WorldWideScience

Sample records for central star wind

  1. Observations of central stars

    Lutz, J.H.

    1978-01-01

    Difficulties occurring in the observation of central stars of planetary nebulae are reviewed with emphasis on spectral classifications and population types, and temperature determination. Binary and peculiar central stars are discussed. (U.M.G.)

  2. Atmospheres of central stars

    Hummer, D.G.

    1978-01-01

    The author presents a brief summary of atmospheric models that are of possible relevance to the central stars of planetary nebulae, and then discusses the extent to which these models accord with the observations of both nebulae and central stars. Particular attention is given to the significance of the very high Zanstra temperature implied by the nebulae He II lambda 4686 A line, and to the discrepancy between the Zanstra He II temperature and the considerably lower temperatures suggested by the appearance of the visual spectrum for some of these objects. (Auth.)

  3. Winds in cataclysmic variable stars

    Cordova, F.A.; Ladd, E.F.; Mason, K.O.

    1984-01-01

    Ultraviolet spectrophotometry of two dwarf novae, CN Ori and RX And, at various phases of their outburst cycles confirms that the far uv flux increases dramatically about 1-2 days after the optical outburst begins. At this time the uv spectral line profiles indicate the presence of a high velocity wind. The detectability of the wind depends more on the steepness of the spectrum, and thus on the flux in the extreme ultraviolet, than on the absolute value of the far uv luminosity. The uv continuum during outburst consists of (at least) two components, the most luminous of which is located behind the wind and is completely absorbed by the wind at the line frequencies. Several pieces of evidence suggest that the uv emission lines that are observed in many cataclysmic variables during quiescence have a different location in the binary than the wind, and are affected very little by the outburst

  4. Winds of AGB stars: does size matter?

    Hoefner, S

    2008-01-01

    Asymptotic giant branch (AGB) stars are showing clear signs of significant mass loss through cool stellar winds. These outflows are attributed to the combined effects of pulsation-induced shocks and radiation pressure on dust grains formed in the outer atmospheric layers. This paper gives an overview of the current status of radiation-hydrodynamical modelling of these processes, and presents a toy model that allows analysis of certain features of detailed models, such as the influence of grain size dependent opacities and basic differences in winds of C- and M-type AGB stars.

  5. NLTE wind models of hot subdwarf stars

    Krtička, J.; Kubát, Jiří

    2010-01-01

    Roč. 329, 1-2 (2010), s. 145-150 ISSN 0004-640X R&D Projects: GA ČR GA205/07/0031 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * winds * outflows Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.437, year: 2010

  6. Stellar Wind Retention and Expulsion in Massive Star Clusters

    Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

    2018-05-01

    Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

  7. DO HYDROGEN-DEFICIENT CARBON STARS HAVE WINDS?

    Geballe, T. R.; Rao, N. Kameswara; Clayton, Geoffrey C.

    2009-01-01

    We present high resolution spectra of the five known hydrogen-deficient carbon (HdC) stars in the vicinity of the 10830 A line of neutral helium. In R Coronae Borealis (RCB) stars the He I line is known to be strong and broad, often with a P Cygni profile, and must be formed in the powerful winds of those stars. RCB stars have similar chemical abundances as HdC stars and also share greatly enhanced 18 O abundances with them, indicating a common origin for these two classes of stars, which has been suggested to be white dwarf mergers. A narrow He I absorption line may be present in the hotter HdC stars, but no line is seen in the cooler stars, and no evidence for a wind is found in any of them. The presence of wind lines in the RCB stars is strongly correlated with dust formation episodes so the absence of wind lines in the HdC stars, which do not make dust, is as expected.

  8. Galactic Winds and the Role Played by Massive Stars

    Heckman, Timothy M.; Thompson, Todd A.

    Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

  9. Interactions between exoplanets and the winds of young stars

    Vidotto A. A.

    2014-01-01

    Full Text Available The topology of the magnetic field of young stars is important not only for the investigation of magnetospheric accretion, but also responsible in shaping the large-scale structure of stellar winds, which are crucial for regulating the rotation evolution of stars. Because winds of young stars are believed to have enhanced mass-loss rates compared to those of cool, main-sequence stars, the interaction of winds with newborn exoplanets might affect the early evolution of planetary systems. This interaction can also give rise to observational signatures which could be used as a way to detect young planets, while simultaneously probing for the presence of their still elusive magnetic fields. Here, we investigate the interaction between winds of young stars and hypothetical planets. For that, we model the stellar winds by means of 3D numerical magnetohydrodynamic simulations. Although these models adopt simplified topologies of the stellar magnetic field (dipolar fields that are misaligned with the rotation axis of the star, we show that asymmetric field topologies can lead to an enhancement of the stellar wind power, resulting not only in an enhancement of angular momentum losses, but also intensifying and rotationally modulating the wind interactions with exoplanets.

  10. Close-binary central stars of planetary nebulae

    Bond, H.E.; Grauer, A.D.

    1987-01-01

    Recent observations of PN central stars identified as binary systems are reviewed. The theoretical significance of binary central stars is discussed, and the characteristics of UU Sge, V 477 Lyr, MT Ser, LSS 2018, VW Pyx, and the central star of HFG 1 are briefly summarized. All of these binaries are shown to have periods less than 1 day, and it is estimated that about 10 percent of all binary central stars are close binaries. 27 references

  11. Theories for the winds from Wolf Rayet stars

    Cassinelli, J.P.

    1982-01-01

    The massive and fast winds of Wolf Rayet stars present a serious momentum problem for the line-driven wind theories that are commonly used to explain the fast winds of early type stars. It is perhaps possible for the winds to be driven by lines, if multiple scattering occurs and if there are a sufficient number of lines in the spectrum so that large fraction of the continuum is blocked by line opacity in the winds. Several other mechanisms are discussed, in particular two that rely on strong magnetic fields: a) Alfven wave driven wind models like those recently developed by Hartmann and MacGregor for late type supergiants and b) the ''Fast Magnetic Rotator'' model that was developed by Belcher and MacGregor for the winds from pre-main sequence stars. In either model, large magnetic fields (approximately equal to 10 4 gauss) are required to drive the massive and fast winds of Wolf Rayet stars. Smaller fields might be possible if the multiple scattering line radiation force can be relied on to provide a final acceleration to terminal velocity. (Auth.)

  12. Thermal radio emission from the winds of single stars

    Abbott, D.C.

    1985-01-01

    Observations of thermal emission at radio wavelengths provides a powerful diagnostic of the rate of mass loss and temperature of the winds of early-type stars. Some winds are also strong sources of nonthermal emission. Case studies of known thermal and nonthermal sources provide empirical criteria for classifying the observed radio radiation. Mass loss rates are derived for 37 OB and Wolf-Rayet stars considered definite or probable thermal wind sources by these criteria. The rate of mass loss is strongly linked to stellar luminosity in OB stars and probably linked to stellar mass in Wolf-Rayet stars, with no measurable correlation with any other stellar property. A few late-type giants and supergiants also have detectable thermal emission, which arises from extended, accelerating, partially-ionized chromospheres. (orig.)

  13. Stellar and wind parameters of massive stars from spectral analysis

    Araya, Ignacio; Curé, Michel

    2017-11-01

    The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

  14. Planetary nebulae and their central stars

    Kaler, J.B.

    1985-01-01

    The present review is devoted primarily to galactic planetaries, while Ford (1983) provides an extensive review of the rapidly expanding study of the extragalactic type. Nebular parameters and observations are discussed, taking into account discovery, distance, motion, structure, spectrophotometry, and nebular properties. It is pointed out that post-AGB, or prewhite dwarf, stars are not as well known as their nebular progeny. Of the fundamental data regarding the central stars, the magnitudes are particularly important. They are used for both temperature and luminosity determinations. Attention is also given to temperatures and luminosities, and the characteristics of the spectra. Questions concerning the evolutionary process are also explored and aspects of observed distribution and evolution are considered. 259 references

  15. IUE observations of variability in winds from hot stars

    Grady, C. A.; Snow, T. P., Jr.

    1981-01-01

    Observations of variability in stellar winds or envelopes provide an important probe of their dynamics. For this purpose a number of O, B, Be, and Wolf-Rayet stars were repeatedly observed with the IUE satellite in high resolution mode. In the course of analysis, instrumental and data handling effects were found to introduce spurious variability in many of the spectra. software was developed to partially compensate for these effects, but limitations remain on the type of variability that can be identified from IUE spectra. With these contraints, preliminary results of multiple observations of two OB stars, one Wolf-Rayet star, and a Be star are discussed.

  16. Wind bubbles within H ii regions around slowly moving stars

    Mackey, Jonathan; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert

    2015-01-01

    Interstellar bubbles around O stars are driven by a combination of the star's wind and ionizing radiation output. The wind contribution is uncertain because the boundary between the wind and interstellar medium is difficult to observe. Mid-infrared observations (e.g., of the H ii region RCW 120) show arcs of dust emission around O stars, contained well within the H ii region bubble. These arcs could indicate the edge of an asymmetric stellar wind bubble, distorted by density gradients and/or stellar motion. We present two-dimensional, radiation-hydrodynamics simulations investigating the evolution of wind bubbles and H ii regions around massive stars moving through a dense (nH = 3000 cm-3), uniform medium with velocities ranging from 4 to 16 km s-1. The H ii region morphology is strongly affected by stellar motion, as expected, but the wind bubble is also very aspherical from birth, even for the lowest space velocity considered. Wind bubbles do not fill their H ii regions (we find filling factors of 10-20 per cent), at least for a main sequence star with mass M⋆ ~ 30 M⊙. Furthermore, even for supersonic velocities the wind bow shock does not significantly trap the ionization front. X-ray emission from the wind bubble is soft, faint, and comes mainly from the turbulent mixing layer between the wind bubble and the H ii region. The wind bubble radiates <1 per cent of its energy in X-rays; it loses most of its energy by turbulent mixing with cooler photoionized gas. Comparison of the simulations with the H ii region RCW 120 shows that its dynamical age is ≲0.4 Myr and that stellar motion ≲4 km s-1 is allowed, implying that the ionizing source is unlikely to be a runaway star but more likely formed in situ. The region's youth, and apparent isolation from other O or B stars, makes it very interesting for studies of massive star formation and of initial mass functions. Movies are available in electronic form at http://www.aanda.org

  17. Modeling pulsations in hot stars with winds

    Noels, Arlette; Godart, Melanie [Institut d' Astrophysique et de Geophysique, Liege (Belgium); Dupret, Marc-Antoine [Observatoire de Paris-Meudon, LESIA (France)], E-mail: Arlette.Noels@ulg.ac.be, E-mail: ma.dupret@obspm.fr, E-mail: Melanie.Godart@ulg.ac.be

    2008-10-15

    The interaction pulsation/mass loss takes different aspects. Pulsations can trigger mass loss as in LBVs and Miras; on the other hand, mass loss can modify the driving conditions within the stars. But the most spectacular aspect is the effect on stellar models which, in turn, opens a royal way to asteroseismology to test physical conditions inside massive stars, such as the extent of convective cores or the appearance of new driving mechanisms. We start with a discussion on MS stars and their strange mode instabilities. We then move on to the excitation of the LBV phenomenon. WR stars and the newly observed MOST period in WR123 are discussed in view of the power of asteroseismology. We then turn to B supergiants, in particular HD163899, and show how asteroseismology can really probe convection, semiconvection and mass loss.

  18. Modeling pulsations in hot stars with winds

    Noels, Arlette; Godart, Melanie; Dupret, Marc-Antoine

    2008-01-01

    The interaction pulsation/mass loss takes different aspects. Pulsations can trigger mass loss as in LBVs and Miras; on the other hand, mass loss can modify the driving conditions within the stars. But the most spectacular aspect is the effect on stellar models which, in turn, opens a royal way to asteroseismology to test physical conditions inside massive stars, such as the extent of convective cores or the appearance of new driving mechanisms. We start with a discussion on MS stars and their strange mode instabilities. We then move on to the excitation of the LBV phenomenon. WR stars and the newly observed MOST period in WR123 are discussed in view of the power of asteroseismology. We then turn to B supergiants, in particular HD163899, and show how asteroseismology can really probe convection, semiconvection and mass loss.

  19. Wind speed forecasting in the central California wind resource area

    McCarthy, E.F. [Wind Economics & Technology, Inc., Martinez, CA (United States)

    1997-12-31

    A wind speed forecasting program was implemented in the summer seasons of 1985 - 87 in the Central California Wind Resource Area (WRA). The forecasting program is designed to use either meteorological observations from the WRA and local upper air observations or upper air observations alone to predict the daily average windspeed at two locations. Forecasts are made each morning at 6 AM and are valid for a 24 hour period. Ease of use is a hallmark of the program as the daily forecast can be made using data entered into a programmable HP calculator. The forecasting program was the first step in a process to examine whether the electrical energy output of an entire wind power generation facility or defined subsections of the same facility could be predicted up to 24 hours in advance. Analysis of the results of the summer season program using standard forecast verification techniques show the program has skill over persistence and climatology.

  20. Polarized bow shocks reveal features of the winds and environments of massive stars

    Shrestha, Manisha

    2018-01-01

    Massive stars strongly affect their surroundings through their energetic stellar winds and deaths as supernovae. The bow shock structures created by fast-moving massive stars contain important information about the winds and ultimate fates of these stars as well as their local interstellar medium (ISM). Since bow shocks are aspherical, the light scattered in the dense shock material becomes polarized. Analyzing this polarization reveals details of the bow shock geometry as well as the composition, velocity, density, and albedo of the scattering material. With these quantities, we can constrain the properties of the stellar wind and thus the evolutionary state of the star, as well as the dust composition of the local ISM.In my dissertation research, I use a Monte Carlo radiative transfer code that I optimized to simulate the polarization signatures produced by both resolved and unresolved stellar wind bow shocks (SWBS) illuminated by a central star and by shock emission. I derive bow shock shapes and densities from published analytical calculations and smooth particle hydrodynamic (SPH) models. In the case of the analytical SWBS and electron scattering, I find that higher optical depths produce higher polarization and position angle rotations at specific viewing angles compared to theoretical predictions for low optical depths. This is due to the geometrical properties of the bow shock combined with multiple scattering effects. For dust scattering, the polarization signature is strongly affected by wavelength, dust grain properties, and viewing angle. The behavior of the polarization as a function of wavelength in these cases can distinguish among different dust models for the local ISM. In the case of SPH density structures, I investigate how the polarization changes as a function of the evolutionary phase of the SWBS. My dissertation compares these simulations with polarization data from Betelgeuse and other massive stars with bow shocks. I discuss the

  1. Massive stars in colliding wind systems: the GLAST perspective

    Reimer, Anita; Reimer, Olaf

    2007-01-01

    Colliding winds of massive stars in binary systems arc considered as candidate sites of high-energy non-thermal photon emission. They are already among the suggested counterparts for a few individual unidentified EGRET sources, but may constitute a detectable source population for the GLAST observatory.The present work investigates such population study of massive colliding wind systems at high-energy gamma-rays. Based on the recent detailed model (Reimer et al. 2006) for non-thermal photon production in prime candidate systems, we unveil the expected characteristics of this source class in the observables accessible at LAT energies. Combining the broadband emission model with the presently cataloged distribution of such systems and their individual parameters allows us to conclude on the expected maximum number of LAT-detections among massive stars in colliding wind binary systems

  2. Winds of Massive Magnetic Stars: Interacting Fields and Flow

    Daley-Yates, S.; Stevens, I. R.

    2018-01-01

    We present results of 3D numerical simulations of magnetically confined, radiatively driven stellar winds of massive stars, conducted using the astrophysical MHD code Pluto, with a focus on understanding the rotational variability of radio and sub-mm emission. Radiative driving is implemented according to the Castor, Abbott and Klein theory of radiatively driven winds. Many magnetic massive stars posses a magnetic axis which is inclined with respect to the rotational axis. This misalignment leads to a complex wind structure as magnetic confinement, centrifugal acceleration and radiative driving act to channel the circumstellar plasma into a warped disk whose observable properties should be apparent in multiple wavelengths. This structure is analysed to calculate free-free thermal radio emission and determine the characteristic intensity maps and radio light curves.

  3. Comoving frame models of hot star winds II. Reduction of O star wind mass-loss rates in global models

    Krtička, J.; Kubát, Jiří

    2017-01-01

    Roč. 606, October (2017), A31/1-A31/12 E-ISSN 1432-0746 R&D Projects: GA ČR GA13-10589S Institutional support: RVO:67985815 Keywords : stars * winds * outflows Subject RIV: BN - Astronomy , Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.014, year: 2016

  4. EVOLUTION OF SUPER STAR CLUSTER WINDS WITH STRONG COOLING

    Wuensch, Richard; Palous, Jan; Silich, Sergiy; Tenorio-Tagle, Guillermo; Munoz-Tunon, Casiana

    2011-01-01

    We study the evolution of super star cluster winds driven by stellar winds and supernova explosions. Time-dependent rates at which mass and energy are deposited into the cluster volume, as well as the time-dependent chemical composition of the re-inserted gas, are obtained from the population synthesis code Starburst99. These results are used as input for a semi-analytic code which determines the hydrodynamic properties of the cluster wind as a function of cluster age. Two types of winds are detected in the calculations. For the quasi-adiabatic solution, all of the inserted gas leaves the cluster in the form of a stationary wind. For the bimodal solution, some of the inserted gas becomes thermally unstable and forms dense warm clumps which accumulate inside the cluster. We calculate the evolution of the wind velocity and energy flux and integrate the amount of accumulated mass for clusters of different mass, radius, and initial metallicity. We also consider conditions with low heating efficiency of the re-inserted gas or mass loading of the hot thermalized plasma with the gas left over from star formation. We find that the bimodal regime and the related mass accumulation occur if at least one of the two conditions above is fulfilled.

  5. Nonspherical Radiation Driven Wind Models Applied to Be Stars

    Arauxo, F. X.

    1990-11-01

    ABSTRACT. In this work we present a model for the structure of a radiatively driven wind in the meridional plane of a hot star. Rotation effects and simulation of viscous forces were included in the motion equations. The line radiation force is considered with the inclusion of the finite disk correction in self-consistent computations which also contain gravity darkening as well as distortion of the star by rotation. An application to a typical BlV star leads to mass-flux ratios between equator and pole of the order of 10 and mass loss rates in the range 5.l0 to Mo/yr. Our envelope models are flattened towards the equator and the wind terminal velocities in that region are rather high (1000 Km/s). However, in the region near the star the equatorial velocity field is dominated by rotation. RESUMEN. Se presenta un modelo de la estructura de un viento empujado radiativamente en el plano meridional de una estrella caliente. Se incluyeron en las ecuaciones de movimiento los efectos de rotaci6n y la simulaci6n de fuerzas viscosas. Se consider6 la fuerza de las lineas de radiaci6n incluyendo la correcci6n de disco finito en calculos autoconsistentes los cuales incluyen oscurecimiento gravitacional asi como distorsi6n de la estrella por rotaci6n. La aplicaci6n a una estrella tipica BlV lleva a cocientes de flujo de masa entre el ecuador y el polo del orden de 10 de perdida de masa en el intervalo 5.l0 a 10 Mo/ano. Nuestros modelos de envolvente estan achatados hacia el ecuador y las velocidads terminales del viento en esa regi6n son bastante altas (1000 Km/s). Sin embargo, en la regi6n cercana a la estrella el campo de velocidad ecuatorial esta dominado por la rotaci6n. Key words: STARS-BE -- STARS-WINDS

  6. Wind Shear Characteristics at Central Plains Tall Towers (presentation)

    Schwartz, M.; Elliott, D.

    2006-06-05

    The objectives of this report are: (1) Analyze wind shear characteristics at tall tower sites for diverse areas in the central plains (Texas to North Dakota)--Turbines hub heights are now 70-100 m above ground and Wind measurements at 70-100+ m have been rare. (2) Present conclusions about wind shear characteristics for prime wind energy development regions.

  7. The central star of the Planetary Nebula NGC 6537

    Pottasch, [No Value

    2000-01-01

    The fact that Space Telescope WFPC2 images of the planetary nebula NGC 6537 fail to show the central star is used to derive a limit to its magnitude: it is fainter than a magnitude of 22.4 in the visible. This is used to derive a lower limit to the temperature of the star. The Zanstra temperature is

  8. Model atmospheres and parameters of central stars of planetary nebulae

    Patriarchi, P.; Cerruti-sola, M.; Perinotto, M.

    1989-01-01

    Non-LTE hydrogen and helium model atmospheres have been obtained for temperatures and gravities relevant to the central stars of planetary nebulae. Low-resolution and high-resolution observations obtained by the IUE satellite have been used along with optical data to determine Zanstra temperatures of the central stars of NGC 1535, NGC 6210, NGC 7009, IC 418, and IC 4593. Comparison of the observed stellar continuum of these stars with theoretical results allowed further information on the stellar temperature to be derived. The final temperatures are used to calculate accurate stellar parameters. 62 refs

  9. Star Formation-Driven Winds in the Early Universe

    Peek, Matthew; Lundgren, Britt; Brammer, Gabriel

    2018-01-01

    Measuring the extent of star formation-driven winds from galaxies in the early universe is crucial for understanding of how galaxies evolve over cosmic time. Using WFC3/IR grism data from the Hubble Space Telescope (HST), we have measured the star formation rates and star formation rate surface densities of several hundred galaxies at redshift (z) = 1, when the universe was roughly half its present age. The galaxies we examine are also probed by background quasars, whose spectra provide information about the extent of metal-enriched gas in their halos. We use a computational pipeline to measure the density of the star formation in each galaxy and correlate these measurements with detections of Mg II absorption in nearby quasar spectra from the Sloan Digital Sky Survey. Our preliminary results support a model in which galaxies with high SFR surface densities drive metal-enriched gas out of the disk and into these galaxies’ extended halos, where that gas is detected in the spectra of more distant quasars.

  10. The origin of carbon revisited: winds of carbon-stars

    Mattsson, L

    2008-01-01

    Chemical evolution models, differing in the nucleosynthesis prescriptions (yields) for carbon, nitrogen and oxygen, have been computed for the Milky Way and Andromeda (NGC 224). All models fit the observed O/H gradients well and reproduce the main characteristics of the gas distributions, but they are also designed to do so. The N/O gradient for NGC 224 cannot be reproduced without ad hoc modifications to the yields and a similar result is obtained for the Milky Way N/O gradient, although in the latter case the slopes of the gradients obtained with unmodified yields are consistent with the observed gradient. For the C/O gradients (obtained from B stars) the results are inconclusive. The C/Fe, N/Fe, O/Fe versus Fe/H, as well as C/O versus O/H trends predicted by the models for the solar neighbourhood were compared with stellar abundances from the literature. For O/Fe versus Fe/H, all models fit the data, but for C/Fe, N/Fe versus Fe/H and C/O versus O/H, only modified sets of yields provide good fits. Since in the best-fit model, the yields were modified such that carbon should be primarily produced in low-mass stars, it is quite possible that in every environment where the peak of star formation happened a few Gyr back in time, the winds of carbon stars are responsible for most of the carbon enrichment, although models with a significant contribution from high-mass stars cannot be ruled out. In the solar neighbourhood, almost two-thirds of the carbon in the interstellar medium may come from carbon stars. Finally, the challenges met by stellar evolution and nucleosynthesis modelling due to this 'carbon star hypothesis' for the origin of carbon are discussed. It is suggested that a mass-loss prescription where the mass-loss rate depends on the carbon excess may act as a self-regulating mechanism for how much carbon a carbon star can deliver to the interstellar medium.

  11. Central Stars of Planetary Nebulae in the SMC

    Bianchi, Luciana

    2004-01-01

    In FUSE cycle 3's program C056 we studied four Central Stars of Planetary Nebulae (CSPN) in the Small Magellanic Could. All FUSE observations have been successfully completed and have been reduced and analyzed. The observation of one object (SMP SMC 5) appeared to be off-target and no useful stellar flux was gathered. For another observation (SMP SMC 1) the voltage problems resulted in the loss of data from one of the SiC detectors, but we were still able to analyze the remaining data. The analysis and the results are summarized below. The FUSE data were reduced using the latest available version of the FUSE calibration pipeline (CALFUSE v2.4). The flux of these SMC post-AGB objects is at the threshold of FUSE S sensitivity, and the targets required many orbit-long exposures, each of which typically had low (target) count-rates. The background subtraction required special care during the reduction, and was done in a similar manner to our FUSE cycle 2 BOO1 objects. The resulting calibrated data from the different channels were compared in the overlapping regions for consistency. The final combined, extracted spectra of each target was then modeled to determine the stellar and nebular parameters. The FUSE spectra, combined with archival HST spectra, have been analyzed using stellar atmospheres codes such as TLUSTY and CMFGEN to derive photospheric and wind parameters of the central stars, and with ISM models to determine the amount and temperature of the surrounding atomic and molecular hydrogen. We have combined these results with those of our cycle 4 (D034) program (CSPN of the LMC) in Herald & Bianchi 2004a (paper in preparation, will be submitted to ApJ in June 2004). Two of the three SMC objects analyzed were found to have significantly lower stellar temperatures than had been predicted using nebular photoionization models, indicating either a hotter ionizing companion or the existence of strong shocks in the nebular environment. The analysis also revealed that

  12. Centralized electricity generation in offshore wind farms using hydraulic networks

    Jarquin Laguna, A.

    2017-01-01

    The work presented in this thesis explores a new way of generation, collection and transmission of wind energy inside a wind farm, in which the electrical conversion does not occur during any intermediate conversion step before the energy has reached the offshore central platform. A centralized

  13. Central stars of planetary nebulae: New spectral classifications and catalogue

    Weidmann, W. A.; Gamen, R.

    2011-02-01

    Context. There are more than 3000 confirmed and probable known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims: We undertook a spectroscopic survey of central stars of PNe at low resolution and compiled a large list of central stars for which information was dispersed in the literature. Methods: We observed 45 PNs using the 2.15 m telescope at Casleo, Argentina. Results: We present a catalogue of 492 confirmed and probable CSPN and provide a preliminary spectral classification for 45 central star of PNe. This revises previous values of the proportion of CSPN with atmospheres poor in hydrogen in at least 30% of cases and provide statistical information that allows us to infer the origin of H-poor stars. Based on data collected at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina.

  14. Atomic Physics of Shocked Plasma in Winds of Massive Stars

    Leutenegger, Maurice A.; Cohen, David H.; Owocki, Stanley P.

    2012-01-01

    High resolution diffraction grating spectra of X-ray emission from massive stars obtained with Chandra and XMM-Newton have revolutionized our understanding of their powerful, radiation-driven winds. Emission line shapes and line ratios provide diagnostics on a number of key wind parameters. Modeling of resolved emission line velocity profiles allows us to derive independent constraints on stellar mass-loss rates, leading to downward revisions of a factor of a few from previous measurements. Line ratios in He-like ions strongly constrain the spatial distribution of Xray emitting plasma, confirming the expectations of radiation hydrodynamic simulations that X-ray emission begins moderately close to the stellar surface and extends throughout the wind. Some outstanding questions remain, including the possibility of large optical depths in resonance lines, which is hinted at by differences in line shapes of resonance and intercombination lines from the same ion. Resonance scattering leads to nontrivial radiative transfer effects, and modeling it allows us to place constraints on shock size, density, and velocity structure

  15. Peculiar early-type galaxies with central star formation

    Ge Chong; Gu Qiusheng

    2012-01-01

    Early-type galaxies (ETGs) are very important for understanding the formation and evolution of galaxies. Recent observations suggest that ETGs are not simply old stellar spheroids as we previously thought. Widespread recent star formation, cool gas and dust have been detected in a substantial fraction of ETGs. We make use of the radial profiles of g — r color and the concentration index from the Sloan Digital Sky Survey database to pick out 31 peculiar ETGs with central blue cores. By analyzing the photometric and spectroscopic data, we suggest that the blue cores are caused by star formation activities rather than the central weak active galactic nucleus. From the results of stellar population synthesis, we find that the stellar population of the blue cores is relatively young, spreading from several Myr to less than one Gyr. In 14 galaxies with H I observations, we find that the average gas fraction of these galaxies is about 0.55. The bluer galaxies show a higher gas fraction, and the total star formation rate (SFR) correlates very well with the H I gas mass. The star formation history of these ETGs is affected by the environment, e.g. in the denser environment the H I gas is less and the total SFR is lower. We also discuss the origin of the central star formation of these early-type galaxies.

  16. On the evolution of central stars of planetary nebulae

    Yahel, R.Z.

    1977-01-01

    The evolution of nuclei of planetary nebulae has been calculated from the end of the ejection stage that produces the nebulae to the white dwarf stage. The structure of the central star is in agreement with the general picture of Finzi (1973) about the mass ejection from the progenitors of planetary nebulae. It has been found that in order to obtain evolutionary track consistent with the Harman-Seaton track (O'Dell, 1968) one has to assume that the masses of the nuclei stars are less than approximately 0.7 solar masses. The calculated evolutionary time scale of the central stars of planetary nebulae is approximately 2 x 10 4 yr. This time scale is negatively correlated with the stellar mass: the heavier the stellar mass, the shorter the evolutionary time scale. (Auth.)

  17. Ages of evolved low mass stars: Central stars of planetary nebulae and white dwarfs

    Costa R.D.D.

    2013-03-01

    Full Text Available We have developed several methods to estimate the ages of central stars of planetary nebulae (CSPN, which are based either on observed nebular properties or on data from the stars themselves. Our goal is to derive the age distribution of these stars and compare the results with empirical distributions for CSPN and white dwarfs. We have initially developed three methods based on nebular abundances, using (i an age-metallicity relation which is also a function of the galactocentric distance; (ii an age-metallicity relation obtained for the galactic disk, and (iii the central star masses derived from the observed nitrogen abundances. In this work we present two new, more accurate methods, which are based on kinematic properties: (I in this method, the expected rotation velocities of the nebulae around the galactic centre at their galactocentric distances are compared with the predicted values for the galactic rotation curve, and the differences are attributed to the different ages of the evolved stars; (II we determine directly the U, V, W, velocity components of the stars, as well as the velocity dispersions, and use the dispersion-age relation by the Geneva-Copenhagen survey. These methods were applied to two large samples of galactic CSPN. We conclude that most CSPN in the galactic disk have ages under 5 Gyr, and that the age distribution is peaked around 1 to 3 Gyr.

  18. Design of the pancake-winding central solenoid coil

    Yoshida, Kiyoshi; Nishi, Masataka; Tsuji, Hirosi

    1995-01-01

    There was a debate over whether a pancake-winding or layer-winding technique is more appropriate for the Central Solenoid (CS) coil for ITER superconducting magnet. The layer-winding CS has the advantage of homogeneous winding supporting the TF centering force without weak joints, but has many difficulties during manufacturing and quality control. On other hand, the pancake-winding has the advantage of better quality control during manufacturing and module testing but has difficulties with joints and feeders, and pipes located in the load path of the bucking force from the toroidal field coils. The compact joints, reinforcement by preformed amour, sharp bending, and double seals are applied to the design of pancake-winding CS coil and demonstrated by hardware developments. The pancake-winding CS coil by using modified existing technology is compatible with the bucking concept of the ITER magnet system. (author)

  19. Suppressing star formation in quiescent galaxies with supermassive black hole winds.

    Cheung, Edmond; Bundy, Kevin; Cappellari, Michele; Peirani, Sébastien; Rujopakarn, Wiphu; Westfall, Kyle; Yan, Renbin; Bershady, Matthew; Greene, Jenny E; Heckman, Timothy M; Drory, Niv; Law, David R; Masters, Karen L; Thomas, Daniel; Wake, David A; Weijmans, Anne-Marie; Rubin, Kate; Belfiore, Francesco; Vulcani, Benedetta; Chen, Yan-mei; Zhang, Kai; Gelfand, Joseph D; Bizyaev, Dmitry; Roman-Lopes, A; Schneider, Donald P

    2016-05-26

    Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 10(10) times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1-4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 10(10) times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy's low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

  20. Wind Climate Analyses for SRTC's Central Climatology Site

    Weber, A.H.

    2003-01-01

    This report was written to present climatological summaries of the wind data at the Central Climatology (CC) tower in a convenient format and to point out some features of the wind speed and direction that have not been widely appreciated in the past. Short-term (two-week) wind roses provide a means to demonstrate the temporal and spatial relationships that wind speed and direction undergo using a ten-year database from the CC tower. These relationships are best demonstrated by examining the figures provided in this report or looking at loops of computer-generated images provided by the authors

  1. Star clusters containing massive, central black holes: evolution calculations

    Marchant, A.B.

    1980-01-01

    This dissertation presents a detailed, two-dimensional simulations of star cluster evolution. A Monte-Carlo method is adapted to simulate the development with time of isolated star clusters. Clusters which evolve on relaxation timescales with and without central black holes are treated. The method is flexible and rugged, rather than highly accurate. It treats the boundary conditions of stellar evaporation and tidal disruption by a central black hole in a precise, stochastic fashion. Dynamical cloning and renormalization and the use of a time-step adjustment algorithm enhance the feasibility of the method which simulates systems with wide ranges of intrinsic length and time scales. First, the method is applied to follow the development and core collapse of an initial Plummer-model cluster without a central black hole. Agreement of these results for early times with the results of previous authors serves as a verification of this method. Three calculations of cluster re-expansion, each beginning with the insertion of a black hole at the center of a highly collapsed cluster core is presented. Each case is characterized by a different value of initial black hole mass or black hole accretion efficiency for the consumption of debris from disrupted stars. It is found that for the special cases examined here substantial, but not catastrophic, growth of the central black hole may accompany core re-expansion. Also, the observability of the evolutionary phases associated with core collapse and re-expansion, constraints on x-ray sources which could be associated with growing black holes, and the observable signature of the cusp of stars surrounding a central black hole are discussed

  2. Identification of faint central stars in extended, low-surface-brightness planetary nebulae

    Kwitter, K.B.; Lydon, T.J.; Jacoby, G.H.

    1988-01-01

    As part of a larger program to study the properties of planetary nebula central stars, a search for faint central stars in extended, low-surface-brightness planetary nebulae using CCD imaging is performed. Of 25 target nebulae, central star candidates have been identified in 17, with certainties ranging from extremely probable to possible. Observed V values in the central star candidates extend to fainter than 23 mag. The identifications are presented along with the resulting photometric measurements. 24 references

  3. Hydrogen-deficient Central Stars of Planetary Nebulae

    Todt, H.; Kniazev, A. Y.; Gvaramadze, V. V.; Hamann, W.-R.; Pena, M.; Graefener, G.; Buckley, D.; Crause, L.; Crawford, S. M.; Gulbis, A. A. S.; Hettlage, C.; Hooper, E.; Husser, T.-O.; Kotze, P.; Loaring, N.; Nordsieck, K. H.; O'Donoghue, D.; Pickering, T.; Potter, S.; Romero-Colmenero, E.; Vaisanen, P.; Williams, T.; Wolf, M.

    2015-06-01

    A significant number of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient and are considered as the progenitors of H-deficient white dwarfs. Almost all of these H-deficient CSPNe show a chemical composition of helium, carbon, and oxygen. Most of them exhibit Wolf-Rayet-like emission line spectra and are therefore classified as of spectral type [WC]. In the last years, CSPNe of other Wolf-Rayet spectral subtypes have been identified, namely PB 8 (spectral type [WN/WC]), IC 4663 and Abell 48 (spectral type [WN]). We performed spectral analyses for a number of Wolf-Rayet type central stars of different evolutionary stages with the help of our Potsdam Wolf-Rayet (PoWR) model code for expanding atmospheres to determine relevant stellar parameters. The results of our recent analyses will be presented in the context of stellar evolution and white dwarf formation. Especially the problems of a uniform evolutionary channel for [WC] stars as well as constraints to the formation of [WN] or [WN/WC] subtype stars will be addressed.

  4. Wind energy resource atlas. Volume 7. The south central region

    Edwards, R.L.; Graves, L.F.; Sprankle, A.C.; Elliott, D.L.; Barchet, W.R.; George, R.L.

    1981-03-01

    This atlas of the south central region combines seven collections of wind resource data: one for the region, and one for each of the six states (Arkansas, Kansas, Louisiana, Missouri, Oklahoma, and Texas). At the state level, features of the climate, topography, and wind resource are discussed in greater detail than that provided in the regional discussion, and the data locations on which the assessment is based are mapped. Variations, over several time scales, in the wind resource at selected stations in each state are shown on graphs of monthly average and interannual wind speed and power, and hourly average wind speed for each season. Other graphs present speed, direction, and duration frequencies of the wind at these locations.

  5. Central stars of planetary nebulae. II. New OB-type and emission-line stars

    Weidmann, W. A.; Gamen, R.

    2011-07-01

    Context. There are more than 3000 confirmed and probably known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims: We have undertaken a spectroscopic survey of the central stars in PNe to identify their spectral types. Methods: We performed spectroscopic observations at low resolution with the 2-m telescope at CASLEO, Argentina. Results: We present the spectra of 46 central stars of PNe, most of them are OB-type and emission-line stars. Based on data collected at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina.The reduced spectra (FITS files) are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A172

  6. Probing the extreme wind confinement of the most magnetic O star with COS spectroscopy

    Petit, Veronique

    2014-10-01

    We propose to obtain phase-resolved UV spectroscopy of the recently discovered magnetic O star NGC 1624-2, which has the strongest magnetic field ever detected in a O-star, by an order of magnitude. We will use the strength and variability of the UV resonance line profiles to diagnose the density, velocity, and ionization structure of NGC 1624-2's enormous magnetosphere that results from entrapment of its stellar wind by its strong, nearly dipolar magnetic field. With this gigantic magnetosphere, NGC 1624-2 represents a new regime of extreme wind confinement that will constrain models of magnetized winds and their surface mass flux properties. A detailed understanding of such winds is necessary to study the rotational braking history of magnetic O-stars, which can shed new light on the fundamental origin of magnetism in massive, hot stars.

  7. Star Formation in the Central Regions of Galaxies

    Tsai, Mengchun

    2015-08-01

    The galactic central region connects the galactic nucleus to the host galaxy. If the central black hole co-evolved with the host galaxies, there should be some evidence left in the central region. We use the environmental properties in the central regions such as star-forming activity, stellar population and molecular abundance to figure out a possible scenario of the evolution of galaxies. In this thesis at first we investigated the properties of the central regions in the host galaxies of active and normal galaxies. We used radio emission around the nuclei of the host galaxies to represent activity of active galactic nuclei (AGNs), and used infrared ray (IR) emission to represent the star-forming activity and stellar population of the host galaxies. We determined that active galaxies have higher stellar masses (SMs) within the central kiloparsec radius than normal galaxies do independent of the Hubble types of the host galaxies; but both active and normal galaxies exhibit similar specific star formation rates (SSFRs). We also discovered that certain AGNs exhibit substantial inner stellar structures in the IR images; most of the AGNs with inner structures are Seyferts, whereas only a few LINERs exhibit inner structures. We note that the AGNs with inner structures show a positive correlation between the radio activity of the AGNs and the SFRs of the host galaxies, but the sources without inner structures show a negative correlation between the radio power and the SFRs. These results might be explained with a scenario of starburst-AGN evolution. In this scenario, AGN activities are triggered following a nuclear starburst; during the evolution, AGN activities are accompanied by SF activity in the inner regions of the host galaxies; at the final stage of the evolution, the AGNs might transform into LINERs, exhibiting weak SF activity in the central regions of the host galaxies. For further investigation about the inner structure, we choose the most nearby and luminous

  8. Dusty disks around central stars of planetary nebulae

    Clayton, Geoffrey C. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); De Marco, Orsola [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Nordhaus, Jason [Center for Computational Relativity and Gravitation, and National Technical Institute for the Deaf, Rochester Institute of Technology, Rochester, NY 14623 (United States); Green, Joel [Department of Astronomy, The University of Texas, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Rauch, Thomas; Werner, Klaus [Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, D-72076 Tübingen (Germany); Chu, You-Hua, E-mail: gclayton@fenway.phys.lsu.edu, E-mail: orsola@science.mq.edu.au, E-mail: nordhaus@astro.rit.edu, E-mail: joel@astro.as.utexas.edu, E-mail: rauch@astro.uni-tuebingen.de, E-mail: werner@astro.uni-tuebingen.de, E-mail: chu@astro.uiuc.edu [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)

    2014-06-01

    Only a few percent of cool, old white dwarfs (WDs) have infrared excesses interpreted as originating in small hot disks due to the infall and destruction of single asteroids that come within the star's Roche limit. Infrared excesses at 24 μm were also found to derive from the immediate vicinity of younger, hot WDs, most of which are still central stars of planetary nebulae (CSPNe). The incidence of CSPNe with this excess is 18%. The Helix CSPN, with a 24 μm excess, has been suggested to have a disk formed from collisions of Kuiper belt-like objects (KBOs). In this paper, we have analyzed an additional sample of CSPNe to look for similar infrared excesses. These CSPNe are all members of the PG 1159 class and were chosen because their immediate progenitors are known to often have dusty environments consistent with large dusty disks. We find that, overall, PG 1159 stars do not present such disks more often than other CSPNe, although the statistics (five objects) are poor. We then consider the entire sample of CSPNe with infrared excesses and compare it to the infrared properties of old WDs, as well as cooler post-asymptotic giant branch (AGB) stars. We conclude with the suggestion that the infrared properties of CSPNe more plausibly derive from AGB-formed disks rather than disks formed via the collision of KBOs, although the latter scenario cannot be ruled out. Finally, there seems to be an association between CSPNe with a 24 μm excess and confirmed or possible binarity of the central star.

  9. Five-Phase Five-Level Open-Winding/Star-Winding Inverter Drive for Low-Voltage/High-Current Applications

    Padmanaban, Sanjeevi Kumar; Blaabjerg, Frede; Wheeler, Patrick

    2016-01-01

    This paper work proposed a five-phase five-level open-/star-winding multilevel AC converter suitable for low-voltage/high-current applications. Modular converter consists of classical two-level five-phase voltage source inverter (VSI) with slight reconfiguration to serve as a multilevel converter...... for open-/star-winding loads. Elaborately, per phase of the VSI is built with one additional bi-directional switch (MOSFET/IGBT) and all five legs links to the neutral through two capacitors. The structure allows multilevel generation to five-level output with greater potential for fault tolerability under...

  10. Episodic mass loss from the hydrogen-deficient central star of the planetary nebula Longmore 4

    Bond, Howard E., E-mail: heb11@psu.edu [Current address: Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA. (United States)

    2014-09-01

    A spectacular transient mass-loss episode from the extremely hot, hydrogen-deficient central star of the planetary nebula (PN) Longmore 4 (Lo 4) was discovered in 1992 by Werner et al. During that event, the star temporarily changed from its normal PG 1159 spectrum to that of an emission-line low-luminosity early-type Wolf-Rayet [WCE] star. After a few days, Lo 4 reverted to its normal, predominantly absorption-line PG 1159 type. To determine whether such events recur, and if so how often, I monitored the optical spectrum of Lo 4 from early 2003 to early 2012. Out of 81 spectra taken at random dates, 4 of them revealed mass-loss outbursts similar to that seen in 1992. This indicates that the episodes recur approximately every 100 days (if the recurrence rate has been approximately constant and the duration of a typical episode is ∼5 days), and that the star is in a high-mass-loss state about 5% of the time. Since the enhanced stellar wind is hydrogen-deficient, it arises from the photosphere and is unlikely to be related to phenomena such as a binary or planetary companion or infalling dust. I speculate on plausible mechanisms for these unique outbursts, including the possibility that they are related to the non-radial GW Vir-type pulsations exhibited by Lo 4. The central star of the PN NGC 246 has stellar parameters similar to those of Lo 4, and it is also a GW Vir-type pulsator with similar pulsation periods. I obtained 167 spectra of NGC 246 between 2003 and 2011, but no mass ejections were found.

  11. The emerging planetary nebula CRL 618 and its unsettled central star(s)

    Balick, B. [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Riera, A. [Departament de Física I Enginyeria Nuclear, EUETIB, Universitat Politècnica de Catalunya, Comte d' Urgell 187, E-08036 Barcelona (Spain); Raga, A.; Velázquez, P. F. [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510 D.F. (Mexico); Kwitter, K. B., E-mail: balick@uw.edu, E-mail: angels.riera@upc.edu, E-mail: raga@nucleares.unam.mx, E-mail: pablo@nucleares.unam.mx, E-mail: kkwitter@williams.edu [Department of Astronomy, Williams College, Williamstown, MA 01267 (United States)

    2014-11-01

    We report deep long-slit emission-line spectra, the line flux ratios, and Doppler profile shapes of various bright optical lines. The low-ionization lines (primarily [N I], [O I], [S II], and [N II]) originate in shocked knots, as reported by many previous observers. Dust-scattered lines of higher ionization are seen throughout the lobes but do not peak in the knots. Our analysis of these line profiles and the readily discernible stellar continuum shows that (1) the central star is an active symbiotic (whose spectrum resembles the central stars of highly bipolar and young planetary nebulae such as M2-9 and Hen2-437) whose compact companion shows a WC8-type spectrum, (2) extended nebular lines of [O III] and He I originate in the heavily obscured nuclear H II region, and (3) the Balmer lines observed throughout the lobes are dominated by reflected Hα emission from the symbiotic star. Comparing our line ratios with those observed historically shows that (1) the [O III]/Hβ and He I/Hβ ratios have been steadily rising by large amounts throughout the nebula, (2) the Hα/Hβ ratio is steadily decreasing while Hγ/Hβ remains nearly constant, and (3) the low-ionization line ratios formed in the shocked knots have been in decline in different ways at various locations. We show that the first two of these results might be expected if the symbiotic central star has been active and if its bright Hα line has faded significantly in the past 20 years.

  12. Assessment of Wind Datasets for Estimating Offshore Wind Energy along the Central California Coast

    Wang, Y. H.; Walter, R. K.; Ruttenberg, B.; White, C.

    2017-12-01

    Offshore renewable energy along the central California coastline has gained significant interest in recent years. We present a comprehensive analysis of near-surface wind datasets available in this region to facilitate future estimates of wind power generation potential. The analyses are based on local NDBC buoys, satellite-based measurements (QuickSCAT and CCMP V2.0), reanalysis products (NARR and MERRA), and a regional climate model (WRF). There are substantial differences in the diurnal signal during different months among the various products (i.e., satellite-based, reanalysis, and modeled) relative to the local buoys. Moreover, the datasets tended to underestimate wind speed under light wind conditions and overestimate under strong wind conditions. In addition to point-to-point comparisons against local buoys, the spatial variations of bias and error in both the reanalysis products and WRF model data in this region were compared against satellite-based measurements. NARR's bias and root-mean-square-error were generally small in the study domain and decreased with distance from coastlines. Although its smaller spatial resolution is likely to be insufficient to reveal local effects, the small bias and error in near-surface winds, as well as the availability of wind data at the proposed turbine hub heights, suggests that NARR is an ideal candidate for use in offshore wind energy production estimates along the central California coast. The framework utilized here could be applied in other site-specific regions where offshore renewable energy is being considered.

  13. The distribution of stars around the Milky Way's central black hole. I. Deep star counts

    Gallego-Cano, E.; Schödel, R.; Dong, H.; Nogueras-Lara, F.; Gallego-Calvente, A. T.; Amaro-Seoane, P.; Baumgardt, H.

    2018-01-01

    Context. The existence of dynamically relaxed stellar density cusps in dense clusters around massive black holes is a long-standing prediction of stellar dynamics, but it has so far escaped unambiguous observational confirmation. Aims: In this paper we aim to revisit the problem of inferring the innermost structure of the Milky Way's nuclear star cluster via star counts, to clarify whether it displays a core or a cusp around the central black hole. Methods: We used judiciously selected adaptive optics assisted high angular resolution images obtained with the NACO instrument at the ESO VLT. Through image stacking and improved point spread function fitting we pushed the completeness limit about one magnitude deeper than in previous, comparable work. Crowding and extinction corrections were derived and applied to the surface density estimates. Known young, and therefore dynamically not relaxed stars, are excluded from the analysis. Contrary to previous work, we analyse the stellar density in well-defined magnitude ranges in order to be able to constrain stellar masses and ages. Results: We focus on giant stars, with observed magnitudes K = 12.5-16, and on stars with observed magnitudes K ≈ 18, which may have similar mean ages and masses than the former. The giants display a core-like surface density profile within a projected radius R ≤ 0.3 pc of the central black hole, in agreement with previous studies, but their 3D density distribution is not inconsistent with a shallow cusp if we take into account the extent of the entire cluster, beyond the radius of influence of the central black hole. The surface density of the fainter stars can be described well by a single power-law at R cluster structure. Conclusions: We conclude that the observed density of the faintest stars detectable with reasonable completeness at the Galactic centre, is consistent with the existence of a stellar cusp around the Milky Way's central black hole, Sagittarius A*. This cusp is well

  14. Emission-line widths and stellar-wind flows in T Tauri stars

    Sa, C.; Lago, M.T.V.T.

    1986-01-01

    Spectra are reported of T Tauri stars taken with the IPCS on the Isaac Newton Telescope at the Observatorio del Roque de los Muchachos at a dispersion of l7 A mm -1 . These were taken in order to determine emission-line widths and hence flow velocities in the winds of these stars following the successful modelling of the wind from RU Lupi using such data. Line widths in RW Aur suggest a similar pattern to the wind flow as in RU Lupi with velocities rising in the inner chromosphere of the star and then entering a 'ballistic' zone. The wind from DFTau is also similar but velocities are generally much lower and the lines sharper. (author)

  15. Influence of X-ray radiation on the hot star wind ionization state and on the radiative force

    Krtička, J.; Kubát, Jiří

    2016-01-01

    Roč. 58, č. 5 (2016), s. 710-718 ISSN 0273-1177 Institutional support: RVO:67985815 Keywords : Stars * winds * early-type stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.401, year: 2016

  16. ENERGY STAR Certified Non-AHRI Central Air Conditioner Equipment and Air Source Heat Pump

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 5.0 ENERGY STAR Program Requirements for Air Source Heat Pump and Central Air Conditioner...

  17. Possibility of star (pyramid) dune development in the area of bimodal wind regime

    Biejat, K.

    2012-04-01

    Star (pyramid) dunes are the largest aeolian landforms. They can occur in three types - simple, complex and compound. Development of this type of dunes is usually connected with multidirectional or complex wind regimes. The aim of this study was to verify a hypothesis that the star dunes can also develop by a bimodal wind regime and by local modifications of nearsurface wind flow directions. Field study was performed on Erg Chebbi, in southern Morocco. Several star and transverse dunes were selected for the study of their shape. The star dunes were analysed concerning their type and position in the dune field. This erg contains all of three types of star dunes together with transverse dunes. The regional wind data show that there are two dominant wind directions - NE (Chergui) and SW (Saheli). To determine the difference in shape of star dunes, we performed topographic surveying by GPS RTK. The results allowed to create 3D models of star dunes. The models were used to determine metric characteristics of star dunes, including area of dune basis, volume, and slope angles. On the basis of 3D models, primary, secondary and, on the compound dunes, tertiary arms were determined. Primary arms on each type of star dunes, as well as crestlines of transverse dunes, have dominant orientation NW-SE, perpendicular to two dominant wind directions. This clearly confirms that star dunes of Erg Chebbi develop by a bimodal wind regime In contrast to primary arms, subsidiary (secondary and tertiary) arms are not connected to general wind regime. The secondary arms of star dunes occur to be differentially developer. There are more subsidiary arms on SW sides in comparison to the E sides of the dunes where inclination of slopes is constant. It can be therefore inferred that sand has been supplied predominantly from SW direction. This is supported by distribution of the dunes on the erg. Most compound star dunes compose a chain along the E margin of the erg. Comparison of compound star

  18. THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

    Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

    2017-01-20

    We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

  19. BINARY CENTRAL STARS OF PLANETARY NEBULAE DISCOVERED THROUGH PHOTOMETRIC VARIABILITY. IV. THE CENTRAL STARS OF HaTr 4 AND Hf 2-2

    Hillwig, Todd C.; Schaub, S. C. [Department of Physics and Astronomy, Valparaiso University, Valparaiso, IN 46383 (United States); Bond, Howard E. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Frew, David J. [Department of Physics, The University of Hong Kong, Pokfulam Road (Hong Kong); Bodman, Eva H. L., E-mail: todd.hillwig@valpo.edu [Southeastern Association for Research in Astronomy (SARA) (United States)

    2016-08-01

    We explore the photometrically variable central stars of the planetary nebulae HaTr 4 and Hf 2-2. Both have been classified as close binary star systems previously based on their light curves alone. Here, we present additional arguments and data confirming the identification of both as close binaries with an irradiated cool companion to the hot central star. We include updated light curves, orbital periods, and preliminary binary modeling for both systems. We also identify for the first time the central star of HaTr 4 as an eclipsing binary. Neither system has been well studied in the past, but we utilize the small amount of existing data to limit possible binary parameters, including system inclination. These parameters are then compared to nebular parameters to further our knowledge of the relationship between binary central stars of planetary nebulae and nebular shaping and ejection.

  20. A-type central stars of planetary nebulae. 2. The central stars of NGC 2346, He 2-36 and NGC 3132

    Mendez, R H [Instituto de Astronomia y Fisica del Espacio, Buenos Aires (Argentina)

    1978-12-01

    Spectrograms, scanner, uvby and ANS ultraviolet measurements of the central stars of NGC 2346, He 2-36 and NGC 3132 are analysed. The observations suggest that the first one is a foreground horizontal-branch star, and the second is above the horizontal branch, presumably in a rapid evolutionary phase. Both objects are probably variable. The central star of NGC 3132 is a slightly evolved main-sequence star with a hot visual companion. The evolutionary status of this system is briefly discussed.

  1. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

    Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

    2012-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  2. Wind estimation around the shipwreck of Oriental Star based on field damage surveys and radar observations.

    Meng, Zhiyong; Yao, Dan; Bai, Lanqiang; Zheng, Yongguang; Xue, Ming; Zhang, Xiaoling; Zhao, Kun; Tian, Fuyou; Wang, Mingjun

    Based on observational analyses and on-site ground and aerial damage surveys, this work aims to reveal the weather phenomena-especially the wind situation-when Oriental Star capsized in the Yangtze River on June 1, 2015. Results demonstrate that the cruise ship capsized when it encountered strong winds at speeds of at least 31 m s -1 near the apex of a bow echo embedded in a squall line. As suggested by the fallen trees within a 2-km radius around the wreck location, such strong winds were likely caused by microburst straight-line wind and/or embedded small vortices, rather than tornadoes.

  3. Effect of rotational mixing and metallicity on the hot star wind mass-loss rates

    Krtička, J.; Kubát, Jiří

    2014-01-01

    Roč. 567, July (2014), A63/1-A63/7 ISSN 0004-6361 R&D Projects: GA ČR GA13-10589S Grant - others:GA MŠk(CZ) LM2010005 Institutional support: RVO:67985815 Keywords : stars: winds * outflows * stars: mass-loss Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  4. Curtain-Lifting Winds Allow Rare Glimpse into Massive Star Factory

    2003-06-01

    of the Swedish-ESO Submillimeter Telescpe (SEST) at the La Silla Observatory. Large-scale mapping of the distribution of the CS-molecule showed the structure and motions of the dense gas in the giant molecular cloud, from which the young stars in NGC 3603 originate. A total of 13 molecular clumps were detected and their sizes, masses and densities were determined. These observations also showed that the intense radiation and strong stellar winds from the hot stars in the central cluster have "carved a cavity" in the molecular cloud; this comparatively empty and transparent region now measures about 8 light-years across. Mid-infrared imaging (at wavelengths 11.9 and 18 µm) was made of selected regions in NGC 3603 with the TIMMI 2 instrument mounted on the ESO 3.6-m telescope. This constitutes the first sub-arcsec resolution mid-IR survey of NGC 3603 and serves in particular to show the warm dust distribution in the region. The survey gives a clear indication of intense, on-going star formation processes. Many different types of objects were detected, including extremely hot Wolf-Rayet stars and protostars; altogether 36 mid-IR point sources and 42 knots of diffuse emission were identified. In the area surveyed, the protostar IRS 9A is found to be the most luminous point source at both wavelengths; two other sources, designated IRS 9B and IRS 9C in the immediate vicinity are also very bright on the TIMMI 2 images, providing further indication that this is the site of an association of protostars in its own right. The collection of high-quality images of the IRS 9 area shown in PR Photo 16b/03 is well suited to investigate the nature and the evolutionary status of the highly obscured objects located there, IRS 9A-C. They are situated on the side of the massive molecular cloud core NGC 3603 MM 2 that faces the central cluster of young stars (PR Photo 16a/03) and were apparently only recently "liberated" from most of their natal gas and dust environment by strong stellar

  5. Stellar winds and coronae of low-mass Population II/III stars

    Suzuki, Takeru K.

    2018-06-01

    We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

  6. CARINA OB STARS: X-RAY SIGNATURES OF WIND SHOCKS AND MAGNETIC FIELDS

    Gagne, Marc; Fehon, Garrett; Savoy, Michael R.; Cohen, David H.; Townsley, Leisa K.; Broos, Patrick S.; Povich, Matthew S.; Corcoran, Michael F.; Walborn, Nolan R.; Remage Evans, Nancy; Moffat, Anthony F. J.; Naze, Yael; Oskinova, Lida M.

    2011-01-01

    The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical L X /L bol relation or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting that it may be a massive binary with a period of >30 days. The visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission components, suggesting embedded wind shocks close to the O2 If* Aa primary and colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic binaries, the long orbital-period systems HD 93343, HD 93403, and QZ Car have higher shock temperatures than short-period systems such as HD 93205 and FO 15. Although the X-rays from most B stars may be produced in the coronae of unseen, low-mass pre-main-sequence companions, a dozen B stars with high L X cannot be explained by a distribution of unseen companions. One of these, SS73 24 in the Treasure Chest cluster, is a new candidate Herbig Be star.

  7. Stellar winds and coronae of low-mass Population II/III stars

    Suzuki, Takeru K.

    2018-04-01

    We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

  8. A-type central stars of planetary nebulae. 1. A radial-velocity study of the central stars of NGC2346 and NGC3132

    Mendez, R H; Niemela, V S [Instituto de Astronomia y Fisica del Espacio, Succuoa, Buenos Aires (Argentina); Lee, P

    1978-08-01

    Radial-velocity measurements of the A-type central stars of NGC2346 and NGC3132 are presented. The first one is almost certainly a spectroscopic binary; no definite statement can be made about the second.

  9. The impact of a central Apennine wind-farm

    Paolo Forconi

    2012-09-01

    Full Text Available We monitored raptors and investigated collision rate of birds with 2 turbines of a central Apennine wind-farm. We detected 1,18/raptors/km2/h. We have not found bird fatalities with turbines. We found 2 carcasses: one Subalpine Warbler, Sylvia cantillans, died by collision with a close communication tower and a Kestrel, Falco tinnunculus, died by electrocution with an MT power-line starting from the communication tower.

  10. Probing the clumpy winds of giant stars with high mass X-ray binaries

    Grinberg, Victoria; Hell, Natalie; Hirsch, Maria; Garcia, Javier; Huenemoerder, David; Leutenegger, Maurice A.; Nowak, Michael; Pottschmidt, Katja; Schulz, Norbert S.; Sundqvists, Jon O.; Townsend, Richard D.; Wilms, Joern

    2016-04-01

    Line-driven winds from early type stars are structured, with small, overdense clumps embedded in tenuous hot gas. High mass X-ray binaries (HMXBs), systems where a neutron star or a black hole accretes from the line-driven stellar wind of an O/B-type companion, are ideal for studying such winds: the wind drives the accretion onto the compact object and thus the X-ray production. The radiation from close to the compact object is quasi-pointlike and effectively X-rays the wind.We used RXTE and Chandra-HETG observations of two of the brightest HMXBs, Cyg X-1 and Vela X-1, to decipher their wind structure. In Cyg X-1, we show that the orbital variability of absorption can be only explained by a clumpy wind model and constrain the porosity of the wind as well as the onion-like structure of the clumps. In Vela X-1 we show, using the newest reference energies for low ionization Si-lines obtained with LLNL’s EBIT-I, that the ionized phase of the circumstellar medium and the cold clumps have different velocities.

  11. Observation of solar wind with radio-star scintillation

    Watanabe, Takashi

    1974-01-01

    Large solar flares occurred in groups in early August 1972, and many interesting phenomena were observed. The solar wind condition during this period, obtained by scintillation observation, is reviewed. The velocity of solar wind has been determined from the observation of interplanetary space scintillation at Toyokawa, Fujigamine and Sugadaira. Four to ten radio wave sources were observed for ten minutes at each southing every day. Strong earth magnetic storm and the Forbush decrease of cosmic ray were observed during the period from August 3rd to 7th. Pioneer 9 observed a solar wind having the maximum velocity as high as 1,100 km/sec, and HEOS-II observed a solar wind having the velocity close to 2,000 km/sec. On the other hand, according to the scintillation of 3C-48 and 3C-144, the velocity of solar wind passing in the interplanetary space on the westside of the earth was only 300 to 400 km/sec. Therefore it is considered that the condition of solar wind on the east side of the earth differs from that on the west side of the earth. Pioneer 9 observed the pass of a shock wave on August 9th. With all radio wave sources, high velocity solar wind was observed and Pioneer 6 positioned on the west side of the earth also observed it. The thickness of this shock wave is at least 0.3 AU. Discussion is made on the cause for the difference between the asymmetric shock wave in the direction of south-west and symmetrical shock wave. The former may be blast wave, and the latter may be piston driven shock wave and the like. (Iwakiri, K.)

  12. Wind estimation around the shipwreck of Oriental Star based on field damage surveys and radar observations

    Meng, Zhiyong; Yao, Dan; Bai, Lanqiang; Zheng, Yongguang; Xue, Ming; Zhang, Xiaoling; Zhao, Kun; Tian, Fuyou; Wang, Mingjun

    2016-01-01

    Based on observational analyses and on-site ground and aerial damage surveys, this work aims to reveal the weather phenomena?especially the wind situation?when Oriental Star capsized in the Yangtze River on June 1, 2015. Results demonstrate that the cruise ship capsized when it encountered strong winds at speeds of at least 31?m?s?1 near the apex of a bow echo embedded in a squall line. As suggested by the fallen trees within a 2-km radius around the wreck location, such strong winds were lik...

  13. Angular Momentum in Disk Wind Revealed in the Young Star MWC 349A

    Zhang, Qizhou; Claus, Brian; Watson, Linda; Moran, James, E-mail: qzhang@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States)

    2017-03-01

    Disk winds are thought to play a critical role in star birth. As winds extract excess angular momentum from accretion disks, matter in the disk can be transported inward to the star to fuel mass growth. However, observational evidence of wind carrying angular momentum has been very limited. We present Submillimeter Array (SMA) observations of the young star MWC 349A in the H26 α and H30 α recombination lines. The high signal-to-noise ratios made possible by the maser emission process allow us to constrain the relative astrometry of the maser spots to milli-arcsecond precision. Previous observations of the H30 α line with the SMA and the Plateau de Bure interferometer (PdBI) showed that masers are distributed in the disk and wind. Our new high-resolution observations of the H26 α line reveal differences in spatial distribution from that of the H30 α line. H26 α line masers in the disk are excited in a thin annulus with a radius of about 25 au, while the H30 α line masers are formed in a slightly larger annulus with a radius of 30 au. This is consistent with expectations for maser excitation in the presence of an electron density variation of approximately R {sup −4}. In addition, the H30 α and H26 α line masers arise from different parts in the wind. This difference is also expected from maser theory. The wind component of both masers exhibits line-of-sight velocities that closely follow a Keplerian law. This result provides strong evidence that the disk wind extracts significant angular momentum, thereby facilitating mass accretion in the young star.

  14. On the Weak-Wind Problem in Massive Stars: X-Ray Spectra Reveal a Massive Hot Wind in mu Columbae

    Huenemoerder, David P.; Oskinova, Lidia M.; Ignace, Richard; Waldron, Wayne L.; Todt, Helge; Hamaguchi, Kenji; Kitamoto, Shunji

    2012-01-01

    Mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"--identified from cool wind UV/optical spectra--is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.

  15. 2D hydrodynamic simulations of super star cluster winds in a bimodal regime

    Wünsch, Richard; Palouš, Jan; Tenorio-Tagle, G.; Silich, S.

    2009-01-01

    Roč. 324, 2-4 (2009), s. 219-223 ISSN 0004-640X R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : stellar winds * star clusters * dynamics of ISM Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.404, year: 2009

  16. The diversity of neutron stars: Nearby thermally emitting neutron stars and the compact central objects in supernova remnants

    Kaplan, David L.

    Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the > 1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population -- instances, ages, and magnetic fields -- the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 10^6 year-old cooling neutron stars with magnetic fields above 10^13 G. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

  17. Possible evidence for the driving of the winds of hot stars by Alfven waves

    Underhill, A.B.

    1983-01-01

    Ultraviolet spectra of the supergiants α Cam (09.5 Ia), HD 105056 (ON9.7 Iae), and 15 Sgr (09.7 Lab) are compared, and it is shown that the terminal outflow velocity ν/sub infinity/, of HD 105056 is one-half that of the other two stars even though HD 105056 has the highest effective temperature of the three stars. This anomaly, together with the fact that the observed ν/sub infinity/ values for early-type stars scatter about an empirical correlation between ν/sub infinity/ and log T/sub eff/ by an amount which is larger than the amount which is larger than the amount expected according to the observational errors in determining ν/sub infinity/ and log T/sub eff/, leads to the conclusion that an agent in addition to radiation. Alfven waves, is driving the winds of early-type stars

  18. Relativistic MHD modeling of magnetized neutron stars, pulsar winds, and their nebulae

    Del Zanna, L.; Pili, A. G.; Olmi, B.; Bucciantini, N.; Amato, E.

    2018-01-01

    Neutron stars are among the most fascinating astrophysical sources, being characterized by strong gravity, densities about the nuclear one or even above, and huge magnetic fields. Their observational signatures can be extremely diverse across the electromagnetic spectrum, ranging from the periodic and low-frequency signals of radio pulsars, up to the abrupt high-energy gamma-ray flares of magnetars, where energies of ∼ {10}46 {erg} are released in a few seconds. Fast-rotating and highly magnetized neutron stars are expected to launch powerful relativistic winds, whose interaction with the supernova remnants gives rise to the non-thermal emission of pulsar wind nebulae, which are known cosmic accelerators of electrons and positrons up to PeV energies. In the extreme cases of proto-magnetars (magnetic fields of ∼ {10}15 G and millisecond periods), a similar mechanism is likely to provide a viable engine for the still mysterious gamma-ray bursts. The key ingredient in all these spectacular manifestations of neutron stars is the presence of strong magnetic fields in their constituent plasma. Here we will present recent updates of a couple of state-of-the-art numerical investigations by the high-energy astrophysics group in Arcetri: a comprehensive modeling of the steady-state axisymmetric structure of rotating magnetized neutron stars in general relativity, and dynamical 3D MHD simulations of relativistic pulsar winds and their associated nebulae.

  19. Photometric investigation of possible binary occurrence in the central stars of seventeen planetary nebulae

    Drummond, J.D. III.

    1980-01-01

    A comprehensive literature search was conducted for all possible bihary central stars in planetary nebulae. The results, which include all known and suspected visual, spectroscopic, and spectrum binaries, as well as all reported variable central stars, are presented in a series of tables. A photoelectric study was conducted in order to determine the status of short period (on the order of hours) variability of the central regions of seventeen planetary nebulae. Only the stellar appearing planetary nebula M1-2 (PK 133-8 0 1) was found to be variable. Its short (4.0002 hours) period suggests that it may be only the second eclipsing binary found among central stars to date. A method of concentric apertures was developed to determine the amount of light contributed by the central star vis-a-vis the nebula through a given aperture and filter. The procedure enabled UBV magnitudes and colors (and the errors) of central stars to be measured, including some in the sample of seventeen for which no previous values have been published. Mean nebular UBV magnitudes, surface brightnesses, and color indices were also found with the technique, and represent the first such published measurements. Various UBV two-parameter were constructed, revealing possible nebular/stellar sequences; a star-plus-nebula two-color diagram identifies three spectral classes of central stars, and two suspected binaries in the seventeen studied

  20. High-entropy ejections from magnetized proto-neutron star winds: implications for heavy element nucleosynthesis

    Thompson, Todd A.; ud-Doula, Asif

    2018-06-01

    Although initially thought to be promising for production of the r-process nuclei, standard models of neutrino-heated winds from proto-neutron stars (PNSs) do not reach the requisite neutron-to-seed ratio for production of the lanthanides and actinides. However, the abundance distribution created by the r-, rp-, or νp-processes in PNS winds depends sensitively on the entropy and dynamical expansion time-scale of the flow, which may be strongly affected by high magnetic fields. Here, we present results from magnetohydrodynamic simulations of non-rotating neutrino-heated PNS winds with strong dipole magnetic fields from 1014 to 1016 G, and assess their role in altering the conditions for nucleosynthesis. The strong field forms a closed zone and helmet streamer configuration at the equator, with episodic dynamical mass ejections in toroidal plasmoids. We find dramatically enhanced entropy in these regions and conditions favourable for third-peak r-process nucleosynthesis if the wind is neutron-rich. If instead the wind is proton-rich, the conditions will affect the abundances from the νp-process. We quantify the distribution of ejected matter in entropy and dynamical expansion time-scale, and the critical magnetic field strength required to affect the entropy. For B ≳1015 G, we find that ≳10-6 M⊙ and up to ˜10-5 M⊙ of high-entropy material is ejected per highly magnetized neutron star birth in the wind phase, providing a mechanism for prompt heavy element enrichment of the universe. Former binary companions identified within (magnetar-hosting) supernova remnants, the remnants themselves, and runaway stars may exhibit overabundances. We provide a comparison with a semi-analytic model of plasmoid eruption and discuss implications and extensions.

  1. THE TWO CENTRAL STARS OF NGC 1514: CAN THEY ACTUALLY BE RELATED?

    Méndez, Roberto H.; Kudritzki, Rolf-Peter [Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Urbaneja, Miguel A., E-mail: mendez@ifa.hawaii.edu [Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstr. 25/8, A-6020 Innsbruck (Austria)

    2016-10-01

    The central star of the planetary nebula NGC 1514 is among the visually brightest central stars in the sky ( V = 9.5). It has long been known to show a composite spectrum, consisting of an A-type star and a much hotter star responsible for the ionization of the surrounding nebula. These two stars have always been assumed to form a binary system. High-resolution spectrograms obtained with Espadons at the Canada–France–Hawaii Telescope on Maunakea have allowed us to measure good radial velocities for both stars: they differ by 13 ± 2 km s{sup −1}. The stellar velocities were unchanged after 500 days. We have also estimated the metallicity of the cooler star. Combining these data with other information available in the literature, we conclude that, unless all the published nebular radial velocities are systematically wrong, the cooler star is just a chance alignment, and the two stars are not orbiting each other. The cooler star cannot have played any role in the formation of NGC 1514.

  2. ON THE LAUNCHING AND STRUCTURE OF RADIATIVELY DRIVEN WINDS IN WOLF–RAYET STARS

    Ro, Stephen; Matzner, Christopher D., E-mail: ro@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)

    2016-04-20

    Hydrostatic models of Wolf–Rayet (WR) stars typically contain low-density outer envelopes that inflate the stellar radii by a factor of several and are capped by a denser shell of gas. Inflated envelopes and density inversions are hallmarks of envelopes that become super-Eddington as they cross the iron-group opacity peak, but these features disappear when mass loss is sufficiently rapid. We re-examine the structures of steady, spherically symmetric wind solutions that cross a sonic point at high optical depth, identifying the physical mechanism through which the outflow affects the stellar structure, and provide an improved analytical estimate for the critical mass-loss rate above which extended structures are erased. Weak-flow solutions below this limit resemble hydrostatic stars even in supersonic zones; however, we infer that these fail to successfully launch optically thick winds. WR envelopes will therefore likely correspond to the strong, compact solutions. We also find that wind solutions with negligible gas pressure are stably stratified at and below the sonic point. This implies that convection is not the source of variability in WR stars, as has been suggested; however, acoustic instabilities provide an alternative explanation. Our solutions are limited to high optical depths by our neglect of Doppler enhancements to the opacity, and do not account for acoustic instabilities at high Eddington factors; yet, they do provide useful insights into WR stellar structures.

  3. Active Power Dispatch Method for a Wind Farm Central Controller Considering Wake Effect

    Tian, Jie; Su, Chi; N. Soltani, Mohsen

    2014-01-01

    With the increasing integration of the wind power into the power system, wind farm are required to be controlled as a single unit and have all the same control tasks as conventional power plants. The wind farm central controller receives control orders from Transmission System Operator (TSO), the...... Optimization (PSO) is used to obtain the optimal wind power for each wind turbine. A case study is carried out. The available wind power of the wind farm was compared between the traditional dispatch method and the proposed dispatch method with the consideration of the wake effect....

  4. The Local ISM and its Interaction with the Winds of Nearby Late-type Stars

    Wood, Brian E.; Linsky, Jeffrey L.

    1998-01-01

    We present new Goddard High-Resolution Spectrograph (GHRS) observations of the Ly-alpha and Mg II absorption lines seen toward the nearby stars 61 Cyg A and 40 Eri A. We use these data to measure interstellar properties along these lines of sight and to search for evidence of circumstellar hydrogen walls, which are produced by collisions between the stellar winds and the Local InterStellar Medium (LISM). We were able to model the Ly-alpha lines of both stars without hydrogen-wall absorption components, but for 61 Cyg A the fit required a stellar Ly-alpha, line profile with an improbably deep self-reversal, and for 40 Eri A the fit required a very low deuterium-to-hydrogen ratio that is inconsistent with previous GHRS measurements. Since these problems could be rectified simply by including stellar hydrogen-wall components with reasonable attributes, our preferred fits to the data include these components. We have explored several ways in which the hydrogen-wall properties measured here and in previous work can be used to study stellar winds and the LISM. We argue that the existence of a hydrogen wall around 40 Eri A and a low H I column density along that line of sight imply that either the interstellar density must decrease toward 40 Eri A or the hydrogen ionization fraction (chi) must increase. We find that hydrogen-wall temperatures are larger for stars with faster velocities through the LISM. The observed temperature-velocity relation is consistent with the predictions of hydromagnetic shock jump conditions. More precise comparison of the data and the jump conditions suggests crude upper limits for both chi and the ratio of magnetic to thermal pressure in the LISM (alpha): chi less than 0.6 and alpha less than 2. The latter upper limit corresponds to a limit on the LISM magnetic field of B less than 5 micro G. These results imply that the plasma Mach number of the interstellar wind flowing into the heliosphere is M(sub A) greater than 1.3, which indicates that

  5. A Survey for hot Central Stars of Planetary Nebulae I. Methods and First Results

    Kanarek, Graham C.; Shara, Michael M.; Faherty, Jacqueline K.; Zurek, David; Moffat, Anthony F. J.

    2015-01-01

    We present the results of initial spectrographic followup with the Very Large Telescope (UT3, Melipal) for $K_s \\ge 14$ Galactic plane CIV emission-line candidates in the near-infrared (NIR). These 7 faint stars all display prominent HeI and CIV emission lines characteristic of a carbon-rich Wolf-Rayet star. They have NIR colours which are much too blue to be those of distant, classical WR stars. The magnitudes and colours are compatible with those expected for central stars of planetary nebu...

  6. 76 FR 41788 - Southern Star Central Gas Pipeline, Inc.; Notice of Intent To Prepare an Environmental Assessment...

    2011-07-15

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [ Docket No. CP11-481-000] Southern Star... Southern Star Central Gas Pipeline, Inc. (Southern Star) in Rice County, Kansas. This EA will be used by... Facility On My Land? What Do I Need To Know?'' was attached to the project notice Southern Star provided to...

  7. 77 FR 43586 - Southern Star Central Gas Pipeline, Inc.; Notice of Intent To Prepare an Environmental Assessment...

    2012-07-25

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket No. CP12-479-000] Southern Star... abandonment of facilities by Southern Star Central Gas Pipeline, Inc. (Southern Star) in Logan and Oklahoma... concern. Southern Star provided landowners with a fact sheet prepared by the FERC entitled ``An Interstate...

  8. HUBBLE SPACE TELESCOPE CONSTRAINTS ON THE WINDS AND ASTROSPHERES OF RED GIANT STARS

    Wood, Brian E. [Naval Research Laboratory, Space Science Division, Washington, DC 20375 (United States); Müller, Hans-Reinhard [Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States); Harper, Graham M., E-mail: brian.wood@nrl.navy.mil [CASA, University of Colorado, Boulder, CO 80309-0389 (United States)

    2016-10-01

    We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope , focusing on spectra of the Mg ii h and k lines near 2800 Å in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus on spectral types between K2 III and M5 III, a spectral type range with stars that are noncoronal, but possessing strong, chromospheric winds. We find a very tight relation between Mg ii surface flux and photospheric temperature, supporting the notion that all K2-M5 III stars are emitting at a basal flux level. Wind velocities ( V {sub w} ) are generally found to decrease with spectral type, with V {sub w} decreasing from ∼40 km s{sup −1} at K2 III to ∼20 km s{sup −1} at M5 III. We find two new detections of astrospheric absorption, for σ Pup (K5 III) and γ Eri (M1 III). This absorption signature had previously only been detected for α Tau (K5 III). For the three astrospheric detections, the temperature of the wind after the termination shock (TS) correlates with V {sub w} , but is lower than predicted by the Rankine–Hugoniot shock jump conditions, consistent with the idea that red giant TSs are radiative shocks rather than simple hydrodynamic shocks. A full hydrodynamic simulation of the γ Eri astrosphere is provided to explore this further.

  9. Central Stars of Mid-Infrared Nebulae Discovered with Spitzer and WISE

    Gvaramadze, V. V.; Kniazev, A. Y.

    2017-02-01

    Searches for compact mid-IR nebulae with the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE), accompanied by spectroscopic observations of central stars of these nebulae led to the discovery of many dozens of massive stars at different evolutionary stages, of which the most numerous are candidate luminous blue variables (LBVs). In this paper, we give a census of candidate and confirmed Galactic LBVs revealed with Spitzer and WISE, and present some new results of spectroscopic observations of central stars of mid-IR nebulae.

  10. Mass distribution and evolutionary scheme for central stars of planetary nebulae

    Heap, S.R.; Augensen, H.J.; Widener Univ., Chester, PA)

    1987-01-01

    IUE data and a distance measuring method that considered central stars in optically thick nebulae were used to examine mass distributions of planetary nebulae. Other data such as spectral type, spatial and kinematic characteristics, etc., were studied to derive relationships between population type and mass distribution. A central star mass range of at least 0.55 solar mass was obtained. Stars with masses of at least 0.64 solar mass, concentrated in the galactic disk, originated from 1.5 solar mass stars. Low mass nuclei originated in old disk or halo populations and evolved from 1.0 solar mass objects. A mass-loss parameter value of 1/3 was calculated for red giants, implying that white dwarfs evolve from stars of under 5 solar masses. Mass distributions around planetary nuclei were concluded to follow patterns associated with the individual mass. 75 references

  11. A new class of galactic discrete gamma ray sources: Chaotic winds of massive stars

    Chen, Wan; White, Richard L.

    1992-01-01

    We propose a new class of galactic discrete gamma-ray sources, the chaotic, high mass-loss-rate winds from luminous early-type stars. Early-type stellar winds are highly unstable due to intrinsic line-driven instabilities, and so are permeated by numerous strong shocks. These shocks can accelerate a small fraction of thermal electrons and ions to relativistic energies via the first-order Fermi mechanism. A power-law-like photon spectrum extending from keV to above 10 MeV energies is produced by inverse Compton scattering of the extremely abundant stellar UV photons by the relativistic electrons. In addition, a typical pi(sup 0)-decay gamma-ray spectrum is generated by proton-ion interactions in the densest part of the winds.

  12. Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

    Martínez-Núñez, Silvia; Kretschmar, Peter; Bozzo, Enrico; Oskinova, Lidia M.; Puls, Joachim; Sidoli, Lara; Sundqvist, Jon Olof; Blay, Pere; Falanga, Maurizio; Fürst, Felix; Gímenez-García, Angel; Kreykenbohm, Ingo; Kühnel, Matthias; Sander, Andreas; Torrejón, José Miguel; Wilms, Jörn

    2017-10-01

    Massive stars, at least ˜10 times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy. In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense "clumps". The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution. Supergiant high mass X-ray binaries (SgXBs) are among the brightest X

  13. Accretion from a clumpy massive-star wind in supergiant X-ray binaries

    El Mellah, I.; Sundqvist, J. O.; Keppens, R.

    2018-04-01

    Supergiant X-ray binaries (SgXB) host a compact object, often a neutron star (NS), orbiting an evolved O/B star. Mass transfer proceeds through the intense line-driven wind of the stellar donor, a fraction of which is captured by the gravitational field of the NS. The subsequent accretion process on to the NS is responsible for the abundant X-ray emission from SgXB. They also display peak-to-peak variability of the X-ray flux by a factor of a few 10-100, along with changes in the hardness ratios possibly due to varying absorption along the line of sight. We use recent radiation-hydrodynamic simulations of inhomogeneities (a.k.a. clumps) in the non-stationary wind of massive hot stars to evaluate their impact on the time-variable accretion process. For this, we run 3D hydrodynamic simulations of the wind in the vicinity of the accretor to investigate the formation of the bow shock and follow the inhomogeneous flow over several spatial orders of magnitude, down to the NS magnetosphere. In particular, we show that the impact of the wind clumps on the time variability of the intrinsic mass accretion rate is severely tempered by the crossing of the shock, compared to the purely ballistic Bondi-Hoyle-Lyttleton estimation. We also account for the variable absorption due to clumps passing by the line of sight and estimate the final effective variability of the column density and mass accretion rate for different orbital separations. Finally, we compare our results to the most recent analysis of the X-ray flux and the hardness ratio in Vela X-1.

  14. Detailed empirical models for the winds of early-type stars

    Olson, G.L.; Castor, J.I.

    1981-01-01

    Owing to the recent accumulation of ultraviolet data from the IUE satellite, of X-ray data from the Einstein (HEAO 2) satellite, of visible data from ground based electronic detectors, and of radio data from the Very Large Array (VLA) telescope, it is becoming possible to build much more complete models for the winds of early-type stars. The present work takes the empirical approach of assuming that there exists a coronal region at the base of a cool wind (T/sub e/roughly-equalT/sub eff/). This will be an extension of previous papers by Olson and by Cassinelli and Olson; however, refinements to the model will be presented, and the model will be applied to seven O stars and one BO star. Ionization equilibria are computed to match the line strengths found in UV spectra. The coronal fluxes that are required to produce the observed abundance of O +5 are compared to the X-ray fluxes observed by the Einstein satellite

  15. SALT reveals the barium central star of the planetary nebula Hen 2-39

    Miszalski, B.; Boffin, H. M. J.; Jones, D.; Karakas, A. I.; Köppen, J.; Tyndall, A. A.; Mohamed, S. S.; Rodríguez-Gil, P.; Santander-García, M.

    2013-12-01

    Classical barium stars are binary systems which consist of a late-type giant enriched in carbon and slow neutron capture (s-process) elements and an evolved white dwarf (WD) that is invisible at optical wavelengths. The youngest observed barium stars are surrounded by planetary nebulae (PNe), ejected soon after the wind accretion of polluted material when the WD was in its preceding asymptotic giant branch (AGB) phase. Such systems are rare but powerful laboratories for studying AGB nucleosynthesis as we can measure the chemical abundances of both the polluted star and the nebula ejected by the polluter. Here, we present evidence for a barium star in the PN Hen 2-39 (PN G283.8-04.2) as one of only a few known systems. The polluted giant is very similar to that found in WeBo 1 (PN G135.6+01.0). It is a cool (Teff = 4250 ± 150 K) giant enhanced in carbon ([C/H] = 0.42 ± 0.02 dex) and barium ([Ba/Fe] = 1.50 ± 0.25 dex). A spectral type of C-R3 C24 nominally places Hen 2-39 amongst the peculiar early R-type carbon stars; however, the barium enhancement and likely binary status mean that it is more likely to be a barium star with similar properties, rather than a true member of this class. An AGB star model of initial mass 1.8 M⊙ and a relatively large carbon pocket size can reproduce the observed abundances well, provided mass is transferred in a highly conservative way from the AGB star to the polluted star (e.g. wind Roche lobe overflow). It also shows signs of chromospheric activity and photometric variability with a possible rotation period of ˜5.5 d likely induced by wind accretion. The nebula exhibits an apparent ring morphology in keeping with the other PNe around barium stars (WeBo 1 and A 70) and shows a high degree of ionization implying the presence of an invisible hot pre-WD companion that will require confirmation with UV observations. In contrast to A 70, the nebular chemical abundance pattern is consistent with non-Type I PNe, in keeping with the

  16. Wolf-Rayet stars in the central region of the Milky Way

    Hamann, Wolf-Rainer; Graefener, Goetz; Oskinova, Lidia; Zinnecker, Hans

    2004-09-01

    We propose to take mid-IR spectra of two Wolf-Rayet stars in the inner part of our Galaxy, within 30pc projected distance from the central Black Hole. Massive stars dominate the central galactic region by their mass-loss and ionizing radiation. A quantitative analysis of this stellar inventory is essential for understanding the energy, momentum and mass budget, for instance with respect to the feeding of the central black hole. Our group developed a highly advanced model code for the expanding atmospheres of WR stars. Recently we extended the spectrum synthesis to IR wavelengths. These models will be applied for the analysis of the Spitzer IRS data. The proposed mid-IR observations will provide a wide spectral range with many lines which are needed to determine the stellar parameters, such as stellar luminosity, effective temperature, mass-loss rate and chemical composition. Near-IR spectra of the program stars are available and will augment the analysis. The capability of our code to reproduce the observed mid-IR spectrum of a WN star has been demonstrated. The two targets we selected are sufficiently isolated, while the Galactic center cluster is too crowded for the size of Spitzer's spectrograph slit. As estimated from the K-band spectra, one of the stars (WR102ka) is of very late subtype (WN9), while the other star (WR102c) has the early subtype WN6. Hence they represent different stages in the evolutionary sequence of massive stars, the late-WN just having entered the Wolf-Rayet phase and the early WN being further evolved. We expect that the parameters of massive stars in the inner galaxy differ from the usual Galactic population. One reason is that higher metallicity should lead to stronger mass-loss, which affects the stellar evolution. The Spitzer IRS, with its high sensitivity, provides a unique opportunity to study representative members of the stellar population in the vicinity of the Galactic center.

  17. Mining the HST "Advanced Spectral Library (ASTRAL)": The Evolution of Winds from non-coronal to hybrid giant stars

    Nielsen, Krister E.; Carpenter, Ken G.; Kober, Gladys V.; Rau, Gioia

    2018-01-01

    The HST/STIS treasury program ASTRAL enables investigations of the character and dynamics of the wind and chromosphere of cool stars, using high quality spectral data. This paper shows how the wind features change with spectral class by comparing the non-coronal objects (Alpha Ori, Gamma Cru) with the hybrid stars (Gamma Dra, Beta Gem). In particular we study the intrinsic strength variation of the numerous FeII profiles observed in the near-ultraviolet HST spectrum that are sensitive to the wind opacity, turbulence and flow velocity. The FeII relative emission strength and wavelengths shifts between the absorption and emission components reflects the acceleration of the wind from the base of the chromosphere. We present the analysis of the outflowing wind characteristics when transitioning from the cool non-coronal objects toward the warmer objects with chromospheric emission from significantly hotter environments.

  18. Eyes in the sky. Interactions between asymptotic giant branch star winds and the interstellar magnetic field

    van Marle, A. J.; Cox, N. L. J.; Decin, L.

    2014-10-01

    Context. The extended circumstellar envelopes (CSEs) of evolved low-mass stars display a large variety of morphologies. Understanding the various mechanisms that give rise to these extended structures is important to trace their mass-loss history. Aims: Here, we aim to examine the role of the interstellar magnetic field in shaping the extended morphologies of slow dusty winds of asymptotic giant branch (AGB) stars in an effort to pin-point the origin of so-called eye shaped CSEs of three carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary nebula (PN) shaping can be responsible for asymmetries observed in PNe. Methods: Hydrodynamical simulations are used to study the effect of typical interstellar magnetic fields on the free-expanding spherical stellar winds as they sweep up the local interstellar medium (ISM). Results: The simulations show that typical Galactic interstellar magnetic fields of 5 to 10 μG are sufficient to alter the spherical expanding shells of AGB stars to appear as the characteristic eye shape revealed by far-infrared observations. The typical sizes of the simulated eyes are in accordance with the observed physical sizes. However, the eye shapes are transient in nature. Depending on the stellar and interstellar conditions, they develop after 20 000 to 200 000 yrs and last for about 50 000 to 500 000 yrs, assuming that the star is at rest relative to the local interstellar medium. Once formed, the eye shape develops lateral outflows parallel to the magnetic field. The explosion of a PN in the centre of the eye-shaped dust shell gives rise to an asymmetrical nebula with prominent inward pointing Rayleigh-Taylor instabilities. Conclusions: Interstellar magnetic fields can clearly affect the shaping of wind-ISM interaction shells. The occurrence of the eyes is most strongly influenced by stellar space motion and ISM density. Observability of this transient phase is favoured for lines-of-sight perpendicular to the

  19. Abell 48 - a rare WN-type central star of a planetary nebula

    Todt, H.; Kniazev, A. Y.; Gvaramadze, V. V.; Hamann, W.-R.; Buckley, D.; Crause, L.; Crawford, S. M.; Gulbis, A. A. S.; Hettlage, C.; Hooper, E.; Husser, T.-O.; Kotze, P.; Loaring, N.; Nordsieck, K. H.; O'Donoghue, D.; Pickering, T.; Potter, S.; Romero-Colmenero, E.; Vaisanen, P.; Williams, T.; Wolf, M.

    2013-04-01

    A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. Almost all of these H-deficient central stars (CSs) display spectra with strong carbon and helium lines. Most of them exhibit emission-line spectra resembling those of massive WC stars. Therefore these stars are classed as CSPNe of spectral type [WC]. Recently, quantitative spectral analysis of two emission-line CSs, PB 8 and IC 4663, revealed that these stars do not belong to the [WC] class. Instead PB 8 has been classified as [WN/WC] type and IC 4663 as [WN] type. In this work we report the spectroscopic identification of another rare [WN] star, the CS of Abell 48. We performed a spectral analysis of Abell 48 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. We find that the expanding atmosphere of Abell 48 is mainly composed of helium (85 per cent by mass), hydrogen (10 per cent) and nitrogen (5 per cent). The residual hydrogen and the enhanced nitrogen abundance make this object different from the other [WN] star IC 4663. We discuss the possible origin of this atmospheric composition.

  20. DETECTION OF THE CENTRAL STAR OF THE PLANETARY NEBULA NGC 6302

    Szyszka, C.; Walsh, J. R.; Zijlstra, Albert A.; Tsamis, Y. G.

    2009-01-01

    NGC 6302 is one of the highest ionization planetary nebulae (PNe) known and shows emission from species with ionization potential > 300 eV. The temperature of the central star must be > 200,000 K to photoionize the nebula, and has been suggested to be up to ∼400,000 K. On account of the dense dust and molecular disk, the central star has not convincingly been directly imaged until now. NGC 6302 was imaged in six narrowband filters by Wide Field Camera 3 on the Hubble Space Telescope as part of the Servicing Mission 4 Early Release Observations. The central star is directly detected for the first time, and is situated at the nebula center on the foreground side of the tilted equatorial disk. The magnitudes of the central star have been reliably measured in two filters (F469N and F673N). Assuming a hot blackbody, the reddening has been measured from the (4688-6766 A) color and a value of c = 3.1, A v = 6.6 mag determined. A G-K main-sequence binary companion can be excluded. The position of the star on the H-R diagram suggests a fairly massive PN central star of about 0.64 M sun close to the white dwarf cooling track. A fit to the evolutionary tracks for (T, L, t) = (200,000 K, 2000 L sun , 2200 yr), where t is the nebular age, is obtained; however, the luminosity and temperature remain uncertain. The model tracks predict that the star is rapidly evolving, and fading at a rate of almost 1% per year. Future observations could test this prediction.

  1. Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256

    Lípari, S.; Díaz, R.; Taniguchi, Y.; Terlevich, R.; Dottori, H.; Carranza, G.

    2000-08-01

    We report detailed evidence for multiple merger, extended massive star formation, galactic wind, and circular/noncircular motions in the luminous infrared galaxy NGC 3256, based on observations of high-resolution imaging (Hubble Space Telescope, ESO NTT), and extensive spectroscopic data (more than 1000 spectra, collected at Estación Astrofísica de Bosque Alegre, Complejo Astronómico el Leoncito, Cerro Tololo InterAmerican Observatory, and IUE observatories). We find in a detailed morphological study (resolution ~15 pc) that the extended massive star formation process detected previously in NGC 3256 shows extended triple asymmetrical spiral arms (r~5 kpc), emanating from three different nuclei. The main optical nucleus shows a small spiral disk (r~500 pc), which is a continuation of the external one and reaches the very nucleus. The core shows blue elongated structure (50 pc×25 pc) and harbors a blue stellar cluster candidate (r~8 pc). We discuss this complex morphology in the framework of an extended massive star formation driven by a multiple merger process (models of Hernquist et al. and Taniguchi et al.). We study the kinematics of this system and present a detailed Hα velocity field for the central region (40''×40'' rmax~30''~5 kpc), with a spatial resolution of 1" and errors of +/-15 km s-1. The color and isovelocity maps show mainly (1) a kinematic center of circular motion with ``spider'' shape, located between the main optical nucleus and the close (5") mid-IR nucleus and (2) noncircular motions in the external parts. We obtained three ``sinusoidal rotation curves'' (from the Hα velocity field) around position angle (P.A.) ~55°, ~90°, and ~130°. In the main optical nucleus we found a clear ``outflow component'' associated with galactic winds plus an ``inflow radial motion.'' The outflow component was also detected in the central and external regions (rstandard models of photoionization, shocks, and starbursts). We present four detailed emission

  2. Simulation of an offshore wind farm using fluid power for centralized electricity generation

    A. Jarquin Laguna

    2017-07-01

    Full Text Available A centralized approach for electricity generation within a wind farm is explored through the use of fluid power technology. This concept considers a new way of generation, collection and transmission of wind energy inside a wind farm, in which electrical conversion does not occur during any intermediate conversion step before the energy has reached the offshore central platform. A numerical model was developed to capture the relevant physics from the dynamic interaction between different turbines coupled to a common hydraulic network and controller. This paper presents a few examples of the time domain simulation results for a hypothetical hydraulic wind farm subject to turbulent wind conditions. The performance and operational parameters of individual turbines are compared with those of a reference wind farm based on conventional wind turbine generator technology using the same wind farm layout and environmental conditions. For the presented case studies, results indicate that the individual wind turbines are able to operate within operational limits. Despite the stochastic turbulent wind conditions and wake effects, the hydraulic wind farm is able to produce electricity with reasonable performance in both below and above rated conditions. With the current pressure control concept, a continuous operation of the hydraulic wind farm is shown including the full stop of one or more turbines.

  3. Discovery of a [WO] central star in the planetary nebula Th 2-A

    Weidmann, W. A.; Gamen, R.; Díaz, R. J.; Niemela, V. S.

    2008-09-01

    Context: About 2500 planetary nebulae are known in our Galaxy but only 224 have central stars with reported spectral types in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Acker et al. 1992; Acker et al. 1996). Aims: We have started an observational program aiming to increase the number of PN central stars with spectral classification. Methods: By means of spectroscopy and high resolution imaging, we identify the position and true nature of the central star. We carried out low resolution spectroscopic observations at CASLEO telescope, complemented with medium resolution spectroscopy performed at Gemini South and Magellan telescopes. Results: As a first outcome of this survey, we present for the first time the spectra of the central star of the PN Th 2-A. These spectra show emission lines of ionized C and O, typical in Wolf-Rayet stars. Conclusions: We identify the position of that central star, which is not the brightest one of the visual central pair. We classify it as of type [WO 3]pec, which is consistent with the high excitation and dynamical age of the nebula. Based on data collected at (i) the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina; (ii) the 6.5 m Magellan Telescopes at Las Campanas Observatory, Chile; (iii) the 8 m Gemini South Telescope, Chile.

  4. Stellar C III Emissions as a New Classification Parameter for (WC) Central Stars

    Feibelman, W. A.

    1999-01-01

    We report detection of stellar C III lambda 1909 emission in International Ultraviolet Explorer (IUE) echelle spectra of early-type [WC] planetary nebula central stars (CSPNs). Additionally, stellar C III emission at lambda 2297 is observed in early- and late-type [WC) CSPNS. Inclusion of these C III features for abundance determinations may resolve a conflict of underabundance of C/O for early type [WC2] - [WC4] CSPNS. A linear dependence on stellar C III lambda 2297 equivalent widths can be used to indicate a new classification of type [WCUV] central stars.

  5. The two young star disks in the central parsec of the Galaxy: properties, dynamics, and formation

    Paumard, T; Genzel, R; Martins, F; Nayakshin, S; Beloborodov, A M; Levin, Y; Trippe, S; Eisenhauer, F; Ott, T; Gillessen, S; Abuter, R; Cuadra, J; Alexander, T; Sternberg, A

    2006-01-01

    We report the definite spectroscopic identification of ≅ 40 OB supergiants, giants and main sequence stars in the central parsec of the Galaxy. Detection of their absorption lines have become possible with the high spatial and spectral resolution and sensitivity of the adaptive optics integral Held spectrometer SPIFFI/SINFONI on the ESO VLT. Several of these OB stars appear to be helium and nitrogen rich. Almost all of the ≅80 massive stars now known in the central parsec (central arcsecond excluded) reside in one of two somewhat thick ((|/R) ≅ 0.14) rotating disks. These stellar disks have fairly sharp inner edges (R ≅ 1'') and surface density profiles that scale as R -2 . We do not detect any OB stars outside the central 0.5 pc. The majority of the stars in the clockwise system appear to be on almost circular orbits, whereas most of those in the 'counter-clockwise' disk appear to be on eccentric orbits. Based on its stellar surface density distribution and dynamics we propose that IRS 13E is an extremely dense cluster (ρ core ∼> 3 x 10 8 M o-dot pc -3 ), which has formed in the counter-clockwise disk. The stellar contents of both systems are remarkably similar, indicating a common age of ≅ 6±2 Myr. The K-band luminosity function of the massive stars suggests a top-heavy mass function and limits the total stellar mass contained in both disks to ≅ 1.5 x 10 4 M o-dot . Our data strongly favor in situ star formation from dense gas accretion disks for the two stellar disks. This conclusion is very clear for the clockwise disk and highly plausible for the counter-clockwise system

  6. HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF WOLF-RAYET STAR WINDS

    Oskinova, L. M.; Hamann, W.-R. [Institute for Physics and Astronomy, University Potsdam, 14476 Potsdam (Germany); Gayley, K. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245 (United States); Huenemoerder, D. P. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 70 Vassar St., Cambridge, MA 02139 (United States); Ignace, R. [Department of Physics and Astronomy, East Tennessee State University, Johnson City, TN 37663 (United States); Pollock, A. M. T., E-mail: lida@astro.physik.uni-potsdam.de [European Space Agency XMM-Newton Science Operations Centre, European Space Astronomy Centre, Apartado 78, Villanueva de la Canada, 28691 Madrid (Spain)

    2012-03-10

    We present the first high-resolution X-ray spectrum of a putatively single Wolf-Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, 'cool' stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at Almost-Equal-To 6.4 keV. The presence of fluorescence is consistent with a two-component medium, where the cool wind is permeated with the hot X-ray emitting plasma. The wind must have a very porous structure to allow the observed amount of X-rays to escape. We find that neither the LDI nor any alternative binary scenario can explain the data. We suggest a scenario where X-rays are produced when the fast wind rams into slow 'sticky clumps' that resist acceleration. Our new data show that the X-rays in single WR star are generated by some special mechanism different from the one operating in the O-star winds.

  7. WR 110: A SINGLE WOLF-RAYET STAR WITH COROTATING INTERACTION REGIONS IN ITS WIND?

    Chene, A.-N.; Moffat, A. F. J.; Fahed, R.; St-louis, N.; Muntean, V.; Chevrotiere, A. De La; Cameron, C.; Matthews, J. M.; Gamen, R. C.; Lefevre, L.; Rowe, J. F.; Guenther, D. B.; Kuschnig, R.; Weiss, W. W.; Rucinski, S. M.; Sasselov, D.

    2011-01-01

    A 30 day contiguous photometric run with the Microvariability and Oscillations of STars (MOST) satellite on the WN5-6b star WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 ± 0.55 days along with a number of harmonics at periods P/n, with n ∼ 2, 3, 4, 5, and 6, and a few other possible stray periodicities and/or stochastic variability on timescales longer than about a day. Spectroscopic radial velocity studies fail to reveal any plausible companion with a period in this range. Therefore, we conjecture that the observed light-curve cusps of amplitude ∼0.01 mag that recur at a 4.08 day timescale may arise in the inner parts, or at the base, of a corotating interaction region (CIR) seen in emission as it rotates around with the star at constant angular velocity. The hard X-ray component seen in WR 110 could then be a result of a high velocity component of the CIR shock interacting with the ambient wind at several stellar radii. Given that most hot, luminous stars showing CIRs have two CIR arms, it is possible that either the fundamental period is 8.2 days or, more likely in the case of WR 110, there is indeed a second weaker CIR arm for P = 4.08 days, that occurs ∼two-thirds of a rotation period after the main CIR. If this interpretation is correct, WR 110 therefore joins the ranks with three other single WR stars, all WN, with confirmed CIR rotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far the lowest amplitude photometric modulation. This illustrates the power of being able to secure intense, continuous high-precision photometry from space-based platforms such as MOST. It also opens the door to revealing low-amplitude photometric variations in other WN stars, where previous attempts have failed. If all WN stars have CIRs at some level, this could be important for revealing sources of magnetism or pulsation in addition to rotation periods.

  8. DISCOVERY OF LOW-METALLICITY STARS IN THE CENTRAL PARSEC OF THE MILKY WAY

    Do, Tuan [Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Kerzendorf, Wolfgang; Støstad, Morten [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Winsor, Nathan [Grenfell Campus—Memorial University of Newfoundland, St. John’s, NL A1B 3X9 (Canada); Morris, Mark R.; Ghez, Andrea M. [UCLA Galactic Center Group, Physics and Astronomy Department, UCLA, Los Angeles, CA 90095-1547 (United States); Lu, Jessica R., E-mail: tdo@astro.ucla.edu [Institute for Astronomy, University of Hawaii, Honolulu, HI (United States)

    2015-08-20

    We present a metallicity analysis of 83 late-type giants within the central 1 pc of the Milky Way. K-band spectroscopy of these stars was obtained with the medium spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guided star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is a large variation in the metallicity, with stars ranging from [M/H] < −1.0 to above solar metallicity. About 6% of the stars have [M/H] < −0.5. This result is in contrast to previous observations with smaller samples that show stars at the Galactic center having approximately solar metallicity with only small variations. Our current measurement uncertainties are dominated by systematics in the model, especially at [M/H] > 0, where there are stellar lines not represented in the model. However, the conclusion that there are low-metallicity stars, as well as large variations in metallicity, is robust. The metallicity may be an indicator of the origin of these stars. The low-metallicity population is consistent with that of globular clusters in the Milky Way, but their small fraction likely means that globular cluster infall is not the dominant mechanism for forming the Milky Way nuclear star cluster. The majority of stars are at or above solar metallicity, which suggests they were formed closer to the Galactic center or from the disk. In addition, our results indicate that it will be important for star formation history analyses using red giants at the Galactic center to consider the effect of varying metallicity.

  9. Temporal and spatial patterns in wind stress and wind stress curl over the central Southern California Bight

    Noble, Marlene A.; Rosenberger, Kurt J.; Rosenfeld, Leslie K.; Robertson, George L.

    2012-01-01

    In 2001, the U.S. Geological Survey, together with several other federal and municipal agencies, began a series of field programs to determine along and cross-shelf transport patterns over the continental shelves in the central Southern California Bight. As a part of these programs, moorings that monitor winds were deployed off the Palos Verdes peninsula and within San Pedro Bay for six 3–4 month summer and winter periods between 2001 and 2008. In addition, nearly continuous records of winds for this 7-year period were obtained from a terrestrial site at the coast and from a basin site offshore of the long-term coastal site. The mean annual winds are downcoast at all sites. The alongshelf components of wind stress, which are the largest part of the low-frequency wind stress fields, are well correlated between basin, shelf and coastal sites. On average, the amplitude of alongshelf fluctuations in wind stress are 3–4 times larger over the offshore basin, compared to the coastal site, irrespective of whether the fluctuations represent the total, or just the correlated portion of the wind stress field. The curl in the large-scale wind stress tends to be positive, especially in the winter season when the mean wind stress is downcoast and larger at the offshore basin site than at the beach. However, since the fluctuation in wind stress amplitudes are usually larger than the mean, periods of weak negative curl do occur, especially in the summer season when the largest normalized differences in the amplitude of wind stress fluctuations are found in the nearshore region of the coastal ocean. Even though the low-frequency wind stress field is well-correlated over the continental shelf and offshore basins, out to distances of 35 km or more from the coast, winds even 10 km inshore of the beach do not represent the coastal wind field, at least in the summer months. The seasonal changes in the spatial structures in wind stress amplitudes suggest that an assessment of the

  10. A combined HST and XMM-Newton campaign for the magnetic O9.7 V star HD 54879. Constraining the weak-wind problem of massive stars

    Shenar, T.; Oskinova, L. M.; Järvinen, S. P.; Luckas, P.; Hainich, R.; Todt, H.; Hubrig, S.; Sander, A. A. C.; Ilyin, I.; Hamann, W.-R.

    2017-10-01

    Context. HD 54879 (O9.7 V) is one of a dozen O-stars for which an organized atmospheric magnetic field has been detected. Despite their importance, little is known about the winds and evolution of magnetized massive stars. Aims: To gain insights into the interplay between atmospheres, winds, and magnetic fields of massive stars, we acquired UV and X-ray data of HD 54879 using the Hubble Space Telescope and the XMM-Newton satellite. In addition, 35 optical amateur spectra were secured to study the variability of HD 54879. Methods: A multiwavelength (X-ray to optical) spectral analysis is performed using the Potsdam Wolf-Rayet (PoWR) model atmosphere code and the xspec software. Results: The photospheric parameters (T∗ = 30.5 kK, log g = 4.0 [cm s-2], log L = 4.45 [L⊙]) are typical for an O9.7 V star. The microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (ξph,vmac,vsini ≤ 4 km s-1). An initial mass of 16 M⊙ and an age of 5 Myr are inferred from evolutionary tracks. We derive a mean X-ray emitting temperature of log TX = 6.7 [K] and an X-ray luminosity of LX = 1 × 1032 erg s-1. Short- and long-scale variability is seen in the Hα line, but only a very long period of P ≈ 5 yr could be estimated. Assessing the circumstellar density of HD 54879 using UV spectra, we can roughly estimate the mass-loss rate HD 54879 would have in the absence of a magnetic field as log ṀB = 0 ≈ -9.0 [M⊙ yr-1]. The magnetic field traps the stellar wind up to the Alfvén radius rA ≳ 12 R∗, implying that its true mass-loss rate is log Ṁ ≲ -10.2 [M⊙ yr-1]. Hence, density enhancements around magnetic stars can be exploited to estimate mass-loss rates of non-magnetic stars of similar spectral types, essential for resolving the weak wind problem. Conclusions: Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence

  11. New Frontiers for Massive Star Winds: Imaging and Spectroscopy with the James Webb Space Telescope

    Sonneborn, George

    2007-01-01

    The James Webb Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2013. JWST will find the first stars and galaxies that formed in the early universe, connecting the Big Bang to our own Milky Way galaxy. JWST will peer through dusty clouds to see stars forming planetary systems, connecting the Milky Way to our own Solar System. JWST's instruments are designed to work primarily in the infrared range of 1 - 28 microns, with some capability in the visible range. JWST will have a large mirror, 6.5 meters in diameter, and will be diffraction-limited at 2 microns (0.1 arcsec resolution). JWST will be placed in an L2 orbit about 1.5 million km from the Earth. The instruments will provide imaging, coronography, and multi-object and integral-field spectroscopy across the full 1 - 28 micron wavelength range. The breakthrough capabilities of JWST will enable new studies of massive star winds from the Milky Way to the early universe.

  12. ENERGY STAR Certified Non-AHRI Central Air Conditioner Equipment and Air Source Heat Pump

    Certified models meet all ENERGY STAR requirements as listed in the Version 5.0 ENERGY STAR Program Requirements for Air Source Heat Pump and Central Air Conditioner Equipment that are effective as of September 15, 2015. A detailed listing of key efficiency criteria are available at http://www.energystar.gov/index.cfm?c=airsrc_heat.pr_crit_as_heat_pumps Listed products have been submitted to EPA by ENERGY STAR partners that do not participate in the AHRI certification program. EPA will continue to update this list with products that are certified by EPA-recognized certification bodies other than AHRI. The majority of ENERGY STAR products, certified by AHRI, can be found on the CEE/AHRI Verified Directory at http://www.ceedirectory.org/

  13. Fluid power network for centralized electricity generation in offshore wind farms

    Jarquin-Laguna, A.

    2014-01-01

    An innovative and completely different wind-energy conversion system is studied where a centralized electricity generation within a wind farm is proposed by means of a hydraulic network. This paper presents the dynamic interaction of two turbines when they are coupled to the same hydraulic network.

  14. Simulation of an offshore wind farm using fluid power for centralized electricity generation

    Jarquin-Laguna, A

    2016-01-01

    A centralized approach for electricity generation within a wind farm is explored through the use of fluid power technology. This concept considers a new way of generation, collection and transmission of wind energy inside a wind farm, in which electrical conversion does not occur during any intermediate conversion step before the energy has reached the offshore central platform. A numerical model was developed to capture the relevant physics from the dynamic interaction between different turbines coupled to a common hydraulic network and controller. This paper presents two examples of the time-domain simulation results for an hypothetical hydraulic wind farm subject to turbulent wind conditions. The performance and operational parameters of individual turbines are compared with those of a reference wind farm with conventional technology turbines, using the same wind farm layout and environmental conditions. For the presented case study, results indicate that the individual wind turbines are able to operate within operational limits with the current pressure control concept. Despite the stochastic turbulent wind input and wake effects, the hydraulic wind farm is able to produce electricity with reasonable performance in both below and above rated conditions. (paper)

  15. Comoving frame models of hot star winds I. Test of the Sobolev approximation in the case of pure line transitions

    Krtička, J.; Kubát, Jiří

    2010-01-01

    Roč. 519, September (2010), A50/1-A50/9 ISSN 0004-6361 R&D Projects: GA ČR GA205/07/0031 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * winds * outflows Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.410, year: 2010

  16. Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis

    David-Uraz, A.; Wade, G.A.; Petit, V.; ud-Doula, A.; Sundqvist, J.O.; Grunhut, J.; Schultz, M.; Neiner, C.; Alecian, E.; Henrichs, H.F.; Bouret, J.-C.

    2014-01-01

    OB stars exhibit various types of spectral variability associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These are proposed to be caused by either magnetic fields or non-radial pulsations. In this paper, we evaluate the possible relation

  17. BINARY CENTRAL STARS OF PLANETARY NEBULAE DISCOVERED THROUGH PHOTOMETRIC VARIABILITY. II. MODELING THE CENTRAL STARS OF NGC 6026 AND NGC 6337

    Hillwig, Todd C.; Bond, Howard E.; Afsar, Melike; De Marco, Orsola

    2010-01-01

    Close-binary central stars of planetary nebulae (CSPNe) provide an opportunity to explore the evolution of PNe, their shaping, and the evolution of binary systems undergoing a common-envelope phase. Here, we present the results of time-resolved photometry of the binary central stars (CSs) of the PNe NGC 6026 and NGC 6337 as well as time-resolved spectroscopy of the CS of NGC 6026. The results of a period analysis give an orbital period of 0.528086(4) days for NGC 6026 and a photometric period of 0.1734742(5) days for NGC 6337. In the case of NGC 6337, it appears that the photometric period reflects the orbital period and that the variability is the result of the irradiated hemisphere of a cool companion. The inclination of the thin PN ring is nearly face-on. Our modeled inclination range for the close central binary includes nearly face-on alignments and provides evidence for a direct binary-nebular shaping connection. For NGC 6026, however, the radial-velocity curve shows that the orbital period is twice the photometric period. In this case, the photometric variability is due to an ellipsoidal effect in which the CS nearly fills its Roche lobe and the companion is most likely a hot white dwarf. NGC 6026 then is the third PN with a confirmed central binary where the companion is compact. Based on the data and modeling using a Wilson-Devinney code, we discuss the physical parameters of the two systems and how they relate to the known sample of close-binary CSs, which comprise 15%-20% of all PNe.

  18. Central regions of LIRGs: rings, hidden starbursts, Supernovae and star clusters

    Väisänen, Petri; Randriamanakoto, Zara; Escala, Andres; Kankare, Erkki; Mattila, Seppo; Reunanen, Juha; Kotilainen, Jari; Rajpaul, Vinesh; Ryder, Stuart; Zijlstra, Albert

    2012-01-01

    We study star formation (SF) in very active environments, in luminous IR galaxies, which are often interacting. A variety of phenomena are detected, such as central starbursts, circumnuclear SF, obscured SNe tracing the history of recent SF, massive super star clusters, and sites of strong off-nuclear SF. All of these can be ultimately used to define the sequence of triggering and propagation of star-formation and interplay with nuclear activity in the lives of gas rich galaxy interactions and mergers. In this paper we present analysis of high-spatial resolution integral field spectroscopy of central regions of two interacting LIRGs. We detect a nuclear 3.3 μm PAH ring around the core of NGC 1614 with thermal-IR IFU observations. The ring's characteristics and relation to the strong star-forming ring detected in recombination lines are presented, as well as a scenario of an outward expanding starburst likely initiated with a (minor) companion detected within a tidal feature. We then present NIR IFU observations of IRAS 19115-2124, aka the Bird, which is an intriguing triple encounter. The third component is a minor one, but, nevertheless, is the source of 3/4 of the SFR of the whole system. Gas inflows and outflows are detected in their nuclei locations. Finally, we briefly report on our on-going NIR adaptive optics imaging survey of several dozen LIRGs. We have detected highly obscured core-collapse SNe in the central kpc, and discuss the statistics of 'missing SNe' due to dust extinction. We are also determining the characteristics of hundreds of super star clusters in and around the core regions of LIRGs, as a function of host-galaxy properties.

  19. The binary fraction of planetary nebula central stars - III. the promise of VPHAS+

    Barker, Helen; Zijlstra, Albert; De Marco, Orsola; Frew, David J.; Drew, Janet E.; Corradi, Romano L. M.; Eislöffel, Jochen; Parker, Quentin A.

    2018-04-01

    The majority of planetary nebulae (PNe) are not spherical, and current single-star models cannot adequately explain all the morphologies we observe. This has led to the Binary Hypothesis, which states that PNe are preferentially formed by binary systems. This hypothesis can be corroborated or disproved by comparing the estimated binary fraction of all PNe central stars (CS) to that of the supposed progenitor population. One way to quantify the rate of CS binarity is to detect near infrared excess indicative of a low-mass main-sequence companion. In this paper, a sample of known PNe within data release 2 of the ongoing VPHAS+ is investigated. We give details of the method used to calibrate VPHAS+ photometry, and present the expected colours of CS and main-sequence stars within the survey. Objects were scrutinized to remove PN mimics from our sample and identify true CS. Within our final sample of seven CS, six had previously either not been identified or confirmed. We detected an i-band excess indicative of a low-mass companion star in three CS, including one known binary, leading us to conclude that VPHAS+ provides the precise photometry required for the IR excess method presented here, and will likely improve as the survey completes and the calibration process finalized. Given the promising results from this trial sample, the entire VPHAS+ catalogue should be used to study PNe and extend the IR excess-tested CS sample.

  20. The UK Infrared Telescope M33 monitoring project - I. Variable red giant stars in the central square kiloparsec

    Javadi, Atefeh; van Loon, Jacco Th.; Mirtorabi, Mohammad Taghi

    2011-02-01

    We have conducted a near-infrared monitoring campaign at the UK Infrared Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive data set was obtained in the K band with the UIST instrument for the central 4 × 4 arcmin2 (1 kpc2) - this contains the nuclear star cluster and inner disc. These data, taken during the period 2003-2007, were complemented by J- and H-band images. Photometry was obtained for 18 398 stars in this region; of these, 812 stars were found to be variable, most of which are asymptotic giant branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the variability survey and the photometric catalogue - which is made publicly available at the Centre de Données astronomiques de Strasbourg - and discuss the properties of the variable stars. The most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey.

  1. The central star candidate of the planetary nebula Sh2-71: photometric and spectroscopic variability

    Močnik, T.; Lloyd, M.; Pollacco, D.; Street, R. A.

    2015-07-01

    We present the analysis of several newly obtained and archived photometric and spectroscopic data sets of the intriguing and yet poorly understood 13.5 mag central star candidate of the bipolar planetary nebula Sh2-71. Photometric observations confirmed the previously determined quasi-sinusoidal light curve with a period of 68 d and also indicated periodic sharp brightness dips, possibly eclipses, with a period of 17.2 d. In addition, the comparison between U and V light curves revealed that the 68 d brightness variations are accompanied by a variable reddening effect of ΔE(U - V) = 0.38. Spectroscopic data sets demonstrated pronounced variations in spectral profiles of Balmer, helium and singly ionized metal lines and indicated that these variations occur on a time-scale of a few days. The most accurate verification to date revealed that spectral variability is not correlated with the 68 d brightness variations. The mean radial velocity of the observed star was measured to be ˜26 km s-1 with an amplitude of ±40 km s-1. The spectral type was determined to be B8V through spectral comparison with synthetic and standard spectra. The newly proposed model for the central star candidate is a Be binary with a misaligned precessing disc.

  2. REVEALING THE ASYMMETRY OF THE WIND OF THE VARIABLE WOLF-RAYET STAR WR1 (HD 4004) THROUGH SPECTROPOLARIZATION

    St-Louis, N., E-mail: stlouis@astro.umontreal.ca [Département de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, C.P. 6128, Succ. Centre Ville, Montréal, QC H3C 3J7 (Canada)

    2013-11-01

    In this paper, high quality spectropolarimetric observations of the Wolf-Rayet (WR) star WR1 (HD 4004) obtained with ESPaDOnS at the Canada-France-Hawaii Telescope are presented. All major emission lines present in the spectrum show depolarization in the relative Stokes parameters Q/I and U/I. From the behavior of the amount of line depolarization as a function of line strength, the intrinsic continuum light polarization of WR1 is estimated to be P/I = 0.443% ± 0.028% with an angle of θ = –26.°2. Although such a level of polarization could in principle be caused by a wind flattened by fast rotation, the scenario in which it is a consequence of the presence of corotating interaction regions (CIRs) in the wind is preferred. This is supported by previous photometric and spectroscopic observations showing periodic variations with a period of 16.9 days. This is now the third WR star thought to exhibit CIRs in its wind that is found to have line depolarization. Previous authors have found a strong correlation between line depolarization and the presence of an ejected nebula, which they interpret as a sign that the star has relatively recently reached the WR phase since the nebula are thought to dissipate very fast. In cases where the presence of CIRs in the wind is favored to explain the depolarization across spectral lines, the above-mentioned correlation may indicate that those massive stars have only very recently transited from the previous evolutionary phase to the WR phase.

  3. Extragalactic gamma-ray background from AGN winds and star-forming galaxies in cosmological galaxy-formation models

    Lamastra, A.; Menci, N.; Fiore, F.; Antonelli, L. A.; Colafrancesco, S.; Guetta, D.; Stamerra, A.

    2017-10-01

    We derive the contribution to the extragalactic gamma-ray background (EGB) from active galactic nuclei (AGN) winds and star-forming galaxies by including a physical model for the γ-ray emission produced by relativistic protons accelerated by AGN-driven and supernova-driven shocks into a state-of-the-art semi-analytic model of galaxy formation. This is based on galaxy interactions as triggers of AGN accretion and starburst activity and on expanding blast waves as the mechanism to communicate outwards the energy injected into the interstellar medium by the active nucleus. We compare the model predictions with the latest measurement of the EGB spectrum performed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) in the range between 100 MeV and 820 GeV. We find that AGN winds can provide 35 ± 15% of the observed EGB in the energy interval Eγ = 0.1-1 GeV, for 73 ± 15% at Eγ = 1-10 GeV, and for 60 ± 20% at Eγ ≳10 GeV. The AGN wind contribution to the EGB is predicted to be larger by a factor of 3-5 than that provided by star-forming galaxies (quiescent plus starburst) in the hierarchical clustering scenario. The cumulative γ-ray emission from AGN winds and blazars can account for the amplitude and spectral shape of the EGB, assuming the standard acceleration theory, and AGN wind parameters that agree with observations. We also compare the model prediction for the cumulative neutrino background from AGN winds with the most recent IceCube data. We find that for AGN winds with accelerated proton spectral index p = 2.2-2.3, and taking into account internal absorption of γ-rays, the Fermi-LAT and IceCube data could be reproduced simultaneously.

  4. On the synthesis of resonance lines in dynamical models of structured hot-star winds

    Puls, J.; Owocki, S. P.; Fullerton, A. W.

    1993-01-01

    We examine basic issues involved in synthesizing resonance-line profiles from 1-D, dynamical models of highly structured hot-star winds. Although these models exhibit extensive variations in density as well as velocity, the density scale length is still typically much greater than the Sobolev length. The line transfer is thus treated using a Sobolev approach, as generalized by Rybicki & Hummer (1978) to take proper account of the multiple Sobolev resonances arising from the nonmonotonic velocity field. The resulting reduced-lambda-matrix equation describing nonlocal coupling of the source function is solved by iteration, and line profiles are then derived from formal solution integration using this source function. Two more approximate methods that instead use either a stationary or a structured, local source function yield qualitatively similar line-profiles, but are found to violate photon conservation by 10% or more. The full results suggest that such models may indeed be able to reproduce naturally some of the qualitative properties long noted in observed UV line profiles, such as discrete absorption components in unsaturated lines, or the blue-edge variability in saturated lines. However, these particular models do not yet produce the black absorption troughs commonly observed in saturated lines, and it seems that this and other important discrepancies (e.g., in acceleration time scale of absorption components) may require development of more complete models that include rotation and other 2-D and/or 3-D effects.

  5. Wind-energy Science, Technology and Research (WindSTAR) Consortium: Curriculum, Workforce Development, and Education Plan Final Report

    Manwell, James [Univ. of Massachusetts, Amherst, MA (United States)

    2013-03-19

    The purpose of the project is to modify and expand the current wind energy curriculum at the University of Massachusetts Amherst and to develop plans to expand the graduate program to a national scale. The expansion plans include the foundational steps to establish the American Academy of Wind Energy (AAWE). The AAWE is intended to be a cooperative organization of wind energy research, development, and deployment institutes and universities across North America, whose mission will be to develop and execute joint RD&D projects and to organize high-level science and education in wind energy

  6. Numerical Simulations of Multiphase Winds and Fountains from Star-forming Galactic Disks. I. Solar Neighborhood TIGRESS Model

    Kim, Chang-Goo; Ostriker, Eve C.

    2018-02-01

    Gas blown away from galactic disks by supernova (SN) feedback plays a key role in galaxy evolution. We investigate outflows utilizing the solar neighborhood model of our high-resolution, local galactic disk simulation suite, TIGRESS. In our numerical implementation, star formation and SN feedback are self-consistently treated and well resolved in the multiphase, turbulent, magnetized interstellar medium. Bursts of star formation produce spatially and temporally correlated SNe that drive strong outflows, consisting of hot (T> 5× {10}5 {{K}}) winds and warm (5050 {{K}} 1 {kpc} from the midplane has mass and energy fluxes nearly constant with d. The hot flow escapes our local Cartesian box barely affected by gravity, and is expected to accelerate up to terminal velocity of {v}{wind}∼ 350{--}500 {km} {{{s}}}-1. The mean mass and energy loading factors of the hot wind are 0.1 and 0.02, respectively. For warm gas, the mean outward mass flux through d=1 {kpc} is comparable to the mean star formation rate, but only a small fraction of this gas is at velocity > 50 {km} {{{s}}}-1. Thus, the warm outflows eventually fall back as inflows. The warm fountain flows are created by expanding hot superbubbles at d< 1 {kpc}; at larger d neither ram pressure acceleration nor cooling transfers significant momentum or energy flux from the hot wind to the warm outflow. The velocity distribution at launching near d∼ 1 {kpc} is a better representation of warm outflows than a single mass loading factor, potentially enabling development of subgrid models for warm galactic winds in arbitrary large-scale galactic potentials.

  7. FIRST INVESTIGATION OF THE COMBINED IMPACT OF IONIZING RADIATION AND MOMENTUM WINDS FROM A MASSIVE STAR ON A SELF-GRAVITATING CORE

    Ngoumou, Judith; Hubber, David; Dale, James E.; Burkert, Andreas

    2015-01-01

    Massive stars shape the surrounding interstellar matter (ISM) by emitting ionizing photons and ejecting material through stellar winds. To study the impact of the momentum from the wind of a massive star on the surrounding neutral or ionized material, we implemented a new HEALPix-based momentum-conserving wind scheme in the smoothed particle hydrodynamics (SPH) code SEREN. A qualitative study of the impact of the feedback from an O7.5-like star on a self-gravitating sphere shows that on its own, the transfer of momentum from a wind onto cold surrounding gas has both a compressing and dispersing effect. It mostly affects gas at low and intermediate densities. When combined with a stellar source's ionizing ultraviolet (UV) radiation, we find the momentum-driven wind to have little direct effect on the gas. We conclude that during a massive star's main sequence, the UV ionizing radiation is the main feedback mechanism shaping and compressing the cold gas. Overall, the wind's effects on the dense gas dynamics and on the triggering of star formation are very modest. The structures formed in the ionization-only simulation and in the combined feedback simulation are remarkably similar. However, in the combined feedback case, different SPH particles end up being compressed. This indicates that the microphysics of gas mixing differ between the two feedback simulations and that the winds can contribute to the localized redistribution and reshuffling of gas

  8. MPC for Wind Power Gradients - Utilizing Forecasts, Rotor Inertia, and Central Energy Storage

    Hovgaard, Tobias Gybel; Larsen, Lars F. S.; Jørgensen, John Bagterp

    2013-01-01

    decentralized energy storage in the turbines’ inertia combined with a central storage unit or deferrable consumers can be utilized to achieve this goal at a minimum cost. We propose a variation on model predictive control to incorporate predictions of wind speed. Due to the aerodynamics of the turbines...

  9. Climate Prediction Center (CPC)Area-averaged 850-hPa Central Pacific Trade Wind Anomalies

    National Oceanic and Atmospheric Administration, Department of Commerce — This is one of the CPC?s Monthly Atmospheric and SST Indices. It is the 850-hPa trade wind anomalies averaged over the area 5oN ? 5oS, 175oW-140oW (central...

  10. Modelling the day to day wind variability offshore central Chile at about 30 deg. south

    Rutllant, J.

    1994-07-01

    Cycles of strengthening and relaxation of the winds offshore 30 degrees S at central Chile, are related to the propagation of coastal-lows, a year-round phenomenon occurring with periodicities of about one in five days. Simple physical modelling of the day to day variability of the alongshore wind component at a coastal strip extending offshore up to the Rossby deformation radius of these wave perturbations, is presented in terms of the relevant horizontal pressure gradients and the ageostrophic components arising from the coastal-low propagation. The results of 5-day composites of 8 wind-events each, at the winter and summer halves of the annual cycle, respectively; lead to a good agreement between the observed phase-lag of the winds with respect to the pressure forcing field, stressing the importance of the ageostrophic wind components at the extremes of the pressure wave perturbation associated with the passage of coastal-lows over the Point Lengua de Vaca (30 15 S) area. A possible contribution of the upwelling-favorable wind enhancement at the time of the pressure rise and subsequent fall, ahead of the coastal-low, is postulated through an upwelling-front low-level jet, that would be carried onshore and closer to the surface by the combination of the enhanced coastal upwelling, the coastal depression of the subsidence inversion base and the coastal ageostrophic wind components during the passage of the leading edge of the coastal lows. (author). 26 refs, 5 figs, 1 tab

  11. VLTI-AMBER Velocity-Resolved Aperture-Synthesis Imaging of Eta Carinae with a Spectral Resolution of 12 000: Studies of the Primary Star Wind and Innermost Wind-Wind Collision Zone

    Weigelt, G.; Hofmann, K.-H.; Schertl, D.; Clementel, N.; Corcoran, M. F.; Damineli, A.; de Wit, W.-J.; Grellmann, R.; Groh, J.; Guieu, S.; hide

    2016-01-01

    The mass loss from massive stars is not understood well. Eta Carinae is a unique object for studying the massive stellar wind during the luminous blue variable phase. It is also an eccentric binary with a period of 5.54 yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. Aims. We want to investigate the structure and kinematics of Car's primary star wind and wind-wind collision zone with a high spatial resolution of approx.6 mas (approx.14 au) and high spectral resolution of R = 12 000. Methods. Observations of Car were carried out with the ESO Very Large Telescope Interferometer (VLTI) and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision. Results. We present velocity-resolved aperture-synthesis images reconstructed in more than 100 di erent spectral channels distributed across the Br(gamma) 2.166 micron emission line. The intensity distribution of the images strongly depends on wavelength. At wavelengths corresponding to radial velocities of approximately -140 to -376 km/s measured relative to line center, the intensity distribution has a fan-shaped structure. At the velocity of -277 km/s, the position angle of the symmetry axis of the fan is 126. The fan-shaped structure extends approximately 8.0 mas (approx.18:8 au) to the southeast and 5.8 mas (approx.13:6 au) to the northwest, measured along the symmetry axis at the 16% intensity contour. The shape of the intensity distributions suggests that the obtained images are the first direct images of the innermost wind-wind collision zone. Therefore, the observations provide velocity-dependent image structures that can be used to test three

  12. A GMOS-N IFU study of the central H II region in the blue compact dwarf galaxy NGC 4449: kinematics, nebular metallicity and star formation

    Kumari, Nimisha; James, Bethan L.; Irwin, Mike J.

    2017-10-01

    We use integral field spectroscopic (IFS) observations from the Gemini Multi-Object Spectrograph North (GMOS-N) to study the central H II region in a nearby blue compact dwarf (BCD) galaxy NGC 4449. The IFS data enable us to explore the variation of physical and chemical conditions of the star-forming region and the surrounding gas on spatial scales as small as 5.5 pc. Our kinematical analysis shows possible signatures of shock ionization and shell structures in the surroundings of the star-forming region. The metallicity maps of the region, created using direct Te and indirect strong line methods (R23, O3N2 and N2), do not show any chemical variation. From the integrated spectrum of the central H II region, we find a metallicity of 12 + log(O/H) = 7.88 ± 0.14 ({˜ }0.15^{+0.06}_{-0.04} Z⊙) using the direct method. Comparing the central H II region metallicity derived here with those of H II regions throughout this galaxy from previous studies, we find evidence of increasing metallicity with distance from the central nucleus. Such chemical inhomogeneities can be due to several mechanisms, including gas loss via supernova blowout, galactic winds or metal-poor gas accretion. However, we find that the localized area of decreased metallicity aligns spatially with the peak of star-forming activity in the galaxy, suggesting that gas accretion may be at play here. Spatially resolved IFS data for the entire galaxy are required to confirm the metallicity inhomogeneity found in this study and determine its possible cause.

  13. Earth Observation Data Quality Monitoring and Control: A Case Study of STAR Central Data Repository

    Han, W.; Jochum, M.

    2017-12-01

    Earth observation data quality is very important for researchers and decision makers involved in weather forecasting, severe weather warning, disaster and emergency response, environmental monitoring, etc. Monitoring and control earth observation data quality, especially accuracy, completeness, and timeliness, is very useful in data management and governance to optimize data flow, discover potential transmission issues, and better connect data providers and users. Taking a centralized near real-time satellite data repository, STAR (Center for Satellite Applications and Research of NOAA) Central Data Repository (SCDR), as an example, this paper describes how to develop new mechanism to verify data integrity, check data completeness, and monitor data latency in an operational data management system. Such quality monitoring and control of large volume satellite data help data providers and managers improve data transmission of near real-time satellite data, enhance its acquisition and management, and overcome performance and management issues to better serve research and development activities.

  14. Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds. III. X-ray emission from wind-embedded shocks

    Carneiro, L. P.; Puls, J.; Sundqvist, J. O.; Hoffmann, T. L.

    2016-05-01

    Context. Extreme ultraviolet (EUV) and X-ray radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres and can be the mechanism responsible for producing highly ionized atomic species detected in stellar wind UV spectra. Aims: To allow for these processes in the context of spectral analysis, we have implemented the emission from wind-embedded shocks and related physics into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. Methods: The shock structure and corresponding emission is calculated as a function of user-supplied parameters (volume filling factor, radial stratification of shock strength, and radial onset of emission). We account for a temperature and density stratification inside the postshock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included in the NLTE network. To test our implementation and to check the resulting effects, we calculated a comprehensive model grid with a variety of X-ray emission parameters. Results: We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of O iv/O v (particularly in dwarfs with Teff~ 45 000 K). Finally, we investigated the frequency dependence and radial behavior of the mass absorption coefficient, κν(r), which is important in the context of X-ray line formation in massive star winds. Conclusions: In almost all of the cases considered, direct ionization is of major influence because of the enhanced EUV radiation field, and Auger ionization only affects N vi

  15. Model-Atmosphere Spectra of Central Stars of Planetary Nebulae - Access via the Virtual Observatory Service TheoSSA

    Rauch, T.; Reindl, N.

    2014-04-01

    In the framework of the Virtual Observatory (VO), the German Astrophysical Virtual Observatory GAVO project provides easy access to theoretical spectral energy distributions (SEDs) within the registered GAVO service TheoSSA (http://dc.g-vo.org/theossa). TheoSSA is based on the well established Tübingen NLTE Model-Atmosphere Package (TMAP) for hot, compact stars. This includes central stars of planetary nebulae. We show examples of TheoSSA in operation.

  16. The extraordinary mass-loss bubble G2.4 + 1.4 and its central star

    Dopita, M.A.; Mcgregor, P.J.; Rawlings, S.J.; Lozinskaia, T.A.

    1990-01-01

    Data are presented on the WR 102 star and the surrounding nebula (G2.4 + 1.4). It is shown that WR 102 and the nebula are associated, the nebula being a mass-loss bubble powered by the central star. From a photoionization analysis of the surrounding nebula, the star was determined to have the following parameters: log T(ion) = 5.20 + or - 0.05; log (R/solar R) = about 0.05; and log (L/solar L) = 5.85 + or - 0.20. 42 refs

  17. Wintering Sandhill Crane exposure to wind energy development in the central and southern Great Plains, USA

    Pearse, Aaron T.; Brandt, David; Krapu, Gary

    2016-01-01

    Numerous wind energy projects have been constructed in the central and southern Great Plains, USA, the main wintering area for midcontinental Sandhill Cranes (Grus canadensis). In an initial assessment of the potential risks of wind towers to cranes, we estimated spatial overlap, investigated potential avoidance behavior, and determined the habitat associations of cranes. We used data from cranes marked with platform transmitting terminals (PTTs) with and without global positioning system (GPS) capabilities. We estimated the wintering distributions of PTT-marked cranes prior to the construction of wind towers, which we compared with current tower locations. Based on this analysis, we found 7% spatial overlap between the distributions of cranes and towers. When we looked at individually marked cranes, we found that 52% would have occurred within 10 km of a tower at some point during winter. Using data from cranes marked after tower construction, we found a potential indication of avoidance behavior, whereby GPS-marked cranes generally used areas slightly more distant from existing wind towers than would be expected by chance. Results from a habitat selection model suggested that distances between crane locations and towers may have been driven more by habitat selection than by avoidance, as most wind towers were constructed in locations not often selected by wintering cranes. Our findings of modest regional overlap and that few towers have been placed in preferred crane habitat suggest that the current distribution of wind towers may be of low risk to the continued persistence of wintering midcontinental Sandhill Cranes in the central and southern Great Plains.

  18. THE TRANSITION MASS-LOSS RATE: CALIBRATING THE ROLE OF LINE-DRIVEN WINDS IN MASSIVE STAR EVOLUTION

    Vink, Jorick S.; Graefener, Goetz, E-mail: jsv@arm.ac.uk [Armagh Observatory, College Hill, BT61 9DG Armagh (United Kingdom)

    2012-06-01

    A debate has arisen regarding the importance of stationary versus eruptive mass loss for massive star evolution. The reason is that stellar winds have been found to be clumped, which results in the reduction of unclumped empirical mass-loss rates. Most stellar evolution models employ theoretical mass-loss rates which are already reduced by a moderate factor of {approx_equal}2-3 compared to non-corrected empirical rates. A key question is whether these reduced rates are of the correct order of magnitude, or if they should be reduced even further, which would mean that the alternative of eruptive mass loss becomes necessary. Here we introduce the transition mass-loss rate M-dot{sub trans} between O and Wolf-Rayet stars. Its novelty is that it is model independent. All that is required is postulating the spectroscopic transition point in a given data set, and determining the stellar luminosity, which is far less model dependent than the mass-loss rate. The transition mass-loss rate is subsequently used to calibrate stellar wind strength by its application to the Of/WNh stars in the Arches cluster. Good agreement is found with two alternative modeling/theoretical results, suggesting that the rates provided by current theoretical models are of the right order of magnitude in the {approx}50 M{sub Sun} mass range. Our results do not confirm the specific need for eruptive mass loss as luminous blue variables, and current stellar evolution modeling for Galactic massive stars seems sound. Mass loss through alternative mechanisms might still become necessary at lower masses, and/or metallicities, and the quantification of alternative mass loss is desirable.

  19. THE TRANSITION MASS-LOSS RATE: CALIBRATING THE ROLE OF LINE-DRIVEN WINDS IN MASSIVE STAR EVOLUTION

    Vink, Jorick S.; Gräfener, Götz

    2012-01-01

    A debate has arisen regarding the importance of stationary versus eruptive mass loss for massive star evolution. The reason is that stellar winds have been found to be clumped, which results in the reduction of unclumped empirical mass-loss rates. Most stellar evolution models employ theoretical mass-loss rates which are already reduced by a moderate factor of ≅2-3 compared to non-corrected empirical rates. A key question is whether these reduced rates are of the correct order of magnitude, or if they should be reduced even further, which would mean that the alternative of eruptive mass loss becomes necessary. Here we introduce the transition mass-loss rate M-dot trans between O and Wolf-Rayet stars. Its novelty is that it is model independent. All that is required is postulating the spectroscopic transition point in a given data set, and determining the stellar luminosity, which is far less model dependent than the mass-loss rate. The transition mass-loss rate is subsequently used to calibrate stellar wind strength by its application to the Of/WNh stars in the Arches cluster. Good agreement is found with two alternative modeling/theoretical results, suggesting that the rates provided by current theoretical models are of the right order of magnitude in the ∼50 M ☉ mass range. Our results do not confirm the specific need for eruptive mass loss as luminous blue variables, and current stellar evolution modeling for Galactic massive stars seems sound. Mass loss through alternative mechanisms might still become necessary at lower masses, and/or metallicities, and the quantification of alternative mass loss is desirable.

  20. IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

    Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

    2017-04-01

    We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

  1. Evolution of Mass Functions of Coeval Stars through Wind Mass Loss and Binary Interactions

    Schneider, F.R.N.; Izzard, R.G.; Langer, N.; de Mink, S.E.

    2015-01-01

    Accurate determinations of stellar mass functions and ages of stellar populations are crucial to much of astrophysics. We analyze the evolution of stellar mass functions of coeval main-sequence stars, including all relevant aspects of single and binary star evolution. We show that the slope of the

  2. Star-disc interaction in galactic nuclei: formation of a central stellar disc

    Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

    2018-05-01

    We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

  3. On-Shore Central Hydraulic Power Generation for Wind and Tidal Energy

    Jones, Jack A.; Bruce, Allan; Lim, Steven; Murray, Luke; Armstrong, Richard; Kimbrall, Richard; Cook-Chenault, Kimberly; DeGennaro, Sean

    2012-01-01

    Tidal energy, offshore wind energy, and onshore wind energy can be converted to electricity at a central ground location by means of converting their respective energies into high-pressure hydraulic flows that are transmitted to a system of generators by high-pressure pipelines. The high-pressure flows are then efficiently converted to electricity by a central power plant, and the low-pressure outlet flow is returned. The Department of Energy (DOE) is presently supporting a project led by Sunlight Photonics to demonstrate a 15 kW tidal hydraulic power generation system in the laboratory and possibly later submerged in the ocean. All gears and submerged electronics are completely eliminated. A second portion of this DOE project involves sizing and costing a 15 MW tidal energy system for a commercial tidal energy plant. For this task, Atlantis Resources Corporation s 18-m diameter demonstrated tidal blades are rated to operate in a nominal 2.6 m/sec tidal flow to produce approximately one MW per set of tidal blades. Fifteen units would be submerged in a deep tidal area, such as in Maine s Western Passage. All would be connected to a high-pressure (20 MPa, 2900 psi) line that is 35 cm ID. The high-pressure HEPG fluid flow is transported 500-m to on-shore hydraulic generators. HEPG is an environmentally-friendly, biodegradable, watermiscible fluid. Hydraulic adaptations to ORPC s cross-flow turbines are also discussed. For 15 MW of wind energy that is onshore or offshore, a gearless, high efficiency, radial piston pump can replace each set of top-mounted gear-generators. The fluid is then pumped to a central, easily serviceable generator location. Total hydraulic/electrical efficiency is 0.81 at full rated wind or tidal velocities and increases to 0.86 at 1/3 rated velocities.

  4. (F)UV Spectral Analysis of 15 Hot, Hydrogen-Rich Central Stars of PNe

    Ziegler, Marc

    2013-07-01

    the sample are still too small to start gravitational settling. For the elements C, N, O, Si, P, and S we find increasing abundances with increasing log(Teff^4/g), while the abundances for Ar and Fe decrease. The latter is unexpected as the higher the Teff^4/g ratio, the more the radiative force dominates the gravitational force and, thus, the elements should be kept in the atmosphere. The determined abundances were compared with previous literature values, with abundances predicted from diusion calculations, with abundances from Asymptotic Giant Branch (AGB) nucleosynthesis calculations, and, if available, with abundances found for the corresponding nebulae. The agreement was of mixed quality. The derived Teff and log g values confirmed some literature values while others had to be revised (e.g. for LSS 1362 and NGC1360). However, most of them agree with the previous literature values within the error limits. No difference in Teff can be found for DAO and O(H)-type stars, but O(H)-type stars have a lower log g (5.4 - 6.0) compared to the DAOs (6.5 - 7.4). The exception is the O(H)-type central star of the planetary nebula (CSPN) of Lo 1 with log g = 7.0. A comparison of the positions of each object with stellar evolutionary tracks for post-AGB stars in the log Teff - log g diagram lead to the respective stellar masses. The derived mean mass of the analyzed sample (M = 0.536 ± 0.023 Msol) agrees within the error limits with the expected mean mass for these objects. In the literature M = 0.638 - 0.145 Msol can be found for DA-type white dwarfs, the immediate successors of DAO-type white dwarfs. For two objects (A 35, Sh 2-174) extremely low masses were found. For A35 the derived mass (M_A35 = 0.523 ± 0.05Msol) lies at the lower end of possible masses predicted for post-AGB stars. The very low mass of Sh 2-174 (M_Sh 2-174 = 0.395 ± 0.05Msol) points at Sh 2-174 being a post-extended horizontal branch (EHB) star and not a CSPN. If a stellar mass is too low, it is

  5. NuSTAR View of the Black Hole Wind in the Galaxy Merger IRAS F11119+3257

    Tombesi, F.; Veilleux, S.; Meléndez, M.; Lohfink, A.; Reeves, J. N.; Piconcelli, E.; Fiore, F.; Feruglio, C.

    2017-12-01

    Galactic winds driven by active galactic nuclei (AGNs) have been invoked to play a fundamental role in the co-evolution between supermassive black holes and their host galaxies. Finding observational evidence of such feedback mechanisms is of crucial importance and it requires a multi-wavelength approach in order to compare winds at different scales and phases. In Tombesi et al., we reported the detection of a powerful ultra-fast outflow (UFO) in the Suzaku X-ray spectrum of the ultra-luminous infrared galaxy IRAS F11119+3257. The comparison with a galaxy-scale OH molecular outflow observed with Herschel in the same source supported the energy-conserving scenario for AGN feedback. The main objective of this work is to perform an independent check of the Suzaku results using the higher sensitivity and wider X-ray continuum coverage of NuSTAR. We clearly detect a highly ionized Fe K UFO in the 100 ks NuSTAR spectrum with parameters N H = (3.2 ± 1.5) × 1024 cm-2, log ξ = {4.0}-0.3+1.2 erg s-1 cm, and {v}{out}={0.253}-0.118+0.061c. The launching radius is likely at a distance of r ≥ 16r s from the black hole. The mass outflow rate is in the range of {\\dot{M}}{out} ≃ 0.5-2 M ⊙ yr-1. The UFO momentum rate and power are {\\dot{P}}{out} ≃ 0.5-2 L AGN/c and {\\dot{E}}{out} ≃ 7%-27% L AGN, respectively. The UFO parameters are consistent between the 2013 Suzaku and the 2015 NuSTAR observations. Only the column density is found to be variable, possibly suggesting a clumpy wind. The comparison with the energetics of molecular outflows estimated in infrared and millimeter wavelengths support a connection between the nuclear and galaxy-scale winds in luminous AGNs.

  6. Relaxing the Small Particle Approximation for Dust-grain opacities in Carbon-star Wind Models

    Mattsson, Lars; Höfner, Susanne

    2010-01-01

    We have computed wind models with time-dependent dust formation and grain-size dependent opacities, where (1) the problem is simplified by assuming a fixed dust-grain size, and where (2) the radiation pressure efficiency is approximated using grain sizes based on various means of the actual grain size distribution. It is shown that in critical cases, the effect of grain sizes can be significant. For well-developed winds, however, the effects on the mass-loss rate and the wind speed are small.

  7. Isotopic anomalies in cosmic rays and winds from Wolf-Rayet stars - a new model

    Maeder, A.

    1984-01-01

    The insufficiency of the metal-rich supernovae model and of the Wolf-Rayet star model for explaining the isotopic anomalies in the galactic cosmic ray source (GCRS) is examined, and a new model for attacking the anomaly problem is proposed. The main properties of WR stars relevant to the study of GCRS are recalled, with particular emphasis on their chemical excesses and the steep galactic gradient in their distribution. The proposed model assumes that GCRs originate from two main sources of different composition and galactic distribution, probably SN's and WR stars. Their properties may change with galactocentric distance. The relevant physical physicochemical relationships are derived, and some approximations which account for the contributions of WR and SN sources in GCRS are worked out for comparison with observations. The model is found to account very well for the observed anomalies. 33 references

  8. Enhancing the rate of tidal disruptions of stars by a self-gravitating disc around a massive central black hole

    Šubr L.

    2012-12-01

    Full Text Available We further study the idea that a self-gravitating accretion disc around a supermassive black hole can increase the rate of gradual orbital decay of stellar trajectories (and hence tidal disruption events by setting some stars on eccentric trajectories. Cooperation between the gravitational field of the disc and the dissipative environment can provide a mechanism explaining the origin of stars that become bound tightly to the central black hole. We examine this process as a function of the black hole mass and conclude that it is most efficient for intermediate central masses of the order of ∼ 104Mʘ. Members of the cluster experience the stage of orbital decay via collisions with an accretion disc and by other dissipative processes, such as tidal effects, dynamical friction and the emission of gravitational waves. Our attention is concentrated on the region of gravitational dominance of the central body. Mutual interaction between stars and the surrounding environment establishes a non-spherical shape and anisotropy of the nuclear cluster. In some cases, the stellar sub-system acquires ring-type geometry. Stars of the nuclear cluster undergo a tidal disruption event as they plunge below the tidal radius of the supermassive black hole.

  9. Effects of wind on the dynamics of the central jet during drop impact onto a deep-water surface

    Liu, Xinan; Wang, An; Wang, Shuang; Dai, Dejun

    2018-05-01

    The cavity and central jet generated by the impact of a single water drop on a deep-water surface in a wind field are experimentally studied. Different experiments are performed by varying the impacting drop diameter and wind speed. The contour profile histories of the cavity (also called crater) and central jet (also called stalk) are measured in detail with a backlit cinematic shadowgraph technique. The results show that shortly after the drop hits the water surface an asymmetrical cavity appears along the wind direction, with a train of capillary waves on the cavity wall. This is followed by the formation of an inclined central jet at the location of the drop impact. It is found that the wind has little effect on the penetration depth of the cavity at the early stage of the cavity expansion, but markedly changes the capillary waves during the retraction of the cavity. The capillary waves in turn shift the position of the central jet formation leeward. The dynamics of the central jet are dominated by two mechanisms: (i) the oblique drop impact produced by the wind and (ii) the wind drag force directly acting on the jet. The maximum height of the central jet, called the stalk height, is drastically affected by the wind, and the nondimensional stalk height H /D decreases with increasing θ Re-1 , where D is the drop diameter, θ is the impingement angle of drop impact, and Re=ρaUwD /μa is the Reynolds number with air density ρa, wind speed Uw, and air viscosity μa.

  10. Influence of extreme ultraviolet radiation on the P v ionization fraction in hot star winds

    Krtička, J.; Kubát, Jiří

    2012-01-01

    Roč. 427, č. 1 (2012), s. 84-90 ISSN 0035-8711 R&D Projects: GA ČR GA205/08/0003 Institutional support: RVO:67985815 Keywords : hydrodynamics * early-type stars * mass-loss Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.521, year: 2012

  11. Fluid power network for centralized electricity generation in offshore wind farms

    Jarquin-Laguna, A

    2014-01-01

    An innovative and completely different wind-energy conversion system is studied where a centralized electricity generation within a wind farm is proposed by means of a hydraulic network. This paper presents the dynamic interaction of two turbines when they are coupled to the same hydraulic network. Due to the stochastic nature of the wind and wake interaction effects between turbines, the operating parameters (i.e. pitch angle, rotor speed) of each turbine are different. Time domain simulations, including the main turbine dynamics and laminar transient flow in pipelines, are used to evaluate the efficiency and rotor speed stability of the hydraulic system. It is shown that a passive control of the rotor speed, as proposed in previous work for a single hydraulic turbine, has strong limitations in terms of performance for more than one turbine coupled to the same hydraulic network. It is concluded that in order to connect several turbines, a passive control strategy of the rotor speed is not sufficient and a hydraulic network with constant pressure is suggested. However, a constant pressure network requires the addition of active control at the hydraulic motors and spear valves, increasing the complexity of the initial concept. Further work needs to be done to incorporate an active control strategy and evaluate the feasibility of the constant pressure hydraulic network

  12. New Solutions to Line-Driven Winds of Hot Massive Stars

    Gormaz-Matamala, Alex C.; Curé, Michel; Cidale, Lydia; Venero, Roberto

    2017-11-01

    In the frame of radiation driven wind theory (Castor et al.1975), we present self-consistent hydrodynamical solutions to the line-force parameters (k, α, δ) under LTE conditions. Hydrodynamic models are provided by HydWind (Curé 2004). We evaluate these results with those ones previously found in literature, focusing in different regions of the optical depth to be used to perform the calculations. The values for mass-loss rate and terminal velocity obtained from our calculations are also presented. We also examine the line-force parameters for the case when large changes in ionization throughout the wind occurs (δ-slow solutions, Curé et al.2011).

  13. A SYSTEMATIC SEARCH FOR COROTATING INTERACTION REGIONS IN APPARENTLY SINGLE GALACTIC WOLF-RAYET STARS. II. A GLOBAL VIEW OF THE WIND VARIABILITY

    Chene, A.-N.; St-Louis, N.

    2011-01-01

    This study is the second part of a survey searching for large-scale spectroscopic variability in apparently single Wolf-Rayet (WR) stars. In a previous paper (Paper I), we described and characterized the spectroscopic variability level of 25 WR stars observable from the northern hemisphere and found 3 new candidates presenting large-scale wind variability, potentially originating from large-scale structures named corotating interaction regions (CIRs). In this second paper, we discuss an additional 39 stars observable from the southern hemisphere. For each star in our sample, we obtained 4-5 high-resolution spectra with a signal-to-noise ratio of ∼100 and determined its variability level using the approach described in Paper I. In total, 10 new stars are found to show large-scale spectral variability of which 7 present CIR-type changes (WR 8, WR 44, WR55, WR 58, WR 61, WR 63, WR 100). Of the remaining stars, 20 were found to show small-amplitude changes and 9 were found to show no spectral variability as far as can be concluded from the data on hand. Also, we discuss the spectroscopic variability level of all single galactic WR stars that are brighter than v ∼ 12.5, and some WR stars with 12.5 < v ≤ 13.5, i.e., all the stars presented in our two papers and four more stars for which spectra have already been published in the literature. We find that 23/68 stars (33.8%) present large-scale variability, but only 12/54 stars (∼22.1%) are potentially of CIR type. Also, we find that 31/68 stars (45.6%) only show small-scale variability, most likely due to clumping in the wind. Finally, no spectral variability is detected based on the data on hand for 14/68 (20.6%) stars. Interestingly, the variability with the highest amplitude also has the widest mean velocity dispersion.

  14. Analysis of Properties of Induction Machine with Combined Parallel Star-Delta Stator Winding

    Schreier, Luděk; Bendl, Jiří; Chomát, Miroslav

    2017-01-01

    Roč. 113, č. 1 (2017), s. 147-153 ISSN 0239-3646 R&D Projects: GA ČR(CZ) GA16-07795S Institutional support: RVO:61388998 Keywords : induction machine * parallel combined stator winding Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering OBOR OECD: Electrical and electronic engineering

  15. Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris

    Ziurys, L. M.; Milam, S. N.; Apponi, A. J.; Woolf, N. J.

    2007-06-01

    The interstellar medium is enriched primarily by matter ejected from old, evolved stars. The outflows from these stars create spherical envelopes, which foster gas-phase chemistry. The chemical complexity in circumstellar shells was originally thought to be dominated by the elemental carbon to oxygen ratio. Observations have suggested that envelopes with more carbon than oxygen have a significantly greater abundance of molecules than their oxygen-rich analogues. Here we report observations of molecules in the oxygen-rich shell of the red supergiant star VY Canis Majoris (VY CMa). A variety of unexpected chemical compounds have been identified, including NaCl, PN, HNC and HCO+. From the spectral line profiles, the molecules can be distinguished as arising from three distinct kinematic regions: a spherical outflow, a tightly collimated, blue-shifted expansion, and a directed, red-shifted flow. Certain species (SiO, PN and NaCl) exclusively trace the spherical flow, whereas HNC and sulphur-bearing molecules (amongst others) are selectively created in the two expansions, perhaps arising from shock waves. CO, HCN, CS and HCO+ exist in all three components. Despite the oxygen-rich environment, HCN seems to be as abundant as CO. These results suggest that oxygen-rich shells may be as chemically diverse as their carbon counterparts.

  16. A climatology of low level wind regimes over Central America using a weather type classification approach.

    Fernán eSáenz

    2015-04-01

    Full Text Available Based on the potential of the weather types classification method to study synoptic features, this study proposes the application of such methodology for the identification of the main large scale patterns related with weather in Central America. Using ERA Interim low-level winds in a domain that encompasses the intra-Americas sea, the eastern tropical Pacific, southern North America, Central America and northern South America; the K-means clustering algorithm was applied to find recurrent regimes of low-level winds. Eleven regimes were identified and good coherency between the results and known features of regional circulation was found. It was determined that the main large scale patterns can be either locally forced or a response to tropical-extratropical interactions. Moreover, the local forcing dominates the summer regimes whereas mid latitude interactions lead winter regimes. The study of the relationship between the large scale patterns and regional precipitation shows that winter regimes are related with the Caribbean-Pacific precipitation seesaw. Summer regimes, on the other hand, enhance the Caribbean-Pacific precipitation contrasting distribution as a function of the dominant regimes. A strong influence of ENSO on the frequency and duration of the regimes was found. It was determined that the specific effect of ENSO on the regimes depends on whether the circulation is locally forced or lead by the interaction between the tropics and the mid-latitudes. The study of the cold surges using the information of the identified regimes revealed that three regimes are linkable with the occurrence of cold surges that affect Central America and its precipitation. As the winter regimes are largely dependent of mid-latitude interaction with the tropics, the effect that ENSO has on the Jet Stream is reflected in the winter regimes. An automated analysis of large scale conditions based on reanalysis and/or model data seems useful for both dynamical

  17. Strongly-sheared wind-forced currents in the nearshore regions of the central Southern California Bight

    Noble, Marlene A.; Rosenberger, Kurt; Robertson, George L.

    2015-01-01

    Contrary to many previous reports, winds do drive currents along the shelf in the central portion of the Southern California Bight (SCB). Winds off Huntington Beach CA are the dominant forcing for currents over the nearshore region of the shelf (water depths less than 20 m). Winds control about 50–70% of the energy in nearshore alongshelf surface currents. The wind-driven current amplitudes are also anomalously high. For a relatively weak 1 dyne/cm2 wind stress, the alongshelf surface current amplitudes in this region can reach 80 cm/s or more. Mid-depth current amplitudes for the same wind stress are around 30–40 cm/s. These wind-driven surface current amplitudes are much larger than previously measured over other nearshore shelf regions, perhaps because this program is one of the few that measured currents within a meter of the surface. The near-bed cross-shelf currents over the nearshore region of the Huntington Beach shelf have an Ekman response to winds in that they upwell (downwell) for down (up) coast winds. This response disappears further offshore. Hence, there is upwelling in the SCB, but it does not occur across the entire shelf. Subthermocline water in the nearshore region that may contain nutrients and plankton move onshore when winds are southeastward, but subthermocline water over the shelf break is not transported to the beach. The currents over the outer shelf are not predominately controlled by winds, consistent with previous reports. Instead, they are mainly driven by cross-shelf pressure gradients that are independent of local wind stress.

  18. Evolutionary effects of mass loss in low-mass stars

    Renzini, A.

    1981-01-01

    The effects of mass loss on the evolution of low-mass stars (actual mass smaller than 1.4 solar masses) are reviewed. The case of globular cluster stars is discussed in some detail, and it is shown that evolutionary theory sets quite precise limits to the mass-loss rate in population II red giants. The effects of mass loss on the final evolutionary stages of stars producing white dwarfs is also discussed. In particular, the interaction of the wind from the hot central star with the surrounding planetary nebula is considered. Finally, the problem of the origin of hydrogen-deficient stars is briefly discussed. (Auth.)

  19. Assessment of electricity generation and energy cost of wind energy conversion systems in north-central Nigeria

    Adaramola, M.S.; Paul, S.S.; Oyedepo, S.O.

    2011-01-01

    Highlights: → The wind energy potential and economic analysis in selected six locations in north central part of Nigeria are investigated. → Economical evaluation of the wind energy in the selected sites was made by using the levelised cost method. → Locations that are suitable electricity generation and small scale applications are identified. - Abstract: In this study, the wind energy potential and economic analysis in selected six locations in north central part of Nigeria were investigated using wind speed data that span between 19 and 37 years measured at 10 m height. The performance of small to medium size commercial wind turbine models were examined and economic evaluation of the wind energy in the selected sites was made by using the levelised cost method. The results showed that the cost of energy production per kWh for the selected sites vary between cents 4.02 and cents 166.79. It was shown that Minna is most viable site while Bida is found to be least among the sites considered. Using three selected wind turbine models (in Minna) as case study, an increase in the escalation rate of operating and maintenance cost from 0% to 10%, lead to an increase in the unit energy cost by about 7%. It was further shown that by increasing the escalation rate of inflation from 0% to 5%, the cost of energy decreases by about 29% while the discount rate (return on investment) decreases from 11.54% to 6.23%.

  20. Comparison of different wind data interpolation methods for a region with complex terrain in Central Asia

    Reinhardt, Katja; Samimi, Cyrus

    2018-01-01

    While climatological data of high spatial resolution are largely available in most developed countries, the network of climatological stations in many other regions of the world still constitutes large gaps. Especially for those regions, interpolation methods are important tools to fill these gaps and to improve the data base indispensible for climatological research. Over the last years, new hybrid methods of machine learning and geostatistics have been developed which provide innovative prospects in spatial predictive modelling. This study will focus on evaluating the performance of 12 different interpolation methods for the wind components \\overrightarrow{u} and \\overrightarrow{v} in a mountainous region of Central Asia. Thereby, a special focus will be on applying new hybrid methods on spatial interpolation of wind data. This study is the first evaluating and comparing the performance of several of these hybrid methods. The overall aim of this study is to determine whether an optimal interpolation method exists, which can equally be applied for all pressure levels, or whether different interpolation methods have to be used for the different pressure levels. Deterministic (inverse distance weighting) and geostatistical interpolation methods (ordinary kriging) were explored, which take into account only the initial values of \\overrightarrow{u} and \\overrightarrow{v} . In addition, more complex methods (generalized additive model, support vector machine and neural networks as single methods and as hybrid methods as well as regression-kriging) that consider additional variables were applied. The analysis of the error indices revealed that regression-kriging provided the most accurate interpolation results for both wind components and all pressure heights. At 200 and 500 hPa, regression-kriging is followed by the different kinds of neural networks and support vector machines and for 850 hPa it is followed by the different types of support vector machine and

  1. Near-infrared variability study of the central 2.3 × 2.3 arcmin2 of the Galactic Centre - II. Identification of RR Lyrae stars in the Milky Way nuclear star cluster

    Dong, Hui; Schödel, Rainer; Williams, Benjamin F.; Nogueras-Lara, Francisco; Gallego-Cano, Eulalia; Gallego-Calvente, Teresa; Wang, Q. Daniel; Rich, R. Michael; Morris, Mark R.; Do, Tuan; Ghez, Andrea

    2017-11-01

    Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K ≥ 15) stellar population in the Milky Way's nuclear star cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the oldest, relative dim stellar population. Recently, we analysed HST/WFC3/IR observations of the central 2.3 × 2.3 arcmin2 of the Milky Way and found 21 variable stars with periods between 0.2 and 1 d. Here, we present a further comprehensive analysis of these stars. The period-luminosity relationship of RR Lyrae is used to derive their extinctions and distances. Using multiple approaches, we classify our sample as 4 RRc stars, 4 RRab stars, 3 RRab candidates and 10 binaries. Especially, the four RRab stars show sawtooth light curves and fall exactly on to the Oosterhoff I division in the Bailey diagram. Compared to the RRab stars reported by Minniti et al., our new RRab stars have higher extinction (AK > 1.8) and should be closer to the Galactic Centre. The extinction and distance of one RRab stars match those for the Milky Way's nuclear star cluster given in previous works. We perform simulations and find that after correcting for incompleteness, there could be not more than 40 RRab stars within the Milky Way's nuclear star cluster and in our field of view. Through comparing with the known globular clusters of the Milky Way, we estimate that if there exists an old, metal-poor (-1.5 < [Fe/H] < -1) stellar population in the Milky Way nuclear star cluster on a scale of 5 × 5 pc, then it contributes at most 4.7 × 105 M⊙, I.e. ˜18 per cent of the stellar mass.

  2. A comparison of different interpolation methods for wind data in Central Asia

    Reinhardt, Katja; Samimi, Cyrus

    2017-04-01

    For the assessment of the global climate change and its consequences, the results of computer based climate models are of central importance. The quality of these results and the validity of the derived forecasts are strongly determined by the quality of the underlying climate data. However, in many parts of the world high resolution data are not available. This is particularly true for many regions in Central Asia, where the density of climatological stations has often to be described as thinned out. Due to this insufficient data base the use of statistical methods to improve the resolution of existing climate data is of crucial importance. Only this can provide a substantial data base for a well-founded analysis of past climate changes as well as for a reliable forecast of future climate developments for the particular region. The study presented here shows a comparison of different interpolation methods for the wind components u and v for a region in Central Asia with a pronounced topography. The aim of the study is to find out whether there is an optimal interpolation method which can equally be applied for all pressure levels or if different interpolation methods have to be applied for each pressure level. The European reanalysis data Era-Interim for the years 1989 - 2015 are used as input data for the pressure levels of 850 hPa, 500 hPa and 200 hPa. In order to improve the input data, two different interpolation procedures were applied: On the one hand pure interpolation methods were used, such as inverse distance weighting and ordinary kriging. On the other hand machine learning algorithms, generalized additive models and regression kriging were applied, considering additional influencing factors, e.g. geopotential and topography. As a result it can be concluded that regression kriging provides the best results for all pressure levels, followed by support vector machine, neural networks and ordinary kriging. Inverse distance weighting showed the worst

  3. Fluctuations at the blue edge of saturated wind lines in IUE spectra of O-type stars

    Owocki, Stanley P.; Fullerton, Alex

    1993-01-01

    We examine basic issues involved in synthesizing resonance-line profiles from 1-D, dynamical models of highly structured hot-star winds. Although these models exhibit extensive variations in density as well as velocity, the density scale length is still typically much greater than the Sobolev length. The line transfer is thus treated using a Sobolev approach, as generalized by Rybicki & Hummer (1978) to take proper account of the multiple Sobolev resonances arising from the nonmonotonic velocity field. The resulting reduced-Lambda-matrix equation describing nonlocal coupling of the source function is solved by iteration, and line profiles and then derived from formal solution integration using this source function. The more appropriate methods that instead use either a stationary or a structured, local source function yield qualitatively similar line-profiles, but are found to violate photon conservation by 10 percent or more. The full results suggest that such models may indeed be able to reproduce naturally some of the qualitative properties long noted in observed UV line profiles, such as discrete absorption components in unsaturated lines, or the blue-edge variability in saturated lines. However, these particular models do not yet produce the black absorption troughs commonly observed in saturated lines, and it seems that this and other important discrepancies (e.g., in acceleration time scale of absorption components) may require development of more complete models that include rotation and other 2-D and/or 3-D effects.

  4. Evaluation of Dynamical Downscaling Resolution Effect on Wind Energy Forecast Value for a Wind Farm in Central Sweden

    Rosgaard, Martin Haubjerg; Hahmann, Andrea N.; Nielsen, Torben Skov

    accuracy metric evaluated for wind speed data consistently translates to an improvement for wind power. For two time series describing the temporal development of the same variable, though by different means, it is assumed that phase errors account for most of the departure from perfect correlation between...... the two time series. Results on limited-area NWP model performance, with focus on the 12th to 48th forecast hour horizon relevant for Elspot auction bidding on the Nord Pool Spot market [2], are presented....

  5. LINEAR RELATION FOR WIND-BLOWN BUBBLE SIZES OF MAIN-SEQUENCE OB STARS IN A MOLECULAR ENVIRONMENT AND IMPLICATION FOR SUPERNOVA PROGENITORS

    Chen Yang; Zhou Ping [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Chu Youhua [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)

    2013-05-20

    We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R{sub b} Almost-Equal-To 1.22 M/M{sub Sun} - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M{sub Sun} will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

  6. Probing the properties of the pulsar wind via studying the dispersive effects in the pulses from the pulsar companion in a double neutron-star binary system

    Yi, Shu-Xu; Cheng, K.-S.

    2017-12-01

    The velocity and density distribution of e± in the pulsar wind are crucial distinction among magnetosphere models, and contain key parameters determining the high-energy emission of pulsar binaries. In this work, a direct method is proposed, which might probe the properties of the wind from one pulsar in a double-pulsar binary. When the radio signals from the first-formed pulsar travel through the relativistic e± flow in the pulsar wind from the younger companion, the components of different radio frequencies will be dispersed. It will introduce an additional frequency-dependent time-of-arrival delay of pulses, which is function of the orbital phase. In this paper, we formulate the above-mentioned dispersive delay with the properties of the pulsar wind. As examples, we apply the formula to the double-pulsar system PSR J0737-3039A/B and the pulsar-neutron star binary PSR B1913+16. For PSR J0737-3039A/B, the time delay in 300 MHz is ≲ 10 μ s-1 near the superior conjunction, under the optimal pulsar wind parameters, which is approximately half of the current timing accuracy. For PSR B1913+16, with the assumption that the neutron-star companion has a typical spin-down luminosity of 1033 erg s-1, the time delay is as large as 10 - 20 μ s-1 in 300 MHz. The best timing precision of this pulsar is ∼ 5 μ s-1 in 1400 MHz. Therefore, it is possible that we can find this signal in archival data. Otherwise, we can set an upper limit on the spin-down luminosity. Similar analysis can be applied to other 11 known pulsar-neutron star binaries.

  7. Evaluation of Dynamical Downscaling Resolution Effect on Wind Energy Forecast Value for a Wind Farm in Central Sweden

    Rosgaard, Martin Haubjerg; Hahmann, Andrea N.; Nielsen, Torben Skov

    2014-01-01

    energy. The present study aims to quantify value added to wind energy forecasts in the 12-48 hour leadtime by downscaling global numerical weather prediction (NWP) data from the National Centers for Environmental Prediction Global Forecast System (GFS) using the limited-area NWP model described...

  8. Wind reduction patterns around isolated biomass for wind erosion control in a desertified area of Central Sudan

    Nasr Al-amin, N.K.; Stigter, C.J.; El-Tayeb Mohammed, A.

    2010-01-01

    The aim of this study was to assess the effectiveness of sparse vegetation, feature common in arid zone, to reduce wind force (velocity) and hence protect the surface and regions downwind from drifting sand and their consequences. Respectively 4 (with heights h of 4, 3.2, 2 and 1.66 m), 2 (with h of

  9. Orbital evolution of colliding star and pulsar winds in 2D and 3D: effects of dimensionality, EoS, resolution, and grid size

    Bosch-Ramon, V.; Barkov, M. V.; Perucho, M.

    2015-05-01

    Context. The structure formed by the shocked winds of a massive star and a non-accreting pulsar in a binary system suffers periodic and random variations of orbital and non-linear dynamical origins. The characterization of the evolution of the wind interaction region is necessary for understanding the rich phenomenology of these sources. Aims: For the first time, we simulate in 3 dimensions the interaction of isotropic stellar and relativistic pulsar winds along one full orbit, on scales well beyond the binary size. We also investigate the impact of grid resolution and size, and of different state equations: a γ̂-constant ideal gas, and an ideal gas with γ̂ dependent on temperature. Methods: We used the code PLUTO to carry out relativistic hydrodynamical simulations in 2 and 3 dimensions of the interaction between a slow dense wind and a mildly relativistic wind with Lorentz factor 2, along one full orbit in a region up to ~100 times the binary size. The different 2-dimensional simulations were carried out with equal and larger grid resolution and size, and one was done with a more realistic equation of state than in 3 dimensions. Results: The simulations in 3 dimensions confirm previous results in 2 dimensions, showing: a strong shock induced by Coriolis forces that terminates the pulsar wind also in the opposite direction to the star; strong bending of the shocked-wind structure against the pulsar motion; and the generation of turbulence. The shocked flows are also subject to a faster development of instabilities in 3 dimensions, which enhances shocks, two-wind mixing, and large-scale disruption of the shocked structure. In 2 dimensions, higher resolution simulations confirm lower resolution results, simulations with larger grid sizes strengthen the case for the loss of the general coherence of the shocked structure, and simulations with two different equations of state yield very similar results. In addition to the Kelvin-Helmholtz instability, discussed in

  10. O Star Wind Mass-Loss Rates and Shock Physics from X-ray Line Profiles in Archival XMM RGS Data

    Cohen, David

    O stars are characterized by their dense, supersonic stellar winds. These winds are the site of X-ray emission from shock-heated plasma. By analyzing high-resolution X-ray spectra of these O stars, we can learn about the wind-shock heating and X-ray production mechanism. But in addition, the X-rays can also be used to measure the mass-loss rate of the stellar wind, which is a key observational quantity whose value affects stellar evolution and energy, momentum, and mass input to the Galactic interstellar medium. We make this X-ray based mass-loss measurement by analyzing the profile shapes of the X-ray emission lines observed at high resolution with the Chandra and XMM-Newton grating spectrometers. One advantage of our method is that it is insensitive to small-scale clumping that affects density-squared diagnostics. We are applying this analysis technique to O stars in the Chandra archive, and are finding mass-loss rates lower than those traditionally assumed for these O stars, and in line with more recent independent determinations that do account for clumping. By extending this analysis to the XMM RGS data archive, we will make significant contributions to the understanding of both X-ray production in O stars and to addressing the issue of the actual mass-loss rates of O stars. The XMM RGS data archive provides several extensions and advantages over the smaller Chandra HETGS archive: (1) there are roughly twice as many O and early B stars in the XMM archive; (2) the longer wavelength response of the RGS provides access to diagnostically important lines of nitrogen and carbon; (3) the very long, multiple exposures of zeta Pup provide the opportunity to study this canonical O supergiant's X-ray spectrum in unprecedented detail, including looking at the time variability of X-ray line profiles. Our research team has developed a sophisticated empirical line profile model as well as a computational infrastructure for fitting the model to high-resolution X-ray spectra

  11. Magnetized hypermassive neutron-star collapse: a central engine for short gamma-ray bursts.

    Shibata, Masaru; Duez, Matthew D; Liu, Yuk Tung; Shapiro, Stuart L; Stephens, Branson C

    2006-01-27

    A hypermassive neutron star (HMNS) is a possible transient formed after the merger of a neutron-star binary. In the latest axisymmetric magnetohydrodynamic simulations in full general relativity, we find that a magnetized HMNS undergoes "delayed" collapse to a rotating black hole (BH) as a result of angular momentum transport via magnetic braking and the magnetorotational instability. The outcome is a BH surrounded by a massive, hot torus with a collimated magnetic field. The torus accretes onto the BH at a quasisteady accretion rate [FORMULA: SEE TEXT]; the lifetime of the torus is approximately 10 ms. The torus has a temperature [FORMULA: SEE TEXT], leading to copious ([FORMULA: SEE TEXT]) thermal radiation that could trigger a fireball. Therefore, the collapse of a HMNS is a promising scenario for generating short-duration gamma-ray bursts and an accompanying burst of gravitational waves and neutrinos.

  12. O stars and Wolf-Rayet stars

    Conti, P.S.; Underhill, A.B.; Jordan, S.; Thomas, R.

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented

  13. O stars and Wolf-Rayet stars

    Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

  14. Supermassive Black Holes as the Regulators of Star Formation in Central Galaxies

    Terrazas, Bryan A.; Bell, Eric F.; Woo, Joanna; Henriques, Bruno M. B.

    2017-01-01

    We present the relationship between the black hole mass, stellar mass, and star formation rate (SFR) of a diverse group of 91 galaxies with dynamically measured black hole masses. For our sample of galaxies with a variety of morphologies and other galactic properties, we find that the specific SFR is a smoothly decreasing function of the ratio between black hole mass and stellar mass, or what we call the specific black hole mass. In order to explain this relation, we propose a physical framework where the gradual suppression of a galaxy’s star formation activity results from the adjustment to an increase in specific black hole mass, and accordingly, an increase in the amount of heating. From this framework, it follows that at least some galaxies with intermediate specific black hole masses are in a steady state of partial quiescence with intermediate specific SFRs, implying that both transitioning and steady-state galaxies live within this region that is known as the “green valley.” With respect to galaxy formation models, our results present an important diagnostic with which to test various prescriptions of black hole feedback and its effects on star formation activity.

  15. Supermassive Black Holes as the Regulators of Star Formation in Central Galaxies

    Terrazas, Bryan A.; Bell, Eric F. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Woo, Joanna; Henriques, Bruno M. B. [Department of Physics, Institute for Astronomy, ETH Zurich, 8093 Zurich (Switzerland)

    2017-08-01

    We present the relationship between the black hole mass, stellar mass, and star formation rate (SFR) of a diverse group of 91 galaxies with dynamically measured black hole masses. For our sample of galaxies with a variety of morphologies and other galactic properties, we find that the specific SFR is a smoothly decreasing function of the ratio between black hole mass and stellar mass, or what we call the specific black hole mass. In order to explain this relation, we propose a physical framework where the gradual suppression of a galaxy’s star formation activity results from the adjustment to an increase in specific black hole mass, and accordingly, an increase in the amount of heating. From this framework, it follows that at least some galaxies with intermediate specific black hole masses are in a steady state of partial quiescence with intermediate specific SFRs, implying that both transitioning and steady-state galaxies live within this region that is known as the “green valley.” With respect to galaxy formation models, our results present an important diagnostic with which to test various prescriptions of black hole feedback and its effects on star formation activity.

  16. Impacts of Wind Farms on Cumulus Cloud Development in the Central Great Plains

    Mahoney, L. C.; Wagner, T. J.; L'Ecuyer, T. S.; Kulie, M.

    2014-12-01

    Cumulus clouds have a net cooling effect on the surface radiative balance by reflecting more downwelling solar radiation than absorbing upwelling terrestrial radiation. As boundary layer cumuli form from buoyant, moist plumes ascending from the surface, their growth may be hindered by the turbulent deformation of the plume by wind farms. A natural laboratory to study the impact of wind farms on cumulus formation are the states of Iowa and Nebraska. Despite their prime location for wind resources and similar synoptic forcings, regulatory issues cause these two states to vary vastly in their wind power offerings. In 2013, Iowa ranked 3rd in the nation for total megawatts installed and generates over a quarter of its electricity from wind energy, more than any other state. In contrast, Nebraska has an order of magnitude fewer turbines installed, and less than five percent of the state's electrical load is wind-generated. This variance in wind power in close proximity makes Iowa and Nebraska a prime area for initial research. This study uses Geostationary Operational Environmental Satellite (GOES) visible satellite imagery from the summer of 2009 to 2013 to investigate cumulus development in these adjacent states, as the majority of large-scale wind farms in Iowa were completed by 2009. Image reflectances in Nebraska and Iowa are compared to determine the magnitude of cumulus growth. Preliminary analysis indicates a reduction in cumulus development near the existing wind farms; a synoptic investigation of these cases will be completed to determine causality.

  17. Large scale hydrogen production from wind energy in the Magallanes area for consumption in the central zone of Chile

    Zolezzi, J.M.; Garay, A.; Reveco, M.

    2010-01-01

    The energy proposal of this research suggests the use of places with abundant wind resources for the production of H 2 on a large scale to be transported and used in the central zone of Chile with the purpose of diversifying the country's energy matrix in order to decrease its dependence on fossil fuels, increase its autonomy, and cover the future increases in energy demand. This research showed that the load factor of the proposed wind park reaches a value of 54.5%, putting in evidence the excellent wind conditions of the zone. This implies that the cost of the electricity produced by the wind park located in the Chilean Patagonia would have a cost of 0.0213 US$ kWh -1 in the year 2030. The low prices of the electricity obtained from the park, thanks to the economy of scale and the huge wind potential, represent a very attractive scenario for the production of H 2 in the future. The study concludes that by the year 2030 the cost of the H 2 generated in Magallanes and transported to the port of Quinteros would be 18.36 US$ MBTU -1 , while by that time the cost of oil would be about 17.241 US$ MBTU -1 , a situation that places H 2 in a very competitive position as a fuel. (author)

  18. The distribution of stars around the Milky Way's central black hole. II. Diffuse light from sub-giants and dwarfs

    Schödel, R.; Gallego-Cano, E.; Dong, H.; Nogueras-Lara, F.; Gallego-Calvente, A. T.; Amaro-Seoane, P.; Baumgardt, H.

    2018-01-01

    Context. This is the second of three papers that search for the predicted stellar cusp around the Milky Way's central black hole, Sagittarius A*, with new data and methods. Aims: We aim to infer the distribution of the faintest stellar population currently accessible through observations around Sagittarius A*. Methods: We used adaptive optics assisted high angular resolution images obtained with the NACO instrument at the ESO VLT. Through optimised PSF fitting we removed the light from all detected stars above a given magnitude limit. Subsequently we analysed the remaining, diffuse light density. Systematic uncertainties were constrained by the use of data from different observing epochs and obtained with different filters. We show that it is necessary to correct for the diffuse emission from the mini-spiral, which would otherwise lead to a systematically biased light density profile. We used a Paschen α map obtained with the Hubble Space Telescope for this purpose. Results: The azimuthally averaged diffuse surface light density profile within a projected distance of R ≲ 0.5 pc from Sagittarius A* can be described consistently by a single power law with an exponent of Γ = 0.26 ± 0.02stat ± 0.05sys, similar to what has been found for the surface number density of faint stars in Paper I. Conclusions: The analysed diffuse light arises from sub-giant and main-sequence stars with Ks ≈ 19-22 with masses of 0.8-1.5 M⊙. These stars can be old enough to be dynamically relaxed. The observed power-law profile and its slope are consistent with the existence of a relaxed stellar cusp around the Milky Way's central black hole. We find that a Nuker law provides an adequate description of the nuclear cluster's intrinsic shape (assuming spherical symmetry). The 3D power-law slope near Sgr A* is γ = 1.13 ± 0.03model ± 0.05sys. The stellar density decreases more steeply beyond a break radius of about 3 pc, which corresponds roughly to the radius of influence of the

  19. The Disk Wind in the Rapidly Spinning Stellar-mass Black Hole 4U 1630-472 Observed with NuSTAR

    King, Ashley L.; Walton, Dominic J.; Miller, Jon M.; Barret, Didier; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Fabian, Andy C.; Furst, Felix; Hailey, Charles J.; hide

    2014-01-01

    We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630-472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we find evidence for a rapidly spinning black hole, a* = 0.985(+0.005/-0.014) (1 sigma statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also report the clear detection of an absorption feature at 7.03 +/- 0.03 keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas (log xi = 3.6(+0.2/-0.3) and is dominated by He-like Fe xxv, the wind has a velocity of v/c = 0.043(+0.002/-0.007) (12900(+600/-2100) km s(exp -1)). If the line is instead associated with a more highly ionized gas (log xi = 6.1(+0.7/-0.6)), and is dominated by Fe xxvi, evidence of a blueshift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200-1100 Rg, and may be magnetically driven.

  20. The wind and fire disturbance in Central European mountain spruce forests: the regeneration after four years

    Monika Budzáková

    2013-03-01

    Full Text Available A strong windstorm in November 2004 resulted in a huge blown-down spruce forest area in the southern part of the Tatra National Park in the Western Carpathians in Slovakia, Central Europe. The aim of this work is to study the vegetation composition of spruce forest at differently managed sites four years after this disturbance. Four study areas were selected for this purpose: (i an area where the fallen trees were extracted and new seedlings were planted; (ii an area, which was hit by a forest fire after the extraction; (iii an area where no active management was applied; (iv a reference forest unaffected by such disturbance. A total of 100 plots were selected, 25 of each area type. The result of DCA and CCA analyses consistently indicated that after this short period the non-extracted and extracted areas are currently most similar to the reference forest area, while the fire affected area differed. A one-way ANOVA comparing species cover for the different plot sizes indicated some significant differences between the extracted and non-extracted plots. The abundance of certain species commonly occurring in spruce forests, such as Dyopteris carthusiana agg., Vaccinium myrtillus and Avenella flexuosa, correlated weli with the non-extracted plots, compared to the extracted plots. Coverage of these species was lowest on burned plots. The lowest Shannon-Wiener’s diversity values were recorded in burned plots. This was most likely a consequence of mono-dominant competitive species spread, (mainly Chamerion angustifolium which profited from the altered ecological conditions following the fire. Although some differences were also registered in the Shannon-Wiener diversity index between the remaining research plots, however these were not statistically significant. The most important results of our investigations include the extensive influence of fire disturbance on vegetation. Study revealed that the wind-disturbed area is able to regenerate

  1. Equatorial thermospheric winds: New results using data from a network of three Fabry-Perot interferometers located in central Peru

    Meriwether, J. W.; Dominquez, L. N.; Milla, M. A.; Chau, J. L.; Makela, J. J.; Fisher, D.

    2013-12-01

    A new observing strategy aimed at improving our understanding of the properties of the equatorial thermosphere wind field, such as the vorticity and divergence, has been developed to generate maps of the thermospheric wind field. Estimates of the neutral wind are obtained from measurements of the Doppler shift of the thermospheric 630.0-nm emission obtained from a sequence of eight evenly spaced azimuthal directions for each of the three Fabry-Perot interferometer (FPI) observatories located in central Peru (Jicamarca, Nazca, and Arequipa). Measurements towards the zenith and a frequency-stabilized laser reference are also included in each sequence, which takes ~25 minutes to complete. Six of the off-zenith observing directions from the Nazca FPI observatory are used to make common volume (CV) measurements, where two of the FPIs observe the same thermospheric volume with a centroid height of ~250 km at orthogonal angles. These CV positions are located ~225 km north and south of the Nazca FPI observatory. The data obtained during a coordinated observation of the two FPIs observing the same CV location are used to compute estimates of the zonal (u) and meridional (v) wind components. The set of Doppler shifts measured by the three FPIs during a single sequence is used to produce a map of the neutral wind field for that period of time. The construction of this map is based upon the use of a first-order polynomial expansion of the neutral wind field relative to the site coordinates of each FPI location. This expansion includes the first-order gradients of u and v with respect to the zonal (x) and meridional (y) directions. Computation of the best fit in a linear least squares sense of the model expansion parameters to the Doppler shift data for all three sites determines the values of these gradient parameters. Results obtained for mid-winter 2013 show the anti-cyclonic circulation expected near the terminator generated by the day-to-night pressure gradient. Sequences

  2. THE NATURE AND FREQUENCY OF OUTFLOWS FROM STARS IN THE CENTRAL ORION NEBULA CLUSTER

    O’Dell, C. R. [Department of Physics and Astronomy, Vanderbilt University, Box 1807-B, Nashville, TN 37235 (United States); Ferland, G. J. [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States); Henney, W. J. [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apartado Postal 3-72, 58090 Morelia, Michoacán, México (Mexico); Peimbert, M. [Instituto de Astronomia, Universidad Nacional Autónoma de México, Apdo, Postal 70-264, 04510 México D. F., México (Mexico); García-Díaz, Ma. T. [Instituto de Astronomia, Universidad Nacional Autónoma de México, Km 103 Carretera Tijuana-Ensenada, 22860 Ensenada, B.C., México (Mexico); Rubin, Robert H., E-mail: cr.odell@vanderbilt.edu [NASA/Ames Research Center, Moffett Field, CA 94035-0001 (United States)

    2015-10-15

    Recent Hubble Space Telescope images have allowed the determination with unprecedented accuracy of motions and changes of shocks within the inner Orion Nebula. These originate from collimated outflows from very young stars, some within the ionized portion of the nebula and others within the host molecular cloud. We have doubled the number of Herbig–Haro objects known within the inner Orion Nebula. We find that the best-known Herbig–Haro shocks originate from relatively few stars, with the optically visible X-ray source COUP 666 driving many of them. While some isolated shocks are driven by single collimated outflows, many groups of shocks are the result of a single stellar source having jets oriented in multiple directions at similar times. This explains the feature that shocks aligned in opposite directions in the plane of the sky are usually blueshifted because the redshifted outflows pass into the optically thick photon-dominated region behind the nebula. There are two regions from which optical outflows originate for which there are no candidate sources in the SIMBAD database.

  3. THE NATURE AND FREQUENCY OF OUTFLOWS FROM STARS IN THE CENTRAL ORION NEBULA CLUSTER

    O’Dell, C. R.; Ferland, G. J.; Henney, W. J.; Peimbert, M.; García-Díaz, Ma. T.; Rubin, Robert H.

    2015-01-01

    Recent Hubble Space Telescope images have allowed the determination with unprecedented accuracy of motions and changes of shocks within the inner Orion Nebula. These originate from collimated outflows from very young stars, some within the ionized portion of the nebula and others within the host molecular cloud. We have doubled the number of Herbig–Haro objects known within the inner Orion Nebula. We find that the best-known Herbig–Haro shocks originate from relatively few stars, with the optically visible X-ray source COUP 666 driving many of them. While some isolated shocks are driven by single collimated outflows, many groups of shocks are the result of a single stellar source having jets oriented in multiple directions at similar times. This explains the feature that shocks aligned in opposite directions in the plane of the sky are usually blueshifted because the redshifted outflows pass into the optically thick photon-dominated region behind the nebula. There are two regions from which optical outflows originate for which there are no candidate sources in the SIMBAD database

  4. Masses of the Planetary Nebula Central Stars in the Galactic Globular Cluster System from HST Imaging and Spectroscopy

    Jacoby, George H. [Lowell Observatory, Flagstaff, AZ 86001 (United States); Marco, Orsola De [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Davies, James [Space Telescope Science Institute, Baltimore MD 21218 (United States); Lotarevich, I. [American Museum of Natural History, New York, NY (United States); Bond, Howard E. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Harrington, J. Patrick [University of Maryland, College Park, MD (United States); Lanz, Thierry, E-mail: gjacoby@lowell.edu, E-mail: orsola.demarco@mq.edu.au, E-mail: jdavies@stsci.edu, E-mail: heb11@psu.edu, E-mail: jph@astro.umd.edu, E-mail: thierry.lanz@oca.eu [Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, F-06304 Nice (France)

    2017-02-10

    The globular cluster (GC) system of our Galaxy contains four planetary nebulae (PNe): K 648 (or Ps 1) in M15, IRAS 18333-2357 in M22, JaFu 1 in Pal 6, and JaFu 2 in NGC 6441. Because single-star evolution at the low stellar mass of present-epoch GCs was considered incapable of producing visible PNe, their origin presented a puzzle. We imaged the PN JaFu 1 with the Hubble Space Telescope (HST) to obtain photometry of its central star (CS) and high-resolution morphological information. We imaged IRAS 18333-2357 with better depth and resolution, and we analyzed its archival HST spectra to constrain its CS temperature and luminosity. All PNe in Galactic GCs now have quality HST data, allowing us to improve CS mass estimates. We find reasonably consistent masses between 0.53 and 0.58 M {sub ⊙} for all four objects, though estimates vary when adopting different stellar evolutionary calculations. The CS mass of IRAS 18333-2357, though, depends strongly on its temperature, which remains elusive due to reddening uncertainties. For all four objects, we consider their CS and nebula masses, their morphologies, and other incongruities to assess the likelihood that these objects formed from binary stars. Although generally limited by uncertainties (∼0.02 M {sub ⊙}) in post-AGB tracks and core mass versus luminosity relations, the high-mass CS in K 648 indicates a binary origin. The CS of JaFu 1 exhibits compact, bright [O iii] and H α emission, like EGB 6, suggesting a binary companion or disk. Evidence is weaker for a binary origin of JaFu 2.

  5. A search for hot pulsators similar to PG1159-035 and the central star of K 1-16

    Bond, H.E.; Grauer, A.D.; Liebert, J.; Fleming, T.; Green, R.F.

    1987-01-01

    The variations of PG1159-035 (GWVir)were discovered by McGraw et al. This object is the prototype of a anew class of pulsating stars located in an instability strip at the left-hand edge of the HR diagram. PG1159-035 and the spectroscopically similar objects PG1707+427 and PG2131+066 display complex non-radial modes with periodicities of order 10 minutes. Grauer and Bond recently discovered that the central star of the planetary nebula Kohoutek 1-16 also exhibits pulsation properties, with dominant periodicities of 25-28 minutes. These four objects display the following characteristics: High effective temperatures (--10 5 Κ) and moderately high surface gravities (log g ≅ 6-8); He II, C IV, and O VI absorption lines in the optical spectra, often reversed with emission cores; No hydrogen lines clearly detected; The pulsational instability has been attributed to partial ionization of carbon and/or oxygen

  6. Isolated/Non-Isolated Quad-Inverter Configuration for Multilevel Symmetrical/Asymmetrical Dual Six-Phase Star-Winding Converter

    Padmanaban, Sanjeevi Kumar; Hontz, Michael R.; Khanna, Raghav

    2016-01-01

    This article presents the developments of a novel isolated/non-isolated quad inverter configuration for multilevel dual six-phase (twelve-phase) star-winding converter. The modular circuit consists of four standard voltage source inverters (VSIs). Each VSI is incorporated with one bi-directional ...... systems, electrical vehicles, AC tractions, and `More-Electric Aircraft' propulsion systems....... converter is numerically modeled using Matlab/PLECS simulation software and the predicted behavior of the system is analyzed and presented. Good agreement is obtained between these results and the theoretical analysis. Suitable applications for the converter include (low-voltage/high-current) medium power...

  7. Radio stars

    Hjellming, R.M.; Gibson, D.M.

    1985-01-01

    Studies of stellar radio emission became an important field of research in the 1970's and have now expanded to become a major area of radio astronomy with the advent of new instruments such as the Very Large Array in New Mexico and transcontinental telescope arrays. This volume contains papers from the workshop on stellar continuum radio astronomy held in Boulder, Colorado, and is the first book on the rapidly expanding field of radio emission from stars and stellar systems. Subjects covered include the observational and theoretical aspects of stellar winds from both hot and cool stars, radio flares from active double star systems and red dwarf stars, bipolar flows from star-forming regions, and the radio emission from X-ray binaries. (orig.)

  8. The photometric and radial velocity variations of the central star of the planetary nebula 1C 418

    Mendez, R.H.; Verga, A.D.; Kriner, A.

    1983-01-01

    This paper brings spectrographic (1979-82) and photometric (January 1983) observations of the central star of the planetary nebula IC 418. We include an improved description of the stellar spectrum. We have found a variable photospheric velocity field, which would imply a fluctuating mass outflow, probably mixed with orbital motion in a close binary system with a period of about 0.2 days. We have also found light variations, on a time scale of one or two hours, with an amplitude of 0.1 mag, which do not appear to be periodic. Our observations are not yet sufficient to rule out definetely the existence of non-radial pulsations; further observations are suggested. (author)

  9. Faint planetary nebulae in the Magellanic Clouds - central star properties and nebular abundances for the Jacoby sample

    Henry, R.B.C.; Liebert, J.; Boroson, T.A.

    1989-01-01

    Forty-four of the LMC and SMC planetary nebulae contained in Jacoby's (1980) sample are studied. Spectrophotometric observations were used to infer the Stoy temperatures, luminosities, and radii of the central stars. For objects in which forbidden O III electron temperatures could be determined, the nebular abundances of He, N, O, and Ne were calculated and compared with values for giant H II regions for the relevant host galaxy. When the present abundance results were compared with previously published results for planetary nebulae in the LMC, SMC, and the Galaxy, a strong correlation was found for O/H versus Ne/H and strong anticorrelations were found for O/H versus forbidden O III temperature, and N/O versus O/H. 69 refs

  10. Impact of wind on ambient noise recorded by the "13 BB star" seismic array in northern Poland

    Lepore, Simone; Markowicz, Krzysztof; Grad, Marek

    2016-04-01

    Seismic interferometry and beam forming techniques were applied to ambient noise recorded during January 2014 at the "13 BB star" array, composed of thirteen seismic stations located in northern Poland, with the aim of evaluating the azimuth of noise sources and the velocities of surface waves. After normalizing the raw recordings in time and frequency domain, the spectral characteristics of the ambient noise were studied to choose a frequency band suitable for the waves' retrieval. To get the velocity of surface waves by seismic interferometry, the crosscorrelation between all station pairs was analysed for the vertical and horizontal components in the 0.05-0.1 Hz, 0.1-1 Hz and 1 10 Hz frequency bands. For each pair, the crosscorrelation was applied to one hour recordings extracted from the ambient noise. The obtained traces were calculated for a complete day, and then summed together: the daily results were stacked for the whole January 2014. In the lowest frequency range, most of the energy is located around the 3.0 km/s line, meaning that the surface waves coming from the uppermost mantle will be retrieved. The intermediate frequency range shows most of the energy between the 2.0 km/s and 1.5 km/s lines: consequently, surface waves originating from the crust will be retrieved. In the highest frequency range, the surface waves are barely visible on the crosscorrelation traces, implying that the associated energy is strongly attenuated. The azimuth variation associated to the noise field was evaluated by means of the beam forming method, using the data from the whole array for all the three components. To that, the beam power was estimated in a small range of frequencies every day for the whole month. For each day, one hour long results of beam forming applications were stacked together. To avoid aliasing and near field effects, the minimum frequency was set at 0.05 Hz and the maximum to 0.1 Hz. In this frequency band, the amplitude maximum was sought

  11. Observations of wind and waves in the central Bay of Bengal during ...

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Time-series wind and wave measurements were carried out onboard INS ... relation for gross estimation of effective depth within which the sound energy is generally trapped during its ..... and wave climate; (USA: Pergamon, Elsevier Science).

  12. Evolution of massive stars

    Loore, C. de

    1984-01-01

    The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

  13. Observations and Predictability of Gap Winds in the Salmon River Canyon of Central Idaho, USA

    Natalie S. Wagenbrenner

    2018-01-01

    Full Text Available This work investigates gap winds in a steep, deep river canyon prone to wildland fire. The driving mechanisms and the potential for forecasting the gap winds are investigated. The onset and strength of the gap winds are found to be correlated to the formation of an along-gap pressure gradient linked to periodic development of a thermal trough in the Pacific Northwest, USA. Numerical simulations are performed using a reanalysis dataset to investigate the ability of numerical weather prediction (NWP to simulate the observed gap wind events, including the timing and flow characteristics within the canyon. The effects of model horizontal grid spacing and terrain representation are considered. The reanalysis simulations suggest that horizontal grid spacings used in operational NWP could be sufficient for simulating the gap flow events given the regional-scale depression in which the Salmon River Canyon is situated. The strength of the events, however, is under-predicted due, at least in part, to terrain smoothing in the model. Routine NWP, however, is found to have mixed results in terms of forecasting the gap wind events, primarily due to problems in simulating the regional sea level pressure system correctly.

  14. Influence of a stellar wind on the evolution of a star of 30 M/sub sun/

    Stothers, R.; Chin, C.

    1980-01-01

    A coarse grid of theoretical evolutionary tracks has been computed for a star of 30 M/sub sun/, in an attempt to delineate the role of mass loss in the star's evolution during core helium burning. For all of the tracks, Cox-Stewart opacities have been adopted, and the free parameters have included the rate of mass loss, criterion for convection, and initial chemical composition. With the use of the Schwarzschild criterion, the star suffers little mass loss during core helium burning and remains almost to the end, a blue supergiant, well separated from main-sequence stars on the H-R diagram. With the use of the Ledoux criterion, the same consequences are obtained only in the case of a relatively low initial hydrogen or initial metals abundance. Otherwise, the star evolves, first, into a red supergiant, whereupon rapid mass loss must be assumed to take place, if the observed paucity of very bright red supergiants is to be accounted for. The stellar remnant then consists of little more than the original helium core, and may appear, for a time, bluer than equally luminous main-sequence stars, provided that the the initial hydrogen and metals abundances are normal. Thus, a wide variety of possible evolutionary tracks can be obtained for an initial mass of 30 M/sub sun/ with reasonable choices of the free parameters

  15. Effects of coronal regions on the x-ray flux and ionization conditions in the winds of ob supergiants and of stars

    Cassinelli, J.P.; Olson, G.L.

    1979-01-01

    The anomalously strong O VI and N V lines in O stars and the C IV lines in B supergiants may be due to Auger ionization by X-rays from a thin coronal zone at the base of the cool stellar winds. We determine the size of a corona that is necessary to produce the overall ionization conditions in zeta Pup as has been deduced by Olson from line profile analysis. In the ionization balance calculations we account for diffuse radiation field in the wind and for the large optical depths in the He II continuum due to radiative and Auger ionization edges of abundant elements. The X-ray flux transmitted through the wind is calculated and compared with upper limits derived for upper limits derived for zeta Pup observations from ANS and Uhuru satellites. It is found that a coronal zone with a temperature of 5x10 6 K and a volume emission measure of 10 58 cm -3 can produce the required ionization in a wind having a temperature of 30,000--35,000 K. The emergent X-ray flux bears little resemblance to the coronal emissivity because of the opacity of the wind. The X-ray flux nearly reaches the upper limits derived from the ANS observations and, at several energy bands, should be detectable by the HEAO B satellite. A simplified analysis of the Auger ionization process is developed and applied to other Of and OB supergiants. We find that the model can explain the presence of C IV and Si IV in supergaints with effective temperatures as low as 12,000 K and can explain the appearance of O VI and N V lines in early type supergiants as late as BO.5 and B2, respectively

  16. THE DISK WIND IN THE RAPIDLY SPINNING STELLAR-MASS BLACK HOLE 4U 1630–472 OBSERVED WITH NuSTAR

    King, Ashley L.; Miller, Jon M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Walton, Dominic J.; Fürst, Felix; Harrison, Fiona A. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Barret, Didier [Université de Toulouse, UPS-OMP, IRAP, Toulouse (France); Boggs, Steven E.; Craig, William W.; Krivonos, Roman; Tomsick, John A. [Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States); Christensen, Finn E. [DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Fabian, Andy C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Hailey, Charles J.; Mori, Kaya [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Natalucci, Lorenzo [Istituto Nazionale di Astrofisica, INAF-IAPS, via del Fosso del Cavaliere, I-00133 Roma (Italy); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109 (United States); Zhang, William W., E-mail: ashking@umich.edu [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2014-03-20

    We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630–472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we find evidence for a rapidly spinning black hole, a{sub ∗}=0.985{sub −0.014}{sup +0.005} (1σ statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also report the clear detection of an absorption feature at 7.03 ± 0.03 keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas (log ξ=3.6{sub −0.3}{sup +0.2}) and is dominated by He-like Fe XXV, the wind has a velocity of v/c=0.043{sub −0.007}{sup +0.002} (12900{sub −2100}{sup +600} km s{sup –1}). If the line is instead associated with a more highly ionized gas (log ξ=6.1{sub −0.6}{sup +0.7}), and is dominated by Fe XXVI, evidence of a blueshift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200-1100 Rg, and may be magnetically driven.

  17. In-Street Wind Direction Variability in the Vicinity of a Busy Intersection in Central London

    Balogun, Ahmed A.; Tomlin, Alison S.; Wood, Curtis R.; Barlow, Janet F.; Belcher, Stephen E.; Smalley, Robert J.; Lingard, Justin J. N.; Arnold, Sam J.; Dobre, Adrian; Robins, Alan G.; Martin, Damien; Shallcross, Dudley E.

    2010-09-01

    We present results from fast-response wind measurements within and above a busy intersection between two street canyons (Marylebone Road and Gloucester Place) in Westminster, London taken as part of the DAPPLE (Dispersion of Air Pollution and Penetration into the Local Environment; www.dapple.org.uk ) 2007 field campaign. The data reported here were collected using ultrasonic anemometers on the roof-top of a building adjacent to the intersection and at two heights on a pair of lamp-posts on opposite sides of the intersection. Site characteristics, data analysis and the variation of intersection flow with the above-roof wind direction ( θ ref ) are discussed. Evidence of both flow channelling and recirculation was identified within the canyon, only a few metres from the intersection for along-street and across-street roof-top winds respectively. Results also indicate that for oblique roof-top flows, the intersection flow is a complex combination of bifurcated channelled flows, recirculation and corner vortices. Asymmetries in local building geometry around the intersection and small changes in the background wind direction (changes in 15- min mean θ ref of 5°-10°) were also observed to have profound influences on the behaviour of intersection flow patterns. Consequently, short time-scale variability in the background flow direction can lead to highly scattered in-street mean flow angles masking the true multi-modal features of the flow and thus further complicating modelling challenges.

  18. Supernova ejecta with a relativistic wind from a central compact object: a unified picture for extraordinary supernovae

    Suzuki, Akihiro; Maeda, Keiichi

    2017-04-01

    The hydrodynamical interaction between freely expanding supernova ejecta and a relativistic wind injected from the central region is studied in analytic and numerical ways. As a result of the collision between the ejecta and the wind, a geometrically thin shell surrounding a hot bubble forms and expands in the ejecta. We use a self-similar solution to describe the early dynamical evolution of the shell and carry out a two-dimensional special relativistic hydrodynamic simulation to follow further evolution. The Rayleigh-Taylor instability inevitably develops at the contact surface separating the shocked wind and ejecta, leading to the complete destruction of the shell and the leakage of hot gas from the hot bubble. The leaking hot materials immediately catch up with the outermost layer of the supernova ejecta and thus different layers of the ejecta are mixed. We present the spatial profiles of hydrodynamical variables and the kinetic energy distributions of the ejecta. We stop the energy injection when a total energy of 1052 erg, which is 10 times larger than the initial kinetic energy of the supernova ejecta, is deposited into the ejecta and follow the subsequent evolution. From the results of our simulations, we consider expected emission from supernova ejecta powered by the energy injection at the centre and discuss the possibility that superluminous supernovae and broad-lined Ic supernovae could be produced by similar mechanisms.

  19. Statistical analysis of the wind around a nuclear power plant; Analisis estadistico del viento alrededor de una central nucleoelectrica

    Tejeda, A; Alvarez, Oscar; Contreras, A. D.; Jauregui, E. [Universidad Veracruzana, (Mexico)

    1996-12-31

    In order to show an appropriate methodology for the climatic analysis of the wind, some of the recent results in the investigation of the field flow around the Laguna Verde Nuclear Power Station, at Veracruz State (Mexico,) through the angular correlation coefficients and contingency tables among the registered wind directions by a meteorological tower at the levels of 10 and 60 meters high are presented. Finally, by applying an objective analysis of the data some conclusions are obtained in connection with the local winds with the mesoscale systems. [Espanol] Con el objeto de mostrar una metodologia apropiada en el analisis climatico del viento, se presentan algunos resultados recientes en la investigacion del campo de flujo en los alrededores de la central nucleoelectrica de Laguna Verde, Veracruz (Mexico), a traves de los coeficientes de correlacion angulares y de tablas de contingencia entre las direcciones del viento registradas por una torre meteorologica en los niveles de 10 y 60 metros de altura. Finalmente, aplicando analisis objetivo de los datos, se obtienen algunas conclusiones sobre la conexion de los vientos locales con los sistemas de mesoescala.

  20. Statistical analysis of the wind around a nuclear power plant; Analisis estadistico del viento alrededor de una central nucleoelectrica

    Tejeda, A; Alvarez, Oscar; Contreras, A D; Jauregui, E [Universidad Veracruzana, (Mexico)

    1997-12-31

    In order to show an appropriate methodology for the climatic analysis of the wind, some of the recent results in the investigation of the field flow around the Laguna Verde Nuclear Power Station, at Veracruz State (Mexico,) through the angular correlation coefficients and contingency tables among the registered wind directions by a meteorological tower at the levels of 10 and 60 meters high are presented. Finally, by applying an objective analysis of the data some conclusions are obtained in connection with the local winds with the mesoscale systems. [Espanol] Con el objeto de mostrar una metodologia apropiada en el analisis climatico del viento, se presentan algunos resultados recientes en la investigacion del campo de flujo en los alrededores de la central nucleoelectrica de Laguna Verde, Veracruz (Mexico), a traves de los coeficientes de correlacion angulares y de tablas de contingencia entre las direcciones del viento registradas por una torre meteorologica en los niveles de 10 y 60 metros de altura. Finalmente, aplicando analisis objetivo de los datos, se obtienen algunas conclusiones sobre la conexion de los vientos locales con los sistemas de mesoescala.

  1. Central Star Properties and C-N-O Abundances in Eight Galactic Planetary Nebulae from New HST/STIS Observations

    Henry, Richard B. C.; Balick, Bruce; Dufour, Reginald J.; Kwitter, Karen B.; Shaw, Richard A.; Corradi, Romano

    2015-01-01

    We present detailed photoionization models of eight Galactic planetary nebulae (IC2165, IC3568, NGC2440, NGC3242, NGC5315, NGC5882, NGC7662, & PB6) based on recently obtained HST STIS spectra. Our interim goal is to infer Teff, luminosity, and current and progenitor masses for each central star, while the ultimate goal is to constrain published stellar evolution models which predict nebular CNO abundances. The models were produced by using the code CLOUDY to match closely the measured line strengths derived from high-quality HST STIS spectra (see poster by Dufour et al., this session) extending in wavelength from 1150-10270 Angstroms. The models assumed a blackbody SED. Variable input parameters included Teff, a radially constant nebular density, a filling factor, and elemental abundances. For the eight PNs we found a birth mass range of 1.5-2.9 Msun, a range in log(L/Lsun) of 3.10-3.88, and a Teff range of 51-150k K. Finally, we compare CNO abundances of the eight successful models with PN abundances of these same elements that are predicted by published stellar evolution models. We gratefully acknowledge generous support from NASA through grants related to the Cycle 19 program GO12600.

  2. The environment of the wind-wind collision region of η Carinae

    Panagiotou, C.; Walter, R.

    2018-02-01

    Context. η Carinae is a colliding wind binary hosting two of the most massive stars and featuring the strongest wind collision mechanical luminosity. The wind collision region of this system is detected in X-rays and γ-rays and offers a unique laboratory for the study of particle acceleration and wind magneto-hydrodynamics. Aim. Our main goal is to use X-ray observations of η Carinae around periastron to constrain the wind collision zone geometry and understand the reasons for its variability. Methods: We analysed 10 Nuclear Spectroscopic Telescope Array (NuSTAR) observations, which were obtained around the 2014 periastron. The NuSTAR array monitored the source from 3 to 30 keV, which allowed us to grasp the continuum and absorption parameters with very good accuracy. We were able to identify several physical components and probe their variability. Results: The X-ray flux varied in a similar way as observed during previous periastrons and largely as expected if generated in the wind collision region. The flux detected within 10 days of periastron is lower than expected, suggesting a partial disruption of the central region of the wind collision zone. The Fe Kα line is likely broadened by the electrons heated along the complex shock fronts. The variability of its equivalent width indicates that the fluorescence region has a complex geometry and that the source obscuration varies quickly with the line of sight.

  3. High-resolution numerical simulation of summer wind field comparing WRF boundary-layer parametrizations over complex Arctic topography: case study from central Spitsbergen

    Láska, K.; Chládová, Zuzana; Hošek, Jiří

    2017-01-01

    Roč. 26, č. 4 (2017), s. 391-408 ISSN 0941-2948 Institutional support: RVO:68378289 Keywords : surface wind field * model evaluation * topographic effect * circulation pattern * Svalbard Subject RIV: DG - Athmosphere Sciences, Meteorology OBOR OECD: Meteorology and atmospheric sciences Impact factor: 1.989, year: 2016 http://www.schweizerbart.de/papers/metz/detail/prepub/87659/High_resolution_numerical_simulation_of_summer_wind_field_comparing_WRF_boundary_layer_parametrizations_over_complex_Arctic_topography_case_study_from_central_Spitsbergen

  4. A review of noise data collection at the central and south west wind farm in Texas

    Moroz, E. [Univ. of Texas, El Paso, TX (United States)

    1996-12-31

    Evaluation of data collected over a 1-year period from a 6 MW wind farm is presented in the paper. Noise propagation prediction methods are compared with each other and with field data. Three forms of regulating noise are also compared: minimum separation distance, absolute noise limit, and relative noise limit.Relative noise limits were found to offer the most comprehensive approach to regulating noise and to allow each location to be treated independently. A hemispherical spreading model appears to be a useful planning tool. 11 refs., 4 tabs.

  5. Star Polymers.

    Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G

    2016-06-22

    Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

  6. Classification of ISO SWS 01 spectra of proto-planetary nebulae: a search for precursors of planetary nebulae with [WR] central stars

    Szczerba, R.; Stasi{ń}ska, G.; Siódmiak, N.; Górny, S. K.

    2002-01-01

    We have analyzed ISO SWS 01 observations for 61 proto-planetary nebulae candidates and classified their spectra according to their dominant chemistry. On the basis of our classification and the more general classification of SWS 01 spectra by Kraemer et al. (2002) we discuss the connection between proto-planetary nebulae candidates and planetary nebulae, with emphasis on possible precursors of planetary nebulae with [WR] central stars.

  7. The formation of secondary stellar generations in massive young star clusters from rapidly cooling shocked stellar winds

    Wünsch, Richard; Palouš, Jan; Tenorio-Tagle, G.; Ehlerová, Soňa

    2017-01-01

    Roč. 835, č. 1 (2017), 60/1-60/15 ISSN 0004-637X R&D Projects: GA ČR GA15-06012S Grant - others:Ga MŠk(CZ) LM2015070 Institutional support: RVO:67985815 Keywords : galaxies * ISM * star clusters Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.533, year: 2016

  8. The symbiotics as binary stars

    Plavec, M.J.

    1982-01-01

    The author envisages at least three models that can give a symbiotic object: He has called them, respectively, the PN symbiotic, the Algol symbiotic, and the novalike symbiotic. Their properties are briefly discussed. The most promising model is one of a binary system in the second stage of mass transfer, actually at the beginning of it: The cool component is a red giant ascending the asymptotic branch, expanding but not yet filling its critical lobe. The hot star is a subdwarf located in the same region of the Hertzsprung-Russell diagram as the central stars of planetary nebulae. It may be closely related to them, or it may be a helium star, actually a remnant of an Algol primary which underwent the first stage of mass transfer. In these cases, accretion on this star may not play a significant role (PN symbiotic). Perhaps more often, the subdwarf is a ''rejuvenated'' degenerate dwarf whose nuclear burning shells were ignited and are maintained by accretion of material coming from the red giant in the form of a stellar wind. Eruptions are often inevitable: this is the novalike symbiotic. A third alternative is a system in the first stage of mass transfer, where the photons needed for ionization of the nebula come from an accretion disk surrounding a main sequence star: an Algol symbiotic. In spite of considerable observational effort, the symbiotics are known so poorly that it is hard to decide between the models, or even decide if all three can actually exist. (Auth.)

  9. La Venta wind power plant, seven months operating experience and growth perspectives; Central eolica La Venta, siete meses de operacion y perspectivas de crecimiento

    Cadena Tovar, Roberto; Lopez Rios, Serafin [Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)

    1995-01-01

    The capacity factor achieved for La Venta Wind Power Plant in Oaxaca State, Mexico was 63.8% during its first seven operating months. There is not similar experience around the world for a wind plant. This paper presents performance plant details and its capacity growth perspectives. [Espanol] En la central eolica La Venta, Oaxaca, Mexico se ha obtenido un factor de planta de 63.8% durante sus primeros siete meses de operacion, no existiendo precedente similar en las centrales eolicas actualmente en operacion en el mundo. En este documento se describen detalles de su comportamiento y se efectua un bosquejo general de las posibilidades de crecimiento del proyecto.

  10. Impact of land use change on wind erosion and dust emission: scenarios from the central US

    There will be significant changes in land cover and land use throughout the central United States in the coming years, particularly as a result of climate change, changes in US rangeland/farm policy, and increasing exploitation of land-intensive sustainable energy sources. The purpose of this study ...

  11. Revealing evolved massive stars with Spitzer

    Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.

    2010-06-01

    Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24-μm data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozen of these central stars, most of which turn out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs. This, in turn, will have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen-burning O stars and helium-burning WR stars. We also report on the detection of an arc-like structure attached to the cLBV HD 326823 and an arc associated with the LBV R99 (HD 269445) in the LMC. Partially based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); fabrika@sao.ru (SF)

  12. A Breath of Fresh Air in Foraging Theory: The Importance of Wind for Food Size Selection in a Central-Place Forager.

    Alma, Andrea Marina; Farji-Brener, Alejandro G; Elizalde, Luciana

    2017-09-01

    Empirical data about food size carried by central-place foragers do not often fit with the optimum predicted by classical foraging theory. Traditionally, biotic constraints such as predation risk and competition have been proposed to explain this inconsistency, leaving aside the possible role of abiotic factors. Here we documented how wind affects the load size of a central-place forager (leaf-cutting ants) through a mathematical model including the whole foraging process. The model showed that as wind speed at ground level increased from 0 to 2 km/h, load size decreased from 91 to 30 mm 2 , a prediction that agreed with empirical data from windy zones, highlighting the relevance of considering abiotic factors to predict foraging behavior. Furthermore, wind reduced the range of load sizes that workers should select to maintain a similar rate of food intake and decreased the foraging rate by ∼70% when wind speed increased 1 km/h. These results suggest that wind could reduce the fitness of colonies and limit the geographic distribution of leaf-cutting ants. The developed model offers a complementary explanation for why load size in central-place foragers may not fit theoretical predictions and could serve as a basis to study the effects of other abiotic factors that influence foraging.

  13. Contribution of stellar winds to the composition of cosmic rays - exotic Ne and Fe from Wolf-Rayet stars

    Blake, J.B.; Dearborn, D.S.P.

    1984-01-01

    The results of previous calculations of the production of Al-26 and the enhancement of heavy isotopes of Fe by Wolf-Rayet (WR) stars are discussed. Mass fractions of Al-26 in WR ejects and in WR H-rich envelopes are given as a function of stellar mass. It is concluded that the predicted mass of Al-26 in the ISM and its galactic distribution are such that WR stars are expected to be a significant if not the major source of the Al-26. The results suggest that He-22 enhancement must be accompanied by 4-8X enhancement of Fe-57, 20-45X enhancement of Fe-58, and 5-10X enhancement of Co-59. The isotopes of Fe are found to be affected before an appreciable enhancement of Ne-22 occurs. The size of the Ne-22 enhancement depends on the details of the mass-loss history whereas the Fe enhancement does not. 11 references

  14. Hydro, wind and solar power as a base for a 100% renewable energy supply for South and Central America.

    Larissa de Souza Noel Simas Barbosa

    Full Text Available Power systems for South and Central America based on 100% renewable energy (RE in the year 2030 were calculated for the first time using an hourly resolved energy model. The region was subdivided into 15 sub-regions. Four different scenarios were considered: three according to different high voltage direct current (HVDC transmission grid development levels (region, country, area-wide and one integrated scenario that considers water desalination and industrial gas demand supplied by synthetic natural gas via power-to-gas (PtG. RE is not only able to cover 1813 TWh of estimated electricity demand of the area in 2030 but also able to generate the electricity needed to fulfil 3.9 billion m3 of water desalination and 640 TWhLHV of synthetic natural gas demand. Existing hydro dams can be used as virtual batteries for solar and wind electricity storage, diminishing the role of storage technologies. The results for total levelized cost of electricity (LCOE are decreased from 62 €/MWh for a highly decentralized to 56 €/MWh for a highly centralized grid scenario (currency value of the year 2015. For the integrated scenario, the levelized cost of gas (LCOG and the levelized cost of water (LCOW are 95 €/MWhLHV and 0.91 €/m3, respectively. A reduction of 8% in total cost and 5% in electricity generation was achieved when integrating desalination and power-to-gas into the system.

  15. Hydro, wind and solar power as a base for a 100% renewable energy supply for South and Central America.

    Barbosa, Larissa de Souza Noel Simas; Bogdanov, Dmitrii; Vainikka, Pasi; Breyer, Christian

    2017-01-01

    Power systems for South and Central America based on 100% renewable energy (RE) in the year 2030 were calculated for the first time using an hourly resolved energy model. The region was subdivided into 15 sub-regions. Four different scenarios were considered: three according to different high voltage direct current (HVDC) transmission grid development levels (region, country, area-wide) and one integrated scenario that considers water desalination and industrial gas demand supplied by synthetic natural gas via power-to-gas (PtG). RE is not only able to cover 1813 TWh of estimated electricity demand of the area in 2030 but also able to generate the electricity needed to fulfil 3.9 billion m3 of water desalination and 640 TWhLHV of synthetic natural gas demand. Existing hydro dams can be used as virtual batteries for solar and wind electricity storage, diminishing the role of storage technologies. The results for total levelized cost of electricity (LCOE) are decreased from 62 €/MWh for a highly decentralized to 56 €/MWh for a highly centralized grid scenario (currency value of the year 2015). For the integrated scenario, the levelized cost of gas (LCOG) and the levelized cost of water (LCOW) are 95 €/MWhLHV and 0.91 €/m3, respectively. A reduction of 8% in total cost and 5% in electricity generation was achieved when integrating desalination and power-to-gas into the system.

  16. Renewable energy management through microgrid central controller design: An approach to integrate solar, wind and biomass with battery

    Zaheeruddin

    2015-11-01

    Full Text Available In this study, an isolated microgrid comprising of renewable energy (RE sources like wind, solar, biogas and battery is considered. Provision of utility grid insertion is also given if total microgrid sources falls short of supplying the total load. To establish an efficient energy management strategy, a central controller takes the decision based on the status of the loads and sources. The status is obtained with the assistance of multi-agent concept (treating each source and load as an agent. The data acquisition system of these renewable sources and loads consists of multiple sensors interconnected through Low Power Radio over one of many GPRS communication. The Microgrid Central Controller (MGCC would use an embedded energy management algorithm to take decisions, which are then transmitted to the controllable RE systems to manage the utilization of their power outputs as per the load-supply power balance. A control strategy is adopted to regulate the power output from the battery in case of supply shortage, which results in a floating battery scheme in steady state.

  17. Marketing research with respect to centralized electric power generation with wind turbines. Verkenning van de markt voor centrale elektriciteitsopwekking met windenergie

    Lenstra, W.J.; Van den Doel, J.C.

    1985-01-01

    The electric utilities so far are not eager to invest in wind power as long as the price per kWh wind power is higher than saved fuel costs. The price the electric utilities are willing to pay for surplus wind power still remains low. Combined with price expectations in the near future for fossil fuels the market does not show great prospects. Wind turbine manufacturers were asked about price-quantity curves of wind turbine types: 3 MW, 1 MW, and 300 kW respectively. Combining the demand and supply side of the market it seems possible in areas having a good wind regime to exploit wind power in a cost-effective way. For a market incentive a wind power capacity of 400 MW: 75-3 MW wind turbines, 120-1 MW wind turbines, 15-300 kW wind turbines and 50 MW for demonstration projects for proving the viability of the technology. 3 figs., 2 tabs.

  18. HM Sagittae - a most remarkable star

    Kwok, S.

    1982-01-01

    The author summarises recent observations of HM Sagittae, a symbiotic star that displays activity in every spectral band from X-ray to radio. He concludes that it is best described as a binary system consisting of a late M giant and a hot compact object which is similar to central stars of planetary nebulae. The presence of a wind from the M giant implies that Roche-lobe overflow is not a necessary condition for mass transfer. The complex structure of the circumstellar nebula is possibly the result of wind interactions. The ongoing spectral evolution of HM Sge after its recent outburst makes it an ideal candidate to test models of the symbiotic phenomenon. (Auth.)

  19. Atmospheric dust events in central Asia: Relationship to wind, soil type, and land use

    Pi, Huawei; Sharratt, Brenton; Lei, Jiaqiang

    2017-06-01

    Xinjiang Province in northwest China is one of the most important source regions of atmospheric dust in the world. Spatial-temporal characteristics of dust events in the province were investigated by time series analysis of annual dust event frequency and meteorological data collected at 101 meteorological stations from 1960 to 2007. Blowing dust frequency (BDF) and dust storm frequency (DSF) decreased with time in North, South, and East Xinjiang whereas floating dust frequency (FDF) decreased with time only in South and East Xinjiang. Dust concentrations were lower in North than in South Xinjiang and decreased with time in East Xinjiang. Wind significantly influenced the temporal trend in FDF, BDF, and DSF in South Xinjiang and DSF in North Xinjiang. Frequency of dust events was smaller by an order of magnitude in North (10.9 d yr-1) than in South Xinjiang (111.3 d yr-1), possibly due in part to higher annual precipitation in North Xinjiang. Floating dust was most frequently observed in East and South Xinjiang, while blowing dust was most frequently observed in North Xinjiang. The high frequency of floating dust in East and South Xinjiang is likely due to the enclosed terrain that characterizes these regions. Land use and soil type also influenced dust events. Although climate influences frequency of dust events, the occurrence of these events may be reduced most effectively by imposing better land management practices in deciduous forests or orchards characterized by saline soils in respectively North and East Xinjiang and meadows characterized by Guanyu soils in South Xinjiang.

  20. Stellar winds

    Weymann, R.J.

    1978-01-01

    It is known that a steady outflow of material at comparable rates of mass loss but vastly different speeds is now known to be ubiquitous phenomenon among both the luminous hot stars and the luminous but cool red giants. The flows are probably massive enough in both cases to give rise to significant effects on stellar evolution and the mass balance between stars and the interstellar medium. The possible mechanisms for these phenomena as well as the methods of observation used are described. In particular, the mass-loss processes in stars other than the sun that also involve a steady flow of matter are considered. The evidence for their existence is described, and then the question of whether the process thought to produce the solar wind is also responsible for producing these stellar winds is explored

  1. Clouds, Wind and the Biogeography of Central American Cloud Forests: Remote Sensing, Atmospheric Modeling, and Walking in the Jungle

    Lawton, R.; Nair, U. S.

    2011-12-01

    Cloud forests stand at the core of the complex of montane ecosystems that provide the backbone to the multinational Mesoamerican Biological Corridor, which seeks to protect a biodiversity conservation "hotspot" of global significance in an area of rapidly changing land use. Although cloud forests are generally defined by frequent and prolonged immersion in cloud, workers differ in their feelings about "frequent" and "prolonged", and quantitative assessments are rare. Here we focus on the dry season, in which the cloud and mist from orographic cloud plays a critical role in forest water relations, and discuss remote sensing of orographic clouds, and regional and atmospheric modeling at several scales to quantitatively examine the distribution of the atmospheric conditions that characterize cloud forests. Remote sensing using data from GOES reveals diurnal and longer scale patterns in the distribution of dry season orographic clouds in Central America at both regional and local scales. Data from MODIS, used to calculate the base height of orographic cloud banks, reveals not only the geographic distributon of cloud forest sites, but also striking regional variation in the frequency of montane immersion in orographic cloud. At a more local scale, wind is known to have striking effects on forest structure and species distribution in tropical montane ecosystems, both as a general mechanical stress and as the major agent of ecological disturbance. High resolution regional atmospheric modeling using CSU RAMS in the Monteverde cloud forests of Costa Rica provides quantitative information on the spatial distribution of canopy level winds, insight into the spatial structure and local dynamics of cloud forest communities. This information will be useful in not only in local conservation planning and the design of the Mesoamerican Biological Corridor, but also in assessments of the sensitivity of cloud forests to global and regional climate changes.

  2. The wind and the magnetospheric accretion onto the T Tauri star S Coronae Australis at sub-au resolution

    Gravity Collaboration; Garcia Lopez, R.; Perraut, K.; Caratti O Garatti, A.; Lazareff, B.; Sanchez-Bermudez, J.; Benisty, M.; Dougados, C.; Labadie, L.; Brandner, W.; Garcia, P. J. V.; Henning, Th.; Ray, T. P.; Abuter, R.; Amorim, A.; Anugu, N.; Berger, J. P.; Bonnet, H.; Buron, A.; Caselli, P.; Clénet, Y.; Coudé Du Foresto, V.; de Wit, W.; Deen, C.; Delplancke-Ströbele, F.; Dexter, J.; Eckart, A.; Eisenhauer, F.; Garcia Dabo, C. E.; Gendron, E.; Genzel, R.; Gillessen, S.; Haubois, X.; Haug, M.; Haussmann, F.; Hippler, S.; Hubert, Z.; Hummel, C. A.; Horrobin, M.; Jocou, L.; Kellner, S.; Kervella, P.; Kulas, M.; Kolb, J.; Lacour, S.; Le Bouquin, J.-B.; Léna, P.; Lippa, M.; Mérand, A.; Müller, E.; Ott, T.; Panduro, J.; Paumard, T.; Perrin, G.; Pfuhl, O.; Ramirez, A.; Rau, C.; Rohloff, R.-R.; Rousset, G.; Scheithauer, S.; Schöller, M.; Straubmeier, C.; Sturm, E.; Thi, W. F.; van Dishoeck, E.; Vincent, F.; Waisberg, I.; Wank, I.; Wieprecht, E.; Wiest, M.; Wiezorrek, E.; Woillez, J.; Yazici, S.; Zins, G.

    2017-12-01

    Aims: To investigate the inner regions of protoplanetary discs, we performed near-infrared interferometric observations of the classical T Tauri binary system S CrA. Methods: We present the first VLTI-GRAVITY high spectral resolution (R 4000) observations of a classical T Tauri binary, S CrA (composed of S CrA N and S CrA S and separated by 1.̋4), combining the four 8m telescopes in dual-field mode. Results: Our observations in the near-infrared K-band continuum reveal a disc around each binary component, with similar half-flux radii of about 0.1 au at d 130 pc, inclinations (i = 28 ± 3° and i = 22 ± 6°), and position angles (PA = 0°± 6° and PA = –2°± 12°), suggesting that they formed from the fragmentation of a common disc. The S CrA N spectrum shows bright He I and Brγ line emission exhibiting inverse P Cygni profiles, typically associated with infalling gas. The continuum-compensated Brγ line visibilities of S CrA N show the presence of a compact Brγ emitting region whose radius is about 0.06 au, which is twice as big as the truncation radius. This component is mostly tracing a wind. Moreover, a slight radius change between the blue- and red-shifted Brγ line components is marginally detected. Conclusions: The presence of an inverse P Cygni profile in the He I and Brγ lines, along with the tentative detection of a slightly larger size of the blue-shifted Brγ line component, hint at the simultaneous presence of a wind and magnetospheric accretion in S CrA N.

  3. On the nature of the symbiotic star BF Cygni

    Mikolajewska, J.; Mikolajewski, M.; Kenyon, S.J.

    1989-01-01

    Optical and ultraviolet spectroscopy of the symbiotic binary BF Cyg obtained during 1979-1988 is discussed. This system consists of a low-mass M5 giant filling about 50 percent of its tidal volume and a hot, luminous compact object similar to the central star of a planetary nebula. The binary is embedded in an asymmetric nebula which includes a small, high-density region and an extended region of lower density. The larger nebula is formed by a slow wind ejected by the cool component and ionized by the hot star, while the more compact nebula is material expelled by the hot component in the form of a bipolar wind. The analysis indicates that disk accretion is essential to maintain the nuclear burning shell of the hot star. 84 refs

  4. Neutron stars

    Irvine, J.M.

    1978-01-01

    The subject is covered in chapters entitled: introduction (resume of stellar evolution, gross characteristics of neutron stars); pulsars (pulsar characteristics, pulsars as neutron stars); neutron star temperatures (neutron star cooling, superfluidity and superconductivity in neutron stars); the exterior of neutron stars (the magnetosphere, the neutron star 'atmosphere', pulses); neutron star structure; neutron star equations of state. (U.K.)

  5. The role of remote wind forcing in the subinertial current variability in the central and northern parts of the South Brazil Bight

    Dottori, Marcelo; Castro, Belmiro Mendes

    2018-05-01

    Data analysis of continental shelf currents and coastal sea level, together with the application of a semi-analytical model, are used to estimate the importance of remote wind forcing on the subinertial variability of the current in the central and northern areas of the South Brazil Bight. Results from both the data analysis and from the semi-analytical model are robust in showing subinertial variability that propagates along-shelf leaving the coast to the left in accordance with theoretical studies of Continental Shelf Waves (CSW). Both the subinertial variability observed in along-shelf currents and sea level oscillations present different propagation speeds for the narrow northern part of the SBB ( 6-7 m/s) and the wide central SBB region ( 11 m/s), those estimates being in agreement with the modeled CSW propagation speed. On the inner and middle shelf, observed along-shelf subinertial currents show higher correlation coefficients with the winds located southward and earlier in time than with the local wind at the current meter mooring position and at the time of measurement. The inclusion of the remote (located southwestward) wind forcing improves the prediction of the subinertial currents when compared to the currents forced only by the local wind, since the along-shelf-modeled currents present correlation coefficients with observed along-shelf currents up to 20% higher on the inner and middle shelf when the remote wind is included. For most of the outer shelf, on the other hand, this is not observed since usually, the correlation between the currents and the synoptic winds is not statistically significant.

  6. Mesoscale modeling of smoke transport over Central Africa: influences of trade winds, subtropical high, ITCZ and vertical statistics

    Yang, Z.; Wang, J.; Hyer, E. J.; Ichoku, C. M.

    2012-12-01

    A fully-coupled meteorology-chemistry-aerosol model, Weather Research and Forecasting model with Chemistry (WRF-Chem), is used to simulate the transport of smoke aerosol over the Central Africa during February 2008. Smoke emission used in this study is specified from the Fire Locating and Modeling of Burning Emissions (FLAMBE) database derived from Moderate Resolution Imaging Spectroradiometer (MODIS) fire products. Model performance is evaluated using MODIS true color images, measured Aerosol Optical Depth (AOD) from space-borne MODIS (550 nm) and ground-based AERONET (500 nm), and Cloud-Aerosol Lidar data with Orthogonal Polarization (CALIOP) level 1 and 2 products. The simulated smoke transport is in good agreement with the validation data. Analyzing from three smoke events, smoke is constrained in a narrow belt between the Equator and 10°N near the surface, with the interplay of trade winds, subtropical high, and ITCZ. At the 700 hpa level, smoke expands farther meridionally. Topography blocks the smoke transport to the southeast of study area, because of high mountains located near the Great Rift Valley region. The simulation with injection height of 650 m is consistent with CALIOP measurements. The particular phenomenon, aerosol above cloud, is studied statistically from CALIOP observations. The total percentage of aerosol above cloud is about 5%.

  7. Potential profiles in the central core of the cathode in the star mode operation in an inertial-electrostatic fusion neutron source

    Yoshikawa, K.; Masuda, K.; Toku, H.

    2003-01-01

    After the successful measurements of the localized electric fields in the center-spot mode operation with relatively large space-charge effects by the laser-induced fluorescence (LIF) method, measurements of potential profiles in the star mode operation with small space-charge effects on helium gas are made in the central cathode core region of an Inertial-Electrostatic Confinement Fusion (IECF) neutron source, which is most suitable to neutron calibration in the fusion devices. Since the high-voltage is required to the star mode operation on deuterium gas, it is predicted to bring about very small beam space charge-related potential. To increase accuracy, we adopted n=4 (2 1 S to 4 1 D:HeI) transition, instead of previous n=3, which is most sensitive to the local electric fields in the Stark transition, and verified using the well-known U-shaped hollow cathode potential. The localized electric fields thus measured by LIF method using n=4 transition show negligible electric fields in the star mode compared with the center-spot mode. (author)

  8. MASSIVE INFANT STARS ROCK THEIR CRADLE

    2002-01-01

    that are responsible for lighting up this cloud of gas. The apparently innocuous-looking star at the very center of the nebula, just below the brightest region, is actually about 30 times more massive and almost 200,000 times brighter than our Sun. The intense light and powerful stellar 'winds' from this ultra-bright star have cleared away the surrounding gas to form a large cavity. The bubble is approximately 25 light-years in diameter - about the same size as the famous star-forming Orion Nebula. The Orion Nebula is sculpted by intense radiation from newly born stars in the same way as N83B. Astronomers estimate that the spherical void in N83B must have been carved out of the nebula very recently - in astronomical terms - maybe as little as 30,000 years ago. The hottest star in N83B is 45 times more massive than the Sun and is embedded in the brightest region in the nebula. This bright region, situated just above the center, is only about 2 light-years across. The region's small size and its intense glow are telltale signs of a very young, massive star. This star is the youngest newcomer to this part of the Large Magellanic Cloud. The Hubble image shows a bright arc structure just below the luminous star. This impressive ridge may have been created in the glowing gas by the hot star's powerful wind. Measurements of the age of this star and neighboring stars in the nebula show that they are younger than the nebula's central star. Their formation may have been 'triggered' by the violent wind from the central star. This 'chain-reaction' of stellar births seems to be common in the Universe. About 20 young and luminous stars have been identified in the region, but it may well be that many more massive stars remain undetected in other areas of the Large Magellanic Cloud, hidden by dust in small clusters like N83B. To the right of the glowing N83B is a much larger diffuse nebula, known as DEM22d, which is partly obscured by an extended lane of dust and gas. This image is

  9. [Estimation of the effect derived from wind erosion of soil and dust emission in Tianjin suburbs on the central district based on WEPS model].

    Chen, Li; Han, Ting-Ting; Li, Tao; Ji, Ya-Qin; Bai, Zhi-Peng; Wang, Bin

    2012-07-01

    Due to the lack of a prediction model for current wind erosion in China and the slow development for such models, this study aims to predict the wind erosion of soil and the dust emission and develop a prediction model for wind erosion in Tianjin by investigating the structure, parameter systems and the relationships among the parameter systems of the prediction models for wind erosion in typical areas, using the U.S. wind erosion prediction system (WEPS) as reference. Based on the remote sensing technique and the test data, a parameter system was established for the prediction model of wind erosion and dust emission, and a model was developed that was suitable for the prediction of wind erosion and dust emission in Tianjin. Tianjin was divided into 11 080 blocks with a resolution of 1 x 1 km2, among which 7 778 dust emitting blocks were selected. The parameters of the blocks were localized, including longitude, latitude, elevation and direction, etc.. The database files of blocks were localized, including wind file, climate file, soil file and management file. The weps. run file was edited. Based on Microsoft Visualstudio 2008, secondary development was done using C + + language, and the dust fluxes of 7 778 blocks were estimated, including creep and saltation fluxes, suspension fluxes and PM10 fluxes. Based on the parameters of wind tunnel experiments in Inner Mongolia, the soil measurement data and climate data in suburbs of Tianjin, the wind erosion module, wind erosion fluxes, dust emission release modulus and dust release fluxes were calculated for the four seasons and the whole year in suburbs of Tianjin. In 2009, the total creep and saltation fluxes, suspension fluxes and PM10 fluxes in the suburbs of Tianjin were 2.54 x 10(6) t, 1.25 x 10(7) t and 9.04 x 10(5) t, respectively, among which, the parts pointing to the central district were 5.61 x 10(5) t, 2.89 x 10(6) t and 2.03 x 10(5) t, respectively.

  10. HUBBLE'S PANORAMIC PORTRAIT OF A VAST STAR-FORMING REGION

    2002-01-01

    NASA's Hubble Space Telescope has snapped a panoramic portrait of a vast, sculpted landscape of gas and dust where thousands of stars are being born. This fertile star-forming region, called the 30 Doradus Nebula, has a sparkling stellar centerpiece: the most spectacular cluster of massive stars in our cosmic neighborhood of about 25 galaxies. The mosaic picture shows that ultraviolet radiation and high-speed material unleashed by the stars in the cluster, called R136 [the large blue blob left of center], are weaving a tapestry of creation and destruction, triggering the collapse of looming gas and dust clouds and forming pillar-like structures that are incubators for nascent stars. The photo offers an unprecedented, detailed view of the entire inner region of 30 Doradus, measuring 200 light-years wide by 150 light-years high. The nebula resides in the Large Magellanic Cloud (a satellite galaxy of the Milky Way), 170,000 light-years from Earth. Nebulas like 30 Doradus are the 'signposts' of recent star birth. High-energy ultraviolet radiation from the young, hot, massive stars in R136 causes the surrounding gaseous material to glow. Previous Hubble telescope observations showed that R136 contains several dozen of the most massive stars known, each about 100 times the mass of the Sun and about 10 times as hot. These stellar behemoths all formed at the same time about 2 million years ago. The stars in R136 are producing intense 'stellar winds' (streams of material traveling at several million miles an hour), which are wreaking havoc on the gas and dust in the surrounding neighborhood. The winds are pushing the gas away from the cluster and compressing the inner regions of the surrounding gas and dust clouds [the pinkish material]. The intense pressure is triggering the collapse of parts of the clouds, producing a new generation of star formation around the central cluster. The new stellar nursery is about 30 to 50 light-years from R136. Most of the stars in the

  11. High-resolution observations of IRAS 08544-4431. Detection of a disk orbiting a post-AGB star and of a slow disk wind

    Bujarrabal, V.; Castro-Carrizo, A.; Winckel, H. Van; Alcolea, J.; Contreras, C. Sánchez; Santander-García, M.; Hillen, M.

    2018-06-01

    Context. Aims: In order to study the effects of rotating disks in the post-asymptotic giant branch (post-AGB) evolution, we observe a class of binary post-AGB stars that seem to be systematically surrounded by equatorial disks and slow outflows. Although the rotating dynamics had only been well identified in three cases, the study of such structures is thought to be fundamental to the understanding of the formation of disks in various phases of the late evolution of binary stars and the ejection of planetary nebulae from evolved stars. Methods: We present ALMA maps of 12CO and 13CO J = 3-2 lines in the source IRAS 08544-4431, which belongs to the above mentioned class of objects. We analyzed the data by means of nebula models, which account for the expectedly composite source and can reproduce the data. From our modeling, we estimated the main nebula parameters, including the structure and dynamics and the density and temperature distributions. We discuss the uncertainties of the derived values and, in particular, their dependence on the distance. Results: Our observations reveal the presence of an equatorial disk in rotation; a low-velocity outflow is also found, probably formed of gas expelled from the disk. The main characteristics of our observations and modeling of IRAS 08544-4431 are similar to those of better studied objects, confirming our interpretation. The disk rotation indicates a total central mass of about 1.8 M⊙, for a distance of 1100 pc. The disk is found to be relatively extended and has a typical diameter of 4 × 1016 cm. The total nebular mass is 2 × 10-2 M⊙, of which 90% corresponds to the disk. Assuming that the outflow is due to mass loss from the disk, we derive a disk lifetime of 10 000 yr. The disk angular momentum is found to be comparable to that of the binary system at present. Assuming that the disk angular momentum was transferred from the binary system, as expected, the high values of the disk angular momentum in this and other

  12. Spectrophotometry of ring nebulae around Wolf-Rayet stars

    Kwitter, K.B.

    1979-01-01

    Spectrophotometric observations of four ring nebulae surrounding population I Wolf-Rayet (WN) stars have been obtained, and four additional filamentary nebulae in order to determine the physical conditions and chemical abundances in these objects. It was concluded that the ring nebulae are enriched in nitrogen and helium as a result of contamination of the ambient interstellar medium by the helium- and nitrogen-rich wind from the central Wolf-Rayet star. Of the additional nebulae studied, two were found to be Peimbert Type I planetary nebulae, overabundant in nitrogen and helium due to mixing of CNO processed material into the parent envelope prior to ejection. One of the remaining objects, a shell around an Oef star, is found to have normal abundances; the other, a small H II region around an early Be star, also exhibits normal abundances. It was attempted to interpret the ring nebulae and the Oef shell as interstellar bubbles, according to recent theory; it met with varying degrees of success. For two of the ring nebulae, the fraction of nebular mass contributed by the central star can be estimated from published stellar abundances. It was found that in these two cases, the stellar wind has provided less than 10% of the observed nebular mass

  13. Trends in surface wind speed and significant wave height as revealed by ERA-Interim wind wave hindcast in the Central Bay of Bengal

    Shanas, P.R.; SanilKumar, V.

    height. The area average analysis is carried out to investigate the sensitivity of the identified trend results for the point location and found similar trends for extreme wind speed and SWH. The high (>5 m) annual maximum SWH in the study area...

  14. The Stars behind the Curtain

    2010-02-01

    ESO is releasing a magnificent VLT image of the giant stellar nursery surrounding NGC 3603, in which stars are continuously being born. Embedded in this scenic nebula is one of the most luminous and most compact clusters of young, massive stars in our Milky Way, which therefore serves as an excellent "local" analogue of very active star-forming regions in other galaxies. The cluster also hosts the most massive star to be "weighed" so far. NGC 3603 is a starburst region: a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust. Located 22 000 light-years away from the Sun, it is the closest region of this kind known in our galaxy, providing astronomers with a local test bed for studying intense star formation processes, very common in other galaxies, but hard to observe in detail because of their great distance from us. The nebula owes its shape to the intense light and winds coming from the young, massive stars which lift the curtains of gas and clouds revealing a multitude of glowing suns. The central cluster of stars inside NGC 3603 harbours thousands of stars of all sorts (eso9946): the majority have masses similar to or less than that of our Sun, but most spectacular are several of the very massive stars that are close to the end of their lives. Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars - extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious explosions known as supernovae. Using another recent set of observations performed with the SINFONI instrument on ESO's Very Large Telescope (VLT), astronomers have confirmed that one of these stars is about 120 times more massive than our Sun, standing out as the most massive star known so far in the Milky Way [1]. The clouds of NGC 3603 provide us with a family picture of stars in different stages of their life, with gaseous structures that are

  15. A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables

    Arneson, R. A.; Gehrz, R. D.; Woodward, C. E.; Shenoy, D. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 106 Pleasant Street S.E., Minneapolis, MN 55455 (United States); Helton, L. A. [USRA-SOFIA Science Center, NASA Ames Research Center, Moffett Field, CA 94035 (United States); Evans, A. [Astrophysics Group, Lennard Jones Laboratory, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Keller, L. D. [Department of Physics and Astronomy, 264 Center for Natural Sciences, Ithaca College, Ithaca, NY 14850 (United States); Hinkle, K. H. [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 (United States); Jura, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Lebzelter, T. [Institute for Astrophysics (IfA), University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria); Lisse, C. M. [Solar System Exploration Branch, Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723 (United States); Rushton, M. T. [Astronomical Institute of the Romanian Academy, Str. Cutitul de Argint 5, Bucharest, 040557 (Romania); Mizrachi, J., E-mail: arneson@astro.umn.edu [Biomedical Engineering Department, Stony Brook University, Stony Brook, NY 11794 (United States)

    2017-07-01

    We present a SOFIA FORCAST grism spectroscopic survey to examine the mineralogy of the circumstellar dust in a sample of post-asymptotic giant branch (post-AGB) yellow supergiants that are believed to be the precursors of planetary nebulae. Our mineralogical model of each star indicates the presence of both carbon-rich and oxygen-rich dust species—contrary to simple dredge-up models—with a majority of the dust in the form of amorphous carbon and graphite. The oxygen-rich dust is primarily in the form of amorphous silicates. The spectra do not exhibit any prominent crystalline silicate emission features. For most of the systems, our analysis suggests that the grains are relatively large and have undergone significant processing, supporting the hypothesis that the dust is confined to a Keplerian disk and that we are viewing the heavily processed, central regions of the disk from a nearly face-on orientation. These results help to determine the physical properties of the post-AGB circumstellar environment and to constrain models of post-AGB mass loss and planetary nebula formation.

  16. Neutron stars: Observational diversity and evolution

    Safi-Harb, S.

    2017-12-01

    Ever since the discovery of the Crab and Vela pulsars in their respective Supernova Remnants, our understanding of how neutron stars manifest themselves observationally has been dramatically shaped by the surge of discoveries and dedicated studies across the electromagnetic spectrum, particularly in the high-energy band. The growing diversity of neutron stars includes the highly magnetized neutron stars (magnetars) and the Central Compact Objects shining in X-rays and mostly lacking pulsar wind nebulae. These two subclasses of high-energy objects, however, seem to be characterized by anomalously high or anomalously low surface magnetic fields (thus dubbed as ‘magnetars’ and ‘anti-magnetars’, respectively), and have pulsar characteristic ages that are often much offset from their associated SNRs’ ages. In addition, some neutron stars act ‘schizophrenic’ in that they occasionally display properties that seem common to more than one of the defined subclasses. I review the growing diversity of neutron stars from an observational perspective, then highlight recent and on-going theoretical and observational work attempting to address this diversity, particularly in light of their magnetic field evolution, energy loss mechanisms, and supernova progenitors’ studies.

  17. Central-engine-powered Bright X-Ray Flares in Short Gamma-Ray Bursts: A Hint of a Black Hole–Neutron Star Merger?

    Mu, Hui-Jun; Gu, Wei-Min; Mao, Jirong; Hou, Shu-Jin; Lin, Da-Bin; Liu, Tong

    2018-05-01

    Short gamma-ray bursts may originate from the merger of a double neutron star (NS) or the merger of a black hole (BH) and an NS. We propose that the bright X-ray flare related to the central engine reactivity may indicate a BH–NS merger, since such a merger can provide more fallback materials and therefore a more massive accretion disk than the NS–NS merger. Based on the 49 observed short bursts with the Swift/X-ray Telescope follow-up observations, we find that three bursts have bright X-ray flares, among which three flares from two bursts are probably related to the central engine reactivity. We argue that these two bursts may originate from the BH–NS merger rather than the NS–NS merger. Our suggested link between the central-engine-powered bright X-ray flare and the BH–NS merger event can be checked by future gravitational wave detections from advanced LIGO and Virgo.

  18. Symbiotic stars

    Boyarchuk, A.A.

    1975-01-01

    There are some arguments that the symbiotic stars are binary, where one component is a red giant and the other component is a small hot star which is exciting a nebula. The symbiotic stars belong to the old disc population. Probably, symbiotic stars are just such an evolutionary stage for double stars as planetary nebulae for single stars. (Auth.)

  19. Local protoplanetary disk ionisation by T Tauri star energetic particles

    Fraschetti, F.; Drake, J.; Cohen, O.; Garraffo, C.

    2017-10-01

    The evolution of protoplanetary disks is believed to be driven largely by viscosity. The ionization of the disk that gives rise to viscosity is caused by X-rays from the central star or by energetic particles released by shock waves travelling into the circumstellar medium. We have performed test-particle numerical simulations of GeV-scale protons traversing a realistic magnetised wind of a young solar mass star with a superposed small-scale turbulence. The large-scale field is generated via an MHD model of a T Tauri wind, whereas the isotropic (Kolmogorov power spectrum) turbulent component is synthesised along the particles' trajectories. We have combined Chandra observations of T Tauri flares with solar flare scaling for describing the energetic particle spectrum. In contrast with previous models, we find that the disk ionization is dominated by X-rays except within narrow regions where the energetic particles are channelled onto the disk by the strongly tangled and turbulent field lines; the radial thickness of such regions broadens with the distance from the central star (5 stellar radii or more). In those regions, the disk ionization due to energetic particles can locally dominate the stellar X-rays, arguably, out to large distances (10, 100 AU) from the star.

  20. Neutron Stars and Pulsars

    Becker, Werner

    2009-01-01

    Neutron stars are the most compact astronomical objects in the universe which are accessible by direct observation. Studying neutron stars means studying physics in regimes unattainable in any terrestrial laboratory. Understanding their observed complex phenomena requires a wide range of scientific disciplines, including the nuclear and condensed matter physics of very dense matter in neutron star interiors, plasma physics and quantum electrodynamics of magnetospheres, and the relativistic magneto-hydrodynamics of electron-positron pulsar winds interacting with some ambient medium. Not to mention the test bed neutron stars provide for general relativity theories, and their importance as potential sources of gravitational waves. It is this variety of disciplines which, among others, makes neutron star research so fascinating, not only for those who have been working in the field for many years but also for students and young scientists. The aim of this book is to serve as a reference work which not only review...

  1. Subluminous Wolf-Rayet stars: Observations

    Heap, S.R.

    1982-01-01

    The author has used the fact that some central stars are WR stars and others are say, O stars, as a focal point for his presentation. In attempting to answer this question he has considered how the properties of WR-type central stars differ from those of O-type stars. The study begins with the classification and calibration of WR spectra, then goes on to the physical properties of WR-type central stars, and at the end returns to the question of what distinguishes a Wolf-Rayet star. The observational data for central stars are neither complete nor precise. Nevertheless, they suggest that what distinguishes a WR central star is not so much its present physical properties (e.g. temperature, gravity), but rather, its fundamental properties (initial and evolutionary history). (Auth.)

  2. IRAS 06562-0337, The Ironclad Nebula: A New Young Star Cluster

    Alves, D.R.; Hoard, D.W.; Rodgers, B.

    1998-01-01

    IRAS 06562-0337 has been the recent subject of a classic debate: is it a proto endash planetary nebula or a young stellar object? We present the first 2 μm image of IRAS 06562-0337, which reveals an extended diffuse nebula containing approximately 70 stars inside a 30 double-prime radius around a bright, possibly resolved, central object. The derived stellar luminosity function is consistent with that expected from a single coeval population, and the brightness of the nebulosity is consistent with the predicted flux of unresolved low-mass stars. The stars and nebulosity are spatially coincident with strong CO line emission. We therefore identify IRAS 06562-0337 as a new young star cluster embedded in its placental molecular cloud. The central object is likely a Herbig Be star, M ∼ 20 M circle-dot , which may be seen in reflection. We present medium-resolution high signal-to-noise ratio 1997 epoch optical spectra of the central object. Comparison with previously published spectra shows new evidence for time-variable permitted and forbidden line emission, including Si ii, Fe ii, [Fe ii], and [O i]. We suggest that the origin is a dynamic stellar wind in the extended stratified atmosphere of the massive central star in IRAS 06562-0337. copyright copyright 1998. The American Astronomical Society

  3. DISCOVERY OF TWIN WOLF-RAYET STARS POWERING DOUBLE RING NEBULAE

    Mauerhan, Jon C.; Wachter, Stefanie; Van Dyk, Schuyler D.; Hoard, D. W.; Morris, Patrick W.

    2010-01-01

    We have spectroscopically discovered a pair of twin, nitrogen-type, hydrogen-rich, Wolf-Rayet stars (WN8-9h) that are both surrounded by circular, mid-infrared-bright nebulae detected with the Spitzer Space Telescope and MIPS instrument. The emission is probably dominated by a thermal continuum from cool dust, but also may contain contributions from atomic line emission. There is no counterpart at shorter Spitzer/IRAC wavelengths, indicating a lack of emission from warm dust. The two nebulae are probably wind-swept stellar ejecta released by the central stars during a prior evolutionary phase. The nebulae partially overlap on the sky and we speculate on the possibility that they are in the early stage of a collision. Two other evolved massive stars have also been identified within the area subtended by the nebulae, including a carbon-type Wolf-Rayet star (WC8) and an O7-8 III-I star, the latter of which appears to be embedded in one of the larger WN8-9h nebulae. The derived distances to these stars imply that they are coeval members of an association lying 4.9 ± 1.2 kpc from Earth, near the intersection of the Galaxy's Long Bar and the Scutum-Centaurus spiral arm. This new association represents an unprecedented display of complex interactions between multiple stellar winds, outflows, and the radiation fields of evolved massive stars.

  4. Mass loss from Wolf-Rayet stars

    Willis, A.J.

    1982-01-01

    Recent results relating to the stellar winds and mass loss rates of the WR stars are reviewed, emphasising new data and their interpretation acquired at UV, IR and Radio wavelengths. The subject is discussed under the headings: physical and chemical properties of WR stars (effective temperatures and radiative luminosities; masses; chemical abundances); velocity, ionisation and excitation structure of WR winds; mass loss rates of WR stars; mass loss properties of WR stars in the LMC; comparisons with theoretical models of mass loss; ring nebulae around WR stars; conclusions. (author)

  5. Very-high-energy gamma-ray observations of pulsar wind nebulae and cataclysmic variable stars with MAGIC and development of trigger systems for IACTs

    Lopez-Coto, Ruben

    2015-07-01

    lowest possible energy threshold with the LSTs of CTA. Together with this work, the trigger of the MAGIC telescopes was improved. We have simulated, tested and commissioned a new concept of stereoscopic trigger. This new system, that uses the information of the position of the showers on each of the MAGIC cameras, is dubbed "Topo-trigger". The scientific fraction of the thesis deals with galactic sources observed with the MAGIC telescopes. In Part III, I talk about the analysis of the VHE γ-ray emission of Pulsar Wind Nebulae (PWNe): the discovery of VHE γ-ray emission from the puzzling PWN 3C 58, the likely remnant of the SN 1181 AD and the weakest PWN detected at VHE to date; the characterization of the VHE tail of the Crab nebula by observing it at the highest zenith angles; and the search for an additional inverse Compton component during the Crab nebula flares reported by Fermi-LAT in the synchrotron regime. Part IV is concerned with searches for VHE γ-ray emission of cataclysmic variable stars. I studied, on a multiwavelength context, the VHE γ-ray nature of the previously claimed pulsed γ-ray emission of the cataclysmic variable AE Aqr. I also performed observations of novae and a dwarf nova to pinpoint the ac- celeration mechanisms taking place in this kind of objects and to discover a putative hadronic component of the soft γ-ray emission. A conclusion chapter summarizes all the work performed and lists prospects related with the topics treated in this thesis.

  6. Directional Bias of TAO Daily Buoy Wind Vectors in the Central Equatorial Pacific Ocean from November 2008 to January 2010

    Ge Peng

    2014-07-01

    Full Text Available This article documents a systematic bias in surface wind directions between the TAO buoy measurements at 0°, 170°W and the ECMWF analysis and forecasts. This bias was of the order 10° and persisted from November 2008 to January 2010, which was consistent with a post-recovery calibration drift in the anemometer vane. Unfortunately, the calibration drift was too time-variant to be used to correct the data so the quality flag for this deployment was adjusted to reflect low data quality. The primary purpose of this paper is to inform users in the modelling and remote-sensing community about this systematic, persistent wind directional bias, which will allow users to make an educated decision on using the data and be aware of its potential impact to their downstream product quality. The uncovering of this bias and its source demonstrates the importance of continuous scientific oversight and effective user-data provider communication in stewarding scientific data. It also suggests the need for improvement in the ability of buoy data quality control procedures of the TAO and ECMWF systems to detect future wind directional systematic biases such as the one described here.

  7. Spectrophotometry of Symbiotic Stars (Abstract)

    Boyd, D.

    2017-12-01

    (Abstract only) Symbiotic stars are fascinating objects - complex binary systems comprising a cool red giant star and a small hot object, often a white dwarf, both embedded in a nebula formed by a wind from the giant star. UV radiation from the hot star ionizes the nebula, producing a range of emission lines. These objects have composite spectra with contributions from both stars plus the nebula and these spectra can change on many timescales. Being moderately bright, they lend themselves well to amateur spectroscopy. This paper describes the symbiotic star phenomenon, shows how spectrophotometry can be used to extract astrophysically useful information about the nature of these systems, and gives results for three symbiotic stars based on the author's observations.

  8. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    Perets, Hagai B. [Technion-Israel Institute of Technology, Haifa (Israel); Kenyon, Scott J., E-mail: hperets@physics.technion.ac.il [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-02-20

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10{sup -5}-10{sup -3} M {sub Sun }, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M {sub Sun }. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  9. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    Perets, Hagai B.; Kenyon, Scott J.

    2013-01-01

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10 –5 -10 –3 M ☉ , with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M ☉ . When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  10. A Heavy Flavor Tracker for STAR

    Xu, Z.; Chen, Y.; Kleinfelder, S.; Koohi, A.; Li, S.; Huang, H.; Tai, A.; Kushpil, V.; Sumbera, M.; Colledani, C.; Dulinski, W.; Himmi,A.; Hu, C.; Shabetai, A.; Szelezniak, M.; Valin, I.; Winter, M.; Miller,M.; Surrow, B.; Van Nieuwenhuizen G.; Bieser, F.; Gareus, R.; Greiner,L.; Lesser, F.; Matis, H.S.; Oldenburg, M.; Ritter, H.G.; Pierpoint, L.; Retiere, F.; Rose, A.; Schweda, K.; Sichtermann, E.; Thomas, J.H.; Wieman, H.; Yamamoto, E.; Kotov, I.

    2005-03-14

    We propose to construct a Heavy Flavor Tracker (HFT) for theSTAR experiment at RHIC. The HFT will bring new physics capabilities toSTAR and it will significantly enhance the physics capabilities of theSTAR detector at central rapidities. The HFT will ensure that STAR willbe able to take heavy flavor data at all luminosities attainablethroughout the proposed RHIC II era.

  11. A Heavy Flavor Tracker for STAR

    Xu, Z.; Chen, Y.; Kleinfelder, S.; Koohi, A.; Li, S.; Huang, H.; Tai, A.; Kushpil, V.; Sumbera, M.; Colledani, C.; Dulinski, W.; Himmi,A.; Hu, C.; Shabetai, A.; Szelezniak, M.; Valin, I.; Winter, M.; Surrow,B.; Van Nieuwenhuizen, G.; Bieser, F.; Gareus, R.; Greiner, L.; Lesser,F.; Matis, H.S.; Oldenburg, M.; Ritter, H.G.; Pierpoint, L.; Retiere, F.; Rose, A.; Schweda, K.; Sichtermann, E.; Thomas, J.H.; Wieman, H.; Yamamoto, E.; Kotov, I.

    2005-03-14

    We propose to construct a Heavy Flavor Tracker (HFT) for the STAR experiment at RHIC. The HFT will bring new physics capabilities to STAR and it will significantly enhance the physics capabilities of the STAR detector at central rapidities. The HFT will ensure that STAR will be able to take heavy flavor data at all luminosities attainable throughout the proposed RHIC II era.

  12. A Heavy Flavor Tracker for STAR

    Xu, Z.; Chen, Y.; Kleinfelder, S.; Koohi, A.; Li, S.; Huang, H.; Tai, A.; Kushpil, V.; Sumbera, M.; Colledani, C.; Dulinski, W.; Himmi, A.; Hu, C.; Shabetai, A.; Szelezniak, M.; Valin, I.; Winter, M.; Surrow, B.; Van Nieuwenhuizen, G.; Bieser, F.; Gareus, R.; Greiner, L.; Lesser, F.; Matis, H.S.; Oldenburg, M.; Ritter, H.G.; Pierpoint, L.; Retiere, F.; Rose, A.; Schweda, K.; Sichtermann, E.; Thomas, J.H.; Wieman, H.; Yamamoto, E.; Kotov, I.

    2005-01-01

    We propose to construct a Heavy Flavor Tracker (HFT) for the STAR experiment at RHIC. The HFT will bring new physics capabilities to STAR and it will significantly enhance the physics capabilities of the STAR detector at central rapidities. The HFT will ensure that STAR will be able to take heavy flavor data at all luminosities attainable throughout the proposed RHIC II era

  13. Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity

    Duez, Matthew D.; Liu, Yuk Tung; Shapiro, Stuart L.; Stephens, Branson C.; Shibata, Masaru

    2006-01-01

    We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can be formed in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both act on differentially rotating stars to redistribute angular momentum. Simulations of these stars are carried out in axisymmetry using our recently developed codes which integrate the coupled Einstein-Maxwell-MHD equations. We consider stars with two different equations of state (EOS), a gamma-law EOS with Γ=2, and a more realistic hybrid EOS, and we evolve them adiabatically. Our simulations show that the fate of the star depends on its mass and spin. For initial data, we consider three categories of differentially rotating, equilibrium configurations, which we label normal, hypermassive and ultraspinning. Normal configurations have rest masses below the maximum achievable with uniform rotation, and angular momentum below the maximum for uniform rotation at the same rest mass. Hypermassive stars have rest masses exceeding the mass limit for uniform rotation. Ultraspinning stars are not hypermassive, but have angular momentum exceeding the maximum for uniform rotation at the same rest mass. We show that a normal star will evolve to a uniformly rotating equilibrium configuration. An ultraspinning star evolves to an equilibrium state consisting of a nearly uniformly rotating central core, surrounded by a differentially rotating torus with constant angular velocity along magnetic field lines, so that differential rotation ceases to wind the magnetic field. In addition, the final state is stable against the MRI, although it has differential rotation. For a hypermassive neutron star, the MHD-driven angular momentum transport leads to catastrophic collapse of the core. The resulting rotating black hole is surrounded by a hot, massive, magnetized torus undergoing quasistationary accretion, and a magnetic field collimated along

  14. SERENDIPITOUS DETECTION OF X-RAY EMISSION FROM THE HOT BORN-AGAIN CENTRAL STAR OF THE PLANETARY NEBULA K 1-16

    Montez, Rodolfo Jr. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Kastner, Joel H., E-mail: rodolfo.montez.jr@gmail.com, E-mail: jhk@cis.rit.edu [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

    2013-03-20

    We report the serendipitous detection of point-like X-ray emission from the hot, PG1159-type central star of the planetary nebula (CSPN) K 1-16 by the XMM-Newton and Chandra X-Ray Observatories. The CSPN lies superimposed on a galaxy cluster that includes an X-ray-bright quasar, but we have successfully isolated the CSPN X-ray emission from the strong diffuse background contributed by the quasar and intracluster gas. We have modeled the XMM-Newton and Chandra X-ray data, taking advantage of the contrasting detection efficiencies of the two observatories to better constrain the low-energy spectral response of Chandra's Advanced CCD Imaging Spectrometer. We find that the CSPN X-ray spectrum is well characterized by the combination of a non-local thermodynamic equilibrium model atmosphere with T{sub *} {approx} 135 kK and a carbon-rich, optically thin thermal plasma with T{sub X} {approx} 1 MK. These results for X-ray emission from the K 1-16 CSPN, combined with those obtained for other PG1159-type objects, lend support to the 'born-again' scenario for Wolf-Rayet and PG1159 CSPNe, wherein a late helium shell flash dredges up carbon-rich intershell material and ejects this material into the circumstellar environment.

  15. Stability of boson stars

    Gleiser, M.

    1988-01-01

    Boson stars are gravitationally bound, spherically symmetric equilibrium configurations of cold, free, or interacting complex scalar fields phi. As these equilibrium configurations naturally present local anisotropy, it is sensible to expect departures from the well-known stability criteria for fluid stars. With this in mind, I investigate the dynamical instability of boson stars against charge-conserving, small radial perturbations. Following the method developed by Chandrasekhar, a variational base for determining the eigenfrequencies of the perturbations is found. This approach allows one to find numerically an upper bound for the central density where dynamical instability occurs. As applications of the formalism, I study the stability of equilibrium configurations obtained both for the free and for the self-interacting [with V(phi) = (λ/4)chemical bondphichemical bond 4 ] massive scalar field phi. Instabilities are found to occur not for the critical central density as in fluid stars but for central densities considerably higher. The departure from the results for fluid stars is sensitive to the coupling λ; the higher the value of λ, the more the stability properties of boson stars approach those of a fluid star. These results are linked to the fractional anisotropy at the radius of the configuration

  16. Gas dynamics in the inner few AU around the Herbig B[e] star MWC297. Indications of a disk wind from kinematic modeling and velocity-resolved interferometric imaging

    Hone, Edward; Kraus, Stefan; Kreplin, Alexander; Hofmann, Karl-Heinz; Weigelt, Gerd; Harries, Tim; Kluska, Jacques

    2017-10-01

    Aims: Circumstellar accretion disks and outflows play an important role in star formation. By studying the continuum and Brγ-emitting region of the Herbig B[e] star MWC297 with high-spectral and high-spatial resolution we aim to gain insight into the wind-launching mechanisms in young stars. Methods: We present near-infrared AMBER (R = 12 000) and CRIRES (R = 100 000) observations of the Herbig B[e] star MWC297 in the hydrogen Brγ-line. Using the VLTI unit telescopes, we obtained a uv-coverage suitable for aperture synthesis imaging. We interpret our velocity-resolved images as well as the derived two-dimensional photocenter displacement vectors, and fit kinematic models to our visibility and phase data in order to constrain the gas velocity field on sub-AU scales. Results: The measured continuum visibilities constrain the orientation of the near-infrared-emitting dust disk, where we determine that the disk major axis is oriented along a position angle of 99.6 ± 4.8°. The near-infrared continuum emission is 3.6 × more compact than the expected dust-sublimation radius, possibly indicating the presence of highly refractory dust grains or optically thick gas emission in the inner disk. Our velocity-resolved channel maps and moment maps reveal the motion of the Brγ-emitting gas in six velocity channels, marking the first time that kinematic effects in the sub-AU inner regions of a protoplanetary disk could be directly imaged. We find a rotation-dominated velocity field, where the blue- and red-shifted emissions are displaced along a position angle of 24° ± 3° and the approaching part of the disk is offset west of the star. The visibility drop in the line as well as the strong non-zero phase signals can be modeled reasonably well assuming a Keplerian velocity field, although this model is not able to explain the 3σ difference that we measure between the position angle of the line photocenters and the position angle of the dust disk. We find that the fit can be

  17. Effects of massive wind power integration on short-term water resource management in central Chile - a grid-wide study

    Haas, J.; Olivares, M. A.; Palma, R.

    2013-12-01

    In central Chile, water from reservoirs and streams is mainly used for irrigation and power generation. Hydropower reservoirs operation is particularly challenging because: i) decisions at each plant impact the entire power system, and ii) the existence of large storage capacity implies inter-temporal ties. An Independent System Operator (ISO) decides the grid-wide optimal allocation of water for power generation, under irrigation-related constraints. To account for the long-term opportunity cost of water, a future cost function is determined and used in the short term planning. As population growth and green policies demand increasing levels of renewable energy in power systems, deployment of wind farms and solar plants is rising quickly. However, their power output is highly fluctuating on short time scales, affecting the operation of power plants, particularly those fast responding units as hydropower reservoirs. This study addresses these indirect consequences of massive introduction of green energy sources on reservoir operations. Short-term reservoir operation, under different wind penetration scenarios, is simulated using a replica of Chile's ISO's scheduling optimization tools. Furthermore, an ongoing study is exploring the potential to augment the capacity the existing hydro-power plants to better cope with the balancing needs due to a higher wind power share in the system. As reservoir releases determine to a great extent flows at downstream locations, hourly time series of turbined flows for 24-hour periods were computed for selected combinations between new wind farms and increased capacity of existing hydropower plants. These time series are compiled into subdaily hydrologic alteration (SDHA) indexes (Zimmerman et al, 2010). The resulting sample of indexes is then analyzed using duration curves. Results show a clear increase in the SDHA for every reservoir of the system as more fluctuating renewables are integrated into the system. High

  18. The disk wind in the rapidly spinning stellar-mass black hole 4U 1630-472 observed with NuSTAR

    King, Ashley L.; Walton, Dominic J.; Miller, Jon M.

    2014-01-01

    We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630-472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we...... find evidence for a rapidly spinning black hole, (1σ statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also...

  19. Strangeon and Strangeon Star

    Xiaoyu, Lai; Renxin, Xu

    2017-06-01

    The nature of pulsar-like compact stars is essentially a central question of the fundamental strong interaction (explained in quantum chromo-dynamics) at low energy scale, the solution of which still remains a challenge though tremendous efforts have been tried. This kind of compact objects could actually be strange quark stars if strange quark matter in bulk may constitute the true ground state of the strong-interaction matter rather than 56Fe (the so-called Witten’s conjecture). From astrophysical points of view, however, it is proposed that strange cluster matter could be absolutely stable and thus those compact stars could be strange cluster stars in fact. This proposal could be regarded as a general Witten’s conjecture: strange matter in bulk could be absolutely stable, in which quarks are either free (for strange quark matter) or localized (for strange cluster matter). Strange cluster with three-light-flavor symmetry is renamed strangeon, being coined by combining “strange nucleon” for the sake of simplicity. A strangeon star can then be thought as a 3-flavored gigantic nucleus, and strangeons are its constituent as an analogy of nucleons which are the constituent of a normal (micro) nucleus. The observational consequences of strangeon stars show that different manifestations of pulsarlike compact stars could be understood in the regime of strangeon stars, and we are expecting more evidence for strangeon star by advanced facilities (e.g., FAST, SKA, and eXTP).

  20. Simulation of coastal winds along the central west coast of India using the MM5 mesoscale model

    Pushpadas, D.; Vethamony, P.; Sudheesh, K.; George, S.; Babu, M.T.; Nair, T.M.B.

    A high-resolution mesoscale numerical model (MM5) has been used to study the coastal atmospheric circulation of the central west coast of India, and Goa in particular. The model is employed with three nested domains. The innermost domain of 3 km...

  1. Veiling and Accretion Around the Young Binary Stars S and VV Corona Australis

    Sullivan, Kendall; Prato, Lisa; Avilez, Ian

    2018-01-01

    S CrA and VV CrA are two young binary star systems with separations of 170 AU and 250 AU, respectively, in the southern star-forming region Corona Australis. The spectral types of the four stars in these two systems are similar, approximately K7 to M1, hence the stellar masses are also similar. The study of young stars just emerging from their natal cloud cores at the very limits of observability allows us to probe the extreme environments in which planet formation begins to occur. Stars in this early evolutionary stage can have circumstellar or circumbinary disks, and sometimes remnants of the envelopes which surrounded them during the protostellar stage. Envelopes accrete onto disks and disks in turn accrete onto the central stars, triggering elevated continuum emission, line emission, outflows, and stellar winds. This violent stage marks the onset of the epoch of planet formation. Using high-resolution near-infrared, H-band spectroscopy from the Keck II telescope using the NIRSPEC instrument over 4-6 epochs, we are probing the chaotic environment surrounding the four stars in these systems. We determine the spectral types for VV CrA A and B for the first time, and examine the variable veiling and emission occurring around each of these stars. This research was supported in part by NSF grants AST-1461200 and AST-1313399.

  2. Spectral Confirmation of New Galactic LBV and WN Stars Associated With Mid-IR Nebulae

    Stringfellow, Guy; Gvaramadze, Vasilii V.

    2014-08-01

    Luminous Blue Variable (LBV) stars represent an extremely rare class and short-lived phase in the lives of very luminous massive stars with high mass loss rates. Extragalactic LBVs are responsible for producing false supernovae (SN), the SN Impostors, and have been directly linked with the progenitors of actual SN, indicating the LBV phase can be a final endpoint for massive star evolution. Yet only a few confirmed LBVs have been identified in the Galaxy. Their stellar evolution is poorly constrained by observations, and the physical reason for their unstable nature, both in terms of moderate spectral and photometric variability of a few magnitudes and the giant eruptions a la η Car that rival SN explosions, remains a mystery. Newly discovered mid-IR shells act as signposts, pointing to the central massive stars (LBV and Wolf-Rayet [WR] stars) that produced them. We have undertaken a spectroscopic survey of possible progenitor stars within these shells and are discovering that many are LBVs and WN-type WR transitional stars. We propose to extend this IR spectral survey to the south to search for new progenitor stars associated with dozens of newly identified shells. This survey should result in a substantial increase of new WRs and candidate LBVs for continued future study. Spectral analysis will yield new insights into the winds and physical properties of these rare and important objects, and lead to a better understanding of the physics driving giant eruptions.

  3. Nonlinear behavior analysis of split-winding dry-type transformer using a new star model and a coupled field-circuit approach

    Azizian Davood

    2016-12-01

    Full Text Available Regarding the importance of short circuit and inrush current simulations in the split-winding transformer, a novel nonlinear equivalent circuit is introduced in this paper for nonlinear simulation of this transformer. The equivalent circuit is extended using the nonlinear inductances. Employing a numerical method, leakage and magnetizing inductances in the split-winding transformer are extracted and the nonlinear model inductances are estimated using these inductances. The introduced model is validated and using this nonlinear model, inrush and short-circuit currents are calculated. It has been seen that the introduced model is valid and suitable for simulations of the split-winding transformer due to various loading conditions. Finally, the effects of nonlinearity of the model inductances are discussed in the following.

  4. 77 FR 48138 - Topaz Solar Farms LLC; High Plains Ranch II, LLC; Bethel Wind Energy LLC; Rippey Wind Energy LLC...

    2012-08-13

    ... Ranch II, LLC; Bethel Wind Energy LLC; Rippey Wind Energy LLC; Pacific Wind, LLC; Colorado Highlands Wind, LLC; Shooting Star Wind Project, LLC; Notice of Effectiveness of Exempt Wholesale Generator or... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket Nos. EG12-63-000; EG12-64-000...

  5. Stars and Star Myths.

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  6. Star Formation at the Galactic Center

    Kohler, Susanna

    2015-08-01

    Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh

  7. A Semi-analytical Model for Wind-fed Black Hole High-mass X-Ray Binaries: State Transition Triggered by Magnetic Fields from the Companion Star

    Yaji, Kentaro; Yamada, Shinya; Masai, Kuniaki [Department of Physics, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo 192-0397 (Japan)

    2017-10-01

    We propose a mechanism of state transition in wind-fed black hole (BH) binaries (high-mass X-ray binaries) such as Cyg X-1 and LMC X-1. Modeling a line-driven stellar wind from the companion by two-dimensional hydrodynamical calculations, we investigate the processes of wind capture by, and accretion onto, the BH. We assume that the wind acceleration is terminated at the He ii ionization front because ions responsible for line-driven acceleration are ionized within the front, i.e., the He iii region. It is found that the mass accretion rate inferred from the luminosity is remarkably smaller than the capture rate. Considering the difference, we construct a model for the state transition based on the accretion flow being controlled by magnetorotational instability. The outer flow is torus-like, and plays an important role to trigger the transition. The model can explain why state transition does occur in Cyg X-1, while not in LMC X-1. Cyg X-1 exhibits a relatively low luminosity, and then the He ii ionization front is located and can move between the companion and BH, depending on its ionizing photon flux. On the other hand, LMC X-1 exhibits too high luminosity for the front to move considerably; the front is too close to the companion atmosphere. The model also predicts that each state of high-soft or low-hard would last fairly long because the luminosity depends weakly on the wind velocity. In the context of the model, the state transition is triggered by a fluctuation of the magnetic field when its amplitude becomes comparable to the field strength in the torus-like outer flow.

  8. Stellar wind theory

    Summers, D.

    1980-01-01

    The theory of stellar winds as given by the equations of classical fluid dynamics is considered. The equations of momentum and energy describing a steady, spherically symmetric, heat-conducting, viscous stellar wind are cast in a dimensionless form which involves a thermal conduction parameter E and a viscosity parameter γ. An asymptotic analysis is carried out, for fixed γ, in the cases E→O and E→infinity (corresponding to small and large thermal conductivity, respectively), and it is found that it is possible to construct critical solutions for the wind velocity and temperature over the entire flow. The E→O solution represents a wind which emanates from the star at low, subsonic speeds, accelerates through a sonic point, and then approaches a constant asymptotic speed, with its temperature varying as r/sup -4/3/ at large distances r from the star; the E→infinity solution represents a wind which, after reaching an approximately constant speed, with temperature varying as r/sup -2/7/, decelerates through a diffuse shock and approaches a finite pressure at infinity. A categorization is made of all critical stellar wind solutions for given values of γ and E, and actual numerical examples are given. Numerical solutions are obtained by integrating upstream 'from infinity' from initial values of the flow parameters given by appropriate asymptotic expansions. The role of viscosity in stellar wind theory is discussed, viscous and inviscid stellar wind solutions are compared, and it is suggested that with certain limitations, the theory presented may be useful in analyzing winds from solar-type stars

  9. Mapping Wind Energy Controversies

    Munk, Anders Kristian

    As part the Wind2050 project funded by the Danish Council for Strategic Research we have mapped controversies on wind energy as they unfold online. Specifically we have collected two purpose built datasets, a web corpus containing information from 758 wind energy websites in 6 different countries......, and a smaller social media corpus containing information from 14 Danish wind energy pages on Facebook. These datasets have been analyzed to answer questions like: How do wind proponents and opponents organize online? Who are the central actors? And what are their matters of concern? The purpose of this report...

  10. Variable accretion of stellar winds onto Sgr A*

    Cuadra, Jorge; Nayakshin, Sergei

    2006-12-01

    We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

  11. Variable accretion of stellar winds onto Sgr A*

    Cuadra, Jorge [Max-Planck-Institut fuer Astrophysik, D-85741 Garching (Germany); Nayakshin, Sergei [Department of Physics and Astronomy, University of Leicester, LEI 7RH (United Kingdom)

    2006-12-15

    We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

  12. Variable accretion of stellar winds onto Sgr A*

    Cuadra, Jorge; Nayakshin, Sergei

    2006-01-01

    We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre

  13. A VERSATILE FAMILY OF GALACTIC WIND MODELS

    Bustard, Chad; Zweibel, Ellen G. [Physics Department, University of Wisconsin-Madison, 1150 University Avenue, Madison, WI 53706 (United States); D’Onghia, Elena, E-mail: bustard@wisc.edu [Department of Astronomy, University of Wisconsin-Madison, 2535 Sterling Hall, 475 N. Charter Street, Madison, WI 53706 (United States)

    2016-03-01

    We present a versatile family of model galactic outflows including non-uniform mass and energy source distributions, a gravitational potential from an extended mass source, and radiative losses. The model easily produces steady-state wind solutions for a range of mass-loading factors, energy-loading factors, galaxy mass, and galaxy radius. We find that, with radiative losses included, highly mass-loaded winds must be driven at high central temperatures, whereas low mass-loaded winds can be driven at low temperatures just above the peak of the cooling curve, meaning radiative losses can drastically affect the wind solution even for low mass-loading factors. By including radiative losses, we are able to show that subsonic flows can be ignored as a possible mechanism for expelling mass and energy from a galaxy compared to the more efficient transonic solutions. Specifically, the transonic solutions with low mass loading and high energy loading are the most efficient. Our model also produces low-temperature, high-velocity winds that could explain the prevalence of low-temperature material in observed outflows. Finally, we show that our model, unlike the well-known Chevalier and Clegg model, can reproduce the observed linear relationship between wind X-ray luminosity and star formation rate (SFR) over a large range of SFR from 1–1000 M{sub ⊙} yr{sup −1} assuming the wind mass-loading factor is higher for low-mass, and hence, low-SFR galaxies. We also constrain the allowed mass-loading factors that can fit the observed X-ray luminosity versus SFR trend, further suggesting an inverse relationship between mass loading and SFR as explored in advanced numerical simulations.

  14. WIND BRAKING OF MAGNETARS

    Tong, H.; Xu, R. X.; Qiao, G. J.; Song, L. M.

    2013-01-01

    We explore the wind braking of magnetars considering recent observations challenging the traditional magnetar model. There is evidence for strong multipole magnetic fields in active magnetars, but the dipole field inferred from spin-down measurements may be strongly biased by particle wind. Recent observations challenging the traditional model of magnetars may be explained naturally by the wind braking scenario: (1) the supernova energies of magnetars are of normal value; (2) the non-detection in Fermi observations of magnetars; (3) the problem posed by low magnetic field soft gamma-ray repeaters; (4) the relation between magnetars and high magnetic field pulsars; and (5) a decreasing period derivative during magnetar outbursts. Transient magnetars with L x rot may still be magnetic dipole braking. This may explain why low luminosity magnetars are more likely to have radio emissions. A strong reduction of the dipole magnetic field is possible only when the particle wind is very collimated at the star surface. A small reduction of the dipole magnetic field may result from detailed considerations of magnetar wind luminosity. In the wind braking scenario, magnetars are neutron stars with a strong multipole field. For some sources, a strong dipole field may no longer be needed. A magnetism-powered pulsar wind nebula will be one of the consequences of wind braking. For a magnetism-powered pulsar wind nebula, we should see a correlation between the nebula luminosity and the magnetar luminosity. Under the wind braking scenario, a braking index smaller than three is expected. Future braking index measurement of a magnetar may tell us whether magnetars are wind braking or magnetic dipole braking.

  15. CO-SPATIAL LONG-SLIT UV/OPTICAL SPECTRA OF TEN GALACTIC PLANETARY NEBULAE WITH HST/STIS. II. NEBULAR MODELS, CENTRAL STAR PROPERTIES, AND He+CNO SYNTHESIS

    Henry, R. B. C.; Miller, T. R. [Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Balick, B. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Dufour, R. J. [Department of Space Physics and Astronomy, Rice University, Houston, TX 77251 (United States); Kwitter, K. B. [Department of Astronomy, Williams College, Williamstown, MA 01267 (United States); Shaw, R. A. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Buell, J. F. [SUNY College of Technology at Alfred, Alfred, NY 14843 (United States); Corradi, R. L. M. [Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain)

    2015-11-10

    The goal of the present study is twofold. First, we employ new HST/STIS spectra and photoionization modeling techniques to determine the progenitor masses of eight planetary nebulae (IC 2165, IC 3568, NGC 2440, NGC 3242, NGC 5315, NGC 5882, NGC 7662, and PB 6). Second, for the first time we are able to compare each object’s observed nebular abundances of helium, carbon, and nitrogen with abundance predictions of these same elements by a stellar model that is consistent with each object’s progenitor mass. Important results include the following: (1) the mass range of our objects’ central stars matches well with the mass distribution of other central stars of planetary nebulae and white dwarfs; (2) He/H is above solar in all of our objects, in most cases likely due to the predicted effects of first dredge-up; (3) most of our objects show negligible C enrichment, probably because their low masses preclude third dredge-up; (4) C/O versus O/H for our objects appears to be inversely correlated, which is perhaps consistent with the conclusion of theorists that the extent of atmospheric carbon enrichment from first dredge-up is sensitive to a parameter whose value increases as metallicity declines; (5) stellar model predictions of nebular C and N enrichment are consistent with observed abundances for progenitor star masses ≤1.5 M{sub ⊙}. Finally, we present the first published photoionization models of NGC 5315 and NGC 5882.

  16. Barium and Tc-poor S stars: Binary masqueraders among carbon stars

    Jorissen, A.; Van Eck, S.

    1997-01-01

    The current understanding of the origin of barium and S stars is reviewed, based on new orbital elements and binary frequencies. The following questions are addressed: (i) Is binarity a necessary condition to produce a barium star? (ii) What is the mass transfer mode (wind accretion or RLOF?) responsible for their formation? (iii) Do barium stars form as dwarfs or as giants? (iv) Do barium stars evolve into Tc-poor S stars? (v) What is the relative frequency of Tc-rich and Tc-poor S stars?

  17. Effects of wind farm construction on concentrations and fluxes of dissolved organic carbon and suspended sediment from peat catchments at Braes of Doune, central Scotland

    I. Grieve

    2008-07-01

    Full Text Available This paper assesses the impacts of disturbance associated with the construction of a wind farm on fluxes of dissolved organic carbon (DOC and suspended sediment from a blanket peat catchment in central Scotland during the period immediately following completion of construction. Six streams draining the site were sampled on six dates from October 2006, when construction was completed, and an additional three control streams to the west of the site were sampled on the same dates. Turbidity and stage were recorded semi-continuously in the two largest streams (one disturbed and one control, which were also sampled during storm events. Absorbance (400 nm and DOC concentrations were determined on all samples, and suspended sediment was determined on the event samples. Absorbance and DOC were closely correlated in both the disturbed and undisturbed streams, with slightly greater absorbance per unit DOC in the disturbed streams. DOC concentrations in disturbed tributaries were always greater than those in undisturbed streams, with mean differences ranging from 2 to around 5 mg L-1. DOC and stage were positively correlated during events with maximum concentrations in excess of 30 mg L 1 at peak flow. Suspended sediment concentrations were markedly elevated in the disturbed stream with maximum concentrations at peak flow some 4–5 times greater than in the control. The colour of the sediment suggested that it was highly organic in nature at peak flow, and suspended particulate organic carbon represented a further loss of C from the site. Using flow-weighted mean DOC concentrations calculated for the storms monitored in autumn 2007, dissolved carbon losses can be estimated for the catchments of the disturbed and control streams. From these data the additional DOC loss related to disturbance associated with the wind farm is estimated at 5 g m-2.

  18. Time-dependent mass loss from hot stars with and without radiative driving

    Castor, J.I.; Owocki, S.P.; Rybicki, G.B.

    1988-01-01

    A numerical hydrodynamics code is used to investigate two aspects of the winds of hot stars. The first is the question of the instability of the massive radiatively-driven wind of an O star that is caused by the line shape mechanism: modulation of the radiation force by velocity fluctuations. The evolution of this instability is studied in a model O star wind, and is found, /ital modulo/ some numerical uncertainty, to lead to wave structures that are compatible with observations of wind instabilities. The other area of investigation is of main-sequence B star winds. Attempts were made to simulate a radiatively-driven and a pulsation-driven wind in a B star, but in each case the wind turned out to be very weak. It is argued that the pulsation-driven wind model is not likely to apply to B stars. 28 refs., 11 figs

  19. Wave Star

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....

  20. Economics of wind energy

    Ranganathan, V.; Kumar, H.P.S.

    1991-01-01

    Conventional economic analysis of wind energy often ignores the fact that it is not an energy source available on tap, but is intermittent. The analysis at times is discriminatory in the sense that the costs of transmission and distribution are added to the central grid alternative but the costs of the locational constraints of wind energy siting are not quantified. This paper evaluates wind energy after correcting for these two factors. The results are not encouraging

  1. MAGNETIC NESTED-WIND SCENARIOS FOR BIPOLAR OUTFLOWS: PREPLANETARY AND YSO NEBULAR SHAPING

    Dennis, Timothy J.; Frank, Adam; Blackman, Eric G.; DeMarco, Orsola; Balick, Bruce; Mitran, Sorin

    2009-01-01

    We present results of a series of magnetohydrodynamic (MHD) and hydrodynamic (HD) 2.5 dimensional simulations of the morphology of outflows driven by nested wide-angle winds, i.e., winds that emanate from a central star as well as from an orbiting accretion disk. While our results are broadly relevant to nested-wind systems, we have tuned the parameters of the simulations to touch on issues in both young stellar objects and planetary nebula (PN) studies. In particular, our studies connect to open issues in the early evolution of PNs. We find that nested MHD winds exhibit marked morphological differences from the single MHD wind case along both dimensions of the flow. Nested HD winds, on the other hand, give rise mainly to geometric distortions of an outflow that is topologically similar to the flow arising from a single stellar HD wind. Our MHD results are insensitive to changes in ambient temperature between ionized and un-ionized circumstellar environments. The results are sensitive to the relative mass-loss rates and the relative speeds of the stellar and disk winds. We also present synthetic emission maps of both nested MHD and HD simulations. We find that nested MHD winds show knots of emission appearing on-axis that do not appear in the HD case.

  2. Wind energy

    Anon.

    1992-01-01

    This chapter discusses the role wind energy may have in the energy future of the US. The topics discussed in the chapter include historical aspects of wind energy use, the wind energy resource, wind energy technology including intermediate-size and small wind turbines and intermittency of wind power, public attitudes toward wind power, and environmental, siting and land use issues

  3. Effects of Combined Stellar Feedback on Star Formation in Stellar Clusters

    Wall, Joshua Edward; McMillan, Stephen; Pellegrino, Andrew; Mac Low, Mordecai; Klessen, Ralf; Portegies Zwart, Simon

    2018-01-01

    We present results of hybrid MHD+N-body simulations of star cluster formation and evolution including self consistent feedback from the stars in the form of radiation, winds, and supernovae from all stars more massive than 7 solar masses. The MHD is modeled with the adaptive mesh refinement code FLASH, while the N-body computations are done with a direct algorithm. Radiation is modeled using ray tracing along long characteristics in directions distributed using the HEALPIX algorithm, and causes ionization and momentum deposition, while winds and supernova conserve momentum and energy during injection. Stellar evolution is followed using power-law fits to evolution models in SeBa. We use a gravity bridge within the AMUSE framework to couple the N-body dynamics of the stars to the gas dynamics in FLASH. Feedback from the massive stars alters the structure of young clusters as gas ejection occurs. We diagnose this behavior by distinguishing between fractal distribution and central clustering using a Q parameter computed from the minimum spanning tree of each model cluster. Global effects of feedback in our simulations will also be discussed.

  4. Topographic Correction of Wind-driven Rainfall for Landslide Analysis in Central Taiwan with Validation from Aerial and Satellite Optical Images

    Jin-King Liu

    2013-05-01

    Full Text Available Rainfall intensity plays an important role in landslide prediction especially in mountain areas. However, the rainfall intensity of a location is usually interpolated from rainfall recorded at nearby gauges without considering any possible effects of topographic slopes. In order to obtain reliable rainfall intensity for disaster mitigation, this study proposes a rainfall-vector projection method for topographic-corrected rainfall. The topographic-corrected rainfall is derived from wind speed, terminal velocity of raindrops, and topographical factors from digital terrain model. In addition, scatter plot was used to present landslide distribution with two triggering factors and kernel density analysis is adopted to enhance the perception of the distribution. Numerical analysis is conducted for a historic event, typhoon Mindulle, which occurred in 2004, in a location in central Taiwan. The largest correction reaches 11%, which indicates that topographic correction is significant. The corrected rainfall distribution is then applied to the analysis of landslide triggering factors. The result with corrected rainfall distribution provides better agreement with the actual landslide occurrence than the result without correction.

  5. Radio emission from symbiotic stars: a binary model

    Taylor, A.R.; Seaquist, E.R.

    1985-01-01

    The authors examine a binary model for symbiotic stars to account for their radio properties. The system is comprised of a cool, mass-losing star and a hot companion. Radio emission arises in the portion of the stellar wind photo-ionized by the hot star. Computer simulations for the case of uniform mass loss at constant velocity show that when less than half the wind is ionized, optically thick spectral indices greater than +0.6 are produced. Model fits to radio spectra allow the binary separation, wind density and ionizing photon luminosity to be calculated. They apply the model to the symbiotic star H1-36. (orig.)

  6. Off-shore Wind Atlas of the Central Aegean Sea: A simple comparison of NCEP/NCAR RE-analysis data, QuickSCAT and ENVISAT Synthetic Aperture Radar (SAR) by use of Wind Atlas Method

    Bingöl, Ferhat; Hasager, Charlotte Bay; Karagali, Ioanna

    2012-01-01

    model results). Unfortunately all of these methods are still under development and do not provide data acceptable for bankable wind assessment reports. On the other hand, they give good indications of the geographical distribution of the wind resources and that is very useful for decision making...... to high costs, but with the new developments in floating turbine design, it seems that offshore wind parks in deep waters will also be a possibility in the future. Whether on-shore or offshore, the first step of a site assessment is to estimate the wind resources. Usually well-known conventional methods...... are used to produce estimates of wind resources by means of at least one year data from a single or multiple points on the terrain. This criterion is dicult to satisfy in offshore locations where measurements are costly and sparse. Therefore other methods are required (e.g satellite imagery or reanalysis...

  7. Moving inhomogeneous envelopes of stars

    Oskinova, L.M.; Kubátová, Brankica; Hamann, W.-R.

    2016-01-01

    Roč. 183, Special Issue (2016), s. 100-112 ISSN 0022-4073. [International Conference on Radiation Mechanisms of Astrophysical Objects - Classics Today. St. Petersburg, 21.09.2016-25.09.2016] Institutional support: RVO:67985815 Keywords : stars * mass-loss * winds Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 2.419, year: 2016

  8. The coupling between pulsation and mass loss in massive stars

    Townsend, Rich

    2007-01-01

    To what extent can pulsational instabilities resolve the mass-loss problem of massive stars? How important is pulsation in structuring and modulating the winds of these stars? What role does pulsation play in redistributing angular momentum in massive stars? Although I cannot offer answers to these questions, I hope at the very least to explain how they come to be asked.

  9. How supernovae launch galactic winds?

    Fielding, Drummond; Quataert, Eliot; Martizzi, Davide; Faucher-Giguère, Claude-André

    2017-09-01

    We use idealized three-dimensional hydrodynamic simulations of global galactic discs to study the launching of galactic winds by supernovae (SNe). The simulations resolve the cooling radii of the majority of supernova remnants (SNRs) and thus self-consistently capture how SNe drive galactic winds. We find that SNe launch highly supersonic winds with properties that agree reasonably well with expectations from analytic models. The energy loading (η _E= \\dot{E}_wind/ \\dot{E}_SN) of the winds in our simulations are well converged with spatial resolution while the wind mass loading (η _M= \\dot{M}_wind/\\dot{M}_\\star) decreases with resolution at the resolutions we achieve. We present a simple analytic model based on the concept that SNRs with cooling radii greater than the local scaleheight break out of the disc and power the wind. This model successfully explains the dependence (or lack thereof) of ηE (and by extension ηM) on the gas surface density, star formation efficiency, disc radius and the clustering of SNe. The winds our simulations are weaker than expected in reality, likely due to the fact that we seed SNe preferentially at density peaks. Clustering SNe in time and space substantially increases the wind power.

  10. Ultraviolet colors of subdwarf O stars

    Wesselius, P.R.

    1978-01-01

    The group of subdwarf O stars consisting of field stars and some central stars of old planetary nebulae does occupy an interesting place in the HR diagram. Greenstein and Sargent (1974) have tried to establish this place, and conclude that especially the hottest ones need ultraviolet data to improve the values of effective temperature and absolute luminosity. The author therefore observed some twenty sdO stars in the far ultraviolet using the spectrophotometer in the Netherlands' satellite ANS. (Auth.)

  11. Compact stars

    Estevez-Delgado, Gabino; Estevez-Delgado, Joaquin

    2018-05-01

    An analysis and construction is presented for a stellar model characterized by two parameters (w, n) associated with the compactness ratio and anisotropy, respectively. The reliability range for the parameter w ≤ 1.97981225149 corresponds with a compactness ratio u ≤ 0.2644959374, the density and pressures are positive, regular and monotonic decrescent functions, the radial and tangential speed of sound are lower than the light speed, moreover, than the plausible stability. The behavior of the speeds of sound are determinate for the anisotropy parameter n, admitting a subinterval where the speeds are monotonic crescent functions and other where we have monotonic decrescent functions for the same speeds, both cases describing a compact object that is also potentially stable. In the bigger value for the observational mass M = 2.05 M⊙ and radii R = 12.957 Km for the star PSR J0348+0432, the model indicates that the maximum central density ρc = 1.283820319 × 1018 Kg/m3 corresponds to the maximum value of the anisotropy parameter and the radial and tangential speed of the sound are monotonic decrescent functions.

  12. Bipolar molecular outflows: T Tauri stars and Herbig-Haro objects

    Choe, S.U.

    1984-01-01

    The relations of Herbig-Haro objects to the observed bipolar molecular outflows with T Tauri stars are studied. An evaporation disk model is proposed to obtain the shape of the disk where gas evaporates and to explain the collimation of the central T Tauri wind. In this case the collimation angle is about 10 0 . The collimated T Tauri wind making a form of de Laval nozzle viscously interacts with the surrounding medium. This interaction enhances the second collimation (about 40 0 ) of the resulting flow, mixing stellar and disk winds with external molecular gas. These viscous outflows are observed in the bipolar molecular outflow of the T Tauri stars. It is also proposed in the model that a Kelvin-Helmholtz instability in the throat of the de Laval nozzle produces clumps, which can be accelerated by the ram pressure of the collimated wind up to the wind speed. The clumps eventually pass through a shock in the outlfow, which results from its encounter with the ambient cloud. The clumps are then moving faster than the surrounding flow. These clumps are identified with Herbig-Haro objects

  13. Economic and financial evaluation of the wind power project in Northeast region, Brazil; Avaliacao economico-financeira de projeto de central eolica na regiao nordeste

    Rocha, Paulo Glicio da; Lima, Maria Angela de Queiroz; Melo Junior, Adalberto de Bastos [Companhia Hidro Eletrica do Sao Francisco (DFPL/CHESF), Recife, PE (Brazil). Div. de Planejamento Economico-Financeiro], Emails: paulogr@chesf.gov.br, angelq@chesf.gov.br, adalbert@chesf.gov.br; Bezerra, Pedro; Bittencourt, Rogerio [Companhia Hidro Eletrica do Sao Francisco (DEFA/CHESF), Recife, PE (Brazil). Div. de Projetos de Fontes Alternativas], E-mails: pbezerra@chesf.gov.br, rogeriob@chesf.gov.br

    2000-07-01

    This work deals with the analysis of economic and financial feasibility of using wind power in the Northeast region for electric power production, considering the new electricity sector model. The case study presented here refers to the design of a 50 MW Wind Farm in the region, based on preliminary data from wind collected in the period from 1993 to 1995. Some programs were used to evaluate this project: ALWIN, which estimates the potential for wind energy production; NEWAVE for determination operating marginal costs and generation plants values and ANAFIN, for economic and financial evaluation of the project, using scenarios, through the deterministic and probabilistic analysis.

  14. A COMPANION AS THE CAUSE OF LATITUDE-DEPENDENT EFFECTS IN THE WIND OF ETA CARINAE

    Groh, J. H.; Madura, T. I.; Weigelt, G.; Hillier, D. J.; Kruip, C. J. H.

    2012-01-01

    We analyze spatially resolved spectroscopic observations of the Eta Carinae binary system obtained with the Hubble Space Telescope/STIS. Eta Car is enshrouded by the dusty Homunculus nebula, which scatters light emitted by the central binary and provides a unique opportunity to study a massive binary system from different vantage points. We investigate the latitudinal and azimuthal dependence of Hα line profiles caused by the presence of a wind-wind collision (WWC) cavity created by the companion star. Using two-dimensional radiative transfer models, we find that the wind cavity can qualitatively explain the observed line profiles around apastron. Regions of the Homunculus which scatter light that propagated through the WWC cavity show weaker or no Hα absorption. Regions scattering light that propagated through a significant portion of the primary wind show stronger P Cygni absorption. Our models overestimate the Hα absorption formed in the primary wind, which we attribute to photoionization by the companion, not presently included in the models. We can qualitatively explain the latitudinal changes that occur during periastron, shedding light on the nature of Eta Car's spectroscopic events. Our models support the idea that during the brief period of time around periastron when the primary wind flows unimpeded toward the observer, Hα absorption occurs in directions toward the central object and Homunculus SE pole, but not toward equatorial regions close to the Weigelt blobs. We suggest that observed latitudinal and azimuthal variations are dominated by the companion star via the WWC cavity, rather than by rapid rotation of the primary star.

  15. Chemistry in T Tauri winds

    Rawlings, J M.C.; Williams, D A; Canto, J

    1988-02-15

    The chemistry occurring in the winds of T Tauri stars is investigated. On the assumption that the wind is dust-free, then routes to H/sub 2/ are inhibited under the conditions in the wind, and subsequent chemistry does not produce substantial molecular abundances. The major losses to the chemical network lie in the geometrical dilution and collisional dissociation rather than in chemical destruction and photodissociation. Mass loading of the wind with dust and H/sub 2/ may, however, occur. This stimulates the chemistry and may in some circumstances lead to a conversion of approx.1-10 per cent of carbon into CO. This gives a column density of CO which is marginally detectable. A positive detection of CO at high wind velocities would imply that the winds must be cool and that mixing of molecular material from a disc, which may play a role in collimating the wind, or the remnants of a disc, must occur.

  16. Radio stars

    Hjellming, R.M.

    1976-01-01

    Any discussion of the radio emission from stars should begin by emphasizing certain unique problems. First of all, one must clarify a semantic confusion introduced into radio astronomy in the late 1950's when most new radio sources were described as radio stars. All of these early 'radio stars' were eventually identified with other galactic and extra-galactic objects. The study of true radio stars, where the radio emission is produced in the atmosphere of a star, began only in the 1960's. Most of the work on the subject has, in fact, been carried out in only the last few years. Because the real information about radio stars is quite new, it is not surprising that major aspects of the subject are not at all understood. For this reason this paper is organized mainly around three questions: what is the available observational information; what physical processes seem to be involved; and what working hypotheses look potentially fruitful. (Auth.)

  17. Small wind power plants : results of the Nordic wind diesel projects for large telecommunications companies; Implantation d'une centrale eolienne comme source d'energie d'appoint pour des stations de telecommunications

    Ilinca, A.; Chaumel, J.L. [ATI Eolien, Rimouski, PQ (Canada); Thibault, G. [Entreprises MB, PQ (Canada)

    2005-07-01

    Two wind-diesel generating stations have been installed at telecommunication towers in the remote communities of Kuujjuarapik and Lac Julien in northern Quebec. The use of wind power contributes to the sustainable development in these remote areas by lowering the reliance on costly helicopter-transported diesel fuel and by reducing the release of greenhouse gases to the atmosphere. The technical characteristics of the Bergey 100 kW turbine with battery charger were presented along with the technical characteristics of the EolDie control panel that controls the supply of electricity from either the wind or diesel power generators. For the first time, the ATI-Wind technology system that was installed can supply the needs of the large telecommunication towers of Bell Canada and Telebec from either the wind or the diesel generators. The system is also capable of shutting down the diesel generators when wind energy is sufficient to take over. Early results from June 2005 showed that the diesel generators could be turned off for 55 per cent of the time. Preliminary results of these 2 projects were discussed by the firms in charge of the diesel and wind aspects and recommendations for improvements to the control systems were presented. 11 figs.

  18. Shooting stars

    Maurette, M.; Hammer, C.

    1985-01-01

    A shooting star passage -even a star shower- can be sometimes easily seen during moonless black night. They represent the partial volatilization in earth atmosphere of meteorites or micrometeorites reduced in cosmic dusts. Everywhere on earth, these star dusts are searched to be gathered. This research made one year ago on the Greenland ice-cap is this article object; orbit gathering projects are also presented [fr

  19. Discovery of a new Wolf-Rayet star and a candidate star cluster in the Large Magellanic Cloud with Spitzer

    Gvaramadze, V. V.; Chené, A.-N.; Kniazev, A. Y.; Schnurr, O.; Shenar, T.; Sander, A.; Hainich, R.; Langer, N.; Hamann, W.-R.; Chu, Y.-H.; Gruendl, R. A.

    2014-08-01

    We report the first-ever discovery of a Wolf-Rayet (WR) star in the Large Magellanic Cloud via detection of a circular shell with the Spitzer Space Telescope. Follow-up observations with Gemini-South resolved the central star of the shell into two components separated from each other by ≈2 arcsec (or ≈0.5 pc in projection). One of these components turns out to be a WN3 star with H and He lines both in emission and absorption (we named it BAT99 3a using the numbering system based on extending the Breysacher et al. catalogue). Spectroscopy of the second component showed that it is a B0 V star. Subsequent spectroscopic observations of BAT99 3a with the du Pont 2.5-m telescope and the Southern African Large Telescope revealed that it is a close, eccentric binary system, and that the absorption lines are associated with an O companion star. We analysed the spectrum of the binary system using the non-LTE Potsdam WR (POWR) code, confirming that the WR component is a very hot (≈90 kK) WN star. For this star, we derived a luminosity of log L/ L⊙ = 5.45 and a mass-loss rate of 10- 5.8 M⊙ yr- 1, and found that the stellar wind composition is dominated by helium with 20 per cent of hydrogen. Spectroscopy of the shell revealed an He III region centred on BAT99 3a and having the same angular radius (≈15 arcsec) as the shell. We thereby add a new example to a rare class of high-excitation nebulae photoionized by WR stars. Analysis of the nebular spectrum showed that the shell is composed of unprocessed material, implying that the shell was swept-up from the local interstellar medium. We discuss the physical relationship between the newly identified massive stars and their possible membership of a previously unrecognized star cluster.

  20. The distribution of heavy metals and 137Cs in the central part of the Polish maritime zone (Baltic Sea) - the area selected for wind farm acquisition

    Zaborska, Agata; Kosakowska, Alicja; Bełdowski, Jacek; Bełdowska, Magdalena; Szubska, Marta; Walkusz-Miotk, Jolanta; Żak, Adam; Ciechanowicz, Agnieszka; Wdowiak, Maciej

    2017-11-01

    Disturbances of the marine sediments that may be induced by offshore wind energy (OWE) construction and functioning may cause reintroduction of contaminants accumulated in the sea bottom over last century. It is thus very important to check in which offshore region of the Polish coast the littlest consequences of the OWE construction may be expected. The area of 9000 km2 in the central part of the Polish economic zone was selected for sediments sampling. In total, sediments from 46 stations were collected by gravity twin corer or geo-vibro corer. Heavy metal (Hg, Pb, Cd, As, Zn, Cu, Cr, Ni, Fe, Mn) concentrations were measured by AAS and ICP-MS while 137 Cs activity concentrations were measured by gamma spectrometer. Sediment accumulation rates were quantified by 210Pb geochronology at 7 stations to follow the history of contaminants accumulation. Study areas located between isobaths of 20 m and 40 m were characterized by the lowest concentration of heavy metals, often below natural environmental background (e.g. Pb = 6.7 - 11.4 μg·g-1, As = 0.3 - 8.4 μg·g-1). The largest contamination by heavy metals (e.g. Pb reached 86.1 μg·g-1 while As = 21.0 μg·g-1) was visible at the outer part of Bornholm Basin and in Słupsk Furrow, the deepest studied regions. Highest accumulation of heavy metals in this area is connected to large fraction of pelite sediments and large proportion of organic matter at those stations. It may be concluded that shallow sandy sediments of the Southern Baltic are unpolluted and appropriate for OWE construction. Deeper sea regions e.g Słupsk Furrow and Bornholm Basin may be regarded as moderately polluted and therefore not recommended for OWE acquisition.

  1. The evolution of massive stars

    Loore, C. de

    1980-01-01

    The evolution of stars with masses between 15 M 0 and 100 M 0 is considered. Stars in this mass range lose a considerable fraction of their matter during their evolution. The treatment of convection, semi-convection and the influence of mass loss by stellar winds at different evolutionary phases are analysed as well as the adopted opacities. Evolutionary sequences computed by various groups are examined and compared with observations, and the advanced evolution of a 15 M 0 and a 25 M 0 star from zero-age main sequence (ZAMS) through iron collapse is discussed. The effect of centrifugal forces on stellar wind mass loss and the influence of rotation on evolutionary models is examined. As a consequence of the outflow of matter deeper layers show up and when the mass loss rates are large enough layers with changed composition, due to interior nuclear reactions, appear on the surface. The evolution of massive close binaries as well during the phase of mass loss by stellar wind as during the mass exchange and mass loss phase due to Roche lobe overflow is treated in detail, and the value of the parameters governing mass and angular momentum losses are discussed. The problem of the Wolf-Rayet stars, their origin and the possibilities of their production either as single stars or as massive binaries is examined. Finally, the origin of X-ray binaries is discussed and the scenario for the formation of these objects (starting from massive ZAMS close binaries, through Wolf-Rayet binaries leading to OB-stars with a compact companion after a supernova explosion) is reviewed and completed, including stellar wind mass loss. (orig.)

  2. Wind: new wind markets

    Cameron, A.

    2005-01-01

    The June 2005 edition of 'Wind Force 12' suggests that wind could generate 12% of global electricity requirements by 2020. But what moves a potential market into an emerging one? Geographical factors include a good wind resource, plenty of open space and the ability to get the generated electricity to end-users. A country's political framework is equally important, with fixed price systems, renewable quota systems and political will all playing a part. Some potential wind markets around the world are thought to have the conditions necessary to become key players in the wind industry. The emerging markets in countries such as Australia, Brazil, Canada, France, Japan and the Philippines are highlighted as examples

  3. A new Wolf-Rayet star and its circumstellar nebula in Aquila

    Gvaramadze, V. V.; Kniazev, A. Y.; Hamann, W.-R.; Berdnikov, L. N.; Fabrika, S.; Valeev, A. F.

    2010-04-01

    We report the discovery of a new Wolf-Rayet star in Aquila via detection of its circumstellar nebula (reminiscent of ring nebulae associated with late WN stars) using the Spitzer Space Telescope archival data. Our spectroscopic follow-up of the central point source associated with the nebula showed that it is a WN7h star (we named it WR121b). We analysed the spectrum of WR121b by using the Potsdam Wolf-Rayet model atmospheres, obtaining a stellar temperature of ~=50kK. The stellar wind composition is dominated by helium with ~20 per cent of hydrogen. The stellar spectrum is highly reddened [E(B - V) = 2.85mag]. Adopting an absolute magnitude of Mv = -5.7, the star has a luminosity of logL/Lsolar = 5.75 and a mass-loss rate of 10-4.7Msolaryr-1, and resides at a distance of 6.3kpc. We searched for a possible parent cluster of WR121b and found that this star is located at ~=1° from the young star cluster embedded in the giant HII region W43 (containing a WN7+a/OB? star - WR121a). We also discovered a bow shock around the O9.5III star ALS9956, located at from the cluster. We discuss the possibility that WR121b and ALS9956 are runaway stars ejected from the cluster in W43. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); wrh@astro.physik.uni-potsdam.de (WRH); berdnik@sai.msu.ru (LNB); fabrika@sao.ru (SF); azamat@sao.ru (AFV)

  4. Wind farm economics

    Milborrow, D.J.

    1995-01-01

    The economics of wind energy are changing rapidly, with improvements in machine performance and increases in size both contributing to reduce costs. These trends are examined and future costs assessed. Although the United Kingdom has regions of high wind speed, these are often in difficult terrain and construction costs are often higher than elsewhere in Europe. Nevertheless, wind energy costs are converging with those of the conventional thermal sources. At present, bank loan periods for wind projects are shorter than for thermal plant, which means that energy prices are higher. Ways of overcoming this problem are explored. It is important, also, to examine the value of wind energy. It is argued that wind energy has a higher value than energy from centralized plant, since it is fed into the low-voltage distribution network. (Author)

  5. NEW X-RAY DETECTIONS OF WNL STARS

    Skinner, Stephen L. [Center for Astrophysics and Space Astronomy (CASA), University of Colorado, Boulder, CO 80309-0389 (United States); Zhekov, Svetozar A. [Space and Solar-Terrestrial Research Institute, Moskovska str. 6, Sofia-1000 (Bulgaria); Guedel, Manuel [Department of Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Schmutz, Werner [Physikalisch-Meteorologisches Observatorium Davos (PMOD), Dorfstrasse 33, CH-7260 Davos Dorf (Switzerland); Sokal, Kimberly R., E-mail: Stephen.Skinner@colorado.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)

    2012-05-15

    Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (L{sub x} ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v{sub {infinity}}). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing L{sub x} with wind luminosity L{sub wind} = (1/2)M-dot v{sup 2}{sub {infinity}}, suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.

  6. NEW X-RAY DETECTIONS OF WNL STARS

    Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner; Sokal, Kimberly R.

    2012-01-01

    Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (L x ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v ∞ ). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing L x with wind luminosity L wind = (1/2)M-dot v 2 ∞ , suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.

  7. Theory of neutron star magnetospheres

    Curtis Michel, F

    1990-01-01

    An incomparable reference for astrophysicists studying pulsars and other kinds of neutron stars, "Theory of Neutron Star Magnetospheres" sums up two decades of astrophysical research. It provides in one volume the most important findings to date on this topic, essential to astrophysicists faced with a huge and widely scattered literature. F. Curtis Michel, who was among the first theorists to propose a neutron star model for radio pulsars, analyzes competing models of pulsars, radio emission models, winds and jets from pulsars, pulsating X-ray sources, gamma-ray burst sources, and other neutron-star driven phenomena. Although the book places primary emphasis on theoretical essentials, it also provides a considerable introduction to the observational data and its organization. Michel emphasizes the problems and uncertainties that have arisen in the research as well as the considerable progress that has been made to date.

  8. Wave Star

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star.......Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star....

  9. Star Imager

    Madsen, Peter Buch; Jørgensen, John Leif; Thuesen, Gøsta

    1997-01-01

    The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol.......The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol....

  10. The evolutionary status of symbiotic stars

    Rudak, B.

    1982-01-01

    The evolutionary relations between symbiotic stars and cataclysmic variables are presented. The symbiotic stars are assumed to be long period detached binaries containing a carbon-oxygen degenerate primary and a red giant losing its mass through a spherically symmetric wind. Such systems can be obtained in Case C evolution, provided a common envelope during a rapid mass transfer phase was not formed. The same way recurrent novae containing a red giant as a secondary component may be produced. The factors influencing the differences between symbiotic stars and nova-type stars are discussed. (Auth.)

  11. The reconstruction of easterly wind directions for the Eifel region (Central Europe during the period 40.3–12.9 ka BP

    K. Seelos

    2010-03-01

    Full Text Available A high resolution continuous reconstruction of last glacial wind directions is based on provenance analysis of eolian sediments in a sediment core from the Dehner dry Maar in the Eifel region (Germany. This Maar is suitable to archive easterly wind directions due to its location west of the Devonian carbonate basins of the Eifel-North-South-Zone. Thus, eolian sediments with high clastic carbonate content can be interpreted as an east wind signal. The detection of such east wind sediments is applied by a new module of the RADIUS grain size analyze technique. The investigated time period from 40.3–12.9 ka BP can be subclassified in three units: The first unit covers the periods of the ending GIS-9, H4, and GIS-8. With the exception of H4 (40–38 ka BP the content of organics in our record is relatively high. With the end of GIS-8 (38–36.5 ka the content of organics decrease and the content of dust increases rapidly. The second time slice (36–24 ka BP has an increased content of dust accumulation and a high amount of east winds layers (up to 19% of the dust storms per century came from the east. In comparison, the subsequent period (24–12.9 ka BP is characterized by lower east wind sediments again. Increased frequencies of east wind occur during the time intervals corresponding with the Heinrich events H1 and H2. The unusual H3 show no higher east wind frequency but so do its former and subsequent Greenland stadials. The late LGM (21–18 ka BP is characterized by a slightly elevated east wind frequency again.

  12. Investigation of conspicuous infrared star cluster and star-forming region RCW 38 IR Cluster

    Gyulbudaghian, A.L.; May, J.

    2008-01-01

    An infrared star cluster RCW 38 IR Cluster, which is also a massive star-forming region, is investigated. The results of observations with SEST (Cerro is Silla, Chile) telescope on 2.6-mm 12 CO spectral line and with SIMBA on 1.2-mm continuum are given. The 12 CO observations revealed the existence of several molecular clouds, two of which (clouds I and 2) are connected with the object RCW 38 IR Cluster. Cloud 1 is a massive cloud, which has a depression in which the investigated object is embedded. It is not excluded that the depression was formed by the wind and/or emission from the young bright stars belonging to the star cluster. Rotation of cloud 2, around the axis having SE-NW direction, with an angular velocity ω 4.6 · 10 -14 s -1 is also found. A red-shifted outflow with velocity ∼+5.6 km/s, in the SE direction and perpendicular to the elongation of cloud 2 has been also found. The investigated cluster is associated with an IR point source IRAS 08573-4718, which has IR colours typical for a, non-evolved embedded (in the cloud) stellar object. The cluster is also connected with a water maser. The SIMBA image shoves the existence of a central bright condensation, coinciding with the cluster itself, and two extensions. One of these extensions (the one with SW-NE direction) coincides, both in place and shape, with cloud 2, so that it is not excluded the possibility that this extension might be also rotating like cloud 2. In the vicinity of these extensions there are condensations resembling HH objects

  13. Binaries discovered by the SPY survey VI. Discovery of a low mass companion to the hot subluminous planetary nebula central star EGB5-a recently ejected common envelope?

    Geier, S.; Napiwotzki, R.; Heber, U.; Nelemans, G.A.

    2011-01-01

    Hot subdwarf B stars (sdBs) in close binary systems are assumed to be formed via common envelope ejection. According to theoretical models, the amount of energy and angular momentum deposited in the common envelope scales with the mass of the companion. That low mass companions near or below the core hydrogen-burning limit are able to trigger the ejection of this envelope is well known. The currently known systems have very short periods $\\simeq0.1-0.3\\,{\\rm d}$. Here we report the discovery ...

  14. Symbiotic stars

    Kafatos, M.; Michalitsianos, A.G.

    1984-01-01

    Among the several hundred million binary systems estimated to lie within 3000 light years of the solar system, a tiny fraction, no more than a few hundred, belong to a curious subclass whose radiation has a wavelength distribution so peculiar that it long defied explanation. Such systems radiate strongly in the visible region of the spectrum, but some of them do so even more strongly at both shorter and longer wavelengths: in the ultraviolet region and in the infrared and radio regions. This odd distribution of radiation is best explained by the pairing of a cool red giant star and an intensely hot small star that is virtually in contact with its larger companion. Such objects have become known as symbiotic stars. On photographic plate only the giant star can be discerned, but evidence for the existence of the hot companion has been supplied by satellite-born instruments capable of detecting ultraviolet radiation. The spectra of symbiotic stars indicate that the cool red giant is surrounded by a very hot ionized gas. Symbiotic stars also flared up in outbursts indicating the ejection of material in the form of a shell or a ring. Symbiotic stars may therefore represent a transitory phase in the evolution of certain types of binary systems in which there is substantial transfer of matter from the larger partner to the smaller

  15. Numerical evidence for 'multiscalar stars'

    Hawley, Scott H.; Choptuik, Matthew W.

    2003-01-01

    We present a class of general relativistic solitonlike solutions composed of multiple minimally coupled, massive, real scalar fields which interact only through the gravitational field. We describe a two-parameter family of solutions we call ''phase-shifted boson stars'' (parametrized by central density ρ 0 and phase δ), which are obtained by solving the ordinary differential equations associated with boson stars and then altering the phase between the real and imaginary parts of the field. These solutions are similar to boson stars as well as the oscillating soliton stars found by Seidel and Suen [E. Seidel and W. M. Suen, Phys. Rev. Lett. 66, 1659 (1991)]; in particular, long-time numerical evolutions suggest that phase-shifted boson stars are stable. Our results indicate that scalar solitonlike solutions are perhaps more generic than has been previously thought

  16. Peering through the veil: near-infrared photometry and extinction for the Galactic nuclear star cluster. Accurate near infrared H, Ks, and L' photometry and the near-infrared extinction-law toward the central parsec of the Galaxy

    Schödel, R.; Najarro, F.; Muzic, K.; Eckart, A.

    2010-02-01

    Context. The nuclear star cluster of the Galaxy is an important template for understanding its extragalactic counterparts, which can currently not be resolved into individual stars. Important drawbacks of observations of the Galactic center are, however, the presence of strong and spatially highly variable interstellar extinction and extreme crowding of the sources, which makes the use of adaptive optics techniques necessary. Both points pose serious obstacles to precise photometry that is needed for analyzing the stellar population. Aims: The aims of this work are to provide accurate photometry in multiple near-infrared broadband filters, to determine the power-law index of the extinction-law toward the central parsec of the Galaxy, to provide measurements of the absolute extinction toward the Galactic center, and finally to measure the spatial variability of extinction on arcsecond scales. Methods: We use observations of the central parsec of the Milky Way that were obtained with the near-infrared camera and adaptive optics system NAOS/CONICA at the ESO VLT unit telescope 4. The photometric method takes into account anisoplanatic effects and limits the corresponding systematic uncertainties to ≲2%. Absolute values for the extinction in the H, Ks, and L'-bands as well as of the power-law indices of the H to Ks and Ks to L' extinction-laws are measured based on the well-known properties of red clump stars. Extinction maps are derived based on H-Ks and Ks-L' colors. Results: We present Ks-band photometry for ~7700 stars, and additionally photometry for stars detected in the H and/or L'-bands. From a number of recently published values we compute a mean distance of the Galactic center of R0=8.03±0.15 kpc, which has an uncertainty of just 2%. Based on this R0 and on the RC method, we derive absolute mean extinction values toward the central parsec of the Galaxy of AH=4.48±0.13 mag, AKs=2.54±0.12 mag, and AL'=1.27±0.18 mag. We estimate values of the power

  17. Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

    2010-07-01

    Using a combination of instruments on ESO's Very Large Telescope, astronomers have discovered the most massive stars to date, one weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The existence of these monsters - millions of times more luminous than the Sun, losing weight through very powerful winds - may provide an answer to the question "how massive can stars be?" A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, has used ESO's Very Large Telescope (VLT), as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail. NGC 3603 is a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust, located 22 000 light-years away from the Sun (eso1005). RMC 136a (more often known as R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away (eso0613). The team found several stars with surface temperatures over 40 000 degrees, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birthweight of as much as 320 times that of the Sun. In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system [1], as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses. Very massive stars produce very powerful outflows. "Unlike humans, these stars are born heavy and lose weight as

  18. Environments of T Tauri stars

    Chevalier, R.A.

    1983-01-01

    The environments of T Tauri stars are probably determined by the interaction of a stellar wind with matter which is falling toward a newly formed star. As shown by Ulrich, the steady infall of cool gas with angular momentum toward the star leads to a density distribution with rhoproportionalr/sup -1/2/ inside a radius r/sub d/ and rhoproportionalr/sup -3/2/ outside r/sub d/. The radius r/sub d/ is determined by the angular momentum of the infalling gas. The expansion of the wind into this medium depends on the parameter α = M/sub w/v/sub w//M/sub in/v/sub in/(r/sub d/), where v/sub in/(r/sub d/) is the free-fall velocity at r/sub d/, M/sub in/ is the mass accretion rate, v/sub w/ is the wind velocity, and M/sub w/ is the mass loss rate. For α 14 cm, v/sub w/ = 150 km s -1 , M/sub in/ = 10 -7 M/sub sun/ yr -1 , and M/sub w/ = 3 x 10 -8 M/sub sun/ yr -1 . The inflow is clumpy. The shocked wind gives the radio emission and nebular emission from T Tauri, and dust within the clumps gives the infrared emission. T Tauri is in a transitory phase in which most of the wind has only recently propagated beyond r/sub d/. The model naturally predicts variable obscuration of T Tauri stars because the infalling clumps move on nonradial trajectories. The infrared emission can vary either because of structural changes in the circumstellar gas or because of variations in the stellar luminosity. Infrared variability should be small at short time scales because of light-travel time effects

  19. The Diversity of Neutron Stars

    Kaplan, David L.

    2004-12-01

    Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the >1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby, isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population---distances, ages, and magnetic fields---the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 1e6 year-old cooling neutron stars with magnetic fields above 1e13 Gauss. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication of central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

  20. Wind models for zeta Orionis

    Olson, G.L.

    1979-01-01

    Several models for the winds of O stars have been proposed to explain the unexpected presence of high ionization potential ions such as N +4 and O +5 . Lamers and Snow (1978) proposed that the winds of stars showing N V and O VI lines have elevated temperatures near 4 +- 2 x 10 5 K while cooler stars with anomalous Si IV lines have Tsub(e) approximately 7+-3 x 10 4 K. Alternately, Cassinelli and Olson (1978, CO) and Olson (1978) have explained the presence of these ions by showing that a thin corona at the base of a cool wind (Tsub(e) < approximately Tsub(eff)) can produce these ions by the Auger photoionization process where a single X-ray photon causes the ejection of two electrons. A third possibility is that the winds are at only slightly elevated temperatures (40 000 to 60 000K) and photoionization in an optically thick wind produces the unexpected ions. The present analysis tests the ability of these three wind models to fit the observations of zeta Orionis A 09.7 Ib. (Auth.)

  1. Star-forming galaxy models: Blending star formation into TREESPH

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

  2. Star formation

    Woodward, P.R.

    1978-01-01

    Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references

  3. Wind Energy

    Rodriguez D, J.M.

    1998-01-01

    The general theory of the wind energy conversion systems is presented. The availability of the wind resource in Colombia and the ranges of the speed of the wind in those which is possible economically to use the wind turbines are described. It is continued with a description of the principal technological characteristics of the wind turbines and are split into wind power and wind-powered pumps; and its use in large quantities grouped in wind farms or in autonomous systems. Finally, its costs and its environmental impact are presented

  4. How Massive Single Stars End Their Life

    Heger, A.; Fryer, C. L.; Woosley, S. E.; Langer, N.; Hartmann, D. H.

    2003-01-01

    How massive stars die-what sort of explosion and remnant each produces-depends chiefly on the masses of their helium cores and hydrogen envelopes at death. For single stars, stellar winds are the only means of mass loss, and these are a function of the metallicity of the star. We discuss how metallicity, and a simplified prescription for its effect on mass loss, affects the evolution and final fate of massive stars. We map, as a function of mass and metallicity, where black holes and neutron stars are likely to form and where different types of supernovae are produced. Integrating over an initial mass function, we derive the relative populations as a function of metallicity. Provided that single stars rotate rapidly enough at death, we speculate on stellar populations that might produce gamma-ray bursts and jet-driven supernovae.

  5. Sounds of a Star

    2001-06-01

    colours show element displacements in opposite directions. Geologists monitor how seismic waves generated by earthquakes propagate through the Earth, and thus learn about the inner structure of our planet. The same technique works for stars. The Sun, our nearest star and a typical middle-age member of its class, has been investigated in this way since the 1960's. With "solar seismology" , astronomers have been able to learn much about the inner parts of the star, and not only the outer layers normally visible to the telescopes. In the Sun, heat is bubbling up from the central regions where enormous amount of energy is created by nuclear reactions . In the so-called convective zone , the gas is virtually boiling, and hot gas-bubbles are rising with a speed that is close to that of sound. Much like you can hear when water starts to boil, the turbulent convection in the Sun creates noise . These sound waves then propagate through the solar interior and are reflected on the surface, making it oscillate. This "ringing" is well observed in the Sun, where the amplitude and frequency of the oscillations provide astronomers with plenty of information about the physical conditions in the solar interior. From the Sun to the stars There is every reason to believe that our Sun is a quite normal star of its type. Other stars that are similar to the Sun are therefore likely to pulsate in much the same way as the Sun. The search for such oscillations in other solar-like stars has, however, been a long and difficult one. The problem is simply that the pulsations are tiny, so very great precision is needed in the measurements. However, the last few years have seen considerable progress in asteroseismology, and François Bouchy and Fabien Carrier from the Geneva Observatory have now been able to detect unambiguous acoustic oscillations in the Solar-twin star, Alpha Centauri A. The bright and nearby star Alpha Centauri Alpha Centauri (Alpha Cen) [1] is the brightest star in the constellation

  6. Wave Star

    Kramer, Morten; Frigaard, Peter

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star....

  7. Wave Star

    Kramer, Morten; Andersen, Thomas Lykke

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star....

  8. H i in Virgo’s “Red and Dead” Dwarf Ellipticals—A Tidal Tail and Central Star Formation

    Hallenbeck, Gregory; Koopmann, Rebecca [Union College, Department of Physics and Astronomy, 807 Union Street, Schenectady NY 12308 (United States); Giovanelli, Riccardo; Haynes, Martha P.; Leisman, Lukas [Cornell Center for Astrophysics and Planetary Science (CCAPS), Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Huang, Shan [CCPP, New York University, 4 Washington Place, New York, NY 10003 (United States); Papastergis, Emmanouil, E-mail: hallenbg@union.edu, E-mail: koopmanr@union.edu, E-mail: riccardo@astro.cornell.edu, E-mail: haynes@astro.cornell.edu, E-mail: leisman@astro.cornell.edu, E-mail: shan.huang@nyu.edu, E-mail: papastergis@astro.rug.nl [Kapteyn Astronomical Institute, University of Groningen, Landleven 12, Groningen NL-9747AD (Netherlands)

    2017-08-01

    We investigate a sample of three dwarf elliptical galaxies in the Virgo Cluster that have significant reservoirs of H i. We present deep optical imaging (from CFHT and KPNO), H i spectra (Arecibo), and resolved H i imaging (VLA) of this sample. These observations confirm their H i content and optical morphologies, and indicate that the gas is unlikely to be recently accreted. The sample has more in common with dwarf transitionals, though dwarf transitionals are generally lower in stellar mass and gas fraction. VCC 190 has an H i tidal tail from a recent encounter with the massive spiral galaxy NGC 4224. In VCC 611, blue star-forming features are observed that were not seen by shallower SDSS imaging.

  9. Stellar parameters for the central star of the planetary nebula PRTM 1 using the German Astrophysical Virtual Observatory service TheoSSA

    Rauch, T.; Demleitner, M.; Hoyer, D.; Werner, K.

    2018-04-01

    The German Astrophysical Virtual Observatory (GAVO) developed the registered service TheoSSA (theoretical stellar spectra access) and the supporting registered VO tool TMAW (Tübingen Model-Atmosphere WWW interface). These allow individual spectral analyses of hot, compact stars with state-of-the-art non-local thermodynamical equilibrium (NLTE) stellar-atmosphere models that presently consider opacities of the elements H, He, C, N, O, Ne, Na, and Mg, without requiring detailed knowledge about the involved background codes and procedures. Presently, TheoSSA provides easy access to about 150 000 pre-calculated stellar spectral energy distributions (SEDs) and is intended to ingest SEDs calculated by any model-atmosphere code. In the case of the exciting star of PN PRTM 1, we demonstrate the easy way to calculate individual NLTE stellar model-atmospheres to reproduce an observed optical spectrum. We measured T_eff = 98 000± 5 000 K, log (g / cm/s^2) = 5.0^{+0.3}_{-0.2}, and photospheric mass fractions of H =7.5 × 10-1 (1.02 times solar), He =2.4 × 10-1 (0.96), C =2.0 × 10-3 (0.84), N =3.2 × 10-4 (0.46), and O =8.5 × 10-3 (1.48) with uncertainties of ±0.2 dex. We determined the stellar mass and luminosity of 0.73^{+0.16}_{-0.15} M_{⊙} and log (L/L⊙) = 4.2 ± 0.4, respectively.

  10. STARS no star on Kauai

    Jones, M.

    1993-01-01

    The island of Kuai, home to the Pacific Missile Range Facility, is preparing for the first of a series of Star Wars rocket launches expected to begin early this year. The Strategic Defense Initiative plans 40 launches of the Stategic Target System (STARS) over a 10-year period. The focus of the tests appears to be weapons and sensors designed to combat multiple-warhead ICBMs, which will be banned under the START II Treaty that was signed in January. The focus of this article is to express the dubious value of testing the STARS at a time when their application will not be an anticipated problem

  11. Flare stars

    Nicastro, A.J.

    1981-01-01

    The least massive, but possibly most numerous, stars in a galaxy are the dwarf M stars. It has been observed that some of these dwarfs are characterized by a short increase in brightness. These stars are called flare stars. These flare stars release a lot of energy in a short amount of time. The process producing the eruption must be energetic. The increase in light intensity can be explained by a small area rising to a much higher temperature. Solar flares are looked at to help understand the phenomenon of stellar flares. Dwarfs that flare are observed to have strong magnetic fields. Those dwarf without the strong magnetic field do not seem to flare. It is believed that these regions of strong magnetic fields are associated with star spots. Theories on the energy that power the flares are given. Astrophysicists theorize that the driving force of a stellar flare is the detachment and collapse of a loop of magnetic flux. The mass loss due to stellar flares is discussed. It is believed that stellar flares are a significant contributor to the mass of interstellar medium in the Milky Way

  12. Self-similar Hot Accretion Flow onto a Neutron Star

    Medvedev, Mikhail V.; Narayan, Ramesh

    2001-06-01

    We consider hot, two-temperature, viscous accretion onto a rotating, unmagnetized neutron star. We assume Coulomb coupling between the protons and electrons, as well as free-free cooling from the electrons. We show that the accretion flow has an extended settling region that can be described by means of two analytical self-similar solutions: a two-temperature solution that is valid in an inner zone, r~102.5. In both zones the density varies as ρ~r-2 and the angular velocity as Ω~r-3/2. We solve the flow equations numerically and confirm that the analytical solutions are accurate. Except for the radial velocity, all gas properties in the self-similar settling zone, such as density, angular velocity, temperature, luminosity, and angular momentum flux, are independent of the mass accretion rate; these quantities do depend sensitively on the spin of the neutron star. The angular momentum flux is outward under most conditions; therefore, the central star is nearly always spun down. The luminosity of the settling zone arises from the rotational energy that is released as the star is braked by viscosity, and the contribution from gravity is small; hence, the radiative efficiency, η=Lacc/Mc2, is arbitrarily large at low M. For reasonable values of the gas adiabatic index γ, the Bernoulli parameter is negative; therefore, in the absence of dynamically important magnetic fields, a strong outflow or wind is not expected. The flow is also convectively stable but may be thermally unstable. The described solution is not advection dominated; however, when the spin of the star is small enough, the flow transforms smoothly to an advection-dominated branch of solution.

  13. Spheroidal Populated Star Systems

    Angeletti, Lucio; Giannone, Pietro

    2008-10-01

    Globular clusters and low-ellipticity early-type galaxies can be treated as systems populated by a large number of stars and whose structures can be schematized as spherically symmetric. Their studies profit from the synthesis of stellar populations. The computation of synthetic models makes use of various contributions from star evolution and stellar dynamics. In the first sections of the paper we present a short review of our results on the occurrence of galactic winds in star systems ranging from globular clusters to elliptical galaxies, and the dynamical evolution of a typical massive globular cluster. In the subsequent sections we describe our approach to the problem of the stellar populations in elliptical galaxies. The projected radial behaviours of spectro-photometric indices for a sample of eleven galaxies are compared with preliminary model results. The best agreement between observation and theory shows that our galaxies share a certain degree of heterogeneity. The gas energy dissipation varies from moderate to large, the metal yield ranges from solar to significantly oversolar, the dispersion of velocities is isotropic in most of the cases and anisotropic in the remaining instances.

  14. A new mechanical stellar wind feedback model for the Rosette Nebula

    Wareing, C. J.; Pittard, J. M.; Wright, N. J.; Falle, S. A. E. G.

    2018-04-01

    The famous Rosette Nebula has an evacuated central cavity formed from the stellar winds ejected from the 2-6 Myr old codistant and comoving central star cluster NGC 2244. However, with upper age estimates of less than 110 000 yr, the central cavity is too young compared to NGC 2244 and existing models do not reproduce its properties. A new proper motion study herein using Gaia data reveals the ejection of the most massive star in the Rosette, HD 46223, from NGC 2244 occurred 1.73 (+0.34, -0.25) Myr (1σ uncertainty) in the past. Assuming this ejection was at the birth of the most massive stars in NGC 2244, including the dominant centrally positioned HD 46150, the age is set for the famous ionized region at more than 10 times that derived for the cavity. Here, we are able to reproduce the structure of the Rosette Nebula, through simulation of mechanical stellar feedback from a 40 M⊙ star in a thin sheet-like molecular cloud. We form the 135 000 M⊙ cloud from thermally unstable diffuse interstellar medium (ISM) under the influence of a realistic background magnetic field with thermal/magnetic pressure equilibrium. Properties derived from a snapshot of the simulation at 1.5 Myr, including cavity size, stellar age, magnetic field, and resulting inclination to the line of sight, match those derived from observations. An elegant explanation is thus provided for the stark contrast in age estimates based on realistic diffuse ISM properties, molecular cloud formation and stellar wind feedback.

  15. INFRARED TWO-COLOR DIAGRAMS FOR AGB STARS, POST-AGB STARS, AND PLANETARY NEBULAE

    Suh, Kyung-Won, E-mail: kwsuh@chungbuk.ac.kr [Department of Astronomy and Space Science, Chungbuk National University, Cheongju-City, 362-763 (Korea, Republic of)

    2015-08-01

    We present various infrared two-color diagrams (2CDs) for asymptotic giant branch (AGB) stars, post-AGB stars, and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use catalogs from the available literature for the sample of 4903 AGB stars (3373 O-rich; 1168 C-rich; 362 S-type), 660 post-AGB stars (326 post-AGB; 334 pre-PN), and 1510 PNe in our Galaxy. For each object in the catalog, we cross-identify the IRAS, AKARI, Midcourse Space Experiment, and 2MASS counterparts. The IR 2CDs can provide useful information about the structure and evolution of the dust envelopes as well as the central stars. To find possible evolutionary tracks from AGB stars to PNe on the 2CDs, we investigate spectral evolution of post-AGB stars by making simple but reasonable assumptions on the evolution of the central star and dust shell. We perform radiative transfer model calculations for the detached dust shells around evolving central stars in the post-AGB phase. We find that the theoretical dust shell model tracks using dust opacity functions of amorphous silicate and amorphous carbon roughly coincide with the densely populated observed points of AGB stars, post-AGB stars, and PNe on various IR 2CDs. Even though some discrepancies are inevitable, the end points of the theoretical post-AGB model tracks generally converge in the region of the observed points of PNe on most 2CDs.

  16. Symbiotic stars

    Kafatos, M.; Michalitsianos, A. G.

    1984-01-01

    The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

  17. THE STAR OFFLINE FRAMEWORK

    FINE, V.; FISYAK, Y.; PEREVOZTCHIKOV, V.; WENAUS, T.

    2000-01-01

    The Solenoidal Tracker At RHIC (STAR) is a-large acceptance collider detector, commissioned at Brookhaven National Laboratory in 1999. STAR has developed a software framework supporting simulation, reconstruction and analysis in offline production, interactive physics analysis and online monitoring environments that is well matched both to STAR's present status of transition between Fortran and C++ based software and to STAR's evolution to a fully OO software base. This paper presents the results of two years effort developing a modular C++ framework based on the ROOT package that encompasses both wrapped Fortran components (legacy simulation and reconstruction code) served by IDL-defined data structures, and fully OO components (all physics analysis code) served by a recently developed object model for event data. The framework supports chained components, which can themselves be composite subchains, with components (''makers'') managing ''data sets'' they have created and are responsible for. An St-DataSet class from which data sets and makers inherit allows the construction of hierarchical organizations of components and data, and centralizes almost all system tasks such as data set navigation, I/O, database access, and inter-component communication. This paper will present an overview of this system, now deployed and well exercised in production environments with real and simulated data, and in an active physics analysis development program

  18. Di-jet Hadron Correlations in Central Au+Au Collisions at √{sNN} = 200 GeV at STAR

    Elsey, Nicholas; STAR Collaboration

    2017-09-01

    Jets and their modifications due to partonic energy loss provide a powerful tool to study the properties of the QGP created in ultrarelativistic heavy-ion collisions. For jets reconstructed with the anti-kT algorithm with resolution parameter R = 0.4 , previous measurements of the di-jet asymmetry AJ at STAR) indicate that the observed imbalance of an initial ``hard-core'' di-jet selection with pTconst > 2.0 GeV/c, pTlead > 20.0 GeV/c and pTsub > 10.0 GeV/c is restored to the balance of the pp reference when soft constituents are included. The lost energy recovered with soft constituents suggests soft gluon radiation by high pT partons. Jet-hadron correlations with respect to di-jets allow a differential assessment of the kinematic properties of the soft gluon radiation spectrum induced by partonic energy loss in the QGP. We present charged hadron correlations with respect to the di-jets found in the above AJ analysis, and compare to similar measurements using a jet trigger at RHIC.

  19. Non-Identical Neutron Star Twins

    Glendenning, Norman K.; Kettner, Christiane

    1998-01-01

    The work of J. A. Wheeler in the mid 1960's showed that for smooth equations of state no stable stellar configurations with central densities above that corresponding to the limiting mass of ``neutron stars'' (in the generic sense) were stable against acoustical vibrational modes. A perturbation would cause any such star to collapse to a black hole or explode. Accordingly, there has been no reason to expect that a stable degenerate family of stars with higher density than the known white dwar...

  20. Properties of hot luminous stars; Proceedings of the First Boulder-Munich Workshop, Boulder, CO, Aug. 6-11, 1988

    Garmany, C.D.

    1990-01-01

    Various papers on the properties of hot luminous stars are presented. Individual topics addressed include: problems in photometry of early-type stars; digital optical morphology of OB spectra; massive-star content of the Magellanic Clouds; observations of massive OB stars; LSS 3074, a new double-lined early O-type binary; non-LTE line blanketing with elements 1-28; non-LTE analysis of four PG1159 stars; rescaling method for model atmospheres of hot stars; stellar wind albedo effects on hot photospheres; atomic data and models for hot star abundance determinations; ring nebulae analysis as a probe for WR atmospheres; coordinated observations of P Cygni; radiation-driven winds of hot luminous stars; winds of O stars: velocities and ionization; methods of radiative transfer in expanding atmospheres; mass loss from extragalactic O stars; H-alpha observations of O- and B-type stars; applicability of steady models for hot-star winds; mass of the O6Iaf star HD 153919; stellar winds in Beta Lyrae; models of WR stars; observational abundances of WR stars, the all-variable WC7 binary HD193793

  1. TURBOVELOCITY STARS: KICKS RESULTING FROM THE TIDAL DISRUPTION OF SOLITARY STARS

    Manukian, Haik; Guillochon, James; Ramirez-Ruiz, Enrico; O'Leary, Ryan M.

    2013-01-01

    The centers of most known galaxies host supermassive black holes (SMBHs). In orbit around these black holes are a centrally concentrated distribution of stars, both in single and in binary systems. Occasionally, these stars are perturbed onto orbits that bring them close to the SMBH. If the star is in a binary system, the three-body interaction with the SMBH can lead to large changes in orbital energy, depositing one of the two stars on a tightly-bound orbit, and its companion into a hyperbolic orbit that may escape the galaxy. In this Letter, we show that the disruption of solitary stars can also lead to large positive increases in orbital energy. The kick velocity depends on the amount of mass the star loses at pericenter, but not on the ratio of black hole to stellar mass, and are at most the star's own escape velocity. We find that these kicks are usually too small to result in the ejection of stars from the Milky Way, but can eject the stars from the black hole's sphere of influence, reducing their probability of being disrupted again. We estimate that ∼ 10 5 stars, ∼ 1% of all stars within 10 pc of the galactic center, are likely to have had mass removed by the central black hole through tidal interaction, and speculate that these 'turbovelocity' stars will at first be redder, but eventually bluer, and always brighter than their unharassed peers.

  2. Power control of a wind farm with active stall wind turbines and AC grid connection

    Hansen, Anca Daniela; Sørensen, Poul; Iov, Florin

    both the control on wind turbine level as well as the central control on the wind farm level. The ability of active stall wind farms with AC grid connection to regulate the power production to the reference power ordered by the operators is assessed and discussed by means of simulations.......This paper describes the design of a centralised wind farm controller for a wind farm made-up exclusively of active stall wind turbines with AC grid connection. The overall aim of such controller is to enable the wind farms to provide the best grid support. The designed wind farm control involves...

  3. Dark stars

    Maselli, Andrea; Pnigouras, Pantelis; Nielsen, Niklas Grønlund

    2017-01-01

    to the formation of compact objects predominantly made of dark matter. Considering both fermionic and bosonic (scalar φ4) equations of state, we construct the equilibrium structure of rotating dark stars, focusing on their bulk properties and comparing them with baryonic neutron stars. We also show that these dark......Theoretical models of self-interacting dark matter represent a promising answer to a series of open problems within the so-called collisionless cold dark matter paradigm. In case of asymmetric dark matter, self-interactions might facilitate gravitational collapse and potentially lead...... objects admit the I-Love-Q universal relations, which link their moments of inertia, tidal deformabilities, and quadrupole moments. Finally, we prove that stars built with a dark matter equation of state are not compact enough to mimic black holes in general relativity, thus making them distinguishable...

  4. Astrospheres and Solar-like Stellar Winds

    Wood Brian E.

    2004-07-01

    Full Text Available Stellar analogs for the solar wind have proven to be frustratingly difficult to detect directly. However, these stellar winds can be studied indirectly by observing the interaction regions carved out by the collisions between these winds and the interstellar medium (ISM. These interaction regions are called "astrospheres", analogous to the "heliosphere" surrounding the Sun. The heliosphere and astrospheres contain a population of hydrogen heated by charge exchange processes that can produce enough H I Ly alpha absorption to be detectable in UV spectra of nearby stars from the Hubble Space Telescope (HST. The amount of astrospheric absorption is a diagnostic for the strength of the stellar wind, so these observations have provided the first measurements of solar-like stellar winds. Results from these stellar wind studies and their implications for our understanding of the solar wind are reviewed here. Of particular interest are results concerning the past history of the solar wind and its impact on planetary atmospheres.

  5. Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

    Vlasov, Andrey D.; Metzger, Brian D.; Lippuner, Jonas; Roberts, Luke F.; Thompson, Todd A.

    2017-06-01

    We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly rotating, strongly magnetized protoneutron stars ('millisecond protomagnetars') for which the magnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the protomagnetar wind trajectories calculated by Vlasov, Metzger & Thompson through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the protoneutron star cooling phase. Although we do not find a successful second or third-peak r-process for any rotation period P, we show that protomagnetars with P ˜ 1-5 ms produce heavy element abundance distributions that extend to higher nuclear mass number than from otherwise equivalent spherical winds (with the mass fractions of some elements enhanced by factors of ≳100-1000). The heaviest elements are synthesized by outflows emerging along flux tubes that graze the closed zone and pass near the equatorial plane outside the light cylinder. Due to dependence of the nucleosynthesis pattern on the magnetic field strength and rotation rate of the protoneutron star, natural variations in these quantities between core collapse events could contribute to the observed diversity of the abundances of weak r-process nuclei in metal-poor stars. Further diversity, including possibly even a successful third-peak r-process, could be achieved for misaligned rotators with non-zero magnetic inclination with respect to the rotation axis. If protomagnetars are central engines for GRBs, their relativistic jets should contain a high-mass fraction of heavy nuclei of characteristic mass number \\bar{A}≈ 100, providing a possible source for ultrahigh energy cosmic rays comprised of heavy nuclei with an energy spectrum that extends beyond the nominal Grezin-Zatsepin-Kuzmin cut-off for protons or iron nuclei.

  6. The Rapid Evolution of the Exciting Star of the Stingray Nebula

    Reindl, N.; Rauch, T.; Parthasarathy, M.; Werner, K.; Kruk, J.W.; Hamann, W. R.; Sander, A.; Todt, H.

    2014-01-01

    Context: SAO244567, the exciting star of the Stingray nebula, is rapidly evolving. Previous analyses suggested that it has heated up from an effective temperature of about 21 kK in 1971 to over 50 kK in the 1990s. Canonical post-asymptotic giant branch evolution suggests a relatively high mass while previous analyses indicate a low-mass star. Aims: A comprehensive model-atmosphere analysis of UV and optical spectra taken during 1988-2006 should reveal the detailed temporal evolution of its atmospheric parameters and provide explanations for the unusually fast evolution. Methods: Fitting line profiles from static and expanding non-LTE model atmospheres to the observed spectra allowed us to study the temporal change of effective temperature, surface gravity, mass-loss rate, and terminal wind velocity. In addition, we determined the chemical composition of the atmosphere. Results: We find that the central star has steadily increased its effective temperature from 38 kK in 1988 to a peak value of 60 kK in 2002. During the same time, the star was contracting, as concluded from an increase in surface gravity from log g = 4.8 to 6.0 and a drop in luminosity. Simultaneously, the mass-loss rate declined from log(M/M (solar mass) yr (exp -1)) = -9.0 to -11.6 and the terminal wind velocity increased from v (infinity) = 1800 km s (exp -1) to 2800 km s (exp -1). Since around 2002, the star stopped heating and has cooled down again to 55 kK by 2006. It has a largely solar surface composition with the exception of slightly subsolar carbon, phosphorus, and sulfur. The results are discussed by considering different evolutionary scenarios. Conclusions: The position of SAO244567 in the log T (sub eff) -log g plane places the star in the region of sdO stars. By comparison with stellar-evolution calculations, we confirm that SAO244567 must be a low-mass star (M nebula with a kinematical age of only about 1000 years. We speculate that the star could be a late He-shell flash object

  7. The Search for New Luminous Blue Variable Stars: Near-Infrared Spectroscopy of Stars With 24 micron Shells

    Stringfellow, Guy; Gvaramadze, Vasilii

    2010-02-01

    Luminous Blue Variable (LBV) stars represent an extremely rare class of very luminous and massive stars. Only about a dozen confirmed Galactic LBV stars are known to date, which precludes us from determining a solid evolutionary connection between LBV and other intermediate (e.g. Ofpe/WN9, WNL) phases in the life of very massive stars. The known LBV stars each have their own unique properties, so new discoveries add insight into the properties and evolutionary status of LBVs and massive stars; even one new discovery of objects of this type could provide break-through results in the understanding of the intermediate stages of massive star evolution. We have culled a prime sample of possible LBV candidates from the Spitzer 24 (micron) archival data. All have circumstellar nebulae, rings, and shells (typical of LBVs and related stars) surrounding reddened central stars. Spectroscopic followup of about two dozen optically visible central stars associated with the shells from this sample showed that they are either candidate LBVs, late WN-type Wolf-Rayet stars or blue supergiants. We propose infrared spectroscopic observations of the central stars for a large fraction (23 stars) of our northern sample to determine their nature and discover additional LBV candidates. These stars have no plausible optical counterparts, so infrared spectra are needed. This program requires two nights of Hale time using TripleSpec.

  8. Effective bending strain estimated from I c test results of a D-shaped Nb3Al CICC coil fabricated with a react-and-wind process for the National Centralized Tokamak

    Ando, T.; Kizu, K.; Miura, Y.M.; Tsuchiya, K.; Matsukawa, M.; Tamai, H.; Ishida, S.; Koizumi, N.; Okuno, K.

    2005-01-01

    Japan National Centralized Tokamak (NCT) is a superconducting tokamak proposed as a modification to JT-60U. As part of the R and D for the National Centralized Tokamak, a two-turn, approximately 2 m tall, D-shaped Nb 3 Al coil was wound and tested using a full-size cable-in-conduit conductor (CICC). The Nb 3 Al cable-in-conductor was bent following the heat treatment reaction with a maximum bending strain of 0.4% to simulate the react-and-wind fabrication. The comparison of the coil performance to the measured strand data shows that the effective axial strain of the conductor strands is essentially zero despite the 0.4% bending strain of the conductor. This suggests that the strands in the cable slipped relatively to each other during bending of the conduit, thus reducing the effective strain transmitted to the strands. This result is very encouraging for the low-cost fabrication of high-current-density fusion coils using the react-and-wind method

  9. Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

    Schneider, F.R.N.; Izzard, R.G.; de Mink, S.E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V.V.; Huβman, B.; Liermann, A.; Sana, H.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass

  10. Star-forming Filament Models

    Myers, Philip C.

    2017-01-01

    New models of star-forming filamentary clouds are presented in order to quantify their properties and to predict their evolution. These 2D axisymmetric models describe filaments that have no core, one low-mass core, and one cluster-forming core. They are based on Plummer-like cylinders and spheroids that are bounded by a constant-density surface of finite extent. In contrast to 1D Plummer-like models, they have specific values of length and mass, they approximate observed column density maps, and their distributions of column density ( N -pdfs) are pole-free. Each model can estimate the star-forming potential of a core-filament system by identifying the zone of gas dense enough to form low-mass stars and by counting the number of enclosed thermal Jeans masses. This analysis suggests that the Musca central filament may be near the start of its star-forming life, with enough dense gas to make its first ∼3 protostars, while the Coronet filament is near the midpoint of its star formation, with enough dense gas to add ∼8 protostars to its ∼20 known stars. In contrast, L43 appears to be near the end of its star-forming life, since it lacks enough dense gas to add any new protostars to the two young stellar objectsalready known.

  11. Star-forming Filament Models

    Myers, Philip C., E-mail: pmyers@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2017-03-20

    New models of star-forming filamentary clouds are presented in order to quantify their properties and to predict their evolution. These 2D axisymmetric models describe filaments that have no core, one low-mass core, and one cluster-forming core. They are based on Plummer-like cylinders and spheroids that are bounded by a constant-density surface of finite extent. In contrast to 1D Plummer-like models, they have specific values of length and mass, they approximate observed column density maps, and their distributions of column density ( N -pdfs) are pole-free. Each model can estimate the star-forming potential of a core-filament system by identifying the zone of gas dense enough to form low-mass stars and by counting the number of enclosed thermal Jeans masses. This analysis suggests that the Musca central filament may be near the start of its star-forming life, with enough dense gas to make its first ∼3 protostars, while the Coronet filament is near the midpoint of its star formation, with enough dense gas to add ∼8 protostars to its ∼20 known stars. In contrast, L43 appears to be near the end of its star-forming life, since it lacks enough dense gas to add any new protostars to the two young stellar objectsalready known.

  12. Strange-quark-matter stars

    Glendenning, N.K.

    1989-11-01

    We investigate the implications of rapid rotation corresponding to the frequency of the new pulsar reported in the supernovae remnant SN1987A. It places very stringent conditions on the equation of state if the star is assumed to be bound by gravity alone. We find that the central energy density of the star must be greater than 13 times that of nuclear density to be stable against the most optimistic estimate of general relativistic instabilities. This is too high for the matter to consist of individual hadrons. We conclude that it is implausible that the newly discovered pulsar, if its half-millisecond signals are attributable to rotation, is a neutron star. We show that it can be a strange quark star, and that the entire family of strange stars can sustain high rotation if strange matter is stable at an energy density exceeding about 5.4 times that of nuclear matter. We discuss the conversion of a neutron star to strange star, the possible existence of a crust of heavy ions held in suspension by centrifugal and electric forces, the cooling and other features. 34 refs., 10 figs., 1 tab

  13. Presupernova evolution of massive stars

    Weaver, T.A.; Zimmerman, G.B.; Woosley, S.E.

    1977-01-01

    Population I stars of 15 M/sub mass/ and 25 M/sub mass/ have been evolved from the zero-age main sequence through iron core collapse utilizing a numerical model that incorporates both implicit hydrodynamics and a detailed treatment of nuclear reactions. The stars end their presupernova evolution as red supergiants with photospheric radii of 3.9 x 10 13 cm and 6.7 x 10 13 cm, respectively, and density structures similar to those invoked to explain Type II supernova light curves on a strictly hydrodynamic basis. Both stars are found to form substantially neutronized ''iron'' cores of 1.56 M/sub mass/ and 1.61 M/sub mass/, and central electron abundances of 0.427 and 0.439 moles/g, respectively, during hydrostatic silicon burning. Just prior to collapse, the abundances of the elements in the 25 M/sub mass/ star (excluding the neutronized iron core) have ratios strikingly close to their solar system values over the mass range from oxygen to calcium, while the 15 M/sub mass/ star is characterized by large enhancements of Ne, Mg, and Si. It is pointed out on nucleosynthetic grounds that the mass of the neutronized core must represent a lower limit to the mass of the neutron star or black hole remnant that stars in this mass range can normally produce

  14. Tornado type wind turbines

    Hsu, Cheng-Ting

    1984-01-01

    A tornado type wind turbine has a vertically disposed wind collecting tower with spaced apart inner and outer walls and a central bore. The upper end of the tower is open while the lower end of the structure is in communication with a wind intake chamber. An opening in the wind chamber is positioned over a turbine which is in driving communication with an electrical generator. An opening between the inner and outer walls at the lower end of the tower permits radially flowing air to enter the space between the inner and outer walls while a vertically disposed opening in the wind collecting tower permits tangentially flowing air to enter the central bore. A porous portion of the inner wall permits the radially flowing air to interact with the tangentially flowing air so as to create an intensified vortex flow which exits out of the top opening of the tower so as to create a low pressure core and thus draw air through the opening of the wind intake chamber so as to drive the turbine.

  15. Hybrid stars

    Hybrid stars. AsHOK GOYAL. Department of Physics and Astrophysics, University of Delhi, Delhi 110 007, India. Abstract. Recently there have been important developments in the determination of neutron ... number and the electric charge. ... available to the system to rearrange concentration of charges for a given fraction of.

  16. Pulsating stars

    Catelan, M?rcio

    2014-01-01

    The most recent and comprehensive book on pulsating stars which ties the observations to our present understanding of stellar pulsation and evolution theory.  Written by experienced researchers and authors in the field, this book includes the latest observational results and is valuable reading for astronomers, graduate students, nuclear physicists and high energy physicists.

  17. Variable stars

    Feast, M.W.; Wenzel, W.; Fernie, J.D.; Percy, J.R.; Smak, J.; Gascoigne, S.C.B.; Grindley, J.E.; Lovell, B.; Sawyer Hogg, H.B.; Baker, N.; Fitch, W.S.; Rosino, L.; Gursky, H.

    1976-01-01

    A critical review of variable stars is presented. A fairly complete summary of major developments and discoveries during the period 1973-1975 is given. The broad developments and new trends are outlined. Essential problems for future research are identified. (B.R.H. )

  18. Oscillations in neutron stars

    Hoeye, Gudrun Kristine

    1999-01-01

    We have studied radial and nonradial oscillations in neutron stars, both in a general relativistic and non-relativistic frame, for several different equilibrium models. Different equations of state were combined, and our results show that it is possible to distinguish between the models based on their oscillation periods. We have particularly focused on the p-, f-, and g-modes. We find oscillation periods of II approx. 0.1 ms for the p-modes, II approx. 0.1 - 0.8 ms for the f-modes and II approx. 10 - 400 ms for the g-modes. For high-order (l → 4) f-modes we were also able to derive a formula that determines II l+1 from II l and II l-1 to an accuracy of 0.1%. Further, for the radial f-mode we find that the oscillation period goes to infinity as the maximum mass of the star is approached. Both p-, f-, and g-modes are sensitive to changes in the central baryon number density n c , while the g-modes are also sensitive to variations in the surface temperature. The g-modes are concentrated in the surface layer, while p- and f-modes can be found in all parts of the star. The effects of general relativity were studied, and we find that these are important at high central baryon number densities, especially for the p- and f-modes. General relativistic effects can therefore not be neglected when studying oscillations in neutron stars. We have further developed an improved Cowling approximation in the non-relativistic frame, which eliminates about half of the gap in the oscillation periods that results from use of the ordinary Cowling approximation. We suggest to develop an improved Cowling approximation also in the general relativistic frame. (Author)

  19. Oscillations in neutron stars

    Hoeye, Gudrun Kristine

    1999-07-01

    We have studied radial and nonradial oscillations in neutron stars, both in a general relativistic and non-relativistic frame, for several different equilibrium models. Different equations of state were combined, and our results show that it is possible to distinguish between the models based on their oscillation periods. We have particularly focused on the p-, f-, and g-modes. We find oscillation periods of II approx. 0.1 ms for the p-modes, II approx. 0.1 - 0.8 ms for the f-modes and II approx. 10 - 400 ms for the g-modes. For high-order (l (>{sub )} 4) f-modes we were also able to derive a formula that determines II{sub l+1} from II{sub l} and II{sub l-1} to an accuracy of 0.1%. Further, for the radial f-mode we find that the oscillation period goes to infinity as the maximum mass of the star is approached. Both p-, f-, and g-modes are sensitive to changes in the central baryon number density n{sub c}, while the g-modes are also sensitive to variations in the surface temperature. The g-modes are concentrated in the surface layer, while p- and f-modes can be found in all parts of the star. The effects of general relativity were studied, and we find that these are important at high central baryon number densities, especially for the p- and f-modes. General relativistic effects can therefore not be neglected when studying oscillations in neutron stars. We have further developed an improved Cowling approximation in the non-relativistic frame, which eliminates about half of the gap in the oscillation periods that results from use of the ordinary Cowling approximation. We suggest to develop an improved Cowling approximation also in the general relativistic frame. (Author)

  20. Formation of stars and star clusters in colliding galaxies

    Belles, Pierre-Emmanuel

    2012-01-01

    Mergers are known to be essential in the formation of large-scale structures and to have a significant role in the history of galaxy formation and evolution. Besides a morphological transformation, mergers induce important bursts of star formation. These starburst are characterised by high Star Formation Efficiencies (SFEs) and Specific Star Formation Rates, i.e., high Star Formation Rates (SFR) per unit of gas mass and high SFR per unit of stellar mass, respectively, compared to spiral galaxies. At all redshifts, starburst galaxies are outliers of the sequence of star-forming galaxies defined by spiral galaxies. We have investigated the origin of the starburst-mode of star formation, in three local interacting systems: Arp 245, Arp 105 and NGC 7252. We combined high-resolution JVLA observations of the 21-cm line, tracing the HI diffuse gas, with UV GALEX observations, tracing the young star-forming regions. We probe the local physical conditions of the Inter-Stellar Medium (ISM) for independent star-forming regions and explore the atomic-to-dense gas transformation in different environments. The SFR/HI ratio is found to be much higher in central regions, compared to outer regions, showing a higher dense gas fraction (or lower HI gas fraction) in these regions. In the outer regions of the systems, i.e., the tidal tails, where the gas phase is mostly atomic, we find SFR/HI ratios higher than in standard HI-dominated environments, i.e., outer discs of spiral galaxies and dwarf galaxies. Thus, our analysis reveals that the outer regions of mergers are characterised by high SFEs, compared to the standard mode of star formation. The observation of high dense gas fractions in interacting systems is consistent with the predictions of numerical simulations; it results from the increase of the gas turbulence during a merger. The merger is likely to affect the star-forming properties of the system at all spatial scales, from large scales, with a globally enhanced turbulence

  1. Star Products and Applications

    Iida, Mari; Yoshioka, Akira

    2010-01-01

    Star products parametrized by complex matrices are defined. Especially commutative associative star products are treated, and star exponentials with respect to these star products are considered. Jacobi's theta functions are given as infinite sums of star exponentials. As application, several concrete identities are obtained by properties of the star exponentials.

  2. Effects of back warming in cocoon stars

    Donnison, J.R.; Williams, I.P.

    1976-01-01

    It is stated that dust shells frequently surround young stars, and attempts have been made to determine some of the properties of these shells. It is probable that the dust absorbs the outgoing radiation from the star and re-emits it in the infrared. If the dust shell does absorb radiation both its inner and outer surfaces will re-emit a certain proportion and some radiation will return to the central star, causing what amounts to 'warming of its own back'. It is interesting to consider how such a star evolves, compared with evolution of a normal pre-main-sequence star. A model for a contracting star that is receiving radiation from an external source has been developed by the authors in connection with the evolution of Jupiter within the radiation field of the Sun (Astrophys. Space Sci., 29:387 (1974)), and this model is here applied to the situation just described. It is emphasised that the discussion is concerned only with the evolution of the central star, the dust being regarded merely as a means of redirecting radiation back on to the surface of this star. Amongst conclusions reached is that a thin shell will cause no significant change in the structure and evolution of the central star, whilst the presence of a thick shell has a substantial effect on the star, slowing down is evolution. Whilst a dust shell is present the star cannot be seen, but only the dust shell emitting in the infrared, but once the dust shell clears the star is seen in a position and with an age that differs considerably from what it would have had if it had evolved without 'back warming' from the dust shell. (U.K.)

  3. Distributed Wind Market Applications

    Forsyth, T.; Baring-Gould, I.

    2007-11-01

    Distributed wind energy systems provide clean, renewable power for on-site use and help relieve pressure on the power grid while providing jobs and contributing to energy security for homes, farms, schools, factories, private and public facilities, distribution utilities, and remote locations. America pioneered small wind technology in the 1920s, and it is the only renewable energy industry segment that the United States still dominates in technology, manufacturing, and world market share. The series of analyses covered by this report were conducted to assess some of the most likely ways that advanced wind turbines could be utilized apart from large, central station power systems. Each chapter represents a final report on specific market segments written by leading experts in this field. As such, this document does not speak with one voice but rather a compendium of different perspectives, which are documented from a variety of people in the U.S. distributed wind field.

  4. Processes and problems in secondary star formation

    Klein, R.I.; Whitaker, R.W.; Sandford, M.T. II.

    1984-03-01

    Recent developments relating the conditions in molecular clouds to star formation triggered by a prior stellar generation are reviewed. Primary processes are those that lead to the formation of a first stellar generation. The secondary processes that produce stars in response to effects caused by existing stars are compared and evaluated in terms of the observational data presently available. We discuss the role of turbulence to produce clumpy cloud structures and introduce new work on colliding inter-cloud gas flows leading to non-linear inhomogeneous cloud structures in an intially smooth cloud. This clumpy morphology has important consequences for secondary formation. The triggering processes of supernovae, stellar winds, and H II regions are discussed with emphasis on the consequences for radiation driven implosion as a promising secondary star formation mechanism. Detailed two-dimensional, radiation-hydrodynamic calculations of radiation driven implosion are discussed. This mechanism is shown to be highly efficient in synchronizing the formation of new stars in congruent to 1-3 x 10 4 years and could account for the recent evidence for new massive star formation in several UCHII regions. It is concluded that, while no single theory adequately explains the variety of star formation observed, a uniform description of star formation is likely to involve several secondary processes. Advances in the theory of star formation will require multiple dimensional calculations of coupled processes. The important non-linear interactions include hydrodynamics, radiation transport, and magnetic fields

  5. Processes and problems in secondary star formation

    Klein, R.I.; Whitaker, R.W.; Sandford, M.T. II

    1985-01-01

    Recent developments relating the conditions in molecular clouds to star formation triggered by a prior stellar generation are reviewed. Primary processes are those that lead to the formation of a first stellar generation. The secondary processes that produce stars in response to effects caused by existing stars are compared and evaluated in terms of observational data presently available. We discuss the role of turbulence to produce clumpy cloud structures and introduce new work on colliding intercloud gas flows leading to nonlinear inhomogeneous cloud structures in an initially smooth cloud. This clumpy morphology has important consequences for secondary formation. The triggering processes of supernovae, stellar winds, and H II regions are discussed with emphasis on the consequences for radiation-driven implosion as a promising secondary star formation mechanism. Detailed two-dimensional, radiation-hydrodynamic calculations of radiation-driven implosion are discussed. This mechanism is shown to be highly efficient in synchronizing the formation of new stars in -- 1-3 x 10/sup 4/ yr and could account for the recent evidence for new massive star formation in several ultracompact H II regions. It is concluded that, while no single theory adequately explains the variety of star formation observed, a uniform description of star formation is likely to involve several secondary processes. Advances in the theory of star formation will require multi-dimensional calculations of coupled processes. Important nonlinear interactions include hydrodynamics, radiation transport, and magnetic fields

  6. NuSTAR Observations of the Powerful Radio-Galaxy Cygnus A

    Reynolds, Christopher S.; Lohfink, Anne M.; Ogle, Patrick M.

    2015-01-01

    We present NuSTAR observations of the powerful radio galaxy Cygnus A,focusing on the central absorbed active galactic nucleus (AGN). Cygnus A is embedded in a cool-core galaxy cluster, and hence we also examine archival XMM-Newton data to facilitate the decomposition of the spectrum into the AGN...... and intracluster medium (ICM) components. NuSTAR gives a source-dominated spectrum of the AGN out to >70keV. In gross terms, the NuSTAR spectrum of the AGN has the form of a power law (Γ~1.6-1.7) absorbed by a neutral column density of NH~1.6x1023 cm-2. However, we also detect curvature in the hard (>10ke......V (90% confidence). Interestingly, the absorbed power-law plus reflection modelleaves residuals suggesting the absorption/emission from a fast(15,000-26,000km/s), high column-density (NW>3x1023 cm-2), highly ionized (ξ~2,500 erg cm/s-1) wind. A second, even faster ionized wind component is also...

  7. The Politics of Star Wars.

    Wilkins, Lee

    George Lucas's Star Wars trilogy is used as the basis for the creation of a political subtext arising from one of America's most enduring literary myths--the American Adam. That subtext, when translated into a modern political context, pinpoints two central issues to face this democracy in the coming years, as well as a national ambivalence about…

  8. Observations of mass loss from OB and Wolf-Rayet stars

    Barlow, M.J.

    1982-01-01

    In this review, three observationally accessible parameters of the winds of OB and Wolf-Rayet stars are discussed: (1) Terminal velocities, (2) Velocity laws, (3) Mass loss rates. In addition, some discussion of the ionisation structure of the winds is included. In general, only the most recent results for OB stars are mentioned. (Auth.)

  9. Are luminous and metal-rich Wolf Rayet stars inflated?

    Petrovic, J.; Pols, O.; Langer, N.

    2006-01-01

    Aims. We investigate the influence of metallicity and stellar wind mass loss on the radius of Wolf-Rayet stars. Methods. We have calculated chemically homogeneous models of Wolf-Rayet stars of 10 to 200 M for two metallicities (Z = 0.02 and Z = 0.001), without mass loss, using OPAL opacities. We

  10. Old and new neutron stars

    Ruderman, M.

    1984-09-01

    The youngest known radiopulsar in the rapidly spinning magnetized neutron star which powers the Crab Nebula, the remnant of the historical supernova explosion of 1054 AD. Similar neutron stars are probably born at least every few hundred years, but are less frequent than Galactic supernova explosions. They are initially sources of extreme relativistic electron and/or positron winds (approx.10 38 s -1 of 10 12 eV leptons) which greatly decrease as the neutron stars spin down to become mature pulsars. After several million years these neutron stars are no longer observed as radiopulsars, perhaps because of large magnetic field decay. However, a substantial fraction of the 10 8 old dead pulsars in the Galaxy are the most probable source for the isotropically distributed γ-ray burst detected several times per week at the earth. Some old neutron stars are spun-up by accretion from companions to be resurrected as rapidly spinning low magnetic field radiopulsars. 52 references, 6 figures, 3 tables

  11. Wind energy

    Kotevski, Darko

    2003-01-01

    Wind is not only free, it is inexhaustible. Wind energy has come a very long way since the prototypes of just 20 years ago. today's wind turbines are state-of-the-art technology - modular and quick to install anywhere where there is sufficient wind potential to provide secure, centralised or distributed generation. It is a global phenomenon, the world's fastest growing energy sector, a clean and effective modern technology that completely avoids pollution and thus reducing the 'green house' effect. (Original)

  12. Preliminary Design of a Multi-Column TLP Foundation for a 5-MW Offshore Wind Turbine

    Yongsheng Zhao; Jianmin Yang; Yanping He

    2012-01-01

    Currently, floating wind turbines (FWTs) may be the more economical and suitable systems with which to exploit offshore wind energy in deep waters. Among the various types of floating foundations for offshore wind farms, a tension leg platform (TLP) foundation can provide a relatively stable platform for currently available offshore wind turbines without requiring major modifications. In this study, a new multi-column TLP foundation (WindStar TLP) was developed for the NREL 5-MW offshore wind...

  13. The theory of radiation driven stellar winds and the Wolf-Rayet phenomenon

    Abbott, D.C.

    1982-01-01

    The author considers the question of whether the mass loss observed from Wolf-Rayet stars can be explained by a version of wind theory which is scaled to the conditions found in the envelopes of Wolf-Rayet stars. He discusses the following topics: - The calculated radiation pressure in OB stars, and its dependence on temperature, density, and chemical composition. - A comparison between predicted and observed mass loss rates and terminal velocities for OB stars. - The applicability of the standard radiation driven wind models to Wolf-Rayet stars. - Speculations on how Wolf-Rayet stars achieve their enormous mass loss rates within the context of the radiation pressure mechanism. (Auth.)

  14. "Wonderful" Star Reveals its Hot Nature

    2005-04-01

    to become a white dwarf. The internal turmoil in Mira A could create magnetic disturbances in the upper atmosphere of the star and lead to the observed X-ray outbursts, as well as the rapid loss of material from the star in a blustery, strong, stellar wind. Some of the gas and dust escaping from Mira A is captured by its companion Mira B. In stark contrast to Mira A, Mira B is thought to be a white dwarf star about the size of the Earth. Some of the material in the wind from Mira A is captured in an accretion disk around Mira B, where collisions between rapidly moving particles produce X-rays. Animation of Interacting Stars Animation of Interacting Stars One of the more intriguing aspects of the observations of Mira AB at both X-ray and ultraviolet wavelengths is the evidence for a faint bridge of material joining the two stars. The existence of a bridge would indicate that, in addition to capturing material from the stellar wind, Mira B is also pulling material directly off Mira A into the accretion disk. Chandra observed Mira with its Advanced CCD Imaging Spectrometer on December 6, 2003 for about 19 hours. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate, Washington. Northrop Grumman of Redondo Beach, Calif., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

  15. Conditions of call for tenders on the offshore wind power plants; Conditions de l'appel d'offres portant sur des centrales eolienne en mer

    NONE

    2003-07-01

    In the framework of the renewable energies sources development, the french government decided to launch a call for tenders for the realization of offshore wind power plants in 2007. The call for tenders conditions concern: the energetic and technical characteristics of the installations as the primary energy, the production technic, the power; the industrial implementing delay; the exploitation and the operating time; the implementing sites; the weighting and the classification principles. The main conditions concerning the utilization of the maritime public land property outside of the harbors. (A.L.B.)

  16. SYMBIOTIC STAR BLOWS BUBBLES INTO SPACE

    2002-01-01

    A tempestuous relationship between an unlikely pair of stars may have created an oddly shaped, gaseous nebula that resembles an hourglass nestled within an hourglass. Images taken with Earth-based telescopes have shown the larger, hourglass-shaped nebula. But this picture, taken with NASA's Hubble Space Telescope, reveals a small, bright nebula embedded in the center of the larger one (close-up of nebula in inset). Astronomers have dubbed the entire nebula the 'Southern Crab Nebula' (He2-104), because, from ground-based telescopes, it looks like the body and legs of a crab. The nebula is several light-years long. The possible creators of these shapes cannot be seen at all in this Wide Field and Planetary Camera 2 image. It's a pair of aging stars buried in the glow of the tiny, central nebula. One of them is a red giant, a bloated star that is exhausting its nuclear fuel and is shedding its outer layers in a powerful stellar wind. Its companion is a hot, white dwarf, a stellar zombie of a burned-out star. This odd duo of a red giant and a white dwarf is called a symbiotic system. The red giant is also a Mira Variable, a pulsating red giant, that is far away from its partner. It could take as much as 100 years for the two to orbit around each other. Astronomers speculate that the interaction between these two stars may have sparked episodic outbursts of material, creating the gaseous bubbles that form the nebula. They interact by playing a celestial game of 'catch': as the red giant throws off its bulk in a powerful stellar wind, the white dwarf catches some of it. As a result, an accretion disk of material forms around the white dwarf and spirals onto its hot surface. Gas continues to build up on the surface until it sparks an eruption, blowing material into space. This explosive event may have happened twice in the 'Southern Crab.' Astronomers speculate that the hourglass-shaped nebulae represent two separate outbursts that occurred several thousand years apart

  17. Wave Star

    Kramer, Morten; Frigaard, Peter; Brorsen, Michael

    Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004.......Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004....

  18. ISOLATED WOLF-RAYET STARS AND O SUPERGIANTS IN THE GALACTIC CENTER REGION IDENTIFIED VIA PASCHEN-α EXCESS

    Mauerhan, J. C.; Stolovy, S. R.; Cotera, A.; Dong, H.; Wang, Q. D.; Morris, M. R.; Lang, C.

    2010-01-01

    We report the discovery of 19 hot, evolved, massive stars near the Galactic center region (GCR). These objects were selected for spectroscopy owing to their detection as strong sources of Paschen-α (Pα) emission-line excess, following a narrowband imaging survey of the central 0. 0 65 x 0. 0 25 (l, b) around Sgr A* with the Hubble Space Telescope. Discoveries include six carbon-type (WC) and five nitrogen-type (WN) Wolf-Rayet stars, six O supergiants, and two B supergiants. Two of the O supergiants have X-ray counterparts having properties consistent with solitary O stars and colliding-wind binaries. The infrared photometry of 17 stars is consistent with the Galactic center distance, but 2 of them are located in the foreground. Several WC stars exhibit a relatively large infrared excess, which is possibly thermal emission from hot dust. Most of the stars appear scattered throughout the GCR, with no relation to the three known massive young clusters; several others lie near the Arches and Quintuplet clusters and may have originated within one of these systems. The results of this work bring the total sample of Wolf-Rayet (WR) stars in the GCR to 88. All sources of strong Pα excess have been identified in the area surveyed with HST, which implies that the sample of WN stars in this region is near completion, and is dominated by late (WNL) types. The current WC sample, although probably not complete, is almost exclusively dominated by late (WCL) types. The observed WR subtype distribution in the GCR is a reflection of the intrinsic rarity of early subtypes (WNE and WCE) in the inner Galaxy, an effect that is driven by metallicity.

  19. Ultra-dense neutron star matter, strange quark stars, and the nuclear equation of state

    Weber, F.; Meixner, M.; Negreiros, R.P.; Malheiro, M.

    2007-01-01

    With central densities way above the density of atomic nuclei, neutron stars contain matter in one of the densest forms found in the universe. Depending of the density reached in the cores of neutron stars, they may contain stable phases of exotic matter found nowhere else in space. This article gives a brief overview of the phases of ultra-dense matter predicted to exist deep inside neutron stars and discusses the equation of state (EoS) associated with such matter. (author)

  20. Storage and Assay of Tritium in STAR

    Longhurst, Glen R.; Anderl, Robert A.; Pawelko, Robert J.; Stoots, Carl J.

    2005-01-01

    The Safety and Tritium Applied Research (STAR) facility at the Idaho National Engineering and Environmental Laboratory (INEEL) is currently being commissioned to investigate tritium-related safety questions for fusion and other technologies. The tritium inventory for the STAR facility will be maintained below 1.5 g to avoid the need for STAR to be classified as a Category 3 nuclear facility. A key capability in successful operation of the STAR facility is the ability to receive, inventory, and dispense tritium to the various experiments underway there. The system central to that function is the Tritium Storage and Assay System (SAS).The SAS has four major functions: (1) receiving and holding tritium, (2) assaying, (3) dispensing, and (4) purifying hydrogen isotopes from non-hydrogen species.This paper describes the design and operation of the STAR SAS and the procedures used for tritium accountancy in the STAR facility

  1. Gamma-ray bursts from tidally spun-up Wolf-Rayet stars?

    Detmers, R.G.; Langer, N.; Podsiadlowski, Ph.; Izzard, R.G.

    2008-01-01

    Context. The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose angular momentum due to their intense stellar winds. Aims. We investigate whether the tidal interaction of a Wolf-Rayet star with a compact

  2. Low-metallicity massive single stars with rotation. Evolutionary models applicable to I Zwicky 18

    Szécsi, D.; Langer, N.; Yoon, S.C.; Sanyal, D.; de Mink, S.; Evans, C.J.; Dermine, T.

    2015-01-01

    Context. Low-metallicity environments such as the early Universe and compact star-forming dwarf galaxies contain many massive stars. These stars influence their surroundings through intense UV radiation, strong winds and explosive deaths. A good understanding of low-metallicity environments requires

  3. Mass-loss rates of cool stars

    Katrien Els Decin, Leen

    2015-08-01

    Over much of the initial mass function, stars lose a significant fraction of their mass through a stellar wind during the late stages of their evolution when being a (super)giant star. As of today, we can not yet predict the mass-loss rate during the (super)giant phase for a given star with specific stellar parameters from first principles. This uncertainty directly impacts the accuracy of current stellar evolution and population synthesis models that predict the enrichment of the interstellar medium by these stellar winds. Efforts to establish the link between the initial physical and chemical conditions at stellar birth and the mass-loss rate during the (super)giant phase have proceeded on two separate tracks: (1) more detailed studies of the chemical and morpho-kinematical structure of the stellar winds of (super)giant stars in our own Milky Way by virtue of the proximity, and (2) large scale and statistical studies of a (large) sample of stars in other galaxies (such as the LMC and SMC) and globular clusters eliminating the uncertainty on the distance estimate and providing insight into the dependence of the mass-loss rate on the metallicity. In this review, I will present recent results of both tracks, will show how recent measurements confirm (some) theoretical predictions, but also how results from the first track admonish of common misconceptions inherent in the often more simplified analysis used to analyse the large samples from track 2.

  4. Stars of strange matter

    Bethe, H.A.; Brown, G.E.; Cooperstein, J.

    1987-01-01

    We investigate suggestions that quark matter with strangeness per baryon of order unity may be stable. We model this matter at nuclear matter densities as a gas of close packed Λ-particles. From the known mass of the Λ-particle we obtain an estimate of the energy and chemical potential of strange matter at nuclear densities. These are sufficiently high to preclude any phase transition from neutron matter to strange matter in the region near nucleon matter density. Including effects from gluon exchange phenomenologically, we investigate higher densities, consistently making approximations which underestimate the density of transition. In this way we find a transition density ρ tr > or approx.7ρ 0 , where ρ 0 is nuclear matter density. This is not far from the maximum density in the center of the most massive neutron stars that can be constructed. Since we have underestimated ρ tr and still find it to be ∝7ρ 0 , we do not believe that the transition from neutron to quark matter is likely in neutron stars. Moreover, measured masses of observed neutron stars are ≅1.4 M sun , where M sun is the solar mass. For such masses, the central (maximum) density is ρ c 0 . Transition to quark matter is certainly excluded for these densities. (orig.)

  5. ON THE HEATING EFFICIENCY DERIVED FROM OBSERVATIONS OF YOUNG SUPER STAR CLUSTERS IN M82

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Torres-Campos, Ana; Munoz-Tunon, Casiana; Monreal-Ibero, Ana; Melo, Veronica

    2009-01-01

    Here, we discuss the mechanical feedback that massive stellar clusters provide to the interstellar medium of their host galaxy. We apply an analytic theory developed in a previous study for M82-A1 to a sample of 10 clusters located in the central zone of the starburst galaxy M82, all surrounded by compact and dense H II regions. We claim that the only way that such H II regions can survive around the selected clusters, is if they are embedded into a high-pressure ISM and if the majority of their mechanical energy is lost within the star cluster volume via strong radiative cooling. The latter implies that these clusters have a low heating efficiency, η, and evolve in the bimodal hydrodynamic regime. In this regime, the shock-heated plasma in the central zones of a cluster becomes thermally unstable, loses its pressure and is accumulated there, whereas the matter injected by supernovae and stellar winds outside this volume forms a high-velocity outflow-the star cluster wind. We calculated the heating efficiency for each of the selected clusters and found that in all cases it does not exceed 10%. Such low heating efficiency values imply a low mechanical energy output and the impact that the selected clusters provide to the ISM of M82 is thus much smaller than what one would expect using stellar cluster synthetic models.

  6. Wind Structure and Wind Loading

    Brorsen, Michael

    The purpose of this note is to provide a short description of wind, i.e. of the flow in the atmosphere of the Earth and the loading caused by wind on structures. The description comprises: causes to the generation of windhe interaction between wind and the surface of the Earthhe stochastic nature...

  7. Symbiotic star AG Dra

    Ipatov, A.P.; Yudin, B.F.; Moskovskij Gosudarstvennyj Univ.

    1986-01-01

    The results obtained from photometric (in the UBVRJHKLM system) and spectrophotometric (in the range 0.33-0.75 μm) observations of symbiotic star AG Dra are presented. The cool component of this star is a red giant with approximately constant brightness (ΔJ ≤ 0 m .3) classified as K4-K5. This red giant fills it's Roche loble and probably is on the assymptotic giant branch of the HR diagramm. The presence of IR excess in 5 μm associated with radiation of the gaseous envelope with the mass of M≅ 10 -6 M sun have been detected. Observations of AG Dra indicate that growing of the bolometric flux of a hot component is accompanied with decreasing effective temperature. The hot component of the system is probably an accerting red dwarf with the mass M≅ 0.4 M sun and disk accretion of matter of cool star with the rate M >or ∼ 10 -4 M sun year in equatorial region. Increase of accretion rate during the outburst of AG Dra leads to the increase of stellar wind from the red dwarf surface and the decrease of it's effective temperature. The hot component of AG Dra may also be considered as a white Dwarf with luminosity L 3 L sun and R eff >or approx. 0.2 R sun . In this case gravitational energy of accreting matter M > or ∼ 10 -6 M sun / year would be the source of the hot component outbursts. The luminosity between outbursts is determined by energy generation from the burning hydrogen layer source

  8. Models for symbiotic stars in the light of the data

    Friedjung, M.

    1982-01-01

    Different single and binary models of symbiotic stars are examined. Single star models encounter a number of problems, and binary models are probable. There are however difficulties in the interpretation of radial velocities. Accretion disks play a role in some cases, but winds especially from the cool component must be taken into account in realistic models. There is some evidence of excess heating of the outer layers of the cool component. Outbursts may be related to sudden changes in the characteristics of the cool star wind. (Auth.)

  9. Wind power

    Gipe, P.

    2007-01-01

    This book is a translation of the edition published in the USA under the title of ''wind power: renewable energy for home, farm and business''. In the wake of mass blackouts and energy crises, wind power remains a largely untapped resource of renewable energy. It is a booming worldwide industry whose technology, under the collective wing of aficionados like author Paul Gipe, is coming of age. Wind Power guides us through the emergent, sometimes daunting discourse on wind technology, giving frank explanations of how to use wind technology wisely and sound advice on how to avoid common mistakes. Since the mid-1970's, Paul Gipe has played a part in nearly every aspect of wind energy development from installing small turbines to promoting wind energy worldwide. As an American proponent of renewable energy, Gipe has earned the acclaim and respect of European energy specialists for years, but his arguments have often fallen on deaf ears at home. Today, the topic of wind power is cropping up everywhere from the beaches of Cape Cod to the Oregon-Washington border, and one wind turbine is capable of producing enough electricity per year to run 200 average American households. Now, Paul Gipe is back to shed light on this increasingly important energy source with a revised edition of Wind Power. Over the course of his career, Paul Gipe has been a proponent, participant, observer, and critic of the wind industry. His experience with wind has given rise to two previous books on the subject, Wind Energy Basics and Wind Power for Home and Business, which have sold over 50,000 copies. Wind Power for Home and Business has become a staple for both homeowners and professionals interested in the subject, and now, with energy prices soaring, interest in wind power is hitting an all-time high. With chapters on output and economics, Wind Power discloses how much you can expect from each method of wind technology, both in terms of energy and financial savings. The book updated models

  10. The iron curtain of WC9 stars

    Hucht, K.A. van der; Willis, A.J.

    1982-01-01

    High resolution (Δlambda approximately equal to 0.1 A) IUE spectra have been obtained of the two WC9 stars HD 164270 and HD 136488, covering the wavelength range lambdalambda1150-2050. The former star shows P Cygni profiles indicating a stellar wind terminal velocity of Vsub(infinity) approximately equal to 1400 km s -1 , and the latter Vsub(infinity) approximately equal to -1800 km s -1 . A common feature in the spectra of both stars is narrow displaced absorptions due to Fe III (UV34) transitions arising from a metastable lower level. These features are displaced at sub-terminal velocities (-830 km s -1 for HD 164270 and -1030 km s -1 for Hd 136488) and are believed to be formed in the deceleration region of their stellar winds. The properties of these inferred Fe III circumstellar shells derived from these data are discussed. (Auth.)

  11. The STAR experiment at RHIC

    Marx, J.N.

    1994-01-01

    STAR (Solenoidal Tracker at RHIC) will be one of two large, sophisticated experiments ready to take data when the Relativistic Heavy Ion Collider (RHIC) comes on-line in 1999. The design of STAR, its construction and commissioning and the physics program using the detector are the responsibility of a collaboration of over 250 members from 30 institutions, world-wide. The overall approach of the STAR Collaboration to the physics challenge of studying collisions of highly relativistic nuclei is to focus on measurements of the properties of the many hadrons produced in the collisions. The STAR detector is optimized to detect and identify hadrons over a large solid angle so that individual events can be characterized, in detail, based on their hadronic content. The broad capabilities of the STAR detector will permit an examination of a wide variety of proposed signatures for the Quark Gluon Plasma (QGP), using the sample of events which, on an event-by-event basis, appear to come from collisions resulting in a large energy density over a nuclear volume. In order to achieve this goal, the STAR experiment is based on a solenoid geometry with tracking detectors using the time projection chamber approach and covering a large range of pseudo-rapidity so that individual tracks can be seen within the very high track density expected in central collisions at RHIC. STAR also uses particle identification by the dE/dx technique and by time-of-flight. Electromagnetic energy is detected in a large, solid-angle calorimeter. The construction of STAR, which will be located in the Wide Angle Hall at the 6 o'clock position at RHIC, formally began in early 1993

  12. Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. I. Solution Topology and Wind Geometry

    Feldmeier, Achim; Shlosman, Isaac

    1999-01-01

    We analyze the dynamics of 2-D stationary, line-driven winds from accretion disks in cataclysmic variable stars. The driving force is that of line radiation pressure, in the formalism developed by Castor, Abbott & Klein for O stars. Our main assumption is that wind helical streamlines lie on straight cones. We find that the Euler equation for the disk wind has two eigenvalues, the mass loss rate and the flow tilt angle with the disk. Both are calculated self-consistently. The wind is characte...

  13. The Contribution of Stellar Winds to Cosmic Ray Production

    Seo, Jeongbhin; Kang, Hyesung; Ryu, Dongsu

    2018-04-01

    Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The wind mechanical energy of a massive star deposited to the interstellar medium can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity by all massive stars in the Galaxy is about Lw ≈ 1.1×1041 ergs, which is about 1/4 of the power of supernova explosions, LSN ≈ 4.8×1041 ergs. If we assume that ˜1-1% of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds are expected to make a significant contribution to GCR production, though lower than that of supernova remnants.

  14. Monte Carlo simulations of the detailed iron absorption line profiles from thermal winds in X-ray binaries

    Tomaru, Ryota; Done, Chris; Odaka, Hirokazu; Watanabe, Shin; Takahashi, Tadayuki

    2018-05-01

    Blueshifted absorption lines from highly ionized iron are seen in some high inclination X-ray binary systems, indicating the presence of an equatorial disc wind. This launch mechanism is under debate, but thermal driving should be ubiquitous. X-ray irradiation from the central source heats disc surface, forming a wind from the outer disc where the local escape velocity is lower than the sound speed. The mass-loss rate from each part of the disc is determined by the luminosity and spectral shape of the central source. We use these together with an assumed density and velocity structure of the wind to predict the column density and ionization state, then combine this with a Monte Carlo radiation transfer to predict the detailed shape of the absorption (and emission) line profiles. We test this on the persistent wind seen in the bright neutron star binary GX 13+1, with luminosity L/LEdd ˜ 0.5. We approximately include the effect of radiation pressure because of high luminosity, and compute line features. We compare these to the highest resolution data, the Chandra third-order grating spectra, which we show here for the first time. This is the first physical model for the wind in this system, and it succeeds in reproducing many of the features seen in the data, showing that the wind in GX13+1 is most likely a thermal-radiation driven wind. This approach, combined with better streamline structures derived from full radiation hydrodynamic simulations, will allow future calorimeter data to explore the detail wind structure.

  15. A Collapsar Model with Disk Wind: Implications for Supernovae Associated with Gamma-Ray Bursts

    Hayakawa, Tomoyasu; Maeda, Keiichi

    2018-02-01

    We construct a simple but self-consistent collapsar model for gamma-ray bursts (GRBs) and SNe associated with GRBs (GRB-SNe). Our model includes a black hole, an accretion disk, and the envelope surrounding the central system. The evolutions of the different components are connected by the transfer of the mass and angular momentum. To address properties of the jet and the wind-driven SNe, we consider competition of the ram pressure from the infalling envelope and those from the jet and wind. The expected properties of the GRB jet and the wind-driven SN are investigated as a function of the progenitor mass and angular momentum. We find two conditions that should be satisfied if the wind-driven explosion is to explain the properties of the observed GRB-SNe: (1) the wind should be collimated at its base, and (2) it should not prevent further accretion even after the launch of the SN explosion. Under these conditions, some relations seen in the properties of the GRB-SNe could be reproduced by a sequence of different angular momentum in the progenitors. Only the model with the largest angular momentum could explain the observed (energetic) GRB-SNe, and we expect that the collapsar model can result in a wide variety of observational counterparts, mainly depending on the angular momentum of the progenitor star.

  16. Ultraviolet spectroscopy of the blue supergiant SBW1: the remarkably weak wind of a SN 1987A analogue

    Smith, Nathan; Groh, Jose H.; France, Kevin; McCray, Richard

    2017-06-01

    The Galactic blue supergiant SBW1 with its circumstellar ring nebula represents the best known analogue of the progenitor of SN 1987A. High-resolution imaging has shown Hα and infrared structures arising in an ionized flow that partly fills the ring's interior. To constrain the influence of the stellar wind on this structure, we obtained an ultraviolet (UV) spectrum of the central star of SBW1 with the Hubble Space Telescope Cosmic Origins Spectrograph. The UV spectrum shows none of the typical wind signatures, indicating a very low mass-loss rate. Radiative transfer models suggest an extremely low rate below 10-10 M⊙ yr-1, although we find that cooling time-scales probably become comparable to (or longer than) the flow time below 10-8 M⊙ yr-1. We therefore adopt this latter value as a conservative upper limit. For the central star, the model yields Teff = 21 000 ± 1000 K, log(geff) = 3.0, L ≃ 5 × 104 L⊙, and roughly Solar composition except for enhanced N abundance. SBW1's very low mass-loss rate may hinder the wind's ability to shape its nebula and to shed angular momentum. The spin-down time-scale for magnetic breaking is more than 500 times longer than the age of the ring. This, combined with the star's slow rotation rate, constrains merger scenarios to form ring nebulae. The mass-loss rate is at least 10 times lower than expected from mass-loss recipes, without any account of clumping. The physical explanation for why SBW1's wind is so weak presents an interesting mystery.

  17. Nuclear processing during star formation

    Newman, M.J.

    1978-01-01

    A preliminary survey was conducted of the thermonuclear energy release expected during star formation. The destruction of primordial deuterium provides substantial amounts of energy at surprisingly low temperatures, and must be considered in any meaningful treatment of star formation carried to stages in which the internal temperature exceeds a few hundred thousand degrees. Significant energy generation from consumption of initial lithium requires higher temperatures, of the order of a few million degrees. Depletion of primordial beryllium and boron may never provide an important energy source. The approach to equilibrium of the carbon--nitrogen cycle is dominant at temperatures approaching those characteristic of the central regions of main sequence stars. The present calculation should serve as a useful guide in choosing those nuclear processes to be included in a more detailed study. 8 figures, 2 tables

  18. Massive stars and X-ray pulsars

    Henrichs, H.

    1982-01-01

    This thesis is a collection of 7 separate articles entitled: long term changes in ultraviolet lines in γ CAS, UV observations of γ CAS: intermittent mass-loss enhancement, episodic mass loss in γ CAS and in other early-type stars, spin-up and spin-down of accreting neutron stars, an excentric close binary model for the X Persei system, has a 97 minute periodicity in 4U 1700-37/HD 153919 really been discovered, and, mass loss and stellar wind in massive X-ray binaries. (Articles 1, 2, 5, 6 and 7 have been previously published). The first three articles are concerned with the irregular mass loss in massive stars. The fourth critically reviews thoughts since 1972 on the origin of the changes in periodicity shown by X-ray pulsars. The last articles indicate the relation between massive stars and X-ray pulsars. (C.F.)

  19. Life of a star

    Henbest, Nigel.

    1988-01-01

    The paper concerns the theory of stellar evolution. A description is given of:- how a star is born, main sequence stars, red giants, white dwarfs, supernovae, neutron stars and black holes. A brief explanation is given of how the death of a star as a supernova can trigger off the birth of a new generation of stars. Classification of stars and the fate of our sun, are also described. (U.K.)

  20. The solar wind in time: a change in the behaviour of older winds?

    O'Fionnagáin, D.; Vidotto, A. A.

    2018-05-01

    In this paper, we model the wind of solar analogues at different ages to investigate the evolution of the solar wind. Recently, it has been suggested that winds of solar type stars might undergo a change in properties at old ages, whereby stars older than the Sun would be less efficient in carrying away angular momentum than what was traditionally believed. Adding to this, recent observations suggest that old solar-type stars show a break in coronal properties, with a steeper decay in X-ray luminosities and temperatures at older ages. We use these X-ray observations to constrain the thermal acceleration of winds of solar analogues. Our sample is based on the stars from the `Sun in Time' project with ages between 120 and 7000 Myr. The break in X-ray properties leads to a break in wind mass-loss rates (\\dot{M}) at roughly 2 Gyr, with \\dot{M} (t 2 Gyr) ∝ t-3.9. This steep decay in \\dot{M} at older ages could be the reason why older stars are less efficient at carrying away angular momentum, which would explain the anomalously rapid rotation observed in older stars. We also show that none of the stars in our sample would have winds dense enough to produce thermal emission above 1-2 GHz, explaining why their radio emissions have not yet been detected. Combining our models with dynamo evolution models for the magnetic field of the Earth, we find that, at early ages (≈100 Myr), our Earth had a magnetosphere that was three or more times smaller than its current size.

  1. Innovative Offshore Wind Plant Design Study

    Hurley, William L. [Glosten Associates, Inc., Seattle, WA (United States); Nordstrom, Charles J. [Glosten Associates, Inc., Seattle, WA (United States); Morrison, Brent J. [Glosten Associates, Inc., Seattle, WA (United States)

    2013-12-18

    Technological advancements in the Glosten PelaStar floating wind turbine system have led to projected cost of energy (COE) reductions from today’s best-in-class offshore wind systems. The PelaStar system is projected to deliver a COE that is 35% lower than that delivered by the current offshore wind plants. Several technology developments have been achieved that directly target significant cost of energy reductions. These include: Application of state-of-the-art steel construction materials and methods, including fatigue-resistant welding techniques and technologies, to reduce hull steel weight; Advancements in synthetic fiber tendon design for the mooring system, which are made possible by laboratory analysis of full-scale sub-rope specimens; Investigations into selected anchor technologies to improve anchor installation methods; Refinement of the installation method, specifically through development of the PelaStar Support Barge design. Together, these technology developments drive down the capital cost and operating cost of offshore wind plants and enable access to superb wind resources in deep water locations. These technology developments also reduce the uncertainty of the PelaStar system costs, which increases confidence in the projected COE reductions.

  2. Do some x-ray stars have white dwarf companions

    Mccollum, Bruce

    1995-01-01

    Some Be stars which are intermittent X-ray sources may have white dwarf companions rather than neutron stars. It is not possible to prove or rule out the existence of Be + WD systems using X-ray or optical data. However, the presence of a white dwarf could be established by the detection of its EUV continuum shortward of the Be star's continuum turnover at 100 A. Either the detection or the nondetection of Be + WD systems would have implications for models of Be star variability, models of Be binary system formation and evolution, and models of wind-fed accretion.

  3. Star Formation in Dwarf Galaxies: Life in a Rough Neighborhood

    Murray, S

    2003-10-16

    Star formation within dwarf galaxies is governed by several factors. Many of these factors are external, including ram-pressure stripping, tidal stripping, and heating by external UV radiation. The latter, in particular, may prevent star formation in the smallest systems. Internal factors include negative feedback in the form of UV radiation, winds and supernovae from massive stars. These act to reduce the star formation efficiency within dwarf systems, which may, in turn, solve several theoretical and observational problems associated with galaxy formation. In this contribution, we discuss our recent work being done to examine the importance of the many factors in the evolution of dwarf galaxies.

  4. Small Wind Energy Systems

    Simoes, Marcelo; Farret, Felix Alberto; Blaabjerg, Frede

    2015-01-01

    devices, and a centralized distribution control. In order to establish a small wind energy system it is important to observe the following: (i) Attending the energy requirements of the actual or future consumers; (ii) Establishing civil liabilities in case of accidents and financial losses due to shortage...... or low quality of energy; (iii) Negotiating collective conditions to interconnect the microgrid with the public network or with other sources of energy that is independent of wind resources; (iv) Establishing a performance criteria of power quality and reliability to end-users, in order to reduce costs...... and guaranteeing an acceptable energy supply. This paper discuss how performance is affected by local conditions and random nature of the wind, power demand profiles, turbine related factors, and presents the technical issues for implementing a self-excited induction generator system, or a permanent magnet based...

  5. PSR1987A: the case for strange-quark stars

    Glendenning, N.K.

    1989-01-01

    The new fast pulsar observed in the remnant of SN1987A, together with other considerations, provide evidence that there are two types of collapsed stars: neutron stars, having moderate central densities and subject to the usual mass constraint, and strange-quark-matter stars. We show that (i) all known pulsar masses and frequencies, with the exception of the new one, can be accounted for by plausible neutron star models; (ii) no known neutron star model can withstand the fast rotation of the new pulsar unless the central energy density is ∼ 15 that of normal nuclei, at which densities hadrons cannot plausibly exist as constituents; and (iii) if strange-quark matter is the true ground state of the strong interactions, strange-quark stars can sustain the high rotation imputed to the new pulsar. In the absence of another plausible structure that can withstand the fast rotation, we provisionally infer that the new pulsar is such a star. (author)

  6. Dust discs around low-mass main-sequence stars

    Wolstencroft, R.D.; Walker, H.J.

    1988-01-01

    Current understanding of the formation of circumstellar discs as a natural accompaniment to the process of low-mass star formation is briefly reviewed. Models of the thermal emission from the dust discs around the prototype stars α Lyr, α PsA, β Pic and ε Eri are discussed, which indicate that the central regions of three of these discs are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest dust lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud that sweeps up grains crossing its orbit. The colour, diameter and thickness of the optical image of β Pic, obtained by coronagraphic techniques, have provided further information on the size, radial distribution of number density and orbital inclination of the grains. The difference in surface brightness on the two sides of the disc is puzzling, but might be explained if the grains are elongated and aligned by the combined effects of a stellar wind and a magnetic field of spiral configuration. Finally, we discuss the orbital evolution and lifetimes of particles in these discs, which are governed primarily by radiation pressure, Poynting-Robertson drag and grain-grain collisions. (author)

  7. THE INFRARED SPECTRAL PROPERTIES OF MAGELLANIC CARBON STARS

    Sloan, G. C. [Cornell Center for Astrophysics and Planetary Science, Cornell Univ., Ithaca, NY 14853-6801 (United States); Kraemer, K. E. [Institute for Scientific Research, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467 (United States); McDonald, I.; Zijlstra, A. A. [Jodrell Bank Centre for Astrophysics, Univ. of Manchester, Manchester M13 9PL (United Kingdom); Groenewegen, M. A. T. [Koninklijke Sterrenwacht van België, Ringlaan 3, B-1180 Brussels (Belgium); Wood, P. R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Lagadec, E. [Observatoire de la Côte d’Azur, F-06300, Nice (France); Boyer, M. L. [CRESST and Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD, 20771 (United States); Kemper, F.; Srinivasan, S. [Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan, R.O.C. (China); Matsuura, M. [School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, CF24 3AA (United Kingdom); Sahai, R. [Jet Propulsion Laboratory, California Institute of Technology, MS 183-900, Pasadena, CA 91109 (United States); Sargent, B. A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Van Loon, J. Th. [Lennard Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); Volk, K., E-mail: sloan@isc.astro.cornell.edu [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)

    2016-07-20

    The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C{sub 2}H{sub 2} at 7.5 μ m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.

  8. THE INFRARED SPECTRAL PROPERTIES OF MAGELLANIC CARBON STARS

    Sloan, G. C.; Kraemer, K. E.; McDonald, I.; Zijlstra, A. A.; Groenewegen, M. A. T.; Wood, P. R.; Lagadec, E.; Boyer, M. L.; Kemper, F.; Srinivasan, S.; Matsuura, M.; Sahai, R.; Sargent, B. A.; Van Loon, J. Th.; Volk, K.

    2016-01-01

    The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C 2 H 2 at 7.5 μ m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.

  9. Wind Farm Decentralized Dynamic Modeling With Parameters

    Soltani, Mohsen; Shakeri, Sayyed Mojtaba; Grunnet, Jacob Deleuran

    2010-01-01

    Development of dynamic wind flow models for wind farms is part of the research in European research FP7 project AEOLUS. The objective of this report is to provide decentralized dynamic wind flow models with parameters. The report presents a structure for decentralized flow models with inputs from...... local models. The results of this report are especially useful, but not limited, to design a decentralized wind farm controller, since in centralized controller design one can also use the model and update it in a central computing node.......Development of dynamic wind flow models for wind farms is part of the research in European research FP7 project AEOLUS. The objective of this report is to provide decentralized dynamic wind flow models with parameters. The report presents a structure for decentralized flow models with inputs from...

  10. Forecasting wind power production from a wind farm using the RAMS model

    Tiriolo, L.; Torcasio, R. C.; Montesanti, S.

    2015-01-01

    of the ECMWF Integrated Forecasting System (IFS), whose horizontal resolution over Central Italy is about 25 km at the time considered in this paper. Because wind observations were not available for the site, the power curve for the whole wind farm was derived from the ECMWF wind operational analyses available......The importance of wind power forecast is commonly recognized because it represents a useful tool for grid integration and facilitates the energy trading. This work considers an example of power forecast for a wind farm in the Apennines in Central Italy. The orography around the site is complex...... and the horizontal resolution of the wind forecast has an important role. To explore this point we compared the performance of two 48 h wind power forecasts using the winds predicted by the Regional Atmospheric Modeling System (RAMS) for the year 2011. The two forecasts differ only for the horizontal resolution...

  11. Wind energy.

    Leithead, W E

    2007-04-15

    From its rebirth in the early 1980s, the rate of development of wind energy has been dramatic. Today, other than hydropower, it is the most important of the renewable sources of power. The UK Government and the EU Commission have adopted targets for renewable energy generation of 10 and 12% of consumption, respectively. Much of this, by necessity, must be met by wind energy. The US Department of Energy has set a goal of 6% of electricity supply from wind energy by 2020. For this potential to be fully realized, several aspects, related to public acceptance, and technical issues, related to the expected increase in penetration on the electricity network and the current drive towards larger wind turbines, need to be resolved. Nevertheless, these challenges will be met and wind energy will, very likely, become increasingly important over the next two decades. An overview of the technology is presented.

  12. Terminal velocities for a large sample of O stars, B supergiants, and Wolf-Rayet stars

    Prinja, R.K.; Barlow, M.J.; Howarth, I.D.

    1990-01-01

    It is argued that easily measured, reliable estimates of terminal velocities for early-type stars are provided by the central velocity asymptotically approached by narrow absorption features and by the violet limit of zero residual intensity in saturated P Cygni profiles. These estimators are used to determine terminal velocities, v(infinity), for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OB stars, the values are typically 15-20 percent smaller than the extreme violet edge velocities, v(edge), while for WR stars v(infinity) = 0.76 v(edge) on average. New mass-loss rates for WR stars which are thermal radio emitters are given, taking into account the new terminal velocities and recent revisions to estimates of distances and to the mean nuclear mass per electron. The relationships between v(infinity), the surface escape velocities, and effective temperatures are examined. 67 refs

  13. Destruction of a Magnetized Star

    Kohler, Susanna

    2017-01-01

    What happens when a magnetized star is torn apart by the tidal forces of a supermassive black hole, in a violent process known as a tidal disruption event? Two scientists have broken new ground by simulating the disruption of stars with magnetic fields for the first time.The magnetic field configuration during a simulation of the partial disruption of a star. Top left: pre-disruption star. Bottom left: matter begins to re-accrete onto the surviving core after the partial disruption. Right: vortices form in the core as high-angular-momentum debris continues to accrete, winding up and amplifying the field. [Adapted from Guillochon McCourt 2017]What About Magnetic Fields?Magnetic fields are expected to exist in the majority of stars. Though these fields dont dominate the energy budget of a star the magnetic pressure is a million times weaker than the gas pressure in the Suns interior, for example they are the drivers of interesting activity, like the prominences and flares of our Sun.Given this, we can wonder what role stars magnetic fields might play when the stars are torn apart in tidal disruption events. Do the fields change what we observe? Are they dispersed during the disruption, or can they be amplified? Might they even be responsible for launching jets of matter from the black hole after the disruption?Star vs. Black HoleIn a recent study, James Guillochon (Harvard-Smithsonian Center for Astrophysics) and Michael McCourt (Hubble Fellow at UC Santa Barbara) have tackled these questions by performing the first simulations of tidal disruptions of stars that include magnetic fields.In their simulations, Guillochon and McCourt evolve a solar-mass star that passes close to a million-solar-mass black hole. Their simulations explore different magnetic field configurations for the star, and they consider both what happens when the star barely grazes the black hole and is only partially disrupted, as well as what happens when the black hole tears the star apart

  14. Hydrodynamic Simulations of the Inner Accretion Flow of Sagittarius A* Fueled By Stellar Winds

    Ressler, S. M.; Quataert, E.; Stone, J. M.

    2018-05-01

    We present Athena++ grid-based, hydrodynamic simulations of accretion onto Sagittarius A* via the stellar winds of the ˜30 Wolf-Rayet stars within the central parsec of the galactic center. These simulations span ˜ 4 orders of magnitude in radius, reaching all the way down to 300 gravitational radii of the black hole, ˜32 times further in than in previous work. We reproduce reasonably well the diffuse thermal X-ray emission observed by Chandra in the central parsec. The resulting accretion flow at small radii is a superposition of two components: 1) a moderately unbound, sub-Keplerian, thick, pressure-supported disc that is at most (but not all) times aligned with the clockwise stellar disc, and 2) a bound, low-angular momentum inflow that proceeds primarily along the southern pole of the disc. We interpret this structure as a natural consequence of a few of the innermost stellar winds dominating accretion, which produces a flow with a broad distribution of angular momentum. Including the star S2 in the simulation has a negligible effect on the flow structure. Extrapolating our results from simulations with different inner radii, we find an accretion rate of ˜ a few × 10-8M⊙/yr at the horizon scale, consistent with constraints based on modeling the observed emission of Sgr A*. The flow structure found here can be used as more realistic initial conditions for horizon scale simulations of Sgr A*.

  15. Unusual Metals in Galactic Center Stars

    Hensley, Kerry

    2018-03-01

    Far from the galactic suburbs where the Sun resides, a cluster of stars in the nucleus of the Milky Way orbits a supermassive black hole. Can chemical abundance measurements help us understand the formation history of the galactic center nuclear star cluster?Studying Stellar PopulationsMetallicity distributions for stars in the inner two degrees of the Milky Way (blue) and the central parsec (orange). [Do et al. 2018]While many galaxies host nuclear star clusters, most are too distant for us to study in detail; only in the Milky Way can we resolve individual stars within one parsec of a supermassive black hole. The nucleus of our galaxy is an exotic and dangerous place, and its not yet clear how these stars came to be where they are were they siphoned off from other parts of the galaxy, or did they form in place, in an environment rocked by tidal forces?Studying the chemical abundances of stars provides a way to separate distinct stellar populations and discern when and where these stars formed. Previous studies using medium-resolution spectroscopy have revealed that many stars within the central parsec of our galaxy have very high metallicities possibly higher than any other region of the Milky Way. Can high-resolution spectroscopy tell us more about this unusual population of stars?Spectral Lines on DisplayTuan Do (University of California, Los Angeles, Galactic Center Group) and collaborators performed high-resolution spectroscopic observations of two late-type giant starslocated half a parsec from the Milky Ways supermassive black hole.Comparison of the observed spectra of the two galactic center stars (black) with synthetic spectra with low (blue) and high (orange) [Sc/Fe] values. Click to enlarge. [Do et al. 2018]In order to constrain the metallicities of these stars, Do and collaborators compared the observed spectra to a grid of synthetic spectra and used a spectral synthesis technique to determine the abundances of individual elements. They found that

  16. 75 FR 11530 - Crystal Lake Wind III, LLC, et al.; Notice of Effectiveness of Exempt Wholesale Generator Status

    2010-03-11

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Crystal Lake Wind III, LLC, et al.; Notice of Effectiveness of Exempt Wholesale Generator Status March 4, 2010. Docket Nos. Crystal Lake Wind III, LLC EG10-6-000 GardenGarden Wind, LLC EG10-7-000 Star Point Wind Project LLC EG10-8-000...

  17. Wind energy in France: impossible?

    Marie-Josette, R.

    2005-01-01

    Since the end of 2004, the European Union is the first producer of wind energy in the world (34205 MW), far beyond the USA (6740 MW) and India (2110 MW). Three countries are in the pole position: Germany (16629 MW), Spain (8263 MW) and Denmark (3117 MW). On the other hand, despite a voluntarist policy, the other countries encounter administrative and local difficulties in the development of wind energy. This is the case with France which has the second biggest potential wind resource of Europe, behind the UK. The French situation is explained by its centralized energy system, by the priority given to nuclear power, by important wind variations, and by a bad image of wind turbines in general (aesthetic, environmental). This situation should change in the future with the scheduling of pluri-annual investments, with adapted tariffs and with improved administrative procedures. (J.S.)

  18. Probabilistic Design of Wind Turbines

    Toft, Henrik Stensgaard

    During the last decades, wind turbines have been continuously developed with the aim of maximizing the life cycle benefits (production of electricity) minus the costs of planning, materials, installation, operation & maintenance as well as possible failure. In order to continue this development...... turbines and the central topics considered are statistical load extrapolation of extreme loads during operation and reliability assessment of wind turbine blades. Wind turbines differ from most civil engineering structures by having a control system which highly influences the loading. In the literature......, methods for estimating the extreme load-effects on a wind turbine during operation, where the control system is active, have been proposed. But these methods and thereby the estimated loads are often subjected to a significant uncertainty which influences the reliability of the wind turbine...

  19. Dust in the Quasar Wind (Artist Concept)

    2007-01-01

    Dusty grains -- including tiny specks of the minerals found in the gemstones peridot, sapphires and rubies -- can be seen blowing in the winds of a quasar, or active black hole, in this artist's concept. The quasar is at the center of a distant galaxy. Astronomers using NASA's Spitzer Space Telescope found evidence that such quasar winds might have forged these dusty particles in the very early universe. The findings are another clue in an ongoing cosmic mystery: where did all the dust in our young universe come from? Dust is crucial for efficient star formation as it allows the giant clouds where stars are born to cool quickly and collapse into new stars. Once a star has formed, dust is also needed to make planets and living creatures. Dust has been seen as far back as when the universe was less than a tenth of its current age, but how did it get there? Most dust in our current epoch forms in the winds of evolved stars that did not exist when the universe was young. Theorists had predicted that winds from quasars growing in the centers of distant galaxies might be a source of this dust. While the environment close to a quasar is too hot for large molecules like dust grains to survive, dust has been found in the cooler, outer regions. Astronomers now have evidence that dust is created in these outer winds. Using Spitzer's infrared spectrograph instrument, scientists found a wealth of dust grains in a quasar called PG2112+059 located at the center of a galaxy 8 billion light-years away. The grains - including corundum (sapphires and rubies); forsterite (peridot); and periclase (naturally occurring in marble) - are not typically found in galaxies without quasars, suggesting they might have been freshly formed in the quasar's winds.

  20. Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation

    Peters, Thomas; /ZAH, Heidelberg; Klessen, Ralf S.; /ZAH, Heidelberg /KIPAC, Menlo Park; Mac Low, Mordecai-Mark; /Amer. Museum Natural Hist.; Banerjee, Robi; /ZAH, Heidelberg

    2010-08-25

    Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

  1. Egyptian "Star Clocks"

    Symons, Sarah

    Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

  2. MAGNETIC FIELDS OF STARS

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

    2008-01-01

    Now it is known about 1212 stars of the main sequence and giants (from them 610 stars - it is chemically peculiarity (CP) stars) for which direct measurements of magnetic fields were spent (Bychkov et al.,2008). Let's consider, what representations were generated about magnetic fields (MT) of stars on the basis of available observations data.

  3. Wind power in modern power systems

    Chen, Zhe

    2013-01-01

    In recent years, wind power is experiencing a rapid growth, and large-scale wind turbines/wind farms have been developed and connected to power systems. However, the traditional power system generation units are centralized located synchronous generators with different characteristics compared...... with wind turbines. This paper presents an overview of the issues about integrating large-scale wind power plants into modern power systems. Firstly, grid codes are introduced. Then, the main technical problems and challenges are presented. Finally, some possible technical solutions are discussed....

  4. Hydrogen deficient stars and related objects

    Hunger, K.; Schoenberner, D.; Kameswara Rao, N.

    1986-01-01

    The central and most startling problem in the field of helium stars is how extreme helium stars are formed and how a star of one solar mass may get rid of all its original hydrogen. A few opposed hypotheses are known, but until now none of them have been very convincing. One of the aims of this book is to explore the various paths which may lead to a solution of the above problems, both theoretically and by means of new methods of observation. One of the points discussed, therefore, is whether the Hubble Space Telescope can be used to this end. (Auth.)

  5. SALT Spectroscopy of Evolved Massive Stars

    Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

    2017-06-01

    Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fiber-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.

  6. Chandra Observations of Neutron Stars: An Overview

    Weisskopf, Martin C.; Karovska, M.; Pavlov, G. G.; Zavlin, V. E.; Clarke, Tracy

    2006-01-01

    We present a brief review of Chandra X-ray Observatory observations of neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present an admittedly biased and overly brief overview of these observations, highlighting some new discoveries made possible by the Observatory's unique capabilities. We also include our analysis of recent multiwavelength observations of the putative pulsar and its pulsar-wind nebula in the IC 443 SNR.

  7. Hydrodynamic ejection of bipolar flows from objects undergoing disk accretion: T Tauri stars, massive pre-main-sequence objects, and cataclysmic variables

    Torbett, M.V.

    1984-01-01

    A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction βapprox.10 -2 to 10 -3 of the accreted mass. These winds are driven by a mechanism that accelerates the flow perpendicular to the plane of the disk and can therefore account for the bipolar geometry of the mass loss observed near young stars. The mass loss contained in these winds is comparable to that inferred for young stars. Thus, disk accretion-driven winds may constitute the T Tauri phase of stellar evolution. This mechanism is generally applicable, and thus massive pre-main-sequence objects as well as cataclysmic variables at times of enhanced accretion are predicted to eject bipolar outflows as well. Unmagnetized accreting neutron stas are also expected to eject bipolar flows. Since this mechanism requires stellar surfaces, however, it will not operate in disk accretion onto black holes

  8. Grid Integration of Offshore Wind | Wind | NREL

    Grid Integration of Offshore Wind Grid Integration of Offshore Wind Much can be learned from the existing land-based integration research for handling the variability and uncertainty of the wind resource Arklow Bank offshore wind park consists of seven GE Wind 3.6-MW wind turbines. Integration and

  9. New white dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 12

    Kepler, S. O.; Pelisoli, Ingrid; Koester, Detlev; Ourique, Gustavo; Romero, Alejandra Daniela; Reindl, Nicole; Kleinman, Scot J.; Eisenstein, Daniel J.; Valois, A. Dean M.; Amaral, Larissa A.

    2015-01-01

    We report the discovery of 6576 new spectroscopically confirmed white dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 12. We obtain Teff, log g and mass for hydrogen atmospherewhite dwarf stars (DAs) and helium atmospherewhite dwarf stars (DBs), estimate the calcium/helium abundances for the white dwarf stars with metallic lines (DZs) and carbon/helium for carbon-dominated spectra (DQs). We found one central star of a planetary nebula, one ultracompact helium binary (AM ...

  10. One of the most massive stars in the Galaxy may have formed in isolation

    Oskinova, L. M.; Steinke, M.; Hamann, W. -R.; Sander, A.; Todt, H.; Liermann, A.

    2013-01-01

    Very massive stars, 100 times heavier than the sun, are rare. It is not yet known whether such stars can form in isolation or only in star clusters. The answer to this question is of fundamental importance. The central region of our Galaxy is ideal for investigating very massive stars and clusters located in the same environment. We used archival infrared images to investigate the surroundings of apparently isolated massive stars presently known in the Galactic Center. We find that two such i...

  11. Wind Energy

    Beurskens, H.J.M. [SET Analysis, Kievitlaan 26, 1742 AD Schagen (Netherlands); Brand, A.J. [Energy research Centre of the Netherlands ECN, Unit Wind Energy, P.O. Box 1, 1755 ZG Petten (Netherlands)

    2013-02-15

    Over the years, wind energy has become a major source of renewable energy worldwide. The present chapter addresses the wind resource, which is available for exploitation for large-scale electricity production, and its specific physical properties. Furthermore, the technical options available to convert the energy of the air flow into mechanical energy and electricity are described. Specific problems of large-scale integration of wind energy into the grid as well as the present and future market developments are described in this chapter. Finally, environmental aspects are discussed briefly.

  12. Multi-Wavelength Polarimetry of Isolated Neutron Stars

    Roberto P. Mignani

    2018-03-01

    Full Text Available Isolated neutron stars are known to be endowed with extreme magnetic fields, whose maximum intensity ranges from 10 12 – 10 15 G, which permeates their magnetospheres. Their surrounding environment is also strongly magnetized, especially in the compact nebulae powered by the relativistic wind from young neutron stars. The radiation from isolated neutron stars and their surrounding nebulae is, thus, supposed to bring a strong polarization signature. Measuring the neutron star polarization brings important information about the properties of their magnetosphere and of their highly magnetized environment. Being the most numerous class of isolated neutron stars, polarization measurements have been traditionally carried out for radio pulsars, hence in the radio band. In this review, I summarize multi-wavelength linear polarization measurements obtained at wavelengths other than radio both for pulsars and other types of isolated neutron stars and outline future perspectives with the upcoming observing facilities.

  13. Pulsar-irradiated stars in dense globular clusters

    Tavani, Marco

    1992-01-01

    We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

  14. Hydrodynamics and stellar winds an introduction

    Maciel, Walter J

    2014-01-01

    Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.

  15. Neutron Stars and NuSTAR

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses

  16. NECESSARY CONDITIONS FOR SHORT GAMMA-RAY BURST PRODUCTION IN BINARY NEUTRON STAR MERGERS

    Murguia-Berthier, Ariadna; Montes, Gabriela; Ramirez-Ruiz, Enrico; De Colle, Fabio; Lee, William H.

    2014-01-01

    The central engine of short gamma-ray bursts (sGRBs) is hidden from direct view, operating at a scale much smaller than that probed by the emitted radiation. Thus we must infer its origin not only with respect to the formation of the trigger—the actual astrophysical configuration that is capable of powering an sGRB—but also from the consequences that follow from the various evolutionary pathways that may be involved in producing it. Considering binary neutron star mergers we critically evaluate, analytically and through numerical simulations, whether the neutrino-driven wind produced by the newly formed hyper-massive neutron star can allow the collimated relativistic outflow that follows its collapse to actually produce an sGRB or not. Upon comparison with the observed sGRB duration distribution, we find that collapse cannot be significantly delayed (≤100 ms) before the outflow is choked, thus limiting the possibility that long-lived hyper-massive remnants can account for these events. In the case of successful breakthrough of the jet through the neutrino-driven wind, the energy stored in the cocoon could contribute to the precursor and extended emission observed in sGRBs

  17. Massive stars evolution with mass-loss. 20-100 M(sun) models

    Chiosi, C; Sreenivasan, S R [Calgary Univ., Alberta (Canada). Dept. of Physics; Nasi, E [Padua Univ. (Italy). Istituto di Astronomia

    1978-02-01

    The evolution of stars with initial masses 20, 30, 40, 60, 80, 100 M(sun) and Population I chemical composition (X = 0.700, Z = 0.02) is calculated, taking into account mass-loss due to stellar winds, from the main sequence up to the early stages of central He-burning. This study incorporates mass-loss rates predicted by the theory of Castor et al. (1975) for the early type phases and a novel way of treating mass-loss rates due to acoustic energy flux driven winds in the later stages analogous to the work of Fusi-Pecci and Renzini (1975a). The results are presented in terms of evolutionary tracks, isochrones, loci of constant mass-loss rates and loci of constant mass in the HR diagram. The effects of mass-loss on the internal structure of the models as well as on the occurrence of semiconvection are also investigated. A detailed comparison of the theoretical predictions and observational results is made and possible implications for O, Of, Wolf-Rayet stars and red supergiants are brought out.

  18. World Wind

    National Aeronautics and Space Administration — World Wind allows any user to zoom from satellite altitude into any place on Earth, leveraging high resolution LandSat imagery and SRTM elevation data to experience...

  19. Wind power

    2009-01-01

    At the end of 2008,the European wind power capacity had risen to 65,247 MW which is a 15,1% increase on 2007. The financial crisis does not appear to have any real consequences of the wind power sector's activity in 2008. At the end of 2008 the European Union accommodated 53,9% of the world's wind power capacity. The top ten countries in terms of installed wind capacities are: 1) Usa with 25,388 MW, 2) Germany with 23,903 MW, 3) Spain with 16,740 MW, 4) China with 12,200 MW, 5) India with 9,645 MW, 6) Italy with 3,736 MW, 7) France with 3,542 MW, 8) U.K. with 3,406 MW, 9) Denmark with 3,166 MW and 10) Portugal with 2,862 MW. (A.C.)

  20. Quasar Winds as Dust Factories at High Redshift

    Elvis, Martin; Marengo, Massimo; Karovska, Margarita

    2003-01-01

    Winds from AGN and quasars will form large amounts of dust, as the cool gas in these winds passes through the (pressure, temperature) region where dust is formed in AGB stars. Conditions in the gas are benign to dust at these radii. As a result quasar winds may be a major source of dust at high redshifts, obviating a difficulty with current observations, and requiring far less dust to exist at early epochs.

  1. Wind power

    1979-01-01

    This publication describes some of the technical, economic, safety and institutional considerations involved in the selection, installation and evaluation of a wind generation system. This information is presented, where possible, in practical, non-technical terms. The first four sections provide background information, theory, and general knowledge, while the remaining six sections are of a more specific nature to assist the prospective owner of a wind generator in his calculations and selections. Meteorological information is provided relating to the wind regime in Nova Scotia. The section on cost analysis discusses some of the factors and considerations which must be examined in order to provide a logical comparison between the alternatives of electricity produced from other sources. The final two sections are brief summaries of the regulations and hazards pertaining to the use of wind generators. The cost of wind-generated electricity is high compared to present Nova Scotia Power Corporation rates, even on Sable Island, Nova Scotia's highest wind area. However, it may be observed that Sable Island is one of the areas of Nova Scotia which is not presently supplied through the power grid and, particularly if there was a significant increase in the price of diesel oil, wind-generated electricity may well be the most economical alternative in that area. Generally speaking, however, where a consumer can purchase electricity at the normal domestic rate, wind generators are not economical, and they will not become economical unless there is a great reduction in their cost, an great increase in electricity rates, or both. Includes glossary. 23 figs., 11 tabs.

  2. Modelación en coordenadas de fase del transformador monofásico con derivación central en el secundario; Modeling in phase-coordinates of the single-phase transformer with center tap in the secondary winding

    Ignacio - Pérez Abril

    2013-10-01

    Full Text Available Existe un modelo en la literatura para representar el transformador monofásico con derivación central en el secundario. No obstante, dicho modelo representa toda la impedancia del transformador en el secundario, lo que difiere de la realidad. La distribución de la impedancia del transformador entre el primario y ambas secciones del secundario tiene una gran influencia en la magnitud de la corriente de cortocircuito de una fase a la derivación central del secundario. Esta corriente supera ampliamente la corriente de cortocircuito de fase a fase en transformadores con devanados entrelazados. El presente trabajo desarrolla el modelo en coordenadas de fase del transformador monofásico con derivación central en el secundario. El modelo desarrollado se prueba con varios ejemplos que demuestran la conveniencia de emplear el modelo presentado para analizar la carga desigual de ambas secciones del devanado secundario o el cortocircuito de una fase a la derivación central del secundario.There exists a model in the literature to representing the single-phase transformer with center tap in the secondary winding. However, this model represents all the impedance of the transformer in the secondary winding, which differs from practice. The distribution of the impedance between primary and the both sections of the secondary winding has a great influence over the magnitude of the short circuit current from a phase to the center tap. This current is much greater than the phase to phase short circuit current in transformers with interlaced windings. The present paper develops a model in phase coordinates for the single-phase transformer with center tap in the secondary winding. The developed model is tested with several examples that shown the convenience of the use of the presented model to analyze the unequal load in both sections of the secondary or the short circuit from a phase to the center tap of the secondary.

  3. Coastal Ohio Wind Project

    Gorsevski, Peter [Bowling Green State Univ., OH (United States); Afjeh, Abdollah [Univ. of Toledo, OH (United States); Jamali, Mohsin [Univ. of Toledo, OH (United States); Bingman, Verner [Bowling Green State Univ., OH (United States)

    2014-04-04

    using different evaluation criteria, and an Android application for collection of field data using mobile and tablet devices . In summary, the simulations of two- and three-blade wind turbines suggested that two-bladed machines could produce comparable annual energy as the three-blade wind turbines but have a lighter tower top weight, which leads to lower cost of energy. In addition, the two-blade rotor configuration potentially costs 20% less than a three blade configuration that produces the same power at the same site. The cost model analysis predicted a potential cost savings of approximately 15% for offshore two-blade wind turbines. The foundation design for a wind turbine in Lake Erie is likely to be driven by ice loads based on the currently available ice data and ice mechanics models. Hence, for Lake Eire, the cost savings will be somewhat smaller than the other lakes in the Great Lakes. Considering the size of cranes and vessels currently available in the Great Lakes, the cost optimal wind turbine size should be 3 MW, not larger. The surveillance data from different monitoring systems suggested that bird and bat passage rates per hour were comparable during heavy migrations in both spring and fall seasons while passage rates were significantly correlated to wind directions and wind speeds. The altitude of migration was higher during heavy migrations and higher over water relative to over land. Notable portions of migration on some spring nights occurred parallel the shoreline, often moving perpendicular to southern winds. The birds approaching the Western basin have a higher propensity to cross than birds approaching the Central basin of Lake Erie and as such offshore turbine development might be a better option further east towards Cleveland than in the Western basin. The high stopover density was more strongly associated with migration volume the following night rather than the preceding night. The processed mean scalar wind speeds with temporal resolutions

  4. Emission Lines in the Near-infrared Spectra of the Infrared Quintuplet Stars in the Galactic Center

    Najarro, F. [Departamento de Astrofísica, Centro de Astrobiología (CSIC-INTA), Ctra. Torrejón a Ajalvir km 4, E-28850 Torrejón de Ardoz (Spain); Geballe, T. R. [Gemini Observatory, 670 North A’ohoku Place, Hilo, HI 96720 (United States); Figer, D. F. [Center for Detectors, Rochester Institute of Technology, 74 Lomb Memorial Drive, Rochester, NY 14623 (United States); Fuente, D. de la [Instituto de Astronomía, Unidad Académica en Ensenada, Universidad Nacional Autónoma de México, Ensenada 22860, México (Mexico)

    2017-08-20

    We report the detection of a number of emission lines in the 1.0–2.4 μ m spectra of four of the five bright-infrared dust-embedded stars at the center of the Galactic center’s (GC) Quintuplet Cluster. Spectroscopy of the central stars of these objects is hampered not only by the large interstellar extinction that obscures all of the objects in the GC, but also by the large amounts of warm circumstellar dust surrounding each of the five stars. The pinwheel morphologies of the dust observed previously around two of them are indicative of Wolf–Rayet colliding wind binaries; however, infrared spectra of each of the five have until now revealed only dust continua steeply rising to long wavelengths and absorption lines and bands from interstellar gas and dust. The emission lines detected, from ionized carbon and from helium, are broad and confirm that the objects are dusty late-type carbon Wolf–Rayet stars.

  5. High-energy X-ray imaging of the pulsar wind nebula MSH 15-52: constraints on particle acceleration and transport

    An, Hongjun; Madsen, Kristin K.; Reynolds, Stephen P.

    2014-01-01

    We present the first images of the pulsar wind nebula (PWN) MSH 15−52 in the hard X-ray band (8 keV), as measured with the Nuclear Spectroscopic Telescope Array (NuSTAR). Overall, the morphology of the PWN as measured by NuSTAR in the 3–7 keV band is similar to that seen in Chandra high-resolutio......We present the first images of the pulsar wind nebula (PWN) MSH 15−52 in the hard X-ray band (8 keV), as measured with the Nuclear Spectroscopic Telescope Array (NuSTAR). Overall, the morphology of the PWN as measured by NuSTAR in the 3–7 keV band is similar to that seen in Chandra high...... of the PWN softens away from the central pulsar B1509−58, and that there exists a roughly sinusoidal variation of spectral hardness in the azimuthal direction. We discuss the results using particle flow models.We find non-monotonic structure in the variation with distance of spectral hardness within 50...... of the pulsar moving in the jet direction, which may imply particle and magnetic-field compression by magnetic hoop stress as previously suggested for this source. We also present two-dimensional maps of spectral parameters and find an interesting shell-like structure in the NH map.We discuss possible origins...

  6. MMT HYPERVELOCITY STAR SURVEY. II. FIVE NEW UNBOUND STARS

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J., E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

    2012-05-20

    We present the discovery of five new unbound hypervelocity stars (HVSs) in the outer Milky Way halo. Using a conservative estimate of Galactic escape velocity, our targeted spectroscopic survey has now identified 16 unbound HVSs as well as a comparable number of HVSs ejected on bound trajectories. A Galactic center origin for the HVSs is supported by their unbound velocities, the observed number of unbound stars, their stellar nature, their ejection time distribution, and their Galactic latitude and longitude distribution. Other proposed origins for the unbound HVSs, such as runaway ejections from the disk or dwarf galaxy tidal debris, cannot be reconciled with the observations. An intriguing result is the spatial anisotropy of HVSs on the sky, which possibly reflects an anisotropic potential in the central 10-100 pc region of the Galaxy. Further progress requires measurement of the spatial distribution of HVSs over the southern sky. Our survey also identifies seven B supergiants associated with known star-forming galaxies; the absence of B supergiants elsewhere in the survey implies there are no new star-forming galaxies in our survey footprint to a depth of 1-2 Mpc.

  7. X-rays from stars

    Güdel, Manuel

    2004-07-01

    Spectroscopic studies available from Chandra and XMM-Newton play a pivotal part in the understanding of the physical processes in stellar (magnetic and non-magnetic) atmospheres. It is now routinely possible to derive densities and to study the influence of ultraviolet radiation fields, both of which can be used to infer the geometry of the radiating sources. Line profiles provide important information on bulk mass motions and attenuation by neutral matter, e.g. in stellar winds. The increased sensitivity has revealed new types of X-ray sources in systems that were thought to be unlikely places for X-rays: flaring brown dwarfs, including rather old, non-accreting objects, and terminal shocks in jets of young stars are important examples. New clues concerning the role of stellar high-energy processes in the modification of the stellar environment (ionization, spallation, etc.) contribute significantly to our understanding of the "astro-ecology" in forming planetary systems. Technological limitations are evident. The spectral resolution has not reached the level where bulk mass motions in cool stars become easily measurable. Higher resolution would also be important to perform X-ray "Doppler imaging" in order to reconstruct the 3-D distribution of the X-ray sources around a rotating star. Higher sensitivity will be required to perform high-resolution spectroscopy of weak sources such as brown dwarfs or embedded pre-main-sequence sources. A new generation of satellites such as Constellation-X or XEUS should pursue these goals.

  8. Influence of orographically steered winds on Mutsu Bay surface currents

    Yamaguchi, Satoshi; Kawamura, Hiroshi

    2005-09-01

    Effects of spatially dependent sea surface wind field on currents in Mutsu Bay, which is located at the northern end of Japanese Honshu Island, are investigated using winds derived from synthetic aperture radar (SAR) images and a numerical model. A characteristic wind pattern over the bay was evidenced from analysis of 118 SAR images and coincided with in situ observations. Wind is topographically steered with easterly winds entering the bay through the terrestrial gap and stronger wind blowing over the central water toward its mouth. Nearshore winds are weaker due to terrestrial blockages. Using the Princeton Ocean Model, we investigated currents forced by the observed spatially dependent wind field. The predicted current pattern agrees well with available observations. For a uniform wind field of equal magnitude and average direction, the circulation pattern departs from observations demonstrating that vorticity input due to spatially dependent wind stress is essential in generation of the wind-driven current in Mutsu Bay.

  9. STAR FORMATION IN 30 DORADUS

    De Marchi, Guido; Spezzi, Loredana; Sirianni, Marco; Andersen, Morten; Paresce, Francesco; Panagia, Nino; Mutchler, Max; Whitmore, Bradley C.; Bond, Howard; Beccari, Giacomo; Balick, Bruce; Dopita, Michael A.; Frogel, Jay A.; Calzetti, Daniela; Marcella Carollo, C.; Disney, Michael J.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.

    2011-01-01

    Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4σ) Hα excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than ∼4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to ∼30 Myr, with a median age of ∼12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136.

  10. WIND VARIABILITY IN BZ CAMELOPARDALIS

    Honeycutt, R. K.; Kafka, S.; Robertson, J. W.

    2013-01-01

    Sequences of spectra of the nova-like cataclysmic variable (CV) BZ Cam were acquired on nine nights in 2005-2006 in order to study the time development of episodes of wind activity known to occur frequently in this star. We confirm the results of Ringwald and Naylor that the P-Cygni absorption components of the lines mostly evolve from higher expansion velocity to lower velocity as an episode progresses. We also commonly find blueshifted emission components in the Hα line profile, whose velocities and durations strongly suggest that they are also due to the wind. Curiously, Ringwald and Naylor reported common occurrences of redshifted Hα emission components in their BZ Cam spectra. We have attributed these emission components in Hα to occasions when gas concentrations in the bipolar wind (both front side and back side) become manifested as emission lines as they move beyond the disk's outer edge. We also suggest, based on changes in the P-Cygni profiles during an episode, that the progression from larger to smaller expansion velocities is due to the higher velocity portions of a wind concentration moving beyond the edge of the continuum light of the disk first, leaving a net redward shift of the remaining absorption profile. We derive a new orbital ephemeris for BZ Cam, using the radial velocity of the core of the He I λ5876 line, finding P = 0.15353(4). Using this period, the wind episodes in BZ Cam are found to be concentrated near the inferior conjunction of the emission line source. This result helps confirm that the winds in nova-like CVs are often phase dependent, in spite of the puzzling implication that such winds lack axisymmetry. We argue that the radiation-driven wind in BZ Cam receives an initial boost by acting on gas that has been lifted above the disk by the interaction of the accretion stream with the disk, thereby imposing flickering timescales onto the wind events, as well as leading to an orbital modulation of the wind due to the non

  11. Giant CP stars

    Loden, L.O.; Sundman, A.

    1989-01-01

    This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary 'non giant' CP stars. There is no clear confirmation of a higher luminosity for 'CP giants', than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members. (author). 50 refs., 5 tabs., 3 figs

  12. Investigating the Magnetospheres of Rapidly Rotating B-type Stars

    Fletcher, C. L.; Petit, V.; Nazé, Y.; Wade, G. A.; Townsend, R. H.; Owocki, S. P.; Cohen, D. H.; David-Uraz, A.; Shultz, M.

    2017-11-01

    Recent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

  13. A SPECTROSCOPIC STUDY OF BLUE SUPERGIANT STARS IN THE SCULPTOR GALAXY NGC 55: CHEMICAL EVOLUTION AND DISTANCE

    Kudritzki, R. P.; Ho, I.-T.; Bresolin, F. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Castro, N. [Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109 (United States); Urbaneja, M. A.; Przybilla, N. [Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstr. 25/8, A-6020 Innsbruck (Austria); Gieren, W.; Pietrzyński, G. [Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción (Chile)

    2016-10-01

    Low-resolution (4.5–5 Å) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities, and metallicities (from iron peak and α -elements). A metallicity gradient of −0.22 ± 0.06 dex/ R {sub 25} is detected. The central metallicity on a logarithmic scale relative to the Sun is [ Z ] = −0.37 ± 0.03. A chemical evolution model using the observed distribution of column densities of the stellar and interstellar medium gas mass reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extraplanar metal-poor H ii regions detected in previous work 1.13 to 2.22 kpc above the galactic plane are ionized by massive stars formed in situ outside the disk. For a subsample of supergiants, for which Hubble Space Telescope photometry is available, the flux-weighted gravity–luminosity relationship is used to determine a distance modulus of 26.85 ± 0.10 mag.

  14. THE Be STAR SPECTRA (BeSS) DATABASE

    Neiner, C.; De Batz, B.; Cochard, F.; Floquet, M.; Mekkas, A.; Desnoux, V.

    2011-01-01

    Be stars vary on many timescales, from hours to decades. A long time base of observations to analyze certain phenomena in these stars is therefore necessary. Collecting all existing and future Be star spectra into one database has thus emerged as an important tool for the Be star community. Moreover, for statistical studies, it is useful to have centralized information on all known Be stars via an up-to-date catalog. These two goals are what the Be Star Spectra (BeSS, http://basebe.obspm.fr) database proposes to achieve. The database contains an as-complete-as-possible catalog of known Be stars with stellar parameters, as well as spectra of Be stars from all origins (any wavelength, any epoch, any resolution, etc.). It currently contains over 54,000 spectra of more than 600 different Be stars among the ∼2000 Be stars in the catalog. A user can access and query this database to retrieve information on Be stars or spectra. Registered members can also upload spectra to enrich the database. Spectra obtained by professional as well as amateur astronomers are individually validated in terms of format and science before being included in BeSS. In this paper, we present the database itself as well as examples of the use of BeSS data in terms of statistics and the study of individual stars.

  15. Continuous-time quantum walks on star graphs

    Salimi, S.

    2009-01-01

    In this paper, we investigate continuous-time quantum walk on star graphs. It is shown that quantum central limit theorem for a continuous-time quantum walk on star graphs for N-fold star power graph, which are invariant under the quantum component of adjacency matrix, converges to continuous-time quantum walk on K 2 graphs (complete graph with two vertices) and the probability of observing walk tends to the uniform distribution.

  16. Rates of star formation

    Larson, R.B.

    1977-01-01

    It is illustrated that a theoretical understanding of the formation and evolution of galaxies depends on an understanding of star formation, and especially of the factors influencing the rate of star formation. Some of the theoretical problems of star formation in galaxies, some approaches that have been considered in models of galaxy evolution, and some possible observational tests that may help to clarify which processes or models are most relevant are reviewed. The material is presented under the following headings: power-law models for star formation, star formation processes (conditions required, ways of achieving these conditions), observational indications and tests, and measures of star formation rates in galaxies. 49 references

  17. Energy production in stars

    Bethe, Hans.

    1977-01-01

    Energy in stars is released partly by gravitation, partly by nuclear reactions. For ordinary stars like our sun, nuclear reactions predominate. However, at the end of the life of a star very large amounts of energy are released by gravitational collapse; this can amount to as much as 10 times the total energy released nuclear reactions. The rotational energy of pulsars is a small remnant of the energy of gravitation. The end stage of small stars is generally a white dwarf, of heavy stars a neutron star of possibly a black hole

  18. Wind turbine/generator set and method of making same

    Bevington, Christopher M.; Bywaters, Garrett L.; Coleman, Clint C.; Costin, Daniel P.; Danforth, William L.; Lynch, Jonathan A.; Rolland, Robert H.

    2013-06-04

    A wind turbine comprising an electrical generator that includes a rotor assembly. A wind rotor that includes a wind rotor hub is directly coupled to the rotor assembly via a simplified connection. The wind rotor and generator rotor assembly are rotatably mounted on a central spindle via a bearing assembly. The wind rotor hub includes an opening having a diameter larger than the outside diameter of the central spindle adjacent the bearing assembly so as to allow access to the bearing assembly from a cavity inside the wind rotor hub. The spindle is attached to a turret supported by a tower. Each of the spindle, turret and tower has an interior cavity that permits personnel to traverse therethrough to the cavity of the wind rotor hub. The wind turbine further includes a frictional braking system for slowing, stopping or keeping stopped the rotation of the wind rotor and rotor assembly.

  19. Evolution of newborn neutron stars: role of quark matter nucleation

    Bombaci, Ignazio; Logoteta, Domenico; Providencia, Constança; Vidaña, Isaac

    2011-01-01

    A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. We study the quark deconfinement phase transition in cold (T = 0) and hot β-stable hadronic matter. Assuming a first order phase transition, we calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) is metastable to the conversion to a quark star (QS) (i.e. hybrid star or strange star). We introduce the concept of critical mass M cr for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass M cr could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars.

  20. The first stars: CEMP-no stars and signatures of spinstars

    Maeder, André; Meynet, Georges; Chiappini, Cristina

    2015-04-01

    Aims: The CEMP-no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s- and r-elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne-Na, and Mg-Al abundances. Methods: We compare the observed abundances to the nucleosynthetic predictions of AGB models and of models of rotating massive stars with internal mixing and mass loss. We also analyze the different behaviors of α- and CNO-elements, as well the abundances of elements involved in the Ne-Na and Mg-Al cycles. Results: We show that CEMP-no stars exhibit products of He-burning that have gone through partial mixing and processing by the CNO cycle, producing low 12C/13C and a broad variety of [C/N] and [O/N] ratios. From a 12C/13C vs. [C/N] diagram, we conclude that neither the yields of AGB stars (in binaries or not) nor the yields of classic supernovae can fully account for the observed CNO abundances in CEMP-no stars. Better agreement is obtained once the chemical contribution by stellar winds of fast-rotating massive stars is taken into account, where partial mixing takes place, leading to various amounts of CNO being ejected. The [(C+N+O)/H] ratios of CEMP-no stars vary linearly with [Fe/H] above [Fe/H] = -4.0 indicating primary behavior by (C+N+O). Below [Fe/H] = -4.0, [(C+N+O)/H] is almost constant as a function of [Fe/H], implying very high [(C+N+O)/Fe] ratios up to 4 dex. In view of the timescales, such abundance ratios reflect more individual nucleosynthetic properties, rather than an average chemical evolution. The high [(C+N+O)/Fe] ratios (as well as the high [(C+N+O)/α-elements]) imply that stellar winds from partially mixed stars were the main source of these excesses of heavy elements now observed in CEMP-no stars. The ranges covered by the variations of [Na/Fe], [Mg/Fe], and [Al/Fe] are much broader than for the α-elements (with an atomic mass number above 24) and are comparable to the wide ranges covered

  1. Regular Generalized Star Star closed sets in Bitopological Spaces

    K. Kannan; D. Narasimhan; K. Chandrasekhara Rao; R. Ravikumar

    2011-01-01

    The aim of this paper is to introduce the concepts of τ1τ2-regular generalized star star closed sets , τ1τ2-regular generalized star star open sets and study their basic properties in bitopological spaces.

  2. Evolution of rotating stars. III. Predicted surface rotation velocities for stars which conserve total angular momentum

    Endal, A.S.; Sofia, S.

    1979-01-01

    Predicted surface rotation velocities are presented for Population I stars at 10, 7, 5, 3, and 1.5M/sub sun/. The surface velocities have been computed for three different cases of angular momentum redistribution: no radial redistribution (rotation on decoupled shells), complete redistribution (rigid-body rotation), and partial redistribution as predicted by detailed consideration of circulation currents in rotation stars. The velocities for these cases are compared to each other and to observed stellar rotation rates (upsilon sin i).Near the main sequence, rotational effects can substantially reduce the moment of inertia of a star, so nonrotating models consistently underestimate the expected velocities for evolving stars. The magnitude of these effects is sufficient to explain the large numbers of Be stars and, perhaps, to explain the bimodal distribution of velocities observed for the O stars.On the red giant branch, angular momentum redistribution reduces the surface velocity by a factor of 2 or more, relative to the velocity expected for no radial redistribution. This removes the discrepancy between predicted and observed rotation rates for the K giants and makes it unlikely that these stars lose significant amounts of angular momentum by stellar winds. Our calculations indicate that improved observations (by the Fourier-transform technique) of the red giants in the Hyades cluster can be used to determine how angular momentum is redistributed by convection

  3. THE NATURE OF STARBURSTS. III. THE SPATIAL DISTRIBUTION OF STAR FORMATION

    McQuinn, Kristen B. W.; Skillman, Evan D. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street, S.E., University of Minnesota, Minneapolis, MN 55455 (United States); Dalcanton, Julianne J.; Weisz, Daniel R.; Williams, Benjamin F. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Holtzman, Jon, E-mail: kmcquinn@astro.umn.edu [Department of Astronomy, New Mexico State University, Box 30001-Department 4500, 1320 Frenger Street, Las Cruces, NM 88003 (United States)

    2012-11-01

    We map the spatial distribution of recent star formation over a few Multiplication-Sign 100 Myr timescales in 15 starburst dwarf galaxies using the location of young blue helium burning stars identified from optically resolved stellar populations in archival Hubble Space Telescope observations. By comparing the star formation histories from both the high surface brightness central regions and the diffuse outer regions, we measure the degree to which the star formation has been centrally concentrated during the galaxies' starbursts, using three different metrics for the spatial concentration. We find that the galaxies span a full range in spatial concentration, from highly centralized to broadly distributed star formation. Since most starbursts have historically been identified by relatively short timescale star formation tracers (e.g., H{alpha} emission), there could be a strong bias toward classifying only those galaxies with recent, centralized star formation as starbursts, while missing starbursts that are spatially distributed.

  4. Gamma rays from active regions in the galaxy: the possible contribution of stellar winds

    Cesarsky, C.J.; Montmerle, Thierry.

    1982-08-01

    Massive stars release a considerable amount of mechanical energy in the form of strong stellar winds. A fraction of this energy may be transferred to relativistic cosmic rays by diffusive shock acceleration at the wind boundary, and/or in the expanding, turbulent wind itself. Massive stars are most frequently found in OB associations, surrounded by H II regions lying at the edge of dense molecular clouds. The interaction of the freshly accelerated particles with matter gives rise to #betta#-ray emission. In this paper, we first briefly review the current knowledge on the energetics of strong stellar winds from O and Wolf-Rayet stars, as well as from T Tauri stars. Taking into account the finite lifetime of these stars, we then proceed to show that stellar winds dominate the energetics of OB associations during the first 4 to 6 million years, after which supernovae take over. In the solar neighborhood, the star formation rate is constant, and a steady-state situation prevails, in which the supernova contribution is found to be dominant. A small, but meaningful fraction of the CO S-B #betta#-ray sources may be fueled by WR and O stellar winds in OB associations, while the power released by T Tauri stars alone is perhaps insufficient to account for the #betta#-ray emission of nearby dark clouds. Finally, we discuss some controversial aspects of the physics of particle acceleration by stellar winds

  5. Properties of O dwarf stars in 30 Doradus

    Sabín-Sanjulián, Carolina; VFTS Collaboration

    2017-11-01

    We perform a quantitative spectroscopic analysis of 105 presumably single O dwarf stars in 30 Doradus, located within the Large Magellanic Cloud. We use mid-to-high resolution multi-epoch optical spectroscopic data obtained within the VLT-FLAMES Tarantula Survey. Stellar and wind parameters are derived by means of the automatic tool iacob-gbat, which is based on a large grid of fastwind models. We also benefit from the Bayesian tool bonnsai to estimate evolutionary masses. We provide a spectral calibration for the effective temperature of O dwarf stars in the LMC, deal with the mass discrepancy problem and investigate the wind properties of the sample.

  6. The slow ionized wind and rotating disklike system that are associated with the high-mass young stellar object G345.4938+01.4677

    Guzmán, Andrés E.; Garay, Guido; Bronfman, Leonardo; Mardones, Diego [Departamento de Astronomía, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago (Chile); Rodríguez, Luis F. [Centro de Radioastronomía y Astrofísica (UNAM), Morelia 58089 (Mexico); Moran, James [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA (United States); Brooks, Kate J. [CSIRO Astronomy and Space Science, P.O. Box 76, Epping, 1710 NSW (Australia); Nyman, Lars-Åke [Joint ALMA Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago (Chile); Sanhueza, Patricio [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States)

    2014-12-01

    We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40α, H42α, and H50β emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562–3959. The HRLs exhibit Voigt profiles, which is a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need for a high-velocity component. The Lorentzian line wings imply electron densities of 5 × 10{sup 7} cm{sup –3} on average. In addition, we detect SO and SO{sub 2} emission arising from a compact (∼3000 AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient that is perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.

  7. Alternative model for the atmospheres of Wolf-Rayet and O stars

    Underhill, A.B.

    1983-01-01

    It is noted that postulating dense spherically symmetric outflow in order to account for the observed radio fluxes from Wolf-Rayet stars requires that much more momentum must be deposited in the wind of a Wolf-Rayet star than is available from the radiation field of the star, and it is shown that the deduced massive winds become opaque in visible wavelengths at stellar radii where the velocity of outflow is several hundred km s - 1 . To attain such a state of motion in the wind requires the action of a strong, unknown source of outward directed momentum in optically thick layers of the star. This is an unreasonable demand. An alternative model for the mantle of a Wolf-Rayet star (the part of the atmosphere in which nonradiative energy and momentum are deposited) is proposed and shown to be feasible

  8. News on the X-ray emission from hot subdwarf stars

    Palombara Nicola La

    2017-12-01

    Full Text Available In latest years, the high sensitivity of the instruments on-board the XMM-Newton and Chandra satellites allowed us to explore the properties of the X-ray emission from hot subdwarf stars. The small but growing sample of X-ray detected hot subdwarfs includes binary systems, in which the X-ray emission is due to wind accretion onto a compact companion (white dwarf or neutron star, as well as isolated sdO stars, in which X-rays are probably due to shock instabilities in the wind. X-ray observations of these low-mass stars provide information which can be useful for our understanding of the weak winds of this type of stars and can lead to the discovery of particularly interesting binary systems. Here we report the most recent results we have recently obtained in this research area.

  9. Wind Generators

    1989-01-01

    When Enerpro, Inc. president, Frank J. Bourbeau, attempted to file a patent on a system for synchronizing a wind generator to the electric utility grid, he discovered Marshall Space Flight Center's Frank Nola's power factor controller. Bourbeau advanced the technology and received a NASA license and a patent for his Auto Synchronous Controller (ASC). The ASC reduces generator "inrush current," which occurs when large generators are abruptly brought on line. It controls voltage so the generator is smoothly connected to the utility grid when it reaches its synchronous speed, protecting the components from inrush current damage. Generator efficiency is also increased in light winds by applying lower than rated voltage. Wind energy is utilized to drive turbines to generate electricity for utility companies.

  10. Wind turbine

    Cheney, Jr., Marvin C.

    1982-01-01

    A wind turbine of the type having an airfoil blade (15) mounted on a flexible beam (20) and a pitch governor (55) which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch, is provided with a limiter (85) which restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows twisting of the beam by the governor under excessive wind velocity conditions to orient the blades in stall pitch positions, thereby preventing overspeed operation of the turbine. In the preferred embodiment, the pitch governor comprises a pendulum (65,70) which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member (90) which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment.

  11. Wind energy potential of coastal Eritrea: an analysis of sparse wind data

    Rosen, K.; Buskirk, R. van; Garbesi, K.

    1999-01-01

    This paper describes an analysis of historical surface wind data for the small country of Eritrea, in northeastern Africa. Winds in this region are directed by summer and winter monsoons in addition to diurnal land-sea effects. An analysis of national Eritrean and historical Italian wind records indicated marginal wind resources in the central highlands near the Eritrean capital of Asmera. An analysis of wind speed records recorded at two sites in the southern port city of Aseb indicate mean annual 10-m wind speeds of 9.5 m s -1 at the windier site. Surface wind speed records for the Red Sea suggest that similar potential may be found along the lower 200 km of the Eritrean coastline. Based on these findings, wind-generated electricity in this region should be substantially cheaper than the current supply generated from imported diesel. (author)

  12. Quark core stars, quark stars and strange stars

    Grassi, F.

    1988-01-01

    A recent one flavor quark matter equation of state is generalized to several flavors. It is shown that quarks undergo a first order phase transition. In addition, this equation of state depends on just one parameter in the two flavor case, two parameters in the three flavor case, and these parameters are constrained by phenomenology. This equation of state is then applied to the hadron-quark transition in neutron stars and the determination of quark star stability, the investigation of strange matter stability and possible strange star existence. 43 refs., 6 figs

  13. Wind turbine spoiler

    Sullivan, W.N.

    An aerodynamic spoiler system for a vertical axis wind turbine includes spoilers on the blades initially stored near the rotor axis to minimize drag. A solenoid latch adjacent the central support tower releases the spoilers and centrifugal force causes the spoilers to move up the turbine blades away from the rotor axis, thereby producing a braking effect and actual slowing of the associated wind turbine, if desired. The spoiler system can also be used as an infinitely variable power control by regulated movement of the spoilers on the blades over the range between the undeployed and fully deployed positions. This is done by the use of a suitable powered reel and cable located at the rotor tower to move the spoilers.

  14. Dynamics of H II regions around exiled O stars

    Mackey, Jonathan; Langer, Norbert; Gvaramadze, Vasilii V.

    2013-11-01

    At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their overpressurized H II regions impart kinetic energy and momentum to the ISM, compress and/or evaporate dense clouds, and can constrain properties of both the star and the ISM. Here, we present one-, two- and (the first) three-dimensional simulations of the H II region around a massive star moving supersonically through a uniform, magnetized ISM, with properties appropriate for the nearby O star ζ Oph. The H II region leaves an expanding overdense shell behind the star and, inside this, an underdense wake that should be filled with hot gas from the shocked stellar wind. The gas column density in the shell is strongly influenced by the ISM magnetic field strength and orientation. Hα emission maps show that H II region remains roughly circular, although the star is displaced somewhat from the centre of emission. For our model parameters, the kinetic energy feedback from the H II region is comparable to the mechanical luminosity of the stellar wind, and the momentum feedback rate is >100 times larger than that from the wind and ≈10 times larger than the total momentum input rate available from radiation pressure. Compared to the star's eventual supernova explosion, the kinetic energy feedback from the H II region over the star's main-sequence lifetime is >100 times less, but the momentum feedback is up to 4 times larger. H II region dynamics are found to have only a small effect on the ISM conditions that a bow shock close to the star would encounter.

  15. 78 FR 29364 - Exelon Corporation, Exelon Wind 1, LLC, Exelon Wind 2, LLC, Exelon Wind 3, LLC, Exelon Wind 4...

    2013-05-20

    ...-005, QF07-55-005, QF07-56-005, QF07-257-004] Exelon Corporation, Exelon Wind 1, LLC, Exelon Wind 2, LLC, Exelon Wind 3, LLC, Exelon Wind 4, LLC, Exelon Wind 5, LLC, Exelon Wind 6, LLC, Exelon Wind 7, LLC, Exelon Wind 8, LLC, Exelon Wind 9, LLC, Exelon Wind 10, LLC, Exelon Wind 11, LLC, High Plains...

  16. ENERGY STAR Certified Displays

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 7.0 ENERGY STAR Program Requirements for Displays that are effective as of July 1, 2016....

  17. ENERGY STAR Certified Boilers

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Boilers that are effective as of October 1,...

  18. ENERGY STAR Certified Televisions

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 7.0 ENERGY STAR Program Requirements for Televisions that are effective as of October 30,...

  19. ENERGY STAR Certified Dehumidifiers

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.0 ENERGY STAR Program Requirements for Dehumidifiers that are effective as of October...

  20. ENERGY STAR Certified Telephones

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Telephony (cordless telephones and VoIP...

  1. Wolf-Rayet stars

    Sahade, J

    1981-12-01

    Aspects of the problems of the Wolf-Rayet stars related to their chemical composition, their evolutionary status, and their apparent dichotomy in two spectral sequences are discussed. Dogmas concerning WR stars are critically discussed, including the belief that WR stars lack hydrogen, that they are helium stars evolved from massive close binaries, and the existence of a second WR stage in which the star is a short-period single-lined binary. The relationship of WR stars with planetary nebulae is addressed, as is the membership of these stars in clusters and associations. The division of WR stars into WN and WC sequences is considered, questioning the reasonability of accounting for WR line formation in terms of abundance differences.

  2. Star formation: Cosmic feast

    Scaringi, Simone

    2017-03-01

    Low-mass stars form through a process known as disk accretion, eating up material that orbits in a disk around them. It turns out that the same mechanism also describes the formation of more massive stars.

  3. HUBBLE CAPTURES THE HEART OF STAR BIRTH

    2002-01-01

    NASA Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) has captured a flurry of star birth near the heart of the barred spiral galaxy NGC 1808. On the left are two images, one superimposed over the other. The black-and-white picture is a ground-based view of the entire galaxy. The color inset image, taken with the Hubble telescope's Wide Field and Planetary Camera 2 (WFPC2), provides a close-up view of the galaxy's center, the hotbed of vigorous star formation. The ground-based image shows that the galaxy has an unusual, warped shape. Most spiral galaxies are flat disks, but this one has curls of dust and gas at its outer spiral arms (upper right-hand corner and lower left-hand corner). This peculiar shape is evidence that NGC 1808 may have had a close interaction with another nearby galaxy, NGC 1792, which is not in the picture Such an interaction could have hurled gas towards the nucleus of NGC 1808, triggering the exceptionally high rate of star birth seen in the WFPC2 inset image. The WFPC2 inset picture is a composite of images using colored filters that isolate red and infrared light as well as light from glowing hydrogen. The red and infrared light (seen as yellow) highlight older stars, while hydrogen (seen as blue) reveals areas of star birth. Colors were assigned to this false-color image to emphasize the vigorous star formation taking place around the galaxy's center. NGC 1808 is called a barred spiral galaxy because of the straight lines of star formation on both sides of the bright nucleus. This star formation may have been triggered by the rotation of the bar, or by matter which is streaming along the bar towards the central region (and feeding the star burst). Filaments of dust are being ejected from the core into a faint halo of stars surrounding the galaxy's disk (towards the upper left corner) by massive stars that have exploded as supernovae in the star burst region. The portion of the galaxy seen in this 'wide-field' image is

  4. Supernovae, compact stars and nuclear physics

    Glendenning, N.K.

    1989-01-01

    We briefly review the current understanding of supernova. We investigate the implications of rapid rotation corresponding to the frequency of the new pulsar reported in the supernovae remnant SN1987A. It places very stringent conditions on the equation of state if the star is assumed to be bound by gravity alone. We find that the central energy density of the star must be greater than 12 times that of nuclear density to be stable against the most optimistic estimate of general relativistic instabilities. This is too high for the matter to plausibly consist of individual hadrons. We conclude that the newly discovered pulsar, if its half-millisecond signals are attributable to rotation, cannot be a neutron star. We show that it can be a strange quark star, and that the entire family of strange stars can sustain high rotation under appropriate conditions. We discuss the conversion of a neutron star to strange star, the possible existence of a crust of heavy ions held in suspension by centrifugal and electric forces, the cooling and other features. 39 refs., 8 figs., 2 tabs

  5. Neutron stars with orbiting light

    Lukacs, B.

    1987-11-01

    There is a wide-spread belief in the literature of relativistic astrophysics concerning nonsingular final states of the stellar evolution: the external gravitational field of a physically nonsingular central symmetric body (e.g. a neutron star) is asymptotically empty and simple, i.e. there are no closed or trapped light-like causal geodesics. Present paper shows that this belief is false: some examples are presented for nonsingular bodies with various equations of state, around which there are closed light-like trajectories: 'orbiting light'. The reality of the used equations of state is discussed in detail. Present state of particle physics does not establish the existence of matter with such equations of state, but the hypothetical subquark level of matter may have such equation of state, thus 'subquark-stars' may exist with orbiting light around them. So the criterion of 'nonsingularity' must be further analyzed and accurately defined. (D.Gy.) 24 refs.; 5 figs

  6. Relativistic stars in vector-tensor theories

    Kase, Ryotaro; Minamitsuji, Masato; Tsujikawa, Shinji

    2018-04-01

    We study relativistic star solutions in second-order generalized Proca theories characterized by a U (1 )-breaking vector field with derivative couplings. In the models with cubic and quartic derivative coupling, the mass and radius of stars become larger than those in general relativity for negative derivative coupling constants. This phenomenon is mostly attributed to the increase of star radius induced by a slower decrease of the matter pressure compared to general relativity. There is a tendency that the relativistic star with a smaller mass is not gravitationally bound for a low central density and hence is dynamically unstable, but that with a larger mass is gravitationally bound. On the other hand, we show that the intrinsic vector-mode couplings give rise to general relativistic solutions with a trivial field profile, so the mass and radius are not modified from those in general relativity.

  7. Autonomous Star Tracker Algorithms

    Betto, Maurizio; Jørgensen, John Leif; Kilsgaard, Søren

    1998-01-01

    Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances.......Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances....

  8. Remote Sensing Wind and Wind Shear System.

    Contents: Remote sensing of wind shear and the theory and development of acoustic doppler; Wind studies; A comparison of methods for the remote detection of winds in the airport environment; Acoustic doppler system development; System calibration; Airport operational tests.

  9. Spectrophotometry at 10 microns of T Tauri stars

    Cohen, M.; Witteborn, F. C.

    1985-01-01

    New 8-13 micron spectra of 32 T Tau, or related young, stars are presented. Silicate emission features are commonly seen. Absorptions occur less frequently but also match the properties of silicate materials. The shape of the emission feature suggests that a more crystalline grain is responsible in the T Tau stars than those of the Trapezium region. The evolution of the silicate component of the circumstellar shell around T Tau stars, and its dependence upon stellar wind activity, visual linear polarization, and extinction are investigated. Several correlations suggest that the shells are likely to be flattened, disklike structures rather than spherical.

  10. Covering tree with stars

    Baumbach, Jan; Guo, Jian-Ying; Ibragimov, Rashid

    2013-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting ...

  11. America's Star Libraries

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  12. Pulsar Magnetohydrodynamic Winds

    Okamoto, Isao; Sigalo, Friday B.

    2006-12-01

    The acceleration and collimation/decollimation of relativistic magnetocentrifugal winds are discussed concerning a cold plasma from a strongly magnetized, rapidly rotating neutron star in a steady axisymmetric state based on ideal magnetohydrodynamics. There exist unipolar inductors associated with the field line angular frequency, α, at the magnetospheric base surface, SB, with a huge potential difference between the poles and the equator, which drive electric current through the pulsar magnetosphere. Any ``current line'' must emanate from one terminal of the unipolar inductor and return to the other, converting the Poynting flux to the kinetic flux of the wind at finite distances. In a plausible field structure satisfying the transfield force-balance equation, the fast surface, SF, must exist somewhere between the subasymptotic and asymptotic domains, i.e., at the innermost point along each field line of the asymptotic domain of \\varpaA2/\\varpi2 ≪ 1, where \\varpiA is the Alfvénic axial distance. The criticality condition at SF yields the Lorentz factor, γF = μ\\varepsilon1/3, and the angular momentum flux, β, as the eigenvalues in terms of the field line angular velocity, α, the mass flux per unit flux tube, η, and one of the Bernoulli integrals, μδ, which are assumed to be specifiable as the boundary conditions at SB. The other Bernoulli integral, μɛ, is related to μδ as μɛ = μδ[1-(α2\\varpiA2/c2)]-1, and both μɛ and \\varpiA2 are eigenvalues to be determined by the criticality condition at SF. Ongoing MHD acceleration is possible in the superfast domain. This fact may be helpful in resolving a discrepancy between the wind theory and the Crab-nebula model. It is argued that the ``anti-collimation theorem'' holds for relativistic winds, based on the curvature of field streamlines determined by the transfield force balance. The ``theorem'' combines with the ``current-closure condition'' as a global condition in the wind zone to produce a

  13. An Optimal Control Scheme to Minimize Loads in Wind Farms

    Soleimanzadeh, Maryam; Wisniewski, Rafal

    2012-01-01

    This work presents a control algorithm for wind farms that optimizes the power production of the farm and helps to increase the lifetime of wind turbines components. The control algorithm is a centralized approach, and it determines the power reference signals for individual wind turbines...

  14. Wind energy

    Portilla S, L.A.

    1995-01-01

    The wind energy or eolic energy is a consequence of solar energy, the one which is absorbed by the atmosphere and is transformed into energy of movement of large bulks of air. In this process the atmosphere acts as the filter to the solar radiation and demotes the ultraviolet beams that result fatal to life in the Earth. The ionosphere is the most external cap and this is ionized by means of absorption process of ultraviolet radiation arising to the Sun. The atmosphere also acts as a trap to the infrared radiation, it that results from the continual process of energetic degradation. In this way, the interaction between Earth - Atmospheres, is behaved as a great greenhouse, maintaining the constant temperatures, including in the dark nights. Processes as the natural convection (that occur by the thermodynamic phenomenon), equatorial calmness, trade winds and against trade winds and global distribution of the air currents are described. The other hand, techniques as the transformation of the wind into energy and its parameters also are shown

  15. Wind power

    2006-06-01

    This road-map proposes by the Group Total aims to inform the public on the wind power. It presents the principles, the technology takes off, its applications and technology focus, the global market trends and the outlooks and Total commitments in the domain. (A.L.B.)

  16. Wind Energy Japan

    Komatsubara, Kazuyo [Embassy of the Kingdom of the Netherlands, Tokyo (Japan)

    2012-06-15

    An overview is given of wind energy in Japan: Background; Wind Energy in Japan; Japanese Wind Energy Industry; Government Supports; Useful Links; Major Japanese Companies; Profiles of Major Japanese Companies; Major Wind Energy Projects in Japan.

  17. Wind energy systems

    Stewart, H. J.

    1978-01-01

    A discussion on wind energy systems involved with the DOE wind energy program is presented. Some of the problems associated with wind energy systems are discussed. The cost, efficiency, and structural design of wind energy systems are analyzed.

  18. Mass loss rates of OB stars derived from infrared observations

    Tanzi, E.G.; Tarenghi, M.; Panagia, N.

    1981-01-01

    In this paper the authors report briefly on a study of the mass loss of early type stars in the infrared. Up to now near infrared (1.25 - 4.8 μ) broad band photometry of 70 southern OB stars of various luminosity class has been secured. Program stars have been selected, among those bright enough in the infrared to give a suitable photometric accuracy, in order to cover a wide range of spectral types. 37 stars are found to exhibit emission in excess over a blackbody photospheric continuum, which is interpreted in terms of gas ejected in the form of an accelerated wind. By means of model calculations the corresponding mass loss rates are derived. The obtained values compare well with those determined independently by various authors for stars in common. Their data show that mass loss rates increase with luminosity and are a decreasing function of surface gravity. (Auth.)

  19. Mass loss by stars on the asymptotic giant branch

    Frantsman, Yu.L.

    1986-01-01

    The theoretical populations of white dwarfs and carbon stars were generated for Salpeter initial mass function and constant stellar birth rate history. The effect of very strong mass loss on the mass distribution of white dwarfs and luminosity distribution of carbon stars is discussed and the results are compared with observations. This comparison suggested that a signioficant mass loss by stars on the asymptotic giant branch occurs besides stellar wind and planetary nebulae ejection. Thus it is possible to explain the absence of carbon stars with Msub(bol) 1.0 Msub(sun). The luminosity of asymptotic giant branch stars in the globular clusters of the Magellanic Clouds appears to be a very good indicator of the age

  20. Formation of Neutral Disk-Like Zone Around the Active Hot Stars in Symbiotic Binaries

    Cariková Z.

    2012-06-01

    Full Text Available In this contribution we present the ionization structure in the enhanced wind from the hot star in symbiotic binaries during active phases. Rotation of the hot star leads to the compression of the outflowing material towards its equatorial plane. As a result, a neutral disk-like zone around the active hot star near the orbital plane is created. We modeled the compression of the wind and calculated the neutral disk-like zone in the enhanced wind from the hot star using the equation of the photoionization equilibrium. the presence of such neutral disk-like zones was also suggested on the basis of the modeling the spectral energy distribution of symbiotic binaries. We confront the calculated ionization structures in the enhanced wind from the hot star with the observations. the calculated column density of the neutral hydrogen atoms in the neutral disk-like zone and the emission measure of the ionized part of the wind from the hot star are in a good agreement with the quantities derived from observations during active phases. the presence of such neutral disk-like zones is transient, being connected with the active phases of symbiotic binaries. During quiescent phases, such neutral disk-like zones cannot be created because of insufficient mass-loss rate from the hot star.