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Sample records for stellar velocity field

  1. 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...

  2. 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

  3. 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

  4. 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.

  5. Analysis of the three-dimensional stellar velocity field using vector spherical functions

    NASA Astrophysics Data System (ADS)

    Vityazev, V. V.; Tsvetkov, A. S.

    2009-02-01

    We apply vector spherical functions to problems of stellar kinematics. Using these functions allows all of the systematic components in the stellar velocity field to be revealed without being attached to a specific physical model. Comparison of the theoretical decomposition coefficients of the equations for a particular kinematical model with observational data can provide precise information about whether the model is compatible with the observations and can reveal systematic components that are not described by this model. The formalism of vector spherical functions is particularly well suited for analyzing the present and future (e.g., GAIA) catalogs containing all three velocity vector components: the propermotions in both coordinates and the radial velocity. We show that there are systematic components in the proper motions of Hipparcos stars that cannot be interpreted in terms of the linear Ogorodnikov-Milne model. The same result is also confirmed by an analysis of the radial velocities for these stars.

  6. Disk Galaxy Stellar Velocity Ellipsoids

    NASA Astrophysics Data System (ADS)

    Westfall, Kyle B.; Bershady, M. A.; Verheijen, M. A. W.; Andersen, D. R.; Swaters, R. A.

    2007-12-01

    We have measured the disk stellar velocity ellipsoids in a subset of spiral galaxies observed for the Disk-Mass Survey, which provide information on disk stability and secular heating mechanisms. Our methodology invokes our 2D ionized gas and stellar kinematics and a suite of dynamical assumptions based on the Jeans' equations. When combined with orthogonal axes from our 2D data, either the epicycle approximation (EA) or asymmetric drift (AD) equation may close the necessary equation set, individually. We have isolated large observational and inherent systematic effects via EA-only, AD-only, and EA+AD ellipsoid decomposition methodologies. In an attempt to minimize these effects and generate robust ellipsoid measurements we explore constraints provided by higher order expansions of the Jeans' equations and direct orbital integrations. We compare our best ellipsoid axial ratio estimates to similar measurements made by, e.g., van der Kruit & de Grijs (1999, A&A, 352, 129) and Shapiro et al. (2003, AJ, 126, 2707). Finally, we discuss possibilities for the measurement of vertical velocity dispersions in low-surface-brightness galaxies by applying the characterization of the stellar velocity ellipsoid in late-type galaxies. This work is supported by the National Science Foundation (AST-0607516).

  7. Kinematic alignment of non-interacting CALIFA galaxies. Quantifying the impact of bars on stellar and ionised gas velocity field orientations

    NASA Astrophysics Data System (ADS)

    Barrera-Ballesteros, J. K.; Falcón-Barroso, J.; García-Lorenzo, B.; van de Ven, G.; Aguerri, J. A. L.; Mendez-Abreu, J.; Spekkens, K.; Lyubenova, M.; Sánchez, S. F.; Husemann, B.; Mast, D.; García-Benito, R.; Iglesias-Paramo, J.; Del Olmo, A.; Márquez, I.; Masegosa, J.; Kehrig, C.; Marino, R. A.; Verdes-Montenegro, L.; Ziegler, B.; McIntosh, D. H.; Bland-Hawthorn, J.; Walcher, C. J.; Califa Collaboration

    2014-08-01

    We present 80 stellar and ionised gas velocity maps from the Calar Alto Legacy Integral Field Area (CALIFA) survey in order to characterise the kinematic orientation of non-interacting galaxies. The study of galaxies in isolation is a key step towards understanding how fast-external processes, such as major mergers, affect kinematic properties in galaxies. We derived the global and individual (projected approaching and receding sides) kinematic position angles (PAs) for both the stellar and ionised gas line-of-sight velocity distributions. When compared to the photometric PA, we find that morpho-kinematic differences are smaller than 22 degrees in 90% of the sample for both stellar and nebular components and that internal kinematic misalignments are generally smaller than 16 degrees. We find a tight relation between the global stellar and ionised gas kinematic PA consistent with circular-flow pattern motions in both components (~90% of the sample has differences smaller than 16 degrees). This relation also holds, generally in barred galaxies across the bar and galaxy disc scales. Our findings suggest that even in the presence of strong bars, both the stellar and the gaseous components tend to follow the gravitational potential of the disc. As a result, kinematic orientation can be used to assess the degree of external distortions in interacting galaxies. Appendices are available in electronic form at http://www.aanda.org

  8. Magnetic Fields in Stellar Jets

    NASA Astrophysics Data System (ADS)

    Hartigan, Patrick; Frank, Adam; Varniére, Peggy; Blackman, Eric G.

    2007-06-01

    Although several lines of evidence suggest that jets from young stars are driven magnetically from accretion disks, existing observations of field strengths in the bow shocks of these flows imply that magnetic fields play only a minor role in the dynamics at these locations. To investigate this apparent discrepancy we performed numerical simulations of expanding magnetized jets with stochastically variable input velocities with the AstroBEAR MHD code. Because the magnetic field B is proportional to the density n within compression and rarefaction regions, the magnetic signal speed drops in rarefactions and increases in the compressed areas of velocity-variable flows. In contrast, B~n0.5 for a steady state conical flow with a toroidal field, so the Alfvén speed in that case is constant along the entire jet. The simulations show that the combined effects of shocks, rarefactions, and divergent flow cause magnetic fields to scale with density as an intermediate power 1>p>0.5. Because p>0.5, the Alfvén speed in rarefactions decreases on average as the jet propagates away from the star. Hence, a typical Alfvén velocity in the jet close to the star is significantly larger than it is in the rarefactions ahead of bow shocks at larger distances. We find that the observed values of weak fields at large distances are consistent with strong fields required to drive the observed mass loss close to the star. Typical velocity perturbations, which form shocks at large distances, will produce only magnetic waves close to the star. For a typical stellar jet the crossover point inside which velocity perturbations of 30-40 km s-1 no longer produce shocks is ~300 AU from the source.

  9. Radial Velocity Planet Detection Biases at the Stellar Rotational Period

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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 radial velocity 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 timescale and amplitude of stellar radial velocity noise as a function of stellar mass. We show that the characteristic timescales of quasi-periodic radial velocity 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. High Precision Measurement of Stellar Radial Velocity Variations

    NASA Technical Reports Server (NTRS)

    Cochran, W. D.

    1984-01-01

    A prototype instrument for measurement of stellar radial velocity variations to a precision of a few meters per second is discussed. The instrument will be used to study low amplitude stellar non-radial oscillations, to search for binary systems with large mass ratios, and ultimately to search for extrasolar planetary systems. The instrument uses a stable Fabry-Perot etalon, in reflection, to impose a set of fixed reference absorption lines on the stellar spectrum before it enters the coude spectrograph of the McDonald Observatory 2.7-m telescope. The spectrum is recorded on the Octicon detector, which consists of eight Reticon arrays placed end to end. Radial velocity variations of the star are detected by measuring the shift of the stellar lines with respect the artificial Fabry-Perot lines, and correcting for the known motions in the solar system.

  11. Principal velocity surfaces in stellar dynamics

    NASA Astrophysics Data System (ADS)

    Lynden-Bell, D.

    2016-05-01

    Recent work by An and Evans has revived interest in the coordinate surfaces that lie along the principal axes of the stress tensor. Here we complete our list of non-axially symmetric systems with local integrals and prove that those principal velocity surfaces exist for all systems with three local integrals. We then demonstrate how systems in non-separable potentials evade the Eddington-An theorem by having distribution functions that lack perfect reflection symmetry in a meridional velocity component, and discuss other consequences of this remarkable theorem.

  12. 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.

  13. Stellar Rotation and Precise Radial Velocities

    NASA Astrophysics Data System (ADS)

    Gray, D. F.

    Two aspects will be considered. First, I will view the spectroscopic measurement of rotation rates as a differential precision radial velocity: how do we get rotation rates; what are the uncertainties stemming from differential rotation, time variable profiles caused by spots, uncertain limb darkening, and the presence of macroturbulence? What do we even mean by the rotation rate when there is differential rotation? Second, I will discuss the effects of rotation on specifying the precise position of spectral lines, i.e., the classical radial velocity of a star. I will present some thoughts on the effects of having our sharp markers of the Doppler effect degraded by rotation, the meaning of line position when the Doppler effects of rotation and convection interact, and the altered shapes of composite spectrum features with increased rotational smearing.

  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. Starspot-Induced Radial Velocity Jitter During a Stellar Cycle

    NASA Astrophysics Data System (ADS)

    Korhonen, Heidi; Andersen, Jan Marie; Järvinen, Silva

    2014-04-01

    Late-type stars exhibit cool regions on their surface, the stellar equivalent of sunspots. These dark starspots can also mimic the radial velocity variations caused by orbiting planets, making it at times difficult to distinguish between planets and activity signatures. The amount of spots on the Sun and other cool stars changes cyclically during an activity cycle, which has length varying from about a year to longer than the solar 11 years. In this work we investigate the influence of varying amount of starspots on the sparsely sampled radial velocity observations - which are the norm in the radial velocity studies searching for exoplanets on wide orbits. We study two simulated cases: one with a random spot configuration, and one where the spot occurrence is concentrated. In addition we use Doppler images of young solar analogue V889 Her as a high activity case.

  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. Surface velocity fields from tidal interactions

    NASA Astrophysics Data System (ADS)

    Koenigsberger, Gloria; Moreno, Edmundo; Harrington, David

    2009-09-01

    Binary stars in eccentric orbits are the clearest example of stars whose equatorial rotation velocity is not synchronized with orbital motion. Under these conditions, the surface velocity field is perturbed from its purely rotational nature, thus modifying the shape of the observationally-detectable photospheric absorption lines on a variety of timescales. Absorption lines are used to derive basic stellar parameters and gain a better physical understanding of the star. Although their variability is often interpreted in terms of non-radial pulsation theory, it is important to understand the nature of the surface velocity fields that are induced by the tidal interactions alone, especially under conditions of rapid rotation and large orbital eccentricity, where the perturbations become highly non-linear. We use a time-marching numerical calculation from first principles to model the surface velocity field due to the tidal interaction (Moreno & Koenigsberger 1999; Toledano et al. 2007). This velocity field is then projected along the line-of-sight to the observer to predict the orbital phase-dependent line-profile variability (Moreno et al. 2005). We compare our model results with very high quality observational data of the B-type binary system α Vir (Spica, HD 116658, P = 4d, e = 0.1), whose variability has in the past been modeled in the context of non-radial pulsations (Smith 1985). Our model reproduces the general features of the observations (Harrington et al. 2009). It is interesting to note that because tidal flows are associated with viscous shear energy dissipation, the question arises as to whether the atmospheric structure of an asynchronously rotating binary star may be reliably modeled using techniques that disregard the dynamical effects on the stellar surface of the tidal interactions.

  19. The evolving velocity field around protostars

    NASA Astrophysics Data System (ADS)

    Brinch, Christian

    2008-10-01

    Using a hydrodynamical simulation of a gravitational collapse and subsequent disk formation, we calculate a time-resolved synthetic data set with a sophisticated molecular excitation and radiation transfer code. These synthetic data consist of a number of molecular gas emission lines that contains information about the density, temperature, and the velocity field. We use this simulated data set to asses how accurately we can extract information about the underlying velocity field from the lines with a simple parameterized velocity model. This model has only two free parameters, the central stellar mass and a geometric angle that describes the ratio of infall to rotation. We find that, by modeling the spectral lines, we can reliably and uniquely describe the underlying velocity field as given by the hydrodynamical simulation and we then assume that by applying the same parameterized model to real data, we can equally well determine the velocity field of observed young stellar objects. We observe two young sources, L1489 IRS in the Taurus star forming region and IRAS2A in NGC-1333. Both sources are observed with single dish telescopes (JCMT, OSO) and with the Submilimeter Array. For L1489~IRS, the interferometric observations reveal a kinematically distinct region on a scale of a few hundred AUs, dominated by rotation, which is still surrounded by some envelope material. Contrary to this, IRAS2A shows no sign of rotation despite the fact that a compact (disk) component is needed in order to interpret the continuum measurements. We do not detect this component in the velocity field and we conclude that IRAS2A is a considerably younger source than L1489 IRS. While this result is based on the gas flow alone, it is entirely consistent with the current classification of IRAS2A as a Class 0 object and L1489~IRS as a Class I object. This thesis also contains a treatment of CO depletion in the disk and envelope. Under certain temperature and density conditions, CO may freeze

  20. Measurement of surface velocity fields

    NASA Technical Reports Server (NTRS)

    Mann, J. A., Jr.

    1979-01-01

    A new technique for measuring surface velocity fields is briefly described. It determines the surface velocity vector as a function of location and time by the analysis of thermal fluctuations of the surface profile in a small domain around the point of interest. The apparatus now being constructed will be used in a series of experiments involving flow fields established by temperature gradients imposed along a surface.

  1. Stellar velocity dispersions to z=2 and tests of stellar population models

    NASA Astrophysics Data System (ADS)

    Franx, Marijn

    2015-08-01

    We have measured stellar velocity dispersions of non-starforming galaxies to a redshift of 2, and we augment our sample with values from literature. We find that the galaxies lie on a well-defined mass Fundamental Plane. We establish a simple relation between restframe colors and mass-to-light ratio, and we show that the M/L can be estimated to 0.25 dex from a single restframe color. In addition, we compare the relation between color with predictions from stellar population models. The galaxies span a wide range in restframe colors, and produce a stringest test of the models. Whereas this test is a classic test of the shape of the IMF, we find thatpopulation models from different authors show substantial differences, comparable to the variations between the predictions due to a different IMF. No single model reproduces the mass-to-light variations in the visual and near-infrared satisfactorily, and a broken IMF models produces the best results. Either the stellar populations are complex, or the models need modification.

  2. Estimating Stellar Radial Velocity Variability from Kepler and GALEX: Implications for the Radial Velocity Confirmation of Exoplanets

    NASA Astrophysics Data System (ADS)

    Cegla, H. M.; Stassun, K. G.; Watson, C. A.; 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' HK . The R' 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-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.

  3. 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.

  4. The Stellar Kinematic Fields of NGC 3379

    NASA Astrophysics Data System (ADS)

    Statler, Thomas S.; Smecker-Hane, Tammy

    1999-02-01

    We have measured the stellar kinematic profiles of NGC 3379 along four position angles, using absorption lines in spectra obtained with the Multiple Mirror Telescope. We derive a far more detailed description of the kinematic fields through the main body of the galaxy than could be obtained from previous work. Our data extend 90" from the center, at essentially seeing-limited resolution out to 17". The derived mean velocities and dispersions have total errors (internal and systematic) better than +/-10 km s^-1, and frequently better than 5 km s^-1, out to 55". We find very weak (3 km s^-1) rotation on the minor axis interior to 12" and no detectable rotation above 6 km s^-1 from 12" to 50" or above 16 km s^-1 out to 90" (95% confidence limits). However, a Fourier reconstruction of the mean velocity field from all four sampled PAs does indicate a ~5 deg twist of the kinematic major axis, in the direction opposite to the known isophotal twist. The h_3 and h_4 parameters are found to be generally small over the entire observed region. The azimuthally averaged dispersion profile joins smoothly at large radii with the velocity dispersions of planetary nebulae. Unexpectedly, we find sharp bends in the major axis rotation curve, also visible (though less pronounced) on the diagonal position angles. The outermost bend closely coincides in position with other sharp kinematic features: an abrupt flattening of the dispersion profile, and local peaks in h_3 and h_4. All of these features are in a photometrically interesting region in which the surface brightness profile departs significantly from an r^1/4 law. Features such as these are not generally known in elliptical galaxies owing to a lack of data at comparable resolution. Very similar behavior, however, is seen the kinematics of the edge-on S0 galaxy NGC 3115. We discuss the suggestion that NGC 3379 could be a misclassified S0 galaxy; preliminary results from dynamical modeling indicate that it may be a flattened, weakly

  5. 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

  6. 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.

  7. STELLAR MASS VERSUS STELLAR VELOCITY DISPERSION: WHICH IS BETTER FOR LINKING GALAXIES TO THEIR DARK MATTER HALOS?

    SciTech Connect

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

    2013-01-01

    It was recently suggested that compared to its stellar mass (M{sub *}), the central stellar velocity dispersion ({sigma}{sub *}) 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{sub *} and {sigma}{sub *}. For this we have estimated the redshift-space cross-correlation function (CCF) between the central galaxies at given M{sub *} and {sigma}{sub *} and a reference galaxy sample, from which we determine both the projected CCF, w{sub p} (r{sub p} ), and the velocity dispersion profile. A halo mass is then obtained from the average velocity dispersion within the virial radius. At fixed M{sub *}, we find very weak or no correlation between halo mass and {sigma}{sub *}. In contrast, strong mass dependence is clearly seen even when {sigma}{sub *} 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 {sigma}{sub *} at fixed M{sub *}, 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.

  8. 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

  9. 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.

  10. Source of the Stellar Age-Velocity Dispersion Relation in Simulated Galaxies

    NASA Astrophysics Data System (ADS)

    Wills, Drew; Christensen, Charlotte

    2016-01-01

    We investigated the source of the stellar age-velocity dispersion relation using six high-resolution simulated galaxies. Observations show that velocity dispersion increases with stellar age. This trend is thought to be due to a combination of the evolution of the velocity dispersion of the interstellar media (ISM), interactions within the disk, and galactic mergers. Our simulated galaxies show redshift zero age-velocity dispersion relations consistent with those of observed galaxies. In order to determine how the velocity dispersion of stars evolves after their formation, we calculated the velocity dispersion versus the age of the stars at both redshift zero and at their time of formation. We found that while the ISM velocity dispersion evolves, it cannot be the sole source of the relation. Additionally, dwarf galaxies display a greater relative change in their velocity dispersion than more massive galaxies. Furthermore, we show that major mergers markedly increase the velocity dispersion of stars.

  11. Using mean polarization profiles to study stellar magnetic fields

    NASA Astrophysics Data System (ADS)

    Shorlin, Stephen L. S.

    2004-12-01

    Approximately 10-20% of moderate mass main sequence stars show marked chemical peculiarities. Characteristic chemical over- and underabundance patterns are well correlated with several physical attributes; most notably the existence or non-existence of large-scale ordered magnetic fields. The details of the origins of both the fields and abundance patterns are topics of continuing study, as are detailed descriptions of field structures in magnetic stars and the possible existence of magnetic fields in the canonically "non-magnetic" stars. We expect that mean spectral line profiles, calculated from entire stellar spectra in polarized and unpolarized light, will be useful in studying these topics. Circular spectropolarimetric observations of 74 survey stars were obtained using the MuSiCoS spectropolarimeter in an attempt to detect magnetic fields. The sample observed includes normal B, A and F stars, emission-line B and A stars, Am stars, HgMn stars, l Boo stars and magnetic Ap stars. Using the multi-line analysis technique known as "Least-Squares Deconvolution" (LSD) to extract mean unpolarized (Stokes I ) and circularly polarized (Stokes V ) signatures from each spectrum, we find absolutely no evidence for magnetic fields in the normal, Am and HgMn stars, with considerably smaller upper limits on longitudinal field measurements than previously obtained for these objects. We conclude that if any magnetic fields exist in the photospheres of these stars, these fields are not ordered as in the magnetic Ap stars, nor do they resemble the fields of active late-type stars. We also detect for the first time a field in the A2pSr star HD 108945 and make new precise measurements of longitudinal fields in five previously known magnetic Ap stars, but do not detect fields in five other stars classified as Ap SrCrEu. Also presented is the first ever exploratory investigation into both the applicability of the LSD technique in analyzing stellar spectra, as well as an examination

  12. 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.

  13. Probabilistic Catalogs for Crowded Stellar Fields

    NASA Astrophysics Data System (ADS)

    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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Interval velocity analysis using wave field continuation

    SciTech Connect

    Zhusheng, Z. )

    1992-01-01

    In this paper, the author proposes a new interval velocity inversion method which, based on wave field continuation theory and fuzzy decision theory, uses CMP seismic gathers to automatically estimate interval velocity and two-way travel time in layered medium. The interval velocity calculated directly from wave field continuation is not well consistent with that derived from VSP data, the former is usually higher than the latter. Three major factors which influence the accuracy of interval velocity from wave field continuation are corrected, so that the two kinds of interval velocity are well consistent. This method brings better interval velocity, adapts weak reflection waves and resists noise well. It is a feasible method.

  20. Binary stellar winds. [flow and magnetic field interactions

    NASA Technical Reports Server (NTRS)

    Siscoe, G. L.; Heinemann, M. A.

    1974-01-01

    Stellar winds from a binary star will interact with each other along a contact discontinuity. We discuss qualitatively the geometry of the flow and field resulting from this interaction in the simplest case where the stars and winds are identical. We consider the shape of the critical surface (defined as the surface where the flow speed is equal to the sound speed) as a function of stellar separation and the role of shock waves in the flow field. The effect of stellar spin and magnetic sectors on the field configuration is given. The relative roles of mass loss and magnetic torque in the evolution of orbital parameters are discussed.

  1. Binary stellar winds. [flow and magnetic field geometry

    NASA Technical Reports Server (NTRS)

    Siscoe, G. L.; Heinemann, M. A.

    1974-01-01

    Stellar winds from a binary star pair will interact with each other along a contact discontinuity. We discuss qualitatively the geometry of the flow and field resulting from this interaction in the simplest case where the stars and winds are identical. We consider the shape of the critical surface (defined as the surface where the flow speed is equal to the sound speed) as a function of stellar separation and the role of shock waves in the flow field. The effect of stellar spin and magnetic sectors on the field configuration is given. The relative roles of mass loss and magnetic torque in the evolution of orbital parameters is discussed.

  2. 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.

  3. 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

  4. Velocity fields in a collectively migrating epithelium.

    PubMed

    Petitjean, L; Reffay, M; Grasland-Mongrain, E; Poujade, M; Ladoux, B; Buguin, A; Silberzan, P

    2010-05-19

    We report quantitative measurements of the velocity field of collectively migrating cells in a motile epithelium. The migration is triggered by presenting free surface to an initially confluent monolayer by using a microstencil technique that does not damage the cells. To avoid the technical difficulties inherent in the tracking of single cells, the field is mapped using the technique of particle image velocimetry. The main relevant parameters, such as the velocity module, the order parameter, and the velocity correlation function, are then extracted from this cartography. These quantities are dynamically measured on two types of cells (collectively migrating Madin-Darby canine kidney (MDCK) cells and fibroblastlike normal rat kidney (NRK) cells), first as they approach confluence, and then when the geometrical constraints are released. In particular, for MDCK cells filling up the patterns, we observe a sharp decrease in the average velocity after the point of confluence, whereas the densification of the monolayer is much more regular. After the peeling off of the stencil, a velocity correlation length of approximately 200 microm is measured for MDCK cells versus only approximately 40 microm for the more independent NRK cells. Our conclusions are supported by parallel single-cell tracking experiments. By using the biorthogonal decomposition of the velocity field, we conclude that the velocity field of MDCK cells is very coherent in contrast with the NRK cells. The displacements in the fingers arising from the border of MDCK epithelia are very oriented along their main direction. They influence the velocity field in the epithelium over a distance of approximately 200 microm. PMID:20441742

  5. 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.

  6. Slipher, Galaxies, and Cosmological Velocity Fields

    NASA Astrophysics Data System (ADS)

    Peacock, J. A.

    2013-04-01

    By 1917, V. M. Slipher had singlehandedly established a general tendency for ‘spiral nebulae’ to be redshifted (21 out of 25 cases). From a modern perspective, it could seem surprising that the discovery of the expansion of the universe was not announced at this point. Examination of the data and arguments contained in Slipher's papers shows that he reached a more subtle conclusion: the identification of cosmological peculiar velocities, including the bulk motion of the Milky Way, leading to a beautiful argument in favor of spiral nebulae as distant stellar systems. Nevertheless, Slipher's data actually contain evidence at >8σ for a positive mean velocity, even after subtracting the best-fitting dipole pattern owing to motion of the observer. In 1929, Hubble provided distance estimates for a sample of no greater depth, using redshifts due almost entirely to Slipher. Hubble's distances turned out to be flawed in two distinct ways: in addition to an incorrect absolute calibration, the largest distances were systematically under-estimated. Nevertheless, he claimed the detection of a linear distance-redshift relation. Statistically, the evidence for such a correlation is less strong than the simple evidence for a positive mean velocity in Hubble's sample. Comparison with modern data shows that a sample of more than twice Hubble's depth would generally be required in order to reveal clearly the global linear expansion in the face of the ‘noise’ from peculiar velocities. When the theoretical context of the time is examined, the role of the de Sitter model and its prediction of a linear distance-redshift relation looms large. A number of searches for this relation were performed prior to Hubble over the period 1924-1928, with a similar degree of success. All were based on the velocities measured by Slipher, whose work from a Century ago stands out both for the precision of his measurements and for the subtle clarity of the arguments he employed to draw correct

  7. On Stellar Wind Bow Shocks with External Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Wilkin, Francis P.

    2016-06-01

    Stellar wind bow shocks have been seen driven by stars of many types, from O to AGB stars as well as pulsars. Recent simulations (e.g. van Marle et al. 2014) have considered the bubble created by a stellar wind of a stationary star in a region of constant magnetic field. By applying a thin-shell formalism, I consider the problem of a stellar wind from a star moving supersonically with respect to a magnetized medium. The properties of the resulting shell are derived, and limitations to the application of the resulting solution are discussed.

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

    PubMed

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

    2009-08-01

    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. PMID:19661911

  9. Rotation and Magnetic Fields: the Evil Twins of Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Charbonneau, P.

    In this paper I give an overview of the numerous ways in which rotation and magnetic fields can interact under stellar interior conditions. I first provide “tutorial” examples of how magnetic fields can (1) alter existing stellar internal flows, (2) generate internal flows, and of how rotation can (3) amplify or (4) destroy magnetic fields. The upshot of all this is that treating rotation or magnetic fields in isolation of one another, as intermediate steps towards the “full picture”, may yield a situation that can only be applied meaningfully under very limited and specific astrophysical circumstances, if any.

  10. 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.

  11. 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.

  12. 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.

  13. The Gaia-ESO Survey: Empirical determination of the precision of stellar radial velocities and projected rotation velocities

    NASA Astrophysics Data System (ADS)

    Jackson, R. J.; Jeffries, R. D.; Lewis, J.; Koposov, S. E.; Sacco, G. G.; Randich, S.; Gilmore, G.; Asplund, M.; Binney, J.; Bonifacio, P.; Drew, J. E.; Feltzing, S.; Ferguson, A. M. N.; Micela, G.; Neguerela, I.; Prusti, T.; Rix, H.-W.; Vallenari, A.; Alfaro, E. J.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme, R.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.; Irwin, M.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.; Walton, N.; Bayo, A.; Bergemann, M.; Carraro, G.; Costado, M. T.; Damiani, F.; Edvardsson, B.; Franciosini, E.; Frasca, A.; Heiter, U.; Hill, V.; Hourihane, A.; Jofré, P.; Lardo, C.; de Laverny, P.; Lind, K.; Magrini, L.; Marconi, G.; Martayan, C.; Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

    2015-08-01

    Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope. Aims: A key aim is to provide precise radial velocities (RVs) and projected equatorial velocities (vsini) for representative samples of Galactic stars, which will complement information obtained by the Gaia astrometry satellite. Methods: We present an analysis to empirically quantify the size and distribution of uncertainties in RV and vsini using spectra from repeated exposures of the same stars. Results: We show that the uncertainties vary as simple scaling functions of signal-to-noise ratio (S/N) and vsini, that the uncertainties become larger with increasing photospheric temperature, but that the dependence on stellar gravity, metallicity and age is weak. The underlying uncertainty distributions have extended tails that are better represented by Student's t-distributions than by normal distributions. Conclusions: Parametrised results are provided, which enable estimates of the RV precision for almost all GES measurements, and estimates of the vsini precision for stars in young clusters, as a function of S/N, vsini and stellar temperature. The precision of individual high S/N GES RV measurements is 0.22-0.26 km s-1, dependent on instrumental configuration. Based on observations collected with the FLAMES spectrograph at VLT/UT2 telescope (Paranal Observatory, ESO, Chile), for the Gaia- ESO Large Public Survey (188.B-3002).Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/580/A75

  14. 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.

  15. 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.

  16. 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.

  17. Toward Understanding Stellar Radial Velocity Jitter as a Function of Wavelength: The Sun as a Proxy

    NASA Astrophysics Data System (ADS)

    Marchwinski, Robert C.; Mahadevan, Suvrath; Robertson, Paul; Ramsey, Lawrence; Harder, Jerald

    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.

  18. Disentangling planetary orbits from stellar activity in radial-velocity surveys

    NASA Astrophysics Data System (ADS)

    Haywood, R. D.; Cameron, A. Collier; Queloz, D.; Barros, S. C. C.; Deleuil, M.; Fares, R.; Gillon, M.; Hatzes, A.; Lanza, A. F.; Lovis, C.; Moutou, C.; Pepe, F.; Pollacco, D.; Santerne, A.; Ségransan, D.; Unruh, Y.

    2014-04-01

    The majority of extra-solar planets have been discovered (or confirmed after follow-up) through radial-velocity (RV) surveys. Using ground-based spectrographs such as High Accuracy Radial Velocity Planetary Search (HARPS) and HARPS-North, it is now possible to detect planets that are only a few times the mass of the Earth. However, the presence of dark spots on the stellar surface produces RV signals that are very similar in amplitude to those caused by orbiting low-mass planets. Disentangling these signals has thus become the biggest challenge in the detection of Earth-mass planets using RV surveys. To do so, we use the star's lightcurve to model the RV variations produced by spots. Here we present this method and show the results of its application to CoRoT-7.

  19. 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.

  20. An updated GPS velocity field for Canada

    NASA Astrophysics Data System (ADS)

    Craymer, M. R.; Henton, J. A.; Piraszewski, M.; Lapelle, E.

    2011-12-01

    In an effort to improve previous continental-scale GPS velocity fields for North America and Canada in particular, we have reprocessed data from nearly all continuous GPS sites in Canada, the northern portions of the US including Alaska, Greenland as well as a set of global sites used to define the reference frame. In addition, repeated high accuracy campaign surveys of the Canadian Base Network were included. Previous velocity fields were derived from coordinate time series of somewhat inhomogeneous GPS results due to: (1) the use of relative antenna calibrations that did not include satellite antennas or account for the presence of antenna radomes, (2) the use of different reference frames, (3) the use of IGS precise orbits based on these calibrations and reference frames, and (4) the use of different (evolving) versions of GPS processing software and procedures. This reprocessing effort of all previous data since 2000 is based on more consistent and accurate absolute antenna calibrations of both station and satellite antennas, the ITRF2005 reference frame and the latest versions of the Bernese GPS Software and IGS processing procedures with their so-called "repro1" reprocessed orbits. Also, more than four additional years of continuous data and a new CBN survey campaign have been included in this velocity field estimation. Furthermore, we have processed all the continuous data with NRCan's Precise Point Positioning (PPP) software using the same IGS repro1 orbits, precise clocks and absolute antenna calibrations together with the Vienna Mapping Function (VMF1) for the tropospheric model. The PPP software has proven to be highly efficient for processing such large networks and the additional solutions have provided much needed redundancy for some regions. The new time series and velocity results from both the Bernese and PPP solutions are compared with each other and with our previous solution. Comparisons are also made with solutions from other GPS analysis

  1. A Gaussian process framework for modelling stellar activity signals in radial velocity data

    NASA Astrophysics Data System (ADS)

    Rajpaul, V.; Aigrain, S.; Osborne, M. A.; Reece, S.; Roberts, S.

    2015-09-01

    To date, the radial velocity (RV) method has been one of the most productive techniques for detecting and confirming extrasolar planetary candidates. Unfortunately, stellar activity can induce RV variations which can drown out or even mimic planetary signals - and it is notoriously difficult to model and thus mitigate the effects of these activity-induced nuisance signals. This is expected to be a major obstacle to using next-generation spectrographs to detect lower mass planets, planets with longer periods, and planets around more active stars. Enter Gaussian processes (GPs) which, we note, have a number of attractive features that make them very well suited to disentangling stellar activity signals from planetary signals. We present here a GP framework we developed to model RV time series jointly with ancillary activity indicators (e.g. bisector velocity spans, line widths, chromospheric activity indices), allowing the activity component of RV time series to be constrained and disentangled from e.g. planetary components. We discuss the mathematical details of our GP framework, and present results illustrating its encouraging performance on both synthetic and real RV data sets, including the publicly available Alpha Centauri B data set.

  2. THE VELOCITY FIELD AROUND GROUPS OF GALAXIES

    SciTech Connect

    Hartwick, F. D. A.

    2011-06-15

    A statistical method is presented for determining the velocity field in the immediate vicinity of groups of galaxies using only positional and redshift information with the goal of studying the perturbation of the Hubble flow around groups more distant than the Local Group. The velocities are assumed to obey a Hubble-like expansion law, i.e., V = H{sub exp} R, where the expansion rate H{sub exp} is to be determined. The method is applied to a large, representative group catalog and evidence is found for a sub-Hubble expansion rate within two well-defined radii beyond the virial radii of the groups. This result is consistent with that of Teerikorpi et al. who found a similar expansion law around three nearby groups and extends it to a more representative volume of space.

  3. 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

  4. WIYN OPEN CLUSTER STUDY. XXXVIII. STELLAR RADIAL VELOCITIES IN THE YOUNG OPEN CLUSTER M35 (NGC 2168)

    SciTech Connect

    Geller, Aaron M.; Mathieu, Robert D.; Braden, Ella K.; Meibom, Soeren; Dolan, Christopher J.; Platais, Imants E-mail: mathieu@astro.wisc.edu E-mail: smeibom@cfa.harvard.edu E-mail: imants@pha.jhu.edu

    2010-04-15

    We present 5201 radial-velocity (RV) measurements of 1144 stars as part of an ongoing study of the young (150 Myr) open cluster M35 (NGC 2168). We have observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN 3.5 m telescope. Our stellar sample covers main-sequence stars over a magnitude range of 13.0 {<=} V {<=} 16.5 (1.6-0.8 M {sub sun}) and extends spatially to a radius of 30 arcmin (7 pc in projection at a distance of 805 pc or {approx}4 core radii). Due to its youth, M35 provides a sample of late-type stars with a range of rotation periods. Therefore, we analyze the RV measurement precision as a function of the projected rotational velocity. For narrow-lined stars (vsin i{<=} 10 km s{sup -1}), the RVs have a precision of 0.5 km s{sup -1}, which degrades to 1.0 km s{sup -1} for stars with vsin i = 50 km s{sup -1}. The RV distribution shows a well-defined cluster peak with a central velocity of -8.16 {+-} 0.05 km s{sup -1}, permitting a clean separation of the cluster and field stars. For stars with {>=}3 measurements, we derive RV membership probabilities and identify RV variables, finding 360 cluster members, 55 of which show significant RV variability. Using these cluster members, we construct a color-magnitude diagram for our stellar sample cleaned of field star contamination. We also compare the spatial distribution of the single and binary cluster members, finding no evidence for mass segregation in our stellar sample. Accounting for measurement precision, we place an upper limit on the RV dispersion of the cluster of 0.81 {+-} 0.08 km s{sup -1}. After correction for undetected binaries, we derive a true RV dispersion of 0.65 {+-} 0.10 km s{sup -1}.

  5. Velocity field of isolated turbulent puffs

    NASA Astrophysics Data System (ADS)

    Ghaem-Maghami, E.; Johari, H.

    2010-11-01

    The velocity field of isolated turbulent puffs was measured using the particle image velocimetry technique and was compared with the steady jet flow field. Puffs were generated by injecting air through a 5 mm diameter nozzle into a flow chamber with a weak coflow. Isolated puffs with a Reynolds number of 5000 were examined in the range of 40-75 diameters downstream of the nozzle. The injection time was varied in order to assess the effects of injection volume and equivalent stroke ratio on the puff structure. The results from phase-locked measurements indicate that as the injection volume increased, puffs elongated in the axial direction and became similar to starting jets in the range considered. The largest scaled fluctuating velocities and turbulent shear stress within the puffs were twice the steady jet values. Inspection of the vorticity field revealed the presence of vorticity throughout the puff volume. Entrainment takes place on the portion of the puff closest to the nozzle and the entrainment rate is greater for the puffs with the smaller injection volume. This is consistent with the observations of rapid mixing and combustion of puffs in previous studies.

  6. [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. PMID:24822441

  7. Stellar magnetic fields: From the photosphere into the corona

    NASA Astrophysics Data System (ADS)

    Liefke, Carolin

    2007-10-01

    Simultaneous X-ray and optical observations of the active M dwarf CN Leo have shown variability in its magnetic flux (as measured through magnetically sensitive lines in the molecular FeH band) on different timescales: within a few days, within one night, and possibly even related to a flare event. We propose to extend these studies to a larger sample of stars and observe the two flare stars Proxima Cen and YZ CMi simultaneously with XMM-Newton and VLT/UVES in order to characterize the amplitudes and time scales of variations in their photospheric magnetic fields together with the behavior of chromospheric emission lines and coronal X-ray emission. This will enable us to trace activity-related changes in the stellar magnetic field through all layers of the stellar atmosphere.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. Velocity Field of Isolated Turbulent Puffs

    NASA Astrophysics Data System (ADS)

    Ghaem-Maghami, Elham; Johari, Hamid

    2006-11-01

    The velocity field of isolated turbulent puffs was investigated by the PIV technique. Particular attention was paid to the entrainment pattern of isolated puffs. Puffs were generated by injecting seeded air through a 5 mm diameter nozzle into a flow chamber with a weak co-flow. Puffs with a Reynolds number of 5,000 were examined in the range of 35 -- 75 diameters downstream of the nozzle. The injection time was varied in order to assess the effect of injection volume and impulse on the puff structure. The results indicate that as the injection volume increased, puffs elongated in the axial direction. The largest mean and fluctuating velocities were within the central portion of the puff. The maximum turbulent shear stress within the puff was as much as 2.5 times the steady jet value. The vorticity field showed the presence of vorticity throughout the puff volume. The ratio of volume flow rate at the puff center to the steady jet volume flux at the same location was largest for the smallest injection volume. The majority of entrainment into the puff occurs below the puff center while the puff cap pushes out into surrounding fluid.

  13. The velocity field in MOND cosmology

    NASA Astrophysics Data System (ADS)

    Candlish, G. N.

    2016-08-01

    The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAYMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAYMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to Λcold dark matter, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard ΛCDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAYMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field is likely an unavoidable consequence of the gravitational modification implemented in MOND, and may represent a clear observational signature of such a modification. It is further suggested that such a signal may be clearest in intermediate-density regions such as cluster outskirts and filaments.

  14. The velocity field in MOND cosmology

    NASA Astrophysics Data System (ADS)

    Candlish, G. N.

    2016-08-01

    The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAyMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAyMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to $\\Lambda$CDM, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard $\\Lambda$CDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAyMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field is likely an unavoidable consequence of the gravitational modification implemented in MOND, and may represent a clear observational signature of such a modification. It is further suggested that such a signal may be clearest in intermediate density regions such as cluster outskirts and filaments.

  15. Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Cantiello, Matteo; Fuller, Jim; Bildsten, Lars

    2016-06-01

    Recent asteroseismic analyses indicate the presence of strong (B ≳ 105 G) magnetic fields in the cores of many red giant stars. Here, we examine the implications of these results for the evolution of stellar magnetic fields, and we make predictions for future observations. Those stars with suppressed dipole modes indicative of strong core fields should exhibit moderate but detectable quadrupole mode suppression. The long magnetic diffusion times within stellar cores ensure that dynamo-generated fields are confined to mass coordinates within the main-sequence (MS) convective core, and the observed sharp increase in dipole mode suppression rates above 1.5 M ⊙ is likely explained by the larger convective core masses and faster rotation of these more massive stars. In clump stars, core fields of ∼105 G can suppress dipole modes, whose visibility should be equal to or less than the visibility of suppressed modes in ascending red giants. High dipole mode suppression rates in low-mass (M ≲ 2 M ⊙) clump stars would indicate that magnetic fields generated during the MS can withstand subsequent convective phases and survive into the compact remnant phase. Finally, we discuss implications for observed magnetic fields in white dwarfs and neutron stars, as well as the effects of magnetic fields in various types of pulsating stars.

  16. 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.

  17. Stellar

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each 'fingertip' is somewhat larger than our own solar system. The pillar is slowly eroding away by the ultraviolet light from nearby hot stars, a process called 'photoevaporation.' As it does, small globules of especially dense gas buried within the cloud is uncovered. These globules have been dubbed 'EGGs' -- an acronym for 'Evaporating Gaseous Globules.' The shadows of the EGGs protect gas behind them, resulting in the finger-like structures at the top of the cloud. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually the stars emerge, as the EGGs themselves succumb to photoevaporation. The stellar EGGS are found, appropriately enough, in the 'Eagle Nebula' (also called M16 -- the 16th object in Charles Messier's 18th century catalog of 'fuzzy' permanent objects in the sky), a nearby star-forming region 7,000 light-years away in the constellation Serpens. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly-ionized oxygen atoms.

  18. 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

  19. Impact of magnetic field on radial velocity measurements.

    NASA Astrophysics Data System (ADS)

    Hébrard, E. M.; Delfosse, X.; Morin, J.; Boisse, I.; Moutou, C.; Hébrard, G.

    2014-12-01

    Very low-mass stars are very promising targets for planet-search programs, in particular to discover super-Earths / Earths located in their habitable zone. Their detection is in principle accessible to the existing velocimeters of highest radial-velocity (RV) precision, but challenging due to activity ( i.e., dark spots and magnetic regions at their surfaces) which generate a noise level in RV curves (RV jitter). It can severely limit our practical ability at detecting Earth-like planets. To overcome this intrinsic limitation, a promising option consists in modeling directly the stellar activity behind the activity jitter, and in particular the magnetic field that gives rise to it. To do this, simultaneous observations in velocimetry (for activity jitter) and in spectropolarimetry (for the Zeeman signatures in spectral lines tracing the presence of a large-scale field) are needed. We present here our first results both on the simulations on the impact of magnetic fields on line profiles (bisectors & RV data), and on the simultaneous observations done thanks to HARPSPol@LaSilla and NARVAL@TBL/SOPHIE@OHP on a small sample.

  20. Stellar coronal magnetic fields and star-planet interaction

    NASA Astrophysics Data System (ADS)

    Lanza, A. F.

    2009-10-01

    Context: Evidence of magnetic interaction between late-type stars and close-in giant planets is provided by the observations of stellar hot spots rotating synchronously with the planets and showing an enhancement of chromospheric and X-ray fluxes. Possible photospheric signatures of such an interaction have also been reported. Aims: We investigate star-planet interaction in the framework of a magnetic field model of a stellar corona, considering the interaction between the coronal field and that of a planetary magnetosphere moving through the corona. This is motivated, among other reasons, by the difficulty of accounting for the energy budgets of the interaction phenomena with previous models. Methods: A linear force-free model is applied to describe the coronal field and study the evolution of its total magnetic energy and relative helicity according to the boundary conditions at the stellar surface and the effects related to the planetary motion through the corona. Results: The energy budget of the star-planet interaction is discussed, assuming that the planet may trigger a release of the energy of the coronal field by decreasing its relative helicity. The observed intermittent character of the star-planet interaction is explained by a topological change in the stellar coronal field, induced by a variation in its relative helicity. The model predicts the formation of many prominence-like structures in the case of highly active stars owing to the accumulation of matter evaporated from the planet inside an azimuthal flux rope in the outer corona. Moreover, the model can explain why stars accompanied by close-in planets have a higher X-ray luminosity than those with distant planets. It predicts that the best conditions for detecting radio emission from the exoplanets and their host stars are achieved when the field topology is characterized by field lines connected to the surface of the star, leading to a chromospheric hot spot rotating synchronously with the planet

  1. 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.

  2. Thermal properties of stellar matter in the strong magnetic field

    NASA Astrophysics Data System (ADS)

    Piloyan, Arpine

    2012-07-01

    Low statistics and selection effects of the existing observational records of neutron stars ( NSs) do not allow to draw a coherent picture of the NSs typology only from observations. From theoretical point of view the unsufficient understanding of the mechanism of Supernovae explosion as well as the uncertainties in the modeling of the stellar matter equation of state make the knowledge of the parameters of the NS's structure and thermal, magnetic field or spin evolution non robust. The model's which are including the effects of superfluidity, superconductivity in dense matter and electro dynamics of super strong magnetic fields due to The complicated physics of matter under extrim conditions need further detailed investigations. The results are demonstrating the influence of magnetic field on the cooling regulators of NSs such as neutrino emissivity, heat conductivity and specific heat in the presence of magnetic fields for the investigations of cooling evolution of magnetars.

  3. 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

  4. Constraining scalar fields with stellar kinematics and collisional dark matter

    SciTech Connect

    Amaro-Seoane, Pau; Barranco, Juan; Bernal, Argelia; Rezzolla, Luciano E-mail: jbarranc@aei.mpg.de E-mail: rezzolla@aei.mpg.de

    2010-11-01

    The existence and detection of scalar fields could provide solutions to long-standing puzzles about the nature of dark matter, the dark compact objects at the centre of most galaxies, and other phenomena. Yet, self-interacting scalar fields are very poorly constrained by astronomical observations, leading to great uncertainties in estimates of the mass m{sub φ} and the self-interacting coupling constant λ of these fields. To counter this, we have systematically employed available astronomical observations to develop new constraints, considerably restricting this parameter space. In particular, by exploiting precise observations of stellar dynamics at the centre of our Galaxy and assuming that these dynamics can be explained by a single boson star, we determine an upper limit for the boson star compactness and impose significant limits on the values of the properties of possible scalar fields. Requiring the scalar field particle to follow a collisional dark matter model further narrows these constraints. Most importantly, we find that if a scalar dark matter particle does exist, then it cannot account for both the dark-matter halos and the existence of dark compact objects in galactic nuclei.

  5. 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

  6. 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

  7. 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

  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. 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.

  10. 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.

    2016-04-01

    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 percent. 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 percent 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.

  11. Field comparison of the point velocity probe with other groundwater velocity measurement methods

    NASA Astrophysics Data System (ADS)

    Labaky, W.; Devlin, J. F.; Gillham, R. W.

    2009-04-01

    Field testing of a new tool for measuring groundwater velocities at the centimeter scale, the point velocity probe (PVP), was undertaken at Canadian Forces Base, Borden, Ontario, Canada. The measurements were performed in a sheet pile-bounded alleyway in which bulk flow rate and direction could be controlled. PVP velocities were compared with those estimated from bulk flow, a Geoflo® instrument, borehole dilution, colloidal borescope measurements, and a forced gradient tracer test. In addition, the velocity profiles were compared with vertical variations in hydraulic conductivity (K) measured by permeameter testing of core samples and in situ high-resolution slug tests. There was qualitative agreement between the trends in velocity and K among all the various methods. The PVP and Geoflo® meter tests returned average velocity magnitudes of 30.2 ± 7.7 to 34.7 ± 13.1 cm/d (depending on prior knowledge of flow direction in PVP tests) and 36.5 ± 10.6, respectively, which were near the estimated bulk velocity (20 cm/d). The other direct velocity measurement techniques yielded velocity estimates 5 to 12 times the bulk velocity. Best results with the PVP instrument were obtained by jetting the instrument into place, though this method may have introduced a slight positive bias to the measured velocities. The individual estimates of point velocity direction varied, but the average of the point velocity directions agreed quite well with the expected bulk flow direction. It was concluded that the PVP method is a viable technique for use in the field, where high-resolution velocity data are required.

  12. 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'. PMID:27185961

  13. 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.

  14. 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.

  15. 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

  16. Environmental dependence of the stellar velocity dispersion at fixed parameters or for different galaxy families in the main galaxy sample of SDSS DR10

    NASA Astrophysics Data System (ADS)

    Deng, Xinfa; Jiang, Peng; Zhong, Shuangying; Ding, Yingping

    2015-01-01

    Using the apparent magnitude-limited Main Galaxy Sample of Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we examine the environmental dependence of the stellar velocity dispersion at fixed parameters or for different galaxy families. Limiting or fixing certain parameters exerts substantial influence on the environmental dependence of the stellar velocity dispersion of the galaxies which suggests that much of the stellar velocity dispersion-density relation is likely attributable to the relations between other galaxy parameters and density. The environmental dependence of the stellar velocity dispersion for red galaxies is very strong in certain redshift bins. This dependence can still be observed in some redshift bins for late-type galaxies, HSM galaxies, and LSM galaxies but is fairly weak in all redshift bins for early-type galaxies and blue galaxies.

  17. CHASING DISK DISPERSAL INDICATORS: THE ORIGIN OF THE [OI] LOW-VELOCITY COMPONENT FROM YOUNG STELLAR OBJECTS

    NASA Astrophysics Data System (ADS)

    Rigliaco, Elisabetta; Pascucci, I.; Gorti, U.; Edwards, S.; Hollenbach, D. J.

    2014-01-01

    The formation time, masses, and location of planets are strongly impacted by the physical mechanisms that disperse protoplanetary disks and the timescale over which protoplanetary material is cleared out. Accretion of matter onto the central star, protostellar winds/jets, magnetic disk winds, and photoevaporative winds operate concurrently. Hence, disentangling their relative contribution to disk dispersal requires identifying diagnostics that trace different star-disk environments. Here, I will discuss the analysis the low velocity component (LVC) of the Oxygen optical forbidden lines, which is found to be blueshifted by a few km/s with respect to the stellar velocity. We find that the [OI] LVC profiles are different from those of other lines tracing disk and photoevaporative winds ([NeII] at 12.81μm and CO at 4.7μm), pointing to different origins for these gas lines. The analysis of the [OI] LVC, and the comparison with the stellar properties favor an origin of the [OI] LVC in a region where OH is photodissociated by stellar FUV photons and argue against thermal emission from an X-ray-heated layer. Detailed modeling of two spectra with the highest S/N and resolution shows that there are two components within the LVC: a broad, centrally peaked component that can be attributed to gas arising in a warm disk surface in Keplerian rotation, and a narrow component that may arise in a cool (<1,000 K) molecular wind.

  18. Stellar Properties of Pulsating B Star Candidates in the Kepler Field

    NASA Astrophysics Data System (ADS)

    Waskie, Steven; McSwain, M. Virginia

    2016-01-01

    We measure physical properties of 31 candidate β Cephei, slowly pulsating B stars (SPB), and hybrid pulsating B stars in the Kepler field. We employ LTE Kurucz ATLAS9 model atmospheres and the TLUSTY BSTAR2006 non-LTE grid to measure the projected rotational velocity, v sin i, effective temperature, Teff, and surface gravity, log g, from blue optical spectra for our stars. Results are plotted against the evolutionary tracks of Ekström et al. for determination of stellar masses, radii, and ages. Accurate determination of these parameters is crucial for asteroseismic analysis as it has been shown by Balona et al. that the predicted parameters in the Kepler Input Catalog (KIC) for these hot stars are unreliable.We would like to thank Lehigh University for supporting this research. This work has been funded by NSF grants AST-1109247 and PHY-11359195.

  19. On the Velocity Field and the 3D Structure of the Galactic Soccer Ball Abell 43

    NASA Astrophysics Data System (ADS)

    Rauch, Thomas; Werner, Klaus; Ercolano, Barbara; Köppen, Joachim

    2005-11-01

    Planetary nebulae (PNe) and their central stars (CSs) are ideal tools to test evolutionary theory: photospheric properties of their exciting stars give stringent constraints for theoretical predictions of stellar evolution. The nebular abundances display the star's photosphere chemical composition at the time of the nebula's ejection which allows to look back into the history of stellar evolution. More importantly, they even provide a possibility to investigate on the chemical evolution of our Galaxy because most of the nuclear processed material goes back into the interstellar medium via PNe. The recent developments in observation techniques and the new three-dimensional photoionization code MOCASSIN (Ercolano et al. 2003) enable us to analyze PNe properties accurately by the construction of consistent models of PNe and CSs. In addition to PNe imaging and spectroscopy, detailed information about the velocity field within the PNe is a pre-requisite to employ de-projection techniques in modeling the physical structure of the PNe.

  20. Velocity field measurement of a round jet using quantitative schlieren.

    PubMed

    Iffa, Emishaw D; Aziz, A Rashid A; Malik, Aamir S

    2011-02-10

    This paper utilizes the background oriented schlieren (BOS) technique to measure the velocity field of a variable density round jet. The density field of the jet is computed based on the light deflection created during the passage of light through the understudy jet. The deflection vector estimation was carried out using phase-based optical flow algorithms. The density field is further exploited to extract the axial and radial velocity vectors with the aid of continuity and energy equations. The experiment is conducted at six different jet-exit temperature values. Additional turbulence parameters, such as velocity variance and power spectral density of the vector field, are also computed. Finally, the measured velocity parameters are compared with the hot wire anemometer measurements and their correlation is displayed. PMID:21343981

  1. Rapid alignment of velocity and magnetic field in magnetohydrodynamic turbulence.

    PubMed

    Matthaeus, W H; Pouquet, A; Mininni, P D; Dmitruk, P; Breech, B

    2008-02-29

    We show that local directional alignment of the velocity and magnetic field fluctuations occurs rapidly in magnetohydrodynamics for a variety of parameters and is seen both in direct numerical simulations and in solar wind data. The phenomenon is due to an alignment between magnetic field and gradients of either pressure or kinetic energy, and is similar to alignment of velocity and vorticity in Navier-Stokes turbulence. This rapid and robust relaxation process leads to a local weakening of nonlinear terms. PMID:18352632

  2. Bayesian 3D velocity field reconstruction with VIRBIUS

    NASA Astrophysics Data System (ADS)

    Lavaux, Guilhem

    2016-03-01

    I describe a new Bayesian-based algorithm to infer the full three dimensional velocity field from observed distances and spectroscopic galaxy catalogues. In addition to the velocity field itself, the algorithm reconstructs true distances, some cosmological parameters and specific non-linearities in the velocity field. The algorithm takes care of selection effects, miscalibration issues and can be easily extended to handle direct fitting of e.g. the inverse Tully-Fisher relation. I first describe the algorithm in details alongside its performances. This algorithm is implemented in the VIRBIUS (VelocIty Reconstruction using Bayesian Inference Software) software package. I then test it on different mock distance catalogues with a varying complexity of observational issues. The model proved to give robust measurement of velocities for mock catalogues of 3000 galaxies. I expect the core of the algorithm to scale to tens of thousands galaxies. It holds the promises of giving a better handle on future large and deep distance surveys for which individual errors on distance would impede velocity field inference.

  3. 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.

  4. Vacuum magnetic field mapping experiments for validated determination of the helical field coil location in stellarators

    SciTech Connect

    Peterson, J.; Hanson, J.; Hartwell, G.; Knowlton, S.

    2010-03-15

    Understanding the behavior of plasmas in magnetic confinement fusion devices typically requires accurate knowledge of the magnetic field structure. In stellarator-type confinement devices, the helical magnetic field is produced by currents in external coils and may be traced experimentally in the absence of plasma through the experimental technique of vacuum magnetic field mapping. Field mapping experiments, such as these, were performed on the recently constructed compact toroidal hybrid to verify the range of accessible magnetic configurations, compare the actual magnetic configuration with the design configuration, and identify any vacuum field errors that lead to perturbations of the vacuum magnetic flux surfaces. Furthermore, through the use of a new coil optimization routine, modifications are made to the simulation coil model such that better agreement exists between the experimental and simulation results. An outline of the optimization procedure is discussed in conjunction with the results of one such optimization process performed on the helical field coil.

  5. Velocity-Field Theory, Boltzmann's Transport Equation and Geometry

    NASA Astrophysics Data System (ADS)

    Ichinose, Shoichi

    Boltzmann equation describes the time development of the velocity distribution in the continuum fluid matter. We formulate the equation using the field theory where the velocity-field plays the central role. The matter (constituent particles) fields appear as the density and the viscosity. Fluctuation is examined, and is clearly discriminated from the quantum effect. The time variable is emergently introduced through the computational process step. The collision term, for the (velocity)**4 potential (4-body interaction), is explicitly obtained and the (statistical) fluctuation is closely explained. The present field theory model does not conserve energy and is an open-system model. (One dimensional) Navier-Stokes equation or Burger's equation, appears. In the latter part, we present a way to directly define the distribution function by use of the geometry, appearing in the mechanical dynamics, and Feynman's path-integral.

  6. Magnetic Cloud Field Intensities and Solar Wind Velocities

    NASA Technical Reports Server (NTRS)

    Gonzalez, Walter D.; Clau de Gonzalez, Alicia D.; Tsurutani, Bruce T.; Arballo, John K.

    1997-01-01

    For the sets of magnetic clouds studied in this work we have shown that there is a general relationship between their magnetic fields strength and velocities. With a clear tendency that the faster the speed of the cloud the higher the magnetic field.

  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. Estimation of Turbulent Wall Jet Velocity Fields for Noise Prediction

    NASA Astrophysics Data System (ADS)

    Nickels, Adam; Ukeiley, Lawrence; Reger, Robert; Cattafesta, Louis

    2015-11-01

    Estimation of the time-dependent turbulent velocity field of a planar wall jet based on discrete surface pressure measurements is performed using stochastic estimation in both the time and frequency domain. Temporally-resolved surface pressure measurements are measured simultaneously with planar Particle Image Velocimetry (PIV) snapshots, obtained at a relatively reduced rate. Proper Orthogonal Decomposition (POD) is then applied to both the surface pressure probes and the PIV snapshots, allowing for the isolation of portions of the wall pressure and velocity field signals that are well correlated. Using the time-varying pressure expansion coefficients as unconditional variables, velocity expansion coefficients are estimated and used to produce reconstructed estimates of the velocity field. Optimization in terms of number of unconditional probes employed, location of probes, and effects of PIV discretization are investigated with regards to the resulting estimates. Coupled with this analysis, Poisson's equation for fluctuating pressure is solved such that the necessary source terms of an acoustic analogy can be calculated for estimates of the far-field acoustics. Specifically in this work, the effects of using estimated velocity fields to solve for the hydrodynamic pressure and acoustic pressure will be studied.

  9. Searching for Non-Circular Motions in Halpha Velocity Fields

    NASA Astrophysics Data System (ADS)

    Peters, Wesley; Kuzio de Naray, Rachel

    2016-01-01

    We present Halpha velocity fields for four spiral galaxies: NGC 2654, NGC 2841, NGC 5746 and NGC 6674. These velocity fields were constructed from SparsePak IFU data taken on the WIYN telescope at KPNO. We use the DiskFit code to model the kinematics of these galaxies and to determine a rotation curve for each object. We find that two of these galaxies, NGC 2654 and NGC 5746, are nearly edge-on and display both photometric and kinematic evidence of a bar. NGC 6674 is closer to face-on and shows the signatures of a bar and ring. The velocity field of NGC 2841 does not show evidence for significant non-circular motions in the disk.

  10. A stochastic filtering technique for fluid flow velocity fields tracking.

    PubMed

    Cuzol, Anne; Mémin, Etienne

    2009-07-01

    In this paper, we present a method for the temporal tracking of fluid flow velocity fields. The technique we propose is formalized within a sequential Bayesian filtering framework. The filtering model combines an Itô diffusion process coming from a stochastic formulation of the vorticity-velocity form of the Navier-Stokes equation and discrete measurements extracted from the image sequence. In order to handle a state space of reasonable dimension, the motion field is represented as a combination of adapted basis functions, derived from a discretization of the vorticity map of the fluid flow velocity field. The resulting nonlinear filtering problem is solved with the particle filter algorithm in continuous time. An adaptive dimensional reduction method is applied to the filtering technique, relying on dynamical systems theory. The efficiency of the tracking method is demonstrated on synthetic and real-world sequences. PMID:19443925

  11. Comparison of the flows and radial electric field in the HSX stellarator to neoclassical calculations

    NASA Astrophysics Data System (ADS)

    Briesemeister, A.; Zhai, K.; Anderson, D. T.; Anderson, F. S. B.; Talmadge, J. N.

    2013-01-01

    Intrinsic flow velocities of up to ˜20 km s-1 have been measured using charge exchange recombination spectroscopy (CHERS) in the quasi-helically symmetric HSX stellarator and are compared with the neoclassical values calculated using an updated version (Lore 2010 Measurement and Transport Modeling with Momentum Conservation of an Electron Internal Transport Barrier in HSX (Madison, WI: University of Wisconsin); Lore et al 2010 Phys. Plasmas 17 056101) of the PENTA code (Spong 2005 Phys. Plasmas. 12 056114). PENTA uses the monoenergetic transport coefficients calculated by the drift kinetic equation solver code (Hirshman et al 1986 Phys. Fluids 29 2951; van Rij and Hirshman 1989 Phys. Fluids B 1 563), but corrects for momentum conservation. In the outer half of the plasma good agreement is seen between the measured parallel flow profile and the calculated neoclassical values when momentum correction is included. The flow velocity in HSX is underpredicted by an order of magnitude when this momentum correction is not applied. The parallel flow is calculated to be approximately equal for the majority hydrogen ions and the C6+ ions used for the CHERS measurements. The pressure gradient of the protons is the primary drive of the calculated parallel flow for a significant portion of the outer half of the plasma. The values of the radial electric field calculated with and without momentum correction were similar, but both were smaller than the measured values in the outer half of the plasma. Differences between the measured and predicted radial electric field are possibly a result of uncertainty in the composition of the ion population and sensitivity of the ion flux calculation to resonances in the radial electric field.

  12. 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.

  13. THE STELLAR VELOCITY DISPERSION OF A COMPACT MASSIVE GALAXY AT z = 1.80 USING X-SHOOTER: CONFIRMATION OF THE EVOLUTION IN THE MASS-SIZE AND MASS-DISPERSION RELATIONS {sup ,}

    SciTech Connect

    Van de Sande, Jesse; Franx, Marijn; Labbe, Ivo; Kriek, Mariska; Van Dokkum, Pieter G.; Bezanson, Rachel; Whitaker, Katherine E.; Brammer, Gabriel; Groot, Paul J.; Kaper, Lex

    2011-07-20

    Recent photometric studies have shown that early-type galaxies at fixed stellar mass were smaller and denser at earlier times. In this Letter, we assess that finding by deriving the dynamical mass of such a compact quiescent galaxy at z = 1.8. We have obtained a high-quality spectrum with full UV-NIR wavelength coverage of galaxy NMBS-C7447 using X-Shooter on the Very Large Telescope. We determined a velocity dispersion of 294 {+-} 51 km s{sup -1}. Given this velocity dispersion and the effective radius of 1.64 {+-} 0.15 kpc (as determined from Hubble Space Telescope Wide Field Camera 3 F160W observations) we derive a dynamical mass of (1.7 {+-} 0.5) x 10{sup 11} M{sub sun}. Comparison of the full spectrum with stellar population synthesis models indicates that NMBS-C774 has a relatively young stellar population (0.40 Gyr) with little or no star formation and a stellar mass of M{sub *} {approx} 1.5 x 10{sup 11} M{sub sun}. The dynamical and photometric stellar masses are in good agreement. Thus, our study supports the conclusion that the mass densities of quiescent galaxies were indeed higher at earlier times, and this earlier result is not caused by systematic measurement errors. By combining available spectroscopic measurements at different redshifts, we find that the velocity dispersion at fixed dynamical mass was a factor of {approx}1.8 higher at z = 1.8 compared with z = 0. Finally, we show that the apparent discrepancies between the few available velocity dispersion measurements at z > 1.5 are consistent with the intrinsic scatter of the mass-size relation.

  14. 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.

  15. Kinematics and Velocity Ellipsoid Parameters of Stellar Groups and Open Star Clusters: II Cool Stars

    NASA Astrophysics Data System (ADS)

    Elsanhoury, W. H.

    2016-06-01

    Based on the galactic space velocity components (U, V, W) and with aid of the vector and matrix analyses, we computed the velocity ellipsoid parameters for 790 late-type stars from CoRoT (Convection, Rotation and Transits) observations and 290 L dwarf stars. We ran the calculations for spectral types F, G, and K for late-type stars and L0, L1, L2, and L3 for L dwarf stars. We found that the ratio of the middle to the major axis in the galaxy ranged from 0.35 to 0.73. The vertex deviation from the galactic center was very small for the samples under investigation, which agrees well with earlier calculations.

  16. First Stellar Radial Velocities with a Laser Frequency Comb: Observations in the NIR H Band

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

    Advances in high precision radial velocity spectroscopy have been hindered by the lack of suitable wavelength references. This has been especially the case in the infrared where until recently radial velocity precision has been limited to 50-100m/s, hindering investigations such as the search for extrasolar planets orbiting cooler M stars at these wavelengths. To redress deficiency this we have developed a 25GHz laser frequency comb spanning the H band and suitable for use with spectrographs with spectral resolution in the range of 40,000 - 60,000, with RV precision limited by instrument stability and object S/N rather than by the lack of a suitable wavelength standard. We will present CU/NIST frequency comb performance and results obtained using the Pennsylvania State University's Pathfinder Spectrograph on the Hobby Eberly Telescope and will discuss lessons learned.

  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. 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

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

    NASA Astrophysics Data System (ADS)

    Hanson, J. D.; Anderson, D. T.; Cianciosa, M.; Franz, P.; Harris, J. H.; Hartwell, G. H.; Hirshman, S. P.; Knowlton, S. F.; Lao, L. L.; Lazarus, E. A.; Marrelli, L.; Maurer, D. A.; Schmitt, J. C.; Sontag, A. C.; Stevenson, B. A.; Terranova, D.

    2013-08-01

    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. Computation of flow pressure fields from magnetic resonance velocity mapping.

    PubMed

    Yang, G Z; Kilner, P J; Wood, N B; Underwood, S R; Firmin, D N

    1996-10-01

    Magnetic resonance phase velocity mapping has unrivalled capacities for acquiring in vivo multi-directional blood flow information. In this study, the authors set out to derive both spatial and temporal components of acceleration, and hence differences of pressure in a flow field using cine magnetic resonance velocity data. An efficient numerical algorithm based on the Navier-Stokes equations for incompressible Newtonian fluid was used. The computational approach was validated with in vitro flow phantoms. This work aims to contribute to a better understanding of cardiovascular dynamics and to serve as a basis for investigating pulsatile pressure/flow relationships associated with normal and impaired cardiovascular function. PMID:8892202

  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. VECTUM. Irregular 2D Velocity Vector Field Plotting Package

    SciTech Connect

    McClurg, F.R.; Mousseau, V.A.

    1992-05-04

    VECTUM is a NCAR Graphics based package, for generating a plot of an irregular 2D velocity vector field. The program reads an ASCII database of x, y, u, v, data pairs and produces a plot in Computer Graphics Metafile (CGM) format. The program also uses an ASCII parameter file for controlling annotation details such as the plot title, arrowhead style, scale of vectors, windowing, etc. Simple geometry (i.e. lines, arcs, splines) can be defined to be included with the velocity vectors. NCAR Graphics drivers can be used to display the CGM file into PostScript, HPGL, HDF, etc, output.

  3. Confronting predictions of stellar evolution theory: the case of single field M dwarf stars

    NASA Astrophysics Data System (ADS)

    Feiden, Gregory A.; Mann, Andrew W.; Gaidos, Eric

    2015-01-01

    Using a homogenous sample of single field M dwarf stars from the CONCH-SHELL catalog, we confront the reliability of predictions from low mass stellar evolution models. Empirical values for the bolometric flux, effective temperature, and stellar radius are typically determined with better than 1%, 2%, and 5% precision, respectively. Coupled with precise [M/H] values, these observations place strong constraints on the accuracy of stellar models. A Markov Chain Monte Carlo (MCMC) formalism is used to establish the most likely stellar properties, with associated uncertainties, by interpolating within a dense grid of Dartmouth stellar evolution models with mass, age, metallicity, and distance as free parameters. The observed effective temperature and bolometric flux are adopted as independent observables in the MCMC likelihood function with the addition of the observed [M/H] and distance as informative Bayesian priors. Results are presented comparing model mass estimates to those from an empirical mass-luminosity calibration, and showing how well stellar models reproduce the observed radii, effective temperatures, and luminosities. Reliability of stellar models is then investigated as a function of mass, [M/H], equivalent width of H-alpha, and X-ray luminosity. Finally, we briefly discuss various physical mechanisms to explain the observed trends, particularly in the context of the hypothesis that magnetic activity is the source of model-observation discrepancies.

  4. Preliminary results of an updated North American GPS velocity field

    NASA Astrophysics Data System (ADS)

    Craymer, M. R.; Henton, J. A.; Piraszewski, M.; Lapelle, E.

    2010-12-01

    In an effort to improve previous continental-scale GPS velocity fields for North America, we and other collaborators in the North American Reference Frame (NAREF) Working Group have reprocessed, or are in the process of reprocessing, data from nearly all continuous GPS sites in North America (as well as a selection of global sites used to define the reference frame). Previous velocity fields were derived from coordinate time series of somewhat inhomogeneous GPS results due to: (1) the use of relative antenna calibrations that did not include satellite antennas or account for the presence of antenna radomes, (2) the use of difference reference frames, (3) the use of IGS precise orbits based on these calibrations and reference frames, and (4) the use of different (evolving) versions of GPS processing software and procedures. This reprocessing effort of all previous data is based on more consistent and accurate absolute antenna calibrations of both station and satellite antennas, the ITRF2005 reference frame and the latest versions of GPS processing software and procedures. Also, more than three additional years of data have been included in the velocity field estimation. The new time series and velocity results from the different NAREF collaborators are compared with each other and with previous reported results. We also compare these results to new precise point positioning (PPP) solutions that are much more efficient for processing large networks and to recent model predictions of glacial isostatic adjustment.

  5. 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

  6. Recovering slant and angular velocity from a linear velocity field: modeling and psychophysics.

    PubMed

    Domini, Fulvio; Caudek, Corrado

    2003-07-01

    The data from two experiments, both using stimuli simulating orthographically rotating surfaces, are presented, with the primary variable of interest being whether the magnitude of the simulated gradient was from expanding vs. contracting motion. One experiment asked observers to report the apparent slant of the rotating surface, using a gauge figure. The other experiment asked observers to report the angular velocity, using a comparison rotating sphere. The results from both experiments clearly show that observers are less sensitive to expanding than to contracting optic-flow fields. These results are well predicted by a probabilistic model which derives the orientation and angular velocity of the projected surface from the properties of the optic flow computed within an extended time window. PMID:12818345

  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. 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.

  9. 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

    2016-07-01

    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.

  10. VELOCITY AND MAGNETIC FIELD DISTRIBUTION IN A FORMING PENUMBRA

    SciTech Connect

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

    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.

  11. 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.

  12. Meeting on Stellar and Planetary Magnetic Fields, Potsdam, East Germany, August 29-September 2, 1983, Proceedings

    NASA Astrophysics Data System (ADS)

    The morphologies and origins of the magnetic fields of the planets, the sun, and different classes of stars are examined in reviews and reports of theoretical and observational investigations. Topics discussed include topological-pumping mechanisms, solar-cyclic oscillatory motions, turbulent heat transfer in convective envelopes, premain-sequence stellar magnetic activity, magnetic starspots, three types of planetary dynamo, and the dynamics and energetics of the earth's core. Consideration is given to mean-field models of the planetary or stellar dynamo, photometry and spectrophotometry of magnetic stars, the binary nature of Beta CrB, and precession-induced long-period variations in magnetic stars.

  13. 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.

  14. 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.

  15. RADIAL VELOCITIES AND PULSATION EPHEMERIDES OF 11 FIELD RR Lyrae STARS

    SciTech Connect

    For, Bi-Qing; Sneden, Christopher; Preston, George W.

    2011-06-01

    We present new radial velocities (RVs), improved pulsation periods, and reference epochs of 11 field RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic. This study is based on high-resolution spectra obtained with the echelle spectrograph of the 2.5 m du Pont telescope at Las Campanas Observatory. We obtained {approx}200 spectra per star (i.e., a total of {approx}2300 spectra), distributed more or less uniformly throughout their pulsation cycles. RV curves and photometric light curves phased to our new ephemerides are presented for all program stars. In a subsequent paper, we will use these spectra to derive stellar atmospheric parameters and chemical compositions throughout the pulsational cycles, based purely on spectroscopic constraints.

  16. Radial Velocities and Pulsation Ephemerides of 11 Field RR Lyrae Stars

    NASA Astrophysics Data System (ADS)

    For, Bi-Qing; Preston, George W.; Sneden, Christopher

    2011-06-01

    We present new radial velocities (RVs), improved pulsation periods, and reference epochs of 11 field RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic. This study is based on high-resolution spectra obtained with the echelle spectrograph of the 2.5 m du Pont telescope at Las Campanas Observatory. We obtained ~200 spectra per star (i.e., a total of ~2300 spectra), distributed more or less uniformly throughout their pulsation cycles. RV curves and photometric light curves phased to our new ephemerides are presented for all program stars. In a subsequent paper, we will use these spectra to derive stellar atmospheric parameters and chemical compositions throughout the pulsational cycles, based purely on spectroscopic constraints.

  17. Stellar Masses from the CANDELS Survey: The GOODS-South and UDS Fields

    NASA Astrophysics Data System (ADS)

    Santini, P.; Ferguson, H. C.; Fontana, A.; Mobasher, B.; Barro, G.; Castellano, M.; Finkelstein, S. L.; Grazian, A.; Hsu, L. T.; Lee, B.; Lee, S.-K.; Pforr, J.; Salvato, M.; Wiklind, T.; Wuyts, S.; Almaini, O.; Cooper, M. C.; Galametz, A.; Weiner, B.; Amorin, R.; Boutsia, K.; Conselice, C. J.; Dahlen, T.; Dickinson, M. E.; Giavalisco, M.; Grogin, N. A.; Guo, Y.; Hathi, N. P.; Kocevski, D.; Koekemoer, A. M.; Kurczynski, P.; Merlin, E.; Mortlock, A.; Newman, J. A.; Paris, D.; Pentericci, L.; Simons, R.; Willner, S. P.

    2015-03-01

    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.

  18. 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.

  19. BAYESIAN INFERENCE OF SOLAR AND STELLAR MAGNETIC FIELDS IN THE WEAK-FIELD APPROXIMATION

    SciTech Connect

    Asensio Ramos, A.

    2011-04-10

    The weak-field approximation is one of the simplest models that allows us to relate the observed polarization induced by the Zeeman effect with the magnetic field vector present on the plasma of interest. It is usually applied for diagnosing magnetic fields in the solar and stellar atmospheres. A fully Bayesian approach to the inference of magnetic properties in unresolved structures is presented. The analytical expression for the marginal posterior distribution is obtained, from which we can obtain statistically relevant information about the model parameters. The role of a priori information is discussed and a hierarchical procedure is presented that gives robust results that are almost insensitive to the precise election of the prior. The strength of the formalism is demonstrated through an application to IMaX data. Bayesian methods can optimally exploit data from filter polarimeters given the scarcity of spectral information as compared with spectro-polarimeters. The effect of noise and how it degrades our ability to extract information from the Stokes profiles is analyzed in detail.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. The Milky Way stellar populations in CFHTLS fields

    NASA Astrophysics Data System (ADS)

    Guittet, M.; Haywood, M.; Schultheis, M.

    2011-12-01

    We investigate the characteristics of the thick disk in the Canada -- France -- Hawaii -- Telescope Legacy Survey (CFHTLS) fields, complemented at bright magnitudes with Sloan Digital Sky Survey (SDSS) data. The ([Fe/H], Z) distributions are derived in the W1 and W3 fields, and compared with simulated maps produced using the Besançon model. It is shown that the thick disk, represented in star-count models by a distinct component, is not an adequate description of the observed ([Fe/H], Z) distributions in these fields.

  7. 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.

  8. 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

  9. Michelson wide-field stellar interferometry: principles and experimental verification.

    PubMed

    Montilla, I; Pereira, S F; Braat, J J M

    2005-01-20

    A new interferometric technique for Michelson wide-field interferometry is presented that consists of a Michelson pupil-plane combination scheme in which a wide field of view can be achieved in one shot. This technique uses a stair-shaped mirror in the intermediate image plane of each telescope in the array, allowing for simultaneous correction of the differential delay for the on-axis and off-axis image positions. Experimental results in a laboratory setup show that it is possible to recover the fringes of on-axis and off-axis stars with an angular separation of 1 arc min simultaneously and with a similar contrast. This new technique represents a considerable extension of the field of view of an interferometer without the need for extra observation time. PMID:15717821

  10. The expansion velocity field within the planetary nebula NGC 7008

    NASA Astrophysics Data System (ADS)

    Sabbadin, F.; Ortolani, S.; Bianchini, A.; Hamzaoglu, E.

    1983-06-01

    The forbidden O III, H-alpha, and forbidden N II expansion velocity fields within the planetary nebula NGC 7008 have been obtained from high dispersion spectrograms. The photographic and spectroscopic data indicate that this nebula is very inhomogeneous. A rough model consists of two coaxial prolate spheroids of moderate ellipticity. Evidence is presented that K 4-44 (93 + 5 deg 1), classified as a distinct planetary nebula in the Catalogue of Galactic Planetary Nebulae of Perek and Kohoutek (1967) is a condensation within NGC 7008.

  11. 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.

    2016-08-01

    Zeeman Doppler imaging 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 form ZDI and activity cycles.

  12. 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.

  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. Elasticity Estimation of Thin Flap Using Optical PIV Velocity Fields

    NASA Astrophysics Data System (ADS)

    Westerdale, John; Belohlavek, Marek; McMahon, Eileen; Jiamsripong, Panupong; Heys, Jeffery; Milano, Michele

    2010-11-01

    We estimate the elasticity of a thin, cellulose acetate flap using forcing data derived from optical particle imaging velocimetry (optical-PIV) velocity fields. The flap is fixed on one end to a stand submerged within a PIV tank and deformed using a water jet pulse. PIV is then performed at the interface between the thin sheet and water jet throughout the deformation cycle; the resulting velocity field allows the determination of instantaneous pressure measurements via Poisson's equation. An optimal estimation technique utilizing ensemble Kalman filtering is coupled with a finite element analysis program to determine the sheet's elasticity. Results show good agreement with actual elasticity measurements for both homogeneous and non-homogeneous elasticity sheets. In addition, we performed a quantitative study to determine the optimal vector density for a given element size to achieve an accurate elasticity estimation value. Considering the success of this technique using optical-PIV, it should also be possible for in-vitro elasticity estimates based on ultrasound-PIV measurements.

  15. 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.

  16. 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.

  17. 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).

  18. Far-ultraviolet stellar photometry: Fields in Sagittarius and Scorpius

    NASA Astrophysics Data System (ADS)

    Schmidt, Edward G.; Carruthers, George R.

    1995-02-01

    Far-ultraviolet photometry for 741 objects in a field in Sagittarius centered near M8 and 541 objects in a field centered near sigma Scorpii is presented. These data were extracted from electographic images obtained with two cameras during a shuttle flight in 1991 April/May. The cameras provided band passes with lambdaeff = 1375 A and lambdaeff = 1781 A. Synthetic colors show that these bands are sensitive to effective temperature for hot stars. Our measurements were placed on a quantitative far-ultraviolet magnitude scale by convolving the spectra of stars observed by IUE with our cameras' spectral response functions. Fifty-eight percent of the ultraviolet objects were identified with visible stars using the SIMBAD database while another 40% of the objects are blends of early type stars too close together to separate with our resolution. Our photometry is compared with that from the TD-1, OAO 2, and ANS satellites and the S201 (Apollo 16) far-ultraviolet camera and found to agree at the level of a few tenths of a magnitude. Unlike previous studies, almost half of the identified visual counterparts to the ultraviolet objects are early B stars. A plot of distance modulus against ultraviolet color excess reveals a significant population of stars with strong ultraviolet excess.

  19. 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}ȯ 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}ȯ /{L}ȯ , 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}ȯ , 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.

  20. 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}ȯ 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}ȯ /{L}ȯ , 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}ȯ , 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.

  1. Empirically Interrelating Stellar Magnetic Activity, Photometric Variability and Radial Velocity “Jitter” to Enhance Planet Discovery

    NASA Astrophysics Data System (ADS)

    Bastien, Fabienne A.

    2014-01-01

    The magnetic activity of Sun-like stars, which can manifest as short time scale photometric and radial velocity (RV) variability, adds to the difficulty of detecting planets, particularly those in the Earth mass range: RV jitter can wash out the very small RV signal of such planets, and photometric “noise” caused by stellar activity can similarly preclude the detection of the tiny transit signature that a planet like ours would produce. Hence, in order to successfully detect Earth-like planets, via either the transit or RV method, the exoplanet community needs a way to characterize the photometric and RV stability of a star in advance. Many studies have examined pair-wise relationships between the magnetic activity, photometric variability and RV jitter of stars. We expand upon this work by using as our foundation the high quality photometric data from NASA's Kepler mission, supplemented by archival Keck RV measurements and our own Ca II H&K magnetic activity measurements, aiming to empirically interrelate all three quantities for both dwarf and evolved Sun-like stars. We find that some of the low level photometric variability correlates poorly with magnetic activity and instead traces granulation, yielding a simple tool to measure surface gravity with a precision of 0.1 dex. We tie the RV jitter of magnetically inactive stars (stars with observed RV jitter ranging from ~3m/s to 135.5m/s but with photometric variations of less than 3 mmag) to the Fourier complexity of the light curve, finding that higher frequency photometric variations drive the RV jitter. Finally, we present initial comparisons between magnetic activity, as traced by Ca II H&K measurements, and other measures of photometric variability, as well as ongoing and future applications of our work.

  2. 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.

  3. 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. PMID:24115059

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

    SciTech Connect

    Bochanski, John J., Jr.; /Washington U., Seattle, Astron. Dept.

    2006-06-01

    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.

  5. Complex Velocity Fields in the Shell of T Pyxidis

    NASA Astrophysics Data System (ADS)

    Margon, Bruce; Deutsch, Eric W.

    1998-05-01

    We present spatially resolved, moderate-resolution spectrophotometry of the recurrent nova T Pyxidis and a portion of the surrounding shell. The spectrum extracted from a strip of width 10'' centered on the star shows well-known, strong emission lines typical of old novae plus a prominent, unfamiliar emission line at 6590 Å. This line, and a weaker companion at 6540 Å, which we also detect, has been previously reported by Shahbaz et al. and attributed to Doppler-shifted Hα emission from a collimated jet emerging from T Pyx. We demonstrate that these lines are instead due to [N II] λλ6548, 6584 from a complex velocity field in the surrounding nebula. The comments of past workers concerning the great strength of He II λ4686 in T Pyx itself are also reiterated.

  6. 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.

  7. 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

  8. THE TRIPLE EVOLUTION DYNAMICAL INSTABILITY: STELLAR COLLISIONS IN THE FIELD AND THE FORMATION OF EXOTIC BINARIES

    SciTech Connect

    Perets, Hagai B.; Kratter, Kaitlin M.

    2012-12-01

    Physical collisions and close approaches between stars play an important role in the formation of exotic stellar systems. Standard theories suggest that collisions are rare, occurring only via random encounters between stars in dense clusters. We present a different formation pathway, the triple evolution dynamical instability (TEDI), in which mass loss in an evolving triple star system causes orbital instability. The subsequent chaotic orbital evolution of the stars triggers close encounters, collisions, exchanges between the stellar components, and the dynamical formation of eccentric compact binaries (including Sirius-like binaries). We demonstrate that the rate of stellar collisions due to the TEDI is approximately 10{sup -4} yr{sup -1} per Milky Way Galaxy, which is nearly 30 times higher than the total collision rate due to random encounters in the Galactic globular clusters. Moreover, we find that the dominant type of stellar collision is qualitatively different; most collisions involve asymptotic giant branch stars, rather than main sequence or slightly evolved stars, which dominate collisions in globular clusters. The TEDI mechanism should lead us to revise our understanding of collisions and the formation of compact, eccentric binaries in the field.

  9. The stellar field in the vicinity of Sirius and the color enigma

    NASA Astrophysics Data System (ADS)

    Bonnet-Bidaud, J. M.; Gry, C.

    1991-12-01

    Several ancient texts suggest that the bright star Sirius was red in the recent past. Evidence is presented from an observation record found in Chinese sources (of about 100 BC) in which mention is made of a color change of Sirius. Photometric observations are reported of the stellar field around Sirius with the aim to find the possible causes of the color change(s) of the stellar system within historical times. Among the possible causes are objects external to Sirius A-B, namely a small interstellar cloud or a third body interacting with the system. Both could have caused an observed reddening effect consistent with the historical record, and two stars in the field may have the right characteristics and orbits to interact with Sirius.

  10. Stellar photometry with the Hubble Space Telescope Wide-field/Planetary camera - A progress report

    NASA Technical Reports Server (NTRS)

    Holtzman, Jon A.; Hunter, Deidre; Groth, Edward J.; Light, Robert M.; Faber, S. M.

    1991-01-01

    The prospects for the use of the Wide-Field/Planetary Camera (WFPC) for stellar photometry are described. The large halos of the point-spread function (PSF) resulting from spherical aberration and from spatial, temporal, and color variations of the PSF are the main limitations to accurate photometry. Degradations caused by crowding are exacerbated by the halos of the PSF. An attempt is made to quantify these effects and determine the current accuracy of stellar photometry with the WFPC. In realistic cases, the brighter stars in crowded fields have 0.09 mag errors; fainter stars have larger errors depending on the degree of crowding. It is shown that measuring Cepheids in Virgo Cluster galaxies is not currently possible without inordinate increases in exposure times.

  11. 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.

  12. 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.

  13. Magnetic Field Line Tracing Calculations for Conceptual PFC Design in the National Compact Stellarator Experiment

    SciTech Connect

    Maingi, R; Kaiser, T; Hill, D N; Lyon, J F; Monticello, D; Zarnstorff, M C

    2006-06-12

    The National Compact Stellarator Experiment (NCSX) is a three-field period compact stellarator presently in the construction phase at Princeton, NJ. The design parameters of the device are major radius R=1.4m, average minor radius = 0.32m, 1.2 {le} toroidal field (B{sub t}) {le} 1.7 T, and auxiliary input power up to 12 MW with neutral beams and radio-frequency heating. The NCSX average aspect ratio of 4.4 lies well below present stellarator experiments and designs, enabling the investigation of high {beta} physics in a compact stellarator geometry. Also the NCSX design choice for a quasi-axisymmetric configuration aims toward the achievement of tokamak-like transport. In this paper, we report on the magnetic field line tracing calculations used to evaluate conceptual plasma facing component (PFC) designs. In contrast to tokamaks, axisymmetric target plates are not required to intercept the majority of the heat flux in stellarators, owing to the nature of the 3-D magnetic field footprint. The divertor plate design investigated in this study covers approximately one half of the toroidal extent in each period. Typical Poincare plots in Figure 1 illustrate the plasma cross-section at several toroidal angles for a computed NCSX high-beta equilibrium. The plates used for these calculations are centered in each period about the elongated cross-section shown in Figure 1a, extending to +/- {pi}/6 in each direction. Two methods for tracing the edge field line topology were used in this study. The first entails use of the VMEC/MFBE-2001 packages, whereas the second entails use of the PIES code with a post-processor by Michael Drevlak; the same field line integration routine was used to evaluate the equilibria for this comparison. Both inputs were generated based on the {beta}=4%, =iota=0.5 equilibrium computed from the final NCSX coil set. We first compare these two methods for a specific plate geometry, and conclude with a comparison of the strike characteristics

  14. 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.

  15. Galaxy Transformation as probed by Morphology and Velocity Fields of Distant Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Ziegler, Bodo

    2005-07-01

    We seek to obtain ACS imaging of four distant {0.3field covered by a 2x2 mosaic to determine morphological and structural parameters of late-type galaxies. We specifically concentrate on peculiarities indicative of past or ongoing interaction processes. The 90 target galaxies have been {Period74} or will be {P75} observed with 3D-spectroscopy at ESO-VLT yielding 2D-velocity fields with unprecedented spatial coverage and sampling. The good spatial resolution of the ground-based data will be further enhanced by a deconvolution method based on the proposed ACS images. The velocity field and the morphology in restframe-UV light will reveal possible transformation mechanisms affecting not only the stellar populations but also the mass distribution of the galaxies. Additionally, it will be possible to pin down the nature of the interaction {e.g. tidally or ram-pressure induced}. This assessment gets supported by our N-body/SPH simulations {including star formation} of different interaction processes that allow the direct comparison of structural and kinematical characteristics at each time step with the observations on an individual basis taking into account all observational constraints for a given galaxy. All together, we will be able to explore the relative efficiency of the various proposed transformation phenomena. In the case of non-disturbed spirals, a rotation curve can be extracted from the full 2D velocity field with unprecedented quality, from which the maximum rotation speed can be derived with high confidence. In combination with accurate size and luminosity determinations from the ACS images, we will be able to establish the Tully-Fisher and Fundamental Plane relations of cluster spiral members at cosmological epochs. At these distances cluster assembly is predicted to peak and we can probe the galaxies' luminosity, size and mass evolution with robust methods. Together with our already existing sample of 200

  16. Variance Anisotropy of Solar Wind Velocity and Magnetic Field Fluctuations

    NASA Astrophysics Data System (ADS)

    Oughton, S.; Matthaeus, W. H.; Wan, M.

    2015-12-01

    At MHD scales in the solar wind, velocity and magnetic fieldfluctuations are typically observed to have much more energy in thecomponents transverse to the mean magnetic field, relative to theparallel components [eg, 1,2]. This is often referred to asvariance anisotropy. Various explanations for it have been suggested,including that the fluctuations are predominantly shear Alfvén waves[1] and that turbulent dynamics leads to such states [eg, 3].Here we investigate the origin and strength of such varianceanisotropies, using spectral method simulations of thecompressible (polytropic) 3D MHD equations. We report on results from runs with several different classes ofinitial conditions. These classes include(i) fluctuations polarized only in the same sense as shear Alfvénwaves (aka toroidal polarization),(ii) randomly polarized fluctuations, and(iii) fluctuations restricted so that most of the energy is inmodes which have their wavevectors perpendicular, or nearly so, to thebackground magnetic field: quasi-2D modes. The plasma beta and Mach number dependence [4] of quantities like the variance anisotropy, Alfven ratio, and fraction of the energy in the toroidal fluctuations will be examined, along with the timescales for the development of any systematic features.Implications for solar wind fluctuations will be discussed. References:[1] Belcher & Davis 1971, J. Geophys. Res, 76, 3534.[2] Oughton et al 2015, Phil Trans Roy Soc A, 373, 20140152.[3] Matthaeus et al 1996, J. Geophys. Res, 101, 7619.[4] Smith et al 2006, J. Geophys. Res, 111, A09111.

  17. Coronal structure of the large scale magnetic field and its influence on stellar rotation.

    NASA Astrophysics Data System (ADS)

    Réville, Victor; Brun, Allan Sacha; Matt, Sean; Strugarek, Antoine; Bouvier, Jérôme

    2015-08-01

    The braking of magnetic stars through the extraction of angular momentum by stellar winds has been studied for decades, leading to several formulations as functions of stellar parameters. We recently demonstrated that the dependency of the braking law on the coronal magnetic field topology can be taken into account through a simple scalar parameter : the open magnetic flux. This parameter can be integrated anywhere beyond the last closed coronal loop in steady-state. The Zeeman-Doppler Imaging technique has brought the community a reliable and precise description of the surface magnetic field of distant stars. However reconstruction of the coronal structure of the large scale magnetic field without running costly numerical simulations of the stellar wind is not trivial. An alternative is to use the classical analytical potential field extrapolation to describe the opening of the field lines by the magnetized wind but this technique relies on knowing the so-called radius of the surface source term which must vary from star to star. To resolve this issue, we use our extended set of 2.5D wind simulations published in 2015, to provide a criteria for the field lines opening as well as a simple tool to assess the surface source term radius and the open magnetic flux. This allows us to derive the magnetic torque applied to the star by the wind from any spectropolarimetric observations. We conclude our talk by discussing the case of 3D wind simulations of the BCool sample ; whose surface magnetic field has been obtained by ZDI and to discuss how non-axisymmetry modifies or not our recent findings.

  18. HIGH ANGULAR RESOLUTION INTEGRAL-FIELD SPECTROSCOPY OF THE GALAXY'S NUCLEAR CLUSTER: A MISSING STELLAR CUSP?

    SciTech Connect

    Do, T.; Ghez, A. M.; Morris, M. R.; Yelda, S.; Larkin, J.; Lu, J. R.; Matthews, K.

    2009-10-01

    We report on the structure of the nuclear star cluster in the innermost 0.16 pc of the Galaxy as measured by the number density profile of late-type giants. Using laser guide star adaptive optics in conjunction with the integral field spectrograph, OSIRIS, at the Keck II telescope, we are able to differentiate between the older, late-type (approx 1 Gyr) stars, which are presumed to be dynamically relaxed, and the unrelaxed young (approx 6 Myr) population. This distinction is crucial for testing models of stellar cusp formation in the vicinity of a black hole, as the models assume that the cusp stars are in dynamical equilibrium in the black hole potential. In the survey region, we classified 60 stars as early-type (22 newly identified) and 74 stars as late-type (61 newly identified). We find that contamination from young stars is significant, with more than twice as many young stars as old stars in our sensitivity range (K' < 15.5) within the central arcsecond. Based on the late-type stars alone, the surface stellar number density profile, SIGMA(R) propor to R {sup -G}AMMA, is flat, with GAMMA = -0.27 +- 0.19. Monte Carlo simulations of the possible de-projected volume density profile, n(r) propor tor {sup -g}amma, show that gamma is less than 1.0 at the 99.7% confidence level. These results are consistent with the nuclear star cluster having no cusp, with a core profile that is significantly flatter than that predicted by most cusp formation theories, and even allows for the presence of a central hole in the stellar distribution. Of the possible dynamical interactions that can lead to the depletion of the red giants observable in this survey-stellar collisions, mass segregation from stellar remnants, or a recent merger event-mass segregation is the only one that can be ruled out as the dominant depletion mechanism. The lack of a stellar cusp around a supermassive black hole would have important implications for black hole growth models and inferences on the

  19. 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.

  20. A Kiloparsec-scale Nuclear Stellar Disk in the Milky Way as a Possible Explanation of the High Velocity Peaks in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Debattista, Victor P.; Ness, Melissa; Earp, Samuel W. F.; Cole, David R.

    2015-10-01

    The Apache Point Observatory Galactic Evolution Experiment has measured the stellar velocities of red giant stars in the inner Milky Way. We confirm that the line of sight velocity distributions (LOSVDs) in the mid-plane exhibit a second peak at high velocities, whereas those at | b| =2^\\circ do not. We use a high resolution simulation of a barred galaxy, which crucially includes gas and star formation, to guide our interpretation of the LOSVDs. We show that the data are fully consistent with the presence of a thin, rapidly rotating, nuclear disk extending to ∼1 kpc. This nuclear disk is orientated perpendicular to the bar and is likely to be composed of stars on x2 orbits. The gas in the simulation is able to fall onto such orbits, leading to stars populating an orthogonal disk.

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

    PubMed

    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

  2. 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.

  3. 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.

  4. Integral field spectroscopy of massive young stellar objects in the N113 H II region in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    The Spitzer Surveying the Agents of Galaxy Evolution (SAGE) survey has allowed the identification and analysis of significant samples of Young Stellar Object (YSO) candidates in the Large Magellanic Cloud (LMC). However, the angular resolution of Spitzer is relatively poor meaning that at the distance of the LMC, it is likely that many of the Spitzer YSO candidates in fact contain multiple components. We present high-resolution K-band integral field spectroscopic observations of the three most prominent massive YSO candidates in the N113 H II region using Very Large Telescope/Spectrograph for INtegral Field Observations in the Near Infrared (VLT/SINFONI). We have identified six K-band continuum sources within the three Spitzer sources and we have mapped the morphology and velocity fields of extended line emission around these sources. Br γ, He I and H2 emission is found at the position of all six K-band sources; we discuss whether the emission is associated with the continuum sources or whether it is ambient emission. H2 emission appears to be mostly ambient emission and no evidence of CO emission arising in the discs of YSOs has been found. We have mapped the centroid velocities of extended Br γ emission and He I emission and found evidence of two expanding compact H II regions. One source shows compact and strong H2 emission suggestive of a molecular outflow. The diversity of spectroscopic properties observed is interpreted in the context of a range of evolutionary stages associated with massive star formation.

  5. 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.

  6. Stability of an ellipsoidal stellar cluster in the tidal force field of the Galaxy

    NASA Astrophysics Data System (ADS)

    Kozhanov, T. S.

    1992-02-01

    Attention is given to the dynamical characteristics of an ellipsoidal stellar cluster which rotates on an elliptical orbit relative to the center of the Galaxy in the field of its tidal forces. Regions of stability and instability of the cluster as a function of its form are defined on the basis of a numerical solution of the equations of the motion of stars inside the cluster. It is shown that, if the flattening of the cluster along the Y-axis, which coincides with the rotation direction, is larger than along the X-axis, which is directed toward the center of the Galaxy), the cluster is unstable.

  7. Velocity-Field Characteristics of Polycrystalline Pentacene Field-Effect Transistors

    SciTech Connect

    Cobb, Brian; Wang, Liang; Dunn, Lawrence; Dodabalapur, Ananth

    2010-06-15

    In this article we report on the carrier velocity of polycrystalline pentacene transistors as a function of electric field in both quasistatic and non-quasistatic regimes. We performed a series of measurements on devices with a range of channel lengths. At moderate electric fields (< 5 x 105 V/cm), the characteristics are similar to those of disordered or amorphous organic semiconductors. The highest velocities we have measured are near 6 x 104 cm/s at room temperature. Additional dynamic measurements, using both step response and frequency response methods, correlate strongly to the quasistatic findings. These results fill an important void between experimental results that have been obtained with disordered/amorphous organic semiconductors and single crystals.

  8. On the latitude dependence of drift velocity of the geomagnetic main field and its secular variation

    NASA Astrophysics Data System (ADS)

    Yukutake, Takesi; Shimizu, Hisayoshi

    2016-08-01

    There is an apparent difference in the westward drift between the geomagnetic main field and its time derivative, secular variation. The drift velocity of the main field is about 0.2°/year, definitely lower than that of the secular variation, 0.3°/year. The drift velocity of the main field appears to change with latitude, being low at high latitudes and higher at low latitudes, whereas the velocity of the secular variation is nearly constant irrespective of latitude. This paper examines what causes this difference by adopting the drifting and standing field model that assumes the geomagnetic field consists of the field steadily drifting westwards and the field remaining at nearly the same location. In this study, we confirm that the existence of the non-drifting standing field significantly affects the estimate of the drift velocity of the total field (i.e., the main field), and makes it slower than that of the secular variation. The drifting field is intense in low latitudes with its maximum at the equator, while the standing field dominates in higher latitudes. As a consequence, reduction of the apparent drifting velocity of the total field by the standing field is conspicuous in higher latitudes and less so in low latitudes. This creates the observed latitudinal structure of the drift velocity of the main field. On the other hand, the drift velocity of the secular variation is less affected by existence of the standing field, and mostly reflects the velocity of the drifting field that is almost constant with latitude. The velocity of the secular variation thus becomes almost uniform independent of latitude. The observed difference between the main field and the secular variation is naturally derived from the drifting and standing field model. This implies that physical mechanisms to generate the drifting and standing fields can be considered independently.

  9. The ejection of shells in the stellar wind of P CYG - The most plausible explanation of the Balmer-line radial velocity variations

    NASA Astrophysics Data System (ADS)

    Markova, N.

    1986-07-01

    Our new data of the Balmer line radial velocities in the P Cygni spectrum are compared to the measurments published by de Groot (1969), Kolka (1983) and Markova (1986). The observed variations are analysed in terms of a model proposed by Kolka (1983) which implies a multiple ejection of shells in the stellar wind of P Cygni. It is shown that all data agree to an ejection time scale of about 200 days. The estimated accelerations for the three data groups are very close which supposes a stability of the ejection mechanism over an interval of about 40 yr. The radial velocities of nalmer and the FeII and FeIII (far UV) lines are compared. The identity of the Balmer and the FeII and FeIII shells is discussed.

  10. Experimental and numerical study of error fields in the CNT stellarator

    NASA Astrophysics Data System (ADS)

    Hammond, K. C.; Anichowski, A.; Brenner, P. W.; Pedersen, T. S.; Raftopoulos, S.; Traverso, P.; Volpe, F. A.

    2016-07-01

    Sources of error fields were indirectly inferred in a stellarator by reconciling computed and numerical flux surfaces. Sources considered so far include the displacements and tilts of the four circular coils featured in the simple CNT stellarator. The flux surfaces were measured by means of an electron beam and fluorescent rod, and were computed by means of a Biot–Savart field-line tracing code. If the ideal coil locations and orientations are used in the computation, agreement with measurements is poor. Discrepancies are ascribed to errors in the positioning and orientation of the in-vessel interlocked coils. To that end, an iterative numerical method was developed. A Newton–Raphson algorithm searches for the coils’ displacements and tilts that minimize the discrepancy between the measured and computed flux surfaces. This method was verified by misplacing and tilting the coils in a numerical model of CNT, calculating the flux surfaces that they generated, and testing the algorithm’s ability to deduce the coils’ displacements and tilts. Subsequently, the numerical method was applied to the experimental data, arriving at a set of coil displacements whose resulting field errors exhibited significantly improved agreement with the experimental results.

  11. 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.

  12. Beyond Phase 3: The FORS1 Catalogue of Stellar Magnetic Fields

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Over the course of a decade of operations, more than 200 nights of telescope time have been granted for magnetic field measurements with the FORS1 instrument on the VLT. Motivated by some conflicting results published in the literature, we have studied the instrument characteristics and critically revised previous magnetic field detections obtained with FORS1. Our study has led to the publication of a catalogue of 1400 magnetic field measurements of a sample of 850 different stars, together with their intensity spectra. This catalogue includes nearly all the circular spectropolarimetric measurements taken during ten years of operation. Here we summarise some of the lessons learned from the analysis of the FORS1 stellar spectropolarimetric archive.

  13. The global velocity field of the filament in NGC 6334

    NASA Astrophysics Data System (ADS)

    Zernickel, A.; Schilke, P.; Smith, R. J.

    2013-06-01

    Aims: Star formation involves the collapse of gas from the scale of giant molecular clouds down to dense cores. Our aim is to trace the velocities in the filamentary, massive star-forming region NGC 6334 and to explain its dynamics. Methods: The main filament was mapped with the single-dish telescope APEX in HCO+ (J = 3-2) at 267.6 GHz to trace the dense gas. In order to reproduce the position-velocity diagram, we use a 3D radiative transfer code and create a model of a cylinder that undergoes a gravitational collapse toward its center. Results: We find a velocity gradient in the filament from the end toward its center, with the highest masses being found at both ends. Similar velocities have been predicted by recent calculations of the gravitational collapse of a sheet or cylinder of gas, and the observed velocities are consistent with these predictions. The 3D structure is revealed by taking the inclination and curvature of the filament into account. The free-fall collapse timescale of the filamentary molecular cloud is estimated to be ~1 Myr. This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.

  14. Glacier surface velocity fields in South Shetland Islands

    NASA Astrophysics Data System (ADS)

    Osmanoglu, B.; Giseke, H.; Navarro, F. J.; Rueckamp, M.; Falk, U.; Corcuera, M. I.; Braun, M.

    2011-12-01

    In this study surface velocity of glaciers in South Shetland Islands (Antarctic Peninsula) are calculated based on synthetic aperture radar data from ALOS PALSAR and TerraSAR-X as well as differential GPS measurements. The obtained glacier velocities will be used to calculate the total glacier mass budget and to better understand the contribution of the study areas to the sea level rise. Only recent studies have examined the region for mass balance and sea level rise estimates. However, larger scale mass budget computations are not yet available. Ice dynamics obtained from satellite data have only been derived in a few occasions, often due to lacking spatial resolution or temporal decorrelation. Hence, any spacebased information on ice dynamics can significantly improve estimates of calving fluxes and mass loss. In this study we analysed over 30 PALSAR and 30 TSX scenes acquired over the King George Island and Livingston Island, the two largest islands in the South Shetland Island group. In the study areas the glacier velocities are calculated using two independent data sets; namely satellite radar imagery and GPS. Feature-tracking methods are applied to the radar imagery to obtain glacier velocities using Gamma Interferometric SAR Processor and TU-Delft DORIS. Results from Gamma and Doris software packages are compared to each other as well as GPS measurements where available. For a subset of the study area tracking results from different acquisitions modes (stripmap and spotlight) and orbits are compared. Comparison of glacier velocities obtained by radar and GPS provide an estimate for the uncertainties in the measured rates. The results obtained from all data sets are then compiled to construct a map of glacier velocities for the entire island group.

  15. 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

  16. 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

  17. 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.

  18. Laboratory Velocity Measurements Used for Recovering Soil Distributions from Field Seismic Data

    SciTech Connect

    Berge, P A; Bertete-Aguirre, H

    1999-10-20

    Recent advances in field methods make it possible to obtain high quality compressional (P) and shear (S) velocity data for the shallow subsurface. Environmental and engineering problems require new methods for interpreting the velocity data in terms of sub-surface soil distribution. Recent advances in laboratory measurement techniques have provided high quality velocity data for soils at low pressures that can be used to improve interpretation of field data. We show how laboratory data can be used to infer lithology from field data. We use laboratory ultrasonic velocity measurements from artificial soils made by combining various amounts of sand and peat moss.

  19. 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.

  20. 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.

  1. 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

  2. VizieR Online Data Catalog: Stellar parameters for CoRoT exoplanet field stars (Cortes+, 2015)

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    The present stellar sample is composed of 138 stars of spectral types F, G, and K, with visual magnitudes V between 10 to 14, located in two exoplanet fields observed by CoRoT, namely the Galactic center (LRc01: Long Run Center 01) and the Galactic anticenter (LRa01: Long Run Anticenter 01) fields. (4 data files).

  3. Global Neuromagnetic Cortical Fields Have Non-Zero Velocity.

    PubMed

    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

  4. 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

  5. Probing the large-scale velocity field with clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Bahcall, Neta A.; Cen, Renyue; Gramann, Mirt

    1994-01-01

    What is the role of clusters of galaxies in probing the large-scale velocity field of the universe? We investigate the distribution of peculiar velocities of clusters of galaxies in the popular low-density (omega = 0.3) flat cold dark matter (CDM) cosmological model, which best fits many large-scale structure observations. An omega = 1 CDM model is also studied for comparison. We find that clusters of galaxies are efficient tracers of the large-scale velocity field. The clusters exhibit a Maxwellian distribution of peculiar velocities, as expected from Gaussian initial density fluctuations. The cluster three-dimensional velocity distribution for the omega = 0.3 model peaks at nu approximately greater than 400 km/s and extends to high velocities of nu approximately 1200 km/s. The rms peculiar velocity of the clusters is 440 km/s. Approximately 10% of all model clusters move with high peculiar velocities nu greater or equal to 700 km/s. The observed velocity distribution of clusters of galaxies is compared with the predictions from cosmological models. The observed data exhibit a larger velocity tail than seen in the model simulations; however, due to the large observational uncertainties, the data are consistent at approximately equal to 3 sigma level with the odel predictions, and with a Gaussian initial density field. The large peculiar velocities reported for some clusters of galaxies (nu approximately greater than 3000 km/s) are likely to be overestimated, if the current model is viable.

  6. Measurement of core velocity fluctuations and the dynamo in a reversed-field pinch

    SciTech Connect

    Den Hartog, D.J.; Craig, D.; Fiksel, G.; Fontana, P.W.; Prager, S.C.; Sarff, J.S.; Chapman, J.T.

    1998-12-31

    Plasma flow velocity fluctuations have been directly measured in the high temperature magnetically confined plasma in the Madison Symmetric Torus (MST) Reversed-Field Pinch (RFP). These measurements show that the flow velocity fluctuations are correlated with magnetic field fluctuations. This initial measurement is subject to limitations of spatial localization and other uncertainties, but is evidence for sustainment of the RFP magnetic field configuration by the magnetohydrodynamic (MHD) dynamo. Both the flow velocity and magnetic field fluctuations are the result of global resistive MHD modes of helicity m = 1, n = 5--10 in the core of MST. Chord-averaged flow velocity fluctuations are measured in the core of MST by recording the Doppler shift of impurity line emission with a specialized high resolution and throughput grating spectrometer. Magnetic field fluctuations are recorded with a large array of small edge pickup coils, which allows spectral decomposition into discrete modes and subsequent correlation with the velocity fluctuation data.

  7. 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.

  8. Comparisons of a standard galaxy model with stellar observations in five fields

    NASA Technical Reports Server (NTRS)

    Bahcall, J. N.; Soneira, R. M.

    1984-01-01

    Modern data on the distribution of stellar colors and on the number of stars as a function of apparent magnitude in five directions in the Galaxy are analyzed. It is found that the standard model is consistent with all the available data. Detailed comparisons with the data for five separate fields are presented. The bright end of the spheroid luminosity function and the blue tip of the spheroid horizontal branch are analyzed. The allowed range of the disk scale heights and of fluctuations in the volume density is determined, and a lower limit is set on the disk scale length. Calculations based on the thick disk model of Gilmore and Reid (1983) are presented.

  9. Stellar Populations in the Kepler and K2 fields: APOGEE-KASC Collaboration

    NASA Astrophysics Data System (ADS)

    Johnson, Jennifer; APOKASC Collaboration

    2016-01-01

    The age distribution, both absolute and relative, of stars throughout the Milky Way reveals the history of star formation and migration and is a key constraint on galaxy formation models. The combination of spectroscopic and asteroseismic information for stars observed by both the APOGEE survey and the Kepler/K2 missions provides ages for field red giants along many lines of sight through the Galaxy. The fundamental stellar properties derived from these data are used to test theories of the formation of the thin and thick disks, the role of radial migration, and the timescales for nucleosynthesis in our Galaxy. We also explore correlations between asteroseismic mass and spectroscopic abundances, with a view towards age calibrations for large current and future spectroscopic surveys.

  10. Estimation of macro velocity models by wave field extrapolation

    NASA Astrophysics Data System (ADS)

    Cox, Hendricus Lambertus Hubertus

    A method to estimate accurate macro velocity models for prediction of traveltimes of seismic waves in the earth's subsurface is developed. The sensitivity of prestack migration is used to estimate the model and since model errors are expressed in the quality of the migration result, the migration process itself can be used to determine these errors. Using an initial model, shot records are downward extrapolated to grid points (depth points) in the subsurface. The extrapolated data can be reordered into so called common depth point (CDP) gathers, image gathers and focus panels. The deviation from horizontal alignment is used to quantify the errors in the model and to apply update corrections accordingly. The analysis can be done before or after stacking over all shot records (CDP stacking). the previously mentioned focus panels are generated by CDP stacking. The alignment analysis reduces then to a simple focusing analysis. The examples discussed show that horizontal alignment gives accurate macro velocity models for prestack depth migration. Focus panels can be difficult to interpret in complicated situations, where it is impossible to converge to the correct solution with focus panels only. The process should be guided by macrogeologic models of the area. In complicated situations, a layer stripping strategy is preferred.

  11. 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.

  12. OBSERVATIONAL CONSTRAINTS ON THE STELLAR RADIATION FIELD IMPINGING ON TRANSITIONAL DISK ATMOSPHERES

    SciTech Connect

    Szulagyi, Judit; Pascucci, Ilaria; Abraham, Peter; Moor, Attila; Apai, Daniel; Bouwman, Jeroen

    2012-11-01

    Mid-infrared atomic and ionic line ratios measured in spectra of pre-main-sequence stars are sensitive indicators of the hardness of the radiation field impinging on the disk surface. We present a low-resolution Spitzer IRS search for [Ar II] at 6.98 {mu}m, [Ne II] at 12.81 {mu}m, and [Ne III] 15.55 {mu}m lines in 56 transitional disks. These objects, characterized by reduced near-infrared but strong far-infrared excess emission, are ideal targets to set constraints on the stellar radiation field onto the disk, because their spectra are not contaminated by shock emission from jets/outflows or by molecular emission lines. After demonstrating that we can detect [Ne II] lines and recover their fluxes from the low-resolution spectra, here we report the first detections of [Ar II] lines toward protoplanetary disks. We did not detect [Ne III] emission in any of our sources. Our [Ne II]/[Ne III] line flux ratios combined with literature data suggest that a soft-EUV or X-ray spectrum produces these gas lines. Furthermore, the [Ar II]/[Ne II] line flux ratios point to a soft X-ray and/or soft-EUV stellar spectrum as the ionization source of the [Ar II] and [Ne II] emitting layer of the disk. If the soft X-ray component dominates over the EUV, then we would expect larger photoevaporation rates and, hence, a reduction of the time available to form planets.

  13. New interpretations of measured antihydrogen velocities and field ionization spectra.

    PubMed

    Pohl, T; Sadeghpour, H R; Gabrielse, G

    2006-10-01

    We present extensive Monte Carlo simulations, showing that cold antihydrogen (H) atoms are produced when antiprotons (p) are gently heated in the side wells of a nested Penning trap. The observed H with high energies, that had seemed to indicate otherwise, are instead explained by a surprisingly effective charge-exchange mechanism. We shed light on the previously measured field-ionization spectrum, and reproduce both the characteristic low-field power law as well as the enhanced H production at higher fields. The latter feature is shown to arise from H toms too deeply bound to be described as guiding center atoms, atoms with internally chaotic motion. PMID:17155247

  14. 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.

  15. 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.

  16. Observation and analysis of abrupt changes in the interplanetary plasma velocity and magnetic field.

    NASA Technical Reports Server (NTRS)

    Martin, R. N.; Belcher, J. W.; Lazarus, A. J.

    1973-01-01

    This paper presents a limited study of the physical nature of abrupt changes in the interplanetary plasma velocity and magnetic field based on 19 day's data from the Pioneer 6 spacecraft. The period was chosen to include a high-velocity solar wind stream and low-velocity wind. Abrupt events were accepted for study if the sum of the energy density in the magnetic field and velocity changes was above a specified minimum. A statistical analysis of the events in the high-velocity solar wind stream shows that Alfvenic changes predominate. This conclusion is independent of whether steady state requirements are imposed on conditions before and after the event. Alfvenic changes do not dominate in the lower-speed wind. This study extends the plasma field evidence for outwardly propagating Alfvenic changes to time scales as small as 1 min (scale lengths on the order of 20,000 km).

  17. Documentation for the machine-readable version of the revised Catalogue of Stellar Rotational Velocities of Uesugi and Fukuda (1982)

    NASA Technical Reports Server (NTRS)

    Warren, W. H., Jr.

    1983-01-01

    The machine-readable catalog provides mean data on the old Slettebak system for 6472 stars. The catalog results from the review, analysis and transformation of 11460 data from 102 sources. Star identification, (major catalog number, name if the star has one, or cluster identification, etc.), a man projected rotational velocity, and a list of source references re included. The references are given in a second file included with the catalog when it is distributed on magnetic tape. The contents and/formats of the the data and reference files of the machine-readable catalog are described to enable users to read and process the data.

  18. 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.

  19. The design of a MSE polarimetry diagnostic for the measurement of radial electric fields on the HSX stellarator

    NASA Astrophysics Data System (ADS)

    Dobbins, T.; Kumar, S. T. A.; Anderson, D. T.; Anderson, F. S. B.

    2014-10-01

    HSX is a quasi-symmetric stellarator that is designed to reduce neoclassical transport. Neoclassical codes estimate a large positive radial electric field (40-50 kV/m) near the core of the HSX plasma. Impurity ion flow measurements could not resolve this large electric field. A single channel, dual PEM (Photo Elastic Modulators) MSE polarimetry diagnostic has therefore been designed for the HSX stellarator to directly measure the radial electric field near the core of the plasma. The design has been optimized to get a maximum change in polarization angle from a radial electric field with a good spatial resolution. A change in radial electric field as small as 1.5 kV/m can be detected with a careful selection of the sightline. The diagnostic design and initial characterization are presented.

  20. Solar subsurface magnetic and velocity fields from tilt angle patterns

    NASA Astrophysics Data System (ADS)

    Baranyi, Tünde; Muraközy, Judit; Ludmány, András

    2015-08-01

    ABSTRACT A refined form of the well known Joy's law has been formulated by using the new Debrecen tilt angle datasets. These data are intercalibrated with the traditional datasets and several determination methods help to make the material reliable. It has been found that the latitudinal distribution of the tilt angles is not merely a monotonously increasing function, but it has a plateau between the latitudes of about 15-25 degrees, where the toroidal field is the strongest. This may provide new constraints for the theoretical investigations about the mechanisms contributing to the observable tilt angles. The new data also allow to demonstrate that the tilts are primarily caused by the Coriolis impact, no signature has been found for the winding up of the global magnetic field. This work has received funding from the European Community's Seventh Framework Programme (FP7/2012-2015) under grant agreement No. 284461 (eHEROES).

  1. 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.

  2. Stellar Populations

    NASA Astrophysics Data System (ADS)

    Peletier, Reynier F.

    2013-10-01

    This is a summary of my lectures during the 2011 Canary Islands Winter School in Puerto de la Cruz. I give an introduction to the field of stellar populations in galaxies, and highlight some new results. Since the title of the Winter School is Secular Evolution in Galaxies I mostly concentrate on nearby galaxies, which are best suited to study this theme. Of course, the understanding of stellar populations is intimately connected to understanding the formation and evolution of galaxies, one of the great outstanding problems of astronomy. We are currently in a situation where very large observational advances have been made in recent years. Galaxies have been detected up to a redshift of ten. A huge effort has to be made so that stellar population theory can catch up with observations. Since most galaxies are far away, information about them has to come from stellar population synthesis of integrated light. Here I will discuss how stellar evolution theory, together with observations in our Milky Way and Local Group, are used as building blocks to analyse these integrated stellar populations.

  3. Simulation and visualization of velocity fields in simple electrokinetic devices

    NASA Astrophysics Data System (ADS)

    Mahanti, Prasun; Taylor, Thomas; Cochran, Douglas; Keebaugh, Michael; Hayes, Mark A.

    2013-12-01

    Capillary electrophoresis and similar techniques which use an electrified contracting-flow interface (gradient elution moving boundary electrophoresis, electrophoretic exclusion, for examples) are widely used, but the detailed flow dynamics and local electric field effects within this zone have only recently been quantitatively investigated. The motivating force behind this work is establishing particle flow based visualization tools enabling advances for arbitrary interfacial designs beyond this traditional flow/electric field interface. These tools work with pre-computed 2-dimensional fundamental interacting fields which govern particle and(or) fluid flow and can now be obtained from various computational fluid dynamics (CFD) software packages. The particle-flow visualization calculations implemented in the tool and are built upon a solid foundation in fluid dynamics. The module developed in here provides a simulated video particle observation tool which generates a fast check for legitimacy. Further, estimating the accuracy and precision of full 2-D and 3-D simulation is notoriously difficult and a centerline estimation is used to quickly and easily quantitate behaviors in support of decision points. This tool and the recent quantitative assessment of particle behavior within the interfacial area have set the stage for new designs which can emphasize advantageous behaviors not offered by the traditional configuration.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. First-order torques and solid-body spinning velocities in intense sound fields

    NASA Technical Reports Server (NTRS)

    Wang, T. G.; Kanber, H.; Rudnick, I.

    1977-01-01

    The letter reports an observation of first-order nonzero time-averaged torques and solid-body spinning velocities in intense acoustic fields. The experimental apparatus consisted of a vertical cylindrical rod supported on an air bearing and passing through a box with two loudspeakers centered on adjoining vertical sides. The rim velocity of the cylinder and the torque on the cylinder are measured as functions of air-particle velocity and the phase difference between the x and y components of the particle velocity. It is found that both rim velocity and torque are linear functions of particle velocity. Difficulties in constructing a proper theoretical description of the observed effects are discussed.

  9. Ultrasonic propagation velocity in magnetic and magnetorheological fluids due to an external magnetic field.

    PubMed

    Bramantya, M A; Motozawa, M; Sawada, T

    2010-08-18

    Ultrasonic propagation velocity in a magnetic fluid (MF) and magnetorheological fluid (MRF) changes with the application of an external magnetic field. The formation of clustering structures inside the MF and MRF clearly has an influence on the ultrasonic propagation velocity. Therefore, we propose a qualitative analysis of these structures by measuring properties of ultrasonic propagation. Since MF and MRF are opaque, non-contact inspection using the ultrasonic technique can be very useful for analyzing the inner structures of MF and MRF. In this study, we measured ultrasonic propagation velocity in a hydrocarbon-based MF and MRF precisely. Based on these results, the clustering structures of these fluids are analyzed experimentally in terms of elapsed time dependence and the effect of external magnetic field strength. The results reveal hysteresis and anisotropy in the ultrasonic propagation velocity. We also discuss differences of ultrasonic propagation velocity between MF and MRF. PMID:21386478

  10. 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.

  11. Determining Stellar Magnetic Fields and Coronal Densities by Radio Spectrum Modeling

    NASA Astrophysics Data System (ADS)

    Deam, Sophie; Stercula, Tyler; Maier, Erin

    2016-01-01

    Radio emission from active stars provides a sensitive measure of stellar coronal characteristics such as temperature, density and magnetic field strengths. Gyro-synchrotron (GS) emission from mildly relativistic electrons spiraling in magnetic fields is commonly detected in hot coronae of stars with extended magnetospheres, and allows for quantitative estimates of coronal features. Another radiation mechanism, thermal gyro-synchrotron (TGS) radiation, which arises from the thermal electron populations in the high energy tail of a Maxwellian energy distribution, depends strongly on the coronal temperature and strength of the magnetic field. Thus, TGS can potentially provide sensitive constraints on these physical parameters. However, TGS radiation has never been observed. Models predict that TGS should be characterized by an increase in flux, and a corresponding sharp increase in fractional circular polarization at high frequencies. Using the Very Large Array (VLA), we observed eight stars of three different classes: pre-main sequence stars, classical flare stars and close binaries, to determine if their spectral energy distributions (SED's) might display these distinguishing features. The VLA observations were made using 4 GHz wide frequency bands between 15 GHz and 44 Ghz, measuring both Stokes I flux and V flux. For six of the eight stars, the results from VLA are consistent with the SED's we expect for GS, not TGS. For the two pre-main sequence stars, we measured a significant increase in the fractional circular polarization at the higher frequency bands. We are in the process of building detailed modeled fits to determine if we can attribute this to TGS. The development of comprehensive models describing SED's for all of the observed stars will allow us to set upper limits constraining the magnetic field strengths for each source, and, in the case of potential TGS detection, refine TGS models.

  12. 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.

  13. 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

  14. Intense velocity-shears, magnetic fields and filaments in diffuse gas

    NASA Astrophysics Data System (ADS)

    Falgarone, Edith; Hily-Blant, Pierre; Levrier, François; Berthet, Manuel; Bastien, Pierre; Clemens, Dan

    2015-03-01

    The dissipation of turbulence is a key process in the evolution of diffuse gas towards denser structures. The vast range of coupled scales and the variety of dissipative processes in interstellar turbulence make it a complex system to analyze. Observations now provide powerful statistics of the gas velocity field, density and magnetic field orientations, opening a rich field of investigation. On-going comparisons of the orientation of intense velocity-shears, magnetic field and tenuous filaments of matter in a turbulent high-latitude cloud are promising.

  15. Drift velocity versus electric field in ⟨ 110 ⟩ Si nanowires: Strong confinement effects

    NASA Astrophysics Data System (ADS)

    Li, Jing; Mugny, Gabriel; Niquet, Yann-Michel; Delerue, Christophe

    2015-08-01

    We have performed atomistic simulations of the phonon-limited high field carrier transport in ⟨ 110 ⟩ Si nanowires with small diameter. The carrier drift velocities are obtained from a direct solution of the non-linear Boltzmann transport equation. The relationship between the drift velocity and the electric field considerably depends on the carrier, temperature, and diameter of the nanowires. In particular, the threshold between the linear and non-linear regimes exhibits important variations. The drift velocity reaches a maximum value and then drops. These trends can be related to the effects of quantum confinement on the band structure of the nanowires. We also discuss the impact of the different phonon modes and show that high-energy phonons can, unexpectedly, increase the drift velocity at a high electric field.

  16. 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.

  17. 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.

  18. Modelling of the solar/stellar wind two-jet structure induced by azimuthal stellar magnetic field

    NASA Astrophysics Data System (ADS)

    Golikov, Evgeniy; Belov, Nickolai; Alexashov, Dmitry; Izmodenov, Vladislav

    2016-07-01

    Opher et al. (2015), Drake et al. (2015) have shown that the heliospheric magnetic field results in formation of two-jet structure of the solar wind flow in the inner heliosheath, i.e. in the subsonic region between the heliospheric termination shock and the heliopause. In this scenario the heliopause has tube-like topology as compared with sheet-like topology in the most models of the global heliosphere (e.g. Izmodenov and Alexashov, 2015). In this paper we explore the two-jet scenario for the simplified astrosphere with the star is at rest with respect to the circumstellar medium and radial magnetic field is neglected as compared with azimuthal component. Our work is further elaboration of Drake et al. (2015) paper. We performed parametric numerical analyses showing how the structure of the flow changes depending on the model parameters. Also, we present three first integrals of the ideal MHD equations for the considered problem and use them to get links between analytical and numerical considerations.

  19. 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).

  20. 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.

  1. Electric field measurements at the magnetopause. I Observation of large convective velocities at rotational magnetopause discontinuities

    NASA Technical Reports Server (NTRS)

    Aggson, T. L.; Maynard, N. C.; Gambardella, P. J.

    1983-01-01

    Large convective electric fields of the order of 10 mV/m (sometimes as high as 22 mV/m) are observed at rotational magnetopause discontinuities. These observations were made with the long cylindrical (179-m base line) probes carried on the ISEE 1 satellite. These electric field observations yield convective velocity magnitudes (equal to the cross product of the vector E and the vector B, the latter divided by the square of the magnitude of B) of the order of 150 km/s. In this format for the convective velocity magnitudes, some of these observations are similar to the high speed plasma velocity observations that were made at the magnetopause with the plasma experiment carried on the ISEE 1 satellite. It is shown that, for many of these magnetopause crossings, there exists a special moving coordinate system where the observed electric fields vanish. Such a unique reference system is often used in theoretical studies of magnetic discontinuities. This special coordinate system does not move at the local plasma velocity but moves instead at a velocity intermediate between the convective velocity and the local Alfven velocity. It is used here as a diagnostic tool for the experimental investigation of rotational discontinuities at the magnetopause.

  2. 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.

  3. Distances and stellar populations of seven low surface brightness galaxies in the field of M101

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter

    2014-10-01

    We have recently discovered seven large, extremely low surface brightness galaxies in the field of the nearby massive spiral galaxy M101. The galaxies were found with Dragonfly, a telescope that is optimized for the detection of low surface brightness emission. If the galaxies are associated with M101, their properties are similar to those of faint dwarf galaxies around the Milky Way and M31, and this would be the first time that a population of "typical", low luminosity dwarfs has been identified around a galaxy outside of the Local Group. Available CFHT imaging does not resolve the galaxies into stars, which makes it difficult to determine their distances and to characterize their stellar populations. Here we propose to obtain ACS imaging of these seven low surface brightness galaxies, with the aim of resolving them into individual stars. The primary goal is to determine their distances using the tip of the red giant branch, and the secondary goal is to constrain their star formation histories from the distribution of stars in the color-magntiude diagram.

  4. Emission line eclipse mapping of velocity fields in dwarf nova accretion discs

    NASA Astrophysics Data System (ADS)

    Makita, M.; Mineshige, S.

    2002-01-01

    We propose a new method, emission-line eclipse mapping, to map the velocity fields in an accretion disc. We apply the usual eclipse mapping technique to the light curves at each of 12-24 wavelengths across the line center to map the region with same line-of-sight velocity, from which we are able to plot the rotational velocity as a function of radius on the assumption of axisymmetric disc. We calculate time changes of the emission line profiles, assuming Keplerian rotation fields (vvarphi propto r-1/2) and the emissivity distribution of j propto r-3/2, and reconstruct emissivity profiles. The results show typically a `two-eye' pattern for high line-of-sight velocities and we can recover the relation, vvarphi propto d-1/2, where d is the separation of two lq eyes.'

  5. 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.

  6. Three-dimensional reconstruction of cardiac flows based on multi-planar velocity fields

    NASA Astrophysics Data System (ADS)

    Falahatpisheh, Ahmad; Pedrizzetti, Gianni; Kheradvar, Arash

    2014-11-01

    Measurement of the three-dimensional flow field inside the cardiac chambers has proven to be a challenging task. This is mainly due to the fact that generalized full-volume velocimetry techniques cannot be easily implemented to the heart chambers. In addition, the rapid pace of the events in the heart does not allow for accurate real-time flow measurements in 3D using imaging modalities such as magnetic resonance imaging, which neglects the transient variations of the flow due to averaging of the flow over multiple heartbeats. In order to overcome these current limitations, we introduce a multi-planar velocity reconstruction approach that can characterize 3D incompressible flows based on the reconstruction of 2D velocity fields. Here, two-dimensional, two-component velocity fields acquired on multiple perpendicular planes are reconstructed into a 3D velocity field through Kriging interpolation and by imposing the incompressibility constraint. Subsequently, the scattered experimental data are projected into a divergence-free vector field space using a fractional step approach. We validate the method in exemplary 3D flows, including the Hill's spherical vortex and a numerically simulated flow downstream of a 3D orifice. During the process of validation, different signal-to-noise ratios are introduced to the flow field, and the method's performance is assessed accordingly. The results show that as the signal-to-noise ratio decreases, the corrected velocity field significantly improves. The method is also applied to the experimental flow inside a mock model of the heart's right ventricle. Taking advantage of the periodicity of the flow, multiple 2D velocity fields in multiple perpendicular planes at different locations of the mock model are measured while being phase-locked for the 3D reconstruction. The results suggest the metamorphosis of the original transvalvular vortex, which forms downstream of the inlet valve during the early filling phase of the right

  7. Classification of Field Dwarfs and Giants in RAVE and Its Use in Stellar Stream Detection

    NASA Astrophysics Data System (ADS)

    Klement, R. J.; Bailer-Jones, C. A. L.; Fuchs, B.; Rix, H.-W.; Smith, K. W.

    2011-01-01

    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 ≈ -160 km s-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

  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. Using a constraint on the parallel velocity when determining electric fields with EISCAT

    NASA Technical Reports Server (NTRS)

    Caudal, G.; Blanc, M.

    1988-01-01

    A method is proposed to determine the perpendicular components of the ion velocity vector (and hence the perpendicular electric field) from EISCAT tristatic measurements, in which one introduces an additional constraint on the parallel velocity, in order to take account of our knowledge that the parallel velocity of ions is small. This procedure removes some artificial features introduced when the tristatic geometry becomes too unfavorable. It is particularly well suited for the southernmost or northernmost positions of the tristatic measurements performed by meridian scan experiments (CP3 mode).

  10. 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.