WorldWideScience

Sample records for central star wind

  1. Stellar and wind properties of massive stars in the central parsec of the Galaxy

    OpenAIRE

    F. Martins; Genzel, R.; Hillier, D. J.; Eisenhauer, F.; Paumard, T.; Gillessen, S.; Ott, T.; Trippe, S.

    2007-01-01

    We study the stellar and wind properties of massive stars in the central cluster of the Galaxy. We use non-LTE atmosphere models including winds and line-blanketing to fit their H and K band spectra obtained with the 3D spectrograph SINFONI on the VLT. We derive the main stellar (Teff, L, abundances, ionizing flux) and wind (mass loss rate, terminal velocity) properties. They are found to be similar to other galactic massive stars. We show that a direct evolutionary link between Ofpe/WN9, WN8...

  2. Fast winds from the central stars of NGC 6543 and NGC 6826

    International Nuclear Information System (INIS)

    The Sobolev exact integration method and high-resolution IUE data are used to examine the properties of the fast winds exhibited by the central stars of the planetary nebulae NGC 6543 and NGC 6826. An attempt is made to evaluate the parameters of the central stars as accurately as possible. The associated mass-loss rates (M) are (4.0 + 10 or - 2.1) x 10 to the -8th and (5.2 + 34 or - 4.5) x 10 to the -8th solar masses/yr for NGC 6543 and NGC 6826, respectively. A comparison with the Population I OB stars in the (log L, log M) diagram shows that the mass-loss phenomenon in these central stars is very likely due to the same mechanism thought to prevail in early-type stars of Population I, i.e., the radiation pressure on heavy ions. 58 references

  3. The central star of the planetary nebula PB 8: a Wolf-Rayet-type wind of an unusual WN/WC chemical composition

    OpenAIRE

    Todt, H.; Peña, M.; Hamann, W. -R.; Gräfener, G.

    2010-01-01

    A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. As a rule, these CSPNe exhibit a chemical composition of helium, carbon, and oxygen with the majority showing Wolf-Rayet-like emission line spectra. These stars are classified as CSPNe of a spectral type [WC]. We perform a spectral analysis of CSPN PB 8 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. The source PB 8 displays wind-broadened emission lines from strong mass loss...

  4. The central star of the planetary nebula PB 8: a Wolf-Rayet-type wind of an unusual WN/WC chemical composition

    CERN Document Server

    Todt, H; Hamann, W -R; Gräfener, G

    2010-01-01

    A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. As a rule, these CSPNe exhibit a chemical composition of helium, carbon, and oxygen with the majority showing Wolf-Rayet-like emission line spectra. These stars are classified as CSPNe of a spectral type [WC]. We perform a spectral analysis of CSPN PB 8 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. The source PB 8 displays wind-broadened emission lines from strong mass loss. Most strikingly, we find that its surface composition is hydrogen-deficient, but not carbon-rich. With mass fractions of 55% helium, 40% hydrogen, 1.3% carbon, 2% nitrogen, and 1.3% oxygen, it differs greatly from the 30-50% of carbon which are typically seen in [WC]-type central stars. The atmospheric mixture in PB 8 has an analogy in the WN/WC transition type among the massive Wolf-Rayet stars. Therefore we suggest to introduce a new spectral type [WN/WC] for CSPNe, with PB 8 as its first member. The central star of P...

  5. Winds of Planet Hosting Stars

    CERN Document Server

    Nicholson, B A; Brookshaw, L; Vidotto, A A; Carter, B D; Marsden, S C; Soutter, J; Waite, I A; Horner, J

    2015-01-01

    The field of exoplanetary science is one of the most rapidly growing areas of astrophysical research. As more planets are discovered around other stars, new techniques have been developed that have allowed astronomers to begin to characterise them. Two of the most important factors in understanding the evolution of these planets, and potentially determining whether they are habitable, are the behaviour of the winds of the host star and the way in which they interact with the planet. The purpose of this project is to reconstruct the magnetic fields of planet hosting stars from spectropolarimetric observations, and to use these magnetic field maps to inform simulations of the stellar winds in those systems using the Block Adaptive Tree Solar-wind Roe Upwind Scheme (BATS-R-US) code. The BATS-R-US code was originally written to investigate the behaviour of the Solar wind, and so has been altered to be used in the context of other stellar systems. These simulations will give information about the velocity, pressur...

  6. Winds and Accretion in Young Stars

    OpenAIRE

    Edwards, Suzan

    2008-01-01

    Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star-disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin-up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer a unique opportunity to study the connection between accretion and winds and their relation to stel...

  7. Radiation-driven winds of hot luminous stars. XVIII. The unreliability of stellar and wind parameter determinations from optical vs. UV spectral analysis of selected central stars of planetary nebulae and the possibility of some CSPNs as single-star supernova Ia progenitors

    Science.gov (United States)

    Hoffmann, T. L.; Pauldrach, A. W. A.; Kaschinski, C. B.

    2016-08-01

    Context. The uncertainty in the degree to which radiation-driven winds of hot stars might be affected by small inhomogeneities in the density leads to a corresponding uncertainty in the determination of the atmospheric mass loss rates from the strength of optical recombination lines and - since the mass loss rate is not a free parameter but a function of the stellar parameters mass, radius, luminosity, and abundances - in principle also in the determination of these stellar parameters. Furthermore, the optical recombination lines also react sensitively to even small changes in the density structure resulting from the (often assumed instead of computed) velocity law of the outflow. This raises the question of how reliable the parameter determinations from such lines are. Aims: The currently existing severe discrepancy between central stars of planetary nebulae (CSPN) stellar and wind parameters derived from model fits to the optical spectra and those derived using hydrodynamically consistent model fits to the UV spectra is to be reassessed via a simultaneous optical/UV analysis using a state-of-the-art model atmosphere code. Methods: We have modified our hydrodynamically consistent model atmosphere code with an implementation of the usual ad hoc treatment of clumping (small inhomogeneities in the density) in the wind. This allows us to re-evaluate, with respect to their influence on the appearance of the UV spectra and their compatibility with the observations, the parameters determined in an earlier study that had employed clumping in its models to achieve a fit to the observed optical spectra. Results: The discrepancy between the optical and the UV analyses is confirmed to be the result of a missing consistency between stellar and wind parameters in the optical analysis. While clumping in the wind does significantly increase the emission in the optical hydrogen and helium recombination lines, the influence of the density (velocity field) is of the same order as

  8. Accretion, winds and outflows in young stars

    Science.gov (United States)

    Günther, H. M.

    2013-02-01

    Young stars and planetary systems form in molecular clouds. After the initial radial infall an accretion disk develops. For classical T Tauri stars (CTTS, F-K type precursors) the accretion disk does not reach down to the central star, but it is truncated near the co-rotation radius by the stellar magnetic field. The inner edge of the disk is ionized by the stellar radiation, so that the accretion stream is funneled along the magnetic field lines. On the stellar surface an accretion shock develops, which is observed over a wide wavelength range as X-ray emission, UV excess, optical veiling and optical and IR emission lines. Some of the accretion tracers, e.g. Hα, can be calibrated to measure the accretion rate. This accretion process is variable on time scales of hours to years due to changing accretion rates, stellar rotation and reconfiguration of the magnetic field. Furthermore, many (if not all) accreting systems also drive strong outflows which are ultimately powered by accretion. However, the exact driving mechanism is still unclear. Several components could contribute to the outflows: slow, wide-angle disk winds, X-winds launched close to the inner disk rim, and thermally driven stellar winds. In any case, the outflows contain material of very different temperatures and speeds. The disk wind is cool and can have a molecular component with just a few tens of km s-1, while the central component of the outflow can reach a few 100 km s-1. In some cases the inner part of the outflow is collimated to a small-angle jet. These jets have an onion-like structure, where the inner components are consecutively hotter and faster. The jets can contain working surfaces, which show up as Herbig-Haro knots. Accretion and outflows in the CTTS phase do not only determine stellar parameters like the rotation rate on the main-sequence, they also can have a profound impact on the environment of young stars. This review concentrates on CTTS in near-by star forming regions where

  9. Accretion, winds and outflows in young stars

    CERN Document Server

    Günther, Hans Moritz

    2012-01-01

    Young stars and planetary systems form in molecular clouds. For classical T Tauri stars (CTTS, F-K type precursors) the accretion disk does not reach down to the central star, but it is truncated near the co-rotation radius. The inner edge of the disk is ionized by the stellar radiation, so that the accretion stream is funneled along the magnetic field lines. On the stellar surface an accretion shock develops, which is observed over a wide wavelength range as X-ray emission, UV excess, optical veiling and optical and IR emission lines. Some of the accretion tracers, e.g. H\\alpha, can be calibrated to measure the accretion rate. This accretion process is variable on time scales of hours to years due to changing accretion rates, stellar rotation and reconfiguration of the magnetic field. Furthermore, many accreting systems also drive strong outflows which are ultimately powered by accretion. Several components could contribute to the outflows: slow, wide-angle disk winds, X-winds launched close to the inner dis...

  10. Multicomponent stellar wind of hot stars

    Czech Academy of Sciences Publication Activity Database

    Votruba, Viktor; Feldmeier, A.; Kubát, Jiří; Rätzel, D.

    Potsdam: Universitätsverlag Potsdam, 2008 - (Hamann, W.; Feldmeier, A.; Oskinova, L.), s. 252-252 ISBN 978-3-940793-33-1. [Clumping in hot-star winds. Potsdam (DE), 18.06.2007-22.06.2007] R&D Projects: GA AV ČR KJB300030701 Institutional research plan: CEZ:AV0Z10030501 Keywords : hot stars * stellar wind * dynamical friction Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  11. Accretion, Outflows, and Winds of Magnetized Stars

    CERN Document Server

    Romanova, M M

    2016-01-01

    Many types of stars have strong magnetic fields that can dynamically influence the flow of circumstellar matter. In stars with accretion disks, the stellar magnetic field can truncate the inner disk and determine the paths that matter can take to flow onto the star. These paths are different in stars with different magnetospheres and periods of rotation. External field lines of the magnetosphere may inflate and produce favorable conditions for outflows from the disk-magnetosphere boundary. Outflows can be particularly strong in the propeller regime, wherein a star rotates more rapidly than the inner disk. Outflows may also form at the disk-magnetosphere boundary of slowly rotating stars, if the magnetosphere is compressed by the accreting matter. In isolated, strongly magnetized stars, the magnetic field can influence formation and/or propagation of stellar wind outflows. Winds from low-mass, solar-type stars may be either thermally or magnetically driven, while winds from massive, luminous O and B type stars...

  12. Winds and Accretion in Young Stars

    CERN Document Server

    Edwards, Suzan

    2008-01-01

    Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star-disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin-up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer a unique opportunity to study the connection between accretion and winds and their relation to stellar spindown. Although spectroscopic indicators of high velocity T Tauri winds have been known for decades, the line of He I 10830 offers a promising new diagnostic to probe the magnetically controlled star-disk interaction and wind-launching region. The high opacity and resonance scattering properties of this line offer a powerful probe of the geometry of both the funnel flow and the inner wind that, together with other atomic and molecular spectral lines covering a wide range of excitation and ionization states, suggest...

  13. Identifying close binary central stars of PN with Kepler

    CERN Document Server

    De Marco, Orsola; Jacoby, George H; Hillwig, T; Kronberger, M; Howell, Steve B; Reindl, N; Margheim, Steve

    2016-01-01

    Six planetary nebulae (PN) are known in the Kepler space telescope field of view, three newly identified. Of the 5 central stars of PN with useful Kepler data, one, J193110888+4324577, is a short-period, post common envelope binary exhibiting relativistic beaming effects. A second, the central star of the newly identified PN Pa5, has a rare O(He) spectral type and a periodic variability consistent with an evolved companion, where the orbital axis is almost aligned with the line of sight. The third PN, NGC~6826 has a fast rotating central star, something that can only be achieved in a merger. Fourth, the central star of the newly identified PN Kn61, has a PG1159 spectral type and a mysterious semi-periodic light variability which we conjecture to be related to the interplay of binarity with a stellar wind. Finally, the central star of the circular PN A61 does not appear to have a photometric variability above 2 mmag. With the possible exception of the variability of Kn61, all other variability behaviour, wheth...

  14. Stellar wind models of subluminous hot stars

    CERN Document Server

    Krticka, J; Krtickova, I

    2016-01-01

    Mass-loss rate is one of the most important stellar parameters. We aim to provide mass-loss rates as a function of subdwarf parameters and to apply the formula for individual subdwarfs, to predict the wind terminal velocities, to estimate the influence of the magnetic field and X-ray ionization on the stellar wind, and to study the interaction of subdwarf wind with mass loss from Be and cool companions. We used our kinetic equilibrium (NLTE) wind models with the radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the wind structure of subluminous hot stars. Our models solve stationary hydrodynamical equations, that is the equation of continuity, equation of motion, and energy equation and predict basic wind parameters. We predicted the wind mass-loss rate as a function of stellar parameters, namely the stellar luminosity, effective temperature, and metallicity. The derived wind parameters (mass-loss rates and terminal velocities) agree with the values derived...

  15. Wind acceleration in AGB stars: Solid ground and loose ends

    CERN Document Server

    Höfner, Susanne

    2015-01-01

    The winds of cool luminous AGB stars are commonly assumed to be driven by radiative acceleration of dust grains which form in the extended atmospheres produced by pulsation-induced shock waves. The dust particles gain momentum by absorption or scattering of stellar photons, and they drag along the surrounding gas particles through collisions, triggering an outflow. This scenario, here referred to as Pulsation-Enhanced Dust-DRiven Outflow (PEDDRO), has passed a range of critical observational tests as models have developed from empirical and qualitative to increasingly self-consistent and quantitative. A reliable theory of mass loss is an essential piece in the bigger picture of stellar and galactic chemical evolution, and central for determining the contribution of AGB stars to the dust budget of galaxies. In this review, I discuss the current understanding of wind acceleration and indicate areas where further efforts by theorists and observers are needed.

  16. Neutrino-driven winds in the aftermath of a neutron star merger: nucleosynthesis and electromagnetic transients

    OpenAIRE

    Martin, Dirk; Perego, Albino; Arcones, Almudena; Thielemann, Friedrich-Karl; Korobkin, Oleg; Rosswog, Stephan

    2015-01-01

    We present a comprehensive nucleosynthesis study of the neutrino-driven wind in the aftermath of a binary neutron star merger. Our focus is the initial remnant phase when a massive central neutron star is present. Using tracers from a recent hydrodynamical simulation, we determine total masses and integrated abundances to characterize the composition of unbound matter. We find that the nucleosynthetic yields depend sensitively on both the life time of the massive neutron star and the polar an...

  17. Magnetised winds in single and binary star systems

    Science.gov (United States)

    Johnstone, Colin

    2016-07-01

    Stellar winds are fundamentally important for the stellar magnetic activity evolution and for the immediate environment surrounding their host stars. Ionised winds travel at hundreds of km/s, impacting planets and clearing out large regions around the stars called astropheres. Winds influence planets in many ways: for example, by compressing the magnetosphere and picking up atmospheric particles, they can cause significant erosion of a planetary atmosphere. By removing angular momentum, winds cause the rotation rates of stars to decrease as they age. This causes the star's magnetic dynamo to decay, leading to a significant decay in the star's levels of X-ray and extreme ultraviolet emission. Despite their importance, little is currently known about the winds of other Sun-like stars. Their small mass fluxes have meant that no direct detections have so far been possible. What is currently known has either been learned indirectly or through analogies with the solar wind. In this talk, I will review what is known about the properties and evolution of the winds of other Sun-like stars. I will also review wind dynamics in binary star systems, where the winds from both stars impact each other, leading to shocks and compression regions.

  18. Nucleosynthesis in neutrino-driven winds after neutron star mergers

    CERN Document Server

    Martin, Dirk; Arcones, Almudena; Thielemann, Friedrich-Karl; Korobkin, Oleg; Rosswog, Stephan

    2015-01-01

    We present a comprehensive nucleosynthesis study of the neutrino-driven wind in the aftermath of a binary neutron star merger. Our focus is the initial remnant phase when a massive central neutron star is present. Using tracers from a recent hydrodynamical simulation, we determine total masses and integrated abundances to characterize the composition of unbound matter. We find that the nucleosynthetic yields depend sensitively on both the life time of the massive neutron star and the polar angle. Matter in excess of up to $9 \\cdot 10^{-3} M_\\odot$ becomes unbound until $\\sim 200~{\\rm ms}$. Due to electron fractions of $Y_{\\rm e} \\approx 0.2 - 0.4$ mainly nuclei with mass numbers $A < 130$ are synthesized, complementing the yields from the earlier dynamic ejecta. Mixing scenarios with these two types of ejecta can explain the abundance pattern in r-process enriched metal-poor stars. Additionally, we calculate heating rates for the decay of the freshly produced radioactive isotopes. The resulting light curve...

  19. Globular cluster winds with central accretion by a massive compact object or subcluster

    International Nuclear Information System (INIS)

    Steady-state isothermal wind flows with accretion by a central mass concentration in spherically symmetric systems of gas-losing stars are computed. Solutions are uniquely determined by two dimensionless parameters lambda and m, where lambda approximately (central escape velocity/sound speed)2 and m approximately (central point mass/cluster core mass). The models are applied to globular clusters for two types of central mass concentration - a single massive black hole and a subcluster of massive stars. A hard (> keV) X-ray source due to a central black hole fed by clusterwide inflow does not provide a consistent model for globular cluster X-ray sources. However, in the case of hot (T approximately > 2 x 105 K) winds, gas trapping by a central subcluster of neutron stars or of binaries containing white dwarfs could explain recent UV and Hα observations. Similar applications to elliptical galaxies are discussed. (author)

  20. Revised element abundances for WC-type central stars

    CERN Document Server

    Todt, H; Hamann, W -R

    2007-01-01

    According to previous spectral analyses of Wolf-Rayet type central stars, late [WC] subtypes show systematically higher carbon-to-helium abundance ratios than early [WC] subtypes. If this were true, it would rule out that these stars form an evolutionary sequence. However, due to the different parameter domains and diagnostic lines, one might suspect systematic errors being the source of this discrepancy. In an ongoing project we are therefore checking the [WC] analyses by means of the last generation of non-LTE models for expanding stellar atmospheres which account for line-blanketing and wind clumping. So far, the abundance discrepancy is not resolved. Further element abundances (H, N, Fe) are determined and compared with evolutionary predictions.

  1. LkH-alpha 101 - The stellar wind, the surrounding nebula, and an associated radio star cluster

    Science.gov (United States)

    Becker, Robert H.; White, Richard L.

    1988-01-01

    Radio observations of LkH-alpha 101 have been taken to determine the characteristics of the stellar wind from the central star as well as to image the surrounding nebulosity. They also revealed the presence of a high concentration of weak compact radio sources in the neighborhood of LkH-alpha 101, four of which have optical stellar counterparts. Spectra of three of the stars indicate two T Tauri stars and a highly obscured B star.

  2. LkH-alpha 101 - the stellar wind, the surrounding nebula, and an associated radio star cluster

    International Nuclear Information System (INIS)

    Radio observations of LkH-alpha 101 have been taken to determine the characteristics of the stellar wind from the central star as well as to image the surrounding nebulosity. They also revealed the presence of a high concentration of weak compact radio sources in the neighborhood of LkH-alpha 101, four of which have optical stellar counterparts. Spectra of three of the stars indicate two T Tauri stars and a highly obscured B star. 15 references

  3. Hot planetary winds near a star: dynamics, wind-wind interactions, and observational signatures

    CERN Document Server

    Carroll-Nellenback, Jonathan; Liu, Baowei; Quillen, Alice C; Blackman, Eric G; Dobbs-Dixon, Ian

    2016-01-01

    Signatures of "evaporative" winds from exo-planets on short (hot) orbits around their host star have been observed in a number of systems. In this paper we present global AMR simulations that track the launching of the winds, their expansion through the circumstellar environment, and their interaction with a stellar wind. We focus on purely hydrodynamic flows including the anisotropy of the wind launching and explore the orbital/fluid dynamics of the resulting flows in detail. In particular we find that a combination of the tidal and Coriolis forces strongly distorts the planetary "Parker" wind creating "up-orbit" and "down-orbit" streams. We characterize the flows in terms of their orbital elements which change depending on their launch position on the planet. We find that the anisotropy in the atmospheric temperature leads to significant backflow on to the planet. The planetary wind interacts strongly with the stellar wind creating instabilities that cause eventual deposition of planetary gas onto the star....

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  5. Attitudes Concerning Wind Energy in Central Illinois

    OpenAIRE

    Theron, Sophie; Winter, J. Randy; David G. Loomis; Spaulding, Aslihan D.

    2011-01-01

    Energy consumption in the United Sates has been increasing and the cost of fossil fuels has been unstable in recent years. Expanding investment in renewable energy is one way to reduce the nation’s dependence on fossil fuels. However, the Not-In-My-Back- Yard (NIMBY) opposition and various concerns raised at public hearings may inhibit the expansion of wind energy in Illinois. This study aims to characterize the public beliefs and opinions toward wind energy in central Illinois.

  6. Interactions between exoplanets and the winds of young stars

    Directory of Open Access Journals (Sweden)

    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.

  7. Atmospheric Heating and Wind Acceleration in Cool Evolved Stars

    CERN Document Server

    Airapetian, Vladimir S

    2014-01-01

    A chromosphere is a universal attribute of stars of spectral type later than ~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae binaries) show extended and highly turbulent chromospheres, which develop into slow massive winds. The associated continuous mass loss has a significant impact on stellar evolution, and thence on the chemical evolution of galaxies. Yet despite the fundamental importance of those winds in astrophysics, the question of their origin(s) remains unsolved. What sources heat a chromosphere? What is the role of the chromosphere in the formation of stellar winds? This chapter provides a review of the observational requirements and theoretical approaches for modeling chromospheric heating and the acceleration of winds in single cool, evolved stars and in eclipsing binary stars, including physical models that have recently been proposed. It describes the successes that have been achieved so far by invoking acoustic and MHD waves to provide a physical description of plasma...

  8. Collimated Outflow Formation via Binary Stars. 3-D Simulations of AGB Wind and Disk Wind Interactions

    OpenAIRE

    Garcia-Arredondo, F.; Frank, Adam

    2003-01-01

    We present three-dimensional hydrodynamic simulations of the interaction of a slow wind from an asymptotic giant branch(AGB) star and a jet blown by an orbiting companion. The jet or "Collimated Fast Wind" is assumed to originate from an accretion disk which forms via Bondi accretion of the AGB wind or Roche lobe overflow. We present two distinct regimes in the wind-jet interaction determined by the ratio of the AGB wind to jet momentum flux. Our results show that when the wind momentum flux ...

  9. O stars with weak winds: the Galactic case

    CERN Document Server

    Martins, F; Hillier, J; Meynadier, F; Heydari-Malayeri, M; Walborn, N; Martins, Fabrice; Schaerer, Daniel; Hillier, John; Meynadier, Frederic; Heydari-Malayeri, Mohammad; Walborn, Nolan

    2005-01-01

    We study the stellar and wind properties of a sample of Galactic O dwarfs to track the conditions under which weak winds (i.e mass loss rates lower than ~ 1e-8 Msol/yr) appear. The sample is composed of low and high luminosity dwarfs including Vz stars and stars known to display qualitatively weak winds. Atmosphere models including non-LTE treatment, spherical expansion and line blanketing are computed with the code CMFGEN. Both UV and Ha lines are used to derive wind properties while optical H and He lines give the stellar parameters. Mass loss rates of all stars are found to be lower than expected from the hydrodynamical predictions of Vink et al. (2001). For stars with log L/Lsol > 5.2, the reduction is by less than a factor 5 and is mainly due to the inclusion of clumping in the models. For stars with log L/Lsol < 5.2 the reduction can be as high as a factor 100. The inclusion of X-ray emission in models with low density is crucial to derive accurate mass loss rates from UV lines. The modified wind mom...

  10. Tracing Slow Winds from T Tauri Stars via Low Velocity Forbidden Line Emission

    Science.gov (United States)

    Simon, Molly; Pascucci, Ilaria; Edwards, Suzan; Feng, Wanda; Rigliaco, Elisabetta; Gorti, Uma; Hollenbach, David J.; Tuttle Keane, James

    2016-06-01

    Protoplanetary disks are a natural result of star formation, and they provide the material from which planets form. The evolutional and eventual dispersal of protoplanetary disks play critical roles in determining the final architecture of planetary systems. Models of protoplanetary disk evolution suggest that viscous accretion of disk gas onto the central star and photoevaporation driven by high-energy photons from the central star are the main mechanisms that drive disk dispersal. Understanding when photoevaporation begins to dominate over viscous accretion is critically important for models of planet formation and planetary migration. Using Keck/HIRES (resolution of ~ 7 km/s) we analyze three low excitation forbidden lines ([O I] 6300 Å, [O I] 5577 Å, and [S II] 6731 Å) previously determined to trace winds (including photoevaporative winds). These winds can be separated into two components, a high velocity component (HVC) with blueshifts between ~30 – 150 km/s, and a low velocity component (LVC) with blueshifts on the order of ~5 km/s (Hartigan et al. 1995). We selected a sample of 32 pre-main sequence T Tauri stars in the Taurus-Auriga star-forming region (plus TW Hya) with disks that span a range of evolutionary stages. We focus on the origin of the LVC specifically, which we are able to separate into a broad component (BC) and a narrow component (NC) due to the high resolution of our optical spectra. We focus our analysis on the [O I] 6300 Å emission feature, which is detected in 30/33 of our targets. Interestingly, we find wind diagnostics consistent with photoevaporation for only 21% of our sample. We can, however, conclude that a specific component of the LVC is tracing a magnetohydrodynamic (MHD) wind rather than a photoevaporative wind. We will present the details behind these findings and the implications they have for planet formation more generally.

  11. Collimated Outflow Formation via Binary Stars. 3-D Simulations of AGB Wind and Disk Wind Interactions

    CERN Document Server

    García-Arredondo, F; Frank, Adam

    2004-01-01

    We present three-dimensional hydrodynamic simulations of the interaction of a slow wind from an asymptotic giant branch(AGB) star and a jet blown by an orbiting companion. The jet or "Collimated Fast Wind" is assumed to originate from an accretion disk which forms via Bondi accretion of the AGB wind or Roche lobe overflow. We present two distinct regimes in the wind-jet interaction determined by the ratio of the AGB wind to jet momentum flux. Our results show that when the wind momentum flux overwhelms the flux in the jet a more dis-ordered outflow outflow results with the jet assuming a corkscrew pattern and multiple shock structures driven into the AGB wind. In the opposite regime the jet dominates and will drive a highly collimated narrow waisted outflow. We compare our results with scenarios described by Soker & Rappaport (2000) and extrapolate the structures observed in PNe and Symbiotic stars.

  12. Determining element abundances of [WC]-type Central Stars for probing stellar evolution and nucleosynthesis

    CERN Document Server

    Todt, H; Hamann, W -R; Gräfener, G

    2007-01-01

    [WC]-type CSPNs are hydrogen-deficient Central Stars of Planetary Nebulae showing strong stellar winds and a carbon-rich chemistry. We have analyzed new high-resolution spectra of [WC]-type CSPNs with the Potsdam Wolf-Rayet (PoWR) non-LTE expanding atmosphere models, using upgraded model atoms and atomic data. Previous analyses are repeated on the basis of the current models which account for iron-line blanketing. We especially focus on determining the chemical composition, including some trace elements like nitrogen which are of key importance for understanding the evolutionary origin of the hydrogen-deficient Central Stars.

  13. Modeling pulsations in hot stars with winds

    International Nuclear Information System (INIS)

    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.

  14. Evolution of Super Star Cluster Winds with Strong Cooling

    OpenAIRE

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

    2011-01-01

    We study the evolution of Super Star Cluster (SSC) winds driven by stellar winds and supernova (SN) 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...

  15. Hot star wind models with new solar abundances

    Czech Academy of Sciences Publication Activity Database

    Krtička, J.; Kubát, Jiří

    2007-01-01

    Roč. 464, č. 2 (2007), L17-L20. ISSN 0004-6361 R&D Projects: GA ČR GA205/04/1267 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * mass-loss * early-type * hydrodynamics * winds outflows Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.259, year: 2007

  16. CNO-driven winds of hot first stars

    Czech Academy of Sciences Publication Activity Database

    Krtička, J.; Kubát, Jiří

    2009-01-01

    Roč. 493, č. 2 (2009), s. 585-593. ISSN 0004-6361 R&D Projects: GA ČR GA205/07/0031 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars winds * outflows * hydrodynamics Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.179, year: 2009

  17. Colliding Winds in Low-Mass Binary Star Systems: wind interactions and implications for habitable planets

    CERN Document Server

    Johnstone, C P; Pilat-Lohinger, E; Bisikalo, D; Güdel, M; Eggl, S

    2015-01-01

    Context. In binary star systems, the winds from the two components impact each other, leading to strong shocks and regions of enhanced density and temperature. Potentially habitable circumbinary planets must continually be exposed to these interactions regions. Aims. We study, for the first time, the interactions between winds from low-mass stars in a binary system, to show the wind conditions seen by potentially habitable circumbinary planets. Methods. We use the advanced 3D numerical hydrodynamic code Nurgush to model the wind interactions of two identical winds from two solar mass stars with circular orbits and a binary separation of 0.5 AU. As input into this model, we use a 1D hydrodynamic simulation of the solar wind, run using the Versatile Advection Code. We derive the locations of stable and habitable orbits in this system to explore what wind conditions potentially habitable planets will be exposed to during their orbits. Results. Our wind interaction simulations result in the formation of two stron...

  18. Multicomponent radiatively driven stellar winds II. Gayley-Owocki heating in multitemperature winds of OB stars

    CERN Document Server

    Krticka, J; Krticka, Jiri; Kubat, Jiri

    2001-01-01

    We show that the so-called Gayley-Owocki (Doppler) heating is important for the temperature structure of the wind of main sequence stars cooler than the spectral type O6. The formula for Gayley-Owocki heating is derived directly from the Boltzmann equation as a direct consequence of the dependence of the driving force on the velocity gradient. Since Gayley-Owocki heating deposits heat directly to the absorbing ions, we also investigated the possibility that individual components of the radiatively driven stellar wind have different temperatures. This effect is negligible in the wind of O stars, whereas a significant temperature difference takes place in the winds of main sequence B stars for stars cooler than B2. Typical temperature difference between absorbing ions and other flow components for such stars is of the order 10^3 K. However, in the case when passive component falls back onto the star the absorbing component reaches temperatures of order 10^6 K, which allows for emission of X-rays. Moreover, we c...

  19. EVOLUTION OF SUPER STAR CLUSTER WINDS WITH STRONG COOLING

    International Nuclear Information System (INIS)

    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.

  20. Wolf-Rayet central stars of planetary nebulae

    Science.gov (United States)

    Todt, H.; Hamann, W.-R.

    A significant number of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient, showing a chemical composition of helium, carbon, and oxygen. Most of them exhibit Wolf-Rayet-like emission line spectra, similar to those of the massive WC Pop I stars, 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, which is of spectral type [WN/C], and IC 4663 and Abell 48, which are of spectral type [WN]. We review spectral analyses of Wolf-Rayet type central stars of different evolutionary stages and discuss the results in the context of stellar evolution. Especially we consider the question of a common evolutionary channel for [WC] stars. The constraints on the formation of [WN] or [WC/N] subtype stars will also be addressed.

  1. Globular cluster winds with central accretion by a massive compact object or subcluster

    Science.gov (United States)

    Durisen, R. H.; Burns, J. O.

    1981-01-01

    Steady-state isothermal wind flows are computed with accretion by a central mass concentration in spherically symmetric systems of gas-losing stars. Solutions are uniquely determined by two dimensionless parameters lambda and m, where lambda is approximately equal to the square of the ratio of the central escape velocity to the sound speed and m is approximately equal to the ratio of the central point mass to the cluster core mass. The models are applied to globular clusters for two types of central mass concentration - a single massive black hole and a subcluster of massive stars. A hard (greater than a keV) X-ray source due to a central black hole fed by clusterwide inflow does not provide a consistent model for globular cluster X-ray sources. However, in the case of hot (T being greater than or approximately equal to 2 x 10 to the 5th K) winds, gas trapping by a central subcluster of neutron stars or of binaries containing white dwarfs could explain recent UV and H-alpha observations. Similar applications to elliptical galaxies are discussed.

  2. A Dynamical Model for Gas Flows, Star Formation, and Nuclear Winds in Galactic Centres

    CERN Document Server

    Krumholz., Mark R; Crocker, Roland M

    2016-01-01

    We present a dynamical model for gas transport, star formation, and winds in the nuclear regions of galaxies, focusing on the Milky Way's Central Molecular Zone (CMZ). In our model angular momentum and mass are transported by a combination of gravitational and bar-driven acoustic instabilities. In gravitationally-unstable regions the gas can form stars, and the resulting feedback drives both turbulence and a wind that ejects mass from the CMZ. We show that the CMZ is in a quasi-steady state where mass deposited at large radii by the bar is transported inward to a star-forming, ring-shaped region at $\\sim 100$ pc from the Galactic Centre, where the shear reaches a minimum. This ring undergoes episodic starbursts, with bursts lasting $\\sim 5-10$ Myr occurring at $\\sim 20-40$ Myr intervals. During quiescence the gas in the ring is not fully cleared, but is driven out of a self-gravitating state by the momentum injected by expanding supernova remnants. Starbursts also drive a wind off the star-forming ring, with ...

  3. Gone With the Wind: Where is the Missing Stellar Wind Energy from Massive Star Clusters?

    CERN Document Server

    Rosen, Anna L; Krumholz, Mark R; Ramirez-Ruiz, Enrico

    2014-01-01

    Star clusters larger than $\\sim 10^{3}$ $M_\\odot$ contain multiple hot stars that launch fast stellar winds. The integrated kinetic energy carried by these winds is comparable to that delivered by supernova explosions, suggesting that at early times winds could be an important form of feedback on the surrounding cold material from which the star cluster formed. However, the interaction of these winds with the surrounding clumpy, turbulent, cold gas is complex and poorly understood. Here we investigate this problem via an accounting exercise: we use empirically determined properties of four well-studied massive star clusters to determine where the energy injected by stellar winds ultimately ends up. We consider a range of kinetic energy loss channels, including radiative cooling, mechanical work on the cold interstellar medium, thermal conduction, heating of dust via collisions by the hot gas, and bulk advection of thermal energy by the hot gas. We show that, for at least some of the clusters, none of these ch...

  4. X-ray diagnostics of massive star winds

    CERN Document Server

    Oskinova, Lidia

    2016-01-01

    Nearly all types of massive stars with radiatively driven stellar winds are X-ray sources that can be observed by the presently operating powerful X-ray telescopes. In this review I briefly address recent advances in our understanding of stellar winds obtained from X-ray observations. The winds of OB dwarfs with subtypes later than O9V may be predominantly in a hot phase, and X-ray observations offer the best window for their studies. The X-ray properties of OB supergiants are largely determined by the effects of radiative transfer in their clumped stellar winds. The recently suggested method to directly measure mass-loss rates of O stars by fitting the shapes of X-ray emission lines is considered but its validity cannot be confirmed. To obtain robust quantitative information on stellar wind parameters from X-ray spectroscopy, a multiwavelength analysis by means of stellar atmosphere models is required. Independent groups are now performing such analyses with encouraging results. Joint analyses of optical, UV...

  5. Magnetic fields, winds and X-rays of the massive stars in the Orion Nebula Cluster

    OpenAIRE

    Petit, V.; Wade, G. A.; Alecian, E.; Drissen, L.; Montmerle, T.; ud-Doula, A.

    2010-01-01

    In some massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind. Although theoretical models and MHD simulations are able to illustrate the dynamics of such a magnetized wind, the impact of this wind-field interaction on the observable properties of a magnetic star - X-ray emission, photometric and spectral variability - is still unclear. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars, b...

  6. Weak magnetic fields in central stars of planetary nebulae?

    CERN Document Server

    Steffen, M; Todt, H; Schöller, M; Hamann, W -R; Sandin, C; Schönberner, D

    2014-01-01

    It is not yet clear whether magnetic fields play an essential role in shaping planetary nebulae (PNe), or whether stellar rotation alone and/or a close binary companion can account for the variety of the observed nebular morphologies. In a quest for empirical evidence verifying or disproving the role of magnetic fields in shaping PNe, we follow up on previous attempts to measure the magnetic field in a representative sample of PN central stars. We obtained low-resolution polarimetric spectra with FORS 2 at VLT for a sample of twelve bright central stars of PNe with different morphology, including two round nebulae, seven elliptical nebulae, and three bipolar nebulae. Two targets are Wolf-Rayet type central stars. For the majority of the observed central stars, we do not find any significant evidence for the existence of surface magnetic fields. However, our measurements may indicate the presence of weak mean longitudinal magnetic fields of the order of 100 Gauss in the central star of the young elliptical pla...

  7. The Cluster Wind from Local Massive Star Clusters

    OpenAIRE

    Stevens, Ian R.; Hartwell, Joanna M.

    2003-01-01

    Results of a study of the theoretically predicted and observed X-ray properties of local massive star clusters are presented, with a focus on understanding the mass and energy flow from these clusters into the ISM via a cluster wind. A simple theoretical model, based on the work of Chevalier & Clegg (1985), is used to predict the theoretical cluster properties, and these are compared to those obtained from recent Chandra observations. The model includes the effect of lower energy transfer eff...

  8. Kinematic ages of central stars of planetary nebulae

    CERN Document Server

    Maciel, W J; Costa, R D D

    2011-01-01

    The age distribution of the central stars of planetary nebulae (CSPN) is estimated using two methods based on their kinematic properties. First, the expected rotation velocities of the nebulae at their Galactocentric distances are compared with the predicted values for the rotation curve, and the differences are attributed to the different ages of the evolved stars. Adopting the relation between the ages and the velocity dispersions determined by the Geneva-Copenhagen survey, the age distribution can be derived. Second, the U, V, W, velocity components of the stars are determined, and the corresponding age-velocity dispersion relations are used to infer the age distribution. These methods have been applied to two samples of PN in the Galaxy. The results are similar for both samples, and show that the age distribution of the PN central stars concentrates in ages lower than 5 Gyr, peaking at about 1 to 3 Gyr.

  9. Improved spectral descriptions of planetary nebulae central stars

    CERN Document Server

    Weidmann, Walter; Gamen, Roberto

    2015-01-01

    Context. At least 492 central stars of Galactic planetary nebulae (CSPNs) have been assigned spectral types. Since many CSPNs are faint, these classification efforts are frequently made at low spectral resolution. However, the stellar Balmer absorption lines are contaminated with nebular emission; therefore in many cases a low-resolution spectrum does not enable the determination of the H abundance in the CSPN photosphere. Whether or not the photosphere is H deficient is arguably the most important fact we should expect to extract from the CSPN spectrum, and should be the basis for an adequate spectral classification system. Aims. Our purpose is to provide accurate spectral classifications and contribute to the knowledge of central stars of planetary nebulae and stellar evolution. Methods. We have obtained and studied higher quality spectra of CSPNs described in the literature as weak emission-line star (WELS). We provide descriptions of 19 CSPN spectra. These stars had been previously classified at low spect...

  10. On the Origin of Wind Line Variability in O Stars

    CERN Document Server

    Massa, D

    2015-01-01

    We analyze 10 UV time series for 5 stars which fulfill specific sampling and spectral criteria to constrain the origin of large-scale wind structure in O stars. We argue that excited state lines must arise close to the stellar surface and are an excellent diagnostic complement to resonance lines which, due to radiative transfer effects, rarely show variability at low velocity. Consequently, we splice dynamic spectra of the excited state line, N IV1718, at low velocity to those of 1393 component of the Si IV 1400 doublet at high velocity in order to examine the temporal evolution of wind line features. These spliced time series reveal that nearly all of the features observed in the time series originate at or very near the stellar surface. Further, we positively identify the observational signature of equatorial co-rotating interaction regions in two of the five stars and possibly two others. In addition, we see no evidence for features originating further out in the wind. We use our results to consolidate the...

  11. Evolution of Super Star Cluster Winds with Strong Cooling

    CERN Document Server

    Wunsch, Richard; Palous, Jan; Tenorio-Tagle, Guillermo; Munoz-Tunon, Casiana

    2011-01-01

    We study the evolution of Super Star Cluster (SSC) winds driven by stellar winds and supernova (SN) 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 consider also conditions with low heating efficiency of ...

  12. Hydrodynamic model atmospheres for WR stars: Self-consistent modeling of a WC star wind

    CERN Document Server

    Gräfener, G

    2004-01-01

    We present the first non-LTE atmosphere models for WR stars that incorporate a self-consistent solution of the hydrodynamic equations. The models account for iron-group line-blanketing and clumping, and compute the hydrodynamic structure of a radiatively driven wind consistently with the non-LTE radiation transport in the co-moving frame. We construct a self-consistent wind model that reproduces all observed properties of an early-type WC star (WC5). We find that the WR-type mass-loss is initiated at high optical depth by the so-called `Hot Iron Bump' opacities (Fe IX-XVI). The acceleration of the outer wind regions is performed by iron-group ions of lower excitation in combination with C and O. Consequently, the wind structure shows two acceleration regions, one close to the hydrostatic wind base in the optically thick part of the atmosphere, and another farther out in the wind. In addition to the radiative acceleration, the `Iron Bump' opacities are responsible for an intense heating of deep atmospheric lay...

  13. Ongoing surveys for close binary central stars and wider implications

    OpenAIRE

    Miszalski, Brent

    2011-01-01

    Binary central stars have long been invoked to explain the vexing shapes of planetary nebulae (PNe) despite there being scant direct evidence to support this hypothesis. Modern large-scale surveys and improved observing strategies have allowed us to significantly boost the number of known close binary central stars and estimate at least 20% of PNe have close binary nuclei that passed through a common-envelope (CE) phase. The larger sample of post-CE nebulae appears to have a high proportion o...

  14. Improved spectral descriptions of planetary nebulae central stars

    Science.gov (United States)

    Weidmann, W. A.; Méndez, R. H.; Gamen, R.

    2015-07-01

    Context. At least 492 central stars of Galactic planetary nebulae (CSPNs) have been assigned spectral types. Since many CSPNs are faint, these classification efforts are frequently made at low spectral resolution. However, the stellar Balmer absorption lines are contaminated with nebular emission; therefore in many cases a low-resolution spectrum does not enable the determination of the H abundance in the CSPN photosphere. Whether or not the photosphere is H deficient is arguably the most important fact we should expect to extract from the CSPN spectrum, and should be the basis for an adequate spectral classification system. Aims: Our purpose is to provide accurate spectral classifications and contribute to the knowledge of central stars of planetary nebulae and stellar evolution. Methods: We have obtained and studied higher quality spectra of CSPNs described in the literature as weak emission-line star (WELS). We provide descriptions of 19 CSPN spectra. These stars had been previously classified at low spectral resolution. We used medium-resolution spectra taken with the Gemini Multi-Object Spectrograph (GMOS). We provide spectral types in the Morgan-Keenan (MK) system whenever possible. Results: Twelve stars in our sample appear to have normal H rich photospheric abundances, and five stars remain unclassified. The rest (two) are most probably H deficient. Of all central stars described by other authors as WELS, we find that at least 26% of them are, in fact, H rich O stars, and at least 3% are H deficient. This supports the suggestion that the denomination WELS should not be taken as a spectral type, because, as a WELS is based on low-resolution spectra, it cannot provide enough information about the photospheric H abundance.

  15. Relating binary-star planetary systems to central configurations

    CERN Document Server

    Veras, Dimitri

    2016-01-01

    Binary-star exoplanetary systems are now known to be common, for both wide and close binaries. However, their orbital evolution is generally unsolvable. Special cases of the N-body problem which are in fact completely solvable include dynamical architectures known as central configurations. Here, I utilize recent advances in our knowledge of central configurations to assess the plausibility of linking them to coplanar exoplanetary binary systems. By simply restricting constituent masses to be within stellar or substellar ranges characteristic of planetary systems, I find that (i) this constraint reduces by over 90 per cent the phase space in which central configurations may occur, (ii) both equal-mass and unequal-mass binary stars admit central configurations, (iii) these configurations effectively represent different geometrical extensions of the Sun-Jupiter-Trojan-like architecture, (iv) deviations from these geometries are no greater than ten degrees, and (v) the deviation increases as the substellar masse...

  16. Peculiar early-type galaxies with central star formation

    Institute of Scientific and Technical Information of China (English)

    Chong Ge; Qiu-Sheng Gu

    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 l gas mass.The star formation history of these ETGs is affected by the environment,e.g.in the denser environment the H 1 gas is less and the total SFR is lower.We also discuss the origin of the central star formation of these early-type galaxies.

  17. VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS

    International Nuclear Information System (INIS)

    We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I λ10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities ∼400 km s–1 appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.

  18. Variable Winds and Dust Formation in R Coronae Borealis Stars

    CERN Document Server

    Clayton, Geoffrey C; Zhang, Wanshu

    2013-01-01

    We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I 10830 lines of twelve R Coronae Borealis (RCB) stars over short (1 month) and long (3 year) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities ~400 km/s appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.

  19. 2D Models for Dust-driven AGB Star Winds

    CERN Document Server

    Woitke, P

    2006-01-01

    New axisymmetric (2D) models for dust-driven winds of C-stars are presented which include hydrodynamics with radiation pressure on dust, equilibrium chemistry and time-dependent dust formation with coupled grey Monte Carlo radiative transfer. Considering the most simple case without stellar pulsation (hydrostatic inner boundary condition) these models reveal a more complex picture of the dust formation and wind acceleration as compared to earlier published spherically symmetric (1D) models. The so-called exterior $\\kappa$-mechanism causes radial oscillations with short phases of active dust formation between longer phases without appreciable dust formation, just like in the 1D models. However, in 2D geometry, the oscillations can be out-of-phase at different places above the stellar atmosphere which result in the formation of dust arcs or smaller caps that only occupy a certain fraction of the total solid angle. These dust structures are accelerated outward by radiation pressure, expanding radially and tangen...

  20. Applicability of steady models for hot-star winds

    International Nuclear Information System (INIS)

    Non-Sobolev models of radiatively driven stellar winds based on a pure-absorption approximation do not have a well-defined steady state. Here the implications of this for flow time-dependence are examined, showing that, under such circumstances, instabilities in the flow attain an absolute character that leads to intrinsic variability. In this case, steady solutions are inherently inapplicable because they do not represent physically realizable states. However, for actual hot-star winds, driving is principally by scattering, not pure absorption. In practice, the relatively weak force associated with slight asymmetries in the diffuse, scattered radiation field may play a crucial role in breaking the solution degeneracy and reducing the instability from an absolute to an advective character. 16 refs

  1. Hot star wind models with new solar abundances

    CERN Document Server

    Krticka, J; Krticka, Jiri; Kubat, Jiri

    2007-01-01

    We compare the hot star wind models calculated assuming older solar abundance determination with models calculated using the recently published values derived from 3D hydrodynamical model atmospheres. We show that the use of new abundances with lower metallicity improves the agreement between wind observation and theory in several aspects: (1) The predicted wind mass-loss rates are lower by a factor of 0.76. This leads to a better agreement with mass-loss rate determinations derived from observations with account of clumping. (2) As a result of the lowering of mass-loss rates, there is a better agreement between predicted modified wind momentum-luminosity relationship and that derived from observations with account of clumping. (3) Both the lower mass fraction of heavier elements and lower mass-loss rates lead to a decrease of the opacity in the X-ray region. This has influence on the prediction of the X-ray line profile shapes. (4) There is a better agreement between predicted PV ionization fractions and tho...

  2. Exploring the central engines of young stars

    Directory of Open Access Journals (Sweden)

    T. P. Ray

    2002-01-01

    Full Text Available Para entender los or genes de los jets de l neas de emisi on de estrellas j ovenes, tenemos que investigar sus ambientes circunestelares inmediatos a escalas de 10UA o menos. Aunque esto es dif cil de hacer en fuentes altamente embebidas, fuentes de ujos opticamente visibles, tales como las estrellas T Tauri cl asicas y estrellas Herbig Ae/Be, a veces nos ofrecen una ventana hacia sus \\m aquinas centrales". Aqu , en particular las l neas de emisi on prohibidas son un diagn ostico extremadamente util. Por ejemplo, en ellas se pueden ver diferencias mayores en las condiciones de excitaci on, velocidad, angulos de apertura, y as sucesivamente, entre los jets opuestos cerca de su fuente. Adem as, en la fuente no solo observamos emisi on de alta velocidad (del jet, sino tambi en ujos de baja velocidad que se mueven a velocidades cercanas a la sist emica de la estrella. El origen de esa emisi on de baja velocidad sigue siendo controversial. Aqu revisamos brevemente descubrimientos recientes en esta area usando im agenes de HST y espectroscop a, como tambi en observaciones espectro-astrom etricas terrestres. El ujo optico de DGTau se usar a como un ejemplo y observaciones recientes de HST se examinar an en el margen de los modelos actuales.

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

    Science.gov (United States)

    Cheung, Edmond; Bundy, Kevin; SDSS-IV/MaNGA

    2016-01-01

    In the last 10 billion years (i.e., since redshift z ~2) the number of quiescent galaxies with little to no ongoing star formation has grown by a factor ~25. This is challenging to understand since galaxy formation models predict that these galaxies will continue to accrete fresh gas over their lifetimes, relatively little of which is required to reignite measurable star formation. It is thought that feedback from fresh gas accreting onto a central active galactic nucleus (AGN) might help such galaxies maintain their quiescence, but observational evidence for such ``maintenance mode feedback'' remains sparse. Using novel imaging spectroscopy from the SDSS-IV MaNGA Survey (Sloan Digital Sky Survey IV: Mapping Nearby Galaxies at Apache Point Observatory), we present evidence for a new maintenance mode phenomenon we term ``red geysers,'' a potentially episodic but relatively low-power AGN driven wind present in typical quiescent field galaxies of moderate mass and spheroidal morphology. We examine an archetypal red geyser that appears to be accreting gas from a low-mass companion but has no corresponding star formation. Instead, we find evidence for a galaxy-scale ionized wind with outflow velocities reaching more than 300 km/s and high velocity dispersions. We also detect a narrow biconical pattern of strong emission line equivalent widths consistent with fast shocks. Given additional confirmation of a radio AGN present in the galaxy, we propose that red geysers such as this may be a common mode in which gas accretion activates an ionized wind feedback mechanism that prevents star formation and helps moderate luminosity quiescent galaxies maintain their quiescence.

  4. Spectral Analysis of Central Stars of Planetary Nebulae

    CERN Document Server

    Rauch, Thomas; Ziegler, Marc; Kruk, Jeffrey W; Oliveira, Cristina M

    2007-01-01

    Spectral analysis by means of NLTE model atmospheres has presently arrived at a high level of sophistication. High-resolution spectra of central stars of planetary nebulae can be reproduced in detail from the infrared to the X-ray wavelength range. In the case of LSV +4621, the exciting star of Sh 2-216, we demonstrate the state-of-the-art in the determination of photospheric properties like, e.g., effective temperature, surface gravity, and abundances of elements from hydrogen to nickel. From such detailed model atmospheres, we can reliably predict the ionizing spectrum of a central star which is a necessary input for the precise analysis of its ambient nebula. NLTE model-atmosphere spectra, however, are not only accessible for specialists. In the framework of the German Astrophysical Virtual Observatory (GAVO), we provide pre-calculated grids of tables with synthetic spectra of hot, compact stars as well as a tool to calculate individual model-atmosphere spectra in order to make the use of synthetic stellar...

  5. Galactic kinematics of planetary nebulae with [WC] central star

    CERN Document Server

    Peña, Miriam; García-Rojas, Jorge

    2013-01-01

    High resolution spectra are used to analyze the galactic kinematics and distribution of a sample of planetary nebulae with [WR] and 'wel' central star ([WR]PN and WLPN). The circular and peculiar velocities (Vpec) of the objects were derived. The results are: a) [WR]PNe are distributed mainly in the galactic disk and they are more concentrated in a thinner disk than WLPNe and normal PNe, which corresponds to a younger population; b) the sample was separated in Peimbert's types, and it is found that Type I PNe have Vpec <50 km s-1, indicating young objects. Most of the [WR]PNe are of Type II showing Vpec <60 km s-1, although a small percentage is of Type III, with larger Vpec showing that the Wolf-Rayet phenomenon in central stars can occur at any stellar mass and in old objects. None of our WLPNe is Type I. Thus, [WR]PNe and WLPNe are unrelated objects.

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

    Science.gov (United States)

    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

  7. Atomic physics of shocked plasma in winds of massive stars

    Energy Technology Data Exchange (ETDEWEB)

    Leutenegger, Maurice A.; Cohen, David H.; Owocki, Stanley P. [NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); CRESST/UMBC (United States); Swarthmore College, Swarthmore, PA 19081 (United States); Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States)

    2012-05-25

    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.

  8. Star Formation in the Central Kiloparsec of Nearby Active Galaxies

    International Nuclear Information System (INIS)

    We investigate star formation (SF) activity in the central kpc of a sample of nearby Active Galactic Nuclei (AGNs). AGN activities are expected to either trigger SF via accreting ISM to the central regions of the host galaxies or quench the SF via the energy feedback of the AGNs. To study the AGN-SF relation we select 113 nearby galaxies that host 8 GHz central radio sources. We use 8 GHz radio emission to represent the AGN activity and 8 micron dust emission in the central kpc regions of these galaxies to estimate the SF rate (SFR). The SFR is found to be correlated with the stellar mass for stellar mass greater than 1010 solar mass and looks scattered for stellar mass less than 1010 solar mass. There is no correlation between the specific SFR (SSFR) and the AGN activity for all sources. However, if we exclude the sources with the central stellar mass greater than 1010 solar mass, we find that the 8 GHz radio emission is well correlated with the SSFR. These results suggest that the AGN activity is significant in triggering SF activity only for small galaxies. Besides, we also select about 20 nearby AGN galaxies to investigate the radial variation of their surface specific star formation rate.

  9. Ongoing surveys for close binary central stars and wider implications

    CERN Document Server

    Miszalski, Brent

    2011-01-01

    Binary central stars have long been invoked to explain the vexing shapes of planetary nebulae (PNe) despite there being scant direct evidence to support this hypothesis. Modern large-scale surveys and improved observing strategies have allowed us to significantly boost the number of known close binary central stars and estimate at least 20% of PNe have close binary nuclei that passed through a common-envelope (CE) phase. The larger sample of post-CE nebulae appears to have a high proportion of bipolar nebulae, low-ionisation structures (especially in SN1987A-like rings) and polar outflows or jets. These trends are guiding our target selection in ongoing multi-epoch spectroscopic and photometric surveys for new binaries. Multiple new discoveries are being uncovered that further strengthen the connection between post-CE trends and close binaries. These ongoing surveys also have wider implications for understanding CE evolution, low-ionisation structure and jet formation, spectral classification of central stars...

  10. Abbott Wave-Triggered Runaway in Line-Driven Winds from Stars and Accretion Disks

    OpenAIRE

    Feldmeier, Achim; Shlosman, Isaac

    2001-01-01

    Line-driven winds from stars and accretion disks are accelerated by scattering in numerous line transitions. The wind is believed to adopt a unique critical solution, out of the infinite variety of shallow and steep solutions. We study the inherent dynamics of the transition towards the critical wind. A new runaway wind mechanism is analyzed in terms of radiative-acoustic (Abbott) waves which are responsible for shaping the wind velocity law and fixing the mass loss. Three different flow type...

  11. Star Formation in the Central Regions of Galaxies

    Science.gov (United States)

    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

  12. Dusty disks around central stars of planetary nebulae

    Energy Technology Data Exchange (ETDEWEB)

    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.

  13. The G305 star-forming complex: the central star clusters Danks 1 and Danks 2

    CERN Document Server

    Davies, Ben; Trombley, Christine; Figer, Donald F; Najarro, Francisco; Crowther, Paul A; Kudritzki, Rolf-Peter; Thompson, Mark; Urquhart, James S; Hindson, Luke

    2011-01-01

    The G305 HII complex (G305.4+0.1) is one of the most massive star forming structures yet identified within the Galaxy. It is host to many massive stars at all stages of formation and evolution, from embedded molecular cores to post main-sequence stars. Here, we present a detailed near-infrared analysis of the two central star clusters Danks 1 and Danks 2, using HST+NICMOS imaging and VLT+ISAAC spectroscopy. We find that the spectro-photometric distance to the clusters is consistent with the kinematic distance to the G305 complex, an average of all measurements giving a distance of 3.8\\pm0.6kpc. From analysis of the stellar populations and the pre-main-sequence stars we find that Danks 2 is the elder of the two clusters, with an age of 3^{+3}_{-1}Myr. Danks 1 is clearly younger with an age of 1.5^{+1.5}_{-0.5}Myr, and is dominated by three very luminous H-rich Wolf-Rayet stars which may have masses \\geq100\\msun. The two clusters have mass functions consistent with the Salpeter slope, and total cluster masses o...

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

    Science.gov (United States)

    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. PMID:27225122

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

    Science.gov (United States)

    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.

    2016-05-01

    Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 1010 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, 2, 3, 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 × 1010 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.

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

    CERN Document Server

    Cheung, Edmond; 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

    2016-01-01

    Quiescent galaxies with little or no ongoing star formation dominate the galaxy population above $M_{*}\\sim 2 \\times 10^{10}~M_{\\odot}$, where their numbers have increased by a factor of $\\sim25$ since $z\\sim2$. Once star formation is initially shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat subsequently accreted gas from stellar mass loss or mergers 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 centers 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 ar...

  17. Decadal predictability of regional scale wind speed and wind energy potentials over Central Europe

    Science.gov (United States)

    Moemken, Julia; Reyers, Mark; Buldmann, Benjamin; Pinto, Joaquim G.

    2016-04-01

    Regional climate predictions on timescales from one year to one decade are gaining importance since this time frame falls within the planning horizon of politics, economy, and society. In this context, decadal predictions are of particular interest for the development of renewable energies such as wind energy. The present study examines the decadal predictability of regional scale wind speed and wind energy potentials in the framework of the MiKlip consortium ("Mittelfristige Klimaprognosen"; www.fona-miklip.de). This consortium aims to develop a model system based on the Max-Planck-Institute Earth System Model (MPI-ESM) that can provide skilful decadal predictions on regional and global scales. Three generations of the decadal prediction system, which differ primarily in their ocean initialisation, are analysed here. Ensembles of uninitialised historical and yearly initialised hindcast experiments are used to assess different skill scores for 10m wind speeds and wind energy output (Eout) over Central Europe, with special focus given to Germany. With this aim, a statistical-dynamical downscaling (SDD) approach is used for the regionalisation of the global datasets. Its added value is evaluated by comparison of skill scores for MPI-ESM large-scale wind speeds and SDD simulated regional wind speeds. All three MPI-ESM ensemble generations show some forecast skill for annual mean wind speed and Eout over Central Europe on yearly and multi-yearly time scales. The forecast skill is mostly limited to the first years after initialisation. Differences between the three ensemble generations are generally small. The regionalisation preserves and sometimes increases the forecast skill of the global runs but results depend on lead time and ensemble generation. Moreover, regionalisation often improves the ensemble spread. Seasonal Eout skills are generally lower than for annual means. Skill scores are lowest during summer, and persist longest in autumn. A large-scale westerly

  18. The Properties of the Progenitor Supernova, Pulsar Wind, and Neutron Star inside PWN G54.1+0.3

    CERN Document Server

    Gelfand, Joseph D; Temim, Tea

    2015-01-01

    The evolution of a pulsar wind nebula (PWN) inside a supernova remnant (SNR) is sensitive to properties of the central neutron star, pulsar wind, progenitor supernova, and interstellar medium. These properties are both difficult to measure directly and critical for understanding the formation of neutron stars and their interaction with the surrounding medium. In this paper, we determine these properties for PWN G54.1+0.3 by fitting its observed properties with a model for the dynamical and radiative evolution of a PWN inside an SNR. Our modeling suggests that the progenitor of G54.1+0.3 was an isolated ~15-20 Solar Mass star which exploded inside a massive star cluster, creating a neutron star initially spinning with period ~30-80ms. We also find that >99.9% of the pulsar's rotational energy is injected into the PWN as relativistic electrons and positrons whose energy spectrum is well characterized by a broken power-law. Lastly, we propose future observations which can both test the validity of this model and...

  19. Echelle spectroscopy of the central stars of planetary nebulae

    International Nuclear Information System (INIS)

    Presented in this work are the results of a spectroscopic study of the central stars of planetary nebulae (CSPN) conducted at high resolution. From detailed comparisons of this photospheric absorption line profiles observed at high signal-to-noise with the NLTE model atmosphere line profiles of Kudritzki, et al., in Munich, West Germany, the photospheric effective temperatures (Teff), surface gravities (g), and helium abundances (y) were derived. Placement of the CSPN in the distance-independent log (g) - log (Teff) diagram allowed central star masses and evolutionary ages to be deduced via comparisons with published evolutionary model calculations. Spectroscopic distances to the CSPN were estimated from the best fit model fluxes, leading to dynamical expansion ages for the surrounding nebulae which were typically much greater than the corresponding CSPN evolutionary ages. Two possible reasons for this timescale disagreement were quantitatively investigated: (1) the nebulae could have experienced a phase of rapid photo-ionization of material ejected while the stars were still on the AGB, or (2) the AGB - CSPN evolutionary times could have been increased by small additional amounts of residual envelope material remaining after the superwind mass loss phase. An important preliminary phase of this project was the design and construction of a CCD echelle spectrography for the Palomar 1.5 m telescope. The scientific objectives of the CSPN study with this new instrument required a thorough investigation into the data reduction process for CCD echelle spectra, and a set of Fortran subroutines were written for this purpose as part of the FIGARO data reduction package

  20. The Emerging Planetary Nebula CRL 618 and its Unsettled Central Star(s)

    CERN Document Server

    Balick, B; Raga, A; Kwitter, K B; Velázquez, P F

    2014-01-01

    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 PNe 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 H{\\alpha} emission from the symbiotic star. Comparing our line ratios with those observed historically shows that (1) the [O III]/H\\b{eta} and He I/H\\b{eta} ratios have been stead...

  1. Polarimetric modeling of corotating interaction regions (CIRs) threading massive-star winds

    CERN Document Server

    Ignace, R; Proulx-Giraldeau, F

    2015-01-01

    Massive star winds are complex radiation-hydrodynamic (sometimes magnetohydrodynamic) outflows that are propelled by their enormously strong luminosities. The winds are often found to be structured and variable, but can also display periodic or quasi-periodic behavior in a variety of wind diagnostics. The regular variations observed in putatively single stars, especially in UV wind lines, have often been attributed to corotating interaction regions (CIRs) like those seen in the solar wind. We present light curves for variable polarization from winds with CIR structures. We develop a model for a time-independent CIR based on a kinematical description. Assuming optically thin electron scattering, we explore the range of polarimetric light curves that result as the curvature, latitude, and number of CIRs are varied. We find that a diverse array of variable polarizations result from an exploration of cases. The net polarization from an unresolved source is weighted more toward the inner radii of the wind. Given t...

  2. Winds driven by super-star clusters: The self-consistent radiative solution

    OpenAIRE

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Rodriguez-Gonzalez, Ary

    2004-01-01

    Here we present a self-consistent stationary solution for spherically symmetric winds driven by massive star clusters under the impact of radiative cooling. We demonstrate that cooling may modify drastically the distribution of temperature if the rate of injected energy approaches a critical value. We also prove that the stationary wind solution does not exist whenever the energy radiated away at the star cluster center exceeds ~ 30% of the energy deposition rate. Finally we thoroughly discus...

  3. Large-scale winds driven by flare-star mass loss

    International Nuclear Information System (INIS)

    The effect of injecting substantial quantities of high-temperature material into the interstellar medium form flare-star activity is examined. Using models like those developed by Mathews and Baker for calculating supernovae-driven elliptical galaxy winds, we consider the effects of flare-star mass loss in elliptical galaxies and globular clusters. It is found that, even in the absence of supernovae, and with a substantially smaller flare-star mass input than may be plausibly expected, steady outflowing winds will develop in these objects. Such winds may explain the observed absence of substantial quantities of interstellar material in globular clusters and elliptical galaxies. Assuming the presence of elliptical galaxy winds in clusters of galaxies, we consider the effects of such winds on intergalactic medium dynamics. We find that a hot intergalactic medium is to be expected and that instabilities resulting in collapse in the center of clusters of galaxies may occur

  4. Impact of Winds from Intermediate-Mass Stars on Molecular Cloud Structure and Turbulence

    CERN Document Server

    Offner, S S R

    2015-01-01

    Observations of nearby molecular clouds detect "shells", which are likely caused by winds from young main sequence stars. However, the progenitors of these observed features are not well characterized and the mass-loss rates inferred from the gas kinematics are several orders of magnitude greater than those predicted by atomic line-driven stellar wind models. We use magnetohydrodynamic simulations to model winds launching within turbulent molecular clouds and explore the impact of wind properties on cloud morphology and turbulence. We find that winds do not produce clear features in turbulent statistics such as the Fourier spectra of density and momentum but do impact the Fourier velocity spectrum. The density and velocity distribution functions, especially as probed by CO spectral lines, strongly indicate the presence and influence of winds. We show that stellar mass-loss rates for individual stars must be $\\dot m_w \\gtrsim 10^{-7}$ Msun yr$^{-1}$, similar to those estimated from observations, to reproduce s...

  5. Orbital elements of barium stars formed through a wind accretion scenario

    CERN Document Server

    Liu, J H; Liang, Y C; Peng, Q H

    2000-01-01

    Taking the total angular momentum conservation in place of the tangential momentum conservation, and considering the square and higher power terms of orbital eccentricity e, the changes of orbital elements of binaries are calculated for wind accretion scenario. These new equations are used to quantitatively explain the observed (e,logP) properties of normal G, K giants and barium stars. Our results reflect the evolution from G, K giant binaries to barium binaries, moreover, the barium stars with longer orbital periods P>1600 days may be formed by accreting part of the ejecta from the intrinsic AGB stars through wind accretion scenario.

  6. Evidence for a warm wind from the red star in symbiotic binaries

    Science.gov (United States)

    Friedjung, M.; Stencel, R. E.; Viotti, R.

    1983-01-01

    A systematic redshift of the high ionization resonance emission lines with respect to the intercombination lines is found from an examination of the ultraviolet spectra of symbiotic stars obtained with IUE. After consideration of other possibilities, this is most probably explained by photon scattering in an expanding envelope optically thick to the resonance lines. Line formation in a wind, or at the base of a wind is therefore suggested. Reasons are also given indicating line formation of the most ionized species in a region with an electron temperature of the order of 100,000 K, probably around the cool star. The behavior of the emission line width with ionization energy seems to support this model. The cool components of symbiotic stars appear to differ from normal red giants, which do not have winds of this temperature. An explanation in terms of a higher rotation velocity due to the binary nature of these stars is suggested.

  7. Puzzling wind properties of young massive stars in SMC-N81

    CERN Document Server

    Martins, F; Hillier, D J; Heydari-Malayeri, M

    2004-01-01

    We present a quantitative study of the stellar and wind properties of massive stars in the compact star forming region SMC-N81. Non-LTE spherically extended atmosphere models including line-blanketing have been computed with the code CMFGEN (Hillier & Miller 1998) and the analysis of UV STIS spectra lead to the following results: 1) The SMC-N81 components are young (~ 0-4 Myrs) O stars with Teff compatible with medium to late subtypes and with luminosities lower than average Galactic O dwarfs, rendering them possible ZAMS candidates; 2) The winds are extremely weak: the mass loss rates (~1e-8/1e-9 Msol/yr) and the modified wind momenta are 1 to 2 orders of magnitude lower than observed so far for Galactic stars, and are lower than the predictions of the most recent hydrodynamical models. The reasons for such weak winds are investigated with special emphasis on the modified wind momenta: 1) There may be a break-down of the wind momentum - luminosity relation (WLR) for dwarf stars at low luminosity (log L/L...

  8. EU Del: exploring the onset of pulsation-driven winds in giant stars

    Science.gov (United States)

    McDonald, I.; Zijlstra, A. A.; Sloan, G. C.; Lagadec, E.; Johnson, C. I.; Uttenthaler, S.; Jones, O. C.; Smith, C. L.

    2016-03-01

    We explore the wind-driving mechanism of giant stars through the nearby (117 pc), intermediate-luminosity (L ≈ 1600 L⊙) star EU Del (HIP 101810, HD 196610). Atacama Pathfinder Experiment observations of the CO (3-2) and (2-1) transitions are used to derive a wind velocity of 9.51 ± 0.02 km s-1, a 12C/13C ratio of 14^{+9}_{-4} and a mass-loss rate of a few × 10-8 M⊙ yr-1. Analysis of published spectra show the star has a metallicity of [Fe/H] = -0.27 ± ˜0.30 dex. The star's dusty envelope lacks a clear 10-μm silicate feature, despite the star's oxygen-rich nature. Radiative transfer modelling cannot fit a wind acceleration model which relies solely on radiation pressure on condensing dust. We compare our results to VY Leo (HIP 53449), a star with similar temperature and luminosity, but different pulsation properties. We suggest the much stronger mass-loss from EU Del may be driven by long-period stellar pulsations, due to its potentially lower mass. We explore the implications for the mass-loss rate and wind velocities of other stars.

  9. Wind Dynamics and Circumstellar Extinction Variations in the T Tauri Star RY Tau

    CERN Document Server

    Babina, Elena V; Petrov, Peter P

    2016-01-01

    The wind interaction with the dusty environment of the classical T Tauri star RY Tau has been investigated. During two seasons of 2013-2015 we carried out a spectroscopic and photometric (BVR) monitoring of the star. A correlation between the stellar brightness and the radial velocity of the wind determined from the H-alpha and Na D line profiles has been found for the first time. The irregular stellar brightness variations are shown to be caused by extinction in a dusty disk wind at a distance of about 0.2 AU from the star. We suppose, that variations of the circumstellar extinction results from cyclic rearrangements of the stellar magnetosphere and coronal mass ejections, which affect the dusty disk wind near the inner boundary of the circumstellar disk.

  10. Abell 41: nebular shaping by a binary central star?

    CERN Document Server

    Jones, D; Santander-García, M; López, J A; Meaburn, J; Mitchell, D L; O'Brien, T J; Pollacco, D; Rubio-Díez, M M; Vaytet, N M H

    2010-01-01

    We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Abell~41, which is known to contain the well-studied close-binary system MT Ser. This object represents an important test case in the study of the evolution of planetary nebulae with binary central stars as current evolutionary theories predict that the binary plane should be aligned perpendicular to the symmetry axis of the nebula. Longslit observations of the \\NII\\ emission from Abell~41 were obtained using the Manchester Echelle Spectrometer on the 2.1-m San Pedro M\\'artir Telescope. These spectra, combined with deep, narrowband imagery acquired using ACAM on the William Herschel Telescope, were used to develop a spatio-kinematical model of \\NII\\ emission from Abell~41. The best fitting model reveals Abell~41 to have a waisted, bipolar structure with an expansion velocity of $\\sim$40\\kms{} at the waist. The symmetry axis of the model nebula is within 5$^\\circ$ of perpendicular to the orbital plane of the central...

  11. Three Concurrent Phases of Massive-Star Evolution in a Pulsar-Wind Nebula

    OpenAIRE

    Morris, Patrick; Van Dyk, Schuyler; Mauerhan, Jon; Hillier, D. John; Lang, Cornelia

    2010-01-01

    The nebular material associated the the SNR G54.1+0.3 (hereafter G54) contains the the first reported instance of triggered star formation in the immediate vicinity of a Pulsar and its Wind Nebula (PWN). With 2MASS and Spitzer colors and followup near-IR spectroscopy, we have discovered the presence of a hot, massive and most likely evolved Be-type star among the cluster of stars hosted by the pulsar. This star has probably triggered cloud collapse and formation of at least 11 YSOs, which rin...

  12. The SAMI Galaxy Survey: extraplanar gas, galactic winds and their association with star formation history

    Science.gov (United States)

    Ho, I.-Ting; Medling, Anne M.; Bland-Hawthorn, Joss; Groves, Brent; Kewley, Lisa J.; Kobayashi, Chiaki; Dopita, Michael A.; Leslie, Sarah K.; Sharp, Rob; Allen, James T.; Bourne, Nathan; Bryant, Julia J.; Cortese, Luca; Croom, Scott M.; Dunne, Loretta; Fogarty, L. M. R.; Goodwin, Michael; Green, Andy W.; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; Lorente, Nuria P. F.; Owers, Matt S.; Richards, Samuel; Sweet, Sarah M.; Tescari, Edoardo; Valiante, Elisabetta

    2016-04-01

    We investigate a sample of 40 local, main-sequence, edge-on disc galaxies using integral field spectroscopy with the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey to understand the link between properties of the extraplanar gas and their host galaxies. The kinematics properties of the extraplanar gas, including velocity asymmetries and increased dispersion, are used to differentiate galaxies hosting large-scale galactic winds from those dominated by the extended diffuse ionized gas. We find rather that a spectrum of diffuse gas-dominated to wind-dominated galaxies exist. The wind-dominated galaxies span a wide range of star formation rates (SFRs; -1 ≲ log (SFR/M⊙ yr-1) ≲ 0.5) across the whole stellar mass range of the sample (8.5 ≲ log (M*/M⊙) ≲ 11). The wind galaxies also span a wide range in SFR surface densities (10- 3-10- 1.5 M⊙ yr- 1 kpc- 2) that is much lower than the canonical threshold of 0.1 M⊙ yr- 1 kpc- 2. The wind galaxies on average have higher SFR surface densities and higher HδA values than those without strong wind signatures. The enhanced HδA indicates that bursts of star formation in the recent past are necessary for driving large-scale galactic winds. We demonstrate with Sloan Digital Sky Survey data that galaxies with high SFR surface density have experienced bursts of star formation in the recent past. Our results imply that the galactic winds revealed in our study are indeed driven by bursts of star formation, and thus probing star formation in the time domain is crucial for finding and understanding galactic winds.

  13. Helium Emission from Classical T Tauri Stars: Dual Origin in Magnetospheric Infall and Hot Wind

    Science.gov (United States)

    Beristain, Georgina; Edwards, Suzan; Kwan, John

    2001-04-01

    High-resolution emission-line profiles of He I and He II in 31 classical T Tauri stars are analyzed with the aim of probing the environs of the star-disk interface in accreting low-mass young stars. The diagnostic power of the helium lines lies in their high-excitation potentials, which restrict their formation to a region either of high temperature or close proximity to a source of ionizing radiation. The He I profiles are decomposed into kinematic components that support the paradigm of magnetically controlled accretion from the disk onto the stellar surface but also require a significant contribution from a hot wind. A narrow component, seen in 28/31 stars, is characterized by relatively uniform line widths and centroid velocities among all the helium lines. Our analysis supports previous conclusions that this feature is consistent with formation in the decelerating postshock gas at the magnetosphere footpoint. A broad component, seen in 22/31 stars, displays a diversity of kinematic properties. Our analysis suggests that in many stars the He I broad component is itself composite. At one extreme are stars where the broad component is redshifted in excess of 8 km s-1, as would occur if helium emission arises primarily from polar angles less than 54.7d in the funnel flow. At the other extreme are stars where the broad component is blueshifted in excess of -30 km s-1, requiring an origin in outflowing gas. The additional occurrence of maximum blue wing velocities exceeding -200 km s-1 in 14 stars leads us to argue that hot winds are present in about half of our sample. The relation between the narrow component and the optical veiling differs between the stars with or without a hot helium wind, suggesting that when the hot wind is present the luminosity and temperature of the accretion shock are reduced. A comparison of broad component helium emission with standard outflow indicators leads us to suggest that there are two sources of inner wind in T Tauri accretion

  14. Illumination in symbiotic binary stars Non-LTE photoionization models; 2, Wind case

    CERN Document Server

    Proga, D; Raymond, J C; Proga, Daniel; Kenyon, Scott J.; Raymond, John C.

    1997-01-01

    We describe a non-LTE photoionization code to calculate the wind structure and emergent spectrum of a red giant wind illuminated by the hot component of a symbiotic binary system. We consider spherically symmetric winds with several different velocity and temperature laws and derive predicted line fluxes as a function of the red giant mass loss rate, \\mdot. Our models generally match observations of the symbiotic stars EG And and AG Peg for \\mdot about 10^{-8} wind as viewed from the hot component is a crucial parameter in these models. Winds with cross-sections of 2--3 red giant radii reproduce the observed fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models favor winds with acceleration regions that either lie far from the red giant photosphere or extend for 2--3 red giant radii.

  15. The interaction of an O star wind with a Herbig-Haro jet

    Science.gov (United States)

    Esquivel, A.; Raga, A. C.; Cantó, J.; Rodríguez-González, A.

    2009-11-01

    Context: Herbig-Haro jets ejected from young, low mass stars in the proximity of O/B stars will interact with the more or less isotropic winds from the more massive stars. An example of this are the jets from the stars within the proplyds near θ-Orionis. Aims: In this paper, we consider the interaction of an externally photoionized HH jet with an isotropic wind ejected from the ionizing photon source. We study this problem through numerical simulations, allowing us to obtain predictions of the detailed structure of the flow and predictions of Hα intensity maps. This is a natural extension of a previously developed analytic model for the interaction between a jet and an isotropic stellar wind. Methods: We present 3D simulations of a bipolar HH jet interacting with an isotropic wind from a massive star, assuming that the radiation from the star photoionizes all of the flow. We describe different possible flow configurations, exploring a limited set of jet and stellar wind parameters and orientations of the jet/counterjet ejection. We have computed 6 models, two of which also include a time-variability in the jet velocity. Results: We compare the locus of the computed jet/counterjet systems with the analytic model, and find very good agreement except for cases in which the direction of the jet (or the counterjet) approaches the direction to the wind source (i.e., the O star). For the models with variable ejection velocities, we find that the internal working surfaces follow straighter trajectories (and the inter-working surface segments more curved trajectories) than the equivalent steady jet model.

  16. Phase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star

    OpenAIRE

    Rauw, Grégor; Mahy, Laurent; Nazé, Yaël; Eenens, P.; Manfroid, Jean; Flores, C. A.

    2014-01-01

    Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star collides with the wind of its O8 II companion, leading to relatively strong X-ray emission. Aims: Measuring the orbital variations of the line-of-sight absorption toward the X-ray emission from the wind-wind interaction zone yields information on the wind densities of both stars. Methods: X-r...

  17. Central Wind Forecasting Programs in North America by Regional Transmission Organizations and Electric Utilities: Revised Edition

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, J.; Porter, K.

    2011-03-01

    The report and accompanying table addresses the implementation of central wind power forecasting by electric utilities and regional transmission organizations in North America. The first part of the table focuses on electric utilities and regional transmission organizations that have central wind power forecasting in place; the second part focuses on electric utilities and regional transmission organizations that plan to adopt central wind power forecasting in 2010. This is an update of the December 2009 report, NREL/SR-550-46763.

  18. New models for the evolution of post-asymptotic giant branch stars and central stars of planetary nebulae

    Science.gov (United States)

    Miller Bertolami, Marcelo Miguel

    2016-04-01

    Context. The post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The two grids of models presently available are based on outdated micro- and macrophysics and do not agree with each other. Studies of the central stars of planetary nebulae (CSPNe) and post-AGB stars in different stellar populations point to significant discrepancies with the theoretical predictions of post-AGB models. Aims: We study the timescales of post-AGB and CSPNe in the context of our present understanding of the micro- and macrophysics of stars. We want to assess whether new post-AGB models, based on the latter improvements in TP-AGB modeling, can help us to understand the discrepancies between observation and theory and within theory itself. In addition, we aim to understand the impact of the previous AGB evolution for post-AGB phases. Methods: We computed a grid of post-AGB full evolutionary sequences that include all previous evolutionary stages from the zero age main sequence to the white dwarf phase. We computed models for initial masses between 0.8 and 4 M⊙ and for a wide range of initial metallicities (Z0 = 0.02, 0.01, 0.001, 0.0001). This allowed us to provide post-AGB timescales and properties for H-burning post-AGB objects with masses in the relevant range for the formation of planetary nebulae (~0.5-0.8 M⊙). We included an updated treatment of the constitutive microphysics and included an updated description of the mixing processes and winds that play a key role during the thermal pulses (TP) on the AGB phase. Results: We present a new grid of models for post-AGB stars that take into account the improvements in the modeling of AGB stars in recent decades. These new models are particularly suited to be inputs in studies of the formation of planetary nebulae and for the determination of the properties of CSPNe from their observational parameters. We find post-AGB timescales that are at

  19. The donor star winds in High-Mass X-ray Binaries

    Science.gov (United States)

    Oskinova, Lida

    2014-10-01

    High-mass X-ray binaries (HMXBs) are essential astrophysical laboratories. These objects represent an advanced stage in the evolution of massive binary systems, after the initially more massive star has already collapsed in a supernova explosion, but its remnant, a neutron star or black hole, remains gravitationally bound. The stellar wind from the OB-type donor is partially accreted onto its compact companion powering its relatively high X-ray luminosity. Since HMXBs accrete from the stellar wind, parameters such as the donor's mass-loss rate, the velocity of the wind, and its clumpiness are of fundamental importance.This proposal takes advantage of the unique capabilities of HST/STIS for UV spectroscopy. We focus on the most populous in the Galaxy class of those HMXBs where the stellar wind of the OB donor is directly accreted onto a neutron star. Recently, a new sub-class of HMXBs - "supergiant fast X-ray transients" - was discovered. It has been proposed that these enigmatic objects can be explained by the specific properties of their donor-star winds. The only way to validate or disprove this hypothesis is by a studying the wind diagnostics lines in the UV spectra of donor stars. The observations proposed here will, for the first time, provide the UV spectra of this important new type of accreting binaries. Our state-of-the art non-LTE expanding stellar atmospheres and 3-D stellar wind simulations allow thorough exploitation of the STIS spectra. As a result we will obtain the wind parameters for a representative sample of six Galactic HMXBs, thus heightening our knowledge thereof considerably.

  20. Temporal variability of the wind from the star τ Boötis

    Science.gov (United States)

    Nicholson, B. A.; Vidotto, A. A.; Mengel, M.; Brookshaw, L.; Carter, B.; Petit, P.; Marsden, S. C.; Jeffers, S. V.; Fares, R.; BCool Collaboration

    2016-06-01

    We present new wind models for τ Boötis (τ Boo), a hot-Jupiter-host-star whose observable magnetic cycles makes it a uniquely useful target for our goal of monitoring the temporal variability of stellar winds and their exoplanetary impacts. Using spectropolarimetric observations from May 2009 to January 2015, the most extensive information of this type yet available, to reconstruct the stellar magnetic field, we produce multiple 3D magnetohydrodynamic stellar wind models. Our results show that characteristic changes in the large-scale magnetic field as the star undergoes magnetic cycles produce changes in the wind properties, both globally and locally at the position of the orbiting planet. Whilst the mass loss rate of the star varies by only a minimal amount (˜4 per cent), the rates of angular momentum loss and associated spin-down time-scales are seen to vary widely (up to ˜140 per cent), findings consistent with and extending previous research. In addition, we find that temporal variation in the global wind is governed mainly by changes in total magnetic flux rather than changes in wind plasma properties. The magnetic pressure varies with time and location and dominates the stellar wind pressure at the planetary orbit. By assuming a Jovian planetary magnetic field for τ Boo b, we nevertheless conclude that the planetary magnetosphere can remain stable in size for all observed stellar cycle epochs, despite significant changes in the stellar field and the resulting local space weather environment.

  1. The Physics of Protoneutron Star Winds Implications for r-Process Nucleosynthesis

    CERN Document Server

    Thompson, T A; Meyer, B S; Thompson, Todd A.; Burrows, Adam; Meyer, Bradley S.

    2001-01-01

    We solve the general-relativistic steady-state eigenvalue problem of neutrino-driven protoneutron star winds, which immediately follow core-collapse supernova explosions. We provide velocity, density, temperature, and composition profiles and explore the systematics and structures generic to such a wind for a variety of protoneutron star characteristics. Furthermore, we derive the entropy, dynamical timescale, and neutron-to-seed ratio in the general relativistic framework essential in assessing this site as a candidate for $r$-process nucleosynthesis. Generally, we find that for a given mass outflow rate ($\\dot{M}$), the dynamical timescale of the wind is significantly shorter than previously thought. We argue against the existence or viability of a high entropy ($\\gtrsim300$ per k$_{\\rm B}$ per baryon), long dynamical timescale $r$-process epoch. In support of this conclusion, we model the protoneutron star cooling phase, calculate nucleosynthetic yields in our steady-state profiles, and estimate the integr...

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

    Czech Academy of Sciences Publication Activity Database

    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 ostatní: 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

  3. Neutral winds from cool young stars - a solution to the line deficit problem

    International Nuclear Information System (INIS)

    The suggestion that IR emission lines from pre-main-sequence stars of relatively low mass originate in primarily neutral winds is examined. In particular, predictions of the Br-alpha line emission for a range of mass loss rates are presented and compared to observations. The low Br-alpha emission for a given mass-loss rate indicated by the observations can be explained if the winds are cool (7000 K, in most cases) and, consequently, primarily neutral. Because the Br-alpha emission is a strong function of both the wind and stellar temperatures, it cannot be used to derive mass-loss rates for these cool stars; but, when used in conjunction with other data, it can provide strong constraints on mechanisms for driving the stellar winds and molecular outflows. 21 references

  4. Dispersion measure contributed by a relativistic neutron star wind and implication for fast radio bursts

    CERN Document Server

    Yu, Yun-Wei

    2014-01-01

    The possible contribution to dispersion measure (DM) by neutron star winds is investigated by introducing a relativistic definition of the DM. On one hand, I propose that the observed fast radio bursts (FRBs) could be produced by activities on some peculiar young Galactic neutron stars, where the large DMs of the FRBs can be ascribed to the neutron star winds rather than the intergalactic medium. On the other hand, in the sight of cosmological origin of FRBs, I also investigate the possible association of the FRBs with the collapses of millisecond magnetars harbored in gamma-ray bursts (GRBs). In particular, as required by the observed bright internal X-ray afterglows, a high intrinsic DM could be contributed by the emitting neutron star winds, which could even exceed the contribution from the intergalactic medium. In any case, such a result is strongly dependent on the uncertain dissipation mechanisms of the winds and more DM measurements of FRBs could provide stringent constraints on the wind physics.

  5. Preface: X-ray emission from hot stars and their winds

    Science.gov (United States)

    Oskinova, Lidia

    2016-09-01

    With the advent of highly sensitive X-ray observatories, X-ray astrophysics has become a versatile tool to study highly energetic processes in a wide variety of astrophysical contexts. Hot stars are no exception to this rule. Indeed, X-rays provide an important observational window for studies of such stars. Observations obtained with modern X-ray telescopes over the last decade and a half have revolutionized our understanding of hot stars and their winds. X-ray spectroscopy, time monitoring, and imaging allow us to probe stellar atmospheres, magnetospheres, stellar winds and give us new insight into their impact on the interstellar medium and the galactic ecology. While some questions about X-ray emission from massive stars have been answered, many unexpected findings point out that our picture of stellar winds is not yet complete. The new theories and models of X-ray emission from hot stars were developed in parallel or, sometimes, ahead of the arrival of the new data. This special issue is aimed at summarizing our current knowledge of X-ray emission from hot stars as well as at opening new avenues for investigation in anticipation of the next generation of X-ray telescopes.

  6. EU Del: exploring the onset of pulsation-driven winds in giant stars

    CERN Document Server

    McDonald, I; Sloan, G C; Lagadec, E; Johnson, C I; Uttenthaler, S; Jones, O C; Smith, C L

    2015-01-01

    We explore the wind-driving mechanism of giant stars through the nearby (117 pc), intermediate-luminosity ($L \\approx 1600$ L$_\\odot$) star EU Del (HIP 101810, HD 196610). APEX observations of the CO (3--2) and (2--1) transitions are used to derive a wind velocity of 9.51 $\\pm$ 0.02 km s$^{-1}$, a $^{12}$C/$^{13}$C ratio of 14 $^{+9}_{-4}$, and a mass-loss rate of a few $\\times$ 10$^{-8}$ M$_\\odot$ yr$^{-1}$. From published spectra, we estimate that the star has a metallicity of [Fe/H] = --0.27 $\\pm$ $\\sim$0.30 dex. The star's dusty envelope lacks a clear 10-$\\mu$m silicate feature, despite the star's oxygen-rich nature. Radiative transfer modelling cannot fit a wind acceleration model which relies solely on radiation pressure on condensing dust. We compare our results to VY Leo (HIP 53449), a star with similar temperature and luminosity, but different pulsation properties. We suggest the much stronger mass loss from EU Del may be driven by long-period stellar pulsations, due to its potentially lower mass. We...

  7. Modelling the cometary structure of the planetary nebula HFG1 based on the evolution of its binary central star V664 Cas

    Science.gov (United States)

    Chiotellis, A.; Boumis, P.; Nanouris, N.; Meaburn, J.; Dimitriadis, G.

    2016-03-01

    HFG1 is the first well-observed planetary nebula (PN) which reveals a cometary-like structure. Its main morphological features consist of a bow-shaped shell, which surrounds the central star, accompanied by a long collimated tail. In this study, we perform two-dimensional hydrodynamic simulations modelling the formation of HFG1 from the interaction of the local ambient medium with the mass outflows of its asymptotic giant branch (AGB) progenitor star. We attribute the cometary appearance of HFG1 to the systemic motion of the PN with respect to the local ambient medium. Due to its vital importance, we re-estimate the distance of HFG1 by modelling the spectral energy distribution of its central star, V664 Cas, and we find a distance of 490 ± 50 pc. Our simulations show that none of our models with time invariant stellar wind and ambient medium properties are able to reproduce simultaneously the extended bow shock and the collimated tail observed in HFG1. Given this, we increase the complexity of our modelling considering that the stellar wind is time variable. The wind description is based on the predictions of the AGB and post-AGB evolution models. Testing a grid of models, we find that the properties of HFG1 are best reproduced by the mass outflows of a 3 M⊙ AGB star. Such a scenario is consistent with the current observed properties of V664 Cas primary star, an O-type subdwarf, and bridges the evolutionary history of HFG1 central star with the observables of the PN. We discuss the implications of our study in the understanding of the evolution of AGB/post-AGB stars towards the formation of O-type subdwarfs surrounded by PNe.

  8. Impact of the central Pacific zonal wind divergence and convergence on the central Pacific El Niño event

    Institute of Scientific and Technical Information of China (English)

    ZUO Tao; CHEN Jinnian; WANG Hongna

    2014-01-01

    The central Pacific (CP) zonal wind divergence and convergence indices are defined, and the forming mech-anism of CP El Niño (La Niña) events is discussed preliminarily. The results show that the divergence and convergence of the zonal wind anomaly (ZWA) are the key process in the forming of CP El Niño (La Niña) events. A correlation analysis between the central Pacific zonal wind divergence and convergence indices and central Pacific El Niño indices indicates that there is a remarkable lag correlation between them. The central Pacific zonal wind divergence and convergence indices can be used to predict the CP events. Based on these results, a linear regression equation is obtained to predict the CP El Niño (La Niña) events 5 months ahead.

  9. Magnetic field measurements and wind-line variability of OB-type stars

    CERN Document Server

    Schnerr, R S; Neiner, C; Verdugo, E; de Jong, J; Geers, V C; Wiersema, K; van Dalen, B; Tijani, A; Plaggenborg, B; Rygl, K L J

    2010-01-01

    Context. The first magnetic fields in O- and B-type stars that do not belong to the Bp-star class, have been discovered. The cyclic UV wind-line variability, which has been observed in a significant fraction of early-type stars, is likely to be related to such magnetic fields. Aims. We attempt to improve our understanding of massive-star magnetic fields, and observe twenty-five carefully-selected, OB-type stars. Methods. Of these stars we obtain 136 magnetic field strength measurements. We present the UV wind-line variability of all selected targets and summarise spectropolarimetric observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL, Pic du Midi, between December 1998 and November 2004. From the average Stokes I and V line profiles, derived using the LSD method, we measure the magnetic field strengths, radial velocities, and first moment of the line profiles. Results. No significant magnetic field is detected in any OB-type star that we observed. Typical 1{\\sigma} errors are betwee...

  10. Mining the Advanced Spectral Library (ASTRAL): Characterizing Winds of Evolved M-Stars

    Science.gov (United States)

    Nielsen, Krister E.; Carpenter, K. G.; Kober, G. V.; Cheng, K.; Ayres, T. R.; Harper, G.

    2013-01-01

    The HST/STIS treasury program Advanced Spectral Library (ASTRAL) enables investigations of the character and dynamics of the wind and chromosphere of cool stars, using high quality spectral data. This paper present the analysis of the outflowing winds of the M3.4 giant Gamma Cru and the M2Iab supergiant Alpha Ori. The outer atmospheres of these objects show strong evidence for significant inhomogeneity in their thermal and kinematic structure, and are in general not well understood. The wind features are characterized by a strong chromospheric emission suppressed by a overlying wind absorption, for many transitions producing a double peak feature. The relative strengths and wavelength shifts between the absorption and emission components of the lines reflect the acceleration of the wind from the base of the chromosphere, as the self-absorption is due to the overlying wind absorption, whose velocity relative to the chromosphere varies with height and thus line opacity. The wind profiles are sensitive to the wind opacity, turbulence and flow velocity, and hence favorable to analyze with the Sobolev source function with Exact Integration of the transfer equation (SEI) code. This paper will show a velocity and intensity analysis of the wind profiles and modeling with the SEI code to derive an improved set of wind parameters, primarily, for Gamma Cru.

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

    OpenAIRE

    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...

  12. IC4663: the first unambiguous [WN] Wolf-Rayet central star of a planetary nebula

    CERN Document Server

    Miszalski, Brent; De Marco, Orsola; Köppen, Joachim; Moffat, Anthony F J; Acker, Agnès; Hillwig, Todd C

    2012-01-01

    Several [WC]-type central stars of planetary nebulae (PNe) are known to mimic the spectroscopic appearance of massive carbon-rich or WC-type Wolf-Rayet stars. In stark contrast, no [WN]-type central stars have yet been identified as clear-cut analogues of the common nitrogen-rich or WN-type Wolf-Rayet stars. We have identified the [WN3] central star of IC4663 to be the first unambiguous example in PNe. The low luminosity nucleus and an asymptotic giant branch (AGB) halo surrounding the main nebula prove the bona-fide PN nature of IC4663. Model atmosphere analysis reveals the [WN3] star to have an exotic chemical composition of helium (95%), hydrogen (O(He), that exists in parallel to the carbon-rich [WC]->PG1159 sequence. This suggests a simpler mechanism, perhaps a binary merger, can better explain H-deficiency in PNe and potentially other H-deficient/He-rich stars. In this respect IC4663 is the best supported case for a possible merged binary central star of a PN.

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

    CERN Document Server

    Krticka, Jiri

    2014-01-01

    Hot star wind mass-loss rates depend on the abundance of individual elements. This dependence is usually accounted for assuming scaled solar chemical composition. However, this approach may not be justified in evolved rotating stars. The rotational mixing brings CNO-processed material to the stellar surface, increasing the abundance of nitrogen at the expense of carbon and oxygen, which potentially influences the mass-loss rates. We study the influence of the modified chemical composition resulting from the rotational mixing on the wind parameters, particularly the wind mass-loss rates. We use our NLTE wind code to predict the wind structure and compare the calculated wind mass-loss rate for the case of scaled solar chemical composition and the composition affected by the CNO cycle. We show that for a higher mass-fraction of heavier elements $Z/Z_\\odot\\gtrsim0.1$ the change of chemical composition from the scaled solar to the CNO-processed scaled solar composition does not significantly affect the wind mass-l...

  14. The astrophysical consequences of the bimodal hydrodynamic solution of the super star cluster winds

    Czech Academy of Sciences Publication Activity Database

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

    2009-01-01

    Roč. 324, 2-4 (2009), s. 195-198. ISSN 0004-640X R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : stellar wind s * star cluster s * HII regions Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.404, year: 2009

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

    Czech Academy of Sciences Publication Activity Database

    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 wind s * star cluster s * dynamics of ISM Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.404, year: 2009

  16. On the origin of variable structures in the winds of hot luminous stars

    Science.gov (United States)

    Michaux, Yannick J. L.; Moffat, Anthony F. J.; Chené, André-Nicolas; St-Louis, Nicole

    2014-05-01

    Examination of the temporal variability properties of several strong optical recombination lines in a large sample of Galactic Wolf-Rayet (WR) stars reveals possible trends, especially in the more homogeneous WC than the diverse WN subtypes, of increasing wind variability with cooler subtypes. This could imply that a serious contender for the driver of the variations is stochastic, magnetic subsurface convection associated with the 170 kK partial-ionization zone of iron, which should occupy a deeper and larger zone of greater mass in cooler WR subtypes. This empirical evidence suggests that the heretofore proposed ubiquitous driver of wind variability, radiative instabilities, may not be the only mechanism playing a role in the stochastic multiple small-scaled structures seen in the winds of hot luminous stars. In addition to small-scale stochastic behaviour, subsurface convection guided by a global magnetic field with localized emerging loops may also be at the origin of the large-scale corotating interaction regions as seen frequently in O stars and occasionally in the winds of their descendant WR stars.

  17. Clumpy wind accretion in supergiant neutron star high mass X-ray binaries

    CERN Document Server

    Bozzo, E; Feldmeier, A; Falanga, M

    2016-01-01

    The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the non-stationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total time scale of several hours), the transition of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the non-stationary wind. Th...

  18. Coronal magnetic field and wind of an aging K-type star

    Science.gov (United States)

    Réville, Victor; Brun, Allan Sacha; Strugarek, Antoine; Jeffers, Sandra; Folsom, Colin; Marsden, Stephen C.; Petit, Pascal

    2015-08-01

    Created at the base of the convective envelope by a nonlinear dynamo process, the large scale magnetic field of a star evolves with its rotational history. Beyond the photosphere, magnetic processes heat the corona above one million Kelvin hence driving a magnetized wind responsible for the braking of main sequence stars. Hence a feedback loop tie those processes. Development of Zeeman-Doppler imaging through spectropolarimetry allows to precisely describe the surface magnetic field of a large sample of stars. Thus the study of the coronal structure and magnetic field with age, magnetochoronology, has developed to extend and complete gyrochronology. We propose a study of the corona and the wind of a sample of K-type stars of different age to follow the evolution of its properties from 20 Myr to 8 Gyr thanks to a set of 3D MHD simulations with the PLUTO code constrained by spectropolarimetric maps of the surface magnetic field obtained by the BCool consortium. To perform those simulations we developed a coherent framework to assess various stellar parameters such as the equilibrium coronal temperature driving the wind. Those assumptions have consequences on UV emissions, wind terminal speed and mass loss that impact planetary systems that could potentially host life.

  19. Evolution of super star cluster winds with strong cooling

    Czech Academy of Sciences Publication Activity Database

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

    2011-01-01

    Roč. 740, č. 2 (2011), A75/1-A75/7. ISSN 0004-637X R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : galaxies * star clusters * HII regions Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 6.024, year: 2011

  20. Delta-slow solution to explain B supergiant stars' winds

    Czech Academy of Sciences Publication Activity Database

    Haucke, M.; Araya, I.; Arcos, C.; Curé, M.; Cidale, L.S.; Kanaan, S.; Venero, R.O.J.; Kraus, Michaela

    Cambridge: Cambridge University Press, 2015, s. 104-105. (Proceedings of the International Astronomical Union. IAU S307). ISBN 9781107078581. ISSN 1743-9213. [Symposium of the International Astronomical Union /307./. Geneva (CH), 23.06.2014-27.06.2014] Institutional support: RVO:67985815 Keywords : stars * mass loss * outflows Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  1. The two central stars of NGC 1514: can they actually be related?

    CERN Document Server

    Mendez, R H; Urbaneja, M A

    2016-01-01

    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 CFHT on Mauna Kea have allowed to measure good radial velocities for both stars. They differ by 13 $\\pm$ 2 km s$^{-1}$. The stellar velocities have not changed 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. Influence of XUV radiation on Pv ionization fraction in hot star winds

    CERN Document Server

    Krticka, Jiri

    2012-01-01

    Different diagnostics of hot star wind mass-loss rates provide results that are difficult to reconcile with each other. The widely accepted presence of clumping in hot star winds implies a significant reduction of observational mass-loss rate estimates from diagnostics that depend on the square of the density. Moreover, the ultraviolet Pv resonance lines indicate a possible need for even stronger reduction of hot star mass-loss rates, provided that Pv is a dominant ionization stage of phosphorus at least in some hot stars. The latter assumption is challenged by a possible presence of the XUV radiation. Here we study the influence of the XUV radiation on the Pv ionization fraction in the hot star winds. By a detailed solution of the hydrodynamical, radiative transfer, and statistical equilibrium equations we confirm that sufficiently strong XUV radiation source may decrease the Pv ionization fraction, possibly depreciating the Pv lines as a reliable mass-loss rate indicator. On the other hand, the XUV radiatio...

  3. Wind modelling of very massive stars up to 300 solar masses

    CERN Document Server

    Vink, Jorick S; Anthonisse, B; de Koter, A; Graefener, G; Langer, N

    2011-01-01

    Some studies have claimed a universal stellar upper-mass limit of 150 Msun. A factor that is often overlooked concerns the fact there might be a difference between the current and initial masses of the most massive stars, due to mass loss. We present Monte Carlo mass-loss predictions for very massive stars in the range 40-300 Msun, with large luminosities and Eddington factors Gamma. Using our new dynamical approach, we find an upturn in the mass-loss vs. Gamma dependence, at the point where the winds become optically thick. This coincides with the location where wind efficiency numbers surpass the single-scattering limit of Eta = 1, reaching values up to Eta = 2.5. Our modelling suggests a transition from common O-type winds to Wolf-Rayet characteristics at the point where the winds become optically thick. This transitional behaviour is also revealed with respect to the wind acceleration parameter beta, which starts at values below 1 for the optically thin O-stars, and naturally reaches values as high as 1.5...

  4. The SILCC project: III. Regulation of star formation and outflows by stellar winds and supernovae

    CERN Document Server

    Gatto, A; Naab, T; Girichidis, P; Wünsch, R; Glover, S C O; Klessen, R S; Clark, P C; Peters, T; Derigs, D; Baczynski, C; Puls, J

    2016-01-01

    We study the impact of stellar winds and supernovae on the multi-phase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)$^2$ x $\\pm$ 5 kpc and a gas surface density of 10 M$_{\\odot}$/pc$^2$. The simulations include an external stellar potential and gas self-gravity, radiative cooling and diffuse heating, sink particles representing star clusters, stellar winds from these clusters which combine the winds from indi- vidual massive stars by following their evolution tracks, and subsequent supernova explosions. Dust and gas (self-)shielding is followed to compute the chemical state of the gas with a chemical network. We find that stellar winds can regulate star (cluster) formation. Since the winds suppress the accretion of fresh gas soon after the cluster has formed, they lead to clusters which have lower average masses (10$^2$ - 10$^{4.3}$ M$_{\\odot}$) and form on shorter timescales (10$^{-3}$ - 10 Myr). In part...

  5. Co-rotating interaction regions in stellar winds: particle acceleration and non-thermal radio emission in hot stars

    International Nuclear Information System (INIS)

    A co-rotating interaction region (CIR) forms in a stellar wind when a fast stream from a rotating star overtakes a slow stream. CIR's have been studied in detail in the solar wind over the past decade primarily because they are efficient sources of particle acceleration. Here, the author points out the usefulness of CIR's in OB star winds to explain two properties of such winds: deposition of nonradiative energy in the wind far from the stellar surfaces and acceleration of non-thermal particles. (orig.)

  6. On the origin of variable structures in the winds of hot luminous stars

    CERN Document Server

    Michaux, Yannick J L; Chene, Andre-Nicolas; Saint-Louis, Nicole

    2013-01-01

    Examination of the temporal variability properties of several strong optical recombination lines in a large sample of Galactic Wolf-Rayet (WR) stars reveals possible trends, especially in the more homogeneous WC than the diverse WN subtypes, of increasing wind variability with cooler subtypes. This could imply that a serious contender for the driver of the variations is stochastic, magnetic subsurface convection associated with the 170 kK partial-ionization zone of iron, which should occupy a deeper and larger zone of greater mass in cooler WR subtypes. This empirical evidence suggests that the heretofore proposed ubiquitous driver of wind variability, radiative instabilities, may not be the only mechanism playing a role in the stochastic multiple small-scaled structures seen in the winds of hot luminous stars. In addition to small-scale stochastic behaviour, subsurface convection guided by a global magnetic field with localized emerging loops may also be at the origin of the large-scale corotating interactio...

  7. Clumpy wind accretion in supergiant neutron star high mass X-ray binaries

    Science.gov (United States)

    Bozzo, E.; Oskinova, L.; Feldmeier, A.; Falanga, M.

    2016-05-01

    The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the nonstationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total timescale of several hours), the transitions of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the nonstationary wind. The X-ray luminosity released by the system is computed at each time step by taking into account the relevant physical processes occurring in the different accretion regimes. Synthetic lightcurves are derived and qualitatively compared with those observed from classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. Although a number of simplifications are assumed in these calculations, we show that taking into account the effects of the centrifugal and magnetic inhibition of accretion significantly reduces the average X-ray luminosity expected for any neutron star wind-fed binary. The present model calculations suggest that long spin periods and stronger magnetic fields are favored in order to reproduce the peculiar behavior of supergiant fast X-ray transients in the X-ray domain.

  8. Polarization of the central star of a recently discovered reflection nebula in Centaurus

    International Nuclear Information System (INIS)

    Vogt et al. have reported the discovery of a faint reflection nebula in Centaurus. The central star is an anonymous GO III star with Asub(v) approx. 4.3 mag. Observations of the wavelength dependence of the polarization associated with the central star have been made. The measured polarization can be fitted by the empirical Serkowski relation for interstellar polarization with psub(max) approx. 5.6 per cent and lambda sub(max) approx. 0.425 μm. However, the position angle of the polarization does not agree with the local direction of the Galactic magnetic field. A circumstellar origin for the polarization seems more attractive. (author)

  9. Action of Winds Inside and Outside of Star Clusters

    Czech Academy of Sciences Publication Activity Database

    Palouš, Jan; Dale, James E.; Wünsch, Richard; Silich, S.; Tenorio-Tagle, G.; Whitworth, A.

    Cambridge: Cambridge University Press, 2011 - (Alves, J.), s. 267-274. (IAU Symposium Proceedings Series. S270). ISBN 9780521766432. ISSN 1743-9213. [Symposium of the International Astronomical Union /270./. Barcelona (ES), 31.05.2010-04.06.2010] R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : globular clusters * open clusters and associations * stars formation Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  10. Dust-driven winds of AGB stars: The critical interplay of atmospheric shocks and luminosity variations

    CERN Document Server

    Liljegren, S; Nowotny, W; Eriksson, K

    2016-01-01

    Winds of AGB stars are thought to be driven by a combination of pulsation-induced shock waves and radiation pressure on dust. In dynamic atmosphere and wind models, the stellar pulsation is often simulated by prescribing a simple sinusoidal variation in velocity and luminosity at the inner boundary of the model atmosphere. We experiment with different forms of the luminosity variation in order to assess the effects on the wind velocity and mass-loss rate, when progressing from the simple sinusoidal recipe towards more realistic descriptions. Using state-of-the-art dynamical models of C-rich AGB stars, a range of different asymmetric shapes of the luminosity variation and a range of phase shifts of the luminosity variation relative to the radial variation are tested. These tests are performed on two stellar atmosphere models. The first model has dust condensation and, as a consequence, a stellar wind is triggered, while the second model lacks both dust and wind. The first model with dust and stellar wind is ve...

  11. Light and heavy metal abundances in hot central stars of planetary nebulae

    CERN Document Server

    Werner, K; Jahn, D; Rauch, T; Reiff, E; Traulsen, I; Kruk, J W; Dreizler, S

    2005-01-01

    We present new results from our spectral analyses of very hot central stars achieved since the last IAU Symposium on planetary nebulae held in Canberra 2001. The analyses are mainly based on UV and far-UV spectroscopy performed with the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer but also on ground-based observations performed at the Very Large Telescope and other observatories. We report on temperature, gravity, and abundance determinations for the CNO elements of hydrogen-rich central stars. In many hydrogen-deficient central stars (spectral type PG1159) we discovered particular neon and fluorine lines, which are observed for the very first time in any astrophysical object. Their analysis strongly confirms the idea that these stars exhibit intershell matter as a consequence of a late helium-shell flash.

  12. Stellar winds and the circumstellar environment of massive first stars

    Czech Academy of Sciences Publication Activity Database

    Krtička, J.; Kubát, Jiří

    Cambridge : Cambridge University Press, 2005 - ( Cill , V.; François, P.; Primas, F.), s. 165-166 [Symposium of te International Astronomical Union /228./. Paris (FR), 23.05.2005-27.05.2005] R&D Projects: GA ČR GA205/04/1267 Institutional research plan: CEZ:AV0Z1003909 Keywords : stellar winds Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  13. Neutrino-driven winds from neutron star merger remnants

    CERN Document Server

    Perego, Albino; Cabezon, Ruben; Korobkin, Oleg; Kaeppeli, Roger; Arcones, Almudena; Liebendoerfer, Matthias

    2014-01-01

    We present a detailed, 3D hydrodynamics study of the neutrino-driven winds that emerge from the remnant of a NS merger. Our simulations are performed with the Newtonian, Eulerian code FISH, augmented by a detailed, spectral neutrino leakage scheme that accounts for heating due to neutrino absorption in optically thin conditions. Consistent with the 2D study of Dessart et al. (2009), we find that a strong baryonic wind is blown out along the original binary rotation axis within $100$ ms after the merger. We compute a lower limit on the expelled mass of $3.5 \\times 10^{-3} M_{\\odot}$, large enough to be relevant for heavy element nucleosynthesis. The physical properties vary significantly between different wind regions. For example, due to stronger neutrino irradiation, the polar regions show substantially larger $Y_e$ than those at lower latitudes. This has its bearings on the nucleosynthesis: the polar ejecta produce interesting r-process contributions from $A\\sim 80$ to about 130, while the more neutron-rich...

  14. Temporal variability of the wind from the star {\\tau} Bo\\"otis

    CERN Document Server

    Nicholson, B A; Mengel, M; Brookshaw, L; Carter, B; Petit, P; Marsden, S C; Jeffers, S V; Fares, R

    2016-01-01

    We present new wind models for {\\tau} Bo\\"otis ({\\tau} Boo), a hot-Jupiter-host-star whose observable magnetic cycles makes it a uniquely useful target for our goal of monitoring the temporal variability of stellar winds and their exoplanetary impacts. Using spectropolarimetric observations from May 2009 to January 2015, the most extensive information of this type yet available, to reconstruct the stellar magnetic field, we produce multiple 3D magnetohydrodynamic stellar wind models. Our results show that characteristic changes in the large-scale magnetic field as the star undergoes magnetic cycles produce changes in the wind properties, both globally and locally at the position of the orbiting planet. Whilst the mass loss rate of the star varies by only a minimal amount ($\\sim$ 4 percent), the rates of angular momentum loss and associated spin-down timescales are seen to vary widely (up to $\\sim$ 140 percent), findings consistent with and extending previous research. In addition, we find that temporal variat...

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

    CERN Document Server

    Schneider, F R N; 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 analyse 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 upper part of the mass function in a stellar cluster can be quite different to the slope of the initial mass function. Wind mass loss from massive stars leads to an accumulation of stars which is visible as a peak at the high mass end of mass functions, thereby flattening the mass function slope. Mass accretion and mergers in close binary systems create a tail of rejuvenated binary products. These blue straggler stars extend the single star mass function by up to a factor of two in mass and can appear up to ten times younger than their parent stellar cluster. Cluster ages derived from their most massive stars that are close to the turn-off may thus be significantly biased. To overcome such difficulties, we propose t...

  16. Ultra-High Energy Cosmic Rays from Young Neutron Star Winds

    OpenAIRE

    P. Blasi(INAF Arcetri); Epstein, R. I.; Olinto, A. V.

    1999-01-01

    The long-held notion that the highest-energy cosmic rays are of distant extragalactic origin is challenged by observations that events above $\\sim 10^{20}$ eV do not exhibit the expected high-energy cutoff from photopion production off the cosmic microwave background. We suggest that these unexpected ultra-high-energy events are due to iron nuclei accelerated from young strongly magnetized neutron stars through relativistic MHD winds. We find that neutron stars whose initial spin periods are ...

  17. The O I] 1641A line as a probe of symbiotic star winds

    OpenAIRE

    Shore, S. N.; Wahlgren, G. M.

    2010-01-01

    The neutral oxygen resonance 1302A line can, if the optical depth is sufficiently high, de-excite by an intercombination transition at 1641A to a metastable state. This has been noted in a number of previous studies but never systematically investigated as a diagnostic of the neutral red giant wind in symbiotic stars and symbiotic-like recurrent novae. We used archival $IUE$ high resolution, and GHRS and STIS medium and high resolution, spectra to study a sample of symbiotic stars. The integr...

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

    Science.gov (United States)

    Rosgaard, Martin; Hahmann, Andrea; Skov Nielsen, Torben; Giebel, Gregor; Ejnar Sørensen, Poul; Madsen, Henrik

    2014-05-01

    For any energy system relying on wind power, accurate forecasts of wind fluctuations are essential for efficient integration into the power grid. Increased forecast precision allows end-users to plan day-ahead operation with reduced risk of penalties which in turn supports the feasibility of wind energy. This study aims to quantify value added to wind energy forecasts in the 12-48 hour leadtime by downscaling global numerical weather prediction (NWP) data using a limited-area NWP model. The accuracy of statistical wind power forecasting tools depends strongly on this NWP input. Typical performance metrics are mean absolute error or root mean square error for predicted- against observed wind power production, and these metrics are closely related to wind speed forecast bias and correlation with observations. Wind speed bias can be handled in the statistical wind power forecasting model, though it is entirely up to it's NWP input to describe the wind speed correlation correctly. The basis of comparison for forecasts is data from the Stor-Rotliden wind farm in central Sweden. The surrounding forest adds to the forecasting challenge, thus motivating the downscaling experiment as the potential for wind power forecast improvement is higher in complex terrain. The 40 Vestas V90 turbines were erected in 2009 and correspond to 78MWe installed electrical capacity. Forecasts from global and limited-area NWP models, together covering five different horizontal computational grid spacings of ~50km down to ~1km, are studied for a yearlong, continuous time period. The preliminary results shown quantify forecast strengths and weaknesses for each NWP model resolution.

  19. GLOBAL MODELING OF X-RAY SPECTRA PRODUCED IN O-TYPE STAR WINDS

    International Nuclear Information System (INIS)

    High-resolution X-ray spectra of O-type stars revealed less wind absorption than expected from smooth winds with conventional mass-loss rates. Various solutions have been proposed, including porous winds, optically thick clumps, or an overall reduction of the mass-loss rates. The latter has a strong impact on the evolution of the star. Our final goal is to analyze high-resolution X-ray spectra of O-type stars with a multi-temperature plasma model in order to determine crucial stellar and wind parameters such as the mass-loss rate, the CNO abundances, and the X-ray temperature plasma distribution in the wind. In this context we are developing a modeling tool to calculate synthetic X-ray spectra. We present here the main ingredients and physics necessary for such a work. Our code uses the most recent version of the AtomDB emissivities to compute the intrinsic emissivity of the hot plasma as well as the CMFGEN model atmosphere code to evaluate the opacity of the cool wind. Following the comparison between two formalisms of stellar wind fragmentation, we introduce, for the first time in X-rays, the effects of a tenuous inter-clump medium. We then explore the quantitative impact of different model parameters on the X-ray spectra such as the position in the wind of the X-ray emitting plasma. For the first time, we also show that the two formalisms of stellar wind fragmentation yield different results, although the differences for individual lines are small and can probably not be tested with the current generation of X-ray telescopes. As an illustration of our method, we compare various synthetic line profiles to the observed O VIII λ18.97 line in the spectrum of ζ Puppis. We illustrate how different combinations of parameters can actually lead to the same morphology of a single line, underlining the need to analyze the whole spectrum in a consistent way when attempting to constrain the parameters of the wind.

  20. MAGNETICALLY DRIVEN WINDS FROM DIFFERENTIALLY ROTATING NEUTRON STARS AND X-RAY AFTERGLOWS OF SHORT GAMMA-RAY BURSTS

    International Nuclear Information System (INIS)

    Besides being among the most promising sources of gravitational waves, merging neutron star binaries also represent a leading scenario to explain the phenomenology of short gamma-ray bursts (SGRBs). Recent observations have revealed a large subclass of SGRBs with roughly constant luminosity in their X-ray afterglows, lasting 10-104 s. These features are generally taken as evidence of a long-lived central engine powered by the magnetic spin-down of a uniformly rotating, magnetized object. We propose a different scenario in which the central engine powering the X-ray emission is a differentially rotating hypermassive neutron star (HMNS) that launches a quasi-isotropic and baryon-loaded wind driven by the magnetic field, which is built-up through differential rotation. Our model is supported by long-term, three-dimensional, general-relativistic, and ideal magnetohydrodynamic simulations, showing that this isotropic emission is a very robust feature. For a given HMNS, the presence of a collimated component depends sensitively on the initial magnetic field geometry, while the stationary electromagnetic luminosity depends only on the magnetic energy initially stored in the system. We show that our model is compatible with the observed timescales and luminosities and express the latter in terms of a simple scaling relation

  1. A Search for O VI in the Winds of B-Type Stars

    OpenAIRE

    Zsargo, J.; Fullerton, A. W.; Lehner, N.; Massa, D.

    2003-01-01

    We have conducted a survey of FUSE spectra of 235 Galactic B-type stars in order to determine the boundaries in the H-R diagram for the production of the superion O VI in their winds. By comparing the locations and morphology of otherwise unidentified absorption features in the vicinity of the O VI resonance doublet with the bona fide wind profiles seen in archival IUE spectra of the resonance lines of N V, Si IV and C IV, we were able to detect blueshifted O VI lines in the spectra of giant ...

  2. Winds of low-metallicity OB-type stars: HST-COS spectroscopy in IC 1613

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, Miriam; Najarro, Francisco [Centro de Astrobiología, CSIC-INTA. Ctra. Torrejón a Ajalvir km.4, E-28850 Torrejón de Ardoz, Madrid (Spain); Herrero, Artemio [Instituto de Astrofísica de Canarias. Vía Láctea s/n, E-38200 La Laguna (S. C. Tenerife) (Spain); Lennon, Daniel J. [European Space Astronomy Centre, Camino Bajo del Castillo, E-28692 Villanueva de la Cañada, Madrid (Spain); Urbaneja, Miguel Alejandro [Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 25/8, A-6020 Innsbruck (Austria)

    2014-06-10

    We present the first quantitative ultraviolet spectroscopic analysis of resolved OB stars in IC 1613. Because of its alleged very low metallicity (≲1/10 Z {sub ☉}, from H II regions), studies in this Local Group dwarf galaxy could become a significant step forward from the Small Magellanic Cloud (SMC) toward the extremely metal-poor massive stars of the early universe. We present HST-COS data covering the ∼1150-1800 Å wavelength range with resolution R ∼ 2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed P Cygni profiles with the Sobolev plus Exact Integration method. The v {sub ∞}-Z relationship has been revisited. The terminal velocity of IC 1613 O stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC 1613 and SMC or LMC analog stars. We find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the v {sub ∞}/v {sub esc} ratio of the whole OB star sample in any of the studied galaxies. Finally, we present the first evidence that the Fe-abundance of IC 1613 OB stars is similar to the SMC, which is in agreement with previous results on red supergiants. With the confirmed ∼1/10 solar oxygen abundances of B-supergiants, our results indicate that IC 1613's α/Fe ratio is sub-solar.

  3. EFFECTS OF A COMPANION STAR ON SLOW NOVA OUTBURSTS—TRANSITION FROM STATIC TO WIND EVOLUTIONS

    International Nuclear Information System (INIS)

    Two types of nova evolutions can occur in low-mass white dwarfs of ∼0.5-0.7 M☉, i.e., an evolution with optically thick winds like in usual classical novae, or an another type of evolution without them like in the symbiotic nova PU Vul. The latter type is characterized by spectra with no indication of strong winds as well as a long-lasting flat optical peak in its light curve. We propose a transition from evolution with no optically thick wind to usual evolution with optically thick winds as a new outburst model for slow novae that show a relatively long-lasting multipeak phase followed by a wind phase like in the slow novae V723 Cas, HR Del, and V5558 Sgr. We calculated nova envelopes with one-dimensional approximation of the companion's effects and found that when the companion star is deeply embedded in the extended nova envelope, the structure of the static envelope approaches that of the optically thick wind solution. Thus, the transition from static to wind solution is triggered by the effect of the companion. The transition occurs in a close binary nova like V723 Cas, but is not triggered in a long-period binary like PU Vul. We reconfirm our previous results that the frictional energy deposition is negligibly small in almost all hydrogen/helium novae because of the low envelope density at the orbit.

  4. A New Grid of Synthetic Spectra for the Analysis of [WC]-type Central Stars of Planetary Nebulae

    CERN Document Server

    Keller, Graziela R; Bianchi, Luciana; Maciel, Walter J; Bohlin, Ralph C; 10.1111/j.1365-2966.2011.19085.x

    2012-01-01

    We present a comprehensive grid of synthetic stellar-atmosphere spectra, suitable for the analysis of high resolution spectra of hydrogen-deficient post-Asymptotic Giant Branch (post-AGB) objects hotter than 50000 K, migrating along the constant luminosity branch of the Hertzsprung-Russell diagram (HRD). The grid was calculated with CMFGEN, a state-of-the-art stellar atmosphere code that properly treats the stellar winds, accounting for expanding atmospheres in non-LTE, line blanketing, soft X-rays, and wind clumping. We include many ionic species that have been previously neglected. Our uniform set of models fills a niche in an important parameter regime, i.e., high effective temperatures, high surface gravities, and a range of mass-loss values. The grid constitutes a general tool to facilitate determination of the stellar parameters and line identifications and to interpret morphological changes of the stellar spectrum as stars evolve through the central star of planetary nebula (CSPN) phase. We show the ef...

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

    OpenAIRE

    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 simulatio...

  6. HST and FUSE Spectroscopy of Hot Hydrogen-Rich Central Stars of Planetary Nebulae

    CERN Document Server

    Traulsen, I; Hoffmann, A I D; Kruk, J W; Rauch, T; Werner, K

    2004-01-01

    High-resolution UV spectra, obtained with HST and FUSE, enable us to analyse hot hydrogen-rich central stars in detail. Up to now, optical hydrogen and helium lines have been used to derive temperature and surface gravity. Those lines, however, are rather insensitive; in particular, neutral helium lines have completely vanished in the hottest central stars. Therefore, we have concentrated on ionization balances of metals, which have a rich line spectrum in the UV, to establish a new temperature scale for our sample. Furthermore, we have determined abundances of light metals, which had been poorly known before. They show considerable variation from star to star. We present results of quantitative spectral analyses performed with non-LTE model atmospheres.

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

    NARCIS (Netherlands)

    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.

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

    Science.gov (United States)

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

    2012-04-01

    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

  9. Suppression of star formation in the galaxy NGC 253 by a starburst-driven molecular wind.

    Science.gov (United States)

    Bolatto, Alberto D; Warren, Steven R; Leroy, Adam K; Walter, Fabian; Veilleux, Sylvain; Ostriker, Eve C; Ott, Jürgen; Zwaan, Martin; Fisher, David B; Weiss, Axel; Rosolowsky, Erik; Hodge, Jacqueline

    2013-07-25

    The under-abundance of very massive galaxies in the Universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable, most of the expelled mass (that is, the total mass flowing out from the nuclear region) is likely to be in atomic and molecular phases that are cooler than the ionized phases. Expanding molecular shells observed in starburst systems such as NGC 253 (ref. 12) and M 82 (refs 13, 14) may facilitate the entrainment of molecular gas in the wind. Although shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution better than 100 parsecs coupled with sensitivity to a wide range of spatial scales, a combination hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (distance ∼ 3.4 megaparsecs) known to possess a wind, that trace the cool molecular wind at 50-parsec resolution. At this resolution, the extraplanar molecular gas closely tracks the Hα filaments, and it appears to be connected to expanding molecular shells located in the starburst region. These observations allow us to determine that the molecular outflow rate is greater than 3 solar masses per year and probably about 9 solar masses per year. This implies a ratio of mass-outflow rate to star-formation rate of at least 1, and probably ∼3, indicating that the starburst-driven wind limits the star-formation activity and the final stellar content. PMID:23887428

  10. K 1-6: an asymmetric planetary nebula with a binary central star

    CERN Document Server

    Frew, David J; Fitzgerald, Michael; Parker, Quentin; Danaia, Lena; McKinnon, David; Guerrero, Martín A; Hedberg, John; Hollow, Robert; An, Yvonne; Bor, Shu Han; Colman, Isabel; Graham-White, Claire; Li, Qing Wen; Mai, Juliette; Papadakis, Katerina; Picone-Murray, Julia; Hoang, Melanie Vo; Yean, Vivian

    2010-01-01

    We present new imaging data and archival multiwavelength observations of the little studied emission nebula K 1-6 and its central star. Narrow-band images in H-alpha (+ [NII]) and [OIII] taken with the Faulkes Telescope North reveal a stratified, asymmetric, elliptical nebula surrounding a central star which has the colours of a late G- or early K-type subgiant or giant. GALEX ultraviolet images reveal a very hot subdwarf or white dwarf coincident in position with this star. The cooler, optically dominant star is strongly variable with a period of 21.312 +/- 0.008 days, and is possibly a high amplitude member of the RS CVn class, although an FK Com classification is also possible. Archival ROSAT data provide good evidence that the cool star has an active corona. We conclude that K 1-6 is most likely an old bona fide planetary nebula at a distance of ~1.0 kpc, interacting with the interstellar medium, and containing a binary or ternary central star. The observations and data analyses reported in this paper wer...

  11. Identifying Close Binary Central Stars of PN From the Kepler K2 Mission

    Science.gov (United States)

    Jacoby, George H.; Long, Joseph; Kronberger, Matthias; De Marco, Orsola; Hillwig, Todd C.

    2016-01-01

    During the Kepler mission, De Marco et al (2015) reported observing 5 PN central stars. Of these, the light curves for 4 central stars exhibited signatures of close binary interactions during their evolution. While suggestive that a large fraction of PN evolve as a binary phenomenon, the sample is far too small to be compelling. We have acquired Kepler K2 data for campaigns 0 and 2 to monitor an additional 6 central stars, and we expect data for another 8-10 targets in campaign 7. We present preliminary results from Kepler K2 campaigns 0 and 2, describe our expectations for campaign 7, and discuss the challenges of using Kepler for these observations.

  12. On the Launching and Structure of Radiatively Driven Winds in Wolf-Rayet Stars

    Science.gov (United States)

    Ro, Stephen; Matzner, Christopher D.

    2016-04-01

    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.

  13. Winds from massive stars: implications for the afterglows of γ-ray bursts

    Science.gov (United States)

    Ramirez-Ruiz, Enrico; Dray, Lynnette M.; Madau, Piero; Tout, Christopher A.

    2001-11-01

    Recent observations suggest that long-duration γ-ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in core-collapse explosions. The pre-explosive ambient medium provides a natural test for the most likely progenitors of GRBs. Those stars that shed their envelopes most readily have short jet crossing times and are more likely to produce a GRB. We construct a simple computational scheme to explore the expected contribution of the presupernova ejecta of single Wolf-Rayet (WR) stars to the circumstellar environment. Using detailed stellar tracks for the evolution of massive stars, we discuss the effects that the initial main-sequence mass, metallicity, rotation and membership in a binary system have on the ambient medium. We extend the theory of GRB afterglows in winds to consider the effect of the relativistic fireball propagating through the WR ejecta. Specific predictions are made for the interaction of the relativistic blast wave with the density bumps that arise when the progenitor star rapidly loses a large fraction of its initial mass or when the ejected wind interacts with the external medium and decelerates. A re-brightening of the afterglow with a spectrum redder than the typical synchrotron spectrum (as seen in GRB 970508, GRB 980326 and GRB 000911) is predicted. We also calculate the luminosity of the reflected echo that arises when circumstellar material Compton-scatters the prompt radiation, and examine the spectral signatures expected from the interaction of the GRB afterglow with the ejected medium.

  14. On the alumina dust production in the winds of O-rich Asymptotic Giant Branch stars

    CERN Document Server

    Dell'Agli, F; Rossi, C; Ventura, P; Di Criscienzo, M; Schneider, R

    2014-01-01

    The O-rich Asymptotic Giant Branch (AGB) stars experience strong mass loss with efficient dust condensation and they are major sources of dust in the interstellar medium. Alumina dust (Al$_2$O$_3$) is an important dust component in O-rich circumstellar shells and it is expected to be fairly abundant in the winds of the more massive and O-rich AGB stars. By coupling AGB stellar nucleosynthesis and dust formation, we present a self-consistent exploration on the Al$_2$O$_3$ production in the winds of AGB stars with progenitor masses between $\\sim$3 and 7 M$_{\\odot}$ and metallicities in the range 0.0003 $\\le$ Z $\\le$ 0.018. We find that Al$_2$O$_3$ particles form at radial distances from the centre between $\\sim2$ and 4 R$_*$ (depending on metallicity), which is in agreement with recent interferometric observations of Galactic O-rich AGB stars. The mass of Al$_2$O$_3$ dust is found to scale almost linearly with metallicity, with solar metallicity AGBs producing the highest amount (about 10$^{-3}$ M$_{\\odot}$) of...

  15. Detection of the Central Star of the Planetary Nebula NGC 6302

    CERN Document Server

    Szyszka, C; Zijlstra, Albert A; Tsamis, Y G

    2009-01-01

    NGC 6302 is one of the highest ionization planetary nebulae known and shows emission from species with ionization potential > 300eV. The temperature of the central star must be >200,000K to photoionize the nebula, and has been suggested to be up to 400,000K. On account of the dense dust and molecular disc, the central star has not convincingly been directly imaged. NGC 6302 was imaged in six narrow band filters by Wide Field Camera 3 on HST as part of the Servicing Mission 4 Early Release Observations. The central star is directly detected for the first time, and is situated, as expected, at the nebula centre and on the foreground (eastern) edge of the equatorial disc. The magnitudes of the central star have been reliably detected in two filters (F469N and F673N). Assuming a hot black body, the reddening has been measured from the 469-673 colour and a value of c=3.1, A_{v}=6.6 mag determined. A main sequence binary companion earlier than K5 can be excluded. The position of the star on the HR diagram suggests ...

  16. Abbott Wave-Triggered Runaway in Line-Driven Winds from Stars and Accretion Disks

    CERN Document Server

    Feldmeier, A; Feldmeier, Achim; Shlosman, Isaac

    2001-01-01

    Line-driven winds from stars and accretion disks are accelerated by scattering in numerous line transitions. The wind is believed to adopt a unique critical solution, out of the infinite variety of shallow and steep solutions. We study the inherent dynamics of the transition towards the critical wind. A new runaway wind mechanism is analyzed in terms of radiative-acoustic (Abbott) waves which are responsible for shaping the wind velocity law and fixing the mass loss. Three different flow types result, depending on the location of perturbations. First, if the shallow solution is perturbed sufficiently far downstream, a single critical point forms in the flow, which is a barrier for Abbott waves, and the solution tends to the critical one. Second, if the shallow solution is perturbed upstream from this critical point, mass overloading results, and the critical point is shifted inwards. This wind exhibits a broad, stationary region of decelerating flow and its velocity law has kinks. Third, for perturbations eve...

  17. Hubble Space Telescope Constraints on the Winds and Astrospheres of Red Giant Stars

    CERN Document Server

    Wood, Brian E; Harper, Graham M

    2016-01-01

    We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope, focusing on spectra of the Mg II h & k lines near 2800 A 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_w) are generally found to decrease with spectral type, with V_w decreasing from ~40 km/s at K2 III to ~20 km/s at M5 III. We find two new detections of astrospheric absorption, for Sigma Pup (K5 III) and Gamma Eri (M1 III). This absorption signature had previously only been detected for Alpha Tau (K5 III). For the three astrospheric detections the temperature of the wind after the termination shock correlates with V_w, but is low...

  18. What controls star formation in the central 500 pc of the Galaxy?

    CERN Document Server

    Kruijssen, J M Diederik; Elmegreen, Bruce G; Murray, Norman; Bally, John; Testi, Leonardo; Kennicutt, Robert C

    2013-01-01

    The star formation rate (SFR) in the Central Molecular Zone (CMZ, i.e. the central 500 pc) of the Milky Way is lower by a factor of >10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. In this paper, we quantify which physical mechanisms could be causing this observation. On scales larger than the disc scale height, the low SFR is found to be consistent with episodic star formation due to secular instabilities or variations of the gas inflow along the Galactic bar. The CMZ is marginally Toomre-stable when including gas and stars, but highly Toomre-stable when only accounting for the gas, indicating that the condensation of self-gravitating clouds may be limited. On small scales, we find that the SFR in the CMZ is consistent with an elevated critical density for star formation due to the high turbulent pressure - potentially aided by weak magnetic effects and an underproduction of massive stars due to a bottom-heavy IMF. The existence of a uni...

  19. Sub-mm free-free emission from the winds of massive stars in the age of ALMA

    CERN Document Server

    Daley-Yates, S; Crossland, T D

    2016-01-01

    The thermal radio and sub-mm emission from the winds of massive stars is investigated and the contribution to the emission due to the stellar wind acceleration region and clumping of the wind is quantified. Building upon established theory, a method for calculating the thermal radio and sub-mm emission using results for a line-driven stellar outflow according to Castor, Abbott & Klein (1975) is presented. The results show strong variation of the spectral index for 10 2 GHz < {\

  20. Discovery of photospheric argon in very hot central stars of planetary nebulae and white dwarfs

    CERN Document Server

    Werner, K; Kruk, J W

    2007-01-01

    We report the first discovery of argon in hot evolved stars and white dwarfs. We have identified the ArVII 1063.55A line in some of the hottest known (Teff=95000-110000 K) central stars of planetary nebulae and (pre-) white dwarfs of various spectral type. We determine the argon abundance and compare it to theoretical predictions from stellar evolution theory as well as from diffusion calculations. We analyze high-resolution spectra taken with the Far Ultraviolet Spectroscopic Explorer. We use non-LTE line-blanketed model atmospheres and perform line-formation calculations to compute synthetic argon line profiles. We find a solar argon abundance in the H-rich central star NGC1360 and in the H-deficient PG1159 star PG1424+535. This confirms stellar evolution modeling that predicts that the argon abundance remains almost unaffected by nucleosynthesis. For the DAO-type central star NGC7293 and the hot DA white dwarfs PG0948+534 and REJ1738+669 we find argon abundances that are up to three orders of magnitude sma...

  1. Far-Ultraviolet Temperature Diagnostics for Hot Central Stars of Planetary Nebulae

    Science.gov (United States)

    Sonneborn, G.; Ipin, R. C.; Herald, J.

    2007-01-01

    The effective temperature of hot central stars of planetary nebulae is usually determined from the ratios of optical He II lines. However, far-ultraviolet spectra from the FUSE satellite of several hot (T(sub eff) > 70,000 K) hydrogen-rich central stars have stellar features that imply a significantly hotter effective temperature than that determined from He II. There are many stellar features in the long wavelength portion of the FUSE spectrum. These include O VI 1146-47, F VI 1039.5, FeVII 1118.6, 1141.4, FeVI 1120.9, 1131.5, and NiVI 1124.2, 1148.2. The strong FVI 1139.5 line is of interest because of the large overabundance (over 100X solar) of F in some PG1159 stars reported recently by Werner et al. (2005). Modeling these spectral features may provide an method for measuring the effective temperature of these stars independent of the He II lines. An example of HD 200516, the central star of NGC 7009 (T(sub eff)= 82000 K from He II vs 95000 K from Far-W metal lines) is presented.

  2. Sub-mm free-free emission from the winds of massive stars in the age of ALMA

    Science.gov (United States)

    Daley-Yates, S.; Stevens, I. R.; Crossland, T. D.

    2016-09-01

    The thermal radio and sub-mm emission from the winds of massive stars is investigated and the contribution to the emission due to the stellar wind acceleration region and clumping of the wind is quantified. Building upon established theory, a method for calculating the thermal radio and sub-mm emission using results for a line-driven stellar outflow according to Castor, Abbott & Klein (1975) is presented. The results show strong variation of the spectral index for 102 GHz range of reasonable mass-loss rates and distances. Consequently both mechanisms need to be included to fully understand the mass-loss rates of massive stars.

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

    CERN Document Server

    David-Uraz, A; Petit, V; ud-Doula, A; Sundqvist, J O; Grunhut, J; Shultz, 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 (NRPs). In this paper, we evaluate the possible relation between large-scale, dipolar magnetic fields and the DAC phenomenon by investigating the magnetic properties of a sample of 13 OB stars exhibiting well-documented DAC behaviour. Using high-precision spectropolarimetric data acquired in part in the context of the Magnetism in Massive Stars (MiMeS) project, we find no evidence for surface dipolar magnetic fields in any of these stars. Using Bayesian inference, we compute upper limits on the strengths of the fields and use these limits to assess two potential mechanisms by which the field may influence wind outflow: magnetic wind confinement and local photospheric brightness enhancements. Within the limits we derive, both mechanisms fail to provide a systematic pro...

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

    CERN Document Server

    Kanarek, Graham C; Faherty, Jacqueline K; Zurek, David; Moffat, Anthony F J

    2016-01-01

    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 nebulae, and are likely to come from massive progenitor populations, and themselves be more massive than any sample of planetary nebulae known. Our survey has identified thousands of such candidates.

  5. The SAMI Galaxy Survey: extraplanar gas, galactic winds, and their association with star formation history

    CERN Document Server

    Ho, I-Ting; Bland-Hawthorn, Joss; Groves, Brent; Kewley, Lisa J; Kobayashi, Chiaki; Dopita, Michael A; Leslie, Sarah K; Sharp, Rob; Allen, James T; Bourne, Nathan; Bryant, Julia J; Cortese, Luca; Croom, Scott M; Dunne, Loretta; Fogarty, L M R; Goodwin, Michael; Green, Andy W; Konstantopoulos, Iraklis S; Lawrence, Jon S; Lorente, Nuria P F; Owers, Matt S; Richards, Samuel; Sweet, Sarah M; Tescari, Edoardo; Valiante, Elisabetta

    2016-01-01

    We investigate a sample of 40 local, main-sequence, edge-on disk galaxies using integral field spectroscopy with the SAMI Galaxy Survey to understand the link between properties of the extraplanar gas and their host galaxies. The kinematics properties of the extraplanar gas, including velocity asymmetries and increased dispersion, are used to differentiate galaxies hosting large-scale galactic winds from those dominated by the extended diffuse ionised gas. We find rather that a spectrum of diffuse gas-dominated to wind dominated galaxies exist. The wind-dominated galaxies span a wide range of star formation rates (-1 < log(SFR / Msun yr^{-1}) < 0.5) across the whole stellar mass range of the sample (8.5 < log(M*/Msun) < 11). The wind galaxies also span a wide range in SFR surface densities (10^{-3} - 10^{-1.5} Msun yr^{-1} kpc^{-2}) that is much lower than the canonical threshold of 0.1 Msun yr^{-1} kpc^{-2}. The wind galaxies on average have higher SFR surface densities and higher Hdelta_A values...

  6. Non-thermal high-energy emission from colliding winds of massive stars

    CERN Document Server

    Reimer, A; Reimer, O

    2005-01-01

    Colliding winds of massive star binary systems are considered as potential sites of non-thermal high-energy photon production. This is motivated merely by the detection of synchrotron radio emission from the expected colliding wind location. Here we investigate the properties of high-energy photon production in colliding winds of long-period WR+OB-systems. We found that in the dominating leptonic radiation process anisotropy and Klein-Nishina effects may yield spectral and variability signatures in the gamma-ray domain at or above the sensitivity of current or upcoming gamma-ray telescopes. Analytical formulae for the steady-state particle spectra are derived assuming diffusive particle acceleration out of a pool of thermal wind particles, and taking into account adiabatic and all relevant radiative losses. For the first time we include their advection/convection in the wind collision zone, and distinguish two regions within this extended region: the acceleration region where spatial diffusion is superior to ...

  7. UV spectral analysis of very hot H-deficient [WCE]-type central stars of planetary nebulae: NGC 2867, NGC 5189, NGC 6905, Pb 6, and Sand 3

    CERN Document Server

    Keller, Graziela R; Maciel, Walter J

    2014-01-01

    We analysed UV FUSE, IUE, and HST/STIS spectra of five of the hottest [WCE]-type central stars of planetary nebulae: NGC 2867, NGC 5189, NGC 6905, Pb 6, and Sand 3. The analysis leveraged on our grid of CMFGEN synthetic spectra, which covers the parameter regime of hydrogen deficient central stars of planetary nebulae and allows a uniform and systematic study of the stellar spectra. The stellar atmosphere models calculated by us include many elements and ionic species neglected in previous analyses, which allowed us to improve the fits to the observed spectra considerably and provided an additional diagnostic line: the Ne VII $\\lambda$ 973 $\\mathrm{\\AA}$, which had not been modelled in [WCE] spectra and which presents, in these stars, a strong P-Cygni profile. We report newly derived photospheric and wind parameters and elemental abundances. The central stars of NGC 2867, NGC 5189, and Pb 6 had their temperatures revised upward in comparison with previous investigations and we found the carbon to helium mass ...

  8. The planetary nebula Abell 48 and its [WN4] central star

    CERN Document Server

    Bojicic, I S; Parker, Q A; Stupar, M; Wachter, S; DePew, K

    2012-01-01

    We have conducted a multi-wavelength study of the planetary nebula Abell 48 and give a revised classification of its nucleus as a hydrogen-deficient star of type [WN4]. The surrounding nebula has a morphology typical of PNe and importantly, is not enriched in nitrogen, and thus not the 'peeled atmosphere' of a massive star. Indeed, no WN4 star is known to be surrounded by such a compact nebula. The ionized mass of the nebula is also a powerful discriminant between the low-mass PN and high-mass WR ejecta interpretations. The ionized mass would be impossibly high if a distance corresponding to a Pop I star was adopted, but at a distance of 2 kpc, the mass is quite typical of moderately evolved PNe. At this distance, the ionizing star then has a luminosity of ~5000 Lsolar, again rather typical for a PN central star. We give a brief discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars.

  9. Discovery of low-metallicity stars in the central parsec of the Milky Way

    CERN Document Server

    Do, Tuan; Winsor, Nathan; Støstad, Morten; Morris, Mark R; Lu, Jessica R; Ghez, Andrea M

    2015-01-01

    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 were obtained with the medium-spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guide star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is large variation in metallicity, with stars ranging from [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 Galac...

  10. X-ray Emission from Ionized Wind-Bubbles around Wolf-Rayet Stars

    CERN Document Server

    Dwarkadas, Vikram V

    2015-01-01

    Using a code that employs a self-consistent method for computing the effects of photoionization on circumstellar gas dynamics, we model the formation of wind-driven nebulae around massive Wolf-Rayet (W-R) stars. Our algorithm incorporates a simplified model of the photo-ionization source, computes the fractional ionization of hydrogen due to the photoionizing flux and recombination, and determines self-consistently the energy balance due to ionization, photo-heating and radiative cooling. We take into account changes in stellar properties and mass-loss over the star's evolution. Our multi-dimensional simulations clearly reveal the presence of strong ionization front instabilities. Using various X-ray emission models, and abundances consistent with those derived for W-R nebulae, we compute the X-ray flux and spectra from our wind bubble models. We show the evolution of the X-ray spectral features with time over the evolution of the star, taking the absorption of the X-rays by the ionized bubble into account. O...

  11. On the Launching and Structure of Radiatively Driven Winds in Wolf-Rayet Stars

    CERN Document Server

    Ro, Stephen

    2016-01-01

    Hydrostatic models of Wolf-Rayet 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 by which 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. Wolf-Rayet envelopes will therefore likely correspond to the strong, compact solutions. We also find that wind solutions with negligible ga...

  12. Wind modelling of very massive stars up to 300 solar masses

    Science.gov (United States)

    Vink, Jorick S.; Muijres, L. E.; Anthonisse, B.; de Koter, A.; Gräfener, G.; Langer, N.

    2011-07-01

    The stellar upper-mass limit is highly uncertain. Some studies have claimed there is a universal upper limit of 150 M⊙. A factor that is often overlooked is that there might be a significant difference between the present-day and the initial masses of the most massive stars - as a result of mass loss. The upper-mass limit may easily supersede 200 M⊙. For these reasons, we present new mass-loss predictions from Monte Carlo radiative transfer models for very massive stars (VMS) in the mass range 40-300 M⊙, and with very high luminosities 6.0 ≤ log (L ⋆ /L⊙) ≤ 7.03, corresponding to large Eddington factors Γ. Using our new dynamical approach, we find an upturn or "kink" in the mass-loss versus Γ dependence, at the point where the model winds become optically thick. This coincides with the location where our wind efficiency numbers surpass the single-scattering limit of η = 1, reaching values up to η ≃ 2.5. In all, our modelling suggests a transition from common O-type winds to Wolf-Rayet characteristics at the point where the winds become optically thick. This transitional behaviour is also revealed with respect to the wind acceleration parameter, β, which starts at values below 1 for the optically thin O-stars, and naturally reaches values as high as 1.5-2 for the optically thick Wolf-Rayet models. An additional finding concerns the transition in spectral morphology of the Of and WN characteristic He ii line at 4686 Å. When we express our mass-loss predictions as a function of the electron scattering Eddington factor Γe L ⋆ /M ⋆ alone, we obtain an Ṁ vs. Γe dependence that is consistent with a previously reported power law Ṁ∝ Γ_e{5} (Vink 2006) that was based on our previous semi-empirical modelling approach. When we express Ṁ in terms of both Γe and stellar mass, we find optically thin winds and Ṁ ∝ Mstar0.68 Γ_e^{2.2} for the Γe range 0.4 ≲ Γe ≲ 0.7, and mass-loss rates that agree with the standard Vink et al. recipe

  13. Polarization of light scattered from the winds of early-type stars

    Science.gov (United States)

    Cassinelli, J. P.; Nordsieck, K. H.; Murison, M. A.

    1987-01-01

    There is evidence from visible wavelength polarimetry that the matter in the winds of early-type stars is not distributed uniformly about the stars. In this paper equations for the observable polarization from an axisymmetric distribution of electrons are derived first from the basic point source model of Brown and McLean (1977) and then from extended atmosphere radiative transfer theory. A factor is derived which corrects the Brown and McLean model for the finite size of stars. This finite disk factor is found to reduce the magnitude of the predicted polarization to less than half of the point source prediction. The effects of having the mass outflow concentrated in a plume are considered. The effects of absorption in an unocculted plume are shown to give rise to a wavelength-dependent polarization that is described using a 'polarization color' parameter. A continuum opacity index is defined that allows for a straightforward interpretation of the polarization of stars of differing effective temperatures.

  14. The Magnetic Coupling of Chromospheres and Winds From Late Type Evolved Stars: Role of MHD Waves

    Science.gov (United States)

    Airapetian, Vladimir; Leake, James; Carpenter, Kenneth

    2015-08-01

    Stellar chromospheres and winds represent universal attributes of stars on the cool portion of H-R diagram. In this paper we derive observational constrains for the chromospheric heating and wind acceleration from cool evolved stars and examine the role of Alfven waves as a viable source of energy dissipation and momentum deposition. We use a 1.5D magnetohydrodynamic code with a generalized Ohm's law to study propagation of Alfven waves generated along a diverging magnetic field in a stellar photosphere at a single frequency. We demonstrate that due to inclusion of the effects of ion-neutral collisions in magnetized weakly ionized chromospheric plasma on resistivity and the appropriate grid resolution, the numerical resistivity becomes 1-2 orders of magnitude smaller than the physical resistivity. The motions introduced by non-linear transverse Alfven waves can explain non-thermally broadened and non-Gaussian profiles of optically thin UV lines forming in the stellar chromosphere of α Tau and other late-type giant and supergiant stars. The calculated heating rates in the stellar chromosphere model due to resistive (Joule) dissipation of electric currents on Pedersen resistivity are consistent with observational constraints on the net radiative losses in UV lines and the continuum from α Tau. At the top of the chromosphere, Alfven waves experience significant reflection, producing downward propagating transverse waves that interact with upward propagating waves and produce velocity shear in the chromosphere. Our simulations also suggest that momentum deposition by non-linear Alfven waves becomes significant in the outer chromosphere within 1 stellar radius from the photosphere that initiates a slow and massive winds from red giants and supergiants.

  15. Fluctuations Mitigation of Variable Speed Wind Turbine through Optimized Centralized Controller

    OpenAIRE

    S. Masoud Barakati; Saeed Tavakoli; Sajjad Farajianpour; Ali Mohammadi

    2012-01-01

    A wind energy conversion system (WECS) including a variable wind turbine in grid-connected mode is considered to control. In this paper, each component of WECS model is systematically presented and then the integrated overall model is validated.Regarding to nonlinear nature of WECS and the complex system structure as multiple-input- multiple-output (MIMO),control procedure counters the problem which strategy to handle.To simplify the control policy, a centralized controller which is compatibl...

  16. ALMA detection of the rotating molecular disk wind from the young star HD 163296

    OpenAIRE

    Klaassen, P. D.; Juhasz, A.; Mathews, G. S.; Mottram, J. C.; de Gregorio-Monsalvo, I.; van Dishoeck, E. F.; Takahashi, S.; Akiyama, E.; Chapillon, E.; Espada, D.; Hales, A.; Hogerheijde, M.R.; Rawlings, M.; Schmalzl, M.; Testi, L.

    2013-01-01

    Disk winds have been postulated as a mechanism for angular momentum release in protostellar systems for decades. HD 163296 is a Herbig Ae star surrounded by a disk and has been shown to host a series of HH knots (HH 409) with bow shocks associated with the farthest knots. Here we present ALMA Science Verification data of CO J=2-1 and J=3-2 emission which are spatially coincident with the blue shifted jet of HH knots, and offset from the disk by -18.6 km/s. The emission has a double corkscrew ...

  17. Star formation in early-type galaxies: the role of stellar winds and kinematics

    CERN Document Server

    Pellegrini, S; Ciotti, L

    2015-01-01

    Early-type galaxies (ETGs) host a hot ISM produced mainly by stellar winds, and heated by Type Ia supernovae and the thermalization of stellar motions. High resolution 2D hydrodynamical simulations showed that ordered rotation in the stellar component results in the formation of a centrifugally supported cold equatorial disc. In a recent numerical investigation we found that subsequent generations of stars are formed in this cold disc; this process consumes most of the cold gas, leaving at the present epoch cold masses comparable to those observed. Most of the new stellar mass formed a few Gyrs ago, and resides in a disc.

  18. Simulating the environment around planet-hosting stars - II. Stellar winds and inner astrospheres

    CERN Document Server

    Alvarado-Gómez, J D; Cohen, O; Drake, J J; Garraffo, C; Grunhut, J; Gombosi, T I

    2016-01-01

    We present the results of a comprehensive numerical simulation of the environment around three exoplanet-host stars (HD 1237, HD 22049, and HD 147513). Our simulations consider one of the latest models currently used for space weather studies in the Heliosphere. Large-scale magnetic field maps, recovered with two implementations of the tomographic technique of Zeeman-Doppler imaging, serve to drive steady-state solutions in each system. This paper contains the description of the stellar wind and inner astrosphere, while the coronal structure was previously discussed in Alvarado-G\\'omez et al. (2016). The analysis includes the magneto-hydrodynamical properties of the stellar wind, the associated mass and angular momentum loss rates, as well as the topology of the astrospheric current sheet in each system. A systematic comparison among the considered cases is performed, including two reference solar simulations covering activity minimum and maximum. For HD 1237, we investigate the interactions between the struc...

  19. Gaps of wind turbines perception in central European space

    Czech Academy of Sciences Publication Activity Database

    Kallabová, Eva; Cetkovský, Stanislav

    Brno : Ústav geoniky AV ČR, 2009 - (Kallabová, E.; Ira, V.). s. 9-10 ISBN 978-80-86407-75-3. [Česko - slovenský geografický akademický seminář/14./. 13.10.2009-15.10.2009, Telč] R&D Projects: GA AV ČR(CZ) KJB700860801 Institutional research plan: CEZ:AV0Z30860518 Keywords : wind turbines * perception * European space Subject RIV: DE - Earth Magnetism, Geodesy, Geography

  20. UV and FUV spectroscopy of the hybrid PG 1159-type central star NGC 7094

    CERN Document Server

    Ziegler, M; Reiff, E; Werner, K; Kruk, J W; Oliveira, C M

    2008-01-01

    Previous studies aiming at the iron-abundance determination in three PG 1159 stars (K 1-16, PG 1159-035, NGC 7094) and a [WC]-PG 1159 transition star (Abell 78) have revealed that no object shows any iron line in the UV spectrum. The stars are iron-deficient by at least 1 dex, typically. A possible explanation is that iron nuclei were transformed by neutron captures into heavier elements (s-process), however, the extent of the iron-destruction would be much stronger than predicted by AGB star models. But if n-captures are the right explanation, then we should observe an enrichment of trans-iron elements. In this paper we report on our search for a possible nickel overabundance in one of the four Fe deficient PG 1159 stars, namely the central star NGC 7094. We are unable to identify any nickel line in HST and FUSE spectra and conclude that Ni is not overabundant. It is conceivable that iron was transformed into even heavier elements, but their identification suffers from the lack of atomic data.

  1. X-ray Emission Line Profiles from Wind Clump Bow Shocks in Massive Stars

    CERN Document Server

    Ignace, R; Cassinelli, J P

    2012-01-01

    The consequences of structured flows continue to be a pressing topic in relating spectral data to physical processes occurring in massive star winds. In a preceding paper, our group reported on hydrodynamic simulations of hypersonic flow past a rigid spherical clump to explore the structure of bow shocks that can form around wind clumps. Here we report on profiles of emission lines that arise from such bow shock morphologies. To compute emission line profiles, we adopt a two component flow structure of wind and clumps using two "beta" velocity laws. While individual bow shocks tend to generate double horned emission line profiles, a group of bow shocks can lead to line profiles with a range of shapes with blueshifted peak emission that depends on the degree of X-ray photoabsorption by the interclump wind medium, the number of clump structures in the flow, and the radial distribution of the clumps. Using the two beta law prescription, the theoretical emission measure and temperature distribution throughout the...

  2. Polarization variability among Wolf-Rayet stars. V - Linear polarization of the bright Cygnus stars and an anticorrelation of variability with wind speed

    International Nuclear Information System (INIS)

    This paper presents polarimetric data for seven of the eight bright WR stars in Cygnus. Six of the stars show only random, low-amplitude modulation on time scales of hours to days. One of these behaves as expected for a long-period WR + O system with an elliptical orbit. The eighth star is the only short-period WR + O binary in the sample. It is confirmed that the degree of random, intrinsic scatter in polarization is correlated with spectral subclass and terminal wind velocity. It is suggested that this is caused by the presence of propagating blobs which form, survive, and/or grow more easily in slower winds. Two models are proposed to explain the origin of the blobs. 93 refs

  3. Cold gas in hot star clusters: the wind from the red supergiant W26 in Westerlund 1

    CERN Document Server

    Mackey, Jonathan; Fossati, Luca; Langer, Norbert

    2015-01-01

    The massive red supergiant (RSG) W26 in Westerlund 1 is one of a growing number of RSGs shown to have winds that are ionized from the outside in. The fate of this dense wind material is important for models of second generation star formation in massive star clusters. Mackey et al. (2014) showed that external photoionization can stall the wind of RSGs and accumulate mass in a dense static shell. We use 1D R-HD simulations of an externally photoionized wind to predict the Halpha and [NII] emission arising from photoionized winds both with and without a dense shell. We analyse spectra of the Halpha and [NII] emission in the environment around W26 and compare them with predicted synthetic emission. Simulations of slow winds that are decelerated into a dense shell show strongly limb-brightened line emission, with line radial velocities that are independent of the wind speed. Faster winds (>22 km/s) do not form a dense shell, have less limb-brightening, and the line radial velocity is a good tracer of the wind spe...

  4. The Low Velocity Wind from the Circumstellar Matter Around the B9V Star sigma Herculis

    CERN Document Server

    Chen, C H

    2003-01-01

    We have obtained FUSE spectra of sigma Her, a nearby binary system, with a main sequence primary, that has a Vega-like infrared excess. We observe absorption in the excited fine structure lines C II* at 1037 A, N II* at 1085 A, and N II** at 1086 A that are blueshifted by as much as ~30 km/sec with respect to the star. Since these features are considerably narrower than the stellar lines and broader than interstellar features, the C II and N II are circumstellar. We suggest that there is a radiatively driven wind, arising from the circumstellar matter, rather than accretion as occurs around beta Pic, because of sigma Her's high luminosity. Assuming that the gas is liberated by collisions between parent bodies at 20 AU, the approximate distance at which blackbody grains are in radiative equilibrium with the star and at which 3-body orbits become unstable, we infer dM/dt ~ 6 * 10^-12 M_{sun}/yr. This wind depletes the minimum mass of parent bodies in less than the estimated age of the system.

  5. Tracing Slow Winds from T Tauri Stars via Low Velocity Forbidden Line Emission

    CERN Document Server

    Simon, M N; Edwards, S; Feng, W; Gorti, U; Hollenbach, D; Rigliaco, E; Keane, J T

    2016-01-01

    Using Keck/HIRES spectra {\\Delta}v ~ 7 km/s, we analyze forbidden lines of [O I] 6300 {\\AA}, [O I] 5577 {\\AA} and [S II] 6731 {\\AA} from 33 T Tauri stars covering a range of disk evolutionary stages. After removing a high velocity component (HVC) associated with microjets, we study the properties of the low velocity component (LVC). The LVC can be attributed to slow disk winds that could be magnetically (MHD) or thermally (photoevaporative) driven. Both of these winds play an important role in the evolution and dispersal of protoplanetary material. LVC emission is seen in all 30 stars with detected [O I] but only in 2 out of eight with detected [S II] , so our analysis is largely based on the properties of the [O I] LVC. The LVC itself is resolved into broad (BC) and narrow (NC) kinematic components. Both components are found over a wide range of accretion rates and their luminosity is correlated with the accretion luminosity, but the NC is proportionately stronger than the BC in transition disks. The FWHM of...

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

    Science.gov (United States)

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

    2012-07-01

    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.

  7. Investigating the potential magnetic origin of wind variability in OB stars

    Science.gov (United States)

    David-Uraz, Alexandre

    2016-05-01

    In this thesis, the origin of large-scale structures in hot star winds, believed to be responsible for the presence of discrete absorption components (DACs) in the absorption troughs of ultraviolet resonance lines, is constrained using both observations and numerical simulations. These structures are understood as arising from bright regions on the stellar surface, although their physical cause remains unknown. First, we use high quality circular spectropolarimetric observations of 13 well-studied OB stars to evaluate the potential role of dipolar magnetic fields in producing DACs. We perform longitudinal field measurements and place limits on the field strength using Bayesian inference, assuming that it is dipolar. No magnetic field was detected within this sample. The derived constraints statistically refute any significant dynamical influence from a magnetic dipole on the wind for all of these stars, ruling out such fields as a cause for DACs. Second, we perform numerical simulations using bright spots constrained by broadband optical photometric observations. We calculate hydrodynamical wind models using three sets of spot sizes and strengths. Co-rotating interaction regions are yielded in each model, and radiative transfer shows that the properties of the variations in the UV resonance lines synthesized from these models are consistent with those found in observed UV spectra, establishing the first consistent link between UV spectroscopic line profile variability and photometric variations and thus supporting the bright spot paradigm (BSP). Finally, we develop and apply a phenomenological model to quantify the measurable effects co-rotating bright spots would have on broadband optical photometry and on the profiles of photospheric lines in optical spectra. This model can be used to evaluate the existence of these spots, and, in the event of their detection, characterize them. Furthermore, a tentative spot evolution model is presented. A preliminary analysis of

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

    CERN Document Server

    Vaisanen, Petri; Kankare, Erkki; Kotilainen, Jari; Mattila, Seppo; Rajpaul, Vinesh; Randriamanakoto, Zara; Reunanen, Juha; 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 um 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 observatio...

  9. Present and Future of Central Production with STAR Detector at RHIC

    International Nuclear Information System (INIS)

    The present status and future of the physics program of Central Production using the STAR detector at RHIC are described. The program focuses on particle production resulting from the Double Pomeron Exchange (DPE) process. Forward protons from the DPE interaction are detected in the Roman Pot system installed at 55.5 m and 58.5 m on both sides of the STAR interaction point. The recoil system of charged particles from the DPE process is measured in the STAR Time Projection Chamber (TPC). The first data were taken during the 2009 RHIC Run 9 using polarized proton-proton collisions at √s = 200 GeV. The preliminary spectra of two pion and four pion invariant mass reconstructed by STAR TPC in central region of pseudo-rapidity abs(η) < 1, are presented. Plans to take data with the current system at √s = 500 GeV and plans to upgrade the forward proton tagging system, so that it can reach higher masses and obtain large data samples in searching for glueballs that could be produced in the DPE process, are discussed. (author)

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

    International Nuclear Information System (INIS)

    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.

  11. Winds from massive stars implications for the afterglows of gamma-ray bursts

    CERN Document Server

    Ramirez-Ruiz, E; Madau, P; Tout, C A; Ramirez-Ruiz, Enrico; Dray, Lynnette M.; Madau, Piero; Tout, Christopher A.

    2001-01-01

    Recent observations suggest that long-duration gamma-ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in core-collapse explosions. The pre-explosive ambient medium provides a natural test for the most likely progenitors of GRBs. Those stars that shed their envelopes most readily have short jet crossing times and are more likely to produce a GRB. We construct a simple computational scheme to explore the expected contribution of the presupernova ejecta of single Wolf-Rayet (WR) stars to the circumstellar environment. Using detailed stellar tracks for the evolution of massive stars, we discuss the effects that the initial main sequence mass, metallicity, rotation and membership in a binary system have on the ambient medium. We extend the theory of GRB afterglows in winds to consider the effect of the relativistic fireball propagating through the WR ejecta. We make specific predictions for the interaction of the relativistic blast wave with the density bumps that arise when ...

  12. WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?

    CERN Document Server

    Chené, A -N; Cameron, C; Fahed, R; Gamen, R C; Lefèvre, L; Rowe, J F; St-Louis, N; Muntean, V; De La Chevrotière, A; Guenther, D B; Kuschnig, R; Matthews, J M; Rucinski, S M; Sasselov, D; Weiss, W W

    2011-01-01

    A 30-day contiguous photometric run with the 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 RV 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 day...

  13. The O I] 1641A line as a probe of symbiotic star winds

    CERN Document Server

    Shore, S N

    2010-01-01

    The neutral oxygen resonance 1302A line can, if the optical depth is sufficiently high, de-excite by an intercombination transition at 1641A to a metastable state. This has been noted in a number of previous studies but never systematically investigated as a diagnostic of the neutral red giant wind in symbiotic stars and symbiotic-like recurrent novae. We used archival $IUE$ high resolution, and GHRS and STIS medium and high resolution, spectra to study a sample of symbiotic stars. The integrated fluxes were measured, where possible, for the O I 1302A and O I] 1641A lines. The intercombination 1641A line is detected in a substantial number of symbiotic stars with optical depths that give column densities comparable with direct eclipse measures (EG And) and the evolution of the recurrent nova RS Oph 1985 in outburst. In four systems (EG And, Z And, V1016 Cyg, and RR Tel), we find that the O I] variations are strongly correlated with the optical light curve and outburst activity. This transition can also be imp...

  14. Using Beta Cen to Probe the Photosphere-Wind Connection to B Stars

    Science.gov (United States)

    MacFarlane, Joseph J.

    2005-01-01

    The goal of the project was to probe the connection between the photospheric pulsations and the X-ray production in the stellar winds of B stars. The B1 III star Beta Centauri is a Beta Cephei variable with a high X-ray count rate, and was observed by XMM. Analysis of XMM X-ray spectra showed characteristic plasma temperatures of 0.1, 0.2 and 0.6 keV. Analysis of He-like forbidden-to-intercombination lines was performed to determine the dominant locations of the X-ray emission. At Prism, work focused on developing and upgrading spectral models to calculate forbidden-to-intercombination line ratios using more detailed atomic models than the simple models typically used in the analysis of X-ray spectral lines, thereby allowing us to assess the effects of a broader variety of populating and depopulating channels for energy levels contributing to the observed X-ray line emission. Based on Ne IX lines, the source location was determined to be no farther than 4 stellar radii. Examination of the time variability of the XMM data for Beta Cen showed no significant correlation with the known optical pulsation period for the star, and also did not find any significant periods of variation at X-ray wavelengths.

  15. Phase resolved X-ray spectroscopy of HDE 228766: Probing the wind of an extreme Of+/WNLha star

    Science.gov (United States)

    Rauw, G.; Mahy, L.; Nazé, Y.; Eenens, P.; Manfroid, J.; Flores, C. A.

    2014-06-01

    Context. HDE 228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star collides with the wind of its O8 II companion, leading to relatively strong X-ray emission. Aims: Measuring the orbital variations of the line-of-sight absorption toward the X-ray emission from the wind-wind interaction zone yields information on the wind densities of both stars. Methods: X-ray spectra have been collected at three key orbital phases to probe the winds of both stars. Optical photometry has been gathered to set constraints on the orbital inclination of the system. Results: The X-ray spectra reveal prominent variations of the intervening column density toward the X-ray emission zone, which are in line with the expectations for a wind-wind collision. We use a toy model to set constraints on the stellar wind parameters by attempting to reproduce the observed variations of the relative fluxes and wind optical depths at 1 keV. Conclusions: The lack of strong optical eclipses sets an upper limit of ~ 68° on the orbital inclination. The analysis of the variations of the X-ray spectra suggests an inclination in the range 54-61° and indicates that the secondary wind momentum ratio exceeds that of the primary by at least a factor 5. Our models further suggest that the bulk of the X-ray emission arises from the innermost region of the wind interaction zone, which is from a region whose outer radius, as measured from the secondary star, lies between 0.5 and 1.5 times the orbital separation. Based on observations collected with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA), and on data collected at the San Pedro Mártir observatory (Mexico).

  16. HST and FUSE Spectroscopy of the DAO-type Central Star LS V+4621

    CERN Document Server

    Rauch, T; Werner, K; Kruk, J W

    2006-01-01

    The DAO-type white dwarf LS V+4621 is the hydrogen-rich central star of the possible planetary nebula Sh 2-216. We have taken high-resolution, high-S/N ultraviolet spectra with STIS aboard the HST and FUSE in order to constrain its photospheric parameters. A detailed spectral analysis by means of state-of-the-art NLTE model-atmosphere techniques is presented which includes the determination the individual abundances of iron-group elements.

  17. Following the rapid evolution of the central star of the Stingray Nebula in real time

    Science.gov (United States)

    Reindl, Nicole

    2014-10-01

    SAO 244567 is an unusually fast evolving star. Within twenty years only, it has turned from a B-type supergiant into the central star of the Stingray nebula. Space and ground-based observations obtained over the last decades have revealed that its spectrum changes noticeably over just a few years, showing stellar evolution in real time. Previous analysis indicates it must be a low mass star and thus the observed fast evolution is in strong contradiction with canonical post-asymptotic giant branch (AGB) evolution. A late He-shell flash is able to account for the rapid evolution. This scenario would predict an evolution back to the AGB, e.g. a decrease of the effective temperature (which is already indicated by the FUSE observations in 2006) and an increase of luminosity. With COS spectroscopy we want to follow the evolution of the surface properties of SAO 244567 to verify this thesis. The very compact nebula of SAO 244567 makes it impossible to derive these parameters from optical spectra, because most of the photospheric lines are blended by nebular emission lines thus they are not suitable for a spectral analysis. The derived surface parameters will establish constraints for late thermal pulse evolutionary calculations. With these calculations we aim not only to explain the nature of SAO 244567, but they also will provide a deeper insight in the formation process of hydrogen deficient stars, which make up 25% of the post AGB-stars and white dwarfs.

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

    Data.gov (United States)

    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...

  19. Cold gas in hot star clusters: the wind from the red supergiant W26 in Westerlund 1

    Science.gov (United States)

    Mackey, Jonathan; Castro, Norberto; Fossati, Luca; Langer, Norbert

    2015-10-01

    The massive red supergiant W26 in Westerlund 1 is one of a growing number of red supergiants shown to have winds that are ionized from the outside in. The fate of this dense wind material is important for models of second generation star formation in massive star clusters. Mackey et al. (2014, Nature, 512, 282) showed that external photoionization can stall the wind of red supergiants and accumulate mass in a dense static shell. We use spherically symmetric radiation-hydrodynamic simulations of an externally photoionized wind to predict the brightness distribution of Hα and [N II] emission arising from photoionized winds both with and without a dense shell. We analyse spectra of the Hα and [N II] emission lines in the circumstellar environment around W26 and compare them with simulations to investigate whether W26 has a wind that is confined by external photoionization. Simulations of slow winds that are decelerated into a dense shell show strongly limb-brightened line emission, with line radial velocities that are independent of the wind speed. Faster winds (≳22 km s-1) do not form a dense shell, have less limb-brightening, and the line radial velocity is a good tracer of the wind speed. The brightness of the [N II] and Hα lines as a function of distance from W26 agrees reasonably well with observations when only the line flux is considered. The radial velocity of the simulated winds disagrees with observations, however: the brightest observed emission is blueshifted by ≈25 km s-1 relative to the radial velocity of the star, whereas a spherically symmetric wind has the brightest emission at zero radial velocity because of limb brightening. Our results show that the bright nebula surrounding W26 must be asymmetric, and we suggest that it is confined by external ram pressure from the extreme wind of the nearby supergiant W9. We obtain a lower limit on the nitrogen abundance within the nebula of 2.35 times solar. The line ratio strongly favours photoionization

  20. Discovery of a galactic wind in the central region of M100

    CERN Document Server

    Jiménez-Vicente, J; Mediavilla, E; Battaner, E

    2007-01-01

    We report the discovery of a galactic wind in the central region of the galaxy M100. This result is based on a careful 2D spectroscopic study performed on observations made with the fibre system INTEGRAL on the WHT. The primary evidence of the wind is the presence of blueshifted interstellar NaD absorption lines. The velocity field of the absorbers show a clear rotation pattern but globally blueshifted ($\\sim$ -115 km/s) with respect to the systemic velocity of the galaxy. The emission lines also present a blueward component arising from the ionized gas phase of the galactic wind. The velocity field of the ionized gas wind component shows no evidences of rotation but exhibits a pattern that can be interpreted in terms of the projection of an outflowing cone or shell. The wind component has [NII]/H$\\alpha$ ratios of about 1.8, typical of shock ionization. The ionized component of the wind can be identified with an expanding shell of shocked gas, and the neutral component with disk gas entrained in the wind at ...

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

    International Nuclear Information System (INIS)

    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

  2. Massive stars and the energy balance of the interstellar medium. II. The 35 solar mass star and a solution to the "missing wind problem"

    CERN Document Server

    Freyer, T; Yorke, H W; Freyer, Tim; Hensler, Gerhard; Yorke, Harold W.

    2006-01-01

    We continue our numerical analysis of the morphological and energetic influence of massive stars on their ambient interstellar medium for a 35 solar mass star that evolves from the main sequence through red supergiant and Wolf-Rayet phases, until it ultimately explodes as a supernova. We find that structure formation in the circumstellar gas during the early main-sequence evolution occurs as in the 60 solar mass case but is much less pronounced because of the lower mechanical wind luminosity of the star. Since on the other hand the shell-like structure of the HII region is largely preserved, effects that rely on this symmetry become more important. At the end of the stellar lifetime 1% of the energy released as Lyman continuum radiation and stellar wind has been transferred to the circumstellar gas. From this fraction 10% is kinetic energy of bulk motion, 36% is thermal energy, and the remaining 54% is ionization energy of hydrogen. The sweeping up of the slow red supergiant wind by the fast Wolf-Rayet wind p...

  3. Narrow He II emission in star-forming galaxies at low metallicity. Stellar wind emission from a population of Very Massive Stars

    CERN Document Server

    Gräfener, G

    2015-01-01

    In a recent study star-forming galaxies with HeII emission at moderate redshifts have been found to occur in two modes, distinguished by the width of their HeII emission lines. Broad HeII emission has been attributed to stellar emission from a population of evolved Wolf-Rayet (WR) stars while narrow HeII emission has been attributed to nebular emission excited by a population of very hot PopIII stars formed in pockets of pristine gas at moderate redshifts. In this work we propose an alternative scenario for the origin of the narrow HeII emission, namely very massive stars (VMS) at low metallicity (Z) which form strong but slow WR-type stellar winds due to their proximity to the Eddington limit. We estimate the expected HeII line fluxes and equivalent widths based on wind models for VMS and population synthesis models, and compare the results with recent observations of star-forming galaxies at moderate redshifts. The observed HeII line strengths and equivalent widths are in line with what is expected for a po...

  4. A unified heuristic X-ray production model for thick and thin winds from single nonmagnetic hot stars

    Science.gov (United States)

    Gayley, K. G.

    2016-09-01

    Observations of X-rays from WR6 and other dense winds require the presence of mechanisms that can produce hot gas at much larger radii than in lower density OB winds. But does this require some new mechanism in Wolf-Rayet winds, or could it simply be that the same hot-gas production is made more visible by denser winds? This article explores the latter perspective, and suggests a unified approach to the X-ray heating in all single nonmagnetic hot stars, as a kind of benchmark for observational testing. The results produce an X-ray generation efficiency that peaks as winds just become optically thick to X-ray reabsorption, but can still maintain detectable efficiencies at the large radii necessary in optically thick WR winds. A key element of the model is that fast terminal speeds serve to rapidly advect the gas being shocked out to large radii where some of the X-ray emission can emerge, even as X-rays emitted deeper down are copiously reabsorbed. An essential requirement is that the turbulence lengthscale increases with the wind acceleration lengthscale, as the latter is seen to be stretched out in Wolf-Rayet winds. Radiative efficiency is maintained at large radii by the high densities in the wind, allowing X-ray heating in an extended spatial "tail" of the normal OB-type emission to become observable. Hence in this scenario, the observation of dense winds serves as a complementary means of spatially resolving the nature of X-ray heating in nonmagnetic single hot-star winds.

  5. New Galactic Planetary Nebulae and the role of Central Star Binarity

    Science.gov (United States)

    Miszalski, B.

    2009-09-01

    : (i) The kinematics of the bulge, and (ii) The role of binary central stars of PNe. Radial velocities of hundreds of PNe towards the bulge were measured from ANU 2.3-m longslit spectroscopy and from deep spectroscopy conducted with the AAT 2dF AAOmega and VLT FLAMES multi-object spectroscopy facilities. Multiple measurements were recorded for many PNe resulting in a more accurate catalogue of "1200 PNe within the |l| role of binarity in the shaping of nebular morphologies. The close binary fraction imposes that at least 10-20% of PNe have been heavily shaped by a close companion, however no clear morphological properties have been identified amongst the very few PNe with close binary CSPN. Nearly 30% of a carefully selected sample of 30 post-CE nebulae are found to have canonical bipolar morphologies. A very plausible bipolar fraction of at least 60% may be reached once the inclination and other effects are considered. This is the strongest indication yet that the morphologies of post-CE nebulae largely satisfy theoretical expectations of a high density contrast established during the CE phase. Low-ionisation structures (LIS) are common amongst post-CE nebulae suggesting they have a binary origin. LIS seem confined to either the orbital plane as radially distributed knots or filaments, or to the polar regions as mostly low surface brightness jets triggered by a dynamo effect. A binary origin may also be responsible for LIS around emission-line nuclei whereby one or more CE phases created the identifiable morphology and dual-dust chemistry. A likely binary formation scenario for LIS includes the distribution of neutral clumps of dust and H2 during the CE phase into the orbital plane that are then photo-ionised by winds during the PN phase. If the binary scenario holds then Nitrogen abundances for PNe with LIS would be rendered meaningless since the [NII] emission observed is not a result of enriched stellar material, but rather reflects shocked emission generated with

  6. Masses and Scaling Relations for Nuclear Star Clusters, and their Coexistence with Central Black Holes

    CERN Document Server

    Georgiev, Iskren Y; Leigh, Natan; Lützgendorf, Nora; Neumayer, Nadine

    2016-01-01

    Galactic nuclei typically host either a Nuclear Star Cluster (NSC, prevalent in galaxies with masses $\\lesssim 10^{10}M_\\odot$) or a Massive Black Hole (MBH, common in galaxies with masses $\\gtrsim 10^{12}M_\\odot$). In the intermediate mass range, some nuclei host both a NSC and a MBH. In this paper, we explore scaling relations between NSC mass (${\\cal M}_{\\rm NSC}$) and host galaxy total stellar mass (${\\cal M}_{\\star,\\rm gal}$) using a large sample of NSCs in late- and early-type galaxies, including a number of NSCs harboring a MBH. Such scaling relations reflect the underlying physical mechanisms driving the formation and (co)evolution of these central massive objects. We find $\\sim\\!1.5\\sigma$ significant differences between NSCs in late- and early-type galaxies in the slopes and offsets of the relations $r_{\\rm eff,NSC}$--${\\cal M}_{\\rm NSC}$, $r_{\\rm eff, NSC}$--${\\cal M}_{\\star,\\rm gal}$ and ${\\cal M}_{\\rm NSC}$--${\\cal M}_{\\star,\\rm gal}$, in the sense that $i)$ NSCs in late-types are more compact at...

  7. QUENCHING OF STAR FORMATION IN SLOAN DIGITAL SKY SURVEY GROUPS: CENTRALS, SATELLITES, AND GALACTIC CONFORMITY

    International Nuclear Information System (INIS)

    We re-examine the fraction of low-redshift Sloan Digital Sky Survey satellites and centrals in which star formation has been quenched, using the environment quenching efficiency formalism that separates out the dependence of stellar mass. We show that the centrals of the groups containing the satellites are responding to the environment in the same way as their satellites (at least for stellar masses above 1010.3 M ☉), and that the well-known differences between satellites and the general set of centrals arise because the latter are overwhelmingly dominated by isolated galaxies. The widespread concept of ''satellite quenching'' as the cause of environmental effects in the galaxy population can therefore be generalized to ''group quenching''. We then explore the dependence of the quenching efficiency of satellites on overdensity, group-centric distance, halo mass, the stellar mass of the satellite, and the stellar mass and specific star formation rate (sSFR) of its central, trying to isolate the effect of these often interdependent variables. We emphasize the importance of the central sSFR in the quenching efficiency of the associated satellites, and develop the meaning of this ''galactic conformity'' effect in a probabilistic description of the quenching of galaxies. We show that conformity is strong, and that it varies strongly across parameter space. Several arguments then suggest that environmental quenching and mass quenching may be different manifestations of the same underlying process. The marked difference in the apparent mass dependencies of environment quenching and mass quenching which produces distinctive signatures in the mass functions of centrals and satellites will arise naturally, since, for satellites at least, the distributions of the environmental variables that we investigate in this work are essentially independent of the stellar mass of the satellite

  8. RADIATION PRESSURE FROM MASSIVE STAR CLUSTERS AS A LAUNCHING MECHANISM FOR SUPER-GALACTIC WINDS

    International Nuclear Information System (INIS)

    Galactic outflows of cool (∼104 K) gas are ubiquitous in local starburst galaxies and in most high-redshift galaxies. Hot gas from supernovae has long been suspected as the primary driver, but this mechanism suffers from its tendency to destroy the cool gas. We propose a modification of the supernova scenario that overcomes this difficulty. Star formation is observed to take place in clusters. We show that, for L* galaxies, the radiation pressure from clusters with Mcl ∼> 106 Msun is able to expel the surrounding gas at velocities in excess of the circular velocity vc of the disk galaxy. This cool gas travels above the galactic disk before supernovae erupt in the driving cluster. Once above the disk, the cool outflowing gas is exposed to radiation and hot gas outflows from the galactic disk, which in combination drive it to distances of ∼50 kpc. Because the radiatively driven clouds grow in size as they travel, and because the hot gas is more dilute at large distance, the clouds are less subject to destruction. Therefore, unlike wind-driven clouds, radiatively driven clouds can give rise to the metal absorbers seen in quasar spectra. We identify these cluster-driven winds with large-scale galactic outflows. The maximum cluster mass in a galaxy is an increasing function of the galaxy's gas surface density, so only starburst galaxies are able to drive cold outflows. We find the critical star formation rate for launching large-scale cool outflows to be Σ-dot*crit approx. 0.05 Msun yr-1 kpc-2, in good agreement with observations.

  9. The soft and hard X-rays thermal emission from star cluster winds with a supernova explosion

    CERN Document Server

    Castellanos-Ramirez, A; Esquivel, A; Toledo-Roy, J C; Olivares, J; Velazquez, P F

    2015-01-01

    Massive young star clusters contain dozens or hundreds of massive stars that inject mechanical energy in the form of winds and supernova explosions, producing an outflow which expands into their surrounding medium, shocking it and forming structures called superbubbles. The regions of shocked material can have temperatures in excess of 10$^6$ K, and emit mainly in thermal X-rays (soft and hard). This X-ray emission is strongly affected by the action of thermal conduction, as well as by the metallicity of the material injected by the massive stars. We present three-dimensional numerical simulations exploring these two effects, metallicity of the stellar winds and supernova explosions, as well as thermal conduction.

  10. Mass Transfer by Stellar Wind

    CERN Document Server

    Boffin, Henri M J

    2014-01-01

    I review the process of mass transfer in a binary system through a stellar wind, with an emphasis on systems containing a red giant. I show how wind accretion in a binary system is different from the usually assumed Bondi-Hoyle approximation, first as far as the flow's structure is concerned, but most importantly, also for the mass accretion and specific angular momentum loss. This has important implications on the evolution of the orbital parameters. I also discuss the impact of wind accretion, on the chemical pollution and change in spin of the accreting star. The last section deals with observations and covers systems that most likely went through wind mass transfer: barium and related stars, symbiotic stars and central stars of planetary nebulae (CSPN). The most recent observations of cool CSPN progenitors of barium stars, as well as of carbon-rich post-common envelope systems, are providing unique constraints on the mass transfer processes.

  11. Implication of the Steady State Equilibrium Condition for Electron-Positron Gas in the Neutrino-driven Wind from Proto-Neutron Star

    CERN Document Server

    Liu, Men-Quan

    2010-01-01

    Based on the steady state equilibrium condition for neutron-proton-electron-positron gas in the neutrino-driven wind from protoneutron star, we estimate the initial electron fraction in the wind in a simple and effective way. We find that the condition in the wind might be propriate for the r-process nucleosynthesis.

  12. Modeling the cometary structure of the planetary nebula HFG1 based on the evolution of its binary central star V664 Cas

    CERN Document Server

    Chiotellis, A; Nanouris, N; Meaburn, J; Dimitriadis, G

    2015-01-01

    HFG1 is the first well observed planetary nebula (PN) which reveals a cometary-like structure. Its main morphological features consist of a bow shaped shell, which surrounds the central star, accompanied by a long collimated tail. In this study we perform two-dimensional hydrodynamic simulations modeling the formation of HFG1 from the interaction of the local ambient medium with the mass outflows of its Asymptotic Giant Branch (AGB) progenitor star. We attribute the cometary appearance of HFG1 to the systemic motion of the PN with respect to the local ambient medium. Due to its vital importance, we re-estimate the distance of HFG1 by modeling the spectral energy distribution of its central star, V664 Cas, and we find a distance of $ 490 \\pm 50$ pc. Our simulations show that none of our models with time invariant stellar wind and ambient medium properties are able to reproduce simultaneously the extended bow shock and the collimated tail observed in HFG1. Given this, we increase the complexity of our modeling ...

  13. Central Exclusive Production in Proton-Proton Collisions with the STAR Experiment at RHIC

    Science.gov (United States)

    Guryn, Włodek

    2016-07-01

    We shall describe the physics program with tagged forward protons, focusing on Central Exclusive Production in polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC), with the STAR detector at √s = 200 GeV. Preliminary results in CEP of two oppositely charged pions and kaons produced in the processes pp → ppπ+π- and pp → ppK+K- shall be presented. Those Double Pomeron Exchange (DPE) processes, allow the final states to be dominated by gluonic exchanges. Silicon strip detectors placed in Roman Pots were used for measuring forward protons. The preliminary results are based on the measurement of the recoil system of charged particles in the STAR experiment's Time Projection Chamber (TPC). Ionization energy loss, dE/dx, of charged particles was used for particle identification (PID).

  14. ALMA detection of the rotating molecular disk wind drom the young star HD 163296

    CERN Document Server

    Klaassen, P D; Mathews, G S; De Gregorio-Monsalvo, J C Mottram I; van Dishoeck, E F; Takahashi, S; Akiyama, E; Chapillon, E; Espada, D; Hales, A; Hogerheijde, M R; Rawlings, M; Schmalzl, M; Testi, L

    2013-01-01

    Disk winds have been postulated as a mechanism for angular momentum release in protostellar systems for decades. HD 163296 is a Herbig Ae star surrounded by a disk and has been shown to host a series of HH knots (HH 409) with bow shocks associated with the farthest knots. Here we present ALMA Science Verification data of CO J=2-1 and J=3-2 emission which are spatially coincident with the blue shifted jet of HH knots, and offset from the disk by -18.6 km/s. The emission has a double corkscrew morphology and extends more than 10" from the disk with embedded emission clumps coincident with jet knots. We interpret this double corkscrew as emission from material in a molecular disk wind, and that the compact emission near the jet knots is being heated by the jet which is moving at much higher velocities. We show that the J=3-2 emission is likely heavily filtered by the interferometer, but the J=2-1 emission suffers less due to the larger beam and measurable angular scales. Excitation analysis suggests temperatures...

  15. Molecular Gas and Star Formation Properties in the Central and Bar Regions of NGC 6946

    CERN Document Server

    Pan, Hsi-An; Koda, Jin; Hirota, Akihiko; Sorai, Kazuo; Kaneko, Hiroyuki

    2015-01-01

    In this work, we investigate the molecular gas and star formation properties in the barred spiral galaxy NGC 6946 using multiple molecular lines and star formation tracers. High-resolution image (100 pc) of $^{13}$CO (1-0) is created by single dish NRO45 and interferometer CARMA for the inner 2 kpc disk, which includes the central region (nuclear ring and bar) and the offset ridges of the primary bar. Single dish HCN (1-0) observations were also made to constrain the amount of dense gas. Physical properties of molecular gas are inferred by (1) the Large Velocity Gradient (LVG) calculations using our observations and archival $^{12}$CO (1-0), $^{12}$CO(2-1) data, (2) dense gas fraction suggested by HCN to $^{12}$CO (1-0) luminosity ratio, and (3) infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. Dense gas fraction of the central region is similar with that of LIRGs/ULIRGs, while the offset ridges are close to the global average of...

  16. The warm circumstellar envelope and wind of the G9 IIb star HR 6902

    Science.gov (United States)

    Kirsch, T.; Baade, R.; Reimers, D.

    2001-12-01

    IUE observations of the eclipsing binary system HR 6902 obtained at various epochs spread over four years indicate the presence of warm circumstellar material enveloping the G9 IIb primary. The spectra show Si Iv and C Iv absorption up to a distance of 3.3 giant radii (Rg). Line ratio diagnostics yields an electron temperature of ~ 78 000 K which appears to be constant over the observed height range. Applying a least square fit absorption line analysis we derive column densities as a function of height. We find that the inner envelope (improved agreement with observations over the whole height regime including the emission line region is obtained with an outflow model. We demonstrate that the common β power-law as well as a P ∝ ρ wind yield appropriate fit models. Adopting a continuous mass outflow we obtain a mass-loss rate of M⊙=0.8 - 3.4 × 10-11 Msolar yr-1 depending on the particular wind model. The emission lines observed during total eclipse are attributed mostly to resonance scattering of B star photons in the extended envelope of the giant. By means of a multi-dimensional line formation study we show that the global envelope properties are consistent with the wind models derived from the absorption line analysis. We argue that future high resolution UV spectroscopy will resolve the large-scale velocity structure of the circumstellar shell. As an illustration we present theoretical Si Iv and C Iv emission profiles showing model-dependent line shifts and asymmetries.

  17. Fluctuations Mitigation of Variable Speed Wind Turbine through Optimized Centralized Controller

    Directory of Open Access Journals (Sweden)

    S. Masoud Barakati

    2012-08-01

    Full Text Available A wind energy conversion system (WECS including a variable wind turbine in grid-connected mode is considered to control. In this paper, each component of WECS model is systematically presented and then the integrated overall model is validated.Regarding to nonlinear nature of WECS and the complex system structure as multiple-input- multiple-output (MIMO,control procedure counters the problem which strategy to handle.To simplify the control policy, a centralized controller which is compatible with systematic modelling introduced, is employed. In other hand to augment the centralized controller performance, an optimization based on genetic algorithm (GA is accomplished. Simulation results demonstate the proper efficiency in fluctuations mitigation.

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

    Science.gov (United States)

    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.

  19. Speckle observations of the central binary star in the Red Rectangle

    International Nuclear Information System (INIS)

    The binary nature of the central star in the Red Rectangle HD 44179 has been confirmed using the Imperial College speckle interferometer on the AAT. The position angle of 146 +- 30 and separation 0.29 +- 0.02 arcsec are given for 1981 November 11. An orbital period of 60 +- 5 yr and a total mass of the two components of the binary approx.= to 31 sun masses are both predicted. No correlation between the inclination of the orbit and the striking geometry of the nebulosity is found. (author)

  20. Iron Abundance in Hydrogen-Rich Central Stars of Planetary Nebulae

    CERN Document Server

    Hoffmann, A I D; Kruk, J W; Rauch, T; Traulsen, I; Werner, K

    2004-01-01

    We report on an on-going analysis of high-resolution UV spectra of hot hydrogen-rich central stars of planetary nebulae (CSPN), obtained with the Hubble Space Telescope and FUSE. Since UV spectra of many CSPN are dominated by Fe and Ni lines, we intend to use them as temperature indicators to check the CSPN temperature scale we have derived earlier from CNO ionization balances. Furthermore, the observed line strengths of heavy metals show large variations between different objects suggesting a possible spread in abundances. We will determine abundances of iron group elements by quantitative spectral analyses with non-LTE model atmospheres.

  1. NGC 6778: Strengthening the link between extreme abundance discrepancy factors and central star binarity in planetary nebulae

    CERN Document Server

    Jones, David; García-Rojas, Jorge; Corradi, Romano L M; Boffin, Henri M J

    2015-01-01

    We present new optical spectra of the nearby, bright, planetary nebula NGC 6778. The nebula has been known to emit strong recombination lines for more than 40 years but this is the first detailed study of its abundances. Heavy element abundances derived from recombination lines are found to exceed those from collisionally excited lines by a factor of ~20 in an integrated spectrum of the nebula, which is among the largest known abundance discrepancy factors. Spatial analysis of the spectra shows that the abundance discrepancy factor is strongly, centrally peaked, reaching ~40 close to the central star. The central star of NGC 6778 is known to be a short period binary, further strengthening the link between high nebular abundance discrepancy factors and central star binarity.

  2. Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks

    CERN Document Server

    Carneiro, Luiz P; Sundqvist, J O; Hoffmann, T L

    2016-01-01

    X-rays/EUV 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 the production of highly ionized species. To allow for these processes in the context of spectral analysis, we have implemented such emission into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. The shock structure and corresponding emission is calculated as a function of user-supplied parameters. We account for a temperature and density stratification inside the post-shock 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 into the NLTE network. We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from s...

  3. The Dust Properties of Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: In Search of the Missing Link

    Science.gov (United States)

    Clayton, Geoffrey C.; De Marco, O.; Whitney, B. A.; Babler, B.; Gallagher, J. S.; Nordhaus, J.; Speck, A. K.; Wolff, M. J.; Freeman, W. R.; Camp, K. A.; Lawson, W. A.; Roman-Duval, J.; Misselt, K. A.; Meade, M.; Sonneborn, G.; Matsuura, M.; Meixner, M.

    2012-01-01

    We present new Spitzer IIRS spectra of two hot R Coronae Borealis (RCB) stars, one in the Galaxy,V348 Sgr, and one lying in the Large Magellanic Cloud, HV 2671. These two objects constitute a link between the RCB stars and the [WCL] class of central stars of planetary nebula (CSPNe) that has little or no hydrogen in their atmospheres such as CPD -560 8032. HV 2671 and V348 Sgr are members of a rare subclass that has significantly higher effective temperatures than most RCB stars, but sharing the traits of hydrogen deficiency and dust formation that define the cooler RCB stars. The [WC] CSPNe star, CPD -560 8032, displays evidence for dual-dust chemistry showing both PAHs and crystalline silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but shows no sign of having crystalline silicates. The spectrum of V348 Sgr is very different from those of CPD -56deg 8032 and HV 2671. The PAH emission seen strongly in the other two stars is only weakly present. Instead, the spectrum is dominated by a broad emission centered at about 8.5 microns. This feature is not identified with either PAHs or silicates. Several other novae and post-asymptotic giant branch stars show similar features in their IR spectra. The mid-IR spectrum of CPD -56deg 8032 shows emission features associated with C60 . The other two stars do not show evidence for C60. The nature of the dust around these stars does not help us in establishing further links that may indicate a common origin.

  4. A dozen colliding wind X-ray binaries in the star cluster R136 in the 30Doradus region

    OpenAIRE

    Portegies Zwart, S.F.; Pooley, D.; Lewin, W.H.G.

    2001-01-01

    We analyzed archival Chandra X-ray observations of the central portion of the 30 Doradus region in the Large Magellanic Cloud. The image contains 20 X-ray point sources with luminosities between $5 \\times 10^{32}$ and $2 \\times 10^{35}$ erg s$^{-1}$ (0.2 -- 3.5 keV). A dozen sources have bright WN Wolf-Rayet or spectral type O stars as optical counterparts. Nine of these are within $\\sim 3.4$pc of R136, the central star cluster of NGC2070. We derive an empirical relation between the X-ray lum...

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

    Science.gov (United States)

    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.

  6. The evolved B[e] star HD 87643 observations and a radiation driven disk-wind model for B[e] stars

    CERN Document Server

    Oudmaijer, R D; Drew, J E; De Winter, D; Oudmaijer, Rene; Proga, Daniel; Drew, Janet; Winter, Dolf de

    1998-01-01

    New high resolution spectroscopic and medium resolution spectropolarimetric data, complemented with optical broad and narrow band imaging, of the B[e] star HD 87643 are presented. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of B[e] stars; a fast wind with an expansion velocity in excess of 1000 km/s is measured in the hydrogen and helium lines, while a slower component is traced by lower excitation lines and forbidden lines. Clues to the geometry of the rapidly expanding circumstellar shell are provided by the startling polarization changes across Halpha. Comparison with published schematic calculations indicates that the polarizing material is located in a slowly rotating, expanding disk structure. A hydrodynamical model is then presented whose results are consistent with the original two-wind concept for B[e] stars and exhibits kinematic properties that may well explain the observed spectral features in HD 87643. The model calculations use as inp...

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

    DEFF Research Database (Denmark)

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

    operationally. It is, however, entirely up to the NWP input to describe the timing of fluctuations correctly. Wind power is nonlinearly transformed wind speed, and the two are monotonically dependent up till wind speeds of ∼25m/s, which is the typical wind farm cut-out. Thus, an improvement in the correlation...

  8. EMCCD photometry reveals two new variable stars in the crowded central region of the globular cluster NGC 6981

    CERN Document Server

    Skottfelt, Jesper; Jaimes, R Figuera; Jørgensen, U G; Kains, N; Harpsoe, K B W; Liebig, C; Penny, M T; Alsubai, K A; Andersen, J M; Bozza, V; Browne, P; Novati, S Calchi; Damerdji, Y; Diehl, C; Dominik, M; Elyiv, A; Giannini, E; Hessman, F; Hinse, T C; Hundertmark, M; Juncher, D; Kerins, E; Korhonen, H; Mancini, L; Martin, R; Rabus, M; Rahvar, S; Southworth, G Scarpetta J; Snodgrass, C; Street, R A; Surdej, J; Tregloan-Reed, J; Vilela, C; Williams, A

    2013-01-01

    Two previously unknown variable stars in the crowded central region of the globular cluster NGC 6981 are presented. The observations were made using the Electron Multiplying CCD (EMCCD) camera at the Danish 1.54m Telescope at La Silla, Chile.The two variables were not previously detected by conventional CCD imaging because of their proximity to a bright star. This discovery demonstrates that EMCCDs are a powerful tool for performing high-precision time-series photometry in crowded fields and near bright stars, especially when combined with difference image analysis (DIA).

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

    International Nuclear Information System (INIS)

    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

  10. The magnetic field and confined wind of the O star $\\theta^1$~Orionis~C

    CERN Document Server

    Wade, G A; Donati, J F; Landstreet, J D; Petit, P; Strasser, S

    2006-01-01

    In this paper we confirm the presence of a globally-ordered, kG-strength magnetic field in the photosphere of the young O star $\\theta^1$~Orionis~C, and examine the properties of its optical line profile variations. A new series of high-resolution MuSiCoS Stokes $V$ and $I$ spectra has been acquired which samples approximately uniformly the rotational cycle of $\\theta^1$~Orionis~C. Using the Least-Squares Deconvolution (LSD) multiline technique, we have succeeded in detecting variable Stokes $V$ Zeeman signatures associated with the LSD mean line profile. These signatures have been modeled to determine the magnetic field geometry. We have furthermore examined the profi le variations of lines formed in both the wind and photosphere using dynamic spectra. Based on spectrum synthesis fitting of the LSD profiles, we determine that the polar strength of the magnetic dipole component is $1150 \\la B_{\\rm d}\\la 1800$~G and that the magnetic obliquity is $27\\degr \\la \\beta \\la 68\\degr$, assuming $i=45\\pm 20\\degr$. The...

  11. Problems for the WELS classification of planetary nebulae central stars: Self-consistent nebular modelling of four candidates

    CERN Document Server

    Basurah, Hassan M; Dopita, Michael A; Alsulami, R; Amer, Morsi A; Alruhaili, A

    2016-01-01

    We present integral field unit (IFU) spectroscopy and self-consistent photoionisation modelling for a sample of four southern Galactic planetary nebulae (PNe) with supposed weak emission-line (WEL) central stars. The Wide Field Spectrograph (WiFeS) on the ANU 2.3 m telescope has been used to provide IFU spectroscopy for NGC 3211, NGC 5979, My 60, and M 4-2 covering the spectral range of 3400-7000{\\AA}. All objects are high excitation non-Type I PNe, with strong He II emission, strong [Ne V] emission, and weak low-excitation lines. They all appear to be predominantly optically-thin nebulae excited by central stars with $T_{\\rm eff} > 10^5$K. Three PNe of the sample have central stars which have been previously classified as weak emission-line stars (WELS), and the fourth also shows the characteristic recombination lines of a WELS. However, the spatially-resolved spectroscopy shows that rather than arising in the central star, the C IV and N III recombination line emission is distributed in the nebula, and in s...

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

    CERN Document Server

    Javadi, Atefeh; Mirtorabi, Mohammad Taghi

    2010-01-01

    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 dataset was obtained in the K-band with the UIST instrument for the central 4'x 4' (1 square kpc) - 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 va...

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

    CERN Document Server

    Bosch-Ramon, V; Perucho, M

    2014-01-01

    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 origin. The characterization of the evolution of the two-wind interaction region is necessary to understand the non-thermal emission from radio to gamma rays. For the first time, we simulate in 3D 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. We carry out, with the code PLUTO, relativistic hydrodynamical simulations in 2 and 3D of the interaction of a slow dense wind and a mildly relativistic wind along one full orbit, up to ~100 times the binary size. The 2-dimensional simulations are carried out with equal and larger grid resolution and size than in 3D. The simulations in 3D confirm previous results in 2D, showing a strong shock induced by Coriolis forces that terminates the pulsar wind in ...

  14. An Ultra-fast X-Ray Disk Wind in the Neutron Star Binary GX 340+0

    Science.gov (United States)

    Miller, J. M.; Raymond, J.; Cackett, E.; Grinberg, V.; Nowak, M.

    2016-05-01

    We present a spectral analysis of a brief Chandra/HETG observation of the neutron star low-mass X-ray binary GX 340+0. The high-resolution spectrum reveals evidence of ionized absorption in the Fe K band. The strongest feature, an absorption line at approximately 6.9 keV, is required at the 5σ level of confidence via an F-test. Photoionization modeling with XSTAR grids suggests that the line is the most prominent part of a disk wind with an apparent outflow speed of v = 0.04c. This interpretation is preferred at the 4σ level over a scenario in which the line is H-like Fe xxvi at a modest redshift. The wind may achieve this speed owing to its relatively low ionization, enabling driving by radiation pressure on lines; in this sense, the wind in GX 340+0 may be the stellar-mass equivalent of the flows in broad absorption line quasars. If the gas has a unity volume filling factor, the mass ouflow rate in the wind is over 10‑5 M ⊙ yr‑1, and the kinetic power is nearly 1039 erg s‑1 (or, 5–6 times the radiative Eddington limit for a neutron star). However, geometrical considerations—including a small volume filling factor and low covering factor—likely greatly reduce these values.

  15. The Interaction of Venus-like, M-dwarf Planets with the Stellar Wind of Their Host Star

    CERN Document Server

    Cohen, O; Drake, J J; Glocer, A; Garraffo, C; Bell, J M; Gombosi, T I

    2015-01-01

    We study the interaction between the atmospheres of Venus-like, non-magnetized exoplanets orbiting an M-dwarf star, and the stellar wind using a multi-species Magnetohydrodynaic (MHD) model. We focus our investigation on the effect of enhanced stellar wind and enhanced EUV flux as the planetary distance from the star decreases. Our simulations reveal different topologies of the planetary space environment for sub- and super-Alfvenic stellar wind conditions, which could lead to dynamic energy deposition in to the atmosphere during the transition along the planetary orbit. We find that the stellar wind penetration for non-magnetized planets is very deep, up to a few hundreds of kilometers. We estimate a lower limit for the atmospheric mass-loss rate and find that it is insignificant over the lifetime of the planet. However, we predict that when accounting for atmospheric ion acceleration, a significant amount of the planetary atmosphere could be eroded over the course of a billion years.

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

    International Nuclear Information System (INIS)

    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

  17. The Central Star Candidate of the Planetary Nebula Sh2-71: Photometric and Spectroscopic Variability

    CERN Document Server

    Močnik, Teo; Pollacco, Don; Street, Rachel A

    2015-01-01

    We present the analysis of several newly obtained and archived photometric and spectroscopic datasets 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 lightcurve with a period of 68 days and also indicated periodic sharp brightness dips, possibly eclipses, with a period of 17.2 days. In addition, the comparison between U and V lightcurves revealed that the 68-day brightness variations are accompanied by a variable reddening effect of $\\Delta E(U-V)=0.38$. Spectroscopic datasets demonstrated pronounced variations in spectral profiles of Balmer, helium and singly ionised 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-day brightness variations. The mean radial velocity of the observed star was measured to be $\\sim$26 km/s with an ...

  18. Problems for the WELS classification of planetary nebula central stars: self-consistent nebular modelling of four candidates

    Science.gov (United States)

    Basurah, Hassan M.; Ali, Alaa; Dopita, Michael A.; Alsulami, R.; Amer, Morsi A.; Alruhaili, A.

    2016-05-01

    We present integral field unit (IFU) spectroscopy and self-consistent photoionization modelling for a sample of four southern Galactic planetary nebulae (PNe) with supposed weak emission-line central stars. The Wide Field Spectrograph on the ANU 2.3 m telescope has been used to provide IFU spectroscopy for NGC 3211, NGC 5979, My 60, and M 4-2 covering the spectral range of 3400-7000 Å. All objects are high-excitation non-Type I PNe, with strong He II emission, strong [Ne V] emission, and weak low-excitation lines. They all appear to be predominantly optically thin nebulae excited by central stars with Teff > 105 K. Three PNe of the sample have central stars which have been previously classified as weak emission-line stars (WELS), and the fourth also shows the characteristic recombination lines of a WELS. However, the spatially resolved spectroscopy shows that rather than arising in the central star, the C IV and N III recombination line emission is distributed in the nebula, and in some cases concentrated in discrete nebular knots. This may suggest that the WELS classification is spurious, and that, rather, these lines arise from (possibly chemically enriched) pockets of nebular gas. Indeed, from careful background subtraction we were able to identify three of the sample as being hydrogen rich O(H)-Type. We have constructed fully self-consistent photoionization models for each object. This allows us to independently determine the chemical abundances in the nebulae, to provide new model-dependent distance estimates, and to place the central stars on the Hertzsprung-Russell diagram. All four PNe have similar initial mass (1.5 < M/M⊙ < 2.0) and are at a similar evolutionary stage.

  19. SPITZER SEARCH FOR DUST DISKS AROUND CENTRAL STARS OF PLANETARY NEBULAE

    International Nuclear Information System (INIS)

    Two types of dust disks have been discovered around white dwarfs (WDs): small dust disks within the Roche limits of their WDs and large dust disks around hot WDs extending to radial distances of 10-102 AU. The majority of the latter WDs are central stars of planetary nebulae (CSPNs). We have therefore used archival Spitzer Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) observations of PNs to search for CSPNs with IR excesses and to make a comparative investigation of dust disks around stars at different evolutionary stages. We have examined available images of 72 resolved PNs in the Spitzer archive and found 56 of them large enough for the CSPN to be resolved from the PN. Among these, only 42 CSPNs are visible in IRAC and/or MIPS images and selected for photometric measurements. From the spectral energy distributions (SEDs) of these CSPNs, we find 19 cases with clear IR excess. Of these, seven are [WC]-type stars, two have apparent visual companions that account for the observed excess emission, two are symbiotic CSPNs, and in eight cases the IR excess originates from an extended emitter, likely a dust disk. For some of these CSPNs, we have acquired follow-up Spitzer MIPS images, Infrared Spectrograph spectra, and Gemini NIRI and Michelle spectroscopic observations. The SEDs and spectra show a great diversity in the emission characteristics of the IR excesses, which may imply different mechanisms responsible for the excess emission. For CSPNs whose IR excesses originate from dust continuum, the most likely dust production mechanisms are (1) breakup of bodies in planetesimal belts through collisions and (2) formation of circumstellar dust disks through binary interactions. A better understanding of post-asymptotic giant branch binary evolution as well as debris disk evolution along with its parent star is needed to distinguish between these different origins. Future observations to better establish the physical parameters of the

  20. Interplay of tidal evolution and stellar wind braking in the rotation of stars hosting massive close-in planets

    CERN Document Server

    Ferraz-Mello, S; Folonier, H; Csizmadia, Sz; Nascimento, J -D do; Pätzold, M

    2015-01-01

    This paper deals with the application of the creep tide theory (Ferraz-Mello, Cel. Mech. Dyn. Astron. vol. 116, 109, 2013) to the study of the rotation of stars hosting massive close-in planets. The stars have nearly the same tidal relaxation factors as gaseous planets and the evolution of their rotation is similar to that of close-in hot Jupiters: they tidally evolve towards a stationary solution. However, stellar rotation may also be affected by stellar wind braking. Thus, while the rotation of a quiet host star evolves towards a stationary attractor with a frequency ($1+6e^2$) times the orbital mean-motion of the companion, the continuous loss of angular momentum in an active star displaces the stationary solution towards slower values: Active host stars with big close-in companions tend to have rotational periods larger than the orbital periods of their companions. The study of some hypothetical examples shows that because of tidal evolution, the rules of gyrochronology cannot be used to estimate the age ...

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

    Science.gov (United States)

    Jarquin-Laguna, A.

    2014-06-01

    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.

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

    International Nuclear Information System (INIS)

    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

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

    DEFF Research Database (Denmark)

    Rosgaard, Martin Haubjerg; Hahmann, Andrea N.; Nielsen, Torben Skov; Giebel, Gregor; Sørensen, Poul Ejnar; Madsen, Henrik

    For any energy system relying on wind power, accurate forecasts of wind fluctuations are essential for efficient integration into the power grid. Increased forecast precision allows end-users to plan day-ahead operation with reduced risk of penalties which in turn supports the feasibility of wind...

  4. On the central abundances of Active Galactic Nuclei and Star-forming Galaxies

    CERN Document Server

    Dors, O L; Hagele, G F; Rodrigues, I; Grebel, E K; Pilyugin, L S; Freitas-Lemes, P; Krabbe, A C

    2015-01-01

    We examine the relation between oxygen abundances in the narrow-line regions (NLRs) of active galactic nuclei (AGNs) estimated from the optical emission lines through the strong-line method (the theoretical calibration of Storchi-Bergmann et al.(1998)), via the direct Te-method, and the central intersect abundances in the host galaxies determined from the radial abundance gradients. We found that the Te-method underestimates the oxygen abundances by up to ~2 dex (with average value of ~0.8 dex) compared to the abundances derived through the strong-line method. This confirms the existence of the so-called "temperature problem" in AGNs. We also found that the abundances in the centres of galaxies obtained from their spectra trough the strong-line method are close to or slightly lower than the central intersect abundances estimated from the radial abundance gradient both in AGNs and Star-forming galaxies. The oxygen abundance of the NLR is usually lower than the maximum attainable abundance in galaxies (~2 times...

  5. Consequences of a possible jet-star interaction in the inner central parsec of Centaurus A

    Science.gov (United States)

    Mueller, C.; Kadler, M.; Mannheim, K.; Perucho, M.; Ojha, R.; Ros, E.; Schulz, R.; Wilms, J.

    The jet-counterjet system of the closest radio-loud active galaxy Centaurus A (Cen A) can be studied with Very Long Baseline Interferometry (VLBI) on unprecedented small linear scales of ~0.018 pc. These high-resolution observations provide essential information on jet emission and propagation within the inner parsec of an AGN jet. We present the results of a kinematic study performed within the framework of the Southern-hemisphere AGN monitoring program TANAMI. Over 3.5 years, the evolution of the central-parsec jet structure of Cen A was monitored with VLBI. These observations reveal complex jet dynamics which are well explained by a spine-sheath structure supported by the downstream acceleration occurring where the jet becomes optically thin. Both moving and stationary jet features are tracked. A persistent local minimum in surface brightness suggests the presence of an obstacle interrupting the jet flow, which can be explained by the interaction of the jet with a star at a distance of ~0.4 pc from the central black hole. We briefly discuss possible implications of such an interaction regarding the expected neutrino and high-energy emission and the effect on a putative planet.

  6. The discovery and characterisation of binary central stars in planetary nebulae

    CERN Document Server

    Jones, David

    2016-01-01

    Close binary central stars of planetary nebulae are key in constraining the poorly-understood common-envelope phase of evolution, which in turn is critical in understanding the formation of a wide-range of astrophysical phenomena (including cataclysmic variables, low-mass X-ray binaries and supernovae type Ia). Here, I present the results of our on-going, targeted search for close-binaries in planetary nebulae which has led to the discovery of more than 10 new central binaries in just the last few years (almost the same as the total discovered during the 1980s and 1990s together). This success has been rooted in the targeted selection of objects for study, based on morphological features deemed typical of binarity, as well as novel observing strategies (including the employment of narrow-band filters for photometry to minimise nebular contamination), both of which are discussed. These new discoveries, coupled with the painstaking characterisation of both newly discovered systems and those from the literature,...

  7. The UK Infrared Telescope M33 monitoring project. III. Feedback from dusty stellar winds in the central square kiloparsec

    CERN Document Server

    Javadi, Atefeh; Khosroshahi, Habib; Mirtorabi, Mohammad Taghi

    2013-01-01

    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. In this third paper of the series, we measure the dust production and rates of mass loss by the pulsating Asymptotic Giant Branch (AGB) stars and red supergiants. To this aim, we combined our time-averaged near-IR photometry with the multi-epoch mid-IR photometry obtained with the Spitzer Space Telescope. The mass-loss rates are seen to increase with increasing strength of pulsation and with increasing bolometric luminosity. Low-mass stars lose most of their mass through stellar winds, but even super-AGB stars and red supergiants lose $\\sim40$% of their mass via a dusty stellar wind. More than three-quarters of the dust return is oxy...

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

    Science.gov (United States)

    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

  9. Stellar and Wind Properties of LMC WC4 stars - A metallicity dependence for Wolf-Rayet mass-loss rates

    CERN Document Server

    Crowther, P A; Hillier, D J; Abbott, J B; Fullerton, A W; Crowther, Paul A.; Dessart, Luc; Abbott, Jay B.; Fullerton, Alex W.

    2002-01-01

    We use ultraviolet space-based (FUSE, HST) and optical/IR ground-based (2.3m MSSSO, NTT) spectroscopy to determine the physical parameters of six WC4-type Wolf-Rayet stars in the Large Magellanic Cloud. Stellar parameters are revised significantly relative to Grafener et al. (1998) based on improved observations and more sophisticated model atmosphere codes, which account for line blanketing and clumping. We find that stellar luminosities are revised upwards by up to 0.4 dex, with surface abundances spanning a lower range of 0.1stars at known distance, and analysed in a similar manner, LMC WC4 stars possess systematically higher stellar luminosities, 0.2dex lower wind densities, yet a similar range of surface chemistries. We illustrate how the classification CIII 5696 line is extremely sensitive to wind density, such that this is the principal difference between the subtype distribution of LMC and Ga...

  10. Exploring wind-driving dust species in cool luminous giants III. Wind models for M-type AGB stars: dynamic and photometric properties

    CERN Document Server

    Bladh, S; Aringer, B; Eriksson, K

    2015-01-01

    Stellar winds observed in asymptotic giant branch (AGB) stars are usually attributed to a combination of stellar pulsations and radiation pressure on dust. Shock waves triggered by pulsations propagate through the atmosphere, compressing the gas and lifting it to cooler regions, which create favourable conditions for grain growth. If sufficient radiative acceleration is exerted on the newly formed grains through absorption or scattering of stellar photons, an outflow can be triggered. Strong candidates for wind-driving dust species in M-type AGB stars are magnesium silicates (Mg$_2$SiO$_4$ and MgSiO$_3$). Such grains can form close to the stellar surface, they consist of abundant materials and, if they grow to sizes comparable to the wavelength of the stellar flux maximum, they experience strong acceleration by photon scattering. We use a frequency-dependent radiation-hydrodynamics code with a detailed description for the growth of Mg$_2$SiO$_4$ grains to calculate the first extensive set of time-dependent wi...

  11. Revealing the Asymmetry of the Wind of the Variable Wolf-Rayet Star WR1 (HD4004) Through Spectropolarization

    CERN Document Server

    St-Louis, Nicole

    2013-01-01

    In this paper, high quality spectropolarimetric observations of the Wolf-Rayet (WR) Star WR1 (HD4004) obtained with ESPaDOnS at CFHT are presented. All major emission lines present in the spectrum show depolarization in the relative Stokes parameters Q/I and U/I. From the behaviour 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 \\pm 0.028 % with an angle of \\theta=-26.2^o. 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 in the wind of Corotating Interaction Regions (CIRs) 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...

  12. Compact planetary nebulae in the Galactic disk: Analysis of the central stars

    Science.gov (United States)

    Moreno-Ibáñez, Manuel; Villaver, Eva; Shaw, Richard A.; Stanghellini, Letizia

    2016-09-01

    Context. We have obtained multi-wavelength observations of compact Galactic planetary nebulae (PNe) to probe post-asymptotic giant branch (AGB) evolution from the onset of nebular ejection. Here we analyze new observations from HST to derive the masses and evolutionary status of their central stars (CSs). Aims: Our objective here is to derive the masses of the CSs hosted by compact PNe in order to better understand the relationship between the CS properties and those of the surrounding nebulae. We also compare this sample with others we obtained using the same technique in different metallicity environments: the Large and Small Magellanic Clouds. Methods: This paper is based on HST/WFC3 images of 51 targets obtained in a snapshot survey (GO-11657). The high spatial resolution of HST allows us to resolve these compact PNe and distinguish the CS emission from that of their surrounding PNe. We derive CS bolometric luminosities and effective temperatures using the Zanstra technique, from a combination of HST photometry and ground-based spectroscopic data. The targets were imaged through the filters F200LP, F350LP, and F814W from which we derive Johnson V and I magnitudes. We infer CS masses by placing the stars on a temperature-luminosity diagram and compare their location with the best available, single star post-AGB evolutionary tracks. Results: We present new, unique photometric measurements of 50 CSs, and we derive effective temperatures and luminosities for most of them. Central star masses for 23 targets were derived with the evolutionary track technique; the remaining masses were indeterminate most likely because of underestimates of the stellar temperature, or because of substantial errors in the adopted statistical distances to these objects. We expect these problems will be largely overcome when the Gaia distance catalog becomes available. We find that objects with the higher ratios of Zanstra temperatures T(H i)/T( He ii ) tend to have lower-mass progenitors

  13. Techno-economic pre-feasibility study of wind and solar electricity generating systems for households in Central Finland

    OpenAIRE

    Alavi, Seyed Mehdi

    2014-01-01

    The objective of this work is to investigate the viability of a wind, PV or hybrid wind-PV system supplemented with battery storage for electricity production to meet the electricity consumption of a typical household apartment in Central Finland. The assessment criteria for the analysis were cost of energy and total net present cost of each system configuration. We selected the Hybrid Optimization Model for Electric Renewables (HOMER) software, RETScreen, and PVsyst in our analysis and final...

  14. Study of a new central compact object: The neutron star in the supernova remnant G15.9+0.2

    CERN Document Server

    Klochkov, D; Sasaki, M; Santangelo, A

    2016-01-01

    We present our study of the central point source CXOU J181852.0-150213 in the young Galactic supernova remnant (SNR) G15.9+0.2 based on the recent ~90 ks Chandra observations. The point source was discovered in 2005 in shorter Chandra observations and was hypothesized to be a neutron star associated with the SNR. Our X-ray spectral analysis strongly supports the hypothesis of a thermally emitting neutron star associated with G15.9+0.2. We conclude that the object belongs to the class of young cooling low-magnetized neutron stars referred to as central compact objects (CCOs). We modeled the spectrum of the neutron star with a blackbody spectral function and with our hydrogen and carbon neutron star atmosphere models, assuming that the radiation is uniformly emitted by the entire stellar surface. Under this assumption, only the carbon atmosphere models yield a distance that is compatible with a source located in the Galaxy. In this respect, CXOU J181852.0-150213 is similar to two other well-studied CCOs, the ne...

  15. Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars

    CERN Document Server

    Lombaert, R; Royer, P; de Koter, A; Cox, N L J; González-Alfonso, E; Neufeld, D; De Ridder, J; Agúndez, M; Blommaert, J A D L; Khouri, T; Groenewegen, M A T; Kerschbaum, F; Cernicharo, J; Vandenbussche, B; Waelkens, C

    2016-01-01

    Context. The recent detection of warm H$_2$O vapor emission from the outflows of carbon-rich asymptotic giant branch (AGB) stars challenges the current understanding of circumstellar chemistry. Two mechanisms have been invoked to explain warm H$_2$O vapor formation. In the first, periodic shocks passing through the medium immediately above the stellar surface lead to H$_2$O formation. In the second, penetration of ultraviolet interstellar radiation through a clumpy circumstellar medium leads to the formation of H$_2$O molecules in the intermediate wind. Aims. We aim to determine the properties of H$_2$O emission for a sample of 18 carbon-rich AGB stars and subsequently constrain which of the above mechanisms provides the most likely warm H$_2$O formation pathway. Methods, Results, and Conclusions. See paper.

  16. Two rings but no fellowship: LoTr 1 and its relation to planetary nebulae possessing barium central stars

    CERN Document Server

    Tyndall, A A; Boffin, H M J; Miszalski, B; Faedi, F; Lloyd, M; López, J A; Martell, S; Pollacco, D; Santander-García, M

    2013-01-01

    LoTr 1 is a planetary nebula thought to contain an intermediate-period binary central star system (that is, a system with an orbital period, P, between 100 and, say, 1500 days). The system shows the signature of a K-type, rapidly rotating giant, and most likely constitutes an accretion-induced post-mass transfer system similar to other PNe such as LoTr 5, WeBo 1 and A70. Such systems represent rare opportunities to further the investigation into the formation of barium stars and intermediate period post-AGB systems -- a formation process still far from being understood. Here, we present the first detailed analyses of both the central star system and the surrounding nebula of LoTr 1 using a combination of spectra obtained with VLT-FORS2, AAT-UCLES and NTT-EMMI, as well as SuperWASP photometry. We confirm the binary nature of the central star of LoTr 1 that consists of a K1 III giant and a hot white dwarf. The cool giant does not present any sign of s-process enhancement but is shown to have a rotation period o...

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

    Directory of Open Access Journals (Sweden)

    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.

  18. The binary fraction of planetary nebula central stars I. A high-precision, I-band excess search

    CERN Document Server

    De Marco, Orsola; Frew, D J; Moe, Maxwell; Jacoby, G H

    2012-01-01

    In an attempt to determine how many planetary nebulae derive from binary interactions, we have started a project to measure their unbiased binary fraction. This number, when compared to the binary fraction of the presumed parent population can give a first handle on the origin of planetary nebulae. By detecting 27 bona fide central stars in the I band we have found that 30% of our sample have an I band excess between one and a few sigmas, possibly denoting companions brighter than M3-4V and with separations smaller than approximately 1000 AU. By accounting for the undetectable companions, we determine a de-biased binary fraction of 67-78% for all companions at all separations. We compare this number to a main sequence binary fraction of (50+/-4)% determined for spectral types F6V-G2V, appropriate if the progenitors of today's PN central star population is indeed the F6V-G2V stars. The error on our estimate could be between 10 and 30%. We conclude that the central star binary fraction may be larger than expect...

  19. DIRECT NUMERICAL SIMULATION OF RADIATION PRESSURE-DRIVEN TURBULENCE AND WINDS IN STAR CLUSTERS AND GALACTIC DISKS

    International Nuclear Information System (INIS)

    The pressure exerted by the radiation of young stars may be an important feedback mechanism that drives turbulence and winds in forming star clusters and the disks of starburst galaxies. However, there is great uncertainty in how efficiently radiation couples to matter in these high optical depth environments. In particular, it is unclear what levels of turbulence the radiation can produce, and whether the infrared radiation trapped by the dust opacity can give rise to heavily mass-loaded winds. In this paper, we report a series of two-dimensional flux-limited diffusion radiation-hydrodynamics calculations performed with the code ORION in which we drive strong radiation fluxes through columns of dusty matter confined by gravity in order to answer these questions. We consider both systems where the radiation flux is sub-Eddington throughout the gas column, and those where it is super-Eddington at the midplane but sub-Eddington in the atmosphere. In the latter, we find that the radiation-matter interaction gives rise to radiation-driven Rayleigh-Taylor instability, which drives supersonic turbulence at a level sufficient to fully explain the turbulence seen in Galactic protocluster gas clouds, and to make a non-trivial contribution to the turbulence observed in starburst galaxy disks. However, the instability also produces a channel structure in which the radiation-matter interaction is reduced compared to time-steady analytic models because the radiation field is not fully trapped. For astrophysical parameters relevant to forming star clusters and starburst galaxies, we find that this effect reduces the net momentum deposition rate in the dusty gas by a factor of ∼2-6 compared to simple analytic estimates, and that in steady state the Eddington ratio reaches unity and there are no strong winds. We provide an approximation formula, appropriate for implementation in analytic models and non-radiative simulations, for the force exerted by the infrared radiation field

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

    International Nuclear Information System (INIS)

    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%.

  1. Status of Centralized Wind Power Forecasting in North America: May 2009-May 2010

    Energy Technology Data Exchange (ETDEWEB)

    Porter, K.; Rogers, J.

    2010-04-01

    Report surveys grid wind power forecasts for all wind generators, which are administered by utilities or regional transmission organizations (RTOs), typically with the assistance of one or more wind power forecasting companies.

  2. Fault tolerant control of triple star-winding flux switching permanent magnet motor drive due to open phase

    OpenAIRE

    Yu, F; Cheng, M.; Hua, W.; Chau, KT

    2015-01-01

    The flux-switching permanent-magnet (PM) (FSPM) motor is a new class of stator-PM brushless machines, which offers the advantages of high reliability, high power density, and high efficiency. In this paper, a nine-phase FSPM motor with triple star-winding sets spatially displaced by 40 degrees fed by three pulse-width modulated voltage source inverters (VSIs) is proposed, and the fault tolerant operation of the proposed FSPM motor is addressed. The key of this paper is to investigate two reme...

  3. Magnetic fields, non-thermal radiation and particle acceleration in colliding winds of WR-O stars

    CERN Document Server

    Falceta-Goncalves, D

    2015-01-01

    Non-thermal emission has been detected in WR-stars for many years at long wavelengths spectral range, in general attributed to synchrotron emission. Two key ingredients are needed to explain such emissions, namely magnetic fields and relativistic particles. Particles can be accelerated to relativistic speeds by Fermi processes at strong shocks. Therefore, strong synchrotron emission is usually attributed to WR binarity. The magnetic field may also be amplified at shocks, however the actual picture of the magnetic field geometry, intensity, and its role on the acceleration of particles at WR binary systems is still unclear. In this work we discuss the recent developments in MHD modelling of wind-wind collision regions by means of numerical simulations, and the coupled particle acceleration processes related.

  4. DUST PRODUCTION FACTORIES IN THE EARLY UNIVERSE: FORMATION OF CARBON GRAINS IN RED-SUPERGIANT WINDS OF VERY MASSIVE POPULATION III STARS

    International Nuclear Information System (INIS)

    We investigate the formation of dust in a stellar wind during the red-supergiant (RSG) phase of a very massive Population III star with a zero-age main sequence mass of 500 M ☉. We show that, in a carbon-rich wind with a constant velocity, carbon grains can form with a lognormal-like size distribution, and that all of the carbon available for dust formation finally condenses into dust for wide ranges of the mass-loss rate ((0.1-3) × 10–3 M ☉ yr–1) and wind velocity (1-100 km s–1). We also find that the acceleration of the wind, driven by newly formed dust, suppresses the grain growth but still allows more than half of the gas-phase carbon to finally be locked up in dust grains. These results indicate that, at most, 1.7 M ☉ of carbon grains can form during the RSG phase of 500 M ☉ Population III stars. Such a high dust yield could place very massive primordial stars as important sources of dust at the very early epoch of the universe if the initial mass function of Population III stars was top-heavy. We also briefly discuss a new formation scenario of carbon-rich ultra-metal-poor stars, considering feedback from very massive Population III stars

  5. UV Spectroscopy of the Central Star of the Planetary Nebula A43

    CERN Document Server

    Ringat, Ellen; Rauch, Thomas; Werner, Klaus; Kruk, Jeffrey W

    2011-01-01

    About 25% of all post-AGB stars are hydrogen-deficient, e.g. the PG1159 stars with a typical abundance pattern He:C:O = 33:50:17 (by mass). Only four of about 40 known PG1159 stars exhibit H in their spectra. The exciting star of the planetary nebula A43 is one of these so-called hybrid PG1159 stars. We present preliminary results of an on-going spectral analysis by means of NLTE model-atmosphere techniques based on UV spectra obtained with FUSE, HST/GHRS, and IUE as well as on optical observations.

  6. An Ultra-Fast X-ray Disk Wind in the Neutron Star Binary GX 340+0

    CERN Document Server

    Miller, J M; Cackett, E; Grinberg, V; Nowak, M

    2016-01-01

    We present a spectral analysis of a brief Chandra/HETG observation of the neutron star low-mass X-ray binary GX~340+0. The high-resolution spectrum reveals evidence of ionized absorption in the Fe K band. The strongest feature, an absorption line at approximately 6.9 keV, is required at the 5 sigma level of confidence via an F-test. Photoionization modeling with XSTAR grids suggests that the line is the most prominent part of a disk wind with an apparent outflow speed of v = 0.04c. This interpretation is preferred at the 4 sigma level over a scenario in which the line is H-like Fe XXVI at a modest red-shift. The wind may achieve this speed owing to its relatively low ionization, enabling driving by radiation pressure on lines; in this sense, the wind in GX 340+0 may be the stellar-mass equivalent of the flows in broad absorption line quasars (BALQSOs). If the gas has a unity volume filling factor, the mass ouflow rate in the wind is over 10^-5 Msun/year, and the kinetic power is nearly 10^39 erg/s (or, 5-6 ti...

  7. Compact Planetary Nebulae in the Galactic Disk: Analysis of the Central Stars

    CERN Document Server

    Moreno-Ibáñez, Manuel; Shaw, Richard A; Stanghellini, Letizia

    2016-01-01

    We have obtained multi-wavelength observations of compact Galactic planetary nebulae (PNe) to probe post-Asymptotic Giant Branch (AGB) evolution from the onset of nebular ejection. We analyze new observations from HST to derive the masses and evolutionary status of their central stars (CSs) in order to better understand the relationship between the CS properties and those of the surrounding nebulae. We also compare this sample with others we obtained using the same technique in different metallicity environments: the Large and Small Magellanic Clouds. We work with HST/WFC3 images of 51 targets obtained in a snapshot survey (GO-11657). The high spatial resolution of HST allows us to resolve these compact PNe and distinguish the CS emission from that of their surrounding PNe. The targets were imaged through the filters F200LP, F350LP, and F814W from which we derive Johnson V and I magnitudes. We derive CS bolometric luminosities and effective temperatures using the Zanstra technique, from a combination of HST p...

  8. Abell 41: shaping of a planetary nebula by a binary central star?

    CERN Document Server

    Jones, D; Santander-García, M; López, J A; Meaburn, J; Mitchell, D L; O'Brien, T J; Pollacco, D; Rubio-Díez, M M; Vaytet, N M H

    2010-01-01

    We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Abell 41, which is known to contain the well-studied close-binary system MT Ser. This object represents an important test case in the study of the evolution of planetary nebulae with binary central stars as current evolutionary theories predict that the binary plane should be aligned perpendicular to the symmetry axis of the nebula. Deep narrowband imaging in the light of [NII], [OIII] and [SII], obtained using ACAM on the William Herschel Telescope, has been used to investigate the ionisation structure of Abell 41. Longslit observations of the H-alpha and [NII] emission were obtained using the Manchester Echelle Spectrometer on the 2.1-m San Pedro M\\'artir Telescope. These spectra, combined with the narrowband imagery, were used to develop a spatio-kinematical model of [NII] emission from Abell 41. The best fitting model reveals Abell 41 to have a waisted, bipolar structure with an expansion velocity of ~40km\\s at...

  9. Consequences of a possible jet-star interaction in the inner central parsec of Centaurus A

    CERN Document Server

    Müller, C; Mannheim, K; Perucho, M; Ojha, R; Ros, E; Schulz, R; Wilms, J

    2015-01-01

    The jet-counterjet system of the closest radio-loud active galaxy Centaurus A (Cen A) can be studied with Very Long Baseline Interferometry (VLBI) on unprecedented small linear scales of ~0.018pc. These high-resolution observations provide essential information on jet emission and propagation within the inner parsec of an AGN jet. We present the results of a kinematic study performed within the framework of the Southern-hemisphere AGN monitoring program TANAMI. Over 3.5years, the evolution of the central-parsec jet structure of Cen A was monitored with VLBI. These observations reveal complex jet dynamics which are well explained by a spine-sheath structure supported by the downstream acceleration occurring where the jet becomes optically thin. Both moving and stationary jet features are tracked. A persistent local minimum in surface brightness suggests the presence of an obstacle interrupting the jet flow, which can be explained by the interaction of the jet with a star at a distance of ~0.4pc from the centra...

  10. Line formation in winds with enhanced equatorial mass-loss rates and its application to the Wolf-Rayet star HD 50896

    International Nuclear Information System (INIS)

    Ultraviolet spectra from the ''Copernicus'' satellite of the Wolf-Rayet star HD 50896 show several P-Cygni profiles whose emission component has a larger equivalent width than the absorption component. For lines with saturated absorption components, such as the N V (lambdalambda1239-1243) line, the excess emission is due to thermal emission from the wind. However, for unsaturated lines which are due to scattering, such as the P V (lambdalambda1118-1128) and O VI (lambdalambda1032-1038) lines, the excess emission suggests that the scattering is not spherically symmetric. Based on this premise, a simple model was developed of a stellar wind whose material is concentrated toward the star's equatorial plane. This model was used to investigate the effect on line formation of the distribution of material in the wind and the orientation of the star-wind system with respect to an observer. In addition, the influence of the wind's velocity structure was investigated for two velocity laws which are schematically depicted. The first distribution has the asymptotic behavior expected for a radiatively accelerated wind. The second one has a similar form in the outer region of the wind, but has a velocity plateau at the inner region, as suggested by ultraviolet to infrared continuum fits of Hartmann and Cassinelli (1977). To simplify calculations, the Sobolev escape probability method was used, and the velocity structure was assumed to be spherically symmetric. (Auth.)

  11. A CHANDRA X-RAY ANALYSIS OF ABELL 1664: COOLING, FEEDBACK, AND STAR FORMATION IN THE CENTRAL CLUSTER GALAXY

    International Nuclear Information System (INIS)

    The brightest cluster galaxy (BCG) in the Abell 1664 cluster is unusually blue and is forming stars at a rate of ∼ 23 M sun yr-1. The BCG is located within 5 kpc of the X-ray peak, where the cooling time of 3.5 x 108 yr and entropy of 10.4 keV cm2 are consistent with other star-forming BCGs in cooling flow clusters. The center of A1664 has an elongated, 'barlike' X-ray structure whose mass is comparable to the mass of molecular hydrogen, ∼1010 M sun in the BCG. We show that this gas is unlikely to have been stripped from interloping galaxies. The cooling rate in this region is roughly consistent with the star formation rate, suggesting that the hot gas is condensing onto the BCG. We use the scaling relations of BIrzan et al. to show that the active galactic nucleus (AGN) is underpowered compared to the central X-ray cooling luminosity by roughly a factor of three. We suggest that A1664 is experiencing rapid cooling and star formation during a low state of an AGN feedback cycle that regulates the rates of cooling and star formation. Modeling the emission as a single-temperature plasma, we find that the metallicity peaks 100 kpc from the X-ray center, resulting in a central metallicity dip. However, a multi-temperature cooling flow model improves the fit to the X-ray emission and is able to recover the expected, centrally peaked metallicity profile.

  12. The central region of M83: Massive star formation, kinematics, and the location and origin of the nucleus

    CERN Document Server

    Knapen, J H; Ryder, S D; Falcon-Barroso, J; Fathi, K; Gutierrez, L

    2010-01-01

    We report new near-IR integral field spectroscopy of the central starburst region of the barred spiral galaxy M83 obtained with CIRPASS on Gemini-S, which we analyse in conjunction with GHaFaS Fabry-Perot data, an AAT IRIS2 Ks-band image, and near- and mid-IR imaging from the Hubble and Spitzer space telescopes. The bulk of the current star formation activity is hidden from optical view by dust extinction, but is seen in the near- and mid-IR to the north of the nucleus. This region is being fed by inflow of gas through the bar of M83, traced by the prominent dust lane entering into the circumnuclear region from the north. An analysis of stellar ages confirms that the youngest stars are indeed in the northwest. A gradual age gradient, with older stars further to the south, characterises the well-known star-forming arc in the central region of M83. Detailed analyses of the Pa beta ionised gas kinematics and near-IR imaging confirm that the kinematic centre coincides with the photometric centre of M83, and that ...

  13. Exploring the crowded central region of 10 Galactic globular clusters using EMCCDs. Variable star searches and new discoveries

    CERN Document Server

    Jaimes, R Figuera; Skottfelt, J; Kains, N; Jørgensen, U G; Horne, K; Dominik, M; Alsubai, K A; Bozza, V; Novati, S Calchi; Ciceri, S; D'Ago, G; Galianni, P; Gu, S -H; Harpsøe, K B W; Haugbølle, T; Hinse, T C; Hundertmark, M; Juncher, D; Korhonen, H; Liebig, C; Mancini, L; Popovas, A; Rabus, M; Rahvar, S; Scarpetta, G; Schmidt, R W; Snodgrass, C; Southworth, J; Starkey, D; Street, R A; Surdej, J; Wang, X -B; Wertz, O

    2015-01-01

    Obtain time-series photometry of the very crowded central regions of Galactic globular clusters with better angular resolution than previously achieved with conventional CCDs on ground-based telescopes to complete, or improve, the census of the variable star population in those stellar systems. Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD and the short-exposure-time images obtained (10 images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. The light curves of 12541 stars in the cores of 10 globular clusters were statistically analysed in order to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 L, 2 SR, 20 RR Lyrae, 1 SX Phe, 3 cataclysmic variables, 1 EW a...

  14. Masses and scaling relations for nuclear star clusters, and their co-existence with central black holes

    Science.gov (United States)

    Georgiev, Iskren Y.; Böker, Torsten; Leigh, Nathan; Lützgendorf, Nora; Neumayer, Nadine

    2016-04-01

    Galactic nuclei typically host either a nuclear star cluster (NSC, prevalent in galaxies with masses ≲1010 M⊙) or a massive black hole (MBH, common in galaxies with masses ≳1012 M⊙). In the intermediate-mass range, some nuclei host both an NSC and an MBH. In this paper, we explore scaling relations between NSC mass (M_NSC) and host-galaxy total stellar mass (M_{star ,gal}) using a large sample of NSCs in late- and early-type galaxies, including a number of NSCs harbouring an MBH. Such scaling relations reflect the underlying physical mechanisms driving the formation and (co)evolution of these central massive objects. We find ˜1.5σ significant differences between NSCs in late- and early-type galaxies in the slopes and offsets of the relations reff,NSC-M_NSC, reff,NSC-M_{star ,gal} and M_NSC-M_{star ,gal}, in the sense that (i) NSCs in late types are more compact at fixed M_NSC and M_{star ,gal}; and (ii) the M_NSC-M_{star ,gal} relation is shallower for NSCs in late types than in early types, similar to the M_BH-M_{star ,bulge} relation. We discuss these results in the context of the (possibly ongoing) evolution of NSCs, depending on host-galaxy type. For NSCs with an MBH, we illustrate the possible influence of an MBH on its host NSC, by considering the ratio between the radius of the MBH sphere of influence and reff,NSC. NSCs harbouring a sufficiently massive black hole are likely to exhibit surface brightness profile deviating from a typical King profile.

  15. GLOBAL STAR FORMATION REVISITED

    International Nuclear Information System (INIS)

    A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

  16. Shape and evolution of wind-blown bubbles of massive stars: on the effect of the interstellar magnetic field

    CERN Document Server

    van Marle, Allard Jan; Marcowith, Alexandre

    2015-01-01

    The winds of massive stars create large (>10 pc) bubbles around their progenitors. As these bubbles expand they encounter the interstellar coherent magnetic field which, depending on its strength, can influence the shape of the bubble. We wish to investigate if, and how much, the interstellar magnetic field can contribute to the shape of an expanding circumstellar bubble around a massive star. We use the MPI-AMRVAC code to make magneto-hydrodynamical simulations of bubbles, using a single star model, combined with several different field strengths: B=5, 10, and 20 muG for the interstellar magnetic field. This covers the typical field strengths of the interstellar magnetic fields found in the galactic disk and bulge. Furthermore, we present two simulations that include both a 5 muG interstellar magnetic field and a 10,000 K interstellar medium and two different ISM densities to demonstrate how the magnetic field can combine with other external factors to influnece the morphology of the circumstellar bubbles. O...

  17. Neutron Star Powered Nebulae: A New View on Pulsar Wind Nebulae with the Fermi Gamma-ray Space Telescope

    CERN Document Server

    Lande, Joshua

    2014-01-01

    Pulsars are rapidly-rotating neutron stars born out of the death of stars. A diffuse nebula is formed when particles stream from these neutron stars and interact with the ambient medium. These pulsar wind nebulae (PWNe) are visible across the electromagnetic spectrum, producing some of the most brilliant objects ever observed. The launch of the Fermi Gamma-ray Space Telescope in 2008 has offered us an unprecedented view of the cosmic gamma-ray sky. Using data from the LAT on board Fermi, we search for new gamma-ray-emitting PWN. With these new observations, we vastly expand the number of PWN observed at these energies. We interpret the observed gamma-ray emission from these PWN in terms of a model where accelerated electrons produce gamma-rays through inverse Compton upscattering when they interact with interstellar photon fields. We conclude by studying how the observed PWN evolve with the age and spin-down power of the host pulsar.

  18. New models for the evolution of Post-Asymptotic Giant Branch stars and Central Stars of Planetary Nebulae

    CERN Document Server

    Bertolami, Marcelo M Miller

    2015-01-01

    The Post Asymptotic Giant Branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The two grids of models presently available are based on outdated micro- and macro-physics and do not agree with each other. We study the timescales of post-AGB and CSPNe in the context of our present understanding of the micro- and macro-physics of stars. We want to assess whether new post-AGB models, based on the latter improvements in TP-AGB modeling, can help to understand the discrepancies between observation and theory and within theory itself. We compute a grid of post-AGB full evolutionary sequences that include all previous evolutionary stages from the Zero Age Main Sequence to the White Dwarf phase. Models are computed for initial masses between 0.8 and 4 $M_\\odot$ and for a wide range of initial metallicities ($Z_0=$0.02, 0.01, 0.001, 0.0001), this allow us to provide post-AGB timescales and properties for H-burning post-AGB objects with masses in the re...

  19. The interplay of disk wind and dynamical ejecta in the aftermath of neutron star - black hole mergers

    CERN Document Server

    Fernández, Rodrigo; Schwab, Josiah; Kasen, Daniel; Rosswog, Stephan

    2014-01-01

    We explore the evolution of the different ejecta components generated during the merger of a neutron star (NS) and a black hole (BH). Our focus is the interplay between material ejected dynamically during the merger, and the wind launched on a viscous timescale by the remnant accretion disk. These components are expected to contribute to an electromagnetic transient and to produce r-process elements, each with a different signature when considered separately. Here we introduce a two-step approach to investigate their combined evolution, using two- and three-dimensional hydrodynamic simulations. Starting from the output of a merger simulation, we identify each component in the initial condition based on its phase space distribution, and evolve the accretion disk in axisymmetry. The wind blown from this disk is injected into a three-dimensional computational domain where the dynamical ejecta is evolved. We find that the wind can suppresses fallback accretion on timescales longer than ~100 ms. Due to self-simila...

  20. Molecules in star formation.

    Science.gov (United States)

    Shu, F. H.

    The author reviews current ideas and models in the problem of star formation from molecular cloud cores that are relatively isolated from the influences of other forming stars. He discusses the time scales, flow dynamics, and density and temperature structures applicable to each of the four stages of the entire process: (1) formation of a magnetized cloud core by ambipolar diffusion and evolution to a pivotal state of gravomagneto catastrophe; (2) self-similar collapse of the pivotal configuration and the formation of protostars, disks, and pseudo-disks; (3) onset of a magnetocentrifugally driven, lightly ionized wind from the interaction of an accretion disk and the magnetosphere of the central star, and the driving of bipolar molecular outflows; (4) evolution of pre-main-sequence stars surrounded by dusty accretion disks. For each of these stages and processes, he considers the characteristics of the molecular diagnostics needed to investigate the crucial aspects of the observational problem.

  1. PO and PN in the wind of the oxygen-rich AGB star IK Tau

    CERN Document Server

    De Beck, E; Patel, N A; Young, K H; Gottlieb, C A; Menten, K M; Decin, L

    2013-01-01

    Phosphorus-bearing compounds have only been studied in the circumstellar environments (CSEs) of the asymptotic giant branch (AGB) star IRC +10216 and the protoplanetary nebula CRL 2688, both C-rich objects, and the O-rich red supergiant VY CMa. The current chemical models cannot reproduce the high abundances of PO and PN derived from observations of VY CMa. No observations have been reported of phosphorus in the CSEs of O-rich AGB stars. We aim to set observational constraints on the phosphorous chemistry in the CSEs of O-rich AGB stars, by focussing on the Mira-type variable star IK Tau. Using the IRAM 30m telescope and the Submillimeter Array (SMA), we observed four rotational transitions of PN (J=2-1,3-2,6-5,7-6) and four of PO (J=5/2-3/2,7/2-5/2,13/2-11/2,15/2-13/2). The IRAM 30m observations were dedicated line observations, while the SMA data come from an unbiased spectral survey in the frequency range 279-355 GHz. We present the first detections of PN and PO in an O-rich AGB star and estimate abundance...

  2. The Eddington factor as the key to understand the winds of the most massive stars. Evidence for a Gamma-dependence of Wolf-Rayet type mass loss

    CERN Document Server

    Gräfener, G; de Koter, A; Langer, N

    2011-01-01

    The most massive stars are thought to be hydrogen-rich Wolf-Rayet stars of late spectral subtype (WNh stars). In previous theoretical studies the enhanced mass loss of these stars has been attributed to their proximity to the Eddington limit. Here we investigate observed trends in the mass-loss properties of such young, very massive stars. We derive theoretical mass-luminosity relations for very massive stars, based on a large grid of stellar structure models. Using these relations, we estimate Eddington factors for a sample of stars, under different assumptions of their evolutionary status. We evaluate the resulting mass-loss relations, and compare them with theoretical predictions. We find observational evidence that the mass loss in the WR regime is dominated by the Eddington parameter Gamma_e, which has important consequences for the way we understand Wolf-Rayet stars and their mass loss. In addition, we derive wind masses that support the picture that the WNh stars in young stellar clusters are very mass...

  3. Exploring the crowded central region of ten Galactic globular clusters using EMCCDs. Variable star searches and new discoveries

    Science.gov (United States)

    Figuera Jaimes, R.; Bramich, D. M.; Skottfelt, J.; Kains, N.; Jørgensen, U. G.; Horne, K.; Dominik, M.; Alsubai, K. A.; Bozza, V.; Calchi Novati, S.; Ciceri, S.; D'Ago, G.; Galianni, P.; Gu, S.-H.; Harpsøe, K. B. W.; Haugbølle, T.; Hinse, T. C.; Hundertmark, M.; Juncher, D.; Korhonen, H.; Mancini, L.; Popovas, A.; Rabus, M.; Rahvar, S.; Scarpetta, G.; Schmidt, R. W.; Snodgrass, C.; Southworth, J.; Starkey, D.; Street, R. A.; Surdej, J.; Wang, X.-B.; Wertz, O.

    2016-04-01

    Aims: We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution thanhas been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems. Methods: Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. Results: The light curves of 12 541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified). Fluxes and photometric measurements for these stars are available in electronic form through the Strasbourg astronomical Data Center. Based on data collected by the MiNDSTEp team with the Danish 1.54m telescope at ESO's La Silla observatory in Chile.Full Table 1 is only available at CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A128

  4. 76 FR 67160 - Southern Star Central Gas Pipeline, Inc.; Notice of Application

    Science.gov (United States)

    2011-10-31

    ... vertically at Southern Star's existing Alden Gas Storage Field located in Rice County, Kansas. Subsequent to... electronic submission of protests and interventions in lieu of paper using the ``eFiling'' link at...

  5. X-Shooter spectroscopy of young stellar objects: V - Slow winds in T Tauri stars

    CERN Document Server

    Natta, A; Alcalá, J M; Rigliaco, E; Covino, E; Stelzer, B; D'Elia, V

    2014-01-01

    Disks around T Tauri stars are known to lose mass, as best shown by the profiles of forbidden emission lines of low ionization species. At least two separate kinematic components have been identified, one characterised by velocity shifts of tens to hundreds km/s (HVC) and one with much lower velocity of few km/s (LVC). The HVC are convincingly associated to the emission of jets, but the origin of the LVC is still unknown. In this paper we analyze the forbidden line spectrum of a sample of 44 mostly low mass young stars in Lupus and $\\sigma$-Ori observed with the X-Shooter ESO spectrometer. We detect forbidden line emission of [OI], [OII], [SII], [NI], and [NII], and characterize the line profiles as LVC, blue-shifted HVC and red-shifted HVC. We focus our study on the LVC. We show that there is a good correlation between line luminosity and both L$_{star}$ and the accretion luminosity (or the mass-accretion rate) over a large interval of values (L$_{star}$ $\\sim 10^{-2} - 1$ L$_\\odot$; L$_{acc}$ $\\sim 10^{-5} ...

  6. A New Numerical Method for Solving Radiation Driven Winds from Hot Stars

    CERN Document Server

    Cure, M; Cure, Michel

    2006-01-01

    We present a general method for solving the non--linear differential equation of monotonically increasing steady--state radiation driven winds. We graphically identify all the singular points before transforming the momentum equation to a system of differential equations with all the gradients explicitly give. This permits a topological classification of all singular points and to calculate the maximum and minimum mass--loss of the wind. We use our method to analyse for the first time the topology of the non--rotating frozen in ionisation m--CAK wind, with the inclusion of the finite disk correction factor and find up to 4 singular points, three of the x--type and one attractor--type. The only singular point (and solution passing through) that satisfies the boundary condition at the stellar surface is the standard m--CAK singular point.

  7. Spatially resolved kinematics, galactic wind, and quenching of star formation in the luminous infrared galaxy IRAS F11506-3851

    CERN Document Server

    Cazzoli, S; Colina, L; Piqueras-Lopez, J; Bellocchi, E; Emonts, B; Maiolino, R

    2014-01-01

    We present a multi-wavelength integral field spectroscopic study of the low-z LIRG IRAS F11506-3851, on the basis of VIMOS and SINFONI (ESO-VLT) observations. The morphology and the 2D kinematics of the gaseous (neutral and ionized) and stellar components have been mapped using the NaD doublet, the H$\\alpha$ line, and the near-IR CO(2-0) and CO(3-1) bands. The kinematics of the ionized gas and the stars are dominated by rotation, with large observed velocity amplitudes and centrally peaked velocity dispersion maps. The stars lag behind the warm gas and represent a dynamically hotter system, as indicated by the observed dynamical ratios. Thanks to these IFS data we have disentangled the contribution of the stars and the ISM to the NaD feature, finding that it is dominated by the absorption of neutral gas clouds in the ISM. The neutral gas 2D kinematics shows a complex structure dominated by two components. On the one hand, the thick slowly rotating disk lags significantly compared to the ionized gas and the st...

  8. On the Role Played by Lines in Radiatively Driven Stellar Winds Depending on the Position of the Stars in the HR Diagram

    Science.gov (United States)

    Migozzi, M. C.; Lafon, J. P. J.

    1985-01-01

    The radiative force due to transfer in ultraviolet lines is always an important mechanism in hot star wind dynamics. However, it is not clear when it is the dominant mechanism and which are the noise parameters. To investigate the efficiency of purely radiative momentum/energy transfer in hot star winds and in various regions of the HR diagram, the Leroy and Lafon model was improved and put to its limits; correlations between the mass loss rate, the luminosity and other parameters and the theoretical and the observational results, looking for observed stars violating the model were compared. It is concluded that in widespread region of the HR diagram, line driven models are consistent with observations, the radiative equilibrium physics is relevant throughout the expanding atmospheres and the mass loss rate is quasilinearly correlated with the luminosity.

  9. The VLT-FLAMES Tarantula Survey. XVII. Physical and wind properties of massive stars at the top of the main sequence

    Science.gov (United States)

    Bestenlehner, J. M.; Gräfener, G.; Vink, J. S.; Najarro, F.; de Koter, A.; Sana, H.; Evans, C. J.; Crowther, P. A.; Hénault-Brunet, V.; Herrero, A.; Langer, N.; Schneider, F. R. N.; Simón-Díaz, S.; Taylor, W. D.; Walborn, N. R.

    2014-10-01

    The evolution and fate of very massive stars (VMS) is tightly connected to their mass-loss properties. Their initial and final masses differ significantly as a result of mass loss. VMS have strong stellar winds and extremely high ionising fluxes, which are thought to be critical sources of both mechanical and radiative feedback in giant H ii regions. However, how VMS mass-loss properties change during stellar evolution is poorly understood. In the framework of the VLT-Flames Tarantula Survey (VFTS), we explore the mass-loss transition region from optically thin O star winds to denser WNh Wolf-Rayet star winds, thereby testing theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and WNh stars, an unprecedented sample of stars with the highest masses and luminosities known. We perform a spectral analysis of optical VFTS as well as near-infrared VLT/SINFONI data using the non-LTE radiative transfer code CMFGEN to obtain both stellar and wind parameters. For the first time, we observationally resolve the transition between optically thin O star winds and optically thick hydrogen-rich WNh Wolf-Rayet winds. Our results suggest the existence of a "kink" between both mass-loss regimes, in agreement with recent Monte Carlo simulations. For the optically thick regime, we confirm the steep dependence on the classical Eddington factor Γe from previous theoretical and observational studies. The transition occurs on the main sequence near a luminosity of 106.1L⊙, or a mass of 80 ... 90 M⊙. Above this limit, we find that - even when accounting for moderate wind clumping (with fv = 0.1) - wind mass-loss rates are enhanced with respect to standard prescriptions currently adopted in stellar evolution calculations. We also show that this results in substantial helium surface enrichment. Finally, based on our spectroscopic analyses, we are able to provide the most accurate ionising fluxes for VMS known to date, confirming the pivotal role of VMS in ionising and

  10. The rapid evolution of the central star of the Stingray Nebula — latest news from the HST

    Science.gov (United States)

    Reindl, Nicole; Rauch, Thomas; Miller Bertolami, Marcelo M.; Werner, Klaus

    2016-07-01

    SAO 244567 is an unusually fast evolving star. Within twenty years only, it had turned from a B-type supergiant into the central star of the Stingray Nebula. Space- and ground-based observations obtained over the last decades have revealed that its spectrum changes noticeably over just a few years, showing stellar evolution in real time. The low mass of SAO 244567 is, however, in strong contradiction with canonical post-asymptotic giant branch evolution. Thus, its fast evolution has been a mystery for decades. We present preliminary results of the non-LTE spectral analyis of the recently obtained HST/COS observations, which finally allow us to shed light on the evolutionary history of this extraordinary object.

  11. Recent X-Recent X-ray observations of the symbiotic star AG Peg: do they signify Colliding Stellar Winds?

    CERN Document Server

    Zhekov, Svetozar A

    2016-01-01

    We present an analysis of recent X-ray observations of the symbiotic star AG Peg. The X-ray emission of AG Peg as observed with Swift in 2015 shows considerable variability on time scale of days as variability on shorter time scales might be present as well. Analysis of the X-ray spectra obtained in 2013 and 2015 confirms that AG Peg is an X-ray source of class $\\beta$ of the X-ray sources amongst the symbiotic stars. The X-ray emission of AG Peg as observed with ROSAT (1993 June) might well originate from colliding stellar winds (CSW) in binary system. On the other hand, the characteristics of the X-ray emission of AG Peg in 2013 and 2015 (Swift) are hard to accommodate in the framework of the CSW picture. Analysis of the light curves in 2015 shows that the power spectrum of the X-ray variability in AG Peg resembles that of the flicker noise (or flickering) being typical for accretion processes in astronomical objects. This is a sign that CSWs did not play a key role for the X-ray emission from AG Peg in 201...

  12. The transition mass-loss rate: Calibrating the role of line-driven winds in massive star evolution

    CERN Document Server

    Vink, Jorick S

    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 (dM/dt)_trans between O and Wolf-Rayet (WR) 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...

  13. Recent X-ray observations of the symbiotic star AG Peg: do they signify Colliding Stellar Winds?

    Science.gov (United States)

    Zhekov, Svetozar A.; Tomov, Toma

    2016-06-01

    We present an analysis of recent X-ray observations of the symbiotic star AG Peg. The X-ray emission of AG Peg as observed with Swift in 2015 shows considerable variability on time scale of days as variability on shorter time scales might be present as well. Analysis of the X-ray spectra obtained in 2013 and 2015 confirms that AG Peg is an X-ray source of class β of the X-ray sources amongst the symbiotic stars. The X-ray emission of AG Peg as observed with ROSAT (1993 June) might well originate from colliding stellar winds (CSW) in binary system. On the other hand, the characteristics of the X-ray emission of AG Peg in 2013 and 2015 (Swift) are hard to accommodate in the framework of the CSW picture. Analysis of the light curves in 2015 shows that the power spectrum of the X-ray variability in AG Peg resembles that of the flicker noise (or flickering) being typical for accretion processes in astronomical objects. This is a sign that CSWs did not play a key role for the X-ray emission from AG Peg in 2013-2015 and a different mechanism (probably accretion) is also getting into play.

  14. Wind Reduction Patterns Around Isolated Biomass for Wind-Erosion Control in a Desertified Area of Central Sudan

    Directory of Open Access Journals (Sweden)

    Nawal Khidir Nasr Al-Amin

    2010-10-01

    Full Text Available 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 3 and 2.5 m and 3 (with h of 1.04, 0.9 and 0.8 m well established single biomass configurations of Leptadenia pyrotechnica trees, Prosopis juliflora trees and Panicum turgidum grass, were selected in the field. Solar powered cup anemometer wind measurements with a data logger system were taken at heights of 0.25 and 0.5 h, at distances 0.5 and 1 h, at four sides of the tree in the prevailing wind direction and perpendicular to it, and additionally at 2, 4 and 6 h windward and leeward. The protection effectiveness of the biomass was calculated as a wind reduction ratio and in terms of objects protection, which was evaluated using the dimensionless protection index (ƒ. The study showed that windward protection provided by Leptadenia and Prosopis at level 0.25h and distance 0.5 h was similar, w ith a wind reduction ratio R0.8, while Panicum showed comparably higher R-values. Even at the 0.5 h level, Panicum showed an R of 0.65 at 0.5 h distance. Leew ard, at 0.25 h level differences were small, R increasing from 0.6/0.7 to 0.8/1 with distance, Leptadenia protecting best. At higher level (0.5 h at distances 0.5 and 1 h Prosopis gave better protection than the other two at distances 0.5, 1 and 2 h. The research is an exam ple of simple experimental work under difficult environmental conditions in Africa. It was part of studies in which additional attention was paid to quantification aspects under such conditions as well as to the problems it helped solve in the African societies concerned as agrometeorological services.

  15. Two bi-stability jumps in theoretical wind models for massive stars and the implications for Luminous Blue Variable supernovae

    CERN Document Server

    Petrov, Blagovest; Gräfener, Götz

    2016-01-01

    Luminous Blue Variables have been suggested to be the direct progenitors of supernova types IIb and IIn, with enhanced mass loss prior to explosion. However, the mechanism of this mass loss is not yet known. Here, we investigate the qualitative behaviour of theoretical stellar wind mass-loss as a function of Teff across two bi-stability jumps in blue supergiant regime and also in proximity to the Eddington limit, relevant for LBVs. To investigate the physical ingredients that play a role in the radiative acceleration we calculate blue supergiant wind models with the CMFGEN non-LTE model atmosphere code over an effective temperature range between 30000 and 8800 K. Although our aim is not to provide new mass-loss rates for BA supergiants, we study and confirm the existence of two bi-stability jumps in mass-loss rates predicted by Vink, de Koter, & Lamers (1999). However, they are found to occur at somewhat lower Teff (20000 and 9000 K, respectively) than found previously, which would imply that stars may ev...

  16. Radiation pressure from massive star clusters as a launching mechanism for super-galactic winds

    OpenAIRE

    Murray, Norman; Ménard, Brice; Thompson, Todd A.

    2010-01-01

    Galactic outflows of low ionization, cool gas are ubiquitous in local starburst galaxies, and in the majority of galaxies at high redshift. How these cool outflows arise is still in question. Hot gas from supernovae has long been suspected as the primary driver, but this mechanism suffers from its tendency to destroy the cool gas as the latter is accelerated. We propose a modification of the supernova scenario that overcomes this difficulty. Star formation is observed to take place in cluster...

  17. Evolution and Nucleosynthesis of Very Massive Stars

    CERN Document Server

    Hirschi, Raphael

    2014-01-01

    In this chapter, after a brief introduction and overview of stellar evolution, we discuss the evolution and nucleosynthesis of very massive stars (VMS: M>100 solar masses) in the context of recent stellar evolution model calculations. This chapter covers the following aspects: general properties, evolution of surface properties, late central evolution, and nucleosynthesis including their dependence on metallicity, mass loss and rotation. Since very massive stars have very large convective cores during the main-sequence phase, their evolution is not so much affected by rotational mixing, but more by mass loss through stellar winds. Their evolution is never far from a homogeneous evolution even without rotational mixing. All VMS at metallicities close to solar end their life as WC(-WO) type Wolf-Rayet stars. Due to very important mass loss through stellar winds, these stars may have luminosities during the advanced phases of their evolution similar to stars with initial masses between 60 and 120 solar masses. A...

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

    Directory of Open Access Journals (Sweden)

    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

  19. ETHOS 1: A high latitude planetary nebula with jets forged by a post common envelope binary central star

    OpenAIRE

    Miszalski, B.; Corradi, R.L.M.; Boffin, H. M. J.; Jones, D.; Sabin, L.; Santander-García, M.; Rodríguez-Gil, P.; Rubio-Díez, M. M.

    2010-01-01

    We report on the discovery of ETHOS 1 (PN G068.1+11.0), the first spectroscopically confirmed planetary nebula (PN) from a survey of the SuperCOSMOS Science Archive for high-latitude PNe. ETHOS 1 stands out as one of the few PNe to have both polar outflows (jets) travelling at $120\\pm10$ km/s and a close binary central star. The lightcurve observed with the Mercator telescope reveals an orbital period of 0.535 days and an extremely large amplitude (0.816 mag) due to irradiation of the compani...

  20. Using Beta Cen to Probe the Photosphere-wind Connection in B Stars

    Science.gov (United States)

    Miller, Nathan A.

    2005-01-01

    In this project we began by identifying the large number of emission lines visible in the XMM-Newton RGS spectra of Beta Cen. A comprehensive analysis of the temperature structure of the hot gas was carried out by simultaneously fitting the data from all the instruments on the spacecraft. This resulted in a measured temperature range of 0.1-0.6 keV. In more detailed analysis, three characteristic plasma temperatures were found: 0.1, 0.2, and 0.6 keV. The research carried out at UW-Eau Claire primarily focused on two aspects of the data: the analysis of the forbidden line to intercombination line ratio for He-like ions and the time variability of the overall X-ray flux as detected in the direct X-ray images of the star. The analysis of the lines from He-like ions indicate that the Ne IX lines are formed no farther than about 4 stellar radii from the star's photosphere, while the N VI lines are formed within 11 stellar radii of the photosphere. X-ray flux variability would be particularly interesting for this star because it is a known Beta Cep-type variable as seen in optical light: similar variation in the X-ray region would forge an interesting link between the two wavebands. Initial analysis of the X-ray flux was complicated by spikes in the count rates early in the observation. Detailed analysis of the spectral characteristics these count rate anomalies indicated that these flares were probably not intrinsic to the star, rather they were contaminations of the data due to the passage of the satellite through soft proton clouds in the Earth's magnetosphere. An analysis of the light curve of the uncontaminated portions of the light curve did not reveal any variation on the known optical period of variation for this star, and a general search for periodic variability also did not find any significant periods of variation.

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

    International Nuclear Information System (INIS)

    The energy proposal of this research suggests the use of places with abundant wind resources for the production of H2 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 H2 in the future. The study concludes that by the year 2030 the cost of the H2 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 H2 in a very competitive position as a fuel. (author)

  2. Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars

    Science.gov (United States)

    Lombaert, R.; Decin, L.; Royer, P.; de Koter, A.; Cox, N. L. J.; González-Alfonso, E.; Neufeld, D.; De Ridder, J.; Agúndez, M.; Blommaert, J. A. D. L.; Khouri, T.; Groenewegen, M. A. T.; Kerschbaum, F.; Cernicharo, J.; Vandenbussche, B.; Waelkens, C.

    2016-04-01

    Context. The recent detection of warm H2O vapor emission from the outflows of carbon-rich asymptotic giant branch (AGB) stars challenges the current understanding of circumstellar chemistry. Two mechanisms have been invoked to explain warm H2O vapor formation. In the first, periodic shocks passing through the medium immediately above the stellar surface lead to H2O formation. In the second, penetration of ultraviolet interstellar radiation through a clumpy circumstellar medium leads to the formation of H2O molecules in the intermediate wind. Aims: We aim to determine the properties of H2O emission for a sample of 18 carbon-rich AGB stars and subsequently constrain which of the above mechanisms provides the most likely warm H2O formation pathway. Methods: Using far-infrared spectra taken with the PACS instrument onboard the Herschel telescope, we combined two methods to identify H2O emission trends and interpreted these in terms of theoretically expected patterns in the H2O abundance. Through the use of line-strength ratios, we analyzed the correlation between the strength of H2O emission and the mass-loss rate of the objects, as well as the radial dependence of the H2O abundance in the circumstellar outflow per individual source. We computed a model grid to account for radiative-transfer effects in the line strengths. Results: We detect warm H2O emission close to or inside the wind acceleration zone of all sample stars, irrespective of their stellar or circumstellar properties. The predicted H2O abundances in carbon-rich environments are in the range of 10-6 up to 10-4 for Miras and semiregular-a objects, and cluster around 10-6 for semiregular-b objects. These predictions are up to three orders of magnitude greater than what is predicted by state-of-the-art chemical models. We find a negative correlation between the H2O/CO line-strength ratio and gas mass-loss rate for Ṁg> 5 × 10-7 M⊙ yr-1, regardless of the upper-level energy of the relevant transitions

  3. Rotating massive O stars with non-spherical 2D winds

    CERN Document Server

    Müller, Patrick E

    2014-01-01

    We present solutions for the velocity field and mass-loss rates for 2D axisymmetric outflows, as well as for the case of mass accretion through the use of the Lambert W-function. For the case of a rotating radiation-driven wind the velocity field is obtained analytically using a parameterised description of the line acceleration that only depends on radius r at any given latitude $\\theta$. The line acceleration g(r) is obtained from Monte-Carlo multi-line radiative transfer calculations. The critical/sonic point of our equation of motion varies with latitude $\\theta$. Furthermore, an approximate analytical solution for the supersonic flow of a rotating wind is derived, which is found to closely resemble the exact solution. For the simultaneous solution of the mass-loss rate and velocity field, we use the iterative method of our 1D method extended to the non-spherical 2D case. We apply the new theoretical expressions with our iterative method to the stellar wind from a differentially rotating 40 $M_{sun}$ O5-V...

  4. New X-ray observations of IQ Aurigae and α2 Canum Venaticorum. Probing the magnetically channeled wind shock model in A0p stars

    Science.gov (United States)

    Robrade, J.; Schmitt, J. H. M. M.

    2011-07-01

    Aims: We re-examine the scenario of X-ray emission from magnetically confined/channeled wind shocks (MCWS) for Ap/Bp stars, a model originally developed to explain the ROSAT detection of the A0p star IQ Aur. Methods: We present new X-ray observations of the A0p stars α2 CVn (Chandra) and IQ Aur (XMM-Newton) and discuss our findings in the context of X-ray generating mechanisms of magnetic, chemically peculiar intermediate mass stars. Results: The X-ray luminosities of IQ Aur with log LX = 29.6 erg s-1 and α2 CVn with log LX ≲ 26.0 erg s-1 differ by at least three orders of magnitude, although both are A0p stars. By studying a sample of comparison stars, we find that X-ray emission is preferably generated by more massive objects such as IQ Aur. Besides a strong, cool plasma component, significant amounts of hot (>10 MK) plasma are present during the quasi-quiescent phase of IQ Aur; moreover, diagnostics of the UV sensitive f/i line ratio in He-like O vii triplet point to X-ray emitting regions well above the stellar surface of IQ Aur. In addition we detect a large flare from IQ Aur with temperatures up to ~100 MK and a peak X-ray luminosity of log LX ≈ 31.5 erg s-1. The flare, showing a fast rise and e-folding decay time of less than half an hour, originates in a fairly compact structure and is accompanied by a significant metallicity increase. The X-ray properties of IQ Aur cannot be described by wind shocks only and require the presence of magnetic reconnection. This is most evident in the, to our knowledge, first X-ray flare reported from an A0p star. Conclusions: Our study indicates that the occurrence the of X-ray emission in A0p stars generated by magnetically channeled wind shocks depends on stellar properties such as luminosity, which promote a high mass loss rate, whereas magnetic field configuration and transient phenomena refine their appearance. While we cannot rule out unknown close companions, the X-ray emission from IQ Aur can be described

  5. Deep Chandra observations of HCG 16. I. Active nuclei, star formation, and galactic winds

    International Nuclear Information System (INIS)

    We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610 MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation, and high-luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe Kα emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infrared and ultraviolet bands to confirm that star formation in both galaxies is probably declining after galaxy-wide starbursts were triggered ∼400-500 Myr ago. We examine the physical properties of their galactic superwinds, and find that both have temperatures of ∼0.8 keV. We also examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in the group, and show that it is dominated by emission from its starburst.

  6. Deep Chandra observations of HCG 16. I. Active nuclei, star formation, and galactic winds

    Energy Technology Data Exchange (ETDEWEB)

    O' Sullivan, E.; Zezas, A.; Vrtilek, J. M.; David, L. P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Giacintucci, S. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Trevisan, M. [Instituto Nacional de Pesquisas Espaciais, Av. dos Astronautas 1758, 12227-010, São José dos Campos (Brazil); Ponman, T. J.; Raychaudhury, S. [School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT (United Kingdom); Mamon, G. A., E-mail: eosullivan@cfa.harvard.edu [Institut d' Astrophysique de Paris (UMR 7095 CNRS and UMPC), 98 bis Bd Arago, F-75014 Paris (France)

    2014-10-01

    We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610 MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation, and high-luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe Kα emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infrared and ultraviolet bands to confirm that star formation in both galaxies is probably declining after galaxy-wide starbursts were triggered ∼400-500 Myr ago. We examine the physical properties of their galactic superwinds, and find that both have temperatures of ∼0.8 keV. We also examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in the group, and show that it is dominated by emission from its starburst.

  7. The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence

    CERN Document Server

    Bestenlehner, Joachim M; Vink, Jorick S; Najarro, F; de Koter, A; Sana, H; Evans, C J; Crowther, P A; Hénault-Brunet, V; Herrero, A; Langer, N; Schneider, F R N; Simón-Díaz, S; Taylor, W D; Walborn, N R

    2014-01-01

    The evolution and fate of very massive stars (VMS) is tightly connected to their mass-loss properties. Their initial and final masses differ significantly as a result of mass loss. VMS have strong stellar winds and extremely high ionising fluxes, which are thought to be critical sources of both mechanical and radiative feedback in giant Hii regions. However, how VMS mass-loss properties change during stellar evolution is poorly understood. In the framework of the VLT-Flames Tarantula Survey (VFTS), we explore the mass-loss transition region from optically thin O to denser WNh star winds, thereby testing theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and WNh stars, an unprecedented sample of stars with the highest masses and luminosities known. We perform a spectral analysis of optical VFTS as well as near-infrared VLT/SINFONI data using the non-LTE radiative transfer code CMFGEN to obtain stellar and wind parameters. For the first time, we observationally resolve the transition between op...

  8. WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?

    OpenAIRE

    Chené, A. -N.; A. F. J. Moffat; Cameron, C; Fahed, R.; Gamen, R. C.; Lefèvre, L.; Rowe, J.F.; St-Louis, N.; Muntean, V; De La Chevrotière, A.; Guenther, D. B.; Kuschnig, R.; Matthews, J. M.; Rucinski, S. M.; Sasselov, D.

    2011-01-01

    A 30-day contiguous photometric run with the 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 RV studies fail to reveal any plausible companion with a period in this range. Therefore, we conjecture that the observed light-curve cusp...

  9. Decoding the Star-Forming Main Sequence or: How I Learned to Stop Worrying and Love the Central Limit Theorem

    CERN Document Server

    Kelson, Daniel D

    2014-01-01

    Star-formation rates (SFR) of disk galaxies strongly correlate with stellar mass, with a small dispersion in SSFR at fixed mass, sigma~0.3 dex. With such small scatter this star-formation main sequence (SFMS) has been interpreted as deterministic and fundamental. Here we demonstrate that it is a simple consequence of the central limit theorem. Our derivation begins by approximating in situ stellar mass growth as a stochastic process, much like a random walk (where the expectation of SFR at any time is equal to the SFR at the previous time). We then derive expectation values for median SSFR of star-forming disks and their scatter over time. We generalize the results for stochastic changes in SFR that are not independent of each other but are correlated over time. For unbiased samples of (disk) galaxies, we derive an expectation that should be independent of mass, decline as 1/T, and have a relative scatter that is independent of mass and time. The derived SFMS and its evolution matches published data to z=10 ...

  10. Deep Chandra Observations of HCG 16 - I. Active Nuclei, Star formation and Galactic Winds

    CERN Document Server

    O'Sullivan, E; Vrtilek, J M; Giacintucci, S; Trevisan, M; David, L P; Ponman, T J; Mamon, G A; Raychaudhury, S

    2014-01-01

    We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope 610~MHz observations of the spiral-galaxy-rich compact group HCG 16, which we use to examine nuclear activity, star formation and the high luminosity X-ray binary populations in the major galaxies. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized nuclear source in NGC 838. All three nuclei are variable on timescales of months to years, and for NGC 833 and NGC 835 this is most likely caused by changes in accretion rate. The deep Chandra observations allow us to detect for the first time an Fe-K$\\alpha$ emission line in the spectrum of the Seyfert 2 nucleus of NGC 835. We find that NGC 838 and NGC 839 are both starburst-dominated systems, with only weak nuclear activity, in agreement with previous optical studies. We estimate the star formation rates in the two galaxies from their X-ray and radio emission, and compare these results with estimates from the infra-red and ultra-vio...

  11. Toward A Self Consistent MHD Model of Chromospheres and Winds From Late Type Evolved Stars

    CERN Document Server

    Airapetian, V S; Carpenter, K G

    2014-01-01

    We present the first magnetohydrodynamic model of the stellar chromospheric heating and acceleration of the outer atmospheres of cool evolved stars, using alpha Tau as a case study. We used a 1.5D MHD code with a generalized Ohm's law that accounts for the effects of partial ionization in the stellar atmosphere to study Alfven wave dissipation and wave reflection. We have demonstrated that due to inclusion of the effects of ion-neutral collisions in magnetized weakly ionized chromospheric plasma on resistivity and the appropriate grid resolution, the numerical resistivity becomes 1-2 orders of magnitude smaller than the physical resistivity. The motions introduced by non-linear transverse Alfven waves can explain non-thermally broadened and non-Gaussian profiles of optically thin UV lines forming in the stellar chromosphere of alpha Tau and other late-type giant and supergiant stars. The calculated heating rates in the stellar chromosphere due to resistive (Joule) dissipation of electric currents, induced by ...

  12. Radiation pressure from massive star clusters as a launching mechanism for super-galactic winds

    CERN Document Server

    Murray, Norman; Thompson, Todd A

    2010-01-01

    Galactic outflows of low ionization, cool gas are ubiquitous in local starburst galaxies, and in the majority of galaxies at high redshift. How these cool outflows arise is still in question. Hot gas from supernovae has long been suspected as the primary driver, but this mechanism suffers from its tendency to destroy the cool gas as the latter is accelerated. We propose a modification of the supernova scenario that overcomes this difficulty. Star formation is observed to take place in clusters; in a given galaxy, the bulk of the star formation is found in the ~20 most massive clusters. We show that, for L* galaxies, the radiation pressure from clusters with M>10^6 M_sun is able to expel the surrounding gas at velocities in excess of the circular velocity of the disk galaxy. This cool gas can travel above the galactic disk in less than 2 Myr, well before any supernovae erupt in the driving cluster. Once above the disk, the cool outflowing gas is exposed to radiation, and supernovae induced hot gas outflows, fr...

  13. High-resolution FUSE and HST ultraviolet spectroscopy of the white dwarf central star of Sh 2-216

    CERN Document Server

    Rauch, T; Werner, K; Kruk, J W; Oliveira, C M; Putte, D Vande; Mignani, R P; Kerber, F

    2007-01-01

    LS V +4621 is the DAO-type central star of the planetary nebula Sh 2-216. We perform a comprehensive spectral analysis of high-resolution, high-S/N ultraviolet observations obtained with FUSE and STIS aboard the HST as well as the optical spectrum of LS V +4621 by means of state-of-the-art NLTE model-atmosphere techniques in order to compare its photospheric properties to theoretical predictions from stellar evolution theory as well as from diffusion calculations. From the N IV - NV, O IV - O VI, Si IV - Si V, and Fe V - Fe VII ionization equilibria, we determined an effective temperature of 95 +/- 2 kK with high precision. The surface gravity is log g = 6.9 +/- 0.2. An unexplained discrepancy appears between the spectroscopic distance d = 224 +46/-58 pc and the parallax distance d = 129 +6/-5 pc of LS V +4621. For the first time, we have identified Mg IV and Ar VI absorption lines in the spectrum of a hydrogen-rich central star and determined the Mg and Ar abundances as well as the individual abundances of i...

  14. ETHOS 1: A high latitude planetary nebula with jets forged by a post common envelope binary central star

    CERN Document Server

    Miszalski, B; Boffin, H M J; Jones, D; Sabin, L; Santander-García, M; Rodríguez-Gil, P; Rubio-Díez, M M

    2010-01-01

    We report on the discovery of ETHOS 1 (PN G068.1+11.0), the first spectroscopically confirmed planetary nebula (PN) from a survey of the SuperCOSMOS Science Archive for high-latitude PNe. ETHOS 1 stands out as one of the few PNe to have both polar outflows (jets) travelling at $120\\pm10$ km/s and a close binary central star. The lightcurve observed with the Mercator telescope reveals an orbital period of 0.535 days and an extremely large amplitude (0.816 mag) due to irradiation of the companion by a very hot pre-white dwarf. ETHOS 1 further strengthens the long suspected link between binary central stars of planetary nebulae (CSPN) and jets. INT IDS and VLT FORS spectroscopy of the CSPN reveals weak N III, C III and C IV emission lines seen in other close binary CSPN and suggests many CSPN with these weak emission lines are misclassified close binaries. We present VLT FORS imaging and Manchester Echelle Spectrometer long slit observations from which a kinematic model of the nebula is built. An unusual combina...

  15. Economic Analysis of Large-Scale Wind Energy Conversion Systems in Central Anatolian Turkey

    OpenAIRE

    Genc, Mustafa Serdar

    2010-01-01

    Clean and renewable energies obtaining from sunlight, wind or water around the earth do not make a net contribution of carbon dioxide to the atmosphere. Therefore, these energy sources should be used to protect our world, because of global warming and the injurious effects of carbon emissions. And so, it should be estimated the windy and sunny fields in Turkey, the unit cost of energy output of various wind and solar energy conversion systems. Today, wind energy seems to be reasonable due to...

  16. On the Dynamics of Proto-Neutron Star Winds and r-Process Nucleosynthesis

    CERN Document Server

    Panov, I V

    2008-01-01

    We study here the formation of heavy r-process nuclei in the high-entropy neutrino-driven wind environment. In particular, we explore the sensitivity of the element creation in the A > 130 region to the low-temperature behavior of the outflows. For this purpose we employ a simplified model of the dynamics and thermodynamical evolution for radiation dominated, adiabatic outflows. It consists of a first stage of fast, exponential cooling, followed by a second phase of slower evolution, either assuming constant density and temperature or a power-law decay of these quantities. This is supposed to capture the most relevant effects associated with a shock deceleration of supersonic winds caused by the collision with the slower, preceding supernova ejecta. We find that not only the transition temperature between the two expansion phases can make a big difference in the formation of the platinum peak, but also the detailed cooling law during the later phase. Unless the transition temperature and corresponding (free n...

  17. Evolution of Massive Stars Up to the End of Central Oxygen Burning

    OpenAIRE

    Eid, Mounib F. El; Meyer, Bradley S.; The, Lih-Sin

    2004-01-01

    We present a detailed study of the evolution of massive stars of masses 15, 20, 25 and 30 $\\msun$ assuming solar-like initial chemical composition. The stellar sequences were evolved through the advanced burning phases up to the end of core oxygen burning. We present a careful analysis of the physical characteristics of the stellar models. In particular, we investigate the effect of the still unsettled reaction $^{12}$C($\\alpha$,$\\gamma$)$^{16}$O on the advanced evolution by using recent comp...

  18. Hierarchical system of shells blown by wind of Cyg OB1 stars

    International Nuclear Information System (INIS)

    The structure and kinematics of gas-dust complex connected with the Cyg OB1 association and open clusters NGC 6913 and IC 4996 have been investigated. the optical and radio brightness distribution along with the radial velocities field provided by the available observations in Hα, CO, HI and recombination radio lines is analyzed. Several new ring nebulae and/or cavities in CO - distribution around the WR and Of stars are distinguished. An hierarchial system of ''inclosed'' shells is revealed: the common shell around Cyg OB1 consists of two components - the shells around NGC 6913 and IC 4996 with small-size WR and Of ring nebulae inside. Interferometric Hα observations of the region provided the common shell expansion velocity Vexp < or approx. 15 km/s. The origin of the multi-stellar structure of the ISM around Cyg OB1 is discussed

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

    Science.gov (United States)

    Pushpadas, Dhanya; Vethamony, P.; Sudheesh, K.; George, Smitha; Babu, M. T.; Balakrishnan Nair, T. M.

    2010-12-01

    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 mesh covers Goa and the surrounding region. Simulations have been carried out for three different seasons—northeast (NE) monsoon, transition period and southwest (SW) monsoon with appropriate physics options to understand the coastal wind system. The simulated wind speed and direction match well with the observations. The model winds show the presence of a sea breeze during the NE monsoon season and transition period, and its absence during the SW monsoon season. In the winter period, the synoptic flow is northeasterly (offshore) and it weakens the sea breeze (onshore flow) resulting in less diurnal variation, while during the transition period, the synoptic flow is onshore and it intensifies the sea breeze. During the northeast monsoon at an altitude of above 750 m, the wind direction reverses, and this is the upper return current, indicating the vertical extent of the sea breeze. A well-developed land sea breeze circulation occurs during the transition period, with vertical extension of 300 and 1,100 m, respectively.

  20. Supernovae in the Central Parsec: A Mechanism for Producing Spatially Anisotropic Hypervelocity Stars

    CERN Document Server

    Zubovas, Kastytis; Gualandris, Alessia

    2013-01-01

    Several tens of hyper-velocity stars (HVSs) have been discovered escaping our Galaxy. These stars share a common origin in the Galactic centre and are distributed anisotropically in Galactic longitude and latitude. We examine the possibility that HVSs may be created as the result of supernovae occurring within binary systems in a disc of stars around Sgr A* over the last 100 Myr. Monte Carlo simulations show that the rate of binary disruption is ~10^-4 yr^-1, comparable to that of tidal disruption models. The supernova-induced HVS production rate (\\Gamma_HVS) is significantly increased if the binaries are hardened via migration through a gaseous disc. Moderate hardening gives \\Gamma_HVS ~ 2*10^-7 yr^-1 and an estimated population of ~20 HVSs in the last 100 Myr. Supernova-induced HVS production requires the internal and external orbital velocity vectors of the secondary binary component to be aligned when the binary is disrupted. This leaves an imprint of the disc geometry on the spatial distribution of the H...

  1. Variable stars and stellar populations in Andromeda XXV: III. A central cluster or the galaxy nucleus?

    CERN Document Server

    Cusano, Felice; Clementini, Gisella; Cignoni, Michele; Federici, Luciana; Marconi, Marcella; Ripepi, Vincenzo; Musella, Ilaria; Testa, Vincenzo; Carini, Roberta; Faccini, Marco

    2016-01-01

    We present B and V time-series photometry of Andromeda XXV, the third galaxy in our program on the Andromeda's satellites, that we have imaged with the Large Binocular Cameras of the Large Binocular Telescope. The field of Andromeda XXV is found to contain 63 variable stars, for which we present light curves and characteristics of the light variation (period, amplitudes, variability type, mean magnitudes, etc.). The sample includes 58 RR Lyrae variables (46 fundamental-mode $-$ RRab, and 12 first-overtone $-$RRc, pulsators), three anomalous Cepheids, one eclipsing binary system and one unclassified variable. The average period of the RRab stars ($\\langle Pab \\rangle$ = 0.60 $\\sigma=0.04$ days) and the period-amplitude diagram place Andromeda XXV in the class of the Oosterhoff-Intermediate objects. From the average luminosity of the RR Lyrae stars we derive for the galaxy a distance modulus of (m-M)$_0$=$24.63\\pm0.17$ mag. The color-magnitude diagram reveals the presence in Andromeda XXV of a single, metal-poo...

  2. An Analysis of Current and Future Wind Energy Gain Potential for Central Iowa

    OpenAIRE

    Sharifi, Farrokh; Hashemi, Nastaran

    2015-01-01

    Using a significant quantity of fossil fuels has adverse impacts on our lives and will affect future generations. Additionally, there are limited and decreasing numbers of nonrenewable resources around the world. In contrast, renewable resources are not depleted and provide energy with negligible pollution. Wind energy is one of the more common renewable energy resources. This project aims to evaluate Iowa's wind energy potential and to provide suggestions to improve the future well‐being of ...

  3. Two bi-stability jumps in theoretical wind models for massive stars and the implications for luminous blue variable supernovae

    Science.gov (United States)

    Petrov, Blagovest; Vink, Jorick S.; Gräfener, Götz

    2016-05-01

    Luminous blue variables (LBVs) have been suggested to be the direct progenitors of supernova Types IIb and IIn, with enhanced mass loss prior to explosion. However, the mechanism of this mass loss is not yet known. Here, we investigate the qualitative behaviour of theoretical stellar wind mass loss as a function of Teff across two bi-stability jumps in blue supergiant regime and also in proximity to the Eddington limit, relevant for LBVs. To investigate the physical ingredients that play a role in the radiative acceleration we calculate blue supergiant wind models with the CMFGEN non-local thermodynamic equilibrium model atmosphere code over an effective temperature range between 30 000 and 8800 K. Although our aim is not to provide new mass-loss rates for BA supergiants, we study and confirm the existence of two bi-stability jumps in mass-loss rates predicted by Vink et al. However, they are found to occur at somewhat lower Teff (20 000 and 9000 K, respectively) than found previously, which would imply that stars may evolve towards lower Teff before strong mass loss is induced by the bi-stability jumps. When the combined effects of the second bi-stability jump and the proximity to Eddington limit are accounted for, we find a dramatic increase in the mass-loss rate by up to a factor of 30. Further investigation of both bi-stability jumps is expected to lead to a better understanding of discrepancies between empirical modelling and theoretical mass-loss rates reported in the literature, and to provide key inputs for the evolution of both normal AB supergiants and LBVs, as well as their subsequent supernova Type II explosions.

  4. STAR FORMATION IN THE CENTRAL 400 PC OF THE MILKY WAY: EVIDENCE FOR A POPULATION OF MASSIVE YOUNG STELLAR OBJECTS

    International Nuclear Information System (INIS)

    The central kpc of the Milky Way might be expected to differ significantly from the rest of the Galaxy with regard to gasdynamics and the formation of young stellar objects (YSOs). We probe this possibility with mid-infrared observations obtained with Infrared Array Camera and Multiband Imaging Photometer on Spitzer and with Midcourse Space Experiment. We use color-color diagrams and spectral energy distribution (SED) fits to explore the nature of YSO candidates (including objects with 4.5 μm excesses possibly due to molecular emission). There is an asymmetry in the distribution of the candidate YSOs, which tend to be found at negative Galactic longitudes; this behavior contrasts with that of the molecular gas, approximately 2/3 of which is at positive longitudes. The small-scale height of these objects suggests that they are within the Galactic center region and are dynamically young. They lie between two layers of infrared dark clouds and may have originated from these clouds. We identify new sites for this recent star formation by comparing the mid-IR, radio, submillimeter, and methanol maser data. The methanol masers appear to be associated with young, embedded YSOs characterized by 4.5 μm excesses. We use the SEDs of these sources to estimate their physical characteristics; their masses appear to range from ∼10 to ∼20 Msun. Within the central 400 x 50 pc (|l| 03 and |b| sun yr-1. Given that the majority of the sources in the population of YSOs are classified as Stage I objects, we suggest that a recent burst of star formation took place within the last 105 yr. This suggestion is also consistent with estimates of SFRs within the last ∼107 yr showing a peak around 105 yr ago. Lastly, we find that the Schmidt-Kennicutt Law applies well in the central 400 pc of the Galaxy. This implies that star formation does not appear to be dramatically affected by the extreme physical conditions in the Galactic center region.

  5. Nucleosynthesis Modes in the High-Entropy-Wind of Type II Supernovae: Comparison of Calculations with Halo-Star Observations

    CERN Document Server

    Farouqi, K; Mashonkina, L I; Pfeiffer, B; Cowan, J J; Thielemann, F -K; Truran, J W

    2009-01-01

    While the high-entropy wind (HEW) of Type II supernovae remains one of the more promising sites for the rapid neutron-capture (r-) process, hydrodynamic simulations have yet to reproduce the astrophysical conditions under which the latter occurs. We have performed large-scale network calculations within an extended parameter range of the HEW, seeking to identify or to constrain the necessary conditions for a full reproduction of all r-process residuals N_{r,\\odot}=N_{\\odot}-N_{s,\\odot} by comparing the results with recent astronomical observations. A superposition of weighted entropy trajectories results in an excellent reproduction of the overall N_{r,\\odot}-pattern beyond Sn. For the lighter elements, from the Fe-group via Sr-Y-Zr to Ag, our HEW calculations indicate a transition from the need for clearly different sources (conditions/sites) to a possible co-production with r-process elements, provided that a range of entropies are contributing. This explains recent halo-star observations of a clear non-cor...

  6. Nucleosynthesis Modes in The High-Entropy Wind of Type II Supernovae: Comparison of Calculations With Halo-Star Observations

    Science.gov (United States)

    Farouqi, K.; Kratz, K.-L.; Mashonkina, L. I.; Pfeiffer, B.; Cowan, J. J.; Thielemann, F.-K.; Truran, J. W.

    2009-03-01

    While the high-entropy wind (HEW) of Type II supernovae remains one of the more promising sites for the rapid neutron-capture (r-) process, hydrodynamic simulations have yet to reproduce the astrophysical conditions under which the latter occurs. We have performed large-scale network calculations within an extended parameter range of the HEW, seeking to identify or to constrain the necessary conditions for a full reproduction of all r-process residuals N r,sun = N sun-N s,sun by comparing the results with recent astronomical observations. A superposition of weighted entropy trajectories results in an excellent reproduction of the overall N r,sun pattern beyond Sn. For the lighter elements, from the Fe group via Sr-Y-Zr to Ag, our HEW calculations indicate a transition from the need for clearly different sources (conditions/sites) to a possible co-production with r-process elements, provided a range of entropies are contributing. This explains recent halo-star observations of a clear noncorrelation of Zn and Ge and a weak correlation of Sr-Zr with heavier r-process elements. Moreover, new observational data on Ru and Pd also seem to confirm a partial correlation with Sr as well as the main r-process elements (e.g., Eu).

  7. Parameter constraints for high-energy models of colliding winds of massive stars: the case WR 147

    CERN Document Server

    Reimer, A

    2009-01-01

    We explore the ability of high energy observations to constrain orbital parameters of long period massive binary systems by means of an inverse Compton model acting in colliding wind environments. This is particular relevant for (very) long period binaries where orbital parameters are often poorly known from conventional methods, as is the case e.g. for the Wolf-Rayet (WR) star binary system WR 147 where INTEGRAL and MAGIC upper limits on the high-energy emission have recently been presented. We conduct a parameter study of the set of free quantities describing the yet vaguely constrained geometry and respective effects on the non-thermal high-energy radiation from WR 147. The results are confronted with the recently obtained high-energy observations and with sensitivities of contemporaneous high-energy instruments like Fermi-LAT. For binaries with sufficient long periods, like WR 147, gamma-ray attenuation is unlikely to cause any distinctive features in the high-energy spectrum. This leaves the anisotropic ...

  8. The stellar-wind envelope around the supernova XRF/GRB060218/SN2006aj massive progenitor star

    CERN Document Server

    Sonbas, E; Fatkhullin, T A; Sokolov, V V; Castro-Tirado, A J; Postigo, A de Ugarte; Gorosabel, J; Guziy, S; Jelinek, M; Sokolova, T N; Chernenkov, V N

    2008-01-01

    In BTA spectra of the supernova SN2006aj, identified with the X-ray flash (XRF) and gamma-ray burst XRF/GRB060218/SN2006aj, we detected details interpreted as hydrogen lines, which is a sign of stellar-wind envelope around a massive progenitor star of the gamma-ray burst. Results of modeling two early spectra obtained with the BTA in 2.55 and 3.55 days after the explosion of Type Ic supernova SN2006aj (z=0.0331) are presented. The spectra were modeled in the Sobolev approximation with the SYNOW code (Branch et al. 2001; Elmhamdi et al. 2006). In the spectra of the optical afterglow of the X-ray flash XRF/GRB060218 we detected spectral features interpreted as (1) the H_alpha PCyg profile for the velocity 33000 km s$^{-1}$ -- a wide and almost unnoticeable deformation of continuum in the range of $\\simeq5600 - 6600\\AA$ for the first epoch (2.55 days) and (2) a part (``remnant'') of the H_alpha PCyg profile in absorption blueshifted by 24000 km s$^{-1}$ -- a wide spectral feature with a minimum at $\\simeq6100\\AA...

  9. The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

    CERN Document Server

    Cherchneff, Isabelle

    2011-01-01

    Aims. We model the chemistry of the inner wind of the carbon star IRC+10216 and consider the effect of periodic shocks induced by the stellar pulsation on the gas to follow the non-equilibrium chemistry in the shocked gas layers. We consider a very complete set of chemical families, including hydrocarbons and aromatics, hydrides, halogens and phosphorous-bearing species. Derived abundances are compared to the latest observational data from large surveys and Herschel. Results. The shocks induce a non-equilibrium chemistry in the dust formation zone of IRC+10216 where the collision destruction of CO in the post-shock gas triggers the formation of O-bearing species (H2O, SiO). Most of the modelled abundances agree very well with the latest values derived from Herschel data on IRC+10216. Hydrides form a family of abundant species that are expelled to the intermediate envelope. In particular, HF traps all the atomic fluorine in the dust formation zone. Halogens are also abundant and their chemistry is independent ...

  10. The central dark matter content of early-type galaxies: scaling relations and connections with star formation histories

    CERN Document Server

    Napolitano, Nicola R; Tortora, Crescenzo

    2010-01-01

    We examine correlations between the masses, sizes, and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar populations models. We confirm an anti-correlation between size and stellar age, and survey for trends with the central content of dark matter (DM). An average relation between central DM density and galaxy size of ~ Reff^-2 provides the first clear indication of cuspy DM haloes in these galaxies -- akin to standard LCDM haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as expected, deviating from suggestions of a universal halo profile for dwarf and late-type galaxies. We introduce a new fundamental constraint on galaxy formation by finding that the central DM fraction decreases with stellar age. This result is only partially explained by the size-age dependencies, and the residual trend is in the opposite direction to basic DM halo expectations. Therefore we suggest that there may be a con...

  11. New X-ray observations of IQ Aurigae and alpha2 Canum Venaticorum - Probing the magnetically channelled wind shock model in A0p stars

    CERN Document Server

    Robrade, J

    2011-01-01

    We present new X-ray observations of the A0p stars alpha^2 CVn (log Lx < 26.0 erg/s) and IQ Aur (log Lx = 29.6 erg/s) and find that their X-ray luminosities differ by at least three orders of magnitude. IQ Aur possesses a strong cool plasma component with X-ray emitting regions located well above the stellar surface, but also significant amounts of hot plasma. Further, a large X-ray flare is detected from IQ Aur, implying the presence of magnetic reconnection. Our comparison study of similar stars indicates that the occurrence of X-ray emission generated by magnetically channelled wind shocks (MCWS) strongly depends on stellar properties. X-ray emission is preferably generated by more luminous and massive objects such as IQ Aur. The MCWS scenario can consistently describe the X-ray emission of these A0p stars, assuming that the very strong magnetic confinement of the stellar wind has led to the build up of a rigidly rotating disk around the star, where magnetic reconnection and centrifugal breakout events ...

  12. The warm circumstellar envelope and wind of the G9 IIb star HR 6902

    CERN Document Server

    Kirsch, T; Reimers, D

    2001-01-01

    IUE observations of the eclipsing binary system HR 6902 obtained at various epochs spread over four years indicate the presence of warm circumstellar material enveloping the G9 IIb primary. The spectra show Si IV and C IV absorption up to a distance of 3.3 giant radii (R_g}. Line ratio diagnostics yields an electron temperature of ~ 78000 K which appears to be constant over the observed height range. Applying a least square fit absorption line analysis we derive column densities as a function of height. We find that the inner envelope (< 3 R_g) of the bright giant is consistent with a hydrostatic density distribution. The derived line broadening velocity of ~ 70 kms^{-1} is sufficient to provide turbulent pressure support for the required scale height. However, an improved agreement with observations over the whole height regime including the emission line region is obtained with an outflow model. We demonstrate that the common beta power-law as well as a P \\propto rho wind yield appropriate fit models. Ad...

  13. The Nature and Frequency of Outflows from Stars in the Central Orion Nebula Cluster

    CERN Document Server

    O'Dell, C R; Henney, W J; Peimbert, M; Garcia-Diaz, 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 a 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 blue shifted because the redshifted outflows pass into the optically thick Photon Dominated Region behind the nebula. There are two regions from which optical outflow...

  14. Comprehensive modelling of the planetary nebula LMC-SMP 61 and its [WC]-type central star

    CERN Document Server

    Stasinska, G; Peña, M; Hamann, W R; Koesterke, L; Szczerba, R

    2003-01-01

    We present a comprehensive study of the Magellanic Cloud planetary nebula SMP 61 and of its nucleus, a Wolf-Rayet type star classified [WC 5-6]. We have performed a detailed spectral analysis of the central star, using the Potsdam code for expanding atmospheres in non-LTE. The fluxes from the model stellar atmosphere were used to compute photoionization models of the nebula. All the available observations, within their error bars, were used to constrain these models. We find that the ionizing fluxes predicted by the stellar model are basically consistent with the fluxes needed by the photoionization model to reproduce the nebular emission, within the error margins. However, there are indications that the stellar model overestimates the number and hardness of Lyman continuum photons. The photoionization models imply a clumped density structure of the nebular material. The observed CIII] 1909/CII 4267 line ratio implies the existence of carbon-rich clumps in the nebula. Such clumps are likely produced by stella...

  15. Fueling the central engine of radio galaxies. III. Molecular gas and star formation efficiency of 3C 293

    Science.gov (United States)

    Labiano, A.; García-Burillo, S.; Combes, F.; Usero, A.; Soria-Ruiz, R.; Piqueras López, J.; Fuente, A.; Hunt, L.; Neri, R.

    2014-04-01

    Context. Powerful radio galaxies show evidence of ongoing active galactic nuclei (AGN) feedback, mainly in the form of fast, massive outflows. But it is not clear how these outflows affect the star formation of their hosts. Aims: We investigate the different manifestations of AGN feedback in the evolved, powerful radio source 3C 293 and their impact on the molecular gas of its host galaxy, which harbors young star-forming regions and fast outflows of H i and ionized gas. Methods: We study the distribution and kinematics of the molecular gas of 3C 293 using high spatial resolution observations of the 12CO(1-0) and 12CO(2-1) lines, and the 3 mm and 1 continuum taken with the IRAM Plateau de Bure interferometer. We mapped the molecular gas of 3C 293 and compared it with the dust and star-formation images of the host. We searched for signatures of outflow motions in the CO kinematics, and re-examined the evidence of outflowing gas in the H i spectra. We also derived the star formation rate (SFR) and star formation efficiency (SFE) of the host with all available SFR tracers from the literature, and compared them with the SFE of young and evolved radio galaxies and normal star-forming galaxies. Results: The 12CO(1-0) emission line shows that the molecular gas in 3C 293 is distributed along a massive (M(H2) ~ 2.2 × 1010M⊙) ~24″(21 kpc-) diameter warped disk, that rotates around the AGN. Our data show that the dust and the star formation are clearly associated with the CO disk. The 12CO(2-1) emission is located in the inner 7 kpc (diameter) region around the AGN, coincident with the inner part of the 12CO(1-0) disk. Both the 12CO(1-0) and 12CO(2-1) spectra reveal the presence of an absorber against the central regions of 3C 293 that is associated with the disk. We do not detect any fast (≳500 km s-1) outflow motions in the cold molecular gas. The host of 3C 293 shows an SFE consistent with the Kennicutt-Schmidt law of normal galaxies and young radio galaxies, and it

  16. Wind energy development in the East Central Europe: divergences, constraints, and directions

    Czech Academy of Sciences Publication Activity Database

    Cetkovský, Stanislav; Frantál, Bohumil

    Washington: Association of American Geographers, 2010. s. 25-25. ISSN N. [2010 Association of American Geographers Annual Meeting. 14.04.2010-18.04.2010, Washington] R&D Projects: GA AV ČR(CZ) KJB700860801 Institutional research plan: CEZ:AV0Z30860518 Keywords : wind energy * renewable energy * Czech Republic Subject RIV: DE - Earth Magnetism, Geodesy, Geography

  17. Wind-driven estuarine turbidity maxima in Mandovi Estuary, central west coast of India

    Indian Academy of Sciences (India)

    Pratima M Kessarkar; V Purnachandra Rao; R Shynu; Ishfaq Mir Ahmad; Prakash Mehra; G S Michael; D Sundar

    2009-08-01

    Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station are ∼20mg/l, 5mg/l, 19mg/l and 5mg/l for June–September, October–January, February–April and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations of the estuary are at least two orders of magnitude greater than those at the river-end during the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the same location in two periods, interrupted by a period with very low SPM concentrations. The ETM occurring in June–September is associated with low salinities; its formation is attributed to the interactions between strong southwesterly winds (5.1–5.6ms−1) and wind-induced waves and tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring in February–April is associated with high salinity and is conspicuous. The strong NW and SW winds (3.2–3.7ms−1) and wind-driven waves and currents seem to have acted effectively at the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears nearly same as that of trade winds and cannot be underestimated in sediment resuspension and deposition.

  18. Wind-driven estuarine turbidity maxima in Mandovi Estuary, central west coast of India

    Science.gov (United States)

    Kessarkar, Pratima M.; Purnachandra Rao, V.; Shynu, R.; Ahmad, Ishfaq Mir; Mehra, Prakash; Michael, G. S.; Sundar, D.

    2009-08-01

    Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station are ˜20mg/l, 5mg/l, 19mg/l and 5mg/l for June-September, October-January, February-April and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations of the estuary are at least two orders of magnitude greater than those at the river-end during the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the same location in two periods, interrupted by a period with very low SPM concentrations. The ETM occurring in June-September is associated with low salinities; its formation is attributed to the interactions between strong southwesterly winds (5.1-5.6ms-1) and wind-induced waves and tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring in February-April is associated with high salinity and is conspicuous. The strong NW and SW winds (3.2-3.7ms-1) and wind-driven waves and currents seem to have acted effectively at the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears nearly same as that of trade winds and cannot be underestimated in sediment resuspension and deposition

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

    Energy Technology Data Exchange (ETDEWEB)

    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. Mining the HST "Advanced Spectral Library (ASTRAL)": Winds of the Evolved M Stars Alpha Ori (M2 Iab) and Gamma Cru (M3.4 III)

    Science.gov (United States)

    Carpenter, Kenneth G.; Nielsen, Krister E.; Kober, Gladys V.; Ayres, Thomas R.

    2015-01-01

    The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) is an HST Cycle 18 Treasury Program that collected a definitive set of representative, high-resolution (R=30,000-100,000) and high signal/noise (S/N>100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and through the ASTRAL website at the University of Colorado at http://casa.colorado.edu/~ayres/ASTRAL/ and will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years. In this paper, we examine the wealth of wind diagnostics contained in the very rich spectra of the two evolved M stars in the sample, the M3.4 III giant Gamma Crucis (GaCrux) and the M2 Iab supergiant Alpha Orionis (Betelgeuse) and characterize the winds at the time of these STIS observations in 2011 and compare the results with those obtained from more limited data taken at earlier epochs with HST/GHRS and IUE. In particular we study the variation of the numerous Fe II profiles with intrinsic strength in the two stars. The shifting wavelengths of the wind absorptions relative to the emission peaks and the changes in relative strengths of the emission peaks reflect the acceleration of the wind from the base of the chromosphere. Although the characteristics of the Gamma Cru wind are relatively stable with time, the Alpha Ori wind outflow appears significantly smaller than seen by Carpenter et al. (1997, ApJ, 479, 970) in GHRS observations taken in 1992 (and in earlier IUE observations). There might in fact be evidence in these STIS spectra that the outflow has turned into an inflow, as reported at epochs prior to IUE by Boesgaard and Magnan (1975 ApJ 198, 369) and Boesgaard (1979 ApJ 232, 485) based on a limited number of lines in the extreme blue end of ground-based spectra.

  1. The central star of the planetary nebula lmc-n66: a Massive accreting white dwarf?

    Directory of Open Access Journals (Sweden)

    M. Peña

    2004-01-01

    Full Text Available La estrella central del sistema PN LMC - N66 present o una impresionante transferencia de masa en 1993 - 1994 y regres o a su condici on inicial alrededor de 8 a~nos m as tarde. Su espectro se parece al de una estrella WN4.5 y es la unica estrella central con rmada de nebulosas planetarias que posee este tipo de espectro. Presentamos el an alisis reciente de los par ametros para la estrella central llevado a cabo por Hamann et al. (2003 que encontraron que durante la transferencia de masa la luminosidad bolom etrica se increment o en un factor mayor que 6. Discutimos los posibles escenarios que fueron propuestos para explicar los excepcionales par ametros estelares y el mecanismo de transferencia de masa. Las caracter sticas estelares, la morfolog a y la cinem atica de la nebulosa planetaria sugieren la presencia de un sistema binario (una estrella masiva con una compa~nera menos masiva o una enana blanca que acreta la materia en un sistema de binarias cercanas, siendo estos los casos que contradicen de manera menos severa las restricciones observacionales.

  2. Molecular gas and triggered star formation surrounding Wolf-Rayet stars

    CERN Document Server

    Liu, Tie; Zhang, Huawei

    2012-01-01

    The environments surrounding nine Wolf-Rayet stars were studied in molecular emission. Expanding shells were detected surrounding these WR stars (see left panels of Figure 1). The average masses and radii of the molecular cores surrounding these WR stars anti-correlate with the WR stellar wind velocities (middle panels of Figure 1), indicating the WR stars has great impact on their environments. The number density of Young Stellar Objects (YSOs) is enhanced in the molecular shells at $\\sim$5 arcmin from the central WR star (lower-right panel of Figure 1). Through detailed studies of the molecular shells and YSOs, we find strong evidences of triggered star formation in the fragmented molecular shells (\\cite[Liu et al. 2010]{liu_etal12}

  3. GTC/OSIRIS observations of RWT 152, a case study of a planetary nebula with an sdO central star

    CERN Document Server

    Aller, A; Olguín, L; Solano, E; Ulla, A

    2015-01-01

    RWT 152 is one of the few planetary nebula with an sdO central star. We present subarcsecond red tunable filter imaging and intermediate-resolution, long-slit spectroscopy of RWT 152, obtained with OSIRIS/GTC, which allow us to describe in detail its morphology and to obtain its physical conditions and chemical abundances.

  4. Roadmap to the deployment of offshore wind energy in the Central and Southern North Sea (2020-2030)

    International Nuclear Information System (INIS)

    This Roadmap represents the final deliverable of the WINDSPEED project. It has a dual objective. Firstly, it aims to present an ambitious but realistic target for offshore wind with minimum negative impacts on other sea functions present in the Central and Southern North Sea basin in the time frame to 2030. Secondly, it aims to identify actions and milestones required to achieve this target. The North Sea countries - Belgium, Denmark, Germany, the Netherlands, Norway and the UK - are facing a number of challenges and opportunities in their quest for rapid expansion of offshore wind energy in the Central and Southern North Sea basin. The WINDSPEED project has carried out an assessment of (ambitious but realistic) deployment potentials under different scenarios to gain better insight into how key uncertainties can impact on OWE developments. An early understanding of how different development perspectives influence challenges and opportunities, as well as uncertainties, will allow for better adaptation of policies and approaches to promote large scale offshore wind energy (OWE). This is particularly important at a time when OWE is strongly driven by EU and national policy needs in attempting to reach overall policy goals of a competitive, secure and sustainable energy system. There is ample space in the Central and Southern North Sea. But many attractive areas for developing OWE within reasonable cost ranges are already occupied by other sea users. Moving OWE further from shore and into deeper waters not only drives costs up, but also raises the issue of the availability of deep sea technology components and the need for an offshore grid. To date, the North Sea countries will have developed a capacity of around 2 GW in the North Sea. It has taken a decade to get this far. Important lessons are being learnt and these must be taken into account in the development of OWE towards 2030. The WINDSPEED project concludes that a capacity of 135 GW of OWE in the Central and

  5. Mass-loading in Galactic Winds: the Role of Photoevaporation and Wind Ablation

    Science.gov (United States)

    Yeh, S. C. C.; Matzner, C. D.

    2012-09-01

    We present a dynamical scenario of instantaneous dense gas entrainment by stellar winds in a wind-dominated HII region. Stellar winds and radiation pressure will become more important in an HII region as the central star or cluster is sufficiently luminous, therefore the region is windswept instead of photoevaporation-dominated. In our model, a cloud is smaller than the region as a whole, hence its mass injection occurs through either ordinary photoevaporation or wind ablation. We predict that the instantaneous wind ablation will cause strong mixing between hot winds and warm gas, and the mass injection rate of the wind-confined photoevaporated flow is higher than that of the ionizing source.

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

    Science.gov (United States)

    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.; Harrison, Fiona A.; Krivonos, Roman; Mori, Kaya; Natalucci, Lorenzo; Stern, Daniel; Tomsick, John A.; Zhang, William W.

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  8. Wind-driven estuarine turbidity maxima in Mandovi Estuary, central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Kessarkar, P.M.; Rao, V.P.; Shynu, R.; Ahmad; Mehra, P.; Michael, G.S.; Sundar, D.

    -driven estuarine turbidity maxima in Mandovi Estuary, central west coast of India Pratima M Kessarkar, V Purnachandra Rao ∗ , R Shynu, Ishfaq Mir Ahmad, Prakash Mehra, G S Michael and D Sundar National Institute of Oceanography, Dona Paula 403 004, Goa, India. ∗ e...

  9. Analysis of chemical abundances in planetary nebulae with [WC] central stars. I. Line intensities and physical conditions

    Science.gov (United States)

    García-Rojas, J.; Peña, M.; Morisset, C.; Mesa-Delgado, A.; Ruiz, M. T.

    2012-02-01

    Context. Planetary nebulae (PNe) around Wolf-Rayet [WR] central stars ([WR]PNe) constitute a particular photoionized nebula class that represents about 10% of the PNe with classified central stars. Aims: We analyse deep high-resolution spectrophotometric data of 12 [WR] PNe. This sample of [WR]PNe represents the most extensive analysed so far, at such high spectral resolution. We aim to select the optimal physical conditions in the nebulae to be used in ionic abundance calculations that will be presented in a forthcoming paper. Methods: We acquired spectra at Las Campanas Observatory with the 6.5-m telescope and the Magellan Inamori Kyocera (MIKE) spectrograph, covering a wavelength range from 3350 Å to 9400 Å. The spectra were exposed deep enough to detect, with signal-to-noise ratio higher than three, the weak optical recombination lines (ORLs) of O ii, C ii, and other species. We detect and identify about 2980 emission lines, which, to date, is the most complete set of spectrophotometric data published for this type of objects. From our deep data, numerous diagnostic line ratios for Te and ne are determined from collisionally excited lines (CELs), ORLs, and continuum measurements (H i Paschen continuum in particular). Results: Densities are closely described by the average of all determined values for objects with ne behaviour of both temperatures agrees with the predictions of the temperature fluctuations paradigm, owing to the large errors in Te(H i). We do not find any evidence of low-temperature, high-density clumps in our [WR]PNe from the analysis of faint O ii and N ii plasma diagnostics, although uncertainties dominate the observed line ratios in most objects. The behaviour of Te([O iii])/Te([N ii]), which is smaller for high ionization degrees, can be reproduced by a set of combined matter-bounded and radiation-bounded models, although, for the smallest temperature ratios, a too high metallicity seem to be required. Based on data obtained at Las

  10. A Central Flash at an Occultation of a Bright Star by Pluto Soon Before New Horizons' Flyby

    Science.gov (United States)

    Pasachoff, Jay M.; Babcock, Bryce A.; Durst, Rebecca F.; Seeger, Christina H.; Levine, Stephen E.; Bosh, Amanda S.; Sickafoose, Amanda A.; Person, Michael J.; Abe, Fumio; Suzuki, Daisuke; Nagakane, Masayuki; Tristam, Paul J.

    2015-11-01

    From the Mt. John Observatory, New Zealand, we were so close to the center of the occultation path on 29 June 2015 UTC that we observed a modest central flash from the focusing of starlight from a 12th-magnitude star. The star was one of the brightest ever in our years of continual monitoring that started in 2002. At the time of Pluto's perihelion in 1989, it was feared from models that Pluto's atmosphere might collapse by now, a motivation for the timely launch of New Horizons; some models now allow Pluto to retain its atmosphere throughout its orbit.We used our frame-transfer CCD at 10 Hz with GPS timing on the 1-m McLellan telescope of Canterbury U. We also observed with a Lowell Obs. infrared camera on the "AAVSO" 0.6-m Optical Craftsman telescope; and obtained 3-color photometry at a slower cadence on a second 0.6-m telescope. We coordinated with the overflight of SOFIA and its 2.5-m telescope, which benefited from last-minute astrometry, and the Auckland Observatory's and other ground-based telescopes.Our light curves show a modest central flash; our tentative geometrical solution shows that we were only about 50 km from the occultation path's centerline. The flash is from rays lower than otherwise accessible in Pluto's atmosphere. Our light curves, at such high cadence that we see spikes caused by atmospheric effects that we had not seen so well since our 2002 Mauna Kea occultation observations, show that Pluto's atmosphere had not changed drastically since our previous year's observations. Our data provide a long-term context for New Horizon's highly-detailed observations of Pluto's atmosphere in addition to providing a chord for the geometrical solution that includes SOFIA's observations.Our observations were supported by NASA Planetary Astronomy grants NNX12AJ29G to Williams College, NNX15AJ82G to Lowell Observatory, and NNX10AB27G to MIT, and by the National Research Foundation of South Africa. We are grateful to Alan Gilmore, Pam Kilmartin, Robert Lucas

  11. Recent star formation in the inner Galactic Bulge seen by ISOGAL II -- The Central Molecular Zone

    CERN Document Server

    Immer, K; Omont, A; Menten, K M

    2011-01-01

    We present 5--38 $\\mu$m spectroscopic observations of a sample of 68 ISOGAL sources with unknown natures, taken with the Spitzer Infrared Spectrograph. Based on the characteristics and the slope of their spectra we classified the sources as young or late-type evolved objects. These sources were selected to test selection criteria based on the ISOGAL [7]--[15] color and the spatial extent parameter $\\sigma_{\\rm 15}$. We revised these criteria until they reliably distinguished between young and late-type evolved objects and then applied them to all ISOGAL sources in the central molecular zone (CMZ), resulting in the selection of 485 sources believed to be young. Furthermore, we added 656 Midcourse Space Experiment (MSX) sources to the CMZ sample that fulfilled $F_{\\rm E}/F_{\\rm D} > 2$ with $F{\\rm D}$ and $F_{\\rm E}$ being the flux densities in the D (15 $\\mu$m) and E (21 $\\mu$m) bands. After obtaining $\\frac{L_{\\rm bol}}{F_{\\rm 15}}$ conversion factors, we calculated the bolometric luminosity, $L_{\\rm bol}$, v...

  12. Discovery of a magnetic field in the rapidly rotating O-type secondary of the colliding-wind binary HD 47129 (Plaskett's star)

    Science.gov (United States)

    Grunhut, J. H.; Wade, G. A.; Leutenegger, M.; Petit, V.; Rauw, G.; Neiner, C.; Martins, F.; Cohen, D. H.; Gagné, M.; Ignace, R.; Mathis, S.; de Mink, S. E.; Moffat, A. F. J.; Owocki, S.; Shultz, M.; Sundqvist, J.; MiMeS Collaboration

    2013-01-01

    We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the Télescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of -810 ± 150 and +680 ± 190 G, implying a minimum surface dipole polar strength of 2850 ± 500 G. In contrast, we derive an upper limit (3σ) to the primary's surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission - previously interpreted as a consequence of colliding stellar winds - in this context. We conclude that HD 47129 represents a heretofore unique stellar system - a close, massive binary with a rapidly rotating, magnetized component - that will be a rich target for further study.

  13. About Galilean transformation on a mass variable system and two bodies gravitational system with variable mass and damping-anti damping effect due to star wind

    CERN Document Server

    Lopez, G V

    2012-01-01

    We make an observation about Galilean transformation on a 1-D mass variable systems which leads us to the right way to deal with these systems. Then using this observation, we study two-bodies gravitational problem where the mass of one of the bodies varies and suffers a damping-anti damping effect due to star wind during its motion. for this system, a constant of motion, a Lagrangian and a Hamiltonian are given for the radial motion, and the period of the body is studied using the constant of motion of the system. An application to the comet motion is given, using the comet Halley as an example.

  14. The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence

    OpenAIRE

    Bestenlehner, J. M.; Gräfener, G.; Vink, J. S.; Najarro, F.; Koter, de, A.; Sana, H.; Evans, C J; Crowther, P. A.; Hénault-Brunet, V.; Herrero, A.; Langer, N.; Schneider, F.R.N.; Simón-Díaz, S.; Taylor, W.D.; N. R. Walborn

    2014-01-01

    The evolution and fate of very massive stars (VMS) is tightly connected to their mass-loss properties. Their initial and final masses differ significantly as a result of mass loss. VMS have strong stellar winds and extremely high ionising fluxes, which are thought to be critical sources of both mechanical and radiative feedback in giant H ii regions. However, how VMS mass-loss properties change during stellar evolution is poorly understood. In the framework of the VLT-Flames Tarantula Survey ...

  15. Evaluation of the variability of wind speed at different heights and its impact on the receiver efficiency of central receiver systems

    Science.gov (United States)

    Delgado, A.; Gertig, C.; Blesa, E.; Loza, A.; Hidalgo, C.; Ron, R.

    2016-05-01

    Typical plant configurations for Central Receiver Systems (CRS) are comprised of a large field of heliostats which concentrate solar irradiation onto the receiver, which is elevated hundreds of meters above the ground. Wind speed changes with altitude above ground, impacting on the receiver thermal efficiency due to variations of the convective heat losses. In addition, the physical properties of air vary at high altitudes to a significant degree, which should be considered in the thermal losses calculation. DNV GL has long-reaching experience in wind energy assessment with reliable methodologies to reduce the uncertainty of the determination of the wind regime. As a part of this study, DNV GL estimates the wind speed at high altitude for different sites using two methods, a detailed estimation applying the best practices used in the wind energy sector based on measurements from various wind sensors and a simplified estimation applying the power law (1, 2) using only one wind measurement and a representative value for the surface roughness. As a result of the study, a comparison of the wind speed estimation considering both methods is presented and the impact on the receiver performance for the evaluated case is estimated.

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

    Science.gov (United States)

    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

  17. A photometric and kinematic study of the stars and interstellar medium in the central two kpc of NGC 3379

    CERN Document Server

    Pastoriza, M G; Ferrari, F; Macchetto, F D; Caon, N; Pastoriza, Miriani G.; Winge, Claudia; Ferrari, Fabricio; Caon, Nicola

    1999-01-01

    HST images of NGC 3379 show that the V and I luminosity profiles in the inner 13 arcsec of this E1 galaxy are represented by two different components: a stellar bulge following a Sersic Law with exponent n = 2.36, and a central core (r < 0.7 arcsec) with a characteristic "cuspy" profile. Subtraction of the underlying stellar component represented by the fitted Sersic profile revealed the presence of a small (r ~ 105 pc) dust disk of about 150 solar masses, oriented at PA = 125 degrees and inclined ~ 77 degrees with respect to the line of sight. The same absorption structure is detected in the color-index (V-I) image. The stellar rotation in the inner 20 arcsec is well represented by a parametric planar disk model, inclined ~ 26 degrees relative to the plane of the sky, and apparent major axis along PA ~ 67 degrees. The gas velocity curves in the inner 5 arcsec show a steep gradient, indicating that the gas rotates much faster than the stars, although in the same direction. The velocity field of the gaseous...

  18. Star Formation in the Central 400 pc of the Milky Way: Evidence for a Population of Massive YSOs

    CERN Document Server

    Yusef-Zadeh, F; Arendt, R G; Whitney, B; Rieke, G; Wardle, M; Hinz, J L; Stolovy, S; Lang, C C; Burton, M G; Ramírez, S

    2009-01-01

    The central kpc of the Milky Way might be expected to differ significantly from the rest of the Galaxy with regard to gas dynamics and the formation of YSOs. We probe this possibility with mid-infrared observations obtained with IRAC and MIPS on Spitzer and with MSX. We use color-color diagrams and SED fits to explore the nature of YSO candidates (including objects with 4.5 micron excesses possibly due to molecular emission). There is an asymmetry in the distribution of the candidate YSOs, which tend to be found at negative Galactic longitudes; this behavior contrasts with that of the molecular gas, approximately 2/3 of which is at positive longitudes. The small scale height of these objects suggests that they are within the Galactic center region and are dynamically young. They lie between two layers of infrared dark clouds and may have originated from these clouds. We identify new sites for this recent star formation. The methanol masers appear to be associated with young, embedded YSOs characterized by 4.5...

  19. Dynamic atmospheres and winds of cool luminous giants, I. Al$_2$O$_3$ and silicate dust in the close vicinity of M-type AGB stars

    CERN Document Server

    Höfner, Susanne; Aringer, Bernhard; Ahuja, Rajeev

    2016-01-01

    High spatial resolution techniques have given valuable insights into the mass loss mechanism of AGB stars, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust. Observations indicate that Al$_2$O$_3$ condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al$_2$O$_3$ grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. We have constructed a new generation of Dynamic Atmosphere & Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth & evaporation for both Al$_2$O$_3$ and Fe-free silicates (Mg$_2$SiO$_4$). The equations describing these dust species are solved in the framework of a frequency-dependent radiation-hydrodynamical model for the atmosphere & wind s...

  20. Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tau as seen by Herschel/HIFI

    CERN Document Server

    Decin, L; De Beck, E; Lombaert, R; de Koter, A; Waters, L B F M

    2010-01-01

    During their asymptotic giant branch, evolution low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the high-resolution HIFI spectrometer onboard Herschel. We report on the first detection of H_2^{16}O and the rarer isotopologues H_2^{17}O and H_2^{18}O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6x10^{-5}, and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H_2O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12CO, 13CO, 28SiO, 29SiO, 30SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized...

  1. Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5

    CERN Document Server

    Whitaker, Katherine E; van Dokkum, Pieter G; Franx, Marijn; van der Wel, Arjen; Brammer, Gabriel; Forster-Schreiber, Natascha M; Giavalisco, Mauro; Labbe, Ivo; Momcheva, Ivelina G; Nelson, Erica J; Skelton, Rosalind

    2016-01-01

    In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at 0.50.5 dex from z~2 to z~0.7. Neither a compact galaxy size nor a high n are sufficient to assess the likelihood of quiescence for the average galaxy; rather, it is the combination of these two parameters together with stellar mass that results in a unique quenching threshold in central density or velocity.

  2. (F)UV spectroscopy of the hybrid PG1159-type central stars of the planetary nebulae NGC 7094 and Abell43

    International Nuclear Information System (INIS)

    Hydrogen-deficient post-AGB stars have experienced a late helium-shell flash that mixes the hydrogen-rich envelope and the helium-rich intershell (between hydrogen- and helium-burning shell). The amount of hydrogen remaining in the stellar envelope depends on the particular moment when this late thermal pulse occurs. Previous spectral analyses of hydrogen-deficient post-AGB stars, namely PG 1159-035 and the central stars of the planetary nebulae (CSPN) K 1-16, NGC 7094, and Abell 78, surprisingly revealed strong iron deficiencies of up to 1 dex. A possible explanation may be neutron captures due to an efficient s-process on the AGB that transformed iron into heavier elements. An increased abundance of these would be a strong indication for this scenario. Since reliable atomic data for highly ionized species heavier than iron is only available for cobalt and nickel, we can presently determine only the nickel abundance. We performed a detailed spectral analysis by means of NLTE model-atmosphere techniques based on high-resolution UV observations of the two PG 1159-type CSPN of NGC 7094 and Abell 43 which are spectroscopic twins, i.e., they exhibit very similar spectra. We confirmed a strong iron-deficiency of at least one dex in both stars. The search for nickel lines in their UV spectra was entirely negative. We find that both stars are even nickel deficient by about one dex.

  3. (F)UV spectroscopy of the hybrid PG1159-type central stars of the planetary nebulae NGC 7094 and Abell43

    Energy Technology Data Exchange (ETDEWEB)

    Ziegler, M; Rauch, T; Werner, K [Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Tuebingen (Germany); Koesterke, L [Texas Advanced Computing Center, University of Texas, Austin (United States); Kruk, J W, E-mail: ziegler@astro.uni-tuebingen.d [Department of Physics and Astronomy, Johns Hopkins University, Baltimore (United States)

    2009-06-01

    Hydrogen-deficient post-AGB stars have experienced a late helium-shell flash that mixes the hydrogen-rich envelope and the helium-rich intershell (between hydrogen- and helium-burning shell). The amount of hydrogen remaining in the stellar envelope depends on the particular moment when this late thermal pulse occurs. Previous spectral analyses of hydrogen-deficient post-AGB stars, namely PG 1159-035 and the central stars of the planetary nebulae (CSPN) K 1-16, NGC 7094, and Abell 78, surprisingly revealed strong iron deficiencies of up to 1 dex. A possible explanation may be neutron captures due to an efficient s-process on the AGB that transformed iron into heavier elements. An increased abundance of these would be a strong indication for this scenario. Since reliable atomic data for highly ionized species heavier than iron is only available for cobalt and nickel, we can presently determine only the nickel abundance. We performed a detailed spectral analysis by means of NLTE model-atmosphere techniques based on high-resolution UV observations of the two PG 1159-type CSPN of NGC 7094 and Abell 43 which are spectroscopic twins, i.e., they exhibit very similar spectra. We confirmed a strong iron-deficiency of at least one dex in both stars. The search for nickel lines in their UV spectra was entirely negative. We find that both stars are even nickel deficient by about one dex.

  4. An extensive spectroscopic time-series of three Wolf-Rayet stars. I. The lifetime of large-scale structures in the wind of WR 134

    Science.gov (United States)

    Aldoretta, E. J.; St-Louis, N.; Richardson, N. D.; Moffat, A. F. J.; Eversberg, T.; Hill, G. M.; Shenar, T.; Artigau, É.; Gauza, B.; Knapen, J. H.; Kubát, J.; Kubátová, B.; Maltais-Tariant, R.; Muñoz, M.; Pablo, H.; Ramiaramanantsoa, T.; Richard-Laferrière, A.; Sablowski, D. P.; Simón-Díaz, S.; St-Jean, L.; Bolduan, F.; Dias, F. M.; Dubreuil, P.; Fuchs, D.; Garrel, T.; Grutzeck, G.; Hunger, T.; Küsters, D.; Langenbrink, M.; Leadbeater, R.; Li, D.; Lopez, A.; Mauclaire, B.; Moldenhawer, T.; Potter, M.; dos Santos, E. M.; Schanne, L.; Schmidt, J.; Sieske, H.; Strachan, J.; Stinner, E.; Stinner, P.; Stober, B.; Strandbaek, K.; Syder, T.; Verilhac, D.; Waldschläger, U.; Weiss, D.; Wendt, A.

    2016-05-01

    During the summer of 2013, a 4-month spectroscopic campaign took place to observe the variabilities in three Wolf-Rayet stars. The spectroscopic data have been analyzed for WR 134 (WN6b), to better understand its behaviour and long-term periodicity, which we interpret as arising from corotating interaction regions (CIRs) in the wind. By analyzing the variability of the He II λ5411 emission line, the previously identified period was refined to P = 2.255 ± 0.008 (s.d.) days. The coherency time of the variability, which we associate with the lifetime of the CIRs in the wind, was deduced to be 40 ± 6 days, or ˜ 18 cycles, by cross-correlating the variability patterns as a function of time. When comparing the phased observational grayscale difference images with theoretical grayscales previously calculated from models including CIRs in an optically thin stellar wind, we find that two CIRs were likely present. A separation in longitude of Δφ ≃ 90° was determined between the two CIRs and we suggest that the different maximum velocities that they reach indicate that they emerge from different latitudes. We have also been able to detect observational signatures of the CIRs in other spectral lines (C IV λλ5802,5812 and He I λ5876). Furthermore, a DAC was found to be present simultaneously with the CIR signatures detected in the He I λ5876 emission line which is consistent with the proposed geometry of the large-scale structures in the wind. Small-scale structures also show a presence in the wind, simultaneously with the larger scale structures, showing that they do in fact co-exist.

  5. An extensive spectroscopic time series of three Wolf-Rayet stars - I. The lifetime of large-scale structures in the wind of WR 134

    Science.gov (United States)

    Aldoretta, E. J.; St-Louis, N.; Richardson, N. D.; Moffat, A. F. J.; Eversberg, T.; Hill, G. M.; Shenar, T.; Artigau, É.; Gauza, B.; Knapen, J. H.; Kubát, J.; Kubátová, B.; Maltais-Tariant, R.; Muñoz, M.; Pablo, H.; Ramiaramanantsoa, T.; Richard-Laferrière, A.; Sablowski, D. P.; Simón-Díaz, S.; St-Jean, L.; Bolduan, F.; Dias, F. M.; Dubreuil, P.; Fuchs, D.; Garrel, T.; Grutzeck, G.; Hunger, T.; Küsters, D.; Langenbrink, M.; Leadbeater, R.; Li, D.; Lopez, A.; Mauclaire, B.; Moldenhawer, T.; Potter, M.; dos Santos, E. M.; Schanne, L.; Schmidt, J.; Sieske, H.; Strachan, J.; Stinner, E.; Stinner, P.; Stober, B.; Strandbaek, K.; Syder, T.; Verilhac, D.; Waldschläger, U.; Weiss, D.; Wendt, A.

    2016-08-01

    During the summer of 2013, a 4-month spectroscopic campaign took place to observe the variabilities in three Wolf-Rayet stars. The spectroscopic data have been analysed for WR 134 (WN6b), to better understand its behaviour and long-term periodicity, which we interpret as arising from corotating interaction regions (CIRs) in the wind. By analysing the variability of the He II λ5411 emission line, the previously identified period was refined to P = 2.255 ± 0.008 (s.d.) d. The coherency time of the variability, which we associate with the lifetime of the CIRs in the wind, was deduced to be 40 ± 6 d, or ˜18 cycles, by cross-correlating the variability patterns as a function of time. When comparing the phased observational grey-scale difference images with theoretical grey-scales previously calculated from models including CIRs in an optically thin stellar wind, we find that two CIRs were likely present. A separation in longitude of Δφ ≃ 90° was determined between the two CIRs and we suggest that the different maximum velocities that they reach indicate that they emerge from different latitudes. We have also been able to detect observational signatures of the CIRs in other spectral lines (C IV λλ5802,5812 and He I λ5876). Furthermore, a DAC was found to be present simultaneously with the CIR signatures detected in the He I λ5876 emission line which is consistent with the proposed geometry of the large-scale structures in the wind. Small-scale structures also show a presence in the wind, simultaneously with the larger scale structures, showing that they do in fact co-exist.

  6. High-resolution FUSE and HST ultraviolet spectroscopy of the white dwarf central star of Sh 2-216

    Science.gov (United States)

    Rauch, T.; Ziegler, M.; Werner, K.; Kruk, J. W.; Oliveira, C. M.; Vande Putte, D.; Mignani, R. P.; Kerber, F.

    2007-07-01

    Context: We perform a comprehensive spectral analysis of LS V +46° 21 in order to compare its photospheric properties to theoretical predictions from stellar evolution theory as well as from diffusion calculations. Aims: LS V +46° 21 is the DAO-type central star of the planetary nebula Sh 2-216. High-resolution, high-S/N ultraviolet observations obtained with FUSE and STIS aboard the HST as well as the optical spectrum have been analyzed in order to determine the photospheric parameters and the spectroscopic distance. Methods: We performed a detailed spectral analysis of the ultraviolet and optical spectrum by means of state-of-the-art NLTE model-atmosphere techniques. Results: From the N IV - N V, O IV - O VI, Si IV - Si V, and Fe V - Fe VII ionization equilibria, we determined an effective temperature of (95± 2) kK with high precision. The surface gravity is log g = 6.9± 0.2. An unexplained discrepancy appears between the spectroscopic distance d = 224+46-58 pc and the parallax distance d = 129+6-5 pc of LS V +46° 21. For the first time, we have identified Mg IV and Ar VI absorption lines in the spectrum of a hydrogen-rich central star and determined the Mg and Ar abundances as well as the individual abundances of iron-group elements (Cr, Mn, Fe, Co, and Ni). With the realistic treatment of metal opacities up to the iron group in the model-atmosphere calculations, the so-called Balmer-line problem (found in models that neglect metal-line blanketing) vanishes. Conclusions: Spectral analysis by means of NLTE model atmospheres has presently arrived at a high level of sophistication, which is now hampered largely by the lack of reliable atomic data and accurate line-broadening tables. Strong efforts should be made to improve upon this situation. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract

  7. The UK Infrared Telescope M33 monitoring project. II. The star formation history in the central square kiloparsec

    CERN Document Server

    Javadi, Atefeh; Mirtorabi, Mohammad Taghi

    2011-01-01

    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. In this second paper of the series, we construct the birth mass function and hence derive the star formation history. The star formation rate has varied between ~0.002 and 0.007 M ̇ yr^-1 kpc^-2. We give evidence of two epochs of a star formation rate enhanced by a factor of a few -- one that happened \\geq 6 Gyr ago and produced \\geq 80% of the total mass in stars, and one around 250 Myr ago that lasted ~ 200 Myr and formed \\leq 6% of the mass in stars. We construct radial and azimuthal distributions in the image plane and in the galaxy plane for populations associated with old first-ascent red giant branch (RGB) stars, intermedia...

  8. Evolution of massive stars

    International Nuclear Information System (INIS)

    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)

  9. An extensive spectroscopic time-series of three Wolf-Rayet stars. I. The lifetime of large-scale structures in the wind of WR 134

    CERN Document Server

    Aldoretta, E J; Richardson, N D; Moffat, A F J; Eversberg, T; Hill, G M; Shenar, T; Artigau, É; Gauza, B; Knapen, J H; Kubát, J; Kubátová, B; Maltais-Tariant, R; Muñoz, M; Pablo, H; Ramiaramanantsoa, T; Richard-Laferrière, A; Sablowski, D P; Simón-Díaz, S; St-Jean, L; Bolduan, F; Dias, F M; Dubreuil, P; Fuchs, D; Garrel, T; Grutzeck, G; Hunger, T; Küsters, D; Langenbrink, M; Leadbeater, R; Li, D; Lopez, A; Mauclaire, B; Moldenhawer, T; Potter, M; Santos, E M dos; Schanne, L; Schmidt, J; Sieske, H; Strachan, J; Stinner, E; Stinner, P; Stober, B; Strandbaek, K; Syder, T; Verilhac, D; Waldschläger, U; Weiss, D; Wendt, A

    2016-01-01

    During the summer of 2013, a 4-month spectroscopic campaign took place to observe the variabilities in three Wolf-Rayet stars. The spectroscopic data have been analyzed for WR 134 (WN6b), to better understand its behaviour and long-term periodicity, which we interpret as arising from corotating interaction regions (CIRs) in the wind. By analyzing the variability of the He II $\\lambda$5411 emission line, the previously identified period was refined to P = 2.255 $\\pm$ 0.008 (s.d.) days. The coherency time of the variability, which we associate with the lifetime of the CIRs in the wind, was deduced to be 40 $\\pm$ 6 days, or $\\sim$ 18 cycles, by cross-correlating the variability patterns as a function of time. When comparing the phased observational grayscale difference images with theoretical grayscales previously calculated from models including CIRs in an optically thin stellar wind, we find that two CIRs were likely present. A separation in longitude of $\\Delta \\phi \\simeq$ 90$^{\\circ}$ was determined between...

  10. The morphology and kinematics of the Fine Ring Nebula, planetary nebula Sp 1, and the shaping influence of its binary central star

    CERN Document Server

    Jones, D; Lloyd, M; Pollacco, D; O'Brien, T J; Meaburn, J; Vaytet, N M H

    2011-01-01

    We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Shapley 1 (Sp 1), which is known to contain a close-binary central star system. Close-binary central stars have been identified as a likely source of shaping in planetary nebulae, but with little observational support to date. Deep narrowband imaging in the light of [O III] {\\lambda}5007A suggests the presence of a large bow-shock to the west of the nebula, indicating that it is undergoing the first stages of an interaction with the interstellar medium. Further narrowband imaging in the light of H{\\alpha}+[NII] {\\lambda}6584A combined with longslit observations of the H{\\alpha} emission have been used to develop a spatio-kinematical model of Sp 1. The model clearly reveals Sp 1 to be a bipolar, axisymmetric structure viewed almost pole-on. The symmetry axis of the model nebula is within a few degrees of perpendicular to the orbital plane of the central binary system - strong evidence that the central close-binary s...

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

    Digital Repository Service at National Institute of Oceanography (India)

    Shanas, P.R.; SanilKumar, V.

    and waves during the southwest monsoon season. We observed statistically declining trends in the mean and extreme wind speed (90th percentile) with increasing trend in extreme significant wave height (SWH). Seasonal analysis also investigated and found...

  12. The velocity dispersion profile of NGC 6388 from resolved-star spectroscopy: no evidence of a central cusp and new constraints on the black hole mass

    CERN Document Server

    Lanzoni, B; Origlia, L; Bellazzini, M; Ferraro, F R; Valenti, E; Miocchi, P; Dalessandro, E; Pallanca, C; Massari, D; -,

    2013-01-01

    By combining high spatial resolution and wide-field spectroscopy performed, respectively, with SINFONI and FLAMES at the ESO/VLT we measured the radial velocities of more than 600 stars in the direction of NGC 6388, a Galactic globular cluster which is suspected to host an intermediate-mass black hole. Approximately 55% of the observed targets turned out to be cluster members. The cluster velocity dispersion has been derived from the radial velocity of individual stars: 52 measurements in the innermost 2", and 276 stars located between 18" and 600". The velocity dispersion profile shows a central value of ~13 km/s, a flat behavior out to ~60" and a decreasing trend outwards. The comparison with spherical and isotropic models shows that the observed density and velocity dispersion profiles are inconsistent with the presence of a central black hole more massive than ~2000 Msol. These findings are at odds with recent results obtained from integrated light spectra, showing a velocity dispersion profile with a ste...

  13. A Static Voltage Security Region for Centralized Wind Power Integration—Part II: Applications

    OpenAIRE

    Tao Ding; Qinglai Guo; Rui Bo; Hongbin Sun; Boming Zhang; Tian-en Huang

    2014-01-01

    In Part I of this work, a static voltage security region was introduced to guarantee the safety of wind farm reactive power outputs under both base conditions and N-1 contingency. In this paper, a mathematical representation of the approximate N-1 security region has further studied to provide better coordination among wind farms and help prevent cascading tripping following a single wind farm trip. Besides, the influence of active power on the security region is studied. The proposed methods...

  14. Feedback in the Antennae Galaxies (NGC 4038/9): I. High-Resolution Infrared Spectroscopy of Winds from Super Star Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Gilbert, A; Graham, J

    2007-06-05

    We present high-resolution (R {approx} 24,600) near-IR spectroscopy of the youngest super star clusters (SSCs) in the prototypical starburst merger, the Antennae Galaxies. These SSCs are young (3-7 Myr old) and massive (10{sup 5}-10{sup 7} M{sub {circle_dot}} for a Kroupa IMF) and their spectra are characterized by broad, extended Brackett {gamma} emission, so we refer to them as emission-line clusters (ELCs) to distinguish them from older SSCs. The Br {gamma} lines of most ELCs have supersonic widths (60-110 km s{sup -1} FWHM) and non-Gaussian wings whose velocities exceed the clusters escape velocities. This high-velocity unbound gas is flowing out in winds that are powered by the clusters massive O and W-R stars over the course of at least several crossing times. The large sizes of some ELCs relative to those of older SSCs may be due to expansion caused by these outflows; many of the ELCs may not survive as bound stellar systems, but rather dissipate rapidly into the field population. The observed tendency of older ELCs to be more compact than young ones is consistent with the preferential survival of the most concentrated clusters at a given age.

  15. NuSTAR observations of the supergiant X-ray pulsar IGR J18027-2016: accretion from the stellar wind and possible cyclotron absorption line

    CERN Document Server

    Lutovinov, A; Postnov, K; Krivonos, R; Molkov, S; Tomsick, J

    2016-01-01

    We report on the first focused hard X-ray view of the absorbed supergiant system IGRJ18027-2016 performed with the NuSTAR observatory. The pulsations are clearly detected with a period of P_{spin}=139.866(1) s and a pulse fraction of about 50-60% at energies from 3 to 80 keV. The source demonstrates an approximately constant X-ray luminosity on a time scale of more than dozen years with an average spin-down rate of dP/dt~6x10^{-10} s/s. This behaviour of the pulsar can be explained in terms of the wind accretion model in the settling regime. The detailed spectral analysis at energies above 10 keV was performed for the first time and revealed a possible cyclotron absorption feature at energy ~23 keV. This energy corresponds to the magnetic field B~3x10^{12} G at the surface of the neutron star, which is typical for X-ray pulsars.

  16. A Generalised Porosity Formalism for Isotropic and Anisotropic Effective Opacity and its Effects on X-ray Line Attenuation in Clumped O Star Winds

    Science.gov (United States)

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

    2011-01-01

    We present a generalised formalism for treating the porosity-associated reduction in continuum opacity that occurs when individual clumps in a stochastic medium become optically thick. As in previous work, we concentrate on developing bridging laws between the limits of optically thin and thick clumps. We consider geometries resulting in either isotropic or anisotropic effective opacity, and, in addition to an idealised model in which all clumps have the same local overdensity and scale, we also treat an ensemble of clumps with optical depths set by Markovian statistics. This formalism is then applied to the specific case of bound-free absorption of X- rays in hot star winds, a process not directly affected by clumping in the optically thin limit. We find that the Markov model gives surprisingly similar results to those found previously for the single clump model, suggesting that porous opacity is not very sensitive to details of the assumed clump distribution function. Further, an anisotropic effective opacity favours escape of X-rays emitted in the tangential direction (the venetian blind effect), resulting in a bump of higher flux close to line centre as compared to profiles computed from isotropic porosity models. We demonstrate how this characteristic line shape may be used to diagnose the clump geometry, and we confirm previous results that for optically thick clumping to significantly influence X-ray line profiles, very large porosity lengths, defined as the mean free path between clumps, are required. Moreover, we present the first X-ray line profiles computed directly from line-driven instability simulations using a 3-D patch method, and find that porosity effects from such models also are very small. This further supports the view that porosity has, at most, a marginal effect on X-ray line diagnostics in O stars, and therefore that these diagnostics do indeed provide a good clumping insensitive method for deriving O star mass-loss rates.

  17. A generalized porosity formalism for isotropic and anisotropic effective opacity and its effects on X-ray line attenuation in clumped O star winds

    Science.gov (United States)

    Sundqvist, Jon O.; Owocki, Stanley P.; Cohen, David H.; Leutenegger, Maurice A.; Townsend, Richard H. D.

    2012-02-01

    We present a generalized formalism for treating the porosity-associated reduction in continuum opacity that occurs when individual clumps in a stochastic medium become optically thick. As in previous work, we concentrate on developing bridging laws between the limits of optically thin and thick clumps. We consider geometries resulting in either isotropic or anisotropic effective opacity, and, in addition to an idealized model in which all clumps have the same local overdensity and scale, we also treat an ensemble of clumps with optical depths set by Markovian statistics. This formalism is then applied to the specific case of bound-free absorption of X-rays in hot star winds, a process not directly affected by clumping in the optically thin limit. We find that the Markov model gives surprisingly similar results to those found previously for the single-clump model, suggesting that porous opacity is not very sensitive to details of the assumed clump distribution function. Further, an anisotropic effective opacity favours escape of X-rays emitted in the tangential direction (the 'venetian blind' effect), resulting in a 'bump' of higher flux close to line centre as compared to profiles computed from isotropic porosity models. We demonstrate how this characteristic line shape may be used to diagnose the clump geometry, and we confirm previous results that for optically thick clumping to significantly influence X-ray line profiles, very large porosity lengths, defined as the mean free path between clumps, are required. Moreover, we present the first X-ray line profiles computed directly from line-driven instability simulations using a 3D patch method, and find that porosity effects from such models also are very small. This further supports the view that porosity has, at most, a marginal effect on X-ray line diagnostics in O stars, and therefore that these diagnostics do indeed provide a good 'clumping insensitive' method for deriving O star mass-loss rates.

  18. Three-dimensional radiative transfer in clumped hot star winds I. Influence of clumping on the resonance line formation

    Czech Academy of Sciences Publication Activity Database

    Šurlan, Brankica; Hamann, W.-R.; Kubát, Jiří; Oskinova, L.M.; Feldmeier, A.

    2012-01-01

    Roč. 541, May (2012), A37/1-A37/11. ISSN 0004-6361 R&D Projects: GA ČR GA205/08/0003; GA ČR GD205/08/H005 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * outflows * mass-loss Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.084, year: 2012

  19. Evidence of suppression of star formation by quasar-driven winds in gas-rich host galaxies at z<1?

    CERN Document Server

    Wylezalek, Dominika

    2016-01-01

    Feedback from active galactic nuclei (AGN) is widely considered to be the main driver in regulating the growth of massive galaxies through heating or driving gas out of the galaxy, preventing further increase in stellar mass. Observational proof for this scenario has, however, been scarce. We have assembled a sample of 132 radio-quiet type-2 and red AGN at 0.1star formation rates and investigate the relationships between AGN luminosities, specific star formation rates (sSFR) and outflow strengths W90 -- the 90\\% velocity width of the [OIII]5007 line power and a proxy for the AGN-driven outflow speed. Outflow strength is independent of sSFR for AGN selected on their mid-IR luminosity, in agreement with previous work demonstrating that star formation is not sufficient to produce the observed ionized gas outflows which have to be powered by AGN activity. More importantly, we find a negative correlation between W90...

  20. Star Polymers.

    Science.gov (United States)

    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. PMID:27299693

  1. Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars

    CERN Document Server

    Trujillo-Gomez, Sebastian; Colin, Pedro; Ceverino, Daniel; Arraki, Kenza; Primack, Joel

    2013-01-01

    Despite recent success in forming realistic disc galaxies at redshift zero, simulations still form the bulk of their stars prematurely. We investigate the process of stellar mass assembly in low-mass simulated galaxies, a dwarf and a typical spiral, focusing on the effects of radiation from young stellar clusters. We employ a novel model of star formation in which stars form deterministically with a small efficiency per free-fall time, as observed in molecular clouds. Stellar feedback includes radiation pressure from massive stars and energy from supernova explosions and stellar winds. In galaxies with masses up to those of typical spirals, radiation efficiently suppresses star formation by dispersing and heating high density gas, mostly in the central regions, preventing the formation of a massive bulge. Once the galaxies reach this radiation-regulated growth regime, their global properties are robust to the specific choice of model parameters. Only when radiative feedback is included, do galaxies exhibit co...

  2. Revealing the Asymmetry of the Wind of the Variable Wolf-Rayet Star WR1 (HD4004) Through Spectropolarization

    OpenAIRE

    St-Louis, Nicole

    2013-01-01

    In this paper, high quality spectropolarimetric observations of the Wolf-Rayet (WR) Star WR1 (HD4004) obtained with ESPaDOnS at CFHT are presented. All major emission lines present in the spectrum show depolarization in the relative Stokes parameters Q/I and U/I. From the behaviour 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 \\pm 0.028 % with an angle of \\theta=-26.2^o. Although such a level...

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

    Digital Repository Service at National Institute of Oceanography (India)

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

    mesh covers Goa and the surrounding region. Simulations have been carried out for three different seasons- northeast (NE) monsoon, transition period and southwest (SW) monsoon with appropriate physics options to understand the coastal wind system...

  4. Observations of wind and waves in the central Bay of Bengal during BOBMEX-99 and their effect on mixed layer depth variability due to forced mixing

    Indian Academy of Sciences (India)

    J Swain; R K Shukla; A Raghunadha Rao; J K Panigrahi; N R Venkitachalam

    2003-06-01

    Time-series wind and wave measurements were carried out onboard INS Sagardhwani in the central Bay of Bengal during BOBMEX-99. Various other marine meteorological and oceanographic measurements relevant to monsoon studies were also collected simultaneously. The observed variations of wind and waves and the associated mixed layer depth (MLD) variability based on both temperature and density criteria at 3 hourly intervals are presented in this paper as a case study. At the time-series location (13°N, 87°E) wind varied between 6 and 16 m/s and the predominant direction was southwesterly. The significant wave height and period varied from 1.9 to 3.7m and 8 to 13 s respectively. Some of the available statistical predictive methods for the determination of MLD by forced mixing are utilized to test the extent of mechanical mixing within the top layer of water by the local wind and wave activity. The same is extended to formulate a new empirical relation for gross estimation of effective depth within which the sound energy is generally trapped during its transmission in the surface duct. The present analysis aiming for estimation of observed MLD variability (35 to 75 m) using the suggested simple empirical relation reveals that, the mixed layer variability observed during the experiment depends on both local ocean variability as well as remote forcing as reported earlier.

  5. The specific star formation rate and stellar mass fraction of low-mass central galaxies in cosmological simulations

    CERN Document Server

    Avila-Reese, V; González-Samaniego, A; Valenzuela, O; Firmani, C; Velázquez, H; Ceverino, D

    2011-01-01

    By means of cosmological simulations of galaxies in the context of the LCDM scenario we explore the specific star formation rates (SSFR=SFR/Ms, Ms is the stellar mass) and stellar mass fractions (Fs=Ms/Mh, Mh is the halo mass) for sub-M* field galaxies at different redshifts (0star-forming galaxies at z<0.3 (at low masses, most of observed field galaxies are actually blue/star-forming); this inconsistency seems to r...

  6. Fundamental Parameters of Massive Stars

    OpenAIRE

    Crowther, Paul A.

    2003-01-01

    We discuss the determination of fundamental parameters of `normal' hot, massive OB-type stars, namely temperatures, luminosities, masses, gravities and surface abundances. We also present methods used to derive properties of stellar winds -- mass-loss rates and wind velocities from early-type stars.

  7. Lightning Attachment to Wind Turbines in Central Kansas: Video Observations, Correlation with the NLDN and in-situ Peak Current Measurements

    Science.gov (United States)

    Myers, J.; Cummins, K. L.; Hutchinson, M.; Nag, A.

    2012-12-01

    Lightning attachment to tall objects has been studied for decades. The attachment of lightning to electric power transmission towers in elevated terrain has driven much of the quantitative assessment of lightning characteristics in the 1970's and 80's. This has led to the understanding that in flat terrain, the probability of upward-initiated lightning is negligible for tower heights less than 100 m. For tower heights greater than 100, the probability increases roughly linearly with the log of height, reaching 100% at a height of 400 m. Additionally, the probability of upward initiation increases when the object resides on locally-elevated terrain. Over the last decade, there has been renewed interest in the study of lightning attachment to tall objects in general, and wind turbines in particular, following the establishment of large "wind farms" in lightning-prone regions. In this study, we present video observations, radiation magnetic field, and in-situ peak current measurements of lightning from an ongoing field program in a large wind farm in north-central Kansas, located in the U.S. Central Great Plains. The terrain variations within the wind farm are small rolling hills with peak variations on the order of 25 m. All turbines had a turbine hub height of 80 m, and a blade tip maximum height of 125 m. Two digital video camera systems (60 fields-per-second) were configured to self-trigger 2-second video sequences using a sequential-field-subtraction scene analysis (ufo-Capture). The two cameras had a common field of view that included 8 of the wind turbines. Nearby NLDN sensors were configured to record information that allows reconstruction of magnetic field waveforms within the bandwidth of the NLDN sensors. Some of the turbines were equipped with semi-quantitative in-situ peak current measuring devices. To date, more than 100 cloud-to-ground (CG) flashes have terminated within the perimeter of the wind farm. Video observations of flashes that attached to

  8. Formation of SiC Grains in Pulsation-Enhanced Dust-Driven Wind Around Carbon Rich Asymptotic Giant Branch Stars

    CERN Document Server

    Yasuda, Yuki

    2011-01-01

    We investigate the formation of silicon carbide (SiC) grains in the framework of dust-driven wind around pulsating carbon-rich Asymptotic Giant Branch (C-rich AGB) stars in order to reveal not only the amount but also the size distribution. Two cases are considered for the nucleation process; one is the LTE case where the vibration temperature of SiC clusters $T_{\\rm v}$ is equal to the gas temperature as usual, and another is the non-LTE case in which $T_{\\rm v}$ is assumed to be the same as the temperature of small SiC grains. The results of hydrodynamical calculations for a model with stellar parameters of mass $M_{\\ast}$=1.0 $M_{\\odot}$, luminosity $L_{\\ast}$=10$^{4}$ $L_{\\odot}$, effective temperature $T_{\\rm eff}$=2600 K, C/O ratio=1.4, and pulsation period $P$=650 days show the followings: In the LTE case, SiC grains condense in accelerated outflowing gas after the formation of carbon grains and the resulting averaged mass ratio of SiC to carbon grains of $\\sim$ 10$^{-8}$ is too small to reproduce the ...

  9. A generalised porosity formalism for isotropic and anisotropic effective opacity and its effects on X-ray line attenuation in clumped O star winds

    CERN Document Server

    Sundqvist, Jon O; Cohen, David H; Leutenegger, Maurice A; Townsend, Richard H D

    2011-01-01

    We present a generalised formalism for treating the porosity-associated reduction in continuum opacity that occurs when individual clumps in a stochastic medium become optically thick. We consider geometries resulting in either isotropic or anisotropic effective opacity, and, in addition to an idealised model in which all clumps have the same local overdensity and scale, we also treat an ensemble of clumps with optical depths set by Markovian statistics. This formalism is then applied to the specific case of bound-free absorption of X-rays in hot star winds, a process not directly affected by clumping in the optically thin limit. We find that the Markov model gives surprisingly similar results to those found previously for the single clump model, suggesting that porous opacity is not very sensitive to details of the assumed clump distribution function. Further, an anisotropic effective opacity favours escape of X-rays emitted in the tangential direction (the `venetian blind' effect), resulting in a 'bump' of ...

  10. 2D Simulations of the Line-Driven Instability in Hot-Star Winds: II. Approximations for the 2D Radiation Force

    CERN Document Server

    Dessart, L; Dessart, Luc

    2005-01-01

    We present initial attempts to include the multi-dimensional nature of radiation transport in hydrodynamical simulations of the small-scale structure that arises from the line-driven instability in hot-star winds. Compared to previous 1D or 2D models that assume a purely radial radiation force, we seek additionally to treat the lateral momentum and transport of diffuse line-radiation, initially here within a 2D context. A key incentive is to study the damping effect of the associated diffuse line-drag on the dynamical properties of the flow, focusing particularly on whether this might prevent lateral break-up of shell structures at scales near the lateral Sobolev angle of ca. $1^{\\rm o}$. We first explore nonlinear simulations that cast the lateral diffuse force in the simple, local form of a parallel viscosity. Second, to account for the lateral mixing of radiation associated with the radial driving, we next explore models in which the radial force is azimuthally smoothed over a chosen scale. Third, to accou...

  11. The analysis of realistic Stellar Gaia mock catalogues. I. Red Clump Stars as tracers of the central bar

    CERN Document Server

    Romero-Gomez, Merce; Antoja, Teresa; Abedi, Hoda; Aguilar, Luis

    2014-01-01

    In this first paper we simulate the population of disc Red Clump stars to be observed by Gaia. We generate a set of test particles and we evolve it in a 3D barred Milky Way like galactic potential. We assign physical properties of the Red Clump trace population and a realistic 3D interstellar extinction model. We add Gaia observational constraints and an error model according to the pre-commissioning scientific performance assessments. We present and analyse two mock catalogues, offered to the community, that are an excellent test bed for testing tools being developed for the future scientific exploitation of Gaia data. The first catalogue contains stars up to Gaia G 20, while the second is the subset containing Gaia radial velocity data with a maximum error of sigmaVr=10 kms. Here we present first attempts to characterise the density structure of the Galactic bar in the Gaia space of observables. The Gaia large errors in parallax and the high interstellar extinction in the inner parts of the Galactic disc pr...

  12. Metal Absorption Profiles from the Central Star of the Planetary Nebula M27 (NGC 6583, PN GO60.8-036, the Dumbbell) -- Photospheric and Nebular Line Identifications

    CERN Document Server

    McCandliss, S R; Candliss, Stephan. R. Mc; Kruk, Jeffrey

    2006-01-01

    High resolution spectra of the hot central star of the planetary nebula (CSPN) M27, acquired with the Far Ultraviolet Spectroscopic Explorer (\\FUSE), have revealed an unusually rich set of narrow molecular hydrogen absorption features. This object is also unique in that the velocity of nebular absorption features are cleanly separated from the velocity of the intervening interstellar medium. These features blend with and in many cases obscure atomic features. We have developed a continuum model of the CSPN including atomic and molecular hydrogen absorption. Using this model we have identified and tabulated the metal lines as arising from either photospheric, nebular and/or non-nebular velocity systems. We find the nebular outflow and ionization balance to be stratified with high ionization states favored at low velocity and low ionization states favored at high velocity. Neutrals and molecules are found at a velocity that marks the transistion between these two regimes. These observations are a challenge to t...

  13. Jet- and Wind-Driven Ionized Outflows in the Superbubble and Star-Forming Disk of NGC 3079

    CERN Document Server

    Cecil, G N; Veilleux, S; Filippenko, A V

    2001-01-01

    HST WFPC2 images are presented that span the inner 19 kpc diameter of the edge-on spiral galaxy NGC 3079; they are combined with ground-based Halpha+[N II] Fabry-Perot spectra and VLA images of radio polarization vectors and rotation measures. Ionized gas filaments within 9 kpc diameter project ~3 kpc above the disk, with the brightest forming the 1 kpc diameter superbubble. They are often resolved into strands ~0."3 (25 pc) wide which emerge from the nuclear CO ring as five distinct gas streams with velocity gradients and dispersions of hundreds of km/s. One stream flows for 250 pc and aligns with the VLBI-scale radio jet, the other four are not connected to the jet, instead curving to the vertical 0.6 kpc above the galaxy disk, then dispersing in a spray of droplets each with ionized mass ~1000 sqrt(f) Msun (volume filling factor f > 0.003 from our data). Shredded clumps of disk gas form a similar structure in hydro models of a galaxy-scale wind. The pattern of magnetic fields and the gas kinematics also su...

  14. Effect of a magnetic field on massive star winds I: mass-loss and velocity for a dipole field

    CERN Document Server

    Bard, Christopher

    2016-01-01

    We generalize the Rigid-Field Hydrodynamic equations to accommodate arbitrary magnetic field topologies, resulting in a new Arbitrary Rigid-Field hydrodynamic (ARFHD) formalism. We undertake a critical point calculation of the steady-state ARFHD equations with a CAK-type radiative acceleration and determine the effects of a dipole magnetic field on the usual CAK mass-loss rate and velocity structure. Enforcing the proper optically-thin limit for the radiative line-acceleration is found to decrease both the mass-loss and wind acceleration, while rotation boosts both properties. We define optically-thin-correction and rotation parameters to quantify these effects on the global mass-loss rate and develop scaling laws for the surface mass-flux as a function of surface colatitude. These scaling laws are found to agree with previous laws derived from magnetohydrodynamic simulations of magnetospheres. The dipole magnetosphere velocity structure is found to differ from a global beta-velocity law, which contradicts a ...

  15. Feeding quasars with stellar winds

    International Nuclear Information System (INIS)

    Quasars may be fueled by stellar mass loss from OB stars and red giants: either normal winds and mass loss or X-ray induced stellar winds in luminous quasars with well developed cusps in the stellar density distribution. The X-ray induced mass loss may furnish part of the broad emission-line gas, as well as an accretion supply for a central black hole during transient bursts of quasar luminosity. The importance of a stellar density cusp may couple stellar dynamical processes with gas-radiative processes in the quasar nucleus, accounting for quasar variability. The coupling of X-ray luminosity with mass supply and stellar population may imply evolution of optical-to-X-ray luminosity ratios with redshift. Most importantly, the evolution of the stellar population away from the initial mass function may explain the scarcity of quasars at low redshift

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

    Science.gov (United States)

    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

  17. Spectral Analysis of the O(He)-Type Central Stars of the Planetary Nebulae K 1-27 and LoTr 4

    Science.gov (United States)

    Reindl, N.; Ringat, E.; Rauch, T.; Werner, K.; Kruk, J. W.

    2011-01-01

    The four known O(He) stars are the only amongst the hottest post-AGB stars whose atmospheres are composed of almost pure helium. Thus, their evolution deviates from the hydrogen-defiCient post-AGB evolutionary sequence of carbon-dominated stars like e.g. PG 1159 stars. The origin of the O(He) stars is still not explained. They might be either post-early AGB stars or the progeny of R Coronae Borealis stars. We present preliminary results of a non-LTE spectral analysis based on FUSE and HST/COS observations.

  18. FORMATION OF SiC GRAINS IN PULSATION-ENHANCED DUST-DRIVEN WIND AROUND CARBON-RICH ASYMPTOTIC GIANT BRANCH STARS

    International Nuclear Information System (INIS)

    We investigate the formation of silicon carbide (SiC) grains in the framework of dust-driven wind around pulsating carbon-rich asymptotic giant branch (C-rich AGB) stars to reveal not only the amount but also the size distribution. Two cases are considered for the nucleation process: one is the local thermal equilibrium (LTE) case where the vibration temperature of SiC clusters Tv is equal to the gas temperature as usual, and another is the non-LTE case in which Tv is assumed to be the same as the temperature of small SiC grains. The results of the hydrodynamical calculations for a model with stellar parameters of mass M* = 1.0 M☉, luminosity L* = 104 L☉, effective temperature Teff = 2600 K, C/O ratio = 1.4, and pulsation period P = 650 days show the following: in the LTE case, SiC grains condense in accelerated outflowing gas after the formation of carbon grains, and the resulting averaged mass ratio of SiC to carbon grains of ∼10–8 is too small to reproduce the value of 0.01-0.3, which is inferred from the radiative transfer models. On the other hand, in the non-LTE case, the formation region of the SiC grains is more internal and/or almost identical to that of the carbon grains due to the so-called inverse greenhouse effect. The mass ratio of SiC to carbon grains averaged at the outer boundary ranges from 0.098 to 0.23 for the sticking probability αs = 0.1-1.0. The size distributions with the peak at ∼0.2-0.3 μm in radius cover the range of size derived from the analysis of the presolar SiC grains. Thus, the difference between the temperatures of the small cluster and gas plays a crucial role in the formation process of SiC grains around C-rich AGB stars, and this aspect should be explored for the formation process of dust grains in astrophysical environments.

  19. Star formation in rotating, magnetized molecular disks

    International Nuclear Information System (INIS)

    The discovery of dense, rotating molecular disks associated with protostars and bipolar outflows suggests that massive (M/sub d/approx.10/sup 1.5/ M/sub sun/) objects have not shed their excessive (happrox.1022 cm2 s-1) angular momentum by the time protostellar activity begins. This paper presents a theory for star formation in rotating disks in which accretion onto the protostellar core produces FUV radiation which heats the disk surfaces out to large radii. A hydromagnetic wind results in which heated gas is driven out along field lines which thread the disk and are aligned with the disk rotation axis. For accretion luminosities of 4 x 1037 ergs s-1, a highly ionized flow inside 1015 cm with M/sub ion/ up to 10-6 M/sub sun/ yr-1 is expected, and a much more massive, neutral component carrying M/sub w/ = 1022 g s-1 from disk radii r>1015 cm. Terminal wind speeds of 50 km s-1 are achieved in this bipolar outflow. The centrifugally driven wind removes angular momentum from the disk at rates high enough to brake it down to protostellar specific values in 105 yr. The wind drives an accretion rate through the disk at rates which are consistent with the accretion luminosity. This global analysis of star formation in a rotating, magnetized disk offers a unifying scheme for understanding both star formation and bipolar outflows. The disks are ''flywheels'' that store rotational energy which is released at a rate dictated self-consistently by the rate at which accretion onto the central protostellar core occurs. The disks in which massive stars form are predicted to be dense (108 cm-3) and have rotation speeds of 4 km s -1, scales of order 5 x 1016 cm, masses of order 102 M/sub sun/, and axial ratios of 0.2

  20. On the impact of radiation pressure on the dynamics and inner structure of dusty wind-driven shells

    OpenAIRE

    Martinez-Gonzalez, Sergio; Silich, Sergiy; Tenorio-Tagle, Guillermo

    2014-01-01

    Massive young stellar clusters are strong sources of radiation and mechanical energy. Their powerful winds and radiation pressure sweep-up interstellar gas into thin expanding shells which trap the ionizing radiation produced by the central clusters affecting the dynamics and the distribution of their ionized gas. Here we continue our comparison of the star cluster winds and radiation pressure effects on the dynamics of shells around young massive clusters. We calculate the impact that radiat...

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

    Science.gov (United States)

    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

  2. Detail of the star WR124 and the surrounding nebula M1-67.

    Science.gov (United States)

    2002-01-01

    The massive, hot central star is known as a Wolf-Rayet star. This extremely rare and short-lived class of super-hot star is going through a violent, transitional phase characterized by the fierce ejection of mass. The blobs may result from the furious stellar wind that does not flow smoothly into space but has instabilities which make it clumpy. This black and white image was made in the light of atomic hydrogen. The contrast has been increased to emphasize the fine detail in the nebula near the central star. Credit: Yves Grosdidier (University of Montreal and Observatoire de Strasbourg), Anthony Moffat (Universitie de Montreal), Gilles Joncas (Universite Laval), Agnes Acker (Observatoire de Strasbourg), and NASA

  3. Analysis of geological aspects and visual impact rising from the realisation of a wind power station in an Italian mountain area (Central Appennines)

    International Nuclear Information System (INIS)

    This study evaluates some aspects of the environmental impacts arising from the wind power station in the Central Appennines of Italy, particularly with reference to the geological and geotechnical conditions of the site and the visual impact on the landscape. Starting from a large-scale analysis that takes into account the Appennines orogeny and their geodynamic process, it is possible to define the geological characteristics of the considered area. It is possible to analyse structural and morphological aspects, in this way it is possible to identify the most suitable location of power generators in the area and to optimise the road network. The geo-stratigraphical study aids decisions about foundations, excavations and works of containments. Considerations on earth traspiration and on rill identify the necessity of controlling surface waters, evolutionary phenomena and the soil stability of the considered areas. Particular attention has been given to analyse effects on the landscape. (author)

  4. Revision of the Wind River faunas, early Eocene of central Wyoming. IX - The oldest known hystricomorphous rodent (Mammalia: Rodentia)

    Science.gov (United States)

    Dawson, Mary R.; Krishtalka, Leonard; Stucky, Richard K.

    1990-01-01

    The rostral portion of the skull of a new genus and species of rodent, Armintomys tullbergi, from the earliest middle Eocene of the Wind River Basin (Wyoming) provides the geologically oldest known record of the hystricomorphous zygomasseteric structure. Armintomys also preserves the oldest known occurrence of incisor enamel that is transitional from pauciserial to uniserial. Other dental characters include: anteriorly grooved incisor, small premolars, and relatively primitive sciuravidlike molars. Analysis of this unique combination of characters implies that Armintomys is the oldest known myomorph rodent and the only known representative of a new family. Armintomyidae, which is referred, with question, to the myomorph superfamily Dipodoidea. Armintomys is more primitive, especially in premolar retention and structure, than the Bridgerian zapodid Elymys from Nevada, but adds to evidence from the latter for an early origin and radiation of dipodoid rodents.

  5. Determination of masses of the central black holes in NGC524 and NGC2549 using Laser Guide Star Adaptive Optics

    CERN Document Server

    Krajnovic, Davor; Cappellari, Michele; Davies, Roger L

    2009-01-01

    [abridged] We present observations of NGC524 and NGC2549 with LGS AO obtained at GEMINI North telescope using the NIFS IFU in the K band. The purpose of these observations, together with previously obtained observations with the SAURON IFU, is to determine the masses (Mbh) of the supermassive black holes (SMBH). The targeted galaxies were chosen to have central light profiles showing a core (NGC524) and a cusp (NGC2549), to probe the feasibility of using the galaxy centre as the NGS required for LGS AO. We employ an innovative `open loop' technique. The data have spatial resolution of 0.23" and 0.17" FWHM, showing that high quality LGS AO observations of these objects are possible. We construct axisymmetric three-integral dynamical models which are constrained with both the NIFS and SAURON data. The best fitting models yield Mbh=(8.3 +2.7 -1.3) x 10^8 Msun for NGC524 and Mbh=(1.4 +0.2 -1.3) x 10^7 Msun for NGC2549 (all errors are at the 3 sigma CL). We demonstrate that the wide-field SAURON data play a crucia...

  6. AMBER-NACO aperture-synthesis imaging of the half-obscured central star and the edge-on disk of the red giant L2 Pup

    CERN Document Server

    Ohnaka, Keiichi; Hofmann, Karl-Heinz; Weigelt, Gerd

    2015-01-01

    The red giant L2 Pup started a dimming event in 1994, which is considered to be caused by the ejection of dust clouds. We present near-IR aperture-synthesis imaging of L2 Pup achieved by combining data from VLT/NACO speckle observations and long-baseline interferometric observations with the AMBER instrument of the Very Large Telescope Interferometer (VLTI). We also extracted an 8.7 micron image from the mid-IR VLTI instrument MIDI. Our aim is to spatially resolve the innermost region of the circumstellar environment. The diffraction-limited image at 2.27 micron obtained by bispectrum speckle interferometry with NACO with a spatial resolution of 57 mas shows an elongated component. The aperture-synthesis imaging combining the NACO speckle data and AMBER data (2.2--2.29 micron) with a spatial resolution of 5.6x7.3 mas further resolves not only this elongated component, but also the central star. The reconstructed image reveals that the elongated component is a nearly edge-on disk with a size of ~180x50 mas lyi...

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

    International Nuclear Information System (INIS)

    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* ∼ 135 kK and a carbon-rich, optically thin thermal plasma with TX ∼ 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.

  8. Beam energy and centrality dependence of the statistical moments of the net-charge and net-kaon multiplicity distributions in Au+Au collisions at STAR

    CERN Document Server

    McDonald, Daniel

    2012-01-01

    In part to search for a possible critical point (CP) in the phase diagram of hot nuclear matter, a Beam Energy Scan was performed at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory. The STAR experiment collected significant Au+Au data sets at beam energies, $\\sqrt{{\\rm s}_{\\rm NN}}$, of 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV. Lattice and phenomenological calculations suggest that the presence of a CP might result in divergences of the thermodynamic susceptibilities and correlation length. The statistical moments of the multiplicity distributions of particles reflecting conserved quantities, such as net-charge and net-strangeness, are expected to depend sensitively on these correlation lengths, making them attractive tools in the search for a possible critical point. The centrality and beam-energy dependence of the statistical moments of the net-charge multiplicity distributions will be discussed. The observables studied include the lowest four statistical moments (mean, variance, ske...

  9. Di-Jet Imbalance Measurements in Central Au+Au Collisions at $\\sqrt{s_{NN}}=200$ GeV from STAR

    CERN Document Server

    ,

    2015-01-01

    The STAR collaboration reports the first measurements of the transverse momentum asymmetry $A_J$ of di-jet pairs in central gold-gold collisions and minimum bias proton-proton collisions at $\\sqrt{s_{NN}}=200$ GeV at RHIC. We focus on anti-$k_T$ di-jets with a leading jet $p_T>20$ GeV/$c$ and a subleading jet $p_T>10$ GeV/$c$, with a constituent cut of 2 GeV/$c$, which reduces the effect of the underlying heavy-ion background. We examine the evolution of $A_J$ while reclustering these same di-jets with a lower constituent cut of 200 MeV/$c$. For the low $p_T$ constituent cut with a resolution parameter of $R=0.4$, the balance between the di-jets is restored to the level of p+p collisions which indicates the lost energy observed for di-jets with a constituent cut of $p_T ^{\\text{Cut}}>2$ GeV/$c$ is recovered. Further variations of $R$ and the constituent \\pT-cutoff indicate that the lost energy is redistributed in the form of soft particles, accompanied by a broadening of the jet structure.

  10. Mass loss from inhomogeneous hot star winds III. An effective-opacity formalism for line radiative transfer in accelerating, clumped two-component media, and first results on theory and diagnostics

    OpenAIRE

    Sundqvist, J. O.; Puls, J.; Owocki, S. P.

    2014-01-01

    [Abridged] We develop and benchmark a fast and easy-to-use effective-opacity formalism for line and continuum radiative transfer in an accelerating two-component clumpy medium. The formalism bridges the limits of optically thin and thick clumps, and is here used to i) design a simple vorosity-modified Sobolev with exact integration (vmSEI) method for analyzing UV wind resonance lines in hot, massive stars, and ii) derive simple correction factors to the line force driving the outflows of such...

  11. Spectra of hot stars

    Science.gov (United States)

    Hillier, D. John

    2015-08-01

    Non-LTE modeling is essential for interpreting the spectra of O stars and their decendents, and much progress has been made. The major uncertainty associated with analyzing photospheric spectra of O stars arises from issues related to microturbulence and macroturbulence. Many supergiants, for example, have microturbulent velocities that approach the sound speed, while macroturbulent velocities are often several times the sound speed. The cause of this turbulence is unknown, but may be related to pulsation, an underlying convection zone associated with the Fe opacity bump, or feedback from the stellar wind. Determining accurate abundances in O stars is hampered by the lack of lines belonging to low-z elements. Many species only have a few observable lines, and some of these are subject to complex non-LTE effects. A characteristic of massive stars is the existence of a stellar wind which is driven by radiation pressure. Radiation driving is inherently unstable, and this leads to winds with an inhomogeneous structure. Major issues that are still unresolved include: How are winds driven through the sonic point? What is the nature of the inhomogeneities, and how do the properties of these inhomogeneities change with density and velocity? How important is spatial porosity, and porosity in velocity space? What is the structure of the shocks, and in what stars do the shocks fail to cool? With Wolf-Rayet (W-R) stars the major uncertainty arises because the classic spectroscopic radius (i.e., the location where τ = 2/3) often refers to a location in the wind — not necessarily the stellar radius associated with stellar evolution models. Derived radii are typically several times those predicted by stellar evolution calculations, although for strong-lined W-R stars it is possible to construct models that are consistent with evolution calculations. The driving of the winds in these stars is strongly coupled to the closeness of the stars to the Eddington limit and to their

  12. On the impact of radiation pressure on the dynamics and inner structure of dusty wind-driven shells

    International Nuclear Information System (INIS)

    Massive young stellar clusters are strong sources of radiation and mechanical energy. Their powerful winds and radiation pressure sweep up interstellar gas into thin expanding shells that trap the ionizing radiation produced by the central clusters affecting the dynamics and the distribution of their ionized gas. Here we continue our comparison of the star cluster winds and radiation pressure effects on the dynamics of shells around young massive clusters. We calculate the impact that radiation pressure has on the distribution of matter and thermal pressure within such shells, as well as on the density-weighted ionization parameter Uw , and put our results on the diagnostic diagram, which allows one to discriminate between the wind-dominated and radiation-dominated regimes. We found that model-predicted values of the ionization parameter agree well with typical values found in local starburst galaxies. Radiation pressure may affect the inner structure and the dynamics of wind-driven shells, but only during the earliest stages of evolution (before ∼3 Myr) or if a major fraction of the star cluster mechanical luminosity is dissipated or radiated away within the star cluster volume and thus the star cluster mechanical energy output is significantly smaller than star cluster synthetic models predict. However, even in these cases radiation dominates over the wind dynamical pressure only if the exciting cluster is embedded into a high-density ambient medium.

  13. Young star clusters in the circumnuclear region of NGC 2110

    Energy Technology Data Exchange (ETDEWEB)

    Durré, Mark; Mould, Jeremy, E-mail: mdurre@swin.edu.au [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122 (Australia)

    2014-03-20

    High-resolution observations in the near infrared show star clusters around the active galactic nucleus (AGN) of the Seyfert 1 NGC 2110, along with a 90 × 35 pc bar of shocked gas material around its nucleus. These are seen for the first time in our imaging and gas kinematics of the central 100 pc with the Keck OSIRIS instrument with adaptive optics. Each of these clusters is two to three times brighter than the Arches cluster close to the center of the Milky Way. The core star formation rate is 0.3 M {sub ☉} yr{sup –1}. The photoionized gas (He I) dynamics imply an enclosed mass of 3-4 × 10{sup 8} M {sub ☉}. These observations demonstrate the physical linkage between AGN feedback, which triggers star formation in massive clusters, and the resulting stellar (and supernovae) winds, which cause the observed [Fe II] emission and feed the black hole.

  14. 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

    Directory of Open Access Journals (Sweden)

    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.

  15. Moving inhomogeneous envelopes of stars

    CERN Document Server

    Oskinova, Lidia M; Hamann, Wolf-Rainer

    2016-01-01

    Massive stars are extremely luminous and drive strong winds, blowing a large part of their matter into the galactic environment before they finally explode as a supernova. Quantitative knowledge of massive star feedback is required to understand our Universe as we see it. Traditionally, massive stars have been studied under the assumption that their winds are homogeneous and stationary, largely relying on the Sobolev approximation. However, observations with the newest instruments, together with progress in model calculations, ultimately dictate a cardinal change of this paradigm: stellar winds are highly inhomogeneous. Hence, we are now advancing to a new stage in our understanding of stellar winds. Using the foundations laid by V.V. Sobolev and his school, we now update and further develop the stellar spectral analysis techniques. New sophisticated 3-D models of radiation transfer in inhomogeneous expanding media elucidate the physics of stellar winds and improve classical empiric mass-loss rate diagnostics...

  16. ROSAT and EUVE observations of B stars

    Science.gov (United States)

    Cassinelli, Joseph P.

    1994-11-01

    Recent observations of the X-ray and EUV emission of non-supergiant B stars are summarized. As compared with O stars, the X-rays of most of the near-main-sequence B stars are soft, and the stars show a departure from the Lx = 1007Lbol relation. Using line driven wind models to provide an estimate of the density distribution, it is concluded that a major fraction of the wind emission measure is hot, whereas in shocked wind theory less than 10 percent of the wind emission measure should be hot. The X-ray observations suggest that all of the B stars are X-ray emitters with a basal X-ray luminosity of about 10-8.5Lbol. For the Be stars, the X-ray emission is that which is expected from a normal B-star wind coming from the poles, as in the Wind Compressed Disk (WCD) model of Be-stars. None of the stars, including the beta Cep stars, show noticeable variability in their X-rays. Extreme Ultraviolet Explorer (EUVE) observations of epsilon CMa B2 II, find it to be the brightest object in the EUV sky at 500 to 700 A. It shows a Lyman continuum flux that is a factor of 30 higher than line blanketed model atmospheres. The EUVE spectra show emission lines both from high stages of ionization ( Fe IX to Fe XVI) and from low stages ( HeII and O III). The He II Lyman alpha results from recombination follwing X-ray photoionization in the wind, and the O III resonance line is found to be present because of the Bowen fluorescence mechanism. Thus, there is and intersting coupling between the wind production by the EUV photospheric emission, the production of X-ray and line EUV emission by winds, and the production of fluorescence by recombination in the wind; all of these processes are now observable in B stars.

  17. 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

    DEFF Research Database (Denmark)

    Bingöl, Ferhat; Hasager, Charlotte Bay; Karagali, Ioanna; Badger, Jake; Badger, Merete; Foussekis, Dimitri; Nielsen, Morten; Topouzelis, Konstantinos

    2012-01-01

    Offshore wind energy is progressing rapidly in many parts of the world including Europe. While our understanding of offshore wind is growing parallel to that, most of the offshore wind development is located in shallow or transitional waters. Deep, open sea was never preferred by developers due to...

  18. Efficiencies of Low-Mass Star and Star Cluster Formation

    OpenAIRE

    Matzner, Christopher D.; McKee, Christopher F.

    2000-01-01

    Using a quantitative model for bipolar outflows driven by hydromagnetic protostellar winds, we calculate the efficiency of star formation assuming that available gas is either converted into stars or ejected in outflows. We estimate the efficiency of a single star formation event in a protostellar core, finding 25%-70% for cores with various possible degrees of flattening. The core mass function and the stellar initial mass function have similar slopes, because the efficiency is not sensitive...

  19. ALMA OBSERVATIONS OF WARM DENSE GAS IN NGC 1614—BREAKING OF THE STAR FORMATION LAW IN THE CENTRAL KILOPARSEC

    Energy Technology Data Exchange (ETDEWEB)

    Xu, C. K.; Cao, C.; Lu, N.; Diaz-Santos, T.; Zhao, Y.-H.; Mazzarella, J. M.; Appleton, P.; Armus, L.; Murphy, E. J. [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Gao, Y. [Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008 (China); Herrero-Illana, R. [Instituto de Astrofísica de Andalucía - CSIC, Glorieta de la Astronomía, s/n, E-18008 Granada (Spain); Meijerink, R. [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Privon, G.; Evans, A. S. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); König, S. [Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, Domaine Universitaire, F-38406 Saint Martin d' Hères (France); Aalto, S. [Department of Earth and Space Sciences, Onsala Observatory, Chalmers University of Technology, SE-439 92 Onsala (Sweden); Charmandaris, V. [Department of Physics, University of Crete, GR-71003 Heraklion (Greece); Chu, J. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96816 (United States); Haan, S. [CSIRO Astronomy and Space Science, ATNF, P.O. Box 76, Epping 1710 (Australia); Inami, H. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); and others

    2015-01-20

    We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 μm dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1{sup ′′}=329 pc). The CO emission is well resolved by the ALMA beam (0.''26 × 0.''20) into a circumnuclear ring, with an integrated flux of f {sub CO(6-5)} = 898 (± 153) Jy km s{sup –1}, which is 63(± 12)% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pcstar formation regions with Σ{sub SFR} ∼ 100 M {sub ☉} yr{sup –1} kpc{sup –2} and Σ{sub Gas}∼10{sup 4} M{sub ⊙} pc{sup −2}. The non-detections of the nucleus in both the CO (6-5) line emission and the 435 μm continuum rule out, with relatively high confidence, a Compton-thick active galactic nucleus in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between Σ{sub Gas} and Σ{sub SFR}, indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of ∼100 pc.

  20. Mass loss from stars

    International Nuclear Information System (INIS)

    This article discusses the different mass-loss processes of stars and how mass-loss rates determine the fate of stars in advanced stages of stellar evolution. Main sequence stars have their atmospheric structure dominated by radiation pressure. The pressure exerted by energetic photons is sufficient to drive gases off into space. This process can impact enormous turbulence to the local interstellar medium. Evolutionary effects keep these stars from fully evaporating, but the very course of their evolution is determined by this mass shedding process. Lower main sequence stars, like the sun, have a turbulent atmosphere enveloped in hot, thin coronal gas, blowing off a light stellar breeze. As the main sequence star evolves to a giant, its corona dissipates and the breeze turns into a strong stellar wind. Intermitten sputters combined with pulsational instabilities can lead to partial ejection of the atmosphere and envelope of a red giant, i.e. a planetary nebula results. The mass-loss from stars through planetary nebule combined with other mass-loss processes such as stellar winds returns a substantial amount of material to the interstellar environment. Mass-loss in binary systems is also discussed

  1. Revised Anatomy of Stars

    CERN Document Server

    Dubin, M; Dubin, Maurice; Soberman, Robert K.

    1997-01-01

    Stars accrete near invisible hydrogen dominated agglomerates. This population, the `dark matter,' effects the nature of stars. Measurements show plasma streams impacting Earth, planets, Sun and stars. This mass-energy source contradicts nebula collapse model for stars. The visual derived model, to which later discoveries (e.g., fusion) were appended, is confounded and contradicted by new observations. Discovery of a quantity of beryllium 7 (53 day half-life) in the Earth's upper atmosphere, fusion produced, hence from the solar outer zone, proves core fusion wrong. Magnetically pinched plasmas from aggregates impact stars at hundreds of km/s, create impulsive conditions for nuclear explosions below the surface. Disks with planets aid cluster capture. Planets modulate the influx varying fusion, hence luminosity (e.g., solar cycle). This population, with no assumptions or ad hoc physics, explains mysterious phenomena, e.g., luminosity/wind variation, sunspots, high temperature corona, CMEs, etc. Standard explan...

  2. Neutron Stars and Pulsars

    CERN Document Server

    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...

  3. Disk reflection and a possible disk wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058

    CERN Document Server

    Degenaar, N; Parker, M; Miller-Jones, J C A; Miller, J M; Heinke, C O; Wijnands, R; Ludlam, R; Parikh, A; Hessels, J W T; Gusinskaia, N; Deller, A T; Fabian, A C

    2016-01-01

    1RXS J180408.9-342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present Nustar, Swift, and Chandra observations obtained around the peak of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of Lx~(2-3)E37 (D/5.8 kpc)^2 erg cm-2 (0.5-10 keV). The Nustar data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disk is viewed at an inclination of i~27-35 degrees and extended close to the neutron star, down to Rin~5-7.5 gravitational radii (~11-17 km). This inner disk radius suggests that the neutron star magnetic field strength is B<2E8 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ~7.64 keV with a significance of ~4.8 sigma. This feature could correspond to blue-shifted Fe xxvi and arise from an accretion disk wind, which would imply an outflow velocity of v~0.086c (~25800...

  4. Solar Wind Ablation of Terrestrial Planet Atmospheres

    Science.gov (United States)

    Moore, Thomas Earle; Fok, Mei-Ching H.; Delcourt, Dominique C.

    2009-01-01

    Internal plasma sources usually arise in planetary magnetospheres as a product of stellar ablation processes. With the ignition of a new star and the onset of its ultraviolet and stellar wind emissions, much of the volatiles in the stellar system undergo a phase transition from gas to plasma. Condensation and accretion into a disk is replaced by radiation and stellar wind ablation of volatile materials from the system- Planets or smaller bodies that harbor intrinsic magnetic fields develop an apparent shield against direct stellar wind impact, but UV radiation still ionizes their gas phases, and the resulting internal plasmas serve to conduct currents to and from the central body along reconnected magnetic field linkages. Photoionization and thermalization of electrons warms the ionospheric topside, enhancing Jeans' escape of super-thermal particles, with ambipolar diffusion and acceleration. Moreover, observations and simulations of auroral processes at Earth indicate that solar wind energy dissipation is concentrated by the geomagnetic field by a factor of 10-100, enhancing heavy species plasma and gas escape from gravity, and providing more current carrying capacity. Thus internal plasmas enable coupling with the plasma, neutral gas and by extension, the entire body. The stellar wind is locally loaded and slowed to develop the required power. The internal source plasma is accelerated and heated, inflating the magnetosphere as it seeks escape, and is ultimately blown away in the stellar wind. Bodies with little sensible atmosphere may still produce an exosphere of sputtered matter when exposed to direct solar wind impact. Bodies with a magnetosphere and internal sources of plasma interact more strongly with the stellar wind owing to the magnetic linkage between the two created by reconnection.

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

    Science.gov (United States)

    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. Blowing bubbles in the cosmos astronomical winds, jets, and explosions

    CERN Document Server

    Hartquist, T W; Ruffle, D P

    2004-01-01

    1. The First Discoveries of Astronomical Winds2. The Magnitudes of Astronomical Quantities3. Stellar Evolution4. Basic Structures of Winds and Windblown Bubbles5. Star Formation and Low-Mass Young Stellar Objects6. Regions of High-Mass Star Formation7. Winds from Main-Sequence and Post-Main-Sequence Stars8. Supernovae and Their Remnants9. Galactic Winds, Starburst Superwinds, and the Epoch of Galaxy Formation10. Active Galaxies and Their Nuclei11. Some Other Windy and Explosive Sources

  7. Role of wind and thermal forcing in the formation of the water circulation variability in the Japan/East Sea Central Basin in 1958-2006

    Science.gov (United States)

    Diansky, N. A.; Stepanov, D. V.; Gusev, A. V.; Novotryasov, V. V.

    2016-03-01

    Based on the numerical experiment on simulation of the Japan/East Sea (JES) water circulation response to the atmospheric forcing for 1958-2006, the analysis is made of its long-term variability in the JES Central Basin (CB). It was found that during the climatic year, the circulation remains cyclonic, strengthening in spring and weakening in autumn. The analysis of mean relative vorticity (MRV) at intermediate depths in the JES CB showed one that the spectrum of its interannual variability is formed mainly by oscillations of periods ˜2, ˜4 and ˜5 years, and in the decadal range with ˜10 and ˜14 years. Along the depth, the spectral composition of MRV variability does not change, but there is a noticeable weakening of decadal variability amplitude, which does not occur with the 4- and 5-year oscillations. Using SVD-analysis, the connection is established between MRV variability, wind stress curl (WSC), as well as sensible heat flux. The strong connection between MRV and WSC is revealed in the range of 4-5 years, and in the decadal range (period is 10 years) the significant connection is with both WSC and air-sea temperature as a result of winter cooling and following deep convection.

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

    Directory of Open Access Journals (Sweden)

    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.

  9. Impact of Large-Scale Wind Power Centralized Access on System Short-Circuit Current%大规模风电集中接入对系统短路电流的影响分析

    Institute of Scientific and Technical Information of China (English)

    周专; 吕盼; 宋新甫; 张增强; 刘建亮

    2015-01-01

    Large-scale wind power centralized access to the power grid caused many problems, such as short-circuit current, equipment selec-tion and mode of operation at middle and low voltage side in booster station etc. Through the different wind turbine generator models (dual-fed and direct drive) and single wind turbine generator of different capacity, this paper analyzed the system short-circuit current. Based on wind tur-bines short-circuit PMU recorded wave curve and wind turbine generator model short-circuit simulation curve, this paper proposed an engineer-ing calculation method to calculate the different models and capacity wind turbine generator equivalent subtransient reactance. Combining with the theoretical calculation model of short-circuit current, this paper analyzed the system short-circuit current provided by the single wind farm and wind power centralized station. The result shows that the large-scale wind power centralized access provides the un-neglected short-circuit current for the system.%规模化风电集中接入电网,将对系统提供一定的短路电流,影响设备选型、升压站中低压侧的运行方式等.通过对不同风电机组型号(双馈式和直驱式)及不同容量的单个风电机组对系统提供的短路电流分析,根据风电机组短路PMU录波曲线和风电机组模型短路仿真曲线,提出了一种工程计算方法,计算出不同型号和不同容量的风电机组等值次暂态电抗,并结合短路电流理论计算模型,分析单个风电场以及风电汇集站对系统提供的短路电流,结果表明,规模化风电的集中接入,对系统提供的短路电流不可忽略.

  10. The True origin of Wolf-Rayet stars

    CERN Document Server

    Vink, Jorick S

    2015-01-01

    The Wolf-Rayet (WR) phenomenon is widespread in astronomy. It involves classical WRs, very massive stars (VMS), WR central stars of planetary nebula CSPN [WRs], and supernovae (SNe). But what is the root cause for a certain type of object to turn into an emission-line star? In this contribution, I discuss the basic aspects of radiation-driven winds that might reveal the ultimate difference between WR stars and canonical O-type stars. I discuss the aspects of (i) self-enrichment via CNO elements, (ii) high effective temperatures Teff, (iii) an increase in the helium abundance Y, and finally (iv) the Eddington factor Gamma. Over the last couple of years, we have made a breakthrough in our understanding of Gamma-dependent mass loss, which will have far-reaching consequences for the evolution and fate of the most massive stars in the Universe. Finally, I discuss the prospects for studies of the WR phenomenon in the highest redshift Ly-alpha and He II emitting galaxies.

  11. Are WNL stars tracers of high metallicity?

    OpenAIRE

    Gräfener, G.; Hamann, W.-R.

    2006-01-01

    We present new atmosphere models for Wolf-Rayet stars that include a self-consistent solution of the wind hydrodynamics. We demonstrate that the formation of optically thick WR winds can be explained by radiative driving on Fe line opacities, implying a strong dependence on metallicity (Z). Z-dependent model calculations for late-type WN stars show that these objects are very massive stars close to the Eddington limit, and that their formation is strongly favored for high metallicity environm...

  12. A Heavy Flavor Tracker for STAR

    International Nuclear Information System (INIS)

    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. A Heavy Flavor Tracker for STAR

    Energy Technology Data Exchange (ETDEWEB)

    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.

  14. A Heavy Flavor Tracker for STAR

    Energy Technology Data Exchange (ETDEWEB)

    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.

  15. A Heavy Flavor Tracker for STAR

    OpenAIRE

    Z. Xu; Chen, Y; Kleinfelder, S.; Koohi, A.; Li, S.; H. Huang; Tai, A.; Kushpil, V.; Sumbera, M; Colledani, C.; Dulinski, W.; Himmi, A.; Hu, C; Shabetai, A.; Szelezniak, M.

    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.

  16. Periodic Variations in Ultraviolet Spectral Lines of the B0.5 Ib Star HD 64760: Evidence for Corotating Wind Streams Rooted in Surface Variations

    Science.gov (United States)

    Owocki, Stanley P.; Cranmer, Steven R.; Fullerton, Alexander W.

    1995-11-01

    We discuss recently observed periodic modulations in the UV wind lines of the B-type supergiant HD 64760, with a focus on the peculiar, upwardly bowed shape seen in isoflux contours of the absorption variations plotted against velocity and time. We show that this qualitative impression of bowed contours is quantitatively confirmed by a peak in the phase for the associated periodic variation at very nearly the same line position as the apparent bow minimum. The bowed shape is significant because it indicates that wind variations evolve both blueward and redward, i.e., toward both larger and smaller line-of-sight velocities. We show here, however, that these characteristics arise naturally from absorption by strictly accelerating corotating wind streams seen in projection against the stellar disk. The quite good agreement obtained with the observed profile variations provides strong evidence for corotating stream modulations in this wind.

  17. Mass loss from Wolf-Rayet stars

    International Nuclear Information System (INIS)

    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)

  18. Rummaging inside the Eskimo's parka: Variable asymmetric PN fast wind and a binary nucleus?

    CERN Document Server

    Prinja, Raman

    2014-01-01

    We report on high-resolution optical time-series spectroscopy of the central star of the `Eskimo' planetary nebula NGC~2392. Datasets were secured with the ESO 2.3m in 2006 March and CFHT 3.6m in 2010 March to diagnose the fast wind and photospheric properties of the central star. The HeI and HeII recombination lines reveal evidence for clumping and temporal structures in the fast wind that are erratically variable on timescales down to ~ 30 min. (i.e. comparable to the characteristic wind flow time). We highlight changes in the overall morphology of the wind lines that cannot plausibly be explained by line-synthesis model predictions with a spherically homogeneous wind. Additionally we present evidence that the UV line profile morphologies support the notion of a high-speed, high-ionization polar wind in NGC~2392. Analyses of deep-seated, near-photospheric absorption lines reveals evidence for low-amplitude radial velocity shifts. Fourier analysis points tentatively to a ~ 0.12-d modulation in the radial vel...

  19. Feedback Regulated Star Formation: From Star Clusters to Galaxies

    CERN Document Server

    Dib, Sami

    2011-01-01

    This paper summarises results from semi-analytical modelling of star formation in protocluster clumps of different metallicities. In this model, gravitationally bound cores form uniformly in the clump following a prescribed core formation efficiency per unit time. After a contraction timescale which is equal to a few times their free-fall times, the cores collapse into stars and populate the IMF. Feedback from the newly formed OB stars is taken into account in the form of stellar winds. When the ratio of the effective wind energy of the winds to the gravitational energy of the system reaches unity, gas is removed from the clump and core and star formation are quenched. The power of the radiation driven winds has a strong dependence on metallicity and increases with increasing metallicity. Thus, winds from stars in the high metallicity models lead to a rapid evacuation of the gas from the protocluster clump and to a reduced star formation efficiency, SFE_{exp}, as compared to their low metallicity counterparts...

  20. Mapping Wind Energy Controversies

    DEFF Research Database (Denmark)

    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...

  1. RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION

    International Nuclear Information System (INIS)

    We report a series of simulations of the formation of a star cluster similar to the Orion Nebula Cluster (ONC), including both radiative transfer and protostellar outflows, and starting from both smooth and self-consistently turbulent initial conditions. Each simulation forms >150 stars and brown dwarfs, yielding a stellar mass distribution that ranges from ☉ to >10 M☉. We show that a simulation that begins with self-consistently turbulent density and velocity fields embedded in a larger turbulent volume, and that includes protostellar outflows, produces an initial mass function (IMF) that is consistent both with that of the ONC and the Galactic field, at least within the statistical power provided by the number of stars formed in our simulations. This is the first simulation published to date that reproduces the observed IMF in a cluster large enough to contain massive stars, and where the peak of the mass function is determined by a fully self-consistent calculation of gas thermodynamics rather than a hand-imposed equation of state. This simulation also produces a star formation rate that, while still somewhat too high, is much closer to observed values than if we omit either the larger turbulent volume or the outflows. Moreover, we show that the combination of outflows, self-consistently turbulent initial conditions, and turbulence continually fed by motions on scales larger than that of the protocluster yields an IMF that is in agreement with observations and invariant with time, resolving the 'overheating' problem in which simulations without these features have an IMF peak that shifts to progressively higher masses over time as more and more of the gas is heated, inconsistent with the observed invariance of the IMF. The simulation that matches the observed IMF also qualitatively reproduces the observed trend of stellar multiplicity strongly increasing with mass. We show that this simulation produces massive stars from distinct massive cores whose

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

    DEFF Research Database (Denmark)

    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...

  3. 77 FR 48138 - Topaz Solar Farms LLC; High Plains Ranch II, LLC; Bethel Wind Energy LLC; Rippey Wind Energy LLC...

    Science.gov (United States)

    2012-08-13

    ...-000; EG12-68-000; EG12-69-000] Topaz Solar Farms LLC; High Plains Ranch II, LLC; Bethel Wind Energy LLC; Rippey Wind Energy LLC; Pacific Wind, LLC; Colorado Highlands Wind, LLC; Shooting Star Wind... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY...

  4. Modelling the Central Constant Emission X-ray component of eta Carinae

    CERN Document Server

    Russell, Christopher M P; Hamaguchi, Kenji; Madura, Thomas I; Owocki, Stanley P; Hillier, D John

    2016-01-01

    The X-ray emission of $\\eta$ Carinae shows multiple features at various spatial and temporal scales. The central constant emission (CCE) component is centred on the binary and arises from spatial scales much smaller than the bipolar Homunculus nebula, but likely larger than the central wind--wind collision region between the stars as it does not vary over the $\\sim$2-3 month X-ray minimum when it can be observed. Using large-scale 3D smoothed particle hydrodynamics (SPH) simulations, we model both the colliding-wind region between the stars, and the region where the secondary wind collides with primary wind ejected from the previous periastron passage. The simulations extend out to one hundred semimajor axes and make two limiting assumptions (strong coupling and no coupling) about the influence of the primary radiation field on the secondary wind. We perform 3D radiative transfer calculations on the SPH output to synthesize the X-ray emission, with the aim of reproducing the CCE spectrum. For the preferred pr...

  5. Stellar Winds on the Main-Sequence I: Wind Model

    CERN Document Server

    Johnstone, C P; Lüftinger, T; Toth, G; Brott, I

    2015-01-01

    Aims: We develop a method for estimating the properties of stellar winds for low-mass main-sequence stars between masses of 0.4 and 1.1 solar masses at a range of distances from the star. Methods: We use 1D thermal pressure driven hydrodynamic wind models run using the Versatile Advection Code. Using in situ measurements of the solar wind, we produce models for the slow and fast components of the solar wind. We consider two radically different methods for scaling the base temperature of the wind to other stars: in Model A, we assume that wind temperatures are fundamentally linked to coronal temperatures, and in Model B, we assume that the sound speed at the base of the wind is a fixed fraction of the escape velocity. In Paper II of this series, we use observationally constrained rotational evolution models to derive wind mass loss rates. Results: Our model for the solar wind provides an excellent description of the real solar wind far from the solar surface, but is unrealistic within the solar corona. We run ...

  6. WIND BRAKING OF MAGNETARS

    Energy Technology Data Exchange (ETDEWEB)

    Tong, H. [Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011 (China); Xu, R. X.; Qiao, G. J. [KIAA and School of Physics, Peking University, Beijing 100871 (China); Song, L. M., E-mail: tonghao@xao.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2013-05-10

    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{sub x}<- E-dot{sub 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.

  7. WIND BRAKING OF MAGNETARS

    International Nuclear Information System (INIS)

    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 Lxrot 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.

  8. Wind Braking of Magnetars

    Science.gov (United States)

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

    2013-05-01

    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.

  9. Mass loss from inhomogeneous hot star winds III. An effective-opacity formalism for line radiative transfer in accelerating, clumped two-component media, and first results on theory and diagnostics

    CERN Document Server

    Sundqvist, J O; Owocki, S P

    2014-01-01

    [Abridged] We develop and benchmark a fast and easy-to-use effective-opacity formalism for line and continuum radiative transfer in an accelerating two-component clumpy medium. The formalism bridges the limits of optically thin and thick clumps, and is here used to i) design a simple vorosity-modified Sobolev with exact integration (vmSEI) method for analyzing UV wind resonance lines in hot, massive stars, and ii) derive simple correction factors to the line force driving the outflows of such stars. We show that (for a given ionization factor) UV resonance doublets may be used to analytically predict the upward corrections in empirically inferred mass-loss rates associated with porosity in velocity space (a.k.a. velocity-porosity, or vorosity), but that severe solution degeneracies exist. For an inter-clump density set to 1 % of the mean density, we for O and B supergiants derive upward empirical mass-loss corrections of typically factors of either ~5 or ~50, depending on which of the two applicable solutions...

  10. Transport of First Rocks of The Solar System by X-winds

    OpenAIRE

    Hu, Renyu

    2010-01-01

    It has been suggested that chondrules and calcium-aluminum-rich inclusions (CAIs) were formed at the inner edge of the protoplanetary disk and then entrained in magnetocentrifugal X-winds. We study trajectories of such solid bodies with the consideration of the central star gravity, the protoplanetary disk gravity, and the gas drag of the wind. The efficiency of the gas drag depends on a parameter $\\eta$, which is the product of the solid body size and density. We find that the gravity of the...

  11. STARs in the CNS.

    Science.gov (United States)

    Ehrmann, Ingrid; Fort, Philippe; Elliott, David J

    2016-08-15

    STAR (signal transduction and activation of RNA) proteins regulate splicing of target genes that have roles in neural connectivity, survival and myelination in the vertebrate nervous system. These regulated splicing targets include mRNAs such as the Neurexins (Nrxn), SMN2 (survival of motor neuron) and MAG (myelin-associated glycoprotein). Recent work has made it possible to identify and validate STAR protein splicing targets in vivo by using genetically modified mouse models. In this review, we will discuss the importance of STAR protein splicing targets in the CNS (central nervous system). PMID:27528753

  12. Discovery of a magnetic field in the rapidly-rotating O-type secondary of the colliding-wind binary HD 47129 (Plaskett's star)

    CERN Document Server

    Grunhut, J H; Leutenegger, M; Petit, V; Rauw, G; Neiner, C; Martins, F; Cohen, D H; Gagné, M; Ignace, R; Mathis, S; de Mink, S E; Moffat, A F J; Owocki, S; Shultz, M; Sundqvist, J

    2012-01-01

    We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star), in the context of the Magnetism in Massive Stars (MiMeS) survey. Eight independent Stokes $V$ observations were acquired using the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the T\\'elescope Bernard Lyot. Using Least-Squares Deconvolution we obtain definite detections of signal in Stokes $V$ in 3 observations. No significant signal is detected in the diagnostic null ($N$) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly-rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable...

  13. Analysis and Design of the Adjustable Central Flap Mechanism of the Second Throat in Wind Tunnel%风洞喉道可调中心体机构分析与设计

    Institute of Scientific and Technical Information of China (English)

    陈建兵; 高鑫宇; 蔡清青

    2012-01-01

    The second throat has important functions in transonic and supersonic wind tunnel. In recent years, the second throat with central flap has been an important structure type and was widely researched abroad. This paper takes the structure design of central flap mechanism of the second throat in transonic wind tunnel as the background, starting with the principle of offset slider-crank mechanism, and combining the characteristics of central flap mechanism of the second throat in 0.3m wind tunnel. The symmetrical offset dual-slider-crank mechanism has been innovatively used, and its kinematic and dynamic characteristics have been analyzed. The results of wind tunnel tests show that this mechanism has better aerodynamic characteristics, and the structure type of the mechanism is reasonable and reliable.%第二喉道在跨超声速风洞中具有重要作用,中心体式第二喉道作为其中一种重要的结构形式近年来国外已开展了大量研究.本文以跨声速风洞第二喉道中心体机构的设计为背景,从偏置曲柄滑块机构原理入手,结合0.3m风洞第二喉道可调中心体机构的结构特点,创新性地运用了对称偏置双曲柄滑块机构,并对其进行了运动学和动力学分析.风洞运行结果表明:该机构具有良好的气动性能,结构形式合理可靠.

  14. The Embedded Massive Star Forming Region RCW 38

    CERN Document Server

    Wolk, Scott J; Vigil, Miquela

    2008-01-01

    RCW~38 is a uniquely young ($<$1 Myr), embedded ($A_V \\sim 10$) stellar cluster surrounding a pair of early O stars ($\\sim$O5.5) and is one of the few regions within 2 kpc other than Orion to contain over 1000 members. X-ray and deep near-infrared observations reveal a dense cluster with over 200 X-ray sources and 400 infrared sources embedded in a diffuse hot plasma within a 1 pc diameter. The central O star has evacuated its immediate surroundings of dust, creating a wind bubble $\\sim$0.1 pc in radius that is confined by the surrounding molecular cloud, as traced by millimeter continuum and molecular line emission. The interface between the bubble and cloud is a region of warm dust and ionized gas, which shows evidence for ongoing star formation. Extended warm dust is found throughout a 2--3 pc region and coincides with extended X-ray plasma. This is evidence that the influence of the massive stars reaches beyond the confines of the O star bubble. RCW~38 appears similar in structure to RCW~49 and M~20 bu...

  15. Star Formation at the Galactic Center

    Science.gov (United States)

    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

  16. Modelling the Central Constant Emission X-ray component of η Carinae

    Science.gov (United States)

    Russell, Christopher M. P.; Corcoran, Michael F.; Hamaguchi, Kenji; Madura, Thomas I.; Owocki, Stanley P.; Hillier, D. John

    2016-05-01

    The X-ray emission of η Carinae shows multiple features at various spatial and temporal scales. The central constant emission (CCE) component is centred on the binary and arises from spatial scales much smaller than the bipolar Homunculus nebula, but likely larger than the central wind-wind collision region between the stars as it does not vary over the ˜2-3 month X-ray minimum when it can be observed. Using large-scale 3D smoothed particle hydrodynamics (SPH) simulations, we model both the colliding-wind region between the stars, and the region where the secondary wind collides with primary wind ejected from the previous periastron passage. The simulations extend out to one hundred semimajor axes and make two limiting assumptions (strong coupling and no coupling) about the influence of the primary radiation field on the secondary wind. We perform 3D radiative transfer calculations on the SPH output to synthesize the X-ray emission, with the aim of reproducing the CCE spectrum. For the preferred primary mass-loss rate dot{M}_A≈ 8.5× 10^{-4} M_{⊙} yr-1, the model spectra well reproduce the observation as the strong- and no-coupling spectra bound the CCE observation for longitude of periastron ω ≈ 252°, and bound/converge on the observation for ω ≈ 90°. This suggests that η Carinae has moderate coupling between the primary radiation and secondary wind, that both the region between the stars and the comoving collision on the backside of the secondary generate the CCE, and that the CCE cannot place constraints on the binary's line of sight. We also discuss comparisons with common X-ray fitting parameters.

  17. 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

    CERN Document Server

    Henry, R B C; Dufour, R J; Kwitter, K B; Shaw, R A; Miller, T R; Buell, J F; Corradi, R L M

    2015-01-01

    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 PB6). 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 PN central stars 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 3rd dredge-up; 4) C/O versus O/H for our objects appears to be inversely correlated, perhaps consistent with the conclusion of theor...

  18. 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

    Science.gov (United States)

    Henry, R. B. C.; Balick, B.; Dufour, R. J.; Kwitter, K. B.; Shaw, R. A.; Miller, T. R.; Buell, J. F.; Corradi, R. L. M.

    2015-11-01

    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⊙. Finally, we present the first published photoionization models of NGC 5315 and NGC 5882. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

  19. A Central Engine for Cosmic $\\gamma$-Ray Burst Sources

    CERN Document Server

    Ruderman, M A; Kluzniak, W

    2000-01-01

    One of a family previously proposed ``central engines'' for cosmic gamma-ray burst sources (Klu\\'zniak & Ruderman 1998) is considered in some detail. A steadily accreting $10^6$ Gauss magnetic white dwarf should ultimately collapse to a strongly differentially rotating, millisecond-rotation-period neutron star for a wide range of steady accretion rates and initial masses if the accreting white dwarf has an evolved O-Ne-Mg composition. A similar neutron star could also result from an initial C-O white dwarf but only for more constrained accretion rates. Because the collapsing white dwarf begins as a $\\gamma=4/3$ polytrope, the final neutron star's spin-rate increases strongly with cylindrical radius. A stable wind-up of magnetic field perpendicular to the stellar spin then produces buoyant magnetic toroids which grow, break loose, rise, and partly penetrate the neutron star surface to form a transient, $B\\approx 10^{17}$ G millisecond spin-period pulsar with a powerful pulsar wind (Usov 1992). This pulsar ...

  20. Stars and Star Myths.

    Science.gov (United States)

    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…

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

    International Nuclear Information System (INIS)

    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

  2. The formation of filamentary structures in radiative cluster winds

    OpenAIRE

    Rodr'iguez-Gonz'alez, A.; Esquivel, A.; A. C. Raga; Cant'o, J.

    2008-01-01

    We explore the dynamics of a ``cluster wind'' flow in the regime in which the shocks resulting from the interaction of winds from nearby stars are radiative. We first show that for a cluster with T Tauri stars and/or Herbig Ae/Be stars, the wind interactions are indeed likely to be radiative. We then compute a set of four, three dimensional, radiative simulations of a cluster of 75 young stars, exploring the effects of varying the wind parameters and the density of the initial ISM that permea...

  3. Modes of clustered star formation

    CERN Document Server

    Pfalzner, S; Olczak, C

    2012-01-01

    The realization that most stars form in clusters, raises the question of whether star/planet formation are influenced by the cluster environment. The stellar density in the most prevalent clusters is the key factor here. Whether dominant modes of clustered star formation exist is a fundamental question. Using near-neighbour searches in young clusters Bressert et al. (2010) claim this not to be the case and conclude that star formation is continuous from isolated to densely clustered. We investigate under which conditions near-neighbour searches can distinguish between different modes of clustered star formation. Near-neighbour searches are performed for model star clusters investigating the influence of the combination of different cluster modes, observational biases, and types of diagnostic and find that the cluster density profile, the relative sample sizes, limitations in observations and the choice of diagnostic method decides whether modelled modes of clustered star formation are detected. For centrally ...

  4. Born from the Wind

    Science.gov (United States)

    2008-10-01

    this mechanism. "We were particularly interested to know what caused this seemingly isolated group of stars to form," says Gouliermis. By combining multi-wavelength data of NGC 346, Gouliermis and his team were able to pinpoint the trigger as a very massive star that blasted apart in a supernova explosion about 50 000 years ago. Fierce winds from the massive dying star, and not radiation, pushed gas and dust together, compressing it into new stars, bringing the isolated young stars into existence. While the remains of this massive star cannot be seen in the image, a bubble created when it exploded can be seen near the large, white spot with a blue halo at the upper left (this white spot is actually a collection of three stars). The finding demonstrates that both wind- and radiation-induced triggered star formation are at play in the same cloud. According to Gouliermis, "the result shows us that star formation is a far more complicated process than we used to think, comprising different competitive or collaborative mechanisms." The analysis was only possible thanks to the combination of information obtained through very different techniques and equipments. It reveals the power of such collaborations and the synergy between ground- and space-based observatories.

  5. CO-0.30-0.07: A Candidate Site of Collision-induced Massive Star Formation in the Milky Way's Central Molecular Zone

    Science.gov (United States)

    Tanaka, K.

    2016-05-01

    Cloud-cloud collision has long been claimed to be an efficient trigger of massive star formation. We present interferometric maps of a candidate site of collision-triggered star formation newly discovered at 40 pc projected distance from the Galactic center. The cloud CO- 0.3 has an extremely broad molecular line emission of a 140 km s-1 velocity width despite of absence of any known energy sources nearby and inside the cloud. Recent observations with the Atacama Large Millimeter and Submillimeter Array have unveiled that the cloud is comprised by two distinctive velocity components which appear to contact at a thin, well-defined interface layer on the plane-of-the-sky, suggesting that the extremely broad emissions originate from shocked regions created by cloud-cloud collision.

  6. The SNR G106.3+2.7 and its Pulsar Wind Nebula: relics of triggered star formation in a complex environment

    OpenAIRE

    Kothes, Roland; Uyaniker, Bulent; Pineault, Serge

    2001-01-01

    We propose that the pulsar nebula associated with the pulsar J2229+6114 and the supernova remnant (SNR) G106.3+2.7 are the result of the same supernova explosion. The whole structure is located at the edge of an HI bubble with extended regions of molecular gas inside. The radial velocities of both the atomic hydrogen and the molecular material suggest a distance of 800 pc. At this distance the SNR is 14 pc long and 6 pc wide. Apparently the bubble was created by the stellar wind and supernova...

  7. Wind farm economics

    International Nuclear Information System (INIS)

    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)

  8. A fast ionised wind in a Star Forming-Quasar system at z~1.5 resolved through Adaptive Optics assisted near-infrared data

    CERN Document Server

    Brusa, M; Cresci, G; Schramm, M; Delvecchio, I; Lanzuisi, G; Mainieri, V; Mignoli, M; Zamorani, G; Berta, S; Bongiorno, A; Comastri, A; Fiore, F; Kakkad, D; Marconi, A; Rosario, D; Contini, T; Lamareille, F

    2016-01-01

    Outflows are invoked in co-evolutionary models to link the growth of SMBH and galaxies through feedback phenomena, and from the analysis of both galaxies and Active Galactic Nuclei (AGN) samples at z$\\sim1-3$, it is becoming clear that powerful winds are quite common in AGN hosts. High-resolution and high S/N observations are needed in order to uncover the physical properties of the wind through kinematics analysis. We exploited VIMOS, SINFONI and Subaru/IRCS Adaptive Optics data to study the kinematics properties on the scale the host galaxy of XID5395, a luminous, X-ray obscured Starburst/Quasar merging system at z$\\sim1.5$ detected in the XMM-COSMOS field, and associated with an extreme [O II] emitter (EW$\\sim200$ \\AA). We mapped, for the first time, at high resolution the kinematics of the [O III] and H$\\alpha$ line complexes and linked them with the [O II] emission. The high spatial resolution achieved allowed us to resolve all the components of the SB-QSO system. Our analysis with a resolution of few kp...

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

    OpenAIRE

    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?

  10. The VLT-FLAMES Tarantula Survey - XI. A census of the hot luminous stars and their feedback in 30 Doradus

    CERN Document Server

    Doran, E I; de Koter, A; Evans, C J; McEvoy, C; Walborn, N R; Bastian, N; Bestenlehner, J M; Grafener, G; Herrero, A; Kohler, K; Apellaniz, J Maiz; Najarro, F; Puls, J; Sana, H; Schneider, F R N; Taylor, W D; van Loon, J Th; Vink, J S

    2013-01-01

    We compile the first comprehensive census of hot luminous stars in the 30 Doradus (30 Dor) star forming region of the LMC. The census extends to a radius of 10arcmin (150pc) from the central cluster, R136. Stars were selected photometrically and combined with the latest spectral types. 1145 candidate hot luminous stars were identified of which >700 were considered genuine early type stars that contribute to feedback. We assess the spectroscopic completeness to be 85% in outer regions (>5pc) but fall to 35% in the vicinity of R136, giving a total of 500 hot luminous stars with spectroscopy. Stellar calibrations and models were used to obtain their physical parameters before integrated values were compared to global observations and the population synthesis code, Starburst99. The 31 W-R and Of/WN stars made large contributions to the total ionising and wind luminosities of ~40% and ~50%, respectively. Stars with Minit>100Msun also showed high contributions to the global feedback, ~25% in both cases. Such massiv...

  11. Envelope Inflation or Stellar Wind?

    Science.gov (United States)

    Ro, S.; Matzner, C. D.

    We an optically-thick, transonic, steady wind model for a H-free Wolf-Rayet star. A bifurcation is found across a critical mass loss rate Mb. Slower winds M < Mb extend by several hydrostatic stellar radii, reproduce features of envelope in ation from Petrovic et al. (2006) and Gräfener et al. (2012), and are energetically unbound. This work is of particular interest for extended envelopes and winds, radiative hydrodynamic instabilities (eg. wind stagnation, clumping, etc.), and NLTE atmospheric models.

  12. Bloated stars as agn broad line clouds the emission line spectrum

    CERN Document Server

    Alexander, T; Tal Alexander; Hagai Netzer

    1994-01-01

    The `Bloated Stars Scenario' proposes that AGN broad line emission originates in the winds or envelopes of bloated stars (BS). Its main advantage over BLR cloud models is the gravitational confinement of the gas and its major difficulty the large estimated number of BSs and resulting high mass loss rate. We calculate the emission line spectrum by a detailed numerical photoionization code for a wide range of wind structures and a detailed QSO nucleus model with L(ion)=7E45 erg/s, M(bh)=8E7 Mo. The size and boundary density of the BS wind are determined by various processes: Comptonization by the central continuum source, calculated self consistently, tidal disruption by the black hole and the limit set by the wind's finite mass. We find that the emission spectrum is mainly determined by the conditions at the boundary of the line emitting fraction of the wind rather than by its internal structure. Comptonization results in very high ionization parameters at the boundary which produces an excess of unobserved br...

  13. MASSIVE STAR FORMATION IN THE MAGELLANIC CLOUDS

    Directory of Open Access Journals (Sweden)

    M. Rubio

    2009-01-01

    Full Text Available Multiwavelenghts studies of massive star formation regions in the LMC and SMC reveal that a second generation of stars is being formed in dense molecular clouds located in the surroundings of the massive clusters. These dense molecular clouds have survive the action of massive star UV radiation elds and winds and they appear as compact dense H2 knots in regions of weak CO emission. We present results of observations obtained towards massive star forming regions in the low metallicity molecular clouds in the Magellanic Clouds and investigate its implication on star formation in the early universe.

  14. UV spectroscopy of the blue supergiant SBW1: the remarkably weak wind of a SN 1987A analog

    OpenAIRE

    Smith, Nathan; Groh, Jose H.; France, Kevin; McCray, Richard

    2016-01-01

    The Galactic blue supergiant SBW1 with its circumstellar ring nebula represents the best known analog of the progenitor of SN 1987A. High-resolution imaging has shown H-alpha and IR 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 HST Cosmic Origins Spectrograph (COS). The UV spectrum shows none of the typical wind signatur...

  15. Stellar magnetism, winds and their effects on planetary environments

    CERN Document Server

    Vidotto, A A

    2016-01-01

    Here, I review some recent works on magnetism of cool, main-sequence stars, their winds and potential impact on surrounding exoplanets. The winds of these stars are very tenuous and persist during their lifetime. Although carrying just a small fraction of the stellar mass, these magnetic winds carry away angular momentum, thus regulating the rotation of the star. Since cool stars are likely to be surrounded by planets, understanding the host star winds and magnetism is a key step towards characterisation of exoplanetary environments. As rotation and activity are intimately related, the spin down of stars leads to a decrease in stellar activity with age. As a consequence, as stars age, a decrease in high-energy (X-ray, extreme ultraviolet) irradiation is observed, which can a ect the evaporation of exoplanetary atmospheres and, thus, also altering exoplanetary evolution.

  16. Magnetic propeller in symbiotic stars

    OpenAIRE

    Panferov, Alexander; Mikolajewski, Maciej

    2000-01-01

    Rapidly spinning magnetic white dwarfs in symbiotic stars may pass through the propeller stage. It is believed that a magnetic propeller acts in two such stars CH Cyg and MWC 560. We review a diversity of manifestations of the propeller there. In these systems in a quiescent state the accretion onto a white dwarf from the strong enough wind of a companion star is suppressed by the magnetic field, and the hot component luminosity is low. Since the gas stored in the envelope eventually settles ...

  17. Hydrodynamical numerical simulation of wind production from black hole hot accretion flows at very large radii

    CERN Document Server

    Bu, De-Fu; Gan, Zhao-Ming; Yang, Xiao-hong

    2015-01-01

    In previous works, it has been shown that strong winds exist in hot accretion flows around black holes. Those works focus only on the region close to the black hole thus it is unknown whether or where the wind production stops at large radii. In this paper, we investigate this problem based on hydrodynamical numerical simulations. For this aim, we have taken into account the gravity of both the central black hole and the nuclear star clusters. When calculating the latter, we assume that the velocity dispersion of stars is a constant and the gravitational potential of the nuclear star cluster $\\propto \\sigma^2 \\ln (r)$, where $\\sigma$ is the velocity dispersion of stars and $r$ is the distance from the center of the galaxy. Different from previous works, we focus on the region where the gravitational potential is dominated by the star cluster. We find that, same as the accretion flow at small radii, the mass inflow rate decreases inward and the flow is convectively unstable. However, trajectory analysis has sh...

  18. Wave Star

    DEFF Research Database (Denmark)

    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....

  19. Ap stars with variable periods

    CERN Document Server

    Mikulášek, Zdeněk; Janík, Jan; Zejda, Miloslav; Henry, Gegory W; Paunzen, Ernst; Žižňovský, Jozef; Zverko, Juraj

    2013-01-01

    The majority of magnetic chemically peculiar (mCP) stars exhibit periodic light, magnetic, radio, and spectroscopic variations that can be adequately modelled as a rigidly-rotating main-sequence star with persistent surface structures. Nevertheless, there is a small sample of diverse mCP stars whose rotation periods vary on timescales of decades while the shapes of their phase curves remain unchanged. Alternating period increases and decreases have been suspected in the hot CP stars CU Vir and V901 Ori, while rotation in the moderately cool star BS Cir has been decelerating. These examples bring new insight into this theoretically unpredicted phenomenon. We discuss possible causes of such behaviour and propose that dynamic interactions between a thin, outer, magnetically-confined envelope braked by the stellar wind, and an inner faster-rotating stellar body are able to explain the observed rotational variability

  20. Circumnuclear Star Formation in the BAT AGN Sample: High Resolution Radio Morphologies and SFRs

    Science.gov (United States)

    Smith, Krista Lynne; Mushotzky, Richard; Vogel, Stuart N.; Miller, Neal A.

    2016-04-01

    It has long been an assumption that active galaxies would obey the same far-infrared (FIR) - radio correlation established for star-forming normal galaxies. This assumption has been used by numerous high-z studies, but has recently come into doubt for two main reasons: the revelation that the AGN itself may contribute non-negligibly to the FIR emission, and different radio emission physics in the vicinity of the active nucleus than in isolated HII regions. Studies have attempted to decompose the FIR spectral energy distributions to remove the AGN contribution and then calculate the star formation rate (SFR). It would then be ideal to compare this to another, independent measure of SFR. We have conducted a high-resolution (0.3-1'') JVLA survey of an unbiased sample of nearby, hard X-ray selected AGN in order to spatially decompose the extended star formation emission from the central compact source. We present these maps of the nuclear regions of 41 AGN from the Swift-BAT sample. The objects exhibit a wide range of circumnuclear radio morphologies, including mini-jets and star-forming rings. When the central compact source is removed, the extended emission does indeed conform to the FIR-radio correlation. A subset of the objects also remain compact in our 1'' and 0.3'' observations, implying very high star formation surface densities which may be capable of driving significant winds.

  1. Spectroscopic analysis of newborn massive stars in SMC N81

    CERN Document Server

    Martins, F; Heydari-Malayeri, M

    2003-01-01

    We present the first results of a spectroscopic study of young massive stars in the SMC High Excitation Blob N81. These stars have Mv values which are ~ 2 mag smaller than those of nor mal dwarf stars. Their UV STIS spectra reveal features typical of O stars, but surprisingly weak wind components. The preliminary modelling of these spectr a with the code CMFGEN (Hillier & Miller 1998) indicates a mass loss rate of the order 10e-9 Mdot/yr. If confirmed, such a weak wind may indicate either a breakdown of the wind-momentum luminosity relation at low luminosity, or a steeper slope of this relation at low metallicity.

  2. Catch a Star!

    Science.gov (United States)

    2006-11-01

    transit" (Lleida, Spain). Some previous winning entries are visible on the Catch a Star! Web site. Detailed entry information can be found on ESO's website, at http://www.eso.org/catchastar/ The deadline for submitting an entry for the 2007 competition is Friday 2 March 2007, 17:00 Central European Time.

  3. The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of HeII 1640 in young star clusters

    CERN Document Server

    Crowther, Paul A; Bostroem, K A; Apellaniz, J Maiz; Schneider, F R N; Walborn, N R; Angus, C R; Brott, I; Bonanos, A; de Koter, A; de Mink, S E; Evans, C J; Grafener, G; Herrero, A; Howarth, I D; Langer, N; Lennon, D J; Puls, J; Sana, H; Vink, J S

    2016-01-01

    We introduce a HST/STIS stellar census of R136a, the central ionizing star cluster of 30 Doradus. We present low resolution far-ultraviolet STIS/MAMA spectroscopy of R136 using 17 contiguous 52x0.2 arcsec slits which together provide complete coverage of the central 0.85 parsec (3.4 arcsec). We provide spectral types of 90% of the 57 sources brighter than m_F555W = 16.0 mag within a radius of 0.5 parsec of R136a1, plus 8 additional nearby sources including R136b (O4\\,If/WN8). We measure wind velocities for 52 early-type stars from CIV 1548-51, including 16 O2-3 stars. For the first time we spectroscopically classify all Weigelt & Baier members of R136a, which comprise three WN5 stars (a1-a3), two O supergiants (a5-a6) and three early O dwarfs (a4, a7, a8). A complete Hertzsprung-Russell diagram for the most massive O stars in R136 is provided, from which we obtain a cluster age of 1.5+0.3_-0.7 Myr. In addition, we discuss the integrated ultraviolet spectrum of R136, and highlight the central role played b...

  4. A fast ionised wind in a star-forming quasar system at z ~ 1.5 resolved through adaptive optics assisted near-infrared data

    Science.gov (United States)

    Brusa, M.; Perna, M.; Cresci, G.; Schramm, M.; Delvecchio, I.; Lanzuisi, G.; Mainieri, V.; Mignoli, M.; Zamorani, G.; Berta, S.; Bongiorno, A.; Comastri, A.; Fiore, F.; Kakkad, D.; Marconi, A.; Rosario, D.; Contini, T.; Lamareille, F.

    2016-04-01

    Aims: Outflow winds are invoked in co-evolutionary models to link the growth of SMBH and galaxies through feedback phenomena, and from the analysis of both galaxies and active galactic nuclei (AGN) samples at z ~ 1-3, it is becoming clear that powerful outflows may be very common in AGN hosts. High-resolution and high S/N observations are needed to uncover the physical properties of the wind through kinematics analysis. Methods: We exploited VLT/VIMOS, VLT/SINFONI, and Subaru/IRCS adaptive optics (AO) data to study the kinematics properties on the scale of the host galaxy of XID5395; this galaxy is a luminous, X-ray obscured starburst/quasar (SB-QSO) merging system at z ~ 1.5, detected in the XMM-COSMOS field, associated with an extreme [O II] emitter (with equivalent width, EW, ~200 Å). For the first time, we mapped the kinematics of the [O III] and Hα line complexes and linked them with the [O II] emission at high resolution. The high spatial resolution achieved allowed us to resolve all the components of the SB-QSO system. Results: Our analysis, with a resolution of few kpc, reveals complexities and asymmetries in and around the nucleus of XID5395. The velocity field measured via non-parametric analysis reveals different kinematic components with maximum blueshifted and redshifted velocities up to ≳ 1300 km s-1 that are not spatially coincident with the nuclear core. These extreme values of the observed velocities and spatial location can be explained by the presence of fast moving material. We also spectroscopically confirm the presence of a merging system at the same redshift as the AGN host. Conclusions: We propose that EW as large as >150 Å in X-ray selected AGN may be an efficient criterion to isolate objects associated with the short, transition phase of "feedback" in the AGN-galaxy co-evolutionary path. This co-evolutionary path subsequently evolves into an unobscured QSO, as suggested from the different observational evidence (e.g. merger, compact

  5. Stars, Galaxies and Quasars

    Directory of Open Access Journals (Sweden)

    Patrick Das Gupta

    2009-05-01

    Full Text Available This article provides a brief introduction to the basics of stars, galaxies and Quasi-stellar objects (QSOs. In stars, the central pressure and temperature must be high in order to halt the stellar gravitational collapse. High temperature leads to thermonuclear fusion in the stellar core, releasing thereby enormous amount of nuclear energy, making the star shine brilliantly. On the other hand, the QSOs are very bright nuclei lying in the centres of some galaxies. Many of these active galactic nuclei, which appear star-like when observed through a telescope and  whose power output are more than 1011 times that of the Sun, exhibit rapid time variability in their X-ray emissions.  Rapid variability along with the existence of a maximum speed limit, c, provide a strong argument in favour of a compact central engine model for QSOs in which a thick disc of hot gas going around a supermassive blackhole is what makes a QSO appear like a bright point source. Hence, unlike stars, QSOs are powered by gravitational potential energy.

  6. Cn2 and wind profiler method to quantify the frozen flow decay using wide-field laser guide stars adaptive optics

    CERN Document Server

    Guesalaga, Andrés; Cortes, Angela; Béchet, Clémentine; Guzmán, Dani

    2014-01-01

    We use spatio-temporal cross-correlations of slopes from five Shack-Hartmann wavefront sensors to analyse the temporal evolution of the atmospheric turbulence layers at different altitudes. The focus is on the verification of the frozen flow assumption. The data is coming from the Gemini South Multi-Conjugate Adaptive Optics System (GeMS). First, the Cn2 and wind profiling technique is presented. This method provides useful information for the AO system operation such as the number of existing turbulence layers, their associated velocities, altitudes and strengths and also a mechanism to estimate the dome seeing contribution to the total turbulence. Next, by identifying the turbulence layers we show that it is possible to estimate the rate of decay in time of the correlation among turbulence measurements. We reduce on-sky data obtained during 2011, 2012 and 2013 campaigns and the first results suggest that the rate of temporal de-correlation can be expressed in terms of a single parameter that is independent ...

  7. High velocity blue-shifted FeII absorption in the dwarf star-forming galaxy PHL293B: Evidence for a wind driven supershell?

    CERN Document Server

    Terlevich, R; Bosch, G; Diaz, A I; Hagele, G; Cardaci, M; Firpo, V

    2014-01-01

    X-shooter and ISIS WHT spectra of the starforming galaxy PHL 293B also known as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper. We find broad (FWHM = 1000km/s) and very broad (FWZI = 4000km/s) components in the Balmer lines, narrow absorption components in the Balmer series blueshifted by 800km/s, previously undetected FeII multiplet (42) absorptions also blueshifted by 800km/s, IR CaII triplet stellar absorptions consistent with [Fe/H] < -2.0 and no broad components or blushifted absorptions in the HeI lines. Based on historical records, we found no optical variability at the 5 sigma level of 0.02 mag between 2005 and 2013 and no optical variability at the level of 0.1mag for the past 24 years. The lack of variability rules out transient phenomena like luminous blue variables or SN IIn as the origin of the blue shifted absorptions of HI and FeII. The evidence points to either a young and dense expanding supershell or a stationary cooling wind, in both cases driven by the young cluster w...

  8. Search for the magnetic field of the O7.5 III star ξ Persei

    NARCIS (Netherlands)

    H.F. Henrichs; R.S. Schnerr; J.A. de Jong; L. Kaper; J.F. Donati; C. Catala

    2008-01-01

    Cyclical wind variability is an ubiquitous but as yet unexplained feature among OB stars. The O7.5 III(n)((f)) star ξ Persei is the brightest representative of this class on the Northern hemisphere. As its prominent cyclical wind properties vary on a rotational time scale (2 or 4 days) the star has

  9. The VLT-FLAMES Tarantula Survey. XI. A census of the hot luminous stars and their feedback in 30 Doradus

    Science.gov (United States)

    Doran, E. I.; Crowther, P. A.; de Koter, A.; Evans, C. J.; McEvoy, C.; Walborn, N. R.; Bastian, N.; Bestenlehner, J. M.; Gräfener, G.; Herrero, A.; Köhler, K.; Maíz Apellániz, J.; Najarro, F.; Puls, J.; Sana, H.; Schneider, F. R. N.; Taylor, W. D.; van Loon, J. Th.; Vink, J. S.

    2013-10-01

    Context. The VLT-FLAMES Tarantula Survey has an extensive view of the copious number of massive stars in the 30 Doradus (30 Dor) star forming region of the Large Magellanic Cloud. These stars play a crucial role in our understanding of the stellar feedback in more distant, unresolved star forming regions. Aims: The first comprehensive census of hot luminous stars in 30 Dor is compiled within a 10 arcmin (150 pc) radius of its central cluster, R136. We investigate the stellar content and spectroscopic completeness of the early type stars. Estimates were made for both the integrated ionising luminosity and stellar wind luminosity. These values were used to re-assess the star formation rate (SFR) of the region and determine the ionising photon escape fraction. Methods: Stars were selected photometrically and combined with the latest spectral classifications. Spectral types were estimated for stars lacking spectroscopy and corrections were made for binary systems, where possible. Stellar calibrations were applied to obtain their physical parameters and wind properties. Their integrated properties were then compared to global observations from ultraviolet (UV) to far-infrared (FIR) imaging as well as the population synthesis code, Starburst99. Results: Our census identified 1145 candidate hot luminous stars within 150 pc of R136 of which >700 were considered to be genuine early type stars and contribute to feedback. We assess the survey to be spectroscopically complete to 85% in the outer regions (>5 pc) but only 35% complete in the region of the R136 cluster, giving a total of 500 hot luminous stars in the census which had spectroscopy. Only 31 were found to be Wolf-Rayet (W-R) or Of/WN stars, but their contribution to the integrated ionising luminosity and wind luminosity was ~40% and ~50%, respectively. Similarly, stars with Minit > 100 M⊙ (mostly H-rich WN stars) also showed high contributions to the global feedback, ~25% in both cases. Such massive stars are not

  10. FUSE Spectroscopy of the DAO-type Central Star LS V+4621: Looking for the Photosphere in the Sea of Interstellar Absorption

    CERN Document Server

    Ziegler, M; Werner, K; Kruk, J W; Oliveira, C

    2006-01-01

    The far-ultraviolet spectrum of the DAO White Dwarf LS V+4621, the exciting star of the possible planetary nebula Sh 2-216,is strongly contaminated by absorption features from the interstellar medium (ISM). For an ongoing spectral analysis, we aim to extract the pure photospheric spectrum in order to identify and model metal lines of species which are not detectable in the near-ultraviolet wavelength range. We have modeled the interstellar absorption precisely and considered it for the simulation of the FUSE (Far Ultraviolet Spectroscopic Explorer) observation. A state-of-the-art NLTE model-atmosphere spectrum which includes 16 elements is combined with the ISM absorption and then compared with the FUSE spectrum.

  11. Quarkonium at STAR

    International Nuclear Information System (INIS)

    The STAR detector is capable of reconstruction the J/ψ meson in its dielectron decay channel, along with continuum dielectrons from heavy quark decay. The limitation is not instrumental--the ability of the STAR detector to identify electrons--rather, the primary limitation is yield. We expect to reconstruct of order 10,000 events per year in the bin of highest centrality, with perhaps ten times that many integrated over all bins of centrality. This is enough for a rather detailed study of J/ψ production. The yields for ψprime and the high pT χ mesons which are in a low enough background region of phase space to permit reconstruction are too small for precision measurements. The only parent of the J/ψ with a large enough yield for clear observation is the b quark. Even limited to just the J/ψ, there is a rich physics program available to STAR: the yield provides information on the gluon flux as well as color screening, especially when compared to the open charm and b -> J/ψX yields. The pT distribution measures energy loss in a nuclear medium, either by comparison with pp data or across different bins in centrality. The STAR quarkonium program should provide several unique windows into the physics of heavy ion collisions at RHIC

  12. A dusty torus around the luminous young star LkHa 101

    CERN Document Server

    Tuthill, P G; Danchi, W C; Tuthill, Peter G.; Monnier, John D.; Danchi, William C.

    2001-01-01

    A star forms when a cloud of dust and gas collapses. It is generally believed that this collapse first produces a flattened rotating disk, through which matter is fed onto the embryonic star at the center of the disk. When the temperature and density at the center of the star pass a critical threshold, thermonuclear fusion begins. The remaining disk, which can still contain up to 0.3 times the mass of the star, is then sculpted and eventually dissipated by the radiation and wind from the newborn star. Unfortunately this picture of the structure and evolution of the disk remains speculative because of the lack of morphological data of sufficient resolution and uncertainties regarding the underlying physical processes. Here we present resolved images of a young star, LkHa 101 in which the structure of the inner accretion disk is resolved. We find that the disk is almost face-on, with a central gap (or cavity) and a hot inner edge. The cavity is bigger than previous theoretical predictions, and we infer that the...

  13. Zeta Pup: the merger of at least two massive stars

    CERN Document Server

    Vanbeveren, Dany

    2011-01-01

    We first discuss the stellar and wind parameters of zeta Pup resulting from detailed UV diagnostics. These parameters together with the runaway nature of the star can most easily be explained by dynamical binary-binary or binary-single star interactions in dense stellar clusters. In this case zeta Pup is most likely the merger of at least two massive stars.

  14. The Electromagnetic Spectrum of Neutron Stars

    CERN Document Server

    Baykal, Altan; Inam, Sitki C; Grebenev, Sergei

    2005-01-01

    Neutron stars hold a central place in astrophysics, not only because they are made up of the most extreme states of the condensed matter, but also because they are, along with white dwarfs and black holes, one of the stable configurations that stars reach at the end of stellar evolution. Neutron stars posses the highest rotation rates and strongest magnetic fields among all stars. They radiate prolifically, in high energy electromagnetic radiation and in the radio band. This book is devoted to the selected lectures presented in the 6th NATO-ASI series entitled "The Electromagnetic Spectrum of Neutron Stars" in Marmaris, Turkey, on 7-18 June 2004. This ASI is devoted to the spectral properties of neutron stars. Spectral observations of neutron stars help us to understand the magnetospheric emission processes of isolated radio pulsars and the emission processes of accreting neutron stars. This volume includes spectral information from the neutron stars in broadest sense, namely neutrino and gravitational radiat...

  15. Theory of wind accretion

    OpenAIRE

    Shakura N.I.; Postnov K.A.; Kochetkova A.Yu.; Hjalmarsdotter L.

    2013-01-01

    A review of wind accretion in high-mass X-ray binaries is presented. We focus attention to different regimes of quasi-spherical accretion onto the neutron star: the supersonic (Bondi) accretion, which takes place when the captured matter cools down rapidly and falls supersonically toward NS magnetospghere, and subsonic (settling) accretion which occurs when plasma remains hot until it meets the magnetospheric boundary. Two regimes of accretion are separated by an X-ray luminosity of about $4\\...

  16. Wind Power

    OpenAIRE

    Makhalas, Kharsan Al; Alsehlli, Faisal

    2015-01-01

    This Bachelor thesis has been written at the Blekinge Institute of Technology. This thesis concentrates on the wind power and their components, also the large wind farm is studied. The electrical power is generated by using the power in wind to drive a wind turbine to produce mechanical power. This mechanical power can be converted into electrical power by using electrical induction generators. There are two types of the wind turbines, the horizontal axis and vertical axis wind turbine, where...

  17. Theoretical mass loss rates of cool main-sequence stars

    CERN Document Server

    Holzwarth, V R

    2006-01-01

    We develop a model for the wind properties of cool main-sequence stars, which comprises their wind ram pressures, mass fluxes, and terminal wind velocities. The wind properties are determined through a polytropic magnetised wind model, assuming power laws for the dependence of the thermal and magnetic wind parameters on the stellar rotation rate. We use empirical data to constrain theoretical wind scenarios, which are characterised by different rates of increase of the wind temperature, wind density, and magnetic field strength. Scenarios based on moderate rates of increase yield wind ram pressures in agreement with most empirical constraints, but cannot account for some moderately rotating targets, whose high apparent mass loss rates are inconsistent with observed coronal X-ray and magnetic properties. For fast magnetic rotators, the magneto-centrifugal driving of the outflow can produce terminal wind velocities far in excess of the surface escape velocity. Disregarding this aspect in the analyses of wind ra...

  18. Quasithermal Neutrinos from Rotating Protoneutron Stars Born during Core Collapse of Massive Stars

    OpenAIRE

    Murase, Kohta; Dasgupta, Basudeb; Thompson, Todd A.

    2013-01-01

    Rotating and magnetized protoneutron stars (PNSs) may drive relativistic magneto-centrifugally accelerated winds as they cool immediately after core collapse. The wind fluid near the star is composed of neutrons and protons, and the neutrons become relativistic while collisionally coupled with the ions. Here, we argue that the neutrons in the flow eventually undergo inelastic collisions around the termination shock inside the stellar material, producing ~0.1-1 GeV neutrinos, without relying o...

  19. The Nature and Origin of the Central Constant Emission Component of Eta Carinae

    Science.gov (United States)

    Hamaguchi, K.; Corcoran, M. F.

    2015-12-01

    The campaign observations of the evolved super massive binary system, η Car, revealed an apparently non-variable X-ray emission component, which was observable only around periastron when the wind-wind colliding (WWC) X-ray emission from the binary system dropped. This central constant emission (CCE) component originates from hot thermal plasma at >50 million degrees Kelvin confined within ˜0.2'' (˜460 AU at 2.3 kpc) of the binary system. The emission suffers weak X-ray absorption at NH˜3 - 5 × 1022 cm-2, so that the plasma should be in front of the binary system. These results suggest that the CCE plasma is thermalized by collision of the secondary wind with the primary wind shell ejected a few orbital cycles before and that it fills the foreground cavity carved by the wind of the secondary star. An apparent change of the line of sight absorption between 2003 and 2009 may suggest a change of the mass loss rate of the primary star around that time.

  20. Constraints on galactic wind models

    CERN Document Server

    Meiksin, Avery

    2016-01-01

    Observational implications are derived for two standard models of supernovae-driven galactic winds: a freely expanding steady-state wind and a wind sourced by a self-similarly expanding superbubble including thermal heat conduction. It is shown that, for the steady-state wind, matching the measured correlation between the soft x-ray luminosity and star formation rate of starburst galaxies is equivalent to producing a scaled wind mass-loading factor relative to the star-formation rate of 0.5 - 3, in agreement with the amount inferred from metal absorption line measurements. The match requires the asymptotic wind velocity v_inf to scale with the star formation rate SFR (in solar masses per year) approximately as v_inf ~ (700 - 1000) km/s SFR^{1/6}. The corresponding mass injection rate is close to the amount naturally provided by thermal evaporation from the wall of a superbubble in a galactic disc, suggesting thermal evaporation may be a major source of mass-loading. The predicted mass-loading factors from the...