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Sample records for modelling stellar coronae

  1. Magnetohydrostatic modelling of stellar coronae

    CERN Document Server

    MacTaggart, David; Neukirch, Thomas; Donati, Jean-Francois

    2015-01-01

    We introduce to the stellar physics community a method of modelling stellar coronae that can be considered to be an extension of the potential field. In this approach, the magnetic field is coupled to the background atmosphere. The model is magnetohydrostatic (MHS) and is a balance between the Lorentz force, the pressure gradient and gravity. Analytical solutions are possible and we consider a particular class of equilibria in this paper. The model contains two free parameters and the effects of these on both the geometry and topology of the coronal magnetic field are investigated. A demonstration of the approach is given using a magnetogram derived from Zeeman-Doppler imaging of the 0.75 M$_{\\odot}$ M-dwarf star GJ 182.

  2. Modeling X-ray emission from stellar coronae

    CERN Document Server

    Gregory, S G; Argiroffi, C; Donati, J -F

    2008-01-01

    By extrapolating from observationally derived surface magnetograms of low-mass stars we construct models of their coronal magnetic fields and compare the 3D field geometry with axial multipoles. AB Dor, which has a radiative core, has a very complex field, whereas V374 Peg, which is completely convective, has a simple dipolar field. We calculate global X-ray emission measures assuming that the plasma trapped along the coronal loops is in hydrostatic equilibrium and compare the differences between assuming isothermal coronae, or by considering a loop temperature profiles. Our preliminary results suggest that the non-isothermal model works well for the complex field of AB Dor, but not for the simple field of V374 Peg.

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

    Science.gov (United States)

    Cohen, O.

    2017-02-01

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

  4. Flare Heating in Stellar Coronae

    CERN Document Server

    Kashyap, V L; Güdel, M; Audard, M; Kashyap, Vinay; Drake, Jeremy; Guedel, Manuel; Audard, Marc

    2002-01-01

    We investigate the contribution of very weak flares to the coronal luminosity of low-mass active stars. We analyze EUVE/DS events data from FK Aqr, V1054 Oph, and AD Leo and conclude that in all these cases the coronal emission is dominated by flares to such an extent that in some cases the entire emission may be ascribed to flare heating. We have developed a new method to directly model for the first time stochastically produced flare emission, including undetectable flares, and their effects on the observed photon arrival times. We find that the index of the power-law distribution of flare energies (dN/dE ~ E^{-alpha}) is 2.6+-0.34, 2.74+-0.35, and 2.03-2.32 for FK Aqr, V1054 Oph, and AD Leo respectively. We also find that the flare component accounts for a large fraction (generally >50 percent) of the total flux.

  5. INDUCED SCATTERING LIMITS ON FAST RADIO BURSTS FROM STELLAR CORONAE

    Energy Technology Data Exchange (ETDEWEB)

    Lyubarsky, Yuri [Physics Department, Ben-Gurion University, P.O.B. 653, Beer-Sheva 84105 (Israel); Ostrovska, Sofiya [Department of Mathematics, Atilim University, Incek 06836, Ankara (Turkey)

    2016-02-10

    The origin of fast radio bursts remains a puzzle. Suggestions have been made that they are produced within the Earth’s atmosphere, in stellar coronae, in other galaxies, or at cosmological distances. If they are extraterrestrial, the implied brightness temperature is very high, and therefore the induced scattering places constraints on possible models. In this paper, constraints are obtained on flares from coronae of nearby stars. It is shown that the radio pulses with the observed power could not be generated if the plasma density within and in the nearest vicinity of the source is as high as is necessary to provide the observed dispersion measure. However, one cannot exclude the possibility that the pulses are generated within a bubble with a very low density and pass through the dense plasma only in the outer corona.

  6. Influence of surface stressing on stellar coronae and winds

    CERN Document Server

    Jardine, M; van Ballegooijen, A; Donati, J -F; Morin, J; Fares, R; Gombosi, T I

    2013-01-01

    The large-scale field of the Sun is well represented by its lowest energy (or potential) state. Recent observations, by comparison, reveal that many solar-type stars show large-scale surface magnetic fields that are highly non-potential - that is, they have been stressed above their lowest-energy state. This non-potential component of the surface field is neglected by current stellar wind models. The aim of this paper is to determine its effect on the coronal structure and wind. We use Zeeman-Doppler surface magnetograms of two stars - one with an almost potential, one with a non-potential surface field - to extrapolate a static model of the coronal structure for each star. We find that the stresses are carried almost exclusively in a band of uni-directional azimuthal field that is confined to mid-latitudes. Using this static solution as an initial state for an MHD wind model, we then find that the final state is determined primarily by the potential component of the surface magnetic field. The band of azimut...

  7. Coronal seismology waves and oscillations in stellar coronae

    CERN Document Server

    Stepanov, Alexander; Nakariakov, Valery M

    2012-01-01

    This concise and systematic account of the current state of this new branch of astrophysics presents the theoretical foundations of plasma astrophysics, magneto-hydrodynamics and coronal magnetic structures, taking into account the full range of available observation techniques -- from radio to gamma. The book discusses stellar loops during flare energy releases, MHD waves and oscillations, plasma instabilities and heating and charged particle acceleration. Current trends and developments in MHD seismology of solar and stellar coronal plasma systems are also covered, while recent p

  8. From solar to stellar corona: the role of wind, rotation and magnetism

    CERN Document Server

    Réville, Victor; Strugarek, Antoine; Matt, Sean P; Bouvier, Jérôme; Folsom, Colin P; Petit, Pascal

    2015-01-01

    Observations of surface magnetic fields are now within reach for many stellar types thanks to the development of Zeeman-Doppler Imaging. These observations are extremely useful for constraining rotational evolution models of stars, as well as for characterizing the generation of magnetic field. We recently demonstrated that the impact of coronal magnetic field topology on the rotational braking of a star can be parametrized with a scalar parameter: the open magnetic flux. However, without running costly numerical simulations of the stellar wind, reconstructing the coronal structure of the large scale magnetic field is not trivial. An alternative -broadly used in solar physics- is to extrapolate the surface magnetic field assuming a potential field in the corona, to describe the opening of the field lines by the magnetized wind. This technique relies on the definition of a so-called source surface radius, which is often fixed to the canonical value of 2.5Rsun. However this value likely varies from star to star...

  9. Global MHD Models of the Solar Corona

    Science.gov (United States)

    Suess, S. T.; Rose, Franklin (Technical Monitor)

    2001-01-01

    Global magnetohydrodynamic (MHD) models of the solar corona are computationally intensive, numerically complex simulations that have produced important new results over the past few years. After a brief overview of how these models usually work, I will address three topics: (1) How these models are now routinely used to predict the morphology of the corona and analyze Earth and space-based remote observations of the Sun; (2) The direct application of these models to the analysis of physical processes in the corona and chromosphere and to the interpretation of in situ solar wind observations; and (3) The use of results from global models to validate the approximations used to make detailed studies of physical processes in the corona that are not otherwise possible using the global models themselves.

  10. Warm gas towards young stellar objects in Corona Australis

    DEFF Research Database (Denmark)

    Lindberg, Johan; Jørgensen, Jes Kristian; D. Green, Joel;

    2014-01-01

    by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented...

  11. Variability of a stellar corona on a time scale of days

    CERN Document Server

    Nordon, Raanan; Drake, Stephen A

    2012-01-01

    Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the First Ionization Potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. We present an analysis of the thermal and chemical structure of the Ei Eri corona as it evolves over the six days. Although the corona is rather steady in its temperature distribution, the emission measure and FIP bias both vary and seem to be correlated. An active region, predating the beginning of the campaign, repeatedly enters into our view at the same phase as it rotates from beyond the stellar limb. As a result, the abundances tend slightly, but consistently, to increa...

  12. Nanoflare heating model for collisionless solar corona

    Indian Academy of Sciences (India)

    U L VISAKH KUMAR; BILIN SUSAN VARGHESE; P J KURIAN

    2017-02-01

    The problem of coronal heating remains one of the greatest unresolved problems in space science. Magnetic reconnection plays a significant role in heating the solar corona. When two oppositely directed magnetic fields come closer to form a current sheet, the current density of the plasma increases due to which magnetic reconnection and conversion of magnetic energy into thermal energy takes place. The present paper deals with a model for reconnection occurring in the solar corona under steady state in collisionless regime. The model predicts that reconnection time in the solar corona varies inversely with the cube of magnetic field and varies directly with the Lindquist number. Our analysis shows that reconnections are occurring within a time interval of600 s in the solar corona, producing nanoflares in the energy range $10^{21}–10^{23}$ erg/s which matches with Yohkoh X-ray observations.

  13. Nanoflare heating model for collisionless solar corona

    Science.gov (United States)

    Visakh Kumar, U. L.; Varghese, Bilin Susan; Kurian, P. J.

    2017-02-01

    The problem of coronal heating remains one of the greatest unresolved problems in space science. Magnetic reconnection plays a significant role in heating the solar corona. When two oppositely directed magnetic fields come closer to form a current sheet, the current density of the plasma increases due to which magnetic reconnection and conversion of magnetic energy into thermal energy takes place. The present paper deals with a model for reconnection occurring in the solar corona under steady state in collisionless regime. The model predicts that reconnection time in the solar corona varies inversely with the cube of magnetic field and varies directly with the Lindquist number. Our analysis shows that reconnections are occurring within a time interval of 600 s in the solar corona, producing nanoflares in the energy range 10 21-10 23 erg /s which matches with Yohkoh X-ray observations.

  14. He-like ions as practical astrophysical plasma diagnostics: From stellar coronae to active galactic nuclei

    CERN Document Server

    Porquet, Delphine; Grosso, Nicolas; 10.1007/s11214-010-9731-2

    2011-01-01

    We review X-ray plasma diagnostics based on the line ratios of He-like ions. Triplet/singlet line intensities can be used to determine electronic temperature and density, and were first developed for the study of the solar corona. Since the launches of the X-ray satellites Chandra and XMM-Newton, these diagnostics have been extended and used (from CV to Si XIII) for a wide variety of astrophysical plasmas such as stellar coronae, supernova remnants, solar system objects, active galactic nuclei, and X-ray binaries. Moreover, the intensities of He-like ions can be used to determine the ionization process(es) at work, as well as the distance between the X-ray plasma and the UV emission source for example in hot stars. In the near future thanks to the next generation of X-ray satellites (e.g., Astro-H and IXO), higher-Z He-like lines (e.g., iron) will be resolved, allowing plasmas with higher temperatures and densities to be probed. Moreover, the so-called satellite lines that are formed closed to parent He-like ...

  15. Advances of plasma diagnostics with high-resolution spectroscopy of stellar coronae

    CERN Document Server

    Ness, J U

    2005-01-01

    X-ray emission from cool stars is an important tracer for stellar activity. The X-ray luminosity reflects different levels of activity and covers four orders of magnitude in stars of spectral types M-F. Low spectral resolution provided by X-ray observations of stellar coronae in the past allowed the determination of temperature distributions and elemental abundances making use of atomic databases (listing line emissivities and bremsstrahlung continuum for a given temperature structure). The new missions XMM-Newton and Chandra carry X-ray gratings providing sufficient spectral resolution to measure the fluxes of strategic emission lines. I describe the different approaches applicable to low-resolution and high-resolution spectra, especially focusing on the new grating spectra with X-ray lines. From only a few lines it is possible to determine plasma temperatures and associated densities, to check for any effects from resonant scattering, and to identify particular abundance anomalies. Line-based temperature- a...

  16. The FIP and Inverse FIP Effects in Solar and Stellar Coronae

    CERN Document Server

    Laming, J Martin

    2015-01-01

    We review our state of knowledge of coronal element abundance anomalies in the Sun and stars. We concentrate on the first ionization potential (FIP) effect observed in the solar corona and slow-speed wind, and in the coronae of solar-like dwarf stars, and the "inverse FIP" effect seen in the corona of stars of later spectral type; specifically M dwarfs. These effects relate to the enhancement or depletion, respectively, in coronal abundance with respect to photospheric values of elements with FIP below about 10~eV. They are interpreted in terms of the ponderomotive force due to the propagation and/or reflection of magnetohydrodynamic waves in the chromosphere. This acts on chromospheric ions, but not neutrals, and so can lead to ion-neutral fractionation. A detailed description of the model applied to closed magnetic loops, and to open field regions is given, accounting for the observed difference in solar FIP fractionation between the slow and fast wind. It is shown that such a model can also account for the...

  17. A Unified Computational Model for Solar and Stellar Flares

    Science.gov (United States)

    Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats

    2015-01-01

    We present a unified computational framework that can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how flare-accelerated charged particles propagate down one-dimensional flux tubes and heat the stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere. These effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

  18. A Unified Computational Model for Solar and Stellar Flares

    CERN Document Server

    Allred, Joel C; Carlsson, Mats

    2015-01-01

    We present a unified computational framework which can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how flare-accelerated charged particles propagate down one-dimensional flux tubes and heat the stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere. These effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and...

  19. Relativistic stellar models

    Indian Academy of Sciences (India)

    A J John; S D Maharaj

    2011-09-01

    We obtain a class of solutions to the Einstein–Maxwell equations describing charged static spheres. Upon specifying particular forms for one of the gravitational potentials and the electric field intensity, the condition for pressure isotropy is transformed into a hypergeometric equation with two free parameters. For particular parameter values we recover uncharged solutions corresponding to specific neutron star models. We find two charged solutions in terms of elementary functions for particular parameter values. The first charged model is physically reasonable and the metric functions and thermodynamic variables are well behaved. The second charged model admits a negative energy density and violates the energy conditions.

  20. A Unified Computational Model for Solar and Stellar Flares

    OpenAIRE

    Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats

    2015-01-01

    We present a unified computational framework which can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into...

  1. Stellar models in Brane Worlds

    CERN Document Server

    Linares, Francisco X; Ureña-Lopez, L Arturo

    2015-01-01

    We consider here a full study of stellar dynamics from the brane-world point of view in the case of constant density and of a polytropic fluid. We start our study cataloguing the minimal requirements to obtain a compact object with a Schwarszchild exterior, highlighting the low and high energy limit, the boundary conditions, and the appropriate behavior of Weyl contributions inside and outside of the star. Under the previous requirements we show an extensive study of stellar behavior, starting with stars of constant density and its extended cases with the presence of nonlocal contributions. Finally, we focus our attention to more realistic stars with a polytropic equation of state, specially in the case of white dwarfs, and study their static configurations numerically. One of the main results is that the inclusion of the Weyl functions from braneworld models allow the existence of more compact configurations than within General Relativity.

  2. Development of Efficient Models of Corona Discharges Around Tall Structures

    Science.gov (United States)

    Tucker, J.; Pasko, V. P.

    2012-12-01

    This work concerns with numerical modeling of glow corona and sreamer corona discharges that occur near tall ground structures under thunderstorm conditions. Glow corona can occur when ambient electric field reaches modest values on the order of 0.2 kV/cm and when the electric field near sharp points of ground structure rises above a geometry dependent critical field required for ionization of air. Air is continuously ionized in a small region close to the surface of the structure and ions diffuse out into the surrounding air forming a corona. A downward leader approaching from a thundercloud causes a further increase in the electric field at the ground level. If the electric field rises to the point where it can support formation of streamers in air surrounding the tall structure, a streamer corona flash, or series of streamer corona flashes can be formed significantly affecting the space charge configuration formed by the preceding glow corona. The streamer corona can heat the surrounding air enough to form a self-propagating thermalized leader that is launched upward from the tall structure. This leader travels upward towards the thundercloud and connects with the downward approaching leader thus causing a lightning flash. Accurate time-dependent modeling of charge configuration created by the glow and streamer corona discharges around tall structure is an important component for understanding of the sequence of events leading to lightning attachment to the tall structure. The present work builds on principal modeling ideas developed previously in [Aleksandrov et al., J. Phys. D: Appl. Phys., 38, 1225, 2005; Bazelyan et al., Plasma Sources Sci. Technol., 17, 024015, 2008; Kowalski, E. J., Honors Thesis, Penn State Univ., University Park, PA, May 2008; Tucker and Pasko, NSF EE REU Penn State Annual Res. J., 10, 13, 2012]. The non-stationary glow and streamer coronas are modeled in spherical geometry up to the point of initiation of the upward leader. The model

  3. Corona graphs as a model of small-world networks

    Science.gov (United States)

    Lv, Qian; Yi, Yuhao; Zhang, Zhongzhi

    2015-11-01

    We introduce recursive corona graphs as a model of small-world networks. We investigate analytically the critical characteristics of the model, including order and size, degree distribution, average path length, clustering coefficient, and the number of spanning trees, as well as Kirchhoff index. Furthermore, we study the spectra for the adjacency matrix and the Laplacian matrix for the model. We obtain explicit results for all the quantities of the recursive corona graphs, which are similar to those observed in real-life networks.

  4. Variability of a Stellar Corona on a Time Scale of Days: Evidence for Abundance Fractionation in an Emerging Coronal Active Region

    Science.gov (United States)

    Nordon, R.; Behar, E.; Drake, S. A.

    2013-01-01

    Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the first ionization potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. We present an analysis of the thermal and chemical structure of the EI Eri corona as it evolves over the six days. Although the corona is rather steady in its temperature distribution, the emission measure and FIP bias both vary and seem to be correlated. An active region, predating the beginning of the campaign, repeatedly enters into our view at the same phase as it rotates from beyond the stellar limb. As a result, the abundances tend slightly, but consistently, to increase for high FIP elements (an inverse FIP effect) with phase. We estimate the abundance increase of high FIP elements in the active region to be of about 75% over the coronal mean. This observed fractionation of elements in an active region on time scales of days provides circumstantial clues regarding the element enrichment mechanism of non-flaring stellar coronae.

  5. Modeling Jets in the Corona and Solar Wind

    CERN Document Server

    Torok, T; Titov, V S; Leake, J E; Mikic, Z; Linker, J A; Linton, M G

    2015-01-01

    Coronal jets are transient, collimated eruptions that occur in regions of predominantly open magnetic field in the solar corona. Our understanding of these events has greatly evolved in recent years but several open questions, such as the contribution of coronal jets to the solar wind, remain. Here we present an overview of the observations and numerical modeling of coronal jets, followed by a brief description of "next-generation" simulations that include an advanced description of the energy transfer in the corona ("thermodynamic MHD"), large spherical computational domains, and the solar wind. These new models will allow us to address some of the open questions.

  6. Warm gas towards young stellar objects in Corona Australis - Herschel/PACS observations from the DIGIT key programme

    CERN Document Server

    Lindberg, Johan E; Green, Joel D; Herczeg, Gregory J; Dionatos, Odysseas; Evans, Neal J; Karska, Agata; Wampfler, Susanne F

    2013-01-01

    The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented. The distribution of CO, OH, H2O, [C II], [O I], and continuum emission is investigated. We have developed a deconvolution algorithm which we use to deconvolve the maps, separating the point-source emission from the extended emission. We also construct rotational diagrams of the molecular species. By deconvolution of the Herschel data, we find large-scale (several thousand AU) dust continuum and spectral line emission not associate...

  7. Semi-analytical modelling of positive corona discharge in air

    Science.gov (United States)

    Pontiga, Francisco; Yanallah, Khelifa; Chen, Junhong

    2013-09-01

    Semianalytical approximate solutions of the spatial distribution of electric field and electron and ion densities have been obtained by solving Poisson's equations and the continuity equations for the charged species along the Laplacian field lines. The need to iterate for the correct value of space charge on the corona electrode has been eliminated by using the corona current distribution over the grounded plane derived by Deutsch, which predicts a cos m θ law similar to Warburg's law. Based on the results of the approximated model, a parametric study of the influence of gas pressure, the corona wire radius, and the inter-electrode wire-plate separation has been carried out. Also, the approximate solutions of the electron number density has been combined with a simplified plasma chemistry model in order to compute the ozone density generated by the corona discharge in the presence of a gas flow. This work was supported by the Consejeria de Innovacion, Ciencia y Empresa (Junta de Andalucia) and by the Ministerio de Ciencia e Innovacion, Spain, within the European Regional Development Fund contracts FQM-4983 and FIS2011-25161.

  8. Model of Ozone Production in the DC Corona Discharge

    Science.gov (United States)

    Chen, Junhong; Davidson, Jane

    2002-10-01

    A comprehensive numerical model of ozone production in clean, dry air by DC corona discharges is presented. This model combines a first-principle corona plasma model with a chemistry and 2-D transport model to obtain the distributions of ozone and other gaseous products in the neighborhood of a corona discharge wire. Electron number density distribution is obtained by solving the continuity equations for electrons and ions and the simplified Maxwell's equation. The non-Maxwellian electron energy distribution is solved from the Boltzmann equation. The chemical kinetics of ozone formation and destruction are based on recent atmospheric chemistry models taking into account the contributions of excited molecules. The transport model includes the conservation equations for total mass, momentum, energy and the mass of individual species and is solved using FLUENT. The predicted ozone production rate agrees well with experimental data. Excited molecules contribute more than 80 percent of the total ozone produced. The effects of discharge polarity, current, wire radius, air temperature, and air velocity (residence time) on the production of ozone are discussed.

  9. Theory of stellar convection - II. First stellar models

    Science.gov (United States)

    Pasetto, S.; Chiosi, C.; Chiosi, E.; Cropper, M.; Weiss, A.

    2016-07-01

    We present here the first stellar models on the Hertzsprung-Russell diagram, in which convection is treated according to the new scale-free convection theory (SFC theory) by Pasetto et al. The aim is to compare the results of the new theory with those from the classical, calibrated mixing-length (ML) theory to examine differences and similarities. We integrate the equations describing the structure of the atmosphere from the stellar surface down to a few per cent of the stellar mass using both ML theory and SFC theory. The key temperature over pressure gradients, the energy fluxes, and the extension of the convective zones are compared in both theories. The analysis is first made for the Sun and then extended to other stars of different mass and evolutionary stage. The results are adequate: the SFC theory yields convective zones, temperature gradients ∇ and ∇e, and energy fluxes that are very similar to those derived from the `calibrated' MT theory for main-sequence stars. We conclude that the old scale dependent ML theory can now be replaced with a self-consistent scale-free theory able to predict correct results, as it is more physically grounded than the ML theory. Fundamentally, the SFC theory offers a deeper insight of the underlying physics than numerical simulations.

  10. Theory of stellar convection II: first stellar models

    CERN Document Server

    Pasetto, S; Chiosi, E; Cropper, M; Weiss, A

    2015-01-01

    We present here the first stellar models on the Hertzsprung-Russell diagram (HRD), in which convection is treated according to the novel scale-free convection theory (SFC theory) by Pasetto et al. (2014). The aim is to compare the results of the new theory with those from the classical, calibrated mixing-length (ML) theory to examine differences and similarities. We integrate the equations describing the structure of the atmosphere from the stellar surface down to a few percent of the stellar mass using both ML theory and SFC theory. The key temperature over pressure gradients, the energy fluxes, and the extension of the convective zones are compared in both theories. The analysis is first made for the Sun and then extended to other stars of different mass and evolutionary stage. The results are adequate: the SFC theory yields convective zones, temperature gradients of the ambient and of the convective element, and energy fluxes that are very similar to those derived from the "calibrated" MT theory for main s...

  11. Stellar Coronae with \\textit{XMM-Newton} RGS. I. Coronal Structure

    CERN Document Server

    Güdel, M; Den Boggende, A J F; Brinkman, A C; Den Herder, J W A; Kaastra, J S; Mewe, R; Raassen, A J J; De Vries, C; Behar, E; Cottam, J; Kahn, S M; Paerels, F B S; Peterson, J M; Rasmussen, A P; Sako, M; Branduardi-Raymont, G; Sakelliou, I; Erd, Christian

    2000-01-01

    First results from high-resolution coronal spectroscopy with the {\\it XMM-Newton} Reflection Grating Spectrometers (RGS) are reviewed. Five stellar systems (HR 1099, Capella, Procyon, YY Gem, AB Dor) have been observed. The emphasis of the present paper is on overall coronal structure. Elemental abundances in {\\it active stars} are found to be `anomalous' in the sense that they tend to increase with increasing First Ionization Potential (FIP - i.e., signifying an inverse FIP effect). Coronal densities are measured at levels of a few times $10^{10}$ cm$^{-3}$ for cooler plasma, although there are indications for very high densities in the hotter plasma components.

  12. The energy input mechanism into the lower transition regions between stellar chromospheres and coronae

    Science.gov (United States)

    Boehm-Vitense, Erika

    1988-01-01

    The ratio of the emission line fluxes for the C II and C IV lines in the lower transition regions (T = 30,000 to 100,000 K) between stellar chromospheres and transition layers is shown to depend mainly on the temperature gradient in the line emitting regions which can therefore be determined from this line ratio. From the observed constant (within the limits of observational error) ratio of the emission line fluxes of the C II (1335 A) and C IV (1550 A) lines it is concluded that the temperature gradients in the lower transition layers are similar for the large majority of stars independently of T sub eff, L, and degree of activity. This means that the temperature dependence of the damping length for the mechanical flux must be the same for all these stars. Since for different kinds of mechanical fluxes the dependence of the damping length on gas pressure and temperature is quite different, it is concluded that the same heating mechanism must be responsible for the heating of all the lower transition layers of these stars, regardless of their chromospheric activity. Only the amount of mechanical flux changes. The T Tauri stars are exceptions: their emission lines are probably mainly due to circumstellar material.

  13. Chemical element transport in stellar evolution models

    Science.gov (United States)

    Cassisi, Santi

    2017-01-01

    Stellar evolution computations provide the foundation of several methods applied to study the evolutionary properties of stars and stellar populations, both Galactic and extragalactic. The accuracy of the results obtained with these techniques is linked to the accuracy of the stellar models, and in this context the correct treatment of the transport of chemical elements is crucial. Unfortunately, in many respects calculations of the evolution of the chemical abundance profiles in stars are still affected by sometimes sizable uncertainties. Here, we review the various mechanisms of element transport included in the current generation of stellar evolution calculations, how they are implemented, the free parameters and uncertainties involved, the impact on the models and the observational constraints.

  14. Formation of Novae and Coronae on Venus. Tectonophysical Modeling Using Gravity Models

    Science.gov (United States)

    Krassilnikov, A. S.

    2001-03-01

    Novae and coronae formation was simulated using caoutchouc as a model of lower ductile part of lithosphere and dry flour as a model of upper brittle part of it. Distribution and character of the deformational structures is described.

  15. Recent advances in modeling stellar interiors (u)

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, Joyce Ann [Los Alamos National Laboratory

    2010-01-01

    Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid {gamma} Dor/{delta} Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as {eta} Car and P Cyg, and the solar abundance problem.

  16. Modeling of Carbon Monoxide Removal by Corona Plasma

    Institute of Scientific and Technical Information of China (English)

    FENG Jingwei; SUN Yabing; ZHAO Dayong; ZHENG Zheng; XU Yuewu; YANG Haifeng; ZHU Hongbiao; ZHOU Xiaoxia

    2009-01-01

    Modeling of carbon monoxide (CO) removal by a corona plasma was conducted in this study.The purification efficiency of CO was calculated theoretically and the factors affecting the removal of CO were analyzed.The results showed that the main removal mechanisms of CO were direct dissociation by generated high-energy electrons and indirect oxidation by generated hydroxyl radicals.The purification efficiency of CO was dependent on the plasma parameters,indoor air humidity and initial concentration of CO.Good consistency between the theoretical calculation and the experimental results was observed.

  17. A few days before the end of the 2008 extreme outburst of EX Lupi: accretion shocks and a smothered stellar corona unveiled by XMM-Newton

    Science.gov (United States)

    Grosso, N.; Hamaguchi, K.; Kastner, J. H.; Richmond, M. W.; Weintraub, D. A.

    2010-11-01

    -ray spectral component is most likely associated with accretion shocks, as opposed to jet activity, given the absence of forbidden emission lines of low-excitation species (e.g., [O i]) in optical spectra of EX Lup obtained during outburst. The hard X-ray spectral component, meanwhile, is most likely associated with a smothered stellar corona. The UV emission is reminiscent of accretion events, such as those already observed with the Optical/UV Monitor from other accreting pre-main sequence stars, and is evidently dominated by emission from accretion hot spots. The large photoelectric absorption of the active stellar corona is most likely due to high-density gas above the corona in accretion funnel flows.

  18. Modelling stellar jets with magnetospheres using as initial states analytical MHD solutions

    CERN Document Server

    Todorov, P; Cayatte, V; Sauty, C; Lima, J J G; Tsinganos, K

    2016-01-01

    In this paper we focus on the construction of stellar outflow models emerging from a polar coronal hole-type region surrounded by a magnetosphere in the equatorial regions during phases of quiescent accretion. The models are based on initial analytical solutions. We adopt a meridionally self-similar solution of the time-independent and axisymmetric MHD equations which describes effectively a jet originating from the corona of a star. We modify appropriately this solution in order to incorporate a physically consistent stellar magnetosphere. We find that the closed fieldline region may exhibit different behaviour depending on the associated boundary conditions and the distribution of the heat flux. However, the stellar jet in all final equilibrium states is very similar to the analytical one prescribed in the initial conditions. When the initial net heat flux is maintained, the magnetosphere takes the form of a dynamical helmet streamer with a quasi steady state slow magnetospheric wind. With no heat flux, a s...

  19. Approximate input physics for stellar modelling

    CERN Document Server

    Pols, O R; Eggleton, P P; Han, Z; Pols, O R; Tout, C A; Eggleton, P P; Han, Z

    1995-01-01

    We present a simple and efficient, yet reasonably accurate, equation of state, which at the moderately low temperatures and high densities found in the interiors of stars less massive than the Sun is substantially more accurate than its predecessor by Eggleton, Faulkner & Flannery. Along with the most recently available values in tabular form of opacities, neutrino loss rates, and nuclear reaction rates for a selection of the most important reactions, this provides a convenient package of input physics for stellar modelling. We briefly discuss a few results obtained with the updated stellar evolution code.

  20. Stellar Winds on the Main-Sequence I: Wind Model

    CERN Document Server

    Johnstone, C P; Lüftinger, T; Toth, G; Brott, I

    2015-01-01

    Aims: We develop a method for estimating the properties of stellar winds for low-mass main-sequence stars between masses of 0.4 and 1.1 solar masses at a range of distances from the star. Methods: We use 1D thermal pressure driven hydrodynamic wind models run using the Versatile Advection Code. Using in situ measurements of the solar wind, we produce models for the slow and fast components of the solar wind. We consider two radically different methods for scaling the base temperature of the wind to other stars: in Model A, we assume that wind temperatures are fundamentally linked to coronal temperatures, and in Model B, we assume that the sound speed at the base of the wind is a fixed fraction of the escape velocity. In Paper II of this series, we use observationally constrained rotational evolution models to derive wind mass loss rates. Results: Our model for the solar wind provides an excellent description of the real solar wind far from the solar surface, but is unrealistic within the solar corona. We run ...

  1. Galactic stellar haloes in the CDM model

    NARCIS (Netherlands)

    Cooper, A. P.; Cole, S.; Frenk, C. S.; White, S. D. M.; Helly, J.; Benson, A. J.; De Lucia, G.; Helmi, A.; Jenkins, A.; Navarro, J. F.; Springel, V.; Wang, J.

    2010-01-01

    We present six simulations of galactic stellar haloes formed by the tidal disruption of accreted dwarf galaxies in a fully cosmological setting. Our model is based on the Aquarius project, a suite of high-resolution N-body simulations of individual dark matter haloes. We tag subsets of particles in

  2. An efficient algorithm for corona simulation with complex chemical models

    Science.gov (United States)

    Villa, Andrea; Barbieri, Luca; Gondola, Marco; Leon-Garzon, Andres R.; Malgesini, Roberto

    2017-05-01

    The simulation of cold plasma discharges is a leading field of applied sciences with many applications ranging from pollutant control to surface treatment. Many of these applications call for the development of novel numerical techniques to implement fully three-dimensional corona solvers that can utilize complex and physically detailed chemical databases. This is a challenging task since it multiplies the difficulties inherent to a three-dimensional approach by the complexity of databases comprising tens of chemical species and hundreds of reactions. In this paper a novel approach, capable of reducing significantly the computational burden, is developed. The proposed method is based on a proper time stepping algorithm capable of decomposing the original problem into simpler ones: each of them has then been tackled with either finite element, finite volume or ordinary differential equations solvers. This last solver deals with the chemical model and its efficient implementation is one of the main contributions of this work.

  3. Stellar wind models of subluminous hot stars

    CERN Document Server

    Krticka, J; Krtickova, I

    2016-01-01

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

  4. Stellar model atmospheres with magnetic line blanketing

    CERN Document Server

    Kochukhov, O; Shulyak, D

    2004-01-01

    Model atmospheres of A and B stars are computed taking into account magnetic line blanketing. These calculations are based on the new stellar model atmosphere code LLModels which implements direct treatment of the opacities due to the bound-bound transitions and ensures an accurate and detailed description of the line absorption. The anomalous Zeeman effect was calculated for the field strengths between 1 and 40 kG and a field vector perpendicular to the line of sight. The model structure, high-resolution energy distribution, photometric colors, metallic line spectra and the hydrogen Balmer line profiles are computed for magnetic stars with different metallicities and are discussed with respect to those of non-magnetic reference models. The magnetically enhanced line blanketing changes the atmospheric structure and leads to a redistribution of energy in the stellar spectrum. The most noticeable feature in the optical region is the appearance of the 5200 A depression. However, this effect is prominent only in ...

  5. Hypervirial Models of Stellar Systems

    CERN Document Server

    Evans, N W

    2005-01-01

    A family of cusped potential-density pairs is introduced for modelling galaxies and dark haloes. The density profile is cusped like 1/r^(2-p) at small radii. The distribution function takes the simple form L^(p-2) E^([3p+1]/2) (where E is the binding energy and L is the angular momentum). The models all possess the remarkable property that the virial theorem holds locally, from which they earn their name as the hypervirial family. Famously, this property was first discovered by Eddington to hold for the Plummer model in 1916. In fact, the seductive properties of the Plummer model extend to the whole hypervirial family, including the members possessing the cosmologically important cusps with density behaving like 1/r or 1/r^1.5 or 1/r^1.33. The intrinsic and projected properties of the family of models are discussed in some detail.

  6. Numerical simulations of stellar winds polytropic models

    CERN Document Server

    Keppens, R

    1999-01-01

    We discuss steady-state transonic outflows obtained by direct numerical solution of the hydrodynamic and magnetohydrodynamic equations. We make use of the Versatile Advection Code, a software package for solving systems of (hyperbolic) partial differential equations. We proceed stepwise from a spherically symmetric, isothermal, unmagnetized, non-rotating Parker wind to arrive at axisymmetric, polytropic, magnetized, rotating models. These represent 2D generalisations of the analytical 1D Weber-Davis wind solution, which we obtain in the process. Axisymmetric wind solutions containing both a `wind' and a `dead' zone are presented. Since we are solving for steady-state solutions, we efficiently exploit fully implicit time stepping. The method allows us to model thermally and/or magneto-centrifugally driven stellar outflows. We particularly emphasize the boundary conditions imposed at the stellar surface. For these axisymmetric, steady-state solutions, we can use the knowledge of the flux functions to verify the...

  7. Intermittent heating in the solar corona employing a 3D MHD model

    CERN Document Server

    Bingert, Sven

    2011-01-01

    We investigate the spatial and temporal evolution of the heating of the corona of a cool star such as our Sun in a three-dimensional magneto-hydrodynamic (3D MHD) model. We solve the 3D MHD problem numerically in a box representing part of the (solar) corona. The energy balance includes Spitzer heat conduction along the magnetic field and optically thin radiative losses. The self-consistent heating mechanism is based on the braiding of magnetic field lines rooted in the convective photosphere. Magnetic stress induced by photospheric motions leads to currents in the atmosphere which heat the corona through Ohmic dissipation. While the horizontally averaged quantities, such as heating rate, temperature or density, are relatively constant in time, the simulated corona is highly variable and dynamic, on average reaching temperatures and densities as found in observations. The strongest heating per particle is found in the transition region from the chromosphere to the corona. The heating is concentrated in curren...

  8. Constraints on photoevaporation models from (lack of) radio emission in the Corona Australis protoplanetary disks

    CERN Document Server

    Galván-Madrid, Roberto; Manara, Carlo Felice; Forbrich, Jan; Pascucci, Ilaria; Carrasco-González, Carlos; Goddi, Ciriaco; Hasegawa, Yasuhiro; Takami, Michihiro; Testi, Leonardo; .,

    2014-01-01

    Photoevaporation due to high-energy stellar photons is thought to be one of the main drivers of protoplanetary disk dispersal. The fully or partially ionized disk surface is expected to produce free-free continuum emission at centimeter (cm) wavelengths that can be routinely detected with interferometers such as the upgraded Very Large Array (VLA). We use deep (rms noise down to 8 $\\mu$Jy beam$^{-1}$ in the field of view center) 3.5 cm maps of the nearby (130 pc) Corona Australis (CrA) star formation (SF) region to constrain disk photoevaporation models. We find that the radio emission from disk sources in CrA is surprisingly faint. Only 3 out of 10 sources within the field of view are detected, with flux densities of order $10^2$ $\\mu$Jy. However, a significant fraction of their emission is non-thermal. Typical upper limits for non-detections are $3\\sigma\\sim 60~\\mu$Jy beam$^{-1}$. Assuming analytic expressions for the free-free emission from extreme-UV (EUV) irradiation, we derive stringent upper limits to ...

  9. Corona noise model of high-voltage AC transmission lines and engineering applications

    Institute of Scientific and Technical Information of China (English)

    Wu Jiuhui; Di Zelong

    2013-01-01

    In order to predict the levels of corona noise from high-voltage alternating current (AC) transmission lines,the mechanism of corona noise and the corresponding theoretical prediction model are investigated.On the basis of Drude model,the motion of positive and negative ions produced by high-voltage corona is analyzed,and the mechanism of corona noise is discovered.The theoretical prediction model is put forward by using Kirchhoff formula,which is verified by the well agreement between our result and others',considering the case of three-phase single lines.Moreover,the calculation results show that for both single and bundled lines,the sound pressure level of the typical frequency,i.e.twice the power frequency,attenuates slowly and leads to an obviously interferential phenomenon near the transmission lines,but the level of the bundled lines is smaller than that of the single ones under the same transmission voltage.Based on the mechanism of corona noise and the prediction model,it is obvious that bundled lines and/or increased line radius can be adopted to reduce corona noise in the practical engineering applications effectively.This model can also provide a theoretical guidance for the high-volt-age AC transmission line design.

  10. Semi-empirical Modeling of the Photosphere, Chromosphere, Transition Region, and Corona of the M-dwarf Host Star GJ 832

    CERN Document Server

    Fontenla, J M; Witbrod, Jesse; France, Kevin; Buccino, A; Mauas, Pablo; Vietes, Mariela; Walkowicz, Lucianne M

    2016-01-01

    Stellar radiation from X-rays to the visible provides the energy that controls the photochemistry and mass loss from exoplanet atmospheres. The important extreme ultraviolet (EUV) region (10--91.2~nm) is inaccessible and should be computed from a reliable stellar model. It is essential to understand the formation regions and physical processes responsible for the various stellar emission features in order to predict how the spectral energy distribution varies with age and activity levels. We compute a state-of-the-art semi-empirical atmospheric model and the emergent high-resolution synthetic spectrum of the moderately active M2~V star GJ~832 as the first of a series of models for stars with different activity levels. Using non-LTE radiative transfer techniques and including many molecular lines, we construct a one-dimensional simple model for the physical structure of the star's chromosphere, chromosphere-corona transition region, and corona. The synthesized spectrum for this model fits the continuum and lin...

  11. Towards a Realistic, Data-Driven Thermodynamic MHD Model of the Global Solar Corona

    CERN Document Server

    Downs, Cooper; van der Holst, Bart; Lugaz, Noé; Sokolov, Igor V; Gombosi, Tamas I

    2009-01-01

    In this work we describe our implementation of a thermodynamic energy equation into the global corona model of the Space Weather Modeling Framework (SWMF), and its development into the new Lower Corona (LC) model. This work includes the integration of the additional energy transport terms of coronal heating, electron heat conduction, and optically thin radiative cooling into the governing magnetohydrodynamic (MHD) energy equation. We examine two different boundary conditions using this model; one set in the upper transition region (the Radiative Energy Balance model), as well as a uniform chromospheric condition where the transition region can be modeled in its entirety. Via observation synthesis from model results and the subsequent comparison to full sun extreme ultraviolet (EUV) and soft X-Ray observations of Carrington Rotation (CR) 1913 centered on Aug 27, 1996, we demonstrate the need for these additional considerations when using global MHD models to describe the unique conditions in the low corona. Th...

  12. Improvements on analytic modelling of stellar spots

    CERN Document Server

    Montalto, M; Oshagh, M; Boisse, I; Bruno, G; Santos, N C

    2014-01-01

    In this work we present the solution of the stellar spot problem using the Kelvin-Stokes theorem. Our result is applicable for any given location and dimension of the spots on the stellar surface. We present explicitely the result up to the second degree in the limb darkening law. This technique can be used to calculate very efficiently mutual photometric effects produced by eclipsing bodies occulting stellar spots and to construct complex spot shapes.

  13. High Performance Computing Application: Solar Dynamo Model Project II, Corona and Heliosphere Component Initialization, Integration and Validation

    Science.gov (United States)

    2015-06-24

    allocate solar heating into any location of the corona . Its total contribution depended on the integration of the unsigned magnetic flux at 1 Rs...AFRL-RD-PS- TR-2015-0028 AFRL-RD-PS- TR-2015-0028 HIGH PERFORMANCE COMPUTING APPLICATION: SOLAR DYNAMO MODEL PROJECT II; CORONA AND HELIOSPHERE...Dynamo Model Project II, Corona and Heliosphere Component Initialization, Integration and Validation 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6

  14. A Novel Approach to Constraining Uncertain Stellar Evolution Models

    Science.gov (United States)

    Rosenfield, Philip; Girardi, Leo; Dalcanton, Julianne; Johnson, L. C.; Williams, Benjamin F.; Weisz, Daniel R.; Bressan, Alessandro; Fouesneau, Morgan

    2017-01-01

    Stellar evolution models are fundamental to nearly all studies in astrophysics. They are used to interpret spectral energy distributions of distant galaxies, to derive the star formation histories of nearby galaxies, and to understand fundamental parameters of exoplanets. Despite the success in using stellar evolution models, some important aspects of stellar evolution remain poorly constrained and their uncertainties rarely addressed. We present results using archival Hubble Space Telescope observations of 10 stellar clusters in the Magellanic Clouds to simultaneously constrain the values and uncertainties of the strength of core convective overshooting, metallicity, interstellar extinction, cluster distance, binary fraction, and age.

  15. Modeling the time evolution of the nanoparticle-protein corona in a body fluid.

    Directory of Open Access Journals (Sweden)

    Daniele Dell'Orco

    Full Text Available BACKGROUND: Nanoparticles in contact with biological fluids interact with proteins and other biomolecules, thus forming a dynamic corona whose composition varies over time due to continuous protein association and dissociation events. Eventually equilibrium is reached, at which point the continued exchange will not affect the composition of the corona. RESULTS: We developed a simple and effective dynamic model of the nanoparticle protein corona in a body fluid, namely human plasma. The model predicts the time evolution and equilibrium composition of the corona based on affinities, stoichiometries and rate constants. An application to the interaction of human serum albumin, high density lipoprotein (HDL and fibrinogen with 70 nm N-iso-propylacrylamide/N-tert-butylacrylamide copolymer nanoparticles is presented, including novel experimental data for HDL. CONCLUSIONS: The simple model presented here can easily be modified to mimic the interaction of the nanoparticle protein corona with a novel biological fluid or compartment once new data will be available, thus opening novel applications in nanotoxicity and nanomedicine.

  16. Confronting Substellar Theoretical Models with Stellar Ages

    CERN Document Server

    Dupuy, Trent J; Ireland, Michael J

    2009-01-01

    By definition, brown dwarfs never reach the main-sequence, cooling and dimming over their entire lifetime, thus making substellar models challenging to test because of the strong dependence on age. Currently, most brown dwarfs with independently determined ages are companions to nearby stars, so stellar ages are at the heart of the effort to test substellar models. However, these models are only fully constrained if both the mass and age are known. We have used the Keck adaptive optics system to monitor the orbit of HD 130948BC, a brown dwarf binary that is a companion to the young solar analog HD 130948A. The total dynamical mass of 0.109+/-0.003 Msun shows that both components are substellar, and the ensemble of available age indicators from the primary star suggests an age comparable to the Hyades, with the most precise age being 0.79 Gyr based on gyrochronology. Therefore, HD 130948BC is unique among field L and T dwarfs as it possesses a well-determined mass, luminosity, and age. Our results indicate tha...

  17. An updated MILES stellar library and stellar population models (Research Note)

    NARCIS (Netherlands)

    Falcon-Barroso, J.; Sanchez-Blazquez, P.; Vazdekis, A.; Ricciardelli, E.; Cardiel, N.; Cenarro, A. J.; Gorgas, J.; Peletier, R. F.

    Aims: We present a number of improvements to the MILES library and stellar population models. We correct some small errors in the radial velocities of the stars, measure the spectral resolution of the library and models more accurately, and give a better absolute flux calibration of the models.

  18. Starspots, stellar cycles and stellar flares: Lessons from solar dynamo models

    Science.gov (United States)

    Choudhuri, Arnab Rai

    2017-01-01

    In this review, we discuss whether the present solar dynamo models can be extrapolated to explain various aspects of stellar activity. We begin with a summary of the following kinds of data for solar-like stars: (i) data pertaining to stellar cycles from Ca H/K emission over many years; (ii) X-ray data indicating hot coronal activity; (iii) starspot data (especially about giant polar spots); and (iv) data pertaining to stellar superflares. Then we describe the current status of solar dynamo modelling—giving an introduction to the flux transport dynamo model, the currently favoured model for the solar cycle. While an extrapolation of this model to solar-like stars can explain some aspects of observational data, some other aspects of the data still remain to be theoretically explained. It is not clear right now whether we need a different kind of dynamo mechanism for stars having giant starspots or producing very strong superflares.

  19. A MHD-turbulence model for solar corona

    Science.gov (United States)

    Romeou, Z.; Velli, M.; Einaudi, G.

    2009-02-01

    The disposition of energy in the solar corona has always been a problem of great interest. It remains an open question how the low temperature photosphere supports the occurence of solar extreme phenomena. In this work, a turbulent heating mechanism for the solar corona through the framework of reduced magnetohydrodynamics (RMHD) is proposed. Two-dimensional incompressible long time simulations of the average energy disposition have been carried out with the aim to reveal the characteristics of the long time statistical behavior of a two-dimensional cross-section of a coronal loop and the importance of the photospheric time scales in the understanding of the underlying mechanisms. It was found that for a slow, shear type photospheric driving the magnetic field in the loop self-organizes at large scales via an inverse MHD cascade. The system undergoes three distinct evolutionary phases. The initial forcing conditions are quickly “forgotten” giving way to an inverse cascade accompanied with and ending up to electric current dissipation. Scaling laws are being proposed in order to quantify the nonlinearity of the system response which seems to become more impulsive for decreasing resistivity. It is also shown that few, if any, qualitative changes in the above results occur by increasing spatial resolution.

  20. An efficient model to simulate stable glow corona discharges and their transition into streamers

    Science.gov (United States)

    Liu, Lipeng; Becerra, Marley

    2017-03-01

    A computationally efficient model to evaluate stable glow corona discharges and their transition into streamers is proposed. The simplified physical model referred to as the SPM is based on the classic hydrodynamic model of charge particles and a quasi-steady state approximation for electrons. The solution follows a two-step segregated procedure, which solves sequentially the stationary continuity equation for electrons and then time-dependent continuity equations for ions. The validity of using the SPM to simulate glow corona discharges and their transition into streamers is demonstrated by performing comparisons with a fully coupled physical model (FPM) and with experimental data available in the literature for air under atmospheric conditions. It is shown that the SPM can obtain estimates similar to those calculated with the FPM and those measured in experiments but using significantly less computation time. Since the proposed model simulates efficiently the ionization layer without prior knowledge of the surface electric field or the discharge current, it is a computationally efficient alternative to calculations of glow corona discharges based on Kaptzov’s approximation (KAM). The model can also be employed to efficiently calculate the conditions for the transition of glow corona into streamers, overcoming the limitations of KAM to provide such estimates.

  1. Improving 1D Stellar Models with 3D Atmospheres

    CERN Document Server

    Mosumgaard, Jakob Rørsted; Weiss, Achim; Christensen-Dalsgaard, Jørgen; Trampedach, Regner

    2016-01-01

    Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature -- also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

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

    CERN Document Server

    Byler, Nell; Conroy, Charlie; Johnson, Benjamin D

    2016-01-01

    Accounting for nebular emission when modeling galaxy spectral energy distributions (SEDs) is important, as both line and continuum emission can contribute significantly to the total observed flux. In this work, we present a new nebular emission model integrated within the Flexible Stellar Population Synthesis code that computes the total line and continuum emission for complex stellar populations using the photoionization code Cloudy. The self-consistent coupling of the nebular emission to the matched ionizing spectrum produces emission line intensities that correctly scale with the stellar population as a function of age and metallicity. This more complete model of galaxy SEDs will improve estimates of global gas properties derived with diagnostic diagrams, star formation rates based on H$\\alpha$, and stellar masses derived from NIR broadband photometry. Our models agree well with results from other photoionization models and are able to reproduce observed emission from H II regions and star-forming galaxies...

  3. GrayStar: Web-based pedagogical stellar modeling

    Science.gov (United States)

    Short, C. Ian

    2017-01-01

    GrayStar is a web-based pedagogical stellar model. It approximates stellar atmospheric and spectral line modeling in JavaScript with visualization in HTML. It is suitable for a wide range of education and public outreach levels depending on which optional plots and print-outs are turned on. All plots and renderings are pure basic HTML and the plotting module contains original HTML procedures for automatically scaling and graduating x- and y-axes.

  4. Numerical modelling of ozone production in a wire-cylinder corona discharge and comparison with a wire-plate corona discharge

    Science.gov (United States)

    Wang, Pengxiang; Chen, Junhong

    2009-02-01

    The effect of electrode configuration on ozone production in the direct-current corona discharge of dry and humid air is studied by a numerical model that combines the electron distribution in the corona plasma, plasma chemistry and transport phenomena. Two electrode configurations are considered: wire-cylinder discharge with air flowing along the wire axis and wire-plate discharge with air flowing transverse to the wire. The ozone distributions in both types of discharges are compared. For both electrode configurations, the ozone production rate is higher in the negative corona than in the positive corona and it decreases with an increase in relative humidity. More importantly, the detailed ozone distribution in the neighbourhood of the discharge wire, together with the ozone kinetics, reveals the possible difference in the ozone production from the two discharges. With the same operating conditions and sufficiently short flow residence time, the ozone production rate is nearly the same for both electrode configurations. When the flow residence time is longer than the characteristic time for homogeneous ozone destruction, the net ozone production is higher in the wire-cylinder discharge than in the wire-plate discharge due to relatively less ozone destruction.

  5. The s Process: Nuclear Physics, Stellar Models, Observations

    CERN Document Server

    Kaeppeler, Franz; Bisterzo, Sara; Aoki, Wako

    2010-01-01

    Nucleosynthesis in the s process takes place in the He burning layers of low mass AGB stars and during the He and C burning phases of massive stars. The s process contributes about half of the element abundances between Cu and Bi in solar system material. Depending on stellar mass and metallicity the resulting s-abundance patterns exhibit characteristic features, which provide comprehensive information for our understanding of the stellar life cycle and for the chemical evolution of galaxies. The rapidly growing body of detailed abundance observations, in particular for AGB and post-AGB stars, for objects in binary systems, and for the very faint metal-poor population represents exciting challenges and constraints for stellar model calculations. Based on updated and improved nuclear physics data for the s-process reaction network, current models are aiming at ab initio solution for the stellar physics related to convection and mixing processes. Progress in the intimately related areas of observations, nuclear...

  6. Uncertainties in stellar evolution models: convective overshoot

    CERN Document Server

    Bressan, Alessandro; Marigo, Paola; Rosenfield, Philip; Tang, Jing

    2014-01-01

    In spite of the great effort made in the last decades to improve our understanding of stellar evolution, significant uncertainties remain due to our poor knowledge of some complex physical processes that require an empirical calibration, such as the efficiency of the interior mixing related to convective overshoot. Here we review the impact of convective overshoot on the evolution of stars during the main Hydrogen and Helium burning phases.

  7. Uncertainties in Stellar Evolution Models: Convective Overshoot

    Science.gov (United States)

    Bressan, Alessandro; Girardi, Léo; Marigo, Paola; Rosenfield, Philip; Tang, Jing

    In spite of the great effort made in the last decades to improve our understanding of stellar evolution, significant uncertainties remain due to our poor knowledge of some complex physical processes that require an empirical calibration, such as the efficiency of the interior mixing related to convective overshoot. Here we review the impact of convective overshoot on the evolution of stars during the main Hydrogen and Helium burning phases.

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

    Energy Technology Data Exchange (ETDEWEB)

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Martinez-Gonzalez, Sergio [Instituto Nacional de Astrofisica Optica y Electronica, AP 51, 72000 Puebla (Mexico); Bisnovatyi-Kogan, Gennadiy, E-mail: silich@inaoep.mx, E-mail: gkogan@iki.rssi.ru [Space Research Institute, 84/32 Profsoyuznaya, Moscow 117810 (Russian Federation)

    2011-12-20

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

  9. Experimental investigation and numerical modelling of positive corona discharge: ozone generation

    Science.gov (United States)

    Yanallah, K; Pontiga, F; Fernández-Rueda, A; Castellanos, A

    2009-03-01

    The spatial distribution of the species generated in a wire-cylinder positive corona discharge in pure oxygen has been computed using a plasma chemistry model that includes the most significant reactions between electrons, ions, atoms and molecules. The plasma chemistry model is included in the continuity equations of each species, which are coupled with Poisson's equation for the electric field and the energy conservation equation for the gas temperature. The current-voltage characteristic measured in the experiments has been used as an input data to the numerical simulation. The numerical model is able to reproduce the basic structure of the positive corona discharge and highlights the importance of Joule heating on ozone generation. The average ozone density has been computed as a function of current intensity and compared with the experimental measurements of ozone concentration determined by UV absorption spectroscopy.

  10. Plasma chemical and electrical modelling of a negative DC corona in pure oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Soria, C [Departamento de Electronica y Electromagnetismo, Universidad de Sevilla, Av. Reina Mercedes s/n, 41012 Sevilla (Spain); Pontiga, F [Departamento de FIsica Aplicada II, Universidad de Sevilla, Av. Reina Mercedes s/n, 41012 Sevilla (Spain); Castellanos, A [Departamento de Electronica y Electromagnetismo, Universidad de Sevilla, Av. Reina Mercedes s/n, 41012 Sevilla (Spain)

    2004-02-01

    A complex plasma chemical and electrical model of a negative stationary wire-to-cylinder corona discharge in pure oxygen is presented. The corona discharge is assumed to have axial and azimuthal symmetry. The experimental current-voltage characteristic is required as input data, but there are no other adjustable or empirical parameters. The experimental validation of the results of the model comes from its prediction of the ozone concentration. The role played by different reactions and species is analysed in detail using the results of the simulation. The effect of the gas temperature and of the decomposition of ozone at the electrodes is also investigated. The agreement between the model and the experiments is excellent when the effect of ozone decomposition at the electrodes is taken into account.

  11. Experimental investigation and numerical modelling of positive corona discharge: ozone generation

    Energy Technology Data Exchange (ETDEWEB)

    Yanallah, K; Castellanos, A [Departamento de Electronica y Electromagnetismo, Universidad de Sevilla (Spain); Pontiga, F; Fernandez-Rueda, A [Departamento de FIsica Aplicada II, Universidad de Sevilla (Spain)

    2009-03-21

    The spatial distribution of the species generated in a wire-cylinder positive corona discharge in pure oxygen has been computed using a plasma chemistry model that includes the most significant reactions between electrons, ions, atoms and molecules. The plasma chemistry model is included in the continuity equations of each species, which are coupled with Poisson's equation for the electric field and the energy conservation equation for the gas temperature. The current-voltage characteristic measured in the experiments has been used as an input data to the numerical simulation. The numerical model is able to reproduce the basic structure of the positive corona discharge and highlights the importance of Joule heating on ozone generation. The average ozone density has been computed as a function of current intensity and compared with the experimental measurements of ozone concentration determined by UV absorption spectroscopy.

  12. Core - Corona Model describes the Centrality Dependence of v_2/epsilon

    CERN Document Server

    Aichelin, J

    2010-01-01

    Event by event EPOS calculations in which the expansion of the system is described by {\\it ideal} hydrodynamics reproduce well the measured centrality dependence of $v_2/\\epsilon_{part}$, although it has been claimed that only viscous hydrodynamics can reproduce these data. This is due to the core - corona effect which manifests itself in the initial condition of the hydrodynamical expansion. The centrality dependence of $v_2/\\epsilon_{part}$ can be understood in the recently advanced core-corona model, a simple parameter free EPOS inspired model to describe the centrality dependence of different observables from SPS to RHIC energies. This model has already been successfully applied to understand the centrality dependence of multiplicities and of the average transverse momentum of identified particles.

  13. Stellar models: firm evidence, open questions and future developments

    CERN Document Server

    Cassisi, Santi

    2009-01-01

    During this last decade our knowledge of the evolutionary properties of stars has significantly improved. This result has been achieved thanks to our improved understanding of the physical behavior of stellar matter in the thermal regimes characteristic of the different stellar mass ranges and/or evolutionary stages. This notwithstanding, the current generation of stellar models is still affected by several, not negligible, uncertainties related to our poor knowledge of some thermodynamical processes and nuclear reaction rates, as well as the efficiency of mixing processes. These drawbacks have to be properly taken into account when comparing theory with observations, to derive evolutionary properties of both resolved and unresolved stellar populations. In this paper we review the major sources of uncertainty along the main evolutionary stages, and emphasize their impact on population synthesis techniques.

  14. 3d Numerical Models of the Chromosphere, Transition Region, and Corona

    CERN Document Server

    Hansteen, Viggo H; Gudiksen, Boris

    2007-01-01

    A major goal in solar physics has during the last five decades been to find how energy flux generated in the solar convection zone is transported and dissipated in the outer solar layers. Progress in this field has been slow and painstaking. However, advances in computer hardware and numerical methods, vastly increased observational capabilities and growing physical insight seem finally to be leading towards understanding. Here we present exploratory numerical MHD models that span the entire solar atmosphere from the upper convection zone to the lower corona. These models include non-grey, non-LTE radiative transport in the photosphere and chromosphere, optically thin radiative losses as well as magnetic field-aligned heat conduction in the transition region and corona.

  15. Accurate Low-Mass Stellar Models of KOI-126

    CERN Document Server

    Feiden, Gregory A; Dotter, Aaron

    2011-01-01

    The recent discovery of an eclipsing hierarchical triple system with two low-mass stars in a close orbit (KOI-126) by Carter et al. (2011) appeared to reinforce the evidence that theoretical stellar evolution models are not able to reproduce the observational mass-radius relation for low-mass stars. We present a set of stellar models for the three stars in the KOI-126 system that show excellent agreement with the observed radii. This agreement appears to be due to the equation of state implemented by our code. A significant dispersion in the observed mass-radius relation for fully convective stars is demonstrated; indicative of the influence of physics currently not incorporated in standard stellar evolution models. We also predict apsidal motion constants for the two M-dwarf companions. These values should be observationally determined to within 1% by the end of the Kepler mission.

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

    Science.gov (United States)

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

    2017-05-01

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

  17. The Steady State Wind Model for Young Stellar Clusters with an Exponential Stellar Density Distribution

    CERN Document Server

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Martinez-Gonzalez, Sergio

    2011-01-01

    A hydrodynamic model for steady state, spherically-symmetric winds driven by young stellar clusters with an exponential stellar density distribution is presented. Unlike in most previous calculations, the position of the singular point R_sp, which separates the inner subsonic zone from the outer supersonic flow, is not associated with the star cluster edge, but calculated self-consistently. When the radiative losses of energy are negligible, the transition from the subsonic to the supersonic flow occurs always at R_sp ~ 4 R_c, where R_c is the characteristic scale for the stellar density distribution, irrespective of other star cluster parameters. This is not the case in the catastrophic cooling regime, when the temperature drops abruptly at a short distance from the star cluster center and the transition from the subsonic to the supersonic regime occurs at a much smaller distance from the star cluster center. The impact from the major star cluster parameters to the wind inner structure is thoroughly discusse...

  18. Model stars for the modelling of galaxies: $\\alpha$-enhancement in stellar populations models

    CERN Document Server

    Coelho, P

    2008-01-01

    Stellar population (SP) models are an essential tool to understand the observations of galaxies and clusters. One of the main ingredients of a SP model is a library of stellar spectra, and both empirical and theoretical libraries can been used for this purpose. Here I will start by giving a short overview of the pros and cons of using theoretical libraries, i.e. model stars, to produce our galaxy models. Then I will address the question on how theoretical libraries can be used to model stellar populations, in particular to explore the effect of $\\alpha$-enhancement on spectral observables.

  19. MODEL STARS FOR THE MODELLING OF GALAXIES: a-ENHANCEMENT IN STELLAR POPULATIONS MODELS

    Directory of Open Access Journals (Sweden)

    P. Coelho

    2009-01-01

    Full Text Available Stellar population (SP models are an essential tool to understand the observations of galaxies and clusters. One of the main ingredients of a SP model is a library of stellar spectra, and both empirical and theoretical libraries can been used for this purpose. Here I will start by giving a short overview of the pros and cons ofusing theoretical libraries, i.e. model stars, to produce our galaxy models. Then I will address the question on how theoretical libraries can be used to model stellar populations, in particular to explore the e ect of -enhancement on spectral observables.

  20. Testing galaxy formation models with galaxy stellar mass functions

    Science.gov (United States)

    Lim, S. H.; Mo, H. J.; Lan, Ting-Wen; Ménard, Brice

    2016-10-01

    We compare predictions of a number of empirical models and numerical simulations of galaxy formation to the conditional stellar mass functions (CSMF) of galaxies in groups of different masses obtained recently by Lan et al. to test how well different models accommodate the data. The observational data clearly prefer a model in which star formation in low-mass halos changes behavior at a characteristic redshift zc ˜ 2. There is also tentative evidence that this characteristic redshift depends on environment, becoming zc ˜ 4 in regions that eventually evolve into rich clusters of galaxies. The constrained model is used to understand how galaxies form and evolve in dark matter halos, and to make predictions for other statistical properties of the galaxy population, such as the stellar mass functions of galaxies at high z, the star formation and stellar mass assembly histories in dark matter halos. A comparison of our model predictions with those of other empirical models shows that different models can make vastly different predictions, even though all of them are tuned to match the observed stellar mass functions of galaxies.

  1. Testing galaxy formation models with galaxy stellar mass functions

    Science.gov (United States)

    Lim, S. H.; Mo, H. J.; Lan, T.-W.; Ménard, B.

    2017-01-01

    We compare predictions of a number of empirical models and numerical simulations of galaxy formation to the conditional stellar mass functions of galaxies in groups of different masses obtained recently by Lan et al. to test how well different models accommodate the data. The observational data clearly prefer a model in which star formation in low-mass haloes changes behaviour at a characteristic redshift zc ˜ 2. There is also tentative evidence that this characteristic redshift depends on environment, becoming zc ˜ 4 in regions that eventually evolve into rich clusters of galaxies. The constrained model is used to understand how galaxies form and evolve in dark matter haloes, and to make predictions for other statistical properties of the galaxy population, such as the stellar mass functions of galaxies at high z, the star formation, and stellar mass assembly histories in dark matter haloes. A comparison of our model predictions with those of other empirical models shows that different models can make vastly different predictions, even though all of them are tuned to match the observed stellar mass functions of galaxies.

  2. Detailed opacity calculations for stellar models

    Science.gov (United States)

    Pain, Jean-Christophe; Gilleron, Franck

    2016-10-01

    We present a state of the art of precise spectral opacity calculations illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments of hot dense plasmas produced by ultra-high-intensity laser interaction. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. Focus is put on iron, due to its crucial role in the understanding of asteroseismic observations of Beta Cephei-type and Slowly Pulsating B stars, as well as in the Sun. For instance, in Beta Cephei-type stars (which should not be confused with Cepheid variables), the iron-group opacity peak excites acoustic modes through the kappa-mechanism. A particular attention is paid to the higher-than-predicted iron opacity measured on Sandia's Z facility at solar interior conditions (boundary of the convective zone). We discuss some theoretical aspects such as orbital relaxation, electron collisional broadening, ionic Stark effect, oscillator-strength sum rules, photo-ionization, or the ``filling-the-gap'' effect of highly excited states.

  3. The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere II. Continuous Emission and Condensed Matter Within the Corona

    Directory of Open Access Journals (Sweden)

    Robitaille P.-M.

    2013-07-01

    Full Text Available The K-corona, a significant portion of the solar atmosphere, displays a continuous spectrum which closely parallels photospheric emission, though without the presence of overlying Fraunhofer lines. The E-corona exists in the same region and is characterized by weak emission lines from highly ionized atoms. For instance, the famous green emission line from coronium (FeXIV is part of the E-corona. The F-corona exists beyond the K/E-corona and, like the photospheric spectrum, is characterized by Fraunhofer lines. The F-corona represents photospheric light scattered by dust particles in the interplanetary medium. Within the gaseous models of the Sun, the K-corona is viewed as photospheric radiation which has been scattered by relativistic electrons. This scattering is thought to broaden the Fraunhofer lines of the solar spectrum such that they can no longer be detected in the K-corona. Thus, the gaseous models of the Sun account for the appearance of the K-corona by distorting photospheric light, since they are unable to have recourse to condensed matter to directly produce such radiation. Conversely, it is now advanced that the continuous emission of the K-corona and associated emission lines from the E-corona must be interpreted as manifestations of the same phenomenon: condensed matter exists in the corona. It is well-known that the Sun expels large amounts of material from its surface in the form of flares and coronal mass ejections. Given a liquid metallic hydrogen model of the Sun, it is logical to assume that such matter, which exists in the condensed state on the solar surface, continues to manifest its nature once expelled into the corona. Therefore, the continuous spectrum of the K-corona provides the twenty-seventh line of evidence that the Sun is composed of condensed matter.

  4. Stellar Models and Yields of Asymptotic Giant Branch Stars

    CERN Document Server

    Karakas, Amanda I

    2007-01-01

    We present stellar yields calculated from detailed models of low and intermediate-mass asymptotic giant branch (AGB) stars. We evolve models with a range of mass from 1 to 6Msun, and initial metallicities from solar to 1/200th of the solar metallicity. Each model was evolved from the zero age main sequence to near the end of the thermally-pulsing AGB phase, and through all intermediate phases including the core He-flash for stars initially less massive than 2.5Msun. For each mass and metallicity, we provide tables containing structural details of the stellar models during the TP-AGB phase, and tables of the stellar yields for 74 species from hydrogen through to sulphur, and for a small number of iron-group nuclei. All tables are available for download. Our results have many applications including use in population synthesis studies and the chemical evolution of galaxies and stellar systems, and for comparison to the composition of AGB and post-AGB stars and planetary nebulae.

  5. Modeling Gyrosynchrotron Coronae of Radio-Loud Stars

    Science.gov (United States)

    Peterson, William M.

    2015-01-01

    Fast gyrosynchrotron codes are used to model the emission in close, active binary star systems. Multiple magnetic field topologies, plasma densities, and scale heights for the emitting plasma are tested for in an attempt to duplicate the emission characteristics detected using high-resolution VLBI imaging of the close active binaries UX Arietis and Algol. Also included are effects of occlusion by the companion star. It is found that a co-orbiting coronal loop oriented toward the companion star with its feet anchored on the poles of the active star is consistent with the observed emission from these two radio-loud stars.

  6. Observations of CMEs and Models of the Eruptive Corona

    Science.gov (United States)

    Gopalswamy, Nat

    2012-01-01

    It is now realized that coronal mass ejections (CMEs) are the most energetic phenomenon in the heliosphere. Although early observations (in the 1970s and 19805) revealed most of the properties of CMEs, it is the extended and uniform data set from the Solar and Heliospheric Observatory (SOHO) mission that helped us consolidate our knowledge on CMEs. The Solar Terrestrial Relations Observatory (STEREO) mission has provided direct confirmation of the three-dimensional structure of CMEs. The broadside view provided by the STEREO coronagraphs helped us estimate the width of the halo CMEs and hence validate CME cone models. Current theoretical ideas on the internal structure of CMEs suggest that a flux rope is central to the CME structure, which has considerable observational support both from remote-sensing and in-situ observations. The flux-rope nature is also consistent with the post-eruption arcades with high-temperature plasma and the charge states observed within CMEs arriving at Earth. The quadrature observations also helped us understand the relation between the radial and expansion speeds of CMEs, which were only known from empirical relations in the past. This paper highlights some of these results obtained during solar cycle 23 and 24 and discusses implications for CME models.

  7. Stellar yields from metal-rich asymptotic giant branch models

    CERN Document Server

    Karakas, Amanda I

    2016-01-01

    We present new theoretical stellar yields and surface abundances for three grids of metal-rich asymptotic giant branch (AGB) models. Post-processing nucleosynthesis results are presented for stellar models with initial masses between 1$M_{\\odot}$ and 7.5$M_{\\odot}$ for $Z=0.007$, and 1$M_{\\odot}$ and 8$M_{\\odot}$ for $Z=0.014$ (solar) and $Z=0.03$. We include stellar surface abundances as a function of thermal pulse on the AGB for elements from C to Bi and for a selection of isotopic ratios for elements up to Fe and Ni (e.g., $^{12}$C/$^{13}$C), which can be obtained from observations of molecules in stars and from the laboratory analysis of meteoritic stardust grains. Ratios of elemental abundances of He/H, C/O, and N/O are also included, which are useful for direct comparison to observations of AGB stars and their progeny including planetary nebulae. The integrated elemental stellar yields are presented for each model in the grid for hydrogen, helium and all stable elements from C to Bi. Yields of Li are al...

  8. Dense Molecular Gas: A Sensitive Probe of Stellar Feedback Models

    CERN Document Server

    Hopkins, Philip F; Murray, Norman; Quataert, Eliot

    2012-01-01

    We show that the mass fraction of GMC gas (n>100 cm^-3) in dense (n>>10^4 cm^-3) star-forming clumps, observable in dense molecular tracers (L_HCN/L_CO(1-0)), is a sensitive probe of the strength and mechanism(s) of stellar feedback. Using high-resolution galaxy-scale simulations with pc-scale resolution and explicit models for feedback from radiation pressure, photoionization heating, stellar winds, and supernovae (SNe), we make predictions for the dense molecular gas tracers as a function of GMC and galaxy properties and the efficiency of stellar feedback. In models with weak/no feedback, much of the mass in GMCs collapses into dense sub-units, predicting L_HCN/L_CO(1-0) ratios order-of-magnitude larger than observed. By contrast, models with feedback properties taken directly from stellar evolution calculations predict dense gas tracers in good agreement with observations. Changing the strength or timing of SNe tends to move systems along, rather than off, the L_HCN-L_CO relation (because SNe heat lower-de...

  9. Late stages of stellar evolution in population models

    Science.gov (United States)

    Maraston, Claudia

    2015-04-01

    My contribution to Roger's celebration symposium focuses on the treatment of late stellar evolutionary phases in stellar population models, reviewing the state of art and discussing some very recent developments, ranging from local stellar clusters up to distant galaxies at high redshift. I shall focus in particular on the Thermally Pulsating Asymptotic Giant Branch, about which a vivid discussion has been ongoing since a few years. I shall present renewed evidence in favour of a sizable contribution from this phase for matching the observed spectral energy distribution of distant massive galaxies. I shall also discuss the possible reasons why such a conclusion has been controversial in the recent literature. Stellar population models are the magic tool to shape the physics of galaxies out of their observed light, and enter virtually all papers presented at this symposium. In a collective effort to properly treat all relevant aspects of the modelling, we split the discussion into six contributions given by experts in the field, as our present to Roger and his outstanding career.

  10. A model for the formation of the active region corona driven by magnetic flux emergence

    Science.gov (United States)

    Chen, F.; Peter, H.; Bingert, S.; Cheung, M. C. M.

    2014-04-01

    Aims: We present the first model that couples the formation of the corona of a solar active region to a model of the emergence of a sunspot pair. This allows us to study when, where, and why active region loops form, and how they evolve. Methods: We use a 3D radiation magnetohydrodynamics (MHD) simulation of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a 3D MHD coronal model. The coronal model accounts for the braiding of the magnetic fieldlines, which induces currents in the corona to heat up the plasma. We synthesize the coronal emission for a direct comparison to observations. Starting with a basically field-free atmosphere we follow the filling of the corona with magnetic field and plasma. Results: Numerous individually identifiable hot coronal loops form, and reach temperatures well above 1 MK with densities comparable to observations. The footpoints of these loops are found where small patches of magnetic flux concentrations move into the sunspots. The loop formation is triggered by an increase in upward-directed Poynting flux at their footpoints in the photosphere. In the synthesized extreme ultraviolet (EUV) emission these loops develop within a few minutes. The first EUV loop appears as a thin tube, then rises and expands significantly in the horizontal direction. Later, the spatially inhomogeneous heat input leads to a fragmented system of multiple loops or strands in a growing envelope. Animation associated with Fig. 2 is available in electronic form at http://www.aanda.org

  11. The Impact of Stellar Model Spectra in Disk Detection

    CERN Document Server

    Sinclair, J A; Greaves, J S

    2010-01-01

    We present a study of the impact of different model groups in the detection of circumstellar debris disks. Almost all previous studies in this field have used Kurucz model spectra to predict the stellar contribution to the flux at the wavelength of observation thus determining the existence of a disk excess. Only recently have other model groups or families like Marcs and NextGen-Phoenix become available to the same extent. This study aims to determine whether the predicted stellar flux of a disk target can change with the choice of model family - can a disk excess be present in the use of one model family whilst being absent from another? A simple comparison of Kurucz model spectra with Mrcs and NextGen model spectra of identical stellar parameters was conducted and differences were present at near-infrared wavelengths. Model spectra often do not extend in wavelength to that of observation and therefore extrapolation of the spectrum is required. In extrapolation of model spectra to the Spitzer MIPS passbands...

  12. Observationally driven 3D MHD model of the solar corona above an active region

    CERN Document Server

    Bourdin, Ph -A; Peter, H

    2013-01-01

    Aims. The goal is to employ a 3D magnetohydrodynamics (MHD) model including spectral synthesis to model the corona in an observed solar active region. This will allow us to judge the merits of the coronal heating mechanism built into the 3D model. Methods. Photospheric observations of the magnetic field and horizontal velocities in an active region are used to drive our coronal simulation from the bottom. The currents induced by this heat the corona through Ohmic dissipation. Heat conduction redistributes the energy that is lost in the end through optically thin radiation. Based on the MHD model, we synthesized profiles of coronal emission lines which can be directly compared to actual coronal observations of the very same active region. Results. In the synthesized model data we find hot coronal loops which host siphon flows or which expand and lose mass through draining. These synthesized loops are at the same location as and show similar dynamics in terms of Doppler shifts to the observed structures. This m...

  13. Development of three-dimensional magnetohydrodynamic model for solar corona and solar wind simulation

    Science.gov (United States)

    Yuan, Xingqiu; Trichtchenko, Larisa; Boteler, David

    Propagation of coronal mass ejections from solar surface to the Earth magnetosphere is strongly influenced by the conditions in solar corona and ambient solar wind. Thus, reliable simulation of the background solar wind is the primary task toward the development of numerical model for the transient events. In this paper we introduce a new numerical model which has been specifically designed for numerical study of the solar corona and ambient solar wind. This model is based on our recently developed three-dimensional Spherical Coordinate Adaptive Magneto-Hydro-Dynamic (MHD) code (SCA-MHD-3D) [Yuan et al., 2009]. Modifications has been done to include the observed magnetic field at the photosphere as inner boundary conditions. The energy source term together with reduced plasma gamma are used in the nonlinear MHD equations in order to simulate the solar wind acceleration from subsonic speed at solar surface to supersonic speed at the inter-heliosphere region, and the absorbing boundary conditions are used at the solar surface. This model has been applied to simulate the background solar wind condition for several different solar rotations, and comparison between the observation and model output have shown that it reproduces many features of solar wind, including open and closed magnetic fields, fast and slow solar wind speed, sector boundaries, etc.

  14. Towards 21st Century Stellar Models: Star Clusters, Supercomputing, and Asteroseismology

    DEFF Research Database (Denmark)

    Campbell, S. W.; Constantino, T. N.; D'Orazi, V.;

    2016-01-01

    Stellar models provide a vital basis for many aspects of astronomy and astrophysics. Recent advances in observational astronomy -- through asteroseismology, precision photometry, high-resolution spectroscopy, and large-scale surveys -- are placing stellar models under greater quantitative scrutin...

  15. Measurements of accretion disc corona size in LMXB: consequences for Comptonization and LMXB models

    OpenAIRE

    M. J. Church; Balucinska-Church, M.

    2003-01-01

    We present results of measurements of the radial extent of the accretion disc corona in low mass X-ray binaries. These results prove conclusively the extended nature of the ADC, with radial extent varying from 20,000 km in the faintest sources to 700,000 km in the brightest, a substantial fraction of the accretion disc radius, typically 15%. This result rules out the Eastern model for LMXB which is extensively used, in which the Comptonizing region is a small central region. The ADC size depe...

  16. A new simple dynamo model for stellar activity cycle

    CERN Document Server

    Yokoi, Nobumitsu; Pipin, Valery; Hamba, Fujihiro

    2016-01-01

    A new simple dynamo model for stellar activity cycle is proposed. By considering an inhomogeneous mean flow effect on turbulence, it is shown that turbulent cross helicity (velocity--magnetic-field correlation) should enter the expression of turbulent electromotive force as the coupling coefficient for the mean absolute vorticity. The inclusion of the cross-helicity effect makes the present model different from the current $\\alpha$--$\\Omega$-type models mainly in two points. First, in addition to the usual $\\alpha$ (helicity effect) and $\\beta$ (turbulent magnetic diffusivity), we consider the $\\gamma$ coefficient (cross-helicity effect). Second, unlike the $\\alpha$ and $\\beta$ coefficients, which are often treated as an adjustable parameter in the current studies, the spatiotemporal evolution of $\\gamma$ coefficient should be solved simultaneously with the mean magnetic-field equations. The basic scenario for the stellar activity cycle in the present model is as follows: In the presence of turbulent cross he...

  17. Old star clusters: Bench tests of low mass stellar models

    Directory of Open Access Journals (Sweden)

    Salaris M.

    2013-03-01

    Full Text Available Old star clusters in the Milky Way and external galaxies have been (and still are traditionally used to constrain the age of the universe and the timescales of galaxy formation. A parallel avenue of old star cluster research considers these objects as bench tests of low-mass stellar models. This short review will highlight some recent tests of stellar evolution models that make use of photometric and spectroscopic observations of resolved old star clusters. In some cases these tests have pointed to additional physical processes efficient in low-mass stars, that are not routinely included in model computations. Moreover, recent results from the Kepler mission about the old open cluster NGC6791 are adding new tight constraints to the models.

  18. Memprot: a program to model the detergent corona around a membrane protein based on SEC–SAXS data

    Energy Technology Data Exchange (ETDEWEB)

    Pérez, Javier, E-mail: javier.perez@synchrotron-soleil.fr [Synchrotron SOLEIL, L’Orme des Merisiers, BP 48, Saint-Aubin, 91192 Gif-sur-Yvette (France); Koutsioubas, Alexandros [Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstrasse 1, 85747 Garching (Germany); Synchrotron SOLEIL, L’Orme des Merisiers, BP 48, Saint-Aubin, 91192 Gif-sur-Yvette (France)

    2015-01-01

    Systematic SAXS simulations have been analysed over a wide range of parameters in order to better understand the detergent corona around a membrane protein. The application of small-angle X-ray scattering (SAXS) to structural investigations of transmembrane proteins in detergent solution has been hampered by two main inherent hurdles. On the one hand, the formation of a detergent corona around the hydrophobic region of the protein strongly modifies the scattering curve of the protein. On the other hand, free micelles of detergent without a precisely known concentration coexist with the protein–detergent complex in solution, therefore adding an uncontrolled signal. To gain robust structural information on such systems from SAXS data, in previous work, advantage was taken of the online combination of size-exclusion chromatography (SEC) and SAXS, and the detergent corona around aquaporin-0, a membrane protein of known structure, could be modelled. A precise geometrical model of the corona, shaped as an elliptical torus, was determined. Here, in order to better understand the correlations between the corona model parameters and to discuss the uniqueness of the model, this work was revisited by analyzing systematic SAXS simulations over a wide range of parameters of the torus.

  19. Parker's Model for Stellar Wind and Magnetohydrodynamic Extensions

    CERN Document Server

    Shivamoggi, B K

    2016-01-01

    In this paper, we first revisit Parker's hydrodynamic model for a stellar wind and make further analytic considerations. We show that the visualization of an effective de Laval type nozzle associated with Parker's model is valid only in a superficial sense and not on the dynamical level. We then make an analytic considerations on the Weber-Davis magnetohydrodynamic (MHD) extension of Parker's model with a view to provide a qualitative understanding of the coupling between the magnetic field and the plasma motion in the stellar wind. We find that, *the MHD azimuthal velocity profile actually resembles that for hydrodynamic Lamb-Oseen vortex; *Keplerian-orbit conditions prevail near a strong rotator even in a magnetized situation; *Parker's hydrodynamic scenario \\cite{Par} seems to reappear in the strong magnetization regime.\\end{itemize}

  20. Semi-empirical Modeling of the Photosphere, Chromosphere, Transition Region, and Corona of the M-dwarf Host Star GJ 832

    Science.gov (United States)

    Fontenla, J. M.; Linsky, Jeffrey L.; Witbrod, Jesse; France, Kevin; Buccino, A.; Mauas, Pablo; Vieytes, Mariela; Walkowicz, Lucianne M.

    2016-10-01

    Stellar radiation from X-rays to the visible provides the energy that controls the photochemistry and mass loss from exoplanet atmospheres. The important extreme ultraviolet (EUV) region (10-91.2 nm) is inaccessible and should be computed from a reliable stellar model. It is essential to understand the formation regions and physical processes responsible for the various stellar emission features to predict how the spectral energy distribution varies with age and activity levels. We compute a state-of-the-art semi-empirical atmospheric model and the emergent high-resolution synthetic spectrum of the moderately active M2 V star GJ 832 as the first of a series of models for stars with different activity levels. We construct a one-dimensional simple model for the physical structure of the star’s chromosphere, chromosphere-corona transition region, and corona using non-LTE radiative transfer techniques and many molecular lines. The synthesized spectrum for this model fits the continuum and lines across the UV-to-optical spectrum. Particular emphasis is given to the emission lines at wavelengths that are shorter than 300 nm observed with the Hubble Space Telescope, which have important effects on the photochemistry of the exoplanet atmospheres. The FUV line ratios indicate that the transition region of GJ 832 is more biased to hotter material than that of the quiet Sun. The excellent agreement of our computed EUV luminosity with that obtained by two other techniques indicates that our model predicts reliable EUV emission from GJ 832. We find that the unobserved EUV flux of GJ 832, which heats the outer atmospheres of exoplanets and drives their mass loss, is comparable to the active Sun. Based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS AR-09525.01A. These observations

  1. Threaded-Field-Lines Model for the Low Solar Corona Powered by the Alfven Wave Turbulence

    CERN Document Server

    Sokolov, Igor V; Manchester, Ward B; Ozturk, Doga Can Su; Szente, Judit; Taktakishvili, Aleksandre; Tóth, Gabor; Jin, Meng; Gombosi, Tamas I

    2016-01-01

    We present an updated global model of the solar corona, including the transition region. We simulate the realistic tree-dimensional (3D) magnetic field using the data from the photospheric magnetic field measurements and assume the magnetohydrodynamic (MHD) Alfv\\'en wave turbulence and its non-linear dissipation to be the only source for heating the coronal plasma and driving the solar wind. In closed field regions the dissipation efficiency in a balanced turbulence is enhanced. In the coronal holes we account for a reflection of the outward propagating waves, which is accompanied by generation of weaker counter-propagating waves. The non-linear cascade rate degrades in strongly imbalanced turbulence, thus resulting in colder coronal holes. The distinctive feature of the presented model is the description of the low corona as almost-steady-state low-beta plasma motion and heat flux transfer along the magnetic field lines. We trace the magnetic field lines through each grid point of the lower boundary of the g...

  2. Spiral Structure Dynamics in Pure Stellar Disk Models

    CERN Document Server

    Valencia-Enriquez, Diego

    2013-01-01

    In order to understand the physical mechanism underlying non-steady stellar spiral arms in disk galaxies we performed a series of N-body simulations with 1.2 and 8 million particles. The initial conditions were chosen to follow Kuijken-Dubinski models. In this work we present the results of a sub-sample of our simulations in which we experiment with different disk central radial velocity dispersion and the disk scale height.

  3. Anisotropic stellar models admitting conformal motion

    Science.gov (United States)

    Banerjee, Ayan; Banerjee, Sumita; Hansraj, Sudan; Ovgun, Ali

    2017-04-01

    We address the problem of finding static and spherically symmetric anisotropic compact stars in general relativity that admit conformal motions. The study is framed in the language of f( R) gravity theory in order to expose opportunity for further study in the more general theory. Exact solutions of compact stars are found under the assumption that spherically symmetric spacetimes admit conformal motion with anisotropic matter distribution in nature. In this work, two cases have been studied for the existence of such solutions: first, we consider the model given by f(R)=R and then f(R)=aR+b . Finally, specific characteristics and physical properties have been explored analytically along with graphical representations for conformally symmetric compact stars in f( R) gravity.

  4. Hybrid modeling of the lower corona using Faraday rotation observations and a MHD thermodynamic simulation

    Science.gov (United States)

    Wexler, David B.; Hollweg, Joseph V.; Jensen, Elizabeth; Lionello, Roberto; Macneice, Peter J.; Coster, Anthea J.

    2017-08-01

    Study of coronal MHD wave energetics relies upon accurate representation of plasma particle number densities (ne) and magnetic field strengths. In the lower corona, these parameters are obtained indirectly, and typically presented as empirical equations as a function of heliocentric radial distance (solar offset, SO). The development of coronal global models using synoptic solar surface magnetogram inputs has provided refined characterization of the coronal plasma organization and magnetic field. We present a cross-analysis between a MHD thermodynamic simulation and Faraday rotation (FR) observations over SO 1.63-1.89 solar radii (Rs) near solar minimum. MESSENGER spacecraft radio signals with a line of sight (LOS) passing through the lower corona were recorded in dual polarization using the Green Bank Telescope in November 2009. Polarization position angle changes were obtained from Stokes parameters. The magnetic field vector (B) and ne along the LOS were obtained from a MHD thermodynamic simulation provided by the Community Coordinated Modeling Center. The modeled FR was computed as the integrated product of ne and LOS-aligned B component. The observations over the given SO range yielded an FR change of 7 radians. The simulation reproduced this change when the modeled ne was scaled up by 2.8x, close to values obtained using the Allen-Baumbach equation. No scaling of B from the model was necessary. A refined fit to the observations was obtained when the observationally based total electron content (TEC) curves were introduced. Changes in LOS TEC were determined from radio frequency shifts as the signal passed to successively lower electron concentrations during egress. A good fit to the observations was achieved with an offset of 7e21 m-2 added. Back-calculating ne along the LOS from the TEC curves, we found that the equivalent ne scaling compared to the model output was higher by a factor of 3. The combination of solar surface magnetogram-based MHD coronal

  5. Experimental modeling of high-voltage corona discharge using design of experiments

    Institute of Scientific and Technical Information of China (English)

    Rezzouga M; Tilmatine A; Gouri R; Medics K; Dascalescu L

    2007-01-01

    Many studies,both experimental and numerical,were devoted to the electric current of corona discharge and some mathematical models were proposed to express it.As it depends on several parameters,it is difficult to find a theoretical or an experimental formula,which considers all the factors.So we opted for the methodology of experimental designs,also called Tagushi's methodology,which represents a powerful tool generally employed when the process has many factors to consider.The objective of this paper is to model current using this experimental methodology.The factors considered were geometrical factors (interelectrode interval,surface of the grounded plane electrode,curvature radius of the point electrode),climatic factors (temperature and relative humidity),and applied high voltage.Results of experiments made it possible to obtain mathematical models and to analyse the interactions between all factors.

  6. Force-free field modeling of twist and braiding-induced magnetic energy in an active-region corona

    CERN Document Server

    Thalmann, J K; Wiegelmann, T

    2013-01-01

    The theoretical concept that braided magnetic field lines in the solar corona may dissipate a sufficient amount of energy to account for the brightening observed in the active-region corona, has been substantiated by high-resolution observations only recently. From the analysis of coronal images obtained with the High Resolution Coronal Imager, first observational evidence of the braiding of magnetic field lines was reported by Cirtain et al. 2013 (hereafter CG13). We present nonlinear force-free reconstructions of the associated coronal magnetic field based on vector SDO/HMI magnetograms. We deliver estimates of the free magnetic energy associated to a braided coronal structure. Our model results suggest (~100 times) more free energy at the braiding site than analytically estimated by CG13, strengthening the possibility of the active-region corona being heated by field line braiding. We were able to assess the coronal free energy appropriately by using vector field measurements and attribute the lower energy...

  7. A new methodology to test galaxy formation models using the dependence of clustering on stellar mass

    CERN Document Server

    Campbell, David J R; Mitchell, Peter D; Helly, John C; Gonzalez-Perez, Violeta; Lacey, Cedric G; Lagos, Claudia del P; Simha, Vimal; Farrow, Daniel J

    2014-01-01

    We present predictions for the two-point correlation function of galaxy clustering as a function of stellar mass, computed using two new versions of the GALFORM semi-analytic galaxy formation model. These models make use of a new high resolution, large volume N-body simulation, set in the WMAP7 cosmology. One model uses a universal stellar initial mass function (IMF), while the other assumes different IMFs for quiescent star formation and bursts. Particular consideration is given to how the assumptions required to estimate the stellar masses of observed galaxies (such as the choice of IMF, stellar population synthesis model and dust extinction) influence the perceived dependence of galaxy clustering on stellar mass. Broad-band spectral energy distribution fitting is carried out to estimate stellar masses for the model galaxies in the same manner as in observational studies. We show clear differences between the clustering signals computed using the true and estimated model stellar masses. As such, we highligh...

  8. The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere V. On the Nature of the Corona

    Directory of Open Access Journals (Sweden)

    Robitaille P.-M.

    2013-07-01

    Full Text Available The E-corona is the site of numerous emission lines associated with high ionization states (i.e. FeXIV-FeXXV. Modern gaseous models of the Sun require that these states are produced by atomic irradiation, requiring the sequential removal of electrons to infinity, without an associated electron acceptor. This can lead to computed temperatures in the corona which are unrealistic (i.e. ∼30–100 MK contrasted to solar core values of ∼16 MK. In order to understand the emission lines of the E-corona, it is vital to recognize that they are superimposed upon the K-corona, which produces a continuous spectrum, devoid of Fraunhofer lines, arising from this same region of the Sun. It has been advanced that the K-corona harbors self-luminous condensed matter (Robitaille P.M. The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere II. Continuous Emission and Condensed Matter Within the Corona. Progr. Phys., 2013, v. 3, L8–L10; Robitaille P.M. The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere III. Importance of Continuous Emission Spectra from Flares, Coronal Mass Ejections, Prominences, and Other Coronal Structures. Progr. Phys., 2013, v. 3, L11–L14. Condensed matter can possess elevated electron affinities which may strip nearby atoms of their electrons. Such a scenario accounts for the high ionization states observed in the corona: condensed matter acts to harness electrons, ensuring the electrical neutrality of the Sun, despite the flow of electrons and ions in the solar winds. Elevated ionization states reflect the presence of materials with high electron affinities in the corona, which is likely to be a form of metallic hydrogen, and does not translate into elevated temperatures in this region of the solar atmosphere. As a result, the many mechanisms advanced to account for coronal heating in the gaseous models of the Sun

  9. Synthetic spectral analysis of a kinetic model for slow-magnetosonic waves in solar corona

    Energy Technology Data Exchange (ETDEWEB)

    Ruan, Wenzhi; He, Jiansen; Tu, Chuanyi; Wang, Linghua [School of Earth and Space Sciences, Peking University, Beijing, 100871, China, E-mail: jshept@gmail.com (China); Zhang, Lei [State Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing 100190 (China); Vocks, Christian [Leibniz-Institut für Astrophysik Potsdam, 14482, Potsdam (Germany); Marsch, Eckart [Institute for Experimental and Applied Physics, Christian-Albrechts-Universität zu Kiel, 24118 Kiel (Germany); Peter, Hardi [Max Plank Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen (Germany)

    2016-03-25

    We propose a kinetic model of slow-magnetosonic waves to explain various observational features associated with the propagating intensity disturbances (PIDs) occurring in the solar corona. The characteristics of slow mode waves, e.g, inphase oscillations of density, velocity, and thermal speed, are reproduced in this kinetic model. Moreover, the red-blue (R-B) asymmetry of the velocity distribution as self-consistently generated in the model is found to be contributed from the beam component, as a result of the competition between Landau resonance and Coulomb collisions. Furthermore, we synthesize the spectral lines and make the spectral analysis, based on the kinetic simulation data of the flux tube plasmas and the hypothesis of the surrounding background plasmas. It is found that the fluctuations of parameters of the synthetic spectral lines are basically consistent with the observations: (1) the line intensity, Doppler shift, and line width are fluctuating in phase; (2) the R-B asymmetry usually oscillate out of phase with the former three parameters; (3) the blueward asymmetry is more evident than the redward asymmetry in the R-B fluctuations. The oscillations of line parameters become weakened for the case with denser surrounding background plasmas. Similar to the observations, there is no doubled-frequency oscillation of the line width for the case with flux-tube plasmas flowing bulkly upward among the static background plasmas. Therefore, we suggest that the “wave + beam flow” kinetic model may be a viable interpretation for the PIDs observed in the solar corona.

  10. Stellar population synthesis models between 2.5 and 5 {\\mu}m based on the empirical IRTF stellar library

    CERN Document Server

    Röck, B; Peletier, R F; Knapen, J H; Falcón-Barroso, J

    2015-01-01

    We present the first single-burst stellar population models in the infrared wavelength range between 2.5 and 5 {\\mu}m which are exclusively based on empirical stellar spectra. Our models take as input 180 spectra from the stellar IRTF (Infrared Telescope Facility) library. Our final single-burst stellar population models are calculated based on two different sets of isochrones and various types of initial mass functions of different slopes, ages larger than 1 Gyr and metallicities between [Fe/H] = -0.70 and 0.26. They are made available online to the scientific community on the MILES web page. We analyse the behaviour of the Spitzer [3.6]-[4.5] colour calculated from our single stellar population models and find only slight dependences on both metallicity and age. When comparing to the colours of observed early-type galaxies, we find a good agreement for older, more massive galaxies that resemble a single-burst population. Younger, less massive and more metal-poor galaxies show redder colours with respect to ...

  11. New Techniques Used in Modeling the 2017 Total Solar Eclipse: Energizing and Heating the Large-Scale Corona

    Science.gov (United States)

    Downs, Cooper; Mikic, Zoran; Linker, Jon A.; Caplan, Ronald M.; Lionello, Roberto; Torok, Tibor; Titov, Viacheslav; Riley, Pete; Mackay, Duncan; Upton, Lisa

    2017-08-01

    Over the past two decades, our group has used a magnetohydrodynamic (MHD) model of the corona to predict the appearance of total solar eclipses. In this presentation we detail recent innovations and new techniques applied to our prediction model for the August 21, 2017 total solar eclipse. First, we have developed a method for capturing the large-scale energized fields typical of the corona, namely the sheared/twisted fields built up through long-term processes of differential rotation and flux-emergence/cancellation. Using inferences of the location and chirality of filament channels (deduced from a magnetofrictional model driven by the evolving photospheric field produced by the Advective Flux Transport model), we tailor a customized boundary electric field profile that will emerge shear along the desired portions of polarity inversion lines (PILs) and cancel flux to create long twisted flux systems low in the corona. This method has the potential to improve the morphological shape of streamers in the low solar corona. Second, we apply, for the first time in our eclipse prediction simulations, a new wave-turbulence-dissipation (WTD) based model for coronal heating. This model has substantially fewer free parameters than previous empirical heating models, but is inherently sensitive to the 3D geometry and connectivity of the coronal field---a key property for modeling/predicting the thermal-magnetic structure of the solar corona. Overall, we will examine the effect of these considerations on white-light and EUV observables from the simulations, and present them in the context of our final 2017 eclipse prediction model.Research supported by NASA's Heliophysics Supporting Research and Living With a Star Programs.

  12. Ultraviolet Radiation from Evolved Stellar Populations -- I. Models

    CERN Document Server

    Dorman, B; O'Connell, R

    1993-01-01

    This series of papers comprises a systematic exploration of the hypothesis that the far ultraviolet radiation from star clusters and elliptical galaxies originates from extremely hot horizontal-branch (HB) stars and their post-HB progeny. This first paper presents an extensive grid of calculations of stellar models from the Zero Age Horizontal Branch through to a point late in post-HB evolution or a point on the white dwarf cooling track. We use the term `Extreme Horizontal Branch' (EHB) to refer to HB sequences of constant mass that do not reach the thermally-pulsing stage on the AGB. These models evolve after core helium exhaustion

  13. Warm stellar matter within the quark-meson-coupling model

    Science.gov (United States)

    Panda, P. K.; Providência, C.; Menezes, D. P.

    2010-10-01

    In the present article, we investigate stellar matter obtained within the quark-meson-coupling (QMC) model for fixed temperature and with the entropy of the order of 1 or 2 Boltzmann units per baryon for neutrino-free matter and matter with trapped neutrinos. A new prescription for the calculation of the baryon effective masses in terms of the free energy is used. Comparing the results of the present work with those obtained from the nonlinear Walecka model, smaller strangeness and neutrino fractions are predicted within QMC. As a consequence, QMC has a smaller window of metastability for conversion into a low-mass blackhole during cooling.

  14. The metastable dynamo model of stellar rotational evolution

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Timothy M., E-mail: tbrown@lcogt.net [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Goleta, CA 93117 (United States)

    2014-07-10

    This paper introduces a new empirical model for the rotational evolution of Sun-like stars—those with surface convection zones and non-convective interior regions. Previous models do not match the morphology of observed (rotation period)-color diagrams, notably the existence of a relatively long-lived 'C-sequence' of fast rotators first identified by Barnes. This failure motivates the Metastable Dynamo Model (MDM) described here. The MDM posits that stars are born with their magnetic dynamos operating in a mode that couples very weakly to the stellar wind, so their (initially very short) rotation periods at first change little with time. At some point, this mode spontaneously and randomly changes to a strongly coupled mode, the transition occurring with a mass-dependent lifetime that is of the order of 100 Myr. I show that with this assumption, one can obtain good fits to observations of young clusters, particularly for ages of 150-200 Myr. Previous models and the MDM both give qualitative agreement with the morphology of the slower-rotating 'I-sequence' stars, but none of them have been shown to accurately reproduce the stellar-mass-dependent evolution of the I-sequence stars, especially for clusters older than a few hundred million years. I discuss observational experiments that can test aspects of the MDM, and speculate that the physics underlying the MDM may be related to other situations described in the literature, in which stellar dynamos may have a multi-modal character.

  15. On the connections between solar and stellar dynamo models

    Science.gov (United States)

    Jouve, Laurène; Kumar, Rohit

    2017-10-01

    We here discuss the various dynamo models which have been designed to explain the generation and evolution of large-scale magnetic fields in stars. We focus on the models that have been applied to the Sun and can be tested for other solar-type stars now that modern observational techniques provide us with detailed stellar magnetic field observations. Mean-field flux-transport dynamo models have been developed for decades to explain the solar cycle and applications to more rapidly-rotating stars are discussed. Tremendous recent progress has been made on 3D global convective dynamo models. They do not however for now produce regular flux emergence that could be responsible for surface active regions and questions about the role of these active regions in the dynamo mechanism are still difficult to address with such models. We finally discuss 3D kinematic dynamo models which could constitute a promising combined approach, in which data assimilation could be applied.

  16. A multipurpose 3-D grid of stellar models

    CERN Document Server

    Apellániz, J Maíz

    2012-01-01

    The last two decades have produced a proliferation of stellar atmosphere grids, evolutionary tracks, and isochrones which are available to the astronomical community from different internet services. However, it is not straightforward (at least for an inexperienced user) to manipulate those models to answer questions of the type: What is the spectral energy distribution of a 9000 K giant? What about its J-band magnitude for different metallicities? What can I tell about the mass of a star if I know that its unreddened B-V color is -0.05 and its luminosity in solar units is 10^5? The answers to those questions are indeed in the models but a series of transformations and combinations involving different variables and models are required to obtain them. To make the available knowledge more user friendly, I have combined a number of state-of-the-art sources to create a 3-D (effective temperature, luminosity, and metallicity) grid of stellar models for which I provide calibrated SEDs and magnitudes as well as auxi...

  17. Truncated $\\gamma$-exponential models for tidal stellar systems

    CERN Document Server

    Gomez-Leyton, Y J

    2016-01-01

    We introduce a parametric family of models to characterize the properties of astrophysical systems in a quasi-stationary evolution under the incidence evaporation. We start from an one-particle distribution $f_{\\gamma}\\left(\\mathbf{q},\\mathbf{p}|\\beta,\\varepsilon_{s}\\right)$ that considers an appropriate deformation of Maxwell-Boltzmann form with inverse temperature $\\beta$, in particular, a power-law truncation at the scape energy $\\varepsilon_{s}$ with exponent $\\gamma>0$. This deformation is implemented using a generalized $\\gamma$-exponential function obtained from the \\emph{fractional integration} of ordinary exponential. As shown in this work, this proposal generalizes models of tidal stellar systems that predict particles distributions with \\emph{isothermal cores and polytropic haloes}, e.g.: Michie-King models. We perform the analysis of thermodynamic features of these models and their associated distribution profiles. A nontrivial consequence of this study is that profiles with isothermal cores and p...

  18. The Stagger-grid: A grid of 3D stellar atmosphere models - VI. Surface appearance of stellar granulation

    CERN Document Server

    Magic, Zazralt

    2014-01-01

    In the surface layers of late-type stars, stellar convection is manifested with its typical granulation pattern due to the presence of convective motions. The resulting photospheric up- and downflows leave imprints in the observed spectral line profiles. We perform a careful statistical analysis of stellar granulation and its properties for different stellar parameters. We employ realistic 3D radiative hydrodynamic (RHD) simulations of surface convection from the Stagger-grid, a comprehensive grid of atmosphere models that covers a large parameter space in terms of Teff, logg, and [Fe/H]. Individual granules are detected from the (bolometric) intensity maps at disk center with an efficient granulation pattern recognition algorithm. From these we derive their respective properties: diameter, fractal dimension (area-perimeter relation), geometry, topology, variation of intensity, temperature, density and velocity with granule size. Also, the correlation of the physical properties at the optical surface are stud...

  19. When the Jeans don't fit: How stellar feedback drives stellar kinematics and complicates dynamical modeling in low-mass galaxies

    CERN Document Server

    El-Badry, Kareem; Geha, Marla; Quataert, Eliot; Hopkins, Philip F; Kereš, Dusan; Chan, T K; Faucher-Giguère, Claude-André

    2016-01-01

    In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments (FIRE) project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies' starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy's dynamical mass dur...

  20. Models of cuspy triaxial stellar systems. II. Regular orbits

    CERN Document Server

    Muzzio, J C; Zorzi, A F

    2012-01-01

    In the first paper of this series we used the N--body method to build a dozen cuspy (gamma ~ 1) triaxial models of stellar systems, and we showed that they were highly stable over time intervals of the order of a Hubble time, even though they had very large fractions of chaotic orbits (more than 85 per cent in some cases). The models were grouped in four sets, each one comprising models morphologically resembling E2, E3, E4 and E5 galaxies, respectively. The three models within each set, although different, had the same global properties and were statistically equivalent. In the present paper we use frequency analysis to classify the regular orbits of those models. The bulk of those orbits are short axis tubes (SATs), with a significant fraction of long axis tubes (LATs) in the E2 models that decreases in the E3 and E4 models to become negligibly small in the E5 models. Most of the LATs in the E2 and E3 models are outer LATs, but the situation reverses in the E4 and E5 models where the few LATs are mainly inn...

  1. Modelling turbulent stellar convection zones: sub-grid scales effects

    CERN Document Server

    Strugarek, A; Brun, A S; Charbonneau, P; Mathis, S; Smolarkiewicz, P K

    2016-01-01

    The impressive development of global numerical simulations of turbulent stellar interiors unveiled a variety of possible differential rotation (solar or anti-solar), meridional circulation (single or multi-cellular), and dynamo states (stable large scale toroidal field or periodically reversing magnetic fields). Various numerical schemes, based on the so-called anelastic set of equations, were used to obtain these results. It appears today mandatory to assess their robustness with respect to the details of the numerics, and in particular to the treatment of turbulent sub-grid scales. We report on an ongoing comparison between two global models, the ASH and EULAG codes. In EULAG the sub-grid scales are treated implicitly by the numerical scheme, while in ASH their effect is generally modelled by using enhanced dissipation coefficients. We characterize the sub-grid scales effect in a turbulent convection simulation with EULAG. We assess their effect at each resolved scale with a detailed energy budget. We deriv...

  2. A stellar model with diffusion in general relativity

    CERN Document Server

    Alho, Artur

    2016-01-01

    We consider a spherically symmetric stellar model in general relativity whose interior consists of a pressureless fluid undergoing microscopic velocity diffusion in a cosmological scalar field. We show that the diffusion dynamics compel the interior to be spatially homogeneous, by which one can infer immediately that within our model, and in contrast to the diffusion-free case, no naked singularities can form in the gravitational collapse. We then study the problem of matching an exterior Bondi type metric to the surface of the star and find that the exterior can be chosen to be a modified Vaidya metric with variable cosmological constant. Finally, we study in detail the causal structure of an explicit, self-similar solution.

  3. Testing galaxy formation models with galaxy stellar mass functions

    CERN Document Server

    Lim, Seunghwan; Lan, Ting-Wen; Ménard, Brice

    2016-01-01

    We compare predictions of a number of empirical models and numerical simulations of galaxy formation to the conditional stellar mass functions (CSMF) of galaxies in groups of different masses obtained recently by Lan et al. to test how well different models accommodate the data. Among all the models considered, only the model of Lu et al. can match the observational data; all other models fail to reproduce the faint-end upturn seen in the observation. The CSMFs are used to update the halo-based empirical model of Lu et al., and the model parameters obtained are very similar to those inferred by Lu et al. from a completely different set of observational constraints. The observational data clearly prefer a model in which star formation in low-mass halos changes behavior at a characteristic redshift $z_c \\sim 2$. There is also tentative evidence that this characteristic redshift depends on environments, becoming $z_c \\sim 4$ in regions that eventually evolve into rich clusters of galaxies. The constrained model ...

  4. Carbon Abundances In The Light Of 3D Model Stellar Atmospheres

    DEFF Research Database (Denmark)

    Collet, Remo

    ) hydrodynamic modelling of stellar atmospheres and stellar spectra. In this contribution, I describe quantitatively the impact of realistic, time-dependent, 3D hydrodynamic model atmospheres on the spectroscopic determination of carbon abundances from CH molecular lines for stars with a wide range of stellar...... carbon abundance corrections on the oxygen abundance in carbon-enhanced metal-poor (CEMP) stars and show that such corrections are extremely sensitive to the atmospheric C/O ratio....

  5. MILES extended : Stellar population synthesis models from the optical to the infrared

    NARCIS (Netherlands)

    Rock, B.; Vazdekis, A.; Ricciardelli, E.; Peletier, R. F.; Knapen, J. H.; Falcon-Barroso, J.

    2016-01-01

    We present the first single-burst stellar population models, which covers the optical and the infrared wavelength range between 3500 and 50 000 angstrom and which are exclusively based on empirical stellar spectra. To obtain these joint models, we combined the extended MILES models in the optical wi

  6. Measurements of accretion disc corona size in LMXB: consequences for Comptonization and LMXB models

    CERN Document Server

    Church, M J

    2004-01-01

    We present results of measurements of the radial extent of the accretion disc corona in low mass X-ray binaries. These results prove conclusively the extended nature of the ADC, with radial extent varying from 20,000 km in the faintest sources to 700,000 km in the brightest, a substantial fraction of the accretion disc radius, typically 15%. This result rules out the Eastern model for LMXB which is extensively used, in which the Comptonizing region is a small central region. The ADC size depends strongly on the 1 - 30 keV source luminosity via a simple relationship r_ADC = L^{0.88 +/- 0.16} (99% confidence) close to a simple proportionality. We also present limited evidence that the ADC size agrees with the Compton radius r_C, or maximum radius for hydrostatic equilibrium. The results are consistent with models in which an extended ADC is formed by illumination of the disc by the central source. The dependence on luminosity may reflect the known decrease of coronal temperature as the source luminosity increas...

  7. The truncation of stellar discs A theoretical model

    CERN Document Server

    Battaner, E; Jiménez-Vicente, J

    1998-01-01

    The truncation of stellar discs is not abrupt but characterized by a continuous distancing from the exponential profile. There exists a truncation curve, $t(r)$, ending at a truncation radius, $r_t$. We present here a theoretical model in which it is assumed that the magnetic hypothesis explaining the flat rotation curve also explains the truncation. Once stars are born, the centripetal magnetic force previously acting on the progenitor gas cloud is suddenly interrupted, and stars must move to larger orbits or escape. The agreement between theoretical and observed truncation curves is very satisfactory. Parameters defining the disc gas rotation curve should therefore be related to those defining the truncation. It is predicted that rotation curves that quickly reach the asymptotic value $\\theta_0 = \\theta (r=\\infty)$ would have small truncation radii. On the contrary, $r_t$ and $\\theta_0$ itself, would be uncorrelated quantities.

  8. A disk-corona model for low/hard state of black hole X-ray binaries

    CERN Document Server

    Wang, Jiu-Zhou; Huang, Chang-Yin

    2013-01-01

    A disk-corona model for fitting low/hard (LH) state of associated steady jet of black hole X-ray binaries (BHXBs) is proposed based on the large-scale magnetic field configuration of the coexistence of the Blandford-Znajek (BZ) and Blandford-Payne (BP) processes,where the magnetic field configuration for the BP process is determined by the requirement of energy conversion from Poynting energy flux into kinetic energy flux in the jet. It is found that corona current is crucial to guarantee the consistency of the jet launching from accretion disk. The relative importance of the BZ to BP processes in powering jets from black hole accretion disk is discussed, and the LH state of several BHXBs is fitted based on our model.In addition, we suggest that magnetic field configuration could be regarded as the second parameter for governing the state transition of BHXBs.

  9. Investigating the X-ray time-lags in PG 1244+026 using an extended corona model

    CERN Document Server

    Chainakun, P

    2016-01-01

    We present an extended corona model based on ray-tracing simulations to investigate X-ray time lags in Active Galactic Nuclei (AGN). This model consists of two axial point sources illuminating an accretion disc that produce the reverberation lags. These lags are due to the time delays between the directly observed and reflection photons and are associated with the light-travel time between the source and the disc, so they allow us to probe the disc-corona geometry. We assume the variations of two X-ray sources are triggered by the same primary variations, but allow the two sources to respond in different ways (i.e. having different source responses). The variations of each source induce a delayed accretion disc response and the total lags consist of a combination of both source and disc responses. We show that the extended corona model can reproduce both the low-frequency hard and high-frequency soft (reverberation) lags. Fitting the model to the timing data of PG~1244+026 reveals the hard and soft X-ray sour...

  10. Investigating the X-ray time lags in PG 1244+026 using an extended corona model

    Science.gov (United States)

    Chainakun, P.; Young, A. J.

    2017-03-01

    We present an extended corona model based on ray-tracing simulations to investigate X-ray time lags in active galactic nuclei (AGNs). This model consists of two axial point sources illuminating an accretion disc that produce the reverberation lags. These lags are due to the time delays between the directly observed and reflection photons and are associated with the light-travel time between the source and the disc, so they allow us to probe the disc-corona geometry. We assume the variations of two X-ray sources are triggered by the same primary variations, but allow the two sources to respond in different ways (i.e. having different source responses). The variations of each source induce a delayed accretion disc response and the total lags consist of a combination of both source and disc responses. We show that the extended corona model can reproduce both the low-frequency hard and high-frequency soft (reverberation) lags. Fitting the model to the timing data of PG 1244+026 reveals the hard and soft X-ray sources at ∼6rg and ∼11rg, respectively. The upper source produces small amounts of reflection and can be interpreted as a relativistic jet, or outflowing blob, whose emission is beamed away from the disc. This explains the observed lag energy in which there is no soft lag at energies possible but only at near the speed of light.

  11. Models of cuspy triaxial stellar systems. IV: Rotating systems

    CERN Document Server

    Carpintero, D D

    2016-01-01

    We built two self-consistent models of triaxial, cuspy, rotating stellar systems adding rotation to non-rotating models presented in previous papers of this series. The final angular velocity of the material is not constant and varies with the distance to the center and with the height over the equator of the systems, but the figure rotation is very uniform in both cases. Even though the addition of rotation to the models modifies their original semiaxes ratios, the final rotating models are considerably flattened and triaxial. An analysis of the orbital content of the models shows that about two thirds of their orbits are chaotic yet the models are very stable over intervals of the order of one Hubble time. The bulk of regular orbits are short axis tubes, while long axis tubes are replaced by tubes whose axes lie on the short-long axes plane, but do not coincide with the major axis. Other types of regular orbits that do not appear in non-rotating systems, like horseshoes and orbits that cross themselves, are...

  12. Towards 21st Century Stellar Models: Star Clusters, Supercomputing, and Asteroseismology

    CERN Document Server

    Campbell, S W; D'Orazi, V; Meakin, C; Stello, D; Christensen-Dalsgaard, J; Kuehn, C; De Silva, G M; Arnett, W D; Lattanzio, J C; MacLean, B T

    2015-01-01

    Stellar models provide a vital basis for many aspects of astronomy and astrophysics. Recent advances in observational astronomy -- through asteroseismology, precision photometry, high-resolution spectroscopy, and large-scale surveys -- are placing stellar models under greater quantitative scrutiny than ever. The model limitations are being exposed and the next generation of stellar models is needed as soon as possible. The current uncertainties in the models propagate to the later phases of stellar evolution, hindering our understanding of stellar populations and chemical evolution. Here we give a brief overview of the evolution, importance, and substantial uncertainties of core helium burning stars in particular and then briefly discuss a range of methods, both theoretical and observational, that we are using to advance the modelling.

  13. Towards 21st century stellar models: Star clusters, supercomputing and asteroseismology

    Science.gov (United States)

    Campbell, S. W.; Constantino, T. N.; D'Orazi, V.; Meakin, C.; Stello, D.; Christensen-Dalsgaard, J.; Kuehn, C.; De Silva, G. M.; Arnett, W. D.; Lattanzio, J. C.; MacLean, B. T.

    2016-09-01

    Stellar models provide a vital basis for many aspects of astronomy and astrophysics. Recent advances in observational astronomy - through asteroseismology, precision photometry, high-resolution spectroscopy, and large-scale surveys - are placing stellar models under greater quantitative scrutiny than ever. The model limitations are being exposed and the next generation of stellar models is needed as soon as possible. The current uncertainties in the models propagate to the later phases of stellar evolution, hindering our understanding of stellar populations and chemical evolution. Here we give a brief overview of the evolution, importance, and substantial uncertainties of core helium burning stars in particular and then briefly discuss a range of methods, both theoretical and observational, that we are using to advance the modelling. This study uses observational data from from HST, VLT, AAT, Kepler, and supercomputing resources in Australia provided by the National Computational Infrastructure (NCI) and Pawsey Supercomputing Centre.

  14. Corona Borealis

    Science.gov (United States)

    Murdin, P.

    2000-11-01

    (the Northern Crown; abbrev. CrB, gen. Coronae Borealis; area 179 sq. deg.) A northern constellation which lies between Boötes and Hercules, and culminates at midnight in mid-May. It represents the crown that in Greek mythology was made by Hephaestus, god of fire, and worn by Princess Ariadne of Crete. Its brightest stars were cataloged by Ptolemy (c. AD 100-175) in the Almagest....

  15. Disk-Corona Model in Active Galactic Nuclei:an Observational Test

    Institute of Scientific and Technical Information of China (English)

    Fang Yang; Chen Hu; Yan-Mei Chen; Jian-Min Wang

    2007-01-01

    We compiled a sample of 98 radio-quiet active galactic nuclei observed by ASCA,Chandra.XMM-Newton,INTEGRAL and Swift with the aim of testing the formation of hot corona and the magnetic shear stress operating in a disk-corona system.We found a strong correlation between the hard X-ray luminosity,bolometric luminosity LBol and Eddington luminosity LEdd.in the sense that the fraction f of hard X-ray to the bolometric luminosity is inversely proportional to the Eddington ratio.This correlation favors the shear stress tensor being of the form of trφ∝ Pgas,with which the disk-corona structure is stable.

  16. A note on magnetized coronae

    CERN Document Server

    Belmont, R

    2008-01-01

    X-ray binaries and AGN show observational evidence for magnetized hot plasmas. Despite years of data, very little is known on these {\\it coronae} especially on the mechanisms responsible for their heating, and most models simply assume their existence. However, understanding its properties has now become a key issue of the AGN and microquasars modelling. Here we consider the effect of a strong vertical magnetic field on the corona AGN and X-ray binaries and show that its modeling (structure, heating) must be reconsidered. As a first step, we present one mechanism that could extract energy from the accretion disks and deposits it in the coronae: the {\\it magnetic pumping

  17. The Evolutionary Population Synthesis Model for Helium-Enhanced Stellar Populations

    Science.gov (United States)

    Chung, Chul; Yoon, Suk-Jin; Lee, Young-Wook

    2017-01-01

    The discovery of multiple stellar populations in the Milky Way globular clusters has stimulated a great deal of researches on the helium enhanced stellar populations. Here, we present the evolutionary population synthesis models for integrated spectro-photometric evolution of simple stellar populations (SSPs) with varied initial helium abundances. The integrated properties of helium-enhanced SSPs depend on metallicity and age as are the normal-helium SSPs, but the properties vary greatly with the initial helium abundance. We will discuss how helium-enhanced stellar populations explain many interesting observations of globular clusters and their host galaxies.

  18. Modeling non-thermal emission from stellar bow shocks

    CERN Document Server

    Pereira, V; Miceli, M; Bonito, R; de Castro, E

    2016-01-01

    Runaway O- and early B-type stars passing throughout the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high energy photons by non-thermal radiative processes, but their efficiency is still debated. We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. We apply our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations failed in detecting high energy emission, and to the transition phase of a supergiant star in the late stages of its life.From our analysis, we confirm that the X-ray emission from the bow shock produced by AE Aurigae can be explained by inverse Compton processes involving the infrared photons of the heated dust. We also predict low high energy fl...

  19. Stellar Models of Multiple Populations in Globular Clusters. I. The Main Sequence of NGC 6752

    CERN Document Server

    Dotter, Aaron; Conroy, Charlie; Milone, A P; Marino, A F; Yong, David

    2014-01-01

    We present stellar atmosphere and evolution models of main sequence stars in two stellar populations of the Galactic globular cluster NGC 6752. These populations represent the two extremes of light-element abundance variations in the cluster. NGC 6752 is a benchmark cluster in the study of multiple stellar populations because of the rich array of spectroscopic abundances and panchromatic Hubble Space Telescope photometry. The spectroscopic abundances are used to compute stellar atmosphere and evolution models. The synthetic spectra for the two populations show significant differences in the ultraviolet and, for the coolest temperatures, in the near-infrared. The stellar evolution models exhibit insignificant differences in the H-R diagram except on the lower main sequence. The appearance of multiple sequences in the colour-magnitude diagrams (CMDs) of NGC 6752 is almost exclusively due to spectral effects caused by the abundance variations. The models reproduce the observed splitting and/or broadening of sequ...

  20. The Effects of Corona on Current Surges Induced on Conducting Lines by EMP (Electromagnetic Pulse): A Comparison of Experiment Data with Results of Analytic Corona Models

    Science.gov (United States)

    1987-09-01

    265-281. 18. Rogers , S.R., and R.A. Perala, "The Effects of Corona and Angle of Arrival on the EMP Response of Cables Lying on the Surface of the...Survivability Organization, Boeing Aerospace COmpany, P. 0. Box 399, Seattle, WA 98124 74. V. L. Chartier , Bonneville Power Administration, P. 0. Box

  1. A model of the generation and transport of ozone in high-tension nozzle driven corona inside a novel diode.

    Science.gov (United States)

    Vijayan, T; Patil, Jagadish G

    2012-12-01

    The genesis and transport of ozone (O(3)) are investigated in a novel plasma diode and described in this paper. The innovative cathode (K) of this axial symmetric diode which operated at the high voltage (φ(0)), has a large number of sharpened nozzles located on different radial planes of its central tubular-mast and is encircled by the anode (A). The nozzles played the dual role of oxygen (O(2)) injection as well as creation of high electric field (E) in the A-K gap, enabled the formation of a cold corona. Electrons in the corona under the influence of E moved towards anode, collided with O(2) and created the O radicals. O in turn joined the free O(2) and formed O(3). The evolution of O(3) here is modeled in various O(2) pressure (P), electron density (n(e)), and temperature (T) in terms of the major reaction modes involving e, O, O(2), and O(3). Typical steady state O(3) density attained so in P ~ bar, n(e) ~ 10(15) m(-3) and T ~ 300 K is over 10(25) m(-3) and that of O lower ~10(20) m(-3). Both the O and O(3) densities increased with an enhanced n(e) of avalanche multiplications in corona. O(3) increased also with a higher P but the temporal O reversed in trend midway and reduced with P towards the steady state. A sharp decline in diode resistance with smaller A-K gap induced finite discharge current and led to the undesired heating of corona. It is shown that the O(3) density reduced with the temperature rise but O density reduced with the T rise up to 500 K and then rose modestly with the further T increase.

  2. A model of the generation and transport of ozone in high-tension nozzle driven corona inside a novel diode

    Science.gov (United States)

    Vijayan, T.; Patil, Jagadish G.

    2012-12-01

    The genesis and transport of ozone (O3) are investigated in a novel plasma diode and described in this paper. The innovative cathode (K) of this axial symmetric diode which operated at the high voltage (ϕ0), has a large number of sharpened nozzles located on different radial planes of its central tubular-mast and is encircled by the anode (A). The nozzles played the dual role of oxygen (O2) injection as well as creation of high electric field (E) in the A-K gap, enabled the formation of a cold corona. Electrons in the corona under the influence of E moved towards anode, collided with O2 and created the O radicals. O in turn joined the free O2 and formed O3. The evolution of O3 here is modeled in various O2 pressure (P), electron density (ne), and temperature (T) in terms of the major reaction modes involving e, O, O2, and O3. Typical steady state O3 density attained so in P ˜ bar, ne ˜ 1015 m-3 and T ˜ 300 K is over 1025 m-3 and that of O lower ˜1020 m-3. Both the O and O3 densities increased with an enhanced ne of avalanche multiplications in corona. O3 increased also with a higher P but the temporal O reversed in trend midway and reduced with P towards the steady state. A sharp decline in diode resistance with smaller A-K gap induced finite discharge current and led to the undesired heating of corona. It is shown that the O3 density reduced with the temperature rise but O density reduced with the T rise up to 500 K and then rose modestly with the further T increase.

  3. The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies

    CERN Document Server

    Conroy, Charlie; White, Martin

    2008-01-01

    The stellar masses, mean ages, metallicities, and star formation histories of galaxies are now commonly estimated via stellar population synthesis (SPS) techniques. SPS relies on stellar evolution calculations from the main sequence to stellar death, stellar spectral libraries, phenomenological dust models, and stellar initial mass functions (IMFs). The present work is the first in a series that explores the impact of uncertainties in key phases of stellar evolution and the IMF on the derived physical properties of galaxies and the expected luminosity evolution for a passively evolving set of stars. A Monte-Carlo Markov-Chain approach is taken to fit near-UV through near-IR photometry of a representative sample of low- and high-redshift galaxies with this new SPS model. Significant results include the following: 1) including uncertainties in stellar evolution, stellar masses at z~0 carry errors of ~0.3 dex at 95% CL with little dependence on luminosity or color, while at z~2, the masses of bright red galaxies...

  4. Modeling turbulent stellar convection zones: Sub-grid scales effects

    Science.gov (United States)

    Strugarek, A.; Beaudoin, P.; Brun, A. S.; Charbonneau, P.; Mathis, S.; Smolarkiewicz, P. K.

    2016-10-01

    The impressive development of global numerical simulations of turbulent stellar interiors unveiled a variety of possible differential rotation (solar or anti-solar), meridional circulation (single or multi-cellular), and dynamo states (stable large scale toroidal field or periodically reversing magnetic fields). Various numerical schemes, based on the so-called anelastic set of equations, were used to obtain these results. It appears today mandatory to assess their robustness with respect to the details of the numerics, and in particular to the treatment of turbulent sub-grid scales. We report on an ongoing comparison between two global models, the ASH and EULAG codes. In EULAG the sub-grid scales are treated implicitly by the numerical scheme, while in ASH their effect is generally modeled by using enhanced dissipation coefficients. We characterize the sub-grid scales effect in a turbulent convection simulation with EULAG. We assess their effect at each resolved scale with a detailed energy budget. We derive equivalent eddy-diffusion coefficients and use the derived diffusivities in twin ASH numerical simulations. We find a good agreement between the large-scale flows developing in the two codes in the hydrodynamic regime, which encourages further investigation in the magnetohydrodynamic regime for various dynamo solutions.

  5. Cepheid models based on self-consistent stellar evolution and pulsation calculations : The right answer?

    NARCIS (Netherlands)

    Baraffe, [No Value; Alibert, Y; Mera, D; Charbrier, G; Beaulieu, JP

    1998-01-01

    We have computed stellar evolutionary models for stars in a mass range characteristic of Cepheid variables (3 stellar evolution calculations are coupled to a linear nonadiabatic stability

  6. Modeling and characterization of field-enhanced corona discharge in ozone-generator diode

    Science.gov (United States)

    Patil, Jagadish G.; Vijayan, T.

    2010-02-01

    Electric field enhanced corona plasma discharge in ozone generator diode of axial symmetry has been investigated and characterized in theory. The cathode K of diode is made of a large number of sharpened nozzles arranged on various radial planes on the axial mast and pervaded in oxygen gas inside the anode cup A, produces high fields over MV/m and aids in the formation of a corona plume of dense ozone cloud over the cathode surface. An r-z finite difference scheme has been devised and employed to numerically determine the potential and electric field distributions inside the diode. The analyses of cathode emissions revealed a field emission domain conformed to modified Child-Langmuir diode-current. Passage of higher currents (over μA) in shorter A-K gaps d gave rise to cathode heated plasma extending from the corona to Saha regimes depending on local temperature. Plasma densities of order 102-106 m-3 are predicted in these. For larger d however, currents are smaller and heating negligible and a negative corona favoring ozone formation is attained. High ozone yields about 20 per cent of oxygen input is predicted in this domain. The generator so developed will be applied to various important applications such as, purification of ambient air /drinking water, ozone therapy, and so on.

  7. Modeling for Stellar Feedback in Galaxy Formation Simulations

    Science.gov (United States)

    Núñez, Alejandro; Ostriker, Jeremiah P.; Naab, Thorsten; Oser, Ludwig; Hu, Chia-Yu; Choi, Ena

    2017-02-01

    Various heuristic approaches to model unresolved supernova (SN) feedback in galaxy formation simulations exist to reproduce the formation of spiral galaxies and the overall inefficient conversion of gas into stars. Some models, however, require resolution-dependent scalings. We present a subresolution model representing the three major phases of supernova blast wave evolution—free expansion, energy-conserving Sedov–Taylor, and momentum-conserving snowplow—with energy scalings adopted from high-resolution interstellar-medium simulations in both uniform and multiphase media. We allow for the effects of significantly enhanced SN remnant propagation in a multiphase medium with the cooling radius scaling with the hot volume fraction, {f}{hot}, as {(1-{f}{hot})}-4/5. We also include winds from young massive stars and AGB stars, Strömgren sphere gas heating by massive stars, and a mechanism that limits gas cooling that is driven by radiative recombination of dense H ii regions. We present initial tests for isolated Milky Way-like systems simulated with the Gadget-based code SPHgal with improved SPH prescription. Compared to pure thermal SN input, the model significantly suppresses star formation at early epochs, with star formation extended both in time and space in better accord with observations. Compared to models with pure thermal SN feedback, the age at which half the stellar mass is assembled increases by a factor of 2.4, and the mass-loading parameter and gas outflow rate from the galactic disk increase by a factor of 2. Simulation results are converged for a variation of two orders of magnitude in particle mass in the range (1.3–130) × 104 solar masses.

  8. A new methodology to test galaxy formation models using the dependence of clustering on stellar mass

    Science.gov (United States)

    Campbell, David J. R.; Baugh, Carlton M.; Mitchell, Peter D.; Helly, John C.; Gonzalez-Perez, Violeta; Lacey, Cedric G.; Lagos, Claudia del P.; Simha, Vimal; Farrow, Daniel J.

    2015-09-01

    We present predictions for the two-point correlation function of galaxy clustering as a function of stellar mass, computed using two new versions of the GALFORM semi-analytic galaxy formation model. These models make use of a high resolution, large volume N-body simulation, set in the 7-year Wilkinson Microwave Anisotropy Probe cosmology. One model uses a universal stellar initial mass function (IMF), while the other assumes different IMFs for quiescent star formation and bursts. Particular consideration is given to how the assumptions required to estimate the stellar masses of observed galaxies (such as the choice of IMF, stellar population synthesis model, and dust extinction) influence the perceived dependence of galaxy clustering on stellar mass. Broad-band spectral energy distribution fitting is carried out to estimate stellar masses for the model galaxies in the same manner as in observational studies. We show clear differences between the clustering signals computed using the true and estimated model stellar masses. As such, we highlight the importance of applying our methodology to compare theoretical models to observations. We introduce an alternative scheme for the calculation of the merger time-scales for satellite galaxies in GALFORM, which takes into account the dark matter subhalo information from the simulation. This reduces the amplitude of small-scale clustering. The new merger scheme offers improved or similar agreement with observational clustering measurements, over the redshift range 0 Public Extragalactic Redshift Survey, depending on the GALFORM model used.

  9. Stellar energy loss rates in the pair-annihilation process beyond the standard model

    Science.gov (United States)

    Hernández-Ruíz, M. A.; Gutiérrez-Rodríguez, A.; González-Sánchez, A.

    2017-01-01

    We calculate the stellar energy loss due to neutrino-pair production in e+e- annihilation in the context of a 331 model, a left-right symmetric model and a simplest little Higgs model in a way that can be used in supernova calculations. We also present some simple estimates which show that such process can act as an efficient energy loss mechanism in the shocked supernova core. We find that the stellar energy loss is almost independent of the parameters of the models in the allowed range for these parameters. This work complements other studies on the stellar energy loss rate in e+e- annihilation.

  10. A Legacy Magellanic Clouds Star Clusters Sample for the Calibration of Stellar Evolution Models

    Science.gov (United States)

    Fouesneau, Morgan

    2014-10-01

    Stellar evolution models are fundamental to all studies in astrophysics. These models are the foundations of the interpretation of colors and luminosities of stars necessary to address problems ranging from galaxy formation to determining the habitable zone of planets and interstellar medium properties. For decades the standard calibration of these models relied on a handful of star clusters. However, large uncertainties remain in the fundamental parameters underlying stellar evolution models. The project we propose is two-fold. First we propose to generate a new high quality reference dataset of the resolved stars in 121 Magellanic Cloud clusters, selected from 18 past programs to efficiently sample a large grid of stellar evolution models. Our team will measure the photometry of individual stars in those clusters and characterize individual completeness and photometric uncertainties. Second, we will migrate the calibration of the stellar evolution into a fully probabilistic framework, that will not only reflect the state-of-the-art, but will also be published with fully characterized uncertainties, based on the entire reference data set, rather than a few select clusters.We have entered an era dominated by large surveys {e.g. SDSS, PanSTARRS, Gaia, LSST} where the variations between families of stellar models are greater than the nominal precision of the instruments. Our proposed program will provide a library needed for a convergence in the stellar models and our understanding of stellar evolution.

  11. Computational Models of Stellar Collapse and Core-Collapse Supernovae

    CERN Document Server

    Ott, C D; Burrows, A; Livne, E; O'Connor, E; Löffler, F

    2009-01-01

    Core-collapse supernovae are among Nature's most energetic events. They mark the end of massive star evolution and pollute the interstellar medium with the life-enabling ashes of thermonuclear burning. Despite their importance for the evolution of galaxies and life in the universe, the details of the core-collapse supernova explosion mechanism remain in the dark and pose a daunting computational challenge. We outline the multi-dimensional, multi-scale, and multi-physics nature of the core-collapse supernova problem and discuss computational strategies and requirements for its solution. Specifically, we highlight the axisymmetric (2D) radiation-MHD code VULCAN/2D and present results obtained from the first full-2D angle-dependent neutrino radiation-hydrodynamics simulations of the post-core-bounce supernova evolution. We then go on to discuss the new code Zelmani which is based on the open-source HPC Cactus framework and provides a scalable AMR approach for 3D fully general-relativistic modeling of stellar col...

  12. Connecting Galaxies with Halos Across Cosmic Time: Stellar mass assembly distribution modeling of galaxy statistics

    CERN Document Server

    Becker, Matthew R

    2015-01-01

    In this work, I explore an empirically motivated model for investigating the relationship between galaxy stellar masses, star formation rates and their halo masses and mass accretion histories. The core statistical quantity in this model is the stellar mass assembly distribution, $P(dM_{*}/dt|\\mathbf{X},a)$, which specifies the probability density distribution of stellar mass assembly rates given a set of halo properties $\\mathbf{X}$ and epoch $a$. Predictions from this model are obtained by integrating the stellar mass assembly distribution (SMAD) over halo merger trees, easily obtained from modern, high-resolution $N$-body simulations. Further properties of the galaxies hosted by the halos can be obtained by post-processing the stellar mass assembly histories with stellar population synthesis models. In my particular example implementation of this model, I use the \\citet{behroozi13a} constraint on the median stellar mass assembly rates of halos as a function of their mass and redshift to construct an exampl...

  13. Massive Warm/Hot Galaxy Coronae as Probed by UV/X-Ray Oxygen Absorption and Emission. I. Basic Model

    Science.gov (United States)

    Faerman, Yakov; Sternberg, Amiel; McKee, Christopher F.

    2017-01-01

    We construct an analytic phenomenological model for extended warm/hot gaseous coronae of L* galaxies. We consider UV O vi Cosmic Origins Spectrograph (COS)-Halos absorption line data in combination with Milky Way (MW) X-ray O vii and O viii absorption and emission. We fit these data with a single model representing the COS-Halos galaxies and a Galactic corona. Our model is multi-phased, with hot and warm gas components, each with a (turbulent) log-normal distribution of temperatures and densities. The hot gas, traced by the X-ray absorption and emission, is in hydrostatic equilibrium in an MW gravitational potential. The median temperature of the hot gas is 1.5× {10}6 K and the mean hydrogen density is ∼ 5× {10}-5 {{cm}}-3. The warm component as traced by the O vi, is gas that has cooled out of the high density tail of the hot component. The total warm/hot gas mass is high and is 1.2× {10}11 {M}ȯ . The gas metallicity we require to reproduce the oxygen ion column densities is 0.5 solar. The warm O vi component has a short cooling time (∼ 2× {10}8 years), as hinted by observations. The hot component, however, is ∼ 80 % of the total gas mass and is relatively long-lived, with {t}{cool}∼ 7× {10}9 years. Our model supports suggestions that hot galactic coronae can contain significant amounts of gas. These reservoirs may enable galaxies to continue forming stars steadily for long periods of time and account for “missing baryons” in galaxies in the local universe.

  14. Building a Predictive Model of Galaxy Formation - I: Phenomenological Model Constrained to the $z=0$ Stellar Mass Function

    CERN Document Server

    Benson, A J

    2014-01-01

    We constrain a highly simplified semi-analytic model of galaxy formation using the $z\\approx 0$ stellar mass function of galaxies. Particular attention is paid to assessing the role of random and systematic errors in the determination of stellar masses, to systematic uncertainties in the model, and to correlations between bins in the measured and modeled stellar mass functions, in order to construct a realistic likelihood function. We derive constraints on model parameters and explore which aspects of the observational data constrain particular parameter combinations. We find that our model, once constrained, provides a remarkable match to the measured evolution of the stellar mass function to $z=1$, although fails dramatically to match the local galaxy HI mass function. Several "nuisance parameters" contribute significantly to uncertainties in model predictions. In particular, systematic errors in stellar mass estimate are the dominant source of uncertainty in model predictions at $z\\approx 1$, with addition...

  15. Towards 21st Century Stellar Models: Star Clusters, Supercomputing, and Asteroseismology

    DEFF Research Database (Denmark)

    Campbell, S. W.; Constantino, T. N.; D'Orazi, V.;

    2016-01-01

    Stellar models provide a vital basis for many aspects of astronomy and astrophysics. Recent advances in observational astronomy -- through asteroseismology, precision photometry, high-resolution spectroscopy, and large-scale surveys -- are placing stellar models under greater quantitative scrutin...... a brief overview of the evolution, importance, and substantial uncertainties of core helium burning stars in particular and then briefly discuss a range of methods, both theoretical and observational, that we are using to advance the modelling....

  16. Unresolved versus resolved: testing the validity of young simple stellar population models with VLT/MUSE observations of NGC 3603

    CERN Document Server

    Kuncarayakti, H; Anderson, J P; Krühler, T; Hamuy, M

    2016-01-01

    CONTEXT. Stellar populations are the building blocks of galaxies including the Milky Way. The majority, if not all extragalactic studies are entangled with the use of stellar population models given the unresolved nature of their observation. Extragalactic systems contain multiple stellar populations with complex star formation histories. However, their study is mainly based upon the principles of simple stellar populations (SSP). Hence, it is critical to examine the validity of SSP models. AIMS. This work aims to empirically test the validity of SSP models. This is done by comparing SSP models against observations of spatially resolved young stellar population in the determination of its physical properties, i.e. age and metallicity. METHODS. Integral field spectroscopy of a young stellar cluster in the Milky Way, NGC 3603, is used to study the properties of the cluster both as a resolved and unresolved stellar population. The unresolved stellar population is analysed using the H$\\alpha$ equivalent width as ...

  17. The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere VII. Further Insights into the Chromosphere and Corona

    Directory of Open Access Journals (Sweden)

    Robitaille P.-M.

    2013-07-01

    Full Text Available In the liquid metallic hydrogen model of the Sun, the chromosphere is responsible for the capture of atomic hydrogen in the solar atmosphere and its eventual re-entry onto the photospheric surface (P.M. Robitaille. The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere IV. On the Nature of the Chromosphere. Prog. Phys., 2013, v. 3, L15–L21. As for the corona, it represents a diffuse region containing both gaseous plasma and condensed matter with elevated electron affinity (P.M. Robitaille. The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere V. On the Nature of the Corona. Prog. Phys., 2013, v. 3, L22–L25. Metallic hydrogen in the corona is thought to enable the continual harvest of electrons from the outer reaches of the Sun, thereby preserving the neutrality of the solar body. The rigid rotation of the corona is offered as the thirty-third line of evidence that the Sun is comprised of condensed matter. Within the context of the gaseous models of the Sun, a 100 km thick transition zone has been hypothesized to exist wherein temperatures increase dramatically from 104–106 K. Such extreme transitional temperatures are not reasonable given the trivial physical scale of the proposed transition zone, a region adopted to account for the ultra-violet emission lines of ions such as C IV, O IV, and Si IV. In this work, it will be argued that the transition zone does not exist. Rather, the intermediate ionization states observed in the solar atmosphere should be viewed as the result of the simultaneous transfer of protons and electrons onto condensed hydrogen structures, CHS. Line emissions from ions such as C IV, O IV, and Si IV are likely to be the result of condensation reactions, manifesting the involvement of species such as CH4, SiH4, H3O+ in the synthesis of CHS in the chromosphere. In addition, given the presence of a true solar surface at the level of the photosphere in the liquid metallic hydrogen model

  18. Three-Dimensional MHD Modeling of The Solar Corona and Solar Wind: Comparison with The Wang-Sheeley Model

    Science.gov (United States)

    Usmanov, A. V.; Goldstein, M. L.

    2003-01-01

    We present simulation results from a tilted-dipole steady-state MHD model of the solar corona and solar wind and compare the output from our model with the Wang-Sheeley model which relates the divergence rate of magnetic flux tubes near the Sun (inferred from solar magnetograms) to the solar wind speed observed near Earth and at Ulysses. The boundary conditions in our model specified at the coronal base and our simulation region extends out to 10 AU. We assumed that a flux of Alfven waves with amplitude of 35 km per second emanates from the Sun and provides additional heating and acceleration for the coronal outflow in the open field regions. The waves are treated in the WKB approximation. The incorporation of wave acceleration allows us to reproduce the fast wind measurements obtained by Ulysses, while preserving reasonable agreement with plasma densities typically found at the coronal base. We find that our simulation results agree well with Wang and Sheeley's empirical model.

  19. Force-free Field Modeling of Twist and Braiding-induced Magnetic Energy in an Active-region Corona

    Science.gov (United States)

    Thalmann, J. K.; Tiwari, S. K.; Wiegelmann, T.

    2014-01-01

    The theoretical concept that braided magnetic field lines in the solar corona may dissipate a sufficient amount of energy to account for the brightening observed in the active-region (AR) corona has only recently been substantiated by high-resolution observations. From the analysis of coronal images obtained with the High Resolution Coronal Imager, first observational evidence of the braiding of magnetic field lines was reported by Cirtain et al. (hereafter CG13). We present nonlinear force-free reconstructions of the associated coronal magnetic field based on Solar Dynamics Observatory/Helioseismic and Magnetic Imager vector magnetograms. We deliver estimates of the free magnetic energy associated with a braided coronal structure. Our model results suggest (~100 times) more free energy at the braiding site than analytically estimated by CG13, strengthening the possibility of the AR corona being heated by field line braiding. We were able to appropriately assess the coronal free energy by using vector field measurements and we attribute the lower energy estimate of CG13 to the underestimated (by a factor of 10) azimuthal field strength. We also quantify the increase in the overall twist of a flare-related flux rope that was noted by CG13. From our models we find that the overall twist of the flux rope increased by about half a turn within 12 minutes. Unlike another method to which we compare our results, we evaluate the winding of the flux rope's constituent field lines around each other purely based on their modeled coronal three-dimensional field line geometry. To our knowledge, this is done for the first time here.

  20. Force-free field modeling of twist and braiding-induced magnetic energy in an active-region corona

    Energy Technology Data Exchange (ETDEWEB)

    Thalmann, J. K. [Institute of Physics/IGAM, University of Graz, Universitätsplatz 5, A-8010 Graz (Austria); Tiwari, S. K.; Wiegelmann, T., E-mail: julia.thalmann@uni-graz.at [Max Plank Institute for Solar System Research, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau (Germany)

    2014-01-01

    The theoretical concept that braided magnetic field lines in the solar corona may dissipate a sufficient amount of energy to account for the brightening observed in the active-region (AR) corona has only recently been substantiated by high-resolution observations. From the analysis of coronal images obtained with the High Resolution Coronal Imager, first observational evidence of the braiding of magnetic field lines was reported by Cirtain et al. (hereafter CG13). We present nonlinear force-free reconstructions of the associated coronal magnetic field based on Solar Dynamics Observatory/Helioseismic and Magnetic Imager vector magnetograms. We deliver estimates of the free magnetic energy associated with a braided coronal structure. Our model results suggest (∼100 times) more free energy at the braiding site than analytically estimated by CG13, strengthening the possibility of the AR corona being heated by field line braiding. We were able to appropriately assess the coronal free energy by using vector field measurements and we attribute the lower energy estimate of CG13 to the underestimated (by a factor of 10) azimuthal field strength. We also quantify the increase in the overall twist of a flare-related flux rope that was noted by CG13. From our models we find that the overall twist of the flux rope increased by about half a turn within 12 minutes. Unlike another method to which we compare our results, we evaluate the winding of the flux rope's constituent field lines around each other purely based on their modeled coronal three-dimensional field line geometry. To our knowledge, this is done for the first time here.

  1. 3D electron density distributions in the solar corona during solar minima: assessment for more realistic solar wind modeling

    CERN Document Server

    de Patoul, Judith; Riley, Pete

    2015-01-01

    Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996-1997 and 2008-2010), devoid of coronal mass ejections. The goals are to derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method and to compare the results between the two solar minima and with two magnetohydrodynamic models. First, we confirm that the values of the density distribution in thermodynamic models are more realistic than in polytropic ones. The tomography provides more accurate distributions in the polar regions, and we find that the density in tomographic and thermodynamic solutions varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the...

  2. Galactic evolution. I - Single-zone models. [encompassing stellar evolution and gas-star dynamic theories

    Science.gov (United States)

    Thuan, T. X.; Hart, M. H.; Ostriker, J. P.

    1975-01-01

    The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

  3. The simplest model of galaxy formation I: A formation history model of galaxy stellar mass growth

    CERN Document Server

    Mutch, Simon J; Poole, Gregory B

    2013-01-01

    We introduce a simple model to self-consistently connect the growth of galaxies to the formation history of their host dark matter halos. Our model is defined by two simple functions: the "baryonic growth function" which controls the rate at which new baryonic material is made available for star formation, and the "physics function" which controls the efficiency with which this material is converted into stars. Using simple, phenomenologically motivated forms for both functions that depend only on a single halo property, we demonstrate the model's ability to reproduce the z=0 red and blue stellar mass functions. Furthermore, by adding redshift as a second input variable to the physics function we show that the reproduction of the global stellar mass function out to z=3 is improved. We conclude by discussing the general utility of our new model, highlighting its usefulness for creating mock galaxy samples which have a number of key advantages over those generated by other techniques.

  4. Validation of the Earth atmosphere models using the EUV solar occultation data from the CORONAS and PROBA 2 instruments

    Science.gov (United States)

    Slemzin, Vladimir; Kuzin, Sergey; Berghmans, David; Pertsov, Andrey; Dominique, Marie; Ulyanov, Artyom; Gaikovich, Konstantin

    Absorption in the atmosphere below 500 km results in attenuation of the solar EUV flux, variation of its spectra and distortion of solar images acquired by solar EUV instruments operating on LEO satellites even on solar synchronous orbits. Occultation measurements are important for planning of solar observations from these satellites, and can be used for monitoring the upper atmosphere as well as for studying its response to the solar activity. We present the results of the occultation measurements of the solar EUV radiation obtained by the CORONAS-F/SPIRIT telescope at high solar activity (2002), by the CORONAS-Photon/TESIS telescope at low activity (2009), and by the SWAP telescope and LYRA radiometer onboard the PROBA 2 satellite at moderate activity (2010). The measured attenuation profiles and the retrieved linear extinction coefficients at the heights 200-500 km are compared with simulations by the NRLMSIS-00 and DTM2013 atmospheric models. It was shown that the results of simulations by the DTM2013 model are well agreed with the data of measurements at all stages of solar activity and in presence of the geomagnetic storm, whereas the results of the NRLMSISE-00 model significantly diverge from the measurements, in particular, at high and low activity. The research leading to these results has received funding from the European Union’s Seventh Programme for Research, Technological Development and Demonstration under Grant Agreement “eHeroes” (project № 284461, www.eheroes.eu).

  5. Coronae of Stars with Supersolar Elemental Abundances

    Science.gov (United States)

    Peretz, Uria; Behar, Ehud; Drake, Stephen A.

    2015-01-01

    Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviation depending on the first ionization potential (FIP). This study focuses on the coronal composition of stars with supersolar photospheric abundances. We present the coronal abundances of six such stars: 11 LMi, iota Hor, HR 7291, tau Boo, and alpha Cen A and B. These stars all have high-statistics X-ray spectra, three of which are presented for the first time. The abundances we measured were obtained using the line-resolved spectra of the Reflection Grating Spectrometer (RGS) in conjunction with the higher throughput EPIC-pn camera spectra onboard the XMM-Newton observatory. A collisionally ionized plasma model with two or three temperature components is found to represent the spectra well. All elements are found to be consistently depleted in the coronae compared to their respective photospheres. For 11 LMi and tau Boo no FIP effect is present, while iota Hor, HR 7291, and alpha Cen A and B show a clear FIP trend. These conclusions hold whether the comparison is made with solar abundances or the individual stellar abundances. Unlike the solar corona, where low-FIP elements are enriched, in these stars the FIP effect is consistently due to a depletion of high-FIP elements with respect to actual photospheric abundances. A comparison with solar (instead of stellar) abundances yields the same fractionation trend as on the Sun. In both cases, a similar FIP bias is inferred, but different fractionation mechanisms need to be invoked.

  6. Core - Corona Model analysis of the Low Energy Beam Scan at RHIC (Relativistic Heavy Ion Collider) in Brookhaven (USA)

    CERN Document Server

    Gemard, M

    2014-01-01

    The centrality dependence of spectra of identified particles in collisions between ultrarelativistic heavy ions with a center of mass energy ($\\sqrt{s}$) of 39 and 11.5 $AGeV$ is analyzed in the core - corona model. We show that at these energies the spectra can be well understood assuming that they are composed of two components whose relative fraction depends on the centrality of the interaction: The core component which describes an equilibrated quark gluon plasma and the corona component which is caused by nucleons close to the surface of the interaction zone which scatter only once and which is identical to that observed in proton-proton collisions. The success of this approach at 39 and 11.5 $AGeV$ shows that the physics does not change between this energy and $\\sqrt{s}=200~ AGeV$ for which this model has been developed (Aichelin 2008). This presents circumstantial evidence that a quark gluon plasma is also created at center of mass energies as low as 11.5 $AGeV$.

  7. Modeling of experimental treatment of acetaldehyde-laden air and phenol-containing water using corona discharge technique.

    Science.gov (United States)

    Faungnawakij, Kajornsak; Sano, Noriaki; Charinpanitkul, Tawatchai; Tanthapanichakoon, Wiwut

    2006-03-01

    Acetaldehyde-laden air and phenol-contaminated water were experimentally treated using corona discharge reactions and gas absorption in a single water-film column. Mathematical modeling of the combined treatment was developed in this work. Efficient removal of the gaseous acetaldehyde was achieved while the corona discharge reactions produced short-lived species such as O and O- as well as ozone. Direct contact of the radicals and ions with water was known to produce aqueous OH radical, which contributes to the decomposition of organic contaminants: phenol, absorbed acetaldehyde, and intermediate byproducts in the water. The influence of initial phenol concentration ranging from 15 to 50 mg L(-1) and that of influent acetaldehyde ranging from 0 to 200 ppm were experimentally investigated and used to build the math model. The maximum energetic efficiency of TOC, phenol, and acetaldehyde were obtained at 25.6 x 10(-9) mol carbon J(-1), 25.0 x 10(-9) mol phenol J(-1), and 2.0 x 10(-9) mol acetaldehyde J(-1), respectively. The predictions for the decomposition of acetaldehyde, phenol, and their intermediates were found to be in good agreement with the experimental results.

  8. Line Shape Modeling for the Diagnostic of the Electron Density in a Corona Discharge

    Directory of Open Access Journals (Sweden)

    Joël Rosato

    2017-09-01

    Full Text Available We present an analysis of spectra observed in a corona discharge designed for the study of dielectrics in electrical engineering. The medium is a gas of helium and the discharge was performed at the vicinity of a tip electrode under high voltage. The shape of helium lines is dominated by the Stark broadening due to the plasma microfield. Using a computer simulation method, we examine the sensitivity of the He 492 nm line shape to the electron density. Our results indicate the possibility of a density diagnostic based on passive spectroscopy. The influence of collisional broadening due to interactions between the emitters and neutrals is discussed.

  9. Stellar models for very low mass main sequence stars the role of model atmospheres

    CERN Document Server

    Brocato, E; Castellani, V

    1997-01-01

    We present Very Low Mass stellar models as computed including non-grey model atmospheres for selected assumptions about the star metallicities. The role of atmospheres is discussed and the models are compared with models based on the Eddington approximation and with similar models appeared in the recent literature. Theoretical predictions concerning both the HR diagram location and the mass-luminosity relation are presented and discussed in terms of expectations in selected photometric bands. Comparison with available observational data concerning both galactic globular clusters and dwarfs in the solar neighborhood reveals a satisfactory agreement together with the existence of some residual mismatches.

  10. On line contribution functions and examining spectral line formation in 3D model stellar atmospheres

    CERN Document Server

    Amarsi, Anish Mayur

    2015-01-01

    Line contribution functions are useful diagnostics for studying spectral line formation in stellar atmospheres. I derive an expression for the contribution function to the abso- lute flux depression that emerges from three-dimensional box-in-a-star model stellar atmospheres. I illustrate the result by comparing the local thermodynamic equilibrium (LTE) spectral line formation of the high-excitation permitted OI777nm lines with the non-LTE case.

  11. The high mass end of the stellar mass function: Dependence on stellar population models and agreement between fits to the light profile

    Science.gov (United States)

    Bernardi, M.; Meert, A.; Sheth, R. K.; Fischer, J.-L.; Huertas-Company, M.; Maraston, C.; Shankar, F.; Vikram, V.

    2017-01-01

    We quantify the systematic effects on the stellar mass function which arise from assumptions about the stellar population, as well as how one fits the light profiles of the most luminous galaxies at z ˜ 0.1. When comparing results from the literature, we are careful to separate out these effects. Our analysis shows that while systematics in the estimated comoving number density which arise from different treatments of the stellar population remain of order ≤0.5 dex, systematics in photometry are now about 0.1 dex, in contrast to some recent claims in the literature. Compared to these more recent analyses, previous work based on Sloan Digital Sky Survey (SDSS) pipeline photometry leads to underestimates of ρ★( ≥ M★) by factors of 3 - 10 in the mass range 1011 - 1011.6M⊙, but up to a factor of 100 at higher stellar masses. This impacts studies which match massive galaxies to dark matter halos. Although systematics which arise from different treatments of the stellar population remain of order ≤0.5 dex, our finding that systematics in photometry now amount to only about 0.1 dex in the stellar mass density is a significant improvement with respect to a decade ago. Our results highlight the importance of using the same stellar population and photometric models whenever low and high redshift samples are compared.

  12. Electro-Hydrodynamics and Kinetic Modeling of Dry and Humid Air Flows Activated by Corona Discharges

    Science.gov (United States)

    P. Sarrette, J.; Eichwald, O.; Marchal, F.; Ducasse, O.; Yousfi, M.

    2016-05-01

    The present work is devoted to the 2D simulation of a point-to-plane Atmospheric Corona Discharge Reactor (ACDR) powered by a DC high voltage supply. The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz. The study compares the results obtained in dry air and in air mixed with a small amount of water vapour (humid air). The simulation involves the electro-dynamics, chemical kinetics and neutral gas hydrodynamics phenomena that influence the kinetics of the chemical species transformation. Each discharge lasts about one hundred of a nanosecond while the post-discharge occurring between two successive discharges lasts one hundred of a microsecond. The ACDR is crossed by a lateral dry or humid air flow initially polluted with 400 ppm of NO. After 5 ms, the time corresponding to the occurrence of 50 successive discharge/post-discharge phases, a higher NO removal rate and a lower ozone production rate are found in humid air. This change is due to the presence of the HO2 species formed from the H primary radical in the discharge zone.

  13. Electro-Hydrodynamics and Kinetic Modeling of Dry and Humid Air Flows Activated by Corona Discharges

    Institute of Scientific and Technical Information of China (English)

    J.P.SARRETTE; O.EICHWALD; F.MARCHAL; O.DUCASSE; M.YOUSFI

    2016-01-01

    The present work is devoted to the 2D simulation of a point-to-plane Atmospheric Corona Discharge Reactor (ACDR) powered by a DC high voltage supply.The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz.The study compares the results obtained in dry air and in air mixed with a small amount of water vapour (humid air).The simulation involves the electro-dynamics,chemical kinetics and neutral gas hydrodynamics phenomena that influence the kinetics of the chemical species transformation.Each discharge lasts about one hundred of a nanosecond while the post-discharge occurring between two successive discharges lasts one hundred of a microsecond.The ACDR is crossed by a lateral dry or humid air flow initially polluted with 400 ppm of NO.After 5 ms,the time corresponding to the occurrence of 50 successive discharge/post-discharge phases,a higher NO removal rate and a lower ozone production rate are found in humid air.This change is due to the presence of the HO2 species formed from the H primary radical in the discharge zone.

  14. Grids of stellar models including second harmonic and colours: Solar composition

    CERN Document Server

    Yildiz, Mutlu

    2015-01-01

    Grids of stellar evolution are required in many fields of astronomy/astrophysics, such as planet hosting stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar evolution models with updated ingredients and {recently determined solar abundaces} is presented. The solar values for the initial abundances of hydrogen, heavy elements and mixing-length parameter are 0.0172, 0.7024 and 1.98, respectively. The mass step is small enough (0.01 M$_\\odot$) that interpolation for a given star mass is not required. The range of stellar mass is 0.74 to 10.00 M$_\\odot$. We present results in different forms of tables for easy and general application. The second stellar harmonic, required for analysis of apsidal motion of eclipsing binaries, is also listed. We also construct rotating models to determine effect of rotation on stellar structure and derive fitting formula for luminosity, radius and the second stellar harmonic as a function of rotational parameter. We also compute and list colo...

  15. AME - Asteroseismology Made Easy. Estimating stellar properties by use of scaled models

    CERN Document Server

    Lundkvist, M; Aguirre, V Silva

    2014-01-01

    We present a new method to obtain stellar properties for stars exhibiting solar-like oscillations in an easy, fast, and transparent way. The method, called Asteroseismology Made Easy (AME), can determine stellar masses, mean-densities, radii, and surface gravities, as well as estimate ages. In this writing we present AME as a visual and powerful tool which could be useful; in particular in the light of the large number of exoplanets being found. AME consists of a set of figures from which the stellar parameters are deduced. These figures are made from a grid of stellar evolutionary models that cover masses ranging from 0.7 Msun to 1.6 Msun in steps of 0.1 Msun and metallicities in the interval -0.3 dex <= [Fe/H] <= +0.3 dex in increments of 0.1 dex. The stellar evolutionary models are computed using the Modules for Experiments in Stellar Astrophysics (MESA) code with simple input physics. We have compared the results from AME with results for three groups of stars; stars with radii determined from inter...

  16. Exponential Disks from Stellar Scattering: III. Stochastic Models

    CERN Document Server

    Elmegreen, Bruce G

    2016-01-01

    Stellar scattering off irregularities in a galaxy disk has been shown to make an exponential radial profile, but no fundamental reason for this has been suggested. Here we show that exponentials are mathematically expected from random scattering in a disk when there is a slight inward bias in the scattering probability. Such a bias was present in our previous scattering experiments that formed exponential profiles. Double exponentials can arise when the bias varies with radius. This is a fundamental property of scattering and may explain why piece-wise exponential profiles are ubiquitous in galaxies, even after minor mergers and other disruptive events.

  17. Single stellar populations in the near-infrared II. Synthesis models

    CERN Document Server

    Meneses-Goytia, S; Trager, S C; Vazdekis, A

    2015-01-01

    We present unresolved single stellar population synthesis models in the near-infrared (NIR) range. The extension to the NIR is important for the study of early-type galaxies, since these galaxies are predominantly old and therefore emit most of their light in this wavelength range. The models are based on a library of empirical stellar spectra, the NASA infrared telescope facility (IRTF) spectral library. Integrating these spectra along theoretical isochrones, while assuming an initial mass function (IMF), we have produced model spectra of single age-metallicity stellar populations at a resolution R~2000. These models can be used to fit observed spectral of globular clusters and galaxies, to derive their age distribution, chemical abundances and IMF. The models have been tested by comparing them to observed colours of elliptical galaxies and clusters in the Magellanic Clouds. Predicted absorption line indices have been compared to published indices of other elliptical galaxies. The comparisons show that our m...

  18. Stellar Activity and Coronal Heating: an overview of recent results

    CERN Document Server

    Testa, Paola; Drake, Jeremy

    2015-01-01

    Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars.

  19. Stellar activity and coronal heating: an overview of recent results

    Science.gov (United States)

    Testa, Paola; Saar, Steven H.; Drake, Jeremy J.

    2015-01-01

    Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars. PMID:25897087

  20. Effects of stellar flybys on planetary systems: 3D modeling of the circumstellar disk's damping effects

    Science.gov (United States)

    Picogna, G.; Marzari, F.

    2014-04-01

    Context. Stellar flybys in star clusters are suspected of affecting the orbital architecture of planetary systems causing eccentricity excitation and orbital misalignment between the planet orbit and the equatorial plane of the star. Aims: We explore whether the impulsive changes in the orbital elements of planets, caused by a hyperbolic stellar flyby, can be fully damped by the circumstellar disk surrounding the star. The time required to disperse stellar clusters is comparable to the circumstellar disk's lifetime. Since we perform 3D simulations, we can also test the inclination, excitation, and damping. Methods: We have modeled in 3D with the SPH code VINE, a system made of a solar-type star surrounded by a low density disk with a giant planet embedded in it approached on a hyperbolic encounter trajectory by a second star of similar mass and with its own disk. Different inclinations between the disks, planet orbit, and star trajectory have been considered to explore various encounter geometries. We focus on an extreme configuration where a very deep stellar flyby perturbs a Jovian planet on an external orbit. This allows us to test in full the ability of the disk to erase the effects of the stellar encounter. Results: We find that the amount of mass lost by the disk during the stellar flyby is less than in 2D models where a single disk was considered. This is mostly related to the mass exchange between the two disks at the encounter. The damping in eccentricity is slightly faster than in 2D models and it occurs on timescales on the order of a few kyr. During the flyby both the disks are warped owing to the mutual interaction and to the stellar gravitational perturbations, but they quickly relax to a new orbital plane. The planet is quickly dragged back within the disk by the tidal interaction with the gas. The only trace of the flyby left in the planet system, after about 104 yr, is a small misalignment, lower than 9°, between the star equatorial plane and the

  1. Effects of stellar flybys on planetary systems: 3D modeling of the circumstellar disks damping effects

    CERN Document Server

    Picogna, Giovanni

    2014-01-01

    Stellar flybys in star clusters are suspected to affect the orbital architecture of planetary systems causing eccentricity excitation and orbital misalignment between the planet orbit and the equatorial plane of the star. We explore whether the impulsive changes in the orbital elements of planets, caused by an hyperbolic stellar flyby, can be fully damped by the circumstellar disk surrounding the star. The time required to disperse stellar clusters is in fact comparable to circumstellar disk's lifetime. We have modelled in 3D a system made of a solar type star surrounded by a low density disk with a giant planet embedded in it approached on a hyperbolic encounter trajectory by a second star, of similar mass and with its own disk. We focus on extreme configurations where a very deep stellar flyby perturbs a Jovian planet on an external orbit. This allows to test in full the ability of the disk to erase the effects of the stellar encounter. We find that the amount of mass lost by the disk during the stellar fly...

  2. Stellar energy loss rates in the pair-annihilation process beyond the standard model

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Ruiz, M.A. [Universidad Autonoma de Zacatecas, Unidad Academica de Ciencias Quimicas, Apartado Postal C-585, Zacatecas (Mexico); Gutierrez-Rodriguez, A. [Universidad Autonoma de Zacatecas, Facultad de Fisica, Apartado Postal C-580, Zacatecas (Mexico); Gonzalez-Sanchez, A. [Universidad Autonoma de Zacatecas, Facultad de Fisica, Apartado Postal C-580, Zacatecas (Mexico); PSL Research University, Observatoire de Paris, LERMA, CNRS UMR 8112, Paris (France)

    2017-01-15

    We calculate the stellar energy loss due to neutrino-pair production in e{sup +}e{sup -} annihilation in the context of a 331 model, a left-right symmetric model and a simplest little Higgs model in a way that can be used in supernova calculations. We also present some simple estimates which show that such process can act as an efficient energy loss mechanism in the shocked supernova core. We find that the stellar energy loss is almost independent of the parameters of the models in the allowed range for these parameters. This work complements other studies on the stellar energy loss rate in e{sup +}e{sup -} annihilation. (orig.)

  3. An XMM-Newton Study of the Coronae of $\\sigma^2$ Coronae Borealis

    CERN Document Server

    Suh, J A; Güdel, M; Paerels, F B S

    2005-01-01

    (Abridged) We present results of XMM-Newton observations of the RS CVn binary $\\sigma^2$ Coronae Borealis. The RGS and EPIC MOS2 spectra were simultaneously fitted with collisional ionization equilibrium plasma models to determine coronal abundances of various elements. Contrary to the solar first ionization potential (FIP) effect in which elements with a low FIP are overabundant in the corona compared to the solar photosphere, and contrary to the ``inverse'' FIP effect observed in several active RS CVn binaries, coronal abundance ratios in $\\sigma^2$ CrB show a complex pattern as supported by similar findings in the Chandra HETGS analysis of $\\sigma^2$ CrB with a different methodology (Osten et al. 2003). Low-FIP elements ($<10$ eV) have their abundance ratios relative to Fe consistent with the solar photospheric ratios, whereas high-FIP elements have their abundance ratios increase with increasing FIP. We find that the coronal Fe abundance is consistent with the stellar photospheric value, indicating tha...

  4. Stellar dynamo models with prominent surface toroidal fields

    CERN Document Server

    Bonanno, Alfio

    2016-01-01

    Recent spectro-polarimetric observations of solar-type stars have shown the presence of photospheric magnetic fields with a predominant toroidal component. If the external field is assumed to be current-free it is impossible to explain these observations within the framework of standard mean-field dynamo theory. In this work it will be shown that if the coronal field of these stars is assumed to be harmonic, the underlying stellar dynamo mechanism can support photospheric magnetic fields with a prominent toroidal component even in the presence of axisymmetric magnetic topologies. In particular it is argued that the observed increase in the toroidal energy in low mass fast rotating stars can be naturally explained with an underlying $\\alpha\\Omega$ mechanism.

  5. Stellar Dynamo Models with Prominent Surface Toroidal Fields

    Science.gov (United States)

    Bonanno, Alfio

    2016-12-01

    Recent spectro-polarimetric observations of solar-type stars have shown the presence of photospheric magnetic fields with a predominant toroidal component. If the external field is assumed to be current-free it is impossible to explain these observations within the framework of standard mean-field dynamo theory. In this work, it will be shown that if the coronal field of these stars is assumed to be harmonic, the underlying stellar dynamo mechanism can support photospheric magnetic fields with a prominent toroidal component even in the presence of axisymmetric magnetic topologies. In particular, it is argued that the observed increase in the toroidal energy in low-mass fast-rotating stars can be naturally explained with an underlying αΩ mechanism.

  6. Ultrasonic corona sensor study

    Science.gov (United States)

    Harrold, R. T.

    1976-01-01

    The overall objective of this program is to determine the feasibility of using ultrasonic (above 20 kHz) corona detection techniques to detect low order (non-arcing) coronas in varying degrees of vacuum within large high vacuum test chambers, and to design, fabricate, and deliver a prototype ultrasonic corona sensor.

  7. A self-consistent model of ionic wind generation by negative corona discharges in air with experimental validation

    Science.gov (United States)

    Chen, She; Nobelen, J. C. P. Y.; Nijdam, S.

    2017-09-01

    Ionic wind is produced by a corona discharge when gaseous ions are accelerated in the electric field and transfer their momentum to neutral molecules by collisions. This technique is promising because a gas flow can be generated without the need for moving parts and can be easily miniaturized. The basic theory of ionic wind sounds simple but the details are far from clear. In our experiment, a negative DC voltage is applied to a needle-cylinder electrode geometry. Hot wire anemometry is used to measure the flow velocity at the downstream exit of the cylinder. The flow velocity fluctuates but the average velocity increases with the voltage. The current consists of a regular train of pulses with short rise time, the well-known Trichel pulses. To reveal the ionic wind mechanism in the Trichel pulse stage, a three-species corona model coupled with gas dynamics is built. The drift-diffusion equations of the plasma together with the Navier–Stokes equations of the flow are solved in COMSOL Multiphysics. The electric field, net number density of charged species, electrohydrodynamic (EHD) body force and flow velocity are calculated in detail by a self-consistent model. Multiple time scales are employed: hundreds of microseconds for the plasma characteristics and longer time scales (∼1 s) for the flow behavior. We found that the flow velocity as well as the EHD body force have opposite directions in the ionization region close to the tip and the ion drift region further away from the tip. The calculated mean current, Trichel pulse frequency and flow velocity are very close to our experimental results. Furthermore, in our simulations we were able to reproduce the mushroom-like minijets observed in experiments.

  8. Propagating Linear Waves in Convectively Unstable Stellar Models: a Perturbative Approach

    CERN Document Server

    Papini, Emanuele; Birch, Aaron C

    2013-01-01

    Linear time-domain simulations of acoustic oscillations are unstable in the stellar convection zone. To overcome this problem it is customary to compute the oscillations of a stabilized background stellar model. The stabilization, however, affects the result. Here we propose to use a perturbative approach (running the simulation twice) to approximately recover the acoustic wave field, while preserving seismic reciprocity. To test the method we considered a 1D standard solar model. We found that the mode frequencies of the (unstable) standard solar model are well approximated by the perturbative approach within $1~\\mu$Hz for low-degree modes with frequencies near $3~\\mu$Hz. We also show that the perturbative approach is appropriate for correcting rotational-frequency kernels. Finally, we comment that the method can be generalized to wave propagation in 3D magnetized stellar interiors because the magnetic fields have stabilizing effects on convection.

  9. A simple model to describe intrinsic stellar noise for exoplanet detection around red giants

    CERN Document Server

    North, Thomas S H; Gilliland, Ronald L; Huber, Daniel; Campante, Tiago L; Handberg, Rasmus; Lund, Mikkel N; Veras, Dimitri; Kuszlewicz, James S; Farr, Will M

    2016-01-01

    In spite of the huge advances in exoplanet research provided by the NASA Kepler Mission, there remain only a small number of transit detections around evolved stars. Here we present a reformulation of the noise properties of red-giant stars, where the intrinsic stellar granulation, and the stellar oscillations described by asteroseismology play a key role. The new noise model is a significant improvement on the current Kepler results for evolved stars. Our noise model may be used to help understand planet detection thresholds for the ongoing K2 and upcoming TESS missions, and serve as a predictor of stellar noise for these missions. As an application of our noise model, we explore the minimum detectable planet radii for red giant stars, and find that Neptune sized planets should be detectable around low luminosity red giant branch stars.

  10. A simple model to describe intrinsic stellar noise for exoplanet detection around red giants

    Science.gov (United States)

    North, Thomas S. H.; Chaplin, William J.; Gilliland, Ronald L.; Huber, Daniel; Campante, Tiago L.; Handberg, Rasmus; Lund, Mikkel N.; Veras, Dimitri; Kuszlewicz, James S.; Farr, Will M.

    2017-02-01

    In spite of the huge advances in exoplanet research provided by the NASA Kepler Mission, there remain only a small number of transit detections around evolved stars. Here, we present a reformulation of the noise properties of red-giant stars, where the intrinsic stellar granulation and the stellar oscillations described by asteroseismology play a key role. The new noise model is a significant improvement on the current Kepler results for evolved stars. Our noise model may be used to help understand planet detection thresholds for the ongoing K2 and upcoming TESSmissions, and serve as a predictor of stellar noise for these missions. As an application of our noise model, we explore the minimum detectable planet radii for red giant stars, and find that Neptune-sized planets should be detectable around low-luminosity red giant branch stars.

  11. MILES extended: Stellar population synthesis models from the optical to the infrared

    Science.gov (United States)

    Röck, B.; Vazdekis, A.; Ricciardelli, E.; Peletier, R. F.; Knapen, J. H.; Falcón-Barroso, J.

    2016-05-01

    We present the first single-burst stellar population models, which covers the optical and the infrared wavelength range between 3500 and 50 000 Å and which are exclusively based on empirical stellar spectra. To obtain these joint models, we combined the extended MILES models in the optical with our new infrared models that are based on the IRTF (Infrared Telescope Facility) library. The latter are available only for a limited range in terms of both age and metallicity. Our combined single-burst stellar population models were calculated for ages larger than 1 Gyr, for metallicities between [ Fe / H ] = - 0.40 and 0.26, for initial mass functions of various types and slopes, and on the basis of two different sets of isochrones. They are available to the scientific community on the MILES web page. We checked the internal consistency of our models and compared their colour predictions to those of other models that are available in the literature. Optical and near infrared colours that are measured from our models are found to reproduce the colours well that were observed for various samples of early-type galaxies. Our models will enable a detailed analysis of the stellar populations of observed galaxies.

  12. Systematic problems with using dark matter simulations to model stellar halos

    Energy Technology Data Exchange (ETDEWEB)

    Bailin, Jeremy [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487-0324 (United States); Bell, Eric F.; Valluri, Monica [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Stinson, Greg S. [Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, D-69117 Heidelberg (Germany); Debattista, Victor P. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Couchman, H. M. P.; Wadsley, James, E-mail: jbailin@ua.edu [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4M1 (Canada)

    2014-03-10

    The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be 'painted' onto dark matter (DM) particles in progenitor satellites; (2) pure DM simulations that do not form a luminous galaxy can be used. We estimate the magnitude of the systematic errors introduced by these assumptions using a controlled set of stellar halo models where we independently vary whether we look at star particles or painted DM particles, and whether we use a simulation in which a baryonic disk galaxy forms or a matching pure DM simulation that does not form a baryonic disk. We find that the 'painting' simplification reduces the halo concentration and internal structure, predominantly because painted DM particles have different kinematics from star particles even when both are buried deep in the potential well of the satellite. The simplification of using pure DM simulations reduces the concentration further, but increases the internal structure, and results in a more prolate stellar halo. These differences can be a factor of 1.5-7 in concentration (as measured by the half-mass radius) and 2-7 in internal density structure. Given this level of systematic uncertainty, one should be wary of overinterpreting differences between observations and the current generation of stellar halo models based on DM-only simulations when such differences are less than an order of magnitude.

  13. General spherical anisotropic Jeans models of stellar kinematics: including proper motions and radial velocities

    CERN Document Server

    Cappellari, Michele

    2015-01-01

    Cappellari (2008) presented a flexible and efficient method to model the stellar kinematics of anisotropic axisymmetric and spherical stellar systems. The spherical formalism could be used to model the line-of-sight velocity second moments allowing for essentially arbitrary radial variation in the anisotropy and general luminous and total density profiles. Here we generalize the spherical formalism by providing the expressions for all three components of the projected second moments, including the two proper motion components. A reference implementation is now included in the public JAM package available at http://purl.org/cappellari/software

  14. Modeling the Near-Infrared Luminosity Functions of Young Stellar Clusters

    CERN Document Server

    Münch, A; Lada, C J; Muench, August A.; Lada, Elizabeth A.; Lada, Charles J.

    1999-01-01

    We present the results of numerical experiments designed to evaluate the usefulness of near-infrared luminosity functions for constraining the Initial Mass Function (IMF) of young stellar populations. From this numerical modeling, we find that the luminosity function of a young stellar population is considerably more sensitive to variations in the underlying initial mass function than to either variations in the star forming history or assumed pre-main-sequence (PMS) mass-to-luminosity relation. To illustrate the potential effectiveness of using the KLF of a young cluster to constrain its IMF, we model the observed K band luminosity function of the nearby Trapezium cluster. Our derived mass function for the Trapezium spans two orders of magnitude in stellar mass (5 Msun to 0.02 Msun), has a peak near the hydrogen burning limit, and has an IMF for Brown Dwarfs which steadily decreases with decreasing mass.

  15. Unresolved versus resolved: testing the validity of young simple stellar population models with VLT/MUSE observations of NGC 3603

    Science.gov (United States)

    Kuncarayakti, H.; Galbany, L.; Anderson, J. P.; Krühler, T.; Hamuy, M.

    2016-09-01

    Context. Stellar populations are the building blocks of galaxies, including the Milky Way. The majority, if not all, extragalactic studies are entangled with the use of stellar population models given the unresolved nature of their observation. Extragalactic systems contain multiple stellar populations with complex star formation histories. However, studies of these systems are mainly based upon the principles of simple stellar populations (SSP). Hence, it is critical to examine the validity of SSP models. Aims: This work aims to empirically test the validity of SSP models. This is done by comparing SSP models against observations of spatially resolved young stellar population in the determination of its physical properties, that is, age and metallicity. Methods: Integral field spectroscopy of a young stellar cluster in the Milky Way, NGC 3603, was used to study the properties of the cluster as both a resolved and unresolved stellar population. The unresolved stellar population was analysed using the Hα equivalent width as an age indicator and the ratio of strong emission lines to infer metallicity. In addition, spectral energy distribution (SED) fitting using STARLIGHT was used to infer these properties from the integrated spectrum. Independently, the resolved stellar population was analysed using the colour-magnitude diagram (CMD) to determine age and metallicity. As the SSP model represents the unresolved stellar population, the derived age and metallicity were tested to determine whether they agree with those derived from resolved stars. Results: The age and metallicity estimate of NGC 3603 derived from integrated spectroscopy are confirmed to be within the range of those derived from the CMD of the resolved stellar population, including other estimates found in the literature. The result from this pilot study supports the reliability of SSP models for studying unresolved young stellar populations. Based on observations collected at the European Organisation

  16. X-ray coronae in simulations of disc galaxy formation

    Science.gov (United States)

    Crain, Robert A.; McCarthy, Ian G.; Frenk, Carlos S.; Theuns, Tom; Schaye, Joop

    2010-09-01

    The existence of X-ray luminous gaseous coronae around massive disc galaxies is a long-standing prediction of galaxy formation theory in the cold dark matter cosmogony. This prediction has garnered little observational support, with non-detections commonplace and detections for only a relatively small number of galaxies which are much less luminous than expected. We investigate the coronal properties of a large sample of bright, disc-dominated galaxies extracted from the GIMIC suite of cosmological hydrodynamic simulations recently presented by Crain et al. Remarkably, the simulations reproduce the observed scalings of X-ray luminosity with K-band luminosity and star formation rate (SFR) and, when account is taken of the density structure of the halo, with disc rotation velocity as well. Most of the star formation in the simulated galaxies (which have realistic stellar mass fractions) is fuelled by gas cooling from a quasi-hydrostatic hot corona. However, these coronae are more diffuse, and of a lower luminosity, than predicted by the analytic models of White & Frenk because of a substantial increase in entropy at z ~ 1-3. Both the removal of low entropy gas by star formation and energy injection from supernovae contribute to this increase in entropy, but the latter is dominant for halo masses M200 <~ 1012.5Msolar. Only a small fraction of the mass of the hot gas is outflowing as a wind but, because of its high density and metallicity, it contributes disproportionally to the X-ray emission. The bulk of the X-ray emission, however, comes from the diffuse quasi-hydrostatic corona which supplies the fuel for ongoing star formation in discs today. Future deep X-ray observations with high spectral resolution (e.g. with NeXT/ASTRO-H or IXO) should be able to map the velocity structure of the hot gas and test this fundamental prediction of current galaxy formation theory.

  17. Corona, Jet, and Relativistic Line Models for Suzaku/RXTE/Chandra-HETG Observations of the Cygnus X-1 Hard State

    Science.gov (United States)

    Nowak, Michael A.; Hanke, Manfred; Trowbridge, Sarah N.; Markoff, Sera B.; Wilms, Joern; Pottschmidt, Katja; Coppi, Paolo; Maitra, Dipankar; Davis, Jhn E.; Tramper, Frank

    2009-01-01

    Using Suzaku and the Rossi X-ray Timing Explorer (RXTE), we have conducted a series of four simultaneous observations of the galactic black hole candidate Cyg X-1 in what were historically faint and spectrally hard "low states". Additionally, all of these observations occurred near superior conjunction with our line of sight to the X-ray source passing through the dense phases of the "focused wind" from the mass donating secondary. One of our observations was also simultaneous with observations by the Chandra-High Energy Transmission Grating (HETG). These latter spectra are crucial for revealing the ionized absorption due to the secondary s focused wind. Such absorption is present and must be accounted for in all four spectra. These simultaneous data give an unprecedented view of the 0.8-300 keV spectrum of Cyg X-1, and hence bear upon both corona and X-ray emitting jet models of black hole hard states. Three models fit the spectra well: coronae with thermal or mixed thermal/non-thermal electron populations, and jets. All three models require a soft component that we fit with a low temperature disk spectrum with an inner radius of only a few tens of GM/c2. All three models also agree that the known spectral break at 10 keV is not solely due to the presence of reflection, but each gives a different underlying explanation for the augmentation of this break. Thus whereas all three models require that there is a relativistically broadened Fe line, the strength and inner radius of such a line is dependent upon the specific model, thus making premature line-based estimates of the black hole spin in the Cyg X-1 system. We look at the relativistic line in detail, accounting for the narrow Fe emission and ionized absorption detected by HETG. Although the specific relativistic parameters of the line are continuum-dependent, none of the broad line fits allow for an inner disk radius that is > 40 GM/c(sup 2).

  18. X-raying clumped stellar winds

    CERN Document Server

    Oskinova, L M; Feldmeier, A

    2008-01-01

    X-ray spectroscopy is a sensitive probe of stellar winds. X-rays originate from optically thin shock-heated plasma deep inside the wind and propagate outwards throughout absorbing cool material. Recent analyses of the line ratios from He-like ions in the X-ray spectra of O-stars highlighted problems with this general paradigm: the measured line ratios of highest ions are consistent with the location of the hottest X-ray emitting plasma very close to the base of the wind, perhaps indicating the presence of a corona, while measurements from lower ions conform with the wind-embedded shock model. Generally, to correctly model the emerging X-ray spectra, a detailed knowledge of the cool wind opacities based on stellar atmosphere models is prerequisite. A nearly grey stellar wind opacity for the X-rays is deduced from the analyses of high-resolution X-ray spectra. This indicates that the stellar winds are strongly clumped. Furthermore, the nearly symmetric shape of X-ray emission line profiles can be explained if t...

  19. The stellar evolution of Luminous Red Galaxies, and its dependence on colour, redshift, luminosity and modelling

    CERN Document Server

    Tojeiro, Rita; Heavens, Alan F; Jimenez, Raul

    2010-01-01

    We present a series of colour evolution models for Luminous Red Galaxies (LRGs) in the 7th spectroscopic data release of the Sloan Digital Sky Survey (SDSS), computed using the full-spectrum fitting code VESPA on high signal-to-noise stacked spectra. The colour-evolution models are computed as a function of colour, luminosity and redshift, and we do not a-priori assume that LRGs constitute a uniform population of galaxies in terms of stellar evolution. By computing star-formation histories from the fossil record, the measured stellar evolution of the galaxies is decoupled from the survey's selection function, which also evolves with redshift. We present these evolutionary models computed using three different sets of Stellar Population Synthesis (SPS) codes. We show that the traditional fiducial model of purely passive stellar evolution of LRGs is broadly correct, but it is not sufficient to explain the full spectral signature. We also find that higher-order corrections to this model are dependent on the SPS ...

  20. The H Corona of Mars

    Science.gov (United States)

    Chaffin, Michael Scott

    The atmosphere of every planet is surrounded by a tenuous cloud of hydrogen gas, referred to as a hydrogen corona. At Mars, a substantial fraction of the H present in the corona is moving fast enough to escape the planet's gravity, permanently removing H from the Martian atmosphere. Because this H is ultimately derived from lower atmospheric water, loss of H from Mars is capable of drying and oxidizing the planet over geologic time. Understanding the processes that supply the H corona and control its escape is therefore essential for a complete understanding of the climate history of Mars and for assessing its habitability. In this thesis, I present the most complete analysis of the H corona ever attempted, surveying eight years of data gathered by the ultraviolet spectrograph SPICAM on Mars Express. Using a coupled radiative transfer and physical density model, I interpret brightness measurements of the corona in terms of escape rates of H from the planet, uncovering an order-of-magnitude variability in the H escape rate never before detected. These variations are interpreted using a completely new photochemical model of the atmosphere, demonstrating that newly discovered high altitude water vapor layers are sufficient to produce the observed variation. Finally, I present first results of the SPICAM successor instrument IUVS, an imaging ultraviolet spectrograph carried by NASA's MAVEN spacecraft. IUVS measurements are producing the most complete dataset ever gathered for the Martian H corona, enabling supply and loss processes to be assessed in more complete detail than ever before. This dataset will allow present-day loss rates to be extrapolated into the past, determining the absolute amount of water Mars has lost to space over the course of its history. Planets the size of Mars may be common throughout the universe; the work of this thesis is one step toward assessing the habitability of such planets in general.

  1. Constraining stellar population models - I. Age, metallicity, and abundance pattern compilation for Galactic globular clusters

    CERN Document Server

    Roediger, Joel C; Graves, Genevieve; Schiavon, Ricardo

    2013-01-01

    We present an extenstive literature compilation of age, metallicity, and chemical abundance pattern information for the 41 Galactic globular clusters (GGCs) studied by Schiavon et al. (2005). Our compilation constitutes a notable improvement over previous similar work, particularly in terms of chemical abundances. Its primary purpose is to enable detailed evaluations of and refinements to stellar population synthesis models designed to recover the above information for unresolved stellar systems based on their integrated spectra. However, since the Schiavon sample spans a wide range of the known GGC parameter space, our compilation may also benefit investigations related to a variety of astrophysical endeavours, such as the early formation of the Milky Way, the chemical evolution of GGCs, and stellar evolution and nucleosynthesis. For instance, we confirm with our compiled data that the GGC system has a bimodal metallicity distribution and is uniformly enhanced in the alpha-elements. When paired with the ages...

  2. Modelling realistic horizontal branch morphologies and their impact on spectroscopic ages of unresolved stellar systems

    CERN Document Server

    Percival, Susan M

    2010-01-01

    The presence of an extended blue horizontal branch (HB) in a stellar population is known to affect the age inferred from spectral fitting to stellar population synthesis models. However, most population synthesis models still rely on theoretical isochrones which do not include realistic modelling of extended HBs. In this work, we create detailed models for a range of old simple stellar populations (SSPs), to create a variety of realistic HB morphologies, from extended red clumps, to extreme blue HBs. We achieve this by utilising stellar tracks from the BaSTI database and implementing a different mass loss prescription for each SSP created, resulting in different HB morphologies. We find that, for each metallicity, there is some HB morphology which maximises Hbeta, making an underlying 14Gyr population look ~5-6Gyr old for the low and intermediate metallicity cases, and as young as 2Gyr for a solar metallicity SSP. We explore whether there are any spectral indices capable of breaking the degeneracy between an ...

  3. The Coronal Global Evolutionary Model (CGEM): Using HMI Vector Magnetogram and Doppler Data to Model the Buildup of Free Magnetic Energy in the Solar Corona

    CERN Document Server

    Fisher, George H; Bercik, David J; Kazachenko, Maria D; Lynch, Benjamin J; Welsch, Brian T; Hoeksema, J Todd; Hayashi, Keiji; Liu, Yang; Norton, Aimee A; Dalda, Alberto Sainz; Sun, Xudong; DeRosa, Marc L; Cheung, Mark C M

    2015-01-01

    The most violent space weather events (eruptive solar flares and coronal mass ejections) are driven by the release of free magnetic energy stored in the solar corona. Energy can build up on timescales of hours to days, and then may be suddenly released in the form of a magnetic eruption, which then propagates through interplanetary space, possibly impacting the Earth's space environment. Can we use the observed evolution of the magnetic and velocity fields in the solar photosphere to model the evolution of the overlying solar coronal field, including the storage and release of magnetic energy in such eruptions? The objective of CGEM, the Coronal Global Evolutionary Model, funded by the NASA/NSF Space Weather Modeling program, is to develop and evaluate such a model for the evolution of the coronal magnetic field. The evolving coronal magnetic field can then be used as a starting point for magnetohydrodynamic (MHD) models of the corona, which can then be used to drive models of heliospheric evolution and predi...

  4. The Coronal Global Evolutionary Model: Using HMI Vector Magnetogram and Doppler Data to Model the Buildup of Free Magnetic Energy in the Solar Corona

    Science.gov (United States)

    Fisher, G. H.; Abbett, W. P.; Bercik, D. J.; Kazachenko, M. D.; Lynch, B. J.; Welsch, B. T.; Hoeksema, J. T.; Hayashi, K.; Liu, Y.; Norton, A. A.; Dalda, A. Sainz; Sun, X.; DeRosa, M. L.; Cheung, M. C. M.

    2015-06-01

    The most violent space weather events (eruptive solar flares and coronal mass ejections) are driven by the release of free magnetic energy stored in the solar corona. Energy can build up on timescales of hours to days, and then may be suddenly released in the form of a magnetic eruption, which then propagates through interplanetary space, possibly impacting the Earth's space environment. Can we use the observed evolution of the magnetic and velocity fields in the solar photosphere to model the evolution of the overlying solar coronal field, including the storage and release of magnetic energy in such eruptions? The objective of CGEM, the Coronal Global Evolutionary Model, funded by the NASA/NSF Space Weather Modeling program, is to develop and evaluate such a model for the evolution of the coronal magnetic field. The evolving coronal magnetic field can then be used as a starting point for magnetohydrodynamic (MHD) models of the corona, which can then be used to drive models of heliospheric evolution and predictions of magnetic field and plasma density conditions at 1AU.

  5. Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

    Science.gov (United States)

    Andrews, Brett H.; Weinberg, David H.; Schönrich, Ralph; Johnson, Jennifer A.

    2017-02-01

    Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]–[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]–[Fe/H] unlike the observed bimodality (separate high-α and low-α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]–[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α-elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.

  6. On the universal stellar law

    Science.gov (United States)

    Krot, Alexander

    In this work, we consider a statistical theory of gravitating spheroidal bodies to derive and develop the universal stellar law for extrasolar systems. Previously, the statistical theory for a cosmogonic body forming (so-called spheroidal body)has been proposed [1-3]. This theory starts from the conception for forming a spheroidal body inside a gas-dust protoplanetary nebula; it permits us to derive the form of distribution functions, mass density, gravitational potentials and strengths both for immovable and rotating spheroidal bodies as well as to find the distribution function of specific angular momentum[1-3]. If we start from the conception for forming a spheroidal body as a protostar (in particular, proto-Sun) inside a prestellar (presolar) nebula then the derived distribution functions of particle (as well as the mass density of an immovable spheroidal body) characterizes the first stage of evolution: from a prestellar molecular cloud (the presolar nebula) to the forming core of protostar (the proto-Sun) together with its shell as a stellar nebula (the solar nebula). This work derives the equation of state of an ideal stellar substance based on conception of gravitating spheroidal body. Using this equation, we obtain the universal stellar law (USL) for the planetary systems connecting temperature, size and mass of each of stars. This work also considers the Solar corona in the connection with USL. Then it is accounting under calculation of the ratio of temperature of the Solar corona to effective temperature of the Sun’ surfaceand modification of USL. To test justice of the modified USLfor different types of stars, the temperature of stellar corona is estimated. The prediction of parameters of stars is carrying out by means of the modified USL,as well as the Hertzsprung-Russell’s dependence [5-7]is derivedby means of USL directly. This paper also shows that knowledge of some characteristics for multi-planet extrasolar systems refines own parameters of

  7. Constraints on galaxy formation models from the galaxy stellar mass function and its evolution

    CERN Document Server

    Rodrigues, Luiz Felippe S; Bower, Richard

    2016-01-01

    We explore the parameter space of the semi-analytic galaxy formation model GALFORM, studying the constraints imposed by measurements of the galaxy stellar mass function (GSMF) and its evolution. We use the Bayesian Emulator method to quickly eliminate vast implausible volumes of the parameter space and zoom in on the most interesting regions, allowing us to identify a set of models that match the observational data within the model uncertainties. We find that the GSMF strongly constrains parameters related to the quiescent star formation in discs, stellar and AGN feedback and the threshold for disc instabilities, but more weakly restricts other parameters. Constraining the model using the local data alone does not usually select models that match the evolution of the mass function well. Nevertheless, we show that a small subset of models provides an acceptable match to GSMF data out to redshift 1.5, without introducing an explicit redshift dependence of feedback parameters. We explore the physical significanc...

  8. A Mega-Grid of CMFGEN Model Atmospheres for Rapid Analysis of Stellar Spectra

    Science.gov (United States)

    Zsargo, J.; Arrieta, A.; Fierro, C.; Klapp, J.; Hillier, D. J.; Arias, L.; Mendoza, J.; Georgiev, L. N.

    2017-02-01

    CMFGEN (Hillier & Miller 1998) is a sophisticated and widely-used non-LTE stellar atmosphere code. It models the full spectrum, and has been used to model OB stars, W-R stars, luminous blue variables, and supernovae. However, it requires the user to have substantial knowledge and experience to run it, and even then a complete analysis of a star can be very difficult and time consuming. Computations and modeling with CMFGEN are greatly eased when suitable initial models are available. To expedite modeling, or to run a quick rudimentary analysis of the stellar spectra, we are undertaking a project to create a mega-grid of pre-calculated CMFGEN models which will be available to the general astronomical community via internet. Tools are also being developed to use this database for analysis.

  9. Modelling realistic horizontal branch morphologies and their impact on spectroscopic ages of unresolved stellar systems

    Science.gov (United States)

    Percival, Susan M.; Salaris, Maurizio

    2011-04-01

    The presence of an extended blue horizontal branch (HB) in a stellar population is known to affect the age inferred from spectral fitting to stellar population synthesis models. This is due to the hot blue component which increases the strength of the Balmer lines and can make an old population look spuriously young. However, most population synthesis models still rely on theoretical isochrones, which do not include realistic modelling of extended HBs. In this work, we create detailed models for a range of old simple stellar populations (SSPs), with metallicities ranging from [Fe/H]=-1.3 to solar, to create a variety of realistic HB morphologies, from extended red clumps, to extreme blue HBs. We achieve this by utilizing stellar tracks from the BaSTI data base and implementing a different mass-loss prescription for each SSP created. This includes setting an average mass and a Gaussian spread in masses of individual stars coming on to the zero-age HB for each model, and hence resulting in different HB morphologies. We find that, for each metallicity, there is some HB morphology which maximizes Hβ, making an underlying 14-Gyr population look ˜5-6 Gyr old for the low- and intermediate-metallicity cases, and as young as 2 Gyr in the case of the solar metallicity SSP. We explore whether there are any spectral indices capable of breaking the degeneracy between an old SSP with extended blue HB and a truly young or intermediate-age SSP, and find that the Ca II index of Rose and the strength of the Mg II doublet at 2800 Å are promising candidates, in combination with Hβ and other metallicity indicators, such as Mgb and Fe5406. We also run Monte Carlo simulations to investigate the level of statistical fluctuations in the spectra of typical stellar clusters. We find that fluctuations in spectral indices are significant even for average to large globular clusters and that various spectral indices are affected in different ways, which has implications for full

  10. Fundamental stellar parameters

    CERN Document Server

    Wittkowski, M

    2004-01-01

    I present a discussion of fundamental stellar parameters and their observational determination in the context of interferometric measurements with current and future optical/infrared interferometric facilities. Stellar parameters and the importance of their determination for stellar physics are discussed. One of the primary uses of interferometry in the field of stellar physics is the measurement of the intensity profile across the stellar disk, both as a function of position angle and of wavelength. High-precision fundamental stellar parameters are also derived by characterizations of binary and multiple system using interferometric observations. This topic is discussed in detail elsewhere in these proceedings. Comparison of observed spectrally dispersed center-to-limb intensity variations with models of stellar atmospheres and stellar evolution may result in an improved understanding of key phenomena in stellar astrophysics such as the precise evolutionary effects on the main sequence, the evolution of meta...

  11. Testing spectral models for stellar populations with star clusters: I. Methodology

    CERN Document Server

    Fernandes, Roberto Cid

    2009-01-01

    High resolution spectral models for simple stellar populations (SSP) developed in the past few years have become a standard ingredient in studies of stellar population of galaxies. As more such models become available, it becomes increasingly important to test them. In this and a companion paper, we test a suite of publicly available evolutionary synthesis models using integrated optical spectra in the blue-near-UV range of 27 well studied star clusters from the work of Leonardi & Rose (2003) spanning a wide range of ages and metallicities. Most (23) of the clusters are from the Magellanic clouds. This paper concentrates on methodological aspects of spectral fitting. The data are fitted with SSP spectral models from Vazdekis and collaborators, based on the MILES library. Best-fit and Bayesian estimates of age, metallicity and extinction are presented, and degeneracies between these parameters are mapped. We find that these models can match the observed spectra very well in most cases, with small formal un...

  12. Properties of Carbon-Oxygen White Dwarfs From Monte Carlo Stellar Models

    CERN Document Server

    Fields, C E; Petermann, I; Iliadis, C; Timmes, F X

    2016-01-01

    We investigate properties of carbon-oxygen white dwarfs with respect to the composite uncertainties in the reaction rates using the stellar evolution toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the probability density functions in the reaction rate library STARLIB. These are the first Monte Carlo stellar evolution studies that use complete stellar models. Focusing on 3 M$_{\\odot}$ models evolved from the pre main-sequence to the first thermal pulse, we survey the remnant core mass, composition, and structure properties as a function of 26 STARLIB reaction rates covering hydrogen and helium burning using a Principal Component Analysis and Spearman Rank-Order Correlation. Relative to the arithmetic mean value, we find the width of the 95\\% confidence interval to be $\\Delta M_{{\\rm 1TP}}$ $\\approx$ 0.019 M$_{\\odot}$ for the core mass at the first thermal pulse, $\\Delta$$t_{\\rm{1TP}}$ $\\approx$ 12.50 Myr for the age, $\\Delta \\log(T_{{\\rm c}}/{\\rm K}) \\approx$ 0.013 for the central temperat...

  13. MILES extended: Stellar population synthesis models from the optical to the infrared

    CERN Document Server

    Röck, B; Ricciardelli, E; Peletier, R F; Knapen, J H; Falcon-Barroso, J

    2016-01-01

    We present the first single-burst stellar population models which covers the optical and the infrared wavelength range between 3500 and 50000 Angstrom and which are exclusively based on empirical stellar spectra. To obtain these joint models, we combined the extended MILES models in the optical with our new infrared models that are based on the IRTF (Infrared Telescope Facility) library. The latter are available only for a limited range in terms of both age and metallicity. Our combined single-burst stellar population models were calculated for ages larger than 1 Gyr, for metallicities between [Fe/H] = -0.40 and 0.26, for initial mass functions of various types and slopes, and on the basis of two different sets of isochrones. They are available to the scientific community on the MILES web page. We checked the internal consistency of our models and compared their colour predictions to those of other models that are available in the literature. Optical and near infrared colours that are measured from our models...

  14. Distance determination for RAVE stars using stellar models II: Most likely values assuming a standard stellar evolution scenario

    CERN Document Server

    Zwitter, T; Breddels, M A; Smith, M C; Helmi, A; Munari, U; Bienaym\\'{e), O; Bland-Hawthorn, J; Boeche, C; Brown, A G A; Campbell, R; Freeman, K C; Fulbright, J; Gibson, B; Gilmore, G; Grebel, E K; Navarro, J F; Parker, Q A; Seabroke, G M; Siebert, A; Siviero, A; Steinmetz, M; Watson, F G; Williams, M; Wyse, R F G

    2010-01-01

    The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of the Milky Way. We use the subsample of spectra with spectroscopically determined values of stellar parameters to determine the distances to these stars. The list currently contains 235,064 high quality spectra which show no peculiarities and belong to 210,872 different stars. The numbers will grow as the RAVE survey progresses. The public version of the catalog will be made available through the CDS services along with the ongoing RAVE public data releases. The distances are determined with a method based on the work by Breddels et al.~(2010). Here we assume that the star undergoes a standard stellar evolution and that its spectrum shows no peculiarities. The refinements include: the use of either of the three isochrone sets, a better account of the stellar ages and masses, use of more realistic errors of stellar parameter values, and application to a larger dataset. The derived distances of both dwarfs and giants match within ~21% to the astr...

  15. Corona helps curb losses

    Energy Technology Data Exchange (ETDEWEB)

    Laasonen, M.; Lahtinen, M.; Lustre, L.

    1996-11-01

    The greatest power losses in electricity transmission arise through a phenomenon called load losses. Corona losses caused by the surface discharge of electricity also constitute a considerable cost item. IVS, the nationwide network company, is investigating corona- induced losses, and has also commissioned similar research from IVO International, the Technical Research Centre of Finland (VTT) and from Tampere University of Technology. The research work strives to gain more in-depth knowledge on the phenomenon of frosting and its impact on corona losses. The correct prediction of frost helps reduce corona losses, while also cutting costs considerably. (orig.)

  16. Corona helps curb losses

    Energy Technology Data Exchange (ETDEWEB)

    Laasonen, M.; Lahtinen, M.; Lustre, L.

    1996-11-01

    The greatest power losses in electricity transmission arise through a phenomenon called load losses. Corona losses caused by the surface discharge of electricity also constitute a considerable cost item. IVS, the nationwide network company, is investigating corona- induced losses, and has also commissioned similar research from IVO International, the Technical Research Centre of Finland (VTT) and from Tampere University of Technology. The research work strives to gain more in-depth knowledge on the phenomenon of frosting and its impact on corona losses. The correct prediction of frost helps reduce corona losses, while also cutting costs considerably. (orig.)

  17. Red Giant Oscillations: Stellar Models and Mode Frequency Calculations

    DEFF Research Database (Denmark)

    Jendreieck, A.; Weiss, A.; Aguirre, Victor Silva

    2012-01-01

    We present preliminary results on modelling KIC 7693833, the so far most metal-poor red-giant star observed by {\\it Kepler}. From time series spanning several months, global oscillation parameters and individual frequencies were obtained and compared to theoretical calculations. Evolution models ......_\\odot$ in radius and of about 2.5 Gyr in age....

  18. Stellar and HI Mass Functions Predicted by a Simple Preheating Galaxy Formation Model

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star formation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.

  19. SMART - a computer program for modelling stellar atmospheres

    CERN Document Server

    Aret, Anna; Poolamäe, Raivo; Sapar, Lili

    2013-01-01

    Program SMART (Spectra and Model Atmospheres by Radiative Transfer) has been composed for modelling atmospheres and spectra of hot stars (O, B and A spectral classes) and studying different physical processes in them (Sapar & Poolam\\"ae 2003, Sapar et al. 2007). Line-blanketed models are computed assuming plane-parallel, static and horizontally homogeneous atmosphere in radiative, hydrostatic and local thermodynamic equilibrium. Main advantages of SMART are its shortness, simplicity, user friendliness and flexibility for study of different physical processes. SMART successfully runs on PC both under Windows and Linux.

  20. Discriminating among stellar population synthesis models of the TP-AGB phase in early quiescent galaxies

    Science.gov (United States)

    MacDougall, Mason; Newman, Andrew; Belli, Sirio; Ellis, Richard S.

    2017-01-01

    Galactic evolution at high redshifts is largely understood through stellar population synthesis (SPS) modeling of spectra and photometry integrated over all starlight of a galaxy. However, complex and poorly understood stellar phases like the unstable thermally-pulsating asymptotic giant branch (TP-AGB) phase make SPS modeling a difficult task. Recent models fail to agree on the TP-AGB contribution to the infrared luminosity, leading to significant discrepancy among the properties derived from modern SPS models when applied to early galaxies. Here we provide a thorough assessment of each of the most widely used SPS models by comparing their results and assessing their accuracy in modeling our unique dataset. We combine high-resolution spectroscopic observations from Keck/MOSFIRE with photometric data for 21 early quiescent galaxies with redshifts of z ~ 2. These galaxies are around the age of peak TP-AGB activity, between ~0.3 and 2 Gyr, and therefore provide an ideal test of the models. We find that models with a “light” TP-AGB contribution provide much better descriptions of our galaxies at ages of ~1 Gyr or less. This is true at high statistical significance and holds for models with or without dust reddening. However, contrary to previous studies, the model-dependent photometrically estimated ages are similar among the models, but they show only moderate agreement with the more model-independent spectroscopic ages derived from stellar absorption lines. The largest discrepancies are found for the Charlot & Bruzual (2007) models which show an artificial clustering of ages around 1 Gyr. The TP-AGB “light” models require more reddening, which can be independently tested by examining dust emission in the mid-infrared. The modeled fluxes are also mostly consistent with mid-infrared observations, with the exception of one model. Resolving these differences among the models will substantially strengthen our estimates of the properties of early quiescent

  1. Empirical Tests of Pre-Main-Sequence Stellar Evolution Models with Eclipsing Binaries

    CERN Document Server

    Stassun, Keivan G; Torres, Guillermo

    2014-01-01

    We examine the performance of standard PMS stellar evolution models against the accurately measured properties of a benchmark sample of 26 PMS stars in 13 EB systems. We provide a definitive compilation of all fundamental properties for the EBs. We also provide a definitive compilation of the various PMS model sets. In the H-R diagram, the masses inferred for the individual stars by the models are accurate to better than 10% above 1 Msun, but below 1 Msun they are discrepant by 50-100%. We find evidence that the failure of the models to match the data is linked to the triples in the EB sample; at least half of the EBs possess tertiary companions. Excluding the triples, the models reproduce the stellar masses to better than ~10% in the H-R diagram, down to 0.5 Msun, below which the current sample is fully contaminated by tertiaries. We consider several mechanisms by which a tertiary might cause changes in the EB properties and thus corrupt the agreement with stellar model predictions. We show that the energies...

  2. Minimum X-ray source size for a lamppost corona in light-bending models for AGN

    Science.gov (United States)

    Dovciak, M.; Done, C.

    2015-07-01

    The `lamppost' model is often used to describe the X-ray source geometry in AGN, where an infinitesimal point source is located on the black hole spin axis. This is especially invoked for Narrow Line Seyfert 1 galaxies, where an extremely broad iron line seen in episodes of low X-ray flux can be explained by extremely strong relativistic effects as the source approaches the black hole horizon. However, the source must also be large enough to intercept sufficient seed photons from the disc to make the hard X-ray Compton continuum which produces the observed iron line/reflected spectrum. This size scale also sets the minimum height of the corona in order that the source can fit above the event horizon. We calculate this using a fully relativistic ray tracing code, and apply to the most extreme NLS1, 1H0707-495. The inferred source size is too big for it to be at a height of less than one gravitational radius above the horizon.

  3. Experimental and modeling study of the oxidation of acetaldehyde in an atmospheric-pressure pulsed corona discharge

    Science.gov (United States)

    Klett, C.; Touchard, S.; Vega-Gonzalez, A.; Redolfi, M.; Bonnin, X.; Hassouni, K.; Duten, X.

    2012-08-01

    This paper reports the results obtained for the degradation of acetaldehyde by an atmospheric plasma corona discharge working in a pulsed regime. It was shown that a few hundred ppm of acetaldehyde diluted in a pure N2 gas flow can be removed up to 80% by a discharge fed with an electric power lower than 1 W. Under the same conditions, adding up to 5% of O2 allowed the removal of up to 95% of the initial acetaldehyde. The main identified end products were CO2, CO and methanol. A quasi-homogeneous zero-dimensional chemical model was developed to investigate the respective efficiency of the discharge and post-discharge periods in the global removal of the pollutant. The identified main pathways of acetaldehyde degradation were quenching of N2 metastable states during plasma pulses and oxidation by O and OH radicals during the post-discharge. This latter contribution increased with input power because of ozone accumulation in the gas mixture acting as an additional oxygen reservoir.

  4. The construction of non-spherical models of quasi-relaxed stellar systems

    CERN Document Server

    Bertin, G

    2008-01-01

    Spherical models of collisionless but quasi-relaxed stellar systems have long been studied as a natural framework for the description of globular clusters. Here we consider the construction of self-consistent models under the same physical conditions, but including explicitly the ingredients that lead to departures from spherical symmetry. In particular, we focus on the effects of the tidal field associated with the hosting galaxy. We then take a stellar system on a circular orbit inside a galaxy represented as a "frozen" external field. The equilibrium distribution function is obtained from the one describing the spherical case by replacing the energy integral with the relevant Jacobi integral in the presence of the external tidal field. Then the construction of the model requires the investigation of a singular perturbation problem for an elliptic partial differential equation with a free boundary, for which we provide a method of solution to any desired order, with explicit solutions to two orders. We outl...

  5. An Iterative Method for the Construction of Equilibrium N-Body Models for Stellar Disks

    CERN Document Server

    Rodionov, S A

    2006-01-01

    One widely used technique for the construction of equilibrium models of stellar disks is based on the Jeans equations and the moments of velocity distribution functions derived using these equations. Stellar disks constructed using this technique are shown to be "not entirely" in equilibrium. Our attempt to abandon the epicyclic approximation and the approximation of infinite isothermal layers, which are commonly adopted in this technique, failed to improve the situation substantially. We conclude that the main drawback of techniques based on the Jeans equations is that the system of equations employed is not closed, and therefore requires adopting an essentially ad hoc additional closure condition. A new iterative approach to constructing equilibrium N-body models with a given density distribution is proposed. The main idea behind this approach is that a model is first constructed using some approximation method, and is then allowed to adjust to an equilibrium state with the specified density and the require...

  6. Comparison of pulsed corona plasma and pulsed electric fields for the decontamination of water containing Legionella pneumophila as model organism.

    Science.gov (United States)

    Banaschik, Robert; Burchhardt, Gerhard; Zocher, Katja; Hammerschmidt, Sven; Kolb, Juergen F; Weltmann, Klaus-Dieter

    2016-12-01

    Pulsed corona plasma and pulsed electric fields were assessed for their capacity to kill Legionella pneumophila in water. Electrical parameters such as in particular dissipated energy were equal for both treatments. This was accomplished by changing the polarity of the applied high voltage pulses in a coaxial electrode geometry resulting in the generation of corona plasma or an electric field. For corona plasma, generated by high voltage pulses with peak voltages of +80kV, Legionella were completely killed, corresponding to a log-reduction of 5.4 (CFU/ml) after a treatment time of 12.5min. For the application of pulsed electric fields from peak voltages of -80kV a survival of log 2.54 (CFU/ml) was still detectable after this treatment time. Scanning electron microscopy images of L. pneumophila showed rupture of cells after plasma treatment. In contrast, the morphology of bacteria seems to be intact after application of pulsed electric fields. The more efficient killing for the same energy input observed for pulsed corona plasma is likely due to induced chemical processes and the generation of reactive species as indicated by the evolution of hydrogen peroxide. This suggests that the higher efficacy and efficiency of pulsed corona plasma is primarily associated with the combined effect of the applied electric fields and the promoted reaction chemistry.

  7. Detecting the growth of structures in Pure Stellar Disk Models

    Science.gov (United States)

    Valencia-Enríquez, D.; Puerari, I.; Chaves-Velasquez, L.

    2017-10-01

    We performed a series of 3D N-body simulations where the initial conditions were chosen to get two sets of models; unbarred and barred ones. In this work, we analyze the growth of spirals and bar structures using 1D, and 2D Fourier transform (FT) methods. Spectrograms and diagrams of the amplitude of the Fourier coefficients as a function of time, radius and pitch angle show that the general morphology of our modeled galaxies is due to the superposition of structures which have different values of pitch angle and number of arms. Also, in barred models a geometric classification of orbits from the bar reference frame was done, showing that the barred potential and the Lagrangian points L4 and L5 catch approximately one-third of the total disk mass.

  8. Modeling the Near-Infrared Luminosity Function of Young Stellar Clusters

    Science.gov (United States)

    Muench, A. A.; Lada, E. A.; Lada, C. J.

    1999-12-01

    We present the results of numerical experiments designed to evaluate the usefulness of near-infrared luminosity functions for constraining the Initial Mass Function (IMF) of young (0-10 Myr) stellar populations. Using Monte Carlo techniques, we create a suite of model luminosity functions systematically varying each of these basic underlying relations: the underlying IMF, cluster star forming history, and theoretical pre-main sequence mass-to-luminosity relations. Our modeling techniques also allow us to explore the effects of unresolved binaries, infrared excess emission from circumstellar disks, and interstellar extinction on the cluster luminosity function. From this numerical modeling, we find that the luminosity function of a young stellar population is considerably more sensitive to variations in the underlying initial mass function than to either variations in the star forming history or assumed pre-main-sequence (PMS) mass-to-luminosity relation. To illustrate the potential effectiveness of using the KLF of a young cluster to constrain its IMF, we model the observed K band luminosity function of the nearby Trapezium cluster. Our derived mass function for the Trapezium spans two orders of magnitude in stellar mass (5>Msun>0.02) and has a peak near the hydrogen burning limit. Below the hydrogen burning limit, the mass function steadily decreases with decreasing mass throughout the brown dwarf regime. We also test the hypothesis of a space varying IMF by performing model fits to the K band luminosity functions of several other young clusters.

  9. Advances In Understanding Solar And Stellar Flares

    Science.gov (United States)

    Kowalski, Adam F.

    2016-07-01

    Flares result from the sudden reconnection and relaxation of magnetic fields in the coronae of stellar atmospheres. The highly dynamic atmospheric response produces radiation across the electromagnetic spectrum, from the radio to X-rays, on a range of timescales, from seconds to days. New high resolution data of solar flares have revealed the intrinsic spatial properties of the flaring chromosphere, which is thought to be where the majority of the flare energy is released as radiation in the optical and near-UV continua and emission lines. New data of stellar flares have revealed the detailed properties of the broadband (white-light) continuum emission, which provides straightforward constraints for models of the transformation of stored magnetic energy in the corona into thermal energy of the lower atmosphere. In this talk, we discuss the physical processes that produce several important spectral phenomena in the near-ultraviolet and optical as revealed from new radiative-hydrodynamic models of flares on the Sun and low mass stars. We present recent progress with high-flux nonthermal electron beams in reproducing the observed optical continuum color temperature of T 10,000 K and the Balmer jump properties in the near-ultraviolet. These beams produce dense, heated chromospheric condensations, which can explain the shape and strength of the continuum emission in M dwarf flares and the red-wing asymmetries in the chromospheric emission lines in recent observations of solar flares from the Interface Region Imaging Spectrograph. Current theoretical challenges and future modeling directions will be discussed, as well as observational synergies between solar and stellar flares.

  10. 3D-modelling of the stellar auroral radio emission

    CERN Document Server

    Leto, P; Buemi, C S; Umana, G; Ingallinera, A; Cerrigone, L

    2016-01-01

    The electron cyclotron maser is the coherent emission process that gives rise to the radio lighthouse effect observed in the hot magnetic chemically peculiar star CU Virginis. It has also been proposed to explain the highly circularly polarized radio pulses observed on some ultra cool dwarfs, with spectral type earlier than M7. Such kind of coherent events resemble the auroral radio emission from the magnetized planets of the solar system. In this paper, we present a tridimensional model able to simulate the timing and profile of the pulses emitted by those stars characterized by a dipolar magnetic field by following the hypothesis of the laminar source model, used to explain the beaming of the terrestrial auroral kilometric radiation. This model proves to be a powerful tool to understand the auroral radio-emission phenomenon, allowing us to derive some general conclusions about the effects of the model's free parameters on the features of the coherent pulses, and to learn more about the detectability of such...

  11. 3D modelling of stellar auroral radio emission

    Science.gov (United States)

    Leto, P.; Trigilio, C.; Buemi, C. S.; Umana, G.; Ingallinera, A.; Cerrigone, L.

    2016-06-01

    The electron cyclotron maser is the coherent emission process that gives rise to the radio lighthouse effect observed in the hot magnetic chemically peculiar star CU Virginis. It has also been proposed to explain the highly circularly polarized radio pulses observed in some ultracool dwarfs with spectral type earlier than M7. Coherent events of this kind resemble auroral radio emission from the magnetized planets of the Solar system. In this article, we present a three-dimensional model able to simulate the timing and profile of the pulses emitted by those stars characterized by a dipolar magnetic field by following the hypothesis of the laminar source model, used to explain the beaming of terrestrial auroral kilometric radiation. This model proves to be a powerful tool with which to understand the auroral radio emission phenomenon, allowing us to derive some general conclusions about the effects of the model's free parameters on the features of coherent pulses and to learn more about the detectability of such pulsed radio emission.

  12. The dependence of AGN activity on stellar and halo mass in Semi-Analytic Models

    CERN Document Server

    Fontanot, Fabio; De Lucia, Gabriella; Bosch, Frank C van den; Somerville, Rachel S; Kang, Xi

    2010-01-01

    AGN feedback is believed to play an important role in shaping a variety of observed galaxy properties, as well as the evolution of their stellar masses and star formation rates. In particular, in the current theoretical paradigm of galaxy formation, AGN feedback is believed to play a crucial role in regulating the levels of activity in galaxies, in relatively massive halos at low redshift. Only in recent years, however, detailed statistical information on the dependence of galaxy activity on stellar mass, parent halo mass and hierarchy has become available. In this paper, we compare the fractions of galaxies belonging to different activity classes (star-forming, AGN and radio active) with predictions from four different and independently developed semi-analytical models. We adopt empirical relations to convert physical properties into observables (H_alpha emission lines, OIII line strength and radio power). We demonstrate that all models used in this study reproduce the overall distributions of galaxies belon...

  13. Role of f(T) gravity on the evolution of collapsing stellar model

    Science.gov (United States)

    Bhatti, M. Zaeem-ul-Haq; Yousaf, Z.; Hanif, Sonia

    2017-06-01

    The aim of this paper is to exhibit the instability epochs of self-gravitating objects coupled with anisotropic radiative matter content. We perform our analysis in the background of f(T) gravity which is the extended version of teleparallel gravity. We probe the instability regions by taking a peculiar model f(T) = T + αT2. We explore the basic equations in order to model stellar interior, including field, dynamical and junction equations. We then study linear perturbations of our system. We formulate the modified collapse equation by using Harrison-Wheeler equation of state. We develop the instability constraints at Newtonian and post-Newtonian regimes. The major outcome of our work reveals that the stiffness parameter plays a significant role in the stability of relativistic anisotropic stellar interior in f(T) gravity.

  14. Ray tracing and ECRH absorption modeling in the HSX stellarator

    Science.gov (United States)

    Weir, G. M.; Likin, K. M.; Marushchenko, N. B.; Turkin, Y.

    2015-09-01

    To increase flexibility in ECRH experiments on the helically symmetric experiment (HSX), a second gyrotron and transmission line have been installed. The second antenna includes a steerable mirror for off-axis heating, and the launched power may be modulated for use in heat pulse propagation experiments. The extraordinary wave at the second harmonic of the electron gyrofrequency or the ordinary wave at the fundamental resonance are used for plasma start-up and heating on HSX. The tracing visualized ray tracing code (Marushchenko et al 2007 Plasma Fusion Res. 2 S1129) is used to estimate single-pass absorption and to model multi-pass wave damping in the three-dimensional HSX geometry. The single-pass absorption of the ordinary wave at the fundamental resonance is calculated to be as high as 30%, while measurements of the total absorption indicate that 45% of the launched power is absorbed. A multi-pass ray tracing model correctly predicts the experimental absorption and indicates that the launched power is absorbed within the plasma core (r/a≤slant 0.2 ).

  15. Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model

    OpenAIRE

    Hirschmann, Michaela; De Lucia, Gabriella; Fontanot, Fabio

    2015-01-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently `anti-hierarchical' evolution of galaxy assembly: massive galaxies appear to be in place since $z\\sim 3$, while a significant increase of the number densities of low mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of GAEA, a new semi-ana...

  16. Local models of stellar convection III: The Strouhal number

    CERN Document Server

    Käpylä, P J; Ossendrijver, M; Tuominen, I

    2004-01-01

    (Abbreviated) We determine the Strouhal number (St), a nondimensional measure of the correlation time, from numerical models of convection. The Strouhal number arises in the mean-field theories of angular momentum transport and dynamos, where its value determines the validity of certain widely used approximations, such as the first order smoothing (FOSA). More specifically, the relevant transport coefficients can be calculated by means of a cumulative series expansion if St < 1 (e.g. Knobloch 1978). We use two independent methods to estimate St. Firstly, we apply the minimal tau-approximation (MTA) in the equation of the time derivative of the Reynolds stress. In this approach the time derivative is essentially replaced by a term containing a relaxation time which can be interpreted as the correlation time of the turbulence. In this approach, the turnover time is estimated simply from the energy carrying scale of the convection and a typical velocity. In the second approach, we determine the correlation an...

  17. Mass content of UGC 6446 and UGC 7524 through H i rotation curves: deriving the stellar discs from stellar population synthesis models

    Science.gov (United States)

    Repetto, P.; Martínez-García, Eric E.; Rosado, M.; Gabbasov, R.

    2017-06-01

    In this work, we study the mass distribution of two irregular galaxies, UGC 6446 and UGC 7524, by means of H i rotation curves derived from high-resolution H i velocity fields obtained through the Westerbork Synthesis Radio Telescope data archive. We constrain the stellar and gas content of both galaxies with stellar population synthesis models and by deriving the H i+He+metals rotation curves from the total H i surface density maps, respectively. The discrepancy between the circular velocity maxima of the stellar plus the H i+He+metals rotation curves and the observed H i rotation curves of both galaxies requires the inclusion of a substantial amount of dark matter. We explore the Navarro Frenk and White, Burkert, Di Cintio, Einasto and Stadel dark matter halo models. We obtain acceptable fits to the observed H i rotation curves of UGC 6446 and UGC 7524 with the cored Burkert, Einasto and Stadel dark matter haloes. In particular, Einasto and Stadel models prove to be an appropriate alternative to the Burkert dark matter halo. This result should increase the empirical basis that justifies the usage of dark matter exponential models to adjust the observed rotation curves of real galaxies.

  18. Constraints on galaxy formation models from the galaxy stellar mass function and its evolution

    Science.gov (United States)

    Rodrigues, Luiz Felippe S.; Vernon, Ian; Bower, Richard G.

    2017-04-01

    We explore the parameter space of the semi-analytic galaxy formation model GALFORM, studying the constraints imposed by measurements of the galaxy stellar mass function (GSMF) and its evolution. We use the Bayesian emulator method to quickly eliminate vast implausible volumes of the parameter space and zoom in on the most interesting regions, allowing us to identify a set of models that match the observational data within model uncertainties. We find that the GSMF strongly constrains parameters related to quiescent star formation in discs, stellar and active galactic nucleus feedback and threshold for disc instabilities, but weakly restricts other parameters. Constraining the model using local data alone does not usually select models that match the evolution of the GSMF well. Nevertheless, we show that a small subset of models provides acceptable match to GSMF data out to redshift 1.5. We explore the physical significance of the parameters of these models, in particular exploring whether the model provides a better description if the mass loading of the galactic winds generated by starbursts (β0,burst) and quiescent discs (β0,disc) is different. Performing a principal component analysis of the plausible volume of the parameter space, we write a set of relations between parameters obeyed by plausible models with respect to GSMF evolution. We find that while β0,disc is strongly constrained by GSMF evolution data, constraints on β0,burst are weak. Although it is possible to find plausible models for which β0,burst = β0,disc, most plausible models have β0,burst > β0,disc, implying - for these - larger stellar feedback efficiency at higher redshifts.

  19. A Model for (Quasi-)Periodic Multi-wavelength Photometric Variability in Young Stellar Objects

    CERN Document Server

    Kesseli, Aurora Y; Wood, Kenneth; Whitney, Barbara A; Hillenbrand, L A; Gregory, Scott G; Stauffer, J R; Morales-Calderon, M; Rebull, L; Alencar, S H P

    2016-01-01

    We present radiation transfer models of rotating young stellar objects (YSOs) with hotspots in their atmospheres, inner disk warps and other 3-D effects in the nearby circumstellar environment. Our models are based on the geometry expected from the magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hotspots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project (Morales-Calderon et al. 2014, Cody et al. 2014) to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting "dipper" behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hotspot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR...

  20. The Effects of Stellar Rotation. II. A Comprehensive Set of Starburst99 Models

    CERN Document Server

    Leitherer, Claus; Meynet, Georges; Schaerer, Daniel; Agienko, Katerina B; Levesque, Emily M

    2014-01-01

    We present a new set of synthesis models for stellar populations obtained with Starburst99, which are based on new stellar evolutionary tracks with rotation. We discuss models with zero rotation velocity and with velocities of 40% of the break-up velocity on the zero-age main-sequence. These values are expected to bracket realistic rotation velocity distributions in stellar populations. The new rotating models for massive stars are more luminous and hotter due to a larger convective core and enhanced surface abundances. This results in pronounced changes in the integrated spectral energy distribution of a population containing massive stars. The changes are most significant at the shortest wavelengths where an increase of the ionizing luminosity by up to a factor of 5 is predicted. We also show that high equivalent widths of recombination lines may not necessarily indicate a very young age but can be achieved at ages as late as 10 Myr. Comparison of these two boundary cases (0 and 40% of the break-up velocity...

  1. Testing stellar evolution models with the retired A star HD 185351

    Science.gov (United States)

    Hjørringgaard, J. G.; Silva Aguirre, V.; White, T. R.; Huber, D.; Pope, B. J. S.; Casagrande, L.; Justesen, A. B.; Christensen-Dalsgaard, J.

    2017-01-01

    The physical parameters of the retired A star HD 185351 were analysed in great detail by Johnson et al. using interferometry, spectroscopy, and asteroseismology. Results from all independent methods are consistent with HD 185351 having a mass in excess of 1.5 M⊙. However, the study also showed that not all observational constraints could be reconciled in stellar evolutionary models, leading to mass estimates ranging from ˜1.6 to 1.9 M⊙ and casting doubts on the accuracy of stellar properties determined from asteroseismology. Here, we solve this discrepancy and construct a theoretical model in agreement with all observational constraints on the physical parameters of HD 185351. The effects of varying input physics are examined as well as the additional constraint of the observed g-mode period spacing is considered. This quantity is found to be sensitive to the inclusion of additional mixing from the convective core during the main sequence, and can be used to calibrate the overshooting efficiency using low-luminosity red giant stars. A theoretical model with metallicity [Fe/H] = 0.16 dex, mixing-length parameter αMLT = 2.00, and convective overshooting efficiency parameter f = 0.030 is found to be in complete agreement with all observational constraints for a stellar mass of M ≃ 1.60 M⊙.

  2. Modelling Accretion Disk and Stellar Wind Interactions: the Case of Sgr A*

    CERN Document Server

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

    2016-01-01

    Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disk, the ram and thermal pressures of the disk terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in $\\sim10^{8}$ cm s$^{-1}$ range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericenter passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly ...

  3. Testing stellar evolution models with the retired A star HD 185351

    Science.gov (United States)

    Hjørringgaard, J. G.; Silva Aguirre, V.; White, T. R.; Huber, D.; Pope, B. J. S.; Casagrande, L.; Justesen, A. B.; Christensen-Dalsgaard, J.

    2016-10-01

    The physical parameters of the retired A star HD 185351 were analysed in great detail by Johnson et al. (2014) using interferometry, spectroscopy and asteroseismology. Results from all independent methods are consistent with HD 185351 having a mass in excess of 1.5M⊙. However, the study also showed that not all observational constraints could be reconciled in stellar evolutionary models, leading to mass estimates ranging from ˜1.6 - 1.9M⊙ and casting doubts on the accuracy of stellar properties determined from asteroseismology. Here we solve this discrepancy and construct a theoretical model in agreement with all observational constraints on the physical parameters of HD 185351. The effects of varying input physics are examined as well as considering the additional constraint of the observed g-mode period spacing. This quantity is found to be sensitive to the inclusion of additional mixing from the convective core during the main sequence, and can be used to calibrate the overshooting efficiency using low-luminosity red giant stars. A theoretical model with metallicity [Fe/H] = 0.16dex, mixing-length parameter αMLT = 2.00, and convective overshooting efficiency parameter f = 0.030 is found to be in complete agreement with all observational constraints for a stellar mass of M ≃ 1.60M⊙.

  4. Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

    CERN Document Server

    Andrews, Brett H; Schönrich, Ralph; Johnson, Jennifer A

    2016-01-01

    Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the IMF, the SNIa delay time distribution, stellar yields, and mixing of stellar populations. Using flexCE, a new, flexible one-zone chemical evolution code, we investigate the effects of individual parameters and the trade-offs between them. Two of the most important parameters are the SFE and outflow mass-loading parameter, which shift the knee in [O/Fe]-[Fe/H] and the equilibrium abundances, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]-[Fe/H] that do not match the observed bimodality in this plane. A mix of one-zone models with variations in their inflow timescales and outflow mass-loading parameters, as motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the high- and low-alpha sequences b...

  5. Properties of Carbon-Oxygen White Dwarfs From Monte Carlo Stellar Models

    Science.gov (United States)

    Fields, C. E.; Farmer, R.; Petermann, I.; Iliadis, C.; Timmes, F. X.

    2016-05-01

    We investigate properties of carbon-oxygen white dwarfs with respect to the composite uncertainties in the reaction rates using the stellar evolution toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the probability density functions in the reaction rate library STARLIB. These are the first Monte Carlo stellar evolution studies that use complete stellar models. Focusing on 3 {M}⊙ models evolved from the pre main-sequence to the first thermal pulse, we survey the remnant core mass, composition, and structure properties as a function of 26 STARLIB reaction rates covering hydrogen and helium burning using a Principal Component Analysis and Spearman Rank-Order Correlation. Relative to the arithmetic mean value, we find the width of the 95% confidence interval to be {{Δ }}{M}{{1TP}} ≈ 0.019 {M}⊙ for the core mass at the first thermal pulse, Δ{t}{{1TP}} ≈ 12.50 Myr for the age, {{Δ }}{log}({T}{{c}}/{{K}}) ≈ 0.013 for the central temperature, {{Δ }}{log}({ρ }{{c}}/{{g}} {{cm}}-3) ≈ 0.060 for the central density, {{Δ }}{Y}{{e,c}} ≈ 2.6 × 10-5 for the central electron fraction, {{Δ }}{X}{{c}}{(}22{{Ne}}) ≈ 5.8 × 10-4, {{Δ }}{X}{{c}}{(}12{{C}}) ≈ 0.392, and {{Δ }}{X}{{c}}{(}16{{O}}) ≈ 0.392. Uncertainties in the experimental 12C(α ,γ {)}16{{O}}, triple-α, and 14N({\\text{}}p,γ {)}15{{O}} reaction rates dominate these variations. We also consider a grid of 1-6 {M}⊙ models evolved from the pre main-sequence to the final white dwarf to probe the sensitivity of the initial-final mass relation to experimental uncertainties in the hydrogen and helium reaction rates.

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

    Science.gov (United States)

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

    2016-07-01

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

  7. Modeling the Near-Infrared Luminosity Functions of Young Stellar Clusters

    Science.gov (United States)

    Muench, August A.; Lada, Elizabeth A.; Lada, Charles J.

    2000-04-01

    We present the results of numerical experiments designed to evaluate the usefulness of near-infrared (NIR) luminosity functions for constraining the initial mass function (IMF) of young stellar populations. We test the sensitivity of the NIR K-band luminosity function (KLF) of a young stellar cluster to variations in the underlying IMF, star-forming history, and pre-main-sequence mass-to-luminosity relations. Using Monte Carlo techniques, we create a suite of model luminosity functions systematically varying each of these basic underlying relations. From this numerical modeling, we find that the luminosity function of a young stellar population is considerably more sensitive to variations in the underlying initial mass function than to either variations in the star-forming history or assumed pre-main-sequence (PMS) mass-to-luminosity relation. Variations in a cluster's star-forming history are also found to produce significant changes in the KLF. In particular, we find that the KLFs of young clusters evolve in a systematic manner with increasing mean age. Our experiments indicate that variations in the PMS mass-to-luminosity relation, resulting from differences in adopted PMS tracks, produce only small effects on the form of the model luminosity functions and that these effects are mostly likely not detectable observationally. To illustrate the potential effectiveness of using the KLF of a young cluster to constrain its IMF, we model the observed KLF of the nearby Trapezium cluster. With knowledge of the star-forming history of this cluster obtained from optical spectroscopic studies, we derive the simplest underlying IMF whose model luminosity function matches the observations. Our derived mass function for the Trapezium spans 2 orders of magnitude in stellar mass (5>Msolar>0.02) and has a peak near the hydrogen-burning limit. Below the hydrogen-burning limit, the mass function steadily decreases with decreasing mass throughout the brown dwarf regime. Comparison

  8. Validation of Earth atmosphere models using solar EUV observations from the CORONAS and PROBA2 satellites in occultation mode

    Directory of Open Access Journals (Sweden)

    Slemzin Vladimir

    2016-01-01

    Full Text Available Aims: Knowledge of properties of the Earth’s upper atmosphere is important for predicting the lifetime of low-orbit spacecraft as well as for planning operation of space instruments whose data may be distorted by atmospheric effects. The accuracy of the models commonly used for simulating the structure of the atmosphere is limited by the scarcity of the observations they are based on, so improvement of these models requires validation under different atmospheric conditions. Measurements of the absorption of the solar extreme ultraviolet (EUV radiation in the upper atmosphere below 500 km by instruments operating on low-Earth orbits (LEO satellites provide efficient means for such validation as well as for continuous monitoring of the upper atmosphere and for studying its response to the solar and geomagnetic activity. Method: This paper presents results of measurements of the solar EUV radiation in the 17 nm wavelength band made with the SPIRIT and TESIS telescopes on board the CORONAS satellites and the SWAP telescope on board the PROBA2 satellite in the occulted parts of the satellite orbits. The transmittance profiles of the atmosphere at altitudes between 150 and 500 km were derived from different phases of solar activity during solar cycles 23 and 24 in the quiet state of the magnetosphere and during the development of a geomagnetic storm. We developed a mathematical procedure based on the Tikhonov regularization method for solution of ill-posed problems in order to retrieve extinction coefficients from the transmittance profiles. The transmittance profiles derived from the data and the retrieved extinction coefficients are compared with simulations carried out with the NRLMSISE-00 atmosphere model maintained by Naval Research Laboratory (USA and the DTM-2013 model developed at CNES in the framework of the FP7 project ATMOP. Results: Under quiet and slightly disturbed magnetospheric conditions during high and low solar activity the

  9. Validation of Earth atmosphere models using solar EUV observations from the CORONAS and PROBA2 satellites in occultation mode

    Science.gov (United States)

    Slemzin, Vladimir; Ulyanov, Artyom; Gaikovich, Konstantin; Kuzin, Sergey; Pertsov, Andrey; Berghmans, David; Dominique, Marie

    2016-02-01

    Aims: Knowledge of properties of the Earth's upper atmosphere is important for predicting the lifetime of low-orbit spacecraft as well as for planning operation of space instruments whose data may be distorted by atmospheric effects. The accuracy of the models commonly used for simulating the structure of the atmosphere is limited by the scarcity of the observations they are based on, so improvement of these models requires validation under different atmospheric conditions. Measurements of the absorption of the solar extreme ultraviolet (EUV) radiation in the upper atmosphere below 500 km by instruments operating on low-Earth orbits (LEO) satellites provide efficient means for such validation as well as for continuous monitoring of the upper atmosphere and for studying its response to the solar and geomagnetic activity. Method: This paper presents results of measurements of the solar EUV radiation in the 17 nm wavelength band made with the SPIRIT and TESIS telescopes on board the CORONAS satellites and the SWAP telescope on board the PROBA2 satellite in the occulted parts of the satellite orbits. The transmittance profiles of the atmosphere at altitudes between 150 and 500 km were derived from different phases of solar activity during solar cycles 23 and 24 in the quiet state of the magnetosphere and during the development of a geomagnetic storm. We developed a mathematical procedure based on the Tikhonov regularization method for solution of ill-posed problems in order to retrieve extinction coefficients from the transmittance profiles. The transmittance profiles derived from the data and the retrieved extinction coefficients are compared with simulations carried out with the NRLMSISE-00 atmosphere model maintained by Naval Research Laboratory (USA) and the DTM-2013 model developed at CNES in the framework of the FP7 project ATMOP. Results: Under quiet and slightly disturbed magnetospheric conditions during high and low solar activity the extinction coefficients

  10. Modeling Active Region Evolution - at the Sun’s Surface and into the Corona

    Science.gov (United States)

    Upton, Lisa; Ugarte-Urra, Ignacio; Warren, Harry; Young, Peter R.

    2017-08-01

    The STEREO mission provides the first opportunity to track the long-term evolution of Active Regions over multiple rotations. The Advective Flux Transport (AFT) model is a state of the art Surface Flux Transport model, which simulates the observed near-surface flows to model the transport of magnetic flux over the entire Sun. Combining STEREO observations with AFT has allowed us to characterize the flux-luminosity relationship for He 304 Å and to validate the far-side evolution of individual active regions produced with AFT. Here, we present recent results in which we extend this radiance - magnetic flux power-law relationship to the AIA 335 Å passband, and the Fe XVIII 93.93 Å spectral line in the 94 Å passband. We use these results to test our current understanding of magnetic flux evolution and coronal heating by modeling the hydrodynamics of individual field lines with the Enthalpy-based Thermal Evolution of Loops (EBTEL) model including steady heating scaled as the ratio of the average field strength and the length (B/L). We find that steady heating is able to partially reproduce the EUV radiance - magnetic flux relationships and their observed temporal evolution. We also discuss how time-dependent heating may be able to explain the remaining discrepancies. This study demonstrates that combined models of magnetic flux transport, magnetic topology and heating can yield realistic estimates for the decay of active region radiances with time.

  11. Revisiting the fundamental properties of Cepheid Polaris using detailed stellar evolution models

    CERN Document Server

    Neilson, Hilding R

    2014-01-01

    Polaris the Cepheid has been observed for centuries, presenting surprises and changing our view of Cepheids and stellar astrophysics, in general. Specifically, understanding Polaris helps anchor the Cepheid Leavitt law, but the distance must be measured precisely. The recent debate regarding the distance to Polaris has raised questions about its role in calibrating the Leavitt law and even its evolutionary status. In this work, I present new stellar evolution models of Cepheids to compare with previously measured CNO abundances, period change and angular diameter. Based on the comparison, I show that Polaris cannot be evolving along the first crossing of the Cepheid instability strip and cannot have evolved from a rapidly-rotating main sequence star. As such, Polaris must also be at least 118 pc away and pulsates in the first overtone, disagreeing with the recent results of Turner et al. (2013).

  12. Bovine respiratory disease model based on dual infections with infection with bovine viral diarrhea virus and bovine corona virus

    Science.gov (United States)

    Bovine respiratory disease complex (BRDC) is the leading cause of economic loss in the U.S. cattle industry. BRDC likely results from simultaneous or sequential infections with multiple pathogens including both viruses and bacteria. Bovine viral diarrhea virus (BVDV) and bovine corona virus (BoCV...

  13. A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones

    CERN Document Server

    Pietrinferni, A; Salaris, M; Castelli, F

    2004-01-01

    We present a large and updated stellar evolution database for low-, intermediate- and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite stellar populations using population synthesis techniques. The stellar mass range is between \\sim0.5Mo and 10Mo with a fine mass spacing. The metallicity [Fe/H] comprises 10 values ranging from -2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y=0.245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Delta Y/Delta Z\\sim 1.4. For each adopted chemical composition, the evolutionary models have been computed without and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. The whole set of evolutionary models can be used to compute isochrones in a wide age range, from \\sim30 Myr to \\sim15Gyr. Both evolutionary tracks and isochrones are available in several observational planes, emp...

  14. Modelling stellar proton event-induced particle radiation dose on close-in exoplanets

    Science.gov (United States)

    Atri, Dimitra

    2017-02-01

    Kepler observations have uncovered the existence of a large number of close-in exoplanets and serendipitously of stellar superflares with emissions several orders of magnitude higher than those observed on the Sun. The interaction between the two and their implications on planetary habitability are of great interest to the community. Stellar proton events (SPEs) interact with planetary atmospheres, generate secondary particles and increase the radiation dose on the surface. This effect is amplified for close-in exoplanets and can be a serious threat to potential planetary life. Monte Carlo simulations are used to model the SPE-induced particle radiation dose on the surface of such exoplanets. The results show a wide range of surface radiation doses on planets in close-in configurations with varying atmospheric column depths, magnetic moments and orbital radii. It can be concluded that for close-in exoplanets with sizable atmospheres and magnetospheres, the radiation dose contributed by stellar superflares may not be high enough to sterilize a planet (for life as we know it) but can result in frequent extinction level events. In light of recent reports, the interaction of hard-spectrum SPEs with the atmosphere of Proxima Centauri b is modelled and their implications on its habitability are discussed.

  15. Dynamical Modelling of the Galactic Bulge and Bar: Pattern Speed, Stellar, and Dark Matter Mass Distributions

    CERN Document Server

    Portail, Matthieu; Wegg, Christopher; Ness, Melissa

    2016-01-01

    We construct a large set of dynamical models of the galactic bulge, bar and inner disk using the Made-to-Measure method. Our models are constrained to match the red clump giant density from a combination of the VVV, UKIDSS and 2MASS infrared surveys together with stellar kinematics in the bulge from the BRAVA and OGLE surveys, and in the entire bar region from the ARGOS survey. We are able to recover the bar pattern speed and the stellar and dark matter mass distributions in the bar region, thus recovering the entire galactic effective potential. We find a bar pattern speed of $39.0 \\pm 3.5 \\,\\rm{km\\,s^{-1}\\,kpc^{-1}}$, placing the bar corotation radius at $6.1 \\pm 0.5 \\, \\rm{kpc}$ and making the Milky Way bar a typical fast rotator. We evaluate the stellar mass of the long bar and bulge structure to be $M_{\\rm{bar/bulge}} = 1.88 \\pm 0.12 \\times 10^{10} \\, \\rm{M}_{\\odot}$, larger than the mass of disk in the bar region, $M_{\\rm{inner\\ disk}} = 1.29\\pm0.12 \\times 10^{10} \\, \\rm{M}_{\\odot}$. The total dynamical...

  16. Disease specific protein corona

    Science.gov (United States)

    Rahman, M.; Mahmoudi, M.

    2015-03-01

    It is now well accepted that upon their entrance into the biological environments, the surface of nanomaterials would be covered by various biomacromolecules (e.g., proteins and lipids). The absorption of these biomolecules, so called `protein corona', onto the surface of (nano)biomaterials confers them a new `biological identity'. Although the formation of protein coronas on the surface of nanoparticles has been widely investigated, there are few reports on the effect of various diseases on the biological identity of nanoparticles. As the type of diseases may tremendously changes the composition of the protein source (e.g., human plasma/serum), one can expect that amount and composition of associated proteins in the corona composition may be varied, in disease type manner. Here, we show that corona coated silica and polystyrene nanoparticles (after interaction with in the plasma of the healthy individuals) could induce unfolding of fibrinogen, which promotes release of the inflammatory cytokines. However, no considerable releases of inflammatory cytokines were observed for corona coated graphene sheets. In contrast, the obtained corona coated silica and polystyrene nanoparticles from the hypofibrinogenemia patients could not induce inflammatory cytokine release where graphene sheets do. Therefore, one can expect that disease-specific protein coronas can provide a novel approach for applying nanomedicine to personalized medicine, improving diagnosis and treatment of different diseases tailored to the specific conditions and circumstances.

  17. Polarized Light from the Sun: Unification of the Corona and Analysis of the Second Solar Spectrum — Further Implications of a Liquid Metallic Hydrogen Solar Model

    Directory of Open Access Journals (Sweden)

    Robitaille P.-M.

    2015-07-01

    Full Text Available In order to account for the slight polarization of the continuum towards the limb, propo- nents of the Standard Solar Model (SSM must have recourse to electron or hydrogen- based scattering of light, as no other mechanism is possible in a gaseous Sun. Con- versely, acceptance that the solar body is comprised of condensed matter opens up new avenues in the analysis of this problem, even if the photospheric surface itself is viewed as incapable of emitting polarized light. Thus, the increased disk polarization, from the center to the limb, can be explained by invoking the scattering of light by the at- mosphere above the photosphere. The former is reminiscent of mechanisms which are known to account for the polarization of sunlight in the atmosphere of the Earth. Within the context of the Liquid Metallic Hydrogen Solar Model (LMHSM, molecules and small particles, not electrons or hydrogen atoms as required by the SSM, would primarily act as scattering agents in regions also partially comprised of condensed hy- drogen structures (CHS. In addition, the well-known polarization which characterizes the K-corona would become a sign of emission polarization from an anisotropic source, without the need for scattering. In the LMHSM, the K, F, and T- coronas can be viewed as emissive and reflective manifestations of a single corona l entity adopting a radially anisotropic structure, while slowly cooling with altitude above the photosphere. The presence of “dust particles”, advanced by proponents of the SSM, would no longer be required to explain the F and T-corona, as a single cooling structure would account for the properties of the K, F, and T coronas. At the same time, the polarized “Second Solar Spectrum”, characterized by the dominance of certain elemental or ionic spectral lines and an abundance of molecular lines, could be explained in the LMHSM, by first invoking interface polarization and coordination of these species with condensed matter

  18. Nonlinear Force-Free Magnetic Field Modeling of the Solar Corona: A Critical Assessment

    Science.gov (United States)

    De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.; Lites, B. W.; Aschwanden, M. J.; McTiernan, J. M.; Régnier, S.; Thalmann, J.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung, M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T.

    2008-12-01

    Nonlinear force-free field (NLFFF) modeling promises to provide accurate representations of the structure of the magnetic field above solar active regions, from which estimates of physical quantities of interest (e.g., free energy and helicity) can be made. However, the suite of NLFFF algorithms have so far failed to arrive at consistent solutions when applied to cases using the highest-available-resolution vector magnetogram data from Hinode/SOT-SP (in the region of the modeling area of interest) and line-of-sight magnetograms from SOHO/MDI (where vector data were not been available). It is our view that the lack of robust results indicates an endemic problem with the NLFFF modeling process, and that this process will likely continue to fail until (1) more of the far-reaching, current-carrying connections are within the observational field of view, (2) the solution algorithms incorporate the measurement uncertainties in the vector magnetogram data, and/or (3) a better way is found to account for the Lorentz forces within the layer between the photosphere and coronal base. In light of these issues, we conclude that it remains difficult to derive useful and significant estimates of physical quantities from NLFFF models.

  19. Corona SDK hotshot

    CERN Document Server

    Flanagan, Nevin

    2013-01-01

    Using a project based approach you will learn the coolest aspects of Corona SDK development. Each project contains step bystep explanations, diagrams, screenshots, and downloadable materials.This book is for users who already have completed at least one simple app using Corona and are familiar with mobile development using another platform and have done Lua programming in another context. Knowledge of the basic functions of Corona routines, as well as an understanding of the Lua programming language's syntax and common libraries, is assumed throughout.

  20. The Cannon 2: A data-driven model of stellar spectra for detailed chemical abundance analyses

    CERN Document Server

    Casey, Andrew R; Ness, Melissa; Rix, Hans-Walter; Ho, Anna Q Y; Gilmore, Gerry

    2016-01-01

    We have shown that data-driven models are effective for inferring physical attributes of stars (labels; Teff, logg, [M/H]) from spectra, even when the signal-to-noise ratio is low. Here we explore whether this is possible when the dimensionality of the label space is large (Teff, logg, and 15 abundances: C, N, O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Mn, Fe, Ni) and the model is non-linear in its response to abundance and parameter changes. We adopt ideas from compressed sensing to limit overall model complexity while retaining model freedom. The model is trained with a set of 12,681 red-giant stars with high signal-to-noise spectroscopic observations and stellar parameters and abundances taken from the APOGEE Survey. We find that we can successfully train and use a model with 17 stellar labels. Validation shows that the model does a good job of inferring all 17 labels (typical abundance precision is 0.04 dex), even when we degrade the signal-to-noise by discarding ~50% of the observing time. The model dependencie...

  1. Evolutionary stellar population synthesis with MILES - II. Scaled-solar and \\alpha-enhanced models

    CERN Document Server

    Vazdekis, A; Cassisi, S; Ricciardelli, E; Falcón-Barroso, J; Sánchez-Blázquez, P; La Barbera, F; Beasley, M A; Pietrinferni, A

    2015-01-01

    We present models that predict spectra of old- and intermediate-aged stellar populations at 2.51\\AA\\ (FWHM) with varying [\\alpha/Fe] abundance. The models are based on the MILES library and on corrections from theoretical stellar spectra. The models employ recent [Mg/Fe] determinations for the MILES stars and BaSTI scaled-solar and \\alpha-enhanced isochrones. We compute models for a suite of IMF shapes and slopes, covering a wide age/metallicity range. Using BaSTI, we also compute "base models" matching The Galactic abundance pattern. We confirm that the \\alpha-enhanced models show a flux excess with respect to the scaled-solar models blue-ward $\\sim$4500\\AA, which increases with age and metallicity. We also confirm that both [MgFe] and [MgFe]' indices are [\\alpha/Fe]-insensitive. We show that the sensitivity of the higher order Balmer lines to [\\alpha/Fe] resides in their pseudo-continua, with narrower index definitions yielding lower sensitivity. We confirm that the \\alpha-enhanced models yield bluer (redde...

  2. Modelling the Global Solar Corona II: Coronal Evolution and Filament Chirality Comparison

    CERN Document Server

    Yeates, A R; Van Ballegooijen, A A

    2007-01-01

    The hemispheric pattern of solar filaments is considered using newly-developed simulations of the real photospheric and 3D coronal magnetic fields over a 6-month period, on a global scale. The magnetic field direction in the simulation is compared directly with the chirality of observed filaments, at their observed locations. In our model the coronal field evolves through a continuous sequence of nonlinear force-free equilibria, in response to the changing photospheric boundary conditions and the emergence of new magnetic flux. In total 119 magnetic bipoles with properties matching observed active regions are inserted. These bipoles emerge twisted and inject magnetic helicity into the solar atmosphere. When we choose the sign of this active-region helicity to match that observed in each hemisphere, the model produces the correct chirality for up to 96% of filaments, including exceptions to the hemispheric pattern. If the emerging bipoles have zero helicity, or helicity of the opposite sign, then this percenta...

  3. Modeling the Corona and Solar Wind using ADAPT Maps that Include Far-Side Observations

    Science.gov (United States)

    2013-11-01

    document for any purpose other than Government procurement does not in any way obligate the U.S. Government. The fact that the Government formulated...Government’s approval or disapproval of its ideas or findings. Approved for public release; distribution is unlimited. REPORT DOCUMENTATION PAGE...Los Alamos National Laboratory ( LANL ) and the National Solar Observatory (NSO), has developed a model that produces more realistic estimates of the

  4. Progress of Solar Corona Study in China

    Institute of Scientific and Technical Information of China (English)

    ZHAO Xinhua; SONG Wenbin

    2008-01-01

    Solar corona study is an important aspect of space weather research.In recent years,great achieVements have been acquired on the solar corona study by the space physics group of China.This paper gives a brief outline of these progresses that have been made during 2006--2008.This kind of research includes observational study of the corona,theoretical investigations,statistical analysis based on a large number of data sets,numerical method for MHD modeling,numerical study of space weather events,and prediction methods for the complicated processes originating from the solar corona.Each is given as a separate part in the following.

  5. UV-extended E-MILES stellar population models: young components in massive early-type galaxies

    Science.gov (United States)

    Vazdekis, A.; Koleva, M.; Ricciardelli, E.; Röck, B.; Falcón-Barroso, J.

    2016-12-01

    We present UV-extended E-MILES stellar population synthesis models covering the spectral range λλ 1680-50 000 Å at moderately high resolution. We employ the NGSL space-based stellar library to compute spectra of single-age, single-metallicity stellar populations in the wavelength range from 1680 to 3540 Å. These models represent a significant improvement in resolution and age/metallicity coverage over previous studies based on earlier space-based libraries. These model spectra were joined with those we computed in the visible using MILES, and other empirical libraries for redder wavelengths. The models span the metallicity range -1.79≤ [M/H]≤ +0.26 and ages above 30 Myr, for a suite of initial mass function types with varying slopes. We focus on the behaviour of colours, spectra and line-strength indices in the UV range as a function of relevant stellar population parameters. Whereas some indices strengthen with increasing age and metallicity, as most metallicity indicators in the visible, other indices peak around 3 Gyr for metal-rich stellar populations, such as Mg at 2800 Å. Our models provide reasonably good fits to the integrated colours and most line strengths of the stellar clusters of the Milky Way and Large Magellanic Cloud. Our full spectrum fits in the UV range for a representative set of early-type galaxies (ETGs) of varying mass yield age and metallicity estimates in very good agreement with those obtained in the optical range. The comparison of UV colours and line strengths of massive ETGs with our models reveals the presence of young stellar components, with ages in the range 0.1-0.5 Gyr and mass fractions 0.1-0.5 per cent, on the top of an old stellar population.

  6. The Surface of Stellar Models - Now with more 3D simulations!

    Directory of Open Access Journals (Sweden)

    Trampedach Regner

    2015-01-01

    Full Text Available We have constructed a grid of 3D hydrodynamic simulations of deep convective and line-blanketed atmospheres. We have developed a new consistent method for computing and employing T(τ relations from these simulations, as surface boundary conditions for 1D stellar structure models. These 1D models have, in turn, had their mixing-length, α, calibrated against the averaged structure of each of the simulations. Both α and T(τ vary significantly with Teff and log g.

  7. Excitation of Solar-like Oscillations: From PMS to MS Stellar Models

    Indian Academy of Sciences (India)

    R. Samadi; M.-J. Goupil; E. Alecian; F. Baudin; D. Georgobiani; R. Trampedach; R. Stein; Å. Nordlund

    2005-06-01

    The amplitude of solar-like oscillations results from a balance between excitation and damping. As in the sun, the excitation is attributed to turbulent motions that stochastically excite the modes in the uppermost part of the convective zone. We present here a model for the excitation mechanism. Comparisons between modeled amplitudes and helio and stellar seismic constraints are presented and the discrepancies discussed. Finally the possibility and the interest of detecting such stochastically excited modes in pre-main sequence stars are also discussed.

  8. Observations and modeling of the fine structure of loops in the transition region and corona

    Science.gov (United States)

    Brooks, David

    2017-08-01

    The physical dimensions of loops hold important clues to the coronal heating process. Theoretical arguments universally indicate that coronal heating should operate on very small spatial scales and loops should be unresolvable by current instrumentation. There are a number of observational results, however, that suggest that coronal loops are organized on spatial scales of several hundred km. For example, recent observations from IRIS have discovered a new class of low-lying dynamic loops structures, and it has been argued that they are the long-postulated unresolved fine structures (UFS) that dominate the emission of the solar transition region. Here we show that the properties of the UFS (intensities, lengths, widths, lifetimes) are consistent with 1-D non-equilibrium ionization simulations of an impulsively heated single strand, suggesting that they are resolved, and that the distribution of UFS widths implies that like coronal loops they are also structured on a spatial scale of a few hundred km. Spatial scales of a few hundred kilometers appear to be typical for a range of chromospheric and coronal structures, but it is unclear whether the true distribution of loop widths is normalized around this scale, or whether it extends to much smaller scales - perhaps by a power-law - below the resolution of current instruments. We have extended our previous modeling of the cross-field intensity profiles of coronal loops observed by EIS and AIA, to investigate what the modeled profiles would look like at Hi-C resolution, what they would look like if loops are composed only of temperatures and densities, and the intensity profiles from the power-law simulations are dominated by emission from the largest strands.

  9. Accelerated complete-linearization method for calculating NLTE model stellar atmospheres

    Science.gov (United States)

    Hubeny, I.; Lanz, T.

    1992-01-01

    Two approaches to accelerating the method of complete linearization for calculating NLTE model stellar atmospheres are suggested. The first one, the so-called Kantorovich variant of the Newton-Raphson method, consists of keeping the Jacobi matrix of the system fixed, which allows us to calculate the costly matrix inversions only a few times and then keep them fixed during the subsequent computations. The second method is an application of the Ng acceleration. Both methods are extremely easy to implement with any model atmosphere code based on complete linearization. It is demonstrated that both methods, and especially their combination, yield a rapidly and globally convergent algorithm, which takes 2 to 5 times less computer time, depending on the model at hand and the required accuracy, than the ordinary complete linearization. Generally, the time gain is more significant for more complicated models. The methods were tested for a broad range of atmospheric parameters, and in all cases they exhibited similar behavior. Ng acceleration applied on the Kantorovich variant thus offers a significant improvement of the standard complete-linearization method, and may now be used for calculating relatively involved NLTE model stellar atmospheres.

  10. Measuring diffuse interstellar bands with cool stars. Improved line lists to model background stellar spectra

    Science.gov (United States)

    Monreal-Ibero, A.; Lallement, R.

    2017-03-01

    Context. Diffuse stellar bands (DIBs) are ubiquitous in stellar spectra. Traditionally, they have been studied through their extraction from hot (early-type) stars because of their smooth continuum. In an era in which there are several ongoing or planned massive Galactic surveys using multi-object spectrographs, cool (late-type) stars constitute an appealing set of targets. However, from the technical point of view, the extraction of DIBs in their spectra is more challenging because of the complexity of the continuum. Aims: In this contribution we provide the community with an improved set of stellar lines in the spectral regions associated with the strong DIBs at λ6196.0, λ6269.8, λ6283.8, and λ6379.3. These lines allow for the creation of better stellar synthetic spectra, reproducing the background emission and a more accurate extraction of the magnitudes associated with a given DIB (e.g., equivalent width, radial velocity). Methods: The Sun and Arcturus were used as representative examples of dwarf and giant stars, respectively. A high quality spectrum for each of them was modeled using TURBOSPECTRUM and the Vienna Atomic Line Database (VALD) stellar line list. The oscillator strength log (gf) and wavelength of specific lines were modified to create synthetic spectra in which the residuals in both the Sun and Arcturus were minimized. Results: The TURBOSPECTRUM synthetic spectra, based on improved line lists, reproduce the observed spectra for the Sun and Arcturus in the mentioned spectral ranges with greater accuracy. Residuals between the synthetic and observed spectra are always ≲10%, which is much better than residuals with previously existing options. We tested the new line lists with some characteristic spectra from a variety of stars, including both giant and dwarf stars, and under different degrees of extinction. As occurred with the Sun and Arcturus, residuals in the fits used to extract the DIB information are smaller when using synthetic spectra

  11. VizieR Online Data Catalog: Stellar models until He burning - III. (Claret+, 1997)

    Science.gov (United States)

    Claret, A.

    1997-04-01

    In this Paper I present grids for the stellar models with a slightly higher metallic content than in the previous works (Claret, 1995A&AS..109..441C; Claret & Gimenez, 1995A&AS..114..549C), say, Z=0.03. The initial helium abundances in mass are Yi=0.42, 0.32 and 0.22; this last value was used only to facilitate interpolations since it is a little bit smaller than the primordial helium abundance. The present computations are based on the radiative opacities with spin-orbi t coupling provided by the Lawrence Livermore group (Iglesias et al., 1992ApJ...397..771I). For the lower temperatures I have used the results by Alexander (1992, priv. comm.). Core overshooting was taken into account as well as mass loss. The models presented here cover the mass range between 1 and 40M⊙. I also compute for all models the internal structure constants kj and the radius of gyration β. For the first time the calculation of the tidal constants E2 and λ2, which are used to evaluate circularization and synchronization times in binary stars, are presented for stellar models as a function of the initial mass and time. The former is related with the dynamical tidal contribution to the total perturbed potential in a binary star while the latter is connected with the external structure of the outer layers. (1 data file).

  12. Modelling of intermediate-age stellar populations III Effects of dust-shells around AGB stars

    CERN Document Server

    Mouhcine, M

    2002-01-01

    In this paper,we present single stellar population models of intermediate age stellar populations where dust-enshrouded AGB stars are introduced. The formation of carbon stars is also accounted for, and is taken to be a function of both initial mass and metallicity. The effect of the dusty envelopes around AGB stars on the optical/near-infrared spectral energy distribution were introduced using semi-emipirical models where the mass-loss and the photospheric chemistry determine the spectral properties of a star along the AGB sequence. The spectral dichotomy between O-rich stars and C-rich stars is taken into account in the modelling. We have investigated the AGB sequence morphology in he near-infrared CMD as a function of time and metallicity. We show that this diaggram is characterized by three morphological features, occupied by optically bright O-rich stars, optically bright C-rich stars, and dust-enshrouded O-rich and C-rich stars respectively. Our models are able to reproduce the distribution of the three...

  13. Stellar abundance analyses in the light of 3D hydrodynamical model atmospheres

    CERN Document Server

    Asplund, M

    2003-01-01

    I describe recent progress in terms of 3D hydrodynamical model atmospheres and 3D line formation and their applications to stellar abundance analyses of late-type stars. Such 3D studies remove the free parameters inherent in classical 1D investigations (mixing length parameters, macro- and microturbulence) yet are highly successful in reproducing a large arsenal of observational constraints such as detailed line shapes and asymmetries. Their potential for abundance analyses is illustrated by discussing the derived oxygen abundances in the Sun and in metal-poor stars, where they seem to resolve long-standing problems as well as significantly alter the inferred conclusions.

  14. Low Mach and Peclet number limit for a model of stellar tachocline and upper radiative zones

    Directory of Open Access Journals (Sweden)

    Donatella Donatelli

    2016-09-01

    Full Text Available We study a hydrodynamical model describing the motion of internal stellar layers based on compressible Navier-Stokes-Fourier-Poisson system. We suppose that the medium is electrically charged, we include energy exchanges through radiative transfer and we assume that the system is rotating. We analyze the singular limit of this system when the Mach number, the Alfven number, the Peclet number and the Froude number approache zero in a certain way and prove convergence to a 3D incompressible MHD system with a stationary linear transport equation for transport of radiation intensity. Finally, we show that the energy equation reduces to a steady equation for the temperature corrector.

  15. Self-consistent models of quasi-relaxed rotating stellar systems

    CERN Document Server

    Varri, A L

    2012-01-01

    Two new families of self-consistent axisymmetric truncated equilibrium models for the description of quasi-relaxed rotating stellar systems are presented. The first extends the spherical King models to the case of solid-body rotation. The second is characterized by differential rotation, designed to be rigid in the central regions and to vanish in the outer parts, where the energy truncation becomes effective. The models are constructed by solving the nonlinear Poisson equation for the self-consistent mean-field potential. For rigidly rotating configurations, the solutions are obtained by an asymptotic expansion on the rotation strength parameter. The differentially rotating models are constructed by means of an iterative approach based on a Legendre series expansion of the density and the potential. The two classes of models exhibit complementary properties. The rigidly rotating configurations are flattened toward the equatorial plane, with deviations from spherical symmetry that increase with the distance f...

  16. Hydrodynamical model atmospheres: Their impact on stellar spectroscopy and asteroseismology of late-type stars

    CERN Document Server

    Ludwig, Hans-G

    2016-01-01

    Hydrodynamical, i.e. multi-dimensional and time-dependent, model atmospheres of late-type stars have reached a high level of realism. They are commonly applied in high-fidelity work on stellar abundances but also allow the study of processes that are not modelled in standard, one-dimensional hydrostatic model atmospheres. Here, we discuss two observational aspects that emerge from such processes, the photometric granulation background and the spectroscopic microturbulence. We use CO5BOLD hydrodynamical model atmospheres to characterize the total granular brightness fluctuations and characteristic time scale for FGK stars. Emphasis is put on the diagnostic potential of the granulation background for constraining the fundamental atmospheric parameters. We find a clear metallicity dependence of the granulation background. The comparison between the model predictions and available observational constraints at solar metallicity shows significant differences, that need further clarification. Concerning microturbule...

  17. Testing spectral models for stellar populations with star clusters: II. Results

    CERN Document Server

    Delgado, Rosa M Gonzalez

    2009-01-01

    High spectral resolution evolutionary synthesis models have become a routinely used ingredient in extragalactic work, and as such deserve thorough testing. Star clusters are ideal laboratories for such tests. This paper applies the spectral fitting methodology outlined in Paper I to a sample of clusters, mainly from the Magellanic Clouds and spanning a wide range in age and metallicity, fitting their integrated light spectra with a suite of modern evolutionary synthesis models for single stellar population. The combinations of model plus spectral library employed in this investigation are Galaxev/STELIB, Vazdekis/MILES, SED@/GRANADA, and Galaxev/MILES+GRANADA, which provide a representative sample of models currently available for spectral fitting work. A series of empirical tests are performed with these models, comparing the quality of the spectral fits and the values of age, metallicity and extinction obtained with each of them. A comparison is also made between the properties derived from these spectral f...

  18. Single stars in the Hyades open cluster. Fiducial sequence for testing stellar and atmospheric models

    Science.gov (United States)

    Kopytova, Taisiya G.; Brandner, Wolfgang; Tognelli, Emanuele; Prada Moroni, Pier Giorgio; Da Rio, Nicola; Röser, Siegfried; Schilbach, Elena

    2016-01-01

    Context. Age and mass determinations for isolated stellar objects remain model-dependent. While stellar interior and atmospheric theoretical models are rapidly evolving, we need a powerful tool to test them. Open clusters are good candidates for this role. Aims: We aim to create a fiducial sequence of stellar objects for testing stellar and atmospheric models. Methods: We complement previous studies on the Hyades multiplicity by Lucky Imaging observations with the AstraLux Norte camera. This allows us to exclude possible binary and multiple systems with companions outside a 2-7 AU separation and to create a single-star sequence for the Hyades. The sequence encompasses 250 main-sequence stars ranging from A5V to M6V. Using the Tool for Astrophysical Data Analysis (TA-DA), we create various theoretical isochrones applying different combinations of interior and atmospheric models. We compare the isochrones with the observed Hyades single-star sequence on J vs. J-Ks, J vs. J-H, and Ks vs. H-Ks color-magnitude diagrams. As a reference we also compute absolute fluxes and magnitudes for all stars from X-ray to mid-infrared based on photometric measurements available in the literature(ROSAT X-ray, GALEX UV, APASS gri, 2MASS JHKs, and WISE W1 to W4). Results: We find that combinations of both PISA and DARTMOUTH stellar interior models with BT-Settl 2010 atmospheric models describe the observed sequence well. We use PISA in combination with BT-Settl 2010 models to derive theoretical predictions for physical parameters (Teff, mass, log g) of 250 single stars in the Hyades. The full sequence covers the mass range of 0.13-2.30 M⊙, and effective temperatures between 3060 K and 8200 K. Conclusions: Within the measurement uncertainties, the current generation of models agree well with the single-star sequence. The primary limitations are the uncertainties in the measurement of the distances to individual Hyades members, and uncertainties in the photometry. Gaia parallaxes

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

    Science.gov (United States)

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

    2011-07-01

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

  20. Cepheid models based on self-consistent stellar evolution and pulsation calculations the right answer?

    CERN Document Server

    Baraffe, I; Méra, D; Chabrier, G; Beaulieu, J P

    1998-01-01

    We have computed stellar evolutionary models for stars in a mass range characteristic of Cepheid variables ($3stellar evolution calculations are coupled to a linear non adiabatic stability analysis to get self-consistent mass-period-luminosity relations. The period - luminosity relation as a function of metallicity is analysed and compared to the recent EROS observations in the Magellanic Clouds. The models reproduce the observed width of the instability strips for the SMC and LMC. We determine a statistical P-L relationship, taking into account the evolutionary timescales and a mass distribution given by a Salpeter mass function. Excellent agreement is found with the SMC PL relationship determined by Sasselov et al. (1997). The models reproduce the change of slope in the P-L relationship near $P\\sim 2.5$ days discovered recently by the EROS collaboration (Bauer 1997; Bauer et al. 1998) and ...

  1. A Stellar Population Synthesis Model for the Study of Ultraviolet Star Counts of the Galaxy

    CERN Document Server

    Pradhan, Ananta C; Robin, A C; Ghosh, S K; Vickers, John J

    2014-01-01

    GALEX, the first all sky imaging UV satellite, has imaged a large part of the sky providing an excellent opportunity for studying UV star counts. The aim of our study is to investigate in detail the observed UV star counts obtained by GALEX vis-a-vis the model simulated catalogs produced by the Besancon model of stellar population synthesis in various Galactic directions, and to explore the potential for studying the structure of our Galaxy from images in multiple NUV and FUV filters of the forthcoming Ultraviolet Imaging Telescope (UVIT) to be flown onboard ASTROSAT. We have upgraded the Besancon model of stellar population synthesis to include the UV bands of GALEX and UVIT. Depending on the availability of contiguous GALEX, SDSS, WISE and 2MASS overlapping regions, we have chosen a set of 19 GALEX fields which spread over a range of Galactic directions. We cross-matched GALEX sources with the WISE+2MASS and SDSS catalogs and UV stars in the GALEX catalog are identified by choosing a suitable IR colour, J -...

  2. Monte Carlo simulation of electrical corona discharge in air

    Energy Technology Data Exchange (ETDEWEB)

    Settaouti, A.; Settaouti, L. [Electrotechnic Department, University of Sciences and Technology, P.O. Box 1505, El-M' naouar, Oran (Algeria)

    2011-01-15

    Electrical discharges play a key role in technologies; there are many industrial applications where the corona discharge is used. Air as insulator is probably the best compromise solution for many applications. All of this reflects on the great importance of the evaluation of the corona performance characteristics. Numerical simulation of the corona discharge helps to better understand the involved phenomena and optimize the corona devices. This paper is aimed at calculating the corona discharge in negative point-plane air gaps. To describe the non-equilibrium behavior of the electronic avalanches and to simulate the development of corona discharge the method of Monte Carlo has been used. This model provides the spatial-temporal local field and particles charged densities variations as well as the ionization front velocity. (author)

  3. Identified Particle Spectra for Au+Au Collisions at $\\sqrt{s}$ = 200 GeV from STAR, PHENIX and BRAHMS in Comparison to Core-Corona Model Predictions

    CERN Document Server

    Schreiber, C; Aichelin, J

    2010-01-01

    The core-corona model describes quite successfully the centrality dependence of multiplicity and $$ of identified particles observed in heavy ion reaction at beam energies between $\\sqrt{s}$ = 17 GeV and 200 GeV. Also the centrality dependence of the elliptic flow, $v_2$, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single particle spectra of identified particles. We concentrate here on protons, antiprotons, kaons and pions which have all been measured by the PHENIX, STAR and BRAHMS collaborations. We find that an analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. For each experience the data agree well with the prediction of the core-corona model but the value of the two necessary parameters depends onthe experiments.

  4. Testing spectral models for stellar populations with star clusters - I. Methodology

    Science.gov (United States)

    Cid Fernandes, Roberto; González Delgado, Rosa M.

    2010-04-01

    High-resolution spectral models for simple stellar populations (SSP) developed in the past few years have become a standard ingredient in studies of stellar population of galaxies. As more such models become available, it becomes increasingly important to test them. In this and a companion paper, we test a suite of publicly available evolutionary synthesis models using integrated optical spectra in the blue-near-UV range of 27 well-studied star clusters from the work of Leonardi and Rose spanning a wide range of ages and metallicities. Most (23) of the clusters are from the Magellanic Clouds. This paper concentrates on the methodological aspects of spectral fitting. The data are fitted with SSP spectral models from Vazdekis and collaborators, based on the Medium-resolution INT Library of Empirical Spectra. Best-fitting and Bayesian estimates of age, metallicity and extinction are presented, and degeneracies between these parameters are mapped. We find that these models can match the observed spectra very well in most cases, with small formal uncertainties in t,Z and AV. In some cases, the spectral fits indicate that the models lack a blue old population, probably associated with the horizontal branch. This methodology, which is mostly based on the publicly available code STARLIGHT, is extended to other sets of models in Paper II, where a comparison with properties derived from spatially resolved data (colour-magnitude diagrams) is presented. The global aim of these two papers is to provide guidance to users of evolutionary synthesis models and empirical feedback to model makers.

  5. The evolution of planetary nebulae VII. Modelling planetary nebulae of distant stellar systems

    CERN Document Server

    Schönberner, D; Sandin, C; Steffen, M

    2010-01-01

    By means of hydrodynamical models we do the first investigations of how the properties of planetary nebulae are affected by their metal content and what can be learned from spatially unresolved spectrograms of planetary nebulae in distant stellar systems. We computed a new series of 1D radiation-hydrodynamics planetary nebulae model sequences with central stars of 0.595 M_sun surrounded by initial envelope structures that differ only by their metal content. At selected phases along the evolutionary path, the hydrodynamic terms were switched off, allowing the models to relax for fixed radial structure and radiation field into their equilibrium state with respect to energy and ionisation. The analyses of the line spectra emitted from both the dynamical and static models enabled us to systematically study the influence of hydrodynamics as a function of metallicity and evolution. We also recomputed selected sequences already used in previous publications, but now with different metal abundances. These sequences w...

  6. A class of exact isotropic solutions of Einstein's equations and relativistic stellar models in general relativity

    Science.gov (United States)

    Murad, Mohammad Hassan; Pant, Neeraj

    2014-03-01

    In this paper we have studied a particular class of exact solutions of Einstein's gravitational field equations for spherically symmetric and static perfect fluid distribution in isotropic coordinates. The Schwarzschild compactness parameter, GM/ c 2 R, can attain the maximum value 0.1956 up to which the solution satisfies the elementary tests of physical relevance. The solution also found to have monotonic decreasing adiabatic sound speed from the centre to the boundary of the fluid sphere. A wide range of fluid spheres of different mass and radius for a given compactness is possible. The maximum mass of the fluid distribution is calculated by using stellar surface density as parameter. The values of different physical variables obtained for some potential strange star candidates like Her X-1, 4U 1538-52, LMC X-4, SAX J1808.4-3658 given by our analytical model demonstrate the astrophysical significance of our class of relativistic stellar models in the study of internal structure of compact star such as self-bound strange quark star.

  7. Equilibrium Reconstructions with V3FIT and Current Evolution Modeling for 3-D Stellarator Plasmas

    Science.gov (United States)

    Schmitt, J. C.; Cianciosa, M.; Geiger, J.; Lazerson, S.

    2016-10-01

    V3FIT is a powerful equilibrium reconstruction tool for magnetic confinement fusion experiments which are inherently 3-D in nature (i.e. stellarators) or have 3-D components (tokamaks with 3-D shaping, reversed field pinches with helical states, etc). Here, we present details of the diagnostic modeling, constraints and the user interface for reconstructions of W7-X plasmas. For typical discharges during the OP1.1 run campaign of W7-X, the net toroidal current and current density profile do not reach steady-state. When modeling the current evolution in 3-D plasmas, both poloidal and toroidal currents are linked with both poloidal and toroidal fluxes. In contrast, in toroidally axisymmetric plasmas, the poloidal flux is linked only with the toroidal current and the toroidal current is linked only with the poloidal flux. Compared to an equivalently-sized axisymmetric configuration, the current diffusion in 3-D plasmas is enhanced, leading to a faster relaxation of the current profile to its steady-state. Implications for the time-evolution of the current and rotational transform profiles in stellarator plasmas are discussed. This work is supported by DoE Grant DE-SC00014529.

  8. Simple Stellar Population Modeling of Low S/N Galaxy Spectra and Quasar Host Galaxy Applications

    CERN Document Server

    Mosby, Gregory; Hooper, Eric; Wolf, Marsha; Sheinis, Andrew; Richards, Joseph

    2014-01-01

    To study the effect of supermassive black holes (SMBHs) on their host galaxies it is important to study the hosts when the SMBH is near its peak activity. A method to investigate the host galaxies of high luminosity quasars is to obtain optical spectra at positions offset from the nucleus where the relative contribution of the quasar and host are comparable. However, at these extended radii the galaxy surface brightness is often low (20-22 mag per arcsec$^{2}$) and the resulting spectrum might have such low S/N that it hinders analysis with standard stellar population modeling techniques. To address this problem we have developed a method that can recover galaxy star formation histories (SFHs) from rest frame optical spectra with S/N $\\sim$ 5~\\AA$^{-1}$. This method uses the statistical technique diffusion k-means to tailor the stellar population modeling basis set. Our diffusion k-means minimal basis set, composed of 4 broad age bins, is successful in recovering a range of galaxy SFHs. Additionally, using an...

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

    CERN Document Server

    Montes, G; Canto, J; Perez-Torres, M A; Alberdi, A

    2011-01-01

    Aims. The interaction of two isotropic stellar winds is studied in order to calculate the free-free emission from the wind collision region. The effects of the binary separation and the wind momentum ratio on the emission from the wind-wind interaction region are investigated. Methods. We developed a semi-analytical model for calculating the thermal emission from colliding stellar winds. Assuming radiative shocks for the compressed layer, which are expected in close binaries, we obtained the emission measure of the thin shell. Then, we computed the total optical depth along each line of sight to obtain the emission from the whole configuration. Results. Here, we present predictions of the free-free emission at radio frequencies from analytic, radiative shock models in colliding wind binaries. It is shown that the emission from the wind collision region mainly arises from the optically thick region of the compressed layer and scales as ~ D^{4/5}, where D is the binary separation. The predicted flux density fro...

  10. Testing stellar evolution models with the retired A star HD 185351

    CERN Document Server

    Hjørringgaard, Jakob G; White, Tim R; Huber, Daniel; Pope, Benjamin J S; Casagrande, Luca; Justesen, Anders B; Christensen-Dalsgaard, Jørgen

    2016-01-01

    The physical parameters of the retired A star HD 185351 were analysed in great detail by Johnson et al. (2014) using interferometry, spectroscopy and asteroseismology. Results from all independent methods are consistent with HD 185351 having a mass in excess of $1.5\\mathrm{M}_{\\odot}$. However, the study also showed that not all observational constraints could be reconciled in stellar evolutionary models, leading to mass estimates ranging from $\\sim 1.6-1.9\\mathrm{M}_{\\odot}$ and casting doubts on the accuracy of stellar properties determined from asteroseismology. Here we solve this discrepancy and construct a theoretical model in agreement with all observational constraints on the physical parameters of HD 185351. The effects of varying input physics are examined as well as considering the additional constraint of the observed g-mode period spacing. This quantity is found to be sensitive to the inclusion of additional mixing from the convective core during the main sequence, and can be used to calibrate the...

  11. Absolute masses and radii determination in multiplanetary systems without stellar models

    CERN Document Server

    Almenara, J M; Mardling, R; Barros, S C C; Damiani, C; Bruno, G; Bonfils, X; Deleuil, M

    2015-01-01

    The masses and radii of extrasolar planets are key observables for understanding their interior, formation and evolution. While transit photometry and Doppler spectroscopy are used to measure the radii and masses respectively of planets relative to those of their host star, estimates for the true values of these quantities rely on theoretical models of the host star which are known to suffer from systematic differences with observations. When a system is composed of more than two bodies, extra information is contained in the transit photometry and radial velocity data. Velocity information (finite speed-of-light, Doppler) is needed to break the Newtonian $MR^{-3}$ degeneracy. We performed a photodynamical modelling of the two-planet transiting system Kepler-117 using all photometric and spectroscopic data available. We demonstrate how absolute masses and radii of single-star planetary systems can be obtained without resorting to stellar models. Limited by the precision of available radial velocities (38 $ms^{...

  12. Stellar Structure Modeling using a Parallel Genetic Algorithm for Objective Global Optimization

    CERN Document Server

    Metcalfe, T S

    2002-01-01

    Genetic algorithms are a class of heuristic search techniques that apply basic evolutionary operators in a computational setting. We have designed a fully parallel and distributed hardware/software implementation of the generalized optimization subroutine PIKAIA, which utilizes a genetic algorithm to provide an objective determination of the globally optimal parameters for a given model against an observational data set. We have used this modeling tool in the context of white dwarf asteroseismology, i.e., the art and science of extracting physical and structural information about these stars from observations of their oscillation frequencies. The efficient, parallel exploration of parameter-space made possible by genetic-algorithm-based numerical optimization led us to a number of interesting physical results: (1) resolution of a hitherto puzzling discrepancy between stellar evolution models and prior asteroseismic inferences of the surface helium layer mass for a DBV white dwarf; (2) precise determination of...

  13. Ground-based observation of emission lines from the corona of a red-dwarf star.

    Science.gov (United States)

    Schmitt, J H; Wichmann, R

    2001-08-02

    All 'solar-like' stars are surrounded by coronae, which contain magnetically confined plasma at temperatures above 106 K. (Until now, only the Sun's corona could be observed in the optical-as a shimmering envelope during a total solar eclipse.) As the underlying stellar 'surfaces'-the photospheres-are much cooler, some non-radiative process must be responsible for heating the coronae. The heating mechanism is generally thought to be magnetic in origin, but is not yet understood even for the case of the Sun. Ultraviolet emission lines first led to the discovery of the enormous temperature of the Sun's corona, but thermal emission from the coronae of other stars has hitherto been detectable only from space, at X-ray wavelengths. Here we report the detection of emission from highly ionized iron (Fe XIII at 3,388.1 A) in the corona of the red-dwarf star CN Leonis, using a ground-based telescope. The X-ray flux inferred from our data is consistent with previously measured X-ray fluxes, and the non-thermal line width of 18.4 km s-1 indicates great similarities between solar and stellar coronal heating mechanisms. The accessibility and spectral resolution (45,000) of the ground-based instrument are much better than those of X-ray satellites, so a new window to the study of stellar coronae has been opened.

  14. Broad-band colours and overall photometric properties of template galaxy models from stellar population synthesis

    Science.gov (United States)

    Buzzoni, Alberto

    2005-08-01

    We present here a new set of evolutionary population synthesis models for template galaxies along the Hubble morphological sequence. The models, which account for the individual evolution of the bulge, disc, and halo components, provide basic morphological features, along with bolometric luminosity and colour evolution (including Johnson/Cousins, Gunn g, r, i, and Washington C, M, T1, T2 photometric systems) between 1 and 15 Gyr. The luminosity contribution from residual gas is also evaluated, both in terms of nebular continuum and Balmer-line enhancement. Our theoretical framework relies on the observed colours of present-day galaxies, coupled with a minimal set of physical assumptions related to simple stellar population (SSP) evolution theory, to constrain the overall distinctive properties of galaxies at earlier epochs. A comparison with more elaborate photometric models, and with empirical sets of reference spectral energy distributions (SEDs) for early- and late-type galaxies is accomplished, in order to test output reliability and investigate the internal uncertainty of the models. The match with observed colours of present-day galaxies tightly constrain the stellar birth rate, b, which smoothly increases from E to Im types. The comparison with the observed supernova (SN) rate in low-redshift galaxies shows, as well, a pretty good agreement, and allows us to tune up the inferred star formation activity and the SN and hypernova rates among the different galaxy morphological types. Among others, these results could find useful application also in cosmological studies, given for instance the claimed relationship between hypernova events and gamma-ray bursts. One outstanding feature of the back-in-time evolution model is the prevailing luminosity contribution of the bulge at early epochs. As a consequence, the current morphological look of galaxies might drastically change when moving to larger distances, and we discuss here how sensibly this bias could affect

  15. Gids of rotating stellar models with masses between 1.0 and 3.0 M⊙

    Institute of Scientific and Technical Information of China (English)

    Wu-Ming Yang; Shao-Lan Bi; Xiang-Cun Meng

    2013-01-01

    We calculated a grid of evolutionary tracks of rotating models with masses between 1.0 and 3.0 M⊙ and resolution δM ≤ 0.02 M⊙,which can be used to study the effects of rotation on stellar evolution and on the characteristics of star clusters.The value of ~ 2.05 M⊙ is a critical mass for the effects of rotation on stellar structure and evolution.For stars with M > 2.05 M⊙,rotation leads to an increase in the convective core and prolongs their lifetime on the main sequence (MS); rotating models evolve more slowly than non-rotating ones; the effects of rotation on the evolution of these stars are similar to those of convective core overshooting.However for stars with 1.1 < M/M⊙ < 2.05,rotation results in a decrease in the convective core and shortens the duration of the MS stage; rotating models evolve faster than non-rotating ones.When the mass has values in the range ~ 1.7-2.0 M⊙,the mixing caused by rotationally induced instabilities is not efficient; the hydrostatic effects dominate processes associated with the evolution of these stars.For models with masses between about 1.6 and 2.0 M⊙,rotating models always exhibit lower effective temperatures than non-rotating ones at the same age during the MS stage.For a given age,the lower the mass,the smaller the change in the effective temperature.Thus rotations could lead to a color spread near the MS turnoff in the color-magnitude diagram for intermediate-age star clusters.

  16. A Grid of MHD Models for Stellar Mass Loss and Spin-down Rates of Solar Analogs

    CERN Document Server

    Cohen, Ofer

    2013-01-01

    Stellar winds are believed to be the dominant factor in spin down of stars over time. However, stellar winds of solar analogs are poorly constrained due to the challenges in observing them. A great improvement has been made in the last decade in our understanding of the mechanisms responsible for the acceleration of the solar wind and in the development of numerical models for solar and stellar winds. In this paper, we present a grid of Magnetohydrodynamic (MHD) models to study and quantify the values of stellar mass-loss and angular momentum loss rates as a function of the stellar rotation period, magnetic dipole component, and coronal base density. We derive simple scaling laws for the loss rates as a function of these parameters, and constrain the possible mass-loss rate of stars with thermally-driven winds. Despite the success of our scaling law in matching the results of the model, we find a deviation between the "solar dipole" case and a real case based on solar observations that overestimates the actua...

  17. Electro-hydrodynamics and kinetic modelling of polluted air flow activated by multi-tip-to-plane corona discharge

    Energy Technology Data Exchange (ETDEWEB)

    Meziane, M.; Eichwald, O.; Ducasse, O.; Marchal, F. [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), Toulouse Cedex 9 F-31062 (France); Sarrette, J. P.; Yousfi, M. [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), Toulouse Cedex 9 F-31062 (France); CNRS, LAPLACE, Toulouse F-31062 (France)

    2013-04-21

    The present paper is devoted to the 2D simulation of an Atmospheric Corona Discharge Reactor (ACDR) involving 10 pins powered by a DC high voltage and positioned 7 mm above a grounded metallic plane. The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz. The simulation involves the electro-dynamic, chemical kinetic, and neutral gas hydrodynamic phenomena that influence the kinetics of the chemical species transformation. Each discharge stage (including the primary and the secondary streamers development and the resulting thermal shock) lasts about one hundred nanoseconds while the post-discharge stages occurring between two successive discharge phases last one hundred microseconds. The ACDR is crossed by a lateral air flow including 400 ppm of NO. During the considered time scale of 10 ms, one hundred discharge/post-discharge cycles are simulated. The simulation involves the radical formation and thermal exchange between the discharges and the background gas. The results show how the successive discharges activate the flow gas and how the induced turbulence phenomena affect the redistribution of the thermal energy and the chemical kinetics inside the ACDR.

  18. Electro-hydrodynamics and kinetic modelling of polluted air flow activated by multi-tip-to-plane corona discharge

    Science.gov (United States)

    Meziane, M.; Eichwald, O.; Sarrette, J. P.; Ducasse, O.; Yousfi, M.; Marchal, F.

    2013-04-01

    The present paper is devoted to the 2D simulation of an Atmospheric Corona Discharge Reactor (ACDR) involving 10 pins powered by a DC high voltage and positioned 7 mm above a grounded metallic plane. The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz. The simulation involves the electro-dynamic, chemical kinetic, and neutral gas hydrodynamic phenomena that influence the kinetics of the chemical species transformation. Each discharge stage (including the primary and the secondary streamers development and the resulting thermal shock) lasts about one hundred nanoseconds while the post-discharge stages occurring between two successive discharge phases last one hundred microseconds. The ACDR is crossed by a lateral air flow including 400 ppm of NO. During the considered time scale of 10 ms, one hundred discharge/post-discharge cycles are simulated. The simulation involves the radical formation and thermal exchange between the discharges and the background gas. The results show how the successive discharges activate the flow gas and how the induced turbulence phenomena affect the redistribution of the thermal energy and the chemical kinetics inside the ACDR.

  19. AN INTEGRATED MODEL FOR THE PRODUCTION OF X-RAY TIME LAGS AND QUIESCENT SPECTRA FROM HOMOGENEOUS AND INHOMOGENEOUS BLACK HOLE ACCRETION CORONAE

    Energy Technology Data Exchange (ETDEWEB)

    Kroon, John J.; Becker, Peter A., E-mail: jkroon@gmu.edu, E-mail: pbecker@gmu.edu [Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030-4444 (United States)

    2016-04-20

    Many accreting black holes manifest time lags during outbursts, in which the hard Fourier component typically lags behind the soft component. Despite decades of observations of this phenomenon, the underlying physical explanation for the time lags has remained elusive, although there are suggestions that Compton reverberation plays an important role. However, the lack of analytical solutions has hindered the interpretation of the available data. In this paper, we investigate the generation of X-ray time lags in Compton scattering coronae using a new mathematical approach based on analysis of the Fourier-transformed transport equation. By solving this equation, we obtain the Fourier transform of the radiation Green’s function, which allows us to calculate the exact dependence of the time lags on the Fourier frequency, for both homogeneous and inhomogeneous coronal clouds. We use the new formalism to explore a variety of injection scenarios, including both monochromatic and broadband (bremsstrahlung) seed photon injection. We show that our model can successfully reproduce both the observed time lags and the time-averaged (quiescent) X-ray spectra for Cyg X-1 and GX 339-04, using a single set of coronal parameters for each source. The time lags are the result of impulsive bremsstrahlung injection occurring near the outer edge of the corona, while the time-averaged spectra are the result of continual distributed injection of soft photons throughout the cloud.

  20. Impacts of planet migration models on planetary populations. Effects of saturation, cooling and stellar irradiation

    CERN Document Server

    Dittkrist, K -M; Klahr, H; Alibert, Y; Henning, T

    2014-01-01

    Context: Several recent studies have found that planet migration in adiabatic discs differs significantly from migration in isothermal discs. Depending on the thermodynamic conditions, i.e., the effectiveness of radiative cooling, and the radial surface density profile, planets migrate inward or outward. Clearly, this will influence the semimajor axis - mass distribution of planets as predicted by population synthesis simulations. Aims: Our goal is to study the global effects of radiative cooling, viscous torque desaturation and gap opening as well as stellar irradiation on the tidal migration of a synthetic planet population. Methods: We combine results from several analytical studies and 3D hydrodynamic simulations in a new semi-analytical migration model for the application in our planet population synthesis calculations. Results: We find a good agreement of our model with torques obtained in a 3D radiative hydrodynamic simulations. We find three convergence zones in a typical disc, towards which planets m...

  1. Ultraviolet Properties of Primeval Galaxies Theoretical Models from Stellar Population Synthesis

    CERN Document Server

    Buzzoni, A

    2002-01-01

    The ultraviolet luminosity evolution of star-forming galaxies is explored from the theoretical point of view, especially focusing on the theory of UV energetics in simple and composite stellar populations and its relationship to the star formation rate and other main evolutionary parameters. Galaxy emission below 3000 Angstroms directly correlates with actual star formation, not depending on the total mass of the system. A straightforward calibration is obtained, in this sense, from the theoretical models at 1600, 2000 and 2800 Angstroms, and a full comparison is carried out with IUE data and other balloon-borne observations for local galaxies. The claimed role of late-type systems as prevailing contributors to the cosmic UV background is reinforced by our results; at 2000 Angstroms Im irregulars are found in fact nearly four orders of magnitude brighter than ellipticals, per unit luminous mass. The role of dust absorption in the observation of high-redshift galaxies is assessed, comparing model output and ob...

  2. Simple stellar population modelling of low S/N galaxy spectra and quasar host galaxy applications

    Science.gov (United States)

    Mosby, G.; Tremonti, C. A.; Hooper, E. J.; Wolf, M. J.; Sheinis, A. I.; Richards, J. W.

    2015-02-01

    To study the effect of supermassive black holes (SMBHs) on their host galaxies it is important to study the hosts when the SMBH is near its peak activity. A method to investigate the host galaxies of high luminosity quasars is to obtain optical spectra at positions offset from the nucleus where the relative contribution of the quasar and host is comparable. However, at these extended radii the galaxy surface brightness is often low (20-22 mag arcsec-2) and the resulting spectrum might have such low signal-to-noise ratio (S/N) that it hinders analysis with standard stellar population modelling techniques. To address this problem, we have developed a method that can recover galaxy star formation histories (SFHs) from rest-frame optical spectra with S/N ˜ 5 Å-1. This method uses the statistical technique diffusion k-means to tailor the stellar population modelling basis set. Our diffusion k-means minimal basis set, composed of four broad age bins, is successful in recovering a range of galaxy SFHs. Additionally, using an analytic prescription for seeing conditions, we are able to simultaneously model scattered quasar light and the SFH of quasar host galaxies (QHGs). We use synthetic data to compare results of our novel method with previous techniques. We also present the modelling results on a previously published QHG and show that galaxy properties recovered from a diffusion k-means basis set are less sensitive to noise added to this QHG spectrum. Our new method has a clear advantage in recovering information from QHGs and could also be applied to the analysis of other low S/N galaxy spectra such as those typically obtained for high redshift objects or integral field spectroscopic surveys.

  3. Heart of Darkness: dust obscuration of the central stellar component in globular clusters younger than ~100Myr in multiple stellar population models

    CERN Document Server

    Longmore, Steven N

    2015-01-01

    To explain the observed anomalies in stellar populations within globular clusters, many globular cluster formation theories require two independent episodes of star formation. A fundamental prediction of these models is that the clusters must accumulate large gas reservoirs as the raw material to form the second stellar generation. We show that young clusters containing the required gas reservoir should exhibit the following observational signatures: (i) a dip in the measured luminosity profile or an increase in measured reddening towards the cluster centre, with Av >10mag within a radius of a few pc; (ii) bright (sub)mm emission from dust grains; (iii) bright molecular line emission once the gas is dense enough to begin forming stars. Unless the IMF is anomalously skewed towards low-mass stars, the clusters should also show obvious signs of star formation via optical emission lines (e.g. H_alpha) after the stars have formed. These observational signatures should be readily observable towards any compact clus...

  4. Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres

    CERN Document Server

    Hayek, W; Pont, F; Asplund, M

    2012-01-01

    We compare limb darkening laws derived from 3D hydrodynamical model atmospheres and 1D hydrostatic MARCS models for the host stars of the two transiting exoplanet systems HD 209458 and HD 189733. The surface brightness distribution of the stellar disks is calculated using 3D LTE spectrum formation and opacity sampling. We test our predictions using least-squares fits of model light curves to primary eclipses that were observed with the Hubble Space Telescope (HST). The limb darkening law derived from the 3D model of HD 209458 between 2900 A and 5700 A produces significantly better fits to the HST data, removing systematic residuals that were previously observed for model light curves based on 1D predictions. This difference arises mainly from the shallower mean temperature structure of the 3D model, which is a consequence of the explicit simulation of surface granulation. In the case of HD 189733, the model atmospheres produce practically equivalent limb darkening curves between 2900 A and 5700 A, partly due ...

  5. An Analytic Model for the Evolution of the Stellar, Gas, and Metal Content of Galaxies

    CERN Document Server

    Davé, Romeel; Oppenheimer, Benjamin D

    2011-01-01

    We present an analytic formalism that describes the evolution of the stellar, gas, and metal content of galaxies. It is based on the idea, inspired by hydrodynamic simulations, that galaxies live in a slowly-evolving equilibrium between inflow, outflow, and star formation. We argue that this formalism broadly captures the behavior of galaxy properties evolving in simulations. The resulting equilibrium equations for the star formation rate, gas fraction, and metallicity depend on three key free parameters that represent ejective feedback, preventive feedback, and re-accretion of ejected material. We schematically describe how these parameters are constrained by models and observations. Galaxies perturbed off the equilibrium relations owing to inflow stochasticity tend to be driven back towards equilibrium, such that deviations in star formation rate at a given mass are correlated with gas fraction and anti-correlated with metallicity. After an early gas accumulation epoch, quiescently star-forming galaxies are...

  6. Model-Independent Stellar and Planetary Masses from Multi-Transiting Exoplanetary Systems

    CERN Document Server

    Montet, Benjamin T

    2012-01-01

    Precise exoplanet characterization requires precise classification of exoplanet host stars. The masses of host stars are commonly estimated by comparing their spectra to those predicted by stellar evolution models. However, spectroscopically determined properties are difficult to measure accurately for stars that are substantially different from the Sun, such as M-dwarfs and evolved stars. Here, we propose a new method to dynamically measure the masses of transiting planets near mean-motion resonances and their host stars by combining observations of transit timing variations with radial velocity measurements. We derive expressions to analytically determine the mass of each member of the system and demonstrate the technique on the Kepler-18 system. We compare these analytic results to numerical simulations and find the two are consistent. We identify eight systems for which our technique could be applied if follow-up radial velocity measurements are collected. We conclude this analysis would be optimal for sy...

  7. The stellar atmosphere simulation code Bifrost

    CERN Document Server

    Gudiksen, Boris V; Hansteen, Viggo H; Hayek, Wolfgang; Leenaarts, Jorrit; Martínez-Sykora, Juan

    2011-01-01

    Context: Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very different physical regimes are present in the convection zone, photosphere, chromosphere, transition region and corona. To understand the details of the atmosphere it is necessary to simulate the whole atmosphere since the different layers interact strongly. These physical regimes are very diverse and it takes a highly efficient massively parallel numerical code to solve the associated equations. Aims: The design, implementation and validation of the massively parallel numerical code Bifrost for simulating stellar atmospheres from the convection zone to the corona. Methods: The code is subjected to a number of validation tests, among them the Sod shock tube test, the Orzag-Tang colliding shock test, boundary condition tests and tests of how the code treats magnetic field advection, chromospheric ...

  8. Self-consistent modeling of radio-frequency plasma generation in stellarators

    Science.gov (United States)

    Moiseenko, V. E.; Stadnik, Yu. S.; Lysoivan, A. I.; Korovin, V. B.

    2013-11-01

    A self-consistent model of radio-frequency (RF) plasma generation in stellarators in the ion cyclotron frequency range is described. The model includes equations for the particle and energy balance and boundary conditions for Maxwell's equations. The equation of charged particle balance takes into account the influx of particles due to ionization and their loss via diffusion and convection. The equation of electron energy balance takes into account the RF heating power source, as well as energy losses due to the excitation and electron-impact ionization of gas atoms, energy exchange via Coulomb collisions, and plasma heat conduction. The deposited RF power is calculated by solving the boundary problem for Maxwell's equations. When describing the dissipation of the energy of the RF field, collisional absorption and Landau damping are taken into account. At each time step, Maxwell's equations are solved for the current profiles of the plasma density and plasma temperature. The calculations are performed for a cylindrical plasma. The plasma is assumed to be axisymmetric and homogeneous along the plasma column. The system of balance equations is solved using the Crank-Nicholson scheme. Maxwell's equations are solved in a one-dimensional approximation by using the Fourier transformation along the azimuthal and longitudinal coordinates. Results of simulations of RF plasma generation in the Uragan-2M stellarator by using a frame antenna operating at frequencies lower than the ion cyclotron frequency are presented. The calculations show that the slow wave generated by the antenna is efficiently absorbed at the periphery of the plasma column, due to which only a small fraction of the input power reaches the confinement region. As a result, the temperature on the axis of the plasma column remains low, whereas at the periphery it is substantially higher. This leads to strong absorption of the RF field at the periphery via the Landau mechanism.

  9. A model for transmission lines through state equations for the effect of frequency on the longitudinal parameters: inclusion and analysis of corona effect; Uma modelagem para linhas de transmissao por meio de equacoes de estado considerando o efeito da frequencia sobre os parametros longitudinais: inclusao e analise do efeito corona

    Energy Technology Data Exchange (ETDEWEB)

    Costa, E.C.M.; Wedy, G.F.; Kurokawa, S.; Prado, A.J.; Bovolato, L.F. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Ilha Solteira (Brazil). Fac. de Engenharia Eletrica. Depto. de Engenharia Eletrica], e-mail: kurokawa@dee.feis.unesp.br; Pissolato, J. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Fac. de Engenharia Eletrica e de Computacao. Depto. de Sistemas e Controle de Energia], email: pisso@dsce.fee.unicamp.br

    2009-07-01

    This paper proposes the inclusion of corona effect on modeling of transmission lines taking into account the effect of frequency on the longitudinal parameters. This paper aims to present a model with acceptable accuracy and easy to implement in the simulation of transients due to corona. To modelling the effect corona is used the Skilling-Umoto model and to reproduce the distributed nature of the line parameters is applied cascade circuits {pi}. The differential equations that represent the electromagnetic transients along the line are presented in state of space and solved using the trapezoidal numerical integration method (trapezoidal rule). The line parameters, obtained using Bessel equations and Carson's infinite series, are reproduced in an approximate way through a rational function F {omega} and then inserted into the cascade circuit {pi}. Finally, simulations are carried out using constant parameters and variable depending on the frequency with scope to check and measure the differences between the methodologies. This work also presents a comparison between data obtained through simulation and empirical data.

  10. Stellar Opacity

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, F J; Iglesias, C A

    1999-11-07

    The monochromatic opacity, {kappa}{sub v}, quantifies the property of a material to remove energy of frequency v from a radiation field. A harmonic average of {kappa}{sub v}, known as the Rosseland mean, {kappa}{sub R}, is frequently used to simplify the calculation of energy transport in stars. The term ''opacity'' is commonly understood to refer to {kappa}{sub R}. Opacity plays an important role in stellar modeling because for most stars radiation is the primary mechanism for transporting energy from the nuclear burning region in the core to the surface. Depending on the mass, convection and electron thermal conduction can also be important modes of stellar energy transport. The efficiency of energy transport is related to the temperature gradient, which is directly proportional to the mean radiative opacity in radiation dominated regions. When the radiative opacity is large, convection can become the more efficient energy transport mechanism. Electron conductive opacity, the resistance of matter to thermal conduction, is inversely proportional to electron thermal conductivity. Thermal conduction becomes the dominant mode of energy transport at high density and low temperature.

  11. Electric Current Equilibrium in the Corona

    CERN Document Server

    Filippov, Boris

    2013-01-01

    A hyperbolic flux-tube configuration containing a null point below the flux rope is considered as a pre-eruptive state of coronal mass ejections that start simultaneously with flares. We demonstrate that this configuration is unstable and cannot exist for a long time in the solar corona. The inference follows from general equilibrium conditions and from analyzing simple models of the flux-rope equilibrium. A direct consequence of the stable flux-rope equilibrium in the corona are separatrices in the horizontal-field distribution in the chromosphere. They can be recognized as specific "herring-bone structures" in a chromospheric fibril pattern.

  12. Electric Current Equilibrium in the Corona

    Science.gov (United States)

    Filippov, Boris

    2013-04-01

    A hyperbolic flux-tube configuration containing a null point below the flux rope is considered as a pre-eruptive state of coronal mass ejections that start simultaneously with flares. We demonstrate that this configuration is unstable and cannot exist for a long time in the solar corona. The inference follows from general equilibrium conditions and from analyzing simple models of the flux-rope equilibrium. A direct consequence of the stable flux-rope equilibrium in the corona are separatrices in the horizontal-field distribution in the chromosphere. They can be recognized as specific "herring-bone structures" in a chromospheric fibril pattern.

  13. XUV exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets II: Hydrogen coronae and ion escape

    CERN Document Server

    Kislyakova, K G; Holmström, M; Panchenko, M; Odert, P; Erkaev, N V; Leitzinger, M; Khodachenko, M L; Kulikov, Yu N; Güdel, M; Hanslmeier, A

    2012-01-01

    The interactions between the stellar wind plasma flow of a typical M star such as GJ 436 and hydrogen-rich upper atmospheres of an Earth-like planet and a "super-Earth" with the radius of 2 R_Earth and a mass of 10 M_Earth, located within the habitable zone at ~0.24 AU are studied. The formation of extended atomic hydrogen coronae under the influence of such factors as the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause) and the heating efficiency on the evolution of the hydrogen-rich upper atmospheres is investigated. XUV fluxes which are 1, 10, 50 and 100 times higher compared to that of the present Sun are considered and the formation of the high-energy neutral hydrogen clouds around the planets due to charge-exchange reaction under various stellar conditions have been modeled. Charge-exchange between stellar wind protons with the planetary hydrogen atoms and photoionization leads to the production of initially cold io...

  14. Constraints on Lithospheric Rheology from Observations of Coronae on Venus

    Science.gov (United States)

    O'Rourke, Joseph G.; Smrekar, Suzanne; Moresi, Louis N.

    2016-10-01

    Coronae are enigmatic, quasi-circular features found in myriad geological environments. They are primarily distinguished as rings of concentric fractures superimposed on various topographic profiles with at least small-scale volcanism. Mantle plumes may produce coronae with interior rises, whereas coronae with central depressions are often attributed to downwellings like Rayleigh-Taylor instabilities. For almost three decades, modelers have attempted to reproduce the topographic and gravity profiles measured at coronae. Until recently, few studies also considered tectonic deformation and melt production. In particular, "Type 2" coronae have complete topographic rims but arcs of fractures extending less than 180°, signifying both brittle and ductile deformation. Only a narrow range of rheological parameters like temperature and volatile content may be compatible with these observations. Ultimately, identifying how lithospheric properties differ between Earth and Venus is critical to understanding what factors permit plate tectonics on rocky, Earth-sized planets.Here we present a hierarchical approach to study the formation of coronae. First, we discuss an observational survey enabled by a new digital elevation model derived from stereo topography for ~20% of the surface of Venus, which offers an order-of-magnitude improvement over the horizontal resolution (10 to 20 kilometers) of altimetry data from NASA's Magellan mission. Next, we search this new dataset for signs of lithospheric flexure around small coronae. Simple, thin-elastic plate models were fit to topographic profiles of larger coronae in previous studies, but data resolution impeded efforts to apply this method to the entire coronae population. Finally, we show simulations of the formation of coronae using Underworld II, an open-source code adaptable to a variety of geodynamical problems. We benchmark our code using models of pure Rayleigh-Taylor instabilities and then investigate the influence of

  15. Variations of the stellar initial mass function in semi-analytical models: implications for the mass assembly and the chemical enrichment of galaxies in the GAEA model

    Science.gov (United States)

    Fontanot, Fabio; De Lucia, Gabriella; Hirschmann, Michaela; Bruzual, Gustavo; Charlot, Stéphane; Zibetti, Stefano

    2017-02-01

    In this paper, we investigate the implications of the integrated galaxy-wide stellar initial mass function (IGIMF) approach in the framework of the semi-analytical model GAEA (GAlaxy Evolution and Assembly), which features a detailed treatment of chemical enrichment and stellar feedback. The IGIMF provides an analytic description of the dependence of the stellar IMF shape on the rate of star formation in galaxies. We find that our model with a universal IMF predicts a rather flat [α/Fe]-stellar mass relation. The model assuming the IGIMF, instead, is able to reproduce the observed increase of α-enhancement with stellar mass, in agreement with previous studies. This is mainly due to the fact that massive galaxies are characterized by larger star formation rates at high redshift, leading to stronger α-enhancement with respect to low-mass galaxies. At the same time, the IGIMF hypothesis does not affect significantly the trend for shorter star formation time-scales for more massive galaxies. We argue that in the IGIMF scenario the [α/Fe] ratios are good tracers of the highest star formation events. The final stellar masses and mass-to-light ratio of our model massive galaxies are larger than those estimated from the synthetic photometry assuming a universal IMF, providing a self-consistent interpretation of similar recent results, based on dynamical analysis of local early-type galaxies.

  16. Mg line formation in late-type stellar atmospheres: I. The model atom

    CERN Document Server

    Osorio, Y; Lind, K; Belyaev, A K; Spielfiedel, A; Guitou, M; Feautrier, N

    2015-01-01

    Mg is often traced in late-type stars using lines of neutral magnesium, which is expected to be subject to departures from LTE. The astrophysical importance of Mg as well as its relative simplicity from an atomic physics point of view, makes it a prime target and test bed for detailed ab initio non-LTE modelling in stellar atmospheres. For the low-lying states of Mg i, electron collision data were calculated using the R-matrix method. Calculations for collisional broadening by neutral hydrogen were also performed where data were missing. These calculations, together with data from the literature, were used to build a model atom. First, the modelling was tested by comparisons with observed spectra of benchmark stars with well-known parameters. Second, the spectral line behaviour and uncertainties were explored by extensive experiments in which sets of collisional data were changed or removed. The modelled spectra agree well with observed spectra. The line-to-line scatter in the derived abundances shows improve...

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

    Science.gov (United States)

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

    1997-12-01

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

  18. Edge Transport Modeling using the 3D EMC3-Eirene code on Tokamaks and Stellarators

    Science.gov (United States)

    Lore, J. D.; Ahn, J. W.; Briesemeister, A.; Ferraro, N.; Labombard, B.; McLean, A.; Reinke, M.; Shafer, M.; Terry, J.

    2015-11-01

    The fluid plasma edge transport code EMC3-Eirene has been applied to aid data interpretation and understanding the results of experiments with 3D effects on several tokamaks. These include applied and intrinsic 3D magnetic fields, 3D plasma facing components, and toroidally and poloidally localized heat and particle sources. On Alcator C-Mod, a series of experiments explored the impact of toroidally and poloidally localized impurity gas injection on core confinement and asymmetries in the divertor fluxes, with the differences between the asymmetry in L-mode and H-mode qualitatively reproduced in the simulations due to changes in the impurity ionization in the private flux region. Modeling of NSTX experiments on the effect of 3D fields on detachment matched the trend of a higher density at which the detachment occurs when 3D fields are applied. On DIII-D, different magnetic field models were used in the simulation and compared against the 2D Thomson scattering diagnostic. In simulating each device different aspects of the code model are tested pointing to areas where the model must be further developed. The application to stellarator experiments will also be discussed. Work supported by U.S. DOE: DE-AC05-00OR22725, DE AC02-09CH11466, DE-FC02-99ER54512, and DE-FC02-04ER54698.

  19. The Stagger-grid: A grid of 3D stellar atmosphere models. I. Methods and general properties

    Science.gov (United States)

    Magic, Z.; Collet, R.; Asplund, M.; Trampedach, R.; Hayek, W.; Chiavassa, A.; Stein, R. F.; Nordlund, Å.

    2013-09-01

    Aims: We present the Stagger-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications besides studies of stellar convection and atmospheres per se, including stellar parameter determination, stellar spectroscopy and abundance analysis, asteroseismology, calibration of stellar evolution models, interferometry, and extrasolar planet search. In this introductory paper, we describe the methods we applied for the computation of the grid and discuss the general properties of the 3D models as well as of their temporal and spatial averages (here denoted ⟨3D⟩ models). Methods: All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~ 220 grid models range in effective temperature, Teff, from 4000 to 7000 K in steps of 500 K, in surface gravity, log g, from 1.5 to 5.0 in steps of 0.5 dex, and metallicity, [Fe/H], from - 4.0 to + 0.5 in steps of 0.5 and 1.0 dex. Results: We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy value of the adiabatic convection zone. The range in intensity contrast is enhanced at lower metallicity. The granule size correlates closely with the pressure scale height sampled at the depth of maximum velocity. We compare the ⟨3D⟩ models with currently widely applied one-dimensional (1D) atmosphere models, as well as with theoretical 1D hydrostatic models generated with the same EOS and opacity tables as the 3D models, in order to isolate the effects of using self-consistent and hydrodynamic modeling of convection, rather than the classical mixing length theory approach. For the first time, we are able to quantify systematically over a broad

  20. Corona SDK application design

    CERN Document Server

    Williams, Daniel

    2013-01-01

    A step by step tutorial that focuses on everything from setup to deployment of basic apps.Have you ever wanted to create your own app? Then this book is for you. You will learn how to create apps using Corona SDK and how to publish your app so others can get a glimpse of your creation. This book is aimed at both Android and iOS app developers. The reader must have basic knowledge of app development.

  1. Haloes light and dark: dynamical models of the stellar halo and constraints on the mass of the Galaxy

    CERN Document Server

    Williams, A A

    2015-01-01

    We develop a flexible set of action-based distribution functions (DFs) for stellar halos. The DFs have five free parameters, controlling the inner and outer density slope, break radius, flattening and anisotropy respectively. The DFs generate flattened stellar halos with a rapidly varying logarithmic slope in density, as well as a spherically aligned velocity ellipsoid with a long axis that points towards the Galactic centre - all attributes possessed by the stellar halo of the Milky Way. We use our action-based distribution function to model the blue horizontal branch stars extracted from the Sloan Digital Sky Survey as stellar halo tracers in a spherical Galactic potential. As the selection function is hard to model, we fix the density law from earlier studies and solve for the anisotropy and gravitational potential parameters. Our best fit model has a velocity anisotropy that becomes more radially anisotropic on moving outwards. It changes from $\\beta \\approx 0.4$ at Galactocentric radius of 15 kpc to $\\ap...

  2. Stellar Differential Rotation and Coronal Timescales

    CERN Document Server

    Gibb, G P S; Mackay, D H

    2014-01-01

    We investigate the timescales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the geometric mean of the lap time and the surface diffusion timescale. In contrast, the lifetime of flux ropes are proportional to the lap time. With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than two days. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on s...

  3. Synthetic polarimetric spectra from stellar prominences

    Science.gov (United States)

    Felipe, T.; Martínez González, M. J.; Asensio Ramos, A.

    2017-02-01

    Stellar prominences detected in rapidly rotating stars serve as probes of the magnetism in the corona of cool stars. We have synthesized the temporal evolution of the Stokes profiles generated in the He I 10 830 and 5876 Å triplets during the rotation of a prominence around a star. The synthesis was performed with the HAZEL code using a cloud model in which the prominence is characterized by a slab located at a fixed latitude and height. It accounts for the scattering polarization and Zeeman and Hanle effects. Several cases with different prominence magnetic field strengths and orientations have been analysed. The results show an emission feature that drifts across the profile while the prominence is out of the stellar disc. When the prominence eclipses the star, the intensity profile shows an absorption. The scattering induced by the prominence generates linear polarization signals in Stokes Q and U profiles, which are modified by the Hanle effect when a magnetic field is present. Due to the Zeeman effect, Stokes V profiles show a signal with very low amplitude when the magnetic field along the line of sight is different from zero. The estimated linear polarization signals could potentially be detected with the future spectropolarimeter Mid-resolution InfRAreD Astronomical Spectrograph, to be attached to Gran Telescopio Canarias telescope.

  4. Synthetic polarimetric spectra from stellar prominences

    CERN Document Server

    Felipe, T; Ramos, A Asensio

    2016-01-01

    Stellar prominences detected in rapidly rotating stars serve as probes of the magnetism in the corona of cool stars. We have synthesized the temporal evolution of the Stokes profiles generated in the He I 10830 and 5876 A triplets during the rotation of a prominence around a star. The synthesis was performed with the HAZEL code using a cloud model in which the prominence is characterized by a slab located at a fixed latitude and height. It accounts for the scattering polarization and Zeeman and Hanle effects. Several cases with different prominence magnetic field strengths and orientations have been analyzed. The results show an emission feature that drifts across the profile while the prominence is out of the stellar disk. When the prominence eclipses the star, the intensity profile shows an absorption. The scattering induced by the prominence generates linear polarization signals in Stokes Q and U profiles, which are modified by the Hanle effect when a magnetic field is present. Due to the Zeeman effect, St...

  5. Corona and solar wind

    Science.gov (United States)

    Withbroe, G. L.

    1986-04-01

    The Pinhole/Occulter Facility is a powerful tool for studying the physics of the extended corona and origins of the solar wind. Spectroscopic data acquired by the P/OF coronal instruments can greatly expand empirical information about temperatures, densities, flow velocities, magnetic fields, and chemical abundances in the corona out to r or approx. 10 solar radii. Such information is needed to provide tight empirical constraints on critical physical processes involved in the transport and dissipation of energy and momentum, the heating and acceleration of plasma, and the acceleration of energetic particles. Because of its high sensitivity, high spatial and temporal resolutions, and powerful capabilities for plasma diagnostics, P/OF can significantly increase our empirical knowledge about coronal streamers and transients and thereby advance the understanding of the physics of these phenomena. P/OF observations can be used to establish the role in solar wind generation, if any, of small-scale dynamical phenomena, such as spicules, macrospicules and coronal bullets, and the role of the fine-scale structures, such as polar plumes. Finally, simultaneous measurements by the P/OF coronal and hard X-ray instruments can provide critical empirical information concerning nonthermal energy releases and acceleration of energetic particles in the corona.

  6. The Chemical Properties of Milky Way and M31 Globular Clusters: II. Stellar Population Model Predictions

    CERN Document Server

    Beasley, M A; Strader, J; Forbes, D A; Proctor, R N; Barmby, P; Huchra, J P; Beasley, Michael A.; Brodie, Jean P.; Strader, Jay; Forbes, Duncan A.; Proctor, Robert N.; Barmby, Pauline; Huchra, John P.

    2004-01-01

    We derive ages, metallicities and [alpha/Fe] ratios from the integrated spectra of 23 globular clusters in M31, by employing multivariate fits to two stellar population models. In parallel we analyze spectra of 21 Galactic globular clusters in order to facilitate a differential analysis. We find that the M31 globular clusters separate into three distinct components in age and metallicity. We identify an old, metal-poor group (7 clusters), an old, metal-rich group (10 clusters) and an intermediate age (3-6 Gyr), intermediate-metallicity ([Z/H]~-1) group (6 clusters). This third group is not identified in the Galactic globular cluster sample. The majority of globular clusters in both samples appear to be enhanced in alpha-elements, the degree of enhancement being model-dependent. The intermediate age GCs appear to be the most enhanced, with [alpha/Fe]~0.4. These clusters are clearly depressed in CN with respect to the models and the bulk of the M31 and Milky Way sample. Compared to the bulge of M31, M32 and NGC...

  7. A Closure Model with Plumes II. Application to the stochastic excitation of stellar p modes

    CERN Document Server

    Belkacem, K; Goupil, M J; Kupka, F; Baudin, F

    2006-01-01

    Amplitudes of stellar p modes result from a balance between excitation and damping processes taking place in the upper-most part of convective zones in solar-type stars and can therefore be used as a seismic diagnostic for the physical properties of these external layers. Our goal is to improve the theoretical modelling of stochastic excitation of p modes by turbulent convection. With the help of the Closure Model with Plume (CMP) developed in a companion paper, we refine the theoretical description of the excitation by the turbulent Reynolds stress term. The CMP is generalized for two-point correlation products so as to apply it to the formalism developed by Samadi & Goupil (2001). The present model gives rise to a frequency dependence of the power supplied into solar p modes which is in agreement with GOLF observations for intermediate and high frequencies. Despite an increase of the Reynolds stress term contribution due to our improved description, an additional source of excitation, identified as the ...

  8. Galaxy assembly, stellar feeback and metal enrichment: the view from the GAEA model

    CERN Document Server

    Hirschmann, Michaela; Fontanot, Fabio

    2015-01-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently "anti-hierarchical" evolution of galaxy assembly: massive galaxies appear to be in place since $z\\sim 3$, while a significant evolution is measured for lower mass galaxies, whose number densities increase significantly with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes. Our analysis is carried out in the framework of GAEA, a new semi-analytic model that includes a self-consistent treatment for the timings of gas, metal and energy recycling, as well for the chemical yields. We show this to be crucial in order to use observational measurements of the metal content as independent and powerful constraints for the adopted feedback schemes. We find that the observed trends can be reproduced in the framework of either a strong ejective or preventive feedback model. In the former case, the gas ejection rate must decreas...

  9. Probing the Solar Corona with VLBI

    Science.gov (United States)

    Soja, Benedikt; Sun, Jing; Heinkelmann, Robert; Schuh, Harald; Böhm, Johannes

    2013-04-01

    Radio observations close to the Sun are sensitive to the dispersive effects of the Sun corona. This has been used to determine (among other parameters) the electron density in the corona during solar conjunctions with spacecrafts. Although geodetic Very Long Baseline Interferometry (VLBI) observations close to the Sun have already been performed before 2002 (but suspended afterwards) they have not yet been used for calculations of corona electron densities. Almost 10 years later the International VLBI Service for Geodesy and Astrometry (IVS) decided to schedule twelve 24 hours VLBI sessions in 2011 and 2012 including observations closer than 15 degrees to the heliocenter. Both the recent and the earlier sessions are analysed in order to determine electron densities of the Sun corona. Based on the ionospheric delay corrections derived from two-frequency VLBI measurements, other dispersive effects like instrumental biases and, most important of all, the Earth's ionosphere effects are estimated and then eliminated. The residual delays are used to successfully determine power-law parameters of the electron density of the Sun corona for several of these sessions. In some cases, scheduled observations close to the Sun had failed, making it impossible to derive meaningful results from them. Both, the successful and the lost observations were analysed including external information like Sunspot numbers and flare occurrences. The estimated electron densities were compared to previous models of the Sun corona derived by radio measurements to spacecrafts during solar conjunctions. Our investigations show that it is possible to use geodetic VLBI sessions with observations close to the Sun to determine electron densities of the corona. The success depends on the geometry, i.e. the source position with respect to the Sun, and on the schedule, which can be optimized for such investigations. Unpredictable disturbances at the Sun's surface, such as flares, play also a role. So far

  10. Evolutionary Stellar Population Synthesis with MILES. Part I: The Base Models and a New Line Index System

    CERN Document Server

    Vazdekis, A; Falcón-Barroso, J; Cenarro, A J; Beasley, M A; Cardiel, N; Gorgas, J; Peletier, R F; 10.1111/j.1365-2966.2010.16407.x

    2010-01-01

    [Abridged]. We present SEDs for single-age, single-metallicity stellar populations (SSPs) covering the optical range at resolution 2.3A (FWHM). These SEDs constitute our base models, as they combine scaled-solar isochrones with MILES empirical stellar library, which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries. The unprecedented stellar parameter coverage of MILES allowed us to safely extend our optical SSP SED predictions from intermediate- to very-old age regimes, and the metallicity coverage of the SSPs from super-solar to [M/H]=-2.3. SSPs with such low metallicities are particularly useful for globular cluster studies. Observed spectra can be studied by means of full spectrum fitting or line-strengths. For the latter we propose a new Line Index System (LIS) to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provid...

  11. Galaxy assembly, stellar feedback and metal enrichment: the view from the GAEA model

    Science.gov (United States)

    Hirschmann, Michaela; De Lucia, Gabriella; Fontanot, Fabio

    2016-09-01

    One major problem of current theoretical models of galaxy formation is given by their inability to reproduce the apparently `anti-hierarchical' evolution of galaxy assembly: massive galaxies appear to be in place since z ˜ 3, while a significant increase of the number densities of low-mass galaxies is measured with decreasing redshift. In this work, we perform a systematic analysis of the influence of different stellar feedback schemes, carried out in the framework of GAEA, a new semi-analytic model of galaxy formation. It includes a self-consistent treatment for the timings of gas, metal and energy recycling, and for the chemical yields. We show this to be crucial to use observational measurements of the metallicity as independent and powerful constraints for the adopted feedback schemes. The observed trends can be reproduced in the framework of either a strong ejective or preventive feedback model. In the former case, the gas ejection rate must decrease significantly with cosmic time (as suggested by parametrizations of the cosmological `FIRE' simulations). Irrespective of the feedback scheme used, our successful models always imply that up to 60-70 per cent of the baryons reside in an `ejected' reservoir and are unavailable for cooling at high redshift. The same schemes predict physical properties of model galaxies (e.g. gas content, colour, age, and metallicity) that are in much better agreement with observational data than our fiducial model. The overall fraction of passive galaxies is found to be primarily determined by internal physical processes, with environment playing a secondary role.

  12. Limb darkening and exoplanets: testing stellar model atmospheres and indentifying biases in transit parameters

    CERN Document Server

    Espinoza, Néstor

    2015-01-01

    Limb-darkening is fundamental in determining transit lightcurve shapes, and is typically modeled by a variety of laws that parametrize the intensity profile of the star that is being transited. Confronted with a transit lightcurve, some authors fix the parameters of these laws, the so-called limb-darkening coefficients (LDCs), while others prefer to let them float in the lightcurve fitting procedure. Which of these is the best strategy, however, is still unclear, as well as how and by how much each of these can bias the retrieved transit parameters. In this work we attempt to clarify those points by first re-calculating these LDCs, comparing them to measured values from Kepler transit lightcurves using an algorithm that takes into account uncertainties in both the geometry of the transit and the parameters of the stellar host. We show there are significant departures from predicted model values, suggesting that our understanding of limb-darkening still needs to improve. Then, we show through simulations that ...

  13. GrayStar: A Web application for pedagogical stellar atmosphere and spectral line modelling and visualisation

    CERN Document Server

    Short, C Ian

    2014-01-01

    GrayStar is a stellar atmospheric and spectral line modelling, post-processing, and visualisation code, suitable for classroom demonstrations and laboratory-style assignments, that has been developed in Java and deployed in JavaScript and HTML. The only software needed to compute models and post-processed observables, and to visualise the resulting atmospheric structure and observables, is a common Web browser. Therefore, the code will run on any common PC or related X86 (-64) computer of the type that typically serves classroom data projectors, is found in undergraduate computer laboratories, or that students themselves own, including those with highly portable form-factors such as net-books and tablets. The user requires no experience with compiling source code, reading data files, or using plotting packages. More advanced students can view the JavaScript source code using the developer tools provided by common Web browsers. The code is based on the approximate gray atmospheric solution and runs quickly eno...

  14. Testing intermediate-age stellar evolution models with VLT photometry of LMC clusters. I. The data

    CERN Document Server

    Gallart, C; Bertelli, G; Chiosi, C; Demarque, P; Girardi, L; Nasi, E; Woo, J H; Yi, S

    2003-01-01

    This is the first of a series of three papers devoted to the calibration of a few parameters of crucial importance in the modeling of the evolution of intermediate-mass stars, with special attention to the amount of convective core overshoot. To this end we acquired deep V and R photometry for three globular clusters of the Large Magellanic Cloud (LMC), namely NGC 2173, SL 556 and NGC 2155, in the age interval 1-3 Gyr. In this first paper, we describe the aim of the project, the VLT observations and data reduction, and we make preliminary comparisons of the color-magnitude diagrams with both Padova and Yonsei-Yale isochrones. Two following papers in this series present the results of a detailed analysis of these data, independently carried out by members of the Yale and Padova stellar evolution groups. This allows us to compare both sets of models and discuss their main differences, as well as the systematic effects that they would have to the determination of the ages and metallicities of intermediate-age si...

  15. Testing intermediate-age stellar evolution models with VLT photometry of LMC clusters. III. Padova results

    CERN Document Server

    Bertelli, G; Girardi, L; Chiosi, C; Zoccali, M; Gallart, C

    2002-01-01

    The color-magnitude diagrams (CMDs) of three intermediate-age LMC clusters, NGC 2173, SL556 and NGC2155 are analyzed to determine their age and metallicity basing on Padova stellar models. Synthetic CMDs are compared with cluster data. The best match is obtained using two fitting functions based on star counts in the different bins of the cluster CMD. Two different criteria are used. One of them takes into account the uncertainties in the color of the red clump stars. Given the uncertainties on the experimental values of the clusters metallicity, we provide a set of acceptable solutions. They define the correspondent values of metallicity, age, reddening and distance modulus (for the assumed IMF). The comparison with Padova models suggests for NGC 2173 a prolonged star formation (spanning a period of about 0.3 Gyr), beginning 1.7 Gyr and ending 1.4 Gyr ago. The metallicity Z is in the range 0.0016 $-$ 0.003. Contrary to what suggested for NGC 2173 a period of extended star formation was not required to fit th...

  16. Ultraviolet Properties of Primeval Galaxies: Theoretical Models from Stellar Population Synthesis

    Science.gov (United States)

    Buzzoni, Alberto

    2002-03-01

    The ultraviolet luminosity evolution of star-forming galaxies is explored from the theoretical point of view, especially focusing on the theory of UV energetics in simple and composite stellar populations and its relationship to the star formation rate and other main evolutionary parameters. Galaxy emission below λ<3000 Å directly correlates with actual star formation, not depending on the total mass of the system. A straightforward calibration is obtained, in this sense, from the theoretical models at 1600, 2000, and 2800 Å, and a full comparison is carried out with IUE data and other balloon-borne observations for local galaxies. The claimed role of late-type systems as prevailing contributors to the cosmic UV background is reinforced by our results; at 2000 Å, Im irregulars are found in fact nearly 4 orders of magnitude brighter than ellipticals, per unit luminous mass. The role of dust absorption in the observation of high-redshift galaxies is assessed, comparing the model output and observed spectral energy distribution of local galaxy samples. Similar to what we observe in our own galaxy, a quick evolution in the dust environment might be envisaged in primeval galaxies, with an increasing fraction of luminous matter that would escape the regions of harder and ``clumpy'' dust absorption on a timescale of some 107 yr, comparable to the lifetime of stars of 5-10 Msolar.

  17. Radial electric field computations with DKES and neoclassical models in TJ-II stellarator

    Science.gov (United States)

    Martinell, Julio; Gutierrez-Tapia, Cesar; Lopez-Bruna, Daniel

    2015-11-01

    Radial electric fields arise due to the non-ambipolar transport in stellarator plasmas and play an important role in determining some improved confinement regimes. In order to calculate this electric field it is necessary to take all particle fluxes that are not ambipolar. The most important contribution to these fluxes comes from neoclassical transport. Here we use particle fluxes obtained from kinetic equation computations using the code DKES to evaluate the radial electric field profiles for certain discharges of the heliac TJ-II. Experimental profiles for the density and temperatures are used together with the diffusion coefficients obtained with DKES. A similar computation of the electric field is performed with three analytical neoclassical models that use an approximation for the magnetic geometry. The ambipolar electric field from the models is compared with the one given by DKES and we find that they are all qualitatively similar. They are also compared with experimental measurements of the electric field obtained with HIBP. It is shown that, although the electric field is reasonably well reproduced by the neoclassical computations, especially in high temperature regimes, the particle fluxes are not. Thus, neoclassical theory provides good Er estimates in TJ-II. Support from CONACyT 152905 and DGAPA IN109115 projects is acknowledged.

  18. A Reduced-order NLTE Kinetic Model for Radiating Plasmas of Outer Envelopes of Stellar Atmospheres

    Science.gov (United States)

    Munafò, Alessandro; Mansour, Nagi N.; Panesi, Marco

    2017-04-01

    The present work proposes a self-consistent reduced-order NLTE kinetic model for radiating plasmas found in the outer layers of stellar atmospheres. A detailed collisional-radiative kinetic mechanism is constructed by leveraging the most up-to-date set of ab initio and experimental data available in the literature. This constitutes the starting point for the derivation of a reduced-order model, obtained by lumping the bound energy states into groups. In order to determine the needed thermo-physical group properties, uniform and Maxwell–Boltzmann energy distributions are used to reconstruct the energy population of each group. Finally, the reduced set of governing equations for the material gas and the radiation field is obtained based on the moment method. Applications consider the steady flow across a shock wave in partially ionized hydrogen. The results clearly demonstrate that adopting a Maxwell–Boltzmann grouping allows, on the one hand, for a substantial reduction of the number of unknowns and, on the other, to maintain accuracy for both gas and radiation quantities. Also, it is observed that, when neglecting line radiation, the use of two groups already leads to a very accurate resolution of the photo-ionization precursor, internal relaxation, and radiative cooling regions. The inclusion of line radiation requires adopting just one additional group to account for optically thin losses in the α, β, and γ lines of the Balmer and Paschen series. This trend has been observed for a wide range of shock wave velocities.

  19. A Connection Between Corona and Jet

    Science.gov (United States)

    Kohler, Susanna

    2017-03-01

    The structure immediately around a supermassive black hole at the heart of an active galaxy can tell us about how material flows in and out of these monsters but this region is hard to observe! A new study provides us with clues of what might be going on in these active and energetic cores of galaxies.In- and OutflowsIn active galactic nuclei (AGN), matter flows both in and out. As material flows toward the black hole via its surrounding accretion disk, much of this gas and dust can then be expelled from the vicinity via highly collimated jets.Top: The fraction of X-rays that is reflected decreases as jet power increases. Bottom: the distance between the corona and the reflecting part of the disk increases as jet power increases. [Adapted from King et al. 2017]To better understand this symbiosis between accretion and outflows, we examine whats known as the corona the hot, X-ray-emitting gas thats located in the closest regions around the black hole. But because the active centers of galaxies are generally obscured by surrounding gas and dust, its difficult for us to learn about the structure of these inner regions near the black hole.Where are the X-rays of the corona produced: in the inner accretion flow, or at the base of the jet? How far away is this corona from the disk? And how does the coronas behavior relate to that of the jet?Reflected ObservationsTo address some of these questions, a group of scientists led by Ashley King (Einstein Fellow at Stanford University) has analyzed X-ray observations from NuSTAR and XMM-Newton of over 40 AGN. The team examined the reflections of the X-rays off of the accretion disk and used two measurements to learn about the structure around the black hole:the fraction of the coronas X-rays that are reflected by the disk, andthe time lag between the original and reflected X-rays, which reveals the distance from the corona to the reflecting part of the disk.A visualization of the authors model for an AGN. The accretion disk is

  20. Stellar ages from asteroseismology

    CERN Document Server

    Lebreton, Yveline

    2008-01-01

    Asteroseismology provides powerful means to probe stellar interiors. The oscillations frequencies are closely related to stellar interior properties via the density and sound speed profiles. Since these are tightly linked with the mass and evolutionary state, we can expect to determine the age and mass of a star from the comparison of its oscillation spectrum with predictions of stellar models. Such a comparison suffers both from the problems we face when modeling a particular star (as the uncertainties on global parameters and chemical composition) and from our misunderstanding of processes at work in stellar interiors (as the transport processes that may lead to core mixing and affect the model ages). For stars where observations have provided precise and numerous oscillation frequencies together with accurate global parameters and additional information (as the radius or the mass if the star is in a binary system, the interferometric radius or the mean density if the star is an exoplanet host), we can also...

  1. Understanding the Kinetics of Protein-Nanoparticle Corona Formation.

    Science.gov (United States)

    Vilanova, Oriol; Mittag, Judith J; Kelly, Philip M; Milani, Silvia; Dawson, Kenneth A; Rädler, Joachim O; Franzese, Giancarlo

    2016-12-27

    When a pristine nanoparticle (NP) encounters a biological fluid, biomolecules spontaneously form adsorption layers around the NP, called "protein corona". The corona composition depends on the time-dependent environmental conditions and determines the NP's fate within living organisms. Understanding how the corona evolves is fundamental in nanotoxicology as well as medical applications. However, the process of corona formation is challenging due to the large number of molecules involved and to the large span of relevant time scales ranging from 100 μs, hard to probe in experiments, to hours, out of reach of all-atoms simulations. Here we combine experiments, simulations, and theory to study (i) the corona kinetics (over 10(-3)-10(3) s) and (ii) its final composition for silica NPs in a model plasma made of three blood proteins (human serum albumin, transferrin, and fibrinogen). When computer simulations are calibrated by experimental protein-NP binding affinities measured in single-protein solutions, the theoretical model correctly reproduces competitive protein replacement as proven by independent experiments. When we change the order of administration of the three proteins, we observe a memory effect in the final corona composition that we can explain within our model. Our combined experimental and computational approach is a step toward the development of systematic prediction and control of protein-NP corona composition based on a hierarchy of equilibrium protein binding constants.

  2. Stellar masses of SDSS-III BOSS galaxies at z~0.5 and constraints to galaxy formation models

    CERN Document Server

    Maraston, Claudia; Henriques, Bruno M; Thomas, Daniel; Wake, David; Brownstein, Joel R; Capozzi, Diego; Bundy, Kevin; Skibba, Ramin A; Beifiori, Alessandra; Nichol, Robert C; Edmondson, Edd; Schneider, Don P; Chen, Yanmei; Masters, Karen L; Steele, Oliver; Bolton, Adam S; York, Donald G; Bizyaev, Dmitry; Brewington, Howard; Malanushenko, Elena; Malanushenko, Viktor; Snedden, Stephanie; Oravetz, Daniel; Pan, Kaike; Shelden, Alaina; Simmons, Audrey

    2012-01-01

    We calculate stellar masses for ~400,000 massive luminous galaxies at redshift ~0.2-0.7 using the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS). Stellar masses are obtained by fitting model spectral energy distributions to u,g,r,i,z magnitudes. Accurate BOSS spectroscopic redshifts are used to constrain the fits. We find that the distribution of stellar masses in BOSS is narrow (Delta log M ~0.5 dex) and peaks at about log M/M_sun ~ 11.3 (for a Kroupa initial stellar mass function), and that the mass sampling is uniform over the redshift range 0.2 to 0.6, in agreement with the intended BOSS target selection. The galaxy masses probed by BOSS extend over ~ 10^{12} M_{sun}, providing unprecedented measurements of the high-mass end of the galaxy mass function. We find that the galaxy number density above ~ 2.5 10^{11} M_{sun} agrees with previous determinations within 2sigma, but there is a slight offset towards lower number densities in BOSS. This alleviates a tension between th...

  3. Measuring Diffuse Interstellar Bands with cool stars. An improved line list to model the background stellar spectra

    CERN Document Server

    Monreal-Ibero, A

    2016-01-01

    DIBs are ubiquitous in stellar spectra. Traditionally, they have been studied through their extraction from hot stars, because of their smooth continuum. In an era where there are several going-on or planned massive Galactic surveys using multi-object spectrographs, cool stars constitute an appealing set of targets. From the technical point of view, the extraction of DIBs in their spectra is more challenging due to the complexity of the continuum. In this contribution we will provide the community with an improved set of stellar lines in the spectral regions associated to the strong DIBs at l6196, l6269, l6284, and l6379. These lines will allow for the creation of better stellar synthetic spectra, reproducing the background emission and a more accurate extraction of the magnitudes associated with a given DIB. The Sun and Arcturus were used as representative examples of dwarf and giant stars, respectively. A high quality spectrum for each of them was modeled using TURBOSPECTRUM and the VALD stellar line list. ...

  4. An intermediate-luminosity-optical-transient (ILOT) model for the young stellar object ASASSN-15qi

    CERN Document Server

    Kashi, Amit

    2016-01-01

    We construct a scenario where the outburst of the young-stellar-object ASASSN-15qi is an intermediate luminosity optical transient (ILOT). In this scenario a sub-Jupiter young planet was tidally destructed on to a young main-sequence star. The system is young, therefore the radius of the planet is larger than its final value, and consequently it has smaller density. The lower density allows the tidal destruction of the young Saturn-like planet on to the main-sequence star of mass $\\approx 2.4 ~M_\\odot$, resulting in a formation of a disc and a gravitationally-powered ILOT. Unlike the case of the more energetic ILOT V838~Mon, the mass of the destroyed planet is too low to inflate a giant envelope, and hence the merger remnant stays hot. If our suggested model holds, this ILOT possesses two interesting properties: (1) its luminosity and total energy are below those of novae, and (2) it is not as red as other ILOTs. The unusual outburst of ASASSN-15qi, if indeed is an ILOT, further increases the diversity of the...

  5. Minimalist coupled evolution model for stellar x-ray activity, rotation, mass loss, and magnetic field

    CERN Document Server

    Blackman, Eric G

    2015-01-01

    Late-type main sequence stars exhibit an x-ray to bolometric flux that depends on the Corolis number $Co$ (product of convective turnover time and angular rotation speed) as $Co^{\\zeta}$ with $2\\le \\zeta \\le 3$ for $Co > 1$. Stars in the unsaturated regime also obey the Skumanich law--- their rotation speeds scale inversely with square root of their age. The associated stellar magnetic field strengths follow a similar decrease with age. While the connection between faster rotators, stronger fields, and higher activity has been well established observationally, a basic theory for the time evolution of x-ray luminosity, rotation, magnetic field and mass loss been lacking. Here we offer a minimalist model for the time evolution of these quantities built from combining a Parker wind with several new ingredients: (1) explicit sourcing of both the thermal energy launching the wind and the x-ray luminosity via dynamo produced magnetic fields; (2) explicit coupling of x-ray activity and mass loss saturation to dynamo...

  6. Star Formation in Galaxy Mergers with Realistic Models of Stellar Feedback & the Interstellar Medium

    CERN Document Server

    Hopkins, Philip F; Hernquist, Lars; Narayanan, Desika; Hayward, Christopher C; Murray, Norman

    2012-01-01

    We use simulations with realistic models for stellar feedback to study galaxy mergers. These high resolution (1 pc) simulations follow formation and destruction of individual GMCs and star clusters. The final starburst is dominated by in situ star formation, fueled by gas which flows inwards due to global torques. The resulting high gas density results in rapid star formation. The gas is self gravitating, and forms massive (~10^10 M_sun) GMCs and subsequent super-starclusters (masses up to 10^8 M_sun). However, in contrast to some recent simulations, the bulk of new stars which eventually form the central bulge are not born in superclusters which then sink to the center of the galaxy, because feedback efficiently disperses GMCs after they turn several percent of their mass into stars. Most of the mass that reaches the nucleus does so in the form of gas. The Kennicutt-Schmidt law emerges naturally as a consequence of feedback balancing gravitational collapse, independent of the small-scale star formation micro...

  7. Implications of WMAP observations on Li abundance and stellar evolution models

    CERN Document Server

    Richard, O; Richer, J; Richard, Olivier; Michaud, Georges; Richer, Jacques

    2004-01-01

    The WMAP determination of the baryon-to-photon ratio implies, through Big Bang nucleosynthesis, a cosmological Li abundance larger, by a factor of 2 to 3, than the Li abundance plateau observed in the oldest Pop II stars. It is however inescapable that there be a reduction by a factor of at least 1.6 to 2.0 of the surface Li abundance during the evolution of Pop II field stars with [Fe/H] < -1.5. That the observed Li be lower than cosmologically produced Li is expected from stellar evolution models. Since at turnoff most of the Li abundance reduction is caused by gravitational settling, the presence of Lithium 6 in some turnoff stars is also understood. Given that the WMAP implications for Li cosmological abundance and the Li Spite plateau can be naturally explained by gravitational settling in the presence of weak turbulence, there appears little need for exotic physics as suggested by some authors. Instead, there is a need for a better understanding of turbulent transport in the radiative zones of stars....

  8. The Meaning and Consequences of Star Formation Criteria in Galaxy Models with Resolved Stellar Feedback

    CERN Document Server

    Hopkins, Philip F; Murray, Norman

    2013-01-01

    We consider the effects of different star formation criteria on galactic scales, in high-resolution simulations with explicitly resolved GMCs and stellar feedback. We compare: (1) a self-gravity criterion (based on the local virial parameter and the assumption that self-gravitating gas collapses to high density in a free-fall time), (2) a fixed density threshold, (3) a molecular-gas law, (4) a temperature threshold, (5) a Jeans-instability requirement, (6) a criteria that cooling times be shorter than dynamical times, and (7) a convergent-flow criterion. We consider these both MW-like and high-density (starburst) galaxies. With feedback present, all models produce identical integrated star formation rates (SFRs), in agreement with the Kennicutt relation. Without feedback all produce orders-of-magnitude excessive SFRs. This is totally dependent on feedback and independent of the SF law. However, the spatial and density distribution of SF depend strongly on the SF criteria. Because cooling rates are generally f...

  9. Measurement, Modeling and Reconstruction of Parallel Currents in the HSX Stellarator

    Science.gov (United States)

    Schmitt, J. C.; Talmadge, J. N.; Lore, J.

    2010-11-01

    Parallel currents are measured with a set of magnetic diagnostics on the HSX. Measurements show that the Pfirsch-Schlüter current is helical due to the lack of toroidal curvature and is reduced in magnitude compared to an equivalent tokamak because of the high effective transform (˜3) in a quasihelically symmetric stellarator. The bootstrap current density is calculated using the PENTA code,^1 which includes momentum conservation between plasma species. The data shows better agreement with a model that includes momentum conservation. HSX plasmas are heated by a 28 GHz gyrotron which allows the electrons to access the low collisionality regime, while the cold ions are generally in the plateau. In HSX, a 3-D plasma with small symmetry-breaking, the calculations show that for two species in different collisionality regimes, the bootstrap current can be strong function of the radial electric field. In the plasma core, multiple stable electric field solutions to the ambipolarity constraint exist. The large positive electric field, the ``electron-root'' solution, can result in a reduction and even a reversal of the bootstrap current. The measured fields and fluxes are used in the V3FIT^2 code to reconstruct the current profile. Supported by DOE grant DE-FG02-93ER54222. ^1D.A. Spong, Phys. Plasmas 12 (2005) 056114. ^2J.D. Hanson, et al, Nucl. Fusion 49 (2009) 075031.

  10. MODEL-INDEPENDENT STELLAR AND PLANETARY MASSES FROM MULTI-TRANSITING EXOPLANETARY SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Montet, Benjamin T. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Johnson, John Asher, E-mail: btm@astro.caltech.edu [Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, MC 170-25, Pasadena, CA 91125 (United States)

    2013-01-10

    Precise exoplanet characterization requires precise classification of exoplanet host stars. The masses of host stars are commonly estimated by comparing their spectra to those predicted by stellar evolution models. However, spectroscopically determined properties are difficult to measure accurately for stars that are substantially different from the Sun, such as M-dwarfs and evolved stars. Here, we propose a new method to dynamically measure the masses of transiting planets near mean-motion resonances and their host stars by combining observations of transit timing variations with radial velocity (RV) measurements. We derive expressions to analytically determine the mass of each member of the system and demonstrate the technique on the Kepler-18 system. We compare these analytic results to numerical simulations and find that the two are consistent. We identify eight systems for which our technique could be applied if follow-up RV measurements are collected. We conclude that this analysis would be optimal for systems discovered by next-generation missions similar to TESS or PLATO, which will target bright stars that are amenable to efficient RV follow-up.

  11. Testing Stellar Population Models with Star Clusters in the Large Magellanic Cloud

    CERN Document Server

    Beasley, M A; Sharples, R M; Beasley, Michael A.; Hoyle, Fiona; Sharples, Ray M.

    2002-01-01

    We present high S/N integrated spectra of 24 star clusters in the LMC obtained using the FLAIR spectrograph at the UK Schmidt. The spectra have been placed onto the Lick/IDS system in order to test the calibration of Simple Stellar Population (SSP) models. We have compared the SSP-predicted metallicities of the clusters with literature Ca-Triplet values, and find that there is good agreement in the range --2.10 0. We present metallicities for 11 clusters with no previous measurements. Comparison of the SSP ages of the clusters (from Balmer lines) with the literature data shows good agreement for the majority. This includes six old globular clusters in our sample, which have ages consistent with their HST CMD turn-offs. However, two clusters, NGC 1754 and NGC 2005, have Hbeta line-strengths which lead to ages which are too young (~8 and ~6 Gyr respectively at 3 sigma) for their HST CMDs. Comparison between the horizontal branch (HB) morphology and Balmer lines of these clusters suggests that blue HBs have inc...

  12. Statistical characteristic in time-domain of direct current corona-generated audible noise from conductor in corona cage

    Science.gov (United States)

    Li, Xuebao; Cui, Xiang; Lu, Tiebing; Ma, Wenzuo; Bian, Xingming; Wang, Donglai; Hiziroglu, Huseyin

    2016-03-01

    The corona-generated audible noise (AN) has become one of decisive factors in the design of high voltage direct current (HVDC) transmission lines. The AN from transmission lines can be attributed to sound pressure pulses which are generated by the multiple corona sources formed on the conductor, i.e., transmission lines. In this paper, a detailed time-domain characteristics of the sound pressure pulses, which are generated by the DC corona discharges formed over the surfaces of a stranded conductors, are investigated systematically in a laboratory settings using a corona cage structure. The amplitude of sound pressure pulse and its time intervals are extracted by observing a direct correlation between corona current pulses and corona-generated sound pressure pulses. Based on the statistical characteristics, a stochastic model is presented for simulating the sound pressure pulses due to DC corona discharges occurring on conductors. The proposed stochastic model is validated by comparing the calculated and measured A-weighted sound pressure level (SPL). The proposed model is then used to analyze the influence of the pulse amplitudes and pulse rate on the SPL. Furthermore, a mathematical relationship is found between the SPL and conductor diameter, electric field, and radial distance.

  13. Statistical characteristic in time-domain of direct current corona-generated audible noise from conductor in corona cage

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xuebao, E-mail: lxb08357x@ncepu.edu.cn; Cui, Xiang, E-mail: x.cui@ncepu.edu.cn; Ma, Wenzuo; Bian, Xingming; Wang, Donglai [State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206 (China); Lu, Tiebing, E-mail: tiebinglu@ncepu.edu.cn [Beijing Key Laboratory of High Voltage and EMC, North China Electric Power University, Beijing 102206 (China); Hiziroglu, Huseyin [Department of Electrical and Computer Engineering, Kettering University, Flint, Michigan 48504 (United States)

    2016-03-15

    The corona-generated audible noise (AN) has become one of decisive factors in the design of high voltage direct current (HVDC) transmission lines. The AN from transmission lines can be attributed to sound pressure pulses which are generated by the multiple corona sources formed on the conductor, i.e., transmission lines. In this paper, a detailed time-domain characteristics of the sound pressure pulses, which are generated by the DC corona discharges formed over the surfaces of a stranded conductors, are investigated systematically in a laboratory settings using a corona cage structure. The amplitude of sound pressure pulse and its time intervals are extracted by observing a direct correlation between corona current pulses and corona-generated sound pressure pulses. Based on the statistical characteristics, a stochastic model is presented for simulating the sound pressure pulses due to DC corona discharges occurring on conductors. The proposed stochastic model is validated by comparing the calculated and measured A-weighted sound pressure level (SPL). The proposed model is then used to analyze the influence of the pulse amplitudes and pulse rate on the SPL. Furthermore, a mathematical relationship is found between the SPL and conductor diameter, electric field, and radial distance.

  14. Stellar Population Synthesis-based Modelling of the Milky Way Using Asteroseismology of Dwarfs and Subgiants from Kepler

    Science.gov (United States)

    Sharma, Sanjib; Stello, Dennis; Huber, Daniel; Bland-Hawthorn, Joss; Bedding, Timothy R.

    2017-02-01

    Early attempts to apply asteroseismology to study the Galaxy have already shown unexpected discrepancies for the mass distribution of stars between the Galactic models and the data; a result that is still unexplained. Here, we revisit the analysis of the asteroseismic sample of dwarf and subgiant stars observed by Kepler and investigate in detail the possible causes for the reported discrepancy. We investigate two models of the Milky Way based on stellar population synthesis, Galaxia and TRILEGAL. In agreement with previous results, we find that TRILEGAL predicts more massive stars compared to Galaxia, and that TRILEGAL predicts too many blue stars compared to 2MASS observations. Both models fail to match the distribution of the stellar sample in ({log} g,{T}{eff}) space, pointing to inaccuracies in the models and/or the assumed selection function. When corrected for this mismatch in ({log} g,{T}{eff}) space, the mass distribution calculated by Galaxia is broader and the mean is shifted toward lower masses compared to that of the observed stars. This behavior is similar to what has been reported for the Kepler red giant sample. The shift between the mass distributions is equivalent to a change of 2% in νmax, which is within the current uncertainty in the νmax scaling relation. Applying corrections to the Δν scaling relation predicted by the stellar models makes the observed mass distribution significantly narrower, but there is no change to the mean.

  15. The Stagger-grid: A Grid of 3D Stellar Atmosphere Models - I. Methods and General Properties

    CERN Document Server

    Magic, Z; Asplund, M; Trampedach, R; Hayek, W; Chiavassa, A; Stein, R F; Nordlund, Å

    2013-01-01

    We present the Stagger-grid, a comprehensive grid of time-dependent, 3D hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications like stellar spectroscopy, asteroseismology and the study of stellar convection. In this introductory paper, we describe the methods used for the computation of the grid and discuss the general properties of the 3D models as well as their temporal and spatial averages (). All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~220 grid models range in Teff from 4000 to 7000K in steps of 500K, in log g from 1.5 to 5.0 in steps of 0.5 dex, and [Fe/H] from -4.0 to +0.5 in steps of 0.5 and 1.0 dex. We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy va...

  16. THE QUADRUPLE PRE-MAIN-SEQUENCE SYSTEM LkCa 3: IMPLICATIONS FOR STELLAR EVOLUTION MODELS

    Energy Technology Data Exchange (ETDEWEB)

    Torres, Guillermo; Latham, David W. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ruiz-Rodriguez, Dary; Prato, L.; Wasserman, Lawrence H. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Badenas, Mariona [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Schaefer, G. H. [CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Mathieu, Robert D., E-mail: gtorres@cfa.harvard.edu [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States)

    2013-08-10

    We report the discovery that the pre-main-sequence (PMS) object LkCa 3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close ({approx}0.''5) visual pair, with one component being a moderately eccentric 12.94 day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented by new near-infrared (NIR) spectroscopy shows both visual components to be double lined; the second one has a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and NIR flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we also detect the rotational signal of the primary in the 4.06 day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these constraints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting that the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa 3 and the well-known quadruple PMS system GG Tau with the widely used models from the Lyon series for a mixing length parameter of {alpha}{sub ML} = 1.0 strongly favor the Dartmouth models.

  17. Probing Atlas model atmospheres at high spectral resolution. Stellar synthesis and reference template validation

    Science.gov (United States)

    Bertone, E.; Buzzoni, A.; Chávez, M.; Rodríguez-Merino, L. H.

    2008-07-01

    Aims: The fast improvement of spectroscopic observations makes mandatory a strong effort on the theoretical side to better reproduce the spectral energy distribution (SED) of stars at high spectral resolution. In this regard, relying on the Kurucz Atlas/Synthe original codes we computed the Bluered library, consisting of 832 synthetic SED of stars, that cover a large parameter space at very high spectral resolution (R = 500 000) along the 3500-7000 Å wavelength range. Methods: Bluered synthetic spectra have been used to assess in finer detail the intrinsic reliability and the performance limits of the Atlas theoretical framework. The continuum-normalized spectra of the Sun, Arcturus, and Vega, plus a selected list of 45 bright stars with high-quality SEDs from the Prugniel & Soubiran Elodie catalog, form our sample designed to probe the global properties of synthetic spectra across the entire range of H-R parameters. Results: Atlas models display a better fitting performance with increasing stellar temperature. High-resolution spectra of Vega, the Sun, and Arcturus have been reproduced at R=100 000, respectively, within a 0.7%, 4.5%, and 8.8% relative scatter in residual flux. In all the three cases, the residual flux distribution shows a significant asymmetry (skewness parameter γ = -2.21, -0.98, -0.67, respectively), which neatly confirms an overall “excess” of theoretical line blanketing. For the Sun, this apparent discrepancy is alleviated, but not recovered, by a systematic decrease (-40%) of the line oscillator strengths, log (gf), especially referring to iron transitions. Definitely, a straight “astrophysical” determination of log (gf) for each individual atomic transition has to be devised to overcome the problem. By neglecting overblanketing effects in theoretical models when fitting high-resolution continuum-normalized spectra of real stars, we lead to a systematically warmer effective temperature (between +80 and +300 K for the solar fit) and a

  18. Kinetics of the formation of a protein corona around nanoparticles.

    Science.gov (United States)

    Zhdanov, Vladimir P; Cho, Nam-Joon

    2016-12-01

    Interaction of metal or oxide nanoparticles (NPs) with biological soft matter is one of the central phenomena in basic and applied biology-oriented nanoscience. Often, this interaction includes adsorption of suspended proteins on the NP surface, resulting in the formation of the protein corona around NPs. Structurally, the corona contains a "hard" monolayer shell directly contacting a NP and a more distant weakly associated "soft" shell. Chemically, the corona is typically composed of a mixture of distinct proteins. The corresponding experimental and theoretical studies have already clarified many aspects of the corona formation. The process is, however, complex, and its understanding is still incomplete. Herein, we present a kinetic mean-field model of the formation of the "hard" corona with emphasis on the role of (i) protein-diffusion limitations and (ii) interplay between competitive adsorption of distinct proteins and irreversible reconfiguration of their native structure. The former factor is demonstrated to be significant only in the very beginning of the corona formation. The latter factor is predicted to be more important. It may determine the composition of the corona on the time scales comparable or longer than a few hours.

  19. Fingering convection induced by atomic diffusion in stars: 3D numerical computations and applications to stellar models

    Energy Technology Data Exchange (ETDEWEB)

    Zemskova, Varvara [Department of Marine Sciences, University of North Carolina at Chapel Hill, 3202 Venable Hall, CB 3300, Chapel Hill, NC 27599-3300 (United States); Garaud, Pascale [Department of Applied Mathematics and Statistics, Baskin School of Engineering, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Deal, Morgan; Vauclair, Sylvie [Institut de Recherche en Astrophysique et Planétologie, 14 avenue Edouard Belin, Université de Toulouse, F-31400-Toulouse (France)

    2014-11-10

    Iron-rich layers are known to form in the stellar subsurface through a combination of gravitational settling and radiative levitation. Their presence, nature, and detailed structure can affect the excitation process of various stellar pulsation modes and must therefore be modeled carefully in order to better interpret Kepler asteroseismic data. In this paper, we study the interplay between atomic diffusion and fingering convection in A-type stars, as well as its role in the establishment and evolution of iron accumulation layers. To do so, we use a combination of three-dimensional idealized numerical simulations of fingering convection (which neglect radiative transfer and complex opacity effects) and one-dimensional realistic stellar models. Using the three-dimensional simulations, we first validate the mixing prescription for fingering convection recently proposed by Brown et al. (within the scope of the aforementioned approximation) and identify what system parameters (total mass of iron, iron diffusivity, thermal diffusivity, etc.) play a role in the overall evolution of the layer. We then implement the Brown et al. prescription in the Toulouse-Geneva Evolution Code to study the evolution of the iron abundance profile beneath the stellar surface. We find, as first discussed by Théado et al., that when the concurrent settling of helium is ignored, this accumulation rapidly causes an inversion in the mean molecular weight profile, which then drives fingering convection. The latter mixes iron with the surrounding material very efficiently, and the resulting iron layer is very weak. However, taking helium settling into account partially stabilizes the iron profile against fingering convection, and a large iron overabundance can accumulate. The opacity also increases significantly as a result, and in some cases it ultimately triggers dynamical convection. The direct effects of radiative acceleration on the dynamics of fingering convection (especially in the

  20. K{sup -} and p-bar spectra for AuAu collisions at {radical}s = 200 GeV from STAR, PHENIX, and BRAHMS in comparison to core-corona model predictions

    Energy Technology Data Exchange (ETDEWEB)

    Schreiber, C.; Werner, K.; Aichelin, J. [Universite de Nantes, SUBATECH (France)

    2012-05-15

    Based on results obtained with event generators we have launched the core-corona model. It describes in a simplified way but quite successfully the centrality dependence of multiplicity and of identified particles observed in heavy-ion reactions at beam energies between {radical}s = 17 and 200 GeV. Also the centrality dependence of the elliptic flow, {upsilon}{sub 2}, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single-particle spectra of K{sup -} and p-bar measured by the PHENIX, STAR, and BRAHMS Collaborations. We find that also for these particles the analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. As for protons and K{sup +}, for each experience the data agree well with the prediction of the core-corona model but the values of the two necessary parameters depend on the experiments. We show as well that the average momentum as a function of the centrality depends in a very sensitive way on the particle species and may be quite different for particles which have about the same mass. Therefore the idea to interpret this centrality dependence as a consequence of a collective expansion of the system, as done in blast way fits, may be premature.

  1. K - and bar p spectra for AuAu collisions at √s = 200 GeV from STAR, PHENIX, and BRAHMS in comparison to core-corona model predictions

    Science.gov (United States)

    Schreiber, C.; Werner, K.; Aichelin, J.

    2012-05-01

    Based on results obtained with event generators we have launched the core-corona model. It describes in a simplified way but quite successfully the centrality dependence of multiplicity and of identified particles observed in heavy-ion reactions at beam energies between √s = 17 and 200 GeV. Also the centrality dependence of the elliptic flow, υ 2, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single-particle spectra of K - and bar p measured by the PHENIX, STAR, and BRAHMS Collaborations. We find that also for these particles the analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. As for protons and K +, for each experience the data agree well with the prediction of the core-corona model but the values of the two necessary parameters depend on the experiments. We show as well that the average momentum as a function of the centrality depends in a very sensitive way on the particle species and may be quite different for particles which have about the same mass. Therefore the idea to interpret this centrality dependence as a consequence of a collective expansion of the system, as done in blast way fits, may be premature.

  2. $K^-$ and $\\bar p$ Spectra for Au+Au Collisions at $\\sqrt{s}$ = 200 GeV from STAR, PHENIX and BRAHMS in Comparison to Core-Corona Model Predictions

    CERN Document Server

    Schreiber, C; Aichelin, J

    2012-01-01

    Based on results obtained with event generators we have launched the core-corona model. It describes in a simplified way but quite successfully the centrality dependence of multiplicity and $$ of identified particles observed in heavy-ion reaction at beam energies between $\\sqrt{s}$ = 17 GeV and 200 GeV. Also the centrality dependence of the elliptic flow, $v_2$, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single particle spectra of $K^-$ and ${\\bar p}$ measured by the PHENIX, STAR and BRAHMS collaborations. We find that also for these particles the analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. As for protons and $K^+$ for each experience the data agree well with the prediction of the core-corona model but the value of the two necessary parameters depends on the experiments. We show as well that...

  3. K- and /line p Spectra for Au+Au Collisions at √ s = 200 GeV from Star, Phenix and Brahms in Comparison to Core-Corona Model Predictions

    Science.gov (United States)

    Schreiber, C.; Werner, K.; Aichelin, J.

    2012-01-01

    Based on results obtained with event generators we have launched the core-corona model. It describes in a simplified way but quite successfully the centrality dependence of multiplicity and of identified particles observed in heavy ion reaction at beam energies between √ s = 17 GeV and 200GeV. Also the centrality dependence of the elliptic flow, ν2, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single particle spectra of K- and /line p measured by the PHENIX, STAR and BRAHMS collaborations. We find that also for these particles the analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. As for protons and K+ for each experience the data agree well with the prediction of the core-corona model but the value of the two necessary parameters depends on the experiments. We show as well that the average momentum as a function of the centrality depends in a very sensitive way on the particle species and may be quite different for particle which have about the same mass. Therefore the idea to interpret this centrality dependence as a consequence of a collective expansion of the system, as done in blast way fits may be premature.

  4. Structural glitches near the cores of red giants revealed by oscillations in g-mode period spacings from stellar models

    CERN Document Server

    Cunha, M S; Avelino, P P; Christensen-Dalsgaard, J; Townsend, R H D

    2015-01-01

    With recent advances in asteroseismology it is now possible to peer into the cores of red giants, potentially providing a way to study processes such as nuclear burning and mixing through their imprint as sharp structural variations -- glitches -- in the stellar cores. Here we show how such core glitches can affect the oscillations we observe in red giants. We derive an analytical expression describing the expected frequency pattern in the presence of a glitch. This formulation also accounts for the coupling between acoustic and gravity waves. From an extensive set of canonical stellar models we find glitch-induced variation in the period spacing and inertia of non-radial modes during several phases of red-giant evolution. Significant changes are seen in the appearance of mode amplitude and frequency patterns in asteroseismic diagrams such as the power spectrum and the \\'echelle diagram. Interestingly, along the red-giant branch glitch-induced variation occurs only at the luminosity bump, potentially providin...

  5. Stellar modelling of Spica, a high-mass spectroscopic binary with a beta Cep variable primary component

    CERN Document Server

    Tkachenko, A; Aerts, C; Pavlovski, K; Papics, P I; Zwintz, K; Cameron, C; Walker, G A H; Kuschnig, R; Degroote, P; Debosscher, J; Moravveji, E; Kolbas, V; Guenther, D B; Moffat, A F J; Rowe, J F; Rucinski, S M; Sasselov, D; Weiss, W W

    2016-01-01

    Binary stars provide a valuable test of stellar structure and evolution, because the masses of the individual stellar components can be derived with high accuracy and in a model-independent way. In this work, we study Spica, an eccentric double-lined spectroscopic binary system with a beta Cep type variable primary component. We use state-of-the-art modelling tools to determine accurate orbital elements of the binary system and atmospheric parameters of both stellar components. We interpret the short-period variability intrinsic to the primary component, detected on top of the orbital motion both in the photometric and spectroscopic data. The non-LTE based spectrum analysis reveals two stars of similar atmospheric chemical composition consistent with the present day cosmic abundance standard defined by Nieva&Przybilla (2012). The masses and radii of the stars are found to be 11.43+/-1.15 M_sun and 7.21+/-0.75 M_sun, and 7.47+/-0.54 R_sun and 3.74+/-0.53 R_sun for the primary and secondary, respectively. W...

  6. Semi-empirical white dwarf initial-final mass relationships: a thorough analysis of systematic uncertainties due to stellar evolution models

    CERN Document Server

    Salaris, Maurizio; Weiss, Achim; Bertolami, Marcelo Miller

    2008-01-01

    Using the most recent results about white dwarfs in 10 open clusters, we revisit semi-empirical estimates of the initial-final mass relation in star clusters, with emphasis on the use of stellar evolution models. We discuss the influence of these models on each step of the derivation. One intention of our work is to use consistent sets of calculations both for the isochrones and the white dwarf cooling tracks. The second one is to derive the range of systematic errors arising from stellar evolution theory. This is achieved by using different sources for the stellar models and by varying physical assumptions and input data. We find that systematic errors, including the determination of the cluster age, are dominating the initial mass values, while observational uncertainties influence the final mass primarily. After having determined the systematic errors, the initial-final mass relation allows us finally to draw conclusions about the physics of the stellar models, in particular about convective overshooting.

  7. The dynamics of general relativistic isotropic stellar cluster models -- Do relativistic extensions of the Plummer model exist?

    CERN Document Server

    De Rijcke, Sven; Boelens, Thomas

    2014-01-01

    We show that the general relativistic theory of the dynamics of isotropic stellar clusters can be developed essentially along the same lines as the Newtonian theory. We prove that the distribution function can be derived from any isotropic momentum moment and that every higher-order moment of the distribution can be written as an integral over a zeroth-order moment. We propose a mathematically simple expression for the distribution function of a family of isotropic general relativistic cluster models and investigate their dynamical properties. In the Newtonian limit, these models obtain a distribution function of the form F(E) ~ (E-E_0)^alpha, with E binding energy and E_0 a constant that determines the model's outer radius. The slope alpha sets the steepness of the distribution function and the corresponding radial density and pressure profiles. We show that the field equations only yield solutions with finite mass for alpha3.5, only Newtonian models exist. In other words: within the context of this family o...

  8. Testing fundamental physics with distant star clusters: theoretical models for pressure-supported stellar systems

    Science.gov (United States)

    Haghi, Hosein; Baumgardt, Holger; Kroupa, Pavel; Grebel, Eva K.; Hilker, Michael; Jordi, Katrin

    2009-05-01

    We investigate the mean velocity dispersion and the velocity dispersion profile of stellar systems in modified Newtonian dynamics (MOND), using the N-body code N-MODY, which is a particle-mesh-based code with a numerical MOND potential solver developed by Ciotti, Londrillo & Nipoti. We have calculated mean velocity dispersions for stellar systems following Plummer density distributions with masses in the range of 104 to 109Msolar and which are either isolated or immersed in an external field. Our integrations reproduce previous analytic estimates for stellar velocities in systems in the deep MOND regime (ai, ae > ae) or constant external accelerations (ae >> ai). In addition, we derive for the first time analytic formulae for the line-of-sight velocity dispersion in the intermediate regime (ai ~ ae ~ a0). This allows for a much-improved comparison of MOND with observed velocity dispersions of stellar systems. We finally derive the velocity dispersion of the globular cluster Pal14 as one of the outer Milky Way halo globular clusters that have recently been proposed as a differentiator between Newtonian and MONDian dynamics.

  9. Use of AO PSF models for the Study of Resolved Stellar Populations

    NARCIS (Netherlands)

    Deep, A.; Fiorentino, G.; Jolissaint, L.; Tolstoy, E.; Clénet, Y.; Conan, J.-M.; Fusco, Th.; Rousset, G.

    2010-01-01

    The full scientific exploitation of AO images to study resolved stellar populations is still in a nascent stage. This requires pushing to the faint limits and carrying out deep and accurate crowded field photometry and astrometry. The main complexity of AO images is that the correction is never perf

  10. Kinematic modeling of the Milky Way using the RAVE and GCS stellar surveys

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, S.; Bland-Hawthorn, J. [Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006 (Australia); Binney, J. [Rudolf Peierls Center for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP (United Kingdom); Freeman, K. C. [RSAA Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, Canberra, ACT 72611 (Australia); Steinmetz, M.; Williams, M. E. K. [Leibniz Institut für Astrophysik Potsdam (AIP), An der Sterwarte 16, D-14482 Potsdam (Germany); Boeche, C.; Grebel, E. K. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, D-69120 Heidelberg (Germany); Bienaymé, O.; Siebert, A. [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, F-67000 Strasbourg (France); Gibson, B. K. [Jeremiah Horrocks Institute for Astrophysics and Super-computing, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Gilmore, G. F.; Kordopatis, G. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Helmi, A. [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Munari, U. [INAF-Astronomical Observatory of Padova, I-36012 Asiago (VI) (Italy); Navarro, J. F. [University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC V8W 3P6 (Canada); Parker, Q. A.; Reid, W. A. [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Seabroke, G. M. [Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT (United Kingdom); Watson, F. [Australian Astronomical Observatory, P.O. Box 296, Epping, NSW 1710 (Australia); and others

    2014-09-20

    We investigate the kinematic parameters of the Milky Way disk using the Radial Velocity Experiment (RAVE) and Geneva-Copenhagen Survey (GCS) stellar surveys. We do this by fitting a kinematic model to the data and taking the selection function of the data into account. For stars in the GCS we use all phase-space coordinates, but for RAVE stars we use only (ℓ, b, v {sub los}). Using the Markov Chain Monte Carlo technique, we investigate the full posterior distributions of the parameters given the data. We investigate the age-velocity dispersion relation for the three kinematic components (σ {sub R}, σ{sub φ}, σ {sub z}), the radial dependence of the velocity dispersions, the solar peculiar motion (U {sub ☉}, V {sub ☉}, W {sub ☉}), the circular speed Θ{sub 0} at the Sun, and the fall of mean azimuthal motion with height above the midplane. We confirm that the Besançon-style Gaussian model accurately fits the GCS data but fails to match the details of the more spatially extended RAVE survey. In particular, the Shu distribution function (DF) handles noncircular orbits more accurately and provides a better fit to the kinematic data. The Gaussian DF not only fits the data poorly but systematically underestimates the fall of velocity dispersion with radius. The radial scale length of the velocity dispersion profile of the thick disk was found to be smaller than that of the thin disk. We find that correlations exist between a number of parameters, which highlights the importance of doing joint fits. The large size of the RAVE survey allows us to get precise values for most parameters. However, large systematic uncertainties remain, especially in V {sub ☉} and Θ{sub 0}. We find that, for an extended sample of stars, Θ{sub 0} is underestimated by as much as 10% if the vertical dependence of the mean azimuthal motion is neglected. Using a simple model for vertical dependence of kinematics, we find that it is possible to match the Sgr A* proper motion without

  11. The Stagger-grid: A grid of 3D stellar atmosphere models. III. The relation to mixing length convection theory

    Science.gov (United States)

    Magic, Z.; Weiss, A.; Asplund, M.

    2015-01-01

    Aims: We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. Methods: The adiabatic entropy value of the deep convection zone, sbot, and the entropy jump, Δs, determined from the 3D RHD models, were matched with the mixing length parameter, αMLT, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derived the mass mixing length parameter, αm, and the vertical correlation length of the vertical velocity, C[vz,vz], directly from the 3D hydrodynamical simulations of stellar subsurface convection. Results: The calibrated mixing length parameter for the Sun is α๏MLT (Sbot) = 1.98. . For different stellar parameters, αMLT varies systematically in the range of 1.7 - 2.4. In particular, αMLT decreases towards higher effective temperature, lower surface gravity and higher metallicity. We find equivalent results for α๏MLT (ΔS). In addition, we find a tight correlation between the mixing length parameter and the inverse entropy jump. We derive an analytical expression from the hydrodynamic mean-field equations that motivates the relation to the mass mixing length parameter, αm, and find that it qualitatively shows a similar variation with stellar parameter (between 1.6 and 2.4) with the solar value of α๏m = 1.83.. The vertical correlation length scaled with the pressure scale height yields 1.71 for the Sun, but only displays a small systematic variation with stellar parameters, the correlation length slightly increases with Teff. Conclusions: We derive mixing length parameters for various stellar parameters that can be used to replace a constant value. Within any convective envelope, αm and related quantities vary strongly. Our results will help to replace a constant αMLT. Appendices are available in electronic form at http

  12. Measurement and Modeling of Large Helical Flows in the HSX Stellarator

    Science.gov (United States)

    Briesemeister, Alexis

    2012-10-01

    Symmetry in a device's magnetic field strength allows large flows to develop, which may reduce turbulent transport. Although symmetry is an inherent feature of tokamaks and other axisymmetric devices, stellarators typically do not have a direction of symmetry. The quasihelically symmetric HSX stellarator is the only device with a helical direction of approximately constant magnetic field strength. We present here first results that verify the capability for the class of quasisymmetric stellarators to have large intrinsic flows. Flow velocities of up to 20 km/s along the helical direction, with no external momentum injection, have been measured using charge exchange recombination spectroscopy in HSX. Measurements are made using the 529 nm C+5 line at 10 radial locations from two viewing directions allowing the flow direction and magnitude to be determined. These measured flows are compared to the neoclassical values calculated by the PENTA code [1]. A non-momentum conserving collision operator is used when solving the drift kinetic equation for stellarators, which typically have large flow damping in all directions. HSX's parallel flow is under-predicted by an order of magnitude by the non-momentum conserving calculations, but good agreement is seen with parallel flows calculated by PENTA when a momentum conservation correction technique [2] is applied. In addition to verifying a key attribute of quasisymmetric stellarators, these results validate a neoclassical code that can calculate plasma flows in a wide range of toroidal devices from perfectly axisymmetric systems to fully 3D configurations. This allows the effects of symmetry breaking magnetic field components, which can increase flow drive as well as damping, to be studied.[4pt] [1] D. Spong, Phys. Plas. 12 (2005) 056114.[0pt] [2] H. Sugama, S. Nishimura, Phys. Plas. 9 (2002) 4637.

  13. The Density of Coronal Plasma in Active Stellar Coronae

    CERN Document Server

    Testa, P; Peres, G; Testa, Paola; Drake, Jeremy J.; Peres, Giovanni

    2004-01-01

    We have analyzed high-resolution X-ray spectra of a sample of 22 active stars observed with the High Energy Transmission Grating Spectrometer on {\\em Chandra} in order to investigate their coronal plasma density. Densities where investigated using the lines of the He-like ions O VII, Mg XI, and Si XIII. While Si XIII lines in all stars of the sample are compatible with the low-density limit, Mg XI lines betray the presence of high plasma densities ($> 10^{12}$ cm$^{-3}$) for most of the sources with higher X-ray luminosity ($> 10^{30}$ erg/s); stars with higher $L_X$ and $L_X/L_{bol}$ tend to have higher densities at high temperatures. Ratios of O VII lines yield much lower densities of a few $10^{10}$ cm$^{-3}$, indicating that the ``hot'' and ``cool'' plasma resides in physically different structures. Our findings imply remarkably compact coronal structures, especially for the hotter plasma emitting the Mg XI lines characterized by coronal surface filling factor, $f_{MgXI}$, ranging from $10^{-4}$ to $10^{-...

  14. Stellar feedback efficiencies: supernovae versus stellar winds

    CERN Document Server

    Fierlinger, Katharina M; Ntormousi, Evangelia; Fierlinger, Peter; Schartmann, Marc; Ballone, Alessandro; Krause, Martin G H; Diehl, Roland

    2015-01-01

    Stellar winds and supernova (SN) explosions of massive stars ("stellar feedback") create bubbles in the interstellar medium (ISM) and insert newly produced heavy elements and kinetic energy into their surroundings, possibly driving turbulence. Most of this energy is thermalized and immediately removed from the ISM by radiative cooling. The rest is available for driving ISM dynamics. In this work we estimate the amount of feedback energy retained as kinetic energy when the bubble walls have decelerated to the sound speed of the ambient medium. We show that the feedback of the most massive star outweighs the feedback from less massive stars. For a giant molecular cloud (GMC) mass of 1e5 solar masses (as e.g. found in the Orion GMCs) and a star formation efficiency of 8% the initial mass function predicts a most massive star of approximately 60 solar masses. For this stellar evolution model we test the dependence of the retained kinetic energy of the cold GMC gas on the inclusion of stellar winds. In our model w...

  15. Snowfall induced by corona discharge

    CERN Document Server

    Ju, Jingjing; Li, Ruxin; Du, Shengzhe; Sun, Haiyi; Liu, Yonghong; Tian, Ye; Bai, Yafeng; Liu, Yaoxiang; Chen, Na; Wang, Jingwei; Wang, Cheng; Liu, Jiansheng; Chin, S L; Xu, Zhizhan

    2016-01-01

    We demonstrated for the first time the condensation and precipitation (or snowfall) induced by a corona discharge inside a cloud chamber. Ionic wind was found to have played a more significant role than ions as extra Cloud Condensation Nuclei (CCN). 2.25 g of net snow enhancement was measured after applying a 30 kV corona discharge for 25 min. In comparison with another newly emerging femtosecond laser filamentation method, the snow precipitation induced by the corona discharge has about 4 orders of magnitude higher wall-plug efficiency under similar conditions.

  16. Tutorial models of the climate and habitability of Proxima Centauri b: a thin atmosphere is sufficient to distribute heat given low stellar flux

    CERN Document Server

    Goldblatt, Colin

    2016-01-01

    Proxima Centauri b, an Earth-size planet in the habitable zone of our nearest stellar neighbour, has just been discovered. A theoretical framework of synchronously rotating planets, in which the risk of a runaway greenhouse on the sunlight side and atmospheric collapse on the reverse side are mutually ameliorated via heat transport is discussed. This is developed via simple (tutorial) models of the climate. These show that lower incident stellar flux means that less heat transport, so less atmospheric mass, is required. The incident stellar flux at Proxima Centauri b is indeed low, which may help enhance habitability if it has suffered some atmospheric loss or began with a low volatile inventory.

  17. Improving the Ni I atomic model for solar and stellar atmospheric models

    CERN Document Server

    Vieytes, Mariela C

    2013-01-01

    Neutral nickel (Ni I) is abundant in the solar atmosphere and is one of the important elements that contribute to the emission and absorption of radiation in the spectral range between 1900 and 3900 A. Previously, the Solar Radiation Physical Modeling (SRPM) models of the solar atmosphere considered only few levels of this species. Here we improve the Ni I atomic model by taking into account 61 levels and 490 spectral lines. We compute the populations of these levels in full NLTE using the SRPM code and compare the resulting emerging spectrum with observations. The present atomic model improves significantly the calculation of the solar spectral irradiance at near-UV wavelengths that are important for Earth atmo spheric studies, and particularly for ozone chemistry.

  18. Time-dependent tomographic reconstruction of the solar corona

    Science.gov (United States)

    Vibert, D.; Peillon, C.; Lamy, P.; Frazin, R. A.; Wojak, J.

    2016-10-01

    Solar rotational tomography (SRT) applied to white-light coronal images observed at multiple aspect angles has been the preferred approach for determining the three-dimensional (3D) electron density structure of the solar corona. However, it is seriously hampered by the restrictive assumption that the corona is time-invariant which introduces significant errors in the reconstruction. We first explore several methods to mitigate the temporal variation of the corona by decoupling the "fast-varying" inner corona from the "slow-moving" outer corona using multiple masking (either by juxtaposition or recursive combination) and radial weighting. Weighting with a radial exponential profile provides some improvement over a classical reconstruction but only beyond ≈ 3R⊙. We next consider a full time-dependent tomographic reconstruction involving spatio-temporal regularization and further introduce a co-rotating regularization aimed at preventing concentration of reconstructed density in the plane of the sky. Crucial to testing our procedure and properly tuning the regularization parameters is the introduction of a time-dependent MHD model of the corona based on observed magnetograms to build a time-series of synthetic images of the corona. Our procedure, which successfully reproduces the time-varying model corona, is finally applied to a set of 53 LASCO-C2 pB images roughly evenly spaced in time from 15 to 29 March 2009. Our procedure paves the way to a time-dependent tomographic reconstruction of the coronal electron density to the whole set of LASCO-C2 images presently spanning 20 years.

  19. STELLAR LOCI II. A MODEL-FREE ESTIMATE OF THE BINARY FRACTION FOR FIELD FGK STARS

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Haibo; Liu, Xiaowei [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Xiang, Maosheng; Huang, Yang; Chen, Bingqiu [Department of Astronomy, Peking University, Beijing 100871 (China); Wu, Yue [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Hou, Yonghui; Zhang, Yong, E-mail: yuanhb4861@pku.edu.cn, E-mail: x.liu@pku.edu.cn [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China)

    2015-02-01

    We propose a stellar locus outlier (SLOT) method to determine the binary fraction of main-sequence stars statistically. The method is sensitive to neither the period nor mass ratio distributions of binaries and is able to provide model-free estimates of binary fraction for large numbers of stars of different populations in large survey volumes. We have applied the SLOT method to two samples of stars from the Sloan Digital Sky Survey (SDSS) Stripe 82, constructed by combining the recalibrated SDSS photometric data with the spectroscopic information from the SDSS and LAMOST surveys. For the SDSS spectroscopic sample, we find an average binary fraction for field FGK stars of 41% ± 2%. The fractions decrease toward late spectral types and are 44% ± 5%, 43% ± 3%, 35% ± 5%, and 28% ± 6% for stars with g – i colors in the range 0.3-0.6 mag, 0.6-0.9 mag, 0.9-1.2 mag, and 1.2-1.6 mag, respectively. A modest metallicity dependence is also found. The fraction decreases with increasing metallicity. For stars with [Fe/H] between –0.5 and 0.0 dex, –1.0 and –0.5 dex, –1.5 and –1.0 dex, and –2.0 and –1.5 dex, the inferred binary fractions are 37% ± 3%, 39% ± 3%, 50% ± 9%, and 53% ± 20%, respectively. We have further divided the sample into stars from the thin disk, the thick disk, the transition zone between them, and the halo. The results suggest that the Galactic thin and thick disks have comparable binary fractions, whereas the Galactic halo contains a significantly larger fraction of binaries. Applying the method to the LAMOST spectroscopic sample yields consistent results. Finally, other potential applications and future work with the method are discussed.

  20. Dynamics of the Transition Corona

    Science.gov (United States)

    Masson, Sophie; McCauley, Patrick; Golub, Leon; Reeves, Katharine K.; DeLuca, Edward E.

    2014-01-01

    Magnetic reconnection between the open and closed magnetic fields in the corona is believed to play a crucial role in the corona/heliosphere coupling. At large scale, the exchange of open/closed connectivity is expected to occur in pseudo-streamer (PS) structures. However, there is neither clear observational evidence of how such coupling occurs in PSs, nor evidence for how the magnetic reconnection evolves. Using a newly developed technique, we enhance the off-limb magnetic fine structures observed with the Atmospheric Imaging Assembly and identify a PS-like feature located close to the northern coronal hole. We first identify that the magnetic topology associated with the observation is a PS, null-point (NP) related topology bounded by the open field. By comparing the magnetic field configuration with the extreme ultraviolet (EUV) emission regions, we determined that most of the magnetic flux associated with plasma emission are small loops below the PS basic NP and open field bounding the PS topology. In order to interpret the evolution of the PS, we referred to a three-dimensional MHD interchange reconnection modeling the exchange of connectivity between small closed loops and the open field. The observed PS fine structures follow the dynamics of the magnetic field before and after reconnecting at the NP obtained by the interchange model. Moreover, the pattern of the EUV plasma emission is the same as the shape of the expected plasma emission location derived from the simulation. These morphological and dynamical similarities between the PS observations and the results from the simulation strongly suggest that the evolution of the PS, and in particular the opening/closing of the field, occurs via interchange/slipping reconnection at the basic NP of the PS. Besides identifying the mechanism at work in the large-scale coupling between the open and closed fields, our results highlight that interchange reconnection in PSs is a gradual physical process that differs

  1. MODELING THE ROSSITER–MCLAUGHLIN EFFECT: IMPACT OF THE CONVECTIVE CENTER-TO-LIMB VARIATIONS IN THE STELLAR PHOTOSPHERE

    Energy Technology Data Exchange (ETDEWEB)

    Cegla, H. M.; Watson, C. A. [Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN (United Kingdom); Oshagh, M.; Figueira, P.; Santos, N. C. [Instituto de Astrofisica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto (Portugal); Shelyag, S., E-mail: h.cegla@qub.ac.uk [Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Clayton, Victoria, 3800 (Australia)

    2016-03-01

    Observations of the Rossiter–McLaughlin (RM) effect provide information on star–planet alignments, which can inform planetary migration and evolution theories. Here, we go beyond the classical RM modeling and explore the impact of a convective blueshift that varies across the stellar disk and non-Gaussian stellar photospheric profiles. We simulated an aligned hot Jupiter with a four-day orbit about a Sun-like star and injected center-to-limb velocity (and profile shape) variations based on radiative 3D magnetohydrodynamic simulations of solar surface convection. The residuals between our modeling and classical RM modeling were dependent on the intrinsic profile width and v sin i; the amplitude of the residuals increased with increasing v sin i and with decreasing intrinsic profile width. For slowly rotating stars the center-to-limb convective variation dominated the residuals (with amplitudes of 10 s of cm s{sup −1} to ∼1 m s{sup −1}); however, for faster rotating stars the dominant residual signature was due a non-Gaussian intrinsic profile (with amplitudes from 0.5 to 9 m s{sup −1}). When the impact factor was 0, neglecting to account for the convective center-to-limb variation led to an uncertainty in the obliquity of ∼10°–20°, even though the true v sin i was known. Additionally, neglecting to properly model an asymmetric intrinsic profile had a greater impact for more rapidly rotating stars (e.g., v sin i = 6 km s{sup −1}) and caused systematic errors on the order of ∼20° in the measured obliquities. Hence, neglecting the impact of stellar surface convection may bias star–planet alignment measurements and consequently theories on planetary migration and evolution.

  2. Stellar Populations

    NARCIS (Netherlands)

    Peletier, Reynier F.

    2013-01-01

    This is a summary of my lectures during the 2011 Canary Islands Winter School in Puerto de la Cruz. I give an introduction to the field of stellar populations in galaxies, and highlight some new results. Since the title of the Winter School is Secular Evolution in Galaxies I mostly concentrate on ne

  3. Stellar remnants

    CERN Document Server

    Kawaler, S D; Srinivasan, G

    1997-01-01

    This volume examines the internal structure, origin and evolution of white dwarfs, neutron stars and black holes, all objects at the final stage of stellar evolution. It covers topics such as: pulsation of white dwarfs; millisecond pulsars; and the dynamics around black holes.

  4. Dynamical modelling of the galactic bulge and bar: the Milky Way's pattern speed, stellar and dark matter mass distribution

    Science.gov (United States)

    Portail, Matthieu; Gerhard, Ortwin; Wegg, Christopher; Ness, Melissa

    2017-02-01

    We construct a large set of dynamical models of the galactic bulge, bar and inner disc using the made-to-measure method. Our models are constrained to match the red clump giant density from a combination of the VVV, UKIDSS and 2MASS infrared surveys together with stellar kinematics in the bulge from the BRAVA and OGLE surveys, and in the entire bar region from the ARGOS Survey. We are able to recover the bar pattern speed and the stellar and dark matter mass distributions in the bar region, thus recovering the entire galactic effective potential. We find a bar pattern speed of 39.0 ± 3.5 km s- 1 kpc- 1, placing the bar corotation radius at 6.1 ± 0.5 kpc and making the Milky Way bar a typical fast rotator. We evaluate the stellar mass of the long bar and bulge structure to be Mbar/bulge = 1.88 ± 0.12 × 1010 M⊙, larger than the mass of disc in the bar region, Minner disc = 1.29 ± 0.12 × 1010 M⊙. The total dynamical mass in the bulge volume is 1.85 ± 0.05 × 1010 M⊙. Thanks to more extended kinematic data sets and recent measurement of the bulge initial mass function, our models have a low dark matter fraction in the bulge of 17 ± 2 per cent. We find a dark matter density profile which flattens to a shallow cusp or core in the bulge region. Finally, we find dynamical evidence for an extra central mass of ∼ 0.2 × 1010 M⊙, probably in a nuclear disc or discy pseudo-bulge.

  5. The Stagger-grid: A grid of 3D stellar atmosphere models - III. The relation to mixing length convection theory

    CERN Document Server

    Magic, Zazralt; Asplund, Martin

    2014-01-01

    We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. The adiabatic entropy value of the deep convection zone, s_bot, and the entropy jump, {\\Delta}s, determined from the 3D RHD models, are matched with the mixing length parameter, {\\alpha}_MLT, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derive the mass mixing length, {\\alpha}_m, and the vertical correlation length of the vertical velocity, C[v_z,v_z], directly from the 3D hydrodynamical simulations of stellar subsurface convection. The calibrated mixing length parameter for the Sun is {\\alpha}_MLT (s_bot) = 1.98. For different stellar parameters, {\\alpha}_MLT varies systematically in the range of 1.7 - 2.4. In particular, {\\alpha}_MLT decreases towards higher effective temperature, lower surface gravity and higher metallicity...

  6. Two-fluid and magnetohydrodynamic modelling of magnetic reconnection in the MAST spherical tokamak and the solar corona

    CERN Document Server

    Browning, P K; Evans, M; Lucini, F Arese; Lukin, V S; McClements, K G; Stanier, A

    2015-01-01

    Twisted magnetic flux ropes are ubiquitous in space and laboratory plasmas, and the merging of such flux ropes through magnetic reconnection is an important mechanism for restructuring magnetic fields and releasing free magnetic energy. The merging-compression scenario is one possible start up scheme for spherical tokamaks, which has been used on the Mega Amp Spherical Tokamak MAST. Two current-carrying plasma rings, or flux ropes, approach each other through the mutual attraction of their like currents, and merge, through magnetic reconnection, into a single plasma torus, with substantial plasma heating. 2D resistive MHD and Hall MHD simulations of this process are reported, and new results for the temperature distribution of ions and electrons are presented. A model of the based on relaxation theory is also described, which is now extended to tight aspect ratio geometry. This model allows prediction of the final merged state and the heating. The implications of the relaxation model for heating of the solar ...

  7. Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC2264

    CERN Document Server

    Landin, N R; Vaz, L P R; Alencar, S H P

    2015-01-01

    Rotational evolution in young stars is described by pMS evolutionary tracks including rotation, conservation of angular momentum (AM), and simulations of disk-locking (DL). By assuming that DL is the regulation mechanism for the stellar angular velocity during the early stages of pMS, we use our models and observational data to constrain disk lifetimes (Tdisk) of a sample of low-mass stars in the ONC and NGC2264. The period distributions of the ONC and NGC2264 are bimodal and depend on the stellar mass. To follow the rotational evolution of these two clusters' stars, we generated some sets of evolutionary tracks. We assumed that the evolution of fast rotators can be modeled by considering conservation of AM during all stages and of moderate rotators by considering conservation of angular velocity during the first stages of evolution. With these models we estimate a mass and an age for all stars. For the ONC, we assume that the secondary peak in the period distribution is due to high-mass objects locked in the...

  8. Modelling the Rossiter-McLaughlin Effect: Impact of the Convective Centre-to-Limb Variations in the Stellar Photosphere

    CERN Document Server

    Cegla, H M; Watson, C A; Figueira, P; Santos, N C; Shelyag, S

    2016-01-01

    Observations of the Rossiter-McLaughlin (RM) effect provide information on star-planet alignments, which can inform planetary migration and evolution theories. Here, we go beyond the classical RM modelling and explore the impact of a convective blueshift that varies across the stellar disc and non-Gaussian stellar photospheric profiles. We simulated an aligned hot Jupiter with a 4 d orbit about a Sun-like star and injected centre-to-limb velocity (and profile shape) variations based on radiative 3D magnetohydrodynamic simulations of solar surface convection. The residuals between our modelling and classical RM modelling were dependent on the intrinsic profile width and v sin i; the amplitude of the residuals increased with increasing v sin i, and with decreasing intrinsic profile width. For slowly rotating stars the centre-to-limb convective variation dominated the residuals (with amplitudes of 10s of cm/s to ~1 m/s); however, for faster rotating stars the dominant residual signature was due a non-Gaussian in...

  9. Evolution of long-lived globular cluster stars I. Grid of stellar models with helium enhancement at [Fe/H] = -1.75

    CERN Document Server

    Chantereau, William; Decressin, Thibaut

    2015-01-01

    Our understanding of the formation and early evolution of globular clusters (GCs) has been totally overthrown with the discovery of the peculiar chemical properties of their long-lived host stars. As a consequence, the interpretation of the observed color-magnitude diagrams and of the properties of the GC stellar populations requires the use of stellar models computed with relevant chemical compositions. We present a grid of 224 stellar evolution for low-mass stars with initial masses between 0.3 and 1.0 Msun and initial helium mass fraction between 0.248 and 0.8 computed for [Fe/H]=-1.75 with the stellar evolution code STAREVOL. This grid is made available to the community. We explore the implications of the assumed initial chemical distribution for the main properties of the stellar models: evolution paths in the Hertzsprung-Russel diagram (HRD), duration and characteristics of the main evolutionary phases, and the chemical nature of the white dwarf remnants. We also provide the ranges in initial stellar ma...

  10. Simulation of low temperature atmospheric pressure corona discharge in helium

    Science.gov (United States)

    Bekasov, Vladimir; Kirsanov, Gennady; Eliseev, Stepan; Kudryavtsev, Anatoly; Sisoev, Sergey

    2015-11-01

    The main objective of this work was to construct a numerical model of corona discharge in helium at atmospheric pressure. The calculation was based on the two-dimensional hybrid model. Two different plasma-chemical models were considered. Models were built for RF corona and negative DC corona discharge. The system of equations is solved by the finite element method in the COMSOL Multiphysics. Main parameters of the discharge (the density of charged and excited particles, the electron temperature) and their dependence on the input parameters of the model (geometry, electrode voltage, power) were calculated. The calculations showed that the shape of the electron distribution near the electrode depends on the discharge power. The neutral gas heating data obtained will allow predicting the temperature of the gases at the designing of atmospheric pressure helium plasma sources.

  11. Gravitational Lensing & Stellar Dynamics

    CERN Document Server

    Koopmans, L V E

    2005-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and mass-anisotropy degeneracies. Second, observational results are presented from the Lenses Structure & Dynamics (LSD) Survey and the Sloan Lens ACS (SLACS) Survey collaborations to illustrate this new methodology in constraining the dark and stellar density profiles, and mass structure, of early-type galaxies to redshifts of unity.

  12. Temporal Variability of Stars and Stellar Systems

    CERN Document Server

    Lister, T A; Brown, T M; Street, R A

    2009-01-01

    Although the Sun is our closest star by many orders of magnitude and despite having sunspot records stretching back to ancient China, our knowledge of the Sun's magnetic field is far from complete. Indeed, even now, after decades of study, the most obvious manifestations of magnetic fields in the Sun (e.g. sunspots, flares and the corona) are scarcely understood at all. These failures in spite of intense effort suggest that to improve our grasp of magnetic fields in stars and of astrophysical dynamos in general, we must broaden our base of examples beyond the Sun; we must study stars with a variety of ages, masses, rotation rates, and other properties, so we can test models against as broad a range of circumstances as possible. Over the next decade, an array of indirect techniques will be supplemented by rapidly maturing new capabilities such as gyrochronology, asteroseismology and precision photometry from space, which will transform our understanding of the temporal variability of stars and stellar systems....

  13. Inflow Generated X-ray Corona Around Supermassive Black Holes and Unified Model for X-ray Emission

    CERN Document Server

    Wang, Lile

    2015-01-01

    Three-dimensional hydrodynamic simulations, covering the spatial domain from hundreds of Schwarzschild radii to $2\\ \\mathrm{pc}$ around the central supermassive black hole of mass $10^8 M_\\odot$, with detailed radiative cooling processes, are performed. Generically found is the existence of a significant amount of shock heated, high temperature ($\\geq 10^8\\ \\mathrm{K}$) coronal gas in the inner ($\\leq 10^4 r_\\mathrm{sch}$) region. It is shown that the composite bremsstrahlung emission spectrum due to coronal gas of various temperatures are in reasonable agreement with the overall ensemble spectrum of AGNs and hard X-ray background. Taking into account inverse Compton processes, in the context of the simulation-produced coronal gas, our model can readily account for the wide variety of AGN spectral shape, which can now be understood physically. The distinguishing feature of our model is that X-ray coronal gas is, for the first time, an integral part of the inflow gas and its observable characteristics are phys...

  14. Gravitational lensing & stellar dynamics

    NARCIS (Netherlands)

    Koopmans, L. V. E.; Mamon, GA; Combes, F; Deffayet, C; Fort, B

    2006-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and mass-ani

  15. Gravitational lensing & stellar dynamics

    NARCIS (Netherlands)

    Koopmans, L. V. E.; Mamon, GA; Combes, F; Deffayet, C; Fort, B

    2006-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and

  16. Gravitational lensing & stellar dynamics

    NARCIS (Netherlands)

    Koopmans, L. V. E.; Mamon, GA; Combes, F; Deffayet, C; Fort, B

    2006-01-01

    Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is powerful in breaking the mass-sheet and mass-ani

  17. Modelling the stellar soft-photon energy density profile of globular clusters

    CERN Document Server

    Prinsloo, P L; Buesching, I; Kopp, A

    2013-01-01

    Recent observations by e.g. Fermi Large Area Telescope (LAT) and the High Energy Stereoscopic System (H.E.S.S.) have revealed globular clusters (GC) to be sources of high-energy (HE) and very-high-energy (VHE) gamma rays. It has been suggested that the presence of large numbers of millisecond pulsars (MSPs) within these clusters may be either directly responsible for these gamma-ray fluxes through emission of pulsed curvature radiation, or indirectly through the injection of relativistic leptons into the cluster. These relativistic particles are plausibly re-accelerated in shocks, created by the collision of stellar winds, before interacting with the soft-photon radiation field set up by the stellar population of the host cluster. Inverse Compton (IC) scattering then produces gamma radiation in the TeV band. In order to calculate the IC spectrum, an accurate profile for the energy density of the soft-photon field is required. We construct such a profile by deriving a radially-dependent expression for the stel...

  18. Detailed Opacity Comparison for an Improved Stellar Modeling of the Envelopes of Massive Stars

    Science.gov (United States)

    Turck-Chièze, S.; Le Pennec, M.; Ducret, J. E.; Colgan, J.; Kilcrease, D. P.; Fontes, C. J.; Magee, N.; Gilleron, F.; Pain, J. C.

    2016-06-01

    Seismic observations have led to doubts or ambiguities concerning the opacity calculations used in stellar physics. Here, we concentrate on the iron-group opacity peak, due to iron, nickel, and chromium, located around T = 200,000 K for densities from {10}-8 {to} {10}-4 {{g}} {{cm}}-3, which creates some convective layers in stellar radiative envelopes for masses between 3 and 18 {M}⊙ . These conditions were extensively studied in the 1980s. More recently, inconsistencies between OP and OPAL opacity calculations have complicated the interpretation of seismic observations as the iron-group opacity peak excites acoustic and gravity modes in SPB, β Cephei, and sdB stars. We investigate the reliability of the theoretical opacity calculations using the modern opacity codes ATOMIC and SCO-RCG. We show their temperature and density dependence for conditions that are achievable in the laboratory and equivalent to astrophysical conditions. We also compare new theoretical opacity spectra with OP spectra and quantify how different approximations impact the Rosseland mean calculations.This detailed study estimates new ATOMIC and SCO-RCG Rosseland mean values for astrophysical conditions which we compare to OP values. Some puzzling questions are still under investigation for iron, but we find a strong increase in the Rosseland mean nickel opacity of a factor between 2 and 6 compared to OP. This appears to be due to the use of extrapolated atomic data for the Ni opacity within the OP calculations. A study on chromium is also shown.

  19. Modeling the gravitational potential of a cosmological dark matter halo with stellar streams

    CERN Document Server

    Sanderson, Robyn E; Helmi, Amina

    2016-01-01

    Stellar streams result from the tidal disruption of satellites and star clusters as they orbit a host galaxy, and can be very sensitive probes of the gravitational potential of the host system. We select and study narrow stellar streams formed in a Milky-Way-like dark matter halo of the Aquarius suite of cosmological simulations, to determine if these streams can be used to constrain the present day characteristic parameters of the halo's gravitational potential. We find that orbits integrated in static spherical and triaxial NFW potentials both reproduce the locations and kinematics of the various streams reasonably well. To quantify this further, we determine the best-fit potential parameters by maximizing the amount of clustering of the stream stars in the space of their actions. We show that using our set of Aquarius streams, we recover a mass profile that is consistent with the spherically-averaged dark matter profile of the host halo, although we ignored both triaxiality and time evolution in the fit. T...

  20. Modeling the Gravitational Potential of a Cosmological Dark Matter Halo with Stellar Streams

    Science.gov (United States)

    Sanderson, Robyn E.; Hartke, Johanna; Helmi, Amina

    2017-02-01

    Stellar streams result from the tidal disruption of satellites and star clusters as they orbit a host galaxy, and can be very sensitive probes of the gravitational potential of the host system. We select and study narrow stellar streams formed in a Milky-Way-like dark matter halo of the Aquarius suite of cosmological simulations, to determine if these streams can be used to constrain the present day characteristic parameters of the halo’s gravitational potential. We find that orbits integrated in both spherical and triaxial static Navarro–Frenk–White potentials reproduce the locations and kinematics of the various streams reasonably well. To quantify this further, we determine the best-fit potential parameters by maximizing the amount of clustering of the stream stars in the space of their actions. We show that using our set of Aquarius streams, we recover a mass profile that is consistent with the spherically averaged dark matter profile of the host halo, although we ignored both triaxiality and time evolution in the fit. This gives us confidence that such methods can be applied to the many streams that will be discovered by the Gaia mission to determine the gravitational potential of our Galaxy.

  1. Can we trust elemental abundances derived in late-type giants with the classical 1D stellar atmosphere models?

    CERN Document Server

    Kucinskas, A; Ivanauskas, A; Ludwig, H -G; Caffau, E; Blazevicius, K; Klevas, J; Prakapavicius, D

    2009-01-01

    We compare the abundances of various chemical species as derived with 3D hydrodynamical and classical 1D stellar atmosphere codes in a late-type giant characterized by T_eff=3640K, log g = 1.0, [M/H] = 0.0. For this particular set of atmospheric parameters the 3D-1D abundance differences are generally small for neutral atoms and molecules but they may reach up to 0.3-0.4 dex in case of ions. The 3D-1D differences generally become increasingly more negative at higher excitation potentials and are typically largest in the optical wavelength range. Their sign can be both positive and negative, and depends on the excitation potential and wavelength of a given spectral line. While our results obtained with this particular late-type giant model suggest that 1D stellar atmosphere models may be safe to use with neutral atoms and molecules, care should be taken if they are exploited with ions.

  2. Absolute dimensions of solar-type eclipsing binaries. EF Aquarii: a G0 test for stellar evolution models

    CERN Document Server

    Vos, J; Jørgensen, U G; Østensen, R H; Claret, A; Hillen, M; Exter, K

    2012-01-01

    Recent studies have shown that stellar chromospheric activity, and its effect on convective energy transport in the envelope, is most likely the cause of significant radius and temperature discrepancies between theoretical evolution models and observations. We aim to determine absolute dimensions and abundances for the solar-type detached eclipsing binary EF Aqr, and to perform a detailed comparison with results from recent stellar evolutionary models. uvby-beta standard photometry was obtained with the Stromgren Automatic Telescope. The broadening function formalism was applied on spectra observed with HERMES at the Mercator telescope in La Palma, to obtain radial velocity curves. Masses and radii with a precision of 0.6% and 1.0% respectively have been established for both components of EF Aqr. The active 0.956 M_sol secondary shows star spots and strong Ca II H and K emission lines. The 1.224 M_sol primary shows signs of activity as well, but at a lower level. An [Fe/H] abundance of 0.00+-0.10 is derived w...

  3. Synthetic photometry for M and K giants and stellar evolution: hydrostatic dust-free model atmospheres and chemical abundances

    Science.gov (United States)

    Aringer, B.; Girardi, L.; Nowotny, W.; Marigo, P.; Bressan, A.

    2016-04-01

    Based on a grid of hydrostatic spherical COMARCS models for cool stars, we have calculated observable properties of these objects, which will be mainly used in combination with stellar evolution tracks and population synthesis tools. The high-resolution opacity sampling and low-resolution convolved spectra as well as bolometric corrections for a large number of filter systems are made electronically available. We exploit those data to study the effect of mass, C/O ratio and nitrogen abundance on the photometry of K and M giants. Depending on effective temperature, surface gravity and the chosen wavelength ranges, variations of the investigated parameters cause very weak to moderate and, in the case of C/O values close to 1, even strong shifts of the colours. For the usage with stellar evolution calculations, they will be treated as correction factors applied to the results of an interpolation in the main quantities. When we compare the synthetic photometry to observed relations and to data from the Galactic bulge, we find in general a good agreement. Deviations appear for the coolest giants showing pulsations, mass-loss and dust shells, which cannot be described by hydrostatic models.

  4. The Stagger-grid: A grid of 3D stellar atmosphere models - V. Fe line shapes, shifts and asymmetries

    CERN Document Server

    Magic, Zazralt; Asplund, Martin

    2014-01-01

    We present a theoretical study of the effects and signatures of realistic velocity field and atmospheric inhomogeneities associated with convective motions at the surface of cool late-type stars on the emergent profiles of iron spectral lines for a large range in stellar parameters. We compute 3D spectral line flux profiles under the assumption of local thermodynamic equilibrium (LTE) by employing state-of-the-art, time-dependent, 3D, radiative-hydrodynamical atmosphere models from the Stagger-grid. A set of 35 real unblended, optical FeI and FeII lines of varying excitation potential are considered. Additionally, fictitious Fe i and Fe ii lines (5000A and 0, 2, 4 eV) are used to construct general curves of growth and enable comparison of line profiles with the same line strength to illustrate systematical trends stemming from the intrinsic structural differences among 3D model atmospheres with different stellar parameters. Theoretical line shifts and bisectors are derived to analyze the shapes, shifts, and a...

  5. The Structure and Dynamics of the Corona - Heliosphere Connection

    Science.gov (United States)

    Antiochos, Spiro K.; Linker, Jon A.; Lionello, Roberto; Mikic, Zoran; Titov, Viacheslav; Zurbuchen, Thomas H.

    2011-01-01

    Determining the source at the Sun of the slow solar wind is one of the major unsolved problems in solar and heliospheric physics. First, we review the existing theories for the slow wind and argue that they have difficulty accounting for both the observed composition of the wind and its large angular extent. A new theory in which the slow wind originates from the continuous opening and closing of narrow open field corridors, the S-Web model, is described. Support for the S-Web model is derived from MHD solutions for the quasisteady corona and wind during the time of the August 1, 2008 eclipse. Additionally, we perform fully dynamic numerical simulations of the corona and heliosphere in order to test the S-Web model as well as the interchange model proposed by Fisk and co-workers. We discuss the implications of our simulations for the competing theories and for understanding the corona - heliosphere connection, in general.

  6. Minimum X-ray source size for a lamp-post corona in light-bending models for AGN

    CERN Document Server

    Dovciak, Michal

    2015-01-01

    The lamppost model is often used to describe the X-ray source geometry in AGN, where an infinitesimal point source is located on the black hole spin axis. This is especially invoked for Narrow Line Seyfert 1 (NLS1) galaxies, where an extremely broad iron line seen in episodes of low X-ray flux can both be explained by extremely strong relativistic effects as the source approaches the black hole horizon. The most extreme spectrum seen from the NLS1 1H0707-495 requires that the source is less than 1Rg above the event horizon in this geometry. However, the source must also be large enough to intercept sufficient seed photons from the disk to make the hard X-ray Compton continuum which produces the observed iron line/reflected spectrum. We use a fully relativistic ray tracing code to show that this implies that the source must be substantially larger than 1Rg in 1H0707-495 if the disk is the source of seed photons. Hence the source cannot fit as close as 1Rg to the horizon, so the observed spectrum and variabilit...

  7. Heating mechanisms of the solar corona

    Science.gov (United States)

    Sakurai, Takashi

    2017-02-01

    The solar corona is a tenuous outer atmosphere of the Sun. Its million-degree temperature was discovered spectroscopically in the 1940s, but its origin has been debated since then without complete convergence. Currently there are two classes of models; the wave theory and the microflare/nanoflare theory. Both models have merits and disadvantages, but the essential issues are nearly pinned down. Recent revival of the wave theory is one of the many contributions from Japanese solar observing satellite Hinode launched in 2006.

  8. Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths"

    CERN Document Server

    Kislyakova, K G; Odert, P; Erkaev, N V; Lammer, H; üftinger, T L; Holmström, M; Khodachenko, M L; üdel, M G

    2013-01-01

    We study the interactions between stellar wind and the extended hydrogen-dominated upper atmospheres of planets and the resulting escape of planetary pick-up ions from the 5 "super-Earths" in the compact Kepler-11 system and compare the escape rates with the efficiency of the thermal escape of neutral hydrogen atoms. Assuming the stellar wind of Kepler-11 is similar to the solar wind, we use a polytropic 1D hydrodynamic wind model to estimate the wind properties at the planetary orbits. We apply a Direct Simulation Monte Carlo Model to model the hydrogen coronae and the stellar wind plasma interaction around Kepler-11b-f within a realistic expected heating efficiency range of 15-40%. The same model is used to estimate the ion pick-up escape from the XUV heated and hydrodynamically extended upper atmospheres of Kepler-11b-f. From the interaction model we study the influence of possible magnetic moments, calculate the charge exchange and photoionization production rates of planetary ions and estimate the loss r...

  9. Synthetic photometry for M and K giants and stellar evolution: hydrostatic dust-free model atmospheres and chemical abundances

    CERN Document Server

    Aringer, Bernhard; Nowotny, Walter; Marigo, Paola; Bressan, Alessandro

    2016-01-01

    Based on a grid of hydrostatic spherical COMARCS models for cool stars we have calculated observable properties of these objects, which will be mainly used in combination with stellar evolution tracks and population synthesis tools. The high resolution opacity sampling and low resolution convolved spectra as well as bolometric corrections for a large number of filter systems are made electronically available. We exploit those data to study the effect of mass, C/O ratio and nitrogen abundance on the photometry of K and M giants. Depending on effective temperature, surface gravity and the chosen wavelength ranges variations of the investigated parameters cause very weak to moderate and, in the case of C/O values close to one, even strong shifts of the colours. For the usage with stellar evolution calculations they will be treated as correction factors applied to the results of an interpolation in the main quantities. When we compare the synthetic photometry to observed relations and to data from the Galactic Bu...

  10. Impact of protein pre-coating on the protein corona composition and nanoparticle cellular uptake.

    Science.gov (United States)

    Mirshafiee, Vahid; Kim, Raehyun; Park, Soyun; Mahmoudi, Morteza; Kraft, Mary L

    2016-01-01

    Nanoparticles (NPs) are functionalized with targeting ligands to enable selectively delivering drugs to desired locations in the body. When these functionalized NPs enter the blood stream, plasma proteins bind to their surfaces, forming a protein corona that affects NP uptake and targeting efficiency. To address this problem, new strategies for directing the formation of a protein corona that has targeting capabilities are emerging. Here, we have investigated the feasibility of directing corona composition to promote targeted NP uptake by specific types of cells. We used the well-characterized process of opsonin-induced phagocytosis by macrophages as a simplified model of corona-mediated NP uptake by a desired cell type. We demonstrate that pre-coating silica NPs with gamma-globulins (γ-globulins) produced a protein corona that was enriched with opsonins, such as immunoglobulins. Although immunoglobulins are ligands that bind to receptors on macrophages and elicit phagocytois, the opsonin-rich protein corona did not increase NP uptake by macrophage RAW 264.7 cells. Immunolabeling experiments indicated that the binding of opsonins to their target cell surface receptors was impeded by other proteins in the corona. Thus, corona-mediated NP targeting strategies must optimize both the recruitment of the desired plasma proteins as well as their accessibility and orientation in the corona layer.

  11. Stellar evolution

    CERN Document Server

    Meadows, A J

    2013-01-01

    Stellar Evolution, Second Edition covers the significant advances in the understanding of birth, life, and death of stars.This book is divided into nine chapters and begins with a description of the characteristics of stars according to their brightness, distance, size, mass, age, and chemical composition. The next chapters deal with the families, structure, and birth of stars. These topics are followed by discussions of the chemical composition and the evolution of main-sequence stars. A chapter focuses on the unique features of the sun as a star, including its evolution, magnetic fields, act

  12. Some new Wyman-Adler type static relativistic charged anisotropic fluid spheres compatible to \\emph{self-bound} stellar modeling

    CERN Document Server

    Murad, Mohammad Hassan

    2014-01-01

    In this work some families of relativistic anisotropic charged fluid spheres have been obtained by solving Einstein-Maxwell field equations with preferred form of one of the metric potentials, a suitable forms of electric charge distribution and pressure anisotropy functions. The resulting equation of state (EOS) of the matter distribution has been obtained. Physical analysis shows that the relativistic stellar structure for matter distribution obtained in this work may reasonably model an electrically charged compact star whose energy density associated with the electric fields is on the same order of magnitude as the energy density of fluid matter itself (e.g. electrically charged bare strange stars). These models permit a simple method of systematically fixing bounds on the maximum possible mass of cold compact electrically charged self-bound stars. It has been demonstrated numerically that the maximum compactness and mass increase in the presence of electric field and anisotropic pressures. Based on the a...

  13. Stellar magnetic cycles

    Science.gov (United States)

    Baliunas, S. L.

    2004-05-01

    Is hope for understanding the solar magnetic cycle to be found in stars? Observations of stars with significant sub-surface convective zones -- masses smaller than about 1.5 solar masses on the lower main sequence and many types of cool, post-main-sequence stars -- indicate the presence of surface and atmospheric inhomogeneities analogous to solar magnetic features, making stellar magnetic activity a cosmically widespread phenomenon. Observations have been made primarily in visible wavelengths, and important information has also been derived from the ultraviolet and x-ray spectrum regions. Interannual to interdecadal variability of spectrum indicators of stellar magnetic features is common, and in some cases similar in appearance to the 11-year sunspot cycle. Successful models of the physical processes responsible for stellar magnetic cycles, typically cast as a magnetohydrodynamic dynamo, require advances in understanding not only convection but also the magnetic field's interaction with it. The observed facts that underpin the hope for models will be summarized. Properties of stellar magnetic cycles will be compared and contrasted with those of the sun, including inferences from paleo-environmental reservoirs that contain information on solar century- to millennial-scale magnetic variability. Partial support of this research came from NASA NAG5-7635, NRC COBASE, CRDF 322, MIT-MSG 5710001241, JPL 1236821, AF 49620-02-1-0194, Richard Lounsberry Foundation, Langley-Abbot, Rollins, Scholarly Studies and James Arthur Funds (Smithsonian Institution) and several generous individuals.

  14. Stellar Structure and Evolution

    CERN Document Server

    Kippenhahn, Rudolf; Weiss, Achim

    2013-01-01

    This long-awaited second edition of the classical textbook on Stellar Structure and Evolution by Kippenhahn and Weigert is a thoroughly revised version of the original text. Taking into account modern observational constraints as well as additional physical effects such as mass loss and diffusion, Achim Weiss and Rudolf Kippenhahn have succeeded in bringing the book up to the state-of-the-art with respect to both the presentation of stellar physics and the presentation and interpretation of current sophisticated stellar models. The well-received and proven pedagogical approach of the first edition has been retained. The book provides a comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star’s life. Just as the first edition, which remained a standard work for more than 20 years after its...

  15. Evidence for wave heating in the solar corona.

    Science.gov (United States)

    Hahn, Michael

    2013-07-01

    The temperature of the Sun increases over a short distance from a few thousand degrees in the photosphere to over a million degrees in the corona. To understand coronal heating is one of the major problems in astrophysics. There is general agreement that the energy source is convective motion in and below the photosphere. It remains to determine how this mechanical energy is transported outward into the corona and then deposited as heat. Two classes of models have been proposed, namely those that rely on magnetic reconnection and those that rely on waves, particularly Alfvén waves. There is increasing evidence that waves are ubiquitous in the corona. However, a difficulty for wave-driven models has been that most theories predict Alfvén waves to be undamped in the corona, and therefore they cannot dissipate their energy into heat. Our research has shown unambiguous observational evidence that the waves do damp at sufficiently low heights in the corona to be important for coronal heating.

  16. Plasma Heating of Titan's Exobase and Corona

    Science.gov (United States)

    Karn, M.; Smith, H. T.; Tucker, O. J.; Johnson, R. E.; de La Haye, V.; Waite, J. H.; Young, D. A.

    2007-12-01

    Cassini data have shown that the dominant heating process for Titan's atmospheric corona and exobase region is as yet uncertain (DeLaHaye et al. 2007). We have speculated that the incident plasma, both the slowed and deflected ambient ions and the pick-up ions, may be responsible for all or a significant fraction of the non-thermal component of Titan's corona (De La Haye et al. 2007). Our earlier models of the net incident plasma heating (Michael et al. 2004; 2005) fall short in describing the coronal structure seen by INMS on Ta, Tb and T5. Since heating of the corona and exobase affects atmospheric escape, it is critical for describing the evolution of Titan's atmosphere (Johnson 2004). Here we describe an empirical approach to this problem. INMS data and the preliminary CAPS flux data clearly indicate, not surprisingly, that the heating is spatially non-uniform and is variable, but there is as yet no correlation with the plasma flow models. Therefore, we haev analyzed INMS data for the atmospheric structure near the exobase for a large number of Cassini passes through the exobase region and we have analyzed certain CAPS data for the plasma flow near the exobase. The goal is to develop a model for the spatial variations in the plasma heating near the exobase with the goal of improving our knowledge of atmospheric escape. De La Haye, V.. et al., JGR 112, A07309, doi:10.1029/2006JA012222, 2007 Johnson, R.E. ApJ 609, L99, 2004 Michael, M., and R. E. Johnson. PSS 53, 1510, 2005. Michael, M., et al. Icarus, 175, 263, 2005.

  17. Stellar streams as gravitational experiments. I. The case of Sagittarius

    Science.gov (United States)

    Thomas, Guillaume F.; Famaey, Benoit; Ibata, Rodrigo; Lüghausen, Fabian; Kroupa, Pavel

    2017-07-01

    Tidal streams of disrupting dwarf galaxies orbiting around their host galaxy offer a unique way to constrain the shape of galactic gravitational potentials. Such streams can be used as "leaning tower" gravitational experiments on galactic scales. The most well-motivated modification of gravity proposed as an alternative to dark matter on galactic scales is Milgromian dynamics (MOND), and we present here the first ever N-body simulations of the dynamical evolution of the disrupting Sagittarius dwarf galaxy in this framework. Using a realistic baryonic mass model for the Milky Way, we attempt to reproduce the present-day spatial and kinematic structure of the Sagittarius dwarf and its immense tidal stream that wraps around the Milky Way. With very little freedom on the original structure of the progenitor, constrained by the total luminosity of the Sagittarius structure and by the observed stellar mass-size relation for isolated dwarf galaxies, we find reasonable agreement between our simulations and observations of this system. The observed stellar velocities in the leading arm can be reproduced if we include a massive hot gas corona around the Milky Way that is flattened in the direction of the principal plane of its satellites. This is the first time that tidal dissolution in MOND has been tested rigorously at these mass and acceleration scales. The movie associated to Fig. 6 is available at http://www.aanda.org

  18. Simulations of stellar convection with CO5BOLD

    CERN Document Server

    Freytag, Bernd; Ludwig, Hans-Günter; Wedemeyer-Böhm, Sven; Schaffenberger, Werner; Steiner, Oskar

    2011-01-01

    High-resolution images of the solar surface show a granulation pattern of hot rising and cooler downward-sinking material -- the top of the deep-reaching solar convection zone. Convection plays a role for the thermal structure of the solar interior and the dynamo acting there, for the stratification of the photosphere, where most of the visible light is emitted, as well as for the energy budget of the spectacular processes in the chromosphere and corona. Convective stellar atmospheres can be modeled by numerically solving the coupled equations of (magneto)hydrodynamics and non-local radiation transport in the presence of a gravity field. The CO5BOLD code described in this article is designed for so-called "realistic" simulations that take into account the detailed microphysics under the conditions in solar or stellar surface layers (equation-of-state and optical properties of the matter). These simulations indeed deserve the label "realistic" because they reproduce the various observables very well -- with on...

  19. Non-local thermodynamic equilibrium stellar spectroscopy with 1D and 3D models - II. Chemical properties of the Galactic metal-poor disk and the halo

    DEFF Research Database (Denmark)

    Bergemann, Maria; Collet, Remo; Schönrich, Ralph

    2016-01-01

    We have analysed high-resolution spectra of 328 stars and derived Mg abundances using non-local thermodynamic equilibrium (NLTE) spectral line formation calculations and plane-parallel model stellar atmospheres derived from the mean stratification of 3D hydrodynamical surface convection simulations....../Fe] ratios close to solar even at [Fe/H] ~ -2. This is at variance with results of classical abundance analyses based on local thermodynamic equilibrium (LTE) and 1D model stellar atmospheres, which argue for a constant elevated [Mg/Fe] in metal-poor stars of the Galactic thick disk and halo....

  20. Characterizing simulated galaxy stellar mass histories

    CERN Document Server

    Cohn, J D

    2014-01-01

    Galaxy formation simulations can now predict many galaxy properties and their evolution through time. To go beyond studying average stellar mass history properties, we classified ensembles of simulated stellar mass histories, holding fixed their z=0 stellar mass. We applied principal component analysis (PCA) to stellar mass histories from the dark matter plus semi-analytic Millennium simulation and the hydrodynamical OverWhelmingly Large Simulations (OWLS) project, finding that a large fraction of the total scatter around the average stellar mass history for each sample is due to only one PCA fluctuation. This fluctuation differs between some different models sharing the same z=0 stellar mass and between lower (<=3e10 M_o) and higher final stellar mass Millennium samples. We correlated the PCA characterization with several $z=0$ galaxy observables (in principle observable in a survey) and galaxy halo history properties. We also explored separating galaxy stellar mass histories into classes, using the large...

  1. Combined stellar structure and atmosphere models for massive stars; 4, The impact on the ionization structure of single star HII regions

    CERN Document Server

    Stasinska, G; Stasinska, Grazyna; Schaerer, Daniel

    1996-01-01

    We study the impact of modern stellar atmospheres that take into account the effects of stellar winds, departures from LTE and line blanketing ("CoStar" models) on the ionization structure of HII regions. Results from a large grid of photoionization models are presented. Due to a flatter energy distribution in the HeI continuum, compared to the widely used Kurucz models, generally higher ionic ratios are obtained. We find that N+/O+ and Ne++/O++ can be safely used as direct indicators of N/O and Ne/O abundance ratios in HII regions, over a wide range of astrophysical situations. The roughly constant observed value of Ne++/O++ ionic ratios in Galactic HII regions is naturally reproduced by photoionization models using CoStar fluxes, while Kurucz models at solar metallicity fail to reproduce this behaviour. This gives support to ionizing fluxes from non-LTE atmospheres including stellar winds and line blanketing. However, we also point out that tests of stellar atmosphere models from observations of HII regions...

  2. Towards a Measurement of the Half-Life of {sup 60}Fe for Stellar and Early Solar System Models

    Energy Technology Data Exchange (ETDEWEB)

    Ostdiek, K.; Anderson, T.; Bauder, W.; Bowers, M.; Collon, P.; Dressler, R.; Greene, J.; Kutschera, W.; Lu, W.; Paul, M.

    2015-10-15

    Radioisotopes, produced in stars and ejected into the Interstellar Medium, are important for constraining stellar and early Solar System (ESS) models. In particular, the half-life of the radioisotope, Fe-60, can have an impact on calculations for the timing for ESS events, the distance to nearby Supernovae, and the brightness of individual, non-steady-state Fe gamma ray sources in the Galaxy. A half-life measurement has been undertaken at the University of Notre Dame and measurements of the Fe-60/Fe-56 concentration of our samples using Accelerator Mass Spectrometry has begun. This result will be coupled with an activity measurement of the isomeric decay in Co-60, which is the decay product of Fe. Preliminary half-life estimates of (2.53 +/- 0.24) x 10(6) years seem to confirm the recent measurement by Rugel et al. (2009). (C) 2015 Elsevier B.V. All rights reserved.

  3. Modeling Stellar Parameters for High Resolution Late-M and Early-L Dwarf SDSS/APOGEE Spectra

    Science.gov (United States)

    Birky, Jessica L.; Aganze, Christian; Burgasser, Adam J.; Theissen, Christopher; Schmidt, Sarah J.; Teske, Johanna K.; Stassun, Keivan G.; Bird, Jonathan C.; UCSD FAST Team

    2017-01-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE) of the Sloan Digital Sky Survey IV has measured high resolution (R~22,500), near-infrared (1.51-1.70 µm) spectra for nearly 100,000 stars within the Milky Way Galaxy. While the APOGEE experiment was designed to research Galactic structure by targeting bright stellar populations in the disk, we have focused attention on the lesser-studied subset of faint and low-temperature late-M and early-L dwarfs, with the objective of characterizing their chemical abundances. Using spectral synthesis routines from the Starfish package, we report preliminary determinations of Teff, logg, and [Fe/H] for a small sample of spectra using PHOENIX models ranging in the 2,300 to 3,000K temperature grids.This work is supported by the SDSS Faculty and Student (FAST) initiative, funded by the Alfred P. Sloan Foundation.

  4. Model equation-of-state for any material in conditions relevant to ICF and to stellar interiors

    Energy Technology Data Exchange (ETDEWEB)

    Atzeni, S.; Caruso, A.; Pais, V.A.

    A simple model Equation-of-State (EOS) for matter in conditions of interest to Inertial Confinement Fusion (ICF) and to Stellar Interiors is developed. It yields pressures and specific energies in good agreement with accurate EOS tabulations, for matter in the density range 10/sup -6/ < rho < 10/sup 4/ g cm/sup -3/ and in the temperature range O <= T < 100 KeV, with the only exception being the liquid and gaseous phases of the undissociated molecular substances. This EOS can be used for any element or mixture, requiring, as input data, only the chemical composition (A, Z, and abundancy of each element of the mixture) and three macroscopic constants of the material.

  5. Towards a measurement of the half-life of {sup 60}Fe for stellar and early Solar System models

    Energy Technology Data Exchange (ETDEWEB)

    Ostdiek, K.; Anderson, T. [University of Notre Dame, Notre Dame, IN 46556 (United States); Bauder, W. [University of Notre Dame, Notre Dame, IN 46556 (United States); Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439 (United States); Bowers, M.; Collon, P. [University of Notre Dame, Notre Dame, IN 46556 (United States); Dressler, R. [Paul Scherrer Institute – Laboratory for Radiochemistry and Environmental Chemistry, 5232 Villigen (Switzerland); Greene, J. [Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439 (United States); Kutschera, W. [Vienna Environmental Research Accelerator Laboratory, Waehringer Strasse 17, 1090 Vienna (Austria); Lu, W. [University of Notre Dame, Notre Dame, IN 46556 (United States); Paul, M. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Robertson, D. [University of Notre Dame, Notre Dame, IN 46556 (United States); Schumann, D. [Paul Scherrer Institute – Laboratory for Radiochemistry and Environmental Chemistry, 5232 Villigen (Switzerland); Skulski, M. [University of Notre Dame, Notre Dame, IN 46556 (United States); Wallner, A. [The Australian National University, Canberra, ACT 0200 (Australia)

    2015-10-15

    Radioisotopes, produced in stars and ejected into the Interstellar Medium, are important for constraining stellar and early Solar System (ESS) models. In particular, the half-life of the radioisotope, {sup 60}Fe, can have an impact on calculations for the timing for ESS events, the distance to nearby Supernovae, and the brightness of individual, non-steady-state {sup 60}Fe gamma ray sources in the Galaxy. A half-life measurement has been undertaken at the University of Notre Dame and measurements of the {sup 60}Fe/{sup 56}Fe concentration of our samples using Accelerator Mass Spectrometry has begun. This result will be coupled with an activity measurement of the isomeric decay in {sup 60}Co, which is the decay product of {sup 60}Fe. Preliminary half-life estimates of (2.53 ± 0.24) × 10{sup 6} years seem to confirm the recent measurement by Rugel et al. (2009).

  6. A New Theoretical Library of High-resolution Stellar Spectra for UV-Optical Population Synthesis Models

    Science.gov (United States)

    Bertone, E.; Rodriguez-Merino, L.; Chavez, M.; Buzzoni, A.

    2003-06-01

    We present a new theoretical library of stellar spectra covering the wavelength interval from 850 to 7000 Å. The library consists of two datasets, one including the far UV-blue spectral region from 850 to 4750 Å at inverse spectral resolution R = 50000, and the latter spanning the range 3500-7000 Å at R = 500000. Both sets are based on the SYNTHE series of codes developed by R.L. Kurucz. For its comprehensive range of physical parameters (i.e. T[eff], logg and [M/H]) and higher spectral resolution, this is the most advanced spectral library currently available in the literature, and could profitably be used for population synthesis models and abundance studies of single stars.

  7. Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths"

    Science.gov (United States)

    Kislyakova, Kristina; Johnstone, Colin; Odert, Petra; Erkaev, Nikolai; Lammer, Helmut; Lüftinger, Theresa; Holmstöm, Mats; Khodachenko, Maxim; Güdel, Manuel

    2014-05-01

    We present the results of modeling of the interactions between stellar wind and the extended hydrogen-dominated upper atmospheres of planets and estimate the resulting escape of planetary pick-up ions from the 5 «super-Earths» in the compact Kepler-11 system. We compare the escape rates with the efficiency of the thermal escape of neutral hydrogen atoms. Assuming the stellar wind of Kepler-11 is similar to the solar wind, we used a polytropic 1D hydrodynamic wind model to estimate the wind properties at the planetary orbits. We applied a Direct Simulation Monte Carlo Model to model the hydrogen coronae and the stellar wind plasma interaction around Kepler-11b-f planets within a realistic expected heating efficiency range of 15-40%. The same model was used to estimate the ion pick-up escape from the XUV heated and hydrodynamically extended upper atmospheres of Kepler-11b-f. Modeling clarifies the influence of possible magnetic moments on escape processes and allows to estimate the charge exchange and photoionization production rates of planetary ions as well as the loss rates of pick-up H+ ions for all five planets. This study presents also the comparison of the results between the five 'super-Earths' and in a more general sense also with the thermal escape rates of the neutral planetary hydrogen atoms. Our results show that for all Kepler-11b-f exoplanets, a huge neutral hydrogen corona is formed around the planet. The non-symmetric form of the corona changes from planet to planet and is defined mostly by radiation pressure, charge-exchange and gravitational effects. According to our estimates, nonthermal escape rates of pick-up ionized hydrogen atoms for Kepler-11 «super-Earths» vary between ~ 6.4 × 1030 s-1 and ~ 4.1 × 1031 s-1 depending on the planet's orbital location and assumed heating efficiency. These values correspond to non-thermal mass loss rates of ~ 1.07 × 107 g·s-1 and ~ 6.8 × 107 g·s-1 respectively, which is a few percent of the thermal

  8. Self-consistent physical parameters for 5 intermediate-age SMC stellar clusters from CMD modelling

    CERN Document Server

    Dias, Bruno; Barbuy, Beatriz; Santiago, Basilio; Ortolani, Sergio; Balbinot, Eduardo

    2013-01-01

    Context. Stellar clusters in the Small Magellanic Cloud (SMC) are useful probes to study the chemical and dynamical evolution of this neighbouring dwarf galaxy, enabling inspection of a large period covering over 10 Gyr. Aims. The main goals of this work are the derivation of age, metallicity, distance modulus, reddening, core radius and central density profile for six sample clusters, in order to place them in the context of the Small Cloud evolution. The studied clusters are: AM 3, HW 1, HW 34, HW 40, Lindsay 2, and Lindsay 3, where HW 1, HW 34, and Lindsay 2 are studied for the first time. Methods. Optical Colour-Magnitude Diagrams (V, B-V CMDs) and radial density profiles were built from images obtained with the 4.1m SOAR telescope, reaching V~23. The determination of structural parameters were carried out applying King profile fitting. The other parameters were derived in a self-consistent way by means of isochrone fitting, which uses the likelihood statistics to identify the synthetic CMDs that best rep...

  9. The Milky Way's Stellar Disk

    CERN Document Server

    Rix, Hans-Walter

    2013-01-01

    A suite of vast stellar surveys mapping the Milky Way, culminating in the Gaia mission, is revolutionizing the empirical information about the distribution and properties of stars in the Galactic stellar disk. We review and lay out what analysis and modeling machinery needs to be in place to test mechanisms of disk galaxy evolution and to stringently constrain the Galactic gravitational potential, using such Galactic star-by-star measurements. We stress the crucial role of stellar survey selection functions in any such modeling; and we advocate the utility of viewing the Galactic stellar disk as made up from `mono-abundance populations' (MAPs), both for dynamical modeling and for constraining the Milky Way's evolutionary processes. We review recent work on the spatial and kinematical distribution of MAPs, and lay out how further study of MAPs in the Gaia era should lead to a decisively clearer picture of the Milky Way's dark matter distribution and formation history.

  10. Research Progress of Solar Corona and Interplanetary Physics in China: 2010-2012

    Institute of Scientific and Technical Information of China (English)

    ZHAO Xinhua; XIANG Changqing

    2012-01-01

    The scientific objective of solar corona and interplanetary research is the understanding of the various phenomena related to solar activities and their effects on the space environments of the Earth. Great progress has been made in the study of solar corona and interplanetary physics by the Chinese space physics community during the past years. This paper will give a brief report about the latest progress of the corona and interplanetary research in China during the years of 2010--2012. The paper can be divided into the following parts: solar corona and solar wind, CME- ICME, magnetic reconnection, energetic particles, space plasma, space weather numerical modeling by 3D SIP-CESE MHD model, space weather prediction methods, and proposed missions. They constitute the abundant content of study for the complicated phenomena that originate from the solar corona, propagate in interplanetary space, and produce geomagnetic disturbances. All these progresses are acquired by the Chinese space physicists, either independently or through international collaborations.

  11. Shape parameters of the solar corona from 1991 to 2016

    Science.gov (United States)

    Priyatikanto, Rhorom

    2016-12-01

    The global structure of the solar corona observed in the optical window is governed by the global magnetic field with different characteristics over a solar activity cycle. The Ludendorff flattening index has become a popular measure of global structure of the solar corona as observed during an eclipse. In this study, 15 digital images of the solar corona from 1991 to 2016 were analyzed in order to construct coronal flattening profiles as a function of radius. In most cases, the profile can be modeled with a 2nd order polynomial function so that the radius with maximum flattening index (Rmax) can be determined. Along with this value, Ludendorff index (a + b) was also calculated. Both Ludendorff index and Rmax show anti-correlation with monthly sunspot number, though the Rmax values are more scattered. The variation in Rmax can be regarded as the impact of the changing coronal brightness profile over the equator.

  12. Shape Parameters of 1991 to 2016 Solar Corona

    CERN Document Server

    Priyatikanto, Rhorom

    2016-01-01

    The global structure of solar corona observed in optical window is governed by the global magnetic field with different characteristics over solar activity cycle. Ludendorff flattening index becomes a popular measure of the global structure of solar corona as observed during eclipse. In this study, 15 digital images of solar corona from 1991 to 2016 were analyzed in order to construct the coronal flattening profiles as a function of radius. In most of the cases, the profile can be modeled with 2nd order polynomial function so that the radius with maximum flattening index ($R_{\\text{max}}$) can be determined. Along with this value, Ludendorff index ($a+b$) was also calculated. Both Ludendorff index and $R_{\\text{max}}$ show anti-correlation with monthly sunspot number, though the $R_{\\text{max}}$ values are more scattered. The variation of $R_{\\text{max}}$ can be regarded as the impact of changing coronal brightness profile over equator.

  13. Triggering Excimer Lasers by Photoionization from Corona Discharges

    Science.gov (United States)

    Xiong, Zhongmin; Duffey, Thomas; Brown, Daniel; Kushner, Mark

    2009-10-01

    High repetition rate ArF (192 nm) excimer lasers are used for photolithography sources in microelectronics fabrication. In highly attaching gas mixtures, preionization is critical to obtaining stable, reproducible glow discharges. Photoionization from a separate corona discharge is one technique for preionization which triggers the subsequent electron avalanche between the main electrodes. Photoionization triggering of an ArF excimer laser sustained in multi-atmosphere Ne/Ar/F2/Xe gas mixtures has been investigated using a 2-dimensional plasma hydrodynamics model including radiation transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron temperature with transport coefficients obtained from solutions of Boltzmann's equation. Photoionizing radiation is produced by a surface discharge which propagates along a corona-bar located adjacent to the discharge electrodes. The consequences of pulse power waveform, corona bar location, capacitance and gas mixture on uniformity, symmetry and gain of the avalanche discharge will be discussed.

  14. Saturation of Stellar Winds from Young Suns

    CERN Document Server

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

    2013-01-01

    (Abridged)We investigate mass losses via stellar winds from sun-like main sequence stars with a wide range of activity levels. We perform forward-type magnetohydrodynamical numerical experiments for Alfven wave-driven stellar winds with a wide range of the input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass loss rate rapidly increases at first owing to the suppression of the reflection of the Alfven waves. The surface materials are lifted up by the magnetic pressure associated with the Alfven waves, and the cool dense chromosphere is intermittently extended to 10-20% of the stellar radius. The densities of the corona and transition region above the chromosphere is also high, which leads to efficient radiative losses. Eventually most of the input Poynting energy from the stellar surface escapes by the radiation. As a result, there is no more sufficient energy remained for the kinetic energy...

  15. Flares on A-type Stars: Evidence for Heating of Solar Corona by Nanoflares?

    Science.gov (United States)

    Švanda, Michal; Karlický, Marian

    2016-11-01

    We analyzed the occurrence rates of flares on stars of spectral types K, G, F, and A, observed by Kepler. We found that the histogram of occurrence frequencies of stellar flares is systematically shifted toward a high-energy tail for A-type stars compared to stars of cooler spectral types. We extrapolated the fitted power laws toward flares with smaller energies (nanoflares) and made estimates for total energy flux to stellar atmospheres by flares. We found that, for A-type stars, the total energy flux density was at least four-times smaller than for G stars. We speculate that this deficit in energy supply may explain the lack of hot coronae on A-type stars. Our results indicate the importance of nanoflares for heating and formation of the solar corona.

  16. Flares on A-type stars: Evidence for heating of solar corona by nanoflares?

    CERN Document Server

    Svanda, M

    2016-01-01

    We analyzed the occurrence rates of flares on stars of spectral types K, G, F, and A, observed by Kepler. We found that the histogram of occurrence frequencies of stellar flares is systematically shifted towards a high-energy tail for A-type stars compared to stars of cooler spectral types. We extrapolated the fitted power laws towards flares with smaller energies (nanoflares) and made estimates for total energy flux to stellar atmospheres by flares. We found that for A-type stars the total energy flux density was at least 4-times smaller than for G-stars. We speculate that this deficit in energy supply may explain the lack of hot coronae on A-type stars. Our results indicate an importance of nanoflares for heating and formation of the solar corona.

  17. Urban Futures - Innovation Engines or Slums? A Stellar Evolution Model of Urban Growth

    Science.gov (United States)

    Shutters, S. T.; Timmes, F.; Desouza, K.

    2015-12-01

    Why, as cities grow in size and density, do some "ignite" into global engines of innovation and prosperity while others grow into dense slums? This is our overarching question as we explore a novel framework for thinking about the evolution of cities and, more specifically, the divergent trajectories they may take. We develop a speculative framework by examining the analogies between the evolution of cities and the evolution of stars. Like cities, stellar gas clouds can grow in mass, eventually reaching temperature and density thresholds at which they ignite the hydrogen fuel in their cores to become full-fledged stars. But not all gas and dust clouds share this fate. Some never achieve the critical conditions and do not unleash the energy we witness emanating from our own star. Some stars, after exhaustion of their initial fuel, evolve to incredible density but lack the temperature to ignite the next fuel needed to maintain the critical interactions that release so much energy. Instead they fade away to an object of intense density, but without the vibrant emission of light and energy associated with non-degenerate stars. The fate of cities, too, depends on the density of interactions - not of gas molecules, but of people. This elevated rate of face-to-face interactions in an urban core is critical for the transition to an innovative and creative economy. Yet, density is not enough, as evidenced both by many megacities in the developing world and degenerate stars. What is this missing element that, along with density, ignites a city and turns it into an innovation engine? With these analogies in mind, we explore whether they are useful for framing future research on cities, what questions they may help pose, and, more broadly, how physical, social, and natural scientists can all contribute to an interdisciplinary endeavor to understand cities more deeply.

  18. Arrested development - a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

    Science.gov (United States)

    Ogilvie, Paula; Gibson, Roger L.

    2017-02-01

    -limiting reaction mechanisms and their petrogenetic signatures in increasingly complex, higher-variance systems has facilitated the refinement of chemical fractionation and partial equilibration diffusion models necessary to more fully understand corona development. Through the application of quantitative physical diffusion models of coronas coupled with phase equilibria modelling utilizing calculated chemical potential gradients, it is possible to model the evolution of a corona through P-T-X-t space by continuous, steady-state and/or sequential, episodic reaction mechanisms. Most coronas in granulites form through a combination of these endmember reaction mechanisms, each characterized by distinct textural and chemical potential signatures with very different petrogenetic implications. An understanding of the inherent petrogenetic limitations of a reaction mechanism model is critical if an appropriate interpretation of P-T evolution is to be inferred from a corona. Since corona modelling employing calculated chemical potential gradients assumes nothing about the sequence in which the layers form and is directly constrained by phase compositional variation within a layer, it allows far more nuanced and robust understanding of corona evolution and its implications for the path of a rock in P-T-X space.

  19. DOLPHOT: Stellar photometry

    Science.gov (United States)

    Dolphin, Andrew

    2016-08-01

    DOLPHOT is a stellar photometry package that was adapted from HSTphot for general use. It supports two modes; the first is a generic PSF-fitting package, which uses analytic PSF models and can be used for any camera. The second mode uses ACS PSFs and calibrations, and is effectively an ACS adaptation of HSTphot. A number of utility programs are also included with the DOLPHOT distribution, including basic image reduction routines.

  20. The DEMO Quasisymmetric Stellarator

    OpenAIRE

    McFadden, Geoffrey B.; Garabedian, Paul R.

    2010-01-01

    The NSTAB nonlinear stability code solves differential equations in conservation form, and the TRAN Monte Carlo test particle code tracks guiding center orbits in a fixed background, to provide simulations of equilibrium, stability, and transport in tokamaks and stellarators. These codes are well correlated with experimental observations and have been validated by convergence studies. Bifurcated 3D solutions of the 2D tokamak problem have been calculated that model persistent disruptions, neo...

  1. Rossiter--McLaughlin models and their effect on estimates of stellar rotation, illustrated using six WASP systems

    CERN Document Server

    Brown, D J A; Doyle, A P; Gillon, M; Lendl, M; Anderson, D R; Cameron, A Collier; Hébrard, G; Hellier, C; Lovis, C; Maxted, P F L; Pepe, F; Pollacco, D; Queloz, D; Smalley, B

    2016-01-01

    We present new measurements of the projected spin--orbit angle $\\lambda$ for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses of previously measured systems using new data (WASP-71, and -79). We use three different models based on two different techniques: radial velocity measurements of the Rossiter--McLaughlin effect, and Doppler tomography. Our comparison of the different models reveals that they produce projected stellar rotation velocities ($v \\sin I_{\\rm s}$) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Bou\\'e model for the Rossiter--McLaughlin effect consistently underestimates the value of $v\\sin I_{\\rm s}$ compared to the Hirano model. Although $v \\sin I_s$ differed, the effect on $\\lambda$ was small for our sample, with all three methods producing values in agreement with each other. Using Doppler tomography, we find that WASP-61\\,b ($\\lambda=4^\\circ.0^{+...

  2. Nebula around R Corona Borealis

    CERN Document Server

    Rao, N Kameswara

    2011-01-01

    The star R Corona Borealis (R CrB) shows forbidden lines of [O II], [N II], and [S II] during the deep minimum when the star is fainter by about 8 to 9 magnitudes from normal brightness, suggesting the presence of nebular material around it. We present low and high spectral resolution observations of these lines during the ongoing deep minimum of R CrB, which started in July 2007. These emission lines show double peaks with a separation of about 170 km/s. The line ratios of [S II] and [O II] suggest an electron density of about 100 cm$^{-3}$. We discuss the physical conditions and possible origins of this low density gas. These forbidden lines have also been seen in other R Coronae Borealis stars during their deep light minima and this is a general characteristic of these stars, which might have some relevance to their origins.

  3. Jet magnetically accelerated from disk-corona around a rotating black hole

    CERN Document Server

    Gong, Xiaolong

    2012-01-01

    A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole is proposed. In the disk-corona scenario, we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations. The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere. It is shown that jet power increases with the increasing black hole (BH) spin, and concentrates in the inner region of the disk-corona. In addition, we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism, and show that our jet formation mechanism can simulate almost all sources with high power jet, that fail to be explained by the Blandford-Znajek (BZ) process.

  4. Dimensions of Attention Associated With the Microstructure of Corona Radiata White Matter.

    Science.gov (United States)

    Stave, Elise A; De Bellis, Michael D; Hooper, Steven R; Woolley, Donald P; Chang, Suk Ki; Chen, Steven D

    2017-01-01

    Mirsky proposed a model of attention that included these dimensions: focus/execute, sustain, stabilize, encode, and shift. The neural correlates of these dimensions were investigated within corona radiata subregions in healthy youth. Diffusion tensor imaging and neuropsychological assessments were conducted in 79 healthy, right-handed youth aged 4-17 years. Diffusion tensor imaging maps were analyzed using standardized parcellation methods. Partial Pearson correlations between neuropsychological standardized scores, representing these attention dimensions, and diffusion tensor imaging measures of corona radiata subregions were calculated after adjusting for gender and IQ. Significant correlations were found between the focus/execute, sustain, stabilize, and shift dimensions and imaging metrics in hypothesized corona radiata subregions. Results suggest that greater microstructural white matter integrity of the corona radiata is partly associated with attention across 4 attention dimensions. Findings suggest that white matter microstructure of the corona radiata is a neural correlate of several, but not all, attention dimensions.

  5. The Role of Magnetic Helicity in Structuring the Solar Corona

    Science.gov (United States)

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

    2017-01-01

    Two of the most widely observed and striking features of the Sun's magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure—filament channels—is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

  6. The Role of Magnetic Helicity in Structuring the Solar Corona

    Science.gov (United States)

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

    2017-01-01

    Two of the most widely observed and striking features of the Suns magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure filament channels is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

  7. Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres. Comparison with 1D models and HST light curve observations

    Science.gov (United States)

    Hayek, W.; Sing, D.; Pont, F.; Asplund, M.

    2012-03-01

    We compare limb darkening laws derived from 3D hydrodynamical model atmospheres and 1D hydrostatic MARCS models for the host stars of two well-studied transiting exoplanet systems, the late-type dwarfs HD 209458 and HD 189733. The surface brightness distribution of the stellar disks is calculated for a wide spectral range using 3D LTE spectrum formation and opacity sampling⋆. We test our theoretical predictions using least-squares fits of model light curves to wavelength-integrated primary eclipses that were observed with the Hubble Space Telescope (HST). The limb darkening law derived from the 3D model of HD 209458 in the spectral region between 2900 Å and 5700 Å produces significantly better fits to the HST data, removing systematic residuals that were previously observed for model light curves based on 1D limb darkening predictions. This difference arises mainly from the shallower mean temperature structure of the 3D model, which is a consequence of the explicit simulation of stellar surface granulation where 1D models need to rely on simplified recipes. In the case of HD 189733, the model atmospheres produce practically equivalent limb darkening curves between 2900 Å and 5700 Å, partly due to obstruction by spectral lines, and the data are not sufficient to distinguish between the light curves. We also analyze HST observations between 5350 Å and 10 500 Å for this star; the 3D model leads to a better fit compared to 1D limb darkening predictions. The significant improvement of fit quality for the HD 209458 system demonstrates the higher degree of realism of 3D hydrodynamical models and the importance of surface granulation for the formation of the atmospheric radiation field of late-type stars. This result agrees well with recent investigations of limb darkening in the solar continuum and other observational tests of the 3D models. The case of HD 189733 is no contradiction as the model light curves are less sensitive to the temperature stratification of

  8. The ILIUM forward modelling algorithm for multivariate parameter estimation and its application to derive stellar parameters from Gaia spectrophotometry

    CERN Document Server

    Bailer-Jones, C A L

    2009-01-01

    I introduce an algorithm for estimating parameters from multidimensional data based on forward modelling. In contrast to many machine learning approaches it avoids fitting an inverse model and the problems associated with this. The algorithm makes explicit use of the sensitivities of the data to the parameters, with the goal of better treating parameters which only have a weak impact on the data. The forward modelling approach provides uncertainty (full covariance) estimates in the predicted parameters as well as a goodness-of-fit for observations. I demonstrate the algorithm, ILIUM, with the estimation of stellar astrophysical parameters (APs) from simulations of the low resolution spectrophotometry to be obtained by Gaia. The AP accuracy is competitive with that obtained by a support vector machine. For example, for zero extinction stars covering a wide range of metallicity, surface gravity and temperature, ILIUM can estimate Teff to an accuracy of 0.3% at G=15 and to 4% for (lower signal-to-noise ratio) sp...

  9. Some new Wyman-Leibovitz-Adler type static relativistic charged anisotropic fluid spheres compatible to self-bound stellar modeling

    Energy Technology Data Exchange (ETDEWEB)

    Murad, Mohammad Hassan [BRAC University, Department of Mathematics and Natural Sciences, Dhaka (Bangladesh); Fatema, Saba [Daffodil International University, Department of Natural Sciences, Dhaka (Bangladesh)

    2015-11-15

    In this work some families of relativistic anisotropic charged fluid spheres have been obtained by solving the Einstein-Maxwell field equations with a preferred form of one of the metric potentials, and suitable forms of electric charge distribution and pressure anisotropy functions. The resulting equation of state (EOS) of the matter distribution has been obtained. Physical analysis shows that the relativistic stellar structure for the matter distribution considered in this work may reasonably model an electrically charged compact star whose energy density associated with the electric fields is on the same order of magnitude as the energy density of fluid matter itself (e.g., electrically charged bare strange stars). Furthermore these models permit a simple method of systematically fixing bounds on the maximum possible mass of cold compact electrically charged self-bound stars. It has been demonstrated, numerically, that the maximum compactness and mass increase in the presence of an electric field and anisotropic pressures. Based on the analytic models developed in this present work, the values of some relevant physical quantities have been calculated by assuming the estimated masses and radii of some well-known potential strange star candidates like PSR J1614-2230, PSR J1903+327, Vela X-1, and 4U 1820-30. (orig.)

  10. Efficiency of gas cooling and accretion at the disc-corona interface

    Science.gov (United States)

    Armillotta, L.; Fraternali, F.; Marinacci, F.

    2016-11-01

    In star-forming galaxies, stellar feedback can have a dual effect on the circumgalactic medium both suppressing and stimulating gas accretion. The trigger of gas accretion can be caused by disc material ejected into the halo in the form of fountain clouds and by its interaction with the surrounding hot corona. Indeed, at the disc-corona interface, the mixing between the cold/metal-rich disc gas (T ≲ 104 K) and the hot coronal gas (T ≳ 106 K) can dramatically reduce the cooling time of a portion of the corona and produce its condensation and accretion. We studied the interaction between fountain clouds and corona in different galactic environments through parsec-scale hydrodynamical simulations, including the presence of thermal conduction, a key mechanism that influences gas condensation. Our simulations showed that the coronal gas condensation strongly depends on the galactic environment, in particular it is less efficient for increasing virial temperature/mass of the haloes where galaxies reside and it is fully ineffective for objects with virial masses larger than 1013 M⊙. This result implies that the coronal gas cools down quickly in haloes with low-intermediate virial mass (Mvir ≲ 3 × 1012 M⊙) but the ability to cool the corona decreases going from late-type to early-type disc galaxies, potentially leading to the switching off of accretion and the quenching of star formation in massive systems.

  11. Cool stars, stellar systems, and the sun; Proceedings of the 6th Cambridge Workshop, Seattle, WA, Sept. 18-21, 1989

    Science.gov (United States)

    Wallerstein, George (Editor)

    1990-01-01

    The present conference on cool stars, stellar systems, and the sun encompasses stellar chromospheres and coronae, binary stars, the stellar evolution of contracting stars and red giants, stellar evolution abundances of the elements, mass loss and envelopes, and stellar pulsation. Specific issues addressed include theories regarding the acoustic and magnetic heating of stellar chromospheres and coronae, stellar granulation, wave heating in magnetic flux tubes, observations of the solar Ca-II lines, longitudinal-transverse magnetic tube waves in the solar atmosphere, radio emission from rapidly rotating cool giant stars, and spot temperatures and area coverages on active dwarf stars. Also addressed are the optical and UV spectra of RS-CVn stars, emission lines from T-Tauri stars, the spectroscopy of HR1614 group stars, red giants in external galaxies, the rotation of evolved stars, the transition from red giant to planetary nebula, and radiative transfer in the dynamic atmospheres of variable stars.

  12. Research on Nanosecond Pulse Corona Discharge Attenuation

    Institute of Scientific and Technical Information of China (English)

    HE Zheng-hao; XU Huai-li; BAI Jing; YU Fu-sheng; HU Feng; LI Jin

    2007-01-01

    A line-to-plate reactor was set-up in the experimental study on the application of nanosecond pulsed corona discharge plasma technology in environmental pollution control.Investigation on the attenuation and distortion of the amplitude of the pulse wave front and the discharge image as well as the waveform along the corona wire was conducted.The results show that the wave front decreases sharply during the corona discharge along the corona wire.The higher the amplitude of the applied pulse is,the more the amplitude of the wave front decreased.The wave attenuation responds in a lower corona discharge inversely.To get a higher efficiency of the line-to-plate reactor a sharp attenuation of the corona has to be considered in practical design.

  13. The Coronae of AR Lac

    CERN Document Server

    Huenemoerder, D P; Drake, J J; Sanz-Forcada, J; Canizares, Claude R.; Drake, Jeremy J.; Huenemoerder, David P.; Sanz-Forcada, Jorge

    2003-01-01

    We observed the coronally active eclipsing binary, AR Lac, with the High Energy Transmission Grating on Chandra for a total of 97 ks, spaced over five orbits, at quadratures and conjunctions. Contemporaneous and simultaneous EUV spectra and photometry were also obtained with the Extreme Ultraviolet Explorer. Significant variability in both X-ray and EUV fluxes were observed, dominated by at least one X-ray flare and one EUV flare. We saw no evidence of primary or secondary eclipses. X-ray flux modulation was largest at high temperature, indicative of flare heating of coronal plasma. Line widths interpreted in terms of Doppler broadening suggest that both binary stellar components are active. From line fluxes obtained from total integrated spectra, we have modeled the emission measure and abundance distributions. A strong maximum was found in the differential emission measure, characterized by peaks at log T = 6.9 and 7.4, together with a weak but significant cooler maximum near log T=6.2, and a moderately str...

  14. Stellar activity and magnetic shielding

    CERN Document Server

    Grießmeier, J -M; Lammer, H; Grenfell, J L; Stadelmann, A; Motschmann, U; 10.1017/S1743921309992961

    2010-01-01

    Stellar activity has a particularly strong influence on planets at small orbital distances, such as close-in exoplanets. For such planets, we present two extreme cases of stellar variability, namely stellar coronal mass ejections and stellar wind, which both result in the planetary environment being variable on a timescale of billions of years. For both cases, direct interaction of the streaming plasma with the planetary atmosphere would entail servere consequences. In certain cases, however, the planetary atmosphere can be effectively shielded by a strong planetary magnetic field. The efficiency of this shielding is determined by the planetary magnetic dipole moment, which is difficult to constrain by either models or observations. We present different factors which influence the strength of the planetary magnetic dipole moment. Implications are discussed, including nonthermal atmospheric loss, atmospheric biomarkers, and planetary habitability.

  15. Nanoparticles-cell association predicted by protein corona fingerprints

    Science.gov (United States)

    Palchetti, S.; Digiacomo, L.; Pozzi, D.; Peruzzi, G.; Micarelli, E.; Mahmoudi, M.; Caracciolo, G.

    2016-06-01

    In a physiological environment (e.g., blood and interstitial fluids) nanoparticles (NPs) will bind proteins shaping a ``protein corona'' layer. The long-lived protein layer tightly bound to the NP surface is referred to as the hard corona (HC) and encodes information that controls NP bioactivity (e.g. cellular association, cellular signaling pathways, biodistribution, and toxicity). Decrypting this complex code has become a priority to predict the NP biological outcomes. Here, we use a library of 16 lipid NPs of varying size (Ø ~ 100-250 nm) and surface chemistry (unmodified and PEGylated) to investigate the relationships between NP physicochemical properties (nanoparticle size, aggregation state and surface charge), protein corona fingerprints (PCFs), and NP-cell association. We found out that none of the NPs' physicochemical properties alone was exclusively able to account for association with human cervical cancer cell line (HeLa). For the entire library of NPs, a total of 436 distinct serum proteins were detected. We developed a predictive-validation modeling that provides a means of assessing the relative significance of the identified corona proteins. Interestingly, a minor fraction of the HC, which consists of only 8 PCFs were identified as main promoters of NP association with HeLa cells. Remarkably, identified PCFs have several receptors with high level of expression on the plasma membrane of HeLa cells.In a physiological environment (e.g., blood and interstitial fluids) nanoparticles (NPs) will bind proteins shaping a ``protein corona'' layer. The long-lived protein layer tightly bound to the NP surface is referred to as the hard corona (HC) and encodes information that controls NP bioactivity (e.g. cellular association, cellular signaling pathways, biodistribution, and toxicity). Decrypting this complex code has become a priority to predict the NP biological outcomes. Here, we use a library of 16 lipid NPs of varying size (Ø ~ 100-250 nm) and surface

  16. PREFACE: A Stellar Journey A Stellar Journey

    Science.gov (United States)

    Asplund, M.

    2008-10-01

    astronomical talk, student lecture, musical concert or theatre play. Another attribute of Bengt is his boundless optimism, which not the least has helped many of his students overcome the unavoidable moments of despair (this is only true as long as one is aware of the well-known BG factor: multiply any of Bengt's estimates for the time required to complete a task by at least a factor of three). His personal traits make working with Bengt always very enjoyable as well as highly educating. Bengt's work also extends well beyond the domain of astronomy, including music, literature, theatre, religion, research ethics, science policy and science popularization. Bengt is an excellent role model for a successful scientist with a rich and rewarding life outside of academia. The symposium A Stellar Journey was divided into five sessions covering basically the main research areas Bengt has worked on: Stellar atmospheres, Solar/stellar spectroscopy, Stellar parameters, Stellar evolution and nucleosynthesis and Stellar populations. In addition, one afternoon was devoted to a session entitled Anything but astronomy (see the symposium program), which tried to showcase Bengt's diverse interests outside of astronomy with talks ranging from religion and history of science over science popularization and future studies to literature and music. My task, as chair of the Scientific Organizing Committee, to put together an exciting scientific program of invited reviews and talks was made considerably easier thanks to the excellent suggestions by the other SOC members: Ann Boesgaard, Sofia Feltzing, John Lattanzio, Andre Maeder, Bertrand Plez and Monique Spite. I believe in the end we were successful in achieving our charge, an impression corroborated by the many encouraging comments from various participants during and after the conference. I am particularly grateful to Nils Bergvall, Bengt Edvardsson and Bertrand Plez for their time-consuming efforts in arranging the extraordinary and greatly

  17. Magellan/M2FS Spectroscopy of Galaxy Clusters: Stellar Population Model and Application to Abell 267

    Science.gov (United States)

    Tucker, Evan; Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W.; Bailey, John I., III; Crane, Jeffrey D.; Shectman, Stephen A.

    2017-09-01

    We report the results of a pilot program to use the Magellan/M2FS spectrograph to survey the galactic populations and internal kinematics of galaxy clusters. For this initial study, we present spectroscopic measurements for 223 quiescent galaxies observed along the line of sight of the galaxy cluster Abell 267 (z∼ 0.23). We develop a Bayesian method for modeling the integrated light from each galaxy as a simple stellar population, with free parameters that specify the redshift ({v}{los}/c) and characteristic age, metallicity ([{Fe}/{{H}}]), alpha-abundance ([α /{Fe}]), and internal velocity dispersion ({σ }{int}) for individual galaxies. Parameter estimates derived from our 1.5 hr observation of A267 have median random errors of {σ }{v{los}}=20 {km} {{{s}}}-1, {σ }{Age}=1.2 {Gyr}, {σ }[{Fe/{{H}}]}=0.11 {dex}, {σ }[α /{Fe]}=0.07 {dex}, and {σ }{σ {int}}=20 {km} {{{s}}}-1. In a companion paper, we use these results to model the structure and internal kinematics of A267.

  18. GrayStar: A Web application for pedagogical stellar atmosphere and spectral line modelling and visualisation II: Methods

    CERN Document Server

    Short, C Ian

    2014-01-01

    GrayStar is a stellar atmospheric and spectral line modelling, post-processing, and visualisation code, suitable for classroom demonstrations and laboratory-style assignments, that has been developed in Java and deployed in JavaScript and HTML. The only software needed to compute models and post-processed observables, and to visualise the resulting atmospheric structure and observables, is a common Web browser. Therefore, the code will run on any common PC or related X86 (-64) computer of the type that typically serves classroom data projectors, is found in undergraduate computer laboratories, or that students themselves own, including those with highly portable form-factors such as net-books and tablets. The user requires no experience with compiling source code, reading data files, or using plotting packages. More advanced students can view the JavaScript source code using the developer tools provided by common Web browsers. The code is based on the approximate gray atmospheric solution and runs quickly eno...

  19. A new model for the structure of the DACs and SACs regions in the Oe and Be stellar atmospheres

    CERN Document Server

    Danezis, E; Lyratzi, E; Popović, L Č; Dimitrijević, M S; Antoniou, A; Theodosiou, E

    2007-01-01

    In this paper we present a new mathematical model for the density regions where a specific spectral line and its SACs/DACs are created in the Oe and Be stellar atmospheres. In the calculations of final spectral line function we consider that the main reasons of the line broadening are the rotation of the density regions creating the spectral line and its DACs/SACs, as well as the random motions of the ions. This line function is able to reproduce the spectral feature and it enables us to calculate some important physical parameters, such as the rotational, the radial and the random velocities, the Full Width at Half Maximum, the Gaussian deviation, the optical depth, the column density and the absorbed or emitted energy. Additionally, we can calculate the percentage of the contribution of the rotational velocity and the ions' random motions of the DACs/SACs regions to the line broadening. Finally, we present two tests and three short applications of the proposed model.

  20. A free-form lensing model of A370 revealing stellar mass dominated BCGs, in Hubble Frontier Fields images

    CERN Document Server

    Diego, Jose M; Broadhurst, Tom; Lam, Daniel; Vega-Ferrero, Jesus; Zheng, Wei; Lee, Slanger; Morishita, Takahiro; Bernstein, Gary; Lim, Jeremy; Silk, Joseph; Ford, Holland

    2016-01-01

    We derive a free-form mass distribution for the unrelaxed cluster A370 (z=0.375), using the latest Hubble Frontier Fields images and GLASS spectroscopy. Starting from a reliable set of 10 multiply lensed systems we produce a free-form lens model that identifies ~ 80 multiple-images. Good consistency is found between models using independent subsamples of these lensed systems, with detailed agreement for the well resolved arcs. The mass distribution has two very similar concentrations centred on the two prominent Brightest Cluster Galaxies (or BCGs), with mass profiles that are accurately constrained by a uniquely useful system of long radially lensed images centred on both BCGs. We show that the lensing mass profiles of these BCGs are mainly accounted for by their stellar mass profiles, with a modest contribution from dark matter within r<100 kpc of each BCG. This conclusion may favour a cooled cluster gas origin for BCGs, rather than via mergers of normal galaxies for which dark matter should dominate ove...

  1. An Integrated Model for the Production of X-Ray Time Lags and Quiescent Spectra from Homogeneous and Inhomogeneous Black Hole Accretion Coronae

    CERN Document Server

    Kroon, John J

    2016-01-01

    Many accreting black holes manifest time lags during outbursts, in which the hard Fourier component typically lags behind the soft component. Despite decades of observations of this phenomenon, the underlying physical explanation for the time lags has remained elusive, although there are suggestions that Compton reverberation plays an important role. However, the lack of analytical solutions has hindered the interpretation of the available data. In this paper, we investigate the generation of X-ray time lags in Compton scattering coronae using a new mathematical approach based on analysis of the Fourier-transformed transport equation. By solving this equation, we obtain the Fourier transform of the radiation Green's function, which allows us to calculate the exact dependence of the time lags on the Fourier frequency, for both homogeneous and inhomogeneous coronal clouds. We use the new formalism to explore a variety of injection scenarios, including both monochromatic and broadband (bremsstrahlung) seed photo...

  2. The Jeans modeling of the Milky Way galaxy: implications of the kinematics of the stellar halo

    Science.gov (United States)

    Samurović, S.; Lalović, A.

    2011-07-01

    Aims: We investigate the predictions of Newtonian dynamics and the MOND theory related to the Milky Way galaxy using the Jeans equation. Methods: We used the measurements of the radial velocities of the blue horizontal branch (BHB) halo stars to test the predictions of Newtonian gravity and to also extend our study to different MOND models, taking orbital anisotropies that we calculate into account. Results: The halo stars of the Galaxy were used as a tracer of the Galaxy's gravitational potential. The Jeans equation was calculated for both the Newtonian and the MOND approaches. We assumed spherical symmetry and calculated the Jeans equation by taking orbital anisotropies into account. Circular velocities for both approaches were also analyzed. Conclusions: We solved the Jeans equation in spherical approximation and confirm that the Newtonian model without dark matter cannot fit the observed velocity dispersion profile and that the truncated flat model with dark matter can provide a good fit to the observed velocity dispersion. For the MOND models, from the Jeans modeling and the models of the circular velocity curves, we found that two models can provide a fit to the data without significant anisotropies whereas two other tested models need various anisotropies to obtain the same result.

  3. Spectropolarimetry of Solar Corona during Solar Eclipses

    Science.gov (United States)

    Qu, Zhongquan

    2017-08-01

    We present the results from spectropolarimetry of solar corona. These observations were conducted during solar eclipses in 2008 China, 2013 Gabon, and probably 2017 United States of America respectively. From the former two observations, it is shown that the patterns of linear polarization of radiation from the solar corona are very abundant, and the abundance may be related to the complexity of mass motions and magnetic configuration in the corona. And the spectropolarimetry during solar eclipses may open a new window to probe precisely the physical features of the local corona, especially its magnetic configuration.

  4. Centrally Concentrated X-Ray Radiation from an Extended Accreting Corona in Active Galactic Nuclei

    Science.gov (United States)

    Liu, B. F.; Taam, Ronald E.; Qiao, Erlin; Yuan, Weimin

    2017-10-01

    The X-ray emission from bright active galactic nuclei (AGNs) is believed to originate in a hot corona lying above a cold, geometrically thin accretion disk. A highly concentrated corona located within ∼10 gravitational radii above the black hole is inferred from observations. Based on the accretion of interstellar medium/wind, a disk corona model has been proposed in which the corona is well coupled to the disk by radiation, thermal conduction, as well as by mass exchange. Such a model avoids artificial energy input to the corona and has been used to interpret the spectral features observed in AGN. In this work, it is shown that the bulk emission size of the corona is very small for the extended accretion flow in our model. More than 80% of the hard X-ray power is emitted from a small region confined within 10 Schwarzschild radii around a non-spinning black hole, which is expected to be even smaller accordingly for a spinning black hole. Here, the corona emission is more extended at higher Eddington ratios. The compactness parameter of the corona, l=\\tfrac{L}{R}\\tfrac{{σ }{{T}}}{{m}{{e}}{c}3}, is shown to be in the range of 1–33 for Eddington ratios of 0.02–0.1. Combined with the electron temperature in the corona, this indicates that electron–positron pair production is not dominant in this regime. A positive relation between the compactness parameter and photon index is also predicted. By comparing the above model predictions with observational features, we find that the model is in agreement with observations.

  5. Stellar population synthesis based modelling of the Milky Way using asteroseismology of 13000 Kepler red giants

    CERN Document Server

    Sharma, Sanjib; Bland-Hawthorn, Joss; Huber, Daniel; Bedding, Timothy R

    2016-01-01

    With current space-based missions it is now possible to obtain age-sensitive asteroseismic information for tens of thousands of red giants. This provides a promising opportunity to study the Galactic structure and evolution. We use asteroseismic data of red giants, observed by Kepler, to test the current theoretical framework of modelling the Galaxy based on population synthesis modeling and the use of asteroseismic scaling relations for giants. We use the open source code Galaxia to model the Milky Way and find the distribution of the masses predicted by Galaxia to be systematically offset with respect to the seismically-inferred observed masses. The Galactic model overestimates the number of low mass stars, and these stars are predominantly old and of low metallicity. Using corrections to the $\\Delta \

  6. Ultraviolet, Optical, and Infrared Constraints on Models of Stellar Populations and Dust Attenuation

    CERN Document Server

    Johnson, Benjamin D; Seibert, Mark; Treyer, Marie; Martin, D Christopher; Barlow, Tom A; Forster, Karl; Friedman, Peter G; Morrissey, Patrick; Neff, Susan G; Small, Todd; Wyder, Ted K; Bianchi, Luciana; Donas, Jose; Heckman, Timothy M; Lee, Young-Wook; Madore, Barry F; Milliard, Bruno; Rich, R Michael; Szalay, A S; Welsh, Barry Y; Yi, Sukyoung K

    2007-01-01

    The color of galaxies is a fundamental property, easily measured, that constrains models of galaxies and their evolution. Dust attenuation and star formation history (SFH) are the dominant factors affecting the color of galaxies. Here we explore the empirical relation between SFH, attenuation, and color for a wide range of galaxies, including early types. These galaxies have been observed by GALEX, SDSS, and Spitzer, allowing the construction of measures of dust attenuation from the ratio of infrared (IR) to ultraviolet (UV) flux and measures of SFH from the strength of the 4000A break. The empirical relation between these three quantities is compared to models that separately predict the effects of dust and SFH on color. This comparison demonstrates the quantitative consistency of these simple models with the data and hints at the power of multiwavelength data for constraining these models. The UV color is a strong constraint; we find that a Milky Way extinction curve is disfavored, and that the UV emission ...

  7. Influence of Air Pressure on Corona at the End of the Generator Stator Bar%气压对发电机定子线棒端部电晕放电特性的影响(英文)

    Institute of Scientific and Technical Information of China (English)

    WANG Youyuan; HE Yingchun; LI Yinwei; GAO Zhan

    2012-01-01

    According to the mechanism of corona discharge at the end of the generator stator bar,a model of stator bar end corona discharge is presented.In a closed corona cage at low atmospheric pressure,the corona discharge characteristics of the stator bar end model were observed using an ultraviolet imaging instrument and an oscilloscope.The influence of atmospheric pressure on the corona inception voltage and discharge intensity was analyzed.The results show that the corona inception voltage is lower under lower atmospheric pressure;the discharge intensity is stronger under lower atmospheric pressure.The particles swarm-optimized support vector machine was employed to analyze the impacts of air pressure and humidity on the corona inception voltage.Error between the calculated value of the established model and the experimental value is less than 5%.The established model can be used to calculate the corona inception voltage of the stator bar end model.

  8. Broad-band colors and overall photometric properties of template galaxy models from stellar population synthesis

    OpenAIRE

    Buzzoni, Alberto

    2005-01-01

    We present here a new set of evolutionary population synthesis models for template galaxies along the Hubble morphological sequence. The models, that account for the individual evolution of the bulge, disk, and halo components, provide basic morphological features, along with bolometric luminosity and color evolution (including Johnson/Cousins "UBVRcIcJHK", Gunn "gri", and Washington "CMT1T2" photometric systems) between 1 and 15 Gyr. Luminosity contribution from residual gas is also evaluate...

  9. Galactic globular clusters as a test for very-low-mass stellar models

    Science.gov (United States)

    Cassisi, S.; Castellani, V.; Ciarcelluti, P.; Piotto, G.; Zoccali, M.

    2000-07-01

    We make use of the `Next Generation' model atmospheres of Allard et al. and Hauschildt, Allard & Baron to compute theoretical models for low- and very-low-mass stars for selected metallicities in the range Z=0.0002 to 0.002. On this basis, we present theoretical predictions covering the sequence of H-burning stars as observed in Galactic globulars from the faint end of the main sequence up to, and beyond, the cluster turn-off. The role played by the new model atmospheres is discussed, showing that present models appear in excellent agreement with models by Baraffe et al. as computed on a quite similar physical basis. One finds that the theoretical mass-luminosity relations based on this updated set of models are in good agreement with the empirical data provided by Henry & McCarthy. Comparison with HST observation discloses that the location on the colour-magnitude diagram of the lower main sequence in Galactic globular clusters appears again in good agreement with the predicted sensitive dependence of these sequences on the cluster metallicity.

  10. A unified model for the maximum mass scales of molecular clouds, stellar clusters and high-redshift clumps

    Science.gov (United States)

    Reina-Campos, Marta; Kruijssen, J. M. Diederik

    2017-08-01

    We present a simple, self-consistent model to predict the maximum masses of giant molecular clouds (GMCs), stellar clusters and high-redshift clumps as a function of the galactic environment. Recent works have proposed that these maximum masses are set by shearing motions and centrifugal forces, but we show that this idea is inconsistent with the low masses observed across an important range of local-Universe environments, such as low-surface density galaxies and galaxy outskirts. Instead, we propose that feedback from young stars can disrupt clouds before the global collapse of the shear-limited area is completed. We develop a shear-feedback hybrid model that depends on three observable quantities: the gas surface density, the epicylic frequency and the Toomre parameter. The model is tested in four galactic environments: the Milky Way, the Local Group galaxy M31, the spiral galaxy M83 and the high-redshift galaxy zC406690. We demonstrate that our model simultaneously reproduces the observed maximum masses of GMCs, clumps and clusters in each of these environments. We find that clouds and clusters in M31 and in the Milky Way are feedback-limited beyond radii of 8.4 and 4 kpc, respectively, whereas the masses in M83 and zC406690 are shear-limited at all radii. In zC406690, the maximum cluster masses decrease further due to their inspiral by dynamical friction. These results illustrate that the maximum masses change from being shear-limited to being feedback-limited as galaxies become less gas rich and evolve towards low shear. This explains why high-redshift clumps are more massive than GMCs in the local Universe.

  11. Rossiter-McLaughlin models and their effect on estimates of stellar rotation, illustrated using six WASP systems

    Science.gov (United States)

    Brown, D. J. A.; Triaud, A. H. M. J.; Doyle, A. P.; Gillon, M.; Lendl, M.; Anderson, D. R.; Cameron, A. Collier; Hébrard, G.; Hellier, C.; Lovis, C.; Maxted, P. F. L.; Pepe, F.; Pollacco, D.; Queloz, D.; Smalley, B.

    2016-09-01

    We present new measurements of the projected spin-orbit angle λ for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses of previously measured systems using new data (WASP-71, and -79). We use three different models based on two different techniques: radial velocity measurements of the Rossiter-McLaughlin effect, and Doppler tomography. Our comparison of the different models reveals that they produce projected stellar rotation velocities (vsin Is) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Boué model for the Rossiter-McLaughlin effect consistently underestimates the value of vsin Is compared to the Hirano model. Although vsin Is differed, the effect on λ was small for our sample, with all three methods producing values in agreement with each other. Using Doppler tomography, we find that WASP-61 b (λ =4.0°+17.1-18.4), WASP-71 b (λ =-1.9°+7.1-7.5), and WASP-78 b (λ = -6.4° ± 5.9) are aligned. WASP-62 b (λ =19.4°+5.1-4.9) is found to be slightly misaligned, while WASP-79 b (λ =-95.2°+0.9-1.0) is confirmed to be strongly misaligned and has a retrograde orbit. We explore a range of possibilities for the orbit of WASP-76 b, finding that the orbit is likely to be strongly misaligned in the positive λ direction.

  12. Role of f(R,T,R{sub μν}T{sup μν}) model on the stability of cylindrical stellar model

    Energy Technology Data Exchange (ETDEWEB)

    Yousaf, Z.; Bhatti, M.Z.; Farwa, Ume [University of the Punjab, Department of Mathematics, Lahore (Pakistan)

    2017-06-15

    The aim of this paper is to investigate the stable/unstable regimes of the non-static anisotropic filamentary stellar models in the framework of f(R,T,R{sub μν}T{sup μν}) gravity. We construct the field equations and conservation laws in the perspective of this model of gravity. The perturbation scheme is applied to the analysis of the behavior of a particular f(R,T,R{sub μν}T{sup μν}) cosmological model on the evolution of cylindrical system. The role of the adiabatic index is also checked in the formulations of the instability regions. We have explored the instability constraints in the Newtonian and post-Newtonian limits. Our results reinforce the significance of the adiabatic index and dark source terms in the stability analysis of celestial objects in modified gravity. (orig.)

  13. Dynamics of nanoparticle-protein corona complex formation: analytical results from population balance equations.

    Directory of Open Access Journals (Sweden)

    Faryad Darabi Sahneh

    Full Text Available BACKGROUND: Nanoparticle-protein corona complex formation involves absorption of protein molecules onto nanoparticle surfaces in a physiological environment. Understanding the corona formation process is crucial in predicting nanoparticle behavior in biological systems, including applications of nanotoxicology and development of nano drug delivery platforms. METHOD: This paper extends the modeling work in to derive a mathematical model describing the dynamics of nanoparticle corona complex formation from population balance equations. We apply nonlinear dynamics techniques to derive analytical results for the composition of nanoparticle-protein corona complex, and validate our results through numerical simulations. RESULTS: The model presented in this paper exhibits two phases of corona complex dynamics. In the first phase, proteins rapidly bind to the free surface of nanoparticles, leading to a metastable composition. During the second phase, continuous association and dissociation of protein molecules with nanoparticles slowly changes the composition of the corona complex. Given sufficient time, composition of the corona complex reaches an equilibrium state of stable composition. We find analytical approximate formulae for metastable and stable compositions of corona complex. Our formulae are very well-structured to clearly identify important parameters determining corona composition. CONCLUSION: The dynamics of biocorona formation constitute vital aspect of interactions between nanoparticles and living organisms. Our results further understanding of these dynamics through quantitation of experimental conditions, modeling results for in vitro systems to better predict behavior for in vivo systems. One potential application would involve a single cell culture medium related to a complex protein medium, such as blood or tissue fluid.

  14. Determination of the position angle of stellar spin axes

    CERN Document Server

    Lesage, Anna-Lea

    2014-01-01

    Measuring the stellar position angle provides valuable information on binary stellar formation or stellar spin axis evolution. We aim to develop a method for determining the absolute stellar position angle using spectro-astrometric analysis of high resolution long-slit spectra. The method has been designed in particular for slowly rotating stars. We investigate its applicability to existing dispersive long-slit spectrographs, identified here by their plate scale, and the size of the resulting stellar sample. The stellar rotation induces a tilt in the stellar lines whose angle depends on the stellar position angle and the orientation of the slit. We developed a rotation model to calculate and reproduce the effects of stellar rotation on unreduced high resolution stellar spectra. Then we retrieved the tilt amplitude using a spectro-astrometric extraction of the position of the photocentre of the spectrum. Finally we present two methods for analysing the position spectrum using either direct measurement of the t...

  15. An interferometric-spectroscopic orbit for the binary HD 195987 Testing models of stellar evolution for metal-poor stars

    CERN Document Server

    Torres, G; Latham, D W; Pan, M; Stefanik, R P; Torres, Guillermo; Boden, Andrew F.; Latham, David W.; Pan, Margaret; Stefanik, Robert P.

    2002-01-01

    We report spectroscopic and interferometric observations of the moderately metal-poor double-lined binary system HD 195987, with an orbital period of 57.3 days. By combining our radial-velocity and visibility measurements we determine the orbital elements and derive absolute masses for the components of M(A) = 0.844 +/- 0.018 Msun and M(B) = 0.6650 +/- 0.0079 Msun, with relative errors of 2% and 1%, respectively. We also determine the orbital parallax, pi(orb) = 46.08 +/- 0.27 mas, corresponding to a distance of 21.70 +/- 0.13 pc. The parallax and the measured brightness difference between the stars in V, H, and K yield the component absolute magnitudes in those bands. We also estimate the effective temperatures of the stars as Teff(A) = 5200 +/- 100 K and Teff(B) = 4200 +/- 200 K. Together with detailed chemical abundance analyses from the literature giving [Fe/H] approximately -0.5 (corrected for binarity) and [alpha/Fe] = +0.36, we use these physical properties to test current models of stellar evolution f...

  16. Absolute properties of the eclipsing binary system AQ Serpentis: A stringent test of convective core overshooting in stellar evolution models

    CERN Document Server

    Torres, Guillermo; Lacy, Claud H Sandberg; Claret, Antonio

    2013-01-01

    We report differential photometric observations and radial-velocity measurements of the detached, 1.69-day period, double-lined eclipsing binary AQ Ser. Accurate masses and radii for the components are determined to better than 1.8% and 1.1%, respectively, and are M1 = 1.417 +/- 0.021 MSun, M2 = 1.346 +/- 0.024 MSun, R1 = 2.451 +/- 0.027 RSun, and R2 = 2.281 +/- 0.014 RSun. The temperatures are 6340 +/- 100 K (spectral type F6) and 6430 +/- 100 K (F5), respectively. Both stars are considerably evolved, such that predictions from stellar evolution theory are particularly sensitive to the degree of extra mixing above the convective core (overshoot). The component masses are different enough to exclude a location in the H-R diagram past the point of central hydrogen exhaustion, which implies the need for extra mixing. Moreover, we find that current main-sequence models are unable to match the observed properties at a single age even when allowing the unknown metallicity, mixing length parameter, and convective o...

  17. Stellar model atmospheres with magnetic line blanketing. II. Introduction of polarized radiative transfer

    CERN Document Server

    Khan, S A

    2006-01-01

    The technique of model atmosphere calculation for magnetic Ap and Bp stars with polarized radiative transfer and magnetic line blanketing is presented. A grid of model atmospheres of A and B stars are computed. These calculations are based on direct treatment of the opacities due to the bound-bound transitions that ensures an accurate and detailed description of the line absorption and anomalous Zeeman splitting. The set of model atmospheres was calculated for the field strengths between 1 and 40 kG. The high-resolution energy distribution, photometric colors and the hydrogen Balmer line profiles are computed for magnetic stars with different metallicities and are compared to those of non-magnetic reference models and to the previous paper of this series. The results of modelling confirmed the main outcomes of the previous study: energy redistribution from UV to the visual region and flux depression at 5200A. However, we found that effects of enhanced line blanketing when transfer for polarized radiation take...

  18. The Probabilities of Orbital-Companion Models for Stellar Radial Velocity Data

    CERN Document Server

    Hou, Fengji; Hogg, David W

    2014-01-01

    The fully marginalized likelihood, or Bayesian evidence, is of great importance in probabilistic data analysis, because it is involved in calculating the posterior probability of a model or re-weighting a mixture of models conditioned on data. It is, however, extremely challenging to compute. This paper presents a geometric-path Monte Carlo method, inspired by multi-canonical Monte Carlo to evaluate the fully marginalized likelihood. We show that the algorithm is very fast and easy to implement and produces a justified uncertainty estimate on the fully marginalized likelihood. The algorithm performs efficiently on a trial problem and multi-companion model fitting for radial velocity data. For the trial problem, the algorithm returns the correct fully marginalized likelihood, and the estimated uncertainty is also consistent with the standard deviation of results from multiple runs. We apply the algorithm to the problem of fitting radial velocity data from HIP 88048 ($\

  19. Abundance analysis of the halo giant HD 122563 with three-dimensional model stellar atmospheres

    Science.gov (United States)

    Collet, R.; Nordlund, Å.; Asplund, M.; Hayek, W.; Trampedach, R.

    We present a preliminary local thermodynamic equilibrium (LTE) abundance analysis of the template halo red giant HD122563 based on a realistic, three-dimensional (3D), time-dependent, hydrodynamical model atmosphere of the very metal-poor star. We compare the results of the 3D analysis with the abundances derived by means of a standard LTE analysis based on a classical, 1D, hydrostatic model atmosphere of the star. Due to the different upper photospheric temperature stratifications predicted by 1D and 3D models, we find large, negative, 3D-1D LTE abundance differences for low-excitation OH and Fe I lines. We also find trends with lower excitation potential in the derived Fe LTE abundances from Fe I lines, in both the 1D and 3D analyses. Such trends may be attributed to the neglected departures from LTE in the spectral line formation calculations.

  20. Abundance Analysis of the Halo Giant HD122563 with Three-Dimensional Model Stellar Atmospheres

    CERN Document Server

    Collet, R; Asplund, M; Hayek, W; Trampedach, R

    2009-01-01

    We present a preliminary local thermodynamic equilibrium (LTE) abundance analysis of the template halo red giant HD122563 based on a realistic, three-dimensional (3D), time-dependent, hydrodynamical model atmosphere of the very metal-poor star. We compare the results of the 3D analysis with the abundances derived by means of a standard LTE analysis based on a classical, 1D, hydrostatic model atmosphere of the star. Due to the different upper photospheric temperature stratifications predicted by 1D and 3D models, we find large, negative, 3D-1D LTE abundance differences for low-excitation OH and Fe I lines. We also find trends with lower excitation potential in the derived Fe LTE abundances from Fe I lines, in both the 1D and 3D analyses. Such trends may be attributed to the neglected departures from LTE in the spectral line formation calculations.

  1. Broad-band colors and overall photometric properties of template galaxy models from stellar population synthesis

    CERN Document Server

    Buzzoni, A

    2005-01-01

    We present here a new set of evolutionary population synthesis models for template galaxies along the Hubble morphological sequence. The models, that account for the individual evolution of the bulge, disk, and halo components, provide basic morphological features, along with bolometric luminosity and color evolution (including Johnson/Cousins "UBVRcIcJHK", Gunn "gri", and Washington "CMT1T2" photometric systems) between 1 and 15 Gyr. Luminosity contribution from residual gas is also evaluated, both in terms of nebular continuum and Balmer-line enhancement.

  2. 基于UV检测的UHV输电线路起晕电压的试验研究%Test Study on Corona Onset Voltage of UHV Transmission Lines Based on UV Detection

    Institute of Scientific and Technical Information of China (English)

    刘云鹏; 王会斌; 陈维江

    2008-01-01

    Corona discharge is being detected by UV imaging detection technology at home and abroad in recent years. This technology is used in the corona tests of conductor bundles in this paper. In order to further research the corona characteristic, optimize geometry parameters and diameter of sub-conductor, and increase corona onset voltage of transmission lines, corona tests of three model conductors which are placed inside the outdoor corona cage are conducted. Corona cage could be used to simulate the corona activities on transmission lines under a low voltage and different conditions in an effective and economical way. Photon which was created by UV light as a result of corona discharge on conductors is detected by the UV detection apparatus. The photon number within unit interval, namely photon counting rate is adopted as the parameter of quantifying the intensity of corona discharge. According to the apparent change of photon number, corona onset voltage can be judged. All tests are conducted under almost same atmosphere condition. Using the method, corona onset voltage is acquired. The results indicate that the tests have a good repeatability, in other words, repeating same test twice same result can be aquired. The corona onset voltage can be acquired exactly from the curve of applied voltage vs. photon counting rate. Therefore UV detection apparatus can not only used to find discharge point exactly, but also applied on corona discharge research and live detection for power equipments. The method using in this paper is proved that is a new available method.

  3. Astronomical performance of the engineering model Ørsted Advanced Stellar Compass

    DEFF Research Database (Denmark)

    Eisenman, Allan R.; Liebe, Carl Christian; Jørgensen, John Leif

    1996-01-01

    large star data bases which enable the computer to recognize star patterns in the field-of-view, to quickly solve the lost-in-space acquisition problem and to derive the attitude of the ASC camera head. The flight model of the camera head has a mass and a power consumption of 127 grams (without baffle...

  4. Ab initio Stellar Astrophysics: Reliable Modeling of Cool White Dwarf Atmospheres

    CERN Document Server

    Kowalski, Piotr M

    2010-01-01

    Over the last decade {\\it ab initio} modeling of material properties has become widespread in diverse fields of research. It has proved to be a powerful tool for predicting various properties of matter under extreme conditions. We apply modern computational chemistry and materials science methods, including density functional theory (DFT), to solve lingering problems in the modeling of the dense atmospheres of cool white dwarfs ($T_{\\rm eff}\\rm <7000 \\, K$). Our work on the revision and improvements of the absorption mechanisms in the hydrogen and helium dominated atmospheres resulted in a new set of atmosphere models. By inclusion of the Ly-$\\rm \\alpha$ red wing opacity we successfully fitted the entire spectral energy distributions of known cool DA stars. In the subsequent work we fitted the majority of the coolest stars with hydrogen-rich models. This finding challenges our understanding of the spectral evolution of cool white dwarfs. We discuss a few examples, including the cool companion to the pulsar...

  5. Simulating halos and coronas in their atmospheric environment.

    Science.gov (United States)

    David Gedzelman, Stanley

    2008-12-01

    Models are developed that simulate the light and color of the sky and of circular halos and coronas as a function of atmospheric pressure, cloud height, width, and optical depth, solar zenith angle, aerosol concentration and size, and ozone content. Halos, coronas, and skylight are treated as singly scattered sunbeams that are depleted in their passage through the atmosphere and cloud. Multiple scattering is included only for background cloud light. Halos produced by hexagonal crystal prisms and coronas produced by monodisperse droplets are visible for cloud optical depths in the range 0.0003 coronas can be bright only at smaller cloud optical depths and tend to be faint at their bottoms when produced in high cloud layers but can be bright at the horizon when produced by narrow cloud cells near ground level.

  6. Modelación del contacto entre dos pares de dientes en las coronas de molinos de caña//Modeling of contact between two pairs of teeth in the sugar cane mills gears

    Directory of Open Access Journals (Sweden)

    Abdel Mendoza‐Fernández

    2013-09-01

    Full Text Available En el trabajo se propone un mecanismo equivalente para la modelación del funcionamiento de las coronas de molino de caña de azúcar cuando teóricamente hay dos pares de dientes en contacto. A través del análisis de movilidad del mecanismo se demuestra que no es posible el contacto simultaneo entre dos pares de dientes y que el coeficiente de recubrimiento en estos engranes es igual o menor que la unidad. A partir de los resultados del análisis cinemático del contacto entre un par de dientes, y combinándolo con la modelación del contacto entre dos pares de dientes se demuestra que el coeficiente de recubrimiento real en estos engranajes es menor que la unidad y se producen impactos entre los dientes al inicio del contacto.Palabras claves: molinos de caña, coronas de molinos, coeficiente de recubrimiento, engranajes._________________________________________________________________________________AbstractThe paper proposes an equivalent mechanism for modeling the functioning of the crowns of sugar cane mill when theoretically there are two pairs of teeth in contact. Through mobility analysis of the mechanism is demonstrated that is not possible the simultaneous contact between two pairs of teeth and that the coating coefficient of these gears is equal or less than unity. Combining kinematic analysis results for the contact between a pair of teeth with the modeling the contact between two pairs of teeth, it is demonstrated that gear ratio of these gears is less than unity and impacts occur between the teeth at the start of contact.Key words: sugar cane mills, sugar cane mills gears, contact ratio, gears.

  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. A spherical, non-LTE, blanketed model stellar atmosphere for Phi CAS (FOIa)

    Science.gov (United States)

    Rosenzweig, Patricia

    By constructing a model atmosphere, the theoretical energy distribution of the emergent radiation that best matches the observed energy distribution of the star Phi Cassiopeiae is calculated; its effective temperature and surface gravity are thus derived. In order to use the pair method to derive the extinction curve for NGC 457 of which Phi Cas is a member, a new method is developed for choosing a lightly reddened comparison star, which consists of matching the equivalent widths of spectral features that are particularly strong and sensitive to temperature and luminosity. The intrinsic energy distribution of Phi Cas was determined from 1500 to 5800 A. A detailed new spherical model atmosphere was constructed. The equation of transfer was solved with the constraints of hydrostatic and pure radiative equilibrium. The statistical equilibrium of 10 to the 6th transitions was treated. Several tests have demonstrated this model to be reliable. Results imply a mass of 6.3 + or - 3.6 solar masses, which agrees with the mass of the main-sequence turnoff of NGC 457.

  9. Why Simple Stellar Population models do not fit the colours of Galactic open clusters

    CERN Document Server

    Piskunov, A E; Schilbach, E; Röser, S; Scholz, R -D; Zinnecker, H

    2009-01-01

    (...) We have found a disagreement between the observed integrated colours of 650 local Galactic clusters and theoretical colours of present-day SSP models and seek an explanation for this discrepancy. We check the hypothesis that the systematic offset between observed and theoretical colours, which is $(B$$-$$V)\\approx 0.3$ \\textbf{and $(J$$-$$K_s)\\approx 0.8$}, is due to neglecting the discrete nature of the underlying mass function. Using Monte Carlo simulations we construct artificial clusters of coeval stars drawn from a mass distribution according to the Salpeter IMF and compare them with corresponding "continuous-IMF" SSP models. If the discreteness of the IMF is taken into account, the model fits the observations perfectly and is able to explain naturally a number of red "outliers" observed in the empirical colour-age relation. We find that the \\textit{systematic} offset between the continuous- and discrete-IMF colours reaches its maximum of about 0.5 in $(B$$-$$V)$ for a cluster mass $M_c=10^2 m_\\odo...

  10. XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part II: hydrogen coronae and ion escape.

    Science.gov (United States)

    Kislyakova, Kristina G; Lammer, Helmut; Holmström, Mats; Panchenko, Mykhaylo; Odert, Petra; Erkaev, Nikolai V; Leitzinger, Martin; Khodachenko, Maxim L; Kulikov, Yuri N; Güdel, Manuel; Hanslmeier, Arnold

    2013-11-01

    We studied the interactions between the stellar wind plasma flow of a typical M star, such as GJ 436, and the hydrogen-rich upper atmosphere of an Earth-like planet and a "super-Earth" with a radius of 2 R(Earth) and a mass of 10 M(Earth), located within the habitable zone at ∼0.24 AU. We investigated the formation of extended atomic hydrogen coronae under the influences of the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause), and the loss of planetary pickup ions on the evolution of hydrogen-dominated upper atmospheres. Stellar XUV fluxes that are 1, 10, 50, and 100 times higher compared to that of the present-day Sun were considered, and the formation of high-energy neutral hydrogen clouds around the planets due to the charge-exchange reaction under various stellar conditions was modeled. Charge-exchange between stellar wind protons with planetary hydrogen atoms, and photoionization, lead to the production of initially cold ions of planetary origin. We found that the ion production rates for the studied planets can vary over a wide range, from ∼1.0×10²⁵ s⁻¹ to ∼5.3×10³⁰ s⁻¹, depending on the stellar wind conditions and the assumed XUV exposure of the upper atmosphere. Our findings indicate that most likely the majority of these planetary ions are picked up by the stellar wind and lost from the planet. Finally, we estimated the long-time nonthermal ion pickup escape for the studied planets and compared them with the thermal escape. According to our estimates, nonthermal escape of picked-up ionized hydrogen atoms over a planet's lifetime within the habitable zone of an M dwarf varies between ∼0.4 Earth ocean equivalent amounts of hydrogen (EO(H)) to <3 EO(H) and usually is several times smaller in comparison to the thermal atmospheric escape rates.

  11. A local leaky-box model for the local stellar surface density-gas surface density-gas phase metallicity relation

    Science.gov (United States)

    Zhu, Guangtun Ben; Barrera-Ballesteros, Jorge K.; Heckman, Timothy M.; Zakamska, Nadia L.; Sánchez, Sebastian F.; Yan, Renbin; Brinkmann, Jonathan

    2017-07-01

    We revisit the relation between the stellar surface density, the gas surface density and the gas-phase metallicity of typical disc galaxies in the local Universe with the SDSS-IV/MaNGA survey, using the star formation rate surface density as an indicator for the gas surface density. We show that these three local parameters form a tight relationship, confirming previous works (e.g. by the PINGS and CALIFA surveys), but with a larger sample. We present a new local leaky-box model, assuming star-formation history and chemical evolution is localized except for outflowing materials. We derive closed-form solutions for the evolution of stellar surface density, gas surface density and gas-phase metallicity, and show that these parameters form a tight relation independent of initial gas density and time. We show that, with canonical values of model parameters, this predicted relation match the observed one well. In addition, we briefly describe a pathway to improving the current semi-analytic models of galaxy formation by incorporating the local leaky-box model in the cosmological context, which can potentially explain simultaneously multiple properties of Milky Way-type disc galaxies, such as the size growth and the global stellar mass-gas metallicity relation.

  12. The Search for Stellar Coronal Mass Ejections

    Science.gov (United States)

    Villadsen, Jacqueline Rose

    2017-05-01

    with the advent of large low-frequency radio telescopes. Wide bandwidth radio dynamic spectroscopy, complemented by high-resolution imaging of the radio corona, is a powerful technique for detecting stellar eruptions and characterizing dynamic processes in the stellar corona.

  13. The Search for Stellar Coronal Mass Ejections

    Science.gov (United States)

    Villadsen, Jacqueline; Hallinan, Gregg; Monroe, Ryan; Bourke, Stephen; Starburst Program Team

    2017-01-01

    -frequency radio telescopes. Wide bandwidth radio dynamic spectroscopy, complemented by high-resolution imaging of the radio corona, is a powerful technique for detecting stellar eruptions and characterizing dynamic processes in the stellar corona.

  14. The condensation of the corona for the correlation between the hard X-ray photon index Γ and the reflection scaling factor ℜ in active galactic nuclei

    Science.gov (United States)

    Qiao, Erlin; Liu, B. F.

    2017-01-01

    Observationally, it is found that there is a strong correlation between the hard X-ray photon index Γ and the Compton reflection scaling factor ℜ in active galactic nuclei. In this paper, we propose that the Γ - ℜ correlation can be explained within the framework of the condensation of the hot corona onto the cold accretion disc around a supermassive black hole. In the model, it is presumed that, initially, a vertically extended hot gas (corona) is supplied to the central supermassive black hole by capturing the interstellar medium and stellar wind. In this scenario, when the initial mass accretion rate dot{M}/ dot{M}_Edd gtrsim 0.01, at a critical radius rd, part of the hot gas begins to condense onto the equatorial disc plane of the black hole, forming an inner cold accretion disc. Then the matter is accreted in the form of the disc-corona structure extending down to the innermost stable circular orbits of the black hole. The size of the inner disc is determined by the initial mass accretion rate. With the increase of the initial mass accretion rate, the size of the inner disc increases, which results in both the increase of the Compton reflection scaling factor ℜ and the increase of the hard X-ray photon index Γ. By comparing with a sample of Seyfert galaxies with well-fitted X-ray spectra, it is found that our model can roughly explain the observations. Finally, we discuss the possibility to apply our model to high mass X-ray binaries, which are believed to be fueled by the hot wind from the companion star.

  15. Inelastic e+Mg collision data and its impact on modelling stellar and supernova spectra

    Science.gov (United States)

    Barklem, P. S.; Osorio, Y.; Fursa, D. V.; Bray, I.; Zatsarinny, O.; Bartschat, K.; Jerkstrand, A.

    2017-09-01

    Results of calculations for inelastic e+Mg effective collision strengths for the lowest 25 physical states of Mg i (up to 3s6p1P), and thus 300 transitions, from the convergent close-coupling (CCC) and the B-spline R-matrix (BSR) methods are presented. At temperatures of interest, 5000 K, the results of the two calculations differ on average by only 4%, with a scatter of 27%. As the methods are independent, this suggests that the calculations provide datasets for e+Mg collisions accurate to this level. Comparison with the commonly used dataset compiled by Mauas et al. (1988, ApJ, 330, 1008), covering 25 transitions among 12 states, suggests the Mauas et al. data are on average 57% too low, and with a very large scatter of a factor of 6.5. In particular the collision strength for the transition corresponding to the Mg i intercombination line at 457 nm is significantly underestimated by Mauas et al., which has consequences for models that employ this dataset. In giant stars the new data leads to a stronger line compared to previous non-LTE calculations, and thus a reduction in the non-LTE abundance correction by 0.1 dex ( 25%). A non-LTE calculation in a supernova ejecta model shows this line becomes significantly stronger, by a factor of around two, alleviating the discrepancy where the 457 nm line in typical models with Mg/O ratios close to solar tended to be too weak compared to observations. Full Tables 2 and 3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A11

  16. Retrievals from GOMOS stellar occultation measurements using characterization of modeling errors

    Directory of Open Access Journals (Sweden)

    V. F. Sofieva

    2010-02-01

    Full Text Available In this paper, we discuss the development of the inversion algorithm for the GOMOS (Global Ozone Monitoring by Occultation of Star instrument on board the Envisat satellite. The proposed algorithm takes accurately into account the wavelength-dependent modeling errors, which are mainly due to the incomplete scintillation correction in the stratosphere. The special attention is paid to numerical efficiency of the algorithm. The developed method is tested on a large data set and its advantages are demonstrated. Its main advantage is a proper characterization of the uncertainties of the retrieved profiles of atmospheric constituents, which is of high importance for data assimilation, trend analyses and validation.

  17. Retrievals from GOMOS stellar occultation measurements using characterization of modeling errors

    Directory of Open Access Journals (Sweden)

    V. F. Sofieva

    2010-08-01

    Full Text Available In this paper, we discuss the development of the inversion algorithm for the GOMOS (Global Ozone Monitoring by Occultation of Star instrument on board the Envisat satellite. The proposed algorithm takes accurately into account the wavelength-dependent modeling errors, which are mainly due to the incomplete scintillation correction in the stratosphere. The special attention is paid to numerical efficiency of the algorithm. The developed method is tested on a large data set and its advantages are demonstrated. Its main advantage is a proper characterization of the uncertainties of the retrieved profiles of atmospheric constituents, which is of high importance for data assimilation, trend analyses and validation.

  18. Asteroseismology of solar-type stars with Kepler: II. Stellar modeling

    DEFF Research Database (Denmark)

    Metcalfe , T.S.; Karoff, Christoffer

    2010-01-01

    Observations from the Kepler satellite were recently published for three bright G-type stars, which were monitored during the first 33.5 days of science operations. One of these stars, KIC 11026764, exhibits a characteristic pattern of oscillation frequencies suggesting that the star has evolved...... significantly. We have derived initial estimates of the properties of KIC 11026764 from the oscillation frequencies observed by Kepler, combined with ground-based spectroscopic data. We present preliminary results from detailed modeling of this star, employing a variety of independent codes and analyses...

  19. Corona Formation and Heat Loss on Venus by Coupled Upwelling and Delamination

    Science.gov (United States)

    Smrekar, Suzanne E.; Stofan, Ellen R.

    1997-01-01

    Coronae are volcanotectonic features that are unique to Venus and are interpreted to be small-scale upwellings. A model in which upwelling causes delamination at the edge of the plume head, along with deformation of a pre-existing depleted mantel Layer, can produce the full range of topographic forms of coronae. If half of the coronae are active, delamination of the lower lithosphere could account for about 10% of venus's heat loss, with another 15% due to upwelling. Delamination may occur in other geologic enviroment and could help account for 'Venus' heat loss 'deficit'.

  20. An Exact Equilibrium Model of an Unbound Stellar System in a Tidal Field

    CERN Document Server

    Fellhauer, M

    2005-01-01

    Star clusters and dwarf galaxies gradually dissolve as they move in the potential of their host galaxy. Once their density falls below a certain critical density (which is comparable with the background density of the galaxy) it is often assumed that their evolution is completed. In fact the remnant of such a system forms a distribution of stars which are unbound to each other and which move on similar orbits in their host potential. With this motivation we study the evolution of an idealised unbound system and follow its expansion and dissolution in the tidal field of a model galaxy. Initially the stars are uniformly distributed (with a density below the critical density) within an ellipsoidal volume. The system itself travels on a circular orbit within a galaxy modelled as an isothermal sphere. The initial velocities of the stars are chosen by assuming that they move on (three-dimensional) epicycles with guiding centre at the centre of the ellipsoid, though the usual epicyclic theory is altered to account f...