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Sample records for supergiant star vy

  1. Diffraction-limited Speckle-Masking Interferometry of the Red Supergiant VY CMa

    CERN Document Server

    Wittkowski, M; Weigelt, G

    1998-01-01

    We present the first diffraction-limited images of the mass-loss envelope of the red supergiant star VY CMa. The two-dimensional optical and NIR images were reconstructed from 3.6 m telescope speckle data using bispectrum speckle interferometry. At the wavelengths ~0.8 \\mum (RG 780 filter), 1.28 \\mum, and 2.17 \\mum the diffraction-limited resolutions of 46 mas, 73 mas, and 124 mas were achieved. All images clearly show that the circumstellar envelope of VY CMa is non-spherical. The RG 780, 1.28 \\mum, and 2.17 mum FWHM Gauss fit diameters are 67 mas * 83 mas, 80 mas * 116 mas and 138 mas * 205 mas, respectively, or 100 AU * 125 AU, 120 AU * 174 AU and 207 AU * 308 AU (for a distance of 1500 pc). We discuss several interpretations for the asymmetric morphology. Combining recent results about the angular momentum evolution of red supergiants and their pulsational properties, we suggest that VY CMa is an immediate progenitor of IRC +10420, a post red supergiant during its transformation into a Wolf-Rayet star.

  2. ALMA observations of anisotropic dust mass loss in the inner circumstellar environment of the red supergiant VY Canis Majoris

    NARCIS (Netherlands)

    O'Gorman, E.; Vlemmings, W.; Richards, A.M.S.; Baudry, A.; De Beck, E.; Decin, L.; Harper, G.M.; Humphreys, E.M.; Kervella, P.; Khouri, T.; Muller, S.

    2015-01-01

    The processes leading to dust formation and the subsequent role it plays in driving mass loss in cool evolved stars is an area of intense study. Here we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These

  3. ALMA observations of anisotropic dust mass loss in the inner circumstellar environment of the red supergiant VY Canis Majoris

    NARCIS (Netherlands)

    O'Gorman, E.; Vlemmings, W.; Richards, A.M.S.; Baudry, A.; De Beck, E.; Decin, L.; Harper, G.M.; Humphreys, E.M.; Kervella, P.; Khouri, T.; Muller, S.

    2015-01-01

    The processes leading to dust formation and the subsequent role it plays in driving mass loss in cool evolved stars is an area of intense study. Here we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These

  4. PACS and SPIRE Spectroscopy of the Red Supergiant VY CMa

    CERN Document Server

    Royer, P; Wesson, R; Barlow, M J; Polehampton, E T; Matsuura, M; Agundez, M; Blommaert, J A D L; Cernicharo, J; Cohen, M; Daniel, F; Degroote, P; De Meester, W; Exter, K; Feuchtgruber, H; Gear, W K; Gomez, H L; Groenewegen, M A T; Hargrave, P C; Huygen, R; Imhof, P; Ivison, R J; Jean, C; Kerschbaum, F; Leeks, S J; Lim, T; Lombaert, R; Olofsson, G; Posch, T; Regibo, S; Savini, G; Sibthorpe, B; Swinyard, B M; Vandenbussche, B; Waelkens, C; Witherick, D K; Yates, J A

    2010-01-01

    With a luminosity > 10^5 Lsun and a mass-loss rate of about 2.10-4 Msun/yr, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VYCMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55 to 672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as 1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.

  5. Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa

    CERN Document Server

    Decin, L; De Koter, A; Justtanont, K; Tielens, A G G M; Waters, L B F M

    2006-01-01

    Context: Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of variations in the mass-loss history of such objects. Aims: By modelling the full line profile of low excitation CO lines emitted in the circumstellar envelope, we can study the mass-loss history of AGB stars. Methods: We have developed a non-LTE radiative transfer code, which calculates the velocity structure and gas kinetic temperature of the envelope in a self-consistent way. The resulting structure of the envelope provides the input for the molecular line radiative calculations which are evaluated in the comoving frame. The code allows for the implementation of modulations in the mass-loss rate. This code has been benchmarked against other radiative transfer codes and is shown to perform well and efficiently. Results: W...

  6. Mass loss from giant and supergiant stars

    Science.gov (United States)

    Wannier, P. G.; Sahai, R.

    1986-01-01

    The 12 m telescope of the National Radio Astronomy Observatory has been used at the J = 2-1 transition of CO to increase the known list of giant and supergiant stars with observable circumstellar envelopes. The candidate objects were generally M-type giants and supergiants, chosen for their strong infrared luminosities. Of the 35 objects which were previously undetected, or only marginally detected, 10 were found to produce detectable CO emission. Physical parameters of the envelopes are derived by source modeling. Mass-loss rates vary from 10 to the -7th to 4 x 10 to the -5th solar mass/yr.

  7. ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY CMa

    CERN Document Server

    O'Gorman, E; Richards, A M S; Baudry, A; De Beck, E; Decin, L; Harper, G M; Humphreys, E M; Kervella, P; Khouri, T; Muller, S

    2014-01-01

    The processes leading to dust formation and the subsequent role it plays in driving mass-loss in cool evolved stars is an area of intense study. Here, we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, allowing us to trace dust on spatial scales down to 11 R$_{\\star}$ (71 AU). Two prominent dust components are detected and resolved. The brightest dust component, C, is located 334 mas (61 R$_{\\star}$) south-east of the star and has a dust mass of at least $2.5\\times 10^{-4} $M$_{\\odot}$. It has an emissivity spectral index of $\\beta =-0.1$ at its peak, implying that it is either optically thick at these frequencies with a cool core of $T_{d}\\lesssim 100$ K, and/or contains very large dust grains. Interestingly, not a single molecule in the ALMA data has emission close to th...

  8. Herschel SPIRE and PACS observations of the red supergiant VY CMa: analysis of the molecular line spectra

    CERN Document Server

    Matsuura, Mikako; Barlow, M J; Swinyard, B M; Royer, P; Cernicharo, J; Decin, L; Wesson, R; Polehampton, E T; Blommaert, J A D L; Groenewegen, M A T; Van de Steene, G C; van Hoof, P A M

    2013-01-01

    We present an analysis of the far-infrared and submillimetre molecular emission line spectrum of the luminous M-supergiant VY CMa, observed with the SPIRE and PACS spectrometers aboard the Herschel Space Observatory. Over 260 emission lines were detected in the 190-650-micron SPIRE FTS spectra, with one-third of the observed lines being attributable to H2O. Other detected species include CO, 13CO, H2^18O, SiO, HCN, SO, SO2, CS, H2S, and NH3. Our model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio of 5.6+-1.8, consistent with measurements of this ratio for other M supergiants, but significantly lower than previously estimated for VY CMa from observations of lower-J lines. The spectral line energy distribution for twenty SiO rotational lines shows two temperature components: a hot component at 1000 K, which we attribute to the stellar atmosphere and inner wind, plus a cooler ~200 K component, which we attribute to an origin in the outer circumstellar envelope. We fit the line fluxes ...

  9. Vigorous atmospheric motion in the red supergiant star Antares

    Science.gov (United States)

    Ohnaka, K.; Weigelt, G.; Hofmann, K.-H.

    2017-08-01

    Red supergiant stars represent a late stage of the evolution of stars more massive than about nine solar masses, in which they develop complex, multi-component atmospheres. Bright spots have been detected in the atmosphere of red supergiants using interferometric imaging. Above the photosphere of a red supergiant, the molecular outer atmosphere extends up to about two stellar radii. Furthermore, the hot chromosphere (5,000 to 8,000 kelvin) and cool gas (less than 3,500 kelvin) of a red supergiant coexist at about three stellar radii. The dynamics of such complex atmospheres has been probed by ultraviolet and optical spectroscopy. The most direct approach, however, is to measure the velocity of gas at each position over the image of stars as in observations of the Sun. Here we report the mapping of the velocity field over the surface and atmosphere of the nearby red supergiant Antares. The two-dimensional velocity field map obtained from our near-infrared spectro-interferometric imaging reveals vigorous upwelling and downdrafting motions of several huge gas clumps at velocities ranging from about -20 to +20 kilometres per second in the atmosphere, which extends out to about 1.7 stellar radii. Convection alone cannot explain the observed turbulent motions and atmospheric extension, suggesting that an unidentified process is operating in the extended atmosphere.

  10. Mass Losing Asymptotic Giant Branch Stars and Supergiants

    CERN Document Server

    Whitelock, Patricia A; Höfner, Susanne; Wittkowski, Markus; Zijlstra, Albert A

    2016-01-01

    This paper presents a summary of four invited and twelve contributed presentations on asymptotic giant branch stars and red supergiants, given over the course of two afternoon splinter sessions at the 19th Cool Stars Workshop. It highlights both recent observations and recent theory, with some emphasis on high spatial resolution, over a wide range of wavelengths. Topics covered include 3D models, convection, binary interactions, mass loss, dust formation and magnetic fields.

  11. Blue supergiants as descendants of magnetic main sequence stars

    Science.gov (United States)

    Petermann, I.; Langer, N.; Castro, N.; Fossati, L.

    2015-12-01

    About 10% of the massive main sequence stars have recently been found to host a strong, large scale magnetic field. Both, the origin and the evolutionary consequences of these fields are largely unknown. We argue that these fields may be sufficiently strong in the deep interior of the stars to suppress convection near the outer edge of their convective core. We performed parametrised stellar evolution calculations and assumed a reduced size of the convective core for stars in the mass range 16M⊙ to 28M⊙ from the zero age main sequence until core carbon depletion. We find that such models avoid the coolest part of the main sequence band, which is usually filled by evolutionary models that include convective core overshooting. Furthermore, our "magnetic" models populate the blue supergiant region during core helium burning, i.e., the post-main sequence gap left by ordinary single star models, and some of them end their life in a position near that of the progenitor of Supernova 1987A in the Hertzsprung-Russell diagram. Further effects include a strongly reduced luminosity during the red supergiant stage, and downward shift of the limiting initial mass for white dwarf and neutron star formation.

  12. The dust condensation sequence in red super-giant stars

    CERN Document Server

    Verhoelst, T; Hony, S; Decin, L; Cami, J; Eriksson, K

    2009-01-01

    Context: Red super-giant (RSG) stars exhibit significant mass loss through a slow and dense wind. They are often considered to be the more massive counter parts of Asymptotic Giant Branch (AGB) stars. While the AGB mass loss is linked to their strong pulsations, the RSG are often only weakly variable. Aim: To study the conditions at the base of the wind, by determining the dust composition in a sample of RSG. The dust composition is thought to be sensitive to the density, temperature and acceleration at the base of the wind. Method: We compile a sample of 27 RSG infrared spectra (ISO-SWS) and supplement these with photometric measurements to obtain the full spectral energy distribution (SED). These data are modelled using a dust radiative transfer code. The results are scrutinised for correlations. Results: We find (1) strong correlations between dust composition, mass-loss rate and stellar luminosity, roughly in agreement with the theoretical dust condensation sequence, (2) the need for a continuous (near-)I...

  13. RAPID FLUCTUATIONS OF WATER MASER EMISSION IN VY CMa

    Institute of Scientific and Technical Information of China (English)

    ZhengXingwu; EugenioScaliseJr; HanFu

    1999-01-01

    The monitoring observations of the short- time variation of the water maser to-ward the supergiant star of VY CMa were carried out from August 26 through September 24 1993, using the 13.7 m telescope at the Qinghai station of the Purple

  14. Dust-forming molecules in VY Canis Majoris (and Betelgeuse)

    CERN Document Server

    Kaminski, T; Schmidt, M R; Patel, N A; Young, K H; Menten, K M; Brunken, S; Muller, H S P; Winters, J M; McCarthy, M C

    2013-01-01

    The formation of inorganic dust in circumstellar environments of evolved stars is poorly understood. Spectra of molecules thought to be most important for the nucleation, i.e. AlO, TiO, and TiO2, have been recently detected in the red supergiant VY CMa. These molecules are effectively formed in VY CMa and the observations suggest that non-equilibrium chemistry must be involved in their formation and nucleation into dust. In addition to exploring the recent observations of VY CMa, we briefly discuss the possibility of detecting these molecules in the dust-poor circumstellar environment of Betelgeuse.

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

    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

  17. Near-infrared spectroscopy of candidate red supergiant stars in clusters

    CERN Document Server

    Messineo, Maria; Ivanov, Valentin D; Figer, Donald F; Davies, Ben; Menten, Karl M; Kudritzki, Rolf P; Chen, C -H Rosie

    2014-01-01

    Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks < 7 mag) in GLIMPSE and 2MASS images. A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 Msun to 15 Msun. Two red supergiants are located at Galactic coordinates (l,b)=(16.7deg,-0.63deg) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b)=(49.3deg,+0.72deg) and at a distance of ~7.0 kpc. Spectroscopic analysis of the brightest stars of detected overdensities and st...

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

    CERN Document Server

    Bozzo, E; Feldmeier, A; Falanga, M

    2016-01-01

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

  19. Probing the structure and dynamics of B[e] supergiant stars' disks

    Science.gov (United States)

    Kraus, M.

    2016-08-01

    B[e] supergiants are a group of evolved massive stars in a short-lived transition phase. During this phase, these objects eject large amounts of material, which accumulates in a circumstellar ring or disk-like structure, revolving around the star on Keplerian orbits. In most objects, the disks seem to be stable over many decades. This guarantees these disks as ideal chemical laboratories to study molecule formation and dust condensation. Combining high-resolution optical and infrared spectroscopic data allows to search for emission features that trace the disk structure, kinematics, and chemical composition at different distances from the star. Certain forbidden emission lines of singly ionized or neutral metals, such as [Caii] and [Oi], are ideal tracers for the innermost gaseous (atomic) regions. Farther out, molecules form. While first-overtone bands of carbon monoxide (CO) mark the hot, inner rim of the molecular disk, more molecules are expected to form and to fill the space between the CO emitting region and the dust condensation zone. Observing campaigns have been initiated to search for these molecules and their emission features, in order to construct a global picture of the properties of the disks around B[e] supergiants. This paper presents an overview of the status of our knowledge about the structure and kinematics of B[e] supergiant stars' disks, based on currently available information from different observational tracers.

  20. Luminous and Variable Stars in M31 and M33. III. The Yellow and Red Supergiants and Post-Red Supergiant Evolution

    CERN Document Server

    Gordon, Michael S; Jones, Terry J

    2016-01-01

    Recent supernova and transient surveys have revealed an increasing number of non-terminal stellar eruptions. Though the progenitor class of these eruptions includes the most luminous stars, little is known of the pre-supernova mechanics of massive stars in their most evolved state, thus motivating a census of possible progenitors. From surveys of evolved and unstable luminous star populations in nearby galaxies, we select a sample of yellow and red supergiant candidates in M31 and M33 for review of their spectral characteristics and spectral energy distributions. Since the position of intermediate and late-type supergiants on the color-magnitude diagram can be heavily contaminated by foreground dwarfs, we employ spectral classification and multi-band photometry from optical and near-infrared surveys to confirm membership. Based on spectroscopic evidence for mass loss and the presence of circumstellar dust in their SEDs, we find that $30-40\\%$ of the yellow supergiants are likely in a post-red supergiant state...

  1. The chemistry of dust formation in red supergiants

    CERN Document Server

    Cherchneff, Isabelle

    2013-01-01

    Massive stars in their late stages of evolution as Red Supergiants experience mass loss. The resulting winds show various degrees of dynamical and chemical complexity and produce molecules and dust grains. This review summarises our knowledge of the molecular and dust components of the wind of Red Supergiants, including VY CMa and Betelgeuse. We discuss the synthesis of dust as a non-equilibrium process in stellar winds, and present the current knowledge of the chemistry involved in the formation of oxygen-rich dust such as silicates and metal oxides.

  2. RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES. III. NLTE EFFECTS IN J-BAND MAGNESIUM LINES

    Energy Technology Data Exchange (ETDEWEB)

    Bergemann, Maria [Max-Planck Institute for Astronomy, D-69117, Heidelberg (Germany); Kudritzki, Rolf-Peter; Gazak, Zach [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Davies, Ben [University of Liverpool (United Kingdom); Plez, Bertrand, E-mail: bergemann@mpia-hd.mpg.de, E-mail: kud@ifa.hawaii.edu, E-mail: zgazak@ifa.hawaii.edu, E-mail: bdavies@ast.cam.ac.uk, E-mail: bertrand.plez@univ-montp2.fr [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France)

    2015-05-10

    Non-local thermodynamic equilibrium (NLTE) calculations for Mg i in red supergiant stellar atmospheres are presented to investigate the importance of NLTE for the formation of Mg i lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated this technique is a very promising tool for investigating the chemical composition of the young stellar population in star forming galaxies. As in previous work, where NLTE effects were studied for iron, titanium, and silicon, substantial effects are found resulting in significantly stronger Mg i absorption lines. For the quantitative spectral analysis the NLTE effects lead to magnesium abundances significantly smaller than in local thermodynamic equilibrium with the NLTE abundance corrections varying smoothly between −0.4 dex and −0.1 dex for effective temperatures between 3400 and 4400 K. We discuss the physical reasons of the NLTE effects and the consequences for extragalactic J-band abundance studies using individual red supergiants in the young massive galactic double cluster h and χ Persei.

  3. The Coolest Stars in the Clouds: Unusual Red Supergiants in the Magellanic Clouds

    CERN Document Server

    Levesque, Emily M; Olsen, K A G; Plez, Bertrand

    2007-01-01

    Red supergiants (RSGs) are a He-burning phase in the evolution of moderately high mass stars (10-25 solar masses). The evolution of these stars, particularly at low metallicities, is still poorly understood. The latest-type RSGs in the Magellanic Clouds are cooler than the current evolutionary tracks allow, occupying the region to the right of the Hayashi limit where stars are no longer in hydrodynamic equilibrium. We have discovered four Cloud RSGs in this region that display remarkably similar unusual behavior. All of them show considerable variations in their V magnitudes and effective temperatures (and spectral types). Two of these stars, HV 11423 and [M2002] SMC 055188, have been observed in an M4.5 I state, considerably later and cooler than any other supergiant in the SMC. These stars suffer dramatic physical changes on timescales of months - when they are at their warmest, they are also brighter, more luminous, and show an increased amount of extinction. This variable extinction is characteristic of t...

  4. ALMA observations of the supergiant B[e] star Wd1-9

    Science.gov (United States)

    Fenech, D. M.; Clark, J. S.; Prinja, R. K.; Morford, J. C.; Dougherty, S.; Blomme, R.

    2017-01-01

    Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible - radiatively driven winds, impulsive ejection and/or binary interaction - remain uncertain. In this Letter, we present Atacama Large Millimetre/Submillimeter Array line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-main-sequence object located within the starburst cluster Westerlund 1 (Wd1). We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41α radio recombination line. We attribute these properties to a low velocity (˜100 km s-1 ) ionized wind, with an extreme mass-loss rate ≳6.4 × 10-5(d/5 kpc)1.5 M⊙yr- 1. External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A. We conclude that these objects are interacting binaries evolving away from the main sequence and undergoing rapid case-A mass transfer. As such they - and by extension the wider class of supergiant B[e] stars - may provide a unique window into the physics of a process that shapes the life-cycle of ˜70 per cent of massive stars found in binary systems.

  5. Spectroscopic Variability of Supergiant Star HD14134, B3Ia

    Indian Academy of Sciences (India)

    Y. M. Y. M. Maharramov

    2017-06-01

    Profile variations in the ${H}\\alpha$ and ${H}\\beta$ lines in the spectra of the star HD14134 are investigated using observations carried out in 2013–2014 and 2016 with the 2-m telescope at the Shamakhy Astrophysical Observatory. The absorption and emission components of the ${H}\\alpha$ line are found to disappear on some observational days, and two of the spectrograms exhibit inverse P-Cyg profile of ${H}\\alpha$. It was revealed that when the ${H}\\alpha$ line disappeared or an inversion of the P-Cyg-type profile is observed in the spectra, the ${H}\\beta$ line is displaced to the longer wavelengths, but no synchronous variabilities were observed in other spectral lines (CII λ 6578.05 Å, λ 6582.88 Å and HeI λ 5875.72 Å) formed in deeper layers of the stellar atmosphere. In addition, the profiles of the ${H}\\alpha$ and ${H}\\beta$ lines have been analysed, as well as their relations with possible expansion, contraction and mixed conditions of the atmosphere of HD14134. We suggest that the observational evidence for the non-stationary atmosphere of HD14134 can be associated in part with the non-spherical stellar wind.

  6. SiO and H2O Maser Observations of Red Supergiants in Star Clusters Embedded in the Galactic Disk

    Science.gov (United States)

    Deguchi, Shuji; Nakashima, Jun-Ichi; Zhang, Yong; Chong, Selina S. N.; Koike, Kazutaka; Kwok, Sun

    2010-04-01

    We present the results of radio observations of red supergiants in a star cluster, Stephenson (1990, AJ, 99, 1867)'s #2, and of candidates for red supergiants in three star clusters, Mercer et al. (2005, ApJ, 635, 560)'s #4, #8, and #13, in the SiO and H2O maser lines. The Stephenson's #2 cluster and nearby aggregation at the southwest contain more than 15 red supergiants. We detected one red supergiant at the center of Stephenson's #2 and three in a southwest aggregation in the SiO maser line; three out of these four were also detected in the H2O maser line. The average radial velocity of the four detected objects is 97 km s-1, giving a kinematic distance of 5.5 kpc, which locates this cluster near the base of the Scutum-Crux spiral arm. We also detected six SiO emitting objects associated with other star clusters. In addition, mapping observations in the CO J = 1-0 line toward these clusters revealed that an appreciable amount of molecular gas still remains around the Stephenson's #2 cluster in contrast to the prototypical red-supergiant cluster, Bica et al. (2003, A&A, 404, 223)'s #122. This indicates that the time scale of gas expulsion differs considerably in individual clusters.

  7. Discovery of magnetic A supergiants: the descendants of magnetic main-sequence B stars

    Science.gov (United States)

    Neiner, Coralie; Oksala, Mary E.; Georgy, Cyril; Przybilla, Norbert; Mathis, Stéphane; Wade, Gregg; Kondrak, Matthias; Fossati, Luca; Blazère, Aurore; Buysschaert, Bram; Grunhut, Jason

    2017-10-01

    In the context of the high resolution, high signal-to-noise ratio, high sensitivity, spectropolarimetric survey BritePol, which complements observations by the BRITE constellation of nanosatellites for asteroseismology, we are looking for and measuring the magnetic field of all stars brighter than V = 4. In this paper, we present circularly polarized spectra obtained with HarpsPol at ESO in La Silla (Chile) and ESPaDOnS at CFHT (Hawaii) for three hot evolved stars: ι Car, HR 3890 and ε CMa. We detected a magnetic field in all three stars. Each star has been observed several times to confirm the magnetic detections and check for variability. The stellar parameters of the three objects were determined and their evolutionary status was ascertained employing evolution models computed with the Geneva code. ε CMa was already known and is confirmed to be magnetic, but our modelling indicates that it is located near the end of the main sequence, i.e. it is still in a core hydrogen burning phase. ι Car and HR 3890 are the first discoveries of magnetic hot supergiants located well after the end of the main sequence on the Hertzsprung-Russell diagram. These stars are probably the descendants of main-sequence magnetic massive stars. Their current field strength (a few G) is compatible with magnetic flux conservation during stellar evolution. These results provide observational constraints for the development of future evolutionary models of hot stars including a fossil magnetic field.

  8. Three-micron spectra of AGB stars and supergiants in nearby galaxies

    CERN Document Server

    Matsuura, M; Van Loon, J T; Yamamura, I; Markwick, A J; Whitelock, P A; Woods, P M; Marshall, J R; Feast, M W; Waters, L B F M

    2005-01-01

    The dependence of stellar molecular bands on the metallicity is studied using infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB stars. The equivalent width of acetylene is found to be high even at low metallicity. The high C2H2 abundance can be explained with a high carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast, the HCN equivalent width is low: fewer than half of the extra-galactic carbon stars show the 3.5micron HCN band, and only a few LMC stars show high HCN equivalent width. HCN abundances are limited by both nitrogen and carbon elemental abundances. The amount of synthesized nitrogen depends on the initial mass, and stars with high luminosity (i.e. high initial mass) could have a high HCN abundance. CH bands are found in...

  9. GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC2

    CERN Document Server

    Origlia, L; Maiolino, R; Mucciarelli, A; Baffa, C; Biliotti, V; Bruno, P; Falcini, G; Gavriousev, V; Ghinassi, F; Giani, E; Gonzalez, M; Leone, F; Lodi, M; Massi, F; Montegriffo, P; Mochi, I; Pedani, M; Rossetti, E; Scuderi, S; Sozzi, M; Tozzi, A

    2013-01-01

    The inner disk of the Galaxy has a number of young star clusters dominated by red supergiants that are heavily obscured by dust extinction and observable only at infrared wavelengths. These clusters are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. During the technical commissioning and as a first science verification of the GIANO spectrograph at the Telescopio Nazionale Galileo, we secured high-resolution (R~50,000) near-infrared spectra of three red supergiants in the young Scutum cluster RSGC2. Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to identify several tens of atomic and molecular lines suitable for chemical abundance determinations. By means of spectral synthesis and line equivalent width measurements, we obtained abundances of Fe and other iron-peak elements such as V, Cr, Ni, of alpha (O, Mg, Si, Ca and Ti) and other light elements (C, N, Na, Al, K, Sc), and of some s-process elements (Y, Sr). ...

  10. GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC3

    CERN Document Server

    Origlia, L; Sanna, N; Mucciarelli, A; Dalessandro, E; Scuderi, S; Baffa, C; Biliotti, V; Carbonaro, L; Falcini, G; Giani, E; Iuzzolino, M; Massi, F; Sozzi, M; Tozzi, A; Ghedina, A; Ghinassi, F; Lodi, M; Harutyunyan, A; Pedani, M

    2015-01-01

    The Scutum complex in the inner disk of the Galaxy has a number of young star clusters dominated by red supergiants that are heavily obscured by dust extinction and observable only at infrared wavelengths. These clusters are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. During the technical commissioning and as a first science verification of the GIANO spectrograph at the Telescopio Nazionale Galileo, we secured high-resolution (R=50,000) near-infrared spectra of five red supergiants in the young Scutum cluster RSGC3. Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to measure several tens of atomic and molecular lines that were suitable for determining chemical abundances. By means of spectral synthesis and line equivalent width measurements, we obtained abundances of Fe and iron-peak elements such as Ni, Cr, and Cu, alpha (O, Mg, Si, Ca, Ti), other light elements (C, N, F, Na, Al, and Sc), and some s-process...

  11. RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES: KMOS OBSERVATIONS IN NGC 6822

    Energy Technology Data Exchange (ETDEWEB)

    Patrick, L. R.; Evans, C. J.; Ferguson, A. M. N. [Institute for Astronomy, University of Edinburgh, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Davies, B. [Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park ic2, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Kudritzki, R-P.; Gazak, J. Z. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Bergemann, M. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Plez, B. [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France)

    2015-04-10

    We present near-IR spectroscopy of red supergiant (RSG) stars in NGC 6822, obtained with the new K-band Multi-Object Spectrograph Very Large Telescope, Chile. From comparisons with model spectra in the J-band we determine the metallicity of 11 RSGs, finding a mean value of [Z] = −0.52 ± 0.21, which agrees well with previous abundance studies of young stars and H ii regions. We also find an indication for a low-significance abundance gradient within the central 1 kpc. We compare our results with those derived from older stellar populations and investigate the difference using a simple chemical evolution model. By comparing the physical properties determined for RSGs in NGC 6822 with those derived using the same technique in the Galaxy and the Magellanic Clouds, we show that there appears to be no significant temperature variation of RSGs with respect to metallicity, in contrast to recent evolutionary models.

  12. Complexes of triggered star formation in supergiant shell of Holmberg II.

    Science.gov (United States)

    Egorov, Oleg V.; Lozinskaya, Tatiana A.; Moiseev, Alexei V.; Shchekinov, Yuri A.

    2016-09-01

    We report a detailed analysis of all regions of current star formation in the walls of the supergiant H I shell (SGS) in the galaxy Holmberg II based on observations with a scanning Fabry-Perot interferometer at the 6-m SAO RAS telescope. We compare the structure and kinematics of ionized gas with that of atomic hydrogen and with the stellar population of the SGS. Our deep Hα images and archival images taken by the HST demonstrate that current star formation episodes are larger and more complicated than previously thought: they represent unified star-forming complexes with sizes of several hundred pc rather than `chains' of separate bright nebulae in the walls of the SGS. The fact that we are dealing with unified complexes is evidenced by identified faint shell-like structures of ionized and neutral gas which connect several distinct bright H II regions. Formation of such complexes is due to the feedback of stars with very inhomogeneous ambient gas in the walls of the SGS. The arguments supporting an idea about the triggering of star formation in SGS by the H I supershells collision are presented. We also found a faint ionized supershell inside the H I SGS expanding with a velocity of no greater than 10 - 15 km s-1. Five OB stars located inside the inner supershell are sufficient to account for its radiation, although a possibility of leakage of ionizing photons from bright H II regions is not ruled out as well.

  13. Complexes of triggered star formation in supergiant shell of Holmberg II

    Science.gov (United States)

    Egorov, Oleg V.; Lozinskaya, Tatiana A.; Moiseev, Alexei V.; Shchekinov, Yuri A.

    2017-01-01

    We report a detailed analysis of all regions of current star formation in the walls of the supergiant H I shell (SGS) in the galaxy Holmberg II based on observations with a scanning Fabry-Perot interferometer at the Russian 6-m telescope. We compare the structure and kinematics of ionized gas with that of atomic hydrogen and with the stellar population of the SGS. Our deep Hα images and archival images taken by the Hubble Space Telescope demonstrate that current star formation episodes are larger and more complicated than previously thought: they represent unified star-forming complexes with sizes of several hundred pc rather than `chains' of separate bright nebulae in the walls of the SGS. The fact that we are dealing with unified complexes is evidenced by identified faint shell-like structures of ionized and neutral gas which connect several distinct bright H II regions. Formation of such complexes is due to the feedback of stars with very inhomogeneous ambient gas in the walls of the SGS. The arguments supporting an idea about the triggering of star formation in SGS by the H I supershells collision are presented. We also found a faint ionized supershell inside the H I SGS expanding with a velocity of no greater than 10-15 km s-1. Five OB stars located inside the inner supershell are sufficient to account for its radiation, although a possibility of leakage of ionizing photons from bright H II regions is not ruled out as well.

  14. Luminous and Variable Stars in M31 and M33. III. The Yellow and Red Supergiants and Post-red Supergiant Evolution

    Science.gov (United States)

    Gordon, Michael S.; Humphreys, Roberta M.; Jones, Terry J.

    2016-07-01

    Recent supernova (SN) and transient surveys have revealed an increasing number of non-terminal stellar eruptions. Though the progenitor class of these eruptions includes the most luminous stars, little is known of the pre-SN mechanics of massive stars in their most evolved state, thus motivating a census of possible progenitors. From surveys of evolved and unstable luminous star populations in nearby galaxies, we select a sample of yellow and red supergiant (RSG) candidates in M31 and M33 for review of their spectral characteristics and spectral energy distributions (SEDs). Since the position of intermediate- and late-type supergiants on the color-magnitude diagram can be heavily contaminated by foreground dwarfs, we employ spectral classification and multi-band photometry from optical and near-infrared surveys to confirm membership. Based on spectroscopic evidence for mass loss and the presence of circumstellar (CS) dust in their SEDs, we find that 30%-40% of the yellow supergiants are likely in a post-RSG state. Comparison with evolutionary tracks shows that these mass-losing, post-RSGs have initial masses between 20 and 40 M ⊙. More than half of the observed RSGs in M31 and M33 are producing dusty CS ejecta. We also identify two new warm hypergiants in M31, J004621.05+421308.06 and J004051.59+403303.00, both of which are likely in a post-RSG state. Based on observations obtained with the Large Binocular Telescope (LBT), an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

  15. LMC Blue Supergiant Stars and the Calibration of the Flux-weighted Gravity-Luminosity Relationship

    Science.gov (United States)

    Urbaneja, M. A.; Kudritzki, R.-P.; Gieren, W.; Pietrzyński, G.; Bresolin, F.; Przybilla, N.

    2017-09-01

    High-quality spectra of 90 blue supergiant stars in the Large Magellanic Cloud are analyzed with respect to effective temperature, gravity, metallicity, reddening, extinction, and extinction law. An average metallicity, based on Fe and Mg abundances, relative to the Sun of [Z] = -0.35 ± 0.09 dex is obtained. The reddening distribution peaks at E(B-V) = 0.08 mag, but significantly larger values are also encountered. A wide distribution of the ratio of extinction to reddening is found ranging from {R}{{V}} = 2 to 6. The results are used to investigate the blue supergiant relationship between flux-weighted gravity, g f ≡ g/{T}{eff}4, and absolute bolometric magnitude M bol. The existence of a tight relationship, the Flux-weighted Gravity-Luminosity Relationship (FGLR), is confirmed. However, in contrast to previous work, the observations reveal that the FGLR is divided into two parts with a different slope. For flux-weighted gravities larger than 1.30 dex, the slope is similar to that found in previous work, but the relationship becomes significantly steeper for smaller values of the flux-weighted gravity. A new calibration of the FGLR for extragalactic distance determinations is provided.

  16. SiO and H2O Maser Observations of Red Supergiants in Star Clusters Embedded in the Galactic Disk

    CERN Document Server

    Deguchi, S; Zhang, Y; Chong, S S N; Koike, K; Kwok, S

    2010-01-01

    We present the result of radio observations of red supergiants in the star cluster, Stephenson's #2, and candidates for red supergiants in the star clusters, Mercer et al. (2005)'s #4, #8, and #13, in the SiO and H$_2$O maser lines.The Stephenson's #2 cluster and nearby aggregation at the South-West contain more than 15 red supergiants. We detected one at the center of Stephenson's #2 and three in the south-west aggregation in the SiO maser line, and three of these 4 were also detected in the H2O maser line. The average radial velocity of the 4 detected objects is 96 km s^{-1}, giving a kinematic distance of 5.5 kpc, which locates this cluster near the base of the Scutum-Crux spiral arm. We also detected 6 SiO emitting objects associated with the other star clusters. In addition, mapping observations in the CO J=1--0 line toward these clusters revealed that an appreciable amount of molecular gas still remains around Stephenson's #2 cluster in contrast to the prototypical red-supergiant cluster, Bica et al.'s ...

  17. Interferometric observations of the supergiant stars alpha Orionis and alpha Herculis with FLUOR at IOTA

    CERN Document Server

    Perrin, G; Foresto, V C; Mennesson, B; Traub, W A; Lacasse, M G

    2004-01-01

    We report the observations in the K band of the red supergiant star alpha Orionis and of the bright giant star alpha Herculis with the FLUOR beamcombiner at the IOTA interferometer. The high quality of the data allows us to estimate limb-darkening and derive precise diameters in the K band which combined with bolometric fluxes yield effective temperatures. In the case of Betelgeuse, data collected at high spatial frequency although sparse are compatible with circular symmetry and there is no clear evidence for departure from circular symmetry. We have combined the K band data with interferometric measurements in the L band and at 11.15 micron. The full set of data can be explained if a 2055 K layer with optical depths $\\tau_{K}=0.060\\pm0.003$, $\\tau_{L}=0.026\\pm0.002$ and $\\tau_{11.15\\mu m}=2.33\\pm0.23$ is added 0.33 $R_{\\star}$ above the photosphere providing a first consistent view of the star in this range of wavelengths. This layer provides a consistent explanation for at least three otherwise puzzling ob...

  18. Complexes of triggered star formation in supergiant shell of Holmberg II

    CERN Document Server

    Egorov, Oleg V; Moiseev, Alexei V; Shchekinov, Yuri A

    2016-01-01

    We report a detailed analysis of all regions of current star formation in the walls of the supergiant HI shell (SGS) in the galaxy Holmberg II based on observations with a scanning Fabry-Perot interferometer at the 6-m SAO RAS telescope. We compare the structure and kinematics of ionized gas with that of atomic hydrogen and with the stellar population of the SGS. Our deep H$\\alpha$ images and archival images taken by the HST demonstrate that current star formation episodes are larger and more complicated than previously thought: they represent unified star-forming complexes with sizes of several hundred pc rather than 'chains' of separate bright nebulae in the walls of the SGS. The fact that we are dealing with unified complexes is evidenced by identified faint shell-like structures of ionized and neutral gas which connect several distinct bright HII regions. Formation of such complexes is due to the feedback of stars with very inhomogeneous ambient gas in the walls of the SGS. The arguments supporting an ide...

  19. Chemical abundances for A-and F-type supergiant stars

    CERN Document Server

    Molina, R E

    2016-01-01

    We present the stellar parameters and elemental abundances of a set of A--F-type supergiant stars HD\\,45674, HD\\,180028, HD\\,194951 and HD\\,224893 using high resolution ($R$\\,$\\sim$\\,42,000) spectra taken from ELODIE library. We present the first results of the abundance analysis for HD\\,45674 and HD\\,224893. We reaffirm the abundances for HD\\,180028 and HD\\,194951 studied previously by Luck (2014) respectively. Alpha-elements indicates that objects belong to the thin disc population. From their abundances and its location on the Hertzsprung-Russell diagram seems point out that HD\\,45675, HD\\,194951 and HD\\,224893 are in the post-first dredge-up (post-1DUP) phase and they are moving in the red-blue loop region. HD~180028, on the contary, shows typical abundances of the population I but its evolutionary status could not be satisfactorily defined.

  20. Chemical abundances for A-and F-type supergiant stars

    Science.gov (United States)

    Molina, R. E.; Rivera, H.

    2016-04-01

    We present the stellar parameters and elemental abundances of a set of A-F-type supergiant stars HD 45674, HD 180028, HD 194951 and HD 224893 using high resolution (R≈ 42,000) spectra taken from ELODIE library. We present the first results of the abundance analysis for HD 45674 and HD 224893. We reaffirm the abundances for HD 180028 and HD 194951 studied previously by Luck. Alpha-elements indicate that the objects belong to the thin disc population. Their abundances and their location on the Hertzsprung-Russell diagram seem to indicate that HD 45675, HD 194951 and HD 224893 are in the post-first dredge-up (post-1DUP) phase, and that they are moving in the red-blue loop region. HD 180028, on the contary, shows typical abundances of Population I, but its evolutionary status cannot be satisfactorily defined.

  1. High-velocity Hα Absorption Events in B8 Ia - A2 Ia Supergiant Stars

    Science.gov (United States)

    Morrison, Nancy D.; Markova, N.; Rother, S. J.

    2009-12-01

    Late B- and early A-type supergiants are notorious for the time variability of their Hα line profiles, but the physical cause of the variations is poorly understood. Usually, the line is filled in by emission, and the blue absorption wing does not extend to the terminal wind speed, which is roughly defined by the blue edges of the ultraviolet resonance lines. On rare occasions, however, the blue wing of Hα goes strongly into absorption over a wide velocity range, from the photospheric velocity almost all the way to the terminal wind speed. This phenomenon was first described by Kaufer et al. (1996, A&A, 314, 599), who denoted it by the term, "High-Velocity Absorption Event." In this report, high-resolution spectra from Ritter Observatory will be combined with published spectra to examine the temporal recurrence behavior and strength distribution of high-velocity absorption events and their incidence as a function of stellar parameters for the available sample of stars. All B8- and A0-type, Ia-class, stars in the sample that have been sufficiently well observed, as well as one A2-type star, show the events. However, there is some evidence that hyperluminous stars (luminosity class Ia+) do not show the events. In one of the most extensively observed stars in the sample (Rigel, B8 Ia), there is no clear periodicity in the recurrence times of the events. In addition to the strong events discovered by Kaufer et al. (1996), there is a broad distribution of more frequent, weaker events. Ritter Observatory receives operating support from the National Science Foundation Program for Research and Education with Small Telescopes (PREST) award AST-0440784.

  2. Chemistry and Kinematics of Red Supergiant Stars in the Young Massive Cluster NGC 2100

    CERN Document Server

    Patrick, L R; Davies, B; Kudritzki, R-P; Hénault-Brunet, V; Bastian, N; Lapenna, E; Bergemann, M

    2016-01-01

    We have obtained K-band Multi-Object Spectrograph (KMOS) near-IR spectroscopy for 14 red supergiant stars (RSGs) in the young massive star cluster NGC 2100 in the Large Magellanic Cloud (LMC). Stellar parameters including metallicity are estimated using the J-band analysis technique, which has been rigorously tested in the Local Universe. We find an average metallicity for NGC 2100 of [Z]=$-$0.38$\\pm$0.20 dex, in good agreement with estimates from the literature for the LMC. Comparing our results in NGC 2100 with those for a Galactic cluster (at Solar-like metallicity) with a similar mass and age we find no significant difference in the location of RSGs in the Hertzsprung--Russell diagram. We combine the observed KMOS spectra to form a simulated integrated-light cluster spectrum and show that, by analysing this spectrum as a single RSG, the results are consistent with the average properties of the cluster. Radial velocities are estimated for the targets and the dynamical properties are estimated for the first...

  3. ALMA observations of the supergiant B[e] star Wd1-9

    CERN Document Server

    Fenech, D; Prinja, R K; Morford, J C; Dougherty, S; Blomme, R

    2016-01-01

    Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible - radiatively driven winds, impulsive ejection and/or binary interaction -remain uncertain. In this paper we present ALMA line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-Main Sequence object located within the starburst cluster Westerlund 1. We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41alpha radio recombination line. We attribute these properties to a low velocity (~100 km/s) ionised wind, with an extreme mass-loss rate 6.4x10^-5(d/5kpc)^1.5 Msol/yr. External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A.We conclude that these objects are interacting binaries evolving a...

  4. The Physical Properties of the Red Supergiant WOH G64: The Largest Star Known?

    CERN Document Server

    Levesque, Emily M; Plez, Bertrand; Olsen, Knut A G

    2009-01-01

    WOH G64 is an unusual red supergiant (RSG) in the Large Magellanic Cloud (LMC), with a number of properties that set it apart from the rest of the LMC RSG population, including a thick circumstellar dust torus, an unusually late spectral type, maser activity, and nebular emission lines. Its reported physical properties are also extreme, including the largest radius for any star known and an effective temperature that is much cooler than other RSGs in the LMC, both of which are at variance with stellar evolutionary theory. We fit moderate-resolution optical spectrophotometry of WOH G64 with the MARCS stellar atmosphere models, determining an effective temperature of 3400 +/- 25 K. We obtain a similar result from the star's broadband V - K colors. With this effective temperature, and taking into account the flux contribution from the aysmmetric circumstellar dust envelope, we calculate log(L/L_sun) = 5.45 +/- 0.05 for WOH G64, quite similar to the luminosity reported by Ohnaka and collaborators based on their r...

  5. HD 179821 (V1427 Aql, IRAS 19114+0002) - a massive post-red supergiant star?

    Science.gov (United States)

    Şahin, T.; Lambert, David L.; Klochkova, Valentina G.; Panchuk, Vladimir E.

    2016-10-01

    We have derived elemental abundances of a remarkable star, HD 179821, with unusual composition (e.g. [Na/Fe] = 1.0 ± 0.2 dex) and extra-ordinary spectral characteristics. Its metallicity at [Fe/H] = 0.4 dex places it among the most metal-rich stars yet analysed. The abundance analysis of this luminous star is based on high-resolution and high-quality (S/N ≈ 120-420) optical echelle spectra from McDonald Observatory and Special Astronomy Observatory. The data includes five years of observations over 21 epochs. Standard 1D local thermodynamic equilibrium analysis provides a fresh determination of the atmospheric parameters over all epochs: Teff = 7350 ± 200 K, log g= +0.6 ± 0.3, and a microturbulent velocity ξ = 6.6 ± 1.6 km s-1 and [Fe/H] = 0.4 ± 0.2, and a carbon abundance [C/Fe] = -0.19 ± 0.30. We find oxygen abundance [O/Fe] = -0.25 ± 0.28 and an enhancement of 0.9 dex in N. A supersonic macroturbulent velocity of 22.0 ± 2.0 km s-1 is determined from both strong and weak Fe I and Fe II lines. Elemental abundances are obtained for 22 elements. HD 179821 is not enriched in s-process products. Eu is overabundant relative to the anticipated [X/Fe] ≈ 0.0. Some peculiarities of its optical spectrum (e.g. variability in the spectral line shapes) is noticed. This includes the line profile variations for H α line. Based on its estimated luminosity, effective temperature and surface gravity, HD 179821 is a massive star evolving to become a red supergiant and finally a Type II supernova.

  6. Chemistry and kinematics of red supergiant stars in the young massive cluster NGC 2100

    Science.gov (United States)

    Patrick, L. R.; Evans, C. J.; Davies, B.; Kudritzki, R.-P.; Hénault-Brunet, V.; Bastian, N.; Lapenna, E.; Bergemann, M.

    2016-06-01

    We have obtained K-band Multi-Object Spectrograph (KMOS) near-IR spectroscopy for 14 red supergiant stars (RSGs) in the young massive star cluster NGC 2100 in the Large Magellanic Cloud (LMC). Stellar parameters including metallicity are estimated using the J-band analysis technique, which has been rigorously tested in the Local Universe. We find an average metallicity for NGC 2100 of [Z] = -0.43 ± 0.10 dex, in good agreement with estimates from the literature for the LMC. Comparing our results in NGC 2100 with those for a Galactic cluster (at Solar-like metallicity) with a similar mass and age we find no significant difference in the location of RSGs in the Hertzsprung-Russell diagram. We combine the observed KMOS spectra to form a simulated integrated-light cluster spectrum and show that, by analysing this spectrum as a single RSG, the results are consistent with the average properties of the cluster. Radial velocities are measured for the targets and the dynamical properties are estimated for the first time within this cluster. The data are consistent with a flat velocity dispersion profile, and with an upper limit of 3.9 kms-1, at the 95 per cent confidence level, for the velocity dispersion of the cluster. However, the intrinsic velocity dispersion is unresolved and could, therefore, be significantly smaller than the upper limit reported here. An upper limit on the dynamical mass of the cluster is derived as Mdyn ≤ 15.2 × 104 M⊙ assuming virial equilibrium.

  7. Seeing Stars Like Never Before: A Multi-Year Interferometric Imaging Study of Red Supergiants in the H-Band.

    Science.gov (United States)

    Norris, Ryan P.; Baron, Fabien

    2017-01-01

    As some of the largest stars, red supergiants (RSG) are ideal candidates for interferometric imaging. 3D radiative hydrodynamic (RHD) models suggest that RSG have large convection cells with lifetimes on the order of 1000s of days. Many imaging projects have hinted at the existence of these features but, until recently, we have lacked the angular resolution to directly compare models to observations. In this presentation, we discuss early results from a multi-year survey of red supergiants using the Michigan InfraRed Combinber (MIRC) on the Center for High Angular Resolution Astronomy (CHARA Array), which has a maximum baseline of 330 m. We will present H-band images of RSG spanning several years developed using a new machine learning based image reconstruction tool for interferometric data. We will also present fundamental parameters for the targets, and discuss the implications of these results on 1D model atmospheres and 3D RHD models of RSG.

  8. The supergiant B[e] star LHA 115-S 18 - binary and/or luminous blue variable?

    CERN Document Server

    Clark, J S; Coe, M J; Dorda, R; Haberl, F; Lamb, J B; Negueruela, I; Udalski, A

    2013-01-01

    The mechanism by which supergiant (sg)B[e] stars support cool, dense dusty discs/tori and their physical relationship with other evolved, massive stars such as luminous blue variables is uncertain. In order to investigate both issues we have analysed the long term behaviour of the canonical sgB[e] star LHA 115-S 18. We employed the OGLE II-IV lightcurve to search for (a-)periodic variability and supplemented these data with new and historic spectroscopy. In contrast to historical expectations for sgB[e] stars, S18 is both photometrically and spectroscopically highly variable. The lightcurve is characterised by rapid aperiodic `flaring' throughout the 16 years of observations. Changes in the high excitation emission line component of the spectrum imply evolution in the stellar temperature - as expected for luminous blue variables - although somewhat surprisingly, spectroscopic and photometric variability appears not to be correlated. Characterised by emission in low excitation metallic species, the cool circum...

  9. Spectroscopic and photometric observations of M supergiants in Carina.

    Science.gov (United States)

    Humphreys, R. M.; Strecker, D. W.; Ney, E. P.

    1972-01-01

    Spectroscopic study of 30 Southern-Hemisphere M supergiants mostly in Carina in the blue and near-infrared, and photometrical study of these stars from 0.4 to 18 microns. The uncertainties in the determinations of interstellar extinction are discussed, and the spatial distribution of the M supergiants in the Carina arm is shown. The presence of the 11-micron excess attributed to silicate dust is a common feature. Stars of the same spectral type and luminosity class are remarkably homogeneous in their long-wave behavior. The silicate feature becomes more prominent in the more luminous stars and in stars of later spectral type. Four composite systems show little long-wave excess. The two VV Cephei objects have excesses probably produced by gas emission, and the other two have little or no excess - supporting the suggestion that the presence of the early star prohibits the formation of a dust envelope. Three stars - VY CMa, VX Sgr, and HD 9767 - appear to be extreme examples of stars with large excesses over the entire long-wave region. It is suggested that these objects are surrounded by large amounts of particulate material over a great range of distances from the stars.

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

    Science.gov (United States)

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

    2015-10-01

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

  11. A Spectroscopic Study of Blue Supergiant Stars in the Sculptor Galaxy NGC 55: Chemical Evolution and Distance

    Science.gov (United States)

    Kudritzki, R. P.; Castro, N.; Urbaneja, M. A.; Ho, I.-T.; Bresolin, F.; Gieren, W.; Pietrzyński, G.; Przybilla, N.

    2016-10-01

    Low-resolution (4.5-5 Å) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities, and metallicities (from iron peak and α-elements). A metallicity gradient of -0.22 ± 0.06 dex/R 25 is detected. The central metallicity on a logarithmic scale relative to the Sun is [Z] = -0.37 ± 0.03. A chemical evolution model using the observed distribution of column densities of the stellar and interstellar medium gas mass reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extraplanar metal-poor H ii regions detected in previous work 1.13 to 2.22 kpc above the galactic plane are ionized by massive stars formed in situ outside the disk. For a subsample of supergiants, for which Hubble Space Telescope photometry is available, the flux-weighted gravity-luminosity relationship is used to determine a distance modulus of 26.85 ± 0.10 mag.

  12. The flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution

    Science.gov (United States)

    Meynet, Georges; Kudritzki, Rolf-Peter; Georgy, Cyril

    2015-09-01

    Context. The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g/T_text{eff ^4}. BSG are the brightest stars in the universe at visual light and the application of the FGLR has become a powerful tool for determining extragalactic distances. Aims: Observationally, the FGLR is a tight relationship with only small scatter. It is, therefore, ideal for using as a constraint for stellar evolution models. The goal of this work is to investigate whether stellar evolution can reproduce the observed FGLR and to develop an improved foundation for the FGLR as an extragalactic distance indicator. Methods: We used different grids of stellar models for initial masses between 9 and 40 M⊙ and for metallicities between Z = 0.002 and 0.014, with and without rotation, which were computed with various mass loss rates during the red supergiant phase. For each of these models, we discuss the details of post-main sequence evolution and construct theoretical FGLRs by means of population synthesis models that we then compare with the observed FGLR. Results: In general, the stellar evolution model FGLRs agree reasonably well with the observed one. There are, however, differences between the models, in particular with regard to the shape and width (scatter) in the flux-weighted gravity-luminosity plane. The best agreement is obtained with models that include the effects of rotation and assume that the large majority, if not all, of the observed BSG evolve toward the red supergiant phase and that only a few are evolving back from this stage. The effects of metallicity on the shape and scatter of the FGLR are small. Conclusions: The shape, scatter, and metallicity dependence of the observed FGLR are explained well by stellar evolution models. This provides a solid theoretical foundation for using this relationship as a robust extragalactic distance indicator.

  13. Near-Infrared Photometric Properties of Red Supergiant Stars in Neaby Galaxies: NGC 4214, NGC 4736 and M51

    Science.gov (United States)

    Jung, DooSeok; Chun, Sang-Hyun; Choudhury, Samyaday; Sohn, Young-Jong

    2017-01-01

    Red supergiant stars (RSGs) are post-main sequence phase of massive stars which can be easily resolved in nearby galaxies due to their bright luminosity as compared to the low-mass stars. RSGs are cool, and hence have a dominant light output at near-infrared (NIR) wavelengths. To investigate the photometric properties of RSGs in a few nearby galaxies, we observed NGC 4214, NGC 4736 and M51 by using the WFCAM detector mounted on the UKIRT telescope at Hawaii, and obtained the NIR (JHK bands) imaging data. After carrying out the photometry, the age ranges of RSGs in each galaxy were estimated by over-plotting PARSEC isochrones to the (J-K, K) colour-magnitude diagram: log(tyr) = 6.9 - 7.3 for NGC 4214; log(tyr) = 7.0 - 8.0 for NGC 4736; and log(tyr) = 6.7 - 6.9 for M51. The effective temperatures and luminosities of RSGs were calculated using MARCS synthetic fluxes, and these results were used to compare the properties of RSGs in Hertzsprung-Russell (H-R) diagram of dominant H II regions within each galaxy, over-plotted with PARSEC evolutionary tracks. The RSGs in NGC 4214 and NGC 4736 are found to have a mass of 9 M⊙ - 30 M⊙, and the maximum luminosities found to be almost constant with log(L/L⊙) = 5.6 - 5.7. However, the location of the RSGs in the H-R diagram are not consistent with the evolutionary tracks for M51.(Key Words: stars: massive - supergiants - galaxies: photometry - galaxies: stellar content - infrared: stars)

  14. The flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution

    CERN Document Server

    Meynet, Georges; Georgy, Cyril

    2015-01-01

    (abridged) The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g = Teff^4. BSG are the brightest stars in the universe at visual light and the application of the FGLR has become a powerful tool to determine extragalactic distances. Observationally, the FGLR is a tight relationship with only small scatter. It is, therefore, ideal to be used as a constraint for stellar evolution models. The goal of this work is to investigate whether stellar evolution can reproduce the observed FGLR and to develop an improved foundation of the FGLR as an extragalactic distance indicator. We use different grids of stellar models for initial masses between 9 and 40 Msun, for metallicities between Z = 0.002 and 0.014, with and without rotation, computed with various mass loss rates during the red supergiant phase. For each of these models we discuss the details of post-main sequence evolution and constru...

  15. vy particles

    DEFF Research Database (Denmark)

    Hansen, Linda Vadgård; Thorarinsdottir, Thordis Linda; Gneiting, Tilmann

    vy particles provide a flexible framework for modelling and simulating threedimensional star-shaped random sets. The radial function of a Lévy particle arises from a kernel smoothing of a Lévy basis, and is associated with an isotropic random field on the sphere. If the kernel is proportional...... to a von Mises–Fisher density, or uniform on a spherical cap, the correlation function of the associated random field admits a closed form expression. Using a Gaussian basis, the fractal or Hausdorff dimension of the surface of the Lévy particle reflects the decay of the correlation function at the origin......, as quantified by the fractal index. Under power kernels we obtain particles with boundaries of any Hausdorff dimension between 2 and 3....

  16. HST Studies of the Chromospheres, Wind, and Mass-Loss Rates of Cool Giant and Supergiant Stars

    Science.gov (United States)

    Carpenter, Kenneth G.

    2000-01-01

    UV spectra of K-M giant and supergiant stars and of carbon stars have been acquired with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). These spectra have been used to measure chromospheric flow and turbulent velocities, study the acceleration of their stellar winds, acquire constraints on their outer atmospheric structure, and enable estimates of their mass-loss rates. Results from our observations of the giant stars Gamma Dra (K5 III hybrid), Alpha Tau (K5 III), Gamma Cru (M3.4 III), Mu Gem (M3 IIIab), and 30 Her (MG III), the supergiants Alpha Ori (M2 Iab) and Lambda Vel (K5 Ib), and the carbon stars TX Psc (NO; C6,2) and TW Hor (NO; C7,2) will be summarized and compared. The high resolution and wavelength accuracy of these data have allowed the direct measurement of the acceleration of the stellar winds in the chromospheres of several of these stars (from initial velocities of 3-9 km/s to upper velocities of 15-25 km/s) and of the chromospheric macroturbulence (-25-35 km/s). The high signal-to-noise and large dynamic range of these spectra have allowed the detection and identification of numerous new emission features, including weak C IV emission indicative of hot transition-region plasma in the non-coronal giant Alpha Tau, many new fluorescent lines of Fe II, and the first detection of fluorescent molecular hydrogen emission and of Ca II recombination lines in the UV spectrum of a giant star. The UV spectrum of two carbon stars have been studied with unprecedented resolution and reveal extraordinarily complicated Mg II lines nearly smothered by circumstellar absorptions. Finally, comparison of synthetic UV emission line profiles computed with the Lamers et al. (1987) Sobolev with Exact Integration (SEI) code with observations of chromospheric emission lines overlain with wind absorption features provides estimates of the mass-loss rates for four of these stars.

  17. On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants

    CERN Document Server

    Jones, O C; Sargent, B A; McDonald, I; Gielen, C; Woods, Paul M; Sloan, G C; Boyer, M L; Zijlstra, A A; Clayton, G C; Kraemer, K E; Srinivasan, S; Ruffle, P M E

    2012-01-01

    We investigate the occurrence of crystalline silicates in oxygen-rich evolved stars across a range of metallicities and mass-loss rates. It has been suggested that the crystalline silicate feature strength increases with increasing mass-loss rate, implying a correlation between lattice structure and wind density. To test this, we analyse Spitzer IRS and Infrared Space Observatory SWS spectra of 217 oxygen-rich asymptotic giant branch stars and 98 red supergiants in the Milky Way, the Large and Small Magellanic Clouds and Galactic globular clusters. These encompass a range of spectral morphologies from the spectrally-rich which exhibit a wealth of crystalline and amorphous silicate features to 'naked' (dust-free) stars. We combine spectroscopic and photometric observations with the GRAMS grid of radiative transfer models to derive (dust) mass-loss rates and temperature. We then measure the strength of the crystalline silicate bands at 23, 28 and 33 microns. We detect crystalline silicates in stars with dust ma...

  18. A grid of NLTE corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia

    CERN Document Server

    Merle, Thibault; Pichon, Bernard; Bigot, Lionel

    2011-01-01

    We investigate NLTE effects for magnesium and calcium in the atmospheres of late-type giant and supergiant stars. The aim of this paper is to provide a grid of NLTE/LTE equivalent width ratios W/W* of Mg and Ca lines for the following range of stellar parameters: Teff in [3500, 5250] K, log g in [0.5, 2.0] dex and [Fe/H] in [-4.0, 0.5] dex. We use realistic model atoms with the best physics available and taking into account the fine structure. The Mg and Ca lines of interest are in optical and near IR ranges. A special interest concerns the lines in the Gaia spectrograph (RVS) wavelength domain [8470, 8740] A. The NLTE corrections are provided as function of stellar parameters in an electronic table as well as in a polynomial form for the Gaia/RVS lines.

  19. Abundance analysis of the supergiant stars HD 80057 and HD 80404 based on their UVES Spectra

    CERN Document Server

    Tanrıverdi, Taner

    2015-01-01

    This study presents elemental abundances of the early A-type supergiant HD 80057 and the late A-type supergiant HD80404. High resolution and high signal-to-noise ratio spectra published by the UVES Paranal Observatory Project (Bagnulo et al., 2003) were analysed to compute their elemental abundances using ATLAS9 (Kurucz, 1993, 2005; Sbordone et al., 2004). In our analysis we assumed local thermodynamic equilibrium. The atmospheric parameters of HD 80057 used in this study are from Firnstein & Przybilla (2012), and that of HD80404 are derived from spectral energy distribution, ionization equilibria of Cr I/II and Fe I/II, and the fits to the wings of Balmer lines and Paschen lines as Teff = 7700 +/- 150 K and log g=1.60 +/- 0.15 (in cgs). The microturbulent velocities of HD 80057 and HD 80404 have been determined as 4.3 +/- 0.1 and 2.2 +/- 0.7 km s^-1 . The rotational velocities are 15 +/-1 and 7 +/- 2 km s^-1 and their macroturbulence velocities are 24 +/-2 and 2+/-1 km s^-1 . We have given the abundances...

  20. Evolved Massive Stars in the Local Group. I. Identification of Red Supergiants in NGC 6822, M31, and M33

    Science.gov (United States)

    Massey, Philip

    1998-07-01

    Knowledge of the red supergiant (RSG) population of nearby galaxies allows us to probe massive star evolution as a function of metallicity; however, contamination by foreground Galactic dwarfs dominates surveys for red stars in Local Group galaxies beyond the Magellanic Clouds. Model atmospheres predict that low-gravity supergiants will have B-V values that are redder by several tenths of a magnitude than foreground dwarfs at a given V-R color, a result that is largely independent of reddening. We conduct a BVR survey of several fields in the Local Group galaxies NGC 6822, M33, and M31 as well as neighboring control fields and identify RSG candidates from CCD photometry. The survey is complete to V = 20.5, corresponding to MV = -4.5 or an Mbol of -6.3 for the reddest stars. Follow-up spectroscopy at the Ca II triplet of 130 stars is used to demonstrate that our photometric criterion for identifying RSGs is highly successful (96% for stars brighter than V = 19.5; 82% for V = 19.5-20.5). Classification spectra are also obtained for a number of stars in order to calibrate color with spectral type empirically. We find that there is a marked progression in the average (B-V)0 and (V-R)0 colors of RSGs in these three galaxies, with the higher metallicity systems having a later average spectral type, which is consistent with previous findings by Elias, Frogel, & Humphreys for the Milky Way and Magellanic Clouds. More significantly, we find that there is a clear progression with metallicity in the relative number of the highest luminosity RSGs, a trend that is apparent both in absolute visual magnitude and in bolometric luminosity. Thus any use of RSGs as distance indicators requires correction for the metallicity of the parent galaxy. Our findings are in accord with the predictions of the ``Conti scenario'' in which higher metallicities result in higher mass-loss rates, resulting in a star of a given luminosity spending an increasing fraction of its He-burning lifetime as

  1. The supergiant shell with triggered star formation in Irr galaxy IC 2574: neutral and ionized gas kinematics

    CERN Document Server

    Egorov, O V; Moiseev, A V; Smirnov-Pinchukov, G V

    2014-01-01

    We analyse the ionized gas kinematics in the star formation regions of the supergiant shell (SGS) of the IC 2574 galaxy using observations with the Fabry-Perot interferometer at the 6-m telescope of SAO RAS; the data of the THINGS survey are used to analyze the neutral gas kinematics in the area. We perform the 'derotation' of the H-alpha and HI data cubes and show its efficiency in kinematics analysis. We confirm the SGS expansion velocity 25 km/s obtained by Walter & Brinks (1999) and conclude that the SGS is located at the far side of the galactic disc plane. We determine the expansion velocities, kinematic ages, and the required mechanical energy input rates for four star formation complexes in the walls of the SGS; for the remaining ones we give the limiting values of the above parameters. A comparison with the age and energy input of the complexes' stellar population shows that sufficient energy is fed to all HII regions except one. We discuss in detail the possible nature of this region and that of...

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

    CERN Document Server

    Mackey, Jonathan; Fossati, Luca; Langer, Norbert

    2015-01-01

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

  3. A spectroscopic study of blue supergiant stars in the Sculptor galaxy NGC 55: chemical evolution and distance

    CERN Document Server

    Kudritzki, Rolf; Castro, Norberto; Ho, I-Ting; Bresolin, Fabio; Gieren, Wolfgang; Pietrzynski, Grzegorz; Przybilla, Norbert

    2016-01-01

    Low resolution (4.5 to 5 Angstroem) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities and metallicities (from iron peak and alpha-elements). A metallicity gradient of -0.22 +/- 0.06$ dex/R_25 is detected. The central metallicity on a logarithmic scale relative to the Sun is [Z] = -0.37 +\\- 0.03. A chemical evolution model using the observed distribution of stellar and interstellar medium gas mass column densities reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extra-planar metal poor HII regions detected in previous work 1.13 to 2.22 kpc above th...

  4. NuSTAR detection of a cyclotron line in the supergiant fast X-ray transient IGR J17544-2619

    DEFF Research Database (Denmark)

    Bhalerao, Varun; Romano, Patrizia; Tomsick, John

    2015-01-01

    We present NuSTAR spectral and timing studies of the supergiant fast X-ray transient (SFXT) IGR J17544-2619. The spectrum is well described by an  ∼ 1 keV blackbody and a hard continuum component, as expected from an accreting X-ray pulsar. We detect a cyclotron line at 17 keV, confirming...... do not find any significant pulsations in the source on time-scales of 1-2000 s....

  5. The supergiant B[e] star LHA 115-S 18 - binary and/or luminous blue variable?

    Science.gov (United States)

    Clark, J. S.; Bartlett, E. S.; Coe, M. J.; Dorda, R.; Haberl, F.; Lamb, J. B.; Negueruela, I.; Udalski, A.

    2013-12-01

    Context. The mechanism by which supergiant (sg)B[e] stars support cool, dense dusty discs/tori and their physical relationship with other evolved, massive stars such as luminous blue variables is uncertain. Aims: In order to investigate both issues we have analysed the long term behaviour of the canonical sgB[e] star LHA 115-S 18. Methods: We employed the OGLE II-IV lightcurve to search for (a-)periodic variability and supplemented these data with new and historic spectroscopy. Results: In contrast to historical expectations for sgB[e] stars, S18 is both photometrically and spectroscopically highly variable. The lightcurve is characterised by rapid aperiodic "flaring" throughout the 16 years of observations. Changes in the high excitation emission line component of the spectrum imply evolution in the stellar temperature - as expected for luminous blue variables - although somewhat surprisingly, spectroscopic and photometric variability appears not to be correlated. Characterised by emission in low excitation metallic species, the cool circumstellar torus appears largely unaffected by this behaviour. Finally, in conjunction with intense, highly variable He ii emission, X-ray emission implies the presence of an unseen binary companion. Conclusions: S18 provides observational support for the putative physical association of (a subset of) sgB[e] stars and luminous blue variables. Given the nature of the circumstellar environment of S18 and that luminous blue variables have been suggested as supernovae progenitors, it is tempting to draw a parallel to the progenitors of SN1987A and SN2009ip. Moreover the likely binary nature of S18 strengthens the possibility that the dusty discs/tori that characterise sgB[e] stars are the result of binary-driven mass-loss; consequently such stars may provide a window on the short lived phase of mass-transfer in massive compact binaries. This work is partly based on observations collected at the European Southern Observatory (programme

  6. Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, and the B[e] Supergiants; How to Tell Them Apart

    CERN Document Server

    Humphreys, Roberta M; Martin, John C; Weis, Kerstin; Hahn, David

    2016-01-01

    In this series of papers we have presented the results of a spectroscopic survey of luminous and variable stars in the nearby spirals M31 and M33. In this paper, we present spectroscopy of 132 additional luminous stars, variables, and emission line objects. Most of the stars have emission line spectra, including LBVs and candidate LBVs, Fe II emission line stars and the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. With this large spectroscopic data set including various types of emission line stars, we examine their similarities and differences and propose the following criteria that can be used to help distinguish these stars in future work: 1. The B[e] supergiants have emission lines of [O I] and [Fe II] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their SEDs. 2. Confirmed LBVs do not have the [O I] emission lines in their spectra. Some LBVs have [Fe II] e...

  7. Sharpest views of Betelgeuse reveal how supergiant stars lose mass-Unveiling the true face of a behemoth

    Science.gov (United States)

    2009-07-01

    Using different state-of-the-art techniques on ESO's Very Large Telescope, two independent teams of astronomers have obtained the sharpest ever views of the supergiant star Betelgeuse. They show that the star has a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface. These discoveries provide important clues to help explain how these mammoths shed material at such a tremendous rate. Betelgeuse - the second brightest star in the constellation of Orion (the Hunter) - is a red supergiant, one of the biggest stars known, and almost 1000 times larger than our Sun [1]. It is also one of the most luminous stars known, emitting more light than 100000 Suns. Such extreme properties foretell the demise of a short-lived stellar king. With an age of only a few million years, Betelgeuse is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight. Red supergiants still hold several unsolved mysteries. One of them is just how these behemoths shed such tremendous quantities of material - about the mass of the Sun - in only 10 000 years. Two teams of astronomers have used ESO's Very Large Telescope (VLT) and the most advanced technologies to take a closer look at the gigantic star. Their combined work suggests that an answer to the long-open mass-loss question may well be at hand. The first team used the adaptive optics instrument, NACO, combined with a so-called "lucky imaging" technique, to obtain the sharpest ever image of Betelgeuse, even with Earth's turbulent, image-distorting atmosphere in the way. With lucky imaging, only the very sharpest exposures are chosen and then combined to form an image much sharper than a single, longer exposure would be. The resulting NACO images almost reach the theoretical limit of sharpness attainable for an 8-metre telescope. The resolution is as fine as 37 milliarcseconds, which is roughly

  8. The Mass-Loss Return from Evolved Stars to the Large Magellanic Cloud IV: Construction and Validation of a Grid of Models for Oxygen-Rich AGB Stars, Red Supergiants, and Extreme AGB Stars

    CERN Document Server

    Sargent, Benjamin A; Meixner, M

    2014-01-01

    To measure the mass loss from dusty oxygen-rich (O-rich) evolved stars in the Large Magellanic Cloud (LMC), we have constructed a grid of models of spherically-symmetric dust shells around stars with constant mass-loss rates using 2Dust. These models will constitute the O-rich model part of the "Grid of Red supergiant and Asymptotic giant branch star ModelS" (GRAMS). This model grid explores 4 parameters - stellar effective temperature from 2100 K - 4700 K; luminosity from 10^3-10^6 L_Sun; dust shell inner radii of 3, 7, 11, and 15 R_Star; and 10.0 micron optical depth from 10^-4 to 26. From an initial grid of ~1200 2Dust models, we create a larger grid of ~69,000 models by scaling to cover the luminosity range required by the data. These models are offered to the public on a website. The matching in color-magnitude diagrams and color-color diagrams to observed O-rich asymptotic giant branch (AGB) and red supergiant (RSG) candidate stars from the SAGE and SAGE-Spec LMC samples and a small sample of OH/IR star...

  9. Pre-supernova outbursts via wave heating in massive stars - I. Red supergiants

    Science.gov (United States)

    Fuller, Jim

    2017-09-01

    Early observations of supernovae (SNe) indicate that enhanced mass-loss and pre-SN outbursts may occur in progenitors of many types of SNe. We investigate the role of energy transport via waves driven by vigorous convection during late-stage nuclear burning of otherwise typical 15 M⊙ red supergiant SN progenitors. Using mesa stellar evolution models including 1D hydrodynamics, we find that waves carry ∼107 L⊙ of power from the core to the envelope during core neon/oxygen burning in the final years before core collapse. The waves damp via shocks and radiative diffusion at the base of the hydrogen envelope, which heats up fast enough to launch a pressure wave into the overlying envelope that steepens into a weak shock near the stellar surface, causing a mild stellar outburst and ejecting a small (≲1 M⊙) amount of mass at low speed (≲50 km s-1) roughly one year before the SN. The wave heating inflates the stellar envelope but does not completely unbind it, producing a non-hydrostatic pre-SN envelope density structure different from prior expectations. In our models, wave heating is unlikely to lead to luminous Type IIn SNe, but it may contribute to flash-ionized SNe and some of the diversity seen in II-P/II-L SNe.

  10. Explosion of red-supergiant stars: Influence of the atmospheric structure on shock breakout and early-time supernova radiation

    Science.gov (United States)

    Dessart, Luc; John Hillier, D.; Audit, Edouard

    2017-09-01

    Early-time observations of Type II supernovae (SNe) 2013cu and 2013fs have revealed an interaction of ejecta with material near the star surface. Unlike Type IIn SN 2010jl, which interacts with a dense wind for 1 yr, the interaction ebbs after 2-3 d, suggesting a dense and compact circumstellar envelope. Here, we use multi-group radiation hydrodynamics and non-local-thermodynamic-equilibrium radiative transfer to explore the properties of red-supergiant (RSG) star explosions embedded in a variety of dense envelopes. We consider the cases of an extended static atmosphere or a steady-state wind, adopting a range of mass loss rates. The shock breakout signal, luminosity and color evolution up to 10 d, and ejecta dynamics are strongly influenced by the properties of this nearby environment. This compromises the use of early-time observations to constrain R⋆. For dense circumstellar envelopes, the time-integrated luminosity over the first 10-15 d can be boosted by a factor of a few. The presence of narrow lines for 2-3 d in 2013fs and 2013cu require a cocoon of material of 0.01 M⊙ out to 5-10 R⋆. Spectral lines evolve from electron scattering to Doppler broadened with a growing blueshift of their emission peaks. Recent studies propose a super-wind phase with a mass loss rate from 0.001 up to 1 M⊙ yr-1 in the last months or years of the life of a RSG, although there is no observational constraint that this external material is a steady-state outflow. Alternatively, observations may be explained by the explosion of a RSG star inside its complex atmosphere. Indeed, spatially resolved observations reveal that RSG stars have extended atmospheres, with the presence of downflows and upflows out to several R⋆, even in a standard RSG such as Betelgeuse. Mass loading in the region intermediate between star and wind can accommodate the 0.01 M⊙ needed to explain the observations of 2013fs. Signatures of interaction in early-time spectra of RSG star explosions may

  11. Aluminium oxide in the optical spectrum of VY Canis Majoris

    CERN Document Server

    Kaminski, T; Menten, K M

    2012-01-01

    We report the first identification of the optical bands of the B-X system of AlO in the red supergiant VY CMa. In addition to TiO, VO, ScO, and YO, which were recognized in the optical spectrum of the star long time ago, AlO is another refractory molecule which displays strong emission bands in this peculiar star. Simulating the bands of AlO, we derive a rotational temperature of the circumstellar gas of Trot=700K. By resolving individual rotational components of the bands, we derive the kinematical characteristics of the gas, finding that the emission is centered at the stellar radial velocity and its intrinsic width is 13.5 km/s (full width at half maximum). It is the narrowest emission among all (thermal) features observed in VY CMa so far. The temperature and line widths suggest that the emission arises in gas located within ~20 stellar radii, where the outflow is still being accelerated. This result contradicts equilibrium-chemistry models which predict substantial AlO abundances only to within a few ste...

  12. VizieR Online Data Catalog: OB and Supergiants stars in LMC (Philip+, 1979)

    Science.gov (United States)

    Philip, A. G. Davis; Sanduleak, N.

    2017-07-01

    An objective-prism survey of the LMC was made with the Lichigan Curtis Schmidt Telescope at the Cerro Tololo Inter-American Observatory. The prims gives a dispersion of 136nm/mm at Hγ and covers the spectral range 330-540nm when used with nitrogen baked, IIIa-J plates. The 60-min exposuers reach stars of apparent magnitude ~16. Accurate positions and more reliable photometry of the stars were added in July 2017, using the finding charts of the authors, and the Aladin tool (Bonnarel et al. 2000A&AS..143...33B) In addition, accurate positions of the B stars in Field 39 as given by Shobbrook and Visvanathan (1987MNRAS.225..947S, Table A1) are presented in the file "pl39.dat". (3 data files).

  13. High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR

    CERN Document Server

    Ohnaka, Keiichi

    2013-01-01

    We present high spectral resolution (R = 30000) spectroscopic observations of the SiO fundamental lines near 8.1 micron in 16 bright red giants and red supergiants using VLT/VISIR. Our sample consists of seven normal K--M giants, three Mira stars, three optically bright red supergiants, two dusty red supergiants, and the enigmatic object GCIRS3 near the Galactic center. We detected SiO fundamental lines in all of our program stars except for GCIRS3. The SiO lines in normal K and M giants as well as optically bright red supergiants do not show P-Cyg profiles or blueshifts, which means the absence of systematic outflows in the SiO line forming region. On the other hand, we detected P-Cyg profiles in the SiO lines in the dusty red supergiants VY CMa and VX Sgr (with the latter being a new detection), which suggest outflow velocities of 27 and 17 km/s, respectively. We derived basic stellar parameters (effective temperature, surface gravity, luminosity, and mass) for the normal K--M giants and optically bright re...

  14. The cool supergiant population of the massive young star cluster RSGC1

    NARCIS (Netherlands)

    Davies, B.; Figer, D.F.; Law, C.J.; Kudritzki, R.-P.; Najarro, F.; Herrero, A.; MacKenty, J.W.

    2008-01-01

    We present new high-resolution near-IR spectroscopy and OH maser observations to investigate the population of cool luminous stars of the young massive Galactic cluster RSGC1. Using the 2.293 mu m CO band-head feature, we make high-precision radial velocity measurements of 16 of the 17 candidate red

  15. The Jet from MWC 137 Points at a Supergiant B[e] Star in a Binary

    Science.gov (United States)

    Mehner, A.; de Wit, W. J.; Groh, J. H.; Oudmaijer, R. D.; Baade, D.; Rivinius, Th.; Selman, F.; Boffin, H. M. J.; Martayan, C.

    2017-02-01

    The Galactic B[e] star MWC 137 is a prime example of an object with an uncertain evolutionary classification. Previous work has suggested that is either a pre- or a post-main sequence object. Integral field spectrograph observations with the Very Large Telescope Multi Unit Spectroscopic Explorer (VLT MUSE) of the host cluster SH 2-266 are used to provide a reliable evolutionary classification. The MUSE data also allowed the discovery of a large collimated outflow, geometrically centered on MWC 137. A color-magnitude diagram analysis of the cluster promotes strongly a post-main sequence stage for MWC 137, while the existence of a jet implies the presence of an accretion disk. A SWIFT X-ray source, which may be associated with MWC 137, hints at the possibility of a neutron star companion.

  16. HD 179821 (V1427 Aql, IRAS 19114+0002) -- A Massive Post-Red Supergiant Star?

    CERN Document Server

    Sahin, Timur; Klochkova, Valentina G; Panchuk, Vladimir E

    2016-01-01

    We have derived elemental abundances of a remarkable star, HD 179821, with unusual composition (e.g. [Na/Fe]=1.0$\\pm$0.2 dex) and extra-ordinary spectral characteristics. Its metallicity at [Fe/H]=0.4 dex places it among the most metal-rich stars yet analyzed. The abundance analysis of this luminous star is based on high resolution and high quality (S/N$\\approx$120--420) optical echelle spectra from McDonald Observatory and Special Astronomy Observatory. The data includes five years of observations over twenty-one epochs. Standard 1D {\\sc LTE} analysis provides a fresh determination of the atmospheric parameters over all epochs: \\Teff = 7350$\\pm$200 \\kelvin, \\logg = +0.6$\\pm$0.3, and a microturbulent velocity $\\xi =$ 6.6$\\pm$1.6 km s$^{\\rm -1}$ and [Fe/H] = 0.4$\\pm$0.2, and a carbon abundance [C/Fe]= $-$0.19$\\pm$0.30. We find oxygen abundance [O/Fe]= $-$0.25$\\pm$0.28 and an enhancement of 0.9 dex in N. A supersonic macroturbulent velocity of 22.0 $\\pm$ 2.0 km s$^{\\rm -1}$ is determined from both strong and we...

  17. NuSTAR Detection Of A Cyclotron Line In The Supergiant Fast X-ray Transient IGR J17544-2619

    CERN Document Server

    Bhalerao, Varun; Tomsick, John; Natalucci, Lorenzo; Smith, David M; Bellm, Eric; Boggs, Steven E; Chakrabarty, Deepto; Christensen, Finn E; Craig, William W; Fuerst, Felix; Hailey, Charles J; Harrison, Fiona A; Krivonos, Roman A; Lu, Ting-Ni; Madsen, Kristin; Stern, Daniel; Younes, George; Zhang, William

    2014-01-01

    We present NuSTAR spectral and timing studies of the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619. The spectrum is well-described by a ~1 keV blackbody and a hard continuum component, as expected from an accreting X-ray pulsar. We detect a cyclotron line at 17 keV, confirming that the compact object in IGR J17544-2619 is indeed a neutron star. This is the first measurement of the magnetic field in a SFXT. The inferred magnetic field strength, B = (1.45 +/- 0.03) * 10^12 G * (1+z) is typical of neutron stars in X-ray binaries, and rules out a magnetar nature for the compact object. We do not find any significant pulsations in the source on time scales of 1-2000 s.

  18. Bringing VY Canis Majoris Down to Size: An Improved Determination of Its Effective Tempeature

    CERN Document Server

    Massey, P; Plez, B; Levesque, Emily M.; Massey, Philip; Plez, Bertrand

    2006-01-01

    The star VY CMa is a late-type M supergiant with many peculiarities, mostly related to the intense circumstellar environment due to the star's high mass-loss rate. Claims have been made that would suggest this star is considerably more luminous (L = 5 x 10^5 Lo) and larger (R=2800 Ro) than other Galactic red supergiants (RSGs). Indeed, such a location in the H-R diagram would be well in the "Hayashi forbidden zone" where stars cannot be in hydrostatic equilibrium. These extraordinary properties, however, rest upon an assumed effective temperature of 2800-3000 K, far cooler than recent work have shown RSGs to be. To obtain a better estimate, we fit newly obtained spectrophotometry in the optical and NIR with the same MARCS models used for our recent determination of the physical properties of other RSGs; we also use $V-K$ and $V-J$ from the literature to derive an effective temperatures. We find that the star likely has a temperature of 3650 K, a luminosity L = 6 x 10^4 Lo, and a radius of 600Ro. These values ...

  19. Large dust grains in the wind of VY Canis Majoris

    CERN Document Server

    Scicluna, P; Wesson, R; Blommaert, J A D L; Kasper, M; Voshchinnikov, N V; Wolf, S

    2015-01-01

    Massive stars live short lives, losing large amounts of mass through their stellar wind. Their mass is a key factor determining how and when they explode as supernovae, enriching the interstellar medium with heavy elements and dust. During the red supergiant phase, mass-loss rates increase prodigiously, but the driving mechanism has proven elusive. Here we present high-contrast optical polarimetric-imaging observations of the extreme red supergiant VY Canis Majoris and its clumpy, dusty, mass-loss envelope, using the new extreme-adaptive-optics instrument SPHERE at the VLT. These observations allow us to make the first direct and unambiguous detection of submicron dust grains in the ejecta; we derive an average grain radius $\\sim$ 0.5 $\\mu$m, 50 times larger than in the diffuse ISM, large enough to receive significant radiation pressure by photon scattering. We find evidence for varying grain sizes throughout the ejecta, highlighting the dynamical nature of the envelope. Grains with 0.5 $\\mu$m sizes are likel...

  20. Kepler sheds new and unprecedented light on the variability of a blue supergiant: Gravity waves in the O9.5Iab star HD 188209

    Science.gov (United States)

    Aerts, C.; Símon-Díaz, S.; Bloemen, S.; Debosscher, J.; Pápics, P. I.; Bryson, S.; Still, M.; Moravveji, E.; Williamson, M. H.; Grundahl, F.; Fredslund Andersen, M.; Antoci, V.; Pallé, P. L.; Christensen-Dalsgaard, J.; Rogers, T. M.

    2017-06-01

    Stellar evolution models are most uncertain for evolved massive stars. Asteroseismology based on high-precision uninterrupted space photometry has become a new way to test the outcome of stellar evolution theory and was recently applied to a multitude of stars, but not yet to massive evolved supergiants.Our aim is to detect, analyse and interpret the photospheric and wind variability of the O9.5 Iab star HD 188209 from Kepler space photometry and long-term high-resolution spectroscopy. We used Kepler scattered-light photometry obtained by the nominal mission during 1460 d to deduce the photometric variability of this O-type supergiant. In addition, we assembled and analysed high-resolution high signal-to-noise spectroscopy taken with four spectrographs during some 1800 d to interpret the temporal spectroscopic variability of the star. The variability of this blue supergiant derived from the scattered-light space photometry is in full in agreement with the one found in the ground-based spectroscopy. We find significant low-frequency variability that is consistently detected in all spectral lines of HD 188209. The photospheric variability propagates into the wind, where it has similar frequencies but slightly higher amplitudes. The morphology of the frequency spectra derived from the long-term photometry and spectroscopy points towards a spectrum of travelling waves with frequency values in the range expected for an evolved O-type star. Convectively-driven internal gravity waves excited in the stellar interior offer the most plausible explanation of the detected variability. Based on photometric observations made with the NASA Kepler satellite and on spectroscopic observations made with four telescopes: the Nordic Optical Telescope operated by NOTSA and the Mercator Telescope operated by the Flemish Community, both at the Observatorio del Roque de los Muchachos (La Palma, Spain) of the Instituto de Astrofísica de Canarias, the T13 2.0 m Automatic Spectroscopic

  1. The Yellow and Red Supergiants of M33

    CERN Document Server

    Drout, Maria R; Meynet, Georges

    2012-01-01

    Yellow and red supergiants are evolved massive stars whose numbers and locations on the HR diagram can provide a stringent test for models of massive star evolution. Previous studies have found large discrepancies between the relative number of yellow supergiants observed as a function of mass and those predicted by evolutionary models, while a disagreement between the predicted and observed locations of red supergiants on the HR diagram was only recently resolved. Here we extend these studies by examining the yellow and red supergiant populations of M33. Unfortunately, identifying these stars is difficult as this portion of the color-magnitude diagram is heavily contaminated by foreground dwarfs. We identify the red supergiants through a combination of radial velocities and a two-color surface gravity discriminant and, after re-characterizing the rotation curve of M33 with our newly selected red supergiants, we identify the yellow supergiants through a combination of radial velocities and the strength of the...

  2. High Resolution, Long - Slit Spectroscopy of VY CMa: The Evidence for Localized High Mass Loss Events

    CERN Document Server

    Humphreys, R M; Ruch, G; Wallerstein, G; Humphreys, Roberta M.; Davidson, Kris; Ruch, Gerald; Wallerstein, George

    2004-01-01

    High spatial and spectral resolution spectroscopy of the OH/IR supergiant VY CMa and its circumstellar ejecta reveals evidence for high mass loss events from localized regions on the star occurring over the past 1000 years. The reflected absorption lines and the extremely strong K I emission lines show a complex pattern of velocities in the ejecta. We show that the large, dusty NW arc, expanding at 50 km/sec with respect to the embedded star, is kinematically distinct from the surrounding nebulosity and was ejected about 400 years ago. Other large, more filamentary loops were probably expelled as much as 800 to 1000 years ago while knots and small arcs close to the star resulted from more recent events 100 to 200 years ago. The more diffuse, uniformly distributed gas and dust is surprisingly stationary with little or no velocity relative to the star. This is not what we would expect for the circumstellar material from an evolved red supergiant with a long history of mass loss. We therefore suggest that the hi...

  3. XMM-Newton and NuSTAR joint observation of the periodic Supergiant Fast X-ray Transient IGR J11215-5952

    Science.gov (United States)

    Sidoli, L.; Paizis, A.; Sguera, V.

    2016-06-01

    IGRJ11215-5952 is the only Supergiant Fast X-ray Transient showing periodic outbursts (every 165 days, the orbital period of the system). The driving mechanism causing the transient X-ray emission in this sub-class of High Mass X-ray Binaries is still a matter of debate, after 10 years from the discovery of the class. To disentangle between magnetar-like neutron stars from models requiring more usual neutron star magnetic fields (1E12G), we observed the SFXT pulsar IGRJ11215-5952 with XMM-Newton coordinated with NuSTAR on 2016, February 14, during the expected peak of the outburst, for a net exposure time of 20 ks. The source was indeed caught in outburst (1E36 erg/s), with several bright flares repeating quasi-periodically with timescales of a few thousand seconds, spanning a dynamic range of two orders of magnitude. The overlapping observation with both XMM-Newton and NuSTAR enabled the study of the simultaneous broad band spectrum from 0.3 to 78 keV. The work is still in progress, given the extreme variability of the X-ray emission. X-ray pulsations were detected at 187.14 s, consistent with the last XMM-Newton observation, performed in 2007. We will discuss XMM+NuSTAR results in light of the different models proposed to explain the SFXTs behavior.

  4. Mid-infrared interferometry on spectral lines III. Ammonia and Silane around IRC+10216 and VY CMa

    CERN Document Server

    Monnier, J D; Hale, D S; Tuthill, P G; Townes, C H

    2000-01-01

    Using the U.C. Berkeley Infrared Spatial Interferometer with an RF filterbank, the first interferometric observations of mid-infrared molecular absorption features of ammonia (NH_3) and silane (SiH_4) with very high spectral resolution (R ~ 100000) were made. Under the assumptions of spherical symmetry and uniform outflow, these new data permitted the molecular stratification around carbon star IRC+10216 and red supergiant VY CMa to be investigated. For IRC+10216, both ammonia and silane were found to form in the dusty outflow significantly beyond both the dust formation and gas acceleration zones. Specifically, ammonia was found to form before silane in a region of decaying gas turbulence (>~ 20 R_star), while the silane is produced in a region of relatively smooth gas flow much further from the star (>~ 80 R_star). The depletion of gas-phase SiS onto grains soon after dust formation may fuel silane-producing reactions on the grain surfaces. For VY CMa, a combination of interferometric and spectral observati...

  5. Near-infrared counterparts to Chandra X-ray sources toward the Galactic Center. II. Discovery of Wolf-Rayet stars and O supergiants

    CERN Document Server

    Mauerhan, Jon C; Morris, Mark R; Stolovy, Susan R; Cotera, Angela S

    2009-01-01

    We present new identifications of infrared counterparts to the population of hard X-ray sources near the Galactic center detected by the Chandra X-ray Observatory. We have confirmed 16 new massive stellar counterparts to the X-ray population, including nitrogen-type (WN) and carbon-type (WC) Wolf-Rayet stars, and O supergiants. For the majority of these sources, the X-ray photometry is consistent with thermal emission from plasma having temperatures in the range of kT=1-8 keV or non-thermal emission having power-law indices in the range of -1stars but are typical of massive binaries, in which the high-energy emission is generated by the collision of supersonic winds, or by accretion onto a compact companion. However, the possibility of intrinsic hard X-ray generation from...

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

    CERN Document Server

    Lutovinov, A; Postnov, K; Krivonos, R; Molkov, S; Tomsick, J

    2016-01-01

    We report on the first focused hard X-ray view of the absorbed supergiant system IGRJ18027-2016 performed with the NuSTAR observatory. The pulsations are clearly detected with a period of P_{spin}=139.866(1) s and a pulse fraction of about 50-60% at energies from 3 to 80 keV. The source demonstrates an approximately constant X-ray luminosity on a time scale of more than dozen years with an average spin-down rate of dP/dt~6x10^{-10} s/s. This behaviour of the pulsar can be explained in terms of the wind accretion model in the settling regime. The detailed spectral analysis at energies above 10 keV was performed for the first time and revealed a possible cyclotron absorption feature at energy ~23 keV. This energy corresponds to the magnetic field B~3x10^{12} G at the surface of the neutron star, which is typical for X-ray pulsars.

  7. The identification of extreme asymptotic giant branch stars and red supergiants in M33 with 24 μm variability

    Energy Technology Data Exchange (ETDEWEB)

    Montiel, Edward J.; Clayton, Geoffrey C.; Johnson, Christopher B. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Srinivasan, Sundar [Academica Sinica, Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei 10617, Taiwan, R. O. C. (China); Engelbracht, Charles W., E-mail: emonti2@lsu.edu [Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2015-02-01

    We present the first detection of 24 μm variability in 24 sources in the Local Group galaxy M33. These results are based on 4 epochs of Multiband Imaging Photometer for Spitzer observations, which are irregularly spaced over ∼750 days. We find that these sources are constrained exclusively to the Holmberg radius of the galaxy, which increases their chances of being members of M33. We have constructed spectral energy distributions (SEDs) ranging from the optical to the submillimeter to investigate the nature of these objects. We find that 23 of our objects are most likely heavily self-obscured, evolved stars, while the remaining source is the Giant H ii region, NGC 604. We believe that the observed variability is the intrinsic variability of the central star reprocessed through their circumstellar dust shells. Radiative transfer modeling was carried out to determine their likely chemical composition, luminosity, and dust production rate (DPR). As a sample, our modeling has determined an average luminosity of (3.8±0.9)×10{sup 4} L{sub ⊙} and a total DPR of (2.3±0.1)×10{sup −5} M{sub ⊙} yr{sup −1}. Most of the sources, given the high DPRs and short wavelength obscuration, are likely extreme asymptotic giant branch (XAGB) stars. Five of the sources are found to have luminosities above the classical AGB limit (M{sub bol} <−7.1 mag, L > 54,000 L{sub ⊙}), which classifies them as probable red supergiants (RSGs). Almost all of the sources are classified as oxygen-rich. As also seen in the LMC, a significant fraction of the dust in M33 is produced by a handful of XAGB and RSG stars.

  8. Discovery and Characterization of Luminous Blue Variables, Wolf-Rayet Stars, and Massive Supergiants and Their Shells Using Spitzer, WISE, and Herschel Data

    Science.gov (United States)

    Stringfellow, Guy

    The extensive WISE all-sky 12 and 22 micron survey data, the Herschel PACS and SPIRE imaging archive (including the GTO and OT Key Programs), as well as the Spitzer IRAC 8 and MIPS 24 micron imaging archival data (GO, GTO, and Legacy Surveys) are being mined for the discovery of new shell and ring-nebulae. Combined with 2MASS data, the progenitor stars are also being identified, and optical and near-IR spectroscopy obtained to confirm their spectral types. Origin of the nebulae arise from a variety of progenitors that include very massive stars, with the vast majority not having been previously identified. Representative classes for the progenitor stars are Luminous Blue Variables (LBVs), Wolf-Rayet (WR), B[e], OB, and Supergiant stars. The discovery potential for these rare massive evolved stars from the mid-IR imaging archives is greater than any other technique utilized over the past several decades, including extensive broadband infrared photometry-color determinations (Hadfield et al. 2007), and near-IR narrowband methods (Shara et al. 2009). The statistics being provided on this new, previously hidden population of evolved stars may very well enable evolutionary pathways to be better delineated, thereby identifying the physics operating in these extreme stars. The data being collected will more tightly define the evolutionary models that apply to these stars, and that enter into modeling and interpretation of extragalactic massive star formation regions (starbursts). Multi-wavelength color-color maps wil be constructed and used to analyze the dust distribution, the energetics of the nebulae and its interaction with the ISM, and identification of nearby star formation perhaps being triggered by the massive stars and the nebulae they produce. As demonstrated in a recent publication presenting the discovery and analysis of two new candidate LBVs found in the early WISE data release (Gvaramadze et al. 2012), much discovery potential yet resides within the

  9. Red supergiants and stellar evolution

    CERN Document Server

    Ekström, Sylvia; Meynet, Georges; Groh, Jose; Granada, Anahí

    2013-01-01

    We review the significant role played by red supergiants (RSGs) in stellar populations, and some challenges and questions they raise for theoretical stellar evolution. We present how metallicity and rotation modify the way stars go to the red part of the Hertzsprung- Russell diagram or come back from it, and how RSGs might keep a trace of their main-sequence evolution. We compare theoretical popu- lation ratios with observed ones.

  10. ALMA observations of TiO$_2$ around VY Canis Majoris

    CERN Document Server

    De Beck, E; Muller, S; Black, J H; O'Gorman, E; Richards, A M S; Baudry, A; Maercker, M; Decin, L; Humphreys, E M

    2015-01-01

    Titanium dioxide, TiO$_2$, is a refractory species that could play a crucial role in the dust-condensation sequence around oxygen-rich evolved stars. To date, gas phase TiO$_2$ has been detected only in the complex environment of the red supergiant VY CMa. We aim to constrain the distribution and excitation of TiO$_2$ around VY CMa in order to clarify its role in dust formation. We analyse spectra and channel maps for TiO$_2$ extracted from ALMA science verification data. We detect 15 transitions of TiO$_2$, and spatially resolve the emission for the first time. The maps demonstrate a highly clumpy, anisotropic outflow in which the TiO$_2$ emission likely traces gas exposed to the stellar radiation field. A roughly east-west oriented, accelerating bipolar-like structure is found, of which the blue component runs into and breaks up around a solid continuum component. A distinct tail to the south-west is seen for some transitions, consistent with features seen in the optical and near-infrared. We find that a si...

  11. Yellow and Red Supergiants in the Large Magellanic Cloud

    CERN Document Server

    Neugent, Kathryn F; Skiff, Brian; Meynet, Georges

    2012-01-01

    Due to their transitionary nature, yellow supergiants provide a critical challenge for evolutionary modeling. Previous studies within M31 and the SMC show that the Geneva evolutionary models do a poor job at predicting the lifetimes of these short-lived stars. Here we extend this study to the LMC while also investigating the galaxy's red supergiant content. This task is complicated by contamination by Galactic foreground stars that color and magnitude criteria alone cannot weed out. Therefore, we use proper motions and the LMC's large systemic radial velocity (\\sim278 km/s) to separate out these foreground dwarfs. After observing nearly 2,000 stars, we identified 317 probable yellow supergiants, 6 possible yellow supergiants and 505 probable red supergiants. Foreground contamination of our yellow supergiant sample was \\sim80%, while that of the the red supergiant sample was only 3%. By placing the yellow supergiants on the H-R diagram and comparing them against the evolutionary tracks, we find that new Geneva...

  12. Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles - II. CO line survey of evolved stars: derivation of mass-loss rate formulae

    CERN Document Server

    De Beck, E; de Koter, A; Justtanont, K; Verhoelst, T; Kemper, F; Menten, K M M

    2010-01-01

    We aim to (1) set up simple and general analytical expressions to estimate mass-loss rates of evolved stars, and (2) from those calculate estimates for the mass-loss rates of asymptotic giant branch (AGB), red supergiant (RSG), and yellow hypergiant stars in our galactic sample. Rotationally excited lines of CO are a very robust diagnostic in the study of circumstellar envelopes (CSEs). When sampling different layers of the CSE, observations of these molecular lines lead to detailed profiles of kinetic temperature, expansion velocity, and density. A state-of-the-art, nonlocal thermal equilibrium, and co-moving frame radiative transfer code that predicts CO line intensities in the CSEs of late-type stars is used in deriving relations between stellar and molecular-line parameters, on the one hand, and mass-loss rate, on the other. We present analytical expressions for estimating the mass-loss rates of evolved stellar objects for 8 rotational transitions of the CO molecule, apply them to our extensive CO data se...

  13. High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR

    Science.gov (United States)

    Ohnaka, K.

    2014-01-01

    Context. The mass-loss mechanism in red giants and red supergiants is not yet understood well. The SiO fundamental lines near 8 μm are potentially useful for probing the outer atmosphere, which is essential for clarifying the mass-loss mechanism. However, these lines have been little explored until now. Aims: We present high spectral resolution spectroscopic observations of the SiO fundamental lines near 8.1 μm in 16 bright red giants and red supergiants. Our sample consists of seven normal (i.e., non-Mira) K-M giants (from K1.5 to M6.5), three Mira stars, three optically bright red supergiants, two dusty red supergiants, and the enigmatic object GCIRS3 near the Galactic center. Methods: Our program stars were observed between 8.088 μm and 8.112 μm with a spectral resolution of 30 000 using VLT/VISIR. Results: We detected SiO fundamental lines in all of our program stars except for GCIRS3. The SiO lines in normal K and M giants as well as optically bright (i.e., not dusty) red supergiants do not show P-Cyg profiles or blueshifts, which means the absence of systematic outflows in the SiO line forming region. We detected P-Cyg profiles in the SiO lines in the dusty red supergiants VY CMa and VX Sgr, with the latter object being a new detection. These SiO lines originate in the outflowing gas with the thermal dust continuum emission seen as the background. The outflow velocities of the SiO line forming region in VY CMa and VX Sgr are estimated to be 27 km s-1 and 17 km s-1, respectively. We derived basic stellar parameters (effective temperature, surface gravity, luminosity, and mass) for the normal K-M giants and optically bright red supergiants in our sample and compared the observed VISIR spectra with synthetic spectra predicted from MARCS photospheric models. Most of the SiO lines observed in the program stars warmer than ~3400 K are reasonably reproduced by the MARCS models, which allowed us to estimate the silicon abundance as well as the 28Si/29Si and 28Si

  14. The Identification of Extreme Asymptotic Giant Branch Stars and Red Supergiants in M33 by 24 {\\mu}m Variability

    CERN Document Server

    Montiel, Edward J; Clayton, Geoffrey C; Engelbracht, Charles W; Johnson, Christopher B

    2014-01-01

    We present the first detection of 24 {\\mu}m variability in 24 sources in the Local Group galaxy M33. These results are based on 4 epochs of MIPS observations, which are irregularly spaced over ~750 days. We find that these sources are constrained exclusively to the Holmberg radius of the galaxy, which increases their chances of being members of M33. We have constructed spectral energy distributions (SEDs) ranging from the optical to the sub-mm to investigate the nature of these objects. We find that 23 of our objects are most likely heavily self-obscured, evolved stars; while the remaining source is the Giant HII region, NGC 604. We believe that the observed variability is the intrinsic variability of the central star reprocessed through their circumstellar dust shells. Radiative transfer modeling was carried out to determine their likely chemical composition, luminosity, and dust production rate (DPR). As a sample, our modeling has determined an average luminosity of (3.8 $\\pm$ 0.9) x 10$^4$ L$_\\odot$ and a ...

  15. New perspectives on red supergiants

    Science.gov (United States)

    Dorda, R.; Negueruela, I.; González-Fernández, C.; Tabernero H. M.

    2017-03-01

    There is a high interest in cool supergiants (CSGs), because they play a key role in the understanding of the evolution and death of massive stars: most high-mass stars pass through this phase at some point of their evolution, and the physical conditions during it will determine their subsequent evolution. In addition, these stars are a powerful high-mass stellar formation tracers and also the main progenitors of core-collapse supernovae (SNe). Despite this, they are poorly characterized in some aspects: their extreme sizes and peculiar conditions defy the predictions of present-day atmospheric and evolutionary models. To bring perspective to this topic, we investigate the behaviour of CSGs as a population. For this, we studied the largest homogeneous multiepoch spectroscopic sample of CSGs (from the SMC and LMC) to date (>500). Our results give a new global view about the physical conditions of CSGs and their evolution

  16. The effects of red supergiant mass loss on supernova ejecta and the circumburst medium

    CERN Document Server

    van Loon, Jacco Th

    2009-01-01

    Massive stars becoming red supergiants lose a significant amount of their mass during that brief evolutionary phase. They then either explode as a hydrogen-rich supernova (SN Type II), or continue to evolve as a hotter supergiant (before exploding). The slow, dusty ejecta of the red supergiant will be over-run by the hot star wind and/or SN ejecta. I will present estimates of the conditions for this interaction and discuss some of the implications.

  17. Luminous and Variable Stars in M31 and M33. II. Luminous Blue Variables, Candidate LBVs, Fe II Emission Line Stars, and Other Supergiants

    CERN Document Server

    Humphreys, Roberta M; Davidson, Kris; Bomans, D J; Burggraf, Birgitta

    2014-01-01

    An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the Luminous Blue Varaibles (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-SN stages of very massive stars. We have begun a survey of the evolved and un stable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we review the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars.We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiesc...

  18. An Interferometric Spectral-Line and Imaging Survey of VY Canis Majoris in the 345 GHz Band

    CERN Document Server

    Kaminski, T; Young, K H; Menten, K M; Patel, N A

    2013-01-01

    A spectral line survey of the oxygen-rich red supergiant VY Canis Majoris was made between 279 and 355 GHz with the Submillimeter Array. Two hundred twenty three spectral features from 19 molecules (not counting isotopic species of some of them) were observed, including the rotational spectra of TiO, TiO2, and AlCl for the first time in this source. The parameters and an atlas of all spectral features is presented. Observations of each line with a synthesized beam of ~0.9 arcsec, reveal the complex kinematics and morphology of the nebula surrounding VY CMa. Many of the molecules are observed in high lying rotational levels or in excited vibrational levels. From these, it was established that the main source of the submillimeter-wave continuum (dust) and the high excitation molecular gas (the star) are separated by about 0.15 arcsec. Apparent coincidences between the molecular gas observed with the SMA, and some of the arcs and knots observed at infrared wavelengths and in the optical scattered light by the Hu...

  19. Gaia TGAS search for Large Magellanic Cloud runaway supergiant stars:Candidate hypervelocity star discovery, and the nature of R71

    CERN Document Server

    Lennon, Daniel J; Lerate, Mercedes Ramos; O'Mullane, William; Sahlmann, Johannes

    2016-01-01

    We search for runaway stars in the Large Magellanic Cloud (LMC) by computing the space velocities of the visually brightest stars in the LMC that are included in the Gaia TGAS proper motion catalog. We compare with predictions from stellar dynamical models to obtain (peculiar) velocities relative to their local stellar environment. Two of the 31 stars have unusually high proper motions. Of the remaining 29 stars we find that most objects in this sample have velocities in very good agreement with model predictions of a circularly rotating disk model. Indeed the excellent fit to the model implies that the TGAS uncertainty estimates are likely overestimated. The fastest outliers in this subsample contain the LBV R71 and a few other well known emission line objects though in no case do we derive velocities consistent with fast (~100 km/s) runaways. Our results imply that R 71 in particular has a moderate deviation from the local stellar velocity field (40 km/s) lending support to the proposition that this object ...

  20. The Red Supergiant Content of M31

    CERN Document Server

    Massey, Philip

    2016-01-01

    We investigate the red supergiant (RSG) population of M31, obtaining radial velocities of 255 stars. These data substantiate membership of our photometrically-selected sample, demonstrating that Galactic foreground stars and extragalactic RSGs can be distinguished on the basis of B-V, V-R two-color diagrams. In addition, we use these spectra to measure effective temperatures and assign spectral types, deriving physical properties for 192 RSGs. Comparison with the solar-metallicity Geneva evolutionary tracks indicates astonishingly good agreement. The most luminous RSGs in M31 are likely evolved from 25-30 Mo stars, while the vast majority evolved from stars with initial masses of 20 Mo or less. There is an interesting bifurcation in the distribution of RSGs with effective temperatures that increases with higher luminosities, with one sequence consisting of early K-type supergiants, and with the other consisting of M-type supergiants that become later (cooler) with increasing luminosities. This separation is o...

  1. The mass-loss rates of red supergiants at low metallicity: Detection of rotational CO emission from two red supergiants in the Large Magellanic Cloud

    CERN Document Server

    Matsuura, Mikako; Swinyard, Bruce; Yates, Jeremy; Royer, P; Barlow, M J; Boyer, Martha; Decin, L; Khouri, Theo; Meixner, Margaret; van Loon, Jacco Th; Woods, Paul M

    2016-01-01

    Using the PACS and SPIRE spectrometers on-board the Herschel Space Observatory, we obtained spectra of two red supergiants (RSGs) in the Large Magellanic Cloud (LMC). Multiple rotational CO emission lines (J=6-5 to 15-14) and 15 H2O lines were detected from IRAS 05280-6910, and one CO line was detected from WOH G64. This is the first time CO rotational lines have been detected from evolved stars in the LMC. Their CO line intensities are as strong as those of the Galactic RSG, VY CMa. Modelling the CO lines and the spectral energy distribution results in an estimated mass-loss rate for IRAS 05280-6910 of 3x10^-4 Msun per yr. The model assumes a gas-to-dust ratio and a CO-to-H2 abundance ratio is estimated from the Galactic values scaled by the LMC metallicity ([Fe/H]~-0.3), i.e., that the CO-to-dust ratio is constant for Galactic and LMC metallicities within the uncertainties of the model. The key factor determining the CO line intensities and the mass-loss rate found to be the stellar luminosity.

  2. Core Hydrogen Burning Red Supergiants in the Young Globular Clusters

    Science.gov (United States)

    Szecsi, Dorottya; Mackey, Jonathan; Langer, Norbert

    2015-08-01

    The first stellar generation in galactic globular clusters contained massive low metallicity stars. We modelled the evolution of this massive stellar population and found that such stars with masses 100-600 Msun evolve into red supergiants. These red supergiants are particularly interesting because they spend not only the helium burning phase but even the last few hundres tousands of years of the core hydrogen burning phase on the RSG branch. Due to the presence of hot massive stars at the same time, we show that the RSG wind is trapped into photoionization confined shells. We simulate the shell formation around such red supergiants and find them to become gravitationally unstable. We propose a scenario in which these shells are responsible for the formation of the second generation low mass stars in globular clusters with anomalous surface abundances.

  3. HIFISTARS Herschel/HIFI observations of VY Canis Majoris. Molecular-line inventory of the envelope around the largest known star

    CERN Document Server

    Alcolea, J; Planesas, P; Teyssier, D; Cernicharo, J; De Beck, E; Decin, L; Dominik, C; Justtanont, K; de Koter, A; Marston, A P; Melnick, G; Menten, K M; Neufeld, D A; Olofsson, H; Schmidt, M; Schöier, F L; Szczerba, R; Waters, L B F M

    2013-01-01

    To gain insight into the physical conditions and kinematics of the warm (100-1000 K) gas around the red hyper-giant VY CMa, we performed sensitive high spectral resolution observations of molecular lines in the sub-mm/FIR using the HIFI instrument of the Herschel Space Observatory. We observed CO, H2O, and other molecular species, sampling excitation energies from a few tens to a few thousand K. These observations are part of the Herschel Guaranteed Time Key Program HIFISTARS. We detected the J=6-5, J=10-9, and J=16-15 lines of 12CO and 13CO at about 100, 300, and 750K above the ground state (and the 13CO J=9-8 line). These lines are crucial for improving the modelling of the internal layers of the envelope around VY CMa. We also detected 27 lines of H2O and its isotopomers, and 96 lines of species such as NH3, SiO, SO, SO2 HCN, OH and others, some of them originating from vibrationally excited levels. Three lines were not unambiguously assigned. Our observations confirm that VY CMa's envelope must consist of...

  4. vy matters

    CERN Document Server

    Bertoin, Jean; Jacod, Jean; Klüppelberg, Claudia

    2010-01-01

    This is the first volume of a subseries of the Lecture Notes in Mathematics which will appear randomly over the next years. Each volume will describe some important topic in the theory or applications of Lévy processes and pay tribute to the state of the art of this rapidly evolving subject with special emphasis on the non-Brownian world. The three expository articles of this first volume have been chosen to reflect the breadth of the area of Lévy processes. The first article by Ken-iti Sato characterizes extensions of the class of selfdecomposable distributions on R^d. The second article by Thomas Duquesne discusses Hausdorff and packing measures of stable trees. The third article by Oleg Reichmann and Christoph Schwab presents numerical solutions to Kolmogoroff equations, which arise for instance in financial engineering, when Lévy or additive processes model the dynamics of the risky assets.

  5. A Study of Hypergiant Mass Loss in the Near-To-Mid Infrared: VY CMa, IRC +10420, mu Cep and rho Cas

    Science.gov (United States)

    Shenoy, Dinesh Prabhakar

    2016-01-01

    Stars of initial mass greater than 9 M_sun become red supergiants (RSGs), a short-lived stage during which they experience mass-loss that strongly influences their post-RSG evolution and end state. The highest luminosity RSGs, referred to here as hypergiants, experience episodic mass-loss whose mechanism remains poorly understood and motivates observations to help constrain it. This thesis studies mass loss from hypergiant stars with near-to-mid infrared imaging over a range of angular scales. The recent mass-loss history of the extreme red supergiant VY Canis Majoris and the warm hypergiant star IRC +10420 are studied at the sub-arcsecond scale with adaptive optics imaging and imaging polarimetry from 1 - 5 micron using LMIRCam on the Large Binocular Telescope (LBT) and MMT-Pol at the MMT Observatory. The nebular features of VY CMa are found to be highly polarized at 1.3 and 3.1 micron, with optically thick scattering required to reproduce the observed surface brightness. The flux of VY CMa's peculiar ``Southwest Clump'' is demonstrated to be due almost entirely to optically thick scattering, with little thermal emission, and with a lower limit mass of 5E-03 M_sun in this single feature. The imaging polarimetry of IRC +10420 at 2.2 micron resolves nebular emission with intrinsic polarization of 30%, with a high surface brightness indicating optically thick scattering largely in the plane of the sky. Using the polarimetry to constrain the scattered light emission, it is shown that the nebula's the emission is mostly thermal with a color temperature well above that for typical astrophysical dust. To probe further into hypergiants' history of mass-loss, mid-IR imaging with MMT/ MIRAC and SOFIA/FORCAST is used to study VY CMa, IRC +10420 and two additional hypergiants: the RSG mu Cep and the warm hypergiant rho Cas. Using DUSTY 1-D radiative transfer models, mu Cep's mass-loss rate is found to have declined by about a factor of 5 over a 13,000 history, ranging from 5E

  6. Supernova shock breakout from a red supergiant.

    Science.gov (United States)

    Schawinski, Kevin; Justham, Stephen; Wolf, Christian; Podsiadlowski, Philipp; Sullivan, Mark; Steenbrugge, Katrien C; Bell, Tony; Röser, Hermann-Josef; Walker, Emma S; Astier, Pierre; Balam, Dave; Balland, Christophe; Carlberg, Ray; Conley, Alex; Fouchez, Dominique; Guy, Julien; Hardin, Delphine; Hook, Isobel; Howell, D Andrew; Pain, Reynald; Perrett, Kathy; Pritchet, Chris; Regnault, Nicolas; Yi, Sukyoung K

    2008-07-11

    Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic "core-collapse" supernova. Such events are usually only detected at least a few days after the star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy Evolution Explorer space telescope reveal a radiative precursor from the supernova shock before the shock reached the surface of the star and show the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve confirm that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a way to probe the physics of core-collapse supernovae and the internal structures of their progenitor stars.

  7. Unveiling the evolutionary phase of B[e] supergiants

    Science.gov (United States)

    Muratore, M. F.; Kraus, M.; Liermann, A.; Schnurr, O.; Cidale, L. S.; Arias, M. L.

    We obtained medium resolution K-band spectra for two B[e] supergiants and one yellow hypergiant (YHG) in the Large Magellanic Cloud (LMC) and found that the spectra of all three stars show enhanced 13CO band emis- sion, in agreement with theoretical predictions for evolved massive stars. Our preliminary results for the two B[e]SGs seem to indicate that one is a pre-RSG star while the other is in a post-RSG phase.

  8. SEARCHING FOR COOL DUST IN THE MID-TO-FAR INFRARED: THE MASS-LOSS HISTORIES OF THE HYPERGIANTS μ Cep, VY CMa, IRC+10420, AND ρ Cas

    Energy Technology Data Exchange (ETDEWEB)

    Shenoy, Dinesh; Humphreys, Roberta M.; Jones, Terry J.; Gehrz, Robert D. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street, SE, Minneapolis, MN 55455 (United States); Marengo, Massimo [Department of Physics, Iowa State University, Ames, IA 50011 (United States); Helton, L. Andrew [USRA-SOFIA Science Center, NASA Ames Research Center, Moffett Field, CA 94035 (United States); Hoffmann, William F.; Skemer, Andrew J.; Hinz, Philip M., E-mail: shenoy@astro.umn.edu [Department of Astronomy/Steward Observatory, University of Arizona, 933N. Cherry Avenue, Tucson, AZ 85721 (United States)

    2016-03-15

    We present mid- and far-IR imaging of four famous hypergiant stars: the red supergiants μ Cep and VY CMa, and the warm hypergiants IRC +10420 and ρ Cas. Our 11–37 μm SOFIA/FORCAST imaging probes cool dust not detected in visual and near-IR imaging studies. Adaptive optics 8–12 μm imaging of μ Cep and IRC +10420 with MMT/MIRAC reveals extended envelopes that are the likely sources of these stars’ strong silicate emission features. We find μ Cep’s mass-loss rate to have declined by about a factor of five over a 13,000 year history, ranging from 5 × 10{sup −6} down to ∼1× 10{sup −6} M{sub ⊙} yr{sup −1}. The morphology of VY CMa indicates a cooler dust component coincident with the highly asymmetric reflection nebulae seen in the visual and near-IR. The lack of cold dust at greater distances around VY CMa indicates that its mass-loss history is limited to the last ∼1200 years, with an average rate of 6 × 10{sup −4} M{sub ⊙} yr{sup −1}. We find two distinct periods in the mass-loss history of IRC +10420 with a high rate of 2 × 10{sup −3} M{sub ⊙} yr{sup −1} until approximately 2000 years ago, followed by an order of magnitude decrease in the recent past. We interpret this change as evidence of its evolution beyond the RSG stage. Our new infrared photometry of ρ Cas is consistent with emission from the expanding dust shell ejected in its 1946 eruption, with no evidence of newer dust formation from its more recent events.

  9. Detection of superhumps in the VY Scl-type nova-like variable KR Aur

    CERN Document Server

    Kozhevnikov, V P

    2007-01-01

    We report on detection of negative superhumps in KR Aur which is the representative member of the VY Scl stars. The observations were obtained with the multi-channel photometer during 107 h. The analysis of the data clearly revealed brightness variations with a period of 3.771 +/- 0.005 h. This is 3.5 per cent less than the orbital period, suggesting it is a negative superhump. Negative superhumps in VY Scl stars are widely spread. The discovery of powerful soft X-rays from V751 Cyg demonstrates that VY Scl stars may contain white dwarfs, at which nuclear burning of the accreted material occur. If this suspicion is correct, we then can suppose that the powerful radiation emerging from the white dwarf may cause the tilt of the accretion disk to the orbital plane, and its retrograde precession may produce negative superhumps in VY Scl stars.

  10. Supernova Shock Breakout from a Red Supergiant

    CERN Document Server

    Schawinski, Kevin; Wolf, Christian; Podsiadlowski, Philipp; Sullivan, Mark; Steenbrugge, Katrien C; Bell, Tony; Roeser, Hermann-Josef; Walker, Emma; Astier, Pierre; Balam, Dave; Balland, Christophe; Basa, Stephane; Carlberg, Ray; Conley, Alex; Fouchez, Dominque; Guy, Julien; Hardin, Delphine; Hook, Isobel; Howell, Andy; Pain, Reynald; Perrett, Kathy; Pritchet, Chris; Regnault, Nicolas; Yi, Sukyoung K

    2008-01-01

    Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic `core-collapse' supernova. Such events are usually detected long after the star has exploded. Here we report the first detection of the radiative precursor from a supernova shock before it has reached the surface of a star followed by the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve show that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a promising and novel way to probe the physics of core-collapse supernovae and the internal structures of their progenitors.

  11. Magnetic fields around late-type stars using water maser observations

    CERN Document Server

    Vlemmings, W H T; Diamond, P J

    2005-01-01

    We present the analysis of the circular polarization, due to Zeeman splitting, of the water masers around a sample of late-type stars to determine the magnetic fields in their circumstellar envelopes. The magnetic field strengths in the water maser regions around the Mira variable stars U Ori and U Her are shown to be several Gauss while those of the supergiants S Per, NML Cyg and VY CMa are several hundred mG. We also show that large scale magnetic fields permeate the CSE of an evolved star; the polarization of the water masers around VX Sgr reveals a dipole field structure. We shortly discuss the coupling of the magnetic field with the stellar outflow, as such fields could possibly be the cause of distinctly aspherical mass-loss and the resulting aspherical planetary nebulae.

  12. Supergiant Fast X-ray Transients

    CERN Document Server

    Sidoli, Lara

    2011-01-01

    The phenomenology of a subclass of High Mass X-ray Binaries hosting a blue supergiant companion, the so-called Supergiant Fast X-ray Transients (SFXTs), is reviewed. Their number is growing, mainly thanks to the discoveries performed by the INTEGRAL satellite, then followed by soft X-rays observations (both aimed at refining the source position and at monitoring the source behavior) leading to the optical identification of the blue supergiant nature of the donor star. Their defining properties are a transient X-ray activity consisting of sporadic, fast and bright flares, (each with a variable duration between a few minutes and a few hours), reaching 1E36-1E37 erg/s. The quiescence is at a luminosity of 1E32 erg/s, while their more frequent state consists of an intermediate X-ray emission of 1E33-1E34 erg/s (1-10 keV). Only the brightest flares are detected by INTEGRAL (>17 keV) during short pointings, with no detected persistent emission. The physical mechanism driving the short outbursts is still debated, al...

  13. The pulsating yellow supergiant V810 Centauri

    CERN Document Server

    Kienzle-Focacci, M N; Burnet, M; Meynet, G

    1998-01-01

    The F8Ia supergiant V810 Centauri is part of a long-term high-precision photometric monitoring program on long period variables started twenty years ago. Time series analysis of this unique set of 500 data points, spanning almost fifteen years in the homogeneous Geneva photometric system, is presented. Cluster membership, physical parameters and evolutionary status of the star are reinvestigated. Radial velocity data do not support the cluster membership to Stock 14}. Ultraviolet and optical spectrophotometry is combined with optical and infrared photometry to evaluate the physical parameters of the yellow supergiant (Teff = 5970 K, M_bol = -8.5, R = 420 R_sun) and of its B0III companion. From theoretical stellar evolutionary tracks, an initial mass of 25 M_sun is estimated for V810 Cen, which is actually at the end of its first redward evolution. V810 Cen is a multi-periodic small amplitude variable star, whose amplitudes are variable with time. The period of the main mode, 156 d, is in agreement with the Pe...

  14. Observational constraints on the X-ray Bright supergiant B[e] stars LHA 115-S18 \\& LHA 120-S 134

    CERN Document Server

    Bartlett, Elizabeth S

    2016-01-01

    We present the preliminary results of an ongoing series of spectroscopic observations of the Small Magellanic Cloud star LHA 115-S 18 (S18), which has demonstrated extreme photospheric and spectroscopic variability that, in some respects, is reminiscent of Luminous Blue Variables (LBVs). In contrast to our previously published results, between 2012-2015 S18 remained in an spectral state intermediate between S18's "hot" and "cool" extremes. In conjunction with contemporaneous OGLE-IV photometric monitoring of S18, these data will be used to determine the characteristic timescale of the variability and search for periodicities, in particular binary modulated periodicity. We also present the results of a pilot study of the LMC star LHA 120-S 134.

  15. An Observational Evaluation of Magnetic Confinement in the Winds of BA Supergiants

    CERN Document Server

    Shultz, M; Petit, V; Grunhut, J; Neiner, C; Hanes, D

    2013-01-01

    Magnetic wind confinement has been proposed as one explanation for the complex wind structures of supergiant stars of spectral types B and A. Observational investigation of this hypothesis was undertaken using high-resolution ({\\lambda}/{\\Delta}{\\lambda} {\\sim} 65,000) circular polarization (Stokes V ) spectra of six late B and early A type supergiants ({\\beta} Ori, B8Iae; 4 Lac, B9Iab; {\\eta} Leo, A0Ib; HR1040, A0Ib; {\\alpha} Cyg, A2Iae; {\

  16. Peculiar Type II Supernovae from Blue Supergiants

    CERN Document Server

    Kleiser, Io K W; Kasen, Daniel; Young, Timothy R; Chornock, Ryan; Filippenko, Alexei V; Challis, Peter; Ganeshalingam, Mohan; Kirshner, Robert P; Li, Weidong; Matheson, Thomas; Nugent, Peter E; Silverman, Jeffrey M

    2011-01-01

    The vast majority of Type II supernovae (SNe) are produced by red supergiants (RSGs), but SN 1987A revealed that blue supergiants (BSGs) can produce members of this class as well, albeit with some peculiar properties. This best studied event revolutionized our understanding of SNe, and linking it to the bulk of Type II events is essential. We present here optical photometry and spectroscopy gathered for SN 2000cb, which is clearly not a standard Type II SN and yet is not a SN 1987A analog. The light curve of SN 2000cb is reminiscent of that of SN 1987A in shape, with a slow rise to a late optical peak, but on substantially different time scales. Spectroscopically, SN 2000cb resembles a normal SN II but with ejecta velocities that far exceed those measured for SN 1987A or normal SNe II, above 18000 km/s for H-alpha at early times. The red colours, high velocities, late photometric peak, and our modeling of this object all point toward a scenario involving the high-energy explosion of a small-radius star, most ...

  17. Characterisation of red supergiants in the Gaia spectral range

    Science.gov (United States)

    Dorda, Ricardo; González-Fernández, Carlos; Negueruela, Ignacio

    2016-11-01

    Context. The infrared calcium triplet and its nearby spectral region have been used for spectral and luminosity classification of late-type stars, but the samples of cool supergiants (CSGs) used have been very limited (in size, metallicity range, and spectral types covered). The spectral range of the Gaia Radial Velocity Spectrograph (RVS) covers most of this region but does not reach the main TiO bands in this region, whose depths define the M sequence. Aims: We study the behaviour of spectral features around the calcium triplet and develop effective criteria to identify and classify CSGs, comparing their efficiency with other methods previously proposed. Methods: We measure the main spectral features in a large sample (almost 600) of red supergiants (RSGs) from three different galaxies, and we analyse their behaviour through a principal component analysis. Using the principal components, we develop an automatised method to differentiate CSGs from other bright late-type stars, and to classify them. Results: The proposed method identifies a high fraction (0.98 ± 0.04) of the supergiants in our test sample, which cover a wide metallicity range (supergiants from the Magellanic Clouds and the Milky Way) and with spectral types from G0 up to late-M. In addition, it is capable to separate most of the non-supergiants in the sample, identifying as supergiants only a very small fraction of them (0.02 ± 0.04). A comparison of this method with other previously proposed shows that it is more efficient and selects less interlopers. A way to automatically assign a spectral type to the supergiants is also developed. We apply this study to spectra at the resolution and spectral range of the Gaia RVS, with a similar success rate. Conclusions: The method developed identifies and classifies CSGs in large samples, with high efficiency and low contamination, even in conditions of wide metallicity and spectral-type ranges. As this method uses the infrared calcium triplet spectral

  18. The Infrared Continuum Spectrum of VY CMa

    CERN Document Server

    Harwit, M; Decin, L; Waelkens, C; Feuchtgruber, H; Melnick, G J; Harwit, Martin; Malfait, Koen; Decin, Leen; Waelkens, Christoffel; Feuchtgruber, Helmut; Melnick, Gary J.

    2001-01-01

    We combine spectra of VY CMa obtained with the short- and long-wavelength spectrometers, SWS and LWS, on the Infrared Space Observatory to provide a first detailed continuum spectrum of this highly luminous star. The circumstellar dust cloud through which the star is observed is partially self-absorbing, which makes for complex computational modeling. We review previous work and comment on the range of uncertainties about the physical traits and mineralogical composition of the modeled disk. We show that these uncertainties significantly affect the modeling of the outflow and the estimated mass loss. In particular, we demonstrate that a variety of quite diverse models can produce good fits to the observed spectrum. If the outflow is steady, and the radiative repulsion on the dust cloud dominates the star's gravitational attraction, we show that the total dust mass-loss rate is $\\sim 4\\times 10^{-6}M_{\\odot}$ yr$^{-1}$, assuming that the star is at a distance of 1.5 kpc. Several indications, however, suggest t...

  19. Understanding A-type supergiants. I. Ultraviolet and visible spectral atlas of A-type supergiants

    CERN Document Server

    Verdugo, E; Gómez de Castro, A I

    1999-01-01

    This paper is the first of a series whose aim is to perform a systematic study of A-type supergiant atmospheres and winds. Here we present a spectral atlas of 41 A-supergiants observed by us in high and medium resolution in the visible and ultraviolet. The atlas consists of profiles of the H alpha , H beta , H gamma , H delta , H epsilon , Ca II (H and K), Na I (D1 and D2), Mg II/sub 4481/, Mg II uv1 and Fe II uv1, uv2, uv3, uv62, uv63, uv161 lines for 41 stars with spectral types ranging from B9 to A9 and luminosity classes Ia, Iab and Ib, and provides the basic data for a thoughtful study of these stars. The overall characteristics of the sample as well as the data reduction procedures are described. We also present some examples of spectral variability. Figures 1-3 are only available in electronic form at http://www.edpsciences.com. (27 refs).

  20. vy-driven queues

    NARCIS (Netherlands)

    K. Dębicki; M. Mandjes

    2012-01-01

    This survey addresses the class of queues with Lévy input, which covers the classical M/G/1 queue and the reflected Brownian motion as special cases. First the stationary behavior is treated, with special attention to the case of the input process having one-sided jumps (i.e., spectrally one-sided L

  1. Infrared observations of circumstellar ammonia in OH/IR supergiants

    Science.gov (United States)

    Mclaren, R. A.; Betz, A. L.

    1980-01-01

    Ammonia has been detected in the circumstellar envelopes of VY Canis Majoris, VX Sagittarii, and IRC +10420 by means of several absorption lines in the nu-2 vibration-rotation band near 950 kaysers. The line profiles are well resolved (0.2 km/sec resolution) and show the gas being accelerated to terminal expansion velocities near 30 km/sec. The observations reveal a method for determining the position of the central star on VLBI maps of OH maser emission to an accuracy of approximately 0.2 arcsec. A firm lower limit of 2 x 10 to the 15th/sq cm is obtained for the NH3 column density in VY Canis Majoris.

  2. Quantitative Studies of the Optical and UV Spectra of Galactic Early B Supergiants

    Science.gov (United States)

    Searle, S. C.; Prinja, R. K.; Massa, D.; Ryans, R.

    2008-01-01

    We undertake an optical and ultraviolet spectroscopic analysis of a sample of 20 Galactic B0-B5 supergiants of luminosity classes Ia, Ib, Iab, and II. Fundamental stellar parameters are obtained from optical diagnostics and a critical comparison of the model predictions to observed UV spectral features is made. Methods. Fundamental parameters (e.g., T(sub eff), log L(sub *), mass-loss rates and CNO abundances) are derived for individual stars using CMFGEN, a nLTE, line-blanketed model atmosphere code. The impact of these newly derived parameters on the Galactic B supergiant Ten scale, mass discrepancy, and wind-momentum luminosity relation is examined. Results. The B supergiant temperature scale derived here shows a reduction of about 1000-3000 K compared to previous results using unblanketed codes. Mass-loss rate estimates are in good agreement with predicted theoretical values, and all of the 20 BO-B5 supergiants analysed show evidence of CNO processing. A mass discrepancy still exists between spectroscopic and evolutionary masses, with the largest discrepancy occuring at log (L/(solar)L approx. 5.4. The observed WLR values calculated for B0-B0.7 supergiants are higher than predicted values, whereas the reverse is true for B1-B5 supergiants. This means that the discrepancy between observed and theoretical values cannot be resolved by adopting clumped (i.e., lower) mass-loss rates as for O stars. The most surprising result is that, although CMFGEN succeeds in reproducing the optical stellar spectrum accurately, it fails to precisely reproduce key UV diagnostics, such as the N v and C IV P Cygni profiles. This problem arises because the models are not ionised enough and fail to reproduce the full extent of the observed absorption trough of the P Cygni profiles. Conclusions. Newly-derived fundamental parameters for early B supergiants are in good agreement with similar work in the field. The most significant discovery, however, is the failure of CMFGEN to predict

  3. Quantitative Studies of the Optical and UV Spectra of Galactic Early B Supergiants

    Science.gov (United States)

    Searle, S. C.; Prinja, R. K.; Massa, D.; Ryans, R.

    2008-01-01

    We undertake an optical and ultraviolet spectroscopic analysis of a sample of 20 Galactic B0-B5 supergiants of luminosity classes Ia, Ib, Iab, and II. Fundamental stellar parameters are obtained from optical diagnostics and a critical comparison of the model predictions to observed UV spectral features is made. Methods. Fundamental parameters (e.g., T(sub eff), log L(sub *), mass-loss rates and CNO abundances) are derived for individual stars using CMFGEN, a nLTE, line-blanketed model atmosphere code. The impact of these newly derived parameters on the Galactic B supergiant Ten scale, mass discrepancy, and wind-momentum luminosity relation is examined. Results. The B supergiant temperature scale derived here shows a reduction of about 1000-3000 K compared to previous results using unblanketed codes. Mass-loss rate estimates are in good agreement with predicted theoretical values, and all of the 20 BO-B5 supergiants analysed show evidence of CNO processing. A mass discrepancy still exists between spectroscopic and evolutionary masses, with the largest discrepancy occuring at log (L/(solar)L approx. 5.4. The observed WLR values calculated for B0-B0.7 supergiants are higher than predicted values, whereas the reverse is true for B1-B5 supergiants. This means that the discrepancy between observed and theoretical values cannot be resolved by adopting clumped (i.e., lower) mass-loss rates as for O stars. The most surprising result is that, although CMFGEN succeeds in reproducing the optical stellar spectrum accurately, it fails to precisely reproduce key UV diagnostics, such as the N v and C IV P Cygni profiles. This problem arises because the models are not ionised enough and fail to reproduce the full extent of the observed absorption trough of the P Cygni profiles. Conclusions. Newly-derived fundamental parameters for early B supergiants are in good agreement with similar work in the field. The most significant discovery, however, is the failure of CMFGEN to predict

  4. A New Survey for Red Supergiants in the Magellanic Clouds

    Science.gov (United States)

    González-Fernández, C.; Negueruela, I.; Dorda, R.

    2016-10-01

    We present a pilot program focused on the red supergiant population of the Magellanic Clouds, with the intent of extending the current known sample to include the unexplored low end of the brightness distribution of these stars, building a more representative dataset with which to extrapolate their behavior to other Galactic and extra-galactic environments. For a pool of candidates selected over near-infrared photometry, we obtain medium resolution multi-object spectroscopy to confirm their nature and their membership in the clouds. Around two hundred new red supergiants have been detected, hinting at a yet-to-be-observed large population. Based on this sample, new a priori classification criteria are investigated, combining mid- and near-infrared photometry to improve the observational efficiency of programs similar to this. A more complete and detailed analysis of this dataset can be found in González- Fernández et al. (2015).

  5. Fast radio bursts counterparts in the scenario of supergiant pulses

    Science.gov (United States)

    Popov, S. B.; Pshirkov, M. S.

    2016-10-01

    We discuss identification of possible counterparts and persistent sources related to fast radio bursts (FRBs) in the framework of the model of supergiant pulses from young neutron stars with large spin-down luminosities. In particular, we demonstrate that at least some of the sources of FRBs can be observed as ultraluminous X-ray sources (ULXs). At the moment no ULXs are known to be coincident with localization areas of FRBs. We searched for a correlation of FRB positions with galaxies in the 2MASS Redshift survey catalogue. Our analysis produced statistically insignificant overabundance (p-value ≈ 4 per cent) of galaxies in error boxes of FRBs. In the very near future with even modestly increased statistics of FRBs and with the help of dedicated X-ray observations and all-sky X-ray surveys it will be possible to decisively prove or falsify the supergiant pulses model.

  6. vy Bases and Extended Subordination

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole

    The concept of subordination of Lévy processes is reinterpreted and then extended to a definition of subordination of Lévy bases. This is extended a step further, and then applied to give an alternative way of volatility/intermittency modulation in the context of ambit fields.......The concept of subordination of Lévy processes is reinterpreted and then extended to a definition of subordination of Lévy bases. This is extended a step further, and then applied to give an alternative way of volatility/intermittency modulation in the context of ambit fields....

  7. The blue supergiant MN18 and its bipolar circumstellar nebula

    CERN Document Server

    Gvaramadze, V V; Bestenlehner, J M; Bodensteiner, J; Langer, N; Greiner, J; Grebel, E K; Berdnikov, L N; Beletsky, Y

    2015-01-01

    We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope. Using the optical spectrum obtained with the Southern African Large Telescope, we classify this star as B1 Ia. The evolved status of MN18 is supported by the detection of nitrogen overabundance in the nebula, which implies that it is composed of processed material ejected by the star. We analysed the spectrum of MN18 by using the code CMFGEN, obtaining a stellar effective temperature of \\approx 21 kK. The star is highly reddened, E(B-V)\\approx 2 mag. Adopting an absolute visual magnitude of M_V=-6.8\\pm0.5 (typical of B1 supergiants), MN18 has a luminosity of log L/Lsun \\approx 5.42\\pm0.30, a mass-loss rate of \\approx (2.8-4.5)\\times10^{-7} Msun/yr, and resides at a distance of \\approx 5.6^{+1.5} _{-1.2} kpc. We discuss the origin of the nebula around MN18 and compare it with similar nebulae produced by other blue supergiants in the Galaxy (She...

  8. Supernovae from yellow, blue supergiants: origin and consequences for stellar evolution

    Science.gov (United States)

    Meynet, Georges; Georgy, Cyril; Saio, Hideyuki; Kudritzki, Rolf-Peter; Groh, Jose

    2015-08-01

    A few core collapse supernovae progenitors have been found to be yellow or blue supergiants. We shall discuss possible scenarios involving single and close binary evolution allowing to explain this kind of core collapse supernova progenitors. According to stellar models for both single and close binaries, blue supergiants, at the end of their nuclear lifetimes and thus progenitors of core collapse supernovae, present very different characteristics for what concerns their surface compositions, rotational surface velocities and pulsational properties with respect to blue supergiants in their core helium burning phase. We discuss how the small observed scatter of the flux-weighted gravity-luminosity (FWGL) relation of blue supergiants constrains the evolution of massive stars after the Main-Sequence phase and the nature of the progenitors of supernovae in the mass range between 12 and 40 solar masses. The present day observed surface abundances of blue supergiants, of their pulsational properties, as well as the small scatter of the FWGL relation provide strong constraints on both internal mixing and mass loss in massive stars and therefore on the end point of their evolution.

  9. Queues and Lévy Fluctuation Theory

    NARCIS (Netherlands)

    Dębicki, K.; Mandjes, M.

    2015-01-01

    The book provides an extensive introduction to queueing models driven by Lévy-processes as well as a systematic account of the literature on Lévy-driven queues. The objective is to make the reader familiar with the wide set of probabilistic techniques that have been developed over the past decades,

  10. Spectroscopic diagnostics for circumstellar disks of B[e] supergiants

    CERN Document Server

    Kraus, Michaela

    2016-01-01

    B[e] supergiants (B[e]SGs) are emission-line objects, presumably in a short-lived phase in the post-main sequence evolution of massive stars. Their intense infrared excess emission indicates large amounts of warm circumstellar dust, and the stars were longtime assumed to possess an aspherical wind consisting of a classical line-driven wind in polar direction and a dense, slow equatorial wind dubbed outflowing disk. The general properties obtained for these disks are in line with this scenario, although current theories have considerable difficulties reproducing the observed quantities. Therefore, more sophisticated observational constraints are needed. These follow from combined optical and infrared spectroscopic studies, which delivered the surprising result that the circumstellar material of B[e]SGs is concentrated in multiple rings revolving the stars on stable Keplerian orbits. Such a scenario requires new ideas for the formation mechanism, in which pulsations might play an important role.

  11. Search for aluminium monoxide in the winds of oxygen-rich AGB stars

    CERN Document Server

    De Beck, E; Ramstedt, S; Olofsson, H; Menten, K M; Patel, N A; Vlemmings, W H T

    2016-01-01

    Aluminium monoxide, AlO, is likely efficiently depleted from the gas around oxygen-rich evolved stars to form alumina clusters and dust seeds. Its presence in the extended atmospheres of evolved stars has been derived from optical spectroscopy. More recently, AlO gas was also detected at long wavelengths around the supergiant VY CMa and the oxygen-rich asymptotic giant branch (AGB) star o Cet (Mira A). In search of AlO, we mined data obtained with APEX, the IRAM 30m telescope, Herschel/HIFI, SMA, and ALMA, which were primarily aimed at studying other molecular species. We report here on observations of AlO towards a sample of eight oxygen-rich AGB stars in different rotational transitions, up to seven for some stars. We present definite detections of one rotational transition of AlO for o Cet and R Aqr, and tentative detections of one transition for R Dor and o Cet, and two for IK Tau and W Hya. The presented spectra of WX Psc, R Cas, and TX Cam show no signature of AlO. For o Cet, R Aqr, and IK Tau, we find ...

  12. The population of OB supergiants in the starburst cluster Westerlund 1

    CERN Document Server

    Negueruela, Ignacio; Ritchie, Ben W

    2010-01-01

    After leaving the main sequence, massive stars undergo complex evolution, still poorly understood. With a population of 100s OB stars, the starburst cluster Westerlund~1 offers an unparallelled environment to study their evolutionary tracks. We used the VLT/FORS2 to obtain intermediate-resolution spectroscopy over the range 5800-9000A of ~ 100 likely members. We developed criteria for their spectral classification using only spectral features in the range observed. We discuss these criteria, useful for spectral classification of early-type stars in the GAIA spectral region, in the appendix. Using these criteria, we obtain spectral classifications, probably accurate to one subtype, for 57 objects, most of which had no previous classification or a generic classification. We identify more than 50 objects as OB supergiants. We find almost 30 luminous early-B supergiants and a number of less luminous late-O supergiants. In addition, we find a few mid B supergiants with very high luminosity, some of them displaying...

  13. Jung and Lévy-Bruhl.

    Science.gov (United States)

    Segal, Robert A

    2007-11-01

    For his knowledge of 'primitive' peoples, C. G. Jung relied on the work of Lucien Lévy-Bruhl (1857-1939), a French philosopher who in mid-career became an armchair anthropologist. In a series of books from 1910 on, Lévy-Bruhl asserted that 'primitive' peoples had been misunderstood by modern Westerners. Rather than thinking like moderns, just less rigorously, 'primitives' harbour a mentality of their own. 'Primitive' thinking is both 'mystical' and 'prelogical'. By 'mystical', Lévy-Bruhl meant that 'primitive' peoples experience the world as identical with themselves. Their relationship to the world, including to fellow human beings, is that of participation mystique. By 'prelogical', Lévy-Bruhl meant that 'primitive' thinking is indifferent to contradictions. 'Primitive' peoples deem all things identical with one another yet somehow still distinct. A human is at once a tree and still a human being. Jung accepted unquestioningly Lévy-Bruhl's depiction of the 'primitive' mind, even when Jung, unlike Lévy-Bruhl, journeyed to the field to see 'primitive' peoples firsthand. But Jung altered Lévy-Bruhl's conception of 'primitive' mentality in three key ways. First, he psychologized it. Whereas for Lévy-Bruhl 'primitive' thinking is to be explained sociologically, for Jung it is to be explained psychologically: 'primitive' peoples think as they do because they live in a state of unconsciousness. Second, Jung universalized 'primitive' mentality. Whereas for Lévy-Bruhl 'primitive' thinking is ever more being replaced by modern thinking, for Jung 'primitive' thinking is the initial psychological state of all human beings. Third, Jung appreciated 'primitive' thinking. Whereas for Lévy-Bruhl 'primitive' thinking is false, for Jung it is true--once it is recognized as an expression not of how the world but of how the unconscious works. I consider, along with the criticisms of Lévy-Bruhl's conception of 'primitive' thinking by his fellow anthropologists and

  14. vy-based growth models

    DEFF Research Database (Denmark)

    Jónsdóttir, Kristjana Ýr; Schmiegel, Jürgen; Jensen, Eva Bjørn Vedel

    2008-01-01

    In the present paper, we give a condensed review, for the nonspecialist reader, of a new modelling framework for spatio-temporal processes, based on Lévy theory. We show the potential of the approach in stochastic geometry and spatial statistics by studying Lévy-based growth modelling of planar...... objects. The growth models considered are spatio-temporal stochastic processes on the circle. As a by product, flexible new models for space–time covariance functions on the circle are provided. An application of the Lévy-based growth models to tumour growth is discussed....

  15. Simultaneous VLBA polarimetric observations of the v=$\\{$1,2$\\}$ J=1-0 and v=1, J=2-1 SiO maser emission toward VY CMa II: component-level polarization analysis

    CERN Document Server

    Richter, L; Jonas, J

    2016-01-01

    This paper presents a component-level comparison of the polarized v=1 J =1-0, v=2 J=1-0 and v=1 J=2-1 SiO maser emission towards the supergiant star VY CMa at milliarcsecond-scale, as observed using the VLBA at $\\lambda=7$mm and $\\lambda=3$mm. An earlier paper considered overall maser morphology and constraints on SiO maser excitation and pumping derived from these data. The goal of the current paper is to use the measured polarization properties of individual co-spatial components detected across multiple transitions to provide constraints on several competing theories for the transport of polarized maser emission. This approach minimizes the significant effects of spatial blending. We present several diagnostic tests designed to distinguish key features of competing theoretical models for maser polarization. The number of coincident features is limited by sensitivity however, particularly in the v=1 J=2-1 transition at 86 GHz, and deeper observations are needed. Preliminary conclusions based on the current ...

  16. Spectroscopic study of the variability of three northern Of+ supergiants

    CERN Document Server

    De Becker, M; Linder, N

    2009-01-01

    The transition from early Of stars to WN type objects is poorly understood. O-type supergiants with emission lines (OIf+) are considered to be intermediate between these two classes. The scope of this paper is to investigate the spectral variability of three Of+ supergiants. We constituted spectral time series of unprecedented quality for our targets (~ 200 spectra in total), essentially in the blue domain, covering time-scales from a few hours up to a few years. Time Variance Spectrum (TVS) and Fourier analyses were performed in order to characterize their spectral variability. We report on a correlated significant line profile variability in the prominent He II \\lambda 4686 and H\\beta lines most likely related to the strong stellar winds. The variability pattern is similar for the three stars investigated (HD14947, HD15570 and HD16691), and the main differences are more quantitative than qualitative. However, the reported time-scales are somewhat different, and the most striking variability pattern is repor...

  17. Searching for supergiant fast X-ray transients with Swift

    CERN Document Server

    Romano, P; Esposito, P; Sbarufatti, B; Haberl, F; Ponti, G; D'Avanzo, P; Ducci, L; Segreto, A; Jin, C; Masetti, N; Del Santo, M; Campana, S; Mangano, V

    2016-01-01

    Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) hosting a neutron star and an OB supergiant companion. We examine the available Swift data, as well as other new or archival/serendipitous data, on three sources: IGR J17407-2808, 2XMM J185114.3-000004, and IGR J18175-2419, whose X-ray characteristics qualify them as candidate SFXT, in order to explore their properties and test whether they are consistent with an SFXT nature. As IGR J17407-2808 and 2XMM J185114.3-000004 triggered the Burst Alert Telescope on board Swift, the Swift data allow us to provide their first arcsecond localisations, leading to an unequivocal identification of the source CXOU J174042.0-280724 as the soft X-ray counterpart of IGR J17407-2808, as well as their first broadband spectra, which can be fit with models generally describing accreting neutron stars in HMXBs. While still lacking optical spectroscopy to assess the spectral type of the companion, we propose 2XMM J185114.3-000004 as a very strong SFXT can...

  18. Queues and Lévy fluctuation theory

    CERN Document Server

    Dębicki, Krzysztof

    2015-01-01

    The book provides an extensive introduction to queueing models driven by Lévy-processes as well as a systematic account of the literature on Lévy-driven queues. The objective is to make the reader familiar with the wide set of probabilistic techniques that have been developed over the past decades, including transform-based techniques, martingales, rate-conservation arguments, change-of-measure, importance sampling, and large deviations. On the application side, it demonstrates how Lévy traffic models arise when modelling current queueing-type systems (as communication networks) and includes applications to finance. Queues and Lévy Fluctuation Theory will appeal to graduate/postgraduate students and researchers in mathematics, computer science, and electrical engineering. Basic prerequisites are probability theory and stochastic processes.

  19. Symmetric Lévy Type Operator

    Institute of Scientific and Technical Information of China (English)

    Jian WANG

    2009-01-01

    The study of symmetric property in the L2-sense for the non-positive definite operator is motivated by the theory of probability and analysis. This paper presents some sufficient conditions for the existence of symmetric measure for Lévy type operator. Some new examples are illustrated. The present study is an important step for considering various ergodic properties and functional inequalities of Lévy type operator.

  20. An Emerging Coherent Picture of Red Supergiant Explosions

    CERN Document Server

    Poznanski, Dovi

    2013-01-01

    A large fraction of supernovae (SNe) arise from the core collapse of red supergiant stars. By comparing the ejecta velocities of a large sample of such SNe with initial stellar masses derived from pre-explosion images of the progenitor star, I find that there is a significant and approximately linear relation between initial mass and ejecta velocity, which in turn implies that the energy released during core collapse and captured by the ejecta depends strongly on this mass as E is proportional to M^3. This correlation naturally explains why most such SNe have almost identical "plateau-phase" durations in their light curves, and places an important constraint on the elusive physics of core collapse.

  1. A new survey of cool supergiants in the Magellanic Clouds

    CERN Document Server

    González-Fernández, Carlos; Negueruela, Ignacio; Marco, Amparo

    2015-01-01

    In this study, we conduct a pilot program aimed at the red supergiant population of the Magellanic Clouds. We intend to extend the current known sample to the unexplored low end of the brightness distribution of these stars, building a more representative dataset with which to extrapolate their behaviour to other Galactic and extra-galactic environments. We select candidates using only near infrared photometry, and with medium resolution multi-object spectroscopy, we perform spectral classification and derive their line-of-sight velocities, confirming the nature of the candidates and their membership to the clouds. Around two hundred new RSGs have been detected, hinting at a yet to be observed large population. Using near and mid infrared photometry we study the brightness distribution of these stars, the onset of mass-loss and the effect of dust in their atmospheres. Based on this sample, new a priori classification criteria are investigated, combining mid and near infrared photometry to improve the observat...

  2. Accretion in supergiant High Mass X-ray Binaries

    Directory of Open Access Journals (Sweden)

    Manousakis Antonios

    2014-01-01

    Full Text Available Supergiant High Mass X-ray Binary systems (sgHMXBs consist of a massive, late type, star and a neutron star. The massive stars exhibits strong, radiatively driven, stellar winds. Wind accretion onto compact object triggers X-ray emission, which alters the stellar wind significantly. Hydrodynamic simulation has been used to study the neutron star - stellar wind interaction it two sgHMXBs: i A heavily obscured sgHMXB (IGR J17252–3616 discovered by INTEGRAL. To account for observable quantities (i.e., absorbing column density we have to assume a very slow wind terminal velocity of about 500 km/s and a rather massive neutron star. If confirmed in other obscured systems, this could provide a completely new stellar wind diagnostics. ii A classical sgHMXB (Vela X-1 has been studied in depth to understand the origin of the off-states observed in this system. Among many models used to account for this observed behavior (clumpy wind, gating mechanism we propose that self-organized criticality of the accretion stream is the likely reason for the observed behavior. In conclusion, the neutron star, in these two examples, acts very effciently as a probe to study stellar winds.

  3. LBT Discovery of a Yellow Supergiant Eclipsing Binary in the Dwarf Galaxy Holmberg IX

    CERN Document Server

    Prieto, J L; Kochanek, C S; Weisz, D R; Baruffolo, A; Bechtold, J; Burwitz, V; DeSantis, C; Gallozzi, S; Garnavich, P M; Giallongo, E; Hill, J M; Pogge, R W; Ragazzoni, R; Speziali, R; Thompson, D J; Wagner, R M

    2007-01-01

    In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (MV ~ -7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 272 days and the light curve is well-fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed by two yellow supergiants (V-I ~ 1 mag, T_eff = 4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however note a second example. The SMC F0 supergiant R47 is a bright (MV ~ -7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well-fit as a contact binary with a 181 day period. We propose that these systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star...

  4. THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR

    Energy Technology Data Exchange (ETDEWEB)

    Bersten, Melina C.; Nomoto, Ken' ichi; Folatelli, Gaston; Maeda, Keiichi [Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan); Benvenuto, Omar G. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, B1900FWA La Plata (Argentina); Ergon, Mattias; Sollerman, Jesper [The Oskar Klein Centre, Department of Astronomy, AlbaNova, SE-106 91 Stockholm (Sweden); Benetti, Stefano; Ochner, Paolo; Tomasella, Lina [INAF-Osservatorio Astronomico di Padova, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Botticella, Maria Teresa [INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli (Italy); Fraser, Morgan; Kotak, Rubina, E-mail: melina.bersten@ipmu.jp [Astrophysics Research Centre, School of Mathematics and Physics, Queen' s University Belfast, Belfast BT7 1NN (United Kingdom)

    2012-09-20

    A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R {approx} 200 R{sub Sun }-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be Almost-Equal-To 2 M{sub Sun }, the explosion energy to be E = (6-10) Multiplication-Sign 10{sup 50} erg, and the {sup 56}Ni mass to be approximately 0.06 M{sub Sun }. The progenitor star was composed of a helium core of 3-4 M{sub Sun} and a thin hydrogen-rich envelope of Almost-Equal-To 0.1M{sub Sun} with a main-sequence mass estimated to be in the range of 12-15 M{sub Sun }. Our models rule out progenitors with helium-core masses larger than 8 M{sub Sun }, which correspond to M{sub ZAMS} {approx}> 25M{sub Sun }. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

  5. The Type IIb Supernova 2011dh from a Supergiant Progenitor

    CERN Document Server

    Bersten, Melina C; Nomoto, Ken'ichi; Ergon, Mattias; Folatelli, Gastón; Sollerman, Jesper; Benetti, Stefano; Botticella, Maria Teresa; Fraser, Morgan; Kotak, Rubina; Maeda, Keiichi; Ochner, Paolo; Tomasella, Lina

    2012-01-01

    A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star ---with R ~200 Rsun---, is needed to reproduce the early light curve of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the SN in deep pre-explosion images is the progenitor star. From the main peak of the bolometric light curve and expansion velocities we constrain the mass of the ejecta to be ~2 Msun, the explosion energy to be E= 6-10 x 10^50 erg, and the 56Ni mass to be approximately 0.06 Msun. The progenitor star was composed of a helium core of 3 to 4 Msun and a thin hydrogen-rich envelope of ~0.1 M_sun with a main sequence mass estimated to be in the range of 12--15 Msun. Our models rule out progenitors with helium-core masses larger than 8 Msun, which correspond to M_ZAMS > 25 Msun. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

  6. ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY CMa

    CERN Document Server

    Decin, L; Millar, T J; Baudry, A; De Beck, E; Homan, W; Smith, N; Van de Sande, M; Walsh, C

    2016-01-01

    (abreviated) We aim to study the inner-wind structure (R<250 Rstar) of the well-known red supergiant VY CMa. We analyse high spatial resolution (~0".24x0".13) ALMA Science Verification (SV) data in band 7 in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ~50 degrees measured from north to east. However, this picture can not capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profi...

  7. The Lévy-Itô decomposition in free probability

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole Eiler; Thorbjørnsen, Steen

    2005-01-01

    In this paper we prove the free analog of the Lévy-Itô decomposition for Lévy processes. A significant part of the proof consists of introducing free Poisson random measures, proving their existence and developing a theory of integration with respect to such measures. The existence of free Poisson...... random measures also yields, via the free Lévy-Itô decomposition, an alternative proof of the general existence of free Lévy processes (in law)....

  8. B[e] Supergiants' circumstellar environment: disks or rings?

    CERN Document Server

    Maravelias, G; Aret, A; Cidale, L; Arias, M L; Fernandes, M Borges

    2016-01-01

    B[e] Supergiants are a phase in the evolution of some massive stars for which we have observational evidence but no predictions by any stellar evolution model. The mass-loss during this phase creates a complex circumstellar environment with atomic, molecular, and dust regions usually found in rings or disk-like structures. However, the detailed structure and the formation of the circumstellar environment are not well-understood, requiring further investigation. To address that we initiated an observing campaign to obtain a homogeneous set of high-resolution spectra in both the optical and NIR (using MPG-ESO/FEROS, GEMINI/Phoenix and VLT/CRIRES, respectively). We monitor a number of Galactic B[e] Supergiants, for which we examined the [OI] and [CaII] emission lines and the bandheads of the CO and SiO molecules to probe the structure and the kinematics of their formation regions. We find that the emission from each tracer forms either in a single or in multiple equatorial rings.

  9. B[e] Supergiants' Circumstellar Environment: Disks or Rings?

    Science.gov (United States)

    Maravelias, G.; Kraus, M.; Aret, A.; Cidale, L.; Arias, M. L.; Borges Fernandes, M.

    2017-02-01

    B[e] supergiants are a phase in the evolution of some massive stars for which we have observational evidence but no predictions by any stellar evolution model. The mass-loss during this phase creates a complex circumstellar environment with atomic, molecular, and dust regions usually found in rings or disk-like structures. However, the detailed structure and the formation of the circumstellar environment are not well-understood, requiring further investigation. To address that we initiated an observing campaign to obtain a homogeneous set of high-resolution spectra in both the optical and NIR (using MPG-ESO/FEROS, GEMINI /Phoenix and VLT/CRIRES, respectively). We monitor a number of Galactic B[e] supergiants, for which we examined the [O I] and [Ca II] emission lines and the bandheads of the CO and SiO molecules to probe the structure and the kinematics of their formation regions. We find that the emission from each tracer forms either in a single or multiple equatorial rings.

  10. Math and physics: Lévy flights and drives

    Science.gov (United States)

    Shlesinger, Michael

    2015-03-01

    Benoit Mandelbrot had a profound influence in the physics community by connecting scaling and geometry. One example is the Lévy flight. In this memorial issue, in honor of Benoit, I review some personal history and ideas on the mathematics of Lévy flights and then introduce Lévy drives for applications to physical problems.

  11. Supergiants transiting towards white dwarf

    CERN Document Server

    Klochkova, V G

    2016-01-01

    Observational manifestations of far evolved stars at the asymptotic giants branch and their nearest descendants are briefly considered. Main results of their chemical composition determinations based on long term high resolution spectroscopy at the 6-m telescope are also briefly summed up. A new kind of peculiarity of optical spectra is found and discussed: splitting or asymmetry of strongest absorptions in the optical spectra of selected post-AGB stars with envelopes and atmospheres enriched in carbon and s-process heavy metals.

  12. ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

    Science.gov (United States)

    Decin, L.; Richards, A. M. S.; Millar, T. J.; Baudry, A.; De Beck, E.; Homan, W.; Smith, N.; Van de Sande, M.; Walsh, C.

    2016-07-01

    Context. At the end of their lives, most stars lose a significant amount of mass through a stellar wind. The specific physical and chemical circumstances that lead to the onset of the stellar wind for cool luminous stars are not yet understood. Complex geometrical morphologies in the circumstellar envelopes prove that various dynamical and chemical processes are interlocked and that their relative contributions are not easy to disentangle. Aims: We aim to study the inner-wind structure (Rarchetype for the class of luminous red supergiant stars experiencing high mass loss. Specifically, the objective is to unravel the density structure in the inner envelope and to examine the chemical interaction between gas and dust species. Methods: We analyse high spatial resolution (~0.̋24×0.̋13) ALMA science verification (SV) data in band 7, in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. Results: For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ~50° measured from north to east. However, this picture cannot capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profiles is significantly lower than the average wind terminal velocity, and much slower than some of the fastest mass ejections, signalling a wide range of characteristic speeds for the mass loss. Gaseous NaCl is detected far beyond the main dust condensation region. Realising the refractory nature of this metal halide, this hints at a

  13. The spin-up of contracting red supergiants

    CERN Document Server

    Heger, A; Heger, Alexander; Langer, Norbert

    1998-01-01

    We report on a mechanism which may lead to a spin-up of the surface of a rotating single star leaving the Hayashi line, which is much stronger than the spin-up expected from the mere contraction of the star. By analyzing rigidly rotating, convective stellar envelopes, we qualitatively work out the mechanism through which these envelopes may be spun up or down by mass loss through their lower or upper boundary, respectively. We find that the first case describes the situation in retreating convective envelopes, which tend to retain most of the angular momentum while becoming less massive, thereby increasing the specific angular momentum in the convection zone and thus in the layers close to the stellar surface. We explore the spin-up mechanism quantitatively in a stellar evolution calculation of a rotating 12 M_sun star, which is found to be spun up to critical rotation after leaving the red supergiant branch. We discuss implications of this spin-up for the circumstellar matter around several types of stars, i...

  14. Red Supergiants in the Inner Galaxy: Stellar Properties

    Science.gov (United States)

    Messineo, Maria; Zhu, Qingfeng; Menten, Karl M.; Ivanov, Valentin D.; Figer, Donald F.; Kudritzki, Rolf-Peter; Chen, C.-H. Rosie

    2017-02-01

    Red supergiants (RSGs) are luminous cool stars detectable in disks of distant spirals. About a thousand are known in the Galaxy. Here, we analyze a sample of late-type stars recently observed by Messineo et al. in the inner Galaxy (10^\\circ 45 Å, ≳M0I). In this work, luminosities are estimated with infrared measurements and distance moduli for 47 spectroscopically classified RSGs; they range from 3.2× {10}4 to 1.3× {10}5 {L}ȯ . Six other RSGs with smaller EW(CO)s are classified according to their luminosities. Using a prescription based on {K}{{s}}{--}[W4], moderate mass-loss rates from 10‑8 to {10}-6.5 {M}ȯ yr‑1 are inferred. In addition, we report on H and K spectra of 26 stars at R = 1500–2200. EWs of the CO at 2.293 and 1.620 μm, and of atomic lines, are consistent with those of nearby RSGs, within uncertainties. Mg i appears to be a useful diagnostic to confirm RSGs at R = 1500–2200. RSG #66 is a member of the cluster Alicante 7. Star #92 is projected onto the overdensity #495 of Camargo et al., but our analysis suggests they are unrelated. Remaining targets are isolated from other known RSGs within ≈3‧.

  15. Probability densities and Lévy densities

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole Eiler

    For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated.......For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated....

  16. Probability densities and Lévy densities

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole Eiler

    For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated.......For positive Lévy processes (i.e. subordinators) formulae are derived that express the probability density or the distribution function in terms of power series in time t. The applicability of the results to finance and to turbulence is briefly indicated....

  17. The evolution of Red Supergiants to supernova in the LMC cluster NGC 2100

    CERN Document Server

    Beasor, Emma R

    2016-01-01

    The mass loss rates of red supergiants (RSGs) govern their evolution towards supernova and dictate the appearance of the resulting explosion. To study how mass-loss rates change with evolution we measure the mass-loss rates (\\mdot) and extinctions of 19 red supergiants in the young massive cluster NGC2100 in the Large Magellanic Cloud. By targeting stars in a coeval cluster we can study the mass-loss rate evolution whilst keeping the variables of mass and metallicity fixed. Mass-loss rates were determined by fitting DUSTY models to mid-IR photometry from WISE and Spitzer/IRAC. We find that the \\mdot\\ in red supergiants increases as the star evolves, and is well described by \\mdot\\ prescription of de Jager, used widely in stellar evolution calculations. We find the extinction caused by the warm dust is negligible, meaning the warm circumstellar material of the inner wind cannot explain the higher levels of extinction found in the RSGs compared to other cluster stars. We discuss the implications of this work in...

  18. Spectral type, temperature and evolutionary stage in cool supergiants

    CERN Document Server

    Dorda, Ricardo; González-Fernández, Carlos; Tabernero, Hugo M

    2016-01-01

    In recent years, temperature scales in cool supergiants (CSGs) have been disputed, and the possibility that spectral types (SpTs) do not depend primarily on temperature has been raised. We explore the relations between different observed parameters and the capability of deriving accurate intrinsic stellar parameters from them through the analysis of the largest spectroscopic sample of CSGs to date from SMC and LMC. We explore possible correlations between different observational parameters, also making use of near- and mid-infrared colours and literature on photometric variability. Direct comparison between the behaviour of atomic lines (Fe I, Ti I, and Ca II) in the observed spectra and synthetic atmospheric models provides compelling evidence that effective temperature is the prime underlying variable driving the SpT sequence in CSGs. However, there is a clear correlation between SpT and luminosity, with later ones tending to correspond to more luminous stars with heavier mass loss. The population of CSGs i...

  19. Long-term spectropolarimetric monitoring of the cool supergiant Betelgeuse

    CERN Document Server

    Bedecarrax, I; Aurière, M; Grunhut, J; Wade, G; Chiavassa, A; Donati, J -F; Konstantinova-Antova, R; Perrin, G

    2013-01-01

    We report on a long-term monitoring of the cool supergiant Betelgeuse, using the NARVAL and ESPaDOnS high-resolution spectropolarimeters, respectively installed at Telescope Bernard Lyot (Pic du Midi Observatory, France) and at the Canada-France-Hawaii Telescope (Mauna Kea Observatory, Hawaii). The data set, constituted of circularly polarized (Stokes V) and intensity (Stokes I) spectra, was collected between 2010 and 2012. We investigate here the temporal evolution of magnetic field, convection and temperature at photospheric level, using simultaneous measurements of the longitudinal magnetic field component, the core emission of the Ca II infrared triplet, the line-depth ratio of selected photospheric lines and the radial velocity of the star.

  20. Two supergiants in the Large Magellanic Cloud with thick dust shells

    Science.gov (United States)

    Elias, J. H.; Frogel, J. A.; Schwering, P. B. W.

    1986-01-01

    Ground-based observations from 0.6 to 20 microns have identified two luminous, evolved stars surrounded by thick dust shells among the Magellanic Cloud sources detected by the Infrared Astronomical Satellite. Their energy distributions resemble those of typical Galactic OH/IR stars, but they have bolometric magnitudes brighter than -9 and the small-amplitude variability of supergiants. One star, IRAS 04553 - 6825, has a special type of M7.5 and a dust shell which absorbs and reradiates roughly 75 percent of the star's luminosity; its radial velocity confirms its LMC membership. The second star, IRAS 05346 - 6949, has an even thicker dust shell, and the central star is not observable.

  1. Extending Lévy search theory from one to higher dimensions: Lévy walking favours the blind

    OpenAIRE

    Reynolds, A. M.

    2015-01-01

    A diverse range of organisms, including T cells, E. coli, honeybees, sharks, turtles, bony fish, jellyfish, wandering albatrosses and even human hunter–gatherers have movement patterns that can be approximated by Lévy walks (LW; sometimes called Lévy flights in the biological and ecological literature). These observations lend support to the ‘Lévy flight foraging hypothesis’ which asserts that natural selection should have led to adaptations for Lévy flight foraging, because Lévy flights can ...

  2. vy matters Lévy-type processes construction, approximation and sample path properties

    CERN Document Server

    Böttcher, Björn; Wang, Jian

    2013-01-01

    This volume presents recent developments in the area of Lévy-type processes and more general stochastic processes that behave locally like a Lévy process. Although written in a survey style, quite a few results are extensions of known theorems, and others are completely new. The focus is on the symbol of a Lévy-type process: a non-random function which is the counterpart of the characteristic exponent of a Lévy process. The class of stochastic processes which can be associated with a symbol is characterized, various schemes constructing a stochastic process from a given symbol are discussed, and it is shown how one can use the symbol in order to describe the sample path properties of the underlying process. Lastly, the symbol is used to approximate and simulate Levy-type processes. This is the third volume in a subseries of the Lecture Notes in Mathematics called Lévy Matters. Each volume describes a number of important topics in the theory or applications of Lévy processes and pays tribute to the stat...

  3. A transient supergiant X-ray binary in IC 10: An extragalactic SFXT?

    Energy Technology Data Exchange (ETDEWEB)

    Laycock, Silas; Cappallo, Rigel; Oram, Kathleen; Balchunas, Andrew [Department of Physics and Applied Physics, Olney Science Center, University of Massachusetts, Lowell, MA 01854 (United States)

    2014-07-01

    We report the discovery of a large amplitude (factor of ∼100) X-ray transient (IC 10 X-2, CXOU J002020.99+591758.6) in the nearby dwarf starburst galaxy IC 10 during our Chandra monitoring project. Based on the X-ray timing and spectral properties, and an optical counterpart observed with Gemini, the system is a high-mass X-ray binary consisting of a luminous blue supergiant and a neutron star. The highest measured luminosity of the source was 1.8 × 10{sup 37} erg s{sup –1}during an outburst in 2003. Observations before, during, and after a second outburst in 2010 constrain the outburst duration to be less than 3 months (with no lower limit). The X-ray spectrum is a hard power law (Γ = 0.3) with fitted column density (N{sub H} = 6.3 × 10{sup 21} atom cm{sup –2}), consistent with the established absorption to sources in IC 10. The optical spectrum shows hydrogen Balmer lines strongly in emission at the correct blueshift (-340 km s{sup –1}) for IC 10. The N III triplet emission feature is seen, accompanied by He II [4686] weakly in emission. Together these features classify the star as a luminous blue supergiant of the OBN subclass, characterized by enhanced nitrogen abundance. Emission lines of He I are seen, at similar strength to Hβ. A complex of Fe II permitted and forbidden emission lines are seen, as in B[e] stars. The system closely resembles galactic supergiant fast X-ray transients, in terms of its hard spectrum, variability amplitude, and blue supergiant primary.

  4. The eccentric short-period orbit of the supergiant fast X-ray transient HD 74194 (=LM Vel)

    CERN Document Server

    Gamen, R; Walborn, N R; Morrell, N I; Arias, J I; Apellániz, J Maíz; Sota, A; Alfaro, E J

    2015-01-01

    Aims. We present the first orbital solution for the O-type supergiant star HD 74194, which is the optical counterpart of the supergiant fast X-ray transient IGR J08408-4503. Methods. We measured the radial velocities in the optical spectrum of HD 74194, and we determined the orbital solution for the first time. We also analysed the complex H{\\alpha} profile. Results. HD 74194 is a binary system composed of an O-type supergiant and a compact object in a short-period ($P=9.5436\\pm0.0002$ d) and high-eccentricity ($e=0.63\\pm0.03$) orbit. The equivalent width of the H{\\alpha} line is not modulated entirely with the orbital period, but seems to vary in a superorbital period ($P=285\\pm10$ d) nearly 30 times longer than the orbital one.

  5. Clumpy molecular structures revolving the B[e] supergiant MWC 137

    CERN Document Server

    Kraus, M; Liimets, T; Cappa, C E; Duronea, N; Gunawan, D S; Oksala, M E; Santander-Garcia, M; Arias, M L; Nickeler, D H; Maravelias, G; Fernandes, M Borges; Cure, M

    2016-01-01

    The peculiar emission-line star MWC 137 with its extended optical nebula was recently classified as B[e] supergiant. To study the spatial distribution of its circumstellar molecular gas on small and large scales, we obtained near-infrared and radio observations using SINFONI and APEX, respectively. We find that the hot CO gas is arranged in moving clumpy ring and shell structures close to the star, while a cold CO envelope is encircling the borders of the optical nebula from the south to the west.

  6. RED SUPERGIANTS AS COSMIC ABUNDANCE PROBES: THE SCULPTOR GALAXY NGC 300

    Energy Technology Data Exchange (ETDEWEB)

    Gazak, J. Zachary; Kudritzki, Rolf; Bresolin, Fabio [Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Dr, Honolulu, HI 96822 (United States); Evans, Chris [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh., EH9 3HJ (United Kingdom); Patrick, Lee [Institute for Astronomy, Royal Observatory Edinburgh, Blackford Hill, Edinburgh., EH9 3HJ (United Kingdom); Davies, Ben [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Bergemann, Maria [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Université de Montpellier, CNRS, F-34095 Montpellier (France); Bender, Ralf; Wegner, Michael [University Observatory Munich, Scheinerstr. 1, D-81679 Munich (Germany); Bonanos, Alceste Z.; Williams, Stephen J. [IAASARS, National Observatory of Athens, GR-15236 Penteli (Greece)

    2015-06-01

    We present a quantitative spectroscopic study of 27 red supergiants (RSGs) in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the Very Large Telescope and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z] = −0.03 ± 0.05 with a gradient of −0.083 ± 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H ii-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual RSG stars beyond the Local Group of galaxies and reveals the great potential of this technique.

  7. A red supergiant nebula at 25 micron: arcsecond scale mass-loss asymmetries of mu Cep

    CERN Document Server

    De Wit, W J; Fujiyoshi, T; Hoare, M G; Honda, M; Kataza, H; Miyata, T; Okamoto, Y K; Onaka, T; Sako, S; Yamashita, T

    2008-01-01

    We present diffraction limited (0.6") 24.5micron Subaru/COMICS images of the red supergiant mu Cep. We report the detection of a circumstellar nebula, that was not detected at shorter wavelengths. It extends to a radius of at least 6" in the thermal infrared. On these angular scales, the nebula is roughly spherical, in contrast, it displays a pronounced asymmetric morphology closer in. We simultaneously model the azimuthally averaged intensity profile of the nebula and the observed spectral energy distribution using spherical dust radiative transfer models. The models indicate a constant mass-loss process over the past 1000 years, for mass-loss rates a few times 10^(-7) Msun/yr. This work supports the idea that at least part of the asymmetries in shells of evolved massive stars and supernovae may be due to the mass-loss process in the red supergiant phase.

  8. The Red Supergiant Progenitor of Supernova 2012aw (PTF12bvh) in Messier 95

    CERN Document Server

    Van Dyk, Schuyler D; Poznanski, Dovi; Arcavi, Iair; Gal-Yam, Avishay; Filippenko, Alexei V; Silverio, Kathryn; Stockton, Alan; Cuillandre, Jean-Charles; Marcy, Geoffrey W; Howard, Andrew W; Isaacson, Howard

    2012-01-01

    We report on the direct detection and characterization of the probable red supergiant progenitor of the intermediate-luminosity Type II-Plateau (II-P) supernova (SN) 2012aw in the nearby (10.0 Mpc) spiral galaxy Messier 95 (M95; NGC 3351). We have identified the star in both Hubble Space Telescope images of the host galaxy, obtained 17-18 yr prior to the explosion, and near-infrared ground-based images, obtained 6-12 yr prior to the SN. The luminous supergiant showed evidence for substantial circumstellar dust, manifested as excess line-of-sight extinction. The effective total-to-selective ratio of extinction to the star was R'_V \\approx 4.35, which is significantly different from that of diffuse interstellar dust (i.e., R_V=3.1), and the total extinction to the star was therefore, on average, A_V \\approx 3.1 mag. We find that the observed spectral energy distribution for the progenitor star is consistent with an effective temperature of 3600 K (spectral type M3), and that the star therefore had a bolometric ...

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

    Energy Technology Data Exchange (ETDEWEB)

    Krticka, Jiri; Skalicky, Jan [Ustav teoreticke fyziky a astrofyziky, Masarykova univerzita, Kotlarska 2, CZ-611 37 Brno (Czech Republic); Kubat, Jiri [Astromomicky ustav Akademie ved Ceske republiky, Fricova 298, CZ-251 65 Ondrejov (Czech Republic)

    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.

  10. Two Ring Nebulae around Blue Supergiants in the Large Magellanic Cloud

    CERN Document Server

    Weis, K; Duschl, W J; Bomans, D J

    1997-01-01

    Ring nebulae are often found around massive stars such as Wolf-Rayet stars, OB and Of stars and Luminous Blue Variables (LBVs). In this paper we report on two ring nebulae around blue supergiants in the Large Magellanic Cloud. The star Sk-69 279 is classified as O9f and is surrounded by a closed shell with a diameter of 4.5 pc. Our echelle observations show an expansion velocity of 14 km/s and a high [N II]6583A/H alpha ratio. This line ratio suggests nitrogen abundance enhancement consistent with those seen in ejectas from LBVs. Thus the ring nebula around Sk-69 279 is a circumstellar bubble. The star Sk-69 271, a B2 supergiant, is surrounded by an H alpha arc resembling an half shell. Echelle observations show a large expanding shell with the arc being part of the approaching surface. The expansion velocity is about 24 km/s and the [N II]6583A/H alpha is not much higher than that of the background emission. The lack of nitrogen abundance anomaly suggests that the expanding shell is an interstellar bubble wi...

  11. Aging ballistic Lévy walks

    Science.gov (United States)

    Magdziarz, Marcin; Zorawik, Tomasz

    2017-02-01

    Aging can be observed for numerous physical systems. In such systems statistical properties [like probability distribution, mean square displacement (MSD), first-passage time] depend on a time span ta between the initialization and the beginning of observations. In this paper we study aging properties of ballistic Lévy walks and two closely related jump models: wait-first and jump-first. We calculate explicitly their probability distributions and MSDs. It turns out that despite similarities these models react very differently to the delay ta. Aging weakly affects the shape of probability density function and MSD of standard Lévy walks. For the jump models the shape of the probability density function is changed drastically. Moreover for the wait-first jump model we observe a different behavior of MSD when ta≪t and ta≫t .

  12. Dynamical continuous time random Lévy flights

    Science.gov (United States)

    Liu, Jian; Chen, Xiaosong

    2016-03-01

    The Lévy flights' diffusive behavior is studied within the framework of the dynamical continuous time random walk (DCTRW) method, while the nonlinear friction is introduced in each step. Through the DCTRW method, Lévy random walker in each step flies by obeying the Newton's Second Law while the nonlinear friction f(v) = - γ0v - γ2v3 being considered instead of Stokes friction. It is shown that after introducing the nonlinear friction, the superdiffusive Lévy flights converges, behaves localization phenomenon with long time limit, but for the Lévy index μ = 2 case, it is still Brownian motion.

  13. Probability Measures, Lévy Measures, and Analyticity in Time

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole Eiler; Hubalek, Friedrich

    , the second method uses convolution integrals of the upper tail integral of the Lévy measure, and the third method uses the analytic continuation of the Lévy density to a complex cone and contour integration. As a byproduct we investigate the smoothness of the semigroup density in time. Several concrete......We investigate the relation of the semigroup probability density of an infinite activity Lévy process to the corresponding Lévy density. For subordinators we provide three methods to compute the former from the latter. The first method is based on approximating compound Poisson distributions...... examples illustrate the three methods and our results....

  14. Characterisation of red supergiants in the Gaia spectral range

    CERN Document Server

    Dorda, Ricardo; Negueruela, Ignacio

    2016-01-01

    The infrared Calcium Triplet and its nearby spectral region have been used for spectral and luminosity classification of late-type stars, but the samples of cool supergiants (CSGs) used have been very limited (in size, metallicity range, and spectral types covered). The spectral range of the Gaia Radial Velocity Spectrograph (RVS) covers most of this region but does not reach the main TiO bands in this region, whose depths define the M sequence. We study the behaviour of spectral features around the Calcium Triplet and develop effective criteria to identify and classify CSGs, comparing their efficiency with other methods previously proposed. We measure the main spectral features in a large sample (almost 600) of CSGs from three different galaxies, and we analyse their behaviour through a principal component analysis. Using the principal components, we develop an automatised method to differentiate CSGs from other bright late-type stars, and to classify them. The proposed method identifies a high fraction of t...

  15. Supernova 2008bk and Its Red Supergiant Progenitor

    CERN Document Server

    Van Dyk, Schuyler D; Elias-Rosa, Nancy; Taubenberger, Stefan; Li, Weidong; Howerton, Stanley; Pignata, Giuliano; Morrell, Nidia; Hamuy, Mario; Filippenko, Alexei V

    2010-01-01

    We have observed Supernova (SN) 2008bk in NGC 7793, both photometrically and spectroscopically, primarily at late times. We find that it is a Type II-Plateau (II-P) SN, which most closely resembles the low-luminosity SN 1999br in NGC 4900. Given the overall similarity between the observed light curves and colors of SNe 2008bk and 1999br, we infer that the total visual extinction to SN 2008bk must be almost entirely due to the Galactic foreground, similar to that for SN 1999br: A_V=0.065 mag, which is substantially less than the 1.0 +/- 0.5 mag assumed by Mattila et al. (2008). Furthermore, we confirm the identification of the putative red supergiant progenitor star of the SN in high-quality g'r'i' Gemini-South images from 2007. Little ambiguity exists in this progenitor identification; besides the connection between the star Sk -69 202 and SN 1987A, it qualifies as one of the best SN progenitor identifications to date. From a combination of the Gemini images with archival, pre-SN, Very Large Telescope JHK_s i...

  16. Simultaneous VLBA polarimetric observations of the v = {1,2} J = 1-0 and v = 1, J = 2-1 SiO maser emission towards VY CMa II: component-level polarization analysis

    Science.gov (United States)

    Richter, L.; Kemball, A.; Jonas, J.

    2016-09-01

    This paper presents a component-level comparison of the polarized v = 1 J = 1-0, v = 2 J = 1-0 and v = 1 J = 2-1 SiO maser emission towards the supergiant star VY CMa at milliarcsecond-scale, as observed using the Very Long Baseline Array at λ = 7 and 3 mm. An earlier paper considered overall maser morphology and constraints on SiO maser excitation and pumping derived from these data. The goal of the current paper is to use the measured polarization properties of individual co-spatial components detected across multiple transitions to provide constraints on several competing theories for the transport of polarized maser emission. This approach minimizes the significant effects of spatial blending. We present several diagnostic tests designed to distinguish key features of competing theoretical models for maser polarization. The number of coincident features is limited by sensitivity however, particularly in the v = 1 J = 2-1 transition at 86 GHz, and deeper observations are needed. Preliminary conclusions based on the current data provide some support for: (i) spin-independent solutions for linear polarization; (ii) the influence of geometry on the distribution of fractional linear polarization with intensity; and, (iii) π/2 rotations in linear polarization position angle arising from transitions across the Van Vleck angle (sin 2θ = 2/3) between the maser line of sight and magnetic field. There is weaker evidence for several enumerated non-Zeeman explanations for circular polarization. The expected 2:1 ratio in circular polarization between J = 1-0 and J = 2-1 predicted by standard Zeeman theory cannot unfortunately be tested conclusively due to insufficient coincident components.

  17. The early-type strong emission-line supergiants of the Magellanic Clouds - A spectroscopic zoology

    Science.gov (United States)

    Shore, S. N.; Sanduleak, N.

    1984-01-01

    The results of a spectroscopic survey of 21 early-type extreme emission line supergiants of the Large and Small Magellanic Clouds using IUE and optical spectra are presented. The combined observations are discussed and the literature on each star in the sample is summarized. The classification procedures and the methods by which effective temperatures, bolometric magnitudes, and reddenings were assigned are discussed. The derived reddening values are given along with some results concerning anomalous reddening among the sample stars. The derived mass, luminosity, and radius for each star are presented, and the ultraviolet emission lines are described. Mass-loss rates are derived and discussed, and the implications of these observations for the evolution of the most massive stars in the Local Group are addressed.

  18. High Mass X-ray Binaries: Progenitors of double neutron star systems

    CERN Document Server

    Chaty, Sylvain

    2015-01-01

    In this review I briefly describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants. A previously unknown population of HMXBs hosting supergiant stars has been revealed in the last years, with multi-wavelength campaigns including high energy (INTEGRAL, Swift, XMM, Chandra) and optical/infrared (mainly ESO) observations. This population is divided between obscured supergiant HMXBs, and supergiant fast X-ray transients (SFXTs), characterized by short and intense X-ray flares. I discuss the characteristics of these types of supergiant HMXBs, propose a scenario describing the properties of these high-energy sources, and finally show how the observations can constrain the accretion models (e.g. clumpy winds, magneto-centrifugal barrier, transitory accretion disc, etc). Because they are the likely progenitors of Luminous Blue Variables (LBVs), and also of double neutron star systems,...

  19. Double bow shocks around young, runaway red supergiants: application to Betelgeuse

    CERN Document Server

    Mackey, Jonathan; Neilson, Hilding R; Langer, Norbert; Meyer, Dominique M -A

    2012-01-01

    A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption of a binary system or ejection from their parent star cluster. The interaction of their wind with the ISM produces a bow shock. In late evolutionary stages these stars may undergo rapid transitions from red to blue and vice versa on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks. Recent 3D simulations of the bow shock produced by the nearby runaway red supergiant (RSG) Betelgeuse, under the assumption of a constant wind, indicate that the bow shock is very young (<30000 years old), hence Betelgeuse may have only recently become a RSG. To test this possibility, we have calculated stellar evolution models for single stars which match the observed properties of Betelgeuse in the RSG phase. The resulting evolving stellar wind is incorporated into 2D hydrodynamic simulations in which we model a runaway blue supergiant (BSG) as i...

  20. Optical spectra of 5 new Be/X-ray Binaries in the Small Magellanic Cloud and the link of the supergiant B[e] star LHA 115-S 18 with an X-ray source

    CERN Document Server

    Maravelias, Grigoris; Antoniou, Vallia; Hatzidimitriou, Despoina

    2013-01-01

    The Small Magellanic Cloud (SMC) is well known to harbor a large number of High-Mass X-ray Binaries (HMXBs). The identification of their optical counterparts provides information on the nature of the donor stars and can help to constrain the parameters of these systems and their evolution. We obtained optical spectra for a number of HMXBs identified in previous Chandra and XMM-Newton surveys of the SMC using the AAOmega/2dF fiber-fed spectrograph at the Anglo-Australian Telescope. We find 5 new Be/X-ray binaries (BeXRBs; including a tentative one), by identifying the spectral type of their optical counterparts, and we confirm the spectral classification of an additional 15 known BeXRBs. We compared the spectral types, orbital periods, and eccentricities of the BeXRB populations in the SMC and the Milky Way and we find marginal evidence for difference between the spectral type distributions, but no statistically significant differences for the orbital periods and the eccentricities. Moreover, our search reveal...

  1. Spectroscopy of unusual emission-line stars

    Science.gov (United States)

    Bopp, Bernard W.

    1988-01-01

    New spectroscopic observations are reported for ten stars that have been identified in the literature as having H-alpha emission with suspected F, G, or K spectral types. Three of the stars are shown to be BE stars, two are confirmed as early-type supergiants, three show composite (F or K + B) spectra, one is a 'post-T Tauri' star, and one is an ordinary F star without emission.

  2. Probability measures, Lévy measures and analyticity in time

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole Eiler; Hubalek, Friedrich

    2008-01-01

    We investigate the relation of the semigroup probability density of an infinite activity Lévy process to the corresponding Lévy density. For subordinators, we provide three methods to compute the former from the latter. The first method is based on approximating compound Poisson distributions...

  3. A Nonstandard Lévy-Khintchine Formula and Lévy Processes

    Institute of Scientific and Technical Information of China (English)

    Siu Ah HG

    2008-01-01

    We use methods from nonstandard analysis to obtain a short and simple derivation of the Lévy-Khintchine formula via an explicit construction of certain laws of the infinitesimal increments.Consequently, any arbitrary Lvy process is representable as the standard part of a hyperfinite sum of infinitesimal increments.

  4. A photometric determination of the metal content for F-G type supergiants in the Large Magellanic Cloud

    Science.gov (United States)

    van Genderen, A. M.; Greidanus, H.; van Driel, W.

    1986-01-01

    A VBLUW photometric analysis is used to derive the metal content of some 100 F- and G type supergiants in the LMC. Using the empirical locus of Pel in the V-B/B-L diagram in conjunction with the relative dependence of theoretical colors on the metal abundance, a metal deficiency of 1.4-1.6 is found for the LMC stars in comparison with those in the solar neighborhood. With an average UBV system foreground reddening of E(B-V) = 0.05 for the LMC, these stars have a metal content of 0.66 + 0.11, -0.03 of the solar abundance. Agreement is found with the result of previous studies. Application to the derivation of the reddenings of most of the galactic supergiants is noted.

  5. Postexplosion hydrodynamics of supernovae in red supergiants

    Science.gov (United States)

    Herant, Marc; Woosley, S. E.

    1994-01-01

    Shock propagation, mixing, and clumping are studied in the explosion of red supergiants as Type II supernovae using a two-dimensional smooth particle hydrodynamic (SPH) code. We show that extensive Rayleigh-Talor instabilities develop in the ejecta in the wake of the reverse shock wave. In all cases, the shell structure of the progenitor is obliterated to leave a clumpy, well-mixed supernova remnant. However, the occurrence of mass loss during the lifetime of the progenitor can significantly reduce the amount of mixing. These results are independent of the Type II supernova explosion mechanism.

  6. Regularizing mappings of Lévy measures

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole Eiler; Thorbjørnsen, Steen

    2006-01-01

    In this paper we introduce and study a regularizing one-to-one mapping from the class of one-dimensional Lévy measures into itself. This mapping appeared implicitly in our previous paper [O.E. Barndorff-Nielsen, S. Thorbjørnsen, A connection between free and classical infinite divisibility, Inf....... Dim. Anal. Quant. Probab. 7 (2004) 573–590], where we introduced a one-to-one mapping from the class of one-dimensional infinitely divisible probability measures into itself. Based on the investigation of in the present paper, we deduce further properties of . In particular it is proved that maps...

  7. A Dark Energy Camera Search for Missing Supergiants in the LMC after the Advanced LIGO Gravitational-wave Event GW150914

    Science.gov (United States)

    Annis, J.; Soares-Santos, M.; Berger, E.; Brout, D.; Chen, H.; Chornock, R.; Cowperthwaite, P. S.; Diehl, H. T.; Doctor, Z.; Drlica-Wagner, A.; Drout, M. R.; Farr, B.; Finley, D. A.; Flaugher, B.; Foley, R. J.; Frieman, J.; Gruendl, R. A.; Herner, K.; Holz, D.; Kessler, R.; Lin, H.; Marriner, J.; Neilsen, E.; Rest, A.; Sako, M.; Smith, M.; Smith, N.; Sobreira, F.; Walker, A. R.; Yanny, B.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Benoit-Lévy, A.; Bernstein, R. A.; Bertin, E.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Castander, F. J.; Cenko, S. B.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Desai, S.; Dietrich, J. P.; Eifler, T. F.; Evrard, A. E.; Fernandez, E.; Fischer, J.; Fong, W.; Fosalba, P.; Fox, D. B.; Fryer, C. L.; Garcia-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Goldstein, D. A.; Gruen, D.; Gutierrez, G.; Honscheid, K.; James, D. J.; Karliner, I.; Kasen, D.; Kent, S.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; Maia, M. A. G.; Martini, P.; Metzger, B. D.; Miller, C. J.; Miquel, R.; Mohr, J. J.; Nichol, R. C.; Nord, B.; Ogando, R.; Peoples, J.; Petravic, D.; Plazas, A. A.; Quataert, E.; Romer, A. K.; Roodman, A.; Rykoff, E. S.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schindler, R.; Schubnell, M.; Sevilla-Noarbe, I.; Sheldon, E.; Smith, R. C.; Stebbins, A.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, R. C.; Tucker, D. L.; Vikram, V.; Wechsler, R. H.; Weller, J.; Wester, W.; DES Collaboration

    2016-06-01

    The collapse of a stellar core is expected to produce gravitational waves (GWs), neutrinos, and in most cases a luminous supernova. Sometimes, however, the optical event could be significantly less luminous than a supernova and a direct collapse to a black hole, where the star just disappears, is possible. The GW event GW150914 was detected by the LIGO Virgo Collaboration via a burst analysis that gave localization contours enclosing the Large Magellanic Cloud (LMC). Shortly thereafter, we used DECam to observe 102 deg2 of the localization area, including 38 deg2 on the LMC for a missing supergiant search. We construct a complete catalog of LMC luminous red supergiants, the best candidates to undergo invisible core collapse, and collected catalogs of other candidates: less luminous red supergiants, yellow supergiants, blue supergiants, luminous blue variable stars, and Wolf-Rayet stars. Of the objects in the imaging region, all are recovered in the images. The timescale for stellar disappearance is set by the free-fall time, which is a function of the stellar radius. Our observations at 4 and 13 days after the event result in a search sensitive to objects of up to about 200 solar radii. We conclude that it is unlikely that GW150914 was caused by the core collapse of a relatively compact supergiant in the LMC, consistent with the LIGO Collaboration analyses of the gravitational waveform as best interpreted as a high mass binary black hole merger. We discuss how to generalize this search for future very nearby core-collapse candidates.

  8. Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198478

    CERN Document Server

    Kraus, M; Cidale, L S; Venero, R O J; Nickeler, D H; Nemeth, P; Niemczura, E; Tomic, S; Aret, A; Kubat, J; Kubatova, B; Oksala, M E; Cure, M; Kaminski, K; Dimitrov, W; Fagas, M; Polinska, M

    2015-01-01

    Blue supergiant stars are known to display photometric and spectroscopic variability that is suggested to be linked to stellar pulsations. Pulsational activity in massive stars strongly depends on the star's evolutionary stage and is assumed to be connected with mass-loss episodes, the appearance of macroturbulent line broadening, and the formation of clumps in the wind. To investigate a possible interplay between pulsations and mass-loss, we carried out an observational campaign of the supergiant 55 Cyg over a period of five years to search for photospheric activity and cyclic mass-loss variability in the stellar wind. We modeled the H, He I, Si II and Si III lines using the nonlocal thermal equilibrium atmosphere code FASTWIND and derived the photospheric and wind parameters. In addition, we searched for variability in the intensity and radial velocity of photospheric lines and performed a moment analysis of the line profiles to derive frequencies and amplitudes of the variations. The Halpha line varies wit...

  9. The Ionized Nebula surrounding the Red Supergiant W26 in Westerlund 1

    CERN Document Server

    Wright, Nicholas J; Drew, Janet E; Barentsen, Geert; Barlow, Michael J; Walsh, Jeremy R; Zijlstra, Albert; Drake, Jeremy J; Eisloffel, Jochen; Farnhill, Hywel J

    2013-01-01

    We present H\\alpha images of an ionized nebula surrounding the M2-5Ia red supergiant (RSG) W26 in the massive star cluster Westerlund 1. The nebula consists of a circumstellar shell or ring ~0.1pc in diameter and a triangular nebula ~0.2pc from the star that in high-resolution Hubble Space Telescope images shows a complex filamentary structure. The excitation mechanism of both regions is unclear since RSGs are too cool to produce ionizing photons and we consider various possibilities. The presence of the nebula, high stellar luminosity and spectral variability suggest that W26 is a highly evolved RSG experiencing extreme levels of mass-loss. As the only known example of an ionized nebula surrounding a RSG W26 deserves further attention to improve our understanding of the final evolutionary stages of massive stars.

  10. Adaptive Lévy processes and area-restricted search in human foraging

    OpenAIRE

    Hills, Thomas Trenholm; Kalff, Christopher; Wiener, Jan M.

    2013-01-01

    A considerable amount of research has claimed that animals’ foraging behaviors display movement lengths with power-law distributed tails, characteristic of Lévy flights and Lévy walks. Though these claims have recently come into question, the proposal that many animals forage using Lévy processes nonetheless remains. A Lévy process does not consider when or where resources are encountered, and samples movement lengths independently of past experience. However, Lévy processes too have come int...

  11. DISTANCE AND KINEMATICS OF THE RED HYPERGIANT VY CMa: VERY LONG BASELINE ARRAY AND VERY LARGE ARRAY ASTROMETRY

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, B. [Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China); Reid, M. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Menten, K. M. [Max-Plank-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany); Zheng, X. W., E-mail: bzhang@mpifr.de [Department of Astronomy, Nanjing University, Nanjing 210093 (China)

    2012-01-01

    We report astrometric results of phase-referencing very long baseline interferometry observations of 43 GHz SiO maser emission toward the red hypergiant VY Canis Majoris (VY CMa) using the Very Long Baseline Array (VLBA). We measured a trigonometric parallax of 0.83 {+-} 0.08 mas, corresponding to a distance of 1.20{sup +0.13}{sub -0.10} kpc. Compared to previous studies, the spatial distribution of SiO masers has changed dramatically, while its total extent remains similar. The internal motions of the maser spots are up to 1.4 mas yr{sup -1}, corresponding to 8 km s{sup -1}, and show a tendency for expansion. After modeling the expansion of maser spots, we derived an absolute proper motion for the central star of {mu}{sub x} = -2.8 {+-} 0.2 and {mu}{sub y} = 2.6 {+-} 0.2 mas yr{sup -1} eastward and northward, respectively. Based on the maser distribution from the VLBA observations, and the relative position between the radio photosphere and the SiO maser emission at 43 GHz from the complementary Very Large Array observations, we estimate the absolute position of VY CMa at mean epoch 2006.53 to be {alpha}{sub J2000} = 07{sup h}22{sup m}58.{sup s}3259 {+-} 0.{sup s}0007, {delta}{sub J2000} = -25 Degree-Sign 46'03.''063 {+-} 0.''010. The position and proper motion of VY CMa from the VLBA observations differ significantly with values measured by the Hipparcos satellite. These discrepancies are most likely associated with inhomogeneities and dust scattering the optical light in the circumstellar envelope. The absolute proper motion measured with VLBA suggests that VY CMa may be drifting out of the giant molecular cloud to the east of it.

  12. Stochastic mutualism model with Lévy jumps

    Science.gov (United States)

    Liu, Qun; Jiang, Daqing; Shi, Ningzhong; Hayat, Tasawar; Alsaedi, Ahmed

    2017-02-01

    In this paper, we consider a stochastic mutualism model with Lévy jumps. First of all, we show that the positive solution of the system is stochastically ultimate bounded. Then under a simple assumption, we establish sufficient and necessary conditions for the stochastic permanence and extinction of the system. The results show an important property of the Lévy jumps: they are unfavorable for the permanence of the species. Moreover, when there are no Lévy jumps, we show that there is a unique ergodic stationary distribution of the corresponding system under certain conditions. Some numerical simulations are introduced to validate the theoretical results.

  13. The Circumstellar Medium of Massive Stars in Motion

    CERN Document Server

    Mackey, Jonathan; Meyer, Dominique M -A; Gvaramadze, Vasilii V; Mohamed, Shazrene; Neilson, Hilding R; Mignone, Andrea

    2014-01-01

    The circumstellar medium around massive stars is strongly impacted by stellar winds, radiation, and explosions. We use numerical simulations of these interactions to constrain the current properties and evolutionary history of various stars by comparison with observed circumstellar structures. Two- and three-dimensional simulations of bow shocks around red supergiant stars have shown that Betelgeuse has probably only recently evolved from a blue supergiant to a red supergiant, and hence its bow shock is very young and has not yet reached a steady state. We have also for the first time investigated the magnetohydrodynamics of the photoionised H II region around the nearby runaway O star Zeta Oph. Finally, we have calculated a grid of models of bow shocks around main sequence and evolved massive stars that has general application to many observed bow shocks, and which forms the basis of future work to model the explosions of these stars into their pre-shaped circumstellar medium.

  14. vy-Feller对流-扩散过程%Lévy-Feller Advection-dispersion Equation

    Institute of Scientific and Technical Information of China (English)

    刘青霞; 刘发旺

    2006-01-01

    考虑Lévy-Feller对流-扩散过程,应用Laplace和Fourier变换及其逆变换导出了用格林函数表示的Lévy-Feller对流-扩散方程的解析解,结果中去掉对流项的特殊情况与Mainardi等的研究结果是一致的.利用Riesz-Feller,Riemann-Li-ouville和Grünwald-Letnikov分数阶导数之间的关系,按照Grünwald-Letnikov定义对Riesz-Feller分数阶导数进行离散,得到了近似Lévy-Feller对流-扩散方程的一种两层的有限差分格式.最后,对上述的两层有限差分格式在一定条件下进行了离散随机游走的解释.

  15. vy matters V functionals of Lévy processes

    CERN Document Server

    Andersen, Lars Nørvang; Aurzada, Frank; Glynn, Peter W; Maejima, Makoto; Pihlsgård, Mats; Simon, Thomas

    2015-01-01

    This three-chapter volume concerns the distributions of certain functionals of Lévy processes. The first chapter, by Makoto Maejima, surveys representations of the main sub-classes of infinitesimal distributions in terms of mappings of certain Lévy processes via stochastic integration. The second chapter, by Lars Nørvang Andersen, Søren Asmussen, Peter W. Glynn and Mats Pihlsgård, concerns Lévy processes reflected at two barriers, where reflection is formulated à la Skorokhod. These processes can be used to model systems with a finite capacity, which is crucial in many real life situations, a most important quantity being the overflow or the loss occurring at the upper barrier.  If a process is killed when crossing the boundary, a natural question concerns its lifetime. Deep formulas from fluctuation theory are the key to many classical results, which are reviewed in the third chapter by Frank Aurzada and Thomas Simon. The main part, however, discusses recent advances and developments in the setting w...

  16. The Discovery of a Massive Cluster of Red Supergiants with GLIMPSE

    CERN Document Server

    Alexander, Michael J; Clemens, Dan P; Jameson, Katherine; Pinnick, April; Pavel, Michael

    2009-01-01

    We report the discovery of a previously unknown massive Galactic star cluster at l=29.22, b=-0.20. Identified visually in mid-IR images from the Spitzer GLIMPSE survey, the cluster contains at least 8 late-type supergiants, based on followup near-IR spectroscopy, and an additional 3-6 candidate supergiant embers having IR photometry consistent with a similar distance and reddening. The cluster lies at a local minimum in the 13-CO column density and 8 micron emission. We interpret this feature as a hole carved by the energetic winds of the evolving massive stars. The 13-CO hole seen in molecular maps at V_LSR ~95 km/s corresponds to near/far kinematic distances of 6.1/8.7+/-1 kpc. We calculate a mean spectrophotometric distance of 7.0^+3.7_-2.4 kpc, broadly consistent with the kinematic distances inferred. This location places it near the northern end of the Galactic bar. For the mean extinction of A_V=12.6+/-0.5 mag (A_K=1.5+/-0.1 mag), the color-magnitude diagram of probable cluster members is well fit by is...

  17. X-ray Emission from an Expanding Supergiant Shell in IC 2574

    CERN Document Server

    Walter, F; Duric, N; Brinks, E; Klein, U; Walter, Fabian; Duric, Neb; Brinks, Elias; Klein, Uli

    1998-01-01

    We present a multi--wavelength study of a supergiant shell within the violent interstellar medium of the nearby dwarf galaxy IC 2574, a member of the M81 group of galaxies. Neutral hydrogen (HI) observations obtained with the Very Large Array (VLA) reveal a prominent expanding supergiant HI shell which is thought to be produced by the combined effects of stellar winds and supernova explosions. It measures roughly 1000 x 500 pc in size and is expanding at about 25 km/s. The HI data suggest an age of about 1.4 x 10^6 yrs; the energy input must have been of order (2.6\\pm 1) x 10^53 ergs. Massive star forming regions, as traced by H$\\alpha$ emission, are situated predominantly on the rim of this HI shell. VLA radio continuum observations at 6 cm show that these star-forming regions are the main sources of radio continuum emission in this galaxy. Soft X-ray emission from within the HI hole is detected by a pointed ROSAT PSPC observation. The emission is resolved, coinciding in size and orientation with the HI shel...

  18. SPECTROSCOPIC AND PHOTOMETRIC VARIABILITY IN THE A0 SUPERGIANT HR 1040

    Energy Technology Data Exchange (ETDEWEB)

    Corliss, David J.; Morrison, Nancy D. [Department of Physics and Astronomy, The University of Toledo, Toledo, OH 43606 (United States); Adelman, Saul J., E-mail: david.corliss@wayne.edu [Department of Physics, The Citadel, 171 Moultrie Street, Charleston, SC 29409 (United States)

    2015-12-15

    A time-series analysis of spectroscopic and photometric observables of the A0 Ia supergiant HR 1040 has been performed, including equivalent widths, radial velocities, and Strömgren photometric indices. The data, obtained from 1993 through 2007, include 152 spectroscopic observations from the Ritter Observatory 1 m telescope and 269 Strömgren photometric observations from the Four College Automated Photoelectric Telescope. Typical of late B- and early A-type supergiants, HR 1040 has a highly variable Hα profile. The star was found to have an intermittent active phase marked by correlation between the Hα absorption equivalent width and blue-edge radial velocity and by photospheric connections observed in correlations to equivalent width, second moment and radial velocity in Si ii λλ6347, 6371. High-velocity absorption (HVA) events were observed only during this active phase. HVA events in the wind were preceded by photospheric activity, including Si ii radial velocity oscillations 19–42 days prior to onset of an HVA event and correlated increases in Si ii W{sub λ} and second moment from 13 to 23 days before the start of the HVA event. While increases in various line equivalent widths in the wind prior to HVA events have been reported in the past in other stars, our finding of precursors in enhanced radial velocity variations in the wind and at the photosphere is a new result.

  19. The impact of mass-loss on the evolution and pre-supernova properties of red supergiants

    CERN Document Server

    Meynet, G; Ekström, S; Georgy, C; Granada, A; Groh, J; Maeder, A; Eggenberger, P; Levesque, E; Massey, P

    2014-01-01

    The post main-sequence evolution of massive stars is very sensitive to many parameters of the stellar models. Key parameters are the mixing processes, the metallicity, the mass-loss rate and the effect of a close companion. We study how the red supergiant lifetimes, the tracks in the Hertzsprung-Russel diagram (HRD), the positions in this diagram of the pre-supernova progenitor as well as the structure of the stars at that time change for various mass-loss rates during the red supergiant phase (RSG), and for two different initial rotation velocities. The surface abundances of RSGs are much more sensitive to rotation than to the mass-loss rates during that phase. A change of the RSG mass-loss rate has a strong impact on the RSG lifetimes and therefore on the luminosity function of RSGs. At solar metallicity, the enhanced mass-loss rate models do produce significant changes on the populations of blue, yellow and red supergiants. When extended blue loops or blue ward excursions are produced by enhanced mass-loss...

  20. A Dark Energy Camera Search for Missing Supergiants in the LMC After the Advanced LIGO Gravitational Wave Event GW150914

    CERN Document Server

    Annis, J; Berger, E; Brout, D; Chen, H; Chornock, R; Cowperthwaite, P S; Diehl, H T; Doctor, Z; Drlica-Wagner, A; Drout, M R; Farr, B; Finley, D A; Flaugher, B; Foley, R J; Frieman, J; Gruendl, R A; Herner, K; Holz, D; Kessler, R; Lin, H; Marriner, J; Neilsen, E; Rest, A; Sako, M; Smith, M; Smith, N; Sobreira, F; Walker, A R; Yanny, B; Abbott, T M C; Abdalla, F B; Allam, S; Benoit-Levy, A; Bernstein, R A; Bertin, E; Buckley-Geer, E; Burke, D L; Capozzi, D; Rosell, A Carnero; Kind, M Carrasco; Carretero, J; Castander, F J; Cenko, S B; Crocce, M; Cunha, C E; D'Andrea, C B; da Costa, L N; Desai, S; Dietrich, J P; Eifler, T F; Evrard, A E; Fernandez, E; Fischer, J; Fong, W; Fosalba, P; Fox, D B; Fryer, C L; Garcia-Bellido, J; Gaztanaga, E; Gerdes, D W; Goldstein, D A; Gruen, D; Gutierrez, G; Honscheid, K; James, D J; Karliner, I; Kasen, D; Kent, S; Kuehn, K; Kuropatkin, N; Lahav, O; Li, T S; Lima, M; Maia, M A G; Martini, P; Metzger, B D; Miller, C J; Miquel, R; Mohr, J J; Nichol, R C; Nord, B; Ogando, R; Peoples, J; Plazas, A A; Quataert, E; Romer, A K; Roodman, A; Rykoff, E S; Sanchez, E; Santiago, B; Scarpine, V; Schindler, R; Schubnell, M; Sevilla-Noarbe, I; Sheldon, E; Smith, R C; Stebbins, A; Swanson, M E C; Tarle, G; Thaler, J; Thomas, R C; Tucker, D L; Vikram, V; Wechsler, R H; Weller, J; Wester, W

    2016-01-01

    The collapse of the core of a star is expected to produce gravitational radiation. While this process will usually produce a luminous supernova, the optical signatue could be subluminous and a direct collapse to a black hole, with the star just disappearing, is possible. The gravitational wave event GW150914 reported by the LIGO Virgo Collaboration (LVC) on 2015 September 16, was detected by a burst analysis and whose high probability spatial localization included the Large Magellanic Cloud. Shortly after the announcement of the event, we used the Dark Energy Camera to observe 102 deg$^2$ of the localization area, including a 38 deg$^2$ area centered on the LMC. Using a catalog of 152 LMC luminous red supergiants, candidates to undergo a core collapse without a visible supernova, we find that the positions of 144 of these are inside our images, and that all are detected - none have disappeared. There are other classes of candidates: we searched existing catalogs of red supergiants, yellow supergiants, Wolf-Ra...

  1. Maximal speed of particles in super-Lévy process

    Institute of Scientific and Technical Information of China (English)

    LIN Zheng-yan; CHENG Zong-mao

    2008-01-01

    We introduce a super-Lévy process and study maximal speed of all particles process is a measure on the set of paths.We study the maximal speed of all particles during a given time period,which turns out to be a function of the packing dimension of the time period.We calculate the Hausdorff dimension of the set of a-fast patlls in the support and the range of the historical super-lévy process.

  2. Entropy Production of Stars

    Directory of Open Access Journals (Sweden)

    Leonid M. Martyushev

    2015-06-01

    Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

  3. From Lévy-type processes to parabolic SPDEs

    CERN Document Server

    Quer-Sardanyons, Lluis

    2016-01-01

    This volume presents the lecture notes from two courses given by Davar Khoshnevisan and René Schilling, respectively, at the second Barcelona Summer School on Stochastic Analysis. René Schilling’s notes are an expanded version of his course on Lévy and Lévy-type processes, the purpose of which is two-fold: on the one hand, the course presents in detail selected properties of the Lévy processes, mainly as Markov processes, and their different constructions, eventually leading to the celebrated Lévy-Itô decomposition. On the other, it identifies the infinitesimal generator of the Lévy process as a pseudo-differential operator whose symbol is the characteristic exponent of the process, making it possible to study the properties of Feller processes as space inhomogeneous processes that locally behave like Lévy processes. The presentation is self-contained, and includes dedicated chapters that review Markov processes, operator semigroups, random measures, etc. In turn, Davar Khoshnevisan’s course inve...

  4. DOUBLE BOW SHOCKS AROUND YOUNG, RUNAWAY RED SUPERGIANTS: APPLICATION TO BETELGEUSE

    Energy Technology Data Exchange (ETDEWEB)

    Mackey, Jonathan; Mohamed, Shazrene; Neilson, Hilding R.; Langer, Norbert; Meyer, Dominique M.-A., E-mail: jmackey@astro.uni-bonn.de [Argelander-Institut fuer Astronomie, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2012-05-20

    A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption of a binary system or ejection from their parent star cluster. The interaction of their wind with the ISM produces a bow shock. In late evolutionary stages these stars may undergo rapid transitions from red to blue and vice versa on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks. Recent three-dimensional simulations of the bow shock produced by the nearby runaway red supergiant (RSG) Betelgeuse, under the assumption of a constant wind, indicate that the bow shock is very young (<30, 000 years old), hence Betelgeuse may have only recently become an RSG. To test this possibility, we have calculated stellar evolution models for single stars which match the observed properties of Betelgeuse in the RSG phase. The resulting evolving stellar wind is incorporated into two-dimensional hydrodynamic simulations in which we model a runaway blue supergiant (BSG) as it undergoes the transition to an RSG near the end of its life. We find that the collapsing BSG wind bubble induces a bow shock-shaped inner shell around the RSG wind that resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We suggest that this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.

  5. Lucien Lévy-Bruhl visto por Norbert Elias Lucien Lévy-Bruhl as Seen by Norbert Elias

    Directory of Open Access Journals (Sweden)

    Vera Weiler

    2008-12-01

    Full Text Available El artículo presenta materiales inéditos que permiten reconstruir la visión de Norbert Elias acerca de Lévy-Bruhl. Se documenta que Elias buscó que Lévy-Bruhl fuera reconsiderado por las ciencias sociales a la luz de un creciente volumen de evidencias que iban confirmando unas diferencias significativas en la organización psíquica de distintas sociedades históricas. Se demuestra que Elias concibió sus propias investigaciones del proceso psicogenético sobre un trasfondo compartido con Lévy-Bruhl. Las dificultades que enfrenta la asimilación de éste por parte de las ciencias humanas, Elias las considera del mismo tipo de las que se presentan a la comprensión de su propia teoría.This article presents unpublished materials enabling to reconstruct Norbert Elias' view of Lévy-Bruhl. It shows that Elias sought to have Lévy-Bruhl reconsidered by the social sciences, in light of the growing volume of evidence that confirmed significant differences in the psychic organization of various historical societies. It shows that Elias conceived of his own research in the psychogenetic process against a background shared by Lévy-Bruhl. Elias regarded the difficulties faced in the assimilation of the latter by human sciences as being of the same kind as those that hampered the understanding of his own theory.

  6. Studying the photometric and spectroscopic variability of the magnetic hot supergiant ζ Orionis Aa

    Science.gov (United States)

    Buysschaert, B.; Neiner, C.; Richardson, N. D.; Ramiaramanantsoa, T.; David-Uraz, A.; Pablo, H.; Oksala, M. E.; Moffat, A. F. J.; Mennickent, R. E.; Legeza, S.; Aerts, C.; Kuschnig, R.; Whittaker, G. N.; Popowicz, A.; Handler, G.; Wade, G. A.; Weiss, W. W.

    2017-06-01

    Massive stars play a significant role in the chemical and dynamical evolution of galaxies. However, much of their variability, particularly during their evolved supergiant stage, is poorly understood. To understand the variability of evolved massive stars in more detail, we present a study of the O9.2Ib supergiant ζ Ori Aa, the only currently confirmed supergiant to host a magnetic field. We have obtained two-color space-based BRIght Target Explorer photometry (BRITE) for ζ Ori Aa during two observing campaigns, as well as simultaneous ground-based, high-resolution optical CHIRON spectroscopy. We perform a detailed frequency analysis to detect and characterize the star's periodic variability. We detect two significant, independent frequencies, their higher harmonics, and combination frequencies: the stellar rotation period Prot = 6.82 ± 0.18 d, most likely related to the presence of the stable magnetic poles, and a variation with a period of 10.0 ± 0.3 d attributed to circumstellar environment, also detected in the Hα and several He I lines, yet absent in the purely photospheric lines. We confirm the variability with Prot/4, likely caused by surface inhomogeneities, being the possible photospheric drivers of the discrete absorption components. No stellar pulsations were detected in the data. The level of circumstellar activity clearlydiffers between the two BRITE observing campaigns. We demonstrate that ζ Ori Aa is a highly variable star with both periodic and non-periodic variations, as well as episodic events. The rotation period we determined agrees well with the spectropolarimetric value from the literature. The changing activity level observed with BRITE could explain why the rotational modulation of the magnetic measurements was not clearly detected at all epochs. Based on data collected by the BRITE Constellation satellite mission, designed, built, launched, operated and supported by the Austrian Research Promotion Agency (FFG), the University of

  7. Inertial Lévy Flight with Nonlinear Friction

    Institute of Scientific and Technical Information of China (English)

    L(U) Yan; BAO Jing-Dong

    2011-01-01

    vy Bight with nonlinear friction is studied. Due to the occurrence of extremely long jumps Levy flights often possess infinite variance and are physically problematic if describing the dynamics of a particle of finite mass. However, by introducing nonlinear friction, we show that the stochastic process subject to Levy noise exhibits finite variance, leading to a well-defined .kinetic energy. In the force-free fiIeld, normal diffusion behavior is observed and the diffusion coefficient decreases with Levy index μ. Furthermore, we find a kinetic resonance of the particle in the harmonic potential to the external oscillating field in the generally underdamped region and the value of the linear friction γo determines whether resonance occurs or not.%Lévy flight with nonlinear friction is studied.Due to the occurrence of extremely long jumps Lévy flights often possess infinite variance and are physically problematic if describing the dynamics of a particle of finite mass.However,by introducing nonlinear friction,we show that the stochastic process subject to Lévy noise exhibits finite variance,leading to a well-defined kinetic energy.In the force-free field,normal diffusion behavior is observed and the diffusion coefficient decreases with Lévy index μ.Furthermore,we find a kinetic resonance of the particle in the harmonic potential to the external oscillating field in the generally underdamped region and the value of the linear friction γ0 determines whether resonance occurs or not.The stable Lévy process,often called the Lévy flight,is used to model various phenomena such as self-diffusion in micelle systems,[1] special problems in reaction dynamics,[2] and even the flight of an albatross.

  8. A note on inverses of non-decreasing Lévy processes

    NARCIS (Netherlands)

    Ferreira, J.A.

    2001-01-01

    We show that, apart from deterministic processes, compound Poisson processes with exponential jumps are the only (shifted) non-decreasing Lévy processes whose inverses are also (shifted) non-decreasing Lévy processes.

  9. Environmental context explains Lévy and Brownian movement patterns of marine predators

    OpenAIRE

    Nicolas E Humphries; Queiroz, Nuno; Dyer, Jennifer R.M.; Pade, Nicolas G.; Musyl, Michael K.; Schaefer, Kurt M.; Fuller, Daniel W.; Brunnschweiler, Juerg M.; Thomas K. Doyle; Jonathan D.R. Houghton; Hays, Graeme C.; Jones, Catherine S.; Noble, Leslie R.; Wearmouth, Victoria J.; Southall, Emily J.

    2010-01-01

    An optimal search theory, the so-called Lévy-flight foraging hypothesis, predicts that predators should adopt search strategies known as Lévy flights where prey is sparse and distributed unpredictably, but that Brownian movement is sufficiently efficient for locating abundant prey. Empirical studies have generated controversy because the accuracy of statistical methods that have been used to identify Lévy behaviour has recently been questioned. Consequently, whether foragers exhibit Lévy flig...

  10. The Type IIb Supernova 2013df and its Cool Supergiant Progenitor

    Science.gov (United States)

    VanDyk, Schuyler D.; Zeng, Weikang; Fox, Ori D.; Cenko, S. Bradley; Clubb, Kelsey I.; Filippenko, Alexei; Foley, Ryan J.; Miller, Adam A.; Smith, Nathan; Kelly, Patrick L.; Lee, William H.; Ben-Ami, Sagi; Gal-Yam, Avishay

    2014-01-01

    We have obtained early-time photometry and spectroscopy of supernova (SN) 2013df in NGC 4414. The SN is clearly of Type II b, with notable similarities to SN 1993J. From its luminosity at secondary maximum light, it appears that less Ni-56 (is approximately less than 0.06M) was synthesized in the SN 2013df explosion than was the case for the SNe II b 1993J, 2008ax, and 2011dh. Based on a comparison of the light curves, the SN 2013df progenitor must have been more extended in radius prior to explosion than the progenitor of SN 1993J. The total extinction for SN 2013dfis estimated to be A(sub V) = 0.30 mag. The metallicity at the SN location is likely to be solar. We have conducted Hubble Space Telescope(HST) Target of Opportunity observations of the SN with the Wide Field Camera 3, and from a precise comparison of these new observations to archival HST observations of the host galaxy obtained 14 yr prior to explosion, we have identified the progenitor of SN 2013df to be a yellow supergiant, somewhat hotter than a red supergiant progenitor for a normal Type II-Plateau SN. From its observed spectral energy distribution, assuming that the light is dominated by one star, the progenitor had effective temperature T(sub eff) = 4250+/-100 K and a bolometric luminosity L(sub bol) =10(exp 4.94+/-0.06) Solar Luminosity. This leads to an effective radius Reff = 545+/-65 Solar Radius. The star likely had an initial mass in the range of 13-17Solar Mass; however, if it was a member of an interacting binary system, detailed modeling of the system is required to estimate this mass more accurately. The progenitor star of SN 2013df appears to have been relatively similar to the progenitor of SN 1993J.

  11. The type IIb supernova 2013df and its cool supergiant progenitor

    Energy Technology Data Exchange (ETDEWEB)

    Van Dyk, Schuyler D. [Spitzer Science Center/Caltech, Mail Code 220-6, Pasadena, CA 91125 (United States); Zheng, WeiKang; Fox, Ori D.; Clubb, Kelsey I.; Filippenko, Alexei V.; Kelly, Patrick L. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Cenko, S. Bradley [Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); Foley, Ryan J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Miller, Adam A. [Jet Propulsion Laboratory, MS 169-506, Pasadena, CA 91109 (United States); Smith, Nathan [Steward Observatory, University of Arizona, Tucson, AZ 85720 (United States); Lee, William H. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, Cd. Universitaria, México DF 04510 (Mexico); Ben-Ami, Sagi; Gal-Yam, Avishay, E-mail: vandyk@ipac.caltech.edu [Benoziyo Center for Astrophysics, The Weizmann Institute of Science, Rehovot 76100 (Israel)

    2014-02-01

    We have obtained early-time photometry and spectroscopy of supernova (SN) 2013df in NGC 4414. The SN is clearly of Type IIb, with notable similarities to SN 1993J. From its luminosity at secondary maximum light, it appears that less {sup 56}Ni (≲ 0.06 M {sub ☉}) was synthesized in the SN 2013df explosion than was the case for the SNe IIb 1993J, 2008ax, and 2011dh. Based on a comparison of the light curves, the SN 2013df progenitor must have been more extended in radius prior to explosion than the progenitor of SN 1993J. The total extinction for SN 2013df is estimated to be A{sub V} = 0.30 mag. The metallicity at the SN location is likely to be solar. We have conducted Hubble Space Telescope (HST) Target of Opportunity observations of the SN with the Wide Field Camera 3, and from a precise comparison of these new observations to archival HST observations of the host galaxy obtained 14 yr prior to explosion, we have identified the progenitor of SN 2013df to be a yellow supergiant, somewhat hotter than a red supergiant progenitor for a normal Type II-Plateau SN. From its observed spectral energy distribution, assuming that the light is dominated by one star, the progenitor had effective temperature T {sub eff} = 4250 ± 100 K and a bolometric luminosity L {sub bol} = 10{sup 4.94±0.06} L {sub ☉}. This leads to an effective radius R {sub eff} = 545 ± 65 R {sub ☉}. The star likely had an initial mass in the range of 13-17 M {sub ☉}; however, if it was a member of an interacting binary system, detailed modeling of the system is required to estimate this mass more accurately. The progenitor star of SN 2013df appears to have been relatively similar to the progenitor of SN 1993J.

  12. vy matters IV estimation for discretely observed Lévy processes

    CERN Document Server

    Belomestny, Denis; Genon-Catalot, Valentine; Masuda, Hiroki; Reiß, Markus

    2015-01-01

    The aim of this volume is to provide an extensive account of the most recent advances in statistics for discretely observed Lévy processes. These days, statistics for stochastic processes is a lively topic, driven by the needs of various fields of application, such as finance, the biosciences, and telecommunication. The three chapters of this volume are completely dedicated to the estimation of Lévy processes, and are written by experts in the field. The first chapter by Denis Belomestny and Markus Reiß treats the low frequency situation, and estimation methods are based on the empirical characteristic function. The second chapter by Fabienne Comte and Valery Genon-Catalon is dedicated to non-parametric estimation mainly covering the high-frequency data case. A distinctive feature of this part is the construction of adaptive estimators, based on deconvolution or projection or kernel methods. The last chapter by Hiroki Masuda considers the parametric situation. The chapters cover the main aspects of the est...

  13. INTEGRAL Long-Term Monitoring of the Supergiant Fast X-Ray Transient XTE J1739-302

    Science.gov (United States)

    Blay, P.; Martinez-Nunez, S.; Negueruela, I.; Pottschmidt, K.; Smith, D. M.; Torrejon, J. M.; Reig, P.; Kretschmar, P.; Kreykenbohm, I.

    2008-01-01

    Context. In the past few years, a new class of High Mass X-Ray Binaries (HMXRB) has been claimed to exist, the Supergiant Fast X-ray Transients (SFXT). These are X-ray binary systems with a compact companion orbiting a supergiant star which show very short and bright outbursts in a series of activity periods overimposed on longer quiescent periods. Only very recently the first attempts to model the behaviour of these sources have been published, some of them within the framework of accretion from clumpy stellar winds. Aims. Our goal is to analyze the properties of XTE J1739-302/IGR J17391-3021 within the context of the clumpy structure of the supergiant wind. Methods. We have used INTEGRAL and RXTE/PCA observations in order to obtain broad band (1 - 200 keV) spectra and light curves of XTE J1739-302 and investigate its X-ray spectrum and temporal variability. Results. We have found that XTE J1739-302 follows a much more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-302 shows periods of high, intermediate, and low flaring activity.

  14. Ring Nebula and Bipolar Outflows Associated with the B1.5 Supergiant Sher #25 in NGC 3603

    CERN Document Server

    Brandner, W; Chu, Y H; Weis, K; Brandner, Wolfgang; Grebel, Eva K.; Chu, You-Hua; Weis, Kerstin

    1996-01-01

    We have identified a ring-shaped emission-line nebula and a possible bipolar outflow centered on the B1.5 supergiant Sher #25 in the Galactic giant HII region NGC 3603 (distance 6 kpc). The clumpy ring around Sher #25 appears to be tilted by 64 deg against the plane of the sky. Its semi-major axis (position angle approx. 165 deg) is 6.9" long, which corresponds to a ring diameter of 0.4 pc. The bipolar outflow filaments, presumably located above and below the ring plane on either side of Sher #25, show a separation of approx. 0.5 pc from the central star. High-resolution spectra show that the ring has a systemic velocity of V_LSR = +19 km/s and a de-projected expansion velocity of 20 km/s, and that one of the bipolar filaments has an outflow speed of approx. 83 km/s. The spectra also show high [NII]/Halpha ratio, suggestive of strong N enrichment. Sher #25 must be an evolved blue supergiant (BSG) past the red supergiant (RSG) stage. We find that the ratio of equatorial to polar mass-loss rate during the red s...

  15. INTEGRAL Long-Term Monitoring of the Supergiant Fast X-Ray Transient XTE J1739-302

    Science.gov (United States)

    Blay, P.; Martinez-Nunez, S.; Negueruela, I.; Pottschmidt, K.; Smith, D. M.; Torrejon, J. M.; Reig, P.; Kretschmar, P.; Kreykenbohm, I.

    2008-01-01

    Context. In the past few years, a new class of High Mass X-Ray Binaries (HMXRB) has been claimed to exist, the Supergiant Fast X-ray Transients (SFXT). These are X-ray binary systems with a compact companion orbiting a supergiant star which show very short and bright outbursts in a series of activity periods overimposed on longer quiescent periods. Only very recently the first attempts to model the behaviour of these sources have been published, some of them within the framework of accretion from clumpy stellar winds. Aims. Our goal is to analyze the properties of XTE J1739-302/IGR J17391-3021 within the context of the clumpy structure of the supergiant wind. Methods. We have used INTEGRAL and RXTE/PCA observations in order to obtain broad band (1 - 200 keV) spectra and light curves of XTE J1739-302 and investigate its X-ray spectrum and temporal variability. Results. We have found that XTE J1739-302 follows a much more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-302 shows periods of high, intermediate, and low flaring activity.

  16. STOCHASTIC PARTIAL DIFFERENTIAL EQUATIONS DRIVEN BY MULTI-PARAMETER WHITE NOISE OF LÉVY PROCESSES

    OpenAIRE

    Øksendal, Bernt

    2007-01-01

    We give a short introduction to the white noise theory for multiparameter Lévy processes and its application to stochastic partial differential equations driven by such processes. Examples include temperature distribution with a Lévy white noise heat source, and heat propagation with a multiplicative Lévy white noise heat source.

  17. Is macroturbulent broadening in OB Supergiants related to pulsations?

    CERN Document Server

    Simón-Díaz, S; Herrero, A; Castro, N; Puls, J; Aerts, C

    2010-01-01

    The spectrum of O and B Supergiants is known to be affected by an important extra line-broadening (usually called \\macro) that adds to stellar rotation. Recent analysis of high resolution spectra has shown that the interpretation of this line-broadening as a consequence of large-scale turbulent motions would imply highly super-sonic velocity fields, making this scenario quite improbable. Stellar oscillations have been proposed as a likely alternative explanation. We present first encouraging results of an observational project aimed at investigating the $macroturbulent$ broadening in O and B Supergiants, and its possible connection with spectroscopic variability phenomena and stellar oscillations: a) all the studied B Supergiants show line profile variations, quantified by means of the first () and third velocity () moments of the lines, b) there is a strong correlation between the peak-to-peak amplitudes of the and variability and the size of the extra-broadening.

  18. Quantitative spectroscopic J-band study of red supergiants in Perseus OB-1

    Energy Technology Data Exchange (ETDEWEB)

    Gazak, J. Zachary; Kudritzki, Rolf [Institute for Astronomy, University of Hawai' i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Davies, Ben [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Bergemann, Maria [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France)

    2014-06-10

    We demonstrate how the metallicities of red supergiant (RSG) stars can be measured from quantitative spectroscopy down to resolutions of ≈3000 in the J-band. We have obtained high resolution spectra on a sample of the RSG population of h and χ Persei, a double cluster in the solar neighborhood. We show that careful application of the MARCS model atmospheres returns measurements of Z consistent with solar metallicity. Using two grids of synthetic spectra–one in pure LTE and one with non-LTE (NLTE) calculations for the most important diagnostic lines–we measure Z = +0.04 ± 0.10 (LTE) and Z = –0.04 ± 0.08 (NLTE) for the sample of eleven RSGs in the cluster. We degrade the spectral resolution of our observations and find that those values remain consistent down to resolutions of less than λ/δλ of 3000. Using measurements of effective temperatures we compare our results with stellar evolution theory and find good agreement. We construct a synthetic cluster spectrum and find that analyzing this composite spectrum with single-star RSG models returns an accurate metallicity. We conclude that the RSGs make ideal targets in the near infrared for measuring the metallicities of star forming galaxies out to 7-10 Mpc and up to 10 times farther by observing the integrated light of unresolved super star clusters.

  19. UV Observations of the Powering Source of the Supergiant Shell in IC2574

    CERN Document Server

    Stewart, S G; Stewart, Susan G.; Walter, Fabian

    2000-01-01

    A multi-band analysis of the region containing the supergiant HI shell in the nearby dwarf irregular galaxy IC2574 presents evidence of a causal relationship between a central star cluster, the surrounding expanding HI shell, and secondary star formation sites on the rim of the HI shell. Comparisons of the far-UV (FUV, 1521 A), optical broad-band, H-alpha, X-ray, and HI morphologies suggest that the region is in an auspicious moment of star formation triggered by the central stellar cluster. The derived properties of the HI shell, the central stellar cluster, and the star forming regions on the rim support this scenario: The kinematic age of the HI shell is <14 Myr and in agreement with the age of the central stellar cluster derived from the FUV observations (sim 11 Myr). An estimate for the mechanical energy input from SN and stellar winds of the central stellar cluster made from FUV photometry and the derived cluster age is 4.1 x 10^52 erg, roughly a few times higher than the kinetic energy of the HI she...

  20. Blue Supergiant X-Ray Binaries in the Nearby Dwarf Galaxy IC 10

    Science.gov (United States)

    Laycock, Silas G. T.; Christodoulou, Dimitris M.; Williams, Benjamin F.; Binder, Breanna; Prestwich, Andrea

    2017-02-01

    In young starburst galaxies, the X-ray population is expected to be dominated by the relics of the most massive and short-lived stars, black hole and neutron-star high-mass X-ray binaries (XRBs). In the closest such galaxy, IC 10, we have made a multi-wavelength census of these objects. Employing a novel statistical correlation technique, we have matched our list of 110 X-ray point sources, derived from a decade of Chandra observations, against published photometric data. We report an 8σ correlation between the celestial coordinates of the two catalogs, with 42 X-ray sources having an optical counterpart. Applying an optical color–magnitude selection to isolate blue supergiant (SG) stars in IC 10, we find 16 matches. Both cases show a statistically significant overabundance versus the expectation value for chance alignments. The blue objects also exhibit systematically higher {f}x/{f}v ratios than other stars in the same magnitude range. Blue SG-XRBs include a major class of progenitors of double-degenerate binaries, hence their numbers are an important factor in modeling the rate of gravitational-wave sources. We suggest that the anomalous features of the IC 10 stellar population are explained if the age of the IC 10 starburst is close to the time of the peak of interaction for massive binaries.

  1. The weak magnetic field of the O9.7 supergiant zeta Orionis A

    CERN Document Server

    Bouret, J -C; Martins, F; Escolano, C; Marcolino, W; Lanz, T; Howarth, Ian

    2008-01-01

    We report here the detection of a weak magnetic field of 50 - 100 G on the O9.7 supergiant zeta Ori A, using spectropolarimetric observations obtained with NARVAL at the 2m Telescope Bernard Lyot atop Pic du Midi (France). zeta Ori A is the third O star known to host a magnetic field (along with theta^1 Ori C and HD 191612), and the first detection on a 'normal' rapidly-rotating O star. The magnetic field of zeta Ori A is the weakest magnetic field ever detected on a massive star. The measured field is lower than the thermal equipartition limit (about 100 G). By fitting NLTE model atmospheres to our spectra, we determined that zeta Ori A is a 40 Msun star with a radius of 25 Rsun and an age of about 5 - 6 Myr, showing no surface nitrogen enhancement and losing mass at a rate of about 2x10^(-6) Msol/yr. The magnetic topology of zeta Ori A is apparently more complex than a dipole and involves two main magnetic polarities located on both sides of the same hemisphere; our data also suggest that zeta Ori A rotates...

  2. Multiwavelength study of the fast rotating supergiant high-mass X-ray binary IGR J16465-4507

    CERN Document Server

    Chaty, Sylvain; Negueruela, Ignacio; Coleiro, Alexis; Castro, Norberto; Simon-Diaz, Sergio; Heras, Juan Antonio Zurita; Goldoni, Paolo; Goldwurm, Andrea

    2016-01-01

    Since its launch, the X-ray and gamma-ray observatory INTEGRAL satellite has revealed a new class of high-mass X-ray binaries (HMXB) displaying fast flares and hosting supergiant companion stars. Optical and infrared (OIR) observations in a multi-wavelength context are essential to understand the nature and evolution of these newly discovered celestial objects. The goal of this multiwavelength study (from ultraviolet to infrared) is to characterise the properties of IGR J16465-4507, to confirm its HMXB nature and that it hosts a supergiant star. We analysed all OIR, photometric and spectroscopic observations taken on this source, carried out at ESO facilities. Using spectroscopic data, we constrained the spectral type of the companion star between B0.5 and B1 Ib, settling the debate on the true nature of this source. We measured a high rotation velocity of v = 320 +/- 8 km/s from fitting absorption and emission lines in a stellar spectral model. We then built a spectral energy distribution from photometric ob...

  3. The evolution of circumstellar medium around rotating massive stars

    NARCIS (Netherlands)

    Chita, S.M.; Marle, A.J.; Langer, N.; García-Segura, G.

    2007-01-01

    A rotating 12Mȯ star, after its main-sequence evolution, becomes a redsupergiant when it starts core He burning. During core helium burning, as consequence of a variation of the hydrogen shell burning efficiency, the star undergoes a so called ``blue loop'', i.e. it evolves into a blue supergiant st

  4. HD 133656 : A new high-latitude supergiant

    NARCIS (Netherlands)

    VanWinckel, H; Oudmaijer, RD; Trams, NR

    1996-01-01

    In the course of our study of post-asymptotic Giant Branch objects, we discovered that the seventh magnitude A supergiant HD 133656 has an infrared excess emission due to cool circumstellar dust, and that its photospheric abundance pattern is population II like. We present a detailed abundance study

  5. POLYNOMIAL RECURRENCE FOR L(E)VY PROCESSES

    Institute of Scientific and Technical Information of China (English)

    ZHAO MINZHI; YING JIANGANG

    2004-01-01

    In this paper, the authors study the ω-transience and ω-recurrence for Lévy processes with any weight function ω, give a relation between ω-recurrence and the last exit times. As a special case, the polynomial recurrence and polynomial transience are also studied.

  6. On spatio-temporal Lévy based Cox processes

    DEFF Research Database (Denmark)

    Prokesova, Michaela; Hellmund, Gunnar; Jensen, Eva Bjørn Vedel

    2006-01-01

    The paper discusses a new class of models for spatio-temporal Cox point processes. In these models, the driving field is defined by means of an integral of a weight function with respect to a Lévy basis. The relations to other Cox process models studied previously are discussed and formulas for t...

  7. vy-based modelling in brain imaging

    DEFF Research Database (Denmark)

    Jónsdóttir, Kristjana Ýr; Rønn-Nielsen, Anders; Mouridsen, Kim

    2013-01-01

    A substantive problem in neuroscience is the lack of valid statistical methods for non-Gaussian random fields. In the present study, we develop a flexible, yet tractable model for a random field based on kernel smoothing of a so-called Lévy basis. The resulting field may be Gaussian, but there ar...

  8. vy targeting and the principle of detailed balance.

    Science.gov (United States)

    Garbaczewski, Piotr; Stephanovich, Vladimir

    2011-07-01

    We investigate confining mechanisms for Lévy flights under premises of the principle of detailed balance. In this case, the master equation of the jump-type process admits a transformation to the Lévy-Schrödinger semigroup dynamics akin to a mapping of the Fokker-Planck equation into the generalized diffusion equation. This sets a correspondence between above two stochastic dynamical systems, within which we address a (stochastic) targeting problem for an arbitrary stability index μ ε (0,2) of symmetric Lévy drivers. Namely, given a probability density function, specify the semigroup potential, and thence the jump-type dynamics for which this PDF is actually a long-time asymptotic (target) solution of the master equation. Here, an asymptotic behavior of different μ-motion scenarios ceases to depend on μ. That is exemplified by considering Gaussian and Cauchy family target PDFs. A complementary problem of the reverse engineering is analyzed: given a priori a semigroup potential, quantify how sensitive upon the choice of the μ driver is an asymptotic behavior of solutions of the associated master equation and thus an invariant PDF itself. This task is accomplished for so-called μ family of Lévy oscillators.

  9. Scientific Works by Wiener and Lévy After Brown

    Science.gov (United States)

    Hida, Takeyuki

    2008-07-01

    Brownian motion was recognized as a scientific research object by R. Brown in 1827, and then many scientists studied the motion within science. Two famous mathematicians, N. Wiener and P. Lévy, studied Browniam motion mainly in mathematics. We appreciate their works and would like to note that their results play very important role in the study of biological phenomena.

  10. The VLT-FLAMES Tarantula Survey . XXIV. Stellar properties of the O-type giants and supergiants in 30 Doradus

    Science.gov (United States)

    Ramírez-Agudelo, O. H.; Sana, H.; de Koter, A.; Tramper, F.; Grin, N. J.; Schneider, F. R. N.; Langer, N.; Puls, J.; Markova, N.; Bestenlehner, J. M.; Castro, N.; Crowther, P. A.; Evans, C. J.; García, M.; Gräfener, G.; Herrero, A.; van Kempen, B.; Lennon, D. J.; Maíz Apellániz, J.; Najarro, F.; Sabín-Sanjulián, C.; Simón-Díaz, S.; Taylor, W. D.; Vink, J. S.

    2017-04-01

    Context. The Tarantula region in the Large Magellanic Cloud (LMC) contains the richest population of spatially resolved massive O-type stars known so far. This unmatched sample offers an opportunity to test models describing their main-sequence evolution and mass-loss properties. Aims: Using ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to determine stellar, photospheric and wind properties of 72 presumably single O-type giants, bright giants and supergiants and to confront them with predictions of stellar evolution and of line-driven mass-loss theories. Methods: We apply an automated method for quantitative spectroscopic analysis of O stars combining the non-LTE stellar atmosphere model fastwind with the genetic fitting algorithm pikaia to determine the following stellar properties: effective temperature, surface gravity, mass-loss rate, helium abundance, and projected rotational velocity. The latter has been constrained without taking into account the contribution from macro-turbulent motions to the line broadening. Results: We present empirical effective temperature versus spectral subtype calibrations at LMC-metallicity for giants and supergiants. The calibration for giants shows a +1kK offset compared to similar Galactic calibrations; a shift of the same magnitude has been reported for dwarfs. The supergiant calibrations, though only based on a handful of stars, do not seem to indicate such an offset. The presence of a strong upturn at spectral type O3 and earlier can also not be confirmed by our data. In the spectroscopic and classical Hertzsprung-Russell diagrams, our sample O stars are found to occupy the region predicted to be the core hydrogen-burning phase by state-of-the-art models. For stars initially more massive than approximately 60 M⊙, the giant phase already appears relatively early on in the evolution; the supergiant phase develops later. Bright giants, however, are not

  11. Asymmetric Lévy flight in financial ratios.

    Science.gov (United States)

    Podobnik, Boris; Valentinčič, Aljoša; Horvatić, Davor; Stanley, H Eugene

    2011-11-01

    Because financial crises are characterized by dangerous rare events that occur more frequently than those predicted by models with finite variances, we investigate the underlying stochastic process generating these events. In the 1960s Mandelbrot [Mandelbrot B (1963) J Bus 36:394-419] and Fama [Fama EF (1965) J Bus 38:34-105] proposed a symmetric Lévy probability distribution function (PDF) to describe the stochastic properties of commodity changes and price changes. We find that an asymmetric Lévy PDF, L, characterized by infinite variance, models several multiple credit ratios used in financial accounting to quantify a firm's financial health, such as the Altman [Altman EI (1968) J Financ 23:589-609] Z score and the Zmijewski [Zmijewski ME (1984) J Accounting Res 22:59-82] score, and models changes of individual financial ratios, ΔX(i). We thus find that Lévy PDFs describe both the static and dynamics of credit ratings. We find that for the majority of ratios, ΔX(i) scales with the Lévy parameter α ≈ 1, even though only a few of the individual ratios are characterized by a PDF with power-law tails X(i)(-1-α) with infinite variance. We also find that α exhibits a striking stability over time. A key element in estimating credit losses is the distribution of credit rating changes, the functional form of which is unknown for alphabetical ratings. For continuous credit ratings, the Altman Z score, we find that P(ΔZ) follows a Lévy PDF with power-law exponent α ≈ 1, consistent with changes of individual financial ratios. Estimating the conditional P(ΔZ|Z) versus Z, we demonstrate how this continuous credit rating approach and its dynamics can be used to evaluate credit risk.

  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

    CERN Document Server

    Gimenez-Garcia, A; Torrejon, J M; Oskinova, L; Martinez-Nunez, S; Hamann, W -R; Rodes-Roca, J J; Gonzalez-Galan, A; Alonso-Santiago, J; Gonzalez-Fernandez, C; Bernabeu, G; Sander, A

    2016-01-01

    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. 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 analyse the spectra of each star in detail and derive their stellar and wind properties. We compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. We find that the stellar para...

  13. The chemical abundances in the Galactic Centre from the atmospheres of Red Supergiants

    CERN Document Server

    Davies, Ben; Kudritzki, Rolf-Peter; Figer, Don F; Rich, R Michael; Najarro, Francisco

    2008-01-01

    The Galactic Centre (GC) has experienced a high degree of recent star-forming activity, as evidenced by the large number of massive stars currently residing there. The relative abundances of chemical elements in the GC may provide insights into the origins of this activity. Here, we present high-resolution $H$-band spectra of two Red Supergiants in the GC (IRS~7 and VR~5-7), and in combination with spectral synthesis we derive abundances for Fe and C, as well as other $\\alpha$-elements Ca, Si, Mg Ti and O. We find that the C-depletion in VR~5-7 is consistent with the predictions of evolutionary models of RSGs, while the heavy depletion of C and O in IRS~7's atmosphere is indicative of deep mixing, possibly due to fast initial rotation and/or enhanced mass-loss. Our results indicate that the {\\it current} surface Fe/H content of each star is slightly above Solar. However, comparisons to evolutionary models indicate that the {\\it initial} Fe/H ratio was likely closer to Solar, and has been driven higher by H-de...

  14. The Chemical composition of the post-AGB F-supergiant CRL 2688

    CERN Document Server

    Ishigaki, Miho N; Reddy, Bacham E; García-Lario, Pedro; Takeda, Yoichi; Aoki, Wako

    2012-01-01

    We present an analysis of a high resolution (R \\sim 30000) optical spectrum of the central region of the proto-planetary nebula CRL 2688. This object is thought to have recently moved off the AGB, and display abundance patterns of CNO and heavy elements that can provide us with important clues to understand the nucleosynthesis, dredge-up and mixing experienced by the envelope of the central star during its AGB stage of evolution. The analysis of the molecular features, presumably originated from the circumstellar matter provides further constraints on the chemistry and velocity of the expanding shell, expelled as a consequence of the strong mass loss experienced by the central star. We confirm that the central star shows a spectrum typical of an F-type supergiant with Teff=7250 K, log g=0.5 and [Fe/H]=-0.3 dex. We find that the abundance pattern of this object is characterized by enhancements of Carbon ([C/Fe]=0.6), Nitrogen ([N/Fe]=1.0) and Na ([Na/Fe]=0.7), similar to other previously known carbon-rich post...

  15. DISCOVERY OF SiO BAND EMISSION FROM GALACTIC B[e] SUPERGIANTS

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, M. [Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov (Czech Republic); Oksala, M. E. [LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, F-92190, Meudon (France); Cidale, L. S.; Arias, M. L.; Torres, A. F. [Departamento de Espectroscopía Estelar, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata (Argentina); Fernandes, M. Borges, E-mail: michaela.kraus@asu.cas.cz [Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro (Brazil)

    2015-02-20

    B[e] supergiants (B[e]SGs) are evolved massive stars in a short-lived transition phase. During this phase, these objects eject large amounts of material, which accumulate in a circumstellar disk-like structure. The expelled material is typically dense and cool, providing the cradle for molecule and dust condensation and for a rich, ongoing chemistry. Very little is known about the chemical composition of these disks, beyond the emission from dust and CO revolving around the star on Keplerian orbits. As massive stars preserve an oxygen-rich surface composition throughout their life, other oxygen-based molecules can be expected to form. As SiO is the second most stable oxygen compound, we initiated an observing campaign to search for first-overtone SiO emission bands. We obtained high-resolution near-infrared L-band spectra for a sample of Galactic B[e]SGs with reported CO band emission. We clearly detect emission from the SiO first-overtone bands in CPD-52 9243 and indications for faint emission in HD 62623, HD 327083, and CPD-57 2874. From model fits, we find that in all these stars the SiO bands are rotationally broadened with a velocity lower than observed in the CO band forming regions, suggesting that SiO forms at larger distances from the star. Hence, searching for and analyzing these bands is crucial for studying the structure and kinematics of circumstellar disks, because they trace complementary regions to the CO band formation zone. Moreover, since SiO molecules are the building blocks for silicate dust, their study might provide insight in the early stage of dust formation.

  16. RED SUPERGIANTS AS COSMIC ABUNDANCE PROBES: THE FIRST DIRECT METALLICITY DETERMINATION OF NGC 4038 IN THE ANTENNAE

    Energy Technology Data Exchange (ETDEWEB)

    Lardo, C.; Davies, B. [Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Kudritzki, R-P.; Gazak, J. Z. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Evans, C. J. [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Patrick, L. R. [Institute for Astronomy, University of Edinburgh, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Bergemann, M. [Max-Planck Institute for Astronomy, D-69117 Heidelberg (Germany); Plez, B. [Laboratoire Univers et Particules de Montpellier, Université de Montpellier, CNRS, F-34095 Montpellier (France)

    2015-10-20

    We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D = 20 Mpc) based on the quantitative analysis of moderate-resolution KMOS/Very Large Telescope spectra of three super star clusters. The method adopted in our analysis has been developed and optimized to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not affected by the biases and poorly understood systematics inherent to strong line H ii methods, which are routinely applied to massive data sets of galaxies. We find [Z] = +0.07 ± 0.03 and compare our measurements to H ii strong line calibrations. Our abundances and literature data suggest the presence of a flat metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction.

  17. Red Supergiants as Cosmic Abundance Probes: The First Direct Metallicity Determination of NGC 4038 in the Antennae

    Science.gov (United States)

    Lardo, C.; Davies, B.; Kudritzki, R.-P.; Gazak, J. Z.; Evans, C. J.; Patrick, L. R.; Bergemann, M.; Plez, B.

    2015-10-01

    We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D = 20 Mpc) based on the quantitative analysis of moderate-resolution KMOS/Very Large Telescope spectra of three super star clusters. The method adopted in our analysis has been developed and optimized to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not affected by the biases and poorly understood systematics inherent to strong line H ii methods, which are routinely applied to massive data sets of galaxies. We find [Z] = +0.07 ± 0.03 and compare our measurements to H ii strong line calibrations. Our abundances and literature data suggest the presence of a flat metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction.

  18. Supergiant Fast X-ray Transients: A Case Study for LOFT

    Science.gov (United States)

    Romano, Patrizia; Mangano, V.; Bozzo, E.; Esposito, P.; Ferrigno, C.

    2013-04-01

    LOFT, the Large Observatory For X-ray Timing, is a new space mission concept selected by ESA in February 2011 and currently competing for a launch of opportunity in 2022. LOFT will carry a coded mask Wide Field Monitor (WFM) and a 10-m^2 class collimated X-ray Large Area Detector (LAD) operating in the energy range 2-80 keV. The instruments on-board LOFT will dramatically deepen our knowledge of Supergiant Fast X-ray Transients, a class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state. The LAD and the WFM will provide simultaneous high S/N broad-band and time-resolved spectroscopy in several intensity states, long term monitoring that will yield new determinations of orbital periods, as well as spin periods. We show the results of an extensive set of simulations based on the Swift broad-band and detailed XMM-Newton observations we collected up to now. Our simulations describe the outbursts at several intensities (F(2-10 keV)=5.9E-9 to 5.5E-10 erg cm-2 s-1), the intermediate and most common state (1E-11 erg cm-2 s-1), and the low state (1.2E-12 to 5E-13 erg cm-2 s-1). We also considered large variations of NH and the presence of emission lines, as observed by Swift and XMM-Newton. We acknowledge financial contribution from ASI-INAF I/004/11/0 and I/021/12/0.

  19. Fractional generalized Lévy random fields as white noise functionals

    Institute of Scientific and Technical Information of China (English)

    HUANG Zhiyuan; LI Peiyan

    2007-01-01

    In this paper, we construct the fractional generalized Lévy random fields (FGLRF) as tempered white noise functionals. We find that this white noise approach is very effective in investigating the properties of these fields. Under some conditions, the fractional Lévy fields in the usual sense are obtained. In addition, we also present a method to construct the anisotropic fractional generalized Lévy random fields (AFGLRF).

  20. VY-BASED ERROR PREDICTION IN CIRCULAR SYSTEMATIC SAMPLING

    Directory of Open Access Journals (Sweden)

    Kristjana Ýr Jónsdóttir

    2013-06-01

    Full Text Available In the present paper, Lévy-based error prediction in circular systematic sampling is developed. A model-based statistical setting as in Hobolth and Jensen (2002 is used, but the assumption that the measurement function is Gaussian is relaxed. The measurement function is represented as a periodic stationary stochastic process X obtained by a kernel smoothing of a Lévy basis. The process X may have an arbitrary covariance function. The distribution of the error predictor, based on measurements in n systematic directions is derived. Statistical inference is developed for the model parameters in the case where the covariance function follows the celebrated p-order covariance model.

  1. Representations of Homogeneous Quantum Lévy Fields

    Indian Academy of Sciences (India)

    V P Belavkin; L Gregory

    2006-11-01

    We study homogeneous quantum Lévy processes and fields with independent additive increments over a noncommutative ∗-monoid. These are described by infinitely divisible generating state functionals, invariant with respect to an endomorphic injective action of a symmetry semigroup. A strongly covariant GNS representation for the conditionally positive logarithmic functionals of these states is constructed in the complex Minkowski space in terms of canonical quadruples and isometric representations on the underlying pre-Hilbert field space. This is of much use in constructing quantum stochastic representations of homogeneous quantum Lévy fields on Itô monoids, which is a natural algebraic way of defining dimension free, covariant quantum stochastic integration over a space-time indexing set.

  2. Filosofický odkaz Luciena Lévy-Bruhla

    Directory of Open Access Journals (Sweden)

    Miloš Kratochvíl

    2011-04-01

    Full Text Available The main aims of the following paper are to sketch general features of Lévy-Bruhl´s attitude to philosophy and its history and to show influence of his thought to 20th century philosophy of science. Lévy-Bruhl´s effort in ethnology and social anthropology, rooted in his philosophical views on human spirit, is presented as an insrument or a method to establish new and scientific theory of knowledge. His work is not presented only as a chapter belonging to history of philosophy, but also to show its influence on some of the most important persons in philosophy of science, namely Piaget, Bachelard and Koyré.

  3. Core collapse supernovae from blue supergiant progenitors : The evolutionary history of SN 1987A

    Science.gov (United States)

    Menon, Athira

    2015-08-01

    SN 1987A is historically one of the most remarkable supernova explosions to be seen from Earth. Due to the proximity of its location in the LMC, it remains the most well-studied object outside the solar system. It was also the only supernova whose progenitor was observed prior to its explosion.SN 1987A however, was a unique and enigmatic core collapse supernova. It was the first Type II supernova to have been observed to have exploded while its progenitor was a blue supergiant (BSG). Until then Type II supernovae were expected to originate from explosions of red supergiants (RSGs). A spectacular triple-ring nebula structure, rich in helium and nitrogen, was observed around the remnant, indicating a recent RSG phase before becoming a BSG. Even today it is not entirely understood what the evolutionary history may have been to cause a BSG to explode. The most commonly accepted hypothesis for its origin is the merger of a massive binary star system.An evolutionary scenario for such a binary system, was proposed by Podsiadlowski (1992) (P92). Through SPH simulations of the merger and the stellar evolution of the post-merger remnant, Ivanova & Podsiadlowski (2002) and (2003) (I&M) could successfully obtain the RSG to BSG transition of the progenitor.The aim of the present work is to produce the evolutionary history of the progenitor of SN 1987A and its explosion. We construct our models based on the results of P92 and I&M. Here, the secondary (less massive) star is accreted on the primary, while being simultaneously mixed in its envelope over a period of 100 years. The merged star is evolved until the onset of core collapse. For this work we use the 1-dimensional, implicit, hydrodynamical stellar evolution code, KEPLER. A large parameter space is explored, consisting of primary (16-20 Ms) and secondary masses (5-8 Ms), mixing boundaries, and accreting timescales. Those models whose end states match the observed properties of the progenitor of SN 1987A are exploded. The

  4. The quest for blue supergiants : The evolution of the progenitor of SN 1987A

    Science.gov (United States)

    Menon, Athira; Heger, Alexander

    2015-08-01

    SN 1987A is historically one of the most remarkable supernova explosions to be seen from Earth. Due to the proximity of its location in the LMC, it remains the most well-studied object outside the solar system. It was also the only supernova whose progenitor was observed prior to its explosion.SN 1987A however, was a unique and enigmatic core collapse supernova. It was the first Type II supernova to have been observed to have exploded while its progenitor was a blue supergiant (BSG). Until then Type II supernovae were expected to originate from explosions of red supergiants (RSGs). A spectacular triple-ring nebula structure, rich in helium and nitrogen, was observed around the remnant, indicating a recent RSG phase before becoming a BSG. Even today it is not entirely understood what the evolutionary history may have been to cause a BSG to explode. The most commonly accepted hypothesis for its origin is the merger of a massive binary star system.An evolutionary scenario for such a binary system, was proposed by Podsiadlowski (1992) (P92). Through SPH simulations of the merger and the stellar evolution of the post-merger remnant, Ivanova & Podsiadlowski (2002) and (2003) (I&M) could successfully obtain the RSG to BSG transition of the progenitor.The aim of the present work is to produce the evolutionary history of the progenitor of SN 1987A and its explosion. We construct our models based on the results of P92 and I&M. Here, the secondary (less massive) star is accreted on the primary, while being simultaneously mixed in its envelope over a period of 100 years. The merged star is evolved until the onset of core collapse. For this work we use the 1-dimensional, implicit, hydrodynamical stellar evolution code, KEPLER. A large parameter space is explored, consisting of primary (16-20 Ms) and secondary masses (5-8 Ms), mixing boundaries, and accreting timescales. Those models whose end states match the observed properties of the progenitor of SN 1987A are exploded. The

  5. Random Dynamics of the Stochastic Boussinesq Equations Driven by Lévy Noises

    Directory of Open Access Journals (Sweden)

    Jianhua Huang

    2013-01-01

    Full Text Available This paper is devoted to the investigation of random dynamics of the stochastic Boussinesq equations driven by Lévy noise. Some fundamental properties of a subordinator Lévy process and the stochastic integral with respect to a Lévy process are discussed, and then the existence, uniqueness, regularity, and the random dynamical system generated by the stochastic Boussinesq equations are established. Finally, some discussions on the global weak solution of the stochastic Boussinesq equations driven by general Lévy noise are also presented.

  6. Stationary distribution and ergodicity of a stochastic food-chain model with Lévy jumps

    Science.gov (United States)

    Yu, Jingyi; Liu, Meng

    2017-09-01

    In this paper, a three-species stochastic food-chain model with Lévy jumps is proposed and analyzed. Sharp sufficient criteria for the existence and uniqueness of an ergodic stationary distribution are established. The effects of Lévy jumps on the existence of the stationary distribution are revealed: in some cases, the Lévy jumps could make the stationary distribution appear, while in some cases, the Lévy jumps could make the stationary distribution disappear. Some numerical simulations are introduced to illustrate the theoretical results.

  7. vy flight artificial bee colony algorithm

    Science.gov (United States)

    Sharma, Harish; Bansal, Jagdish Chand; Arya, K. V.; Yang, Xin-She

    2016-08-01

    Artificial bee colony (ABC) optimisation algorithm is a relatively simple and recent population-based probabilistic approach for global optimisation. The solution search equation of ABC is significantly influenced by a random quantity which helps in exploration at the cost of exploitation of the search space. In the ABC, there is a high chance to skip the true solution due to its large step sizes. In order to balance between diversity and convergence in the ABC, a Lévy flight inspired search strategy is proposed and integrated with ABC. The proposed strategy is named as Lévy Flight ABC (LFABC) has both the local and global search capability simultaneously and can be achieved by tuning the Lévy flight parameters and thus automatically tuning the step sizes. In the LFABC, new solutions are generated around the best solution and it helps to enhance the exploitation capability of ABC. Furthermore, to improve the exploration capability, the numbers of scout bees are increased. The experiments on 20 test problems of different complexities and five real-world engineering optimisation problems show that the proposed strategy outperforms the basic ABC and recent variants of ABC, namely, Gbest-guided ABC, best-so-far ABC and modified ABC in most of the experiments.

  8. Subexponential loss rate asymptotics for Lévy processes

    DEFF Research Database (Denmark)

    Andersen, Lars Nørvang

    We consider a Lévy process reflected in barriers at 0 and K > 0. The loss rate is the mean time spent at the upper barrier K at time 1 when the process is started in stationarity, and is a natural continuous-time analogue of the stationary expected loss rate for a reflected random walk. We derive...... asymptotics for the loss rate when K tends to infinity, when the mean of the Lévy process is negative and the positive jumps are subexponential. In the course of this derivation, we achieve a formula, which is a generalization of the celebrated Pollaczeck-Khinchine formula.......We consider a Lévy process reflected in barriers at 0 and K > 0. The loss rate is the mean time spent at the upper barrier K at time 1 when the process is started in stationarity, and is a natural continuous-time analogue of the stationary expected loss rate for a reflected random walk. We derive...

  9. Subexponential loss rate asymptotics for Lévy processes

    DEFF Research Database (Denmark)

    Andersen, Lars Nørvang

    2011-01-01

    We consider a Lévy process reflected in barriers at 0 and K > 0. The loss rate is the mean of the local time at K at time 1 when the process is started in stationarity, and is a natural continuous-time analogue of the stationary expected loss rate for a reflected random walk. We derive asymptotic...... for the loss rate when K tends to infinity, when the mean of the Lévy process is negative and the positive jumps are subexponential. In the course of this derivation, we achieve a formula, which is a generalization of the celebrated Pollaczeck-Khinchine formula.......We consider a Lévy process reflected in barriers at 0 and K > 0. The loss rate is the mean of the local time at K at time 1 when the process is started in stationarity, and is a natural continuous-time analogue of the stationary expected loss rate for a reflected random walk. We derive asymptotics...

  10. Fluctuations of Lévy processes with applications introductory lectures

    CERN Document Server

    Kyprianou, Andreas E

    2014-01-01

    vy processes are the natural continuous-time analogue of random walks and form a rich class of stochastic processes around which a robust mathematical theory exists. Their application appears in the theory of many areas of classical and modern stochastic processes including storage models, renewal processes, insurance risk models, optimal stopping problems, mathematical finance, continuous-state branching processes and positive self-similar Markov processes. This textbook is based on a series of graduate courses concerning the theory and application of Lévy processes from the perspective of their path fluctuations. Central to the presentation is the decomposition of paths in terms of excursions from the running maximum as well as an understanding of short- and long-term behaviour. The book aims to be mathematically rigorous while still providing an intuitive feel for underlying principles. The results and applications often focus on the case of Lévy processes with jumps in only one direction, for which r...

  11. From Lévy walks to superdiffusive shock acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Zimbardo, Gaetano; Perri, Silvia, E-mail: gaetano.zimbardo@fis.unical.it, E-mail: silvia.perri@fis.unical.it [Dipartimento di Fisica, Università della Calabria, Ponte P. Bucci, Cubo 31C, I-87036 Arcavacata di Rende (Italy)

    2013-11-20

    In this paper, we present a general scenario for nondiffusive transport and we investigate the influence of anomalous, superdiffusive transport on Fermi acceleration processes at shocks. We explain why energetic particle superdiffusion can be described within the Lévy walk framework, which is based on a power-law distribution of free path lengths and on a coupling between free path length and free path duration. A self-contained derivation of the particle mean square displacement, which grows as (Δx {sup 2}) = 2D {sub α} t {sup α} with α > 1, and the particle propagator, is presented for Lévy walks, making use of a generalized version of the Montroll-Weiss equation. We also derive for the first time an explicit expression for the anomalous diffusion coefficient D {sub α} and we discuss how to obtain these quantities from energetic particle observations in space. The results are applied to the case of particle acceleration at an infinite planar shock front. Using the scaling properties of the Lévy walk propagator, the energy spectral indices are found to have values smaller than the ones predicted by the diffusive shock acceleration theory. Furthermore, when applying the results to ions with energies of a few MeV accelerated at the solar wind termination shock, the estimation of the anomalous diffusion coefficient associated with the superdiffusive motion gives acceleration times much smaller than the ones related to normal diffusion.

  12. vy processes on a generalized fractal comb

    Science.gov (United States)

    Sandev, Trifce; Iomin, Alexander; Méndez, Vicenç

    2016-09-01

    Comb geometry, constituted of a backbone and fingers, is one of the most simple paradigm of a two-dimensional structure, where anomalous diffusion can be realized in the framework of Markov processes. However, the intrinsic properties of the structure can destroy this Markovian transport. These effects can be described by the memory and spatial kernels. In particular, the fractal structure of the fingers, which is controlled by the spatial kernel in both the real and the Fourier spaces, leads to the Lévy processes (Lévy flights) and superdiffusion. This generalization of the fractional diffusion is described by the Riesz space fractional derivative. In the framework of this generalized fractal comb model, Lévy processes are considered, and exact solutions for the probability distribution functions are obtained in terms of the Fox H-function for a variety of the memory kernels, and the rate of the superdiffusive spreading is studied by calculating the fractional moments. For a special form of the memory kernels, we also observed a competition between long rests and long jumps. Finally, we considered the fractal structure of the fingers controlled by a Weierstrass function, which leads to the power-law kernel in the Fourier space. This is a special case, when the second moment exists for superdiffusion in this competition between long rests and long jumps.

  13. Human memory retrieval as Lévy foraging

    Science.gov (United States)

    Rhodes, Theo; Turvey, Michael T.

    2007-11-01

    When people attempt to recall as many words as possible from a specific category (e.g., animal names) their retrievals occur sporadically over an extended temporal period. Retrievals decline as recall progresses, but short retrieval bursts can occur even after tens of minutes of performing the task. To date, efforts to gain insight into the nature of retrieval from this fundamental phenomenon of semantic memory have focused primarily upon the exponential growth rate of cumulative recall. Here we focus upon the time intervals between retrievals. We expected and found that, for each participant in our experiment, these intervals conformed to a Lévy distribution suggesting that the Lévy flight dynamics that characterize foraging behavior may also characterize retrieval from semantic memory. The closer the exponent on the inverse square power-law distribution of retrieval intervals approximated the optimal foraging value of 2, the more efficient was the retrieval. At an abstract dynamical level, foraging for particular foods in one's niche and searching for particular words in one's memory must be similar processes if particular foods and particular words are randomly and sparsely located in their respective spaces at sites that are not known a priori. We discuss whether Lévy dynamics imply that memory processes, like foraging, are optimized in an ecological way.

  14. The Envelopes of B[e] Supergiants in the Magellanic Clouds as Seen by Polarimetry

    Science.gov (United States)

    Seriacopi, D. B.; Carciofi, A. C.; Magalhães, A. M.

    2017-02-01

    B[e] supergiants (sgB[e]) are rare, massive post-main sequence stars. Their evolutionary status with respect to other objects on the H-R diagram is still unknown. These stars are surrounded by a non-spherically symmetric circumstellar envelope, from which arises a net intrinsic polarization. Therefore, spectropolarimetry is a very useful tool in the study of these objects. Since emission, absorption, and scattering processes are imprinted in the polarized flux, this technique can provide useful information about the circumstellar structure. We present a study of the envelope structure of RMC 82, a sgB[e] in the Large Magellanic Cloud, based on spectropolarimetric data. Our observations were obtained with the 8.2 m VLT/UT1 telescope at the Paranal Observatory (ESO). We analyzed the Balmer line formation loci, and their corresponding physical conditions. The data was modeled by a bimodal wind model of the circumstellar envelope, consisting of a slow, dense equatorial wind and a fast polar wind. The calculations were done with the radiative transfer code HDUST. Our results suggest that this geometry is indeed consistent with the RMC 82 data. Our best fit parameters are an opening angle of the disk of 15° and a total mass loss rate of 1.0×10-5 M⊙ yr-1 sr-1.

  15. Similarities in the structure of the circumstellar environments of B[e] supergiants and yellow hypergiants

    CERN Document Server

    Aret, Anna; Kraus, Michaela; Maravelias, Grigoris

    2016-01-01

    Yellow Hypergiants (YHGs) and B[e] supergiants (B[e]SGs), though in different phases in their evolution, display many features in common. This is partly due to the fact that both types of objects undergo strong, often asymmetric mass loss, and the ejected material accumulates in shells, rings, or disk-like structures, giving rise to emission from warm molecules and dust. We performed an optical spectroscopic survey of northern Galactic emission-line stars aimed at identifying tracers for the structure and kinematics of circumstellar environments. We identified two sets of lines, [O I] and [Ca II], which originate from the discs of B[e]SGs. The same set of lines is observed in V1302 Aql and V509 Cas, which are both hot YHGs. While V1302 Aql is known to have a disc-like structure, the kinematical broadening of the lines in V509 Cas suggest a Keplerian disk or ring around this star alike their hotter B[e]SG counterparts.

  16. Neutral and ionized gas around the post-Red Supergiant IRC+10420 at au size scales

    CERN Document Server

    Oudmaijer, Rene

    2012-01-01

    IRC +10420 is one of the few known massive stars in rapid transition from the Red Supergiant phase to the Wolf-Rayet or Luminous Blue Variable phase. The star has an ionised wind and using the Br gamma hydrogen recombination emission we assess the mass-loss on spatial scales of order 1 au. We present new VLT Interferometer AMBER data which are combined with all other AMBER data in the literature. The final dataset covers a position angle range of 180 degrees and baselines up to 110 meters. The spectrally dispersed visibilities, differential phases and line flux are conjointly analyzed and modelled. We also present AMBER/FINITO observations which cover a larger wavelength range and allow us to observe the Na I doublet at 2.2 micron. The data are complemented by X-Shooter data, which provide a higher spectral resolution view. The Brackett gamma line and the Na I doublet are both spatially resolved. After correcting the AMBER data for the fact that the lines are not spectrally resolved, we find that Br gamma tra...

  17. DISCOVERY OF THE FIRST B[e] SUPERGIANTS IN M 31

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, M.; Oksala, M. E. [Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov (Czech Republic); Cidale, L. S.; Arias, M. L. [Departamento de Espectroscopía Estelar, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, B1900FWA La Plata (Argentina); Borges Fernandes, M., E-mail: kraus@sunstel.asu.cas.cz [Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro (Brazil)

    2014-01-01

    B[e] supergiants (B[e]SGs) are transitional objects in the post-main sequence evolution of massive stars. The small number of B[e]SGs known so far in the Galaxy and the Magellanic Clouds indicates that this evolutionary phase is short. Nevertheless, the strong aspherical mass loss occurring during this phase, which leads to the formation of rings or disk-like structures, and the similarity to possible progenitors of SN1987 A emphasize the importance of B[e]SGs for the dynamics of the interstellar medium as well as stellar and galactic chemical evolution. The number of objects and their mass-loss behavior at different metallicities are essential ingredients for accurate predictions from stellar and galactic evolution calculations. However, B[e]SGs are not easily identified, as they share many characteristics with luminous blue variables (LBVs) in their quiescent (hot) phase. We present medium-resolution near-infrared K-band spectra for four stars in M 31, which have been assigned a hot LBV (candidate) status. Applying diagnostics that were recently developed to distinguish B[e]SGs from hot LBVs, we classify two of the objects as bonafide LBVs; one of them currently in outburst. In addition, we firmly classify the two stars 2MASS J00441709+4119273 and 2MASS J00452257+4150346 as the first B[e]SGs in M 31 based on strong CO band emission detected in their spectra, and infrared colors typical for this class of stars.

  18. Quantitative Spectroscopy of BA-type Supergiants

    CERN Document Server

    Przybilla, N; Becker, S R; Kudritzki, R P

    2005-01-01

    Luminous BA-SGs allow topics ranging from NLTE physics and the evolution of massive stars to the chemical evolution of galaxies and cosmology to be addressed. A hybrid NLTE technique for the quantitative spectroscopy of BA-SGs is discussed. Thorough tests and first applications of the spectrum synthesis method are presented for four bright Galactic objects. Stellar parameters are derived from spectroscopic indicators. The internal accuracy of the method allows the 1sigma-uncertainties to be reduced to <1-2% in Teff and to 0.05-0.10dex in log g. Elemental abundances are determined for over 20 chemical species, with many of the astrophysically most interesting in NLTE. The NLTE computations reduce random errors and remove systematic trends in the analysis. Inappropriate LTE analyses tend to systematically underestimate iron group abundances and overestimate the light and alpha-process element abundances by up to factors of 2-3 on the mean. Contrary to common assumptions, significant NLTE abundance correction...

  19. The advanced stages of stellar evolution: impact of mass loss, rotation, and link with B[e] stars

    CERN Document Server

    Georgy, Cyril; Ekström, Sylvia; Meynet, Georges

    2016-01-01

    In this paper, we discuss some consequences of rotation and mass loss on the evolved stages of massive star evolution. The physical reasons of the time evolution of the surface velocity are explained, and then we show how the late-time evolution of massive stars are impacted in combination with the effects of mass loss. The most interesting result is that in some cases, a massive star can have a blue-red-blue evolution, opening the possibility that Blue Supergiants are composed by two distinct populations of stars: one just leaving the main sequence and crossing the HRD for the first time, and the other one evolving back to the blue side of the HRD after a Red Supergiant phase. We discuss a few possible observational tests that can allow to distinguish these two populations, and how supergiant B[e] stars fit in this context.

  20. Infrared spectroscopy of radio-luminous OH/IR stars

    Science.gov (United States)

    Jones, Terry Jay; Hyland, A. R.; Fix, John D.; Cobb, Michael L.

    1988-01-01

    Low-resolution 1.5-2.5-micron spectra for 21 radio-luminous OH/IR stars are presented. These spectra divide into two broad classes. Those with very strong water-vapor absorption closely resemble the spectra of classical Mira variables and are classified Type VM. Those with weaker water-vapor absorption, but still showing strong CO absorption, resemble the spectra of true core-burning supergiants and are classified Type SG. Comparison of the classification of 30 radio-luminous OH/IR stars with their Delta(V)s and luminosities suggests this classification is a good indicator of the intrinsic nature of the underlying star. There is some evidence, however, that some true supergiants (massive main-sequence progenitors) develop the pulsation properties and photospheric characteristics of the Mira-like OH/IR stars when they become optically obscured OH/IR stars.

  1. VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), sigma Oph, BM Sco, and HD 206859

    CERN Document Server

    Wittkowski, M; Marcaide, J M; Abellan, F J; Chiavassa, A; Guirado, J C

    2016-01-01

    We add four warmer late-type supergiants to our previous spectro-interferometric studies of red giants and supergiants. V766 Cen (=HR 5171 A) is found to be a high-luminosity log(L/L_sun)=5.8+-0.4 source of Teff 4290+-760 K and radius 1490+-540 Rsun located close to both the Hayashi and Eddington limits; this source is consistent with a 40 Msun evolutionary track without rotation and current mass 27-36 Msun. It exhibits NaI in emission arising from a shell of radius 1.5 Rphot and a photocenter displacement of about 0.1 Rphot. V766 Cen shows strong extended molecular (CO) layers and a dusty circumstellar background component. This suggest an optically thick pseudo-photosphere at about 1.5 Rphot at the onset of the wind. V766 Cen is a red supergiant located close to the Hayashi limit instead of a yellow hypergiant already evolving back toward warmer Teff as previously discussed. The stars sigma Oph, BM Sco, and HD 206859 are found to have lower luminosities of about log(L/Lsun)=3.4-3.5 and Teff of 3900-5300 K, ...

  2. Pricing Bermudan options under local Lévy models with default

    NARCIS (Netherlands)

    A. Borovykh (Anastasia); A. Pascucci; C.W. Oosterlee (Cornelis)

    2017-01-01

    textabstractWe consider a defaultable asset whose risk-neutral pricing dynamics are described by an exponential Lévy-type martingale. This class of models allows for a local volatility, local default intensity and a locally dependent Lévy measure. We present a pricing method for Bermudan options

  3. Experimental evidence for inherent Lévy search behaviour in foraging animals

    NARCIS (Netherlands)

    Kölzsch, A.; Alzate, A.; Bartumeus, F.; de Jager, M.; Weerman, E.; Hengeveld, G.M.; Naguib, M.; Nolet, B.A.; Van de Koppel, J.

    2015-01-01

    Recently, Lévy walks have been put forward as a new paradigm for animal search and many cases have been made for its presence in nature. However, it remains debated whether Lévy walks are an inherent behavioural strategy or emerge from the animal reacting to its habitat. Here, we demonstrate signatu

  4. Quantifying the Statistics of Animal Motion: Lévy Flights of the Wandering Albatross

    Science.gov (United States)

    Viswanathan, Gandhimohan M.

    1998-03-01

    vy flights are commonly observed in physical and biological systems(See, e.g., M. F. Shlesinger, G. Zaslavsky and U. Frisch, eds., Lévy flights and Related Topics in Physics) (Springer, Berlin, 1995)., raising the possibility that similar random walks may be used to describe animal motion. Here we discuss recent findings showing that the Wandering Albatross and other animals may perform Lévy flights when foraging( G. M. Viswanathan, V. Afanasyev, S. V. Buldyrev, E. J. Murphy, P. A. Prince and H. E. Stanley, ``Lévy Flight Search Patterns of Wandering Albatrosses,'' Nature) 381, 413--415 (1996). We further examine how such random walks may confer biological advantages and discuss recent findings which suggest that under certain conditions there is a universal power law exponent which characterizes Lévy flight foraging ( G. M. Viswanathan, Sergey V. Buldyrev, Shlomo Havlin, M. G. E. da Luz, E. P. Raposo and H. E. Stanley, preprint.).

  5. Resolved photometry of extragalactic young massive star clusters

    CERN Document Server

    Larsen, S S; Eldridge, J J; Langer, N; Bastian, N; Seth, A; Smith, L J; Brodie, J; Efremov, Y N

    2011-01-01

    We present colour-magnitude diagrams (CMDs) for a sample of seven young massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793. The clusters have ages in the range 5-50 million years and masses of 10^5 -10^6 Msun. Although crowding prevents us from obtaining photometry in the central regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters, along with the brighter main sequence stars. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergi...

  6. Bilateral V-Y rotation advancement flap for fingertip amputations.

    Science.gov (United States)

    Sungur, Nezih; Kankaya, Yüksel; Yıldız, Kaya; Dölen, Utku Can; Koçer, Uğur

    2012-03-01

    Fingertip amputation is the most common type of injury in the upper limb. Goals in fingertip amputation reconstruction are covering the defect, establishing maximum tactile gnosis, keeping the length of the finger, protecting the joint function, acquiring a well-padded pulp tissue, providing a bed for growing nail, obtaining a satisfactory cosmetic appearance and allowing the patient to return to work as soon as possible. Adjacent skin and soft tissue are the best covers for fingertip injuries. However, local homodigital flaps lack enough tissue to cover the defect. To solve this problem, we used V-Y rotation advancement flap bilaterally in fingertip amputations which meets all the reconstruction goals. Rotation besides advancement makes this flap more mobile and easier to cover larger defects in all amputation planes. Between 2007 and 2009, we performed bilateral V-Y rotation advancement flap on seven male patients' pulpa (average age, 37.6 years) whose fingertips were not replantable. Fourteen flaps were made on 7 fingers. There was neither total nor partial flap loss. Patients had neither cold intolerance nor scar hypersensitivity. Stiffness of the PIP joint did not occur. No obvious hooked nail occurred in patients who have remaining nail matrix. Because flaps contain neurovascular bundle, there was no difference in sensation and perfusion between the finger's pre-operative and post-operative status. The result was satisfactory with painless pinching. In addition to the various and versatile fingertip reconstruction methods, we want to present V-Y rotation advancement flap as a quick, reliable and aesthetic method.

  7. vy-Student distributions for halos in accelerator beams.

    Science.gov (United States)

    Cufaro Petroni, Nicola; De Martino, Salvatore; De Siena, Silvio; Illuminati, Fabrizio

    2005-12-01

    We describe the transverse beam distribution in particle accelerators within the controlled, stochastic dynamical scheme of stochastic mechanics (SM) which produces time reversal invariant diffusion processes. This leads to a linearized theory summarized in a Schrödinger-like (SL) equation. The space charge effects have been introduced in recent papers by coupling this S-L equation with the Maxwell equations. We analyze the space-charge effects to understand how the dynamics produces the actual beam distributions, and in particular we show how the stationary, self-consistent solutions are related to the (external and space-charge) potentials both when we suppose that the external field is harmonic (constant focusing), and when we a priori prescribe the shape of the stationary solution. We then proceed to discuss a few other ideas by introducing generalized Student distributions, namely, non-Gaussian, Lévy infinitely divisible (but not stable) distributions. We will discuss this idea from two different standpoints: (a) first by supposing that the stationary distribution of our (Wiener powered) SM model is a Student distribution; (b) by supposing that our model is based on a (non-Gaussian) Lévy process whose increments are Student distributed. We show that in the case (a) the longer tails of the power decay of the Student laws and in the case (b) the discontinuities of the Lévy-Student process can well account for the rare escape of particles from the beam core, and hence for the formation of a halo in intense beams.

  8. vy night flights by the jellyfish Periphylla periphylla

    KAUST Repository

    Ugland, KI

    2014-10-22

    Jellyfish blooms occur in marine environments around the world and have been linked to over-fishing, eutrophication and climatic change. In some coastal areas of Norway, the circumglobal Periphylla periphylla has increased to exceptionally high abundances and has replaced fish as the main planktivorous predator despite the ineffectiveness of its non-visual predation compared to visual fish predation. Using data from a bottom-mounted acoustic platform, we collected 12341 in situ measurements of individual vertical movements of large individuals of P. periphylla. These jellyfish are characterized by a stepwise vertical movement. The distribution of their vertical swimming distances was extremely left skewed; about 85% of the swimming distances were less than 3 m, and a few displacements were extremely long with a maximum of 85 m. Chi-square tests of goodness of fit to the tail and Akaike’s information criterion gave overwhelming evidence of the truncated power law. There was a clear diel pattern in the exponent with values significantly larger than 3 during the daytime and significantly lower than 3 at night. This pattern means that P. periphylla switches from relatively limited movements during the day to Lévy-like flights during the night. Since the abundance of zooplankton is large in the P. periphylla fjord, Brownian motion, rather than Lévy flight, is predicted by the optimal foraging hypothesis. It is therefore possible that the Lévy-like search pattern has evolved in the food-scarce oceanic environment, which is the main natural habitat of P. periphylla. Alternatively, the large individuals of the population addressed here may forage on scarcer prey sources than the main prevailing zooplankton in Lurefjorden.

  9. Outflowing disk winds in B[e] Supergiants

    CERN Document Server

    Cur'e, M; Cidale, L; Cur\\'{e}, Michel; Rial, Diego F.; Cidale, Lydia

    2005-01-01

    The effects of rapid rotation and bi--stability upon the density contrast between the equatorial and polar directions of a B[e] supergiant are investigated. Based on a new slow solution for different high rotational radiation--driven winds and the fact that bi--stability allows a change in the line--force parameters ($\\alpha$, $k$, and $\\delta$), the equatorial densities are about $10^2$--$10^3$ times higher than the polar ones. These values are in qualitative agreement with the observations. This calculation also permits to obtain the aperture angle of the disk.

  10. Rimo Tumino "Vyšnių sodas" : gyvenimo komedija

    OpenAIRE

    Balevičiūtė, Ramunė

    2010-01-01

    Straipsnyje aptariamos Antono Čechovo absurdo dramaturgijos interpretavimo tendencijos. Analizuojama, kaip režisierius Rimas Tuminas spektaklyje „Vyšnių sodas“ (1990), jungdamas psichologinio ir žaidybinio teatro strategijas, konkretizavo kai kuriuos Čechovo pasaulėjautos ir kūrybos bruožus, siejusius jį su absurdo teatru. [autoriaus tekstas] The article analyses the absurdist tendencies of the interpretation of Anton Chekhov’ plays and is based on the production of Rimas Tuminas’ “Cherry ...

  11. The VLT-FLAMES Tarantula Survey XXV. Surface nitrogen abundances of O-type giants and supergiants

    CERN Document Server

    Grin, N J; de Koter, A; Sana, H; Puls, J; Brott, I; Crowther, P A; Dufton, P L; Evans, C J; Graefener, G; Herrero, A; Langer, N; Lennon, D J; van Loon, J Th; Markova, N; de Mink, S E; Najarro, F; Schneider, F R N; Taylor, W D; Tramper, F; Vink, J S; Walborn, W R

    2016-01-01

    Theoretically, rotation-induced chemical mixing in massive stars has far reaching evolutionary consequences, affecting the sequence of morphological phases, lifetimes, nucleosynthesis, and supernova characteristics. Using a sample of 72 presumably single O-type giants to supergiants observed in the context of the VLT-FLAMES Tarantula Survey (VFTS), we aim to investigate rotational mixing in evolved core-hydrogen burning stars initially more massive than $15\\,M_\\odot$ by analysing their surface nitrogen abundances. Using stellar and wind properties derived in a previous VFTS study, we constrained the nitrogen abundance by fitting the equivalent widths of relatively strong lines that are sensitive to changes in the abundance of this element. Given the quality of the data, we constrained the nitrogen abundance in 38 cases; for 34 stars only upper limits could be derived, which includes almost all stars rotating at $v_\\mathrm{e}\\sin i >200\\,\\mathrm{km s^{-1}}$. We analysed the nitrogen abundance as a function of ...

  12. 2D radiaition-hydrodynamic simulations of supernova shock breakout in bipolar explosions of a blue supergiant progenitor

    CERN Document Server

    Suzuki, Akihiro; Shigeyama, Toshikazu

    2016-01-01

    A two-dimensional special relativistic radiation-hydrodynamics code is developed and applied to numerical simulations of supernova shock breakout in bipolar explosions of a blue supergiant. Our calculations successfully simulate the dynamical evolution of a blast wave in the star and its emergence from the surface. Results of the model with spherical energy deposition show a good agreement with previous simulations. Furthermore, we calculate several models with bipolar energy deposition and compare their results with the spherically symmetric model. The bolometric light curves of the shock breakout emission are calculated by a ray-tracing method. Our radiation-hydrodynamic models indicate that the early part of the shock breakout emission can be used to probe the geometry of the blast wave produced as a result of the gravitational collapse of the iron core.

  13. Olivier Chesneau's work on massive stars

    CERN Document Server

    Millour, Florentin

    2016-01-01

    Olivier Chesneau challenged several fields of observational stellar astrophysics with bright ideas and an impressive amount of work to make them real in the span of his career, from his first paper on P Cygni in 2000, up to his last one on V838 Mon in 2014. He was using all the so-called high-angular resolution techniques since it helped his science to be made, namely study in details the inner structure of the environments around stars, be it small mass (AGBs), more massive (supergiant stars), or explosives (Novae). I will focus here on his work on massive stars.

  14. Chemical Composition of RM_1-390 - Large Magellanic Cloud Red Supergiant

    Directory of Open Access Journals (Sweden)

    Alexander V. Yushchenko

    2017-09-01

    Full Text Available A high resolution spectroscopic observation of the red supergiant star RM_1-390 in the Large Magellanic Cloud was made from a 3.6 m telescope at the European Southern Observatory. Spectral resolving power was R=20,000, with a signal-to-noise ratio S/N > 100. We found the atmospheric parameters of RM_1-390 to be as follows: the effective temperature Teff = 4,250 ± 50 K, the surface gravity log g = 0.16 ± 0.1, the microturbulent velocity vmicro = 2.5 km/s, the macroturbulence velocity vmacro = 9 km/s and the iron abundance [Fe/H] = -0.73 ± 0.11. The abundances of 18 chemical elements from silicon to thorium in the atmosphere of RM_1-390 were found using the spectrum synthesis method. The relative deficiencies of all elements are close to that of iron. The fit of abundance pattern by the solar system distribution of r- and s-element isotopes shows the importance of the s-process. The plot of relative abundances as a function of second ionization potentials of corresponding chemical elements allows us to find a possibility of convective energy transport in the photosphere of RM_1-390.

  15. SN 2004A: Another Type II-P Supernova with a Red Supergiant Progenitor

    CERN Document Server

    Hendry, M A; Cenko, S B; Crockett, R M; Fox, D W; Gal-Yam, A; Kudritzki, R P; Maund, J R; Moon, D S; Smartt, S J

    2006-01-01

    We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion HST images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em and estimate an explosion epoch of 2004 January 6. We also calculate three new distances to NGC 6207 of 21.0 +/-4.3, 21.4 +/-3.5 and 25.1 +/-1.7Mpc. The former was calculated using the Standard Candle Method (SCM) for SNe II-P, and the latter two from the Brightest Supergiants Method (BSM). We combine these three distances with existing kinematic distances, to derive a mean value of 20.3 +/-3.4Mpc. Using this distance we estimate that the ejected nickel mass in the explosion is 0.046(+0.031,-0.017) Msolar. The progenitor of SN 2004A is identified in pre-explosion WFPC2 F814W images with a magnitude of mF814W = 24.3 +/-0.3, but is below the detection limit of the F606W images. We show th...

  16. The eclipsing, double-lined, Of supergiant binary Cygnus OB2-B17

    Science.gov (United States)

    Stroud, V. E.; Clark, J. S.; Negueruela, I.; Roche, P.; Norton, A. J.; Vilardell, F.

    2010-02-01

    Context. Massive, eclipsing, double-lined, spectroscopic binaries are not common but are necessary to understand the evolution of massive stars as they are the only direct way to determine stellar masses. They are also the progenitors of energetic phenomena such as X-ray binaries and γ-ray bursts. Aims: We present a photometric and spectroscopic analysis of the candidate binary system Cyg OB2-B17 to show that it is indeed a massive evolved binary. Methods: We utilise V band and white-light photometry to obtain a light curve and period of the system, and spectra at different resolutions to calculate preliminary orbital parameters and spectral classes for the components. Results: Our results suggest that B17 is an eclipsing, double-lined, spectroscopic binary with a period of 4.0217±0.0004 days, with two massive evolved components with preliminary classifications of O7 and O9 supergiants. The radial velocity and light curves are consistent with a massive binary containing components with similar luminosities, and in turn with the preliminary spectral types and age of the association.

  17. The eclipsing, double-lined, Of supergiant binary Cyg OB2-B17

    CERN Document Server

    Stroud, V E; Negueruela, I; Roche, P; Norton, A J; Vilardell, F

    2010-01-01

    Massive, eclipsing, double-lined, spectroscopic binaries are not common but are necessary to understand the evolution of massive stars as they are the only direct way to determine stellar masses. They are also the progenitors of energetic phenomena such as X-ray binaries and gamma-ray bursts. We present a photometric and spectroscopic analysis of the candidate binary system Cyg OB2-B17 to show that it is indeed a massive evolved binary. We utilise V band and white-light photometry to obtain a light curve and period of the system, and spectra at different resolutions to calculate preliminary orbital parameters and spectral classes for the components. Our results suggest that B17 is an eclipsing, double-lined, spectroscopic binary with a period of 4.0217+/-0.0004 days, with two massive evolved components with preliminary classifications of O7 and O9 supergiants. The radial velocity and light curves are consistent with a massive binary containing components with similar luminosities, and in turn with the prelimi...

  18. Quantitative Spectroscopic J-band Study of Red Supergiants in Perseus OB-1

    CERN Document Server

    Gazak, J Zachary; Kudritzki, Rolf; Bergemann, Maria; Plez, Bertrand

    2014-01-01

    We demonstrate how the metallicities of red supergiant (RSG) stars can be measured from quantitative spectroscopy down to resolutions of ~3000 in the J-band. We have obtained high resolution spectra on a sample of the RSG population of h and chi Persei, a double cluster in the solar neighborhood. We show that careful application of the MARCS model atmospheres returns measurements of Z consistent with solar metallicity. Using two grids of synthetic spectra--one in pure LTE and one with NLTE calculations for the most important diagnostic lines--we measure Z = +0.04 +/- 0.10 (LTE) and Z = -0.04 +/- 0.08 (NLTE) for the sample of eleven RSGs in the cluster. We degrade the spectral resolution of our observations and find that those values remain consistent down to resolutions of less than R of 3000. Using measurements of effective temperatures we compare our results with stellar evolution theory and find good agreement. We construct a synthetic cluster spectrum and find that analyzing this composite spectrum with s...

  19. THE ULTRA-LONG GAMMA-RAY BURST 111209A: THE COLLAPSE OF A BLUE SUPERGIANT?

    Energy Technology Data Exchange (ETDEWEB)

    Gendre, B.; Cutini, S.; D' Elia, V. [ASI Science Data Center, via Galileo Galilei, I-00044 Frascati (Italy); Stratta, G. [Osservatorio Astronomico di Roma, OAR-INAF, via Frascati 33, I-00040, Monte Porzio Catone (Italy); Atteia, J. L.; Klotz, A. [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France); Basa, S. [Aix Marseille Universite, CNRS, LAM (Laboratoire d' Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France); Boeer, M. [CNRS, ARTEMIS, UMR 7250, Boulevard de l' Observatoire, BP 4229, F-06304 Nice Cedex 4 (France); Coward, D. M.; Howell, E. J [University of Western Australia, School of Physics, University of Western Australia, Crawley WA 6009 (Australia); Piro, L., E-mail: bruce.gendre@gmail.com [Istituto di Astrofisica e Planetologia Spaziali di Roma, INAF, via fosso del cavaliere 100, I-00133 Roma (Italy)

    2013-03-20

    We present optical, X-ray and gamma-ray observations of GRB 111209A, observed at a redshift of z = 0.677. We show that this event was active in its prompt phase for about 25000 s, making it the longest burst ever observed. This rare event could have been detected up to z {approx} 1.4 in gamma-rays. Compared to other long gamma-ray bursts (GRBs), GRB 111209A is a clear outlier in the energy-fluence and duration plane. The high-energy prompt emission shows no sign of a strong blackbody component, the signature of a tidal disruption event, or a supernova shock breakout. Given the extreme longevity of this event, and lack of any significant observed supernova signature, we propose that GRB 111209A resulted from the core-collapse of a low-metallicity blue supergiant star. This scenario is favored because of the necessity to supply enough mass to the central engine over a duration of thousands of seconds. Hence, we suggest that GRB 111209A could have more in common with population III stellar explosions, rather than those associated with normal long GRBs.

  20. A Transient Supergiant X-ray Binary in IC10. An Extragalactic SFXT?

    CERN Document Server

    Laycock, Silas; Oram, Kathleen; Balchunas, Andrew

    2014-01-01

    We report the discovery of a large amplitude (factor of $\\sim$100) X-ray transient (IC 10 X-2, CXOU J002020.99+591758.6) in the nearby dwarf starburst galaxy IC10 during our Chandra monitoring project. Based on the X-ray timing and spectral properties, and an optical counterpart observed with Gemini, the system is a high mass X-ray binary (HMXB) consisting of a luminous blue supergiant and a neutron star (NS). The highest measured luminosity of the source was 1.8$\\times$10$^{37}$ erg s$^{-1}$ during an outburst in 2003. Observations before, during and after a second outburst in 2010 constrain the outburst duration to be less than 3 months (with no lower limit). The X-ray spectrum is a hard powerlaw ($\\Gamma$=0.3) with fitted column density ($N_H$=6.3$\\times$10$^{21}$ atom cm$^{-2}$) consistent with the established absorption to sources in IC10. The optical spectrum shows hydrogen Balmer lines strongly in emission, at the correct blueshift (-340 km/s) for IC10. The NIII triplet emission feature is seen, accomp...

  1. Photometric and Spectroscopic Study of the Supergiant with an Infrared Excess V1027 Cygni

    CERN Document Server

    Arkhipova, V P; Ikonnikova, N P; Esipov, V F; Komissarova, G V; Shenavrin, V I; Burlak, M A

    2016-01-01

    We present the results of our $UBV$ and $JHKLM$-photometry for the semiregular pulsating variable V1027~Cyg, a supergiant with an infrared excess, over the period from 1991 to 2015. Our search for a periodicity in the $UBV$ brightness variations has led to several periods from $P=212^{d}$ to $P=320^{d}$ in different time intervals. We have found the period $P=237^{d}$ based on our infrared photometry. The variability amplitude, the light-curve shape, and the magnitude of V1027~Cyg at maximum light change noticeably from cycle to cycle. An ambiguous correlation of the $B-V$ and $U-B$ colors with the brightness has been revealed. The spectral energy distribution for V1027~Cyg from our photometry in the range 0.36 ($U$)-5.0 ($M$) $\\mu$m corresponds to spectral types from G8I to K3I at different phases of the pulsation cycle. Low-resolution spectra of V1027 Cyg in the range $\\lambda$4400--9200 \\AA\\ were taken during 16 nights over the period 1995--2015. At the 1995 and 2011 photometric minima the star's spectrum ...

  2. Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

    CERN Document Server

    Kraus, M; Arias, M L; Maravelias, G; Nickeler, D H; Torres, A F; Fernandes, M Borges; Aret, A; Cure, M; Vallverdu, R; Barba, R H

    2016-01-01

    We aim to improve our knowledge on the structure and dynamics of the circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution optical and near-IR spectroscopic data were obtained over a period of 16 and 7 years, respectively. The spectra cover the diagnostic emission lines from [CaII] and [OI], as well as the CO bands. These features trace the disk at different distances from the star. We analyzed the kinematics of the individual emission regions by modeling their emission profiles. A low-resolution mid-infrared spectrum was obtained as well, which provides information on the composition of the dusty disk. All diagnostic emission features display double-peaked line profiles, which we interpret as due to Keplerian rotation. We find that LHA 120-S 73 is surrounded by at least four individual rings of material with alternating densities (or by a disk with strongly non-monotonic radial density distribution). Moreover, we find that the molecular ring must have gaps or at least strong density inh...

  3. Level Statistics and Localization Transitions of Lévy Matrices.

    Science.gov (United States)

    Tarquini, E; Biroli, G; Tarzia, M

    2016-01-08

    This work provides a thorough study of Lévy, or heavy-tailed, random matrices (LMs). By analyzing the self-consistent equation on the probability distribution of the diagonal elements of the resolvent we establish the equation determining the localization transition and obtain the phase diagram. Using arguments based on supersymmetric field theory and Dyson Brownian motion we show that the eigenvalue statistics is the same one as of the Gaussian orthogonal ensemble in the whole delocalized phase and is Poisson-like in the localized phase. Our numerics confirm these findings, valid in the limit of infinitely large LMs, but also reveal that the characteristic scale governing finite size effects diverges much faster than a power law approaching the transition and is already very large far from it. This leads to a very wide crossover region in which the system looks as if it were in a mixed phase. Our results, together with the ones obtained previously, now provide a complete theory of Lévy matrices.

  4. Level Statistics and Localization Transitions of Lévy Matrices

    Science.gov (United States)

    Tarquini, E.; Biroli, G.; Tarzia, M.

    2016-01-01

    This work provides a thorough study of Lévy, or heavy-tailed, random matrices (LMs). By analyzing the self-consistent equation on the probability distribution of the diagonal elements of the resolvent we establish the equation determining the localization transition and obtain the phase diagram. Using arguments based on supersymmetric field theory and Dyson Brownian motion we show that the eigenvalue statistics is the same one as of the Gaussian orthogonal ensemble in the whole delocalized phase and is Poisson-like in the localized phase. Our numerics confirm these findings, valid in the limit of infinitely large LMs, but also reveal that the characteristic scale governing finite size effects diverges much faster than a power law approaching the transition and is already very large far from it. This leads to a very wide crossover region in which the system looks as if it were in a mixed phase. Our results, together with the ones obtained previously, now provide a complete theory of Lévy matrices.

  5. Stable Lévy motion with inverse Gaussian subordinator

    Science.gov (United States)

    Kumar, A.; Wyłomańska, A.; Gajda, J.

    2017-09-01

    In this paper we study the stable Lévy motion subordinated by the so-called inverse Gaussian process. This process extends the well known normal inverse Gaussian (NIG) process introduced by Barndorff-Nielsen, which arises by subordinating ordinary Brownian motion (with drift) with inverse Gaussian process. The NIG process found many interesting applications, especially in financial data description. We discuss here the main features of the introduced subordinated process, such as distributional properties, existence of fractional order moments and asymptotic tail behavior. We show the connection of the process with continuous time random walk. Further, the governing fractional partial differential equations for the probability density function is also obtained. Moreover, we discuss the asymptotic distribution of sample mean square displacement, the main tool in detection of anomalous diffusion phenomena (Metzler et al., 2014). In order to apply the stable Lévy motion time-changed by inverse Gaussian subordinator we propose a step-by-step procedure of parameters estimation. At the end, we show how the examined process can be useful to model financial time series.

  6. Nucleosynthesis and Evolution of Massive Metal-Free Stars

    CERN Document Server

    Heger, Alexander

    2008-01-01

    The evolution and explosion of metal-free stars with masses 10--100 solar masses are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. When the supernova yields are integrated over a Salpeter initial mass function, the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 <= Z <= 13. Neglecting the contribution of the neutrino wind from the neutron stars that they make, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] ~< -3. Most of the stars end their lives as blue supergiants and make supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen by dredge up and become red supergiants. A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and initial mass function in the large model ...

  7. Pair Instability Supernovae of Very Massive Population III Stars

    CERN Document Server

    Chen, Ke-Jung; Woosley, Stan; Almgren, Ann; Whalen, Daniel

    2014-01-01

    Numerical studies of primordial star formation suggest that the first stars in the universe may have been very massive. Stellar models indicate that non-rotating Population III stars with initial masses of 140-260 Msun die as highly energetic pair-instability supernovae. We present new two-dimensional simulations of primordial pair-instability supernovae done with the CASTRO code. Our simulations begin at earlier times than previous multidimensional models, at the onset of core collapse, to capture any dynamical instabilities that may be seeded by collapse and explosive burning. Such instabilities could enhance explosive yields by mixing hot ash with fuel, thereby accelerating nuclear burning, and affect the spectra of the supernova by dredging up heavy elements from greater depths in the star at early times. Our grid of models includes both blue supergiants and red supergiants over the range in progenitor mass expected for these events. We find that fluid instabilities driven by oxygen and helium burning ari...

  8. Water in stars: expected and unexpected

    Science.gov (United States)

    Tsuji, T.; Aoki, W.; Ohnaka, K.

    1999-03-01

    We have confirmed the presence of water in the early M giant α Cet (M1.5III) and supergiant KK Per (M2Iab) by the highest resolution grating mode of SWS, but this result is quite unexpected from present model atmospheres. In late M giant and supergiant stars, water observed originates partly in the photosphere as expected by the model atmospheres, but ISO SWS has revealed that the 2.7 mic\\ absorption bands appear to be somewhat stronger than predicted while 6.5 mic\\ bands weaker, indicating the contamination by an emission component. In the mid-infrared region extending to 45 mic, pure rotation lines of hho\\ appear as distinct emission on the high resolution SWS spectra of 30g Her (M7III) and S Per (M4-7Ia), along with the dust emission at 10, 13, 20 mic\\ and a new unidentified feature at 30 mic. Thus, together with the dust, water contributes to the thermal balance of the outer atmosphere already in the mid-infrared. The excitation temperature of hho\\ gas is estimated to be 500 - 1000 K. In view of this result for late M (super)giants, unexpected water observed in early M (super)giants should also be of non-photospheric in origin. Thus, ISO has finally established the presence of a new component of the outer atmosphere - a warm molecular envelope - in red giant and supergiant stars from early to late types. Such a rather warm molecular envelope will be a site of various activities such as chemical reactions, dust formation, mass-outflow etc.

  9. vy noise improves the electrical activity in a neuron under electromagnetic radiation.

    Science.gov (United States)

    Wu, Juan; Xu, Yong; Ma, Jun

    2017-01-01

    As the fluctuations of the internal bioelectricity of nervous system is various and complex, the external electromagnetic radiation induced by magnet flux on membrane can be described by the non-Gaussian type distribution of Lévy noise. Thus, the electrical activities in an improved Hindmarsh-Rose model excited by the external electromagnetic radiation of Lévy noise are investigated and some interesting modes of the electrical activities are exhibited. The external electromagnetic radiation of Lévy noise leads to the mode transition of the electrical activities and spatial phase, such as from the rest state to the firing state, from the spiking state to the spiking state with more spikes, and from the spiking state to the bursting state. Then the time points of the firing state versus Lévy noise intensity are depicted. The increasing of Lévy noise intensity heightens the neuron firing. Also the stationary probability distribution functions of the membrane potential of the neuron induced by the external electromagnetic radiation of Lévy noise with different intensity, stability index and skewness papremeters are analyzed. Moreover, through the positive largest Lyapunov exponent, the parameter regions of chaotic electrical mode of the neuron induced by the external electromagnetic radiation of Lévy noise distribution are detected.

  10. Search for aluminium monoxide in the winds of oxygen-rich AGB stars

    Science.gov (United States)

    De Beck, E.; Decin, L.; Ramstedt, S.; Olofsson, H.; Menten, K. M.; Patel, N. A.; Vlemmings, W. H. T.

    2017-01-01

    Context. Aluminium monoxide (AlO) is likely efficiently depleted from the gas around oxygen-rich evolved stars to form alumina (Al2O3) clusters and dust seeds. The presence of AlO gas in the extended atmospheres of evolved stars has been derived from optical spectroscopy. More recently, AlO gas was also detected at long wavelengths around the supergiant VY CMa and the oxygen-rich asymptotic giant branch star o Cet (Mira A). The central role aluminium might play in dust formation and wind driving, in combination with these first detections of AlO at long wavelengths, shows the need for a wider search for this molecule in the winds of evolved stars. Aims: The detection at long wavelengths of emission in rotational transitions of AlO towards asymptotic giant branch stars can help constrain the presence and location of AlO gas in the outflows and ultimately also the efficiency of the depletion process. Methods: In search of AlO, we mined data obtained with APEX, the IRAM 30 m telescope, Herschel/HIFI, SMA, and ALMA, which were primarily aimed at studying other species around asymptotic giant branch stars. We report here on observations of AlO towards a sample of eight oxygen-rich asymptotic giant branch stars in different rotational transitions, up to seven for some stars. Results: We present definite detections of one rotational transition of AlO for o Cet and R Aqr, and tentative detections of one transition for R Dor and o Cet and two transitions for IK Tau and W Hya. The presented spectra of WX Psc, R Cas, and TX Cam show no signature of AlO. For o Cet, R Aqr, and IK Tau, we find that the AlO (N = 9-8) emission likely traces the inner parts of the wind, out to only a few tens of AU, where the gas has not yet been accelerated to its terminal velocity. This is in agreement with recently published results from a detailed study on o Cet. Conclusions: The conclusive detections of AlO emission in the case of o Cet and R Aqr confirm the presence of AlO in the gas phase in

  11. Revisiting Lévy flight search patterns of wandering albatrosses, bumblebees and deer

    Science.gov (United States)

    Edwards, Andrew M.; Phillips, Richard A.; Watkins, Nicholas W.; Freeman, Mervyn P.; Murphy, Eugene J.; Afanasyev, Vsevolod; Buldyrev, Sergey V.; da Luz, M. G. E.; Raposo, E. P.; Stanley, H. Eugene; Viswanathan, Gandhimohan M.

    2007-10-01

    The study of animal foraging behaviour is of practical ecological importance, and exemplifies the wider scientific problem of optimizing search strategies. Lévy flights are random walks, the step lengths of which come from probability distributions with heavy power-law tails, such that clusters of short steps are connected by rare long steps. Lévy flights display fractal properties, have no typical scale, and occur in physical and chemical systems. An attempt to demonstrate their existence in a natural biological system presented evidence that wandering albatrosses perform Lévy flights when searching for prey on the ocean surface. This well known finding was followed by similar inferences about the search strategies of deer and bumblebees. These pioneering studies have triggered much theoretical work in physics (for example, refs 11, 12), as well as empirical ecological analyses regarding reindeer, microzooplankton, grey seals, spider monkeys and fishing boats. Here we analyse a new, high-resolution data set of wandering albatross flights, and find no evidence for Lévy flight behaviour. Instead we find that flight times are gamma distributed, with an exponential decay for the longest flights. We re-analyse the original albatross data using additional information, and conclude that the extremely long flights, essential for demonstrating Lévy flight behaviour, were spurious. Furthermore, we propose a widely applicable method to test for power-law distributions using likelihood and Akaike weights. We apply this to the four original deer and bumblebee data sets, finding that none exhibits evidence of Lévy flights, and that the original graphical approach is insufficient. Such a graphical approach has been adopted to conclude Lévy flight movement for other organisms, and to propose Lévy flight analysis as a potential real-time ecosystem monitoring tool. Our results question the strength of the empirical evidence for biological Lévy flights.

  12. UV, optical and near-IR diagnostics of massive stars

    CERN Document Server

    Martins, F

    2010-01-01

    We present an overview of a few spectroscopic diagnostics of massive stars. We explore the following wavelength ranges: UV (1000 to 2000 A), optical (4000--7000 A) and near-infrared (mainly H and K bands). The diagnostics we highlight are available in O and Wolf-Rayet stars as well as in B supergiants. We focus on the following parameters: effective temperature, gravity, surface abundances, luminosity, mass loss rate, terminal velocity, wind clumping, rotation/macroturbulence and surface magnetic field.

  13. On critical cases in limit theory for stationary increments Lévy driven moving averages

    DEFF Research Database (Denmark)

    Basse-O'Connor, Andreas; Podolskij, Mark

    averages. The limit theory heavily depends on the interplay between the given order of the increments, the considered power, the Blumenthal-Getoor index of the driving pure jump Lévy process L and the behavior of the kernel function g at 0. In this work we will study the critical cases, which were......In this paper we present some limit theorems for power variation of stationary increments Lévy driven moving averages in the setting of critical regimes. In [5] the authors derived first and second order asymptotic results for k-th order increments of stationary increments Lévy driven moving...

  14. Excursion sets of infinitely divisible random fields with convolution equivalent Lévy measure

    DEFF Research Database (Denmark)

    Rønn-Nielsen, Anders; Jensen, Eva B. Vedel

    We consider a continuous, infinitely divisible random field in R d , d = 1, 2, 3, given as an integral of a kernel function with respect to a Lévy basis with convolution equivalent Lévy measure. For a large class of such random fields we compute the asymptotic probability that the excursion set a...... at level x contains some rotation of an object with fixed radius as x → ∞. Our main result is that the asymptotic probability is equivalent to the right tail of the underlying Lévy measure...

  15. Repair of minor true hare lip using V-Y plasty: How i do it

    Directory of Open Access Journals (Sweden)

    Abdelrahman EM Ezzat

    2015-01-01

    Full Text Available Background: Minor true hare lip is rare central midline deficiency of the upper lip. There are multiple techniques but little consensus on the preferred surgical technique. Materials And Methods: A transoral approach for repair using mucosal V-Y plasty is described by employing a vertical inverted V incision. Result: The contour of the free labial border immediately improves with avoidance of skin scar. Conclusions: The midline cleft lip notch or minor true (hare lip midline clefts can be effectively treated by mucosal lengthening using a V-Y plasty. Moreover, the ability to augment the tubercle with mucosa through a VY plasty is simple and easy.

  16. Polarimetry and the Envelopes of Magellanic B[e] Supergiants

    CERN Document Server

    Magalhães, A M; Melgarejo, R; Pereyra, A

    2006-01-01

    We discuss the nature of the circumstellar envelopes around the B[e] supergiants (B[e]SG) in the Magellanic Clouds (MC). Contrary to those in the Galaxy, the MC B[e]SG have a well defined luminosity and can be considered members of a well defined class. We discuss spectroscopy and optical broadband polarimetry and spectropolarimetry data. These data show for the first time detailed changes in the polarization across several spectral features. We show that the envelopes of the B[e]SG are generally variable. Broadband polarimetry data show that the envelopes are definitely non-spherically symmetric and large non-axisymmetric ejections may occur. In addition to that, spectropolarimetry is coming of age as a tool to study the B[e]SG envelope structure.

  17. A numerical investigation of wind accretion in persistent Supergiant X-ray Binaries I - Structure of the flow at the orbital scale

    CERN Document Server

    Mellah, I El

    2016-01-01

    Classical Supergiant X-ray Binaries host a neutron star orbiting a supergiant OB star and display persistent X-ray luminosities of 10$^{35}$ to 10$^{37}$ erg/s. The stellar wind from the massive companion is believed to be the main source of matter accreted by the compact object. With this first paper, we introduce a ballistic model to characterize the structure of the wind at the orbital scale as it accelerates, from the stellar surface to the vicinity of the accretor. Thanks to the parametrization we retained and the numerical pipeline we designed, we can investigate the supersonic flow and the subsequent observables as a function of a reduced set of characteristic numbers and scales. We show that the shape of the permanent flow is entirely determined by the mass ratio, the filling factor, the Eddington factor and the $\\alpha$-force multiplier which drives the stellar wind acceleration. Provided scales such as the orbital period are known, we can trace back the observables to evaluate the mass accretion rat...

  18. On Comparison Theorem and Solutions of BSDEs for Lévy Processes

    Institute of Scientific and Technical Information of China (English)

    Qing Zhou

    2007-01-01

    In this paper, we consider backward stochastic differential equations driven by a Lévy process. A comparison theorem and an existence and uniqueness theorem of BSDEs with non-Lipschitz coefficients are obtained.

  19. Escape of an inertial Lévy flight particle from a truncated quartic potential well

    Science.gov (United States)

    Bai, Zhan-Wu; Hu, Meng

    2017-08-01

    Motivated by that the quartic potential can confined Lévy flights, we investigate the escape rate of an inertial Lévy particle from a truncated quartic potential well via Langevin simulation. The escape rate still depends on the noise intensity in a power-law form in low noise intensity, but the exponent and the inverse coefficient vary significantly for different Lévy indexes compared with previous works. Trimodal structure of the probability density function was found in simulations. The probability density function in a quasi-stable state exhibits transition among unimodal, bimodal, and trimodal structures. A metastable state by stable state approach is developed to calculate the escape rate analytically, which may be applied to extensive escape problems. The theoretical approach is confirmed by Langevin simulation for the Cauchy case of Lévy flight in the applied potential.

  20. Finite difference methods for option pricing under Lévy processes: Wiener-Hopf factorization approach

    National Research Council Canada - National Science Library

    Kudryavtsev, Oleg

    2013-01-01

    In the paper, we consider the problem of pricing options in wide classes of Lévy processes. We propose a general approach to the numerical methods based on a finite difference approximation for the generalized Black-Scholes equation...

  1. Some path properties of generalized Lévy sheet

    Institute of Scientific and Technical Information of China (English)

    ZHANG Rongmao; LIN Zhengyan

    2006-01-01

    Let X(t) be an N parameter generalized Lévy sheet taking values in Rd with a lower index α,sR = {(s,t] = ∏iN=1(si,ti],si < ti},E(x,Q) = {t ∈ Q: X(t) = x},Q ∈ sR be the level set of X at x and X(Q) = {x: (E)t ∈ Q such that X(t) = x} be the image of X on Q.In this paper,the problems of the existence and increment size of the local times for X(t) are studied.In addition,the Hausdorff dimension of E(x,Q) and the upper bound of a uniform dimension for X(Q) are also established.

  2. Numerical Methods for the Lévy LIBOR Model

    DEFF Research Database (Denmark)

    Papapantoleon, Antonis; Skovmand, David

    are generally slow. We propose an alternative approximation scheme based on Picard iterations. Our approach is similar in accuracy to the full numerical solution, but with the feature that each rate is, unlike the standard method, evolved independently of the other rates in the term structure. This enables......The aim of this work is to provide fast and accurate approximation schemes for the Monte-Carlo pricing of derivatives in the Lévy LIBOR model of Eberlein and Özkan (2005). Standard methods can be applied to solve the stochastic differential equations of the successive LIBOR rates but the methods...... simultaneous calculation of derivative prices of different maturities using parallel computing. We include numerical illustrations of the accuracy and speed of our method pricing caplets....

  3. vy Flights due to Anisotropic Disorder in Graphene

    Science.gov (United States)

    Gattenlöhner, S.; Gornyi, I. V.; Ostrovsky, P. M.; Trauzettel, B.; Mirlin, A. D.; Titov, M.

    2016-07-01

    We study transport properties of graphene with anisotropically distributed on-site impurities (adatoms) that are randomly placed on every third line drawn along carbon bonds. We show that stripe states characterized by strongly suppressed backscattering are formed in this model in the direction of the lines. The system reveals Lévy-flight transport in the stripe direction such that the corresponding conductivity increases as the square root of the system length. Thus, adding this type of disorder to clean graphene near the Dirac point strongly enhances the conductivity, which is in stark contrast with a fully random distribution of on-site impurities, which leads to Anderson localization. The effect is demonstrated both by numerical simulations using the Kwant code and by an analytical theory based on the self-consistent T -matrix approximation.

  4. Numerical Methods for the Lévy LIBOR model

    DEFF Research Database (Denmark)

    Papapantoleon, Antonis; Skovmand, David

    The aim of this work is to provide fast and accurate approximation schemes for the Monte-Carlo pricing of derivatives in the Lévy LIBOR model of Eberlein and Özkan (2005). Standard methods can be applied to solve the stochastic differential equations of the successive LIBOR rates but the methods ...... reduce this growth from exponential to quadratic in an approximation using truncated expansions of the product terms. We include numerical illustrations of the accuracy and speed of our method pricing caplets, swaptions and forward rate agreements........ This enables simultaneous calculation of derivative prices of different maturities using parallel computing. Secondly, the product terms occuring in the drift of a LIBOR Market model driven by a jump process grow exponentially as a function of the number of rates, quickly rendering the model intractable. We...

  5. The VLT-FLAMES Tarantula Survey. XXV. Surface nitrogen abundances of O-type giants and supergiants

    Science.gov (United States)

    Grin, N. J.; Ramírez-Agudelo, O. H.; de Koter, A.; Sana, H.; Puls, J.; Brott, I.; Crowther, P. A.; Dufton, P. L.; Evans, C. J.; Gräfener, G.; Herrero, A.; Langer, N.; Lennon, D. J.; van Loon, J. Th.; Markova, N.; de Mink, S. E.; Najarro, F.; Schneider, F. R. N.; Taylor, W. D.; Tramper, F.; Vink, J. S.; Walborn, N. R.

    2017-04-01

    Context. Theoretically, rotation-induced chemical mixing in massive stars has far reaching evolutionary consequences, affecting the sequence of morphological phases, lifetimes, nucleosynthesis, and supernova characteristics. Aims: Using a sample of 72 presumably single O-type giants to supergiants observed in the context of the VLT-FLAMES Tarantula Survey (VFTS), we aim to investigate rotational mixing in evolved core-hydrogen burning stars initially more massive than 15 M⊙ by analysing their surface nitrogen abundances. Methods: Using stellar and wind properties derived in a previous VFTS study we computed synthetic spectra for a set of up to 21 N ii-v lines in the optical spectral range, using the non-LTE atmosphere code FASTWIND. We constrained the nitrogen abundance by fitting the equivalent widths of relatively strong lines that are sensitive to changes in the abundance of this element. Given the quality of the data, we constrained the nitrogen abundance in 38 cases; for 34 stars only upper limits could be derived, which includes almost all stars rotating at νesini> 200 km s-1. Results: We analysed the nitrogen abundance as a function of projected rotation rate νesini and confronted it with predictions of rotational mixing. We found a group of N-enhanced slowly-spinning stars that is not in accordance with predictions of rotational mixing in single stars. Among O-type stars with (rotation-corrected) gravities less than log gc = 3.75 this group constitutes 30-40 percent of the population. We found a correlation between nitrogen and helium abundance which is consistent with expectations, suggesting that, whatever the mechanism that brings N to the surface, it displays CNO-processed material. For the rapidly-spinning O-type stars we can only provide upper limits on the nitrogen abundance, which are not in violation with theoretical expectations. Hence, the data cannot be used to test the physics of rotation induced mixing in the regime of high spin rates

  6. A moment symbolic representation of Lévy processes with applications

    OpenAIRE

    Oliva, Immacolata

    2012-01-01

    By using a symbolic method, known in the literature as the classical umbral calculus, a symbolic representation of Lévy processes is given and a new family of time-space harmonic polynomials with respect to such processes, which includes and generalizes the exponential complete Bell polynomials, is introduced. The usefulness of time-space harmonic polynomials with respect to Lévy processes is that it is a martingale the stochastic process obtained by replacing the indeterminate x of the p...

  7. The Lévy flight foraging hypothesis in a pelagic seabird.

    Science.gov (United States)

    Focardi, Stefano; Cecere, Jacopo G

    2014-03-01

    vy flight foraging represents an innovative paradigm for the analysis of animal random search by including models of heavy-tailed distribution of move length, which complements the correlated random walk paradigm that is founded on Brownian walks. Theory shows that the efficiency of the different foraging tactics is a function of prey abundance and dynamics with Lévy flight being especially efficient in poor prey fields. Lévy flights have been controversial in some quarters, because they previously have been wrongly ascribed to many species through the employment of inappropriate statistical techniques and by misunderstanding movement pattern data. More recent studies using state-of-the-art statistical tools have, however, provided seemingly compelling evidence for Lévy flights. In this study, we employ these maximum-likelihood methods and their Bayesian equivalents by analysing both turning angles and move length distributions. We tested, for compliance with Lévy flight foraging, a set of 77 independent foraging trajectories of Cory's shearwaters Calonectris diomedea diomedea. Birds were tagged with high-resolution GPS loggers in two Mediterranean colonies (Linosa and Tremiti) during both incubation and chick rearing. We found that the behaviour of six birds was fitted by a correlated random walk; the movement of 32 birds was better represented by adaptive correlated random walks by switching from intensive to extensive searches; and the trajectories of 36 birds were fitted by a Lévy flight pattern of movement. The probability of performing Lévy flights was higher for trips during chick provisioning when shearwaters were forced to forage in suboptimal areas. This study supports Lévy flight foraging as an appropriate framework to analyse search tactics in this pelagic bird species and highlights that the adoption of a given search strategy is a function of biological and ecological constraints.

  8. Crossing the Yellow Void: Spatially Resolved Spectroscopy of the Post-Red Supergiant IRC +10420 and Its Circumstellar Ejecta

    Science.gov (United States)

    Humphreys, Roberta M.; Davidson, Kris; Smith, Nathan

    2002-08-01

    IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his collaborators have called the ``yellow void.'' We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long-slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double-peaked Hα emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass-loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently, the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a ``rain'' model, in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass-loss rate, IRC +10420 may be about to shed its opaque wind, cross the yellow void, and emerge as a hotter star. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  9. Sieve-based confidence intervals and bands for L\\'{e}vy densities

    CERN Document Server

    Figueroa-López, José E

    2011-01-01

    The estimation of the L\\'{e}vy density, the infinite-dimensional parameter controlling the jump dynamics of a L\\'{e}vy process, is considered here under a discrete-sampling scheme. In this setting, the jumps are latent variables, the statistical properties of which can be assessed when the frequency and time horizon of observations increase to infinity at suitable rates. Nonparametric estimators for the L\\'{e}vy density based on Grenander's method of sieves was proposed in Figueroa-L\\'{o}pez [IMS Lecture Notes 57 (2009) 117--146]. In this paper, central limit theorems for these sieve estimators, both pointwise and uniform on an interval away from the origin, are obtained, leading to pointwise confidence intervals and bands for the L\\'{e}vy density. In the pointwise case, our estimators converge to the L\\'{e}vy density at a rate that is arbitrarily close to the rate of the minimax risk of estimation on smooth L\\'{e}vy densities. In the case of uniform bands and discrete regular sampling, our results are consis...

  10. VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), σ Oph, BM Sco, and HD 206859

    Science.gov (United States)

    Wittkowski, M.; Arroyo-Torres, B.; Marcaide, J. M.; Abellan, F. J.; Chiavassa, A.; Guirado, J. C.

    2017-01-01

    Aims: We add four warmer late-type supergiants to our previous spectro-interferometric studies of red giants and supergiants. Methods: We measure the near-continuum angular diameter, derive fundamental parameters, discuss the evolutionary stage, and study extended atmospheric atomic and molecular layers. Results: V766 Cen (=HR 5171 A) is found to be a high-luminosity (log L/L⊙ = 5.8 ± 0.4) source of effective temperature 4290 ± 760 K and radius 1490 ± 540 R⊙, located in the Hertzsprung-Russell (HR) diagram close to both the Hayashi limit and Eddington limit; this source is consistent with a 40 M⊙ evolutionary track without rotation and current mass 27-36 M⊙. V766 Cen exhibits Na i in emission arising from a shell of radius 1.5 RPhot and a photocenter displacement of about 0.1 RPhot. It shows strong extended molecular (CO) layers and a dusty circumstellar background component. The other three sources are found to have lower luminosities of about log L/L⊙ = 3.4-3.5, corresponding to 5-9 M⊙ evolutionary tracks. They cover effective temperatures of 3900 K to 5300 K and radii of 60-120 R⊙. They do not show extended molecular layers as observed for higher luminosity RSGs of our sample. BM Sco shows an unusually strong contribution by an over-resolved circumstellar dust component. Conclusions: V766 Cen is a red supergiant located close to the Hayashi limit instead of a yellow hypergiant already evolving back toward warmer effective temperatures as discussed in the literature. Our observations of the Na i line and the extended molecular layers suggest an optically thick pseudo-photosphere at about 1.5 RPhot at the onset of the wind. The stars σ Oph, BM Sco, and HD 206859 are more likely high-mass red giants instead of RSGs as implied by their luminosity class Ib. This leaves us with an unsampled locus in the HR diagram corresponding to luminosities log L/L⊙ 3.8-4.8 or masses 10-13 M⊙, possibly corresponding to the mass region where stars explode as

  11. UV spectroscopy of the blue supergiant SBW1: the remarkably weak wind of a SN 1987A analog

    CERN Document Server

    Smith, Nathan; France, Kevin; McCray, Richard

    2016-01-01

    The Galactic blue supergiant SBW1 with its circumstellar ring nebula represents the best known analog of the progenitor of SN 1987A. High-resolution imaging has shown H-alpha and IR structures arising in an ionized flow that partly fills the ring's interior. To constrain the influence of the stellar wind on this structure, we obtained an ultraviolet (UV) spectrum of the central star of SBW1 with the HST Cosmic Origins Spectrograph (COS). The UV spectrum shows none of the typical wind signatures, indicating a very low mass-loss rate. Radiative transfer models suggest an extremely low rate below 10$^{-10}$ Msun/yr, although we find that cooling timescales probably become comparable to or longer than the flow time below 10$^{-8}$ Msun/yr. We therefore adopt this latter value as a conservative upper limit. For the central star, the model yields $T_{\\rm eff}$=21,000$\\pm$1000 K, $L\\simeq$5$\\times$10$^4$ $L_{\\odot}$, and roughly Solar composition except for enhanced N abundance. SBW1's very low mass-loss rate may hi...

  12. High-amplitude supergiant V5112 Sgr: enrichment of the envelope with heavy s-process metals

    CERN Document Server

    Klochkova., V G

    2013-01-01

    High-resolution (R=60000) echelle spectroscopy of the post-AGB supergiant V5112 Sgr performed in 1996-2012 with the 6-m telescope BTA has revealed peculiarities of the star optical spectrum and has allowed the variability of the velocity field in the stellar atmosphere and envelope to be studied in detail. An asymmetry and splitting of strong absorption lines with a low lower-level excitation potential have been detected for the first time. The effect is maximal in BaII lines whose profile is split into three components. The profile shape and positions of the split lines change with time. The blue components of the split absorption lines are shown to be formed in a structured circumstellar envelope, suggesting an efficient dredge-up of the heavy metals produced during the preceding evolution of this star into the envelope. The envelope expansion velocities have been estimated to be 20 and 30 km/s. The mean radial velocity from diffuse bands in the spectrum of V5112 Sgr coincides with that from the short-wavel...

  13. Life Cycle of Stars

    Science.gov (United States)

    1999-01-01

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

  14. Structure of Supergiant Shells in the Large Magellanic Cloud

    CERN Document Server

    Book, Laura G; Gruendl, Robert A

    2007-01-01

    Nine supergiant shells (SGSs) have been identified in the Large Magellanic Cloud (LMC) based on H-alpha images, and twenty-three SGSs have been reported based on HI 21-cm line observations, but these sets do not always identify the same structures. We have examined the physical structure of the optically identified SGSs using HI channel maps and P-V diagrams to analyze the gas kinematics. There is good evidence for seven of the nine optically identified SGSs to be true shells. Of these seven H-alpha SGSs, four are the ionized inner walls of HI SGSs, while three are an ionized portion of a larger and more complex HI structure. All of the H-alpha SGSs are identified as such because they have OB associations along the periphery or in the center, with younger OB associations more often found along the periphery. After roughly 12 Myrs, if no new OB associations have been formed a SGS will cease to be identifiable at visible wavelengths. Thus, the presence and location of ionizing sources is the main distinction be...

  15. Signatures of active and passive optimized Lévy searching in jellyfish.

    Science.gov (United States)

    Reynolds, Andy M

    2014-10-06

    Some of the strongest empirical support for Lévy search theory has come from telemetry data for the dive patterns of marine predators (sharks, bony fishes, sea turtles and penguins). The dive patterns of the unusually large jellyfish Rhizostoma octopus do, however, sit outside of current Lévy search theory which predicts that a single search strategy is optimal. When searching the water column, the movement patterns of these jellyfish change over time. Movement bouts can be approximated by a variety of Lévy and Brownian (exponential) walks. The adaptive value of this variation is not known. On some occasions movement pattern data are consistent with the jellyfish prospecting away from a preferred depth, not finding an improvement in conditions elsewhere and so returning to their original depth. This 'bounce' behaviour also sits outside of current Lévy walk search theory. Here, it is shown that the jellyfish movement patterns are consistent with their using optimized 'fast simulated annealing'--a novel kind of Lévy walk search pattern--to locate the maximum prey concentration in the water column and/or to locate the strongest of many olfactory trails emanating from more distant prey. Fast simulated annealing is a powerful stochastic search algorithm for locating a global maximum that is hidden among many poorer local maxima in a large search space. This new finding shows that the notion of active optimized Lévy walk searching is not limited to the search for randomly and sparsely distributed resources, as previously thought, but can be extended to embrace other scenarios, including that of the jellyfish R. octopus. In the presence of convective currents, it could become energetically favourable to search the water column by riding the convective currents. Here, it is shown that these passive movements can be represented accurately by Lévy walks of the type occasionally seen in R. octopus. This result vividly illustrates that Lévy walks are not necessarily

  16. Minimizing Banking Risk in a Lévy Process Setting

    Directory of Open Access Journals (Sweden)

    F. Gideon

    2007-01-01

    Full Text Available The primary functions of a bank are to obtain funds through deposits from external sources and to use the said funds to issue loans. Moreover, risk management practices related to the withdrawal of these bank deposits have always been of considerable interest. In this spirit, we construct Lévy process-driven models of banking reserves in order to address the problem of hedging deposit withdrawals from such institutions by means of reserves. Here reserves are related to outstanding debt and acts as a proxy for the assets held by the bank. The aforementioned modeling enables us to formulate a stochastic optimal control problem related to the minimization of reserve, depository, and intrinsic risk that are associated with the reserve process, the net cash flows from depository activity, and cumulative costs of the bank's provisioning strategy, respectively. A discussion of the main risk management issues arising from the optimization problem mentioned earlier forms an integral part of our paper. This includes the presentation of a numerical example involving a simulation of the provisions made for deposit withdrawals via treasuries and reserves.

  17. Robert Lévy-Mandel (1923-2010)

    CERN Document Server

    2010-01-01

    Former CERN Director Robert Lévy-Mandel passed away on 3 July at the age of 87.   After obtaining a diploma from the Institut polytechnique in Grenoble, in 1948 he started work at the CEA, and was involved in the development and construction of the Saclay institute's first particle accelerator, a Van de Graaff machine. From 1954 to 1957 he was responsible for the coordination, development and construction of the CEA’s Saturne synchrotron, which entered service in 1958. In 1963 he was appointed head of the Saturne Synchrotron Department. The team led the construction of the Gargamelle bubble chamber, which was installed at CERN, and made contributions to other major facilities, including the Big European Bubble Chamber (BEBC). In 1971 he was invited to come to Geneva by John Adams, who was in charge of the SPS accelerator project. With the start of the SPS project, CERN had two laboratories, one at Meyrin and one at Prévessin, each with its own Director General: ...

  18. Intrinsic Lévy behaviour in organisms - searching for a mechanism. Comment on "Liberating Lévy walk research from the shackles of optimal foraging" by A.M. Reynolds

    Science.gov (United States)

    Sims, David W.

    2015-09-01

    The seminal papers by Viswanathan and colleagues in the late 1990s [1,2] proposed not only that scale-free, superdiffusive Lévy walks can describe the free-ranging movement patterns observed in animals such as the albatross [1], but that the Lévy walk was optimal for searching for sparsely and randomly distributed resource targets [2]. This distinct advantage, now shown to be present over a much broader set of conditions than originally theorised [3], implied that the Lévy walk is a search strategy that should be found very widely in organisms [4]. In the years since there have been several influential empirical studies showing that Lévy walks can indeed be detected in the movement patterns of a very broad range of taxa, from jellyfish, insects, fish, reptiles, seabirds, humans [5-10], and even in the fossilised trails of extinct invertebrates [11]. The broad optimality and apparent deep evolutionary origin of movement (search) patterns that are well approximated by Lévy walks led to the development of the Lévy flight foraging (LFF) hypothesis [12], which states that "since Lévy flights and walks can optimize search efficiencies, therefore natural selection should have led to adaptations for Lévy flight foraging".

  19. Dynamics of a stochastic multi-strain SIS epidemic model driven by Lévy noise

    Science.gov (United States)

    Chen, Can; Kang, Yanmei

    2017-01-01

    A stochastic multi-strain SIS epidemic model is formulated by introducing Lévy noise into the disease transmission rate of each strain. First, we prove that the stochastic model admits a unique global positive solution, and, by the comparison theorem, we show that the solution remains within a positively invariant set almost surely. Next we investigate stochastic stability of the disease-free equilibrium, including stability in probability and pth moment asymptotic stability. Then sufficient conditions for persistence in the mean of the disease are established. Finally, based on an Euler scheme for Lévy-driven stochastic differential equations, numerical simulations for a stochastic two-strain model are carried out to verify the theoretical results. Moreover, numerical comparison results of the stochastic two-strain model and the deterministic version are also given. Lévy noise can cause the two strains to become extinct almost surely, even though there is a dominant strain that persists in the deterministic model. It can be concluded that the introduction of Lévy noise reduces the disease extinction threshold, which indicates that Lévy noise may suppress the disease outbreak.

  20. Broad Balmer Wings in BA Hyper/Supergiants Distorted by Diffuse Interstellar Bands: Five Examples in the 30 Doradus Region from the VLT-FLAMES Tarantula Survey

    CERN Document Server

    Walborn, Nolan R; Evans, Christopher J; Taylor, William D; Sabbi, Elena; Barbá, Rodolfo H; Morrell, Nidia I; Apellániz, Jesús Maíz; Sota, Alfredo; Dufton, Philip L; McEvoy, Catherine M; Clark, J Simon; Markova, Nevena; Ulaczyk, Krzysztof

    2015-01-01

    Extremely broad emission wings at H$\\beta$ and H$\\alpha$ have been found in VFTS data for five very luminous BA supergiants in or near 30 Doradus in the Large Magellanic Cloud. The profiles of both lines are extremely asymmetrical, which we have found to be caused by very broad diffuse interstellar bands (DIBs) in the longward wing of H$\\beta$ and the shortward wing of H$\\alpha$. These DIBs are well known to interstellar but not to many stellar specialists, so that the asymmetries may be mistaken for intrinsic features. The broad emission wings are generally ascribed to electron scattering, although we note difficulties for that interpretation in some objects. Such profiles are known in some Galactic hyper/supergiants and are also seen in both active and quiescent Luminous Blue Variables. No prior or current LBV activity is known in these 30 Dor stars, although a generic relationship to LBVs is not excluded; subject to further observational and theoretical investigation, it is possible that these very luminou...

  1. The Massive Star Population in M101

    Science.gov (United States)

    Grammer, Skyler H.

    An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. Very little is known about the origin of these giant eruptions and their progenitors which are presumably very-massive, evolved stars such as luminous blue variables, hypergiants, and supergiants. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the luminous and evolved massive star populations in several nearby galaxies. We aim to identify the likely progenitors of the giant eruptions, study the spatial variations in the stellar populations, and examine the relationship between massive star populations and their environment. The work presented here is focused on stellar populations in the relatively nearby, giant, spiral galaxy M101 from sixteen archival BVI HST/ACS images. We create a catalog of stars in the direction to M101 with photometric errors history (SFH) for the stellar populations in five 2' wide annuli by fitting the color-magnitude diagrams. Binning the SFH into time frames corresponding to populations traced by Halpha, far ultraviolet (FUV), and near ultraviolet (NUV) emission, we show that the fraction of stellar populations young enough to contribute in Halpha is 15% " 35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of Halpha emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into the modeled ratios, we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed

  2. Tsallis statistics and gradually truncated Lévy flight-distribution of an economical index

    Science.gov (United States)

    Gupta, Hari M.; Campanha, José R.

    2002-06-01

    Tsallis postulated a generalized form for entropy and give rise to a new statistics now known as Tsallis statistics. In the present work, we compare the Tsallis statistics with the gradually truncated Lévy flight, and discuss the distribution of an economical index-the Standard and Poor's 500-using the values of standard deviation as calculated by our model. We find that both statistics give almost the same distribution. Thus we feel that gradual truncation of Lévy distribution, after certain critical step size for describing complex systems, is a requirement of generalized thermodynamics or similar. The gradually truncated Lévy flight is based on physical considerations and bring a better physical picture of the dynamics of the whole system. Tsallis statistics gives a theoretical support. Both statistics together can be utilized for the development of a more exact portfolio theory or to understand better the complexities in human and financial behaviors. A comparison of both statistics is made.

  3. Markov Regime Switching of Stochastic Volatility Lévy Model on Approximation Mode

    Directory of Open Access Journals (Sweden)

    Arthit Intarasit

    2013-01-01

    Full Text Available This paper deals with financial modeling to describe the behavior of asset returns, through consideration of economic cycles together with the stylized empirical features of asset returns such as fat tails. We propose that asset returns are modeled by a stochastic volatility Lévy process incorporating a regime switching model. Based on the risk-neutral approach, there exists a large set of candidates of martingale measures due to the driving of a stochastic volatility Lévy process in the proposed model which renders the market incomplete in general. We first establish an equivalent martingale measure for the proposed model introduced in risk-neutral version. Regime switching of stochastic volatility Lévy process is employed in an approximation mode for model calibration and the calibration of parameters model done based on EM algorithm. Finally, some empirical results are illustrated via applications to the Bangkok Stock Exchange of Thailand index.

  4. Numerical approximation of Lévy-Feller fractional diffusion equation via Chebyshev-Legendre collocation method

    Science.gov (United States)

    Sweilam, N. H.; Abou Hasan, M. M.

    2016-08-01

    This paper reports a new spectral algorithm for obtaining an approximate solution for the Lévy-Feller diffusion equation depending on Legendre polynomials and Chebyshev collocation points. The Lévy-Feller diffusion equation is obtained from the standard diffusion equation by replacing the second-order space derivative with a Riesz-Feller derivative. A new formula expressing explicitly any fractional-order derivatives, in the sense of Riesz-Feller operator, of Legendre polynomials of any degree in terms of Jacobi polynomials is proved. Moreover, the Chebyshev-Legendre collocation method together with the implicit Euler method are used to reduce these types of differential equations to a system of algebraic equations which can be solved numerically. Numerical results with comparisons are given to confirm the reliability of the proposed method for the Lévy-Feller diffusion equation.

  5. Non-Gaussian distributions of melodic intervals in music: The Lévy-stable approximation

    Science.gov (United States)

    Niklasson, Gunnar A.; Niklasson, Maria H.

    2015-11-01

    The analysis of structural patterns in music is of interest in order to increase our fundamental understanding of music, as well as for devising algorithms for computer-generated music, so called algorithmic composition. Musical melodies can be analyzed in terms of a “music walk” between the pitches of successive tones in a notescript, in analogy with the “random walk” model commonly used in physics. We find that the distribution of melodic intervals between tones can be approximated with a Lévy-stable distribution. Since music also exibits self-affine scaling, we propose that the “music walk” should be modelled as a Lévy motion. We find that the Lévy motion model captures basic structural patterns in classical as well as in folk music.

  6. vy Distributions for One-Dimensional Analysis of the Bose–Einstein Correlations

    Directory of Open Access Journals (Sweden)

    V. A. Okorokov

    2017-01-01

    Full Text Available A general study of relations between the parameters of two centrally symmetric Lévy distributions, often used for one-dimensional investigation of Bose–Einstein correlations, is given for the first time. These relations of the strength of correlations and of the radius of the emission region take into account possible various finite ranges of the Lorentz invariant four-momentum difference for two centrally symmetric Lévy distributions. In particular, special cases of the relations are investigated for Cauchy and normal (Gaussian distributions. The mathematical formalism is verified using the recent measurements given that a generalized centrally symmetric Lévy distribution is used. The reasonable agreement is observed between estimations and experimental results for all available types of strong interaction processes and collision energies.

  7. Stellar atmospheres, atmospheric extension and fundamental parameters: weighing stars using the stellar mass index

    CERN Document Server

    Neilson, Hilding R; Norris, Ryan; Kloppenborg, Brian; Lester, John B

    2016-01-01

    One of the great challenges in understanding stars is measuring their masses. The best methods for measuring stellar masses include binary interaction, asteroseismology and stellar evolution models, but these methods are not ideal for red giant and supergiant stars. In this work, we propose a novel method for inferring stellar masses of evolved red giant and supergiant stars using interferometric and spectrophotometric observations combined with spherical model stellar atmospheres to measure what we call the stellar mass index, defined as the ratio between the stellar radius and mass. The method is based on the correlation between different measurements of angular diameter, used as a proxy for atmospheric extension, and fundamental stellar parameters. For a given star, spectrophotometry measures the Rosseland angular diameter while interferometric observations generally probe a larger limb-darkened angular diameter. The ratio of these two angular diameters is proportional to the relative extension of the stel...

  8. State of matter for quark stars

    CERN Document Server

    Lai, X Y

    2009-01-01

    It depends on the state of matter at supra-nuclear density to model pulsar's structure, which is unfortunately not certain due to the difficulties in physics. In cold quark matter at realistic baryon densities of compact stars (with an average value of $\\sim 2-3\\rho_0$), the interaction between quarks is so strong that they would condensate in position space to form quark-clusters. We argue that quarks in quark stars are grouped in clusters, then we apply two phenomenological models for quark stars, the polytropic model and Lennard-Jones model. Both of the two models have stiffer EoS, and larger maximum mass for quark stars (larger than 2 $M_\\odot$). The gravitational energy releases during the AIQ process could explain the observed energy of three supergiant flares from soft gamma-ray repeaters ($\\sim 10^{47}$ ergs).

  9. Explicit Forms of q-Deformed Lévy-Meixner Polynomials and Their Generating Functions

    Institute of Scientific and Technical Information of China (English)

    Zhi Yuan HUANG; Pei Yan LI; Ying WU

    2008-01-01

    The classical Lévy-Meixner polynomials are distinguished through the special forms of their generating functions. In fact, they are completely determined by 4 parameters: c 1, c 2, γ and β .Inthis paper, for - 1 vy-Meixner polynomials and their generating functions in term of c 1, c 2, γand β , which is shown to be a reasonable interpolation between classical case (q=1) and fermionic case (q=-1). In particular, when q = 0 it's also compatible with the free case.

  10. A Stroock formula for a certain class of Lévy processes and applications to finance

    Directory of Open Access Journals (Sweden)

    M. Eddahbi

    2005-01-01

    Full Text Available We find a Stroock formula in the setting of generalized chaos expansion introduced by Nualart and Schoutens for a certain class of Lévy processes, using a Malliavin-type derivative based on the chaotic approach. As applications, we get the chaotic decomposition of the local time of a simple Lévy process as well as the chaotic expansion of the price of a financial asset and of the price of a European call option. We also study the behavior of the tracking error in the discrete delta neutral hedging under both the equivalent martingale measure and the historical probability.

  11. Continuous dependence estimate for conservation laws with Lévy noise

    Science.gov (United States)

    Biswas, Imran H.; Koley, Ujjwal; Majee, Ananta K.

    2015-11-01

    We are concerned with multidimensional stochastic balance laws driven by Lévy processes. Using bounded variation (BV) estimates for vanishing viscosity approximations, we derive an explicit continuous dependence estimate on the nonlinearities of the entropy solutions under the assumption that Lévy noise only depends on the solution. This result is used to show the error estimate for the stochastic vanishing viscosity method. In addition, we establish fractional BV estimate for vanishing viscosity approximations in case the noise coefficient depends on both the solution and spatial variable.

  12. European Option Pricing with Transaction Costs in Lévy Jump Environment

    Directory of Open Access Journals (Sweden)

    Jiayin Li

    2014-01-01

    Full Text Available The European option pricing problem with transaction costs is investigated for a risky asset price model with Lévy jump. By the aid of arbitrage pricing theory and the generalized Itô formula (which includes Poisson jump, the explicit solution to the risk asset price model is given. According to arbitrage-free principle, we first discretize the continuous-time model. Then, in each small time interval, the transaction costs are introduced. By using the Δ-hedging strategy, the explicit solutions of the European options pricing formula with transaction costs are given for the risky asset price model with Lévy jump.

  13. ELEMENTARY BIFURCATIONS FOR A SIMPLE DYNAMICAL SYSTEM UNDER NON-GAUSSIAN L(é)VY NOISES

    Institute of Scientific and Technical Information of China (English)

    Chen Huiqin; Duan Jinqiao; Zhang Chengjian

    2012-01-01

    Nonlinear dynamical systems are sometimes under the influence of random fluctuations.It is desirable to examine possible bifurcations for stochastic dynamical systems when a parameter varies.@@A computational analysis is conducted to investigate bifurcations of a simple dynamical system under non-Gaussian α-stable Lévy motions,by examining the changes in stationary probability density functions for the solution orbits of this stochastic system.The stationary probability density functions are obtained by solving a nonlocal Fokker-Planck equation numerically.This allows numerically investigating phenomenological bifurcation,or P-bifurcation,for stochastic differential equations with non-Gaussian Lévy noises.

  14. Alternative Specifications for the Lévy Libor Market Model: An Empirical Investigation

    DEFF Research Database (Denmark)

    Skovmand, David; Nicolato, Elisa

    This paper introduces and analyzes specications of the Lévy Market Model originally proposed by Eberlein and Özkan (2005). An investigation of the term structure of option implied moments rules out the Brownian motion and homogeneous Lévy processes as suitable modeling devices, and consequently...... of the estimation show that pricing performances are improved when a high frequency jump component is incorporated. Specifically, excellent results are achieved with the 4 parameter Sato-Variance Gamma model, which is able to fit an entire surface of caps with an average absolute percentage pricing error of less...

  15. Massive Stars in the Quintuplet Cluster

    CERN Document Server

    Figer, D F; Morris, M; Figer, Donald F.; Lean, Ian S. Mc

    1999-01-01

    We present near-infrared photometry and K-band spectra of newly-identified massive stars in the Quintuplet Cluster, one of the three massive clusters projected within 50 pc of the Galactic Center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any cluster in the Galaxy, and over a dozen stars in earlier stages of evolution, i.e., LBV, Ofpe/WN9, and OB supergiants. One newly identified star is the second ``Luminous Blue Variable'' in the cluster, after the ``Pistol Star.'' Given the evolutionary stages of the identified stars, the cluster appears to be about 4 \\pm 1 Myr old, assuming coeval formation. The total mass in observed stars is $\\sim 10^3 \\Msun$, and the implied mass is initial mass function. The implied mass density in stars is at least a few thousand $\\Msun pc^{-3}$. The newly-identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 10^{50.9...

  16. AI canis minoris, a pulsating low-mass supergiant at an early transition phase from the AGB to the post-AGB stage of evolution

    Science.gov (United States)

    Arkhipova, V. P.; Ikonnikova, N. P.; Esipov, V. F.; Komissarova, G. V.

    2017-06-01

    The U BV photometry and low-resolution spectroscopy for the semiregular variable AI CMi, a candidate for post-AGB objects, performed in 1996-2016 and 2000-2013, respectively, are presented. The star showed multiperiodic brightness variations with an amplitude up to 1\\underset{\\cdot}{m} 5 in the V band, a significant (up to 0\\underset{\\cdot}{m} 4) bluing of the B - V and U - B colors as the star faded, and a change of its spectrum from G5 I to K3-5 I, depending on its brightness. A possible long-term fading of AI CMi below 8\\underset{\\cdot}{m} 5 in the period from May 2013 to early 2015 is observed in the light curve. The colors in this episode did not change the pattern of their unusual behavior with brightness. The main feature of the spectrum for AI CMi is the appearance and strengthening of TiO absorption bands as its brightness declines, which are atypical in the spectra of ordinary G5-K3 supergiants. The bluing of the B - V and U - B colors is interpreted as the blanketing of stellar radiation predominantly in V (and to a lesser extent in B) by the TiO absorption bands whose intensity increases dramatically with decreasing brightness. Another cause of the bluing can be the scattering of stellar radiation by small dust particles in the gas-dust shell of AI CMi. The star's continuum-normalized spectra over the period from 2000 to 2013 in the wavelength range 4200 to 7700 or 9200 Å are presented. These were taken at different phases of the pulsation cycle and clearly demonstrate the behavior of the TiO absorption bands depending on the V magnitude and B - V color. The equivalent widths of individual TiO bands weremeasured, and their correlation with the photometric parameters of the star is shown. AI CMi belongs to the O-rich branch of AGB/post-AGB supergiants and has a luminosity of 4000 L ⊙ at a distance of 1500 ± 700 pc. The mass of AI CMi is most likely small and close to the lower mass limit for post-AGB stars. The connection of the star

  17. The emission-line regions in the nucleus of NGC 1313 probed with GMOS-IFU: a supergiant/hypergiant candidate and a kinematically cold nucleus

    Science.gov (United States)

    Menezes, R. B.; Steiner, J. E.

    2017-04-01

    NGC 1313 is a bulgeless nearby galaxy, classified as SB(s)d. Its proximity allows high spatial resolution observations. We performed the first detailed analysis of the emission-line properties in the nuclear region of NGC 1313, using an optical data cube obtained with the Gemini Multi-object Spectrograph. We detected four main emitting areas, three of them (regions 1, 2 and 3) having spectra typical of H II regions. Region 1 is located very close to the stellar nucleus and shows broad spectral features characteristic of Wolf-Rayet stars. Our analysis revealed the presence of one or two WC4-5 stars in this region, which is compatible with results obtained by previous studies. Region 4 shows spectral features (as a strong Hα emission line, with a broad component) typical of a massive emission-line star, such as a luminous blue variable, a B[e] supergiant or a B hypergiant. The radial velocity map of the ionized gas shows a pattern consistent with rotation. A significant drop in the values of the gas velocity dispersion was detected very close to region 1, which suggests that the young stars there were formed from this cold gas, possibly keeping low values of velocity dispersion. Therefore, although detailed measurements of the stellar kinematics were not possible (due to the weak stellar absorption spectrum of this galaxy), we predict that NGC 1313 may also show a drop in the values of the stellar velocity dispersion in its nuclear region.

  18. TYC 3159-6-1: a runaway blue supergiant

    Science.gov (United States)

    Gvaramadze, V. V.; Miroshnichenko, A. S.; Castro, N.; Langer, N.; Zharikov, S. V.

    2014-01-01

    We report the results of optical spectroscopy of a candidate evolved massive star in the Cygnus-X region, TYC 3159-6-1, revealed via detection of its curious circumstellar nebula in archival data of the Spitzer Space Telescope. We classify TYC 3159-6-1 as an O9.5-O9.7 Ib star and derive its fundamental parameters by using the stellar atmosphere code FASTWIND. The He and CNO abundances in the photosphere of TYC 3159-6-1 are consistent with the solar abundances, suggesting that the star only recently evolved off the main sequence. Proper motion and radial velocity measurements for TYC 3159-6-1 show that it is a runaway star. We propose that Dolidze 7 is its parent cluster. We discuss the origin of the nebula around TYC 3159-6-1 and suggest that it might be produced in several successive episodes of enhanced mass-loss rate (outbursts) caused by rotation of the star near the critical Ω limit.

  19. TYC 3159-6-1: a runaway blue supergiant

    CERN Document Server

    Gvaramadze, V V; Castro, N; Langer, N; Zharikov, S V

    2013-01-01

    We report the results of optical spectroscopy of a candidate evolved massive star in the Cygnus X region, TYC 3159-6-1, revealed via detection of its curious circumstellar nebula in archival data of the Spitzer Space Telecope. We classify TYC 3159-6-1 as an O9.5-O9.7 Ib star and derive its fundamental parameters by using the stellar atmosphere code FASTWIND. The He and CNO abundances in the photosphere of TYC 3159-6-1 are consistent with the solar abundances, suggesting that the star only recently evolved off the main sequence. Proper motion and radial velocity measurements for TYC 3159-6-1 show that it is a runaway star. We propose that Dolidze 7 is its parent cluster. We discuss the origin of the nebula around TYC 3159-6-1 and suggest that it might be produced in several successive episodes of enhanced mass-loss rate (outbursts) caused by rotation of the star near the critical, \\Omega-limit.

  20. The past and future evolution of a star like Betelgeuse

    CERN Document Server

    Meynet, Georges; Ekstrom, Sylvia; Georgy, Cyril; Groh, Jose; Maeder, Andre

    2013-01-01

    We discuss the physics and the evolution of a typical massive star passing through an evolutionary stage similar to that of Betelgeuse. After a brief introduction recalling various observed parameters of Betelgeuse, we discuss the Pre-Main-Sequence phase (PMS), the Main-Sequence (MS) phase, the physics governing the duration of the first crossing of the HR diagram, the red supergiant stage (RSG), the post-red supergiant phases and the final fate of solar metallicity stars with masses between 9 and 25 M$_\\odot$. We examine the impact of different initial rotation and of various prescriptions for the mass loss rates during the red supergiant phase. We show that, whatever the initial rotation rate (chosen between 0 and 0.7$\\times\\upsilon_{\\rm crit}$, $\\upsilon_{\\rm crit}$ being the surface equatorial velocity producing a centrifugal acceleration balancing exactly the gravity) and the mass loss rates during the RSG stage (varied between a standard value and 25 times that value), a 15 M$_\\odot$ star always ends it...

  1. Swift/XRT orbital monitoring of the candidate supergiant fast X-ray transient IGR J17354-3255

    CERN Document Server

    Ducci, L; Esposito, P; Bozzo, E; Krimm, H A; Vercellone, S; Mangano, V; Kennea, J A

    2013-01-01

    We report on the Swift/X-ray Telescope (XRT) monitoring of the field of view around the candidate supergiant fast X-ray transient (SFXT) IGR J17354-3255, which is positionally associated with the AGILE/GRID gamma-ray transient AGL J1734-3310. Our observations, which cover 11 days for a total on-source exposure of about 24 ks, span 1.2 orbital periods (P_orb=8.4474 d) and are the first sensitive monitoring of this source in the soft X-rays. These new data allow us to exploit the timing variability properties of the sources in the field to unambiguously identify the soft X-ray counterpart of IGR J17354-3255. The soft X-ray light curve shows a moderate orbital modulation and a dip. We investigated the nature of the dip by comparing the X-ray light curve with the prediction of the Bondi-Hoyle-Lyttleton accretion theory, assuming both spherical and nonspherical symmetry of the outflow from the donor star. We found that the dip cannot be explained with the X-ray orbital modulation. We propose that an eclipse or the...

  2. Low-amplitude rotational modulation rather than pulsations in the CoRoT B-type supergiant HD 46769

    CERN Document Server

    Aerts, C; Catala, C; Neiner, C; Briquet, M; Castro, N; Schmid, V S; Scardia, M; Rainer, M; Poretti, E; Papics, I; Degroote, P; Bloemen, S; Oestensen, R H; Auvergne, M; Baglin, A; Baudin, F; Michel, E; Samadi, R

    2013-01-01

    {We aim to detect and interpret photometric and spectroscopic variability of the bright CoRoT B-type supergiant target HD\\,46769 ($V=5.79$). We also attempt to detect a magnetic field in the target.} {We analyse a 23-day oversampled CoRoT light curve after detrending, as well as spectroscopic follow-up data, by using standard Fourier analysis and Phase Dispersion Minimization methods. We determine the fundamental parameters of the star, as well as its abundances from the most prominent spectral lines. We perform a Monte Carlo analysis of spectropolarimetric data to obtain an upper limit of the polar magnetic field, assumping a dipole field.} {In the CoRoT data, we detect a dominant period of 4.84\\,d with an amplitude of 87\\,ppm, and some of its (sub-)multiples. Given the shape of the phase-folded light curve and the absence of binary motion, we interpret the dominant variability in terms of rotational modulation, with a rotation period of 9.69\\,d. Subtraction of the rotational modulation signal does not revea...

  3. Periodic mass loss episodes due to an oscillation mode with variable amplitude in the hot supergiant HD50064

    CERN Document Server

    Aerts, C; Baglin, A; Degroote, P; Oreiro, R; Vuckovic, M; Smolders, K; Acke, B; Verhoelst, T; Desmet, M; Godart, M; Noels, A; Dupret, M -A; Auvergne, M; Baudin, F; Catala, C; Michel, E; Samadi, R

    2010-01-01

    We aim to interpret the photometric and spectroscopic variability of the luminous blue variable supergiant HD\\,50064 ($V=8.21$).CoRoT space photometry and follow-up high-resolution spectroscopy, with a time base of 137\\,d and 169\\,d, respectively, was gathered, analysed and interpreted using standard time series analysis and light curve modelling methods as well as spectral line diagnostics.The space photometry reveals one period of 37\\,d, which undergoes a sudden amplitude change with a factor 1.6. The pulsation period is confirmed in the spectroscopy, which additionally reveals metal line radial velocity values differing by $\\sim 30\\,$km\\,s$^{-1}$ depending on the spectral line and on the epoch. We estimate \\teff$\\sim$13\\,500\\,K, \\logg$\\sim$1.5 from the equivalent width of Si lines. The Balmer lines reveal that the star undergoes episodes of changing mass loss on a time scale similar to the changes in the photometric and spectroscopic variability, with an average value of $\\log\\dot{\\rm M}\\simeq-5$ (in M$_\\o...

  4. Detection of the 128 day radial velocity variations in the supergiant {\\alpha} Persei. Rotational modulations, pulsations, or a planet?

    CERN Document Server

    Lee, Byeong-Cheol; Park, Myeong-Gu; Kim, Kang-Min; Mkrtichian, David E

    2012-01-01

    Aims. In order to search for and study the nature of the low-amplitude and long-periodic radial velocity (RV) variations of massive stars, we have been carrying out a precise RV survey for supergiants that lie near or inside the Cepheid instability strip. Methods. We have obtained high-resolution spectra of {\\alpha} Per (F5 Ib) from November 2005 to September 2011 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO). Results. Our measurements reveal that {\\alpha} Per shows a periodic RV variation of 128 days and a semi-amplitude of 70 m/s. We find no strong correlation between RV variations and bisector velocity span (BVS), but the 128-d peak is indeed present in the BVS variations among several other significant peaks in periodogram. Conclusions. {\\alpha} Per may have an exoplanet, but the combined data spanning over 20 years seem to suggest that the 128-d RV variations have not been stable on long-term scale, which is somewhat difficult to r...

  5. The XMM-Newton view of Supergiant Fast X-ray Transients: the case of IGRJ16418-4532

    CERN Document Server

    Sidoli, L; Sguera, V; Pizzolato, F

    2011-01-01

    We report on a 40 ks long, uninterrupted X-ray observation of the candidate supergiant fast X-ray transient (SFXT) IGRJ16418-4532 performed with XMM-Newton on February 23, 2011. This high mass X-ray binary lies in the direction of the Norma arm, at an estimated distance of 13 kpc. During the observation, the source showed strong variability exceeding two orders of magnitudes, never observed before from this source. Its X-ray flux varied in the range from 0.1 counts/s to about 15 counts/s, with several bright flares of different durations (from a few hundreds to a few thousands seconds) and sometimes with a quasi-periodic behavior. This finding supports the previous suggestion that IGRJ16418-4532 is a member of the SFXTs class. In our new observation we measured a pulse period of 1212+/-6 s, thus confirming that this binary contains a slowly rotating neutron star. During the periods of low luminosity the source spectrum is softer and more absorbed than during the flares. A soft excess is present below 2 keV in...

  6. Cold Dust in Three Massive Evolved Stars in the LMC

    CERN Document Server

    Boyer, M L; van Loon, J Th; Srinivasan, S; Clayton, G C; Kemper, F; Smith, L J; Matsuura, M; Woods, Paul M; Marengo, M; Meixner, M; Engelbracht, C; Gordon, K D; Hony, S; Indebetouw, R; Misselt, K; Okumura, K; Panuzzo, P; Riebel, D; Roman-Duval, J; Sauvage, M; Sloan, G C

    2010-01-01

    Massive evolved stars can produce large amounts of dust, and far-infrared (IR) data are essential for determining the contribution of cold dust to the total dust mass. Using Herschel, we search for cold dust in three very dusty massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red supergiant. We model the spectral energy distributions using radiative transfer codes and find that these three stars have mass-loss rates up to 10^-3 solar masses/year, suggesting that high-mass stars are important contributors to the life-cycle of dust. We found far-IR excesses in two objects, but these excesses appear to be associated with ISM and star-forming regions. Cold dust (T < 100 K) may thus not be an important contributor to the dust masses of evolved stars.

  7. ON THE NATURE OF RAPIDLY ROTATING SINGLE EVOLVED STARS

    Energy Technology Data Exchange (ETDEWEB)

    Da Silva, R. Rodrigues; Canto Martins, B. L.; De Medeiros, J. R., E-mail: renan@dfte.ufrn.br [Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal RN (Brazil)

    2015-03-01

    We present an analysis of the nature of the rapidly rotating, apparently single giant based on rotational and radial velocity measurements carried out by the CORAVEL spectrometers. From the analyzed sample, composed of 2010 spectroscopic, apparently single, evolved stars of luminosity classes IV, III, II, and Ib with spectral types G and K, we classified 30 stars that presented unusual, moderate to rapid rotation. This work reports, for the first time, the presence of these abnormal rotators among subgiant, bright giant, and Ib supergiant stars. To date, this class of stars was reported only among giant stars of luminosity class III. Most of these abnormal rotators present an IRAS infrared excess, which, in principle, can be related to dust around these stars.

  8. Photometry of the Variable Bright Red Supergiant Betelgeuse from the Ground and from Space with the BRITE Nano-satellites

    Science.gov (United States)

    Minor, Robert; Guinan, Edward F.

    2016-01-01

    Robert B. Minor, Edward Guinan, Richard Wasatonic Betelgeuse (Alpha Orionis) is a large, luminous semi-regular red supergiant of spectral class M1.5-2Iab. It is the 8th brightest star in the night sky. Betelgeuse is 30,000 times more luminous than the Sun and 700 times larger. It has an estimated age of ~8 +/- 2 Myr. Betelgeuse explode in a Type II supernova (anytime within the next million years). When it explodes, it will shine with about the intensity of a full moon and may be visible during the day. However, it is too far away to cause any major damage to Earth. Photometry of this pre-supernova star has been ongoing at Villanova for nearly 45 years. These observations are being used to define the complex brightness variations of this star. Semi-regular periodic light variations have been found with periods of 385 days up to many years. These light variations are used to study its unstable atmosphere and resulting complex pulsations. Over the last 15 years, it has been observed by Wasatonic who has accumulated a large photometric database. The ground-based observations are limited to precisions of 1.5%, and due to poor weather, limit observations to about 1-2 times per week. However, with the recent successful launch of the BRITE Nano-satellites (http://www.brite-constellation.at) during 2013-14, it is possible to secure high precision photometry of bright stars, including Betelgeuse, continuously for up to 3 months. Villanova has participated in the BRITE guest investigators program and has been awarded observing time and data rights many bright stars, including Betelgeuse. BRITE blue and red observations of Betelgeuse were carried out during the Nov-Feb 2013-14 season and the 2014-15. These datasets were given to Villanova and have been combined with coexistent photometry from Wasatonic. Although BRITE's red data is saturated, the blue data is useable. The BRITE datasets were combined with our ground-based V, red, and near-IR photometry. Problems were

  9. Intrinsic Lévy behaviour in organisms – searching for a mechanism: Comment on “Liberating Lévy walk research from the shackles of optimal foraging” by A.M. Reynolds

    OpenAIRE

    Sims, David W.

    2015-01-01

    The seminal papers by Viswanathan and colleagues in the late 1990s [1] and [2] proposed not only that scale-free, superdiffusive Lévy walks can describe the free-ranging movement patterns observed in animals such as the albatross [1], but that the Lévy walk was optimal for searching for sparsely and randomly distributed resource targets [2]. This distinct advantage, now shown to be present over a much broader set of conditions than originally theorised [3], implied that the Lévy walk is a sea...

  10. Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

    Science.gov (United States)

    Kraus, M.; Cidale, L. S.; Arias, M. L.; Maravelias, G.; Nickeler, D. H.; Torres, A. F.; Borges Fernandes, M.; Aret, A.; Curé, M.; Vallverdú, R.; Barbá, R. H.

    2016-10-01

    Context. B[e] supergiants are evolved massive stars, enshrouded in a dense wind and surrounded by a molecular and dusty disk. The mechanisms that drive phases of enhanced mass loss and mass ejections, responsible for the shaping of the circumstellar material of these objects, are still unclear. Aims: We aim to improve our knowledge on the structure and dynamics of the circumstellar disk of the Large Magellanic Cloud B[e] supergiant LHA 120-S 73. Methods: High-resolution optical and near-infrared spectroscopic data were obtained over a period of 16 and 7 yr, respectively. The spectra cover the diagnostic emission lines from [Ca ii] and [O i], as well as the CO bands. These features trace the disk at different distances from the star. We analyzed the kinematics of the individual emission regions by modeling their emission profiles. A low-resolution mid-infrared spectrum was obtained as well, which provides information on the composition of the dusty disk. Results: All diagnostic emission features display double-peaked line profiles, which we interpret as due to Keplerian rotation. We find that the profile of each forbidden line contains contributions from two spatially clearly distinct rings. In total, we find that LHA 120-S 73 is surrounded by at least four individual rings of material with alternating densities (or by a disk with strongly non-monotonic radial density distribution). Moreover, we find that the molecular ring must have gaps or at least strong density inhomogeneities, or in other words, a clumpy structure. The optical spectra additionally display a broad emission feature at 6160-6180 Å, which we interpret as molecular emission from TiO. The mid-infrared spectrum displays features of oxygen- and carbon-rich grain species, which indicates a long-lived, stable dusty disk. We cannot confirm the previously reported high value for the stellar rotation velocity. He i λ 5876 is the only clearly detectable pure atmospheric absorption line in our data. Its

  11. The dustiest Post-Main sequence stars in the Magellanic Clouds

    CERN Document Server

    Jones, Olivia C; Sargent, Benjamin A; Boyer, Martha L; Sewilo, Marta; Hony, Sacha; Roman-Duval, Julia

    2015-01-01

    Using observations from the {\\em Herschel} Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds, we have found thirty five evolved stars and stellar end products that are bright in the far-infrared. These twenty eight (LMC) and seven (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found thirteen low- to intermediate mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae and a symbiotic star. We also identify ten high mass stars, including four of the fifteen known B[e] stars in the Magellanic Clouds, three extreme red supergiants wh...

  12. Bilateral V-Y flap for a perianal basal cell carcinoma: A case report

    Directory of Open Access Journals (Sweden)

    José P. Rivera-Chavarría

    2016-01-01

    Conclusion: Treatment modalities include early wide local excision to clear margins, ensuring further local recurrence and distant metastasis. The use of local V-Y advancement fasciocutaneous flaps may be another valid option for the reconstruction of perianal skin defects, with less morbidity than other flaps described in the literature.

  13. The Light-Time Effect in the Eclipsing Binaries GK Cep and VY Cet

    CERN Document Server

    Liakos, Alexios

    2014-01-01

    New times of minima of the eclipsing binaries GK Cep and VY Cet, obtained at the Observatory of the University of Athens, have been used together with all reliable timings found in the literature in order to study the period variation and search for the presence of third body in the systems.

  14. [Phenotype analysis and mutant gene location of ventral yellow mouse (VY(Slac))].

    Science.gov (United States)

    Shi, Mei-Lian; Xu, Ping; Yin, Xiao-Shu; Yang, Wei-Wei; Gu, Mei-Er; Yu, Li-Ping; Liu, Gui-Jie; Wu, Bao-Jin

    2012-06-01

    The ventri-yellow pigmentation mouse (temporarily named VY(Slac)) arose spontaneously in the C57BL/6J inbred mouse strain, found and bred by Shanghai SLAC Laboratory Animal Co., Ltd. VY(Slac) presented a special phenotype marked by yellow coat on the ventral surface of neck and trunk that was without melanin deposition but maintained a normal structure. The number of melanocytes in epidermis and melanin in hair follicle of the abdominal skin of the mutant mouse were less than that of their background strain, while there was no significant difference between the dorsal skins of the two strains. This mutant phenotype was inherited as single-gene dominant inheritance, confirmed by genetic experiment, and there was no significant difference between VY(Slac) and B(6) for other biological parameters such as weight, anatomic and histological structures of major organs and blood physiology. When the linkage relationship between the genomic DNA samples of F(2) 48 mice (VY(Slac)D(2)F(1)×D(2)) and mutant phenotype were evaluated, the mutant gene was confirmed on chromosome 2 near D2Mit229. New microsatellite and SNP markers were selected to amplify genomic DNA samples of 196 F(2) mice and the mutant gene was narrowed down to 5.3 Mb region between rs13476833 and rs27310903 on chromosome 2. The preliminary results of our phenotype analysis and gene location provides a solid basis for further identification of this mutant gene.

  15. Leapover lengths and first passage time statistics for Lévy flights

    DEFF Research Database (Denmark)

    Koren, Tal; Lomholt, Michael A; Chechkin, Aleksei V

    2007-01-01

    Exact results for the first passage time and leapover statistics of symmetric and one-sided Lévy flights (LFs) are derived. LFs with a stable index alpha are shown to have leapover lengths that are asymptotically power law distributed with an index alpha for one-sided LFs and, surprisingly...

  16. Exact solution of a Lévy walk model for anomalous heat transport

    Science.gov (United States)

    Dhar, Abhishek; Saito, Keiji; Derrida, Bernard

    2013-01-01

    The Lévy walk model is studied in the context of the anomalous heat conduction of one-dimensional systems. In this model, the heat carriers execute Lévy walks instead of normal diffusion as expected in systems where Fourier's law holds. Here we calculate exactly the average heat current, the large deviation function of its fluctuations, and the temperature profile of the Lévy walk model maintained in a steady state by contact with two heat baths (the open geometry). We find that the current is nonlocally connected to the temperature gradient. As observed in recent simulations of mechanical models, all the cumulants of the current fluctuations have the same system-size dependence in the open geometry. For the ring geometry, we argue that a size-dependent cutoff time is necessary for the Lévy walk model to behave like mechanical models. This modification does not affect the results on transport in the open geometry for large enough system sizes.

  17. Finite Difference Methods for Option Pricing under Lévy Processes: Wiener-Hopf Factorization Approach

    National Research Council Canada - National Science Library

    Kudryavtsev, Oleg

    2013-01-01

      In the paper, we consider the problem of pricing options in wide classes of Lévy processes. We propose a general approach to the numerical methods based on a finite difference approximation for the generalized Black-Scholes equation...

  18. Optimal Stopping Problems Driven by Lévy Processes and Pasting Principles

    NARCIS (Netherlands)

    Surya, B.A.

    2007-01-01

    Solving optimal stopping problems driven by Lévy processes has been a challenging task and has found many applications in modern theory of mathematical finance. For example situations in which optimal stopping typically arise include the problem of finding the arbitrage-free price of the American p

  19. Global solutions of stochastic 2D Navier-Stokes equations with Lévy noise

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    In this paper,we prove the global existence and uniqueness of the strong and weak solutions for 2D Navier-Stokes equations on the torus T2 perturbed by a Lévy process.The existence of invariant measure of the solutions are proved also.

  20. Generalized Backward Doubly Stochastic Differential Equations Driven by Lévy Processes with Continuous Coefficients

    Institute of Scientific and Technical Information of China (English)

    Auguste AMAN; Jean Marc OWO

    2012-01-01

    A new class of generalized backward doubly stochastic differential equations (GBDSDEs in short) driven by Teugels martingales associated with Lévy process are investigated.We establish a comparison theorem which allows us to derive an existence result of solutions under continuous and linear growth conditions.

  1. Exact tail asymptotics of the supremum attained by a Lévy process

    NARCIS (Netherlands)

    Asghari, N.M.; Dębicki, K.; Mandjes, M.

    2015-01-01

    In this short communication we analyze the tail asymptotics corresponding to the maximum value attained by a Lévy process with negative drift. The note has two contributions: a short and elementary proof of these asymptotics, and an importance sampling algorithm to estimate the rare-event probabilit

  2. Feller processes: the next generation in modeling. Brownian motion, Lévy processes and beyond.

    Science.gov (United States)

    Böttcher, Björn

    2010-12-03

    We present a simple construction method for Feller processes and a framework for the generation of sample paths of Feller processes. The construction is based on state space dependent mixing of Lévy processes. Brownian Motion is one of the most frequently used continuous time Markov processes in applications. In recent years also Lévy processes, of which Brownian Motion is a special case, have become increasingly popular. Lévy processes are spatially homogeneous, but empirical data often suggest the use of spatially inhomogeneous processes. Thus it seems necessary to go to the next level of generalization: Feller processes. These include Lévy processes and in particular brownian motion as special cases but allow spatial inhomogeneities. Many properties of Feller processes are known, but proving the very existence is, in general, very technical. Moreover, an applicable framework for the generation of sample paths of a Feller process was missing. We explain, with practitioners in mind, how to overcome both of these obstacles. In particular our simulation technique allows to apply Monte Carlo methods to Feller processes.

  3. vy-noise-induced transport in a rough triple-well potential

    Science.gov (United States)

    Li, Yongge; Xu, Yong; Kurths, Jürgen; Yue, Xiaole

    2016-10-01

    Rough energy landscape and noisy environment are two common features in many subjects, such as protein folding. Due to the wide findings of bursting or spiking phenomenon in biology science, small diffusions mixing large jumps are adopted to model the noisy environment that can be properly described by Lévy noise. We combine the Lévy noise with the rough energy landscape, modeled by a potential function superimposed by a fast oscillating function, and study the transport of a particle in a rough triple-well potential excited by Lévy noise, rather than only small perturbations. The probabilities of a particle staying in the middle well are considered under different amplitudes of roughness to find out how roughness affects the steady-state probability density function. Variations in the mean first passage time from the middle well to the right well have been investigated with respect to Lévy parameters and amplitudes of the roughness. In addition, we have examined the influences of roughness on the splitting probabilities of the first escape from the middle well. We uncover that the roughness can enhance significantly the first escape of a particle from the middle well, especially for different skewness parameters, but weak differences are found for stability index and noise intensity on the probabilities a particle staying in the middle well and splitting probability to the right.

  4. [Andreeva, E. and Belobrovtseva, I. "Tol'ko Vy poimete sleduiushchii tekst..."] / Avril Pyman

    Index Scriptorium Estoniae

    Pyman, Avril

    2014-01-01

    Arvustus: Andreeva, E. and Belobrovtseva, I. "Tol'ko Vy poimete sleduiushchii tekst...". Perepiska N. E. Andreeva i L. F. Zurova. Baltiiskii arkhiv: Russkaia kult'tura v Pribaltike, 13. Tallinna Ülikooli Slaavi Keelte ja Kultuuride Instituut, Tallinn, 2013

  5. The Ergodicity of Stochastic Partial Differential Equations with Lévy Jump

    Institute of Scientific and Technical Information of China (English)

    Guo Li ZHOU; Zhen Ting HOU

    2011-01-01

    In this article,the authors prove the uniqueness in law of a class of stochastic equations in infinite dimension,then we apply it to establish the existence and uniqueness of invariant measure of the generalized stochastic partial differential equation perturbed by Lévy process.

  6. An HST COS 'SNAPSHOT' spectrum of the K supergiant λ Vel (K4Ib-II)

    Energy Technology Data Exchange (ETDEWEB)

    Carpenter, Kenneth G. [NASA/GSFC Code 667, Greenbelt, MD 20771 (United States); Ayres, Thomas R. [University of Colorado, CASA, 389-UCB, Boulder, CO 80309 (United States); Harper, Graham M. [School of Physics, Trinity College, Dublin 2 (Ireland); Kober, Gladys; Nielsen, Krister E.; Wahlgren, Glenn M., E-mail: Kenneth.G.Carpenter@nasa.gov [Deptartment of Physics, Catholic University of America, Washington, DC 20064 (United States)

    2014-10-10

    We present a far-ultraviolet spectrum of the K4 Ib-II supergiant λ Vel obtained with the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) as a part of the SNAPshot program 'SNAPing coronal iron' (GO 11687). The observation covers a wavelength region (1326-1467 Å) not previously recorded for λ Vel at a spectral resolving power of R ∼ 20,000 and displays strong emission and absorption features, superposed on a bright chromospheric continuum. Fluorescent excitation is responsible for much of the observed emission, mainly powered by strong H I Lyα and the O I (UV 2) triplet emission near λ1304. The molecular CO and H{sub 2} fluorescences are weaker than in the early-K giant α Boo while the Fe II and Cr II lines, also pumped by H I Lyα, are stronger in λ Vel. This pattern of relative line strengths between the two stars is explained by the lower iron-group element abundance in α Boo, which weakens that star's Fe II and Cr II emission without reducing the molecular fluorescences. The λ Vel spectrum shows fluorescent Fe II, Cr II, and H{sub 2} emission similar to that observed in the M supergiant α Ori, but more numerous well-defined narrow emissions from CO. The additional CO emissions are visible in the spectrum of λ Vel since that star does not have the cool, opaque circumstellar shells that surround α Ori and produce broad circumstellar CO (A-X) band absorptions that hide those emissions in the cooler star. The presence of Si IV emission in λ Vel indicates a ∼8 × 10{sup 4} K plasma that is mixed into the cooler chromosphere. Evidence of the stellar wind is seen in the C II λλ1334,1335 lines and in the blueshifted Fe II and Ni II wind absorption lines. Line modeling using Sobolev with Exact Integration for the C II lines indicates a larger terminal velocity (∼45 versus ∼30 km s{sup –1}) and turbulence (∼27 versus <21 km s{sup –1}) with a more quickly accelerating wind (β = 0.35 versus 0.7) at the time of

  7. Spectroscopic survey of emission-line stars. I. B[e] stars

    CERN Document Server

    Aret, Anna; Šlechta, Miroslav

    2015-01-01

    Emission-line stars are typically surrounded by dense circumstellar material, often in form of rings or disc-like structures. Line emission from forbidden transitions trace a diversity of density and temperature regimes. Of particular interest are the forbidden lines of [O I] {\\lambda}{\\lambda}6300, 6364 and [Ca II] {\\lambda}{\\lambda}7291, 7324. They arise in complementary, high-density environments, such as the inner-disc regions around B[e] supergiants. To study physical conditions traced by these lines and to investigate how common they are, we initiated a survey of emission-line stars. Here, we focus on a sample of nine B[e] stars in different evolutionary phases. Emission of the [O I] lines is one of the characteristics of B[e] stars. We find that four of the objects display [Ca II] line emission: for the B[e] supergiants V1478 Cyg and 3 Pup the kinematics obtained from the [O I] and [Ca II] line profiles agrees with a Keplerian rotating disc scenario; the forbidden lines of the compact planetary nebula ...

  8. Carbon abundance and the N/C ratio in atmospheres of A-, F- and G-type supergiants and bright giants

    CERN Document Server

    Lyubimkov, Leonid S; Korotin, Sergey A; Rachkovskaya, Tamara M; Poklad, Dmitry B

    2014-01-01

    Based on our prior accurate determination of fundamental parameters for 36 Galactic A-, F- and G-type supergiants and bright giants (luminosity classes I and II), we undertook a non-LTE analysis of the carbon abundance in their atmospheres. It is shown that the non-LTE corrections to the C abundances derived from C I lines are negative and increase with the effective temperature Teff; the corrections are especially significant for the infrared C I lines with wavelengths 9060-9660 \\AA. The carbon underabundance as a general property of the stars in question is confirmed; a majority of the stars studied has the carbon deficiency [C/Fe] between -0.1 and -0.5 dex, with a minimum at -0.7 dex. When comparing the derived C deficiency with the N excess found by us for the same stars earlier, we obtain a pronounced N vs. C anti-correlation, which could be expected from predictions of the theory.We found that the ratio [N/C] spans mostly the range from 0.3 to 1.7 dex. Both these enhanced [N/C] values and the C and N an...

  9. NEW LUMINOUS ON SPECTRA FROM THE GALACTIC O-STAR SPECTROSCOPIC SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Walborn, Nolan R. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Morrell, Nidia I. [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile); Barbá, Rodolfo H. [Departamento de Física y Astronomía, Universidad de La Serena, Cisternas 1200 Norte, La Serena (Chile); Sota, Alfredo, E-mail: walborn@stsci.edu, E-mail: nmorrell@lco.cl, E-mail: rbarba@dfuls.cl, E-mail: sota@iaa.es [Instituto de Astrofísica de Andalucía—CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain)

    2016-04-15

    Two new ON supergiant spectra (bringing the total known to seven) and one new ONn giant (total of this class now eight) are presented; they have been discovered by the Galactic O-Star Spectroscopic Survey. These rare objects represent extremes in the mixing of CNO-cycled material to the surfaces of evolved, late-O stars, by uncertain mechanisms in the first category but likely by rotation in the second. The two supergiants are at the hot edge of the class, which is a selection effect from the behavior of defining N iii and C iii absorption blends, related to the tendency toward emission (Of effect) in the former. An additional N/C criterion first proposed by Bisiacchi et al. is discussed as a means to alleviate that effect, and it is relevant to the two new objects. The entire ON supergiant class is discussed; they display a fascinating diversity of detail undoubtedly related to the complexities of their extended atmospheres and winds that are sensitive to small differences in physical parameters, as well as to binary effects in some cases. Serendipitously, we have found significant variability in the spectrum of a little-known hypergiant with normal N, C spectra selected as a comparison for the anomalous objects. In contrast to the supergiants, the ONn spectra are virtual (nitrogen)-carbon copies of one another except for the degrees of line broadening, which emphasizes their probable unique origin and hence amenability to definitive astrophysical interpretation.

  10. Evolved star water maser cloud size determined by star size

    CERN Document Server

    Richards, A M S; Gray, M D; Lekht, E E; Mendoza-Torres, J E; Murakawa, K; Rudnitskij, G; Yates, J A

    2012-01-01

    Cool, evolved stars undergo copious mass loss but the details of how the matter is returned to the ISM are still under debate. We investigated the structure and evolution of the wind at 5 to 50 stellar radii from Asymptotic Giant Branch and Red Supergiant stars. 22-GHz water masers around seven evolved stars were imaged using MERLIN, at sub-AU resolution. Each source was observed at between 2 and 7 epochs (several stellar periods). We compared our results with long-term Pushchino single dish monitoring. The 22-GHz emission is located in ~spherical, thick, unevenly filled shells. The outflow velocity doubles between the inner and outer shell limits. Water maser clumps could be matched at successive epochs separated by <2 years for AGB stars, or at least 5 years for RSG. This is much shorter than the decades taken for the wind to cross the maser shell, and comparison with spectral monitoring shows that some features fade and reappear. In 5 sources, most of the matched features brighten or dim in concert from...

  11. The Onset of Chaos in Pulsating Variable Stars

    CERN Document Server

    Turner, David G; Percy, J R; Abdel-Latif, Mohamed Abdel-Sabour

    2011-01-01

    Random changes in pulsation period occur in cool pulsating Mira variables, Type A, B, and C semiregular variables, RV Tauri variables, and in most classical Cepheids. The physical processes responsible for such fluctuations are uncertain, but presumably originate in temporal modifications of the envelope convection in such stars. Such fluctuations are seemingly random over a few pulsation cycles of the stars, but are dominated by the regularity of the primary pulsation over the long term. The magnitude of stochasticity in pulsating stars appears to be linked directly to their dimensions, although not in simple fashion. It is relatively larger in M supergiants, for example, than in short-period Cepheids, but is common enough that it can be detected in visual observations for many types of pulsating stars. Although chaos was discovered in such stars 80 years ago, detection of its general presence in the group has only been possible in recent studies.

  12. Persistence and extinction of a stochastic non-autonomous Gilpin-Ayala system driven by Lévy noise

    Science.gov (United States)

    Liu, Qun; Liang, Yanlai

    2014-10-01

    In this paper, we consider the persistence and extinction of a stochastic non-autonomous Gilpin-Ayala system driven by Lévy noise. Sufficient criteria for extinction, non-persistence in the mean and weak persistence of the system are established. The threshold between weak persistence and extinction is obtained. From the results we can see that both persistence and extinction have close relationships with Lévy noise. Some simulation figures are introduced to demonstrate the analytical findings.

  13. Copernicus observations of the N v resonance doublet in 53 early-type stars

    Science.gov (United States)

    Abbott, D. C.; Bohlin, R. C.; Savage, B. D.

    1982-01-01

    UV spectra in the wavelength interval 1170-1270 A are presented for 53 early-type stars ranging in spectral type from O6.5 V to B2.5 IV. The sample includes four Wolf-Rayet stars, seven known Oe-Be stars, and six galactic halo OB stars. A qualitative analysis of the stellar N v doublet reveals that: (1) N v is present in all stars hotter and more luminous than type B0 for the main sequence, B1 for giants, and B2 for supergiants; (2) shell components of N v and an unidentified absorption feature at 1230 A are present in about half of the stars; (3) the column density of N v is well correlated with bolometric luminosity over the spectral range O6 to B2; and (4) the ratio of emission to absorption equivalent width is a factor of 2 smaller in the main sequence stars than in supergiants, which suggests that the wind structure changes as a star evolves. For several stars, this ratio is too small to be explained by traditional wind models.

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

    Science.gov (United States)

    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).

  15. Fractional L\\'{e}vy-driven Ornstein--Uhlenbeck processes and stochastic differential equations

    CERN Document Server

    Fink, Holger; 10.3150/10-BEJ281

    2011-01-01

    Using Riemann-Stieltjes methods for integrators of bounded $p$-variation we define a pathwise integral driven by a fractional L\\'{e}vy process (FLP). To explicitly solve general fractional stochastic differential equations (SDEs) we introduce an Ornstein-Uhlenbeck model by a stochastic integral representation, where the driving stochastic process is an FLP. To achieve the convergence of improper integrals, the long-time behavior of FLPs is derived. This is sufficient to define the fractional L\\'{e}vy-Ornstein-Uhlenbeck process (FLOUP) pathwise as an improper Riemann-Stieltjes integral. We show further that the FLOUP is the unique stationary solution of the corresponding Langevin equation. Furthermore, we calculate the autocovariance function and prove that its increments exhibit long-range dependence. Exploiting the Langevin equation, we consider SDEs driven by FLPs of bounded $p$-variation for $p<2$ and construct solutions using the corresponding FLOUP. Finally, we consider examples of such SDEs, includin...

  16. Alternative Specifications for the Lévy Libor Market Model: An Empirical Investigation

    DEFF Research Database (Denmark)

    Skovmand, David; Nicolato, Elisa

    This paper introduces and analyzes specications of the Lévy Market Model originally proposed by Eberlein and Özkan (2005). An investigation of the term structure of option implied moments rules out the Brownian motion and homogeneous Lévy processes as suitable modeling devices, and consequently...... a variety of more appropriate models is proposed. Besides a diffusive component the models have jump structures with low or high frequency combined with constant or stochastic volatility. The models are subjected to an empirical analysis using a time series of data for Euribor caps. The results...... of the estimation show that pricing performances are improved when a high frequency jump component is incorporated. Specifically, excellent results are achieved with the 4 parameter Sato-Variance Gamma model, which is able to fit an entire surface of caps with an average absolute percentage pricing error of less...

  17. Stochastic expansions using continuous dictionaries: L\\'{e}vy adaptive regression kernels

    CERN Document Server

    Wolpert, Robert L; Tu, Chong; 10.1214/11-AOS889

    2011-01-01

    This article describes a new class of prior distributions for nonparametric function estimation. The unknown function is modeled as a limit of weighted sums of kernels or generator functions indexed by continuous parameters that control local and global features such as their translation, dilation, modulation and shape. L\\'{e}vy random fields and their stochastic integrals are employed to induce prior distributions for the unknown functions or, equivalently, for the number of kernels and for the parameters governing their features. Scaling, shape, and other features of the generating functions are location-specific to allow quite different function properties in different parts of the space, as with wavelet bases and other methods employing overcomplete dictionaries. We provide conditions under which the stochastic expansions converge in specified Besov or Sobolev norms. Under a Gaussian error model, this may be viewed as a sparse regression problem, with regularization induced via the L\\'{e}vy random field p...

  18. Evolution of optimal Lévy-flight strategies in human mental searches

    Science.gov (United States)

    Radicchi, Filippo; Baronchelli, Andrea

    2012-06-01

    Recent analysis of empirical data [Radicchi, Baronchelli, and Amaral, PloS ONE1932-620310.1371/journal.pone.0029910 7, e029910 (2012)] showed that humans adopt Lévy-flight strategies when exploring the bid space in online auctions. A game theoretical model proved that the observed Lévy exponents are nearly optimal, being close to the exponent value that guarantees the maximal economical return to players. Here, we rationalize these findings by adopting an evolutionary perspective. We show that a simple evolutionary process is able to account for the empirical measurements with the only assumption that the reproductive fitness of the players is proportional to their search ability. Contrary to previous modeling, our approach describes the emergence of the observed exponent without resorting to any strong assumptions on the initial searching strategies. Our results generalize earlier research, and open novel questions in cognitive, behavioral, and evolutionary sciences.

  19. Structure of Shocks in Burgers Turbulence with Lévy Noise Initial Data

    Science.gov (United States)

    Abramson, Joshua

    2013-08-01

    We study the structure of the shocks for the inviscid Burgers equation in dimension 1 when the initial velocity is given by Lévy noise, or equivalently when the initial potential is a two-sided Lévy process ψ 0. When ψ 0 is abrupt in the sense of Vigon or has bounded variation with lim sup| h|↓0 h -2 ψ 0( h)=∞, we prove that the set of points with zero velocity is regenerative, and that in the latter case this set is equal to the set of Lagrangian regular points, which is non-empty. When ψ 0 is abrupt we show that the shock structure is discrete. When ψ 0 is eroded we show that there are no rarefaction intervals.

  20. Numerical solution of stochastic differential equations with Poisson and Lévy white noise

    Science.gov (United States)

    Grigoriu, M.

    2009-08-01

    A fixed time step method is developed for integrating stochastic differential equations (SDE’s) with Poisson white noise (PWN) and Lévy white noise (LWN). The method for integrating SDE’s with PWN has the same structure as that proposed by Kim [Phys. Rev. E 76, 011109 (2007)], but is established by using different arguments. The integration of SDE’s with LWN is based on a representation of Lévy processes by sums of scaled Brownian motions and compound Poisson processes. It is shown that the numerical solutions of SDE’s with PWN and LWN converge weakly to the exact solutions of these equations, so that they can be used to estimate not only marginal properties but also distributions of functionals of the exact solutions. Numerical examples are used to demonstrate the applications and the accuracy of the proposed integration algorithms.

  1. Option pricing for stochastic volatility model with infinite activity Lévy jumps

    Science.gov (United States)

    Gong, Xiaoli; Zhuang, Xintian

    2016-08-01

    The purpose of this paper is to apply the stochastic volatility model driven by infinite activity Lévy processes to option pricing which displays infinite activity jumps behaviors and time varying volatility that is consistent with the phenomenon observed in underlying asset dynamics. We specially pay attention to three typical Lévy processes that replace the compound Poisson jumps in Bates model, aiming to capture the leptokurtic feature in asset returns and volatility clustering effect in returns variance. By utilizing the analytical characteristic function and fast Fourier transform technique, the closed form formula of option pricing can be derived. The intelligent global optimization search algorithm called Differential Evolution is introduced into the above highly dimensional models for parameters calibration so as to improve the calibration quality of fitted option models. Finally, we perform empirical researches using both time series data and options data on financial markets to illustrate the effectiveness and superiority of the proposed method.

  2. Procesos de Lévy: propiedades e integración estocástica

    OpenAIRE

    Chávez Bedoya Mercado, Luis Carlos

    2006-01-01

    Los procesos de Lévy son procesos estocásticos que poseen incrementos estacionarios e independientes, y además son continuos en probabilidad. Muchas de las investigaciones teóricas y aplicaciones actuales de los procesos estocásticos en ingeniería, economía y finanzas están basadas en procesos de Lévy; tomamos esto como motivación para profundizar en el estudio de dichos procesos así como para difundir sus aspectos teóricos y prácticos. Asimismo, el cálculo estocástico es una de las principal...

  3. Subcutaneous pedicled V-Y advancement flap for surgical reconstruction of the auricle of the ear.

    Science.gov (United States)

    González-Sixto, B; Pérez-Bustillo, A; Otero-Rivas, M M; Rodríguez-Prieto, M Á

    2014-05-01

    The subcutaneous pedicled V-Y advancement flap is useful for the repair of small and medium-sized defects in areas where it is easy to obtain a good subcutaneous pedicle (upper lip, cheek, eyebrow, and nasal tip and ala). The almost complete absence of subcutaneous tissue on the anterior aspect of the auricle of the ear can limit the use of this approach in this region. We present 4 patients in whom subcutaneous pedicled V-Y advancement flaps were used to repair surgical defects of the helix, scaphoid fossa, and antitragus, achieving a good functional and aesthetic result in all cases. Copyright © 2012 Elsevier España, S.L. and AEDV. All rights reserved.

  4. An Upper Mass Limit on a Red Supergiant Progenitor for the Type II-Plateau Supernova SN 2006my

    Science.gov (United States)

    Leonard, Douglas C.; Gal-Yam, Avishay; Fox, Derek B.; Cameron, P. B.; Johansson, Erik M.; Kraus, Adam L.; Le Mignant, David; van Dam, Marcos A.

    2008-12-01

    We analyze two pre-supernova (SN) and three post-SN high-resolution images of the site of the Type II-Plateau supernova SN 2006my in an effort to either detect the progenitor star or to constrain its properties. Following image registration, we find that an isolated stellar object is not detected at the location of SN 2006my in either of the two pre-SN images. In the first, an I-band image obtained with the Wide-Field and Planetary Camera 2 on board the Hubble Space Telescope, the offset between the SN 2006my location and a detected source (“Source 1”) is too large: ≥0.08‧‧, which corresponds to a confidence level of non-association of 96% from our most liberal estimates of the transformation and measurement uncertainties. In the second, a similarly obtained V-band image, a source is detected (“Source 2”) that has overlap with the SN 2006my location but is definitively an extended object. Through artificial star tests carried out on the precise location of SN 2006my in the images, we derive a 3 σ upper bound on the luminosity of a red supergiant that could have remained undetected in our pre-SN images of log L/L⊙ = 5.10, which translates to an upper bound on such a star’s initial mass of 15 M⊙ from the STARS stellar evolutionary models. Although considered unlikely, we can not rule out the possibility that part of the light comprising Source 1, which exhibits a slight extension relative to other point sources in the image, or part of the light contributing to the extended Source 2, may be due to the progenitor of SN 2006my. Only additional, high-resolution observations of the site taken after SN 2006my has faded beyond detection can confirm or reject these possibilities. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was

  5. Semi-analytical Formulas for the Fundamental Parameters of Galactic Early B Supergiants

    Directory of Open Access Journals (Sweden)

    Zaninetti, L.

    2009-12-01

    Full Text Available The publication of new tables of calibration of some fundamental parameters of Galactic B0-B5 supergiants in the two classes $I_mathrm{a}$ and $I_mathrm{b} $ allows to particularize the eight parameters conjecture that model five fundamental parameters. The numerical expressions for visual magnitude, radius, mass, luminosity and surface gravity are derived for supergiants in the range of temperature between 29700 K and 15200 K. The availability of accurate tables of calibration allows us to estimate the efficiency of the derived formulas in reproducing the observed values. The average efficiency of the new formulas, expressed in percent, is 94 for the visual magnitude, 81 for the mass, 96 for the radius, 99 for the logarithm of the luminosity and 97 for the logarithm of the surface gravity.

  6. A Survey of Local Group Galaxies Currently Forming Stars: \\\\II. UBVRI Photometry of Stars in Seven Dwarfs

    CERN Document Server

    Massey, P; Hodge, P W; Jacoby, G H; McNeill, R T; Smith, R C; Strong, S B; Massey, Philip; Hodge, Paul W.; Jacoby, George H.; Neill, Reagin T. Mc; Strong, Shay B.

    2007-01-01

    We have obtained UBVRI images with the Kitt Peak and Cerro Tololo 4-m telescopes and Mosaic cameras of seven dwarfs in (or near) the Local Group, all of which have known evidence of recent star formation: IC10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus,and Phoenix. We construct color-magnitude diagrams (CMDs) of these systems, as well as neighboring regions that can be used to evaluate the degree of foreground contamination by stars in the Milky Way. Inter-comparison of these CMDs with those of M31, M33, the LMC, and the SMC permits us to determine improved reddening values for a typical OB star found within these galaxies. All of the CMDs reveal a strong or modest number of blue supergiants. All but Pegasus and Phoenix also show the clear presence of red supergiants in the CMD, although IC10 appears to be deficient in these objects given its large WR population. The bright stars of intermediate color in the CMD are badly contaminated by foreground stars (30-100%), and considerable spectroscopy is needed b...

  7. Mid-infrared observations of O-type stars: spectral morphology

    Science.gov (United States)

    Marcolino, W. L. F.; Bouret, J.-C.; Lanz, T.; Maia, D. S.; Audard, M.

    2017-09-01

    We present mid-infrared (mid-IR) observations for a sample of 16 O-type stars. The data were acquired with the NASA Spitzer Space Telescope, using the IRS instrument at moderate resolution (R ∼ 600), covering the range of ∼10-37 μm. Our sample includes early, mid and late O supergiants and dwarfs. We explore for the first time their mid-IR spectral morphology in a quantitative way. We use NLTE expanding atmosphere models to help with line identifications, analyse profile contributions and line-formation regions. The O supergiants present a rich emission line spectra. The most intense features are from hydrogen - 6 α, 7 α and 8 α - that have non-negligible contributions of He i or He ii lines, depending on the spectral type. The spectrum of early O supergiants is a composite of H i and He ii lines, He i lines being absent. On the other hand, late O supergiants present features composed mainly by H i and He i lines. All emission lines are formed throughout the stellar wind. We found that O dwarfs exhibit a featureless mid-IR spectrum. Two stars of our sample exhibit very similar mid-IR features, despite having a very different optical spectral classification. The analysis of O-type stars based on mid-IR spectra alone to infer spectral classes or to estimate physical parameters may thus be prone to substantial errors. Our results may therefore inform spectroscopic observations of massive stars located in heavily obscured regions and help establish an initial framework for observations of massive stars using the Mid-Infrared Instrument on the James Webb Space Telescope.

  8. Integer-valued Lévy processes and low latency financial econometrics

    DEFF Research Database (Denmark)

    Barndorff-Nielsen, Ole; Pollard, David G.; Shephard, Neil

    Motivated by features of low latency data in financial econometrics we study in detail integervalued Lévy processes as the basis of price processes for high frequency econometrics. We propose using models built out of the difference of two subordinators. We apply these models in practice to low...... latency data for a variety of different types of futures contracts.futures markets, high frequency econometrics, low latency data, negative binomial, Skellam, tempered stable...

  9. Stability analysis of a stochastic Gilpin-Ayala model driven by Lévy noise

    Science.gov (United States)

    Zhang, Xinhong; Wang, Ke

    2014-05-01

    A stochastic one-dimensional Gilpin-Ayala model driven by Lévy noise is presented in this paper. Firstly, we show that this model has a unique global positive solution under certain conditions. Then sufficient conditions for the almost sure exponential stability and moment exponential stability of the trivial solution are established. Results show that the jump noise can make the trivial solution stable under some conditions. Numerical example is introduced to illustrate the results.

  10. Fast Fourier Transform Approximation of Foreign Currency Option Pricing Based on Exponential Lévy Model

    Institute of Scientific and Technical Information of China (English)

    CHEN Xu; WAN Jian-ping

    2007-01-01

    To study the approximation of foreign currency option prices when the underlying assets'price dynamics are described by exponential Lévy processes, the convolution representations for option pricing formulas were given, and then the fast Fourier transform(FFT) algorithm was used to get the approximate values of option prices. Finally, a numerical example was given to demonstrate the calculate steps to the option price by FFT.

  11. Stochastic control of Itô-Lévy processes with applications to finance

    OpenAIRE

    Øksendal, Bernt; Sulem, Agnès

    2014-01-01

    We give a short introduction to the stochastic calculus for Itô-Lévy processes and review briefly the two main methods of optimal control of systems described by such processes: (i) Dynamic programming and the Hamilton-Jacobi-Bellman (HJB) equation (ii) The stochastic maximum principle and its associated backward stochastic differential equation (BSDE). The two methods are illustrated by application to the classical portfolio optimization problem in finance. A second application is t...

  12. Transitions in a genetic transcriptional regulatory system under Lévy motion

    OpenAIRE

    Zheng, Yayun; Serdukova, Larissa; Duan, Jinqiao; Kurths, Jürgen

    2016-01-01

    Based on a stochastic differential equation model for a single genetic regulatory system, we examine the dynamical effects of noisy fluctuations, arising in the synthesis reaction, on the evolution of the transcription factor activator in terms of its concentration. The fluctuations are modeled by Brownian motion and α-stable Lévy motion. Two deterministic quantities, the mean first exit time (MFET) and the first escape probability (FEP), are used to analyse the transitions from the low to hi...

  13. Dynamical Mass of the O-Type Supergiant in Zeta Orionis A

    Science.gov (United States)

    2013-01-01

    A&A 554, A52 (2013) DOI: 10.1051/0004-6361/201321434 c© ESO 2013 Astronomy & Astrophysics Dynamical mass of the O-type supergiant in ζ Orionis A C...STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES Astronomy & Astrophysics, 554, A52 (2013),7 pgs 14. ABSTRACT...MJD 51143 to 51160). For the purpose of this work, deriving the orbital radial velocity (RV) variations, spectra within one season have been

  14. HD 187885 and s-process elements in high galactic latitude supergiants

    NARCIS (Netherlands)

    VanWinckel, H; Waelkens, C; Waters, LBFM

    1996-01-01

    We present an accurate LTE chemical analysis of HD 187885 on the basis of high-resolution, high signal-to-noise spectra. The low iron abundance of [Fe/H] = -0.5 confirms the old, low-mass nature of the supergiant. With [C/Fe] = +0.9, [N/Fe] = +0.7, [O/Fe] = +0.6 and above all the high s-process elem

  15. HD 187885 and s-process elements in high galactic latitude supergiants

    NARCIS (Netherlands)

    VanWinckel, H; Waelkens, C; Waters, LBFM

    We present an accurate LTE chemical analysis of HD 187885 on the basis of high-resolution, high signal-to-noise spectra. The low iron abundance of [Fe/H] = -0.5 confirms the old, low-mass nature of the supergiant. With [C/Fe] = +0.9, [N/Fe] = +0.7, [O/Fe] = +0.6 and above all the high s-process

  16. Low-amplitude rotational modulation rather than pulsations in the CoRoT B-type supergiant HD 46769

    Science.gov (United States)

    Aerts, C.; Simón-Díaz, S.; Catala, C.; Neiner, C.; Briquet, M.; Castro, N.; Schmid, V. S.; Scardia, M.; Rainer, M.; Poretti, E.; Pápics, P. I.; Degroote, P.; Bloemen, S.; Østensen, R. H.; Auvergne, M.; Baglin, A.; Baudin, F.; Michel, E.; Samadi, R.

    2013-09-01

    Aims: We aim to detect and interpret photometric and spectroscopic variability of the bright CoRoT B-type supergiant target HD 46769 (V = 5.79). We also attempt to detect a magnetic field in the target. Methods: We analyse a 23-day oversampled CoRoT light curve after detrending and spectroscopic follow-up data using standard Fourier analysis and phase dispersion minimization methods. We determine the fundamental parameters of the star, as well as its abundances from the most prominent spectral lines. We perform a Monte Carlo analysis of spectropolarimetric data to obtain an upper limit of the polar magnetic field, assuming a dipole field. Results: In the CoRoT data, we detect a dominant period of 4.84 d with an amplitude of 87 ppm and some of its (sub-)multiples. Given the shape of the phase-folded light curve and the absence of binary motion, we interpret the dominant variability in terms of rotational modulation, with a rotation period of 9.69 d. Subtraction of the rotational modulation signal does not reveal any sign of pulsations. Our results are consistent with the absence of variability in the Hipparcos light curve. The spectroscopy leads to a projected rotational velocity of 72 ± 2 km s-1 and does not reveal periodic variability or the need to invoke macroturbulent line broadening. No signature of a magnetic field is detected in our data. A field stronger than ~500 G at the poles can be excluded, unless the possible non-detected field were more complex than dipolar. Conclusions: The absence of pulsations and macroturbulence of this evolved B-type supergiant is placed into the context of instability computations and of observed variability of evolved B-type stars. Based on CoRoT space-based photometric data; the CoRoT space mission was developed and operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. Based on observations collected at La Silla Observatory, ESO

  17. vy-driven polling systems and continuous-state branching processes

    Directory of Open Access Journals (Sweden)

    Michel Mandjes

    2011-01-01

    Full Text Available In this paper we consider a ring of N ≥ 1 queues served by a single server in a cyclic order. After having served a queue (according to a service discipline that may vary from queue to queue, there is a switch-over period and then the server serves the next queue and so forth. This model is known in the literature as a polling model.Each of the queues is fed by a non-decreasing Lévy process, which can be different during each of the consecutive periods within the server's cycle. The N-dimensional Lévy processes obtained in this fashion are described by their (joint Laplace exponent, thus allowing for non-independent input streams. For such a system we derive the steady-state distribution of the joint workload at embedded epochs, i.e. polling and switching instants. Using the Kella-Whitt martingale, we also derive the steady-state distribution at an arbitrary epoch.Our analysis heavily relies on establishing a link between fluid (Lévy input polling systems and multi-type Jiřina processes (continuous-state discrete-time branching processes. This is done by properly defining the notion of the branching property for a discipline, which can be traced back to Fuhrmann and Resing. This definition is broad enough to contain the most important service disciplines, like exhaustive and gated.

  18. Phylogenetic analysis using Lévy processes: finding jumps in the evolution of continuous traits.

    Science.gov (United States)

    Landis, Michael J; Schraiber, Joshua G; Liang, Mason

    2013-03-01

    Gaussian processes, a class of stochastic processes including Brownian motion and the Ornstein-Uhlenbeck process, are widely used to model continuous trait evolution in statistical phylogenetics. Under such processes, observations at the tips of a phylogenetic tree have a multivariate Gaussian distribution, which may lead to suboptimal model specification under certain evolutionary conditions, as supposed in models of punctuated equilibrium or adaptive radiation. To consider non-normally distributed continuous trait evolution, we introduce a method to compute posterior probabilities when modeling continuous trait evolution as a Lévy process. Through data simulation and model testing, we establish that single-rate Brownian motion (BM) and Lévy processes with jumps generate distinct patterns in comparative data. We then analyzed body mass and endocranial volume measurements for 126 primates. We rejected single-rate BM in favor of a Lévy process with jumps for each trait, with the lineage leading to most recent common ancestor of great apes showing particularly strong evidence against single-rate BM.

  19. Synchronisation of networked Kuramoto oscillators under stable Lévy noise

    Science.gov (United States)

    Kalloniatis, Alexander C.; Roberts, Dale O.

    2017-01-01

    We study the Kuramoto model on several classes of network topologies examining the dynamics under the influence of Lévy noise. Such noise exhibits heavier tails than Gaussian and allows us to understand how 'shocks' influence the individual oscillator and collective system behaviour. Skewed α-stable Lévy noise, equivalent to fractional diffusion perturbations, are considered. We perform numerical simulations for Erdős-Rényi (ER) and Barabási-Albert (BA) scale free networks of size N = 1000 while varying the Lévy index α for the noise. We find that synchrony now assumes a surprising variety of forms, not seen for Gaussian-type noise, and changing with α: a noise-generated drift, a smooth α dependence of the point of cross-over of ER and BA networks in the degree of synchronisation, and a severe loss of synchronisation at low values of α. We also show that this robustness of the BA network across most values of α can also be understood as a consequence of the Laplacian of the graph working within the fractional Fokker-Planck equation of the linearised system, close to synchrony, with both eigenvalues and eigenvectors alternately contributing in different regimes of α.

  20. Reconstruction in extensive axillary Hidradenitis suppurativa with local fasciocutaneous V-Y advancement flaps

    Directory of Open Access Journals (Sweden)

    Sharma Ramesh

    2006-01-01

    Full Text Available We present our experience with the use of local fasciocutaneous V-Y advancement flaps in the reconstruction of 10 axillae in 6 patients for large defects following wide excision of long-standing Hidradenitis suppurativa of the axilla. The defects were closed with local V-Y subcutaneous island flaps. A single flap from the chest wall was sufficient for moderate defects. However, for larger defects, an additional flap was taken from the medial side of the ipsilateral arm. The donor defects could be closed primarily in all the patients. The local areas of the lateral chest wall and the medial side of the arm have a plentiful supply of cutaneous perforators and the flaps can be designed in a V-Y fashion without resorting to preoperative marking of the perforator. The flaps were freed sufficiently to allow adequate movement for closure of the defects. Although no attempt was made to identify the perforators specifically, many perforators were seen entering the flap. Some perforators can be safely divided to increase reach of the flap. All the flaps survived completely. A follow up of 2.5 years is presented.

  1. SUPERGIANT SHELLS AND MOLECULAR CLOUD FORMATION IN THE LARGE MAGELLANIC CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Dawson, J. R.; Dickey, John M. [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia); McClure-Griffiths, N. M. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield NSW 2122 (Australia); Wong, T. [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States); Hughes, A. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany); Fukui, Y. [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya (Japan); Kawamura, A., E-mail: joanne.dawson@utas.edu.au [National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan)

    2013-01-20

    We investigate the influence of large-scale stellar feedback on the formation of molecular clouds in the Large Magellanic Cloud (LMC). Examining the relationship between H I and {sup 12}CO(J = 1-0) in supergiant shells (SGSs), we find that the molecular fraction in the total volume occupied by SGSs is not enhanced with respect to the rest of the LMC disk. However, the majority of objects ({approx}70% by mass) are more molecular than their local surroundings, implying that the presence of a supergiant shell does on average have a positive effect on the molecular gas fraction. Averaged over the full SGS sample, our results suggest that {approx}12%-25% of the molecular mass in supergiant shell systems was formed as a direct result of the stellar feedback that created the shells. This corresponds to {approx}4%-11% of the total molecular mass of the galaxy. These figures are an approximate lower limit to the total contribution of stellar feedback to molecular cloud formation in the LMC, and constitute one of the first quantitative measurements of feedback-triggered molecular cloud formation in a galactic system.

  2. Probing Hypergiant Mass Loss with Adaptive Optics Imaging & Polarimetry in the Infrared: MMT-Pol and LMIRCam observations of IRC +10420 & VY Canis Majoris

    CERN Document Server

    Shenoy, Dinesh P; Packham, Chris; Lopez-Rodriguez, Enrique

    2015-01-01

    We present 2 - 5 micron adaptive optics (AO) imaging and polarimetry of the famous hypergiant stars IRC +10420 and VY Canis Majoris. The imaging polarimetry of IRC +10420 with MMT-Pol at 2.2 micron resolves nebular emission with intrinsic polarization of 30%, with a high surface brightness indicating optically thick scattering. The relatively uniform distribution of this polarized emission both radially and azimuthally around the star confirms previous studies that place the scattering dust largely in the plane of the sky. Using constraints on scattered light consistent with the polarimetry at 2.2 micron, extrapolation to wavelengths in the 3 - 5 micron band predicts a scattered light component significantly below the nebular flux that is observed in our LBT/LMIRCam 3 - 5 micron AO imaging. Under the assumption this excess emission is thermal, we find a color temperature of ~ 500 K is required, well in excess of the emissivity-modified equilibrium temperature for typical astrophysical dust. The nebular featur...

  3. The discovery of nonthermal radio emission from magnetic Bp-Ap stars

    Science.gov (United States)

    Drake, Stephen A.; Abbott, David C.; Bastian, T. S.; Bieging, J. H.; Churchwell, E.

    1987-01-01

    In a VLA survey of chemically peculiar B- and A-type stars with strong magnetic fields, five of the 34 stars observed have been identified as 6 cm continuum sources. Three of the detections are helium-strong early Bp stars (Sigma Ori E, HR 1890, and Delta Ori C), and two are helium weak, silicon-strong stars with spectral types near A0p (IQ Aur = HD 34452, Babcock's star = HD 215441). The 6 cm luminosities L6 (ergs/s Hz) range from log L6 = 16.2 to 17.9, somewhat less than the OB supergiants and W-R stars. Three-frequency observations indicate that the helium-strong Bp stars are variable nonthermal sources.

  4. The nature of FS CMa stars as revealed by host young clusters

    Science.gov (United States)

    de la Fuente, D.; Najarro, F.; Trombley, C.; Davies, B.; Figer, D. F.

    2015-05-01

    The nature and evolutionary state of the diverse objects displaying the B[e] phenomenon are reasonably known, except for a rare subtype named FS CMa stars. These are surrounded by compact disks of warm dust whose origin is unclear. Although the luminosity of these objects corresponds to main-sequence stars, mass loss rates derived from emission lines are 2 orders of magnitude larger than predicted by wind theory. Hitherto, FS CMa stars have been only found in isolation, which hinders the study of their nature. In this contribution, we present the discovery of FS CMa stars in two young Galactic clusters, which host Wolf-Rayet stars and OB supergiants. Membership to these coeval populations allows us to constrain the luminosity, circumstellar extinction and age of FS CMa stars in an unprecedented way. Due to their relatively low brightness when compared with coeval evolved massive stars, a high number of these objects may remain unnoticed in young clusters.

  5. The Puppis region and the last crusade for faint OB stars

    Science.gov (United States)

    Orsatti, Ana M.

    1992-08-01

    UBV photoelectric and photographic measurements of OB stars from a list of 397 OB stars and 5 early-type supergiants and from the Luminous Stars Survey are presented. The galactic distribution of the OB stars in the region shows concentrations around the open clusters Ruprecht 44 and Ruprecht 55, and the presence of an important grouping of young stars located far below the plane. The distribution in latitude shows that young stars in the region are not restricted to a thin sheet around the plane but are spread over negative latitudes reaching at least b = -5 deg. In longitude, the OB distribution exhibits a concentration of Ob stars in the interval 244-251 deg; this is argued to be due to the presence of the local arm extension.

  6. Evolution of intermediate mass and massive binary stars: physics, mass loss, and rotation

    CERN Document Server

    Vanbeveren, D

    2016-01-01

    In the present review we discuss the past and present status of the interacting OB-type binary frequency. We critically examine the popular idea that Be-stars and supergiant sgB[e] stars are binary evolutionary products. The effects of rotation on stellar evolution in general, stellar population studies in particular, and the link with binaries will be evaluated. Finally a discussion is presented of massive double compact star binary mergers as possible major sites of chemical enrichment of r-process elements and as the origin of recent aLIGO GW events.

  7. Pulsations as a mass-loss trigger in evolved hot stars

    CERN Document Server

    Kraus, Michaela; Haucke, Maximiliano; Cidale, Lydia; Venero, Roberto; Fernandes, Marcelo Borges; Tomic, Sanja; Cure, Michel

    2013-01-01

    During the post-main sequence evolution massive stars pass through several short-lived phases, in which they experience enhanced mass loss in the form of clumped winds and mass ejection events of unclear origin. The discovery that stars populating the blue, luminous part of the Hertzsprung-Russell diagram can pulsate hence suggests that stellar pulsations might influence or trigger enhanced mass loss and eruptions. We present recent results for two objects in different phases: a B[e] star at the end of the main sequence and a B-type supergiant.

  8. From B[e] to A[e]. On the peculiar variations of the SMC supergiant LHA 115-S 23 (AzV 172)

    CERN Document Server

    Kraus, Michaela; Kubat, Jiri; de Araujo, Francisco X

    2008-01-01

    Optical observations from 1989 of the SMC B[e] supergiant star S23 revealed the presence of photospheric HeI absorption lines. In our high-resolution optical spectra from 2000, however, we could not identify any HeI line. The observed changes in spectral behaviour of S23 lead to different spectral classifications at different observing epochs. The aim of this research is, therefore, to find and discuss possible scenarios that might cause a disappearance of the photospheric HeI absorption lines within a period of only 11 years. From our high-resolution optical spectra, we perform a detailed investigation of the different spectral appearances of S23. We further determine the projected rotational velocities of S23 in the two epochs of observations. Based on its spectral appearance in 2000, we classify S23 as A1Ib star with an effective temperature of about 9000 K. Further, an interstellar extinction value of E(B-V) = 0.03 is derived. This is considerably lower than the previously published value, which means tha...

  9. Identification of the Red Supergiant Progenitor of Supernova 2005cs: Do the Progenitors of Type II-P Supernovae Have Low Mass?

    CERN Document Server

    Li, W; Filippenko, A V; Cuillandre, J C; Jha, S; Bloom, J S; Riess, A G; Livio, M; Li, Weidong; Dyk, Schuyler D. Van; Filippenko, Alexei V.; Cuillandre, Jean-Charles; Jha, Saurabh; Bloom, Joshua S.; Riess, Adam G.; Livio, Mario

    2006-01-01

    The stars that end their lives as supernovae (SNe) have been directly observed in only a handful of cases, due mainly to the extreme difficulty in identifying them in images obtained prior to the SN explosions. Here we report the identification of the progenitor for the recent Type II-plateau (core-collapse) SN 2005cs in pre-explosion archival images of the Whirlpool Galaxy (M51) obtained with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). From high-quality ground-based images of the SN from the Canada-France-Hawaii Telescope, we precisely determine the position of the SN and are able to isolate the SN progenitor to within 0".04 in the HST/ACS optical images. We further pinpoint the SN location to within 0".005 from HST/ACS ultraviolet images of the SN, confirming our progenitor identification. From photometry of the SN progenitor obtained with the pre-SN ACS images, and also limits to its brightness in pre-SN HST/NICMOS images, we infer that the progenitor is a red supergiant star of spe...

  10. Observations and theory of mass loss in late-type stars

    Science.gov (United States)

    Hartmann, L.

    1981-01-01

    The presented review is mainly concerned with the ubiquitous mass loss which occurs during most of a star's existence as a cool giant or supergiant. Observations of mass loss are considered, taking into account wind components and kinematics, and the temperature structure of cool winds. Theories of mass loss are examined, giving attention to radiation pressure on dust, radiation pressure in Lyman alpha, and magnetic wave-driven winds. It is pointed out that the study of mass loss from late-type stars appears to be entering a promising new phase. In this phase, the behavior of cool giants and supergiants is considered from a solar perspective, a perspective which contains important implications concerning the nature of solar activity.

  11. Observational consequences of turbulent pressure in the envelopes of massive stars

    CERN Document Server

    Grassitelli, Luca; Simon-Diaz, Sergio; Langer, Norbert; Castro, Norberto; Sanyal, Debashis

    2015-01-01

    The major mass fraction of the envelope of hot luminous stars is radiatively stable. However, the partial ionisation of hydrogen, helium and iron gives rise to extended sub-surface convection zones in all of them. In this work, we investigate the effect of the pressure induced by the turbulent motion in these zones based on the mixing length theory, and search for observable consequences. We find that the turbulent pressure fraction can amount up to ~5% in OB supergiants, and to ~30% in cooler supergiants. The resulting structural changes are, however, not significantly affecting the evolutionary tracks compared to previous calculations. Instead, a comparison of macroturbulent velocities derived from high quality spectra of OB stars with the turbulent pressure fraction obtained in corresponding stellar models reveals a strong correlation of these two quantities. We discuss a possible physical connection, and conclude that turbulent pressure fluctuations may drive high-order oscillations, which - as conjecture...

  12. External Shaping of Circumstellar Envelopes of Evolved Stars

    Science.gov (United States)

    Cox, N. L. J.

    2015-08-01

    The circumstellar envelopes of asymptotic giant branch (AGB) stars and red supergiants (RSGs) are complex chemical and physical environments, and the specifics of their mass-loss history are important for both stellar and galactic evolution. One key aspect in this is to understand how the circumstellar medium of these stars can be shaped and affected by both internal and external mechanisms. These influences can skew our view on the (dust) chemistry and mass-loss history of these stars, and hence their role in the chemical enrichment of galaxies. This contribution focuses on the external mechanism related to the interaction between the slow dusty stellar wind and the local ambient medium. I will discuss what recent observations and hydrodynamical simulations have revealed and how these can help us learn more about AGB stars and RSGs, as well as the interstellar medium (ISM).

  13. Massive Stars in the W33 Giant Molecular Complex

    CERN Document Server

    Messineo, Maria; Figer, Donald F; Kudritzki, Rolf-Peter; Najarro, Francisco; Rich, R Michael; Menten, Karl M; Ivanov, Valentin D; Valenti, Elena; Trombley, Christine; Chen, C -H Rosie; Davies, Ben

    2015-01-01

    Rich in HII regions, giant molecular clouds are natural laboratories to study massive stars and sequential star formation. The Galactic star forming complex W33 is located at l=~12.8deg and at a distance of 2.4 kpc, has a size of ~10 pc and a total mass of (~0.8 - ~8.0) X 10^5 Msun. The integrated radio and IR luminosity of W33 - when combined with the direct detection of methanol masers, the protostellar object W33A, and protocluster embedded within the radio source W33 main - mark the region out as a site of vigorous ongoing star formation. In order to assess the long term star formation history, we performed an infrared spectroscopic search for massive stars, detecting for the first time fourteen early-type stars, including one WN6 star and four O4-7 stars. The distribution of spectral types suggests that this population formed during the last ~2-4 Myr, while the absence of red supergiants precludes extensive star formation at ages 6-30 Myr. This activity appears distributed throughout the region and does ...

  14. Evidence of the evolved nature of the B[e] star MWC 137

    Energy Technology Data Exchange (ETDEWEB)

    Muratore, M. F.; Arias, M. L.; Cidale, L. [Departamento de Espectroscopía Estelar, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, and Instituto de Astrofísica de La Plata, CCT La Plata, CONICET-UNLP, Paseo del Bosque S/N, B1900FWA, La Plata (Argentina); Kraus, M.; Oksala, M. E. [Astronomický ústav, Akademie věd České Republiky, Fričova 298, 251 65 Ondřejov (Czech Republic); Fernandes, M. Borges [Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro (Brazil); Liermann, A., E-mail: fmuratore@carina.fcaglp.unlp.edu.ar [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany)

    2015-01-01

    The evolutionary phase of B[e] stars is difficult to establish due to the uncertainties in their fundamental parameters. For instance, possible classifications for the Galactic B[e] star MWC 137 include pre-main-sequence and post-main-sequence phases, with a large range in luminosity. Our goal is to clarify the evolutionary stage of this peculiar object, and to study the CO molecular component of its circumstellar medium. To this purpose, we modeled the CO molecular bands using high-resolution K-band spectra. We find that MWC 137 is surrounded by a detached cool (T=1900±100 K) and dense (N=(3±1)×10{sup 21} cm{sup −2}) ring of CO gas orbiting the star with a rotational velocity, projected to the line of sight, of 84 ± 2 km s{sup −1}. We also find that the molecular gas is enriched in the isotope {sup 13}C, excluding the classification of the star as a Herbig Be. The observed isotopic abundance ratio ({sup 12}C/{sup 13}C = 25 ± 2) derived from our modeling is compatible with a proto-planetary nebula, main-sequence, or supergiant evolutionary phase. However, based on some observable characteristics of MWC 137, we propose that the supergiant scenario seems to be the most plausible. Hence, we suggest that MWC 137 could be in an extremely short-lived phase, evolving from a B[e] supergiant to a blue supergiant with a bipolar ring nebula.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-06-10

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

  16. vy Stable Distribution and [0, 2] Power Law Dependence of Acoustic Absorption on Frequency in Various Lossy Media

    Institute of Scientific and Technical Information of China (English)

    CHEN Wen

    2005-01-01

    @@ Absorption of acoustic wave propagation in a large variety of lossy media is characterized by an empirical power law function of frequency, αo|ω|y. It has long been noted that the exponent y ranges from 0 to 2 for diverse media. Recently, the present author [J. Acoust. Soc. Am. 115 (2004) 1424] developed a fractional Laplacian wave equation to accurately model the power law dissipation, which can be further reduced to the fractional Laplacian diffusion equation. The latter is known underlying the Lévy stable distribution theory. Consequently,the parameters y is found to be the Lévy stability index, which is known to be bounded within 0 < y ≤ 2. This finding first provides a theoretical explanation of empirical observations y ∈ [0, 2]. Statistically, the frequencydependent absorption can thus be understood a Lévy stable process, where the parameter y describes the fractal nature of attenuative media.

  17. Backward Stochastic Differential Equations and Feynman-Kac Formula for Multidimensional L\\'{e}vy Processes, with Applications in Finance

    CERN Document Server

    Lin, Jianzhong

    2012-01-01

    In this paper we show the existence and form uniqueness of a solution for multidimensional backward stochastic differential equations driven by a multidimensional L\\'{e}vy process with moments of all orders. The results are important from a pure mathematical point of view as well as in the world of finance: an application to Clark-Ocone and Feynman-Kac formulas for multidimensional L\\'{e}vy processes is presented. Moreover, the Feynman-Kac formula and the related partial differential integral equations provide an analogue of the famous Black-Scholes partial differential equation and thus can be used for the purpose of option pricing in a multidimensional L\\'{e}vy market.

  18. Fluctuation effects in the pair-annihilation process with Lévy dynamics.

    Science.gov (United States)

    Homrighausen, Ingo; Winkler, Anton A; Frey, Erwin

    2013-07-01

    We investigate the density decay in the pair-annihilation process A+A→∅ in the case when the particles perform anomalous diffusion on a cubic lattice. The anomalous diffusion is realized via Lévy flights, which are characterized by long-range jumps and lead to superdiffusive behavior. As a consequence, the critical dimension depends continuously on the control parameter of the Lévy flight distribution. This instance is used to study the system close to the critical dimension by means of the nonperturbative renormalization group theory. Close to the critical dimension, the assumption of well-stirred reactants is violated by anticorrelations between the particles, and the law of mass action breaks down. The breakdown of the law of mass action is known to be caused by long-range fluctuations. We identify three interrelated consequences of these fluctuations. First, despite being a nonuniversal quantity and thus depending on the microscopic details, the renormalized reaction rate λ(0) can be approximated by a universal law close to the critical dimension. The emergence of universality relies on the fact that long-range fluctuations suppress the influence of the underlying microscopic details. Second, as criticality is approached, the macroscopic reaction rate decreases such that the law of mass action loses its significance. And third, additional nonanalytic power law corrections complement the analytic law of mass action term. An increasing number of those corrections accumulate and give an essential contribution as the critical dimension is approached. We test our findings for two implementations of Lévy flights that differ in the way they cross over to the normal diffusion in the limit σ→2.

  19. The intrinsic values and color excesses of (B-V) for 115 F-K supergiants

    Science.gov (United States)

    Kelsall, T.

    1972-01-01

    Color excesses in B-V are determined indirectly from a study of Stromgren's b-y color for a sample of F0 - K5 supergiants. The resulting E(B-V)'s are estimated to have an expected precision of + or - 0.05. With the calculated color excesses and the observed values of B-V given in various catalogs, the run of B-V with spectral type is obtained. This B-V/(spectral type) relationship is compared with those found previously by other investigators.

  20. Sodium Enrichment in Yellow Supergiants: a Perspective from the Uncertainties of Reaction Rates

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Sodium overabundance in yellow supergiants has stumped people for more than 20 years. The purpose of this paper is to explore this problem from the perspective of nuclear physics. We investigate carefully the CNO and NeNa cycles that are responsible for sodium production. We investigate some key reactions in the appropriate network. We show whether and how the sodium output can be affected by the rate uncertainties in these reactions. In this way, we evaluate if a reaction is important enough to deserve a better determination of its rate in terrestrial laboratories.

  1. Synchronization of Coupled Stochastic Systems Driven by α-Stable Lévy Noises

    Directory of Open Access Journals (Sweden)

    Anhui Gu

    2013-01-01

    Full Text Available The synchronization of the solutions to coupled stochastic systems of N-Marcus stochastic ordinary differential equations which are driven by α-stable Lévy noises is investigated (N∈ℕ,1<α<2. We obtain the synchronization between two solutions and among different components of solutions under certain dissipative conditions. The synchronous phenomena persist no matter how large the intensity of the environment noises. These results generalize the work of two Marcus canonical equations in X. M. Liu et al.' s (2010.

  2. Convexity of Ruin Probability and Optimal Dividend Strategies for a General Lévy Process

    Science.gov (United States)

    Yuen, Kam Chuen; Shen, Ying

    2015-01-01

    We consider the optimal dividends problem for a company whose cash reserves follow a general Lévy process with certain positive jumps and arbitrary negative jumps. The objective is to find a policy which maximizes the expected discounted dividends until the time of ruin. Under appropriate conditions, we use some recent results in the theory of potential analysis of subordinators to obtain the convexity properties of probability of ruin. We present conditions under which the optimal dividend strategy, among all admissible ones, takes the form of a barrier strategy. PMID:26351655

  3. Differential Evolution with Adaptive Mutation and Parameter Control Using Lévy Probability Distribution

    Institute of Scientific and Technical Information of China (English)

    Ren-Jie He; Zhen-Yu Yang

    2012-01-01

    Differential evolution (DE) has become a very popular and effective global optimization algorithm in the area of evolutionary computation.In spite of many advantages such as conceptual simplicity,high efficiency and ease of use,DE has two main components,i.e.,mutation scheme and parameter control,which significantly influence its performance.In this paper we intend to improve the performance of DE by using carefully considered strategies for both of the two components.We first design an adaptive mutation scheme,which adaptively makes use of the bias of superior individuals when generating new solutions.Although introducing such a bias is not a new idea,existing methods often use heuristic rules to control the bias.They can hardly maintain the appropriate balance between exploration and exploitation during the search process,because the preferred bias is often problem and evolution-stage dependent.Instead of using any fixed rule,a novel strategy is adopted in the new adaptive mutation scheme to adjust the bias dynamically based on the identified local fitness landscape captured by the current population.As for the other component,i.e.,parameter control,we propose a mechanism by using the Lévy probability distribution to adaptively control the scale factor F of DE.For every mutation in each generation,an Fi is produced from one of four different Lévy distributions according to their historical performance.With the adaptive mutation scheme and parameter control using Lévy distribution as the main components,we present a new DE variant called Lévy DE (LDE).Experimental studies were carried out on a broad range of benchmark functions in global numerical optimization.The results show that LDE is very competitive,and both of the two main components have contributed to its overall performance.The scalability of LDE is also discussed by conducting experiments on some selected benchmark functions with dimensions from 30 to 200.

  4. Error analysis in Fourier methods for option pricing for exponential Lévy processes

    KAUST Repository

    Crocce, Fabian

    2015-01-07

    We derive an error bound for utilising the discrete Fourier transform method for solving Partial Integro-Differential Equations (PIDE) that describe european option prices for exponential Lévy driven asset prices. We give sufficient conditions for the existence of a L? bound that separates the dynamical contribution from that arising from the type of the option n in question. The bound achieved does not rely on information of the asymptotic behaviour of option prices at extreme asset values. In addition, we demonstrate improved numerical performance for select examples of practical relevance when compared to established bounding methods.

  5. Convexity of Ruin Probability and Optimal Dividend Strategies for a General Lévy Process

    Directory of Open Access Journals (Sweden)

    Chuancun Yin

    2015-01-01

    Full Text Available We consider the optimal dividends problem for a company whose cash reserves follow a general Lévy process with certain positive jumps and arbitrary negative jumps. The objective is to find a policy which maximizes the expected discounted dividends until the time of ruin. Under appropriate conditions, we use some recent results in the theory of potential analysis of subordinators to obtain the convexity properties of probability of ruin. We present conditions under which the optimal dividend strategy, among all admissible ones, takes the form of a barrier strategy.

  6. Chaotic Teaching-Learning-Based Optimization with Lévy Flight for Global Numerical Optimization

    Directory of Open Access Journals (Sweden)

    Xiangzhu He

    2016-01-01

    Full Text Available Recently, teaching-learning-based optimization (TLBO, as one of the emerging nature-inspired heuristic algorithms, has attracted increasing attention. In order to enhance its convergence rate and prevent it from getting stuck in local optima, a novel metaheuristic has been developed in this paper, where particular characteristics of the chaos mechanism and Lévy flight are introduced to the basic framework of TLBO. The new algorithm is tested on several large-scale nonlinear benchmark functions with different characteristics and compared with other methods. Experimental results show that the proposed algorithm outperforms other algorithms and achieves a satisfactory improvement over TLBO.

  7. Chaotic Teaching-Learning-Based Optimization with Lévy Flight for Global Numerical Optimization.

    Science.gov (United States)

    He, Xiangzhu; Huang, Jida; Rao, Yunqing; Gao, Liang

    2016-01-01

    Recently, teaching-learning-based optimization (TLBO), as one of the emerging nature-inspired heuristic algorithms, has attracted increasing attention. In order to enhance its convergence rate and prevent it from getting stuck in local optima, a novel metaheuristic has been developed in this paper, where particular characteristics of the chaos mechanism and Lévy flight are introduced to the basic framework of TLBO. The new algorithm is tested on several large-scale nonlinear benchmark functions with different characteristics and compared with other methods. Experimental results show that the proposed algorithm outperforms other algorithms and achieves a satisfactory improvement over TLBO.

  8. Optimal harvesting of a stochastic delay logistic model with Lévy jumps

    Science.gov (United States)

    Qiu, Hong; Deng, Wenmin

    2016-10-01

    The optimal harvesting problem of a stochastic time delay logistic model with Lévy jumps is considered in this article. We first show that the model has a unique global positive solution and discuss the uniform boundedness of its pth moment with harvesting. Then we prove that the system is globally attractive and asymptotically stable in distribution under our assumptions. Furthermore, we obtain the existence of the optimal harvesting effort by the ergodic method, and then we give the explicit expression of the optimal harvesting policy and maximum yield.

  9. vy stable two-sided distributions: exact and explicit densities for asymmetric case.

    Science.gov (United States)

    Górska, K; Penson, K A

    2011-06-01

    We investigate functions g(α,β;x) which are heavy-tailed Lévy stable probability distributions of index 0econophysics, geology, hydrology, internet traffic, dynamics of human relations, etc. We present an ensemble of exact and explicit solutions of g(α,β;x) for all admissible rational values of α and β. We reproduce all the previously known cases and furnish distributions for values α and β which were previously inaccessible. We point out many instances of experimental and statistical data that could be described by our results.

  10. Comparison principles for integro-differential equations with L{\\'e}vy operators - the case of spacial depending jumps -

    CERN Document Server

    Arisawa, M

    2010-01-01

    A comparison principle for the integro-differential equation with the L{\\'e}vy operator corresponding to the spacial depending jump process is presented in this paper. The jump $\\beta(x,z)$ at a point $x$ and the L{\\'e}vy measure $dq(z)$ satisfy conditions given independently for each of them, which is a major difference from other works. Moreover, a useful form of the viscosity solution is presented, which is equivalent to more "classical" definitions, and is used to prove the comparison principle easily.

  11. Aesthetic Subunit Reconstruction Facilitated with V-Y Island Advancement Flaps on the Face: A Case Report

    Directory of Open Access Journals (Sweden)

    Jaime Eduardo Pachón Suárez, MD

    2014-05-01

    Full Text Available Summary: The reconstruction of complex facial soft-tissue defects is a challenge that is often encountered by the plastic surgeon. Careful planning and knowledge of the aesthetic subunits that border the defect are paramount to achieve optimal results. We present a case of a 56-year-old woman who underwent excision of a large disfiguring chronic xanthelasma that extended from canthus to canthus across the nasal bridge. An aesthetic outcome was achieved by use of bilateral V-Y nasolabial flaps combined with a V-Y glabella advancement, which allowed for a tension-free like-for-like subunit reconstruction.

  12. e-MERLIN 21cm constraints on the mass-loss rates of OB stars in Cyg OB2

    CERN Document Server

    Morford, Jack; Prinja, Raman; Blomme, Ronnie; Yates, Jeremy

    2016-01-01

    We present e-MERLIN 21 cm (L-band) observations of single luminous OB stars in the Cygnus OB2 association, from the COBRaS Legacy programme. The radio observations potentially offer the most straightforward, least model-dependent, determinations of mass-loss rates, and can be used to help resolve current discrepancies in mass-loss rates via clumped and structured hot star winds. We report here that the 21 cm flux densities of O3 to O6 supergiant and giant stars are less than ~ 70 microJy. These fluxes may be translated to `smooth' wind mass-loss upper limits of ~ 4.4 - 4.8 x 10^(-6) M_sol/yr for O3 supergiants and < 2.9 x 10^(-6) M_sol/yr for B0 to B1 supergiants. The first ever resolved 21 cm detections of the hypergiant (and LBV candidate) Cyg OB2 #12 are discussed; for multiple observations separated by 14 days, we detect a ~ 69% increase in its flux density. Our constraints on the upper limits for the mass-loss rates of evolved OB stars in Cyg OB2 support the model that the inner wind region close to t...

  13. e-MERLIN 21 cm constraints on the mass-loss rates of OB stars in Cyg OB2

    Science.gov (United States)

    Morford, J. C.; Fenech, D. M.; Prinja, R. K.; Blomme, R.; Yates, J. A.

    2016-11-01

    We present e-MERLIN 21 cm (L-band) observations of single luminous OB stars in the Cygnus OB2 association, from the Cyg OB2 Radio Survey Legacy programme. The radio observations potentially offer the most straightforward, least model-dependent, determinations of mass-loss rates, and can be used to help resolve current discrepancies in mass-loss rates via clumped and structured hot star winds. We report here that the 21 cm flux densities of O3 to O6 supergiant and giant stars are less than ˜70 μJy. These fluxes may be translated to `smooth' wind mass-loss upper limits of ˜4.4-4.8 × 10-6 M⊙ yr -1 for O3 supergiants and ≲2.9 × 10-6 M⊙ yr -1 for B0 to B1 supergiants. The first ever resolved 21 cm detections of the hypergiant (and luminous blue variable candidate) Cyg OB2 #12 are discussed; for multiple observations separated by 14 d, we detect an ˜69 per cent increase in its flux density. Our constraints on the upper limits for the mass-loss rates of evolved OB stars in Cyg OB2 support the model that the inner wind region close to the stellar surface (where Hα forms) is more clumped than the very extended geometric region sampled by our radio observations.

  14. Is mass loss from red giant stars dust driven?

    Science.gov (United States)

    Yates, J. A.

    1992-12-01

    Long period variable stars on the Asymptotic Giant Branch are observed to be losing mass in the form of cool dusty molecular stellar winds at rates from 10-7 to 10-4 Msunyr-1. The driving force for this mass loss is thought to be radiation pressure on dust particles. The dust transfers its momentum to gas molecules via collisions. This paper discusses the existing evidence for this scenario. New results, from analysis of 22 GHz H2O maser observations made by Merlin, show that the cruical acceleration past the stellar escape velocity of the central star takes place in the inner circumstellar envelope around the central star. The analysis of the velocity fields of the circumstellar envelopes of VX Sgr and VY CMa using the model described by Chapman and Cohen (1986) are discussed.

  15. VLT spectroscopy of massive stars in NGC55

    Directory of Open Access Journals (Sweden)

    N. Castro

    2007-01-01

    Full Text Available We present the first spectroscopy study of massive stars in NGC55. The data, taken with VLT-FORS2 allow us to provide spectral classification for 200 objects located through- out the galaxy. From this sample, suitable B-type supergiants are chosen for subsequent higher resolution spectroscopic observations that will enable a quantitative study. The stellar abundances will be a key point in the study of galaxy chemical evolution. We also discuss how GTC-OSIRIS can be a valuable tool for similar studies.

  16. A Spectroscopic Survey of Massive Stars in M31 and M33

    Science.gov (United States)

    Massey, Philip; Neugent, Kathryn F.; Smart, Brianna M.

    2016-09-01

    We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of them for the first time. Our study has identified many foreground stars, and established membership for hundreds of early- and mid-type supergiants. We have also found nine new candidate luminous blue variables and a previously unrecognized Wolf-Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates, and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars are more rare and fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20-40 M ⊙ range. The spectroscopic observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. MMT telescope time was granted by NOAO, through the Telescope System Instrumentation Program (TSIP). TSIP is funded by the National Science Foundation. This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory.

  17. THE MASSIVE STAR POPULATION IN M101. III. SPECTRA AND PHOTOMETRY OF THE LUMINOUS AND VARIABLE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Grammer, Skyler H.; Humphreys, Roberta M. [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota , Minneapolis, MN 55455 (United States); Gerke, Jill, E-mail: grammer@astro.umn.edu, E-mail: roberta@umn.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

    2015-05-15

    We discuss moderate-resolution spectra, multicolor photometry, and light curves of 31 of the most luminous stars and variables in the giant spiral M101. The majority are intermediate A- to F-type supergiants. We present new photometry and light curves for three known “irregular blue variables,” V2, V4, and V9, and identify a new candidate. Their spectra and variability confirm that they are luminous blue variable (LBV) candidates and V9 may be in an LBV-like maximum light state or eruption.

  18. Atmospheric Heating and Wind Acceleration in Cool Evolved Stars

    CERN Document Server

    Airapetian, Vladimir S

    2014-01-01

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

  19. Triggered star formation in giant HI supershells: ionized gas

    CERN Document Server

    Egorov, O V; Moiseev, A V

    2015-01-01

    We considered the regions of triggered star formation inside kpc-sized HI supershells in three dwarf galaxies: IC 1613, IC 2574 and Holmberg II. The ionized and neutral gas morphology and kinematics were studied based on our observations with scanning Fabry-Perot interferometer at the SAO RAS 6-m telescope and 21 cm archival data of THINGS and LITTLE THINGS surveys. The qualitative analysis of the observational data performed in order to highlight the two questions: why the star formation occurred very locally in the supershells, and how the ongoing star formation in HI supershells rims influence its evolution? During the investigation we discovered the phenomenon never observed before in galaxies IC 2574 and Holmberg II: we found faint giant (kpc-sized) ionized shells in H-alpha and [SII]6717,6731 lines inside the supergiant HI shells.

  20. Dynamical mass of the O-type supergiant in Zeta Orionis A

    CERN Document Server

    Hummel, C A; Nieva, M -F; Stahl, O; van Belle, G; Zavala, R T

    2013-01-01

    A close companion of Zeta Orionis A was found in 2000 with the Navy Precision Optical Interferometer (NPOI), and shown to be a physical companion. Because the primary is a supergiant of type O, for which dynamical mass measurements are very rare, the companion was observed with NPOI over the full 7-year orbit. Our aim was to determine the dynamical mass of a supergiant that, due to the physical separation of more than 10 AU between the components, cannot have undergone mass exchange with the companion. The interferometric observations allow measuring the relative positions of the binary components and their relative brightness. The data collected over the full orbital period allows all seven orbital elements to be determined. In addition to the interferometric observations, we analyzed archival spectra obtained at the Calar Alto, Haute Provence, Cerro Armazones, and La Silla observatories, as well as new spectra obtained at the VLT on Cerro Paranal. In the high-resolution spectra we identified a few lines tha...

  1. The Intermediate Luminosity Optical Transient SN 2010da: The Progenitor, Eruption and Aftermath of an Unusual Supergiant High-mass X-ray Binary

    Science.gov (United States)

    Villar, Victoria; Berger, Edo; Chornock, Ryan; Laskar, Tanmoy; Margutti, Raffaella; Brown, Peter J.

    2016-06-01

    We present high- and medium-resolution optical spectroscopy, optical/UV imaging and archival Chandra, Hubble and Spitzer observations of the intermediate luminosity optical transient (ILOT) SN 2010da, discovered in the nearby galaxy NGC 300 (d=1.86 Mpc). SN 2010da had a peak absolute magnitude of M ~ -10.4 mag, dimmer than other recent ILOTs and supernova impostors. We detect hydrogen Balmer, Paschen and Ca II emission lines in our high-resolution spectra, which indicate a dusty and complex circumstellar environment. Based on SN 2010da's light curve and multi-epoch SEDs, we conclude that the progenitor of SN 2010da is a ~10-12 Msol yellow supergiant possibly transitioning into a blue loop phase. Since the 2010 eruption, the star has brightened by a factor of ~5 and remains highly variable in the optical. SN 2010da is a unique ILOT which seems to stem from a different physical origin than red SN 2008S-like events and luminous blue variable outbursts. Furthermore, we detect SN 2010da in archival Swift observations as an ultraluminous X-ray source. We additionally attribute He II 4686 and coronal Fe emission in addition to a steady X-ray luminosity of ~10^{37} erg/s to the presence of a compact companion.

  2. The Intermediate Luminosity Optical Transient SN 2010da: The Progenitor, Eruption, and Aftermath of a Peculiar Supergiant High-mass X-Ray Binary

    Science.gov (United States)

    Villar, V. A.; Berger, E.; Chornock, R.; Margutti, R.; Laskar, T.; Brown, P. J.; Blanchard, P. K.; Czekala, I.; Lunnan, R.; Reynolds, M. T.

    2016-10-01

    We present optical spectroscopy, ultraviolet-to-infrared imaging, and X-ray observations of the intermediate luminosity optical transient (ILOT) SN 2010da in NGC 300 (d = 1.86 Mpc) spanning from ‑6 to +6 years relative to the time of outburst in 2010. Based on the light-curve and multi-epoch spectral energy distributions of SN 2010da, we conclude that the progenitor of SN 2010da is a ≈10–12 M ⊙ yellow supergiant possibly transitioning into a blue-loop phase. During outburst, SN 2010da had a peak absolute magnitude of M bol ≲ ‑10.4 mag, dimmer than other ILOTs and supernova impostors. We detect multi-component hydrogen Balmer, Paschen, and Ca ii emission lines in our high-resolution spectra, which indicate a dusty and complex circumstellar environment. Since the 2010 eruption, the star has brightened by a factor of ≈5 and remains highly variable in the optical. Furthermore, we detect SN 2010da in archival Swift and Chandra observations as an ultraluminous X-ray source (L X ≈ 6 × 1039 erg s‑1). We additionally attribute He ii 4686 Å and coronal Fe emission lines in addition to a steady X-ray luminosity of ≈1037 erg s‑1 to the presence of a compact companion.

  3. The Intermediate Luminosity Optical Transient SN 2010da: The Progenitor, Eruption and Aftermath of a Peculiar Supergiant High-mass X-ray Binary

    CERN Document Server

    Villar, V Ashley; Chornock, Ryan; Margutti, Raffaella; Laskar, Tanmoy; Brown, Peter J; Blanchard, Peter K; Czekala, Ian; Lunnan, Ragnhild; Reynolds, Mark T

    2016-01-01

    We present optical spectroscopy, ultraviolet to infrared imaging and X-ray observations of the intermediate luminosity optical transient (ILOT) SN 2010da in NGC 300 (d=1.86 Mpc) spanning from -6 to +6 years relative to the time of outburst in 2010. Based on the light curve and multi-epoch SEDs of SN 2010da, we conclude that the progenitor of SN 2010da is a ~10-12 Msol yellow supergiant possibly transitioning into a blue loop phase. During outburst, SN 2010da had a peak absolute magnitude of M<-10.4 mag, dimmer than other ILOTs and supernova impostors. We detect multi-component hydrogen Balmer, Paschen, and Ca II emission lines in our high-resolution spectra, which indicate a dusty and complex circumstellar environment. Since the 2010 eruption, the star has brightened by a factor of ~5 and remains highly variable in the optical. Furthermore, we detect SN 2010da in archival Swift and Chandra observations as an ultraluminous X-ray source (L~6x10^{39} erg/s). We additionally attribute He II 4686 Angstrom and c...

  4. Orbital motions and light curves of young binaries XZ Tau and VY Tau

    CERN Document Server

    Dodin, A V; Zharova, A V; Lamzin, S A; Malogolovets, E V; Roe, J M

    2015-01-01

    The results of our speckle interferometric observations of young binaries VY Tau and XZ Tau are presented. For the first time, we found a relative displacement of VY Tau components as well as a preliminary orbit for XZ Tau. It appeared that the orbit is appreciably non-circular and is inclined by $i \\lesssim 47^o$ from the plane of the sky. It means that the rotation axis of XZ Tau A and the axis of its jet are significantly non-perpendicular to the orbital plane. We found that the average brightness of XZ Tau had been increasing from the beginning of the last century up to the mid-thirties and then it decreased by $\\Delta B > 2$ mag. The maximal brightness has been reached significantly later on the time of periastron passage. The total brightness of XZ Tau's components varied in a non-regular way from 1970 to 1985 when eruptions of hot gas from XZ Tau A presumably had occurred. In the early nineties the variations became regular following which a chaotic variability had renewed. We also report that a flare ...

  5. ISOLATION AND CHARACTERIZATION OF STREPTOMYCES RISHIRIENSIS (VY31 WITH ANTIBIOTIC ACTIVITY AGAINST VARIOUS PATHOGENIC MICROORGANISMS

    Directory of Open Access Journals (Sweden)

    Ivana Charousová

    2015-02-01

    Full Text Available Actinomycete strain VY31 was isolated from agriculture soil of region Východná, Slovakia. Morphological, physiological and biochemical studies indicated that this isolate belongs to the genus Streptomyces. The 16S rRNA sequence data supported the assignment of the isolate to the genus Streptomyces rishiriensis (sequence similarity 97%. Tested isolate was able to produce melanin dark pigment and exopigments on ISP6, ISP7 and SSM+T cultivating media. The optimal pH range was from 6-8 and optimal temperature at 30 °C. The strain exhibited salt tolerance up to 5 % and utilized the carbon sources such as glucose, arabinose, xylose, inositol, mannose, fructose, rhamnose and rafinose. Using ApiZym® stripes, the highest production of enzymes was determined for phosphatase alkaline, leucinearylamidase, valinearylamidase, phosphatase acid, naphtol-AS-BI-phosphohydrolase, galactosidase and glucosidase (>40 nmol. According to ApiCoryne® results, positive reaction was confirmed in case of esculin, alkaline phosphatase, and this strain was also able to hydrolyze gelatine. Minimum Inhibitory Concentration (MIC of the purified extract of isolate was evaluated against Gram-positive bacteria Staphylococcus aureus and Enterococcus faecium, Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa and against yeast Candida albicans. On the basis of MIC results, strain VY31 had noticeable antibacterial activity against Staphylococcus aures N315 (MRSA from collection database of University Hospital in Hamburg, Germany. This isolate could be used in the development of new antibiotics for pharmaceutical purposes.

  6. Emergence of Lévy walks in systems of interacting individuals

    Science.gov (United States)

    Fedotov, Sergei; Korabel, Nickolay

    2017-03-01

    We propose a model of superdiffusive Lévy walk as an emergent nonlinear phenomenon in systems of interacting individuals. The aim is to provide a qualitative explanation of recent experiments [G. Ariel et al., Nat. Commun. 6, 8396 (2015), 10.1038/ncomms9396] revealing an intriguing behavior: swarming bacteria fundamentally change their collective motion from simple diffusion into a superdiffusive Lévy walk dynamics. We introduce microscopic mean-field kinetic equations in which we combine two key ingredients: (1) alignment interactions between individuals and (2) non-Markovian effects. Our interacting run-and-tumble model leads to the superdiffusive growth of the mean-squared displacement and the power-law distribution of run length with infinite variance. The main result is that the superdiffusive behavior emerges as a cooperative effect without using the standard assumption of the power-law distribution of run distances from the inception. At the same time, we find that the collision and repulsion interactions lead to the density-dependent exponential tempering of power-law distributions. This qualitatively explains the experimentally observed transition from superdiffusion to the diffusion of mussels as their density increases [M. de Jager et al., Proc. R. Soc. B 281, 20132605 (2014), 10.1098/rspb.2013.2605].

  7. Finite difference methods for option pricing under Lévy processes: Wiener-Hopf factorization approach.

    Science.gov (United States)

    Kudryavtsev, Oleg

    2013-01-01

    In the paper, we consider the problem of pricing options in wide classes of Lévy processes. We propose a general approach to the numerical methods based on a finite difference approximation for the generalized Black-Scholes equation. The goal of the paper is to incorporate the Wiener-Hopf factorization into finite difference methods for pricing options in Lévy models with jumps. The method is applicable for pricing barrier and American options. The pricing problem is reduced to the sequence of linear algebraic systems with a dense Toeplitz matrix; then the Wiener-Hopf factorization method is applied. We give an important probabilistic interpretation based on the infinitely divisible distributions theory to the Laurent operators in the correspondent factorization identity. Notice that our algorithm has the same complexity as the ones which use the explicit-implicit scheme, with a tridiagonal matrix. However, our method is more accurate. We support the advantage of the new method in terms of accuracy and convergence by using numerical experiments.

  8. Portfolio Strategy of Financial Market with Regime Switching Driven by Geometric Lévy Process

    Directory of Open Access Journals (Sweden)

    Liuwei Zhou

    2014-01-01

    Full Text Available The problem of a portfolio strategy for financial market with regime switching driven by geometric Lévy process is investigated in this paper. The considered financial market includes one bond and multiple stocks which has few researches up to now. A new and general Black-Scholes (B-S model is set up, in which the interest rate of the bond, the rate of return, and the volatility of the stocks vary as the market states switching and the stock prices are driven by geometric Lévy process. For the general B-S model of the financial market, a portfolio strategy which is determined by a partial differential equation (PDE of parabolic type is given by using Itô formula. The PDE is an extension of existing result. The solvability of the PDE is researched by making use of variables transformation. An application of the solvability of the PDE on the European options with the final data is given finally.

  9. Helical Lévy walks: Adjusting searching statistics to resource availability in microzooplankton

    Science.gov (United States)

    Bartumeus, Frederic; Peters, Francesc; Pueyo, Salvador; Marrasé, Cèlia; Catalan, Jordi

    2003-10-01

    The searching trajectories of different animals can be described with a broad class of flight length (lj) distributions with P(lj) = lj-μ. Theoretical studies have shown that changes in these distributions (i.e., different μ values) are key to optimizing the long-term encounter statistics under certain searcher-resource scenarios. In particular, they predict the advantage of Lévy searching (μ 2) over Brownian motion (μ =" BORDER="0"> 3) for low-prey-density scenarios. Here, we present experimental evidence of predicted optimal changes in the flight-time distribution of a predator's walk in response to gradual density changes of its moving prey. Flight times of the dinoflagellate Oxyrrhis marina switched from an exponential to an inverse square power-law distribution when the prey (Rhodomonas sp.) decreased in abundance. Concomitantly, amplitude and frequency of the short-term helical path increased. The specific biological mechanisms involved in these searching behavioral changes are discussed. We suggest that, in a three-dimensional environment, a stronger helical component combined with a Lévy walk searching strategy enhances predator's encounter rates. Our results support the idea of universality of the statistical laws in optimal searching processes despite variations in the biological details of the organisms.

  10. Truncated Lévy walks and an emerging market economic index

    Science.gov (United States)

    Miranda, L. Couto; Riera, R.

    2001-08-01

    In this paper, we perform a statistical analysis of the major stock index in Latin America, the São Paulo Stock Exchange Index in Brazil (IBOVESPA). Database contains daily records for the 15-year period 1986-2000. We find that the time evolution of the index of share prices is well described by an Exponentially Truncated Lévy Flight (ETLF) characterized by a Lévy exponent α≃1.6-1.7 and a cutoff exponent λ≃1.7. The ETLF statistics accounts for the observed short-term large fluctuations of the financial data time series and describes the long-term convergence to the Gaussian regime. We derive the characteristic crossover time scale Nc dependence on α and λ according to this model as well as the volatility dependence on α, λ and Nc. We find an uncorrelated behaviour of the historical data and Nc≃20 trading days which are in numerical agreement with the analytical results. This dynamic model provides a framework within which it is possible to develop an efficient risk management and option pricing practice for emerging economies.

  11. vy noise-induced escape in an excitable system

    Science.gov (United States)

    Cai, Rui; Chen, Xiaoli; Duan, Jinqiao; Kurths, Jürgen; Li, Xiaofan

    2017-06-01

    This paper considers the dynamics of escape in the stochastic FitzHugh-Nagumo (FHN) neuronal model driven by symmetric α-stable Lévy noise. External or internal stimulation may make the excitable system produce a pulse or not, which can be interpreted as an escape problem. A new method to analyse the state transition from the rest state to the excitatory state is presented. This approach consists of two deterministic indices: the first escape probability (FEP) and the mean first exit time (MFET). We find that higher FEP in the rest state (equilibrium) promotes such a transition and MFET reflects the stability of the rest state directly with the selected escape region. The developed two dimensional numerical simulation method to calculate FEP and MFET can not only avoid a dimension reduction, but is also applicable for the cases with large noise. In addition, FEP provides us with a new perspective to understand the seperatrix of the stochastic FHN model. It can be seen that smaller jumps of the Lévy motion and relatively small noise intensity are conducive to the production of spikes. In order to characterize the effect of noise on the selected escape region in which the equilibrium lies, the area of higher FEP and MFET in the escape region are calculated. Meanwhile, Brownian motion as a special case is also taken into account for comparison. This work was partly supported by the NSF grant 1620449, and NSFC grants 11531006, 11371367 and 11271290.

  12. Territory covered by N Lévy flights on d-dimensional lattices

    Science.gov (United States)

    Berkolaiko, G.; Havlin, S.

    1997-02-01

    We study the territory covered by N Lévy flights by calculating the mean number of distinct sites, , visited after n time steps on a d-dimensional, d>=2, lattice. The Lévy flights are initially at the origin and each has a probability Al-(d+α) to perform an l-length jump in a randomly chosen direction at each time step. We obtain asymptotic results for different values of α. For d=2 and N-->∞ we find ~CαN2/(2+α)n4/(2+α), when α~N2/(2+α)n2/α, when α>2. For d=2 and n-->∞ we find ~Nn for α~Nn/ln n for α>2. The last limit corresponds to the result obtained by Larralde et al. [Phys. Rev. A 45, 7128 (1992)] for bounded jumps. We also present asymptotic results for on d>=3 dimensional lattices.

  13. First supernova companion star found

    Science.gov (United States)

    2004-01-01

    Supernova 1993J exploding hi-res Size hi-res: 222 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Supernova 1993J exploding (artist’s impression) New observations with the Hubble Space Telescope allow a look into a supernova explosion under development. In this artist’s view the red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). This interaction process happened over about 250 years and affected the supernova explosion to such an extent that SN 1993J was later known as one of the most peculiar supernovae ever seen. Supernova 1993J exploding hi-res Size hi-res: 4200 kb Credits: ESA and Justyn R. Maund (University of Cambridge) The site of the Supernova 1993J explosion A virtual journey into one of the spiral arms of the grand spiral Messier 81 (imaged with the Isaac Newton Telescope on La Palma, left) reveals the superb razor-sharp imaging power of the NASA/ESA Hubble Space Telescope (Hubble’s WFPC2 instrument, below). The close-up (with Hubble’s ACS, to the right) is centred on the newly discovered companion star to Supernova 1993J that itself is no longer visible. The quarter-circle around the supernova companion is a so-called light echo originating from sheets of dust in the galaxy reflecting light from the original supernova explosion. Supernova 1993J explosing site hi-res Size hi-res: 1502 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Close-up of the Supernova 1993J explosion site (ACS/HRC image) This NASA/ESA Hubble Space Telescope image shows the area in Messier 81 where Supernova 1993J exploded. The companion to the supernova ‘mother star’ that remains after the explosion is seen in the centre of the image. The image is taken with Hubble’s Advanced Camera for Surveys and is a combination of four exposures taken with ACS’ High Resolution Camera. The exposures were taken through two near-UV filters (250W

  14. The Na-O anticorrelation in horizontal branch stars. II. NGC1851

    CERN Document Server

    Gratton, R G; Carretta, E; Bragaglia, A; D'Orazi, V; Momany, Y Al; Sollima, A; Salaris, M; Cassisi, S

    2012-01-01

    We studied the Na-O anti-correlation from moderately high resolution spectra for 35 stars on the blue HB (BHB), one RR Lyrae, and 55 stars are on the red HB (RHB) of NGC1851. We also derived abundances for He and N in BHB stars, and Ba and upper limits for N in RHB stars. The RHB stars clearly separate into two groups: the vast majority are O-rich and Na-poor, while about 10-15% are Na-rich and moderately O-poor. Most Na-rich RHB stars are also Ba-rich and there is an overall correlation between Na and Ba abundances within the RHB. The group of Ba-rich RHB stars resides on the warmer edge and includes ~10% of the RHB stars. We propose that they are the descendant of the stars on the RGB sequence with very red v-y colour. This sequence is known also to consist of Ba and perhaps CNO-rich stars. However, the upper limit we obtain for N ([N/Fe]<1.55) for one of the Ba-rich stars coupled with the low C-abundances for RGB Ba-rich stars from the literature suggests that the total CNO might not be particularly hig...

  15. Search reliability and search efficiency of combined Lévy-Brownian motion: long relocations mingled with thorough local exploration

    Science.gov (United States)

    Palyulin, Vladimir V.; Chechkin, Aleksei V.; Klages, Rainer; Metzler, Ralf

    2016-09-01

    A combined dynamics consisting of Brownian motion and Lévy flights is exhibited by a variety of biological systems performing search processes. Assessing the search reliability of ever locating the target and the search efficiency of doing so economically of such dynamics thus poses an important problem. Here we model this dynamics by a one-dimensional fractional Fokker-Planck equation combining unbiased Brownian motion and Lévy flights. By solving this equation both analytically and numerically we show that the superposition of recurrent Brownian motion and Lévy flights with stable exponent α \\lt 1, by itself implying zero probability of hitting a point on a line, leads to transient motion with finite probability of hitting any point on the line. We present results for the exact dependence of the values of both the search reliability and the search efficiency on the distance between the starting and target positions as well as the choice of the scaling exponent α of the Lévy flight component.

  16. Optimal harvesting policy of a stochastic two-species competitive model with Lévy noise in a polluted environment

    Science.gov (United States)

    Zhao, Yu; Yuan, Sanling

    2017-07-01

    As well known that the sudden environmental shocks and toxicant can affect the population dynamics of fish species, a mechanistic understanding of how sudden environmental change and toxicant influence the optimal harvesting policy requires development. This paper presents the optimal harvesting of a stochastic two-species competitive model with Lévy noise in a polluted environment, where the Lévy noise is used to describe the sudden climate change. Due to the discontinuity of the Lévy noise, the classical optimal harvesting methods based on the explicit solution of the corresponding Fokker-Planck equation are invalid. The object of this paper is to fill up this gap and establish the optimal harvesting policy. By using of aggregation and ergodic methods, the approximation of the optimal harvesting effort and maximum expectation of sustainable yields are obtained. Numerical simulations are carried out to support these theoretical results. Our analysis shows that the Lévy noise and the mean stress measure of toxicant in organism may affect the optimal harvesting policy significantly.

  17. Discovery of a red supergiant counterpart to RX~J004722.4-252051, a ULX in NGC 253

    CERN Document Server

    Heida, M; Jonker, P G; Servillat, M; Repetto, S; Roberts, T P; Walton, D J; Moon, D -S; Harrison, F A

    2015-01-01

    We present two epochs of near-infrared spectroscopy of the candidate red supergiant counterpart to RX~J004722.4-252051, a ULX in NGC 253. We measure radial velocities of the object and its approximate spectral type by cross-correlating our spectra with those of known red supergiants. Our VLT/X-shooter spectrum is best matched by that of early M-type supergiants, confirming the red supergiant nature of the candidate counterpart. The radial velocity of the spectrum, taken on 2014, August 23, is $417 \\pm 4$ km/s. This is consistent with the radial velocity measured in our spectrum taken with Magellan/MMIRS on 2013, June 28, of $410 \\pm 70$ km/s, although the large error on the latter implies that a radial velocity shift expected for a black hole of tens of $M_\\odot$ can easily be hidden. Using nebular emission lines we find that the radial velocity due to the rotation of NGC 253 is 351 $\\pm$ 4 km/s at the position of the ULX. Thus the radial velocity of the counterpart confirms that the source is located in NGC ...

  18. Uncovering the monster stars in W49: the most luminous star-forming region in the Milky Way

    Science.gov (United States)

    Wu, Shiwei; Bik, Arjan; Henning, Thomas; Pasquali, Anna; Brandner, Wolfgang; Stolte, Andrea

    2015-08-01

    As a part of the LOBSTAR project (Luci OBservations of STARburst regions), which aims at understanding the stellar content of some of the most massive star-forming regions, we present our result on the high-mass stellar content of W49. K-band spectra of the candidate massive stars from VLT/ISAAC and LBT/LUCI provide us with reliable spectral types of dozens of massive stars in this HII region.The first results show that this region hosts several of the most massive stars in our galaxy. Two most brightest stars, one in the core of the central cluster and one in W49 South, were identified as very massive stars (M > 100 M⊙). Their K-band spectra exhibit strong stellar wind features, and they are classified as O2-3.5If* supergiant stars. After comparison to the Geneva evolutionary models, the mass range of W49nr1 was estimated to be between 100 M⊙ and 180 M⊙. Additionally we find 12 O stars with spectral types between O7V and O3V and masses from 25 M⊙ to 125 M⊙, respectively.These results allow us to derive the fundamental parameters of the cluster (mass, age) as well as the total energy output in the form of ionising photons. This will enable us to study the feedback effects of this extreme star forming region in great detail. To our surprise, two young stellar objects with infrared excess feature showing CO emission lines in their spectra are identified. This suggests that circumstellar disks can survive even in this extreme environment. Finally the spatial distribution of the massive stars is analysed to discuss the star formation history and identify potential runaway stars. The extreme properties of this region makes it a good template for more extreme star formation outside our galaxy.

  19. New Luminous ON Spectra from the Galactic O-Star Spectroscopic Survey

    CERN Document Server

    Walborn, Nolan R; Barba, Rodolfo H; Sota, Alfredo

    2016-01-01

    Two new ON supergiant spectra (bringing the total known to seven) and one new ONn giant (total of this class now eight) are presented; they have been discovered by the Galactic O-Star Spectroscopic Survey. These rare objects represent extremes in the mixing of CNO-cycled material to the surfaces of evolved, late-O stars, by uncertain mechanisms in the first category but likely by rotation in the second. The two supergiants are at the hot edge of the class, which is a selection effect from the behavior of defining N III and C III absorption blends, related to the tendency toward emission (Of effect) in the former. An additional N/C criterion first proposed by Bisiacchi et al. is discussed as a means to alleviate that effect, and it is relevant to the two new objects. The entire ON supergiant class is discussed; they display a fascinating diversity of detail undoubtedly related to the complexities of their extended atmospheres and winds that are sensitive to small differences in physical parameters, as well as ...

  20. Star Clusters

    OpenAIRE

    Gieles, M.

    1993-01-01

    Star clusters are observed in almost every galaxy. In this thesis we address several fundamental problems concerning the formation, evolution and disruption of star clusters. From observations of (young) star clusters in the interacting galaxy M51, we found that clusters are formed in complexes of stars and star clusters. These complexes share similar properties with giant molecular clouds, from which they are formed. Many (70%) of the young clusters will not survive the fist 10 Myr, due to t...

  1. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

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

  2. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

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

  3. Massive stars in their death-throes

    CERN Document Server

    Eldridge, J J

    2008-01-01

    The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently there are 8 detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants as theory has long predicted. However no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae which, given the expected progenitors, is an unlikely result. Also observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict current stellar evolution theory. This suggests that we may need to update our understanding.

  4. Massive stars in their death throes.

    Science.gov (United States)

    Eldridge, John J

    2008-12-13

    The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently, there are eight detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants, as theory has long predicted. However, no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae, which, given the expected progenitors, is an unlikely result. Also, observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict the current stellar evolution theory. This suggests that we may need to update our understanding.

  5. Spots, activity cycles, and differential rotation on cool stars

    Science.gov (United States)

    Alekseev, I. Yu.

    2005-01-01

    The first results are reported from a search for activity cycles in stars similar to the sun based on modelling their spotting with an algorithm developed at the Crimean Astrophysical Observatory. Of the more than thirty program stars, 10 manifested a cyclical variation in their central latitudes and total starspot area. The observed cycles have durations of 4-15 years, i.e., analogous to the 11 year Schwabe sunspot cycle. Most of the stars have a rough analog of the solar butterfly pattern, with a reduction in the average latitude of the spots as their area increases. A flip-flop effect during the epoch of the maximum average latitude is noted in a number of these objects (e.g., the analog LQ Hya of the young sun or the RS CVn-type variable V711 Tau), as well as a reduction in the photometric rotation period of a star as the spots drift toward the equator, an analog of the differential rotation effect in the sun. Unlike in the sun, the observed spot formation cycles do not correlate uniquely with other indicators of activity— chromospheric emission in the CaII HK lines (Be Cet, EK Dra, Dx Leo), H line emission (LQ Hya, VY Ari, EV Lac), or cyclical flare activity (EV Lac). In V833 Tau, BY Dra, EK Dra, and VY Ari short Schwabe cycles coexist with long cycles that are analogous to the Gleissberg solar cycle, in which the spotted area can approach half the entire area of the star.

  6. Massive Stars in the Quintuplet Cluster

    Science.gov (United States)

    Figer, Donald F.; McLean, Ian S.; Morris, Mark

    1999-03-01

    We present near-infrared photometry and K-band spectra of newly identified massive stars in the Quintuplet cluster, one of the three massive clusters projected within 50 pc of the Galactic center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any cluster in the Galaxy, and over a dozen stars in earlier stages of evolution, i.e., luminous blue variables (LBVs), Ofpe/WN9, and OB supergiants. One newly identified star is the second luminous blue variable in the cluster, after the ``Pistol star.'' Although we are unable to provide certain spectral classifications for the five enigmatic Quintuplet-proper members, we tentatively propose that they are extremely dusty versions of the WC stars found elsewhere in the cluster and similar to the dozen or so known examples in the Galaxy. Although the cluster parameters are uncertain because of photometric errors and uncertainties in stellar models, i.e., extrapolating initial masses and estimating ionizing fluxes, we have the following conclusions. Given the evolutionary stages of the identified stars, the cluster appears to be about 4+/-1 Myr old, assuming coeval formation. The total mass in observed stars is ~103 Msolar, and the implied mass is ~104 Msolar, assuming a lower mass cutoff of 1 Msolar and a Salpeter initial mass function. The implied mass density in stars is greater than or similar to a few thousand Msolar pc-3. The newly identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 1050.9 photons s-1, or roughly what is required to ionize the nearby ``Sickle'' H II region (G0.18-0.04). The total luminosity from the massive cluster stars is ~107.5 Lsolar, enough to account for the heating of the nearby molecular cloud, M0.20-0.033. We propose a picture that integrates most of the major features in this part of the sky, excepting the nonthermal filaments. We

  7. Measuring the self-similarity exponent in Lévy stable processes of financial time series

    Science.gov (United States)

    Fernández-Martínez, M.; Sánchez-Granero, M. A.; Trinidad Segovia, J. E.

    2013-11-01

    Geometric method-based procedures, which will be called GM algorithms herein, were introduced in [M.A. Sánchez Granero, J.E. Trinidad Segovia, J. García Pérez, Some comments on Hurst exponent and the long memory processes on capital markets, Phys. A 387 (2008) 5543-5551], to efficiently calculate the self-similarity exponent of a time series. In that paper, the authors showed empirically that these algorithms, based on a geometrical approach, are more accurate than the classical algorithms, especially with short length time series. The authors checked that GM algorithms are good when working with (fractional) Brownian motions. Moreover, in [J.E. Trinidad Segovia, M. Fernández-Martínez, M.A. Sánchez-Granero, A note on geometric method-based procedures to calculate the Hurst exponent, Phys. A 391 (2012) 2209-2214], a mathematical background for the validity of such procedures to estimate the self-similarity index of any random process with stationary and self-affine increments was provided. In particular, they proved theoretically that GM algorithms are also valid to explore long-memory in (fractional) Lévy stable motions. In this paper, we prove empirically by Monte Carlo simulation that GM algorithms are able to calculate accurately the self-similarity index in Lévy stable motions and find empirical evidence that they are more precise than the absolute value exponent (denoted by AVE onwards) and the multifractal detrended fluctuation analysis (MF-DFA) algorithms, especially with a short length time series. We also compare them with the generalized Hurst exponent (GHE) algorithm and conclude that both GM2 and GHE algorithms are the most accurate to study financial series. In addition to that, we provide empirical evidence, based on the accuracy of GM algorithms to estimate the self-similarity index in Lévy motions, that the evolution of the stocks of some international market indices, such as U.S. Small Cap and Nasdaq100, cannot be modelized by means of a

  8. X-ray diagnostics of massive star winds

    Science.gov (United States)

    Oskinova, Lidia M.

    2016-09-01

    Nearly all types of massive stars with radiatively driven stellar winds are X-ray sources that can be observed by the presently operating powerful X-ray telescopes. In this review I briefly address recent advances in our understanding of stellar winds obtained from X-ray observations. X-rays may strongly influence the dynamics of weak winds of main sequence B-type stars. X-ray pulsations were detected in a β Cep type variable giving evidence of tight photosphere-wind connections. The winds of OB dwarfs with subtypes later than O9V may be predominantly in a hot phase, and X-ray observations offer the best window for their studies. The X-ray properties of OB supergiants are largely determined by the effects of radiative transfer in their clumped stellar winds. The recently suggested method to directly measure mass-loss rates of O stars by fitting the shapes of X-ray emission lines is considered but its validity cannot be confirmed. To obtain robust quantitative information on stellar wind parameters from X-ray spectroscopy, a multiwavelength analysis by means of stellar atmosphere models is required. Independent groups are now performing such analyses with encouraging results. Joint analyses of optical, UV, and X-ray spectra of OB supergiants yield consistent mass-loss rates. Depending on the adopted clumping parameters, the empirically derived mass-loss rates are a factor of a few smaller or comparable to those predicted by standard recipes (Vink et al., 2001). All sufficiently studied O stars display variable X-ray emission that might be related to corotating interaction regions in their winds. In the latest stages of stellar evolution, single red supergiants (RSG) and luminous blue variable (LBV) stars do not emit observable amounts of X-rays. On the other hand, nearly all types of Wolf-Rayet (WR) stars are X-ray sources. X-ray spectroscopy allows a sensitive probe of WR wind abundances and opacities.

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

    Science.gov (United States)

    2010-07-01

    raises the challenge to theorists still further. "Either they were born so big or smaller stars merged together to produce them," explains Crowther. Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants, either neutron stars or black holes. Having now established the existence of stars weighing between 150 and 300 solar masses, the astronomers' findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae" that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years. Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the Sun. "Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon," concludes Crowther. Notes [1] The star A1 in NGC 3603 is a double star, with an orbital period of 3.77 days. The two stars in the system have, respectively, 120 and 92 times the mass of the Sun, which means that they have formed as stars weighing, respectively, 148 and 106 solar masses. [2] The team used the SINFONI, ISAAC and MAD instruments, all attached to ESO's Very Large Telescope at Paranal, Chile. [3] (note added on 26 July 2010) The "bigger" in the title does not imply that these stars are the biggest observed. Such stars, called red supergiants, can have radii up to about a thousand solar radii, while R136a1, which is blue, is about 35 times as large as the Sun. However, R136a1 is the star with the greatest mass known to date. More information This work is presented in an article published in the Monthly Notices of the Royal Astronomical Society ("The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit", by

  10. The Massive Star Population in M101. II. Spatial Variations in the Recent Star Formation History

    CERN Document Server

    Grammer, Skyler

    2014-01-01

    We investigate the star formation history (SFH) as a function of radius in M101 using archival HST/ACS photometry. We derive the SFH from the resolved stellar populations in five 2' wide annuli. Binning the SFH into time frames corresponding to stellar populations traced by H$\\alpha$, far ultraviolet (FUV), and near ultraviolet (NUV) emission, we find that the fraction of stellar populations young enough to contribute in H$\\alpha$ is 15%-35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of H$\\alpha$ emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into modeled ratios, we find that we a...

  11. The Massive Star Population in M101. II. Spatial Variations in the Recent Star Formation History

    Science.gov (United States)

    Grammer, Skyler; Humphreys, Roberta M.

    2014-09-01

    We investigate star formation history (SFH) as a function of radius in M101 using archival Hubble Space Telescope Advanced Camera for Surveys photometry. We derive the SFH from the resolved stellar populations in five 2' wide annuli. Binning the SFH into time frames corresponding to stellar populations traced by Hα, far-ultraviolet, and near-ultraviolet emission, we find that the fraction of stellar populations young enough to contribute in Hα is 15%-35% in the inner regions, compared to less than 5% in the outer regions. This provides a sufficient explanation for the lack of Hα emission at large radii. We also model the blue to red supergiant ratio in our five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into modeled ratios, we find that we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant.

  12. The Swift Supergiant Fast X-Ray Transients Project:. [A Review, New Results and Future Perspectives

    Science.gov (United States)

    Romano, P.; Mangano, V.; Ducci, L.; Esposito, P.; Vercellone, S.; Bocchino, F.; Burrows, D. N.; Kennea, J. A.; Krimm, H. A.; Gehrels, N.; Farinelli, R.; Ceccobello, C.

    2013-01-01

    We present a review of the Supergiant Fast X-ray Transients (SFXT) Project, a systematic investigation of the properties of SFXTs with a strategy that combines Swift monitoring programs with outburst follow-up observations. This strategy has quickly tripled the available sets of broad-band data of SFXT outbursts, and gathered a wealth of out-of-outburst data, which have led us to a broad-band spectral characterization, an assessment of the fraction of the time these sources spend in each phase, and their duty cycle of inactivity. We present some new observational results obtained through our outburst follow-ups, as fitting examples of the exceptional capabilities of Swift in catching bright flares and monitor them panchromatically.

  13. Risk finance for catastrophe losses with Pareto-calibrated Lévy-stable severities.

    Science.gov (United States)

    Powers, Michael R; Powers, Thomas Y; Gao, Siwei

    2012-11-01

    For catastrophe losses, the conventional risk finance paradigm of enterprise risk management identifies transfer, as opposed to pooling or avoidance, as the preferred solution. However, this analysis does not necessarily account for differences between light- and heavy-tailed characteristics of loss portfolios. Of particular concern are the decreasing benefits of diversification (through pooling) as the tails of severity distributions become heavier. In the present article, we study a loss portfolio characterized by nonstochastic frequency and a class of Lévy-stable severity distributions calibrated to match the parameters of the Pareto II distribution. We then propose a conservative risk finance paradigm that can be used to prepare the firm for worst-case scenarios with regard to both (1) the firm's intrinsic sensitivity to risk and (2) the heaviness of the severity's tail.

  14. Stable Equilibrium Based on Lévy Statistics:A Linear Boltzmann Equation Approach

    Science.gov (United States)

    Barkai, Eli

    2004-06-01

    To obtain further insight on possible power law generalizations of Boltzmann equilibrium concepts, we consider stochastic collision models. The models are a generalization of the Rayleigh collision model, for a heavy one dimensional particle M interacting with ideal gas particles with a mass mlaw equilibrium. We show, under certain conditions, that the velocity distribution function of the heavy particle is Lévy stable, the Maxwellian distribution being a special case. We demonstrate our results with numerical examples. The relation of the power law equilibrium obtained here to thermodynamics is discussed. In particular we compare between two models: a thermodynamic and an energy scaling approaches. These models yield insight into questions like the meaning of temperature for power law equilibrium, and into the issue of the universality of the equilibrium (i.e., is the width of the generalized Maxwellian distribution functions obtained here, independent of coupling constant to the bath).

  15. Contraction Options and Optimal Multiple-Stopping in Spectrally Negative Lévy Models

    Energy Technology Data Exchange (ETDEWEB)

    Yamazaki, Kazutoshi, E-mail: kyamazak@kansai-u.ac.jp [Kansai University, Department of Mathematics, Faculty of Engineering Science (Japan)

    2015-08-15

    This paper studies the optimal multiple-stopping problem arising in the context of the timing option to withdraw from a project in stages. The profits are driven by a general spectrally negative Lévy process. This allows the model to incorporate sudden declines of the project values, generalizing greatly the classical geometric Brownian motion model. We solve the one-stage case as well as the extension to the multiple-stage case. The optimal stopping times are of threshold-type and the value function admits an expression in terms of the scale function. A series of numerical experiments are conducted to verify the optimality and to evaluate the efficiency of the algorithm.

  16. MASTER OT J190519.41+301524.4: New Eclipsing Cataclysmic Variable of VY Scl Type

    CERN Document Server

    Martinelli, F

    2016-01-01

    MASTER OT J190519.41+301524.4 was discovered as an optical transient of 15.7m by the Mobile Astronomical System of TElescope-Robots in March 2014. We report the results of photometric observations of this variable performed at Lajatico Astronomical Center in June-July 2015. The light curve is showing deep V-shaped eclipses with an amplitude of two magnitudes. The orbital period was determined to be 0.129694 d (3.113 h). Based on the archival observations and the shape of the orbital curve we suggest that MASTER OT J190519.41+301524.4 is a new cataclysmic variable of VY Scl type ("anti-nova") with an inclination angle close to 90 deg.

  17. A cuckoo search algorithm by Lévy flights for solving reliability redundancy allocation problems

    Science.gov (United States)

    Valian, Ehsan; Valian, Elham

    2013-11-01

    A new metaheuristic optimization algorithm, called cuckoo search (CS), was recently developed by Yang and Deb (2009, 2010). This article uses CS and Lévy flights to solve the reliability redundancy allocation problem. The redundancy allocation problem involves setting reliability objectives for components or subsystems in order to meet the resource consumption constraint, e.g. the total cost. The difficulties facing the redundancy allocation problem are to maintain feasibility with respect to three nonlinear constraints, namely, cost, weight and volume-related constraints. The redundancy allocation problems have been studied in the literature for decades, usually using mathematical programming or metaheuristic optimization algorithms. The performance of the algorithm is tested on five well-known reliability redundancy allocation problems and is compared with several well-known methods. Simulation results demonstrate that the optimal solutions obtained by CS are better than the best solutions obtained by other methods.

  18. Optimal variational principle for backward stochastic control systems associated with Lévy processes

    Institute of Scientific and Technical Information of China (English)

    TANG MaoNing; ZHANG Qi

    2012-01-01

    The paper is concerned with optimal control of backward stochastic differential equation (BSDE)driven by Teugel's martingales and an independent multi-dimensional Brownian motion,where Teugel's martingales are a family of pairwise strongly orthonormal martingales associated with Lévy processes (see e.g.,Nualart and Schoutens' paper in 2000).We derive the necessary and sufficient conditions for the existence of the optimal control by means of convex variation methods and duality techniques.As an application,the optimal control problem of linear backward stochastic differential equation with a quadratic cost criteria (or backward linear-quadratic problem,or BLQ problem for short) is discussed and characterized by a stochastic Hamilton system.

  19. The Stars behind the Curtain

    Science.gov (United States)

    2010-02-01

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

  20. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

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

  1. The quantitative assessment of UV extinction derived from IUE data of giants and supergiants

    Science.gov (United States)

    Cardelli, Jason A.; Sembach, Kenneth R.; Mathis, John S.

    1992-01-01

    It is shown here that the UV interstellar extinction towards hot luminous stars can be determined as accurately as for hot main-sequence stars. An atlas of IUE dereddened fluxes is presented for 13 lightly reddened stars within the 1160-3125 A range. The fluxes of these stars how absorption line strengths that allow a rather accurate determination of relative temperatures and luminosities which is more suitable for the determination of UV extinction via the pair method than choosing a comparison star based on quoted optical MK classifications.

  2. Low resolution spectroscopy of hot post-AGB candidates II. LS, LSS, LSE stars and additional IRAS sources

    CERN Document Server

    Parthasarathy, M; Vijapurkar, J; Takeda, Y

    2011-01-01

    Hot (OB) post-AGB stars are immediate progenitors of planetary nebulae (PNe). Very few hot post-AGB stars are known. Detecting new hot post-AGB candidates and follow-up multiwavelength studies will enable us to further understand the processes during the post-AGB evolution that lead to the formation of PNe. Case-Hamburg OB star surveys and their extension (LS, LSS, and LSE catalogues) and IRAS (point source) catalogues are good sources for detecting new hot post-AGB candidates from low resolution spectroscopy. Spectral types are determined from low resolution optical spectra of 44 stars selected from the LS, LSS, and LSE catalogues. Unlike the stars in the first paper, the stars in this paper were selected using criteria other than positional coincidence with an IRAS source with far IR (IRAS) colours similar to post-AGB supergiants and planetary nebulae. These included high galactic latitude, spectral types of O, B, A supergiants, emission lines in the spectrum and known spectral peculiarity. From the present...

  3. Massive Stars

    Science.gov (United States)

    Livio, Mario; Villaver, Eva

    2009-11-01

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

  4. Do the albatross Lévy flights below the spandrels of St Mark?. Comment on "Liberating Lévy walk research from the shackles of optimal foraging" by A.M. Reynolds

    Science.gov (United States)

    Focardi, Stefano

    2015-09-01

    Because of the strong technological developments and device miniaturization, (the so-called biologging revolution [1]) ecology is currently witnessing important conceptual transformations and a new scientific branch "the movement ecology" is quickly developing [2]. In this context the proposals by Reynolds [3] of a new theoretical approach for the explanation of animal movement, which overrides at once the established paradigms of correlated random walk [4] and the new Lévy flight foraging hypothesis [5] is really welcome.

  5. Conjunction Risks of Near-Earth Objects to Artificial Satellites: The Case of Asteroid 2015 VY105

    Science.gov (United States)

    Ryan, W.; Ryan, E.

    2016-09-01

    The close approach of near-Earth object 2015 VY105 on November 15, 2015 occurred less than 24 hours after discovery by the Catalina Sky Survey (located in Tucson, AZ). Based on the discovery metric information and follow up data from Magdalena Ridge Observatory (MRO) observations, it was clear that this asteroid would pass through the geostationary satellite belt. In particular, data indicated that although 2015 VY105 would come within approximately 200 km of the DirectTV 11 and 14 satellites, it would not impact either. The details of this analysis as well as characterization results acquired are presented. Further, examples of various other asteroids that have made close approaches within geostationary distances in the past (with both long and short lead times) are included for risk context.

  6. Monte Carlo Analysis of the Lévy Stability and Multi-fractal Spectrum in e+e- Collisions

    Institute of Scientific and Technical Information of China (English)

    陈刚; 刘连寿

    2002-01-01

    The Lévy stability analysis is carried out for e+e- collisions at Z0 mass using the Monte Carlo method. The Lévy index μ is found to be μ = 1.701 ± 0.043. The self-slmilar generalized dimensions D(q) and multi-fractal spectrum f(а) are presented. The Rényi dimension D(q) decreases with increasing q. The self-similar multifractal spectrum is a convex curve with a maximum at q = 0, а = 1.169 ± 0.011. The right-hand side of the spectrum, corresponding to negative values of q, is obtained through analytical continuation.

  7. Optimal portfolio selection in a Lévy market with uncontrolled cash flow and only risky assets

    Science.gov (United States)

    Zeng, Yan; Li, Zhongfei; Wu, Huiling

    2013-03-01

    This article considers an investor who has an exogenous cash flow evolving according to a Lévy process and invests in a financial market consisting of only risky assets, whose prices are governed by exponential Lévy processes. Two continuous-time portfolio selection problems are studied for the investor. One is a benchmark problem, and the other is a mean-variance problem. The first problem is solved by adopting the stochastic dynamic programming approach, and the obtained results are extended to the second problem by employing the duality theory. Closed-form solutions of these two problems are derived. Some existing results are found to be special cases of our results.

  8. Optimality of the barrier strategy in de Finetti's dividend problem for spectrally negative Lévy processes: An alternative approach

    Science.gov (United States)

    Yin, Chuancun; Wang, Chunwei

    2009-11-01

    The optimal dividend problem proposed in de Finetti [1] is to find the dividend-payment strategy that maximizes the expected discounted value of dividends which are paid to the shareholders until the company is ruined. Avram et al. [9] studied the case when the risk process is modelled by a general spectrally negative Lévy process and Loeffen [10] gave sufficient conditions under which the optimal strategy is of the barrier type. Recently Kyprianou et al. [11] strengthened the result of Loeffen [10] which established a larger class of Lévy processes for which the barrier strategy is optimal among all admissible ones. In this paper we use an analytical argument to re-investigate the optimality of barrier dividend strategies considered in the three recent papers.

  9. Approximation of the Lévy Feller advection dispersion process by random walk and finite difference method

    Science.gov (United States)

    Liu, Q.; Liu, F.; Turner, I.; Anh, V.

    2007-03-01

    In this paper we present a random walk model for approximating a Lévy-Feller advection-dispersion process, governed by the Lévy-Feller advection-dispersion differential equation (LFADE). We show that the random walk model converges to LFADE by use of a properly scaled transition to vanishing space and time steps. We propose an explicit finite difference approximation (EFDA) for LFADE, resulting from the Grünwald-Letnikov discretization of fractional derivatives. As a result of the interpretation of the random walk model, the stability and convergence of EFDA for LFADE in a bounded domain are discussed. Finally, some numerical examples are presented to show the application of the present technique.

  10. Hadron star models. [neutron stars

    Science.gov (United States)

    Cohen, J. M.; Boerner, G.

    1974-01-01

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

  11. Mass loss rate determinations of southern OB stars

    CERN Document Server

    Benaglia, P; Koribalski, B S

    2001-01-01

    A sample of OB stars (eleven Of, one O and one B supergiant) has been surveyed with the Australia Telescope Compact Array at 4.8 and 8.64 GHz with a resolution of 2'' -- 4''. Five stars were detected; three of them have negative spectral indices, consistent with non-thermal emission, and two have positive indices. The thermal radiation from HD 150135 and HD 163181 can be explained as coming from an optically thick ionized stellar wind. The non-thermal radiation from CD-47 4551, HD 124314 and HD 150136 possibly comes from strong shocks in the wind itself and/or in the wind colliding region if the stars have a massive early-type companion. The percentage of non-thermal emitters among detected O stars has increased up to ~50%. The Of star HD 124314 clearly shows flux density variations. Mass loss rates (or upper limits) were derived for all the observed stars and the results compared with non-radio measurements and theoretical predictions.

  12. Combining observational techniques to constrain convection in evolved massive star models

    CERN Document Server

    Georgy, C; Meynet, G

    2014-01-01

    Recent stellar evolution computations indicate that massive stars in the range ~ 20 - 30 Msun are located in the blue supergiant (BSG) region of the Hertzsprung-Russell diagram at two different stages of their life: immediately after the main sequence (MS, group 1) and during a blueward evolution after the red supergiant phase (group 2). From the observation of the pulsationnal properties of a subgroup of variable BSGs (alpha Cyg variables), one can deduce that these stars belongs to group 2. It is however difficult to simultaneously fit the observed surface abundances and gravity for these stars, and this allows to constrain the physical processes of chemical species transport in massive stars. We will show here that the surface abundances are extremely sensitive to the physics of convection, particularly the location of the intermediate convective shell that appears at the ignition of the hydrogen shell burning after the MS. Our results show that the use of the Ledoux criterion to determine the convective r...

  13. Further Results from the Galactic O-Star Spectroscopic Survey: Rapidly Rotating Late ON Giants

    CERN Document Server

    Walborn, Nolan R; Sota, Alfredo; Alfaro, Emilio J; Morrell, Nidia I; Barba, Rodolfo H; Arias, Julia I; Gamen, Roberto C

    2011-01-01

    With new data from the Galactic O-Star Spectroscopic Survey, we confirm and expand the ONn category of late-O, nitrogen-enriched (N), rapidly rotating (n) giants. In particular, we have discovered two "clones" (HD 102415 and HD 117490) of one of the most rapidly rotating O stars previously known (HD 191423, "Howarth's Star"). We compare the locations of these objects in the theoretical HR Diagram to those of slowly rotating ON dwarfs and supergiants. All ON giants known to date are rapid rotators, whereas no ON dwarf or supergiant is; but all ON stars are small fractions of their respective spectral-type/luminosity-class/rotational subcategories. The ONn giants, displaying both substantial processed material and high rotation at an intermediate evolutionary stage, may provide significant information about the development of those properties. They may have preserved high initial rotational velocities or been spun up by TAMS core contraction; but alternatively and perhaps more likely, they may be products of bi...

  14. Bispectrum speckle interferometry observations and radiative transfer modelling of the red supergiant NML Cyg. Multiple dust-shell structures evidencing previous superwind phases

    Science.gov (United States)

    Blöcker, T.; Balega, Y.; Hofmann, K.-H.; Weigelt, G.

    2001-04-01

    NML Cyg is a highly evolved OH/IR supergiant, one of the most prominent infrared objects due to its strong obscuration by dust, and supposed to be among the most luminous supergiants in the galaxy. We present the first diffraction-limited 2.13 mu m observations of NML Cyg with 73 mas resolution. The speckle interferograms were obtained with the 6 m telescope at the Special Astrophysical Observatory, and the image reconstruction is based on the bispectrum speckle-interferometry method. The visibility function declines towards the diffraction limit to ~ 0.6. Radiative transfer calculations have been carried out to model the spectral energy distribution, given by ground-based photometry and ISO spectroscopy, and our 2.13 mu m visibility function. Additionally, mid-infrared visibility functions at 11 mu m were considered. The observed dust shell properties do not appear to be in accordance with standard single-shell (uniform outflow) models but seem to require multiple components. Considering previous periods of enhanced mass-loss, various density enhancements in the dust shell were taken into account. An extensive grid of models was calculated for different locations and strenghts of such superwind regions in the dust shell. To match the observations from the optical to the sub-mm domain requires at least two superwind regions embedded in the shell. The best model includes a dust shell with a temperature of 1000 K at its inner radius of 6.2 R*, a close embedded superwind shell extending from 15.5 R* to 21.7 R* with an amplitude (factor of density enhancement) of 10, and a far-out density enhancement at 186 R* with an amplitude of 5. The angular diameters of the central star and of the inner rim of the dust shell amount to 16.2 mas and 105 mas, resp. The diameter of the embedded close superwind region extends from 263 mas to 368 mas, and the inner boundary of the distant superwind region has a diameter of 3\\farcs 15. In the near-infrared the dust condensation zone is

  15. Spectroscopic evolution of massive stars on the main sequence

    Science.gov (United States)

    Martins, F.; Palacios, A.

    2017-02-01

    Context. The evolution of massive stars depends on several parameters, and the relation between different morphological types is not fully constrained. Aims: We aim to provide an observational view of evolutionary models in the Hertzsprung-Russell diagram, on the main sequence. This view should help compare observations and model predictions. Methods: We first computed evolutionary models with the code STAREVOL for initial masses between 15 and 100 M⊙. We subsequently calculated atmosphere models at specific points along the evolutionary tracks, using the code CMFGEN. Synthetic spectra obtained in this way were classified as if they were observational data: we assigned them a spectral type and a luminosity class. We tested our spectral classification by comparison to observed spectra of various stars with different spectral types. We also compared our results with empirical data of a large number of OB stars. Results: We obtain spectroscopic sequences along evolutionary tracks. In our computations, the earliest O stars (O2-3.5) appear only above 50 M⊙. For later spectral types, a similar mass limit exists, but is lower. A luminosity class V does not correspond to the entire main sequence. This only holds for the 15 M⊙ track. As mass increases, a larger portion of the main sequence is spent in luminosity class III. Above 50 M⊙, supergiants appear before the end of core-hydrogen burning. Dwarf stars (luminosity class V) do not occur on the zero-age main sequence above 80 M⊙. Consequently, the distribution of luminosity class V in the HR diagram is not a diagnostic of the length of the main sequence (above 15 M⊙) and cannot be used to constrain the size of the convective core. The distribution of dwarfs and giants in the HR diagram that results from our calculations agrees well with the location of stars analyzed by means of quantitative spectroscopy. For supergiants, there is a slight discrepancy in the sense that luminosity class I is observed slightly

  16. Expected number of distinct sites visited by N Lévy flights on a one-dimensional lattice

    Science.gov (United States)

    Berkolaiko, G.; Havlin, S.; Larralde, H.; Weiss, G. H.

    1996-06-01

    We calculate asymptotic forms for the expected number of distinct sites, , visited by N noninteracting n-step symmetric Lévy flights in one dimension. By a Lévy flight we mean one in which the probability of making a step of j sites is proportional to 1/\\|j\\|1+α in the limit j-->∞. All values of α>~0 are considered. In our analysis each Lévy flight is initially at the origin and both N and n are assumed to be large. Different asymptotic results are obtained for different ranges in α. When n is fixed and N-->∞ we find that is proportional to (Nn2)1/(1+α) for α~1. When α exceeds 2 the second moment is finite and one expects the results of Larralde et al. [Phys. Rev. A 45, 7128 (1992)] to be valid. We give results for both fixed n and N-->∞ and N fixed and n-->∞. In the second case the analysis leads to the behavior predicted by Larralde et al.

  17. Freestyle-Like V-Y Flaps of the Eyebrow: A New Outlook and Indication of an Historical Technique

    Directory of Open Access Journals (Sweden)

    Angelo Alberto Leto Barone

    2013-01-01

    Full Text Available The eyebrow region is of utmost importance for facial movement, symmetry, and the overall cosmetic appearance of the face. Trauma or tumor resection often leave scars that may dislocate the eyebrow producing an alteration both in static symmetry of the face and in the dynamic expressivity. The authors present a technique for eyebrow’s defects repair using the remaining eyebrow advancement by means of a “freestyle-like” V-Y flap. In the past two years a total of eight consecutive patients underwent excision of skin lesions in the superciliary region and immediate reconstruction with this technique. On histology, six patients were affected from basal cell carcinomas, one from squamous cell carcinoma, and one from congenital intradermal melanocytic nevus. The pedicle of the flap included perforators from the supratrochlear, supraorbital, or superficial temporalis artery. Advancement of the entire aesthetic subunit that includes the eyebrow using a V-Y perforator flap was performed successfully in all cases achieving full, tension-free closure of defects up to 3.0 cm. “Freestyle-like” V-Y flaps should be considered as a first-line choice for partial defects of the eyebrow. The greater mobility compared to random subcutaneous flaps allows to reconstruct large defects providing an excellent cosmetic result.

  18. The MiMeS Survey of Magnetism in Massive Stars: CNO surface abundances of Galactic O stars

    CERN Document Server

    Martins, F; Bouret, J -C; Marcolino, W; Wade, G A; Neiner, C; Alecian, E; Grunhut, J; Petit, V

    2014-01-01

    The evolution of massive stars is still partly unconstrained. Mass, metallicity, mass loss and rotation are the main drivers of stellar evolution. Binarity and magnetic field may also significantly affect the fate of massive stars. Our goal is to investigate the evolution of single O stars in the Galaxy. For that, we use a sample of 74 objects comprising all luminosity classes and spectral types from O4 to O9.7. We rely on optical spectroscopy obtained in the context of the MiMeS survey of massive stars. We perform spectral modelling with the code CMFGEN. We determine the surface properties of the sample stars, with special emphasis on abundances of carbon, nitrogen and oxygen. Most of our sample stars have initial masses in the range 20 to 50 Msun. We show that nitrogen is more enriched and carbon/oxygen more depleted in supergiants than in dwarfs, with giants showing intermediate degrees of mixing. CNO abundances are observed in the range of values predicted by nucleosynthesis through the CNO cycle. More ma...

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

    CERN Document Server

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

    2006-01-01

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

  20. Le primitif et le mystique chez Lévy-Bruhl, Bergson et Bataille.

    Directory of Open Access Journals (Sweden)

    Frédéric Keck

    2004-04-01

    Full Text Available L’assimilation du fou, du primitif et de l’enfant a été souvent analysée comme une opposition de l’archaïque par rapport au civilisé ou du normal par rapport au pathologique. On veut montrer ici que le mystique s’ajoute à cette liste, celle-ci désignant alors plutôt des figures de l’altérité qui défient la raison. On étudie alors les liens entre la figure du primitif et celle du mystique dans la sociologie de Lévy-Bruhl, la métaphysique de Bergson et la pratique littéraire de Bataille. Par-delà les divergences entre ces trois œuvres, on montre que le lien entre primitif et mystique vise à élargir le champ de l’expérience en l’ouvrant à une altérité radicale, et en même temps prépare le terrain pour cette expérience vide et formelle que pensera le structuralisme.French human sciences at the beginning of the 20th century used to assimilate the figures of the mad person, the primitive and the child. The Author shows that this assimilation should not be interpreted in the sense of an opposition between the archaic and the developed, or the normal and the pathological, but, once the figure of the mystic is added to this list, in the sense of an opposition between rationality and its other. Three examples allows to analyse the link between the figures of the primitive and the mystic : the sociology of Lévy-Bruhl, the metaphysics of Bergson, the literature of Bataille. Through the reading of these three works, the Author shows that the link between the figures of the primitive and the mystic allows to think a larger experience by opening it to an alterity, and at the same time prepares the ground for an empty and formal experience that will be explored by structuralism.