WorldWideScience

Sample records for central star wind

  1. 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...

  2. 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...

  3. 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...

  4. 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

  5. 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

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. Accretion of Supersonic Winds on Boson Stars

    CERN Document Server

    Gracia-Linares, M

    2016-01-01

    We present the evolution of a supersonic wind interacting with a Boson Star (BS) and compare the resulting wind density profile with that of the shock cone formed when the wind is accreted by a non-rotating Black Hole (BH) of the same mass. The physical differences between these accretors are that a BS, unlike a BH has no horizon, it does not have a mechanical surface either and thus the wind is expected to trespass the BS. Despite these conditions, on the BS space-time the gas achieves a stationary flux with the gas accumulating in a high density elongated structure comparable to the shock cone formed behind a BH. The highest density resides in the center of the BS whereas in the case of the BH it is found on the downstream part of the BH near the event horizon. The maximum density of the gas is smaller in the BS than in the BH case. Our results indicate that the highest density of the wind is more similar on the BS to that on the BH when the BS has high self-interaction, when it is more compact and when the...

  11. 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...

  12. 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.

  13. 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...

  14. 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.

  15. 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....

  16. 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.

  17. 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.

  18. 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.

  19. Wind bubbles within H II regions around slowly moving stars

    CERN Document Server

    Mackey, Jonathan; Mohamed, Shazrene; Langer, Norbert

    2014-01-01

    Interstellar bubbles around O stars are driven by a combination of the star's wind and ionizing radiation output. The wind contribution is uncertain because the boundary between the wind and interstellar medium is difficult to observe. Mid-infrared observations (e.g., of the H II region RCW 120) show arcs of dust emission around O stars, contained well within the H II region bubble. These arcs could indicate the edge of an asymmetric stellar wind bubble, distorted by density gradients and/or stellar motion. We present two-dimensional, radiation-hydrodynamics simulations investigating the evolution of wind bubbles and H II regions around massive stars moving through a dense (n=3000 cm^{-3}), uniform medium with velocities ranging from 4 to 16 km/s. The H II region morphology is strongly affected by stellar motion, as expected, but the wind bubble is also very aspherical from birth, even for the lowest space velocity considered. Wind bubbles do not fill their H II regions (we find filling factors of 10-20%), at...

  20. Theory of Winds from Hot, Luminous Massive Stars

    CERN Document Server

    Owocki, Stanley

    2014-01-01

    The high luminosities of massive stars drive strong stellar winds, through line scattering of the star's continuum radiation. This paper reviews the dynamics of such line driving, building first upon the standard CAK model for steady winds, and deriving the associated analytic scalings for the mass loss rate and wind velocity law. It next summarizes the origin and nature of the strong Line Deshadowing Instability (LDI) intrinsic to such line-driving, including also the role of a diffuse-line-drag effect that stabilizes the wind base, and then describes how both instability and drag are incorporated in the Smooth Source Function (SSF) method for time-dependent simulations of the nonlinear evolution of the resulting wind structure. The review concludes with a discussion of the effect of the resulting extensive structure in temperature, density and velocity for interpreting observational diagnostics. In addition to the usual clumping effect on density-squared diagnostics, the spatial porosity of optically thick ...

  1. 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 ...

  2. 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...

  3. 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.

  4. 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.

  5. 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.

  6. Effects of anisotropic winds on massive stars evolution

    CERN Document Server

    Cyril, Georgy; André, Maeder

    2010-01-01

    Whenever stars are rotating very fast ($\\Omega/\\Omega_\\mathrm{crit} > 0.7$, with $\\Omega_\\mathrm{crit}$ the Keplerian angular velocity of the star accounting for its deformation) radiative stellar winds are enhanced in polar regions. This theoretical prediction is now confirmed by interferometric observations of fast rotating stars.} Polar winds remove less angular momentum than spherical winds and thus allow the star to keep more angular momentum. We quantitatively assess the importance of this effect. First we use a semi-analytical approach to estimate the variation of the angular momentum loss when the rotation parameter increases. Then we compute complete 9 M$_\\odot$ stellar models at very high angular velocities (starting on the ZAMS with $\\Omega/\\Omega_\\mathrm{crit} = 0.8$ and reaching the critical velocity during the Main Sequence) with and without radiative wind anisotropies. When wind anisotropies are accounted for, the angular momentum loss rate is reduced by less than $4%$ for $\\Omega/\\Omega_\\mathr...

  7. X-ray diagnostics of massive star winds

    Science.gov (United States)

    Oskinova, Lidia M.

    2016-09-01

    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. X-rays may strongly influence the dynamics of weak winds of main sequence B-type stars. X-ray pulsations were detected in a β Cep type variable giving evidence of tight photosphere-wind connections. 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, and X-ray spectra of OB supergiants yield consistent mass-loss rates. Depending on the adopted clumping parameters, the empirically derived mass-loss rates are a factor of a few smaller or comparable to those predicted by standard recipes (Vink et al., 2001). All sufficiently studied O stars display variable X-ray emission that might be related to corotating interaction regions in their winds. In the latest stages of stellar evolution, single red supergiants (RSG) and luminous blue variable (LBV) stars do not emit observable amounts of X-rays. On the other hand, nearly all types of Wolf-Rayet (WR) stars are X-ray sources. X-ray spectroscopy allows a sensitive probe of WR wind abundances and opacities.

  8. Wind accretion in binary stars - I. Mass accretion ratio

    CERN Document Server

    Nagae, T; Matsuda, T; Fujiwara, H; Hachisu, I; Boffin, H M J

    2004-01-01

    Three-dimensional hydrodynamic calculations are performed in order to investigate mass transfer in a close binary system, in which one component undergoes mass loss through a wind. The mass ratio is assumed to be unity. The radius of the mass-losing star is taken to be about a quarter of the separation between the two stars. Calculations are performed for gases with a ratio of specific heats gamma=1.01 and 5/3. Mass loss is assumed to be thermally driven so that the other parameter is the sound speed of the gas on the mass-losing star. Here, we focus our attention on two features: flow patterns and mass accretion ratio, which we define as the ratio of the mass accretion rate onto the companion to the mass loss rate from the mass-losing primary star. We characterize the flow by the mean normal velocity of wind on the critical Roche surface of the mass-losing star, Vr. When Vr0.7 A Omega we observe wind accretion. We find very complex flow patterns in between these two extreme cases. We derive an empirical form...

  9. The Self-Regulated Winds of Long Period Variable Stars

    CERN Document Server

    Struck, C; Willson, L A; Turner, G; Bowen, G H; Struck, Curtis; Smith, Daniel C.; Willson, Lee Anne; Turner, Gary; Bowen, George H.

    2004-01-01

    Numerical models of the extended atmospheres of long period variable or Mira stars have shown that their winds have a very simple, power law structure when averaged over the pulsation cycle. This structure is stable and robust despite the pulsational wave disturbances, and appears to be strongly self-regulated. Observational studies support these conclusions. The models also show that dust-free winds are nearly adiabatic, with little heating or cooling. The classical, steady, adiabatic wind solution to the hydrodynamic equations fails to account for an extensive region of nearly constant outflow velocity. We investigate analytic solutions which include the effects of wave pressure, heating, and the resulting entropy changes. Wave pressure is represented by a term like that in the Reynolds turbulence equation for the mean velocity. Although the pressure from individual waves is modest, the waves are likely the primary agent of self-regulation of dust-free winds. In models of dusty winds, the gas variables also...

  10. 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...

  11. Massive Stars in Colliding Wind Systems: the GLAST Perspective

    Energy Technology Data Exchange (ETDEWEB)

    Reimer, Anita; Reimer, Olaf; /Stanford U., HEPL /KIPAC, Menlo Park

    2011-11-29

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

  12. FUSE observations of the central star of Abell 78

    CERN Document Server

    Werner, K; Koesterke, L; Kruk, J W

    2002-01-01

    FUSE high resolution spectra of two PG1159 type central stars (K1-16 and NGC 7094) have revealed an unexpected iron deficiency of at least 1 or 2 dex (Miksa et al. 2002). Here we present early results of FUSE spectroscopy of the CSPN Abell 78. It is shown that iron is strongly deficient in this star, too.

  13. IC 4663: The first unambiguous [WN] Wolf-Rayet central star of a planetary nebula

    CERN Document Server

    Miszalski, B; De Marco, O; Köppen, J; Moffat, A F J; Acker, A; Hillwig, T C

    2012-01-01

    We report on the serendipitous discovery of the first central star of a planetary nebula (PN) that mimics the helium- and nitrogen-rich WN sequence of massive Wolf-Rayet (WR) stars. The central star of IC 4663 (PN G346.2-08.2) is dominated by broad He II and N V emission lines which correspond to a [WN3] spectral type. Unlike previous [WN] candidates, the surrounding nebula is unambiguously a PN. At an assumed distance of 3.5 kpc, corresponding to a stellar luminosity of 4000 Lsun, the V=16.9 mag central star remains 4-6 mag fainter than the average luminosity of massive WN3 stars even out to an improbable d=8 kpc. The nebula is typical of PNe with an elliptical morphology, a newly discovered Asymptotic Giant Branch (AGB) halo, a relatively low expansion velocity (v_exp=30 km/s) and a highly ionised spectrum with an approximately Solar chemical abundance pattern. The [WN3] star is hot enough to show Ne VII emission (T_*=140+/-20 kK) and exhibits a fast wind (v_infty=1900 km/s), which at d=3.5 kpc would yield ...

  14. A barium-rich binary central star in Abell 70

    CERN Document Server

    Boffin, Henri M J; Frew, D J; Acker, A; Köppen, J; Moffat, A F J; Parker, Q A

    2011-01-01

    We have found the central star of Abell 70 (PN G038.1-25.4, hereafter A 70) to be a binary consisting of a G8 IV-V secondary and a hot white dwarf. The secondary shows enhanced Ba II and Sr II features, firmly classifying it as a barium star. The nebula is found to have Type-I chemical abundances with helium and nitrogen enrichment, which combined with future abundance studies of the central star, will establish A 70 as a unique laboratory for studying s-process AGB nucleosynthesis.

  15. 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.

  16. 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 ...

  17. 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...

  18. Central stars of planetary nebulae: The white dwarf connection

    CERN Document Server

    Werner, K

    2011-01-01

    This paper is focused on the transition phase between central stars and white dwarfs, i.e. objects in the effective temperature range 100,000 - 200,000 K. We confine our review to hydrogen-deficient stars because the common H-rich objects are subject of the paper by Ziegler et al. in these proceedings. We address the claimed iron-deficiency in PG1159 stars and [WC] central stars. The discovery of new Ne VII and Ne VIII lines in PG1159 stars suggests that the identification of O VII and O VIII lines that are used for spectral classification of [WCE] stars is wrong. We then present evidence for two distinct post-AGB evolutionary sequences for H-deficient stars based on abundance analyses of the He-dominated O(He) stars and the hot DO white dwarf KPD0005+5106. Finally, we report on evidence for an H-deficient post-super AGB evolution sequence represented by the hottest known, carbon/oxygen-atmosphere white dwarf H1504+65 and the recently discovered carbon-atmosphere "hot DQ" white dwarfs.

  19. Atmospheric NLTE-models for the spectroscopic analysis of luminous blue stars with winds.

    Science.gov (United States)

    Santolaya-Rey, A. E.; Puls, J.; Herrero, A.

    1997-07-01

    We present a new, fast and easy to use NLTE line formation code for ``unified atmospheres'' with spherical extension and stellar winds, developed for the (routine) spectroscopic analysis of luminous blue stars, covering the spectral range from ``A'' to ``O'' and including central stars of planetary nebulae. The major features of our code are: Data driven input of atomic models; consistent photospheric stratification including continuum radiative acceleration and photospheric extension; ``β-velocity law'' for the wind; comoving frame or Sobolev plus continuum line transfer; fast solution algorithm for calculating line profiles, allowing for a consistent treatment of incoherent electron scattering. We describe the code and perform thorough tests for models with H/He opacity, especially with respect to a comparison with plane-parallel, hydrostatic models in cases of thin winds. Our conclusions are: Due in particular to our numerical treatment of the radiative transfer in the ionization and recombination integrals, the convergence rate of the solution algorithm is fast. The flux conservation is good, (maximum flux errors of order 2 to 3%), unless the atmospheric conditions are extreme, either with respect to mass-loss or to a large extension of the photosphere. (In these cases, our treatment of the temperature structure has to be improved). A comparison with plane-parallel results shows perfect agreement with the thin wind case. However, this comparison also reveals two interesting effects: First, the strength of the Hei lines in hot O-stars is very sensitive to the treatment of electron scattering in the EUV. This might affect the effective temperature scale of early O spectral types. Second, the effects of photospheric extension become decisive for the gravity determination of stars close to the Eddington limit. Finally, we demonstrate the differences in using the Sobolev vs. the comoving line transfer in the rate equations. We conclude that, in cases of moderate

  20. 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...

  1. 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...

  2. 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.

  3. Wind collisions in three massive stars of Cyg OB2

    CERN Document Server

    Cazorla, Constantin; Rauw, Gregor

    2013-01-01

    Aims: We wish to study the origin of the X-ray emission of three massive stars in the Cyg OB2 association: Cyg OB2 #5, #8A, #12. Methods: To this aim, dedicated X-ray observations from XMM and Swift are used, as well as archival ROSAT and Suzaku data. Results: Our results on Cyg OB2 #8A improve the phase coverage of the orbit and confirm previous studies: the signature of a wind-wind collision is conspicuous. In addition, signatures of a wind-wind collision are also detected in Cyg OB2 #5, but the X-ray emission appears to be associated with the collision between the inner binary and the tertiary component orbiting it with a 6.7yr period, without a putative collision inside the binary. The X-ray properties strongly constrain the orbital parameters, notably allowing us to discard some proposed orbital solutions. To improve the knowledge of the orbit, we revisit the light curves and radial velocity of the inner binary, looking for reflex motion induced by the third star. Finally, the X-ray emission of Cyg OB2 #...

  4. Instabilities in the Envelopes and Winds of Very Massive Stars

    CERN Document Server

    Owocki, Stanley P

    2014-01-01

    The high luminosity of Very Massive Stars (VMS) means that radiative forces play an important, dynamical role both in the structure and stability of their stellar envelope, and in driving strong stellar-wind mass loss. Focusing on the interplay of radiative flux and opacity, with emphasis on key distinctions between continuum vs. line opacity, this chapter reviews instabilities in the envelopes and winds of VMS. Specifically, we discuss how: 1) the iron opacity bump can induce an extensive inflation of the stellar envelope; 2) the density dependence of mean opacity leads to strange mode instabilities in the outer envelope; 3) desaturation of line-opacity by acceleration of near-surface layers initiates and sustains a line-driven stellar wind outflow; 4) an associated line-deshadowing instability leads to extensive small-scale structure in the outer regions of such line-driven winds; 5) a star with super-Eddington luminosity can develop extensive atmospheric structure from photon bubble instabilities, or from ...

  5. Powerful Winds from Low-Mass Stars: V374 Peg

    CERN Document Server

    Vidotto, A A; Opher, M; Donati, J -F; Gombosi, T I

    2010-01-01

    The rapid rotation (P=0.44 d) of the M dwarf V374Peg (M4) along with its intense magnetic field point toward magneto-centrifugal acceleration of a coronal wind. In this work, we investigate the structure of the wind of V374Peg by means of 3D magnetohydrodynamical (MHD) numerical simulations. For the first time, an observationally derived surface magnetic field map is implemented in MHD models of stellar winds for a low mass star. We show that the wind of V374Peg deviates greatly from a low-velocity, low-mass-loss rate solar-type wind. We find general scaling relations for the terminal velocities, mass-loss rates, and spin-down times of highly magnetized M dwarfs. In particular, for V374Peg, our models show that terminal velocities across a range of stellar latitudes reach ~(1500-2300) n_{12}^{-1/2} km/s, where n_{12} is the coronal wind base density in units of 10^{12} cm^{-3}, while the mass-loss rates are about 4 x 10^{-10} n_{12}^{1/2} Msun/yr. We also evaluate the angular-momentum loss of V374Peg, which p...

  6. 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 ...

  7. 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...

  8. Wind energy resource atlas. Volume 2. The North Central Region

    Energy Technology Data Exchange (ETDEWEB)

    Freeman, D.L.; Hadley, D.L.; Elliott, D.L.; Barchet, W.R.; George, R.L.

    1981-02-01

    The North Central atlas assimilates six collections of wind resource data: one for the region and one for each of the five states that compose the North Central region (Iowa, Minnesota, Nebraska, North Dakota, and South Dakota). At the state level, features of the climate, topography and wind resource are discussed in greater detail than is provided in the regional discussion, and that data locations on which the assessment is based are mapped. Variations, over several time scales, in the wind resource at selected stations in each state are shown on graphs of monthly average and international wind speed and power, and hourly average wind speed for each season. Other graphs present speed direction and duration frequencies of the wind at these locations.

  9. The enigmatic central star of the planetary nebula PRTM 1

    CERN Document Server

    Boffin, Henri M J; Jones, David

    2012-01-01

    The central star of the planetary nebula PRTM 1 (PN G243.8-37.1) was previously found to be variable by M. Pena and colleagues. As part of a larger programme aimed towards finding post common-envelope binary central stars we have monitored the central star of PRTM 1 spectroscopically and photometrically for signs of variability. Over a period of ~3 months we find minimal radial velocity (<10 km/s) and photometric (< 0.2 mag) variability. The data suggest a close binary nucleus can be ruled out at all but the lowest orbital inclinations, especially considering the spherical morphology of the nebula which we reveal for the first time. Although the current data strongly support the single star hypothesis, the true nature of the central star of PRTM 1 remains enigmatic and will require further radial velocity monitoring at higher resolution to rule out a close binary. If in the odd case that it is a close binary, it would be the first such case in a spherical planetary nebula, in contradiction to current th...

  10. 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...

  11. 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...

  12. 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.

  13. 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...

  14. 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.

  15. 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.

  16. Relating binary-star planetary systems to central configurations

    Science.gov (United States)

    Veras, Dimitri

    2016-11-01

    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 10°, and (v) the deviation increases as the substellar masses increase. This study may help restrict future stability analyses to architectures which resemble exoplanetary systems, and might hint at where observers may discover dust, asteroids and/or planets in binary-star systems.

  17. A barium central star binary in the Type-I diamond ring planetary nebula Abell 70

    CERN Document Server

    Miszalski, B; Frew, D J; Acker, A; Köppen, J; Moffat, A F J; Parker, Q A

    2011-01-01

    Abell 70 (PN G038.1-25.4, hereafter A 70) is a planetary nebula (PN) known for its diamond ring appearance due a superposition with a background galaxy. The previously unstudied central star is found to be a binary consisting of a G8IV-V secondary at optical wavelengths and a hot white dwarf (WD) at UV wavelengths. The secondary shows Ba II and Sr II features enhanced for its spectral type that, combined with the chromospheric Halpha emission and possible 20-30 km/s radial velocity amplitude, firmly classifies the binary as a Barium star. The proposed origin of Barium stars is intimately linked to PNe whereby wind accretion pollutes the companion with dredged-up material rich in carbon and s-process elements when the primary is experiencing thermal pulses on the Asymptotic Giant Branch (AGB). A 70 provides further evidence for this scenario together with the other very few examples of Barium central stars. The nebula is found to have Type-I chemical abundances with helium and nitrogen enrichment, which when c...

  18. 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.

  19. 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

  20. 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...

  1. 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...

  2. 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.

  3. NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS

    Energy Technology Data Exchange (ETDEWEB)

    Martin, D.; Perego, A.; Arcones, A. [Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstr. 2, Darmstadt D-64289 (Germany); Thielemann, F.-K. [Department of Physics, University of Basel, Klingelbergstraße 82, 4056, Basel (Switzerland); Korobkin, O.; Rosswog, S., E-mail: dirk.martin@physik.tu-darmstadt.de [The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden)

    2015-11-01

    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 × 10{sup −3} M{sub ⊙} becomes unbound until ∼200 ms. Due to electron fractions of Y{sub e} ≈ 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 peaks in the blue band after about 4 hr. Furthermore, high opacities due to heavy r-process nuclei in the dynamic ejecta lead to a second peak in the infrared after 3–4 days.

  4. 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...

  5. 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.

  6. 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...

  7. 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

  8. 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

    2016-05-25

    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.

  9. Variable central stars of young planetary nebulae. I. Photometric multisite observations of IC 418.

    Science.gov (United States)

    Handler, G.; Mendez, R. H.; Medupe, R.; Costero, R.; Birch, P. V.; Alvarez, M.; Sullivan, D. J.; Kurtz, D. W.; Herrero, A.; Guerrero, M. A.; Ciardullo, R.; Breger, M.

    1997-04-01

    We report the results of a photometric multisite campaign devoted to HD 35914, the variable central star of the Planetary Nebula IC 418. From the analysis of 120 hours of data acquired with a variety of techniques, we find that HD 35914 exhibits two distinct kinds of variability: irregular light modulation with a time scale of days, as well as cyclic variations with a time scale of 6.5 hours. The short-term variations are not strictly periodic, and cannot be reasonably explained by multiperiodicity; they appear to be semiregular. The star is generally redder when it is brighter; this behavior appears to be connected with the long-term variability. A re-analysis of most of the older data obtained for HD 35914 by various researchers suggests that the basic behavior of the star did not change during the last 15 years. We carefully discuss all the possible causes for the light variations of the star. Rotational modulation of surface features cannot explain the observations, and binarity is unlikely. Pulsations may be excited, but wind variability (or a combination of both) can also not be ruled out.

  10. 77 FR 41975 - Southern Star Central Gas Pipeline, Inc.; Notice of Application

    Science.gov (United States)

    2012-07-17

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Application Take notice that on June 27, 2012, Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700 Highway 56, Owensboro, Kentucky 42301, filed...

  11. 77 FR 38622 - Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization

    Science.gov (United States)

    2012-06-28

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization Take notice that on June 4, 2012, Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700 Highway 56, Owensboro,...

  12. 78 FR 68835 - Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization

    Science.gov (United States)

    2013-11-15

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization Take notice that on October 31, 2013, Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700 Highway 56, Owensboro,...

  13. 78 FR 25264 - Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization

    Science.gov (United States)

    2013-04-30

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization Take notice that on April 16, 2013, Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700 Highway 56, Owensboro,...

  14. 78 FR 53746 - Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization

    Science.gov (United States)

    2013-08-30

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization Take notice that on August 13, 2013, Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700 Highway 56, Owensboro,...

  15. 77 FR 14517 - Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization

    Science.gov (United States)

    2012-03-12

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization Take notice that on February 21, 2012 Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700 State Highway 56,...

  16. 78 FR 13663 - Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization

    Science.gov (United States)

    2013-02-28

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization Take notice that on February 11, 2013, Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700 Highway 56, P.O. Box...

  17. 75 FR 8053 - Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization

    Science.gov (United States)

    2010-02-23

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Request Under Blanket Authorization February 16, 2010. Take notice that on January 29, 2010, Southern Star Central Gas Pipeline, Inc. (Southern Star), 4700...

  18. 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...

  19. 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...

  20. 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

  1. Massive star formation in the central regions of spiral galaxies

    CERN Document Server

    Knapen, J H; Böker, T; Shlosman, I; Colina, L; Combes, F; Axon, D J

    2005-01-01

    Context: The morphology of massive star formation in the central regions of galaxies is an important tracer of the dynamical processes that govern the evolution of disk, bulge, and nuclear activity. Aims: We present optical imaging of the central regions of a sample of 73 spiral galaxies in the H alpha line and in optical broad bands, and derive information on the morphology of massive star formation. Methods: We obtained images with the William Herschel Telescope, mostly at a spatial resolution of below one second of arc. For most galaxies, no H alpha imaging is available in the literature. We outline the observing and data reduction procedures, list basic properties, and present the I-band and continuum-subtracted H alpha images. We classify the morphology of the nuclear and circumnuclear H alpha emission and explore trends with host galaxy parameters. Results: We confirm that late-type galaxies have a patchy circumnuclear appearance in H alpha, and that nuclear rings occur primarily in spiral types Sa-Sbc....

  2. 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

  3. 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...

  4. The kinematics of the quadrupolar nebula M 1-75 and the identification of its central star

    Science.gov (United States)

    Santander-García, M.; Rodríguez-Gil, P.; Hernandez, O.; Corradi, R. L. M.; Jones, D.; Giammanco, C.; Beckman, J. E.; Carignan, C.; Fathi, K.; Rubio-Díez, M. M.; Jiménez-Luján, F.; Benn, C. R.

    2010-09-01

    Context. The link between how bipolar planetary nebulae are shaped and their central stars is still poorly understood. Aims: This paper investigates the kinematics and shaping of the multipolar nebula M 1-75, and briefly discusses the location and nature of its central star. Methods: Fabry-Perot data from GHαFAS on the WHT that samples the Doppler shift of the [Nii] 658.3 nm line are used to study the dynamics of the nebula by means of a detailed 3D spatio-kinematical model. Multi-wavelength images and spectra from the WFC and IDS on the INT, as well as from ACAM on the WHT, allowed us to constrain the parameters of the central star. Results: The two pairs of lobes, angularly separated by ~22°, were ejected simultaneously approx. ~3500-5000 years ago, at the adopted distance range from 3.5 to 5.0 kpc. The larger lobes show a slight degree of point symmetry. The formation of the nebula could be explained by wind interaction in a system consisting of a post-AGB star surrounded by a disc warped by radiative instabilities. This requires the system to be a close binary or a single star that engulfed a planet as it died. On the other hand, we present broad- and narrow-band images and a low S/N optical spectrum of the highly-reddened, previously unnoticed star that is likely the nebular progenitor. Its estimated V-I colour allows us to derive a rough estimate of the parameters and nature of the central star. Based on observations made with the 4.2 m William Herschel Telescope and the 2.5 m Isaac Newton Telescope, both operated on the island of la Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

  5. 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.

  6. 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...

  7. 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.

  8. 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.

  9. 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...

  10. 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.

  11. 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.

  12. 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...

  13. THE CHANDRA PLANETARY NEBULA SURVEY (ChanPlaNS). III. X-RAY EMISSION FROM THE CENTRAL STARS OF PLANETARY NEBULAE

    Energy Technology Data Exchange (ETDEWEB)

    Montez, R. Jr. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37212 (United States); Kastner, J. H.; Freeman, M. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, Rochester, NY 14623 (United States); and others

    2015-02-10

    We present X-ray spectral analysis of 20 point-like X-ray sources detected in Chandra Planetary Nebula Survey observations of 59 planetary nebulae (PNe) in the solar neighborhood. Most of these 20 detections are associated with luminous central stars within relatively young, compact nebulae. The vast majority of these point-like X-ray-emitting sources at PN cores display relatively ''hard'' (≥0.5 keV) X-ray emission components that are unlikely to be due to photospheric emission from the hot central stars (CSPN). Instead, we demonstrate that these sources are well modeled by optically thin thermal plasmas. From the plasma properties, we identify two classes of CSPN X-ray emission: (1) high-temperature plasmas with X-ray luminosities, L {sub X}, that appear uncorrelated with the CSPN bolometric luminosity, L {sub bol} and (2) lower-temperature plasmas with L {sub X}/L {sub bol} ∼ 10{sup –7}. We suggest these two classes correspond to the physical processes of magnetically active binary companions and self-shocking stellar winds, respectively. In many cases this conclusion is supported by corroborative multiwavelength evidence for the wind and binary properties of the PN central stars. By thus honing in on the origins of X-ray emission from PN central stars, we enhance the ability of CSPN X-ray sources to constrain models of PN shaping that invoke wind interactions and binarity.

  14. 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.

  15. 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

  16. Central Stars of Planetary Nebulae in the Large Magellanic Cloud: A Far-UV Spectroscopic Analysis

    CERN Document Server

    Herald, J E

    2004-01-01

    We observed seven central stars of planetary nebulae (CSPN) in the Large Magellanic Cloud (LMC) with the Far Ultraviolet Spectroscopic Explorer (FUSE), and performed a model-based analysis of these spectra in conjunction with Hubble Space Telescope (HST) spectra in the UV and optical range to determine the stellar and nebular parameters. Most of the objects show wind features, and they have effective temperatures ranging from 38 to 60 kK with mass-loss rates of ~= 5x10^-8 Msun/yr. Five of the objects have typical LMC abundances. One object (SMP LMC 61) is a [WC4] star, and we fit its spectra with He/C/O-rich abundances typical of the [WC] class, and find its atmosphere to be iron-deficient. Most objects have very hot (T ~> 2000 K) molecular hydrogen in their nebulae, which may indicate a shocked environment. One of these (SMP LMC 62) also displays OVI 1032-38 nebular emission lines, rarely observed in PN.

  17. Stellar winds near massive black holes: The case of the S-stars

    CERN Document Server

    Lützgendorf, Nora; Pelupessy, Inti; Zwart, Simon Portegies

    2015-01-01

    The Galactic center provides a unique laboratory to study the interaction of a supermassive black hole (SMBH) with its gaseous and stellar environment. Simulations to determine the accretion of stellar winds from the surrounding O-stars onto the black hole have been performed earlier, but in those the presence of the S-star system was ignored. The S-stars are a group of young massive B-stars in relatively close orbits around the black hole. Here we simulate those stars in order to study their contribution to the accretion rate, without taking the more distant and massive O-stars into account. We use the Astrophysical Multi-purpose Software Environment (AMUSE) to combine gravitational physics, stellar evolution and hydrodynamics in a single simulation of the S-stars orbiting the supermassive black hole, and use this framework to determine the amount of gas that is accreted onto the black hole. We find that the accretion rate is sensitive to the wind properties of the S-stars (rate of mass-loss and terminal vel...

  18. 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.

  19. Far-UV Spectroscopic Analyses of Four Central Stars of Planetary Nebulae

    CERN Document Server

    Herald, J E

    2004-01-01

    We analyze the Far-UV/UV spectra of four central stars of planetary nebulae with strong wind features -- NGC 2371, Abell 78, IC 4776 and NGC 1535, and derive their photospheric and wind parameters by modeling high-resolution FUSE (Far-Ultraviolet Spectroscopic Explorer) data in the Far-UV and HST-STIS and IUE data in the UV with spherical non-LTE line-blanketed model atmospheres. Abell 78 is a hydrogen-deficient transitional [WR]-PG 1159 object, and we find NGC 2371 to be in the same stage, both migrating from the constant-luminosity phase to the white dwarf cooling sequence with Teff ~= 120 kK, Mdot ~= 5x10^-8 Msun/yr. NGC 1535 is a ``hydrogen-rich'' O(H) CSPN, and the exact nature of IC 4776 is ambiguous, although it appears to be helium burning. Both objects lie on the constant-luminosity branch of post-AGB evolution and have Teff ~= 65 kK, Mdot ~= 1x10^-8 Msun/yr. Thus, both the H-rich and H-deficient channels of PN evolution are represented in our sample. We also investigate the effects of including high...

  20. Observations and 3D Hydrodynamical models of planetary nebulae with Wolf Rayet type central stars

    CERN Document Server

    Rechy-García, J S; Peña, M; Raga, A C

    2016-01-01

    We present high-resolution, long-slit spectroscopic observations of two planetary nebulae with [WC] central stars located near the galactic bulge, M 1-32 and M 3-15. The observations were obtained with the 2.1-m telescope at the Observatorio Astron\\'omico Nacional, San Pedro M\\'artir. M 1-32 shows wide wings on the base of its emission lines and M 3-15 has two very faint high-velocity knots. In order to model both PNe we built a three-dimensional model consisting of a jet interacting with an equatorially concentrated slow wind, emulating the presence of a dense torus, using the Yguaz\\'u hydrodynamical code. From our hydrodynamical models, we obtained position-velocity (PV) diagrams in the [N II]$\\lambda$6583 line for comparison with the observations. We find that the spectral characteristics of M 1-32 and M 3-15 can be explained with the same physical model -a jet moving inside an AGB wind- using different parameters (physical conditions and position angles of the jet). In agreement with our model and observa...

  1. Observations and 3D Hydrodynamical models of planetary nebulae with Wolf Rayet type central stars

    Science.gov (United States)

    Rechy-García, J. S.; Velázquez, P. F.; Peña, M.; Raga, A. C.

    2016-10-01

    We present high-resolution, long-slit spectroscopic observations of two planetary nebulae with [WC] central stars located near the galactic bulge, M 1-32 and M 3-15. The observations were obtained with the 2.1-m telescope at the Observatorio Astronómico Nacional, San Pedro Mártir. M 1-32 shows wide wings on the base of its emission lines and M 3-15 has two very faint high-velocity knots. In order to model both PNe we built a three-dimensional model consisting of a jet interacting with an equatorially concentrated slow wind, emulating the presence of a dense torus, using the Yguazú hydrodynamical code. From our hydrodynamical models, we obtained position-velocity (PV) diagrams in the [N II]λ6583 line for comparison with the observations. We find that the spectral characteristics of M 1-32 and M 3-15 can be explained with the same physical model -a jet moving inside an AGB wind- using different parameters (physical conditions and position angles of the jet). In agreement with our model and observations, these objects contain a dense torus seeing pole-on and a bipolar jet escaping thorough the poles. Then we propose to classify this kind of objects as spectroscopic bipolar nebulae, although they have been classified morphologically as compact, round, or elliptical nebulae or with "close collimated lobes".

  2. High-Resolution Spectroscopy of Winds Associated with T Tauri Stars

    Science.gov (United States)

    Iguchi, Naoto; Itoh, Yoichi

    2016-02-01

    We carried out optical high-resolution spectroscopy of T Tauri stars using the Subaru Telescope. Using archived data from the Keck Telescope and the Very Large Telescope, we detected forbidden lines of [S II] at 4069 Å, in addition to those of [O I] at 5577 Å and 6300 Å, for 13 T Tauri stars. We consider that low-velocity components of these forbidden lines emanate from the wind associated with T Tauri stars. Using two flux ratios of the three lines, we simultaneously determined the hydrogen density and temperature of the winds. The winds of T Tauri stars have a hydrogen density of 2.5 × 106 cm‑3 ‑ 2.5 × 109 cm‑3 and a temperature of 10800 –18 000 K. The mass loss rates by the wind are estimated to lie in the range from 2.0 × 10‑10 M⊙ yr‑1 to 1.4 × 10‑9 M⊙ yr‑1. The mass loss rates are found to increase with increasing mass accretion rates. The ratio of the mass loss rate to the mass accretion rate is 0.001–0.1 for classical T Tauri stars and 0.1–1 for transitional disk objects.

  3. Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars

    CERN Document Server

    Abate, C; Izzard, R G; Mohamed, S S; de Mink, S E

    2013-01-01

    Carbon-enhanced metal-poor stars (CEMP) are observed as a substantial fraction of the very metal-poor stars in the Galactic halo. Most CEMP stars are also enriched in s-process elements and these are often found in binary systems. This suggests that the carbon enrichment is due to mass transfer in the past from an asymptotic giant branch (AGB) star on to a low-mass companion. Models of binary population synthesis are not able to reproduce the observed fraction of CEMP stars without invoking non-standard nucleosynthesis or a substantial change in the initial mass function. This is interpreted as evidence of missing physical ingredients in the models. Recent hydrodynamical simulations show that efficient wind mass transfer is possible in the case of the slow and dense winds typical of AGB stars through a mechanism called wind Roche-lobe overflow (WRLOF), which lies in between the canonical Bondi-Hoyle-Lyttleton (BHL) accretion and Roche-lobe overflow. WRLOF has an effect on the accretion efficiency of mass tran...

  4. 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.

  5. The IUE Mega Campaign: Wind Variability and Rotation in Early-Type Stars

    Science.gov (United States)

    Massa, D.; Fullerton, A. W.; Nichols, J. S.; Owocki, S. P.; Prinja, R. K.; St-Louis, N.; Willis, A. J.; Altner, B.; Bolton, C. T.; Cassinelli, J. P.; Cohen, D.; Cooper, R. G.; Feldmeier, A.; Gayley, K. G.; Harries, T.; Heap, S. R.; Henriksen, R. N.; Howarth, I. D.; Hubeny, I.; Kambe, E.

    1995-01-01

    Wind variability in OB stars may be ubiquitous and a connection between projected stellar rotation velocity and wind activity is well established. However, the origin of this connection is unknown. To probe the nature of the rotation connection, several of the attendees at the workshop on Instability and Variability of Hot-Star Winds drafted an IUE observing proposal. The goal of this program was to follow three stars for several rotations to determine whether the rotation connection is correlative or causal. The stars selected for monitoring all have rotation periods less than or equal to 5 days. They were HD 50896 (WN5), HD 64760 (BO.5 Ib), and HD 66811 (zeta Pup; 04 If(n)). During 16 days of nearly continuous observations in 1995 January (dubbed the 'MEGA' campaign), 444 high-dispersion IUE spectra of these stars were obtained. This Letter presents an overview of the results of the MEGA campaign and provides an introduction to the three following Letters, which discuss the results for each star.

  6. 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.

  7. 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...

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

    CERN Document Server

    Krticka, Jiri

    2016-01-01

    Hot stars emit large amounts of X-rays, which are assumed to originate in the supersonic stellar wind. Part of the emitted X-rays is subsequently absorbed in the wind and influences its ionization state. Because hot star winds are driven radiatively, the modified ionization equilibrium affects the radiative force. We review the recent progress in modelling the influence of X-rays on the radiative equilibrium and on the radiative force. We focus particularly on single stars with X-rays produced in wind shocks and on binaries with massive components, which belong to the most luminous objects in X-rays.

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

    Science.gov (United States)

    Krtička, Jiří; Kubát, Jiří

    2016-09-01

    Hot stars emit large amounts of X-rays, which are assumed to originate in the supersonic stellar wind. Part of the emitted X-rays is subsequently absorbed in the wind and influences its ionization state. Because hot star winds are driven radiatively, the modified ionization equilibrium affects the radiative force. We review the recent progress in modeling the influence of X-rays on the radiative equilibrium and on the radiative force. We focus particularly on single stars with X-rays produced in wind shocks and on binaries with massive components, which belong to the most luminous objects in X-rays.

  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. 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...

  13. 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...

  14. 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.

  15. 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.

  16. 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...

  17. 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.

  18. 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.)

  19. 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...

  20. 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...

  1. Wind energy resource atlas. Volume 5: the East Central Region

    Energy Technology Data Exchange (ETDEWEB)

    Brode, R.; Stoner, R.; Elliott, D.L.; Barchet, W.R.; George, R.L.

    1980-01-01

    This atlas of the wind energy resource is composed of introductory and background information, a regional summary of the wind resource, and assessments of the wind resource in each state of the region. Background is presented on how the wind resource is assessed and on how the results of the assessment should be interpreted. A description of the wind resource on a regional scale is then given. The results of the wind energy assessments for each state are assembled into an overview and summary of the various features of the regional wind energy resource. Assessments for individual states are presented as separate chapters. The state wind energy resources are described in greater detail than is the regional wind energy resource, and features of selected stations are discussed. This preface outlines the use and interpretation of the information found in the state chapters. States include Delaware, Maryland, Kentucky, North Carolina, Tennessee, Virginia, and West Virginia.

  2. The Two Central Stars of NGC 1514: Can They Actually Be Related?

    Science.gov (United States)

    Méndez, Roberto H.; Kudritzki, Rolf-Peter; Urbaneja, Miguel A.

    2016-10-01

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

  3. 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.

  4. 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...

  5. 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.

  6. 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...

  7. Ultra-High-Energy Cosmic Rays from a Magnetized Strange Star Central Engine for Gamma-Ray Bursts

    CERN Document Server

    Esquivel, O

    2008-01-01

    Ultra-high-energy cosmic rays (UHECRs) have been tried to be related to the most varied and powerful sources known in the universe. Gamma-ray bursts (GRBs) are natural candidates. Here, we argue that cosmic rays can be accelerated by large amplitude electromagnetic waves (LAEMWs) when the MHD approximation of the field in the wind generated by the GRB's magnetized central engine breaks down. The central engine considered here is a strange star born with differential rotation from the accretion induced conversion of a neutron star into a strange star in a low-mass X-ray binary system. The LAEMWs generated this way accelerate light ions to the highest energies $E = q\\eta\\Delta\\Phi_{max}$ with an efficiency $\\eta \\sim 10^{-1}$ that accounts for all plausible energy losses. Alternatively, we also consider the possibility that, once formed, the LAEMWs are unstable to creation of a relativistically strong electromagnetic turbulence due to an overturn instability. Under this assumption, a lower limit to the efficien...

  8. Central stars of mid-infrared nebulae discovered with Spitzer and WISE

    CERN Document Server

    Gvaramadze, V V

    2016-01-01

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

  9. Wind-driven gas networks and star formation in galaxies: reaction-advection hydrodynamic simulations

    Science.gov (United States)

    Chappell, David; Scalo, John

    2001-07-01

    The effects of wind-driven star formation feedback on the spatio-temporal organization of stars and gas in galaxies is studied using two-dimensional intermediate-representational quasi-hydrodynamical simulations. The model retains only a reduced subset of the physics, including mass and momentum conservation, fully non-linear fluid advection, inelastic macroscopic interactions, threshold star formation, and momentum forcing by winds from young star clusters on the surrounding gas. Expanding shells of swept-up gas evolve through the action of fluid advection to form a `turbulent' network of interacting shell fragments which have the overall appearance of a web of filaments (in two dimensions). A new star cluster is formed whenever the column density through a filament exceeds a critical threshold based on the gravitational instability criterion for an expanding shell, which then generates a new expanding shell after some time delay. A filament-finding algorithm is developed to locate the potential sites of new star formation. The major result is the dominance of multiple interactions between advectively distorted shells in controlling the gas and star morphology, gas velocity distribution and mass spectrum of high mass density peaks, and the global star formation history. The gas morphology strongly resembles the model envisioned by Norman & Silk, and observations of gas in the Large Magellanic Cloud (LMC)Q1 and local molecular clouds. The dependence of the frequency distribution of present-to-past average global star formation rate on a number of parameters is investigated. Bursts of star formation only occur when the time-averaged star formation rate per unit area is low, or the system is small. Percolation does not play a role. The broad distribution observed in late-type galaxies can be understood as a result of either small size or small metallicity, resulting in larger shell column densities required for gravitational instability. The star formation rate

  10. 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...

  11. KMOS view of the Galactic centre. I. Young stars are centrally concentrated

    Science.gov (United States)

    Feldmeier-Krause, A.; Neumayer, N.; Schödel, R.; Seth, A.; Hilker, M.; de Zeeuw, P. T.; Kuntschner, H.; Walcher, C. J.; Lützgendorf, N.; Kissler-Patig, M.

    2015-12-01

    Context. The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4 pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also ≳100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3-8 Myr old. Aims: Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5 pc of the Galactic centre. The distribution and kinematics of early-type stars are essential to understand the formation and growth of the nuclear star cluster. Methods: We cover the central >4 pc2 (0.75 sq. arcmin) of the Galactic centre using the integral-field spectrograph KMOS (VLT). We extracted more than 1000 spectra from individual stars and identified early-type stars based on their spectra. Results: Our data set contains 114 bright early-type stars: 6 have narrow emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and 76 are O/B type stars. Our wide-field spectroscopic data confirm that the distribution of young stars is compact, with 90% of the young stars identified within 0.5 pc of the nucleus. We identify 24 new O/B stars primarily at large radii. We estimate photometric masses of the O/B stars and show that the total mass in the young population is ≳12 000 M⊙. The O/B stars all appear to be bound to the Milky Way nuclear star cluster, while less than 30% belong to the clockwise rotating disk. We add one new star to the sample of stars affiliated with this disk. Conclusions: The central concentration of the early-type stars is a strong argument that they have formed in situ. An alternative scenario, in which the stars formed outside the Galactic centre in a cluster that migrated to the centre, is refuted. A large part of the young O/B stars is not on the disk, which either means that the early-type stars did not all form on the same disk or

  12. 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...

  13. 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...

  14. Age dependence of wind properties for solar type stars: a 3d study

    CERN Document Server

    Réville, Victor; Strugarek, Antoine; Brun, Allan Sacha

    2016-01-01

    Young and rapidly rotating stars are known for intense, dynamo generated magnetic fields. Spectropolarimetric observations of those stars in precisely aged clusters are key input for gyrochronology and magnetochronology. We use ZDI maps of several young K-type stars of similar mass and radius but with various ages and rotational periods, to perform 3D numerical MHD simulations of their coronae and follow the evolution of their magnetic properties with age. Those simulations yield the coronal structure as well as the instant torque exerted by the magnetized, rotating wind on the star. As stars get older, we find that the angular momentum loss decreases with $\\Omega^3$, which is the reason for the convergence on the Skumanich law. For the youngest stars of our sample, the angular momentum loss show signs of saturation around $8\\Omega_{\\odot}$, which is a common value used in spin evolution models for K-type stars. We compare these results to semi-analytical models and existing braking laws. We observe a complex...

  15. 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...

  16. 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.

  17. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, Daniel M.; Ciolfi, Riccardo; Rezzolla, Luciano [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, D-14476 Potsdam-Golm (Germany)

    2014-04-10

    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 10-10{sup 4} 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.

  19. Magnetically driven winds from differentially rotating neutron stars and X-ray afterglows of short gamma-ray bursts

    CERN Document Server

    Siegel, Daniel M; Rezzolla, Luciano

    2014-01-01

    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 10-10^4 s. These features are generally taken as evidence for 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 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 sensitivel...

  20. Luminous Infrared Galaxies; 3, Multiple Merger, Extended Massive Star Formation, Galactic-Wind and Nuclear-Inflow in NGC 3256

    CERN Document Server

    Lipari, S; Taniguchi, Y; Terlevich, R J; Dottori, H; Carranza, G

    1999-01-01

    We find in a detailed morphological study (at 15 pc resolution) that the extended massive star formation process, shows: (i) extended triple asymmetrical spiral arms structure (r = 5 kpc); and (ii) the spiral arms emanate from three different nuclei. The main optical nucleus shows a small spiral-disk (r = 500 pc) which is a continuation of the external one and reach the very nucleus. And this very nucleus shows blue elongate structure (63 pc x 30 pc), and luminous blue star cluster properties. We study the kinematics of this system and present a detailed Halpha velocity field for the central region (r = 5 kpc). In the main optical nucleus we found a clear "outflow component" associated to galactic-winds and a "inflow radial motion" (in the spiral-disk nuclear structure, r = 700 pc). In addition we detected the outflow component in the central and external regions (r < 5-6 kpc), with a very wide opening angle of 140. We found that the mean value of the inflow region (at PA = 80) is practically perpendicular...

  1. 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.

  2. X-ray Spectroscopy of the Radiation-Driven Winds of Massive Stars: Line Profile and Line Ratio Diagnostics

    CERN Document Server

    Cohen, David H

    2009-01-01

    Massive stars drive powerful, supersonic winds via the radiative momentum associated with the thermal UV emission from their photospheres. Shock phenomena are ubiquitous in these winds, heating them to millions, and sometimes tens of millions, of degrees. The emission line spectra from the shock-heated plasma provide powerful diagnostics of the winds' physical conditions, which in turn provide constraints on models of wind shock heating. Here I show how x-ray line transfer is affected by photoelectric absorption in the partially ionized component of the wind and how it can be modeled to determine the astrophysically important mass-loss rates of these stellar winds. I also discuss how photoexcitation out of metastable excited levels of helium-like ions can provide critical information about the location of the hot plasma in magnetically channeled massive star winds.

  3. Disk wind and magnetospheric accretion in emission from the Herbig Ae star MWC 480

    Science.gov (United States)

    Tambovtseva, L. V.; Grinin, V. P.; Potravnov, I. S.; Mkrtichian, D. E.

    2016-09-01

    The young Herbig Ae star MWC 480 (HD 31648) is one of the comprehensively spectroscopically studied stars in the ultraviolet, optical, and infrared spectral ranges. Using non-LTE modeling of its hydrogen spectrum, we have calculated the contribution to the hydrogen emission from such important regions of the circumstellar environment as the disk wind and the magnetosphere. We have used our own observations of the stellar spectrum performed with the 2.4-m telescope at the Thai National Observatory to quantitatively check our theoretical calculations. In addition, all of the visible and infrared spectra available in the literature have been used for a qualitative comparison. The modeling results have revealed a significant role of the magneto-centrifugal disk wind in the formation of atomic hydrogen emission. The cause of the emission line variability in the spectrum ofMWC 480 is discussed.

  4. 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.

  5. Two bodies gravitational system with variable mass and damping-antidamping effect due to star wind

    CERN Document Server

    López, G V

    2009-01-01

    We study two-bodies gravitational problem where the mass of one of the bodies varies and suffers a damping-antidamping effect due to star wind during its motion. A constant of motion, a Lagrangian and a Hamiltonian are given for the radial motion of the system, 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.

  6. 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...

  7. 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.

  8. Modeling the early evolution of massive OB stars with an experimental wind routine

    CERN Document Server

    Keszthelyi, Zsolt; Wade, Gregg

    2016-01-01

    Stellar evolution models of massive stars are very sensitive to the adopted mass-loss scheme. The magnitude and evolution of mass-loss rates significantly affect the main sequence evolution, and the properties of post-main sequence objects, including their rotational velocities. Driven by potential discrepancies between theoretically predicted and observationally derived mass-loss rates in the OB star range, we particularly aim to investigate the response to mass-loss rates that are lower than currently adopted, in parallel with the mass-loss behavior at the "first" bi-stability jump. We perform 1D hydrodynamical model calculations of single $20 - 60 \\, M_{\\odot}$ Galactic ($Z = 0.014$) stars where the effects of stellar winds are already significant during the main sequence phase. We develop an experimental wind routine to examine the behavior and response of the models under the influence of different mass-loss rates. This observationally guided, simple and flexible wind routine is not a new mass-loss descr...

  9. 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

  10. 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.

    2012-01-01

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

  11. Star Formation Quenching Timescale of Central Galaxies in a Hierarchical Universe

    CERN Document Server

    Hahn, ChangHoon; Wetzel, Andrew R

    2016-01-01

    Central galaxies make up the majority of the galaxy population, including the majority of the quiescent population at $\\mathcal{M}_* > 10^{10}\\mathrm{M}_\\odot$. Thus, the mechanism(s) responsible for quenching central galaxies plays a crucial role in galaxy evolution as whole. We combine a high resolution cosmological $N$-body simulation with observed evolutionary trends of the "star formation main sequence," quiescent fraction, and stellar mass function at $z < 1$ to construct a model that statistically tracks the star formation histories and quenching of central galaxies. Comparing this model to the distribution of central galaxy star formation rates in a group catalog of the SDSS Data Release 7, we constrain the timescales over which physical processes cease star formation in central galaxies. Over the stellar mass range $10^{9.5}$ to $10^{11} \\mathrm{M}_\\odot$ we infer quenching e-folding times that span $1.5$ to $0.5\\; \\mathrm{Gyr}$ with more massive central galaxies quenching faster. For $\\mathcal{M}...

  12. 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.

  13. 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...

  14. 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...

  15. 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...

  16. 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 ...

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

    Science.gov (United States)

    Jarquin-Laguna, A.

    2016-09-01

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

  18. Spin Evolution of Accreting Young Stars. II. Effect of Accretion-Powered Stellar Winds

    CERN Document Server

    Matt, Sean P; Greene, Thomas P; Pudritz, Ralph E

    2011-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind. For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1--10 days in the age range of 1--3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to s...

  19. Wolf-Rayet Central Stars and the Binary Evolution Channel

    Directory of Open Access Journals (Sweden)

    Orsola De Marco

    2003-01-01

    Full Text Available Cálculos recientes de la evolución de estrellas sencillas han tenido éxito en reproducir la composicion de estrellas Wolf-Rayet (WR deficientes en hidrogeno que son además estrellas centrales de nebulosas planetarias. Sin embargo, las observaciones infrarrojas mas recientes dejan claro que el esquema de estrellas sencillas no concuerda con las propiedades del polvo que rodea a muchas estrellas centrales tipo WR. Por otro lado, la binariedad podría explicar las observaciones en el infrarrojo asi como ofrecer una posibilidad de remover la envoltura rica en H de la estrella. En este trabajo proponemos dos esquemas con estrellas binarias originalmente propuestos por De Marco & Soker en relación a las estrellas centrales tipo WR. En el primero, un sistema binario cercano da como resultado el regreso de material eyectado a la estrella y eventualmente una estrella central deficiente en H. Este esquema se invoca para explicar la estrella central CPD-56º8032 en [WC10] y su disco de polvo. El segundo esquema propone que la mayoría de las estrellas centrales tipo WR son resultado de una fusión con una compañera de baja masa durante la fase AGB. Modelamos este esquema por medio de simulaciones hidrodinámicas en 3D, que simulan la fase de envolvente común entre una estrella AGB y una compañera de entre 0.1 and 0.2-M๏ durante el primer y décimo pulso térmico.

  20. 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 < {\

  1. 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.

  2. 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...

  3. 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...

  4. 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...

  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| 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 models that assume standard abundances.

  6. 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...

  7. 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 wind acceleration region and clumping of the wind, leading to a strong dependence on the wind velocity law and clumping parameters. The Atacama Large Millimeter/sub-mm Array (ALMA) is the first observatory to have both the spectral window and sensitivity to observe at the high frequencies required to probe the acceleration regions of massive stars. The deviations in the predicted flux levels as a result of the inclusion of the wind acceleration region and clumping are sufficient to be detected by ALMA, through deviations in the spectral index in different portions of the radio/sub-mm spectra of massive stars, for a 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.

  8. 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...

  9. 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.

  10. Towards a multi-scale understanding of the gas-star formation cycle in the Central Molecular Zone

    CERN Document Server

    Kruijssen, J M Diederik

    2016-01-01

    The Central Molecular Zone (CMZ, the central 500 pc of the Milky Way) contains the largest reservoir of high-density molecular gas in the Galaxy, but forms stars at a rate 10-100 times below commonly-used star formation relations. We discuss recent efforts in understanding how the nearest galactic nucleus forms its stars. The latest models of the gas inflow, star formation, and feedback duty cycle reproduce the main observable features of the CMZ, showing that star formation is episodic and that the CMZ currently resides at a star formation minimum. Using orbital modelling, we derive the three-dimensional geometry of the CMZ and show how the orbital dynamics and the star formation potential of the gas are closely coupled. We discuss how this coupling reveals the physics of star formation and feedback under the conditions seen in high-redshift galaxies, and promotes the formation of the densest stellar clusters in the Galaxy.

  11. 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...

  12. 76 FR 78636 - Southern Star Central Gas Pipeline, Inc.; Supplemental Notice of Intent To Prepare an...

    Science.gov (United States)

    2011-12-19

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Supplemental Notice of Intent To Prepare an Environmental Assessment for the Proposed Alden Gas Storage Field Expansion Project and Request for Comments On Environmental...

  13. 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

  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. 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.

  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. 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...

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

    CERN Document Server

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

    2013-01-01

    Classical barium stars are binary systems which consist of a late-type giant enriched in carbon and slow neutron capture (s-process) elements and an evolved white dwarf (WD) that is invisible at optical wavelengths. The youngest observed barium stars are surrounded by planetary nebulae (PNe), ejected soon after the wind accretion of polluted material when the WD was in its preceeding asymptotic giant branch (AGB) phase. Such systems are rare but powerful laboratories for studying AGB nucleosynthesis as we can measure the chemical abundances of both the polluted star and the nebula ejected by the polluter. Here we present evidence for a barium star in the PN Hen 2-39. The polluted giant is very similar to that found in WeBo 1. It is a cool (Teff=4250 +/- 150 K) giant enhanced in carbon ([C/H]=0.42 +/- 0.02 dex) and barium ([Ba/Fe]=1.50 +/- 0.25 dex). A spectral type of C-R3 C_24 nominally places Hen 2-39 amongst the peculiar early R-type carbon stars, however the barium enhancement and likely binary status mea...

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

    Science.gov (United States)

    Wood, Brian E.; Müller, Hans-Reinhard; Harper, Graham M.

    2016-10-01

    We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope, focusing on spectra of the Mg ii h and k lines near 2800 Å in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus on spectral types between K2 III and M5 III, a spectral type range with stars that are noncoronal, but possessing strong, chromospheric winds. We find a very tight relation between Mg ii surface flux and photospheric temperature, supporting the notion that all K2-M5 III stars are emitting at a basal flux level. Wind velocities (V w ) are generally found to decrease with spectral type, with V w decreasing from ˜40 km s-1 at K2 III to ˜20 km s-1 at M5 III. We find two new detections of astrospheric absorption, for σ Pup (K5 III) and γ Eri (M1 III). This absorption signature had previously only been detected for α Tau (K5 III). For the three astrospheric detections, the temperature of the wind after the termination shock (TS) correlates with V w , but is lower than predicted by the Rankine-Hugoniot shock jump conditions, consistent with the idea that red giant TSs are radiative shocks rather than simple hydrodynamic shocks. A full hydrodynamic simulation of the γ Eri astrosphere is provided to explore this further. Based on observations made 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 NAS 5-26555. These observations are associated with program GO-13462. This paper also presents observations obtained with the Harlan J. Smith Telescope at McDonald Observatory of the University of Texas at Austin.

  20. 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...

  1. MOLECULAR GAS AND STAR-FORMATION PROPERTIES IN THE CENTRAL AND BAR REGIONS OF NGC 6946

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Hsi-An; Sorai, Kazuo [Department of Physics, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810 (Japan); Kuno, Nario [Division of Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, Tennodai, Tsukuba, Ibaraki 305-8571 (Japan); Koda, Jin [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States); Hirota, Akihiko [Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Kaneko, Hiroyuki, E-mail: hapan@astro1.sci.hokudai.ac.jp [Nobeyama Radio Observatory, NAOJ, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)

    2015-12-10

    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. A high-resolution image (100 pc) of {sup 13}CO (1–0) is created for the inner 2 kpc disk by the single-dish Nobeyama Radio Observatory 45 m telescope and interferometer Combined Array for Research in Millimeter-wave Astronomy, including 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. The physical properties of molecular gas are inferred from (1) the large velocity gradient calculations using our observations and archival {sup 12}CO (1–0), {sup 12}CO(2–1) data, (2) the dense gas fraction suggested by the luminosity ratio of HCN to {sup 12}CO (1–0), and (3) the infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. The dense gas fraction of the central region is similar to that of luminous infrared galaxies/ultraluminous infrared galaxies, whereas the offset ridges are close to the global average of normal galaxies. The coolest and least-dense region is found in a spiral-like structure, which was misunderstood to be part of the southern primary bar in previous low-resolution observations. The star-formation efficiency (SFE) changes by about five times in the inner disk. The variation of SFE agrees with the prediction in terms of star formation regulated by the galactic bar. We find a consistency between the star-forming region and the temperature inferred by the infrared color, suggesting that the distribution of subkiloparsec-scale temperature is driven by star formation.

  2. The post-common-envelope, binary central star of the planetary nebula Hen 2-11

    Science.gov (United States)

    Jones, D.; Boffin, H. M. J.; Miszalski, B.; Wesson, R.; Corradi, R. L. M.; Tyndall, A. A.

    2014-02-01

    We present a detailed photometric study of the central star system of the planetary nebula Hen 2-11, selected for study because of its low-ionisation filaments and bipolar morphology - traits which have been strongly linked with central star binarity. Photometric monitoring with NTT-EFOSC2 reveals a highly irradiated, double-eclipsing, post-common-envelope system with a period of 0.609 d. Modelling of the lightcurve indicates that the nebular progenitor is extremely hot, while the secondary in the system is probably a K-type main sequence star. The chemical composition of the nebula is analysed, showing Hen 2-11 to be a medium-excitation non-Type i nebula. A simple photoionisation model is constructed determining abundance ratios of C/O and N/O which would be consistent with the common-envelope cutting short the AGB evolution of the nebular progenitor. The detection of a post-common-envelope binary system at the heart of Hen 2-11 further strengthens the link between binary progeny and the formation of axisymmetric planetary nebulae with patterns of low-ionisation filaments, clearly demonstrating their use as morphological indicators of central star binarity. Extracted 1D spectra, reduced 2D spectra, and table of photometry are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/562/A89

  3. 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.

  4. 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...

  5. Astrometry with Hubble Space Telescope: A Parallax of the Central Star of the Planetary Nebula NGC 6853

    CERN Document Server

    Benedict, G F; Fredrick, L W; Harrison, T E; Skrutskie, M F; Slesnick, C L; Rhee, J; Patterson, R J; Nelan, E; Jefferys, W H; Van Altena, W; Montemayor, T; Shelus, P J; Franz, O G; Wasserman, L H; Hemenway, P D; Duncombe, R L; Story, D; Whipple, A L; Bradley, A J

    2003-01-01

    We present an absolute parallax and relative proper motion for the central star of the planetary nebula NGC 6853 (The Dumbell). We obtain these with astrometric data from FGS 3, a white-light interferometer on {\\it HST}. Spectral classifications and VRIJHKT$_2$M and DDO51 photometry of the stars comprising the astrometric reference frame provide spectrophotometric estimates of their absolute parallaxes. Introducing these into our model as observations with error, we find $\\pi_{abs} = 2.10 \\pm 0.48$ mas for the DAO central star of NGC 6853. A weighted average with a previous ground-based USNO determination yields $\\pi_{abs} = 2.40 \\pm 0.32$. We assume that the extinction suffered by the reference stars nearest (in angular separation and distance) to the central star is the same as for the central star. Correcting for color differences, we find $$ = 0.30 $ \\pm $ 0.06 for the central star, hence, an absolute magnitude M$_V = 5.48^{-0.16}_{+0.15}$. A recent determination of the central star effective temperature ...

  6. 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.

  7. 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...

  8. 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

  9. 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).

  10. 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...

  11. 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.

  12. The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity

    CERN Document Server

    Goldman, Steven R; Zijlstra, Albert A; Green, James A; Wood, Peter R; Nanni, Ambra; Imai, Hiroshi; Whitelock, Patricia A; Matsuura, Mikako; Groenewegen, Martin A T; Gómez, José F

    2016-01-01

    We present the results of our survey of 1612 MHz circumstellar OH maser emission from asymptotic giant branch (AGB) stars and red supergiants (RSGs) in the Large Magellanic Cloud. We have discovered four new circumstellar maser sources in the LMC, and increased the number of reliable wind speeds from IR stars in the LMC from 5 to 13. Using our new wind speeds, as well as those from Galactic sources, we have derived an updated relation for dust driven winds: $v_{exp} \\propto Z L^{0.4}$. We compare the sub-solar metallicity LMC OH/IR stars with carefully selected samples of more metal-rich OH/IR stars, also at known distances, in the Galactic Centre and Galactic Bulge. For 8 of the Bulge stars we derive pulsation periods for the first time, using near-IR photometry from the VVV survey. We have modeled our LMC OH/IR stars and developed an empirical method of deriving gas-to-dust ratios and mass loss rates by scaling the models to the results from maser profiles. We have done this also for samples in the Galactic...

  13. 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.

  14. 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)

  15. The iron abundance in hot central stars of planetary nebulae derived from IUE spectra

    CERN Document Server

    Deetjen, J L; Rauch, T; Werner, K

    1999-01-01

    We present the first attempt to determine the iron abundance in hot central stars of planetary nebulae. We perform an analysis with fully metal-line blanketed NLTE model atmospheres for a sample of ten stars (T_eff >= 70.000 K) for which high-resolution UV spectra are available from the IUE archive. In all cases lines of Fe VI or Fe VII can be identified. As a general trend, the iron abundance appears to be subsolar by 0.5-1 dex, however, the S/N of the IUE spectra is not sufficient to exclude a solar abundance in any specific case. Improved spectroscopy by either FUSE or HST is necessary to verify the possibility of a general iron deficiency in central stars. The suspected deficiency may be the result of gravitational settling in the case of three high-gravity objects. For the other stars with low gravity and high luminosity dust fractionation during the previous AGB phase is a conceivable origin.

  16. Gravitational Lensing of stars in the central arcsecond of our Galaxy

    CERN Document Server

    Bozza, V

    2005-01-01

    In the neighborhood of Sgr A*, several stars (S2, S12, S14, S1, S8, S13) enjoy an accurate determination of their orbital parameters. General Relativity predicts that the central black hole acts as a gravitational lens on these stars, generating a secondary image and two infinite series of relativistic images. For each of these six stars, we calculate the light curves for the secondary and the first two relativistic images, in the Schwarzschild black hole hypothesis, throughout their orbital periods. The curves are peaked around the periapse epoch, but two subpeaks may arise in nearly edge-on orbits, when the source is behind or in front of Sgr A*. We show that for most of these stars the secondary image should be observable during its brightness peak. In particular, S14 is the best candidate, since its secondary image reaches K=23.3 with an angular separation of 0.125 mas from the apparent horizon of the central black hole. The detection of such images by future instruments could represent the first observat...

  17. Gravitational Lensing of Stars in the Central Arcsecond of Our Galaxy

    Science.gov (United States)

    Bozza, V.; Mancini, L.

    2005-07-01

    In the neighborhood of Sgr A*, several stars (S2, S12, S14, S1, S8, and S13) enjoy an accurate determination of their orbital parameters. General relativity predicts that the central black hole acts as a gravitational lens on these stars, generating a secondary image and two infinite series of relativistic images. For each of these six stars, we calculate the light curves for the secondary and the first two relativistic images, in the Schwarzschild black hole hypothesis, throughout their orbital periods. The curves are peaked around the periapse epoch, but two subpeaks may arise in nearly edge-on orbits, when the source is behind or in front of Sgr A*. We show that for most of these stars the secondary image should be observable during its brightness peak. In particular, S14 is the best candidate, since its secondary image reaches K=23.3 with an angular separation of 0.125 mas from the apparent horizon of the central black hole. The detection of such images by future instruments could represent the first observation of gravitational lensing beyond the weak-field approximation.

  18. 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...

  19. Full Three Dimensional Orbits For Multiple Stars on Close Approaches to the Central Supermassive Black Hole

    CERN Document Server

    Ghez, A M; Duchêne, G; Hornstein, S D; Morris, M; Salim, S; Tanner, A

    2003-01-01

    With the advent of adaptive optics on the W. M. Keck 10 m telescope, two significant steps forward have been taken in building the case for a supermassive black hole at the center of the Milky Way and understanding the black hole's effect on its environment. Using adaptive optics and speckle imaging to study the motions of stars in the plane of sky with +-~2 mas precision over the past 7 years, we have obtained the first simultaneous orbital solution for multiple stars. Among the included stars, three are newly identified (S0-16, S0-19, S0-20). The most dramatic orbit is that of the newly identified star S0-16, which passed a mere 60 AU from the central dark mass at a velocity of 9,000 km/s in 1999. The orbital analysis results in a new central dark mass estimate of 3.6(+-0.4)x10^6(D/8kpc)^3 Mo. This dramatically strengthens the case for a black hole at the center of our Galaxy, by confining the dark matter to within a radius of 0.0003 pc or 1,000 Rsh and thereby increasing the inferred dark mass density by f...

  20. Temperature Scale and Iron Abundances of Very Hot Central Stars of Planetary Nebulae

    CERN Document Server

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

    2002-01-01

    The determination of effective temperatures of very hot central stars (Teff>70000K) by model atmosphere analyses of optical H and He line profiles is afflicted with considerable uncertainty, primarily due to the lack of neutral helium lines. Ionization balances of metals, accessible only with UV lines, allow more precise temperature estimates. The potential of iron lines is pointed out. At the same time iron and other metal abundances, hardly investigated until today, may be derived from UV spectra. We describe recent HST spectroscopy performed for this purpose. A search for iron lines in FUV spectra of the hottest H-deficient central stars (PG1159-type, Teff>100000K) taken with FUSE was unsuccessful. The derived deficiency is interpreted in terms of iron depletion due to n-capture nucleosynthesis in intershell matter, which is now exposed at the stellar surface as a consequence of a late He shell flash.

  1. The role of binarity in Wolf-Rayet central stars of planetary nebulae

    CERN Document Server

    Miszalski, Brent; McBride, Vanessa

    2015-01-01

    Nearly 50 post-common-envelope (post-CE) close binary central stars of planetary nebulae (CSPNe) are now known. Most contain either main sequence or white dwarf (WD) companions that orbit the WD primary in around 0.1-1.0 days. Only PN~G222.8-04.2 and NGC~5189 have post-CE CSPNe with a Wolf-Rayet star primary (denoted [WR]), the low-mass analogues of massive Wolf-Rayet stars. It is not well understood how H-deficient [WR] CSPNe form, even though they are relatively common, appearing in over 100 PNe. The discovery and characterisation of post-CE [WR] CSPNe is essential to determine whether proposed binary formation scenarios are feasible to explain this enigmatic class of stars. The existence of post-CE [WR] binaries alone suggests binary mergers are not necessarily a pathway to form [WR] stars. Here we give an overview of the initial results of a radial velocity monitoring programme of [WR] CSPNe to search for new binaries. We discuss the motivation for the survey and the associated strong selection effects. T...

  2. Post-common-envelope Wolf-Rayet central stars of planetary nebulae

    CERN Document Server

    Miszalski, Brent; McBride, Vanessa

    2015-01-01

    Nearly 50 post-common-envelope (post-CE) close binary central stars of planetary nebulae (CSPNe) are now known. Most contain either main sequence or white dwarf (WD) companions that orbit the WD primary in around 0.1-1.0 days. Only PN~G222.8-04.2 and NGC~5189 have post-CE CSPNe with a Wolf-Rayet star primary (denoted [WR]), the low-mass analogues of massive Wolf-Rayet stars. It is not well understood how H-deficient [WR] CSPNe form, even though they are relatively common, appearing in over 100 PNe. The discovery and characterisation of post-CE [WR] CSPNe is essential to determine whether proposed binary formation scenarios are feasible to explain this enigmatic class of stars. The existence of post-CE [WR] binaries alone suggests binary mergers are not necessarily a pathway to form [WR] stars. Here we give an overview of the initial results of a radial velocity monitoring programme of [WR] CSPNe to search for new binaries. We discuss the motivation for the survey and the associated strong selection effects. T...

  3. Measuring the shock-heating rate in the winds of O stars using X-ray line spectra

    CERN Document Server

    Cohen, David H; Gayley, Kenneth G; Owocki, Stanley P; Sundqvist, Jon O; Petit, Veronique; Leutenegger, Maurice A

    2014-01-01

    We present a new method for using measured X-ray emission line fluxes from O stars to determine the shock-heating rate due to instabilities in their radiation-driven winds. The high densities of these winds means that their embedded shocks quickly cool by local radiative emission, while cooling by expansion should be negligible. Ignoring for simplicity any non-radiative mixing or conductive cooling, the method presented here exploits the idea that the cooling post-shock plasma systematically passes through the temperature characteristic of distinct emission lines in the X-ray spectrum. In this way, the observed flux distribution among these X-ray lines can be used to construct the cumulative probability distribution of shock strengths that a typical wind parcel encounters as it advects through the wind. We apply this new method (Gayley 2014) to Chandra grating spectra from five O stars with X-ray emission indicative of embedded wind shocks in effectively single massive stars. Correcting for wind absorption of...

  4. Bar-induced central star formation as revealed by integral field spectroscopy from CALIFA

    CERN Document Server

    Lin, Lin; He, Yanqin; Xiao, Ting; Wang, Enci

    2016-01-01

    We investigate the recent star formation history (SFH) in the inner region of 57 nearly face-on spiral galaxies selected from the Calar Alto Legacy Integral Field Area (CALIFA) survey. For each galaxy we use the integral field spectroscopy from CALIFA to obtain two-dimensional maps and radial profiles of three parameters that are sensitive indicators of the recent SFH: the 4000\\AA\\ break (D$_n$(4000)), and the equivalent width of H$\\delta$ absorption (EW(H$\\delta_A$)) and H$\\alpha$ emission (EW(H$\\alpha$)). We have also performed photometric decomposition of bulge/bar/disk components based on SDSS optical image. We identify a class of 17 "turnover" galaxies whose central region present significant drop in D$_n$(4000), and most of them correspondingly show a central upturn in EW(H$\\delta_A$) and EW(H$\\alpha$). This indicates that the central region of the turnover galaxies has experienced star formation in the past 1-2 Gyr, which makes the bulge younger and more star-forming than surrounding regions. We find a...

  5. 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...

  6. 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...

  7. 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.

  8. 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

  9. 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 ...

  10. 77 FR 33210 - Shooting Star Wind Project, LLC; Supplemental Notice That Initial Market-Based Rate Filing...

    Science.gov (United States)

    2012-06-05

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Shooting Star Wind Project, LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes Request for Blanket Section 204 Authorization This is a supplemental notice in the above-referenced proceeding...

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

    NARCIS (Netherlands)

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

    2014-01-01

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

  12. 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.

  13. Simulations of Winds of Weak-Lined T Tauri Stars. II.: The Effects of a Tilted Magnetosphere and Planetary Interactions

    CERN Document Server

    Vidotto, A A; Jatenco-Pereira, V; Gombosi, T I

    2010-01-01

    Based on our previous work (Vidotto et al. 2009a), we investigate the effects on the wind and magnetospheric structures of weak-lined T Tauri stars due to a misalignment between the axis of rotation of the star and its magnetic dipole moment vector. In such configuration, the system loses the axisymmetry presented in the aligned case, requiring a fully 3D approach. We perform 3D numerical MHD simulations of stellar winds and study the effects caused by different model parameters. The system reaches a periodic behavior with the same rotational period of the star. We show that the magnetic field lines present an oscillatory pattern and that by increasing the misalignment angle, the wind velocity increases. Our wind models allow us to study the interaction of a magnetized wind with a magnetized extra-solar planet. Such interaction gives rise to reconnection, generating electrons that propagate along the planet's magnetic field lines and produce electron cyclotron radiation at radio wavelengths. We find that a cl...

  14. 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.

  15. 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...

  16. The post-common-envelope, binary central star of the planetary nebula Hen 2-11

    CERN Document Server

    Jones, David; Miszalski, Brent; Wesson, Roger; Corradi, Romano L M; Tyndall, Amy A

    2014-01-01

    We present a detailed photometric study of the central star system of the planetary nebula Hen 2-11, selected for study because of its low-ionisation filaments and bipolar morphology - traits which have been strongly linked with central star binarity. Photometric monitoring with NTT-EFOSC2 reveals a highly irradiated, double-eclipsing, post-common-envelope system with a period of 0.609 d. Modelling of the lightcurve indicates that the nebular progenitor is extremely hot, while the secondary in the system is probably a K-type main sequence star. The chemical composition of the nebula is analysed, showing Hen 2-11 to be a medium-excitation non-Type I nebula. A simple photoionisation model is constructed determining abundance ratios of C/O and N/O which would be consistent with the common-envelope cutting short the AGB evolution of the nebular progenitor. The detection of a post-common-envelope binary system at the heart of Hen 2-11 further strengthens the link between binary progeny and the formation of axisymm...

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

    Energy Technology Data Exchange (ETDEWEB)

    Knobel, Christian; Lilly, Simon J.; Woo, Joanna; Kovač, Katarina, E-mail: christian.knobel@phys.ethz.ch [Institute for Astronomy, ETH Zurich, CH-8093 Zurich (Switzerland)

    2015-02-10

    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 10{sup 10.3} M {sub ☉}), 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.

  18. 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...

  19. RY Scuti: Infrared and radio observations of the mass-loss wind of a massive binary star system

    Science.gov (United States)

    Gehrz, R. D.; Hayward, T. L.; Houck, J. R.; Miles, J. W.; Hjellming, R. M.; Jones, T. J.; Woodward, Charles E.; Prentice, Ricarda; Forrest, W. J.; Libonate, S.

    1995-01-01

    We report infrared (IR) imaging, IR photometry, IR spectroscopy, optical/IR photopolarimetry, and Very Large Array (VLA) radio observations of the peculiar binary star RY Scuti. These observations provide an unprecedented view of the detailed spatial structure of the equatorial mass-loss wind of a massive, luminous, 'overcontact' binary system. The binary star (0.43 AU separation) is surrounded by a flattened equatorial disk with an outer radius of approximately = 3 x 10(exp 16) cm (2000 AU) that emits strongly in the IR and radio. The inside of the disk is ionized and emits free-free radiation from hydrogen and 12.8 micrometers forbidden-line emission from (Ne II); the outside of the disk emits thermal radiation from silicate dust. Radio continuum emission is also produced in a compact H II region surrounding the binary. The dust may have a polycyclic aromatic hydrocarbon (PAH) component. We use a rudimentary geometric model in which the thermal IR and radio emission from the disk are assumed to arise in a pair of concentric toroidal rings to estimate the physical properties of the disk. The mean radius of the ionized gas toroid is approximately = 1.3 x 10(exp 16) cm (870 AU), and the mean radius of the dust toroid is approximately = 2.2 x 10(exp 16) cm (1470 AU). RY Scuti has a small intrinsic polarization, with the electric vector perpendicular to the equatorial disk, that is probably caused by electron scattering from hot gas close to the central binary. We conclude that neon in the nebula is overabundant with respect to hydrogen and helium by a factor of between 1.6 and 10. Our IR/radio image data suggest that the circumstellar disk is part of an extensive radiation driven mass-loss outflow that is strongly confined to the equatorial plane of the binary system. The sharp spatial separation of the outer dust torous from the inner ionized gas torus confirms earlier suggestions that dust formation in the circumstellar ejecta of very hot stars must occur in

  20. 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 ...

  1. 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).

  2. The growth of the central region by acquisition of counter-rotating gas in star-forming galaxies

    CERN Document Server

    Chen, Yan-Mei; Tremonti, Christy A; Bershady, Matt; Merrifield, Michael; Emsellem, Eric; Jin, Yi-Fei; Huang, Song; Fu, Hai; Wake, David A; Bundy, Kevin; Stark, David; Lin, Lihwai; Argudo-Fernandez, Maria; Bergmann, Thaisa Storchi; Bizyaev, Dmitry; Brownstein, Joel; Bureau, Martin; Chisholm, John; Drory, Niv; Guo, Qi; Hao, Lei; Hu, Jian; Li, Cheng; Li, Ran; Lopes, Alexandre Roman; Pan, Kai-Ke; Riffel, Rogemar A; Thomas, Daniel; Wang, Lan; Westfall, Kyle; Yan, Ren-Bin

    2016-01-01

    Galaxies grow through both internal and external processes. In about 10% of nearby red galaxies with little star formation, gas and stars are counter-rotating, demonstrating the importance of external gas acquisition in these galaxies. However, systematic studies of such phenomena in blue, star-forming galaxies are rare, leaving uncertain the role of external gas acquisition in driving evolution of blue galaxies. Based on new measurements with integral field spectroscopy of a large representative galaxy sample, we find an appreciable fraction of counter-rotators among blue galaxies (9 out of 489 galaxies). The central regions of blue counter-rotators show younger stellar populations and more intense, ongoing star formation than their outer parts, indicating ongoing growth of the central regions. The result offers observational evidence that the acquisition of external gas in blue galaxies is possible; the interaction with pre-existing gas funnels the gas into nuclear regions (< 1 kpc) to form new stars.

  3. 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...

  4. 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.

  5. 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...

  6. 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.

  7. 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.

  8. Supermassive black holes and central star clusters: Connection with the host galaxy kinematics and color

    Science.gov (United States)

    Zasov, A. V.; Cherepashchuk, A. M.

    2013-11-01

    The relationship between the masses of the central, supermassive black holes ( M bh) and of the nuclear star clusters ( M nc) of disk galaxies with various parameters galaxies are considered: the rotational velocity at R = 2 kpc V (2), the maximum rotational velocity V max, the indicative dynamical mass M 25, the integrated mass of the stellar population M *, and the integrated color index B-V. The rotational velocities andmasses of the central objects were taken from the literature. Themass M nc correlatesmore closely with the kinematic parameters and the disk mass than M bh, including with the velocity V max, which is closely related to the virial mass of the dark halo. On average, lenticular galaxies are characterized by higher masses M bh compared to other types of galaxies with similar characteristics. The dependence of the blackhole mass on the color index is bimodal: galaxies of the red group (red-sequence) with B-V >0.6-0.7 which are mostly early-type galaxies with weak star formation, differ appreciably from blue galaxies, which have higher values of M nc and M bh. At the dependences we consider between the masses of the central objects and the parameters of the host galaxies (except for the dependence of M bh on the central velocity dispersion), the red-group galaxies have systematically higher M bh values, even when the host-galaxy parameters are similar. In contrast, in the case of nuclear star clusters, the blue and red galaxies form unified sequences. The results agree with scenarios in which most red-group galaxies form as a result of the partial or complete loss of interstellar gas in a stage of high nuclear activity in galaxies whose central black-hole masses exceed 106-107 M ⊙ (depending on the mass of the galaxy itself). The bulk of disk galaxies with M bh > 107 M ⊙ are lenticular galaxies (types S0, E/S0) whose disks are practically devoid of gas.

  9. The Dust Properties of Two Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: in Search of a Possible Link

    CERN Document Server

    Clayton, Geoffrey C; 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

    2011-01-01

    We present new Spitzer/IRS spectra of two hot R Coronae Borealis (RCB) stars, one in the Galaxy,V348 Sgr, and one lying in the LMC, HV 2671. These two objects may constitute a link between the RCB stars and the late Wolf-Rayet ([WCL]) class of central stars of planetary nebula (CSPNe) such as CPD -56 8032 that has little or no hydrogen in their atmospheres. 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 -56 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 -56 8032 and HV 2671. The PAH emission seen strongly in the other two stars is not present. Instead, the spectrum is dominated by a broad emission c...

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

    Science.gov (United States)

    Airapetian, V. S.; Leake, J. E.; Carpenter, Kenneth G.

    2015-01-01

    We present the first magnetohydrodynamic model of the stellar chromospheric heating and acceleration of the outer atmospheres of cool evolved stars, using α 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 Alfvén 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 Alfvé 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 due to resistive (Joule) dissipation of electric currents, induced by upward propagating non-linear Alfvé waves, 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, Alfvé 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 Alfvé waves becomes significant in the outer chromosphere at 1 stellar radius from the photosphere. The calculated terminal velocity and the mass loss rate are consistent with the observationally derived wind properties in α Tau.

  11. Discovery of close binary central stars in the planetary nebulae NGC 6326 and NGC 6778

    CERN Document Server

    Miszalski, B; Rodríguez-Gil, P; Boffin, H M J; Corradi, R L M; Santander-García, M

    2011-01-01

    We present observations proving the close binary nature of the central stars belonging to the planetary nebulae (PNe) NGC 6326 and NGC 6778. Photometric monitoring reveals irradiated lightcurves with orbital periods of 0.372 and 0.1534 days, respectively, constituting firm evidence that they passed through a common-envelope (CE) phase. Unlike most surveys for close binary central stars (CSPN) however, the binary nature of NGC 6326 was first revealed spectroscopically and only later did photometry obtain an orbital period. Gemini South observations revealed a large 160 km/s shift between the nebula and emission lines of C III and N III well known to originate from irradiated atmospheres of main-sequence companions. These so-called weak emission lines are fairly common in PNe and measurement of their radial velocity shifts in spectroscopic surveys could facilitate the construction of a statistically significant sample of post-CE nebulae. There is growing evidence that this process can be further accelerated by ...

  12. 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...

  13. 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.

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    turbine can increase the total available wind power of the wind farm. This paper proposed a new dispatch method which dispatches the wind power reference to each wind turbine proportional to each wind turbine’s optimal wind power to increase the available wind power of the whole wind farm. Particle Swarm...... efficient of upstream wind turbines in the wind farm influences the downstream wind speed which determines the available wind power of the downstream wind turbine. Optimize the wind power production of each wind turbine in the wind farm by the optimization of the pitch angle and tip-speed-ratio of each...... Optimization (PSO) is used to obtain the optimal wind power for each wind turbine. A case study is carried out. The available wind power of the wind farm was compared between the traditional dispatch method and the proposed dispatch method with the consideration of the wake effect....

  15. 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

  16. 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...

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

    Science.gov (United States)

    Jones, D.; Lloyd, M.; 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.

    2010-11-01

    We present the first detailed spatiokinematical 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 narrow-band imaging in the light of [NII]6584Å, [OIII]5007 Å and [SII]6717+6731Å, obtained using ACAM on the William Herschel Telescope, has been used to investigate the ionization structure of Abell 41. Long-slit observations of the Hα and [NII]6584Å emission were obtained using the Manchester Echelle Spectrometer on the 2.1-m San Pedro Mártir Telescope. These spectra, combined with the narrow-band imagery, were used to develop a spatiokinematical model of [NII]6584Å emission from Abell 41. The best-fitting model reveals Abell 41 to have a waisted, bipolar structure with an expansion velocity of ~40 km s-1 at the waist. The symmetry axis of the model nebula is within 5° of perpendicular to the orbital plane of the central binary system. This provides strong evidence that the close-binary system, MT Ser, has directly affected the shaping of its nebula, Abell 41. Although the theoretical link between bipolar planetary nebulae and binary central stars is long established, this nebula is only the second to have this link, between nebular symmetry axis and binary plane, proved observationally. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. E-mail: david.jones-3@postgrad.manchester.ac.uk

  18. 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).

  19. VLTI-AMBER velocity-resolved aperture-synthesis imaging of η Carinae with a spectral resolution of 12 000. Studies of the primary star wind and innermost wind-wind collision zone

    Science.gov (United States)

    Weigelt, G.; Hofmann, K.-H.; Schertl, D.; Clementel, N.; Corcoran, M. F.; Damineli, A.; de Wit, W.-J.; Grellmann, R.; Groh, J.; Guieu, S.; Gull, T.; Heininger, M.; Hillier, D. J.; Hummel, C. A.; Kraus, S.; Madura, T.; Mehner, A.; Mérand, A.; Millour, F.; Moffat, A. F. J.; Ohnaka, K.; Patru, F.; Petrov, R. G.; Rengaswamy, S.; Richardson, N. D.; Rivinius, T.; Schöller, M.; Teodoro, M.; Wittkowski, M.

    2016-10-01

    Context. The mass loss from massive stars is not understood well. η Carinae is a unique object for studying the massive stellar wind during the luminous blue variable phase. It is also an eccentric binary with a period of 5.54 yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. Aims: We want to investigate the structure and kinematics of η Car's primary star wind and wind-wind collision zone with a high spatial resolution of ~6 mas (~14 au) and high spectral resolution of R = 12 000. Methods: Observations of η Car were carried out with the ESO Very Large Telescope Interferometer (VLTI) and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision. Results: We present velocity-resolved aperture-synthesis images reconstructed in more than 100 different spectral channels distributed across the Brγ 2.166 μm emission line. The intensity distribution of the images strongly depends on wavelength. At wavelengths corresponding to radial velocities of approximately -140 to - 376 km s-1 measured relative to line center, the intensity distribution has a fan-shaped structure. At the velocity of - 277 km s-1, the position angle of the symmetry axis of the fan is ~126°. The fan-shaped structure extends approximately 8.0 mas (~18.8 au) to the southeast and 5.8 mas (~13.6 au) to the northwest, measured along the symmetry axis at the 16% intensity contour. The shape of the intensity distributions suggests that the obtained images are the first direct images of the innermost wind-wind collision zone. Therefore, the observations provide velocity-dependent image structures that can be used to test three

  20. Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet and wels type central stars

    CERN Document Server

    Girard, P; Acker, A

    2006-01-01

    Aims: Chemical compositions and other properties of planetary nebulae around central stars of spectral types [WC], [WO], and wels are compared with those of `normal' central stars, in order to clarify the evolutionary status of each type and their interrelation. Methods: We use plasma diagnostics to derive from optical spectra the plasma parameters and chemical compositions of 48 planetary nebulae. We also reanalyze the published spectra of a sample of 167 non-WR PN. The results as well as the observational data are compared in detail with those from other studies of the objects in common. Results: The central star's spectral type is clearly correlated with electron density, temperature and excitation class of the nebula, [WC] nebulae tend to be smaller than the other types. All this corroborates the view of an evolutionary sequence from cool [WC 11] central stars inside dense, low excitation nebulae towards hot [WO 1] stars with low density, high excitation nebulae. The wels PN, however, appear to be a separ...

  1. 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...

  2. 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.

  3. 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.

  4. THE INTERACTION OF VENUS-LIKE, M-DWARF PLANETS WITH THE STELLAR WIND OF THEIR HOST STAR

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, O.; Drake, J. J.; Garraffo, C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138 (United States); Ma, Y. [Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California (United States); Glocer, A. [NASA/GSFC, Code 673 Greenbelt, MD 20771 (United States); Bell, J. M. [Center for Planetary Atmospheres and Flight Sciences, National Institute of Aerospace, Hampton, VA 23666 (United States); Gombosi, T. I. [Center for Space Environment Modeling, University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109 (United States)

    2015-06-10

    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 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-Alfvénic stellar wind conditions, which could lead to dynamic energy deposition into 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.

  5. 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 ...

  6. Brackett γ radiation from the inner gaseous accretion disk, magnetosphere, and disk wind region of Herbig AeBe stars

    Science.gov (United States)

    Tambovtseva, L. V.; Grinin, V. P.; Weigelt, G.

    2016-05-01

    Various disk and outflow components such as the magnetosphere, the disk wind, the gaseous accretion disk, and other regions may contribute to the hydrogen line emission of young Herbig AeBe stars. Non-LTE modeling was performed to show the influence of the model parameters of each emitting region on the intensity and shape of the Brγ line profile, to present the spatial brightness distribution of each component, and to compare the contribution of each component to the total line emission. The modeling shows that the disk wind is the dominant contributor to the Brγ line rather than the magnetosphere and inner gaseous accretion disk. The contribution of the disk wind region to the Hα line is also considered.

  7. 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...

  8. 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 ...

  9. A Link Between Star Formation Quenching and Inner Stellar Mass Density in SDSS Central Galaxies

    CERN Document Server

    Fang, Jerome J; Koo, David C; Dekel, Avishai

    2013-01-01

    We study the correlation between galaxy structure and the quenching of star formation using a sample of SDSS central galaxies with stellar masses 9.75< log M_*/M_sun<11.25 and redshifts z<0.075. GALEX UV data are used to cleanly divide the sample into star-forming and quenched galaxies, and to identify galaxies in transition (the green valley). Despite a stark difference in visual appearance between blue and red galaxies, their average radial stellar mass density profiles are remarkably similar (especially in the outer regions) at fixed mass. The inner stellar mass surface density within a radius of 1 kpc, \\Sigma_1, is used to quantify the growth of the bulge as galaxies evolve. When galaxies are divided into narrow mass bins, their distribution in the color-\\Sigma_1 plane at fixed mass forms plausible evolutionary tracks. \\Sigma_1 seems to grow as galaxies evolve through the blue cloud, and once it crosses a threshold value, galaxies are seen to quench at fixed \\Sigma_1. The \\Sigma_1 threshold for q...

  10. VLTI-AMBER velocity-resolved aperture-synthesis imaging of Eta Carinae with a spectral resolution of 12000. Studies of the primary star wind and innermost wind-wind collision

    CERN Document Server

    Weigelt, G; Schertl, D; Clementel, N; Corcoran, M F; Damineli, A; de Wit, W -J; Grellmann, R; Groh, J; Guieu, S; Gull, T; Heininger, M; Hillier, D J; Hummel, C A; Kraus, S; Madura, T; Mehner, A; Mérand, A; Millour, F; Moffat, A F J; Ohnaka, K; Patru, F; Petrov, R G; Rengaswamy, S; Richardson, N D; Rivinius, T; Schöller, M; Teodoro, M; Wittkowski, M

    2016-01-01

    Context. The mass loss from massive stars is not understood well. Eta Car is a unique object for studying the massive stellar wind during the LBV phase. It is also an eccentric binary with a period of 5.54 yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. Methods. Observations of Eta Car were carried out with the ESO VLTI and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision. Results. We present velocity-resolved aperture-synthesis images reconstructed in more than 100 different spectral channels distributed across the Br Gamma 2.166 micrometer emission line. The intensity distribution of the images strongly depends on wavelength....

  11. 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 ...

  12. 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.

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

    Science.gov (United States)

    Klochkov, D.; Suleimanov, V.; Sasaki, M.; Santangelo, A.

    2016-08-01

    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 neutron stars in Cas A and in HESS J1731-347, for which carbon atmosphere models were used to reconcile their emission with the known or estimated distances.

  14. The Star-Forming Main Sequence as a Natural Consequence of the Central Limit Theorem

    Science.gov (United States)

    Kelson, Daniel David

    2015-08-01

    Star-formation rates (SFR) of disk galaxies correlate with stellar mass, with a small dispersion in SSFR at fixed mass, sigma~0.3 dex. With such scatter this star-formation main sequence (SFMS) has been interpreted as deterministic and fundamental. Here I demonstrate that such a correlation arises naturally from the central limit theorem. The 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. The SFRs of real galaxies, however, do not experience wholly random stochastic changes over time, but change in a highly correlated fashion due to the long reach of gravity and the correlation of structure in the universe. We therefore generalize the results for star-formation as a stochastic process that has random correlations over random and potentially infinite timescales. For unbiased samples of (disk) galaxies we derive expectation values for SSFR and its scatter, such that =2/T, and Sig[SFR/M]=. Note that this relative scatter is independent of mass and time. This derived correlation between SFR and stellar mass, and its evolution, matches published data to z=10 with sufficient accuracy to constrain cosmological parameters from the data. This statistical approach to the diversity of star-formation histories reproduces several important observables, including: the scatter in SSFR at fixed mass; the forms of SFHs of nearby dwarf galaxies and the Milky Way. At least one additional process beyond a single one responsible for in situ stellar mass growth will be required to match the evolution of the stellar mass function, and we discuss ways to generalize the framework. The implied dispersion in SFHs, and the SFMS's insensitivity to timescales of stochasticity, thus substantially limits the ability to connect massive galaxies to their progenitors over long cosmic baselines. Such analytical work shows promise for statisically

  15. First Investigation of the Combined Impact of Ionizing Radiation and Momentum Winds from a Massive Star on a Self-Gravitating Core

    CERN Document Server

    Ngoumou, Judith; Dale, James E; Burkert, Andreas

    2014-01-01

    Massive stars shape the surrounding 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 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 formati...

  16. 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

  17. 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...

  18. 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.

  19. 76 FR 41788 - Southern Star Central Gas Pipeline, Inc.; Notice of Intent To Prepare an Environmental Assessment...

    Science.gov (United States)

    2011-07-15

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Intent To Prepare an Environmental Assessment for the Proposed Alden Gas Storage Field Expansion Project and Request for Comments on Environmental Issues The staff...

  20. 77 FR 43586 - Southern Star Central Gas Pipeline, Inc.; Notice of Intent To Prepare an Environmental Assessment...

    Science.gov (United States)

    2012-07-25

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Southern Star Central Gas Pipeline, Inc.; Notice of Intent To Prepare an Environmental Assessment for the Proposed Line V Pipeline Retirement Project and Request for Comments On Environmental Issues The staff of...

  1. 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,...

  2. 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.

  3. 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...

  4. 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...

  5. 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...

  6. 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

  7. 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.

  8. 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

  9. 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...

  10. 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.

  11. 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;

    For any energy system relying on wind power, accurate forecasts of wind fluctuations are essential for efficient utilisation in the power grid. Statistical wind power prediction tools [1] use numerical weather prediction (NWP) model data along with measurements and can correct magnitude errors...... the two time series. Results on limited-area NWP model performance, with focus on the 12th to 48th forecast hour horizon relevant for Elspot auction bidding on the Nord Pool Spot market [2], are presented....

  12. 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.

  13. 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...

  14. 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...

  15. 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;

    2014-01-01

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

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

    Science.gov (United States)

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

    2015-01-01

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

  17. 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.

  18. Star formation in the central 0.5 pc of the Milky Way

    CERN Document Server

    Paumard, Thibaut

    2008-01-01

    The supermassive black hole candidate at the Galactic Center is surrounded by a parsec-scale star cluster, which contains a number of early type stars. The presence of such stars has been called a "paradox of youth" as star formation in the immediate vicinity of a supermassive black hole seemed difficult, as well as the transport of stars from far out in a massive-star lifetime. I will recall 30 years of technological developments which led to the current understanding of the nuclear cluster stellar population. The number of early type stars known at present is sufficient to access the 3D structure of this population and its dynamics, which in turn allows discriminating between the various possible origins proposed along the years.

  19. Evidence of suppression of star formation by quasar-driven winds in gas-rich host galaxies at z < 1?

    Science.gov (United States)

    Wylezalek, Dominika; Zakamska, Nadia L.

    2016-10-01

    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 0.1 < z < 1. We measure the kinematics of the AGN-ionized gas, the host galaxies' stellar masses and star formation rates (SFRs) and investigate the relationships between AGN luminosities, specific star formation rates (sSFRs) and outflow strengths W90 - the 90 per cent velocity width of the [O III]λ5007Å 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 and sSFR in the AGN hosts with the highest SFRs, i.e. with the highest gas content, where presumably the coupling of the AGN-driven wind to the gas is strongest. This implies that AGN with strong outflow signatures are hosted in galaxies that are more `quenched' than galaxies with weaker outflow signatures. Despite the galaxies' high SFRs, we demonstrate that the outflows are not star formation driven but indeed due to AGN powering. This observation is consistent with the AGN having a net suppression, `negative' impact, through feedback on the galaxies' star formation history.

  20. 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.)

  1. 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...

  2. 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...

  3. Direct Numerical Simulation of Radiation Pressure-Driven Turbulence and Winds in Star Clusters and Galactic Disks

    CERN Document Server

    Krumholz, Mark R

    2012-01-01

    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 numerical experiments performed with the radiation-hydrodynamics 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 Rayl...

  4. Zonda downslope winds in the central Andes of South America in a 20-year climate simulation with the Eta model

    Science.gov (United States)

    Antico, Pablo L.; Chou, Sin Chan; Mourão, Caroline

    2015-12-01

    The Zonda wind is a local version of the alpine foehn in the central Andes Mountains in South America. It blows on the eastern slopes and produces an extremely warm and dry condition in Argentina. In this study, the occurrence of Zonda wind events during a 20-year simulation from the regional Eta model is analyzed and results are compared to previous studies of Zonda wind events based on weather observations. We define a set of parameters to account for the zonal pressure gradient across the mountain, vertical movement, and air humidity typical of Zonda wind events. These parameters are applied to characterize Zonda wind events in model run and to classify them as surface-level or high-level episodes. The resulting annual distribution of Zonda occurrences based on composite analyses shows a preference for winter and spring with rare occurrences during summer. For the surface-level Zonda wind events, the highest frequency occurs during spring. Whereas surface-level Zonda wind episodes more commonly initiate in the afternoon, high-level Zonda wind events show no preference for a given initiation time. Our results are mostly in agreement with previous observational results.

  5. 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.

  6. 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...

  7. 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 ...

  8. 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...

  9. Breaking news from the HST: The central star of the Stingray Nebula is now returning towards the AGB

    CERN Document Server

    Reindl, N; Bertolami, M M Miller; Todt, H; Werner, K

    2016-01-01

    SAO244567 is a rare example of a star that allows us to witness stellar evolution in real time. Between 1971 and 1990 it changed from a B-type star into the hot central star of the Stingray Nebula. This observed rapid heating has been a mystery for decades, since it is in strong contradiction with the low mass of the star and canonical post-asymptotic giant branch (AGB) evolution. We speculated that SAO244567 might have suffered from a late thermal pulse (LTP) and obtained new observations with HST/COS to follow the evolution of the surface properties of SAO244567 and to verify the LTP hypothesis. Our non-LTE spectral analysis reveals that the star cooled significantly since 2002 and that its envelope is now expanding. Therefore, we conclude that SAO244567 is currently on its way back towards the AGB, which strongly supports the LTP hypothesis. A comparison with state-of-the-art LTP evolutionary calculations shows that these models cannot fully reproduce the evolution of all surface parameters simultaneously,...

  10. 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...

  11. Evolution of solitary density waves in stellar winds of early-type stars: A simple explanation of discrete absorption component behavior

    Science.gov (United States)

    Waldron, Wayne L.; Klein, Larry; Altner, Bruce

    1994-01-01

    We model the evolution of a density shell propagating through the stellar wind of an early-type star, in order to investigate the effects of such shells on UV P Cygni line profiles. Unlike previous treatments, we solve the mass, momentum, and energy conservation equations, using an explicit time-differencing scheme, and present a parametric study of the density, velocity, and temperature response. Under the assumed conditions, relatively large spatial scale, large-amplitude density shells propagate as stable waves through the supersonic portion of the wind. Their dynamical behavior appears to mimic propagating 'solitary waves,' and they are found to accelerate at the same rate as the underlying steady state stellar wind (i.e., the shell rides the wind). These hydrodynamically stable structures quantitatively reproduce the anomalous 'discrete absorption component' (DAC) behavior observed in the winds of luminous early-type stars, as illustrated by comparisons of model predictions to an extensive International Ultraviolet Explorer (IUE) time series of spectra of zeta Puppis (O4f). From these comparisons, we find no conclusive evidence indicative of DACs accelerating at a significantly slower rate than the underlying stellar wind, contrary to earlier reports. In addition, these density shells are found to be consistent within the constraints set by the IR observations. We conclude that the concept of propagating density shells should be seriously reconsidered as a possible explanation of the DAC phenomenon in early-type stars.

  12. 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...

  13. 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...

  14. 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...

  15. Cometary shaped sources at the Galactic Center - Evidence for a wind from the central 0.2 pc

    CERN Document Server

    Muzic, K; Schoedel, R; Buchholz, R; Zamaninasab, M

    2010-01-01

    In 2007 we reported two cometary shaped sources in the vicinity of Sgr A* (0.8" and 3.4" projected distance), named X7 and X3. The symmetry axes of the two sources are aligned to within 5 degrees in the plane of the sky and the tips of their bow-shocks point towards Sgr A*. Our measurements show that the proper motion vectors of both features are pointing in directions more than 45 deg away from the line that connects them with Sgr A*. This misalignment of the bow-shock symmetry axes and their proper motion vectors, combined with the high proper motion velocities of several 100 km/s, suggest that the bow-shocks must be produced by an interaction with some external fast wind, possibly coming from Sgr A*, or stars in its vicinity. We have developed a bow-shock model to fit the observed morphology and constrain the source of the external wind. The result of our modeling allows us to estimate the velocity of the external wind, making sure that all likely stellar types of the bow-shock stars are considered. We sho...

  16. Neutrino signatures and the neutrino-driven wind in Binary Neutron Star Mergers

    CERN Document Server

    Dessart, Luc; Burrows, Adam; Rosswog, Stefan; Livne, Eli

    2008-01-01

    We present VULCAN/2D multi-group flux-limited-diffusion radiation hydrodynamics simulations of binary neutron star (BNS) mergers, using the Shen equation of state, covering ~100 ms, and starting from azimuthal-averaged 2D slices obtained from 3D SPH simulations of Rosswog & Price for 1.4 Msun (baryonic) neutron stars with no initial spins, co-rotating spins, and counter-rotating spins. Snapshots are post-processed at 10 ms intervals with a multi-angle neutrino-transport solver. We find polar-enhanced neutrino luminosities, dominated by $\\bar{\

  17. 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

  18. 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} ...

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

    NARCIS (Netherlands)

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

    2011-01-01

    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 lo

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

    NARCIS (Netherlands)

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

    2011-01-01

    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 lo

  1. 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.

  2. 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

  3. 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...

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

    NARCIS (Netherlands)

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

    2010-01-01

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

  5. 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...

  6. 3D models of radiatively driven colliding winds in massive O+O star binaries - III. Thermal X-ray emission

    CERN Document Server

    Pittard, J M

    2009-01-01

    The X-ray emission from the wind-wind collision in short-period massive O+O-star binaries is investigated. The emission is calculated from three-dimensional hydrodynamical models which incorporate gravity, the driving of the winds, orbital motion of the stars, and radiative cooling of the shocked plasma. Changes in the amount of stellar occultation and circumstellar attenuation introduce phase-dependent X-ray variability in systems with circular orbits, while strong variations in the intrinsic emission also occur in systems with eccentric orbits. The X-ray emission in eccentric systems can display strong hysteresis, with the emission softer after periastron than at corresponding orbital phases prior to periastron, reflecting the physical state of the shocked plasma at these times. Furthermore, the rise of the luminosity to maximum does not necessarily follow a 1/D law. Our models further demonstrate that the effective circumstellar column can be highly energy dependent. We simulate Chandra and Suzaku observat...

  7. 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...

  8. 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

    2016-09-01

    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 (CSWs) 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.

  9. 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...

  10. 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...

  11. 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.

  12. 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...

  13. Boundary layer evolution over the central Himalayas from radio wind profiler and model simulations

    Science.gov (United States)

    Singh, Narendra; Solanki, Raman; Ojha, Narendra; Janssen, Ruud H. H.; Pozzer, Andrea; Dhaka, Surendra K.

    2016-08-01

    We investigate the time evolution of the Local Boundary Layer (LBL) for the first time over a mountain ridge at Nainital (79.5° E, 29.4° N, 1958 m a.m.s.l.) in the central Himalayan region, using a radar wind profiler (RWP) during November 2011 to March 2012, as a part of the Ganges Valley Aerosol Experiment (GVAX). We restrict our analysis to clear-sunny days, resulting in a total of 78 days of observations. The standard criterion of the peak in the signal-to-noise ratio (S / N) profile was found to be inadequate in the characterization of mixed layer (ML) top at this site. Therefore, we implemented a criterion of S / N > 6 dB for the characterization of the ML and the resulting estimations are shown to be in agreement with radiosonde measurements over this site. The daytime average (05:00-10:00 UTC) observed boundary layer height ranges from 440 ± 197 m in November (late autumn) to 766 ± 317 m above ground level (a.g.l.) in March (early spring). The observations revealed a pronounced impact of mountain topography on the LBL dynamics during March, when strong winds (> 5.6 m s-1) lead to LBL heights of 650 m during nighttime. The measurements are further utilized to evaluate simulations from the Weather Research and Forecasting (WRF) model. WRF simulations captured the day-to-day variations up to an extent (r2 = 0.5), as well as the mean diurnal variations (within 1σ variability). The mean biases in the daytime average LBL height vary from -7 % (January) to +30 % (February) between model and observations, except during March (+76 %). Sensitivity simulations using a mixed layer model (MXL/MESSy) indicated that the springtime overestimation of LBL would lead to a minor uncertainty in simulated surface ozone concentrations. However, it would lead to a significant overestimation of the dilution of black carbon aerosols at this site. Our work fills a gap in observations of local boundary layer over this complex terrain in the Himalayas, and highlights the need for

  14. 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.

  15. 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

  16. 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

  17. 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...

  18. 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...

  19. 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.

  20. 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.

  1. 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

  2. Massive Stars

    Science.gov (United States)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  3. 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...

  4. 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 ...

  5. 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...

  6. 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.

  7. 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...

  8. 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...

  9. Femtolens imaging of a quasar central engine using a dwarf star telescope

    CERN Document Server

    Gould, A; Gould, Andrew; Gaudi, B Scott

    1996-01-01

    We show that it is possible to image the structure of a distant quasar on scales of \\sim 1\\,AU by constructing a telescope which uses a nearby dwarf star as its ``primary lens'' together with a satellite-borne ``secondary''. The image produced by the primary is magnified by \\sim 10^5 in one direction but is contracted by 0.5 in the other, and therefore contains highly degenerate one-dimensional information about the two-dimensional source. We discuss various methods for extracting information about the second dimension including ``femtolens interferometry'' where one measures the interference between different parts of the one-dimensional image with each other. Assuming that the satellite could be dispatched to a position along a star-quasar line of sight at a distance r from the Sun, the nearest available dwarf-star primary is likely to be at \\sim 15\\,\\pc\\,(r/40\\,\\rm AU)^{-2}. The secondary should consist of a one-dimensional array of mirrors extending \\sim 700\\,m to achieve 1 AU resolution, or \\sim 100\\,m t...

  10. 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...

  11. Fractional Slot Concentrated Windings: A New Method to Manage the Mutual Inductance between Phases in Three-Phase Electrical Machines and Multi-Star Electrical Machines

    Directory of Open Access Journals (Sweden)

    Olivier Barre

    2015-06-01

    Full Text Available Mutual inductance is a phenomenon caused by the circulation of the magnetic flux in the core of an electrical machine. It is the result of the effect of the current flowing in one phase on the other phases. In conventional three-phase machines, such an effect has no influence on the electrical behaviour of the device. Although these machines are powered by power inverters, no problem should occur. The result is not the same for multi-star machines. If these machines are using a conventional winding structure, namely distributed windings, and are powered by voltage source converters, current ripples appear in the power supply lines. These current ripples are related to magnetic couplings between the stars. Designers should check these current ripples in order to stay within the limits imposed by the specifications. These electric current disturbances also provide torque ripples. With concentrated windings, a new degree of freedom appears; the configuration—number of slots/number of poles—can have a positive impact. The circulation of the magnetic flux is the initial phenomenon that produces the mutual inductance. The main goal of this discussion is to describe a design method that is able to produce not only a machine with low mutual inductance between phases, but also a multi-star machine where the stars and the phases are magnetically decoupled or less coupled. This discussion only takes into account the machines that use permanent magnets mounted on the rotor surface. This article is part of a study aimed at designing a high efficiency generator using fractional-slot concentrated-windings (FSCW.

  12. 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 ...

  13. Assessment of centralized grid connected wind power cost in coastal area of Pakistan

    Energy Technology Data Exchange (ETDEWEB)

    Harijan, Khanji; Memon, Mujeebuddin [Department of Mechanical Engineering, Mehran University of Engineering and Technology, Jamshoro 76062 (Pakistan); Uqaili, Mohammad A. [Department of Electrical Engineering, Mehran University of Engineering and Technology, Jamshoro 76062 (Pakistan); Mirza, Umar K. [Pakistan Institute of Engineering and Applied Sciences, P.O. Nilore, Islamabad 45650 (Pakistan)

    2009-02-15

    This work presents an assessment of per unit cost of electricity generated from 15 MW wind farm at 40 locations in the coastal areas of Pakistan using the method of net present value analysis. The Nordex N43/600 wind turbine has been selected and used as reference wind turbine. Wind duration curves were developed and utilized to calculate per unit cost of electricity generated from chosen wind turbine. In Sindh province, the minimum cost of electricity generated was found to be 4.2 cents /kWh at Jamshoro, while the corresponding maximum was 7.4 cents /kWh at Kadhan site. In Balochistan, the minimum cost of electricity generated was found to be 6.3 cents /kWh at Aghore, while the corresponding maximum was 21.0 cents /kWh at Mand site. The study concludes that at most of the locations especially in Sindh province, wind power is competitive to conventional grid connected thermal power even without considering the externalities. (author)

  14. 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...

  15. 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 ...

  16. 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 ...

  17. 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...

  18. 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...

  19. 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...

  20. 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

  1. 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.

  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. Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit

    CERN Document Server

    Graefener, G

    2008-01-01

    The mass loss from Wolf-Rayet (WR) stars is of fundamental importance for the final fate of massive stars and their chemical yields. Its Z-dependence is discussed in relation to the formation of long-duration Gamma Ray Bursts (GRBs) and the yields from early stellar generations. However, the mechanism of formation of WR-type stellar winds is still under debate. We present the first fully self-consistent atmosphere/wind models for late-type WN stars. We investigate the mechanisms leading to their strong mass loss, and examine the dependence on stellar parameters, in particular on the metallicity Z. We identify WNL stars as very massive stars close to the Eddington limit, potentially still in the phase of central H-burning. Due to their high L/M ratios, these stars develop optically thick, radiatively driven winds. These winds show qualitatively different properties than the thin winds of OB stars. The resultant mass loss depends strongly on Z, but also on the Eddington factor, and the stellar temperature. We c...

  4. 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.

  5. 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.

  6. NGC 6826: A UNIFIED STUDY OF THE PLANETARY NEBULA AND ITS CENTRAL STARS

    Directory of Open Access Journals (Sweden)

    C. R. Fierro

    2011-01-01

    Full Text Available Presentamos una metodología de trabajo para obtener un modelo estelar-nebular autoconsistente. Determinamos la distancia usando las trazas evolutivas teóricas de estrellas centrales de nebulosas planetarias. Se aplicó esta metodología a la nebulosa planetaria galáctica NGC 6826. El modelo unificado requiere más trabajo pero disminuye las incertidumbres debido al mayor número de restricciones observacionales.

  7. 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.

  8. V838 Monocerotis: the central star and its environment a decade after outburst

    CERN Document Server

    Chesneau, Olivier; De Marco, Orsola; Bright, S N; Spang, Alain; Banerjee, D P K; Ashok, N M; Kaminski, T; Wisniewski, John P; Meilland, Anthony; Lagadec, Eric

    2014-01-01

    Aims. V838 Monocerotis erupted in 2002, brightened in a series of outbursts, and eventually developed a spectacular light echo. A very red star emerged a few months after the outburst. The whole event has been interpreted as the result of a merger. Methods. We obtained near-IR and mid-IR interferometric observations of V838 Mon with the AMBER and MIDI recombiners located at the Very Large Telescope Interferometer (VLTI) array. The MIDI two-beam observations were obtained with the 8m Unit Telescopes between October 2011 and February 2012. The AMBER three-beam observations were obtained with the compact array (B≤35m) in April 2013 and the long array (B≤140m) in May 2014, using the 1.8m Auxiliary Telescopes. Results. A significant new result is the detection of a compact structure around V838 Mon, as seen from MIDI data. The extension of the structure increases from a FWHM of 25 mas at 8 {\\mu}m to 70 mas at 13 {\\mu}m. At the adopted distance of D = 6.1 $\\pm$ 0.6 kpc, the dust is distributed from about ...

  9. 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.

  10. Effect of a magnetic field on massive-star winds - I. Mass-loss and velocity for a dipole field

    Science.gov (United States)

    Bard, Christopher; Townsend, Richard H. D.

    2016-11-01

    We generalize the Rigid-Field Hydrodynamic equations to accommodate arbitrary magnetic field topologies, resulting in a new Arbitrary Rigid-Field Hydrodynamic (ARFHD) formalism. We undertake a critical point calculation of the steady-state ARFHD equations with a CAK-type radiative acceleration and determine the effects of a dipole magnetic field on the usual CAK mass-loss rate and velocity structure. Enforcing the proper optically thin limit for the radiative line-acceleration is found to decrease both the mass-loss and wind acceleration, while rotation boosts both properties. We define optically thin correction and rotation parameters to quantify these effects on the global mass-loss rate and develop scaling laws for the surface mass-flux as a function of surface colatitude. These scaling laws are found to agree with previous laws derived from magnetohydrodynamic simulations of magnetospheres. The dipole magnetosphere velocity structure is found to differ from a global beta-velocity law, which contradicts a central assumption of the previously developed XADM model of X-ray emission from magnetospheres.

  11. 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.

  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. 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

  14. 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

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

    Science.gov (United States)

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

    2011-05-01

    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 ± 10 km s-1 and a close binary central star. The light curve observed with the Mercator Telescope reveals an orbital period of 0.535 d 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 PNe (CSPN) and jets. The Isaac Newton Telescope/Intermediate Dispersion Spectrograph and Very Large Telescope (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 that 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 combination of bipolar outflows and a spherical nebula conspires to produce an X-shaped appearance. The kinematic age of the jets (1750 ± 250 yr kpc-1) is found to be more than that of the inner nebula (900 ± 100 yr kpc-1), consistent with previous studies of similar PNe. Emission-line ratios of the jets are found to be consistent with that of reverse-shock models for fast low-ionization emitting regions (FLIERs) in PNe. Further large-scale surveys for close binary CSPN will be required to securely establish whether FLIERs are launched by close binaries. Based on observations made with the Flemish Mercator Telescope and Isaac Newton Telescope of the Observatorio del Roque de Los Muchachos and the VLT at the Paranal Observatory under programs 083.D-0654(A) and 085.D-0629(A).

  16. 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.

  17. 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 ...

  18. 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

  19. 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...

  20. Tests of the Galactic planetary nebula distance scale with the initial Gaia parallax distances of their central stars

    CERN Document Server

    Stanghellini, Letizia; Lattanzi, Mario G; Morbidelli, Roberto

    2016-01-01

    We used the "primary dataset" of Gaia Data Release 1 (DR1) to search for parallax measurements of central stars (CSs) of Galactic planetary nebulae (PNe), to determine PN distances. We found that a trigonometric parallax is available for 16 CSs, seven of which with relative uncertainty below 80%. The limited comparison of these trigonometric distances to other reliable individual determinations discloses good correlation between the two sets, with the Gaia parallax distances being lower by a factor of ~0.1 dex in the logarithmic distances. We tested with the Gaia parallaxes the most popular Galactic PN distance scales, namely, the physical radius vs. surface brightness, and the ionized mass vs. inverse optical thickness scales. While the number of available calibrators may still be too low, and their relative uncertainties too high, to derive a working distance scale, we were able to assess the current sample and to reveal the very promising potential of the future Gaia releases for a recalibration of the dis...

  1. 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.

  2. 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...

  3. 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...

  4. Late Pleistocene paleoclimatology of the central equatorial Pacific: Sea surface response to the southeast Trade Winds

    Science.gov (United States)

    Pisias, Nicklas G.; Rea, David K.

    1988-02-01

    Proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data, and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late Pleistocene: All indicators fluctuate at higher frequencies than the 100,000-year glacial-interglacial cycle, display reduced amplitude variations since 300,000 years ago, exhibit a change in the record character at about 300,000 years ago (the mid-Brunhes climatic event), and have higher amplitude variations in sediments 300,000-850,000 years old. Time series analyses were conducted to determine the spectral character of each record (δ18O of planktonic foraminifer, sea surface temperature values, equatorial divergence indicators, and wind intensity indicators) and to quantify interrecord coherence and phase relationships. The record was divided at the 300,000-year clear change in climatic variability (nonstationarity). The δ18O-based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402,000-774,000 years. The δ18O spectra show 100,000- and 41,000-year power in the younger portion, 0-300,000 years, and 100,000-, 41,000- and 23,000-year power in the older interval, all highly coherent and in phase with the SPECMAP average stacked isotope record. Unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31,000 years. This period is also important in the sea surface temperature signal where the dominant spectral peak is 100,000 years. The 31,000-year spectral component is coherent and in phase between the eolian and divergence records, confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record. Since the 31,000-year power appears in independent data sets within this core and also appears in other equatorial records [J. Imbrie personal communication, 1987], we assume it to be real and

  5. Discovery of Eclipsing Binary Central Stars in the Planetary Nebulae M 3-16, H 2-29 and M 2-19

    CERN Document Server

    Miszalski, B; Moffat, A F J; Parker, Q A; Udalski, A

    2008-01-01

    Progress in understanding the formation and evolution of planetary nebulae (PN) has been restricted by a paucity of well-determined central star masses. To address this deficiency we aim to (i) significantly increase the number of known eclipsing binary central stars of PN (CSPN), and subsequently (ii) directly obtain their masses and absolute dimensions by combining their light-curve parameters with planned radial velocity data. Using photometric data from the third phase of the Optical Gravitational Lensing Experiment (OGLE) we have searched for periodic variability in a large sample of PN towards the Galactic Bulge using Fourier and phase-dispersion minimisation techniques. Among some dozen periodically variable CSPN found, we report here on three new eclipsing binaries: M 3-16, H 2-29 and M 2-19. We present images, confirmatory spectroscopy and light-curves of the systems.

  6. 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.

  7. 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.

  8. 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.

  9. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-03-20

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

  11. THE GALACTIC CENTER S-STARS AND THE HYPERVELOCITY STARS IN THE GALACTIC HALO: TWO FACES OF THE TIDAL BREAKUP OF STELLAR BINARIES BY THE CENTRAL MASSIVE BLACK HOLE?

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Fupeng; Lu Youjun [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Yu Qingjuan [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)

    2013-05-10

    In this paper, we investigate the link between the hypervelocity stars (HVSs) discovered in the Galactic halo and the Galactic center (GC) S-stars, under the hypothesis that they are both the products of the tidal breakup of the same population of stellar binaries by the central massive black hole (MBH). By adopting several hypothetical models for binaries to be injected into the vicinity of the MBH and doing numerical simulations, we realize the tidal breakup processes of the binaries and their follow-up dynamical evolution. We find that many statistical properties of the detected HVSs and GC S-stars could be reproduced under some binary injecting models, and their number ratio can be reproduced if the stellar initial mass function is top-heavy (e.g., with slope {approx} - 1.6). The total number of the captured companions is {approx}50 that have masses in the range {approx}3-7 M{sub Sun} and semimajor axes {approx}< 4000 AU and survive to the present within their main-sequence lifetime. The innermost one is expected to have a semimajor axis {approx}300-1500 AU and a pericenter distance {approx}10-200 AU, with a significant probability of being closer to the MBH than S2. Future detection of such a close star would offer an important test to general relativity. The majority of the surviving ejected companions of the GC S-stars are expected to be located at Galactocentric distances {approx}< 20 kpc, and have heliocentric radial velocities {approx} - 500-1500 km s{sup -1} and proper motions up to {approx}5-20 mas yr{sup -1}. Future detection of these HVSs may provide evidence for the tidal breakup formation mechanism of the GC S-stars.

  12. 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

  13. 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...

  14. 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...

  15. X-RAY SPECTRAL RESIDUALS IN NGC 5408 X-1: DIFFUSE EMISSION FROM STAR FORMATION, OR THE SIGNATURE OF A SUPER-EDDINGTON WIND?

    Energy Technology Data Exchange (ETDEWEB)

    Sutton, Andrew D [Astrophysics Office, NASA Marshall Space Flight Center, ZP12, Huntsville, Al 35812 (United States); Roberts, Timothy P. [Centre for Extragalactic Astronomy, Department of Physics, University of Durham, South Road, Durham, DH1 3LE (United Kingdom); Middleton, Matthew J, E-mail: andrew.d.sutton@nasa.gov [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom)

    2015-11-20

    If ultraluminous X-ray sources (ULXs) are powered by accretion onto stellar remnant black holes, then many must be accreting at super-Eddington rates. It is predicted that such high accretion rates should give rise to massive, radiatively driven winds. However, observational evidence of a wind, in the form of absorption or emission features, has remained elusive. As such, the reported detection of X-ray spectral residuals in XMM-Newton spectra of NGC 5408 X-1, which could be related to absorption in a wind is potentially very exciting. However, it has previously been assumed by several authors that these features simply originate from background diffuse plasma emission related to star formation in the ULX’s host galaxy. In this work we utilize the spatial resolving power of Chandra to test whether we can rule out this latter interpretation. We demonstrate that the majority of the luminosity in these spectral features is emitted from a highly localized region close to the ULX, and appears point-like even with Chandra. It is therefore highly likely that the spectral features are associated with the ULX itself, and little of the flux in this spectral component originates from spatially extended emission in the host galaxy. This may be consistent with the suggestion of absorption in an optically thin phase of a super-Eddington wind. Alternatively, we could be seeing emission from collisionally ionized material close to the black hole, but critically this would be difficult to reconcile with models where the source inclination largely determines the observed X-ray spectral and timing properties.

  16. 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...

  17. 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...

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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...

  3. Metallicity effects on the modified wind momentum of CSPN

    CERN Document Server

    Maciel, W J; Costa, R D D

    2008-01-01

    Recent investigations on the central stars of planetary nebulae (CSPN) indicate that the masses based on model atmospheres can be much larger than the masses derived from theoretical mass-luminosity relations. Also, the dispersion in the relation between the modified wind momentum and the luminosity depends on the mass spread of the CSPN, and is larger than observed in massive hot stars. Since the wind characteristics probably depend on the metallicity, we analyze the effects on the modified wind momentum by considering the dispersion in this quantity caused by the stellar metallicity. Our CSPN masses are based on a relation between the core mass and the nebular abundances. We conclude that these masses agree with the known mass distribution both for CSPN and white dwarfs, and that the spread in the modified wind momentum can be explained by the observed metallicity variations.

  4. 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

    Energy Technology Data Exchange (ETDEWEB)

    Lanzoni, B.; Mucciarelli, A.; Ferraro, F. R.; Miocchi, P.; Dalessandro, E.; Pallanca, C.; Massari, D. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Origlia, L.; Bellazzini, M. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Valenti, E., E-mail: barbara.lanzoni3@unibo.it [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München (Germany)

    2013-06-01

    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{sup –1}, a flat behavior out to ∼60'' and a decreasing trend outward. 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 M {sub ☉}. These findings are at odds with recent results obtained from integrated light spectra, showing a velocity dispersion profile with a steep central cusp of 23-25 km s{sup –1} at r < 2'' and suggesting the presence of a black hole with a mass of ∼1.7 × 10{sup 4} M {sub ☉}. We also found some evidence of systemic rotation with amplitude A {sub rot} ∼ 8 km s{sup –1} in the innermost 2'' (0.13 pc), decreasing to A {sub rot} = 3.2 km s{sup –1} at 18'' < r < 160''.

  5. 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...

  6. 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.

    . 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...

  7. 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...

  8. Iron abundance in hot hydrogen-deficient central stars and white dwarfs from FUSE, HST, and IUE spectroscopy

    CERN Document Server

    Miksa, S; Dreizler, S; Kruk, J W; Rauch, T; Werner, K

    2002-01-01

    We present a first systematic investigation of the iron abundance in very hot (Teff>50,000K) hydrogen-deficient post-AGB stars. Our sample comprises 16 PG1159 stars and four DO white dwarfs. We use recent FUSE observations as well as HST and IUE archival data to perform spectral analyses with line blanketed NLTE model atmospheres. Iron is not detected in any PG1159 star. In most cases this is compatible with a solar iron abundance due to limited quality of HST and IUE data, although the tendency to an iron underabundance may be recognized. However, the absence of iron lines in excellent FUSE spectra suggests an underabundance by at least 1 dex in two objects (K1-16 NGC 7094). A similar result has been reported recently in the [WC]-PG1159 transition object Abell 78 (Werner et al. 2002). We discuss dust fractionation and s-process neutron-captures as possible origins. We also announce the first identification of sulfur in PG1159 stars.

  9. X-ray emission from the double neutron star binary B1534+12: Powered by the pulsar wind?

    CERN Document Server

    Kargaltsev, O; Garmire, G P

    2006-01-01

    We report the detection of the double neutron star binary (DNSB) B1534+12 (= J1537+1155) with the Chandra X-ray Observatory. This DNSB (orbital period 10.1 hr) consists of the millisecond (recycled) pulsar J1537+1155A (P_A=37.9 ms) and a neutron star not detected in the radio. After the remarkable double pulsar binary J0737-3039, it is the only other DNSB detected in X-rays. We measured the flux of (2.2\\pm 0.6)\\times10^{-15} ergs s^{-1} cm^{-2} in the 0.3-6 keV band. The small number of collected counts allows only crude estimates of spectral parameters. The power-law fit yields the photon index of 3.2\\pm 0.5 and the unabsorbed 0.2-10 keV luminosity L_X=6\\times10^{29} ergs s^{-1} = 3\\times 10^{-4}Edot_A, where Edot_A is the spin-down power of J1537+1155A. Alternatively, the spectrum can be fitted by a blackbody model with T = 2.2 MK and the projected emitting area of ~ 5\\times 10^3 m^2. The distribution of photon arrival times over binary orbital phase shows a deficit of X-ray emission around apastron, which ...

  10. The Chandra Planetary Nebulae Survey (ChanPlaNS): III. X-ray Emission from the Central Stars of Planetary Nebulae

    CERN Document Server

    Montez, R; Balick, B; Behar, E; Blackman, E; Bujarrabal, V; Chu, Y -H; Corradi, R L M; De Marco, O; Frank, A; Freeman, M; Frew, D J; Guerrero, M A; Jones, D; Lopez, J A; Miszalski, B; Nordhaus, J; Parker, Q A; Sahai, R; Sandin, C; Schonberner, D; Soker, N; Sokoloski, J L; Steffen, M; Toalá, J A; Ueta, T; Villaver, E; Zijlstra, A

    2014-01-01

    We present X-ray spectral analysis of 20 point-like X-ray sources detected in Chandra Planetary Nebula Survey (ChanPlaNS) observations of 59 planetary nebulae (PNe) in the solar neighborhood. Most of these 20 detections are associated with luminous central stars within relatively young, compact nebulae. The vast majority of these point-like X-ray-emitting sources at PN cores display relatively "hard" ($\\geq0.5$~keV) X-ray emission components that are unlikely to be due to photospheric emission from the hot central stars (CSPN). Instead, we demonstrate that these sources are well modeled by optically-thin thermal plasmas. From the plasma properties, we identify two classes of CSPN X-ray emission: (1) high-temperature plasmas with X-ray luminosities, $L_{\\rm X}$, that appear uncorrelated with the CSPN bolometric luminosity, $L_{\\rm bol}$; and (2) lower-temperature plasmas with $L_{\\rm X}/L_{\\rm bol}\\sim10^{-7}$. We suggest these two classes correspond to the physical processes of magnetically active binary comp...

  11. 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.

  12. 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...

  13. 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 ...

  14. 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...

  15. 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 ...

  16. 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

  17. 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 ...

  18. 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...

  19. 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...

  20. 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

  1. MASSIVE INFANT STARS ROCK THEIR CRADLE

    Science.gov (United States)

    2002-01-01

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

  2. Modeling the X-rays from the Central Compact Object PSR J1852+0040 in Kesteven 79: Evidence for a Strongly Magnetized Neutron Star

    CERN Document Server

    Bogdanov, Slavko

    2014-01-01

    I present modeling of the X-ray pulsations from the central compact object (CCO) PSR J1852+0040 in the Galactic supernova remnant Kesteven 79. In the context of thermal surface radiation from a rotating neutron star, a conventional polar cap model can reproduce the broad, large-amplitude X-ray pulse only with a "pencil plus fan" beam emission pattern, which is characteristic of strongly magnetized ($\\gtrsim$10^12 Gauss) neutron star atmospheres, substantially stronger than the ~10^10 Gauss external dipole field inferred from the pulsar spin-down rate. This discrepancy can be explained by an axially displaced dipole. For other beaming patterns, it is necessary to invoke high-aspect-ratio emitting regions that are greatly longitudinally elongated, possibly due to an extremely offset dipole. For all assumed emission models, the existence of strong internal magnetic fields ($\\gtrsim$10^14} Gauss) that preferentially channel internal heat to only a portion of the exterior is required to account for the implied hig...

  3. Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058

    Science.gov (United States)

    Degenaar, N.; Altamirano, D.; 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.

    2016-10-01

    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 brightness of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of LX ≃ (2-3) × 1037(D/5.8 kpc)2 erg s-1 (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 disc is viewed at an inclination of i ≃ 27°-35° and extended close to the neutron star, down to Rin ≃ 5-7.5 gravitational radii (≃11-17 km). This inner disc radius suggests that the neutron star magnetic field strength is B ≲ 2 × 108 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ≃7.64 keV with a significance of ≃4.8σ. This feature could correspond to blueshifted Fe XXVI and arise from an accretion disc wind, which would imply an outflow velocity of vout ≃ 0.086c (≃25 800 km s-1). However, this would be extreme for an X-ray binary and it is unclear if a disc wind should be visible at the low inclination angle that we infer from our reflection analysis. Finally, we discuss how the X-ray and optical properties of 1RXS J180408.9-342058 are consistent with a relatively small (Porb ≲ 3 h) binary orbit.

  4. The Stars behind the Curtain

    Science.gov (United States)

    2010-02-01

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

  5. Locating the Launching Region of T Tauri Winds: The Case of DG Tauri

    Science.gov (United States)

    Anderson, Jeffrey M.; Li, Zhi-Yun; Krasnopolsky, Ruben; Blandford, Roger D.

    2003-06-01

    It is widely believed that T Tauri winds are driven magnetocentrifugally from accretion disks close to the central stars. The exact launching conditions are uncertain. We show that a general relation exists between the poloidal and toroidal velocity components of a magnetocentrifugal wind at large distances and the rotation rate of the launching surface, independent of the uncertain launching conditions. We discuss the physical basis of this relation and verify it by using a set of numerically determined large-scale wind solutions. Both velocity components are in principle measurable from spatially resolved spectra, as has been done for the extended low-velocity component (LVC) of the DG Tauri wind by Bacciotti et al. For this particular source, we infer that the spatially resolved LVC originates from a region on the disk extending from ~0.3 to ~4.0 AU from the star, which is consistent with, and a refinement over, the rough estimate of Bacciotti et al.

  6. 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

  7. 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...

  8. 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 f...

  9. The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016

    CERN Document Server

    Federrath, C; Longmore, S N; Kruijssen, J M D; Bally, J; Contreras, Y; Crocker, R M; Garay, G; Jackson, J M; Testi, L; Walsh, A J

    2016-01-01

    Star formation is primarily controlled by the interplay between gravity, turbulence, and magnetic fields. However, the turbulence and magnetic fields in molecular clouds near the Galactic Center may differ substantially from spiral-arm clouds. Here we determine the physical parameters of the central molecular zone (CMZ) cloud G0.253+0.016, its turbulence, magnetic field and filamentary structure. Using column-density maps based on dust-continuum emission observations with ALMA+Herschel, we identify filaments and show that at least one dense core is located along them. We measure the filament width W_fil=0.17$\\pm$0.08pc and the sonic scale {\\lambda}_sonic=0.15$\\pm$0.11pc of the turbulence, and find W_fil~{\\lambda}_sonic. A strong velocity gradient is seen in the HNCO intensity-weighted velocity maps obtained with ALMA+Mopra, which is likely caused by large-scale shearing of G0.253+0.016, producing a wide double-peaked velocity PDF. After subtracting the gradient to isolate the turbulent motions, we find a near...

  10. X-ray Emission from the Binary Central Stars of the Planetary Nebulae HFG 1, DS 1, and LoTr 5

    CERN Document Server

    Montez, Rodolfo; Kastner, Joel H; Chu, You-Hua

    2010-01-01

    Close binary systems undergoing mass transfer or common envelope interactions can account for the morphological properties of some planetary nebulae. The search for close binary companions in planetary nebulae is hindered by the difficulty of detecting cool, late-type, main sequence companions in binary systems with hot pre-white dwarf primaries. However, models of binary PN progenitor systems predict that mass accretion or tidal interactions can induce rapid rotation in the companion, leading to X-ray-emitting coronae. To test such models, we have searched for, and detected, X-ray emission from three binary central stars within planetary nebulae: the post-common envelope close binaries in HFG 1 and DS 1 consisting of O-type subdwarfs with late-type, main sequence companions, and the binary system in LoTr 5 consisting of O-type subdwarf and rapidly rotating, late-type giant companion. The X-ray emission in each case is best characterized by spectral models consisting of two optically-thin thermal plasma compo...

  11. 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...

  12. 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...

  13. 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...

  14. 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.

  15. 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.

  16. 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...

  17. 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...

  18. Self-Regulated Fueling of Galaxy Centers: Evidence for Star-Formation Feedback in IC342's Nucleus

    CERN Document Server

    Schinnerer, E; Meier, D S; Calzetti, D

    2008-01-01

    Using new, high-resolution interferometric observations of the CO and HCN molecules, we directly compare the molecular and ionized components of the interstellar medium in the center of the nearby spiral galaxy IC342, on spatial scales of ~ 10pc. The morphology of the tracers suggests that the molecular gas flow caused by a large-scale stellar bar has been strongly affected by the mechanical feedback from recent star formation activity within the central 100pc in the nucleus of the galaxy. Possibly, stellar winds and/or supernova shocks originating in the nuclear star cluster have compressed, and likely pushed outward, the infalling molecular gas, thus significantly reducing the gas supply to the central 10pc. Although our analysis currently lacks kinematic confirmation due to the face-on orientation of IC342, the described scenario is supported by the generally observed repetitive nature of star formation in the nuclear star clusters of late-type spiral galaxies.

  19. 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...

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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...

  6. 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)

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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;

    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 high costs, but with the new developments in floating turbine design, it seems that offshore wind parks in deep waters will also be a possibility in the future. Whether on-shore or offshore, the first step of a site assessment is to estimate the wind resources. Usually well-known conventional methods...

  12. 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...

  13. 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.

  14. 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...

  15. 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.

  16. 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.

  17. 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 this report...

  18. 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...

  19. 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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-11-10

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

  20. 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 ...

  1. 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...

  2. 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...

  3. 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

  4. 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...

  5. 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.

  6. 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.

  7. 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

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

    Directory of Open Access Journals (Sweden)

    K. Seelos

    2009-09-01

    Full Text Available A continuous reconstruction of last glacial wind directions is based on provenance analysis of eolian sediments in a sediment core from the Dehner dry Maar in the Eifel region (Germany. This Maar is suitable to archive paleo wind directions due to its location west of the Devonian carbonate basins of the Eifel-North-South-Zone. Thus, eolian sediments with high clastic carbonate content can be interpreted as an east wind signal. The detection of such east wind sediments is applied by a new module of the RADIUS grain size analyze technique. Increased frequencies of east wind occur during the time intervals corresponding with the Heinrich events H1 and H2. The unusual H3 show no higher east wind frequency but so do its former and subsequent Greenland stadials. The LGM (21–18 ka BP is characterized by a slightly elevated east wind activity. The investigated time period from 40.3–12.9 ka BP can be subclassified in three units: The first time period during Marine Isotope Stage 3 (40.3–36 ka BP is controlled by relative warm climate leading to an enriched content of organic matter in the sediment. Thus, there is only little accumulation of dust in the Eifel region and Heinrich 4 is not recorded in the archive by our dust proxy. The second time slice (36–24 ka BP has an increased content of dust accumulation and a high amount of east winds layers (up to 19% of the dust storms per century came from the east. In comparison, the subsequent period (24–12.9 ka BP is characterized by lower east winds sediments again.

  9. 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…

  10. Star Product and Star Exponential

    OpenAIRE

    Tomihisa, Toshio; Yoshioka, Akira

    2010-01-01

    Here we extend the star products by means of complex symmetric matrices. In this way we obtain a family of star products. Next we consider the star exponentials with respect to these star products, and finally we obtain several interesting identities.

  11. 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.

  12. Galaxy Evolution in Cosmological Simulations With Outflows I: Stellar Masses and Star Formation Rates

    CERN Document Server

    Davé, Romeel; Finlator, Kristian

    2011-01-01

    We examine the growth of the stellar content of galaxies from z=3-0 in cosmological hydrodynamic simulations incorporating parameterised galactic outflows. Without outflows, galaxies overproduce stellar masses (M*) and star formation rates (SFRs) compared to observations. Winds introduce a three-tier form for the galaxy stellar mass and star formation rate functions, where the middle tier depends on differential (i.e. mass-dependent) recycling of ejected wind material back into galaxies. A tight M*-SFR relation is a generic outcome of all these simulations, and its evolution is well-described as being powered by cold accretion, although current observations at z>2 suggest that star formation in small early galaxies must be highly suppressed. Roughly one-third of z=0 galaxies at masses below M^* are satellites, and star formation in satellites is not much burstier than in centrals. All models fail to suppress star formation and stellar mass growth in massive galaxies at z<2, indicating the need for an exter...

  13. 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?

  14. 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...

  15. Mass fluxes for hot stars

    CERN Document Server

    Lucy, L B

    2009-01-01

    In an attempt to understand the extraordinarily small mass-loss rates of late-type O dwarfs, mass fluxes in the relevant part of (Teff, g)-space are derived from first principles using a previously-described code for constructing moving reversing layers. From these mass fluxes, a weak-wind domain is identified within which a star's rate of mass loss by a radiatively-driven wind is less than that due to nuclear burning. The five weak-wind stars recently analysed by Marcolino et al. (2009) fall within or at the edge of this domain. But although the theoretical mass fluxes for these stars are approximately 1.4 dex lower than those derived with the formula of Vink et al. (2000), the observed rates are still not matched, a failure that may reflect our poor understanding of low-density supersonic outflows. Mass fluxes are also computed for two strong-wind O4 stars analysed by Bouret et al. (2005). The predictions agree with the sharply reduced mass loss rates found when wind clumping is taken into account.

  16. Mass fluxes for hot stars

    Science.gov (United States)

    Lucy, L. B.

    2010-03-01

    In an attempt to understand the extraordinarily small mass-loss rates of late-type O dwarfs, mass fluxes in the relevant part of (Teff, g)-space are derived from first principles using a previously-described code for constructing moving reversing layers. From these mass fluxes, a weak-wind domain is identified within which a star's rate of mass loss by a radiatively-driven wind is less than that due to nuclear burning. The five weak-wind stars recently analysed by Marcolino et al. (2009, A&A, 498, 837) fall within or at the edge of this domain. But although the theoretical mass fluxes for these stars are ≈1.4 dex lower than those derived with the formula of Vink et al. (2000), the observed rates are still not matched, a failure that may reflect our poor understanding of low-density supersonic outflows. Mass fluxes are also computed for two strong-wind O4 stars analysed by Bouret et al. (2005, A&A, 438, 301). The predictions agree with the sharply reduced mass loss rates found when Bouret et al. take wind clumping into account.

  17. 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...

  18. 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...

  19. 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.

  20. 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...

  1. 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 ...

  2. 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.

  3. 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

  4. 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...

  5. 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.

  6. 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....

  7. Wind-load analysis for collector subsystem for the 10-MW/sub e/ solar-thermal central-receiver pilot plant. Phase 1

    Energy Technology Data Exchange (ETDEWEB)

    None

    1978-12-01

    A computer model with 61 grid points and 85 members was used to predict the structural deformations of all the heliostat structural components from the pedestal/foundation interface to the mirror reflective surfaces. The mirror surface rotations are tabulated. The results indicate the current structural configuration will meet requirements of 1.62 mrad standard deviation for structural deflections of the heliostat subject to 27 mph wind and gravity. These values will be optimized with adjustments that compensate for gravity. Stress analyses are in process on all the heliostat structural components and mechanisms. These are based on the maximum loads (90 mph winds at 10/sup 0/ angle of attack and 50 mph winds with the heliostat in any orientation). The initial calculations on the bar joists and gear drive mechanism components show acceptable safety factors.

  8. 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.

  9. 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.

  10. Constraints on galactic wind models

    Science.gov (United States)

    Meiksin, Avery

    2016-09-01

    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∞ to scale with the star formation rate dot{M}_{ast } (in M⊙ yr-1) approximately as v_∞ ≃ (700-1000) {{km s^{-1}}} {dot{M}_{ast }}^{1/6}. The implied mass injection rate is close to the amount naturally provided by thermal evaporation from the wall of a superbubble in a galactic disc, suggesting that thermal evaporation may be a major source of mass loading. The predicted mass-loading factors from thermal evaporation within the galactic disc alone, however, are somewhat smaller, 0.2-2, so that a further contribution from cloud ablation or evaporation within the wind may be required. Both models may account for the 1.4 GHz luminosity of unresolved radio sources within starburst galaxies for plausible parameters describing the distribution of relativistic electrons. Further observational tests to distinguish the models are suggested.

  11. 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

  12. 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...

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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...

  18. 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 ...

  19. GALEX Detection of Shock Breakout in Type II-P Supernova PS1-13arp: Implications for the Progenitor Star Wind

    CERN Document Server

    Gezari, S; Sanders, N E; Soderberg, A M; Hung, T; Heinis, S; Smartt, S J; Rest, A; Scolnic, D; Chornock, R; Berger, E; Foley, R J; Huber, M E; Stubbs, P Price C W; Riess, A G; Kirshner, R P; Smith, K; Wood-Vasey, W M; Schiminovich, D; Martin, D C; Burgett, W S; Chambers, K C; Flewelling, H; Kaiser, N; Tonry, J L; Wainscoat, R

    2015-01-01

    We present the GALEX detection of a UV burst at the time of explosion of an optically normal Type II-P supernova (PS1-13arp) from the Pan-STARRS1 survey at z=0.1665. The temperature and luminosity of the UV burst match the theoretical predictions for shock breakout in a red supergiant, but with a duration a factor of ~50 longer than expected. We compare the $NUV$ light curve of PS1-13arp to previous GALEX detections of Type IIP SNe, and find clear distinctions that indicate that the UV emission is powered by shock breakout, and not by the subsequent cooling envelope emission previously detected in these systems. We interpret the ~ 1 d duration of the UV signal with a shock breakout in the wind of a red supergiant with a pre-explosion mass-loss rate of ~ 10^-3 Msun yr^-1. This mass-loss rate is enough to prolong the duration of the shock breakout signal, but not enough to produce an excess in the optical plateau light curve or narrow emission lines powered by circumstellar interaction. This detection of non-st...

  20. Life Cycle of Stars

    Science.gov (United States)

    1999-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper left of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

  1. Chronology of star formation and disk evolution in the Eagle Nebula

    CERN Document Server

    Guarcello, M G; Peres, G; Prisinzano, L; Sciortino, S

    2010-01-01

    Massive SFR are characterized by intense ionizing fluxes, strong stellar winds and supernovae explosions, all of which have important effects on the surrounding media, on the star-formation (SF) process and on the evolution of YSOs and their disks. We present a multiband study of the massive young cluster NGC6611 and M16, to study how OB stars affect the early stellar evolution and the SF. We search for evidence of triggered SF by OB stars in NGC6611 on a large spatial scale (~10 pc) and how the efficiency of disks photoevaporation depends on the central stars mass. We assemble a multiband catalog with photometric data, from B band to 8.0micron, and X-ray data obtained with 2 new and 1 archival ACIS-I observation. We select the stars with disks from IR photometry and disk-less from X-ray emission, both in NGC6611 and the outer region of M16. We study induced photoevaporation searching for the spatial variation of disk frequency for distinct stellar mass ranges. The triggering of SF by OB stars has been invest...

  2. Hadron star models. [neutron stars

    Science.gov (United States)

    Cohen, J. M.; Boerner, G.

    1974-01-01

    The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

  3. Young star cluster evolution and metallicity

    CERN Document Server

    Mapelli, M

    2013-01-01

    Young star clusters (SCs) are the cradle of stars and the site of important dynamical processes. We present N-body simulations of young SCs including recipes for metal-dependent stellar evolution and mass loss by stellar winds. We show that metallicity affects significantly the collapse and post-core collapse phase, provided that the core collapse timescale is of the same order of magnitude as the lifetime of massive stars. In particular, the reversal of core collapse is faster for metal-rich SCs, where stellar winds are stronger. As a consequence, the half-mass radius of metal-poor SCs expands more than that of metal-rich SCs.

  4. A Real Shooting Star

    Science.gov (United States)

    2007-01-01

    [figure removed for brevity, see original site] Click on the image for movie of A Real Shooting Star This artist's animation illustrates a star flying through our galaxy at supersonic speeds, leaving a 13-light-year-long trail of glowing material in its wake. The star, named Mira (pronounced my-rah) after the latin word for 'wonderful,' sheds material that will be recycled into new stars, planets and possibly even life. NASA's Galaxy Evolution Explorer discovered the long trail of material behind Mira during its survey of the entire sky in ultraviolet light. The animation begins by showing a close-up of Mira -- a red-giant star near the end of its life. Red giants are red in color and extremely bloated; for example, if a red giant were to replace our sun, it would engulf everything out to the orbit of Mars. They constantly blow off gas and dust in the form of stellar winds, supplying the galaxy with molecules, such as oxygen and carbon, that will make their way into new solar systems. Our sun will mature into a red giant in about 5 billion years. As the animation pulls out, we can see the enormous trail of material deposited behind Mira as it hurls along between the stars. Like a boat traveling through water, a bow shock, or build up of gas, forms ahead of the star in the direction of its motion. Gas in the bow shock is heated and then mixes with the cool hydrogen gas in the wind that is blowing off Mira. This heated hydrogen gas then flows around behind the star, forming a turbulent wake. Why does the trailing hydrogen gas glow in ultraviolet light? When it is heated, it transitions into a higher-energy state, which then loses energy by emitting ultraviolet light - a process known as fluorescence. Finally, the artist's rendering gives way to the actual ultraviolet image taken by the Galaxy Evolution Explorer Mira is located 350 light-years from Earth in the constellation Cetus, otherwise known as the whale. Coincidentally, Mira and its 'whale of a tail' can be

  5. 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\\...

  6. Multi-phase environment of compact galactic nuclei: the role of the Nuclear Star Cluster

    CERN Document Server

    Różańska, A; Czerny, B; Adhikari, T P; Karas, V

    2016-01-01

    We study the conditions for the onset of Thermal Instability in the innermost regions of compact galactic nuclei, where the properties of the interstellar environment are governed by the interplay of quasi-spherical accretion onto a supermassive black hole (SMBH) and the heating/cooling processes of gas in a dense nuclear star cluster. Stellar winds are the source of material for radiatively inefficient (quasi-spherical, non-magnetised) inflow/outflow onto the central SMBH, where a stagnation point develops within the Bondi type accretion. We study the local thermal equilibrium to determine the parameter space which allows cold and hot phases in mutual contact to co-exist. We include the effects of mechanical heating by stellar winds and radiative cooling/heating by the ambient field of the dense star cluster. We consider two examples: the Nuclear Star Cluster (NSC) in the Milky Way central region (including the gaseous Mini-spiral of Sgr~A*), and the Ultra-Compact Dwarf galaxy M60-UCD1. We find that the two ...

  7. Young stellar clusters and star formation throughout the Galaxy

    CERN Document Server

    Feigelson, Eric; Allen, Lori; Bergin, Edwin; Bally, John; Balog, Zoltan; Bourke, Tyler; Brogan, Crystal; Chu, You-Hua; Churchwell, Edward; Gagne, Marc; Getman, Konstantin; Hunter, Todd; Morgan, Larry; Massey, Philip; Mac Low, Mordecai-Mark; Mamajek, Eric; Megeath, S Thomas; O'Dell, C Robert; Rathborne, Jill; Rebull, Luisa; Stahler, Steven; Townsley, Leisa; Wang, Junfeng; Williams, Jonathan

    2009-01-01

    Most stars are born in rich young stellar clusters (YSCs) embedded in giant molecular clouds. The most massive stars live out their short lives there, profoundly influencing their natal environments by ionizing HII regions, inflating wind-blown bubbles, and soon exploding as supernovae. Thousands of lower-mass pre-main sequence stars accompany the massive stars, and the expanding HII regions paradoxically trigger new star formation as they destroy their natal clouds. While this schematic picture is established, our understanding of the complex astrophysical processes involved in clustered star formation have only just begun to be elucidated. The technologies are challenging, requiring both high spatial resolution and wide fields at wavelengths that penetrate obscuring molecular material and remove contaminating Galactic field stars. We outline several important projects for the coming decade: the IMFs and structures of YSCs; triggered star formation around YSC; the fate of OB winds; the stellar populations of...

  8. 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...

  9. The elusive origin of Carbon-Enhanced Metal-Poor stars

    CERN Document Server

    Abate, C; Izzard, R G; Mohamed, S S; de Mink, S E

    2013-01-01

    Carbon-enhanced metal-poor (CEMP) stars count for 9-25% of all the very metal-poor stars of the halo. In at least some CEMP stars the chemical enrichment is believed to be due to wind mass transfer in the past from an AGB donor star on to a low-mass companion. However, binary population synthesis models predict much lower CEMP fractions. As an alternative to the canonical Bondi-Hoyle-Lyttleton (BHL) wind accretion model, recent hydrodynamical simulations suggest an efficient mode of wind mass transfer, called wind Roche-lobe overflow (WRLOF), can reproduce observations of AGB winds in binary systems. We use our population synthesis model to test the consequences of WRLOF on a population of CEMP stars. Compared to previous predictions based on the BHL model we find a modest increase of the fraction of CEMP stars and substantial differences in the distributions of carbon and periods in the population of CEMP stars.

  10. Uniformly rotating neutron stars

    CERN Document Server

    Boshkayev, Kuantay

    2016-01-01

    In this chapter we review the recent results on the equilibrium configurations of static and uniformly rotating neutron stars within the Hartle formalism. We start from the Einstein-Maxwell-Thomas-Fermi equations formulated and extended by Belvedere et al. (2012, 2014). We demonstrate how to conduct numerical integration of these equations for different central densities ${\\it \\rho}_c$ and angular velocities $\\Omega$ and compute the static $M^{stat}$ and rotating $M^{rot}$ masses, polar $R_p$ and equatorial $R_{\\rm eq}$ radii, eccentricity $\\epsilon$, moment of inertia $I$, angular momentum $J$, as well as the quadrupole moment $Q$ of the rotating configurations. In order to fulfill the stability criteria of rotating neutron stars we take into considerations the Keplerian mass-shedding limit and the axisymmetric secular instability. Furthermore, we construct the novel mass-radius relations, calculate the maximum mass and minimum rotation periods (maximum frequencies) of neutron stars. Eventually, we compare a...

  11. Shooting stars

    Energy Technology Data Exchange (ETDEWEB)

    Maurette, M.; Hammer, C.

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

  12. Multicomponent radiatively driven stellar winds IV. On the helium decoupling in the wind of sigma Ori E

    OpenAIRE

    Krticka, Jiri; Kubat, Jiri; Groote, Detlef

    2006-01-01

    We study the possibility of the helium decoupling in the stellar wind of sigma Ori E. To obtain reliable wind parameters for this star we first calculate an NLTE wind model and derive wind mass-loss rate and terminal velocity. Using corresponding force multipliers we study the possibility of helium decoupling. We find that helium decoupling is not possible for realistic values of helium charge (calculated from NLTE wind models). Helium decoupling seems only possible for a very low helium char...

  13. downburst wind with rainfall

    Directory of Open Access Journals (Sweden)

    Chao Zhou

    2015-03-01

    Full Text Available There have been many reports recently on unanticipated galloping and collapse accidents of tower-line systems due to downburst wind with rainfall. Although wet downburst is characterized by high-velocity wind with rainfall, very little research work is involved with galloping of high-voltage transmission line induced by the downburst wind with rainfall. Thus, this article proposes a preliminary theoretical study aiming to provide an analytical model of the high-voltage transmission line subjected to the downburst wind with rainfall to explain some phenomena observed from field measurements. Through wind or rain–wind tunnel experiments, we obtained aerodynamic characteristics of the high-voltage conductor with different yaw angles and rainfall rates. Considering the variations of several factors such as wind velocity, rainfall rate, yaw angle, and attack angle, the proposed analytical model was created by finite element method and central differences with the obtained aerodynamic coefficients of the high-voltage conductor. The theoretical results accord well with the experimental data. The analytical model enables better comprehension of the galloping of the high-voltage transmission line subjected to the downburst wind with rainfall.

  14. Theory of neutron star magnetospheres

    CERN Document Server

    Curtis Michel, F

    1990-01-01

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

  15. Cool Stars and Space Weather

    CERN Document Server

    Vidotto, A A; Cameron, A C; Morin, J; Villadsen, J; Saar, S; Alvarado, J; Cohen, O; Holzwarth, V; Poppenhaeger, K; Reville, V

    2014-01-01

    Stellar flares, winds and coronal mass ejections form the space weather. They are signatures of the magnetic activity of cool stars and, since activity varies with age, mass and rotation, the space weather that extra-solar planets experience can be very different from the one encountered by the solar system planets. How do stellar activity and magnetism influence the space weather of exoplanets orbiting main-sequence stars? How do the environments surrounding exoplanets differ from those around the planets in our own solar system? How can the detailed knowledge acquired by the solar system community be applied in exoplanetary systems? How does space weather affect habitability? These were questions that were addressed in the splinter session "Cool stars and Space Weather", that took place on 9 Jun 2014, during the Cool Stars 18 meeting. In this paper, we present a summary of the contributions made to this session.

  16. NuSTAR Observations of the Powerful Radio Galaxy Cygnus A

    Science.gov (United States)

    Reynolds, Christopher S.; Lohfink, Anne M.; Ogle, Patrick M.; Harrison, Fiona A.; Madsen, Kristin K.; Fabian, Andrew C.; Wik, Daniel R.; Madejski, Grzegorz; Ballantyne, David R.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Fuerst, Felix; Hailey, Charles J.; Lanz, Lauranne; Miller, Jon M.; Saez, Cristian; Stern, Daniel; Walton, Dominic J.; Zhang, William

    2015-08-01

    We present NuSTAR observations of the powerful radio galaxy Cygnus A, focusing on the central absorbed active galactic nucleus (AGN). Cygnus A is embedded in a cool-core galaxy cluster, and hence we also examine archival XMM-Newton data to facilitate the decomposition of the spectrum into the AGN and intracluster medium components. NuSTAR gives a source-dominated spectrum of the AGN out to \\gt 70 keV. In gross terms, the NuSTAR spectrum of the AGN has the form of a power law ({{Γ }}∼ 1.6-1.7) absorbed by a neutral column density of {N}{{H}}∼ 1.6× {10}23 {{cm}}-2. However, we also detect curvature in the hard (\\gt 10 keV) spectrum resulting from reflection by Compton-thick matter out of our line of sight to the X-ray source. Compton reflection, possibly from the outer accretion disk or obscuring torus, is required even permitting a high-energy cut off in the continuum source; the limit on the cut-off energy is {E}{cut}\\gt 111 keV(90% confidence). Interestingly, the absorbed power law plus reflection model leaves residuals suggesting the absorption/emission from a fast (15,000-26,000 {km} {{{s}}}-1 ), high column-density ({N}W\\gt 3× {10}23 {{cm}}-2), highly ionized (ξ ∼ 2500 {erg} {cm} {{{s}}}-1) wind. A second, even faster ionized wind component is also suggested by these data. We show that the ionized wind likely carries a significant mass and momentum flux, and may carry sufficient kinetic energy to exercise feedback on the host galaxy. If confirmed, the simultaneous presence of a strong wind and powerful jets in Cygnus A demonstrates that feedback from radio-jets and sub-relativistic winds are not mutually exclusive phases of AGN activity but can occur simultaneously.

  17. Mass loss and evolution of stars and star clusters: a personal historical perspective

    NARCIS (Netherlands)

    Lamers, H.J.G.L.M.

    2008-01-01

    The development and progress of the studies of winds and mass loss from hot stars, from about 1965 up to now, is discussed in a personal historical perspective. The present state of knowledge about stellar winds, based on papers presented at this workshop, is described. About ten years ago the mecha

  18. Conditions of call for tenders on the offshore wind power plants; Conditions de l'appel d'offres portant sur des centrales eolienne en mer

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2003-07-01

    In the framework of the renewable energies sources development, the french government decided to launch a call for tenders for the realization of offshore wind power plants in 2007. The call for tenders conditions concern: the energetic and technical characteristics of the installations as the primary energy, the production technic, the power; the industrial implementing delay; the exploitation and the operating time; the implementing sites; the weighting and the classification principles. The main conditions concerning the utilization of the maritime public land property outside of the harbors. (A.L.B.)

  19. On the Fast Magnetic Rotator Regime of Stellar Winds

    CERN Document Server

    Johnstone, C P

    2016-01-01

    Aims: We study the acceleration of the stellar winds of rapidly rotating low mass stars and the transition between the slow magnetic rotator and fast magnetic rotator regimes. We aim to understand the properties of stellar winds in the fast magnetic rotator regime and the effects of magneto-centrifugal forces on wind speeds and mass loss rates. Methods: We extend the solar wind model of Johnstone et al. (2015b) to 1D magnetohydrodynamic (MHD) simulations of the winds of rotating stars. We test two assumptions for how to scale the wind temperature to other stars and assume the mass loss rate scales as Mdot ~ Rstar^2 OmegaStar^1.33 Mstar^-3.36, in the unsaturated regime, as estimated by Johnstone et al. (2015a). Results: For 1.0 Msun stars, the winds can be accelerated to several thousand km/s, and the effects of magneto-centrifugal forces are much weaker for lower mass stars. We find that the different assumptions for how to scale the wind temperature to other stars lead to significantly different mass loss ra...

  20. Grand unification of neutron stars

    Science.gov (United States)

    Kaspi, Victoria M.

    2010-01-01

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical “grand unification” of this wealth of observational phenomena, and comment on possibilities for Chandra’s next decade in this field. PMID:20404205