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Sample records for photoionized stellar wind

  1. X-Ray Spectral Study of the Photoionized Stellar Wind in Vela X-1

    SciTech Connect

    Watanabe, Shin; Sako, Masao; Ishida, Manabu; Ishisaki, Yoshitaka; Kahn, Steven M.; Kohmura, Takayoshi; Nagase, Fumiaki; Paerels, Frederik; Takahashi, Tadayuki; /JAXA, Sagamihara /KIPAC, Menlo Park /Tokyo Metropolitan U. /Kogakuin U. /Columbia U., Astron. Astrophys.

    2006-07-10

    We present results from quantitative modeling and spectral analysis of the high mass X-ray binary system Vela X-1 obtained with the Chandra High Energy Transmission Grating Spectrometer. The observations cover three orbital phase ranges within a single binary orbit. The spectra exhibit emission lines from H-like and He-like ions driven by photoionization, as well as fluorescent emission lines from several elements in lower charge states. The properties of these X-ray lines are measured with the highest accuracy to date. In order to interpret and make full use of the high-quality data, we have developed a simulator, which calculates the ionization and thermal structure of a stellar wind photoionized by an X-ray source, and performs Monte Carlo simulations of X-ray photons propagating through the wind. The emergent spectra are then computed as a function of the viewing angle accurately accounting for photon transport in three dimensions including dynamics. From comparisons of the observed spectra with results from the simulator, we are able to find the ionization structure and the geometrical distribution of material in the stellar wind of Vela X-1 that can reproduce the observed spectral line intensities and continuum shapes at different orbital phases remarkably well. We find that the stellar wind profile can be represented by a CAK-model with a star mass loss rate of (1.5-2.0) x 10{sup -6} M{sub {circle_dot}} yr{sup -1}, assuming a terminal velocity of 1100 km s{sup -1}. It is found that a large fraction of X-ray emission lines from highly ionized ions are formed in the region between the neutron star and the companion star. We also find that the fluorescent X-ray lines must be produced in at least three distinct regions: (1) the extended stellar wind, (2) reflection off the stellar photosphere, and (3) in a distribution of dense material partially covering and possibly trailing the neutron star, which may be associated with an accretion wake. Finally, from

  2. Stellar Winds

    NASA Astrophysics Data System (ADS)

    Owocki, Stan

    A "stellar wind" is the continuous, supersonic outflow of matter from the surface layers of a star. Our sun has a solar wind, driven by the gas-pressure expansion of the hot (T > 106 K) solar corona. It can be studied through direct in situ measurement by interplanetary spacecraft; but analogous coronal winds in more distant solar-type stars are so tenuous and transparent that that they are difficult to detect directly. Many more luminous stars have winds that are dense enough to be opaque at certain wavelengths of the star's radiation, making it possible to study their wind outflows remotely through careful interpretation of the observed stellar spectra. Red giant stars show slow, dense winds that may be driven by the pressure from magnetohydrodyanmic waves. As stars with initial mass up to 8 M ⊙ evolve toward the Asymptotic Giant Branch (AGB), a combination of stellar pulsations and radiative scattering off dust can culminate in "superwinds" that strip away the entire stellar envelope, leaving behind a hot white dwarf stellar core with less than the Chandrasekhar mass of ˜ ​​ 1. 4M ⊙. The winds of hot, luminous, massive stars are driven by line-scattering of stellar radiation, but such massive stars can also exhibit superwind episodes, either as Red Supergiants or Luminous Blue Variable stars. The combined wind and superwind mass loss can strip the star's hydrogen envelope, leaving behind a Wolf-Rayet star composed of the products of earlier nuclear burning via the CNO cycle. In addition to such direct effects on a star's own evolution, stellar winds can be a substantial source of mass, momentum, and energy to the interstellar medium, blowing open large cavities or "bubbles" in this ISM, seeding it with nuclear processed material, and even helping trigger the formation of new stars, and influencing their eventual fate as white dwarves or core-collapse supernovae. This chapter reviews the properties of such stellar winds, with an emphasis on the various

  3. PHOTOIONIZATION IN THE SOLAR WIND

    SciTech Connect

    Landi, E.; Lepri, S. T.

    2015-10-20

    In this work we investigate the effects of photoionization on the charge state composition of the solar wind. Using measured solar EUV and X-ray irradiance, the Michigan Ionization Code and a model for the fast and slow solar wind, we calculate the evolution of the charge state distribution of He, C, N, O, Ne, Mg, Si, S, and Fe with and without including photoionization for both types of wind. We find that the solar radiation has significant effects on the charge state distribution of C, N, and O, causing the ionization levels of these elements to be higher than without photoionization; differences are largest for oxygen. The ions commonly observed for elements heavier than O are much less affected, except in ICMEs where Fe ions more ionized than 16+ can also be affected by the solar radiation. We also show that the commonly used O{sup 7+}/O{sup 6+} density ratio is the most sensitive to photoionization; this sensitivity also causes the value of this ratio to depend on the phase of the solar cycle. We show that the O{sup 7+}/O{sup 6+} ratio needs to be used with caution for solar wind classification and coronal temperature estimates, and recommend the C{sup 6+}/C{sup 4+} ratio for these purposes.

  4. Photoionized gaseous nebulae and magnetized stellar winds: The evolution and shaping of H II regions and planetary nebulae

    NASA Astrophysics Data System (ADS)

    Franco, José; García-Segura, Guillermo; Kurtz, Stan E.; López, José A.

    2001-05-01

    The early evolution of hydrogen+ (H II) regions is controlled by the properties of the star-forming cloud cores. The observed density distributions in some young H II regions indicate that the power-law stratifications can be steeper than r-2. Ionization fronts can overrun these gradients and the ionized outflows are strongly accelerated along these steep density distributions. Thus, photoionized regions can either reach pressure equilibrium inside the inner parts of the high-pressure cores [with sizes and densities similar to those observed in ultra compact (UC) H II regions], or create bright H II regions with extended emission. The density inhomogeneities engulfed within the ionization fronts create corrugations in the front, which in turn drive instabilities in the ionization-shock (I-S) front. These instabilities grow on short time scales and lead to the fragmentation of the dense shells generated by the shock fronts. Thus, new clumps are continuously created from the fragmented shell, and the resulting finger-like structures can explain the existence of elephant trunks and cometary-like globules in most H II regions. In the case of planetary nebulae (PNe), wind asymmetries and magnetic fields from rotating stars, along with precession of the rotation axis, can create the wide range of observed PNe morphologies and collimated outflows (jets). Magnetic collimation and jet formation in PNe become very efficient after the flow has passed through the reverse shock of the PN.

  5. Introduction to Stellar Winds

    NASA Astrophysics Data System (ADS)

    Lamers, Henny J. G. L. M.; Cassinelli, Joseph P.

    1999-06-01

    Preface; 1. Historical overview; 2. Observations of stellar winds; 3. Basic concepts: isothermal winds; 4. Basic concepts: non-isothermal winds; 5. Coronal winds; 6. Sound wave driven winds; 7. Dust driven winds; 8. Line driven winds; 9. Magnetic rotator theory; 10. Alfvén wave driven winds; 11. Outflowing disks from rotating stars; 12. Winds colliding with the interstellar medium; 13. The effects of mass loss on stellar evolution; 14. Problems; Appendices; Bibliography; Object index; Index.

  6. AXISYMMETRIC SIMULATIONS OF HOT JUPITER–STELLAR WIND HYDRODYNAMIC INTERACTION

    SciTech Connect

    Christie, Duncan; Arras, Phil; Li, Zhi-Yun

    2016-03-20

    Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyα transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point.

  7. X-RAY PHOTOIONIZED BUBBLE IN THE WIND OF VELA X-1 PULSAR SUPERGIANT COMPANION

    SciTech Connect

    Krticka, Jiri; Skalicky, Jan; Kubat, Jiri

    2012-10-01

    Vela X-1 is the archetype of high-mass X-ray binaries (HMXBs), composed of a neutron star and a massive B supergiant. The supergiant is a source of a strong radiatively driven stellar wind. The neutron star sweeps up this wind and creates a huge amount of X-rays as a result of energy release during the process of wind accretion. Here, we provide detailed NLTE models of the Vela X-1 envelope. We study how the X-rays photoionize the wind and destroy the ions responsible for the wind acceleration. The resulting decrease of the radiative force explains the observed reduction of the wind terminal velocity in a direction to the neutron star. The X-rays create a distinct photoionized region around the neutron star filled with a stagnating flow. The existence of such photoionized bubbles is a general property of HMXBs. We unveil a new principle governing these complex objects, according to which there is an upper limit to the X-ray luminosity the compact star can have without suspending the wind due to inefficient line driving.

  8. Stellar winds of hot stars

    NASA Astrophysics Data System (ADS)

    Stee, Ph.; Chesneau, O.

    2014-09-01

    In this paper, we summarize the basic properties of radiative stellar winds from the theoretical and observational point of views. We illustrate two examples of a radiative code applied to stellar physics: the SIMECA code successfully used to constrain the physics of the circumstellar environment of the Be star α Arae constrained by VLTI-AMBER spectrally resolved measurements and the CMFGEN code applied to the BA supergiants Deneb and Rigel constrained by CHARA-VEGA measurements.

  9. Envelope Inflation or Stellar Wind?

    NASA Astrophysics Data System (ADS)

    Ro, S.; Matzner, C. D.

    We an optically-thick, transonic, steady wind model for a H-free Wolf-Rayet star. A bifurcation is found across a critical mass loss rate Mb. Slower winds M < Mb extend by several hydrostatic stellar radii, reproduce features of envelope in ation from Petrovic et al. (2006) and Gräfener et al. (2012), and are energetically unbound. This work is of particular interest for extended envelopes and winds, radiative hydrodynamic instabilities (eg. wind stagnation, clumping, etc.), and NLTE atmospheric models.

  10. Transonic canards and stellar wind

    NASA Astrophysics Data System (ADS)

    Carter, Paul; Knobloch, Edgar; Wechselberger, Martin

    2017-03-01

    Parker’s classical stellar wind solution [20] describing steady spherically symmetric outflow from the surface of a star is revisited. Viscous dissipation is retained. The resulting system of equations has slow-fast structure and is amenable to analysis using geometric singular perturbation theory. This technique leads to a reinterpretation of the sonic point as a folded saddle and the identification of shock solutions as canard trajectories in space [22]. The results shed light on the location of the shock and its sensitivity to the system parameters. The related spherically symmetric stellar accretion solution of Bondi [4] is described by the same theory.

  11. Astrospheres and Solar-like Stellar Winds.

    PubMed

    Wood, Brian E

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

  12. STELLAR WIND INFLUENCE ON PLANETARY DYNAMOS

    SciTech Connect

    Heyner, Daniel; Glassmeier, Karl-Heinz; Schmitt, Dieter

    2012-05-10

    We examine the possible influence of early stellar wind conditions on the evolution of planetary dynamo action. In our model, the dynamo operates within a significant ambient magnetospheric magnetic field generated by the interaction between the stellar wind and the planetary magnetic field. This provides a negative feedback mechanism which quenches the dynamo growth. The external magnetic field magnitude which the dynamo experiences, and thus the strength of the quenching, depends on the stellar wind dynamic pressure. As this pressure significantly changes during stellar evolution, we argue that under early stellar system conditions the coupling between the stellar wind and the interior dynamics of a planet is much more important than has been thought up to now. We demonstrate the effects of the feedback coupling in the course of stellar evolution with a planet at a similar distance to the central star as Mercury is to the Sun.

  13. Stellar wind models of subluminous hot stars

    NASA Astrophysics Data System (ADS)

    Krtička, J.; Kubát, J.; Krtičková, I.

    2016-09-01

    Context. Mass-loss rate is one of the most important stellar parameters. Mass loss via stellar winds may influence stellar evolution and modifies stellar spectrum. Stellar winds of subluminous hot stars, especially subdwarfs, have not been studied thoroughly. Aims: We aim to provide mass-loss rates as a function of subdwarf parameters and to apply the formula for individual subdwarfs, to predict the wind terminal velocities, to estimate the influence of the magnetic field and X-ray ionization on the stellar wind, and to study the interaction of subdwarf wind with mass loss from Be and cool companions. Methods: We used our kinetic equilibrium (NLTE) wind models with the radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the wind structure of subluminous hot stars. Our models solve stationary hydrodynamical equations, that is the equation of continuity, equation of motion, and energy equation and predict basic wind parameters. Results: We predicted the wind mass-loss rate as a function of stellar parameters, namely the stellar luminosity, effective temperature, and metallicity. The derived wind parameters (mass-loss rates and terminal velocities) agree with the values derived from the observations. The radiative force is not able to accelerate the homogeneous wind for stars with low effective temperatures and high surface gravities. We discussed the properties of winds of individual subdwarfs. The X-ray irradiation may inhibit the flow in binaries with compact components. In binaries with Be components, the winds interact with the disk of the Be star. Conclusions: Stellar winds exist in subluminous stars with low gravities or high effective temperatures. Despite their low mass-loss rates, they are detectable in the ultraviolet spectrum and cause X-ray emission. Subdwarf stars may lose a significant part of their mass during the evolution. The angular momentum loss in magnetic subdwarfs with wind may explain their

  14. Blocking Metal Accretion onto Population III Stars by Stellar Wind

    NASA Astrophysics Data System (ADS)

    Tanaka, Shuta J.; Chiaki, Gen; Tominaga, Nozomu; Susa, Hajime

    2017-08-01

    Low-mass population III (PopIII) stars of ≲ 0.8 {M}⊙ could survive up until the present. The nondetection of low-mass PopIII stars in our Galaxy has already put a stringent constraint on the initial mass function (IMF) of PopIII stars, suggesting that PopIII stars have a top-heavy IMF. On the other hand, some claim that the lack of such stars stems from metal enrichment of their surfaces by the accretion of heavy elements from the interstellar medium (ISM). We investigate the effects of the stellar wind on metal accretion onto low-mass PopIII stars because accretion of the local ISM onto the Sun is prevented by the solar wind, even for neutrals. The stellar wind and radiation of low-mass PopIII stars are modeled based on knowledge of nearby low-mass stellar systems, including our Sun. We find that low-mass PopIII stars traveling across the Galaxy form a stellar magnetosphere in most of their life. Once the magnetosphere is formed, most of the neutral interstellar particles are photoionized before reaching the stellar surface and are blown away by the wind. Especially, the accretion abundance of iron will be reduced by a factor of < {10}-12 compared with Bondi-Hoyle-Lyttleton accretion. The metal accretion can enhance iron abundance [Fe/H] only up to ˜-14. This demonstrates that low-mass PopIII stars remain pristine and will be found as metal-free stars and that further searches for them are valuable in constraining the IMF of PopIII stars.

  15. Powerful, Rotating Disk Winds from Stellar-mass Black Holes

    NASA Astrophysics Data System (ADS)

    Miller, J. M.; Fabian, A. C.; Kaastra, J.; Kallman, T.; King, A. L.; Proga, D.; Raymond, J.; Reynolds, C. S.

    2015-12-01

    We present an analysis of ionized X-ray disk winds found in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630-47, GRO J1655-40, H 1743-322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe xxv line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe xxvi line is detected as a spin-orbit doublet. The data require 2-3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are rotating with the orbital velocity of the underlying disk, and provides a new means of estimating launching radii—crucial to understanding wind driving mechanisms. Some aspects of the wind velocities and radii correspond well to the broad-line region in active galactic nuclei (AGNs), suggesting a physical connection. We discuss these results in terms of prevalent models for disk wind production and disk accretion itself, and implications for massive black holes in AGNs.

  16. The Photoionized Disk Wind in MWC 349AOrigin of the photo-ionized wind in MWC349A

    NASA Astrophysics Data System (ADS)

    Báez-Rubio, A.; Martín-Pintado, J.

    2017-02-01

    Establishing how dense photo-ionized winds around stars are formed is key to understanding which physical mechanisms have an important role in the evolution of their circumstellar disks. In the case of the massive star MWC 349A, the extensive research carried out since the discovery of its hydrogen recombination lines has lead to a profound knowledge of the characteristics of the system formed by its ionized wind and disk. We present a summary of the current knowledge of their kinematics, which suggests that its dense wind is formed by photoevaporation of the circumstellar disk at a distance of ˜ 24 AU from the central star. We briefly discuss the reasons why disk-wind models are favored because of the radius where its launching occurs. Finally, we compare our results with the recent discovery of maser recombination lines toward another B[e] star, MWC 922, by Sanchez Contreras et al. (in prep.). This finding opens new prospects for studying the origin of winds around stars showing the B[e] phenomenon.

  17. Kinetic efficiencies of stellar wind bubbles

    NASA Technical Reports Server (NTRS)

    Van Buren, D.

    1986-01-01

    The theoretical fraction of a stellar wind's energy converted into the kinetic energy of an expanding swept-up shell is 20 percent in the classical theory of stellar wind bubbles. Observational estimates of this conversion factor based on the amount of ionized material in wind-swept shells about Wolf-Rayet stars generally yield results of 1 percent. If there is a substantial amount of neutral material in the shell, it will not be counted and the kinetic efficiency will be underestimated. Presented here is a dynamical estimate which accounts for this neutral material in deducing the kinetic efficiencies of stellar wind bubbles. Bubbles classified as wind-blown shells have kinetic efficiencies in line with theoretical expectations for energy-conserving evolution in a homogeneous medium. Ringlike nebulae have significantly lower efficiencies, probably because they have been 'poisoned' by the photoevaporation of clouds engulfed during evolution into a cloudy substrate.

  18. Solar and stellar coronae and winds

    NASA Astrophysics Data System (ADS)

    Jardine, Moira

    2017-10-01

    Solar-like stars influence their environments through their coronal emis- sion and winds. These processes are linked through the physics of the stellar magnetic field, whose strength and geometry has now been explored for a large number of stars through spectropolarimetric observations. We have now detected trends with mass and rotation rate in the distribution of magnetic energies in different geometries and on also different length scales. This has implications both for the dynamo processes that generate the fields and also for the dynamics and evolution of the coronae and winds. Modelling of the surface driving processes on stars of various masses and rotation rates has revealed tantalising clues about the dynamics of stellar coronae and their ejecta. These new observations have also prompted a resurgence in the modelling of stellar winds, which is now uncovering the range of different interplanetary conditions that exoplanets might experience as they evolve.

  19. Angular Momentum Loss Via Stellar Winds

    NASA Astrophysics Data System (ADS)

    Matt, Sean; Pinzon, G.; Greene, T. P.

    2010-01-01

    The evolution of stellar spin rates observed during star formation is not yet understood, due primarily to the fact that it is still not clear which mechanism(s) is responsible for removing angular momentum. Stellar winds may exert significant torques during pre-main-sequence evolution, provided that the mass loss rates are enhanced by several orders of magnitude relative to their main sequence values. This may be possible, if the winds are powered by the accretion process. We present new calculations of the angular momentum loss from enhanced stellar winds and address how this may help our understanding of young star spins. SPM was supported by an appointment to the NASA Postdoctoral Program at Ames Research Center, administered by ORAU through a contract with NASA.

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

    NASA Astrophysics Data System (ADS)

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

    2017-10-01

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

  1. Stellar winds driven by Alfven waves

    NASA Technical Reports Server (NTRS)

    Belcher, J. W.; Olbert, S.

    1973-01-01

    Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds.

  2. Saturation of Stellar Winds from Young Suns

    NASA Astrophysics Data System (ADS)

    Suzuki, Takeru K.; Imada, Shinsuke; Kataoka, Ryuho; Kato, Yoshiaki; Matsumoto, Takuma; Miyahara, Hiroko; Tsuneta, Saku

    2013-10-01

    We investigated mass losses via stellar winds from Sun-like main-sequence stars with a wide range of activity levels. We performed forward-type magnetohydrodynamical numerical experiments for Alfvén wave-driven stellar winds with a wide range of input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass-loss rate rapidly at first increases, owing to suppression of the reflection of the Alfvén waves. The surface materials are lifted up by the magnetic pressure associated with the Alfvén waves, and the cool dense chromosphere is intermittently extended to 10%#8211;20% of the stellar radius. The dense atmospheres enhance the radiative losses, and eventually most of the input Poynting energy from the stellar surface escapes by radiation. As a result, there is no more sufficient energy remaining for the kinetic energy of the wind; the stellar wind saturates in very active stars, as observed in Wood et al. (2002, ApJ, 574, 412; 2005, ApJ, 628, L143). The saturation level is positively correlated with Br,0 f0, where Br,0 and f0 are the magnetic field strength and the filling factor of open flux tubes at the photosphere. If Br,0 f0 is relatively large gtrsim 5 G, the mass-loss rate could be as high as 1000 times. If such a strong mass loss lasts for ˜ 1 billion years, the stellar mass itself would be affected, which could be a solution to the faint young Sun paradox. We derived a Reimers-type scaling relation that estimates the mass-loss rate from an energetics consideration of our simulations. Finally, we derived the evolution of the mass-loss rates, dot;{M} ∝ t-1.23, of our simulations, combining with an observed time evolution of X-ray flux from Sun-like stars, which are shallower than dot;{M} ∝ t-2.33±0.55 in Wood et al. (2005).

  3. An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ 436 b

    NASA Astrophysics Data System (ADS)

    Bourrier, V.; Lecavelier des Etangs, A.; Ehrenreich, D.; Tanaka, Y. A.; Vidotto, A. A.

    2016-06-01

    Observations of the warm Neptune GJ 436 b were performed with HST/STIS at three different epochs (2012, 2013, 2014) in the stellar Lyman-α line. They showed deep, repeated transits that were attributed to a giant exosphere of neutral hydrogen. The low radiation pressure from the M-dwarf host star was shown to play a major role in the dynamics of the escaping gas and its dispersion within a large volume around the planet. Yet by itself it cannot explain the specific time-variable spectral features detected in each transit. Here we investigate the combined role of radiative braking and stellar wind interactions using numerical simulations with the EVaporating Exoplanet code (EVE) and we derive atmospheric and stellar properties through the direct comparison of simulated and observed spectra. The first epoch of observations is difficult to interpret because of the lack of out-of-transit data. In contrast, the results of our simulations match the observations obtained in 2013 and 2014 well. The sharp early ingresses observed in these epochs come from the abrasion of the planetary coma by the stellar wind. Spectra observed at later times during the transit can be produced by a dual exosphere of planetary neutrals (escaped from the upper atmosphere of the planet) and neutralized protons (created by charge-exchange with the stellar wind). We find similar properties at both epochs for the planetary escape rate (~2.5 × 108 g s-1), the stellar photoionization rate (~2 × 10-5 s-1), the stellar wind bulk velocity (~85 km s-1), and its kinetic dispersion velocity (~10 km s-1, corresponding to a kinetic temperature of 12 000 K). We also find high velocities for the escaping gas (~50-60 km s-1) that may indicate magnetohydrodynamic (MHD) waves that dissipate in the upper atmosphere and drive the planetary outflow. In 2014 the high density of the stellar wind (~3 × 103 cm-3) led to the formation of an exospheric tail that was mainly composed of neutralized protons and produced

  4. The axisymmetric stellar wind of AG Carinae

    NASA Technical Reports Server (NTRS)

    Schulte-Ladbeck, Regina E.; Clayton, Geoffrey C.; Hillier, D. John; Harries, Tim J.; Howarth, Ian D.

    1994-01-01

    We present optical linear spectropolarimetry of the Luminous Blue Variable AG Carinae obtained after a recent visual brightness increase. The absence of He II lambda 4686 emission, together with the weakening of the He I spectrum and the appearance of Fe lines in the region around 5300 A, confirm that AG Car has started a new excursion across the HR diagram. The H alpha line profile exhibits very extended line wings that are polarized differently in both amount and position angle from either the continuum or the line core. The polarization changes across H alpha, together with variable continuum polarization, indicate the presence of intrinsic polarization. Coexistence of the line-wing polarization with extended flux-line wings evidences that both are formed by electron scattering in a dense wind. The position angle rotates across the line profiles, in a way that presently available models suggest is due to rotation and expansion of the scattering material. AG Car displays very large variations of its linear polarization with time, Delta P approximately 1.2%, indicating significant variations in envelope opacity. We find that the polarization varies along a preferred position angle of approximately 145 deg (with a scatter of +/- 10 deg) which we interpret as a symmetry axis of the stellar wind (with an ambiguity of 90 deg). This position angle is co-aligned with the major axis of the AG Car ring nebula and perpendicular to the AG Car jet. Our observations thus suggest that the axisymmetric geometry seen in the resolved circumstellar environment at various distances already exists within a few stellar radii of AG Car. From the H alpha polarization profile we deduce an interstellar polarization of Q = 0.31%, U = -1.15% at H alpha. The inferred interstellar polarization implies that the intrinsic polarization is not always of the same sign. This indicates either significant temporal changes in the envelope geometry, or it may arise from effects of multiple scattering

  5. The axisymmetric stellar wind of AG Carinae

    NASA Technical Reports Server (NTRS)

    Schulte-Ladbeck, Regina E.; Clayton, Geoffrey C.; Hillier, D. John; Harries, Tim J.; Howarth, Ian D.

    1994-01-01

    We present optical linear spectropolarimetry of the Luminous Blue Variable AG Carinae obtained after a recent visual brightness increase. The absence of He II lambda 4686 emission, together with the weakening of the He I spectrum and the appearance of Fe lines in the region around 5300 A, confirm that AG Car has started a new excursion across the HR diagram. The H alpha line profile exhibits very extended line wings that are polarized differently in both amount and position angle from either the continuum or the line core. The polarization changes across H alpha, together with variable continuum polarization, indicate the presence of intrinsic polarization. Coexistence of the line-wing polarization with extended flux-line wings evidences that both are formed by electron scattering in a dense wind. The position angle rotates across the line profiles, in a way that presently available models suggest is due to rotation and expansion of the scattering material. AG Car displays very large variations of its linear polarization with time, Delta P approximately 1.2%, indicating significant variations in envelope opacity. We find that the polarization varies along a preferred position angle of approximately 145 deg (with a scatter of +/- 10 deg) which we interpret as a symmetry axis of the stellar wind (with an ambiguity of 90 deg). This position angle is co-aligned with the major axis of the AG Car ring nebula and perpendicular to the AG Car jet. Our observations thus suggest that the axisymmetric geometry seen in the resolved circumstellar environment at various distances already exists within a few stellar radii of AG Car. From the H alpha polarization profile we deduce an interstellar polarization of Q = 0.31%, U = -1.15% at H alpha. The inferred interstellar polarization implies that the intrinsic polarization is not always of the same sign. This indicates either significant temporal changes in the envelope geometry, or it may arise from effects of multiple scattering

  6. Constraining Stellar Feedbacks: Photo-ionization vs. Shock-ionization in Local Starburst Galaxies

    NASA Astrophysics Data System (ADS)

    Hong, Sungryong; Calzetti, D.; Chandar, R.; Gallagher, J. S.; Kennicutt, R. C.; Martin, C.; Pellerin, A.; Strickland, D.; Dopita, M. A.

    2010-01-01

    We present the small- and intermediate-scale structure of interstellar medium(ISM) of five local starburst galaxies; NGC1569, NGC4449, Holmberg II, NGC5236, and HE2-10. Each galaxy has four narrow band images for H-beta(4861A), [OIII](5007A), H-alpha(6563A), and [SII](6717,6731A) (or [NII](6583A)), imaged by Advanced Camera for Survey(ACS), Wide Field Planetary Camera 2(WFPC2), and Wide Field Camera 3(WFC3) of the Hubble Space Telescope(HST). We produce line diagnostics diagrams from those narrow band images on a pixel-by-pixel basis and discriminate shock-ionized gas (pixels) by using the ``maximum starburst line'' of Kewley et al. (2001). The properties of line ratios, [SII]/H-alpha vs [OIII]/H-beta, H-alpha vs [OIII]/H-beta, and H-alpha vs [SII]/H-alpha, for photo-ionized gas are well explained by the photo-ionization model of Kewley et al. (2001). When comparing the four galaxies, NGC3077, NGC4214, NGC5236, and NGC5253, previously studied in Calzetti et al. (2004) with our galaxies, we have found similar groups which share the same trend in line ratio plots. The origin of the groups can be explained by the effects of different metallicity and different starforming strength with respect to potential depth, which are strongly related to cooling rate and galactic wind driving mechanism. We compare the shock-ionized gas with shock-ionization model of Allen et al. (2008). Although the ``maximum starburst line'' gives us conservative estimation of shock-ionized gas, our rough estimation of shock velocity 250km/s of HE2-10 is consistent with Mendez et al. (1999). As an Appendix, we present a new objective technique for continuum subtraction from narrow-band image. We have found that skewness values of continuum subtracted images show a transitional feature around the optimal subtraction. We present some real applications and discuss about the strong points and the weak points of this technique.

  7. Scientists Track Collision of Powerful Stellar Winds

    NASA Astrophysics Data System (ADS)

    2005-04-01

    Wolf-Rayet stars and of the wind-collision region," Dougherty said. The stars in WR 140 complete an orbital cycle in 7.9 years. The astronomers tracked the system for a year and a half, noting dramatic changes in the wind collision region. "People have worked out theoretical models for these collision regions, but the models don't seem to fit what our observations have shown," said Mark Claussen, of the National Radio Astronomy Observatory in Socorro, New Mexico. "The new data on this system should provide the theorists with much better information for refining their models of how Wolf-Rayet stars evolve and how wind-collision regions work," Claussen added. The scientists watched the changes in the stellar system as the star's orbits carried them in paths that bring them nearly as close to each other as Mars is to the Sun and as far as Neptune is from the Sun. Their detailed analysis gave them new information on the Wolf-Rayet star's strong wind. At some points in the orbit, the wind collision region strongly emitted radio waves, and at other points, the scientists could not detect the collison region. Wolf-Rayet stars are giant stars nearing the time when they will explode as supernovae. "No other telescope in the world can see the details revealed by the VLBA," Claussen said. "This unmatched ability allowed us to determine the masses and other properties of the stars, and will help us answer some basic questions about the nature of Wolf-Rayet stars and how they develop." he added. The astronomers plan to continue observing WR 140 to follow the system's changes as the two massive stars continue to circle each other. Dougherty and Claussen worked with Anthony Beasley of the Atacama Large Millimeter Array office, Ashley Zauderer of the University of Maryland and Nick Bolingbroke of the University of Victoria, British Columbia. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated

  8. On the fast magnetic rotator regime of stellar winds

    NASA Astrophysics Data System (ADS)

    Johnstone, C. P.

    2017-01-01

    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 a solar wind model to 1D magnetohydrodynamic 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 dot{M_star ∝ R_star2 Ω_star1.33 M_star-3.36}, in the unsaturated regime, as estimated from observed rotational evolution. Results: For 1.0 M⊙ stars, the winds can be accelerated to several thousand km s-1, 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 rates for the rapid rotators. If we assume a constant temperature, the mass loss rates of solar mass stars do not saturate at rapid rotation, which we show to be inconsistent with observed rotational evolution. If we assume the wind temperatures scale positively with rotation, the mass loss rates are only influenced significantly at rotation rates above 75 Ω⊙. We suggest that models with increasing wind speed for more rapid rotators are preferable to those that assume a constant wind speed. If this conclusion is confirmed by more sophisticated wind modelling. it might provide an interesting observational constraint on the properties of stellar winds. All of the codes and output data used in this paper can be downloaded from http://https://zenodo.org/record/160052#.V_y6drWkVC1 or obtained by contacting the author.

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

    NASA Astrophysics Data System (ADS)

    Araya, I.; Curé, M.

    2017-07-01

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

  10. On the effects of stellar winds on exoplanetary magnetospheres

    NASA Astrophysics Data System (ADS)

    See, V.; Jardine, M.; Vidotto, A. A.; Petit, P.; Marsden, S. C.; Jeffers, S. V.

    2014-08-01

    The habitable zone is the range of orbital distances from a host star in which an exoplanet would have a surface temperature suitable for maintaining liquid water. This makes the orbital distance of exoplanets an important variable when searching for extra-solar Earth analogues. However, the orbital distance is not the only important factor determining whether an exoplanet is potentially suitable for life. The ability of an exoplanet to retain an atmosphere is also vital since it helps regulate surface temperatures. One mechanism by which a planetary atmosphere can be lost is erosion due to a strong stellar wind from the host star. The presence of a magnetosphere can help to shield a planetary atmosphere from this process. Using a simple stellar wind model, we present the impact that stellar winds might have on magnetospheric sizes of exoplanets. This is done with the aim of further constraining the parameter space in which we look for extra-solar Earth analogues.

  11. Wind blown bubbles in realistic young and old stellar environments

    NASA Astrophysics Data System (ADS)

    Delamarter, Guy Ralph

    2001-06-01

    We explore the Generalized Wind Blown Bubble (GWBB) paradigm and its ability to explain the morphology of a few classes of objects: Young Stellar Object (YSO) molecular outflows, FU Orionis (time dependent wind) outflows, and Proto Planetary Nebulae (PPNe). These objects represent stages at opposite ends of a stellar lifecycle. We apply two-dimensional hydrodynamic simulation to follow the non-linear evolution of interactions between the circumstellar winds and surrounding environments. The simulations include the effects of atomic and molecular cooling microphysics, stellar gravity, and angular momentum. Synthetic observations are produced from the simulation data and compared to contemporary object observations. Using parameters relevant for YSO molecular outflows, we analyze how the variation in the balance of ram pressure between wind and infalling ambient gas affects the morphology of the resulting outflows. Assuming non- spherical cloud collapse, we find that relatively strong winds can carve out wide, conical outflow cavities and that relatively weak winds can be strongly collimated. If the winds become weak enough, they can be cut off entirely by the infalling environment. We investigate the interaction of multi-stage winds in a proto-planetary nebula, namely those of a pulsed slow wind, a medium velocity wind in the shape of a circumstellar torus, and a final fast wind. The results are compared closely with the well studied object CRL2688 (Egg Nebula). Comparisons to other nebulae are also made. Using several arrangements for the winds and applying synthetic observations it is found that it is difficult to recover the shape of CRL2688 if the final stage fast wind is not precollimated. More complicated dynamics or magnetic fields are suggested to resolve the discrepancy in that case. An examination is made of the interaction of a pulsing wind with an infalling environment. The hydrodynamic simulations are motivated by the FU Orionis and EXor classes of YSOs

  12. Cosmic-ray acceleration at stellar wind terminal shocks

    NASA Technical Reports Server (NTRS)

    Webb, G. M.; Axford, W. I.; Forman, M. A.

    1985-01-01

    Steady-state spherically symmetric analytic solutions of the cosmic-ray transport equations, applicable to the problem of acceleration of cosmic rays at the terminal shock to a stellar wind, are studied. The spectra, graidents, and flow patterns of particles modulated and accelerated by the stellar wind and shock are investigated by means of monoenergetic-source solutions at finite radius, as well as solutions with monoenergetic and power-law galactic spectra. On the basis of calculations given, early-type stars could supply a significant fraction of the 3 x 10 to the 40th ergs/sec required by galactic cosmic rays.

  13. Stellar Magnetism, Winds and their Effects on Planetary Environments

    NASA Astrophysics Data System (ADS)

    Vidotto, A. A.

    2016-08-01

    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.

  14. Colliding stellar winds in O-type close binary systems

    NASA Technical Reports Server (NTRS)

    Gies, Douglas R.

    1991-01-01

    A study of the stellar wind properties of O-type close binary systems is presented. The main objective of this program was to search for colliding winds in four systems, AO Cas, iota Ori, Plaskett's star, and 29 UW CMa, through an examination of high dispersion UV spectra from IUE and optical spectra of the H alpha and He I lambda 6678 emission lines.

  15. On star formation in stellar systems. II - Photoionization in protodwarf galaxies

    NASA Technical Reports Server (NTRS)

    Noriega-Crespo, A.; Bodenheimer, P.; Lin, D. N. C.; Tenorio-Tagle, G.

    1989-01-01

    Numerical hydrodynamical calculations are used to study the effects of the onset of star formation on the residual gas in a primordial low-mass Local-Group dwarf spheroidal galaxy in the size range 0.3-1.0 kpc. It is demonstrated that photoionization in the presence of a moderate gas-density gradient can be responsible for gas ejection on a time-scale of a few times 10 to the 7th yr. The results indicate that, given a normal initial mass function, many protodwarf galaxies may have been dispersed by the onset of star formation.

  16. Stellar evolution at high mass including the effect of a stellar wind

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.-W.

    1979-01-01

    The effect of a stellar wind on the evolution of stars in the mass range from 15 to 120 solar masses is investigated. All the stellar models are constructed with the use of Cox-Stewart opacities. Four possible cases of mass loss are considered: (1) no mass loss at all; (2) substantial mass loss from stars in all stages of evolution; (3) heavy mass loss from red supergiants only; and (4) sudden and very heavy mass loss from luminous yellow supergiants. The assumption of mass loss during the main-sequence phase of evolution is found to lead to a lowering of the luminosity and, unless the mass loss is extremely heavy, of the effective temperature as well. A comparison of the adopted mass-loss rates with observed rates suggests that stellar winds are probably not an important factor in the evolution of main-sequence stars and supergiants unless the initial masses are greater than about 30 solar masses.

  17. Multiline Transfer and the Dynamics of Stellar Winds

    NASA Technical Reports Server (NTRS)

    Abbott, D. C.; Lucy, L. B.

    1985-01-01

    A Monte Carlo technique for treating multiline transfer in stellar winds is described. With a line list containing many thousands of transitions and with fairly realistic treatments of ionization, excitation and line formation, the resulting code allows the dynamic effects of overlapping lines the investigation of and provides the means to directly synthesize the complete spectrum of a star and its wind. It is found that the computed mass loss rate for data Puppis agrees with the observed rate. The synthesized spectrum of zeta Puppis also agrees with observational data. This confirms that line driving is the dominant acceleration mechanism in this star's wind.

  18. The homunculus of Eta Carinae: An interacting stellar winds paradigm

    NASA Technical Reports Server (NTRS)

    Frank, Adam; Balick, Bruce; Davidson, Kris

    1995-01-01

    We simulate the origin and evolution of the bipolar nebula surrounding Eta Car using numerical two-dimensional gasdynamic models. The generalized interacting stellar winds scenario, wherein a stellar wind interacts with an aspherical circumstellar environment, is adopted. The eruption wind of 1840-1860, which is taken to be spherically symmetric, interacts with a preeruption toroidal density environment. Using reasonable assumptions of initial conditions and eruption parameters based on archival data, we have performed over 30 simulations in an effort to bracket the initial parameters which produce models that best match observations. We find that models with high pole-to-equator density contrasts (greater than 100) and toroidal density configurations nicely account for the observed morphology and kinematics of the homunculus.

  19. Stellar Parameters and Winds of Red Supergiants in Binaries

    NASA Astrophysics Data System (ADS)

    Bennett, K.

    The proposed target stars (zeta Aur, 31 Cyg) are eclipsing binary systems with K supergiant primaries and B-type main sequence companions. From these binaries, we will determine key information about fundamental stellar parameters and outer atmospheric structure that can not be obtained from observations of single red supergiants. The proposed observations are directed towards understanding the mass loss process driving the massive winds of red supergiants. In particular, the proposed FUSE observations will support the following analyses: -- detailed model atmosphere analyses of the B-stars' continua -- determining accurate radial velocities of the B-type secondaries -- analyses of the wind absorption features of the red supergiant primaries. From these FUSE observations, we will determine improved fundamental stellar parameters of red supergiants (effective temperatures, radii, masses and luminosities) and wind properties (velocity laws and mass loss rates).

  20. Mineral formation in stellar winds. V. Formation of calcium carbonate

    NASA Astrophysics Data System (ADS)

    Ferrarotti, A. S.; Gail, H.-P.

    2005-02-01

    An emission band around 92 μm found in a few IR spectra from highly evolved stars was proposed to be due to the presence of carbonate dust grains in the circumstellar material (Kemper et al. \\cite{Kem02a}, Nature, 415, 295). This contribution presents the results of a model calculation for the condensation of calcite (CaCO_3) in the stellar wind of AGB stars. It is shown that the quantities of carbonate dust formed relative to the quantities of silicate dust are negligibly small. This results from the fact that carbonates form at a much lower temperature than the silicate dust components. Carbonate dust formation then is suppressed by the strong acceleration of the wind material by radiation pressure on the silicate dust and the subsequent rapid dilution of the wind material. This makes it highly improbable that carbonate dust can be formed in stellar outflows.

  1. Observational Constraints on Stellar Winds from the Hubble Space Telescope

    NASA Astrophysics Data System (ADS)

    Wood, Brian

    2017-05-01

    Planetary atmospheres are affected by both radiation and particle fluxes from their host stars. The former is well constrained by observations, but there are unfortunately few such constraints on the latter. The only means by which the coronal winds of Sun-like stars have ever been perceived at all is by detecting circumstellar H Lyman-alpha absorption from the wind/ISM interaction regions (i.e., "astrospheres"). I will review the existing Lyman-alpha constraints on stellar winds, all of them based on UV spectra from the Hubble Space Telescope. One unexpected result is that the two most active main sequence stars with detected astrospheres, EV Lac (M3.5 V) and Pi1 UMa (G1.5 V), are inferred to have winds comparable to or even weaker than the solar wind. I will explore the utility of the solar example for interpreting this result.

  2. Estimating stellar wind parameters from low-resolution magnetograms

    NASA Astrophysics Data System (ADS)

    Jardine, M.; Vidotto, A. A.; See, V.

    2017-02-01

    Stellar winds govern the angular momentum evolution of solar-like stars throughout their main-sequence lifetime. The efficiency of this process depends on the geometry of the star's magnetic field. There has been a rapid increase recently in the number of stars for which this geometry can be determined through spectropolarimetry. We present a computationally efficient method to determine the 3D geometry of the stellar wind and to estimate the mass-loss rate and angular momentum loss rate based on these observations. Using solar magnetograms as examples, we quantify the extent to which the values obtained are affected by the limited spatial resolution of stellar observations. We find that for a typical stellar surface resolution of 20o-30o, predicted wind speeds are within 5 per cent of the value at full resolution. Mass-loss rates and angular momentum loss rates are within 5-20 per cent. In contrast, the predicted X-ray emission measures can be underestimated by one-to-two orders of magnitude, and their rotational modulations by 10-20 per cent.

  3. Clump formation through colliding stellar winds in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Calderón, Diego

    2016-07-01

    The gas cloud G2 is currently being tidally disrupted by the Galactic Center super-massive black hole, Sgr A*. The region around the black hole is populated by ˜30 Wolf-Rayet stars, which produce strong outflows. Following an analytical approach, we explore the possibility that gas clumps, such as G2, originate from the collision of identical stellar winds via the Non-Linear Thin Shell Instability. We have found that the collision of relatively slow (<750 km s^{-1}) and strong (˜10^{-5} M_{⊙} yr^{-1}) stellar winds from stars at short separations (<2000 AU) is a process that indeed could produce clumps of G2's mass and above. Such short separation encounters of single stars along their orbits are not common in the Galactic Centre, however close binaries, such as IRS 16SW, are promising clump sources (see Calderón et al. 2016). We also present the first results of 2D models of colliding wind systems using the hydrodynamics adaptive mesh refinement code RAMSES, aiming to obtain a clump mass function, and the rate of clump formation and ejection to the ISM. We study the effect of parameters such as wind properties, stellar separation and orbital motion, in order to understand how likely the formation of G2 is in this context.

  4. The Stellar Wind from the Central Star of NGC 7009

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Iping, Rosina; Chu, You-Hua; Gruendl, Robert

    2006-01-01

    Observations of NGC 7009, including its central star HD 200516, have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, providing spectra covering 905-1187 A with spectral resolution of 15 km/sec. One observation was made with the 30x30 arcsec aperture and includes the star plus the entire nebula. A second observation used the 1.25x20arcsec slit significantly reducing the nebular 'contamination' of the stellar spectrum. This poster discusses the spectrum of the central star. A strong FUV continuum, as expected for Teff=82,000K, dominates the spectrum. The most prominent spectral feature is a very strong P-Cygni profile of O VI 1032-1038. This paper presents models of the stellar spectrum and the wind features to further refine the stellar parameters and mass loss rate.

  5. The Stellar Wind from the Central Star of NGC 7009

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Iping, Rosina; Chu, You-Hua; Gruendl, Robert

    2006-01-01

    Observations of NGC 7009, including its central star HD 200516, have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, providing spectra covering 905-1187 A with spectral resolution of 15 km/sec. One observation was made with the 30x30 arcsec aperture and includes the star plus the entire nebula. A second observation used the 1.25x20arcsec slit significantly reducing the nebular 'contamination' of the stellar spectrum. This poster discusses the spectrum of the central star. A strong FUV continuum, as expected for Teff=82,000K, dominates the spectrum. The most prominent spectral feature is a very strong P-Cygni profile of O VI 1032-1038. This paper presents models of the stellar spectrum and the wind features to further refine the stellar parameters and mass loss rate.

  6. The dynamic of stellar wind accretion and the HMXB zoo

    NASA Astrophysics Data System (ADS)

    Walter, Roland; Manousakis, Antonios

    2016-07-01

    The dynamic of the accretion of stellar wind on the pulsar in Vela X-1 is dominated by unstable hydrodynamical flows. Off-states, 10^{37} erg/s flares, quasi-periodic oscillations and log normal flux distribution can all be reproduced by hydrodynamical simulations and reveal the complex motion of bow shocks moving either towards or away from the neutron star. These behaviors are enlightening the zoo of HMXB and suggest new phenomenology to be detected.

  7. The stellar wind velocity field of HD 77581

    NASA Astrophysics Data System (ADS)

    Manousakis, A.; Walter, R.

    2015-12-01

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

  8. THE STEADY-STATE WIND MODEL FOR YOUNG STELLAR CLUSTERS WITH AN EXPONENTIAL STELLAR DENSITY DISTRIBUTION

    SciTech Connect

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Martinez-Gonzalez, Sergio; Bisnovatyi-Kogan, Gennadiy E-mail: gkogan@iki.rssi.ru

    2011-12-20

    A hydrodynamic model for steady-state, spherically symmetric winds driven by young stellar clusters with an exponential stellar density distribution is presented. Unlike in most previous calculations, the position of the singular point R{sub sp}, which separates the inner subsonic zone from the outer supersonic flow, is not associated with the star cluster edge, but calculated self-consistently. When the radiative losses of energy are negligible, the transition from the subsonic to the supersonic flow occurs always at R{sub sp} Almost-Equal-To 4R{sub c} , where R{sub c} is the characteristic scale for the stellar density distribution, irrespective of other star cluster parameters. This is not the case in the catastrophic cooling regime, when the temperature drops abruptly at a short distance from the star cluster center, and the transition from the subsonic to the supersonic regime occurs at a much smaller distance from the star cluster center. The impact from the major star cluster parameters to the wind inner structure is thoroughly discussed. Particular attention is paid to the effects which radiative cooling provides to the flow. The results of the calculations for a set of input parameters, which lead to different hydrodynamic regimes, are presented and compared to the results from non-radiative one-dimensional numerical simulations and to those from calculations with a homogeneous stellar mass distribution.

  9. Prevention of accretion onto white dwarfs by stellar winds

    NASA Technical Reports Server (NTRS)

    Macdonald, James

    1992-01-01

    There is indirect observational evidence that hot white dwarfs may have weak stellar winds. In this paper, the interaction between such a wind and the flow of ISM material in the gravitational field of the white dwarf is investigated with the aim of finding limits on the mass-loss rate and terminal velocity of winds capable of preventing accretion from the ISM. The limiting cases of no relative motion of the star and the ISM and supersonic relative motion of the star through ISM are separately investigated. Each case is treated by generalizing models for the interaction between the solar wind and the local ISM to include the effects of gravity. It is found that, for wind velocities expected for radiatively driven winds, mass-loss rates as low as 10 exp -21 solar mass/yr are sufficient to prevent accretion from the hot phase of the ISM. To prevent accretion during passages through cold clouds, wind mass-loss rates of order 10 exp -18 to 10 exp -17 are required.

  10. Prevention of accretion onto white dwarfs by stellar winds

    NASA Technical Reports Server (NTRS)

    Macdonald, James

    1992-01-01

    There is indirect observational evidence that hot white dwarfs may have weak stellar winds. In this paper, the interaction between such a wind and the flow of ISM material in the gravitational field of the white dwarf is investigated with the aim of finding limits on the mass-loss rate and terminal velocity of winds capable of preventing accretion from the ISM. The limiting cases of no relative motion of the star and the ISM and supersonic relative motion of the star through ISM are separately investigated. Each case is treated by generalizing models for the interaction between the solar wind and the local ISM to include the effects of gravity. It is found that, for wind velocities expected for radiatively driven winds, mass-loss rates as low as 10 exp -21 solar mass/yr are sufficient to prevent accretion from the hot phase of the ISM. To prevent accretion during passages through cold clouds, wind mass-loss rates of order 10 exp -18 to 10 exp -17 are required.

  11. Gravitational damping of Alfven waves in stellar atmospheres and winds

    NASA Technical Reports Server (NTRS)

    Khabibrakhmanov, I. K.; Mullan, D. J.

    1994-01-01

    We consider how gravity affects the propagation of Alfven waves in a stellar atmosphere. We show that when the ion gyrofrequency exceeds the collision rate, the waves are absorbed at a rate proportional to the gravitational acceleration g. Estimates show that this mechanism can readily account for the observed energy losses in the solar chromosphere. The mechanism predicts that the pressure at the top of the chromosphere P(sub Tc) should scale with g as P(sub Tc) proportional to g(exp delta), where delta approximately equals 2/3; this is close to empirical results which suggest delta approximately equals 0.6. Gravitational damping leads to deposition of energy at a rate proportional to the mass of the particles. Hence, heavier ion are heated more effectively than protons. This is consistent with the observed proportionality between ion temperature and mass in the solar wind. Gravitational damping causes the local g to be effectively decreased by an amount proportional to the wave energy. This feature affects the acceleration of the solar wind. Gravitational damping may also lead to self-regulation of the damping of Alfven waves in stellar winds: this is relevant in the context of slow massive winds in cool giants.

  12. Light elements as probes of weak stellar winds

    NASA Astrophysics Data System (ADS)

    Landstreet, J. D.; Dolez, N.; Vauclair, S.

    1998-05-01

    The possibility that stars of the upper main sequence possess weak winds (of order 10(-14) to 10(-12) Msun yr(-1) ) that may compete with atomic diffusion has been suggested by several authors, particularly by Babel & Michaud (1991a) and Babel (1992). Such winds may affect the chemical abundances that appear in the atmospheres of these stars. However, obtaining unambiguous evidence for the existence of a weak wind is not easy. We consider the possibility that naturally abundant chemical elements such as C, O and Ne, which are not expected to be made overabundant in a stellar atmosphere by radiative levitation, may accumulate in or near the photosphere of a mass-losing star, thus serving as tracers of mass loss. We first show that the most abundant elements are not expected to be overabundant in the atmospheres of main sequence stars in the range 8000 <= T_e <= 15000K due to radiative acceleration. We next show that hydrogen mass loss from the atmosphere, at a rate in the range of roughly 10(-14) <= dot {M} <= 10(-12) \\ M_{sunyr(-1}) , could lead to accumulation of a few abundant elements in or not far below the stellar photosphere, provided that any turbulence in the wind at the level of the photosphere is not sufficient to prevent diffusion. We find that such mass loss in late B stars should lead to observable overabundance of Ne, while in early A stars, such mass loss causes O to accumulate in the atmosphere. Detection of overabundances of these elements would provide direct evidence of the presence of weak mass loss. The few available Ne abundance determinations do not allow us to decide whether such weak winds are present in any B stars, but numerous measurements of O abundance imply that either winds in this mass loss range do not occur, or else that atmospheric diffusion is prevented by turbulence in early A stars.

  13. Stellar winds and the evolution of luminous stars

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.-W.

    1978-01-01

    The effect of a stellar wind on the evolution of stars in the mass range 7-60 solar masses has been investigated for stellar models in which Carson's opacities have been employed. Several cases of mass loss have been considered. It is found that the assumption of heavy mass loss from both blue and red supergiants can account well for the relevant observations of OBN stars, WN stars, and very luminous supergiants of all spectral types. But no amount of mass loss can account adequately for the properties of the B supergiants of lowest luminosity. A critical comparison is made between the present results and some earlier results based on the adoption of Cox-Stewart opacities.

  14. Gone with the wind: Where is the missing stellar wind energy from massive star clusters?

    NASA Astrophysics Data System (ADS)

    Rosen, Anna L.; Lopez, Laura A.; Krumholz, Mark R.; Ramirez-Ruiz, Enrico

    2014-08-01

    Star clusters larger than ˜103 M⊙ contain multiple hot stars that launch fast stellar winds. The integrated kinetic energy carried by these winds is comparable to that delivered by supernova explosions, suggesting that at early times winds could be an important form of feedback on the surrounding cold material from which the star cluster formed. However, the interaction of these winds with the surrounding clumpy, turbulent, cold gas is complex and poorly understood. Here, we investigate this problem via an accounting exercise: we use empirically determined properties of four well-studied massive star clusters to determine where the energy injected by stellar winds ultimately ends up. We consider a range of kinetic energy loss channels, including radiative cooling, mechanical work on the cold interstellar medium, thermal conduction, heating of dust via collisions by the hot gas, and bulk advection of thermal energy by the hot gas. We show that, for at least some of the clusters, none of these channels can account for more than a small fraction of the injected energy. We suggest that turbulent mixing at the hot-cold interface or physical leakage of the hot gas from the H II region can efficiently remove the kinetic energy injected by the massive stars in young star clusters. Even for the clusters where we are able to account for all the injected kinetic energy, we show that our accounting sets strong constraints on the importance of stellar winds as a mechanism for feedback on the cold interstellar medium.

  15. Clump formation through colliding stellar winds in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Calderón, D.; Ballone, A.; Cuadra, J.; Schartmann, M.; Burkert, A.; Gillessen, S.

    2016-02-01

    The gas cloud G2 is currently being tidally disrupted by the Galactic Centre supermassive black hole, Sgr A*. The region around the black hole is populated by ˜30 Wolf-Rayet stars, which produce strong outflows. We explore the possibility that gas clumps, such as G2, originate from the collision of stellar winds via the non-linear thin shell instability. Following an analytical approach, we study the thermal evolution of slabs formed in the symmetric collision of winds, evaluating whether instabilities occur, and estimating possible clump masses. We find that the collision of relatively slow (≲750 km s-1) and strong (˜10-5 M⊙ yr-1) stellar winds from stars at short separations (<10 mpc) is a process that indeed could produce clumps of G2's mass and above. Such short separation encounters of single stars along their known orbits are not common in the Galactic Centre, making this process a possible but unlikely origin for G2. We also discuss clump formation in close binaries such as IRS 16SW and in asymmetric encounters as promising alternatives that deserve further numerical study.

  16. Observational overview of clumping in hot stellar winds

    NASA Astrophysics Data System (ADS)

    Moffat, Anthony F. J.

    2008-04-01

    In the old days (pre ˜1990) hot stellar winds were assumed to be smooth, which made life fairly easy and bothered no one. Then after suspicious behaviour had been revealed, e.g. stochastic temporal variability in broadband polarimetry of single hot stars, it took the emerging CCD technology developed in the preceding decades (˜1970-80’s) to reveal that these winds were far from smooth. It was mainly high-S/N, time-dependent spectroscopy of strong optical recombination emission lines in WR, and also a few OB and other stars with strong hot winds, that indicated all hot stellar winds likely to be pervaded by thousands of multiscale (compressible supersonic turbulent?) structures, whose driver is probably some kind of radiative instability. Quantitative estimates of clumping-independent mass-loss rates came from various fronts, mainly dependent directly on density (e.g. electron-scattering wings of emission lines, UV spectroscopy of weak resonance lines, and binary-star properties including orbital-period changes, electron-scattering, and X-ray fluxes from colliding winds) rather than the more common, easier-to-obtain but clumping-dependent density-squared diagnostics (e.g. free-free emission in the IR/radio and recombination lines, of which the favourite has always been Hα). Many big questions still remain, such as: What do the clumps really look like? Do clumping properties change as one recedes from the mother star? Is clumping universal? Does the relative clumping correction depend on dot{M} itself?

  17. Polarization Signatures of Bow Shocks in Stellar Winds

    NASA Astrophysics Data System (ADS)

    Shrestha, M.; Hoffman, J. L.

    2015-12-01

    Bow shocks around massive stars provide important information regarding the motion of the star, the stellar wind properties, and the density of the surrounding interstellar medium. We use a Monte Carlo radiative transfer code to investigate the polarization created when photons from a central star scatter from electrons or dust grains in a surrounding bow shock. We discuss the behavior of the polarization with respect to viewing angle as a function of parameters such as optical depth and scattering medium in both the resolved and unresolved cases.

  18. Modeling the effects of latitudinal gradients in stellar winds, with application to the solar wind

    NASA Technical Reports Server (NTRS)

    Nerney, S.; Suess, S. T.

    1985-01-01

    A steady, axisymmetric, quasi-radial, global model previously developed for stellar winds with embedded magnetic fields has been extended to include latitudinal gradient effects on the azimuthal velocity and magnetic field. The linear results at large radii are presented for large-amplitude latitudinal variations in the radial magnetic field, mass loss rate, and radial velocity of the wind. The magnetohydrodynamic (MHD) equations predict meridional flows that develop naturally from internal magnetic stresses. The flows open flux tubes in the star's equatorial plane, redistributing mass and magnetic flux as a function of stellar latitude. The plasma spins up to conserve angular momentum in fields and plasma. The results are generally applicable to stellar winds (including radiatively driven winds), provided that the internal structure is not dominated by rotation. The asymptotic solutions do not explicitly depend on the form of the energy equation, although the assumed O(1) state which drives these solutions depends on the deposition of energy and momentum throughout the wind.

  19. Braking down an accreting protostar: disc-locking, disc winds, stellar winds, X-winds and Magnetospheric Ejecta

    NASA Astrophysics Data System (ADS)

    Ferreira, J.

    2013-09-01

    Classical T Tauri stars are low mass young forming stars that are surrounded by a circumstellar accretion disc from which they gain mass. Despite this accretion and their own contraction that should both lead to their spin up, these stars seem to conserve instead an almost constant rotational period as long as the disc is maintained. Several scenarios have been proposed in the literature in order to explain this puzzling "disc-locking" situation: either deposition in the disc of the stellar angular momentum by the stellar magnetosphere or its ejection through winds, providing thereby an explanation of jets from Young Stellar Objects. In this lecture, these various mechanisms will be critically detailed, from the physics of the star-disc interaction to the launching of self-confined jets (disc winds, stellar winds, X-winds, conical winds). It will be shown that no simple model can account alone for the whole bulk of observational data and that "disc locking" requires a combination of some of them.

  20. Momentum and energy balance in late-type stellar winds

    NASA Technical Reports Server (NTRS)

    Macgregor, K. B.

    1981-01-01

    Observations at ultraviolet and X-ray wavelengths indicate that the classical picture of a static stellar atmosphere containing a radiative equilibrium temperature distribution is inapplicable to the majority of late type stars. Mass loss and the presence of atmospheric regions characterized by gas temperatures in excess of the stellar effective temperature appear to be almost ubiquitous throughout the HR diagram. Evidence pertaining to the thermal and dynamical structure of the outer envelopes of cool stars is summarized. These results are compared with the predictions of several theoretical models which were proposed to account for mass loss from latetype stars. Models in which the outflow is thermally radiatively, or wave driven are considered for identification of the physical processes responsible for the observed wind properties. The observed variation of both the wind, thermal and dynamical structure as one proceeds from the supergiant branch toward the main sequence in the cool portion of the HR diagram give consideration to potential mechanisms for heating and cooling the flow from low gravity stars.

  1. [WC] Stellar Wind Turbulent Outflows Feeding the ISM

    NASA Astrophysics Data System (ADS)

    Grosdidier, Y.; Acker, A.; Moffat, A. F. J.

    2000-11-01

    In the framework of our study of wind fluctuations in [WC 8--9]-type central stars of planetary nebulae, we describe spectroscopic observations taken at the Observatoire de Haute-Provence (France), Observatoire du mont Mégantic(Canada), and the European Southern Observatory (Chile). Moving features seen on the top of the CIII5696 and CIV5801/12 emission lines of HD 826 (=NGC 40) and BD +30 3639 are interpreted as outflowing clumps which are radially accelerated outwards in the Wolf-Rayet winds. The amplitudes of the variations range from ~ 5%, up to ~ 25-30% of the adjacent continuum flux, over timescales of hours. The blue-shifted absorption component of the lines exhibiting P-Cygni profiles is significantly more variable than the emission component, which suggests linear sizes for the clumps of ~1 R*. The subpeaks show large measurable velocity shifts during their lifetime: subpeaks (or gaps) on the top of the CIII line generally move towards the nearest line edge in a symmetric fashion in the blue and the red. Kinematic parameters of the blobs have been derived and compared to those observed for massive Wolf-Rayet stars: the wind fragmentation process appears as a purely atmospheric phenomenon, independent of the strong differences between both types of hot star. In addition, the β velocity field is found to possibly underestimate the true gradient within the stellar wind flow. On the whole, the winds are highly stochastically variable on a very short time-scale, which supports a turbulent origin. Unlike the ISM, we see clumps forming and dissipating in real time. The consequences of clumping in hot-star winds are manifold, including substantial constraints on the effective mass-loss rates, and their impact on the surrounding nebula itself.

  2. Non-thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind

    NASA Astrophysics Data System (ADS)

    de la Cita, V. M.; Bosch-Ramon, V.; Paredes-Fortuny, X.; Khangulyan, D.; Perucho, M.

    2017-02-01

    Context. Binaries hosting a massive star and a non-accreting pulsar are powerful non-thermal emitters owing to the interaction of the pulsar and the stellar wind. The winds of massive stars are thought to be inhomogeneous, which could have an impact on the non-thermal emission. Aims: We study numerically the impact of the presence of inhomogeneities or clumps in the stellar wind on the high-energy non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. Methods: We compute the trajectories and physical properties of the streamlines in the shocked pulsar wind without clumps, with a small clump, and with a large clump. This information is used to characterize the injection and the steady state distribution of non-thermal particles accelerated at shocks formed in the pulsar wind. The synchrotron and inverse Compton emission from these non-thermal particles is calculated, accounting also for the effect of gamma-ray absorption through pair creation. A specific study is done for PSR B1259-63/LS2883. Results: When stellar wind clumps perturb the two-wind interaction region, the associated non-thermal radiation in the X-ray band, of synchrotron origin, and in the GeV-TeV band, of inverse Compton origin, is affected by several equally important effects: (i) strong changes in the plasma velocity direction that result in Doppler boosting factor variations; (ii) strengthening of the magnetic field that mainly enhances the synchrotron radiation; (iii) strengthening of the pulsar wind kinetic energy dissipation at the shock, potentially available for particle acceleration; and (iv) changes in the rate of adiabatic losses that affect the lower energy part of the non-thermal particle population. The radiation above 100 GeV detected, presumably, during the post-periastron crossing of the Be star disc in PSR B1259-63/LS2883, can be roughly reproduced assuming that the crossing of the disc is modelled as the encounter with a large inhomogeneity. Conclusions

  3. Closed and open magnetic fields in stellar winds

    SciTech Connect

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

    1983-03-15

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

  4. Model structure of a cosmic-ray mediated stellar or solar wind

    NASA Technical Reports Server (NTRS)

    Lee, M. A.; Axford, W. I.

    1988-01-01

    An idealized hydrodynamic model is presented for the mediation of a free-streaming stellar wind by galactic cosmic rays or energetic particles accelerated at the stellar wind termination shock. The spherically-symmetric stellar wind is taken to be cold; the only body force is the cosmic ray pressure gradient. The cosmic rays are treated as a massless fluid with an effective mean diffusion coefficient k proportional to radial distance r. The structure of the governing equations is investigated both analytically and numerically. Solutions for a range of values of k are presented which describe the deceleration of the stellar wind and a transition to nearly incompressible flow and constant cosmic ray pressure at large r. In the limit of small k the transition steepens to a strong stellar wind termination shock. For large k the stellar wind is decelerated gradually with no shock transition. It is argued that the solutions provide a simple model for the mediation of the solar wind by interstellar ions as both pickup ions and the cosmic ray anomalous component which together dominate the pressure of the solar wind at large r.

  5. Stellar winds with non-WKB Alfven waves 1: Wind models for solar coronal conditions

    NASA Astrophysics Data System (ADS)

    MacGregor, K. B.; Charbonneau, P.

    1994-07-01

    We have constructed numerical models for stationary, wind-type outflows that include treatment of the force produced by propagating Alfven waves. We make no assumptions regarding the relative sizes of the wavelengths of such disturbances and the scale lengths that characterize the variation of the physical properties of the expanding stellar atmosphere. Consequently, our models take account the process of Alfven wave reflection, and provide for dynamical effects arising from the simultaneous presence of outward and inward traveling waves in the wind. For physical conditions like those prevailing in the outer solar corona and wind, we find that even relatively high frequency, short wavelength waves can suffer some reflection from the gradient in Alfven speed at the vase of the flow. Among the consequences of the interaction between outward and inward directed perturbations in the sub-Alfvenic portion of the wind is a reduction in the magnitude of the time-averaged wave force relative to its value in the Wentzel-Kramer-Brillouin (WKB) (i.e., short-wavelenght) limit. As a result, the flow velocities of our models interior to the Alfven radius are smaller than those of corresponding WKB models. For models containing very low frequency, long wavelength waves, a substantial amount of wave reflection can also take place in the super-Alvenic portion of the wind. The resulting modifications to the spatial dependences of the eave magnetic and velocity amplitudes can lead to a wave force whose magnitude at large distances exceeds that of an equivalent WKB solution.

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

    NASA Astrophysics Data System (ADS)

    Ignace, Richard

    1996-05-01

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

  7. Equatorial disk formation around rotating stars due to ram pressure confinement by the stellar wind

    NASA Technical Reports Server (NTRS)

    Bjorkman, J. E.; Cassinelli, J. P.

    1993-01-01

    The axisymmetric 2D supersonic solution of a rotating, radiation-driven stellar wind presently obtained by a simple approximation predicts the formation of a dense equatorial disk, when the star's rotation rate lies above a threshold value that depends on the ratio of the wind's terminal speed to the escape speed of the star. The disk is formed because the trajectories of the wind leaving the stellar surface at high latitudes carry it down to the equatorial plane; there, the material passes through a standing oblique shock atop the disk; it is therefore the ram pressure of the polar wind that compresses and confines the disk.

  8. Wind Variability of B Supergiants. No. 2; The Two-component Stellar Wind of gamma Arae

    NASA Technical Reports Server (NTRS)

    Prinja, R. K.; Massa, D.; Fullerton, A. W.; Howarth, I. D.; Pontefract, M.

    1996-01-01

    The stellar wind of the rapidly rotating early-B supergiant, gamma Ara, is studied using time series, high-resolution IUE spectroscopy secured over approx. 6 days in 1993 March. Results are presented based on an analysis of several line species, including N(N), C(IV), Si(IV), Si(III), C(II), and Al(III). The wind of this star is grossly structured, with evidence for latitude-dependent mass loss which reflects the role of rapid rotation. Independent, co-existing time variable features are identified at low-velocity (redward of approx. -750 km/s) and at higher-speeds extending to approx. -1500 km/s. The interface between these structures is 'defined' by the appearance of a discrete absorption component which is extremely sharp (in velocity space). The central velocity of this 'Super DAC' changes only gradually, over several days, between approx. -400 and -750 km/s in most of the ions. However, its location is shifted redward by almost 400 km/s in Al(III) and C(II), indicating that the physical structure giving rise to this feature has a substantial velocity and ionization jump. Constraints on the relative ionization properties of the wind structures are discussed, together with results based on SEI line-profile-fitting methods. The overall wind activity in gamma Ara exhibits a clear ion dependence, such that low-speed features are promoted in low-ionization species, including Al(III), C(II), and Si(III). We also highlight that - in contrast to most OB stars - there are substantial differences in the epoch-to-epoch time-averaged wind profiles of gamma Ara. We interpret the results in terms of a two-component wind model for gamma Ara, with an equatorially compressed low ionization region, and a high speed, higher-ionization polar outflow. This picture is discussed in the context of the predicted bi-stability mechanism for line-driven winds in rapidly rotating early-B type stars, and the formation of compressed wind regions in rapidly rotating hot stars. The apparent

  9. The Formation of Secondary Stellar Generations in Massive Young Star Clusters from Rapidly Cooling Shocked Stellar Winds

    NASA Astrophysics Data System (ADS)

    Wünsch, R.; Palouš, J.; Tenorio-Tagle, G.; Ehlerová, S.

    2017-01-01

    We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 107 M⊙ and half-mass-radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, ηhe, and the mass loading, ηml. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if ηhe ≲ 10%, which is suggested by the observations. Furthermore, for low ηhe, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

  10. Corotating Interaction Regions in Stellar Winds: Particle Acceleration and Non-thermal Radio Emission in Hot Stars

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1985-01-01

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

  11. YOUNG STELLAR CLUSTERS WITH A SCHUSTER MASS DISTRIBUTION. I. STATIONARY WINDS

    SciTech Connect

    Palous, Jan; Wuensch, Richard; Hueyotl-Zahuantitla, Filiberto; Martinez-Gonzalez, Sergio; Silich, Sergiy; Tenorio-Tagle, Guillermo

    2013-08-01

    Hydrodynamic models for spherically symmetric winds driven by young stellar clusters with a generalized Schuster stellar density profile are explored. For this we use both semi-analytic models and one-dimensional numerical simulations. We determine the properties of quasi-adiabatic and radiative stationary winds and define the radius at which the flow turns from subsonic to supersonic for all stellar density distributions. Strongly radiative winds significantly diminish their terminal speed and thus their mechanical luminosity is strongly reduced. This also reduces their potential negative feedback into their host galaxy interstellar medium. The critical luminosity above which radiative cooling becomes dominant within the clusters, leading to thermal instabilities which make the winds non-stationary, is determined, and its dependence on the star cluster density profile, core radius, and half-mass radius is discussed.

  12. Self-Consistent Hydrodynamical Models For Stellar Winds

    NASA Astrophysics Data System (ADS)

    Boulangier, Jels; Homan, Ward; van Marle, Allard Jan; Decin, Leen; de Koter, Alex

    2016-07-01

    model, arguing this is the dominant cooling factor. Using dissociative H2 cooling allows the ratio of the H-H2 gas mixture to vary, making the cooling efficiency time and space dependent. This will affect local cooling, in turn affecting the hydrodynamics and chemical composition, hereby introducing a feedback loop. Secondly, most significant radiative heating/cooling sources will be introduced to obtain the most realistic temperature structure. Next, dust acceleration will be introduced in the regions cool enough for dust condensation to exists. Hereby laying the basis of our hydrodynamical chemistry model for stellar winds of evolved stars.

  13. The Effect of Magnetic Spots on Stellar Winds and Angular Momentum Loss

    NASA Astrophysics Data System (ADS)

    Cohen, O.; Drake, J. J.; Kashyap, V. L.; Gombosi, T. I.

    2009-07-01

    We simulate the effect of latitudinal variations in the location of star spots, as well as their magnetic field strength, on stellar angular momentum loss (AML) to the stellar wind. We use the Michigan solar corona global magnetohydrodynamic model, which incorporates realistic relation between the magnetic field topology and the wind distribution. We find that the spots' location significantly affects the stellar wind structure, and as a result, the total mass loss rate and AML rate. In particular, we find that the AML rate is controlled by the mass flux when spots are located at low latitudes but is controlled by an increased plasma density between the stellar surface and the Alfvén surface when spots are located at high latitudes. Our results suggest that there might be a feedback mechanism between the magnetic field distribution, wind distribution, AML through the wind, and the motions at the convection zone that generate the magnetic field. This feedback might explain the role of coronal magnetic fields in stellar dynamos.

  14. THE EFFECT OF MAGNETIC SPOTS ON STELLAR WINDS AND ANGULAR MOMENTUM LOSS

    SciTech Connect

    Cohen, O.; Drake, J. J.; Kashyap, V. L.; Gombosi, T. I.

    2009-07-10

    We simulate the effect of latitudinal variations in the location of star spots, as well as their magnetic field strength, on stellar angular momentum loss (AML) to the stellar wind. We use the Michigan solar corona global magnetohydrodynamic model, which incorporates realistic relation between the magnetic field topology and the wind distribution. We find that the spots' location significantly affects the stellar wind structure, and as a result, the total mass loss rate and AML rate. In particular, we find that the AML rate is controlled by the mass flux when spots are located at low latitudes but is controlled by an increased plasma density between the stellar surface and the Alfven surface when spots are located at high latitudes. Our results suggest that there might be a feedback mechanism between the magnetic field distribution, wind distribution, AML through the wind, and the motions at the convection zone that generate the magnetic field. This feedback might explain the role of coronal magnetic fields in stellar dynamos.

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

    NASA Technical Reports Server (NTRS)

    Ahmad, Imad A.; Stencel, Robert E.

    1988-01-01

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

  16. AGN Obscuration from Winds: From Dusty Infrared-Driven to Warm and X-Ray Photoionized

    NASA Technical Reports Server (NTRS)

    Dorodnitsyn, A.; Kallman, T.

    2012-01-01

    We present calculations of AGN winds at approximate parsec scales, along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L=0.05 - 0.6L(sub Edd) the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72? -75? regardless of the luminosity. At L 0.1 the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations (theta) greater than or approximately 70? and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR supported flow. At luminosities less than or equal to 0.1L(sub Edd) episodes of outflow are followed by extended periods when the wind switches to slow accretion.

  17. The SILCC project - III. Regulation of star formation and outflows by stellar winds and supernovae

    NASA Astrophysics Data System (ADS)

    Gatto, Andrea; Walch, Stefanie; Naab, Thorsten; Girichidis, Philipp; Wünsch, Richard; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul C.; Peters, Thomas; Derigs, Dominik; Baczynski, Christian; Puls, Joachim

    2017-04-01

    We study the impact of stellar winds and supernovae on the multiphase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)2 × ±5 kpc and a gas surface density of 10 M⊙ 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 that combine the winds from individual 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 that have lower average masses (102-104.3 M⊙) and form on shorter time-scales (10-3-10 Myr). In particular, we find an anticorrelation of cluster mass and accretion time-scale. Without winds, the star clusters easily grow to larger masses for ∼5 Myr until the first supernova explodes. Overall, the most massive stars provide the most wind energy input, while objects beginning their evolution as B-type stars contribute most of the supernova energy input. A significant outflow from the disc (mass loading ≳1 at 1 kpc) can be launched by thermal gas pressure if more than 50 per cent of the volume near the disc mid-plane can be heated to T > 3 × 105 K. Stellar winds alone cannot create a hot volume-filling phase. The models that are in best agreement with observed star formation rates drive either no outflows or weak outflows.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    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, with turbulent Alfvén wave dissipation as the source of coronal heating and stellar wind acceleration. 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 discussed in a previous paper. 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 structure of the developed stellar wind, and a possible magnetosphere around the Jupiter-mass planet in this system. We find that the process of particle injection into the planetary atmosphere is dominated by the density distribution rather than the velocity profile of the stellar wind. In this context, we predict a maximum exoplanetary radio emission of 12 mJy at 40 MHz in this system, assuming the crossing of a high-density streamer during periastron passage. Furthermore, in combination with the analysis performed in the first paper of this study, we obtain for the first time a fully simulated mass loss-activity relation. This relation is compared and discussed in the context of the previously proposed observational counterpart, derived from astrospheric detections. Finally, we provide a characterisation of the global 3D properties of the stellar wind of these systems, at the inner

  19. Super-Eddington stellar winds driven by near-surface energy deposition

    NASA Astrophysics Data System (ADS)

    Quataert, Eliot; Fernández, Rodrigo; Kasen, Daniel; Klion, Hannah; Paxton, Bill

    2016-05-01

    We develop analytic and numerical models of the properties of super-Eddington stellar winds, motivated by phases in stellar evolution when super-Eddington energy deposition (via, e.g. unstable fusion, wave heating, or a binary companion) heats a region near the stellar surface. This appears to occur in the giant eruptions of luminous blue variables (LBVs), Type IIn supernovae progenitors, classical novae, and X-ray bursts. We show that when the wind kinetic power exceeds Eddington, the photons are trapped and behave like a fluid. Convection does not play a significant role in the wind energy transport. The wind properties depend on the ratio of a characteristic speed in the problem v_crit˜ (dot{E} G)^{1/5} (where dot{E} is the heating rate) to the stellar escape speed near the heating region vesc(rh). For vcrit ≳ vesc(rh), the wind kinetic power at large radii dot{E}_w ˜ dot{E}. For vcrit ≲ vesc(rh), most of the energy is used to unbind the wind material and thus dot{E}_w ≲ dot{E}. Multidimensional hydrodynamic simulations without radiation diffusion using FLASH and one-dimensional hydrodynamic simulations with radiation diffusion using MESA are in good agreement with the analytic predictions. The photon luminosity from the wind is itself super-Eddington but in many cases the photon luminosity is likely dominated by `internal shocks' in the wind. We discuss the application of our models to eruptive mass-loss from massive stars and argue that the wind models described here can account for the broad properties of LBV outflows and the enhanced mass-loss in the years prior to Type IIn core-collapse supernovae.

  20. Detection of the Compressed Primary Stellar Wind in eta Carinae

    NASA Technical Reports Server (NTRS)

    Teodoro, Mairan Macedo; Madura, Thomas I.; Gull, Theodore R.; Corcoran, Michael F.; Hamaguchi, K.

    2014-01-01

    A series of three HST/STIS spectroscopic mappings, spaced approximately one year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving outward from eta Carinae. We identify these arcs with the shell-like structures, seen in the 3D hydrodynamical simulations, formed by compression of the primary wind by the secondary wind during periastron passages.

  1. Theory of Hot Coronae in T Tauri Stellar Winds

    NASA Astrophysics Data System (ADS)

    Kuin, N. P. M.

    Using IUE data of RU Lupi, it is shown that the energy transport into the transition region is most likely by Alfvén waves. It is argued that the chromospheric activity is proportional to the magnetic field strength. A relation between X-ray activity and age is predicted. It is argued that a magnetic field declining with age will cause a transition from a cool, to a warm, to a hot coronal wind. A calculation extending the cool to warm wind model of Hartmann et al. (1981) to a hot coronal wind model is given. The coronal emission measure is computed.

  2. Realistic NLTE Radiative Transfer for Modeling Stellar Winds

    NASA Technical Reports Server (NTRS)

    Bennett, Philip D.

    1999-01-01

    This NASA grant supported the development of codes to solve the non-LTE multi-level spherical radiative transfer problem in the presence of velocity fields. Much of this work was done in collaboration with Graham Harper (CASA, University of Colorado). These codes were developed for application to the cool, low-velocity winds of evolved late-type stars. Particular emphasis was placed on modeling the wind of lambda Velorum (K4 lb), the brightest K supergiant in the sky, based on extensive observations of the ultraviolet spectrum with the HST/GHRS from GO program 5307. Several solution techniques were examined, including the Eddington factor Approach described in detail by Bennett & Harper (1997). An Eddington factor variant of Harper's S-MULTI code (Harper 1994) for stationary atmospheres was developed and implemented, although full convergence was not realized. The ratio of wind terminal velocity to turbulent velocity is large (approx. 0.3-0.5) in these cool star winds so this assumption of stationarity provides reasonable starting models. Final models, incorporating specified wind laws, were converged using the comoving CRD S-MULTI code. Details of the solution procedure were published by Bennett & Harper (1997). Our analysis of the wind of lambda Vel, based on wind absorption superimposed on chromospheric emission lines in the ultraviolet, can be found in Carpenter et al. (1999). In this paper, we compare observed wind absorption features to an exact CRD calculation in the comoving frame, and also to a much quicker, but approximate, method using the SEI (Sobolev with Exact Integration) code of Lamers, Cerruti-Sola, & Perinotto (1987). Carpenter et al. (1999) provide detailed comparisons of the exact CRD and approximate SEI results and discuss when SEI is adequate to use for computing wind line profiles. Unfortunately, the observational material is insufficient to unambiguously determine the wind acceleration law for lambda Vel. Relatively few unblended Fe II lines

  3. Realistic NLTE Radiative Transfer for Modeling Stellar Winds

    NASA Technical Reports Server (NTRS)

    Bennett, Philip D.

    1999-01-01

    This NASA grant supported the development of codes to solve the non-LTE multi-level spherical radiative transfer problem in the presence of velocity fields. Much of this work was done in collaboration with Graham Harper (CASA, University of Colorado). These codes were developed for application to the cool, low-velocity winds of evolved late-type stars. Particular emphasis was placed on modeling the wind of lambda Velorum (K4 lb), the brightest K supergiant in the sky, based on extensive observations of the ultraviolet spectrum with the HST/GHRS from GO program 5307. Several solution techniques were examined, including the Eddington factor Approach described in detail by Bennett & Harper (1997). An Eddington factor variant of Harper's S-MULTI code (Harper 1994) for stationary atmospheres was developed and implemented, although full convergence was not realized. The ratio of wind terminal velocity to turbulent velocity is large (approx. 0.3-0.5) in these cool star winds so this assumption of stationarity provides reasonable starting models. Final models, incorporating specified wind laws, were converged using the comoving CRD S-MULTI code. Details of the solution procedure were published by Bennett & Harper (1997). Our analysis of the wind of lambda Vel, based on wind absorption superimposed on chromospheric emission lines in the ultraviolet, can be found in Carpenter et al. (1999). In this paper, we compare observed wind absorption features to an exact CRD calculation in the comoving frame, and also to a much quicker, but approximate, method using the SEI (Sobolev with Exact Integration) code of Lamers, Cerruti-Sola, & Perinotto (1987). Carpenter et al. (1999) provide detailed comparisons of the exact CRD and approximate SEI results and discuss when SEI is adequate to use for computing wind line profiles. Unfortunately, the observational material is insufficient to unambiguously determine the wind acceleration law for lambda Vel. Relatively few unblended Fe II lines

  4. DETECTION OF THE COMPRESSED PRIMARY STELLAR WIND IN {eta} CARINAE

    SciTech Connect

    Teodoro, M.; Madura, T. I.; Gull, T. R.; Corcoran, M. F.; Hamaguchi, K.

    2013-08-10

    A series of three Hubble Space Telescope/Space Telescope Imaging Spectrograph spectroscopic mappings, spaced approximately one year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving outward from {eta} Carinae. We identify these arcs with the shell-like structures, seen in the three-dimensional hydrodynamical simulations, formed by compression of the primary wind by the secondary wind during periastron passages.

  5. Detection of the Compressed Primary Stellar Wind in eta Carinae*

    NASA Technical Reports Server (NTRS)

    Teodoro, M.; Madura, T. I.; Gull, T. R.; Corcoran, M. F.; Hamaguchi, K.

    2013-01-01

    A series of three Hubble Space Telescope Space Telescope Imaging Spectrograph (HST/STIS) spectroscopic mappings, spaced approximately one year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving outward from ? Carinae. We identify these arcs with the shell-like structures, seen in the 3D hydrodynamical simulations, formed by compression of the primary wind by the secondary wind during periastron passages.

  6. The magnetically controlled stellar wind of HD 21699

    NASA Technical Reports Server (NTRS)

    Brown, D. N.; Shore, S. N.; Sonneborn, G.

    1985-01-01

    The discovery of a magnetically controlled stellar mass outflow in the helium-weak sn star HD 21699 = HR 1063 is reported. IUE observations show that the C IV resonance doublet is variable on the rotational time scale of about 2.5 days, and that there are no other observable spectrum variations in the UV. The magnetic field reverses sign on the rotational time scale. An interpretation of the observations in terms of magnetically structured jets is presented.

  7. DEVIATION OF STELLAR ORBITS FROM TEST PARTICLE TRAJECTORIES AROUND SGr A* DUE TO TIDES AND WINDS

    SciTech Connect

    Psaltis, Dimitrios; Li, Gongjie; Loeb, Abraham E-mail: gli@cfa.harvard.edu

    2013-11-01

    Monitoring the orbits of stars around Sgr A* offers the possibility of detecting the precession of their orbital planes due to frame dragging, of measuring the spin and quadrupole moment of the black hole, and of testing the no-hair theorem. Here we investigate whether the deviations of stellar orbits from test-particle trajectories due to wind mass loss and tidal dissipation of the orbital energy compromise such measurements. We find that the effects of stellar winds are, in general, negligible. On the other hand, for the most eccentric orbits (e > 0.96) for which an optical interferometer, such as GRAVITY, will detect orbital plane precession due to frame dragging, the tidal dissipation of orbital energy occurs at timescales comparable to the timescale of precession due to the quadrupole moment of the black hole. As a result, this non-conservative effect is a potential source of systematic uncertainty in testing the no-hair theorem with stellar orbits.

  8. Deviation of Stellar Orbits from Test Particle Trajectories around Sgr A* Due to Tides and Winds

    NASA Astrophysics Data System (ADS)

    Psaltis, Dimitrios; Li, Gongjie; Loeb, Abraham

    2013-11-01

    Monitoring the orbits of stars around Sgr A* offers the possibility of detecting the precession of their orbital planes due to frame dragging, of measuring the spin and quadrupole moment of the black hole, and of testing the no-hair theorem. Here we investigate whether the deviations of stellar orbits from test-particle trajectories due to wind mass loss and tidal dissipation of the orbital energy compromise such measurements. We find that the effects of stellar winds are, in general, negligible. On the other hand, for the most eccentric orbits (e > 0.96) for which an optical interferometer, such as GRAVITY, will detect orbital plane precession due to frame dragging, the tidal dissipation of orbital energy occurs at timescales comparable to the timescale of precession due to the quadrupole moment of the black hole. As a result, this non-conservative effect is a potential source of systematic uncertainty in testing the no-hair theorem with stellar orbits.

  9. Colliding planetary and stellar winds: charge exchange and transit spectroscopy in neutral hydrogen

    NASA Astrophysics Data System (ADS)

    Tremblin, Pascal; Chiang, Eugene

    2013-01-01

    When transiting their host stars, hot Jupiters absorb about 10 per cent of the light in the wings of the stellar Lyman α emission line. The absorption occurs at wavelengths Doppler-shifted from line centre by ±100 km s-1 - larger than the thermal speeds with which partially neutral, ˜104 K hydrogen escapes from hot Jupiter atmospheres. It has been proposed that the absorption arises from ˜106 K hydrogen from the host stellar wind, made momentarily neutral by charge exchange with planetary H i. The ±100 km s-1 velocities would then be attributed to the typical velocity dispersions of protons in the stellar wind - as inferred from spacecraft measurements of the solar wind. To test this proposal, we perform 2D hydrodynamic simulations of colliding hot Jupiter and stellar winds, augmented by a chemistry module to compute the amount of hot neutral hydrogen produced by charge exchange. We observe the contact discontinuity where the two winds meet to be Kelvin-Helmholtz unstable. The Kelvin-Helmholtz instability mixes the two winds; in the mixing layer, charge exchange reactions establish, within tens of seconds, a chemical equilibrium in which the neutral fraction of hot stellar hydrogen equals the neutral fraction of cold planetary hydrogen (about 20 per cent). In our simulations, enough hot neutral hydrogen is generated to reproduce the transit observations, and the amount of absorption converges with both spatial resolution and time. Our calculations support the idea that charge transfer between colliding winds correctly explains the Lyman α transit observations - modulo the effects of magnetic fields, which we do not model but which may suppress mixing. Other neglected effects include, in order of decreasing importance, rotational forces related to orbital motion, gravity and stellar radiation pressure; we discuss quantitatively the errors introduced by our approximations. How hot stellar hydrogen cools when it collides with cold planetary hydrogen is also

  10. Neutral stellar winds that drive bipolar outflows in low-mass protostars

    NASA Technical Reports Server (NTRS)

    Lizano, Susana; Heiles, Carl; Koo, Bon-Ghul; Shu, Frank H.; Rodriguez, Luis F.

    1988-01-01

    The Arecibo radio telescope at the 21-cm line of atomic hydrogen has been used to detect a neutral atomic wind in the bipolar flow source HH 7-11. An atomic mass of about 0.015 solar associated with the rapidly flowing gas is deduced. The stellar mass-loss rate is roughly 3 x 10 to the -6th solar mass/yr if the crossing time of the decelerating wind is 5000 yr. The excess emission in the H I line core gives a total duration of the outflow of about 70,000 yr. A detailed analysis of the H I line shape yields a reasonable deceleration rate for the atomic wind if the stellar wind continuously entrains ambient molecular gas as it propagates from the protostar. A stellar wind with the described characteristics and a terminal velocity of 170 km/s would be more than sufficient to drive the known extended CO bipolar outflow in HH 7-11.

  11. Neutral stellar winds that drive bipolar outflows in low-mass protostars

    NASA Technical Reports Server (NTRS)

    Lizano, Susana; Heiles, Carl; Koo, Bon-Ghul; Shu, Frank H.; Rodriguez, Luis F.

    1988-01-01

    The Arecibo radio telescope at the 21-cm line of atomic hydrogen has been used to detect a neutral atomic wind in the bipolar flow source HH 7-11. An atomic mass of about 0.015 solar associated with the rapidly flowing gas is deduced. The stellar mass-loss rate is roughly 3 x 10 to the -6th solar mass/yr if the crossing time of the decelerating wind is 5000 yr. The excess emission in the H I line core gives a total duration of the outflow of about 70,000 yr. A detailed analysis of the H I line shape yields a reasonable deceleration rate for the atomic wind if the stellar wind continuously entrains ambient molecular gas as it propagates from the protostar. A stellar wind with the described characteristics and a terminal velocity of 170 km/s would be more than sufficient to drive the known extended CO bipolar outflow in HH 7-11.

  12. Spectroscopy of the Stellar Wind in the Cygnus X-1 System

    NASA Technical Reports Server (NTRS)

    Miskovicova, Ivica; Hanke, Manfred; Wilms, Joern; Nowak, Michael A.; Pottschmidt, Katja; Schultz, Norbert

    2010-01-01

    The X-ray luminosity of black holes is produced through the accretion of material from their companion stars. Depending on the mass of the donor star, accretion of the material falling onto the black hole through the inner Lagrange point of the system or accretion by the strong stellar wind can occur. Cygnus X-1 is a high mass X-ray binary system, where the black hole is powered by accretion of the stellar wind of its supergiant companion star HDE226868. As the companion is close to filling its Roche lobe, the wind is not symmetric, but strongly focused towards the black hole. Chandra-HETGS observations allow for an investigation of this focused stellar wind, which is essential to understand the physics of the accretion flow. We compare observations at the distinct orbital phases of 0.0, 0.2, 0.5 and 0.75. These correspond to different lines of sights towards the source, allowing us to probe the structure and the dynamics of the wind.

  13. Cosmic ray-modified stellar winds. I - Solution topologies and singularities

    NASA Technical Reports Server (NTRS)

    Ko, C. M.; Webb, G. M.

    1987-01-01

    In the present two-fluid hydrodynamical model for stellar wind flow modification due to its interaction with Galactic cosmic rays, these rays are coupled to the stellar wind by either hydromagnetic wave scattering or background flow irregularity propagation. The background flow is modified by the cosmic rays via their pressure gradient. The system of equations used possesses a line of singularities in (r, u, P sub c)-space, or a two-dimensional hypersurface of singularities in (r, u, P sub c, dP sub c/dr)-space, where r, u, and P sub c are respectively the radial distance from the star, the radial wind flow speed, and the cosmic ray pressure. The singular points may be nodes, foci, or saddle points.

  14. The slow ionized wind and rotating disklike system that are associated with the high-mass young stellar object G345.4938+01.4677

    SciTech Connect

    Guzmán, Andrés E.; Garay, Guido; Bronfman, Leonardo; Mardones, Diego; Rodríguez, Luis F.; Moran, James; Brooks, Kate J.; Nyman, Lars-Åke; Sanhueza, Patricio

    2014-12-01

    We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40α, H42α, and H50β emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562–3959. The HRLs exhibit Voigt profiles, which is a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need for a high-velocity component. The Lorentzian line wings imply electron densities of 5 × 10{sup 7} cm{sup –3} on average. In addition, we detect SO and SO{sub 2} emission arising from a compact (∼3000 AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient that is perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.

  15. Modelling accretion disc and stellar wind interactions: the case of Sgr A*

    NASA Astrophysics Data System (ADS)

    Christie, I. M.; Petropoulou, M.; Mimica, P.; Giannios, D.

    2016-07-01

    Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disc, the ram and thermal pressures of the disc terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in ˜108 cm s-1 range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericentre passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly a month long X-ray flare with a peak luminosity of L ≈ 4 × 1033 erg s-1 for a stellar mass-loss rate, disc number density, and thermal pressure strength of dot{M}_w= 10^{-7} M_{⊙} yr^{-1}, nd = 105 cm-3, and α = 0.1, respectively. This peak luminosity is comparable to the quiescent X-ray emission detected from Sgr A* and is within the detection capabilities of current X-ray observatories. Its detection could constrain the density and thickness of the disc at a distance of ˜3000 gravitational radii from the supermassive black hole.

  16. Modelling accretion disc and stellar wind interactions: the case of Sgr A.

    PubMed

    Christie, I M; Petropoulou, M; Mimica, P; Giannios, D

    2016-07-01

    Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disc, the ram and thermal pressures of the disc terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in ∼10(8) cm s(-1) range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericentre passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly a month long X-ray flare with a peak luminosity of L ≈ 4 × 10(33) erg s(-1) for a stellar mass-loss rate, disc number density, and thermal pressure strength of [Formula: see text], nd = 10(5) cm(-3), and α = 0.1, respectively. This peak luminosity is comparable to the quiescent X-ray emission detected from Sgr A* and is within the detection capabilities of current X-ray observatories. Its detection could constrain the density and thickness of the disc at a distance of ∼3000 gravitational radii from the supermassive black hole.

  17. Using a Neutron Star as a Stellar Wind Probe

    NASA Astrophysics Data System (ADS)

    Gregory, P. C.; Neish, C.

    2002-12-01

    LS I+61o303 is a remarkable X-ray and γ -ray emitting Be + neutron star binary, with periodic (26.5 day) radio outbursts. A recent Bayesian analysis demonstrates that the orbital phase and peak flux density of the radio outbursts exhibit a 4.6 year periodic modulation. We present a model that accounts for the radio properties of LS I+61o303 in terms of variable accretion by the neutron star in an eccentric orbit embedded within the dense equatorial wind from the rapidly rotating Be star. The neutron star thus acts as a probe of the wind speed and density. The analysis indicates that the 4.6 year modulation in radio properties results from an outward moving density enhancement or shell in the Be star equatorial disk. We propose that each new shell ejection may be triggered by the interaction of a short lived relativistic wind (ejector phase) from the neutron star, with the rapidly rotating Be star. Our best estimates of the mass accretion rate of the neutron star are in the range ~ 0.001 to ~ 0.01 of the Eddington accretion limit. This translates to an expected luminosity range of ~ 1035 to ~ 1036 ergs s-1 which is comparable to estimates of the total X-ray and γ -ray luminosity for LS I +61o 303. This research was supported in part by a grant from the Canadian Natural Sciences and Engineering Research Council at the University of British Columbia.

  18. Latitude-Dependent Effects in the Stellar Wind of Eta Carinae

    NASA Technical Reports Server (NTRS)

    Smith, Nathan; Davidson, Kris; Gull, Theodore R.; Ishibashi, Kazunori; Hillier, D. John

    2002-01-01

    The Homunculus reflection nebula around eta Carinae provides the rare opportunity to observe the spectrum of a star from more than one direction. In the case of eta Car, the nebula's geometry is known well enough to infer how wind profiles vary with latitude. We present STIS spectra of several positions in the Homunculus, showing directly that eta Car has an aspherical and axisymmetric stellar wind. P Cygni absorption in Balmer lines depends on latitude, with relatively high velocities and strong absorption near the polar axis. Stronger absorption at high latitudes is surprising, and it suggests higher mass flux toward the poles, perhaps resulting from equatorial gravity darkening on a rotating star. Reflected profiles of He I lines are more puzzling, and offer clues to eta Car's wind geometry and ionization structure. During eta Car's high-excitation state in March 2000, the wind had a fast, dense polar wind, with higher ionization at low latitudes. Older STIS data obtained since 1998 reveal that this global stellar-wind geometry changes during eta Car's 5.5 year cycle, and may suggest that this star s spectroscopic events are shell ejections. Whether or not a companion star triggers these outbursts remains ambiguous. The most dramatic changes in the wind occur at low latitudes, while the dense polar wind remains relatively undisturbed during an event. The apparent stability of the polar wind also supports the inferred bipolar geometry. The wind geometry and its variability have critical implications for understanding the 5.5 year cycle and long-term variability, but do not provide a clear alternative to the binary hypothesis for generating eta Car s X-rays.

  19. A model for the thermal radio-continuum emission from radiative shocks in colliding stellar winds

    NASA Astrophysics Data System (ADS)

    Montes, G.; González, R. F.; Cantó, J.; Pérez-Torres, M. A.; Alberdi, A.

    2011-07-01

    Context. In massive-star binary systems, the interaction of the strong stellar winds results in a wind collision region (WCR) between the stars, which is limited by two shock fronts. Besides the nonthermal emission resulting from the shock acceleration, these shocks emit thermal (free-free) radiation detectable at radio frequencies that increase the expected emission from the stellar winds. Observations and theoretical studies of these sources show that the shocked gas is an important, but not dominant, contributor to the total emission in wide binary systems, while it plays a very substantial role in close binaries. Aims: The interaction of two isotropic stellar winds is studied in order to calculate the free-free emission from the WCR. The effects of the binary separation and the wind momentum ratio on the emission from the wind-wind interaction region are investigated. Methods: We developed a semi-analytical model for calculating the thermal emission from colliding stellar winds. Assuming radiative shocks for the compressed layer, which are expected in close binaries, we obtained the emission measure of the thin shell. Then, we computed the total optical depth along each line of sight to obtain the emission from the whole configuration. Results: Here, we present predictions of the free-free emission at radio frequencies from analytic, radiative shock models in colliding wind binaries. It is shown that the emission from the WCR mainly arises from the optically thick region of the compressed layer and scales as ~D4/5, where D is the binary separation. The predicted flux density Sν from the WCR becomes more important as the frequency ν increases, showing higher spectral indices than the expected 0.6 value (Sν ∝ να, where α = 0.6) from the unshocked winds. We also investigate the emission from short-period WR+O systems calculated with our analytic formulation. In particular, we apply the model to the binary systems WR 98 and WR 113 and compare our results

  20. Simulations of stellar/pulsar-wind interaction along one full orbit

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

    Context. The winds from a non-accreting pulsar and a massive star in a binary system collide forming a bow-shaped shock structure. The Coriolis force induced by orbital motion deflects the shocked flows, strongly affecting their dynamics. Aims: We study the evolution of the shocked stellar and pulsar winds on scales in which the orbital motion is important. Potential sites of non-thermal activity are investigated. Methods: Relativistic hydrodynamical simulations in two dimensions, performed with the code PLUTO and using the adaptive mesh refinement technique, are used to model interacting stellar and pulsar winds on scales ~80 times the distance between the stars. The hydrodynamical results suggest the suitable locations of sites for particle acceleration and non-thermal emission. Results: In addition to the shock formed towards the star, the shocked and unshocked components of the pulsar wind flowing away from the star terminate by means of additional strong shocks produced by the orbital motion. Strong instabilities lead to the development of turbulence and an effective two-wind mixing in both the leading and trailing sides of the interaction structure, which starts to merge with itself after one orbit. The adopted moderate pulsar-wind Lorentz factor already provides a good qualitative description of the phenomena involved in high-mass binaries with pulsars, and can capture important physical effects that would not appear in non-relativistic treatments. Conclusions: Simulations show that shocks, instabilities, and mass-loading yield efficient mass, momentum, and energy exchanges between the pulsar and the stellar winds. This renders a rapid increase in the entropy of the shocked structure, which will likely be disrupted on scales beyond the simulated ones. Several sites of particle acceleration and low- and high-energy emission can be identified. Doppler boosting will have significant and complex effects on radiation. A movie of the simulation is available in

  1. THE GALACTIC CENTER CLOUD G2-A YOUNG LOW-MASS STAR WITH A STELLAR WIND

    SciTech Connect

    Scoville, N.; Burkert, A.

    2013-05-10

    We explore the possibility that the G2 gas cloud falling in toward SgrA* is the mass-loss envelope of a young T Tauri star. As the star plunges to smaller radius at 1000-6000 km s{sup -1}, a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA*. For a stellar mass-loss rate of 4 Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1} and wind velocity 100 km s{sup -1}, the bow shock will have an emission measure (EM = n {sup 2} vol) at a distance {approx}10{sup 16} cm, similar to that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA*, while the latter will have increasing emission at lesser distances. In this model, the star and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter ({approx}3 AU for a stellar mass of 2 M{sub Sun }). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.

  2. A Comparison between Physics-based and Polytropic MHD Models for Stellar Coronae and Stellar Winds of Solar Analogs

    NASA Astrophysics Data System (ADS)

    Cohen, O.

    2017-02-01

    The development of the Zeeman–Doppler Imaging (ZDI) technique has provided synoptic observations of surface magnetic fields of low-mass stars. This led the stellar astrophysics community to adopt modeling techniques that have been used in solar physics using solar magnetograms. However, many of these techniques have been neglected by the solar community due to their failure to reproduce solar observations. Nevertheless, some of these techniques are still used to simulate the coronae and winds of solar analogs. Here we present a comparative study between two MHD models for the solar corona and solar wind. The first type of model is a polytropic wind model, and the second is the physics-based AWSOM model. We show that while the AWSOM model consistently reproduces many solar observations, the polytropic model fails to reproduce many of them, and in the cases where it does, its solutions are unphysical. Our recommendation is that polytropic models, which are used to estimate mass-loss rates and other parameters of solar analogs, must first be calibrated with solar observations. Alternatively, these models can be calibrated with models that capture more detailed physics of the solar corona (such as the AWSOM model) and that can reproduce solar observations in a consistent manner. Without such a calibration, the results of the polytropic models cannot be validated, but they can be wrongly used by others.

  3. Stellarators

    SciTech Connect

    Hartmann, D.A.

    2004-03-15

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

  4. Interacting supernovae from photoionization-confined shells around red supergiant stars.

    PubMed

    Mackey, Jonathan; Mohamed, Shazrene; Gvaramadze, Vasilii V; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M-A; Moriya, Takashi J; Neilson, Hilding R

    2014-08-21

    Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction.

  5. Interacting supernovae from photoionization-confined shells around red supergiant stars

    NASA Astrophysics Data System (ADS)

    Mackey, Jonathan; Mohamed, Shazrene; Gvaramadze, Vasilii V.; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M.-A.; Moriya, Takashi J.; Neilson, Hilding R.

    2014-08-01

    Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction.

  6. A STELLAR WIND ORIGIN FOR THE G2 CLOUD: THREE-DIMENSIONAL NUMERICAL SIMULATIONS

    SciTech Connect

    De Colle, Fabio; Raga, A. C.; Contreras-Torres, Flavio F.; Toledo-Roy, Juan C.

    2014-07-10

    We present three-dimensional, adaptive mesh refinement simulations of G2, a cloud of gas moving in a highly eccentric orbit toward the galactic center. We assume that G2 originates from a stellar wind interacting with the environment of the Sgr A* black hole. The stellar wind forms a cometary bubble which becomes increasingly elongated as the star approaches periastron. A few months after periastron passage, streams of material begin to accrete on the central black hole with accretion rates M-dot ∼10{sup −8} M {sub ☉} yr{sup –1}. Predicted Brγ emission maps and position-velocity diagrams show an elongated emission resembling recent observations of G2. A large increase in luminosity is predicted by the emission coming from the shocked wind region during periastron passage. The observations, showing a constant Brγ luminosity, remain puzzling, and are explained here assuming that the emission is dominated by the free-wind region. The observed Brγ luminosity (∼8 × 10{sup 30} erg s{sup –1}) is reproduced by a model with a v{sub w} = 50 km s{sup –1} wind velocity and a 10{sup –7} M {sub ☉} yr{sup –1} mass-loss rate if the emission comes from the shocked wind. A faster and less dense wind reproduces the Brγ luminosity if the emission comes from the inner, free-wind region. The extended cometary wind bubble, largely destroyed by the tidal interaction with the black hole, reforms a few years after periastron passage. As a result, the Brγ emission is more compact after periastron passage.

  7. Newborn stars and stellar winds in Barnard 228

    NASA Technical Reports Server (NTRS)

    Heyer, Mark H.; Graham, J. A.

    1989-01-01

    Imaging and spectroscopic observations of premain-sequence stars in the B228 molecular cloud have identified three sites of extended, shock-excited nebulosity. A highly collimated, blueshifted jet is associated with the T Tauri star Sz68 (CoD -33:10685 deg). A candidate Herbig-Haro object is found near Sz68 and the T Tauri star Sz69. A third region of shock-excited nebulosity is identified near the embedded newborn star IRAS 15398-3359. IR excesses observed toward these stellar sources may imply a relationship between outflow activity and the presence of a circumstellar disk. Only one of the two outflow sources with well-defined orientations is aligned with the large-scale, magnetic-field geometry of the cloud in contrast to the global alignment of outflows in the Taurus cloud complex. Data for three previously unidentified emission-line stars are presented. A faint 18th magnitude dMe star located 48 arcsecs west of Sz68 is identified.

  8. Newborn stars and stellar winds in Barnard 228

    NASA Astrophysics Data System (ADS)

    Heyer, Mark H.; Graham, J. A.

    1989-09-01

    Imaging and spectroscopic observations of premain-sequence stars in the B228 molecular cloud have identified three sites of extended, shock-excited nebulosity. A highly collimated, blueshifted jet is associated with the T Tauri star Sz68 (CoD -33:10685 deg). A candidate Herbig-Haro object is found near Sz68 and the T Tauri star Sz69. A third region of shock-excited nebulosity is identified near the embedded newborn star IRAS 15398-3359. IR excesses observed toward these stellar sources may imply a relationship between outflow activity and the presence of a circumstellar disk. Only one of the two outflow sources with well-defined orientations is aligned with the large-scale, magnetic-field geometry of the cloud in contrast to the global alignment of outflows in the Taurus cloud complex. Data for three previously unidentified emission-line stars are presented. A faint 18th magnitude dMe star located 48 arcsecs west of Sz68 is identified.

  9. Radiative waves in stellar winds with line scattering

    NASA Astrophysics Data System (ADS)

    Thomas, Timon; Feldmeier, Achim

    2016-08-01

    Photospheric radiation can drive winds from hot, massive stars by direct momentum transfer through scattering in bound-bound transitions of atmospheric ions. The line radiation force should cause a new radiative wave mode. The dispersion relation from perturbations of the line force was analysed so far either in Sobolev approximation or for pure line absorption. The former does not include the line-driven instability, and the latter cannot account for upstream propagating, radiative waves. We consider a non-Sobolev line force that includes scattering in a simplified way, accounting however for the important line-drag effect. We derive a new dispersion relation for radiative waves, and analyse wave propagation using Fourier methods, and by numerical solution of an integro-differential equation. The existence of an upstream propagating, dispersive radiative wave mode is demonstrated.

  10. TESTING MODELS OF ACCRETION-DRIVEN CORONAL HEATING AND STELLAR WIND ACCELERATION FOR T TAURI STARS

    SciTech Connect

    Cranmer, Steven R.

    2009-11-20

    Classical T Tauri stars are pre-main-sequence objects that undergo simultaneous accretion, wind outflow, and coronal X-ray emission. The impact of plasma on the stellar surface from magnetospheric accretion streams is likely to be a dominant source of energy and momentum in the upper atmospheres of these stars. This paper presents a set of models for the dynamics and heating of three distinct regions on T Tauri stars that are affected by accretion: (1) the shocked plasmas directly beneath the magnetospheric accretion streams, (2) stellar winds that are accelerated along open magnetic flux tubes, and (3) closed magnetic loops that resemble the Sun's coronal active regions. For the loops, a self-consistent model of coronal heating was derived from numerical simulations of solar field-line tangling and turbulent dissipation. Individual models are constructed for the properties of 14 well-observed stars in the Taurus-Auriga star-forming region. Predictions for the wind mass-loss rates are, on average, slightly lower than the observations, which suggests that disk winds or X-winds may also contribute to the measured outflows. For some of the stars, however, the modeled stellar winds do appear to contribute significantly to the measured mass fluxes. Predictions for X-ray luminosities from the shocks and loops are in general agreement with existing observations. The stars with the highest accretion rates tend to have X-ray luminosities dominated by the high-temperature (5-10 MK) loops. The X-ray luminosities for the stars having lower accretion rates are dominated by the cooler accretion shocks.

  11. THERMAL X-RAY EMISSION FROM THE SHOCKED STELLAR WIND OF PULSAR GAMMA-RAY BINARIES

    SciTech Connect

    Zabalza, V.; Paredes, J. M.; Bosch-Ramon, V.

    2011-12-10

    Gamma-ray-loud X-ray binaries are binary systems that show non-thermal broadband emission from radio to gamma rays. If the system comprises a massive star and a young non-accreting pulsar, their winds will collide producing broadband non-thermal emission, most likely originated in the shocked pulsar wind. Thermal X-ray emission is expected from the shocked stellar wind, but until now it has neither been detected nor studied in the context of gamma-ray binaries. We present a semi-analytic model of the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries, and find that the thermal X-ray emission increases monotonically with the pulsar spin-down luminosity, reaching luminosities of the order of 10{sup 33} erg s{sup -1}. The lack of thermal features in the X-ray spectrum of gamma-ray binaries can then be used to constrain the properties of the pulsar and stellar winds. By fitting the observed X-ray spectra of gamma-ray binaries with a source model composed of an absorbed non-thermal power law and the computed thermal X-ray emission, we are able to derive upper limits on the spin-down luminosity of the putative pulsar. We applied this method to LS 5039, the only gamma-ray binary with a radial, powerful wind, and obtain an upper limit on the pulsar spin-down luminosity of {approx}6 Multiplication-Sign 10{sup 36} erg s{sup -1}. Given the energetic constraints from its high-energy gamma-ray emission, a non-thermal to spin-down luminosity ratio very close to unity may be required.

  12. A radiation-driven stellar wind model with a line force cutoff

    NASA Technical Reports Server (NTRS)

    Abbott, Mark J.; Friend, David B.

    1989-01-01

    This paper presents a model for a radiation-driven stellar wind in which the driving force is abruptly cut off at an adjustable distance from the star. The model is intended to give a first approximation of the effects of ionizing shocks in a stellar wind on the terminal velocity and mass-loss rate. As expected, the wind velocity is found to decrease after the line force is cut off. The terminal velocity depends directly on the velocity of the wind at the point where the driving force is cut off. The mass-loss rate is found to be unaffected as long as the cutoff is outside the critical point of the flow. The model is applied to the star Tau Sco, a strong X-ray source with an anomalously low terminal velocity. It is shown that this low terminal velocity can be caused by a cutoff of the line force at a distance which is consistent with the idea that the observed X-rate emission is produced by shocks in the wind.

  13. Faraday Rotation Distributions from Stellar Magnetism in Wind-blown Bubbles

    NASA Astrophysics Data System (ADS)

    Ignace, R.; Pingel, N. M.

    2013-03-01

    Faraday rotation is a valuable tool for detecting magnetic fields. Here, the technique is considered in relation to wind-blown bubbles. In the context of spherical winds with azimuthal or split monopole stellar magnetic field geometries, we derive maps of the distribution of position angle (P.A.) rotation of linearly polarized radiation across projected bubbles. We show that the morphology of maps for split monopole fields are distinct from those produced by the toroidal field topology; however, the toroidal case is the one most likely to be detectable because of its slower decline in field strength with distance from the star. We also consider the important case of a bubble with a spherical sub-volume that is field-free to approximate crudely a "swept-up" wind interaction between a fast wind (or possibly a supernova ejecta shell) overtaking a slower magnetized wind from a prior state of stellar evolution. With an azimuthal field, the resultant P.A. map displays two arc-like features of opposite rotation measure, similar to observations of the supernova remnant G296.5+10.0. We illustrate how P.A. maps can be used to disentangle Faraday rotation contributions made by the interstellar medium versus the bubble. Although our models involve simplifying assumptions, their consideration leads to a number of general robust conclusions for use in the analysis of radio mapping data sets.

  14. Analytical solutions of stellar winds in B-A type supergiants stars

    NASA Astrophysics Data System (ADS)

    Araya, Ignacio; Cure, Michel

    2013-06-01

    An analytical solution for the δ-slow hydrodynamic solution (Cure et al. 2011) in B-A type supergiants stars is developed. The methodology is based on the analytical solutions of a) Villata (1992), which is described in terms of the stellar and wind parameters and b) Muller & Vink (2008), which is described in terms of fitting parameters from a numerical solution (hydrodynamic). These methodologies only apply for fast solutions, for that reason the line acceleration term (gL) of Muller & Vink method is modified in order to obtain an analytical solution for the δ-slow solution. To find a relationship between the parameters from the fit and the stellar and wind parameters, a computational grid, based on the grid of stellar models from Ekstrom et al. (2012), is created for B-A type supergiants stars with δ-slow hydrodynamic solution. Finally, an analytical solution for B-A type supergiants stars is obtained based on the Lambert W function (Corless et al. 1996). Comparing with the numerical solutions, the terminal velocity has a median relative error below 4% and the mass loss rate has a median relative error below 5%. In addition, we calculated the wind-momentum luminosity relationship (WLR) with the models from the computational grid and compared with the observations, showing a very good agreement.

  15. Spin Evolution of Accreting Young Stars. II. Effect of Accretion-powered Stellar Winds

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  16. The stellar wind as a key to the understanding of the spectral activity of IN Com

    NASA Astrophysics Data System (ADS)

    Kozlova, O. V.; Alekseev, I. Yu.

    2014-06-01

    We present long-term spectral observations ( R = 20000) of IN Com in the region of the Hα, Hβ, and He I 5876 lines. One distinguishing characteristic of the stellar spectrum is the presence in the Hα line of an extended two-component emission with limits up to ±400 km/s. Emission parameters show the rotation modulation with the stellar rotation period and a significant variability on the long-term scale. Similar emissions are also observed in the Hβ and He I 5876 lines. Our results allow us to conclude that observational emission profiles are formed in an optically thin hot gas. This is a result of the presence of a circumstellar gas disk around IN Com. Its size does not exceed several stellar radii. The material for the disk is supported by the stellar wind from IN Com. The detected variability of Hα-emission parameters shows a clear connection with the photopolarimetric activity of the star. This fact allows us to associate the long-term spectral variability with cycles of stellar activity of IN Com.

  17. The effects of the stellar wind and orbital motion on the jets of high-mass microquasars

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    Context. High-mass microquasar jets propagate under the effect of the wind from the companion star, and the orbital motion of the binary system. The stellar wind and the orbit may be dominant factors determining the jet properties beyond the binary scales. Aims: This is an analytical study, performed to characterise the effects of the stellar wind and the orbital motion on the jet properties. Methods: Accounting for the wind thrust transferred to the jet, we derive analytical estimates to characterise the jet evolution under the impact of the stellar wind. We include the Coriolis force effect, induced by orbital motion and enhanced by the wind's presence. Large-scale evolution of the jet is sketched, accounting for wind-to-jet thrust transfer, total energy conservation, and wind-jet flow mixing. Results: If the angle of the wind-induced jet bending is larger than its half-opening angle, the following is expected: (i) a strong recollimation shock; (ii) bending against orbital motion, caused by Coriolis forces and enhanced by the wind presence; and (iii) non-ballistic helical propagation further away. Even if disrupted, the jet can re-accelerate due to ambient pressure gradients, but wind entrainment can weaken this acceleration. On large scales, the opening angle of the helical structure is determined by the wind-jet thrust relation, and the wind-loaded jet flow can be rather slow. Conclusions: The impact of stellar winds on high-mass microquasar jets can yield non-ballistic helical jet trajectories, jet partial disruption and wind mixing, shocks, and possibly non-thermal emission. Among other observational diagnostics, such as radiation variability at any band, the radio morphology on milliarcsecond scales can be informative on the wind-jet interaction.

  18. On the Origin and Evolution of Stellar Chromospheres, Coronae and Winds

    NASA Technical Reports Server (NTRS)

    Musielak, Z. E.

    2000-01-01

    This grant was awarded by NASA to The University of Alabama in Huntsville (UAH) to construct state-of-the-art, theoretical, two-component, chromospheric models for single stars of different spectral types and different evolutionary status. In our proposal, we suggested to use these models to predict the level of the "basal flux", the observed range of variation of chromospheric activity for a given spectral type, and the decrease of this activity with stellar age. In addition, for red giants and supergiants, we also proposed to construct self-consistent, purely theoretical wind models, and used these models to investigate the origin of "dividing lines" in the H-R diagram. In the following, we describe our completed work. We have accomplished the first main goal of our proposal by constructing first purely theoretical, time-dependent and two-component models of stellar chromospheres.1 The models require specifying only three basic stellar parameters, namely, the effective temperature, gravity and rotation rate, and they take into account non-magnetic and magnetic regions in stellar chromospheres. The non-magnetic regions are heated by acoustic waves generated by the turbulent convection in the stellar subphotospheric layers. The magnetic regions are identified with magnetic flux tubes uniformly distributed over the entire stellar surface and they are heated by longitudinal tube waves generated by turbulent motions in the subphotospheric and photospheric layers. The coverage of stellar surface by magnetic regions (the so-called filling factor) is estimated for a given rotation rate from an observational relationship. The constructed models are time-dependent and are based on the energy balance between the amount of mechanical energy supplied by waves and radiative losses in strong Ca II and Mg II emission lines. To calculate the amount of wave energy in the non-magnetic regions, we have used the Lighthill-Stein theory for sound generation.

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

    NASA Astrophysics Data System (ADS)

    Brown, Timothy M.

    2015-08-01

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

  20. Learning from our Sun: The Interaction of Stellar with Interstellar Winds

    NASA Astrophysics Data System (ADS)

    Opher, M.; Liewer, P. C.; Velli, M.; Gombosi, T. I.; Manchester, W.; DeZeeuw, D. L.; Toth, G.; Sokolov, I. V.

    2004-05-01

    Stars have winds which interact with the interstellar medium. The intensity of the winds can be 10 million times greater than that of the solar wind. The magnetic fields of these stars can be orders of magnitude greater than that of the Sun. The rotation periods can be appreciably different from that of the Sun. A detailed description of the interaction of stellar winds with the interstellar winds has never been made. The interaction between the Sun and Interstellar Medium creates three major structures: Termination Shock, Heliopause and Bow Shock. Recently, we found (Opher et al. 2003, 2004) that beyond the region where the solar wind become subsonic, the Termination Shock, a jet-sheet structure forms in the equatorial plane of the Sun rotation axis. This structure forms due to the compression of the solar magnetic field by the interstellar wind. The structure of the jet-sheet resembles a the "brim of a baseball cap"- it extends beyond the Termination Shock for 150 AU (almost touching the Bow Shock) and has a width of 10AU. This result is due to a novel application of a state-of-art 3D Magnetohydrodynamic (MHD) code with a highly refined grid (0.75 AU 4 orders of magnitude smaller than the physical dimensions of the system). The jet-sheet is unstable and oscillates up and down due to a velocity shear instability. We showed that the sinuous mode is the dominant mode that develops into a velocity-shear-instability with a growth rate of 0.027 years-1. We are the first to predict the formation of this structure at the equatorial region in the interaction of magnetized rotating star and an external wind (for a stellar rotation and magnetic field axis aligned). In this work, we extend our previous solar studies and investigate the effect in other solar-like stars. We present the dependence of the jet-sheet structure and the velocity-shear instability on the star mass-loss rate and magnetic field. We discuss further applications to other stellar wind interactions and the

  1. Phase-Dependent Changes in O VI and Other Stellar Wind Lines in SMC X-1

    NASA Astrophysics Data System (ADS)

    Sonneborn, G.; Iping, R. C.; Massa, D. L.; Gruber, D.; Schlegel, E. M.; Hutchings, J. B.

    2004-12-01

    The accretion-powered high-mass X-ray binary SMC X-1/Sk 160 was observed for one complete orbit (3.89 days) with the Far Ultraviolet Spectroscopic Explorer (FUSE) to study how the strong X-ray source modulates the stellar wind of the B0 I primary. The observations were obtained primarily on 2003 July 19-23, with additional observations on 2003 Oct 27 and 2004 Aug 23 filling some phase gaps and duplicating others. Interstellar lines of molecular hydrogen and O VI 1032 from foreground Milky Way and SMC gas were modelled and used to correct the observed stellar O VI 1032 P-Cygni line profiles. The O VI absorption shows that the wind is highly asymmetry around the orbit. The line is at maximum strength during the eclipse of the pulsar (phase 0.0), with a total column density of N(O VI) = 7E17 cm-2. The O VI line virtually disappears near phase 0.4. The terminal velocity (700 km/s) drops to near zero at phase 0.3-0.4. These results are qualitatively consistent with 3D-hydrodynamic models of the disrupted stellar wind of SMC X-1 (Blondin and Woo 1995, ApJ, 445, 889). Archival HST/STIS spectra of SMC X-1 obtained in 2000 and 2001 show that the N V 1238-42 and C IV 1548-50 stellar wind features have phase dependences similar to that seen in O VI. The line profile variations do not appear to be correlated with X-ray high or low states of the 60-day super-orbital period. Other stellar wind lines in the FUSE spectrum of SMC X-1 (S IV 1073, P V 1117, Si IV 1122, C III 1176) show much smaller orbital modulation effects than are seen in O VI. These lines are present at approximately the same strength at all phases. This work was supported in part by NASA grant NNG04GK79G to Catholic University of America for FUSE GI program D175.

  2. STELLAR WIND INDUCED SOFT X-RAY EMISSION FROM CLOSE-IN EXOPLANETS

    SciTech Connect

    Kislyakova, K. G.; Lammer, H.; Fossati, L.; Johnstone, C. P.; Holmström, M.; Zaitsev, V. V.

    2015-01-30

    In this Letter, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX), which produces soft X-ray emission, is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted as a result of the charge exchange between heavy ions in the solar wind and the atmospheric neutral particles. In the solar system, comets produce X-rays mostly through the SWCX mechanism, but it has also been shown to operate in the heliosphere, in the terrestrial magnetosheath, and on Mars, Venus, and the Moon. Since the number of emitted photons is proportional to the solar wind mass flux, this mechanism is not very effective for the solar system giants. Here we present a simple estimate of the X-ray emission intensity that can be produced by close-in extrasolar giant planets due to charge exchange with the heavy ions of the stellar wind. Using the example of HD 209458b, we show that this mechanism alone can be responsible for an X-ray emission of ≈10{sup 22} erg s{sup –1}, which is 10{sup 6} times stronger than the emission from the Jovian aurora. We discuss also the possibility of observing the predicted soft X-ray flux of hot Jupiters and show that despite high emission intensities they are unobservable with current facilities.

  3. On the Origin and Evolution of Stellar Chromospheres, Coronae and Winds

    NASA Technical Reports Server (NTRS)

    Musielak, Z. E.

    1997-01-01

    The final report discusses work completed on proposals to construct state-of-the-art, theoretical, two-component, chromospheric models for single stars of different spectral types and different evolutionary status. We suggested to use these models to predict the level of the "basal flux", the observed range of variation of chromospheric activity for a given spectral type, and the decrease of this activity with stellar age. In addition, for red giants and supergiants, we also proposed to construct self-consistent, purely theoretical, chromosphere-wind models, and investigate the origin of "dividing lines" in the H-R diagram. In the report, we list the following six specific goals for the first and second year of the proposed research and then describe the completed work: (1) To calculate the acoustic and magnetic wave energy fluxes for stars located in different regions of the H-R diagram; (2) To investigate the transfer of this non-radiative energy through stellar photospheres and to estimate the amount of energy that reaches the chromosphere; (3) To identify major sources of radiative losses in stellar chromospheres and calculate the amount of emitted energy; (4) To use (1) through (3) to construct purely theoretical, two-component, chromospheric models based on the local energy balance. The models will be constructed for stars of different spectral types and different evolutionary status; (5) To explain theoretically the "basal flux", the location of stellar temperature minima and the observed range of chromospheric activity for stars of the same spectral type; and (6) To construct self-consistent, time-dependent stellar wind models based on the momentum deposition by finite amplitude Alfven waves.

  4. M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets

    NASA Astrophysics Data System (ADS)

    Vidotto, A. A.; Jardine, M.; Morin, J.; Donati, J. F.; Opher, M.; Gombosi, T. I.

    2014-02-01

    We perform three-dimensional numerical simulations of stellar winds of early-M-dwarf stars. Our simulations incorporate observationally reconstructed large-scale surface magnetic maps, suggesting that the complexity of the magnetic field can play an important role in the angular momentum evolution of the star, possibly explaining the large distribution of periods in field dM stars, as reported in recent works. In spite of the diversity of the magnetic field topologies among the stars in our sample, we find that stellar wind flowing near the (rotational) equatorial plane carries most of the stellar angular momentum, but there is no preferred colatitude contributing to mass-loss, as the mass flux is maximum at different colatitudes for different stars. We find that more non-axisymmetric magnetic fields result in more asymmetric mass fluxes and wind total pressures ptot (defined as the sum of thermal, magnetic and ram pressures). Because planetary magnetospheric sizes are set by pressure equilibrium between the planet's magnetic field and ptot, variations of up to a factor of 3 in ptot (as found in the case of a planet orbiting at several stellar radii away from the star) lead to variations in magnetospheric radii of about 20 per cent along the planetary orbital path. In analogy to the flux of cosmic rays that impact the Earth, which is inversely modulated with the non-axisymmetric component of the total open solar magnetic flux, we conclude that planets orbiting M-dwarf stars like DT Vir, DS Leo and GJ 182, which have significant non-axisymmetric field components, should be the more efficiently shielded from galactic cosmic rays, even if the planets lack a protective thick atmosphere/large magnetosphere of their own.

  5. Stellar Wind Bubbles: H-Deficient Stars and X-Ray Spectra

    NASA Astrophysics Data System (ADS)

    Mellema, G.

    2003-01-01

    We present simplified one-dimensional numerical models for stellar wind bubbles (SWB), investigating two aspects: the effect of H-deficient winds, such as observed in [WR]-type centrals stars of planetary nebulae (PN) and massive Wolf-Rayet stars (WR), and the X-ray spectra produced by SWBs. For the H-deficient winds, we find that the extra cooling caused by the extremely high metal abundances influences the structure and evolution of their SWBs, although they remain mostly energy-driven. For the X-ray spectra we find that a standard SWB model cannot explain the observed spectra, and some extra physical effect is needed. We show that thermal conduction with low efficiency can be this effect.

  6. Detecting stellar-wind bubbles through infrared arcs in H ii regions

    NASA Astrophysics Data System (ADS)

    Mackey, Jonathan; Haworth, Thomas J.; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert; Harries, Tim J.

    2016-02-01

    Mid-infrared arcs of dust emission are often seen near ionizing stars within H ii regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional, radiation-hydrodynamics simulations of wind bubbles within H ii regions around individual stars to predict the infrared emission properties of the dust within the H ii region. We assume that dust and gas are dynamically well-coupled and that dust properties (composition, size distribution) are the same in the H ii region as outside it, and that the wind bubble contains no dust. We post-process the simulations to make synthetic intensity maps at infrared wavebands using the torus code. We find that the outer edge of a wind bubble emits brightly at 24 μm through starlight absorbed by dust grains and re-radiated thermally in the infrared. This produces a bright arc of emission for slowly moving stars that have asymmetric wind bubbles, even for cases where there is no bow shock or any corresponding feature in tracers of gas emission. The 24 μm intensity decreases exponentially from the arc with increasing distance from the star because the dust temperature decreases with distance. The size distribution and composition of the dust grains has quantitative but not qualitative effects on our results. Despite the simplifications of our model, we find good qualitative agreement with observations of the H ii region RCW 120, and can provide physical explanations for any quantitative differences. Our model produces an infrared arc with the same shape and size as the arc around CD -38°11636 in RCW 120, and with comparable brightness. This suggests that infrared arcs around O stars in H ii regions may be revealing the extent of stellar wind bubbles, although we have not excluded other explanations.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  8. Collisions versus stellar winds in the runaway merger scenario: place your bets

    NASA Astrophysics Data System (ADS)

    Mapelli, Michela

    The runaway merger scenario is one of the most promising mechanisms to explain the formation of intermediate-mass black holes (IMBHs) in young dense star clusters (SCs). On the other hand, the massive stars that participate in the runaway merger lose mass by stellar winds. This effect is tremendously important, especially at high metallicity. We discuss N-body simulations of massive (˜{}6×{}104 M_ȯ) SCs, in which we added new recipes for stellar winds and supernova explosion at different metallicity. At solar metallicity, the mass of the final merger product spans from few solar masses up to ˜{}30 M_ȯ. At low metallicity (0.01-0.1 Z_ȯ) the maximum remnant mass is ˜{}250 M_ȯ, in the range of IMBHs. A large fraction (˜{}0.6) of the massive remnants are not ejected from the parent SC and acquire stellar or black hole companions. Finally, I discuss the importance of this result for gravitational wave detection.

  9. Momentum and energy deposition in late-type stellar atmospheres and winds

    NASA Technical Reports Server (NTRS)

    Hartmann, L.; Macgregor, K. B.

    1980-01-01

    The present study calculates the response of the outer atmospheres of cool low-gravity stars to the passage of the mechanical energy fluxes of solar magnitude in the form of acoustic waves and Alfven waves. It is shown that Alfven waves are efficient in generating outflow, and can account for the order of magnitude of observed mass loss in late-type luminous stars. However, unless these magnetic waves undergo some dissipation within several stellar radii of the surface, the predicted terminal velocities of the resulting stellar winds are far too high. Alfven wave dissipation should give rise to extended warm chromospheres in low-gravity late-type stars, a prediction which can be observationally tested.

  10. Assisted stellar suicide: the wind-driven evolution of the recurrent nova T Pyxidis

    NASA Astrophysics Data System (ADS)

    Knigge, Ch.; King, A. R.; Patterson, J.

    2000-12-01

    We show that the extremely high luminosity of the short-period recurrent nova T Pyx in quiescence can be understood if this system is a wind-driven supersoft x-ray source (SSS). In this scenario, a strong, radiation-induced wind is excited from the secondary star and accelerates the binary evolution. The accretion rate is therefore much higher than in an ordinary cataclysmic binary at the same orbital period, as is the luminosity of the white dwarf primary. In the steady state, the enhanced luminosity is just sufficient to maintain the wind from the secondary. The accretion rate and luminosity predicted by the wind-driven model for T Pyx are in good agreement with the observational evidence. X-ray observations with Chandra or XMM may be able to confirm T Pyx's status as a SSS. T Pyx's lifetime in the wind-driven state is on the order of a million years. Its ultimate fate is not certain, but the system may very well end up destroying itself, either via the complete evaporation of the secondary star, or in a Type Ia supernova if the white dwarf reaches the Chandrasekhar limit. Thus either the primary, the secondary, or both may currently be committing assisted stellar suicide.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  12. Do stellar winds prevent the formation of supermassive stars by accretion?

    NASA Astrophysics Data System (ADS)

    Nakauchi, Daisuke; Hosokawa, Takashi; Omukai, Kazuyuki; Saio, Hideyuki; Nomoto, Ken'ichi

    2017-03-01

    Supermassive stars (SMSs; ∼105 M⊙) formed from metal-free gas in the early Universe attract attention as progenitors of supermassive black holes observed at high redshifts. To form SMSs by accretion, central protostars must accrete at as high rates as ∼0.1-1 M⊙ yr-1. Such protostars have very extended structures with bloated envelopes, like supergiant stars, and are called supergiant protostars (SGPSs). Under the assumption of hydrostatic equilibrium, SGPSs have density-inverted layers, where the luminosity becomes locally super-Eddington, near the surface. If the envelope matter is allowed to flow out, however, a stellar wind could be launched and hinder the accretion growth of SGPSs before reaching the supermassive regime. We examine whether radiation-driven winds are launched from SGPSs by constructing steady and spherically symmetric wind solutions. We find that the wind velocity does not reach the escape velocity in any case considered. This is because once the temperature falls below ∼104 K, the opacity plummet drastically owing to the recombination of hydrogen and the acceleration ceases suddenly. This indicates that, in realistic non-steady cases, even if outflows are launched from the surface of SGPSs, they would fall back again. Such a 'wind' does not result in net mass-loss and does not prevent the growth of SGPSs. In conclusion, SGPSs will grow to SMSs and eventually collapse to massive black holes of ∼105 M⊙, as long as the rapid accretion is maintained.

  13. Probing the Abundance of SiO and HCN throughout the Stellar Wind of R Dor

    NASA Astrophysics Data System (ADS)

    Van de Sande, Marie; Decin, Leen; Lombaert, Robin; Millar, T. J.; Walsh, Catherine; Li, Xiaohu

    2016-07-01

    R Dor is an oxygen-rich AGB star characterised by a low mass-loss rate. Using retrieval methods, we found abundance profiles for SiO and HCN, two chemically important molecules. By comparing these results to those of forward chemistry modelling we will be able to constrain the dominant chemical pathways within the stellar wind. They will also enable us to improve the forward chemistry models, through incorporating dust-gas reactions. The same methodologies will be applied to the abundance profiles retrieved for the O-rich AGB star IK Tau (Decin et al. 2010), which is characterised by a high mass-loss rate.

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

    NASA Astrophysics Data System (ADS)

    Pellegrini, Silvia; Negri, Andrea; Ciotti, Luca

    2015-08-01

    Early-Type galaxies (ETGs) host a hot ISM produced mainly by stellar winds, and heated by Type Ia supernovae (SNIa) and the thermalization of stellar motions. Recent high resolution 2D hydrodynamical simulations (Negri et al. 2014) showed that ordered rotation in the stellar component alters significantly the evolution of the hot ISM, and results in the formation of a centrifugally supported cold equatorial disc. This agrees well with the recent evidence that approximately 50% of massive ETGs host significant quantities of cold gas (Morganti et al. 2006; Young et al. 2014), often in settled configurations, sharing the same kinematics of the stars. In particular, in a systematic investigation of the ATLAS3D sample, the most massive fast-rotating ETGs always have kinematically aligned gas, which suggests an internal origin for it, and molecular gas is detected only in fast rotators (Davis et al. 2011). The observed cold gas seems also to provide material for low level star formation (SF) activity (Combes et al. 2007, Davis et al. 2014). Interestingly, in the ATLAS3D sample, SF and young stellar populations are detected only in fast rotators (Sarzi et al. 2013). In a recent work we investigated whether and how SF takes place in the cold gas disc typically produced in rotating ETGs by our previous 2D simulations, by adding to them the possibility for the gas to form stars (Negri et al. 2015). We also inserted the injection of mass, momentum and energy appropriate for the newly (and continuously) forming stellar population. We found that subsequent generations of stars are formed, and that most of the extended and massive cold disc is consumed by this process, leaving at the present epoch cold gas masses that compare well with those observed. The mass in secondary generations of stars resides mostly in a disc, and could be related to a younger, more metal rich disky stellar component indeed observed in fast rotator ETGs (Cappellari et al. 2013). Most of the mass in

  15. Formation of standing shocks in stellar winds and related astrophysical flows

    NASA Technical Reports Server (NTRS)

    Tsinganos, K.; Habbal, S. R.; Rosner, R.

    1983-01-01

    Stellar winds and other analogous astrophysical flows can be described, to lowest order, by the familiar one dimensional hydrodynamic equations which, being nonlinear, admit in some instances discontinuous as well as continuous transonic solutions for identical inner boundary conditions. The characteristics of the time dependent differential equations of motion are described to show how a perturbation changes profile in time and, under well defined conditions, develops into a stationary shock discontinuity. The formation of standing shocks in wind type astrophysical flows depends on the fulfillment of appropriate necessary conditions, which are determined by the conservation of mass, momentum and energy across the discontinuity, and certain sufficient conditions, which are determined by the flow's history.

  16. The effects of stellar winds on the magnetospheres and potential habitability of exoplanets

    NASA Astrophysics Data System (ADS)

    See, V.; Jardine, M.; Vidotto, A. A.; Petit, P.; Marsden, S. C.; Jeffers, S. V.; do Nascimento, J. D.

    2014-10-01

    Context. The principle definition of habitability for exoplanets is whether they can sustain liquid water on their surfaces, i.e. that they orbit within the habitable zone. However, the planet's magnetosphere should also be considered, since without it, an exoplanet's atmosphere may be eroded away by stellar winds. Aims: The aim of this paper is to investigate magnetospheric protection of a planet from the effects of stellar winds from solar-mass stars. Methods: We study hypothetical Earth-like exoplanets orbiting in the host star's habitable zone for a sample of 124 solar-mass stars. These are targets that have been observed by the Bcool Collaboration. Using two wind models, we calculate the magnetospheric extent of each exoplanet. These wind models are computationally inexpensive and allow the community to quickly estimate the magnetospheric size of magnetised Earth-analogues orbiting cool stars. Results: Most of the simulated planets in our sample can maintain a magnetosphere of ~5 Earth radii or larger. This suggests that magnetised Earth analogues in the habitable zones of solar analogues are able to protect their atmospheres and is in contrast to planets around young active M dwarfs. In general, we find that Earth-analogues around solar-type stars, of age 1.5 Gyr or older, can maintain at least a Paleoarchean Earth sized magnetosphere. Our results indicate that planets around 0.6-0.8 solar-mass stars on the low activity side of the Vaughan-Preston gap are the optimum observing targets for habitable Earth analogues. Appendix A is available in electronic form at http://www.aanda.org

  17. From Solar to Stellar Corona: The Role of Wind, Rotation, and Magnetism

    NASA Astrophysics Data System (ADS)

    Réville, Victor; Brun, Allan Sacha; Strugarek, Antoine; Matt, Sean P.; Bouvier, Jérôme; Folsom, Colin P.; Petit, Pascal

    2015-12-01

    Observations of surface magnetic fields are now within reach for many stellar types thanks to the development of Zeeman-Doppler Imaging. These observations are extremely useful for constraining rotational evolution models of stars, as well as for characterizing the generation of the magnetic field. We recently demonstrated that the impact of coronal magnetic field topology on the rotational braking of a star can be parameterized with a scalar parameter: the open magnetic flux. However, without running costly numerical simulations of the stellar wind, reconstructing the coronal structure of the large-scale magnetic field is not trivial. An alternative—broadly used in solar physics—is to extrapolate the surface magnetic field assuming a potential field in the corona, to describe the opening of the field lines by the magnetized wind. This technique relies on the definition of a so-called source surface radius, which is often fixed to the canonical value of 2.5{R}⊙ . However this value likely varies from star to star. To resolve this issue, we use our extended set of 2.5D wind simulations published in 2015 to provide a criterion for the opening of field lines as well as a simple tool to assess the source surface radius and the open magnetic flux. This allows us to derive the magnetic torque applied to the star by the wind from any spectropolarimetric observation. We conclude by discussing some estimations of spin-down timescales made using our technique and compare them to observational requirements.

  18. Numerical Simulation of Interacting Stellar Winds Model Using Smoothed Particle Hydrodynamics (SPH)

    NASA Astrophysics Data System (ADS)

    Thronson, H. A., Jr.; Li, P. S.; Kwok, S.

    1997-12-01

    In the past decade, the Interacting Stellar Winds (ISW) model has been shown to be successful in explaining the formation of planetary nebulae, Wolf-Rayet nebulae, slow novae, and supernovae. Since analytical methods applied to the ISW model have been limited to the spherical symmetric (1D) geometry, numerical methods are necessary for axisymmetric (2D) or arbitrary (3D) geometries, such as the study of formation and evolution of planetary nebulae, and for symbiotic nova outbursts. The Smoothed Particle Hydrodynamics (SPH) algorithm has been developed to study hydrodynamics using the particle method. This algorithm has been applied in many different fields successfully. In this paper, we apply the SPH algorithm using the TREE code to the problem of interacting winds dynamics. We present three simulations: (1) the interaction of two winds in spherical symmetry to demonstrate the validity of the algorithm in dealing with ISW modeling, (2) the formation and evolution of an axisymmetric nebula in the first 500 years, and (3) the interacting-colliding winds caused by a slow nova outburst in a symbiotic system. It is the first time that the SPH algorithm has been applied to an ISW simulation. The SPH algorithm is proved to be an accurate and powerful tool in studying ISW model. This work is supported by NASA's US ISO program and the University of Calgary.

  19. Phase-locked photospheric and stellar-wind variations of θ^1^Orionis C.

    NASA Astrophysics Data System (ADS)

    Stahl, O.; Kaufer, A.; Rivinius, T.; Szeifert, T.; Wolf, B.; Gaeng, T.; Gummersbach, C. A.; Jankovics, I.; Kovacs, J.; Mandel, H.; Pakull, M. W.; Peitz, J.

    1996-08-01

    We have obtained a long series of optical spectra and new IUE spectra of θ^1^Ori C, the brightest star in the Orion Trapezium and the main source of ionization of the Orion nebula (M 42). With these data, we have improved the accuracy of the period of the optical emission-line variations and the UV stellar-wind absorption-line variations. We find a period of 15.422 +/- 0.002 days. The high accuracy of the period makes it possible to phase correctly our new data and archival IUE data obtained more than fifteen years ago. The stellar wind absorption is weakest when the emission lines have maximum strength. In addition, we have detected periodic variations in the strength of photospheric spectral lines. Lines from HeI, HeII, C IV and OIII all vary in phase. The absorption of these lines is strongest when the emission is at its maximum. These variations appear to be due to a rotating surface feature which spatially coincides with the emission region.

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

    NASA Technical Reports Server (NTRS)

    Becker, Robert H.; White, Richard L.

    1988-01-01

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

  1. Gadolinium photoionization process

    DOEpatents

    Paisner, Jeffrey A.; Comaskey, Brian J.; Haynam, Christopher A.; Eggert, Jon H.

    1993-01-01

    A method is provided for selective photoionization of the odd-numbered atomic mass gadolinium isotopes 155 and 157. The selective photoionization is accomplished by circular or linear parallel polarized laser beam energy effecting a three-step photoionization pathway.

  2. Gadolinium photoionization process

    DOEpatents

    Paisner, J.A.; Comaskey, B.J.; Haynam, C.A.; Eggert, J.H.

    1993-04-13

    A method is provided for selective photoionization of the odd-numbered atomic mass gadolinium isotopes 155 and 157. The selective photoionization is accomplished by circular or linear parallel polarized laser beam energy effecting a three-step photoionization pathway.

  3. Extended red objects and stellar-wind bow shocks in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Sexton, Remington O.; Povich, Matthew S.; Smith, Nathan; Babler, Brian L.; Meade, Marilyn R.; Rudolph, Alexander L.

    2015-01-01

    We report the results of infrared photometry on 39 extended red objects (EROs) in the Carina Nebula, observed with the Spitzer Space Telescope. Most EROs are identified by bright, extended 8.0 μm emission, which ranges from 10 arcsec to 40 arcsec in size, but our sample also includes four EROs identified by extended 24 μm emission. Of particular interest are nine EROs associated with late O- or early B-type stars and characterized by arc-shaped morphology, suggesting dusty, stellar-wind bow shocks. These objects are preferentially oriented towards the central regions of the Carina Nebula, suggesting that these bow shocks are generally produced by the interactions of OB winds with the bulk expansion of the H II region rather than high proper motion. We identify preferred regions of mid-infrared colour space occupied by our bow shock candidates, which also contain bow shock candidates in M17 and RCW 49 but are well separated from polycyclic aromatic hydrocarbon emission or circumstellar discs. Colour cuts identify an additional 12 marginally resolved bow shock candidates, 10 of which are also associated with known late O or early B stars. H II region expansion velocities derived from bow shock candidate standoff distances are ˜10 km s-1, assuming typical H II region gas densities, comparable to expansion velocities derived from bow shocks in M17 and RCW 49. One candidate bow shock provides direct evidence of physical interaction between the massive stellar winds originating in the Trumpler 15 and Trumpler 14 clusters, supporting the conclusion that both clusters are at similar heliocentric distances.

  4. The HEAO-2 Guest Investigator Program: Non-linear growth of instabilities in line-driven stellar winds

    NASA Technical Reports Server (NTRS)

    Rybicki, G. B.

    1985-01-01

    The linear instability of line-driven stellar winds to take proper account of the dynamical effect of scattered radiation were analyzed. It is found that: (1) the drag effect of the mean scattered radiation does greatly reduce the contribution of scattering lines to the instability at the very base of the wind, but the instability growth rate associated with such lines rapidly increases as the flow moves outward from the base, reaching more than 50% of the growth rate for pure absorption lines within a stellar radius of the surface, and eventually reaching 80% of that rate at large radii; (2) perturbations in the scattered radiation field may be important for the propagation of wind disturbances, but they have little effect on the wind instability; and (3) the contribution of strongly shadowed lines to the wind instability is often reduced compared to that of unshadowed lines, but their overall effect is not one of damping in the outer parts of the wind. It is concluded that, even when all scattering effects are taken into account, the bulk of the flow in a line-driven stellar wind is still highly unstable.

  5. FUSE Observations of Stellar Wind Variability in {Sk -67°166}

    NASA Astrophysics Data System (ADS)

    Fullerton, A. W.; Massa, D. L.; Howarth, I. D.; Owocki, S. P.; Prinja, R. K.; Willis, A. J.

    2000-12-01

    We present results from an 18-day campaign to monitor stellar wind variability in {Sk -67°166} (HDE 269698), an O4 If+ star in the Large Magellanic Cloud, with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Optical depth enhancements that progress from blue to red through the absorption trough are prominent in all unsaturated P Cygni profiles, particularly the resonance doublets of {S 4} and {P 5}. Related variability is evident in the resonance lines of {S 6} and {O 6}. The variations are qualitatively similar to those observed in the {Si 4} wind lines of the Galactic supergiant ζ Puppis [O4 I(n)f] during a 16-day monitoring campaign with IUE. However, the FUSE observations contain more diagnostic information about the nature of the structures responsible for the observed variability. In particular, the relative amplitudes of the variations in {S 4} and {S 6} provide the first empirical constraint on the ionization equilibrium of these structures in an O star wind, while the variability of {O 6} traces the distribution of very hot gas. This work is based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.

  6. EXPLORING THE EFFECTS OF STELLAR ROTATION AND WIND CLEARING: DEBRIS DISKS AROUND F STARS

    SciTech Connect

    Mizusawa, Trisha F.; Rebull, Luisa M.; Stauffer, John R.; Bryden, Geoffrey; Meyer, Michael; Song, Inseok

    2012-11-01

    We have conducted a study of debris disks around F stars in order to explore correlations between rotation, stellar winds, and circumstellar disks. We obtained new 24 {mu}m photometry from the Multiband Imaging Photometer for Spitzer (MIPS) camera for a sample of 188 relatively nearby F dwarfs with various rotation rates and optical colors, and combined it with archival MIPS data for 66 more F stars, as well as Wide-field Infrared Survey Explorer data for the entire sample, plus 9 more F stars. Based on the objects' K{sub s} - [24] and [3.4] - [22] colors, we identify 22 stars in our sample as having 22 and/or 24 {mu}m excesses above our detection limit, 13 of which are new discoveries. Our overall disk detection rate is 22/263, or 8%, consistent with previous determinations of disk fractions in the solar neighborhood. While fast-rotating stars are expected to have strong winds capable of efficiently removing dust, we find no correlation between rotational velocity and infrared excess. Similarly, we find no significant difference in excess detection rate between late-type F stars, which have convective surfaces, and early-type F stars, which have fully radiative envelopes. However, the essentially unknown range of ages in this sample may be washing out any effects relating rotation, winds, and disks.

  7. TIDALLY ENHANCED STELLAR WIND: A WAY TO MAKE THE SYMBIOTIC CHANNEL TO TYPE Ia SUPERNOVA VIABLE

    SciTech Connect

    Chen, X.; Han, Z.

    2011-07-10

    In the symbiotic (or WD+RG) channel of the single-degenerate scenario for type Ia supernovae (SNe Ia), the explosions occur a relatively long time after star formation. The birthrate from this channel would be too low to account for all observed SNe Ia were it not for some mechanism to enhance the rate of accretion on to the white dwarf. A tidally enhanced stellar wind, of the type which has been postulated to explain many phenomena related to giant star evolution in binary systems, can do this. Compared to mass stripping, this model extends the space of SNe Ia progenitors to longer orbital periods and hence increases the birthrate to about 0.0069 yr{sup -1} for the symbiotic channel. Two symbiotic stars, T CrB and RS Oph, considered to be the most likely progenitors of SNe Ia through the symbiotic channel, are well inside the period-companion mass space predicted by our models.

  8. The variable stellar wind of Rigel probed at high spatial and spectral resolution

    NASA Astrophysics Data System (ADS)

    Chesneau, O.; Kaufer, A.; Stahl, O.; Colvinter, C.; Spang, A.; Dessart, L.; Prinja, R.; Chini, R.

    2014-06-01

    Context. Luminous BA-type supergiants are the brightest stars in the visible that can be observed in distant galaxies and are potentially accurate distance indicators. The impact of the variability of the stellar winds on the distance determination remains poorly understood. Aims: Our aim is to probe the inhomogeneous structures in the stellar wind using spectro-interferometric monitoring. Methods: We present a spatially resolved, high-spectral resolution (R = 12 000) K-band temporal monitoring of the bright supergiant β Orionis (Rigel, B8 Iab) using AMBER at the Very Large Telescope Interferometer (VLTI). Rigel was observed in the Brγ line and its nearby continuum once per month over 3 months in 2006-2007, and 5 months in 2009-2010. These unprecedented observations were complemented by contemporaneous optical high-resolution spectroscopy. We analyse the near-IR spectra and visibilities with the 1D non-LTE radiative-transfer code CMFGEN. The differential and closure phase signals are evidence of asymmetries that are interpreted as perturbations of the wind. Results: A systematic visibility decrease is observed across the Brγ line indicating that at a radius of about 1.25 R∗ the photospheric absorption is filled by emission from the wind. During the 2006-2007 period the Brγ and likely the continuum forming regions were larger than in the 2009-2010 epoch. Using CMFGEN we infer a mass-loss rate change of about 20% between the two epochs. We also find time variations in the differential visibilities and phases. The 2006-2007 period is characterised by noticeable variations in the differential visibilities in Doppler position and width and by weak variations in differential and closure phase. The 2009-2010 period is much quieter with virtually no detectable variations in the dispersed visibilities but a strong S-shaped signal is observed in differential phase coinciding with a strong ejection event discernible in the optical spectra. The differential phase signal

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

    SciTech Connect

    Cohen, O.; Drake, J. J.; Garraffo, C.; Ma, Y.; Glocer, A.; Gombosi, T. I.

    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.

  10. Time-dependent models of radiatively driven stellar winds. I - Nonlinear evolution of instabilities for a pure absorption model

    NASA Technical Reports Server (NTRS)

    Owocki, Stanley P.; Castor, John I.; Rybicki, George B.

    1988-01-01

    Numerical radiation-hydrodynamics simulations of the nonlinear evolution of instabilities in radiatively driven stellar winds have been performed. The results show a strong tendency for the unstable flow to form rather sharp rarefactions in which the highest speed material has very low density. The qualitative features of the model agree well with the reqirements of displaced narrow absorption components in UV lines.

  11. Geometry and physical conditions in the stellar wind of AG Carinae

    NASA Technical Reports Server (NTRS)

    Leitherer, Claus; Allen, Richard; Altner, Bruce; Damineli, Augusto; Drissen, Laurent; Idiart, Thais; Lupie, Olivia; Nota, Antonella; Robert, Carmelle; Schmutz, Werner

    1994-01-01

    AG Carinae is one of the prototypes of the class of Luminous Blue Variables (LBVs). Since 1990 the star has continuously brightened in its visual continuum. We report on a multi-instrument and -wavelength observing campaign to monitor the current activity phase of AG Car. Ground-based photometry, polarimetry, spectroscopy, and space-ultraviolet spectroscopy and spectropolarimetry have been obtained. From the variability of the polarization at ultraviolet and optical wavelengths we detect significant intrinsic polarization. P(sub int) greater than or equal to 0.5% is a large value for a hot, luminous star, suggesting departure from spherical symmetry in the wind of AG Car. The intrinsic polarization is variable on a timescale of 2 months or less. The measured ultraviolet polarization (intrinsic + interstellar) dropped to 0.5% in 1992 May and returned to 1% in 1992 July. The results are interpreted in terms of a variable outflow with a density enhancement in the equatorial plane. A similar model was suggested for the related object R127 in the Large Magellanic Cloud (LMC). This geometry is reminiscent of the large-scale morphology of the gas nebula and dust 'jet' surrounding AG Car. It is therefore likely that physical conditions close to the stellar surface are responsible for the geometry of the spatially resolved circumstellar material around AG Car. Despite the drastic change of the photospheric conditions, the mass-loss rate did not increase. We find no evidence for a positive correlation between wind density and stellar radius. This makes models that explain the radius increase by opacity effects in the outflow unlikely. The mechanism responsible for the temperature and radius variations is still unknown but most likely has its origin in subphotospheric regions.

  12. Geometry and physical conditions in the stellar wind of AG Carinae

    NASA Technical Reports Server (NTRS)

    Leitherer, Claus; Allen, Richard; Altner, Bruce; Damineli, Augusto; Drissen, Laurent; Idiart, Thais; Lupie, Olivia; Nota, Antonella; Robert, Carmelle; Schmutz, Werner

    1994-01-01

    AG Carinae is one of the prototypes of the class of Luminous Blue Variables (LBVs). Since 1990 the star has continuously brightened in its visual continuum. We report on a multi-instrument and -wavelength observing campaign to monitor the current activity phase of AG Car. Ground-based photometry, polarimetry, spectroscopy, and space-ultraviolet spectroscopy and spectropolarimetry have been obtained. From the variability of the polarization at ultraviolet and optical wavelengths we detect significant intrinsic polarization. P(sub int) greater than or equal to 0.5% is a large value for a hot, luminous star, suggesting departure from spherical symmetry in the wind of AG Car. The intrinsic polarization is variable on a timescale of 2 months or less. The measured ultraviolet polarization (intrinsic + interstellar) dropped to 0.5% in 1992 May and returned to 1% in 1992 July. The results are interpreted in terms of a variable outflow with a density enhancement in the equatorial plane. A similar model was suggested for the related object R127 in the Large Magellanic Cloud (LMC). This geometry is reminiscent of the large-scale morphology of the gas nebula and dust 'jet' surrounding AG Car. It is therefore likely that physical conditions close to the stellar surface are responsible for the geometry of the spatially resolved circumstellar material around AG Car. Despite the drastic change of the photospheric conditions, the mass-loss rate did not increase. We find no evidence for a positive correlation between wind density and stellar radius. This makes models that explain the radius increase by opacity effects in the outflow unlikely. The mechanism responsible for the temperature and radius variations is still unknown but most likely has its origin in subphotospheric regions.

  13. ACTIVE GALACTIC NUCLEUS OBSCURATION FROM WINDS: FROM DUSTY INFRARED-DRIVEN TO WARM AND X-RAY PHOTOIONIZED

    PubMed Central

    Dorodnitsyn, A.; Kallman, T.

    2016-01-01

    We present calculations of AGN winds at ~parsec scales, along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L=0.05 – 0.6Ledd, the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72° – 75° regardless of the luminosity. At L ≳ 0.1 the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations θ ≳ 70° and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR supported flow. At luminosities ≤0.1Ledd episodes of outflow are followed by extended periods when the wind switches to slow accretion. PMID:27642184

  14. Active Galactic Nucleus Obscuration from Winds: From Dusty Infrared-Driven to Warm and X-Ray Photoionized

    NASA Technical Reports Server (NTRS)

    Dorodnitsyn, Anton V.; Kallman, Timothy R.

    2012-01-01

    We present calculations of active galactic nucleus winds at approx.parsec scales along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L = 0.05-0.6 L(sub Edd), the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72deg - 75deg regardless of the luminosity. At L > or approx. 0.1, the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations (theta) > or approx.70deg and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR-supported flow. At luminosities < or = 0.1 L(sub Edd) episodes of outflow are followed by extended periods when the wind switches to slow accretion. Key words: acceleration of particles . galaxies: active . hydrodynamics . methods: numerical Online-only material: color figures

  15. ACTIVE GALACTIC NUCLEUS OBSCURATION FROM WINDS: FROM DUSTY INFRARED-DRIVEN TO WARM AND X-RAY PHOTOIONIZED.

    PubMed

    Dorodnitsyn, A; Kallman, T

    2012-12-10

    We present calculations of AGN winds at ~parsec scales, along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L=0.05 - 0.6Ledd, the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72° - 75° regardless of the luminosity. At L ≳ 0.1 the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations θ ≳ 70° and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR supported flow. At luminosities ≤0.1Ledd episodes of outflow are followed by extended periods when the wind switches to slow accretion.

  16. ACTIVE GALACTIC NUCLEUS OBSCURATION FROM WINDS: FROM DUSTY INFRARED-DRIVEN TO WARM AND X-RAY PHOTOIONIZED

    SciTech Connect

    Dorodnitsyn, A.; Kallman, T.

    2012-12-10

    We present calculations of active galactic nucleus winds at {approx}parsec scales along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L = 0.05-0.6 L{sub Edd}, the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72 Degree-Sign -75 Degree-Sign regardless of the luminosity. At L {approx}> 0.1, the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations {theta} {approx}> 70 Degree-Sign and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR-supported flow. At luminosities {<=}0.1 L{sub Edd} episodes of outflow are followed by extended periods when the wind switches to slow accretion.

  17. Magnetization of Stellar Wind in the High-Mass X-Ray Binary OAO 1657-415

    NASA Astrophysics Data System (ADS)

    Kim, V. Yu.; Ikhsanov, N. R.

    2017-06-01

    Spin evolution of the X-ray pulsar OAO 1657-415 in a wind-fed High Mass X-ray Binary (HMXB) is discussed. We suggest that its regular spin-up behaviour superposed with the spin-up/down episodes can be explained in terms of the Magnetic Levitation Accretion scenario (MLA scenario). This implies that the neutron star captures matter from a magnetized stellar wind of its massive companion. The magnetic field of the wind at a distance of the orbital separation within this scenario can be limited within the range of 20-70 mG.

  18. Simulating 3D Stellar Winds and Diffuse X-ray Emissions from Gases in Non-equilibrium Ionization State

    NASA Astrophysics Data System (ADS)

    Long, Min; Sun, Wei; Niu, Shu; Zhou, Xin; Ji, Li

    2017-08-01

    We investigate the physical properties of stellar winds launched in super stellar clusters (SSCs). Chandra observations have detected the presence of diffuse X-ray emission caused by hot gas from such winds in SSCs, and provide the best probe for understanding interactions between the stellar winds and the complex nursery regions. However, the details of the origin of cluster winds, the mass and energy ejection, the formation of diffuse X-ray emission, the fraction of winds contribution to the distribution of diffuse X-ray emission still remain unclear. We developed a multiphysics hydrodynamic model including self-gravity, head conduction and performed 3D simulations with an unprecedented grid resolution due to adaptive mesh refinement (AMR) capability in a case study of NGC 3603, as a supplement to the analysis of the archived 500 ks Chandra observations. The synthetic emission will be computed by assuming the gas in a non-equilibrium ionization (NEI) state indicated by Chandra observation, not coronal ionization equilibrium (CIE) that most works assumed, by using a customized NEI calculation module based on AtomDB. The results will be compared to the Chandra observations.

  19. Estimation of the stellar effective temperature and stellar wind detection in a Herbig Ae/Be type star from spectra acquired in Bogotá - Colombia

    NASA Astrophysics Data System (ADS)

    Guasca Garnica, I. L.; Ramírez Suárez, O. L.; Oostra Vannoppen, B.; Chaparro Molano, G.; Restrepo Gaitán, O. A.

    2017-07-01

    We present the results of spectroscopic observations in the range of 4280-6800 Å of AB Aur, a Herbig Ae/Be type star. These observations were carried out at the Observatory of the Universidad de los Andes in Bogotá - Colombia in 2015. We select the 4280-6000 Å spectral window for fitting our data to a black-body model of the star. In this range, the effects due to circumstellar disk emission are negligible and the nighborhood of the prominent accretion Hα emission line is neglected. In this window the dominant lines due atomic processes are the Balmer series lines Hβ and Hγ. We remove data around 3σ for each of these lines in order to ignore quantum effects. We model the stellar continuum by doing a Monte Carlo bootstrap-sampled fitting of three parameters: (i) a bolometric correction factor due to atmospheric absorption and/or defect electronics, (ii) measured (relative) continuum flux, and (iii) stellar temperature Teff. We obtain a value for the stellar temperature of 9400K-9700K, in agreement with the temperature reported by Tannirkulam et al. 2008. We also successfully fitted the H lines using a two-component gaussian fit, which shows the effects of stellar wind on top of the gas accretion onto the star. Our measurements strongly suggest that even in the harsh observational conditions present in Colombia, it is possible to obtain quality astronomical data for teaching astrophysics at an undergraduate level.

  20. Time-dependent models of radiatively driven stellar winds. I - Nonlinear evolution of instabilities for a pure absorption model

    NASA Astrophysics Data System (ADS)

    Owocki, Stanley P.; Castor, John I.; Rybicki, George B.

    1988-12-01

    The authors describe results of numerical radiation-hydrodynamics simulations of the nonlinear evolution of instabilities in radiatively driven stellar winds. The wind is idealized as a spherically symmetric, isothermal flow driven by pure absorption of stellar radiation in a fixed ensemble of spectral lines. The simulations indicate that there is a strong tendency for the unstable flow to form rather sharp rarefactions in which the highest speed material has very low density. The growth of wave perturbations thus remains nearly exponential well beyond the linear regime, until the waves are kinematically steepened into strong shocks. The strongest shocks here are reverse shocks that arise to decelerate high-speed, rarefied flow as it impacts slower material that has been compressed into dense shells. The subsequent wind evolution shows a slow decay of the shocks and the gradual thermal decompression and interaction of the dense shells.

  1. The First Extrasolar Measurement of Stellar He II and O III Bowen Fluorescence Emission in the EUV: A New Diagnostic of Hot Star Wind Conditions Applied to ɛ Canis Majoris (B 2 II)

    NASA Astrophysics Data System (ADS)

    Cohen, David H.; Macfarlane, Joseph J.; Cassinelli, Joseph P.; Owocki, Stanley P.

    1999-11-01

    The B bright giant ɛ CMa is one of only two OB stars observable with the Extreme Ultraviolet Explorer (EUVE) spectrometers (between 70 Åand 760ÅOne of the most interesting aspects of this unique spectrum is the presence of strong emission lines at 304 ÅHe II Lyman-α) and 374 ÅO III) due to the Bowen fluorescence mechanism. In this process, the He II 304 Åline pumps a resonance line of O III and the subsequent radiative decay yields several UV emission lines between 3000 Åand 4000 ÅThese lines are observed in nebulae, AGN, and novae, but the final O III transition leads to emission near 400 Åwhich had never before been seen in any astrophysical object outside of the solar system. The Bowen emission lines are formed in the radiation-driven stellar wind of ɛ CMa, as is shown by the Doppler-broadened 304 Åline profile. Our modeling indicates that the He II 304 Åline is sensitive to the X-ray emission in the wind of ɛ CMa, due to the importance of X-rays photoionization in controlling the ionization of helium. We also explore the temperature-sensitivity of the 374 ÅÅand 435 ÅO III lines, and use the non-detection of the latter two lines to place an upper limit on the wind temperature.

  2. Feedback from winds and supernovae in massive stellar clusters - II. X-ray emission

    NASA Astrophysics Data System (ADS)

    Rogers, H.; Pittard, J. M.

    2014-06-01

    The X-ray emission from a simulated massive stellar cluster is investigated. The emission is calculated from a 3D hydrodynamical model which incorporates the mechanical feedback from the stellar winds of three O stars embedded in a giant molecular cloud (GMC) clump containing 3240 M⊙ of molecular material within a 4 pc radius. A simple prescription for the evolution of the stars is used, with the first supernova (SN) explosion at t = 4.4 Myr. We find that the presence of the GMC clump causes short-lived attenuation effects on the X-ray emission of the cluster. However, once most of the material has been ablated away by the winds, the remaining dense clumps do not have a noticeable effect on the attenuation compared with the assumed interstellar medium (ISM) column. We determine the evolution of the cluster X-ray luminosity, LX, and spectra, and generate synthetic images. The intrinsic X-ray luminosity drops from nearly 1034 erg s-1 while the winds are `bottled up', to a near-constant value of 1.7 × 1032 erg s-1 between t = 1 and 4 Myr. LX reduces slightly during each star's red supergiant stage due to the depressurization of the hot gas. However, LX increases to ≈1034 erg s-1 during each star's Wolf-Rayet stage. The X-ray luminosity is enhanced by two to three orders of magnitude to ˜1037 erg s-1 for at least 4600 yr after each SN explosion, at which time the blast wave leaves the grid and the X-ray luminosity drops. The X-ray luminosity of our simulation is generally considerably fainter than predicted from spherically symmetric bubble models, due to the leakage of hot gas material through gaps in the outer shell. This process reduces the pressure within our simulation and thus the X-ray emission. However, the X-ray luminosities and temperatures which we obtain are comparable to similarly powerful massive young clusters.

  3. Scientists Find X Rays from Stellar Winds That May Play Significant Role in Galactic Evolution

    NASA Astrophysics Data System (ADS)

    2001-09-01

    Colorful star-forming regions that have captivated stargazers since the advent of the telescope 400 years ago contain gas thousands of times more energetic than previously recognized, powered by colliding stellar winds. This multimillion-degree gas radiated as X rays is one of the long-sought sources of energy and elements in the Milky Way galaxy's interstellar medium. A team led by Leisa Townsley, a senior research associate in astronomy and astrophysics at Penn State University, uncovered this wind phenomenon in the Rosette Nebula, a stellar nursery. With the Chandra X-ray Observatory, the team found that the most massive stars in the nebula produce winds that slam into each other, create violent shocks, and infuse the region with 6-million-degree gas. The findings are presented in Washington, D.C., today at a conference entitled "Two Years of Science with Chandra." "A ghostly glow of diffuse X-ray emission pervades the Rosette Nebula and perhaps many other similar star-forming regions throughout the Galaxy," said Townsley. "We now have a new view of the engine lighting the beautiful Rosette Nebula and new evidence for how the interstellar medium may be energized." Townsley and her colleagues created a striking X-ray panorama of the Rosette Molecular Cloud from four images with Chandra's Advanced CCD Imaging Spectrometer. This is a swath of the sky nearly 100 light years across sprayed with hundreds of X-ray-emitting young stars. In one corner of the Rosette Molecular Cloud lies the Rosette Nebula, called an "H II region" because the hydrogen gas there has been stripped of its electrons due to the strong ultraviolet radiation from its young stars. This region, about 5,000 light years away in the constellation Monoceros, the Unicorn, has long been a favorite among amateur astronomers. The wispy, colorful display is visible with small telescopes. The Chandra survey reveals, for the first time, 6-million-degree gas at the center of the Rosette Nebula, occupying a

  4. Probing the stellar wind environment of Vela X-1 with MAXI

    NASA Astrophysics Data System (ADS)

    Malacaria, C.; Mihara, T.; Santangelo, A.; Makishima, K.; Matsuoka, M.; Morii, M.; Sugizaki, M.

    2016-04-01

    Context. Vela X-1 is one of the best-studied and most luminous accreting X-ray pulsars. The supergiant optical companion produces a strong radiatively driven stellar wind that is accreted onto the neutron star, producing highly variable X-ray emission. A complex phenomenology that is due to both gravitational and radiative effects needs to be taken into account to reproduce orbital spectral variations. Aims: We have investigated the spectral and light curve properties of the X-ray emission from Vela X-1 along the binary orbit. These studies allow constraining the stellar wind properties and its perturbations that are induced by the pulsating neutron star. Methods: We took advantage of the All Sky Monitor MAXI/GSC data to analyze Vela X-1 spectra and light curves. By studying the orbital profiles in the 4-10 and 10-20 keV energy bands, we extracted a sample of orbital light curves (~15% of the total) showing a dip around the inferior conjunction, that is, a double-peaked shape. We analyzed orbital phase-averaged and phase-resolved spectra of both the double-peaked and the standard sample. Results: The dip in the double-peaked sample needs NH ~ 2 × 1024cm-2 to be explained by absorption alone, which is not observed in our analysis. We show that Thomson scattering from an extended and ionized accretion wake can contribute to the observed dip. Fit by a cutoff power-law model, the two analyzed samples show orbital modulation of the photon index that hardens by ~0.3 around the inferior conjunction, compared to earlier and later phases. This indicates a possible inadequacy of this model. In contrast, including a partial covering component at certain orbital phase bins allows a constant photon index along the orbital phases, indicating a highly inhomogeneous environment whose column density has a local peak around the inferior conjunction. We discuss our results in the framework of possible scenarios.

  5. The Physics of Wind-Fed Accretion

    SciTech Connect

    Mauche, C W; Liedahl, D A; Akiyama, S; Plewa, T

    2008-05-27

    We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global models of the radiatively-driven photoionized winds and accretion flows of HMXBs, with particular attention to the prototypical system Vela X-1. The models combine XSTAR photoionization calculations, HULLAC emission models appropriate to X-ray photoionized plasmas, improved models of the radiative driving of photoionized winds, FLASH time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo radiation transport. We present two- and three-dimensional maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of representative X-ray emission lines, as well as synthetic global Monte Carlo X-ray spectra. Such models help to better constrain the properties of the winds of HMXBs, which bear on such fundamental questions as the long-term evolution of these binaries and the chemical enrichment of the interstellar medium.

  6. The Physics of Wind-Fed Accretion

    SciTech Connect

    Mauche, Christopher W.; Liedahl, Duane A.; Akiyama, Shizuka

    2008-09-30

    We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global models of the radiatively-driven photoionized winds and accretion flows of HMXBs, with particular attention to the prototypical system Vela X-l. The models combine XSTAR photoionization calculations, HULLAC emission models appropriate to X-ray photoionized plasmas, improved models of the radiative driving of photoionized winds, FLASH time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo radiation transport. We present two- and three-dimensional maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of representative X-ray emission lines, as well as synthetic global Monte Carlo X-ray spectra. Such models help to better constrain the properties of the winds of HMXBs, which bear on such fundamental questions as the long-term evolution of these binaries and the chemical enrichment of the interstellar medium.

  7. Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

    NASA Astrophysics Data System (ADS)

    Chiang, Eugene; Fung, Jeffrey

    2017-10-01

    We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star’s wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the “avalanche zone”—located on AU Mic’s primary “birth” ring at a true distance of ∼35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind’s magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.

  8. GRB 110731A: Early Afterglow in Stellar Wind Powered By a Magnetized Outflow

    NASA Astrophysics Data System (ADS)

    Fraija, N.

    2015-05-01

    One of the most energetic gamma-ray bursts, GRB 110731A, was observed from an optical to GeV energy range. Previous analysis of the prompt phase revealed similarities between the Large Area Telescope (LAT) bursts observed by Fermi: (1) a delayed onset of the high-energy emission (\\gt 100 MeV), (2) a short-lasting bright peak at later times, and (3) a temporally extended component from this phase, lasting hundreds of seconds. Additionally to the prompt phase, multiwavelength observations over different epochs showed that the spectral energy distribution was better fitted by a wind afterglow model. We present a leptonic model based on an early afterglow that evolves in a stellar wind of its progenitor. We apply this model to interpret the temporally extended LAT emission and the brightest LAT peak exhibited by the prompt phase of GRB 110731A. Additionally, using the same set of parameters, we describe the multiwavelength afterglow observations. The origin of the temporally extended LAT, X-ray, and optical flux is explained through synchrotron radiation from the forward shock (FS) and the brightest LAT peak is described, evoking the synchrotron self-Compton emission from the reverse shock (RS). The bulk Lorentz factor required in this model (Γ ≃ 520) lies in the range of values demanded for most LAT-detected GRBs. We show that the strength of the magnetic field in the RS region is ∼50 times stronger than that in the FS region. This result suggests that, for GRB 110731A, the central engine is likely entrained with strong magnetic fields.

  9. Nonthermal X-rays and Gamma Rays from Supernova Remnants in Stellar-Wind Bubbles

    NASA Astrophysics Data System (ADS)

    Reynolds, S. P.

    1997-12-01

    Electrons are expected to be accelerated in strong shock waves to energies limited by radiative losses, by the finite age of the shock, or by escape. Young supernova remnants can easily produce electron distributions that, while steepening from the slope at radio energies, still contain significant numbers of electrons at energies of 100 TeV or higher, where they produce synchrotron X-rays to 10 keV and above. In addition, these electrons can inverse-Compton scatter cosmic microwave background photons up to energies in excess of 100 GeV. For remnants of core-collapse supernovae expanding into stellar-wind bubbles, the upstream density is likely to drop as r(-2) while the upstream magnetic field is wrapped into a tight spiral, resulting in an almost perpendicular shock everywhere. Such shocks can be extremely effective in accelerating electrons to high energies. I describe spectra and images for spherical remnants, assuming the dynamics are given by the Sedov self-similar solution appropriate for an ambient r(-2) density profile (r_sh t(2/3) ). Both images and spectra differ significantly from those for remnants expanding into uniform magnetic fields, and should be distinguishable. Remnants expanding into spherical wind bubbles should show little azimuthal variation in synchrotron brightness for any viewing angle. Except at the highest photon energies, their brightness profiles peak somewhat inside the outermost edge of emission. X-ray halos caused by electrons diffusing ahead of the shock are generally narrow and faint. I shall describe inverse-Compton gamma-ray spectra produced by these electron distributions as well.

  10. Gusty, gaseous flows of FIRE: galactic winds in cosmological simulations with explicit stellar feedback

    NASA Astrophysics Data System (ADS)

    Muratov, Alexander L.; Kereš, Dušan; Faucher-Giguère, Claude-André; Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

    2015-12-01

    We present an analysis of the galaxy-scale gaseous outflows from the Feedback in Realistic Environments (FIRE) simulations. This suite of hydrodynamic cosmological zoom simulations resolves formation of star-forming giant molecular clouds to z = 0, and features an explicit stellar feedback model on small scales. Our simulations reveal that high-redshift galaxies undergo bursts of star formation followed by powerful gusts of galactic outflows that eject much of the interstellar medium and temporarily suppress star formation. At low redshift, however, sufficiently massive galaxies corresponding to L* progenitors develop stable discs and switch into a continuous and quiescent mode of star formation that does not drive outflows far into the halo. Mass-loading factors for winds in L* progenitors are η ≈ 10 at high redshift, but decrease to η ≪ 1 at low redshift. Although lower values of η are expected as haloes grow in mass over time, we show that the strong suppression of outflows with decreasing redshift cannot be explained by mass evolution alone. Circumgalactic outflow velocities are variable and broadly distributed, but typically range between one and three times the circular velocity of the halo. Much of the ejected material builds a reservoir of enriched gas within the circumgalactic medium, some of which could be later recycled to fuel further star formation. However, a fraction of the gas that leaves the virial radius through galactic winds is never regained, causing most haloes with mass Mh ≤ 1012 M⊙ to be deficient in baryons compared to the cosmic mean by z = 0.

  11. The initial mass function and global rates of mass, momentum, and energy input to the interstellar medium via stellar winds

    NASA Technical Reports Server (NTRS)

    Van Buren, D.

    1985-01-01

    Published observational data are compiled and analyzed, using theoretical stellar-evolution models to determine the global rates of mass, momentum, and energy injected into the interstellar medium (ISM) by stellar winds. Expressions derived include psi = 0.00054 x (M to the -1.03) stars formed/sq kpc yr log M (where M is the initial mass function in solar mass units) and mass-loss = (2 x 10 to the -13th) x (L to the 1.25) solar mass/yr (with L in solar luminosity units). It is found that the wind/supernova injection of energy into the ISM and the mass loss from stars of 5 solar mass or more are approximately balanced by the dissipation of energy by cloud-cloud collisions and the formation of stars, respectively.

  12. The initial mass function and global rates of mass, momentum, and energy input to the interstellar medium via stellar winds

    NASA Technical Reports Server (NTRS)

    Van Buren, D.

    1985-01-01

    Published observational data are compiled and analyzed, using theoretical stellar-evolution models to determine the global rates of mass, momentum, and energy injected into the interstellar medium (ISM) by stellar winds. Expressions derived include psi = 0.00054 x (M to the -1.03) stars formed/sq kpc yr log M (where M is the initial mass function in solar mass units) and mass-loss = (2 x 10 to the -13th) x (L to the 1.25) solar mass/yr (with L in solar luminosity units). It is found that the wind/supernova injection of energy into the ISM and the mass loss from stars of 5 solar mass or more are approximately balanced by the dissipation of energy by cloud-cloud collisions and the formation of stars, respectively.

  13. The distant future of solar activity: A case study of Beta Hydri. III - Transition region, corona, and stellar wind

    NASA Technical Reports Server (NTRS)

    Dravins, D.; Linde, P.; Ayres, T. R.; Linsky, J. L.; Monsignori-Fossi, B.; Simon, T.; Wallinder, F.

    1993-01-01

    The paper investigates the secular decay of solar-type activity through a detailed comparison of the present sun with the very old solar-type star, Beta Hyi, taken as a proxy of the future sun. Analyses of successive atmospheric layers are presented, with emphasis of the outermost parts. The FUV emission lines for the transition zone are among the faintest so far seen in any solar-type star. The coronal soft X-ray spectrum was measured through different filters on EXOSAT and compared to simulated X-ray observations of the sun seen as a star. The flux from Beta Hyi is weaker than that from the solar corona and has a different spectrum. It is inferred that a thermally driven stellar wind can no longer be supported, which removes the mechanism from further rotational braking of the star through a magnetic stellar wind.

  14. Mapping the latitude dependence of the primary stellar wind of eta Carinae using the spectrum reflected on the Homunculus nebula

    NASA Astrophysics Data System (ADS)

    Odessey, Rachel

    2016-01-01

    The binary star Eta Carinae underwent a massive eruption in the 1840s, resulting in a huge nebula of ejected material, called the Homunculus. Despite preventing us from the direct view from the central source, the Homunculus acts like a mirror, allowing us to see the spectrum of the central binary system from different stellar latitudes. Therefore, by mapping the spectrum along the nebula we are actually probing the dependence of the spectrum with stellar latitude. Our project focuses on the P Cyg absorption component of H lines mostly in the optical and near-infrared wavelengths. in order to investigate the structure of the primary stellar wind. A full spectral mapping of the entire nebula was constructed by combining multiple dithered long slit observations using the ESO/X-Shooter high-resolution spectrograph. Such mapping allowed us to assemble a data cube containing the spectrum of each position along the nebula. Preliminary analysis confirms that the primary wind indeed has a deeper absorption component at high stellar latitudes (polar region). Also, contrary to our expectations, our analysis indicates that the polar region does not seem entirely radially symmetric in terms of density, which invites further investigation into the source of these discrepancies.

  15. Narrow components in the profiles of ultraviolet resonance lines - Evidence for a two-component stellar wind for O and B stars

    NASA Technical Reports Server (NTRS)

    Lamers, H. J. G. L. M.; Gathier, R.; Snow, T. P., Jr.

    1982-01-01

    The presence of narrow, shifted absorption features superposed on the wide P Cygni profiles of the UV resonance lines in the spectra of O and B stars is studied and possible explanations of the narrow components are discussed. Spectra from 26 stars of spectral types O4f to B1 Ib were examined for the presence of narrow components in the absorption part of the profiles, and positive evidence was detected in 17. The central velocities of the features are found to be similar for different ions of the same star, and typically equal to 0.75 times the terminal velocity of the stellar wind. The width of the narrow absorptions is about 18% of the terminal stellar wind velocity, with a column density generally not correlated with the effective temperature or mass loss rate. Possible explanations for the narrow components include peaks in the degree of ionization, a stationary stellar shell, a plateau in the stellar wind velocity law, a decelerating stellar wind, a variable mass loss rate or a two component stellar wind with low-velocity, low-density material found at a distance greater than 2 stellar radii, which explanation appears most likely.

  16. Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination

    NASA Technical Reports Server (NTRS)

    Wargelin, B.

    2003-01-01

    The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory to study the X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in the existing experimental and theoretical data and are needed to explain all or part of the observed X-ray emission from the Galactic Ridge, solar and stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae.

  17. Radiation-driven winds of hot luminous stars. XI - Frictional heating in a multicomponent stellar wind plasma and decoupling of radiatively accelerated ions

    NASA Astrophysics Data System (ADS)

    Springmann, U. W. E.; Pauldrach, A. W. A.

    1992-09-01

    It is shown that the usual assumption of regarding radiatively driven winds of hot stars as a one-component fluid is wrong under certain circumstances. A detailed investigation of the mechanism of momentum transfer from radiatively accelerated ions to the bulk matter of a stellar wind plasma via Coulomb collisions shows that, at least for thin winds, the one-fluid description is not justified. Instead, for objects with thin winds (candidates are late OV and early BV stars, central stars of planetary nebulae, and subdwarf O-stars) a multicomponent model is required because ionic decoupling occurs, which leads to a 'runaway mechanism' for the accelerated ions and hence terminates the momentum transfer from ions to the bulk matter of the wind (e.g. H and He). As a consequence the predicted one-fluid terminal wind velocities are significantly reduced. This is shown for the late main sequence O-star Tau Scorpii (O9.5V). Furthermore, the collisionally induced momentum transfer is inevitably accompanied by the production of entropy in the form of frictional heating, which dominates the energy balance in the case of thin winds and thus enhances the runaway mechanism.

  18. Effect of scattering on the transonic solution topology and intrinsic variability of line-driven stellar winds

    NASA Astrophysics Data System (ADS)

    Sundqvist, Jon O.; Owocki, Stanley P.

    2015-11-01

    For line-driven winds from hot, luminous OB stars, we examine the subtle but important role of diffuse, scattered radiation in determining both the topology of steady-state solutions and intrinsic variability in the transonic wind base. We use a smooth source function formalizm to obtain non-local, integral expressions for the direct and diffuse components of the line-force that account for deviations from the usual localized, Sobolev forms. As the scattering source function is reduced, we find the solution topology in the transonic region transitions from X-type, with a unique wind solution, to a nodal type, characterized by a degenerate family of solutions. Specifically, in the idealized case of an optically thin source function and a uniformly bright stellar disc, the unique X-type solution proves to be a stable attractor to which time-dependent numerical radiation-hydrodynamical simulations relax. But in models where the scattering strength is only modestly reduced, the topology instead turns nodal, with the associated solution degeneracy now manifest by intrinsic structure and variability that persist down to the photospheric wind base. This highlights the potentially crucial role of diffuse radiation for the dynamics and variability of line-driven winds, and seriously challenges the use of Sobolev theory in the transonic wind region. Since such Sobolev-based models are commonly used in broad applications like stellar evolution and feedback, this prompts development of new wind models, not only for further quantifying the intrinsic variability found here, but also for computing new theoretical predictions of global properties like velocity laws and mass-loss rates.

  19. Radio-continuum emission from the ionized stellar winds of warm supergiants

    NASA Technical Reports Server (NTRS)

    Drake, S. A.; Linsky, J. L.

    1989-01-01

    The Very Large Array has been used at an observing wavelength of 6 cm to survey 25 supergiants of spectral types between B2 and F8. Only one of these stars (Beta Ori, or Rigel) has been detected as a radio-continuum source, with an inferred 6 cm luminosity L6 of 7 x 10 to the 16th ergs/sec per Hz. Rigel may also be an X-ray source (and, if it were, would be the only X-ray detected star out of the 12 stars in this sample that were observed by Einstein. An extended source of more than 10 mJy flux density with the same angular dimensions and location as He 1-5, the planetary nebula surrounding the peculiar supergiant FG Sge, and a weak localized source of roughly 0.1-0.2 mJy somewhat offset from the center of the extended radio emission have also been detected. The upper limits to L6 for the F Ib stars are as much as an order of magnitude below the level at which Rigel was detected. If the radio emission from Rigel is interpreted as free-free radiation from its stellar wind, the inferred ionized mass-loss rate is 2.5 x 10 th the 7th solar mass/yr. The most stringent upper limits to the ionized mass-loss rates obtained for the F and A supergiants are not greater than 10 to the -8th solar mass/yr and less than or equal to 10 to the -7th solar mass/yr, respectively.

  20. Instabilities in line-driven stellar winds. III - Wave propagation in the case of pure line absorption

    NASA Technical Reports Server (NTRS)

    Owocki, S. P.; Rybicki, G. B.

    1986-01-01

    The spatial and temporal evolution of small-amplitude velocity perturbations is examined in the idealized case of a stellar wind that is driven by pure line absorption of the star's continuum radiation. It is established that the instability in the supersonic region is of the advective type relative to the star, but of the absolute type relative to the wind itself. It is also shown that the inward propagation of information in such a wind is limited to the sound speed, in contrast to the theory of Abbott, which predicts inward propagation faster than sound. This apparent contradiction is resolved through an extensive discussion of the analytically soluble case of zero sound speed.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  2. Solar Wind Ablation of Terrestrial Planet Atmospheres

    NASA Technical Reports Server (NTRS)

    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. The steady state solutions of radiatively driven stellar winds for a non-Sobolev, pure absorption model

    NASA Technical Reports Server (NTRS)

    Poe, C. H.; Owocki, S. P.; Castor, J. I.

    1990-01-01

    The steady state solution topology for absorption line-driven flows is investigated for the condition that the Sobolev approximation is not used to compute the line force. The solution topology near the sonic point is of the nodal type with two positive slope solutions. The shallower of these slopes applies to reasonable lower boundary conditions and realistic ion thermal speed v(th) and to the Sobolev limit of zero of the usual Castor, Abbott, and Klein model. At finite v(th), this solution consists of a family of very similar solutions converging on the sonic point. It is concluded that a non-Sobolev, absorption line-driven flow with a realistic values of v(th) has no uniquely defined steady state. To the extent that a pure absorption model of the outflow of stellar winds is applicable, radiatively driven winds should be intrinsically variable.

  4. Synchrotron radiation from the winds of O supergiants - Tb = 10 to the 7. 6th K at 60 stellar radii

    SciTech Connect

    Phillips, R.B.; Titus, M.A. )

    1990-08-01

    Results are presented on VLBI measurements of the nonthermal radio components around two O supergiant stars: Cyg OB2 No. 9 and HD 167971. The measurements were used to characterize the brightness temperature of the emission and to measure the size of compact 5-10 mJy components in these stars, reported by Bieging et al. (1989). The sizes found for the 5-10 mJy components are consistent with the free-free wind radii, indicating that the compact companions are not the sources of nonthermal radiation. Results suggest that there is a small fractional population (10 to the -4th to 10 to the -7th) of ultrarelativistic electrons (Teff of about 10 to the 11th K) coexisting with the stellar wind, which emit optically thin synchrotron radiation. This is in agreement with the synchrotron model of White (1985). 21 refs.

  5. Photoionization of molecular clusters

    NASA Astrophysics Data System (ADS)

    Andres, R. P.; Calo, J. M.

    1981-12-01

    An experimental apparatus consisting of a novel multiple expansion cluster source coupled with a molecular beam system and photoionization mass spectrometer has been designed and constructed. This apparatus has been thoroughly tested and preliminary measurements of the growth kinetics of water clusters and the photoionization cross section of the water dimer have been carried out.

  6. NLTE models of line-driven stellar winds - II. O stars in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Krtička, Jiří

    2006-04-01

    We calculate non-local thermodynamic equilibrium (NLTE) line-driven wind models of selected O stars in the spectral range of O4 to O9 in the Small Magellanic Cloud (SMC). We compare predicted basic wind properties, i.e. the terminal velocity and the mass-loss rate with values derived from observation. We found relatively good agreement between theoretical and observed terminal velocities. On the other hand, predicted mass-loss rates and mass-loss rates derived from observation are in a good agreement only for higher mass-loss rates. Theoretical mass-loss rates lower than approximately 10-7Msolaryr-1 are significantly higher than those derived from observation. These results confirm the previously reported problem of weak winds, since our calculated mass-loss rates are in fair agreement with predictions of Vink et al. We study multicomponent models for these winds. For this purpose we develop a more detailed description of wind decoupling. We show that the instability connected with the decoupling of individual wind elements may occur for low-density winds. In the case of winds with very low observed mass-loss rates the multicomponent effects are important for the wind structure, however this is not able to explain consistently the difference between the predicted mass-loss rate and the mass-loss rate derived from observation for these stars. Similar to previous studies, we found the level of dependence of the wind parameters on the metallicity. We conclude that the wind mass-loss rate significantly increases with metallicity as , whereas the terminal velocity of wind on average depends on metallicity only slightly, namely v∞~Z0.06 (for studied stars).

  7. Exploring the innermost wind region of the massive star QV Nor.

    NASA Astrophysics Data System (ADS)

    Torrejon, Jose M.

    2014-11-01

    QV Nor is the B0I donor of the HMXB 4U1538-52. The neutron star orbits its massive companion in less than 4 days probing, along its eccentric orbit, the innermost (r < 1.4R*) wind regions of the stellar wind. In this work we will present the first high resolution X-ray spectrum of QV Nor, using Chandra HETG. We will present and analysis of the emission lines arising in its photoionized wind as well as the fluorescence Fe K alpha line probing the dense and cold matter. The implications for the wind structure in early type stars will be discussed.

  8. A Wolf-Rayet-Like Progenitor of SN 2013cu from Spectral Observations of a Stellar Wind

    NASA Technical Reports Server (NTRS)

    Gal-Yam, Avishay; Arcavi, I.; Ofek, E. O.; Ben-Ami, S.; Cenko, S. B.; Kasliwal, M. M.; Cao, Y.; Yaron, O.; Tal, D.; Silverman, J. M.; hide

    2014-01-01

    The explosive fate of massive Wolf-Rayet stars (WRSs) is a key open question in stellar physics. An appealing option is that hydrogen- deficient WRSs are the progenitors of some hydrogen-poor supernova explosions of types IIb, Ib and Ic. A blue object, having luminosity and colours consistent with those of some WRSs, has recently been identified in pre-explosion images at the location of a supernova of type Ib, but has not yet been conclusively determined to have been the progenitor. Similar work has so far only resulted in non-detections. Comparison of early photometric observations of type Ic supernovae with theoretical models suggests that the progenitor stars had radii of less than 10(exp 12) centimetres, as expected for some WRSs. The signature of WRSs, their emission line spectra, cannot be probed by such studies. Here we report the detection of strong emission lines in a spectrum of type IIb supernova 2013cu (iPTF13ast) obtained approximately 15.5 hours after explosion (by 'flash spectroscopy', which captures the effects of the supernova explosion shock breakout flash on material surrounding the progenitor star).We identify Wolf-Rayet-like wind signatures, suggesting a progenitor of the WN(h) subclass (those WRSs with winds dominated by helium and nitrogen, with traces of hydrogen). The extent of this dense wind may indicate increased mass loss from the progenitor shortly before its explosion, consistent with recent theoretical predictions.

  9. High efficiency photoionization detector

    DOEpatents

    Anderson, D.F.

    1984-01-31

    A high efficiency photoionization detector is described using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36 [+-] 0.02 eV, and a vapor pressure of 0.35 torr at 20 C. 6 figs.

  10. High efficiency photoionization detector

    DOEpatents

    Anderson, David F.

    1984-01-01

    A high efficiency photoionization detector using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36.+-.0.02 eV, and a vapor pressure of 0.35 torr at 20.degree. C.

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

    NASA Technical Reports Server (NTRS)

    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. Measuring Doppler Shifts of X-Ray Lines to Determine the Stellar Wind X-Ray Locations in OB Stars

    NASA Astrophysics Data System (ADS)

    Waldron, Wayne

    1999-09-01

    For almost 20 years we have been trying to determine the source of the X-ray emission in OB stars. It is generally believed that this emission is caused by a distribution of stellar wind shocks. The AXAF grating spectrometers will provide the ultimate test of X-ray models. The shock model predicts that X-ray lines must be Doppler blue-shifted, hence, our primary objective is to measure these blue-shifts. MARX simulations show that the expected X-ray line shifts will be at least 4 times the MEG1 energy resolution limit. ASCA observations have provided stronger constraints on X-ray models, but they have also raised additional questions (e.g., X-ray abundance anomalies). The large number of X-ray lines predicted by MARX simulations will allow us to probe X-ray densities and abundances.

  13. Orbital period changes and possible stellar wind mass loss in the algol-type binary system AT Pegasi

    NASA Astrophysics Data System (ADS)

    Hanna, Magdy A.

    2012-12-01

    An analysis of the measurements of mid-eclipse times of AT Peg has been presented. It indicates a period decrease rate of dP/dt = -4.2 × 10-7 d/yr, which can be interpreted in terms of mass loss from the system via stellar wind with a rate between (1 and 2) × 10-8 Mʘ/yr. The O-C diagram shows a growing sine wave covering two different cycles of 13 yr and 31.9 yr with amplitudes equal to 0.026 and 0.032 day, respectively. These unequal durations of the cycles may be explained by magnetic activity cycling variations due to star spots. The obtained characteristics of the second cycle are consistent with similar systems when applying Applegate’s mechanism.

  14. ORFEUS observations of SVI, OVI and PV in the stellar wind from the nucleus of NGC 6543.

    NASA Astrophysics Data System (ADS)

    Zweigle, J.; Grewing, M.; Barnstedt, J.; Goelz, M.; Gringel, W.; Haas, C.; Hopfensitz, W.; Kappelmann, N.; Kraemer, G.; Appenzeller, I.; Krautter, J.; Mandel, H.

    1997-05-01

    During the ORFEUS-SPAS (Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer on the Shuttle Pallet Satellite) mission STS-51, flown in September 1993, we observed, to our knowledge for the first time, the central star of the planetary nebula NGC 6543 in the far ultraviolet (90nm-115nm) wavelength region using the University of California, Berkeley spectrometer. The spectral resolution of the instrument during the flight was about 0.03nm. The observed stellar continuum energy distribution can be approximated by a modelled stellar atmosphere from Clegg and Middlemass with a temperature of 50000K and a gravity of log(g)=4.5, using an extinction of E(B-V)=0.08. In addition to narrow absorption lines of atomic species (e.g. HI, CI, NI, OI) the spectrum shows narrow absorption lines of molecular hydrogen and strong P-Cygni line profiles of the SVI (93.3nm, 94.5nm), OVI (103.2nm, 103.8nm) and PV (111.8nm, 112.8nm) resonance doublets. The analysis of these three P-Cygni line doublets using the escape probability method yields together with the consideration of the NV (123.9nm, 124.3nm), SiIV (139.4nm, 140.3nm) and CIV (154.8nm, 155.1nm) P-Cygni line doublets from IUE spectra as a mean value for the lower limit of the central star's mass loss rate 2.8x10^-9^Msun_/yr. This value for the stellar mass loss rate of the nucleus of NGC 6543 is compatible within a factor of two with the expected mass loss rate from the approximate radiation driven wind theory for an evolved star with a mass of 0.62Msun_, a luminosity of 3030Lsun_ and an effective temperature of 50000K.

  15. Simplified models of stellar wind anatomy for interpreting high-resolution data. Analytical approach to embedded spiral geometries

    NASA Astrophysics Data System (ADS)

    Homan, Ward; Decin, Leen; de Koter, Alex; van Marle, Allard Jan; Lombaert, Robin; Vlemmings, Wouter

    2015-07-01

    Context. Recent high-resolution observations have shown that stellar winds harbour complexities that strongly deviate from spherical symmetry, which generally is assumed as standard wind model. One such morphology is the Archimedean spiral, which is generally believed to be formed by binary interactions, as has been directly observed in multiple sources. Aims: We seek to investigate the manifestation in the observables of spiral structures embedded in the spherical outflows of cool stars. We aim to provide an intuitive bedrock with which upcoming ALMA data can be compared and interpreted. Methods: By means of an extended parameter study, we modelled rotational CO emission from the stellar outflow of asymptotic giant branch stars. To this end, we developed a simplified analytical parametrised description of a 3D spiral structure. This model is embedded into a spherical wind and fed into the 3D radiative transfer code LIME, which produces 3D intensity maps throughout velocity space. Subsequently, we investigated the spectral signature of rotational transitions of CO in the models, as well as the spatial aspect of this emission by means of wide-slit position-velocity (PV) diagrams. Additionally, we quantified the potential for misinterpreting the 3D data in a 1D context. Finally, we simulated ALMA observations to explore the effect of interferometric noise and artefacts on the emission signatures. Results: The spectral signatures of the CO rotational transition v = 0J = 3 - 2 are very efficient at concealing the dual nature of the outflow. Only a select few parameter combinations allow for the spectral lines to disclose the presence of the spiral structure. If the spiral cannot be distinguished from the spherical signal, this might result in an incorrect interpretation in a 1D context. Consequently, erroneous mass-loss rates would be calculated. The magnitude of these errors is mainly confined to a factor of a few, but in extreme cases can exceed an order of magnitude

  16. Modeling the thermal X-ray emission around the Galactic center from colliding stellar winds

    NASA Astrophysics Data System (ADS)

    Russell, Christopher Michael Post; Wang, Daniel; Cuadra, Jorge

    2016-04-01

    The Galactic center is a hotbed of astrophysical activity. Powering these processes is the injection of wind material from ˜30 massive Wolf-Rayet (WR) stars orbiting within 12" of the super-massive black hole (SMBH). Hydrodynamic simulations of such colliding and accreting winds produce a complex density and temperature structure of cold wind material shocking with the ambient medium, creating a large reservoir of hot, X-ray-emitting gas. A Chandra X-ray Visionary Program that observed the Galactic center for 3 Ms resolved this diffuse emission. This work computes the X-ray emission from these hydrodynamic simulations of the WR winds with the aim of reproducing the Chandra observations, amid exploring a variety of SMBH feedback mechanisms. The success of the model is the spectrum from the 2"-5" ring around the SMBH matches the shape of the observed spectrum very well. This naturally explains that the hot gas comes from colliding WR winds, and that the winds speeds of these stars are in general well constrained. The model flux in this ring and over the ±6" images of 4-9keV is ˜2.2× lower than the observations, with stronger feedback mechanisms leading to weaker X-ray emission since more hot, X-ray-emitting gas is cleared from the spherical r < 12" simulation volume. Possible improvements to rectify this flux discrepancy are increasing the mass loss rates of the WRs and/or adding more gas into the simulation, such as from the O stars and their winds, so the adiabatic WR shocks occur closer to their stars, thereby becoming brighter in X-rays.

  17. Extrasolar Giant Magnetospheric Response to Steady-state Stellar Wind Pressure at 10, 5, 1, and 0.2 au

    NASA Astrophysics Data System (ADS)

    Tilley, Matt A.; Harnett, Erika M.; Winglee, Robert M.

    2016-08-01

    A three-dimensional, multifluid simulation of a giant planet’s magnetospheric interaction with steady-state stellar wind from a Sun-like star was performed for four different orbital semimajor axes—10, 5, 1, and 0.2 au. We simulate the effect of the increasing, steady-state stellar wind pressure related to the planetary orbital semimajor axis on the global magnetospheric dynamics for a Saturn-like planet, including an Enceladus-like plasma torus. Mass-loss processes are shown to vary with orbital distance, with the centrifugal interchange instability displayed only in the 10 and 5 au cases, which reach a state of mass-loss equilibrium more slowly than the 1 or 0.2 au cases. The compression of the magnetosphere in the 1 and 0.2 au cases contributes to the quenching of the interchange process by increasing the ratio of total plasma thermal energy to corotational energy. The strength of field-aligned currents, associated with auroral radio emissions, is shown to increase in magnitude and latitudinal coverage with a corresponding shift equatorward from increased dynamic ram pressure experienced in the hotter orbits. Similar to observed hot Jovian planets, the warm exo-Saturn simulated in the current work shows enhanced ion density in the magnetosheath and magnetopause regions, as well as the plasma torus, which could contribute to altered transit signals, suggesting that for planets in warmer (>0.1 au) orbits, planetary magnetic field strengths and possibly exomoons—via the plasma torus—could be observable with future missions.

  18. Extrasolar giant magnetospheric response to steady-state stellar wind pressure at 10, 5, 1, and 0.2 AU

    NASA Astrophysics Data System (ADS)

    Tilley, Matt; Harnett, Erika; Winglee, Robert

    2016-10-01

    A three-dimensional, multifluid simulation of a giant planet's magnetospheric interaction with steady-state stellar wind from a Sun-like star was performed for four different orbital semi-major axes - 10, 5, 1 and 0.2 AU. We simulate the effect of the increasing, steady-state stellar wind pressure related to the planetary orbital semi-major axis on the global magnetospheric dynamics for a Saturn-like planet, including an Enceladus-like plasma torus. Mass loss processes are shown to vary with orbital distance, with the centrifugal interchange instability displayed only in the 10 AU and 5 AU cases which reach a state of mass loss equilibrium more slowly than the 1 AU or 0.2 AU cases. The compression of the magnetosphere in the 1 AU and 0.2 AU cases contributes to the quenching of the interchange process by increasing the ratio of total plasma thermal energy to corotational energy. The strength of field-aligned currents (FAC), associated with auroral radio emissions, are shown to increase in magnitude and latitudinal coverage with a corresponding shift equatorward from increased dynamic ram pressure experienced in the hotter orbits. Similar to observed hot Jovian planets, the warm exo-Saturn simulated in the current work shows enhanced ion density in the magnetosheath and magnetopause regions, as well as the plasma torus which could contribute to altered transit signals, suggesting that for planets in warmer (> 0.1 AU) orbits, planetary magnetic field strengths and possibly exomoons - via the plasma torus - could be observable with future missions.

  19. Polarization signatures of bow shocks: A diagnostic tool to constrain the properties of stellar winds and ISM

    NASA Astrophysics Data System (ADS)

    Shrestha, Manisha; Hoffman, Jennifer L.; Nielson, Hilding R.; Ignace, Richard

    2017-01-01

    When a stellar wind traveling at supersonic speed interacts with almost stationary ISM, a bow shock shape is formed. By studying a bow shock, we can obtain information about the properties of the stellar wind as well as the surrounding ISM. Bow shocks are asymmetric structures, and thus produce net polarization even if they are unresolved. Hence, polarization studies of bow shocks can provide complementary constraints on their properties.We simulate the polarization signatures of circumstellar material with bow shock geometries using a Monte Carlo radiative transfer code called SLIP. We use the analytic solution from Wilkin (1996) to define the geometry and mass surface density of the bow shock in our models. We present results from our simulations showing how changing CSM optical depth, CSM albedo, photon source, and scattering particles (electrons or different types of dust particles) affects the observed polarization in both resolved and unresolved cases. In the optically thin regime of the unresolved electron-scattering case, the polarization peaks at an inclination angle of 90°, in agreement with analytical single-scattering models. In optically thick cases, a second polarization peak appears near 130°, which we propose is due to multiple scattering. Given these results, an observed polarization value can constrain the inclination of an unresolved bow shock to two possible angles, which in turn constrain the motion of the star. In case of resolved bow shocks, our simulations produce polarization maps which we compare with observations.We also present results from our dust-scattering simulations, which show that multicolor broadband polarization observations can constrain the characteristics of the dust in a resolved or unresolved bow shock-shaped CSM configuration.

  20. Fractionated stellar wind and the H/He abundance anomalies in BP stars

    NASA Astrophysics Data System (ADS)

    Hunger, K.; Groote, D.

    1999-11-01

    Radiatively driven winds occur in all main sequence stars (Babel \\cite{Bab1}, \\cite{Bab2}). However, due to the weak coupling between the photon absorbing metals and the inert elements H and He, the wind in the low temperature domain is fractionated: He decouples from the wind at T_eff < 25 000 K, and below 17 000 K even H. The decoupled elements fall back to the surface of the star thus creating overabundances and abundance stratifications. These anomalies, however, become manifest only if atmospheric turbulence is suppressed (say by magnetic fields). In order to prove the validity of the described scenario, all B_p stars for which reliable fundamental parameters exist, are discussed on the basis of the (augmented) (g, T_eff)-diagram of Babel (\\cite{Bab2}). It is shown that the fractionation process is able to explain the observed temperature sequence of He-rich and He-poor stars, additionally to classical diffusion processes. A necessary condition is that a magnetic field is present. This explains why only a fraction of B stars exhibits H/He anomalies. While classical diffusion operates in the quiet zones (no wind) of a star, fractionation takes place above the wind bases.

  1. Feeding the monster: Wind accretion in Cygnus X-1

    NASA Astrophysics Data System (ADS)

    Miskovicova, Ivica

    2012-07-01

    Stellar wind in HMXBs is highly structured: dense clumps of low temperatures are embedded in highly ionized material. We present analysis of the focused stellar wind in the hard state of Cygnus X-1 from high-resolution Chandra-HETGS observations at four distinct orbital phases: phi~0, ~0.2, ~0.5 and ~0.75. All light curves but the one at phi~0.5 show strong absorption dips that are believed to be caused by the clumps. We compare the spectral properties between dips and persistent flux: while the H-like and He-like absorption lines reveal the highly photoionized wind, the lines of lower ionization stages visible only in the dip spectra constrain the properties of the clumps. Comparison between different orbital phases allows us to study the complex structure and dynamics of the wind.

  2. Photoionization of Ar VIII

    NASA Astrophysics Data System (ADS)

    Liang, Liang; Jiang, Wen-xian; Zhou, Chao

    2017-01-01

    The photoionization cross section, energy levels and widths of 22 Rydberg series (in the autoionization region) for Na-like Ar VIII were investigated by using of R-matrix method. The relativistic distorted-wave method is used to calculate the radial functions, and QB method of Quigly-Berrington [Quigley et al. 1998] is employed to calculate the resonance levels and widths. We have identified the formant in the figure of the photoionization cross section.

  3. The Zeeman effect in the Sobolev approximation: applications to spherical stellar winds

    NASA Astrophysics Data System (ADS)

    Ignace, R.; Gayley, K. G.

    2003-05-01

    Modern spectropolarimeters are capable of detecting subkilogauss field strengths using the Zeeman effect in line profiles from the static photosphere, but supersonic Doppler broadening makes it more difficult to detect the Zeeman effect in the wind lines of hot stars. Nevertheless, the recent advances in observational capability motivate an assessment of the potential for detecting the magnetic fields threading such winds. We incorporate the weak-field longitudinal Zeeman effect in the Sobolev approximation to yield integral expressions for the flux of circularly polarized emission. To illustrate the results, two specific wind flows are considered: (i) spherical constant expansion with v(r) =v∞ and (ii) homologous expansion with v(r) ~r. Axial and split monopole magnetic fields are used to schematically illustrate the polarized profiles. For constant expansion, optically thin lines yield the well-known `flat-topped' total intensity emission profiles and an antisymmetric circularly polarized profile. For homologous expansion, we include occultation and wind absorption to provide a more realistic observational comparison. Occultation severely reduces the circularly polarized flux in the redshifted component, and in the blueshifted component, the polarization is reduced by partially offsetting emission and absorption contributions. We find that for a surface field of approximately 100 G, the largest polarizations result for thin but strong recombination emission lines. Peak polarizations are approximately 0.05 per cent, which presents a substantial although not inconceivable sensitivity challenge for modern instrumentation.

  4. THE MYSTERIOUS SICKLE OBJECT IN THE CARINA NEBULA: A STELLAR WIND INDUCED BOW SHOCK GRAZING A CLUMP?

    SciTech Connect

    Ngoumou, Judith; Preibisch, Thomas; Ratzka, Thorsten; Burkert, Andreas

    2013-06-01

    Optical and near-infrared images of the Carina Nebula show a peculiar arc-shaped feature, which we call the ''Sickle'', next to the B-type star Trumpler 14 MJ 218. We use multi-wavelength observations to explore and constrain the nature and origin of the nebulosity. Using submillimeter data from APEX/LABOCA as well as Herschel far-infrared maps, we discovered a dense, compact clump with a mass of {approx}40 M{sub Sun} located close to the apex of the Sickle. We investigate how the B star MJ 218, the Sickle, and the clump are related. Our numerical simulations show that, in principle, a B-type star located near the edge of a clump can produce a crescent-shaped wind shock front, similar to the observed morphology. However, the observed proper motion of MJ 218 suggests that the star moves with high velocity ({approx}100 km s{sup -1}) through the ambient interstellar gas. We argue that the star is just about to graze along the surface of the clump, and the Sickle is a bow shock induced by the stellar wind, as the object moves supersonically through the density gradient in the envelope of the clump.

  5. Hydrodynamic simulations of stellar wind disruption by a compact X-ray source

    NASA Technical Reports Server (NTRS)

    Blondin, John M.; Kallman, Timothy R.; Fryxell, Bruce A.; Taam, Ronald E.

    1990-01-01

    This paper presents two-dimensional numerical simulations of the gas flow in the orbital plane of a massive X-ray binary system, in which the mass accretion is fueled by a radiation-driven wind from an early-type companion star. These simulations are used to examine the role of the compact object (either a neutron star or a black hole) in disturbing the radiatively accelerating wind of the OB companion, with an emphasis on understanding the origin of the observed soft X-ray photoelectric absorption seen at late orbital phases in these systems. On the basis of these simulations, it is suggested that the phase-dependent photoelectric absorption seen in several of these systems can be explained by dense filaments of compressend gas formed in the nonsteady accreation bow shock and wake of the compact object.

  6. Simultaneous visible and ultraviolet spectroscopy of stellar wind variability in Zeta Puppis

    NASA Technical Reports Server (NTRS)

    Wegner, G. A.; Snow, T. P., Jr.

    1978-01-01

    Spectra of He II 4686 A and H-alpha in Zeta Pup were obtained simultaneously with Copernicus ultraviolet scans of several P Cygni profiles in this O4 If supergiant with strong mass loss. The visible-wavelength data show significant variations in the profiles of both lines, consisting of doubling of the emission over times of less than a day. Recent theoretical calculations show that the observed profile variations in 4686 A can be produced by significant fluctuations in the wind density. The Copernicus data show less variability, although in one scan of the 1400-A Si IV doublet there appears to be a significant enhancement of the emission which may be correlated with one of the doublings observed in 4686 A and H-alpha, as though a density enhancement formed at low levels and then moved outward in the wind.

  7. The Production Phase for the National Compact Stellarator Experiment (NCSX) Modular Coil Winding Forms

    SciTech Connect

    Heitzenroeder, P.; Brown, T.; Neilson, G.; Malinowski, F.; Sutton, L.; Nelson, B.; Williamson, D.; Horton, N.; Goddard, B.; Edwards, J.; Bowling, K.; Hatzilias, K.

    2005-10-20

    The production phase for the NCSX modular coil winding forms has been underway for approximately one year as of this date. This is the culmination of R&D efforts performed in 2001-4. The R&D efforts included limited manufacturing studies while NCSX was in its conceptual design phase followed by more detailed manufacturing studies by two teams which included the fabrication of full scale prototypes. This provided the foundation necessary for the production parts to be produced under a firm price and schedule contract that was issued in September 2004. This paper will describe the winding forms, the production team and team management, details of the production process, and the achievements for the first year.

  8. Colliding stellar winds in the eclipsing Wolf-Rayet binary V444 Cygni

    NASA Technical Reports Server (NTRS)

    Brown, Douglas N.; Shore, Steven N.

    1988-01-01

    High resolution spectra of V444 Cygni have been obtained using the International Ultraviolet Explorer Satellite. These spectra span both eclipses and include one observation at third quadrature. Together with seven archival spectra, they provide reasonably complete phase coverage for the system. The variations in the P Cygni profiles of the He(II) and N(IV) lines, imply the existence of a low density region in the WR wind. This region occupies a relatively narrow range of orbital phase coinciding with the highest terminal velocities observed in C IV. These data are interpreted to be evidence of an interaction region separating the winds of the O-star and Wolf-Rayet star.

  9. Simultaneous visible and ultraviolet spectroscopy of stellar wind variability in Zeta Puppis

    NASA Technical Reports Server (NTRS)

    Wegner, G. A.; Snow, T. P., Jr.

    1978-01-01

    Spectra of He II 4686 A and H-alpha in Zeta Pup were obtained simultaneously with Copernicus ultraviolet scans of several P Cygni profiles in this O4 If supergiant with strong mass loss. The visible-wavelength data show significant variations in the profiles of both lines, consisting of doubling of the emission over times of less than a day. Recent theoretical calculations show that the observed profile variations in 4686 A can be produced by significant fluctuations in the wind density. The Copernicus data show less variability, although in one scan of the 1400-A Si IV doublet there appears to be a significant enhancement of the emission which may be correlated with one of the doublings observed in 4686 A and H-alpha, as though a density enhancement formed at low levels and then moved outward in the wind.

  10. The sn stars - Magnetically controlled stellar winds among the helium-weak stars

    NASA Technical Reports Server (NTRS)

    Shore, Steven N.; Brown, Douglas N.; Sonneborn, George

    1987-01-01

    The paper reports observations of magnetically controlled stellar mass outflows in three helium-weak sn stars: HD 21699 = HR 1063; HD 5737 = Alpha Scl; and HD 79158 = 36 Lyn. IUE observations show that the C IV resonance doublet is variable on the rotational timescale but that there are no other strong-spectrum variations in the UV. Magnetic fields, which reverse sign on the rotational timescale, are present in all three stars. This phenomenology is interpreted in terms of jetlike mass loss above the magnetic poles, and these objects are discussed in the context of a general survey of the C IV and Si IV profiles of other more typical helium-weak stars.

  11. Influence of a stellar wind on the evolution of a star of 30 solar masses

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.

    1980-01-01

    A coarse grid of theoretical evolutionary tracks was calculated for a 30 solar mass star to determine the role of mass loss in the evolution of the star during core He burning. The Cox-Stewart opacities were applied, and the rate of mass loss, criterion for convection, and initial chemical composition were taken into consideration. Using the Schwarzschild criterion, the star undergoes little mass loss during core He burning and remains a blue supergiant separated from main sequence stars on the H-R diagram. The stellar remnant consists of the original He core and may appear bluer than equally luminous main sequence stars; a variety of possible evolutionary tracks can be obtained for an initial solar mass of 30 with proper choices of free parameters.

  12. Microlensing of circumstellar envelopes. III. Line profiles from stellar winds in homologous expansion

    NASA Astrophysics Data System (ADS)

    Hendry, M. A.; Ignace, R.; Bryce, H. M.

    2006-05-01

    This paper examines line profile evolution due to the linear expansion of circumstellar material obsverved during a microlensing event. This work extends our previous papers on emission line profile evolution from radial and azimuthal flow during point mass lens events and fold caustic crossings. Both "flavours" of microlensing were shown to provide effective diagnostics of bulk motion in circumstellar envelopes. In this work a different genre of flow is studied, namely linear homologous expansion, for both point mass lenses and fold caustic crossings. Linear expansion is of particular relevance to the effects of microlensing on supernovae at cosmological distances. We derive line profiles and equivalent widths for the illustrative cases of pure resonance and pure recombination lines, modelled under the Sobolev approximation. The efficacy of microlensing as a diagnostic probe of the stellar environs is demonstrated and discussed.

  13. Influence of a stellar wind on the evolution of a star of 30 solar masses

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.

    1980-01-01

    A coarse grid of theoretical evolutionary tracks was calculated for a 30 solar mass star to determine the role of mass loss in the evolution of the star during core He burning. The Cox-Stewart opacities were applied, and the rate of mass loss, criterion for convection, and initial chemical composition were taken into consideration. Using the Schwarzschild criterion, the star undergoes little mass loss during core He burning and remains a blue supergiant separated from main sequence stars on the H-R diagram. The stellar remnant consists of the original He core and may appear bluer than equally luminous main sequence stars; a variety of possible evolutionary tracks can be obtained for an initial solar mass of 30 with proper choices of free parameters.

  14. Waves and Turbulence in Stellar Winds across the H-R Diagram

    NASA Technical Reports Server (NTRS)

    Cranmer, Steven R.; Frogel, Jay (Technical Monitor)

    2005-01-01

    During the first year of this project, the PI began work in several areas that are expected to yield a substantial increase in our understanding of how and why stars form winds and disks. The approach outlined in the original proposal comprised four complementary pieces (cool and hot stars; observations and theory for each), and the accomplishments in this report are thus divided into these four categories.

  15. Accretion, jets and winds: High-energy emission from young stellar objects

    NASA Astrophysics Data System (ADS)

    Günther, H. M.

    2011-06-01

    This article summarizes the processes of high-energy emission in young stellar objects. Stars of spectral type A and B are called Herbig Ae/Be (HAeBe) stars in this stage, all later spectral types are termed classical T Tauri stars (CTTS). Both types are studied by high-resolution X-ray and UV spectroscopy and modeling. Three mechanisms contribute to the high-energy emission from CTTS: 1) CTTS have active coronae similar to main-sequence stars, 2) the accreted material passes through an accretion shock at the stellar surface, which heats it to a few MK, and 3) some CTTS drive powerful outflows. Shocks within these jets can heat the plasma to X-ray emitting temperatures. Coronae are already well characterized in the literature; for the latter two scenarios models are shown. The magnetic field suppresses motion perpendicular to the field lines in the accretion shock, thus justifying a 1D geometry. The radiative loss is calculated as optically thin emission. A mixture of shocked and coronal gas is fitted to X-ray observations of accreting CTTS. Specifically, the model explains the peculiar line-ratios in the He-like triplets of Ne IX and O VII. All stars require only small mass accretion rates to power the X-ray emission. In contrast, the HAeBe HD 163296 has line ratios similar to coronal sources, indicating that neither a high density nor a strong UV-field is present in the region of the X-ray emission. This could be caused by a shock in its jet. Similar emission is found in the deeply absorbed CTTS DG Tau. Shock velocities between 400 and 500 km s-1 are required to explain the observed spectrum. Doctoral Thesis Award Lecture 2010

  16. The Geometry of the Stellar Winds and Shock Structure in V444 Cyg

    NASA Astrophysics Data System (ADS)

    Hoffman, Jennifer

    Given the importance of mass loss in the evolution of massive stars, it is imperative that we improve our understanding of the processes by which the outer layers of a star may be lost to its environment. The eclipsing nature of the Wolf-Rayet binary star V444 Cyg provides us with a unique opportunity to study the detailed characteristics of the radiatively driven mass loss in colliding-wind systems. Our multi-technique study combines X-ray spectroscopic and optical spectropolarimetric methods to describe the three-dimensional nature of the shock and wind structure in V444 Cyg. In support of this project, we have won new X-ray observations of V444 Cyg using the XMM-Newton telescope through the Guest Observer program in AO-11 (proposal ID #069281). We will combine these new data with six archival XMM-Newton observations and with optical spectropolarimetry obtained with the newly refurbished Half-Wave Spectropolarimeter (HPOL) at Ritter Observatory in Toledo, OH and archival data from both HPOL and the ESPaDOnS instrument at CFHT. Detailed X-ray light curve analysis and modeling of the X-ray spectra will constrain the location of the wind collision region and the mass-loss properties of the system. Polarized light curves in optical broad bands and emission lines combined with spectropolarimetric line profile analysis and radiative transfer simulations will trace the geometrical structure of various emission and scattering regions within the winds. Joint analysis of these two data sets will allow us to construct a self-consistent, physically realistic three-dimensional model of the complex winds in V444 Cyg and quantify its mass loss characteristics. We request support for data analysis and interpretation of our four new XMM-Newton observations. This will consist primarily of salaries for program personnel, who will analyze the new data in conjunction with previous X-ray results, carry out detailed radiation-hydrodynamic simulations to investigate the effect of

  17. Photoionization and Recombination

    NASA Technical Reports Server (NTRS)

    Nahar, Sultana N.

    2000-01-01

    Theoretically self-consistent calculations for photoionization and (e + ion) recombination are described. The same eigenfunction expansion for the ion is employed in coupled channel calculations for both processes, thus ensuring consistency between cross sections and rates. The theoretical treatment of (e + ion) recombination subsumes both the non-resonant recombination ("radiative recombination"), and the resonant recombination ("di-electronic recombination") processes in a unified scheme. In addition to the total, unified recombination rates, level-specific recombination rates and photoionization cross sections are obtained for a large number of atomic levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling, calculations are carried out in the close coupling approximation using the R-matrix method. Although the calculations are computationally intensive, they yield nearly all photoionization and recombination parameters needed for astrophysical photoionization models with higher precision than hitherto possible, estimated at about 10-20% from comparison with experimentally available data (including experimentally derived DR rates). Results are electronically available for over 40 atoms and ions. Photoionization and recombination of He-, and Li-like C and Fe are described for X-ray modeling. The unified method yields total and complete (e+ion) recombination rate coefficients, that can not otherwise be obtained theoretically or experimentally.

  18. The binary systems IC 10 X-1 and NGC 300 X-1: Accretion of matter from an intense Wolf-Rayet stellar wind onto a black hole

    NASA Astrophysics Data System (ADS)

    Tutukov, A. V.; Fedorova, A. V.

    2016-01-01

    The current evolutionary stage of the binary systems IC 10 X-1 and NGC 300 X-1, which contain a massive black hole and a Wolf-Rayet star with a strong stellar wind that does not fill its Roche lobe, is considered. The high X-ray luminosity and X-ray properties testify to the presence of accretion disks in these systems. The consistency of the conditions for the existence of such a disk and the possibility of reproducing the observed X-ray luminosity in the framework of the Bondi-Hoyle-Littleton theory for a spherically symmetric stellar wind is analyzed. A brief review of information about the mass-loss rates of Wolf-Rayet stars and the speeds of their stellar winds is given. The evolution of these systems at the current stage is computed. Estimates made using the derived parameters show that it is not possible to achieve consistency, since the conditions for the existence of an accretion disk require that the speed of the Wolf-Rayetwind be appreciably lower than is required to reproduce the observedX-ray luminosity. Several explanations of this situation are possible: (1) the real pattern of the motion of the stellar-wind material in the binary is substantially more complex than is assumed in the Bondi-Hoyle-Littleton theory, changing the conditions for the formation of an accretion disk and influencing the accretion rate onto the black hole; (2) some of the accreting material leaves the accretor due to X-ray heating; (3) the accretion efficiency in these systems is nearly an order of magnitude lower than in the case of accretion through a thin disk onto a non-rotating black hole; (4) the intensity of the Wolf-Rayet wind is one to two orders of magnitude lower than has been suggested by modern studies.

  19. Flash-photoionized nebulae

    NASA Technical Reports Server (NTRS)

    Katz, J. I.

    1989-01-01

    Under conditions of high radiation intensity and low gas density, recombination may be neglected in determining the ionization state of a photoionized gas. Calculations of the ionization structure of nebulae in this 'flash-photoionized' regime are reported. Very hard spectra of ionizing ultraviolet radiation may be produced by filtration of the ionizing flux through a neutral hydrogen layer which preferentially absorbs photons just above the hydrogen photoionization threshold. Fluxes with these hard spectra produce gas layer in which helium is largely doubly ionized while hydrogen is largely neutral. Such a layer leads to anomalously high ratios of He II to H I recombination line strengths. These results are applied to the problem of the spectrum of the arc in the cluster of galaxies A370. It is found that the spectrum may possibly be reconciled with the light echo model.

  20. Flash-photoionized nebulae

    SciTech Connect

    Katz, J.I.

    1989-05-01

    Under conditions of high radiation intensity and low gas density, recombination may be neglected in determining the ionization state of a photoionized gas. Calculations of the ionization structure of nebulae in this 'flash-photoionized' regime are reported. Very hard spectra of ionizing ultraviolet radiation may be produced by filtration of the ionizing flux through a neutral hydrogen layer which preferentially absorbs photons just above the hydrogen photoionization threshold. Fluxes with these hard spectra produce gas layer in which helium is largely doubly ionized while hydrogen is largely neutral. Such a layer leads to anomalously high ratios of He II to H I recombination line strengths. These results are applied to the problem of the spectrum of the arc in the cluster of galaxies A370. It is found that the spectrum may possibly be reconciled with the light echo model. 25 refs.

  1. Radiation Pressure--driven Magnetic Disk Winds in Broad Absorption Line Quasi-stellar Objects

    NASA Astrophysics Data System (ADS)

    de Kool, Martijn; Begelman, Mitchell C.

    1995-12-01

    We explore a model in which QSO broad absorption lines (BALs) are formed in a radiation pressure- driven wind emerging from a magnetized accretion disk. The magnetic field threading the disk material is dragged by the flow and is compressed by the radiation pressure until it is dynamically important and strong enough to contribute to the confinement of the BAL clouds. We construct a simple self-similar model for such radiatively driven magnetized disk winds, in order to explore their properties. It is found that solutions exist for which the entire magnetized flow is confined to a thin wedge over the surface of the disk. For reasonable values of the mass-loss rate, a typical magnetic field strength such that the magnetic pressure is comparable to the inferred gas pressure in BAL clouds, and a moderate amount of internal soft X-ray absorption, we find that the opening angle of the flow is approximately 0.1 rad, in good agreement with the observed covering factor of the broad absorption line region.

  2. Radiation Pressure-Driven Magnetic Disk Winds in Broad Absorption Line Quasi-Stellar Objects

    NASA Technical Reports Server (NTRS)

    DeKool, Martin; Begelman, Mitchell C.

    1995-01-01

    We explore a model in which QSO broad absorption lines (BALS) are formed in a radiation pressure-driven wind emerging from a magnetized accretion disk. The magnetic field threading the disk material is dragged by the flow and is compressed by the radiation pressure until it is dynamically important and strong enough to contribute to the confinement of the BAL clouds. We construct a simple self-similar model for such radiatively driven magnetized disk winds, in order to explore their properties. It is found that solutions exist for which the entire magnetized flow is confined to a thin wedge over the surface of the disk. For reasonable values of the mass-loss rate, a typical magnetic field strength such that the magnetic pressure is comparable to the inferred gas pressure in BAL clouds, and a moderate amount of internal soft X-ray absorption, we find that the opening angle of the flow is approximately 0.1 rad, in good agreement with the observed covering factor of the broad absorption line region.

  3. Double Photoionization Near Threshold

    NASA Technical Reports Server (NTRS)

    Wehlitz, Ralf

    2007-01-01

    The threshold region of the double-photoionization cross section is of particular interest because both ejected electrons move slowly in the Coulomb field of the residual ion. Near threshold both electrons have time to interact with each other and with the residual ion. Also, different theoretical models compete to describe the double-photoionization cross section in the threshold region. We have investigated that cross section for lithium and beryllium and have analyzed our data with respect to the latest results in the Coulomb-dipole theory. We find that our data support the idea of a Coulomb-dipole interaction.

  4. VLT/FLAMES-ARGUS observations of stellar wind-ISM cloud interactions in NGC 6357

    NASA Astrophysics Data System (ADS)

    Westmoquette, M. S.; Slavin, J. D.; Smith, L. J.; Gallagher, J. S., III

    2010-02-01

    We present optical/near-IR integral field unit observations of a gas pillar in the Galactic HII region NGC 6357 containing the young open star cluster Pismis 24. These observations have allowed us to examine in detail the gas conditions of the strong wind-clump interactions taking place on its surface. By accurately decomposing the Hα line profile, we identify the presence of a narrow (~20kms-1) and broad (50-150kms-1) component, both of which we can associate with the pillar and its surroundings. Furthermore, the broadest broad component widths are found in a region that follows the shape of the eastern pillar edge. These connections have allowed us to firmly associate the broad component with emission from ionized gas within turbulent mixing layers on the pillar's surface set up by the shear flows of the winds from the O stars in the cluster. We discuss the implications of our findings in terms of the broad emission-line component that is increasingly found in extragalactic starburst environments. Although the broad linewidths found here are narrower, we conclude that the mechanisms producing both must be the same. The difference in linewidths may result from the lower total mechanical wind energy produced by the O stars in Pismis 24 compared to that from a typical young massive star cluster found in a starburst galaxy. The pillar's edge is also clearly defined by dense (<~5000cm-3), hot (>~20000K) and excited (via the [NII]/Hα and [SII]/Hα ratios) gas conditions, implying the presence of a D-type ionization front propagating into the pillar surface. Although there must be both photoevaporation outflows produced by the ionization front and mass loss through mechanical ablation, we see no evidence for any significant bulk gas motions on or around the pillar. We postulate that the evaporated/ablated gas must be rapidly heated before being entrained. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere

  5. Simulations of stellar winds and planetary bodies: Ionosphere-rich obstacles in a super-Alfvénic flow

    NASA Astrophysics Data System (ADS)

    Vernisse, Y.; Riousset, J. A.; Motschmann, U.; Glassmeier, K.-H.

    2017-03-01

    We classify the interactions of planetary obstacles with an upstream stellar wind. The investigation of each type of interaction is made using a three dimensional simulation code based on the hybrid modeling of the interplanetary plasma (the AIKEF code). The aim is to fill up the parameter space of magnetospheric interactions. In this work, we focus on highly resistive obstacles, non-magnetized but possessing an ionosphere. We examine different ionospheric types by focusing on one parameter: the ionospheric production. Two types of ionospheric ions are used: H+ and O+, to show the influence of ionospheric ion mass on the interaction region configuration. The interaction types are classified using an equivalent conductivity of the ionosphere. The resulting induced magnetospheric interactions are described using the currents flowing throughout the interaction region. The essence of the interaction region structure is summarized into three-dimensional diagrams of the current distribution. The results show three main stages of development. The first is a lunar-type interaction with raising asymmetries. The second is depicted by the presence of a growing induced magnetopause and an interaction region which asymmetry depends on the mass of the ionospheric ions. The last stage is a fully developed induced magnetosphere, or Venus-like interaction, with a symmetric magnetosphere.

  6. Photoionization-photoelectron research

    SciTech Connect

    Berkowitz, J.; Ruscic, B.

    1993-12-01

    The photoionization research program is aimed at understanding the basic processes of interaction of vacuum ultraviolet (VUV) light with atoms and molecules. This research provides valuable information on both thermochemistry and dynamics. Recent studies include atoms, clusters, hydrides, sulfides and an important fluoride.

  7. Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination

    NASA Technical Reports Server (NTRS)

    Wargelin, B.

    2002-01-01

    The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory (LLNL) to study X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in existing experimental and theoretical understanding of this atomic physics process, and are needed to explain all or part of the observed X-ray emission from the soft X-ray background, stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae. Progress made during the first year of the grant is described, as is work planned for the second year.

  8. Stellar wind-magnetosphere interaction at exoplanets: computations of auroral radio powers

    NASA Astrophysics Data System (ADS)

    Nichols, J. D.; Milan, S. E.

    2016-09-01

    We present calculations of the auroral radio powers expected from exoplanets with magnetospheres driven by an Earth-like magnetospheric interaction with the solar wind. Specifically, we compute the twin cell-vortical ionospheric flows, currents, and resulting radio powers resulting from a Dungey cycle process driven by dayside and nightside magnetic reconnection, as a function of planetary orbital distance and magnetic field strength. We include saturation of the magnetospheric convection, as observed at the terrestrial magnetosphere, and we present power-law approximations for the convection potentials, radio powers and spectral flux densities. We specifically consider a solar-age system and a young (1 Gyr) system. We show that the radio power increases with magnetic field strength for magnetospheres with saturated convection potential, and broadly decreases with increasing orbital distance. We show that the magnetospheric convection at hot Jupiters will be saturated, and thus unable to dissipate the full available incident Poynting flux, such that the magnetic Radiometric Bode's Law (RBL) presents a substantial overestimation of the radio powers for hot Jupiters. Our radio powers for hot Jupiters are ˜5-1300 TW for hot Jupiters with field strengths of 0.1-10 BJ orbiting a Sun-like star, while we find that competing effects yield essentially identical powers for hot Jupiters orbiting a young Sun-like star. However, in particular, for planets with weaker magnetic fields, our powers are higher at larger orbital distances than given by the RBL, and there are many configurations of planet that are expected to be detectable using SKA.

  9. The Galactic Plane region near ℓ = 93°. II. A stellar wind bubble surrounding SNR 3C 434.1

    NASA Astrophysics Data System (ADS)

    Foster, T.; Routledge, D.; Kothes, R.

    2004-04-01

    New Canadian Galactic Plane Survey λ 21 cm H I line observations towards supernova remnant (SNR) 3C 434.1 (G94.0+1.0) are presented. We find a fragmented and thin-walled atomic hydrogen shell inside which the SNR is seen to be contained at v≃ -80 km s-1, which we report to be a highly evolved stellar wind bubble (SWB) associated with the remnant. A dark area in the midst of otherwise bright line emission is also seen near -71 km s-1. An absorption profile to the extragalactic continuum source 4C 51.45 (superimposed on the shell's north face) allows us to probe the shell's optical depth, kinetic temperature and expansion velocity. The material in the dark area has the same properties as material in the fragmented shell, suggesting that the dark area is actually the far-side ``cap'' of the shell seen absorbing emission from warm background gas, the first instance of H I Self Absorption (HISA) seen in such a structure. We show that the kinematic distance of 10 kpc derived from a flat Galactic rotation model is highly improbable, and that this bubble/SNR system is most likely resident in the Perseus Spiral Arm, lying 5.2 kpc distant. We model the SWB shell in three dimensions as a homologously expanding ellipsoid. Physical and dynamical characteristics of the bubble are determined, showing its advanced evolutionary state. Finally, from a photometric search for one or more stars associated with the SWB, we determine that three B0V stars and one O4V star currently inhabit this bubble, and that the progenitor of 3C 434.1 was at latest also an O4 type star.

  10. Galaxy formation with local photoionization feedback - I. Methods

    NASA Astrophysics Data System (ADS)

    Kannan, R.; Stinson, G. S.; Macciò, A. V.; Hennawi, J. F.; Woods, R.; Wadsley, J.; Shen, S.; Robitaille, T.; Cantalupo, S.; Quinn, T. R.; Christensen, C.

    2014-01-01

    We present a first study of the effect of local photoionizing radiation on gas cooling in smoothed particle hydrodynamics simulations of galaxy formation. We explore the combined effect of ionizing radiation from young and old stellar populations. The method computes the effect of multiple radiative sources using the same tree algorithm as used for gravity, so it is computationally efficient and well resolved. The method foregoes calculating absorption and scattering in favour of a constant escape fraction for young stars to keep the calculation efficient enough to simulate the entire evolution of a galaxy in a cosmological context to the present day. This allows us to quantify the effect of the local photoionization feedback through the whole history of a galaxy's formation. The simulation of a Milky Way-like galaxy using the local photoionization model forms ˜40 per cent less stars than a simulation that only includes a standard uniform background UV field. The local photoionization model decreases star formation by increasing the cooling time of the gas in the halo and increasing the equilibrium temperature of dense gas in the disc. Coupling the local radiation field to gas cooling from the halo provides a preventive feedback mechanism which keeps the central disc light and produces slowly rising rotation curves without resorting to extreme feedback mechanisms. These preliminary results indicate that the effect of local photoionizing sources is significant and should not be ignored in models of galaxy formation.

  11. The X-ray absorption spectrum of 4U 1700-37 and its implications for the stellar wind of the companion HD 153919

    NASA Technical Reports Server (NTRS)

    White, N. E.; Kallman, T. R.; Swank, J. H.

    1983-01-01

    The first high resolution non-dispersive 2-60 keV X-ray spectra at 4U1700-37 is presented. The continuum is typical of that found from X-ray pulsars; that is a flat powr law between 2 and 10 keV and, beyond 10 keV, an exponential decay of characteristic energy varying between 10 and 20 keV. No X-ray pulsations were detected between 160 ms and 6 min with an amplitude greater than approximately 2 percent. The absorption measured at binary phases approximately 0.72 is comparable to that expected from the stellar wind of the primary. The gravitational capture of material in the wind is found to be more than enough to power the X-ray source. The increase in the average absorption after phi of approximately 0.5 is confirmed. The minimum level of adsorption is a factor of 2 or 3 lower than that reported by previous observers, which may be related to a factor of approximately 10 decline in the average X-ray luminosity over the same interval. Short term approximately 50 percent variations in adsorption are seen for the first time which appear to be loosely correlated with approximately 10 min flickering activity in the X-ray flux. These most likely originate from inhomogeneities in the stellar wind of the primary. Previously announced in STAR as N83-14034

  12. The X-ray absorption spectrum of 4U1700-37 and its implications for the stellar wind of the companion HD153919

    NASA Technical Reports Server (NTRS)

    White, N. E.; Kallman, T. R.; Swank, J. H.

    1982-01-01

    The first high resolution non-dispersive 2-60 KeV X-ray spectra of 4U1700-37 is presented. The continuum is typical of that found from X-ray pulsars; that is a flat power law between 2 and 10 keV and, beyond 10 keV, an exponential decay of characteristic energy varying between 10 and 20 keV. No X-ray pulsations were detected between 160 ms and 6 min with an amplitude greater than approximately 2%. The absorption measured at binary phases approximately 0.72 is comparable to that expected from the stellar wind of the primary. The gravitational capture of material in the wind is found to be more than enough to power the X-ray source. The increase in the average absorption after phi o approximately 0.5 is confirmed. The minimum level of adsorption is a factor of 2 or 3 lower than that reported by previous observers, which may be related to a factor of approximately 10 decline in the average X-ray luminosity over the same interval. Short term approximately 50% variations in adsorption are seen for the first time which appear to be loosely correlated with approximately 10 min flickering activity in the X-ray flux. These most likely originate from inhomogeneities in the stellar wind of the primary.

  13. The chemical evolution of local star-forming galaxies: radial profiles of ISM metallicity, gas mass, and stellar mass and constraints on galactic accretion and winds

    NASA Astrophysics Data System (ADS)

    Kudritzki, Rolf-Peter; Ho, I.-Ting; Schruba, Andreas; Burkert, Andreas; Zahid, H. Jabran; Bresolin, Fabio; Dima, Gabriel I.

    2015-06-01

    The radially averaged metallicity distribution of the interstellar medium (ISM) and the young stellar population of a sample of 20 disc galaxies is investigated by means of an analytical chemical evolution model which assumes constant ratios of galactic wind mass-loss and accretion mass gain to star formation rate. Based on this model, the observed metallicities and their gradients can be described surprisingly well by the radially averaged distribution of the ratio of stellar mass to ISM gas mass. The comparison between observed and model-predicted metallicity is used to constrain the rate of mass-loss through galactic wind and accretion gain in units of the star formation rate. Three groups of galaxies are found: galaxies with either mostly winds and only weak accretion, or mostly accretion and only weak winds, and galaxies where winds are roughly balanced by accretion. The three groups are distinct in the properties of their gas discs. Galaxies with approximately equal rates of mass-loss and accretion gain have low metallicity, atomic-hydrogen-dominated gas discs with a flat spatial profile. The other two groups have gas discs dominated by molecular hydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential decline, which is on average steeper for the galaxies with small accretion rates. The rates of accretion ( ≲ 1.0 × SFR) and outflow ( ≲ 2.4 × SFR) are relatively low. The latter depend on the calibration of the zero-point of the metallicity determination from the use of H II region strong emission lines.

  14. Photoionization of the Buckminsterfullerene Cation.

    PubMed

    Douix, Suzie; Duflot, Denis; Cubaynes, Denis; Bizau, Jean-Marc; Giuliani, Alexandre

    2017-01-05

    Photoionization of a buckminsterfullerene ion is investigated using an ion trap and a merged beam setup coupled to synchrotron radiation beamlines and compared to theoretical calculations. Absolute measurements derived from the ion trap experiment allow discrepancies concerning the photoionization cross section of C60(+) to be solved.

  15. Radio Jets in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Anglada, Guillem

    Radio continuum emission in the centimeter range has already been detected in association with a large number of the youngest stellar objects. This emission, dominated by a thermal free-free component, is in general weak, but sensitive interferometric observations at these wavelengths have become one of the most important tools to detect and study the objects (particularly those most deeply embedded) that are powering the outflows frequently found in the star forming regions. Observations carried out with high (subarcsecond) angular resolution reveal that these centimeter sources are tracing collimated ionized outflows, i.e. "thermal radio jets". These radio jets constitute, at present, the best evidence for collimated outflow at the smallest scale (~100 AU). For objects of low bolometric luminosity (for which no significant photoionization is expected), there is a correlation between the momentum rate in the large scale outflow and the centimeter continuum luminosity, as expected if the emission is originated in shock-ionized gas, produced when a stellar wind shocks against surrounding high density material. This result provides important evidence favoring a connection between small scale jets and molecular outflows.

  16. Photoionization of FE3+ Ions

    SciTech Connect

    Ovchinnikov, O.; Schlachter, F.

    2003-01-01

    Photoionization of Fe3+ ions was studied for the first time using synchrotron radiation from the Advanced Light Source (ALS) and the merged-beams technique. Fe3+ ions were successfully produced using ferrocene in an electron cyclotron resonance ion source (ECR). The measured yield of Fe4+ photoions as a function of photon energy revealed the presence of resonances that correspond to excitation of autoionizing states. These resonances are superimposed upon the photoion yield produced by direct photoionization, which is a smooth, slowly decreasing function of energy. The spectra for the photoionization of Fe3+ will be analyzed and compared with theory. The data collected will also serve to test models for the propagation of light through ionized matter.

  17. Narrow He II emission in star-forming galaxies at low metallicity. Stellar wind emission from a population of very massive stars

    NASA Astrophysics Data System (ADS)

    Gräfener, G.; Vink, J. S.

    2015-06-01

    Context. In a recent study, star-forming galaxies with He ii λ1640 emission at moderate redshifts between 2 and 4.6 have been found to occur in two modes that are distinguished by the width of their He ii emission lines. Broad He ii emission has been attributed to stellar emission from a population of evolved Wolf-Rayet (WR) stars. The origin of narrow He ii emission is less clear but has been attributed to nebular emission excited by a population of very hot Pop III stars formed in pockets of pristine gas at moderate redshifts. Aims: We propose an alternative scenario for the origin of the narrow He ii 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. Methods: We estimated the expected He ii line fluxes and equivalent widths based on wind models for VMS and Starburst99 population synthesis models and compared the results with recent observations of star-forming galaxies at moderate redshifts. Results: The observed He ii line strengths and equivalent widths are in line with what is expected for a population of VMS in one or more young super-clusters located within these galaxies. Conclusions: In our scenario the two observed modes of He ii emission originate from massive stellar populations in distinct evolutionary stages at low Z (~0.01 Z⊙). If this interpretation is correct, there is no need to postulate the existence of Pop III stars at moderate redshifts to explain the observed narrow He ii emission. An interesting possibility is the existence of self-enriched VMS with similar WR-type spectra at extremely low Z. Stellar He ii emission from such very early generations of VMS may be detectable in future studies of star-forming galaxies at high redshifts with the James Webb Space Telescope (JWST). The fact that the He ii emission of VMS is largely neglected in current population synthesis models will generally affect the interpretation of the

  18. High-efficiency photoionization detector

    SciTech Connect

    Anderson, D.F.

    1981-05-12

    A high efficiency photoionization detector using tetraaminoethylenes in a gaseous state having a low ionization potential and a relative photoionization cross section which closely matches the emission spectrum of xenon gas. Imaging proportional counters are also disclosed using the novel photoionization detector of the invention. The compound of greatest interest is TMAE which comprises tetrakis(dimethylamino)ethylene which has a measured ionization potential of 5.36 +- 0.02 eV, and a vapor pressure of 0.35 torr at 20/sup 0/C.

  19. Photoelectron photoion molecular beam spectroscopy

    SciTech Connect

    Trevor, D.J.

    1980-12-01

    The use of supersonic molecular beams in photoionization mass spectroscopy and photoelectron spectroscopy to assist in the understanding of photoexcitation in the vacuum ultraviolet is described. Rotational relaxation and condensation due to supersonic expansion were shown to offer new possibilities for molecular photoionization studies. Molecular beam photoionization mass spectroscopy has been extended above 21 eV photon energy by the use of Stanford Synchrotron Radiation Laboratory (SSRL) facilities. Design considerations are discussed that have advanced the state-of-the-art in high resolution vuv photoelectron spectroscopy. To extend gas-phase studies to 160 eV photon energy, a windowless vuv-xuv beam line design is proposed.

  20. Stellarator hybrids

    SciTech Connect

    Furth, H.P.; Ludescher, C.

    1984-08-01

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

  1. Photoionization of sodium clusters

    SciTech Connect

    Peterson, K.I.; Dao, P.D.; Farley, R.W.; Castleman, A.W. Jr.

    1984-03-01

    Sodium clusters, Na/sub x/ (2< or =x< or =8), were produced in a supersonic jet by coexpansion with argon and subjected to analysis via photoionization coupled with mass spectrometry. The present measurements, made at somewhat higher resolution than earlier literature studies, yield ionization potentials in excellent agreement for x = 1 to 4 and x = 7, and reveal heretofore unreported structure in the post-threshold spectra. The present measurements enable a more definitive assignment of the ionization potentials, giving a lower value for x = 6 and pointing to lower ones for x = 5 and 8. The frequently discussed odd--even alternation in ionization potentials is no longer evident beyond the pentamer. Values for the binding energies of Na to Na/sup +//sub x/ (3< or =x< or =8) are deduced.

  2. Photoionization-photoelectron research.

    SciTech Connect

    Ruscic, B.

    1998-03-06

    In the broad sense of a general definition, the fundamental goal of this research program is to explore, understand, and utilize the basic processes of interaction of vacuum UV light with atoms and molecules. In practical terms, this program uses photoionization mass spectrometry and other related techniques to study chemically relevant transient and metastable species that are intimately connected to energy-producing processes, such as combustion, or play-prominent roles in the associated environmental issues. Some recent examples of species that have been studied are: CH{sub 3}, CH{sub 2}, CH{sub 3}O, CH{sub 2}OH, CH{sub 3}S, CH{sub 2}SH, HCS, HNCO, NCO, HNCS, NCS, the isomers of C{sub 2}H{sub 5}O, HOBr, CF{sub 3} and CF{sub 3}OH. The ephemeral species of interest are produced in situ using various suitable techniques, such as sublimation, pyrolysis, microwave discharge, chemical abstraction reactions with H or F atoms, laser photodissociation, on-line synthesis, and others. The desired information is obtained by applying a variety of suitable photoionization methods, which use both conventional and coherent light sources in the vacuum W region. The spiritus movens of our studies is the need to provide the chemical community with essential information on the species of interest, such as accurate and reliable thermochemical, spectroscopic and structural data, and thus contribute to the global comprehension of the underlying chemical processes. The scientific motivation is also fueled by the necessity to unveil useful generalities, such as bonding patterns within a class of related compounds, or systematic behavior in the ubiquitous autoionization processes. In addition, the nature of the results obtained in this program is such that it generates a significant impetus for further theoretical work. The experimental work of this program is coordinated with other related experimental and theoretical efforts of the Chemical Dynamics Group to provide a broad perspective

  3. Spectra of resonance surface photoionization

    SciTech Connect

    Antsiferov, V.V.; Smirnov, G.I.; Telegin, G.G.

    1995-09-01

    The theory of nonactivated electron transfer between atoms interacting reasonantly with coherent radiation and a metal surface is developed. The spectral resonances in photoabsorption and surface photoionization are found to be related to nonlinear interference effects in the interaction between discrete atomic levels and the continuum formed by the quasi-continuous electron spectrum of a normal metal. The asymmetry in the resonance surface photoionization spectrum is shown to have a shape typical of the Fano autoionization resonances. 18 refs.

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

    NASA Technical Reports Server (NTRS)

    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.

  5. UNDERSTANDING THE UNUSUAL X-RAY EMISSION PROPERTIES OF THE MASSIVE, CLOSE BINARY WR 20a: A HIGH ENERGY WINDOW INTO THE STELLAR WIND INITIATION REGION

    SciTech Connect

    Montes, Gabriela; Ramirez-Ruiz, Enrico; De Colle, Fabio; Strickler, Rachel

    2013-11-10

    The problem of explaining the X-ray emission properties of the massive, close binary WR 20a is discussed. Located near the cluster core of Westerlund 2, WR 20a is composed of two nearly identical Wolf-Rayet stars of 82 and 83 solar masses orbiting with a period of only 3.7 days. Although Chandra observations were taken during the secondary optical eclipse, the X-ray light curve shows no signs of a flux decrement. In fact, WR 20a appears slightly more X-ray luminous and softer during the optical eclipse, opposite to what has been observed in other binary systems. To aid in our interpretation of the data, we compare with the results of hydrodynamical simulations using the adaptive mesh refinement code Mezcal which includes radiative cooling and a radiative acceleration force term. It is shown that the X-ray emission can be successfully explained in models where the wind-wind collision interface in this system occurs while the outflowing material is still being accelerated. Consequently, WR 20a serves as a critical test-case for how radiatively driven stellar winds are initiated and how they interact. Our models not only procure a robust description of current Chandra data, which cover the orbital phases between 0.3 and 0.6, but also provide detailed predictions over the entire orbit.

  6. Understanding the Unusual X-Ray Emission Properties of the Massive, Close Binary WR 20a: A High Energy Window into the Stellar Wind Initiation Region

    NASA Astrophysics Data System (ADS)

    Montes, Gabriela; Ramirez-Ruiz, Enrico; De Colle, Fabio; Strickler, Rachel

    2013-11-01

    The problem of explaining the X-ray emission properties of the massive, close binary WR 20a is discussed. Located near the cluster core of Westerlund 2, WR 20a is composed of two nearly identical Wolf-Rayet stars of 82 and 83 solar masses orbiting with a period of only 3.7 days. Although Chandra observations were taken during the secondary optical eclipse, the X-ray light curve shows no signs of a flux decrement. In fact, WR 20a appears slightly more X-ray luminous and softer during the optical eclipse, opposite to what has been observed in other binary systems. To aid in our interpretation of the data, we compare with the results of hydrodynamical simulations using the adaptive mesh refinement code Mezcal which includes radiative cooling and a radiative acceleration force term. It is shown that the X-ray emission can be successfully explained in models where the wind-wind collision interface in this system occurs while the outflowing material is still being accelerated. Consequently, WR 20a serves as a critical test-case for how radiatively driven stellar winds are initiated and how they interact. Our models not only procure a robust description of current Chandra data, which cover the orbital phases between 0.3 and 0.6, but also provide detailed predictions over the entire orbit.

  7. Photoionization modeling of the LWS fine-structure lines in IR bright galaxies

    NASA Technical Reports Server (NTRS)

    Satyapal, S.; Luhman, M. L.; Fischer, J.; Greenhouse, M. A.; Wolfire, M. G.

    1997-01-01

    The long wavelength spectrometer (LWS) fine structure line spectra from infrared luminous galaxies were modeled using stellar evolutionary synthesis models combined with photoionization and photodissociation region models. The calculations were carried out by using the computational code CLOUDY. Starburst and active galactic nuclei models are presented. The effects of dust in the ionized region are examined.

  8. Goddard high-resolution spectrograph observations of narrow discrete stellar wind absorption features in the ultraviolet spectrum of the O7.5 III star Xi Persei

    NASA Technical Reports Server (NTRS)

    Shore, Steven N.; Altner, Bruce; Bolton, C. T.; Cardelli, Jason A.; Ebbets, Dennis C.

    1993-01-01

    We report the observation of transient narrow absorption components (NACs) in the stellar wind of the O giant Xi Per. Two sets of GHRS observations of the Si IV ultraviolet resonance doublet have been obtained. These features are extremely weak, with column densities of approximately 10 exp 12/sq cm and optical depths of order 0.1. The features are narrow, less than 30 km/s, and seem to occur in groups. If the NACs are due to the 1393 A component, they represent previously undetected low-velocity discrete absorption components at V(rad) below -600 km/s. If they are high-velocity features on the 1402 A doublet component, they may represent the decay phase of the discrete absorption components at the terminal velocity. In either case, they are a new aspect of the NAC phenomenon that could not have been detected with previous ultraviolet spectrographs.

  9. Goddard high-resolution spectrograph observations of narrow discrete stellar wind absorption features in the ultraviolet spectrum of the O7.5 III star Xi Persei

    NASA Technical Reports Server (NTRS)

    Shore, Steven N.; Altner, Bruce; Bolton, C. T.; Cardelli, Jason A.; Ebbets, Dennis C.

    1993-01-01

    We report the observation of transient narrow absorption components (NACs) in the stellar wind of the O giant Xi Per. Two sets of GHRS observations of the Si IV ultraviolet resonance doublet have been obtained. These features are extremely weak, with column densities of approximately 10 exp 12/sq cm and optical depths of order 0.1. The features are narrow, less than 30 km/s, and seem to occur in groups. If the NACs are due to the 1393 A component, they represent previously undetected low-velocity discrete absorption components at V(rad) below -600 km/s. If they are high-velocity features on the 1402 A doublet component, they may represent the decay phase of the discrete absorption components at the terminal velocity. In either case, they are a new aspect of the NAC phenomenon that could not have been detected with previous ultraviolet spectrographs.

  10. Two Regimes of Interaction of a Hot Jupiter’s Escaping Atmosphere with the Stellar Wind and Generation of Energized Atomic Hydrogen Corona

    NASA Astrophysics Data System (ADS)

    Shaikhislamov, I. F.; Khodachenko, M. L.; Lammer, H.; Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.; Prokopov, P. A.; Berezutsky, A. G.; Zakharov, Yu. P.; Posukh, V. G.

    2016-12-01

    The interaction of escaping the upper atmosphere of a hydrogen-rich non-magnetized analog of HD 209458b with a stellar wind (SW) of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic (HD) model. A realistic Sun-like spectrum of X-ray and ultraviolet radiation, which ionizes and heats the planetary atmosphere, together with hydrogen photochemistry, as well as stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric HD outflow. Two different regimes of the planetary and SW interaction have been modeled. These are: (1) the “captured by the star” regime, when the tidal force and pressure gradient drive the planetary material beyond the Roche lobe toward the star, and (2) the “blown by the wind” regime, when sufficiently strong SW confines the escaping planetary atmosphere and channels it into the tail. The model simulates in detail the HD interaction between the planetary atoms, protons and the SW, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge exchange between planetary atoms and stellar protons. The revealed location and shape of the ENA cloud, either as a paraboloid shell between the ionopause and bowshock (for the “blown by the wind” regime), or a turbulent layer at the contact boundary between the planetary stream and SW (for the “captured by the star” regime) are of importance for the interpretation of Lyα absorption features in exoplanetary transit spectra and characterization of the plasma environments.

  11. Common Envelope Wind Tunnel: Coefficients of Drag and Accretion in a Simplified Context for Studying Flows around Objects Embedded within Stellar Envelopes

    NASA Astrophysics Data System (ADS)

    MacLeod, Morgan; Antoni, Andrea; Murguia-Berthier, Ariadna; Macias, Phillip; Ramirez-Ruiz, Enrico

    2017-03-01

    This paper examines the properties of flows around objects embedded within common envelopes in the simplified context of a “wind tunnel.” We establish characteristic relationships between key common envelope flow parameters like the Mach number and density scale height. Our wind tunnel is a three-dimensional, Cartesian geometry hydrodynamic simulation setup that includes the gravity of the primary and secondary stars and allows us to study the coefficients of drag and accretion experienced by the embedded object. Accretion and drag lead to a transformation of an embedded object and its orbit during a common envelope phase. We present two suites of simulations spanning a range of density gradients and Mach numbers—relevant for flow near the limb of a stellar envelope to the deep interior. In one suite, we adopt an ideal gas adiabatic exponent of γ =5/3, in the other, γ =4/3. We find that coefficients of drag rise in flows with steeper density gradients and that coefficients of drag and accretion are consistently higher in the more compressible, γ =4/3 flow. We illustrate the impact of these newly derived coefficients by integrating the inspiral of a secondary object through the envelopes of 3{M}⊙ (γ ≈ 5/3) and 80{M}⊙ (γ ≈ 4/3) giants. In these examples, we find a relatively rapid initial inspiral because, near the stellar limb, dynamical friction drag is generated mainly from dense gas focused from deeper within the primary-star’s envelope. This rapid initial inspiral timescale carries potential implications for the timescale of transients from early common envelope interaction.

  12. Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries

    NASA Astrophysics Data System (ADS)

    Giménez-García, A.; Shenar, T.; Torrejón, J. M.; Oskinova, L.; Martínez-Núñez, S.; Hamann, W.-R.; Rodes-Roca, J. J.; González-Galán, A.; Alonso-Santiago, J.; González-Fernández, C.; Bernabeu, G.; Sander, A.

    2016-06-01

    Context. Classical supergiant X-ray binaries (SGXBs) and supergiant fast X-ray transients (SFXTs) are two types of high-mass X-ray binaries (HMXBs) that present similar donors but, at the same time, show very different behavior in the X-rays. The reason for this dichotomy of wind-fed HMXBs is still a matter of debate. Among the several explanations that have been proposed, some of them invoke specific stellar wind properties of the donor stars. Only dedicated empiric analysis of the donors' stellar wind can provide the required information to accomplish an adequate test of these theories. However, such analyses are scarce. Aims: To close this gap, we perform a comparative analysis of the optical companion in two important systems: IGR J17544-2619 (SFXT) and Vela X-1 (SGXB). We analyze the spectra of each star in detail and derive their stellar and wind properties. As a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. Methods: We use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (NLTE) Potsdam Wolf-Rayet model atmosphere code. We derive the physical properties of the stars and their stellar winds, accounting for the influence of X-rays on the stellar winds. Results: We find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). The distance to the sources have been revised and also agree well with the estimations already available in the literature. In IGR J17544-2619 we are able to narrow the uncertainty to d = 3.0 ± 0.2 kpc. From the stellar radius of the donor and its X-ray behavior, the eccentricity of IGR J17544-2619 is constrained to e< 0.25. The derived chemical abundances point to certain mixing during the lifetime of the donors. An important difference between the stellar winds of the

  13. FUSE Observations of the SMC 16 day Wolf-Rayet Binary Sanduleak 1 (WO4+O4): Atmospheric Eclipses and Colliding Stellar Winds

    NASA Astrophysics Data System (ADS)

    St-Louis, Nicole; Moffat, Anthony F. J.; Marchenko, Sergey; Pittard, Julian Mark

    2005-08-01

    In this paper we present the results of a FUSE monitoring campaign of the SMC WO4+O4 V Wolf-Rayet binary Sanduleak 1. Our 18 spectra obtained during a little more than one orbital cycle in 2000 October combined with four archival spectra show variability in the S VI, C III, C IV, and O VI P Cygni profiles, which we attribute to emission from the shock cone resulting from the collision between the two strong winds and to atmospheric eclipses of the O star continuum light by the W-R wind. All the lines vary in concert indicating that the cooling is such that even lines such as the OVI λλ1032, 1038 doublet form in the linear part of the cone. We have also applied both a simple geometrical model and profile fits, including emission from the normal wind, extra emission from the shock cone, and the atmospheric eclipse. Adopting an orbital inclination of ~40°, we deduce a total cone opening angle of ~80° and a streaming velocity for the gas along the shock cone of ~3000 km s-1. The luminosity ratio required to fit our spectra is LO/LW-R=3.5, and the stellar radii are 3.5 and 12 Rsolar, respectively, for the W-R and O stars. We also present radiative driving models for this binary system having two massive stars with strong winds and discuss radiative inhibition and braking effects. In particular, we address the coupling of the O star radiation with the W-R star wind. Finally, we present a PICA hydrodynamic colliding-wind model for Sand 1. We find an opening angle for the shock cone similar to that deduced from the line-profile fitting, but significantly longer cooling lengths along the shock cone. However, the model reveals some cold gas that is stripped off the O4 surface and mixed with the hotter WO4 material, thereby accelerating its cooling. This could very well explain why shorter cooling lengths are inferred from the profile fits. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by Johns Hopkins

  14. Stellar winds and planetary bodies simulations: Magnetized obstacles in super-Alfvénic and sub-Alfvénic flows

    NASA Astrophysics Data System (ADS)

    Vernisse, Y.; Riousset, J. A.; Motschmann, U.; Glassmeier, K.-H.

    2017-03-01

    Most planetary bodies are moving in the solar wind, in a stellar wind, or in a plasma flow within the magnetosphere of a planet. The interaction of the body with the flowing plasma provides us with various interaction types, which mainly depend on the flow speed, the magnetization of the body, its conductivity, the presence of an ionosphere, and the size of the body. We establish two cornerstones representing highly magnetized obstacles embedded in a super-Alfvénic and sub-Alfvénic plasma. Those two cornerstones complete the two cornerstones defined in our previous study on inert obstacles in super-Alfvénic and sub-Alfvénic regimes. Tracking the transitions between these cornerstones enable better understanding of the feedback of the obstacle onto the plasma flow. Each interaction is studied by means of the hybrid model simulation code AIKEF. The results are summarized in three dimensional diagrams showing the current structures, which serve as a basis for our descriptions. We identify the major currents such as telluric, magnetosonic, Chapman-Ferraro, and bow-shock currents as the signatures of the particular state of development of the interaction region. We show that each type of interactions can be identified by studying the shape and the magnitude of its specific currents.

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

    NASA Astrophysics Data System (ADS)

    Rzaev, A. Kh.

    2007-12-01

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

  16. Photoionization Dynamics of Small Molecules

    SciTech Connect

    Dehmer, Joseph L.; Dill, Dan; Parr, Albert C.

    1985-01-01

    The last decade has witnessed remarkable progress in characterizing dynamical aspects of the molecular photoionization process. The general challenge is to gain physical insight into those processes occuring during photo excitation and eventual escape of the photoelectron through the anisotropic molecular field, in terms of various observables such as photoionization cross-sections and branching ratios, photoelectron angular distributions and even newer probes mentioned below. Much of the progress in this field has mirrored earlier work in atomic photoionization dynamics where many key ideas were developed (e.g., channel interaction, quantum defect analysis, potential barrier phenomena and experimental techniques). However, additional concepts and techniques were required to deal with the strictly molecular aspects of the problem, particularly the anisotropy of the multicenter molecular field and the interaction among rovibronic modes.

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

    SciTech Connect

    King, Ashley L.; Miller, Jon M.; Walton, Dominic J.; Fürst, Felix; Harrison, Fiona A.; Barret, Didier; Boggs, Steven E.; Craig, William W.; Krivonos, Roman; Tomsick, John A.; Christensen, Finn E.; Fabian, Andy C.; Hailey, Charles J.; Mori, Kaya; Natalucci, Lorenzo; Stern, Daniel; Zhang, William W.

    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.

  18. Properties of a B0 I stellar wind and interstellar grains derived from Ginga observations of the binary X-ray pulsar 4U 1538-52

    NASA Technical Reports Server (NTRS)

    Clark, George W.; Woo, Jonathan W.; Nagase, Fumiaki

    1994-01-01

    From measurements of the X-ray eclipse phenomena of the binary X-ray pulsar 4U 1538-52, we derive properties of the stellar wind of its B0 I companion, QV Nor, and a constraint on models of interstellar grains. Estimates of the wind density as a function of the distance from the center of QV Nor are obtained from an analysis of the variation of X-ray attenuation during an eclipse egress. A Monte Carlo computation of the absorption and scattering of X-rays in the X-ray-ionized wind accounts for approximately two-thirds of the spectrum of X-rays with energies above 4.5 keV observed during the eclipse. Our upper limit on R(sub XV) is 0.06/mag, which implies that the X-ray scattering efficiency of interstellar dust is less than expected for solid grains with a size distribution of the form n(sub g)(a) approximately a(exp -3.5) in the range from 0.005 to 0.25 microns and composed of silicate (R(sub XV) = 0.22/mag) or a silicate-graphite mixture (R(sub XV) = 0.11/mag) as derived from the calculations of Martin & Rouleau (1991). This lends support to the idea (Mathis & Whiffen 1989) that interstellar grains are 'fluffy' aggregates with an average bulk density less than that of their constitutent particles. Such aggregates would have a smaller ratio of X-ray scattering efficiency to optical extinction efficiency compared with solid grains of the same material.

  19. A spectroscopic search for colliding stellar winds in O-type close binary systems. III - 29 UW Canis Majoris

    NASA Astrophysics Data System (ADS)

    Wiggs, Michael S.; Gies, Douglas R.

    1993-04-01

    The orbital-phase variations in the optical emission lines and UV P Cygni lines of the massive O-type binary 29 UW Canis Majoris are investigated in a search for evidence of colliding winds. High SNR spectra of the H-alpha and He I 6678-A emission lines are presented, and radial velocity curves for several features associated with the photosphere of the more luminous primary star are given. The H-alpha features consists of a P Cygni component that shares the motion of the primary, and which probably originates at the base of its wind, and a broad, stationary emission component. It is proposed that the broad emission forms in a plane midway between the stars where the winds collide. A simple geometric model is used to show that this placement of the broad component can explain the lack of orbital velocity shifts, the near-constancy of the emission strength throughout the orbit, the large velocities associated with the H-alpha wings, and the constancy of the velocity range observed.

  20. Modeling the magnetospheres of luminous stars: Interactions between supersonic radiation-driven winds and stellar magnetic fields

    NASA Astrophysics Data System (ADS)

    Owocki, Stan; Townsend, Rich; Ud-Doula, Asif

    2007-05-01

    Hot, luminous stars (spectral types O and B) lack the hydrogen recombination convection zones that drive magnetic dynamo generation in the sun and other cool stars. Nonetheless, observed rotational modulation of spectral lines formed in the strong, radiatively driven winds of hot stars suggests magnetic perturbations analogous to those that induce ``co-rotating interaction regions'' in the solar wind. Indeed, recent advances in spectropolarimetric techniques have now led to direct detection of moderate to strong (100-10 000 G), tilted dipole magnetic fields in several hot stars. Using a combination of analytic and numerical magnetohydrodynamic models, this paper focuses on the role of such magnetic fields in channeling, and sometimes confining, the radiatively driven mass outflows from such stars. The results show how ``magnetically confined wind shocks'' can explain the moderately hard x-ray emission seen from the O7V star Theta-1 Ori C, and how the trapping of material in a ``rigidly rotating magnetosphere'' can explain the periodically modulated Balmer line emission seen from the magnetic B2pV star Sigma Ori E. In addition, magnetic reconnection heating from episodic centrifugal breakout events might explain the occasional very hard x-ray flares seen from the latter star. The paper concludes with a brief discussion on the generation of hot-star fields and the broader relationship to other types of magnetospheres.

  1. A spectroscopic search for colliding stellar winds in O-type close binary systems. III - 29 UW Canis Majoris

    NASA Technical Reports Server (NTRS)

    Wiggs, Michael S.; Gies, Douglas R.

    1993-01-01

    The orbital-phase variations in the optical emission lines and UV P Cygni lines of the massive O-type binary 29 UW Canis Majoris are investigated in a search for evidence of colliding winds. High SNR spectra of the H-alpha and He I 6678-A emission lines are presented, and radial velocity curves for several features associated with the photosphere of the more luminous primary star are given. The H-alpha features consists of a P Cygni component that shares the motion of the primary, and which probably originates at the base of its wind, and a broad, stationary emission component. It is proposed that the broad emission forms in a plane midway between the stars where the winds collide. A simple geometric model is used to show that this placement of the broad component can explain the lack of orbital velocity shifts, the near-constancy of the emission strength throughout the orbit, the large velocities associated with the H-alpha wings, and the constancy of the velocity range observed.

  2. A spectroscopic search for colliding stellar winds in O-type close binary systems. III - 29 UW Canis Majoris

    NASA Technical Reports Server (NTRS)

    Wiggs, Michael S.; Gies, Douglas R.

    1993-01-01

    The orbital-phase variations in the optical emission lines and UV P Cygni lines of the massive O-type binary 29 UW Canis Majoris are investigated in a search for evidence of colliding winds. High SNR spectra of the H-alpha and He I 6678-A emission lines are presented, and radial velocity curves for several features associated with the photosphere of the more luminous primary star are given. The H-alpha features consists of a P Cygni component that shares the motion of the primary, and which probably originates at the base of its wind, and a broad, stationary emission component. It is proposed that the broad emission forms in a plane midway between the stars where the winds collide. A simple geometric model is used to show that this placement of the broad component can explain the lack of orbital velocity shifts, the near-constancy of the emission strength throughout the orbit, the large velocities associated with the H-alpha wings, and the constancy of the velocity range observed.

  3. Spitzer Space Telescope IRS Spectral Mapping of Photoionized Columns in M16 and the Carina HII Regions

    NASA Astrophysics Data System (ADS)

    Cotera, Angela; Simpson, J. P.; Sellgren, K.; Stolovy, S. R.

    2013-01-01

    Photoevaporated columns of dust and gas - also called elephant trunks, pillars or fingers - are found in the periphery of many H II regions. They have been observed within the Galaxy, the SMC and the LMC. These features are thought to be sites of current star formation, but the question remains whether the columns persist because stars formed in the denser regions prior to interactions with the UV radiation and stellar winds of nearby massive stars, or because of core collapse resulting from these interactions. We have obtained Spitzer IRS spectral maps of three columns within M 16 and three columns within the Carina nebula, to test our understanding of the impact on these transitory features of differing stellar populations and initial conditions. We use the wealth of molecular, atomic and PAH emission lines located within the spectral range of the high resolution IRS modes (9.9-37.2 micron) to determine the excitation state, dust and gas temperatures, and probe the shock characteristics within the columns as a function of location. Using the IRS spectral mapping mode, in conjunction with the CUBISM tool and the CLOUDY H II region model code, we have constructed detailed maps of the accessible emission lines and derived parameters for each column. Mapping the distribution of the physical states of the dust and gas in these columns is enhancing our understanding of the competing processes within these dynamic objects. The data presented here represent the only IRS spectral maps of photoionized pillars.

  4. Re-analysis of the 2003-Nov-14 Stellar Occultation by Titan with New Haze and Methane Optical Constants: Implications for Vertical Structure and Zonal Winds

    NASA Astrophysics Data System (ADS)

    Young, Eliot F.; Zalucha, A.

    2012-10-01

    Zalucha et al. (2007) looked at the 2003-Nov-14 stellar occultation by Titan using lightcurves obtained with the ULTRACAM instrument (Dhillon et a. 2007). Previous occultations, beginning with the 28 Sgr occultation in 1989 (Hubbard et al. 1993; Sicardy et al. 1990), measured central flashes that served as extremely sensitive constraints on Titan's atmospheric figure. The ULTRACAM lightcurves were obtained at 30 Hz in three simultaneous passbands (u', g' and i', with effective centers at 358, 487 and 758 nm). The i' and g' bands show a central flash event. In the i' band, the central flash shows three clear large peaks and two small peaks. The 30-Hz cadence of the ULTRACAM observations corresponds to a sampling rate of 375 m on the sky (given the event velocity of 11.25 km/sec), actually smaller than the Fresnel scale of around 600 m and the estimated stellar diameter of about 730 m at Titan. Using Titan haze optical parameters from Huygens/DISR instrument (Tomasko et al. 2008), we retrieve temperature and haze opacity profiles between altitudes of roughly 200 to 600 km with a vertical resolution better than 5 km. Unlike Zalucha et al. (2007), we use a forward model to iteratively generate and compare model lightcurves to the u', g' and i' observations. The forward modeling approach lets us investigate lightcurves from atmospheres with arbitrary haze distributions, temperature fluctuations and wind distortions. We discuss solutions that are consistent with the ULTRACAM observations and compare results to ISS vertical haze profiles. Hubbard et al. 1993, A&A 269, 541. Sicardy et al. 1990, Nature 343, 350. Tomasko et al. 2008, P&SS 56, 669. Zalucha et al. 2007, Icarus 192, 503.

  5. Mass-Selective Laser Photoionization.

    ERIC Educational Resources Information Center

    Smalley, R. E.

    1982-01-01

    Discusses the nature and applications of mass-selective laser photoionization. The ionization can be done with a single intense laser pulse lasting a few billionths of a second with no molecular fragmentation. Applications focus on: (1) benzene clusters, excimers, and exciplexes; (2) metal clusters; and (3) triplet formation and decay. (Author/JN)

  6. Mass-Selective Laser Photoionization.

    ERIC Educational Resources Information Center

    Smalley, R. E.

    1982-01-01

    Discusses the nature and applications of mass-selective laser photoionization. The ionization can be done with a single intense laser pulse lasting a few billionths of a second with no molecular fragmentation. Applications focus on: (1) benzene clusters, excimers, and exciplexes; (2) metal clusters; and (3) triplet formation and decay. (Author/JN)

  7. Shining a light on galactic outflows: photoionized outflows

    NASA Astrophysics Data System (ADS)

    Chisholm, John; Tremonti, Christy A.; Leitherer, Claus; Chen, Yanmei; Wofford, Aida

    2016-04-01

    We study the ionization structure of galactic outflows in 37 nearby, star-forming galaxies with the Cosmic Origins Spectrograph on the Hubble Space Telescope. We use the O I, Si II, Si III, and Si IV ultraviolet absorption lines to characterize the different ionization states of outflowing gas. We measure the equivalent widths, line widths, and outflow velocities of the four transitions, and find shallow scaling relations between them and galactic stellar mass and star formation rate. Regardless of the ionization potential, lines of similar strength have similar velocities and line widths, indicating that the four transitions can be modelled as a comoving phase. The Si equivalent width ratios (e.g. Si IV/Si II) have low dispersion, and little variation with stellar mass; while ratios with O I and Si vary by a factor of 2 for a given stellar mass. Photoionization models reproduce these equivalent width ratios, while shock models under predict the relative amount of high ionization gas. The photoionization models constrain the ionization parameter (U) between -2.25 < log (U) < -1.5, and require that the outflow metallicities are greater than 0.5 Z⊙. We derive ionization fractions for the transitions, and show that the range of ionization parameters and stellar metallicities leads to a factor of 1.15-10 variation in the ionization fractions. Historically, mass outflow rates are calculated by converting a column density measurement from a single metal ion into a total hydrogen column density using an ionization fraction, thus mass outflow rates are sensitive to the assumed ionization structure of the outflow.

  8. The lack of X-ray pulsations in the extreme helium star BD+37°442 and its possible stellar wind X-ray emission

    NASA Astrophysics Data System (ADS)

    Mereghetti, Sandro; La Palombara, Nicola; Tiengo, Andrea; Esposito, Paolo

    2017-04-01

    We report the results of a new XMM-Newton observation of the helium-rich hot subdwarf BD+37°442 carried out in 2016 February. The possible periodicity at 19 s seen in a 2011 shorter observation is not confirmed, thus dismissing the evidence for a binary nature. This implies that the observed soft X-ray emission, with a luminosity of a few 1031 erg s-1, originates in BD+37°442 itself, rather than in an accreting neutron star companion. The X-ray spectrum is well fit by thermal plasma emission with a temperature of 0.22 keV and non-solar element abundances. Besides the overabundance of He, C and N already known from optical/UV studies, the X-ray spectra indicate also a significant excess of Ne. The soft X-ray spectrum and the ratio of X-ray to bolometric luminosity, LX/LBOL ˜ 2 × 10-7, are similar to those observed in massive early-type stars. This indicates that the mechanisms responsible for plasma shock-heating can work also in the weak stellar winds (mass-loss rates dot{M}_W≤ 10^{-8} M⊙ yr-1) of low-mass hot stars.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  10. Stellar evolution.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  11. Dirac R-matrix calculations of photoionization cross-sections of Ni XIII

    NASA Astrophysics Data System (ADS)

    Sardar, S.; Bilal, M.; Bari, M. A.; Nazir, R. T.; Hannan, A.; Salahuddin, M.; Nasim, M. H.

    2016-05-01

    In this paper, we report total photoionization cross-sections of Ni XIII in the ground state (3P2) and four excited states (3P1,0, 1D2, 1S0) for the first time over the photon energy range 380-480 eV. The target wavefunctions are constructed with fully relativistic atomic structure GRASP code. Our calculated energy levels and oscillator strengths of core ion Ni XIV agree well with available experimental and theoretical results. The ionization threshold value of ground state of Ni XIII is found to be more closer to the experimental ionization energy and improved over the previous calculations. The photoionization cross-sections are calculated using the fully relativistic DARC code with an appropriate energy step of 0.01 eV to delineate the resonance structures. The calculated ionization cross-sections are important for the modelling of features of photoionized plasmas and for stellar opacities.

  12. Photoionization of oxidized metal clusters

    SciTech Connect

    Dao, P.D.; Peterson, K.I.; Castleman, A.W. Jr.

    1984-01-01

    Oxidized metal clusters (Na/sub x/O and K/sub x/O for 2< or =x< or =4) were formed in a gas phase reaction between metal clusters and an oxidizing gas using a double expansion technique. Their appearance potentials were measured using a molecular beam-photoionization mass spectrometer system. These first photoionization data for oxidized clusters provide information on trends of ionization potentials as a function of the degree of aggregation. The ionization potentials do not differ greatly from the analogous metallic species, but in the case of the sodium tetramer the value does fall below that of the bare metal cluster. This finding is in accord with what has been observed as an influence of impurities on the work function of the bulk sodium. The results are also of interest concerning questions of octet rule violations and hypervalency.

  13. On the Evolution of Low-Mass X-Ray Binaries under the Influence of a Donor Stellar Wind Induced by X-Rays from the Accretor

    NASA Astrophysics Data System (ADS)

    Iben, Icko, Jr.; Tutukov, Alexander V.; Fedorova, Alexandra V.

    1997-09-01

    In a low-mass X-ray binary (LMXB), an intense stellar wind from the mass donor may be a consequence of the absorption of X-rays from the mass-accreting neutron star or black hole, and such a wind could change the evolution of these binaries dramatically compared with the evolution of cataclysmic variables (CVs), which are close binaries in which the accretor is a white dwarf. An analytical study and numerical models show that, in the closest and brightest LMXBs, a relativistic companion can capture up to ~10% of the mass lost in the induced stellar wind (ISW) from the main-sequence or subgiant donor, and this is enough to keep the X-ray luminosity of a typical LMXB on the level of LX ~ 5000 L⊙ and to accelerate the rotation of an old neutron star with a low magnetic field into the millisecond-period range. A self-sustained ISW may exist even if the donor does not fill its Roche lobe, but the system can be bright (LX > 100 L⊙) only if the radius of the donor is a substantial fraction (>~0.8) of the Roche lobe radius. A lower limit on the Roche lobe filling factor follows from the circumstance that both the rate Ėwind at which work must be done to lift wind matter off the donor and the rate Ėabs at which the donor absorbs X-ray energy are proportional to ṀISW (the ISW mass-loss rate) and from the requirement that Ėwind<Ėabs in order for energy to be conserved. The observed number (~100) of bright LMXBs in our Galaxy can be understood as the product of a relatively short lifetime (a few × 107 yr) and a small theoretical birthrate (~2 × 10-6-8 × 10-6 yr-1), which is comparable to semiempirical estimates of the birthrate of LMXBs and millisecond pulsars (~2 × 10-6 yr-1). The theoretical lifetime is ~10-60 times shorter than when the ISW is not taken into account, and the theoretical birthrate is ~3-6 times smaller, because of the fact that the ISW acts to expand the orbit and reduce the number of systems that can evolve through an X-ray bright stage under

  14. Stellar Dynamos

    NASA Astrophysics Data System (ADS)

    Charbonneau, Paul

    This chapter steps finally away from the sun and towards the stars, the idea being to apply the physical insight gained so far to see how much of stellar magnetism can be understood in terms of dynamo action. Dynamo action in the convective core of massive main-sequence stars is first considered and shown viable. For intermediate-mass main-sequence stars the fossil field hypothesis will carry the day, although possible dynamo alternatives are also briefly discussed. The extension of the solar dynamo models investigated in Chap. 3 (10.1007/978-3-642-32093-4_3) to other solar-type stars will first take us through an important detour in first having to understand rotational evolution in response to angular momentum loss in a magnetized wind. Dynamo action in fully convective stars comes next, and the chapter closes with an overview of the situation for pre- and post-main-sequence stars and compact objects, leading finally to the magnetic fields of galaxies and beyond.

  15. Solar Wind Five

    NASA Technical Reports Server (NTRS)

    Neugebauer, M. (Editor)

    1983-01-01

    Topics of discussion were: solar corona, MHD waves and turbulence, acceleration of the solar wind, stellar coronae and winds, long term variations, energetic particles, plasma distribution functions and waves, spatial dependences, and minor ions.

  16. IONIS: Approximate atomic photoionization intensities

    NASA Astrophysics Data System (ADS)

    Heinäsmäki, Sami

    2012-02-01

    A program to compute relative atomic photoionization cross sections is presented. The code applies the output of the multiconfiguration Dirac-Fock method for atoms in the single active electron scheme, by computing the overlap of the bound electron states in the initial and final states. The contribution from the single-particle ionization matrix elements is assumed to be the same for each final state. This method gives rather accurate relative ionization probabilities provided the single-electron ionization matrix elements do not depend strongly on energy in the region considered. The method is especially suited for open shell atoms where electronic correlation in the ionic states is large. Program summaryProgram title: IONIS Catalogue identifier: AEKK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKK_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1149 No. of bytes in distributed program, including test data, etc.: 12 877 Distribution format: tar.gz Programming language: Fortran 95 Computer: Workstations Operating system: GNU/Linux, Unix Classification: 2.2, 2.5 Nature of problem: Photoionization intensities for atoms. Solution method: The code applies the output of the multiconfiguration Dirac-Fock codes Grasp92 [1] or Grasp2K [2], to compute approximate photoionization intensities. The intensity is computed within the one-electron transition approximation and by assuming that the sum of the single-particle ionization probabilities is the same for all final ionic states. Restrictions: The program gives nonzero intensities for those transitions where only one electron is removed from the initial configuration(s). Shake-type many-electron transitions are not computed. The ionized shell must be closed in the initial state. Running time: Few seconds for a

  17. Biomedical applications of laser photoionization

    NASA Astrophysics Data System (ADS)

    Xiong, Xiaoxiong; Moore, Larry J.; Fassett, John R.; O'Haver, Thomas C.

    1991-07-01

    Trace elements are important for many essential metabolic functions. Zinc is a structural/functional component in more than 200 enzymes active in the biochemistry of cell division and tissue growth, neurology and endocrine control. Calcium is involved in intracellular control mechanisms and in skeletal bone building and resorption processes related to osteoporosis. Sensitive and selective laser photoionization is being developed to understand mechanisms in smaller samples and biological units approaching the cellular domain. Zinc has an ionization potential of 9.4 eV, or 75766.8 cm-1. Several processes are being explored, including two-photon resonant, three- photon ionization utilizing sequential UV transitions, e.g., 4s2 1S0 yields 4s4p 3P1 and 4s4p 3P1 yields 4s5d 3D1. Preliminary zinc stable isotope ratio data obtained by thermal atomization and laser photoionization agree with accepted values within 2 to 5%, except for anomalous 67Zn. Photoionization of calcium is being studied for isotope enrichment and ratio measurement using narrow and medium bandwidth lasers. Several ionization pathways, e.g., 4s2 1S0 - 2hv1 yields 4s10s - hv2 yields Ca+ (4s2S), are being investigated for isotopically selective ionization. Auto-ionization pathways are explored for greater efficiency in isotopic analysis. All studies have utilized a Nd:YAG- pumped laser system with one or two frequency-doubled tunable dye lasers coupled either to a magnetic sector or time-of-flight mass spectrometer.

  18. Stellar Metamorphosis:

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [TOP LEFT AND RIGHT] The Hubble Space Telescope's Wide Field and Planetary Camera 2 has captured images of the birth of two planetary nebulae as they emerge from wrappings of gas and dust, like butterflies breaking out of their cocoons. These images highlight a fleeting phase in the stellar burnout process, occurring just before dying stars are transformed into planetary nebulae. The left-hand image is the Cotton Candy nebula, IRAS 17150-3224; the right-hand image, the Silkworm nebula, IRAS 17441-2411. Called proto-planetary nebulae, these dying stars have been caught in a transition phase between a red giant and a planetary nebula. This phase is only about 1,000 years long, very short in comparison to the 1 billion-year lifetime of a star. These images provide the earliest snapshots of the transition process. Studying images of proto-planetary nebulae is important to understanding the process of star death. A star begins to die when it has exhausted its thermonuclear fuel - hydrogen and helium. The star then becomes bright and cool (red giant phase) and swells to several tens of times its normal size. It begins puffing thin shells of gas off into space. These shells become the star's cocoon. In the Hubble images, the shells are the concentric rings seen around each nebula. But the images also reveal the nebulae breaking out from those shells. The butterfly-like wings of gas and dust are a common shape of planetary nebulae. Such butterfly shapes are created by the 'interacting winds' process, in which a more recent 'fast wind' - material propelled by radiation from the hot central star - punches a hole in the cocoon, allowing the nebula to emerge. (This 'interacting wind' theory was first proposed by Dr. Sun Kwok to explain the origin of planetary nebulae, and has been subsequently proven successful in explaining their shapes.) The nebulae are being illuminated by light from the invisible central star, which is then reflected toward us. We are viewing the nebulae

  19. Stellar Metamorphosis:

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [TOP LEFT AND RIGHT] The Hubble Space Telescope's Wide Field and Planetary Camera 2 has captured images of the birth of two planetary nebulae as they emerge from wrappings of gas and dust, like butterflies breaking out of their cocoons. These images highlight a fleeting phase in the stellar burnout process, occurring just before dying stars are transformed into planetary nebulae. The left-hand image is the Cotton Candy nebula, IRAS 17150-3224; the right-hand image, the Silkworm nebula, IRAS 17441-2411. Called proto-planetary nebulae, these dying stars have been caught in a transition phase between a red giant and a planetary nebula. This phase is only about 1,000 years long, very short in comparison to the 1 billion-year lifetime of a star. These images provide the earliest snapshots of the transition process. Studying images of proto-planetary nebulae is important to understanding the process of star death. A star begins to die when it has exhausted its thermonuclear fuel - hydrogen and helium. The star then becomes bright and cool (red giant phase) and swells to several tens of times its normal size. It begins puffing thin shells of gas off into space. These shells become the star's cocoon. In the Hubble images, the shells are the concentric rings seen around each nebula. But the images also reveal the nebulae breaking out from those shells. The butterfly-like wings of gas and dust are a common shape of planetary nebulae. Such butterfly shapes are created by the 'interacting winds' process, in which a more recent 'fast wind' - material propelled by radiation from the hot central star - punches a hole in the cocoon, allowing the nebula to emerge. (This 'interacting wind' theory was first proposed by Dr. Sun Kwok to explain the origin of planetary nebulae, and has been subsequently proven successful in explaining their shapes.) The nebulae are being illuminated by light from the invisible central star, which is then reflected toward us. We are viewing the nebulae

  20. Photoionization of methanol and formaldehyde

    NASA Technical Reports Server (NTRS)

    Warneck, P.

    1971-01-01

    Photoions produced in methanol and formaldehyde by radiation in the spectral region 450-1150 A were analyzed mass spectrometrically, and their relative yields were determined as a function of wavelength. First ionization potentials were determined, and the ion yield curves were interpreted in terms of ionization processes in conjunction with other data. Fragment ions were detected on mass numbers of 31, 30, 29, 15, and 14 for methanol, and 29, 2, and 1 for formaldehyde. The associated appearance potentials were determined and were used to calculate heats of formation of the ions CH2OH(+) and HCO(+), and the radicals CH3, CH2, and HCO.

  1. Model Atmospheres for Irradiated Red Giant Stars with Winds

    NASA Astrophysics Data System (ADS)

    Aufdenberg, J. P.; Barman, T. S.

    2002-12-01

    We will present exploratory model atmosphere calculations applicable to symbiotic binary systems, where a hot white dwarf illuminates the extended atmosphere of a red giant. While sophisticated non-LTE photoionization models exist for these systems (e.g. Proga et al. 1998), detailed models for the ionized-to-neutral transition region in the red giant wind have lacked molecular line opacities. To make improvements in this area, we employ a new version of the PHOENIX stellar atmosphere and planetary radiative transfer code which combines the stellar wind module of Aufdenberg et al. (2002), now modified to treat the winds of cool stars, with the external illumination module of Barman, Hauschildt, & Allard (2001). Our present calculations include illuminated spherically symmetric models, with conditions similar to those found in EG And, that include non-LTE line blanketing, molecular opacity, and a realistic description of the incident white dwarf flux. Our goals include the prediction of changes in the red giant absorption-line spectrum with orbital phase, the prediction of emission-line strengths from the coolest, densest portions of the recombination region, and the detailing modeling of eclipse mapping observations. JPA is supported by a Harvard-Smithsonian Center for Astrophysics Postdoctoral Fellowship. Some of the calculations for this work were computed on the IBM SP ``Blue Horizon'' of the San Diego Supercomputer Center (SDSC), with support from the National Science Foundation, and on the IBM SP of the NERSC with support from the DOE.

  2. Photoionization Efficiencies of Five Polycyclic Aromatic Hydrocarbons.

    PubMed

    Johansson, K Olof; Campbell, Matthew F; Elvati, Paolo; Schrader, Paul E; Zádor, Judit; Richards-Henderson, Nicole K; Wilson, Kevin R; Violi, Angela; Michelsen, Hope A

    2017-06-15

    We have measured photoionization-efficiency curves for pyrene, fluoranthene, chrysene, perylene, and coronene in the photon energy range of 7.5-10.2 eV and derived their photoionization cross-section curves in this energy range. All measurements were performed using tunable vacuum ultraviolet (VUV) radiation generated at the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory. The VUV radiation was used for photoionization, and detection was performed using a time-of-flight mass spectrometer. We measured the photoionization efficiency of 2,5-dimethylfuran simultaneously with those of pyrene, fluoranthene, chrysene, perylene, and coronene to obtain references of the photon flux during each measurement from the known photoionization cross-section curve of 2,5-dimethylfuran.

  3. Photoionization Efficiencies of Five Polycyclic Aromatic Hydrocarbons

    DOE PAGES

    Johansson, K. Olof; Campbell, Matthew F.; Elvati, Paolo; ...

    2017-05-18

    We have measured photoionization-efficiency curves for pyrene, fluoranthene, chrysene, perylene, and coronene in the photon energy range of 7.5-10.2 eV and derived their photoionization cross-section curves in this energy range. All measurements were performed using tunable vacuum ultraviolet (VUV) radiation generated at the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory. The VUV radiation was used for photoionization, and detection was performed using a time-of-flight mass spectrometer. We measured the photoionization efficiency of 2,5-dimethylfuran simultaneously with those of pyrene, fluoranthene, chrysene, perylene, and coronene to obtain references of the photon flux during each measurement from the known photoionization cross-sectionmore » curve of 2,5- dimethylfuran.« less

  4. Hubble Space Telescope WFPC2 Imaging of M16: Photoevaporation and Emerging Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Hester, J. J.; Scowen, P. A.; Sankrit, R.; Lauer, T. R.; Ajhar, E. A.; Baum, W. A.; Code, A.; Currie, D. G.; Danielson, G. E.; Ewald, S. P.; Faber, S. M.; Grillmair, C. J.; Groth, E. J.; Holtzman, J. A.; Hunter, D. A.; Kristian, J.; Light, R. M.; Lynds, C. R.; Monet, D. G.; O'Neil, E. J., Jr.; Shaya, E. J.; Seidelmann, P. K.; Westphal, J. A.

    1996-06-01

    We present Hubble Space Telescope WFPC2 images of elephant trunks in the H II region M16. There are three principle results of this study. First, the morphology and stratified ionization structure of the interface between the dense molecular material and the interior of the H II region is well understood in terms of photoionization of a photoevaporative flow. Photoionization models of an empirical density profile capture the essential features of the observations, including the extremely localized region of [S II] emission at the interface and the observed offset between emission peaks in lower and higher ionization lines. The details of this structure are found to be a sensitive function both of the density profile of the interface and of the shape of the ionizing continuum. Interpretation of the interaction of the photoevaporative flow with gas in the interior of the nebula supports the view that much of the emission from H II regions may arise in such flows. Photoionization of photoevaporative flows may provide a useful paradigm for interpreting a wide range of observations of H II regions. Second, we report the discovery of a population of small cometary globules that are being uncovered as the main bodies of the elephant trunks are dispersed. Several lines of evidence connect these globules to ongoing star formation, including the association of a number of globules with stellar objects seen in IR images of M16 or in the continuum HST images themselves. We refer to these structures as evaporating gaseous globules, or "EGGs." These appear to be the same type of object as the nebular condensations seen previously in M42. The primary difference between the two cases is that in M16 we are seeing the objects from the side, while in M42 the objects are seen more nearly face-on against the backdrop of the ionized face of the molecular cloud. We find that the "evaporating globule" interpretation naturally accounts for the properties of objects in both nebulae, while

  5. IPOPv2: Photoionization of Ni XIV - a test case

    NASA Astrophysics Data System (ADS)

    Delahaye, F.; Palmeri, P.; Quinet, P.; Zeippen, C. J.

    2013-12-01

    Several years ago, M. Asplund and coauthors (2004) proposed a revision of the Solar composition. The use of this new prescription for Solar abundances in standard stellar models generated a strong disagreement between the predictions and the observations of Solar observables. Many claimed that the Standard Solar Model (SSM) was faulty, and more specifically the opacities used in such models. As a result, activities around the stellar opacities were boosted. New experiments (J. Bailey at Sandia on Z-Pinch, The OPAC consortium at LULI200) to measure directly absorbtion coefficients have been realized or are underway. Several theoretical groups (CEA-OPAS, Los Alamos Nat. Lab., CEA-SCORCG, The Opacity Project - The Iron Project (IPOPv2)) have started new sets of calculations using different approaches and codes. While the new results seem to confirm the good quality of the opacities used in SSM, it remains important to improve and complement the data currently available. We present recent results in the case of the photoionization cross sections for Ni XIV (Ni13+) from IPOPv2 and possible implications on stellar modelling.

  6. Blowin in the Stellar Wind

    NASA Image and Video Library

    2011-06-13

    This image of the Elephant Trunk nebula from NASA Wide-field Survey Explorer shows clouds of dust and gas being pushed and eroded by a massive star. The bright trunk of the nebula near the center is an especially dense cloud.

  7. Dust formation and mass loss around intermediate-mass AGB stars with initial metallicity Zini ≤ 10-4 in the early Universe - I. Effect of surface opacity on stellar evolution and the dust-driven wind

    NASA Astrophysics Data System (ADS)

    Tashibu, Shohei; Yasuda, Yuki; Kozasa, Takashi

    2017-04-01

    Dust formation and the resulting mass loss around asymptotic giant branch (AGB) stars with initial metallicity in the range 0 ≤ Zini ≤ 10-4 and initial mass 2 ≤ Mini/M⊙ ≤ 5 are explored by hydrodynamical calculations of the dust-driven wind (DDW) along the AGB evolutionary tracks. We employ the MESA code to simulate the evolution of stars, assuming an empirical mass-loss rate in the post-main-sequence phase and considering three types of low-temperature opacity (scaled-solar, CO-enhanced and CNO-enhanced opacity) to elucidate the effect on stellar evolution and the DDW. We find that the treatment of low-temperature opacity strongly affects dust formation and the resulting DDW; in the carbon-rich AGB phase, the maximum dot{M} of Mini ≥ 3 M⊙ stars with the CO-enhanced opacity is at least one order of magnitude smaller than that with the CNO-enhanced opacity. A wide range of stellar parameters being covered, the necessary condition for driving efficient DDW with dot{M} ≥ 10^{-6} M⊙ yr-1 is expressed as effective temperature Teff ≲ 3850 K and log (δCL/κRM) ≳ 10.43log Teff - 32.33, with the carbon excess δC defined as εC - εO, the Rosseland mean opacity κR in units of cm2 g-1 in the surface layer and the stellar mass (luminosity) M(L) in solar units. The fitting formulae derived for gas and dust mass-loss rates in terms of input stellar parameters could be useful for investigating the dust yield from AGB stars in the early Universe being consistent with stellar evolution calculations.

  8. Photoionization of rare gas clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Huaizhen

    This thesis concentrates on the study of photoionization of van der Waals clusters with different cluster sizes. The goal of the experimental investigation is to understand the electronic structure of van der Waals clusters and the electronic dynamics. These studies are fundamental to understand the interaction between UV-X rays and clusters. The experiments were performed at the Advanced Light Source at Lawrence Berkeley National Laboratory. The experimental method employs angle-resolved time-of-flight photoelectron spectrometry, one of the most powerful methods for probing the electronic structure of atoms, molecules, clusters and solids. The van der Waals cluster photoionization studies are focused on probing the evolution of the photoelectron angular distribution parameter as a function of photon energy and cluster size. The angular distribution has been known to be a sensitive probe of the electronic structure in atoms and molecules. However, it has not been used in the case of van der Waals clusters. We carried out outer-valence levels, inner-valence levels and core-levels cluster photoionization experiments. Specifically, this work reports on the first quantitative measurements of the angular distribution parameters of rare gas clusters as a function of average cluster sizes. Our findings for xenon clusters is that the overall photon-energy-dependent behavior of the photoelectrons from the clusters is very similar to that of the corresponding free atoms. However, distinct differences in the angular distribution point at cluster-size-dependent effects were found. For krypton clusters, in the photon energy range where atomic photoelectrons have a high angular anisotropy, our measurements show considerably more isotropic angular distributions for the cluster photoelectrons, especially right above the 3d and 4p thresholds. For the valence electrons, a surprising difference between the two spin-orbit components was found. For argon clusters, we found that the

  9. 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

    NASA Astrophysics Data System (ADS)

    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

  10. Double photoionization of halogenated benzene

    SciTech Connect

    AlKhaldi, Mashaal Q.; Wehlitz, Ralf

    2016-01-28

    We have experimentally investigated the double-photoionization process in C{sub 6}BrF{sub 5} using monochromatized synchrotron radiation. We compare our results with previously published data for partially deuterated benzene (C{sub 6}H{sub 3}D{sub 3}) over a wide range of photon energies from threshold to 270 eV. A broad resonance in the ratio of doubly to singly charged parent ions at about 65 eV appears shifted in energy compared to benzene data. This shift is due to the difference in the bond lengths in two molecules. A simple model can explain the shape of this resonance. At higher photon energies, we observe another broad resonance that can be explained as a second harmonic of the first resonance.

  11. Nondipole effects in helium photoionization

    NASA Astrophysics Data System (ADS)

    Argenti, Luca; Moccia, Roberto

    2010-12-01

    An accurate calculation of the nondipole anisotropy parameter γ in the photoionization of helium below the N = 2 threshold is presented. The calculated results are in fairly good agreement with the experimental results of Krässig et al (2002 Phys. Rev. Lett. 88 203002), but not as good as the accuracy of the calculation should have warranted. A careful examination of the possible causes for the observed discrepancies between theory and experiment seems to rule out any role either of the multipolar terms higher than the electric quadrupole, or of the singlet-triplet spin-orbit mixing. It is argued that such discrepancies might have an instrumental origin, due to the difficulty of measuring vanishingly small total cross sections σtot with the required accuracy. In such eventuality, it might be more appropriate to use a parameter other than γ, such as for instance the drag current, to measure the nondipole anisotropy of the photoelectron angular distribution.

  12. Photoionization of ClII

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana; Hernández, E.; Antillón, A.; Morales, A.; González, O.; Macaluso, D.; Hanstorp, D.; Aguilar, A.; Juárez, A.; Hinojosa, G.

    2014-05-01

    The cross section and spectrum for the process of single photoionization of the chlorine cation was measured in the energy range of 19.5 to 28.0 eV with a photon energy resolution of 20 meV. Over a non resonant cross section, resonant structures originated from initinal Cl+ 3P(J=0,1,2) manifold converging mainly to 2P(J=3/2) and 2D(J=5/2) are identified. A theoretical calculation based on the close coupling R-matrix is under progress. CONACYT CB-2011 167631. US National Science Fundation, DGAPA IN106813, The ALS is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. DOE Cntrct. DE-AC02-05CH11231. Montana Space Grant Consortium, Swedish Research Council.

  13. Indirect double photoionization of water

    NASA Astrophysics Data System (ADS)

    Resccigno, T. N.; Sann, H.; Orel, A. E.; Dörner, R.

    2011-05-01

    The vertical double ionization thresholds of small molecules generally lie above the dissociation limits corresponding to formation of two singly charged fragments. This gives the possibility of populating singly charged molecular ions by photoionization in the Franck-Condon region at energies below the lowest dication state, but above the dissociation limit into two singly charged fragment ions. This process can produce a superexcited neutral fragment that autoionizes at large internuclear separation. We study this process in water, where absorption of a photon produces an inner-shell excited state of H2O+ that fragments to H++OH*. The angular distribution of secondary electrons produced by OH* when it autoionizes produces a characteristic asymmetric pattern that reveals the distance, and therefore the time, at which the decay takes place. LBNL, Berkeley, CA, J. W. Goethe Universität, Frankfurt, Germany. Work performed under auspices of US DOE and supported by OBES, Div. of Chemical Sciences.

  14. 2006 Photoions, Photoionization & Photodetachment held on January 29-February 3, 2006

    SciTech Connect

    Robert Continetti Nancy Ryan Gray

    2006-09-06

    The 4th Gordon Conference on Photoions, Photoionization and Photodetachment will be held January 29-February 3, 2006 at the Santa Ynez Valley Marriott in Buellton, California. This meeting will continue to cover fundamentals and applications of photoionization and photodetachment, including valence and core-level phenomena and applications to reaction dynamics, ultrashort laser pulses and the study of exotic molecules and anions. Further information will be available soon at the Gordon Conference Website, and will be announced.

  15. Alignment of photoions far from threshold

    NASA Astrophysics Data System (ADS)

    Das, Romith; Wu, Chuanyong; Mihill, A. G.; Poliakoff, E. D.; Wang, Kwanghsi; McKoy, V.

    1994-09-01

    We present results of measurements and calculations of the alignment for CO+(B 2Σ+) photoions over an extended energy range (0≤Ek≤210 eV). The polarization of CO+(B 2Σ+→X 2Σ+) fluorescence indicates that the photoions retain significant alignment even at high energies. Agreement between the measured and calculated polarization of the fluorescence is excellent.

  16. Stellar chromospheres

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1980-01-01

    Developments in the understanding and use of chromospheric diagnostics are discussed with emphasis on the following aspects: (1) trends emerging from semiempirical models of single stars; (2) the validity of claims that theoretical models of chromospheres are becoming realistic; (3) the correlation between the widths of Ca 2 H and K line emission cores and stellar absolute luminosity extending over 15 magnitudes (Wilson-Bappu relation); and (4) the existence of systematic flow patterns in stellar chromospheres.

  17. The Herschel Planetary Nebula Survey (HerPlaNS): A Comprehensive Dusty Photoionization Model of NGC6781

    NASA Astrophysics Data System (ADS)

    Otsuka, Masaaki; Ueta, Toshiya; van Hoof, Peter A. M.; Sahai, Raghvendra; Aleman, Isabel; Zijlstra, Albert A.; Chu, You-Hua; Villaver, Eva; Leal-Ferreira, Marcelo L.; Kastner, Joel; Szczerba, Ryszard; Exter, Katrina M.

    2017-08-01

    We perform a comprehensive analysis of the planetary nebula (PN) NGC 6781 to investigate the physical conditions of each of its ionized, atomic, and molecular gas and dust components and the object’s evolution, based on panchromatic observational data ranging from UV to radio. Empirical nebular elemental abundances, compared with theoretical predictions via nucleosynthesis models of asymptotic giant branch (AGB) stars, indicate that the progenitor is a solar-metallicity, 2.25{--}3.0 {M}⊙ initial-mass star. We derive the best-fit distance of 0.46 kpc by fitting the stellar luminosity (as a function of the distance and effective temperature of the central star) with the adopted post-AGB evolutionary tracks. Our excitation energy diagram analysis indicates high-excitation temperatures in the photodissociation region (PDR) beyond the ionized part of the nebula, suggesting extra heating by shock interactions between the slow AGB wind and the fast PN wind. Through iterative fitting using the Cloudy code with empirically derived constraints, we find the best-fit dusty photoionization model of the object that would inclusively reproduce all of the adopted panchromatic observational data. The estimated total gas mass (0.41 {M}⊙ ) corresponds to the mass ejected during the last AGB thermal pulse event predicted for a 2.5 {M}⊙ initial-mass star. A significant fraction of the total mass (about 70%) is found to exist in the PDR, demonstrating the critical importance of the PDR in PNe that are generally recognized as the hallmark of ionized/H+ regions. Herschel is an ESA Space Observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  18. The Herschel Planetary Nebula Survey (HerPlaNS): A Comprehensive Dusty Photoionization Model of NGC6781.

    PubMed

    Otsuka, Masaaki; Ueta, Toshiya; van Hoof, Peter A M; Sahai, Raghvendra; Aleman, Isabel; Zijlstra, Albert A; Chu, You-Hua; Villaver, Eva; Leal-Ferreira, Marcelo L; Kastner, Joel; Szczerba, Ryszard; Exter, Katrina M

    2017-08-01

    We perform a comprehensive analysis of the planetary nebula (PN) NGC 6781 to investigate the physical conditions of each of its ionized, atomic, and molecular gas and dust components and the object's evolution, based on panchromatic observational data ranging from UV to radio. Empirical nebular elemental abundances, compared with theoretical predictions via nucleosynthesis models of asymptotic giant branch (AGB) stars, indicate that the progenitor is a solar-metallicity, 2.25-3.0 M⊙ initial-mass star. We derive the best-fit distance of 0.46 kpc by fitting the stellar luminosity (as a function of the distance and effective temperature of the central star) with the adopted post-AGB evolutionary tracks. Our excitation energy diagram analysis indicates high-excitation temperatures in the photodissociation region (PDR) beyond the ionized part of the nebula, suggesting extra heating by shock interactions between the slow AGB wind and the fast PN wind. Through iterative fitting using the Cloudy code with empirically derived constraints, we find the best-fit dusty photoionization model of the object that would inclusively reproduce all of the adopted panchromatic observational data. The estimated total gas mass (0.41 M⊙) corresponds to the mass ejected during the last AGB thermal pulse event predicted for a 2.5 M⊙ initial-mass star. A significant fraction of the total mass (about 70%) is found to exist in the PDR, demonstrating the critical importance of the PDR in PNe that are generally recognized as the hallmark of ionized/H(+) regions.

  19. 2001 Gordon Research Conference on Photoions, Photoionization and Photodetachment. Final progress report [agenda and attendees list

    SciTech Connect

    Johnson, Mark

    2001-07-13

    The Gordon Research Conference on Photoions, Photoionization and Photodetachment was held at Williams College, Williamstown, Massachusetts, July 8-13, 2001. The 72 conference attendees represented the spectrum of endeavor in this field, coming from academia, industry, and government laboratories, and including US and foreign scientists, senior researchers, young investigators, and students. Emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate discussion about the key issues in the field today. Time for formal presentations was limited. Sessions included the following topics: Vibrational structure, Time resolved studies: nuclear wavepackets, Valence photoionization, Clusters and networks, Resonance structures and decay mechanisms, Ultrafast photoionization, Threshold photoionization, Molecule fixed properties, and Collisional phenomena.

  20. Double Photoionization of Atomic Beryllium

    NASA Astrophysics Data System (ADS)

    Yip, Frank L.; McCurdy, C. William; Rescigno, Thomas N.

    2010-03-01

    One-photon double ionization (DPI) of beryllium represents the next step in the evolution of DPI investigations that began with helium in order to sensitively probe electron correlation. Beryllium is the simplest atomic species of the alkaline earth elements which, in general, possess two electrons outside of a fully occupied inner shell that spherically screens the nucleus. This provides a natural basis for comparison to 1s^2 helium DPI. However, the valence state of beryllium has n=2, thus making the valence excited target 2s2p more accessible relative to the 2s^2 ground state as compared to ground-state and metastable helium. Also, the symmetry of photoionizing from either the ^1S or ^1P initial state will have consequences for the angular distributions for double ionization. Triply differential cross sections (TDCS) are presented for DPI from both ground state 2s^2 and excited state 2s2p beryllium calculated using exterior complex scaling (ECS) for the valence electrons.

  1. Stellar Ablation of Planetary Atmospheres

    NASA Technical Reports Server (NTRS)

    Moore, Thomas E.; Horwitz, J. L.

    2007-01-01

    We review observations and theories of the solar ablation of planetary atmospheres, focusing on the terrestrial case where a large magnetosphere holds off the solar wind, so that there is little direct atmospheric impact, but also couples the solar wind electromagnetically to the auroral zones. We consider the photothermal escape flows known as the polar wind or refilling flows, the enhanced mass flux escape flows that result from localized solar wind energy dissipation in the auroral zones, and the resultant enhanced neutral atom escape flows. We term these latter two escape flows the "auroral wind." We review observations and theories of the heating and acceleration of auroral winds, including energy inputs from precipitating particles, electromagnetic energy flux at magnetohydrodynamic and plasma wave frequencies, and acceleration by parallel electric fields and by convection pickup processes also known as "centrifugal acceleration." We consider also the global circulation of ionospheric plasmas within the magnetosphere, their participation in magnetospheric disturbances as absorbers of momentum and energy, and their ultimate loss from the magnetosphere into the downstream solar wind, loading reconnection processes that occur at high altitudes near the magnetospheric boundaries. We consider the role of planetary magnetization and the accumulating evidence of stellar ablation of extrasolar planetary atmospheres. Finally, we suggest and discuss future needs for both the theory and observation of the planetary ionospheres and their role in solar wind interactions, to achieve the generality required for a predictive science of the coupling of stellar and planetary atmospheres over the full range of possible conditions.

  2. Stellar Ablation of Planetary Atmospheres

    NASA Technical Reports Server (NTRS)

    Moore, Thomas E.; Horwitz, J. L.

    2007-01-01

    We review observations and theories of the solar ablation of planetary atmospheres, focusing on the terrestrial case where a large magnetosphere holds off the solar wind, so that there is little direct atmospheric impact, but also couples the solar wind electromagnetically to the auroral zones. We consider the photothermal escape flows known as the polar wind or refilling flows, the enhanced mass flux escape flows that result from localized solar wind energy dissipation in the auroral zones, and the resultant enhanced neutral atom escape flows. We term these latter two escape flows the "auroral wind." We review observations and theories of the heating and acceleration of auroral winds, including energy inputs from precipitating particles, electromagnetic energy flux at magnetohydrodynamic and plasma wave frequencies, and acceleration by parallel electric fields and by convection pickup processes also known as "centrifugal acceleration." We consider also the global circulation of ionospheric plasmas within the magnetosphere, their participation in magnetospheric disturbances as absorbers of momentum and energy, and their ultimate loss from the magnetosphere into the downstream solar wind, loading reconnection processes that occur at high altitudes near the magnetospheric boundaries. We consider the role of planetary magnetization and the accumulating evidence of stellar ablation of extrasolar planetary atmospheres. Finally, we suggest and discuss future needs for both the theory and observation of the planetary ionospheres and their role in solar wind interactions, to achieve the generality required for a predictive science of the coupling of stellar and planetary atmospheres over the full range of possible conditions.

  3. Advanced stellarators

    NASA Astrophysics Data System (ADS)

    Schlüter, Arnulf

    1983-03-01

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

  4. Stellar Imager

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth

    2007-01-01

    The Stellar Imager (SI) is one of NASA's "Vision Missions" - concepts for future, space-based, strategic missions that could enormously increase our capabilities for observing the Cosmos. SI is designed as a UV/Optical Interferometer which will enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI, with a characteristic angular resolution of 0.1 milli-arcseconds at 2000 Angstroms, represents an advance in image detail of several hundred times over that provided by the Hubble Space Telescope. The Stellar Imager will zoom in on what today-with few exceptions - we only know as point sources, revealing processes never before seen, thus providing a tool as fundamental to astrophysics as the microscope is to the study of life on Earth. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. It's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives, in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. Stellar Imager is included as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005) and as such is a candidate mission for the 2025-2030 timeframe. An artist's drawing of the current "baseline" concept for SI is presented.

  5. Theory of attosecond delays in molecular photoionization

    NASA Astrophysics Data System (ADS)

    Baykusheva, Denitsa; Wörner, Hans Jakob

    2017-03-01

    We present a theoretical formalism for the calculation of attosecond delays in molecular photoionization. It is shown how delays relevant to one-photon-ionization, also known as Eisenbud-Wigner-Smith delays, can be obtained from the complex dipole matrix elements provided by molecular quantum scattering theory. These results are used to derive formulae for the delays measured by two-photon attosecond interferometry based on an attosecond pulse train and a dressing femtosecond infrared pulse. These effective delays are first expressed in the molecular frame where maximal information about the molecular photoionization dynamics is available. The effects of averaging over the emission direction of the electron and the molecular orientation are introduced analytically. We illustrate this general formalism for the case of two polyatomic molecules. N2O serves as an example of a polar linear molecule characterized by complex photoionization dynamics resulting from the presence of molecular shape resonances. H2O illustrates the case of a non-linear molecule with comparably simple photoionization dynamics resulting from a flat continuum. Our theory establishes the foundation for interpreting measurements of the photoionization dynamics of all molecules by attosecond metrology.

  6. The Winds of B Supergiants

    NASA Technical Reports Server (NTRS)

    Fullerton, A. W.; Massa, D. L.; Prinja, R. K.; Owocki, S. P.; Cranmer, S. R.

    1998-01-01

    This report summarizes the progress of the work conducted under the program "The Winds of B Supergiants," conducted by Raytheon STX Corporation. The report consists of a journal article "Wind variability in B supergiants III. Corotating spiral structures in the stellar wind of HD 64760." The first step in the project was the analysis of the 1996 time series of 2 B supergiants and an O star. These data were analyzed and reported on at the ESO workshop, "Cyclical Variability in Stellar Winds."

  7. EUV optics in photoionization experiments

    NASA Astrophysics Data System (ADS)

    Bartnik, Andrzej; Wachulak, Przemysław; Fiedorowicz, Henryk; Fok, Tomasz; Jarocki, Roman; Kostecki, Jerzy; Szczurek, Anna; Szczurek, Mirosław; Pina, Ladislav; Sveda, Libor

    2013-05-01

    In this work photoionized plasmas were created by irradiation of He, Ne and Ar gases with a focused EUV beam from one of two laser-plasma sources employing Nd:YAG laser systems of different parameters. First of them was a 10-Hz laser-plasma EUV source, based on a double-stream gas-puff target, irradiated with the 3-ns/0.8J laser pulse. EUV radiation in this case was focused using a gold-plated grazing incidence ellipsoidal collector in the wavelength range λ = 9÷70 nm. The most intense emission was in the relatively narrow spectral region centred at λ = 11 +/- 1 nm. The second source was based on a 10 ns/10 J/10 Hz laser system. In this case EUV radiation was focused using a gold-plated grazing incidence multifoil collector or a Mo-coated ellipsoidal collector. The most intense emission in this case was in the 5 ÷ 15 nm spectral region. Radiation fluence ranged from 60 mJ/cm2 to 400 mJ/cm2. Different gases were injected into the interaction region, perpendicularly to an optical axis of the irradiation system, using an auxiliary gas puff valve. Irradiation of the gases resulted in ionization and excitation of atoms and ions. Spectra in EUV range were measured using a grazing incidence, flat-field spectrometer (McPherson Model 251), equipped with a 450 lines/mm toroidal grating. In all cases the most intense emission lines were assigned to singly charged ions. The other emission lines belong to atoms or doubly charged ions. The spectra were excited in low density gases of the order of 1 ÷ 10% atmospheric density.

  8. THE OUTER SHOCK OF THE OXYGEN-RICH SUPERNOVA REMNANT G292.0+1.8: EVIDENCE FOR THE INTERACTION WITH THE STELLAR WINDS FROM ITS MASSIVE PROGENITOR

    SciTech Connect

    Lee, Jae-Joon; Park, Sangwook; Burrows, David N.; Hughes, John P.; Slane, Patrick O.; Gaensler, B. M.; Ghavamian, Parviz

    2010-03-10

    We study the outer-shock structure of the oxygen-rich supernova remnant G292.0+1.8 using a deep observation with the Chandra X-ray Observatory. We measure radial variations of the electron temperature and emission measure that we identify as the outer shock propagating into a medium with a radially decreasing density profile. The inferred ambient density structure is consistent with models for the circumstellar wind of a massive progenitor star rather than for a uniform interstellar medium. The estimated wind density (n{sub H} = 0.1-0.3 cm{sup -3}) at the current outer radius ({approx} 7.7 pc) of the remnant is consistent with a slow wind from a red supergiant (RSG) star. The total mass of the wind is estimated to be {approx}15-40 M{sub sun} (depending on the estimated density range), assuming that the wind extended down to near the surface of the progenitor. The overall kinematics of G292.0+1.8 are consistent with the remnant expanding through the RSG wind.

  9. The Properties of the local Interstellar Medium and the Interaction of the Stellar Winds of epsilon Indi and lambda Andromedae with the Interstellar Environment

    NASA Technical Reports Server (NTRS)

    Wood, Brian E.; Alexander, William R.; Linsky, Jeffrey L.

    1996-01-01

    We present new observations of the Ly alpha lines of Epsilon Indi (K5 5) and A Andromedae (G8 4-3 + ?) These data were obtained by the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. Analysis of the interstellar H 1 and D 1 absorption lines reveals that the velocities and temperatures inferred from the H 1 lines are inconsistent with the parameters inferred from the D 1 lines, unless the H 1 absorption is assumed to be produced by two absorption components. One absorption component is produced by interstellar material. For both lines of sight observed, the velocity of this component is consistent with the velocity predicted by the local flow vector. For the Epsilon Indi data, the large velocity separation between the stellar emission and the interstellar absorption allows us to measure the H 1 column density independent of the shape of the intrinsic stellar Ly alpha profile. This approach permits us to quote an accurate column density and to assess its uncertainty with far more confidence than in previous analyses, for which the errors were dominated by uncertainties in the assumed stellar profiles.

  10. Photo-ionization rate coefficients for the rare gases

    NASA Astrophysics Data System (ADS)

    Pang, Xuexia

    2005-01-01

    By introducing the converting method from electron-impact ionization cross sections to rate coefficients through using a semi-experiential formula, we try to probe a semi-experiential formula for converting the photo-ionization cross sections into photo-ionization rate coefficient. It"s found that photo-ionization rate coefficient is direct proportion to photo-ionization cross sections, the rate S is related with light resource.

  11. Vacuum Ultraviolet Photoionization of Complex Chemical Systems.

    PubMed

    Kostko, Oleg; Bandyopadhyay, Biswajit; Ahmed, Musahid

    2016-05-27

    Tunable vacuum ultraviolet (VUV) radiation coupled to mass spectrometry is applied to the study of complex chemical systems. The identification of novel reactive intermediates and radicals is revealed in flame, pulsed photolysis, and pyrolysis reactors, leading to the elucidation of spectroscopy, reaction mechanisms, and kinetics. Mass-resolved threshold photoelectron photoion coincidence measurements provide unprecedented access to vibrationally resolved spectra of free radicals present in high-temperature reactors. Photoionization measurements in water clusters, nucleic acid base dimers, and their complexes with water provide signatures of proton transfer in hydrogen-bonded and π-stacked systems. Experimental and theoretical methods to track ion-molecule reactions and fragmentation pathways in intermolecular and intramolecular hydrogen-bonded systems in sugars and alcohols are described. Photoionization of laser-ablated molecules, clusters, and their reaction products inform thermodynamics and spectroscopy that are relevant to astrochemistry and catalysis. New directions in coupling VUV radiation to interrogate complex chemical systems are discussed.

  12. Vacuum Ultraviolet Photoionization of Complex Chemical Systems

    NASA Astrophysics Data System (ADS)

    Kostko, Oleg; Bandyopadhyay, Biswajit; Ahmed, Musahid

    2016-05-01

    Tunable vacuum ultraviolet (VUV) radiation coupled to mass spectrometry is applied to the study of complex chemical systems. The identification of novel reactive intermediates and radicals is revealed in flame, pulsed photolysis, and pyrolysis reactors, leading to the elucidation of spectroscopy, reaction mechanisms, and kinetics. Mass-resolved threshold photoelectron photoion coincidence measurements provide unprecedented access to vibrationally resolved spectra of free radicals present in high-temperature reactors. Photoionization measurements in water clusters, nucleic acid base dimers, and their complexes with water provide signatures of proton transfer in hydrogen-bonded and π-stacked systems. Experimental and theoretical methods to track ion-molecule reactions and fragmentation pathways in intermolecular and intramolecular hydrogen-bonded systems in sugars and alcohols are described. Photoionization of laser-ablated molecules, clusters, and their reaction products inform thermodynamics and spectroscopy that are relevant to astrochemistry and catalysis. New directions in coupling VUV radiation to interrogate complex chemical systems are discussed.

  13. Early stellar evolution

    NASA Technical Reports Server (NTRS)

    Stahler, Steven W.

    1994-01-01

    Research into the formation and early evolution of stars is currently an area of great interest and activity. The theoretical and observational foundations for this development are reviewed in this paper. By now, the basic physics governing cloud collapse is well understood, as is the structure of the resulting protostars. However, the theory predicts protostellar luminosities that are greater than those of most infrared sources. Observationally, it is thought that protostars emit powerful winds that push away remnant cloud gas, but both the origin of these winds and the nature of their interaction with ambient gas are controversial. Finally, the theory of pre-main-sequence stars has been modified to incorporate more realistic initial conditions. This improvement helps to explain the distribution of such stars in the H-R diagram. Many important issues, such as the origin of binary stars and stellar clusters, remain as challenges for future research.

  14. Early stellar evolution

    NASA Technical Reports Server (NTRS)

    Stahler, Steven W.

    1994-01-01

    Research into the formation and early evolution of stars is currently an area of great interest and activity. The theoretical and observational foundations for this development are reviewed in this paper. By now, the basic physics governing cloud collapse is well understood, as is the structure of the resulting protostars. However, the theory predicts protostellar luminosities that are greater than those of most infrared sources. Observationally, it is thought that protostars emit powerful winds that push away remnant cloud gas, but both the origin of these winds and the nature of their interaction with ambient gas are controversial. Finally, the theory of pre-main-sequence stars has been modified to incorporate more realistic initial conditions. This improvement helps to explain the distribution of such stars in the H-R diagram. Many important issues, such as the origin of binary stars and stellar clusters, remain as challenges for future research.

  15. Double photoionization of hydrocarbons and aromatic molecules

    NASA Astrophysics Data System (ADS)

    Wehlitz, R.

    2016-11-01

    This article reviews the recent progress in the field of double photoionization of hydrocarbons and aromatic molecules using synchrotron radiation. First I will describe the importance of carbon-based molecules, which are all around us and are literally part of our life. They exhibit intriguing properties some of which can be probed via double photoionization, i.e., the simultaneous emission of two electrons. Furthermore, I will discuss the different mechanisms that can lead to a doubly charged organic molecule and will highlight those findings by comparing them with the results for atoms and other (simple) molecules. Finally, I will give an outlook on future directions on this subject.

  16. Correlation between photoeletron and photoion in ultrafast multichannel photoionization of Ar

    SciTech Connect

    Itakura, R.; Fushitani, M.; Hishikawa, A.; Sako, T.

    2015-12-31

    We theoretically investigate coherent dynamics of ions created through ultrafast multichannel photoionization from a viewpoint of photoelectron-photoion correlation. The model calculation on single-photon ionization of Ar reveals that the coherent hole dynamics in Ar{sup +} associated with a superposition of the spin-orbit states {sup 2}PJ (J = 3/2 and 1/2) can be identified by monitoring only the photoion created by a Fourier-transform limited extreme ultraviolet (EUV) pulse with the fs pulse duration, while the coherence is lost by a chirped EUV pulse. It is demonstrated that by coincidence detection of the photoelectron and photoion the coherent hole dynamics can be extracted even in the case of ionization by a chirped EUV pulse with the sufficiently wide bandwidth.

  17. Rotational distributions of molecular photoions following resonant excitation

    NASA Astrophysics Data System (ADS)

    Poliakoff, E. D.; Chan, Jeffrey C. K.; White, M. G.

    1986-11-01

    We demonstrate that the photoelectron energy mediates the rotational energy distribution of N+2 ions created by photoionization, and conversely, that rotational energy determinations probe resonant excitation in molecular photoionization. Experimentally, this is accomplished by monitoring the dispersed fluorescence from N+2 (B 2Σ+u) photoions to determine their rotational energy distribution. These results demonstrate that while dipole selection rules constrain the total angular momentum of the electron-ion complex, the partitioning of angular momentum between the photoelectron and photoion depends on the photoejection dynamics. Implications for photoionization and electron impact ionizatin studies are discussed.

  18. A stellar-interstellar counterflow configuration with transversal plasma compressibility

    NASA Astrophysics Data System (ADS)

    Scherer, Klaus; Fahr, Hans J.; Ratkiewicz, Roma

    1994-07-01

    In general, a stellar wind system is in relative motion with respect to its ambient intersellar medium. Thus the stellar wind plasma eventually has to enter into an asymptotic outflow geometry appropriately adapted to this counterflow situation. We start out from a general description of the flow configuration describing the interaction of a subsonic interstellar plasma with the stellar wind plasma which either is subsonic from the very beginning (stellar breeze solution) or has already undergone an inner-shock transition before its encounter with the outer medium. We assume irrotational flows and allow for a transversal plasma compressibility, i.e. density gradients normal to the flowlines. This enables the determination of the velocity field as solution of the Laplacian differential equation. With the associated specific solutions of the density field, the pressure can consistently be calculated, providing the complete hydrodynamical data field of the counterflow configuration. From this theoretical hydrodynamical context it can then be proven that a finite net momentum loss of the stellar wind source is naturally connected with this form of an adapted wind, as was already shown for the case of incompressible plasmas by Fahr & Scherer (1993). The associated force acting upon the wind-driving star is calculated here and shows that such stars accelerate with respect to the ambient interstellar medium. Hereby, of course, the net reaction force has to be mediated through the stellar wind regime down to its source (i.e. the stellar corona). In case that, close to the star, a supersonic wind prevails, it has to adapt to the associated, asymmetric, outer boundary conditions which the distant stellar wind has to meet. Thus the adapted inner supersonic stellar wind has to be developed in an asymmetric form if the outer wind pattern is to be maintained in its calculated form.

  19. Absolute partial photoionization cross sections of ozone.

    SciTech Connect

    Berkowitz, J.; Chemistry

    2008-04-01

    Despite the current concerns about ozone, absolute partial photoionization cross sections for this molecule in the vacuum ultraviolet (valence) region have been unavailable. By eclectic re-evaluation of old/new data and plausible assumptions, such cross sections have been assembled to fill this void.

  20. HST imaging of hydrogen-poor ejecta in Abell 30 and Abell 78 - Wind-blown cometary structures

    NASA Technical Reports Server (NTRS)

    Borkowski, Kazimierz J.; Harrington, J. P.; Tsvetanov, Zlatan; Clegg, Robin E. S.

    1993-01-01

    HST Faint Object Camera images of hydrogen-poor gas in the planetary nebulae A30 and A78 have revealed remarkable 'cometary' structures in the O III 5007-A forbidden line. Most of these cometary structures, consisting of compact (0.15-0.5 arcsec) knots with radial tails several arcsec in length, are located in an equatorial plane in both nebulae. In addition, two bright, compact (0.3 arcsec) polar knots are present in A30, one of them forming a bow shock. Corresponding polar features in A78 are more diffuse. The central stars of both nebulae have energetic winds which are most likely responsible for the 'cometary' knot morphology. We interpret this morphology in terms of dense (several thousand electrons per cu cm) H-poor condensations whose outer expanding layers are swept outward by stellar winds. Photoionization modeling indicates that while dense knot cores are mostly heated by atomic photoionization, expanding tenuous gas is heated by photoelectrons ejected from abundant dust grains. Our models predict steep temperature gradients for which there is observational evidence and possible abrupt phase transitions in the expanding gas.

  1. Photoionization studies of oxygen and hydrogen

    NASA Astrophysics Data System (ADS)

    Padmanabhan, Arathi

    A toroidal spectrometer designed to perform (gamma, 2e) studies, was for the first time employed for Threshold Photoelectron Photoion Coincidence (TPEPICO) study. The angular distributions of O+(4S) ions produced from dissociative photoionization (DPI) of O2 + c4Sigma-u(nu =0,1) using the TPEPICO technique, i.e. by measuring the coincidence yield between threshold photoelectrons and photoions have been investigated. The results for lifetimes, taunu, corresponding to the vibrational levels nu = 0,1, along with the value obtained for inherent anisotropic photoion angular distribution betaO+, are presented. Recently, Fernandez and Martin (New J Phys 11 34 (2009)), have performed an extensive ab initio study of DPI in H2, in which large oscillatory behaviour in the electron angular distribution, as a function of electron energy, has been predicted. The result of their ab anitio calculations reveal that the electron angular, theta, distributions oscillate between a cos2theta pattern and isotropic with less than a 1 eV.change in electron energy. Due to the very low cross section and the requirement for high energy resolution in the electron detection system, these measurements require sensitive instrumentation that is now available at the Canadian Light Source. For this particular H 2 study, the electron angular distributions as a function of electron energy are the signature of quantum mechanical interference between, essentially, two specific doubly excited states (namely, 1Q11Sigma u+ and 1Q21piu) decaying at different internuclear distances. While interference between 'direct' photoionization and autoionization is well-known, the first unambiguous observation of interference between two autoionization processes, occurring on the femtosecond timescale is presented. A simple semi-classical model captures the essence of both our experimental observations and the results of full ab initio calculations. It does this through explicitly linking the electron angular

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

    NASA Technical Reports Server (NTRS)

    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.

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

    NASA Technical Reports Server (NTRS)

    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.

  4. THE EFFECT OF LIMITED SPATIAL RESOLUTION OF STELLAR SURFACE MAGNETIC FIELD MAPS ON MAGNETOHYDRODYNAMIC WIND AND CORONAL X-RAY EMISSION MODELS

    SciTech Connect

    Garraffo, C.; Cohen, O.; Drake, J. J.; Downs, C.

    2013-02-10

    We study the influence of the spatial resolution on scales of 5 Degree-Sign and smaller of solar surface magnetic field maps on global magnetohydrodynamic solar wind models, and on a model of coronal heating and X-ray emission. We compare the solutions driven by a low-resolution Wilcox Solar Observatory magnetic map, the same map with spatial resolution artificially increased by a refinement algorithm, and a high-resolution Solar and Heliospheric Observatory Michelson Doppler Imager map. We find that both the wind structure and the X-ray morphology are affected by the fine-scale surface magnetic structure. Moreover, the X-ray morphology is dominated by the closed loop structure between mixed polarities on smaller scales and shows significant changes between high- and low-resolution maps. We conclude that three-dimensional modeling of coronal X-ray emission has greater surface magnetic field spatial resolution requirements than wind modeling, and can be unreliable unless the dominant mixed polarity magnetic flux is properly resolved.

  5. Chandra X-ray spectroscopy of focused wind in the Cygnus X-1 system. II. The non-dip spectrum in the low/hard state - modulations with orbital phase

    NASA Astrophysics Data System (ADS)

    Miškovičová, Ivica; Hell, Natalie; Hanke, Manfred; Nowak, Michael A.; Pottschmidt, Katja; Schulz, Norbert S.; Grinberg, Victoria; Duro, Refiz; Madej, Oliwia K.; Lohfink, Anne M.; Rodriguez, Jérôme; Cadolle Bel, Marion; Bodaghee, Arash; Tomsick, John A.; Lee, Julia C.; Brown, Gregory V.; Wilms, Jörn

    2016-05-01

    Accretion onto the black hole in the system HDE 226868/Cygnus X-1 is powered by the strong line-driven stellar wind of the O-type donor star. We study the X-ray properties of the stellar wind in the hard state of Cyg X-1, as determined using data from the Chandra High Energy Transmission Gratings. Large density and temperature inhomogeneities are present in the wind, with a fraction of the wind consisting of clumps of matter with higher density and lower temperature embedded in a photoionized gas. Absorption dips observed in the light curve are believed to be caused by these clumps. This work concentrates on the non-dip spectra as a function of orbital phase. The spectra show lines of H-like and He-like ions of S, Si, Na, Mg, Al, and highly ionized Fe (Fe xvii-Fe xxiv). We measure velocity shifts, column densities, and thermal broadening of the line series. The excellent quality of these five observations allows us to investigate the orbital phase-dependence of these parameters. We show that the absorber is located close to the black hole. Doppler shifted lines point at a complex wind structure in this region, while emission lines seen in some observations are from a denser medium than the absorber. The observed line profiles are phase-dependent. Their shapes vary from pure, symmetric absorption at the superior conjunction to P Cygni profiles at the inferior conjunction of the black hole.

  6. Photoionization models of the CALIFA H II regions. I. Hybrid models

    NASA Astrophysics Data System (ADS)

    Morisset, C.; Delgado-Inglada, G.; Sánchez, S. F.; Galbany, L.; García-Benito, R.; Husemann, B.; Marino, R. A.; Mast, D.; Roth, M. M.

    2016-10-01

    Photoionization models of H ii regions require as input a description of the ionizing spectral energy distribution (SED) and of the gas distribution, in terms of ionization parameter U and chemical abundances (e.g., O/H and N/O).A strong degeneracy exists between the hardness of the SED and U, which in turn leads to high uncertainties in the determination of the other parameters, including abundances. One way to resolve the degeneracy is to fix one of the parameters using additional information. For each of the ~20 000 sources of the CALIFA H ii regions catalog, a grid of photoionization models is computed assuming the ionizing SED to be described by the underlying stellar population obtained from spectral synthesis modeling. The ionizing SED is then defined as the sum of various stellar bursts of different ages and metallicities. This solves the degeneracy between the shape of the ionizing SED and U. The nebular metallicity (associated with O/H) is defined using the classical strong line method O3N2 (which gives our models the status of "hybrids"). The remaining free parameters are the abundance ratio N/O and the ionization parameter U, which are determined by looking for the model fitting [N ii]/Hα and [O iii]/Hβ. The models are also selected to fit [O ii]/Hβ. This process leads to a set of ~3200 models that reproduce the three observations simultaneously. We find that the regions associated with young stellar bursts (i.e., ionized by OB stars) are affected by leaking of ionizing photons,the proportion of escaping photons having a median of 80%. The set of photoionization models satisfactorily reproduces the electron temperature derived from the [O iii]λ4363/5007 line ratio. We determine new relations between the nebular parameters, like the ionization parameter U and the [O ii]/[O iii] or [S ii]/[S iii] line ratios. A new relation between N/O and O/H is obtained, mostly compatible with previous empirical determinations (and not with previous results obtained

  7. Photoionization of Co+ and electron-impact excitation of Co2 + using the Dirac R-matrix method

    NASA Astrophysics Data System (ADS)

    Tyndall, N. B.; Ramsbottom, C. A.; Ballance, C. P.; Hibbert, A.

    2016-11-01

    Modelling of massive stars and supernovae (SNe) plays a crucial role in understanding galaxies. From this modelling we can derive fundamental constraints on stellar evolution, mass-loss processes, mixing, and the products of nucleosynthesis. Proper account must be taken of all important processes that populate and depopulate the levels (collisional excitation, de-excitation, ionization, recombination, photoionization, bound-bound processes). For the analysis of Type Ia SNe and core collapse SNe (Types Ib, Ic and II) Fe group elements are particularly important. Unfortunately little data is currently available and most noticeably absent are the photoionization cross-sections for the Fe-peaks which have high abundances in SNe. Important interactions for both photoionization and electron-impact excitation are calculated using the relativistic Dirac atomic R-matrix codes (DARC) for low-ionization stages of Cobalt. All results are calculated up to photon energies of 45 eV and electron energies up to 20 eV. The wavefunction representation of Co III has been generated using GRASP0 by including the dominant 3d7, 3d6[4s, 4p], 3p43d9 and 3p63d9 configurations, resulting in 292 fine structure levels. Electron-impact collision strengths and Maxwellian averaged effective collision strengths across a wide range of astrophysically relevant temperatures are computed for Co III. In addition, statistically weighted level-resolved ground and metastable photoionization cross-sections are presented for Co II and compared directly with existing work.

  8. Does feedback help or hinder star formation? The effect of photoionization on star formation in giant molecular clouds

    NASA Astrophysics Data System (ADS)

    Shima, Kazuhiro; Tasker, Elizabeth J.; Habe, Asao

    2017-05-01

    We investigated the effect of photoionizing feedback inside turbulent star-forming clouds, comparing the resultant star formation in both idealized profiles and more realistic cloud structures drawn from a global galaxy simulation. We performed a series of numerical simulations that compared the effect of star formation alone, photoionization and photoionization plus supernovae feedback. In the idealized cloud, photoionization suppresses gas fragmentation at early times, resulting in the formation of more massive stars and an increase in the star formation efficiency. At later times, the dispersal of the dense gas causes the radiative feedback effect to switch from positive to negative as the star formation efficiency drops. In the cloud extracted from the global simulation, the initial cloud is heavily fragmented prior to the stellar-feedback beginning and is largely structurally unaffected by the late injection of radiation energy. The result is a suppression of the star formation. We conclude that the efficiency of feedback is heavily dependent on the gas structure, with negative feedback dominating when the density is high.

  9. Winds from Low Mass Protostars

    NASA Astrophysics Data System (ADS)

    Shu, Frank H.; Lizano, Susana; Adams, Fred C.; Ruden, Steven P.

    In its last stages, star formation in molecular clouds includes the onset of a stellar wind that helps to clear away the surrounding placenta of gas and dust, thereby making the young stellar object optically visible. The authors discuss new observational evidence that the emerging wind is largely neutral and atomic in low-mass protostars. They then suggest a simple theoretical mechanism for the generation of such powerful neutral winds.

  10. Photoionization and Dissociative Photoionization Study of Cholesterol by IR Laser Desorption/Tunable Synchrotron VUV Photoionization Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Pan, Yang; Zhang, Li-dong; Guo, Hui-jun; Yin, Hao; Qi, Fei

    2009-04-01

    Elementary cholesterol was analyzed with IR laser desorption/tunable synchrotron vacuum ultraviolet photoionization mass spectrometry. An exclusive molecular ion of cholesterol is observed by near threshold single-photon ionization with high efficiency. Fragments are yielded with the increase of photon energy. The structures of various fragments are determined with commercial electron ionization time-of-flight mass spectrometry. Dominant fragmentation pathways are discussed in detail with the aid of ab initio calculations.

  11. Stellar shrapnel

    NASA Image and Video Library

    2016-08-15

    Several thousand years ago, a star some 160 000 light-years away from us exploded, scattering stellar shrapnel across the sky. The aftermath of this energetic detonation is shown here in this striking image from the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3. The exploding star was a white dwarf located in the Large Magellanic Cloud, one of our nearest neighbouring galaxies. Around 97% of stars within the Milky Way that are between a tenth and eight times the mass of the Sun are expected to end up as white dwarfs. These stars can face a number of different fates, one of which is to explode as supernovae, some of the brightest events ever observed in the Universe. If a white dwarf is part of a binary star system, it can siphon material from a close companion. After gobbling up more than it can handle — and swelling to approximately one and a half times the size of the Sun — the star becomes unstable and ignites as a Type Ia supernova. This was the case for the supernova remnant pictured here, which is known as DEM L71. It formed when a white dwarf reached the end of its life and ripped itself apart, ejecting a superheated cloud of debris in the process. Slamming into the surrounding interstellar gas, this stellar shrapnel gradually diffused into the separate fiery filaments of material seen scattered across this skyscape.

  12. Stellar cannibalism

    NASA Astrophysics Data System (ADS)

    Astronomers have obtained evidence that stars can literally swallow other stars, leading to the ejection of stellar material into space and the formation of extremely close pairs of stars, according to the National Science Foundation (NSF). The discovery supports theoretical predictions of the evolution of double stars.While studying the central stars of planetary nebulae—disk-shaped gas clouds that vaguely resemble planets—Albert D. Grauer of the University of Arkansas at Little Rock and Howard E. Bond of Louisiana State University at Baton Rouge found that several of these central stars are actually very close stellar pairs. Previously, it had been thought that the central star in a planetary nebula was a single star that expelled a gas cloud as it neared the end of its life. Their latest discovery, the central star of planetary nebula Abell 41, consists of a pair of stars that orbit each other in 2 hours and 43 minutes. The researchers also have found three other central star pairs that have orbital periods of between 11 and 16 hours.

  13. Time-dependent Cooling in Photoionized Plasma

    NASA Astrophysics Data System (ADS)

    Gnat, Orly

    2017-02-01

    I explore the thermal evolution and ionization states in gas cooling from an initially hot state in the presence of external photoionizing radiation. I compute the equilibrium and nonequilibrium cooling efficiencies, heating rates, and ion fractions for low-density gas cooling while exposed to the ionizing metagalactic background radiation at various redshifts (z = 0 ‑ 3), for a range of temperatures (108–104 K), densities (10‑7–103 cm‑3), and metallicities (10‑3–2 times solar). The results indicate the existence of a threshold ionization parameter, above which the cooling efficiencies are very close to those in photoionization equilibrium (so that departures from equilibrium may be neglected), and below which the cooling efficiencies resemble those in collisional time-dependent gas cooling with no external radiation (and are thus independent of density).

  14. Photoionization of P+: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Nahar, S. N.; Hernández, E. M.; Hernández, L.; Antillón, A.; Morales-Mori, A.; González, O.; Covington, A. M.; Chartkunchand, K. C.; Hanstorp, D.; Juárez, A. M.; Hinojosa, G.

    2017-01-01

    An experimental and theoretical study of the single photoionization cross section of the P+ cation of phosphorus is presented. Photoionization (PI) cross sections are instrumental for the determination of abundances in the interstellar medium. The experiment was performed by merging an ion beam with a photon beam. The photon beam was nearly monochromatic and had an energy resolution of 24 meV. Calculations were carried out using the Breit-Pauli R-matrix method. The combined study was developed in the photon energy interval from 18 eV (68.9 nm) to 50 eV (24.8 nm). Comparison between the measured and the calculated cross section shows good agreement in general and identifies features of the process and existence of states in the experimental beam. The present results should provide for more accurate modeling of P+.

  15. Photoionization of atomic hydrogen in electric field

    SciTech Connect

    Gorlov, Timofey V; Danilov, Viatcheslav V

    2010-01-01

    Laser assisted ionization of high energy hydrogen beams in magnetic fields opens wide application possibilities in accelerator physics and other fields. The key theoretical problem of the method is the calculation of the ionization probability of a hydrogen atom affected by laser and static electric fields in the particle rest frame. A method of solving this problem with the temporal Schr dinger equation including a continuum spectrum is presented in this paper in accurate form for the first time. This method allows finding the temporal evolution of the wave function of the hydrogen atom as a function of laser and static electric fields. Solving the problem of photoionization reveals quantum effects that cannot be described by the cross sectional approach. The effects play a key role in the problems of photoionization of H0 beams with the large angular or energy spread.

  16. Neon photoionized plasma experiment at Z

    NASA Astrophysics Data System (ADS)

    Mayes, D. C.; Mancini, R. C.; Bailey, J. E.; Loisel, G. P.; Rochau, G. A.

    2016-10-01

    We discuss an experimental effort to study the atomic kinetics in neon photoionized plasmas via K-shell line absorption spectroscopy. The experiment employs the intense x-ray flux emitted at the collapse of a Z-pinch to heat and backlight a photoionized plasma contained within a cm-scale gas cell placed at various distances from the Z-pinch and filled with neon gas pressures in the range from 3.5 to 30 torr. The experimental platform affords an order of magnitude range in the ionization parameter characterizing the photoionized plasma from about 3 to 80 erg*cm/s. An x-ray crystal spectrometer capable of collecting both time-integrated and time-gated spectra is used to collect absorption spectra. A suite of IDL programs has been developed to process the experimental data to produce transmission spectra. The spectra show line absorption by several ionization stages of neon, including Be-, Li-, He-, and H-like ions. Analysis of these spectra yields ion areal-densities and charge state distributions, which can be compared with results from atomic kinetics codes. In addition, the electron temperature is extracted from level population ratios of nearby energy levels in Li- and Be-like ions, which can be used to test heating models of photoionized plasmas. This work was sponsored in part by the DOE National Nuclear Security Administration Grant DE-FG52-09NA29551, DOE Office of Science Grant DE-SC0014451, and the Z Facility Fundamental Science Program of SNL.

  17. STELLARATOR INJECTOR

    DOEpatents

    Post, R.F.

    1962-09-01

    A method and means are described for injecting energetic neutral atoms or molecular ions into dense magnetically collimated plasma columns of stellarators and the like in such a manner that the atoms or ions are able to significantly penetrate the column before being ionized by collision with the plasma constituent particles. Penetration of the plasma column by the neutral atoms or molecular ions is facilitated by superposition of two closely spaced magnetic mirrors on the plasma confinement field. The mirrors are moved apart to magnetically sweep plasma from a region between the mirrors and establish a relatively low plasma density therein. By virture of the low density, neutral atoms or molecular ions injected into the region significantly penetrate the plasma column before being ionized. Thereafter, the mirrors are diminished to permit the injected material to admix with the plasma in the remainder of the column. (AEC)

  18. Photoionization of atoms and molecules. [of hydrogen, helium, and xenon

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1976-01-01

    A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

  19. Nebular Continuum and Line Emission in Stellar Population Synthesis Models

    NASA Astrophysics Data System (ADS)

    Byler, Nell; Dalcanton, Julianne J.; Conroy, Charlie; Johnson, Benjamin D.

    2017-05-01

    Accounting for nebular emission when modeling galaxy spectral energy distributions (SEDs) is important, as both line and continuum emissions can contribute significantly to the total observed flux. In this work, we present a new nebular emission model integrated within the Flexible Stellar Population Synthesis code that computes the line and continuum emission for complex stellar populations using the photoionization code Cloudy. The self-consistent coupling of the nebular emission to the matched ionizing spectrum produces emission line intensities that correctly scale with the stellar population as a function of age and metallicity. This more complete model of galaxy SEDs will improve estimates of global gas properties derived with diagnostic diagrams, star formation rates based on Hα, and physical properties derived from broadband photometry. Our models agree well with results from other photoionization models and are able to reproduce observed emission from H ii regions and star-forming galaxies. Our models show improved agreement with the observed H ii regions in the Ne iii/O ii plane and show satisfactory agreement with He ii emission from z = 2 galaxies, when including rotating stellar models. Models including post-asymptotic giant branch stars are able to reproduce line ratios consistent with low-ionization emission regions. The models are integrated into current versions of FSPS and include self-consistent nebular emission predictions for MIST and Padova+Geneva evolutionary tracks.

  20. Flexible helical-axis stellarator

    DOEpatents

    Harris, Jeffrey H.; Hender, Timothy C.; Carreras, Benjamin A.; Cantrell, Jack L.; Morris, Robert N.

    1988-01-01

    An 1=1 helical winding which spirals about a conventional planar, circular central conductor of a helical-axis stellarator adds a significant degree of flexibility by making it possible to control the rotational transform profile and shear of the magnetic fields confining the plasma in a helical-axis stellarator. The toroidal central conductor links a plurality of toroidal field coils which are separately disposed to follow a helical path around the central conductor in phase with the helical path of the 1=1 winding. This coil configuration produces bean-shaped magnetic flux surfaces which rotate around the central circular conductor in the same manner as the toroidal field generating coils. The additional 1=1 winding provides flexible control of the magnetic field generated by the central conductor to prevent the formation of low-order resonances in the rotational transform profile which can produce break-up of the equilibrium magnetic surfaces. Further, this additional winding can deepen the magnetic well which together with the flexible control provides increased stability.

  1. NuSTAR observations of the supergiant X-ray pulsar IGR J18027-2016: accretion from the stellar wind and possible cyclotron absorption line

    NASA Astrophysics Data System (ADS)

    Lutovinov, Alexander A.; Tsygankov, Sergey S.; Postnov, Konstantin A.; Krivonos, Roman A.; Molkov, Sergey V.; Tomsick, John A.

    2017-04-01

    We report on the first focused hard X-ray view of the absorbed supergiant system IGR J18027-2016 performed with the Nuclear Spectroscopic Telescope Array observatory. The pulsations are clearly detected with a period of Pspin = 139.866(1) s and a pulse fraction of about 50-60 per cent 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 dot{P}≃ 6× 10^{-10} s s-1. 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 ≃ 3 × 1012 G at the surface of the neutron star, which is typical for X-ray pulsars.

  2. Radiation-driven winds of hot stars. V - Wind models for central stars of planetary nebulae

    NASA Technical Reports Server (NTRS)

    Pauldrach, A.; Puls, J.; Kudritzki, R. P.; Mendez, R. H.; Heap, S. R.

    1988-01-01

    Wind models using the recent improvements of radiation driven wind theory by Pauldrach et al. (1986) and Pauldrach (1987) are presented for central stars of planetary nebulae. The models are computed along evolutionary tracks evolving with different stellar mass from the Asymptotic Giant Branch. We show that the calculated terminal wind velocities are in agreement with the observations and allow in principle an independent determination of stellar masses and radii. The computed mass-loss rates are in qualitative agreement with the occurrence of spectroscopic stellar wind features as a function of stellar effective temperature and gravity.

  3. Radiation-driven winds of hot stars. V - Wind models for central stars of planetary nebulae

    NASA Technical Reports Server (NTRS)

    Pauldrach, A.; Puls, J.; Kudritzki, R. P.; Mendez, R. H.; Heap, S. R.

    1988-01-01

    Wind models using the recent improvements of radiation driven wind theory by Pauldrach et al. (1986) and Pauldrach (1987) are presented for central stars of planetary nebulae. The models are computed along evolutionary tracks evolving with different stellar mass from the Asymptotic Giant Branch. We show that the calculated terminal wind velocities are in agreement with the observations and allow in principle an independent determination of stellar masses and radii. The computed mass-loss rates are in qualitative agreement with the occurrence of spectroscopic stellar wind features as a function of stellar effective temperature and gravity.

  4. Stellarmak a hybrid stellarator: Spheromak

    SciTech Connect

    Hartman, C.W.

    1980-01-04

    This paper discusses hybridization of modified Stellarator-like transform windings (T-windings) with a Spheromak or Field-Reversed-Mirror configuration. This configuration, Stellarmak, retains the important topological advantage of the Spheromak or FRM of having no plasma linking conductors or blankets. The T-windings provide rotational transformation in toroidal angle of the outer poloidal field lines, in effect creating a reversed B/sub Toroidal/ Spheromak or adding average B/sub T/ to the FRM producing higher shear, increased limiting ..beta.., and possibly greater stability to kinks and tilt. The presence of field ripple in the toroidal direction may be sufficient to inhibit cancellation of directed ion current by electron drag to allow steady state operation with the toroidal as well as poloidal current maintained by neutral beams.

  5. Devastated Stellar Neighborhood

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image from NASA's Spitzer Space Telescope shows the nasty effects of living near a group of massive stars: radiation and winds from the massive stars (white spot in center) are blasting planet-making material away from stars like our sun. The planetary material can be seen as comet-like tails behind three stars near the center of the picture. The tails are pointing away from the massive stellar furnaces that are blowing them outward.

    The picture is the best example yet of multiple sun-like stars being stripped of their planet-making dust by massive stars.

    The sun-like stars are about two to three million years old, an age when planets are thought to be growing out of surrounding disks of dust and gas. Astronomers say the dust being blown from the stars is from their outer disks. This means that any Earth-like planets forming around the sun-like stars would be safe, while outer planets like Uranus might be nothing more than dust in the wind.

    This image shows a portion of the W5 star-forming region, located 6,500 light-years away in the constellation Cassiopeia. It is a composite of infrared data from Spitzer's infrared array camera and multiband imaging photometer. Light with a wavelength of 3.5 microns is blue, while light from the dust of 24 microns is orange-red.

  6. 2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008

    SciTech Connect

    Klaus Muller-Dethefs Nancy Ryan GRay

    2009-03-31

    This conference brings together scientists interested in a range of basic phenomena linked to the ejection and scattering of electrons from atoms, molecules, clusters, liquids and solids by absorption of light. Photoionization, a highly sensitive probe of both structure and dynamics, can range from perturbative single-photon processes to strong-field highly non-perturbative interactions. It is responsible for the formation and destruction of molecules in astrophysical and plasma environments and successfully used in advanced analytical techniques. Positive ions, which can be produced and studied most effectively using photoionization, are the major components of all plasmas, vital constituents of flames and important intermediates in many chemical reactions. Negative ions are significant as transient species and, when photodetached, the corresponding neutral species often undergoes remarkable, otherwise non-observable, dynamics. The scope of the meeting spans from novel observations in atomic and molecular physics, such as Coulomb Crystals, highly excited states and cold Rydberg plasmas, to novel energy resolved or ultrafast time-resolved experiments, photoionization in strong laser fields, theoretical method development for electron scattering, photoionization and photodetachment and more complex phenomena such as charge transfer and DNA and protein conductivity, important for biological and analytical applications.

  7. Astronomy: A turbulent stellar atmosphere in full view

    NASA Astrophysics Data System (ADS)

    Schaefer, Gail H.

    2017-08-01

    The dynamic motion of gas in the outer atmosphere of a red supergiant star has been mapped, providing clues to the mysterious mechanism that causes massive stars to lose mass through stellar winds. See Letter p.310

  8. On the onset of secondary stellar generations in giant star-forming regions and massive star clusters

    SciTech Connect

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-09-10

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ∼ 10{sup 4} K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ∼ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  9. Stellar Ro

    NASA Astrophysics Data System (ADS)

    Featherstone, Nicholas

    2017-05-01

    Our understanding of the interior dynamics that give rise to a stellar dynamo draws heavily from investigations of similar dynamics in the solar context. Unfortunately, an outstanding gap persists in solar dynamo theory. Convection, an indispensable component of the dynamo, occurs in the midst of rotation, and yet we know little about how the influence of that rotation manifests across the broad range of convective scales present in the Sun. We are nevertheless well aware that the interaction of rotation and convection profoundly impacts many aspects of the dynamo, including the meridional circulation, the differential rotation, and the helicity of turbulent EMF. The rotational constraint felt by solar convection ultimately hinges on the characteristic amplitude of deep convective flow speeds, and such flows are difficult to measure helioseismically. Those measurements of deep convective power which do exist disagree by orders of magnitude, and until this disagreement is resolved, we are left with the results of models and those less ambiguous measurements derived from surface observations of solar convection. I will present numerical results from a series of nonrotating and rotating convection simulations conducted in full 3-D spherical geometry. This presentation will focus on how convective spectra differ between the rotating and non-rotating models and how that behavior changes as simulations are pushed toward more turbulent and/or more rotationally-constrained regimes. I will discuss how the surface signature of rotationally-constrained interior convection might naturally lead to observable signatures in the surface convective pattern, such as supergranulation and a dearth of giant cells.

  10. Complete characterization of double photoionization processes

    NASA Astrophysics Data System (ADS)

    Ivanov, I. A.; Kheifets, A. S.

    2011-06-01

    We analyze correlated photoelectron spectra of single-photon two-electron ionization [double photoionization (DPI)] of helium to reconstruct the phase of the spectral amplitude of this process. The phase can be reconstructed reliably in a wide range of photoelectron momenta, thus allowing one to retrieve information about the wave function of the DPI process and its temporal evolution. Our simulation indicates that the proposed phase reconstruction technique can be applied in experiment to trace dynamics of the DPI process with attosecond precision.

  11. Spin effects in double photoionization of lithium

    NASA Astrophysics Data System (ADS)

    Kheifets, A. S.; Fursa, D. V.; Hines, C. W.; Bray, I.; Colgan, J.; Pindzola, M. S.

    2010-02-01

    We apply the nonperturbative convergent close-coupling (CCC) and time-dependent close coupling (TDCC) formalisms to calculate fully differential energy and angular resolved cross sections of double photoionization (DPI) of lithium. The equal energy sharing case is considered in which dynamics of the DPI process can be adequately described by two symmetrized singlet and triplet amplitudes. The angular width of these amplitudes serves as a measure of the strength of the angular correlation between the two ejected electrons. This width is interpreted in terms of the spin of the photoelectron pair.

  12. Spin effects in double photoionization of lithium

    SciTech Connect

    Kheifets, A. S.; Fursa, D. V.; Hines, C. W.; Bray, I.; Colgan, J.; Pindzola, M. S.

    2010-02-15

    We apply the nonperturbative convergent close-coupling (CCC) and time-dependent close coupling (TDCC) formalisms to calculate fully differential energy and angular resolved cross sections of double photoionization (DPI) of lithium. The equal energy sharing case is considered in which dynamics of the DPI process can be adequately described by two symmetrized singlet and triplet amplitudes. The angular width of these amplitudes serves as a measure of the strength of the angular correlation between the two ejected electrons. This width is interpreted in terms of the spin of the photoelectron pair.

  13. Complete characterization of double photoionization processes

    SciTech Connect

    Ivanov, I. A.; Kheifets, A. S.

    2011-06-15

    We analyze correlated photoelectron spectra of single-photon two-electron ionization [double photoionization (DPI)] of helium to reconstruct the phase of the spectral amplitude of this process. The phase can be reconstructed reliably in a wide range of photoelectron momenta, thus allowing one to retrieve information about the wave function of the DPI process and its temporal evolution. Our simulation indicates that the proposed phase reconstruction technique can be applied in experiment to trace dynamics of the DPI process with attosecond precision.

  14. Double Photoionization of Aligned Molecular Hydrogen

    SciTech Connect

    Vanroose, Wim; Horner, Daniel A.; Martin, Fernando; Rescigno,Thomas N.; McCurdy, C. William

    2006-07-21

    We present converged, completely ab initio calculations ofthe triple differential cross sections for double photoionization ofaligned H2 molecules for a photon energy of 75.0 eV. The method ofexterior complex scaling, implemented with both the discrete variablerepresentation and B-splines, is used to solve the Schroedinger equationfor a correlated continuum wave function corresponding to a single photonhaving been absorbed by a correlated initial state. Results for a fixedinternuclear distance are compared with recent experiments and show thatintegration over experimental angular and energy resolutions is necessaryto produce good qualitative agreement, but does not eliminate somediscrepancies. Limitations of current experimental resolution are shownto sometimes obscure interesting details of the crosssection.

  15. K-shell photoionization cross-sections.

    NASA Technical Reports Server (NTRS)

    Daltabuit, E.; Cox, D. P.

    1972-01-01

    Approximate values for the threshold energies, threshold cross sections, and energy dependence of the cross sections for K-shell photoionization are tabulated for H, He, C, N, O, Ne, Mg, Si, and S in all stages of ionization. The approximation of these data is based on the assumptions that the threshold energy is a simple function of the nuclear charge and the number of electrons present in the atom, and that the threshold values and energy dependence of the cross sections are determined only by the threshold energy.

  16. Photoionization of zinc by TDLDA calculations

    NASA Astrophysics Data System (ADS)

    Stener, M.; Decleva, P.

    1997-10-01

    Absolute photoionization cross section profiles of Zn have been calculated at TDLDA and LDA level, employing a very accurate B-spline basis set and the modified Sternheimer approach. The van Leeuwen - Baerends exchange correlation potential has been used, since its correct asymptotic behaviour is able to support virtual states and describe core-excited resonances. A comparison with available theoretical and experimental data has been performed when possible. The present method has been proven to be robust to analyse wide photon energy regions (from threshold up to 200 eV) and discuss the various shapes of one-electron resonances.

  17. Atomic photoionization experiment by harmonic-generation spectroscopy

    NASA Astrophysics Data System (ADS)

    Frolov, M. V.; Sarantseva, T. S.; Manakov, N. L.; Fulfer, K. D.; Wilson, B. P.; Troß, J.; Ren, X.; Poliakoff, E. D.; Silaev, A. A.; Vvedenskii, N. V.; Starace, Anthony F.; Trallero-Herrero, C. A.

    2016-03-01

    Measurements of the high-order-harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter.

  18. Calculated photoionization cross sections using Quantemol-N

    NASA Astrophysics Data System (ADS)

    Brigg, Will J.; Harvey, Alex G.; Dzarasova, Anna; Mohr, Sebastian; Brambila, Danilo S.; Morales, Felipe; Smirnova, Olga; Tennyson, Jonathan

    2015-06-01

    Quantemol-N is an expert system designed to run the widely used UK Molecular R-matrix code (UKRMol). Originally designed to consider electron-molecule collision problems, here we present an extension to treat molecular photoionization. Sample results are given for the photoionization of molecular nitrogen and methane. Comparisons are made with experimental results showing good agreement.

  19. Stellar Feedback Up and Close

    NASA Astrophysics Data System (ADS)

    Gadotti, Dimitri; Timer Team

    2017-07-01

    We report the serendipitous discovery of ongoing stellar feedback in the star-bursting nuclear ring of a nearby spiral galaxy, as part of the TIMER survey with MUSE. Combining MUSE and ALMA data we show bubbles of ionised gas expanding from the ring and shocking with the cold ISM. We demonstrate how much energy is being released into the ISM corresponding to the star formation observed, how fast the heated ISM is expanding from the centre, and provide a physical description of the shocks happening at the interface between the heated and cold phases of the ISM. Further, we quantitatively show how the exchange of energy between the two phases impacts the dynamics of the cold ISM. Finally, applying a model to the spatially-resolved spectral properties of this system, we find that about 60% of the energy input into the ISM is produced via the direct transfer of momentum from photons scattering onto dust grains, and 27% produced by mass loss in supernova explosions. The remaining energy input is produced via photoionisation heating ( 12%) and stellar winds ( 1%). These analyses provide invaluable measurements against which our theoretical understanding of stellar feedback can be compared, particularly state-of-the-art simulations that aim at reproducing star formation and stellar feedback in galaxies.

  20. Determining the partial photoionization cross-sections of ethyl radicals.

    PubMed

    FitzPatrick, B L; Maienschein-Cline, M; Butler, L J; Lee, S-H; Lin, J J

    2007-12-13

    Using a crossed laser-molecular beam scattering apparatus, these experiments photodissociate ethyl chloride at 193 nm and detect the Cl and ethyl products, resolved by their center-of-mass recoil velocities, with vacuum ultraviolet photoionization. The data determine the relative partial cross-sections for the photoionization of ethyl radicals to form C2H5+, C2H4+, and C2H3+ at 12.1 and 13.8 eV. The data also determine the internal energy distribution of the ethyl radical prior to photoionization, so we can assess the internal energy dependence of the photoionization cross-sections. The results show that the C2H4++H and C2H3++H2 dissociative photoionization cross-sections strongly depend on the photoionization energy. Calibrating the ethyl radical partial photoionization cross-sections relative to the bandwidth-averaged photoionization cross-section of Cl atoms near 13.8 eV allows us to use these data in conjunction with literature estimates of the Cl atom photoionization cross-sections to put the present bandwidth-averaged cross-sections on an absolute scale. The resulting bandwidth-averaged cross-section for the photoionization of ethyl radicals to C2H5+ near 13.8 eV is 8+/-2 Mb. Comparison of our 12.1 eV data with high-resolution ethyl radical photoionization spectra allows us to roughly put the high-resolution spectrum on the same absolute scale. Thus, one obtains the photoionization cross-section of ethyl radicals to C2H5+ from threshold to 12.1 eV. The data show that the onset of the C2H4++H dissociative photoionization channel is above 12.1 eV; this result offers a simple way to determine whether the signal observed in photoionization experiments on complex mixtures is due to ethyl radicals. We discuss an application of the results for resolving the product branching in the O+allyl bimolecular reaction.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Studies of x-ray emission properties of photoionized plasmas

    NASA Astrophysics Data System (ADS)

    Wang, Feilu; Han, Bo; Jin, Rui; Salzmann, David; Liang, Guiyun; Wei, Huigang; Zhong, Jiayong; Zhao, Gang; Li, Jia-ming

    2016-03-01

    In this paper three aspects of photoionized plasmas are discussed in both laboratory and astrophysical contexts. First, the importance of accurate atomic/ionic data for the analysis of photoionized plasmas is shown. Second, an overview of present computer codes for the analysis of photoionized plasmas is given. We introduce our computer model, radiative-collisional code based on the flexible atomic code (RCF), for calculations of the properties of such plasmas. RCF uses database generated by the flexible atomic code. Using RCF it is shown that incorporating the satellite lines from doubly excited Li-like ions into the He{}α triplet lines is necessary for reliable analysis of observational spectra from astrophysical objects. Finally, we introduce a proposal to generate photoionized plasmas by x-ray free electron laser, which may facilitate the simulation in lab of astrophysical plasmas in photoionization equilibrium.

  3. Double photoionization of helium with synchrotron x-rays: Proceedings

    SciTech Connect

    Not Available

    1994-01-01

    This report contains papers on the following topics: Overview and comparison of photoionization with charged particle impact; The ratio of double to single ionization of helium: the relationship of photon and bare charged particle impact ionization; Double photoionization of helium at high energies; Compton scattering of photons from electrons bound in light elements; Electron ionization and the Compton effect in double ionization of helium; Elimination of two atomic electrons by a single energy photon; Double photoionization of helium at intermediate energies; Double Photoionization: Gauge Dependence, Coulomb Explosion; Single and Double Ionization by high energy photon impact; The effect of Compton Scattering on the double to single ionization ratio in helium; and Double ionization of He by photoionization and Compton scattering. These papers have been cataloged separately for the database.

  4. An Extreme X-ray Disk Wind in the Black Hole Candidate IGR J17091-3624

    NASA Technical Reports Server (NTRS)

    King, A. L.; Miller, J. M.; Raymond, J.; Fabian, A. C.; Reynolds, C. S.; Kallman, T. R.; Maitra, D.; Cackett, E. M.; Rupen, M. P.

    2012-01-01

    Chandra spectroscopy of transient stellar-mass black holes in outburst has clearly revealed accretion disk winds in soft, disk-dominated states, in apparent anti-correlation with relativistic jets in low/hard states. These disk winds are observed to be highly ionized. dense. and to have typical velocities of approx 1000 km/s or less projected along our line of sight. Here. we present an analysis of two Chandra High Energy Transmission Grating spectra of the Galactic black hole candidate IGR J17091-3624 and contemporaneous EVLA radio observations. obtained in 2011. The second Chandra observation reveals an absorption line at 6.91+/-0.01 keV; associating this line with He-like Fe XXV requires a blue-shift of 9300(+500/-400) km/ s (0.03c. or the escape velocity at 1000 R(sub schw)). This projected outflow velocity is an order of magnitude higher than has previously been observed in stellar-mass black holes, and is broadly consistent with some of the fastest winds detected in active galactic nuclei. A potential feature at 7.32 keV, if due to Fe XXVI, would imply a velocity of approx 14600 km/s (0.05c), but this putative feature is marginal. Photoionization modeling suggests that the accretion disk wind in IGR J17091-3624 may originate within 43,300 Schwarzschild radii of the black hole, and may be expelling more gas than accretes. The contemporaneous EVLA observations strongly indicate that jet activity was indeed quenched at the time of our Chandra observations. We discuss the results in the context of disk winds, jets, and basic accretion disk physics in accreting black hole systems

  5. AN EXTREME X-RAY DISK WIND IN THE BLACK HOLE CANDIDATE IGR J17091-3624

    SciTech Connect

    King, A. L.; Miller, J. M.; Maitra, D.; Raymond, J.; Fabian, A. C.; Cackett, E. M.; Reynolds, C. S.; Kallman, T. R.; Rupen, M. P.

    2012-02-20

    Chandra spectroscopy of transient stellar-mass black holes in outburst has clearly revealed accretion disk winds in soft, disk-dominated states, in apparent anti-correlation with relativistic jets in low/hard states. These disk winds are observed to be highly ionized, dense, and to have typical velocities of {approx}1000 km s{sup -1} or less projected along our line of sight. Here, we present an analysis of two Chandra High Energy Transmission Grating spectra of the Galactic black hole candidate IGR J17091-3624 and contemporaneous Expanded Very Large Array (EVLA) radio observations, obtained in 2011. The second Chandra observation reveals an absorption line at 6.91 {+-} 0.01 keV; associating this line with He-like Fe XXV requires a blueshift of 9300{sup +500}{sub -400} km s{sup -1} (0.03c, or the escape velocity at 1000 R{sub Schw}). This projected outflow velocity is an order of magnitude higher than has previously been observed in stellar-mass black holes, and is broadly consistent with some of the fastest winds detected in active galactic nuclei. A potential feature at 7.32 keV, if due to Fe XXVI, would imply a velocity of {approx}14, 600 km s{sup -1} (0.05c), but this putative feature is marginal. Photoionization modeling suggests that the accretion disk wind in IGR J17091-3624 may originate within 43,300 Schwarzschild radii of the black hole and may be expelling more gas than it accretes. The contemporaneous EVLA observations strongly indicate that jet activity was indeed quenched at the time of our Chandra observations. We discuss the results in the context of disk winds, jets, and basic accretion disk physics in accreting black hole systems.

  6. Radiation-magnetohydrodynamic simulations of the photoionization of magnetized globules

    NASA Astrophysics Data System (ADS)

    Henney, William J.; Arthur, S. Jane; de Colle, Fabio; Mellema, Garrelt

    2009-09-01

    We present the first three-dimensional radiation-magnetohydrodynamic simulations of the photoionization of a dense, magnetized molecular globule by an external source of ultraviolet radiation. We find that, for the case of a strong ionizing field, significant deviations from the non-magnetic evolution are seen when the initial magnetic field threading the globule has an associated magnetic pressure that is greater than 100 times the gas pressure. In such a strong-field case, the photoevaporating globule will adopt a flattened or `curled up' shape, depending on the initial field orientation, and magnetic confinement of the ionized photoevaporation flow can lead to recombination and subsequent fragmentation during advanced stages of the globule evolution. We find suggestive evidence that such magnetic effects may be important in the formation of bright, bar-like emission features in HII regions. We include simple but realistic fits to heating and cooling rates in the neutral and molecular gas in the vicinity of a high-mass star cluster, and show that the frequently used isothermal approximation can lead to an overestimate of the importance of gravitational instability in the radiatively imploded globule. For globules within 2 pc of a high-mass star cluster, we find that heating by stellar X-rays prevents the molecular gas from cooling below 50 K. Based in part on numerical simulations carried out using the Kan Balam supercomputer, operated by the Departamento de Supercómputo, Dirección General de Servicios de Cómputo Académico, Universidad Nacional Autónoma de México. E-mail: w.henney@astrosmo.unam.mx

  7. Prospects for ALMA Studies of the Solar-Stellar Connection

    NASA Astrophysics Data System (ADS)

    Linsky, Jeffrey

    2016-07-01

    ALMA provides a splendid opportunity to observe a wide range of star types at millimeter wavelengths to investigate the solar-stellar connection. I will compare the sensitivities and wavelength coverages of ALMA and the JVLA to highlight the discovery space that ALMA has for stellar astronomy. At millimeter wavelengths, ALMA will be able to detect thermal and gyroresonance emission from nearby stellar chromospheres and transition regions. Comparison of millimeter fluxes from ALMA with centimeter fluxes from JVLA may be able to separate thermal from gyrosynchrotron emission from stellar coronae and thereby measure magnetic field strengths in stellar coronae. Measurements of stellar wind mass-loss rates are feasible with ALMA for giants but will be difficult for main sequence stars. The study of stellar flares should be an active area of research with ALMA.

  8. Gas-Phase Photoionization Of A Protein

    NASA Astrophysics Data System (ADS)

    Milosavljevic, A. R.; Giuliani, A.; Nicolas, C.; Gil, J.-F.; Lemaire, J.; Refregiers, M.; Nahon, L.

    2010-07-01

    We present preliminary results on gas phase photoionization of electrosprayproduced multiply protonated cytochrome c protein (104 amino acids; ˜12.4 kDa), which has been achieved with a newly developed experimental system for spectroscopy of electrosprayed ions in a linear quadrupole ion trap using a monochromatized vacuum ultraviolet (VUV) synchrotron radiation and tandem mass spectrometry method. The investigation of proteins in the gas phase, where they are free of the influence of counterions and solvent molecules, offer a possibility to understand their intrinsic molecular properties. However, due to limited both ion densities and available number of photons, the use of synchrotron radiation for the trapped ions spectroscopy is a rather challenging task. The feasibility of coupling a Fourier transform ion cyclotron resonance ion trap with soft x-ray synchrotron beamline and the first successful use of synchrotron radiation for spectroscopy of electrosprayed negative ions stored in a three-dimensional quadrupole ion trap have been demonstrated only recently (R. Thissen et al., 2008, Phys. Rev. Lett., 100, 223001; A. Giulliani et al., Proc. 57th ASMS Conf., Philadelphia, 2009). The present results are the first reported on photoionization of kDa species in the gas phase and are valuable regarding both a fundamental interest of accessing physical properties of large biological ions isolated in vacuo and potential development of a new technique for proteomics.

  9. Photoionization of aligned molecular excited states

    NASA Astrophysics Data System (ADS)

    Appling, J. R.; White, M. G.; Kessler, W. J.; Fernandez, R.; Poliakoff, E. D.

    1988-02-01

    Photoelectron angular distributions of several excited states of NO have been measured in an effort to better elucidate the role of alignment in resonant multiphoton excitation processes of molecules. In contrast to previous molecular REMPI measurements on NO, (2+1) angular distributions taken for low rotational levels of the E 2Σ+ (4sσ) Rydberg state of NO exhibit complex angular behavior which is characteristic of strong spatial alignment of the optically prepared levels. Photoelectron angular distributions were also found to be strongly branch and J dependent with the lowest rotational levels of the R21+S11 branch exhibiting the full anisotropy expected for an overall three-photon process. Fluorescence anisotropies extracted from complementary two-photon fluorescence angular distribution measurements reveal small, but nonzero alignment in all rotational levels with J>1/2, in contrast to the photoelectron results. Additional photoelectron angular distributions taken for (1+1) REMPI via the A 2Σ+ (3sσ), v=0 state exhibit near ``cos2θ'' distributions characteristic of photoionization of unaligned target states. The observed photoelectron data are qualitatively interpreted on the basis of the angular momentum constraints of the excitation-induced alignment and photoionization dynamics which determine the observable moments in the angular distribution.

  10. Double photoionization of doubly-excited lithium

    NASA Astrophysics Data System (ADS)

    Armstrong, G.; Pindzola, M. S.; Kheifets, A.; Schuricke, M.; Veeravalli, G.; Dornes, Ch.; Zhu, G.; Joachimsmeyer, K.; Treusch, R.; Dorn, A.; Colgan, J.

    2012-06-01

    We present triple differential cross sections and recoil ion momentum distributions for double photoionization of the 1s2s2p state of lithium. Double ionization of lithium may be treated as a two-active-electron process, where the ``active'' 2s and 2p electrons move in the field of the ``frozen-core'' Li^2+ 1s state.The time-dependent close-coupling (TDCC) method is used to solve the two-electron time-dependent Schr"odinger equation in full dimensionality. This work is motivated by recent FLASH experiments, which have obtained recoil-ion momentum distributions at a photon energy of 59 eV, where the 1s2s2p state is first reached via a 1s-2p photoexcitation from the initial ground state, and may then be doubly-ionized after the absorption of a second photon. The TDCC calculations in this work treat the subsequent photoionization of this doubly-excited state. The results are compared to those obtained by the convergent close-coupling method and to measurement, and provide a first comparison between theory and experiment in this fundamental few-photon few-body problem.

  11. Mode specific photoionization dynamics in polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Rathbone, Gerald Jeffery

    2002-11-01

    The work presented in this dissertation presents new work on polyatomic photoionization. In these investigations, the broad range behavior of both allowed and forbidden vibrational modes in linear triatomic systems were studied to understand mode specific aspects of photoionization. The current study is made possible by the experimental strategy of exploiting high resolution photoelectron spectroscopy and the high brightness of third generation synchrotron radiation sources. The data is taken typically tens of eV's past the ionization potential. The strategy that I employ is to probe alternative vibrational modes which are frequently affected differently following resonant ionization. Such vibrationally resolved data can be used to understand how the correlation between vibration and electron energy reveals microscopic insights into the photoelectron scattering process. Moreover, the mode specific behavior contains a wealth of information not only regarding allowed transitions, but also contains information on how forbidden transitions gain surprising amounts of intensity. A previously overlooked mechanism for the appearance of forbidden nontotally symmetric vibrations was discovered---resonantly amplified vibronic symmetry breaking. The photoelectron the culprit for the symmetry breaking which induces the excitation of nominally forbidden vibrational excitations. In a more general sense, these results will demonstrate that some fundamental spectroscopic approximations are not always valid, and can lead to surprising consequences.

  12. The Winds of B Supergiants

    NASA Technical Reports Server (NTRS)

    Massa, D.; Fullerton, A. W.; Prinja, R. K.

    1998-01-01

    This quarterly report is comprised of a paper, "Rotational Modulation of B Supergiant Winds" presented at the ESO workshop "Cyclical Variability in Stellar Winds." Presented is a 30-day IUE time series of the BO Ia HD 91969, a member of the Carina open cluster NGC 3293, which showed, among other things, that wind lines that probe more deeply into the wind vary more regularly.

  13. The Stellar Extreme-Ultraviolet Radiation Field

    NASA Astrophysics Data System (ADS)

    Vallerga, John

    1998-04-01

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

  14. Photoionization research on atomic beams. 2: The photoionization cross section of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Comes, F. J.; Speier, F.; Elzer, A.

    1982-01-01

    An experiment to determine the absolute value of the photo-ionization cross section of atomic oxygen is described. The atoms are produced in an electrical discharge in oxygen gas with 1% hydrogen added. In order to prevent recombination a crossed beam technique is employed. The ions formed are detected by a time-of-flight mass spectrometer. The concentration of oxygen atoms in the beam is 57%. The measured photoionization cross section of atomic oxygen is compared with theoretical data. The results show the participation of autoionization processes in ionization. The cross section at the autoionizing levels detected is considerably higher than the absorption due to the unperturbed continuum. Except for wavelengths where autoionization occurs, the measured ionization cross section is in fair agreement with theory. This holds up to 550 A whereas for shorter wavelengths the theoretical values are much higher.

  15. Hydrodynamic and Spectral Simulations of HMXB Winds

    SciTech Connect

    Mauche, C W; Liedahl, D A; Akiyama, S; Plewa, T

    2007-03-30

    We describe preliminary results of a global model of the radiatively-driven photoionized wind and accretion flow of the high-mass X-ray binary Vela X-1. The full model combines FLASH hydrodynamic calculations, XSTAR photoionization calculations, HULLAC atomic data, and Monte Carlo radiation transport. We present maps of the density, temperature, velocity, and ionization parameter from a FLASH two-dimensional time-dependent simulation of Vela X-1, as well as maps of the emissivity distributions of the X-ray emission lines.

  16. Absorption spectroscopy of a laboratory photoionized plasma experiment at Z

    SciTech Connect

    Hall, I. M.; Durmaz, T.; Mancini, R. C.; Bailey, J. E.; Rochau, G. A.; Golovkin, I. E.; MacFarlane, J. J.

    2014-03-15

    The Z facility at the Sandia National Laboratories is the most energetic terrestrial source of X-rays and provides an opportunity to produce photoionized plasmas in a relatively well characterised radiation environment. We use detailed atomic-kinetic and spectral simulations to analyze the absorption spectra of a photoionized neon plasma driven by the x-ray flux from a z-pinch. The broadband x-ray flux both photoionizes and backlights the plasma. In particular, we focus on extracting the charge state distribution of the plasma and the characteristics of the radiation field driving the plasma in order to estimate the ionisation parameter.

  17. Advanced stellarator power plants

    SciTech Connect

    Miller, R.L.

    1994-07-01

    The stellarator is a class of helical/toroidal magnetic fusion devices. Recent international progress in stellarator power plant conceptual design is reviewed and comparisons in the areas of physics, engineering, and economics are made with recent tokamak design studies.

  18. Photodetachment and photoionization rainbows and glories

    NASA Astrophysics Data System (ADS)

    Cohen, S.; Kalaitzis, P.; Danakas, S.; Lépine, F.; Bordas, C.

    2017-03-01

    Quantum scattering has many similarities with the physics of the atmospheric rainbow. Diffraction effects, including rainbows and glories, have long been introduced in the physics of scattering, and particularly in nuclear, atomic and molecular physics. In this paper we describe the striking similarity between the optics of the primary rainbow and supernumerary bows and photodetachment microscopy, with the latter term referring to the photodetachment of a structureless anion in the presence of a static electric field. Further, we extend the aforementioned analogy to the more complex and fertile case of photoionization microscopy. Despite the fact that in the latter situation the analogy is only approximate, we demonstrate the emergence of additional features that are also found in classical optics, like higher-order bows and glories. Finally, based on the conclusions drawn from the above analyses, we discuss the significant contribution of glories in threshold photoelectron spectroscopy.

  19. Nondipole Effects in Double Photoionization of He

    SciTech Connect

    Istomin, A. Y.; Starace, A. F.; Manakov, N. L.; Meremianin, A. V.

    2006-01-09

    Lowest-order nondipole effects are studied in double photoionization (DPI) of the He atom. Ab initio parametrizations of the quadrupole transition amplitude for DPI from the 1S0-state are presented in terms of the exact two-electron reduced matrix elements. Parametrizations for the dipole-quadrupole triply differential cross section (TDCS) and doubly differential cross section (DDCS) are presented in terms of polarization-independent amplitudes for the case of an elliptically polarized photon. Expressions for the DDCS in terms of the reduced two-electron matrix elements are also given. A general analysis of retardation-induced asymmetries of the TDCS including the circular dichroism effect at equal energy sharing is presented. Our numerical results exhibit a nondipole forward-backward asymmetry in the TDCS for DPI of He at an excess energy of 450 eV that is in qualitative agreement with existing experimental data.

  20. Double photoionization of tropone and cyclooctatetraene

    NASA Astrophysics Data System (ADS)

    Hartman, Tim; Wehlitz, Ralf

    2017-05-01

    We have studied the double-photoionization process of tropone (C7H6O) and cyclooctatetraene (C8H8) as a function of photon energy using monochromatized synchrotron radiation between 18 and 270 eV. We compare our results with previously published data for partially deuterated benzene (C6H3D3), which exhibits three distinct features in the ratio of doubly to singly charged parent ions, whereas pyrrole (C4H4N) exhibits only two of these features. The question that we address in this paper is how molecules with different molecular structures (pentagonal, hexagonal, heptagonal, and octagonal carbon rings) affect the photon-energy dependence of this ratio.

  1. Electron localization following attosecond molecular photoionization.

    PubMed

    Sansone, G; Kelkensberg, F; Pérez-Torres, J F; Morales, F; Kling, M F; Siu, W; Ghafur, O; Johnsson, P; Swoboda, M; Benedetti, E; Ferrari, F; Lépine, F; Sanz-Vicario, J L; Zherebtsov, S; Znakovskaya, I; L'huillier, A; Ivanov, M Yu; Nisoli, M; Martín, F; Vrakking, M J J

    2010-06-10

    For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10(-15)-s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale has become possible only with the recent development of isolated attosecond (10(-18)-s) laser pulses. Such pulses have been used to investigate atomic photoexcitation and photoionization and electron dynamics in solids, and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H(2) and D(2) was monitored on femtosecond timescales and controlled using few-cycle near-infrared laser pulses. Here we report a molecular attosecond pump-probe experiment based on that work: H(2) and D(2) are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.

  2. Stellarator status, 1989

    SciTech Connect

    Lyon, J.F. ); Grieger, G.; Rau, F. ); Iiyoshi, A. ); Navarro, A.P. ); Kovrizhnykh, L.M. . Inst. Obshchey Fiziki); Pavlichenko, O.S. (AN Ukrain

    1990-07-01

    The present status of stellarator experiments and recent progress in stellarator research (both experimental and theoretical) are reported by groups in the United States, the USSR, Japan, Australia, and the European Community (the Federal Republic of Germany and Spain). Experiments under construction and studies of large, next-generation stellarators are also described. 73 refs., 11 figs., 4 tabs.

  3. Stellar duplicity and nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Izzard, Rob

    2014-09-01

    Half or more of all stars more massive than our Sun are orbited by one (or more) companion stars. Many companions are close enough that the evolution of both stars is greatly altered by the transfer of mass and angular momentum from one star to the other. Such mass transfer is highly likely during the late stages of evolution, such as on the giant branches, which are quite coincidentally also when stars undergo interesting nucleosynthesis. Direct mass transfer truncates the (A)GB prematurely compared to single stars and the ensuing stellar envelope is ejected perhaps to form a (chemically peculiar?) planetary nebula. In wider binaries, where one star has captured material from a long-dead companion, we can probe the nucleosynthesis that happened in ancient stars as well as fundamental astrophysical phenomena like wind accretion and circumbinary disc formation. I will focus on recent quantitative work on nucleosynthesis in mass-transfer systems, such as carbon-enhanced metal-poor and barium stars, and highlight some of the key open questions - and opportunities - that will dominate the next decade of duplicitous nucleosynthesis.

  4. Winds from cool stars

    NASA Technical Reports Server (NTRS)

    Dupree, A. K.

    1995-01-01

    Spectral observations of cool stars enable study of the presence and character of winds and the mass loss process in objects with effective temperatures, gravities, and atmospheric compositions which differ from that of the Sun. A wealth of recent spectroscopic measurements from the Hubble Space Telescope, and the Extreme Ultraviolet Explorer complement high resolution ground-based measures in the optical and infrared spectral regions. Such observations when combined with realistic semi-empirical atmospheric modeling allow us to estimate the physical conditions in the atmospheres and winds of many classes of cool stars. Line profiles support turbulent heating and mass motions. In low gravity stars, evidence is found for relatively fast (approximately 200 km s(exp -1)), warm winds with rapid acceleration occurring in the chromosphere. In some cases outflows commensurate with stellar escape velocities are present. Our current understanding of cool star winds will be reviewed including the implications of stellar observations for identification of atmospheric heating and acceleration processes.

  5. Photoionization of psoralen derivatives in micelles: Imperatorin and alloimperatorin

    NASA Astrophysics Data System (ADS)

    El-Gogary, Sameh R.

    2010-11-01

    The fluorescence properties of psoralen derivatives, 8-methoxypsoralen (8-MOP), imperatorin (IMP) and alloimperatorin (ALLOI), were investigated in various solvent and micellar solutions. The variation in intensity and maxima of the fluorescence in micellar solutions suggest that psoralens are located in the micelle-water interface region. Radical cations and hydrated electrons were generated by photoionization in micellar solution upon excitation at 266 nm. A nonlinear relationship between transient yield and photon fluency was obtained for each compound, indicating that a two-photon mechanism is predominant in the photoionization of the sensitizers. The photoionization efficiencies are significantly higher in anionic sodium dodecyl sulfate (SDS) than in cationic cetyltrimethylammonium bromide (CTAB) micelles, reflecting the influence of micelle charge on the efficiency of the separation of the photoproduced charge carriers. The photoionization efficiencies of IMP and ALLOI are similar.

  6. Photoionization of noble-gas atoms by ultrashort electromagnetic pulses

    SciTech Connect

    Astapenko, V. A. Svita, S. Yu.

    2014-11-15

    The photoionization of atoms of noble gases (Ar, Kr, and Xe) by ultrashort electromagnetic pulses of a corrected Gaussian shape is studied theoretically. Computations are performed in the context of perturbation theory using a simple expression for the total probability of photoionization of an atom by electromagnetic pulses. The features of this process are revealed and analyzed for various ranges of the parameters of the problem.

  7. An Atomic Photoionization Experiment by Harmonic Generation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Trallero, Carlos; Frolov, Mikhail; Sarantseva, Tatiana S.; Manakov, Nikolay; Fulfer, Kristen D.; Wilson, Benjamin; Troß, Jan; Ren, Xiaoming; Poliakoff, Erwin; Silaev, Alexander A.; Vvedenskii, Nikolay; Starace, Anthony

    2016-05-01

    Measurements of the high-order harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter. NSF EPSCoR Track II Nebraska-Kansas Awards No. 1430519 and No. 1430493.

  8. Initiating solar system formation through stellar shock waves

    NASA Technical Reports Server (NTRS)

    Boss, A. P.; Myhill, E. A.

    1993-01-01

    Isotopic anomalies in presolar grains and other meteoritical components require nucleosynthesis in stellar interiors, condensation into dust grains in stellar envelopes, transport of the grains through the interstellar medium by stellar outflows, and finally injection of the grains into the presolar nebula. The proximity of the presolar cloud to these energetic stellar events suggests that a shock wave from a stellar outflow might have initiated the collapse of an otherwise stable presolar cloud. We have begun to study the interactions of stellar shock waves with thermally supported, dense molecular cloud cores, using a three spatial dimension (3D) radiative hydrodynamics code. Supernova shock waves have been shown by others to destroy quiescent clouds, so we are trying to determine if the much smaller shock speeds found in, e.g., asymptotic giant branch (AGB) star winds, are strong enough to initiate collapse in an otherwise stable, rotating, solar-mass cloud core, without leading to destruction of the cloud.

  9. Photoionization and photofragmentation of SF6 in helium nanodroplets.

    PubMed

    Peterka, Darcy S; Kim, Jeong Hyun; Wang, Chia C; Neumark, Daniel M

    2006-10-12

    The photoionization of He droplets doped with SF6 was investigated using tunable vacuum ultraviolet (VUV) synchrotron radiation from the Advanced Light Source (ALS). The resulting ionization and photofragmentation dynamics were characterized using time-of-flight mass spectrometry combined with photofragment and photoelectron imaging. Results are compared to those of gas-phase SF6 molecules. We find dissociative photoionization to SF5+ to be the dominant channel, in agreement with previous results. Key new findings are that (a) the photoelectron spectrum of the SF6 in the droplet is similar but not identical to that of the gas-phase species, (b) the SF5+ photofragment velocity distribution is considerably slower upon droplet photoionization, and (c) fragmentation to SF4+ and SF3+ is much less than in the photoionization of bare SF6. From these measurements we obtain new insights into the mechanism of SF6 photoionization within the droplet and the cooling of the hot photofragment ions produced by dissociative photoionization.

  10. Chandra Spectroscopy of MAXI J1305-704: Detection of an Infalling Black Hole Disk Wind?

    NASA Astrophysics Data System (ADS)

    Miller, J. M.; Raymond, J.; Kallman, T. R.; Maitra, D.; Fabian, A. C.; Proga, D.; Reynolds, C. S.; Reynolds, M. T.; Degenaar, N.; King, A. L.; Cackett, E. M.; Kennea, J. A.; Beardmore, A.

    2014-06-01

    We report on a high-resolution Chandra/HETG X-ray spectrum of the transient X-ray binary MAXI J1305-704. A rich absorption complex is detected in the Fe L band, including density-sensitive lines from Fe XX, Fe XXI, and Fe XXII. Spectral analysis over three wavelength bands with a large grid of XSTAR photoionization models generally requires a gas density of n >= 1017 cm-3. Assuming a luminosity of L = 1037 erg s-1, fits to the 10-14 Å band constrain the absorbing gas to lie within r = (3.9 ± 0.7) × 103 km from the central engine, or about r = 520 ± 90 (M/5 M ⊙) rg , where rg = GM/c 2. At this small distance from the compact object, gas in stable orbits should have a gravitational redshift of z = v/c ~= (3 ± 1) × 10-3 (M/5 M ⊙), and any tenuous inflowing gas should have a free-fall velocity of v/c ~= (6 ± 1) × 10-2 (M/5 M ⊙)1/2. The best-fit single-zone photoionization models measure a redshift of v/c = (2.6-3.2) × 10-3. Models with two absorbing zones provide significantly improved fits, and the additional zone is measured to have a redshift of v/c = (4.6-4.9) × 10-2 (models including two zones suggest slightly different radii and may point to lower densities). Thus, the observed shifts are broadly consistent with those expected at the photoionization radius. The absorption spectrum revealed in MAXI J1305-704 may be best explained in terms of a "failed wind" like those predicted in some recent numerical simulations of black hole accretion flows. The robustness of the velocity shifts was explored through detailed simulations with the Chandra/MARX ray-tracing package and analysis of the zeroth-order ACIS-S3 spectrum. These tests are particularly important given the anomalously large angle between the source and the optical axis in this observation. The simulations and ACIS spectrum suggest that the shifts are not instrumental; however, strong caution is warranted. We discuss our results in the context of accretion flows in stellar-mass black holes and

  11. Chandra spectroscopy of MAXI J1305–704: Detection of an infalling black hole disk wind?

    SciTech Connect

    Miller, J. M.; Maitra, D.; Reynolds, M. T.; Degenaar, N.; King, A. L.; Raymond, J.; Kallman, T. R.; Fabian, A. C.; Proga, D.; Reynolds, C. S.; Cackett, E. M.; Kennea, J. A.; Beardmore, A.

    2014-06-10

    We report on a high-resolution Chandra/HETG X-ray spectrum of the transient X-ray binary MAXI J1305–704. A rich absorption complex is detected in the Fe L band, including density-sensitive lines from Fe XX, Fe XXI, and Fe XXII. Spectral analysis over three wavelength bands with a large grid of XSTAR photoionization models generally requires a gas density of n ≥ 10{sup 17} cm{sup –3}. Assuming a luminosity of L = 10{sup 37} erg s{sup –1}, fits to the 10-14 Å band constrain the absorbing gas to lie within r = (3.9 ± 0.7) × 10{sup 3} km from the central engine, or about r = 520 ± 90 (M/5 M {sub ☉}) r{sub g} , where r{sub g} = GM/c {sup 2}. At this small distance from the compact object, gas in stable orbits should have a gravitational redshift of z = v/c ≅ (3 ± 1) × 10{sup –3} (M/5 M {sub ☉}), and any tenuous inflowing gas should have a free-fall velocity of v/c ≅ (6 ± 1) × 10{sup –2} (M/5 M {sub ☉}){sup 1/2}. The best-fit single-zone photoionization models measure a redshift of v/c = (2.6-3.2) × 10{sup –3}. Models with two absorbing zones provide significantly improved fits, and the additional zone is measured to have a redshift of v/c = (4.6-4.9) × 10{sup –2} (models including two zones suggest slightly different radii and may point to lower densities). Thus, the observed shifts are broadly consistent with those expected at the photoionization radius. The absorption spectrum revealed in MAXI J1305–704 may be best explained in terms of a 'failed wind' like those predicted in some recent numerical simulations of black hole accretion flows. The robustness of the velocity shifts was explored through detailed simulations with the Chandra/MARX ray-tracing package and analysis of the zeroth-order ACIS-S3 spectrum. These tests are particularly important given the anomalously large angle between the source and the optical axis in this observation. The simulations and ACIS spectrum suggest that the shifts are not instrumental; however

  12. High-Resolution Photoelectron and Photoionization Spectroscopy

    NASA Astrophysics Data System (ADS)

    Merkt, F.

    2012-06-01

    Since its development in the late 1950s and early 1960s, photoelectron spectroscopy has established itself as an important method to study the electronic structure of molecules, their photoionization dynamics, and the structure and dynamics of molecular cations. In recent years, and particularly since the development of pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy, considerable progress has been made in the resolution that can be achieved by photoelectron spectroscopy. This progress relies on the systematic exploitation of the unusual physical properties of high Rydberg states and enables one today to resolve the rotational structure in the photoelectron spectra of even large molecules and the hyperfine structure in the photoelectron spectra of small molecules. This talk will begin with a brief historical review of photoelectron spectroscopy. Then, the relationship between photoelectron spectroscopy, photoionization spectroscopy and the spectroscopy of high Rydberg states will be discussed. It will be explained how this relationship is currently exploited to improve the resolution achievable by PFI-ZEKE photoelectron spectroscopy. Then, the physical principles that are at the heart of the latest methods related to high-resolution photoelectron spectroscopy will be described together with their fundamental limitations. Depending on the resolution and the spectral range needed to address a specific scientific problem, a choice can be made between several different methods with spectral resolutions ranging from 30 GHz to better than 1 MHz. The talk will summarize the current state of the art in gas-phase photoelectron spectroscopy and be illustrated by several examples, primarily taken from the research in my group, in which photoelectron spectroscopy has contributed to answer questions concerning the structure and dynamics of small-sized molecular cations. F. I. Vilesov, B. C. Kurbatov, and N. Terrenin, Soviet Phys. (Doklady) 6

  13. Energy-limited escape revised. The transition from strong planetary winds to stable thermospheres

    NASA Astrophysics Data System (ADS)

    Salz, M.; Schneider, P. C.; Czesla, S.; Schmitt, J. H. M. M.

    2016-01-01

    Gas planets in close proximity to their host stars experience photoevaporative mass loss. The energy-limited escape concept is generally used to derive estimates for the planetary mass-loss rates. Our photoionization hydrodynamics simulations of the thermospheres of hot gas planets show that the energy-limited escape concept is valid only for planets with a gravitational potential lower than log 10(-ΦG)< 13.11 erg g-1 because in these planets the radiative energy input is efficiently used to drive the planetary wind. Massive and compact planets with log 10(-ΦG) ≳ 13.6 erg g-1 exhibit more tightly bound atmospheres in which the complete radiative energy input is re-emitted through hydrogen Lyα and free-free emission. These planets therefore host hydrodynamically stable thermospheres. Between these two extremes the strength of the planetary winds rapidly declines as a result of a decreasing heating efficiency. Small planets undergo enhanced evaporation because they host expanded atmospheres that expose a larger surface to the stellar irradiation. We present scaling laws for the heating efficiency and the expansion radius that depend on the gravitational potential and irradiation level of the planet. The resulting revised energy-limited escape concept can be used to derive estimates for the mass-loss rates of super-Earth-sized planets as well as massive hot Jupiters with hydrogen-dominated atmospheres.

  14. The stellar accretion origin of stellar population gradients in massive galaxies at large radii

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela; Naab, Thorsten; Ostriker, Jeremiah P.; Forbes, Duncan A.; Duc, Pierre-Alain; Davé, Romeel; Oser, Ludwig; Karabal, Emin

    2015-05-01

    We investigate the evolution of stellar population gradients from z = 2 to 0 in massive galaxies at large radii (r > 2Reff) using 10 cosmological zoom simulations of haloes with 6 × 1012 M⊙ < Mhalo < 2 × 1013 M⊙. The simulations follow metal cooling and enrichment from SNII, SNIa and asymptotic giant branch winds. We explore the differential impact of an empirical model for galactic winds that reproduces the mass-metallicity relation and its evolution with redshift. At larger radii the galaxies, for both models, become more dominated by stars accreted from satellite galaxies in major and minor mergers. In the wind model, fewer stars are accreted, but they are significantly more metal-poor resulting in steep global metallicity (<∇Zstars> = -0.35 dex dex-1) and colour (e.g. <∇g - r> = -0.13 dex dex-1) gradients in agreement with observations. In contrast, colour and metallicity gradients of the models without winds are inconsistent with observations. Age gradients are in general mildly positive at z = 0 (<∇Agestars> = 0.04 dex dex-1) with significant differences between the models at higher redshift. We demonstrate that for the wind model, stellar accretion is steepening existing in situ metallicity gradients by about 0.2 dex by the present day and helps to match observed gradients of massive early-type galaxies at large radii. Colour and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results. The effect of stellar migration of in situ formed stars to large radii is discussed. This study highlights the importance of stellar accretion for stellar population properties of massive galaxies at large radii, which can provide important constraints for formation models.

  15. Vacuum ultraviolet photoionization of carbohydrates and nucleotides

    SciTech Connect

    Shin, Joong-Won; Bernstein, Elliot R.

    2014-01-28

    Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5{sup ′}-monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C–C and C–O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results.

  16. Extreme ultraviolet-induced photoionized plasmas

    NASA Astrophysics Data System (ADS)

    Bartnik, Andrzej; Wachulak, Przemyslaw; Fiedorowicz, Henryk; Fok, Tomasz; Jarocki, Roman; Szczurek, Miroslaw

    2014-05-01

    In this work photoionized plasmas were created by irradiation of He or Ne gases with a focused extreme ultraviolet (EUV) beam from one of two laser-plasma sources employing Nd:YAG laser systems. The first of them was a 10 Hz laser-plasma EUV source, based on a double-stream gas-puff target, irradiated with a 3 ns per 0.8 J laser pulse. EUV radiation in this case was focused using a gold-plated grazing incidence ellipsoidal collector. The second source was based on a 10 ns per 10 J per 10 Hz laser system. In this case EUV radiation was focused using a gold-plated grazing incidence multifoil collector. Gases were injected into the interaction region, perpendicularly to an optical axis of the irradiation system, using an auxiliary gas puff valve. Spectral measurements in the EUV range were performed. In all cases the most intense emission lines were assigned to singly charged ions. The other emission lines belong to atoms or doubly charged ions.

  17. Cooling and Heating Functions of Photoionized Gas

    NASA Astrophysics Data System (ADS)

    Gnedin, Nickolay Y.; Hollon, Nicholas

    2012-10-01

    Cooling and heating functions of cosmic gas are crucial ingredients for any study of gas dynamics and thermodynamics in the interstellar and intergalactic media. As such, they have been studied extensively in the past under the assumption of collisional ionization equilibrium. However, for a wide range of applications, the local radiation field introduces a non-negligible, often dominant, modification to the cooling and heating functions. In the most general case, these modifications cannot be described in simple terms and would require a detailed calculation with a large set of chemical species using a radiative transfer code (the well-known code Cloudy, for example). We show, however, that for a sufficiently general variation in the spectral shape and intensity of the incident radiation field, the cooling and heating functions can be approximated as depending only on several photoionization rates, which can be thought of as representative samples of the overall radiation field. This dependence is easy to tabulate and implement in cosmological or galactic-scale simulations, thus economically accounting for an important but rarely included factor in the evolution of cosmic gas. We also show a few examples where the radiation environment has a large effect, the most spectacular of which is a quasar that suppresses gas cooling in its host halo without any mechanical or non-radiative thermal feedback.

  18. Intergalactic magnetogenesis at Cosmic Dawn by photoionization

    NASA Astrophysics Data System (ADS)

    Durrive, J.-B.; Langer, M.

    2015-10-01

    We present a detailed analysis of an astrophysical mechanism that generates cosmological magnetic fields during the Epoch of Reionization. It is based on the photoionization of the intergalactic medium by the first sources formed in the Universe. First the induction equation is derived, then the characteristic length and time-scales of the mechanism are identified, and finally numerical applications are carried out for first stars, primordial galaxies and distant powerful quasars. In these simple examples, the strength of the generated magnetic fields varies between the order of 10-23 G on hundreds of kiloparsecs and 10-19 G on hundreds of parsecs in the neutral intergalactic medium between the Strömgren spheres of the sources. Thus, this mechanism contributes to the premagnetization of the whole Universe before large-scale structures are in place. It operates with any ionizing source, at any time during the Epoch of Reionization. Finally, the generated fields possess a characteristic spatial configuration which may help discriminate these seeds from those produced by different mechanisms.

  19. Vacuum ultraviolet photoionization of carbohydrates and nucleotides

    NASA Astrophysics Data System (ADS)

    Shin, Joong-Won; Bernstein, Elliot R.

    2014-01-01

    Carbohydrates (2-deoxyribose, ribose, and xylose) and nucleotides (adenosine-, cytidine-, guanosine-, and uridine-5'-monophosphate) are generated in the gas phase, and ionized with vacuum ultraviolet photons (VUV, 118.2 nm). The observed time of flight mass spectra of the carbohydrate fragmentation are similar to those observed [J.-W. Shin, F. Dong, M. Grisham, J. J. Rocca, and E. R. Bernstein, Chem. Phys. Lett. 506, 161 (2011)] for 46.9 nm photon ionization, but with more intensity in higher mass fragment ions. The tendency of carbohydrate ions to fragment extensively following ionization seemingly suggests that nucleic acids might undergo radiation damage as a result of carbohydrate, rather than nucleobase fragmentation. VUV photoionization of nucleotides (monophosphate-carbohydrate-nucleobase), however, shows that the carbohydrate-nucleobase bond is the primary fragmentation site for these species. Density functional theory (DFT) calculations indicate that the removed carbohydrate electrons by the 118.2 nm photons are associated with endocyclic C-C and C-O ring centered orbitals: loss of electron density in the ring bonds of the nascent ion can thus account for the observed fragmentation patterns following carbohydrate ionization. DFT calculations also indicate that electrons removed from nucleotides under these same conditions are associated with orbitals involved with the nucleobase-saccharide linkage electron density. The calculations give a general mechanism and explanation of the experimental results.

  20. Photoionization Models for the Semi-forbidden C III] 1909 Emission in Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Jaskot, A. E.; Ravindranath, S.

    2016-12-01

    The increasing neutrality of the intergalactic medium at z > 6 suppresses Lyα emission, and spectroscopic confirmation of galaxy redshifts requires the detection of alternative ultraviolet lines. The strong [C iii] λ1907+C iii] λ1909 doublet frequently observed in low-metallicity, actively star-forming galaxies is a promising emission feature. We present CLOUDY photoionization model predictions for C iii] equivalent widths (EWs) and line ratios as a function of starburst age, metallicity, and ionization parameter. Our models include a range of C/O abundances, dust content, and gas density. We also examine the effects of varying the nebular geometry and optical depth. Only the stellar models that incorporate binary interaction effects reproduce the highest observed C iii] EWs. The spectral energy distributions from the binary stellar population models also generate observable C iii] over a longer timescale relative to single-star models. We show that diagnostics using C iii] and nebular He ii λ1640 can separate star-forming regions from shock-ionized gas. We also find that density-bounded systems should exhibit weaker C iii] EWs at a given ionization parameter, and C iii] EWs could, therefore, select candidate Lyman continuum-leaking systems. In almost all models, C iii] is the next strongest line at <2700 Å after Lyα, and C iii] reaches detectable levels for a wide range of conditions at low metallicity. C iii] may therefore serve as an important diagnostic for characterizing galaxies at z > 6.

  1. VUV photoionization and dissociative photoionization spectroscopy of the interstellar molecule aminoacetonitrile: Theory and experiment

    NASA Astrophysics Data System (ADS)

    Bellili, A.; Schwell, M.; Bénilan, Y.; Fray, N.; Gazeau, M.-C.; Mogren Al-Mogren, M.; Guillemin, J.-C.; Poisson, L.; Hochlaf, M.

    2015-09-01

    Aminoacetonitrile (AAN) is a key compound in astrochemistry and astrobiology. We present a combined theoretical and experimental investigation concerning the single photoionization of gas-phase AAN and the fragmentation pathways of the resulting cation. At present, we measured photoelectron photoion coincidence (PEPICO) spectra in the 9.8-13.6 eV energy regime using synchrotron radiation as exciting light source. In order to interpret the VUV experimental data obtained, we explored the ground potential energy surface (PES) of AAN and of its cation using standard and explicitly correlated quantum chemical methodologies. This allowed us to deduce accurate thermochemical data for this molecule. We also determined, for the first time, the adiabatic ionization energy of AAN to lie at AIE = (10.085 ± 0.03) eV. The unimolecular decomposition pathways of the resulting AAN+ parent cation are also investigated. The appearance energies of five fragments are determined for the first time, with 30 meV accuracy. Interestingly, our work shows the possibility of the formation of both HCN and HNC isomeric forms. The implications for the evolution of prebiotic molecules under VUV irradiation are briefly discussed.

  2. Spectroscopic observations of selected stellar systems

    NASA Technical Reports Server (NTRS)

    Conti, P. S.; Garmany, C. D.

    1985-01-01

    Spectra of very luminous, high temperature stars, the o-type stars with the largest masses among stars, and the Wolf-Rayet (W-R) stars are studied. These stars are characterized by strong stellar winds which produce signiicant mass loss. The nature and evolution of these winds are studied to learn the densities, velocity structue, ionization balance, and composition. The IUE satellite provides the best way to study these phenomena because many of the most important ground state and excited state lines of common highly ionized species are found in the spectral range.

  3. On star formation in stellar systems. I - Photoionization effects in protoglobular clusters

    NASA Technical Reports Server (NTRS)

    Tenorio-Tagle, G.; Bodenheimer, P.; Lin, D. N. C.; Noriega-Crespo, A.

    1986-01-01

    The progressive ionization and subsequent dynamical evolution of nonhomogeneously distributed low-metal-abundance diffuse gas after star formation in globular clusters are investigated analytically, taking the gravitational acceleration due to the stars into account. The basic equations are derived; the underlying assumptions, input parameters, and solution methods are explained; and numerical results for three standard cases (ionization during star formation, ionization during expansion, and evolution resulting in a stable H II region at its equilibrium Stromgren radius) are presented in graphs and characterized in detail. The time scale of residual-gas loss in typical clusters is found to be about the same as the lifetime of a massive star on the main sequence.

  4. Photoionization of Highly Charged Argon Ions and Their Diagnostic Lines

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2012-06-01

    %TEXT OF YOUR ABSTRACT Lines of highly charged He-like and Li-like ions in the ultraviolet and X-ray regions provide useful diagnostics for the physical and chemical conditions of the astrophysical as well as fusion plasmas. For example, Ar XVII lines in a Syfert galaxy have been measured by the X-ray space observatory Chandra. Results on photoionization of Ar XVI and Ar XVII obtained from relativistic Breit-Pauli R-matrix method and close-coupling approximation will be presented. Important features for level-specific photoionization for the diagnostic w, x, y, z lines of He-like Ar XVII in the ultraviolet region will be illustrated. Although monotonous decay dominates the low energy photoionization for these ions, strong resonances appear in the high energy region indicating higher recombination, inverse process of photoionization, at high temperature. The spectra of the well known 22 diagnostics dielectronic satellite lines of Li-like Ar XVI will be shown produced from the the KLL resonances in photoionization. Acknowledgement: Partially supported by DOE, NSF; Computational work was carried out at the Ohio Supercomputer Center

  5. Stability in straight stellarators

    SciTech Connect

    Kulsrud, R.M.; Yoshikawa, S.

    1981-07-01

    The stability of the straight stellarator against localized interchange modes is investigated employing the Mercier-Greene-Johnson criterion. Critical values of ..beta.. are obtained both numerically and analytically. The conclusion is that for classical helical stellarators the average limiting ..beta..'s are quite low of order three to four percent.

  6. Triggering Excimer Lasers by Photoionization from Corona Discharges

    NASA Astrophysics Data System (ADS)

    Xiong, Zhongmin; Duffey, Thomas; Brown, Daniel; Kushner, Mark

    2009-10-01

    High repetition rate ArF (192 nm) excimer lasers are used for photolithography sources in microelectronics fabrication. In highly attaching gas mixtures, preionization is critical to obtaining stable, reproducible glow discharges. Photoionization from a separate corona discharge is one technique for preionization which triggers the subsequent electron avalanche between the main electrodes. Photoionization triggering of an ArF excimer laser sustained in multi-atmosphere Ne/Ar/F2/Xe gas mixtures has been investigated using a 2-dimensional plasma hydrodynamics model including radiation transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron temperature with transport coefficients obtained from solutions of Boltzmann's equation. Photoionizing radiation is produced by a surface discharge which propagates along a corona-bar located adjacent to the discharge electrodes. The consequences of pulse power waveform, corona bar location, capacitance and gas mixture on uniformity, symmetry and gain of the avalanche discharge will be discussed.

  7. Design of Laboratory Experiments to Study Photoionization Fronts

    NASA Astrophysics Data System (ADS)

    Gray, William James; Davis, Josh; Drake, R. Paul

    2017-06-01

    Here we present the theoretical foundation for a laboratory experiment to study photoionization fronts. Photoionization fronts play important roles in the formation and evolution of structure in the Universe. A properly designed experiment will have to control the recombination rate, electron impact ionization rate, and the initial thermal spectrum. We show that such an experiment can be designed, but requires the use of the largest high-energy-density laser facilities, such as Omega, Z, and NIF. We also show that prior experiments do not actually generate photoionization fronts, rather a heat front is produced by heat conductions. We show some initial simulation results of the current experimental design and characterize the ionization front.

  8. Absolute measurements of chlorine Cl+ cation single photoionization cross section

    NASA Astrophysics Data System (ADS)

    Hernández, E. M.; Juárez, A. M.; Kilcoyne, A. L. D.; Aguilar, A.; Hernández, L.; Antillón, A.; Macaluso, D.; Morales-Mori, A.; González-Magaña, O.; Hanstorp, D.; Covington, A. M.; Davis, V.; Calabrese, D.; Hinojosa, G.

    2015-01-01

    The photoionization of Cl+ leading to Cl2+ was measured in the photon energy range of 19.5-28.0 eV. A spectrum with a photon energy resolution of 15 meV normalized to absolute cross-section measurements is presented. The measurements were carried out by merging a Cl+ ion beam with a photon beam of highly monochromatic synchrotron radiation at the Advanced Light Source at Lawrence Berkeley National Laboratory. The measured photoionization of Cl+ consists of several autoionization resonances surperimposed on the direct photoionization signal. Most of the prominent resonances are assigned to members of Rydberg series originating from the singlet ground state and from metastable triplet levels within the ground-state configuration of Cl+. The direct ionization cross section is no larger than 12 Mb.

  9. Depth-resolved subcycle dynamics of photoionization in solids

    NASA Astrophysics Data System (ADS)

    Zhokhov, P. A.; Zheltikov, A. M.

    2017-09-01

    We develop a theoretical framework for the analysis of ultrafast dynamics of photoionization in solids that treats the electron density buildup resolved within the field cycle jointly with the propagation dynamics of the laser driver. We show that while the standard, cycle-averaging photoionization models predict a monotonic buildup of the electron density within the driver pulse, the cycle-resolved photoionization model used in this work reveals a subcycle modulation of optical properties of a solid, giving rise to complex patterns of reflected and transmitted fields and providing a source for optical harmonic generation. Propagation effects are shown to heavily distort the spectra of high-order harmonics. Still, the analysis of harmonic spectra and the temporal structure of the harmonic field reveals physically significant properties of the nonlinear-optical response, suggesting the existence of attosecond bursts of interband optical-harmonic emission.

  10. The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

    NASA Astrophysics Data System (ADS)

    Belkus, H.; van Bever, J.; Vanbeveren, D.

    In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

  11. Dynamics of photoionization of hydrogenlike ions in Debye plasmas

    SciTech Connect

    Qi, Y. Y.; Wang, J. G.; Janev, R. K.

    2009-12-15

    Photoionization processes for the ground state and n<=3 excited states of hydrogenlike ions embedded in a weakly coupled plasma are investigated in the entire energy range of a nonrelativistic regime. The plasma screening of the Coulomb interaction between charged particles is described by the Debye-Hueckel model. The energy levels and wave functions for both the bound and continuum states are calculated by solving the Schroedinger equation numerically by the symplectic integrator. The screening of Coulomb interactions reduces the number of bound electron states, decreases their binding energies, broadens the radial distribution of electron wave functions of these states, and changes significantly the phases and the amplitudes of continuum wave functions. These changes strongly affect the dipole matrix elements between the bound and continuum states and, hence, the photoionization cross sections. The most significant effects of the screened Coulomb interactions on the energy behavior of photoionization cross sections are manifested in its low-energy behavior (Wigner threshold law), the appearance of multiple shape and virtual-state resonances when the energy levels of upper bound states enter the continuum after certain critical strength of the screening, and in the (slight) reduction of the cross section at high photon energies. All these features of the photoionization cross section are related to the short-range character of the Debye-Hueckel potential. The effects of the potential screening on the Combet-Farnoux and Cooper minima in the photoionization cross section are also investigated. Comparison of calculated photoionization cross sections with the results of other authors, when available, is made.

  12. The Influences of Stellar Activity on Planetary Atmospheres

    NASA Astrophysics Data System (ADS)

    Johnstone, Colin P.

    2017-10-01

    On evolutionary timescales, the atmospheres of planets evolve due to interactions with the planet's surface and with the planet's host star. Stellar X-ray and EUV (='XUV') radiation is absorbed high in the atmosphere, driving photochemistry, heating the gas, and causing atmospheric expansion and mass loss. Atmospheres can interact strongly with the stellar winds, leading to additional mass loss. In this review, I summarise some of the ways in which stellar output can influence the atmospheres of planets. I will discuss the importance of simultaneously understanding the evolution of the star's output and the time dependent properties of the planet's atmosphere.

  13. Testing Cosmic-Ray Acceleration in Young, Embedded Stellar Clusters

    NASA Astrophysics Data System (ADS)

    Nukri, Komin; Marcowith, Alexandre; Lamanna, Giovanni; Maurin, Gilles; Krayzel, Fabien

    2016-07-01

    Most of the massive stars appear grouped in clusters located in giant molecular clouds. Their strong wind activity generates large structures known as stellar wind bubbles and induces collective effects which could accelerate particles up to high energy and produce gamma-rays. The best objects to observe these effects are young massive star clusters in which no supernova explosion has occurred yet. We model these star clusters as a spherical leaky box (the molecular cloud) surrounding a central cosmic ray source (the stellar cluster). We developed a phenomenological model to estimate the cosmic and gamma-ray production for a set of 8 selected clusters. We compare the predicted gamma-ray emission with data obtained with the Fermi-LAT telescope. No significant emission has been detected from any of the selected cluster. Comparing the upper limit on the gamma-ray flux with the prediction from our phenomenological model indicates that not more than 10% of the stellar wind luminosity of the stellar clusters is converted into cosmic rays. If all O-type stars do not contribute more than 10% of their stellar wind luminosity to cosmic-ray acceleration they do not contribute to more than on percent of the total cosmic-ray luminosity.

  14. Two-electron photoionization of ground-state lithium

    SciTech Connect

    Kheifets, A. S.; Fursa, D. V.; Bray, I.

    2009-12-15

    We apply the convergent close-coupling (CCC) formalism to single-photon two-electron ionization of the lithium atom in its ground state. We treat this reaction as single-electron photon absorption followed by inelastic scattering of the photoelectron on a heliumlike Li{sup +} ion. The latter scattering process can be described accurately within the CCC formalism. We obtain integrated cross sections of single photoionization leading to the ground and various excited states of the Li{sup +} ion as well as double photoionization extending continuously from the threshold to the asymptotic limit of infinite photon energy. Comparison with available experimental and theoretical data validates the CCC model.

  15. Relativistic theory of the double photoionization of heliumlike atoms

    SciTech Connect

    Yerokhin, Vladimir A.; Surzhykov, Andrey

    2011-09-15

    A fully relativistic calculation of the double photoionization of heliumlike atoms is presented. The approach is based on the partial-wave representation of the Dirac continuum states and accounts for the retardation in the electron-electron interaction as well as the higher-order multipoles of the absorbed photon. The electron-electron interaction is taken into account to the leading order of the perturbation theory. The relativistic effects are shown to become prominent already for the medium-Z ions, changing the shape and the asymptotic behavior of the photon energy dependence of the ratio of the double-to-single photoionization cross section.

  16. Photoionization spectrum of the B2A' state of HCO

    NASA Astrophysics Data System (ADS)

    Foltynowicz, Robert J.; Rupp, Wolfgang; Hedderich, Hartmut G.; Grant, Edward R.

    1999-12-01

    Formyl radicals, excited to specific rovibrational levels of the strongly bent B2A' state are photoionized to form vibrationally excited states of the linear cation by the absorption of a tunable pulse of ultraviolet light from a second laser. Strong and essentially continuous photoionization spectra, which appear at intervals lying 7000 and 12 000 cm -1 above the adiabatic threshold, establish that formyl radicals can be efficiently ionized with a large geometry change at both energies. Non-Franck-Condon intensities suggest multiquantum pathways for vibrational autoionization.

  17. Double K-shell photoionization and universal scaling laws

    NASA Astrophysics Data System (ADS)

    Hoszowska, J.; Kheifets, A. K.; Dousse, J.-Cl; Berset, M.; Bray, I.; Cao, W.; Fennane, K.; Kayser, Y.; Kavčič, M.; Szlachetko, J.; Szlachetko, M.

    2009-11-01

    The photon energy dependence of the double K-shell ionization cross sections for light atoms and He-like ions is reported. The K-shell double photoionization DPI cross-sections for hollow atom production are compared to those of the corresponding He-like counterparts. The relative contribution of the initial-state correlations and final-state electron-electron interactions to the K-shell DPI is addressed. A semiempirical universal scaling of the double photoionization cross sections with the effective nuclear charge for neutral atoms in the range 2 <= Z <= 47 is established.

  18. Absolute Photoionization Cross Sections of Two Cyclic Ketones: Cyclopentanone & Cyclohexanone.

    PubMed

    Price, Chelsea; Fathi, Yasmin; Meloni, Giovanni

    2017-02-23

    Absolute photoionization cross sections for cyclopentanone and cyclohexanone, as well as partial ionization cross sections for the dissociative ionized fragments, are presented in this investigation. Experiments are performed via a multiplexed photoionization mass spectrometer utilizing VUV synchrotron radiation supplied by the Advanced Light Source of Lawrence Berkeley National Laboratory. These results allow the quantification of these species that is relevant to investigate the kinetics and combustion reactions of potential biofuels. The CBS-QB3 calculated values for the adiabatic ionization energies agree well with the experimental values and the identification of possible dissociative fragments is discussed for both systems.

  19. Atmospheric pressure photoionization using tunable VUV synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Giuliani, A.; Giorgetta, J.-L.; Ricaud, J.-P.; Jamme, F.; Rouam, V.; Wien, F.; Laprévote, O.; Réfrégiers, M.

    2012-05-01

    We report here the first coupling of an atmospheric pressure photoionization (APPI) source with a synchrotron radiation beamline in the vacuum ultra-violet (VUV). A commercial APPI source of a QStar Pulsar i from AB Sciex was modified to receive photons from the DISCO beamline at the SOLEIL synchrotron radiation facility. Photons are delivered at atmospheric pressure in the 4-20 eV range. The advantages of this new set up, termed SR-APPI, over classical APPI are spectral purity and continuous tunability. The technique may also be used to perform tunable photoionization mass spectrometry on fragile compounds difficult to vaporize by classical methods.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    Signatures of 'evaporative' winds from exoplanets on short (hot) orbits around their host star have been observed in a number of systems. In this paper, we present global adaptive mesh refinement 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 that 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 may cause eventual deposition of planetary gas on to the star. We present synthetic observations of both transit and absorption line-structure for our simulations. For our initial conditions, we find that the orbiting wind material produces absorption signatures at significant distances from the planet and substantial orbit-to-orbit variability. Lyα absorption shows red- and blueshifted features out to 70 km s-1. Finally, using semi-analytic models we constrain the effect of radiation pressure, given the approximation of uniform stellar absorption.

  1. Disk-driven hydromagnetic winds as a key ingredient of active galactic nuclei unification schemes

    NASA Technical Reports Server (NTRS)

    Konigl, Arieh; Kartje, John F.

    1994-01-01

    Centrifugally driven winds from the surfaces of magnetized accretion disks have been recognized as an attractive mechanism of removing the angular momentum of the accreted matter and of producing the bipolar outflows and jets that are often associated with compact astronomical objects. As previously suggested in the context of young stellar objects, such winds have unique observational manifestations stemming from their highly stratified density and velocity structure and from their exposure to the strong continuum radiation field of the compact object. We have applied this scenario to active galactic nuclei (AGNs) and investigated the properties of hydromagnetic outflows that originate within approximately 10(M(sub 8)) pc of the central 10(exp 8)(M(sub 8)) solar mass black hole. On the basis of our results, we propose that hydromagnetic disk-driven winds may underlie the classification of broad-line and narrow-line AGNs (e.g., the Seyfert 1/Seyfert 2 dichotomy) as well as the apparent dearth of luminous Seyfert 2 galaxies. More generally, we demonstrate that such winds could strongly influence the spectral characteristics of Seyfert galaxies, QSOs, and BL Lac objects (BLOs). In our picture, the torus is identified with the outer regions of the wind where dust uplifted from the disk surfaces by gas-grain collisions is embedded in the outflow. Using an efficient radiative transfer code, we show that the infrared emission of Seyfert galaxies and QSOs can be attributed to the reprocessing of the UV/soft X-ray AGN continuum by the dust in the wind and the disk. We demonstrate that the radiation pressure force flattens the dust distribution in objects with comparatively high (but possibly sub-Eddington) bolometric luminosities, and we propose this as one likely reason for the apparent paucity of narrow-line objects among certain high-luminosity AGNs. Using the XSTAR photoionization code, we show that the inner regions of the wind could naturally account for the warm

  2. Disk-driven hydromagnetic winds as a key ingredient of active galactic nuclei unification schemes

    NASA Technical Reports Server (NTRS)

    Konigl, Arieh; Kartje, John F.

    1994-01-01

    Centrifugally driven winds from the surfaces of magnetized accretion disks have been recognized as an attractive mechanism of removing the angular momentum of the accreted matter and of producing the bipolar outflows and jets that are often associated with compact astronomical objects. As previously suggested in the context of young stellar objects, such winds have unique observational manifestations stemming from their highly stratified density and velocity structure and from their exposure to the strong continuum radiation field of the compact object. We have applied this scenario to active galactic nuclei (AGNs) and investigated the properties of hydromagnetic outflows that originate within approximately 10(M(sub 8)) pc of the central 10(exp 8)(M(sub 8)) solar mass black hole. On the basis of our results, we propose that hydromagnetic disk-driven winds may underlie the classification of broad-line and narrow-line AGNs (e.g., the Seyfert 1/Seyfert 2 dichotomy) as well as the apparent dearth of luminous Seyfert 2 galaxies. More generally, we demonstrate that such winds could strongly influence the spectral characteristics of Seyfert galaxies, QSOs, and BL Lac objects (BLOs). In our picture, the torus is identified with the outer regions of the wind where dust uplifted from the disk surfaces by gas-grain collisions is embedded in the outflow. Using an efficient radiative transfer code, we show that the infrared emission of Seyfert galaxies and QSOs can be attributed to the reprocessing of the UV/soft X-ray AGN continuum by the dust in the wind and the disk. We demonstrate that the radiation pressure force flattens the dust distribution in objects with comparatively high (but possibly sub-Eddington) bolometric luminosities, and we propose this as one likely reason for the apparent paucity of narrow-line objects among certain high-luminosity AGNs. Using the XSTAR photoionization code, we show that the inner regions of the wind could naturally account for the warm

  3. Chandra X-ray Spectroscopy of the Focused Wind In the Cygnus X-1 System I. The Non-Dip Spectrum in the Low/Hard State

    NASA Technical Reports Server (NTRS)

    Hanke, Manfred; Wilms, Jorn; Nowak, Michael A.; Pottschmidt, Katja; Schultz, Norbert S.; Lee, Julia C.

    2008-01-01

    We present analyses of a 50 ks observation of the supergiant X-ray binary system CygnusX-1/HDE226868 taken with the Chandra High Energy Transmission Grating Spectrometer (HETGS). CygX-1 was in its spectrally hard state and the observation was performed during superior conjunction of the black hole, allowing for the spectroscopic analysis of the accreted stellar wind along the line of sight. A significant part of the observation covers X-ray dips as commonly observed for CygX-1 at this orbital phase, however, here we only analyze the high count rate non-dip spectrum. The full 0.5-10 keV continuum can be described by a single model consisting of a disk, a narrow and a relativistically broadened Fe K line, and a power law component, which is consistent with simultaneous RXTE broad band data. We detect absorption edges from overabundant neutral O, Ne and Fe, and absorption line series from highly ionized ions and infer column densities and Doppler shifts. With emission lines of He-like Mg XI, we detect two plasma components with velocities and densities consistent with the base of the spherical wind and a focused wind. A simple simulation of the photoionization zone suggests that large parts of the spherical wind outside of the focused stream are completely ionized, which is consistent with the low velocities (<200 km/s) observed in the absorption lines, as the position of absorbers in a spherical wind at low projected velocity is well constrained. Our observations provide input for models that couple the wind activity of HDE 226868 to the properties of the accretion flow onto the black hole.

  4. STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

    SciTech Connect

    Matzner, Christopher D.; Jumper, Peter H.

    2015-12-10

    During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when its column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive.

  5. Double-helix stellarator

    SciTech Connect

    Moroz, P.E.

    1997-09-01

    A new stellarator configuration, the Double-Helix Stellarator (DHS), is introduced. This novel configuration features a double-helix center post as the only helical element of the stellarator coil system. The DHS configuration has many unique characteristics. One of them is the extreme low plasma aspect ratio, A {approx} 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-{beta} MHD equilibria. Moreover, the DHS features improved transport characteristics caused by the absence of the magnetic field ripple on the outboard of the torus. Compactness, simplicity and modularity of the coil system add to the DHS advantages for fusion applications.

  6. Spectroscopy of Stellar Coronae

    NASA Astrophysics Data System (ADS)

    Laming, J. Martin

    I review the important spectroscopic results that have come from observations of stellar coronae, mainly by EUVE and ASCA, but also from HST. The plasma parameters that can be determined from such spectra include the electron density and temperature distributions, and relative element abundances. With high resolution spectra dynamical information can be obtained. Such parameters can then be used to put constraints on models of the heating and structure of stellar coronae. Throughout, I try to emphasise the similarities and differences between stellar coronal spectroscopy and that of the solar corona.

  7. Frontiers of stellar evolution

    NASA Technical Reports Server (NTRS)

    Lambert, David L. (Editor)

    1991-01-01

    The present conference discusses theoretical and observational views of star formation, spectroscopic constraints on the evolution of massive stars, very low mass stars and brown dwarfs, asteroseismology, globular clusters as tests of stellar evolution, observational tests of stellar evolution, and mass loss from cool evolved giant stars. Also discussed are white dwarfs and hot subdwarfs, neutron stars and black holes, supernovae from single stars, close binaries with evolved components, accretion disks in interacting binaries, supernovae in binary systems, stellar evolution and galactic chemical evolution, and interacting binaries containing compact components.

  8. Colliding Winds and Infall Confinement of Protostellar Winds

    NASA Astrophysics Data System (ADS)

    Wilkin, F. P.; Stahler, S. W.

    1996-12-01

    We consider the hydrodynamic influence of the protostellar environment on the confinement of protostellar winds by modeling the collision of a stellar wind with anisotropic infall from a rotating cloud core. The stellar wind and infall collide supersonically, yielding a thin, radiative shocked shell. We calculate the structure of the shocked layer using a quasi-steady formulation similar to that used for stellar-wind bow shocks. At any time the shell structure is determined by simple conservation laws involving the fluxes of mass, momentum, and angular momentum of the incident wind and infall material, and including the effects of rotation and the stellar gravity. The gravitational forces are critical to the shell structure because in order for the infall ram pressure to be comparable to the wind ram pressure and allow normal force balance, the shell must be deep inside the gravitational well. We find that self-consistent, bowshock-like steady-state solutions only exist when the stellar gravity is included. There are two solution families (an inner and an outer solution), which both move outward in quasi-steady fashion with time due to the evolving infall structure. These solutions will be described and compared to new analytic solutions for bow shocks[1] and colliding winds[2] from spherically-symmetric sources. Fully non-steady calculations of the evolution will be presented in the future. [1] Wilkin, F.P. 1996, ApJ, 459, L31. [2] Canto, J., Raga, A.C., & Wilkin, F.P. 1996, ApJ, 469, 729

  9. Protonation enhancement by dichloromethane doping in low-pressure photoionization

    NASA Astrophysics Data System (ADS)

    Shu, Jinian; Zou, Yao; Xu, Ce; Li, Zhen; Sun, Wanqi; Yang, Bo; Zhang, Haixu; Zhang, Peng; Ma, Pengkun

    2016-12-01

    Doping has been used to enhance the ionization efficiency of analytes in atmospheric pressure photoionization, which is based on charge exchange. Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH2Cl2) doping. CH2Cl2 is not a common dopant due to its high ionization energy (11.33 eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6 eV and was operated at ~500–1000 Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7 ± 122.4, 197.8 ± 18.8, 87.3 ± 7.8, and 93.5 ± 35.5 times after doping 291 ppmv CH2Cl2, meanwhile CH2Cl2 almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization.

  10. Protonation enhancement by dichloromethane doping in low-pressure photoionization

    PubMed Central

    Shu, Jinian; Zou, Yao; Xu, Ce; Li, Zhen; Sun, Wanqi; Yang, Bo; Zhang, Haixu; Zhang, Peng; Ma, Pengkun

    2016-01-01

    Doping has been used to enhance the ionization efficiency of analytes in atmospheric pressure photoionization, which is based on charge exchange. Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH2Cl2) doping. CH2Cl2 is not a common dopant due to its high ionization energy (11.33 eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6 eV and was operated at ~500–1000 Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7 ± 122.4, 197.8 ± 18.8, 87.3 ± 7.8, and 93.5 ± 35.5 times after doping 291 ppmv CH2Cl2, meanwhile CH2Cl2 almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization. PMID:27905552

  11. Helium 23S photoionization up to the N = 5 threshold

    NASA Astrophysics Data System (ADS)

    Argenti, Luca; Moccia, Roberto

    2008-02-01

    We present the results of an accurate B-spline K-matrix calculation of total and partial cross sections and asymmetry parameters for the photoionization of the metastable 23Se state of helium up to the N = 5 threshold. The effect of the [040]+5 intruder state below N = 4 is shown.

  12. Photodissociation of Acetaldehyde and the Photoionization Cross Section of HCO

    NASA Astrophysics Data System (ADS)

    Shubert, V. Alvin; Pratt, Stephen T.

    2010-06-01

    Acetaldehyde was photodissociated with near UV laser light, and the methyl (CH_3) and formyl (HCO) radical fragments were photoionized with vacuum ultraviolet (VUV) light. The fragments were detected by using both time of flight mass spectrometry and velocity ion map imaging. With the former technique, simultaneous detection of both fragments provided the intensity of HCO+ relative to CH_3+ with I(HCO+)/I(CH_3+) ≈ 0.8. Because the absolute photoionization cross section of the CH_3 radical has been characterized (≈ 5 Mb) at the VUV energies of interest, the absolute photoionization cross section of HCO could be determined from the intensity ratio, yielding an HCO cross section of ≈ 4 Mb at 10.3 eV. However, because some of the HCO fragments could be formed with enough internal energy to undergo secondary dissociation, velocity ion map imaging was employed to determine the extent of any secondary dissociation that occurred. The translational energy distributions obtained for both the CH_3 and HCO fragments are nearly identical, indicating that no HCO fragments underwent secondary dissociation. A surprising result was the smaller photoionization cross section of HCO relative to CH_3. Comparison to the isoelectronic species of NO will be discussed and a potential explanation will be offered for this observation. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under contract No. DE-AC02-06CH11357.

  13. Photoionization of hydrogen-like ions in dense quantum plasmas

    NASA Astrophysics Data System (ADS)

    Qi, Y. Y.; Wang, J. G.; Janev, R. K.

    2017-06-01

    The photoionization of hydrogen-like ions in n ≤ 3 bound states, embedded in cold, dense quantum plasmas, is investigated in detail. The electron energies and wave functions for the bound and continuum states are determined by numerically solving the scaled Schrödinger equation by the fourth-order symplectic integration scheme. The monotonic behavior of the photoionization cross section for a pure Coulomb potential is dramatically changed due to the plasma screening effects described by the cosine-Debye-Hückel potential. In the region of low photoelectron energies, the photoionization cross section, besides the usual Wigner-law threshold behavior, exhibits a rich structure of shape and virtual-state resonances when the plasma screening parameter takes values around the critical screening parameter for which a bound state enters the continuum. It is observed that a shape resonance is followed by a Cooper minimum in the photoionization cross section when the principal quantum number of continuum quasi-bound state is equal to the one of the initial bound states.

  14. Atomic kinetics of a neon photoionized plasma experiment at Z

    NASA Astrophysics Data System (ADS)

    Mayes, Daniel C.; Mancini, Roberto; E Bailey, James; Loisel, Guillaume; Rochau, Gregory

    2017-06-01

    We discuss an experimental effort to study the atomic kinetics in neon photoionized plasmas via K-shell line absorption spectroscopy. The experiment employs the intense x-ray flux emitted at the collapse of a Z-pinch to heat and backlight a photoionized plasma contained within a cm-scale gas cell placed at various distances from the Z-pinch and filled with neon gas pressures in the range from 3.5 to 30 torr. The experimental platform affords an order of magnitude range in the ionization parameter characterizing the photoionized plasma from about 3 to 80 erg*cm/s. Thus, the experiment allows for the study of trends in ionization distribution as a function of the ionization parameter. An x-ray crystal spectrometer capable of collecting both time-integrated and time-gated spectra is used to collect absorption spectra. A suite of IDL programs has been developed to process the experimental data to produce transmission spectra. The spectra show line absorption by several ionization stages of neon, including Be-, Li-, He-, and H-like ions. Analysis of these spectra yields ion areal-densities and charge state distributions, which can be compared with results from atomic kinetics codes. In addition, the electron temperature is extracted from level population ratios of nearby energy levels in Li- and Be-like ions, which can be used to test heating models of photoionized plasmas.

  15. Dissociative photoionization of ethyl acrylate: Theoretical and experimental insights

    NASA Astrophysics Data System (ADS)

    Song, Yanlin; Chen, Jun; Ding, Mengmeng; Wei, Bin; Cao, Maoqi; Shan, Xiaobin; Zhao, Yujie; Huang, Chaoqun; Sheng, Liusi; Liu, Fuyi

    2015-08-01

    The photoionization and dissociation of ethyl acrylate have been investigated by time-of-flight mass spectrometer with tunable vacuum ultraviolet (VUV) source in the range of 9.0-20.0 eV. The photoionization mass spectrum (PIMS) for ethyl acrylate and photoionization efficiency (PIE) curves for its major fragment ions: C5H7O2+, C4H5O2+, C3H5O2+, C3H4O+, C3H3O+, C2H5O+, C2H3O+, C2H5+ and C2H4+ have been obtained. The formation channels of main fragments are predicted by Gaussian 09 program at G3B3 level and examined via their dissociation energies from experimental results. Based on our analysis, nine main dissociative photoionization channels are proposed: C5H7O2+ + H, C4H5O2+ + CH3, C3H5O2+ + C2H3, C3H4O+ + C2H4O, C3H3O+ + C2H5O, C2H5O+ + C3H3O, C2H3O+ + C3H5O, C2H5+ + C3H3O2, C2H4+ + C3H4O2, respectively. The results of this work lead to a better understanding of photochemistry in the environment.

  16. Electron scattering from and photoionization of open- shell atoms

    NASA Astrophysics Data System (ADS)

    Lin, Dong

    1999-09-01

    The multiconfiguration Hartree-Fock (MCHF) approach, developed by Dr. H. P. Saha et al, has been proved to be extremely successful in the past few years in reproducing experimental results at a very high level of accuracy. The research projects we are interested consist of two areas. In the first area we performed ab initio calculations on elastic scattering of electrons from open-shell sulfur atoms. In the second area, in order to understand the electronic dynamics in photoionization of atoms, we carried out accurate calculations on valence and K-shell photoionization of three-electron systems from lithium through neon for photon energies from threshold to very high energies; to further identify the autoionization resonances which were observed near threshold and to understand the dynamics, we modifies the MCHF method to include relativistic effects and performed calculation on partial photoionization cross section, resonance structure and effect of spin-orbit interaction in photoionization of atomic bromine. The calculated results obtained in each of these investigations are compared with available experimental and theoretical data and are found to be in very good agreement. The research contribution made for the fulfillment of the degree, we understand, will be a valuable addition towards a better understanding of the open-shell systems.

  17. Correlation Effects in the Photoionization of Confined Calcium and Zinc

    NASA Astrophysics Data System (ADS)

    Varma, R. Hari; Manson, S. T.

    2005-05-01

    Studies of atoms confined in an endohedral environment have aroused significant recent interest [1]. In this work, the photoionization @Ca and @Zn have been studied using the Relativistic-Random-Phase Approximation, modified to include the confinement potential. Photoionization of the 4s and 3p subshells of free and confined atomic calcium, along with the 4s, 3d, 3p and 3s subshells of free and confined atomic zinc, have been studied. The photoionization parameters of confined atoms differ significantly from those of their ``free'' counterparts. The dipole cross sections and angular distribution asymmetry parameters exhibit oscillations with energy arising from the back scattering of the escaping electron by the confining potential, i.e., ``confinement resonances'' [2]. These oscillations persist when nondipole matrix elements are also included as is reflected in the nondipole cross section and angular distribution asymmetry parameters [3]; the relative strengths of the oscillations due to back-scattering in the E1 and E2 photoionization parameters have qualitatively different profiles as a function of photon energy. [1] V. K. Dolmatov, A. S. Baltenkov, J.-P. Connerade and S. T. Manson, Radiation Phys. Chem. 70, 417 (2004). [2] M. Ya. Amusia, A. S. Baltenkov, V. K. Dolmatov, S. T. Manson and A. Z. Msezane, Phys. Rev. A 70, 023201 (2004). [3] P.C. Deshmukh, Tanima Banerjee, K. P. Sunanda and R. Hari Varma, Radiation Phys. and Chem (submitted).

  18. Photoionization of Ca XV with high energy features

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2017-02-01

    Photoionization cross sections of (Ca XV + hν → Ca XVI + e), with high energy resonant photo-absorption phenomena, of a large number of bound states, 701 in total with n ≤ 10 and l ≤ 9, are reported. They are obtained using the R-matrix method with a close coupling (CC) wavefunction expansion of 29 states of n = 2,3 complexes of the core ion Ca XVI. Characteristic features found in photoionization of the ion are illustrated with examples. The cross section (σPI) of the ground 2s22p2(3P) state is found to be unaffected by the size of the wavefunction expansion except for weak sparse resonances in high energy region. However, effects on excited states are considerable as the core excitations to n = 3 states are manifested in huge resonant absorption in high energy photoionization. They show existence of prominent high peak resonant features and enhancement in the background that were not studied before for Ca XV. In addition photoionization of the excited states with a single valence electron is dominated by Seaton resonant structures formed by the photo-excitation-of-core in the high energy region. These features will impact other quantities, such as the opacity, electron-ion recombination in high temperature plasmas where the ion exists, and hence will play important role in determination of elemental abundances in the astronomical objects.

  19. Protonation enhancement by dichloromethane doping in low-pressure photoionization.

    PubMed

    Shu, Jinian; Zou, Yao; Xu, Ce; Li, Zhen; Sun, Wanqi; Yang, Bo; Zhang, Haixu; Zhang, Peng; Ma, Pengkun

    2016-12-01

    Doping has been used to enhance the ionization efficiency of analytes in atmospheric pressure photoionization, which is based on charge exchange. Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH2Cl2) doping. CH2Cl2 is not a common dopant due to its high ionization energy (11.33 eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6 eV and was operated at ~500-1000 Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7 ± 122.4, 197.8 ± 18.8, 87.3 ± 7.8, and 93.5 ± 35.5 times after doping 291 ppmv CH2Cl2, meanwhile CH2Cl2 almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization.

  20. Evolving sparse stellar populations

    NASA Astrophysics Data System (ADS)

    Bruzual, Gustavo; Gladis Magris, C.; Hernández-Pérez, Fabiola

    2017-03-01

    We examine the role that stochastic fluctuations in the IMF and in the number of interacting binaries have on the spectro-photometric properties of sparse stellar populations as a function of age and metallicity.

  1. Stellar atmospheric structural patterns

    NASA Technical Reports Server (NTRS)

    Thomas, R. N.

    1983-01-01

    The thermodynamics of stellar atmospheres is discussed. Particular attention is given to the relation between theoretical modeling and empirical evidence. The characteristics of distinctive atmospheric regions and their radical structures are discussed.

  2. Stellar X-Ray Polarimetry

    NASA Technical Reports Server (NTRS)

    Swank, J.

    2011-01-01

    Most of the stellar end-state black holes, pulsars, and white dwarfs that are X-ray sources should have polarized X-ray fluxes. The degree will depend on the relative contributions of the unresolved structures. Fluxes from accretion disks and accretion disk corona may be polarized by scattering. Beams and jets may have contributions of polarized emission in strong magnetic fields. The Gravity and Extreme Magnetism Small Explorer (GEMS) will study the effects on polarization of strong gravity of black holes and strong magnetism of neutron stars. Some part of the flux from compact stars accreting from companion stars has been reflected from the companion, its wind, or accretion streams. Polarization of this component is a potential tool for studying the structure of the gas in these binary systems. Polarization due to scattering can also be present in X-ray emission from white dwarf binaries and binary normal stars such as RS CVn stars and colliding wind sources like Eta Car. Normal late type stars may have polarized flux from coronal flares. But X-ray polarization sensitivity is not at the level needed for single early type stars.

  3. Oscillations in stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Costa, A.; Ringuelet, A. E.; Fontenla, J. M.

    1989-01-01

    Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized.

  4. Oscillations in stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Costa, A.; Ringuelet, A. E.; Fontenla, J. M.

    1989-01-01

    Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized.

  5. New Insights into Radiation Line-Driven Winds

    NASA Astrophysics Data System (ADS)

    Cidale, L.; Venero, R. O. J.; Curé, M.; Haucke, M.

    2017-02-01

    The classical theory of radiatively driven stellar winds reproduces the observed stellar wind conditions (mass loss and terminal velocity) of massive supergiants fairly well. However, some differences are still found between the wind parameters predicted by theory and those observed in mid-B, late-B, and A-type supergiants. Inclusion of rotation in the models brought a remarkable progress in the development of the theory of stellar winds. Three types of stationary wind regimes are currently known: the classical fast solution, the Ω-slow solution that arises for fast rotators, and the δ-slow solution that takes place in highly ionized winds. We show synthetic line profiles and discuss all the hydrodynamical solutions in the context of the observed wind properties of B and B[e] supergiants. We also discuss the variability of spectral lines formed in the wind of B-supergiants.

  6. Photoionization of the cerium isonuclear sequence and cerium endohedral fullerene

    NASA Astrophysics Data System (ADS)

    Habibi, Mustapha

    This dissertation presents an experimental photoionization study of the cerium isonuclear sequence ions in the energy range of the 4d inner-shell giant resonance. In addition, single and double photoionization and photofragmentation cross sections of the cerium endohedral ion Ce C+82 were also measured and studied in the 4d excitation-ionization energy range of cerium. Relative and absolute cross-section measurements were performed at undulator beamline 10.0.1 of the Advanced Light Source (ALS) for nine parent cerium ions: Ce+ - Ce9+. Double-to-single ionization cross-section ratios were measured for photoionization of the endohedral Ce C+82 and empty fullerene C C+82 molecular ions. The merged ion and photon beams technique was used to conduct the experiments. Multiconfiguration Hartree-Fock calculations were performed as an aid to interpret the experimental data. Four Rydberg series for 4d → nf (n ≥ 4) and 4d → np (n ≥ 6) autoionizing excitations were assigned using the quantum defect theory for the Ce3+ photoionization cross section. The experimental data show the collapse of the nf wavefunctions (n ≥ 4) with increasing ionization stage as outer-shell electrons are stripped from the parent ion. The nf orbital collapse occurs partially for Ce2+ and Ce3+ ion and completely for Ce4+, where these wavefunctions penetrate the core region of the ion. A strong contribution to the total oscillator strength was observed in the double and triple photoionization channels for low charge states (Ce +, Ce2+, and Ce3+), whereas most of the 4d excitations of the higher charge states decay by ejection of one electron.

  7. Photoionization of ground and excited levels of P II

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2017-01-01

    Photoionization cross section (σPI) of P II, (hν + P II → P III + e), from ground and a large number of excited levels are presented. The study includes the resonant structures and the characteristics of the background in photoionization cross sections. The present calculations were carried out in the Breit-Pauli R-matrix (BPRM) method that includes relativistic effects. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. A singular resonance, formed by the coupling of channels in fine structure but not allowed in LS coupling, is seen at the ionization threshold of photoionization for the ground and many excited levels. The background cross section is seen enhanced compared to smooth decay for the excited levels. Examples are presented to illustrate the enhanced background cross sections at the energies of the core levels, 4P3/2 and 2D3/2, that are allowed for electric dipole transitions by the core ground level 2 P1/2o. In addition strong Seaton or photo-excitation-of-core (PEC) resonances are found in the photoionization of single valence electron excited levels. Calculations used a close coupling wave function expansion that included 18 fine structure levels of core P III from configurations 3s23p, 3s3p2, 3s23d, 3s24s, 3s24p and 3p3. Photoionization cross sections are presented for all 475 fine structure levels of P II found with n ≤ 10 and l ≤ 9. The present results will provide high precision parameters of various applications involving this less studied ion.

  8. Photodissociation and photoionization of organosulfur radicals

    SciTech Connect

    Hsu, Chia-Wei

    1994-05-27

    The dynamics of S(3P2,1,0, 1D2) production from the 193 nm photodissociation of CH3SCH3, H2S and CH3SH have been studied using 2 + 1 resonance-enhanced multiphoton ionization (REMPI) techniques. The 193 nm photodissociation cross sections for the formation of S from CH3S and HS initially prepared in the photodissociation of CH3SCH3 and H2S are estimated to be 1 x 10-18 and 1.1 x 10-18 cm2, respectively. The dominant product from CH3S is S(1D), while that from SH is S(3P). Possible potential energy surfaces involved in the 193 nm photodissociation of CH3S($\\tilde{X}$) and SH(X) have been also examined. Threshold photoelectron (PE) spectra for SH and CH3S formed in the ultraviolet photodissociation of H2S and CH3SH, respectively, have been measured using the nonresonant two-photon pulsed field ionization (N2P-PFI) technique. The rotationally resolved N2P-PFI-PE spectrum obtained for SH indicates that photoionization dynamics favors the rotational angular momentum change ΔN < 0 with the ΔN value up to -3, an observation similar to that found in the PFI-PE spectra of OH (OD) and NO. The ionization energies for SH(X2Π3,2) and CH3S($\\tilde{X}$2E3/2) are determined to be 84,057.5 ± 3 cm-1 and 74,726 ± 8 cm-1 respectively. The spin-orbit splittings for SH(X2Π3/2, 1/2) and CH3S($\\tilde{X}$2E3/2, 1/2) are found to be 377 ± 2 and 257 ± 5 cm-1, respectively, in agreement with previous measurements. The C-S stretching frequency for CH3S+($\\tilde{X}$3A2) is 733 ± 5 cm-1. This study illustrates that the PFI-PE detection method can be a

  9. The SOHO-Stellar Connection

    NASA Technical Reports Server (NTRS)

    Ayres, Thomas R.

    1999-01-01

    I discusses practical aspects of the so-called "solar-stellar" connection; namely, the fundamental principles, the tools at the disposal of the stellar astronomer, and a few recent examples of the connection in action. I provide an overall evolutionary context for coronal activity, calling attention to the very different circumstances of low mass main sequence stars like the Sun, which are active mainly early in their lives; compared with more massive stars, whose coronally active phase occurs near the end of their lives, during their brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow and then red giants. On the instrumental slide, I concentrate primarily on spectroscopy, in the ultraviolet and X-ray bands where coronae leave their most obvious signatures. I present an early glimpse of the type of moderate resolution spectra we can expect from the recently launched Chandra observatory, and contemporaneous HST STIS high-resolution UV measurements of the CXO calibration star Capella (alpha Aur; G8 III + G1 III). I compare STIS spectra of solar-type dwarfs-zeta Dor (F7 V), an active coronal source; and alpha Cen A (G2 V), a near twin of the Sun-to a trace obtained with the SOHO SUMER imaging UV spectrometer. I also compare STIS line profiles of the active coronal dwarf to the corresponding features in the mixed-activity "hybrid-chromosphere" bright giant alpha TrA (K2 II) and the archetype "noncoronal" red giant Arcturus (alpha Boo; K2 III). The latter shows dramatic evidence for a "cool absorber" in its outer atmosphere that is extinguishing the "hot lines" (like Si IV lambda1393 and N V lambda1238) below about 1500 A, probably through absorption in the Si I lambda1525 and C I lambda1240 photoionization continua. The disappearance of coronae across the "Linsky-Haisch" dividing line near K1 III thus apparently is promoted by a dramatic overturning in the outer atmospheric structure, namely the coronae of the red giants seem to lie beneath

  10. The SOHO-Stellar Connection

    NASA Technical Reports Server (NTRS)

    Ayres, Thomas R.

    1999-01-01

    I discusses practical aspects of the so-called "solar-stellar" connection; namely, the fundamental principles, the tools at the disposal of the stellar astronomer, and a few recent examples of the connection in action. I provide an overall evolutionary context for coronal activity, calling attention to the very different circumstances of low mass main sequence stars like the Sun, which are active mainly early in their lives; compared with more massive stars, whose coronally active phase occurs near the end of their lives, during their brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow and then red giants. On the instrumental slide, I concentrate primarily on spectroscopy, in the ultraviolet and X-ray bands where coronae leave their most obvious signatures. I present an early glimpse of the type of moderate resolution spectra we can expect from the recently launched Chandra observatory, and contemporaneous HST STIS high-resolution UV measurements of the CXO calibration star Capella (alpha Aur; G8 III + G1 III). I compare STIS spectra of solar-type dwarfs-zeta Dor (F7 V), an active coronal source; and alpha Cen A (G2 V), a near twin of the Sun-to a trace obtained with the SOHO SUMER imaging UV spectrometer. I also compare STIS line profiles of the active coronal dwarf to the corresponding features in the mixed-activity "hybrid-chromosphere" bright giant alpha TrA (K2 II) and the archetype "noncoronal" red giant Arcturus (alpha Boo; K2 III). The latter shows dramatic evidence for a "cool absorber" in its outer atmosphere that is extinguishing the "hot lines" (like Si IV lambda1393 and N V lambda1238) below about 1500 A, probably through absorption in the Si I lambda1525 and C I lambda1240 photoionization continua. The disappearance of coronae across the "Linsky-Haisch" dividing line near K1 III thus apparently is promoted by a dramatic overturning in the outer atmospheric structure, namely the coronae of the red giants seem to lie beneath

  11. Detailed opacity calculations for stellar models

    NASA Astrophysics Data System (ADS)

    Pain, Jean-Christophe; Gilleron, Franck

    2016-10-01

    We present a state of the art of precise spectral opacity calculations illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments of hot dense plasmas produced by ultra-high-intensity laser interaction. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. Focus is put on iron, due to its crucial role in the understanding of asteroseismic observations of Beta Cephei-type and Slowly Pulsating B stars, as well as in the Sun. For instance, in Beta Cephei-type stars (which should not be confused with Cepheid variables), the iron-group opacity peak excites acoustic modes through the kappa-mechanism. A particular attention is paid to the higher-than-predicted iron opacity measured on Sandia's Z facility at solar interior conditions (boundary of the convective zone). We discuss some theoretical aspects such as orbital relaxation, electron collisional broadening, ionic Stark effect, oscillator-strength sum rules, photo-ionization, or the ``filling-the-gap'' effect of highly excited states.

  12. VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: Theory and experiment

    SciTech Connect

    Bellili, A.; Hochlaf, M. E-mail: martin.schwell@lisa.u-pec.fr; Schwell, M. E-mail: martin.schwell@lisa.u-pec.fr; Bénilan, Y.; Fray, N.; Gazeau, M.-C.; Mogren Al-Mogren, M.; Guillemin, J.-C.; Poisson, L.

    2014-10-07

    The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals. In view of the interpretation of vacuum ultraviolet (VUV) experimental data obtained using synchrotron radiation, we explored the ground potential energy surface (PES) of acetyl cyanide and of its cation using standard and recently implemented explicitly correlated methodologies. Our PES covers the regions of tautomerism (between keto and enol forms) and of the lowest fragmentation channels. This allowed us to deduce accurate thermochemical data for this astrobiologically relevant molecule. Unimolecular decomposition of the AC cation turns out to be very complex. The implications for the evolution of prebiotic molecules under VUV irradiation are discussed.

  13. VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: Theory and experiment

    NASA Astrophysics Data System (ADS)

    Bellili, A.; Schwell, M.; Bénilan, Y.; Fray, N.; Gazeau, M.-C.; Mogren Al-Mogren, M.; Guillemin, J.-C.; Poisson, L.; Hochlaf, M.

    2014-10-01

    The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals. In view of the interpretation of vacuum ultraviolet (VUV) experimental data obtained using synchrotron radiation, we explored the ground potential energy surface (PES) of acetyl cyanide and of its cation using standard and recently implemented explicitly correlated methodologies. Our PES covers the regions of tautomerism (between keto and enol forms) and of the lowest fragmentation channels. This allowed us to deduce accurate thermochemical data for this astrobiologically relevant molecule. Unimolecular decomposition of the AC cation turns out to be very complex. The implications for the evolution of prebiotic molecules under VUV irradiation are discussed.

  14. Stellar feedback in dwarf galaxy formation.

    PubMed

    Mashchenko, Sergey; Wadsley, James; Couchman, H M P

    2008-01-11

    Dwarf galaxies pose substantial challenges for cosmological models. In particular, current models predict a dark-matter density that is divergent at the center, which is in sharp contrast with observations that indicate a core of roughly constant density. Energy feedback, from supernova explosions and stellar winds, has been proposed as a major factor shaping the evolution of dwarf galaxies. We present detailed cosmological simulations with sufficient resolution both to model the relevant physical processes and to directly assess the impact of stellar feedback on observable properties of dwarf galaxies. We show that feedback drives large-scale, bulk motions of the interstellar gas, resulting in substantial gravitational potential fluctuations and a consequent reduction in the central matter density, bringing the theoretical predictions in agreement with observations.

  15. Simulating Stellar Cluster Formation and Early Evolution

    NASA Astrophysics Data System (ADS)

    Wall, Joshua; McMillan, Stephen L. W.; Mac Low, Mordecai-Mark; Ibañez-Mejia, Juan; Portegies Zwart, Simon; Pellegrino, Andrew

    2017-01-01

    We present our current development of a model of stellar cluster formation and evolution in the presence of stellar feedback. We have integrated the MHD code Flash into the Astrophysical Multi-Use Software Environment (AMUSE) and coupled the gas dynamics to an N-body code using a Fujii gravity bridge. Further we have integrated feedback from radiation using the FERVENT module for Flash, supernovae by thermal and kinetic energy injection, and winds by kinetic energy injection. Finally we have developed a method of implementing star formation using the Jeans criterion of the gas. We present initial results from our cluster formation model in a cloud using self-consistent boundary conditions drawn from a model of supernova-driven interstellar turbulence.

  16. PREFACE: A Stellar Journey A Stellar Journey

    NASA Astrophysics Data System (ADS)

    Asplund, M.

    2008-10-01

    The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

  17. Feedback in Clouds II: UV photoionization and the first supernova in a massive cloud

    NASA Astrophysics Data System (ADS)

    Geen, Sam; Hennebelle, Patrick; Tremblin, Pascal; Rosdahl, Joakim

    2016-12-01

    Molecular cloud structure is regulated by stellar feedback in various forms. Two of the most important feedback processes are UV photoionization and supernovae from massive stars. However, the precise response of the cloud to these processes, and the interaction between them, remains an open question. In particular, we wish to know under which conditions the cloud can be dispersed by feedback, which, in turn, can give us hints as to how feedback regulates the star formation inside the cloud. We perform a suite of radiative magnetohydrodynamic simulations of a 105 solar mass cloud with embedded sources of ionizing radiation and supernovae, including multiple supernovae and a hypernova model. A UV source corresponding to 10 per cent of the mass of the cloud is required to disperse the cloud, suggesting that the star formation efficiency should be of the order of 10 per cent. A single supernova is unable to significantly affect the evolution of the cloud. However, energetic hypernovae and multiple supernovae are able to add significant quantities of momentum to the cloud, approximately 1043 g cm s-1 of momentum per 1051 erg of supernova energy. We argue that supernovae alone are unable to regulate star formation in molecular clouds. We stress the importance of ram pressure from turbulence in regulating feedback in molecular clouds.

  18. Las Campanas Stellar Library

    NASA Astrophysics Data System (ADS)

    Chilingarian, Igor; Zolotukhin, Ivan; Beletsky, Yuri; Worthey, Guy

    2015-08-01

    Stellar libraries are fundamental tools required to understand stellar populations in star clusters and galaxies as well as properties of individual stars. Comprehensive libraries exist in the optical domain, but the near-infrared (NIR) domain stays a couple of decades behind. Here we present the Las Campanas Stellar Library project aiming at obtaining high signal-to-noise intermediate-resolution (R=8000) NIR spectra (0.83<λ<2.5μm) for a sample of 1200 stars in the Southern sky using the Folded-port InfraRed Echelette spectrograph at the 6.5-m Magellan Baade telescope. We developed a dedicated observing strategy and customized the telescope control software in order to achieve the highest possible level of data homogeniety. As of 2015, we observed about 600 stars of all spectral types and luminosity classes making our library the largest homogeneous collection of stellar spectra covering the entire NIR domain. We also re-calibrated in flux and wavelength the two existing optical stellar libraries, INDO-US and UVES-POP and followed up about 400 non-variable stars in the NIR in order to get complete optical-NIR coverage. Worth mentioning that our current sample includes about 80 AGB stars and a few dozens of bulge/LMC/SMC stars.

  19. Innovations in Quasi-Poloidal Stellarator Design

    NASA Astrophysics Data System (ADS)

    Nelson, B. E.; Lyon, J. F.; Freudenberg, K. D.; Fogarty, P. J.; Benson, R. D.; Madhukar, M.

    2006-10-01

    The Quasi-Poloidal Stellarator (QPS) is being developed with very low plasma aspect ratio, 1/2-1/4 that of existing stellarators. Design innovation is driven by both the complex 3-D geometry and the need for reduced cost and risk in fabrication, so QPS differs significantly in design and construction from other toroidal devices. An internally cooled, compacted cable conductor consisting of stranded copper filaments wound around an internal copper cooling tube was developed that can be wound into complex 3-D shapes. This conductor is wound directly onto the complex, highly accurate, stainless steel coil winding forms. Simplified coil winding procedures lead to faster fabrication and reduced technical risk. A full-size prototype of the largest and most complex of the winding forms has been cast using a patternless process (machined sand molds) and a high-temperature pour, which resulted in <1/10 the major weld repairs of similar sand castings using conventional patterns, and machined to high precision. A vacuum-tight cover is welded over each coil pack and a high-temperature cyanate ester resin is used for vacuum pressure impregnation of the coils because it has several important advantages over the usual epoxy. The completed coils are then installed in an external vacuum vessel.

  20. Mild evolution of the stellar metallicity gradients of disc galaxies

    NASA Astrophysics Data System (ADS)

    Tissera, Patricia B.; Machado, Rubens E. G.; Vilchez, José M.; Pedrosa, Susana E.; Sanchez-Blazquez, Patricia; Varela, Silvio

    2017-08-01

    Context. The metallicity gradients of the stellar populations in disc galaxies and their evolution store relevant information on the disc formation history and on those processes which could mix stars a posteriori, such as migration, bars and/or galaxy-galaxy interactions. Aims: We aim to investigate the evolution of the metallicity gradients of the whole stellar populations in disc components of simulated galaxies in a cosmological context. Methods: We analyse simulated disc galaxies selected from a cosmological hydrodynamical simulation that includes chemical evolution and a physically motivated supernova feedback capable of driving mass-loaded galactic winds. Results: We detect a mild evolution with redshift in the metallicity slopes of - 0.02 ± 0.01 dex kpc-1 from z 1. If the metallicity profiles are normalised by the effective radius of the stellar disc, the slopes show no clear evolution for z< 1, with a median value of approximately - 0.23 dex reff-1. As a function of stellar mass, we find that metallicity gradients steepen for stellar masses smaller than 1010.3M⊙ while the trend reverses for higher stellar masses, in the redshift range z = [ 0,1 ]. Galaxies with small stellar masses have discs with larger reff and flatter metallicity gradients than expected. We detect migration albeit weaker than in previous works. Conclusions: Our stellar discs show a mild evolution of the stellar metallicity slopes up to z 1, which is well-matched by the evolution calculated archeologically from the abundance distributions of mono-age stellar populations at z 0. The dispersion in the relations allows for stronger individual evolutions. Overall, supernova feedback could explain the trends but an impact of migration can not be totally discarded. Galaxy-galaxy interactions or small satellite accretions can also contribute to modify the metallicity profiles in the outer parts. Disentangling the effects of these processes for individual galaxies is still a challenge in a

  1. Origins of Stellar Halos

    NASA Astrophysics Data System (ADS)

    Johnston, Kathryn V.

    2016-08-01

    This contribution reviews ideas about the origins of stellar halos. It includes discussion of the theoretical understanding of and observational evidence for stellar populations formed ``in situ'' (meaning formed in orbits close to their current ones), ``kicked-out'' (meaning formed in the inner galaxy in orbits unlike their current ones) and ``accreted'' (meaning formed in a dark matter halo other than the one they currently occupy). At this point there is general agreement that a significant fraction of any stellar halo population is likely ``accreted''. There is modest evidence for the presence of a ``kicked-out'' population around both the Milky Way and M31. Our theoretical understanding of and the observational evidence for an ``in situ'' population are less clear.

  2. The Galactic stellar disc

    NASA Astrophysics Data System (ADS)

    Feltzing, S.; Bensby, T.

    2008-12-01

    The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Also based on observations collected at the Nordic Optical Telescope on La Palma, Spain, and at the European Southern Observatories on La Silla and Paranal, Chile, Proposals no. 65.L-0019(B), 67.B-0108(B), 69.B-0277.

  3. Clumping in hot-star winds

    NASA Astrophysics Data System (ADS)

    Hamann, Wolf-Rainer; Feldmeier, Achim; Oskinova, Lidia M.

    2008-04-01

    Stellar winds play an important role for the evolution of massive stars and their cosmic environment. Multiple lines of evidence, coming from spectroscopy, polarimetry, variability, stellar ejecta, and hydrodynamic modeling, suggest that stellar winds are non-stationary and inhomogeneous. This is referred to as 'wind clumping'. The urgent need to understand this phenomenon is boosted by its far-reaching implications. Most importantly, all techniques to derive empirical mass-loss rates are more or less corrupted by wind clumping. Consequently, mass-loss rates are extremely uncertain. Within their range of uncertainty, completely different scenarios for the evolution of massive stars are obtained. Settling these questions for Galactic OB, LBV and Wolf-Rayet stars is prerequisite to understanding stellar clusters and galaxies, or predicting the properties of first-generation stars. In order to develop a consistent picture and understanding of clumped stellar winds, an international workshop on 'Clumping in Hot Star Winds' was held in Potsdam, Germany, from 18. - 22. June 2007. About 60 participants, comprising almost all leading experts in the field, gathered for one week of extensive exchange and discussion. The Scientific Organizing Committee (SOC) included John Brown (Glasgow), Joseph Cassinelli (Madison), Paul Crowther (Sheffield), Alex Fullerton (Baltimore), Wolf-Rainer Hamann (Potsdam, chair), Anthony Moffat (Montreal), Stan Owocki (Newark), and Joachim Puls (Munich). These proceedings contain the invited and contributed talks presented at the workshop, and document the extensive discussions.

  4. Outflow Collimation in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Noriega-Crespo, A.; Frank, A.

    1993-05-01

    Recent results of long-slit spectroscopy of the forbidden lines of the outflow in the young star DG Tau [7] suggest that its wind is well collimated very close to it, leading to the formation of its jet. The analysis of the width of stellar jets, on the other hand, seems to indicate that the collimation of the jets takes place at larger scales [5]. In other to understand this discrepancy, we are studying by means of a two dimensional hydrodynamical code [1][3], the collimation driven by the interaction of the stellar wind with the surrounding density structure left by the star formation process [8][9]. We have found in our adiabatic outflow simulations (using physical parameters similar to those for the HH 34 bipolar stellar jet [2]) that a spherical wind is well collimated near the source resembling a de Laval Nozzle [4][6]. ANC research is supported by NSF grant AST-91-14888. \\ References [1] Frank, A. 1992, PhD Thesis, University of Washington. [2] Heathcote, S. & Reipurth, B. 1992, AJ 104, 2193. [3] Icke, V., 1988 A&A 202, 177. [4] Konigl, A. 1982, ApJ 261, 115. [5] Mundt, R., Ray, T.P., & Raga, A.C. 1991, A&A 252, 740. [6] Raga A.C., & Canto, J. 1989, ApJ 344, 404. [7] Solf, J., & Bohm, K.H. 1993, ApJL (in press). [8] Terebey, S., Shu, F.H., & Cassen, P. 1984, ApJ 286, 529. [9] Yorke, H.W., Bodenheimer, P., & Laughlin, G. 1993, ApJ (in press).

  5. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2008-02-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  6. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2003-05-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  7. Time-Dependent Photoionization of Gas Outflows in AGN

    NASA Astrophysics Data System (ADS)

    Elhoussieny, Ehab E.; Bautista, M.; Garcia, J.; Kallman, T. R.

    2013-01-01

    Gas outflows are fundamental components of Active Galactic Nuclei (AGN) activity. Time-variability of ionizing radiation, which is characteristic of AGN in various different time scales, may produce non-equilibrium photoionization conditions over a significant fraction of the flow and yields supersonically moving cooling/heating fronts. These fast fronts create pressure imbalances that can only be resolved by fragmentation of the flow and acceleration of such fragments. This mechanism can explain the kinematic structure of low ionization BAL systems (FeLoBAL). This mechanism may also have significant effects on other types of outflows given the wide range of variability time scales in AGN. We will study these effects in detail by constructing time-dependent photoionization models of the outflows and incorporating these models into radiative-hydrodynamic simulations.

  8. Photoionization of Endohedral Atoms: Collective, Reflective and Collateral Emissions

    NASA Astrophysics Data System (ADS)

    Chakraborty, Himadri S.; McCune, Matthew A.; Madjet, Mohamed E.; Hopper, Dale E.; Manson, Steven T.

    2009-12-01

    The photoionization properties of a fullerene-confined atom differ dramatically from that of an isolated atom. In the low energy region, where the fullerene plasmons are active, the electrons of the confined atom emerge through a collective channel carrying a significant chunk of plasmon with it. The photoelectron angular distribution of the confined atom however shows far lesser impact of the effect. At higher energies, the interference between two single-electron ionization channels, one directly from the atom and another reflected off the fullerene cage, producuces oscillatory cross sections. But for the outermost atomic level, which transfers some electrons to the cage, oscillations are further modulated by the collateral emission from the part of the atomic charge density transferred to the cage. These various modes of emissions are studied for the photoionization of Ar endohedrally confined in C60.

  9. K -shell double photoionization of Be, Mg, and Ca

    NASA Astrophysics Data System (ADS)

    Kheifets, A. S.; Bray, Igor; Hoszowska, J.

    2009-04-01

    We perform convergent close-coupling calculations of double photoionization (DPI) of the K -shell of alkaline-earth metal atoms (Be, Mg, and Ca) from the threshold to the nonrelativistic limit of infinite photon energy. Theoretical double-to-single photoionization cross-section ratios for Mg and Ca are compared with experimental values derived from high-resolution x-ray spectra following the radiative decay of the K -shell double vacancy. We investigate the role of many-electron correlations in the ground and doubly-ionized final states played in the DPI process. Universal scaling of DPI cross section with an effective nuclear charge is examined in neutral atoms in comparison with corresponding heliumlike ions.

  10. Double Photoionization into Double Core-Hole States in Xe

    SciTech Connect

    Hikosaka, Y.; Kaneyasu, T.; Shigemasa, E.; Lablanquie, P.; Penent, F.; Eland, J. H. D.; Aoto, T.; Ito, K.

    2007-05-04

    Double photoionization (DPI) leading to double core-hole states of Xe{sup 2+} 4d{sup -2} has been studied using a magnetic bottle time-of-flight spectrometer. The assignments of the Xe{sup 2+} 4d{sup -2} states are confirmed by the Auger lines extracted from fourfold coincidences including two photoelectrons and two Auger electrons. It is estimated that the core-core DPI into Xe{sup 2+} 4d{sup -2} at a photon energy of 301.6 eV has a favored cross section of about 0.3 MB. The intense core-core DPI is due to mixing of the 4d{sup -2} continuum with the 4p single photoionization, which is manifested in the relative intensities of the Xe{sup 2+} 4d{sup -2} components.

  11. Vibrationally resolved shape resonant photoionization of SiF4

    NASA Astrophysics Data System (ADS)

    Kakar, Sandeep; Poliakoff, E. D.; Rosenberg, R. A.

    1992-01-01

    We have measured vibrationally resolved fluorescence from SiF+4(D˜ 2A1) photoions to determine the vibrational branching ratio σ[v=(1,0,0,0)]/σ[v=(0,0,0,0)] in the excitation energy range 22photoionization are discussed.

  12. Fluorescence probes of spectroscopic and dynamical aspects of molecular photoionization

    NASA Astrophysics Data System (ADS)

    Poliakoff, Erwin D.

    1988-11-01

    Studies were made of vibrationally resolved aspects of shape resonant excitation in the photoionization of N(2)0. This experiment was performed by generating dispersed fluorescence spectra from electronically excited photoions. These results are the first vibrationally resolved results on a polyatomic shape resonance. In vibrationally resolved measurements, different internuclear configurations are probed by sampling alternative vibrational levels of the ion. As a result, the continuum electron behavior can be mapped out most clearly, and the qualitative aspects of the electron ejection can be understood clearly. A central motivation for studying polyatomic shape resonances is that alternative vibrational modes may be explored, revealing facets that are nonexistent for diatomic systems, which are the only systems that have been characterized previously.

  13. Communication: The influence of vibrational parity in chiral photoionization dynamics

    SciTech Connect

    Powis, Ivan

    2014-03-21

    A pronounced vibrational state dependence of photoelectron angular distributions observed in chiral photoionization experiments is explored using a simple, yet realistic, theoretical model based upon the transiently chiral molecule H{sub 2}O{sub 2}. The adiabatic approximation is used to separate vibrational and electronic wavefunctions. The full ionization matrix elements are obtained as an average of the electronic dipole matrix elements over the vibrational coordinate, weighted by the product of neutral and ion state vibrational wavefunctions. It is found that the parity of the vibrational Hermite polynomials influences not just the amplitude, but also the phase of the transition matrix elements, and the latter is sufficient, even in the absence of resonant enhancements, to account for enhanced vibrational dependencies in the chiral photoionization dynamics.

  14. Spatially resolved photoionization of ultracold atoms on an atom chip

    SciTech Connect

    Kraft, S.; Guenther, A.; Fortagh, J.; Zimmermann, C.

    2007-06-15

    We report on photoionization of ultracold magnetically trapped Rb atoms on an atom chip. The atoms are trapped at 5 {mu}K in a strongly anisotropic trap. Through a hole in the chip with a diameter of 150 {mu}m, two laser beams are focused onto a fraction of the atomic cloud. A first laser beam with a wavelength of 778 nm excites the atoms via a two-photon transition to the 5D level. With a fiber laser at 1080 nm the excited atoms are photoionized. Ionization leads to depletion of the atomic density distribution observed by absorption imaging. The resonant ionization spectrum is reported. The setup used in this experiment is suitable not only to investigate mixtures of Bose-Einstein condensates and ions but also for single-atom detection on an atom chip.

  15. Double-photoionization of helium including quadrupole radiation effects

    SciTech Connect

    Colgan, James; Ludlow, J A; Lee, Teck - Ghee; Pindzola, M S; Robicheaux, F

    2009-01-01

    Non-perturbative time-dependent close-coupling calculations are carried out for the double photoionization of helium including both dipole and quadrupole radiation effects. At a photon energy of 800 eV, accessible at CUlTent synchrotron light sources, the quadrupole interaction contributes around 6% to the total integral double photoionization cross section. The pure quadrupole single energy differential cross section shows a local maxima at equal energy sharing, as opposed to the minimum found in the pure dipole single energy differential cross section. The sum of the pure dipole and pure quadrupole single energy differentials is insensitive to non-dipole effects at 800 eV. However, the triple differential cross section at equal energy sharing of the two ejected electrons shows strong non-dipole effects due to the quadrupole interaction that may be experimentally observable.

  16. Photoionization of Endohedral Atoms: Collective, Reflective and Collateral Emissions

    SciTech Connect

    Chakraborty, Himadri S.; McCune, Matthew A.; Hopper, Dale E.; Madjet, Mohamed E.; Manson, Steven T.

    2009-12-03

    The photoionization properties of a fullerene-confined atom differ dramatically from that of an isolated atom. In the low energy region, where the fullerene plasmons are active, the electrons of the confined atom emerge through a collective channel carrying a significant chunk of plasmon with it. The photoelectron angular distribution of the confined atom however shows far lesser impact of the effect. At higher energies, the interference between two single-electron ionization channels, one directly from the atom and another reflected off the fullerene cage, producuces oscillatory cross sections. But for the outermost atomic level, which transfers some electrons to the cage, oscillations are further modulated by the collateral emission from the part of the atomic charge density transferred to the cage. These various modes of emissions are studied for the photoionization of Ar endohedrally confined in C{sub 60}.

  17. Photoionization and electron-ion recombination of P II

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2017-08-01

    A study of the inverse processes of photoionization and electron-ion recombination of P ii is reported. Phosphorus, a little studied cosmic element, requires atomic parameters such as those presented here for spectral analysis. The unified method of Nahar and Pradhan, which incorporates two methods of recombination - radiative recombination (RR) and dielectronic recombination (DR) - and the interference between them, is used to obtain the total electron-ion recombination. This method implements the framework of the {R}-matrix close-coupling approximation. The present results include the partial photoionization cross-sections σPI(Jπ) leaving the residual ion in the ground level and level-specific recombination rate coefficients, αRC(Jπ), of 475 fine-structure levels of P ii with n ≤10. In photoionization of the ground and many excited levels, a sharp resonance is found to form at the ionization threshold from couplings of relativistic fine-structure channels. These, with other resonances in the near-threshold energy region, yield a slight curvature, in contrast to typical smooth decay, at a very low temperature of about 330 K in the total recombination rate coefficient αRC. The presence of other Rydberg and Seaton resonances in the photoionization cross-section introduces features in the level-specific recombination rate coefficients and a DR bump at high temperature at 105 K for the total recombination rate coefficient. Considerable interference between RR and DR is noted around 6700 K. The recombination spectrum with respect to photoelectron energy αRC(E) is also presented. The results are expected to provide accurate models for astrophysical plasmas up to ∼1 MK.

  18. Nonperturbative theory of double photoionization of the hydrogen molecule

    SciTech Connect

    Vanroose, W.; Martin, F.; Rescigno, T.N.; McCurdy, C.W.

    2004-10-01

    We present completely ab initio nonperturbative calculations of the integral and single differential cross sections for double photoionization of H2 for photon energies from 53.9 to 75.7 eV. The method of exterior complex scaling, implemented with B-splines, is used to solve the Schrodinger equation for a correlated continuum wave function corresponding to a single photon having been absorbed by a correlated initial state. The results are in good agreement with experimental integral cross sections.

  19. Differential cross-sections for the double photoionization of lithium

    NASA Astrophysics Data System (ADS)

    Kheifets, A. S.; Fursa, D. V.; Bray, Igor; Colgan, J.; Pindzola, M. S.

    2012-11-01

    We apply the convergent close-coupling (CCC) and time-dependent close- coupling (TDCC) methods to describe energy and angular resolved double photoionization (DPI) of lithium at arbitrary energy sharing. By doing so, we are able to evaluate the recoil ion momentum distribution of DPI of Li and make a comparison with recent measurements of Zhu et al. [Phys. Rev. Lett. 103, 103008 (2009)].

  20. Differential cross sections of double photoionization of lithium

    SciTech Connect

    Kheifets, A. S.; Fursa, D. V.; Bray, I.; Colgan, J.; Pindzola, M. S.

    2010-08-15

    We extend our previous application of the convergent close-coupling (CCC) and time-dependent close-coupling (TDCC) methods [Phys. Rev. A 81, 023418 (2010)] to describe energy and angular resolved double photoionization (DPI) of lithium at arbitrary energy sharing. By doing so, we are able to evaluate the recoil ion momentum distribution of DPI of Li and make a comparison with recent measurements of Zhu et al. [Phys. Rev. Lett. 103, 103008 (2009)].

  1. Tunable Wavelength Soft Photoionization of Ionic Liquid Vapors (Preprint)

    DTIC Science & Technology

    2009-11-18

    determined using the atomic absorption line spectrum of an argon gas filter located between the light Preprint Distribution A: Approved for public...Journal of the American Society for Mass Spectrometry; 19, 1347 (2008). 28. P.B. Corkum, Plasma Perspective on Strong-Field Multiphoton Ionization...Physical Review Letters; 71, 1994 (1993). 29. L. Belau et al., Vacuum ultraviolet ( VUV ) photoionization of small water clusters. Journal of

  2. Photoionization of an aluminum plasma by a tantalum X source

    NASA Astrophysics Data System (ADS)

    Renaudin, Patrick; Back, Christina A.; Chenais-Popovics, Claude; Audebert, Patrick; Geindre, Jean-Paul; Gauthier, Jean-Claude

    1991-05-01

    Photoionization of a helium like aliminum plasma is carried out by an external x-source. The laser beam used corresponds to the 3d to 4F transition level of tantalum. The experimental spectrum of tantalum is shown superimposed over the emission spectrum of aluminum on diagrammatic form. Good correspondence is seen between the 3d to 4F emissions of tantalum and helium like aluminum. Plasma pumping is obtained by exposure of a tantalum target to laser rays.

  3. Excitation of the symmetry forbidden bending mode in molecular photoionization

    NASA Astrophysics Data System (ADS)

    Miller, J. Scott; Poliakoff, E. D.; Miller, Thomas F.; Natalense, Alexandra P. P.; Lucchese, Robert R.

    2001-03-01

    We present results on the energy dependence of the vibrational branching ratio for the bending mode in CO2 3σu-1 photoionization. Specifically, we determine the v+=(0,1,0)/v+=(0,0,0) intensity ratio by detecting dispersed fluorescence from the electronically excited photoions. The results exhibit large deviations over a very wide energy range, 18photoionization spectroscopies. The magnitude of these deviations display the utility of vibrationally resolved studies, and the extent over which these changes occur underscores the necessity of broad range studies to elucidate slowly varying characteristics in photoionization continua.

  4. Rotationally resolved fluorescence as a probe of molecular photoionization dynamics

    NASA Astrophysics Data System (ADS)

    Kakar, Sandeep; Choi, Heung-Cheun; Poliakoff, E. D.

    1992-11-01

    We present rotationally resolved data for the v'=0 and v'=1 levels of N2+(B 2Σu+) produced via 2σu-1 photoionization of N2. The data are obtained over a broad photon energy range (19≤hνexc≤35 eV). This is made possible by using synchrotron radiation excitation in conjunction with dispersed fluorescence detection. The results exhibit both resonant and nonresonant effects.

  5. Precision measurements on the photoionization of neutral atomic species

    NASA Astrophysics Data System (ADS)

    Stolte, Wayne

    2016-05-01

    In contrast to studies on rare gas atoms, experimental studies of open-shell atoms offers very challenging problems, such as creation of the atom, low signal, purity and stability. Because of this, studies of inner-shell excitations for open shell atoms are limited. In this talk I will discuss precision experimental measurements for photoionization of atomic oxygen, nitrogen, and chlorine over the last two decades on various beamlines at Lawrence Berkeley National Laboratories, Advanced Light Source.

  6. Lyman alpha initiated winds in late-type stars

    NASA Technical Reports Server (NTRS)

    Haisch, B. M.; Linsky, J. L.; Vanderhucht, K. A.

    1979-01-01

    The IUE survey of late-type stars revealed a sharp division in the HR diagram between stars with solar type spectra (chromosphere and transition region lines) and those with non-solar type spectra (only chromosphere lines). Models of both hot coronae and cool wind flows were calculated using stellar model chromospheres as starting points for stellar wind calculations in order to investigate the possibility of having a supersonic transition locus in the HR diagram dividing hot coronae from cool winds. From these models, it is concluded that the Lyman alpha flux may play an important role in determining the location of a stellar wind critical point. The interaction of Lyman alpha radiation pressure with Alfven waves in producing strong, low temperature stellar winds in the star Arcturus is examined.

  7. Photoionization sensors for non-invasive medical diagnostics

    NASA Astrophysics Data System (ADS)

    Mustafaev, Aleksandr; Rastvorova, Iuliia; Khobnya, Kristina; Podenko, Sofia

    2016-09-01

    The analysis of biomarkers can help to identify the significant number of diseases: lung cancer, tuberculosis, diabetes, high levels of stress, psychosomatic disorders etc. To implement continuous monitoring of the state of human health, compact VUV photoionization detector with current-voltage measurement is designed by Saint-Petersburg Mining University Plasma Research Group. This sensor is based on the patented method of stabilization of electric parameters - CES (Collisional Electron Spectroscopy). During the operation at atmospheric pressure VUV photoionization sensor measures the energy of electrons, produced in the ionization with the resonance photons, whose wavelength situated in the vacuum ultraviolet (VUV). A special software was developed to obtain the second-order derivative of the I-U characteristics, taken by the VUV sensor, to construct the energy spectra of the characteristic electrons. VUV photoionization detector has an unique set of parameters: small size (10*10*1 mm), low cost, wide range of recognizable molecules, as well as accuracy, sufficient for using this instrument for the medical purposes. This device can be used for non-invasive medical diagnostics without compromising the quality of life, for control of environment and human life. Work supported by Foundation for Assistance to Small Innovative Enterprises in Science and Technology.

  8. Photoionization Modeling and the K Lines of Iron

    NASA Technical Reports Server (NTRS)

    Kallman, T. R.; Palmeri, P.; Bautista, M. A.; Mendoza, C.; Krolik, J. H.

    2004-01-01

    We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases, and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7-9 keV energy band. We show that the centroid of the ensemble of K(alpha) lines, the K(beta) energy, and the ratio of the K(alpha(sub 1)) to K(alpha(sub 2)) components are all diagnostics of the ionization parameter of our model slabs.

  9. Turbulence in giant molecular clouds: the effect of photoionization feedback

    NASA Astrophysics Data System (ADS)

    Boneberg, D. M.; Dale, J. E.; Girichidis, P.; Ercolano, B.

    2015-02-01

    Giant molecular clouds (GMCs) are observed to be turbulent, but theory shows that without a driving mechanism turbulence should quickly decay. The question arises by which mechanisms turbulence is driven or sustained. It has been shown that photoionizing feedback from massive stars has an impact on the surrounding GMC and can for example create vast H II bubbles. We therefore address the question of whether turbulence is a consequence of this effect of feedback on the cloud. To investigate this, we analyse the velocity field of simulations of high-mass star-forming regions by studying velocity structure functions and power spectra. We find that clouds whose morphology is strongly affected by photoionizing feedback also show evidence of driving of turbulence by preserving or recovering a Kolmogorov-type velocity field. On the contrary, control run simulations without photoionizing feedback have a velocity distribution that bears the signature of gravitational collapse and of the dissipation of energy, where the initial Kolmogorov-type structure function is erased.

  10. 2s photoionization and subsequent Auger cascade in atomic Si

    SciTech Connect

    Partanen, L.; Fritzsche, S.; Jaenkaelae, K.; Huttula, M.; Osmekhin, S.; Aksela, H.; Aksela, S.; Urpelainen, S.

    2010-06-15

    The 2s photoionization and subsequent Auger transition cascade in atomic Si were studied by means of synchrotron-radiation-induced electron spectroscopy. After the 2s photoionization, the core hole states decay predominantly by a two-step Auger transition cascade into the triply ionized [Ne]nl states. The ionization channels of the 2s core-ionized Si{sup +} atoms to Si{sup 3+} ions were observed by measuring the conventional Auger electron spectra of the L{sub 1}-L{sub 2,3}M Coster-Kronig transitions and the L{sub 2,3}M-MMM Auger transitions. The observed L{sub 1}-L{sub 2,3}M and L{sub 2,3}M-MMM Auger spectra were analyzed by means of extensive multiconfiguration Dirac-Fock computations. We found that the electron correlation plays a prominent role in the Auger cascade, especially for the final-step Auger L{sub 2,3}M-MMM spectrum. Additionally, it was seen that the L{sub 2,3}M-MMM Auger spectrum of Si includes more Auger groups than the isoelectronic L{sub 2,3}-MM Auger spectrum of Al. Thus, more information on the intermediate ionic states is obtained if they are produced by Auger cascade rather than by direct photoionization.

  11. Solvent jet desorption capillary photoionization-mass spectrometry.

    PubMed

    Haapala, Markus; Teppo, Jaakko; Ollikainen, Elisa; Kiiski, Iiro; Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

    2015-03-17

    A new ambient mass spectrometry method, solvent jet desorption capillary photoionization (DCPI), is described. The method uses a solvent jet generated by a coaxial nebulizer operated at ambient conditions with nitrogen as nebulizer gas. The solvent jet is directed onto a sample surface, from which analytes are extracted into the solvent and ejected from the surface in secondary droplets formed in collisions between the jet and the sample surface. The secondary droplets are directed into the heated capillary photoionization (CPI) device, where the droplets are vaporized and the gaseous analytes are ionized by 10 eV photons generated by a vacuum ultraviolet (VUV) krypton discharge lamp. As the CPI device is directly connected to the extended capillary inlet of the MS, high ion transfer efficiency to the vacuum of MS is achieved. The solvent jet DCPI provides several advantages: high sensitivity for nonpolar and polar compounds with limit of detection down to low fmol levels, capability of analyzing small and large molecules, and good spatial resolution (250 μm). Two ionization mechanisms are involved in DCPI: atmospheric pressure photoionization, capable of ionizing polar and nonpolar compounds, and solvent assisted inlet ionization capable of ionizing larger molecules like peptides. The feasibility of DCPI was successfully tested in the analysis of polar and nonpolar compounds in sage leaves and chili pepper.

  12. Vacuum ultraviolet (VUV) photoionization of small water clusters.

    PubMed

    Belau, Leonid; Wilson, Kevin R; Leone, Stephen R; Ahmed, Musahid

    2007-10-11

    Tunable vacuum ultraviolet (VUV) photoionization studies of water clusters are performed using 10-14 eV synchrotron radiation and analyzed by reflectron time-of-flight (TOF) mass spectrometry. Photoionization efficiency (PIE) curves for protonated water clusters (H2O)(n)H+ are measured with 50 meV energy resolution. The appearance energies of a series of protonated water clusters are determined from the photoionization threshold for clusters composed of up to 79 molecules. These appearance energies represent an upper limit of the adiabatic ionization energy of the corresponding parent neutral water cluster in the supersonic molecular beam. The experimental results show a sharp drop in the appearance energy for the small neutral water clusters (from 12.62 +/- 0.05 to 10.94 +/- 0.06 eV, for H2O and (H2O)4, respectively), followed by a gradual decrease for clusters up to (H2O)23 converging to a value of 10.6 eV (+/-0.2 eV). The dissociation energy to remove a water molecule from the corresponding neutral water cluster is derived through thermodynamic cycles utilizing the dissociation energies of protonated water clusters reported previously in the literature. The experimental results show a gradual decrease of the dissociation energy for removal of one water molecule for small neutral water clusters (3

  13. Excitons in Cuprous Oxide: Photoionization and Other Multiphoton Processes

    NASA Astrophysics Data System (ADS)

    Frazer, Nicholas Laszlo

    In cuprous oxide (Cu2O), momentum from the absorption of two infrared photons to make an orthoexciton is conserved and detected through the photon component of a resulting mixed exciton/photon (quadrupole exciton polariton) state. I demonstrated that this process, which actually makes the photon momentum more precisely defined, is disrupted by photoionization of excitons. Some processes are known to affect exciton propagation in both the pump and exciton stages, such as phonon emission, exciton-exciton (Auger) scattering, and third harmonic generation. These processes alone were not able to explain all observed losses of excitons or all detected scattering products, which lead me to design an optical pump-probe experiment to measure the exciton photoionization cross section, which is (3.9+/-0.2) x 10-22 m2. This dissertation describes the synthesis of cuprous oxide crystals using oxidation of copper, crystallization from melt with the optical floating zone method, and annealing. The cuprous oxide crystals were characterized using time and space resolved luminescence, leading to the discovery of new defect properties. Selection rules and overall efficiency of third harmonic generation in these crystals were characterized. Exciton photoionization was demonstrated through the depletion of polariton luminescence by an optical probe, the production of phonon linked luminescence as a scattering product, temporal delay of the probe, and time resolved luminescence. The results are integrated with the traditional dynamical model of exciton densities. An additional investigation of copper/cuprous oxide/gold photovoltaic devices is appended.

  14. VUV photoionization cross sections of HO2, H2O2, and H2CO.

    PubMed

    Dodson, Leah G; Shen, Linhan; Savee, John D; Eddingsaas, Nathan C; Welz, Oliver; Taatjes, Craig A; Osborn, David L; Sander, Stanley P; Okumura, Mitchio

    2015-02-26

    The absolute vacuum ultraviolet (VUV) photoionization spectra of the hydroperoxyl radical (HO2), hydrogen peroxide (H2O2), and formaldehyde (H2CO) have been measured from their first ionization thresholds to 12.008 eV. HO2, H2O2, and H2CO were generated from the oxidation of methanol initiated by pulsed-laser-photolysis of Cl2 in a low-pressure slow flow reactor. Reactants, intermediates, and products were detected by time-resolved multiplexed synchrotron photoionization mass spectrometry. Absolute concentrations were obtained from the time-dependent photoion signals by modeling the kinetics of the methanol oxidation chemistry. Photoionization cross sections were determined at several photon energies relative to the cross section of methanol, which was in turn determined relative to that of propene. These measurements were used to place relative photoionization spectra of HO2, H2O2, and H2CO on an absolute scale, resulting in absolute photoionization spectra.

  15. Femtosecond pump-probe photoionization-photofragmentation spectroscopy: Photoionization-induced twisting and coherent vibrational motion of azobenzene cation

    NASA Astrophysics Data System (ADS)

    Ho-Wei, Jr.; Chen, Wei-Kan; Cheng, Po-Yuan

    2009-10-01

    We report studies of ultrafast dynamics of azobenzene cation using femtosecond photoionization-photofragmentation spectroscopy. In our experiments, a femtosecond pump pulse first produces an ensemble of azobenzene cations via photoionization of the neutrals. A delayed probe pulse then brings the evolving ionic system to excited states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cation are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place in this time scale.

  16. Progress Toward Attractive Stellarators

    SciTech Connect

    Neilson, G H; Brown, T G; Gates, D A; Lu, K P; Zarnstorff, M C; Boozer, A H; Harris, J H; Meneghini, O; Mynick, H E; Pomphrey, N; Reiman, A H; Xanthopoulos, P

    2011-01-05

    The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.

  17. Stellar Ontogeny: From Dust...

    ERIC Educational Resources Information Center

    MOSAIC, 1978

    1978-01-01

    Discusses the process of star formation. Infrared and radio astronomy, particularly microwave astronomy is used to provide information on different stages of stellar formation. The role of dust and gas which swirl through the interstellar regions of a galaxy and the collapse of a cloud in star formation are also presented. (HM)

  18. Stellar Ontogeny: From Dust...

    ERIC Educational Resources Information Center

    MOSAIC, 1978

    1978-01-01

    Discusses the process of star formation. Infrared and radio astronomy, particularly microwave astronomy is used to provide information on different stages of stellar formation. The role of dust and gas which swirl through the interstellar regions of a galaxy and the collapse of a cloud in star formation are also presented. (HM)

  19. A Stellar Demonstrator

    ERIC Educational Resources Information Center

    Ros, Rosa M.

    2009-01-01

    The main purpose of the stellar demonstrator is to help explain the movement of stars. In particular, students have difficulties understanding why, if they are living in the Northern Hemisphere, they may observe starts in the Southern Hemisphere, or why circumpolar stars are not the same in different parts of Europe. Using the demonstrator, these…

  20. Introduction to Stellar Astrophysics

    NASA Astrophysics Data System (ADS)

    Böhm-Vitense, Erika

    1992-01-01

    This book is the final one in a series of three texts which together provide a modern, complete and authoritative account of our present knowledge of the stars. It discusses the internal structure and the evolution of stars, and is completely self-contained. There is an emphasis on the basic physics governing stellar structure and the basic ideas on which our understanding of stellar structure is based. The book also provides a comprehensive discussion of stellar evolution. Careful comparison is made between theory and observation, and the author has thus provided a lucid and balanced introductory text for the student. As for volumes 1 and 2, volume 3 is self-contained and can be used as an independent textbook. The author has not only taught but has also published many original papers in this subject. Her clear and readable style should make this text a first choice for undergraduate and beginning graduate students taking courses in astronomy and particularly in stellar astrophysics.