012-12-01

    In the present study, impact behavior of Kevlar/Epoxy composite plates has been carried out experimentally by considering different thicknesses and lay-up sequences and compared with analytical results. The effect of thickness, lay-up sequence on energy absorbing capacity has been studied for high velocity impact. Four lay-up sequences and four thickness values have been considered. Initial velocities and residual velocities are measured experimentally to calculate the energy absorbing capacity of laminates. Residual velocity of projectile and energy absorbed by laminates are calculated analytically. The results obtained from analytical study are found to be in good agreement with experimental results. It is observed from the study that 0/90 lay-up sequence is most effective for impact resistance. Delamination area is maximum on the back side of the plate for all thickness values and lay-up sequences. The delamination area on the back is maximum for 0/90/45/-45 laminates compared to other lay-up sequences.

  2. Analysis of a High Velocity Oxygen-Fuel (HVOF) thermal spray torch. Part 2, Computational results

    SciTech Connect

    Oberkampf, W.L.; Talpallikar, M.

    1993-12-31

    The fluid dynamics inside and outside a High Velocity Oxygen-Fuel (HVOF) torch are analyzed using computational fluid dynamic (CFD) techniques. The thermal spray device analyzed is similar to a Metco Diamond Jet torch with powder injection. The spray nozzle is axisymmetric with powder injected on the centerline, premixed fuel and oxygen fed from an annulus, and air cooling injected along the interior surface of the aircap choked flow conditions occur at the exit of the aircap and a supersonic, under-expanded jet develops externally. The details of the CFD simulation are given in a companion paper. This paper describes the general gas dynamic features of HVOF spraying and then gives a detailed discussion of the computational predictions of the present analysis. The gas velocity, temperature, pressure and Mach number distributions are presented for various locations inside and outside the torch. Characteristics of the metal spray particle velocity, temperature, Mach number, trajectory, and phase state (solid or liquid) are also presented and discussed. Extensive numerical flow visualization is provided to show flow features such as mixing layers, shock waves, and expansion waves.

  3. Searching for dark matter annihilation in the Smith high-velocity cloud

    SciTech Connect

    Drlica-Wagner, Alex; Gómez-Vargas, Germán A.; Hewitt, John W.; Linden, Tim; Tibaldo, Luigi

    2014-07-20

    Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use γ-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant γ-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (∼ 3 × 10{sup –26} cm{sup 3} s{sup –1}) for dark matter masses ≲ 30 GeV annihilating via the b b-bar or τ{sup +}τ{sup –} channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

  4. A High-velocity Cloud Impact Forming a Supershell in the Milky Way

    NASA Astrophysics Data System (ADS)

    Park, Geumsook; Koo, Bon-Chul; Kang, Ji-hyun; Gibson, Steven J.; Peek, J. E. G.; Douglas, Kevin A.; Korpela, Eric J.; Heiles, Carl E.

    2016-08-01

    Neutral atomic hydrogen (H i) gas in interstellar space is largely organized into filaments, loops, and shells, the most prominent of which are “supershells.” These gigantic structures, which require ≳ 3× {10}52 erg to form, are generally thought to be produced by either the explosion of multiple supernovae (SNe) in OB associations or, alternatively, by the impact of high-velocity clouds (HVCs) falling into the Galactic disk. Here, we report the detection of a kiloparsec (kpc)-size supershell in the outskirts of the Milky Way with the compact HVC 040 + 01-282 (hereafter, CHVC040) at its geometrical center using the “Inner-Galaxy Arecibo L-band Feed Array” H i 21 cm survey data. The morphological and physical properties of both objects suggest that CHVC040, which is either a fragment of a nearby disrupted galaxy or a cloud that originated from an intergalactic accreting flow, collided with the disk ˜5 Myr ago to form the supershell. Our results show that some compact HVCs can survive their trip through the Galactic halo and inject energy and momentum into the Milky Way disk.

  5. Energy evaluation of the High Velocity Algae Raceway Integrated Design (ARID-HV)

    NASA Astrophysics Data System (ADS)

    Attalah, Said

    The original ARID (Algae Raceway Integrated Design) raceway was an effective method to increase temperature toward the optimal growth range. However, the energy input was high and flow mixing was poor. Thus, the ARID-HV (High Velocity Algae Raceway Integrated Design) raceway was developed to reduce energy input requirements and improve flow mixing. This was accomplished by improving pumping efficiency and using a serpentine flow pattern in which the water flows through channels instead of over barriers. A prototype ARID-HV system was installed in Tucson, Arizona, and the constructability, reliability of components, drainage of channels, and flow and energy requirements of the ARID-HV raceway were evaluated. Each of the electrical energy inputs to the raceway (air sparger, air tube blower, canal lift pump, and channel recirculation pump) was quantified, some by direct measurement and others by simulation. An algae growth model was used to determine the algae production rate vs. flow depth and time of year. Then the electrical energy requirement of the most effective flow depth was calculated. Channel hydraulics was evaluated with Manning's equation and the corner head loss equation. In this way, the maximum length of channels for several raceway slopes and mixing velocities were determined. Algae production in the ARID-HV raceway was simulated with a temperature and light growth model. An energy efficient design for the ARID-HV raceway was developed.

  6. Experimental Characterization of Magnetogasdynamic Phenomena in Ultra-High Velocity Pulsed Plasma Jets

    NASA Astrophysics Data System (ADS)

    Loebner, Keith; Wang, Benjamin; Cappelli, Mark

    2014-10-01

    The formation and propagation of high velocity plasma jets in a pulsed, coaxial, deflagration-type discharge is examined experimentally. A sensitive, miniaturized, immersed probe array is used to map out magnetic flux density and associated radial current density as a function of time and axial position. This array is also used to probe the magnetic field gradient across the exit of the accelerator and in the jet formation region. Sensitive interferometry via a continuous-wave helium-neon laser source is used to probe the structure of the plasma jet over multiple chords and axial locations. A two dimensional plasma density gradient profile at an instant in time during jet formation is compiled via Shack-Hartmann wavefront sensor analysis. The qualitative characteristics of rarefaction and/or shock wave formation as a function of chamber back-pressure is examined via fast-framing ICCD imaging. These measurements are compared to existing resistive MHD simulations of the coaxial deflagration accelerator and the ensuing rarefaction jet that is expelled from the electrode assembly. The physical mechanisms governing the behavior of the discharge and the formation of these high energy density plasma jets are proposed and validated against both theoretical models and numerically simulated behavior. This research was conducted with Government support under and awarded by DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a.

  7. Suspension High Velocity Oxy-Fuel (SHVOF)-Sprayed Alumina Coatings: Microstructure, Nanoindentation and Wear

    NASA Astrophysics Data System (ADS)

    Murray, J. W.; Ang, A. S. M.; Pala, Z.; Shaw, E. C.; Hussain, T.

    2016-10-01

    Suspension high velocity oxy-fuel spraying can be used to produce thermally sprayed coatings from powdered feedstocks too small to be processed by mechanical feeders, allowing formation of nanostructured coatings with improved density and mechanical properties. Here, alumina coatings were produced from submicron-sized feedstock in aqueous suspension, using two flame combustion parameters yielding contrasting microstructures. Both coatings were tested in dry sliding wear conditions with an alumina counterbody. The coating processed with high combustion power of 101 kW contained 74 wt.% amorphous phase and 26 wt.% crystalline phase (95 wt.% gamma and 3 wt.% alpha alumina), while the 72-kW coating contained lower 58 wt.% amorphous phase and 42 wt.% crystalline phases (73 wt.% was alpha and 26 wt.% gamma). The 101-kW coating had a dry sliding specific wear rate between 4 and 4.5 × 10-5 mm3/Nm, 2 orders of magnitude higher than the 72-kW coating wear rate of 2-4.2 × 10-7 mm3/Nm. A severe wear regime dominated by brittle fracture and grain pullout of the coating was responsible for the wear of the 101-kW coating, explained by mean fracture toughness three times lower than the 72-kW coating, owing to the almost complete absence of alpha alumina.

  8. Removal of Interproximal Dental Biofilms by High-velocity Water Microdrops

    PubMed Central

    Rmaile, A.; Carugo, D.; Capretto, L.; Aspiras, M.; De Jager, M.; Ward, M.; Stoodley, P.

    2014-01-01

    The influence of the impact of a high-velocity water microdrop on the detachment of Streptococcus mutans UA159 biofilms from the interproximal (IP) space of teeth in a training typodont was studied experimentally and computationally. Twelve-day-old S. mutans biofilms in the IP space were exposed to a prototype AirFloss delivering 115 µL water at a maximum exit velocity of 60 m/sec in a 30-msec burst. Using confocal microscopy and image analysis, we obtained quantitative measurements of the percentage removal of biofilms from different locations in the IP space. The 3D geometry of the typodont and the IP spaces was obtained by micro-computed tomography (µ-CT) imaging. We performed computational fluid dynamics (CFD) simulations to calculate the wall shear stress (τw) distribution caused by the drops on the tooth surface. A qualitative agreement and a quantitative relationship between experiments and simulations were achieved. The wall shear stress (τw) generated by the prototype AirFloss and its spatial distribution on the teeth surface played a key role in dictating the efficacy of biofilm removal in the IP space. PMID:24170371

  9. Cryogenic spray vaporization in high-velocity helium, argon and nitrogen gasflows

    NASA Technical Reports Server (NTRS)

    Ingebo, Robert D.

    1993-01-01

    Effects of gas properties on cryogenic liquid-jet atomization in high-velocity helium, nitrogen, and argon gas flows were investigated. Volume median diameter, D(sub v.5e), data were obtained with a scattered-light scanning instrument. By calculating the change in spray drop size, -Delta D(sub v.5)(exp 2), due to droplet vaporization, it was possible to calculate D(sub v.5C). D(sub v.5C) is the unvaporized characteristic drop size formed at the fuel-nozzle orifice. This drop size was normalized with respect to liquid-jet diameter, D(sub O). It was then correlated with several dimensionless groups to give an expression for the volume median diameter of cryogenic LN2 sprays. This expression correlates drop size D(sub v.5c) with aerodynamic and liquid-surface forces so that it can be readily determined in the design of multiphase-flow propellant injectors for rocket combustors.

  10. Analysis of a High Velocity Oxygen-Fuel (HVOF) thermal spray torch. Part 1, Numerical formulation

    SciTech Connect

    Oberkampf, W.L.; Talpallikar, M.

    1994-01-01

    The fluid and particle dynamics of a High Velocity Oxygen-Fuel (HVOF) torch are analyzed using computational fluid dynamic (CFD) techniques. The thermal spray device analyzed is similar to a Metco Diamond Jet torch with powder injection. The spray nozzle is axisymmetric with powder injection on the centerline, premixed fuel and oxygen fed from an annulus, and air cooling injected along the interior surface of the aircap. Choked flow conditions occur at the exit of the aircap and a supersonic, under-expanded jet develops externally. The CFD simulation assumes three injection streams (solid metal particles with argon as a carrier gas, premixed oxygen/fuel, and air) inside the aircap and solves the combusting two-phase flow until the external spray stream decays to sonic conditions. The numerical formulation solves the mass, momentum, and energy transfer for both the gas and particle phase and strongly couples each phase. The combustion process is modeled using approximate equilibrium chemistry with dissociation of the gas with a total of nine species. Melting and re-solidification of the metal panicles is modeled as a lumped-mass system. Turbulent flow is modeled by a two equation k-{epsilon} turbulence model, including compressibility effects on turbulent dissipation. A time iterative, implicit, finite volume numerical method is used to solve the partial differential equations. A companion paper [10] presents the results of the numerical simulation and gives a detailed discussion of the gas and panicle dynamics.

  11. Computational fluid dynamic analysis of a High-Velocity Oxygen-Fuel (HVOF) thermal spray torch

    SciTech Connect

    Hassan, B.; Oberkampf, W.L.; Neiser, R.A.; Roemer, T.J.

    1995-09-01

    The gas dynamics of a High-Velocity Oxygen-Fuel (HVOF) torch are analyzed using computational fluid dynamics (CFD) techniques. The thermal spray device analyzed is similar to a Metco Diamond Jet torch with powder feed. The injection nozzle is assumed to be axisymmetric with premixed fuel and oxygen fed from an annulus, and air cooling injected along the interior surface of the aircap. The aircap, a cronically converging nozzle, achieves choked flow conditions at the exit and a supersonic, under-expanded jet develops externally. Finite difference equations for mass, momentum, and energy conservation are solved for the gas dynamics. The combustion process is modeled using a single-step and a 12-step quasi-global finite-rate chemistry model with dissociation of the gas and a total of nine species. Turbulent flow inside the aircap and in the free-jet decay is modeled using a two-equation k-{epsilon} model. An iterative, implicit, finite volume numerical method is used to solve the gas dynamic equations inside and outside the torch . The CFD results are compared with recent experimental measurements of pressure inside the HVOF aircap. Comparisons are made for two flow rates of premixed fuel and oxygen and air cooling. This paper presents the first published comparisons of CFD predictions and experimental measurements for HVOF tbermal spraying.

  12. Cryogenic spray vaporization in high-velocity helium, argon and nitrogen gasflows

    NASA Astrophysics Data System (ADS)

    Ingebo, Robert D.

    1993-10-01

    Effects of gas properties on cryogenic liquid-jet atomization in high-velocity helium, nitrogen, and argon gas flows were investigated. Volume median diameter, D(sub v.5e), data were obtained with a scattered-light scanning instrument. By calculating the change in spray drop size, -Delta D(sub v.5)(exp 2), due to droplet vaporization, it was possible to calculate D(sub v.5C). D(sub v.5C) is the unvaporized characteristic drop size formed at the fuel-nozzle orifice. This drop size was normalized with respect to liquid-jet diameter, D(sub O). It was then correlated with several dimensionless groups to give an expression for the volume median diameter of cryogenic LN2 sprays. This expression correlates drop size D(sub v.5c) with aerodynamic and liquid-surface forces so that it can be readily determined in the design of multiphase-flow propellant injectors for rocket combustors.

  13. HIGH-VELOCITY CLOUDS IN THE GALACTIC ALL SKY SURVEY. I. CATALOG

    SciTech Connect

    Moss, V. A.; Kummerfeld, J. K.; McClure-Griffiths, N. M.; Murphy, T.; Pisano, D. J.; Curran, J. R.

    2013-11-01

    We present a catalog of high-velocity clouds (HVCs) from the Galactic All Sky Survey (GASS) of southern sky neutral hydrogen, which has 57 mK sensitivity and 1 km s{sup –1} velocity resolution and was obtained with the Parkes Telescope. Our catalog has been derived from the stray-radiation-corrected second release of GASS. We describe the data and our method of identifying HVCs and analyze the overall properties of the GASS population. We catalog a total of 1693 HVCs at declinations <0°, including 1111 positive velocity HVCs and 582 negative velocity HVCs. Our catalog also includes 295 anomalous velocity clouds (AVCs). The cloud line-widths of our HVC population have a median FWHM of ∼19 km s{sup –1}, which is lower than that found in previous surveys. The completeness of our catalog is above 95% based on comparison with the HIPASS catalog of HVCs upon which we improve by an order of magnitude in spectral resolution. We find 758 new HVCs and AVCs with no HIPASS counterpart. The GASS catalog will shed unprecedented light on the distribution and kinematic structure of southern sky HVCs, as well as delve further into the cloud populations that make up the anomalous velocity gas of the Milky Way.

  14. Effect of Operating Parameters on a Dual-Stage High Velocity Oxygen Fuel Thermal Spray System

    NASA Astrophysics Data System (ADS)

    Khan, Mohammed N.; Shamim, Tariq

    2014-08-01

    High velocity oxygen fuel (HVOF) thermal spray systems are being used to apply coatings to prevent surface degradation. The coatings of temperature sensitive materials such as titanium and copper, which have very low melting points, cannot be applied using a single-stage HVOF system. Therefore, a dual-stage HVOF system has been introduced and modeled computationally. The dual-spray system provides an easy control of particle oxidation by introducing a mixing chamber. In addition to the materials being sprayed, the thermal spray coating quality depends to a large extent on flow behavior of reacting gases and the particle dynamics. The present study investigates the influence of various operating parameters on the performance of a dual-stage thermal spray gun. The objective is to develop a predictive understanding of various parameters. The gas flow field and the free jet are modeled by considering the conservation of mass, momentum, and energy with the turbulence and the equilibrium combustion sub models. The particle phase is decoupled from the gas phase due to very low particle volume fractions. The results demonstrate the advantage of a dual-stage system over a single-stage system especially for the deposition of temperature sensitive materials.

  15. The collision of high-velocity clouds with a galactic disk

    NASA Technical Reports Server (NTRS)

    Tenorio-Tagle, G.; Bodenheimer, P.; Rozyczka, M.; Franco, J.

    1986-01-01

    Two-dimensional hydrodynamic simulations for the interaction of high-velocity clouds with a galactic disk are presented. The impinging clouds are assumed to be spherical and the target disk is represented by a constant density slab, n(g) = 1/cu cm, with a total width W(g) = 200 pc. The numerical experiments cover a wide range of cloud densities, between 0.1 and 100/cu cm, and velocities between 100 and 300 km/s. At a time approximately 10 to the 7th yr after impact, two types of final configurations are found. In the first case, the infalling cloud is completely shocked in a time short compared with the crossing time of the disk. Then, the generated cavity has time to grow sideways and large scale structures with a round shape, and in some cases nearly spherical, are produced. In the second case, which occurs for high density clouds, the cloud is shocked on a time scale longer than or comparable to the crossing time. The resultant cylindrical holes drilled across the entire disk have the dimensions of the impinging cloud. Cloud-galaxy interactions are compared with other energy sources and the morphologies of the resultant structures are suggested to resemble the large scale structures observed in H I.

  16. Estimation of Fuel Rate on the Galactic Disk from High Velocity Clouds (HVCs) Infall

    NASA Astrophysics Data System (ADS)

    Sung, Kwang Hyun; Kwak, Kyujin

    2016-06-01

    Continuous accretion of metal-poor gas can explain the discrepancy between the number of observed G-Dwarfs and the number predicted by the “simple model” of galactic evolution. The maximum accretion rate estimated based upon approaching high velocity clouds (HVCs) can be up to ~0.4 M⊙yr-1 which is comparable with the accretion rate required by many chemical evolution models that is at least ~0.45 M⊙yr-1. However, it is not clear to what extent the exchange of gas between the disk and the cloud can occur when a HVC collides with the galactic disk. Therefore, we examined a series of HVC-Disk collision simulations using the FLASH2.5 hydrodynamics simulation code. Our simulation results show that an HVC will more likely take away substances from the galactic disk rather than adding new material to the disk. We define this as a “negative fuel rate” event. Further outcomes in our study present that the fuel rate, which is defined as how much material is transferred to the galactic disk from the colliding HVC, can change depending on the combination among density, radius and velocity of an approaching HVC as well as the modeled galactic disk.

  17. Flow mechanism of Forchheimer's cubic equation in high-velocity radial gas flow through porous media

    SciTech Connect

    Ezeudembah, A.S.; Dranchuk, P.M.

    1982-01-01

    Formal derivation of Forchheimer's cubic equation is made by considering the kinetic energy equation of mean flow and dimensional relations for one-dimensional, linear, incompressible fluid flow. By the addition of the cubic term, this equation is regarded as a modified Forchheimer's quadratic equation which accounts for the flow rates obtained beyond the laminar flow condition. The cubic equation spans a wide range of flow rates and regimes. For suitable use in gas flow studies, this equation has been adapted, modified, and corrected for the gas slippage effect. The physical basis of the cubic term has been established by using boundary layer theory to explain the high-velocity, high-pressure flow behavior through a porous path. Gamma, the main parameter in the cubic term, is related directly to a characteristic, dimensionless shape factor which is significant at higher flow rates. It is inversely related to viscosity, but has no dependence on the gas slippage coefficient in the higher flow regime. 25 references.

  18. A High-velocity Cloud Impact Forming a Supershell in the Milky Way

    NASA Astrophysics Data System (ADS)

    Park, Geumsook; Koo, Bon-Chul; Kang, Ji-hyun; Gibson, Steven J.; Peek, J. E. G.; Douglas, Kevin A.; Korpela, Eric J.; Heiles, Carl E.

    2016-08-01

    Neutral atomic hydrogen (H i) gas in interstellar space is largely organized into filaments, loops, and shells, the most prominent of which are “supershells.” These gigantic structures, which require ≳ 3× {10}52 erg to form, are generally thought to be produced by either the explosion of multiple supernovae (SNe) in OB associations or, alternatively, by the impact of high-velocity clouds (HVCs) falling into the Galactic disk. Here, we report the detection of a kiloparsec (kpc)-size supershell in the outskirts of the Milky Way with the compact HVC 040 + 01‑282 (hereafter, CHVC040) at its geometrical center using the “Inner-Galaxy Arecibo L-band Feed Array” H i 21 cm survey data. The morphological and physical properties of both objects suggest that CHVC040, which is either a fragment of a nearby disrupted galaxy or a cloud that originated from an intergalactic accreting flow, collided with the disk ˜5 Myr ago to form the supershell. Our results show that some compact HVCs can survive their trip through the Galactic halo and inject energy and momentum into the Milky Way disk.

  19. Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

    NASA Technical Reports Server (NTRS)

    Drlica-Wagner, Alex; Gomez-Vargas, German A.; Hewitt, John W.; Linden, Tim; Tibaldo, Luigi

    2014-01-01

    Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (approximately 3 x 10 (sup -26) cubic centimeters per second) for dark matter masses less than or approximately 30 gigaelectronvolts annihilating via the B/B- bar oscillation or tau/antitau channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

  20. Analysis of particle behavior in High-Velocity Oxy-Fuel thermal spraying process

    NASA Astrophysics Data System (ADS)

    Katanoda, Hiroshi; Matsuo, Kazuyasu

    2003-08-01

    This paper analyzes the behavior of coating particle as well as the gas flow both of inside and outside the High-Velocity Oxy-Fuel (HVOF) thermal spraying gun by using quasi-one-dimensional analysis and numerical simulation. The HVOF gun in the present analysis is an axisymmetric convergent-divergent nozzle with the design Mach number of 2.0 followed by a straight passage called barrel. In the present analysis it is assumed that the influence of the particles injected in the gas flow is neglected, and the interaction between the particles is also neglected. The gas flow in the gun is assumed to be quasi-one-dimensional adiabatic flow. The velocity, temperature and density of gas in the jet discharged from the barrel exit are predicted by solving Navier-Stokes equations numerically. The particle equation of motion is numerically integrated using three-step Runge-Kutta method. The drag coefficient of the particle is calculated by linear interpolation of the experimental data obtained in the past. Particle mean temperature is calculated by using Ranz and Marchalls’ correlation for spherical particles. From the present analysis, the distributions of velocity and temperature of the coating particles flying inside and outside the HVOF gun are predicted.

  1. Variability of the high-velocity outflow in the quasar PDS 456

    SciTech Connect

    Reeves, J. N.; Gofford, J.; Costa, M.; Matzeu, G.; Braito, V.; Sim, S. A.; Behar, E.; Kaspi, S.; Miller, L.; O'Brien, P.; Turner, T. J.; Ward, M.

    2014-01-01

    We present a comparison of two Suzaku X-ray observations of the nearby (z = 0.184), luminous (L {sub bol} ∼ 10{sup 47} erg s{sup –1}) type I quasar, PDS 456. A new 125 ks Suzaku observation in 2011 caught the quasar during a period of low X-ray flux and with a hard X-ray spectrum, in contrast with a previous 190 ks Suzaku observation in 2007 when the quasar appeared brighter and had a steep (Γ > 2) X-ray spectrum. The 2011 X-ray spectrum contains a pronounced trough near 9 keV in the quasar rest frame, which can be modeled with blueshifted iron K-shell absorption, most likely from the He- and H-like transitions of iron. The absorption trough is observed at a similar rest-frame energy as in the earlier 2007 observation, which appears to confirm the existence of a persistent high-velocity wind in PDS 456, at an outflow velocity of 0.25-0.30c. The spectral variability between 2007 and 2011 can be accounted for by variations in a partial covering absorber, increasing in covering fraction from the brighter 2007 observation to the hard and faint 2011 observation. Overall, the low-flux 2011 observation can be explained if PDS 456 is observed at relatively low inclination angles through a Compton-thick wind, originating from the accretion disk, which significantly attenuates the X-ray flux from the quasar.

  2. Episodic High-velocity Outflows from V899 Mon: A Constraint On The Outflow Mechanisms

    NASA Astrophysics Data System (ADS)

    Ninan, J. P.; Ojha, D. K.; Philip, N. S.

    2016-07-01

    We report the detection of large variations in the outflow wind velocity from a young eruptive star, V899 Mon, during its ongoing high accretion outburst phase. Such large variations in the outflow velocity (from -722 to -425 km s-1) have never been reported previously in this family of objects. Our continuous monitoring of this source shows that the multi-component, clumpy, and episodic high velocity outflows are stable in the timescale of a few days, and vary over the timescale of a few weeks to months. We detect significant decoupling in the instantaneous outflow strength to accretion rate. From the comparison of various possible outflow mechanisms in magnetospheric accretion of young stellar objects, we conclude magnetically driven polar winds to be the most consistent mechanism for the outflows seen in V899 Mon. The large scale fluctuations in outflow over the short period makes V899 Mon the most ideal source to constrain various magnetohydrodynamics simulations of magnetospheric accretion. Based on observations made with the Southern African Large Telescope (SALT).

  3. Studying counterstreaming high velocity plasma flows relevant to astrophysical collisionless shock

    NASA Astrophysics Data System (ADS)

    Ross, James Steven; Amendt, Peter; Divol, Laurent; Pollock, Brad; Remington, Bruce; Ryutov, Dmitri; rozmus, Wojciech; Turnbull, David; Froula, Dustin; morita, taichi; Sakawa, Youichi; Takabe, Hideke; Drake, R. Paul; Kuranz, Carolyn C.; Gregori, Gianluca; Meinecke, Jena; Koenig, Michel; Spitkovsky, Anatoly; Park, Hye-Sook

    2015-08-01

    In a broad range of low-density astrophysical plasmas the flow has a high Mach number, making the ion-ion collisional mean free path very large compared to the scale lengths of various observed astrophysical shocks. These shocks are believed to be “collisionless,” driven by plasma instabilities and self-generated magnetic fields. A series of experiments at the NIF and Omega laser facilities is underway to study the formation of collisionless shocks under scaled laboratory conditions, using high velocity counterstreaming and interpenetrating plasma flows. Double CH2, and CH/CD planar foils have been irradiated with a laser intensity of ~1016 W/cm2. The laser-ablated plasma between the two foils was characterized using a suite of diagnostics, including Thomson scattering and x-ray radiography. On the Omega laser facility clear interpenetration and instability growth are observed, although our experimental conditions reached only ~50 ion skin depths (c/wpi) and were insufficient to fully form a collisionless shock. Initial NIF experimental results using 50x more laser energy than the Omega experiments will be presented.

  4. The First Distance Constraint on the Renegade High-velocity Cloud Complex WD

    NASA Astrophysics Data System (ADS)

    Peek, J. E. G.; Bordoloi, Rongmon; Sana, Hugues; Roman-Duval, Julia; Tumlinson, Jason; Zheng, Yong

    2016-09-01

    We present medium-resolution, near-ultraviolet Very Large Telescope/FLAMES observations of the star USNO-A0600-15865535. We adapt a standard method of stellar typing to our measurement of the shape of the Balmer ɛ absorption line to demonstrate that USNO-A0600-15865535 is a blue horizontal branch star, residing in the lower stellar halo at a distance of 4.4 kpc from the Sun. We measure the H & K lines of singly ionized calcium and find two isolated velocity components, one originating in the disk, and one associated with the high-velocity cloud complex WD. This detection demonstrated that complex WD is closer than ˜4.4 kpc and is the first distance constraint on the +100 km s-1 Galactic complex of clouds. We find that complex WD is not in corotation with the Galactic disk, which has been assumed for decades. We examine a number of scenarios and find that the most likely scenario is that complex WD was ejected from the solar neighborhood and is only a few kiloparsecs from the Sun.

  5. The First Distance Constraint on the Renegade High-velocity Cloud Complex WD

    NASA Astrophysics Data System (ADS)

    Peek, J. E. G.; Bordoloi, Rongmon; Sana, Hugues; Roman-Duval, Julia; Tumlinson, Jason; Zheng, Yong

    2016-09-01

    We present medium-resolution, near-ultraviolet Very Large Telescope/FLAMES observations of the star USNO-A0600-15865535. We adapt a standard method of stellar typing to our measurement of the shape of the Balmer ɛ absorption line to demonstrate that USNO-A0600-15865535 is a blue horizontal branch star, residing in the lower stellar halo at a distance of 4.4 kpc from the Sun. We measure the H & K lines of singly ionized calcium and find two isolated velocity components, one originating in the disk, and one associated with the high-velocity cloud complex WD. This detection demonstrated that complex WD is closer than ∼4.4 kpc and is the first distance constraint on the +100 km s‑1 Galactic complex of clouds. We find that complex WD is not in corotation with the Galactic disk, which has been assumed for decades. We examine a number of scenarios and find that the most likely scenario is that complex WD was ejected from the solar neighborhood and is only a few kiloparsecs from the Sun.

  6. Stability analysis of confined V-shaped flames in high-velocity streams.

    PubMed

    El-Rabii, Hazem; Joulin, Guy; Kazakov, Kirill A

    2010-06-01

    The problem of linear stability of confined V-shaped flames with arbitrary gas expansion is addressed. Using the on-shell description of flame dynamics, a general equation governing propagation of disturbances of an anchored flame is obtained. This equation is solved analytically for V-flames anchored in high-velocity channel streams. It is demonstrated that dynamics of the flame disturbances in this case is controlled by the memory effects associated with vorticity generated by the perturbed flame. The perturbation growth rate spectrum is determined, and explicit analytical expressions for the eigenfunctions are given. It is found that the piecewise linear V structure is unstable for all values of the gas expansion coefficient. Despite the linearity of the basic pattern, however, evolutions of the V-flame disturbances are completely different from those found for freely propagating planar flames or open anchored flames. The obtained results reveal strong influence of the basic flow and the channel walls on the stability properties of confined V-flames. PMID:20866527

  7. High-Velocity Gas in the SN1991T/3C273 Sightline

    NASA Astrophysics Data System (ADS)

    Meyer, David M.

    Meyer & Roth (1991) have recently obtained high SIN observations of the Ca II absorption toward SN1991T and 3C273 which exhibit weak components at vLSR=-87, +215, and +263 km s^-1 toward SN1991T that are absent in the adjacent (sep.=1.4degrees) 3C273 sightline. In this proposal, we discuss our plans to test the local hypothesis for these high-velocity clouds (HVCs) by observing the interstellar Mg II absorption toward several stars in the SN1991T/3C273 field with IUE. Although the many HVCs observed in H I 21 cm emission have not yet been conclusively detected in metal absorption against any Galactic source (Wakker 1991), our particular search is worthwhile given that: (1) the general issue of HVC distances remains unclear due to metallicity uncertainties and, (2) the SN1991T/3C273 sightline presents a possibly unique case where there is radio continuum evidence of a local disturbance.

  8. H ii REGIONS WITHIN A COMPACT HIGH VELOCITY CLOUD. A NEARLY STARLESS DWARF GALAXY?

    SciTech Connect

    Bellazzini, M.; Magrini, L.; Mucciarelli, A.; Fraternali, F.; Ibata, R.; Martin, N.; Battaglia, G.; Testa, V.; Fumana, M.; Marchetti, A.; Correnti, M.

    2015-02-10

    Within the SECCO survey we identified a candidate stellar counterpart to the Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123 that was suggested by Adams et al. to be a possible mini halo within the Local Group of galaxies. The spectroscopic follow-up of the brightest sources within the candidate reveals the presence of two H ii regions whose radial velocity is compatible with a physical association with the UVHVC. The available data do not allow us to give a definite answer on the nature of the newly identified system. A few alternative hypotheses are discussed. However, the most likely possibility is that we have found a new faint dwarf galaxy residing in the Virgo cluster of galaxies, which we name SECCO 1. Independently of its actual distance, SECCO 1 displays a ratio of neutral hydrogen mass to V luminosity of M{sub H} {sub I}/L{sub V}≳20, by far the largest among local dwarfs. Hence, it appears to be a nearly starless galaxy and it may be an example of the missing links between normal dwarfs and the dark mini halos that are predicted to exist in large numbers according to the currently accepted cosmological model.

  9. Detection Of New High Velocity Clouds Using The Leiden-Argentina-Bonn Hi All-sky Survey

    NASA Astrophysics Data System (ADS)

    Engel, Tyler; Wakker, B.; Witt, C.; Gostisha, M. C.; Thomson, E.; Stratman, L.; Benjamin, R. A.

    2011-01-01

    We describe a new effort to use the Leiden/Argentina/Bonn (LAB) Galactic HI survey to update the high-velocity clouds catalog of Wakker and van Woerden (1991). The LAB survey (Kalberla et al 2005) combined the Leiden-Dwingeloo survey (Hartmann and Burton 1997) with a complementary southern sky survey (Arnal et al 2000). This survey provides improved angular spacing (0.5 deg vs. 1 deg) and velocity resolution (1 km/s vs. 16 km/s), although it was less sensitive than previous surveys. We describe how we fit the LAB high velocity gas with Gaussian components, providing three levels of review for the quality of fits, and compare the resulting high velocity cloud catalog to previous results for galactic latitudes greater than b=45 degrees. This research was supported by NASA ATP grant NNX10AI70G to the University of Wisconsin-Whitewater.

  10. SN 2010mb: Direct evidence for a supernova interacting with a large amount of hydrogen-free circumstellar material

    SciTech Connect

    Ben-Ami, Sagi; Gal-Yam, Avishay; Rabinak, Itay; Yaron, Ofer; Arcavi, Iair; Ofek, Eran O.; Mazzali, Paolo A.; Gnat, Orly; Modjaz, Maryam; Sullivan, Mark; Bildsten, Lars; Poznanski, Dovi; Bloom, Joshua S.; Nugent, Peter E.; Horesh, Assaf; Kulkarni, Shrinivas R.; Perley, Daniel; Kasliwal, Mansi M.; Quimby, Robert; Xu, Dong

    2014-04-10

    We present our observations of SN 2010mb, a Type Ic supernova (SN) lacking spectroscopic signatures of H and He. SN 2010mb has a slowly declining light curve (LC) (∼600 days) that cannot be powered by {sup 56}Ni/{sup 56}Co radioactivity, the common energy source for Type Ic SNe. We detect signatures of interaction with hydrogen-free circumstellar material including a blue quasi-continuum and, uniquely, narrow oxygen emission lines that require high densities (∼10{sup 9} cm{sup –3}). From the observed spectra and LC, we estimate that the amount of material involved in the interaction was ∼3 M {sub ☉}. Our observations are in agreement with models of pulsational pair-instability SNe described in the literature.

  11. AXAOTHER XL -- A spreadsheet for determining doses for incidents caused by tornadoes or high-velocity straight winds

    SciTech Connect

    Simpkins, A.A.

    1996-09-01

    AXAOTHER XL is an Excel Spreadsheet used to determine dose to the maximally exposed offsite individual during high-velocity straight winds or tornado conditions. Both individual and population doses may be considered. Potential exposure pathways are inhalation and plume shine. For high-velocity straight winds the spreadsheet has the capability to determine the downwind relative air concentration, however for the tornado conditions, the user must enter the relative air concentration. Theoretical models are discussed and hand calculations are performed to ensure proper application of methodologies. A section has also been included that contains user instructions for the spreadsheet.

  12. NEAR-INFRARED SPECTROSCOPY OF THE TYPE IIn SN 2010jl: EVIDENCE FOR HIGH VELOCITY EJECTA

    SciTech Connect

    Borish, H. Jacob; Huang, Chenliang; Chevalier, Roger A.; Breslauer, Benjamin M.; Kingery, Aaron M.; Privon, George C.

    2015-03-01

    The Type IIn supernova SN 2010jl was relatively nearby and luminous, allowing detailed studies of the near-infrared (NIR) emission. We present 1-2.4 μm spectroscopy over the age range of 36-565 days from the earliest detection of the supernova. On day 36, the H lines show an unresolved narrow emission component along with a symmetric broad component that can be modeled as the result of electron scattering by a thermal distribution of electrons. Over the next hundreds of days, the broad components of the H lines shift to the blue by 700 km s{sup –1}, as is also observed in optical lines. The narrow lines do not show a shift, indicating they originate in a different region. He I λ10830 and λ20587 lines both show an asymmetric broad emission component, with a shoulder on the blue side that varies in prominence and velocity from –5500 km s{sup –1} on day 108 to –4000 km s{sup –1} on day 219. This component may be associated with the higher velocity flow indicated by X-ray observations of the supernova. The absence of the feature in the H lines suggests that this is from a He-rich ejecta flow. The He I λ10830 feature has a narrow P Cygni line, with absorption extending to ∼100 km s{sup –1} and strengthening over the first 200 days, and an emission component which weakens with time. At day 403, the continuum emission becomes dominated by a blackbody spectrum with a temperature of ∼1900 K, suggestive of dust emission.

  13. EVIDENCE FOR ASYMMETRIC DISTRIBUTION OF CIRCUMSTELLAR MATERIAL AROUND TYPE Ia SUPERNOVAE

    SciTech Connect

    Foerster, Francisco; Gonzalez-Gaitan, Santiago; Anderson, Joseph; Marchi, Sebastian; Gutierrez, Claudia; Hamuy, Mario; Cartier, Regis; Pignata, Giuliano

    2012-08-01

    We study the properties of low-velocity material in the line of sight toward nearby Type Ia supernovae (SNe Ia) that have measured late phase nebular velocity shifts (v{sub neb}), thought to be an environment-independent observable. We have found that the distribution of equivalent widths of narrow blended Na I D1 and D2 and Ca II H and K absorption lines differs significantly between those SNe Ia with negative and positive v{sub neb}, with generally stronger absorption for SNe Ia with v{sub neb} {>=} 0. A similar result had been found previously for the distribution of colors of SNe Ia, which was interpreted as a dependence of the temperature of the ejecta with viewing angle. Our work suggests that (1) a significant part of these differences in color should be attributed to extinction, (2) this extinction is caused by an asymmetric distribution of circumstellar material (CSM), and (3) the CSM absorption is generally stronger on the side of the ejecta opposite to where the ignition occurs. Since it is difficult to explain (3) via any known physical processes that occur before explosion, we argue that the asymmetry of the CSM is originated after explosion by a stronger ionizing flux on the side of the ejecta where ignition occurs, probably due to a stronger shock breakout and/or more exposed radioactive material on one side of the ejecta. This result has important implications for both progenitor and explosion models.

  14. Uvby-B Photometry of High Velocity Stars. Photometric Parallaxes and Preliminary Kinematic Results

    NASA Astrophysics Data System (ADS)

    Schuster, W. J.

    1990-11-01

    RESUMEN. Se han explorado dos metodos para la determinaci6n de paralajes fotometricos usando fotometrfa uv - . Estos metodos dependen de las relaciones estandar de Crawford (1975) y de Olsen (1984) y de colores y magnitudes sinteticas de VandenBerg y Bell (1985). Ambos metodos incluyen una correcci6n evolucionaria de forma f6c0. Se calculan las distancias para las 711 estrellas de alta velocidad y pobres en metales en el catalogo uvby-p de Schuster y Nissen (1988). Se comparan estas con las distancias de Sandage y Fouts (1987) y Laird, Carney y Latham (1988) para las estrellas en comtfin. Tambien son aplicables nuestros metodos a estrellas de paralaje. En general las comparaciones son satisfactorias y las sistematicas son despreciables o pequefias. Las distancias finales de nuestras 711 estrellas se aplican a un numero de problemas cinematicos. Se estudian algunos diagramas interesantes, tales como el diagrama de energia de Toomre y el diagrama V(rot) versus [Fe/H]. ABSTRACT Two methods for the determination of parallaxes using uvbyP photometry are being explored. These methods depend upon the standard relations of Crawford (1975) and of Olsen (1984) and upon synthetic colors and magnitudes of VandenBerg and Bell (1985). Both include an evolutionary correction of the form f6c0. Distances are calculated for the 711 high-velocity and metal-poor stars in the uvby-P catalogue of Schuster and Nissen (1988). These are compared to the distances of Sandage and Fouts (1987) and Laird, Carney, and Lathain (1988) for stars in common. Also our methods are applied to parallax stars. In general the comparisons are good with negligible or small systematic differences. The final distances of our 711 stars are applied to a number of kinematical problems. Several interesting diagrams are studied, sucl as Toomre energy diagram and the plot of V(rot) versus [Fe/H]. Key words: DISTANCES - PHOTOMETRY - STARS-POPULATION II

  15. Shear instability of plastically-deforming metals in high-velocity impact welding

    NASA Astrophysics Data System (ADS)

    Nassiri, Ali; Kinsey, Brad; Chini, Greg

    2016-10-01

    High-speed oblique impact of two metal plates results in the development of an intense shear region at their interface leading to interfacial profile distortion and interatomic bonding. If the relative velocity is sufficient, a distinct wavy morphology with a well-defined amplitude and wavelength is observed. Emergence of this morphology below the melting point of the metal plates is usually taken as evidence of a successful weld. Amongvarious proposed mechanisms, instability owing to large tangential velocity variations near the interface has received significant attention. With one exception, the few quantitative stability analyses of this proposed mechanism have treated an anti-symmetric/shear-layer base profile (i.e., a Kelvin-Helmholtz configuration) and employed an inviscid or Newtonian viscous fluid constitutive relation. The former stipulation implies the energy source for the instability is the presumed relative shearing motion of the two plates, while the latter is appropriate only if melting occurs locally near the interface. In this study, these restrictions, which are at odds with the conditions realized in high-velocity impact welding, are relaxed. A quantitative temporal linear stability analysis is performed to investigate whether the interfacial wave morphology could be the signature of a shear-driven high strain-rate instability of a perfectly plastic material undergoing a jet-like deformation near the interface. The resulting partial differential eigenvalue problem is solved numerically using a spectral collocation method in which customized boundary conditions near the interface are implemented to properly treat the singularity arising from the vanishing of the base flow strain-rate at the symmetry plane of the jet. The solution of the eigenvalue problem yields the wavelength and growth rate of the dominant wave-like disturbances along the interface and confirms that a shear instability of a plastically-deforming material is compatible with the

  16. WSRT HI imaging of ultra-compact high velocity clouds: gas-bearing dark matter minihalos?

    NASA Astrophysics Data System (ADS)

    Adams, Elizabeth A.; Oosterloo, Tom; Giovanelli, Riccardo; Haynes, Martha P.; Cannon, John M.; Faerman, Yakov; Janesh, William; Janowiecki, Steven; Munoz, Ricardo; Rhode, Katherine L.; Salzer, John Joseph; Sternberg, Amiel

    2015-01-01

    A long standing problem in cosmology is the mismatch between the number of low mass dark matter halos predicted by simulations and the number of low mass galaxies observed in the Local Volume. We recently presented a set of isolated ultra-compact high velocity clouds (UCHVCs) identified within the dataset of the Arecibo Legacy Fast ALFA (ALFALFA) HI line survey that are consistent with representing low-mass gas-bearing dark matter halos within the Local Volume (Adams+ 2013). At distances of ~1 Mpc, the UCHVCs have HI masses of ~10^5 Msun and indicative dynamical masses of 10^7-10^8 Msun. The HI diameters of the UCHVCs range from 4' to 20', or 1 to 6 kpc at a distance of 1 Mpc.We have selected the most compact and isolated UCHVCs with the highest average column densities as representing the best galaxy candidates. These systems have been observed with the Westerbork Synthesis Radio Telescope (WSRT) to enable higher spatial resolution (~60") studies of the HI distribution. The HI morphology revealed by the WSRT data offers clues to the environment and origin of the UCHVCs, the kinematics of the HI allow the underlying mass distribution to be constrained, and the combination of spatial and spectral resolution allow the detection of a cold neutral medium component to the HI. The WSRT HI observations discriminate among the selected galaxy candidates for those objects that are most likely gas-bearing dark matter halos.One UCHVC, AGC198606, is of particular interest as it is located 16 km/s and 1.2 degrees from Leo T and has similar HI properties within the ALFALFA dataset. The WSRT HI observations reveal a smooth HI morphology and a velocity gradient along the HI major axis of the system consistent with rotation. These properties are consistent with the hypothesis that this object is a gas-bearing low-mass dark matter halo.

  17. Characteristics of MCrAlY coatings sprayed by high velocity oxygen-fuel spraying system

    SciTech Connect

    Itoh, Y.; Saitoh, M.; Tamura, M.

    2000-01-01

    High velocity oxygen-fuel (HVOF) spraying system in open air has been established for producing the coatings that are extremely clean and dense. It is thought that the HVOF sprayed MCrAlY (M is Fe, Ni and/or Co) coatings can be applied to provide resistance against oxidation and corrosion to the hot parts of gas turbines. Also, it is well known that the thicker coating can be sprayed in comparison with any other thermal spraying systems due to improved residual stresses. However, thermal and mechanical properties of HVOF coatings have not been clarified. Especially, the characteristics of residual stress, that are the most important property from the view point of production technique, have not been made clear. In this paper, the mechanical properties of HVOF sprayed MCrAlY coatings were measured in both the case of as-sprayed and heat-treated coatings in comparison with a vacuum plasma sprayed MCrAlY coatings. It was confirmed that the mechanical properties of HVOF sprayed MCrAlY coatings could be improved by a diffusion heat treatment to equate the vacuum plasma sprayed MCrAlY coatings. Also, the residual stress characteristics were analyzed using a deflection measurement technique and a X-ray technique. The residual stress of HVOF coating was reduced by the shot-peening effect comparable to that of a plasma spray system in open air. This phenomena could be explained by the reason that the HVOF sprayed MCrAlY coating was built up by poorly melted particles.

  18. Monitoring High Velocity Salt Tracer via 4D Electrical Resistivity Tomography - Possibility for Salt Tracer Tomography

    NASA Astrophysics Data System (ADS)

    Doro, K. O.; Cirpka, O. A.; Patzelt, A.; Leven, C.

    2014-12-01

    Hydrogeological testing in a tomographic sequence as shown by the use of hydraulic tomography, allows an improvement of the spatial resolution of subsurface parameters. In this regard, recent studies show increasing interest in tracer tomography which involves sequential and spatially separated tracer injections and the measurement of their corresponding tracer breakthrough at different locations and depths. Such concentration measurements however require large experimental efforts and can be simplified by geophysical tracer monitoring techniques such as electrical resistivity. In this study, we present the use of 4-D, cross-hole electrical resistivity tomography (ERT) for monitoring salt tracer experiments in high velocity flow fields. For our study, we utilized a set up that enables the conduction of salt tracer experiments with complete recovery within 84 hours over a transport distance of 16 m. This allows the repetition of the experiments with different injection depths for a tomographic salt tracer testing. For ERT monitoring, we designed modular borehole electrodes for repeated usage in a flexible manner. We also assess the use of a high speed resistivity data acquisition mode for field scale tracer monitoring ensuring high spatial and temporal resolution without sacrificing data accuracy. We applied our approach at the Lauswiesen test site, Tübingen, Germany. In our 10 m × 10 m tracer monitoring domain with 16 borehole electrodes, we acquired 4650 data points in less than 18 minutes for each monitoring cycle. Inversion results show that the tracer could be successfully imaged using this approach. The results show that repeated salt tracer tests can be efficiently monitored at a high resolution with ERT which gives the possibility for salt tracer tomography at field scale. Our results also provide a data base for extending current hydrogeophysical inversion approaches to field scale data.

  19. H II Regions Within a Compact High Velocity Cloud. A Nearly Starless Dwarf Galaxy?

    NASA Astrophysics Data System (ADS)

    Bellazzini, M.; Magrini, L.; Mucciarelli, A.; Beccari, G.; Ibata, R.; Battaglia, G.; Martin, N.; Testa, V.; Fumana, M.; Marchetti, A.; Correnti, M.; Fraternali, F.

    2015-02-01

    Within the SECCO survey we identified a candidate stellar counterpart to the Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123 that was suggested by Adams et al. to be a possible mini halo within the Local Group of galaxies. The spectroscopic follow-up of the brightest sources within the candidate reveals the presence of two H ii regions whose radial velocity is compatible with a physical association with the UVHVC. The available data do not allow us to give a definite answer on the nature of the newly identified system. A few alternative hypotheses are discussed. However, the most likely possibility is that we have found a new faint dwarf galaxy residing in the Virgo cluster of galaxies, which we name SECCO 1. Independently of its actual distance, SECCO 1 displays a ratio of neutral hydrogen mass to V luminosity of {{M}H I}/{{L}V}≳ 20, by far the largest among local dwarfs. Hence, it appears to be a nearly starless galaxy and it may be an example of the missing links between normal dwarfs and the dark mini halos that are predicted to exist in large numbers according to the currently accepted cosmological model. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

  20. The effects of varying resistance-training loads on intermediate- and high-velocity-specific adaptations.

    PubMed

    Jones, K; Bishop, P; Hunter, G; Fleisig, G

    2001-08-01

    The purpose of this study was to compare changes in velocity-specific adaptations in moderately resistance-trained athletes who trained with either low or high resistances. The study used tests of sport-specific skills across an intermediate- to high-velocity spectrum. Thirty NCAA Division I baseball players were randomly assigned to either a low-resistance (40-60% 1 repetition maximum [1RM]) training group or a high-resistance (70-90% 1RM) training group. Both of the training groups intended to maximallv accelerate each repetition during the concentric phase (IMCA). The 10 weeks of training consisted of 4 training sessions a week using basic core exercises. Peak force, velocity, and power were evaluated during set angle and depth jumps as well as weighted jumps using 30 and 50% 1RM. Squat 1RMs were also tested. Although no interactions for any of the jump tests were found, trends supported the hypothesis of velocity-specific training. Percentage gains suggest that the combined use of heavier training loads (70-90% 1RM) and IMCA tend to increase peak force in the lower-body leg and hip extensors. Trends also show that the combined use of lighter training loads (40-60% 1RM) and IMCA tend to increase peak power and peak velocity in the lower-body leg and hip extensors. The high-resistance group improved squats more than the low-resistance group (p < 0.05; +22.7 vs. + 16.1 kg). The results of this study support the use of a combination of heavier training loads and IMCA to increase 1RM strength in the lower bodies of resistance-trained athletes.

  1. Cognate xenoliths in Mt. Etna lavas: witnesses of the high-velocity body beneath the volcano

    NASA Astrophysics Data System (ADS)

    Corsaro, Rosa Anna; Rotolo, Silvio Giuseppe; Cocina, Ornella; Tumbarello, Gianvito

    2014-01-01

    Various xenoliths have been found in lavas of the 1763 ("La Montagnola"), 2001, and 2002-03 eruptions at Mt. Etna whose petrographic evidence and mineral chemistry exclude a mantle origin and clearly point to a cognate nature. Consequently, cognate xenoliths might represent a proxy to infer the nature of the high-velocity body (HVB) imaged beneath the volcano by seismic tomography. Petrography allows us to group the cognate xenoliths as follows: i) gabbros with amphibole and amphibole-bearing mela-gabbros, ii) olivine-bearing leuco-gabbros, iii) leuco-gabbros with amphibole, and iv) Plg-rich leuco gabbros. Geobarometry estimates the crystallization pressure of the cognate xenoliths between 1.9 and 4.1 kbar. The bulk density of the cognate xenoliths varies from 2.6 to 3.0 g/cm3. P wave velocities (V P ), calculated in relation to xenolith density, range from 4.9 to 6.1 km/s. The integration of mineralogical, compositional, geobarometric data, and density-dependent V P with recent literature data on 3D V P seismic tomography enabled us to formulate the first hypothesis about the nature of the HVB which, in the depth range of 3-13 km b.s.l., is likely made of intrusive gabbroic rocks. These are believed to have formed at the "solidification front", a marginal zone that encompasses a deep region (>5 km b.s.l.) of Mt. Etna's plumbing system, within which magma crystallization takes place. The intrusive rocks were afterwards fragmented and transported as cognate xenoliths by the volatile-rich and fast-ascending magmas of the 1763 "La Montagnola", 2001 and 2002-03 eruptions.

  2. COLLISIONS BETWEEN DARK MATTER CONFINED HIGH VELOCITY CLOUDS AND MAGNETIZED GALACTIC DISKS: THE SMITH CLOUD

    SciTech Connect

    Galyardt, Jason; Shelton, Robin L. E-mail: rls@physast.uga.edu

    2016-01-01

    The Galaxy’s population of High Velocity Clouds (HVCs) may include a subpopulation that is confined by dark matter minihalos and falling toward the Galactic disk. We present the first magnetohydrodynamic simulational study of dark-matter-dominated HVCs colliding with a weakly magnetized galactic disk. Our HVCs have baryonic masses of 5 × 10{sup 6}M{sub ⊙} and dark matter minihalo masses of 0, 3 × 10{sup 8}, or 1 × 10{sup 9} M{sub ⊙}. They are modeled on the Smith Cloud, which is said to have collided with the disk 70 Myr ago. We find that, in all cases, the cloud’s collision with the galactic disk creates a hole in the disk, completely disperses the cloud, and forms a bubble-shaped structure on the far side of the disk. In contrast, when present, the dark matter minihalo continues unimpeded along its trajectory. Later, as the minihalo passes through the bubble structure and galactic halo, it accretes up to 6.0 × 10{sup 5} M{sub ⊙} in baryonic material, depending on the strengths of the magnetic field and minihalo gravity. These simulations suggest that if the Smith Cloud is associated with a dark matter minihalo and collided with the Galactic disk, the minihalo has accreted the observed gas. However, if the Smith Cloud is dark-matter-free, it is on its first approach toward the disk. These simulations also suggest that the dark matter is most concentrated either at the head of the cloud or near the cloud, depending upon the strength of the magnetic field, a point that could inform indirect dark matter searches.

  3. Chemical abundances in a high-velocity RR Lyrae star near the bulge

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; Rich, R. M.; Koch, A.; Xu, S.; Kunder, A.; Ludwig, H.-G.

    2016-05-01

    Low-mass variable high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high- or hyper-velocity stars were young stars thought to originate from the Galactic center. Wide-area surveys such as APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities higher than 350 km s-1. In this study we present the first abundance analysis of a low-mass RR Lyrae star that is located close to the Galactic bulge, with a space motion of ~-400 km s-1. Using medium-resolution spectra, we derived abundances (including upper limits) of 11 elements. These allowed us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] =-0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, its retrograde orbit and the derived abundances combined suggest that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star might have been stripped from a stellar cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  4. Observational parameters of the dusty plasma line during high velocity meteor streams

    NASA Astrophysics Data System (ADS)

    Musatenko, S.; Musatenko, Yu.; Kurochka, E.; Choliy, V.; Lastochkin, A.; Slipchenko, O.

    The parameters of the dusty plasma line were determined from the observations of the high velocity meteor streams: Perseids, Orionids, Leonids whose velocities are greater than 70 km/sec. The observed line frequency variation is in 12-60 Hz range. The outline of the line is asymmetric, it contains a set of peaks 2-3 Hz wide and some of them may be approximated by gaussian. In some cases the line is accompanied with higher frequency satellite at the distance 3-5 Hz. The spectral behavior of the line during observation time is very individual for concrete meteor shower. In the Leonids-2000 campaign the sharp line intensity maximum was registered between 02-04 LT, whereas during Leonids-2003 there were no maxima found. During Perseids-1999 the line was detectable all the night time. From these follows that dusty component of ionosphere plasma was either cloud shaped or consisted of streams of different scale. The line could be detected with high confidence during low or middle solar activity. We failed to detect the line when the storm (Dst=235nT, F10.7=195) took place during Perseids-2000 campaign. It was impossible for us to make some conclusion about the influence of solar bursts hard emission on the line characteristics due to poor statistics. Also, some of the low velocity meteor streams like Geminids-2000 may produce weak line. We have evidence of line arising even when regular meteor showers are absent (our experiment in June 2000 when no any of the streams were awaited). Basing on characteristics of plasma line the structure of dust clouds created by meteor streams in Earth ionosphere could be determined.

  5. Petrophysical models of high velocity lower crust on the South Atlantic rifted margins: whence the asymmetry?

    NASA Astrophysics Data System (ADS)

    Trumbull, Robert B.; Franke, Dieter; Bauer, Klaus; Sobolev, Stephan V.

    2015-04-01

    Lower crustal bodies with high seismic velocity (Vp > 7km/s) underlie seaward-dipping reflector wedges on both margins of the South Atlantic, as on many other volcanic rifted margins worldwide. A comprehensive geophysical study of the South Atlantic margins by Becker et al. (Solid Earth, 5: 1011-1026, 2014) showed a strong asymmetry in the development of high-velocity lower crust (HVLC), with about 4 times larger volumes of HVLC on the African margin. That study also found interesting variations in the vertical position of HVLC relative to seaward-dipping reflectors which question a simple intrusive vs. extrusive relationship between these lower- and upper crustal features. The asymmetry of HVLC volumes on the conjugate margins is paradoxically exactly the opposite to that of surface lavas in the Paraná-Etendeka flood basalt province, which are much more voluminous on the South American margin. This contribution highlights the asymmetric features of magma distribution on the South Atlantic margins and explores their geodynamic significance. Petrophysical models of the HVLC are presented in the context of mantle melt generation, based on thickness-velocity (H-Vp) relations. These suggest that the greater volumes and average Vp values of HVLC on the African margin are due to active upwelling and high temperature, whereas passive upwelling under a thick lithospheric lid suppressed magma generation on the South American margin. The contrast in mantle upwelling rate and lithospheric thickness on the two margins predictably causes differential uplift, and this may help explain the greater accomodation space for surface lavas on the South American side although melt generation was strongest under the African margin.

  6. Energy Productivity of the High Velocity Algae Raceway Integrated Design (ARID-HV)

    SciTech Connect

    Attalah, Said; Waller, Peter M.; Khawam, George; Ryan, Randy D.; Huesemann, Michael H.

    2015-06-03

    The original Algae Raceway Integrated Design (ARID) raceway was an effective method to increase algae culture temperature in open raceways. However, the energy input was high and flow mixing was poor. Thus, the High Velocity Algae Raceway Integrated Design (ARID-HV) raceway was developed to reduce energy input requirements and improve flow mixing in a serpentine flow path. A prototype ARID-HV system was installed in Tucson, Arizona. Based on algae growth simulation and hydraulic analysis, an optimal ARID-HV raceway was designed, and the electrical energy input requirement (kWh ha-1 d-1) was calculated. An algae growth model was used to compare the productivity of ARIDHV and conventional raceways. The model uses a pond surface energy balance to calculate water temperature as a function of environmental parameters. Algae growth and biomass loss are calculated based on rate constants during day and night, respectively. A 10 year simulation of DOE strain 1412 (Chlorella sorokiniana) showed that the ARID-HV raceway had significantly higher production than a conventional raceway for all months of the year in Tucson, Arizona. It should be noted that this difference is species and climate specific and is not observed in other climates and with other algae species. The algae growth model results and electrical energy input evaluation were used to compare the energy productivity (algae production rate/energy input) of the ARID-HV and conventional raceways for Chlorella sorokiniana in Tucson, Arizona. The energy productivity of the ARID-HV raceway was significantly greater than the energy productivity of a conventional raceway for all months of the year.

  7. Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud

    NASA Astrophysics Data System (ADS)

    Galyardt, Jason; Shelton, Robin L.

    2016-01-01

    The Galaxy’s population of High Velocity Clouds (HVCs) may include a subpopulation that is confined by dark matter minihalos and falling toward the Galactic disk. We present the first magnetohydrodynamic simulational study of dark-matter-dominated HVCs colliding with a weakly magnetized galactic disk. Our HVCs have baryonic masses of 5 × 106M⊙ and dark matter minihalo masses of 0, 3 × 108, or 1 × 109 M⊙. They are modeled on the Smith Cloud, which is said to have collided with the disk 70 Myr ago. We find that, in all cases, the cloud’s collision with the galactic disk creates a hole in the disk, completely disperses the cloud, and forms a bubble-shaped structure on the far side of the disk. In contrast, when present, the dark matter minihalo continues unimpeded along its trajectory. Later, as the minihalo passes through the bubble structure and galactic halo, it accretes up to 6.0 × 105 M⊙ in baryonic material, depending on the strengths of the magnetic field and minihalo gravity. These simulations suggest that if the Smith Cloud is associated with a dark matter minihalo and collided with the Galactic disk, the minihalo has accreted the observed gas. However, if the Smith Cloud is dark-matter-free, it is on its first approach toward the disk. These simulations also suggest that the dark matter is most concentrated either at the head of the cloud or near the cloud, depending upon the strength of the magnetic field, a point that could inform indirect dark matter searches.

  8. Type I Superluminous Supernovae as Explosions inside Non-hydrogen Circumstellar Envelopes

    NASA Astrophysics Data System (ADS)

    Sorokina, Elena; Blinnikov, Sergei; Nomoto, Ken'ichi; Quimby, Robert; Tolstov, Alexey

    2016-09-01

    A number of Type I (hydrogenless) superluminous supernova (SLSN) events have been discovered recently. However, their nature remains debatable. One of the most promising ideas is the shock interaction mechanism, but only simplified semi-analytical models have been applied so far. We simulate light curves for several Type I SLSN (SLSN-I) models enshrouded by dense, non-hydrogen circumstellar (CS) envelopes, using a multi-group radiation hydrodynamics code that predicts not only bolometric, but also multicolor light curves. We demonstrate that the bulk of SLSNe-I including those with relatively narrow light curves like SN 2010gx or broad ones like PTF09cnd can be explained by the interaction of the SN ejecta with the CS envelope, though the range of parameters for these models is rather wide. Moderate explosion energy (˜(2-4) × 1051 erg) is sufficient to explain both narrow and broad SLSN-I light curves, but ejected mass and envelope mass differ for those two cases. Only 5-10 M ⊙ of non-hydrogen material is needed to reproduce the light curve of SN 2010gx, while the best model for PTF09cnd is very massive: it contains almost 50 M ⊙ in the CS envelope and only 5 M ⊙ in the ejecta. The CS envelope for each case extends from 10 R ⊙ to ˜105 R ⊙ (7 × 1015 cm), which is about an order of magnitude larger than typical photospheric radii of standard SNe near the maximum light. We briefly discuss possible ways to form such unusual envelopes.

  9. The Velocity Structure of SN 1987A's Outer Circumstellar Envelope

    NASA Astrophysics Data System (ADS)

    Crotts, A. P. S.; Heathcote, S. R.

    1997-12-01

    We present high-resolution optical spectroscopy, (obtained with the CTIO 4-meter/echelle spectrograph over many epochs between 1989 and 1997) of the circumstellar nebula of SN 1987A, including the outer rings (within 3 arcsec of the SN), the inner (equatorial) ring, and fainter features at larger radii never studied before spectroscopically. We report velocity displacements for portions of the outer rings, up to 26 km s(-1) with respect the SN centroid velocity, with blueshifted components in the location of the southern outer ring and the redshifted portions of the northern outer ring. The largest shifts are near the SN, as predicted by a model in which the outer rings are the crowns of an expanding, bipolar nebula with the inner ring at its waist. We also confirm that the inner ring shows a velocity full-width of about 13 km s(-1) , which, along with the geometry of the rings and our outer ring velocity measurements, allows us to estimate a characteristic timescale of about 20,000 y for each of the three rings, implying that all are coeval. This contrasts with measurements by others of compositional ratios in the inner versus outer rings indicating that they were, perhaps, ejected at different times from the progenitor's star's outer envelope. Additionally, we measure the velocity of low surface brightness features at larger radii indicating that circumstellar material even farther from the SN was ejected up to 400,000 y before the explosion. Finally, we note the presence of transient emission features within the circumstellar nebula and describe their behaviour, and consider what implications our observations may have for the coming transformation of this nebula into Supernova Remnant 1987A.

  10. Mean gas opacity for circumstellar environments and equilibrium temperature degeneracy

    NASA Astrophysics Data System (ADS)

    Malygin, M. G.; Kuiper, R.; Klahr, H.; Dullemond, C. P.; Henning, Th.

    2014-08-01

    Context. In a molecular cloud dust opacity typically dominates over gas opacity, yet in the vicinities of forming stars dust is depleted, and gas is the sole provider of opacity. In the optically thin circumstellar environments the radiation temperature cannot be assumed to be equal to the gas temperature, hence the two-temperature Planck means are necessary to calculate the radiative equilibrium. Aims: By using the two-temperature mean opacity one does obtain the proper equilibrium gas temperature in a circumstellar environment, which is in a chemical equilibrium. A careful consideration of a radiative transfer problem reveals that the equilibrium temperature solution can be degenerate in an optically thin gaseous environment. Methods: We compute mean gas opacities based on the publicly available code DFSYNTHE by Kurucz and Castelli. We performed the calculations assuming local thermodynamic equilibrium and an ideal gas equation of state. The values were derived by direct integration of the high-resolution opacity spectrum. Results: We produced two sets of gas opacity tables: Rosseland means and two-temperature Planck means. For three metallicities [Me/H] = 0.0, ± 0.3 we covered the parameter range 3.48 ≤ log Trad [K] ≤ 4.48 in radiation temperature, 2.8 ≤ log Tgas [K] ≤ 6.0 in gas temperature, and -10 ≤ log P [dyn cm-2] ≤ 6 in gas pressure. We show that in the optically thin circumstellar environment for a given stellar radiation field and local gas density there are several equilibrium gas temperatures possible. Conclusions: We conclude that, in general, equilibrium gas temperature cannot be determined without treating the temperature evolution. The opacity tables 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/568/A91 as well as via http://www.mpia.de/~malygin

  11. Cepheids at high angular resolution: circumstellar envelope and pulsation

    NASA Astrophysics Data System (ADS)

    Gallenne, Alexandre

    2011-12-01

    In 2005, interferometric observations with VLTI/VINCI and CHARA/FLUOR revealed the existence of a circumstellar envelope (CSE) around some Cepheids. This surrounding material is particularly interesting for two reasons: it could have an impact on the distance estimates and could be linked to a past or on-going mass loss. The use of Baade-Wesselink methods for independent distance determinations could be significantly biased by the presence of these envelopes. Although their observations are difficult because of the high contrast between the photosphere of the star and the CSE, several observation techniques have the potential to improve our knowledge about their physical properties. In this thesis, I discuss in particular high angular resolution techniques that I applied to the study of several bright Galactic Cepheids. First, I used adaptive optic observations with NACO of the Cepheid RS Puppis, in order to deduce the flux ratio between the CSE and the photosphere of the star. In addition, I could carry out a statistical study of the speckle noise and inspect a possible asymmetry. Secondly, I analysed VISIR data to study the spectral energy distribution of a sample of Cepheids. These diffraction-limited images enabled me to carry out an accurate photometry in the N band and to detect an IR excess linked to the presence of a circumstellar component. On the other hand, applying a Fourier analysis I showed that some components are resolved. I then explored the K' band with the recombination instrument FLUOR for some bright Cepheids. Thanks to new set of data of Y Oph, I improved the study of its circumstellar envelope, using a ring-like model for the CSE. For two other Cepheids, U Vul and S Sge, I applied the interferometric Baade-Wesselink method in order to estimate their distance.

  12. Evidence for dust grain growth in young circumstellar disks.

    PubMed

    Throop, H B; Bally, J; Esposito, L W; McCaughrean, M J

    2001-06-01

    Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.

  13. Studies of Interstellar and Circumstellar Magnetic Field with Aligned Atoms

    NASA Astrophysics Data System (ADS)

    Lazarian, A.; Yan, H.

    2004-12-01

    Population of levels of the hyperfine and fine split ground state of an atom is affected by radiative transitions induced by anisotropic radiation flux. Such aligned atoms precess in the external magnetic field and this affects properties of polarized radiation arising from both scattering and absorption by atoms. As the result the degree of light polarization depends on the direction of the magnetic field. This provides a new tool for studies of astrophysical magnetic fields using optical and UV polarimetry. We provide calculations for several atoms and ions that can be used to study magnetic fields in interplanetary medium, interstellar medius, circumstellar regions and quasars.

  14. Detection of circumstellar gas associated with GG Tauri

    NASA Technical Reports Server (NTRS)

    Skrutskie, M. F.; Snell, R. L.; Strom, K. M.; Strom, S. E.; Edwards, S.; Fukui, Y.; Mizuno, A.; Hayashi, M.; Ohashi, N.

    1993-01-01

    Double-peaked (C-12)O (1-0) emission centered on the young T Tauri star GG Tau possesses a line profile which may be modeled on the assumption that CO emission arises in an extended circumstellar disk. While bounds on the observed gas mass can be estimated on this basis, it is suggested that a large amount of mass could lie within a small and optically thick region, escaping detection due to beam-dilution effects. In addition, CO may no longer accurately trace the gas mass due to its dissociation, or freezing into grains, or due to the locking-up of carbon into more complex molecules.

  15. Photochemistry and molecular ions in oxygen-rich circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Mamon, G. A.; Glassgold, A. E.; Omont, A.

    1987-01-01

    A theory for the ionization of the circumstellar envelopes around O-rich red giants is developed from the photochemical model. The main source of ionization is photoionization of H2O, OH, and C by the interstellar UV radiation field, supplemented by cosmic-ray ionization of hydrogen. Significant amounts of H3O(+) and HCO(+) are produced, with peak abundances of about 10 to the -7th at intermediate distances from the star. Although H3O(+) may be difficult to detect with current instrumentation, HCO(+) is probably detectable in nearby O-rich envelopes with large millimeter-wave telescopes.

  16. Iron containing vitamins and dietary supplements: control of the iron state using Mössbauer spectroscopy with high velocity resolution

    NASA Astrophysics Data System (ADS)

    Oshtrakh, M. I.; Semionkin, V. A.; Milder, O. B.; Novikov, E. G.

    2009-04-01

    Control of the iron state in iron containing vitamins and dietary supplements using Mössbauer spectroscopy with high velocity resolution was done. An improvement of velocity resolution appeared to be useful in determination of impurities and analysis of the main components in iron containing pharmaceuticals with better quality.

  17. High- and low-temperature-stable thermite composition for producing high-pressure, high-velocity gases

    DOEpatents

    Halcomb, Danny L.; Mohler, Jonathan H.

    1990-10-16

    A high- and low-temperature-stable thermite composition for producing high-pressure and high-velocity gases comprises an oxidizable metal, an oxidizing reagent, and a high-temperature-stable gas-producing additive selected from the group consisting of metal carbides and metal nitrides.

  18. High velocity Van de Graaff shots of mineral dust: application to STARDUST and other in situ space missions

    NASA Astrophysics Data System (ADS)

    Postberg, Frank; Srama, Ralf; Trieloff, Mario; Hillier, Jon; Gainsforth, Zack; Westphal, Andrew; Grün, Eberhard; Armes, Steve; Kearsley, Anton

    2010-05-01

    The detection and collection of high velocity interplanetary or interstellar dust grains by space missions is a nontrivial task, as high speed impacts on collectors or detectors may cause significant structural and chemical modification. Hence, simulation of high speed dust impacts is required, e.g. into STARDUST aerogel or foils [1], or impact ionisation time-of-flight mass spectrometers as onboard CASSINI [2,3]. Particle speeds up to 50 km/sec can only be achieved by a Van de Graaff accelerator as operated at the Max-Planck-Institut für Kernphysik (Heidelberg). Here, only charged particles can be ac-celerated: While metals (e.g., Fe, Al) or magnetite work well, ac-celeration of silicates or organics requires a complex chemical coating procedure, to achieve acceptable levels of conductivity. A thin platinum coating [4] was successfully applied to analogue ma-terial like silicates (quartz, orthopyroxene, anorthite, olivine), and carbon rich particles (silicon carbide). Organic and sulfide (e.g. pyrrhotite) grains have been coated with a thin conductive layer of Polypyrrole [5], which allows acceleration in the Van de Graaff. All coated grains were successfully accelerated and provided im-pacts with speeds between 1 - 40 km/s. Impact signals as well as high resolution impact ionisation mass spectra were evaluated using the large area mass analyzer [6] (LAMA). These TOF spectra provide a mass resolution of about 200 and allow for qualitative determination of mineral compounds and isotopes in individual grains. However, while for these kinds of experiments active selection of suitable particle impacts is possible, the preparation for shots into STARDUST collectors requires com-plete control of particle size and speed by an improved new version of specific Particle Selection Unit, which is currently implemented. This provides a clear advantage over shots with a light gas gun where single shots of selected grain within a narrow mass and speed range are not achievable

  19. The Small-Scale Structure of High-Velocity Na I Absorption Toward M81

    NASA Astrophysics Data System (ADS)

    Roth, K. C.; Meyer, D. M.; Lauroesch, J. T.

    2000-12-01

    We present high-resolution (R=20,000) integral field spectra of the Na I absorption toward the nucleus of the nearby spiral galaxy M81 (NGC 3031) obtained in April 2000 with the WIYN 3.5-m telescope and the DensePak fiber optic bundle. Our DensePak map covers the central 27 x 43 arcsec of M81 at a spatial resolution of 4 arcsec which corresponds to a projected length scale of 63 pc at the distance of the galaxy (3.25 Mpc). These data were intended to explore the spatial extent of high-velocity (v = 110-130 km/s) gas seen in Na I, Mg I and Mg II absorption toward SN 1993J by Bowen et al. (1994), which they proposed is due to tidal material associated with interactions between M81 and nearby M82 (Yun, Ho & Lo 1993). No H I gas at these velocities has been detected in 21 cm interferometry maps near the position of SN 1993J (2.6 arcmin SW of the M81 nucleus). Our Na I map of the M81 core shows no evidence of the strong absorption seen at v = 110-130 km/s toward SN 1993J. However, our map does reveal a strong Na I component at v = 220 km/s in several fibers that appears to trace a filamentary structure running from the SW to the NE across the M81 nuclear region. The origin and distance of this filament are unknown. No H I gas at v = 220 km/s has previously been detected in 21 cm studies of the core. At the location of SN 1993J, Bowen et al. measured weak Mg II absorption at this velocity but found no evidence of corresponding Na I absorption. The only known H I gas that corresponds to this velocity in the M81 group are the H I streamers found around M82 by Yun, Ho, & Lo that they interpreted as tidally disrupted M82 disk material.

  20. On the Metallicity and Origin of the Smith High-velocity Cloud

    NASA Astrophysics Data System (ADS)

    Fox, Andrew J.; Lehner, Nicolas; Lockman, Felix J.; Wakker, Bart P.; Hill, Alex S.; Heitsch, Fabian; Stark, David V.; Barger, Kathleen A.; Sembach, Kenneth R.; Rahman, Mubdi

    2016-01-01

    The Smith Cloud (SC) is a gaseous high-velocity cloud (HVC) in an advanced state of accretion, only 2.9 kpc below the Galactic plane and due to impact the disk in ≈27 Myr. It is unique among HVCs in having a known distance (12.4 ± 1.3 kpc) and a well-constrained 3D velocity (296 km s-1), but its origin has long remained a mystery. Here we present the first absorption-line measurements of its metallicity, using Hubble Space Telescope/COS UV spectra of three active galactic nuclei lying behind the Cloud together with Green Bank Telescope 21 cm spectra of the same directions. Using Voigt-profile fitting of the S ii λλ1250, 1253, 1259 triplet together with ionization corrections derived from photoionization modeling, we derive the sulfur abundance in each direction; a weighted average of the three measurements gives [S/H] = -0.28 ± 0.14, or {0.53}-0.15+0.21 solar metallicity. The finding that the SC is metal-enriched lends support to scenarios where it represents recycled Galactic material, rather than the remnant of a dwarf galaxy or accreting intergalactic gas. The metallicity and trajectory of the Cloud are both indicative of an origin in the outer disk. However, its large mass and prograde kinematics remain to be fully explained. If the cloud has accreted cooling gas from the corona during its fountain trajectory, as predicted in recent theoretical work, its current mass would be higher than its launch mass, alleviating the mass concern. Based on observations taken under program 13840 of the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555, and under program GBT09A_17 of the Robert C. Byrd Green Bank Telescope (GBT) of the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under a cooperative agreement by Associated Universities, Inc.

  1. Force Criterion Prediction of Damage for Carbon/Epoxy Composite Panels Impacted by High Velocity Ice

    NASA Astrophysics Data System (ADS)

    Rhymer, Jennifer D.

    The use of advanced fiber-reinforced polymer matrix composites in load-bearing aircraft structures is increasing, as evident by the various composites-intensive transport aircraft presently under development. A major impact source of concern for these structures is hail ice, which affects design and skin-sizing (skin thickness determination) at various locations of the aircraft. Impacts onto composite structures often cause internal damage that is not visually detectable due to the high strength and resiliency of the composite material (unlike impacts onto metallic structures). This internal damage and its effect on the performance of the structure are of great concern to the aircraft industry. The prediction of damage in composite structures due to SHI impact has been accomplished via experimental work, explicit dynamic nonlinear finite element analysis (FEA) and the definition of design oriented relationships. Experiments established the critical threshold and corresponding analysis provided contact force results not readily measurable in high velocity SHI impact experiments. The design oriented relationships summarize the FEA results and experimental database into contact force estimation curves that can be easily applied for damage prediction. Failure thresholds were established for the experimental conditions (panel thickness ranging from 1.56 to 4.66 mm and ice diameters from 38.1 to 61.0 mm). Additionally, the observations made by high-speed video during the impact event, and ultrasonic C-scan post-impact, showed how the ice failed during impact and the overall shape and location of the panel damage. Through analysis, the critical force, the force level where damage occurs above but not below, of a SHI impact onto the panel was found to be dependent only on the target structure. However, the peak force generated during impact was dependent on both the projectile and target. Design-oriented curves were generated allowing the prediction of the allowable

  2. High Velocity Linear Induction Launcher with Exit-Edge Compensation for Testing of Aerospace Components

    NASA Technical Reports Server (NTRS)

    Kuznetsov, Stephen; Marriott, Darin

    2008-01-01

    Advances in ultra high speed linear induction electromagnetic launchers over the past decade have focused on magnetic compensation of the exit and entry-edge transient flux wave to produce efficient and compact linear electric machinery. The paper discusses two approaches to edge compensation in long-stator induction catapults with typical end speeds of 150 to 1,500 m/s. In classical linear induction machines, the exit-edge effect is manifest as two auxiliary traveling waves that produce a magnetic drag on the projectile and a loss of magnetic flux over the main surface of the machine. In the new design for the Stator Compensated Induction Machine (SCIM) high velocity launcher, the exit-edge effect is nulled by a dual wavelength machine or alternately the airgap flux is peaked at a location prior to the exit edge. A four (4) stage LIM catapult is presently being constructed for 180 m/s end speed operation using double-sided longitudinal flux machines. Advanced exit and entry edge compensation is being used to maximize system efficiency, and minimize stray heating of the reaction armature. Each stage will output approximately 60 kN of force and produce over 500 G s of acceleration on the armature. The advantage of this design is there is no ablation to the projectile and no sliding contacts, allowing repeated firing of the launcher without maintenance of any sort. The paper shows results of a parametric study for 500 m/s and 1,500 m/s linear induction launchers incorporating two of the latest compensation techniques for an air-core stator primary and an iron-core primary winding. Typical thrust densities for these machines are in the range of 150 kN/sq.m. to 225 kN/sq.m. and these compete favorably with permanent magnet linear synchronous machines. The operational advantages of the high speed SCIM launcher are shown by eliminating the need for pole-angle position sensors as would be required by synchronous systems. The stator power factor is also improved.

  3. Titanium dioxide reinforced hydroxyapatite coatings deposited by high velocity oxy-fuel (HVOF) spray.

    PubMed

    Li, H; Khor, K A; Cheang, P

    2002-01-01

    Hydroxyapatite (HA) coatings with titania addition were produced by the high velocity oxy-fuel (HVOF) spray process. Mechanical properties of the as-sprayed coatings in terms of adhesive strength, shear strength and fracture toughness were investigated to reveal the effect of the titania reinforcement on HA. Qualitative phase analysis with X-ray diffraction (XRD) showed that mutual chemical reaction between TiO2 and HA, that formed CaTiO3 occurred during coating formation. Differential scanning calorimetry (DSC) analysis of the starting powders showed that the mutual chemical reaction temperature was approximately 1410 degrees C and the existence of TiO2 can effectively inhibit the decomposition of HA at elevated temperatures. The positive influence of TiO2 addition on the shear strength was revealed. The incorporation of 10 vol% TiO2 significantly improved the Young's modulus of HA coatings from 24.82 (+/- 2.44) GPa to 43.23 (+/- 3.20) GPa. It decreased to 38.51 (+/- 3.65) GPa as the amount of TiO2 increased to 20 vol%. However, the addition of TiO2 has a negative bias on the adhesive strength of HA coatings especially when the content of TiO2 reached 20 vol%. This is attributed to the weak chemical bonding and brittle phases existing at the splats' interface that resulted from mutual chemical reactions. The fracture toughness exhibited values of 0.48 (+/- 0.08) MPa m0.5, 0.60 (+/- 0.07) MPa m0.5 and 0.67 (+/- 0.06) MPa m0.5 for the HA coating, 10 vol% TiO2 blended HA coating and 20 vol% TiO2 blended HA coating respectively. The addition of TiO2 in HA coating with the amount of less than 20 vol% is suggested for satisfactory toughening effect in HVOF HA coating. PMID:11762858

  4. Global properties of the HI high velocity sky. A statistical investigation based on the LAB survey

    NASA Astrophysics Data System (ADS)

    Kalberla, P. M. W.; Haud, U.

    2006-08-01

    Context.Since 1973, it has been known that some H i high velocity clouds (HVCs) have a core-envelope structure. Recent observations of compact HVCs confirm this, but more general investigations have been missing so far.Aims.We study the properties of all major HVC complexes from a sample compiled in 1991 by Wakker & van Woerden (WvW). Methods.We use the Leiden/Argentine/Bonn all sky 21-cm line survey and decompose the profiles into Gaussian components.Results.We find the WvW line widths and column densities to be underestimated by ~40%. In 1991, these line widths could not be measured directly, but had to be estimated with the help of higher resolution data. We find a well-defined multi-component structure for most of the HVC complexes. The cold HVC phase has lines with typical velocity dispersions of σ = 3 km s-1 and exists only within more extended broad line regions, typically with σ = 12 km s-1. The motions of the cores relative to the envelopes are characterized by Mach numbers M = (vcore-venvelope)/σenvelope ˜ 1.5. The center velocities of the cores within a HVC complex have typical dispersions of 20 km s-1. The well-defined two-component structure of some prominent HVC complexes in the outskirts of the Milky Way is remakable: Complex H lies approximately in the Galactic plane, and the most plausible distance estimate of R ˜ 33 kpc places it at the edge of the disk. The Magellanic Stream and the Leading Arm (complex EP) reach higher latitudes and are probably more distant, R ˜ 50 kpc. There might be some indications for an interaction between HVCs and disk gas at intermediate velocities. This is possible for complex H, M, C, WB, WD, WE, WC, R, G, GCP, and OA, but not for complex A, MS, ACVHV, EN, WA, and P. Conclusions.The line widths, determined by us, imply that estimates of HVC masses, as far as those derived from the WvW database are concerned, need to be scaled up by a factor 1.4. Correspondingly, guesses for the external pressure of a confining

  5. Earthquake Energy Dissipation in Light of High-Velocity, Slip-Pulse Shear Experiments

    NASA Astrophysics Data System (ADS)

    Reches, Z.; Liao, Z.; Chang, J. C.

    2014-12-01

    We investigated the energy dissipation during earthquakes by analysis of high-velocity shear experiments conducted on room-dry, solid samples of granite, tonalite, and dolomite sheared at slip-velocity of 0.0006-1m/s, and normal stress of 1-11.5MPa. The experimental fault were loaded in one of three modes: (1) Slip-pulse of abrupt, intense acceleration followed by moderate deceleration; (2) Impact by a spinning, heavy flywheel (225 kg); and (3) Constant velocity loading. We refer to energy dissipation in terms of power-density (PD=shear stress*slip-velocity; units of MW/m^2), and Coulomb-energy-density (CED= mechanical energy/normal stress; units of m). We present two aspects: Relative energy dissipation of the above loading modes, and relative energy dissipation between impact experiments and moderate earthquakes. For the first aspect, we used: (i) the lowest friction coefficient of the dynamic weakening; (ii) the work dissipated before reaching the lowest friction; and (iii) the cumulative mechanical work during the complete run. The results show that the slip-pulse/impact modes are energy efficient relatively to the constant-velocity mode as manifested by faster, more intense weakening and 50-90% lower energy dissipation. Thus, for a finite amount of pre-seismic crustal energy, the efficiency of slip-pulse would amplify earthquake instability. For the second aspect, we compare the experimental CED of the impact experiments to the reported breakdown energy (EG) of moderate earthquakes, Mw = 5.6 to 7.2 (Chang et al., 2012). In is commonly assumed that the seismic EG is a small fraction of the total earthquake energy, and as expected in 9 out of 11 examined earthquakes, EG was 0.005 to 0.07 of the experimental CED. We thus speculate that the experimental relation of Coulomb-energy-density to total slip distance, D, CED = 0.605 × D^0.933, is a reasonable estimate of total earthquake energy, a quantity that cannot be determined from seismic data.

  6. Ultraviolet Spectroscopy of Narrow CMEs

    NASA Astrophysics Data System (ADS)

    Dobrzycka, D.; Raymond, J. C.; Biesecker, D. A.; Li, J.; Ciaravella, A.

    2002-12-01

    Coronal mass ejections (CMEs) are commonly described as new, discrete, bright features appearing in the field of view of a white light coronagraph and moving outward over a period of minutes to hours. Apparent angular widths of the CMEs cover a wide range, from few to 360°. The very narrow structures (narrower than ~15-20°) form only a small subset of all the observed CMEs and are usually referred to as rays, spikes, fans, etc. Recently, Gilbert et al. (2001, ApJ, 550, 1093) reported LASCO white light observations of 15 selected narrow CMEs. We extended the study and analyzed ultraviolet spectroscopy of narrow ejections, including several events listed by Gilbert et al. The data were obtained by the Ultraviolet Coronagraph Spectrometer (UVCS/SOHO). We present comparison of narrow and large CMEs and discuss the relation of the narrow CMEs to coronal jets and/or other narrow transient events. This work is supported by NASA under Grant NAG5-11420 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  7. An energetic stellar outburst accompanied by circumstellar light echoes.

    PubMed

    Bond, Howard E; Henden, Arne; Levay, Zoltan G; Panagia, Nino; Sparks, William B; Starrfield, Sumner; Wagner, R Mark; Corradi, R L M; Munari, U

    2003-03-27

    Some classes of stars, including novae and supernovae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of approximately 10(4). Unlike a supernova or nova, it did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into the surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of those light echoes, which allow us to set direct geometric distance limits to the object. At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behaviour, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation. PMID:12660776

  8. Far-Infrared Water Line Emissions from Circumstellar Outflows

    NASA Technical Reports Server (NTRS)

    Chen, Wesley; Neufeld, David A.

    1995-01-01

    We have modeled the far-infrared water line emission expected from circumstellar outflows from oxygen-rich late-type stars, as a function of the mass-loss rate and the terminal outflow velocity. For each mass-loss rate and terminal outflow velocity considered, we computed self-consistently the gas density, temperature, outflow velocity, and water abundance as a function of distance from the star. We then used an escape probability method to solve for the equilibrium level populations of 80 rotational states of water and thereby obtained predictions for the luminosity of a large number of far-infrared rotational transitions of water. In common with previous models, our model predicts that water will be copiously produced in the warm circumstellar gas and that water rotational emission will dominate the radiative cooling. However, our use of a realistic radiative cooling function for water leads to a lower gas temperature than that predicted in previous models. Our predictions for the far-infrared water line luminosities are consequently significantly smaller than those obtained in previous studies. Observations to be carried out by the Infrared Space Observatory will provide a crucial test of the models presented here.

  9. A Radiative Instability in Post-shock-cooling Circumstellar Gas

    NASA Astrophysics Data System (ADS)

    Schirrmacher, V.; Woitke, P.; Sedlmayr, E.

    Investigations on non-LTE radiative heating and cooling processes behind shock waves in circumstellar environments have revealed the existence of a radiative/thermal instability in the post-shock cooling gas. The results have been obtained in the framework of spherical symmetric, hydrodynamical model calculations for dust-enshrouded circumstellar envelopes (CSEs) of Asymptotic Giant Branch (AGB) stars, which combine a time-dependent treatment of dust formation with grey radiative transfer and tabulated non-LTE state functions. The instability occurs in a situation, where thin and hot atomic gas behind a shock wave cools down to the molecular domain where it remains in pressure equilibrium with its environment. Radiative cooling in this case causes a temperature decrease and a density increase which both favour molecule formation. The molecules, in return, accelerate the radiative cooling. Thereby, a self-amplifying feedback loop is established, which in the model leads to the amplification of small density fluctuations in the post-shock cooling region to large density inhomogeneities of more than one order of magnitude. This radiative/thermal instability is not restricted to one spatial dimension (as in the model) and is possibly capable to generate a strongly non-homogeneous density distribution around pulsating stars, which can, for example lead to dust cloud formation. In this presentation, we discuss the parameter range for this instability as well as the underlying thermodynamical concept of the model calculations.

  10. Attenuation of supersoft X-ray sources by circumstellar material

    NASA Astrophysics Data System (ADS)

    Nielsen, M. T. B.; Gilfanov, M.

    2015-11-01

    Recent studies have suggested the possibility of significantly obscuring supersoft X-ray sources in relatively modest amounts of local matter lost from the binaries themselves. If correct, then this would have explained the paucity of observed supersoft X-ray sources and would have significance for the search for single-degenerate Type Ia supernova progenitors. We point out that earlier studies of circumbinary obscuration ignored photoionizations of the gas by the emission from the supersoft X-ray source. We revisit the problem using a full, self-consistent calculation of the ionization state of the circumbinary material photoionized by the radiation of the central source. Our results show that the circumstellar mass-loss rates required for obscuration of supersoft X-ray sources is about an order of magnitude larger than those reported in earlier studies, for comparable model parameters. While this does not entirely rule out the possibility of circumstellar material obscuring supersoft X-ray sources, it makes it unlikely that this effect alone can account for the majority of the missing supersoft X-ray sources. We discuss the observational appearance of hypothetical obscured nuclear-burning white dwarfs and show that they have signatures making them distinct from photoionized nebulae around supersoft X-ray sources imbedded in the low-density interstellar medium.

  11. Probing Pre-Supernova Mass Loss With Circumstellar Dust Shells

    NASA Astrophysics Data System (ADS)

    Fox, Ori; Filippenko, Alex; Skrutskie, Mike; van Dyk, Schuyler; Kelly, Pat

    2013-10-01

    Late-time (>100 day) mid-infrared (mid-IR) observations of supernovae (SNe) offer a valuable probe of the progenitor mass-loss. Already, this technique has been exemplified with the Type IIn subclass, which often have large, dusty, pre-existing shells formed in pre-SN eruptions. While other SN subclasses are generally thought of having relatively low density circumstellar environments, a growing number of objects in other subclasses now show evidence for significant pre-SN mass loss and similar mid-IR characteristics. Long after the SN radioactive tail disappears, warm dust can stay bright at mid-IR wavelengths due to alternative heating mechanisms, such as shocks. The success of Spitzer archival studies has already been highlighted by the work of several members of this team. Here we propose a SNAPSHOT survey of a well-studied and high-profile SN sample, extending over a range of subclasses, and including both recent and historical events with evidence of a dense CSM and/or dust. This program will (a) discover new SNe with warm dust and (b) monitor the evolution of warm dust in previously detected SNe. Expanding upon our previous mid-IR work on SNe IIn, these observations will probe the similarities in and differences between the subclasses' circumstellar environments, pre-SN mass-loss, and ultimately, the progenitors themselves.

  12. Probing Pre-Supernova Mass Loss With Circumstellar Dust Shells

    NASA Astrophysics Data System (ADS)

    Fox, Ori; Filippenko, Alex; Skrutskie, Mike; van Dyk, Schuyler; Kelly, Pat

    2014-12-01

    Late-time (>100 day) mid-infrared (mid-IR) observations of supernovae (SNe) offer a valuable probe of the progenitor system's mass-loss. Already, this technique has been demonstrated with the Type IIn subclass, which often have large, dusty, pre-existing shells formed in pre-SN eruptions. While other SN subclasses are thought of having relatively low density circumstellar environments, a growing number of objects in other subclasses now show evidence for significant pre-SN mass loss and similar mid-IR characteristics. Long after the SN radioactive tail fades, warm dust can stay bright at mid-IR wavelengths due to alternative heating mechanisms, such as shocks. Here we propose a SNAPSHOT survey of a well-studied and high-profile SN sample, extending over a range of subclasses, including both recent and historical events with evidence of a dense CSM and/or dust. This program will (a) discover new SNe with warm dust and (b) monitor the evolution of warm dust in previously detected SNe. Harnessing the success of our previous Spitzer programs, these observations will expand upon that work by probing the similarities in and differences between the subclasses' circumstellar environments, pre-SN mass-loss, and ultimately, the progenitors themselves.

  13. An energetic stellar outburst accompanied by circumstellar light echoes.

    PubMed

    Bond, Howard E; Henden, Arne; Levay, Zoltan G; Panagia, Nino; Sparks, William B; Starrfield, Sumner; Wagner, R Mark; Corradi, R L M; Munari, U

    2003-03-27

    Some classes of stars, including novae and supernovae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of approximately 10(4). Unlike a supernova or nova, it did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into the surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of those light echoes, which allow us to set direct geometric distance limits to the object. At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behaviour, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation.

  14. Are young supernova remnants interacting with circumstellar gas

    SciTech Connect

    Chevalier, R.A.

    1982-08-15

    The young remnants of galactic Type I supernovae (SN 1006, SN 1572, and SN 1604) appear to be interacting with moderately dense gas (n/sub O/> or =0.1 cm/sup -3/). If the gas in the ambient interstellar medium, the observations suggest that gas of this density is fairly pervasive. If the gas is circumstellar, there are important implications for the progenitors of Type I supernovae. A plausible density distribution for circumstellar gas is rhoinfinityr/sup -2/. The expansion of a supernova into such a medium is examined and is compared with expansion into a uniform medium. The two cases can be distinguished on the basis of their density profiles and their rates of expansion. Currently available data factor the hypothesis of expansion in a uniform medium for all three Type I remnants; the evidence is the strongest for SN 1572 and the weakest for SN 1604. Further X-ray and radio observations of the galactic remnants and of extragalactic Type I supernovae should serve to test this hypothesis.

  15. Archival legacy investigations of circumstellar environments: overview and first results

    NASA Astrophysics Data System (ADS)

    Choquet, Élodie; Pueyo, Laurent; Hagan, J. Brendan; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D.; Debes, John; Golimowski, David; Hines, Dean C.; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian; Soummer, Rémi

    2014-08-01

    We are currently conducting a comprehensive and consistent re-processing of archival HST-NICMOS coronagraphic surveys using advanced PSF subtraction methods, entitled the Archival Legacy Investigations of Circumstellar Environments program (ALICE, HST/AR 12652). This virtual campaign of about 400 targets has already produced numerous new detections of previously unidentified point sources and circumstellar structures. We present five newly spatially resolved debris disks revealed in scattered light by our analysis of the archival data. These images provide new views of material around young solar-type stars at ages corresponding to the period of terrestrial planet formation in our solar system. We have also detected several new candidate substellar companions, for which there are ongoing followup campaigns (HST/WFC3 and VLT/SINFONI in ADI mode). Since the methods developed as part of ALICE are directly applicable to future missions (JWST, AFTA coronagraph) we emphasize the importance of devising optimal PSF subtraction methods for upcoming coronagraphic imaging missions. We describe efforts in defining direct imaging high-level science products (HLSP) standards that can be applicable to other coronagraphic campaigns, including ground-based (e.g., Gemini Planet Imager), and future space instruments (e.g., JWST). ALICE will deliver a first release of HLSPs to the community through the MAST archive at STScI in 2014.

  16. Ultra-compact high velocity clouds in the ALFALFA HI survey: Candidate Local Group galaxies?

    NASA Astrophysics Data System (ADS)

    Adams, Elizabeth Ann Kovenz

    The increased sensitivity and spatial resolution of the ALFALFA HI survey has resulted in the detection of ultra-compact high velocity clouds (UCHVCs). These objects are good candidates to represent low mass gas-rich galaxies in the Local Group and Local Volume with stellar populations that are too faint to be detected in extant optical surveys. This idea is referred to as the "minihalo hypothesis". We identify the UCHVCs within the ALFALFA dataset via the use of a 3D matched filtering signal identification algorithm. UCHVCs are selected based on a compact size (< 30'), separation from Galactic HI (|upsilon LSR| > 120 km s-1) and isolation. Within the 40% complete ALFALFA survey (alpha.40), 59 UCHVCs are identified; 19 are in a most-isolated subset and are the best galaxy candidates. Due to the presence of large HVC complexes in the fall sky, most notably the Magellanic Stream, the association of UCHVCs with existing structure cannot be ruled out. In the spring sky, the spatial and kinematic distribution of the UCHVCs is consistent with simulations of dark matter halos within the Local Group. In addition, the HI properties of the UCHVCs (if placed at 1 Mpc) are consistent with both theoretical and observational predictions for low mass gas-rich galaxies. Importantly, the HI properties of the UCHVCs are consistent with those of two recently discovered low mass gas-rich galaxies in the Local Group and Local Volume, Leo T and Leo P. Detailed follow-up observations are key for addressing the minihalo hypothesis. High resolution HI observations can constrain the environment of a UCHVC and offer evidence for a hosting dark matter halo through evidence of rotation support and comparison to theoretical models. Observations of one UCHVC at high resolution (15'') reveal the presence of a clumpy HI distribution, similar to both low mass galaxies and circumgalactic compact HVCs. An extended envelope containing ˜50% of the HI flux is resolved out by the array configuration

  17. Frictional behavior of talc at seismic slip rates: preliminary results from high-velocity experiments.

    NASA Astrophysics Data System (ADS)

    Boutareaud, S.; Hirose, T.; Doan, M. L.; Andréani, M.; Calugaru, D. G.

    2009-04-01

    Talc is one of the few minerals not following the Byerlee law, its static friction velocity is 0.2-0.25. Talc has been identified in the San Andreas Fault, and is expected to occur within subduction zone. Talc can then affect their seismic behavior. Yet, the details of its frictional properties are poorly known, especially at seismic velocities. Our study aims at understanding its behavior at these velocities. The properties of the talc were studied during high-velocity rotary-shear experiments carried out at from 0.01 m/s to 1.31 m/s, at normal stresses of 0.6 to 1.4 MPa, using the frictional testing apparatus of the JAMSTEC. The experimental gouge is a pure natural talc schist powder (99.9% wt). The samples were test used in dry (i.e. at room moisture conditions) or wet conditions. During experiments, we were able to measure simulated fault thickness evolution, moisture release and to calculate friction coefficient. Even though it is from the start a weak material, talc schist follows a slip weakening law, which appears to depend strongly on the saturation of the sample. Dry samples sliding at speed of 1.31m/s an exponential decrease of friction coefficient from a peak value of 0.98-0.71 to a steady state value between 0.18 and 0.59. This weakening is strongly dependent on normal stress. Dry sample also experienced large gouge dilation. Results from experiments on wet samples are different. The friction peak values of 0.52-0.36 drop to a steady state value between 0.1 and 0.18. Moreover the steady state friction seems to be independent on the applied normal stress. Finally, the wet samples do not experience dilation, but a large release of water steam. This preliminary work suggests two different weakening processes for dry and wet conditions, respectively. To understand the talc friction behavior, we performed studies on talc schist decomposition, in case flash heating would locally alter the talc structure. Differential thermal analysis (DTA) combined to

  18. Electrospray Charging of Minerals: Surface Chemistry and Applications to High-Velocity Microparticle Impacts

    NASA Astrophysics Data System (ADS)

    Daly, T.; Call, S.; Austin, D. E.

    2010-12-01

    charge detector measures the electrosprayed mineral particles’ speed and charge. Quartz microparticles have been successfully electrosprayed. Variation in quartz microparticles’ charge as a function of pH is being evaluated. In addition, we are studying how to completely desolvate electrosprayed mineral particles. Desolvation is not trivial and often requires more than the passive passage of the droplets from the needle to the grounded plate and into vacuum. We are testing two desolvation methods: a heated beam tube and a heated capillary. Preliminary data suggests we have achieved complete desolvation with a hot beam tube. Although quartz’s surface chemistry is rather unique, successful electrospray of quartz microparticles strongly suggests that other minerals may also be electrosprayed. We are preparing olivine samples for electrospray. In addition, an instrument that creates high-velocity microparticle impacts using electrospray-charged mineral microparticles is being developed. This instrument will not only permit minerals to be used as projectiles, but also allows direction characterization of chemical speciation occurring during microparticle impacts.

  19. Long-term carbide development in high-velocity oxygen fuel/high-velocity air fuel Cr3C2-NiCr coatings heat treated at 900 °C

    NASA Astrophysics Data System (ADS)

    Matthews, S.; Hyland, M.; James, B.

    2004-12-01

    During the deposition of Cr3C2-NiCr coatings, compositional degradation occurs, primarily through the dissolution of the carbide phase into the matrix. Exposure at an elevated temperature leads to transformations in the compositional distribution and microstructure. While these have been investigated in short-term trials, no systematic investigations of the long-term microstructural development have been presented for high-velocity sprayed coatings. In this work, high-velocity air fuel (HVAF) and high-velocity oxygen fuel (HVOF) coatings were treated at 900 °C for up to 60 days. Rapid refinement of the supersaturated matrix phase occurred, with the degree of matrix phase alloying continuing to decrease over the following 20 to 40 days. Carbide nucleation in the HVAF coatings occurred preferentially on the retained carbide grains, while that in the HVOF coatings developed in the regions of greatest carbide dissolution. This difference resulted in a variation in carbide morphologies. Preferential horizontal growth was evident in both coatings over the first 20 to 30 days of exposure, beyond which spheroidization of the microstructure occurred. After 30 days, the carbide morphology of both coatings was comparable, tending toward an expansive structure of coalesced carbide grains. The development of the carbide phase played a significant role in the microhardness variation of these coatings with time.

  20. Two Point Space-Time Correlation of Density Fluctuations Measured in High Velocity Free Jets

    NASA Technical Reports Server (NTRS)

    Panda, Jayanta

    2006-01-01

    Two-point space-time correlations of air density fluctuations in unheated, fully-expanded free jets at Mach numbers M(sub j) = 0.95, 1.4, and 1.8 were measured using a Rayleigh scattering based diagnostic technique. The molecular scattered light from two small probe volumes of 1.03 mm length was measured for a completely non-intrusive means of determining the turbulent density fluctuations. The time series of density fluctuations were analyzed to estimate the integral length scale L in a moving frame of reference and the convective Mach number M(sub c) at different narrow Strouhal frequency (St) bands. It was observed that M(sub c) and the normalized moving frame length scale L*St/D, where D is the jet diameter, increased with Strouhal frequency before leveling off at the highest resolved frequency. Significant differences were observed between data obtained from the lip shear layer and the centerline of the jet. The wave number frequency transform of the correlation data demonstrated progressive increase in the radiative part of turbulence fluctuations with increasing jet Mach number.

  1. The η Car Campaign with UVES at the ESO VLT II. Interstellar and circumstellar absorption lines

    NASA Astrophysics Data System (ADS)

    Weis, K.; Bomans, D. J.; Stahl, O.; Davidson, K.; Humphreys, R. M.; Gull, T. R.

    2005-09-01

    We monitored η Car and the Homunculus using the ESO VLT UVES spectrograph between 2002 and 2004 (see Weis et al., this proceedings). In these high dispersion spectra practically all interstellar absorption features known in the 3000 Å to 10000 Å regime are present (e.g. 4 Ti II lines, 3 Fe I lines, the Ca I line, both Na I doublets, the two K I doublets, and the Ca II doublets, several molecular lines, and a number of diffuse interstellar bands). Near-UV STIS spectra show many low ionization absorption lines (e.g. Gull et al., this proceedings), but there are several differences in the velocity structure and line strengths between these lines of sight, e.g. we do not detect multiple absorption components between -350 to -550 km s-1 in the UVES spectra. Changes over time are present in e.g. the Ca II lines, with small column density changes in the (probably interstellar) +80 km s-1 component and large changes in the -510 km s-1 component, which is most probably located in the outer shell of the Homunculus (see e.g. Nielsen et al., this proceedings). Similar changes in the Ti II 3384 Å component at -147 km s-1 are present, too. With the data set, we not only follow the temporal evolution of the circumstellar absorption components (presumably originating near η Car and in the Homunculus) before, during and after the event, but also search for changes along our long-slits centered on the star and on FOS4. Indeed, the -147 km s-1 component of the Ti II 3384 Å lines shows line strength variations over the southeast lobe of the Homunculus. A preliminary search for very high velocity absorption lines from the outer ejected using only one of our spectra already yielded a possible detection at -1500 km s-1. Clearly a detailed analysis of the absorption lines in the UVES data will provide many new insights into the structure and physics of η Car's ejecta.

  2. Searching for the Circumstellar Ejecta Around Cool Hypergiants

    NASA Astrophysics Data System (ADS)

    Schuster, M. T.; Humphreys, R. M.; Marengo, M.; Gehrz, R. D.; Woodward, C. E.; Polomski, E.

    2005-05-01

    We present HST and Spitzer images of several of the most luminous cool stars in the Galaxy. These highly unstable, very massive stars lie on or near the empirical upper luminosity boundary in the H-R diagram, and are characterized by high mass loss phenomena, sometimes violent, which may be responsible for the upper boundary. These observations are designed to search for circumstellar structures close to the star as well as more distant nebulosity. We discuss the presence, or lack of, ejecta around these hypergiants, and the evolutionary implications. Our high-resolution WFPC2 images show compact nebulosity around the cool M-type hypergiants NML Cyg, VX Sgr and S Per. The powerful OH/IR source NML Cyg exhibits a small, peculiar bean-shaped asymmetric nebula that closely matches the distribution of the surrounding H2O vapor masers. NML Cyg's concave outer envelope is likely shaped by photo-dissociation from the powerful, nearby association Cyg OB2 inside the Cygnus X superbubble. VX Sgr and S Per, also OH/IR sources, have marginally resolved envelopes. S Per's circumstellar nebula appears elongated in a NE/SW orientation similar to that for its surrounding OH and H2O masers, while VX Sgr is obscured by a spheroidal envelope. We find no evidence in our WFPC2 images for circumstellar nebulosity around the intermediate-type hypergiants ρ Cas, HR 8752, HR 5171a nor the normal M-type supergiant μ Cep. We conclude that very likely, there has been no high mass loss event prior to 500-1000 yrs ago for these four stars. Our IRAC images (ρ Cas, HR 8752, and R 150) also show no evidence for extended structure. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work is in part provided by NASA through contracts 1256406 and 1215746 issued by JPL/Caltech to the University of Minnesota.

  3. The Three-dimensional Circumstellar Environment of SN 1987A

    NASA Astrophysics Data System (ADS)

    Sugerman, Ben E. K.; Crotts, Arlin P. S.; Kunkel, William E.; Heathcote, Stephen R.; Lawrence, Stephen S.

    2005-07-01

    Surrounding SN 1987A is a three-ring nebula attributed to interacting stellar winds, yet no model has successfully reproduced this system. Fortunately, the progenitor's mass-loss history can be reconstructed using light echoes, in which scattered light from the supernova traces the three-dimensional morphology of its circumstellar dust. In this paper, we construct and analyze the most complete map to date of the progenitor's circumstellar environment, using ground- and space-based imaging from the past 16 years. PSF-matched difference-imaging analyses of data from 1988 through 1997 reveal material between 1 and 28 lt-yr from the SN. Previously known structures, such as an inner hourglass, Napoleon's Hat, and a contact discontinuity, are probed in greater spatial detail than before. Previously unknown features are also discovered, such as a southern counterpart to Napoleon's Hat. Careful analyses of these echoes allows the reconstruction of the probable circumstellar environment, revealing a richly structured bipolar nebula. An outer, double-lobed ``Peanut,'' which is believed to be the contact discontinuity between red supergiant and main-sequence winds, is a prolate shell extending 28 lt-yr along the poles and 11 lt-yr near the equator. Napoleon's Hat, previously believed to be an independent structure, is the waist of this Peanut, which is pinched to a radius of 6 lt-yr. Interior to this is a cylindrical hourglass, 1 lt-yr in radius and 4 lt-yr long, which connects to the Peanut by a thick equatorial disk. The nebulae are inclined 41° south and 8° east of the line of sight, slightly elliptical in cross section, and marginally offset west of the SN. From the hourglass to the large, bipolar lobes, echo fluxes suggest that the gas density drops from 1-3 to >~0.03 cm-3, while the maximum dust-grain size increases from ~0.2 to 2 μm, and the silicate:carbonaceous dust ratio decreases. The nebulae have a total mass of ~1.7 Msolar. The geometry of the three rings is

  4. Microstructural and Tribological Investigation of High-Velocity Suspension Flame Sprayed (HVSFS) Al2O3 Coatings

    NASA Astrophysics Data System (ADS)

    Bolelli, Giovanni; Rauch, Johannes; Cannillo, Valeria; Killinger, Andreas; Lusvarghi, Luca; Gadow, Rainer

    2009-03-01

    Al2O3 coatings were manufactured by the high-velocity suspension flame spraying (HVSFS) technique using a nanopowder suspension. Their structural and microstructural characteristics, micromechanical behavior, and tribological properties were studied and compared to conventional atmospheric plasma sprayed and high-velocity oxygen-fuel-sprayed Al2O3 coatings manufactured using commercially available feedstock. The HVSFS process enables near full melting of the nanopowder particles, resulting in very small and well flattened lamellae (thickness range 100 nm to 1 μm), almost free of transverse microcracking, with very few unmelted inclusions. Thus, porosity is much lower and pores are smaller than in conventional coatings. Moreover, few interlamellar or intralamellar cracks exist, resulting in reduced pore interconnectivity (evaluated by electrochemical impedance spectroscopy). Such strong interlamellar cohesion favors much better dry sliding wear resistance at room temperature and at 400 °C.

  5. Effects of pulsed, high-velocity water flow on larval robust redhorse and V-lip redhorse

    USGS Publications Warehouse

    Weyers, R.S.; Jennings, C.A.; Freeman, Mary C.

    2003-01-01

    The pulsed, high-velocity water flow characteristic of water-flow patterns downstream from hydropower-generating dams has been implicated in the declining abundance of both aquatic insects and fishes in dam-regulated rivers. This study examined the effects of 0, 4, and 12 h per day of pulsed, high-velocity water flow on the egg mortality, hatch length, final length, and survival of larval robust redhorse Moxostoma robusturn, a presumedly extinct species that was rediscovered in the 1990s, and V-lip redhorse M. collapsum (previously synonomized with the silver redhorse M. anisurum) over a 3-5 week period in three separate experiments. Twelve 38.0-L aquaria (four per treatment) were modified to simulate pulsed, high-velocity water flow (>35 cm/s) and stable, low-velocity water flow (<10 cm/s). Temperature, dissolved oxygen, zooplankton density, and water quality variables were kept the same across treatments. Fertilized eggs were placed in gravel nests in each aquarium. Hatch success was estimated visually at greater than 90%, and the mean larval length at 24 h posthatch was similar in each experiment. After emergence from the gravel nest, larvae exposed to 4 and 12 h of pulsed, high-velocity water flow grew significantly more slowly and had lower survival than those in the 0-h treatment. These results demonstrate that the altered water-flow patterns that typically occur when water is released during hydropower generation can have negative effects on the growth and survival of larval catostomid suckers.

  6. Study of maghemite nanoparticles as prepared and coated with DMSA using Mössbauer spectroscopy with a high velocity resolution

    NASA Astrophysics Data System (ADS)

    Oshtrakh, M. I.; Ushakov, M. V.; Semionkin, V. A.; Lima, E. C. D.; Morais, P. C.

    2014-04-01

    Study of maghemite nanoparticles, native and coated with DMSA as magnetic fluid for biomedical applications, was carried out using Mössbauer spectroscopy with a high velocity resolution at 295 and 90 K. The obtained results demonstrated differences in Mössbauer hyperfine parameters for uncoated and DMSA-coated nanoparticles which were related to the interactions of DMSA molecules with Fe3+ ions on maghemite nanoparticle's surface.

  7. A Case Report of Spinal Cord Injury Patient From a High Velocity Gunshot Wound to the Lumbar Spine

    PubMed Central

    Kim, Juyong; Kim, Je Ho

    2013-01-01

    We report on operational and rehabilitation management, as well as the outcome, of a patient who with sustained spinal cord injury from a high velocity gunshot wound to the lumbar spine. More specifically, a patient with a gunshot wound to the spine is more likely to sustain a complete injury and have a poor prognosis. As such, there should be concerns regarding associated and extended injuries related to bullet fragmentation as well as the possibility of long-term sequelae. PMID:23526072

  8. Phase contrast ultrashort TE: A more reliable technique for measurement of high-velocity turbulent stenotic jets.

    PubMed

    O'Brien, Kieran R; Myerson, Saul G; Cowan, Brett R; Young, Alistair A; Robson, Matthew D

    2009-09-01

    Accurate measurement of peak velocity is critical to the assessment of patients with stenotic valvular disease. Conventional phase contrast (PC) methods for imaging high-velocity jets in aortic stenosis are susceptible to intravoxel dephasing signal loss, which can result in unreliable measurements. The most effective method for reducing intravoxel dephasing is to shorten the echo time (TE); however, the amount that TE can be shortened in conventional sequences is limited. A new sequence incorporating velocity-dependent slice excitation and ultrashort TE (UTE) centric radial readout trajectories is proposed that reduces TE from 2.85 to 0.65 ms. In a high-velocity stenotic jet phantom, a conventional sequence had >5% flow error at a flow rate of only 400 mL/s (velocity >358 cm/s), whereas the PC-UTE showed excellent agreement (<5% error) at much higher flow rates (1080 mL/s, 965 cm/s). In vivo feasibility studies demonstrated that by measuring velocity over a shorter time the PC-UTE approach is more robust to intravoxel dephasing signal loss. It also has less inherent higher-order motion encoding. This sequence therefore demonstrates potential as a more robust method for measuring peak velocity and flow in high-velocity turbulent stenotic jets.

  9. THE HIGH-VELOCITY MOLECULAR OUTFLOWS IN MASSIVE CLUSTER-FORMING REGION G10.6-0.4

    SciTech Connect

    Liu Hauyu Baobab; Ho, Paul T. P.; Zhang Qizhou E-mail: pho@asiaa.sinica.edu.t

    2010-12-20

    We report the arcsecond resolution Submillimeter Array observations of the {sup 12}CO (2-1) transition in the massive cluster-forming region G10.6-0.4. In these observations, the high-velocity {sup 12}CO emission is resolved into individual outflow systems, which have a typical size scale of a few arcseconds. These molecular outflows are energetic and are interacting with the ambient molecular gas. By inspecting the shock signatures traced by CH{sub 3}OH, SiO, and HCN emissions, we suggest that abundant star formation activities are distributed over the entire 0.5 pc scale dense molecular envelope. The star formation efficiency over one global free-fall timescale (of the 0.5 pc molecular envelope, {approx}10{sup 5} years) is about a few percent. The total energy feedback of these high-velocity outflows is higher than 10{sup 47} erg, which is comparable to the total kinetic energy in the rotational motion of the dense molecular envelope. From order-of-magnitude estimations, we suggest that the energy injected from the protostellar outflows is capable of balancing the turbulent energy dissipation. No high-velocity bipolar molecular outflow associated with the central OB cluster is directly detected, which can be due to the photoionization.

  10. The High-velocity Molecular Outflows in Massive Cluster-forming Region G10.6-0.4

    NASA Astrophysics Data System (ADS)

    Liu, Hauyu Baobab; Ho, Paul T. P.; Zhang, Qizhou

    2010-12-01

    We report the arcsecond resolution Submillimeter Array observations of the 12CO (2-1) transition in the massive cluster-forming region G10.6-0.4. In these observations, the high-velocity 12CO emission is resolved into individual outflow systems, which have a typical size scale of a few arcseconds. These molecular outflows are energetic and are interacting with the ambient molecular gas. By inspecting the shock signatures traced by CH3OH, SiO, and HCN emissions, we suggest that abundant star formation activities are distributed over the entire 0.5 pc scale dense molecular envelope. The star formation efficiency over one global free-fall timescale (of the 0.5 pc molecular envelope, ~105 years) is about a few percent. The total energy feedback of these high-velocity outflows is higher than 1047 erg, which is comparable to the total kinetic energy in the rotational motion of the dense molecular envelope. From order-of-magnitude estimations, we suggest that the energy injected from the protostellar outflows is capable of balancing the turbulent energy dissipation. No high-velocity bipolar molecular outflow associated with the central OB cluster is directly detected, which can be due to the photoionization.

  11. EVIDENCE OF HOT HIGH VELOCITY PHOTOIONIZED PLASMA FALLING ON ACTIVELY ACCRETING T TAURI STARS

    SciTech Connect

    Gómez de Castro, Ana Ines

    2013-10-01

    The He II (1640 Å) line and the resonance doublet of N V (UV1) provide a good diagnostic tool to constrain the excitation mechanism of hot (T{sub e} > 40,000 K) atmospheric/magnetospheric plasmas in T Tauri stars (TTSs). Making use of the data available in the Hubble Space Telescope archive, this work shows that there are at least two distinct physical components contributing to the radiation in these tracers: the accretion flow sliding on the magnetosphere and the atmosphere. The N V profiles in most sources are symmetric and at rest with respect to the star. The velocity dispersion of the profile increases from non-accreting (σ = 40 km s{sup –1}) to accreting (σ = 120 km s{sup –1}) TTSs, suggesting that the macroturbulence field in the line formation region decreases as the stars approach the main sequence. Evidence of the N V line being formed in a hot solar-like wind has been found in RW Aur, HN Tau, and AA Tau. The He II profile has a strong narrow component that dominates the line flux; the dispersion of this component ranges from 20 to 60 km s{sup –1}. Current data suggest that both accretion shocks and atmospheric emission might contribute to the line flux. In some sources, the He II line shows a broad and redward-shifted emission component often accompanied by semiforbidden O III] emission that has a critical electron density of ∼3.4 × 10{sup 10} cm{sup 3}. In spite of their different origins (inferred from the kinematics of the line formation region), N V and He II fluxes are strongly correlated, with only the possible exception of some of the heaviest accretors.

  12. Circumstellar debris and pollution at white dwarf stars

    NASA Astrophysics Data System (ADS)

    Farihi, J.

    2016-04-01

    Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

  13. Astrobiological Effects of Stellar Radiation in Circumstellar Environments

    NASA Astrophysics Data System (ADS)

    Cuntz, Manfred; Gurdemir, Levent; Guinan, Edward F.; Kurucz, Robert L.

    2006-10-01

    The centerpiece of all life on Earth is carbon-based biochemistry. Previous scientific research has suggested that biochemistry based on carbon may also play a decisive role in extraterrestrial life forms, i.e., alien life outside of Earth, if existent. In the following, we explore if carbon-based macromolecules (such as DNA) in the environments of stars other than the Sun are able to survive the effects of energetic stellar radiation, such as UV-C in the wavelength band between 200 and 290 nm. We focus on main-sequence stars akin to the Sun, but of hotter (F-type stars) and cooler (K- and M-type stars) surface temperature. Emphasis is placed on investigating the radiative environment in stellar habitable zones (HZs). Stellar habitable zones have an important relevance in astrobiology because they constitute circumstellar regions in which a planet of suitable size can have surface temperatures for water to exist in liquid form.

  14. PAH formation in carbon-rich circumstellar envelopes

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.; Frenklach, Michael

    1989-01-01

    While there is growing observational evidence that some fraction of interstellar carbon is in polycyclic aromatic hydrocarbons (PAH's), the mechanisms by which these molecules might be formed have not been extensively studied. A detailed investigation of PAH production in the outflowing molecular envelopes of carbon-rich red giant star is presented. The gasphase kinetics of a chemical reaction mechanism developed to study soot production in hydrocarbon flames is modified to apply in circumstellar environments. It was found that astrophysically significant quantities of PAH's can be formed in carbon star envelopes provided the gas is sufficiently dense and resides for a long time in the temperature range of 900 to 1100 k. The precise yield of PAH's is very sensitive to astronomical parameters of the envelope (e.g., mass loss rate, outflow velocity, and acetylene abundance) and certain poorly determined chemical reaction rates.

  15. Flash Heating of Circumstellar Clouds by Gamma-Ray Bursts.

    PubMed

    Dermer; Böttcher

    2000-05-10

    The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV. Low-energy photons that subsequently pass through the hot plasma will be scattered to higher energies, hardening the intrinsic spectrum. This effect resolves the "line-of-death" objection to the synchrotron shock model. Illuminated clouds near GRBs will form relativistic plasmas containing large numbers of electron-positron pairs that can be detected within approximately 1-2 days of the explosion before expanding and dissipating. Localized regions of pair annihilation radiation in the Galaxy would reveal past GRB explosions.

  16. Circumstellar envelope manifestations in the optical spectra of evolved stars

    NASA Astrophysics Data System (ADS)

    Klochkova, V. G.

    2014-07-01

    We analyze the peculiarities of the optical spectra of luminous stars with circumstellar gas and dust envelopes: the time variability of the absorption-emission profiles of the H α line, the presence of stationary emission and absorption molecular bands, multicomponent absorption-emission profiles of the Na I D doublet lines. We show that the peculiarities of the line profiles (the presence of an emission component in the Na I D doublet lines, the specific type of the molecular features, the asymmetry and splitting of the profiles of strong absorption features with low excitation potential of the low level) can be associated with the kinematic and chemical properties of the envelope and its morphological type.

  17. Molecular anion chemistry in interstellar and circumstellar environments

    NASA Astrophysics Data System (ADS)

    Cordiner, M. A.; Millar, T. J.; Herbst, E.; Chuimin, R. Ni; Walsh, C.

    2007-12-01

    The recent detection of C4H-, C6H- and C8H- in TMC-1 and IRC+10216 led us to investigate the synthesis of hydrocarbon anions in a variety of interstellar and circumstellar environments. We find that the anion/neutral abundance ratio can be quite large, on the order of at least a few percent, once the neutral has more than five carbon atoms. Detailed modeling shows that the column densities of C6H- observed in IRC+10216 and TMC-1 can be reproduced. Our calculations also predict that hydrocarbon anions CnH- (for n = 4, 6, 8) are viable candidates for detection in photon-dominated regions such as the Horsehead Nebula and the Orion Bar.

  18. Hydrocarbon Anions in Interstellar Clouds and Circumstellar Envelopes

    NASA Astrophysics Data System (ADS)

    Millar, T. J.; Walsh, C.; Cordiner, M. A.; Ní Chuimín, R.; Herbst, Eric

    2007-06-01

    The recent detection of the hydrocarbon anion C6H- in the interstellar medium has led us to investigate the synthesis of hydrocarbon anions in a variety of interstellar and circumstellar environments. We find that the anion/neutral abundance ratio can be quite large, on the order of at least a few percent, once the neutral has more than five carbon atoms. Detailed modeling shows that the column densities of C6H- observed in IRC +10 216 and TMC-1 can be reproduced. Our calculations also predict that other hydrocarbon anions, such as C4H- and C8H-, are viable candidates for detection in IRC +10 216, TMC-1, and photon-dominated regions such as the Horsehead Nebula.

  19. Archival Legacy Investigation of Circumstellar Environments (ALICE). Survey results

    NASA Astrophysics Data System (ADS)

    Soummer, Remi; Choquet, Elodie; Pueyo, Laurent; Brendan Hagan, J.; Gofas-Salas, Elena; Rajan, Abhijith; Chen, Christine; Perrin, Marshall D.; Debes, John H.; Golimowski, David A.; Hines, Dean C.; N'Diaye, Mamadou; Schneider, Glenn; Mawet, Dimitri; Marois, Christian

    2016-01-01

    We report on the status of the ALICE project (Archival Legacy Investigation of Circumstellar Environments. HST/AR-12652), which consists in a consistent reanalysis of the entire HST-NICMOS coronagraphic archive with advanced post-processing techniques. Over the last two years, we have developed a sophisticated pipeline able to handle the data of the 400 stars of the archive. We present the results of the overall reduction campaign and discuss the first statistical analysis of the candidate detections. As we will deliver high-level science products to the STScI MAST archive, we are defining a new standard format for high-contrast science products, which will be compatible with every new high-contrast imaging instrument and used by the JWST coronagraphs. We present here an update and overview of the specifications of this standard.

  20. The Circumstellar Disk of HD 141569 Imaged with NICMOS.

    PubMed

    Weinberger; Becklin; Schneider; Smith; Lowrance; Silverstone; Zuckerman; Terrile

    1999-11-01

    Coronagraphic imaging with the Near-Infrared Camera and Multiobject Spectrometer on the Hubble Space Telescope reveals a large, approximately 400 AU (4&arcsec;) radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected light image at 1.1 µm shows the disk oriented at a position angle of 356&j0;+/-5&j0; and inclined to our line of sight by 51&j0;+/-3&j0;; the intrinsic scattering function of the dust in the disk makes the side inclined toward us, the eastern side, brighter. The disk flux density peaks 185 AU (1&farcs;85) from the star and falls off to both larger and smaller radii. A region of depleted material, or a gap, in the disk is centered 250 AU from the star. The dynamical effect of one or more planets may be necessary to explain this morphology. PMID:10511512

  1. Polarimetric Models of Circumstellar Discs Including Aggregate Dust Grains

    NASA Astrophysics Data System (ADS)

    Mohan, Mahesh

    The work conducted in this thesis examines the nature of circumstellar discs by investigating irradiance and polarization of scattered light. Two circumstellar discs are investigated. Firstly, H-band high contrast imaging data on the transitional disc of the Herbig Ae/Be star HD169142 are presented. The images were obtained through the polarimetric differential imaging (PDI) technique on the Very Large Telescope (VLT) using the adaptive optics system NACO. Our observations use longer exposure times, allowing us to examine the edges of the disc. Analysis of the observations shows distinct signs of polarization due to circumstellar material, but due to excessive saturation and adaptive optics errors further information on the disc could not be inferred. The HD169142 disc is then modelled using the 3D radiative transfer code Hyperion. Initial models were constructed using a two disc structure, however recent PDI has shown the existence of an annular gap. In addition to this the annular gap is found not to be devoid of dust. This then led to the construction of a four-component disc structure. Estimates of the mass of dust in the gap (2.10E-6 Msun) are made as well as for the planet (1.53E-5 Msun (0.016 Mjupiter)) suspected to be responsible for causing the gap. The predicted polarization was also estimated for the disc, peaking at ~14 percent. The use of realistic dust grains (ballistic aggregate particles) in Monte Carlo code is also examined. The fortran code DDSCAT is used to calculate the scattering properties for aggregates which are used to replace the spherical grain models used by the radiative transfer code Hyperion. Currently, Hyperion uses four independent elements to define the scattering matrix, therefore the use of rotational averaging and a 50/50 percent population of grains and their enantiomers were explored to reduce the number of contributing scattering elements from DDSCAT. A python script was created to extract the scattering data from the DDSCAT

  2. The circumstellar environments of intermediate mass main sequence stars

    NASA Technical Reports Server (NTRS)

    Grady, Carol A.

    1993-01-01

    Analysis of archival Infrared Astronomy Satellite (IRAS) and International Ultraviolet Explorer (IUE) data resulted in identification of accreting gas toward a 2.8 Myr post-Herbig Be star in the R CrA star formation region, and identification of accreting gas toward HD 93563, previously identified as a classical Be star. Accreting gas was also detected toward two B(e) stars of previously controversial evolutionary state, resulting in identification of these systems as pre-Main Sequence Herbig Be stars viewed edge-on to their circumstellar disks. In parallel with this effort, accreting gas was detected toward the Herbig Ae star HR 5999, resulting in development of identification criteria for edge-on PMS proto-planetary disk systems. The work on individual stars is described.

  3. Warm Circumstellar Debris Disks: Dynamical Excitation by Massive External Perturbers?

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika; Naoz, Smadar; Vican, Laura; Vican, Laura; Zuckerman, Ben M.; Holmbeck, Erika

    2016-01-01

    Observations of circumstellar debris disks have revealed that a subset of this population are warm disks (~300 K). A dynamically excited disk may indicate the presence of an exoplanet orbiting within and stirring the disk. However, observations suggest another possible mechanism for heating a debris disk: an external stellar-mass perturber exciting the eccentricities and inclinations of the particles in a disk.We explore the consequences of an external perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. The perturber excites the eccentricities of the particles in the disk via the Kozai-Lidov mechanism, triggering a collisional cascade among the planetesimals. These collisions produce smaller dust grains and damp the particles' larger eccentricities.We present the results of our study and discuss the connections to observations of warm disks and the implications for planet formation.

  4. TIDALLY INDUCED BROWN DWARF AND PLANET FORMATION IN CIRCUMSTELLAR DISKS

    SciTech Connect

    Thies, Ingo; Kroupa, Pavel; Goodwin, Simon P.; Stamatellos, Dimitrios; Whitworth, Anthony P.

    2010-07-01

    Most stars are born in clusters and the resulting gravitational interactions between cluster members may significantly affect the evolution of circumstellar disks and therefore the formation of planets and brown dwarfs (BDs). Recent findings suggest that tidal perturbations of typical circumstellar disks due to close encounters may inhibit rather than trigger disk fragmentation and so would seem to rule out planet formation by external tidal stimuli. However, the disk models in these calculations were restricted to disk radii of 40 AU and disk masses below 0.1 M{sub sun}. Here, we show that even modest encounters can trigger fragmentation around 100 AU in the sorts of massive ({approx}0.5 M{sub sun}), extended ({>=}100 AU) disks that are observed around young stars. Tidal perturbation alone can do this; no disk-disk collision is required. We also show that very low mass binary systems can form through the interaction of objects in the disk. In our computations, otherwise non-fragmenting massive disks, once perturbed, fragment into several objects between about 0.01 and 0.1 M{sub sun}, i.e., over the whole BD mass range. Typically, these orbit on highly eccentric orbits or are even ejected. While probably not suitable for the formation of Jupiter- or Neptune-type planets, our scenario provides a possible formation mechanism for BDs and very massive planets which, interestingly, leads to a mass distribution consistent with the canonical substellar initial mass function. As a minor outcome, a possible explanation for the origin of misaligned extrasolar planetary systems is discussed.

  5. Beta Pic-like Circumstellar Gas Disk Around 2 And

    NASA Technical Reports Server (NTRS)

    Cheng, Patricia

    2003-01-01

    This grant was awarded to support the data analysis and publication of results from our project entitled P Pic-like Circumstellar Gas Disk Around 2 And . We proposed to obtain FUSE observations of 2 And and study the characteristics and origin of its circumstellar gas. We observed 2 Andromedae with FUSE on 3-4 July 2001 in 11 exposures with a total exposure time of 21,289 seconds through the LWRS aperture. Our data were calibrated with Version 1.8.7 of the CALFUSE pipeline processing software. We corrected the wavelength scale for the heliocentric velocity error in this version of the CALFUSE software. The relative accuracy of the calibrated wavelength scale is +/- 9 km/s . We produced a co-added spectrum in the LiF 1B and LiF 2A channels (covering the 1100 to 1180 A region) by cross-correlating the 11 individual exposures and doing an exposure-time weighted average flux. The final co-added spectra have a signal-to-noise ratio in the stellar continuum near 1150 A of about 20. To obtain an absolute wavelength calibration, we cross-correlated our observed spectra with a model spectrum to obtain the best fit for the photospheric C I lines. Because the photospheric lines are very broad, this yields an absolute accuracy for the wavelength scale of approx.+/- 15 km/s. We then rebinned 5 original pixels to yield the optimal sampling of .033 A for each new pixel, because the calibrated spectra oversample the spectral resolution for FUSE+LWRS (R = 20,000 +/- 2,000).

  6. AKARI INFRARED OBSERVATIONS OF THE SUPERNOVA REMNANT G292.0+1.8: UNVEILING CIRCUMSTELLAR MEDIUM AND SUPERNOVA EJECTA

    SciTech Connect

    Lee, Ho-Gyu; Sakon, Itsuki; Onaka, Takashi; Koo, Bon-Chul; Moon, Dae-Sik; Jeong, Woong-Seob; Kaneda, Hidehiro; Nozawa, Takaya; Kozasa, Takashi E-mail: isakon@astron.s.u-tokyo.ac.j E-mail: koo@astrohi.snu.ac.k E-mail: jeongws@kasi.re.k E-mail: tnozawa@mail.sci.hokudai.ac.j

    2009-11-20

    We present the results of AKARI observations of the O-rich supernova remnant (SNR) G292.0+1.8 using six Infrared Camera (IRC) and four Far-Infrared Surveyor bands covering 2.7-26.5 mum and 50-180 mum, respectively. The AKARI images show two prominent structures; a bright equatorial ring (ER) structure along the east-west direction and an outer elliptical shell structure surrounding the remnant. The ER structure is clumpy and incomplete with its western end opened. The outer shell is almost complete and slightly squeezed along the north-south direction. The central position of the outer shell is approx1' northwest from the embedded pulsar and coincides with the center of the ER structure. In the northern and southwestern regions, there is also faint emission with a sharp boundary beyond the bright shell structure. The ER and the elliptical shell structures were partly visible in optical and/or X-rays, but they are much more clearly revealed in our AKARI images. There is no evident difference in infrared colors of the two prominent structures, which is consistent with the previous proposition that both structures are of circumstellar origin. However, we have detected faint infrared emission of a considerably high 15/24 mum ratio associated with the supernova (SN) ejecta in the southeastern and northwestern areas. Our IRC spectra show that the high ratio is at least partly due to the emission lines from Ne ions in the SN ejecta material. In addition, we detect a narrow, elongated feature outside the SNR shell. We derive the physical parameters of the infrared-emitting dust grains in the shocked circumstellar medium (CSM) and compare the result with model calculations of dust destruction by an SN shock. The AKARI results suggest that the progenitor was at the center of the infrared circumstellar shell in the red supergiant stage and that the observed asymmetry in the SN ejecta could be a result of either a dense CSM in the equatorial plane and/or an asymmetric

  7. Early Experience & Multisensory Perceptual Narrowing

    PubMed Central

    Lewkowicz, David J.

    2014-01-01

    Perceptual narrowing is a reflection of early experience and contributes in key ways to perceptual and cognitive development. In general, findings have shown that unisensory perceptual sensitivity in early infancy is broadly tuned such that young infants respond to, and discriminate, native as well as non-native sensory inputs, whereas older infants only respond to native inputs. Recently, my colleagues and I discovered that perceptual narrowing occurs at the multisensory processing level as well. The present article reviews this new evidence and puts it in the larger context of multisensory perceptual development and the role that perceptual experience plays in it. Together, the evidence on unisensory and multisensory narrowing shows that early experience shapes the emergence of perceptual specialization and expertise. PMID:24435505

  8. Polarimetry with the Gemini Planet Imager. Methods, performance at first light, and the circumstellar ring around HR 4796A

    DOE PAGESBeta

    Perrin, Marshall D.; Duchene, Gaspard; Millar-Blanchaer, Max; Fitzgerald, Michael P.; Graham, James R.; Wiktorowicz, Sloane J.; Kalas, Paul G.; Macintosh, Bruce; Bauman, Brian; Cardwell, Andrew; et al

    2015-01-28

    We report he first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI’s advanced adaptive optics system reveals the disk clearly evenmore » prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side ≳9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. In conclusion, these findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn’s F ring.« less

  9. Narrow rings - Observations and theory

    NASA Astrophysics Data System (ADS)

    Porco, C. C.

    Voyager 1 and 2 observations have revealed that within the rings of Saturn lies a set of narrow, eccentric rings resembling those of Uranus. Voyager 2 observations have proven crucial in refining the Uranian ring orbit models to a remarkable level of precision. All these rings share some common structural and kinematical characteristics, such as spatially variable radial widths and uniform precession; however, interesting differences exist which provoke attention and may be related to the differing dynamical environments in which these rings dwell. The current state of the knowledge of the shape, behavior, and confinement of narrow rings is discussed.

  10. Bursting SN 1996cr's bubble: hydrodynamic and X-ray modelling of its circumstellar medium

    NASA Astrophysics Data System (ADS)

    Dwarkadas, V. V.; Dewey, D.; Bauer, F.

    2010-09-01

    SN1996cr is one of the five closest supernovae (SNe) to explode in the past 30 yr. Due to its fortuitous location in the Circinus galaxy at ~3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485-ks Chandra high-energy transmission grating spectrum. In order to interpret these data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at four epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium (CSM), the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium before interacting with a dense shell of material about 0.03 pc away from the progenitor star. We speculate that the shell could be due to the interaction of a blue supergiant or Wolf-Rayet wind with a previously existing red supergiant (RSG) wind. The shock wave has now exited the shell and is expanding in the medium exterior to it, possibly the undisturbed continuation of the dense RSG wind. The narrow lines that earned SN 1996cr its IIn designation possibly arise from dense, shocked clumps in the CSM. Although the possibility for a luminous blue variable progenitor for this Type IIn SN cannot be completely excluded, it is inconsistent with much of the data. These calculations allow us to probe the stellar mass-loss in the very last phases (<104 yr) of a massive star's life (>106 yr), and provide another means to deducing the progenitor of the SN.

  11. An Optical Study of the Circumstellar Environment Around the Crab Nebula

    NASA Technical Reports Server (NTRS)

    Fesen, Robert A.; Shull, J. Michael; Hurford, Alan P.

    1997-01-01

    Long-slit spectra of two peripheral regions around the Crab Nebula show no H(alpha) emission down to a flux level of 1.5 x 10(exp -7)erg/sq cm s sr (0.63 Rayleigh), corresponding to an emission measure limit of 4.2 cm(sup - 6) pc (3(sigma)) assuming A(sub V)= 1.6(sup m) and T(sub e)=7000 K. This is below the flux levels reported by Murdin & Clark (Nature, 294, 543 (198 1)) for an H(alpha) halo around the Crab. Narrow H(beta) emission as described by Murdin (MNRAS, 269, 89 (1994)) is detected but appears to be Galactic emission unassociated with the remnant. A review of prior searches indicates no convincing observational evidence to support either a high- or low-velocity envelope around the remnant. Spectral scans confirm a well-organized, N-S expansion asymmetry of the filaments with a approx. 500 km/s central velocity constriction as described by MacAlpine et al. (ApJ, 342, 364 (1989)) and Lawrence et (it. (AJ, 109, 2635 (1995)] but questioned by Hester et al. (ApJ, 448, 240 (1995)). The velocity pinching appears to coincide with an cast-west chain of bright [O III] and helium-rich filaments. This expansion asymmetry might be the result of ejecta interaction with a disk of circumstellar matter, but such a model may be inconsistent with H and He filament abundances in the velocity constriction zone. A re-analysis of the remnant's total mass suggests that the filaments contain 4.6 +/- 1.8 M(solar) in ionized and neutral cas, about twice that of earlier estimates. For a 10M(solar) progenitor, this suggests that approx.equals 4M(solar) remains to be detected in an extended halo or wind.

  12. FIRST DETECTION OF NEAR-INFRARED LINE EMISSION FROM ORGANICS IN YOUNG CIRCUMSTELLAR DISKS

    SciTech Connect

    Mandell, Avi M.; Mumma, Michael J.; Villanueva, Geronimo; Bast, Jeanette; Van Dishoeck, Ewine F.; Blake, Geoffrey A.; Salyk, Colette

    2012-03-10

    We present an analysis of high-resolution spectroscopy of several bright T Tauri stars using the CRIRES spectrograph on the Very Large Telescope and NIRSPEC spectrograph on the Keck Telescope, revealing the first detections of emission from HCN and C{sub 2}H{sub 2} in circumstellar disks at near-infrared wavelengths. Using advanced data reduction techniques, we achieve a dynamic range with respect to the disk continuum of {approx}500 at 3 {mu}m, revealing multiple emission features of H{sub 2}O, OH, HCN, and C{sub 2}H{sub 2}. We also present stringent upper limits for two other molecules thought to be abundant in the inner disk, CH{sub 4} and NH{sub 3}. Line profiles for the different detected molecules are broad but centrally peaked in most cases, even for disks with previously determined inclinations of greater than 20 Degree-Sign , suggesting that the emission has both a Keplerian and non-Keplerian component as observed previously for CO emission. We apply two different modeling strategies to constrain the molecular abundances and temperatures: we use a simplified single-temperature local thermal equilibrium (LTE) slab model with a Gaussian line profile to make line identifications and determine a best-fit temperature and initial abundance ratios, and we compare these values with constraints derived from a detailed disk radiative transfer model assuming LTE excitation but utilizing a realistic temperature and density structure. Abundance ratios from both sets of models are consistent with each other and consistent with expected values from theoretical chemical models, and analysis of the line shapes suggests that the molecular emission originates from within a narrow region in the inner disk (R < 1 AU).

  13. X-rays from High-Velocity Clouds: XMM-Newton Observations of MS30.7-81.4-118

    NASA Astrophysics Data System (ADS)

    Shelton, Robin

    Recently, XMM-Newton and Chandra observations have shown evidence of enhanced X- ray emission associated with compact high-velocity clouds (HVCs). While the Chandra detections are of low significance, XMM-Newton observed a 6.4sigma X-ray enhancement associated with the HVC MS30.7-81.4-118 (hereafter, MS30.7), which is part of the Magellanic Stream. As there is currently only one detection of X-rays from a compact HVC with any great significance, it is important to confirm that this enhancement is real, and not due to some transient event. If it is real, then X-ray enhancements associated with HVCs potentially provide a new way to study HVCs and their interaction with the Galaxy. Both the morphology and the spectrum of the emission provide clues to the mechanism that produces the hot X-ray-emitting gas, as different physical processes predict different morphologies and spectral properties. For example, shock-heating of the ambient gas leads to X-ray emission in front the HVC, while mixing of the cool cloud material with hot ambient material leads to enhanced emission behind the cloud. (Note that in the case of MS30.7, we know its likely direction of motion on the sky, as it is likely moving toward the Magellanic Clouds.) On the spectral side, different physical processes lead to different temperatures for the X-ray-emitting gas. Strong adiabatic shocks with speeds of 300-400 km/s (the speed of the Magellanic Stream) will yield temperatures of ~1e6-2e6 K. Slower and/or radiative shocks will yield lower temperatures, while magnetic reconnection is predicted to lead to temperatures of >~ 6e6 K. Furthermore, spectral models generated from hydrodynamical simulations, such as those carried out by our group, can be used to narrow down the region of parameter space relevant to the X-ray enhancement. In the most recent XMM-Newton proposal round (AO-10), we were awarded a second observation of MS30.7 (PI: Shelton), to the east of the existing observation. We are applying for

  14. PAHs in circumstellar disks around T Tauri stars

    NASA Astrophysics Data System (ADS)

    Geers, Vincent C.; Augereau, Jean-Charles; Pontoppidan, Klaus M.; Dullemond, Cornelis P.; Visser, Ruud; van Dishoeck, Ewine F.; C2d Irs Team

    We have begun to investigate the emission from Polycyclic Aromatic Hydrocarbons seen toward circumstellar disks around young low mass pre-main-sequence (T Tauri) stars, observed as part of our Spitzer Legacy program "From Molecular Cores to Planet-Forming Disks" (Evans et al. 2003). In this poster we will present some of our first Spitzer spectra of PAH features in T Tauri stars and discuss these features in the context of the disk structure and the UV radiation field needed to excite the PAH molecules. Laboratory measurements show that PAH molecules are strongly heated/excited when they absorb a single UV photon, and that they re-radiate the energy through C-H and C-C stretch and C-H bending mode transitions, in the form of infrared photons. These give rise to characteristic PAH features at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.8 microns. These emission features have now been observed toward about 60% of intermediate mass Herbig Ae/Be stars with the ISO satellite (Acke & van den Ancker 2004) and for a few of these sources, ground-based spatially resolved spectroscopy has confirmed that the emission originates from the inner ~100-150 AU region around the star (Geers et al. 2004, van Boekel et al. 2004, Habart et al. 2004), so typically on the scale of circumstellar disks. Our investigation of PAHs in disks around young stars takes two approaches. On the one hand, we address the question how the PAH abundance evolves in these disks during this period of planet formation and how their presence can have an impact on the circumstellar environment. The observed PAH emission is believed to originate from the surface layers of the disk, where the large molecules / small grains are mixed with the gas. The high opacity of PAHs to FUV radiation can significantly reduce the stellar UV field in the inner parts of the disk, while at the same time, through the photo-electric effect, PAHs can provide an important heating mechanism for the gas in the surrounding environment through

  15. PAHs in circumstellar disks around T Tauri stars

    NASA Astrophysics Data System (ADS)

    Geers, Vincent C.; Augereau, Jean-Charles; Pontoppidan, Klaus M.; Dullemond, Cornelis P.; Visser, Ruud; van Dishoeck, Ewine F.; C2d Irs Team

    We have begun to investigate the emission from Polycyclic Aromatic Hydrocarbons seen toward circumstellar disks around young low mass pre-main-sequence (T Tauri) stars, observed as part of our Spitzer Legacy program "From Molecular Cores to Planet-Forming Disks" (Evans et al. 2003). In this poster we will present some of our first Spitzer spectra of PAH features in T Tauri stars and discuss these features in the context of the disk structure and the UV radiation field needed to excite the PAH molecules. Laboratory measurements show that PAH molecules are strongly heated/excited when they absorb a single UV photon, and that they re-radiate the energy through C-H and C-C stretch and C-H bending mode transitions, in the form of infrared photons. These give rise to characteristic PAH features at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.8 microns. These emission features have now been observed toward about 60% of intermediate mass Herbig Ae/Be stars with the ISO satellite (Acke & van den Ancker 2004) and for a few of these sources, ground-based spatially resolved spectroscopy has confirmed that the emission originates from the inner ~100-150 AU region around the star (Geers et al. 2004, van Boekel et al. 2004, Habart et al. 2004), so typically on the scale of circumstellar disks. Our investigation of PAHs in disks around young stars takes two approaches. On the one hand, we address the question how the PAH abundance evolves in these disks during this period of planet formation and how their presence can have an impact on the circumstellar environment. The observed PAH emission is believed to originate from the surface layers of the disk, where the large molecules / small grains are mixed with the gas. The high opacity of PAHs to FUV radiation can significantly reduce the stellar UV field in the inner parts of the disk, while at the same time, through the photo-electric effect, PAHs can provide an important heating mechanism for the gas in the surrounding environment through

  16. Models for circumstellar nebulae around red and blue supergiants

    NASA Astrophysics Data System (ADS)

    Chita, S. M.

    2011-10-01

    In this thesis, we model the circumstellar medium of stars with initial masses of 8, 12, 18 and 20 solar masses, over their entire life from the main sequence until their supernova explosion. During the post-main-sequence stages, stars can evolve through several blue and red supergiant stages depending on their initial mass, composition and rotation rate. The models considered in the second Chapter have long-lasting RSG stages starting after the MS. In this phase, they develop shells of RSG wind material at the location where the free streaming RSG wind is stalled by the thermal pressure of the hot MS bubble, close to the central star. The RSG shells develop violent Rayleigh-Taylor instabilities. Once these start to grow non-linear, the RSG shell becomes highly structured as clumps form, and shell material mixes with material in the hot bubble. Later, the stars evolve to the BSG stage, during which the RSG shells are completely destroyed. These models return to the RSG stage, and build new RSG shells, which are more massive than those formed earlier. RSG shells are essential for our understanding of bipolar emission nebulae around BSGs. In the third Chapter are shown the results of the wind-wind interaction model of single star with 12 solar masses. On a time scale of a few 10000 yr, a BSG hour-glas shaped nebula expands into the sphere defined by the RSG shell. The faster polar parts of the hour glass hit the inner edge of the RSG shell first. The collision creates a pair of hot and dense polar caps. As time passes, the collision zone moves to lower latitudes of the RSG shell and becomes more confined in latitude. At the same time, the interaction of the BSG wind with the equatorial disk defines a second, ring shaped collision zone in the equatorial plane. These structures are reminiscent of the observed nebulae around the blue supergiant Sher 25. In the Chapter 3 we present calculations that predict the properties of the circumstellar medium for rapidly rotating

  17. Si IV Column Densities Predicted from Non-equilibrium Ionization Simulations of Turbulent Mixing Layers and High-velocity Clouds

    NASA Astrophysics Data System (ADS)

    Kwak, Kyujin; Shelton, Robin L.; Henley, David B.

    2015-10-01

    We present predictions of the Si iv ions in turbulent mixing layers (TMLs) between hot and cool gas and in cool high-velocity clouds (HVCs) that travel through a hot halo, complementing the C iv, N v, and O vi predictions in Kwak & Shelton, Kwak et al., and Henley et al. We find that the Si iv ions are most abundant in regions where the hot and cool gases first begin to mix or where the mixed gas has cooled significantly. The predicted column densities of high velocity Si iv and the predicted ratios of Si iv to C iv and O vi found on individual sightlines in our HVC simulations are in good agreement with observations of high velocity gas. Low velocity Si iv is also seen in the simulations, as a result of decelerated gas in the case of the HVC simulations and when looking along directions that pass perpendicular to the direction of motion in the TML simulations. The ratios of low velocity Si iv to C iv and O vi in the TML simulations are in good agreement with those recorded for Milky Way halo gas, while the ratio of Si iv to O vi from the decelerated gas in the HVC simulations is lower than that observed at normal velocity in the Milky Way halo. We attribute the shortfall of normal velocity Si iv to not having modeled the effects of photoionization and, following Henley et al., consider a composite model that includes decelerated HVC gas, supernova remnants, galactic fountain gas, and the effect of photoionization.

  18. Study of variable extinction of hot stars with circumstellar dust shells

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Various projects on the topic of hot stars with circumstellar dust are reported. The surface temperature, wind speed, and interstellar reddening were determined for the variable WC7 star HD 193793. Circumstellar carbon monoxide molecules were detected around a hot star. The dust envelope of the star W90 in the young cluster NGC2264 is discussed, and the spectra of low-redshift and X-ray emitting quasars are mentioned.

  19. The Copernicus observations - Interstellar or circumstellar material. [UV spectra of early stars

    NASA Technical Reports Server (NTRS)

    Steigman, G.; Strittmatter, P. A.; Williams, R. E.

    1975-01-01

    It is suggested that the sharp absorption lines observed in the ultraviolet spectra of early-type stars by the Copernicus satellite may be entirely accounted for by the circumstellar material in the H II regions and associated transition zones around the observed stars. If this interpretation is correct, the Copernicus results yield little information on the state of any interstellar (as opposed to circumstellar) gas and, in particular, shed little light on the degree of element depletion in interstellar space.

  20. High velocity flyer plates launched by magnetic pressure on pulsed power generator CQ-4 and applied in shock Hugoniot experiments

    NASA Astrophysics Data System (ADS)

    Zhang, Xuping; Wang, Guiji; Zhao, Jianheng; Tan, Fuli; Luo, Binqiang; Sun, Chengwei

    2014-05-01

    High velocity flyer plates with good flatness and some thickness have being widely used to the field of shock physics for characterizations of materials under dynamical loading. The techniques of magnetically driven high-velocity flyer plates are further researched based on our pulsed power generators CQ-4 and some good results got on Sandia's Z machine. With large current of several mega-amperes, the loading surface of electrode panel will suffer acute phase transitions caused from magnetic diffusion and Joule heating, and the thickness and flatness of the flyer plates will change with time. In order to obtain the flyer plates with high performances for shock physics, some researches on electrode panels were done by means of LS-DYNA980 software with electro-magnetic package. Two typical configurations for high velocity flyer plates were compared from distribution uniformity of magnetic field in simulation. The results show that the configuration with counter-bore with "notch" and "ear" is better than the other. Then, with the better configuration panels, some experiments were designed and done to validate the simulation results and obtain high velocity flyer plates with good flatness for one-dimensional strain shock experiments on CQ-4. The velocity profiles of the flyer plates were measured by displacement interferometer systems for any reflectors. And the planarity of flyer plates was measured by using the optical fiber pins array for recording the flyer arrival time. The peak velocities of 8.7 km/s with initial dimension of 10 × 7.2 × 0.62 mm for aluminum flyer plates have been achieved. And the flyer plate with initial size of 12 × 9.2 × 0.73 mm was accelerated to velocity of 6.5 km/s with the flatness of less than 11 ns in the central region of 6 mm in diameter and the effective thickness of about 0.220 mm. Based on these work, the symmetrical impact experiments were performed to obtain the high accuracy Hugoniot data of OFHC (oxygen free high conductance

  1. Oxidation and thermal fatigue of coated and uncoated NX-188 nickel-base alloy in a high velocity gas stream

    NASA Technical Reports Server (NTRS)

    Johnson, J. R.; Young, S. G.

    1972-01-01

    A cast nickel-base superalloy, NX-188, coated and uncoated, was tested in a high-velocity gas stream for resistance to oxidation and thermal fatigue by cycling between room temperature and 980, 1040, and 1090 C. Contrary to the behavior of more conventional nickel-base alloys, uncoated NX-188 exhibited the greatest weight loss at the lowest test temperature. In general, on the basis of weight change and metallographic observations a coating consisting of vapor-deposited Fe-Cr-Al-Y over a chromized substrate exhibited the best overall performance in resistance to oxidation and thermal fatigue.

  2. Plane-wave and common-translation-factor treatments of He sup 2+ +H collisions at high velocities

    SciTech Connect

    Errea, L.F. ); Harel, C.; Jouin, H. ); Maidagan, J.M.; Mendez, L. ); Pons, B. ); Riera, A. )

    1992-11-01

    We complement previous work that showed that the molecular approach, modified with plane-wave translation factors, is able to reproduce the fall of charge-exchange cross sections in He{sup 2+}+H collisions, by presenting the molecular data, and studying the corresponding mechanism. We test the accuracy of simplifications of the method that have been employed in the literature, and that lead to very simple calculations. We show that the common-translation-factor method is also successful at high nuclear velocities, provided that sufficiently excited states are included in the basis; moreover, it yields a simple picture of the mechanism and a description of ionization processes at high velocities.

  3. Transition-Metal Oxides in Warm Circumstellar Environments

    NASA Astrophysics Data System (ADS)

    Schmidt, Mirosław R.; Kaminski, Tomasz; Tylenda, Romuald

    2013-06-01

    We report on detections and simulations of electronic bands of transition-metal oxides, i.e. ScO, TiO, VO, CrO, YO, and of AlO, in spectra of two red novae V838 Mon and V4332 Sgr. These objects experienced a stellar merger event in 2002 and 1994, respectively, and have very rich circumstellar environments abundant in dust and molecules. We analyzed optical spectra of V838 Mon which show a presence of outflowing material. In this object, electronic systems of oxides are observed in absorption against a photospheric spectrum which resembles that of a late-type supergiant. We present simulations of the absorption bands which allowed us to derive the excitation temperatures of 300-500 K and constrain column densities, which turned out to be very high. Among many interesting features discovered, we identified forbidden transitions of TiO in the b^1Π-X^3Δ and c^{1}Φ-X^{3}Δ systems, which are seen owing to the high column densities and the relatively low temperatures. In the case of the older red nova V4332 Sgr, the main object is surrounded by a circumstellar disc which is seen almost edge-on and obscures the central star. The molecular spectra are seen in emission in this object, what is very unusual in astrophysical sources observed at optical wavelengths. We show that these emission bands arise owing to the special geometry of the star-disk system and that radiative pumping is responsible for excitation of the molecules. From the shapes of the rotational contours, we derive temperatures of about 120 K in this object. Remarkably, the spectra of V4332 Sgr contain features of CrO, which is the first identified signature of this molecule in an astrophysical object. In addition to the excitation and radiative-transfer analysis of the molecular spectra, we discuss chemical pathways that could lead to the observed variety of metal oxides seen in these enigmatic sources. T. Kaminski, M. Schmidt, R. Tylenda, M. Konacki, and M. Gromadzki ApJSuppl., {182} (33), 2009. T

  4. Kinetic narrowing of size distribution

    NASA Astrophysics Data System (ADS)

    Dubrovskii, V. G.

    2016-05-01

    We present a model that reveals an interesting possibility for narrowing the size distribution of nanostructures when the deterministic growth rate changes its sign from positive to negative at a certain stationary size. Such a behavior occurs in self-catalyzed one-dimensional III-V nanowires and more generally whenever a negative "adsorption-desorption" term in the growth rate is compensated by a positive "diffusion flux." By asymptotically solving the Fokker-Planck equation, we derive an explicit representation for the size distribution that describes either Poissonian broadening or self-regulated narrowing depending on the parameters. We show how the fluctuation-induced spreading of the size distribution can be completely suppressed in systems with size self-stabilization. These results can be used for obtaining size-uniform ensembles of different nanostructures.

  5. ON THE EXCITATION AND FORMATION OF CIRCUMSTELLAR FULLERENES

    SciTech Connect

    Bernard-Salas, J.; Jones, A. P.; Groenewegen, M. A. T.

    2012-09-20

    We compare and analyze the Spitzer mid-infrared spectrum of three fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds: Tc1, SMP SMC 16, and SMP LMC 56. The three planetary nebulae share many spectroscopic similarities. The strongest circumstellar emission bands correspond to the infrared active vibrational modes of the fullerene species C{sub 60} and little or no emission is present from polycyclic aromatic hydrocarbons. The strengths of the fullerene bands in the three planetary nebulae are very similar, while the ratios of the [Ne III]15.5 {mu}m/[Ne II]12.8 {mu}m fine structure lines, an indicator of the strength of the radiation field, are markedly different. This raises questions about their excitation mechanism and we compare the fullerene emission to fluorescent and thermal models. In addition, the spectra show other interesting and common features, most notably in the 6-9 {mu}m region, where a broad plateau with substructure dominates the emission. These features have previously been associated with mixtures of aromatic/aliphatic hydrocarbon solids. We hypothesize on the origin of this band, which is likely related to the fullerene formation mechanism, and compare it with modeled hydrogenated amorphous carbon that present emission in this region.

  6. Probing NH3 Formation in Oxygen-rich Circumstellar Envelopes

    NASA Astrophysics Data System (ADS)

    Wong, K. T.; Menten, K. M.; Kamiński, T.; Wyrowski, F.

    2015-08-01

    The chemistry of ammonia (NH3) in the circumstellar envelopes (CSEs) of AGB stars and red supergiants is poorly understood. Thermodynamic equilibrium (TE) chemistry predicts an abundance of ≲10-8, orders of magnitudes below values reported from observations (˜10-7-10-6). To date, there is no consistent model explaining the origin of such high abundances. To better understand the physical conditions necessary for the formation of NH3, we analysed the NH3 rotational and inversion lines observed in the spectrum of IK Tauri. The strength of the rotational lines clearly confirms the high abundances as compared to the TE predictions. From 1D radiative transfer modelling including infrared pumping via vibrational bands, we infer a total NH3 abundance of 7.5× 10-7, along with an ortho-to-para ratio (OPR) of ≤ 1.5 : 1, slightly above the statistical equilibrium value of 1. We discuss these preliminary results and the possible origin of NH3 in oxygen-rich CSEs.

  7. High angular resolution millimeter observations of circumstellar disks

    NASA Astrophysics Data System (ADS)

    Testi, Leonard; Leurini, Silvia

    2008-06-01

    In this lecture, we review the properties of protoplanetary disks as derived from high angular resolution observations at millimeter wavelengths. We discuss how the combination of several different high angular resolution techniques allow us to probe different regions of the disk around young stellar objects and to derive the properties of the dust when combined with sophisticated disk models. The picture that emerges is that the dust in circumstellar disks surrounding pre-main sequence stars is in many cases significantly evolved compared to the dust in molecular clouds and the interstellar medium. It is however still difficult to derive a consistent picture and timeline for dust evolution in disks as the observations are still limited to small samples of objects. We also review the evidence for and properties of disks around high-mass young stellar objects and the implications on their formation mechanisms. The study of massive YSOs is complicated by their short lifetimes and larger average distances. In most cases high angular resolution data at millimeter wavelengths are the only method to probe the structure of disks in these objects. We provide a summary of the characteristics of available high angular resolution millimeter and submillimeter observatories. We also describe the characteristics of the ALMA observatory being constructed in the Chilean Andes. ALMA is going to be the world leading observatory at millimeter wavelengths in the coming decades, the project is now in its main construction phase with early science activities envisaged for 2010 and full science operations for 2012.

  8. On circumstellar disks: Spitzer identifies two possible evolutionary paths

    NASA Astrophysics Data System (ADS)

    Teixeira, Paula S.; Lada, Charles J.; Marengo, Massimo; Lada, Elizabeth

    Multi-wavelength surveys have vastly improved our understanding of many astrophysical objects, in particular, circumstellar disks. We present our results for the disk population of the young cluster NGC 2264. Our study was based on data obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer on board the Spitzer Space Telescope combined with previously published optical data. We divide the disk population into 3 classes based on their spectral energy distribution shapes: optically thick disks, homologously depleted anemic disks, and radially depleted transition disks. We find that there are two distinct evolutionary paths for disks: a homologous one, where the disk emission decreases uniformly in NIR and mid-infrared wavelengths (anemic disks) and throughout which most sources pass, and a radially differential one where the emission from the inner region of the disk decreases more rapidly than from the outer region (transition disks). Whether a disk evolves in a homologously or radially depleted fashion is still unknown and may depend on the nature of planet formation in the disk.

  9. Observation of Circumstellar Gas in the Neighborhood of RZ Psc

    NASA Astrophysics Data System (ADS)

    Potravnov, I. S.; Grinin, V. P.; Ilyin, I. V.

    2013-12-01

    The first evidence is found of the existence of circumstellar gas in the nearest surroundings of the UX Ori star RZ Psc. Spectra obtained at the Terskol Observatory, Special Astrophysical Observatory (SAO), and the Nordic Optical Telescope (NOT) reveal a strong variability in the sodium doublet lines that is indicative of a sporadic outflow of matter. Weak variability was also observed in the core of the Hα line. One nontrivial feature of this discovery is that RZ Psc is of spectral class K0 IV. This means that the star has no intrinsic energy resources for creating the observed outflow of matter. There are no emission lines in the star's spectrum which might indicate that matter is falling into the star so that the observed outflow could be related to an accretion process. We suggest, nevertheless, that the ejection of gas is related to residual (slow) accretion and is driven by a propeller mechanism. The latter is possible if the star has a sufficiently high (on the order of 103 G) magnetic field.

  10. A WISE survey of circumstellar disks in Taurus

    SciTech Connect

    Esplin, T. L.; Luhman, K. L.; Mamajek, E. E.

    2014-04-01

    We have compiled photometry at 3.4, 4.6, 12, and 22 μm from the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) for all known members of the Taurus complex of dark clouds. Using these data and photometry from the Spitzer Space Telescope, we have identified members with infrared excess emission from circumstellar disks and have estimated the evolutionary stages of the detected disks, which include 31 new full disks and 16 new candidate transitional, evolved, evolved transitional, and debris disks. We have also used the WISE All-Sky Source Catalog to search for new disk-bearing members of Taurus based on their red infrared colors. Through optical and near-infrared spectroscopy, we have confirmed 26 new members with spectral types of M1-M7. The census of disk-bearing stars in Taurus should now be largely complete for spectral types earlier than ∼M8 (M ≳ 0.03 M {sub ☉}).

  11. Grain growth and dust trapping in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Pinilla, Paola

    2015-08-01

    Circumstellar disks around young stars are known to be the birthplace of planets. Planet formation starts with the coagulation of micron-sized particles to larger dust aggregates. This process, which covers more than forty orders of magnitude in mass, has different physical challenges. One of the oldest mysteries is how planetesimals are formed, in spite of fragmentation collisions and rapid inward drift. Radial drift theory is in disagreement with the observations of millimetre grains in the cold regions of protoplanetary disks. Nevertheless, a disk model that includes dust coagulation, fragmentation, and the presence of long-lived pressure bumps, which moderate the rapid inward migration of particles, leads to a better agreement between observations and theory. Disks with a dust depleted inner cavity, known as transition disks, are excellent candidates to investigate the dust evolution under the existence of a pressure bump. Millimetre observations of transition disks reveal crescent- and ring-shaped emissions that lend credence to the notion than planetesimals may form in localised hotspots or pressure traps. Recent ALMA observations have showed astonishing dust structures in transition disks, which together with data of CO and its isotopologues, have been giving major support for particle trapping induced by embedded planets, which can solve the old paradigm of radial drift.

  12. Secular resonances in circumstellar systems in binary stars

    NASA Astrophysics Data System (ADS)

    Bazso, A.; Pilat-Lohinger, E.; Eggl, S.; Funk, B.; Bancelin, D.

    2016-02-01

    Planet formation around single stars is already a complicated matter, but extrasolar planets are also present in binary and multiple star systems. We investigate circumstellar planets in binary star systems with stellar separations below 100 astronomical units. For a selection of 11 systems with at least one detected giant planet we determine the location and extension of the habitable zone (HZ), subject to the incident stellar flux from both stars. We work out the stability of additional hypothetical terrestrial planets in or close to the HZ in these systems. To study the secular dynamics we apply a semi-analytical method. This method employs a first-order perturbation theory to determine the secular frequencies of objects moving under the gravitational influence of two much more massive perturbers. The other part uses a single numerical integration of the equations of motion and a frequency analysis of the obtained time-series to determine the apsidal precession frequencies of the massive bodies. By combining these two parts we are able to find the location of the most important secular resonances and the regions of chaotic motion. We demonstrate that terrestrial planets interior to the giant planet’s orbit may suffer from a linear secular resonance that could prevent the existence of habitable planets. Contrary to this, close-in giant planets are less of a problem, but one has to take into account the general relativistic precession of the pericenter that can also lead to resonances.

  13. ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

    SciTech Connect

    Spalding, Christopher; Batygin, Konstantin; Adams, Fred C. E-mail: kbatygin@gps.caltech.edu

    2014-12-20

    Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function.

  14. Rapid disappearance of a warm, dusty circumstellar disk.

    PubMed

    Melis, Carl; Zuckerman, B; Rhee, Joseph H; Song, Inseok; Murphy, Simon J; Bessell, Michael S

    2012-07-04

    Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution typically is ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amount of cooler dust. Such a phase of rapid ejecta evolution has not been previously predicted or observed, and no currently available physical model satisfactorily explains the observations.

  15. Rapid disappearance of a warm, dusty circumstellar disk.

    PubMed

    Melis, Carl; Zuckerman, B; Rhee, Joseph H; Song, Inseok; Murphy, Simon J; Bessell, Michael S

    2012-07-01

    Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution typically is ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amount of cooler dust. Such a phase of rapid ejecta evolution has not been previously predicted or observed, and no currently available physical model satisfactorily explains the observations. PMID:22763553

  16. Polarization of circumstellar bow shocks due to electron scattering

    NASA Astrophysics Data System (ADS)

    Shrestha, Manisha; Hoffman, J. L.; Neilson, H.; Ignace, R.

    2014-01-01

    Circumstellar material (CSM) provides a link between interacting supernovae and their massive progenitor stars. This CSM arises from stellar winds, outflows, or eruptions from a massive star before it explodes and can be detected around stars or supernovae with polarimetric observations. We use a Monte Carlo based radiative transfer code (SLIP) to investigate the polarization created by different models for the CSM surrounding a central source such as supernovae or massive stars. We vary parameters such as the shape, optical depth, temperature, and brightness of the CSM and compare the simulated flux and polarization behavior with observational data. We present results from new simulations that assume a bow shock shape for the CSM. Bow shocks are commonly observed around massive stars; this shape forms when a star moving more quickly than the speed of sound in the local interstellar medium emits a stellar wind that drives a shock wave into the ISM. Since a bow shock projects an aspherical shape onto the sky, light from the central source that scatters in the shock region becomes polarized. We present electron-scattering polarization maps for this geometry and discuss the behavior of observed polarization with viewing angle in the unresolved case.

  17. The circumstellar envelope of S 106 - IRS 4

    NASA Astrophysics Data System (ADS)

    Felli, M.; Simon, M.; Fischer, J.; Hamann, F.

    1985-04-01

    The authors present new observations that help set the parameters of the ionized circumstellar envelope of S 106-IRS 4. The part of the envelope that is optically thick at 1.35 cm wavelength is smaller than 0arcsec.15 diameter which corresponds to 90 AU at 600 pc distance. The profiles of the Brackett-α and -γ lines are somewhat different with half power widths of 121±10 and 181±15 km s-1, respectively. The He I (21P-21S) line is detected at the S 106 nebula but not at IRS 4. The He I line emission of the nebula indicates that the central star of IRS 4 must have an effective temperature of about 35,000K. Comparison of the wind model scenario presented by Felli et al. (1984) with the present data and the Paschen line and Paschen edge data of McGregor et al. (1984) shows that the model encounters difficulties when observables that require details of the velocity field and of the innermost regions of the flow are considered.

  18. The Circumstellar Environments of Born-Again Giants

    NASA Astrophysics Data System (ADS)

    Helton, L. Andrew; Evans, Aneurin; Gehrz, Robert D.; Woodward, Charles; Eyres, Stewart

    2015-08-01

    When a solar-mass star reaches the end of its main sequence life, has shed a planetary nebula or become a proto-planetary nebula, and is heading towards the white dwarf phase of its evolution, the star may reignite residual surface helium and be "reborn". It retraces its path on the HR diagram and once again becomes a giant: it undergoes a Very Late Thermal Pulse (VLTP) and becomes a "Born-Again Giant" (BAG). This alternate scenario for the demise of low mass stars may occur in as many as 20% of cases. During this phase the star may become a prolific dust producer such that the star is completely obscured and the only means of monitoring its evolution is by observing the ejected dust.Over the past 10-20 years we have used ground-based, spaceborne and airborne infrared (IR) facilities to monitor the spectral energy distributions of the dust shells of stars that have recently undergone VLTPs. Covering a time period from ~1996 to the present, and with recent SOFIA observations that extend the spectral coverage from 1 - 38 microns, we have been able to determine mass-loss rates from the stars, and the physical state, nature and extent of their circumstellar dust shells.Our observations throw light on a phase of the evolution of low mass stars that is very rare, poorly observed, and little understood. Understanding these phenomena can potentially give us a glimpse of the ultimate fate of the Sun.

  19. The effect of low- and high-velocity tendon excursion on the mechanical properties of human cadaver subsynovial connective tissue.

    PubMed

    Filius, Anika; Thoreson, Andrew R; Yang, Tai-Hua; Vanhees, Matthias; An, Kai-Nan; Zhao, Chunfeng; Amadio, Peter C

    2014-01-01

    Fibrosis of the subsynovial connective tissue (SSCT) in the carpal tunnel is the most common histological finding in carpal tunnel syndrome (CTS). Fibrosis may result from damaged SSCT. Previous studies found that with low-velocity (2 mm/s), tendon excursions can irreversibly damage the SSCT. We investigated the effect of tendon excursion velocity in the generation of SSCT damage. Nine human cadaver wrists were used. Three repeated cycles of ramp-stretch testing were performed simulating 40%, 60%, 90%, and 120% of the middle finger flexor tendon superficialis physiological excursion with an excursion velocity of 60 mm/s. Energy and force were calculated and normalized by values obtained in the first cycle for each excursion level. Data were compared with low-velocity excursion data. For high-velocity excursions, a significant drop in the excursion energy ratio was first observed at an excursion level of 60% physiological excursion (p < 0.024) and that for low-velocity excursions was first observed at 90% physiological excursion (p < 0.038). Furthermore, the energy ratio was lower at 60% for high velocities (p ≤ 0.039). Increasing velocity lowers the SSCT damage threshold. This finding may be relevant for understanding the pathogenesis of SSCT fibrosis, such as that accompanying CTS, and a relationship with occupational factors.

  20. Stimulated Raman scattering as an explanation for the extreme high-velocity features of water maser emission

    NASA Astrophysics Data System (ADS)

    Deguchi, Shuji

    1994-01-01

    Extreme high-velocity features in the water maser spectra with velocity shifts of about +/- 900 km/s have recently been detected in the extragalactic water maser source, NGC 4258. We explain these extreme high-velocity features of water masers by stimulated Raman scattering in the plasma of the electron density of about 106-107/cu cm. For the Raman masers to occur, the brightness temperature of the original masers must be greater than about 1016-1019 K (depending on the maser beam solid angles, etc.), and the amplification path length of the maser must be about 3 x 1014 cm. We show that the frequency-downshifted (Stokes) photons are produced by the backward scattering and that upshifted (anti-Stokes) photons are created by interacting intersecting masers in the plasma. The intensity of the upshifted component is slightly lower than the intensity of the downshifted component. Time variations of upshifted and downshifted features must be independent. A crucial test for the Raman maser model is proposed.

  1. Characterization of High-Velocity Solution Precursor Flame-Sprayed Manganese Cobalt Oxide Spinel Coatings for Metallic SOFC Interconnectors

    NASA Astrophysics Data System (ADS)

    Puranen, Jouni; Laakso, Jarmo; Kylmälahti, Mikko; Vuoristo, Petri

    2013-06-01

    A modified high-velocity oxy-fuel spray (HVOF) thermal spray torch equipped with liquid feeding hardware was used to spray manganese-cobalt solutions on ferritic stainless steel grade Crofer 22 APU substrates. The HVOF torch was modified in such a way that the solution could be fed axially into the combustion chamber through 250- and 300-μm-diameter liquid injector nozzles. The solution used in this study was prepared by diluting nitrates of manganese and cobalt, i.e., Mn(NO3)2·4H2O and Co(NO3)2·6H2O, respectively, in deionized water. The as-sprayed coatings were characterized by X-ray diffraction and field-emission scanning electron microscopy operating in secondary electron mode. Chemical analyses were performed on an energy dispersive spectrometer. Coatings with remarkable density could be prepared by the novel high-velocity solution precursor flame spray (HVSPFS) process. Due to finely sized droplet formation in the HVSPFS process and the use of as delivered Crofer 22 APU substrate material having very low substrate roughness ( R a < 0.5 μm), thin and homogeneous coatings, with thicknesses lower than 10 μm could be prepared. The coatings were found to have a crystalline structure equivalent to MnCo2O4 spinel with addition of Co-oxide phases. Crystallographic structure was restored back to single-phase spinel structure by heat treatment.

  2. 3 mm band line survey toward the high-velocity compact cloud CO-0.40-0.22

    NASA Astrophysics Data System (ADS)

    Oka, T.; Tanaka, K.; Matsumura, S.; Miura, K.; Takekawa, S.; Takahata, Y.; Nishino, Akihiko

    2014-05-01

    High-velocity compact clouds (HVCCs) are a population of molecular clouds which have compact appearance (d < 10 pc) and large velocity width (Δ V > 50 km s-1), and are found in the central molecular zone of our Galaxy. We performed a 3 mm band line survey toward CO-0.40-0.22, a spatially unresolved HVCC with an extremely large velocity width (Δ V ≃ 90 km s-1), using the Mopra 22 m telescope. We surveyed the frequency range between 76 GHz and 116 GHz with a 0.27 MHz frequency resolution. We detect at least 54 lines from 32 molecules. Many line profiles show a prominent peak at vLSR ˜ 70 km s-1 with very large velocity width, indicating they are emitted by the HVCC. Detections of largish molecules are indicative of non-equilibrium chemistry. We extracted some prominent lines based on velocity structure, intensity ratios, and PCA analyses. Shock diagnostic lines (SiO, SO, CH3OH, HNCO) and dense gas probes (HCN, HCO+) appear to be prominent. Excitation analysis of CH3OH lines show an enhancement in T rot in the negative high-velocity end of the profile. These results suggest that CO-0.40-0.22 has experienced a shock, acceleration, compression, and heating in the recent past.

  3. Severe lung contusion and death after high-velocity behind-armor blunt trauma: relation to protection level.

    PubMed

    Gryth, Dan; Rocksén, David; Persson, Jonas K E; Arborelius, Ulf P; Drobin, Dan; Bursell, Jenny; Olsson, Lars-Gunnar; Kjellström, Thomas B

    2007-10-01

    The most-used safety recommendation for protective vests is that the impact should not cause more than a 44-mm impression in plasticine. The aim of this study was to investigate whether this criterion was sufficient if the vest was exposed to a high-velocity projectile. We tested the hypothesis with pigs divided into a 40-mm group (n = 10) and a 34-mm group (n = 8) protected by a vest allowing a 40-mm or 34-mm impression in plasticine, respectively. Five (50%) of 10 animals in the 40-mm group and 2 (25%) of 8 in the 34-mm group died due to the trauma. We observed severe lung hematoma, impaired circulation, desaturation, and electroencephalogram changes. These effects were more aggravated in the 40-mm group compared to the 34-mm group. Based on our results, the overall judgment is that the safety criterion of 44-mm impression is insufficient when a vest is exposed to a high-velocity projectile. PMID:17985777

  4. High-velocity frictional properties and microstructures of clay-rich fault gouge in megasplay fault zone, Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Ujiie, K.; Tsutsumi, A.

    2010-12-01

    In accretionary margins, a large out-of-sequence fault system (the megasplay fault) commonly branches from the megathrust and intersects the seafloor along the lower slope of the margin. Detailed seismic reflection surveys and theoretical studies have suggested that the propagation of earthquake rupture occurred repeatedly along the megasplay fault during great subduction earthquakes. Recently, IODP Expedition 316 drilled into the shallow portion of the megasplay fault zone in the Nankai subduction zone offshore the Kii Peninsula, southwest Japan and found the evidence for the slip localization and past frictional heating along ~10-mm-thick dark gouges in the microbreccia. Thus, high-velocity frictional properties of the megasplay fault material are crucial for understanding whether the megasplay fault efficiently transfers displacement toward the seafloor and fosters a tsunami genesis during a subduction earthquake. We conducted high-velocity friction experiments on clay-rich fault gouge taken from the Nankai megasplay fault zone at a slip rate of 1.3 m/s and normal stresses of 0.6-2.0 MPa under dry and wet conditions. After the experiments, the microstructures of the fault gouges were examined by optical microscope and SEM. In the dry tests, dehydration of clay minerals occurred by frictional heating, and the slip weakening is related to the fault gouge expansion due to a water phase transition from liquid to vapor. The water is derived from the dehydration of clay minerals by frictional heating. The resulting microstructure in the gouge layer is a random distribution of spherical clay-clast aggregates (CCA) in the optically isotropic, dark matrix. In the wet tests, the slip weakening is caused by pore-fluid pressurization resulting from shear-enhanced compaction of the water-saturated gouge and frictional heating. Compared to the dry tests, the wet tests show smaller dynamic stress drops and slip weakening distance. The steady-state shear stress in the wet tests

  5. Detection of High Velocity Absorption Components in the He I Lines of Eta Carinae near the Time of Periastron

    NASA Technical Reports Server (NTRS)

    Richardson, Noel D.; St-Jean, Lucas; Gull, Theodore R.; Madura, Thomas; Hillier, D. John; Teodoro, Mairan; Moffat, Anthony; Corcoran, Michael; Damineli, Augusto

    2014-01-01

    We have obtained a total of 58 high spectral resolution (R90,000) spectra of the massive binary star eta Carinae since 2012 in an effort to continue our orbital and long-term echelle monitoring of this extreme binary (Richardson et al. 2010, AJ, 139, 1534) with the CHIRON spectrograph on the CTIO 1.5 m telescope (Tokovinin et al. 2013, PASP, 125, 1336) in the 45507500A region. We have increased our monitoring efforts and observation frequency as the periastron event of 2014 has approached. We note that there were multiple epochs this year where we observe unusual absorption components in the P Cygni troughs of the He I triplet lines. In particular, we note high velocity absorption components related to the following epochs for the following lines: He I 4713: HJD 2456754- 2456795 (velocity -450 to -560 kms) He I 5876: HJD 2456791- 2456819 (velocity -690 to -800 kms) He I 7065: HJD 2456791- 2456810 (velocity -665 to -730 kms) Figures: Note that red indicates a high-velocity component noted above. He I 4713: http:www.astro.umontreal.carichardson4713.png He I 5876: http:www.astro.umontreal.carichardson5876.png He I 7065: http:www.astro.umontreal.carichardson7065.png These absorptions are likely related to the wind-wind collision region and bow shock, as suggested by the high-velocity absorption observed by Groh et al. (2010, AA, 519, 9) in the He I 10830 Atransition. In these cases, we suspect that we look along an arm of the shock cone and that we will see a fast absorption change from the other collision region shortly after periastron. We suspect that this is related to the multiple-components of the He II 4686 line that was noted by Walter (ATel6334), and is confirmed in our data. Further, high spectral resolution data are highly encouraged,especially for resolving powers greater than 50,000.These observations were obtained with the CTIO 1.5 m telescope, operated by the SMARTS Consortium, and were obtained through both SMARTS and NOAO programs 2012A-0216,2012B-0194

  6. First g(2+) measurement on neutron-rich 72Zn, and the high-velocity transient field technique for radioactive heavy-ion beams

    NASA Astrophysics Data System (ADS)

    Fiori, E.; Georgiev, G.; Stuchbery, A. E.; Jungclaus, A.; Balabanski, D. L.; Blazhev, A.; Cabaret, S.; Clément, E.; Danchev, M.; Daugas, J. M.; Grevy, S.; Hass, M.; Kumar, V.; Leske, J.; Lozeva, R.; Lukyanov, S.; Mertzimekis, T. J.; Modamio, V.; Mouginot, B.; Nowacki, F.; Penionzhkevich, Yu. E.; Perrot, L.; Pietralla, N.; Sieja, K.; Speidel, K.-H.; Stefan, I.; Stodel, C.; Thomas, J. C.; Walker, J.; Zell, K. O.

    2012-03-01

    The high-velocity transient-field (HVTF) technique was used to measure the g factor of the 2+ state of 72Zn produced as a radioactive beam. The transient-field strength was probed at high velocity in ferromagnetic iron and gadolinium hosts using 76Ge beams. The potential of the HVTF method is demonstrated and the difficulties that need to be overcome for a reliable use of the TF technique with high-Z, high-velocity radioactive beams are revealed. The polarization of K-shell vacancies at high velocity, which shows more than an order of magnitude difference between Z=20 and Z=30 is discussed. The g-factor measurement hints at the theoretically predicted transition in the structure of the Zn isotopes near N=40.

  7. A Collisional Algorithm for Modeling Circumstellar Debris Disks

    NASA Technical Reports Server (NTRS)

    Nesvold, Erika; Kuchner, Marc

    2011-01-01

    Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm.

  8. Thermal desorption of circumstellar and cometary ice analogs

    NASA Astrophysics Data System (ADS)

    Martín-Doménech, R.; Muñoz Caro, G. M.; Bueno, J.; Goesmann, F.

    2014-04-01

    Context. Thermal annealing of interstellar ices takes place in several stages of star formation. Knowledge of this process comes from a combination of astronomical observations and laboratory simulations under astrophysically relevant conditions. Aims: For the first time we present the results of temperature programmed desorption (TPD) experiments with pre-cometary ice analogs composed of up to five molecular components: H2O, CO, CO2, CH3OH, and NH3. Methods: The experiments were performed with an ultra-high vacuum chamber. A gas line with a novel design allows the controlled preparation of mixtures with up to five molecular components. Volatiles desorbing to the gas phase were monitored using a quadrupole mass spectrometer, while changes in the ice structure and composition were studied by means of infrared spectroscopy. Results: The TPD curves of water ice containing CO, CO2, CH3OH, and NH3 present desorption peaks at temperatures near those observed in pure ice experiments, volcano desorption peaks after water ice crystallization, and co-desorption peaks with water. Desorption peaks of CH3OH and NH3 at temperatures similar to the pure ices takes place when their abundance relative to water is above ~3% in the ice matrix. We found that CO, CO2, and NH3 also present co-desorption peaks with CH3OH, which cannot be reproduced in experiments with binary water-rich ice mixtures. These are extensively used in the study of thermal desorption of interstellar ices. Conclusions: These results reproduce the heating of circumstellar ices in hot cores and can be also applied to the late thermal evolution of comets. In particular, TPD curves represent a benchmark for the analysis of the measurements that mass spectrometers on board the ESA-Rosetta cometary mission will perform on the coma of comet 67P/Churyumov-Gerasimenko, which will be active before the arrival of Rosetta according to our predictions.

  9. ALMA Observations of HD 141569’s Circumstellar Disk

    NASA Astrophysics Data System (ADS)

    White, J. A.; Boley, A. C.; Hughes, A. M.; Flaherty, K. M.; Ford, E.; Wilner, D.; Corder, S.; Payne, M.

    2016-09-01

    We present ALMA band 7 (345 GHz) continuum and 12CO(J = 3-2) observations of the circumstellar disk surrounding HD 141569. At an age of about 5 Myr, the disk has a complex morphology that may be best interpreted as a nascent debris system with gas. Our 870 μm ALMA continuum observations resolve a dust disk out to approximately 56 au from the star (assuming a distance of 116 pc) with 0.″38 resolution and 0.07 mJy beam-1 sensitivity. We measure a continuum flux density for this inner material of 3.8 ± 0.4 mJy (including calibration uncertainties). The 12CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated 12CO(3-2) line flux density is 15.7 ± 1.6 Jy km s-1. We estimate the mass of the millimeter debris and 12CO(3-2) gas to be ≳0.04 M ⊕ and ˜2 × 10-3 M ⊕, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk (<50 au) has ˜160 M ⊕ contained within objects less than 50 km in radius, depending on the planetesimal size distribution and density assumptions. Markov Chain Monte Carlo modeling of the system reveals a disk morphology with an inclination of 53.°4 centered around an M = 2.39 M ⊙ host star (Msin(i) = 1.92 M ⊙). We discuss whether the gas in HD 141569's disk may be second generation. If it is, the system can be used to study the clearing stages of planet formation.

  10. Circumstellar medium around rotating massive stars at solar metallicity

    NASA Astrophysics Data System (ADS)

    Georgy, Cyril; Walder, Rolf; Folini, Doris; Bykov, Andrei; Marcowith, Alexandre; Favre, Jean M.

    2013-11-01

    Aims: Observations show nebulae around some massive stars but not around others. If observed, their chemical composition is far from homogeneous. Our goal is to put these observational features into the context of the evolution of massive stars and their circumstellar medium (CSM) and, more generally, to quantify the role of massive stars for the chemical and dynamical evolution of the ISM. Methods: Using the A-MAZE code, we perform 2d-axisymmetric hydrodynamical simulations of the evolution of the CSM, shaped by stellar winds, for a whole grid of massive stellar models from 15 to 120 M⊙ and following the stellar evolution from the zero-age main-sequence to the time of supernova explosion. In addition to the usual quantities, we also follow five chemical species: H, He, C, N, and O. Results: We show how various quantities evolve as a function of time: size of the bubble, position of the wind termination shock, chemical composition of the bubble, etc. The chemical composition of the bubble changes considerably compared to the initial composition, particularly during the red-supergiant (RSG) and Wolf-Rayet (WR) phases. In some extreme cases, the inner region of the bubble can be completely depleted in hydrogen and nitrogen, and is mainly composed of carbon, helium, and oxygen. We argue why the bubble typically expands at a lower rate than predicted by self-similarity theory. In particular, the size of the bubble is very sensitive to the density of the ISM, decreasing by a factor of ~2.5 for each additional dex in ISM density. The bubble size also decreases with the metallicity of the central star, because low-metallicity stars have weaker winds. Our models qualitatively fit the observations of WR ejecta nebulae.

  11. Standard Stars for the High-velocity and Metal-poor project at San Pedro Mártir

    NASA Astrophysics Data System (ADS)

    Schuster, W. J.; Parrao, L.; Contreras, M. E.

    2016-04-01

    The main documentation for the primary and secondary standard stars used in the high-velocity and metal-poor stars project is presented. Observations were taken using the Strömgren-Crawford, uvby-Hβ, 6-channel, spectrophotometric equipment with the H.L. Johnson 1.5-m telescope at the Observatorio Astronómico Nacional, San Pedro Mártir, between 1987 and 2007. Standard photometric values from the literature are reported for our standard stars, as well as transformed standard values, errors in the instrumental system, the transformation coefficients obtained for the standard system, the transformation errors, and the methods used to obtain such photometric observations and their standard transformations.

  12. Titanium K-Shell X-Ray Production from High Velocity Wire Arrays Implosions on the 20-MA Z Accelerator

    SciTech Connect

    Apruzese, J.P.; Beg, F.N.; Clark, R.C.; Coverdale, C.A.; Davis, J.; Deeney, C.; Douglas, M.R.; Nash, T.J.; Ruiz-Comacho, J.; Spielman, R.B.; Struve, K.W.; Thornhill, J.W.; Whitney, K.G.

    1999-01-27

    The advent of the 20-MA Z accelerator [R.B. Spielman, C. Deeney, G.A. Chandler, et al., Phys. Plasmas 5, 2105, (1997)] has enabled implosions of large diameter, high-wire-number arrays of titanium to begin testing Z-pinch K-shell scaling theories. The 2-cm long titanium arrays, which were mounted on a 40-mm diameter, produced between 75{+-}15 to 125{+-}20 kJ of K-shell x-rays. Mass scans indicate that, as predicted, higher velocity implosions in the series produced higher x-ray yields. Spectroscopic analyses indicate that these high velocity implosions achieved peak electron temperatures from 2.7{+-}0.1 to 3.2{+-}0.2 keV and obtained a K-shell emission mass participation of up to 12%.

  13. The Space Density of Primordial Gas Clouds near Galaxies and Groups and their Relation to Galactic High-Velocity Clouds.

    PubMed

    Zwaan; Briggs

    2000-02-20

    The Arecibo H i Strip Survey probed the halos of approximately 300 cataloged galaxies and the environments of approximately 14 groups with sensitivity to neutral hydrogen masses >/=107 M middle dot in circle. The survey detected no objects with properties resembling the high-velocity clouds (HVCs) associated with the Milky Way or Local Group. If the HVCs were typically MHi=107.5 M middle dot in circle objects distributed throughout groups and galaxy halos at distances of approximately 1 Mpc, the survey should have made approximately 70 HVC detections in groups and approximately 250 detections around galaxies. The null detection implies that HVCs are deployed at typical distances of

  14. Wear Behavior of High Velocity Arc Spraying FeNiCrAlBRE/Ni95Al Composite Coatings

    NASA Astrophysics Data System (ADS)

    Tian, H. L.; Wei, S. C.; Chen, Y. X.; Tong, H.; Liu, Y.; Xu, B. S.

    Wear-resistant FeNiCrAlBRE/Ni95Al composite coatings were deposited on carbon steel plate by high velocity arc spraying. Adhesive strength of the composite coating was improved by spraying Ni95Al cored wires as transition layer between working coating and substrate. Scanning electron microscopy and Vickers hardness testing were used to evaluate coatings structure and mechanical properties. For quantitative investigation of porosity, a computer image analyzer was used. The forming, the wear resistance and its mechanism of the coatings were studied. The results show that coating has relatively high average hardness about 550 HV0.1 and adhesive strength is 47 MPa. The worn surface characterized shallow grooves and few of debris on the coating manifested that the coating has better wear resistance under dry sliding conditions.

  15. Surface Remelting Treated High Velocity arc Sprayed FeNiCrAlBRE Coating by Tungsten Inert Gas

    NASA Astrophysics Data System (ADS)

    Tian, H. L.; Wei, S. C.; Chen, Y. X.; Tong, H.; Liu, Y.; Xu, B. S.

    This study aims at evaluating the effect of the TIG (Tungsten Inert Gas) remelting treatment of self-fluxing FeNiCrAlBRE alloy coatings, formed by means of high velocity arc spraying on steel surfaces. The treated and untreated samples were subjected to comparative structural examination using scanning electron microscopes. For quantitative investigation of porosity, a computer image analyser was used. Additionally, the wear resistance and wear volume loss of the worn tracks before and after the remelting process were contrastively evaluated in details. After the sprayed coatings were treated by TIG remelting in a proper conditions, the microstructure examination of the remelted coatings showed that a change of the microstructure from lamellar to cellular structure. Also, the results show that the remelting process decrease the coating defects and make the coating more wearable.

  16. Gamma-ray bursts from the accretion of solid bodies onto high-velocity Galactic neutron stars

    SciTech Connect

    Colgate, S.A.; Leonard, P.J.T.

    1993-12-31

    We propose a simple model for the gamma-ray bursts based on high- velocity Galactic neutron stars that have accretion disks. The latter are formed from a mixture of material from the supernova shell and that ablated from a pre-supernova binary companion. Accretion onto the neutron star from this disk when the disk is still largely gaseous may result in a soft gamma-ray repeater phase. Much later, after the neutron star has moved away from its birthplace, solid bodies form in the disk, and some are perturbed into hitting the neutron star to create gamma-ray bursts. This model makes several predictions that are consistent with the observations. The observed combination of a high degree of isotropy on the sky coupled with the observed value of < V/V{sub max}> is not, at first glance, predicted, but is not impossible to attain in our model.

  17. Precise Astrometry in the Core of the Globular Cluster 47 Tuc: a Complete Census of High-Velocity Stars

    NASA Astrophysics Data System (ADS)

    Meylan, Georges

    1995-07-01

    Binary stars play an essential role during the late phases of the dynamical evolution of a globular cluster. They transfer energy to passing stars, and so can strongly influence the cluster evolution - enough to delay, halt, and even reverse core collapse. Hard binaries are known to exist in cluster cores, e.g., in the form of millisecond pulsars. The presence of hard binaries may also be revealed by searching for the by- products of close encounters: high-velocity stars. Two such stars were serendipitously discovered in the core of 47 Tuc by Meylan et al. (1991), and similar stars have since been detected by Pryor et al. (1994). This represents the limit of the radial velocity data which can be obtained from the ground. If more progress is to be made in the search for high- velocity stars in 47 Tuc it must be made by obtaining proper motions - a task for which only HST is suitable. We propose to use WFPC2 to obtain deep U (F300W) images of the core of 47 Tuc at three different epochs over two years. This will allow us to measure differential proper motions to a 1 sigma limit of 0.23 mas/yr - this corresponds to a 5 sigma detection of all stars with velocities greater than 22 km/s. The choice of F300W will allow stars to be measured over the whole color-magnitude diagram - from the red-giant branch to well down the main sequence. Such a complete census will provide unique constraints on relaxation processes, collision and ejection rates, and velocity distributions.

  18. Precise Astrometry in the Core of the Globular Cluster 47 Tuc: A Complete Census of High-Velocity Stars

    NASA Astrophysics Data System (ADS)

    Meylan, Georges

    1996-07-01

    Binary stars play an essential role during the late phases of the dynamical evolution of a globular cluster. They transfer energy to passing stars, and so can strongly influence the cluster evolution. Hard binaries are known to exist in cluster cores, e.g., in the form of millisecond pulsars. The presence of hard binaries may also be revealed by searching for the by- products of close encounters: high-velocity stars. Two such stars were serendipitously discovered in the core of 47 Tuc by Meylan et al. {1991}, and similar stars have since been detected by Pryor et al. {1994}. This represents the limit of the radial velocity data from the ground. If more progress is to be made in the search for high-velocity stars in 47 Tuc, it must be made by obtaining proper motions, a task for which only HST is suitable. We propose to continue {Cycle 5 observations are scheduled for the fall of 1995} to use WFPC2 to obtain deep U {F300W} images of the core of 47 Tuc at three different epochs over two years. This will allow us to measure differential proper motions to a 1-Sigma limit of 0.23 mas/yr - this corresponds to a 5-Sigma detection of all stars with velocities greater than 22 km/s. The choice of F300W will allow stars to be measured over the whole color-magnitude diagram, from the red-giant branch to well down the main sequence. Such a complete census will provide unique constraints on relaxation processes, collision and ejection rates, and velocity distribution, as a function of the stellar mass.

  19. Precise Astrometry in the Core of the Globular Cluster 47 Tuc: A Complete Census of High-Velocity Stars

    NASA Astrophysics Data System (ADS)

    Meylan, Georges

    1997-07-01

    We propose to obtain the third and final epoch for our measurement of differential proper motions in the core of 47 Tuc using deep U {F300W} and V {F555W} WFPC2 images over two years {1^st epoch: Oct. 1995; 2^nd: Cycle 6 scheduled}. The resulting motions will have a 1-Sigma uncertainty of 0.23 mas/yr - corresponds to a 5-Sigma detection of all stars with velocities greater than 22 km/s. The choice of F300W will allow stars to be measured over the whole color-magnitude diagram, from the red-giant branch to well down the main sequence. Such a complete census will provide unique constraints on relaxation processes, collision and ejection rates, and the velocity distribution, as a function of the stellar mass. Binary stars play an essential role during the late phases of the dynamical evolution of a globular cluster. They transfer energy to passing stars, and so can strongly influence the cluster evolution. Hard binaries are known to exist in cluster cores, e.g., in th e form of millisecond pulsars. Th e presence of hard binaries may also be revealed by searching for the by-products of close encounters: high-velocity stars. Two such stars were serendipitously discovered in the core of 47 Tuc by Meylan et al. {1991}, and similar stars have since been detected by Pryor et al. {1994}. This represents the limit of the radial velocity data from the ground. If more progress is to be made in the search for high-velocity stars in 47 Tuc, it must be made by obtaining proper motions, a task for which only HST is suitable.

  20. Large- and small-scale structure of the intermediate- and high-velocity clouds towards the LMC and SMC

    NASA Astrophysics Data System (ADS)

    Smoker, J. V.; Fox, A. J.; Keenan, F. P.

    2015-08-01

    We employ Ca II K and Na I D interstellar absorption-line spectroscopy of early-type stars in the Large and Small Magellanic Clouds (LMC, SMC) to investigate the large- and small-scale structure in foreground intermediate- and high-velocity clouds (I/HVCs). Data include FLAMES-GIRAFFE Ca II K observations of 403 stars in four open clusters, plus FEROS or UVES spectra of 156 stars in the LMC and SMC. The FLAMES observations are amongst the most extensive probes to date of Ca II structures on ˜20 arcsec scales in Magellanic I/HVCs. From the FLAMES data within a 0.5° field of view, the Ca II K equivalent width in the I/HVC components towards three clusters varies by factors of ≥10. There are no detections of molecular gas in absorption at intermediate or high velocities, although molecular absorption is present at LMC and Galactic velocities towards some sightlines. The FEROS/UVES data show Ca II K I/HVC absorption in ˜60 per cent of sightlines. The range in the Ca II/Na I ratio in I/HVCs is from -0.45 to +1.5 dex, similar to previous measurements for I/HVCs. In 10 sightlines we find Ca II/O I ratios in I/HVC gas ranging from 0.2 to 1.5 dex below the solar value, indicating either dust or ionization effects. In nine sightlines I/HVC gas is detected in both H I and Ca II at similar velocities, implying that the two elements form part of the same structure.

  1. A CATALOG OF ULTRA-COMPACT HIGH VELOCITY CLOUDS FROM THE ALFALFA SURVEY: LOCAL GROUP GALAXY CANDIDATES?

    SciTech Connect

    Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P. E-mail: riccardo@astro.cornell.edu

    2013-05-01

    We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s{sup -1}, median angular diameters of 10', and median velocity widths of 23 km s{sup -1}. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of {approx}1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of {approx}10{sup 5}-10{sup 6} M{sub Sun }, H I diameters of {approx}2-3 kpc, and indicative dynamical masses within the H I extent of {approx}10{sup 7}-10{sup 8} M{sub Sun }, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.

  2. Highly Ionized Gas in the Galactic Halo and the High Velocity Clouds Toward PG 1116+215

    NASA Astrophysics Data System (ADS)

    Ganguly, R.; Sembach, K. R.; Tripp, T. M.; Savage, B. D.

    2003-12-01

    Recent observations of extragalactic objects with FUSE have revealed the presence of high ionization OVI absorption associated with high velocity clouds (HVCs), defined as gas which lies at absolute velocities beyond 100 km/s in the Local Standard of Rest. We have acquired high spectral resolution observations with STIS ( ˜ 10 km/s) and FUSE ( ˜ 20 km/s) of the quasar PG 1116+215. The spectra show absorption at Vlsr=184km/s from a wide range of ionization species:CIV, OI, OVI, MgII, SiII, SiIII, SiIV, and FeII. The strong and broad O VI absorption in this HVC extends from ˜ 120 to 230 km/s with a weak wing of absorption to 300km/s. Although the HVC is not seen in HI 21 cm emission down to N(HI) ˜ 2x1018 cm-2, it is seen in the HI Lyman series up to at least the 918.13Å line. In addition, we have non-detection constraints on the column denisties of CI, NI, NV, and SII. We can rule out photoionization in an ultra-low density (n ˜ 10-6 cm-3) Local Group medium adopted by some investigators to explain the O VI and O VII absorption detected in several directions. We are currently in the process of determining if these data either support or rule out other models of HVCs, such as the Warm-Hot Intergalactic Medium, Dark Matter dominated mini-halos, or interactions with a low density (10-4-10-5 cm-3) Galactic corona or Local Group medium. In addition, we will also use abundance infomation to study the enrichment history and constrain possible sources for the high velocity gas, such as tidal debris from cannibalized galaxies.

  3. A Catalog of Ultra-compact High Velocity Clouds from the ALFALFA Survey: Local Group Galaxy Candidates?

    NASA Astrophysics Data System (ADS)

    Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P.

    2013-05-01

    We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s-1, median angular diameters of 10', and median velocity widths of 23 km s-1. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of ~1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of ~105-106 M ⊙, H I diameters of ~2-3 kpc, and indicative dynamical masses within the H I extent of ~107-108 M ⊙, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.

  4. Spectral Narrowing in Semiconductor Microcavities

    NASA Astrophysics Data System (ADS)

    La Rocca, G. C.; Bassani, F.; Agranovich, V. M.

    1998-03-01

    The notion of in-plane motional narrowing of cavity polariton (CP) lines has been recently considered ( D.M. Whittaker et al.), Phys. Rev. Lett. 77, 4792 (1996); V. Savona et al.. Phys. Rev. Lett. 78, 4470 (1997). We point out that, in the presence of N>1 resonating quantum wells (QWs), the exciton component in a CP is coherently delocalized over all the individual QWs. Besides the two CP branches, also a dark exciton branch is present given by N-1 states similarly delocalized, but orthogonal to the cavity photon mode. If the QW disorder potential is weak compared to the Rabi splitting, it is seen by a CP as reduced by a factor 1/√N because of averaging along the cavity axis (G.C. La Rocca, F. Bassani, V.M. Agranovich, JOSA B 15), (1998). As for the in-plane motional narrowing, a simple scaling procedure shows that it would imply that the inhomogeneous linewidth of a CP be reduced by about four orders of magnitude compared to a QW exciton, which is incompatible with the experimental observations. The physical reason of such a shortcoming is that the disorder introduces localized exciton states which can resonantly scatter CPs, mixing them with states having a large k vector as well as with dark exciton states.

  5. High velocity acoustics

    NASA Astrophysics Data System (ADS)

    Legendre, R.

    1992-09-01

    Different types of aerodynamically generated noise of practical interest are examined using a novel, physically based, approach. A simple source model for turbulence noise is proposed. The prediction for turbulent mixing layer noise, produced by this model based on a simple monopole-type source mechanism, is that the radiated sound power varies as the eighth power of the relative velocity. The model is too simple to allow calculations to be carried further to the extent of determining the radiated sound power level, so that an empirical factor must still be considered, as in the case of Lighthill's formula.

  6. HIGH-DENSITY CIRCUMSTELLAR INTERACTION IN THE LUMINOUS TYPE IIn SN 2010jl: THE FIRST 1100 DAYS

    SciTech Connect

    Fransson, Claes; Ergon, Mattias; Sollerman, Jesper; Challis, Peter J.; Kirshner, Robert P.; Marion, G. H.; Milisavljevic, Dan; Friedman, Andrew S.; Chornock, Ryan; Czekala, Ian; Soderberg, Alicia; Chevalier, Roger A.; France, Kevin; Smith, Nathan; Bufano, Filomena; Kangas, Tuomas; Larsson, Josefin; Mattila, Seppo; Benetti, Stefano

    2014-12-20

    Hubble Space Telescope and ground-based observations of the Type IIn supernova (SN) 2010jl are analyzed, including photometry and spectroscopy in the ultraviolet, optical, and near-IR bands, 26-1128 days after first detection. At maximum, the bolometric luminosity was ∼3 × 10{sup 43} erg s{sup –1} and even at 850 days exceeds 10{sup 42} erg s{sup –1}. A near-IR excess, dominating after 400 days, probably originates in dust in the circumstellar medium (CSM). The total radiated energy is ≳ 6.5 × 10{sup 50} erg, excluding the dust component. The spectral lines can be separated into one broad component that is due to electron scattering and one narrow with expansion velocity ∼100 km s{sup –1} from the CSM. The broad component is initially symmetric around zero velocity but becomes blueshifted after ∼50 days, while remaining symmetric about a shifted centroid velocity. Dust absorption in the ejecta is unlikely to explain the line shifts, and we attribute the shift instead to acceleration by the SN radiation. From the optical lines and the X-ray and dust properties, there is strong evidence for large-scale asymmetries in the CSM. The ultraviolet lines indicate CNO processing in the progenitor, while the optical shows a number of narrow coronal lines excited by the X-rays. The bolometric light curve is consistent with a radiative shock in an r {sup –2} CSM with a mass-loss rate of M-dot ∼0.1  M{sub ⊙} yr{sup −1}. The total mass lost is ≳ 3 M {sub ☉}. These properties are consistent with the SN expanding into a CSM characteristic of a luminous blue variable progenitor with a bipolar geometry. The apparent absence of nuclear processing is attributed to a CSM that is still opaque to electron scattering.

  7. The inner circumstellar disk of the UX Orionis star V1026 Scorpii

    NASA Astrophysics Data System (ADS)

    Vural, J.; Kreplin, A.; Kishimoto, M.; Weigelt, G.; Hofmann, K.-H.; Kraus, S.; Schertl, D.; Dugué, M.; Duvert, G.; Lagarde, S.; Massi, F.

    2014-04-01

    Context. The UX Ori type variables (named after the prototype of their class) are intermediate-mass pre-main sequence objects. One of the most likely causes of their variability is the obscuration of the central star by orbiting dust clouds. Aims: We investigate the structure of the circumstellar environment of the UX Ori star V1026 Sco (HD 142666) and test whether the disk inclination is large enough to explain the UX Ori variability. Methods: We observed the object in the low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument and derived H- and K-band visibilities and closure phases. We modeled our AMBER observations, published Keck Interferometer observations, archival MIDI/VLTI visibilities, and the spectral energy distribution using geometric and temperature-gradient models. Results: Employing a geometric inclined-ring disk model, we find a ring radius of 0.15 ± 0.06 AU in the H band and 0.18 ± 0.06 AU in the K band. The best-fit temperature-gradient model consists of a star and two concentric, ring-shaped disks. The inner disk has a temperature of 1257+133-53 K at the inner rim and extends from 0.19 ± 0.01 AU to 0.23 ± 0.02 AU. The outer disk begins at 1.35+0.19-0.20 AU and has an inner temperature of 334+35-17 K. The derived inclination of 48.6+2.9-3.6° approximately agrees with the inclination derived with the geometric model (49 ± 5° in the K band and 50 ± 11° in the H band). The position angle of the fitted geometric and temperature-gradient models are 163 ± 9° (K band; 179 ± 17° in the H band) and 169.3+4.2-6.7°, respectively. Conclusions: The narrow width of the inner ring-shaped model disk and the disk gap might be an indication for a puffed-up inner rim shadowing outer parts of the disk. The intermediate inclination of ~50° is consistent with models of UX Ori objects where dust clouds in the inclined disk obscure the central star. Based on observations made with ESO telescopes at the La Silla Paranal Observatory

  8. Circumstellar matter and the nature of the SN1987A progenitor star

    NASA Technical Reports Server (NTRS)

    Chevalier, R. A.; Fransson, C.

    1987-01-01

    It is argued that radio observations of the supernova 1987A can be interpreted in terms of its interaction with circumstellar matter. The early turn-on of the radio emission implies a relatively low density circumstellar medium. The optical properties of the supernova imply that the progenitor star had a smaller radius than that of a typical type II supernova progenitor. The mass loss properties are consistent with this hypothesis. The thermal X-ray luminosity of the supernova is predicted and noted to be below the current upper limit. A bright infrared dust echo is not expected, although a weak echo from an earlier mass loss phase is possible. Weak ultraviolet emission lines from cicumstellar gas may be visible. Although the circumstellar density is low, it is possible that the progenitor star did lose a substantial fraction of its mass prior to the supernova explosion.

  9. The chemical history of molecules in circumstellar disks. I. Ices

    NASA Astrophysics Data System (ADS)

    Visser, R.; van Dishoeck, E. F.; Doty, S. D.; Dullemond, C. P.

    2009-03-01

    Context: Many chemical changes occur during the collapse of a molecular cloud to form a low-mass star and the surrounding disk. One-dimensional models have been used so far to analyse these chemical processes, but they cannot properly describe the incorporation of material into disks. Aims: The goal of this work is to understand how material changes chemically as it is transported from the cloud to the star and the disk. Of special interest is the chemical history of the material in the disk at the end of the collapse. Methods: A two-dimensional, semi-analytical model is presented that, for the first time, follows the chemical evolution from the pre-stellar core to the protostar and circumstellar disk. The model computes infall trajectories from any point in the cloud and tracks the radial and vertical motion of material in the viscously evolving disk. It includes a full time-dependent radiative transfer treatment of the dust temperature, which controls much of the chemistry. A small parameter grid is explored to understand the effects of the sound speed and the mass and rotation of the cloud. The freeze-out and evaporation of carbon monoxide (CO) and water (H2O), as well as the potential for forming complex organic molecules in ices, are considered as important first steps towards illustrating the full chemistry. Results: Both species freeze out towards the centre before the collapse begins. Pure CO ice evaporates during the infall phase and re-adsorbs in those parts of the disk that cool below the CO desorption temperature of ~18 K. Water remains solid almost everywhere during the infall and disk formation phases and evaporates within ~10 AU of the star. Mixed CO-H2O ices are important in keeping some solid CO above 18 K and in explaining the presence of CO in comets. Material that ends up in the planet- and comet-forming zones of the disk (~5-30 AU from the star) is predicted to spend enough time in a warm zone (several 104 yr at a dust temperature of 20-40 K

  10. TYPE Ia SUPERNOVAE STRONGLY INTERACTING WITH THEIR CIRCUMSTELLAR MEDIUM

    SciTech Connect

    Silverman, Jeffrey M.; Nugent, Peter E.; Gal-Yam, Avishay; Arcavi, Iair; Ben-Ami, Sagi; Sullivan, Mark; Howell, D. Andrew; Graham, Melissa L.; Filippenko, Alexei V.; Bloom, Joshua S.; Cenko, S. Bradley; Clubb, Kelsey I.; Cao, Yi; Horesh, Assaf; Kulkarni, Shrinivas R.; Chornock, Ryan; Foley, Ryan J.; Coil, Alison L.; Griffith, Christopher V.; Kasliwal, Mansi M.; and others

    2013-07-01

    Owing to their utility for measurements of cosmic acceleration, Type Ia supernovae (SNe Ia) are perhaps the best-studied class of SNe, yet the progenitor systems of these explosions largely remain a mystery. A rare subclass of SNe Ia shows evidence of strong interaction with their circumstellar medium (CSM), and in particular, a hydrogen-rich CSM; we refer to them as SNe Ia-CSM. In the first systematic search for such systems, we have identified 16 SNe Ia-CSM, and here we present new spectra of 13 of them. Six SNe Ia-CSM have been well studied previously, three were previously known but are analyzed in depth for the first time here, and seven are new discoveries from the Palomar Transient Factory. The spectra of all SNe Ia-CSM are dominated by H{alpha} emission (with widths of {approx}2000 km s{sup -1}) and exhibit large H{alpha}/H{beta} intensity ratios (perhaps due to collisional excitation of hydrogen via the SN ejecta overtaking slower-moving CSM shells); moreover, they have an almost complete lack of He I emission. They also show possible evidence of dust formation through a decrease in the red wing of H{alpha} 75-100 days past maximum brightness, and nearly all SNe Ia-CSM exhibit strong Na I D absorption from the host galaxy. The absolute magnitudes (uncorrected for host-galaxy extinction) of SNe Ia-CSM are found to be -21.3 mag {<=} M{sub R} {<=} -19 mag, and they also seem to show ultraviolet emission at early times and strong infrared emission at late times (but no detected radio or X-ray emission). Finally, the host galaxies of SNe Ia-CSM are all late-type spirals similar to the Milky Way, or dwarf irregulars like the Large Magellanic Cloud, which implies that these objects come from a relatively young stellar population. This work represents the most detailed analysis of the SN Ia-CSM class to date.

  11. Analysis of the flux and polarization spectra of the type Ia supernova SN 2001el: Exploring the geometry of the high-velocity Ejecta

    SciTech Connect

    Kasen, Daniel; Nugent, Peter; Wang, Lifan; Howell, D.A.; Wheeler, J. Craig; Hoeflich, Peter; Baade, Dietrich; Baron, E.; Hauschildt, P.H.

    2003-01-15

    SN 2001el is the first normal Type Ia supernova to show a strong, intrinsic polarization signal. In addition, during the epochs prior to maximum light, the CaII IR triplet absorption is seen distinctly and separately at both normal photospheric velocities and at very high velocities. The unusual, high-velocity triplet absorption is highly polarized, with a different polarization angle than the rest of the spectrum. The unique observation allows us to construct a relatively detailed picture of the layered geometrical structure of the supernova ejecta: in our interpretation, the ejecta layers near the photosphere (v approximately 10,000 km/s) obey a near axial symmetry, while a detached, high-velocity structure (v approximately 18,000-25,000 $ km/s) of CaII line opacity deviates from the photospheric axisymmetry. By partially obscuring the underlying photosphere, the high-velocity structure causes a more incomplete cancellation of the polarization of the photospheric light, and so gives rise to the polarization peak of the high-velocity IR triplet feature. In an effort to constrain the ejecta geometry, we develop a technique for calculating 3-D synthetic polarization spectra and use it to generate polarization profiles for several parameterized configurations. In particular, we examine the case where the inner ejecta layers are ellipsoidal and the outer, high-velocity structure is one of four possibilities: a spherical shell, an ellipsoidal shell, a clumped shell, or a toroid. The synthetic spectra rule out the clearly discriminated if observations are obtained from several different lines of sight. Thus, assuming the high velocity structure observed for SN 2001el is a consistent feature of at least known subset of type Ia supernovae, future observations and analyses such as these may allow one to put strong constraints on the ejecta geometry and hence on supernova progenitors and explosion mechanisms.

  12. Seismic Technology Adapted to Analyzing and Developing Geothermal Systems Below Surface-Exposed High-Velocity Rocks Final Report

    SciTech Connect

    Hardage, Bob A.; DeAngelo, Michael V.; Ermolaeva, Elena; Hardage, Bob A.; Remington, Randy; Sava, Diana; Wagner, Donald; Wei, Shuijion

    2013-02-01

    The objective of our research was to develop and demonstrate seismic data-acquisition and data-processing technologies that allow geothermal prospects below high-velocity rock outcrops to be evaluated. To do this, we acquired a 3-component seismic test line across an area of exposed high-velocity rocks in Brewster County, Texas, where there is high heat flow and surface conditions mimic those found at numerous geothermal prospects. Seismic contractors have not succeeded in creating good-quality seismic data in this area for companies who have acquired data for oil and gas exploitation purposes. Our test profile traversed an area where high-velocity rocks and low-velocity sediment were exposed on the surface in alternating patterns that repeated along the test line. We verified that these surface conditions cause non-ending reverberations of Love waves, Rayleigh waves, and shallow critical refractions to travel across the earth surface between the boundaries of the fast-velocity and slow-velocity material exposed on the surface. These reverberating surface waves form the high level of noise in this area that does not allow reflections from deep interfaces to be seen and utilized. Our data-acquisition method of deploying a box array of closely spaced geophones allowed us to recognize and evaluate these surface-wave noise modes regardless of the azimuth direction to the surface anomaly that backscattered the waves and caused them to return to the test-line profile. With this knowledge of the surface-wave noise, we were able to process these test-line data to create P-P and SH-SH images that were superior to those produced by a skilled seismic data-processing contractor. Compared to the P-P data acquired along the test line, the SH-SH data provided a better detection of faults and could be used to trace these faults upward to the boundaries of exposed surface rocks. We expanded our comparison of the relative value of S-wave and P-wave seismic data for geothermal

  13. The influence of slip velocity and temperature on permeability during and after high-velocity fault slip

    NASA Astrophysics Data System (ADS)

    Tanikawa, W.; Mukoyoshi, H.; Tadai, O.; Hirose, T.; Lin, W.

    2011-12-01

    Fluid transport properties in fault zones play an important role in dynamic processes during large earthquakes. If the permeability in a fault zone is low, high pore-fluid pressures caused by thermal pressurization (Sibson, 1973) or shear-induced compaction (Blanpied et al., 1992) can lead to an apparent reduction of fault strength. Changes in porosity and permeability of fault rocks within a fault zone during earthquakes and the subsequent progressive recovery of these properties may have a large influence on earthquake recurrence (Sleep and Blanpied, 1992). A rotary shear apparatus was used to investigate changes of fluid transport properties in a fault zone by real-time measurement of gas flow rates during and after shearing of hollow sandstone and granite cylinders at various slip rates. Our apparatus measures permeability parallel to the slip plane in both the slip zone and wall rocks. In all cases, permeability decreased rapidly with an increase of friction, but recovered soon after slip, reaching a steady state within several tens of minutes. The rate of reduction of permeability increased with increasing slip velocity. Permeability did not recover to pre-slip levels after low-velocity tests but recovered to exceed them after high-velocity tests. Frictional heating of gases at the slip surface increased gas viscosity, which increased gas flow rate to produce an apparent permeability increase. The irreversible permeability changes of the low-velocity tests were caused by gouge formation due to wearing and smoothing of the slip surface. The increase of permeability after high-velocity tests was caused by mesoscale fracturing in response to rapid temperature rise. Changes of pore fluid viscosity contributed more to changes of flow rate than did permeability changes caused by shear deformation, although test results from different rocks and pore fluids might be different. References Blanpied, M.L., Lockner, D.A., Byerlee, J.D., 1992. An earthquake mechanism

  14. High-velocity Frictional Behavior of Dunite, Biotite Gneiss, Phyllite and Coal Show Evidence for Melting and Thermal Degasing

    NASA Astrophysics Data System (ADS)

    O'Hara, K. D.; Mizoguchi, K.; Shimamoto, T.

    2004-12-01

    We conducted high-velocity frictional experiments on dunite, biotite gneiss, phyllite gouge and coal gouge at Kyoto University using a rotary high-velocity frictional testing machine. The purpose was to examine the effect of frictional melting in various rock types and to explore the effect of thermal degassing using coal as an analogue for a volatile fault zone. Experiments were conducted dry at equivalent slip rates of 1 m/s (1200 rpm) at normal stresses of 0.6-16 MPa for distances up to 90 m. Solid cylinders (25 mm diameter) of dunite and biotite gneiss were sheared with aluminum-alloy jackets at high stress, whereas phyllite and coal gouges were sheared with Teflon sleeves at low stress. The metal jackets allow high stress experiments to be performed and are inferred to melt before rock melting occurs. Dunite sheared at 10-16 MPa shows a weakening-strengthening followed by second weakening on melting, similar to previous experiments on gabbro without a metal jacket. Dunite melting is confirmed by, as yet unidentified, dendritic microlites, and a rapid reduction of steady-state frictional strength to 0.15. Under similar conditions, biotite gneiss shows apparent melting, but undergoes continuous strengthening without reaching steady state. Bituminous coal gouge sheared at 0.6 MPa undergoes a highly reproducible rapid weakening from 0.75 to 0.2, with odorous white gas emissions, sometimes accompanied by liquid hydrocarbons. Shear stress decreases prior to gasification and rapidly oscillating sample shortening/elongation occurs during gas emission. A slowly sheared sample (15 rpm) did not show weakening or gas emission. This is the first experimental demonstration of weakening associated with devolatilization during rapid slip. Vitrinite reflectance measurements on sheared coal samples may provide constraints on the temperature during gasification. Phyllite gouge sheared under the same conditions shows a gradual weakening to a steady-state strength of about 0

  15. High-Velocity Frictional Properties of Westerly Granite and the Role of Thermal Cracking on Gouge Production

    NASA Astrophysics Data System (ADS)

    Passelegue, F. X.; Di Toro, G.; Spagnuolo, E.; Violay, M.; Nielsen, S. B.; Schubnel, A.

    2015-12-01

    With the advent of high-velocity rotary shear apparatus, several experimental studies have been conducted in the last decades improving our understanding of fault friction at seismic slip rates (0.1 < Vs < 10 m/s). Here, we present the results of a series of tests conducted on Westerly granite with the Slow to HIgh Velocity Apparatus (SHIVA - INGV Rome), coupled with a high frequency acoustic monitoring (4 MHz sampling rate). Experiments were conducted under normal stress (σn) ranging from 5 to 20 MPa and at Vs between 3 mm/s and 3 m/s. Additional experiments were conducted in the presence of pore fluid at equivalent effective normal stress. In dry conditions, two friction drops are observed: the first drop at Vs > 0.1 m/s is explained by flash heating mechanism while the second drop is due to the formation and growth of a continuous melt layer on the fault surface. In wet conditions, only the second drop of friction is observed. Average values of the fracture energy are independent of normal stress and sliding velocity. However, measurements of elastic wave velocities travelling through the fault strongly suggest that higher damage is induced for 0.1< Vs <0.3 m/s for equivalent final displacement. This observation is also supported by acoustic emission (AEs) recordings. Indeed, most the AEs are recorded after the initiation of the second friction drop, that is, once the fault surface temperature is high, suggesting they may be due to thermal cracking induced by heat diffusion. In addition, the presence of pore fluid pressure (water) delayed the appearance of AEs, supporting the link between AEs and the production and diffusion of heat. Using the thermo-elastic crack model, we demonstrate that damage can indeed be induced by heat diffusion. Our theoretical results predict accurately the amount of sample wear, supporting the idea that gouge production and gouge comminution is in fact largely controlled by thermal cracking. Finally, we show that this new fracture

  16. Cryogenic Detectors (Narrow Field Instruments)

    NASA Astrophysics Data System (ADS)

    Hoevers, H.; Verhoeve, P.

    Two cryogenic imaging spectrometer arrays are currently considered as focal plane instruments for XEUS. The narrow field imager 1 (NFI 1) will cover the energy range from 0.05 to 3 keV with an energy resolution of 2 eV, or better, at 500 eV. A second narrow field imager (NFI 2) covers the energy range from 1 to 15 keV with an energy resolution of 2 eV (at 1 keV) and 5 eV (at 7 keV), creating some overlap with part of the NFI 1 energy window. Both narrow field imagers have a 0.5 arcmin field of view. Their imaging capabilities are matched to the XEUS optics of 2 to 5 arcsec leading to 1 arcsec pixels. The detector arrays will be cooled by a closed cycle system comprising a mechanical cooler with a base temperature of 2.5 K and either a low temperature 3He sorption pump providing the very low temperature stage and/or an Adiabatic Demagnetization Refrigerator (ADR). The ADR cooler is explicitly needed to cool the NFI 2 array. The narrow field imager 1} Currently a 48 times 48 element array of superconducting tunnel junctions (STJ) is envisaged. Its operating temperature is in the range between 30 and 350 mK. Small, single Ta STJs (20-50 mum on a side) have shown 3.5 eV (FWHM) resolution at E = 525 eV and small arrays have been successfully demonstrated (6 times 6 pixels), or are currently tested (10 times 12 pixels). Alternatively, a prototype Distributed Read-Out Imaging Device (DROID), consisting of a linear superconducting Ta absorber of 20 times 100 mum2, including a 20 times 20 mum STJ for readout at either end, has shown a measured energy resolution of 2.4 eV (FWHM) at E = 500 eV. Simulations involving the diffusion properties as well as loss and tunnel rates have shown that the performance can be further improved by slight modifications in the geometry, and that the size of the DROIDS can be increased to 0.5-1.0 mm without loss in energy resolution. The relatively large areas and good energy resolution compared to single STJs make DROIDS good candidates for the

  17. High velocity circuit resistance training improves cognition, psychiatric symptoms and neuromuscular performance in overweight outpatients with severe mental illness.

    PubMed

    Strassnig, Martin T; Signorile, Joseph F; Potiaumpai, Melanie; Romero, Matthew A; Gonzalez, Carolina; Czaja, Sara; Harvey, Philip D

    2015-09-30

    We developed a physical exercise intervention aimed at improving multiple determinants of physical performance in severe mental illness. A sample of 12 (9M, 3F) overweight or obese community-dwelling patients with schizophrenia (n=9) and bipolar disorder (n=3) completed an eight-week, high-velocity circuit resistance training, performed twice a week on the computerized Keiser pneumatic exercise machines, including extensive pre/post physical performance testing. Participants showed significant increases in strength and power in all major muscle groups. There were significant positive cognitive changes, objectively measured with the Brief Assessment of Cognition Scale: improvement in composite scores, processing speed and symbol coding. Calgary Depression Scale for Schizophrenia and Positive and Negative Syndrome Scale total scores improved significantly. There were large gains in neuromuscular performance that have functional implications. The cognitive domains that showed the greatest improvements (memory and processing speed) are most highly predictive of disability in schizophrenia. Moreover, the improvements seen in depression suggest this type of exercise intervention may be a valuable add-on therapy for bipolar depression.

  18. Improvement of corrosion resistance of high-velocity oxyfuel-sprayed stainless steel coatings by addition of molybdenum

    NASA Astrophysics Data System (ADS)

    Kawakita, Jin; Kuroda, Seiji; Fukushima, Takeshi; Kodama, Toshiaki

    2005-06-01

    To improve the marine corrosion resistance of stainless steel coatings fabricated by high-velocity oxyfuel (HVOF) spraying with a gas shroud attachment, the molybdenum (Mo) content of stainless steel was increased to form coatings with a chemical composition of Fe balance-18mass%Cr-22mass%Ni-2˜8mass%Mo. These coatings were highly dense, with <0.1 vol.% in porosity, and less oxidized, with 0.5 mass% in oxygen content at most. The corrosion mechanism and resistance of the coatings were investigated by electrochemical measurement, chemical analysis, and statistical processing. The general corrosion resistance of the coatings in 0.5 mol/dm3 sulfuric acid was improved with increases in Mo content, and the corrosion rate could be decreased to 8.8 × 10-2 mg/cm2 per hour (˜1 mm/year) at 8 mass% Mo. The pitting corrosion resistance of the coatings in artificial seawater was improved with increases in Mo content and was superior to that of the 316L stainless steel coating. The crevice corrosion resistance of the coatings in artificial seawater was improved and the number of rust spots at 4 mass% Mo was decreased to 38% of that for the 316L coating. Accordingly, Mo is highly effective in improving the corrosion resistance of the stainless steel coatings by HVOF spraying.

  19. Comparative characteristic and erosion behavior of NiCr coatings deposited by various high-velocity oxyfuel spray processes

    NASA Astrophysics Data System (ADS)

    Sidhu, Hazoor Singh; Sidhu, Buta Singh; Prakash, S.

    2006-12-01

    The purpose of this study is to analyze and compare the mechanical properties and microstructure details at the interface of high-velocity oxyfuel (HVOF)-sprayed NiCr-coated boiler tube steels, namely ASTM-SA-210 grade A1, ASTM-SA213-T-11, and ASTM-SA213-T-22. Coatings were developed by two different techniques, and in these techniques liquefied petroleum gas was used as the fuel gas. First, the coatings were characterized by metallographic, scanning electron microscopy/energy-dispersive x-ray analysis, x-ray diffraction, surface roughness, and microhardness, and then were subjected to erosion testing. An attempt has been made to describe the transformations taking place during thermal spraying. It is concluded that the HVOF wire spraying process offers a technically viable and cost-effective alternative to HVOF powder spraying process for applications in an energy generation power plant with a point view of life enhancement and to minimize the tube failures because it gives a coating having better resistance to erosion.

  20. Manufacturing and Properties of High-Velocity Oxygen Fuel (HVOF)-Sprayed FeVCrC Coatings

    NASA Astrophysics Data System (ADS)

    Sassatelli, Paolo; Bolelli, Giovanni; Lusvarghi, Luca; Manfredini, Tiziano; Rigon, Rinaldo

    2016-09-01

    This paper studies the microstructure, sliding wear behavior and corrosion resistance of high-velocity oxygen fuel (HVOF)-sprayed FeVCrC-based coatings. Various process parameters were tested to evaluate their effects on the coating properties, which were also compared to those of HVOF-sprayed NiCrBSi and Stellite-6 coatings. The Fe alloy coatings are composed of flattened splats, originating from molten droplets and consisting of a super-saturated solid solution, together with rounded particles, coming from partially unmolten material and containing V- and Fe-based carbide precipitates. All process parameters, apart from "extreme" settings with excess comburent in the flame, produce dense coatings, indicating that the feedstock powder is quite easily processable by HVOF. These coatings, with a microhardness of 650-750 HV0.3, exhibit wear rates of ≈2 × 10-6 mm3/(Nm) in ball-on-disk tests against sintered Al2O3 spheres. They perform far better than the reference coatings, and better than other Fe- and Ni-based alloy coatings tested in previous research. On the other hand, the corrosion resistance of the coating material (tested by electrochemical polarization in 0.1 M HCl solution) is quite low. Even in the absence of interconnected porosity, this results in extensive, selective damage to the Fe-based matrix. This coating material is therefore unadvisable for severely corrosive environments.

  1. An Extremely High Velocity Molecular Jet Surrounded by an Ionized Cavity in the Protostellar Source Serpens SMM1

    NASA Astrophysics Data System (ADS)

    Hull, Charles L. H.; Girart, Josep M.; Kristensen, Lars E.; Dunham, Michael M.; Rodríguez-Kamenetzky, Adriana; Carrasco-González, Carlos; Cortés, Paulo C.; Li, Zhi-Yun; Plambeck, Richard L.

    2016-06-01

    We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of a one-sided, high-velocity (˜80 km s-1) CO(J = 2\\to 1) jet powered by the intermediate-mass protostellar source Serpens SMM1-a. The highly collimated molecular jet is flanked at the base by a wide-angle cavity; the walls of the cavity can be seen in both 4 cm free-free emission detected by the Very Large Array and 1.3 mm thermal dust emission detected by ALMA. This is the first time that ionization of an outflow cavity has been directly detected via free-free emission in a very young, embedded Class 0 protostellar source that is still powering a molecular jet. The cavity walls are ionized either by UV photons escaping from the accreting protostellar source or by the precessing molecular jet impacting the walls. These observations suggest that ionized outflow cavities may be common in Class 0 protostellar sources, shedding further light on the radiation, outflow, and jet environments in the youngest, most embedded forming stars.

  2. Discovery of star formation in the extreme outer galaxy possibly induced by a high-velocity cloud impact

    SciTech Connect

    Izumi, Natsuko; Kobayashi, Naoto; Hamano, Satoshi; Yasui, Chikako; Tokunaga, Alan T.; Saito, Masao

    2014-11-01

    We report the discovery of star formation activity in perhaps the most distant molecular cloud in the extreme outer galaxy. We performed deep near-infrared imaging with the Subaru 8.2 m telescope, and found two young embedded clusters at two CO peaks of 'Digel Cloud 1' at the kinematic distance of D = 16 kpc (Galactocentric radius R {sub G} = 22 kpc). We identified 18 and 45 cluster members in the two peaks, and the estimated stellar densities are ∼5 and ∼3 pc{sup –2}, respectively. The observed K-band luminosity function suggests that the age of the clusters is less than 1 Myr and also that the distance to the clusters is consistent with the kinematic distance. On the sky, Cloud 1 is located very close to the H I peak of high-velocity cloud Complex H, and there are some H I intermediate velocity structures between the Complex H and the Galactic disk, which could indicate an interaction between them. We suggest the possibility that Complex H impacting on the Galactic disk has triggered star formation in Cloud 1 as well as the formation of the Cloud 1 molecular cloud.

  3. Computational analysis of a three-dimensional High-Velocity Oxygen-Fuel (HVOF) Thermal Spray torch

    SciTech Connect

    Hassan, B.; Lopez, A.R.; Oberkampf, W.L.

    1995-07-01

    An analysis of a High-Velocity Oxygen-Fuel Thermal Spray torch is presented using computational fluid dynamics (CFD). Three-dimensional CFD results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco Diamond Jet Rotating Wire torch, but wire feed is not simulated. To the authors` knowledge, these are the first published 3-D results of a thermal spray device. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Argon is injected through the center of the nozzle. Pre-mixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled assuming instantaneous chemistry. A standard, two-equation, K-{var_epsilon} turbulence model is employed for the turbulent flow field. An implicit, iterative, finite volume numerical technique is used to solve the coupled conservation of mass, momentum, and energy equations for the gas in a sequential manner. Flow fields inside and outside the aircap are presented and discussed.

  4. Computational fluid dynamics analysis of a wire-feed, high-velocity oxygen-fuel (HVOF) thermal spray torch

    SciTech Connect

    Lopez, A.R.; Hassan, B.; Oberkampf, W.L.; Neiser, R.A.; Roemer, T.J.

    1996-09-01

    The fluid and particle dynamics of a High-Velocity Oxygen-Fuel Thermal Spray torch are analyzed using computational and experimental techniques. Three-dimensional Computational Fluid Dynamics (CFD) results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco Diamond Jet Rotating Wire (DJRW) torch. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Premixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled using a single-step finite-rate chemistry model with a total of 9 gas species which includes dissociation of combustion products. A continually-fed steel wire passes through the center of the nozzle and melting occurs at a conical tip near the exit of the aircap. Wire melting is simulated computationally by injecting liquid steel particles into the flow field near the tip of the wire. Experimental particle velocity measurements during wire feed were also taken using a Laser Two-Focus (L2F) velocimeter system. Flow fields inside and outside the aircap are presented and particle velocity predictions are compared with experimental measurements outside of the aircap.

  5. Hot corrosion resistance of high-velocity oxyfuel sprayed coatings on a nickel-base superalloy in molten salt environment

    NASA Astrophysics Data System (ADS)

    Sidhu, T. S.; Prakash, S.; Agrawal, R. D.

    2006-09-01

    No alloy is immune to hot corrosion attack indefinitely. Coatings can extend the lives of substrate materials used at higher temperatures in corrosive environments by forming protective oxides layers that are reasonably effective for long-term applications. This article is concerned with studying the performance of high-velocity oxyfuel (HVOF) sprayed NiCrBSi, Cr3C2-NiCr, Ni-20Cr, and Stellite-6 coatings on a nickel-base superalloy at 900 °C in the molten salt (Na2SO4-60% V2O5) environment under cyclic oxidation conditions. The thermogravimetric technique was used to establish kinetics of corrosion. Optical microscope, x-ray diffraction, scanning electron microscopy/electron dispersive analysis by x-ray (SEM/EDAX), and electron probe microanalysis (EPMA) techniques were used to characterize the as-sprayed coatings and corrosion products. The bare superalloy suffered somewhat accelerated corrosion in the given environmental conditions. whereas hot corrosion resistance of all the coated superalloys was found to be better. Among the coating studied, Ni-20Cr coated superalloy imparted maximum hot corrosion resistance, whereas Stellite-6 coated indicated minimum resistance. The hot corrosion resistance of all the coatings may be attributed to the formation of oxides and spinels of nickel, chromium, or cobalt.

  6. AN EXTREME HIGH-VELOCITY BIPOLAR OUTFLOW IN THE PRE-PLANETARY NEBULA IRAS 08005-2356

    SciTech Connect

    Sahai, R.; Patel, N. A.

    2015-09-01

    We report interferometric mapping of the bipolar pre-planetary nebula IRAS 08005-2356 (I 08005) with an angular resolution of ∼1″–5″, using the Submillimeter Array, in the {sup 12}CO J = 2–1, 3–2, {sup 13}CO J = 2–1, and SiO J = 5–4 (v = 0) lines. Single-dish observations, using the SMT 10 m, were made in these lines as well as in the CO J = 4–3 and SiO J = 6–5 (v = 0) lines. The line profiles are very broad, showing the presence of a massive (>0.1 M{sub ⊙}), extreme high velocity outflow (V ∼ 200 km s{sup −1}) directed along the nebular symmetry axis derived from the Hubble Space Telescope imaging of this object. The outflow's scalar momentum far exceeds that available from radiation pressure of the central post-AGB star, and it may be launched from an accretion disk around a main-sequence companion. We provide indirect evidence for such a disk from its previously published, broad Hα emission profile, which we propose results from Lyβ emission generated in the disk followed by Raman-scattering in the innermost regions of a fast, neutral wind.

  7. Influence of Processing Parameters on Residual Stress of High Velocity Oxy-Fuel Thermally Sprayed WC-Co-Cr Coating

    NASA Astrophysics Data System (ADS)

    Gui, M.; Eybel, R.; Asselin, B.; Radhakrishnan, S.; Cerps, J.

    2012-10-01

    Residual stress in high velocity oxy-fuel (HVOF) thermally sprayed WC-10Co-4Cr coating was studied based on design of experiment (DOE) with five factors of oxygen flow, fuel gas hydrogen flow, powder feed rate, stand-off distance, and surface speed of substrate. In each DOE run, the velocity and temperature of in-flight particle in flame, and substrate temperature were measured. Almen-type N strips were coated, and their deflections after coating were used for evaluation of residual stress level in the coating. The residual stress in the coating obtained in all DOE runs is compressive. In the present case of HVOF thermally sprayed coating, the residual stress is determined by three types of stress: peening, quenching, and cooling stress generated during spraying or post spraying. The contribution of each type stress to the final compressive residual stress in the coating depends on material properties of coating and substrate, velocity and temperature of in-flight particle, and substrate temperature. It is found that stand-off distance is the most important factor to affect the final residual stress in the coating, following by two-factor interaction of oxygen flow and hydrogen flow. At low level of stand-off distance, higher velocity of in-flight particle in flame and higher substrate temperature post spraying generate more peening stress and cooling stress, resulting in higher compressive residual stress in the coating.

  8. THE APACHE POINT OBSERVATORY GALACTIC EVOLUTION EXPERIMENT: FIRST DETECTION OF HIGH-VELOCITY MILKY WAY BAR STARS

    SciTech Connect

    Nidever, David L.; Zasowski, Gail; Majewski, Steven R.; Beaton, Rachael L.; Wilson, John C.; Skrutskie, Michael F.; O'Connell, Robert W.; Bird, Jonathan; Schoenrich, Ralph; Johnson, Jennifer A.; Sellgren, Kris; Robin, Annie C.; Schultheis, Mathias; Martinez-Valpuesta, Inma; Gerhard, Ortwin; Shetrone, Matthew; Schiavon, Ricardo P.; Weiner, Benjamin; Schneider, Donald P.; Allende Prieto, Carlos; and others

    2012-08-20

    Commissioning observations with the Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, have produced radial velocities (RVs) for {approx}4700 K/M-giant stars in the Milky Way (MW) bulge. These high-resolution (R {approx} 22, 500), high-S/N (>100 per resolution element), near-infrared (NIR; 1.51-1.70 {mu}m) spectra provide accurate RVs ({epsilon}{sub V} {approx} 0.2 km s{sup -1}) for the sample of stars in 18 Galactic bulge fields spanning -1 Degree-Sign -32 Degree-Sign . This represents the largest NIR high-resolution spectroscopic sample of giant stars ever assembled in this region of the Galaxy. A cold ({sigma}{sub V} {approx} 30 km s{sup -1}), high-velocity peak (V{sub GSR} Almost-Equal-To +200 km s{sup -1}) is found to comprise a significant fraction ({approx}10%) of stars in many of these fields. These high RVs have not been detected in previous MW surveys and are not expected for a simple, circularly rotating disk. Preliminary distance estimates rule out an origin from the background Sagittarius tidal stream or a new stream in the MW disk. Comparison to various Galactic models suggests that these high RVs are best explained by stars in orbits of the Galactic bar potential, although some observational features remain unexplained.

  9. Burst Speed of Wild Fishes under High-Velocity Flow Conditions Using Stamina Tunnel with Natural Guidance System in River

    NASA Astrophysics Data System (ADS)

    Izumi, Mattashi; Yamamoto, Yasuyuki; Yataya, Kenichi; Kamiyama, Kohhei

    Swimming experiments were conducted on wild fishes in a natural guidance system stamina tunnel (cylindrical pipe) installed in a fishway of a local river under high-velocity flow conditions (tunnel flow velocity : 211 to 279 cm·s-1). In this study, the swimming characteristics of fishes were observed. The results show that (1) the swimming speeds of Tribolodon hakonensis (Japanese dace), Phoxinus lagowshi steindachneri (Japanese fat-minnow), Plecoglossus altivelis (Ayu), and Zacco platypus (Pale chub) were in proportion to their body length under identical water flow velocity conditions; (2) the maximum burst speed of Japanese dace and Japanese fat-minnow (measuring 4 to 6 cm in length) was 262 to 319 cm·s-1 under high flow velocity conditions (225 to 230 cm·s-1), while the maximum burst speed of Ayu and Pale chub (measuring 5 cm to 12 cm in length) was 308 to 355 cm·s-1 under high flow velocity conditions (264 to 273 cm·s-1) ; (3) the 50cm-maximum swimming speed of swimming fishes was 1.07 times faster than the pipe-swimming speed; (4) the faster the flow velocity, the shorter the swimming distance became.

  10. Manufacturing and Properties of High-Velocity Oxygen Fuel (HVOF)-Sprayed FeVCrC Coatings

    NASA Astrophysics Data System (ADS)

    Sassatelli, Paolo; Bolelli, Giovanni; Lusvarghi, Luca; Manfredini, Tiziano; Rigon, Rinaldo

    2016-10-01

    This paper studies the microstructure, sliding wear behavior and corrosion resistance of high-velocity oxygen fuel (HVOF)-sprayed FeVCrC-based coatings. Various process parameters were tested to evaluate their effects on the coating properties, which were also compared to those of HVOF-sprayed NiCrBSi and Stellite-6 coatings. The Fe alloy coatings are composed of flattened splats, originating from molten droplets and consisting of a super-saturated solid solution, together with rounded particles, coming from partially unmolten material and containing V- and Fe-based carbide precipitates. All process parameters, apart from "extreme" settings with excess comburent in the flame, produce dense coatings, indicating that the feedstock powder is quite easily processable by HVOF. These coatings, with a microhardness of 650-750 HV0.3, exhibit wear rates of ≈2 × 10-6 mm3/(Nm) in ball-on-disk tests against sintered Al2O3 spheres. They perform far better than the reference coatings, and better than other Fe- and Ni-based alloy coatings tested in previous research. On the other hand, the corrosion resistance of the coating material (tested by electrochemical polarization in 0.1 M HCl solution) is quite low. Even in the absence of interconnected porosity, this results in extensive, selective damage to the Fe-based matrix. This coating material is therefore unadvisable for severely corrosive environments.

  11. Teaching and Assessment of High-Velocity, Low-Amplitude Techniques for the Spine in Predoctoral Medical Education.

    PubMed

    Channell, Millicent King

    2016-09-01

    Although national didactic criteria have been set for predoctoral education and assessment in osteopathic manipulative treatment, there is no criterion standard for teaching methods and assessments of osteopathic manipulative treatment competence in colleges of osteopathic medicine. This issue is more pressing with the creation of the single graduate medical education accreditation system by the American Osteopathic Association and Accreditation Council for Graduate Medical Education, which introduced the creation of "osteopathic recognition" for residencies that want to incorporate osteopathic principles and practice into their programs. Residencies with osteopathic recognition may include both osteopathic and allopathic graduates. Increased standardization at the predoctoral level, however, is recommended as osteopathic principles and practice training applications are expanded. The objectives of this article are to review the standards for teaching osteopathic medical students high-velocity, low-amplitude (HVLA) techniques for the spine; to review and discuss the methods used to assess medical students' proficiency in using HVLA; and to propose baseline standards for teaching and assessing HVLA techniques among medical students.

  12. Establishing force and speed training targets for lumbar spine high-velocity, low-amplitude chiropractic adjustments*

    PubMed Central

    Owens, Edward F.; Hosek, Ronald S.; Sullivan, Stephanie G.B.; Russell, Brent S.; Mullin, Linda E.; Dever, Lydia L.

    2016-01-01

    Objective: We developed an adjusting bench with a force plate supporting the lumbar portion to measure loads transmitted during lumbar manual adjustment. It will be used to provide force-feedback to enhance student learning in technique labs. The study goal is to define the learning target loads and speeds, with instructors as expert models. Methods: A total of 11 faculty members experienced in teaching Gonstead technique methods performed 81 simulated adjustments on a mannequin on the force plate. Adjustments were along 9 lumbopelvic “listings” at 3 load levels: light, normal, and heavy. We analyzed the thrusts to find preload, peak load, duration, and thrust rate. Results: Analysis of 891 thrusts showed wide variations between doctors. Peak loads ranged from 100 to 1400 N. All doctors showed clear distinctions between peak load levels, but there was overlap between high and low loads. Thrust rates were more uniform across doctors, averaging 3 N/ms. Conclusion: These faculty members delivered a range of thrusts, not unlike those seen in the literature for high velocity, low amplitude manipulation. We have established at least minimum force and speed targets for student performance, but more work must be done to create a normative adjustment to guide refinement of student learning. PMID:26600272

  13. Patient-centered outcomes of high-velocity, low-amplitude spinal manipulation for low back pain: a systematic review.

    PubMed

    Goertz, C M; Pohlman, K A; Vining, R D; Brantingham, J W; Long, C R

    2012-10-01

    Low back pain (LBP) is a well-recognized public health problem with no clear gold standard medical approach to treatment. Thus, those with LBP frequently turn to treatments such as spinal manipulation (SM). Many clinical trials have been conducted to evaluate the efficacy or effectiveness of SM for LBP. The primary objective of this paper was to describe the current literature on patient-centered outcomes following a specific type of commonly used SM, high-velocity low-amplitude (HVLA), in patients with LBP. A systematic search strategy was used to capture all LBP clinical trials of HVLA using our predefined patient-centered outcomes: visual analogue scale, numerical pain rating scale, Roland-Morris Disability Questionnaire, and the Oswestry Low Back Pain Disability Index. Of the 1294 articles identified by our search, 38 met our eligibility criteria. Like previous SM for LBP systematic reviews, this review shows a small but consistent treatment effect at least as large as that seen in other conservative methods of care. The heterogeneity and inconsistency in reporting within the studies reviewed makes it difficult to draw definitive conclusions. Future SM studies for LBP would benefit if some of these issues were addressed by the scientific community before further research in this area is conducted.

  14. AN EXPERIMENTAL STUDY OF SHOCK WAVES RESULTING FROM THE IMPACT OF HIGH VELOCITY MISSILES ON ANIMAL TISSUES

    PubMed Central

    Harvey, E. Newton; McMillen, J. Howard

    1947-01-01

    The spark shadowgram method of studying shock waves is described. It has been used to investigate the properties of such waves produced by the impact of a high velocity missile on the surface of water. The method can be adapted for study of behavior of shock waves in tissue by placing the tissue on a water surface or immersing it in water. Spark shadowgrams then reveal waves passing from tissue to water or reflected from tissue surfaces. Reflection and transmission of shock waves from muscle, liver, stomach, and intestinal wall are compared with reflection from non-living surfaces such as gelatin gel, steel, plexiglas, cork, and air. Because of its heterogeneous structure, waves transmitted by tissue are dispersed and appear as a series of wavelets. When the accoustical impedance (density x wave velocity) of a medium is less than that in which the wave is moving, reflection will occur with inversion of the wave; i.e., a high pressure wave will become a low pressure wave. This inversion occurs at an air surface and is illustrated by shadowgrams of reflection from stomach wall, from a segment of colon filled with gas, and from air-filled rubber balloons. Bone (human skull and beef ribs) shows good reflection and some transmission of shock waves. When steel is directly hit by a missile, clearly visible elastic waves pass from metal to water, but a similar direct hit on bone does not result in elastic waves strong enough to be detected by a spark shadowgram. PMID:19871617

  15. Teaching and Assessment of High-Velocity, Low-Amplitude Techniques for the Spine in Predoctoral Medical Education.

    PubMed

    Channell, Millicent King

    2016-09-01

    Although national didactic criteria have been set for predoctoral education and assessment in osteopathic manipulative treatment, there is no criterion standard for teaching methods and assessments of osteopathic manipulative treatment competence in colleges of osteopathic medicine. This issue is more pressing with the creation of the single graduate medical education accreditation system by the American Osteopathic Association and Accreditation Council for Graduate Medical Education, which introduced the creation of "osteopathic recognition" for residencies that want to incorporate osteopathic principles and practice into their programs. Residencies with osteopathic recognition may include both osteopathic and allopathic graduates. Increased standardization at the predoctoral level, however, is recommended as osteopathic principles and practice training applications are expanded. The objectives of this article are to review the standards for teaching osteopathic medical students high-velocity, low-amplitude (HVLA) techniques for the spine; to review and discuss the methods used to assess medical students' proficiency in using HVLA; and to propose baseline standards for teaching and assessing HVLA techniques among medical students. PMID:27571298

  16. Thermal metamorphism of Si2O3 - (A circumstellar dust analog)

    NASA Technical Reports Server (NTRS)

    Nuth, J. A.; Donn, B.

    1984-01-01

    The thermal behavior of Si2O3, the metastable condensate from SiO vapor,has been studied experimentally. Si2O3 and its successor, amorphous quartz, have previously been shown to have infrared spectral features similar to some that appear in the spectra of grains in oxygen-rich circumstellar regions. Thermal annealing experiments show that only one Si2O3 decay process operates over the range between 750-1000 K. This process is a unimolecular disproportionation. The rate of this transformation can be expressed as k/hr = 10 to the 9th exp (-40 kcal/mole/RT). By using this rate constant, it is found that a significant fraction of freshly nucleated circumstellar grains can survive passage through a typical circumstellar shell virtually unaltered in structure. It is emphasized that this is only the first in a series of laboratory experiments intended to study the metamorphism of newly condensed circumstellar material ejected into the interstellar medium. Grains similar to these might have been incorporated into the primitive solar nebula, provided that they could also survive passage through the general interstellar medium.

  17. Organic chemistry in circumstellar envelopes: Setting the stage for prebiotic synthesis

    NASA Astrophysics Data System (ADS)

    Ziurys, Lucy M.

    2008-10-01

    One of the few carbon-rich environments found in interstellar space is the ejecta of asymptotic giant branch (AGB) stars. Such material, which forms a circumstellar envelope, becomes enriched in carbon due to “dredge-up” phenomena associated with nucleosynthesis. A unique organic synthesis flourishes in the gas phase in these envelopes, and radio and millimeter observations have identified a wide range of C-bearing compounds, including long acetylenic chains such as HC5N, HC7N, C4H, C6H, C8H, C6H-, C8H-, and C3O. Oxygen-rich envelopes also have a non-negligible carbon chemistry, fostering species such as HCN and HCO+. Phosphorus chemistry appears to be active as well in circumstellar shells, as evidenced by the recent detections of HCP, CCP, and PO. Radio observations also indicate that some fraction of the circumstellar molecular material survives into the planetary nebula stage, and then becomes incorporated into diffuse, and eventually, dense clouds. The complex organic molecules found in dense clouds such as Sgr B2(N) may be the products of “seed” material that can be traced back to the carbon-enriched circumstellar gas.

  18. A Bagel-shaped Envelope To Model Circumstellar Material Around Rapidly Rotating Be-type Stars

    NASA Astrophysics Data System (ADS)

    Touhami, Yamina; Gies, D.; Coudé du Foresto, V.; Schaefer, G.

    2009-01-01

    The circumstellar material around Be stars have essentially been studied spectroscopically and interferometrically with disc-shaped models (Waters et al. 1987, Hummel 1994, Gies et al. 2007), where the physical properties are still not very well defined. Schmitz et al. 1983 and Rohrmann et al. 1997, have applied the kinetic theory of gases to steady-state isothermal gaseous masses with differential rotation, and predict bagel-shaped circumstellar envelopes. The theory of a circumstellar torus could very well explain the short and long lived photometric outbursts that have been reported by Mennickent et al.2002, Hubert et al. 1998, and other irregular behaviors such as the spectroscopic transition from a standard B-type star to a Be-type star (Pavlovski et al. 1997). The purpose of this study is to show results on how to model a low-density circumstellar torus around the Be star and to generate visibility curves that could be comparable to observational data obtained with the CHARA long baseline infrared interferometer.

  19. Finding success in ACA narrow networks.

    PubMed

    Daly, Rich

    2015-12-01

    Health systems should carefully consider the specific details of their local market before deciding to launch a narrow network plan or to join an existing insurer's narrow network. Key steps to take in the evaluation process include: Determining insurer interest in forming a true partnership. Assessing capability for greater efficiency. Assessing insurer priorities. Obtaining access to enrollee data. Identifying capabilities that differentiate it from other narrow networks. PMID:26793944

  20. Narrow gap electronegative capacitive discharges

    NASA Astrophysics Data System (ADS)

    Kawamura, E.; Lieberman, M. A.; Lichtenberg, A. J.

    2013-10-01

    Narrow gap electronegative (EN) capacitive discharges are widely used in industry and have unique features not found in conventional discharges. In this paper, plasma parameters are determined over a range of decreasing gap length L from values for which an electropositive (EP) edge exists (2-region case) to smaller L-values for which the EN region connects directly to the sheath (1-region case). Parametric studies are performed at applied voltage Vrf=500 V for pressures of 10, 25, 50, and 100 mTorr, and additionally at 50 mTorr for 1000 and 2000 V. Numerical results are given for a parallel plate oxygen discharge using a planar 1D3v (1 spatial dimension, 3 velocity components) particle-in-cell (PIC) code. New interesting phenomena are found for the case in which an EP edge does not exist. This 1-region case has not previously been investigated in detail, either numerically or analytically. In particular, attachment in the sheaths is important, and the central electron density ne0 is depressed below the density nesh at the sheath edge. The sheath oscillations also extend into the EN core, creating an edge region lying within the sheath and not characterized by the standard diffusion in an EN plasma. An analytical model is developed using minimal inputs from the PIC results, and compared to the PIC results for a base case at Vrf=500 V and 50 mTorr, showing good agreement. Selected comparisons are made at the other voltages and pressures. A self-consistent model is also developed and compared to the PIC results, giving reasonable agreement.

  1. Narrow gap electronegative capacitive discharges

    SciTech Connect

    Kawamura, E.; Lieberman, M. A.; Lichtenberg, A. J.

    2013-10-15

    Narrow gap electronegative (EN) capacitive discharges are widely used in industry and have unique features not found in conventional discharges. In this paper, plasma parameters are determined over a range of decreasing gap length L from values for which an electropositive (EP) edge exists (2-region case) to smaller L-values for which the EN region connects directly to the sheath (1-region case). Parametric studies are performed at applied voltage V{sub rf}=500 V for pressures of 10, 25, 50, and 100 mTorr, and additionally at 50 mTorr for 1000 and 2000 V. Numerical results are given for a parallel plate oxygen discharge using a planar 1D3v (1 spatial dimension, 3 velocity components) particle-in-cell (PIC) code. New interesting phenomena are found for the case in which an EP edge does not exist. This 1-region case has not previously been investigated in detail, either numerically or analytically. In particular, attachment in the sheaths is important, and the central electron density n{sub e0} is depressed below the density n{sub esh} at the sheath edge. The sheath oscillations also extend into the EN core, creating an edge region lying within the sheath and not characterized by the standard diffusion in an EN plasma. An analytical model is developed using minimal inputs from the PIC results, and compared to the PIC results for a base case at V{sub rf}=500 V and 50 mTorr, showing good agreement. Selected comparisons are made at the other voltages and pressures. A self-consistent model is also developed and compared to the PIC results, giving reasonable agreement.

  2. Anger perceptually and conceptually narrows cognitive scope.

    PubMed

    Gable, Philip A; Poole, Bryan D; Harmon-Jones, Eddie

    2015-07-01

    For the last 50 years, research investigating the effect of emotions on scope of cognitive processing was based on models proposing that affective valence determined cognitive scope. More recently, our motivational intensity model suggests that this past work had confounded valence with motivational intensity. Research derived from this model supports the idea that motivational intensity, rather than affective valence, explains much of the variance emotions have on cognitive scope. However, the motivational intensity model is limited in that the empirical work has examined only positive affects high in approach and negative affects high in avoidance motivation. Thus, perhaps only approach-positive and avoidance-negative states narrow cognitive scope. The present research was designed to clarify these conceptual issues by examining the effect of anger, a negatively valenced approach-motivated state, on cognitive scope. Results revealed that anger narrowed attentional scope relative to a neutral state and that attentional narrowing to anger was similar to the attentional narrowing caused by high approach-motivated positive affects (Study 1). This narrowing of attention was related to trait approach motivation (Studies 2 and Study 3). Anger also narrowed conceptual cognitive categorization (Study 4). Narrowing of categorization related to participants' approach motivation toward anger stimuli. Together, these results suggest that anger, an approach-motivated negative affect, narrows perceptual and conceptual cognitive scope. More broadly, these results support the conceptual model that motivational intensity per se, rather than approach-positive and avoidance-negative states, causes a narrowing of cognitive scope.

  3. Dozens of compact and high velocity-dispersion, early-type galaxies in Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Saulder, Christoph; van den Bosch, Remco C. E.; Mieske, Steffen

    2015-06-01

    Context. Passive galaxies at high redshift are much smaller than equally massive early types today. If this size evolution is caused by stochastic merging processes, then a small fraction of the compact galaxies should persist until today. Up to now it has not been possible to systematically identify the existence of such objects in Sloan Digital Sky Survey (SDSS). Aims: We aim at finding potential survivors of these compact galaxies in SDSS, as targets for more detailed follow-up observations. Methods: From the virial theorem, it is expected that for a given mass, compact galaxies have stellar velocity dispersion higher than the mean owing to their smaller sizes. Therefore velocity dispersion, coupled with size (or mass), is an appropriate method of selecting relics, independent of the stellar population properties. Based on these considerations, we designed a set of criteria the use the distribution of early-type galaxies from SDSS on the log 10(R0) - log 10(σ0) plane to find the most extreme objects on it. We thus selected compact massive galaxy candidates by restricting them to high velocity dispersions σ0> 323.2 km s-1 and small sizes R0< 2.18 kpc. Results: We find 76 galaxies at 0.05

  4. High-Velocity Frictional Properties of Westerly Granite and the Role of Thermal Cracking on Gouge Production

    NASA Astrophysics Data System (ADS)

    Passelegue, Francois; Spanuolo, Elena; Violay, Marie; Nielsen, Stefan; Di Toro, Giulio; Schubnel, Alexandre

    2016-04-01

    With the advent of high-velocity shear apparatus, several experimental studies have been conducted in recent years improving our understanding of fault friction at seismic slip rates (0.1-10 m/s). Here, we present the results of a series of tests conducted on Westerly granite, at INGV Roma, on a Slow to HIgh Velocity Apparatus (SHIVA), coupled with a high frequency monitoring (4MHz sampling rate). Experiments were conducted under normal stress (σn) ranging from 5 to 20 MPa and at sliding velocities (V) comprised between 3 mm/s and 3 m/s. Additional experiments were conducted in the presence of pore fluid at equivalent effective normal stress. In dry conditions, two friction drops are observed. The first drop is independent of the normal stress and occurs when V become higher than a critical value (Vc≈0.15 m/s). The second friction drop occurs after a critical slip weakening distance which decreases as a power law with the power density (τV). The first, abrupt, drop is explained by flash heating and weakening mechanism while the second, smooth, drop is due to the formation and growth of molten patches on the fault surface. In wet conditions, only the second drop of friction is observed. Average values of the fracture energy are independent of normal stress and sliding velocity at V > 0.01 m/s. However, measurements of elastic wave velocities travelling through the fault strongly suggest that higher damage is induced for 0.1 < V < 0.3 m/s for a same finite displacement. This observation is also supported by acoustic emission (AE) recordings. Indeed, most the AEs are recorded after the initiation of the second friction drop, that is, once the fault surface temperature is high. Some AEs are even recorded few seconds after the end of the experiments, suggesting they may be due to thermal cracking induced by heat diffusion. In addition, the presence of pore fluid pressure (water) delayed the apparition of AEs at equivalent effective pressure, supporting the link

  5. Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

    NASA Astrophysics Data System (ADS)

    Luo, Jun; Cai, Zhenbing; Mo, Jiliang; Peng, Jinfang; Zhu, Minhao

    2016-05-01

    Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed (HVOF) technique WC-17Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffractrometry (XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy (OM), and surface topography. The experimental results reveal that the WC-17Co coating adjusted the boundary between the partial slip regime (PSR) and the slip regime (SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17Co coating in prevention of rotational fretting wear.

  6. Spatially extended and high-velocity dispersion molecular component in spiral galaxies: Single-dish versus interferometric observations

    SciTech Connect

    Caldú-Primo, Anahi; Walter, Fabian; Schruba, Andreas; Leroy, Adam; Bolatto, Alberto D.; Vogel, Stuart

    2015-02-01

    Recent studies of the molecular medium in nearby galaxies have provided mounting evidence that the molecular gas can exist in two phases: one that is clumpy and organized as molecular clouds and another one that is more diffuse. This last component has a higher velocity dispersion than the clumpy one. In order to investigate these two molecular components further, we compare the fluxes and line widths of CO in NGC 4736 and NGC 5055, two nearby spiral galaxies for which high-quality interferometric as well as single-dish data sets are available. Our analysis leads to two main results: (1) employing three different methods, we determine the flux recovery of the interferometer as compared to the single-dish to be within a range of 35%–74% for NGC 4736 and 81%–92% for NGC 5055, and (2) when focusing on high (S/N ≥ 5) lines of sight (LOSs), the single-dish line widths are larger by ∼(40 ± 20)% than the ones derived from interferometric data, which is in agreement with stacking all LOSs. These results point to a molecular gas component that is distributed over spatial scales larger than 30″(∼1 kpc), and is therefore filtered out by the interferometer. The available observations do not allow us to distinguish between a truly diffuse gas morphology and a uniform distribution of small clouds that are separated by less than the synthesized beam size (∼3″ or ∼100 pc), as they would both be invisible for the interferometer. This high velocity dispersion component has a dispersion similar to what is found in the atomic medium, as traced through observations of the H i line.

  7. Optimization of magnetically accelerated, ultra-high velocity aluminum flyer plates for use in plate impact, shock wave experiments.

    SciTech Connect

    Cochrane, Kyle Robert; Knudson, Marcus D.; Slutz, Stephen A.; Lemke, Raymond William; Davis, J. P.; Harjes, Henry Charles III; Giunta, Anthony Andrew; Bliss, David Emery

    2005-05-01

    The intense magnetic field produced by the 20 MA Z accelerator is used as an impulsive pressure source to accelerate metal flyer plates to high velocity for the purpose of performing plate impact, shock wave experiments. This capability has been significantly enhanced by the recently developed pulse shaping capability of Z, which enables tailoring the rise time to peak current for a specific material and drive pressure to avoid shock formation within the flyer plate during acceleration. Consequently, full advantage can be taken of the available current to achieve the maximum possible magnetic drive pressure. In this way, peak magnetic drive pressures up to 490 GPa have been produced, which shocklessly accelerated 850 {micro}m aluminum (6061-T6) flyer plates to peak velocities of 34 km/s. We discuss magnetohydrodynamic (MHD) simulations that are used to optimize the magnetic pressure for a given flyer load and to determine the shape of the current rise time that precludes shock formation within the flyer during acceleration to peak velocity. In addition, we present results pertaining to plate impact, shock wave experiments in which the aluminum flyer plates were magnetically accelerated across a vacuum gap and impacted z-cut, {alpha}-quartz targets. Accurate measurements of resulting quartz shock velocities are presented and analyzed through high-fidelity MHD simulations enhanced using optimization techniques. Results show that a fraction of the flyer remains at solid density at impact, that the fraction of material at solid density decreases with increasing magnetic pressure, and that the observed abrupt decrease in the quartz shock velocity is well correlated with the melt transition in the aluminum flyer.

  8. A Comprehensive Archival Search for Counterparts to Ultra-compact High-Velocity Clouds: Five Local Volume Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Sand, D. J.; Crnojević, D.; Bennet, P.; Willman, B.; Hargis, J.; Strader, J.; Olszewski, E.; Tollerud, E. J.; Simon, J. D.; Caldwell, N.; Guhathakurta, P.; James, B. L.; Koposov, S.; McLeod, B.; Morrell, N.; Peacock, M.; Salinas, R.; Seth, A. C.; Stark, D. P.; Toloba, E.

    2015-06-01

    We report five Local Volume dwarf galaxies (two of which are presented here for the first time) uncovered during a comprehensive archival search for optical counterparts to ultra-compact high-velocity clouds (UCHVCs). The UCHVC population of HI clouds are thought to be candidate gas-rich, low-mass halos at the edge of the Local Group and beyond, but no comprehensive search for stellar counterparts to these systems has been presented. Careful visual inspection of all publicly available optical and ultraviolet imaging at the position of the UCHVCs revealed six blue, diffuse counterparts with a morphology consistent with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all six candidate dwarf counterparts show that five have an Hα-derived velocity consistent with the coincident HI cloud, confirming their association; the sixth diffuse counterpart is likely a background object. The size and luminosity of the UCHVC dwarfs is consistent with other known Local Volume dwarf irregular galaxies. The gas fraction ({{M}HI}/{{M}star}) of the five dwarfs are generally consistent with that of dwarf irregular galaxies in the Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC HVC274.68+74.70-123) has a very high {{M}HI}/{{M}star} ˜ 40. Despite the heterogenous nature of our search, we demonstrate that the current dwarf companions to UCHVCs are at the edge of detectability due to their low surface brightness, and that deeper searches are likely to find more stellar systems. If more sensitive searches do not reveal further stellar counterparts to UCHVCs, then the dearth of such systems around the Local Group may be in conflict with ΛCDM simulations.

  9. A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Crnojevic, Denija; Sand, David J.

    2015-08-01

    We report the discovery of five Local Volume dwarf galaxies uncovered during a comprehensive archival search for optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC population of HI clouds are thought to be candidate gas-rich, low mass halos at the edge of the Local Group and beyond, but no comprehensive search for stellar counterparts to these systems has been presented. Careful visual inspection of all publicly available optical and ultraviolet imaging at the position of the UCHVCs revealed six blue, diffuse counterparts with a morphology consistent with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all six candidate dwarf counterparts show that five have an Halpha-derived velocity consistent with the coincident HI cloud, confirming their association; the sixth diffuse counterpart is likely a background object. The size and luminosity of the UCHVC dwarfs is consistent with other known Local Volume dwarf irregular galaxies. The gas fraction (M_HI/M_star) of the five dwarfs are generally consistent with that of dwarf irregular galaxies in the Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC HVC274.68+74.70-123) has a very high M_HI/M_star~40. Despite the heterogenous nature of our search, we demonstrate that the current dwarf companions to UCHVCs are at the edge of detectability due to their low surface brightness, and that deeper searches are likely to find more stellar systems. If more sensitive searches do not reveal further stellar counterparts to UCHVCs, then the dearth of such systems around the Local Group may be in conflict with LambdaCDM simulations.

  10. Searching for Optical Counterparts to Ultra-compact High Velocity Clouds: Possible Detection of a Counterpart to AGC 198606

    NASA Astrophysics Data System (ADS)

    Janesh, William; Rhode, Katherine L.; Salzer, John J.; Janowiecki, Steven; Adams, Elizabeth A. K.; Haynes, Martha P.; Giovanelli, Riccardo; Cannon, John M.; Muñoz, Ricardo R.

    2015-09-01

    We report initial results from a campaign to obtain optical imaging of Ultra Compact High Velocity Clouds (UCHVCs) discovered by the Arecibo Legacy Fast ALFA (ALFALFA) Hi survey. UCHVCs have properties consistent with their being low-mass dwarf galaxies in the Local Volume, but do not have identified optical counterparts. We are using the WIYN 3.5 m telescope to image these objects and search for an associated stellar population. Here we present our observational strategy and method for searching for resolved stellar counterparts to the UCHVCs. We combine careful photometry, a color–magnitude filter, and spatial smoothing techniques to search for stellar overdensities in the g- and i-band images. We also run statistical tests to quantify the likelihood that detected overdensities are real and not chance superpositions of sources. We demonstrate the method by applying it to WIYN imaging of two objects: Leo P, a UCHVC discovered by ALFALFA and shown to be a star-forming dwarf galaxy in the Local Volume and AGC 198606, an ALFALFA source near in position and velocity to the Local Group dwarf galaxy Leo T. Applying the search method to the Leo P data yields an unambiguous detection (>99% confidence) of the galaxy’s stellar population. Applying the method to the AGC 198606 imaging yields a possible detection (92% confidence) of an optical counterpart located ∼2.5 arcmin from the centroid of AGC 198606's Hi distribution and within the Hi disk. We estimate a distance to the stellar counterpart of 373–393 kpc, an absolute magnitude Mi = ‑4.67 ± 0.09, and an Hi-to-stellar mass ratio of ∼45–110.

  11. PRESENT-DAY GALACTIC EVOLUTION: LOW-METALLICITY, WARM, IONIZED GAS INFLOW ASSOCIATED WITH HIGH-VELOCITY CLOUD COMPLEX A

    SciTech Connect

    Barger, K. A.; Haffner, L. M.; Wakker, B. P.; Hill, Alex S.; Madsen, G. J.; Duncan, A. K. E-mail: haffner@astro.wisc.edu E-mail: wakker@astro.wisc.edu

    2012-12-20

    The high-velocity cloud Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin H{alpha} Mapper kinematically resolved observations of Complex A over the velocity range of -250 to -50 km s{sup -1} in the local standard of rest reference frame. These observations include the first full H{alpha} intensity map of Complex A across (l, b) = (124 Degree-Sign , 18 Degree-Sign ) to (171 Degree-Sign , 53 Degree-Sign ) and deep targeted observations in H{alpha}, [S II] {lambda}6716, [N II] {lambda}6584, and [O I] {lambda}6300 toward regions with high H I column densities, background quasars, and stars. The H{alpha} data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than 10{sup 6} M{sub Sun }. We find that the Bland-Hawthorn and Maloney model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7-8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 10{sup 4} K or for gas with a high fraction of singly ionized nitrogen and sulfur.

  12. A HIGH-METALLICITY, HIGH-VELOCITY CLOUD ALONG THE Mrk 421 SIGHT LINE: A TRACER OF COMPLEX M?

    SciTech Connect

    Yao Yangsen; Shull, J. Michael; Danforth, Charles W. E-mail: michael.shull@colorado.edu

    2011-02-10

    We present a new measurement, 0.85-3.5 Z{sub sun}, of the metallicity of high-velocity cloud (HVC) Complex M by analyzing ultraviolet spectroscopic observations of the blazar Mrk 421 taken with the Cosmic Origins Spectrograph on the Hubble Space Telescope and the Far-Ultraviolet Spectroscopic Explorer. Although an HVC at V{sub LSR} = -131 km s{sup -1} is not visible in 21 cm emission (log N{sub H{sub I}} < 18.38; 3{sigma}), it is detected in ultraviolet absorption lines of C II, N I, O I, O VI, Si II, Si III, Si IV, Fe II, and H I. By referencing velocities to the intermediate-velocity cloud at -60 km s{sup -1} and jointly analyzing H I absorption from high-order H I Lyman lines, we measure log N{sub H{sub I}} = 16.84{sup +0.34}{sub -0.13} (1{sigma}) in the HVC. Comparing H I and O I, we find an HVC metallicity [O/H] =0.32{sup +0.22}{sub -0.39}. Because the sight line passes {approx}4{sup 0} from the HVCs in Complex M, the detected HVC may represent the highest velocity component of the Complex, and our measurements provide a lower limit to its metallicity. The high, possibly super-solar metallicity, together with the low distance, z < 3.5 kpc, above the Galactic plane suggests that Complex M is condensed returning gas from a Galactic fountain.

  13. Present-day Galactic Evolution: Low-metallicity, Warm, Ionized Gas Inflow Associated with High-velocity Cloud Complex A

    NASA Astrophysics Data System (ADS)

    Barger, K. A.; Haffner, L. M.; Wakker, B. P.; Hill, Alex. S.; Madsen, G. J.; Duncan, A. K.

    2012-12-01

    The high-velocity cloud Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin Hα Mapper kinematically resolved observations of Complex A over the velocity range of -250 to -50 km s-1 in the local standard of rest reference frame. These observations include the first full Hα intensity map of Complex A across (\\mathit {l, b}) = (124{^\\circ }, 18{^\\circ }) to (171°, 53°) and deep targeted observations in Hα, [S II] λ6716, [N II] λ6584, and [O I] λ6300 toward regions with high H I column densities, background quasars, and stars. The Hα data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than 106 M ⊙. We find that the Bland-Hawthorn & Maloney model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7-8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 104 K or for gas with a high fraction of singly ionized nitrogen and sulfur.

  14. Neural responses to the mechanical parameters of a high velocity, low amplitude spinal manipulation: effect of preload parameters

    PubMed Central

    Reed, William. R.; Long, Cynthia R.; Kawchuk, Gregory N.; Pickar, Joel G.

    2014-01-01

    Objective The purpose of this study was to determine how the preload that precedes a high velocity low amplitude spinal manipulation (HVLA-SM) affects muscle spindle input from lumbar paraspinal muscles both during and after the HVLA-SM. Methods Primary afferent activity from muscle spindles in lumbar paraspinal muscles were recorded from the L6 dorsal root in anesthetized cats. HVLA-SM of the L6 vertebra was preceded either by no preload or by systematic changes in the preload magnitude, duration, and the presence or absence of a downward incisural point (DIP). Immediate effects of preload on muscle spindle responses to the HVLA-SM were determined by comparing mean instantaneous discharge frequencies (MIF) during the HVLA-SM’s thrust phase with baseline. Longer lasting effects of preload on spindle responses to the HVLA-SM were determined by comparing MIF during slow ramp and hold movement of the L6 vertebra before and following the HVLA-SM. Results The smaller compared to the larger preload magnitude and the longer compared to the shorter preload duration significantly increased (P=0.02 and P=0.04) respectively) muscle spindle responses during the HVLA-SM thrust. The absence of preload had the greatest effect on the change in MIF. Interactions between preload magnitude, duration and DIP often produced statistically significant but arguably physiologically modest changes in the passive signaling properties of the muscle spindle following the manipulation. Conclusion Because preload parameters in this animal model were shown to affect neural responses to an HVLA-SM, preload characteristics should be taken into consideration when judging this intervention’s therapeutic benefit in both clinical efficacy studies and in clinical practice. PMID:24387888

  15. The Silicon and Calcium High-velocity Features in Type Ia Supernovae from Early to Maximum Phases

    NASA Astrophysics Data System (ADS)

    Zhao, Xulin; Wang, Xiaofeng; Maeda, Keiichi; Sai, Hanna; Zhang, Tianmeng; Zhang, Jujia; Huang, Fang; Rui, Liming; Zhou, Qi; Mo, Jun

    2015-09-01

    The high-velocity features (HVFs) in optical spectra of type Ia supernovae (SNe Ia) are examined with a large sample including very early-time spectra (e.g., t < -7 days). Multiple Gaussian fits are applied to examine the HVFs and their evolutions, using constraints on expansion velocities for the same species (i.e., Si ii 5972 and Si ii 6355). We find that strong HVFs tend to appear in SNe Ia with smaller decline rates (e.g., Δm15(B) ≲ 1.4 {mag}), clarifying that the finding by Childress et al. for the Ca-HVFs in near-maximum-light spectra applies both to the Si-HVFs and Ca-HVFs in the earlier phase. The Si-HVFs seem to be more common in rapidly expanding SNe Ia, which is different from the earlier result that Ca-HVFs are associated with SNe Ia that have slower Si ii 6355 velocities at maximum light (i.e., VSimax). Moreover, SNe Ia with both stronger HVFs at early phases and larger VSimax are found to have noticeably redder B-V colors and to occur preferentially in the inner regions of their host galaxies, while those with stronger HVFs but smaller VSimax show opposite tendencies, suggesting that these two subclasses have different explosion environments and their HVFs may have different origins. We further examine the relationships between the absorption features of Si ii 6355 and Ca ii IR lines, and find that their photospheric components are well correlated in velocity and strength but that the corresponding HVFs show larger scatter. These results cannot be explained with ionization and/or thermal processes alone, and different mechanisms are required for the creation of HVF-forming regions in SNe Ia.

  16. Development of wear resistant nanostructured duplex coatings by high velocity oxy-fuel process for use in oil sands industry.

    PubMed

    Saha, Gobinda C; Khan, Tahir I; Glenesk, Larry B

    2009-07-01

    Oil sands deposits in Northern Alberta, Canada represent a wealth of resources attracting huge capital investment and significant research focus in recent years. As of 2005, crude oil production from the current oil sands operators accounted for 50% of Canada's domestic production. Alberta's oil sands deposits contain approximately 1.7 trillion barrels of bitumen, of which over 175 billion are recoverable with current technology, and 315 billion barrels are ultimately recoverable with technological advances. A major problem of operating machinery and equipment in the oil sands is the unpredictable failure from operating in this highly aggressive environment. One of the significant causes of that problem is premature material wear. An approach to minimize this wear is the use of protective coatings and, in particular, a cermet thin coating. A high level of coating homogeneity is critical for components such as bucketwheels, draglines, conveyors, shovels, heavyhauler trucks etc. that are subjected to severe degradation through abrasive wear. The identification, development and application of optimum wear solutions for these components pose an ongoing challenge. Nanostructured cermet coatings have shown the best results of achieving the degree of homogeneity required for these applications. In this study, WC-17Co cermet powder with nanocrystalline WC core encapsulated with 'duplex' Co layer was used to obtain a nanostructured coating. To apply this coating, high velocity oxy-fuel (HVOF) thermal spraying technique was used, as it is known for producing wear-resistant coatings superior to those obtained from plasma-based techniques. Mechanical, sliding wear and microstructural behavior of the coating was compared with those of the microstructured coating obtained from spraying WC-10Co-4Cr cermet powder by HVOF technique. Results from the nanostructured coating, among others, showed an average of 25% increase in microhardness, 30% increase in sliding wear resistance and

  17. Exocomet Circumstellar Fe I Absorption in the Beta Pictoris Gas Disk

    NASA Astrophysics Data System (ADS)

    Welsh, Barry Y.; Montgomery, Sharon

    2016-06-01

    We present an archival study of 27 circumstellar Fe i (λ3860 Å) and Ca ii (λ3933 Å) absorption spectra of the β Pictoris system recorded over the 2003-2014 timeframe. We have detected several transient absorption events at velocities red-shifted by >+20 km s-1 from the main central absorption line profiles of both Fe i and Ca ii. Such events can be attributed to the presence of kilometer-sized infalling evaporating bodies (i.e., exocomets) on their grazing approach to the central star. The majority of the transient absorption events detected in the Fe i profiles occur at velocities in the +35 to +50 km s-1 range. This is consistent with that found for Ca ii gas that has been sublimated from the “D” family of β Pictoris exocomets recently found by Kiefer et al. These spectra also reveal that the strength of the main component of the Fe i absorption line at V helio ˜ +21 km s-1 has weakened by ˜30% since 2011. Since neutrals, when ionized, are the main source of the ion-braking mechanism of Brandeker for circumstellar gas in the β Pictoris system, then this may have some measurable effect on the size and/or location of the main circumstellar gas disk. Finally we note that we have failed to detect any circumstellar Fe i absorption in our previously reported spectra of similar gas disks surrounding 28 young A-type stars. Thus, it would appear that the β Pictoris is anomalous with regards to circumstellar Fe i absorption.

  18. The circumstellar nature of the metallic features in a hot DA white dwarf

    NASA Technical Reports Server (NTRS)

    Holberg, J. B.; Bruhweiler, F. C.; Andersen, J.

    1995-01-01

    A new co-added IUE echelle spectrum of the bright DA white dwarf CD -38 deg 10980, together with a newly determined radial velocity for this star, indicate that the sharp lined Si and C absorption features seen in the UV are clearly circumstellar in origin. Absorption in both excited and ground state transitions occurs at a velocity displaced by -12.1 +/- 2.0 km.s with respect to the photospheric velocity. Weak features due to the Si IV doublet are seen at a velocity intermediate between that of the circumstellar features and the photosphere. First time estimates of column densities for excited and ground states of C II, Si II, and Si III are derived. These quantities are used with electron density estimates derived from these species to determine the location and physical conditions of the circumstellar gas in the vicinity of CD -38 deg 10980. If collisional excitation alone is responsible for the excited levels of Si III observed in CD -38 deg 10980, then electron densities in the circumstellar gas must exceed 10(exp 9)/cu cm. Substantially lower electron densities are possible if the circumstellar gas is located near enough to the star so that photoexcitation is the dominant process responsible for the excited lines seen in the UV. Strong limits are placed on the photospheric abundance of Si and C in the star itself. These limits are in sharp contrast to the theoretical predictions of radiative levitation in which Si, but not C, is expected in the photosphere of a white dwarf such as CD -38 deg 10980. The interstellar line of sight to CD -38 deg 10980 is also investigated.

  19. 31. TACOMA NARROWS BRIDGE, LOOKING WEST ACROSS TOLL PLAZA, 29 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    31. TACOMA NARROWS BRIDGE, LOOKING WEST ACROSS TOLL PLAZA, 29 AUGUST 1940. (ELDRIDGE, CLARK M. TACOMA NARROWS BRIDGE, TACOMA, WASHINGTON, FINAL REPORT ON DESIGN AND CONSTRUCTION, 1941) - Tacoma Narrows Bridge, Spanning Narrows at State Route 16, Tacoma, Pierce County, WA

  20. 30. TACOMA NARROWS BRIDGE, LOOKING EAST THROUGH TOLL LANES, 29 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    30. TACOMA NARROWS BRIDGE, LOOKING EAST THROUGH TOLL LANES, 29 AUGUST 1940. (ELDRIDGE, CLARK H. TACOMA NARROWS BRIDGE, TACOMA, WASHINGTON, FINAL REPORT ON DESIGN AND CONSTRUCTION, 1941) - Tacoma Narrows Bridge, Spanning Narrows at State Route 16, Tacoma, Pierce County, WA

  1. Massive stars exploding in a He-rich circumstellar medium - VIII. PSN J07285387+3349106, a highly reddened supernova Ibn

    NASA Astrophysics Data System (ADS)

    Pastorello, A.; Tartaglia, L.; Elias-Rosa, N.; Morales-Garoffolo, A.; Terreran, G.; Taubenberger, S.; Noebauer, U. M.; Benetti, S.; Cappellaro, E.; Ciabattari, F.; Dennefeld, M.; Dimai, A.; Ishida, E. E. O.; Harutyunyan, A.; Leonini, S.; Ochner, P.; Sollerman, J.; Taddia, F.; Zaggia, S.

    2015-12-01

    We present spectroscopic and photometric observations for the Type Ibn supernova (SN) dubbed PSN J07285387+3349106. Using data provided by amateur astronomers, we monitored the photometric rise of the SN to maximum light, occurred on 2015 February 18.8 UT (JDmax(V) = 245 7072.0 ± 0.8). PSN J07285387+3349106 exploded in the inner region of an infrared luminous galaxy, and is the most reddened SN Ibn discovered so far. We apply multiple methods to derive the total reddening to the SN, and determine a total colour excess E(B - V)tot = 0.99 ± 0.48 mag. Accounting for the reddening correction, which is affected by a large uncertainty, we estimate a peak absolute magnitude of MV = -20.30 ± 1.50. The spectra are dominated by continuum emission at early phases, and He I lines with narrow P-Cygni profiles are detected. We also identify weak Fe III and N II features. All these lines show an absorption component which is blueshifted by about 900-1000 km s-1. The spectra also show relatively broad He I line wings with low contrast, which extend to above 3000 km s-1. From about two weeks past maximum, broad lines of O I, Mg II and the Ca II near-infrared triplet are identified. The composition and the expansion velocity of the circumstellar material, and the presence of He I and α-elements in the SN ejecta indicate that PSN J07285387+3349106 was produced by the core collapse of a stripped-envelope star. We suggest that the precursor was WNE-type Wolf-Rayet star in its dense, He-rich circumstellar cocoon.

  2. Infants Experience Perceptual Narrowing for Nonprimate Faces

    ERIC Educational Resources Information Center

    Simpson, Elizabeth A.; Varga, Krisztina; Frick, Janet E.; Fragaszy, Dorothy

    2011-01-01

    Perceptual narrowing--a phenomenon in which perception is broad from birth, but narrows as a function of experience--has previously been tested with primate faces. In the first 6 months of life, infants can discriminate among individual human and monkey faces. Though the ability to discriminate monkey faces is lost after about 9 months, infants…

  3. Do narrow {Sigma}-hypernuclear states exist?

    SciTech Connect

    Chrien, R.E.

    1995-12-31

    Reports of narrow states in {Sigma}-hypernucleus production have appeared from time to time. The present experiment is a repeat of the first and seemingly most definitive such experiment, that on a target of {sup 9}Be, but with much better statistics. No narrow states were observed.

  4. Study of irradiated Hadfield steel using transmission Mössbauer spectroscopy with high velocity resolution and conversion electron Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Semionkin, V. A.; Neshev, F. G.; Tsurin, V. A.; Milder, O. B.; Oshtrakh, M. I.

    2010-03-01

    Proton irradiated Hadfield steel foil was studied using transmission Mössbauer spectroscopy with high velocity resolution and conversion electron Mössbauer spectroscopy. It was shown that proton irradiation leads to structural changes in the foil as well as to surface oxidation with ferric hydrous oxide formation (ferrihydrite). Moreover, oxidation on the foil underside was higher than on the foil right side.

  5. Infrared and X-Ray Evidence for Circumstellar Grain Destruction by the Blast Wave of Supernova 1987A

    NASA Technical Reports Server (NTRS)

    Dwek, Eliahu; Arendt, Richard G.; Bouchet, Patrice; Burrows, David N.; Challis, Peter; Danziger, John; DeBuizer James M.; Gehrz, Robert D.; Kirshner, Robert P.; McCray, Richard; Park, Sangwok; Polomski, Elisha; Woodward, Charles

    2007-01-01

    Multiwavelength observations of supernova remnant (SNR) 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared, and radio wavelengths as the blast wave from the explosion expands into the circumstellar equatorial ring, produced by mass loss from the progenitor star. The observed infrared (IR) radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray emitting plasma component of the shocked gas. Spitzer IRS spectra at 5 - 30 microns taken on day 6190 since the explosion show that the emission arises from approx. 1.1 x 10(exp -6) solar mass of silicate grains radiating at a temperature of approx. 180+/-(15-20) K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) is consistent with that of a dusty plasma with standard LMC dust abundances. This flux ratio has decreased by a factor of approx. 2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding SN blast wave on dynamic time scales. Detailed models consistent with the observed dust temperature, the ionization fluence of the soft X-ray emission component, and the evolution of IRX suggest that the radiating si1icate grains are immersed in a 3.5 x 10(exp 6) K plasma with a density of (0.3 - 1) x 10(exp 4)/cu cm, and have a size distribution that is confined to a narrow range of radii between 0.02 and 0.2 microns. Smaller grains may have been evaporated by the initial UV flash from the supernova.

  6. Narrow band gap amorphous silicon semiconductors

    DOEpatents

    Madan, A.; Mahan, A.H.

    1985-01-10

    Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

  7. Characterizing high-velocity angular vestibulo-ocular reflex function in service members post-blast exposure.

    PubMed

    Scherer, Matthew R; Shelhamer, Mark J; Schubert, Michael C

    2011-02-01

    Blasts (explosions) are the most common mechanism of injury in modern warfare. Traumatic brain injury (TBI) and dizziness are common sequelae associated with blasts, and many service members (SMs) report symptoms worsen with activity. The purpose of this study was to measure angular vestibulo-ocular reflex gain (aVOR) of blast-exposed SMs with TBI during head impulse testing. We also assessed their symptoms during exertion. Twenty-four SMs recovering from TBI were prospectively assigned to one of two groups based on the presence or absence of dizziness. Wireless monocular scleral search coil and rate sensor were used to characterize active and passive yaw and pitch head and eye rotations. Visual analog scale (VAS) was used to monitor symptoms during fast walking/running. For active yaw head impulses, aVOR gains were significantly lower in the symptomatic group (0.79 ± 0.15) versus asymptomatic (0.87 ± 0.18), but not for passive head rotation. For pitch head rotation, the symptomatic group had both active (0.915 ± 0.24) and passive (0.878 ± 0.22) aVOR gains lower than the asymptomatic group (active 1.03 ± 0.27, passive 0.97 ± 0.23). Some SMs had elevated aVOR gain. VAS scores for all symptoms were highest during exertion. Our data suggest symptomatic SMs with TBI as a result of blast have varied aVOR gain during high-velocity head impulses and provide compelling evidence of pathology affecting the vestibular system. Potential loci of injury in this population include the following: disruption of pathways relaying vestibular efference signals, differential destruction of type I vestibular hair cells, or selective damage to irregular afferent pathways-any of which may explain the common discrepancy between reports of vestibular-like symptoms and laboratory testing results. Significantly reduced pitch aVOR in symptomatic SMs and peak symptom severity during exertional testing support earlier findings in the chronic blast-exposed active duty SMs.

  8. Searching for Stellar Counterparts to ALFALFA Ultra-Compact High Velocity Clouds with WIYN / pODI

    NASA Astrophysics Data System (ADS)

    Janesh, William; Rhode, Katherine L.; Salzer, John Joseph; Janowiecki, Steven; Adams, Elizabeth A.; Haynes, Martha P.; Giovanelli, Riccardo; Cannon, John M.; Munoz, Ricardo

    2015-01-01

    A current issue in cosmology is the disagreement between models and observations regarding the number of low-mass galaxies in the Local Volume. While simulations of structure formation in a Lambda-CDM universe predict large numbers of low-mass dark matter halos, observational campaigns have not yet found sufficient numbers of faint, low-mass galaxies to match the models. The ALFALFA neutral hydrogen (HI) survey has detected a sample of isolated ultra-compact high-velocity HI clouds (UCHVCs) with kinematic properties that make them likely members of the Local Volume. This UCHVC sample as a group possesses properties similar to other known ultra-faint dwarf galaxies like Leo T (at 1 Mpc, HI masses of ~105-106 M⊙, HI diameters of ~2-3 kpc, and dynamical masses of ~107-108 M⊙). We have initiated a campaign to obtain deep optical imaging of the UCHVCs using the 24' x 24' pODI camera on the WIYN 3.5-m telescope. Here we present a technique to search for faint but resolved stellar counterparts to the UCHVCs in our optical images. We begin by processing and stacking the pipeline-reduced pODI g'- and i'-band images in order to maximize the number of sources we can detect while preserving the photometric integrity of the data. We then remove extended sources and measure calibrated g' and i' magnitudes for all the resulting point sources in the images. We apply a color-magnitude filter, constructed using theoretical isochrones for old stellar populations, to select stars in a single population and at a given distance. The spatial distribution of the point sources selected by the filter is then smoothed on a number of spatial scales. Strong overdensities in the resulting smoothed spatial distributions indicate the possible presence of a dwarf galaxy counterpart to the UCHVC. We have also developed statistical tests that quantify the likelihood of detecting true stellar overdensities in our images. We show recent examples of our results.

  9. Proper motion with HST: Searching for high-velocity stars in the core of the globular cluster 47 Tucanae

    SciTech Connect

    Meylan, G.; Minniti, D.; Pryor, C.; Tinney, C.G.; Phinney, E.S.; Sams, B.

    1996-02-13

    Binary stars play an essential role during the late phases of the dynamical evolution of a globular cluster. They transfer energy to passing stars and so can strongly influence the cluster evolution, enough to delay, halt, and even reverse core collapse. Hard binaries are known to exist in cluster cores, e.g., in the form of millisecond pulsars (about half of the millisecond pulsars observed in 47 Tucanae are such hard binaries). The presence of hard binaries may also be revealed by searching for the by-products of close encounters: high- velocity stars, such as those discovered in the core of 47 Tuc by Meylan et al. (1991) and Gebhardt et al. (1995). These studies represent the limit of the radial velocity data which can be obtained from the ground. If more progress is to be made, it must come through obtaining proper motions--a task for which {ital only} the Hubble Space Telescope (HST) is suitable. We are using WFPC2 to obtain deep U (F300W) images of the core of 47 Tuc at three different epochs over two years, with which we will measure differential proper motions to a 1-{sigma} limit of 0.23 mas/yr. This--rather conservative--estimate corresponds to a 5-{sigma} detection of all stars with tangential velocities greater than 22 km s{sup -1}. By using the F300W filter we can measure stars over the whole color-magnitude diagram, from the red-giant branch to well down the main sequence. Such a complete census will provide unique constraints as a function of the stellar mass on relaxation processes, collision and ejection rates, and the velocity distribution. Here we report on the first-epoch (Cycle 5) observations of this project. Although no proper motions are available yet, some preliminary by-product results are presented. These include luminosity functions and color-magnitude diagrams for the core of 47 Tuc and the light curves of variable blue straggler stars and of a candidate X-ray source. 32 refs., 5 figs.

  10. High-velocity extended molecular outflow in the star-formation dominated luminous infrared galaxy ESO 320-G030

    NASA Astrophysics Data System (ADS)

    Pereira-Santaella, M.; Colina, L.; García-Burillo, S.; Alonso-Herrero, A.; Arribas, S.; Cazzoli, S.; Emonts, B.; Piqueras López, J.; Planesas, P.; Storchi Bergmann, T.; Usero, A.; Villar-Martín, M.

    2016-10-01

    We analyze new high spatial resolution (~60 pc) ALMA CO(2-1) observations of the isolated luminous infrared galaxy ESO 320-G030 (d = 48 Mpc) in combination with ancillary Hubble Space Telescope optical and near infrared (IR) imaging, as well as VLT/SINFONI near-IR integral field spectroscopy. We detect a high-velocity (~450 km s-1) spatially resolved (size~2.5 kpc; dynamical time ~3 Myr) massive (~107 M⊙; Ṁ ~ 2-8 M⊙ yr-1) molecular outflow that has originated in the central ~250 pc. We observe a clumpy structure in the outflowing cold molecular gas with clump sizes between 60 and 150 pc and masses between 105.5 and 106.4 M⊙. The mass of the clumps decreases with increasing distance, while the velocity is approximately constant. Therefore, both the momentum and kinetic energy of the clumps decrease outwards. In the innermost (~100 pc) part of the outflow, we measure a hot-to-cold molecular gas ratio of 7 × 10-5, which is similar to that measured in other resolved molecular outflows. We do not find evidence of an ionized phase in this outflow. The nuclear IR and radio properties are compatible with strong and highly obscured star-formation (Ak ~ 4.6 mag; star formation rate ~ 15 M⊙ yr-1). We do not find any evidence for the presence of an active galactic nucleus. We estimate that supernova explosions in the nuclear starburst (νSN ~ 0.2 yr-1) can power the observed molecular outflow. The kinetic energy and radial momentum of the cold molecular phase of the outflow correspond to about 2% and 20%, respectively, of the supernovae output. The cold molecular outflow velocity is lower than the escape velocity, so the gas will likely return to the galaxy disk. The mass loading factor is ~0.1-0.5, so the negative feedback owing to this star-formation-powered molecular outflow is probably limited. The reduced images and datacubes (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

  11. Characterizing high-velocity angular vestibulo-ocular reflex function in service members post-blast exposure

    PubMed Central

    Scherer, Matthew R.; Shelhamer, Mark J.; Schubert, Michael C.

    2011-01-01

    Blasts (explosions) are the most common mechanism of injury in modern warfare. Traumatic brain injury (TBI) and dizziness are common sequelae associated with blasts, and many service members (SMs) report symptoms worsen with activity. The purpose of this study was to measure angular vestibulo-ocular reflex gain (aVOR) of blast-exposed SMs with TBI during head impulse testing. We also assessed their symptoms during exertion. Twenty-four SMs recovering from TBI were prospectively assigned to one of two groups based on the presence or absence of dizziness. Wireless monocular scleral search coil and rate sensor were used to characterize active and passive yaw and pitch head and eye rotations. Visual analog scale (VAS) was used to monitor symptoms during fast walking/running. For active yaw head impulses, aVOR gains were significantly lower in the symptomatic group (0.79 ± 0.15) versus asymptomatic (0.87 ± 0.18), but not for passive head rotation. For pitch head rotation, the symptomatic group had both active (0.915 ± 0.24) and passive (0.878 ± 0.22) aVOR gains lower than the asymptomatic group (active 1.03 ± 0.27, passive 0.97 ± 0.23). Some SMs had elevated aVOR gain. VAS scores for all symptoms were highest during exertion. Our data suggest symptomatic SMs with TBI as a result of blast have varied aVOR gain during high-velocity head impulses and provide compelling evidence of pathology affecting the vestibular system. Potential loci of injury in this population include the following: disruption of pathways relaying vestibular efference signals, differential destruction of type I vestibular hair cells, or selective damage to irregular afferent pathways—any of which may explain the common discrepancy between reports of vestibular-like symptoms and laboratory testing results. significantly reduced pitch aVOR in symptomatic SMs and peak symptom severity during exertional testing support earlier findings in the chronic blast-exposed active duty SMs. PMID:21113582

  12. Fault strength evolution during high velocity friction experiments with slip-pulse and constant-velocity loading

    NASA Astrophysics Data System (ADS)

    Liao, Z.; Chang, J. C.; Reches, Z.

    2014-12-01

    Seismic analyses show that slip during large earthquakes evolves in a slip-pulse mode that is characterized by abrupt, intense acceleration followed by moderate deceleration. We experimentally analyze the friction evolution under slip-pulse proxy of a large earthquake, and compare it with the evolution at loading modes of constant-velocity and changing-velocity. We present a series of 42 experiments conducted on granite samples sheared in a high-velocity rotary apparatus. The experiments were conducted on room-dry, solid granite samples at slip-velocities of 0.0006-1 m/s, and normal stress of 1-11.5 MPa. The constitutive relations are presented with respect to mechanical power-density: PD= [shear stress * slip velocity], with units of power per area (MW/m^2). The experimental constitutive relations strongly depend on the loading mode. Constant velocity mode displays initial weakening with increasing PD that is followed by strengthening for PD = 0.02-0.5 MW/m^2, and abrupt weakening at PD > 0.5 MW/m^2. Changing-velocity modes display gentle strengthening for PD < 0.2 MW/m^2 that is followed by abrupt weakening as PD reaches 0.7-0.8 MW/m^2. Beyond this level of power-density, the two loading modes diverge: in changing-velocity of quake-mode the experimental fault continues to weaken with friction coefficient approaching 0.2, whereas in changing-velocity of ramp-mode the fault strengthens with friction coefficient approaching 1.0. The analysis demonstrates that (1) the strength evolution and constitutive parameters of the granite fault strongly depend on the loading mode, and (2) the slip-pulse mode is energy efficient relatively to the constant-velocity mode as manifested by faster, more intense weakening and 50-90% lower energy dissipation. The results suggest that the frictional strength determined in slip-pulse experiments, is more relevant to simulations of earthquake rupture than frictional strength determined in constant-velocity experiments.Figure 1. Friction

  13. Search for and study of hot circumstellar dust envelopes

    NASA Astrophysics Data System (ADS)

    Shenavrin, V. I.; Taranova, O. G.; Nadzhip, A. E.

    2011-01-01

    Long-term (1984-2008) JHKLM photometry for 254 objects is presented. The observations were carried out in the standard JHKLM photometric system using an original method and a modern IR photometer designed and built at the Sternberg Astronomical Institute. Our program of studies included searches for and studies of relatively hot circumstellar dust envelopes. The most important results obtained using these observations include the following. We have detected relatively hot dust envelopes in a number of objects for the first time, including the RCB star UV Cas, RX Cas, several classical symbiotic stars, etc. A model has been calculated for the dust envelope of FG Sge, which formed around the star as a result of several successive cycles of dust condensation beginning in Autumn 1992. Several dust-condensation episodes have been traced in the envelopes of symbiotic systems (CH Cyg, V1016 Cyg, HM Sge, etc.), as well as the role of the hot component in the formation of the dust envelopes. We have established from variations of the IR emission that the cool components in the symbiotic novae V1016 Cyg and HM Sge, and possibly CH Cyg, are Miras. The binarity of V1016 Cyg and HM Sge has also been firmly established. The variability of a whole series of object has been studied, including the stellar components of close binary systems and several dozen Mira and semi-regular variables. The ellipsoidality of the components in the RX Cas system (a prototype W Ser star) and the cool component in the symbiotic systems CI Cyg and BF Cyg has been firmly established. We have obtained the first IR light curve for the eclipsing system V444 Cyg (WN5+O6), and determined the wavelength dependence of the obtained parameters of the WN5 star. Analysis of the IR light curves of several novae indicate the condensation of dust envelopes in the transition periods of Cygnus 1992, Aquila 1993, and Aquila 1995. The IR light curve of R CrB has been obtained over a long period and analyzed. IR

  14. EARLY THERMAL X-RAY EMISSION FROM LONG GAMMA-RAY BURSTS AND THEIR CIRCUMSTELLAR ENVIRONMENTS

    SciTech Connect

    Suzuki, Akihiro; Shigeyama, Toshikazu

    2013-02-10

    We performed a series of hydrodynamical calculations of an ultrarelativistic jet propagating through a massive star and the circumstellar matter (CSM) to investigate the interaction between the ejecta and the CSM. We succeed in distinguishing two qualitatively different cases in which the ejecta are shocked and adiabatically cool. To examine whether the cocoon expanding at subrelativistic speeds emits any observable signal, we calculate the expected photospheric emission from the cocoon. It is found that the emission can explain early thermal X-ray emission recently found in some long gamma-ray bursts (GRBs). The result implies that the difference of the circumstellar environment of long GRBs can be probed by observing their early thermal X-ray emission.

  15. CIRCUMSTELLAR MAGNETITE FROM THE LAP 031117 CO3.0 CHONDRITE

    SciTech Connect

    Zega, Thomas J.; Haenecour, Pierre; Floss, Christine; Stroud, Rhonda M.

    2015-07-20

    We report the first microstructural confirmation of circumstellar magnetite, identified in a petrographic thin section of the LaPaz Icefield 031117 CO3.0 chondrite. The O-isotopic composition of the grain indicates an origin in a low-mass (∼2.2 M{sub ⊙}), approximately solar metallicity red/asymptotic giant branch (RGB/AGB) star undergoing first dredge-up. The magnetite is a single crystal measuring 750 × 670 nm, is free of defects, and is stoichiometric Fe{sub 3}O{sub 4}. We hypothesize that the magnetite formed via oxidation of previously condensed Fe dust within the circumstellar envelope of its progenitor star. Using an empirically derived rate constant for this reaction, we calculate that such oxidation could have occurred over timescales ranging from approximately ∼9000–500,000 years. This timescale is within the lifetime of estimates for dust condensation within RGB/AGB stars.

  16. Diffraction-limited spatial resolution of circumstellar shells at 10 microns

    NASA Technical Reports Server (NTRS)

    Bloemhof, E. E.; Townes, C. H.; Vanderwyck, A. H. B.

    1983-01-01

    A new spatial array instrument provided diffraction-limited mid-infrared intensity profiles of the type-M supergiant stars alpha Orionis and alpha Scorpii, both of which are known to exhibit excess 10 microns radiation due to the presence of circumstellar dust shells. In the case of alpha Ori, there is a marked asymmetry in the dust distribution, with peak intensity of dust emission a distance of 0.9 inches from the star.

  17. Herbig Ae/Be stars - Intermediate-mass stars surrounded by massive circumstellar accretion disks

    NASA Technical Reports Server (NTRS)

    Hillenbrand, Lynne A.; Strom, Stephen E.; Vrba, Frederick J.; Keene, Jocelyn

    1992-01-01

    The proposition that Herbig Ae/Be stars are young intermediate mass stars surrounded by optically thick accretion disks is explored. From a study of 47 such objects, a subset of 30 stars is identified whose spectral energy distributions can be interpreted convincingly in terms of pre-main sequence stars surrounded by massive optically thick circumstellar accretion disks. Constraints on the physical properties of the disks, such as size, mass, accretion rate, lifetime, and radial structure are derived from the photometric data.

  18. Correlation of circumstellar SiO maser spot distribution with the stellar light curve

    NASA Astrophysics Data System (ADS)

    Oyadomari, M.; Imai, H.; Nagayama, T.; Oyama, T.; Matsumoto, N.; Nakashima, J.; Cho, S.-H.

    2016-07-01

    We have investigated the distributions of silicon monoxide (SiO) v = 2 and v = 3 J = 1 → 0 masers around long-period variables (LPVs) in VLBI observations using the VLBI Exploration of Radio Astrometry (VERA) combined with the Nobeyama 45 m telescope. We find some examples of correlation of a maser spot distribution with the stellar light curve, which may provide a clue to elucidating the pumping mechanism of circumstellar SiO masers.

  19. High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

    NASA Astrophysics Data System (ADS)

    Tanii, Ryoko; Itoh, Yoichi; Kudo, Tomoyuki; Hioki, Tomonori; Oasa, Yumiko; Gupta, Ranjan; Sen, Asoke K.; Wisniewski, John P.; Muto, Takayuki; Grady, Carol A.; Hashimoto, Jun; Fukagawa, Misato; Mayama, Satoshi; Hornbeck, Jeremy; Sitko, Michael L.; Russell, Ray W.; Werren, Chelsea; Curé, Michel; Currie, Thayne; Ohashi, Nagayoshi; Okamoto, Yoshiko; Momose, Munetake; Honda, Mitsuhiko; Inutsuka, Shu-ichi; Takeuchi, Taku; Dong, Ruobing; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph; Egner, Sebastian E.; Feldt, Markus; Fukue, Tsubasa; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kusakabe, Nobuhiko; Kuzuhara, Masayuki; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-ichi; Moro-Martín, Amaya; Nishimura, Tetsuro; Pyo, Tae-Soo; Serabyn, Eugene; Suto, Hiroshi; Suzuki, Ryuji; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2012-12-01

    We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.''15 (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A, which extends to 120 AU, at a spatial resolution of 0.''1 (14 AU). It is inclined by 46° ± 2°, since the west side is nearest. Although SED modeling and sub-millimeter imagery have suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25-30 AU, we detect no evidence of a gap at the limit of our inner working angle (23 AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66%) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh-scattering nor Mie-scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with radii of 30μm is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations, and have grown in the circumstellar disk of UX Tau A.

  20. High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

    NASA Technical Reports Server (NTRS)

    Serabyn, G.; Grady, C. A.; Currie, T.

    2012-01-01

    We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.15" (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a spatial resolution of 0.1" (14 AU). It is inclined by 46 degrees plus or minus 2 degrees as the west side is nearest. Although SED modeling and sub-millimeter imagery suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at the limit of our inner working angle (23AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66 %) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh scattering nor Mie scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with the radii of 30 micrometers is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations and have grown in the circumstellar disk of UX Tau A.

  1. Observing the Circumstellar Environment of the Eruptive FUor/EXor Protostar V1647 Ori with ALMA

    NASA Astrophysics Data System (ADS)

    Principe, David; Cieza, Lucas A.; Zhu, Zhaohuan; Tobin, John J.; Prieto, Jose Luis

    2016-01-01

    Fu Ori (FUor) and EXor objects represent a short-lived stage of protostellar evolution characterized by intense mass accretion events which cause extreme variability in the form of outbursts. While it is well demonstrated that these objects exhibit sudden outbursts (ΔV~2-6), the mechanism causing such variability is not well understood. High spatial and spectral resolution observations of the circumstellar environment of these objects are essential to distinguish between different outbursting mechanisms. We present ALMA observations of the FUor/EXor object V1647 Ori as part of an ALMA campaign, which has observed a combined eight FUor and EXor type objects. Deeply embedded in the dark cloud LDN 1630 (L1630), V1647 Ori is one of a few FUor/EXor objects to have been extensively studied at multiple wavelengths before, during and after an outburst. We present preliminary results derived from ALMA 12CO, 13CO, C18O and continuum observations of the circumstellar environment of V1647 Ori. By measuring gas/dust masses and gas kinematics of the circumstellar disk, we investigate the potential mechanisms producing variability in these eruptive protostars during an essential, yet rarely observed, stage of pre-main sequence stellar evolution.

  2. Hot Wax Sweeps Debris From Narrow Passages

    NASA Technical Reports Server (NTRS)

    Ricklefs, Steven K.

    1990-01-01

    Safe and effective technique for removal of debris and contaminants from narrow passages involves entrainment of undesired material in thermoplastic casting material. Semisolid wax slightly below melting temperature pushed along passage by pressurized nitrogen to remove debris. Devised to clean out fuel passages in main combustion chamber of Space Shuttle main engine. Also applied to narrow, intricate passages in internal-combustion-engine blocks, carburetors, injection molds, and other complicated parts.

  3. Imaging spectrophotometry of ionized gas in NGC 1068. I - Kinematics of the narrow-line region

    NASA Technical Reports Server (NTRS)

    Cecil, Gerald; Bland, Jonathan; Tully, R. Brent

    1990-01-01

    The kinematics of collisionally excited forbidden N II 6548, 6583 across the inner 1 arcmin diameter of the nearby Seyfert galaxy NGC 1068 is mapped using an imaging Fabry-Perot interferometer and low-noise CCD. The stack of monochromatic images, which spatially resolved the high-velocity gas, was analyzed for kinematic and photometric content. Profiles agree well with previous long-slit work, and their complete spatial coverage makes it possible to constrain the gas volume distribution. It is found that the narrow-line region is distributed in a thick center-darkened, line-emitting cylinder that envelopes the collimated radio jet. Three distinct kinematic subsystems, of which the cylinder is composed, are discussed in detail. Detailed behavior of the emission-line profiles, at the few points in the NE quadrant with simple kinematics, argues that the ionized gas develops a significant component of motion perpendicular to the jet axis.

  4. PHL 1092: A narrow-line quasar emerging from the darkness

    NASA Astrophysics Data System (ADS)

    Gallo, Luigi

    2013-10-01

    The radio quiet, narrow line quasar, PHL1092 exhibits the extreme behaviour associated with 1H0707 and IRAS13224, but at a high redshift (z=0.396) and with high luminosity (~10^45 erg/s). From a short, bright state observation of PHL1092 we discovered a super soft excess, possible relativistically broadened FeL and K emission, high radiative efficiency, and possible high velocity outflow. Follow up observations between 2008-10 caught the quasar in a deep minimum that could be attributed to disruption of the corona. We will monitor PHL1092 with Swift to catch the quasar emerging from its current low-flux state so that we can study the bright state of the AGN with a triggered 130ks XMM observation.

  5. High-velocity interstellar gas in the lines of sight to the Wolf-Rayet stars HD 97152 and HD 96548

    NASA Technical Reports Server (NTRS)

    Nichols-Bohlin, Joy; Fesen, Robert A.

    1990-01-01

    The interstellar medium was studied in the direction to the WR stars HD 96548 and HD 97152, and the results are reported. New observational data on the UV spectra of several field stars near both these WR stars are presented. The high-velocity gas seen in the spectra of these stars suggests that the detected expanding interstellar gas structure consists of two OB cluster supershells. The presence of high-velocity absorption components in one of five field star spectra in the direction of the more isolated WR star HD 96548 suggests that this expanding gas does not originate from the optical ring nebula RCW 58 surrounding HD 96548, as previously believed, but instead indicates the detection of a previously unknown expanding interstellar shell in this line of sight.

  6. Numerical Simulation of the Twin-Wire Arc Spraying Process: Modeling the High Velocity Gas Flow Field Distribution and Droplets Transport

    NASA Astrophysics Data System (ADS)

    Chen, Yongxiong; Liang, Xiubing; Wei, Shicheng; Chen, Xi; Xu, Binshi

    2012-03-01

    During the twin-wire arc spraying, a high velocity gas stream is used to accelerate the arc-melting materials and propel the droplets toward the substrate surface. This study is aimed at investigating the gas flow formation and droplets transport processes using numerical simulation method. Results from the 3-D gas flow field model show that the distribution of the gas flow velocity on the twin-wire intersection plane is quite different from that on the twin-wire vertical plane. Based on the 3-D model, the convergence amplitude of the high velocity zone in the jet center is improved by modifying the gun head design. It is also observed that a flat substrate existed downstream from the gas nozzle exit results in decreasing close to zero in velocity of the gas jet near the substrate. In addition, the predicted droplet trajectories and velocity distributions exhibited good agreement with experimentally observations.

  7. Characterization of impact damage resistance of CF/PEEK and CF/toughened epoxy laminates under low and high velocity impact tests

    SciTech Connect

    Morita, Hideo; Adachi, Tadaharu; Tateishi, Yasuhiro; Matsumoto, Hiroyuki

    1995-12-31

    In order to use composite materials in aeronautical turbo engines, their resistance to impact damage must be understood. In this work the subperforation flat-wise impact resistance of three kinds of high resistance material systems were evaluated under low and high velocity impact tests. Tested systems were AS4/PEEK (APC-2/AS4, ICI-Fiberite), AS4/PEEK+IL, which consists of APC-2 prepreg and PEEK film inserted between layers as an interleave, and toughened epoxy system T800/{number_sign}3900 (Toray). To investigate the effects of stacking sequence on resistance, three lay-ups -- (0/+30/0/{minus}30)s, (0/+60/0/{minus}60)s, and (0/+45/90/{minus}45)s -- were tested. A drop weight system was used for the low velocity tests, where the velocity ranged from 1.5 to 3.1 m/s. An air gun system was used for the high velocity tests, where the velocity range was between 50 and 100 m/s. The relation between damage area (DA) and impact energy (IE) was linear, and the ratio of the DA/IE quantified the impact resistance of each specimen. The value of DA/IE for the high velocity tests was larger than the value for low velocity tests. To estimate the lay-up effect, a stacking parameter {beta}, which indicates the difference of the inplane stiffness between the adjacent laminae, was proposed. A proportional relation between the DA/IE and the {beta} was obtained. The value of (DA/IE)/{beta}, which was independent of stacking sequence, indicated the impact resistance of the tested material systems for both velocity levels. The ratio of (DA/IE)/{beta} for the high velocity to the value for the low velocity changed with material systems.

  8. Impact of an inhomogeneous density distribution on selected observational characteristics of circumstellar disks

    NASA Astrophysics Data System (ADS)

    Brauer, R.; Wolf, S.

    2016-01-01

    Context. Analysis of observations of circumstellar disks around young stellar objects is often based on disk models with smooth and continuous density distribution. However, spatially resolved observations with increasing angular resolution and dynamical models indicate that circumstellar disks are highly structured. Aims: We investigate the influence of different clumpy density distributions on selected physical properties and on the observable characteristics of circumstellar disks. In particular, these are the temperature distribution, the spectral energy distribution (SED), the radial brightness profile and the degree of polarization of scattered stellar radiation. Methods: Based on radiative transfer modeling we calculated the temperature structure of the disk and simulate observational quantities in the thermal re-emission and scattering regime. The clumpy density distributions are realized using a two-phase medium approach with phases for the clumps and the medium in between. We compared our results to those obtained for a smooth and continuous density distribution to quantify the influence of clumps on internal physical parameters and observable quantities of circumstellar disks. Results: Within the considered model space, the clumpiness has a significant impact on the disk temperature distribution. For instance, in the transition region from the optically thin upper disk layers to the disk interior, it causes a decrease in the mean temperature by up to 12 K (corresponding to ~15%), if compared to continuous disks. In addition, circumstellar disks with clumpy density distributions generally feature a lower spectral index in the submm/mm range of the SED than continuous disks. The strength of this decrease can be varied by changing the dust mass or grain size, but not by changing the inclination of the disk. As a consequence of the lower spectral index, the dust grain size derived from the submm/mm-slope of the SED may be overestimated, if the inhomogeneity

  9. Real-Time Thermographic-Phosphor-Based Temperature Measurements of Thermal Barrier Coating Surfaces Subjected to a High-Velocity Combustor Burner Environment

    NASA Technical Reports Server (NTRS)

    Eldridge, Jeffrey I.; Jenkins, Thomas P.; Allison, Stephen W.; Cruzen, Scott; Condevaux, J. J.; Senk, J. R.; Paul, A. D.

    2011-01-01

    Surface temperature measurements were conducted on metallic specimens coated with an yttria-stabilized zirconia (YSZ) thermal barrier coating (TBC) with a YAG:Dy phosphor layer that were subjected to an aggressive high-velocity combustor burner environment. Luminescence-based surface temperature measurements of the same TBC system have previously been demonstrated for specimens subjected to static furnace or laser heating. Surface temperatures were determined from the decay time of the luminescence signal of the YAG:Dy phosphor layer that was excited by a pulsed laser source. However, the furnace and laser heating provides a much more benign environment than that which exists in a turbine engine, where there are additional challenges of a highly radiant background and high velocity gases. As the next step in validating the suitability of luminescence-based temperature measurements for turbine engine environments, new testing was performed where heating was provided by a high-velocity combustor burner rig at Williams International. Real-time surface temperature measurements during burner rig heating were obtained from the decay of the luminescence from the YAG:Dy surface layer. The robustness of several temperature probe designs in the sonic velocity, high radiance flame environment was evaluated. In addition, analysis was performed to show whether the luminescence decay could be satisfactorily extracted from the high radiance background.

  10. Exploration of the interaction of type Ia supernovae with the circumstellar environment

    NASA Astrophysics Data System (ADS)

    Dragulin, Paul

    . The free parameters are: the a) mass loss dot{m}, b) wind velocity v_w, c) density distributions ∝ r. {-s} of theISM, and d)} the duration of the wind prior to the supernova explosion. I discuss the observational signatures with respect to light curves and high resolution spectra as tools to probe the environment of SNe˜Ia. The specific properties and evolution of the progenitor systems are found to leave unique imprints. During the progenitor evolution and with typical parameters in the SD scenario, the winds create a low density bubble surrounding the progenitor system and a high-density shell. It is also found that accretion disk winds dominate the environment formation. Within a distance of several light-years (ly), the densities are smaller by factors of 10. {2...4} compared to theenvironment. This explains the general lack of observed interaction in late time Supernova (SN) light curves for, at least, several years. The overdensities of the shells are between a factor of 4 to several hundred in case of constant density ISM and environments produced by stellar winds, respectively. The expansion velocity and width of the shell are typically 1-10 % of both v_w and the contact discontinuity R_C and may produce narrow spectral lines as observed in some SNe˜Ia. Typically, narrow circumstellar lines of equivalent width ≈ 100 m{Å are found for uniform ISM typical in Spiral galaxies and ≈ 1 m{Å} for wind environments. The outer layers of a SNe˜Ia expands with velocities of 10 to 30 % of the speed of light and we may expect some interaction with the shells several years after the explosion. I apply the analysis to SN2014J and discuss several scenarios. For SN˜2014J, the environment is likely formed by the AD wind running into a region produced by the Red Giant (RG) wind from the progenitor star prior to its WD stage. The delay times between the formation of the WD and the explosion is suggested to be short, ˜ 10. 5˜yr. Finally the same analysis is

  11. Detection of narrow C 4 and Si 4 absorption features in spectra of stars within 200 pc f the Sun

    NASA Technical Reports Server (NTRS)

    Molaro, P.; Beckman, J. E.; Franco, M.; Morossi, C.; Ramella, M.

    1984-01-01

    Detection of narrow (Beta lambda 0.5 A) absorption features in C 4 at lambda lambda 1548 and 1550 have been made in the spectra of 4 late B dwarfs within 200 pc of the Sun; the Si4 doublet at lambda lambda 1393 and 1403 shows up in two of them. It is argued that it is difficult to account for the strengths, widths, shapes, and C IV/Si IV ratios in terms consistent with a circumstellar origin except possibly for an asymmetric C IV component in one star (HD 185037). The most probable source is semi-torrid gas in the 50,000 K range forming the interfaces between cooler H 1 clouds and the ambient medium at coronal temperatures. Late B rapid rotators are used for local interstellar medium probing of this kind.

  12. Sulphur molecules in the circumstellar envelopes of M-type AGB stars

    NASA Astrophysics Data System (ADS)

    Danilovich, T.; De Beck, E.; Black, J. H.; Olofsson, H.; Justtanont, K.

    2016-04-01

    Aims: The sulphur compounds SO and SO2 have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO2 lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. Methods: We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO2 line emission. We use molecular data files for both SO and SO2 that are more extensive than those previously available. Results: Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of (6.7 ± 0.9) × 10-6 and an SO2 abundance of 5 × 10-6 with both species having high abundances close to the star. We also modelled 34SO and found an abundance of (3.1 ± 0.8) × 10-7, giving an 32SO/34SO ratio of 21.6 ± 8.5. We derive similar results for the circumstellar SO and SO2 abundances and their distributions for the low mass-loss rate object W Hya. For the higher mass-loss rate stars, we find shell-like SO distributions with peak abundances that decrease and peak abundance radii that increase with increasing mass-loss rate. The positions of the peak SO abundance agree very well with the photodissociation radii of H2O. We also modelled SO2 in two higher mass-loss rate stars but our models for these were less conclusive. Conclusions: We conclude that for the low mass-loss rate stars, the circumstellar SO and SO2 abundances are much higher than predicted by chemical models of the extended stellar atmosphere. These two species may also account for all the available sulphur. For the higher mass-loss rate stars we find evidence that SO is most efficiently formed in the circumstellar envelope, most likely through the photodissociation of H2O and the subsequent reaction between S and OH. The S

  13. A search for ultraviolet circumstellar gas absorption features in alpha Piscis Austrinus (Fomalhaut), a possible Beta Pictoris-like system

    NASA Technical Reports Server (NTRS)

    Cheng, K.-P.; Bruhweiler, Fred C.; Kondo, Yoji

    1994-01-01

    Archival high-dispersion International Ultraviolet Explorer (IUE) spectra have been used to search for circumstellar gas absorption features in alpha PsA (A3 V), a nearby (6.7 pc) proto-planetary system candidate. Recent sub-millimeter mapping observations around the region of alpha PsA indicate a spatially resolved dust disk like the one seen around Beta Pic. To determine how closely this putative disk resembles that of Beta Pic, we have searched for signatures of circumstellar gaseous absorption in all the available IUE high-dispersion data of alpha PsA. Examination of co-added IUE spectra shows weak circumstellar absorptions from excited levels in the resonance multiplet of Fe II near 2600 A. We also conclude that the sharp C I feature near 1657 A, previously identified as interstellar absorption toward alpha PsA, likely has a circumstellar origin. However, because the weakness of these absorption features, we will consider the presence of circumstellar gas as tentative and should be verified by using the Goddard High-Resolution Spectrograph aboard the Hubble Space Telescope. No corresponding circumstellar absorption is detected in higher ionization Fe III and Al III. Since the collisionally ionized nonphotospheric Al III resonance absorption seen in Beta Pic is likely formed close to the stellar surface, its absence in the UV spectra of alpha PsA could imply that, in contrast with Beta Pic, there is no active gaseous disk infall onto the central star. In the alpha PsA gaseous disk, if we assume a solar abundance for iron and all the iron is in the form of Fe II, plus a disk temperature of 5000 K, the Fe II UV1 absorption at 2611.8743 A infers a total hydrogen column density along the line of sight through the circumstellar disk of N(H) approximately equals 3.8 x 10(exp 17)/cm.

  14. Atomic momentum patterns with narrower intervals

    NASA Astrophysics Data System (ADS)

    Yang, Baoguo; Jin, Shengjie; Dong, Xiangyu; Liu, Zhe; Yin, Lan; Zhou, Xiaoji

    2016-10-01

    We studied the atomic momentum distribution of a superposition of Bloch states in the lowest band of an optical lattice after the action of the standing-wave pulse. By designing the imposing pulse on this superposed state, an atomic momentum pattern appears with a narrow interval between the adjacent peaks that can be far less than double recoil momentum. The patterns with narrower interval come from the effect of the designed pulse on the superposition of many Bloch states with quasimomenta throughout the first Brillouin zone. Our experimental result of narrow interval peaks is consistent with the theoretical simulation. The patterns of multiple modes with different quasimomenta may be helpful for precise measurement and atomic manipulation.

  15. Narrow-bandwidth unstable laser resonator

    SciTech Connect

    Reintjes, J.F.; Tankersley, L.L.; Cooper, D.

    1988-10-21

    The present invention relates to unstable laser resonators, particularly to unstable laser resonators, and particularly to an unstable laser resonator that produces optical radiation that simultaneously has the high output power diffraction-limited divergence characteristic of an unstable laser resonator and also the narrow bandwidth that can usually be obtained only with a stable laser resonator. Some success was achieved in the frequency narrowing of the laser radiation from an unstable laser resonator cavity by using a diffraction grating. This technique was works best with lasers that have sharp line structure, such as molecular lasers. For example, selection of a single line in a hydrogen-fluoride laser has been reported in several configurations involving the insertion of a diffraction grating into a standard unstable laser resonator cavity. Although currently available, unstable laser resonators have the configuration of choice for producing high-power, low-divergence radiation from laser cavities; they are not compatible with a simultaneous requirement of narrow bandwidth.

  16. Discovery of a narrow line quasar

    NASA Technical Reports Server (NTRS)

    Stocke, J.; Liebert, J.; Maccacaro, T.; Griffiths, R. E.; Steiner, J. E.

    1982-01-01

    A stellar object is reported which, while having X-ray and optical luminosities typical of quasars, has narrow permitted and forbidden emission lines over the observed spectral range. The narrow-line spectrum is high-excitation, the Balmer lines seem to be recombinational, and a redder optical spectrum than that of most quasars is exhibited, despite detection as a weak radio source. The object does not conform to the relationships between H-beta parameters and X-ray flux previously claimed for a large sample of the active galactic nuclei. Because reddish quasars with narrow lines, such as the object identified, may not be found by the standard techniques for the discovery of quasars, the object may be a prototype of a new class of quasars analogous to high-luminosity Seyfert type 2 galaxies. It is suggested that these objects cannot comprise more than 10% of all quasars.

  17. Atomic and Molecular Isotope Ratios in Circumstellar Envelopes: Fractionation vs. Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Milam, Stefanie

    The long standing question of "What are the origin, evolution, and fate of our Universe and/or Galaxy?" has puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolutionary state of a galaxy. Stars are the factories of heavy elements, including carbon, nitrogen, and oxygen, that are key to the chemical complexity associated with planetary systems. Primitive materials, such as meteorites and IDPs, have revealed a component of "atypical" isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive is essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to analyze data obtained from the Herschel Space Observatory of circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. This proposal augments completed programs from the Herschel Space Observatory, namely the the HIFISTARS program (PI: Bujarrabal), which at the time of proposal submission a significant portion of data will no longer be under proprietary regulations (https://nhscsci.ipac.caltech.edu/sc/).) The broader implications for this study include fundamental data necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace their natal, nucleosynthetic isotope ratios. We will analyze Herschel data obtained for a survey of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry

  18. Herschel Studies of Circumstellar Volatile Isotopes: Supporting Observations from the Ground and SOFIA

    NASA Astrophysics Data System (ADS)

    Milam, Stefanie

    The long standing question of ''What are the origin, evolution, and fate of our Universe and/or Galaxy?" has puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolution of a galaxy. Stars are the factories of heavy elements, including carbon, nitrogen, and oxygen, that are fundamental in chemical complexity associated with planetary systems. Primitive materials have revealed a component of “atypical” isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive are essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to perform a comprehensive program of radioastronomical and infrared observations in circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. These data augment current programs underway with the Herschel Space Observatory. The broad implications for this study include fundamental values necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace the natal, nucleosynthetic isotope ratio. We will survey a sample of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry (e.g. oxygen-rich vs. carbon-rich). The isotope ratios of 12C/13C, 14N/15N, 16O/17O, and 16O/18O will be obtained and compared to previous studies conducted on species now considered to be affected by chemical effects in the circumstellar shell

  19. Spitzer/MIPS Infrared Imaging of the Extremely Extended Circumstellar Dust Shell of HD 161796.

    NASA Astrophysics Data System (ADS)

    Speck, A. K.; Ueta, T.; Stencel, R.; MIRIAD Collaboration

    2005-12-01

    Evolved intermediate mass stars are major contributors to the interstellar medium. However, the mechanisms by which they do this are not well understood. Asymptotic giant branch (AGB) stars suffer mass loss which leads to the formation of a circumstellar shell of gas and dust. At the end of the AGB phase, mass loss stops and the circumstellar shell begins to drift away from the star. If the velocity of the AGB wind has been relatively constant, then dust furthest from the star represents the oldest mass loss, while material closer to the star represents more recent mass loss. Hence, circumstellar shells of AGB and post-AGB stars contain the fossil record of their mass loss, and therefore have the potential to verify many aspects of stellar evolution. IRAS and ISO data indicate that huge dust shells exist around many such objects, extending several parsecs from the central star. Furthermore, some of these large dust shells show evidence for mass-loss variations that correlate with evolutionary changes in the star itself. Previous observations lacked the sensitivity and spatial resolution to investigate the full extent and detailed structure of these large dust shells. Using Spitzer/MIPS's unique sensitivity and mapping capabilities, we have obtained a 160μ m image of the very extended dust shell around post-AGB star HD161796, which confirms that it exhibits weak extended emission out to a radius of several hundred arcseconds. We present preliminary studies of this observation and compare to previous FIR observations of this and other post-AGB stars. From this study we will be able to (a) constrain the mass of the progenitor star; (b) test theories of stellar evolution and mass-loss mechanisms; (c) determine the effect of dust chemistry on mass loss (and therefore on stellar evolution).

  20. ON ABSORPTION BY CIRCUMSTELLAR DUST, WITH THE PROGENITOR OF SN 2012aw AS A CASE STUDY

    SciTech Connect

    Kochanek, C. S.; Khan, R.; Dai, X.

    2012-11-01

    We use the progenitor of SN 2012aw to illustrate the consequences of modeling circumstellar dust using Galactic (interstellar) extinction laws that (1) ignore dust emission in the near-IR and beyond, (2) average over dust compositions, and (3) mischaracterize the optical/UV absorption by assuming that scattered photons are lost to the observer. The primary consequences for the progenitor of SN 2012aw are that both the luminosity and the absorption are significantly overestimated. In particular, the stellar luminosity is most likely in the range 10{sup 4.8} < L {sub *}/L {sub Sun} < 10{sup 5.0} and the star was not extremely massive for a Type IIP progenitor, with M {sub *} < 15 M {sub Sun }. Given the properties of the circumstellar dust and the early X-ray/radio detections of SN 2012aw, the star was probably obscured by an ongoing wind with M-dot {approx}10{sup -5.5} to 10{sup -5.0} M {sub Sun} yr{sup -1} at the time of the explosion, roughly consistent with the expected mass-loss rates for a star of its temperature (T{sub *} {approx_equal} 3600{sup +300} {sub -200} K) and luminosity. In the spirit of Galactic extinction laws, we supply simple interpolation formulae for circumstellar extinction by dusty graphitic and silicate shells as a function of wavelength ({lambda} {>=} 0.3 {mu}m) and total (absorption plus scattering) V-band optical depth ({tau}{sub V} {<=} 20). These do not include the contributions of dust emission, but provide a simple, physical alternative to incorrectly using interstellar extinction laws.