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Sample records for stellar velocity field

  1. Velocity Fields in Stellar Atmospheres Probed by Tomography

    NASA Astrophysics Data System (ADS)

    Jorissen, Alain; Van Eck, Sophie; Kravchenko, Kateryna

    A tomographic method to probe velocity fields within stellar atmospheres is described. It relies on the design of spectral masks collecting lines forming at given, pre-specified ranges of optical depths. Different masks thus probe different line-formation depths in the stellar atmosphere. The masks are cross-correlated with the observed spectrum to yield cross-correlation functions (CCFs). The cross-correlation has two advantages: (i) to overcome line crowding, and (ii) to reveal minute line asymmetries by adding together many lines. In pulsating stars (long-period variables or Cepheids), the CCFs are double-peaked around maximum light, when the shock front associated with the stellar pulsation is located in the layer probed by the considered mask. Double-peaked CCFs originate in stellar layers where upward- and downward-moving matter co-exist, on each side of the shock front. The application of the tomographic method to long-period variables and supergiants is illustrated.

  2. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Makarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism.We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) = (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) = (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star...

  3. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Makarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism.We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) = (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) = (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star...

  4. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Markarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0 +/- 1.4, B=13.1 +/- 1.2, K=1.1 +/- 1.8, and C=2.9 +/- 1.4 km s(exp -1) kpc(exp -1). The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at approximately -20 km s(exp -1) kpc(exp -1). A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z greater than 1 kpc

  5. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Astrophysics Data System (ADS)

    Makarov, V. V.; Murphy, D. W.

    2007-07-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (VX,VY,VZ)=(10.5,18.5,7.3)+/-0.1 km s-1 not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (VX,VY,VZ)=(9.9,15.6,6.9)+/-0.2 km s-1. The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0+/-1.4, B=-13.1+/-1.2, K=1.1+/-1.8, and C=-2.9+/-1.4 km s-1 kpc-1. The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at ~-20 km s-1 kpc-1. A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z>1 kpc), but here we surmise its existence in the thin disk at z<200 pc. The most unexpected and unexplained term within

  6. The stellar wind velocity field of HD 77581

    NASA Astrophysics Data System (ADS)

    Manousakis, A.; Walter, R.

    2015-12-01

    Aims: The early acceleration of stellar winds in massive stars is poorly constrained. The scattering of hard X-ray photons emitted by the pulsar in the high-mass X-ray binary Vela X-1 can be used to probe the stellar wind velocity and density profile close to the surface of its supergiant companion HD 77581. Methods: We built a high signal-to-noise and high resolution hard X-ray lightcurve of Vela X-1 measured by Swift/BAT over 300 orbital periods of the system and compared it with the predictions of a grid of hydrodynamic simulations. Results: We obtain very good agreement between observations and simulations for a narrow set of parameters, implying that the wind velocity close to the stellar surface is twice higher than usually assumed with the standard beta law. Locally a velocity gradient of β ~ 0.5 is favoured. Even if still incomplete, hydrodynamic simulations successfully reproduce several observational properties of Vela X-1.

  7. Mass-loss rates, ionization fractions, shock velocities, and magnetic fields of stellar jets

    NASA Technical Reports Server (NTRS)

    Hartigan, Patrick; Morse, Jon A.; Raymond, John

    1994-01-01

    In this paper we calculate emission-line ratios from a series of planar radiative shock models that cover a wide range of shock velocities, preshock densities, and magnetic fields. The models cover the initial conditions relevant to stellar jets, and we show how to estimate the ionization fractions and shock velocities in jets directly from observations of the strong emission lines in these flows. The ionization fractions in the HH 34, HH 47, and HH 111 jets are approximately 2%, considerably smaller than previous estimates, and the shock velocities are approximately 30 km/s. For each jet the ionization fractions were found from five different line ratios, and the estimates agree to within a factor of approximately 2. The scatter in the estimates of the shock velocities is also small (+/- 4 km/s). The low ionization fractions of stellar jets imply that the observed electron densities are much lower than the total densities, so the mass-loss rates in these flows are correspondingly higher (approximately greater than 2 x 10(exp -7) solar mass/yr). The mass-loss rates in jets are a significant fraction (1%-10%) of the disk accretion rates onto young stellar objects that drive the outflows. The momentum and energy supplied by the visible portion of a typical stellar jet are sufficient to drive a weak molecular outflow. Magnetic fields in stellar jets are difficult to measure because the line ratios from a radiative shock with a magnetic field resemble those of a lower velocity shock without a field. The observed line fluxes can in principle indicate the strength of the field if the geometry of the shocks in the jet is well known.

  8. The BRAVE Program. I. Improved Bulge Stellar Velocity Dispersion Estimates for a Sample of Active Galaxies

    NASA Astrophysics Data System (ADS)

    Batiste, Merida; Bentz, Misty C.; Manne-Nicholas, Emily R.; Onken, Christopher A.; Bershady, Matthew A.

    2017-02-01

    We present new bulge stellar velocity dispersion measurements for 10 active galaxies with secure MBH determinations from reverberation mapping. These new velocity dispersion measurements are based on spatially resolved kinematics from integral-field (IFU) spectroscopy. In all but one case, the field of view of the IFU extends beyond the effective radius of the galaxy, and in the case of Mrk 79 it extends to almost one half the effective radius. This combination of spatial resolution and field of view allows for secure determinations of stellar velocity dispersion within the effective radius for all 10 target galaxies. Spatially resolved maps of the first (V) and second (σ⋆) moments of the line of sight velocity distribution indicate the presence of kinematic substructure in most cases. In future projects we plan to explore methods of correcting for the effects of kinematic substructure in the derived bulge stellar velocity dispersion measurements.

  9. Radial velocity planet detection biases at the stellar rotational period

    NASA Astrophysics Data System (ADS)

    Vanderburg, Andrew; Plavchan, Peter; Johnson, John Asher; Ciardi, David R.; Swift, Jonathan; Kane, Stephen R.

    2016-07-01

    Future generations of precise radial velocity (RV) surveys aim to achieve sensitivity sufficient to detect Earth mass planets orbiting in their stars' habitable zones. A major obstacle to this goal is astrophysical RV noise caused by active areas moving across the stellar limb as a star rotates. In this paper, we quantify how stellar activity impacts exoplanet detection with radial velocities as a function of orbital and stellar rotational periods. We perform data-driven simulations of how stellar rotation affects planet detectability and compile and present relations for the typical time-scale and amplitude of stellar RV noise as a function of stellar mass. We show that the characteristic time-scales of quasi-periodic RV jitter from stellar rotational modulations coincides with the orbital period of habitable-zone exoplanets around early M-dwarfs. These coincident periods underscore the importance of monitoring the targets of RV habitable-zone planet surveys through simultaneous photometric measurements for determining rotation periods and activity signals, and mitigating activity signals using spectroscopic indicators and/or RV measurements at different wavelengths.

  10. The Evolution of Stellar Velocity Dispersion in Galaxy Mergers

    NASA Astrophysics Data System (ADS)

    Stickley, Nathaniel Roland

    Stellar velocity dispersion is a key measurable quantity in galactic astronomy, yet its variation during galaxy mergers is not well-understood theoretically. Thus, while it is fairly common to measure velocity dispersion in galaxies that are in the process of merging, it is unclear how these measurements should be interpreted. In this dissertation, I provide a theoretical analysis of the evolution of stellar velocity dispersion during galaxy mergers. This is done using a set of numerical simulations. The temporal and directional evolution of velocity dispersion are examined in detail for a variety of merger simulations. I also examine the effects that dust attenuation and star formation have on measurements of velocity dispersion by creating detailed, Doppler broadened galaxy spectra. Velocity dispersions are measured from the synthetic spectra using the same technique that is employed for observations of real galaxies. I find that velocity dispersion increases rapidly and significantly as two galaxies pass through one another. As galaxies recede from a collision, their velocity dispersions rapidly decrease and nearly return to their pre-collision values. Velocity dispersion increases in all directions during collisions, however the enhancement is most significant along the collision axis. After the nuclei of the progenitor system coalesce, the velocity dispersion oscillates slightly of the coalesced system oscillated around its final equilibrium value for up to several dynamical timescales. I also find that the mean velocity dispersion of young stars tends to be lower than the velocity dispersion of the galaxy as a whole. The young stars become dynamically heated with time. In most cases, the youngest stars are found in dusty environments. Thus, dust preferen- tially obscures young stars, partially removing them from the flux-weighted velocity dispersion measurement. This causes flux-weighted velocity dispersion measurements to be elevated with respect to mass

  11. Measuring Stellar Radial Velocities with a LISA Spectrograph

    NASA Astrophysics Data System (ADS)

    Boyd, David

    2016-05-01

    Conventional wisdom says it should not be possible to measure stellar radial velocities with a useful degree of precision with a spectrograph having spectral resolution of 1000. This paper will demonstrate that with a combination of careful observational technique and the use of cross correlation it is possible to far exceed initial expectations. This is confirmed by reproducing the known radial velocity of a catalogued SB1 star with a precision of 5.2 km/s. To demonstrate the scientific potential of such a spectrograph, we use radial velocity measurements to confirm the binary nature and measure the orbital period and parameters of a suspected post common envelope binary.

  12. Stellarator bootstrap current and plasma flow velocity at low collisionality

    NASA Astrophysics Data System (ADS)

    Helander, P.; Parra, F. I.; Newton, S. L.

    2017-04-01

    The bootstrap current and flow velocity of a low-collisionality stellarator plasma are calculated. As far as possible, the analysis is carried out in a uniform way across all low-collisionality regimes in general stellarator geometry, assuming only that the confinement is good enough that the plasma is approximately in local thermodynamic equilibrium. It is found that conventional expressions for the ion flow speed and bootstrap current in the low-collisionality limit are accurate only in the -collisionality regime and need to be modified in the -regime. The correction due to finite collisionality is also discussed and is found to scale as 2/5$ .

  13. High-velocity stars from decay of small stellar systems

    NASA Astrophysics Data System (ADS)

    Kiseleva, L. G.; Colin, J.; Dauphole, B.; Eggleton, P.

    1998-12-01

    In this paper we present numerical results on the decay of small stellar systems under different initial conditions (multiplicity 3<=N<=10, and various mass spectra, initial velocities and initial configurations). The numerical treatment uses the CHAIN1 code (Mikkola & Aarseth). Particular attention is paid to the distribution of high-velocity escapers: we define these as stars with velocity above 30 km s^-1. These numerical experiments confirm that small N-body systems are dynamically unstable and produce cascades of escapers in the process of their decay. It is shown that the fraction of stars that escape from small dense stellar systems with an escape velocity greater than 30 km s^-1 is ~1 per cent for all systems treated here. This relatively small fraction must be considered in relation to the rate of star formation in the Galaxy in small groups: this could explain some moderately high-velocity stars observed in the Galactic disc and possibly some young stars with relatively high metallicity in the thick disc.

  14. Stellar velocity dispersion in dissipative galaxy mergers with star formation

    SciTech Connect

    Stickley, Nathaniel R.; Canalizo, Gabriela

    2014-05-01

    In order to better understand stellar dynamics in merging systems, such as NGC 6240, we examine the evolution of central stellar velocity dispersion (σ{sub *}) in dissipative galaxy mergers using a suite of binary disk merger simulations that include feedback from stellar formation and active galactic nuclei (AGNs). We find that σ{sub *} undergoes the same general stages of evolution that were observed in our previous dissipationless simulations: coherent oscillation, then phase mixing, followed by dynamical equilibrium. We also find that measurements of σ{sub *} that are based only upon the youngest stars in simulations consistently yield lower values than measurements based upon the total stellar population. This finding appears to be consistent with the so-called 'σ{sub *} discrepancy', observed in real galaxies. We note that quasar-level AGN activity is much more likely to occur when σ{sub *} is near its equilibrium value rather than during periods of extreme σ{sub *}. Finally, we provide estimates of the scatter inherent in measuring σ{sub *} in ongoing mergers.

  15. Proxima Centauri reloaded: Unravelling the stellar noise in radial velocities

    NASA Astrophysics Data System (ADS)

    Damasso, M.; Del Sordo, F.

    2017-03-01

    Context. The detection and characterisation of Earth-like planets with Doppler signals of the order of 1 m s-1 currently represent one of the greatest challenge for extrasolar-planet hunters. As results for such findings are often controversial, it is desirable to provide independent confirmations of the discoveries. Testing different models for the suppression of non-Keplerian stellar signals usually plaguing radial velocity data is essential to ensuring findings are robust and reproducible. Aims: Using an alternative treatment of the stellar noise to that discussed in the discovery paper, we re-analyse the radial velocity dataset that led to the detection of a candidate terrestrial planet orbiting the star Proxima Centauri. We aim to confirm the existence of this outstanding planet, and test the existence of a second planetary signal. Methods: Our technique jointly modelled Keplerian signals and residual correlated signals in radial velocities using Gaussian processes. We analysed only radial velocity measurements without including other ancillary data in the fitting procedure. In a second step, we have compared our outputs with results coming from photometry, to provide a consistent physical interpretation. Our analysis was performed in a Bayesian framework to quantify the robustness of our findings. Results: We show that the correlated noise can be successfully modelled as a Gaussian process regression, and contains a periodic term modulated on the stellar rotation period and characterised by an evolutionary timescale of the order of one year. Both findings appear to be robust when compared with results obtained from archival photometry, thus providing a reliable description of the noise properties. We confirm the existence of a coherent signal described by a Keplerian orbit equation that can be attributed to the planet Proxima b, and provide an independent estimate of the planetary parameters. Our Bayesian analysis dismisses the existence of a second planetary

  16. Short-period terrestrial planets and radial velocity stellar jitter.

    NASA Astrophysics Data System (ADS)

    Dumusque, Xavier

    2015-01-01

    Stellar jitter is the main limitation to ultra-precise radial velocity (RV) measurements. It currently precludes our ability to detect a planet like the Earth. Short-period terrestrial planets present first the advantage of inducing a stronger RV signal. In addition, the signal produced by these planets have a period completely different than stellar activity. This allows us, when the observational strategy is adequate, to decorrelate the planetary signal from the jitter induced by the star using filtering techniques. I will show the examples of Kepler-78b and Corot-7b, where the amplitude of the planetary signal can be detected, despite the stellar activity jitter that is 5 and 3 times larger, respectively. The cases of Alpha Cen Bb will also be reviewed, with a new reduction of the published data that increases the significance of the planetary signal.This project is funded by ETAEARTH, a transnational collaboration between European countries and the US (the Swiss Space Office, the Harvard Origin of Life Initiative, the Scottish Universities Physics Alliance, the University of Geneva, the Smithsonian Astrophysical Observatory, the Italian National Astrophysical Institute, the University of St. Andrews, Queens University Belfast, and the University of Edinburgh) setup to optimize the synergy between space-and ground-based data whose scientific potential for the characterization of extrasolar planets can only be fully exploited when analyzed together.

  17. Radial velocity fitting challenge. I. Simulating the data set including realistic stellar radial-velocity signals

    NASA Astrophysics Data System (ADS)

    Dumusque, X.

    2016-08-01

    Context. Stellar signals are the main limitation for precise radial-velocity (RV) measurements. These signals arise from the photosphere of the stars. The m s-1 perturbation created by these signals prevents the detection and mass characterization of small-mass planetary candidates such as Earth-twins. Several methods have been proposed to mitigate stellar signals in RV measurements. However, without precisely knowing the stellar and planetary signals in real observations, it is extremely difficult to test the efficiency of these methods. Aims: The goal of the RV fitting challenge is to generate simulated RV data including stellar and planetary signals and to perform a blind test within the community to test the efficiency of the different methods proposed to recover planetary signals despite stellar signals. Methods: In this first paper, we describe the simulation used to model the measurements of the RV fitting challenge. Each simulated planetary system includes the signals from instrumental noise, stellar oscillations, granulation, supergranulation, stellar activity, and observed and simulated planetary systems. In addition to RV variations, this simulation also models the effects of instrumental noise and stellar signals on activity observables obtained by HARPS-type high-resolution spectrographs, that is, the calcium activity index log (R'HK) and the bisector span and full width at half maximum of the cross-correlation function. Results: We publish the 15 systems used for the RV fitting challenge including the details about the planetary systems that were injected into each of them. Based on observations collected at the La Silla Parana Observatory, ESO (Chile), with the HARPS spectrograph at the 3.6-m telescope.The simulated data sets are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/593/A5 and at the wiki of the RV fitting challenge http://https://rv-challenge.wikispaces.com.

  18. Stellar Activity with BRITE: the ``Aurigae'' field

    NASA Astrophysics Data System (ADS)

    Strassmeier, K. G.

    2008-01-01

    Photometric time series of active stars can pin down some of the ingredients that govern the stellar magnetic field, itself being the driver of all non-thermal stellar emissions. Among the most important -- and least understood -- astrophysical ingredients is stellar rotation and its subtle latitudinal dependence called differential rotation. Rotation switches on and maintains the internal dynamo, itself a phenomenon from the interaction of turbulent plasma motions and large-scale shearing forces in the deep stellar interior. I propose to observe the active binary Capella, made up of two giants in exposed locations in the HR-diagram. Along with Capella (α Aur), another eight stars brighter than 4th magnitude would be in the field-of-view of BRITE, among them such benchmark variables as ζ Aur or θ Aur.

  19. The Scaling of Stellar Mass and Central Stellar Velocity Dispersion for Quiescent Galaxies at z<0.7

    NASA Astrophysics Data System (ADS)

    Zahid, H. Jabran; Geller, Margaret J.; Fabricant, Daniel G.; Hwang, Ho Seong

    2016-12-01

    We examine the relation between stellar mass and central stellar velocity dispersion—the M * σ relation—for massive quiescent galaxies at z < 0.7. We measure the local relation from the Sloan Digital Sky Survey and the intermediate redshift relation from the Smithsonian Hectospec Lensing Survey. Both samples are highly complete (>85%) and we consistently measure the stellar mass and velocity dispersion for the two samples. The M * σ relation and its scatter are independent of redshift with σ \\propto {M}* 0.3 for M * ≳ 1010.3 M ⊙. The measured slope of the M * σ relation is the same as the scaling between the total halo mass and the dark matter halo velocity dispersion obtained by N-body simulations. This consistency suggests that massive quiescent galaxies are virialized systems, where the central dark matter concentration is either a constant or negligible fraction of the stellar mass. The relation between the total galaxy mass (stellar + dark matter) and the central stellar velocity dispersion is consistent with the observed relation between the total mass of a galaxy cluster and the velocity dispersion of the cluster members. This result suggests that the central stellar velocity dispersion is directly proportional to the velocity dispersion of the dark matter halo. Thus, the central stellar velocity dispersion is a fundamental, directly observable property of galaxies, which may robustly connect galaxies to dark matter halos in N-body simulations. To interpret the results further in the context of ΛCDM, it would be useful to analyze the relationship between the velocity dispersion of stellar particles and the velocity dispersion characterizing their dark matter halos in high-resolution cosmological hydrodynamic simulations.

  20. Estimating stellar radial velocity variability from Kepler and GALEX: Implications for the radial velocity confirmation of exoplanets

    SciTech Connect

    Cegla, H. M.; Watson, C. A.; Stassun, K. G.; Bastien, F. A.; Pepper, J.

    2014-01-01

    We cross match the GALEX and Kepler surveys to create a unique dataset with both ultraviolet (UV) measurements and highly precise photometric variability measurements in the visible light spectrum. As stellar activity is driven by magnetic field modulations, we have used UV emission from the magnetically heated gas in the stellar atmosphere to serve as our proxy for the more well-known stellar activity indicator, R' {sub HK}. The R' {sub HK} approximations were in turn used to estimate the level of astrophysical noise expected in radial velocity (RV) measurements and these were then searched for correlations with photometric variability. We find significant scatter in our attempts to estimate RV noise for magnetically active stars, which we attribute to variations in the phase and strength of the stellar magnetic cycle that drives the activity of these targets. However, for stars we deem to be magnetically quiet, we do find a clear correlation between photometric variability and estimated levels of RV noise (with variability up to ∼10 m s{sup –1}). We conclude that for these quiet stars, we can use photometric measurements as a proxy to estimate the RV noise expected. As a result, the procedure outlined in this paper may help select targets best-suited for RV follow-up necessary for planet confirmation.

  1. THE EVOLUTION OF STELLAR VELOCITY DISPERSION DURING DISSIPATIONLESS GALAXY MERGERS

    SciTech Connect

    Stickley, Nathaniel R.; Canalizo, Gabriela

    2012-03-01

    Using N-body simulations, we studied the detailed evolution of central stellar velocity dispersion, {sigma}{sub *}, during dissipationless binary mergers of galaxies. Stellar velocity dispersion was measured using the common mass-weighting method as well as a flux-weighting method designed to simulate the technique used by observers. A toy model for dust attenuation was introduced in order to study the effect of dust attenuation on measurements of {sigma}{sub *}. We found that there are three principal stages in the evolution of {sigma}{sub *} in such mergers: oscillation, phase mixing, and dynamical equilibrium. During the oscillation stage, {sigma}{sub *} undergoes damped oscillations of increasing frequency. The oscillation stage is followed by a phase mixing stage during which the amplitude of the variations in {sigma}{sub *} is smaller and more chaotic than in the oscillation stage. Upon reaching dynamical equilibrium, {sigma}{sub *} assumes a stable value. We used our data regarding the evolution of {sigma}{sub *} during mergers to characterize the scatter inherent in making measurements of {sigma}{sub *} in non-quiescent systems. In particular, we found that {sigma}{sub *} does not fall below 70% nor exceed 200% of its final, quiescent value during a merger and that a random measurement of {sigma}{sub *} in such a system is much more likely to fall near the equilibrium value than near an extremum. Our toy model of dust attenuation suggested that dust can systematically reduce observational measurements of {sigma}{sub *} and increase the scatter in {sigma}{sub *} measurements.

  2. Stellar Mass Versus Stellar Velocity Dispersion: Which is Better for Linking Galaxies to Their Dark Matter Halos?

    NASA Astrophysics Data System (ADS)

    Li, Cheng; Wang, Lixin; Jing, Y. P.

    2013-01-01

    It was recently suggested that compared to its stellar mass (M *), the central stellar velocity dispersion (σ*) of a galaxy might be a better indicator for its host dark matter halo mass. Here we test this hypothesis by estimating the dark matter halo mass for central galaxies in groups as a function of M * and σ*. For this we have estimated the redshift-space cross-correlation function (CCF) between the central galaxies at given M * and σ* and a reference galaxy sample, from which we determine both the projected CCF, wp (rp ), and the velocity dispersion profile. A halo mass is then obtained from the average velocity dispersion within the virial radius. At fixed M *, we find very weak or no correlation between halo mass and σ*. In contrast, strong mass dependence is clearly seen even when σ* is limited to a narrow range. Our results thus firmly demonstrate that the stellar mass of central galaxies is still a good (if not the best) indicator for dark matter halo mass, better than the stellar velocity dispersion. The dependence of galaxy clustering on σ* at fixed M *, as recently discovered by Wake et al., may be attributed to satellite galaxies, for which the tidal stripping occurring within halos has stronger effect on stellar mass than on central stellar velocity dispersion.

  3. Preflare magnetic and velocity fields

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

    1986-01-01

    A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

  4. The impact of stellar feedback on the density and velocity structure of the interstellar medium

    NASA Astrophysics Data System (ADS)

    Grisdale, Kearn; Agertz, Oscar; Romeo, Alessandro B.; Renaud, Florent; Read, Justin I.

    2017-04-01

    We study the impact of stellar feedback in shaping the density and velocity structure of neutral hydrogen (H I) in disc galaxies. For our analysis, we carry out ∼4.6 pc resolution N-body+adaptive mesh refinement hydrodynamic simulations of isolated galaxies, set up to mimic a Milky Way and a Large and Small Magellanic Cloud. We quantify the density and velocity structure of the interstellar medium using power spectra and compare the simulated galaxies to observed H I in local spiral galaxies from THINGS (The H I Nearby Galaxy Survey). Our models with stellar feedback give an excellent match to the observed THINGS H I density power spectra. We find that kinetic energy power spectra in feedback-regulated galaxies, regardless of galaxy mass and size, show scalings in excellent agreement with supersonic turbulence (E(k) ∝ k-2) on scales below the thickness of the H I layer. We show that feedback influences the gas density field, and drives gas turbulence, up to large (kpc) scales. This is in stark contrast to density fields generated by large-scale gravity-only driven turbulence. We conclude that the neutral gas content of galaxies carries signatures of stellar feedback on all scales.

  5. Kriging interpolating cosmic velocity field

    NASA Astrophysics Data System (ADS)

    Yu, Yu; Zhang, Jun; Jing, Yipeng; Zhang, Pengjie

    2015-10-01

    Volume-weighted statistics of large-scale peculiar velocity is preferred by peculiar velocity cosmology, since it is free of the uncertainties of galaxy density bias entangled in observed number density-weighted statistics. However, measuring the volume-weighted velocity statistics from galaxy (halo/simulation particle) velocity data is challenging. Therefore, the exploration of velocity assignment methods with well-controlled sampling artifacts is of great importance. For the first time, we apply the Kriging interpolation to obtain the volume-weighted velocity field. Kriging is a minimum variance estimator. It predicts the most likely velocity for each place based on the velocity at other places. We test the performance of Kriging quantified by the E-mode velocity power spectrum from simulations. Dependences on the variogram prior used in Kriging, the number nk of the nearby particles to interpolate, and the density nP of the observed sample are investigated. First, we find that Kriging induces 1% and 3% systematics at k ˜0.1 h Mpc-1 when nP˜6 ×1 0-2(h-1 Mpc )-3 and nP˜6 ×1 0-3(h-1 Mpc )-3 , respectively. The deviation increases for decreasing nP and increasing k . When nP≲6 ×1 0-4(h-1 Mpc )-3 , a smoothing effect dominates small scales, causing significant underestimation of the velocity power spectrum. Second, increasing nk helps to recover small-scale power. However, for nP≲6 ×1 0-4(h-1 Mpc )-3 cases, the recovery is limited. Finally, Kriging is more sensitive to the variogram prior for a lower sample density. The most straightforward application of Kriging on the cosmic velocity field does not show obvious advantages over the nearest-particle method [Y. Zheng, P. Zhang, Y. Jing, W. Lin, and J. Pan, Phys. Rev. D 88, 103510 (2013)] and could not be directly applied to cosmology so far. However, whether potential improvements may be achieved by more delicate versions of Kriging is worth further investigation.

  6. Stellarators

    SciTech Connect

    Hartmann, D.A.

    2004-03-15

    Stellarators are toroidal devices where the required rotational transform of the magnetic field lines is generated by external field coils and not via an induced net toroidal plasma current. This confinement scheme has the advantages that, in principle, steady-state plasma operation is possible and that it does not have to brace itself against disruptions of a toroidal plasma current. At the cost of having to give up toroidal symmetry the properties of the stellarator field can be tailored to suit reactor needs. Research focuses on the plasma confinement properties of different stellarator fields and investigates the problems arising when one extrapolates to reactor parameters.

  7. Extremely high-velocity molecular flows in young stellar objects

    NASA Astrophysics Data System (ADS)

    Koo, Bon-Chul

    1989-02-01

    Very sensitive, wideband CO J = 1-0, J = 2-1, and HCO+ J = 1-0 spectra of several young stellar objects are presented. Extremely weak and very broad extremely high velocity (EHV) wings are found in GL 4909, HH 7-11, S140, and MWC 1080. The line profiles of EHV wings are smooth or flat, quite different from steep HV wings. In L551 and HL Tau, EHV wings as broad as other sources are not found, which would be due to the inclination of the bipolar flows to the line of sight. From the excitation temperature of about 10 K derived for the EHV flows, the estimated column density of CO yields a number density too small to explain the observed ratio of CO J = 2-1 to J = 1-0 intensity. It is concluded that either EHV flows are composed of small dense clumps or most of the carbon in the flow is atomic carbon, unless the kinetic temperature of the flow is much higher than 100 K.

  8. Stellar Radial Velocities with IGRINS at McDonald Observatory

    NASA Astrophysics Data System (ADS)

    Mace, Gregory; Jaffe, Daniel; Park, Chan; Lee, Jae-Joon

    2016-06-01

    Exoplanet searches with dedicated instrumentation have made 1 m/s radial velocity (RV) precision routine.Yet, RVs for large samples of stars generally remain at the 1km/s level.TheImmersion Grating Infrared Spectrometer (IGRINS) is a revolutionary instrument that exploits broad spectral coverage at high-resolution in the near-infrared.IGRINS on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory is nearly as sensitive as CRIRES at the 8 meter Very Large Telescope. However, IGRINS at R=45,000 has more than 30 times the spectral grasp of CRIRES.The use of a silicon immersion grating facilitates a compact cryostat while providing simultaneous wavelength coverage from 1.45 - 2.45 microns. Wehave developed a pipeline to cross-correlate the more than 20,000 resolution elements in two IGRINS exposures and provide relative RVs with uncertainties of 50m/s (<1% of a resolution element). Absolute RVs are limited by thezero point uncertainty, which is 150m/s.IGRINS RVs will be provided for thousands of objects per year as a default procedure of the data reduction pipeline, creating a legacy product for multi-epoch studies of low-mass, stellar and substellar multiplicity.

  9. Detecting exoplanets: jointly modeling radial velocity and stellar activity time series

    NASA Astrophysics Data System (ADS)

    Jones, David Edward; Stenning, David; Ford, Eric B.; Wolpert, Robert L.; Loredo, Thomas J.

    2017-06-01

    The radial velocity method is one of the most successful techniques for detecting exoplanets, but stellar activity often corrupts the radial velocity signal. This corruption can make it difficult to detect low mass planets and planets orbiting more active stars. A principled approach to recovering planet radial velocity signals in the presence of stellar activity was proposed by Rajpaul et al. (2015) and involves the use of dependent Gaussian processes to jointly model the corrupted radial velocity signal and multiple proxies for stellar activity. We build on this work in two ways: (i) we propose using dimension reduction techniques to construct more informative stellar activity proxies; (ii) we extend the Rajpaul et al. (2015) model to a larger class of models and use a model comparison procedure to select the best model for the particular stellar activity proxies at hand. Our framework enables us to compare the performance of various proxies in terms of the resulting statistical power for planet detection.

  10. 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

  11. The energy budget of stellar magnetic fields

    NASA Astrophysics Data System (ADS)

    See, V.; Jardine, M.; Vidotto, A. A.; Donati, J.-F.; Folsom, C. P.; Boro Saikia, S.; Bouvier, J.; Fares, R.; Gregory, S. G.; Hussain, G.; Jeffers, S. V.; Marsden, S. C.; Morin, J.; Moutou, C.; do Nascimento, J. D.; Petit, P.; Rosén, L.; Waite, I. A.

    2015-11-01

    Spectropolarimetric observations have been used to map stellar magnetic fields, many of which display strong bands of azimuthal fields that are toroidal. A number of explanations have been proposed to explain how such fields might be generated though none are definitive. In this paper, we examine the toroidal fields of a sample of 55 stars with magnetic maps, with masses in the range 0.1-1.5 M⊙. We find that the energy contained in toroidal fields has a power-law dependence on the energy contained in poloidal fields. However the power index is not constant across our sample, with stars less and more massive than 0.5 M⊙ having power indices of 0.72 ± 0.08 and 1.25 ± 0.06, respectively. There is some evidence that these two power laws correspond to stars in the saturated and unsaturated regimes of the rotation-activity relation. Additionally, our sample shows that strong toroidal fields must be generated axisymmetrically. The latitudes at which these bands appear depend on the stellar rotation period with fast rotators displaying higher latitude bands than slow rotators. The results in this paper present new constraints for future dynamo studies.

  12. Polarized radiation diagnostics of stellar magnetic fields

    NASA Astrophysics Data System (ADS)

    Mathys, Gautier

    The main techniques used to diagnose magnetic fields in stars from polarimetric observations are presented. First, a summary of the physics of spectral line formation in the presence of a magnetic field is given. Departures from the simple case of linear Zeeman effect are briefly considered: partial Paschen-Back effect, contribution of hyperfine structure, and combined Stark and Zeeman effects. Important approximate solutions of the equation of transfer of polarized light in spectral lines are introduced. The procedure for disk-integration of emergent Stokes profiles, which is central to stellar magnetic field studies, is described, with special attention to the treatment of stellar rotation. This formalism is used to discuss the determination of the mean longitudinal magnetic field (through the photographic technique and through Balmer line photopolarimetry). This is done within the specific framework of Ap stars, which, with their unique large-scale organized magnetic fields, are an ideal laboratory for studies of stellar magnetism. Special attention is paid to those Ap stars whose magnetically split line components are resolved in high-dispersion Stokes I spectra, and to the determination of their mean magnetic field modulus. Various techniques of exploitation of the information contained in polarized spectral line profiles are reviewed: the moment technique (in particular, the determination of the crossover and of the mean quadratic field), Zeeman-Doppler imaging, and least-squares deconvolution. The prospects that these methods open for linear polarization studies are sketched. The way in which linear polarization diagnostics complement their Stokes I and V counterparts is emphasized by consideration of the results of broad band linear polarization measurements. Illustrations of the use of various diagnostics to derive properties of the magnetic fields of Ap stars are given. This is used to show the interest of deriving more physically realistic models of the

  13. A Complex Stellar Line-of-Sight Velocity Distribution in the Lenticular Galaxy NGC 524

    NASA Astrophysics Data System (ADS)

    Katkov, I.; Chilingarian, I.; Sil'chenko, O.; Zasov, A.; Afanasiev, V.

    2011-08-01

    We present a detailed study of the stellar and gaseous kinematics in the luminous early-type galaxy NGC 524, derived from the long-slit spectroscopic observations obtained with the Russian 6 m telescope and the IFU data from the SAURON survey. The stellar line-of-sight velocity distribution (LOSVD) of NGC 524 exhibits strong asymmetry. We performed a comprehensive analysis of the LOSVD using two complementary approaches by the nbursts full spectral fitting technique: (a) a non-parametric LOSVD recovery and (b) a parametric recovery of two Gaussian kinematical components having different stellar populations. We discuss the origin of the complex stellar LOSVD of NGC 524.

  14. PROBABILISTIC CATALOGS FOR CROWDED STELLAR FIELDS

    SciTech Connect

    Brewer, Brendon J.; Foreman-Mackey, Daniel; Hogg, David W.

    2013-07-01

    We present and implement a probabilistic (Bayesian) method for producing catalogs from images of stellar fields. The method is capable of inferring the number of sources N in the image and can also handle the challenges introduced by noise, overlapping sources, and an unknown point-spread function. The luminosity function of the stars can also be inferred, even when the precise luminosity of each star is uncertain, via the use of a hierarchical Bayesian model. The computational feasibility of the method is demonstrated on two simulated images with different numbers of stars. We find that our method successfully recovers the input parameter values along with principled uncertainties even when the field is crowded. We also compare our results with those obtained from the SExtractor software. While the two approaches largely agree about the fluxes of the bright stars, the Bayesian approach provides more accurate inferences about the faint stars and the number of stars, particularly in the crowded case.

  15. The Stellar Extreme-Ultraviolet Radiation Field

    NASA Astrophysics Data System (ADS)

    Vallerga, John

    1998-04-01

    The local extreme ultraviolet (EUV) radiation field from stellar sources has been determined by combining the EUV spectra of 54 stars, taken with the spectrometers aboard the Extreme Ultraviolet Explorer satellite. The resultant spectrum over the range 70-730 Å is estimated to be 95% complete above 400 Å and 90% complete above 200 Å. The flux contributed by two B stars and three hot white dwarfs dominate the spectrum except at the shortest wavelengths, where an assortment of EUV source types contribute. The high electron densities measured toward nearby stars can be accounted for by photoionization from this radiation field, but the spectrum is too soft to explain the overionization of helium with respect to hydrogen recently measure in the Local Cloud.

  16. Polarized Line Formation in Non-monotonic Velocity Fields

    NASA Astrophysics Data System (ADS)

    Sampoorna, M.; Nagendra, K. N.

    2016-12-01

    For a correct interpretation of the observed spectro-polarimetric data from astrophysical objects such as the Sun, it is necessary to solve the polarized line transfer problems taking into account a realistic temperature structure, the dynamical state of the atmosphere, a realistic scattering mechanism (namely, the partial frequency redistribution—PRD), and the magnetic fields. In a recent paper, we studied the effects of monotonic vertical velocity fields on linearly polarized line profiles formed in isothermal atmospheres with and without magnetic fields. However, in general the velocity fields that prevail in dynamical atmospheres of astrophysical objects are non-monotonic. Stellar atmospheres with shocks, multi-component supernova atmospheres, and various kinds of wave motions in solar and stellar atmospheres are examples of non-monotonic velocity fields. Here we present studies on the effect of non-relativistic non-monotonic vertical velocity fields on the linearly polarized line profiles formed in semi-empirical atmospheres. We consider a two-level atom model and PRD scattering mechanism. We solve the polarized transfer equation in the comoving frame (CMF) of the fluid using a polarized accelerated lambda iteration method that has been appropriately modified for the problem at hand. We present numerical tests to validate the CMF method and also discuss the accuracy and numerical instabilities associated with it.

  17. VizieR Online Data Catalog: Bibliography of stellar radial velocities (Abt+ 1972)

    NASA Astrophysics Data System (ADS)

    Abt, H. A.; Biggs, E. S.

    2015-09-01

    The data file contains a bibliography of 44,000 radial velocities for about 25,000 stars, from a compilation of about 2340 publications (see the "Note (3)" below). The authors estimate that 99% of stellar radial velocities published by June 1970 are contained in the surveyed volumes. (1 data file).

  18. MERIDIONAL TILT OF THE STELLAR VELOCITY ELLIPSOID DURING BAR BUCKLING INSTABILITY

    SciTech Connect

    Saha, Kanak; Pfenniger, Daniel; Taam, Ronald E.

    2013-02-20

    The structure and evolution of the stellar velocity ellipsoid play an important role in shaping galaxies undergoing bar-driven secular evolution and the eventual formation of a boxy/peanut bulge such as is present in the Milky Way. Using collisionless N-body simulations, we show that during the formation of such a boxy/peanut bulge, the meridional shear stress of stars, which can be measured by the meridional tilt of the velocity ellipsoid, reaches a characteristic peak in its time evolution. It is shown that the onset of a bar buckling instability is closely connected to the maximum meridional tilt of the stellar velocity ellipsoid. Our findings bring a new insight to this complex gravitational instability of the bar which complements the buckling instability studies based on orbital models. We briefly discuss the observed diagnostics of the stellar velocity ellipsoid during such a phenomenon.

  19. Analytic representation of three-dimensional stellarator field

    SciTech Connect

    Yoshikawa, S.

    1983-09-01

    The stellarator configuration can be greatly simplified when toroidal harmonics are introduced. The toroidal function satisfies Laplace's equation and together with toroidal field and vertical field, a small-aspect-ratio stellarator can be constructed with an aspect ratio as low as 3.6. This functional presentation suggests a very fast computation of particle orbits and magnetic configuration.

  20. VizieR Online Data Catalog: General Catalogue of Stellar Radial Velocities (Wilson, 1953)

    NASA Astrophysics Data System (ADS)

    Wilson, R. E.

    2010-01-01

    The General Catalogue of Stellar Radial Velocity is a compilation of the radial velocities for about 15,000 stars, available to the author up to January 1951. Systematic differences were carefully studied and removed, providing therefore velocities in an homogenized system. The electronic version of the catalog is not identical to the printed version: notes and designations from "Personal lists" are not included and galactic coordinates were added. The velocities computed here can also be found in the "WEB Catalog of Radial Velocities" (Duflot et al. 1995, Cat. III/190) (1 data file).

  1. Measuring the Stellar Halo Velocity Anisotropy With 3D Kinematics

    NASA Astrophysics Data System (ADS)

    Cunningham, Emily C.; Deason, Alis J.; Guhathakurta, Puragra; Rockosi, Constance M.; van der Marel, Roeland P.; Sohn, S. Tony

    2016-08-01

    We present the first measurement of the anisotropy parameter β using 3D kinematic information outside of the solar neighborhood. Our sample consists of 13 Milky Way halo stars with measured proper motions and radial velocities in the line of sight of M31. Proper motions were measured using deep, multi-epoch HST imaging, and radial velocities were measured from Keck II/DEIMOS spectra. We measure β = -0.3-0.9 +0.4, which is consistent with isotropy, and inconsistent with measurements in the solar neighborhood. We suggest that this may be the kinematic signature of a relatively early, massive accretion event, or perhaps several such events.

  2. Asymmetric metallicity patterns in the stellar velocity space with RAVE

    NASA Astrophysics Data System (ADS)

    Antoja, T.; Kordopatis, G.; Helmi, A.; Monari, G.; Famaey, B.; Wyse, R. F. G.; Grebel, E. K.; Steinmetz, M.; Bland-Hawthorn, J.; Gibson, B. K.; Bienaymé, O.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G.; Siebert, A.; Siviero, A.; Zwitter, T.

    2017-05-01

    Context. The chemical abundances of stars encode information on their place and time of origin. Stars formed together in e.g. a cluster, should present chemical homogeneity. Also disk stars influenced by the effects of the bar and the spiral arms might have distinct chemical signatures depending on the type of orbit that they follow, e.g. from the inner versus outer regions of the Milky Way. Aims: We explore the correlations between velocity and metallicity and the possible distinct chemical signatures of the velocity over-densities of the local Galactic neighbourhood. Methods: We use the large spectroscopic survey RAVE and the Geneva Copenhagen Survey. We compare the metallicity distribution of regions in the velocity plane (vR,vφ) with that of their symmetric counterparts (-vR,vφ). We expect similar metallicity distributions if there are no tracers of a sub-population (e.g. a dispersed cluster, accreted stars), if the disk of the Galaxy is axisymmetric, and if the orbital effects of the bar and the spiral arms are weak. Results: We find that the metallicity-velocity space of the solar neighbourhood is highly patterned. A large fraction of the velocity plane shows differences in the metallicity distribution when comparing symmetric vR regions. The typical differences in the median metallicity are of 0.05 dex with statistical significant of at least 95% confidence, and with values up to 0.6 dex. For stars with low azimuthal velocity vφ, the ones moving outwards. These include stars in the Hercules and Hyades moving groups and other velocity branch-like structures. For higher vφ, the stars moving inwards have higher metallicity than those moving outwards. We have also discovered a positive gradient in vφ with respect to metallicity at high metallicities, apart from the two known positive and negative gradients for the thick and thin disks. Conclusions: The most likely interpretation of the metallicity asymmetry is that it is mainly due to the orbital effects of

  3. On Animating 2D Velocity Fields

    NASA Technical Reports Server (NTRS)

    Kao, David; Pang, Alex

    2000-01-01

    A velocity field. even one that represents a steady state flow implies a dynamical system. Animated velocity fields is an important tool in understanding such complex phenomena. This paper looks at a number of techniques that animate velocity fields and propose two new alternatives, These are texture advection and streamline cycling. The common theme among these techniques is the use of advection on some texture to generate a realistic animation of the velocity field. Texture synthesis and selection for these methods are presented. Strengths and weaknesses of the techniques are also discussed in conjunction with several examples.

  4. On Animating 2D Velocity Fields

    NASA Technical Reports Server (NTRS)

    Kao, David; Pang, Alex; Yan, Jerry (Technical Monitor)

    2001-01-01

    A velocity field, even one that represents a steady state flow, implies a dynamical system. Animated velocity fields is an important tool in understanding such complex phenomena. This paper looks at a number of techniques that animate velocity fields and propose two new alternatives. These are texture advection and streamline cycling. The common theme among these techniques is the use of advection on some texture to generate a realistic animation of the velocity field. Texture synthesis and selection for these methods are presented. Strengths and weaknesses of the techniques are also discussed in conjunctions with several examples.

  5. New GNSS velocity field and preliminary velocity model for Ecuador

    NASA Astrophysics Data System (ADS)

    Luna-Ludeña, Marco P.; Staller, Alejandra; Gaspar-Escribano, Jorge M.; Belén Benito, M.

    2016-04-01

    In this work, we present a new preliminary velocity model of Ecuador based on the GNSS data of the REGME network (continuous monitoring GNSS network). To date, there is no velocity model available for the country. The only existing model in the zone is the regional model VEMOS2009 for South America and Caribbean (Drewes and Heidbach, 2012). This model was developed from the SIRGAS station positions, the velocities of the SIRGAS-CON stations, and several geodynamics projects performed in the region. Just two continuous GNSS (cGNSS) stations of Ecuador were taking into account in the VEMOS2009 model. The first continuous station of the REGME network was established in 2008. At present, it is composed by 32 continuous GNSS stations, covering the country. All the stations provided data during at least two years. We processed the data of the 32 GNSS stations of REGME for the 2008-2014 period, as well as 20 IGS stations in order to link to the global reference frame IGb08 (ITRF2008). GPS data were processed using Bernese 5.0 software (Dach et al., 2007). We obtained and analyzed the GNSS coordinate time series of the 32 REGME stations and we calculated the GPS-derived horizontal velocity field of the country. Velocities in ITRF2008 were transformed into a South American fixed reference frame, using the Euler pole calculated from 8 cGNSS stations throughout this plate. Our velocity field is consistent with the tectonics of the country and contributes to a better understanding of it. From the horizontal velocity field, we determined a preliminary model using the kriging geostatistical technique. To check the results we use the cross-validation method. The differences between the observed and estimated values range from ± 5 mm. This is a new velocity model obtained from GNSS data for Ecuador.

  6. A method to deconvolve stellar rotational velocities II. The probability distribution function via Tikhonov regularization

    NASA Astrophysics Data System (ADS)

    Christen, Alejandra; Escarate, Pedro; Curé, Michel; Rial, Diego F.; Cassetti, Julia

    2016-10-01

    Aims: Knowing the distribution of stellar rotational velocities is essential for understanding stellar evolution. Because we measure the projected rotational speed v sin i, we need to solve an ill-posed problem given by a Fredholm integral of the first kind to recover the "true" rotational velocity distribution. Methods: After discretization of the Fredholm integral we apply the Tikhonov regularization method to obtain directly the probability distribution function for stellar rotational velocities. We propose a simple and straightforward procedure to determine the Tikhonov parameter. We applied Monte Carlo simulations to prove that the Tikhonov method is a consistent estimator and asymptotically unbiased. Results: This method is applied to a sample of cluster stars. We obtain confidence intervals using a bootstrap method. Our results are in close agreement with those obtained using the Lucy method for recovering the probability density distribution of rotational velocities. Furthermore, Lucy estimation lies inside our confidence interval. Conclusions: Tikhonov regularization is a highly robust method that deconvolves the rotational velocity probability density function from a sample of v sin i data directly without the need for any convergence criteria.

  7. The stellar wind velocity function for red supergiants determined in eclipsing binaries

    NASA Technical Reports Server (NTRS)

    Ahmad, Imad A.; Stencel, Robert E.

    1988-01-01

    The potential for direct measurement of the acceleration of stellar winds from the supergiant component of Zeta Aurigae-type binary stars is discussed. The aberration angle of the interaction shock cone centered on the hot star provides a measure of the velocity of the cool star wind at the orbit of the secondary. This is confirmed by direct observations of stellar wind (P Cygni) line profile variations. This velocity is generally smaller than the final (terminal) velocity of the wind, deduced from the P Cygni line profiles. The contrast between these results and previously published supergiant wind models is discussed. The implication on the physics of energy source dissipation predicted in the theoretical models is considered.

  8. Velocity asymmetries in young stellar object jets. Intrinsic and extrinsic mechanisms

    NASA Astrophysics Data System (ADS)

    Matsakos, T.; Vlahakis, N.; Tsinganos, K.; Karampelas, K.; Sauty, C.; Cayatte, V.; Matt, S. P.; Massaglia, S.; Trussoni, E.; Mignone, A.

    2012-09-01

    Context. It is well established that some YSO jets (e.g. RW Aur) display different propagation speeds between their blue and red shifted parts, a feature possibly associated with the central engine or the environment in which the jet propagates. Aims: To understand the origin of asymmetric YSO jet velocities, we investigate the efficiency of two candidate mechanisms, one based on the intrinsic properties of the system and the other on the role of the external medium. In particular, a parallel or anti-parallel configuration between the protostellar magnetosphere and the disk magnetic field is considered, and the resulting dynamics examined both in an ideal and in a resistive magneto-hydrodynamical (MHD) regime. Moreover, we explore the effects of a potential difference in the pressure of the environment, as a consequence of the nonuniform density distribution of molecular clouds. Methods: Ideal and resistive axisymmetric numerical simulations were carried out for a variety of models, all of which are based on a combination of two analytical solutions, a disk wind and a stellar outflow. The initial two-component jet is modified by either inverting the orientation of its inner magnetic field or imposing a constant surrounding pressure. The velocity profiles are studied by assuming steady flows as well as after strong time variable ejection is incorporated. Results: Discrepancies between the speeds of the two outflows in opposite directions can indeed occur both due to unaligned magnetic fields and different outer pressures. In the former case, the asymmetry appears only on the dependence of the velocity on the cylindrical distance, but the implied observed value is significantly altered when the density distribution is also taken into account. On the other hand, a nonuniform medium collimates the two jets unevenly, directly affecting their propagation speed. A further interesting feature of the pressure-confined outflow simulations is the formation of static knots

  9. Theoretical and Observational Consequences of Rotation and Magnetic Fields in Stellar Winds

    NASA Astrophysics Data System (ADS)

    Ignace, Richard

    1996-05-01

    My dissertation concerns the study of stellar winds from theoretical modeling of the wind structure and the development of observational diagnostics. First, I have investigated the effects of stellar rotation for the wind structure of stars across the H-R Diagram. The effect of rotation is to increase the wind density at the equator while decreasing the density near the poles. The model, known as the Wind-Compressed Zone (WCZ) model, predicts that equatorial wind compressions are most likely to occur for stars with rapid rotation, low terminal speeds, and/or radial velocity distributions that increase gradually from the base of the wind. It is found that in favorable cases, stellar rotation can play a significant role in shaping the winds of Wolf Rayet stars, B supergiants, Asymptotic Giant Branch stars, and even some novae. The second major part of my thesis relates to the fact that the WCZ model will predict the magnetic field structure in the wind, if the field strength is relatively weak. However, there are generally no good diagnostics of stellar magnetic fields in the weak field limit, where Zeeman splitting is smaller than Doppler broadening. Thus, I have explored applications of the Hanle effect for probing magnetic fields in stellar winds. This effect (which has been used in studies of the solar atmosphere) deals with the modification of resonance line scattering polarization by a magnetic field. Solutions for the Hanle effect in optically thin axisymmetric extended stellar envelopes have been derived. Relative to the zero field case, the Hanle effect can result in significant changes of the line polarization, in some cases causing a position angle flip of 90(deg) . With multiline observations the Hanle effect is a viable diagnostic of stellar magnetic fields in the range 1-1000 Gauss. This thesis work was completed under the supervision of Joseph Cassinelli and in collaboration with Kenneth Nordsieck and Jon Bjorkman.

  10. On the velocity fields of elliptical galaxies

    NASA Technical Reports Server (NTRS)

    Statler, Thomas S.

    1991-01-01

    A family of self-consistent maximum entropy dynamical models is presented for the triaxial 'perfect ellipsoids'. These models are projected in different viewing geometries to explore the possible morphologies of the 2D radial-velocity fields of elliptical galaxies. It is found that, typically, about half the time an 'ordinary' velocity field is seen with a mixture of major- and minor-axis rotation. For other lines of sight, the velocity fields are more complicated, showing multiple peaks, steep gradients, strongly twisted contours, or kinematically distinct or counter-rotating cores. The origin of each of these velocity field morphologies is explained in terms of competing contributions from the major families of tube orbits.

  11. INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

    SciTech Connect

    Cortés, Juan R.; Hardy, Eduardo; Kenney, Jeffrey D. P. E-mail: ehardy@nrao.cl

    2015-01-01

    We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between the optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ {sub R}. An evaluation of the galaxies in the λ {sub R} ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects.

  12. Limitations of Precise Radial-Velocity Measurements in Pulsating Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Vinkó, J.; Kaszás, G.; Kiss, L. L.

    We have studied the velocities of specific stellar absorption lines emerging from the atmospheres of Cepheid-type variable stars using newly obtained high-resolution echelle spectra. The spectra covered the interval 5860 - 6660 Angstroms with a resolution of 40,000. Both the cross-correlation method and the line bisector method using individual lines with specific excitation potential were applied to derive radial velocities. Our tests showed that these methods have internal accuracy of better than 100 m/s. Typical velocity differences of 3 - 5 km/s were found between photospheric lines having low- and high-excitation potentials in the case of long-period (P > 10 days) Cepheids. These differences are smaller, about 1 km/s or less, for the shorter period Cepheids. Furthermore, we have compared two very accurate techniques (Coravel and iodine-cell method) using recently published radial velocities. Systematic differences have been found between the shapes of these velocity curves, especially around the phase of velocity reversal. We conclude that these velocity differences could cause a few km/s ambiguity even in the best-quality Cepheid radial velocity curves that were obtained averaging the velocities of many lines. This may result in an uncertainty of Cepheid radii derived from Baade-Wesselink methods.

  13. Velocity modulation of microtubules in electric fields.

    PubMed

    Dujovne, Irene; van den Heuvel, Martin; Shen, Yi; de Graaff, Martijn; Dekker, Cees

    2008-12-01

    We show that the speed of microtubules gliding over a kinesin-coated surface can be controlled over a wide range of values by the application of an electric field. The speed can be increased by up to a factor of 5 compared to the speed at zero field when assisting forces are applied and slowed down to zero velocity for opposing fields. Sideways applied fields also induce significant motion. The kinesin surface density impacts the rate of velocity change, whereas the ATP concentration does not seem to play a major role, provided that it is nonzero. A simple grab-and-release model is presented that explains the velocity change with applied electric fields.

  14. The rising stellar velocity dispersion of M87 from integrated starlight

    SciTech Connect

    Murphy, Jeremy D.; Gebhardt, Karl; Cradit, Mason

    2014-04-20

    We have measured the line-of-sight velocity distribution from integrated stellar light at two points in the outer halo of M87 (NGC 4486), the second-rank galaxy in the Virgo Cluster. The data were taken at R = 480'' (∼41.5 kpc) and R = 526'' (∼45.5 kpc) along the SE major axis. The second moment for a non-parametric estimate of the full velocity distribution is 420 ± 23 km s{sup –1} and 577 ± 35 km s{sup –1}, respectively. There is intriguing evidence in the velocity profiles for two kinematically distinct stellar components at the position of our pointing. Under this assumption, we employ a two-Gaussian decomposition and find the primary Gaussian having rest velocities equal to M87 (consistent with zero rotation) and second moments of 383 ± 32 km s{sup –1} and 446 ± 43 km s{sup –1}, respectively. The asymmetry seen in the velocity profiles suggests that the stellar halo of M87 is not in a relaxed state and confuses a clean dynamical interpretation. That said, either measurement (full or two component model) shows a rising velocity dispersion at large radii, consistent with previous integrated light measurements, yet significantly higher than globular cluster measurements at comparable radial positions. These integrated light measurements at large radii, and the stark contrast they make to the measurements of other kinematic tracers, highlight the rich kinematic complexity of environments like the center of the Virgo Cluster and the need for caution when interpreting kinematic measurements from various dynamical tracers.

  15. A high stellar velocity dispersion for a compact massive galaxy at redshift z = 2.186.

    PubMed

    van Dokkum, Pieter G; Kriek, Mariska; Franx, Marijn

    2009-08-06

    Recent studies have found that the oldest and most luminous galaxies in the early Universe are surprisingly compact, having stellar masses similar to present-day elliptical galaxies but much smaller sizes. This finding has attracted considerable attention, as it suggests that massive galaxies have grown in size by a factor of about five over the past ten billion years (10 Gyr). A key test of these results is a determination of the stellar kinematics of one of the compact galaxies: if the sizes of these objects are as extreme as has been claimed, their stars are expected to have much higher velocities than those in present-day galaxies of the same mass. Here we report a measurement of the stellar velocity dispersion of a massive compact galaxy at redshift z = 2.186, corresponding to a look-back time of 10.7 Gyr. The velocity dispersion is very high at km s(-1), consistent with the mass and compactness of the galaxy inferred from photometric data. This would indicate significant recent structural and dynamical evolution of massive galaxies over the past 10 Gyr. The uncertainty in the dispersion was determined from simulations that include the effects of noise and template mismatch. However, we cannot exclude the possibility that some subtle systematic effect may have influenced the analysis, given the low signal-to-noise ratio of our spectrum.

  16. THE STELLAR VELOCITY DISTRIBUTION IN THE SOLAR NEIGHBORHOOD: DEVIATIONS FROM THE SCHWARZSCHILD DISTRIBUTION

    SciTech Connect

    Griv, Evgeny; Gedalin, Michael; Eichler, David

    2009-03-15

    The idea of the collisionless relaxation of the stellar disk of the Milky Way is elaborated. Jeans' gravitationally unstable stellar disk is considered by applying the procedure of the quasi-linear kinetic approach. It is shown that unstable gravity perturbations (e.g., those produced by a spontaneous disturbance) grow almost aperiodically in the main part of the disk between the inner and outer Lindblad resonances and affect the in-plane averaged velocity distribution of stars. The diffusion equation in velocity space is derived describing the secular increase in the dispersion of the peculiar velocities of stars with time after star formation in the rotationally supported Galactic disk. Our previous investigation is extended by including the minor second-order terms of the theory to describe the small distortion in the local distribution function of stars away from the standard Schwarzschild distribution. It is shown that the residual velocity distributions along the radial and azimuthal coordinates in velocity space are non-Gaussian in the sense that the central peaks are more populated and the higher energy portions of the distributions are somewhat underpopulated. For a subsystem of relatively old stars with ages (2-3)x10{sup 9} years, the quantitative change is of the order of 10%-15%. The observational test of the theory is also suggested.

  17. Characterizing the convective velocity fields in massive stars

    SciTech Connect

    Chatzopoulos, Emmanouil; Graziani, Carlo; Couch, Sean M.

    2014-11-01

    We apply the mathematical formalism of vector spherical harmonics decomposition to convective stellar velocity fields from multidimensional hydrodynamics simulations and show that the resulting power spectra furnish a robust and stable statistical description of stellar convective turbulence. Analysis of the power spectra helps identify key physical parameters of the convective process such as the dominant scale of the turbulent motions that influence the structure of massive evolved pre-supernova stars. We introduce the numerical method that can be used to calculate vector spherical harmonics power spectra from two-dimensional (2D) and three-dimensional (3D) convective shell simulation data. Using this method we study the properties of oxygen shell burning and convection for a 15 M {sub ☉} star simulated by the hydrodynamics code FLASH in 2D and 3D. We discuss the importance of realistic initial conditions to achieving successful core-collapse supernova explosions in multidimensional simulations. We show that the calculated power spectra can be used to generate realizations of the velocity fields of presupernova convective shells. We find that the slope of the solenoidal mode power spectrum remains mostly constant throughout the evolution of convection in the oxygen shell in both 2D and 3D simulations. We also find that the characteristic radial scales of the convective elements are smaller in 3D than in 2D, while the angular scales are larger in 3D.

  18. Jovian cloud structure and velocity fields

    NASA Technical Reports Server (NTRS)

    Mitchell, J. L.; Terrile, R. J.; Collins, S. A.; Smith, B. A.; Muller, J.-P.; Hunt, G. E.; Ingersoll, A. P.; Beebe, R. F.

    1979-01-01

    A global view of Jovian small-scale morphologies and zonal velocity profiles has been discussed previously. In the present paper, a regional comparison is made of the structures and velocity fields (meridional and zonal velocities) in the Jovian atmosphere as observed by Voyager I imaging system. The cloud structures discussed are fairly independent of the visual wavelength. The analysis shows that although both Jovian hemispheres exhibit similar patterns of diminishing and alternating eastward and westward jets as one progresses polewards, there is a pronounced asymmetry in the structural appearance of the two hemispheres.

  19. Reliability of the Measured Velocity Anisotropy of the Milky Way Stellar Halo

    NASA Astrophysics Data System (ADS)

    Hattori, Kohei; Valluri, Monica; Loebman, Sarah R.; Bell, Eric F.

    2017-06-01

    Determining the velocity distribution of halo stars is essential for estimating the mass of the Milky Way and for inferring its formation history. Since the stellar halo is a dynamically hot system, the velocity distribution of halo stars is well described by the three-dimensional velocity dispersions ({σ }r,{σ }θ ,{σ }φ ) or by the velocity anisotropy parameter β =1-({σ }θ 2+{σ }φ 2)/(2{σ }r2). Direct measurements of ({σ }r,{σ }θ ,{σ }φ ) consistently suggest β = 0.5-0.7 for nearby halo stars. In contrast, the value of β at large Galactocentric radius r is still controversial, since reliable proper motion data are available for only a handful of stars. In the last decade, several authors have tried to estimate β for distant halo stars by fitting the observed line-of-sight velocities at each radius with simple velocity distribution models (local fitting methods). Some results of local fitting methods imply β < 0 at r≳ 20 {kpc}, which is inconsistent with recent predictions from cosmological simulations. Here we perform mock-catalog analyses to show that the estimates of β based on local fitting methods are reliable only at r≤slant 15 {kpc} with the current sample size (˜103 stars at a given radius). As r increases, the line-of-sight velocity (corrected for the solar reflex motion) becomes increasingly closer to the Galactocentric radial velocity, so it becomes increasingly more difficult to estimate the tangential velocity dispersion ({σ }θ ,{σ }φ ) from the line-of-sight velocity distribution. Our results suggest that the forthcoming Gaia data will be crucial for understanding the velocity distribution of halo stars at r≥slant 20 {kpc}.

  20. Rotating field mass and velocity analyzer

    NASA Technical Reports Server (NTRS)

    Smith, Steven Joel (Inventor); Chutjian, Ara (Inventor)

    1998-01-01

    A rotating field mass and velocity analyzer having a cell with four walls, time dependent RF potentials that are applied to each wall, and a detector. The time dependent RF potentials create an RF field in the cell which effectively rotates within the cell. An ion beam is accelerated into the cell and the rotating RF field disperses the incident ion beam according to the mass-to-charge (m/e) ratio and velocity distribution present in the ion beam. The ions of the beam either collide with the ion detector or deflect away from the ion detector, depending on the m/e, RF amplitude, and RF frequency. The detector counts the incident ions to determine the m/e and velocity distribution in the ion beam.

  1. A Titius-Bode like law for stellar populations in the velocity space

    NASA Astrophysics Data System (ADS)

    Alcobé, Santiago; Cubarsi, Rafael

    2007-05-01

    A large sample from HIPPARCOS catalogue with known full space motions is used. The statistical algorithm MEMPHIS (Maximum Entropy of the Mixture Probability from HIerarchical Segregation) is applied for segregating the kinematic populations contained in the solar neighbourhood. A discrete set of stellar groups is obtained and they are associated with Galactic components. The velocity dispersions of Gaussian elements seem to follow a geometrical progression which allows us to do an analogy with the old Titius-Bode distribution for Keplerian orbits. Such Titius-Bode like law in the velocity space for stellar kinematics could be indeed already seen in previous published kinematic parameters of Galactic components. As in the Keplerian case, one should argue that values for the velocity dispersions are too approximated and may not be fit in a general law. But, even taking into account the rude approximations, it is not possible to ignore anymore the similarities between the geometrical progression distribution of Keplerian orbits and kinematics of the elements building the Galactic Disk. The empiric distribution σ=6.6(4/3)n for n=2, 3, 5, 8 is interpreted as the energy levels corresponding to discrete populations. For the intervals n ≤ 5 and n ≥ 7 instead, what it describes is the velocity-age evolution of thin and thick disk components.

  2. Laser Frequency Comb Supported Stellar Radial Velocity Determination in the NIR: Initial Results.

    NASA Astrophysics Data System (ADS)

    Osterman, Steve; Diddams, S.; Quinlan, F.; Ycas, G.; Mahadevan, S.; Ramsey, L.; Bender, C.; Terrien, R.; Botzer, B.; Redman, S.

    2011-09-01

    The laser frequency comb presents the potential for a revolutionary increase in radial velocity precision by providing a calibration reference of unprecedented quality in terms of wavelength knowledge, repeatability, number, density and regularity of lines. Promising first steps have been taken leading to the derivation of stellar radial velocities in the NIR H band, a wavelength range well suited to the observation of M dwarfs. These stars, with low mass and low luminosity, are the most prevalent class of stars within 10 parsecs and can be expected to yield a higher reflex velocity for a terrestrial mass planet in the liquid water habitable zone than would be the case with a more massive star such as our own. We present the design and both laboratory and on-sky performance of an H-band laser frequency comb used in conjunction with the Penn State Pathfinder testbed spectrograph and discuss lessons learned and plans for follow on testing.

  3. Velocity Field in a Vertical Foam Film

    NASA Astrophysics Data System (ADS)

    Seiwert, Jacopo; Kervil, Ronan; Nou, Soniraks; Cantat, Isabelle

    2017-01-01

    The drainage of vertical foam films governs their lifetime. For a foam film supported on a rectangular solid frame, when the interface presents a low resistance to shear, the drainage dynamics involves a complex flow pattern at the film scale, leading to a drainage time proportional to the frame width. Using an original velocimetry technique, based on fluorescent foam films and photobleaching, we measure the horizontal and vertical components of the velocity in a draining film, thus providing the first quantitative experimental evidence of this flow pattern. Upward velocities up to 10 cm /s are measured close to the lateral menisci, whereas a slower velocity field is obtained in the center of the film, with comparable downwards and horizontal components. Scaling laws are proposed for all characteristic velocities, coupling gravitational effects, and capillary suction.

  4. STELLAR VELOCITY DISPERSION MEASUREMENTS IN HIGH-LUMINOSITY QUASAR HOSTS AND IMPLICATIONS FOR THE AGN BLACK HOLE MASS SCALE

    SciTech Connect

    Grier, C. J.; Martini, P.; Peterson, B. M.; Pogge, R. W.; Zu, Y.; Watson, L. C.; Bentz, M. C.; Dasyra, K. M.; Dietrich, M.; Ferrarese, L.

    2013-08-20

    We present new stellar velocity dispersion measurements for four luminous quasars with the Near-Infrared Integral Field Spectrometer instrument and the ALTAIR laser guide star adaptive optics system on the Gemini North 8 m telescope. Stellar velocity dispersion measurements and measurements of the supermassive black hole (BH) masses in luminous quasars are necessary to investigate the coevolution of BHs and galaxies, trace the details of accretion, and probe the nature of feedback. We find that higher-luminosity quasars with higher-mass BHs are not offset with respect to the M{sub BH}-{sigma}{sub *} relation exhibited by lower-luminosity active galactic nuclei (AGNs) with lower-mass BHs, nor do we see correlations with galaxy morphology. As part of this analysis, we have recalculated the virial products for the entire sample of reverberation-mapped AGNs and used these data to redetermine the mean virial factor (f) that places the reverberation data on the quiescent M{sub BH}-{sigma}{sub *} relation. With our updated measurements and new additions to the AGN sample, we obtain (f) = 4.31 {+-} 1.05, which is slightly lower than, but consistent with, most previous determinations.

  5. Modified methods of stellar magnetic field measurements

    NASA Astrophysics Data System (ADS)

    Kholtygin, A. F.

    2014-12-01

    The standard methods of the magnetic field measurement, based on an analysis of the relation between the Stokes V-parameter and the first derivative of the total line profile intensity, were modified by applying a linear integral operator \\hat{L} to both sides of this relation. As the operator \\hat{L}, the operator of the wavelet transform with DOG-wavelets is used. The key advantage of the proposed method is an effective suppression of the noise contribution to the line profile and the Stokes parameter V. The efficiency of the method has been studied using model line profiles with various noise contributions. To test the proposed method, the spectropolarimetric observations of the A0 star α2 CVn, the Of?p star HD 148937, and the A0 supergiant HD 92207 were used. The longitudinal magnetic field strengths calculated by our method appeared to be in good agreement with those determined by other methods.

  6. Low-velocity variability in the stellar wind of HD 152408 (O8: Iafpe)

    NASA Technical Reports Server (NTRS)

    Prinja, Raman K.; Fullerton, A. W.

    1994-01-01

    We describe high-quality, spectroscopic time series observations of variability at low velocities in the stellar wind of the extreme O-supergiant HD 152408. These observations were obtained during a monitoring campaign coordinated between Australia and Chile in 1992 July. Systematic variability on hourly time scales is particularly apparent in the He I lambda 5876 P Cygni profile, which diagnoses the deeper, denser region of the wind. These changes indicate the presence of evolving wind structure, which takes the form of blueward-migrating, discrete optical depth enhancements. Four distinct features are identified over approximately 5 days, spanning a velocity range of about -50 km/s at formation to about -500 km/s (i.e., greater than or approximately equal to 0.5 of the terminal velocity) at the blue edge of the He I absorption trough. Sympathetic variations are also apparent in the Balmer emission lines of HD 152408. The characteristics of these features, including their widths, column densities, and accelerations, suggest similarities to discrete absorption components commonly seen at larger velocities in UV P Cygni profiles of other O-type stars. These optical results demonstrate that frequent, systematic wind variability is present down to very large depths, and provide constraints on the stability of the low-velocity regime of hot-star winds.

  7. Radial velocities of K-M dwarfs and local stellar kinematics

    NASA Astrophysics Data System (ADS)

    Sperauskas, J.; Bartašiūtė, S.; Boyle, R. P.; Deveikis, V.; Raudeliūnas, S.; Upgren, A. R.

    2016-12-01

    Aims: The goal of this paper is to present complete radial-velocity data for the spectroscopically selected McCormick sample of nearby K-M dwarfs and, based on these and supplementary data, to determine the space-velocity distributions of late-type stars in the solar neighborhood. Methods: We analyzed nearly 3300 measurements of radial velocities for 1049 K-M dwarfs, that we obtained during the past decade with a CORAVEL-type instrument, with a primary emphasis on detecting and eliminating from kinematic calculations the spectroscopic binaries and binary candidates. Combining radial-velocity data with Hipparcos/Tycho-2 astrometry we calculated the space-velocity components and parameters of the galactic orbits in a three-component model potential for the stars in the sample, that we use for kinematical analysis and for the identification of possible candidate members of nearby stellar kinematic groups. Results: We present the catalog of our observations of radial velocities for 959 stars which are not suspected of velocity variability, along with the catalog of U,V,W velocities and Galactic orbital parameters for a total of 1088 K-M stars which are used in the present kinematic analysis. Of these, 146 stars were identified as possible candidate members of the known nearby kinematic groups and suspected subgroups. The distributions of space-velocity components, orbital eccentricities, and maximum distances from the Galactic plane are consistent with the presence of young, intermediate-age and old populations of the thin disk and a small fraction ( 3%) of stars with the thick disk kinematics. The kinematic structure gives evidence that the bulk of K-M type stars in the immediate solar vicinity represents a dynamically relaxed stellar population. The star MCC 869 is found to be on a retrograde Galactic orbit (V = -262 km s-1) of low inclination (4°) and can be a member of stellar stream of some dissolved structure. The Sun's velocity with respect to the Local

  8. TOWARD UNDERSTANDING STELLAR RADIAL VELOCITY JITTER AS A FUNCTION OF WAVELENGTH: THE SUN AS A PROXY

    SciTech Connect

    Marchwinski, Robert C.; Mahadevan, Suvrath; Robertson, Paul; Ramsey, Lawrence; Harder, Jerald E-mail: suvrath@astro.psu.edu E-mail: lwr@psu.edu

    2015-01-01

    Using solar spectral irradiance measurements from the SORCE spacecraft and the F/F' technique, we have estimated the radial velocity (RV) scatter induced on the Sun by stellar activity as a function of wavelength. Our goal was to evaluate the potential advantages of using new near-infrared (NIR) spectrographs to search for low-mass planets around bright F, G, and K stars by beating down activity effects. Unlike M dwarfs, which have higher fluxes and therefore greater RV information content in the NIR, solar-type stars are brightest at visible wavelengths, and, based solely on information content, are better suited to traditional optical RV surveys. However, we find that the F/F' estimated RV noise induced by stellar activity is diminished by up to a factor of four in the NIR versus the visible. Observations with the upcoming future generation of NIR instruments can be a valuable addition to the search for low-mass planets around bright FGK stars in reducing the amount of stellar noise affecting RV measurements.

  9. Light Curves as Predictors of Good Radial Velocity Planet Search Targets in New Stellar Domains

    NASA Astrophysics Data System (ADS)

    Bastien, Fabienne A.; Wright, Jason; Sigurdsson, Steinn; Dumusque, Xavier; Luhn, Jacob K.; Howard, Andrew

    2017-01-01

    As Kepler and K2 have collectively found thousands of exoplanet candidates, their discoveries have strained ground-based radial velocity (RV) follow-up resources, which are unable to simultaneously keep up with the pace of transit discoveries by measuring masses for all of the candidates and maintain vigorous RV searches for planets that do not transit their parent star. The burden to the RV community is expected to worsen with the upcoming TESS mission, even as new RV instruments are slated to come online in the coming years. Observations that can enable the RV community to prioritize targets on the basis of their stellar RV variability in advance and, ideally, independently of the RV instruments themselves, can therefore permit us to reserve our RV resources for the stars most likely to yield the highest payoff. We show that the light curves from space-based transit surveys may not only be used as predictors of good RV search targets for the stars predominantly targeted by the exoplanet community but also for stars usually avoided by both RV and transit surveys due to their high intrinsic levels of stellar variability. We also briefly present recommendations to the RV planet search community on how to improve prospects for finding Earth analogs from the recent workshop at the Aspen Center for Physics, “Approaching the Stellar Astrophysical Limits of Exoplanet Detection: Getting to 10cm/s.”

  10. Velocity Selective Coherences in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Liu, L.; Cashen, M.; Metcalf, H.

    2001-05-01

    We have studied VSCPT(M. Doery et al., Phys. Rev: A52), 2295 (1995) and references therein. in metastable He in a B field and have begun to unravel the connection to magnetically induced velocity selective resonances (VSR)(S.Q. Shang et al., Phys. Rev. Lett 65), 826 (1990).. One very obvious difference between these is the two-peaked velocity distribution split by 2vr ≡ 2 hbar k/M of VSCPT, and the single peak of rms width < vr of VSR. But the evidence for a strong connection is that both phenomena produce velocity distributions with rms widths below vr when a velocity-selective Raman resonance is achieved by matching the Doppler and Zeeman shifts of two ground states |1> and |2>. The coherence produced by such a resonance suggests a basis |± > = \\|1> ± |2> √2, where |-> is a dark state^2. Thus there are two time scales, one for the excitation of |+ > that quickly pumps its atoms away from velocities near the Raman resonance, and Γ^', a much slower rate for atoms in |- > to evolve to |+ > and be pumped, often into the velocity trapped dark state^2. When Bz neq 0 the VSCPT signals are centered at 2 k \\cdot v = g Δ M μB |B|/hbar instead of v=0, just as in VSR, as long as the interaction time satisfies Γ^' τ_int > few. But if a B field compromises the optical selection rules so atoms can be pumped out of |- >, or if the laser parameters make Γ^' < few/τ_int, then only a single peak appears^2. We will present an appealing semi-classical model of these phenomena.

  11. A Clear Age-Velocity Dispersion Correlation in Andromeda’s Stellar Disk

    NASA Astrophysics Data System (ADS)

    Dorman, Claire E.; Guhathakurta, Puragra; Seth, Anil C.; Weisz, Daniel R.; Bell, Eric F.; Dalcanton, Julianne J.; Gilbert, Karoline M.; Hamren, Katherine M.; Lewis, Alexia R.; Skillman, Evan D.; Toloba, Elisa; Williams, Benjamin F.

    2015-04-01

    The stellar kinematics of galactic disks are key to constraining disk formation and evolution processes. In this paper, for the first time, we measure the stellar age-velocity dispersion correlation in the inner 20 kpc (˜3.5 disk scale lengths) of M31 and show that it is dramatically different from that in the Milky Way (MW). We use optical Hubble Space Telescope/Advanced Camera for Surveys photometry of 5800 individual stars from the Panchromatic Hubble Andromeda Treasury survey and Keck/DEIMOS radial velocity measurements of the same stars from the Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo survey. We show that the average line-of-sight dispersion is a steadily increasing function of age exterior to R = 10 kpc, increasing from 30 km {{s}-1} for the main-sequence stars to 90 km s-1 for the red giant branch stars. This monotonic increase implies that a continuous or recurring process contributed to the evolution of the disk. Both the slope and normalization of the dispersion versus age relation are significantly larger than in the MW, allowing for the possibility that the disk of M31 has had a more violent history than the disk of the MW, more in line with Λ cold dark matter predictions. We also find evidence for an inhomogeneous distribution of stars from a second kinematical component in addition to the dominant disk component. One of the largest and hottest high-dispersion patches is present in all age bins and may be the signature of the end of the long bar.

  12. River Surface Velocity Fields Observed From Space

    NASA Astrophysics Data System (ADS)

    Kääb, A.; Prowse, T. D.

    2011-12-01

    Knowledge of water-surface velocities in rivers is useful for understanding a wide range of lotic processes and systems, such as water and ice fluxes and forces, mixing, solute and sediment transport, bed and bank stability, aquatic and riparian ecology, and extreme hydrologic events. In cold regions, river-ice break up and the associated downstream transport of ice debris is often the most important hydrological event of the year, producing flood levels that commonly exceed those for the open-water period and dramatic consequences for river infrastructure and ecology. Quantification of river surface velocity and currents has relied mostly on very scarce in situ measurements or particle tracking in laboratory models, with few attempts to cover entire river reaches. Accurate and complete surface-velocity fields on rivers have rarely been produced. In this study, we use river-ice debris as an index of surface water velocity, and track it over a time period of about one minute, which is the typical time lapse between the two or more images that form a stereo data set in spaceborne, along-track optical-stereo mapping. Using this novel approach, we measure and visualize for the first time the almost complete two-dimensional surface velocity fields over many tens of kilometers long river reaches. We present the types of short time-delay imagery suitable for the measurements and discuss application examples on a number of North-American (e.g. Figs. 1 and 2) and Siberian rivers, using a range of high and medium resolution imagery. The methodology and results of the novel approach will be valuable to a number of disciplines requiring detailed information about river flow, such as hydraulics, hydrology, river ecology and natural-hazard management.

  13. Optical Velocity Field in NGC 3310

    NASA Astrophysics Data System (ADS)

    Sharp, N. A.

    1994-12-01

    NGC 3310 is a peculiar SAB(r)bc galaxy with giant Hii regions, star-burst nuclear activity, and evidence of a past merger. I present a variety of long-slit spectroscopic data covering both the nuclear region and the outer linear feature (the `arrow' in the poetic `bow-and-arrow' description of this galaxy). The spectral coverage includes several emission lines. The velocity field(s) and some line ratios derived from these data are discussed in the context of other work.

  14. Optical Velocity Field in NGC3310

    NASA Astrophysics Data System (ADS)

    Sharp, N. A.

    1996-12-01

    NGC 3310 is a peculiar SAB(r)bc galaxy with giant Hii regions, star-burst nuclear activity, and evidence of a past merger. I present a variety of long-slit spectroscopic data covering both the nuclear region and the outer linear feature (the `arrow' in the poetic `bow-and-arrow' description of this galaxy). The spectral coverage includes several emission lines. The velocity field(s) and some line ratios derived from these data are discussed in the context of other work.

  15. Optical Velocity Field in NGC3310

    NASA Astrophysics Data System (ADS)

    Sharp, N. A.

    2000-12-01

    NGC 3310 is a peculiar SAB(r)bc galaxy with giant Hii regions, star-burst nuclear activity, and evidence of a past merger. I present a variety of long-slit spectroscopic data covering both the nuclear region and the outer linear feature (the `arrow' in the poetic `bow-and-arrow' description of this galaxy). The spectral coverage includes several emission lines. The velocity field(s) and some line ratios derived from these data are discussed in the context of other work.

  16. Performances of four photometry softwares in very dense stellar fields

    NASA Astrophysics Data System (ADS)

    Dubout-Crillon, R.; Llebaria, A.

    2002-06-01

    We assess the relative performances of the softwares DAOPHOT, DAOPHOT/ ALLSTAR, CAPELLA, SEXTRACTOR for stellar fields with irregular backgrounds and asymmetric PSFs. The first three packages use PSF fit- tings, the fourth performs fixed aperture photometry and a small aperture was used in order to minimize the contaminating fluxes. A typical extragalactic stellar field has been used to built synthetic counterparts in order to test the photometric accuracy with respect to the blend extent. The results show in which cases DAOPHOT, DAOPHOT/ ALLSTAR and SEXTRACTOR overestimate the fluxes of blended stars. SEXTRACTOR results dispersions are near the ALLSTAR ones, but as we can expect, systematic overestimation appears for the severely blended stars. For stars merged in the wings of brighter stars, CAPELLA reaches the best accuracy. For isolated and moderately blended stars, ALLSTAR, CAPELLA and SEXTRACTOR results are near.

  17. [The radial velocity measurement accuracy of different spectral type low resolution stellar spectra at different signal-to-noise ratio].

    PubMed

    Wang, Feng-Fei; Luo, A-Li; Zhao, Yong-Heng

    2014-02-01

    The radial velocity of the star is very important for the study of the dynamics structure and chemistry evolution of the Milky Way, is also an useful tool for looking for variable or special objects. In the present work, we focus on calculating the radial velocity of different spectral types of low-resolution stellar spectra by adopting a template matching method, so as to provide effective and reliable reference to the different aspects of scientific research We choose high signal-to-noise ratio (SNR) spectra of different spectral type stellar from the Sloan Digital Sky Survey (SDSS), and add different noise to simulate the stellar spectra with different SNR. Then we obtain theradial velocity measurement accuracy of different spectral type stellar spectra at different SNR by employing a template matching method. Meanwhile, the radial velocity measurement accuracy of white dwarf stars is analyzed as well. We concluded that the accuracy of radial velocity measurements of early-type stars is much higher than late-type ones. For example, the 1-sigma standard error of radial velocity measurements of A-type stars is 5-8 times as large as K-type and M-type stars. We discuss the reason and suggest that the very narrow lines of late-type stars ensure the accuracy of measurement of radial velocities, while the early-type stars with very wide Balmer lines, such as A-type stars, become sensitive to noise and obtain low accuracy of radial velocities. For the spectra of white dwarfs stars, the standard error of radial velocity measurement could be over 50 km x s(-1) because of their extremely wide Balmer lines. The above conclusion will provide a good reference for stellar scientific study.

  18. Quasi-Axially Symmetric Stellarators with 3 Field Periods

    NASA Astrophysics Data System (ADS)

    Garabedian, Paul; Ku, Long-Poe

    1998-11-01

    Compact hybrid configurations with 2 field periods have been studied recently as candidates for a proof of principle experiment at PPPL, cf. A. Reiman et al., Physics design of a high beta quasi-axially symmetric stellarator, J. Plas. Fus. Res. SERIES 1, 429(1998). This enterprise has led us to the discovery of a family of quasi-axially symmetric stellarators with 3 field periods that seem to have significant advantages, although their aspect ratios are a little larger. They have reversed shear and perform better in a local analysis of ballooning modes. Nonlinear equilibrium and stability calculations predict that the average beta limit may be as high as 6% if the bootstrap current turns out to be as big as that expected in comparable tokamaks. The concept relies on a combination of helical fields and bootstrap current to achieve adequate rotational transform at low aspect ratio. A detailed manuscript describing some of this work will be published soon, cf. P.R. Garabedian, Quasi-axially symmetric stellarators, Proc. Natl. Acad. Sci. USA 95 (1998).

  19. Warm and dense stellar matter under strong magnetic fields

    SciTech Connect

    Rabhi, A.; Panda, P. K.; Providencia, C.

    2011-09-15

    We investigate the effects of strong magnetic fields on the equation of state of warm stellar matter as it may occur in a protoneutron star. Both neutrino-free and neutrino-trapped matter at a fixed entropy per baryon are analyzed. A relativistic mean-field nuclear model, including the possibility of hyperon formation, is considered. A density-dependent magnetic field with a magnitude of 10{sup 15} G at the surface and not more than 3x10{sup 18} G at the center is considered. The magnetic field gives rise to a neutrino suppression, mainly at low densities, in matter with trapped neutrinos. It is shown that a hybrid protoneutron star will not evolve into a low-mass black hole if the magnetic field is strong enough and the magnetic field does not decay. However, the decay of the magnetic field after cooling may give rise to the formation of a low-mass black hole.

  20. Axonal Velocity Distributions in Neural Field Equations

    PubMed Central

    Bojak, Ingo; Liley, David T. J.

    2010-01-01

    By modelling the average activity of large neuronal populations, continuum mean field models (MFMs) have become an increasingly important theoretical tool for understanding the emergent activity of cortical tissue. In order to be computationally tractable, long-range propagation of activity in MFMs is often approximated with partial differential equations (PDEs). However, PDE approximations in current use correspond to underlying axonal velocity distributions incompatible with experimental measurements. In order to rectify this deficiency, we here introduce novel propagation PDEs that give rise to smooth unimodal distributions of axonal conduction velocities. We also argue that velocities estimated from fibre diameters in slice and from latency measurements, respectively, relate quite differently to such distributions, a significant point for any phenomenological description. Our PDEs are then successfully fit to fibre diameter data from human corpus callosum and rat subcortical white matter. This allows for the first time to simulate long-range conduction in the mammalian brain with realistic, convenient PDEs. Furthermore, the obtained results suggest that the propagation of activity in rat and human differs significantly beyond mere scaling. The dynamical consequences of our new formulation are investigated in the context of a well known neural field model. On the basis of Turing instability analyses, we conclude that pattern formation is more easily initiated using our more realistic propagator. By increasing characteristic conduction velocities, a smooth transition can occur from self-sustaining bulk oscillations to travelling waves of various wavelengths, which may influence axonal growth during development. Our analytic results are also corroborated numerically using simulations on a large spatial grid. Thus we provide here a comprehensive analysis of empirically constrained activity propagation in the context of MFMs, which will allow more realistic studies

  1. Binaries at Birth: Stellar multiplicity in embedded clusters from radial velocity variations in the IN-SYNC survey

    NASA Astrophysics Data System (ADS)

    Oskar Jaehnig, Karl; Stassun, Keivan; Tan, Jonathan C.; Covey, Kevin R.; Da Rio, Nicola

    2016-01-01

    We study the nature of stellar multiplicity in young stellar systems using the INfrared Spectroscopy of Young Nebulous Clusters (IN-SYNC) survey, carried out in SDSS III with the APOGEE spectrograph. Multi-epoch observations of thousands of low-mass stars in Orion A, NGC2264, NGC1333 and IC348 have been carried out, yielding H-band spectra with R=22,500 for sources with H<12 mag. Radial velocity sensitivities ~0.3 km/s can be achieved, depending on the spectral type of the star. We search the IN-SYNC radial velocity catalog to identify sources with radial velocity variations indicative of spectroscopically undetected companions, analyze their spectral properties and discuss the implications for the overall multiplicity of stellar populations in young, embedded star clusters.

  2. Stellar radial velocities using a laser frequency comb: Application and observations in the near infrared

    NASA Astrophysics Data System (ADS)

    Osterman, Steve

    2011-04-01

    The laser frequency comb presents the potential for a revolutionary increase in radial velocity precision by providing a calibration reference of unprecedented quality in terms of wavelength knowledge, repeatability, number, density, and regularity of lines. However, implementation has proven challenging, particularly in the near infrared. Nevertheless, with the right combination of comb and instrument, promising first steps have been taken, allowing for the derivation of stellar radial velocities in a wavelength range which is well suited to the observation of M dwarfs. These stars, with low mass and low luminosity, are the most prevalent class of stars within 10 parsecs and can be expected to yield a higher reflex velocity for a terrestrial mass planet in the liquid water habitable zone than would be the case with a more massive star such as our own. We present the design and both laboratory and on-sky performance of an H-band laser frequency comb used in conjunction with the Penn State Pathfinder testbed spectrograph and discuss lessons learned and plans for follow on testing with both the Pathfinder and the CSHELL instruments.

  3. AN UPPER LIMIT TO THE VELOCITY DISPERSION OF RELAXED STELLAR SYSTEMS WITHOUT MASSIVE BLACK HOLES

    SciTech Connect

    Miller, M. Coleman; Davies, Melvyn B.

    2012-08-10

    Massive black holes have been discovered in all closely examined galaxies with high velocity dispersion. The case is not as clear for lower-dispersion systems such as low-mass galaxies and globular clusters. Here we suggest that above a critical velocity dispersion {approx}40 km s{sup -1}, massive central black holes will form in relaxed stellar systems at any cosmic epoch. This is because above this dispersion primordial binaries cannot support the system against deep core collapse. If, as previous simulations show, the black holes formed in the cluster settle to produce a dense subcluster, then given the extremely high densities reached during core collapse the holes will merge with each other. For low velocity dispersions and hence low cluster escape speeds, mergers will typically kick out all or all but one of the holes due to three-body kicks or the asymmetric emission of gravitational radiation. If one hole remains, it will tidally disrupt stars at a high rate. If none remain, one is formed after runaway collisions between stars, and then it tidally disrupts stars at a high rate. The accretion rate after disruption is many orders of magnitude above Eddington. If, as several studies suggest, the hole can accept matter at that rate because the generated radiation is trapped and advected, then it will grow quickly and form a massive central black hole.

  4. Uncovering the planets and stellar activity of CoRoT-7 using only radial velocities

    NASA Astrophysics Data System (ADS)

    Faria, J. P.; Haywood, R. D.; Brewer, B. J.; Figueira, P.; Oshagh, M.; Santerne, A.; Santos, N. C.

    2016-04-01

    Stellar activity can induce signals in the radial velocities of stars, complicating the detection of orbiting low-mass planets. We present a method to determine the number of planetary signals present in radial-velocity datasets of active stars, using only radial-velocity observations. Instead of considering separate fits with different number of planets, we use a birth-death Markov chain Monte Carlo algorithm to infer the posterior distribution for the number of planets in a single run. In a natural way, the marginal distributions for the orbital parameters of all planets are also inferred. This method is applied to HARPS data of CoRoT-7. We confidently recover the orbits of both CoRoT-7b and CoRoT-7c although the data show evidence for the presence of additional signals. All data and software presented in this article are available online at http://https://github.com/j-faria/exoBD-CoRoT7

  5. Inverse methods for stellarator error-fields and emission

    NASA Astrophysics Data System (ADS)

    Hammond, K. C.; Anichowski, A.; Brenner, P. W.; Diaz-Pacheco, R.; Volpe, F. A.; Wei, Y.; Kornbluth, Y.; Pedersen, T. S.; Raftopoulos, S.; Traverso, P.

    2016-10-01

    Work at the CNT stellarator at Columbia University has resulted in the development of two inverse diagnosis techniques that infer difficult-to-measure properties from simpler measurements. First, CNT's error-field is determined using a Newton-Raphson algorithm to infer coil misalignments based on measurements of flux surfaces. This is obtained by reconciling the computed flux surfaces (a function of coil misalignments) with the measured flux surfaces. Second, the plasma emissivity profile is determined based on a single CCD camera image using an onion-peeling method. This approach posits a system of linear equations relating pixel brightness to emission from a discrete set of plasma layers bounded by flux surfaces. Results for both of these techniques as applied to CNT will be shown, and their applicability to large modular coil stellarators will be discussed.

  6. Resolving stellar populations with crowded field 3D spectroscopy

    NASA Astrophysics Data System (ADS)

    Kamann, S.; Wisotzki, L.; Roth, M. M.

    2013-01-01

    We describe a new method of extracting the spectra of stars from observations of crowded stellar fields with integral field spectroscopy (IFS). Our approach extends the well-established concept of crowded field photometry in images into the domain of 3-dimensional spectroscopic datacubes. The main features of our algorithm follow. (1) We assume that a high-fidelity input source catalogue already exists, e.g. from HST data, and that it is not needed to perform sophisticated source detection in the IFS data. (2) Source positions and properties of the point spread function (PSF) vary smoothly between spectral layers of the datacube, and these variations can be described by simple fitting functions. (3) The shape of the PSF can be adequately described by an analytical function. Even without isolated PSF calibrator stars we can therefore estimate the PSF by a model fit to the full ensemble of stars visible within the field of view. (4) By using sparse matrices to describe the sources, the problem of extracting the spectra of many stars simultaneously becomes computationally tractable. We present extensive performance and validation tests of our algorithm using realistic simulated datacubes that closely reproduce actual IFS observations of the central regions of Galactic globular clusters. We investigate the quality of the extracted spectra under the effects of crowding with respect to the resulting signal-to-noise ratios (S/N) and any possible changes in the continuum level, as well as with respect to absorption line spectral parameters, radial velocities, and equivalent widths. The main effect of blending between two nearby stars is a decrease in the S/N in their spectra. The effect increases with the crowding in the field in a way that the maximum number of stars with useful spectra is always ~0.2 per spatial resolution element. This balance breaks down when exceeding a total source density of one significantly detected star per resolution element. We also explore the

  7. High-precision measurements of global stellar magnetic fields

    NASA Astrophysics Data System (ADS)

    Plachinda, S. I.

    2014-06-01

    This paper presents a brief history of the development of devices and techniques for high-precision measurements of stellar magnetic fields. Two main approaches for the processing of spectral-polarimetric observations are described: the method of least-squares deconvolution (LSD), which is used to find a mean-weighted average of the normalized polarization profile using a set of spectral lines, and a method in which each individual spectral line is used to determine the magnetic field, viz., the single line method (SL). The advantages and disadvantages of the LSD and SL methods are discussed.

  8. Stellar Dynamo Models with Prominent Surface Toroidal Fields

    NASA Astrophysics Data System (ADS)

    Bonanno, Alfio

    2016-12-01

    Recent spectro-polarimetric observations of solar-type stars have shown the presence of photospheric magnetic fields with a predominant toroidal component. If the external field is assumed to be current-free it is impossible to explain these observations within the framework of standard mean-field dynamo theory. In this work, it will be shown that if the coronal field of these stars is assumed to be harmonic, the underlying stellar dynamo mechanism can support photospheric magnetic fields with a prominent toroidal component even in the presence of axisymmetric magnetic topologies. In particular, it is argued that the observed increase in the toroidal energy in low-mass fast-rotating stars can be naturally explained with an underlying αΩ mechanism.

  9. Velocity dispersion and the stellar population in the central 1.2 parsecs of the Galaxy

    NASA Technical Reports Server (NTRS)

    Sellgren, K.; Mcginn, M. T.; Becklin, E. E.; Hall, D. N.

    1990-01-01

    New observations of the 2.3 micron absorption band head of CO in integrated stellar light in the central 1.2 pc of the Galaxy are presented. These data confirm that the velocity dispersion of the stars increases toward the Galactic center and totally dominates their systematic rotation at small radii. The velocity dispersion is constant an average value of 125 km/s within about 30 arcsec projected diameter central region. The strength of the CO features decreases in the integrated faint light within the same region. These observations are all consistent with the hypothesis that both the diffuse 2 micron light and the bright 2 micron point sources in the central region are dominated by sources that have little or no CO absorption feature. The observed CO feature at projected distances less than 0.6 pc thus actually arises in stars that are at true radii greater than 0.6 pc. The mass distribution at radius between 3.7 and 0.6 pc from IRS 16 is strong evidence for an increasing mass/2 micron radiation ratio toward the Galactic center.

  10. Velocity dispersion and the stellar population in the central 1.2 parsecs of the Galaxy

    NASA Technical Reports Server (NTRS)

    Sellgren, K.; Mcginn, M. T.; Becklin, E. E.; Hall, D. N.

    1990-01-01

    New observations of the 2.3 micron absorption band head of CO in integrated stellar light in the central 1.2 pc of the Galaxy are presented. These data confirm that the velocity dispersion of the stars increases toward the Galactic center and totally dominates their systematic rotation at small radii. The velocity dispersion is constant an average value of 125 km/s within about 30 arcsec projected diameter central region. The strength of the CO features decreases in the integrated faint light within the same region. These observations are all consistent with the hypothesis that both the diffuse 2 micron light and the bright 2 micron point sources in the central region are dominated by sources that have little or no CO absorption feature. The observed CO feature at projected distances less than 0.6 pc thus actually arises in stars that are at true radii greater than 0.6 pc. The mass distribution at radius between 3.7 and 0.6 pc from IRS 16 is strong evidence for an increasing mass/2 micron radiation ratio toward the Galactic center.

  11. On generating and derived magnitudes of stellar magnetic fields

    NASA Astrophysics Data System (ADS)

    Gerth, E.; Glagolevskij, Yu. V.

    2004-10-01

    The structure of the stellar surface magnetic field is covered from direct observation by many mixing processes. The discovery of the topographic surface structure requires an inversion procedure but does not reveal the origin of the magnetic field. Modelling of magnetic stars, however, has to start from the generating magnitudes and is a matter of construction by a strategy of forward calculation. The model of the star is fitted to the observed appearance of the real object by variation of parameters and optimizing. The magnetic field strength on the surface of the star -- including the magnetic poles -- is a derived magnitude, which should not be taken as a parameter for modeling. At the present time two versions of magnetic modeling are discussed: 1) expansion of spherical harmonics, 2) magnetic charge distribution. Both methods claim for the application of parameters, which determine the magnetic field. In this paper the question is investigated, what the generating and the derived magnitudes of the magnetic field are. Tracing back the observed spherical distribution of the magnetic field to its origin, one is led to the eigen values as the solution of Legendre's differential equation. We regard the eigen values as the generating magnitudes of the magnetic field, the physical quantities of which are the constituents of any vector field, namely the sources and vortices, from which the field originates. This interpretation is substantiated by graphical representations of magnetic maps with topographical features like poles -- derived from the field-generating sources: the virtual magnetic charges.

  12. StarFinder: A code for stellar field analysis

    NASA Astrophysics Data System (ADS)

    Diolaiti, Emiliano; Bendinelli, Orazio; Bonaccini, Domenico; Close, Laird M.; Currie, Doug G.; Parmeggiani, Gianluigi

    2000-11-01

    StarFinder is an IDL code for the deep analysis of stellar fields, designed for Adaptive Optics well-sampled images with high and low Strehl ratio. The Point Spread Function is extracted directly from the frame, to take into account the actual structure of the instrumental response and the atmospheric effects. The code is written in IDL language and organized in the form of a self-contained widget-based application, provided with a series of tools for data visualization and analysis. A description of the method and some applications to Adaptive Optics data are presented.

  13. Data reduction, radial velocities and stellar parameters from spectra in the very low signal-to-noise domain

    NASA Astrophysics Data System (ADS)

    Malavolta, Luca

    2013-10-01

    Large astronomical facilities usually provide data reduction pipeline designed to deliver ready-to-use scientific data, and too often as- tronomers are relying on this to avoid the most difficult part of an astronomer job Standard data reduction pipelines however are usu- ally designed and tested to have good performance on data with av- erage Signal to Noise Ratio (SNR) data, and the issues that are related with the reduction of data in the very low SNR domain are not taken int account properly. As a result, informations in data with low SNR are not optimally exploited. During the last decade our group has collected thousands of spec- tra using the GIRAFFE spectrograph at Very Large Telescope (Chile) of the European Southern Observatory (ESO) to determine the ge- ometrical distance and dynamical state of several Galactic Globular Clusters but ultimately the analysis has been hampered by system- atics in data reduction, calibration and radial velocity measurements. Moreover these data has never been exploited to get other informa- tions like temperature and metallicity of stars, because considered too noisy for these kind of analyses. In this thesis we focus our attention on data reduction and analysis of spectra with very low SNR. The dataset we analyze in this thesis comprises 7250 spectra for 2771 stars of the Globular Cluster M 4 (NGC 6121) in the wavelength region 5145-5360Å obtained with GIRAFFE. Stars from the upper Red Giant Branch down to the Main Sequence have been observed in very different conditions, including nights close to full moon, and reaching SNR - 10 for many spectra in the dataset. We will first review the basic steps of data reduction and spec- tral extraction, adapting techniques well tested in other field (like photometry) but still under-developed in spectroscopy. We improve the wavelength dispersion solution and the correction of radial veloc- ity shift between day-time calibrations and science observations by following a completely

  14. Galaxy luminosities, stellar masses, sizes, velocity dispersions as a function of morphological type

    NASA Astrophysics Data System (ADS)

    Bernardi, M.; Shankar, F.; Hyde, J. B.; Mei, S.; Marulli, F.; Sheth, R. K.

    2010-06-01

    We provide fits to the distribution of galaxy luminosity, size, velocity dispersion and stellar mass as a function of concentration index Cr and morphological type in the Sloan Digital Sky Survey (SDSS). (Our size estimate, a simple analogue of the SDSS cmodel magnitude, is new: it is computed using a combination of seeing-corrected quantities in the SDSS data base, and is in substantially better agreement with results from more detailed bulge/disc decompositions.) We also quantify how estimates of the fraction of `early'- or `late'-type galaxies depend on whether the samples were cut in colour, concentration or light profile shape, and compare with similar estimates based on morphology. Our fits show that ellipticals account for about 20 per cent of the r-band luminosity density, , and 25 per cent of the stellar mass density, ρ* including S0s and Sas increases these numbers to 33 per cent and 40 per cent, and 50 per cent and 60 per cent, respectively. The values of and ρ*, and the mean sizes, of E, E+S0 and E+S0+Sa samples are within 10 per cent of those in the Hyde & Bernardi, Cr >= 2.86 and Cr >= 2.6 samples, respectively. Summed over all galaxy types, we find ρ* ~ 3 × 108MsolarMpc-3 at z ~ 0. This is in good agreement with expectations based on integrating the star formation history. However, compared to most previous work, we find an excess of objects at large masses, up to a factor of ~10 at M* ~ 5 × 1011Msolar. The stellar mass density further increases at large masses if we assume different initial mass functions for elliptical and spiral galaxies, as suggested by some recent chemical evolution models, and results in a better agreement with the dynamical mass function. We also show that the trend for ellipticity to decrease with luminosity is primarily because the E/S0 ratio increases at large L. However, the most massive galaxies, M* >= 5 × 1011Msolar, are less concentrated and not as round as expected if one extrapolates from lower L, and they are

  15. Transport in stellar radiation zones with magnetic field

    NASA Astrophysics Data System (ADS)

    Mathis, S.; Zahn, J.-P.

    We examine the interaction between meridian circulation and turbulence in rotating stars with an axisymetric magnetic field. In the same way as Zahn (1992) and Spiegel and Zahn (1992), the turbulence is assumed to be anisotropic, due to the stratification, with stronger transport in the horizontal directions than in the vertical. We keep the 'shellular rotation' hypothesis, but we expand the differential rotation in latitude to higher order, which allow us to treat simultaneously the radiative interior and the tachocline(s). We derive the partial differential equations which govern the transport of magnetic field, temperature, angular momentum and chemical elements with taking into account the non-stationarity of the problem, the mu-gradients, the effect of horizontal turbulence in thermal imbalance and a general equation of state like in Maeder and Zahn (1998). Finally, we apply the beta-viscosity prescription which has been derived from Couette-Taylor experiments (Richard and Zahn (1999)) to the problem of transport in stellar interiors to obtain a new expression for the horizontal component of the turbulent viscosity, nuh, and its companion the horizontal diffusivity, Dh. The next step will be to implement these new equations in existing stellar structure codes, to model the evolution of rotating stars.

  16. Space density distribution of galaxies in the absolute magnitude - rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA stellar kinematics

    NASA Astrophysics Data System (ADS)

    Bekeraité, S.; Walcher, C. J.; Falcón-Barroso, J.; Garcia Lorenzo, B.; Lyubenova, M.; Sánchez, S. F.; Spekkens, K.; van de Ven, G.; Wisotzki, L.; Ziegler, B.; Aguerri, J. A. L.; Barrera-Ballesteros, J.; Bland-Hawthorn, J.; Catalán-Torrecilla, C.; García-Benito, R.

    2016-10-01

    We measured the distribution in absolute magnitude - circular velocity space for a well-defined sample of 199 rotating galaxies of the Calar Alto Legacy Integral Field Area Survey (CALIFA) using their stellar kinematics. Our aim in this analysis is to avoid subjective selection criteria and to take volume and large-scale structure factors into account. Using stellar velocity fields instead of gas emission line kinematics allows including rapidly rotating early-type galaxies. Our initial sample contains 277 galaxies with available stellar velocity fields and growth curve r-band photometry. After rejecting 51 velocity fields that could not be modelled because of the low number of bins, foreground contamination, or significant interaction, we performed Markov chain Monte Carlo modelling of the velocity fields, from which we obtained the rotation curve and kinematic parameters and their realistic uncertainties. We performed an extinction correction and calculated the circular velocity vcirc accounting for the pressure support of a given galaxy. The resulting galaxy distribution on the Mr-vcirc plane was then modelled as a mixture of two distinct populations, allowing robust and reproducible rejection of outliers, a significant fraction of which are slow rotators. The selection effects are understood well enough that we were able to correct for the incompleteness of the sample. The 199 galaxies were weighted by volume and large-scale structure factors, which enabled us to fit a volume-corrected Tully-Fisher relation (TFR). More importantly, we also provide the volume-corrected distribution of galaxies in the Mr-vcirc plane, which can be compared with cosmological simulations. The joint distribution of the luminosity and circular velocity space densities, representative over the range of -20 > Mr > -22 mag, can place more stringent constraints on the galaxy formation and evolution scenarios than linear TFR fit parameters or the luminosity function alone. Galaxies main

  17. Closed and open magnetic fields in stellar winds

    SciTech Connect

    Mullan, D.J.; Steinolfson, R.S.

    1983-03-15

    We report on a numerical study of the interaction between a thermal wind and a global dipole field in the Sun and in a giant star. In order for closed field lines to persist near the equator (where a helmet-streamer-like configuration appears), the coronal temperature must be less than a critical value T/sub c/, which scales as M/R. This condition is found to be equivalent to the following: for a static helmet streamer to persist, the sonic point above the helmet must not approach closer to the star than 2.2--2.6 stellar radii. Implications for rapid mass loss and X-ray emission from cool giants are pointed out. Our results strengthen the case for identifying empirical dividing lines in the H-R diagram with a magnetic topology transition locus (MTTL). Support for the MTTL concept is also provided by considerations of the breakdown of magnetostatic equilibrium.

  18. A consistent solution for the velocity field and mass-loss rate of massive stars

    NASA Astrophysics Data System (ADS)

    Müller, P. E.; Vink, J. S.

    2008-12-01

    Stellar winds are an important aspect of our understanding of the evolution of massive stars and their input into the interstellar medium. Here we present solutions for the velocity field and mass-loss rates for stellar outflows as well as for the case of mass accretion through the use of the so-called Lambert W-function. For the case of a radiation-driven wind, the velocity field is obtained analytically using a parameterised description for the line acceleration that only depends on radius, which we obtain from Monte-Carlo multi-line radiative transfer calculations. In our form of the equation of motion the critical point is the sonic point. We also derive an approximate analytical solution for the supersonic flow which closely resembles our exact solution. For the simultaneous solution of the mass-loss rate and velocity field, we describe a new iterative method. We apply our theoretical expressions and our iterative method to the stellar wind from a typical O5-V main sequence star, and find good agreement with empirical values. Our computations represent a self-consistent mass-loss calculation including the effect of multi-line scattering for an O-type star, opening up the possibility of applying Monte Carlo mass-loss calculations in regions of the Universe for which empirical constraints cannot be readily obtained.

  19. Narrow-band imaging and velocity maps of young stellar objects - Initial results

    NASA Technical Reports Server (NTRS)

    Morgan, J. S.; Wolff, S. C.; Strom, S. E.; Strom, K. M.

    1984-01-01

    The first trials of a new technique, designed to map low-excitation ionized gas surrounding young stellar objects, are reported. The region surrounding the T Tau stars HL Tau and XZ Tau, that near HH 101, and that near IRS 5 in L1551 have been imaged through a narrow-band (4.7 A FWHM) forbidden S II filter; three-phase CCD chip was used as the detector. By tilting the narrow-band filter, it is possible to vary the wavelength of peak transmission and thus to detect high-velocity radial flows as well as map the morphology of the excited gas near these young stars. Evidence of an apparently helical outflow is found for HH 101. Redshifted gas appears to extend southward from HL Tau toward HH 30; a blueshifted jet extends northeastward of HL Tau. A series of forbidden S II knots is seen to extend along a jet directed southwestward from the infrared source IRS 5; the knot chain appears to delineate a blueshifted outflow that decelerates as it recedes from IRS 5.

  20. Magnetic Fields In Early Stellar Evolution: Improving Mass And Age Estimates For Young Stars

    NASA Astrophysics Data System (ADS)

    Feiden, Gregory A.

    2016-11-01

    Inhibition of convection by strong magnetic fields has been implicated as a potential culprit for the observed systematic errors with stellar models predictions. I test this hypothesis using stellar evolution models that include effects of strong magnetic fields on stellar structure and the efficiency of convection. I show that models including inhibition of convection due to magnetic fields producebetter age consistency across effective temperature domains and alterthe slope of the mass-radius relation to predict an age consistentwith the HR diagram.

  1. RADIAL VELOCITY VARIABILITY OF FIELD BROWN DWARFS

    SciTech Connect

    Prato, L.; Mace, G. N.; Rice, E. L.; McLean, I. S.; Kirkpatrick, J. Davy; Burgasser, A. J.; Kim, Sungsoo S.

    2015-07-20

    We present paper six of the NIRSPEC Brown Dwarf Spectroscopic Survey, an analysis of multi-epoch, high-resolution (R ∼ 20,000) spectra of 25 field dwarf systems (3 late-type M dwarfs, 16 L dwarfs, and 6 T dwarfs) taken with the NIRSPEC infrared spectrograph at the W. M. Keck Observatory. With a radial velocity (RV) precision of ∼2 km s{sup −1}, we are sensitive to brown dwarf companions in orbits with periods of a few years or less given a mass ratio of 0.5 or greater. We do not detect any spectroscopic binary brown dwarfs in the sample. Given our target properties, and the frequency and cadence of observations, we use a Monte Carlo simulation to determine the detection probability of our sample. Even with a null detection result, our 1σ upper limit for very low mass binary frequency is 18%. Our targets included seven known, wide brown dwarf binary systems. No significant RV variability was measured in our multi-epoch observations of these systems, even for those pairs for which our data spanned a significant fraction of the orbital period. Specialized techniques are required to reach the high precisions sensitive to motion in orbits of very low-mass systems. For eight objects, including six T dwarfs, we present the first published high-resolution spectra, many with high signal to noise, that will provide valuable comparison data for models of brown dwarf atmospheres.

  2. THE EFFECT OF THE PRE-DETONATION STELLAR INTERNAL VELOCITY PROFILE ON THE NUCLEOSYNTHETIC YIELDS IN TYPE Ia SUPERNOVA

    SciTech Connect

    Kim, Yeunjin; Jordan, G. C. IV; Graziani, Carlo; Lamb, D. Q.; Truran, J. W.; Meyer, B. S.

    2013-07-01

    A common model of the explosion mechanism of Type Ia supernovae is based on a delayed detonation of a white dwarf. A variety of models differ primarily in the method by which the deflagration leads to a detonation. A common feature of the models, however, is that all of them involve the propagation of the detonation through a white dwarf that is either expanding or contracting, where the stellar internal velocity profile depends on both time and space. In this work, we investigate the effects of the pre-detonation stellar internal velocity profile and the post-detonation velocity of expansion on the production of {alpha}-particle nuclei, including {sup 56}Ni, which are the primary nuclei produced by the detonation wave. We perform one-dimensional hydrodynamic simulations of the explosion phase of the white dwarf for center and off-center detonations with five different stellar velocity profiles at the onset of the detonation. In order to follow the complex flows and to calculate the nucleosynthetic yields, approximately 10,000 tracer particles were added to every simulation. We observe two distinct post-detonation expansion phases: rarefaction and bulk expansion. Almost all the burning to {sup 56}Ni occurs only in the rarefaction phase, and its expansion timescale is influenced by pre-existing flow structure in the star, in particular by the pre-detonation stellar velocity profile. We find that the mass fractions of the {alpha}-particle nuclei, including {sup 56}Ni, are tight functions of the empirical physical parameter {rho}{sub up}/v{sub down}, where {rho}{sub up} is the mass density immediately upstream of the detonation wave front and v{sub down} is the velocity of the flow immediately downstream of the detonation wave front. We also find that v{sub down} depends on the pre-detonation flow velocity. We conclude that the properties of the pre-existing flow, in particular the internal stellar velocity profile, influence the final isotopic composition of burned

  3. The Effect of the Pre-detonation Stellar Internal Velocity Profile on the Nucleosynthetic Yields in Type Ia Supernova

    NASA Astrophysics Data System (ADS)

    Kim, Yeunjin; Jordan, G. C., IV; Graziani, Carlo; Meyer, B. S.; Lamb, D. Q.; Truran, J. W.

    2013-07-01

    A common model of the explosion mechanism of Type Ia supernovae is based on a delayed detonation of a white dwarf. A variety of models differ primarily in the method by which the deflagration leads to a detonation. A common feature of the models, however, is that all of them involve the propagation of the detonation through a white dwarf that is either expanding or contracting, where the stellar internal velocity profile depends on both time and space. In this work, we investigate the effects of the pre-detonation stellar internal velocity profile and the post-detonation velocity of expansion on the production of α-particle nuclei, including 56Ni, which are the primary nuclei produced by the detonation wave. We perform one-dimensional hydrodynamic simulations of the explosion phase of the white dwarf for center and off-center detonations with five different stellar velocity profiles at the onset of the detonation. In order to follow the complex flows and to calculate the nucleosynthetic yields, approximately 10,000 tracer particles were added to every simulation. We observe two distinct post-detonation expansion phases: rarefaction and bulk expansion. Almost all the burning to 56Ni occurs only in the rarefaction phase, and its expansion timescale is influenced by pre-existing flow structure in the star, in particular by the pre-detonation stellar velocity profile. We find that the mass fractions of the α-particle nuclei, including 56Ni, are tight functions of the empirical physical parameter ρup/v down, where ρup is the mass density immediately upstream of the detonation wave front and v down is the velocity of the flow immediately downstream of the detonation wave front. We also find that v down depends on the pre-detonation flow velocity. We conclude that the properties of the pre-existing flow, in particular the internal stellar velocity profile, influence the final isotopic composition of burned matter produced by the detonation.

  4. Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars

    NASA Astrophysics Data System (ADS)

    Orlando, S.; Bonito, R.; Argiroffi, C.; Reale, F.; Peres, G.; Miceli, M.; Matsakos, T.; Stehlé, C.; Ibgui, L.; de Sa, L.; Chièze, J. P.; Lanz, T.

    2013-11-01

    Context. According to the magnetospheric accretion model, hot spots form on the surface of classical T Tauri stars (CTTSs) in regions where accreting disk material impacts the stellar surface at supersonic velocity, generating a shock. Aims: We investigate the dynamics and stability of postshock plasma that streams along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. Methods: We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model considers the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction (including the effects of heat flux saturation). We explore different configurations and strengths of the magnetic field. Results: The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic field. In the case of weak magnetic fields (plasma β ≳ 1 in the postshock region), a large component of B may develop perpendicular to the stream at the base of the accretion column, which limits the sinking of the shocked plasma into the chromosphere and perturbs the overstable shock oscillations induced by radiative cooling. An envelope of dense and cold chromospheric material may also develop around the shocked column. For strong magnetic fields (β < 1 in the postshock region close to the chromosphere), the field configuration determines the position of the shock and its stand-off height. If the field is strongly tapered close to the chromosphere, an oblique shock may form well above the stellar surface at the height where the plasma β ≈ 1. In general, we find that a nonuniform magnetic field makes the distribution of emission measure vs. temperature of the postshock plasma at T > 106 K lower than when there is uniform magnetic field

  5. Effective diffusion equation in a random velocity field

    NASA Technical Reports Server (NTRS)

    Vinals, Jorge; Sekerka, Robert F.

    1992-01-01

    The effects are studied of assumed random velocity fields on diffusion in a binary fluid. Random velocity fields can result, for example, from the high-frequency components of residual accelerations onboard spacecraft (often called g-jitter). An effective diffusion equation is derived for an average concentration which includes spatial and temporal correlations induced by the fluctuating velocity fields assumed to be Gaussianly distributed. The resulting equation becomes nonlocal, and if correlations between different components of the velocity field exist, it is also anisotropic. The simple limiting case of short correlation times is discussed and an effective diffusivity is obtained which reflects the enhanced mixing caused by the velocity fields. The results obtained in the limit of short correlation times are valid even if the probability distribution of the velocity field is not Gaussian.

  6. McDonald Observatory Planetary Search - A high precision stellar radial velocity survey for other planetary systems

    NASA Technical Reports Server (NTRS)

    Cochran, William D.; Hatzes, Artie P.

    1993-01-01

    The McDonald Observatory Planetary Search program surveyed a sample of 33 nearby F, G, and K stars since September 1987 to search for substellar companion objects. Measurements of stellar radial velocity variations to a precision of better than 10 m/s were performed as routine observations to detect Jovian planets in orbit around solar type stars. Results confirm the detection of a companion object to HD114762.

  7. Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity

    NASA Astrophysics Data System (ADS)

    Hatzes, A. P.; Cochran, W. D.; Endl, M.; Guenther, E. W.; MacQueen, P.; Hartmann, M.; Zechmeister, M.; Han, I.; Lee, B.-C.; Walker, G. A. H.; Yang, S.; Larson, A. M.; Kim, K.-M.; Mkrtichian, , D. E.; Döllinger, M.; Simon, , A. E.; Girardi, L.

    2015-08-01

    Aims: We investigate the nature of the long-period radial velocity variations in α Tau first reported over 20 yr ago. Methods: We analyzed precise stellar radial velocity measurements for α Tau spanning over 30 yr. An examination of the Hα and Ca II λ8662 spectral lines, and Hipparcos photometry was also done to help discern the nature of the long-period radial velocity variations. Results: Our radial velocity data show that the long-period, low amplitude radial velocity variations are long-lived and coherent. Furthermore, Hα equivalent width measurements and Hipparcos photometry show no significant variations with this period. Another investigation of this star established that there was no variability in the spectral line shapes with the radial velocity period. An orbital solution results in a period of P = 628.96 ± 0.90 d, eccentricity, e = 0.10 ± 0.05, and a radial velocity amplitude, K = 142.1 ± 7.2 m s-1. Evolutionary tracks yield a stellar mass of 1.13 ± 0.11 M⊙, which corresponds to a minimum companion mass of 6.47 ± 0.53 MJup with an orbital semi-major axis of a = 1.46 ± 0.27 AU. After removing the orbital motion of the companion, an additional period of ≈520 d is found in the radial velocity data, but only in some time spans. A similar period is found in the variations in the equivalent width of Hα and Ca II. Variations at one-third of this period are also found in the spectral line bisector measurements. The ~520 d period is interpreted as the rotation modulation by stellar surface structure. Its presence, however, may not be long-lived, and it only appears in epochs of the radial velocity data separated by ~10 yr. This might be due to an activity cycle. Conclusions: The data presented here provide further evidence of a planetary companion to α Tau, as well as activity-related radial velocity variations. Based in part on observations obtained at the 2-m-Alfred Jensch Telescope at the Thüringer Landessternwarte Tautenburg and the

  8. PROJECTED ROTATIONAL VELOCITIES AND STELLAR CHARACTERIZATION OF 350 B STARS IN THE NEARBY GALACTIC DISK

    SciTech Connect

    Braganca, G. A.; Daflon, S.; Cunha, K.; Bensby, T.; Oey, M. S.; Walth, G.

    2012-11-01

    Projected rotational velocities (v sin i) are presented for a sample of 350 early B-type main-sequence stars in the nearby Galactic disk. The stars are located within {approx}1.5 kpc from the Sun, and the great majority within 700 pc. The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5 m telescope at the Las Campanas Observatory in Chile. Spectral types were estimated based on relative intensities of some key line absorption ratios and comparisons to synthetic spectra. Effective temperatures were estimated from the reddening-free Q index, and projected rotational velocities were then determined via interpolation on a published grid that correlates the synthetic FWHM of the He I lines at 4026, 4388 and 4471 A with v sin i. As the sample has been selected solely on the basis of spectral types, it contains a selection of B stars in the field, in clusters, and in OB associations. The v sin i distribution obtained for the entire sample is found to be essentially flat for v sin i values between 0 and 150 km s{sup -1}, with only a modest peak at low projected rotational velocities. Considering subsamples of stars, there appears to be a gradation in the v sin i distribution with the field stars presenting a larger fraction of the slow rotators and the cluster stars distribution showing an excess of stars with v sin i between 70 and 130 km s{sup -1}. Furthermore, for a subsample of potential runaway stars we find that the v sin i distribution resembles the distribution seen in denser environments, which could suggest that these runaway stars have been subject to dynamical ejection mechanisms.

  9. Study on a multi-delay spectral interferometry for stellar radial velocity measurement

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Jiang, Haijiao; Tang, Jin; Ji, Hangxin; Zhu, Yongtian; Wang, Liang

    2014-08-01

    High accuracy radial velocity measurement isn't only one of the most important methods for detecting earth-like Exoplanets, but also one of the main developing fields of astronomical observation technologies in future. Externally dispersed interferometry (EDI) generates a kind of particular interference spectrum through combining a fixed-delay interferometer with a medium-resolution spectrograph. It effectively enhances radial velocity measuring accuracy by several times. Another further study on multi-delay interferometry was gradually developed after observation success with only a fixed-delay, and its relative instrumentation makes more impressive performance in near Infrared band. Multi-delay is capable of giving wider coverage from low to high frequency in Fourier field so that gives a higher accuracy in radial velocity measurement. To study on this new technology and verify its feasibility at Guo Shoujing telescope (LAMOST), an experimental instrumentation with single fixed-delay named MESSI has been built and tested at our lab. Another experimental study on multi-delay spectral interferometry given here is being done as well. Basically, this multi-delay experimental system is designed in according to the similar instrument named TEDI at Palomar observatory and the preliminary test result of MESSI. Due to existence of LAMOST spectrograph at lab, a multi-delay interferometer design actually dominates our work. It's generally composed of three parts, respectively science optics, phase-stabilizing optics and delay-calibrating optics. To switch different fixed delays smoothly during observation, the delay-calibrating optics is possibly useful to get high repeatability during switching motion through polychromatic interferometry. Although this metrology is based on white light interferometry in theory, it's different that integrates all of interference signals independently obtained by different monochromatic light in order to avoid dispersion error caused by

  10. Stability of toroidal magnetic fields in stellar interiors

    NASA Astrophysics Data System (ADS)

    Ibáñez-Mejía, J. C.; Braithwaite, J.

    2015-06-01

    Aims: Magnetic fields play an important role during the formation and evolution of stars. Of particular interest in stellar evolution is what effect they have on the transport angular momentum and mixing of chemical elements along the radial direction in radiative regions. Current theories suggest a dynamo loop as the mechanism responsible for maintaining the magnetic field in the radiative zone. This loop consists of differential rotation on one side and magnetohydrodynamic (MHD) instability - the so-called Tayler instability - on the other. However, how this might work quantitatively is still an unsettled question, largely because we do not yet understand all the properties of the instability in question. In this paper we explore some properties of the Tayler instability. Methods: We present 3D MHD simulations of purely toroidal and mixed poloidal-toroidal magnetic field configurations to study the behavior of the Tayler instability. For the first time the simultaneous action of rotation and magnetic diffusion are taken into account and the effects of a poloidal field on the dynamic evolution of unstable toroidal magnetic fields is included. Results: In the absence of diffusion, fast rotation (rotation rate, Ω∥, compared to Alfvén frequency, ωA,φ) is able to suppress the instability when the rotation and magnetic axes are aligned and when the radial field strength gradient p< 1.5 (where p ≡ ∂lnB/∂lnϖ and ϖ is the cylindrical radius coordinate). When diffusion is included, this system turns unstable for diffusion dominated and marginally diffusive dominated regions. If the magnetic and rotation axes are perpendicular to each other, Ω⊥, the stabilizing effect induced by the Coriolis force is scale dependent and decreases with increasing wavenumber. In toroidal fields with radial field gradients bigger than p> 1.5, rapid rotation does not suppress the instability but instead introduces a damping factor ωA/ 2Ω∥ to the growth rate, in agreement

  11. OB associations in four stellar fields of M 31

    NASA Astrophysics Data System (ADS)

    Battinelli, P.

    1992-05-01

    The problem of the real spatial distribution of OB stars in M 31, with particular attention on whether these stars follow a hierarchical distribution in agreement with the scenario of star formation proposed by Elmegreen & Elmegreen (1983), is addressed. The first step in this direction would be to provide an objective identification of the OB associations in M 31 and then to study their spatial distribution. Unfortunately, this task is made difficult by the fact that the catalogs of OB stars in M 31 available in the literature are mainly limited to supergiant stars. The recent PLC identification technique for OB associations (Battinelli, 1991) is therefore applied in four stellar fields of M 31 for which high-resolution photometric data ensure that almost all of the OB stars have been identified. Results are in agreement with other works in the literature and show that the sizes of the OB associations in these fields of M 31 are similar to the sizes of their counterparts in the Milky Way and in the Magellanic Clouds.

  12. Linear relation between H I circular velocity and stellar velocity dispersion in early-type galaxies, and slope of the density profiles

    NASA Astrophysics Data System (ADS)

    Serra, Paolo; Oosterloo, Tom; Cappellari, Michele; den Heijer, Milan; Józsa, Gyula I. G.

    2016-08-01

    We report a tight linear relation between the H I circular velocity measured at 6 Re and the stellar velocity dispersion measured within 1 Re for a sample of 16 early-type galaxies with stellar mass between 1010 and 1011 M⊙. The key difference from previous studies is that we only use spatially resolved vcirc(H I) measurements obtained at large radius for a sizeable sample of objects. We can therefore link a kinematical tracer of the gravitational potential in the dark-matter dominated outer regions of galaxies with one in the inner regions, where baryons control the distribution of mass. We find that vcirc(H I)= 1.33 σe with an observed scatter of just 12 per cent. This indicates a strong coupling between luminous and dark matter from the inner- to the outer regions of early-type galaxies, analogous to the situation in spirals and dwarf irregulars. The vcirc(H I)-σe relation is shallower than those based on vcirc measurements obtained from stellar kinematics and modelling at smaller radius, implying that vcirc declines with radius - as in bulge-dominated spirals. Indeed, the value of vcirc(H I) is typically 25 per cent lower than the maximum vcirc derived at ˜0.2 Re from dynamical models. Under the assumption of power-law total density profiles ρ ∝ r-γ, our data imply an average logarithmic slope <γ> = 2.18 ± 0.03 across the sample, with a scatter of 0.11 around this value. The average slope and scatter agree with recent results obtained from stellar kinematics alone for a different sample of early-type galaxies.

  13. THE GEMINI SPECTRAL LIBRARY OF NEAR-IR LATE-TYPE STELLAR TEMPLATES AND ITS APPLICATION FOR VELOCITY DISPERSION MEASUREMENTS

    SciTech Connect

    Winge, Claudia

    2009-11-01

    We present a spectroscopic library of late spectral type stellar templates in the near-IR range 2.15-2.42 {mu}m, at R = 5300-5900 resolution, oriented to support stellar kinematics studies in external galaxies, such as the direct determination of the masses of supermassive black holes in nearby active (or non-active) galaxies. The combination of high spectral resolution and state-of-the-art instrumentation available in 8 m class telescopes has made the analysis of circumnuclear stellar kinematics using the near-IR CO band heads one of the most used techniques for such studies, and this library aims to provide the supporting data sets required by the higher spectral resolution and larger spectral coverage currently achieved with modern near-IR spectrographs. Examples of the application for kinematical analysis are given for data obtained with two Gemini instruments, but the templates can be easily adjusted for use with other near-IR spectrographs at similar or lower resolution. The example data sets are also used to revisit the 'template mismatch' effect and the dependence of the velocity dispersion values obtained from the fitting process with the characteristics of the stellar templates. The library is available in electronic form from the Gemini Web pages.

  14. VELOCITY DISPERSIONS AND STELLAR POPULATIONS OF THE MOST COMPACT AND MASSIVE EARLY-TYPE GALAXIES AT REDSHIFT {approx}1

    SciTech Connect

    Martinez-Manso, Jesus; Guzman, Rafael; Barro, Guillermo; Cardiel, Nicolas; Gallego, Jesus; Cenarro, Javier; Perez-Gonzalez, Pablo; Sanchez-Blazquez, Patricia; Trujillo, Ignacio; Balcells, Marc; Hempel, Angela; Prieto, Mercedes

    2011-09-10

    We present Gran-Telescopio-Canarias/OSIRIS optical spectra of four of the most compact and massive early-type galaxies (ETGs) in the Groth Strip Survey at redshift z {approx} 1, with effective radii R{sub e} = 0.5-2.4 kpc and photometric stellar masses M{sub *} = (1.2-4) x 10{sup 11} M{sub sun}. We find that these galaxies have velocity dispersions {sigma} = 156-236 km s{sup -1}. The spectra are well fitted by single stellar population models with approximately 1 Gyr of age and solar metallicity. We find that (1) the dynamical masses of these galaxies are systematically smaller by a factor of {approx}6 than the published stellar masses using BRIJK photometry, and (2) when estimating stellar masses as 0.7x M{sub dyn}, a combination of passive luminosity fading with mass/size growth due to minor mergers can plausibly evolve our objects to match the properties of the local population of ETGs.

  15. Universal Velocity-Field Characteristics for a Nanowire Arbitrary Degeneracy

    SciTech Connect

    Chek, Desmond C. Y.; Hashim, Abdul Manaf; Tan, Michael Loong Peng; Arora, Vijay K.

    2011-05-25

    The effects of electric field on the carrier motion and drift velocity in nanowire (NW) are presented in this paper. When the electric field is applied in NW, the electron is expected to move in anti-parallel direction to the electric field. This is so-called randomness motion is transformed into streamlined motion in extremely high electric field. The normalized Fermi energy and relative electron population as a function of electric field are examined for various degeneracies. It was found that the electric field has lesser influence on the relative electron population with the increased degeneracy. The drift velocity in NW is shown to increase with electric field until it reaches the saturation velocity. Two approximations have been made to simplify the theoretical equation. It is also shown in this paper that when the quantum emission is taken into account, the drift and saturation velocity degrades.

  16. Stellar Radial Velocities in the Old Open Cluster M67 (NGC 2682). I. Memberships, Binaries, and Kinematics

    NASA Astrophysics Data System (ADS)

    Geller, Aaron M.; Latham, David W.; Mathieu, Robert D.

    2015-09-01

    We present results from 13776 radial-velocity (RV) measurements of 1278 candidate members of the old (4 Gyr) open cluster M67 (NGC 2682). The measurements are the results of a long-term survey that includes data from seven telescopes with observations for some stars spanning over 40 years. For narrow-lined stars, RVs are measured with precisions ranging from about 0.1 to 0.8 km s-1. The combined stellar sample reaches from the brightest giants in the cluster down to about 4 mag below the main-sequence turnoff (V=16.5), covering a mass range of about 1.34 {M}⊙ to 0.76 {M}⊙ . Spatially, the sample extends to a radus of 30 arcmin (7.4 pc in projection at a distance of 850 pc or 6-7 core radii). We find M67 to have a mean RV of +33.64 km s-1 (with an internal precision of ±0.03 km s-1) well separated from the mean velocity of the field. For stars with ≥slant 3 measurements, we derive RV membership probabilities and identify RV variables, finding 562 cluster members, 142 of which show significant RV variability. We use these cluster members to construct a color-magnitude diagram and identify a rich sample of stars that lie far from the standard single star isochrone, including the well-known blue stragglers, sub-subgiants and yellow giants. These exotic stars have a binary frequency of (at least) 80%, more than three times that detected for stars in the remainder of the sample. We confirm that the cluster is mass segregated, finding the binaries to be more centrally concentrated than the single stars in our sample at the 99.8% confidence level (and at the 98.7% confidence level when only considering main-sequence stars). The blue stragglers are centrally concentrated as compared to the solar-type main-sequence single stars in the cluster at the 99.7% confidence level. Accounting for measurement precision, we derive an RV dispersion in M67 of 0.80 ± 0.04 km s-1 for our sample of single main-sequence stars, subgiants and giants with V≤slant 15.5. When corrected

  17. Reconstruction of velocity fields in electromagnetic flow tomography

    PubMed Central

    Lehtikangas, Ossi; Karhunen, Kimmo

    2016-01-01

    Electromagnetic flow meters (EMFMs) are the gold standard in measuring flow velocity in process industry. The flow meters can measure the mean flow velocity of conductive liquids and slurries. A drawback of this approach is that the velocity field cannot be determined. Asymmetric axial flows, often encountered in multiphase flows, pipe elbows and T-junctions, are problematic and can lead to serious systematic errors. Recently, electromagnetic flow tomography (EMFT) has been proposed for measuring velocity fields using several coils and a set of electrodes attached to the surface of the pipe. In this work, a velocity field reconstruction method for EMFT is proposed. The method uses a previously developed finite-element-based computational forward model for computing boundary voltages and a Bayesian framework for inverse problems. In the approach, the vz-component of the velocity field along the longitudinal axis of the pipe is estimated on the pipe cross section. Different asymmetric velocity fields encountered near pipe elbows, solids-in-water flows in inclined pipes and in stratified or multiphase flows are tested. The results suggest that the proposed reconstruction method could be used to estimate velocity fields in complicated pipe flows in which the conventional EMFMs have limited accuracy. This article is part of the themed issue ‘Supersensing through industrial process tomography’. PMID:27185961

  18. Reconstruction of velocity fields in electromagnetic flow tomography.

    PubMed

    Lehtikangas, Ossi; Karhunen, Kimmo; Vauhkonen, Marko

    2016-06-28

    Electromagnetic flow meters (EMFMs) are the gold standard in measuring flow velocity in process industry. The flow meters can measure the mean flow velocity of conductive liquids and slurries. A drawback of this approach is that the velocity field cannot be determined. Asymmetric axial flows, often encountered in multiphase flows, pipe elbows and T-junctions, are problematic and can lead to serious systematic errors. Recently, electromagnetic flow tomography (EMFT) has been proposed for measuring velocity fields using several coils and a set of electrodes attached to the surface of the pipe. In this work, a velocity field reconstruction method for EMFT is proposed. The method uses a previously developed finite-element-based computational forward model for computing boundary voltages and a Bayesian framework for inverse problems. In the approach, the vz-component of the velocity field along the longitudinal axis of the pipe is estimated on the pipe cross section. Different asymmetric velocity fields encountered near pipe elbows, solids-in-water flows in inclined pipes and in stratified or multiphase flows are tested. The results suggest that the proposed reconstruction method could be used to estimate velocity fields in complicated pipe flows in which the conventional EMFMs have limited accuracy. This article is part of the themed issue 'Supersensing through industrial process tomography'.

  19. Velocity fields in non-Gaussian cold dark matter models

    NASA Astrophysics Data System (ADS)

    Lucchin, F.; Matarrese, S.; Messina, A.; Moscardini, L.; Tormen, G.

    1995-02-01

    We analyse the large-scale velocity field obtained by N-body simulations of cold dark matter (CDM) models with non-Gaussian primordial density fluctuations, considering models with both positive and negative primordial skewness in the density fluctuation distribution. We study the velocity probability distribution and calculate the dependence of the bulk flow, one-point velocity dispersion and cosmic Mach number on the filtering size. We find that the sign of the primordial skewness of the density field provides poor discriminatory power on the evolved velocity field. All non-Gaussian models considered here tend to have lower velocity dispersion and bulk flow than the standard Gaussian CDM model, while the cosmic Mach number turns out to be a poor statistic in characterizing the models. We also compare the large-scale velocity field of a composite sample of optically selected galaxies as described by the Local Group properties, bulk flow, velocity correlation function and cosmic Mach number with the velocity field of mock catalogues extracted from the N-body simulations. The comparison does not clearly single out the best model: the standard Gaussian model is, however, marginally preferred by the maximum likelihood analysis.

  20. Velocity field measurements of a laminar starting plume

    NASA Astrophysics Data System (ADS)

    Tanny, J.; Shlien, D. J.

    1985-04-01

    The region of buoyant fluid resulting from the initiation of heating of an infinite fluid is called the starting plume. Here, velocity field measurements of this flow pattern are presented for the first time. The measurements were carried out by processing digitized tracer particle path photographs. Similarity of the velocity field of the starting plume as it rises was found to exist in the limited range of heat injection rates investigated. The vorticity computed from the velocity field was diffuse, there being no evidence of a distinctive core. Additional flow visualization experiments show the spiral structure in the starting plume cap.

  1. Using GIS for calculation and visualization of the velocity field

    NASA Astrophysics Data System (ADS)

    Grzempowski, P.; Kontny, B.,; Bogusz, J.; Kłos, A.

    2012-04-01

    In the paper structure of the system to collect data about the GPS permanent station velocities and velocity field modelling were described. The system includes modules for data managements, calculation and visualization. These modules were created in Visual Basic. Data management and visualization modules use ArcGIS .NET library for manage the data structure and drawing. This allows to visualize the velocity field and integrate spatial data and data (qualitative and quantitative) described the phenomenon and accompanying factors. This system allows to develop a model of the strain field in triangle network (TIN strain model) and model of the velocity field in regular grid. Some functions and procedures like spatial analysis are used to split points into separate sets, which are connected with tectonic units. Thus, it is possible to develop velocity fields in the sub-areas. System operation was described on the example of modeling the velocity field on the Poland area. Inputs to the model were velocities of the ASG-EUPOS stations.

  2. STUDYING THE INTERSTELLAR MAGNETIC FIELD FROM ANISOTROPIES IN VELOCITY CHANNELS

    SciTech Connect

    Esquivel, A.; Lazarian, A.; Pogosyan, D. E-mail: lazarian@astro.wisc.edu

    2015-11-20

    Turbulence in the interstellar medium is anisotropic due to the ubiquitous magnetic fields. This anisotropy depends on the strength of the magnetic field and leaves an imprint on observations of spectral line maps. We use a grid of ideal magnetohydrodynamic simulations of driven turbulence and produce synthetic position–position–velocity maps to study the turbulence anisotropy in velocity channels of various resolutions. We found that the average structure function of velocity channels is aligned with the projection of the magnetic field on the plane of the sky. We also found that the degree of such anisotropy increases with the magnitude of the magnetic field. For thick velocity channels (low velocity resolution), the anisotropy is dominated by density, and the degree of anisotropy in these maps allows one to distinguish sub-Alfvénic and super-Alfvénic turbulence regimes, but it also depends strongly on the sonic Mach number. For thin channels (high velocity resolution), we find that the anisotropy depends less on the sonic Mach number. An important limitation of this technique is that it only gives a lower limit on the magnetic field strength because the anisotropy is related only to the magnetic field component on the plane of the sky. It can, and should, be used in combination with other techniques to estimate the magnetic field, such as the Fermi-Chandrasekhar method, anisotropies in centroids, Faraday rotation measurements, or direct line-of-sight determinations of the field from Zeeman effect observations.

  3. Lagrangian statistical model for transport in highly heterogeneous velocity fields.

    PubMed

    Le Borgne, Tanguy; Dentz, Marco; Carrera, Jesus

    2008-08-29

    We define an effective Lagrangian statistical model in phase space (x, t, v) for describing transport in highly heterogeneous velocity fields with complex spatial organizations. The spatial Markovian nature (and temporal non-Markovian nature) of Lagrangian velocities leads to an effective transport description that turns out to be a correlated continuous time random walk. This model correctly captures the Lagrangian velocity correlation properties and is demonstrated to represent a forward model for predicting transport in highly heterogeneous porous media for different types of velocity organizations.

  4. Accuracy Progressive Calculation of Lagrangian Trajectories from Gridded Velocity Field

    DTIC Science & Technology

    2014-01-01

    velocity, 29 temperature, salinity, and other variables, which are commonly represented in satellite 30 observations, modeling, simulation, and...13514. 400 401 Gandin, L.S., 1965: Objective analysis of meteorological fields, Israel Program for Scientific 402 Translation, Jerusalem , 242 pp

  5. The winds of O-stars. II - The terminal velocities of stellar winds of O-type stars

    NASA Technical Reports Server (NTRS)

    Groenewegen, M. A. T.; Lamers, H. J. G. L. M.; Pauldrach, A. W. A.

    1989-01-01

    The SEI method (Lamers et al., 1987) is used to obtain P Cygni profiles of the UV resonance lines of C IV, N V, and S IV and of the subordinate UV lines of N IV and C III observed in the spectra of 27 O-type stars. Theoretical profiles which include the turbulence effects agree well with the observations, and they can account for the deep absorption troughs, the shape of the violet absorption wings, and the wavelength of the emission peak. The resulting terminal velocities of the stellar winds are found to be systematically lower by about 400 km/s than previous estimates obtained using the Sobolev approximation (Castor and Lamers, 1979), suggesting that the narrow absorption components, observed in the UV resonance lines of O and B stars, reach the terminal velocity of the winds.

  6. Anomalous cross-field velocities in a CIV laboratory experiment

    NASA Astrophysics Data System (ADS)

    Axnaes, Ingvar

    1988-10-01

    The axial and radial ion velocities and the electron radial velocity were determined in coaxial plasma gun operated under critical velocity conditions. The particle velocities were determined from probe measurements together with He I 3889 A absolute intensity measurements and the consideration of the total momentum balance of the current sheet. The ions were found to move axially and the electrons radially much faster than predicted by the Electrified/Magnetic Field (E/B) drift in the macroscopic fields. These results agree with what can be expected from the instability processes, which has earlier been proposed to operate in these experiments. It is therefore a direct experimental demonstration that instability processes have to be invoked not only for the electron heating, but also to explain the macroscopic velocities and currents.

  7. Approximate quasi-isodynamicity at a finite aspect ratio in a stellarator vacuum magnetic field

    SciTech Connect

    Mikhailov, M. I.; Nührenberg, J. Zille, R.

    2015-12-15

    A stellarator vacuum field is found in which, at a finite aspect ratio (A ≈ 40), the contours of the second adiabatic invariant of nearly all particles reflected inside that surface are poloidally closed.

  8. Monte Carlo Estimation of the Electric Field in Stellarators

    NASA Astrophysics Data System (ADS)

    Bauer, F.; Betancourt, O.; Garabedian, P.; Ng, K. C.

    1986-10-01

    The BETA computer codes have been developed to study ideal magnetohydrodynamic equilibrium and stability of stellarators and to calculate neoclassical transport for electrons as well as ions by the Monte Carlo method. In this paper a numerical procedure is presented to select resonant terms in the electric potential so that the distribution functions and confinement times of the ions and electrons become indistinguishable.

  9. Influence of flow velocity on flow field's optical tomography diagnosis

    NASA Astrophysics Data System (ADS)

    Chen, Yun-yun; Yu, Yang; Zhong, Xia; Zhang, Ying-ying

    2017-01-01

    The effect of flow velocity is usually neglected when optical computerized tomography (OCT) methods are chosen to measure the temperature distribution of the flow fields up to now. In this paper, two sets of experiment are supplied to verify the effect of flow velocity on flow field's moiré tomography. Specifically speaking, the temperature results with the assumption that it is an isobaric process (omit the effect of flow velocity) in the measured flame flow fields, manifest that the isobaric supposition is not suitable for all the flames. And then, a condition, which can be adopted to judge that when the effect of flow velocity on its temperature reconstruction can not be neglected any more, is proposed. This study would provide some reference to the temperature diagnosis by the optical methods which are based on the measurement of the refractive index.

  10. Revisiting the Influence of Unidentified Binaries on Velocity Dispersion Measurements in Ultra-faint Stellar Systems

    NASA Astrophysics Data System (ADS)

    McConnachie, Alan W.; Côté, Patrick

    2010-10-01

    Velocity dispersion measurements of recently discovered Milky Way satellites with MV >~ -7 imply that they posses high mass-to-light ratios. The expected velocity dispersions due to their baryonic mass are ~0.2 km s-1, but values gsim3 km s-1 are measured. We perform Monte Carlo simulations of mock radial velocity measurements of these systems assuming that they have mass-to-light ratios similar to globular clusters and posses an unidentified binary star population, to determine if these stars could boost the velocity dispersion to the observed values. We find that this hypothesis is unlikely to produce dispersions much in excess of ~4.5 km s-1, in agreement with previous work. However, for the systems with the potentially smallest velocity dispersions, values consistent with observations are produced in 5%-40% of our simulations for binary fractions in excess of f bin(P <= 10 yr)~ 5%. This sample includes the dwarf galaxy candidates that lie closest to classical globular clusters in MV - rh space. Considered as a population, it is unlikely that all of these dwarf galaxy candidates have mass-to-light ratios typical of globular clusters, but boosting of the observed dispersion by binaries from near-zero values cannot be ruled out at high confidence for several individual dwarf galaxy candidates. Given the importance of obtaining accurate velocity dispersions and dynamical masses for the faintest satellites, it is clearly desirable to directly exclude the possible effect of binaries on these systems. This requires multi-epoch radial velocity measurements with individual uncertainties of lsim1 km s-1 to identify spectroscopic binaries with orbital velocities of the order of the observed velocity dispersion.

  11. Heat and mass transport in nonhomogeneous random velocity fields.

    PubMed

    Mauri, Roberto

    2003-12-01

    The effective equation describing the transport of passive tracers in nonsolenoidal velocity fields is determined, assuming that the velocity field U(r,t) is a function of both position r and time t, albeit remaining locally random. Assuming a strong separation of scales and applying the method of homogenization, we find a Fickian constitutive relation for the coarse-grained particle flux, as the sum of a convective part, V(E)c, and a diffusive term, -D(s). Inverted Delta c, where V(E) is the Eulerian mean tracer velocity, c the average particle concentration, and D(s) the effective diffusivity. The latter can be written as D(s)(r,t)=D(0)I+D(r,r,t), where D0 is the molecular diffusivity, I the unit dyadic and D(r(1),r(2),t) the cross diffusion dyadic. Conversely, the Eulerian mean velocity V(E)(r,t) is the sum of the microscale mean tracer velocity V(r,t) and a particle drift velocity, V(d)(r,t)=-[(delta/delta r(2)).D(T)(r,r(2),t)](r(2)=r), which depends on the nonhomogeneity of the velocity field at the macroscale. The microscale mean particle velocity, in turn, is the sum of the mean fluid velocity and the ballistic tracer velocity, which is due to the local nonuniformity of the concentration field and is therefore structurally different from the tracer drift velocity. In the limit of large Peclet numbers, D(s) coincides with the self-diffusion dyadic, as it measures the local temporal growth of the mean square displacement of a tracer particle from its average position. In this case, the motion of a tracer particle is a random process in the manner of Stratonovich, where the smoothly varying mean tracer velocity equals the microscale mean tracer velocity and the fluctuating term is described through the cross diffusion dyadic D(r(1),r(2),t).

  12. NLTE solar flare models with stationary velocity fields

    NASA Astrophysics Data System (ADS)

    Nejezchleba, T.

    1998-02-01

    A method of calculating NLTE models of a plan-parallel solar flare atmosphere with stationary plasma flows is presented. To solve the radiative transfer equation, equations of statistical equilibrium (ESE) and the stationary momentum equation, we use the multilevel approximate lambda iteration (MALI) approach. The numerical code is based on the method recently developed by \\cite[Rybicky & Hummer (1991, 1992)]{ri91} and allows to take into account macroscopic velocity fields in observer's frame formulation. The preconditioned ESE, constructed by this method, are finally linearized with respect to level populations and electron densities to treat the the hydrogen ionization balance. The numerical code based on this method is used to compute a grid of NLTE flare models with various velocity fields in order to show the influence of the velocity fields on the Hα -line asymmetries. The analysis of the results lead to conclusions that would improve interpretations of flare line asymmetries: 1) The velocities affect the level populations, 2) The type of asymmetry depends on the changes in the optical depth scales and on the run of the source function in the atmosphere. 3) A monotonous velocity affects only one wing of the line profile. 4) To get the velocity field from an observed profile the bisector method should be modified.

  13. The conducting shell stellarator: A simple means for producing complicated fields

    SciTech Connect

    Sheffield, G.V.

    1997-01-01

    One of the main characteristics of stellarators, both helical and modular, is that their coil sets must take difficult shapes in order to produce the complicated stellarator magnetic fields. The complex coil shapes make fabrication difficult and costly compared to say the toroidal field, TF, coil set of a tokamak. The conducting shell stellarator, CSS, configuration described in this report shows that complicated stellarator fields can be produced by inducing eddy currents in a conducting shell from a simple TF coil set (a field that varies like 1/R). This technique is applicable not only to a pulsed system at room or cryogenic temperatures, but can be implemented for a superconducting TF with a superconducting shell in a stellarator reactor. The CSS has the added benefit that within this device the metallic shell which can be made up of discrete plates can be changed out and replaced with new plates to create a different stellarator configuration within the same TF coil set. The work of creating the complicated magnetics is done by the passive conductor reshaping the simple TF field.

  14. Velocity Dispersion, Size, Sérsic Index, and D n 4000: The Scaling of Stellar Mass with Dynamical Mass for Quiescent Galaxies

    NASA Astrophysics Data System (ADS)

    Zahid, H. Jabran; Geller, Margaret J.

    2017-05-01

    We examine the relation between stellar mass, velocity dispersion, size, Sérsic index, and {D}n4000 for a volume-limited sample of ˜40,000 quiescent galaxies in the SDSS. At a fixed stellar mass, galaxies with higher {D}n4000 have larger velocity dispersions and smaller sizes. {D}n4000 is a proxy for stellar population age, thus these trends suggest that older galaxies typically have larger velocity dispersions and smaller sizes. We combine velocity dispersion and size into a dynamical mass estimator, {σ }2R. At a fixed stellar mass, {σ }2R depends on {D}n4000. The Sérsic index is also correlated with {D}n4000. The dependence of {σ }2R and Sérsic index on {D}n4000 suggests that quiescent galaxies are not structurally homologous systems. We derive an empirical correction for non-homology which is consistent with the analytical correction derived from the virial theorem. After accounting for non-homologous galactic structure, we measure {M}* \\propto {M}d0.998+/- 0.004, where M * is the stellar mass and M d is the dynamical mass derived from the velocity dispersion and size; stellar mass is directly proportional to dynamical mass. Quiescent galaxies appear to be in approximate virial equilibrium, and deviations of the fundamental plane parameters from the expected virial relation may result from mass-to-light ratio variations, selection effects, and the non-homology of quiescent galaxies. We infer the redshift evolution of velocity dispersion and size for galaxies in our sample assuming purely passive evolution. The inferred evolution is inconsistent with direct measurements at higher redshifts. Thus quiescent galaxies do not passively evolve. Quiescent galaxies have properties that are consistent with standard galaxy formation in ΛCDM. They form at different epochs and evolve modestly, increasing their size, velocity dispersion, and Sérsic index after they cease star formation.

  15. Tip vortex core pressure estimates derived from velocity field measurements

    NASA Astrophysics Data System (ADS)

    Sinding, Kyle; Krane, Michael

    2016-11-01

    We present estimates of tip vortex core pressure derived from velocity field measurements of a high Reynolds number flow over a lifting surface. Tip vortex cavitation decreases propulsor efficiency and contributes to both unwanted noise and surface damage. Coordinated load cell, pressure, and velocity measurements were performed in the 12-inch tunnel at the Applied Research Laboratory at Penn State University, over a range of angles of attack and flow speeds. Stereo PIV imaging planes were oriented normal to the tunnel axis. Pressure estimates in each measurement plane were estimated from the velocity field. Visual cavitation calls were performed over the same range of conditions as the optical velocity measurements, by varying the tunnel pressure until tip vortex cavitation was observed to initiate. The pressure differences between the tip vortex and the tunnel ambient pressure obtained with these two methods were then compared.

  16. The statistical properties of sea ice velocity fields

    NASA Astrophysics Data System (ADS)

    Agarwal, S.; Wettlaufer, J. S.

    2016-12-01

    Thorndike and Colony (1982) showed that more than 70% of the variance of the ice motion can be explained by the geostrophic winds. This conclusion was reached by analyzing only 2 years of data. Due to the importance of ice motion in Arctic climate we ask how persistent is such a prediction. In so doing, we study and develop a stochastic model for the Arctic sea ice velocity fields based on the observed sea ice velocity fields from satellites and buoys for the period 1978 - 2012. Having previously found that the Arctic Sea Equivalent Ice Extent (EIE) has a white noise structure on annual to bi-annual time scales (Agarwal et. al. 2012), we assess the connection to ice motion. We divide the Arctic into dynamic and thermodynamic components, with focus on the dynamic part i.e. the velocity fields of sea ice driven by the geostrophic winds over the Arctic. We show (1) the stationarity of the spatial correlation structure of the velocity fields, and (2) the robustness of white noise structure present in the velocity fields on annual to bi-annual time scales, which combine to explain the white noise characteristics of the EIE on these time scales. S. Agarwal, W. Moon and J.S. Wettlaufer, Trends, noise and reentrant long-term persistence in Arctic sea ice, Proc. R. Soc. A, 468, 2416 (2012). A.S. Thorndike and R. Colony, Sea ice motion in response to geostrophic winds, J. Geophys. Res. 87, 5845 (1982).

  17. Stellar evolution.

    NASA Technical Reports Server (NTRS)

    Chiu, H.-Y. (Editor); Muriel, A.

    1972-01-01

    Aspects of normal stellar evolution are discussed together with evolution near the main sequence, stellar evolution from main sequence to white dwarf or carbon ignition, the structure of massive main-sequence stars, and problems of stellar stability and stellar pulsation. Other subjects considered include variable stars, white dwarfs, close binaries, novae, early supernova luminosity, neutron stars, the photometry of field horizontal-branch stars, and stellar opacity. Transport mechanisms in stars are examined together with thermonuclear reactions and nucleosynthesis, the instability problem in nuclear burning shells, stellar coalescence, and intense magnetic fields in astrophysics. Individual items are announced in this issue.

  18. New Program for Measuring Stellar Magnetic Fields Observed with the 6-m BTA

    NASA Astrophysics Data System (ADS)

    Semenko, E.; Semenova, E.

    2017-06-01

    The program aimed at detecting and measuring stellar magnetic fields of CP-stars which has been carried out with the 6-meter telescope at SAO RAS for almost 40 years remains to be one of the most successful so far. Since the outcome of the program depends on the massive measurements of polarized stellar spectra exhibiting the Zeeman effect, it seems of great importance to improve the accuracy of measurements and save the consistency with all previously gathered data.

  19. Non-axisymmetric equilibrium reconstruction for stellarators, reversed field pinches and tokamaks

    SciTech Connect

    Hanson, James D.; Anderson, D.T.; Cianciosa, M.; Franz, P.; Hartwell, G. H.; Hirshman, Steven Paul; Knowlton, Stephen F.; Lao, Lang L.; Lazarus, Edward Alan; Marrelli, L.; Maurer, D. A.; Schmitt, J. C.; Sontag, A. C.; Stevenson, B. A.; Terranova, D.

    2013-01-01

    Axisymmetric equilibrium reconstruction using magnetohydrodynamic equilibrium solutions to the Grad Shafranov equation has long been an important tool for interpreting tokamak experiments. This paper describes recent results in non-axisymmetric (three-dimensional) equilibrium reconstruction of nominally axisymmetric plasmas (tokamaks and reversed field pinches (RFPs)), and fully non-axisymmetric plasmas (stellarators). Results from applying the V3FIT code to CTH and HSX stellarator plasmas, RFX-mod RFP plasmas and the DIII-D tokamak are presented.

  20. Preferential Excitation of Stellar Oscillations of a Magnetar with a Tangled Magnetic Field

    NASA Astrophysics Data System (ADS)

    Bretz, Joseph; van Eysden, Anthony; Link, Bennett

    2017-01-01

    Magnetars are strongly magnetized ( 1015 Gauss) neutron stars. Some of them produce giant flares that exhibit quasi-periodic oscillations which have been attributed to stellar oscillations that modulate the emission. A tangled magnetic field model introduces a spectrum of magnetic normal modes that can explain the observed quasi-periodic oscillations, as expected from stability considerations. We show that reasonable initial conditions preferentially excite stellar oscillations, and find promising agreement with data. Funding support from Montana Space Grant Apprenticeship Program

  1. Sound field separation with sound pressure and particle velocity measurements.

    PubMed

    Fernandez-Grande, Efren; Jacobsen, Finn; Leclère, Quentin

    2012-12-01

    In conventional near-field acoustic holography (NAH) it is not possible to distinguish between sound from the two sides of the array, thus, it is a requirement that all the sources are confined to only one side and radiate into a free field. When this requirement cannot be fulfilled, sound field separation techniques make it possible to distinguish between outgoing and incoming waves from the two sides, and thus NAH can be applied. In this paper, a separation method based on the measurement of the particle velocity in two layers and another method based on the measurement of the pressure and the velocity in a single layer are proposed. The two methods use an equivalent source formulation with separate transfer matrices for the outgoing and incoming waves, so that the sound from the two sides of the array can be modeled independently. A weighting scheme is proposed to account for the distance between the equivalent sources and measurement surfaces and for the difference in magnitude between pressure and velocity. Experimental and numerical studies have been conducted to examine the methods. The double layer velocity method seems to be more robust to noise and flanking sound than the combined pressure-velocity method, although it requires an additional measurement surface. On the whole, the separation methods can be useful when the disturbance of the incoming field is significant. Otherwise the direct reconstruction is more accurate and straightforward.

  2. Stellar Populations across the Black Hole Mass-Velocity Dispersion Relation

    NASA Astrophysics Data System (ADS)

    Martín-Navarro, Ignacio; Brodie, Jean P.; van den Bosch, Remco C. E.; Romanowsky, Aaron J.; Forbes, Duncan A.

    2016-11-01

    Coevolution between supermassive black holes (BH) and their host galaxies is universally adopted in models for galaxy formation. In the absence of feedback from active galactic nuclei (AGNs), simulated massive galaxies keep forming stars in the local universe. From an observational point of view, however, such coevolution remains unclear. We present a stellar population analysis of galaxies with direct BH mass measurements and the BH mass-σ relation as a working framework. We find that over-massive BH galaxies, i.e., galaxies lying above the best-fitting BH mass-σ line, tend to be older and more α-element-enhanced than under-massive BH galaxies. The scatter in the BH mass-σ-[α/Fe] plane is significantly lower than that in the standard BH mass-σ relation. We interpret this trend as an imprint of AGN feedback on the star formation histories of massive galaxies.

  3. Normalized velocity profiles of field-measured turbidity currents

    USGS Publications Warehouse

    Xu, Jingping

    2010-01-01

    Multiple turbidity currents were recorded in two submarine canyons with maximum speed as high as 280 cm/s. For each individual turbidity current measured at a fixed station, its depth-averaged velocity typically decreased over time while its thickness increased. Some turbidity currents gained in speed as they traveled downcanyon, suggesting a possible self-accelerating process. The measured velocity profiles, first in this high resolution, allowed normalizations with various schemes. Empirical functions, obtained from laboratory experiments whose spatial and time scales are two to three orders of magnitude smaller, were found to represent the field data fairly well. The best similarity collapse of the velocity profiles was achieved when the streamwise velocity and the elevation were normalized respectively by the depth-averaged velocity and the turbidity current thickness. This normalization scheme can be generalized to an empirical function Y = exp(–αXβ) for the jet region above the velocity maximum. Confirming theoretical arguments and laboratory results of other studies, the field turbidity currents are Froude-supercritical.

  4. The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. II. Sensitivity of the survey and the atlas of synthetic dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Beccari, G.; Bellazzini, M.; Battaglia, G.; Ibata, R.; Martin, N.; Testa, V.; Cignoni, M.; Correnti, M.

    2016-06-01

    The searching for StEllar Counterparts of COmpact high velocity clouds (SECCO) survey is devoted to the search for stellar counterparts within ultra compact high velocity clouds that are candidate low-mass, low-luminosity galaxies. We present the results of a set of simulations aimed at the quantitative estimate of the sensitivity of the survey as a function of the total luminosity, size, and distance of the stellar systems we are looking for. For all of our synthetic galaxies we assumed an exponential surface brightness profile and an old and metal-poor population. The synthetic galaxies are simulated both on the images and on the photometric catalogues, taking all the observational effects into account. In the fields where the available observational material is of top quality (≃36% of the SECCO fields), we detect synthetic galaxies as ≥5σ over-densities of resolved stars down to μV,h ≃ 30.0 mag/arcsec2, for D ≤ 1.5 Mpc, and down to μV,h ≃ 29.5 mag/arcsec2, for D ≤ 2.5 Mpc. In the field with the worst observational material of the whole survey, we detect synthetic galaxies with μV,h ≤ 28.8 mag/arcsec2 out to D ≤ 1.0 Mpc, and those with μV,h ≤ 27.5 mag/arcsec2 out to D ≤ 2.5 Mpc. Dwarf galaxies with MV = -10.0, with sizes in the range spanned by known dwarfs, are detected by visual inspection of the images up to D = 5 Mpc independent of the image quality. In the best quality images, dwarfs are partially resolved into stars up to D = 3.0 Mpc and completely unresolved at D = 5 Mpc. As an independent test of the sensitivity of our images to low surface brightness galaxies, we report on the detection of several dwarf spheroidal galaxies probably located in the Virgo cluster with MV ≲ -8.0 and μV,h ≲ 26.8 mag/arcsec2. The nature of the previously discovered SECCO 1 stellar system, also likely located in the Virgo cluster, is rediscussed in comparison with these dwarfs. While specific for the SECCO survey, our study may also provide general

  5. A non-parametric model for the cosmic velocity field

    NASA Astrophysics Data System (ADS)

    Branchini, E.; Teodoro, L.; Frenk, C. S.; Schmoldt, I.; Efstathiou, G.; White, S. D. M.; Saunders, W.; Sutherland, W.; Rowan-Robinson, M.; Keeble, O.; Tadros, H.; Maddox, S.; Oliver, S.

    1999-09-01

    We present a self-consistent non-parametric model of the local cosmic velocity field derived from the distribution of IRAS galaxies in the PSCz redshift survey. The survey has been analysed using two independent methods, both based on the assumptions of gravitational instability and linear biasing. The two methods, which give very similar results, have been tested and calibrated on mock PSCz catalogues constructed from cosmological N-body simulations. The denser sampling provided by the PSCz survey compared with previous IRAS galaxy surveys allows an improved reconstruction of the density and velocity fields out to large distances. The most striking feature of the model velocity field is a coherent large-scale streaming motion along the baseline connecting Perseus-Pisces, the Local Supercluster, the Great Attractor and the Shapley Concentration. We find no evidence for back-infall on to the Great Attractor. Instead, material behind and around the Great Attractor is inferred to be streaming towards the Shapley Concentration, aided by the compressional push of two large nearby underdensities. The PSCz model velocities compare well with those predicted from the 1.2-Jy redshift survey of IRAS galaxies and, perhaps surprisingly, with those predicted from the distribution of Abell/ACO clusters, out to 140h^-1Mpc. Comparison of the real-space density fields (or, alternatively, the peculiar velocity fields) inferred from the PSCz and cluster catalogues gives a relative (linear) bias parameter between clusters and IRAS galaxies of b_c=4.4+/-0.6. Finally, we implement a likelihood analysis that uses all the available information on peculiar velocities in our local Universe to estimate beta_Omega 0 0.6 b_0.6 -0.15 +0.22 (1sigma), where b is the bias parameter for IRAS galaxies.

  6. Magnetic and velocity fields of a solar pore

    NASA Astrophysics Data System (ADS)

    Sobotka, M.; Del Moro, D.; Jurčák, J.; Berrilli, F.

    2012-01-01

    Context. Solar pores are intermediate-size magnetic flux features that emerge at the surface of the Sun. The absence of a filamentary penumbra indicates that there is a relatively simple magnetic structure with a prevailing vertical magnetic field. Aims: Relations between the magnetic field components, line-of-sight velocities, and horizontal motions in and around a large pore (Deff = 8''.5) are analysed to provide observational constraints on theoretical models and numerical simulations. Methods: Spectropolarimetric observations in Fe I 617.3 nm of the pore NOAA 11005 with the IBIS spectrometer attached to the Dunn Solar Telescope are inverted into series of maps of thermal, magnetic, and velocity parameters using the SIR code. Horizontal velocities are obtained from series of white-light images by means of local correlation tracking. Results: The magnetic field B extends from the visible pore border of more than 3''.5 and has a radial structure in a form of spines that are co-spatial with dark intergranular lanes. The horizontal component Bhor is more extended than the vertical component Bz. The temperature linearly decreases with increasing Bz, by about - 300 K kG-1 in the photosphere and - 800 K kG-1 in the umbra. The temperature contrast of granulation increases with increasing magnetic field strength and is then suppressed for Bz > 1200 G. Granular upflows dominate in regions with Bz < 600-700 G. Line-of-sight velocities are lower in stronger fields, except for fast isolated downflows at the pore's border. The velocity signature of granulation is suppressed completely for Bhor > 1000 G. Horizontal motions of granules start to be damped for Bz > 500 G and recurrently exploding granules appear only in magnetic fields comparable to or weaker than the equipartition field strength 400 G.

  7. Velocity field calculation for non-orthogonal numerical grids

    SciTech Connect

    Flach, G. P.

    2015-03-01

    Computational grids containing cell faces that do not align with an orthogonal (e.g. Cartesian, cylindrical) coordinate system are routinely encountered in porous-medium numerical simulations. Such grids are referred to in this study as non-orthogonal grids because some cell faces are not orthogonal to a coordinate system plane (e.g. xy, yz or xz plane in Cartesian coordinates). Non-orthogonal grids are routinely encountered at the Savannah River Site in porous-medium flow simulations for Performance Assessments and groundwater flow modeling. Examples include grid lines that conform to the sloping roof of a waste tank or disposal unit in a 2D Performance Assessment simulation, and grid surfaces that conform to undulating stratigraphic surfaces in a 3D groundwater flow model. Particle tracking is routinely performed after a porous-medium numerical flow simulation to better understand the dynamics of the flow field and/or as an approximate indication of the trajectory and timing of advective solute transport. Particle tracks are computed by integrating the velocity field from cell to cell starting from designated seed (starting) positions. An accurate velocity field is required to attain accurate particle tracks. However, many numerical simulation codes report only the volumetric flowrate (e.g. PORFLOW) and/or flux (flowrate divided by area) crossing cell faces. For an orthogonal grid, the normal flux at a cell face is a component of the Darcy velocity vector in the coordinate system, and the pore velocity for particle tracking is attained by dividing by water content. For a non-orthogonal grid, the flux normal to a cell face that lies outside a coordinate plane is not a true component of velocity with respect to the coordinate system. Nonetheless, normal fluxes are often taken as Darcy velocity components, either naively or with accepted approximation. To enable accurate particle tracking or otherwise present an accurate depiction of the velocity field for a non

  8. Gyrokinetic Calculations of the Neoclassical Radial Electric Field in Stellarator Plasmas

    SciTech Connect

    Lewandowski, J.L.V.; Williams, J.; Boozer, A.H.; Lin, Z.

    2001-04-09

    A novel method to calculate the neoclassical radial electric field in stellarator plasmas is described. The method, which does not have the inconvenience of large statistical fluctuations (noise) of standard Monte Carlo technique, is based on the variation of the combined parallel and perpendicular pressures on a magnetic surface. Using a three-dimensional gyrokinetic delta f code, the calculation of the radial electric field in the National Compact Stellarator Experiment has been carried out. It is shown that a direct evaluation of radial electric field based on a direct calculation of the radial particle flux is not tractable due to the considerable noise.

  9. ZFIRE: Similar Stellar Growth in Halpha-emitting Cluster and Field Galaxies at z~2

    NASA Astrophysics Data System (ADS)

    Tran, Kim-Vy; Alcorn, Leo; Kacprzak, Glenn; Nanayakkara, Themiya; Straatman, Caroline; Yuan, Tiantian; Cowley, Michael; Dave, Romeel; Glazebrook, Karl; Kewley, Lisa J.; Labbe, Ivo; martizzi, davide; Papovich, Casey J.; Quadri, Ryan; Spitler, Lee; Tomczak, Adam R.

    2017-01-01

    We compare galaxy scaling relations as a function of environment at z~2 with our ZFIRE survey where we have measured Halpha fluxes for 90 galaxies selected from a mass-limited sample based on ZFOURGE. The cluster galaxies (37) are part of a spectroscopically confirmed system at z=2.095 and the field galaxies (53) have redshifts of 1.9field populations when comparing their star formation rate (SFR), stellar mass, galaxy size, star formation rate surface density, and stellar age distributions. Approximately 20-25% of Halpha-emitting galaxies in both the cluster and field are IR-luminous. In our combined cluster and field sample, IR-luminous galaxies have ~5 times more stellar mass and radii that are ~70% larger than the low-IR galaxies. To track stellar growth, we separate galaxies into those that lie above, on, and below the Halpha star-forming main sequence (SFMS) using delta[SFR]=+/-0.2 dex. Galaxies above the SFMS (starbursts) tend to have higher Halpha SFR surface densities and younger stellar ages compared to galaxies below the SFMS. Our results indicate that starbursts (+SFMS) in the cluster and field at z~2 are growing their stellar cores. Lastly, we compare to the (SFR-stellar mass) relation predicted by the RHAPSODY galaxy cluster simulations and find that the predicted slope is nominally consistent with the observations. However, the predicted cluster SFRs tend to be too low by a factor of ~2 which suggests that simulations may be over-predicting how efficient environment is at quenching star formation.

  10. Stellar photometry with the Wide Field/Planetary Camera of the Hubble Space Telescope

    SciTech Connect

    Holtzman, J.A. )

    1990-07-01

    Simulations of Wide Field/Planetary Camera (WF/PC) images are analyzed in order to discover the most effective techniques for stellar photometry and to evaluate the accuracy and limitations of these techniques. The capabilities and operation of the WF/PC and the simulations employed in the study are described. The basic techniques of stellar photometry and methods to improve these techniques for the WF/PC are discussed. The correct parameters for star detection, aperture photometry, and point-spread function (PSF) fitting with the DAOPHOT software of Stetson (1987) are determined. Consideration is given to undersampling of the stellar images by the detector; variations in the PSF; and the crowding of the stellar images. It is noted that, with some changes DAOPHOT, is able to generate photometry almost to the level of photon statistics. 10 refs.

  11. Determining Pressure and Velocity Fields from Experimental Schlieren Data

    NASA Astrophysics Data System (ADS)

    Lee, Frank M.; Allshouse, Michael R.; Morrison, P. J.; Swinney, Harry L.

    2015-11-01

    Internal gravity waves generated by tidal flow over bottom topography in the ocean are important because they contribute significantly to the energy composition of the ocean. Determination of the instantaneous internal wave energy flux requires knowledge of the pressure and velocity fields, each of which is difficult to measure in the ocean or the laboratory. However, the density perturbation field can be measured using a laboratory technique known as ``synthetic schlieren.'' We present an analytical method for deducing both the pressure and velocity fields from the density perturbation field. This yields the instantaneous energy flux of linear internal waves. Our method is verified in tests with data from a Navier-Stokes direct numerical simulation. The method is then applied to laboratory schlieren data obtained for the conditions in the numerical simulations. MRA and HLS were supported by ONR. FML and PJM supported by DOE contract DE-FG02-04ER-54742.

  12. Electric field measurements during the Condor critical velocity experiment

    NASA Technical Reports Server (NTRS)

    Kelley, M. C.; Pfaff, R. F.; Haerendel, G.

    1986-01-01

    The instrumentation of the Condor critical velocity Ba experiment (Wescott et al., 1986) for the measurements of the energetic particles and the electric field associated with a Ba explosion is described. The Ba explosion created a complex electric field pulse detected in situ by a single-axis double electric-field probe on a separate spacecraft. The measurements provide evidence of several important links in the critical-velocity chain, and are consistent with two hypotheses. The first hypothesis involves the creation of large polarization electric field due to charge separation; the second hypothesis implies a polarization of the beam by currents flowing across it. The chain of physical processes inferred from the observations is in agreement with most theories for the Alfven process.

  13. Electric field measurements during the Condor critical velocity experiment

    NASA Technical Reports Server (NTRS)

    Kelley, M. C.; Pfaff, R. F.; Haerendel, G.

    1986-01-01

    The instrumentation of the Condor critical velocity Ba experiment (Wescott et al., 1986) for the measurements of the energetic particles and the electric field associated with a Ba explosion is described. The Ba explosion created a complex electric field pulse detected in situ by a single-axis double electric-field probe on a separate spacecraft. The measurements provide evidence of several important links in the critical-velocity chain, and are consistent with two hypotheses. The first hypothesis involves the creation of large polarization electric field due to charge separation; the second hypothesis implies a polarization of the beam by currents flowing across it. The chain of physical processes inferred from the observations is in agreement with most theories for the Alfven process.

  14. Interstellar Turbulence. I. Retrieval of Velocity Field Statistics

    NASA Astrophysics Data System (ADS)

    Brunt, Christopher M.; Heyer, Mark H.

    2002-02-01

    We demonstrate the capability of principal component analysis (PCA) as applied by Heyer & Schloerb to extract the statistics of turbulent interstellar velocity fields as measured by the energy spectrum, E(k)~k-β. Turbulent velocity and density fields with known statistics are generated from fractional Brownian motion simulations. These fields are translated to the observational domain, T(x,y,v), considering the excitation of molecular rotational energy levels and radiative transfer. Using PCA and the characterization of velocity and spatial scales from the eigenvectors and eigenimages, respectively, a relationship is identified that describes the magnitude of line profile differences, δv, and the scale, L, over which these differences occur, δv~Lα. From a series of models with varying values of β, we find α=0.33β-0.05 for 1<β<3. This provides the basic calibration between the intrinsic velocity field statistics to observational measures and a diagnostic for turbulent flows in the interstellar medium. We also investigate the effects of noise, line opacity, and finite resolution on these results.

  15. Tracing magnetic fields and identifying star formation with velocity gradients

    NASA Astrophysics Data System (ADS)

    Lazarian, Alex; Gonzalez Casanova, Diego; Yuen, Ka Ho

    2017-01-01

    We are presenting a new technique of tracing magnetic fields utilizing Doppler broadened spectral lines. We demonstrate that for subAlfvenic turbulence, i.e. for regions with turbulence velocities less than Alfven speed, the velocity gradients (VGs) are well aligned with magnetic fields both in 3D data cubes and in synthetic observations. For the latter case the VGs are calculated using velocity centroids and their alignment with the projected magnetic field is studied. We demonstraed this by comparing the HI data with the PLANCK polarization maps. We conclude that velocity gradients present a new promissing way of studying magnetic fields in diffuse media. We also explored the properties of VGs in dense gas and found that starting with a particular density threshold value the VGs tend to be perpendicular to magnetic fields. We also compare the alignment of VGs and the density gradients (DGs) and find that these measures are well aligned in the absense of self-gravity, although in diffuse regions the VGs trace magnetic field better than the DGs. The advantage of VGs for tracing magnetic fields gets more obvious as the Mach number increases. Self-gravity acts differently on the VGs and the DGs. For self-gravitating regions the VGs and the DGs tend to get orthogonal to each other, revealing the the regions of ongoing star formation. This misalignment of the VGs and DGs is also evident in synthetic observations. We conclude that the VGs present(a) a new promising way of tracing magnetic field in diffuse media, (b) in combination with polarimety they reveal shocked gas,(c) in combination with the DGs they reveal star forming regions.

  16. Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters

    NASA Astrophysics Data System (ADS)

    Erkaev, N. V.; Odert, P.; Lammer, H.; Kislyakova, K. G.; Fossati, L.; Mezentsev, A. V.; Johnstone, C. P.; Kubyshkina, D. I.; Shaikhislamov, I. F.; Khodachenko, M. L.

    2017-10-01

    We investigate the interaction between the magnetized stellar wind plasma and the partially ionized hydrodynamic hydrogen outflow from the escaping upper atmosphere of non-magnetized or weakly magnetized hot Jupiters. We use the well-studied hot Jupiter HD 209458b as an example for similar exoplanets, assuming a negligible intrinsic magnetic moment. For this planet, the stellar wind plasma interaction forms an obstacle in the planet's upper atmosphere, in which the position of the magnetopause is determined by the condition of pressure balance between the stellar wind and the expanded atmosphere, heated by the stellar extreme ultraviolet radiation. We show that the neutral atmospheric atoms penetrate into the region dominated by the stellar wind, where they are ionized by photoionization and charge exchange, and then mixed with the stellar wind flow. Using a 3D magnetohydrodynamic (MHD) model, we show that an induced magnetic field forms in front of the planetary obstacle, which appears to be much stronger compared to those produced by the solar wind interaction with Venus and Mars. Depending on the stellar wind parameters, because of the induced magnetic field, the planetary obstacle can move up to ≈0.5-1 planetary radii closer to the planet. Finally, we discuss how estimations of the intrinsic magnetic moment of hot Jupiters can be inferred by coupling hydrodynamic upper planetary atmosphere and MHD stellar wind interaction models together with UV observations. In particular, we find that HD 209458b should likely have an intrinsic magnetic moment of 10-20 per cent that of Jupiter.

  17. A LOCAL BASELINE OF THE BLACK HOLE MASS SCALING RELATIONS FOR ACTIVE GALAXIES. II. MEASURING STELLAR VELOCITY DISPERSION IN ACTIVE GALAXIES

    SciTech Connect

    Harris, Chelsea E.; Bennert, Vardha N.; Auger, Matthew W.; Treu, Tommaso; Woo, Jong-Hak; Malkan, Matthew A. E-mail: mauger@physics.ucsb.edu E-mail: vbennert@calpoly.edu E-mail: malkan@astro.ucla.edu

    2012-08-01

    We derive spatially resolved stellar kinematics for a sample of 84 out of 104 observed local (0.02 < z < 0.09) galaxies hosting type-1 active galactic nuclei (AGNs), based on long-slit spectra obtained at the 10 m W. M. Keck-1 Telescope. In addition to providing central stellar velocity dispersions, we measure major axis rotation curves and velocity dispersion profiles using three separate wavelength regions, including the prominent Ca H and K, Mg Ib, and Ca II NIR stellar features. In this paper, we compare kinematic measurements of stellar velocity dispersion obtained for different apertures, wavelength regions, and signal-to-noise ratios, and provide recipes to cross-calibrate the measurements reducing systematic effects to the level of a few percent. We also provide simple recipes based on readily observable quantities such as global colors and Ca H and K equivalent width that will allow observers of high-redshift AGN hosts to increase the probability of obtaining reliable stellar kinematic measurements from unresolved spectra in the region surrounding the Ca H and K lines. In subsequent papers in this series, we will combine this unprecedented spectroscopic data set with surface photometry and black hole mass measurements to study in detail the scaling relations between host galaxy properties and black hole mass.

  18. Near field acoustic holography with particle velocity transducers

    NASA Astrophysics Data System (ADS)

    Jacobsen, Finn; Liu, Yang

    2005-11-01

    Near field acoustic holography is usually based on measurement of the pressure. This paper describes an investigation of an alternative technique that involves measuring the normal component of the acoustic particle velocity. A simulation study shows that there is no appreciable difference between the quality of predictions of the pressure based on knowledge of the pressure in the measurement plane and predictions of the particle velocity based on knowledge of the particle velocity in the measurement plane. However, when the particle velocity is predicted close to the source on the basis of the pressure measured in a plane further away, high spatial frequency components corresponding to evanescent modes are not only amplified by the distance but also by the wave number ratio (kz/k). By contrast, when the pressure is predicted close to the source on the basis of the particle velocity measured in a plane further away, high spatial frequency components are reduced by the reciprocal wave number ratio (k/kz). For the same reason holography based on the particle velocity is less sensitive to transducer mismatch than the conventional technique based on the pressure. These findings are confirmed by an experimental investigation made with a p-u sound intensity probe produced by Microflown.

  19. The ATLAS3D project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

    NASA Astrophysics Data System (ADS)

    Scott, Nicholas; Cappellari, Michele; Davies, Roger L.; Kleijn, Gijs Verdoes; Bois, Maxime; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    2013-07-01

    We explore the connection between the local escape velocity, Vesc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-of-the-art photometry in the literature with residuals of 0.04 mag. We utilize these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local Vesc derived from the surface brightness. We find that the local Vesc is tightly correlated with the Mg b and Fe5015 line strengths and optical colours, and anti-correlated with the Hβ line strength. In the case of the Mg b and colour-Vesc relations we find that the relation within individual galaxies follows the global relation between different galaxies. We intentionally ignored any uncertain contribution due to dark matter since we are seeking an empirical description of stellar population gradients in early-type galaxies that is ideal for quantitative comparison with model predictions. We also make use of single stellar population (SSP) modelling to transform our line strength index measurements into the SSP-equivalent parameters age (t), metallicity ([Z/H]) and α-enhancement [α/Fe]. The residuals from the relation are correlated with age, [α/Fe], molecular gas mass and local environmental density. We identify a population of galaxies that occur only at low Vesc that exhibit negative gradients in the Mg b- and Colour-Vesc relations. These galaxies typically have young central stellar populations and contain significant amounts of molecular gas and dust. Combining these results with N-body simulations of binary mergers we use the Mg b-Vesc relation to constrain the possible number of dry mergers experienced by

  20. The MASSIVE Survey - V. Spatially resolved stellar angular momentum, velocity dispersion, and higher moments of the 41 most massive local early-type galaxies

    NASA Astrophysics Data System (ADS)

    Veale, Melanie; Ma, Chung-Pei; Thomas, Jens; Greene, Jenny E.; McConnell, Nicholas J.; Walsh, Jonelle; Ito, Jennifer; Blakeslee, John P.; Janish, Ryan

    2017-01-01

    We present spatially resolved two-dimensional stellar kinematics for the 41 most massive early-type galaxies (ETGs; MK ≲ -25.7 mag, stellar mass M* ≳ 1011.8 M⊙) of the volume-limited (D < 108 Mpc) MASSIVE survey. For each galaxy, we obtain high-quality spectra in the wavelength range of 3650-5850 Å from the 246-fibre Mitchell integral-field spectrograph at McDonald Observatory, covering a 107 arcsec × 107 arcsec field of view (often reaching 2 to 3 effective radii). We measure the 2D spatial distribution of each galaxy's angular momentum (λ and fast or slow rotator status), velocity dispersion (σ), and higher order non-Gaussian velocity features (Gauss-Hermite moments h3 to h6). Our sample contains a high fraction (˜80 per cent) of slow and non-rotators with λ ≲ 0.2. When combined with the lower mass ETGs in the ATLAS3D survey, we find the fraction of slow rotators to increase dramatically with galaxy mass, reaching ˜50 per cent at MK ˜ -25.5 mag and ˜90 per cent at MK ≲ -26 mag. All of our fast rotators show a clear anticorrelation between h3 and V/σ, and the slope of the anticorrelation is steeper in more round galaxies. The radial profiles of σ show a clear luminosity and environmental dependence: the 12 most luminous galaxies in our sample (MK ≲ -26 mag) are all brightest cluster/group galaxies (except NGC 4874) and all have rising or nearly flat σ profiles, whereas five of the seven `isolated' galaxies are all fainter than MK = -25.8 mag and have falling σ. All of our galaxies have positive average h4; the most luminous galaxies have average h4 ˜ 0.05, while less luminous galaxies have a range of values between 0 and 0.05. Most of our galaxies show positive radial gradients in h4, and those galaxies also tend to have rising σ profiles. We discuss the implications for the relationship among dynamical mass, σ, h4, and velocity anisotropy for these massive galaxies.

  1. Turbulence in Flowing Soap Films: Velocity, Vorticity, and Thickness Fields

    SciTech Connect

    Rivera, M.; Vorobieff, P.; Ecke, R.E.

    1998-08-01

    We report experimental measurements of the velocity, vorticity, and thickness fields of turbulent flowing soap films using a modified particle-image velocimetry technique. These data yield the turbulent energy and enstrophy of the two-dimensional flows with microscale Reynolds numbers of about 100 and demonstrate the effects of compressibility arising from variations in film thickness. Despite the compressibility of the flow, real-space correlations of velocity, vorticity, and enstrophy flux are consistent with theoretical predictions for two-dimensional turbulence. {copyright} {ital 1998} {ital The American Physical Society }

  2. Rotational Velocities of Field Blue Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Weafer, V. K.; Fulbright, J. P.

    2001-12-01

    This study is motivated by interest in the much-debated ``second-parameter" problem. Deep mixing, driven by angular momentum, has been proposed as a second parameter controlling horizontal-branch colour morphology (Sweigart & Mengel 1979). Observations of low-metallicity field giant stars show little evidence of deep mixing (Kraft 1994, Wallerstein et al. 1997, Gratton et al. 2000). We therefore expect that field horizontal branch stars may show little evidence of rotation. We have used high-resolution spectra from Keck and Lick observatories to find the projected rotational velocity (v sin i) of 44 blue (-0.04 <= B-V <= 0.20) horizontal branch stars in the halo field. Selected Fe and Ti absorption lines were co-added in velocity space to create an average line profile for each star. To find v sin i, the average profile was compared to similarly-averaged synthesised lines. We have compared the v sin i values of the sample to those of the blue horizontal branch stars in the second-parameter globular-cluster pair, M3 and M13 (Peterson et al. 1995). Although further work is needed to completely establish the velocity distribution of the sample, we have found that the sample has rotational velocities more similar to M13 than to M3, with at least 5 stars showing v sin i > = 25 km/s.

  3. STELLAR MASSES FROM THE CANDELS SURVEY: THE GOODS-SOUTH AND UDS FIELDS

    SciTech Connect

    Santini, P.; Fontana, A.; Castellano, M.; Grazian, A.; Amorin, R.; Ferguson, H. C.; Mobasher, B.; Barro, G.; Hsu, L. T.; Salvato, M.; Wuyts, S.; Galametz, A.; Lee, B.; Lee, S.-K.; Pforr, J.; Wiklind, T.; Almaini, O.; Cooper, M. C.; Weiner, B.; and others

    2015-03-10

    We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey project. We combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age <100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 Myr sources) if nebular contribution is ignored.

  4. Velocity-map imaging at low extraction fields

    NASA Astrophysics Data System (ADS)

    Horke, Daniel A.; Roberts, Gareth M.; Lecointre, Julien; Verlet, Jan R. R.

    2012-06-01

    We present a velocity-map imaging (VMI) setup for photoelectron imaging that utilizes low electric extraction fields. This avoids any complications that could arise from electrostatic interactions between the extraction field and the molecular properties that are probed and has a minimal effect on the trajectory of ions in ion beam experiments. By using an attractive potential supplied to the detector, and keeping the electrodes at ground (zero) potential, we show that fringe fields between the VMI arrangement and the vacuum chamber can be eliminated, which is important in experiments on ions.

  5. Velocity-map imaging at low extraction fields

    SciTech Connect

    Horke, Daniel A.; Roberts, Gareth M.; Lecointre, Julien; Verlet, Jan R. R.

    2012-06-15

    We present a velocity-map imaging (VMI) setup for photoelectron imaging that utilizes low electric extraction fields. This avoids any complications that could arise from electrostatic interactions between the extraction field and the molecular properties that are probed and has a minimal effect on the trajectory of ions in ion beam experiments. By using an attractive potential supplied to the detector, and keeping the electrodes at ground (zero) potential, we show that fringe fields between the VMI arrangement and the vacuum chamber can be eliminated, which is important in experiments on ions.

  6. Radial velocities in three fields along the southern galactic equator

    NASA Astrophysics Data System (ADS)

    Denoyelle, J.

    1987-09-01

    A list of radial velocities for 764 stars is given for three fields in the Vela-Carina region of the Galaxy. They were obtained from GPO-plates taken at La Silla and reduced following Fehrenbach's method. Slit-spectra were collected with the 152 cm-spectrographic telescope at La Silla, to derive an accurate radial velocity for a sufficient number of calibration stars: out of the 29 stars, 26 had no formerly published value. The global motions of 10 to 14 km/s can be considered as normal on the basis of galactic rotation. Some stars however show high velocities. The case of HD 81471 (Sp type A7 Iab) suggest that a detailed study of this star is to be recommended.

  7. Development of a Data Reduction Pipeline to Measure Stellar Radial Velocities Using Kutztown University's On-Campus Research Observatory

    NASA Astrophysics Data System (ADS)

    Fox, Odysseus; Reed, Phillip A.

    2016-01-01

    The Kutztown University Observatory (KUO) houses a 0.6m Ritchey-Chrétien telescope with a focal ratio of f/8. It is a dedicated observatory collecting data every clear night using the eShel model (Shelyak Instruments) echelle spectrograph. The spectral resolution is R = 11,000 and the final dispersion is 0.050 Å/pixel over the range of 4300 Å to 8100 Å.It is paramount to ensure accurate radial velocity (RV) measurements when conducting projects for research and education. RV measurements at KUO are used to determine the masses of spectroscopic binary stars, study pulsations of stellar photospheres (Cepheid variables), and to perform reconnaissance RV measurements of exoplanet candidates (reflex motion of host star).We present a data reduction pipeline program that produces RV measurements from observed spectra. After using the eShel's built in ThAr lamp for wavelength calibration, the program continuum normalizes the spectrum, creates a non-moving template (synthetic and/or observed spectrum), and corrects for barycentric motion. Finally, the program performs a cross correlation of the data and template to produce accurate RV measurements.Examples of completed and on-going projects at KUO are presented. We also demonstrate our ability to observe stellar RV's with uncertainties as good as 0.13 km/s. The eShel spectrograph is commercially available and is becoming popular among users of smaller telescopes. This data reduction pipeline will be useful to the increasing number of researchers utilizing the eShel spectrograph.

  8. Three-dimensional photogrammetric measurement of magnetic field lines in the WEGA stellarator.

    PubMed

    Drewelow, Peter; Bräuer, Torsten; Otte, Matthias; Wagner, Friedrich; Werner, Andreas

    2009-12-01

    The magnetic confinement of plasmas in fusion experiments can significantly degrade due to perturbations of the magnetic field. A precise analysis of the magnetic field in a stellarator-type experiment utilizes electrons as test particles following the magnetic field line. The usual fluorescent detector for this electron beam limits the provided information to two-dimensional cut views at certain toroidal positions. However, the technique described in this article allows measuring the three-dimensional structure of the magnetic field by means of close-range photogrammetry. After testing and optimizing the main diagnostic components, measurements of the magnetic field lines were accomplished with a spatial resolution of 5 mm. The results agree with numeric calculations, qualifying this technique as an additional tool to investigate magnetic field configurations in a stellarator. For a possible future application, ways are indicated on how to reduce experimental error sources.

  9. LAMOST Observations in the Kepler Field. Analysis of the Stellar Parameters Measured with LASP Based on Low-resolution Spectra

    NASA Astrophysics Data System (ADS)

    Ren, Anbing; Fu, Jianning; De Cat, Peter; Wu, Yue; Yang, Xiaohu; Shi, Jianrong; Luo, Ali; Zhang, Haotong; Dong, Subo; Zhang, Ruyuan; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Cao, Zihuang; Du, Bing

    2016-08-01

    All 14 subfields of the Kepler field were observed at least once with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (lamost, Xinglong Observatory, China) during the 2012-2014 observation seasons. There are 88,628 reduced spectra with a signal-to-noise ratio in the g band (S/N g ) ≥ 6 after the first round (2012-2014) of observations of the lamost- Kepler project (LK-project). By adopting the upgraded version of the lamost Stellar Parameter pipeline (lasp), we have determined the atmospheric parameters ({T}{eff}, {log}g, and [Fe/H]) and heliocentric radial velocity v rad for 51,406 stars with 61,226 spectra. Compared with the atmospheric parameters derived from both high-resolution spectroscopy and asteroseismology for common stars in Huber et al., an external calibration of lasp atmospheric parameters was made, leading to the determination of the external errors for giants and dwarfs. Multiple spectroscopic observations of the same objects in the LK-project were used to estimate the internal uncertainties of the atmospheric parameters as a function of S/N g with the unbiased estimation method. The lasp atmospheric parameters were calibrated based on both the external and internal uncertainties for the giants and dwarfs. A general statistical analysis of the stellar parameters leads to the discovery of 106 candidate metal-poor stars, 9 candidate very metal-poor stars, and 18 candidate high-velocity stars. Fitting formulae were obtained segmentally for both the calibrated atmospheric parameters of the LK-project and the Kepler Input Catalog (KIC) parameters with common stars. The calibrated atmospheric parameters and radial velocities of the LK-project will be useful for studying stars in the Kepler field. ) located at the Xinglong Observatory, China.

  10. The DiskMass Survey. VI. Gas and stellar kinematics in spiral galaxies from PPak integral-field spectroscopy

    NASA Astrophysics Data System (ADS)

    Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Bershady, Matthew A.; Schechtman-Rook, Andrew; Andersen, David R.; Swaters, Rob A.

    2013-09-01

    We present ionized-gas ([Oiii]λ5007 Å) and stellar kinematics (velocities and velocity dispersions) for 30 nearly face-on spiral galaxies out to as many as three K-band disk scale lengths (hR). These data have been derived from PPak integral-field-unit spectroscopy from 4980-5370 Å observed at a mean resolution of λ/Δλ = 7700 (σinst = 17 km s-1). These data are a fundamental product of our survey and will be used in companion papers to, e.g., derive the detailed (baryonic+dark) mass budget of each galaxy in our sample. Our presentation provides a comprehensive description of the observing strategy and data reduction, including a robust measurement and removal of shift, scale, and rotation effects in the data due to instrumental flexure. Using an in-plane coordinate system determined by fitting circular-speed curves to our velocity fields, we derive azimuthally averaged rotation curves and line-of-sight velocity dispersion (σLOS) and luminosity profiles for both the stars and [Oiii]-emitting gas. Along with a clear presentation of the data, we demonstrate: (1) The [Oiii] and stellar rotation curves exhibit a clear signature of asymmetric drift with a rotation difference that is 11% of the maximum rotation speed of the galaxy disk, comparable to measurements in the solar neighborhood in the Milky Way. (2) The e-folding length of the stellar velocity dispersion (hσ) is 2hR on average, as expected for a disk with a constant scale height and mass-to-light ratio, with a scatter that is notably smaller for massive, high-surface-brightness disks in the most luminous galaxies. (3) At radii larger than 1.5hR, σLOS tends to decline slower than the best-fitting exponential function, which may be due to an increase in the disk mass-to-light ratio, disk flaring, or disk heating by the dark-matter halo. (4) A strong correlation exists between the central vertical stellar velocity dispersion of the disks (σz,0) and their circular rotational speed at 2.2hR (V2.2h

  11. A Stellar Velocity Dispersion for a Strongly-lensed, Intermediate-mass Quiescent Galaxy at z=2.8

    NASA Astrophysics Data System (ADS)

    Hill, Allison. R.; Muzzin, Adam; Franx, Marijn; van de Sande, Jesse

    2016-03-01

    Measuring stellar velocity dispersions of quiescent galaxies beyond z˜ 2 is observationally challenging. Such measurements require near-infrared spectra with a continuum detection of at least moderate signal to noise, often necessitating long integrations. In this paper, we present deep X-Shooter spectroscopy of one of only two known gravitationally lensed massive quiescent galaxies at z\\gt 2. This galaxy is quadruply imaged, with the brightest images magnified by a factor of ˜5. The total exposure time of our data is 9.8 hr on-source; however, the magnification, and the slit placement encompassing two images, provides a total equivalent exposure time of 215 hr. From this deep spectrum we measure a redshift of ({z}{spec}=2.756+/- 0.001), making this one of the highest redshift quiescent galaxies that is spectroscopically confirmed. We simultaneously fit both the spectroscopic and photometric data to determine stellar population parameters and conclude that this galaxy is relatively young ({560}-80+100 {Myr}), of intermediate mass ({log} {M}*/{M}⊙ ={10.59}-0.05+0.04), consistent with low dust content ({A}V={0.20}-0.20+0.26), and has quenched only relatively recently. This recent quenching is confirmed by strong Balmer absorption, particularly Hδ (H{δ }A={6.66}-0.92+0.96). Remarkably, this proves that at least some intermediate-mass galaxies have already quenched as early as z˜ 2.8. Additionally, we have measured a velocity dispersion of (σ =187+/- 43 {km} {{{s}}}-1), making this the highest-redshift quiescent galaxy with a dispersion measurement. We confirm that this galaxy falls on the same mass fundamental plane (MFP) as galaxies at z = 2.2, consistent with little to no evolution in the MFP up to z = 2.8. Overall this galaxy is proof of the existence of intermediate-mass quenched galaxies in the distant universe, and that lensing is a powerful tool for determining their properties with improved accuracy.

  12. Visualizing 3D velocity fields near contour surfaces

    SciTech Connect

    Max, N.; Crawfis, R.; Grant, C.

    1994-03-01

    Vector field rendering is difficult in 3D because the vector icons overlap and hide each other. We propose four different techniques for visualizing vector fields only near surfaces. The first uses motion blurred particles in a thickened region around the surface. The second uses a voxel grid to contain integral curves of the vector field. The third uses many antialiased lines through the surface, and the fourth uses hairs sprouting from the surface and then bending in the direction of the vector field. All the methods use the graphite pipeline, allowing real time rotation and interaction, and the first two methods can animate the texture to move in the flow determined by the velocity field.

  13. Stellar magnetic fields from four Stokes parameter observations

    NASA Astrophysics Data System (ADS)

    Rusomarov, N.; Kochukhov, O.; Piskunov, N.

    2015-01-01

    Magnetic Doppler imaging (MDI) from observations of four Stokes parameters can uncover new information that is of interest to the evolution and structure of magnetic fields of intermediate and high-mass stars. Our MDI study of the chemically peculiar star HD 24712 from four Stokes parameter observations, obtained with the HARPSpol instrument at the 3.6-m ESO telescope, revealed a magnetic field with strong dipolar component and weak small-scale contributions. This finding gives evidence for the hypothesis that old Ap stars have predominantly dipolar magnetic fields.

  14. Newly velocity field of Sulawesi Island from GPS observation

    NASA Astrophysics Data System (ADS)

    Sarsito, D. A.; Susilo, Simons, W. J. F.; Abidin, H. Z.; Sapiie, B.; Triyoso, W.; Andreas, H.

    2017-07-01

    Sulawesi microplate Island is located at famous triple junction area of the Eurasian, India-Australian, and Philippine Sea plates. Under the influence of the northward moving Australian plate and the westward motion of the Philippine plate, the island at Eastern part of Indonesia is collide and with the Eurasian plate and Sunda Block. Those recent microplate tectonic motions can be quantitatively determine by GNSS-GPS measurement. We use combine GNSS-GPS observation types (campaign type and continuous type) from 1997 to 2015 to derive newly velocity field of the area. Several strategies are applied and tested to get the optimum result, and finally we choose regional strategy to reduce error propagation contribution from global multi baseline processing using GAMIT/GLOBK 10.5. Velocity field are analyzed in global reference frame ITRF 2008 and local reference frame by fixing with respect alternatively to Eurasian plate - Sunda block, India-Australian plate and Philippine Sea plates. Newly results show dense distribution of velocity field. This information is useful for tectonic deformation studying in geospatial era.

  15. Velocity and Magnetic Field Distribution in a Forming Penumbra

    NASA Astrophysics Data System (ADS)

    Romano, P.; Frasca, D.; Guglielmino, S. L.; Ermolli, I.; Tritschler, A.; Reardon, K. P.; Zuccarello, F.

    2013-07-01

    We present results from the analysis of high-resolution spectropolarimetric and spectroscopic observations of the solar photosphere and chromosphere, obtained shortly before the formation of a penumbra in one of the leading polarity sunspots of NOAA active region 11490. The observations were performed at the Dunn Solar Telescope of the National Solar Observatory on 2012 May 28, using the Interferometric Bidimensional Spectrometer. The data set is comprised of a 1 hr time sequence of measurements in the Fe I 617.3 nm and Fe I 630.25 nm lines (full Stokes polarimetry) and in the Ca II 854.2 nm line (Stokes I only). We perform an inversion of the Fe I 630.25 nm Stokes profiles to derive magnetic field parameters and the line-of-sight (LOS) velocity at the photospheric level. We characterize chromospheric LOS velocities by the Doppler shift of the centroid of the Ca II 854.2 nm line. We find that, before the formation of the penumbra, an annular zone of 3''-5'' width is visible around the sunspot. In the photosphere, we find that this zone is characterized by an uncombed structure of the magnetic field although no visible penumbra has formed yet. We also find that the chromospheric LOS velocity field shows several elongated structures characterized by downflow and upflow motions in the inner and outer parts of the annular zone, respectively.

  16. Lattice Models for Granular-Like Velocity Fields: Hydrodynamic Description

    NASA Astrophysics Data System (ADS)

    Manacorda, Alessandro; Plata, Carlos A.; Lasanta, Antonio; Puglisi, Andrea; Prados, Antonio

    2016-08-01

    A recently introduced model describing—on a 1d lattice—the velocity field of a granular fluid is discussed in detail. The dynamics of the velocity field occurs through next-neighbours inelastic collisions which conserve momentum but dissipate energy. The dynamics is described through the corresponding Master Equation for the time evolution of the probability distribution. In the continuum limit, equations for the average velocity and temperature fields with fluctuating currents are derived, which are analogous to hydrodynamic equations of granular fluids when restricted to the shear modes. Therefore, the homogeneous cooling state, with its linear instability, and other relevant regimes such as the uniform shear flow and the Couette flow states are described. The evolution in time and space of the single particle probability distribution, in all those regimes, is also discussed, showing that the local equilibrium is not valid in general. The noise for the momentum and energy currents, which are correlated, are white and Gaussian. The same is true for the noise of the energy sink, which is usually negligible.

  17. Field-effect transistor having a superlattice channel and high carrier velocities at high applied fields

    DOEpatents

    Chaffin, R.J.; Dawson, L.R.; Fritz, I.J.; Osbourn, G.C.; Zipperian, T.E.

    1984-04-19

    In a field-effect transistor comprising a semiconductor having therein a source, a drain, a channel and a gate in operational relationship, there is provided an improvement wherein said semiconductor is a superlattice comprising alternating quantum well and barrier layers, the quantum well layers comprising a first direct gap semiconductor material which in bulk form has a certain bandgap and a curve of electron velocity versus applied electric field which has a maximum electron velocity at a certain electric field, the barrier layers comprising a second semiconductor material having a bandgap wider than that of said first semiconductor material, wherein the layer thicknesses of said quantum well and barrier layers are sufficiently thin that the alternating layers constitute a superlattice having a curve of electron velocity versus applied electric field which has a maximum electron velocity at a certain electric field, and wherein the thicknesses of said quantum well layers are selected to provide a superlattice curve of electron velocity versus applied electric field whereby, at applied electric fields higher than that at which the maximum electron velocity occurs in said first material when in bulk form, the electron velocities are higher in said superlattice than they are in said first semiconductor material in bulk form.

  18. Resistive dissipation and magnetic field topology in the stellar corona

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1993-01-01

    Tangential discontinuities, or current sheets, in a magnetic field embedded in a fluid with vanishing resistivity are created by discontinuous fluid motion. Tangential discontinuities are also created when a magnetic field is allowed to relax to magnetostatic equilibrium after mixing by fluid motions (either continuous or discontinuous) into any but the simplest topologies. This paper shows by formal examples that the current sheets arising solely from discontinuous fluid motions do not contribute significantly to the dissipation of magnetic free energy when a small resistivity is introduced. Dissipation that is significant under coronal conditions occurs only by rapid reconnection, which arises when, and only when, the current sheets are required by the field topology. Hence it is topological dissipation that is primarily responsible for heating tenuous coronal gases in astronomical settings, whether the fluid displacements of the field are continuous or discontinuous.

  19. Stellar magnetic fields - The role of a magnetic field in the peculiar M giant, HD 4174

    NASA Technical Reports Server (NTRS)

    Stencel, R. E.; Ionson, J. A.

    1979-01-01

    Principles of coronal heating via basic electrodynamic effects, viz., resonant absorption of Alfven surface waves (quiescent) and magnetic tearing instabilities (impulsive), are detailed to argue three principles which may have application to late-type evolved stars. First, if one observes that B-squared/8 pi is much greater than rho times v-squared in a stellar atmosphere, then the observed magnetic field must originate in an interior dynamo. Second, low mass-loss rates could imply the presence of closed magnetic flux loops within the outer atmosphere, which constrain hydrodynamic flows when the magnetic body forces exceed the driving forces. Third, given that such magnetic loops effect an enhancement of the local heating rate, a positive correlation is predicted between the existence of a corona and low mass-loss rates. Application of these principles is made in the case of the peculiar M giant star HD 4174, which is purported to have a kilogauss magnetic field. Several of its spectroscopic peculiarities are shown to be consistent with the above principles, and further observational checks are suggested. Possible application to dMe and RS CVn objects is sketched.

  20. The FORS1 catalogue of stellar magnetic field measurements

    NASA Astrophysics Data System (ADS)

    Bagnulo, S.; Fossati, L.; Landstreet, J. D.; Izzo, C.

    2015-11-01

    Context. The FORS1 instrument on the ESO Very Large Telescope was used to obtain low-resolution circular polarised spectra of nearly a thousand different stars, with the aim of measuring their mean longitudinal magnetic fields. Magnetic fields were measured by different authors, and using different methods and software tools. Aims: A catalogue of FORS1 magnetic measurements would provide a valuable resource with which to better understand the strengths and limitations of this instrument and of similar low-dispersion, Cassegrain spectropolarimeters. However, FORS1 data reduction has been carried out by a number of different groups using a variety of reduction and analysis techniques. Our understanding of the instrument and our data reduction techniques have both improved over time. A full re-analysis of FORS1 archive data using a consistent and fully documented algorithm would optimise the accuracy and usefulness of a catalogue of field measurements. Methods: Based on the ESO FORS pipeline, we have developed a semi-automatic procedure for magnetic field determinations, which includes self-consistent checks for field detection reliability. We have applied our procedure to the full content of circular spectropolarimetric measurements of the FORS1 archive. Results: We have produced a catalogue of spectro-polarimetric observations and magnetic field measurements for ~1400 observations of ~850 different objects. The spectral type of each object has been approximately classified. We have also been able to test different methods for data reduction is a systematic way. The resulting catalogue has been used to produce an estimator for an upper limit to the uncertainty in a field strength measurement of an early type star as a function of the signal-to-noise ratio of the observation. Conclusions: While FORS1 is not necessarily an optimal instrument for the discovery of weak magnetic fields, it is very useful for the systematic study of larger fields, such as those found in Ap

  1. MEASUREMENTS OF STELLAR MAGNETIC FIELDS USING AUTOCORRELATION OF SPECTRA

    SciTech Connect

    Borra, E. F.; Deschatelets, D.

    2015-11-15

    We present a novel technique that uses the autocorrelation of the spectrum of a star to measure the line broadening caused by the modulus of its average surface magnetic field. The advantage of the autocorrelation comes from the fact that it can detect very small spectral line broadening effects because it averages over many spectral lines and therefore gives an average with a very high signal-to-noise ratio. We validate the technique with the spectra of known magnetic stars and obtain autocorrelation curves that are in full agreement with published magnetic curves obtained with Zeeman splitting. The autocorrelation also gives less noisy curves so that it can be used to obtain very accurate curves. We degrade the resolution of the spectra of these magnetic stars to lower spectral resolutions where the Zeeman splitting is undetectable. At these resolutions, the autocorrelation still gives good quality curves, thereby showing that it can be used to measure magnetic fields in spectra where the Zeeman splitting is significantly smaller than the width of the spectral line. This would therefore allow observing magnetic fields in very faint Ap stars with low-resolution spectrographs, thereby greatly increasing the number of known magnetic stars. It also demonstrates that the autocorrelation can measure magnetic fields in rapidly rotating stars as well as weak magnetic fields that give a Zeeman splitting smaller than the intrinsic width of the spectral lines. Finally, it shows that the autocorrelation can be used to find unknown magnetic stars in low-resolution spectroscopic surveys.

  2. Electric Field-Induced Fluid Velocity Field Distribution in DNA Solution

    NASA Astrophysics Data System (ADS)

    Zhang, Ling-Yun; Wang, Peng-Ye

    2008-10-01

    We present an analytical solution for fluid velocity Geld distribution of polyelectrolyte DNA. Both the electric field force and the viscous force in the DNA solution are considered under a suitable boundary condition. The solution of electric potential is analytically obtained by using the linearized Poisson-Boltzmann equation. The fluid velocity along the electric field is dependent on the cylindrical radius and concentration. It is shown that the electric field-induced fluid velocity will be increased with the increasing cylindrical radius, whose distribution also varies with the concentration.

  3. REVEALING VELOCITY DISPERSION AS THE BEST INDICATOR OF A GALAXY's COLOR, COMPARED TO STELLAR MASS, SURFACE MASS DENSITY, OR MORPHOLOGY

    SciTech Connect

    Wake, David A.; Van Dokkum, Pieter G.; Franx, Marijn

    2012-06-01

    Using data of nearby galaxies from the Sloan Digital Sky Survey we investigate whether stellar mass (M{sub star}), central velocity dispersion ({sigma}), surface mass density ({Sigma}), or the Sersic n parameter is best correlated with a galaxy's rest-frame color. Specifically, we determine how the mean color of galaxies varies with one parameter when another is fixed. When M{sub star} is fixed we see that strong trends remain with all other parameters, whereas residual trends are weaker when {Sigma}, n, or {sigma} is fixed. Overall {sigma} is the best indicator of a galaxy's typical color, showing the largest residual color dependence when any of the other three parameters are fixed, and M{sub star} is the poorest. Other studies have indicated that both the central black hole mass and possibly host dark matter halo properties (mass or concentration) are also better correlated with {sigma} than with M{sub star}, {Sigma}, or n. Therefore, it could be the case that the strong correlation between color and {sigma} reflects an underlying relationship between a galaxy's star formation history and/or present star formation rate and the properties of its dark matter halo and/or the feedback from its central supermassive black hole.

  4. Constraints on the original ejection velocity fields of asteroid families

    NASA Astrophysics Data System (ADS)

    Carruba, V.; Nesvorný, D.

    2016-04-01

    Asteroid families form as a result of large-scale collisions among main belt asteroids. The orbital distribution of fragments after a family-forming impact could inform us about their ejection velocities. Unfortunately, however, orbits dynamically evolve by a number of effects, including the Yarkovsky drift, chaotic diffusion, and gravitational encounters with massive asteroids, such that it is difficult to infer the ejection velocities eons after each family's formation. Here, we analyse the inclination distribution of asteroid families, because proper inclination can remain constant over long time intervals, and could help us to understand the distribution of the component of the ejection velocity that is perpendicular to the orbital plane (vW). From modelling the initial break up, we find that the distribution of vW of the fragments, which manage to escape the parent body's gravity, should be more peaked than a Gaussian distribution (i.e. be leptokurtic) even if the initial distribution was Gaussian. We surveyed known asteroid families for signs of a peaked distribution of vW using a statistical measure of the distribution peakedness or flatness known as kurtosis. We identified eight families whose vW distribution is significantly leptokurtic. These cases (e.g. the Koronis family) are located in dynamically quiet regions of the main belt, where, presumably, the initial distribution of vW was not modified by subsequent orbital evolution. We suggest that, in these cases, the inclination distribution can be used to obtain interesting information about the original ejection velocity field.

  5. STABILITY OF THE TOROIDAL MAGNETIC FIELD IN STELLAR RADIATION ZONES

    SciTech Connect

    Bonanno, Alfio; Urpin, Vadim E-mail: vadim.urpin@uv.es

    2012-03-10

    The stability of the magnetic field in radiation zones is of crucial importance for mixing, angular momentum transport, etc. We consider the stability properties of a star containing a predominant toroidal field in spherical geometry by means of a linear stability in the Boussinesq approximation taking into account the effect of thermal conductivity. We calculate the growth rate of instability and analyze in detail the effects of stable stratification and heat transport. We argue that the stabilizing influence of gravity can never entirely suppress the instability caused by electric currents in radiation zones. However, the stable stratification can essentially decrease the growth rate of instability.

  6. The connection between stellar activity cycles and magnetic field topology

    NASA Astrophysics Data System (ADS)

    See, V.; Jardine, M.; Vidotto, A. A.; Donati, J.-F.; Boro Saikia, S.; Bouvier, J.; Fares, R.; Folsom, C. P.; Gregory, S. G.; Hussain, G.; Jeffers, S. V.; Marsden, S. C.; Morin, J.; Moutou, C.; do Nascimento, J. D.; Petit, P.; Waite, I. A.

    2016-11-01

    Zeeman-Doppler imaging (ZDI) has successfully mapped the large-scale magnetic fields of stars over a large range of spectral types, rotation periods and ages. When observed over multiple epochs, some stars show polarity reversals in their global magnetic fields. On the Sun, polarity reversals are a feature of its activity cycle. In this paper, we examine the magnetic properties of stars with existing chromospherically determined cycle periods. Previous authors have suggested that cycle periods lie on multiple branches, either in the cycle period-Rossby number plane or the cycle period-rotation period plane. We find some evidence that stars along the active branch show significant average toroidal fields that exhibit large temporal variations while stars exclusively on the inactive branch remain dominantly poloidal throughout their entire cycle. This lends credence to the idea that different shear layers are in operation along each branch. There is also evidence that the short magnetic polarity switches observed on some stars are characteristic of the inactive branch while the longer chromospherically determined periods are characteristic of the active branch. This may explain the discrepancy between the magnetic and chromospheric cycle periods found on some stars. These results represent a first attempt at linking global magnetic field properties obtained from ZDI and activity cycles.

  7. Understanding solar and stellar magnetic fields through helio- and asteroseismology

    NASA Astrophysics Data System (ADS)

    Broomhall, Anne-Marie

    Global helioseismology uses the Sun’s natural acoustic oscillations to study the solar interior, where the solar magnetic field is generated. At any one time thousands of acoustic oscillations are trapped in different but overlapping regions of the solar interior. Therefore, by studying the properties of these oscillations, such as their frequency and amplitude, we can probe inside the Sun. Often models designed to describe the helioseismic oscillations are based on the assumption that no magnetic field is present. However, this is clearly a simplistic view: The properties of these acoustic oscillations are affected by the presence of a magnetic field. By studying variations in the oscillations through the solar cycle we can learn about the Sun’s internal magnetic field and can feedback into MHD models of the solar interior. Similar techniques can be used to study the magnetic activity cycles of stars other than the Sun (through asteroseismology), using data from, for example, NASA’s Kepler satellite. While studying the Sun’s magnetic cycle helps us to understand the magnetic activity observed on other stars, activity cycles on other stars could prove vital in unravelling the mysteries of the Sun’s magnetic activity cycle.

  8. Velocity field measurements on high-frequency, supersonic microactuators

    NASA Astrophysics Data System (ADS)

    Kreth, Phillip A.; Ali, Mohd Y.; Fernandez, Erik J.; Alvi, Farrukh S.

    2016-05-01

    The resonance-enhanced microjet actuator which was developed at the Advanced Aero-Propulsion Laboratory at Florida State University is a fluidic-based device that produces pulsed, supersonic microjets by utilizing a number of microscale, flow-acoustic resonance phenomena. The microactuator used in this study consists of an underexpanded source jet that flows into a cylindrical cavity with a single, 1-mm-diameter exhaust orifice through which an unsteady, supersonic jet issues at a resonant frequency of 7 kHz. The flowfields of a 1-mm underexpanded free jet and the microactuator are studied in detail using high-magnification, phase-locked flow visualizations (microschlieren) and two-component particle image velocimetry. These are the first direct measurements of the velocity fields produced by such actuators. Comparisons are made between the flow visualizations and the velocity field measurements. The results clearly show that the microactuator produces pulsed, supersonic jets with velocities exceeding 400 m/s for roughly 60 % of their cycles. With high unsteady momentum output, this type of microactuator has potential in a range of ow control applications.

  9. A dissipative random velocity field for fully developed fluid turbulence

    NASA Astrophysics Data System (ADS)

    Chevillard, Laurent; Pereira, Rodrigo; Garban, Christophe

    2016-11-01

    We investigate the statistical properties, based on numerical simulations and analytical calculations, of a recently proposed stochastic model for the velocity field of an incompressible, homogeneous, isotropic and fully developed turbulent flow. A key step in the construction of this model is the introduction of some aspects of the vorticity stretching mechanism that governs the dynamics of fluid particles along their trajectory. An additional further phenomenological step aimed at including the long range correlated nature of turbulence makes this model depending on a single free parameter that can be estimated from experimental measurements. We confirm the realism of the model regarding the geometry of the velocity gradient tensor, the power-law behaviour of the moments of velocity increments, including the intermittent corrections, and the existence of energy transfers across scales. We quantify the dependence of these basic properties of turbulent flows on the free parameter and derive analytically the spectrum of exponents of the structure functions in a simplified non dissipative case. A perturbative expansion shows that energy transfers indeed take place, justifying the dissipative nature of this random field.

  10. The velocity field induced by a helical vortex tube

    NASA Astrophysics Data System (ADS)

    Fukumoto, Y.; Okulov, V. L.

    2005-10-01

    The influence of finite-core thickness on the velocity field around a vortex tube is addressed. An asymptotic expansion of the Biot-Savart law is made to a higher order in a small parameter, the ratio of core radius to curvature radius, which consists of the velocity field due to lines of monopoles and dipoles arranged on the centerline of the tube. The former is associated with an infinitely thin core and is featured by the circulation alone. The distribution of vorticity in the core reflects on the strength of dipole. This result is applied to a helical vortex tube, and the induced velocity due to a helical filament of the dipoles is obtained in the form of the Kapteyn series, which augments Hardin's [Phys. Fluids 25, 1949 (1982)] solution for the monopoles. Using a singularity-separation technique, a substantial part of the series is represented in a closed form for both the mono- and the dipoles. It is found from numerical calculation that the smaller the helix pitch is, the larger the relative influence of the dipoles is as the cylinder wound by the helix is approached.

  11. Simulated stellar kinematics studies of high-redshift galaxies with the HARMONI Integral Field Spectrograph

    NASA Astrophysics Data System (ADS)

    Kendrew, S.; Zieleniewski, S.; Houghton, R. C. W.; Thatte, N.; Devriendt, J.; Tecza, M.; Clarke, F.; O'Brien, K.; Häußler, B.

    2016-05-01

    We present a study into the capabilities of integrated and spatially resolved integral field spectroscopy of galaxies at z = 2-4 with the future HARMONI spectrograph for the European Extremely Large Telescope (E-ELT) using the simulation pipeline, HSIM. We focus particularly on the instrument's capabilities in stellar absorption line integral field spectroscopy, which will allow us to study the stellar kinematics and stellar population characteristics. Such measurements for star-forming and passive galaxies around the peak star formation era will provide a critical insight into the star formation, quenching and mass assembly history of high-z, and thus present-day galaxies. First, we perform a signal-to-noise study for passive galaxies at a range of stellar masses for z = 2-4, assuming different light profiles; for this population, we estimate that integrated stellar absorption line spectroscopy with HARMONI will be limited to galaxies with M* ≳ 1010.7 M⊙. Secondly, we use HSIM to perform a mock observation of a typical star-forming 1010 M⊙ galaxy at z = 3 generated from the high-resolution cosmological simulation NUTFB. We demonstrate that the input stellar kinematics of the simulated galaxy can be accurately recovered from the integrated spectrum in a 15-h observation, using common analysis tools. Whilst spatially resolved spectroscopy is likely to remain out of reach for this particular galaxy, we estimate HARMONI's performance limits in this regime from our findings. This study demonstrates how instrument simulators such as HSIM can be used to quantify instrument performance and study observational biases on kinematics retrieval; and shows the potential of making observational predictions from cosmological simulation output data.

  12. Pressure and velocity fields produced by an underwater explosion

    NASA Astrophysics Data System (ADS)

    Hunter, Kendall S.; Geers, Thomas L.

    2002-11-01

    A model for a moderately deep underwater explosion bubble has recently been developed that integrates the initial shock wave phase and the subsequent oscillation phase of the motion [T. L. Geers and K. S. Hunter, J. Acoust. Soc. Am. 111, 1584-1601 (2002)]. A hyperacoustic volume-acceleration model for the shock wave phase employs an empirical pressure-profile expression for the far field to determine bubble radius as a function of time, thereby providing initial conditions for the subsequent oscillation phase. The model for the oscillation phase yields bubble-response equations that incorporate first-order wave effects in both the external liquid and the internal gas. In this paper, a radiation model consistent with the bubble model is formulated and evaluated. The far-field pressure and velocity fields produced during the shock wave phase derive from the previously mentioned pressure-profile expression. Those produced during the oscillation phase derive from a matched-asymptotic-expansion solution for a translating acoustic source/dipole [F. G. Leppington and H. Levine, Proc. R. Soc. London, Ser. A 412, 199-221 (1987)]. Computed far-field pressure and velocity histories and snapshots are shown. Comparisons with existing data exhibit good agreement. [Research sponsored by ONR.

  13. Chandrasekhar's relation and stellar rotation in the Kepler field

    SciTech Connect

    Silva, J. R. P.; Soares, B. B.; De Freitas, D. B. E-mail: brauliosoares@uern.br

    2014-11-20

    According to the statistical law of large numbers, the expected mean of identically distributed random variables of a sample tends toward the actual mean as the sample increases. Under this law, it is possible to test the Chandrasekhar's relation (CR), (V) = (π/4){sup –1}(Vsin i), using a large amount of Vsin i and V data from different samples of similar stars. In this context, we conducted a statistical test to check the consistency of the CR in the Kepler field. In order to achieve this, we use three large samples of V obtained from Kepler rotation periods and a homogeneous control sample of Vsin i to overcome the scarcity of Vsin i data for stars in the Kepler field. We used the bootstrap-resampling method to estimate the mean rotations ((V) and (Vsin i)) and their corresponding confidence intervals for the stars segregated by effective temperature. Then, we compared the estimated means to check the consistency of CR, and analyzed the influence of the uncertainties in radii measurements, and possible selection effects. We found that the CR with (sin i) = π/4 is consistent with the behavior of the (V) as a function of (Vsin i) for stars from the Kepler field as there is a very good agreement between such a relation and the data.

  14. Velocity and Attenuation Structure of the Geysers Geothermal Field, California

    SciTech Connect

    Zucca, J. J.; Hutchings, L. J.; Kasameyer, P. W.

    1993-01-01

    The Geysers geothermal field is located in northern California and is one of the world's largest producers of electricity from geothermal energy. The resource consists of primarily dry steam which is produced from a low, porosity fractured graywacke. Over the last several years steam pressure at the Geysers has been dropping. Concern over decline of the resource has prompted research to understand its fundamental nature. A key issue is the distribution of fluid in the matrix of the reservoir rock. In this paper we interpret seismic compressional-wave velocity and attenuation data at the Geysers in terms of the geologic structure and fluid saturation in the reservoir. Our data consist of approximately 300 earthquakes that are of magnitude 1.2 and are distributed in depth between sea level and 2.5 km. Using compressional-wave arrival times, we invert for earthquake location, origin time, and velocity along a three-dimensional grid. Using the initial pulse width of the compressional-wave, we invert for the initial pulse width associated with the source, and the one-dimensional Q structure. We find that the velocity structure correlates with known mapped geologic units, including a velocity high that is correlated with a felsite body at depth that is known from drilling. The dry steam reservoir, which is also known from drilling, is mostly correlated with low velocity. The Q increases with depth to the top of the dry steam reservoir and decreases with depth within the reservoir. The decrease of Q with depth probably indicates that the saturation of the matrix of the reservoir rock increases with depth.

  15. Shear velocity of the Rotokawa geothermal field using ambient noise

    NASA Astrophysics Data System (ADS)

    Civilini, F.; Savage, M. K.; Townend, J.

    2014-12-01

    Ambient noise correlation is an increasingly popular seismological technique that uses the ambient seismic noise recorded at two stations to construct an empirical Green's function. Applications of this technique include determining shear velocity structure and attenuation. An advantage of ambient noise is that it does not rely on external sources of seismic energy such as local or teleseismic earthquakes. This method has been used in the geothermal industry to determine the depths at which magmatic processes occur, to distinguish between production and non-production areas, and to observe seismic velocity perturbations associated with fluid extraction. We will present a velocity model for the Rotokawa geothermal field near Taupo, New Zealand, produced from ambient noise cross correlations. Production at Rotokawa is based on the "Rotokawa A" combined cycle power station established in 1997 and the "Nga Awa Purua" triple flash power plant established in 2010. Rotokawa Joint Venture, a partnership between Mighty River Power and Tauhara North No. 2 Trust currently operates 174 MW of generation at Rotokawa. An array of short period seismometers was installed in 2008 and occupies an area of roughly 5 square kilometers around the site. Although both cultural and natural noise sources are recorded at the stations, the instrument separation distance provides a unique challenge for analyzing cross correlations produced by both signal types. The inter-station spacing is on the order of a few kilometers, so waves from cultural sources generally are not coherent from one station to the other, while the wavelength produced by natural noise is greater than the station separation. Velocity models produced from these two source types will be compared to known geological models of the site. Depending on the amount of data needed to adequately construct cross-correlations, a time-dependent model of velocity will be established and compared with geothermal production processes.

  16. The HII regions and the velocity field of NGC 7331

    NASA Astrophysics Data System (ADS)

    Marcelin, M.; Petrosian, A. R.; Amram, P.; Boulesteix, J.

    1994-02-01

    The galaxy NGC 7331 has been observed with an IPCS through an H alpha filter for direct imagery and through a scanning Fabry-Perot interferometer at H aplha wavelength with the 2.60 m Byurakan telescope to study the main physical parameters of 47 H II regions, diameter and luminosity, as well as their velocities. The cumulative diameter distribution of H II regions is well represented by an exponential function with the parameters N0 = 272 and D0 = 95 pc. The H alpha luminosity function is described by a power law with index - 1.6. The H alpha velocity field of the galaxy is in good agreement with radio observations. Much less extended but offering a higher spatial resolution, it reveals non-circular motions, like the classical wiggles of the isovelocity lines when crossing a spiral arm, or the Z shape distortions of the isovelocity lines in the center possibly revealing an unseen bar.

  17. The effects of flaring in H1 on the observed velocity field of spirals

    NASA Technical Reports Server (NTRS)

    Olling, Rob; Vangorkom, J. H.

    1993-01-01

    This work is part of a larger project in which we want to determine the shapes of dark halos around spiral galaxies. Rotation curves 'probe' the halos in the radial direction. The derived halo mass distributions are badly constrained. The local halo densities fully determine the width of the gas distribution once the gaseous velocity dispersion is known. There where the dark halo dominates, the Full Width at Half Maximum (FWHM) of the gas layer is proportional to (rho(sub halo))(exp -0.5). Therefore, measuring the width of the gas layer probes the halo density directly. In a dark halo dominated potential, the FWHM of the gas layer increases linearly with radius. This increase of the thickness of the gas layer is known as 'flaring'. Flaring has been found inside the stellar disk. Beyond the edge of the stellar disk, the analysis is hampered by the onset of the warp. Since the galaxy we are studying, NGC 4244, has no significant warp we hope to extend Rupen's analysis into the halo dominated regime. The usual method to derive a rotation curve from an observed 2-dimensional velocity field is to assume that the hydrogen is distributed in infinitely thin rings. For a flaring disk, any line of sight samples many different parts of the galaxy, all having different densities and projected velocities. In order to fully exploit the information contained in the gas distribution, we have to understand the effects of flaring on the observables (the spectrum for each point of the galaxy). We have investigated the effects of a flaring disk on the observed velocity field. It is obvious that the largest (kinematical) effects are to be expected for low density dark halos at large inclinations. For low mass galaxies we expect that the flaring of the H1 layer will have a major effect on the observed kinematics. For galaxy with intermediate V(sub max,halo) seen at intermediate inclinations, one overestimates Vsin(i) typically by a few percent. For more massive galaxies, any effects

  18. Stellar Rotation in the Orion Nebula Cluster Flanking Fields

    NASA Astrophysics Data System (ADS)

    Rebull, L.

    1999-12-01

    We present an optical study of four 45' x 45' fields centered 35' north, south, east, and west of the Orion Nebula Cluster center. We have measured V and I C photometry for 5000 stars in three of these fields, and U photometry for 1600 of those. We have obtained spectral classifications for 300 of the stars with UVI C photometry plus an additional 200 stars located outside the area of our photometric survey. Based on these data, we find 230 active accretion disk candidates. We have also obtained time-series data for stars in each of these four fields, and 300 periods derived from these data will be presented and discussed. In recent months, several investigators have presented rotation rates for stars in the Trapezium and its immediate environs. The paradigm (e.g. Choi and Herbst 1996) until now has been that the slow rotators are still (magnetically) locked to their disks, and that the fast rotators have dissipated their disks sufficiently as to allow spinup. Herbst et al. (2000) claim they see a bimodal distribution of rotators in Orion; Stassun et al. (1999) claim not to see such a distribution in a very similar region, and in fact cast doubt on the bimodality of the original distribution. Different selection effects (as well as different numbers of stars) are likely to be affecting these conclusions; the addition of data presented here will clarify the issues. This research has made use of data taken at McDonald Observatory (by R. Makidon and M. Adams), data taken at the KPNO 0.9m (with B. Patten and C. Pavlovsky), data taken through the WIYN-Queue program, software written by B. Patten, and partial funding via NASA Origins Grants (L. Hillenbrand and S. Strom).

  19. The Magellanic Analog Dwarf Companions and Stellar Halos (MADCASH) Survey: Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

    NASA Astrophysics Data System (ADS)

    Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Peter, Annika; Price, Paul A.; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

    2017-01-01

    We discuss the first results of our observational program to comprehensively map nearly the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. These will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. We will detail our discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

  20. Eye Velocity Gain Fields in MSTd During Optokinetic Stimulation

    PubMed Central

    Brostek, Lukas; Büttner, Ulrich; Mustari, Michael J.; Glasauer, Stefan

    2015-01-01

    Lesion studies argue for an involvement of cortical area dorsal medial superior temporal area (MSTd) in the control of optokinetic response (OKR) eye movements to planar visual stimulation. Neural recordings during OKR suggested that MSTd neurons directly encode stimulus velocity. On the other hand, studies using radial visual flow together with voluntary smooth pursuit eye movements showed that visual motion responses were modulated by eye movement-related signals. Here, we investigated neural responses in MSTd during continuous optokinetic stimulation using an information-theoretic approach for characterizing neural tuning with high resolution. We show that the majority of MSTd neurons exhibit gain-field-like tuning functions rather than directly encoding one variable. Neural responses showed a large diversity of tuning to combinations of retinal and extraretinal input. Eye velocity-related activity was observed prior to the actual eye movements, reflecting an efference copy. The observed tuning functions resembled those emerging in a network model trained to perform summation of 2 population-coded signals. Together, our findings support the hypothesis that MSTd implements the visuomotor transformation from retinal to head-centered stimulus velocity signals for the control of OKR. PMID:24557636

  1. ZFIRE: Similar Stellar Growth in Hα-emitting Cluster and Field Galaxies at z ~ 2

    NASA Astrophysics Data System (ADS)

    Tran, Kim-Vy H.; Alcorn, Leo Y.; Kacprzak, Glenn G.; Nanayakkara, Themiya; Straatman, Caroline; Yuan, Tiantian; Cowley, Michael; Davé, Romeel; Glazebrook, Karl; Kewley, Lisa J.; Labbé, Ivo; Martizzi, Davidé; Papovich, Casey; Quadri, Ryan; Spitler, Lee R.; Tomczak, Adam

    2017-01-01

    We compare galaxy scaling relations as a function of environment at z∼ 2 with our ZFIRE survey12 where we have measured Hα fluxes for 90 star-forming galaxies selected from a mass-limited ({log}({M}\\star /{M}ȯ )> 9) sample based on ZFOURGE.13 The cluster galaxies (37) are part of a confirmed system at z = 2.095 and the field galaxies (53) are at 1.9< z< 2.4; all are in the COSMOS legacy field. There is no statistical difference between Hα-emitting cluster and field populations when comparing their star formation rate (SFR), stellar mass ({M}\\star ), galaxy size ({r}{eff}), SFR surface density (Σ({{H}}{α }{star})), and stellar age distributions. The only difference is that at fixed stellar mass, the Hα-emitting cluster galaxies are {log}({r}{eff}) ∼ 0.1 larger than in the field. Approximately 19% of the Hα emitters in the cluster and 26% in the field are IR-luminous ({L}{IR} > 2 × 1011 {L}ȯ ). Because the luminous IR galaxies in our combined sample are ∼5 times more massive than the low-IR galaxies, their radii are ∼70% larger. To track stellar growth, we separate galaxies into those that lie above, on, or below the Hα star-forming main sequence (SFMS) using ΔSFR({M}\\star ) = ±0.2 dex. Galaxies above the SFMS (starbursts) tend to have higher Hα SFR surface densities and younger light-weighted stellar ages than galaxies below the SFMS. Our results indicate that starbursts (+SFMS) in the cluster and field at z∼ 2 are growing their stellar cores. Lastly, we compare to the (SFR–{M}\\star ) relation from Rhapsody-G cluster simulations and find that the predicted slope is nominally consistent with the observations. However, the predicted cluster SFRs tend to be too low by a factor of ∼2, which seems to be a common problem for simulations across environment.

  2. Velocity field and star formation in the Horsehead nebula

    NASA Astrophysics Data System (ADS)

    Hily-Blant, P.; Teyssier, D.; Philipp, S.; Güsten, R.

    2005-09-01

    Using large scale maps in C18O(2-1) and in the continuum at 1.2 mm obtained at the IRAM-30 m antenna with the Heterodyne Receiver Array (HERA) and MAMBO2, we investigated the morphology and the velocity field probed in the inner layers of the Horsehead nebula. The data reveal a non-self-gravitating (m/m_vir≈ 0.3) filament of dust and gas (the “neck”, \\varnothing = 0.15-0.30 pc) connecting the Horsehead western ridge, a Photon-Dominated Region illuminated by σOri, to its parental cloud L1630. Several dense cores are embedded in the ridge and the neck. One of these cores appears particularly peaked in the 1.2 mm continuum map and corresponds to a feature seen in absorption on ISO maps around 7 μm. Its C18O emission drops at the continuum peak, suggestive of molecular depletion onto cold grains. The channel maps of the Horsehead exhibit an overall north-east velocity gradient whose orientation swivels east-west, showing a somewhat more complex structure than was recently reported by Pound et al. (2003) using BIMA CO(1-0) mapping. In both the neck and the western ridge, the material is rotating around an axis extending from the PDR to L1630 (angular velocity =1.5-4.0 km s-1). Moreover, velocity gradients along the filament appear to change sign regularly (3 km s-1 pc-1, period = 0.30 pc) at the locations of embedded integrated intensity peaks. The nodes of this oscillation are at the same velocity. Similar transverse cuts across the filament show a sharp variation of the angular velocity in the area of the main dense core. The data also suggest that differential rotation is occurring in parts of the filament. We present a new scenario for the formation and evolution of the nebula and discuss dense core formation inside the filament.

  3. A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra-diffuse Galaxy Dragonfly 44

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Danieli, Shany; Merritt, Allison; Mowla, Lamiya; Romanowsky, Aaron; Zhang, Jielai

    2016-09-01

    Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these ultra-diffuse galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here, we present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck II telescope. We find a velocity dispersion of σ ={47}-6+8 {km} {{{s}}}-1, which implies a dynamical mass of {M}{dyn}(\\lt {r}1/2)={0.7}-0.2+0.3× {10}10 {M}⊙ within its deprojected half-light radius of {r}1/2=4.6+/- 0.2 {kpc}. The mass-to-light ratio is M/{L}I(\\lt {r}1/2)={48}-14+21 {M}⊙ /{L}⊙ , and the dark matter fraction is 98% within {r}1/2. The high mass of Dragonfly 44 is accompanied by a large globular cluster population. From deep Gemini imaging taken in 0\\buildrel{\\prime\\prime}\\over{.} 4 seeing we infer that Dragonfly 44 has {94}-20+25 globular clusters, similar to the counts for other galaxies in this mass range. Our results add to other recent evidence that many UDGs are “failed” galaxies, with the sizes, dark matter content, and globular cluster systems of much more luminous objects. We estimate the total dark halo mass of Dragonfly 44 by comparing the amount of dark matter within r=4.6 {kpc} to enclosed mass profiles of NFW halos. The enclosed mass suggests a total mass of ˜ {10}12 {M}⊙ , similar to the mass of the Milky Way. The existence of nearly dark objects with this mass is unexpected, as galaxy formation is thought to be maximally efficient in this regime.

  4. THE BLACK HOLE MASS-STELLAR VELOCITY DISPERSION RELATIONSHIP FOR QUASARS IN THE SLOAN DIGITAL SKY SURVEY DATA RELEASE 7

    SciTech Connect

    Salviander, S.; Shields, G. A.

    2013-02-10

    We assess evolution in the M {sub BH}-{sigma}{sub *} relationship for quasars in the Sloan Digital Sky Survey Data Release 7 for the redshift range 0.1 < z < 1.2. We estimate the black hole mass, M {sub BH}, using the 'photoionization method', with the broad H{beta} or Mg II emission line and the quasar continuum luminosity. For the stellar velocity dispersion, we use the narrow [O III] or [O II] emission line as a surrogate. This study is a follow-up to an earlier study in which we investigated evolution in the M {sub BH}-{sigma}{sub *} relationship in quasars from Data Release 3. The greatly increased number of quasars in our new sample has allowed us to break our lower-redshift subsample into black hole mass bins and probe the M {sub BH}-{sigma}{sub *} relationship for constant black hole mass. The M {sub BH}-{sigma}{sub *} relationship for the highest-mass (M {sub BH} > 10{sup 9.0} M {sub Sun }) and lowest-mass (M {sub BH} < 10{sup 7.5} M {sub Sun }) black holes appears to evolve significantly; however, most or all of this apparent evolution can be accounted for by various observational biases due to intrinsic scatter in the relationship and to uncertainties in observed quantities. The M {sub BH}-{sigma}{sub *} relationship for black holes in the middle mass range (10{sup 7.5} < M {sub BH} < 10{sup 9.0} M {sub Sun }) shows minimal change with redshift. The overall results suggest a limit of {+-}0.2 dex on any evolution in the M {sub BH}-{sigma}{sub *} relationship for quasars out to z Almost-Equal-To 1 compared with the relationship observed in the local universe. Intrinsic scatter may also provide a plausible way to reconcile the wide range of results of several different studies of the black hole-galaxy relationships.

  5. M dwarfs in the Local Milky Way: The Field Low-Mass Stellar Luminosity and Mass Functions

    SciTech Connect

    Bochanski, Jr, John J.

    2008-01-01

    Modern sky surveys, such as the Sloan Digital Sky Survey (SDSS) and the Two-Micron All Sky Survey, have revolutionized how Astronomy is done. With millions of photometric and spectroscopic observations, global observational properties can be studied with unprecedented statistical significance. Low-mass stars dominate the local Milky Way, with tens of millions observed by SDSS within a few kpc. Thus, they make ideal tracers of the Galactic potential, and the thin and thick disks. In this thesis dissertation, I present my efforts to characterize the local low-mass stellar population, using a collection of observations from the Sloan Digital Sky Survey (SDSS). First, low-mass stellar template spectra were constructed from the co-addition of thousands of SDSS spectroscopic observations. These template spectra were used to quantify the observable changes introduced by chromospheric activity and metallicity. Furthermore, the average ugriz colors were measured as a function of spectral type. Next, the local kinematic structure of the Milky Way was quantified, using a special set of SDSS spectroscopic observations. Combining proper motions and radial velocities (measured using the spectral templates), along with distances, the full UVW space motions of over 7000 low-mass stars along one line of sight were computed. These stars were also separated kinematically to investigate other observational differences between the thin and thick disks. Finally, this dissertation details a project designed to measure the luminosity and mass functions of low-mass stars. Using a new technique optimized for large surveys, the field luminosity function (LF) and local stellar density profile are measured simultaneously. The sample size used to estimate the LF is nearly three orders of magnitude larger than any previous study, offering a definitive measurement of this quantity. The observed LF is transformed into a mass function (MF) and compared to previous studies.

  6. Are the outflows in FU Orionis systems driven by the stellar magnetic field?

    NASA Astrophysics Data System (ADS)

    Königl, Arieh; Romanova, Marina M.; Lovelace, Richard V. E.

    2011-09-01

    FU Orionis (FUOR) outbursts are major optical brightening episodes in low-mass protostars that evidently correspond to rapid mass accretion events in the innermost region of a protostellar disc. The outbursts are accompanied by strong outflows, with the inferred mass outflow rates reaching ˜10 per cent of the mass inflow rates. Shu et al. proposed that the outflows represent accreted disc material that is driven centrifugally from the spun-up surface layers of the protostar by the stellar magnetic field. This model was critiqued by Calvet et al., who argued that it cannot reproduce the photospheric absorption-line shifts observed in the prototype object FU Ori. Calvet et al. proposed that the wind is launched, instead, from the surface of the disc on scales of a few stellar radii by a non-stellar magnetic field. In this paper we present results from numerical simulations of disc accretion on to a slowly rotating star with an aligned magnetic dipole moment that gives rise to a kilogauss-strength surface field. We demonstrate that, for parameters appropriate to FU Ori, such a system can develop a strong, collimated disc outflow of the type previously identified by Romanova et al. in simulations of protostars with low and moderate accretion rates. At the high accretion rate that characterizes the FUOR outburst phase, the radius rm at which the disc is truncated by the stellar magnetic field moves much closer to the stellar surface, but the basic properties of the outflow, which is launched from the vicinity of rm along opened-up stellar magnetic field lines, remain the same. These properties are distinct from those of the X-celerator (or the closely related X-wind) mechanism proposed by Shu et al. - in particular, the outflow is driven from the start by the magnetic pressure gradient force, not centrifugally, and it is more strongly collimated. We show that the simulated outflow can in principle account for the main observed characteristics of FUOR winds, including

  7. Ion and electron cyclotron wall conditioning in stellarator and tokamak magnetic field configuration on WEGA

    SciTech Connect

    Wauters, T.; Louche, F.; Urlings, P.

    2014-02-12

    Discharge wall conditioning is an effective tool to improve plasma performance in tokamaks and stellarators. RF Discharge Conditioning (RFDC) techniques are envisaged for use during operational campaigns on superconducting devices like the ITER tokamak and W7-X stellarator, as alternative to DC Glow Discharge Conditioning which is inefficient in presence of magnetic fields. This contribution investigates RFDC in both the ion and electron cyclotron range of frequencies (ICRF and ECRF) on the WEGA device (Max-Planck-Institute for Plasma Physics, Greifswald, Germany) as preparation for W7-X operation. ECRF discharges produced by localised absorption of RF power at EC resonance layers suffer from poor radial discharge homogeneity in the tokamak vacuum magnetic field configuration, severely limiting the plasma wetted wall areas and consequently the conditioning efficiency. The non-localised production of ICRF discharges by collisional RF power absorption features much improved discharge homogeneity making Ion Cyclotron Wall Conditioning (ICWC) the favoured RFDC technique for superconducting tokamaks. RFDC with the stellarator vacuum magnetic field needs to aim at sufficient plasma densities at and outside the last closed flux surface (LCFS), maximising the convective plasma flux along the open field lines to the wall. Whereas for ICRF discharges this condition is easily fulfilled, on WEGA for He-ECRF discharges this could be achieved as well by off axis heating close to the LCFS. In stellarator magnetic field configuration it is found that He-ICWC for wall desaturation is at least one order of magnitude more efficient than He-ECWC. Novel ECWC methods are proposed that can decrease this efficiency gap with ICWC to a factor 2-3. The efficiency difference is less pronounced in case of H{sub 2}-ICWC and ECWC for isotopic exchange.

  8. Ion and electron cyclotron wall conditioning in stellarator and tokamak magnetic field configuration on WEGA

    NASA Astrophysics Data System (ADS)

    Wauters, T.; Laqua, H. P.; Otte, M.; Preynas, M.; Stange, T.; Urlings, P.; Altenburg, Y.; Aßmus, D.; Birus, D.; Louche, F.

    2014-02-01

    Discharge wall conditioning is an effective tool to improve plasma performance in tokamaks and stellarators. RF Discharge Conditioning (RFDC) techniques are envisaged for use during operational campaigns on superconducting devices like the ITER tokamak and W7-X stellarator, as alternative to DC Glow Discharge Conditioning which is inefficient in presence of magnetic fields. This contribution investigates RFDC in both the ion and electron cyclotron range of frequencies (ICRF and ECRF) on the WEGA device (Max-Planck-Institute for Plasma Physics, Greifswald, Germany) as preparation for W7-X operation. ECRF discharges produced by localised absorption of RF power at EC resonance layers suffer from poor radial discharge homogeneity in the tokamak vacuum magnetic field configuration, severely limiting the plasma wetted wall areas and consequently the conditioning efficiency. The non-localised production of ICRF discharges by collisional RF power absorption features much improved discharge homogeneity making Ion Cyclotron Wall Conditioning (ICWC) the favoured RFDC technique for superconducting tokamaks. RFDC with the stellarator vacuum magnetic field needs to aim at sufficient plasma densities at and outside the last closed flux surface (LCFS), maximising the convective plasma flux along the open field lines to the wall. Whereas for ICRF discharges this condition is easily fulfilled, on WEGA for He-ECRF discharges this could be achieved as well by off axis heating close to the LCFS. In stellarator magnetic field configuration it is found that He-ICWC for wall desaturation is at least one order of magnitude more efficient than He-ECWC. Novel ECWC methods are proposed that can decrease this efficiency gap with ICWC to a factor 2-3. The efficiency difference is less pronounced in case of H2-ICWC and ECWC for isotopic exchange.

  9. Full field gas phase velocity measurements in microgravity

    NASA Technical Reports Server (NTRS)

    Griffin, Devon W.; Yanis, William

    1995-01-01

    Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.

  10. The velocity field under breaking waves: coherent structures and turbulence

    NASA Astrophysics Data System (ADS)

    Melville, W. Kendall; Veron, Fabrice; White, Christopher J.

    2002-03-01

    Digital particle image velocimetry (DPIV) measurements of the velocity field under breaking waves in the laboratory are presented. The region of turbulent fluid directly generated by breaking is too large to be imaged in one video frame and so an ensemble-averaged representation of the flow is built up from a mosaic of image frames. It is found that breaking generates at least one coherent vortex that slowly propagates downstream at a speed consistent with the velocity induced by its image in the free surface. Both the kinetic energy of the flow and the vorticity decay approximately as t[minus sign]1. The Reynolds stress of the turbulence also decays as t[minus sign]1 and is, within the accuracy of the measurements, everywhere negative, consistent with downward transport of streamwise momentum. Estimates of the mometum flux from waves to currents based on the measurements of the Reynolds stress are consistent with earlier estimates. The implications of the measurements for breaking in the field are discussed. Based on geometrical optics and wave action conservation, we suggest that the presence of the breaking-induced vortex provides an explanation for the suppression of short waves by breaking. Finally, in Appendices, estimates of the majority of the terms in the turbulent kinetic energy budget are presented at an early stage in the evolution of the turbulence, and comparisons with independent acoustical measurements of breaking are presented.

  11. Recovering the full velocity and density fields from large-scale redshift-distance samples

    NASA Technical Reports Server (NTRS)

    Bertschinger, Edmund; Dekel, Avishai

    1989-01-01

    A new method for extracting the large-scale three-dimensional velocity and mass density fields from measurements of the radial peculiar velocities is presented. Galaxies are assumed to trace the velocity field rather than the mass. The key assumption made is that the Lagrangian velocity field has negligible vorticity, as might be expected from perturbations that grew by gravitational instability. By applying the method to cosmological N-body simulations, it is demonstrated that it accurately reconstructs the velocity field. This technique promises a direct determination of the mass density field and the initial conditions for the formation of large-scale structure from galaxy peculiar velocity surveys.

  12. Recovering the full velocity and density fields from large-scale redshift-distance samples

    NASA Technical Reports Server (NTRS)

    Bertschinger, Edmund; Dekel, Avishai

    1989-01-01

    A new method for extracting the large-scale three-dimensional velocity and mass density fields from measurements of the radial peculiar velocities is presented. Galaxies are assumed to trace the velocity field rather than the mass. The key assumption made is that the Lagrangian velocity field has negligible vorticity, as might be expected from perturbations that grew by gravitational instability. By applying the method to cosmological N-body simulations, it is demonstrated that it accurately reconstructs the velocity field. This technique promises a direct determination of the mass density field and the initial conditions for the formation of large-scale structure from galaxy peculiar velocity surveys.

  13. The SLUGGS Survey: Wide-field Stellar Kinematics of Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Arnold, Jacob A.; Romanowsky, Aaron J.; Brodie, Jean P.; Forbes, Duncan A.; Strader, Jay; Spitler, Lee R.; Foster, Caroline; Blom, Christina; Kartha, Sreeja S.; Pastorello, Nicola; Pota, Vincenzo; Usher, Christopher; Woodley, Kristin A.

    2014-08-01

    We present stellar kinematics of 22 nearby early-type galaxies (ETGs), based on two-dimensional (2D) absorption line stellar spectroscopy out to ~2-4 R e (effective radii), as part of the ongoing SLUGGS Survey. The galaxies span a factor of 20 in intrinsic luminosity, as well as a full range of environment and ETG morphology. Our data consist of good velocity resolution (σinst ~ 25 km s-1) integrated stellar-light spectra extracted from the individual slitlets of custom made Keck/DEIMOS slitmasks. We extract stellar kinematics measurements (V, σ, h 3, and h 4) for each galaxy. Combining with literature values from smaller radii, we present 2D spatially resolved maps of the large-scale kinematic structure in each galaxy. We find that the kinematic homogeneity found inside 1 R e often breaks down at larger radii, where a variety of kinematic behaviors are observed. While central slow rotators remain slowly rotating in their halos, central fast rotators show more diversity, ranging from rapidly increasing to rapidly declining specific angular momentum profiles in the outer regions. There are indications that the outer trends depend on morphological type, raising questions about the proposed unification of the elliptical and lenticular (S0) galaxy families in the ATLAS3D survey. Several galaxies in our sample show multiple lines of evidence for distinct disk components embedded in more slowly rotating spheroids, and we suggest a joint photometric-kinematic approach for robust bulge-disk decomposition. Our observational results appear generally consistent with a picture of two-phase (in-situ plus accretion) galaxy formation.

  14. The SLUGGS survey: wide-field stellar kinematics of early-type galaxies

    SciTech Connect

    Arnold, Jacob A.; Romanowsky, Aaron J.; Brodie, Jean P.; Woodley, Kristin A.; Forbes, Duncan A.; Blom, Christina; Kartha, Sreeja S.; Pastorello, Nicola; Pota, Vincenzo; Usher, Christopher; Strader, Jay; Spitler, Lee R.; Foster, Caroline

    2014-08-20

    We present stellar kinematics of 22 nearby early-type galaxies (ETGs), based on two-dimensional (2D) absorption line stellar spectroscopy out to ∼2-4 R {sub e} (effective radii), as part of the ongoing SLUGGS Survey. The galaxies span a factor of 20 in intrinsic luminosity, as well as a full range of environment and ETG morphology. Our data consist of good velocity resolution (σ{sub inst} ∼ 25 km s{sup –1}) integrated stellar-light spectra extracted from the individual slitlets of custom made Keck/DEIMOS slitmasks. We extract stellar kinematics measurements (V, σ, h {sub 3}, and h {sub 4}) for each galaxy. Combining with literature values from smaller radii, we present 2D spatially resolved maps of the large-scale kinematic structure in each galaxy. We find that the kinematic homogeneity found inside 1 R {sub e} often breaks down at larger radii, where a variety of kinematic behaviors are observed. While central slow rotators remain slowly rotating in their halos, central fast rotators show more diversity, ranging from rapidly increasing to rapidly declining specific angular momentum profiles in the outer regions. There are indications that the outer trends depend on morphological type, raising questions about the proposed unification of the elliptical and lenticular (S0) galaxy families in the ATLAS{sup 3D} survey. Several galaxies in our sample show multiple lines of evidence for distinct disk components embedded in more slowly rotating spheroids, and we suggest a joint photometric-kinematic approach for robust bulge-disk decomposition. Our observational results appear generally consistent with a picture of two-phase (in-situ plus accretion) galaxy formation.

  15. The PAndAS field of streams: Stellar structures in the milky way halo toward Andromeda and Triangulum

    SciTech Connect

    Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael; Collins, Michelle L. M.; Fardal, Mark A.; Irwin, Michael J.; Lewis, Geraint F.; Bate, Nicholas F.; Conn, Anthony R.; McConnachie, Alan W.; Babul, Arif; Navarro, Julio F.; Chapman, Scott C.; Crnojević, Denija; Ferguson, Annette M. N.; Peñarrubia, Jorge; Mackey, A. Dougal; Tanvir, Nial T.; Valls-Gabaud, David

    2014-05-20

    We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ∼5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ∼17 kpc. With a surface brightness of Σ {sub V} ∼ 32-32.5 mag arcsec{sup –2}, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s{sup –1} at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.

  16. The PAndAS Field of Streams: Stellar Structures in the Milky Way Halo toward Andromeda and Triangulum

    NASA Astrophysics Data System (ADS)

    Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael; Collins, Michelle L. M.; Fardal, Mark A.; Irwin, Michael J.; Lewis, Geraint F.; McConnachie, Alan W.; Babul, Arif; Bate, Nicholas F.; Chapman, Scott C.; Conn, Anthony R.; Crnojević, Denija; Ferguson, Annette M. N.; Mackey, A. Dougal; Navarro, Julio F.; Peñarrubia, Jorge; Tanvir, Nial T.; Valls-Gabaud, David

    2014-05-01

    We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ~5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ~17 kpc. With a surface brightness of Σ V ~ 32-32.5 mag arcsec-2, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s-1 at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.

  17. Improved methods for the measurement and analysis of stellar magnetic fields

    NASA Technical Reports Server (NTRS)

    Saar, Steven H.

    1988-01-01

    The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.

  18. Improved methods for the measurement and analysis of stellar magnetic fields

    NASA Technical Reports Server (NTRS)

    Saar, Steven H.

    1988-01-01

    The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.

  19. GeMS/GSAOI Photometric and Astrometric Performance in Dense Stellar Fields

    NASA Astrophysics Data System (ADS)

    Dalessandro, E.; Saracino, S.; Origlia, L.; Marchetti, E.; Ferraro, F. R.; Lanzoni, B.; Geisler, D.; Cohen, R. E.; Mauro, F.; Villanova, S.

    2016-12-01

    Ground-based imagers at 8 m class telescopes assisted by multi-conjugate adaptive optics are primary facilities with which to obtain accurate photometry and proper motions in dense stellar fields. We observed the central region of the globular clusters Liller 1 and NGC 6624 with the Gemini Multi-conjugate Adaptive Optics System (GeMS) feeding the Gemini South Adaptive Optics Imager (GSAOI) currently available at the Gemini South telescope, under different observing conditions. We characterized the stellar point-spread function (PSF) in terms of FWHM, Strehl ratio (SR), and encircled energy (EE), over the field of view (FOV). We found that, for sub-arcsecond seeing at the observed airmass, we can obtain the diffraction-limited PSF (FWHM ≈ 80 mas), SR ∼ 40%, and EE ≥ 50% with a dispersion around 10% over the FOV of 85″ × 85″, in the K s band. In the J band the best images provide FWHMs between 60 and 80 mas, SR \\gt 10 % , and {EE}\\gt 40 % . For seeing at the observed airmass exceeding 1″, the performance worsens but it is still possible to perform PSF fitting photometry with 25% EE in J and 40% in K s . We also computed the geometric distortions of GeMS/GSAOI and we obtained corrected images with an astrometric accuracy of ∼1 mas in a stellar field with high crowding.

  20. Velocity Vector Fields from Sea Surface Temperature Images Using Multiresolution

    NASA Astrophysics Data System (ADS)

    Tonsmann, G.; Tyler, J. M.; Walker, N. D.; Wiseman, W.; Rouse, L. J.

    2001-12-01

    This paper presents a new method for the estimation of oceanic surface velocity vector fields using multiresolution. Wavelet analysis is used to achieve multiresolution. The new method requires two sea surface temperature (SST) satellite images of the same region taken within a known time interval. Wavelet analysis is performed on both images to decompose them into sub-images of decreasing resolution levels. These sub-images are organized into two quadtrees, one for each SST image. The method compares equivalent sub-images between quadtrees to produce vector fields to represent local displacements of features within the images. Comparisons are performed by maximization of cross correlation of regions in the sub-images. The vector fields are smoothed to eliminate noise and to produce coherent vector fields at each resolution level. Vector fields at levels of higher resolution are used as refinements to vector fields at lower resolution levels. Operational parameters for the new method were optimized. It was determined that wavelet filters with smaller support were best for analysis and smoothing. Validation of the methodology was performed with SST images of the Gulf of Mexico from NOAA satellites during the period October 1993 through July 1994. Image pairs within this set were selected with a time interval of 24 hours between them to minimize biases in SST values that may be introduced by the day-night cycle and to filter out the effects of the diurnal tide, which dominates in the Gulf of Mexico. Comparisons with daily average velocities calculated from drifters from the Surface Current and Lagrangian-drift Program I (SCULP-I) were also performed. Agreement with drifter data was partially achieved. Some discrepancies were discovered in featureless image regions where cross correlation calculations produce unreliable results. The discrepancies could also be explained by differences in the features captured in the satellite images and the factors that influence

  1. An algorithm to estimate unsteady and quasi-steady pressure fields from velocity field measurements.

    PubMed

    Dabiri, John O; Bose, Sanjeeb; Gemmell, Brad J; Colin, Sean P; Costello, John H

    2014-02-01

    We describe and characterize a method for estimating the pressure field corresponding to velocity field measurements such as those obtained by using particle image velocimetry. The pressure gradient is estimated from a time series of velocity fields for unsteady calculations or from a single velocity field for quasi-steady calculations. The corresponding pressure field is determined based on median polling of several integration paths through the pressure gradient field in order to reduce the effect of measurement errors that accumulate along individual integration paths. Integration paths are restricted to the nodes of the measured velocity field, thereby eliminating the need for measurement interpolation during this step and significantly reducing the computational cost of the algorithm relative to previous approaches. The method is validated by using numerically simulated flow past a stationary, two-dimensional bluff body and a computational model of a three-dimensional, self-propelled anguilliform swimmer to study the effects of spatial and temporal resolution, domain size, signal-to-noise ratio and out-of-plane effects. Particle image velocimetry measurements of a freely swimming jellyfish medusa and a freely swimming lamprey are analyzed using the method to demonstrate the efficacy of the approach when applied to empirical data.

  2. Is there a relation between stellar wind braking and the spatial structure of surface magnetic fields?

    NASA Astrophysics Data System (ADS)

    Brown, Timothy M.

    2015-08-01

    For open cluster ages between about 100 Myr and 500 Myr, plots of rotational period vs. color (or equivalently, stellar mass) are almost bimodal, with distinct groups fast and slow rotators at all masses between roughly 0.5 and 1.3 M_sun. One cannot explain these diagrams without invoking some process with a lifetime of a few hundred Myr, that for some but not all stars isolates most of the stellar angular momentum from the torque caused by a magnetized stellar wind. The prevailing theory [e.g. Epstein & Pinsonneault 2014 (ApJ 780, 159) and references therein] locates this process at the base of the stellar convection zone, allowing the wind to spin down the convection zone without much affecting the core. In Brown 2014 (ApJ 789,101) I suggested rather that the break occurs above the stellar photosphere, with different spatial structures of the stellar dynamos accounting for drastically different degrees of magnetic coupling to the stellar wind. In this talk I will describe preliminary results from two observing programs that aim to test the latter hypothesis.One program uses photometry from the LCOGT (ground-based, world-wide) telescope network to measure rotational periods of stars in fairly young open clusters, to improve comparisons between modeled and observed period-color diagrams by increasing sample sizes. The LCOGT network proves nearly ideal for this kind of work, having already provided good data sets for the clusters NGC 6281 and NGC 3532. These clusters are both about 300 Myr old, filling a gap in the current age distribution of observed clusters. The second program uses K2 photometry combined with multicolor photometry (from LCOGT) and spectroscopy (from the ARC 3.5m telescope) to search for rotation-dependent differences in possible proxies for the typical spatial scale of surface magnetic fields. These include the spot/photosphere temperature contrast, and short-timescale variations in various diagnostics of projected starspot area.

  3. Velocity field measurements in the wake of a propeller model

    NASA Astrophysics Data System (ADS)

    Mukund, R.; Kumar, A. Chandan

    2016-10-01

    Turboprop configurations are being revisited for the modern-day regional transport aircrafts for their fuel efficiency. The use of laminar flow wings is an effort in this direction. One way to further improve their efficiency is by optimizing the flow over the wing in the propeller wake. Previous studies have focused on improving the gross aerodynamic characteristics of the wing. It is known that the propeller slipstream causes early transition of the boundary layer on the wing. However, an optimized design of the propeller and wing combination could delay this transition and decrease the skin friction drag. Such a wing design would require the detailed knowledge of the development of the slipstream in isolated conditions. There are very few studies in the literature addressing the requirements of transport aircraft having six-bladed propeller and cruising at a high propeller advance ratio. Low-speed wind tunnel experiments have been conducted on a powered propeller model in isolated conditions, measuring the velocity field in the vertical plane behind the propeller using two-component hot-wire anemometry. The data obtained clearly resolved the mean velocity, the turbulence, the ensemble phase averages and the structure and development of the tip vortex. The turbulence in the slipstream showed that transition could be close to the leading edge of the wing, making it a fine case for optimization. The development of the wake with distance shows some interesting flow features, and the data are valuable for flow computation and optimization.

  4. Towards a Dense Velocity Field for Central Europe

    NASA Astrophysics Data System (ADS)

    Caporali, Alessandro

    2013-04-01

    Twelve measurement campaigns between 1994 and 2011 with epoch and permanent GNSS stations make the CEGRN network one of the most regularly and accurately surveyed networks for scientific applications. Recently, the CEGRN GNSS data have been reprocessed with consistent orbits and IGS05 antenna models. On the other hand, the EUREF Permanent Network (EPN) represents the backbone geodetic infrastructure for Europe and realizes the ETRS89 system prescriptions with the ETRF2000 reference frame. Recently EUREF prepared its densification of the ITRF2008 and the IGS08 reference frames and resulting in cumulative SINEX files: by stacking reprocessed weekly normal equation files from 1996 to present, high accuracy positions and velocities of IGS and EPN stations in Europe could be obtained in a consistent reference frame throughout the temporal range. It is finally worth noting that both the IAG Working Group on "Integration of Dense Velocity Fields in the ITRF" and the EUREF Working Group on Deformation Models encourage initiatives aiming at estimating velocities of GNSS sites in a rigorous manner, both for reference frame applications and 3D tectonic deformation problems. Within this framework it is then natural to attempt a combination of the EPN and CEGRN networks with the intent to bring down to regional, i.e. Central European, scale the same standard of accuracy of the EPN long-term solution, without reprocessing the entire set of raw GNSS data. This paper presents the first results of the EPN+CEGRN combination: we review the common properties of the input SINEX files, the processing software Bernese 5.0 and CATREF, the adopted processing strategies and the results, in terms of positions, velocities and Helmert parameters. We discuss the pros and cons of three possible processing strategies: one consists in stacking the individual, weekly CEGRN campaign solutions with the cumulative EPN solution; the second consists in stacking the two cumulative solutions, CEGRN and

  5. Large-scale velocity fields. [of solar rotation

    NASA Technical Reports Server (NTRS)

    Howard, Robert F.; Kichatinov, L. L.; Bogart, Richard S.; Ribes, Elizabeth

    1991-01-01

    The present evaluation of recent observational results bearing on the nature and characteristics of solar rotation gives attention to the status of current understanding on such large-scale velocity-field-associated phenomena as solar supergranulation, mesogranulation, and giant-scale convection. Also noted are theoretical suggestions reconciling theory and observations of giant-scale solar convection. The photosphere's global meridional circulation is suggested by solar rotation models requiring pole-to-equator flows of a few m/sec, as well as by the observed migration of magnetic activity over the solar cycle. The solar rotation exhibits a latitude and cycle dependence which can be understood in terms of a time-dependent convective toroidal roll pattern.

  6. Transformations based on continuous piecewise-affine velocity fields

    DOE PAGES

    Freifeld, Oren; Hauberg, Soren; Batmanghelich, Kayhan; ...

    2017-01-11

    Here, we propose novel finite-dimensional spaces of well-behaved Rn → Rn transformations. The latter are obtained by (fast and highly-accurate) integration of continuous piecewise-affine velocity fields. The proposed method is simple yet highly expressive, effortlessly handles optional constraints (e.g., volume preservation and/or boundary conditions), and supports convenient modeling choices such as smoothing priors and coarse-to-fine analysis. Importantly, the proposed approach, partly due to its rapid likelihood evaluations and partly due to its other properties, facilitates tractable inference over rich transformation spaces, including using Markov-Chain Monte-Carlo methods. Its applications include, but are not limited to: monotonic regression (more generally, optimization overmore » monotonic functions); modeling cumulative distribution functions or histograms; time-warping; image warping; image registration; real-time diffeomorphic image editing; data augmentation for image classifiers. Our GPU-based code is publicly available.« less

  7. Molecular Strong Field Ionization viewed with Photoelectron Velocity Map Imaging

    NASA Astrophysics Data System (ADS)

    Sandor, Peter

    In this thesis, work is presented on molecular strong-field ionization, during which an electron is removed from polyatomic molecules in the presence of strong laser fields. This is a process which is the basis of a number of experimental techniques to uncover electronic dynamics in atoms and molecules on the femtosecond and attosecond timescale. 'Strong' refers to an electric field strength which leads to a response from the system which can not be modeled perturbatively. These fields can be easily produced in the focus of femtosecond laser radiation, as is done in this work. With the use of velocity map imaging of the photoelectron in coincidence with the fragment ion, multiple ionization--dissociation pathways can be distinguished. It is shown that as opposed to early attempts to model the process, multiple low-lying states are populated in the ion, and also the signatures of multielectron dynamics are revealed. By changing the laser pulse duration from 30 fs to below 10 fs, control is demonstrated over which quantum states of the ion are populated. It is also shown that for pulses shorter than 10 fs (which is a timescale below the shortest vibrational period in molecules), ionization pathways that involve motion of the nuclei are almost completely shut off. Finally, the origin of electrons with <1 meV kinetic energy is discussed. A two-step model is proposed for creating the electrons: the first step is population transfer to high-lying excited states of the neutral molecule by the laser field; the second step is ionization. Different ionization mechanisms are examined and their viability is checked against available data.

  8. Could the stellar magnetic field explain the vertical structures in the AU Mic debris disk?

    NASA Astrophysics Data System (ADS)

    Sezestre, É.; Augereau, J.-C.

    2016-12-01

    Recent observations of the edge-on debris disk of AU Mic have revealed asymmetric, fast-moving wave-like structures above its disk midplane. Although asymmetries are frequent in debris disks, no model can readily explain these features.} {In this paper, we present a model aiming to reproduce such structures, particularly the wave morphology and the high projected speeds. We test the hypothesis of dust emitted by a point source, interacting with the stellar wind and the large-scale magnetic field of the star.} {We perform numerical simulations of test particle trajectories to explore the available parameter space. The impact of the stellar wind and the magnetic field on the dust dynamics is discussed separately, then together.} {The stellar wind and, to a smaller extent, the magnetic topology, can reproduce the arches. The observed structures cannot be explained by a single trajectory common to all dust grains emitted intermittently by a fixed point source in space.} {This excludes a giant collision as the emission process. Therefore, our preferred scenario relies on an orbiting source of dust, possibly a planetary companion, emitting at different epochs.

  9. STELLAR MAGNETIC FIELDS AS A HEATING SOURCE FOR EXTRASOLAR GIANT PLANETS

    SciTech Connect

    Buzasi, D.

    2013-03-10

    It has been observed that hot Jupiters located within 0.08 AU of their host stars commonly display radii in excess of those expected based on models. A number of theoretical explanations for this phenomenon have been suggested, but the ability of any one mechanism to account for the full range of observations remains to be rigorously proven. I identify an additional heating mechanism, arising from the interaction of the interplanetary magnetic field and the planetary magnetosphere, and show that this is capable of providing enough energy to explain the observed planetary radii. Such a model predicts that the degree of heating should be dependent on the stellar magnetic field, for which stellar activity serves as a proxy. Accordingly, I examine populations of hot Jupiters from the Kepler database and confirm that stellar activity (determined using Kepler CDPP levels) is correlated with the presence of planetary radii inflated beyond the basal level of R = 0.87 R{sub J} identified by previous researchers. I propose that the primary mechanism for transferring energy from the magnetosphere to the planetary interior is Joule heating arising from global electric circuits analogous to those seen in solar system objects.

  10. Instantaneous velocity field imaging instrument for supersonic reacting flows

    NASA Technical Reports Server (NTRS)

    Allen, M. G.; Davis, S. J.; Kessler, W. J.; Legner, H. H.; Mcmanus, K. R.; Mulhall, P. A.; Parker, T. E.; Sonnenfroh, D. M.

    1993-01-01

    The technical tasks conducted to develop and demonstrate a new gas velocity measurement technique for high enthalpy reacting flows is described. The technique is based on Doppler-shifted Planar Laser-induced Fluorescence (PLIF) imaging of the OH radical. The imaging approach permits, in principle, single-shot measurements of the 2-D distribution of a single velocity component in the measurement plane, and is thus a technique of choice for applications in high enthalpy transient flow facilities. In contrast to previous work in this area, the present program demonstrated an approach which modified the diagnostic technique to function under the constraints of practical flow conditions of engineering interest, rather than vice-versa. In order to accomplish the experimental demonstrations, the state-of-the-art in PLIF diagnostic techniques was advanced in several ways. Each of these tasks is described in detail and is intended to serve as a reference in supporting the transition of this new capability to the fielded PLIF instruments now installed at several national test facilities. Among the new results of general interest in LlF-based flow diagnostics, a detailed set of the first measurements of the collisional broadening and shifting behavior of OH (1,0) band transitions in H7-air combustion environments is included. Such measurements are critical in the design of a successful strategy for PLIF velocity imaging; they also relate to accurate concentration and temperature measurements, particularly in compressible flow regimes. Furthermore, the results shed new light on the fundamental relationship between broadening and energy transfer collisions in OH A(sup 2)Sigma(+)v(sup ') = 1. The first single-pulse, spectrally-resolved measurements of the output of common pulsed dye lasers were also produced during the course of this effort. As with the OH broadening measurements, these data are a significant aspect of a successful velocity imaging strategy, and also have

  11. Zeeman-Doppler Imaging of Stellar Magnetic Fields with Atomic and Molecular Lines

    NASA Astrophysics Data System (ADS)

    Sennhauser, C.; Berdyugina, S. V.; Fluri, D. M.

    2009-06-01

    We have developed a new code for Zeeman-Doppler Imaging (ZDI) of stellar magnetic fields using the Occamian approach for solving inverse problems. The inversions are applied to Stokes I and V parameter sets obtained by solving the full set of polarized radiative transfer equations for both atomic and molecular lines. For the first time we demonstrate that molecular polarization strongly constrains the ZDI maps and is crucial for obtaining a realistic solution from Stokes I and V only observed at a few stellar rotational phases. We also present an enhanced LSD technique, which allows analytic separation of blended line profiles. The resulting LSD profiles are free from systematic effects induced by blends, which are typical for other multi-line techniques.

  12. ROTATION AND STABILITY OF THE TOROIDAL MAGNETIC FIELD IN STELLAR RADIATION ZONES

    SciTech Connect

    Bonanno, Alfio; Urpin, Vadim E-mail: vadim.urpin@uv.es

    2013-03-20

    The stability of the magnetic field in radiation zones is of crucial importance for mixing and angular momentum transport in the stellar interior. We consider the stability properties of stars containing a predominant toroidal field in spherical geometry by means of a linear stability in the Boussinesq approximation taking into account the effect of thermal conductivity. We calculate the growth rate of instability and analyze in detail the effects of stable stratification and heat transport. We argue that the stabilizing influence of gravity can never entirely suppress the instability caused by electric currents in radiation zones. However, the stable stratification can essentially decrease the growth rate of instability.

  13. The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars

    SciTech Connect

    Allende Prieto, C.; Sivarani, T.; Beers, T.C.; Lee, Y.S.; Koesterke, L.; Shetrone, M.; Sneden, C.; Lambert, D.L.; Wilhelm, R.; Rockosi, C.M.; Lai, D.

    2007-10-01

    The authors report high-resolution spectroscopy of 125 field stars previously observed as part of the Sloan Digital Sky Survey and its program for Galactic studies, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). These spectra are used to measure radial velocities and to derive atmospheric parameters, which they compare with those reported by the SEGUE Stellar Parameter Pipeline (SSPP). The SSPP obtains estimates of these quantities based on SDSS ugriz photometry and low-resolution (R {approx} 2000) spectroscopy. For F- and G-type stars observed with high signal-to-noise ratios (S/N), they empirically determine the typical random uncertainties in the radial velocities, effective temperatures, surface gravities, and metallicities delivered by the SSPP to be 2.4 km s{sup -1}, 130 K (2.2%), 0.21 dex, and 0.11 dex, respectively, with systematic uncertainties of a similar magnitude in the effective temperatures and metallicities. They estimate random errors for lower S/N spectra based on numerical simulations.

  14. Multi-Line Spectro-Polarimetry of Stellar Magnetic Fields Using Principal Components Analysis

    NASA Astrophysics Data System (ADS)

    Semel, M.; Rees, D. E.; Ramírez Vélez, J. C.; Stift, M. J.; Leone, F.

    2006-12-01

    Zeeman-Doppler-Imaging (ZDI) is a technique for the diagnosis of stellar magnetic fields from observations of circularly polarized light, based on the weak-field approximation. This approach has proved adequate in numerous studies of the magnetic fields of solar-type stars. To improve the signal-to-noise ratio, one can add the contributions of different lines to the polarization signature. However, this multi-line extension has been limited by a number of assumptions (e.g., the weak-field approximation). Here we present a novel approach. We created a database of synthetic polarized spectra for different combinations of magnetic-field intensities and orientations. Principal Components Analysis was used to compress the database, so that only few Principal Components are needed to represent all the calculated spectra.

  15. On The Stability of A General Magnetic Field Topology In Stellar Radiative Zones

    NASA Astrophysics Data System (ADS)

    Augustson, Kyle; Mathis, Stéphane; Strugarek, Antoine

    2016-10-01

    This paper provides a brief overview of the formation of stellar fossil magnetic fields and what potential instabilities may occur given certain configurations of the magnetic field. In particular, a purely magnetic instability can occur for poloidal, toroidal, and mixed poloidal-toroidal axisymmetric magnetic field configurations as originally studied in Tayler (1973), Markey & Tayler (1973), and Tayler (1980). However, most of the magnetic field configurations observed at the surface of massive stars are non- axisymmetric. Thus, extending earlier studies of the axisymmetric Tayler instability in spherical geometry (Goossens, 1980), we introduce a formulation for the global change in the potential energy contained in a convectively-stable region given an arbitrary Lagrangian perturbation, which permits the inclusion of both axisymmetric and non-axisymmetric magnetic fields. With this tool in hand, a path is shown by which more general stability criterion can be established.

  16. Stellar Flares in the CSTAR Field: Results from the 2008 Data Set

    NASA Astrophysics Data System (ADS)

    Liang, En-Si; Wang, Songhu; Zhou, Ji-Lin; Zhou, Xu; Zhang, Hui; Xie, Jiwei; Liu, Huigen; Wang, Lifan; Ashley, M. C. B.

    2016-12-01

    The Chinese Small Telescope ARray (CSTAR) is the first Chinese astronomical instrument placed in Antarctica. It is a group of four identical, fully automatic 14.5 {cm} telescopes, with a field of view (FOV) of 20 {\\deg }2 centered on the South Celestial Pole. Placed at Antarctic Dome A, CSTAR is designed to provide high-cadence photometry for site monitoring and variable sources detection. During the 2008 observing season, CSTAR took high-precision photometric data of 18,145 stars around the South Celestial Pole. At i=7.5 and 12, the photometric precision reaches ∼8 mmag and ∼30 mmag with a cadence of 20 s or 30 s, respectively. Using a robust detection method, we have found 15 stellar flares on 13 sources, including two classified variables. We have also found a linear relation between the decay times and the total durations of the stellar flares. The details of all the detected flares along with their stellar properties are presented in this work.

  17. Variable Field Analytical Ultracentrifugation: II. Gravitational Sweep Sedimentation Velocity

    PubMed Central

    Ma, Jia; Zhao, Huaying; Sandmaier, Julia; Alexander Liddle, J.; Schuck, Peter

    2016-01-01

    Sedimentation velocity (SV) analytical ultracentrifugation is a classical biophysical technique for the determination of the size-distribution of macromolecules, macromolecular complexes, and nanoparticles. SV has traditionally been carried out at a constant rotor speed, which limits the range of sedimentation coefficients that can be detected in a single experiment. Recently we have introduced methods to implement experiments with variable rotor speeds, in combination with variable field solutions to the Lamm equation, with the application to expedite the approach to sedimentation equilibrium. Here, we describe the use of variable-field sedimentation analysis to increase the size-range covered in SV experiments by ∼100-fold with a quasi-continuous increase of rotor speed during the experiment. Such a gravitational-sweep sedimentation approach has previously been shown to be very effective in the study of nanoparticles with large size ranges. In the past, diffusion processes were not accounted for, thereby posing a lower limit of particle sizes and limiting the accuracy of the size distribution. In this work, we combine variable field solutions to the Lamm equation with diffusion-deconvoluted sedimentation coefficient distributions c(s), which further extend the macromolecular size range that can be observed in a single SV experiment while maintaining accuracy and resolution. In this way, approximately five orders of magnitude of sedimentation coefficients, or eight orders of magnitude of particle mass, can be probed in a single experiment. This can be useful, for example, in the study of proteins forming large assemblies, as in fibrillation process or capsid self-assembly, in studies of the interaction between very dissimilar-sized macromolecular species, or in the study of broadly distributed nanoparticles. PMID:26745414

  18. Variable Field Analytical Ultracentrifugation: II. Gravitational Sweep Sedimentation Velocity.

    PubMed

    Ma, Jia; Zhao, Huaying; Sandmaier, Julia; Alexander Liddle, J; Schuck, Peter

    2016-01-05

    Sedimentation velocity (SV) analytical ultracentrifugation is a classical biophysical technique for the determination of the size-distribution of macromolecules, macromolecular complexes, and nanoparticles. SV has traditionally been carried out at a constant rotor speed, which limits the range of sedimentation coefficients that can be detected in a single experiment. Recently we have introduced methods to implement experiments with variable rotor speeds, in combination with variable field solutions to the Lamm equation, with the application to expedite the approach to sedimentation equilibrium. Here, we describe the use of variable-field sedimentation analysis to increase the size-range covered in SV experiments by ∼100-fold with a quasi-continuous increase of rotor speed during the experiment. Such a gravitational-sweep sedimentation approach has previously been shown to be very effective in the study of nanoparticles with large size ranges. In the past, diffusion processes were not accounted for, thereby posing a lower limit of particle sizes and limiting the accuracy of the size distribution. In this work, we combine variable field solutions to the Lamm equation with diffusion-deconvoluted sedimentation coefficient distributions c(s), which further extend the macromolecular size range that can be observed in a single SV experiment while maintaining accuracy and resolution. In this way, approximately five orders of magnitude of sedimentation coefficients, or eight orders of magnitude of particle mass, can be probed in a single experiment. This can be useful, for example, in the study of proteins forming large assemblies, as in fibrillation process or capsid self-assembly, in studies of the interaction between very dissimilar-sized macromolecular species, or in the study of broadly distributed nanoparticles.

  19. The velocity fields of gas and stars within five KPC of the sun

    NASA Astrophysics Data System (ADS)

    Ovenden, M. W.; Pryce, M. H. L.; Shuter, W. L. H.

    A mathematical expression is considered for the most probable value of the line of sight velocity, Vr, of an element at a certain galactic longitude and a certain distance projected onto the plane of the galactic disk. Attention is given to the velocity field of O and B stars, the velocity field for idealized circular motion, the velocity field of 112 kinematically distinct H II regions, and the velocity field of nearby 21 cm emission. It is found that the velocity field describing the O and B stars is very close to pure circular motion. On the basis of plots presented in the investigation and an extensive statistical error analysis conducted by Pryce (1983), it is seen that the velocity fields for the nearby gas and H II regions and that of the stars are different.

  20. Analysis of isoplanatic high resolution stellar fields by the StarFinder code

    NASA Astrophysics Data System (ADS)

    Diolaiti, E.; Bendinelli, O.; Bonaccini, D.; Close, L.; Currie, D.; Parmeggiani, G.

    2000-12-01

    We describe a new code for the deep analysis of stellar fields, designed for Adaptive Optics (AO) Nyquist-sampled images with high and low Strehl ratio. The Point Spread Function (PSF) is extracted directly from the image frame, to take into account the actual structure of the instrumental response and the atmospheric effects. The code is written in IDL language and organized in the form of a self-contained widget-based application, provided with a series of tools for data visualization and analysis. A description of the method and some applications to AO data are presented.

  1. A new present-day velocity field for eastern Iran

    NASA Astrophysics Data System (ADS)

    Walpersdorf, A.; Tavakoli, F.; Hatzfeld, D.; Jadidi, A.; Vergnolle, M.; Djamour, Y.; Nankali, H. R.; Sedighi, M.; Bellier, O.; Shabanian, E.

    2009-04-01

    Since 2004, extensive GPS campaigns and the upcoming Iranian permanent GPS network are monitoring the present-day deformation in eastern Iran. We present a new GPS velocity field that extends from Central Iran to the Turkmen shield and the Hellmand block on the Eurasian plate. It permits to monitor the right lateral shear across the aseismic Lut block between Central Iran and the Hellmand block, and the resulting shortening across the Kopeh Dagh mountain belt limiting NE Iran towards Turkmenistan. The present-day deformation pattern is used to verify existing tectonic models. Individual instantaneous fault slip rates are compared to short term and long term geological estimates. We find that GPS slip rates are generally coherent with short term geologic determinations (from dating of geomorphologic offsets over some 10-100 ka). Some differences with respect to long term estimates (from total geologic fault offsets and onset ages of several Ma) indicate non-constant slip rates over different time scales or that the onset of the present-day deformation presumed to 3-7 Ma in eastern Iran has to be revised.

  2. The Direct Effect of Toroidal Magnetic Fields on Stellar Oscillations: An Analytical Expression for the General Matrix Element

    NASA Astrophysics Data System (ADS)

    Kiefer, René; Schad, Ariane; Roth, Markus

    2017-09-01

    Where is the solar dynamo located and what is its modus operandi? These are still open questions in solar physics. Helio- and asteroseismology can help answer them by enabling us to study solar and stellar internal structures through global oscillations. The properties of solar and stellar acoustic modes are changing with the level of magnetic activity. However, until now, the inference on subsurface magnetic fields with seismic measures has been very limited. The aim of this paper is to develop a formalism to calculate the effect of large-scale toroidal magnetic fields on solar and stellar global oscillation eigenfunctions and eigenfrequencies. If the Lorentz force is added to the equilibrium equation of motion, stellar eigenmodes can couple. In quasi-degenerate perturbation theory, this coupling, also known as the direct effect, can be quantified by the general matrix element. We present the analytical expression of the matrix element for a superposition of subsurface zonal toroidal magnetic field configurations. The matrix element is important for forward calculations of perturbed solar and stellar eigenfunctions and frequency perturbations. The results presented here will help to ascertain solar and stellar large-scale subsurface magnetic fields, and their geometric configuration, strength, and change over the course of activity cycles.

  3. Spatially Resolved Stellar Kinematics of Field Early-Type Galaxies at z = 1: Evolution of the Rotation Rate

    NASA Astrophysics Data System (ADS)

    van der Wel, Arjen; van der Marel, Roeland P.

    2008-09-01

    We use the spatial information of our previously published VLT/FORS2 absorption-line spectroscopy to measure mean stellar velocity and velocity dispersion profiles of 25 field early-type galaxies at a median redshift z = 0.97 (full range 0.6 < z < 1.2). This provides the first detailed study of early-type galaxy rotation at these redshifts. From surface brightness profiles from HST imaging we calculate two-integral oblate axisymmetric Jeans equation models for the observed kinematics. Fits to the data yield for each galaxy the degree of rotational support and the mass-to-light ratio M/LJeans. S0 and Sa galaxies are generally rotationally supported, whereas elliptical galaxies rotate less rapidly or not at all. Down to MB = - 19.5 (corrected for luminosity evolution), we find no evidence for evolution in the fraction of rotating early-type (E+S0) galaxies between z ~ 1 (63% +/- 11% ) and the present (61% +/- 5% ). We interpret this as evidence for little or no change in the field S0 fraction with redshift. We compare M/LJeans with M/Lvir inferred from the virial theorem and globally averaged quantities and assuming homologous evolution. There is good agreement for nonrotating (mostly E) galaxies. However, for rotationally supported galaxies (mostly S0) M/LJeans is on average ~40% higher than M/Lvir. We discuss possible explanations and the implications for the evolution of M/L between z = 1 and the present and its dependence on mass. Based on observations collected at the European Southern Observatory, Chile (169.A-0458), and on observations with the Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  4. Induced velocity field of a jet in a crossflow

    NASA Technical Reports Server (NTRS)

    Fearn, R. L.; Weston, R. P.

    1978-01-01

    An experimental investigation of a subsonic round jet exhausting perpendicularly from a flat plate into a subsonic crosswind of the same temperature was conducted. Velocity and pressure measurements were made in planes perpendicular to the path of the jet for ratios of jet velocity to crossflow velocity ranging from 3 to 10. The results of these measurements are presented in tabular and graphical forms. A pair of diffuse contrarotating vortices is identified as a significant feature of the flow, and the characteristics of the vortices are discussed.

  5. Stellar parameters for stars of the CoRoT exoplanet field

    NASA Astrophysics Data System (ADS)

    Cortés, C.; Maciel, S. C.; Vieira, S.; Ferreira Lopes, C. E.; Leão, I. C.; de Oliveira, G. P.; Correia, C.; Canto Martins, B. L.; Catelan, M.; De Medeiros, J. R.

    2015-09-01

    Context. Spectroscopic observations represent a fundamental step in the physical characterization of stars and, in particular, in the precise location of stars in the HR diagram. Rotation is also a key parameter, impacting stellar properties and evolution, which modulates the interior and manifests itself on the surface of stars. To date, the lack of analysis based on large samples has prevented our understanding of the real impact of stellar parameters and rotation on the stellar evolution as well as on the behavior of surface abundances. The space missions, CoRoT and Kepler, are providing us with rotation periods for thousands of stars, thus enabling a robust assessment of the behavior of rotation for different populations and evolutionary stages. For these reasons, the follow-up programs are fundamental to increasing the returns of these space missions. An analysis that combines spectroscopic data and rotation/modulation periods obtained from these space missions provides the basis for establishing the evolutionary behavior of the angular momentum of solar-like stars at different evolutionary stages, and the relation of rotation with other relevant physical and chemical parameters. Aims: To support the computation and evolutionary interpretation of periods associated with the rotational modulation, oscillations, and variability of stars located in the CoRoT fields, we are conducting a spectroscopic survey for stars located in the fields already observed by the satellite. These observations allow us to compute physical and chemical parameters for our stellar sample. Methods: Using spectroscopic observations obtained with UVES/VLT and Hydra/Blanco, and based on standard analysis techniques, we computed physical and chemical parameters (Teff, log (g), [Fe/H], vmic, vrad, vsin (i), and A(Li)) for a large sample of CoRoT targets. Results: We provide physical and chemical parameters for a sample comprised of 138 CoRoT targets. Our analysis shows the stars in our

  6. Experimental investigation of the velocity field in buoyant diffusion flames using PIV and TPIV algorithm

    Treesearch

    L. Sun; X. Zhou; S.M. Mahalingam; D.R. Weise

    2005-01-01

    We investigated a simultaneous temporally and spatially resolved 2-D velocity field above a burning circular pan of alcohol using particle image velocimetry (PIV). The results obtained from PIV were used to assess a thermal particle image velocimetry (TPIV) algorithm previously developed to approximate the velocity field using the temperature field, simultaneously...

  7. Radial electric field computations with DKES and neoclassical models in TJ-II stellarator

    NASA Astrophysics Data System (ADS)

    Martinell, Julio; Gutierrez-Tapia, Cesar; Lopez-Bruna, Daniel

    2015-11-01

    Radial electric fields arise due to the non-ambipolar transport in stellarator plasmas and play an important role in determining some improved confinement regimes. In order to calculate this electric field it is necessary to take all particle fluxes that are not ambipolar. The most important contribution to these fluxes comes from neoclassical transport. Here we use particle fluxes obtained from kinetic equation computations using the code DKES to evaluate the radial electric field profiles for certain discharges of the heliac TJ-II. Experimental profiles for the density and temperatures are used together with the diffusion coefficients obtained with DKES. A similar computation of the electric field is performed with three analytical neoclassical models that use an approximation for the magnetic geometry. The ambipolar electric field from the models is compared with the one given by DKES and we find that they are all qualitatively similar. They are also compared with experimental measurements of the electric field obtained with HIBP. It is shown that, although the electric field is reasonably well reproduced by the neoclassical computations, especially in high temperature regimes, the particle fluxes are not. Thus, neoclassical theory provides good Er estimates in TJ-II. Support from CONACyT 152905 and DGAPA IN109115 projects is acknowledged.

  8. ACS and WFPC2 Stellar Photometry in the Kepler Mission Target Field

    NASA Astrophysics Data System (ADS)

    Borucki, William

    2004-07-01

    We will observe three regions at the Galactic Equator {GE} to determine the number of stars in the magnitude range from 18 to 25 in the target field of the NASA Kepler mission. This mission will search for Earth-size planets orbiting other stars. The field is a twelve by twelve degree square in Cygnus. It abuts the GE. The detection technique is to search photometrically for planetary transits. Faint eclipsing binaries that are not spatially resolved from the target star by Kepler may cause confusion, leading to false positive detections. The HST is uniquely capable of determining the potential magnitude of the issue in the region of the GE, where stellar densities are extremely high.

  9. Defining the Velocity Field of Root Cells in Arabidopsis Seedlings Using Open Source Image Processing Tools

    NASA Astrophysics Data System (ADS)

    Craig, Amy E.; Higgins, Brad R.; Guy, Tracy; Durham Brooks, Tessa; Wentworth, Christopher D.

    2011-11-01

    The velocity field for cells in a growing root is a function of a cell's position with respect to the root apex and time. For many species of plant this function has the same general sigmoid shape described by a modified logistics curve. In this investigation we obtain microscopic images of Arabidopsis seedling roots over a 20 minute period of time, measure the velocity field for root cells using an application developed with the open source mathematics application Octave, and test whether the velocity field can be described by the modified logistics function. We find support for describing the velocity field by the modified logistics function.

  10. Peculiar velocity field: Constraining the tilt of the Universe

    SciTech Connect

    Ma Yinzhe; Gordon, Christopher; Feldman, Hume A.

    2011-05-15

    A large bulk flow, which is in tension with the Lambda cold dark matter ({Lambda}CDM) cosmological model, has been observed. In this paper, we provide a physically plausible explanation of this bulk flow, based on the assumption that some fraction of the observed dipole in the cosmic microwave background is due to an intrinsic fluctuation, so that the subtraction of the observed dipole leads to a mismatch between the cosmic microwave background defined rest frame and the matter rest frame. We investigate a model that takes into account the relative velocity (hereafter the tilted velocity) between the two frames, and develop a Bayesian statistic to explore the likelihood of this tilted velocity. By studying various independent peculiar velocity catalogs, we find that (1) the magnitude of the tilted velocity u is around 400 km/s, and its direction is close to what is found from previous bulk flow analyses; for most catalogs analyzed, u=0 is excluded at about the 2.5{sigma} level; (2) constraints on the magnitude of the tilted velocity can result in constraints on the duration of inflation, due to the fact that inflation can neither be too long (no dipole effect) nor too short (very large dipole effect); (3) under the assumption of a superhorizon isocurvature fluctuation, the constraints on the tilted velocity require that inflation lasts at least 6 e-folds longer (at the 95% confidence interval) than that required to solve the horizon problem. This opens a new window for testing inflation and models of the early universe from observations of large scale structure.

  11. Magnetic Field Line Topology of the Scrape-Off Layer in the Compact Stellarator NCSX

    NASA Astrophysics Data System (ADS)

    Grossman, Arthur; Mioduszewski, Peter; Fenstermacher, Max; Koniges, Alice; Rognlien, Tom

    2001-10-01

    The magnetic topology of the plasma boundary of the proposed compact stellarator NCSX is investigated using the MFBE[1] and VMEC2000[2] codes. The VMEC code provides a free boundary equilibrium and the magnetics from external coils and bootstrap plasma currents inside the last closed magnetic surface (LCMS). The MFBE code uses these results to calculate the magnetic fields of these finite beta equilibria outside the LCMS in a form suitable for line tracing. The Poincaré plots of field lines started outside the LCMS indicate preservation of initial radial ordering of field lines up to intersections with vacuum vessel and plasma facing components. A large flux expansion of field lines is observed between the midplane and tips of the banana shaped cross-section, due to the presence of a nearby poloidal field null used to create the banana shape. TRIM coils used to heal islands just within the LCMS appear to reduce stochasticity just outside the LCMS as well as enhance an island structure outside the LCMS. Field lines are observed to move in and out radially as they are followed toroidally. Power and particle control design based on these observations include the limiting structure geometry and baffles designed to intersect islands outside the LCMS. [1] E.Strumberger, Nuclear Fusion 37 1997 19. [2] S.Hirshman, Comp. Phys. Commun. 43 1986 143.

  12. Resolving the extended stellar haloes of nearby galaxies: the wide-field PISCeS survey

    NASA Astrophysics Data System (ADS)

    Crnojevic, Denija; Sand, David J.; Caldwell, Nelson; Guhathakurta, Puragra; McLeod, Brian A.; Seth, Anil; Simon, Joshua D.; Strader, Jay; Toloba, Elisa

    2015-08-01

    I will present results from the wide-field Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS): we investigate the resolved stellar haloes of two nearby galaxies (the spiral NGC253 and the elliptical Centaurus A, D~3.7 Mpc) out to a galactocentric radius of 150 kpc with Magellan/Megacam. The survey led to the discovery of ~20 faint satellites and stunning streams/substructures in two environments substantially different from the Local Group, i.e. the loose Sculptor group of galaxies and the Centaurus A group dominated by an elliptical. These discoveries clearly testify the past and ongoing accretion processes shaping the haloes of these nearby galaxies, and provide the first complete census of their satellite systems down to an unprecedented M_V<-8. This effectively enables the first direct comparison of external galaxies' resolved haloes to the PAndAS survey. The detailed characterization of the stellar content, shape and gradients in the extended haloes of NGC253, Centaurus A and in their satellites represent crucial constraints to theoretical models of galaxy formation and evolution.

  13. AMUSE-Field I: NUCLEAR X-RAY PROPERTIES OF LOCAL FIELD AND GROUP SPHEROIDS ACROSS THE STELLAR MASS SCALE

    SciTech Connect

    Miller, Brendan; Gallo, Elena; Treu, Tommaso; Woo, Jong-Hak

    2012-03-01

    We present the first results from AMUSE-Field, a Chandra survey designed to characterize the occurrence and intensity of low-level accretion onto supermassive black holes (SMBHs) at the center of local early-type field galaxies. This is accomplished by means of a Large Program targeting a distance-limited (<30 Mpc) sample of 103 early types spanning a wide range in stellar masses. We acquired new ACIS-S observations for 61 objects down to a limiting (0.3-10 keV) luminosity of 2.5 Multiplication-Sign 10{sup 38} erg s{sup -1}, and we include an additional 42 objects with archival (typically deeper) coverage. A nuclear X-ray source is detected in 52 out of the 103 galaxies. After accounting for potential contamination from low-mass X-ray binaries, we estimate that the fraction of accreting SMBHs within the sample is 45% {+-} 7%, which sets a firm lower limit on the occupation fraction within the field. The measured nuclear X-ray luminosities are invariably highly sub-Eddington, with L{sub X}/L{sub Edd} ratios between {approx}10{sup -4} and 10{sup -8}. As also found in a companion survey targeting Virgo early types, the active fraction increases with increasing host galaxy stellar mass, reflective of 'Eddington incompleteness' within the lower-mass objects. For the Field sample, the average nuclear X-ray luminosity scales with the host stellar mass as M{sup 0.71{+-}0.10}{sub star}, with an intrinsic scatter of 0.73 {+-} 0.09 dex. Qualitatively similar results hold for morphologically homogeneous (type E) or uniform sensitivity (new observations only) subsets. A majority of the AMUSE-Field galaxies (78%) inhabit groups, enabling us to investigate the influence of group richness on nuclear activity. We see no evidence for a positive correlation between nuclear X-ray luminosity, normalized to host properties, and galaxy density. Rather, while the scatter is substantial, it appears that the Eddington-scaled X-ray luminosity of group members may be slightly lower than for

  14. AMUSE-Field I: Nuclear X-Ray Properties of Local Field and Group Spheroids across the Stellar Mass Scale

    NASA Astrophysics Data System (ADS)

    Miller, Brendan; Gallo, Elena; Treu, Tommaso; Woo, Jong-Hak

    2012-03-01

    We present the first results from AMUSE-Field, a Chandra survey designed to characterize the occurrence and intensity of low-level accretion onto supermassive black holes (SMBHs) at the center of local early-type field galaxies. This is accomplished by means of a Large Program targeting a distance-limited (<30 Mpc) sample of 103 early types spanning a wide range in stellar masses. We acquired new ACIS-S observations for 61 objects down to a limiting (0.3-10 keV) luminosity of 2.5 × 1038 erg s-1, and we include an additional 42 objects with archival (typically deeper) coverage. A nuclear X-ray source is detected in 52 out of the 103 galaxies. After accounting for potential contamination from low-mass X-ray binaries, we estimate that the fraction of accreting SMBHs within the sample is 45% ± 7%, which sets a firm lower limit on the occupation fraction within the field. The measured nuclear X-ray luminosities are invariably highly sub-Eddington, with L X/L Edd ratios between ~10-4 and 10-8. As also found in a companion survey targeting Virgo early types, the active fraction increases with increasing host galaxy stellar mass, reflective of "Eddington incompleteness" within the lower-mass objects. For the Field sample, the average nuclear X-ray luminosity scales with the host stellar mass as M 0.71 ± 0.10 star, with an intrinsic scatter of 0.73 ± 0.09 dex. Qualitatively similar results hold for morphologically homogeneous (type E) or uniform sensitivity (new observations only) subsets. A majority of the AMUSE-Field galaxies (78%) inhabit groups, enabling us to investigate the influence of group richness on nuclear activity. We see no evidence for a positive correlation between nuclear X-ray luminosity, normalized to host properties, and galaxy density. Rather, while the scatter is substantial, it appears that the Eddington-scaled X-ray luminosity of group members may be slightly lower than for isolated galaxies, and that this trend continues to cluster early types.

  15. Star-gas decoupling and a non-rotating stellar core in He 2-10. Integral field spectroscopy with FLAMES/ARGUS

    NASA Astrophysics Data System (ADS)

    Marquart, T.; Fathi, K.; Östlin, G.; Bergvall, N.; Cumming, R. J.; Amram, P.

    2007-10-01

    Aims:We study the two-dimensional distribution and kinematics of the stellar and gaseous components in the centre of the blue compact dwarf galaxy He 2-10. The aim is to compare the kinematics of gas and stars in order to determine whether they are consistent with one another, or if stars and gas can be decoupled due to gravitational perturbations and feedback from star formation. Methods: We have used the integral field unit ARGUS, part of FLAMES on the European Southern Observatory's Very Large Telescope, to target the Ca ii λλ8498,8542,8662 Å triplet in the central 300 × 480 parsecs of He 2-10. The selected wavelength regime includes several prominent spectral features, including the Paschen series and the [S iii] emission-line, which we have used to derive the kinematics of the ionised interstellar medium. Results: We find no systematic trend in the velocities of the stars over the observed field of view and conclude that the stellar kinematics is governed by random motions. This is in contrast to the motions the ionised interstellar medium, where we find spatial velocity variations up to 60 km s-1. Our gas velocity field is consistent with previous studies of both the molecular gas and the feedback-driven outflow in He 2-10. We interpret the kinematic decoupling between the stars and the gas as He 2-10 being in the process of transformation to a dwarf elliptical galaxy. Based on observations collected at the European Southern Observatory, Paranal, Chile, under observing programme 74.B-0771.

  16. State of the Field: Extreme Precision Radial Velocities

    NASA Astrophysics Data System (ADS)

    Fischer, Debra A.; Anglada-Escude, Guillem; Arriagada, Pamela; Baluev, Roman V.; Bean, Jacob L.; Bouchy, Francois; Buchhave, Lars A.; Carroll, Thorsten; Chakraborty, Abhijit; Crepp, Justin R.; Dawson, Rebekah I.; Diddams, Scott A.; Dumusque, Xavier; Eastman, Jason D.; Endl, Michael; Figueira, Pedro; Ford, Eric B.; Foreman-Mackey, Daniel; Fournier, Paul; Fűrész, Gabor; Gaudi, B. Scott; Gregory, Philip C.; Grundahl, Frank; Hatzes, Artie P.; Hébrard, Guillaume; Herrero, Enrique; Hogg, David W.; Howard, Andrew W.; Johnson, John A.; Jorden, Paul; Jurgenson, Colby A.; Latham, David W.; Laughlin, Greg; Loredo, Thomas J.; Lovis, Christophe; Mahadevan, Suvrath; McCracken, Tyler M.; Pepe, Francesco; Perez, Mario; Phillips, David F.; Plavchan, Peter P.; Prato, Lisa; Quirrenbach, Andreas; Reiners, Ansgar; Robertson, Paul; Santos, Nuno C.; Sawyer, David; Segransan, Damien; Sozzetti, Alessandro; Steinmetz, Tilo; Szentgyorgyi, Andrew; Udry, Stéphane; Valenti, Jeff A.; Wang, Sharon X.; Wittenmyer, Robert A.; Wright, Jason T.

    2016-06-01

    The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm s-1 measurement precision. The presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this bold precision are summarized here. Beginning with the High Accuracy Radial Velocity Planet Searcher spectrograph, technological advances for precision radial velocity (RV) measurements have focused on building extremely stable instruments. To reach still higher precision, future spectrometers will need to improve upon the state of the art, producing even higher fidelity spectra. This should be possible with improved environmental control, greater stability in the illumination of the spectrometer optics, better detectors, more precise wavelength calibration, and broader bandwidth spectra. Key data analysis challenges for the precision RV community include distinguishing center of mass (COM) Keplerian motion from photospheric velocities (time correlated noise) and the proper treatment of telluric contamination. Success here is coupled to the instrument design, but also requires the implementation of robust statistical and modeling techniques. COM velocities produce Doppler shifts that affect every line identically, while photospheric velocities produce line profile asymmetries with wavelength and temporal dependencies that are different from Keplerian signals. Exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. However, higher precision RV measurements are required to serve as a discovery technique for potentially habitable worlds, to confirm and characterize detections from transit missions, and to provide mass measurements for other space-based missions. The future of exoplanet science has very different trajectories depending on the precision that can

  17. An Updated Homogeneous GPS Velocity Field for Studies of Earthquake Hazard Prediction and Assessment in Turkey

    NASA Astrophysics Data System (ADS)

    Ozener, H.; Aktug, B.; Dogru, A.; Tasci, L.; Acar, M.

    2016-12-01

    While the GPS-based crustal deformation studies in Turkey date back to early 1990s, a homogenous velocity field utilizing all the available data is still missing. Regional studies employing different site distributions, observation plans, processing software and methodology not only create reference frame variations but also heterogeneous stochastic models. While the reference frame effect between different velocity fields could easily be removed by estimating a set of rotations, the homogenization of the stochastic models of the individual velocity fields requires a more detailed analysis. Using a rigorous Variance Component Estimation (VCE) methodology, we estimated the variance factors for each of the contributing velocity fields and combined them into a single homogenous velocity field covering whole Turkey. Results show that variance factors between velocity fields including the survey mode and continuous observations can vary a few orders of magnitude.In this study, we present the most complete velocity field in Turkey rigorously combined from 20 individual velocity fields including the 146 station CORS network with 8 years continuous stations. In addition, two GPS campaigns were performed at 35 stations along the North Anatolian Fault to fill the gap between existing velocity fields. The homogenously combined new velocity field is nearly complete in terms of geographic coverage, and will serve as the basis for further analyses such as the estimation of the deformation rates and the determination of the slip rates across main fault zones. As the Active Fault Map of Turkey was recently revised and 500 faults were tagged as having the potential of generating destructive earthquakes, the new velocity field is also expected to have a direct impact on the earthquake hazard studies.

  18. Stellar magnetic fields. 1: The role of a magnetic field in the peculiar M giant, HD 4174

    NASA Technical Reports Server (NTRS)

    Stencel, R. E.; Ionson, J. A.

    1979-01-01

    Coronal heating by resonant absorption of Alfvenic surface waves (quiescent), and magnetic tearing instabilities (impulsive), is discussed with emphasis on three principles which may have application to late-type evolved stars. (1) If sq B/8 pi greater than sq. rho V is observed 2 in a stellar atmosphere, then the observed magnetic field must originate in an interior dynamo. (2) Low mass loss rates could imply the presence of closed magnetic flux loops within the outer atmosphere which constrain hydrodynamic flows when the magnetic body forces exceed the driving forces. (3) given that such magnetic loops effect an enhancement of the local heating rate, a positive correlation is predicted between the existence of a corona and low mass loss rates. These principles are applied to the M giant star HD 4174, which is purported to have a kilogauss magnetic field. Several of its spectroscopic peculiarities are shown to be consistent with the above principles, and further observational checks are suggested.

  19. Magnetic field and temperature dependence of the critical vortex velocity in type-II superconducting films.

    PubMed

    Grimaldi, G; Leo, A; Cirillo, C; Attanasio, C; Nigro, A; Pace, S

    2009-06-24

    We study the vortex dynamics in the instability regime induced by high dissipative states well above the critical current in Nb superconducting strips. The magnetic field and temperature behavior of the critical vortex velocity corresponding to the observed dynamic instability is ascribed to intrinsic non-equilibrium phenomena. The Larkin-Ovchinnikov (LO) theory of electronic instability in high velocity vortex motion has been applied to interpret the temperature dependence of the critical vortex velocity. The magnetic field dependence of the vortex critical velocity shows new features in the low-field regime not predicted by LO.

  20. Seismic imaging for velocity and attenuation structure in geothermal fields

    SciTech Connect

    Zucca, J.J. ); Evans, J.R. )

    1989-06-01

    We have applied the attenuation inversion technique developed by Evans and Zucca (1988) to a seismic tomographic data set taken at Newberry Volcano by Achauer et al. (1988). Our preliminary results suggest that the interpretation of the velocity data by Achauer et al. that a magma chamber is present 3 km beneath the caldera is not confirmed by the attenuation data.

  1. Determination of radial electric field from Pfirsch–Schlüter flows in the HSX stellarator

    NASA Astrophysics Data System (ADS)

    Kumar, S. T. A.; Talmadge, J. N.; Dobbins, T. J.; Anderson, F. S. B.; Likin, K. M.; Anderson, D. T.

    2017-03-01

    Inboard/outboard asymmetry in the impurity ion parallel flow is observed in the HSX stellarator using charge exchange recombination spectroscopy (CHERS). This observation shows the presence of counter-streaming Pfirsch–Schlüter flow predicted by neoclassical theory. The asymmetry of the flow is used to calculate the magnitude and direction of the radial electric field (E r), as well as the mean flow, using computed magnetic geometry factors. This method enables calculation of E r near the core of the HSX plasma where the E r obtained from the radial force balance equation has large uncertainties due to the relatively large width of the diagnostic neutral beam with respect to the plasma minor radius.

  2. Dynamical population synthesis: constructing the stellar single and binary contents of galactic field populations

    NASA Astrophysics Data System (ADS)

    Marks, Michael; Kroupa, Pavel

    2011-11-01

    The galactic field's late-type stellar single and binary populations are calculated on the observationally well-constrained supposition that all stars form as binaries with invariant properties in discrete star formation events. A recently developed tool (Marks, Kroupa & Oh) is used to evolve the binary star distributions in star clusters for a few million years until an equilibrium situation is achieved which has a particular mixture of single and binary stars. On cluster dissolution the population enters the galactic field with these characteristics. The different contributions of single stars and binaries from individual star clusters, which are selected from a power-law-embedded star cluster mass function, are then added up. This gives rise to integrated galactic field binary distribution functions (IGBDFs), resembling a galactic field's stellar content (dynamical population synthesis). It is found that the binary proportion in the galactic field of a galaxy is larger the lower the minimum cluster mass, Mecl, min, the lower the star formation rate, SFR, the steeper the embedded star cluster mass function (described by index β) and the larger the typical size of forming star clusters in the considered galaxy. In particular, period, mass ratio and eccentricity IGBDFs for the Milky Way (MW) are modelled using Mecl, min= 5 M⊙, SFR = 3 M⊙ yr-1 and β= 2 which are justified by observations. For rh≈ 0.1-0.3 pc, the half-mass radius of an embedded cluster, the aforementioned theoretical IGBDFs agree with independently observed distributions, suggesting that the individual discrete star formation events in the MW generally formed compact star clusters. Of all late-type binaries, 50 per cent stem from Mecl≲ 300 M⊙ clusters, while 50 per cent of all single stars were born in Mecl≳ 104 M⊙ clusters. Comparison of the G-dwarf and M-dwarf binary populations indicates that the stars are formed in mass-segregated clusters. In particular, it is pointed out that

  3. Virgo cluster and field dwarf ellipticals in 3D - III. Spatially and temporally resolved stellar populations

    NASA Astrophysics Data System (ADS)

    Ryś, Agnieszka; Koleva, Mina; Falcón-Barroso, Jesús; Vazdekis, Alexandre; Lisker, Thorsten; Peletier, Reynier; van de Ven, Glenn

    2015-09-01

    We present the stellar population analysis of a sample of 12 dwarf elliptical galaxies, observed with the SAURON integral field unit, using the full-spectrum fitting method. We show that star formation histories (SFHs) resolved into two populations can be recovered even within a limited wavelength range, provided that high signal-to-noise ratio (S/N) data are used. We confirm that dEs have had complex SFHs, with star formation extending to (more) recent epochs: for the majority of our galaxies star formation activity was either still strong a few (≲5) Gyr ago or they experienced a secondary burst of star formation roughly at that time. This latter possibility is in agreement with the proposed dE formation scenario where tidal harassment drives the gas remaining in their progenitors inwards and induces a star formation episode. For one of our field galaxies, ID 0918, we find a correlation between its stellar population and kinematic properties, pointing to a possible merger origin of its kinematically decoupled core. One of our cluster objects, VCC 1431, appears to be composed exclusively of an old population (≳10-12 Gyr). Combining this with our earlier dynamical results, we conclude that the galaxy was either ram-pressure stripped early on in its evolution in a group environment and subsequently tidally heated, or that it evolved in situ in the cluster's central parts, compact enough to avoid tidal disruption. These are only two of the examples illustrating the SFH richness of these objects confirmed with our data.

  4. Some features of the radial-velocity variations of lines of different intensity in the spectrum of HD 93521. Variability of the stellar wind

    NASA Astrophysics Data System (ADS)

    Rzaev, A. Kh.

    2007-12-01

    CCD spectra taken with the PFES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences are used to perform a detailed study of the variability of the profiles of Hell, H β, and H α lines in the spectrum of HD 93521. The pattern and nature of the variability of the Hell lines are similar to those of weak HeI lines and are due to nonradial pulsations. The period and amplitude of the radial-velocity variations are the same for the blue and red halves of the absorption profile but their phases are opposite. The behavior of the variations of H β and H α hydrogen lines relative to their mean profiles is the same as that of strong HeI line and is due to nonradial pulsations. The period and phase of the radial-velocity oscillations are the same for the blue and red halves of the absorption profile but their amplitude are different. The behavior of the radial-velocity variations of the absorption and emission components of the H α line indicates that the latter also are caused by nonradial pulsations. All this is indicative of the complex structure of the stellar wind in the region of its origin. The behavior of variability and wind kinematics differ in different directions and for different regions of the atmosphere and/or envelope.

  5. Far-Field and Middle-Field Vertical Velocities Associated with Megathrust Earthquakes

    NASA Astrophysics Data System (ADS)

    Fleitout, L.; Trubienko, O.; Klein, E.; Vigny, C.; Garaud, J.; Shestakov, N.; Satirapod, C.; Simons, W. J.

    2013-12-01

    The recent megathrust earthquakes (Sumatra, Chili and Japan) have induced far-field postseismic subsidence with velocities from a few mm/yr to more than 1cm/yr at distances from 500 to 1500km from the earthquake epicentre, for several years following the earthquake. This subsidence is observed in Argentina, China, Korea, far-East Russia and in Malaysia and Thailand as reported by Satirapod et al. ( ASR, 2013). In the middle-field a very pronounced uplift is localized on the flank of the volcanic arc facing the trench. This is observed both over Honshu, in Chile and on the South-West coast of Sumatra. In Japan, the deformations prior to Tohoku earthquake are well measured by the GSI GPS network: While the East coast was slightly subsiding, the West coast was raising. A 3D finite element code (Zebulon-Zset) is used to understand the deformations through the seismic cycle in the areas surrounding the last three large subduction earthquakes. The meshes designed for each region feature a broad spherical shell portion with a viscoelastic asthenosphere. They are refined close to the subduction zones. Using these finite element models, we find that the pattern of the predicted far-field vertical postseismic displacements depends upon the thicknesses of the elastic plate and of the low viscosity asthenosphere. A low viscosity asthenosphere at shallow depth, just below the lithosphere is required to explain the subsidence at distances from 500 to 1500km. A thick (for example 600km) asthenosphere with a uniform viscosity predicts subsidence too far away from the trench. Slip on the subduction interface is unable tot induce the observed far-field subsidence. However, a combination of relaxation in a low viscosity wedge and slip or relaxation on the bottom part of the subduction interface is necessary to explain the observed postseismic uplift in the middle-field (volcanic arc area). The creep laws of the various zones used to explain the postseismic data can be injected in

  6. Massive spectroscopic analysis of the stellar populations in three of the CoRoT/Exoplanet fields

    NASA Astrophysics Data System (ADS)

    Gazzano, J.-C.; Deleuil, M.; de Laverny, P.; Kordopatis, G.; Moutou, C.; Recio-Blanco, A.; Bijaoui, A.; Bouchy, F.; Ordenovic, C.

    2010-12-01

    We derived the atmospheric parameters (teff, logg, met, alf), řad, and šini for 1227 CoRoT/Exoplanet targets in three of the fields observed by CoRoT. We derived the corresponding absolute magnitude using evolutionary models. We combined 2MASS colours with a new implementation of the infrared flux method, and the teff from matisse to constrain the interstellar extinction. These steps allowed us to measure the stellar distances, hence deriving kinematics information. This opened the path to the study of the stellar populations found in these \\corot fields.These studies showed the potential of combining a multi-fiber instrument like FLAMES/GIRAFFE, with an automatic tool to determine efficiently atmospheric stellar parameters, as MATISSE.

  7. Characterizing the original ejection velocity field of the Koronis family

    NASA Astrophysics Data System (ADS)

    Carruba, V.; Nesvorný, D.; Aljbaae, S.

    2016-06-01

    An asteroid family forms as a result of a collision between an impactor and a parent body. The fragments with ejection speeds higher than the escape velocity from the parent body can escape its gravitational pull. The cloud of escaping debris can be identified by the proximity of orbits in proper element, or frequency, domains. Obtaining estimates of the original ejection speed can provide valuable constraints on the physical processes occurring during collision, and used to calibrate impact simulations. Unfortunately, proper elements of asteroids families are modified by gravitational and non-gravitational effects, such as resonant dynamics, encounters with massive bodies, and the Yarkovsky effect, such that information on the original ejection speeds is often lost, especially for older, more evolved families. It has been recently suggested that the distribution in proper inclination of the Koronis family may have not been significantly perturbed by local dynamics, and that information on the component of the ejection velocity that is perpendicular to the orbital plane (vW), may still be available, at least in part. In this work we estimate the magnitude of the original ejection velocity speeds of Koronis members using the observed distribution in proper eccentricity and inclination, and accounting for the spread caused by dynamical effects. Our results show that (i) the spread in the original ejection speeds is, to within a 15% error, inversely proportional to the fragment size, and (ii) the minimum ejection velocity is of the order of 50 m/s, with larger values possible depending on the orbital configuration at the break-up.

  8. Solar velocity field determined tracking coronal bright points

    NASA Astrophysics Data System (ADS)

    Brajša, R.; Sudar, D.; Skokić, I.; Saar, S. H.; Žic, T.

    Preliminary data from Atmospheric Imaging Assembly (AIA) instrumenton board Solar Dynamics Observatory (SDO) satellite were used to determine solar differential rotation and related phenomena. A segmentation algorithm, which uses multiple AIA channels in search for intensity enhancements in EUV and X-ray parts of the spectrum compared to the background intensity, was applied to obtain positional information of coronal bright points (CBPs). More than 60000 position measurements of more than 10000 identified CBPs from the period 1 - 2 January 2011 were analyzed. Rotational and meridional velocities were determined by tracking identified CBPs and various filters were used to exclude erroneous results. Also, proper motions of CBPs were calculated from rotation velocity residuals and meridional velocities. Proper motions of CBPs were investigated using a random walk model and the diffusion constant was calculated. These results were compared with the previous ones obtained by other instruments and methods (especially with the SOHO-EIT and Hinode data) and a striking agreement of the obtained diffusion constant with results from other studies was found.

  9. Global Neuromagnetic Cortical Fields Have Non-Zero Velocity

    PubMed Central

    Alexander, David M.; Nikolaev, Andrey R.; Jurica, Peter; Zvyagintsev, Mikhail; Mathiak, Klaus; van Leeuwen, Cees

    2016-01-01

    Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain activity measures across-trials, whether prior to source localization or for estimating inter-areal coherence. We analyzed, at single-trial level, whole head MEG recorded during an observer-triggered apparent motion task. Episodes of globally coherent activity occurred in the delta, theta, alpha and beta bands of the signal in the form of large-scale waves, which propagated with a variety of velocities. Their mean speed at each frequency band was proportional to temporal frequency, giving a range of 0.06 to 4.0 m/s, from delta to beta. The wave peaks moved over the entire measurement array, during both ongoing activity and task-relevant intervals; direction of motion was more predictable during the latter. A large proportion of the cortical signal, measurable at the scalp, exists as large-scale coherent motion. We argue that the distribution of observable phase velocities in MEG is dominated by spatial filtering considerations in combination with group velocity of cortical activity. Traveling waves may index processes involved in global coordination of cortical activity. PMID:26953886

  10. Velocity Reconstruction of Arbitrary Shaped Incompressible Flow Field with Noises Using Seamless Immersed Boundary Method

    NASA Astrophysics Data System (ADS)

    Nishida, Hidetoshi

    In order to reconstruct the arbitrary shaped incompressible velocity field with noises, a new data-processing fluid dynamics (DFD) based upon the seamless immersed boundary method is proposed. The velocity field with noises is reconstructed by the Helmholtz's decomposition. The performance of DFD is demonstrated first for the reconstruction of velocity with noises and erroneous vectors. Also, the seamless immersed boundary method is incorporated into the velocity reconstruction for complicated flow geometry. Some fundamental flow fields, i.e., the square cavity flows with a circular cylinder and a square cylinder, are considered. As a result, it is concluded that the present DFD based upon the seamless immersed boundary method is very versatile technique for velocity reconstruction of the arbitrary shaped incompressible velocity with noises.

  11. K- band integral field spectroscopy and optical spectroscopy of massive young stellar objects in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Ward, J. L.; Oliveira, J. M.; van Loon, J. Th.; Sewiło, M.

    2017-01-01

    We present K-band integral field spectroscopic observations towards 17 massive young stellar objects (YSOs) in the low-metallicity Small Magellanic Cloud (SMC) and two YSO candidates in the compact H II regions N81 and N88 A (also in the SMC). These sources, originally identified using Spitzer photometry and/or spectroscopy, have been resolved into 29 K-band continuum sources. By comparing Brγ emission luminosities with those presented for a Galactic sample of massive YSOs, we find tentative evidence for increased accretion rates in the SMC. Around half of our targets exhibit emission-line (Brγ, He I and H2) morphologies that extend significantly beyond the continuum source and we have mapped both the emission morphologies and the radial velocity fields. This analysis also reveals evidence for the existence of ionized low-density regions in the centre outflows from massive YSOs. Additionally, we present an analysis of optical spectra towards a similar sample of massive YSOs in the SMC, revealing that the optical emission is photoexcited and originates near the outer edges of molecular clouds, and is therefore consistent with a high mean-free path of UV photons in the interstellar medium (ISM) of the SMC. Finally, we discuss the sample of YSOs in an evolutionary context incorporating the results of previous infrared and radio observations, as well as the near-infrared and optical observations presented in this work. Our spectroscopic analysis in both the K band and the optical regimes, combined with previously obtained infrared and radio data, exposes differences between properties of massive YSOs in our own Galaxy and the SMC, including tracers of accretion, discs and YSO-ISM interactions.

  12. Magnetic domain-wall velocity enhancement induced by a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Yang, Jusang; Beach, Geoffrey S. D.; Knutson, Carl; Erskine, James L.

    2016-01-01

    Spin dynamics of field-driven domain walls (DWs) guided by permalloy nanowires are studied by high-speed magneto-optic polarimetry and numerical simulations. DW velocities and spin configurations are determined as functions of longitudinal drive field, transverse bias field, and nanowire width. Nanowires having cross-sectional dimensions large enough to support vortex wall structures exhibit regions of drive-field strength (at zero bias field) that have enhanced DW velocity resulting from coupled vortex structures that suppress oscillatory motion. Factor of 10 enhancements of the DW velocity are observed above the critical longitudinal drive-field (that marks the onset of oscillatory DW motion) when a transverse bias field is applied. Nanowires having smaller cross-sectional dimensions that support transverse wall structures also exhibit a region of higher mobility above the critical field, and similar transverse-field induced velocity enhancement but with a smaller enhancement factor. The bias-field enhancement of DW velocity is explained by numerical simulations of the spin distribution and dynamics within the propagating DW that reveal dynamic stabilization of coupled vortex structures and suppression of oscillatory motion in the nanowire conduit resulting in uniform DW motion at high speed. The enhanced velocity and drive field range are achieved at the expense of a less compact DW spin distribution.

  13. Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars

    NASA Astrophysics Data System (ADS)

    Bychkov, V. D.; Bychkova, L. V.; Madej, J.

    2003-08-01

    This paper presents the catalogue and the method of determination of averaged quadratic effective magnetic fields < B_e > for 596 main sequence and giant stars. The catalogue is based on measurements of the stellar effective (or mean longitudinal) magnetic field strengths B_e, which were compiled from the existing literature. We analysed the properties of 352 chemically peculiar A and B stars in the catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, and all ApSr type stars. We have found that the number distribution of all chemically peculiar (CP) stars vs. averaged magnetic field strength is described by a decreasing exponential function. Relations of this type hold also for stars of all the analysed subclasses of chemical peculiarity. The exponential form of the above distribution function can break down below about 100 G, the latter value representing approximately the resolution of our analysis for A type stars. Table A.1 and its references are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9 are only available in electronic form at http://www.edpsciences.org

  14. Disorder-induced domain wall velocity shift at high fields in perpendicularly magnetized thin films

    NASA Astrophysics Data System (ADS)

    Voto, Michele; Lopez-Diaz, Luis; Torres, Luis; Moretti, Simone

    2016-11-01

    Domain wall dynamics in a perpendicularly magnetized system is studied by means of micromagnetic simulations in which disorder is introduced as a dispersion of both the easy-axis orientation and the anisotropy constant over regions reproducing a granular structure of the material. High field dynamics show a linear velocity-field relationship and an additional grain size dependent velocity shift, weakly dependent on both applied field and intrinsic Gilbert's damping parameter. We find the origin of this velocity shift in the nonhomogeneous in-plane effective field generated by the tilting of anisotropy easy axis introduced by disorder. We show that a one-dimensional analytical approach cannot predict the observed velocities and we augment it with the additional dissipation of energy arising from internal domain wall dynamics triggered by disorder. This way we prove that the main cause of higher velocity is the ability of the domain wall to irradiate energy into the domains, acquired with a precise feature of disorder.

  15. Advanced stellarators

    NASA Astrophysics Data System (ADS)

    Schlüter, Arnulf

    1983-03-01

    Toroidal confinement of a plasma by an external magnetic field is not compatible with axisymmetry, in contrast to confinement by the pinch effect of induced electric currents as in a tokomak or by the reversed field pinch configuration. The existence of magnetic surfaces throughout the region in which grad p ≠ 0 is therefore not guaranteed in such configurations, though it is necessary for MHD-equilibrium when the lines of force possess a finite twist (or "rotational transform"). These twisted equilibria are called stellarators. The other type of external confinement requires all lines of force to be closed upon themselves and p to be function of the well defined quantity Q = φ d l/ B only. The resulting "bumpy" tori are sometimes also referred to as being M + S like. By discussing specific examples it is shown that stellarator configurations exist which retain as much as possible the properties of M + S like configurations, combine these with the magnetic well, and with an approximation to the isodynamic requirement of D. Palumbo. These so-called Advanced Stellarators shown an improvement in predicted particle confinement and beta-limit compared to the classical stellarators. They can also be viewed as forming a system of linked stabilized mirrors of small mirror ratio. These fields can be produced by modular coils. A prototype of such a configuration is being designed by the stellarator division of IPP under the name of Wendelstein VII-AS. Expected physical data and technical details of W VII-AS are given.

  16. Investigating magnetic activity in very stable stellar magnetic fields. Long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Pegasi

    NASA Astrophysics Data System (ADS)

    Vida, K.; Kriskovics, L.; Oláh, K.; Leitzinger, M.; Odert, P.; Kővári, Zs.; Korhonen, H.; Greimel, R.; Robb, R.; Csák, B.; Kovács, J.

    2016-05-01

    The ultrafast-rotating (Prot ≈ 0.44 d) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in a stable magnetic topology. As an observable proxy for the stellar magnetic field, we study the stability of the light curve, hence the spot configuration. We also measure the occurrence rate of flares and coronal mass ejections (CMEs). We have analysed spectroscopic observations, BV(RI)C photometry covering 5 yrs, and additional RC photometry that expands the temporal base over 16 yr. The light curve suggests an almost rigid-body rotation and a spot configuration that is stable over about 16 yrs, confirming the previous indications of a very stable magnetic field. We observed small changes on a nightly timescale and frequent flaring, including a possible sympathetic flare. The strongest flares seem to be more concentrated around the phase where the light curve indicates a smaller active region. Spectral data suggest a complex CME with falling-back and re-ejected material with a maximal projected velocity of ~675 km s-1. We observed a CME rate that is much lower than expected from extrapolations of the solar flare-CME relation to active stars. Tables of the photometry 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/590/A11

  17. Ultra-diffuse Galaxies in Clusters and the Field: Masses and Stellar Populations

    NASA Astrophysics Data System (ADS)

    Romanowsky, Aaron; Laine, Seppo; Krick, Jessica; van Dokkum, Pieter; Villaume, Alexa; Brodie, Jean

    2016-08-01

    Ultra-diffuse galaxies (UDGs) were recognized only last year as a novel class of galaxies, with luminosities like dwarfs but sizes like giants. Although some UDGs appear to be just unusually extended dwarfs, others show evidence of being very different and unexpected: their dark matter halos are overmassive by factors of ~10, with one UDG even being arguably a 'failed Milky Way.' These exotic galaxies might be a byproduct of environmental processes within galaxy clusters, but UDGs have also now been found in the field. It is crucial for understanding their origins to test if UDGs have the same properties in cluster and field environments. Here we propose studying the stellar populations (ages and metallicities) of seven UDGs using Spitzer/IRAC 3.6- and 4.5-micron imaging combined with optical photometry, along with mass estimation of three of the UDGs using HST/ACS imaging to provide globular cluster number counts and colors (proxies for halo mass). This ultra low surface brightness photometry in the near infrared, on an important new class of galaxies, could become a legacy result from the Spitzer mission.

  18. Electric field due to velocity space particle loss in field-reversed configurations

    SciTech Connect

    Hsiao, M.; Staudenmeier, J.L.; Chiang, P.

    1989-02-01

    Particle confinement criteria for velocity space particle loss are used to calculate the radial and axial electric potential profiles in field-reversed configurations (FRC's). Assuming Vlasov equilibrium distribution functions for both electrons and ions, the density profile and the potential profile are calculated self-consistently. With rest Maxwellian distribution functions for both species and the Hill's vortex magnetic configuration, a radial electric field of about 0--70 V/cm and an axial electric field of about 0--4 V/cm, depending on positions, have been found for a typical set of experimental parameters: electron temperature T/sub e/ = 100 eV, ion temperature T/sub i/ = 200 eV, magnetic field B/sub 0/ = 5500 G, separatrix radius r/sub s/ = 12 cm, and elongation factor k = 5. The corresponding density profile has behavior similar to profiles observed in the experiments. Cases using rigid-rotor distribution functions with different rigid rotating frequencies are also studied.

  19. Laser transit anemometer measurements of a JANNAF nozzle base velocity flow field

    NASA Technical Reports Server (NTRS)

    Hunter, William W., Jr.; Russ, C. E., Jr.; Clemmons, J. I., Jr.

    1990-01-01

    Velocity flow fields of a nozzle jet exhausting into a supersonic flow were surveyed. The measurements were obtained with a laser transit anemometer (LTA) system in the time domain with a correlation instrument. The LTA data is transformed into the velocity domain to remove the error that occurs when the data is analyzed in the time domain. The final data is shown in velocity vector plots for positions upstream, downstream, and in the exhaust plane of the jet nozzle.

  20. Properties of velocity field in the vicinity of synthetic jet generator

    NASA Astrophysics Data System (ADS)

    Strzelczyk, P.; Gil, P.

    2016-10-01

    The paper presents the results of experimental investigation of velocity field in the vicinity of synthetic jet actuator as a function of Stokes number and for constant Reynolds number. A constant temperature hot-wire anemometer with tungsten-platinum coated single wire probe used for the velocity measurements. Synthetic jet flow visualization was presented, especially process of vortex ring development. Synthetic jet velocity profiles were compared with a solution to fully-developed pipe flow with an oscillating pressure gradient.

  1. Metallicities and radial velocities of two stellar clusters located in the outer regions of the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Gramajo, L. V.; Parisi, M. C.; Clariá, J. J.; Geisler, D.; Vásquez, S.; Da Costa, G.; Grebel, E. K.

    2016-08-01

    We studied near-infrared spectra of red giant stars in two Small Magellanic Cloud (SMC) clusters. We used the Caii lines to measure radial velocities as well as the equivalent widths of these lines to determine metallicity. The two studied clusters (L32 and L38) are projected on the outer regions of the SMC so they are particularly interesting to examine the possible existence of a change of sign in the metallicity gradient in the outer regions, as suggested by a recent study.

  2. VELOCITY-FIELD MEASUREMENTS OF A SHOCK-ACCELERATED FLUID INSTABILITY

    SciTech Connect

    K. PRESTRIDGE; C. ZOLID; ET AL

    2001-05-01

    A cylinder of heavy gas (SF{sub 6}) in air is hit by a Mach 1.2 shock. The resultant Richtmyer-Meshkov instability is observed as it propagates through the test section of the shock tube. Six images are taken after shock impact, and the velocity field at one time is measured using Particle Image Velocimetry (PIV). The images of the density field show the development of a secondary instability in the cylinder. The velocity field provides us with information about the magnitudes of the velocities as well as the magnitude of the vorticity in the flow.

  3. Fast measurements of average flow velocity by Low-Field ¹H NMR.

    PubMed

    Osán, T M; Ollé, J M; Carpinella, M; Cerioni, L M C; Pusiol, D J; Appel, M; Freeman, J; Espejo, I

    2011-04-01

    In this paper, we describe a method for measuring the average flow velocity of a sample by means of Nuclear Magnetic Resonance. This method is based on the Carr-Purcell-Meiboom-Gill (CPMG) sequence and does not require the application of any additional static or pulsed magnetic field gradients to the background magnetic field. The technique is based on analyzing the early-time behavior of the echo amplitudes of the CPMG sequence. Measurements of average flow velocity of water are presented. The experimental results show a linear relationship between the slope/y-intercept ratio of a linear fit of the first echoes in the CPMG sequence, and the average flow velocity of the flowing fluid. The proposed method can be implemented in low-cost Low-Field NMR spectrometers allowing a continuous monitoring of the average velocity of a fluid in almost real-time, even if the flow velocity changes rapidly.

  4. Velocity field control of a class of electrically-driven manipulators

    NASA Astrophysics Data System (ADS)

    Moreno-Valenzuela, Javier; Campa, Ricardo; Santibáñez, Víctor

    2014-03-01

    This article addresses the control of robotic manipulators under the assumption that the desired motion in the operational space is encoded through a velocity field. In other words, a vectorial function assigns a velocity vector to each point in the robot workspace. Thus, the control objective is to design a control input such that the actual operational space velocity of the robot end-effector asymptotically tracks the desired velocity from the velocity field. This control formulation is known in the literature as velocity field control. A new velocity field controller together with a rigorous stability analysis is introduced in this article. The controller is developed for a class of electrically-driven manipulators. In this class of manipulators, the passivity property from the servo-amplifier voltage input to the joint velocity is not satisfied. However, global exponential stability of the state space origin of the closed-loop system is proven. Furthermore, the closed-loop system is proven to be and output strictly passive map from an auxiliary input to a filtered error signal. To confirm the theoretical conclusions, a detailed experimental study in a two degrees-of-freedom direct-drive manipulator is provided. Particularly, experiments consist of comparing the performance of a simple PI controller and a high-gain PI controller with respect to the new control scheme.

  5. Looking for imprints of the first stellar generations in metal-poor bulge field stars

    NASA Astrophysics Data System (ADS)

    Siqueira-Mello, C.; Chiappini, C.; Barbuy, B.; Freeman, K.; Ness, M.; Depagne, E.; Cantelli, E.; Pignatari, M.; Hirschi, R.; Frischknecht, U.; Meynet, G.; Maeder, A.

    2016-09-01

    Context. Efforts to look for signatures of the first stars have concentrated on metal-poor halo objects. However, the low end of the bulge metallicity distribution has been shown to host some of the oldest objects in the Milky Way and hence this Galactic component potentially offers interesting targets to look at imprints of the first stellar generations. As a pilot project, we selected bulge field stars already identified in the ARGOS survey as having [Fe/H] ≈-1 and oversolar [α/Fe] ratios, and we used FLAMES-UVES to obtain detailed abundances of key elements that are believed to reveal imprints of the first stellar generations. Aims: The main purpose of this study is to analyse selected ARGOS stars using new high-resolution (R ~ 45 000) and high-signal-to-noise (S/N> 100) spectra. We aim to derive their stellar parameters and elemental ratios, in particular the abundances of C, N, the α-elements O, Mg, Si, Ca, and Ti, the odd-Z elements Na and Al, the neutron-capture s-process dominated elements Y, Zr, La, and Ba, and the r-element Eu. Methods: High-resolution spectra of five field giant stars were obtained at the 8 m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. Spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fe i and Fe ii. The abundance analysis was performed with a MARCS LTE spherical model atmosphere grid and the Turbospectrum spectrum synthesis code. Results: We confirm that the analysed stars are moderately metal-poor (-1.04 ≤ [Fe/H] ≤-0.43), non-carbon-enhanced (non-CEMP) with [C/Fe] ≤ + 0.2, and α-enhanced. We find that our three most metal-poor stars are nitrogen enhanced. The α-enhancement suggests that these stars were formed from a gas enriched by core-collapse supernovae, and that the values are in agreement with results in the literature for bulge stars in the same metallicity range. No abundance anomalies (Na - O, Al - O, Al - Mg anti-correlations) were

  6. Hα LINE PROFILE ASYMMETRIES AND THE CHROMOSPHERIC FLARE VELOCITY FIELD

    SciTech Connect

    Kuridze, D.; Mathioudakis, M.; Kennedy, M.; Keenan, F. P.; Simões, P. J. A.; Voort, L. Rouppe van der; Fletcher, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski, A. F.; Graham, D.

    2015-11-10

    The asymmetries observed in the line profiles of solar flares can provide important diagnostics of the properties and dynamics of the flaring atmosphere. In this paper the evolution of the Hα and Ca ii λ8542 lines are studied using high spatial, temporal, and spectral resolution ground-based observations of an M1.1 flare obtained with the Swedish 1 m Solar Telescope. The temporal evolution of the Hα line profiles from the flare kernel shows excess emission in the red wing (red asymmetry) before flare maximum and excess in the blue wing (blue asymmetry) after maximum. However, the Ca ii λ8542 line does not follow the same pattern, showing only a weak red asymmetry during the flare. RADYN simulations are used to synthesize spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. We show that the red asymmetry observed in Hα is not necessarily associated with plasma downflows, and the blue asymmetry may not be related to plasma upflows. Indeed, we conclude that the steep velocity gradients in the flaring chromosphere modify the wavelength of the central reversal in the Hα line profile. The shift in the wavelength of maximum opacity to shorter and longer wavelengths generates the red and blue asymmetries, respectively.

  7. Velocity Field Measurements Downstream of a Reynolds Ridge

    NASA Astrophysics Data System (ADS)

    Vogel, M. J.; Hirsa, A. H.; Kelley, J. S.; Korenowski, G. M.

    1999-11-01

    Reported values of the intrinsic interfacial viscosities for a surfactant-influenced air/water interface have been inconsistent despite their importance in the governing flow equations. The present experiment involves a steady, planar geometry that readily allows the determination of surfactant surface concentration and interfacial velocities and their derivatives which can be used with the stress boundary condition to determine the interfacial viscosities. A surface-piercing barrier is placed in a clean free-surface water tunnel and a hemicyanine monomolecular layer is subsequently deposited on the surface. When flow is started in the tunnel a Reynolds Ridge is formed, marking the leading edge of the now compressed monolayer which is characterized by a free-surface boundary layer and a surfactant concentration profile in the direction of flow. A single laser beam was used for second harmonic generation measurements of surfactant concentration profile, as well as boundary-fitted digital particle image velocimetry (DPIV) measurements of subsurface flow. This presentation focuses on the DPIV measurements at the interface.

  8. Rotation and strain rate of Sulawesi from geometrical velocity field

    NASA Astrophysics Data System (ADS)

    Sarsito, D. A.; Susilo, Simons, W. J. F.; Abidin, H. Z.; Sapiie, B.; Triyoso, W.; Andreas, H.

    2017-07-01

    One of methods that can be used to determine the tectonic deformation status is rate estimation from geometric rotation and strain using quantitative velocity data from GPS observations. Microplate Sulawesi region located in the zone of triple junction (Eurasia, Australia and Philippine Sea Plates) has very complex tectonic and seismic condition, which is why become very important to know its recent deformation status in order to study neo-tectonic and disaster mitigation. Deformation rate quantification is estimated in two parameters: rotation and geodetic strain rate of each GPS station Delaunay triangle in the study area. The analysis in this study is not done using the grids since there is no rheological information at location that can be used as the interpolation-extrapolation constraints. Our analysis reveals that Sulawesi is characterized by rapid rotation in several different domains and compression-strain pattern that varies depending on the type and boundary conditions of microplate. This information is useful for studying neo tectonic deformation status and earthquake disaster mitigation.

  9. MHD dynamo in Reversed Field Pinch Plasmas: electrostatic drift nature of the dynamo velocity field

    NASA Astrophysics Data System (ADS)

    Cappello, Susanna

    2005-10-01

    Within the framework of MHD numerical modelling, the Reversed Field Pinch (RFP) has been found to develop turbulent or laminar regimes switching from the former to the latter in a continuous way depending on the strength of dissipative forces. The laminar solution corresponds to a simple global helical deformation of the current channel and is associated to an electrostatic dynamo field. In this work we show that the associated drift yields the main component of the dynamo velocity. While quite natural in the stationary helical state, this analysis is shown to extend also to the dynamic turbulent regime for a sustained RFP. The continuity of the transition between the two regimes suggests that the simple helical symmetric solution can provide a fruitful intuitive description of the RFP dynamo in general. Many of the MHD predictions are in good agreement with experimental findings. References: [1] S. Cappello and D.F. Escande, ``Bifurcation in viscoresistive MHD: the Hartmann number and the RFP,'' Phys. Rev. Lett. 85, 3838 (2000) [2] S. Cappello, ``Bifurcation in the MHD behaviour of a self-organizing system: the RFP,'' Plasma Phys. Control. Fusion 46, B313 (2004) [3] D. Bonfiglio, S. Cappello, D.F. Escande, ``Dominant electrostatic nature of the Reversed Field Pinch dynamo,'' Phys. Rev. Lett. 94, 145001 (2005) In collaboration with D.F. Escande and D. Bonfiglio.

  10. HATNET Variability Survey in the High Stellar Density ``Kepler Field'' with Millimagnitude Image Subtraction Photometry

    NASA Astrophysics Data System (ADS)

    Hartman, J. D.; Bakos, G.; Stanek, K. Z.; Noyes, R. W.

    2004-10-01

    The Hungarian-made Automated Telescope Network (HATnet) is an ongoing project to detect transiting extrasolar planets using small-aperture (11 cm diameter) robotic telescopes. In this paper, we present the results from using image subtraction photometry to reduce a crowded stellar field observed with one of the HATnet telescopes (HAT-5). This field was chosen to overlap with the planned Kepler mission. We obtained I-band light curves for 98,000 objects in a 67 square degree field of view centered at J2000 (α,δ) = (19h44m00s0, +37°32'00.0"), near the Galactic plane in the constellations Cygnus and Lyra. These observations include 788 exposures of 5 minutes' length over 30 days. For the brightest stars (I~8.0) we achieved a precision of 3.5 mmag, falling to 0.1 mag at the faint end (I~14). From these light curves we identify 1617 variable stars, of which 1439 are newly discovered. The fact that nearly 90% of the variables were previously undetected further demonstrates the vast number of variables yet to be discovered even among fairly bright stars in our Galaxy. We also discuss some of the most interesting cases. These include V1171 Cyg, a triple system with the inner two stars in a P=1.462 day period eclipsing orbit and the outer star a P=4.86 day Cepheid; HD 227269, an eccentric eclipsing system with a P=4.86 day period that also shows P=2.907 day pulsations; WW Cyg, a well-studied eclipsing binary; V482 Cyg, an R Coronae Borealis star; and V546 Cyg, a PV Telescopii variable. We also detect a number of small-amplitude variables, in some cases with full amplitude as low as 10 mmag.

  11. Inferred properties of stellar granulation

    SciTech Connect

    Gray, D.F.; Toner, C.G.

    1985-06-01

    Apparent characteristics of stellar granulation in F and G main-sequence stars are inferred directly from observed spectral-line asymmetries and from comparisons of numerical simulations with the observations: (1) the apparent granulation velocity increases with effective temperature, (2) the dispersion of granule velocities about their mean velocity of rise increases with the apparent granulation velocity, (3) the mean velocity of rise of granules must be less than the total line broadening, (4) the apparent velocity difference between granules and dark lanes corresponds to the granulation velocity deduced from stellar line bisectors, (5) the dark lanes show velocities of fall approximately twice as large as the granule rise velocities, (6) the light contributed to the stellar flux by the granules is four to ten times more than the light from the dark lanes. Stellar rotation is predicted to produce distortions in the line bisectors which may give information on the absolute velocity displacements of the line bisectors. 37 references.

  12. The velocity field created by a shallow bump in a boundary layer

    NASA Technical Reports Server (NTRS)

    Gaster, Michael; Grosch, Chester E.; Jackson, Thomas L.

    1994-01-01

    We report the results of measurements of the disturbance velocity field generated in a boundary layer by a shallow three-dimensional bump oscillating at a very low frequency on the surface of a flat plate. Profiles of the mean velocity, the disturbance velocity at the fundamental frequency and at the first harmonic are presented. These profiles were measured both upstream and downstream of the oscillating bump. Measurements of the disturbance velocity were also made at various spanwise and downstream locations at a fixed distance from the boundary of one displacement thickness. Finally, the spanwise spectrum of the disturbances at three locations downstream of the bump are presented.

  13. Measurement of velocity and vorticity fields in the wake of an airfoil in periodic pitching motion

    NASA Technical Reports Server (NTRS)

    Booth, Earl R., Jr.

    1987-01-01

    The velocity field created by the wake of an airfoil undergoing a prescribed pitching motion was sampled using hot wire anemometry. Data analysis methods concerning resolution of velocity components from cross wire data, computation of vorticity from velocity time history data, and calculation of vortex circulation from vorticity field data are discussed. These data analysis methods are applied to a flow field relevant to a two dimensional blade-vortex interaction study. Velocity time history data were differentiated to yield vorticity field data which are used to characterize the wake of the pitching airfoil. Measurement of vortex strength in sinusoidal and nonsinusoidal wakes show vortices in the sinusoidal wake have stronger circulation and more concentrated vorticity distributions than the tailored nonsinusoidal wake.

  14. Measurement of velocity and vorticity fields in the wake of an airfoil in periodic pitching motion

    NASA Astrophysics Data System (ADS)

    Booth, Earl R., Jr.

    1987-12-01

    The velocity field created by the wake of an airfoil undergoing a prescribed pitching motion was sampled using hot wire anemometry. Data analysis methods concerning resolution of velocity components from cross wire data, computation of vorticity from velocity time history data, and calculation of vortex circulation from vorticity field data are discussed. These data analysis methods are applied to a flow field relevant to a two dimensional blade-vortex interaction study. Velocity time history data were differentiated to yield vorticity field data which are used to characterize the wake of the pitching airfoil. Measurement of vortex strength in sinusoidal and nonsinusoidal wakes show vortices in the sinusoidal wake have stronger circulation and more concentrated vorticity distributions than the tailored nonsinusoidal wake.

  15. Variability of solar/stellar activity and magnetic field and its influence on planetary atmosphere evolution

    NASA Astrophysics Data System (ADS)

    Lammer, Helmut; Güdel, Manuel; Kulikov, Yuri; Ribas, Ignasi; Zaqarashvili, Teimuraz V.; Khodachenko, Maxim L.; Kislyakova, Kristina G.; Gröller, Hannes; Odert, Petra; Leitzinger, Martin; Fichtinger, Bibiana; Krauss, Sandro; Hausleitner, Walter; Holmström, Mats; Sanz-Forcada, Jorge; Lichtenegger, Herbert I. M.; Hanslmeier, Arnold; Shematovich, Valery I.; Bisikalo, Dmitry; Rauer, Heike; Fridlund, Malcolm

    2012-02-01

    It is shown that the evolution of planetary atmospheres can only be understood if one recognizes the fact that the radiation and particle environment of the Sun or a planet's host star were not always on the same level as at present. New insights and the latest observations and research regarding the evolution of the solar radiation, plasma environment and solar/stellar magnetic field derived from the observations of solar proxies with different ages will be given. We show that the extreme radiation and plasma environments of the young Sun/stars have important implications for the evolution of planetary atmospheres and may be responsible for the fact that planets with low gravity like early Mars most likely never build up a dense atmosphere during the first few 100 Myr after their origin. Finally we present an innovative new idea on how hydrogen clouds and energetic neutral atom (ENA) observations around transiting Earth-like exoplanets by space observatories such as the WSO-UV, can be used for validating the addressed atmospheric evolution studies. Such observations would enhance our understanding on the impact on the activity of the young Sun on the early atmospheres of Venus, Earth, Mars and other Solar System bodies as well as exoplanets.

  16. Note on the velocity and related fields of steady irrotational two-dimensional surface gravity waves.

    PubMed

    Clamond, Didier

    2012-04-13

    The velocity and other fields of steady two-dimensional surface gravity waves in irrotational motion are investigated numerically. Only symmetric waves with one crest per wavelength are considered, i.e. Stokes waves of finite amplitude, but not the highest waves, nor subharmonic and superharmonic bifurcations of Stokes waves. The numerical results are analysed, and several conjectures are made about the velocity and acceleration fields.

  17. Measurement of temperature and velocity fields of freezing water using liquid crystal tracers

    NASA Astrophysics Data System (ADS)

    Kowalewski, Tomasz A.

    A new experimental technique based on a computational analysis of the colour and displacement of thermochromic liquid crystal tracers was applied to determine both the temperature and velocity fields of freezing water. The technique combines Digital Particle Image Thermometry and Digital Particle Image Velocimetry. Full 2-D temperature and velocity fields are determined from a pair or a longer sequence, of colour images taken for the selected cross-section of the flow.

  18. Clear and Measurable Signature of Modified Gravity in the Galaxy Velocity Field

    NASA Astrophysics Data System (ADS)

    Hellwing, Wojciech A.; Barreira, Alexandre; Frenk, Carlos S.; Li, Baojiu; Cole, Shaun

    2014-06-01

    The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v12 are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ12(r) is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon f(R) gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the (5-10)σ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.

  19. Clear and measurable signature of modified gravity in the galaxy velocity field.

    PubMed

    Hellwing, Wojciech A; Barreira, Alexandre; Frenk, Carlos S; Li, Baojiu; Cole, Shaun

    2014-06-06

    The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v_{12} are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ_{12}(r) is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon f(R) gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the (5-10)σ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.

  20. An exact solution of solute transport by one-dimensional random velocity fields

    USGS Publications Warehouse

    Cvetkovic, V.D.; Dagan, G.; Shapiro, A.M.

    1991-01-01

    The problem of one-dimensional transport of passive solute by a random steady velocity field is investigated. This problem is representative of solute movement in porous media, for example, in vertical flow through a horizontally stratified formation of variable porosity with a constant flux at the soil surface. Relating moments of particle travel time and displacement, exact expressions for the advection and dispersion coefficients in the Focker-Planck equation are compared with the perturbation results for large distances. The first- and second-order approximations for the dispersion coefficient are robust for a lognormal velocity field. The mean Lagrangian velocity is the harmonic mean of the Eulerian velocity for large distances. This is an artifact of one-dimensional flow where the continuity equation provides for a divergence free fluid flux, rather than a divergence free fluid velocity. ?? 1991 Springer-Verlag.

  1. Phototactic Clustering of Swimming Microorganisms in a Turbulent Velocity Field

    NASA Astrophysics Data System (ADS)

    Torney, Colin; Neufeld, Zoltán

    2008-08-01

    We study the distribution of swimming microorganisms advected by a two-dimensional smooth turbulent flow and attracted towards a light source through phototaxis. It is shown that particles aggregate along a dynamical attractor with fractal measure whose dimension depends on the strength of the phototaxis. Using an effective diffusion approximation for the flow, we derive an analytic expression for the increase in light exposure over the aggregate and by extension an accurate prediction for the fractal dimension based on the properties of the advection and the statistics of the attracting field.

  2. Stellarator hybrids

    SciTech Connect

    Furth, H.P.; Ludescher, C.

    1984-08-01

    The present paper briefly reviews the subject of tokamak-stellarator and pinch-stellarator hybrids, and points to two interesting new possibilities: compact-torus-stellarators and mirror-stellarators.

  3. Radiography by selective detection of scatter field velocity components

    NASA Technical Reports Server (NTRS)

    Jacobs, Alan M. (Inventor); Dugan, Edward T. (Inventor); Shedlock, Daniel (Inventor)

    2007-01-01

    A reconfigurable collimated radiation detector, system and related method includes at least one collimated radiation detector. The detector has an adjustable collimator assembly including at least one feature, such as a fin, optically coupled thereto. Adjustments to the adjustable collimator selects particular directions of travel of scattered radiation emitted from an irradiated object which reach the detector. The collimated detector is preferably a collimated detector array, where the collimators are independently adjustable. The independent motion capability provides the capability to focus the image by selection of the desired scatter field components. When an array of reconfigurable collimated detectors is provided, separate image data can be obtained from each of the detectors and the respective images cross-correlated and combined to form an enhanced image.

  4. A simple measuring technique of surface flow velocity to analyze the behavior of velocity fields in hydraulic engineering applications.

    NASA Astrophysics Data System (ADS)

    Tellez, Jackson; Gomez, Manuel; Russo, Beniamino; Redondo, Jose M.

    2015-04-01

    An important achievement in hydraulic engineering is the proposal and development of new techniques for the measurement of field velocities in hydraulic problems. The technological advances in digital cameras with high resolution and high speed found in the market, and the advances in digital image processing techniques now provides a tremendous potential to measure and study the behavior of the water surface flows. This technique was applied at the Laboratory of Hydraulics at the Technical University of Catalonia - Barcelona Tech to study the 2D velocity fields in the vicinity of a grate inlet. We used a platform to test grate inlets capacity with dimensions of 5.5 m long and 4 m wide allowing a zone of useful study of 5.5m x 3m, where the width is similar of the urban road lane. The platform allows you to modify the longitudinal slopes from 0% to 10% and transversal slope from 0% to 4%. Flow rates can arrive to 200 l/s. In addition a high resolution camera with 1280 x 1024 pixels resolution with maximum speed of 488 frames per second was used. A novel technique using particle image velocimetry to measure surface flow velocities has been developed and validated with the experimental data from the grate inlets capacity. In this case, the proposed methodology can become a useful tools to understand the velocity fields of the flow approaching the inlet where the traditional measuring equipment have serious problems and limitations. References DigiFlow User Guide. (2012), (June). Russo, B., Gómez, M., & Tellez, J. (2013). Methodology to Estimate the Hydraulic Efficiency of Nontested Continuous Transverse Grates. Journal of Irrigation and Drainage Engineering, 139(10), 864-871. doi:10.1061/(ASCE)IR.1943-4774.0000625 Teresa Vila (1), Jackson Tellez (1), Jesus Maria Sanchez (2), Laura Sotillos (1), Margarita Diez (3, 1), and J., & (1), M. R. (2014). Diffusion in fractal wakes and convective thermoelectric flows. Geophysical Research Abstracts - EGU General Assembly 2014

  5. SOAP 2.0: A Tool to Estimate the Photometric and Radial Velocity Variations Induced by Stellar Spots and Plages

    NASA Astrophysics Data System (ADS)

    Dumusque, X.; Boisse, I.; Santos, N. C.

    2014-12-01

    This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i <=8 km s-1. A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD 189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star α Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation. . The work in this paper is based on observations made with the MOST satellite, the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory (Chile), and the SOPHIE instrument at the Observatoire de Haute Provence (France).

  6. SOAP 2.0: a tool to estimate the photometric and radial velocity variations induced by stellar spots and plages

    SciTech Connect

    Dumusque, X.; Boisse, I.; Santos, N. C.

    2014-12-01

    This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i ≤8 km s{sup –1}. A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD 189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star α Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation.

  7. Locating earthquakes in west Texas oil fields using 3-D anisotropic velocity models

    SciTech Connect

    Hua, Fa; Doser, D.; Baker, M. . Dept. of Geological Sciences)

    1993-02-01

    Earthquakes within the War-Wink gas field, Ward County, Texas, that have been located with a 1-D velocity model occur near the edges and top of a naturally occurring overpressured zone. Because the War-Wink field is a structurally controlled anticline with significant velocity anisotropy associated with the overpressured zone and finely layered evaporites, the authors have attempted to re-locate earthquakes using a 3-D anisotropic velocity model. Preliminary results with this model give the unsatisfactory result that many earthquakes previously located at the top of the overpressured zone (3-3.5 km) moved into the evaporites (1-1.5 km) above the field. They believe that this result could be caused by: (1) aliasing the velocity model; or (2) problems in determining the correct location minima when several minima exist. They are currently attempting to determine which of these causes is more likely for the unsatisfactory result observed.

  8. CLASSIFICATION OF FIELD DWARFS AND GIANTS IN RAVE AND ITS USE IN STELLAR STREAM DETECTION

    SciTech Connect

    Klement, R. J.; Bailer-Jones, C. A. L.; Rix, H.-W.; Smith, K. W.; Fuchs, B. E-mail: fuchs@ari.uni-heidelberg.de

    2011-01-10

    Samples of bright stars, as they emerge from surveys such as RAVE, contain comparable fractions of dwarf and giant stars. An efficient separation of these two luminosity classes is therefore important, especially for studies in which distances are estimated through photometric parallax relations. We use the available spectroscopic log g estimates from the second RAVE data release (DR2) to assign each star a probability for being a dwarf or subgiant/giant based on mixture model fits to the log g distribution in different color bins. We further attempt to use these stars as a labeled training set in order to classify stars which lack log g estimates into dwarfs and giants with a Support Vector Machine algorithm. We assess the performance of this classification against different choices of the input feature vector. In particular, we use different combinations of reduced proper motions, 2MASS JHK, DENIS IJK, and USNO-B B2R2 apparent magnitudes. Our study shows that-for our color ranges-the infrared bands alone provide no relevant information to separate dwarfs and giants. Even when optical bands and reduced proper motions are added, the fraction of true giants classified as dwarfs (the contamination) remains above 20%. Using only the dwarfs with available spectroscopic log g and distance estimates (the latter from Breddels et al.), we then repeat the stream search by Klementet al. (KFR08), which assumed that all stars were dwarfs and claimed the discovery of a new stellar stream at V {approx} -160 km s{sup -1} in a sample of 7015 stars from RAVE DR1. The existence of the KFR08 stream has been supported by two recent studies using other independent data sets. Our re-analysis of the pure DR2 dwarf sample exhibits an overdensity of five stars at the phase-space position of the KFR08 stream, with a metallicity distribution that appears inconsistent with that of stars at comparably low rotational velocities. Compared to several smooth Milky Way models, the mean standardized

  9. Intermittency of a passive scalar advected by a quasifrozen velocity field

    NASA Astrophysics Data System (ADS)

    Ching, Emily S. C.; Pang, C. S.; Tsang, Y. K.; Wang, X. H.

    1999-08-01

    We use a two-dimensional lattice model to study the intermittency problem of a passive scalar advected by a velocity field of finite correlation time. The stream function generating the incompressible velocity field is modeled by a random Gaussian noise that is identically independently distributed at each lattice point and is updated every certain finite time interval. A fixed scalar difference is maintained across one direction of the lattice. There are three time scales in the problem: the correlation or update time of the velocity field τc, the diffusion time of the scalar τdiff, and the advection time of the velocity field τadv. Interesting behavior is observed when τdiff<τc. In this regime the passive scalar field is found to be intermittent while its dynamics between the updates of the velocity field is dominated by diffusion. The intermittency can be described by log-Poisson statistics and is independent of the ratio τc/τadv. On the other hand, the passive scalar field exhibits dissipative scaling and is thus nonintermittent when τdiff⩾τc.

  10. Measuring the velocity field from type Ia supernovae in an LSST-like sky survey

    NASA Astrophysics Data System (ADS)

    Odderskov, Io; Hannestad, Steen

    2017-01-01

    In a few years, the Large Synoptic Survey Telescope will vastly increase the number of type Ia supernovae observed in the local universe. This will allow for a precise mapping of the velocity field and, since the source of peculiar velocities is variations in the density field, cosmological parameters related to the matter distribution can subsequently be extracted from the velocity power spectrum. One way to quantify this is through the angular power spectrum of radial peculiar velocities on spheres at different redshifts. We investigate how well this observable can be measured, despite the problems caused by areas with no information. To obtain a realistic distribution of supernovae, we create mock supernova catalogs by using a semi-analytical code for galaxy formation on the merger trees extracted from N-body simulations. We measure the cosmic variance in the velocity power spectrum by repeating the procedure many times for differently located observers, and vary several aspects of the analysis, such as the observer environment, to see how this affects the measurements. Our results confirm the findings from earlier studies regarding the precision with which the angular velocity power spectrum can be determined in the near future. This level of precision has been found to imply, that the angular velocity power spectrum from type Ia supernovae is competitive in its potential to measure parameters such as σ8. This makes the peculiar velocity power spectrum from type Ia supernovae a promising new observable, which deserves further attention.

  11. Volumetric Velocity Fields Downstream of a 2-Bladed Turbine

    NASA Astrophysics Data System (ADS)

    Troolin, Daniel

    2013-11-01

    Tip vortices of axial-flow turbines are important in understanding the mean and turbulent characteristics of the wake. Volumetric 3-component velocimetry (V3V) was used to examine the flow downstream of a model two-bladed turbine in air. The turbine had a diameter of 177.8 mm and was powered by a motor operating at approximately 150 rpm. The measurement volume (50 × 50 × 20 mm) was positioned approximately 5 mm downstream of the blade tip, in order to examine the tip vortex structure. The V3V system utilized three 4MP cameras with 85 mm lenses positioned in a fixed triangular frame located at a distance of 450 mm from the back of the measurement volume. The illumination source was a 200 mJ dual-head pulsed Nd:YAG laser operating at 7.25 Hz and illuminating 1 micron olive oil droplets as tracer particles. The particle images were then analyzed to produce volumetric vector fields. The focus was placed on visualizing the complex interaction between the turbine tip vortices. Insights on the tip vortex dynamics and three dimensional characteristics of the wake flow will be discussed.

  12. Velocity field measurements in oblique static divergent vocal fold models

    NASA Astrophysics Data System (ADS)

    Erath, Byron

    2005-11-01

    During normal phonation, the vocal fold cycle is characterized by the glottal opening transitioning from a convergent to a divergent passage and then closing before the cycle is repeated. Under ordinary phonatory conditions, both vocal folds, which form the glottal passage, move in phase with each other, creating a time-varying symmetric opening. However, abnormal pathological conditions, such as unilateral paralysis, and polyps, can result in geometrical asymmetries between the vocal folds throughout the phonatory cycle. This study investigates pulsatile flow fields through 7.5 times life-size vocal fold models with included divergence angles of 5 to 30 degrees, and obliquities between the vocal folds of up to 15 degrees. Flow conditions were scaled to match physiological parameters. Data were taken at the anterior posterior mid-plane using phase-averaged Particle Image Velocimetry (PIV). Viscous flow phenomena including the Coanda effect, flow separation points, and jet "flapping" were investigated. The results are compared to previously reported work of flow through symmetric divergent vocal fold models.

  13. The relationship between the instantaneous velocity field and the rate of moment release in the lithosphere

    USGS Publications Warehouse

    Pollitz, F.F.

    2003-01-01

    Instantaneous velocity gradients within the continental lithosphere are often related to the tectonic driving forces. This relationship is direct if the forces are secular, as for the case of loading of a locked section of a subduction interface by the downgoing plate. If the forces are static, as for the case of lateral variations in gravitational potential energy, then velocity gradients can be produced only if the lithosphere has, on average, zero strength. The static force model may be related to the long-term velocity field but not the instantaneous velocity field (typically measured geodetically over a period of several years) because over short time intervals the upper lithosphere behaves elastically. In order to describe both the short- and long-term behaviour of an (elastic) lithosphere-(viscoelastic) asthenosphere system in a self-consistent manner, I construct a deformation model termed the expected interseismic velocity (EIV) model. Assuming that the lithosphere is populated with faults that rupture continually, each with a definite mean recurrence time, and that the Earth is well approximated as a linear elastic-viscoelastic coupled system, I derive a simple relationship between the instantaneous velocity field and the average rate of moment release in the lithosphere. Examples with synthetic fault networks demonstrate that velocity gradients in actively deforming regions may to a large extent be the product of compounded viscoelastic relaxation from past earthquakes on hundreds of faults distributed over large ( ≥106 km2) areas.

  14. Lattice models for granular-like velocity fields: finite-size effects

    NASA Astrophysics Data System (ADS)

    Plata, C. A.; Manacorda, A.; Lasanta, A.; Puglisi, A.; Prados, A.

    2016-09-01

    Long-range spatial correlations in the velocity and energy fields of a granular fluid are discussed in the framework of a 1d lattice model. The dynamics of the velocity field occurs through nearest-neighbour inelastic collisions that conserve momentum but dissipate energy. A set of equations for the fluctuating hydrodynamics of the velocity and energy mesoscopic fields give a first approximation for (i) the velocity structure factor and (ii) the finite-size correction to the Haff law, both in the homogeneous cooling regime. At a more refined level, we have derived the equations for the two-site velocity correlations and the total energy fluctuations. First, we seek a perturbative solution thereof, in powers of the inverse of system size. On the one hand, when scaled with the granular temperature, the velocity correlations tend to a stationary value in the long time limit. On the other hand, the scaled standard deviation of the total energy diverges, that is, the system shows multiscaling. Second, we find an exact solution for the velocity correlations in terms of the spectrum of eigenvalues of a certain matrix. The results of numerical simulations of the microscopic model confirm our theoretical results, including the above described multiscaling phenomenon.

  15. The black hole mass of NGC 4151. II. Stellar dynamical measurement from near-infrared integral field spectroscopy

    SciTech Connect

    Onken, Christopher A.; Ferrarese, Laura; Valluri, Monica; Brown, Jonathan S.; McGregor, Peter J.; Peterson, Bradley M.; Pogge, Richard W.; Bentz, Misty C.; Vestergaard, Marianne; Storchi-Bergmann, Thaisa; Riffel, Rogemar A. E-mail: mvalluri@umich.edu

    2014-08-10

    We present a revised measurement of the mass of the central black hole (M{sub BH} ) in the Seyfert 1 galaxy NGC 4151. The new stellar dynamical mass measurement is derived by applying an axisymmetric orbit-superposition code to near-infrared integral field data obtained using adaptive optics with the Gemini Near-infrared Integral Field Spectrograph (NIFS). When our models attempt to fit both the NIFS kinematics and additional low spatial resolution kinematics, our results depend sensitively on how χ{sup 2} is computed—probably a consequence of complex bar kinematics that manifest immediately outside the nuclear region. The most robust results are obtained when only the high spatial resolution kinematic constraints in the nuclear region are included in the fit. Our best estimates for the black hole mass and H-band mass-to-light ratio are M{sub BH} ∼ 3.76 ± 1.15 × 10{sup 7} M{sub ☉} (1σ error) and Y{sub H} ∼ 0.34 ± 0.03 M{sub ☉}/L{sub ☉} (3σ error), respectively (the quoted errors reflect the model uncertainties). Our black hole mass measurement is consistent with estimates from both reverberation mapping (3.57{sub −0.37}{sup +0.45}×10{sup 7} M{sub ⊙}) and gas kinematics (3.0{sub −2.2}{sup +0.75}×10{sup 7} M{sub ⊙}; 1σ errors), and our best-fit mass-to-light ratio is consistent with the photometric estimate of Y{sub H} = 0.4 ± 0.2 M{sub ☉}/L{sub ☉}. The NIFS kinematics give a central bulge velocity dispersion σ{sub c} = 116 ± 3 km s{sup –1}, bringing this object slightly closer to the M{sub BH}-σ relation for quiescent galaxies. Although NGC 4151 is one of only a few Seyfert 1 galaxies in which it is possible to obtain a direct dynamical black hole mass measurement—and thus, an independent calibration of the reverberation mapping mass scale—the complex bar kinematics makes it less than ideally suited for this purpose.

  16. Reconstructing the galaxy density field with photometric redshifts. I. Methodology and validation on stellar mass functions

    NASA Astrophysics Data System (ADS)

    Malavasi, N.; Pozzetti, L.; Cucciati, O.; Bardelli, S.; Cimatti, A.

    2016-01-01

    Context. Measuring environment for large numbers of galaxies in the distant Universe is an open problem in astrophysics, as environment is important in determining many properties of galaxies during their formation and evolution. In order to measure galaxy environments, we need galaxy positions and redshifts. Photometric redshifts are more easily available for large numbers of galaxies, but at the price of larger uncertainties than spectroscopic redshifts. Aims: We study how photometric redshifts affect the measurement of galaxy environment and how the reconstruction of the density field may limit an analysis of the galaxy stellar mass function (GSMF) in different environments. Methods: Through the use of mock galaxy catalogues, we measured galaxy environment with a fixed aperture method, using each galaxy's true and photometric redshifts. We varied the parameters defining the fixed aperture volume and explored different configurations. We also used photometric redshifts with different uncertainties to simulate the case of various surveys. We then computed GSMF of the mock galaxy catalogues as a function of redshift and environment to see how the environmental estimate based on photometric redshifts affects their analysis. Results: We found that the most extreme environments can be reconstructed in a fairly accurate way only when using high-precision photometric redshifts with σΔz/ (1 + z) ≲ 0.01, with a fraction ≥ 60 ÷ 80% of galaxies placed in the correct density quartile and a contamination of ≤10% by opposite quartile interlopers. A length of the volume in the radial direction comparable to the ±1.5σ error of photometric redshifts and a fixed aperture radius of a size similar to the physical scale of the studied environment grant a better reconstruction than other volume configurations. When using this kind of an estimate of the density field, we found that any difference between the starting GSMF (divided accordingly to the true galaxy environment

  17. Stellar Loci II. A Model-free Estimate of the Binary Fraction for Field FGK Stars

    NASA Astrophysics Data System (ADS)

    Yuan, Haibo; Liu, Xiaowei; Xiang, Maosheng; Huang, Yang; Chen, Bingqiu; Wu, Yue; Hou, Yonghui; Zhang, Yong

    2015-02-01

    We propose a stellar locus outlier (SLOT) method to determine the binary fraction of main-sequence stars statistically. The method is sensitive to neither the period nor mass ratio distributions of binaries and is able to provide model-free estimates of binary fraction for large numbers of stars of different populations in large survey volumes. We have applied the SLOT method to two samples of stars from the Sloan Digital Sky Survey (SDSS) Stripe 82, constructed by combining the recalibrated SDSS photometric data with the spectroscopic information from the SDSS and LAMOST surveys. For the SDSS spectroscopic sample, we find an average binary fraction for field FGK stars of 41% ± 2%. The fractions decrease toward late spectral types and are 44% ± 5%, 43% ± 3%, 35% ± 5%, and 28% ± 6% for stars with g - i colors in the range 0.3-0.6 mag, 0.6-0.9 mag, 0.9-1.2 mag, and 1.2-1.6 mag, respectively. A modest metallicity dependence is also found. The fraction decreases with increasing metallicity. For stars with [Fe/H] between -0.5 and 0.0 dex, -1.0 and -0.5 dex, -1.5 and -1.0 dex, and -2.0 and -1.5 dex, the inferred binary fractions are 37% ± 3%, 39% ± 3%, 50% ± 9%, and 53% ± 20%, respectively. We have further divided the sample into stars from the thin disk, the thick disk, the transition zone between them, and the halo. The results suggest that the Galactic thin and thick disks have comparable binary fractions, whereas the Galactic halo contains a significantly larger fraction of binaries. Applying the method to the LAMOST spectroscopic sample yields consistent results. Finally, other potential applications and future work with the method are discussed.

  18. Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Antonini, Fabio; Toonen, Silvia; Hamers, Adrian S.

    2017-06-01

    We consider the formation of binary black hole (BH) mergers through the evolution of field massive triple stars. In this scenario, favorable conditions for the inspiral of a BH binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. We use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (Lidov-Kozai cycles) with stellar evolution. After a BH triple is formed, its dynamical evolution is computed using either the orbit-averaged equations of motion, or a high-precision direct integrator for triples with weaker hierarchies for which the secular perturbation theory breaks down. Most BH mergers in our models are produced in the latter non-secular dynamical regime. We derive the properties of the merging binaries and compute a BH merger rate in the range (0.3-1.3) Gpc-3 yr-1, or up to ≈2.5 Gpc-3 yr-1 if the BH orbital planes have initially random orientation. Finally, we show that BH mergers from the triple channel have significantly higher eccentricities than those formed through the evolution of massive binaries or in dense star clusters. Measured eccentricities could therefore be used to uniquely identify binary mergers formed through the evolution of triple stars. While our results suggest up to ≈10 detections per year with Advanced-LIGO, the high eccentricities could render the merging binaries harder to detect with planned space based interferometers such as LISA.

  19. Uncertainty in calculating vorticity from 2D velocity fields using circulation and least-squares approaches

    NASA Astrophysics Data System (ADS)

    Abrahamson, S.; Lonnes, S.

    1995-11-01

    The most common method for determining vorticity from planar velocity information is the circulation method. Its performance has been evaluated using a plane of velocity data obtained from a direct numerical simulation (DNS) of a three dimensional plane shear layer. Both the ability to reproduce the vorticity from the exact velocity field and one perturbed by a 5% random “uncertainty” were assessed. To minimize the sensitivity to velocity uncertainties, a new method was developed using a least-squares approach. The local velocity data is fit to a model velocity field consisting of uniform translation, rigid rotation, a point source, and plane shear. The least-squares method was evaluated in the same manner as the circulation method. The largest differences between the actual and calculated vorticity fields were due to the filter-like nature of the methods. The new method is less sensitive to experimental uncertainty. However the circulation method proved to be slightly better at reproducing the DNS field. The least-squares method provides additional information beyond the circulation method results. Using the correlation overline {Pω ω } and a vorticity threshold criteria to identify regions of rigid rotation (or eddies), the rigid rotation component of the least-squares method indicates these same regions.

  20. Numerical method for determination of resonance electron velocities in periodic electric fields

    SciTech Connect

    Tarnev, Khristo

    2014-11-18

    A Monte Carlo method is applied for modeling of a plasma source with a periodic structure of a radiofrequency electric field. The method is modified in order to detect resonance increase of the electron energy at given velocities of the electrons as expected from theoretical considerations. The numerical model is validated by comparison with known analytical results. The applicability of the method for detection of resonance velocities in plasma sources with electric field variation parallel or perpendicular to the electric field vector is proven.

  1. An industrial light-field camera applied for 3D velocity measurements in a slot jet

    NASA Astrophysics Data System (ADS)

    Seredkin, A. V.; Shestakov, M. V.; Tokarev, M. P.

    2016-10-01

    Modern light-field cameras have found their application in different areas like photography, surveillance and quality control in industry. A number of studies have been reported relatively low spatial resolution of 3D profiles of registered objects along the optical axis of the camera. This article describes a method for 3D velocity measurements in fluid flows using an industrial light-field camera and an alternative reconstruction algorithm based on a statistical approach. This method is more accurate than triangulation when applied for tracking small registered objects like tracer particles in images. The technique was used to measure 3D velocity fields in a turbulent slot jet.

  2. Creating analytically divergence-free velocity fields from grid-based data

    NASA Astrophysics Data System (ADS)

    Ravu, Bharath; Rudman, Murray; Metcalfe, Guy; Lester, Daniel R.; Khakhar, Devang V.

    2016-10-01

    We present a method, based on B-splines, to calculate a C2 continuous analytic vector potential from discrete 3D velocity data on a regular grid. A continuous analytically divergence-free velocity field can then be obtained from the curl of the potential. This field can be used to robustly and accurately integrate particle trajectories in incompressible flow fields. Based on the method of Finn and Chacon (2005) [10] this new method ensures that the analytic velocity field matches the grid values almost everywhere, with errors that are two to four orders of magnitude lower than those of existing methods. We demonstrate its application to three different problems (each in a different coordinate system) and provide details of the specifics required in each case. We show how the additional accuracy of the method results in qualitatively and quantitatively superior trajectories that results in more accurate identification of Lagrangian coherent structures.

  3. Ensemble Monte Carlo Simulation of a Velocity-Modulation Field Effect Transistor (VMT)

    NASA Astrophysics Data System (ADS)

    Kizilyalli, I. C.; Hess, K.

    1987-09-01

    We present numerical simulations of velocity modulated field effect transistors as proposed by Sakaki. Using self-consistent particle-field Monte Carlo analysis, we assess possible advantages of these novel device structures with respect to switching speed and show the qualitative correctness of Sakaki’s ideas. Quantitatively, delays are introduced by the redistribution of electrons in the separated channels.

  4. Stellar Populations of Late-Type Bulges at z ≃ 1 in the Hubble Ultra Deep Field

    NASA Astrophysics Data System (ADS)

    Hathi, N. P.; Ferreras, I.; Pasquali, A.; Malhotra, S.; Rhoads, J. E.; Pirzkal, N.; Windhorst, R. A.; Xu, C.

    2009-01-01

    We combine the exceptional depth of the Hubble Ultra Deep Field (HUDF) images and the deep GRism Advanced Camera for Surveys Program for Extragalactic Science (GRAPES) grism spectroscopy to explore the stellar populations of 34 bulges belonging to late-type galaxies at 0.8 <= z <= 1.3. The sample is selected based on the presence of a noticeable 4000 Å break in their GRAPES spectra, and by visual inspection of the HUDF images. The HUDF images are used to measure the bulge color and Sérsic index. The narrow extraction of the GRAPES data around the galaxy center enables us to study the spectrum of the bulges in these late-type galaxies, minimizing the contamination from the disk of the galaxy. We use the low-resolution (R ≃ 50) spectral energy distribution (SED) around the 4000 Å break to estimate redshifts and stellar ages. The SEDs are compared with models of galactic chemical evolution to determine the stellar mass, and to characterize the age distribution. We find that (1) the average age of late-type bulges in our sample is ~1.3 Gyr with stellar masses in the range 106.5-1010 M sun. (2) Late-type bulges are younger than early-type galaxies at similar redshifts and lack a trend of age with respect to redshift, suggesting a more extended period of star formation. (3) Bulges and inner disks in these late-type galaxies show similar stellar populations, and (4) late-type bulges are better fitted by exponential surface brightness profiles. The overall picture emerging from the GRAPES data is that, in late-type galaxies at z ≃ 1 bulges form through secular evolution and disks via an inside-out process.

  5. Validation of a scaling law for the coronal magnetic field strength and loop length of solar and stellar flares

    NASA Astrophysics Data System (ADS)

    Namekata, Kosuke; Sakaue, Takahito; Watanabe, Kyoko; Asai, Ayumi; Shibata, Kazunari

    2017-02-01

    Shibata and Yokoyama (1999, ApJ, 526, L49; 2002, ApJ, 577, 422) proposed a method of estimating the coronal magnetic field strength (B) and magnetic loop length (L) of solar and stellar flares, on the basis of magnetohydrodynamic simulations of the magnetic reconnection model. Using the scaling law provided by Shibata and Yokoyama (1999, ApJ, 526, L49; 2002, ApJ, 577, 422), we obtain B and L as functions of the emission measure (EM = n2L3) and temperature (T) at the flare peak. Here, n is the coronal electron density of the flares. This scaling law enables the estimation of B and L for unresolved stellar flares from the observable physical quantities EM and T, which is helpful for studying stellar surface activities. To apply this scaling law to stellar flares, we discuss its validity for spatially resolved solar flares. Quantities EM and T are calculated from GOES (Geostationary Operational Environmental Satellite) soft X-ray flux data, and B and L are theoretically estimated using the scaling law. For the same flare events, B and L were also observationally estimated with images taken by the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) Magnetogram and Atmospheric Imaging Assembly (AIA) 94 Å pass band. As expected, a positive correlation was found between the theoretically and observationally estimated values. We interpret this result as indirect evidence that flares are caused by magnetic reconnection. Moreover, this analysis makes us confident about the validity of applying this scaling law to stellar flares as well as solar flares.

  6. 3-D seismic velocity and attenuation structures in the geothermal field

    SciTech Connect

    Nugraha, Andri Dian; Syahputra, Ahmad; Fatkhan,; Sule, Rachmat

    2013-09-09

    We conducted delay time tomography to determine 3-D seismic velocity structures (Vp, Vs, and Vp/Vs ratio) using micro-seismic events in the geothermal field. The P-and S-wave arrival times of these micro-seismic events have been used as input for the tomographic inversion. Our preliminary seismic velocity results show that the subsurface condition of geothermal field can be fairly delineated the characteristic of reservoir. We then extended our understanding of the subsurface physical properties through determining of attenuation structures (Qp, Qs, and Qs/Qp ratio) using micro-seismic waveform. We combined seismic velocities and attenuation structures to get much better interpretation of the reservoir characteristic. Our preliminary attanuation structures results show reservoir characterization can be more clearly by using the 3-D attenuation model of Qp, Qs, and Qs/Qp ratio combined with 3-D seismic velocity model of Vp, Vs, and Vp/Vs ratio.

  7. Correlation algorithm for computing the velocity fields in microchannel flows with high resolution

    NASA Astrophysics Data System (ADS)

    Karchevskiy, M. N.; Tokarev, M. P.; Yagodnitsyna, A. A.; Kozinkin, L. A.

    2015-11-01

    A cross-correlation algorithm, which enables the obtaining of the velocity field in the flow with a spatial resolution up to a single pixel per vector, has been realized in the work. It gives new information about the structure of microflows as well as increases considerably the accuracy of the measurement of the flow velocity field. In addition, the realized algorithm renders information about the velocity fluctuations in the flow structure. The algorithm was tested on synthetic data at a different number of test images the velocity distribution on which was specified by the Siemens star. The experimental validation was done on the data provided within the international project "4th International PIV Challenge". Besides, a detailed comparison with the Particle Image Velocimetry algorithm, which was realized previously, was carried out.

  8. Spatiotemporal properties of Sub-Rayleigh and supershear rupture velocity fields: Theory and experiments

    NASA Astrophysics Data System (ADS)

    Mello, Michael; Bhat, Harsha S.; Rosakis, Ares J.

    2016-08-01

    Fundamental spatiotemporal field properties and particle velocity waveform signatures of sub-Rayleigh and supershear ruptures were experimentally investigated through a series of laboratory earthquake experiments. We appeal to dynamic rupture theory to extract and highlight previously unnoticed aspects and results, which are of direct relevance to our new experiments. Kinematic relationships derived from both singular and non-singular solutions are applied to analyze and interpret various features observed in these experiments. A strong correspondence is demonstrated between particle velocity records obtained in lab experiments and synthetic particle velocity waveform profiles derived from theory. Predicted temporal profiles, sense of particle motion, and amplitude decay properties of sub-Rayleigh and supershear particle velocity waveforms are experimentally verified. In a particular set of supershear rupture experiments, the fault-normal (FN) and fault-parallel (FP) velocity waveforms were simultaneously recorded at fixed, off-fault field points as a shear Mach front swept these locations. Particle velocity records collected over a broad range of stable supershear rupture speeds validate the predicted scaling relationship δu˙1s / δu˙2s =√{Vr2 / Cs2-1 } =βs, between the FP (δu1ṡ) and the FN (δu2ṡ) velocity jumps propagated by a shear Mach front. Additional experimental findings include detailed rupture speed measurements of sub-Rayleigh and supershear ruptures and the observation of a supershear daughter crack with vanishing shear Mach front.

  9. Kinematics of the Suez-Sinai area from combined GPS velocity field

    NASA Astrophysics Data System (ADS)

    Pietrantonio, G.; Devoti, R.; Mahmoud, S.; Riguzzi, F.

    2016-12-01

    A combined GPS velocity solution covering a wide area from Egypt to Middle East allowed us to infer the current rates across the main, already well known, tectonic features. We have estimated 126 velocities from time series of 90 permanent and 36 non permanent GPS sites located in Africa (Egypt), Eurasia and Arabia plates in the time span 1996-2015, the largest available for the Egyptian sites. We have combined our velocity solution in a least-squares sense with two other recent velocity solutions of networks located around the eastern Mediterranean, obtaining a final IGb08 velocity field of about 450 sites. Then, we have estimated the IGb08 Euler poles of Africa, Sinai and Arabia, analyzing the kinematics of the Sinai area, particular velocity profiles, and estimating the 2D strain rate field. We show that it is possible to reliably model the rigid motion of Sinai block only including some GPS sites located south of the Carmel Fault. The estimated relative motion with respect to Africa is of the order of 2-3 mm/yr, however there is a clear mismatch between the modeled and the observed velocities in the southern Sinai sites. We have also assessed the NNE left shear motion along the Dead Sea Transform Fault, estimating a relative motion between Arabia and Africa of about 6 mm/yr in the direction of the Red Sea opening.

  10. The velocity field near the orifice of a Helmholtz resonator in grazing flow

    NASA Technical Reports Server (NTRS)

    Charwat, A. F.; Walker, B. E.

    1981-01-01

    Measurement of the time-dependent velocities induced inside and outside the opening of acoustically excited, two-dimensional Helmholtz resonator imbedded in a grazing flow are presented. The remarkably clear structure of the perturbation field which evokes a pulsating source and a coherently pulsating vortex-image pair is described. The simple phenomenological "lid-model" which correlates the variation in the components of the acoustic impedance with the velocity of the grazing flow is discussed and extended.

  11. The effect of spatially varying velocity field on the transport of radioactivity in a porous medium.

    PubMed

    Sen, Soubhadra; Srinivas, C V; Baskaran, R; Venkatraman, B

    2016-10-01

    In the event of an accidental leak of the immobilized nuclear waste from an underground repository, it may come in contact of the flow of underground water and start migrating. Depending on the nature of the geological medium, the flow velocity of water may vary spatially. Here, we report a numerical study on the migration of radioactivity due to a space dependent flow field. For a detailed analysis, seven different types of velocity profiles are considered and the corresponding concentrations are compared.

  12. Instantaneous velocity field measurement of objects in coaxial rotation using digital image velocimetry

    NASA Technical Reports Server (NTRS)

    Cho, Y.-C.; Park, H.

    1990-01-01

    The instantaneous velocity fields of time-dependent flows, or of a collection of objects moving with spatially varying velocities, can be measured by means of digital image velocimetry (DIV). DIV overcomes several shortcomings of such existing techniques as laser-speckle or particle-image velocimetry. Attention is presently given to numerically generated images representing objects in uniform motion which are then used for the experimental validation of DIV.

  13. Second-order solution for determining density and velocity fields of galaxies

    NASA Technical Reports Server (NTRS)

    Gramann, Mirt

    1993-01-01

    In this Letter, I use second-order Lagrangian perturbation theory to calculate an analytical expression relating density to velocity in a gravitating system. This solution can be used to compare peculiar velocity field measurements with observations of large-scale structure. The predictions of both linear theory and second-order theory are compared with the results of N-body simulations. While linear theory systematically overestimates the velocity flows in high-density regions, the second-order corrections calculated herein remove this systematic error.

  14. Stellar magnetic field parameters from a Bayesian analysis of high-resolution spectropolarimetric observations

    NASA Astrophysics Data System (ADS)

    Petit, V.; Wade, G. A.

    2012-02-01

    In this paper we describe a Bayesian statistical method designed to infer the magnetic properties of stars observed using high-resolution circular spectropolarimetry in the context of large surveys. This approach is well suited for analysing stars for which the stellar rotation period is not known, and therefore the rotational phases of the observations are ambiguous. The model assumes that the magnetic observations correspond to a dipole oblique rotator, a situation commonly encountered in intermediate- and high-mass stars. Using reasonable assumptions regarding the model parameter prior probability density distributions, the Bayesian algorithm determines the posterior probability densities corresponding to the surface magnetic field geometry and strength by performing a comparison between the observed and computed Stokes V profiles. Based on the results of numerical simulations, we conclude that this method yields a useful estimate of the surface dipole field strength based on a small number (i.e. one or two) of observations. On the other hand, the method provides only weak constraints on the dipole geometry. The odds ratio, a parameter computed by the algorithm that quantifies the relative appropriateness of the magnetic dipole model versus the non-magnetic model, provides a more sensitive diagnostic of the presence of weak magnetic signals embedded in noise than traditional techniques. To illustrate the application of the technique to real data, we analyse seven ESPaDOnS and Narval observations of the early B-type magnetic star LP Ori. Insufficient information is available to determine the rotational period of the star and therefore the phase of the data; hence traditional modelling techniques fail to infer the dipole strength. In contrast, the Bayesian method allows a robust determination of the dipole polar strength, ? G. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) and at the Télescope Bernard Lyot (TBL). CFHT is operated by

  15. Automatic NMO Correction and Full Common Depth Point NMO Velocity Field Estimation in Anisotropic Media

    NASA Astrophysics Data System (ADS)

    Sedek, Mohamed; Gross, Lutz; Tyson, Stephen

    2017-01-01

    We present a new computational method of automatic normal moveout (NMO) correction that not only accurately flattens and corrects the far offset data, but simultaneously provides NMO velocity (v_nmo) for each individual seismic trace. The method is based on a predefined number of NMO velocity sweeps using linear vertical interpolation of different NMO velocities at each seismic trace. At each sweep, we measure the semblance between the zero offset trace (pilot trace) and the next seismic trace using a trace-by-trace rather than sample-by-sample based semblance measure; then after all the sweeps are done, the one with the maximum semblance value is chosen, which is assumed to be the most suitable NMO velocity trace that accurately flattens seismic reflection events. Other traces follow the same process, and a final velocity field is then extracted. Isotropic, anisotropic and lateral heterogenous synthetic geological models were built to test the method. A range of synthetic background noise, ranging from 10 to 30 %, was applied to the models. In addition, the method was tested on Hess's VTI (vertical transverse isotropy) model. Furthermore, we tested our method on a real pre-stack seismic CDP gathered from a gas field in Alaska. The results from the presented examples show an excellent NMO correction and extracted a reasonably accurate NMO velocity field.

  16. Determining cardiac velocity fields and intraventricular pressure distribution from a sequence of Ultrafast CT cardiac images

    SciTech Connect

    Song, S.M.; Napel, S. ); Leahy, R.M. . Signal and Image Processing Inst.); Brundage, B.H. . Div. of Cardiology); Boyd, D.P.

    1994-06-01

    A method of computing the velocity field and pressure distribution from a sequence of Ultrafast CT (UFCT) cardiac images is demonstrated. UFCT multi-slice cine imaging gives a series of tomographic slices covering the volume of the heart at a rate of 17 frames per second. The complete volume data set can be modeled using equations of continuum theory and through regularization, velocity vectors of both blood and tissue can be determined at each voxel in the volume. The authors present a technique to determine the pressure distribution throughout the volume of the left ventricle using the computed velocity field. A numerical algorithm is developed by discretizing the pressure Poisson equation (PPE), which is based on the Navier-Stokes equation. The algorithm is evaluated using a mathematical phantom of known velocity and pressure -- Couette flow. It is shown that the algorithm based on the PPE can reconstruct the pressure distribution using only the velocity data. Furthermore, the PPE is shown to be robust in the presence of noise. The velocity field and pressure distribution derived from a UFCT study of a patient are also presented.

  17. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    SciTech Connect

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J.; Basu, S.; Deheuvels, S.; Brandao, I. M.; Cunha, M. S.; Sousa, S. G.; Dogan, G.; Metcalfe, T. S.; Serenelli, A. M.; Garcia, R. A.; Ballot, J.; Weiss, A.; Appourchaux, T.; Casagrande, L.; Cassisi, S.; Creevey, O. L.; Lebreton, Y.; Noels, A.; and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  18. A Unified Geodetic Vertical Velocity Field (UGVVF), Version 1.0

    NASA Astrophysics Data System (ADS)

    Schmalzle, G.; Wdowinski, S.

    2014-12-01

    Tectonic motion, volcanic inflation or deflation, as well as oil, gas and water pumping can induce vertical motion. In southern California these signals are inter-mingled. In tectonics, properly identifying regions that are contaminated by other signals can be important when estimating fault slip rates. Until recently vertical deformation rates determined by high precision Global Positioning Systems (GPS) had large uncertainties compared to horizontal components and were rarely used to constrain tectonic models of fault motion. However, many continuously occupied GPS stations have been operating for ten or more years, often delivering uncertainties of ~1 mm/yr or less, providing better constraints for tectonic modeling. Various processing centers produced GPS time series and estimated vertical velocity fields, each with their own set of processing techniques and assumptions. We compare vertical velocity solutions estimated by seven data processing groups as well as two combined solutions (Figure 1). These groups include: Central Washington University (CWU) and New Mexico Institute of Technology (NMT), and their combined solution provided by the Plate Boundary Observatory (PBO) through the UNAVCO website. Also compared are the Jet Propulsion Laboratory (JPL) and Scripps Orbit and Permanent Array Center (SOPAC) and their combined solution provided as part of the NASA MEaSUREs project. Smaller velocity fields included are from Amos et al., 2014, processed at the Nevada Geodetic Laboratory, Shen et al., 2011, processed by UCLA and called the Crustal Motion Map 4.0 (CMM4) dataset, and a new velocity field provided by the University of Miami (UM). Our analysis includes estimating and correcting for systematic vertical velocity and uncertainty differences between groups. Our final product is a unified velocity field that contains the median values of the adjusted velocity fields and their uncertainties. This product will be periodically updated when new velocity fields

  19. Trace projection transformation: a new method for measurement of debris flow surface velocity fields

    NASA Astrophysics Data System (ADS)

    Yan, Yan; Cui, Peng; Guo, Xiaojun; Ge, Yonggang

    2016-12-01

    Spatiotemporal variation of velocity is important for debris flow dynamics. This paper presents a new method, the trace projection transformation, for accurate, non-contact measurement of a debris-flow surface velocity field based on a combination of dense optical flow and perspective projection transformation. The algorithm for interpreting and processing is implemented in C ++ and realized in Visual Studio 2012. The method allows quantitative analysis of flow motion through videos from various angles (camera positioned at the opposite direction of fluid motion). It yields the spatiotemporal distribution of surface velocity field at pixel level and thus provides a quantitative description of the surface processes. The trace projection transformation is superior to conventional measurement methods in that it obtains the full surface velocity field by computing the optical flow of all pixels. The result achieves a 90% accuracy of when comparing with the observed values. As a case study, the method is applied to the quantitative analysis of surface velocity field of a specific debris flow.

  20. Effects of the mean velocity field on the renormalized turbulent viscosity and correlation function

    NASA Astrophysics Data System (ADS)

    Kumar, Abhishek; Verma, Mahendra

    2015-11-01

    We perform renormalization group analysis of the Navier Stokes equation in the Eulerian framework in the presence of mean velocity field U0, and observe that that the renormalized viscosity ν (k) is independent of U0, where k is the wavenumber. Thus we show that ν (k) in the Eulerian field theory is Galilean invariant. We also compute ν (k) using numerical simulations and verify the above theoretical prediction. The velocity-velocity correlation function however exhibits damped oscillations whose time period of oscillation and damping time scales are given by 1 / kU0 and 1 / (ν (k) k2) respectively. In a modified form of Kraichnan's direct interaction approximation (DIA), the ``random mean velocity field'' of the large eddies sweeps the small-scale fluctuations. The DIA calculations also reveal that in the weak turbulence limit, the energy spectrum E (k) ~k - 3 / 2 , but for the strong turbulence limit, the random velocity field of the large-scale eddies is scale-dependent that leads to Kolmogorov's energy spectrum.

  1. Methods for measuring 1/1 error field in Wendelstein 7-X stellarator

    NASA Astrophysics Data System (ADS)

    Bozhenkov, S. A.; Lazerson, S.; Otte, M.; Gates, D. A.; Pedersen, T. Sunn; Wolf, R. C.

    2016-07-01

    Wendelstein 7-X is an optimized helical axis stellarator that came into operation at the end of 2015. A m/n  =  5/5 island chain is used in most of its configurations to form a divertor. This island chain at \

  2. A RADIAL VELOCITY AND CALCIUM TRIPLET ABUNDANCE SURVEY OF FIELD SMALL MAGELLANIC CLOUD GIANTS

    SciTech Connect

    De Propris, Roberto; Rich, R. Michael; Mallery, Ryan C.; Howard, Christian D.

    2010-05-10

    We present the results of a pilot wide-field radial velocity and metal abundance survey of red giants in 10 fields in the Small Magellanic Cloud (SMC). The targets lie at projected distances of 0.9 and 1.9 kpc from the SMC center (m - M = 18.79) to the north, east, south, and west. Two more fields are to the east at distances of 3.9 and 5.1 kpc. In this last field, we find only a few to no SMC giants, suggesting that the edge of the SMC in this direction lies approximately at 6 kpc from its center. In all eastern fields, we observe a double peak in the radial velocities of stars, with a component at the classical SMC recession velocity of {approx}160 km s{sup -1} and a high-velocity component at about 200 km s{sup -1}, similar to observations in H I. In the most distant field (3.9 kpc), the low-velocity component is at 106 km s{sup -1}. The metal abundance distribution in all fields is broad and centered at about [Fe/H] {approx}-1.25, reaching to solar and possibly slightly supersolar values and down to [Fe/H] of about -2.5. In the two innermost (0.9 kpc) northern and southern fields, we observe a secondary peak at metallicities of about {approx}-0.6. This may be evidence of a second episode of star formation in the center, possibly triggered by the interactions that created the Stream and Bridge.

  3. A Simple Method to Predict Threshold Shear Velocity in the Field

    NASA Astrophysics Data System (ADS)

    Li, J.; Okin, G. S.; Herrick, J. E.; Miller, M. E.; Munson, S. M.; Belnap, J.

    2009-12-01

    A very important parameter in predicting wind erosion is the threshold shear velocity, which is the minimal shear velocity required to initiate deflation of soil particles. Modeling and wind tunnel are primary methods in predicting threshold shear velocity. However, most models have limited applications in the presence of roughness elements, and running a wind tunnel in the field is labor-intensive and time-consuming. Soil crust (both physical and biological) is known to be a crucial factor affecting soil stability and threshold shear velocity. In this report, a simple and portable field method was tested in multiple locations of Utah for the estimation of threshold shear velocity. This method includes measuring size of holes (length and width) induced by shooting a “bullet ball” or “BB” gun, applying a pocket penetrometer, and a torvane on soil surface in the field. In the first stage of the experiment, a conventional wind tunnel was run in combination with BB gun, penetrometer, and torvane in field conditions for a range of soil texture. Results from both the BB gun and penetrometer applied at 45 degree to the ground were significantly correlated with the threshold shear velocity obtained using the wind tunnel (R2=0.70, P<0.001). In the second stage, BB gun and penetrometer method was applied to a serial of sites which have BSNE wind erosion monitors and known horizontal sediment fluxes. Our results showed that a combination of BB gun and penetrometer is able to provide decent prediction of threshold shear velocity in the presence of vegetation under different soil physical and biological conditions.

  4. Mass-conservative reconstruction of Galerkin velocity fields for transport simulations

    NASA Astrophysics Data System (ADS)

    Scudeler, C.; Putti, M.; Paniconi, C.

    2016-08-01

    Accurate calculation of mass-conservative velocity fields from numerical solutions of Richards' equation is central to reliable surface-subsurface flow and transport modeling, for example in long-term tracer simulations to determine catchment residence time distributions. In this study we assess the performance of a local Larson-Niklasson (LN) post-processing procedure for reconstructing mass-conservative velocities from a linear (P1) Galerkin finite element solution of Richards' equation. This approach, originally proposed for a-posteriori error estimation, modifies the standard finite element velocities by imposing local conservation on element patches. The resulting reconstructed flow field is characterized by continuous fluxes on element edges that can be efficiently used to drive a second order finite volume advective transport model. Through a series of tests of increasing complexity that compare results from the LN scheme to those using velocity fields derived directly from the P1 Galerkin solution, we show that a locally mass-conservative velocity field is necessary to obtain accurate transport results. We also show that the accuracy of the LN reconstruction procedure is comparable to that of the inherently conservative mixed finite element approach, taken as a reference solution, but that the LN scheme has much lower computational costs. The numerical tests examine steady and unsteady, saturated and variably saturated, and homogeneous and heterogeneous cases along with initial and boundary conditions that include dry soil infiltration, alternating solute and water injection, and seepage face outflow. Typical problems that arise with velocities derived from P1 Galerkin solutions include outgoing solute flux from no-flow boundaries, solute entrapment in zones of low hydraulic conductivity, and occurrences of anomalous sources and sinks. In addition to inducing significant mass balance errors, such manifestations often lead to oscillations in concentration

  5. STELLAR LOCI II. A MODEL-FREE ESTIMATE OF THE BINARY FRACTION FOR FIELD FGK STARS

    SciTech Connect

    Yuan, Haibo; Liu, Xiaowei; Xiang, Maosheng; Huang, Yang; Chen, Bingqiu; Wu, Yue; Hou, Yonghui; Zhang, Yong E-mail: x.liu@pku.edu.cn

    2015-02-01

    We propose a stellar locus outlier (SLOT) method to determine the binary fraction of main-sequence stars statistically. The method is sensitive to neither the period nor mass ratio distributions of binaries and is able to provide model-free estimates of binary fraction for large numbers of stars of different populations in large survey volumes. We have applied the SLOT method to two samples of stars from the Sloan Digital Sky Survey (SDSS) Stripe 82, constructed by combining the recalibrated SDSS photometric data with the spectroscopic information from the SDSS and LAMOST surveys. For the SDSS spectroscopic sample, we find an average binary fraction for field FGK stars of 41% ± 2%. The fractions decrease toward late spectral types and are 44% ± 5%, 43% ± 3%, 35% ± 5%, and 28% ± 6% for stars with g – i colors in the range 0.3-0.6 mag, 0.6-0.9 mag, 0.9-1.2 mag, and 1.2-1.6 mag, respectively. A modest metallicity dependence is also found. The fraction decreases with increasing metallicity. For stars with [Fe/H] between –0.5 and 0.0 dex, –1.0 and –0.5 dex, –1.5 and –1.0 dex, and –2.0 and –1.5 dex, the inferred binary fractions are 37% ± 3%, 39% ± 3%, 50% ± 9%, and 53% ± 20%, respectively. We have further divided the sample into stars from the thin disk, the thick disk, the transition zone between them, and the halo. The results suggest that the Galactic thin and thick disks have comparable binary fractions, whereas the Galactic halo contains a significantly larger fraction of binaries. Applying the method to the LAMOST spectroscopic sample yields consistent results. Finally, other potential applications and future work with the method are discussed.

  6. Methods of measuring velocity fields in the problem with a channel with periodic hills

    NASA Astrophysics Data System (ADS)

    Kozinkin, L. A.; Karchevskiy, M. N.

    2016-11-01

    The work studies the flow characteristics in a channel with periodic hills on the basis of three algorithms for calculating the flow velocity fields through the images: Particle Image Velocimetry, Particle Tracking Velocimetry, and Pyramid Correlation. Descriptions of algorithms, detailed information about the experiment and parameters of the received data processing, as well as the results of calculations of instantaneous velocity fields at selected time points obtained by corresponding methods are provided. In addition, the presented techniques are compared on the basis of experimental data.

  7. Particle size, magnetic field, and blood velocity effects on particle retention in magnetic drug targeting.

    PubMed

    Cherry, Erica M; Maxim, Peter G; Eaton, John K

    2010-01-01

    A physics-based model of a general magnetic drug targeting (MDT) system was developed with the goal of realizing the practical limitations of MDT when electromagnets are the source of the magnetic field. The simulation tracks magnetic particles subject to gravity, drag force, magnetic force, and hydrodynamic lift in specified flow fields and external magnetic field distributions. A model problem was analyzed to determine the effect of drug particle size, blood flow velocity, and magnetic field gradient strength on efficiency in holding particles stationary in a laminar Poiseuille flow modeling blood flow in a medium-sized artery. It was found that particle retention rate increased with increasing particle diameter and magnetic field gradient strength and decreased with increasing bulk flow velocity. The results suggest that MDT systems with electromagnets are unsuitable for use in small arteries because it is difficult to control particles smaller than about 20 microm in diameter.

  8. Group velocity effect on resonant, long-range wake-fields in slow wave structures

    NASA Astrophysics Data System (ADS)

    Smirnov, A. V.

    2002-03-01

    Synchronous wake-fields in a dispersive waveguide are derived in a general explicit form on the basis of a rigorous electro-dynamical approach using Fourier transformations. The fundamental role of group velocity in wake-field propagation, calculation of attenuation, amplitudes, form-factors and loss-factors is analyzed for single bunch radiation. Adiabatic tapering of the waveguide and bunch density variation is taken into account analytically for the time-domain fields. Effects of field "compression/expansion" and group delays are demonstrated. The role of these effects is discussed for single bunch wake-fields, transient beam loading, BBU and HOMs. A novel waveguide structure with central rf coupling and both positive and negative velocities is proposed. It can be used effectively in both high-energy accelerators and single-section linacs.

  9. Measurement of temperature and velocity fields in a convective fluid flow in air using schlieren images.

    PubMed

    Martínez-González, A; Moreno-Hernández, D; Guerrero-Viramontes, J A

    2013-08-01

    A convective fluid flow in air could be regulated if the physical process were better understood. Temperature and velocity measurements are required in order to obtain a proper characterization of a convective fluid flow. In this study, we show that a classical schlieren system can be used for simultaneous measurements of temperature and velocity in a convective fluid flow in air. The schlieren technique allows measurement of the average fluid temperature and velocity integrated in the direction of the test beam. Therefore, in our experiments we considered surfaces with isothermal conditions. Temperature measurements are made by relating the intensity level of each pixel in a schlieren image to the corresponding knife-edge position measured at the exit focal plane of the schlieren system. The same schlieren images were also used to measure the velocity of the fluid flow by using optical flow techniques. The algorithm implemented analyzes motion between consecutive schlieren frames to obtain a tracked sequence and finally velocity fields. The proposed technique was applied to measure the temperature and velocity fields in natural convection of air due to unconfined and confined heated rectangular plates.

  10. GIRAFFE multiple integral field units at VLT: A unique tool to recover velocity fields of distant galaxies

    NASA Astrophysics Data System (ADS)

    Flores, H.; Puech, M.; Hammer, F.; Garrido, O.; Hernandez, O.

    2004-06-01

    The GIRAFFE spectrograph is unique in providing the integral field spectroscopy of fifteen distant galaxies at the same time. It has been successfully implemented at the second VLT unit within the FLAMES facility. We present GIRAFFE observations acquired during the Guaranteed Time Observation of the Paris Observatory, using total exposure times ranging from 6 to 12 h. The reduced 3D cube of each galaxy has been deconvolved using our new package DisGal3D. This software has been written using the only assumption that UV light traces the emission line regions. The comparison between GIRAFFE spectra and HST imagery allows us to recover details on velocity fields as small as 0.3-0.4 arcsec. It has been successfully tested using Fabry Perot observations of nearby galaxies purposely redshifted to large distances. We present here preliminary results for three distant galaxies at 0.45< z < 0.65, whose velocity fields have been derived with exquisite spectral (R=10 000) and spatial resolutions. Observed velocity fields range from disturbed fields expected in major merger events to those of regular spiral with minor perturbations. For the latter, one could accurately derive the dynamical major axis and the maximal rotational velocity. We conclude that dynamical properties of a large number of distant galaxies can be routinely derived at VLT. This opens a new avenue towards the understanding of the galaxy formation and evolution during the last 8 Gyr. Based on ESO GTO programs No 71.A-0322(A) and 72.A-0169(A).

  11. Kriging interpolating cosmic velocity field. II. Taking anistropies and multistreaming into account

    NASA Astrophysics Data System (ADS)

    Yu, Yu; Zhang, Jun; Jing, Yipeng; Zhang, Pengjie

    2017-02-01

    Measuring the volume-weighted peculiar velocity statistics from inhomogeneously and sparsely distributed galaxies/halos, by existing velocity assignment methods, suffers from a significant sampling artifact. As an alternative, the Kriging interpolation based on Gaussian processes was introduced and evaluated [Y. Yu, J. Zhang, Y. Jing, and P. Zhang, Phys. Rev. D 92, 083527 (2015), 10.1103/PhysRevD.92.083527]. Unfortunately, the most straightforward application of Kriging does not perform better than the existing methods in the literature. In this work, we investigate two physically motivated extensions. The first takes into account of the anisotropic velocity correlations. The second introduces the nugget effect, on account of multistreaming of the velocity field. We find that the performance is indeed improved. For sparsely sampled data [nP≲6 ×10-3(h-1 Mpc )-3 ] where the sampling artifact is the most severe, the improvement is significant and is two-fold: 1) The scale of reliable measurement of the velocity power spectrum is extended by a factor ˜1.6 , and 2) the dependence on the velocity correlation prior is weakened by a factor of ˜2 . We conclude that such extensions are desirable for accurate velocity assignment by Kriging.

  12. Time-lapse Measurements of Scholte Wave Velocity Over a Compacting Oil Field

    NASA Astrophysics Data System (ADS)

    Wills, P. B.; Hatchell, P. J.

    2007-12-01

    Acquisition of time-lapse seismic data over producing oil and gas fields is a proven method for optimizing hydrocarbon production. Most current data have been acquired using towed-streamer seismic vessels but new systems incorporating permanent Ocean Bottom Cable (OBC) systems are gaining in popularity, both as a way to achieve better repeatability and also to reduce the cost of acquiring many time-lapse repeats of the baseline survey. Over the last three years, more than seven repeat data sets have been acquired at the permanent OBC system installed (by the operator, BP) over the Valhall oil field located offshore Norway. This system contains ~2400 four-component receiver stations that are recorded using a dense areal shot grid ("carpet" shoot) that provides high fold and has delivered excellent time-lapse signals starting from the first repeat occurring just three months after the baseline. Time-lapse OBC data are conventionally used to measure amplitude and velocity changes of body wave reflections (PP and PS) but other measurements are also possible. In particular, Scholte waves are strongly visible on records acquired everywhere in the field on appropriately processed data and, given the high fold (because of the dense shots), Scholte wave velocity and anisotropy time-lapse changes obtained with both hydrophone and geophone sensors are accurately and robustly estimated. The resulting shallow velocity maps are very sensitive to the seabed strains and show large velocity changes overlying deep production. Also, reconstruction of compressional "head wave" velocity difference measurements and vertically propagating shear wave shallow time-lapse statics produce maps that resemble the Scholte wave maps, with differences that reflect the physics of the propagation modes and effective fold. A reservoir model that includes deep reservoir volume changes together with appropriate geomechanical properties in the overburden and a shallow conversion of strain to velocity is

  13. Measurements of Dendritic Growth Velocities in Undercooled Melts of Pure Nickel Under Static Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Gao, Jianrong; Zhang, Zongning; Zhang, Yingjie

    2012-01-01

    Dendritic growth velocities in undercooled melts of pure Ni have been intensively studied over the past fifty years. However, the literature data are at marked variance with the prediction of the widely accepted model for rapid dendritic growth both at small and at large undercoolings. In the present work, bulk melts of pure Ni samples of high purity were undercooled by glass fluxing treatment under a static magnetic field. The recalescence processes of the samples at different undercoolings were recorded using a high-speed camera, and were modeled using a software to determine the dendritic growth velocities. The present data confirmed the effect of melt flow on dendritic growth velocities at undercoolings below 100 K. A comparison of the present data with previous measurements on a lower purity material suggested an effect of impurities on dendritic growth velocities at undercoolings larger than 200 K as well.

  14. Full-field velocity imaging of red blood cells in capillaries with spatiotemporal demodulation autocorrelation.

    PubMed

    Wang, Mingyi; Zeng, Yaguang; Dong, Nannan; Liao, Riwei; Yang, Guojian

    2016-03-01

    We propose a full-field optical method for the label-free and quantitative mapping of the velocities of red blood cells (RBCs) in capillaries. It integrates spatiotemporal demodulation and an autocorrelation algorithm, and measures RBC velocity according to the ratio of RBC length to lag time. Conventionally, RBC length is assumed to be a constant and lag time is taken as a variable, while our method treats both of them as variables. We use temporal demodulation and the Butterworth spatial filter to separate RBC signal from background signal, based on which we obtain the RBC length by image segmentation and lag time by autocorrelation analysis. The RBC velocity calculated now is more accurate. The validity of our method is verified by an in vivo experiment on a mouse ear. Owing to its higher image signal-to-noise ratio, our method can be used for mapping RBC velocity in the turbid tissue case.

  15. Time evolution of the lateral-velocity distribution for a strong-field-ionization process

    NASA Astrophysics Data System (ADS)

    Ivanov, I. A.

    2016-05-01

    We study time development of a cusp in the lateral-velocity distribution for the process of strong-field ionization. The lateral-velocity distribution is computed using an ab initio quantum mechanical procedure for the moments of time inside and after the end of the laser pulse. We show that at the moment of time corresponding to the midpoint of the laser pulse the lateral-velocity distribution is a smooth Gaussian curve, its parameters agreeing very well with the predictions of the tunelling theories. At the moment of time corresponding to the end of the pulse the lateral-velocity distribution narrows considerably, showing the initial stage of the cusp-formation process due to the Coulomb focusing effect. Following evolution of the ionized wave packet yet further in time we consider the cusp formation in detail.

  16. Full-field velocity imaging of red blood cells in capillaries with spatiotemporal demodulation autocorrelation

    NASA Astrophysics Data System (ADS)

    Wang, Mingyi; Zeng, Yaguang; Dong, Nannan; Liao, Riwei; Yang, Guojian

    2016-03-01

    We propose a full-field optical method for the label-free and quantitative mapping of the velocities of red blood cells (RBCs) in capillaries. It integrates spatiotemporal demodulation and an autocorrelation algorithm, and measures RBC velocity according to the ratio of RBC length to lag time. Conventionally, RBC length is assumed to be a constant and lag time is taken as a variable, while our method treats both of them as variables. We use temporal demodulation and the Butterworth spatial filter to separate RBC signal from background signal, based on which we obtain the RBC length by image segmentation and lag time by autocorrelation analysis. The RBC velocity calculated now is more accurate. The validity of our method is verified by an in vivo experiment on a mouse ear. Owing to its higher image signal-to-noise ratio, our method can be used for mapping RBC velocity in the turbid tissue case.

  17. Evaluating a campaign GNSS velocity field derived from an online precise point positioning service

    NASA Astrophysics Data System (ADS)

    Holden, L.; Silcock, D.; Choy, S.; Cas, R.; Ailleres, L.; Fournier, N.

    2016-10-01

    Traditional processing of Global Navigation Satellite System (GNSS) data using dedicated scientific software has provided the highest levels of positional accuracy, and has been used extensively in geophysical deformation studies. To achieve these accuracies a significant level of understanding and training is required, limiting their availability to the general scientific community. Various online GNSS processing services, now freely available, address some of these difficulties and allow users to easily process their own GNSS data and potentially obtain high quality results. Previous research into these services has focused on Continually Operating Reference Station (CORS) GNSS data. Less research exists on the results achievable with these services using large campaign GNSS datasets, which are inherently noisier than CORS data. Even less research exists on the quality of velocity fields derived from campaign GNSS data processed through online PPP services. Particularly, whether they are suitable for geodynamic and deformation studies where precise and reliable velocities are needed. In this research, we process a very large campaign GPS dataset (spanning ten years) with the online Jet Propulsion Laboratory (JPL) Automated Precise Positioning Service (APPS) service. This dataset is taken from a GNSS network specifically designed and surveyed to measure deformation through the central North Island of New Zealand (NZ). This includes regional CORS stations. We then use these coordinates to derive a horizontal and vertical velocity field. This is the first time that a large campaign GPS dataset has been processed solely using an online service and the solutions used to determine a horizontal and vertical velocity field. We compared this velocity field to that of another well utilised GNSS scientific software package. The results show a good agreement between the CORS positions and campaign station velocities obtained from the two approaches. We discuss the

  18. Evaluating a campaign GNSS velocity field derived from an online precise point positioning service

    NASA Astrophysics Data System (ADS)

    Holden, L.; Silcock, D.; Choy, S.; Cas, R.; Ailleres, L.; Fournier, N.

    2017-01-01

    Traditional processing of Global Navigation Satellite System (GNSS) data using dedicated scientific software has provided the highest levels of positional accuracy, and has been used extensively in geophysical deformation studies. To achieve these accuracies a significant level of understanding and training is required, limiting their availability to the general scientific community. Various online GNSS processing services, now freely available, address some of these difficulties and allow users to easily process their own GNSS data and potentially obtain high quality results. Previous research into these services has focused on Continually Operating Reference Station (CORS) GNSS data. Less research exists on the results achievable with these services using large campaign GNSS data sets, which are inherently noisier than CORS data. Even less research exists on the quality of velocity fields derived from campaign GNSS data processed through online precise point positioning services. Particularly, whether they are suitable for geodynamic and deformation studies where precise and reliable velocities are needed. In this research, we process a very large campaign GPS data set (spanning 10 yr) with the online Jet Propulsion Laboratory Automated Precise Positioning Service. This data set is taken from a GNSS network specifically designed and surveyed to measure deformation through the central North Island of New Zealand. This includes regional CORS stations. We then use these coordinates to derive a horizontal and vertical velocity field. This is the first time that a large campaign GPS data set has been processed solely using an online service and the solutions used to determine a horizontal and vertical velocity field. We compared this velocity field to that of another well utilized GNSS scientific software package. The results show a good agreement between the CORS positions and campaign station velocities obtained from the two approaches. We discuss the implications

  19. Investigation of the Velocity Field and Flow Regime of David Glacier and Drygalski Ice Tongue, Antarctica

    NASA Astrophysics Data System (ADS)

    Wuite, J.; Jezek, K. C.

    2005-12-01

    Recent observations of outlet glaciers in both Greenland and Antarctica show surprising and unexpectedly rapid changes in flow velocities. Outlet glaciers drain the majority of the polar ice sheets and consequently these changes threaten their stability and can lead to rising sea levels. It is therefore important to investigate their flow governing processes and document changes. We measured surface velocity over large portions of David Glacier and its floating seaward extension Drygalski Ice Tongue. This is the largest outlet glacier on the Scott Coast draining a section of the East Antarctic Ice Sheet into the Ross Sea. Giant iceberg B15-A recently collided with the ice tongue and broke off a significant section. To obtain velocities we used combinations of intensity feature tracking, interferometric speckle tracking and phase interferometry using RADARSAT-1 images acquired during the AMM-1 and MAMM missions. We compare short term velocities, 3-year averaged velocities and earlier studies to analyze spatial and temporal variability of the surface velocity field. We use obtained velocities, in combination with isostatically derived ice thickness from ICESat data, to estimate basal melting along the glacier. Also we investigate the role of lateral drag through force-budget theory and determine the equilibrium profile of the ice tongue. Unlike for example the West Antarctic Ice Streams and Jakobshavn Isbrae, our data suggests that the David Glacier velocity field has remained relatively constant from about 1991 - 2000 and likely much longer. The pattern of melting and freezing along the base of the glacier is consistent with an ice pump mechanism. In the fjord lateral drag opposes approximately 90% of the driving stress; this gradually drops to the point where most resistance comes from longitudinal stress gradients. We find the modeled and ICESat derived profile agree favorably suggesting steady state conditions

  20. IAG Working Group on Regional Dense Velocity Fields: First Results and Steps Ahead

    NASA Astrophysics Data System (ADS)

    Bruyninx, Carine

    2010-05-01

    The IAG Working Group (WG) on "Regional Dense Velocity Fields" was created within IAG sub-commission 1.3 "Regional Reference Frames" at the IUGG General Assembly in Perugia in 2007. The goal of the Working Group is to densify the latest realization of the ITRS and provide regional dense velocity information in a common global reference frame. For that purpose, working group members join efforts with the regional sub-commissions (AFREF, NAREF, SIRGAS, EUREF, …) and analysis groups processing data from local/regional continuous and episodic GNSS stations. Up to now, dedicated region coordinators have gathered velocity solutions (in accordance with the WG requirements) for their region and combined these solutions with the sub-commission regional solutions to produce a regional cumulative combined solution. Two combination coordinators performed a first test combination of these regional solutions together with global solutions in order to identify the main problems when producing a dense velocity field based on multiple cumulative position and velocity solutions. First comparisons between different velocity solutions show an RMS agreement between 0.3 mm/yr and 0.5 mm/yr resp. for the horizontal and vertical velocities. In some cases, significant disagreements between the velocities of some of the networks are seen, but these are primarily caused by the inconsistent handling of discontinuity epochs and solution numbers. Consequently, this test identified the urgent need for a consensus on the attribution of discontinuity epochs for stations common to several solutions. Due to the use of different analysis strategies and software packages by the individual contributors, finding such a consensus is a challenge as most probably not the same discontinuities are seen by different people. A possible way to go ahead for the Working Group could be to combine solutions at the weekly level. This approach is one of the alternative procedures which are presently under

  1. Exploiting SENTINEL-1 Amplitude Data for Glacier Surface Velocity Field Measurements: Feasibility Demonstration on Baltoro Glacier

    NASA Astrophysics Data System (ADS)

    Nascetti, A.; Nocchi, F.; Camplani, A.; Di Rico, C.; Crespi, M.

    2016-06-01

    The leading idea of this work is to continuously retrieve glaciers surface velocity through SAR imagery, in particular using the amplitude data from the new ESA satellite sensor Sentinel-1 imagery. These imagery key aspects are the free access policy, the very short revisit time (down to 6 days with the launch of the Sentinel-1B satellite) and the high amplitude resolution (up to 5 m). In order to verify the reliability of the proposed approach, a first experiment has been performed using Sentinel-1 imagery acquired over the Karakoram mountain range (North Pakistan) and Baltoro and other three glaciers have been investigated. During this study, a stack of 11 images acquired in the period from October 2014 to September 2015 has been used in order to investigate the potentialities of the Sentinel-1 SAR sensor to retrieve the glacier surface velocity every month. The aim of this test was to measure the glacier surface velocity between each subsequent pair, in order to produce a time series of the surface velocity fields along the investigated period. The necessary coregistration procedure between the images has been performed and subsequently the glaciers areas have been sampled using a regular grid with a 250 × 250 meters posting. Finally the surface velocity field has been estimated, for each image pair, using a template matching procedure, and an outlier filtering procedure based on the signal to noise ratio values has been applied, in order to exclude from the analysis unreliable points. The achieved velocity values range from 10 to 25 meters/month and they are coherent to those obtained in previous studies carried out on the same glaciers and the results highlight that it is possible to have a continuous update of the glacier surface velocity field through free Sentinel-1 imagery, that could be very useful to investigate the seasonal effects on the glaciers fluid-dynamics.

  2. The Crustal Velocity Field Mosaic of the Alpine Mediterranean Area: Insight from New Geodetic Data

    NASA Astrophysics Data System (ADS)

    Farolfi, G.; Del Ventisette, C.

    2016-08-01

    Geodetic techniques, such as Global Navigation Satellite System (GNSS), Synthetic Aperture Radar (SAR), satellite gravity missions, etc., have made significant contributions in monitoring temporal and spatial changes in Earth's lithosphere and atmosphere.A new crustal velocity field for the Alpine Mediterranean area (Farolfi & Del Ventisette, 2015) was determined by using a time series spanning 6.5 years of GNSS permanent stations. Thus, processing was performed by using state-of-the-art antenna phase center model, new recomputed satellite orbits and a new more accurate tropospheric model.The aim of this work is to calculate and analyze the spatial variations of continuous time series of GNSS permanent stations, to estimate crustal velocities in the Alpine Mediterranean area. The resulting velocity field gives a strong contribution in the framework of the contemporary geodynamics.

  3. Velocity-Space Diffusion Coefficients Due to Full-Wave ICRF Fields in Toroidal Geometry

    SciTech Connect

    Harvey, R.W.; Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D.; Ershov, N.M.; Smirnov, A.P.; Bonoli, P.; Wright, J.C.; Smithe, D.N.

    2005-09-26

    Jaeger et al. have calculated bounce-averaged QL diffusion coefficients from AORSA full-wave fields, based on non-Maxwellian distributions from CQL3D Fokker-Planck code. A zero banana-width approximation is employed. Complementing this calculation, a fully numerical calculation of ion velocity diffusion coefficients using the full-wave fields in numerical tokamak equilibria has been implemented to determine the finite orbit width effects. The un-approximated Lorentz equation of motion is integrated to obtain the change in velocity after one complete poloidal transit of the tokamak. Averaging velocity changes over initial starting gyro-phase and toroidal angle gives bounce-averaged diffusion coefficients. The coefficients from the full-wave and Lorentz orbit methods are compared for an ITER DT second harmonic tritium ICRF heating case: the diffusion coefficients are similar in magnitude but reveal substantial finite orbit effects.

  4. Quantum mechanical E × B drift velocity in a weakly inhomogeneous electromagnetic field

    NASA Astrophysics Data System (ADS)

    Chan, Poh Kam; Oikawa, Shun-ichi; Kosaka, Wataru

    2017-07-01

    The analytical solution for the quantum mechanical drift velocity for a non-relativistic spinless charged particle of E × B drift in the presence of a weakly inhomogeneous electric and magnetic field for the magnetized plasma is presented. Using the Heisenberg equation of motion, the time evolution of the position and momentum operators for the charged particle is solved. From the time dependent operators, the analytical solution of the time dependent momenta operators and position operators is derived. The quantum mechanical expansion rates of variances are shown to agree with the numerical results. Most importantly, the quantum mechanical E × B drift velocity coincides perfectly with the classical drift velocity in the limit of Planck's constant being zero. With higher order electric field inhomogeneity, low energy particles would drift faster than what the classical drift theory predicts.

  5. Effects of magnetic field and Hall current to the blood velocity and LDL transfer

    NASA Astrophysics Data System (ADS)

    Abdullah, I.; Naser, N.; Talib, A. H.; Mahali, S.

    2015-09-01

    The magnetic field and Hall current effects have been considered on blood velocity and concentration of low-density lipoprotein (LDL). It is important to observe those effects to the flowing blood in a stenosed artery. The analysis from the obtained results may be useful to some clinical procedures, such as MRI, where the radiologists may have more information in the investigations before cardiac operations could be done. In this study, the uniform magnetic field and Hall current are applied to the Newtonian blood flow through an artery having a cosine-shaped stenosis. The governing equations are coupled with mass transfer and solved employing a finite difference Marker and Cell (MAC) method with an appropriate initial and boundary conditions. The graphical results of velocity profiles and LDL concentration are presented in this paper and the results show that the velocity increases and concentration decreases as Hall parameter increased.

  6. Arctic sea ice velocity field: General circulation and turbulent-like fluctuations

    NASA Astrophysics Data System (ADS)

    Rampal, P.; Weiss, J.; Marsan, D.; Bourgoin, M.

    2009-10-01

    Using buoy trajectories of the IABP data set, we analyze the Arctic sea ice velocity field as the superposition of a mean field and fluctuations. We study how the mean field can be objectively defined, using appropriate spatial and temporal averaging scales depending on the season considered: 400 km and 5 ? months for winter (i.e., approximately all the polar winter duration), and 200 km and 2 ? months for summer (i.e., approximately all the polar summer duration). The mean velocity field shows a strong intra-annual (between winter and the following summer) as well as interannual variability. The fluctuations, i.e., the remaining part of the velocity field after subtracting the mean field, are analyzed in terms of diffusion properties. Although the Arctic sea ice cover is a solid, we show that the fluctuations follow the same diffusion regimes as the ones predicted for turbulent flows, as observed in geophysical fluids like the ocean or the atmosphere. We found that the integral time and the diffusivity of sea ice are in the same ranges as those estimated for the ocean, i.e., 1.5 days in winter and 1.3 days in summer and 0.44 × 103 m2/s for winter and 0.45 × 103 m2/s in summer, respectively. However, the statistics of the sea ice fluctuating velocity deviate from classical turbulence theory, as they show exponential instead of Gaussian distributions. Sea ice velocity and acceleration are intermittent, and both are characterized by a multifractal scaling. The oceanic and atmospheric dynamic forcing cannot explain solely the statistical properties of sea ice kinematics and dynamics. We argue that sea ice dynamic is significantly influenced by the interplay of multiple fractures that are activated intermittently within the ice pack.

  7. On Density and Velocity Fields and beta from the IRAS PSCZ Survey

    NASA Astrophysics Data System (ADS)

    Schmoldt, Inga M.; Saar, Veikko; Saha, Prasenjit; Branchini, E.; Efstathiou, G. P.; Frenk, C. S.; Keeble, O.; Maddox, S.; McMahon, R.; Oliver, S.; Rowan-Robinson, M.; Saunders, W.; Sutherland, W. J.; Tadros, H.; White, S. D. M.

    1999-09-01

    We present a version of the Fourier-Bessel method first introduced by Fisher and coworkers and Zaroubi and coworkers with two extensions: (1) we amend the formalism to allow a generic galaxy weight that can be constant, rather than the more conventional overweighting of galaxies at high distances, and (2) we correct for the masked zones by extrapolation of Fourier-Bessel modes rather than by cloning from the galaxy distribution in neighboring regions. We test the procedure extensively on N-body simulations and find that it gives generally unbiased results but that the reconstructed velocities tend to be overpredicted in high-density regions. Applying the formalism to the PSCz redshift catalog, we find that beta=0.7+/-0.5 from a comparison of the reconstructed Local Group velocity to the cosmic microwave background dipole. From an anisotropy test of the velocity field, we find that beta=1 cold dark matter models normalized to the current cluster abundance can be excluded with 90% confidence. The density and velocity fields reconstructed agree with the fields found by Branchini and coworkers on most points. We find a back infall into the Great Attractor region (Hydra-Centaurus region), but tests suggest that this may be an artifact. We identify all the major clusters in our density field and confirm the existence of some previously identified possible ones.

  8. Probing High-Velocity Transient-Field Strength Using Heavy-ions Traversing Fe and Gd

    SciTech Connect

    Fiori, E.; Georgiev, G.; Cabaret, S.; Lozeva, R.; Jungclaus, A.; Modamio, V.; Walker, J.; Balabanski, D. L.; Blazhev, A.; Clement, E.; Grevy, S.; Stodel, C.; Thomas, J. C.; Danchev, M.; Daugas, J. M.; Hass, M.; Kumar, V.; Leske, J.; Pietralla, N.

    2009-08-26

    The transient field strength for {sup 76}Ge ions, passing through iron and gadolinium layers at velocities approxZv{sub 0}, has been measured. Although a sizeable value has been obtained for Gd, a vanishing strength has been observed in Fe.

  9. A simple method to estimate threshold friction velocity of wind erosion in the field

    USDA-ARS?s Scientific Manuscript database

    Nearly all wind erosion models require the specification of threshold friction velocity (TFV). Yet determining TFV of wind erosion in field conditions is difficult as it depends on both soil characteristics and distribution of vegetation or other roughness elements. While several reliable methods ha...

  10. Conditions for similitude between the fluid velocity and electric field in electroosmotic flow

    SciTech Connect

    E. B. Cummings; S. K. Griffiths; R. H. Nilson; P. H. Paul

    1999-04-01

    Electroosmotic flow is fluid motion driven by an electric field acting on the net fluid charge produced by charge separation at a fluid-solid interface. Under many conditions of practical interest, the resulting fluid velocity is proportional to the local electric field, and the constant of proportionality is everywhere the same. Here the authors show that the main conditions necessary for this similitude are a steady electric field, uniform fluid and electric properties, an electric Debye layer that is thin compared to any physical dimension, and fluid velocities on all inlet and outlet boundaries that satisfy the Helmholtz-Smoluchowski relation normally applicable to fluid-solid boundaries. Under these conditions, the velocity field can be determined directly from the Laplace equation governing the electric potential, without solving either the continuity or momentum equations. Three important consequences of these conditions are that the fluid motion is everywhere irrotational, that fluid velocities in two-dimensional channels bounded by parallel planes are independent of the channel depth, and that such flows exhibit no dependence on the Reynolds number.

  11. Acoustic reconstruction of the velocity field in a furnace using a characteristic flow model.

    PubMed

    Li, Yanqin; Zhou, Huaichun; Chen, Shiying; Zhang, Yindi; Wei, Xinli; Zhao, Jinhui

    2012-06-01

    An acoustic method can provide a noninvasive, efficient and full-field reconstruction of aerodynamic fields in a furnace. A simple yet reasonable model is devised for reconstruction of a velocity field in a cross section of a tangential furnace from acoustic measurements based on typical physical characteristics of the field. The solenoidal component of the velocity field is modeled by a curved surface, derived by rotating a curve of Gaussian distribution, determined by six characteristic parameters, while the nonrotational component is governed by a priori knowledge. Thus the inverse problem is translated into determination of the characteristic parameters using a set of acoustic projection data. First numerical experiments were undertaken to simulate the acoustic measurement, so as to preliminarily validate the effectiveness of the model. Based on this, physical experiments under different operating conditions were performed in a pilot-scale setup to provide a further test. Hot-wire anemometry and strip floating were applied to compare with acoustic measurements. The acoustic measurements provided satisfactory consistency with both of these approaches. Nevertheless, for a field with a relatively large magnitude of air velocities, the acoustic measurement can give more reliable reconstructions. Extension of the model to measurements of hot tangential furnaces is also discussed.

  12. Shape coexistence effects on stellar weak interaction rates of proton-rich nuclei within beyond-mean-field approach

    NASA Astrophysics Data System (ADS)

    Petrovici, A.; Andrei, O.

    2017-06-01

    Relevant for the astrophysical rp-process, proton-rich A˜70 nuclei manifesting shape coexistence have been investigated in the frame of the beyond-mean-field complex Excited Vampir variational model with symmetry projection before variation using the effective interaction obtained from a G-matrix based on BonnA/BonnCD potential. Reliable predictions on stellar weak interaction rates emerged starting from the realistic description of the experimentally accesible properties. The influence of shape coexistence and mixing in the structure of the low-lying parent states as well as in the independently calculated daughter states on weak interaction rates under X-ray burst environment is discussed.

  13. In vivo PIV measurement of red blood cell velocity field in microvessels considering mesentery motion.

    PubMed

    Sugii, Yasuhiko; Nishio, Shigeru; Okamoto, Koji

    2002-05-01

    As endothelial cells are subject to flow shear stress, it is important to determine the detailed velocity distribution in microvessels in the study of mechanical interactions between blood and endothelium. Recently, particle image velocimetry (PIV) has been proposed as a quantitative method of measuring velocity fields instantaneously in experimental fluid mechanics. The authors have developed a highly accurate PIV technique with improved dynamic range. spatial resolution and measurement accuracy. In this paper, the proposed method was applied to images of the arteriole in the rat mesentery using an intravital microscope and high-speed digital video system. Taking the mesentery motion into account, the PIV technique was improved to measure red blood cell (RBC) velocity. Velocity distributions with spatial resolutions of 0.8 x 0.8 microm were obtained even near the wall in the centre plane of the arteriole. The arteriole velocity profile was blunt in the centre region of the vessel cross-section and sharp in the near-wall region. Typical flow features for non-Newtonian fluid were shown. Time-averaged velocity profiles in six cross sections with different diameters were compared.

  14. Effect of Range and Angular Velocity of Passive Movement on Somatosensory Evoked Magnetic Fields.

    PubMed

    Sugawara, Kazuhiro; Onishi, Hideaki; Yamashiro, Koya; Kojima, Sho; Miyaguchi, Shota; Kotan, Shinichi; Tsubaki, Atsuhiro; Kirimoto, Hikari; Tamaki, Hiroyuki; Shirozu, Hiroshi; Kameyama, Shigeki

    2016-09-01

    To clarify characteristics of each human somatosensory evoked field (SEF) component following passive movement (PM), PM1, PM2, and PM3, using high spatiotemporal resolution 306-channel magnetoencephalography and varying PM range and angular velocity. We recorded SEFs following PM under three conditions [normal range-normal velocity (NN), small range-normal velocity (SN), and small range-slow velocity (SS)] with changing movement range and angular velocity in 12 participants and calculated the amplitude, equivalent current dipole (ECD) location, and the ECD strength for each component. All components were observed in six participants, whereas only PM1 and PM3 in the other six. Clear response deflections at the ipsilateral hemisphere to PM side were observed in seven participants. PM1 amplitude was larger under NN and SN conditions, and mean ECD location for PM1 was at primary motor area. PM3 amplitude was larger under SN condition and mean ECD location for PM3 under SS condition was at primary somatosensory area. PM1 amplitude was dependent on the angular velocity of PM, suggesting that PM1 reflects afferent input from muscle spindle, whereas PM3 amplitude was dependent on the duration. The ECD for PM3 was located in the primary somatosensory cortex, suggesting that PM3 reflects cutaneous input. We confirmed the hypothesis for locally distinct generators and characteristics of each SEF component.

  15. The implications of groundwater velocity variations on microbial transport and wellhead protection - review of field evidence.

    PubMed

    Taylor, Richard; Cronin, Aidan; Pedley, Steve; Barker, John; Atkinson, Tim

    2004-07-01

    Current strategies to protect groundwater sources from microbial contamination (e.g., wellhead protection areas) rely upon natural attenuation of microorganisms between wells or springs and potential sources of contamination and are determined using average (macroscopic) groundwater flow velocities defined by Darcy's Law. However, field studies of sewage contamination and microbial transport using deliberately applied tracers provide evidence of groundwater flow paths that permit the transport of microorganisms by rapid, statistically extreme velocities. These paths can be detected because of (i) the high concentrations of bacteria and viruses that enter near-surface environments in sewage or are deliberately applied as tracers (e.g., bacteriophage); and (ii) low detection limits of these microorganisms in water. Such paths must comprise linked microscopic pathways (sub-paths) that are biased toward high groundwater velocities. In media where microorganisms may be excluded from the matrix (pores and fissures), the disparity between the average linear velocity of groundwater flow and flow velocities transporting released or applied microorganisms is intensified. It is critical to recognise the limited protection afforded by source protection measures that disregard rapid, statistically extreme groundwater velocities transporting pathogenic microorganisms, particularly in areas dependent upon untreated groundwater supplies.

  16. Present-day velocity field and block kinematics of Tibetan Plateau from GPS measurements

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Qiao, Xuejun; Yang, Shaomin; Wang, Dijin

    2016-11-01

    In this study, we present a new synthesis of GPS velocities for tectonic deformation within the Tibetan Plateau and its surrounding areas, a combined dataset of ˜1854 GPS-derived horizontal velocity vectors. Assuming that crustal deformation is localized along major faults, a block modeling approach is employed to interpret the GPS velocity field. We construct a 30-element block model to describe present-day deformation in western China, with half of them located within the Tibetan Plateau, and the remainder located in its surrounding areas. We model the GPS velocities simultaneously for the effects of block rotations and elastic strain induced by the bounding faults. Our model yields a good fit to the GPS data with a mean residual of 1.08 mm/a compared to the mean uncertainty of 1.36 mm/a for each velocity component, indicating a good agreement between the predicted and observed velocities.The major strike-slip faults such as the Altyn Tagh, Xianshuihe, Kunlun and Haiyuan faults have relatively uniform slip rates in a range of 5-12 mm/a along most of their segments, and the estimated fault slip rates agree well with previous geologic and geodetic results. Blocks having significant residuals are located at the southern and southeastern Tibetan Plateau, suggesting complex tectonic settings and further refinement of accurate definition of block geometry in these regions.

  17. Present-day velocity field and block kinematics of Tibetan Plateau from GPS measurements

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Qiao, Xuejun; Yang, Shaomin; Wang, Dijin

    2017-02-01

    In this study, we present a new synthesis of GPS velocities for tectonic deformation within the Tibetan Plateau and its surrounding areas, a combined data set of ˜1854 GPS-derived horizontal velocity vectors. Assuming that crustal deformation is localized along major faults, a block modelling approach is employed to interpret the GPS velocity field. We construct a 30-element block model to describe present-day deformation in western China, with half of them located within the Tibetan Plateau, and the remainder located in its surrounding areas. We model the GPS velocities simultaneously for the effects of block rotations and elastic strain induced by the bounding faults. Our model yields a good fit to the GPS data with a mean residual of 1.08 mm a-1 compared to the mean uncertainty of 1.36 mm a-1 for each velocity component, indicating a good agreement between the predicted and observed velocities. The major strike-slip faults such as the Altyn Tagh, Xianshuihe, Kunlun and Haiyuan faults have relatively uniform slip rates in a range of 5-12 mm a-1 along most of their segments, and the estimated fault slip rates agree well with previous geologic and geodetic results. Blocks having significant residuals are located at the southern and southeastern Tibetan Plateau, suggesting complex tectonic settings and further refinement of accurate definition of block geometry in these regions.

  18. Field assessment of noncontact stream gauging using portable surface velocity radars (SVR)

    NASA Astrophysics Data System (ADS)

    Welber, Matilde; Le Coz, Jérôme; Laronne, Jonathan B.; Zolezzi, Guido; Zamler, Daniel; Dramais, Guillaume; Hauet, Alexandre; Salvaro, Martino

    2016-02-01

    The applicability of a portable, commercially available surface velocity radar (SVR) for noncontact stream gauging was evaluated through a series of field-scale experiments carried out in a variety of sites and deployment conditions. Comparisons with various concurrent techniques showed acceptable agreement with velocity profiles, with larger uncertainties close to the banks. In addition to discharge error sources shared with intrusive velocity-area techniques, SVR discharge estimates are affected by flood-induced changes in the bed profile and by the selection of a depth-averaged to surface velocity ratio, or velocity coefficient (α). Cross-sectional averaged velocity coefficients showed smaller fluctuations and closer agreement with theoretical values than those computed on individual verticals, especially in channels with high relative roughness. Our findings confirm that α = 0.85 is a valid default value, with a preferred site-specific calibration to avoid underestimation of discharge in very smooth channels (relative roughness ˜ 0.001) and overestimation in very rough channels (relative roughness > 0.05). Theoretically derived and site-calibrated values of α also give accurate SVR-based discharge estimates (within 10%) for low and intermediate roughness flows (relative roughness 0.001 to 0.05). Moreover, discharge uncertainty does not exceed 10% even for a limited number of SVR positions along the cross section (particularly advantageous to gauge unsteady flood flows and very large floods), thereby extending the range of validity of rating curves.

  19. Full-field spreading velocity measurement inside droplets impinging on a dry solid surface

    NASA Astrophysics Data System (ADS)

    Erkan, Nejdet; Okamoto, Koji

    2014-11-01

    Liquid droplet impacts onto solid surfaces have attracted enormous amount of attention from wide range of research fields including experimental and numerical investigations. Unlike experimental efforts, numerical and analytical studies generated various sets of data. In this study, we investigated the spreading velocities inside the water droplets impinging onto a dry glass substrate using time-resolved PIV. The method, together with the high spatiotemporal resolution and the additional treatments improving the robustness, allowed us to resolve the radial velocity profiles efficiently in the spreading phase. Several impact velocity cases ranging from 0.40 to 0.96 m/s were studied. They correspond to low and moderate level Weber numbers (4.9-27.6). We observed that instantaneous radial velocity distributions exhibit linear and nonlinear modes. The nonlinearity is caused by the vortical flows formed at outer regions of the spreading liquid lamella. We demonstrated that even at low impact velocities the linear parts of the profiles obey a quasi-one-dimensional theory proposed in the literature. The comparison of obtained results with a literature-based numerical study, performed for high range of Weber numbers, confirmed the simultaneous existence of linear and nonlinear parts in the radial velocity profiles. In spite of the scale differences in terms of Weber number, the agreements in the tendencies of the profiles imply the validity of the mechanism considered in the numerical study even at low and moderate level range of Weber numbers.

  20. Separation of non-stationary sound fields with single layer pressure-velocity measurements.

    PubMed

    Bi, Chuan-Xing; Geng, Lin; Zhang, Xiao-Zheng

    2016-02-01

    This paper examines the feasibility of extracting the non-stationary sound field generated by a target source in the presence of disturbing source from single layer pressure-velocity measurements. Unlike the method described in a previous paper [Bi, Geng, and Zhang, J. Acoust. Soc. Am. 135(6), 3474-3482 (2014)], the proposed method allows measurements of pressure and particle velocity signals on a single plane instead of pressure signals on two planes, and the time-dependent pressure generated by the target source is extracted by a simple superposition of the measured pressure and the convolution between the measured particle velocity and the corresponding impulse response function. Because the particle velocity here is measured directly, the error caused by the finite difference approximation can be avoided, which makes it possible to perform the separation better than the previous method. In this paper, a Microflown pressure-velocity probe is used to perform the experimental measurements, and the calibration procedure of the probe in the time domain is given. The experimental results demonstrate that the proposed method is effective in extracting the desired non-stationary sound field generated by the target source from the mixed one in both time and space domains, and it obtains more accurate results than the previous method.

  1. Velocity Measurements of Free Surface Liquid Metal Flows in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Pfeffer, Scott; Ji, Hantao; Nornberg, Mark; Rhoads, John

    2008-11-01

    A potential probe diagnostic was developed and calibrated to map the velocity profile of free-surface liquid metal channel flow and quantify the effect an applied magnetic field played in shaping the velocity profile. The setup for this experiment consists of a wide aspect ratio channel sealed from the air, with argon replacing the air in the channel, placed within an electromagnet capable of producing more than a 2000 Gauss field perpendicular to the flow. An alloy of GaInSn, which is liquid at room temperature, is pumped through the channel by a screw pump at a specified rate. The velocity profile is obtained by measuring the voltage across pairs of probes. Various materials were used to determine which probe material would maximize the signal from the voltage induced by the Hall effect and reduce the voltage due to thermoelectric effects. Extensive calibration was then carried out to ensure an accurate velocity measurement. After amplification and filtering this signal gives us a good measurement of the velocity of the liquid metal over the cross-section of a specific probe.

  2. Kinematics of the Suez-Sinai area from an updated combined GPS velocity field

    NASA Astrophysics Data System (ADS)

    Pietrantonio, Grazia; Devoti, Roberto; Mahmoud, Salah; Riguzzi, Federica

    2017-04-01

    Many studies based on GPS data, have been carried out to shed light on the current kinematics of the Suez-Sinai area, where the interaction of the African and Arabian plates is active. A combined GPS velocity solution covering a wide area from Egypt to Middle East allowed us to infer the current rates across the plate margins. We have estimated 126 velocities from time series of 90 permanent and 36 non permanent GPS sites located in Africa (Egypt), Eurasia and Arabia plates in the time span 1996-2015, the largest available for the Egyptian sites. We have combined our velocity solution in a least-squares sense with two other recent velocity solutions of networks located around the eastern Mediterranean, obtaining a final IGb08 velocity field of about 450 sites. Then, we have estimated the IGb08 Euler poles of Africa, Sinai and Arabia, analyzing the kinematics of the Sinai area, particular velocity profiles, and estimating the 2D strain rate field. We show that it is possible to reliably model the rigid motion of Sinai block only including some GPS sites located south of the Carmel Fault. The estimated relative motion with respect to Africa is of the order of 2-3 mm/yr, however there is a clear mismatch between the modeled and the observed velocities in the southern Sinai sites. We have also assessed the NNE left shear motion along the Dead Sea Transform Fault, estimating a relative motion between Arabia and Africa of about 6 mm/yr in the direction of the Red Sea opening.

  3. Near-field Oblique Remote Sensing of Stream Water-surface Elevation, Slope, and Surface Velocity

    NASA Astrophysics Data System (ADS)

    Minear, J. T.; Kinzel, P. J.; Nelson, J. M.; McDonald, R.; Wright, S. A.

    2014-12-01

    A major challenge for estimating discharges during flood events or in steep channels is the difficulty and hazard inherent in obtaining in-stream measurements. One possible solution is to use near-field remote sensing to obtain simultaneous water-surface elevations, slope, and surface velocities. In this test case, we utilized Terrestrial Laser Scanning (TLS) to remotely measure water-surface elevations and slope in combination with surface velocities estimated from particle image velocimetry (PIV) obtained by video-camera and/or infrared camera. We tested this method at several sites in New Mexico and Colorado using independent validation data consisting of in-channel measurements from survey-grade GPS and Acoustic Doppler Current Profiler (ADCP) instruments. Preliminary results indicate that for relatively turbid or steep streams, TLS collects tens of thousands of water-surface elevations and slopes in minutes, much faster than conventional means and at relatively high precision, at least as good as continuous survey-grade GPS measurements. Estimated surface velocities from this technique are within 15% of measured velocity magnitudes and within 10 degrees from the measured velocity direction (using extrapolation from the shallowest bin of the ADCP measurements). Accurately aligning the PIV results into Cartesian coordinates appears to be one of the main sources of error, primarily due to the sensitivity at these shallow oblique look angles and the low numbers of stationary objects for rectification. Combining remotely-sensed water-surface elevations, slope, and surface velocities produces simultaneous velocity measurements from a large number of locations in the channel and is more spatially extensive than traditional velocity measurements. These factors make this technique useful for improving estimates of flow measurements during flood flows and in steep channels while also decreasing the difficulty and hazard associated with making measurements in these

  4. New experimental technique for the measurement of the velocity field in thin films falling over obstacles

    NASA Astrophysics Data System (ADS)

    Landel, Julien R.; Daglis, Ana; McEvoy, Harry; Dalziel, Stuart B.

    2014-11-01

    We present a new experimental technique to measure the surface velocity of a thin falling film. Thin falling films are important in various processes such as cooling in heat exchangers or cleaning processes. For instance, in a household dishwasher cleaning depends on the ability of a thin draining film to remove material from a substrate. We are interested in the impact of obstacles attached to a substrate on the velocity field of a thin film flowing over them. Measuring the velocity field of thin falling films is a challenging experimental problem due to the small depth of the flow and the large velocity gradient across its depth. We propose a new technique based on PIV to measure the plane components of the velocity at the surface of the film over an arbitrarily large area and an arbitrarily large resolution, depending mostly on the image acquisition technique. We perform experiments with thin films of water flowing on a flat inclined surface, made of glass or stainless steel. The typical Reynolds number of the film is of the order of 100 to 1000, computed using the surface velocity, the film thickness and the kinematic viscosity of the film. We measure the modification to the flow field, from a viscous-gravity regime, caused by small solid obstacles, such as three-dimensional hemispherical obstacles and two-dimensional steps. We compare our results with past theoretical and numerical studies. This material is based upon work supported by the Defense Threat Reduction Agency under Contract No. HDTRA1-12-D-0003-0001.

  5. Experimental study of the free surface velocity field in an asymmetrical confluence

    NASA Astrophysics Data System (ADS)

    Creelle, Stephan; Mignot, Emmanuel; Schindfessel, Laurent; De Mulder, Tom

    2017-04-01

    The hydrodynamic behavior of open channel confluences is highly complex because of the combination of different processes that interact with each other. To gain further insights in how the velocity uniformization between the upstream channels and the downstream channel is proceeding, experiments are performed in a large scale 90 degree angled concrete confluence flume with a chamfered rectangular cross-section and a width of 0.98m. The dimensions and lay-out of the flume are representative for a prototype scale confluence in e.g. drainage and irrigation systems. In this type of engineered channels with sharp corners the separation zone is very large and thus the velocity difference between the most contracted section and the separation zone is pronounced. With the help of surface particle tracking velocimetry the velocity field is recorded from upstream of the confluence to a significant distance downstream of the confluence. The resulting data allow to analyze the evolution of the incoming flows (with a developed velocity profile) that interact with the stagnation zone and each other, causing a shear layer between the two bulk flows. Close observation of the velocity field near the stagnation zone shows that there are actually two shear layers in the vicinity of the upstream corner. Furthermore, the data reveals that the shear layer observed more downstream between the two incoming flows is actually one of the two shear layers next to the stagnation zone that continues, while the other shear layer ceases to exist. The extensive measurement domain also allows to study the shear layer between the contracted section and the separation zone. The shear layers of the stagnation zone between the incoming flows and the one between the contracted flow and separation zone are localized and parameters such as the maximum gradient, velocity difference and width of the shear layer are calculated. Analysis of these data shows that the shear layer between the incoming flows

  6. Velocity fields in a low-latitude coronal hole - Results from the Solar Maximum Mission

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.; Waldron, W. L.

    1987-01-01

    The Solar Maximum Mission (SMM) satellite has been used to observe Doppler signatures in C IV in a low-latitude coronal hole as it crossed the central meridian (1985 February 2-8). Scatter plots of C IV emission intensity versus velocity do not show the pronounced positive correlation which has been reported in other regions on the sun. These data suggest that the coronal hole may control the gross velocity field in the solar atmosphere at the level where C IV is formed. Some localized regions of upflow coincide with EUV bright points in the coronal hole.

  7. Online computing of non-stationary distributions velocity fields by an accuracy controlled growing neural gas.

    PubMed

    Frezza-Buet, Hervé

    2014-12-01

    This paper presents a vector quantization process that can be applied online to a stream of inputs. It enables to set up and maintain a dynamical representation of the current information in the stream as a topology preserving graph of prototypical values, as well as a velocity field. The algorithm relies on the formulation of the accuracy of the quantization process, that allows for both the updating of the number of prototypes according to the stream evolution and the stabilization of the representation from which velocities can be extracted. A video processing application is presented. Copyright © 2014 Elsevier Ltd. All rights reserved.

  8. The influence of polyvinylacetate additive in water on turbulent velocity field and drag reduction

    NASA Astrophysics Data System (ADS)

    Lodes, A.; Macho, V.

    1989-06-01

    The effect of polymer concentration on drag reduction was studied experimentally with diluted water solutions of polyvinylacetate in a 2.4 cm I. D. pipe. The instantaneous local velocities of the velocity fields were measured by a one-channel differential laser-Doppler anemometer DISA Mark II, with forward scattering. Concentrations of water-polyvinylacetate over the range from 10 to 2,000 ppm were used. The drag reduction coefficient is proportional to the concentration and hydrolysis degree of the saponificated polyvinylacetate (PVAC) employed. A mechanical degradation in the turbulent shear flow was not observed.

  9. Cooling tower irrigator layout with allowances for non-uniformity of the airflow velocity field

    NASA Astrophysics Data System (ADS)

    Pushnov, A. S.; Ryabushenko, A. S.

    2016-07-01

    This article covers the results of analysis of aerodynamic processes in the cooling tower irrigator and provides the approaches to optimal layout of preformed packing blocks (of the irrigator) developed based on these results. The analysis of the airflow velocity field in the cooling towers shows that the irrigation space can be broken down into the following zones: the peripheral zone of the cooling tower near the airblast windows, the zone near the cooling tower center, and the intermediate zone. Furthermore, the highest level of nonuniformity of the airflow velocity field in cooling towers is in the zone adjoining the tower's airblast windows. The proposed concept of the cooling tower irrigator's layout is made with allowances for the airflow velocity field characteristics in the cross-section of the irrigation space of the cooling tower. Based on this concept, we suggest that higher irrigator blocks should be placed in the zone of increased airflow consumption, which provides the possibility to enhance the hydraulic resistance and, respectively, decrease the gas flow velocity as well as to boost the efficiency of chilling the circulating water in the cooling tower. For this purpose, additional irrigator blocks can be of the same design as the main irrigator. As an option, it is possible to use blocks of the geometry and design other than the main irrigator block in the cooling tower.

  10. Imaginary particle tracking accelerometry based on time-resolved velocity fields

    NASA Astrophysics Data System (ADS)

    Wang, Zhongyi; Gao, Qi; Pan, Chong; Feng, Lihao; Wang, Jinjun

    2017-09-01

    An accurate calculation of material acceleration is important for particle image velocimetry-based pressure reconstruction. Therefore, an imaginary particle tracking accelerometry (IPTA) approach based on time-resolved velocity fields is described in this paper for a better determination of acceleration. Multi-velocity fields and a least squares polynomial fitting of the velocity along imaginary particle trajectories are introduced to improve the acceleration accuracy. The process of imaginary particle tracking is operated iteratively until a convergence condition is satisfied. Then the Lagrangian acceleration (or the material acceleration in the Eulerian coordinates) is acquired by the first-order time derivation of the fitting polynomial. In addition, the sensitivity of the IPTA approach to different levels of noise and parameters that affect its performance is investigated. A criterion is proposed to determine these parameters when using IPTA to calculate the acceleration. Performance of the IPTA method is compared with other velocity-based accelerometry methods, including both Eulerian and Lagrangian methods. Assessments are conducted in a synthetic solid body rotation flow, a synthetic flow of a vortex ring, and an experimental jet flow. The results show that IPTA is a robust method for experimental acceleration determination that can both improve the accuracy of acceleration and provide better physical characteristics of the flow field.

  11. Velocity controlled sound field reproduction by non-uniformly spaced loudspeakers

    NASA Astrophysics Data System (ADS)

    Shin, Mincheol; Nelson, Philip A.; Fazi, Filippo M.; Seo, Jeongil

    2016-05-01

    One approach to the reproduction of a sound field is to ensure the reproduction of the acoustic pressure on the surface bounding the volume within which reproduction is sought. However, this approach suffers from technical limitations when the loudspeakers used for the reproduction of the surface acoustic pressures are unevenly spaced. It is shown in this paper that sound field reproduction with a spatially non-uniform loudspeaker arrangement can be considerably improved by changing the physical quantity to be controlled on the bounding surface from pressure to particle velocity. One of the main advantages of the velocity control method is the simplicity with which the inverse problem can be regularized, irrespective of the direction of arrival of the sound to be reproduced. In addition, the velocity controlled sound field shows better reproduction of the time averaged intensity flow in the reproduction region which in turn appears to be closely linked with better human perception of sound localization. Furthermore, the proposed method results in smoother "panning functions" that describe the variation of the source outputs as a function of the angle of incidence of the sound to be reproduced. The performance of the velocity matching method has been evaluated by comparison to the conventional pressure matching method and through simulations with several non-uniform loudspeaker layouts. The simulated results were also verified with experiments and subjective tests.

  12. An optical flow-based method for velocity field of fluid flow estimation

    NASA Astrophysics Data System (ADS)

    Głomb, Grzegorz; Świrniak, Grzegorz; Mroczka, Janusz

    2017-06-01

    The aim of this paper is to present a method for estimating flow-velocity vector fields using the Lucas-Kanade algorithm. The optical flow measurements are based on the Particle Image Velocimetry (PIV) technique, which is commonly used in fluid mechanics laboratories in both research institutes and industry. Common approaches for an optical characterization of velocity fields base on computation of partial derivatives of the image intensity using finite differences. Nevertheless, the accuracy of velocity field computations is low due to the fact that an exact estimation of spatial derivatives is very difficult in presence of rapid intensity changes in the PIV images, caused by particles having small diameters. The method discussed in this paper solves this problem by interpolating the PIV images using Gaussian radial basis functions. This provides a significant improvement in the accuracy of the velocity estimation but, more importantly, allows for the evaluation of the derivatives in intermediate points between pixels. Numerical analysis proves that the method is able to estimate even a separate vector for each particle with a 5× 5 px2 window, whereas a classical correlation-based method needs at least 4 particle images. With the use of a specialized multi-step hybrid approach to data analysis the method improves the estimation of the particle displacement far above 1 px.

  13. Synchrotron microimaging technique for measuring the velocity fields of real blood flows

    SciTech Connect

    Lee, Sang-Joon; Kim, Guk Bae

    2005-03-15

    Angiography and Doppler methods used for diagnosing vascular diseases give information on the shape of blood vessels and pointwise blood speed but do not provide detailed information on the flow fields inside the blood vessels. In this study, we developed a method for visualizing blood flow by using coherent synchrotron x rays. This method, which does not require the addition of any contrast agent or tracer particles, visualizes the flow pattern of blood by enhancing the diffraction and interference characteristics of the blood cells. This was achieved by optimizing the sample- (blood) to-detector (charge-coupled device camera) distance and the sample thickness. The proposed method was used to extract quantitative velocity field information from blood flowing inside an opaque microchannel by applying a two-frame particle image velocimetry algorithm to enhanced x-ray images of the blood flow. The measured velocity field data showed a flow structure typical of flow in a macrochannel.

  14. Potential, velocity, and density fields from sparse and noisy redshift-distance samples - Method

    NASA Technical Reports Server (NTRS)

    Dekel, Avishai; Bertschinger, Edmund; Faber, Sandra M.

    1990-01-01

    A method for recovering the three-dimensional potential, velocity, and density fields from large-scale redshift-distance samples is described. Galaxies are taken as tracers of the velocity field, not of the mass. The density field and the initial conditions are calculated using an iterative procedure that applies the no-vorticity assumption at an initial time and uses the Zel'dovich approximation to relate initial and final positions of particles on a grid. The method is tested using a cosmological N-body simulation 'observed' at the positions of real galaxies in a redshift-distance sample, taking into account their distance measurement errors. Malmquist bias and other systematic and statistical errors are extensively explored using both analytical techniques and Monte Carlo simulations.

  15. Conductivity, electric field and electron drift velocity within the equatorial electrojet

    NASA Astrophysics Data System (ADS)

    Rastogi, R. G.; Chandra, H.

    2006-08-01

    Rocket-borne in-situ measurements of electron density and current density made from Thumba, India, on four occasions between 1966 and 1973 and on one flight from Peru in 1965 are studied along with the corresponding ground magnetometer data. The Cowling conductivity is computed using the yearly mean magnetic field values of 1965 and the atmospheric density values from the MSIS 1986 model. The rocket-borne measurements from Thumba cover different geophysical conditions of strong, moderate and partial counter-electrojet events. The vertical profiles of the measured current density and electron density are presented along with the computed Cowling conductivity, electron drift velocity and electric field. The peak current density occurred at 106-107 km over Thumba and at 109 km over Peru compared to 104 km over Brazil. Cowling conductivity peaks occurred at 102 km over Huancayo and 101 km over Thumba, while electron drift velocity and electric field peaks occurred at approximately 105-107 km over Thumba, 108 and 110 km over Huancayo and 104 km over Brazil, respectively. While the electron density near the level of peak current density shows some variability, electron drift velocity and electric field show large variability. We conclude that the local electric field plays an important role in the spatial and temporal variability of the strength of the electrojet.

  16. Underwater patch near-field acoustical holography based on particle velocity and vector hydrophone array

    NASA Astrophysics Data System (ADS)

    Hu, Bo; Yang, DeSen; Li, SiChun; Sun, Yu; Mo, ShiQi; Shi, ShengGuo

    2012-11-01

    One-step patch near-field acoustical holography (PNAH) is a powerful tool for identifying noise sources from the partially known sound pressure field. The acoustical property to be reconstructed on the surface of interest is related to the partially measured pressure on the hologram surface in terms of sampling and bandlimiting matrices, which cost more in computation. A one-step procedure based on measuring of the normal component of the particle velocity is described, including the mathematical formulation. The numerical simulation shows that one-step PNAH based on particle velocity can obtain more accurately reconstructed results and it is also less sensitive to noise than the method based on pressure. These findings are confirmed by an underwater near-field acoustical holography experiment conducted with a vector hydrophone array. The experimental results have illustrated the high performance of one-step PNAH based on particle velocity in the reconstruction of sound field and the advantages of a vector hydrophone array in an underwater near-field measurement.

  17. Electric-field control of magnetic domain-wall velocity in ultrathin cobalt with perpendicular magnetization.

    PubMed

    Chiba, D; Kawaguchi, M; Fukami, S; Ishiwata, N; Shimamura, K; Kobayashi, K; Ono, T

    2012-06-06

    Controlling the displacement of a magnetic domain wall is potentially useful for information processing in magnetic non-volatile memories and logic devices. A magnetic domain wall can be moved by applying an external magnetic field and/or electric current, and its velocity depends on their magnitudes. Here we show that the applying an electric field can change the velocity of a magnetic domain wall significantly. A field-effect device, consisting of a top-gate electrode, a dielectric insulator layer, and a wire-shaped ferromagnetic Co/Pt thin layer with perpendicular anisotropy, was used to observe it in a finite magnetic field. We found that the application of the electric fields in the range of ± 2-3 MV cm(-1) can change the magnetic domain wall velocity in its creep regime (10(6)-10(3) m s(-1)) by more than an order of magnitude. This significant change is due to electrical modulation of the energy barrier for the magnetic domain wall motion.

  18. A comparison of measured and modeled velocity fields for a laminar flow in a porous medium

    NASA Astrophysics Data System (ADS)

    Wood, B. D.; Apte, S. V.; Liburdy, J. A.; Ziazi, R. M.; He, X.; Finn, J. R.; Patil, V. A.

    2015-11-01

    Obtaining highly-resolved velocity data from experimental measurements in porous media is a significant challenge. The goal of this work is to compare the velocity fields measured in a randomly-packed porous medium obtained from particle image velocimetry (PIV) with corresponding fields predicted from direct numerical simulation (DNS). Experimentally, the porous medium was comprised of 15 mm diameter spherical beads made of optical glass placed in a glass flow cell to create the packed bed. A solution of ammonium thiocyanate was refractive-index matched to the glass creating a medium that could be illuminated with a laser sheet without distortion. The bead center locations were quantified using the imaging system so that the geometry of the porous medium was known very accurately. Two-dimensional PIV data were collected and processed to provide high-resolution velocity fields at a single plane within the porous medium. A Cartesian-grid-based fictitious domain approach was adopted for the direct numerical simulation of flow through the same geometry as the experimental measurements and without any adjustable parameters. The uncertainties associated with characterization of the pore geometry, PIV measurements, and DNS predictions were all systematically quantified. Although uncertainties in bead position measurements led to minor discrepancies in the comparison of the velocity fields, the axial and normal velocity deviations exhibited normalized root mean squared deviations (NRMSD) of only 11.32% and 4.74%, respectively. The high fidelity of both the experimental and numerical methods have significant implications for understanding and even for engineering the micro-macro relationship in porous materials. The ability to measure and model sub-pore-scale flow features also has relevance to the development of upscaled models for flow in porous media, where physically reasonable closure models must be developed at the sub-pore scale. These results provide valuable data

  19. Tracing Interstellar Magnetic Field Using Velocity Gradient Technique: Application to Atomic Hydrogen Data

    NASA Astrophysics Data System (ADS)

    Yuen, Ka Ho; Lazarian, A.

    2017-03-01

    The advancement of our understanding of MHD turbulence opens ways to develop new techniques to probe magnetic fields. In MHD turbulence, the velocity gradients are expected to be perpendicular to magnetic fields and this fact was used by González-Casanova & Lazarian to introduce a new technique to trace magnetic fields using velocity centroid gradients (VCGs). The latter can be obtained from spectroscopic observations. We apply the technique to GALFA-H i survey data and then compare the directions of magnetic fields obtained with our technique to the direction of magnetic fields obtained using PLANCK polarization. We find an excellent correspondence between the two ways of magnetic field tracing, which is obvious via the visual comparison and through the measuring of the statistics of magnetic field fluctuations obtained with the polarization data and our technique. This suggests that the VCGs have a potential for measuring of the foreground magnetic field fluctuations, and thus provide a new way of separating foreground and CMB polarization signals.

  20. The Magellan PFS Planet Search Program: Radial Velocity and Stellar Abundance Analyses of the 360 au, Metal-poor Binary “Twins” HD 133131A & B

    NASA Astrophysics Data System (ADS)

    Teske, Johanna K.; Shectman, Stephen A.; Vogt, Steve S.; Díaz, Matías; Butler, R. Paul; Crane, Jeffrey D.; Thompson, Ian B.; Arriagada, Pamela

    2016-12-01

    We present a new precision radial velocity (RV) data set that reveals multiple planets orbiting the stars in the ˜360 au, G2+G2 “twin” binary HD 133131AB. Our six years of high-resolution echelle observations from MIKE and five years from the Planet Finder Spectrograph (PFS) on the Magellan telescopes indicate the presence of two eccentric planets around HD 133131A with minimum masses of 1.43 ± 0.03 and 0.63 ± 0.15 {{ M }}{{J}} at 1.44 ± 0.005 and 4.79 ± 0.92 au, respectively. Additional PFS observations of HD 133131B spanning five years indicate the presence of one eccentric planet of minimum mass 2.50 ± 0.05 {{ M }}{{J}} at 6.40 ± 0.59 au, making it one of the longest-period planets detected with RV to date. These planets are the first to be reported primarily based on data taken with the PFS on Magellan, demonstrating the instrument’s precision and the advantage of long-baseline RV observations. We perform a differential analysis between the Sun and each star, and between the stars themselves, to derive stellar parameters and measure a suite of 21 abundances across a wide range of condensation temperatures. The host stars are old (likely ˜9.5 Gyr) and metal-poor ([Fe/H] ˜ -0.30), and we detect a ˜0.03 dex depletion in refractory elements in HD 133131A versus B (with standard errors ˜0.017). This detection and analysis adds to a small but growing sample of binary “twin” exoplanet host stars with precise abundances measured, and represents the most metal-poor and likely oldest in that sample. Overall, the planets around HD 133131A and B fall in an unexpected regime in planet mass-host star metallicity space and will serve as an important benchmark for the study of long-period giant planets. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  1. Stellar wind models of subluminous hot stars

    NASA Astrophysics Data System (ADS)

    Krtička, J.; Kubát, J.; Krtičková, I.

    2016-09-01

    Context. Mass-loss rate is one of the most important stellar parameters. Mass loss via stellar winds may influence stellar evolution and modifies stellar spectrum. Stellar winds of subluminous hot stars, especially subdwarfs, have not been studied thoroughly. Aims: We aim to provide mass-loss rates as a function of subdwarf parameters and to apply the formula for individual subdwarfs, to predict the wind terminal velocities, to estimate the influence of the magnetic field and X-ray ionization on the stellar wind, and to study the interaction of subdwarf wind with mass loss from Be and cool companions. Methods: We used our kinetic equilibrium (NLTE) wind models with the radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the wind structure of subluminous hot stars. Our models solve stationary hydrodynamical equations, that is the equation of continuity, equation of motion, and energy equation and predict basic wind parameters. Results: We predicted the wind mass-loss rate as a function of stellar parameters, namely the stellar luminosity, effective temperature, and metallicity. The derived wind parameters (mass-loss rates and terminal velocities) agree with the values derived from the observations. The radiative force is not able to accelerate the homogeneous wind for stars with low effective temperatures and high surface gravities. We discussed the properties of winds of individual subdwarfs. The X-ray irradiation may inhibit the flow in binaries with compact components. In binaries with Be components, the winds interact with the disk of the Be star. Conclusions: Stellar winds exist in subluminous stars with low gravities or high effective temperatures. Despite their low mass-loss rates, they are detectable in the ultraviolet spectrum and cause X-ray emission. Subdwarf stars may lose a significant part of their mass during the evolution. The angular momentum loss in magnetic subdwarfs with wind may explain their

  2. Dynamic Measurements of High Explosive Velocity Fields using Particle Image Velocimetry

    NASA Astrophysics Data System (ADS)

    Wilson, Brandon; Wood, Wm. M.; Olson, Russ

    2015-06-01

    A non-invasive technique for measuring dynamic particle velocities using pRad images ahead and behind an HE detonation burn front is presented. The technique uses proven principles from particle image velocimetry (PIV). Time-resolved radiographs of detonated HE (PBX 9501 and 9502) doped with tungsten particles (<= 10 μ m) are captured at pRad at Los Alamos National Laboratory. From sequential radiographs, resolved velocity fields are measured by local cross-correlations of tungsten tracer positions. With this technique, we resolve the Taylor wave and can measure the particle velocity directly behind the detonation front. Results for single detonation waves and colliding detonation waves are presented. We also discuss the capabilities, limitations, applications, and future of this technique.

  3. Velocity Field Measurements of Human Coughing Using Time Resolved Particle Image Velocimetry

    NASA Astrophysics Data System (ADS)

    Khan, T.; Marr, D. R.; Higuchi, H.; Glauser, M. N.

    2003-11-01

    Quantitative fluid mechanics analysis of human coughing has been carried out using new Time Resolved Particle Image Velocimetry (TRPIV). The study involves measurement of velocity vector time-histories and velocity profiles. It is focused on the average normal human coughing. Some work in the past on cough mechanics has involved measurement of flow rates, tidal volumes and sub-glottis pressure. However, data of unsteady velocity vector field of the exiting highly time-dependent jets is not available. In this study, human cough waveform data are first acquired in vivo using conventional respiratory instrumentation for various volunteers of different gender/age groups. The representative waveform is then reproduced with a coughing/breathing simulator (with or without a manikin) for TRPIV measurements and analysis. The results of this study would be useful not only for designing of indoor air quality and heating, ventilation and air conditioning systems, but also for devising means of protection against infectious diseases.

  4. Random Field Sampling for a Simplified Model of Melt-Blowing Considering Turbulent Velocity Fluctuations

    NASA Astrophysics Data System (ADS)

    Hübsch, Florian; Marheineke, Nicole; Ritter, Klaus; Wegener, Raimund

    2013-03-01

    In melt-blowing very thin liquid fiber jets are spun due to high-velocity air streams. In literature there is a clear, unsolved discrepancy between the measured and computed jet attenuation (thinning). In this paper we will verify numerically that the turbulent velocity fluctuations causing a random aerodynamic drag on the fiber jets—that has been neglected so far—are the crucial effect to close this gap. For this purpose, we model the velocity fluctuations as vector Gaussian random fields on top of a k- ɛ turbulence description and develop an efficient sampling procedure. Taking advantage of the special covariance structure the effort of the sampling is linear in the discretization and makes the realization possible. Numerical results are discussed for a simplified melt-blowing model consisting of a system of random ordinary differential equations.

  5. Estimates of the seasonal mean vertical velocity fields of the extratropical Northern Hemisphere

    NASA Technical Reports Server (NTRS)

    White, G. H.

    1983-01-01

    Indirect methods are employed to estimate the wintertime and summertime mean vertical velocity fields of the extratropical Northern Hemisphere and intercomparisons are made, together with comparisons with mean seasonal patterns of cloudiness and precipitation. Twice-daily NMC operational analyses produced general circulation statistics for 11 winters and 12 summers, permitting calculation of the seasonal NMC averages for 6 hr forecasts, solution of the omega equation, integration of continuity equation downward from 100 mb, and solution of the thermodynamic energy equation in the absence of diabatic heating. The methods all yielded similar vertical velocity patterns; however, the magnitude of the vertical velocities could not be calculated with great accuracy. Orography was concluded to have less of an effect in summer than in winter, when winds are stronger.

  6. Velocity-Field Measurements of an Axisymmetric Separated Flow Subjected to Amplitude-Modulated Excitation

    NASA Technical Reports Server (NTRS)

    Trosin, Barry James

    2007-01-01

    Active flow control was applied at the point of separation of an axisymmetric, backward-facing-step flow. The control was implemented by employing a Helmholtz resonator that was externally driven by an amplitude-modulated, acoustic disturbance from a speaker located upstream of the wind tunnel. The velocity field of the separating/reattaching flow region downstream of the step was characterized using hotwire velocity measurements with and without flow control. Conventional statistics of the data reveal that the separating/reattaching flow is affected by the imposed forcing. Triple decomposition along with conditional averaging was used to distinguish periodic disturbances from random turbulence in the fluctuating velocity component. A significant outcome of the present study is that it demonstrates that amplitude-modulated forcing of the separated flow alters the flow in the same manner as the more conventional method of periodic excitation.

  7. Interpretation of the electric fields measured in an ionospheric critical ionization velocity experiment

    NASA Technical Reports Server (NTRS)

    Brenning, N.; Faelthammar, C.-G.; Marklund, G.; Haerendel, G.; Kelley, M. C.; Pfaff, R.

    1991-01-01

    The quasi-dc electric fields measured in the CRIT I ionospheric release experiment are studied. In the experiment, two identical barium shaped charges were fired toward a main payload, and three-dimensional measurements of the electric field inside the streams were made. The relevance of proposed mechanisms for electron heating in the critical ionization velocity (CIV) mechanism is addressed. It is concluded that both the 'homogeneous' and the 'ionizing front' models probably are valid, but in different parts of the streams. It is also possible that electrons are directly accelerated by a magnetic field-aligned component of the electric field. The coupling between the ambient ionosphere and the ionized barium stream is more complicated that is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes.

  8. Multifractal Analysis of Velocity Vector Fields and a Continuous In-Scale Cascade Model

    NASA Astrophysics Data System (ADS)

    Fitton, G.; Tchiguirinskaia, I.; Schertzer, D.; Lovejoy, S.

    2012-04-01

    In this study we have compared the multifractal analyses of small-scale surface-layer wind velocities from two different datasets. The first dataset consists of six-months of wind velocity and temperature measurements at the heights 22, 23 and 43m. The measurements came from 3D sonic anemometers with a 10Hz data output rate positioned on a mast in a wind farm test site subject to wake turbulence effects. The location of the test site (Corsica, France) meant the large scale structures were subject to topography effects that therefore possibly caused buoyancy effects. The second dataset (Germany) consists of 300 twenty minute samples of horizontal wind velocity magnitudes simultaneously recorded at several positions on two masts. There are eight propeller anemometers on each mast, recording velocity magnitude data at 2.5Hz. The positioning of the anemometers is such that there are effectively two grids. One grid of 3 rows by 4 columns and a second of 5 rows by 2 columns. The ranges of temporal scale over which the analyses were done were from 1 to 103 seconds for both datasets. Thus, under the universal multifractal framework we found both datasets exhibit parameters α ≈ 1.5 and C1 ≈ 0.1. The parameters α and C1, measure respectively the multifractality and mean intermittency of the scaling field. A third parameter, H, quantifies the divergence from conservation of the field (e.g. H = 0 for the turbulent energy flux density). To estimate the parameters we used the ratio of the scaling moment function of the energy flux and of the velocity increments. This method was particularly useful when estimating the parameter α over larger scales. In fact it was not possible to obtain a reasonable estimate of alpha using the usual double trace moment method. For each case the scaling behaviour of the wind was almost isotropic when the scale ranges remained close to the sphero-scale. For the Corsica dataset this could be seen by the agreement of the spectral exponents of

  9. Effect of a magnetic field on massive-star winds - I. Mass-loss and velocity for a dipole field

    NASA Astrophysics Data System (ADS)

    Bard, Christopher; Townsend, Richard H. D.

    2016-11-01

    We generalize the Rigid-Field Hydrodynamic equations to accommodate arbitrary magnetic field topologies, resulting in a new Arbitrary Rigid-Field Hydrodynamic (ARFHD) formalism. We undertake a critical point calculation of the steady-state ARFHD equations with a CAK-type radiative acceleration and determine the effects of a dipole magnetic field on the usual CAK mass-loss rate and velocity structure. Enforcing the proper optically thin limit for the radiative line-acceleration is found to decrease both the mass-loss and wind acceleration, while rotation boosts both properties. We define optically thin correction and rotation parameters to quantify these effects on the global mass-loss rate and develop scaling laws for the surface mass-flux as a function of surface colatitude. These scaling laws are found to agree with previous laws derived from magnetohydrodynamic simulations of magnetospheres. The dipole magnetosphere velocity structure is found to differ from a global beta-velocity law, which contradicts a central assumption of the previously developed XADM model of X-ray emission from magnetospheres.

  10. B fields in OB stars (BOB): The magnetic triple stellar system HD 164492C in the Trifid nebula

    NASA Astrophysics Data System (ADS)

    González, J. F.; Hubrig, S.; Przybilla, N.; Carroll, T.; Nieva, M.-F.; Ilyin, I.; Järvinen, S.; Morel, T.; Schöller, M.; Castro, N.; Barbá, R.; de Koter, A.; Schneider, F. R. N.; Kholtygin, A.; Butler, K.; Veramendi, M. E.; Langer, N.; BOB Collaboration

    2017-01-01

    HD 164492C is a spectroscopic triple stellar system that has been recently detected to possess a strong magnetic field. We have obtained high-resolution spectroscopic and spectropolarimetric observations over a timespan of two years and derived physical, chemical, and magnetic properties for this object. The system is formed by an eccentric close spectroscopic binary (Ca1-Ca2) with a period of 12.5 days, and a massive tertiary Cb. We calculated the orbital parameters of the close pair, reconstructed the spectra of the three components, and determined atmospheric parameters and chemical abundances by spectral synthesis. From spectropolarimetric observations, multi-epoch measurements of the longitudinal magnetic fields were obtained. The magnetic field is strongly variable on timescales of a few days, with a most probable period in the range of 1.4-1.6 days. Star Cb with Teff ˜ 25 000 K is the apparently fastest rotator and the most massive star of this triple system and has anomalous chemical abundances with a marked overabundance of helium, 0.35±0.04 by number. We identified this star as being responsible for the observed magnetic field, although the presence of magnetic fields in the components of the Ca pair cannot be excluded. Star Ca1 with a temperature of about 24 000 K presents a normal chemical pattern, while the least massive star Ca2 is a mid-B type star (Teff ˜ 15 000 K) with an overabundance of silicon. The obtained stellar parameters of the system components suggest a distance of 1.5 kpc and an age of 10-15 Myr.

  11. B fields in OB stars (BOB): The magnetic triple stellar system HD 164492C in the Trifid nebula

    NASA Astrophysics Data System (ADS)

    González, J. F.; Hubrig, S.; Przybilla, N.; Carroll, T.; Nieva, M.-F.; Ilyin, I.; Järvinen, S.; Morel, T.; Schöller, M.; Castro, N.; Barbá, R.; de Koter, A.; Schneider, F. R. N.; Kholtygin, A.; Butler, K.; Veramendi, M. E.; Langer, N.; BOB Collaboration

    2017-05-01

    HD 164492C is a spectroscopic triple stellar system that has been recently detected to possess a strong magnetic field. We have obtained high-resolution spectroscopic and spectropolarimetric observations over a time span of two years and derived physical, chemical and magnetic properties for this object. The system is formed by an eccentric close spectroscopic binary (Ca1-Ca2) with a period of 12.5 d, and a massive tertiary Cb. We calculated the orbital parameters of the close pair, reconstructed the spectra of the three components and determined atmospheric parameters and chemical abundances by spectral synthesis. From spectropolarimetric observations, multi-epoch measurements of the longitudinal magnetic fields were obtained. The magnetic field is strongly variable on time-scales of a few days, with a most probable period in the range of 1.4-1.6 d. Star Cb with Teff ˜ 25 000 K is apparently the fastest rotator and the most massive star of this triple system and has anomalous chemical abundances with a marked overabundance of helium, 0.35±0.04 by number. We identified this star as being responsible for the observed magnetic field, although the presence of magnetic fields in the components of the Ca pair cannot be excluded. Star Ca1 with a temperature of about 24 000 K presents a normal chemical pattern, while the least massive star Ca2 is a mid-B-type star (Teff ˜ 15 000 K) with an overabundance of silicon. The obtained stellar parameters of the system components suggest a distance of 1.5 kpc and an age of 10-15 Myr.

  12. Assessment of velocity fields through open-channel flows with an empiric law.

    PubMed

    Bardiaux, J B; Vazquez, J; Mosé, R

    2008-01-01

    Most sewer managers are currently confronted with the evaluation of the water discharges, that flow through their networks or go to the discharge system, i.e. rivers in the majority of cases. In this context, the Urban Hydraulic Systems laboratory of the ENGEES is working on the relation between velocity fields and metrology assessment through a partnership with the Fluid and Solid Mechanics Institute of Strasbourg (IMFS). The responsibility is clearly to transform a velocity profile measurement, given by a Doppler sensor developed by the IMFS team, into a water discharge evaluation. The velocity distribution in a cross section of the flow in a channel has attracted the interests of many researchers over the years, due to its practical applications. In the case of free surface flows in narrow open channels the maximum velocity is below the free surface. This phenomenon, usually called "dip-phenomenon", amongst other things, raises the problem of the area explored in the section of measurements. The work presented here tries to create a simple relation making possible to associate the flow with the velocity distribution. This step allows to insert the sensor position into the flow calculation.

  13. Field-derived relationships for flow velocity and resistance in high-gradient streams

    NASA Astrophysics Data System (ADS)

    Comiti, Francesco; Mao, Luca; Wilcox, Andrew; Wohl, Ellen E.; Lenzi, Mario A.

    2007-06-01

    SummaryWe measured velocity and channel geometry in 10 reaches (bed gradient = 0.08-0.21) of a predominantly step-pool channel, the Rio Cordon, Italy, over a range of discharges (3-80% of the bankfull discharge). The resulting data were used to compute flow resistance. At-a-station hydraulic geometry relations indicate that in most reaches, the exponent describing the rate of velocity increases with discharge was between 0.48 and 0.6, which is within the range of published values for pool-riffle channels. The Rio Cordon data are also combined with published hydraulics data from step-pool streams to explore non-dimensional relationships between velocity and flow resistance and factors including unit discharge, channel gradient, and step geometry. Multiple regression analysis of this combined field dataset indicated that dimensionless unit discharge ( q∗) is the most important independent variable overall in explaining variations in velocity and flow resistance, followed by channel slope and the ratio of step height to step length. Empirical equations are provided both for dimensionless velocity and flow resistance, but prediction of the former variable appears more reliable.

  14. Measurement of a velocity field in microvessels using a high resolution PIV technique.

    PubMed

    Sugii, Yasuhiko; Nishio, Shigeru; Okamoto, Koji

    2002-10-01

    Because endothelial cells are subject to flow shear stress, it is important to determine the velocity distribution in microvessels during studies of the mechanical interactions between the blood and the endothelium. Particle image velocimetry (PIV) is a quantitative method for measuring velocity fields instantaneously in experimental fluid mechanics. The authors have developed a high-resolution PIV technique that improves the dynamic flow range, spatial resolution, and measurement accuracy. The proposed method was applied to images of the arteriole in the rat mesentery, using an intravital microscope and high-speed digital video system. Taking the mesentery motion into account, the PIV technique was improved to measure red blood cell (RBC) velocity. Velocity distributions with spatial resolutions of 0.8 3 0.8 mm were obtained even near the wall in the center plane of the arteriole. The arteriole velocity profile was blunt in the center region of the vessel cross-section and sharp in the near-wall region. Typical flow features for non-Newtonian fluid are shown.

  15. An Inexpensive Field-Widened Monolithic Michelson Interferometer for Precision Radial Velocity Measurements

    NASA Astrophysics Data System (ADS)

    Mahadevan, Suvrath; Ge, Jian; Fleming, Scott W.; Wan, Xiaoke; DeWitt, Curtis; van Eyken, Julian C.; McDavitt, Dan

    2008-09-01

    We have constructed a thermally compensated field-widened monolithic Michelson interferometer that can be used with a medium-resolution spectrograph to measure precise Doppler radial velocities of stars. Our prototype monolithic fixed-delay interferometer is constructed with off-the-shelf components and assembled using a hydrolysis bonding technique. We installed and tested this interferometer in the Exoplanet Tracker (ET) instrument at the Kitt Peak 2.1 m telescope, an instrument built to demonstrate the principles of dispersed fixed-delay interferometry. An iodine cell allows the interferometer drift to be accurately calibrated, relaxing the stability requirements on the interferometer itself. When using our monolithic interferometer, the ET instrument has no moving parts (except the iodine cell), greatly simplifying its operation. We demonstrate differential radial velocity precision of a few m s-1 on well known radial velocity standards and planet bearing stars when using this interferometer. Such monolithic interferometers will make it possible to build relatively inexpensive instruments that are easy to operate and capable of precision radial velocity measurements. A larger multiobject version of the Exoplanet Tracker will be used to conduct a large scale survey for planetary systems as part of the Sloan Digital Sky Survey III (SDSS III). Variants of the techniques and principles discussed in this paper can be directly applied to build large monolithic interferometers for such applications, enabling the construction of instruments capable of efficiently observing many stars simultaneously at high velocity precision.

  16. Field-derived relationships for flow velocity and resistance in high-gradient streams

    USGS Publications Warehouse

    Comiti, F.; Mao, L.; Wilcox, A.; Wohl, E.E.; Lenzi, M.A.

    2007-01-01

    We measured velocity and channel geometry in 10 reaches (bed gradient = 0.08-0.21) of a predominantly step-pool channel, the Rio Cordon, Italy, over a range of discharges (3-80% of the bankfull discharge). The resulting data were used to compute flow resistance. At-a-station hydraulic geometry relations indicate that in most reaches, the exponent describing the rate of velocity increases with discharge was between 0.48 and 0.6, which is within the range of published values for pool-riffle channels. The Rio Cordon data are also combined with published hydraulics data from step-pool streams to explore non-dimensional relationships between velocity and flow resistance and factors including unit discharge, channel gradient, and step geometry. Multiple regression analysis of this combined field dataset indicated that dimensionless unit discharge (q*) is the most important independent variable overall in explaining variations in velocity and flow resistance, followed by channel slope and the ratio of step height to step length. Empirical equations are provided both for dimensionless velocity and flow resistance, but prediction of the former variable appears more reliable. ?? 2007 Elsevier B.V. All rights reserved.

  17. Italy - Adriatic Sea - Barbara - A giant gas field marked by seismic velocity anomaly - A subtle trap

    SciTech Connect

    Ianniello, A.; Bolelli, W.; Di Scala, L. )

    1990-09-01

    Barbara gas field, discovered in 1971, is located in the northern sector of the Adriatic offshore. The field is a gentle anticline involving Quaternary clastic sediments and shaped by carbonate Mesozoic morphology. The presence of shallow gas pockets at the crest of the structure distort the seismic signal to such an extent that structural reconstruction using seismic data is not possible. Moreover, time delays and ray-path anomalies do not allow the use of staking velocities for the depth conversion. Seismic attribute analysis, instead of velocities, and time delays on the isochrone maps are providing a key to the understanding of seismic anomalies and are an indirect tool for reconstructing the real structural configuration of the field. The appraisal story of the field illustrates how the previously mentioned complications influenced its delineation and how an understanding of these complications helped in upgrading the reserves from an initial value of 10 billion ECM of gas to 40 billion ECM. Additional data acquired with the development wells tend to increase the estimate. Therefore, Barbara field is the most important Italian gas field of the decade. The producing formation is composed of very thin-bedded sandstone and shale intercalations, representing the peculiarity of this reservoir. Development of the field is being achieved with six production platforms and 72 wells.

  18. The velocity field of a coronal mass ejection: The event of September 1, 1980

    SciTech Connect

    Low, B.C.; Hundhausen, A.J. )

    1987-03-01

    A coronal mass ejection with the appearance of two sets of overlapping loops occurred at about 0600 UT on September 1, 1980, over the northwest limb of the sun. It was one of the fastest events observed by the Solar Maximum Mission coronagraph during the 1980 epoch, with apparent radial velocity components of several features approaching 1,000 km s{sup {minus}1}. A study of the slow evolution of H{sub {alpha}} prominence filaments and coronal structures in the northwest solar sector suggests that the mass ejection resulted form the disruption of a helmet streamer in association with, possibly, two filaments to give rise to the double-loop structure. This event is well covered by 10 coronagraph images of good quality so that the complex velocity field, defined by the apparent motions of many different parts of the mass ejection, can be mapped out as a function of space and time. The results of such an analysis are presented and related to current concerns in the theoretical understanding of mass ejections In particular, it is concluded that a self-similar description of the velocity field is a gross oversimplification and that although some evidence of wave propagation can be found, the bright features in this mass ejection are plasma structures moving (presumably) with frozen-in magnetic fields, rather that waves propagating through plasma and magnetic fields.

  19. High-Resolution Hα Velocity Fields of Nearby Spiral Galaxies with the Southern African Large Telescope

    NASA Astrophysics Data System (ADS)

    Mitchell, Carl; Williams, Ted; Spekkens, Kristine; Lee-Waddell, Karen; Kuzio de Naray, Rachel; Sellwood, Jerry

    2016-01-01

    In an effort to test ΛCDM predictions of galaxy mass distributions, we have obtained spectrophotometric observations of several nearby spiral galaxies with the Southern African Large Telescope (SALT) Fabry-Pérot (FP) interferometer as part of the RSS Imaging spectroscopy Nearby Galaxy Survey. Utilizing the SALT FP's 8 arcmin field of view and 2 arcsec angular resolution, we have derived 2D velocity fields of the Hα emission line to high spatial resolution at large radii. We have modeled these velocity fields with the DiskFit software package and found them to be in good agreement with lower-resolution velocity fields of the HI 21 cm line for the same galaxies. Here we present our Hα kinematic map of the barred spiral galaxy NGC 578. At the distance to this galaxy (22 Mpc), our kinematic data has a spatial resolution of 185 pc and extends to galactocentric radii of 13 kpc. The high spatial resolution of this data allows us to resolve the inner rising part of the rotation curves, which is compromised by beam smearing in lower-resolution observations. We are using these Hα kinematic data, combined with HI 21 cm kinematics and broadband photometric observations, to place constraints on NGC 578's mass distribution.

  20. Comparison of remotely sensed chlorophyll and Lagrangian Coherent Structures for velocity field validation

    NASA Astrophysics Data System (ADS)

    Goldman, Ron; Efrati, Shai; Lehahn, Yoav; Gertman, Isaac; Heifetz, Eyal

    2014-05-01

    We present a tool for daily validation of modeled or satellite derived velocity fields in the southeastern region of the Mediterranean. Within this tool, spatial patterns of Lagrangian Coherent Structures (LCS) derived from the velocity field are compared to distribution patterns of satellite derived surface chlorophyll. This comparison is advantageous to pollution spread predictions since it compares the location of fronts in passive tracer spread. The suggested methodology is based on Lagrangian tools that were shown to be very effective in reconstructing the specific effect of horizontal stirring on individual oceanic patterns. Lagrangian techniques are based, in general, on the identification of the velocity field characteristics along particle trajectories. They are well suited for diagnosing properties of tracers like chlorophyll, since they allow to quantify the dynamical properties experienced by a parcel of water during its motion. The Lagrangian diagnostics performed in this tool are based on analyzing the spatial structure of LCS from calculation of finite size Lyapunov exponents (FSLE). These LCS induce in advected tracer fields filament patterns with typical length in the range of 10 - 100 km and lifetime in the range of days/weeks (though it can be much longer if the patterns are associated to long-lived and energetic mesoscale features with low temporal variability). Since LCS represent transport barriers and tracer boundaries, they separate between water bodies with possibly different physical - biogeochemical properties. Daily analyses ( available online at http://isramar.ocean.org.il/isramar2009/cosem/fsle.aspx ) of LCS is performed on AVISO altimetry derived velocity fields and on operational numerical circulation forecasts, which are produced as part of the South Eastern Levantine Israeli Prediction System (SELIPS). The LCS analyses are then placed atop maps of surface Chlorophyll concentrations, which is provided within the MyOcean project. A

  1. Cluster Analysis of Velocity Field Derived from Dense GNSS Network of Japan

    NASA Astrophysics Data System (ADS)

    Takahashi, A.; Hashimoto, M.

    2015-12-01

    Dense GNSS networks have been widely used to observe crustal deformation. Simpson et al. (2012) and Savage and Simpson (2013) have conducted cluster analyses of GNSS velocity field in the San Francisco Bay Area and Mojave Desert, respectively. They have successfully found velocity discontinuities. They also showed an advantage of cluster analysis for classifying GNSS velocity field. Since in western United States, strike-slip events are dominant, geometry is simple. However, the Japanese Islands are tectonically complicated due to subduction of oceanic plates. There are many types of crustal deformation such as slow slip event and large postseismic deformation. We propose a modified clustering method of GNSS velocity field in Japan to separate time variant and static crustal deformation. Our modification is performing cluster analysis every several months or years, then qualifying cluster member similarity. If a GNSS station moved differently from its neighboring GNSS stations, the station will not belong to in the cluster which includes its surrounding stations. With this method, time variant phenomena were distinguished. We applied our method to GNSS data of Japan from 1996 to 2015. According to the analyses, following conclusions were derived. The first is the clusters boundaries are consistent with known active faults. For examples, the Arima-Takatsuki-Hanaore fault system and the Shimane-Tottori segment proposed by Nishimura (2015) are recognized, though without using prior information. The second is improving detectability of time variable phenomena, such as a slow slip event in northern part of Hokkaido region detected by Ohzono et al. (2015). The last one is the classification of postseismic deformation caused by large earthquakes. The result suggested velocity discontinuities in postseismic deformation of the Tohoku-oki earthquake. This result implies that postseismic deformation is not continuously decaying proportional to distance from its epicenter.

  2. Velocity overshoot decay mechanisms in compound semiconductor field-effect transistors with a submicron characteristic length

    SciTech Connect

    Jyegal, Jang

    2015-06-15

    Velocity overshoot is a critically important nonstationary effect utilized for the enhanced performance of submicron field-effect devices fabricated with high-electron-mobility compound semiconductors. However, the physical mechanisms of velocity overshoot decay dynamics in the devices are not known in detail. Therefore, a numerical analysis is conducted typically for a submicron GaAs metal-semiconductor field-effect transistor in order to elucidate the physical mechanisms. It is found that there exist three different mechanisms, depending on device bias conditions. Specifically, at large drain biases corresponding to the saturation drain current (dc) region, the velocity overshoot suddenly begins to drop very sensitively due to the onset of a rapid decrease of the momentum relaxation time, not the mobility, arising from the effect of velocity-randomizing intervalley scattering. It then continues to drop rapidly and decays completely by severe mobility reduction due to intervalley scattering. On the other hand, at small drain biases corresponding to the linear dc region, the velocity overshoot suddenly begins to drop very sensitively due to the onset of a rapid increase of thermal energy diffusion by electrons in the channel of the gate. It then continues to drop rapidly for a certain channel distance due to the increasing thermal energy diffusion effect, and later completely decays by a sharply decreasing electric field. Moreover, at drain biases close to a dc saturation voltage, the mechanism is a mixture of the above two bias conditions. It is suggested that a large secondary-valley energy separation is essential to increase the performance of submicron devices.

  3. The velocity and vorticity fields of the turbulent near wake of a circular cylinder

    NASA Technical Reports Server (NTRS)

    Wallace, James; Ong, Lawrence; Moin, Parviz

    1995-01-01

    The purpose of this research is to provide a detailed experimental database of velocity and vorticity statistics in the very near wake (x/d less than 10) of a circular cylinder at Reynolds number of 3900. This study has determined that estimations of the streamwise velocity component in flow fields with large nonzero cross-stream components are not accurate. Similarly, X-wire measurements of the u and v velocity components in flows containing large w are also subject to the errors due to binormal cooling. Using the look-up table (LUT) technique, and by calibrating the X-wire probe used here to include the range of expected angles of attack (+/- 40 deg), accurate X-wire measurements of instantaneous u and v velocity components in the very near wake region of a circular cylinder has been accomplished. The approximate two-dimensionality of the present flow field was verified with four-wire probe measurements, and to some extent the spanwise correlation measurements with the multisensor rake. Hence, binormal cooling errors in the present X-wire measurements are small.

  4. Molecular clouds. [significance in stellar evolution

    NASA Technical Reports Server (NTRS)

    Thaddeus, P.

    1977-01-01

    An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

  5. Molecular clouds. [significance in stellar evolution

    NASA Technical Reports Server (NTRS)

    Thaddeus, P.

    1977-01-01

    An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

  6. High-Resolution Velocity Fields of Low-Mass Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Truong, Phuongmai N.

    obtained using both algorithms. In general, the CO rotation curves are consistent with Halpha rotation curves of the same galaxies. Using the CO rotation curves, along with information on the stellar distribution from optical and infrared imaging, we model the velocity data including contributions from stars and the dark matter halo, which we parameterized using a generalized Navarro, Frenk & White profile. The results show that the inner power-law slope alpha of the density profile varies over a large range from below 0.38 (cored) to 1.76 (cuspy), with a mean value of 0.58 +/- 0.45 (mean +/- scatter) or 0.64 +/- 0.49 if we assume the stellar distribution derived from r-band data or IRAC 4.5- micron data, respectively. The density profile slope is generally robust as the baryonic M/L is varied from minimum- to maximum-disk estimates. Our galaxies show low stellar mass- to-light ratios: M*/L = 0.10+/-0.02 for IRAC channel-2 data and 0.49+/-0.33 for r-band data. Considering our results in combination with recent studies from the literature, we find weak correlations between the dark matter profile inner slope, dynamical mass and distance of the galaxies, where more distant and more massive galaxies have steeper slopes. In addition, we find no statistically significant correlation between the slope and the stellar mass, which may suggest that baryonic feedback models alone cannot fully explain the flattening behavior of the inner profiles of dwarf galaxies.

  7. Large-scale peculiar velocity field in flat models of the universe

    SciTech Connect

    Vittorio, N.; Turner, M.S.

    1987-05-01

    The inflationary universe scenario predicts a flat universe and both adiabatic and isocurvature primordial density perturbations with the Zel'dovich spectrum. The two simplest realizations, models dominated by hot or cold dark matter, seem to be in conflict with observations. Flat models with two components of mass density, where one of the components of mass density is smoothly distributed, are examined, and the large-scale peculiar velocity field for these models is computed. For the smooth component the authors consider relativistic particles, a relic cosmological term, and light strings. At present the observational situation is unsettled, but, in principle, the large-scale peculiar velocity field is a very powerful discriminator between these different models. 66 references.

  8. Lift distribution and velocity field measurements for a three-dimensional, steady blade/vortex interaction

    NASA Technical Reports Server (NTRS)

    Dunagan, Stephen E.; Norman, Thomas R.

    1987-01-01

    A wind tunnel experiment simulating a steady three-dimensional helicopter rotor blade/vortex interaction is reported. The experimental configuration consisted of a vertical semispan vortex-generating wing, mounted upstream of a horizontal semispan rotor blade airfoil. A three-dimensional laser velocimeter was used to measure the velocity field in the region of the blade. Sectional lift coefficients were calculated by integrating the velocity field to obtain the bound vorticity. Total lift values, obtained by using an internal strain-gauge balance, verified the laser velocimeter data. Parametric variations of vortex strength, rotor blade angle of attack, and vortex position relative to the rotor blade were explored. These data are reported (with attention to experimental limitations) to provide a dataset for the validation of analytical work.

  9. The large-scale peculiar velocity field in flat models of the universe

    NASA Technical Reports Server (NTRS)

    Vittorio, Nicola; Turner, Michael S.

    1987-01-01

    The inflationary universe scenario predicts a flat universe and both adiabatic and isocurvature primordial density perturbations with the Zel'dovich spectrum. The two simplest realizations, models dominated by hot or cold dark matter, seem to be in conflict with observations. Flat models with two components of mass density, where one of the components of mass density is smoothly distributed, are examined, and the large-scale peculiar velocity field for these models is computed. For the smooth component the authors consider relativistic particles, a relic cosmological term, and light strings. At present the observational situation is unsettled, but, in principle, the large-scale peculiar velocity field is a very powerful discriminator between these different models.

  10. Comment on "Diffusion by a random velocity field" [Phys. Fluids 13, 22 (1970)

    NASA Astrophysics Data System (ADS)

    Saad, Tony; Sutherland, James C.

    2016-11-01

    This comment aims at addressing a mass conservation issue in a paper published in the physics of fluids. The paper [R. H. Kraichnan, "Diffusion by a random velocity field," Phys. Fluids 13(1), 22 (1970)] introduces a novel method to generate synthetic isotropic turbulence for computational purposes. The method has been used in the literature to generate inlet boundary conditions and to model aeroacoustic noise as well as for validation and verification purposes. However, the technique uses a continuous formulation to derive the mass conservation constraint. In this comment, we argue that the continuous constraint is invalid on a discrete grid and provide an alternative derivation using the discrete divergence. In addition, we present an analysis to quantify the impact of a pressure projection on the kinetic energy of a non-solenoidal velocity field.

  11. Velocity field in a vicinity of cylinder bouncing off horizontal wall

    NASA Astrophysics Data System (ADS)

    Chara, Z.; Kysela, B.; Dolansky, J.

    2016-06-01

    The paper describes experimental and numerical investigations of velocity fields around a circular cylinder colliding perpendicularly with a plane wall. The cylinder of the diameter D = 20 mm was moving vertically in a water tank and the motion was recorded by a fast digital camera. Reynolds numbers ranged from 3000 to 8100 and the initial positions L of the cylinder above the wall were L/D = 2.5; 3.5; 4.5 and 5.5. An evolution of fluid agitation in an area close to the impact point was based on the results of the velocity field measurements. The numerical simulations were performed using a 2D-LES model.

  12. Application of Helical Characteristics of the Velocity Field to Evaluate the Intensity of Tropical Cyclones

    NASA Astrophysics Data System (ADS)

    Levina, G.; Glebova, E.; Naumov, A.; Trosnikov, I.

    The paper presents results of numerical analysis for helical features of velocity field to investigate the process of tropical cyclone formation, namely, the downward helicity flux through the upper boundary of the viscous atmospheric turbulent boundary layer has been calculated. The simulation was carried out by use of the regional atmospheric ETA model and NCEP reanalysis global data. Calculations were performed for two tropical cyclones - Wilma (Atlantic basin, 2005) and Man-Yi (North-West Pacific, 2007). It has been found, that the chosen helical characteristic reveals an adequate response to basic trends in variation of such important meteorological fields as pressure and wind velocity during the hurricane vortex evolution. The analysis carried out in the paper shows that the helicity flux can be used as an illustrative characteristic to describe the intensity and destructive power of tropical cyclones.

  13. Reconstruction of divergence-free velocity fields from cine 3D phase-contrast flow measurements.

    PubMed

    Busch, Julia; Giese, Daniel; Wissmann, Lukas; Kozerke, Sebastian

    2013-01-01

    Three-dimensional phase-contrast velocity vector field mapping shows great potential for clinical applications; however measurement inaccuracies may limit the utility and robustness of the technique. While parts of the error in the measured velocity fields can be minimized by background phase estimation in static tissue and magnetic field monitoring, considerable inaccuracies remain. The present work introduces divergence-reduction processing of 3D phase-contrast flow data based on a synergistic combination of normalized convolution and divergence-free radial basis functions. It is demonstrated that this approach effectively addresses erroneous flow for image reconstructions from both fully sampled and undersampled data. Using computer simulations and in vivo data acquired in the aorta of healthy subjects and a stenotic valve patient it is shown that divergence arising from measurement imperfections can be reduced by up to 87% resulting in improved vector field representations. Based on the results obtained it is concluded that integration of the divergence-free condition into postprocessing of vector fields presents an efficient approach to addressing flow field inaccuracies. Copyright © 2012 Wiley Periodicals, Inc.

  14. VLA Observations of the Magnetic Field of the Smith High Velocity Cloud

    NASA Astrophysics Data System (ADS)

    Betti, Sarah; Hill, Alex S.; Mao, Sui Ann; McClure-Griffiths, Naomi M.; Lockman, Felix J.; Benjamin, Robert A.; Gaensler, Bryan M.

    2017-01-01

    High velocity clouds (HVCs) are hydrogen gas clouds around galaxies with velocities inconsistent with Galactic rotation. HVCs may fuel future star formation and drive galaxy evolution. The Smith Cloud is an HVC with an orbit suggesting it has made at least one passage through the disk. A measured magnetic field suggests how it survived passage through the Galactic halo. The Faraday rotation measure (RM) provides information about the strength and direction of the magnetic field. We use the Karl G. Jansky Very Large Array (VLA) to obtain reliable RMs towards ~950 background point sources to measure the geometry of the magnetic field of the Smith Cloud. These RMs constrain the strength of the magnetic field at the head, tail, and body of the Smith Cloud while RMs directly behind the Smith Cloud suggest there is ionized gas associated with the cloud that has not previously been detected. The confirmation of the magnetic field of the Smith Cloud along with a detailed morphology of the magnetic field structure will constrain how HVCs pass through the Galactic halo without losing their gas and survive the passage through the intergalactic and interstellar media.

  15. Visualizing flow fields using acoustic Doppler current profilers and the Velocity Mapping Toolbox

    USGS Publications Warehouse

    Jackson, P. Ryan

    2013-01-01

    The purpose of this fact sheet is to provide examples of how the U.S. Geological Survey is using acoustic Doppler current profilers for much more than routine discharge measurements. These instruments are capable of mapping complex three-dimensional flow fields within rivers, lakes, and estuaries. Using the Velocity Mapping Toolbox to process the ADCP data allows detailed visualization of the data, providing valuable information for a range of studies and applications.

  16. Characterization of Stellar Sub-Structure in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Kunder, Andrea; De Propris, Roberto; Rich, R. Michael; Koch, Andreas; Johnson, Christian I.

    2014-02-01

    We have discovered a group of 7 bulge giants with radial velocities of +300 km/s in a two degree field toward the Galactic bulge at (l,b)=(-6,-8). They are separated from the highest velocity bulge members by ~100 km/s. Recently, ARGOS reported a group of 4 kinematically distinct metal-poor bulge stars in their bulge fields at l=-20. Coincidentally, these stars have radial velocities of +300 km/sec. Given the scarcity of stars with velocities of +300 km/s in the bulge, these stellar features are likely related and part of a large independent stream or moving group in the inner Galaxy. We propose to search for connecting stars that link these two features and trace the extent of this newly discovered stream and understand their stellar system of origin, via their chemical composition.

  17. Kernel Bundle Diffeomorphic Image Registration Using Stationary Velocity Fields and Wendland Basis Functions.

    PubMed

    Pai, Akshay; Sommer, Stefan; Sorensen, Lauge; Darkner, Sune; Sporring, Jon; Nielsen, Mads

    2016-06-01

    In this paper, we propose a multi-scale, multi-kernel shape, compactly supported kernel bundle framework for stationary velocity field-based image registration (Wendland kernel bundle stationary velocity field, wKB-SVF). We exploit the possibility of directly choosing kernels to construct a reproducing kernel Hilbert space (RKHS) instead of imposing it from a differential operator. The proposed framework allows us to minimize computational cost without sacrificing the theoretical foundations of SVF-based diffeomorphic registration. In order to recover deformations occurring at different scales, we use compactly supported Wendland kernels at multiple scales and orders to parameterize the velocity fields, and the framework allows simultaneous optimization over all scales. The performance of wKB-SVF is extensively compared to the 14 non-rigid registration algorithms presented in a recent comparison paper. On both MGH10 and CUMC12 datasets, the accuracy of wKB-SVF is improved when compared to other registration algorithms. In a disease-specific application for intra-subject registration, atrophy scores estimated using the proposed registration scheme separates the diagnostic groups of Alzheimer's and normal controls better than the state-of-the-art segmentation technique. Experimental results show that wKB-SVF is a robust, flexible registration framework that allows theoretically well-founded and computationally efficient multi-scale representation of deformations and is equally well-suited for both inter- and intra-subject image registration.

  18. GNSS-based densification of the ITRF velocity field through a collaborative approach

    NASA Astrophysics Data System (ADS)

    Legrand, Juliette; Bruyninx, Carine; Craymer, Michael; Dawson, John; Griffiths, Jake; Kenyeres, Ambrus; Rebischung, Paul; Sánchez, Laura; Santamaría-Gómez, Alvaro; Saria, Elifuraha; Altamimi, Zuheir

    2015-04-01

    The objective of the IAG Working Group "Integration of Dense Velocity Fields in the ITRF" is to provide a GNSS-based dense, unified and reliable velocity field globally referenced in the ITRF (International Terrestrial Reference Frame) and useful for geodynamical and geophysical interpretations. The WG is embedded in IAG Sub-Commission 1.3 "Regional Reference Frames" where it coexists with the Regional Reference Frame Sub-Commissions AFREF (Africa), APREF (Asia & Pacific), EUREF (Europe), NAREF (North America), SCAR (Antarctica), SIRGAS (Latin America & Caribbean). These IAG Regional Reference Frame sub-commissions are responsible for providing GNSS-based densified weekly solutions for their region. To obtain such a densified velocity field, the WG combined the individual weekly solutions from 7 individual contributors (AFREF, APREF, EUREF, NAREF (NGS, GSB), SIRGAS, IGS) and then stacked these weekly combined solutions in order to derive a ITRF2008 densification as well as the associated residual position time series for more than 2800 sites. Here we present the latest densification results.

  19. Kernel bundle diffeomorphic image registration using stationary velocity fields and Wendland basis functions.

    PubMed

    Pai, Akshay; Sommer, Stefan; Sorensen, Lauge; Darkner, Sune; Sporring, Jon; Nielsen, Mads

    2015-12-23

    In this paper, we propose a multi-scale, multi-kernel shape, compactly supported kernel bundle framework for stationary velocity field-based image registration (Wendland kernel bundle stationary velocity field, wKB-SVF). We exploit the possibility of directly choosing kernels to construct a reproducing kernel Hilbert space (RKHS) instead of imposing it from a differential operator. The proposed framework allows us to minimize computational cost without sacrificing the theoretical foundations of SVF-based diffeomorphic registration. In order to recover deformations occurring at different scales, we use compactly supported Wendland kernels at multiple scales and orders to parameterize the velocity fields, and the framework allows simultaneous optimization over all scales. The performance of wKB-SVF is extensively compared to the 14 non-rigid registration algorithms presented in a recent comparison paper. On both MGH10 and CUMC12 datasets, the accuracy of wKB-SVF is improved when compared to other registration algorithms. In a disease-specific application for intra-subject registration, atrophy scores estimated using the proposed registration scheme separates the diagnostic groups of Alzheimer's and normal controls better than the state-of-the-art segmentation technique. Experimental results show that wKB-SVF is a robust, flexible registration framework that allows theoretically well-founded and computationally efficient multi-scale representation of deformations and is equally well-suited for both inter- and intra-subject image registration.

  20. Image registration using stationary velocity fields parameterized by norm-minimizing Wendland kernel

    NASA Astrophysics Data System (ADS)

    Pai, Akshay; Sommer, Stefan; Sørensen, Lauge; Darkner, Sune; Sporring, Jon; Nielsen, Mads

    2015-03-01

    Interpolating kernels are crucial to solving a stationary velocity field (SVF) based image registration problem. This is because, velocity fields need to be computed in non-integer locations during integration. The regularity in the solution to the SVF registration problem is controlled by the regularization term. In a variational formulation, this term is traditionally expressed as a squared norm which is a scalar inner product of the interpolating kernels parameterizing the velocity fields. The minimization of this term using the standard spline interpolation kernels (linear or cubic) is only approximative because of the lack of a compatible norm. In this paper, we propose to replace such interpolants with a norm-minimizing interpolant - the Wendland kernel which has the same computational simplicity like B-Splines. An application on the Alzheimer's disease neuroimaging initiative showed that Wendland SVF based measures separate (Alzheimer's disease v/s normal controls) better than both B-Spline SVFs (p<0.05 in amygdala) and B-Spline freeform deformation (p<0.05 in amygdala and cortical gray matter).

  1. Plasma Disruption Avoidance and Mitigation using Strong Non-Axisymmetric Shaping with Stellarator Fields

    NASA Astrophysics Data System (ADS)

    Archmiller, Matthew C.

    2013-10-01

    The avoidance and mitigation of major disruptions remains a critical challenge for ITER and future burning tokamak plasmas. Early stellarator experiments with toroidal plasma current were found to operate without disruptions if the vacuum rotational transform produced by external coils was greater than a threshold value of ιvac (a) >= 0 . 14. Strong 3-D shaping produced by externally generated rotational transform is also observed to suppress disruptive phenomena of current-carrying discharges in the Compact Toroidal Hybrid (CTH), with the amount of ιvac (a) required for suppression dependent upon the disruption scenario. Current-driven disruptions are deliberately generated in CTH by (1) raising the plasma density, (2) operating at low edge safety factor q (a) , or (3) by not compensating against the vertical instability of plasmas with high elongation. While the density limit is found to agree with the empirical Greenwald limit at low edge vacuum transform (ιvac (a) = 0 . 04), the experimental densities exceed this limit by up to a factor of three as the vacuum transform is raised to - 8 muιvac (a) = 0 . 25 . Low- q disruptions near q (a) = 2 are observed at low vacuum transform but no longer occur when the vacuum transform is raised above, even though q (a) falls below a value of 2. Passive suppression of the vertical instability of elongated plasmas is observed with the addition of external transform, and the amount required is in agreement with an analytic calculation of marginal stability in current-carrying stellarators. Work supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610.

  2. Uncertainty of InSAR velocity fields for measuring long-wavelength displacement

    NASA Astrophysics Data System (ADS)

    Fattahi, H.; Amelung, F.

    2014-12-01

    Long-wavelength artifacts in InSAR data are the main limitation to measure long-wavelength displacement; they are traditionally attributed mainly to the inaccuracy of the satellite orbits (orbital errors). However, most satellites are precisely tracked resulting in uncertainties of orbits of 2-10 cm. Orbits of these satellites are thus precise enough to obtain precise velocity fields with uncertainties better than 1 mm/yr/100 km for older satellites (e.g. Envisat) and better than 0.2 mm/yr/100 km for modern satellites (e.g. TerraSAR-X and Sentinel-1) [Fattahi & Amelung, 2014]. Such accurate velocity fields are achievable if long-wavelength artifacts from sources other than orbital errors are identified and corrected for. We present a modified Small Baseline approach to measure long-wavelength deformation and evaluate the uncertainty of these measurements. We use a redundant network of interferograms for detection and correction of unwrapping errors to ensure the unbiased estimation of phase history. We distinguish between different sources of long-wavelength artifacts and correct those introduced by atmospheric delay, topographic residuals, timing errors, processing approximations and hardware issues. We evaluate the uncertainty of the velocity fields using a covariance matrix with the contributions from orbital errors and residual atmospheric delay. For contributions from the orbital errors we consider the standard deviation of velocity gradients in range and azimuth directions as a function of orbital uncertainty. For contributions from the residual atmospheric delay we use several approaches including the structure functions of InSAR time-series epochs, the predicted delay from numerical weather models and estimated wet delay from optical imagery. We validate this InSAR approach for measuring long-wavelength deformation by comparing InSAR velocity fields over ~500 km long swath across the southern San Andreas fault system with independent GPS velocities and

  3. Crustal velocity field near the big bend of California's San Andreas fault

    USGS Publications Warehouse

    Snay, R.A.; Cline, M.W.; Philipp, C.R.; Jackson, D.D.; Feng, Y.; Shen, Z.-K.; Lisowski, M.

    1996-01-01

    We use geodetic data spanning the 1920-1992 interval to estimate the horizontal velocity field near the big bend segment of California's San Andreas fault (SAF). More specifically, we estimate a horizontal velocity vector for each node of a two-dimensional grid that has a 15-min-by-15-min mesh and that extends between latitudes 34.0??N and 36.0??N and longitudes 117.5??W and 120.5??W. For this estimation process, we apply bilinear interpolation to transfer crustal deformation information from geodetic sites to the grid nodes. The data include over a half century of triangulation measurements, over two decades of repeated electronic distance measurements, a decade of repeated very long baseline interferometry measurements, and several years of Global Positioning System measurements. Magnitudes for our estimated velocity vectors have formal standard errors ranging from 0.7 to 6.8 mm/yr. Our derived velocity field shows that (1) relative motion associated with the SAF exceeds 30 mm/yr and is distributed on the Earth's surface across a band (> 100 km wide) that is roughly centered on this fault; (2) when velocities are expressed relative to a fixed North America plate, the motion within our primary study region has a mean orientation of N44??W ?? 2?? and the surface trace of the SAF is congruent in shape to nearby contours of constant speed yet this trace is oriented between 5?? and 10?? counterclockwise relative to these contours; and (3) large strain rates (shear rates > 150 nrad/yr and/or areal dilatation rates < -150 nstr/yr) exist near the Garlock fault, near the White Wolf fault, and in the Ventura basin.

  4. Regulation of conduction velocity in axons from near-field receptors of the crayfish antennule.

    PubMed

    Mellon, DeForest

    2010-11-15

    The antennular flagella of the crayfish Procambarus clarkii each possess a linear array of near-field receptors, termed standing feathered sensilla, that are extremely sensitive to movement of the surrounding water. Previously it had been shown that, within each flagellum, the axonal conduction velocity of the sensory neuron pair associated with each feathered sensillum was linearly related to the position of the sensillum along the flagellar axis. In the current studies I show that the conduction velocity of axons within the proximal three segments of the antennules, between the flagellum and the brain, is somewhat higher than the corresponding conduction velocity of the same axons in the flagellum, especially for those whose flagellar conduction velocity is between 1 and 3 m s(-1), even though there is no net change in axonal diameter within this part of the afferent pathway. One consequence of this change in axonal conduction properties is an effective compression of the temporal spread - potentially by as much as tenfold - which otherwise would occur in arrival times of initial spikes from each sensillum following a mechanical stimulus to the antennule. Furthermore, the pattern signature of initial spike volleys at the brain following a global hydrodynamic stimulus to the flagellum is remarkably consistent and conceivably could be recognized as such by central processing centers. I conclude that conduction velocity adjustments improve temporal summation and resolution from input volleys that originate in the highly sensitive and, hence, inherently noisy near-field receptors, thereby more effectively triggering startle response circuitry at the approach of potential predators.

  5. The Effects Of Stellar Activity On Detecting And Characterising Planets

    NASA Astrophysics Data System (ADS)

    Aigrain, Suzanne; Angus, R.; Barstow, J.; Rajpaul, V.; Gillen, E.; Parviainen, H.; Pope, B.; Roberts, S.; McQuillan, A.; Gibson, N.; Mazeh, T.; Pont, F.; Zucker, S.

    2016-08-01

    Intrinsic stellar variability associated with magnetic activity, rotation and convection, affects the detection of exoplanets via the transit and radial velocity methods, and the characterisation of their atmospheres. I will review the increasingly sophisticated methods developed in the last few years to mitigate this problem, and outline how stellar variability is likely to impact the field of exoplanets in the future. Planetary transits last a few hours, much shorter than the rotational modulation of star spots (day to weeks), but smaller-scale variability is nonetheless an important limiting factor in our ability to detect transits of Earth analogs in Kepler and Plato data. In radial velocity, the problem is even more severe, as the planet's signal occurs on the orbital timescale, which can coincide with the range expected for stellar rotation periods or activity cycles - but the spectra used to extract radial velocities contain a wealth of information about stellar activity that can be used to disentangle the two types of signals. Finally, when using transits or phase curves to probe the composition and dynamics of planetary atmospheres, star spots must be accounted for very carefully, as they can mimic or mask planetary atmosphere signals. On the positive side, the sensitivity of planet search and characterisation experiments to stellar activity means that they are a treasure trove of information about stellar activity. The continued success of exoplanet surveys depends on our making the best possible use of this information.

  6. Effects of Data Sampling on the Results of Fourier Analysis of Radial-Velocity Fields in Spiral-Galaxy Disks

    NASA Astrophysics Data System (ADS)

    Burlak, A. N.; Zasov, A. V.; Fridman, A. M.; Khoruzhi, O. V.

    2000-12-01

    Our main goal is to investigate the effects of data incompleteness on the results of Fourier analysis of line-of-sight velocity fields in the disks of spiral galaxies. We have carried out a number of numerical experiments, first with an artificially created simple velocity field and then with the velocity fields of two real galaxies, which qualitatively differ in data filling: NGC 157 and NGC 3631 with good and bad data filling, respectively. The field of purely circular velocities is chosen as the simplest artificial velocity field, because the circular velocities of spiral galaxies are much high than the residual (noncircular) velocities. Superimposing a "mask" simulating blank spots (holes) in the map of observational data on this artificial field has no effect on the results of Fourier analysis of this simplest field. A similar result is obtained for real galaxies with good data filling of the observed velocity fields. Superimposing arbitrarily shaped masks on the observed velocity field of NGC 157 in such a way that the field was filled by a mere 50% (at each radius) could not change appreciably the radial variations of large-scale Fourier harmonics. The situation qualitatively changes in attempting to fill the holes in the observed velocity field of NGC 3631 in some way. When missing velocities are artificially introduced by using the simplest model of purely circular gas rotation, the amplitudes and phases of the principal Fourier harmonics are distorted. In particular, a substantial distortion of the third harmonic also causes an increase in the error when determining the corotation radius from data of the filled field. When the filling of the velocity field is increased by degrading the spatial resolution, the amplitudes of most harmonics decrease throughout the entire disk region; as a result, their radial variations are smoothed out and the behavior of harmonic phases in the range of moderately high initial amplitudes can be distorted. An abnormal

  7. Pulse-shape-dependent strong-field ionization viewed with velocity-map imaging

    SciTech Connect

    Geissler, Dominik; Weinacht, Thomas C.; Rozgonyi, Tamas; Gonzalez-Vazquez, Jesus

    2011-11-15

    We explore strong field molecular ionization with velocity map imaging of fragment ions produced by dissociation following ionization. Our measurements and ab initio electronic structure calculations allow us to identify various electronic states of the molecular cation populated during ionization, with multiple pathways to individual states highlighted by the pulse shape dependence. In addition, we show that relative populations can be reconstructed from our measurements. The results illustrate how strong field molecular ionization can be complicated by the presence and interaction of multiple cationic states during ionization.

  8. Velocity dependence of the dynamic magnetic field acting on swift O and Sm ions

    NASA Astrophysics Data System (ADS)

    Shu, N. K. B.; Melnik, D.; Brennan, J. M.; Semmler, W.; Benczer-Koller, #.

    1980-05-01

    The hyperfine dynamic field acting on fast ions traversing polarized iron foils has been measured as a function of the ion velocity in the region 0.03field increases with velocity but not linearly. The same conclusions were obtained from measurements on oxygen ions traversing thin iron foils or stopping in thick iron foils. All available data on dynamic-field measurements at ions with 8field. The region of validity of this parametrization of the dynamic field, as well as possible explanations of its origin, are discussed. NUCLEAR REACTIONS 150,152Sm(16O, 16O')150,152Sm(2+1), 150,152Sm(32S, 32S')150,152Sm(2+1), and 16O(α,α')16O(3-1): E0~40 MeV, Es~70-80 MeV, Eα=17.55 MeV; measured W(θ,B,∞) through polarized iron; deduced BDYNAMIC(v); compiled existing data to obtain general parametrization for BDYNAMIC(v,Z).

  9. Numerical Analysis of the Turbine 99 Draft Tube Flow Field Provoked by Redesigned Inlet Velocity Profiles.

    NASA Astrophysics Data System (ADS)

    Galván, S.; Reggio, M.; Guibault, F.; Castro, L.

    2014-03-01

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic flow field at the runner outlet determines the diffuser efficiency affecting the overall performance of the turbine. This flow field, for which the principal characteristics are the flow rate and the inlet swirling flow intensity, is mostly developed on turbines designed for low head (high specific velocity) and operated away from their best efficiency point. To identify factors of the flow field responsible for loosing draft- tube efficiency, the correlations between the flow pattern along the diffuser and both swirl intensity and flow rate have been examined. An analytical representation of inlet flow field has been manipulated by a Multi Island Genetic Algorithm through the automatic coupling of multidisciplinary commercial software systems in order to obtain redesigned inlet velocity profiles. This loop allowed determining the profile for which the minimum energy loss factor was reached. With different flow field patterns obtained during the optimization process it was possible to undertake a qualitative and quantitative analysis which has helped to understand how to suppress or at least mitigate undesirable draft tube flow characteristics. The direct correlation between the runner blade design and the kinematics of the swirl at the draft tube inlet should suppose the perfect coupling at the runner-draft tube interface without compromising the overall flow stability of the machine.

  10. Ab initio velocity-field curves in monoclinic β-Ga2O3

    NASA Astrophysics Data System (ADS)

    Ghosh, Krishnendu; Singisetti, Uttam

    2017-07-01

    We investigate the high-field transport in monoclinic β-Ga2O3 using a combination of ab initio calculations and full band Monte Carlo (FBMC) simulation. Scattering rate calculation and the final state selection in the FBMC simulation use complete wave-vector (both electron and phonon) and crystal direction dependent electron phonon interaction (EPI) elements. We propose and implement a semi-coarse version of the Wannier-Fourier interpolation method [Giustino et al., Phys. Rev. B 76, 165108 (2007)] for short-range non-polar optical phonon (EPI) elements in order to ease the computational requirement in FBMC simulation. During the interpolation of the EPI, the inverse Fourier sum over the real-space electronic grids is done on a coarse mesh while the unitary rotations are done on a fine mesh. This paper reports the high field transport in monoclinic β-Ga2O3 with deep insight into the contribution of electron-phonon interactions and velocity-field characteristics for electric fields ranging up to 450 kV/cm in different crystal directions. A peak velocity of 2 × 107 cm/s is estimated at an electric field of 200 kV/cm.

  11. Repeating firing fields of CA1 neurons shift forward in response to increasing angular velocity.

    PubMed

    Cowen, Stephen L; Nitz, Douglas A

    2014-01-01

    Self-motion information influences spatially-specific firing patterns exhibited by hippocampal neurons. Moreover, these firing patterns can repeat across similar subsegments of an environment, provided that there is similarity of path shape and head orientations across subsegments. The influence of self-motion variables on repeating fields remains to be determined. To investigate the role of path shape and angular rotation on hippocampal activity, we recorded the activity of CA1 neurons from rats trained to run on spiral-shaped tracks. During inbound traversals of circular-spiral tracks, angular velocity increases continuously. Under this condition, most neurons (74%) exhibited repeating fields across at least three adjacent loops. Of these neurons, 86% exhibited forward shifts in the angles of field centers relative to centers on preceding loops. Shifts were absent on squared-spiral tracks, minimal and less reliable on concentric-circle tracks, and absent on outward-bound runs on circular-spiral tracks. However, outward-bound runs on the circular-spiral track in the dark were associated with backward shifts. Together, the most parsimonious interpretation of the results is that continuous increases or decreases in angular velocity are particularly effective at shifting the center of mass of repeating fields, although it is also possible that a nonlinear integration of step counts contributes to the shift. Furthermore, the unexpected absence of field shifts during outward journeys in light (but not darkness) suggests visual cues around the goal location anchored the map of space to an allocentric reference frame.

  12. Modeling of integrated sunlight velocity measurements: The effect of surface darkening by magnetic fields

    NASA Technical Reports Server (NTRS)

    Ulrich, R. K.; Henney, C. J.; Schimpf, S.; Fossat, E.; Gelly, B.; Grec, G.; Loudagh, S.; Schmider, F.-X; Palle, P.; Regulo, C.

    1993-01-01

    It has been known since the work by Claverie et al. (1982) that integrated-sunlight velocities measured with the resonance scattering technique show variations with time scales of weeks to months. The cause can be understood in terms of the effects of solar activity as was pointed out by Edmunds & Gough (1983) and Andersen & Maltby (1983). The latter authors included a model calculation based on sunspot areas which showed good promise of being able to quantitatively reproduce the observed velocity shifts. We discuss in this paper a new modeling effort based on daily magnetograms obtained at the 150-ft tower on Mt. Wilson. This type of database is more quantitative than sunspot area. Similar maps of magnetically sensitive quantities will be measured on a continuous time base as part of several planned helioseismology experiments (from space with the Solar Oscillations Imagery/Michelson Doppler Imager (SOI/MDI) experiment on the Solar and Heliospheric Observatory (SOHO), see Scherrer et al. (1991) or with ground-based networks, see Hill & Leibacher (1991)). We discuss the correlations between various magnetically sensitive quantities and develop a new model for the effects of magnetic field on line profiles and surface brightness. From these correlations we integrate the line profile changes over the solar surface using observed magnetic field strengths measured at lambda 5250.2. The final output is a new model for the effects of magnetic fields on integrated sunlight velocities which we compare with daily offset velocities derived from the International Research on the Interior of the Sun (IRIS)-T instrument at the Observatorio del Teide.

  13. Coupled human erythrocyte velocity field and aggregation measurements at physiological haematocrit levels.

    PubMed

    Dusting, Jonathan; Kaliviotis, Efstathios; Balabani, Stavroula; Yianneskis, Michael

    2009-07-22

    Simultaneous measurement of erythrocyte (RBC) velocity fields and aggregation properties has been successfully performed using an optical shearing microscope and Particle Image Velocimetry (PIV). Blood at 45% haematocrit was sheared at rates of 5.4< or =gamma < or = 252 s(-1) and imaged using a high speed camera. The images were then processed to yield aggregation indices and flow velocities. Negligible levels of aggregation were observed for gamma > or = 54.0 s(-1), while high levels of aggregation and network formation occurred for gamma < or = 11.7 s(-1). The results illustrate that the velocity measurements are dependent on the extent of RBC aggregation. High levels of network formation cause the velocities at gamma > or = 5.4 s(-1) to deviate markedly from the expected solid body rotation profile. The effect of aggregation level on the PIV accuracy was assessed by monitoring the two-dimensional (2D) correlation coefficients. Lower levels of aggregation result in poorer image correlation, from which it can be inferred that PIV accuracy is reduced. Moreover, aggregation is time-dependent, and consequently PIV accuracy may decrease during recording as the cells break up. It is therefore recommended that aggregation and its effects are taken into account in future when undertaking blood flow studies using PIV. The simplicity of the technique, which requires no lasers, filters, or special pretreatments, demonstrates the potential wide-spread applicability of the data acquisition system for accurate blood flow PIV and aggregation measurement.

  14. On the velocity in the Effective Field Theory of Large Scale Structures

    SciTech Connect

    Mercolli, Lorenzo; Pajer, Enrico E-mail: enrico.pajer@gmail.com

    2014-03-01

    We compute the renormalized two-point functions of density, divergence and vorticity of the velocity in the Effective Field Theory of Large Scale Structures. Because of momentum and mass conservation, the corrections from short scales to the large-scale power spectra of density, divergence and vorticity must start at order k{sup 4}. For the vorticity this constitutes one of the two leading terms. Exact (approximated) self-similarity of an Einstein-de Sitter (ΛCDM) background fixes the time dependence so that the vorticity power spectrum at leading order is determined by the symmetries of the problem and the power spectrum around the non-linear scale. We show that to cancel all divergences in the velocity correlators one needs new counterterms. These fix the definition of velocity and do not represent new properties of the system. For an Einstein-de Sitter universe, we show that all three renormalized cross- and auto-correlation functions have the same structure but different numerical coefficients, which we compute. We elucidate the differences between using momentum and velocity.

  15. High-speed non-intrusive measurements of fuel velocity fields at high-pressure injectors

    NASA Astrophysics Data System (ADS)

    Gürtler, Johannes; Schlüßler, Raimund; Fischer, Andreas; Czarske, Jürgen

    2017-03-01

    Using a single high-speed camera and a frequency modulated laser, a novel approach is presented for fast velocity field measurements in unsteady spray flows. The velocity range is from zero up to several 100 m/s, which requires a high measurement rate and a large dynamic. Typically, flow measurements require to seed tracer particles to the fluid. A paradigm shift to seeding-free measurements is presented. The light scattered at the phase boundaries of the fluid droplets is evaluated. In order to validate the high-speed measurement system, a detailed uncertainty analysis is performed by means of measurements as well as simulations. Thereby, variations of the scattered light intensity, which are based on the high temporal velocity gradients, are found to be the main contribution to the uncertainty. The eventually measurement results, obtained at a measurement rate of 500 kHz, exhibit spray velocities ranging from 0 m/s up to 400 m/s in less than 1 ms, and the detection of unsteady and irregular flow phenomena with a characteristic time of several μs is achieved. This demonstrates the high measurement rate, the high temporal resolution and the large measurement range of the proposed high-speed measurement system.

  16. Rapid analysis of non-uniformly sampled pulsed field gradient data for velocity estimation.

    PubMed

    Raghavan, K; Park, J C; Pavlovskaya, G E; Gibbs, S J

    2001-06-01

    Bretthorst's recent generalization of the Lomb-Scargle periodogram shows that a sufficient statistic for frequency estimation from non-uniformly, but simultaneously sampled quadrature data is equivalent to the FFT of those data with the missing samples replaced by zeros. We have applied this concept to the rapid analysis of pulsed field gradient MRI data which have been non-uniformly sampled in the velocity encoding wave vector q. For a small number of q samples, it is more computationally efficient to calculate the periodogram directly rather than using the FFT algorithm with a large number of zeros. The algorithm we have implemented for finding the peak of the generalized periodogram is simple and robust; it involves repeated apodization and grid searching of the periodogram until the desired velocity resolution is achieved. The final estimate is refined by quadratic interpolation. We have tested the method for fully developed Poiseuille flow of a Newtonian fluid and have demonstrated substantial improvement in the precision of velocity measurement achievable in a fixed acquisition time with non-uniform sampling. The method is readily extendible to multidimensional data. Analysis of a 256 by 256 pixel image with 8 q samples and an effective velocity resolution of better than 1/680 of the Nyquist range requires approximately 1 minute computation time on a 400 MHz SUN Ultrasparc II processor.

  17. IGS Working Group "Regional Dense Velocity Fields": Objectives and Work Plan

    NASA Astrophysics Data System (ADS)

    Bruyninx, C.; Altamimi, Z.; Becker, M.; Craymer, M.; Combrinck, L.; Combrink, A.; Fernandes, R.; Govind, R.; Herring, T.; Kenyeres, A.; King, B.; Kreemer, C.; Lavallee, D.; Legrand, J.; Moore, M.; Sanchez, L.; Sella, G.; Woppelmann, G.

    2008-12-01

    The IAG Working Group (WG) on "Regional Dense Velocity Fields" was created within IAG sub-commission 1.3 "Regional Reference Frames" at the IUGG General Assembly in Perugia in 2007. The goal of the Working Group is to densify the latest realization of the ITRS and provide regional dense velocity information in a common global reference frame. For that purpose, working group members join efforts with the regional sub-commissions (AFREF, NAREF, SIRGAS, EUREF, ·s ) and analysis groups processing data from local/regional continuous and episodic GNSS stations. In a first step, dedicated region coordinators will gather as many as possible velocity solutions for their region (in accordance with the WG requirements) and combine these solutions with the sub-commission regional solutions to produce a regional cumulative combined solution in the SINEX format. In a second step, combination coordinators will perform combinations of the regional SINEX submissions and SINEX solutions from global GNSS networks like e.g. TIGA. The purpose of multiple combination coordinators is to evaluate both the results and different approaches. To assist in this task regional coordinators will solicit discontinuity tables in addition to the weekly SINEX solutions. At the same time, the WG will also study the strengths and shortcomings of local/regional and continuous/episodic GNSS solutions to determine site velocities, and define optimal strategies for the combination of regional and global SINEX solutions.

  18. Imaging of Time and Space Variation of Vortex Wind Velocity Fields Using Acoustic Tomography

    NASA Astrophysics Data System (ADS)

    Li, Haiyue; Ueki, Takaaki; Yamada, Akira

    2008-05-01

    A technique for monitoring the strong vortex wind field is much required with the rapid increase in global warming. For the realization of the technique, the acoustic tomography of two-dimensional vortex air flow profile was proposed, which can be reconstructed by arraying approximately 10 pairs of transmitters and receivers in parallel. To show the feasibility of the present method, experimental results of performance evaluation using an indoor simulation system are presented. In particular, the reproducibilities of time and space variations of the vortex wind fields passing through the monitoring region were examined. To achieve the real-time capability, a correction scheme for the error caused by the time lag in the sequential sampling was introduced. As a result, vortex wind velocity fields could be reconstructed with a high-speed frame rate while keeping a satisfactory tractability against time and space vortex wind field variations.

  19. A new velocity field for Greece: Implications for the kinematics and dynamics of the Aegean

    NASA Astrophysics Data System (ADS)

    Floyd, M. A.; Billiris, H.; Paradissis, D.; Veis, G.; Avallone, A.; Briole, P.; McClusky, S.; Nocquet, J.-M.; Palamartchouk, K.; Parsons, B.; England, P. C.

    2010-10-01

    A new set of geodetic velocities for Greece and the Aegean, derived from 254 survey-mode and continuous GPS sites, is used to test kinematic and dynamic models for this area of rapid continental deformation. Modeling the kinematics of the Aegean by the rotation of a small number (3-6) of blocks produces RMS misfits of ˜5 mm yr-1 in the southern Aegean and western Peloponnese, indicating significant internal strain within these postulated blocks. It is possible to fit the observed velocities to within 2-3 mm yr-1 (RMS) by models that contain 10 or more blocks, but many such models can be found, with widely varying arrangements of blocks, that fit the data equally well provided that the horizontal dimension of those blocks is not larger than 100-200 km. A continuous field of velocity calculated from the GPS velocities by assuming that strain rates are homogeneous on the scale of ˜120 km fits the observed velocities to better than 2-3 mm yr-1 (RMS), with systematic misfits, representing more localized strain, confined to a region approximately 100 × 100 km in size around the western Gulf of Corinth. This velocity field accounts for the major active tectonic features of Greece and the Aegean, including the widespread north-south extensional deformation and the distributed strike-slip deformation in the NE Aegean and western Greece. The T axes of earthquakes are aligned with the principal axes of elongation in the geodetic field, major active normal fault systems are perpendicular to those axes, and ˜90% of the large earthquakes in this region during the past 120 years took place within the areas in which the geodetic strain rate exceeds 30 nanostrain yr-1. These observations suggest that the faulting within the upper crust of the Aegean region is driven by forces that are coherent over a scale that is significantly greater than 100 km. It is likely that those forces arise primarily from differences in gravitational potential energy within the lithosphere of the

  20. GPS Velocity and Strain Rate Fields in Southwest Anatolia from Repeated GPS Measurements

    PubMed Central

    Erdoğan, Saffet; Şahin, Muhammed; Tiryakioğlu, İbrahim; Gülal, Engin; Telli, Ali Kazım

    2009-01-01

    Southwestern Turkey is a tectonically active area. To determine kinematics and strain distribution in this region, a GPS network of sixteen stations was established. We have used GPS velocity field data for southwest Anatolia from continuous measurements covering the period 2003 to 2006 to estimate current crustal deformation of this tectonically active region. GPS data were processed using GAMIT/GLOBK software and velocity and strain rate fields were estimated in the study area. The measurements showed velocities of 15–30 mm/yr toward the southwest and strain values up to 0.28–8.23×10−8. Results showed that extension has been determined in the Burdur-Isparta region. In this study, all of strain data reveal an extensional neotectonic regime through the northeast edge of the Isparta Angle despite the previously reported compressional neotectonic regime. Meanwhile, results showed some small differences relatively with the 2006 model of Reilinger et al. As a result, active tectonic movements, in agreement with earthquake fault plane solutions showed important activity. PMID:22573998

  1. Effects of light illumination on electron velocity of AlGaN/GaN heterostructures under high electric field

    SciTech Connect

    Guo, Lei; Yang, Xuelin Cheng, Jianpeng; Sang, Ling; Xu, Fujun; Tang, Ning; Feng, Zhihong; Lv, Yuanjie; Wang, Xinqiang; Shen, B.; Ge, Weikun

    2014-12-15

    We have investigated the variation of electron velocity in AlGaN/GaN heterostructures depending on illuminating light intensity and wavelength. It is shown that the electron velocity at high electric field increases under above-band light illumination. This electron velocity enhancement is found to be related to the photo-generated cold holes which interact with hot electrons and thus accelerate the energy relaxation at high electric field. The results suggest an alternative way to improve the electron energy relaxation rate and hence the electron velocity in GaN based heterostructures.

  2. Wide-Field Infrared Survey Explorer Observations of Young Stellar Objects in the Lynds 1509 Dark Cloud in Auriga

    NASA Technical Reports Server (NTRS)

    Liu, Wilson M.; Padgett, Deborah L.; Terebey, Susan; Angione, John; Rebull, Luisa M.; McCollum, Bruce; Fajardo-Acosta, Sergio; Leisawitz, David

    2015-01-01

    The Wide-Field Infrared Survey Explorer (WISE) has uncovered a striking cluster of young stellar object (YSO) candidates associated with the L1509 dark cloud in Auriga. The WISE observations, at 3.4, 4.6, 12, and 22 microns, show a number of objects with colors consistent with YSOs, and their spectral energy distributions suggest the presence of circumstellar dust emission, including numerous Class I, flat spectrum, and Class II objects. In general, the YSOs in L1509 are much more tightly clustered than YSOs in other dark clouds in the Taurus-Auriga star forming region, with Class I and flat spectrum objects confined to the densest aggregates, and Class II objects more sparsely distributed. We estimate a most probable distance of 485-700 pc, and possibly as far as the previously estimated distance of 2 kpc.

  3. Wide-field infrared survey explorer observations of young stellar objects in the Lynds 1509 dark cloud in Auriga

    SciTech Connect

    Liu, Wilson M.; McCollum, Bruce; Fajardo-Acosta, Sergio; Padgett, Deborah L.; Terebey, Susan; Angione, John; Rebull, Luisa M.; Leisawitz, David

    2014-06-01

    The Wide-Field Infrared Survey Explorer (WISE) has uncovered a striking cluster of young stellar object (YSO) candidates associated with the L1509 dark cloud in Auriga. The WISE observations, at 3.4 μm, 4.6 μm, 12 μm, and 22 μm, show a number of objects with colors consistent with YSOs, and their spectral energy distributions suggest the presence of circumstellar dust emission, including numerous Class I, flat spectrum, and Class II objects. In general, the YSOs in L1509 are much more tightly clustered than YSOs in other dark clouds in the Taurus-Auriga star forming region, with Class I and flat spectrum objects confined to the densest aggregates, and Class II objects more sparsely distributed. We estimate a most probable distance of 485-700 pc, and possibly as far as the previously estimated distance of 2 kpc.

  4. Effective filtering and interpolation of 2D discrete velocity fields with Navier-Stokes equations

    NASA Astrophysics Data System (ADS)

    Saumier, Louis-Philippe; Khouider, Boualem; Agueh, Martial

    2016-11-01

    We introduce a new variational technique to interpolate and filter a two-dimensional velocity vector field which is discretely sampled in a region of {{{R}}}2 and sampled only once at a time, on a small time-interval [0,{{Δ }}t]. The main idea is to find a solution of the Navier-Stokes equations that is closest to a prescribed field in the sense that it minimizes the l 2 norm of the difference between this solution and the target field. The minimization is performed on the initial vorticity by expanding it into radial basis functions of Gaussian type, with a fixed size expressed by a parameter ɛ. In addition, a penalty term with parameter k e is added to the minimizing functional in order to select a solution with a small kinetic energy. This additional term makes the minimizing functional strongly convex, and therefore ensures that the minimization problem is well-posed. The interplay between the parameters k e and ɛ effectively contributes to smoothing the discrete velocity field, as demonstrated by the numerical experiments on synthetic and real data.

  5. Magnetic Field Strength in an Intermediate-velocity Ionized Filament in the First Galactic Quadrant

    NASA Astrophysics Data System (ADS)

    Stil, J. M.; Hryhoriw, A.

    2016-08-01

    We investigate the magnetic field in an intermediate-velocity filament for which the Hα intensity in the WHAM survey correlates with excess Faraday rotation of extragalactic radio sources over the length of the filament from b ≈ 20° to b ≈ 55°. The density-weighted mean magnetic field is 2.8 +/- 0.8 μ {{G}}, derived from rotation measures and an empirical relation between Hα emission measure and dispersion measure from Berkhuijsen et al. In view of the uncertainties in the derived magnetic field strength, we propose an alternative use of the available data, rotation measure, and emission measure, to derive a lower limit to the Alfvén speed, weighted by electron density {n}e3/2. We find lower limits to the Alfvén speed that are comparable to or larger than the sound speed in a {10}4 {{K}} plasma, and conclude that the magnetic field is dynamically important. We discuss the role of intermediate-velocity gas as a locus of Faraday rotation in the interstellar medium, and propose that this lower limit to the Alfvén speed may also be applicable to Faraday rotation by galaxy clusters.

  6. AN ALMA SURVEY OF SUBMILLIMETER GALAXIES IN THE EXTENDED CHANDRA DEEP FIELD SOUTH: NEAR-INFRARED MORPHOLOGIES AND STELLAR SIZES

    SciTech Connect

    Chen, Chian-Chou; Smail, Ian; Swinbank, A. M.; Simpson, J. M.; Ma, Cheng-Jiun; Alexander, D. M.; Danielson, A. L. R.; Edge, A. C.; Biggs, A. D.; Ivison, R. J.; Brandt, W. N.; Chapman, S. C.; Coppin, K. E. K.; Dannerbauer, H.; Greve, T. R.; Karim, A.; Menten, Karl M.; Schinnerer, E.; Walter, F.; Wardlow, J. L.; and others

    2015-02-01

    We analyze Hubble Space Telescope WFC3/H {sub 160}-band observations of a sample of 48 Atacama Large Millimeter/submillimeter Array detected submillimeter galaxies (SMGs) in the Extended Chandra Deep Field South field, to study their stellar morphologies and sizes. We detect 79% ± 17% of the SMGs in the H {sub 160}-band imaging with a median sensitivity of 27.8 mag, and most (80%) of the nondetections are SMGs with 870 μm fluxes of S {sub 870} < 3 mJy. With a surface brightness limit of μ {sub H} ∼ 26 mag arcsec{sup –2}, we find that 82% ± 9% of the H {sub 160}-band-detected SMGs at z = 1-3 appear to have disturbed morphologies, meaning they are visually classified as either irregulars or interacting systems, or both. By determining a Sérsic fit to the H {sub 160} surface brightness profiles, we derive a median Sérsic index of n = 1.2 ± 0.3 and a median half-light radius of r{sub e} = 4.4{sub −0.5}{sup +1.1} kpc for our SMGs at z = 1-3. We also find significant displacements between the positions of the H {sub 160} component and 870 μm emission in these systems, suggesting that the dusty starburst regions and less-obscured stellar distribution are not colocated. We find significant differences in the sizes and the Sérsic index between our z = 2-3 SMGs and z ∼ 2 quiescent galaxies, suggesting that a major transformation of the stellar light profile is needed in the quenching processes if SMGs are progenitors of the red-and-dead z ∼ 2 galaxies. Given the short-lived nature of SMGs, we postulate that the majority of the z = 2-3 SMGs with S {sub 870} ≳ 2 mJy are early/mid-stage major mergers.

  7. A redshift survey of IRAS galaxies. III - Reconstruction of the velocity and density fields in N-body model universes

    NASA Technical Reports Server (NTRS)

    Davis, Marc; Strauss, Michael A.; Yahil, Amos

    1991-01-01

    N-body simulations of a 'cold dark matter' universe are presently used to calibrate the accuracy, and assess the limitations, of the procedure previously employed to predict the velocity field within 8000 km/sec of the Local Group through the application of linear gravitational theory to a full-sky, flux-limited sample of IRAS galaxies. The rms difference between the one-dimensional acceleration and velocity of field particles is an increasing function of local density; linear theory can in this way account for all but one-sixth of kinetic energy. A series of artificial IRAS catalogs closely matching the real sample in space density and clustering amplitude is constructed. Velocity correlation functions are used to demonstrate that the predicted velocity fields are in good agreement with the true velocity fields on large scales.

  8. A redshift survey of IRAS galaxies. III - Reconstruction of the velocity and density fields in N-body model universes

    NASA Technical Reports Server (NTRS)

    Davis, Marc; Strauss, Michael A.; Yahil, Amos

    1991-01-01

    N-body simulations of a 'cold dark matter' universe are presently used to calibrate the accuracy, and assess the limitations, of the procedure previously employed to predict the velocity field within 8000 km/sec of the Local Group through the application of linear gravitational theory to a full-sky, flux-limited sample of IRAS galaxies. The rms difference between the one-dimensional acceleration and velocity of field particles is an increasing function of local density; linear theory can in this way account for all but one-sixth of kinetic energy. A series of artificial IRAS catalogs closely matching the real sample in space density and clustering amplitude is constructed. Velocity correlation functions are used to demonstrate that the predicted velocity fields are in good agreement with the true velocity fields on large scales.