Science.gov

Sample records for astrophysical disk models

  1. On Vertically Global, Horizontally Local Models for Astrophysical Disks

    NASA Astrophysics Data System (ADS)

    McNally, Colin P.; Pessah, Martin E.

    2015-10-01

    Disks with a barotropic equilibrium structure, for which the pressure is only a function of the density, rotate on cylinders in the presence of a gravitational potential, so that the angular frequency of such a disk is independent of height. Such disks with barotropic equilibria can be approximately modeled using the shearing box framework, representing a small disk volume with height-independent angular frequency. If the disk is in baroclinic equilibrium, the angular frequency does generally depend on height, and it is thus necessary to go beyond the standard shearing box approach. In this paper, we show that given a global disk model, it is possible to develop approximate models that are local in horizontal planes without an expansion in height with shearing-periodic boundary conditions. We refer to the resulting framework as the vertically global shearing box (VGSB). These models can be non-axisymmetric for globally barotropic equilibria but should be axisymmetric for globally baroclinic equilibria. We provide explicit equations for this VGSB which can be implemented in standard magnetohydrodynamic codes by generalizing the shearing-periodic boundary conditions to allow for a height-dependent angular frequency and shear rate. We also discuss the limitations that result from the radial approximations that are needed in order to impose height-dependent shearing periodic boundary conditions. We illustrate the potential of this framework by studying a vertical shear instability and examining the modes associated with the magnetorotational instability.

  2. Rossby Wave Instability in Astrophysical Disks

    NASA Astrophysics Data System (ADS)

    Lovelace, Richard; Li, Hui

    2014-10-01

    A brief review is given of the Rossby wave instability in astrophysical disks. In non-self-gravitating discs, around for example a newly forming stars, the instability can be triggered by an axisymmetric bump at some radius r0 in the disk surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation (proportional to Exp[im ϕ], m = 1,2,...) in the vicinity of r0 consisting of anticyclonic vortices. These vortices are regions of high pressure and consequently act to trap dust particles which in turn can facilitate planetesimal growth in protoplanetary disks. The Rossby vortices in the disks around stars and black holes may cause the observed quasi-periodic modulations of the disk's thermal emission. Stirling Colgate's long standing interest in all types of vortices - particularly tornados - had an important part in stimulating the research on the Rossby wave instability.

  3. Saturn's Rings: An Accessible Astrophysical Disk

    NASA Astrophysics Data System (ADS)

    Tiscareno, Matthew S.; Cassini Imaging Team

    2007-12-01

    Saturn's ring system is an astrophysical disk that is neither light-years away nor billions of years in the past. We can visit this disk at close range and observe a number of phenomena that also operate in disks of other kinds. As a result, we see small-scale processes that shape ring texture, connect those processes to the bodies and structures that cause them, and watch closely as the disk changes with time. Recent observations include: 1) "self-gravity wakes” (see Julian and Toomre 1966) dominating the texture of some ring regions; 2) km-sized "propeller-shaped” features caused by small (100-meter) moonlets embedded in the disk; 3) irregular edge shapes in the gaps opened up by larger ( 10 km) moons, which may hold clues to angular momentum transport; 4) resonant spiral density waves excited by more distant large moons, which serve as in situ probes of local disk density and viscosity; 5) waves whose form changes with time, due to the varying orbits of the moons Janus and Epimetheus. The latest results from the Cassini mission will be presented.

  4. Transient dynamics of perturbations in astrophysical disks

    NASA Astrophysics Data System (ADS)

    Razdoburdin, D. N.; Zhuravlev, V. V.

    2015-11-01

    We review some aspects of a major unsolved problem in understanding astrophysical (in particular, accretion) disks: whether the disk interiors can be effectively viscous in spite of the absence of magnetorotational instability. A rotational homogeneous inviscid flow with a Keplerian angular velocity profile is spectrally stable, making the transient growth of perturbations a candidate mechanism for energy transfer from regular motion to perturbations. Transient perturbations differ qualitatively from perturbation modes and can grow substantially in shear flows due to the nonnormality of their dynamical evolution operator. Because the eigenvectors of this operator, also known as perturbation modes, are not pairwise orthogonal, they can mutually interfere, resulting in the transient growth of their linear combinations. Physically, a growing transient perturbation is a leading spiral whose branches are shrunk as a result of the differential rotation of the flow. We discuss in detail the transient growth of vortex shearing harmonics in the spatially local limit, as well as methods for identifying the optimal (fastest growth) perturbations. Special attention is given to obtaining such solutions variationally by integrating the respective direct and adjoint equations forward and backward in time. The presentation is intended for experts new to the subject.

  5. Integrated accretion disk angular momentum removal and astrophysical jet acceleration mechanism

    NASA Astrophysics Data System (ADS)

    Bellan, Paul

    2015-11-01

    A model has been developed for how accretion disks discard angular momentum while powering astrophysical jets. The model depends on the extremely weak ionization of disks. This causes disk ions to be collisionally locked to adjacent disk neutrals so a clump of disk ions and neutrals has an effective cyclotron frequency αωci where α is the fractional ionization. When αωci is approximately twice the Kepler orbital frequency, conservation of canonical momentum shows that the clump spirals radially inwards producing a radially inward disk electric current as electrons cannot move radially in the disk. Upon reaching the jet radius, this current then flows axially away from the disk plane along the jet, producing a toroidal magnetic field that drives the jet. Electrons remain frozen to poloidal flux surfaces everywhere and electron motion on flux surfaces in the ideal MHD region outside the disk completes the current path. Angular momentum absorbed from accreting material in the disk by magnetic counter-torque -JrBz is transported by the electric circuit and ejected at near infinite radius in the disk plane. This is like an electric generator absorbing angular momentum and wired to a distant electric motor that emits angular momentum. Supported by USDOE/NSF Partnership in Plasma Science.

  6. Global Simulations of Dynamo and Magnetorotational Instability in Madison Plasma Experiments and Astrophysical Disks

    SciTech Connect

    Ebrahimi, Fatima

    2014-07-31

    Large-scale magnetic fields have been observed in widely different types of astrophysical objects. These magnetic fields are believed to be caused by the so-called dynamo effect. Could a large-scale magnetic field grow out of turbulence (i.e. the alpha dynamo effect)? How could the topological properties and the complexity of magnetic field as a global quantity, the so called magnetic helicity, be important in the dynamo effect? In addition to understanding the dynamo mechanism in astrophysical accretion disks, anomalous angular momentum transport has also been a longstanding problem in accretion disks and laboratory plasmas. To investigate both dynamo and momentum transport, we have performed both numerical modeling of laboratory experiments that are intended to simulate nature and modeling of configurations with direct relevance to astrophysical disks. Our simulations use fluid approximations (Magnetohydrodynamics - MHD model), where plasma is treated as a single fluid, or two fluids, in the presence of electromagnetic forces. Our major physics objective is to study the possibility of magnetic field generation (so called MRI small-scale and large-scale dynamos) and its role in Magneto-rotational Instability (MRI) saturation through nonlinear simulations in both MHD and Hall regimes.

  7. Astrophysical Model Selection in Gravitational Wave Astronomy

    NASA Technical Reports Server (NTRS)

    Adams, Matthew R.; Cornish, Neil J.; Littenberg, Tyson B.

    2012-01-01

    Theoretical studies in gravitational wave astronomy have mostly focused on the information that can be extracted from individual detections, such as the mass of a binary system and its location in space. Here we consider how the information from multiple detections can be used to constrain astrophysical population models. This seemingly simple problem is made challenging by the high dimensionality and high degree of correlation in the parameter spaces that describe the signals, and by the complexity of the astrophysical models, which can also depend on a large number of parameters, some of which might not be directly constrained by the observations. We present a method for constraining population models using a hierarchical Bayesian modeling approach which simultaneously infers the source parameters and population model and provides the joint probability distributions for both. We illustrate this approach by considering the constraints that can be placed on population models for galactic white dwarf binaries using a future space-based gravitational wave detector. We find that a mission that is able to resolve approximately 5000 of the shortest period binaries will be able to constrain the population model parameters, including the chirp mass distribution and a characteristic galaxy disk radius to within a few percent. This compares favorably to existing bounds, where electromagnetic observations of stars in the galaxy constrain disk radii to within 20%.

  8. Spiral waves and instability in magnetized astrophysical disks

    SciTech Connect

    Tagger, M.; Henriksen, R.N.; Sygnet, J.F.; Pellat, R. CNRS, Institut d'Astrophysique, Paris Ecole Polytechnique, Palaiseau )

    1990-04-01

    It is shown that an ionized disk in a vertical magnetic field (e.g., the dipole field of the central object for an accretion or planetary disk) is subject to spiral instabilities of low azimuthal wavenumber, driven by differential rotation. The amplification is due to the Swing mechanism already known for the spiral instability of galactic disks, with self-gravity replaced by magnetic forces. In realistic cases the growth time is a few tens of rotation periods. Such instabilities, or waves driven by irregularities in the ambient magnetic field, might be important in particular for accretion disks, and to explain the spokes in Saturn's rings. 11 refs.

  9. Reaction models in nuclear astrophysics

    NASA Astrophysics Data System (ADS)

    Descouvemont, Pierre

    2016-05-01

    We present different reaction models commonly used in nuclear astrophysics, in particular for the nucleosynthesis of light elements. Pioneering works were performed within the potential model, where the internal structure of the colliding nuclei is completely ignored. Significant advances in microscopic cluster models provided the first microscopic description of the 3He(α,&gamma)7 Be reaction more than thirty years ago. In this approach, the calculations are based on an effective nucleon-nucleon interaction, but the cluster approximation should be made to simplify the calculations. Nowadays, modern microscopic calculations are able to go beyond the cluster approximation, and aim at finding exact solutions of the Schrödinger equation with realistic nucleon-nucleon interactions. We discuss recent examples on the d+d reactions at low energies.

  10. Numerical MHD codes for modeling astrophysical flows

    NASA Astrophysics Data System (ADS)

    Koldoba, A. V.; Ustyugova, G. V.; Lii, P. S.; Comins, M. L.; Dyda, S.; Romanova, M. M.; Lovelace, R. V. E.

    2016-05-01

    We describe a Godunov-type magnetohydrodynamic (MHD) code based on the Miyoshi and Kusano (2005) solver which can be used to solve various astrophysical hydrodynamic and MHD problems. The energy equation is in the form of entropy conservation. The code has been implemented on several different coordinate systems: 2.5D axisymmetric cylindrical coordinates, 2D Cartesian coordinates, 2D plane polar coordinates, and fully 3D cylindrical coordinates. Viscosity and diffusivity are implemented in the code to control the accretion rate in the disk and the rate of penetration of the disk matter through the magnetic field lines. The code has been utilized for the numerical investigations of a number of different astrophysical problems, several examples of which are shown.

  11. Do Accretion Disks Exist in High Energy Astrophysics?

    NASA Astrophysics Data System (ADS)

    Coppi, B.

    2006-10-01

    The familiar concept of an accretion disk is based on its gas dynamic description where, in particular, the vertical equilibrium is maintained by the (weak) vertical component of the gravitational force due to the central object. When a plasma structure differentially rotating around the same kind of object is considered in which the magnetic field diffusion due to finite resistivity is realistically weak, a radially periodic sequence of pairs of opposite current channels is found. Moreover, the vertical confinement of the structure is maintained by the resulting Lorentz force rather than by gravity. Thus, a ``Lorentz compression'' occurs. In addition, sequences of plasma rings^2 rather than disks emerge. (Note that H. Alfvén had proposed that planetary rings may be ``fossils'' of pre- existing envisioned plasma rings. Moreover, a large ring is the most prominent feature emerging from the high resolution X- ray image of the Crab). The ``seed'' magnetic field in which the structure is immersed is considerably smaller than that produced by the internal toroidal currents. The magnetic pressure is of the order of the plasma pressure. Thus, ring sequence configurations can be suitable for the emergence of a jet from their center. Two coupled non-linear equations have been solved, representing the vertical and the horizontal equilibrium conditions for the structure.*Sponsored in part by the U.S. D.O.E. B. Coppi, Phys. Plasmas 12, 057301, (2005) B. Coppi and F. Rousseau, Ap. J. 641 (1), 458 (2006)

  12. A model for astrophysical spallation reactions

    NASA Technical Reports Server (NTRS)

    Schmitt, W. F.; Ayres, C. L.; Merker, M.; Shen, B. S. P.

    1974-01-01

    A Monte-Carlo model (RENO) for spallation reactions is described which can treat both the spallations induced by a free nucleon and those induced by a complex nucleus. It differs from other such models in that it employs a discrete-nucleon representation of the nucleus and allows clusters of nucleons to form and to participate in the reaction. The RENO model is particularly suited for spallations involving the relatively light nuclei of astrophysical and cosmic-ray interest.

  13. Optimizing a tandem disk model

    SciTech Connect

    Healey, J.V.

    1983-07-01

    A very simple physicomathematical model, in which thin straight blades with zero drag skim across a plane rectangular disk, shows that the maximum power coefficient attains the classical maximum of 0.593 over a range of T and a zero or small negative value of alpha/sub 0/. This maximum appears independent of sigma and there are values of T and alpha/sub 0/ for which the speed through the disk becomes complex and the model breaks down. Extending this model to a tandem disk system leads to a difficulty in defining the power coefficient. Attempts to optimize the system output based on reference areas A/sub 1/, A/sub 2/, and A/sub 4/ prove futile and the sum of the coefficients is chosen for this purpose. For thin blades and zero drag the analytic solution is available and it shows that the maximum value of 2 X 0.593 is attained over a narrow range of slightly negative alpha/sub 0/ (blade nose in) and medium values of T. The maximum is independent of sigma. As T is increased, the model breaks down either after C /SUB psum/ becomes large and negative or after backflow through the downwind disk occurs. There appears to be no requirement on load distribution between the disks. By comparison, modeling a machine with NACA 0012 blades at Re = 1.34 X 10/sup 6/ shows that the maximum value of C /SUB psum/ depends on the solidity. For example, at sigma = 0.4, the maximum value of C /SUB psum/ is 83% of 2 X 0.593. At such high values of sigma, however, the ranges of alpha/sub 0/ and T over which solutions are available become very limited.

  14. Simple analytic model for astrophysical S factors

    SciTech Connect

    Yakovlev, D. G.; Beard, M.; Gasques, L. R.; Wiescher, M.

    2010-10-15

    We propose a physically transparent analytic model of astrophysical S factors as a function of a center-of-mass energy E of colliding nuclei (below and above the Coulomb barrier) for nonresonant fusion reactions. For any given reaction, the S(E) model contains four parameters [two of which approximate the barrier potential, U(r)]. They are easily interpolated along many reactions involving isotopes of the same elements; they give accurate practical expressions for S(E) with only several input parameters for many reactions. The model reproduces the suppression of S(E) at low energies (of astrophysical importance) due to the shape of the low-r wing of U(r). The model can be used to reconstruct U(r) from computed or measured S(E). For illustration, we parametrize our recent calculations of S(E) (using the Sao Paulo potential and the barrier penetration formalism) for 946 reactions involving stable and unstable isotopes of C, O, Ne, and Mg (with nine parameters for all reactions involving many isotopes of the same elements, e.g., C+O). In addition, we analyze astrophysically important {sup 12}C+{sup 12}C reaction, compare theoretical models with experimental data, and discuss the problem of interpolating reliably known S(E) values to low energies (E < or approx. 2-3 MeV).

  15. Astrophysical constraints on scalar field models

    SciTech Connect

    Bertolami, O.; Paramos, J.

    2005-01-15

    We use stellar structure dynamics arguments to extract bounds on the relevant parameters of two scalar field models: the putative scalar field mediator of a fifth force with a Yukawa potential and the new variable mass particle models. We also analyze the impact of a constant solar inbound acceleration, such as the one reported by the Pioneer anomaly, on stellar astrophysics. We consider the polytropic gas model to estimate the effect of these models on the hydrostatic equilibrium equation and fundamental quantities such as the central temperature. The current bound on the solar luminosity is used to constrain the relevant parameters of each model.

  16. DiskJockey: Protoplanetary disk modeling for dynamical mass derivation

    NASA Astrophysics Data System (ADS)

    Czekala, Ian

    2016-03-01

    DiskJockey derives dynamical masses for T Tauri stars using the Keplerian motion of their circumstellar disks, applied to radio interferometric data from the Atacama Large Millimeter Array (ALMA) and the Submillimeter Array (SMA). The package relies on RADMC-3D (ascl:1202.015) to perform the radiative transfer of the disk model. DiskJockey is designed to work in a parallel environment where the calculations for each frequency channel can be distributed to independent processors. Due to the computationally expensive nature of the radiative synthesis, fitting sizable datasets (e.g., SMA and ALMA) will require a substantial amount of CPU cores to explore a posterior distribution in a reasonable timeframe.

  17. Astrophysical Plasmas: Codes, Models, and Observations

    NASA Astrophysics Data System (ADS)

    Canto, Jorge; Rodriguez, Luis F.

    2000-05-01

    The conference Astrophysical Plasmas: Codes, Models, and Observations was aimed at discussing the most recent advances, arid some of the avenues for future work, in the field of cosmical plasmas. It was held (hiring the week of October 25th to 29th 1999, at the Centro Nacional de las Artes (CNA) in Mexico City, Mexico it modern and impressive center of theaters and schools devoted to the performing arts. This was an excellent setting, for reviewing the present status of observational (both on earth and in space) arid theoretical research. as well as some of the recent advances of laboratory research that are relevant, to astrophysics. The demography of the meeting was impressive: 128 participants from 12 countries in 4 continents, a large fraction of them, 29% were women and most of them were young persons (either recent Ph.Ds. or graduate students). This created it very lively and friendly atmosphere that made it easy to move from the ionization of the Universe and high-redshift absorbers, to Active Galactic Nucleotides (AGN)s and X-rays from galaxies, to the gas in the Magellanic Clouds and our Galaxy, to the evolution of H II regions and Planetary Nebulae (PNe), and to the details of plasmas in the Solar System and the lab. All these topics were well covered with 23 invited talks, 43 contributed talks. and 22 posters. Most of them are contained in these proceedings, in the same order of the presentations.

  18. Crystalline structure of accretion disks: Features of a global model

    NASA Astrophysics Data System (ADS)

    Montani, Giovanni; Benini, Riccardo

    2011-08-01

    In this paper, we develop the analysis of a two-dimensional magnetohydrodynamical configuration for an axially symmetric and rotating plasma (embedded in a dipolelike magnetic field), modeling the structure of a thin accretion disk around a compact astrophysical object. Our study investigates the global profile of the disk plasma, in order to fix the conditions for the existence of a crystalline morphology and ring sequence, as outlined by the local analysis pursued in Coppi [Phys. PlasmasPHPAEN1070-664X10.1063/1.1883667 12, 7302 (2005)] and Coppi and Rousseau [Astrophys. J.AJLEEY0004-637X10.1086/500315 641, 458 (2006)]. In the linear regime, when the electromagnetic back-reaction of the plasma is small enough, we show the existence of an oscillating radial behavior for the flux surface function, which very closely resembles the one outlined in the local model, apart from a radial modulation of the amplitude. In the opposite limit, corresponding to a dominant back-reaction in the magnetic structure over the field of central object, we can recognize the existence of a ringlike decomposition of the disk, according to the same modulation of the magnetic flux surface, and a smoother radial decay of the disk density, with respect to the linear case. In this extreme nonlinear regime, the global model seems to predict a configuration very close to that of the local analysis, but here the thermostatic pressure, crucial for the equilibrium setting, is also radially modulated. Among the conditions requested for the validity of such a global model, the confinement of the radial coordinate within a given value sensitive to the disk temperature and to the mass of the central objet, stands; however, this condition corresponds to dealing with a thin disk configuration.

  19. Optical - IR stellar astrophysics: Models vs. Observations

    NASA Astrophysics Data System (ADS)

    Ferguson, J. W.; Penley, J. J.; Alexander, D. R.; Allard, F.; Hauschildt, P. H.

    2001-12-01

    Recent observational catalogs by Lancon & Wood (2000, A&AS, 146, 217) and Pickles (1998, PASP, 110, 863) among others include the spectra of dozens of stars covering an unprecedented wavelength range from the optical to near-infrared. These observations include a wide range of stellar temperatures, and many types of stars including some with unusual chemical compositions. Such observations are a vast improvement over previous "optical-only" or "infrared-only" spectra. Having good observations with such a broad wavelength range make it possible to better model the conditions of these stars. Carefully fitting the effects of molecules such as H2O, CO, VO, and TiO in the spectra of these stars is paramount in our effort to better understand these stars. We show the results of PHOENIX (Hauschildt & Baron, 1999, J. Comp. Appl. Math., 102, 41) stellar atmosphere models with recent improvements in the TiO, H2O and a few other minor molecular opacity sources. Models computed with different sources of molecular opacity (H2O for example) show varying degrees of accuracy of fit, although none of the sources given are perfect fits to the observed spectral shape. Comparisons with the observations are made and the resulting effective temperature/spectral class scale is shown. Low temperature astrophysics at Wichita State University is supported by NSF grant No. EPS-9874732 with matching support from the State of Kansas, by a NASA EPSCoR grant NCC5-168 and NASA LTSA grant NAG5-3435.

  20. Modeling collisions in circumstellar debris disks

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika

    2015-10-01

    Observations of resolved debris disks show a spectacular variety of features and asymmetries, including inner cavities and gaps, inclined secondary disks or warps, and eccentric, sharp-edged rings. Embedded exoplanets could create many of these features via gravitational perturbations, which sculpt the disk directly and by generating planetesimal collisions. In this thesis, I present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. I show that SMACK is stable to numerical viscosity and numerical heating over 107 yr, and that it can reproduce analytic models of disk evolution. As an example of the algorithm's capabilities, I use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit and demonstrate that differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring. To demonstrate SMACK's utility in studying debris disk physics, I apply SMACK to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (alpha = 2/7). I find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index alpha of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by alpha = 0.32(t/ tcoll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion

  1. Modelling Molecular Emission from Young Embedded Disks

    NASA Astrophysics Data System (ADS)

    Harsono, D.; Visser, R.; van Dishoeck, E. F.; Kristensen, L.; Bruderer, S.; Brinch, C. Hogerheijde, M.

    2011-05-01

    Circumstellar disks play an important role in the formation of stars and planets. Recent observations and models have placed strong constraints on the later stages of their evolution (the T Tauri or Herbig Ae/Be phase), when an envelope is no longer present. However, little is known of the disk structure and evolution during the embedded phase of star formation. With Herschel and the VLT, and soon ALMA, we will be able to detect and characterize the early stages of disk formation. Sophisticated modeling including both physical and chemical structure of the system would be needed to interpret the high quality of data. We present a two-dimensional, semi-analytical model of disk formation as also used in Visser et al. (2009) and Visser and Dullemond (2010). The dust temperature is determined using a three-dimensional dust continuum radiative transfer code (RADMC-3D). Molecular abundances are calculated by following freeze-out and evaporation from the pre-stellar core up to the formation of the circumstellar disk. Synthetic spectra of CO and H2O within the wavelength ranges observable with Herschel and VLT-CRIRES are then produced at a series of time steps, tracing the different stages of disk formation. We also present simulated ALMA images. We discuss the evolution of the molecular emission and the possibility of identifying the presence of embedded disks.

  2. An MCMC Circumstellar Disks Modeling Tool

    NASA Astrophysics Data System (ADS)

    Wolff, Schuyler; Perrin, Marshall D.; Mazoyer, Johan; Choquet, Elodie; Soummer, Remi; Ren, Bin; Pueyo, Laurent; Debes, John H.; Duchene, Gaspard; Pinte, Christophe; Menard, Francois

    2016-01-01

    We present an enhanced software framework for the Monte Carlo Markov Chain modeling of circumstellar disk observations, including spectral energy distributions and multi wavelength images from a variety of instruments (e.g. GPI, NICI, HST, WFIRST). The goal is to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in the derived properties. This modular code is designed to work with a collection of existing modeling tools, ranging from simple scripts to define the geometry for optically thin debris disks, to full radiative transfer modeling of complex grain structures in protoplanetary disks (using the MCFOST radiative transfer modeling code). The MCMC chain relies on direct chi squared comparison of model images/spectra to observations. We will include a discussion of how best to weight different observations in the modeling of a single disk and how to incorporate forward modeling from PCA PSF subtraction techniques. The code is open source, python, and available from github. Results for several disks at various evolutionary stages will be discussed.

  3. GeV excess and phenomenological astrophysics modeling

    NASA Astrophysics Data System (ADS)

    Huang, Xiaoyuan; Enßlin, Torsten; Selig, Marco

    2016-05-01

    Predefined spatial templates to describe the background of γ-ray emission from astrophysical processes, like cosmic ray interactions, are used in previous searches for the γ-ray signatures of annihilating galactic dark matter. In this proceeding, we investigate the GeV excess in the inner Galaxy using an alternative approach, in which the astrophysical components are identified solely by their spectral and morphological properties. We confirm the reported GeV excess and derive related parameters for dark matter interpretation, which are consistent with previous results. We investigate the morphology of this spectral excess as preferred by the data only. This emission component exhibits a central Galaxy cusp as expected for a dark matter annihilation signal. However, Galactic disk regions with a morphology of that of the hot interstellar medium also host such a spectral component. This points to a possible astrophysical origin of the excess and requests a more detailed understanding of astrophysical γ-ray emitting processes in the galactic center region before definite claims about a dark matter annihilation signal can be made.

  4. Are Bulges and Disks Real? Decomposing Spectral Data Cubes Into Their Astrophysical Components

    NASA Astrophysics Data System (ADS)

    Merrifield, Michael; Tabor, Martha; Aragon-Salamanca, Alfonso; Cappellari, Michele; Johnston, Evelyn

    2016-01-01

    Decomposing galaxies photometrically into bulge and disk components is now a well-established technique, but it remains unclear how distinct and real these components are, and how they relate to each other. To address these questions, we have been developing novel techniques to extract the various structural components from integral field unit (IFU) spectral observations of galaxies, in order to study simultaneously their spectral and spatial properties.As a first approach, by spatially decomposing each wavelength in a spectral data cube, we can discover how much light comes from the separate components as a function of wavelength, and hence derive unprecedentedly high quality spectra of bulge and disk for detailed analysis of their stellar populations.In addition, we have decomposed spectral data cubes by fitting the spectrum at each location with the sum of two components, with the spectral properties left entirely free to fit both kinematic and stellar population properties, subject only to the constraint that the relative flux contributions match those of a conventional bulge-disk decomposition.Initial results applied to MaNGA and other IFU surveys show the power of these techniques when applied to such high quality data. The first method allows us to understand the formation sequence of bulges and disks, with, for example, bulges showing the younger stellar populations in S0 galaxies, implying that this was where the last gasp of star formation occurred. The second technique reveals subtle population gradients within individual components, but also confirms that the decomposition into separate components is a credible procedure, as the resulting bulges and disks have entirely plausible kinematic properties that are in no way imposed by the decomposition.Although our initial application of these decomposition techniques has been to studying bulges and disks in S0 galaxies, the methods have much wider application to the spectral data cubes that MaNGA and other

  5. Calculation of astrophysical spallation reactions using the RENO model

    NASA Technical Reports Server (NTRS)

    Ayres, C. L.; Schmitt, W. F.; Merker, M.; Shen, B. S. P.

    1974-01-01

    The RENO model for the Monte-Carlo treatment of astrophysical spallation reactions has been used to generate preliminary cross-sections for the purpose of illustrating the discrete-nucleon approach to spallation modeling and to exhibit differences between two versions of RENO. Comparisons with experimental, theoretical, and semiempirical data demonstrate the practicability of the discrete-nucleon approach.-

  6. Relativistic static thin disks: The counterrotating model

    NASA Astrophysics Data System (ADS)

    González, Guillermo A.; Espitia, Omar A.

    2003-11-01

    A detailed study is presented of the counterrotating model (CRM) for generic finite static axially symmetric thin disks with nonzero radial pressure. A general constraint over the counterrotating tangential velocities, needed to cast the surface energy-momentum tensor of the disk as the superposition of two counterrotating perfect fluids, and expressions for the energy density and pressure of the counterrotating fluids are obtained. We show that, in general, it is not possible to take the two counterrotating fluids as circulating along geodesics nor take the two counterrotating tangential velocities as equal and opposite. A simple family of disks is studied that admits some CRMs with well defined counterrotating tangential velocities and stable against radial perturbations.

  7. Modeling of Radiative Transfer in Protostellar Disks

    NASA Technical Reports Server (NTRS)

    VonAllmen, Paul; Turner, Neal

    2007-01-01

    This program implements a spectral line, radiative transfer tool for interpreting Spitzer Space Telescope observations by matching them with models of protostellar disks for improved understanding of planet and star formation. The Spitzer Space Telescope detects gas phase molecules in the infrared spectra of protostellar disks, with spectral lines carrying information on the chemical composition of the material from which planets form. Input to the software includes chemical models developed at JPL. The products are synthetic images and spectra for comparison with Spitzer measurements. Radiative transfer in a protostellar disk is primarily affected by absorption and emission processes in the dust and in molecular gases such as H2, CO, and HCO. The magnitude of the optical absorption and emission is determined by the population of the electronic, vibrational, and rotational energy levels. The population of the molecular level is in turn determined by the intensity of the radiation field. Therefore, the intensity of the radiation field and the population of the molecular levels are inter-dependent quantities. To meet the computational challenges of solving for the coupled radiation field and electronic level populations in disks having wide ranges of optical depths and spatial scales, the tool runs in parallel on the JPL Dell Cluster supercomputer with C++ and Fortran compiler with a Message Passing Interface. Because this software has been developed on a distributed computing platform, the modeling of systems previously beyond the reach of available computational resources is possible.

  8. ON THE TRANSITIONAL DISK CLASS: LINKING OBSERVATIONS OF T TAURI STARS AND PHYSICAL DISK MODELS

    SciTech Connect

    Espaillat, C.; Andrews, S.; Qi, C.; Wilner, D.; Ingleby, L.; Calvet, N.; Hernandez, J.; Furlan, E.; D'Alessio, P.; Muzerolle, J. E-mail: sandrews@cfa.harvard.edu E-mail: dwilner@cfa.harvard.edu E-mail: ncalvet@umich.edu E-mail: Elise.Furlan@jpl.nasa.gov E-mail: muzerol@stsci.edu

    2012-03-10

    Two decades ago 'transitional disks' (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC 2068 and IC 348. One group has a 'dip' in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We find that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects 'transitional disks' and 'pre-transitional disks' (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term 'transitional' only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks.

  9. WAVE-VORTEX MODE COUPLING IN ASTROPHYSICAL ACCRETION DISKS UNDER COMBINED RADIAL AND VERTICAL STRATIFICATION

    SciTech Connect

    Salhi, A.; Lehner, T.; Godeferd, F.; Cambon, C.

    2013-07-10

    We examine accretion disk flow under combined radial and vertical stratification utilizing a local Cartesian (or ''shearing box'') approximation. We investigate both axisymmetric and nonaxisymmetric disturbances with the Boussinesq approximation. Under axisymmetric disturbances, a new dispersion relation is derived. It reduces to the Solberg-Hoieland criterion in the case without vertical stratification. It shows that, asymptotically, stable radial and vertical stratification cannot induce any linear instability; Keplerian flow is accordingly stable. Previous investigations strongly suggest that the so-called bypass concept of turbulence (i.e., that fine-tuned disturbances of any inviscid smooth shear flow can reach arbitrarily large transient growth) can also be applied to Keplerian disks. We present an analysis of this process for three-dimensional plane-wave disturbances comoving with the shear flow of a general rotating shear flow under combined stable radial and vertical rotation. We demonstrate that large transient growth occurs for K{sub 2}/k{sub 1} >> 1 and k{sub 3} = 0 or k{sub 1} {approx} k{sub 3}, where k{sub 1}, K{sub 2}, and k{sub 3} are the azimuthal, radial, and vertical components of the initial wave vector, respectively. By using a generalized ''wave-vortex'' decomposition of the disturbance, we show that the large transient energy growth in a Keplerian disk is mainly generated by the transient dynamics of the vortex mode. The analysis of the power spectrum of total (kinetic+potential) energy in the azimuthal or vertical directions shows that the contribution coming from the vortex mode is dominant at large scales, while the contribution coming from the wave mode is important at small scales. These findings may be confirmed by appropriate numerical simulations in the high Reynolds number regime.

  10. Astrophysical models of r-process nucleosynthesis: An update

    SciTech Connect

    Qian Yongzhong

    2012-11-12

    An update on astrophysical models for nucleosynthesis via rapid neutron capture, the r process, is given. A neutrino-induced r process in supernova helium shells may have operated up to metallicities of {approx} 10{sup -3} times the solar value. Another r-process source, possibly neutron star mergers, is required for higher metallicities.

  11. Spinning Unmagnetized Plasma for Laboratory Studies of Astrophysical Accretion Disks & Dynamos

    NASA Astrophysics Data System (ADS)

    Collins, Cami

    2015-11-01

    A technique for creating a large, fast-flowing, unmagnetized plasma has been demonstrated experimentally. This marks an important first step towards laboratory studies of phenomenon such as magnetic field generation through self-excited dynamos, or the magnetorotational instability (MRI), the mechanism of interest for its role in the efficient outward transport of angular momentum in accretion disks. In the Plasma Couette Experiment (PCX), a sufficiently hot, steady-state plasma is confined in a cylindrical, axisymmetric multicusp magnetic field, with Te<10 eV, Ti<1 eV, and n<1011 cm-3. Azimuthal flows are driven by JxB torque using toroidally localized, biased hot cathodes in the magnetized edge region. Measurements show that momentum couples viscously from the magnetized edge to the unmagnetized core, and the core rotates when collisional ion viscosity overcomes the drag due to ion-neutral collisions. Torque can be applied at the inner or outer boundaries, resulting in controlled, differential rotation. Maximum speeds are observed (He ~ 12 km/s, Ne ~ 4 km/s, Ar ~ 3.2 km/s, Xe ~ 1.4 km/s), consistent with a critical ionization velocity limit reported to occur in partially ionized plasmas. PCX has achieved magnetic Reynolds numbers of Rm ~ 65 and magnetic Prandtl numbers of Pm ~ 0.2-10, which are approaching regimes shown to excite the MRI in a global Hall-MHD stability analysis. Ion-neutral collisions effectively add a body force that undesirably changes the flow profile shape. Recent upgrades have increased the ionization fraction with an additional 6 kW of microwave heating power and stronger magnets that reduce loss area and increase plasma volume by 150%. In addition, an alternative scheme using volume-applied JxB force will maintain the shear profile and destabilize the MRI at more easily achievable plasma parameters.

  12. Galactic dark matter search via phenomenological astrophysics modeling

    NASA Astrophysics Data System (ADS)

    Huang, Xiaoyuan; Enßlin, Torsten; Selig, Marco

    2016-04-01

    Previous searches for the γ-ray signatures of annihilating galactic dark matter used predefined spatial templates to describe the background of γ-ray emission from astrophysical processes like cosmic ray interactions. In this work, we aim to establish an alternative approach, in which the astrophysical components are identified solely by their spectral and morphological properties. To this end, we adopt the recent reconstruction of the diffuse γ-ray sky from Fermi data by the D3PO algorithm and the fact that more than 90% of its flux can be represented by only two spectral components, resulting form the dense and dilute interstellar medium. Under these presumptions, we confirm the reported DM annihilation-like signal in the inner Galaxy and derive upper limits for dark matter annihilation cross sections. We investigate whether the DM signal could be a residual of the simplified modeling of astrophysical emission by inspecting the morphology of the regions, which favor a dark matter component. The central galactic region favors strongest for such a component with the expected spherically symmetric and radially declining profile. However, astrophysical structures, in particular sky regions which seem to host most of the dilute interstellar medium, obviously would benefit from a DM annihilation-like component {as well}. Although these regions do not drive the fit, they warn that a more detailed understanding of astrophysical γ-ray emitting processes in the galactic center region are necessary before definite claims about a DM annihilation signal can be made. The regions off the Galactic plane actually disfavor the best fit DM annihilation cross section from the inner Galactic region unless the radial decline of the Galactic DM density profile in the outer regions is significantly steeper than that usually assumed.

  13. Towards a Global Evolutionary Model of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Bai, Xue-Ning

    2016-04-01

    A global picture of the evolution of protoplanetary disks (PPDs) is key to understanding almost every aspect of planet formation, where standard α-disk models have been continually employed for their simplicity. In the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. However, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in PPDs. I present a framework of global PPD evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. Disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. The timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. In addition, because wind launching requires a sufficient level of ionization at the disk surface (mainly via external far-UV (FUV) radiation), wind kinematics is also affected by the FUV penetration depth and disk geometry. For a typical disk lifetime of a few million years, the disk loses approximately the same amount of mass through the wind as through accretion onto the protostar, and most of the wind mass loss proceeds from the outer disk via a slow wind. Fractional wind mass loss increases with increasing disk lifetime. Significant wind mass loss likely substantially enhances the dust-to-gas mass ratio and promotes planet formation.

  14. Self-Consistent Models of Accretion Disks

    NASA Technical Reports Server (NTRS)

    Narayan, Ramesh

    1997-01-01

    The investigations of advection-dominated accretion flows (ADAFs), with emphasis on applications to X-ray binaries containing black holes and neutron stars is presented. This work is now being recognized as the standard paradigm for understanding the various spectral states of black hole X-ray Binaries (BHXBs). Topics discussed include: (1) Problem in BHXBS, namely that several of these binaries have unusually large concentrations of lithium in their companion stars; (2) A novel test to show that black holes have event horizons; (3) Application of the ADAF model to the puzzling X-ray delay in the recent outburst of the BHXB, GRO J1655-40; (4) Description of the various spectral states in BHXBS; (5) Application of the ADAF model to the famous supermassive black hole at the center of our Galaxy, Sgr A(*); (6) Writing down and solving equations describing steady-state, optically thin, advection-dominated accretion onto a Kerr black hole; (7) The effect of "photon bubble" instability on radiation dominated accretion disks; and (8) Dwarf nova disks in quiescence that have rather low magnetic Reynolds number, of order 10(exp 3).

  15. Models of unsaturated Compton disks around supermassive black holes

    NASA Technical Reports Server (NTRS)

    Liang, E. P. T.; Thompson, K. A.

    1979-01-01

    Two inverse-Compton disk models for the hard X-ray spectra of quasi-stellar objects and active galactic nuclei are studied and compared. One is a slightly generalized version of the Shapiro, Lightman and Eardley optically thin disk model, and the other is a conduction-stabilized Corona model. Observational distinctions between the two models are discussed.

  16. GLOBAL SIMULATIONS OF ACCRETION DISKS. I. CONVERGENCE AND COMPARISONS WITH LOCAL MODELS

    SciTech Connect

    Sorathia, Kareem A.; Reynolds, Christopher S.; Stone, James M.; Beckwith, Kris

    2012-04-20

    Grid-based magnetohydrodynamic (MHD) simulations have proven invaluable for the study of astrophysical accretion disks. However, the fact that angular momentum transport in disks is mediated by MHD turbulence (with structure down to very small scales) raises the concern that the properties of the modeled accretion disks are affected by the finite numerical resolution of the simulation. By implementing an orbital advection algorithm into the Athena code in cylindrical geometry, we have performed a set of global (but unstratified) Newtonian disk simulations extending up to resolutions previously unattained. We study the convergence of these models as a function of spatial resolution and initial magnetic field geometry. The usual viscosity parameter ({alpha}) or the ratio of thermal-to-magnetic pressure ({beta}) is found to be a poor diagnostic of convergence, whereas the average tilt angle of the magnetic field in the (r, {phi})-plane is a very good diagnostic of convergence. We suggest that this is related to the saturation of the MHD turbulence via parasitic modes of the magnetorotational instability. Even in the case of zero-net magnetic flux, we conclude that our highest resolution simulations (with 32 zones and 64 zones per vertical scale height) have achieved convergence. Our global simulations reach resolutions comparable to those used in local, shearing-box models of MHD disk turbulence. We find that the saturation predictors derived from local simulations correspond well to the instantaneous correlations between local flux and stress found in our global simulations. However, the conservation of magnetic flux implicit in local models is not realized in our global disks. Thus, the magnetic connectivity of an accretion disk represents physics that is truly global and cannot be captured in any ab initio local model.

  17. A wind-type model for the generation of astrophysical jets

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    Wind-type solutions for the generation of astrophysical jets from active galactic nuclei and stellar sources, such as those associated with SS 433 and protostellar objects, are discussed. Acceleration, collimation, and morphology are consistently interpreted in terms of a flow starting from the galactic or stellar core inside the 'throat' of a thick accretion disk.

  18. EMPIRE: A Reaction Model Code for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Palumbo, A.; Herman, M.; Capote, R.

    2014-06-01

    The correct modeling of abundances requires knowledge of nuclear cross sections for a variety of neutron, charged particle and γ induced reactions. These involve targets far from stability and are therefore difficult (or currently impossible) to measure. Nuclear reaction theory provides the only way to estimate values of such cross sections. In this paper we present application of the EMPIRE reaction code to nuclear astrophysics. Recent measurements are compared to the calculated cross sections showing consistent agreement for n-, p- and α-induced reactions of strophysical relevance.

  19. EMPIRE: A Reaction Model Code for Nuclear Astrophysics

    SciTech Connect

    Palumbo, A.; Herman, M.; Capote, R.

    2014-06-15

    The correct modeling of abundances requires knowledge of nuclear cross sections for a variety of neutron, charged particle and γ induced reactions. These involve targets far from stability and are therefore difficult (or currently impossible) to measure. Nuclear reaction theory provides the only way to estimate values of such cross sections. In this paper we present application of the EMPIRE reaction code to nuclear astrophysics. Recent measurements are compared to the calculated cross sections showing consistent agreement for n-, p- and α-induced reactions of strophysical relevance.

  20. Cosmological and astrophysical constraints on tachyon dark energy models

    NASA Astrophysics Data System (ADS)

    Martins, C. J. A. P.; Moucherek, F. M. O.

    2016-06-01

    Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant α . Here we take advantage of recent observational progress and use a combination of background cosmological observations of type Ia supernovas and astrophysical and local measurements of α to improve constraints on this class of models. We show that the constraints on α imply that the field dynamics must be extremely slow, leading to a constraint of the present-day dark energy equation of state (1 +w0)<2.4 ×10-7 at the 99.7% confidence level. Therefore current and forthcoming standard background cosmology observational probes cannot distinguish this class of models from a cosmological constant, while detections of α variations could possibly do so since they would have a characteristic redshift dependence.

  1. Laboratory Plasma Source as an MHD Model for Astrophysical Jets

    NASA Technical Reports Server (NTRS)

    Mayo, Robert M.

    1997-01-01

    The significance of the work described herein lies in the demonstration of Magnetized Coaxial Plasma Gun (MCG) devices like CPS-1 to produce energetic laboratory magneto-flows with embedded magnetic fields that can be used as a simulation tool to study flow interaction dynamic of jet flows, to demonstrate the magnetic acceleration and collimation of flows with primarily toroidal fields, and study cross field transport in turbulent accreting flows. Since plasma produced in MCG devices have magnetic topology and MHD flow regime similarity to stellar and extragalactic jets, we expect that careful investigation of these flows in the laboratory will reveal fundamental physical mechanisms influencing astrophysical flows. Discussion in the next section (sec.2) focuses on recent results describing collimation, leading flow surface interaction layers, and turbulent accretion. The primary objectives for a new three year effort would involve the development and deployment of novel electrostatic, magnetic, and visible plasma diagnostic techniques to measure plasma and flow parameters of the CPS-1 device in the flow chamber downstream of the plasma source to study, (1) mass ejection, morphology, and collimation and stability of energetic outflows, (2) the effects of external magnetization on collimation and stability, (3) the interaction of such flows with background neutral gas, the generation of visible emission in such interaction, and effect of neutral clouds on jet flow dynamics, and (4) the cross magnetic field transport of turbulent accreting flows. The applicability of existing laboratory plasma facilities to the study of stellar and extragalactic plasma should be exploited to elucidate underlying physical mechanisms that cannot be ascertained though astrophysical observation, and provide baseline to a wide variety of proposed models, MHD and otherwise. The work proposed herin represents a continued effort on a novel approach in relating laboratory experiments to

  2. A weakened cascade model for turbulence in astrophysical plasmas

    SciTech Connect

    Howes, G. G.; TenBarge, J. M.; Dorland, W.

    2011-10-15

    A refined cascade model for kinetic turbulence in weakly collisional astrophysical plasmas is presented that includes both the transition between weak and strong turbulence and the effect of nonlocal interactions on the nonlinear transfer of energy. The model describes the transition between weak and strong MHD turbulence and the complementary transition from strong kinetic Alfven wave (KAW) turbulence to weak dissipating KAW turbulence, a new regime of weak turbulence in which the effects of shearing by large scale motions and kinetic dissipation play an important role. The inclusion of the effect of nonlocal motions on the nonlinear energy cascade rate in the dissipation range, specifically the shearing by large-scale motions, is proposed to explain the nearly power-law energy spectra observed in the dissipation range of both kinetic numerical simulations and solar wind observations.

  3. Modeling Dust Emission of HL Tau Disk Based on Planet-Disk Interactions

    NASA Astrophysics Data System (ADS)

    Jin, Sheng; Li, Shengtai; Isella, Andrea; Li, Hui; Ji, Jianghui

    2016-02-01

    We use extensive global two-dimensional hydrodynamic disk gas+dust simulations with embedded planets, coupled with three-dimensional radiative transfer calculations, to model the dust ring and gap structures in the HL Tau protoplanetary disk observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We include the self-gravity of disk gas and dust components and make reasonable choices of disk parameters, assuming an already settled dust distribution and no planet migration. We can obtain quite adequate fits to the observed dust emission using three planets with masses of 0.35, 0.17, and 0.26 MJup at 13.1, 33.0, and 68.6 AU, respectively. Implications for the planet formation as well as the limitations of this scenario are discussed.

  4. Consistent dust and gas models for protoplanetary disks. I. Disk shape, dust settling, opacities, and PAHs

    NASA Astrophysics Data System (ADS)

    Woitke, P.; Min, M.; Pinte, C.; Thi, W.-F.; Kamp, I.; Rab, C.; Anthonioz, F.; Antonellini, S.; Baldovin-Saavedra, C.; Carmona, A.; Dominik, C.; Dionatos, O.; Greaves, J.; Güdel, M.; Ilee, J. D.; Liebhart, A.; Ménard, F.; Rigon, L.; Waters, L. B. F. M.; Aresu, G.; Meijerink, R.; Spaans, M.

    2016-02-01

    We propose a set of standard assumptions for the modelling of Class II and III protoplanetary disks, which includes detailed continuum radiative transfer, thermo-chemical modelling of gas and ice, and line radiative transfer from optical to cm wavelengths. The first paper of this series focuses on the assumptions about the shape of the disk, the dust opacities, dust settling, and polycyclic aromatic hydrocarbons (PAHs). In particular, we propose new standard dust opacities for disk models, we present a simplified treatment of PAHs in radiative equilibrium which is sufficient to reproduce the PAH emission features, and we suggest using a simple yet physically justified treatment of dust settling. We roughly adjust parameters to obtain a model that predicts continuum and line observations that resemble typical multi-wavelength continuum and line observations of Class II T Tauri stars. We systematically study the impact of each model parameter (disk mass, disk extension and shape, dust settling, dust size and opacity, gas/dust ratio, etc.) on all mainstream continuum and line observables, in particular on the SED, mm-slope, continuum visibilities, and emission lines including [OI] 63 μm, high-J CO lines, (sub-)mm CO isotopologue lines, and CO fundamental ro-vibrational lines. We find that evolved dust properties, i.e. large grains, often needed to fit the SED, have important consequences for disk chemistry and heating/cooling balance, leading to stronger near- to far-IR emission lines in general. Strong dust settling and missing disk flaring have similar effects on continuum observations, but opposite effects on far-IR gas emission lines. PAH molecules can efficiently shield the gas from stellar UV radiation because of their strong absorption and negligible scattering opacities in comparison to evolved dust. The observable millimetre-slope of the SED can become significantly more gentle in the case of cold disk midplanes, which we find regularly in our T Tauri models

  5. Eccentric-Disk Models for the Nucleus of M31

    NASA Astrophysics Data System (ADS)

    Peiris, Hiranya V.; Tremaine, Scott

    2003-12-01

    We construct dynamical models of the ``double'' nucleus of M31 in which the nucleus consists of an eccentric disk of stars orbiting a central black hole. The principal approximation in these models is that the disk stars travel in a Keplerian potential; i.e., we neglect the mass of the disk relative to the black hole. We consider both ``aligned'' models, in which the eccentric disk lies in the plane of the large-scale M31 disk, and ``nonaligned'' models, in which the orientation of the eccentric disk is fitted to the data. Both types of model can reproduce the double structure and overall morphology seen in Hubble Space Telescope photometry. In comparison with the best available ground-based spectroscopy, the models reproduce the asymmetric rotation curve, the peak height of the dispersion profile, and the qualitative behavior of the Gauss-Hermite coefficients h3 and h4. Aligned models fail to reproduce the observation that the surface brightness at P1 is higher than at P2 and yield significantly poorer fits to the kinematics; thus, we favor nonaligned models. Eccentric-disk models fitted to ground-based spectroscopy are used to predict the kinematics observed at much higher resolution by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, and we find generally satisfactory agreement.

  6. An analytic performance model of disk arrays and its application

    NASA Technical Reports Server (NTRS)

    Lee, Edward K.; Katz, Randy H.

    1991-01-01

    As disk arrays become widely used, tools for understanding and analyzing their performance become increasingly important. In particular, performance models can be invaluable in both configuring and designing disk arrays. Accurate analytic performance models are desirable over other types of models because they can be quickly evaluated, are applicable under a wide range of system and workload parameters, and can be manipulated by a range of mathematical techniques. Unfortunately, analytical performance models of disk arrays are difficult to formulate due to the presence of queuing and fork-join synchronization; a disk array request is broken up into independent disk requests which must all complete to satisfy the original request. We develop, validate, and apply an analytic performance model for disk arrays. We derive simple equations for approximating their utilization, response time, and throughput. We then validate the analytic model via simulation and investigate the accuracy of each approximation used in deriving the analytical model. Finally, we apply the analytical model to derive an equation for the optimal unit of data striping in disk arrays.

  7. Sharp Eccentric Rings in Planetless Hydrodynamical Models of Debris Disks

    NASA Technical Reports Server (NTRS)

    Lyra, W.; Kuchner, M. J.

    2013-01-01

    Exoplanets are often associated with disks of dust and debris, analogs of the Kuiper Belt in our solar system. These "debris disks" show a variety of non-trivial structures attributed to planetary perturbations and utilized to constrain the properties of the planets. However, analyses of these systems have largely ignored the fact that, increasingly, debris disks are found to contain small quantities of gas, a component all debris disks should contain at some level. Several debris disks have been measured with a dust-to-gas ratio around unity where the effect of hydrodynamics on the structure of the disk cannot be ignored. Here we report that dust-gas interactions can produce some of the key patterns seen in debris disks that were previously attributed to planets. Through linear and nonlinear modeling of the hydrodynamical problem, we find that a robust clumping instability exists in this configuration, organizing the dust into narrow, eccentric rings, similar to the Fomalhaut debris disk. The hypothesis that these disks might contain planets, though thrilling, is not necessarily required to explain these systems.

  8. On Numerical Considerations for Modeling Reactive Astrophysical Shocks

    SciTech Connect

    Papatheodore, Thomas L; Messer, Bronson

    2014-01-01

    Simulating detonations in astrophysical environments is often complicated by numerical approximations to shock structure. A common prescription to ensure correct detonation speeds (and associated quantities) is to prohibit burning inside the numerically broadened shock (Fryxell et al. 1989). We have performed a series of simulations to verify the efficacy of this approximation and to understand how resolution and dimensionality might affect its use. Our results show that, in one dimension, prohibiting burning in the shock is important wherever the carbon burning length is not resolved, in keeping with the results of Fryxell et al. (1989). In two dimensions, we find that the prohibition of shock burning effectively inhibits the development of cellular structure for all but the most highly-resolved cases. We discuss the possible impacts this outcome may have on sub-grid models and detonation propagation in Type Ia supernovae.

  9. A Collisional Algorithm for Modeling Circumstellar Debris Disks

    NASA Technical Reports Server (NTRS)

    Nesvold, Erika; Kuchner, Marc

    2011-01-01

    Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm.

  10. Protoplanetary Disk Structure with Grain Evolution: The ANDES Model

    NASA Astrophysics Data System (ADS)

    Akimkin, V.; Zhukovska, S.; Wiebe, D.; Semenov, D.; Pavlyuchenkov, Ya.; Vasyunin, A.; Birnstiel, T.; Henning, Th.

    2013-03-01

    We present a self-consistent model of a protoplanetary disk: "ANDES" ("AccretioN disk with Dust Evolution and Sedimentation"). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R <~ 50 AU) and lower in the outer disk (R >~ 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO2, NH2CN, HNO, H2O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

  11. PROTOPLANETARY DISK STRUCTURE WITH GRAIN EVOLUTION: THE ANDES MODEL

    SciTech Connect

    Akimkin, V.; Wiebe, D.; Pavlyuchenkov, Ya.; Zhukovska, S.; Semenov, D.; Henning, Th.; Vasyunin, A.; Birnstiel, T. E-mail: dwiebe@inasan.ru E-mail: zhukovska@mpia.de E-mail: henning@mpia.de E-mail: tbirnstiel@cfa.harvard.edu

    2013-03-20

    We present a self-consistent model of a protoplanetary disk: 'ANDES' ('AccretioN disk with Dust Evolution and Sedimentation'). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R {approx}< 50 AU) and lower in the outer disk (R {approx}> 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO{sub 2}, NH{sub 2}CN, HNO, H{sub 2}O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

  12. Model of magnetic reconnection in space and astrophysical plasmas

    SciTech Connect

    Boozer, Allen H.

    2013-03-15

    Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.

  13. Model of magnetic reconnection in space and astrophysical plasmas

    NASA Astrophysics Data System (ADS)

    Boozer, Allen H.

    2013-03-01

    Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.

  14. On the importance of having accurate data for astrophysical modelling

    NASA Astrophysics Data System (ADS)

    Lique, Francois

    2016-06-01

    The Herschel telescope and the ALMA and NOEMA interferometers have opened new windows of observation for wavelengths ranging from far infrared to sub-millimeter with spatial and spectral resolutions previously unmatched. To make the most of these observations, an accurate knowledge of the physical and chemical processes occurring in the interstellar and circumstellar media is essential.In this presentation, I will discuss what are the current needs of astrophysics in terms of molecular data and I will show that accurate molecular data are crucial for the proper determination of the physical conditions in molecular clouds.First, I will focus on collisional excitation studies that are needed for molecular lines modelling beyond the Local Thermodynamic Equilibrium (LTE) approach. In particular, I will show how new collisional data for the HCN and HNC isomers, two tracers of star forming conditions, have allowed solving the problem of their respective abundance in cold molecular clouds. I will also present the last collisional data that have been computed in order to analyse new highly resolved observations provided by the ALMA interferometer.Then, I will present the calculation of accurate rate constants for the F+H2 → HF+H and Cl+H2 ↔ HCl+H reactions, which have allowed a more accurate determination of the physical conditions in diffuse molecular clouds. I will also present the recent work on the ortho-para-H2 conversion due to hydrogen exchange that allow more accurate determination of the ortho-to-para-H2 ratio in the universe and that imply a significant revision of the cooling mechanism in astrophysical media.

  15. Modeling transiting circumstellar disks: characterizing the newly discovered eclipsing disk system OGLE LMC-ECL-11893

    SciTech Connect

    Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.; Quillen, Alice C.; Moolekamp, Fred; Bell, Cameron P. M.

    2014-12-10

    We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ∼1.4 mag, preceded by a plateau of ∼0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ∼150 Myr and mass ∼4 M {sub ☉}. The disk appears to have an outer radius of ∼0.2 AU with predicted temperatures of ∼1100-1400 K. We model the eclipses as being due to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.

  16. Modeling Transiting Circumstellar Disks: Characterizing the Newly Discovered Eclipsing Disk System OGLE LMC-ECL-11893

    NASA Astrophysics Data System (ADS)

    Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.; Quillen, Alice C.; Moolekamp, Fred; Bell, Cameron P. M.

    2014-12-01

    We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ~1.4 mag, preceded by a plateau of ~0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ~150 Myr and mass ~4 M ⊙. The disk appears to have an outer radius of ~0.2 AU with predicted temperatures of ~1100-1400 K. We model the eclipses as being due to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.

  17. PAH bombardment by energetic particles: models and astrophysical implications

    NASA Astrophysics Data System (ADS)

    Micelotta, E.; Jones, A.; Tielens, A.

    2011-05-01

    Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of the Interstellar Medium (ISM) of galaxies. Interstellar PAHs are apparently able to withstand the rigors of the harsh environment of the ISM for some some 100 million years and thus are resilient against processing by UV and X-ray photons and supernova shock waves. PAHs in space are mainly studied through their characteristic emission bands, due to infrared fluorescence following the absorption of UV photons. This is the reason why the photophysics of PAHs in space has been extensively investigated. On the other hand, PAHs are also strongly affected by collisional processes, i.e. bombardment by high-velocity ions and electrons, arising from interstellar shocks, hot gas and cosmic rays. However, very little was known about the physics of the interaction between PAHs and high energy particles, especially in terms of PAH damage and destruction. This lack of information had made the interpretation of PAH observations difficult in regions subjected to such processes. Our research aims to fill this key gap in our understanding of the physics behind collisional processing of PAHs and to clarify how this affects the PAH evolution in the astrophysical context. We first describe the models we have developed, that take into account the molecular nature of the target PAH and allow for the first time a quantitative description of the collisional processing of PAH molecules by ions and electrons with energies between 10 eV and 10 keV (in shocks and hot gas) and between 5 MeV and 10 GeV (in cosmic rays). Specific models were needed because PAHs are molecules and not small solid fragments, thus the classical approach from solid state physics cannot be applied. We then show the applications of our models to observations, estimating the lifetime of PAHs against collisional processing in specific objects. We discuss the astrophysical implications of our findings on the considered sample, which

  18. No evidence for Bardeen-Petterson alignment in GRMHD simulations and semi-analytic models of moderately thin, prograde, tilted accretion disks

    SciTech Connect

    Zhuravlev, Viacheslav V.; Ivanov, Pavel B.; Teixeira, Danilo Morales

    2014-12-01

    In this paper, we introduce the first results that use data extracted directly from numerical simulations as inputs to the analytic twisted disk model of Zhuravlev and Ivanov. In both numerical and analytic approaches, fully relativistic models of tilted and twisted disks having a moderate effective viscosity around a slowly rotating Kerr black hole are considered. Qualitatively, the analytic model demonstrates the same dynamics as the simulations, although with some quantitative offset. Namely, the general relativistic magnetohydrodynamic simulations typically give smaller variations of tilt and twist across the disk. When the black hole and the disk rotate in the same direction, the simulated tilted disk and analytic model show no sign of Bardeen-Petterson alignment, even in the innermost parts of the disk where the characteristic time for relaxation to a quasi-stationary configuration is of the same order as the computation time. In the opposite case, when the direction of the disk's rotation is opposite to that of the black hole, a partial alignment is observed, in agreement with previous theoretical estimates. Thus, both fully numerical and analytic schemes demonstrate that the Bardeen-Petterson effect may not be possible for the case of prograde rotation provided that disk's effective viscosity is sufficiently small. This may have implications in modeling of different astrophysical phenomena such as disk spectra and jet orientation.

  19. Constraining Dark Matter and Dark Energy Models using Astrophysical Surveys

    NASA Astrophysics Data System (ADS)

    Cieplak, Agnieszka M.

    This thesis addresses astrophysical probes to constrain dark matter (DM) and dark energy models. Primordial black holes (PBHs) remain one of the few DM candidates within the Standard Model of Particle Physics. This thesis presents a new probe of this PBH DM, using the microlensing of the source stars monitored by the already existing Kepler satellite. With its photometric precision and the large projected cross section of the nearby stars, it is found that previous constraints on PBH DM could theoretically be extended by two orders of magnitude. Correcting a well-known microlensing formula, a limb-darkening analysis is included, and a new approximation is calculated for future star selection. A preliminary prediction is calculated for the planned Wide-Field Infrared Survey Telescope. A preliminary study of the first two years of publicly available Kepler data is presented. The investigation yields many new sources of background error not predicted in the theoretical calculations, such as stellar flares and comets in the field of view. Since no PBH candidates are detected, an efficiency of detection is therefore calculated by running a Monte Carlo with fake limb-darkened finite-source microlensing events. It is found that with just the first 8 quarters of data, a full order of magnitude of the PBH mass range can be already constrained. Finally, one of the astrophysical probes of dark energy is also addressed - specifically, the baryon acoustic oscillations (BAO) measurement in the gas distribution, as detected in quasar absorption lines. This unique measurement of dark energy at intermediate redshifts is being measured by current telescope surveys. The last part of this thesis therefore focuses on understanding the systematic effects in such a detection. Since the bias between the underlying dark matter distribution and the measured gas flux distribution is based on gas physics, hydrodynamic simulations are used to understand the evolution of neutral hydrogen over

  20. Search for the Galactic Disk and Halo Components in the Arrival Directions of High-Energy Astrophysical Neutrinos

    NASA Astrophysics Data System (ADS)

    Troitsky, S. V.

    2015-12-01

    The arrival directions of 40 neutrino events with energies ≳100 TeV, observed by the IceCube experiment, are studied. Their distribution in the Galactic latitude and in the angular distance to the Galactic Center allow searching for the Milky-Way disk and halo-related components, respectively. No statistically significant evidence for the disk component is found, though even 100% disk origin of the flux is allowed at the 90% confidence level. Contrary, the Galactic Center-Anticenter dipole anisotropy, specific for dark-matter decays (annihilation) or for interactions of cosmic rays with the extended halo of the circumgalactic gas, is clearly favored over the isotropic distribution (the probability of fluctuation of the isotropic signal is ~2%).

  1. Properties of the δ Scorpii Circumstellar Disk from Continuum Modeling

    NASA Astrophysics Data System (ADS)

    Carciofi, A. C.; Miroshnichenko, A. S.; Kusakin, A. V.; Bjorkman, J. E.; Bjorkman, K. S.; Marang, F.; Kuratov, K. S.; García-Lario, P.; Calderón, J. V. Perea; Fabregat, J.; Magalhães, A. M.

    2006-12-01

    We present optical WBVR and infrared JHKL photometric observations of the Be binary system δ Sco obtained in 2000-2005, and mid-infrared (10 and 18 μm) photometry and optical (λλ3200-10500) spectropolarimetry obtained in 2001. Our optical photometry confirms the results of a frequent visual monitoring being done by amateurs. The 2001 spectral energy distribution and polarization are successfully modeled with a three-dimensional non-LTE Monte Carlo code that self-consistently calculates the hydrogen level populations, electron temperature, and gas density for hot star disks. Our disk model is hydrostatically supported in the vertical direction and radially controlled by viscosity. Such a disk model has essentially only two free parameters, viz., the equatorial mass-loss rate and the disk outer radius, if one assumes a prescription for the viscosity. We find that the primary companion is surrounded by a small (7R*), geometrically-thin disk, which is highly nonisothermal and fully ionized. Our model requires an average equatorial mass-loss rate of 1.5×10-9 Msolar yr-1 to successfully explain the observations. In 2005, we detected a significant simultaneous decrease in the object's optical and near-infrared brightness, which is associated with a continuous rise in the hydrogen line equivalent widths. We discuss possible causes for this unusual phenomenon, which is difficult to explain in view of current models of Be star disks.

  2. Modeling Layered Accretion and the Magnetorotational Instability in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Lesniak, Michael V., III

    2012-05-01

    Understanding the temperature structure of protoplanetary disks (PPDs) is paramount to modeling disk evolution and future planet formation. PPDs around T Tauri stars have two primary heating sources, protostellar irradiation, which depends on the flaring of the disk, and accretional heating as viscous coupling between annuli dissipate energy. I have written a "1.5-D" radiative transfer code to calculate disk temperatures assuming hydrostatic and radiative equilibrium. The model solves for the temperature at all locations simultaneously using Rybicki's method, converges rapidly at high optical depth, and retains full frequency dependence. The likely cause of accretional heating in PPDs is the magnetorotational instability (MRI), which acts where gas ionization is sufficiently high for gas to couple to the magnetic field. This will occur in surface layers of the disk, leaving the interior portions of the disk inactive ("dead zone"). I calculate temperatures in PPDs undergoing such "layered accretion." Since the accretional heating is concentrated far from the midplane, temperatures in the disk's interior are lower than in PPDs modeled with vertically uniform accretion. The method is used to study for the first time disks evolving via the magnetorotational instability, which operates primarily in surface layers. I find that temperatures in layered accretion disks do not significantly differ from those of "passive disks," where no accretional heating exists. Emergent spectra are insensitive to active layer thickness, making it difficult to observationally identify disks undergoing layered vs. uniform accretion. I also calculate the ionization chemistry in PPDs, using an ionization network including multiple charge states of dust grains. Combined with a criterion for the onset of the MRI, I calculate where the MRI can be initiated and the extent of dead zones in PPDs. After accounting for feedback between temperature and active layer thickness, I find the surface

  3. Parametric Model for Astrophysical Proton-Proton Interactions and Applications

    SciTech Connect

    Karlsson, Niklas

    2007-01-01

    Observations of gamma-rays have been made from celestial sources such as active galaxies, gamma-ray bursts and supernova remnants as well as the Galactic ridge. The study of gamma rays can provide information about production mechanisms and cosmic-ray acceleration. In the high-energy regime, one of the dominant mechanisms for gamma-ray production is the decay of neutral pions produced in interactions of ultra-relativistic cosmic-ray nuclei and interstellar matter. Presented here is a parametric model for calculations of inclusive cross sections and transverse momentum distributions for secondary particles--gamma rays, e±, ve, $\\bar{v}$e, vμ and $\\bar{μ}$e--produced in proton-proton interactions. This parametric model is derived on the proton-proton interaction model proposed by Kamae et al.; it includes the diffraction dissociation process, Feynman-scaling violation and the logarithmically rising inelastic proton-proton cross section. To improve fidelity to experimental data for lower energies, two baryon resonance excitation processes were added; one representing the Δ(1232) and the other multiple resonances with masses around 1600 MeV/c2. The model predicts the power-law spectral index for all secondary particle to be about 0.05 lower in absolute value than that of the incident proton and their inclusive cross sections to be larger than those predicted by previous models based on the Feynman-scaling hypothesis. The applications of the presented model in astrophysics are plentiful. It has been implemented into the Galprop code to calculate the contribution due to pion decays in the Galactic plane. The model has also been used to estimate the cosmic-ray flux in the Large Magellanic Cloud based on HI, CO and gamma-ray observations. The transverse momentum distributions enable calculations when the proton distribution is anisotropic. It is shown that the gamma-ray spectrum and flux due to a

  4. A model for neutrino emission from nuclear accretion disks

    NASA Astrophysics Data System (ADS)

    Deaton, Michael

    2015-04-01

    Compact object mergers involving at least one neutron star can produce short-lived black hole accretion engines. Over tens to hundreds of milliseconds such an engine consumes a disk of hot, nuclear-density fluid, and drives changes to its surrounding environment through luminous emission of neutrinos. The neutrino emission may drive an ultrarelativistic jet, may peel off the disk's outer layers as a wind, may irradiate those winds or other forms of ejecta and thereby change their composition, may change the composition and thermodynamic state of the disk itself, and may oscillate in its flavor content. We present the full spatial-, angular-, and energy-dependence of the neutrino distribution function around a realistic model of a nuclear accretion disk, to inform future explorations of these types of behaviors. Spectral Einstein Code (SpEC).

  5. Simulations of Accretion Disk Wind Models

    NASA Astrophysics Data System (ADS)

    Brooks, Craig L.; Yong, Suk Yee; O'Dowd, Matthew; Webster, Rachel L.; Bate, Nicholas

    2016-01-01

    The kinematics of the broad emission line region (BELR) in quasars is largely unknown, however there is strong evidence that outflows may be a key component. For example, in approximately 15% of quasars we observe broad, blue-shifted absorption features which may be ubiquitous based on line-of-sight arguments. We use a new mathematical description of an outflowing disk-wind with an initial rotational component to predict surface brightness distributions of this wind at different orientations. These surface brightness distributions will allow us to simulate gravitational microlensing of BELR light, with a view to mapping the structure and better understanding the kinematics of these flows.

  6. Structure Formation in Astrophysics

    NASA Astrophysics Data System (ADS)

    Chabrier, Gilles

    2009-01-01

    Part I. Physical Processes and Numerical Methods Common to Structure Formations in Astrophysics: 1. The physics of turbulence E. Levêque; 2. The numerical simulation of turbulence W. Schmidt; 3. Numerical methods for radiation magnetohydrodynamics in astrophysics R. Klein and J. Stone; 4. The role of jets in the formation of planets, stars, and galaxies R. Banerjee, R. Pudritz and R. Ouyed; 5. Advanced numerical methods in astrophysical fluid dynamics A. Hujeirat and F. Heitsch; Part II. Structure and Star Formation in the Primordial Universe: 6. New frontiers in cosmology and galaxy formation challenges for the future R. Ellis and J. Silk; 7. Galaxy formation physics T. Abel, G. Bryan and R. Teyssier; 8. First stars formation, evolution, feedback effects V. Bromm, A. Ferrara and A. Heger; Part III. Contemporary Star and Brown Dwarf Formation: a) Cloud Formation and Fragmentation: 9. Diffuse interstellar medium and the formation of molecular clouds P. Hennebelle, M. Mac Low and E. Vazquez-Semadeni; 10. The formation of distributed and clustered stars in molecular clouds T. Megeath, Z. -Y. Li and A. Nordlund; b) Core Fragmentation and Star Formation: 11. The formation and evolution of prestellar cores P. André, S. Basu and S. Inutsuka; 12. Models for the formation of massive stars; Part IV. Protoplanetary Disks and Planet Formation M. Krumholz and I. Bonnell: 13. Observational properties of disks and young stellar objects G. Duchêne, F. Ménard, J. Muzzerolle and S. Mohanty; 14. Structure and dynamics of protoplanetary disks C. Dullemond, R. Durisen and J. Papaloizou; 15. Planet formation and evolution theory and observation Y. Alibert, I. Baraffe, W. Benz, G. Laughlin and S. Udry; 16. Planet formation assembling the puzzle G. Wurm and T. Guillot; Part V. Summary: 17. Open issues in small- and large-scale structure formation R. Klessen and M. Mac Low; 18. Final word E. Salpeter.

  7. Structure Formation in Astrophysics

    NASA Astrophysics Data System (ADS)

    Chabrier, Gilles

    2011-02-01

    Part I. Physical Processes and Numerical Methods Common to Structure Formations in Astrophysics: 1. The physics of turbulence E. Levêque; 2. The numerical simulation of turbulence W. Schmidt; 3. Numerical methods for radiation magnetohydrodynamics in astrophysics R. Klein and J. Stone; 4. The role of jets in the formation of planets, stars, and galaxies R. Banerjee, R. Pudritz and R. Ouyed; 5. Advanced numerical methods in astrophysical fluid dynamics A. Hujeirat and F. Heitsch; Part II. Structure and Star Formation in the Primordial Universe: 6. New frontiers in cosmology and galaxy formation challenges for the future R. Ellis and J. Silk; 7. Galaxy formation physics T. Abel, G. Bryan and R. Teyssier; 8. First stars formation, evolution, feedback effects V. Bromm, A. Ferrara and A. Heger; Part III. Contemporary Star and Brown Dwarf Formation: a) Cloud Formation and Fragmentation: 9. Diffuse interstellar medium and the formation of molecular clouds P. Hennebelle, M. Mac Low and E. Vazquez-Semadeni; 10. The formation of distributed and clustered stars in molecular clouds T. Megeath, Z. -Y. Li and A. Nordlund; b) Core Fragmentation and Star Formation: 11. The formation and evolution of prestellar cores P. André, S. Basu and S. Inutsuka; 12. Models for the formation of massive stars; Part IV. Protoplanetary Disks and Planet Formation M. Krumholz and I. Bonnell: 13. Observational properties of disks and young stellar objects G. Duchêne, F. Ménard, J. Muzzerolle and S. Mohanty; 14. Structure and dynamics of protoplanetary disks C. Dullemond, R. Durisen and J. Papaloizou; 15. Planet formation and evolution theory and observation Y. Alibert, I. Baraffe, W. Benz, G. Laughlin and S. Udry; 16. Planet formation assembling the puzzle G. Wurm and T. Guillot; Part V. Summary: 17. Open issues in small- and large-scale structure formation R. Klessen and M. Mac Low; 18. Final word E. Salpeter.

  8. Relativistic Astrophysics

    NASA Astrophysics Data System (ADS)

    Jones, Bernard J. T.; Markovic, Dragoljub

    1997-06-01

    Preface; Prologue: Conference overview Bernard Carr; Part I. The Universe At Large and Very Large Redshifts: 2. The size and age of the Universe Gustav A. Tammann; 3. Active galaxies at large redshifts Malcolm S. Longair; 4. Observational cosmology with the cosmic microwave background George F. Smoot; 5. Future prospects in measuring the CMB power spectrum Philip M. Lubin; 6. Inflationary cosmology Michael S. Turner; 7. The signature of the Universe Bernard J. T. Jones; 8. Theory of large-scale structure Sergei F. Shandarin; 9. The origin of matter in the universe Lev A. Kofman; 10. New guises for cold-dark matter suspects Edward W. Kolb; Part II. Physics and Astrophysics Of Relativistic Compact Objects: 11. On the unification of gravitational and inertial forces Donald Lynden-Bell; 12. Internal structure of astrophysical black holes Werner Israel; 13. Black hole entropy: external facade and internal reality Valery Frolov; 14. Accretion disks around black holes Marek A. Abramowicz; 15. Black hole X-ray transients J. Craig Wheeler; 16. X-rays and gamma rays from active galactic nuclei Roland Svensson; 17. Gamma-ray bursts: a challenge to relativistic astrophysics Martin Rees; 18. Probing black holes and other exotic objects with gravitational waves Kip Thorne; Epilogue: the past and future of relativistic astrophysics Igor D. Novikov; I. D. Novikov's scientific papers and books.

  9. The Disk Wind Model of the Broad Line Regions in Active Galactic Nuclei and Cataclysmic Variables

    NASA Technical Reports Server (NTRS)

    Begelman, Mitchell

    2002-01-01

    This is the final progress report for our Astrophysics Theory Program (NRA 97-OSS12) grant NAG5-7723. We have made considerable progress on incorporating photoionization calculations with a 2.5D hydrodynamical code to model disk winds in AGNs. Following up on our simultaneous broad band monitoring campaign of the type I Seyfert galaxy NGC 5548, we have investigated the constraints imposed on models of accretion in Seyfert galaxies by their optical, UV, and X-ray spectral energy distributions (SEDs). Using results from thermal Comptonization models that relate the physical properties of the hot inner accretion flow to the thermal reprocessing that occurs in the surrounding colder thin disk, we find that we can constrain the central black hole mass, accretion rate and size scale of the hot central flow. We have applied our model to observations of Seyfert galaxies NGC 3516, NGC 7469 and NGC 5548. Our mass and accretion rate estimates for these objects roughly agree with those found using other methods.

  10. APPLICATION OF THE DISK EVAPORATION MODEL TO ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Liu, B. F.

    2009-12-10

    The disk corona evaporation model extensively developed for the interpretation of observational features of black hole X-ray binaries (BHXRBs) is applied to active galactic nuclei (AGNs). Since the evaporation of gas in the disk can lead to its truncation for accretion rates less than a maximal evaporation rate, the model can naturally account for the soft spectrum in high-luminosity AGNs and the hard spectrum in low-luminosity AGNs. The existence of two different luminosity levels describing transitions from the soft to hard state and from the hard to soft state in BHXRBs, when applied to AGNs, suggests that AGNs can be in either spectral state within a range of luminosities. For example, at a viscosity parameter, alpha, equal to 0.3, the Eddington ratio from the hard-to-soft transition and from the soft-to-hard transition occurs at 0.027 and 0.005, respectively. The differing Eddington ratios result from the importance of Compton cooling in the latter transition, in which the cooling associated with soft photons emitted by the optically thick inner disk in the soft spectral state inhibits evaporation. When the Eddington ratio of the AGN lies below the critical value corresponding to its evolutionary state, the disk is truncated. With decreasing Eddington ratios, the inner edge of the disk increases to greater distances from the black hole with a concomitant increase in the inner radius of the broad-line region, R {sub BLR}. The absence of an optically thick inner disk at low luminosities (L) gives rise to region in the R {sub BLR}-L plane for which the relation R {sub BLR} propor to L {sup 1/2} inferred at high luminosities is excluded. As a result, a lower limit to the accretion rate is predicted for the observability of broad emission lines, if the broad-line region is associated with an optically thick accretion disk. Thus, true Seyfert 2 galaxies may exist at very low accretion rates/luminosities. The differences between BHXRBs and AGNs in the framework of

  11. Planetary rings and astrophysical discs

    NASA Astrophysics Data System (ADS)

    Latter, Henrik

    2016-05-01

    Disks are ubiquitous in astrophysics and participate in some of its most important processes. Of special interest is their role in star, planet and moon formation, the growth of supermassive black holes, and the launching of jets. Although astrophysical disks can be up to ten orders of magnitude larger than planetary rings and differ hugely in composition, all disks share to some extent the same basic dynamics and many physical phenomena. This review explores these areas of overlap. Topics covered include disk formation, accretion, collisions, instabilities, and satellite-disk interactions.

  12. An X-Ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies

    NASA Astrophysics Data System (ADS)

    Chiang, James

    2002-06-01

    Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, & Ryde for the X-ray binary Cyg X-1 and later applied to Seyfert galaxies by Zdziarski, Lubiński, & Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum and, as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those that have been observed from these objects can, in principle, be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate that satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the heretofore poorly measured hard X-ray continuum above ~50 keV in type 1 Seyfert galaxies. Conversely, forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft γ-ray telescopes, such as those aboard the International Gamma-Ray Astrophysics Laboratory, in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.

  13. An X-Ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies

    NASA Technical Reports Server (NTRS)

    Chiang, James; White, Nicholas E. (Technical Monitor)

    2002-01-01

    Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert. galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, and Ryde for the X-ray binary Cygnus X-1 and later applied to Seyfert galaxies by Zdziarski, Lubifiski, and Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum, and as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those which have been observed from these objects can, in principle, be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate which satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the heretofore poorly measured hard X-ray continuum above approximately 50 keV in type 1 Seyfert galaxies. Conversely, forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft gamma-ray telescopes, such as those aboard the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.

  14. Planet formation in transition disks: Modeling, spectroscopy, and theory

    NASA Astrophysics Data System (ADS)

    Liskowsky, Joseph Paul

    due to either a massive planet accreting the material onto it or via a photoevaporation process whereby the central star's radiation field ejects material from the inner disk out of the bound system in the the interstellar medium. It is presumed that this phase is the last gasp of the planetary disk's evolution before the debris disk stage and before a fully formed solar system evolves. Our work specifically focuses on one object of this transition disk class: HD100546. We add to the understanding of transition disks by showing that a model where ro-vibrational OH emission in the NIR is preferentially emitted along the 'wall' of the disk is consistent with observations, and furthermore that adding an eccentricity to this `wall' component is required to generate the necessary observed line shape. In conjunction with this observation we present supporting material which motivates the usage of such an eccentric wall component in light of predictions of the influence of giant planet formation occurring within the disk.

  15. Structure of relativistic accretion disk with non-standard model

    NASA Astrophysics Data System (ADS)

    Khesali, A. R.; Salahshoor, K.

    2016-07-01

    The structure of stationary, axisymmetric advection-dominated accretion disk (ADAF) around rotating black hole, using non-standard model, was examined. In this model, the transport efficiency of the angular momentum α was dependent on the magnetic Prandtl number α ∝ Pm^{δ } . The full relativistic shear stress recently obtained by a new manner, was used. By considering black hole spin and Prandtl number instantaneously, the structure of ADAFs was changed in inner and outer region of the disk. It was discovered that the accretion flow was denser and hotter in the inner region, due to the black hole spin, and in the outer region, due to the presence of Prandtl parameter. Inasmuch as the rotation of the black hole affected the transport efficiency of angular momentum in parts of the disk very close to the even horizon, then in these regions, the viscosity depended on the rotation of black hole. Also, it was discovered that the effect of the black hole spin on the structure of the disk was related to the presence of Prandtl parameter.

  16. Modeling Disk Cracks in Rotors by Utilizing Speed Dependent Eccentricity

    NASA Astrophysics Data System (ADS)

    Gyekenyesi, Andrew L.; Sawicki, Jerzy T.; Haase, Wayne C.

    2010-03-01

    This paper discusses the feasibility of vibration-based structural health monitoring for detecting disk cracks in rotor systems. The approach of interest assumes that a crack located on a rotating disk causes a minute change in the system’s center of mass due to the centrifugal force induced opening of the crack. The center of mass shift is expected to reveal itself in the vibration vector (i.e., whirl response; plotted as amplitude and phase versus speed) gathered during a spin-up and/or spin-down test. Here, analysis is accomplished by modeling a Jeffcott rotor that is characterized by analytical, numerical, and experimental data. The model, which has speed dependent eccentricity, is employed in order to better understand the sensitivity of the approach. For the experimental set-up emulated here (i.e., a single disk located mid-span on a flexible shaft), it appears that a rather sizable flaw in the form of a through-thickness notch could be detected by monitoring the damage-induced shift in center of mass. Although, identifying actual disk cracks in complex “real world” environments, where noncritical crack lengths are small and excessive mechanical and/or electrical noise are present, would prove to be rather challenging. Further research is needed in this regard.

  17. An Analytic Model for Buoyancy Resonances in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Lubow, Stephen H.; Zhu, Zhaohuan

    2014-04-01

    Zhu et al. found in three-dimensional shearing box simulations a new form of planet-disk interaction that they attributed to a vertical buoyancy resonance in the disk. We describe an analytic linear model for this interaction. We adopt a simplified model involving azimuthal forcing that produces the resonance and permits an analytic description of its structure. We derive an analytic expression for the buoyancy torque and show that the vertical torque distribution agrees well with the results of the Athena simulations and a Fourier method for linear numerical calculations carried out with the same forcing. The buoyancy resonance differs from the classic Lindblad and corotation resonances in that the resonance lies along tilted planes. Its width depends on damping effects and is independent of the gas sound speed. The resonance does not excite propagating waves. At a given large azimuthal wavenumber ky > h -1 (for disk thickness h), the buoyancy resonance exerts a torque over a region that lies radially closer to the corotation radius than the Lindblad resonance. Because the torque is localized to the region of excitation, it is potentially subject to the effects of nonlinear saturation. In addition, the torque can be reduced by the effects of radiative heat transfer between the resonant region and its surroundings. For each azimuthal wavenumber, the resonance establishes a large scale density wave pattern in a plane within the disk.

  18. Constraining Collisional Models of Planetesimals in Debris Disks

    NASA Astrophysics Data System (ADS)

    MacGregor, Meredith A.; Wilner, David J.; Hughes, A. Meredith; Steele, Amy; Ricci, Luca; Andrews, Sean M.; Chandler, Claire J.; Tahli Maddison, Sarah

    2016-01-01

    Debris disks around main-sequence stars are produced by the ongoing collisional erosion of planetesimals, analogous to Kuiper Belt Objects (KBOs) or comets in our own Solar System. Observations of these dusty belts offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. In particular, the millimeter/radio spectral index of thermal dust emission encodes information on the grain size distribution that can be used to test proposed collisional models of planetesimals. We have made sensitive Jansky Very Large Array (JVLA) observations of a sample of 7 nearby debris disks at 9 mm and combine these with archival Australia Telescope Compact Array (ATCA) observations of 8 additional debris disks at 7 mm. Using measurements at (sub)millimeter wavelengths from the literature, we place tight constraints on the millimeter spectral indices and thus grain size distributions of this sample of debris disks. Our analysis gives a weighted mean for the slope of the power-law grain distribution that is close to the classical prediction for a steady-state collisional cascade (q=3.5), but not consistent with the steeper distributions predicted by recent models that include more complex fragmentation processes. To interpret this result, we explore the effects of material strengths, velocity distributions, and small-size cutoffs on the steady-state grain size distribution.

  19. An analytic model for buoyancy resonances in protoplanetary disks

    SciTech Connect

    Lubow, Stephen H.; Zhu, Zhaohuan E-mail: zhzhu@astro.princeton.edu

    2014-04-10

    Zhu et al. found in three-dimensional shearing box simulations a new form of planet-disk interaction that they attributed to a vertical buoyancy resonance in the disk. We describe an analytic linear model for this interaction. We adopt a simplified model involving azimuthal forcing that produces the resonance and permits an analytic description of its structure. We derive an analytic expression for the buoyancy torque and show that the vertical torque distribution agrees well with the results of the Athena simulations and a Fourier method for linear numerical calculations carried out with the same forcing. The buoyancy resonance differs from the classic Lindblad and corotation resonances in that the resonance lies along tilted planes. Its width depends on damping effects and is independent of the gas sound speed. The resonance does not excite propagating waves. At a given large azimuthal wavenumber k{sub y} > h {sup –1} (for disk thickness h), the buoyancy resonance exerts a torque over a region that lies radially closer to the corotation radius than the Lindblad resonance. Because the torque is localized to the region of excitation, it is potentially subject to the effects of nonlinear saturation. In addition, the torque can be reduced by the effects of radiative heat transfer between the resonant region and its surroundings. For each azimuthal wavenumber, the resonance establishes a large scale density wave pattern in a plane within the disk.

  20. Modelling Relativistic Astrophysics at the Large and Small Scale

    NASA Astrophysics Data System (ADS)

    Haugboelle, Troels

    2005-10-01

    In this thesis different numerical methods, as well as applications of the methods to a number of current problems in relativistic astrophysics, are presented. In the first part the theoretical foundation and numerical implementation of a new general relativistic magnetohydrodynamics code is discussed. A new form of the equations of motion using global coordinates, but evolving the dynamical variables from the point of view of a local observer is presented. No assumptions are made about the background metric and the design is ready to be coupled with methods solving the full Einstein equations. In the second part of the thesis important results concerning the understanding of collisionless shocks, obtained from experiments with a relativistic charged particle code, are presented. Relativistic collisionless shocks are important in a range of astrophysical objects; in particular in gamma ray burst afterglows and other relativistic jets. It is shown that a strong small scale, fluctuating, and predominantly transversal magnetic field is unavoidably generated by a two-stream instability. The magnetic energy density reaches a few percent of equipartition. A new acceleration mechanism for electrons in ion-electron collisionless shocks is proposed. The mechanism is capable of creating a powerlaw electron distribution in a collisionless shocked region. The non-thermal acceleration of the electrons is directly related to the ion current channels generated by the two-stream instability and is local in nature. Thus the observed radiation field may be tied directly to the local conditions of the plasma and could be a strong handle on the physical processes. (abridged)

  1. Microstructure Modeling of Third Generation Disk Alloys

    NASA Technical Reports Server (NTRS)

    Jou, Herng-Jeng

    2010-01-01

    The objective of this program was to model, validate, and predict the precipitation microstructure evolution, using PrecipiCalc (QuesTek Innovations LLC) software, for 3rd generation Ni-based gas turbine disc superalloys during processing and service, with a set of logical and consistent experiments and characterizations. Furthermore, within this program, the originally research-oriented microstructure simulation tool was to be further improved and implemented to be a useful and user-friendly engineering tool. In this report, the key accomplishments achieved during the third year (2009) of the program are summarized. The activities of this year included: Further development of multistep precipitation simulation framework for gamma prime microstructure evolution during heat treatment; Calibration and validation of gamma prime microstructure modeling with supersolvus heat treated LSHR; Modeling of the microstructure evolution of the minor phases, particularly carbides, during isothermal aging, representing the long term microstructure stability during thermal exposure; and the implementation of software tools. During the research and development efforts to extend the precipitation microstructure modeling and prediction capability in this 3-year program, we identified a hurdle, related to slow gamma prime coarsening rate, with no satisfactory scientific explanation currently available. It is desirable to raise this issue to the Ni-based superalloys research community, with hope that in future there will be a mechanistic understanding and physics-based treatment to overcome the hurdle. In the mean time, an empirical correction factor was developed in this modeling effort to capture the experimental observations.

  2. Radiation Hydrodynamical Models of the Inner Rim in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Flock, Mario

    2016-06-01

    Many stars host planets orbiting within one astronomical unit (AU). These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric, and include starlight heating, silicate grains sublimating and condensing to equilibrium at the local, timedependent temperature and density, and accretion stresses parametrizing the results of MHD magneto-rotational turbulence models. The results compare well with radiation hydrostatic solutions, and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rims’s location. A small optically-thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops at the position of thermal ionization at temperatures about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are su ciently high for annealing to form crystalline silicates.

  3. Constraints on Planetesimal Collision Models in Debris Disks

    NASA Astrophysics Data System (ADS)

    MacGregor, Meredith A.; Wilner, David J.; Chandler, Claire; Ricci, Luca; Maddison, Sarah T.; Cranmer, Steven R.; Andrews, Sean M.; Hughes, A. Meredith; Steele, Amy

    2016-06-01

    Observations of debris disks offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. In particular, the millimeter spectral index of thermal dust emission encodes information on the grain size distribution. We have made new VLA observations of a sample of seven nearby debris disks at 9 mm, with 3\\prime\\prime resolution and ∼5 μJy beam‑1rms. We combine these with archival ATCA observations of eight additional debris disks observed at 7 mm, together with up-to-date observations of all disks at (sub)millimeter wavelengths from the literature, to place tight constraints on the millimeter spectral indices and thus grain size distributions. The analysis gives a weighted mean for the slope of the power-law grain size distribution, n(a)\\propto {a}-q, of < q> =3.36+/- 0.02, with a possible trend of decreasing q for later spectral type stars. We compare our results to a range of theoretical models of collisional cascades, from the standard self-similar, steady-state size distribution (q = 3.5) to solutions that incorporate more realistic physics such as alternative velocity distributions and material strengths, the possibility of a cutoff at small dust sizes from radiation pressure, and results from detailed dynamical calculations of specific disks. Such effects can lead to size distributions consistent with the data, and plausibly the observed scatter in spectral indices. For the AU Mic system, the VLA observations show clear evidence of a highly variable stellar emission component; this stellar activity obviates the need to invoke the presence of an asteroid belt to explain the previously reported compact millimeter source in this system.

  4. Microstructure Modeling of 3rd Generation Disk Alloy

    NASA Technical Reports Server (NTRS)

    Jou, Herng-Jeng

    2008-01-01

    The objective of this initiative, funded by NASA's Aviation Safety Program, is to model, validate, and predict, with high fidelity, the microstructural evolution of third-generation high-refractory Ni-based disc superalloys during heat treating and service conditions. This initiative is a natural extension of the DARPA-AIM (Accelerated Insertion of Materials) initiative with GE/Pratt-Whitney and with other process simulation tools. Strong collaboration with the NASA Glenn Research Center (GRC) is a key component of this initiative and the focus of this program is on industrially relevant disk alloys and heat treatment processes identified by GRC. Employing QuesTek s Computational Materials Dynamics technology and PrecipiCalc precipitation simulator, physics-based models are being used to achieve high predictive accuracy and precision. Combining these models with experimental data and probabilistic analysis, "virtual alloy design" can be performed. The predicted microstructures can be optimized to promote desirable features and concurrently eliminate nondesirable phases that can limit the reliability and durability of the alloys. The well-calibrated and well-integrated software tools that are being applied under the proposed program will help gas turbine disk alloy manufacturers, processing facilities, and NASA, to efficiently and effectively improve the performance of current and future disk materials.

  5. A Multiphysics and Multiscale Software Environment for Modeling Astrophysical Systems

    NASA Astrophysics Data System (ADS)

    Portegies Zwart, Simon; McMillan, Steve; O'Nualláin, Breanndán; Heggie, Douglas; Lombardi, James; Hut, Piet; Banerjee, Sambaran; Belkus, Houria; Fragos, Tassos; Fregeau, John; Fuji, Michiko; Gaburov, Evghenii; Glebbeek, Evert; Groen, Derek; Harfst, Stefan; Izzard, Rob; Jurić, Mario; Justham, Stephen; Teuben, Peter; van Bever, Joris; Yaron, Ofer; Zemp, Marcel

    We present MUSE, a software framework for tying together existing computational tools for different astrophysical domains into a single multiphysics, multiscale workload. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly-coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for a generalized stellar systems workload. MUSE has now reached a "Noah's Ark" milestone, with two available numerical solvers for each domain. MUSE can treat small stellar associations, galaxies and everything in between, including planetary systems, dense stellar clusters and galactic nuclei. Here we demonstrate an examples calculated with MUSE: the merger of two galaxies. In addition we demonstrate the working of MUSE on a distributed computer. The current MUSE code base is publicly available as open source at http://muse.li.

  6. A multiphysics and multiscale software environment for modeling astrophysical systems

    NASA Astrophysics Data System (ADS)

    Portegies Zwart, Simon; McMillan, Steve; Harfst, Stefan; Groen, Derek; Fujii, Michiko; Nualláin, Breanndán Ó.; Glebbeek, Evert; Heggie, Douglas; Lombardi, James; Hut, Piet; Angelou, Vangelis; Banerjee, Sambaran; Belkus, Houria; Fragos, Tassos; Fregeau, John; Gaburov, Evghenii; Izzard, Rob; Jurić, Mario; Justham, Stephen; Sottoriva, Andrea; Teuben, Peter; van Bever, Joris; Yaron, Ofer; Zemp, Marcel

    2009-05-01

    We present MUSE, a software framework for combining existing computational tools for different astrophysical domains into a single multiphysics, multiscale application. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for studying generalized stellar systems. We have now reached a "Noah's Ark" milestone, with (at least) two available numerical solvers for each domain. MUSE can treat multiscale and multiphysics systems in which the time- and size-scales are well separated, like simulating the evolution of planetary systems, small stellar associations, dense stellar clusters, galaxies and galactic nuclei. In this paper we describe three examples calculated using MUSE: the merger of two galaxies, the merger of two evolving stars, and a hybrid N-body simulation. In addition, we demonstrate an implementation of MUSE on a distributed computer which may also include special-purpose hardware, such as GRAPEs or GPUs, to accelerate computations. The current MUSE code base is publicly available as open source at http://muse.li.

  7. Asymmetric mass models of disk galaxies. I. Messier 99

    NASA Astrophysics Data System (ADS)

    Chemin, Laurent; Huré, Jean-Marc; Soubiran, Caroline; Zibetti, Stefano; Charlot, Stéphane; Kawata, Daisuke

    2016-04-01

    Mass models of galactic disks traditionally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, such as lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk midplane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M 99, the new strategy shows that circular velocities are highly nonuniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M 99, in the usual case where luminous and dark matter share the same center. The impact of the velocity nonuniformity is to make the inner profile less steep, although the density remains cuspy. On another hand, a model where the halo is core dominated and shifted by 2.2-2.5 kpc from the luminous mass center is more appropriate to explain most of the kinematical lopsidedness evidenced in the velocity field of M 99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions: possibly a lopsided distribution of dark matter.

  8. One-dimensional disk model simulation for klystron design

    SciTech Connect

    Yonezawa, H.; Okazaki, Y.

    1984-05-01

    In 1982, one of the authors (Okazaki), of Toshiba Corporation, wrote a one-dimensional, rigid-disk model computer program <1> to serve as a reliable design tool for the 150 MW klystron development project. This is an introductory note for the users of this program. While reviewing the so-called disk programs presently available, hypotheses such as gridded interaction gaps, a linear relation between phase and position, and so on, were found. These hypotheses bring serious limitations and uncertainties into the computational results. JPNDISK was developed to eliminate these defects, to follow the equations of motion as rigorously as possible, and to obtain self-consistent solutions for the gap voltages and the electron motion. Although some inaccuracy may be present in the relativistic region, JPNDISK, in its present form, seems a most suitable tool for klystron design; it is both easy and inexpensive to use.

  9. Drag-o-llision Models of Extrasolar Planets in Debris Disks

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc

    2009-01-01

    An extrasolar planet sculpts the famous debris disk around Fomalhaut; probably many other debris disks contain planets that we could locate if only we could better recognize their signatures in the dust that surrounds them. But the interaction between planets and debris disks involves both orbital resonances and collisions among grains and rocks in the disks---difficult processes to model simultaneously. The author describes new 3-D models of debris disk dynamics, Drag-o-llision models, that incorporate both collisions and resonant trapping of dust for the first time. The author also discusses the implications of these models for coronagraphic imaging with Gemini and other telescopes.

  10. Astrophysics today

    SciTech Connect

    Cameron, A.G.W.

    1984-01-01

    Examining recent history, current trends, and future possibilities, the author reports the frontiers of research on the solar system, stars, galactic physics, and cosmological physics. The book discusses the great discoveries in astronomy and astrophysics and examines the circumstances in which they occurred. It discusses the physics of white dwarfs, the inflationary universe, the extinction of dinosaurs, black hole, cosmological models, and much more.

  11. The Behavior of Accretion Disks in Low Mass X-ray Binaries: Disk Winds and Alpha Model

    NASA Astrophysics Data System (ADS)

    Bayless, Amanda J.

    2010-01-01

    This dissertation presents research on two low mass X-ray binaries. The eclipsing low-mass X-ray binary 4U 1822-371 is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectroscopy with the ACS/SBC on the Hubble Space Telescope and new V- and J-band photometry with the 1.3-m SMARTS telescope at CTIO. We show that the accretion disk in the system has a strong wind with projected velocities up to 4000 km/s as determined from the Doppler width of the C IV emission line. The broad and shallow eclipse indicates that the disk has a vertically-extended, optically-thick component at optical wavelengths. This component extends almost to the edge of the disk and has a height equal to 50% of the disk radius. As it has a low brightness temperature, we identify it as the optically-thick base of the disk wind. V1408 Aql (=4U 1957+115) is a low mass X-ray binary which continues to be a black hole candidate. We have new photometric data of this system from the Otto Struve 2.1-m telescope's high speed CCD photometer at McDonald Observatory. The light curve is largely sinusoidal which we model with two components: a constant light source from the disk and a sinusoidal modulation at the orbital period from the irradiated face of the companion star. This is a radical re-interpretation of the orbital light curve. We do not require a large or asymmetric disk rim to account for the modulation in the light curve. Thus, the orbital inclination is unconstrained in our new model, removing the foundation for any claims of the compact object being a black hole.

  12. X-Ray Binary Stars and Ovarian Follicle Growth: Math Models in Astrophysics and Physiology

    NASA Astrophysics Data System (ADS)

    Sarty, Gordon E.; Saxton, Curtis; Wu, Kinwah; Pierson, Roger

    2010-10-01

    The scientific investigation of Nature relies on mathematics. While mathematics itself is precise, its application to the understanding of nature always involves an approximation. The approximate nature of mathematical application ultimately limits the scientific approach to Nature, but the freedom to make appropriate approximations allows us to understand complex phenomena on the basis of a few simple principles in approaches that are limited only by imagination. Here we review and compare two mathematical models of natural phenomena in astrophysics and physiology. The astrophysical model describes the emission of polarized radiation from a magnetic cataclysmic variable; the physiological model describes growth and competition among ovarian follicles under the influence of circulating hormones. In each case, the understanding offered by the mathematical model must be verified by fitting the model to data; this is part of the usual scientific method. In the follicle model case, we show how model fits may also be used for medical diagnostic purposes.

  13. MODELING MAGNETOROTATIONAL TURBULENCE IN PROTOPLANETARY DISKS WITH DEAD ZONES

    SciTech Connect

    Okuzumi, Satoshi; Hirose, Shigenobu

    2011-12-01

    Turbulence driven by magnetorotational instability (MRI) crucially affects the evolution of solid bodies in protoplanetary disks. On the other hand, small dust particles stabilize MRI by capturing ionized gas particles needed for the coupling of the gas and magnetic fields. To provide an empirical basis for modeling the coevolution of dust and MRI, we perform three-dimensional, ohmic-resistive MHD simulations of a vertically stratified shearing box with an MRI-inactive 'dead zone' of various sizes and with a net vertical magnetic flux of various strengths. We find that the vertical structure of turbulence is well characterized by the vertical magnetic flux and three critical heights derived from the linear analysis of MRI in a stratified disk. In particular, the turbulent structure depends on the resistivity profile only through the critical heights and is insensitive to the details of the resistivity profile. We discover scaling relations between the amplitudes of various turbulent quantities (velocity dispersion, density fluctuation, vertical diffusion coefficient, and outflow mass flux) and vertically integrated accretion stresses. We also obtain empirical formulae for the integrated accretion stresses as a function of the vertical magnetic flux and the critical heights. These empirical relations allow us to predict the vertical turbulent structure of a protoplanetary disk for a given strength of the magnetic flux and a given resistivity profile.

  14. Radiation Hydrodynamics Models of the Inner Rim in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Flock, M.; Fromang, S.; Turner, N. J.; Benisty, M.

    2016-08-01

    Many stars host planets orbiting within a few astronomical units (AU). The occurrence rate and distributions of masses and orbits vary greatly with the host star’s mass. These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric and include starlight heating silicate grains sublimating and condensing to equilibrium at the local, time-dependent temperature and density and accretion stresses parameterizing the results of MHD magnetorotational turbulence models. The results compare well with radiation hydrostatic solutions and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rim’s location. A small optically thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops near the location of thermal ionization at temperatures of about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are sufficiently high for annealing to form crystalline silicates.

  15. A method for comparing non-nested models with application to astrophysical searches for new physics

    NASA Astrophysics Data System (ADS)

    Algeri, Sara; Conrad, Jan; van Dyk, David A.

    2016-05-01

    Searches for unknown physics and decisions between competing astrophysical models to explain data both rely on statistical hypothesis testing. The usual approach in searches for new physical phenomena is based on the statistical likelihood ratio test and its asymptotic properties. In the common situation, when neither of the two models under comparison is a special case of the other i.e. when the hypotheses are non-nested, this test is not applicable. In astrophysics, this problem occurs when two models that reside in different parameter spaces are to be compared. An important example is the recently reported excess emission in astrophysical γ-rays and the question whether its origin is known astrophysics or dark matter. We develop and study a new, simple, generally applicable, frequentist method and validate its statistical properties using a suite of simulations studies. We exemplify it on realistic simulated data of the Fermi-Large Area Telescope γ-ray satellite, where non-nested hypotheses testing appears in the search for particle dark matter.

  16. Thermodynamic model of MHD turbulence and some of its applications to accretion disks

    NASA Astrophysics Data System (ADS)

    Kolesnichenko, A. V.; Marov, M. Ya.

    2008-06-01

    Within the framework of the main problem of cosmogony related to the reconstruction of the evolution of the protoplanetary gas-dust cloud that surrounded the proto-Sun at an early stage of its existence, we have derived a closed system of magnetohydrodynamic equations for the scale of mean motion in the approximation of single-fluid magnetohydrodynamics designed to model the shear and convective turbulent flows of electrically conducting media in the presence of a magnetic field. These equations are designed for schematized formulations and the numerical solution of special problems to interconsistently model intense turbulent flows of cosmic plasma in accretion disks and associated coronas, in which the magnetic field noticeably affects the dynamics of astrophysical processes. In developing the model of a conducting turbulized medium, apart from the conventional probability-theoretical averaging of the MHD equations, we systematically use the weighted Favre averaging. The latter allows us to considerably simplify the writing of the averaged equations of motion for a compressible fluid and the analysis of the mechanisms of macroscopic field amplification by turbulent flows. To clearly interpret the individual components of the plasma and field-energy balance, we derive various energy equations that allow us to trace the possible energy conversions from one form into another, in particular, to understand the transfer mechanisms of the gravitational and kinetic energies of the mean motion into magnetic energy. Special emphasis is placed on the method for obtaining the closure relations for the total (with allowance made for the magnetic field) kinetic turbulent stress tensor in an electrically conducting medium and the turbulent electromotive force (or the so-called magnetic Reynolds tensor). This method also makes it possible to analyze the constraints imposed on the turbulent transport coefficients by the entropy growth condition. As applied to the problem of

  17. Modeling Planet-Building Stellar Disks with Radiative Transfer Code

    NASA Astrophysics Data System (ADS)

    Swearingen, Jeremy R.; Sitko, Michael L.; Whitney, Barbara; Grady, Carol A.; Wagner, Kevin Robert; Champney, Elizabeth H.; Johnson, Alexa N.; Warren, Chelsea C.; Russell, Ray W.; Hammel, Heidi B.; Lisse, Casey M.; Cure, Michel; Kraus, Stefan; Fukagawa, Misato; Calvet, Nuria; Espaillat, Catherine; Monnier, John D.; Millan-Gabet, Rafael; Wilner, David J.

    2015-01-01

    Understanding the nature of the many planetary systems found outside of our own solar system cannot be completed without knowledge of the beginnings these systems. By detecting planets in very young systems and modeling the disks of material around stars from which they form, we can gain a better understanding of planetary origin and evolution. The efforts presented here have been in modeling two pre-transitional disk systems using a radiative transfer code. With the first of these systems, V1247 Ori, a model that fits the spectral energy distribution (SED) well and whose parameters are consistent with existing interferometry data (Kraus et al 2013) has been achieved. The second of these two systems, SAO 206462, has presented a different set of challenges but encouraging SED agreement between the model and known data gives hope that the model can produce images that can be used in future interferometry work. This work was supported by NASA ADAP grant NNX09AC73G, and the IR&D program at The Aerospace Corporation.

  18. Model-based Clustering of High-Dimensional Data in Astrophysics

    NASA Astrophysics Data System (ADS)

    Bouveyron, C.

    2016-05-01

    The nature of data in Astrophysics has changed, as in other scientific fields, in the past decades due to the increase of the measurement capabilities. As a consequence, data are nowadays frequently of high dimensionality and available in mass or stream. Model-based techniques for clustering are popular tools which are renowned for their probabilistic foundations and their flexibility. However, classical model-based techniques show a disappointing behavior in high-dimensional spaces which is mainly due to their dramatical over-parametrization. The recent developments in model-based classification overcome these drawbacks and allow to efficiently classify high-dimensional data, even in the "small n / large p" situation. This work presents a comprehensive review of these recent approaches, including regularization-based techniques, parsimonious modeling, subspace classification methods and classification methods based on variable selection. The use of these model-based methods is also illustrated on real-world classification problems in Astrophysics using R packages.

  19. Computer Modeling of Electrostatic Aggregation of Granular Materials in Planetary and Astrophysical Settings

    NASA Technical Reports Server (NTRS)

    Marshall, J.; Sauke, T.

    1999-01-01

    Electrostatic forces strongly influence the behavior of granular materials in both dispersed (cloud) systems and semi-packed systems. These forces can cause aggregation or dispersion of particles and are important in a variety of astrophysical and planetary settings. There are also many industrial and commercial settings where granular matter and electrostatics become partners for both good and bad. This partnership is important for human exploration on Mars where dust adheres to suits, machines, and habitats. Long-range Coulombic (electrostatic) forces, as opposed to contact-induced dipoles and van der Waals attractions, are generally regarded as resulting from net charge. We have proposed that in addition to net charge interactions, randomly distributed charge carriers on grains will result in a dipole moment regardless of any net charge. If grains are unconfined, or fluidized, they will rotate so that the dipole always induces attraction between grains. Aggregates are readily formed, and Coulombic polarity resulting from the dipole produces end-to-end stacking of grains to form filamentary aggregates. This has been demonstrated in USML experiments on Space Shuttle where microgravity facilitated the unmasking of static forces. It has also been demonstrated in a computer model using grains with charge carriers of both sign. Model results very closely resembled micro-g results with actual sand grains. Further computer modeling of the aggregation process has been conducted to improve our understanding of the aggregation process, and to provide a predictive tool for microgravity experiments slated for Space Station. These experiments will attempt to prove the dipole concept as outlined above. We have considerably enhanced the original computer model: refinements to the algorithm have improved the fidelity of grain behavior during grain contact, special attention has been paid to simulation time steps to enable establishment of a meaningful, quantitative time axis

  20. Parameterized reduced order modeling of misaligned stacked disks rotor assemblies

    NASA Astrophysics Data System (ADS)

    Ganine, Vladislav; Laxalde, Denis; Michalska, Hannah; Pierre, Christophe

    2011-01-01

    Light and flexible rotating parts of modern turbine engines operating at supercritical speeds necessitate application of more accurate but rather computationally expensive 3D FE modeling techniques. Stacked disks misalignment due to manufacturing variability in the geometry of individual components constitutes a particularly important aspect to be included in the analysis because of its impact on system dynamics. A new parametric model order reduction algorithm is presented to achieve this goal at affordable computational costs. It is shown that the disks misalignment leads to significant changes in nominal system properties that manifest themselves as additional blocks coupling neighboring spatial harmonics in Fourier space. Consequently, the misalignment effects can no longer be accurately modeled as equivalent forces applied to a nominal unperturbed system. The fact that the mode shapes become heavily distorted by extra harmonic content renders the nominal modal projection-based methods inaccurate and thus numerically ineffective in the context of repeated analysis of multiple misalignment realizations. The significant numerical bottleneck is removed by employing an orthogonal projection onto the subspace spanned by first few Fourier harmonic basis vectors. The projected highly sparse systems are shown to accurately approximate the specific misalignment effects, to be inexpensive to solve using direct sparse methods and easy to parameterize with a small set of measurable eccentricity and tilt angle parameters. Selected numerical examples on an industrial scale model are presented to illustrate the accuracy and efficiency of the algorithm implementation.

  1. The Vertical Structure of Nuclear Starburst Disks: Testing a Model of AGN Obscuration

    NASA Astrophysics Data System (ADS)

    Ballantyne, David R.; Gohil, Raj

    2016-04-01

    Nuclear starburst disks are Eddington-limited, radiation pressure supported disks that may be active in the nuclear environment of active galaxies (ULIRGS and AGNs). Earlier analytical models suggested that, under certain conditions, these disks may be geometrically thick on pc-scales, and thus could be a viable source for AGN obscuration, partcularly at z≤1, when gas factions in galaxies are still significant. Here, we present early results from numerical 2D models of nuclear starburst disks where the vertical structure is calculated explicitly from solving the hydrostatic balance and radiative transfer equations. We quantitatively assess under which conditions the starburst disk may present substantial obscuring columns for AGN observations.

  2. Modelling Cosmic-Ray Effects in the Protosolar Disk

    NASA Technical Reports Server (NTRS)

    Wilson, Thomas L.

    2010-01-01

    The role that Galactic cosmic rays (GCRs) and solar energetic particles (SEPs) play in the dynamic evolution of protosolar disks and the origin of our Solar System is a fundamental one. The GCRs are an important component of the interstellar medium (ISM), and even play a role in correcting the age determinations of some irons versus CAIs (calcium-aluminum inclusions) in meteoroids . Because CRs also are one of the energy transport mechanisms in a planetary nebula, the question of modelling their effect upon this broad subject is a serious topic for planetary science. The problem is addressed here.

  3. Disk-Corona Model of Active Galactic Nuclei with Nonthermal Pairs

    NASA Technical Reports Server (NTRS)

    Tsuruta, Sachiko; Kellen, Michael

    1995-01-01

    As a promising model for the X-ray emission from radio-quiet quasars and Seyfert 1 nuclei, we present a nonthermal disk-corona model, where soft photons from a disk are Comptonized by the nonthermal electron-positron pairs in a coronal region above the disk. Various characteristics of our model are qualitatively similar to the homogeneous, spherical, nonthermal pair models previously studied, but the important difference is that in our disk-corona model gamma-ray depletion is far more efficient, and, moreover, the gamma-ray annihilation line is much less prominent. Consequently, this model naturally satisfies the observed constraints on active galactic nuclei.

  4. Optical model and optimal output coupler for a continuous wave Yb:YAG thin-disk laser with multiple-disk configuration.

    PubMed

    Zhu, Guangzhi; Zhu, Xiao; Zhu, Changhong; Shang, Jianli

    2012-09-10

    This article presents the fundamental principles of operational performance of a continuous wave (cw) thin-disk laser with multiple disks in one resonator. Based on the model of an end-pumped Yb:YAG thin-disk laser with nonuniform temperature distribution, the effect of the multiple disks in one resonator is considered. The analytic expressions are derived to analyze the laser output intensity, laser intensity in the resonator, threshold intensity, and the optical efficiency of a thin-disk laser with multiple disks arranged in series. The dependence of output coupler reflectivity and the number of thin disks on various parameters are investigated, which are useful to determine the optimal output coupler reflectivity of the thin-disk lasers and control the laser intensity in the resonator. PMID:22968282

  5. Eddington's Stellar Models and Early Twentieth Century Astrophysics

    NASA Astrophysics Data System (ADS)

    Eisberg, Joann

    1991-06-01

    Between 1916 and 1926, Arthur Stanley Eddington developed models of the temperature, pressure and density in the interior of stars. The models generated a relationship between stellar mass and luminosity that agreed well with observation. Coupled with the evolutionary theory that astronomers then thought governed stars, the models explained the distribution of stars upon the Hertzsprung-Russell diagram. This thesis argues that Eddington's models were shaped by the cosmological concerns that had preoccupied the British astronomical community in the preceding decade. British astronomers participated in a program of statistical cosmology, spearheaded by the Dutch astronomer, J. C. Kapteyn, to map the universe by studying the distribution of stars in neighborhoods successively more distant from the sun. The parameters of chief concern in this program were proper motion, which was used to measure stellar distance, and luminosity, considered the most important inherent characteristic of a star. In 1913 Henry Norris Russell published an empirical diagram of stellar luminosity and spectral type, on which he based a new theory of the evolution of stars from bright, red giants to bright, blue giants, to faint red dwarfs. British astronomers recognized the theory and diagram as fruits of the statistical program, and they rapidly accepted its parameters as the ones a stellar model should generate. Prompted by his interest in cepheid variable stars to construct a model of stars in radiative equilibrium, Eddington's first concern was to reproduce the features of Russell's diagram. Russell's evolutionary theory played so large a role in Eddington's work that when his own mass -luminosity relationship threatened to overturn it, he tailored his theory of stellar energy generation to preserve it.

  6. Automated optic disk boundary detection by modified active contour model.

    PubMed

    Xu, Juan; Chutatape, Opas; Chew, Paul

    2007-03-01

    This paper presents a novel deformable-model-based algorithm for fully automated detection of optic disk boundary in fundus images. The proposed method improves and extends the original snake (deforming-only technique) in two aspects: clustering and smoothing update. The contour points are first self-separated into edge-point group or uncertain-point group by clustering after each deformation, and these contour points are then updated by different criteria based on different groups. The updating process combines both the local and global information of the contour to achieve the balance of contour stability and accuracy. The modifications make the proposed algorithm more accurate and robust to blood vessel occlusions, noises, ill-defined edges and fuzzy contour shapes. The comparative results show that the proposed method can estimate the disk boundaries of 100 test images closer to the groundtruth, as measured by mean distance to closest point (MDCP) <3 pixels, with the better success rate when compared to those obtained by gradient vector flow snake (GVF-snake) and modified active shape models (ASM). PMID:17355059

  7. Challenges in Modeling Astrophysical Phenomena Involving Radiative, Reactive, and Multiphase Flows

    NASA Astrophysics Data System (ADS)

    Leung, C. M.

    1994-05-01

    Computer modeling is an indispensable research tool in advancing our understanding of astrophysical phenomena. With the rapid increase in both quality and quantity of astronomical data from ground-based and space-based facilities, a major challenge facing computational astrophysicists is to construct models with increasing degree of realism (in terms of physical and chemical processes, as well as source geometry) to interpret these data. The continuing advance in computer hardware and the associated increase in computing power allow the inclusion of more realistic microphysics and physico- chemical processes in the models. While many astrophysical phenomena are dominated by the collective effects of gas dynamics, there are many situations in which radiation transport, heterogeneous chemical kinetics, and gas dynamics all play an important role, making the modeling of radiative and reactive flow problems difficult. In particular, the modeling of astrophysical phenomena involving radiative, reactive, and multiphase flows not only increases the number of simultaneous processes occurring but also expands the range of both time and space scales in the problem. Counterintuitive behavior arises from the interactions of the various local, diffusive, convective, and oscillatory phenomena in the flow. Some examples are chemical and dynamical evolution of interstellar clouds involving both gas-phase and grain-surface chemistry, dust formation in radiation-driven stellar winds, and grain alignment in magnetohydrodynamic shocks. In this talk I will first review the basic concepts and computational techniques in modeling astrophysical systems involving radiation hydrodynamics, chemical kinetics, and heterogeneous components. I will describe a few selected results to demonstrate some recent progress made and identify the technical challenges that we still need to overcome.

  8. Searching for Simpler Models of Astrophysical Pattern Formation

    NASA Astrophysics Data System (ADS)

    Cangi, Eryn; Abrams, Daniel M.

    2016-01-01

    While theories of synchronization in two- or three-body astronomical systems are well understood, a generalization to many-bodied systems remains largely unexplored. Historically, problems of resonant capture among astronomical bodies have been treated primarily using methods from conservative classical mechanics. We investigate the possibility of using nonconservative models together with perturbation theory and numerical methods to understand the phenomenon of resonant capture in large-scale structures such as rings, planetary systems and galactic spiral arms. In particular, we focus on N-body dissipative systems such as circumplanetary discs and use methods drawn from the study of coupled oscillators. One such method is inspired by the Kuramoto model, which describes mean-field behavior in large ensembles of coupled nonlinear oscillators. The Kuramoto model can be modified to allow for non-mean-field coupling, leading to the existence of chimera states, in which most of the oscillators synchronize. These chimera states can appear as clusters or spirals of synced oscillators, and may be suggestive of objects in astronomical contexts. As an illustrative example, we develop a mean-field model for N small particles in a dust ring around a massive planet and integrate it numerically using code developed in MATLAB and Python. Preliminary results show promise that this approach will yield new insight into astronomical synchronization phenomena across a wide range of length scales.

  9. Astrophysical constraints on unparticle-inspired models of gravity

    SciTech Connect

    Bertolami, O.; Paramos, J.; Santos, P.

    2009-07-15

    We use stellar dynamics arguments to constrain the relevant parameters of unparticle-inspired models of gravity. We show that resulting bounds do constrain the parameters of the theory of unparticles, as far as its energy scale satisfies the condition {lambda}{sub U}{>=}1 TeV and d{sub U} is close to unity.

  10. Three-dimensional modelling of film flows over spinning disks

    NASA Astrophysics Data System (ADS)

    Zhao, Kun; Wray, Alex; Yang, Junfeng; Matar, Omar

    2014-11-01

    Film flows over spinning disks are of central importance to a wide array of industrial processes, such as the augmentation of heat and mass transfer in chemical reactors, or power production in metallurgy. As a result they have been extensively investigated experimentally. Theoretically they constitute an interesting problem due to the interplay of inertial, capillary, centrifugal and Coriolis forces. However, modelling efforts have typically been restricted to the consideration of the one-dimensional axisymmetric situation. We extend the existing models to incorporate azimuthal variations. The resultant system is solved via the use of an operator-splitting method. In addition, we have performed Direct Numerical Simulations of the system. We compare the low order model, the direct simulations and the results of experiments, to reveal a wide variety of different flow regimes in accordance with existing literature. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.

  11. Microscopic nuclear models for astrophysics: The Brussels BRUSLIB nuclear library and beyond

    NASA Astrophysics Data System (ADS)

    Arnould, M.; Goriely, S.

    2006-10-01

    Astrophysics is in need of a broad variety of nuclear data. This concerns static ground state properties, characteristics of excited nuclei, spontaneous decay properties, or interactions of nuclei with (mainly) nucleons, α-particles or photons. A strong theoretical activity complementing laboratory efforts is also mandatory. A large variety of highly ‘exotic’ laboratory-unreachable nuclei are indeed involved in the astrophysics modelling. Even when laboratory-studied nuclei are considered, theory has very often to be called for. Mastering the huge volume of nuclear information and making it available in an accurate and usable form for incorporation into astrophysics models is clearly of pivotal importance. The recognition of this necessity has been the driving motivation for the construction of the Brussels library (BRUSLIB) of computed data of astrophysics relevance. It provides an extended information in tabular form on masses, nuclear level densities and partition functions, fission barriers, and thermonuclear reaction rates. In addition of the unprecedented broadness of its scope, BRUSLIB has the unique and most important feature of relying to the largest possible extent on global and coherent microscopic nuclear models. The models of this sort that we have developed to predict the basic properties of the nuclei and of their interactions are briefly reviewed. The content of the BRUSLIB library that relies on these models is described, as well as a user-friendly nuclear network generator (NETGEN) complementing BRUSLIB. Finally, an application of BRUSLIB and NETGEN to the p-process nucleosynthesis during He detonation in sub-Chandrasekhar CO white dwarfs is proposed.

  12. Radiative Magnetic Reconnection in Astrophysics

    NASA Astrophysics Data System (ADS)

    Uzdensky, D. A.

    In this chapter we review a new and rapidly growing area of research in high-energy plasma astrophysics—radiative magnetic reconnection, defined here as a regime of reconnection where radiation reaction has an important influence on the reconnection dynamics, energetics, and/or nonthermal particle acceleration. This influence be may be manifested via a variety of radiative effects that are critical in many high-energy astrophysical applications. The most notable radiative effects in astrophysical reconnection include radiation-reaction limits on particle acceleration, radiative cooling, radiative resistivity, braking of reconnection outflows by radiation drag, radiation pressure, viscosity, and even pair creation at highest energy densities. The self-consistent inclusion of these effects into magnetic reconnection theory and modeling sometimes calls for serious modifications to our overall theoretical approach to the problem. In addition, prompt reconnection-powered radiation often represents our only observational diagnostic tool available for studying remote astrophysical systems; this underscores the importance of developing predictive modeling capabilities to connect the underlying physical conditions in a reconnecting system to observable radiative signatures. This chapter presents an overview of our recent theoretical progress in developing basic physical understanding of radiative magnetic reconnection, with a special emphasis on astrophysically most important radiation mechanisms like synchrotron, curvature, and inverse-Compton. The chapter also offers a broad review of key high-energy astrophysical applications of radiative reconnection, illustrated by multiple examples such as: pulsar wind nebulae, pulsar magnetospheres, black-hole accretion-disk coronae and hot accretion flows in X-ray Binaries and Active Galactic Nuclei and their relativistic jets, magnetospheres of magnetars, and Gamma-Ray Bursts. Finally, this chapter discusses the most critical

  13. Magnetically Torqued Thin Accretion Disks

    NASA Astrophysics Data System (ADS)

    Kluźniak, W.; Rappaport, S.

    2007-12-01

    We compute the properties of a geometrically thin, steady accretion disk surrounding a central rotating, magnetized star. The magnetosphere is assumed to entrain the disk over a wide range of radii. The model is simplified in that we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal component of the magnetic field as a function of radial distance. We find a solution for the angular velocity profile tending to corotation close to the central star and smoothly matching a Keplerian curve at a radius where the viscous stress vanishes. The value of this ``transition'' radius is nearly the same for both of our adopted B-field models. We then solve analytically for the torques on the central star and for the disk luminosity due to gravity and magnetic torques. When expressed in a dimensionless form, the resulting quantities depend on one parameter alone, the ratio of the transition radius to the corotation radius. For rapid rotators, the accretion disk may be powered mostly by spin-down of the central star. These results are independent of the viscosity prescription in the disk. We also solve for the disk structure for the special case of an optically thick alpha disk. Our results are applicable to a range of astrophysical systems including accreting neutron stars, intermediate polar cataclysmic variables, and T Tauri systems.

  14. Tilted Accretion Disk Models of Sgr A* Flares

    NASA Astrophysics Data System (ADS)

    Dexter, Jason; Fragile, P. C.

    2013-01-01

    Sagittarius A* (Sgr A*), the Galactic center massive black hole candidate, is an unparalleled laboratory for low-luminosity accretion theory. First discovered as a compact radio source, Sgr A* has since been observed to undergo rapid, large amplitude NIR/X-ray flares. The many proposed phenomenological models cannot simultaneously explain both the flaring emission and the peak of the SED in the submillimeter. I will describe flares seen in numerical simulations of black hole accretion flows where the disk angular momentum is misaligned from that of the black hole. Eccentric fluid orbits driven by gravitational torques converge and form strong shocks, which can lead to significant particle heating. The resulting NIR emission can reproduce the observations, and is completely unrelated to the submillimeter emission, which is included in these models and is also in excellent agreement with observations. I will describe the prospects for testing accretion theory and constraining the properties of Sgr A* with exciting ongoing multi-wavelength observations.

  15. Numerical modeling of the interstellar medium in galactic disks

    NASA Technical Reports Server (NTRS)

    Rosen, A.; Bregman, J. N.; Norman, Michael L.

    1993-01-01

    We have been developing detailed hydrodynamic models of the global interstellar medium in the hope of understanding the mass and volume occupied by various phases, as well as their structure and kinematics. In our model, the gas is modeled by one fluid while representative Pop 1 stars are modeled by a second fluid. The two fluids are coupled in that the gas forms into stars at a rate given by a Schmidt law while stellar mass loss returns matter into the gas phase (on a time scale of 100 Myr). Also, the stars heat the gas through stellar winds and the gas cools through optically thin radiation. The time behavior of these two fluids is studied in two spatial dimensions with the Eulerian finite difference numerical hydrodynamic code Zen. The two spatial dimensions are along the plane of a disk (x, total length of 2 kpc) and perpendicular to the disk (z, total height of +/- 15 kpc) and a galactic gravitational field in the z direction, typical of that at the solar circle, is imposed upon the simulation; self-gravity and rotation are absent. For the boundary conditions, outflow is permitted at the top and bottom of the grid (z = +/- 15 kpc) while periodic boundary conditions are imposed upon left and right sides of the grid. As initial conditions, we assumed a gaseous distribution like that seen for the H1 by earlier researchers, although the results are insensitive to the initial conditions. We have run simulations in which the heating due to stars, parameterized as a stellar wind velocity, a, is varied from low (a = 150 km/s), to intermediate (a = 300 km/s), to high (a = 600 km/s). Since the intermediate case is roughly equivalent to the Galactic energy injection rate from supernovae, this summary will concentrate on results from this simulation.

  16. A Model Study of the Thermal Evolution of Astrophysical Ices

    NASA Technical Reports Server (NTRS)

    Loeffler, M. J.; Teolis, B. D.; Baragiola, R. A.

    2006-01-01

    We address the question of the evolution of ices that have been exposed to radiation from stellar sources and cosmic rays. We studied in the laboratory the thermal evolution of a model ice sample: a mixture of water, hydrogen peroxide, dioxygen, and ozone produced by irradiating solid H2O2 with 50 keV H(+) at 17 K. The changes in composition and release of volatiles during warming to 200 K were monitored by infrared spectroscopy, mass spectrometry, and microbalance techniques. We find evidence for voids in the water component from the infrared bands due to dangling H bonds. The absorption from these bands increases during heating and can be observed at temperatures as high as approx. 155 K. More O2 is stored in the radiolyzed film than can be retained by codeposition of O2 and H2O. This O2 remains trapped until approx. 155 K, where it desorbs in an outburst as water ice crystallizes. Warming of the ice also drastically decreases the intrinsic absorbance of O2 by annealing defects in the ice. We also observe loss of O3 in two stages during heating, which correlates with desorption and possibly chemical reactions with radicals stored in the ice, triggered by the temperature increase.

  17. Generalized Mittag-Leffler Distributions and Processes for Applications in Astrophysics and Time Series Modeling

    NASA Astrophysics Data System (ADS)

    Jose, Kanichukattu Korakutty; Uma, Padmini; Lekshmi, Vanaja Seetha; Haubold, Hans Joachim

    Geometric generalized Mittag-Leffler distributions having the Laplace transform 1/(1+βlog(1+tα)), 0 < α ≤ 2, β > 0 is introduced and its properties are discussed. Autoregressive processes with Mittag-Leffler and geometric generalized Mittag-Leffler marginal distributions are developed. Haubold and Mathai (Astrophysics and Space Science 273 53-63, 2000) derived a closed form representation of the fractional kinetic equation and thermonuclear function in terms of Mittag-Leffler function. Saxena et al. (2002; Astrophysics and Space Science 209 299-310 2004a; Physica A 344 657-664 2004b) extended the result and derived the solutions of a number of fractional kinetic equations in terms of generalized Mittag-Leffler functions. These results are useful in explaining various fundamental laws of physics. Here we develop first-order autoregressive time series models and the properties are explored. The results have applications in various areas like astrophysics, space sciences, meteorology, financial modeling and reliability modeling.

  18. MODELING COLLISIONAL CASCADES IN DEBRIS DISKS: THE NUMERICAL METHOD

    SciTech Connect

    Gaspar, Andras; Psaltis, Dimitrios; Oezel, Feryal; Rieke, George H.; Cooney, Alan E-mail: dpsaltis@as.arizona.edu E-mail: grieke@as.arizona.edu

    2012-04-10

    We develop a new numerical algorithm to model collisional cascades in debris disks. Because of the large dynamical range in particle masses, we solve the integro-differential equations describing erosive and catastrophic collisions in a particle-in-a-box approach, while treating the orbital dynamics of the particles in an approximate fashion. We employ a new scheme for describing erosive (cratering) collisions that yields a continuous set of outcomes as a function of colliding masses. We demonstrate the stability and convergence characteristics of our algorithm and compare it with other treatments. We show that incorporating the effects of erosive collisions results in a decay of the particle distribution that is significantly faster than with purely catastrophic collisions.

  19. Tests and consequences of disk plus halo models of gamma-ray burst sources

    NASA Technical Reports Server (NTRS)

    Smith, I. A.

    1995-01-01

    The gamma-ray burst observations made by the Burst and Transient Source Experiment (BATSE) and by previous experiments are still consistent with a combined Galactic disk (or Galactic spiral arm) plus extended Galactic halo model. Testable predictions and consequences of the disk plus halo model are discussed here; tests performed on the expanded BATSE database in the future will constrain the allowed model parameters and may eventually rule out the disk plus halo model. Using examples, it is shown that if the halo has an appropriate edge, BATSE will never detect an anisotropic signal from the halo of the Andromeda galaxy. A prediction of the disk plus halo model is that the fraction of the bursts observed to be in the 'disk' population rises as the detector sensitivity improves. A careful reexamination of the numbers of bursts in the two populations for the pre-BATSE databases could rule out this class of models. Similarly, it is predicted that different satellites will observe different relative numbers of bursts in the two classes for any model in which there are two different spatial distribiutions of the sources, or for models in which there is one spatial distribution of the sources that is sampled to different depths for the two classes. An important consequence of the disk plus halo model is that for the birthrate of the halo sources to be small compared to the birthrate of the disk sources, it is necessary for the halo sources to release many orders of magnitude more energy over their bursting lifetime than the disk sources. The halo bursts must also be much more luminous than the disk bursts; if this disk-halo model is correct, it is necessary to explain why the disk sources do not produce halo-type bursts.

  20. Particle astrophysics

    SciTech Connect

    Sadoulet, B. |

    1992-12-31

    In the last few years, particle astrophysics has emerged as a new field at the frontier between high energy astrophysics, cosmology, and particle physics. Two spectacular achievements of this new field in the last decade have been the establishment of neutrino astronomy with the detection of solar neutrinos by two independent experiments and the spectacular observation of the neutrinos from the supernova SN1987A. In addition, the field has produced tantalizing hints of new physics beyond the standard models of astrophysics and particle physics, generating enthusiastic attempts to confirm these potential effects. This new field involves some two hundred experimentalists and a similar number of theorists, most of them coming from particle and nuclear physics, and as scientist will see, their effort is to a large extent complementary to accelerator based high energy physics. This review attempts, at the beginning of this workshop, to capture the excitement of this new field. Summary talks will describe in more detail some of the topics discussed in the study groups.

  1. THE MISSING CAVITIES IN THE SEEDS POLARIZED SCATTERED LIGHT IMAGES OF TRANSITIONAL PROTOPLANETARY DISKS: A GENERIC DISK MODEL

    SciTech Connect

    Dong, R.; Rafikov, R.; Zhu, Z.; Brandt, T.; Janson, M.; Hartmann, L.; Whitney, B.; Muto, T.; Hashimoto, J.; Kuzuhara, M.; Grady, C.; Follette, K.; Tanii, R.; Itoh, Y.; Thalmann, C.; Wisniewski, J.; Mayama, S.; Abe, L.; Brandner, W.; Carson, J.; and others

    2012-05-10

    Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 {mu}m in their spectral energy distributions, recently measured by the Spitzer Infrared Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for {mu}m-sized grains, with little discontinuity in the surface density of the {mu}m-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the {mu}m-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models.

  2. The Thermodynamic Model of a Moon Forming Disk Based on SPH Simulations

    NASA Astrophysics Data System (ADS)

    Nakajima, M.; Stevenson, D. J.

    2011-12-01

    According to the giant impact hypothesis, a Mars size body hits the proto-Earth in the late stage of Earth forming event (e.g. Benz et al., 1986, Thompson and Stevenson 1988). The impact generates a debris disk around the proto-Earth, from which the Moon is accreted. SPH simulations suggest that the silicate disk has high temperature (~ a few thousands K) and partially vaporized (~10-30% by mass) (Canup 2004). However, SPH does not determine the state of the resulting hydrostatic disk. To do this, we have taken the output of SPH, applied conservation of entropy, mass and angular momentum and corrected for the additional energy released upon quick relaxation to the hydrostatic Keplerian state. We find that the disk is remarkably uniform in entropy but is of lower entropy than the adjacent outer shell of Earth. Constant entropy implies a temperature variation, typically from 4500K (inner disk) to 2500K (outer disk) at the midplane. For grazing impact cases (impact angles: 40 - 60 degrees, impact velocity: escape velocity, mantle material: forsterite), 90% of the disk mass is within 10 Earth radius. The disk vapor mass fractions are about 10-20%, which are consistent with Canup (2004) results. This may be an underestimate because iron is more volatile than magnesium. Mass loss from this disk will be small. The effects of initial condition differences will be discussed in the presentation. This is the first attempt to create a bridge between SPH results and a thermodynamic disk model.

  3. Circumstellar disks in binary star systems. Models for γ Cephei and α Centauri

    NASA Astrophysics Data System (ADS)

    Müller, T. W. A.; Kley, W.

    2012-03-01

    Context. As of today, over 50 planetary systems have been discovered in binary star systems, some of which have binary separations that are smaller than 20 AU. In these systems the gravitational forces from the binary have a strong influence on the evolution of the protoplanetary disk and hence the planet formation process. Aims: We study the evolution of viscous and radiative circumstellar disks under the influence of a companion star. We focus on the eccentric γ Cephei and α Centauri system as examples and compare disk quantities such as disk eccentricity and precession rate to previous isothermal simulations. Methods: We performed two-dimensional hydrodynamical simulations of the binary star systems under the assumption of coplanarity of the disk, host star and binary companion. We used the grid-based, staggered mesh code FARGO with an additional energy equation to which we added radiative cooling based on opacity tables. Results: The eccentric binary companion perturbs the disk around the primary star periodically. Upon passing periastron, spirals arms are induced that wind from the outer disk towards the star. In isothermal simulations this results in disk eccentricities up to edisk ≈ 0.2, but in more realistic radiative models we obtain much smaller eccentricities of about edisk ≈ 0.04-0.06 with no real precession. Models with varying viscosity and disk mass indicate that disks with less mass have lower temperatures and higher disk eccentricity. Conclusions: The fairly high disk eccentricities, as indicated in previous isothermal disk simulations, implied a more difficult planet formation in the γ Cephei system caused by the enhanced collision velocities of planetesimals. We have shown that under more realistic conditions with radiative cooling the disk becomes less eccentric and thus planet formation may be made easier. However, we estimate that the viscosity in the disk has to very low, with α ≲ 0.001, because otherwise the disk's lifetime will be

  4. Studying Wake Deflection of Wind Turbines in Yaw using Drag Disk Experiments and Actuator Disk Modeling in LES

    NASA Astrophysics Data System (ADS)

    Howland, Michael; Bossuyt, Juliaan; Meyers, Johan; Meneveau, Charles

    2015-11-01

    Recently, there has been a push towards the optimization in the power output of entire large wind farms through the control of individual turbines, as opposed to operating each turbine in a maximum power point tracking manner. In this vane, the wake deflection by wind turbines in yawed conditions has generated considerable interest in recent years. In order to effectively study the wake deflection according to classical actuator disk momentum theory, a 3D printed drag disk model with a coefficient of thrust of approximately 0.75 - 0.85 and a diameter of 3 cm is used, studied under uniform inflow in a wind tunnel with test section of 1 m by 1.3 m, operating with a negligible inlet turbulence level at an inflow velocity of 10 m/s. Mean velocity profile measurements are performed using Pitot probes. Different yaw angles are considered, including 10, 20, and 30 degrees. We confirm earlier results that (e.g.) a 30 degree yaw angle deflects the center of the wake around 1/2 of a rotor diameter when it impinges on a downstream turbine. Detailed comparisons between the experiments and Large Eddy Simulations using actuator disk model for the wind turbines are carried out in order to help validate the CFD model. Work supported by NSF (grants CBET-113380 and IIA-1243482, the WINDINSPIRE project) and by ERC (ActiveWindFarms, grant no. 306471).

  5. Laboratory astrophysics

    SciTech Connect

    Springer, P.T.; Goldstein, W.H.; Iglesias, C.A.; Wilson, B.G.; Rogers, F.J.; Stewart, R.E.

    1995-05-01

    We propose an experiment to test opacity models for stellar atmospheres. Particularly important is to perform experiments at very low density and temperature where line shape treatments give large differences in Rosseland mean opacities for astrophysical mixtures, and to test the range of validity for the unresolved transition array treatments. Experimental requirements are ultra high spectral resolution combined with large homogenous plasma sources lasting tens of nanoseconds, and with Planckian radiation fields. These requirements dovetail nicely with emerging pulsed power capabilities. We propose a high resolution measurement of the frequency dependent opacity, for ultra low density iron plasmas in radiatively driven equilibrium plasmas.

  6. Protoplanetary disk formation and evolution models: DM Tau and GM Aur

    NASA Astrophysics Data System (ADS)

    Hueso, R.; Guillot, T.

    2002-09-01

    We study the formation and evolution of protoplanetary disks using an axisymmetric turbulent disk model. We compare model results with observational parameters derived for the DM Tau and GM Aur systems. These are relatively old T Tauri stars with large and massive protoplanetary disks. Early disk formation is studied in the standard scenario of slowly rotating isothermal collapsing spheres and is strongly dependent on the initial angular momentum and the collapse accretion rate. The viscous evolution of the disk is integrated in time using the classical Alpha prescription of turbulence. We follow the temporal evolution of the disks until their characteristics fit the observed characteristics of DM Tau and GM Aur. We therefore obtain the set of model parameters that are able to explain the present state of these disks. We also study the disk evolution under the Beta parameterization of turbulence, recently proposed for sheared flows on protoplanetary disks. Both parameterizations allow explaining the present state of both DM Tau and GM Aur. We infer a value of Alpha between 5x10-3 to 0.02 for DM Tau and one order of magnitude smaller for GM Aur. Values of the Beta parameter are in accordance with theoretical predictions of Beta around 2x10-5 but with a larger dispersion on other model parameters, which make us favor the Alpha parameterization of turbulence. Implications for planetary system development in these systems are presented. In particular, GM Aur is a massive and slowly evolving disk where conditions are very favorable for planetesimal growth. The large value of present disk mass and the relatively small observed accretion rate of this system may also be indicative of the presence of an inner gas giant planet. Acknowledgements: This work has been supported by Programme Nationale de Planetologie. R. Hueso acknowledges a post-doctoral fellowship from Gobierno Vasco.

  7. Searching for inflation in simple string theory models: An astrophysical perspective

    NASA Astrophysics Data System (ADS)

    Hertzberg, Mark P.; Tegmark, Max; Kachru, Shamit; Shelton, Jessie; Özcan, Onur

    2007-11-01

    Attempts to connect string theory with astrophysical observation are hampered by a jargon barrier, where an intimidating profusion of orientifolds, Kähler potentials, etc. dissuades cosmologists from attempting to work out the astrophysical observables of specific string theory solutions from the recent literature. We attempt to help bridge this gap by giving a pedagogical exposition with detailed examples, aimed at astrophysicists and high energy theorists alike, of how to compute predictions for familiar cosmological parameters when starting with a 10-dimensional string theory action. This is done by investigating inflation in string theory, since inflation is the dominant paradigm for how early universe physics determines cosmological parameters. We analyze three explicit string models from the recent literature, each containing an infinite number of vacuum solutions. Our numerical investigation of some natural candidate inflatons, the so-called “moduli fields,” fails to find inflation. We also find in the simplest models that, after suitable field redefinitions, vast numbers of these vacua differ only in an overall constant multiplying the effective inflaton potential, a difference which affects neither the potential’s shape nor its ability to support slow-roll inflation. This illustrates that even having an infinite number of vacua does not guarantee having inflating ones. This may be an artifact of the simplicity of the models that we study. Instead, more complicated string theory models appear to be required, suggesting that identifying the inflating subset of the string landscape will be challenging.

  8. Power-law Wrinkling Turbulence-Flame Interaction Model for Astrophysical Flames

    NASA Astrophysics Data System (ADS)

    Jackson, Aaron P.; Townsley, Dean M.; Calder, Alan C.

    2014-04-01

    We extend a model for turbulence-flame interactions (TFI) to consider astrophysical flames with a particular focus on combustion in Type Ia supernovae. The inertial range of the turbulent cascade is nearly always under-resolved in simulations of astrophysical flows, requiring the use of a model in order to quantify the effects of subgrid-scale wrinkling of the flame surface. We provide implementation details to extend a well-tested TFI model to low-Prandtl number flames for use in the compressible hydrodynamics code FLASH. A local, instantaneous measure of the turbulent velocity is calibrated for FLASH and verification tests are performed. Particular care is taken to consider the relation between the subgrid rms turbulent velocity and the turbulent flame speed, especially for high-intensity turbulence where the turbulent flame speed is not expected to scale with the turbulent velocity. Finally, we explore the impact of different TFI models in full-star, three-dimensional simulations of Type Ia supernovae.

  9. Power-law wrinkling turbulence-flame interaction model for astrophysical flames

    SciTech Connect

    Jackson, Aaron P.; Townsley, Dean M.; Calder, Alan C.

    2014-04-01

    We extend a model for turbulence-flame interactions (TFI) to consider astrophysical flames with a particular focus on combustion in Type Ia supernovae. The inertial range of the turbulent cascade is nearly always under-resolved in simulations of astrophysical flows, requiring the use of a model in order to quantify the effects of subgrid-scale wrinkling of the flame surface. We provide implementation details to extend a well-tested TFI model to low-Prandtl number flames for use in the compressible hydrodynamics code FLASH. A local, instantaneous measure of the turbulent velocity is calibrated for FLASH and verification tests are performed. Particular care is taken to consider the relation between the subgrid rms turbulent velocity and the turbulent flame speed, especially for high-intensity turbulence where the turbulent flame speed is not expected to scale with the turbulent velocity. Finally, we explore the impact of different TFI models in full-star, three-dimensional simulations of Type Ia supernovae.

  10. MODELING MID-INFRARED VARIABILITY OF CIRCUMSTELLAR DISKS WITH NON-AXISYMMETRIC STRUCTURE

    SciTech Connect

    Flaherty, K. M.; Muzerolle, J.

    2010-08-20

    Recent mid-infrared observations of young stellar objects have found significant variations possibly indicative of changes in the structure of the circumstellar disk. Previous models of this variability have been restricted to axisymmetric perturbations in the disk. We consider simple models of a non-axisymmetric variation in the inner disk, such as a warp or a spiral wave. We find that the precession of these non-axisymmetric structures produces negligible flux variations but a change in the height of these structures can lead to significant changes in the mid-infrared flux. Applying these models to observations of the young stellar object LRLL 31 suggests that the observed variability could be explained by a warped inner disk with variable scale height. This suggests that some of the variability observed in young stellar objects could be explained by non-axisymmetric disturbances in the inner disk and this variability would be easily observable in future studies.

  11. Simulating the Timescale-Dependent Color Variation in Quasars with a Revised Inhomogeneous Disk Model

    NASA Astrophysics Data System (ADS)

    Cai, Zhen-Yi; Wang, Jun-Xian; Gu, Wei-Min; Sun, Yu-Han; Wu, Mao-Chun; Huang, Xing-Xing; Chen, Xiao-Yang

    2016-07-01

    The UV–optical variability of active galactic nuclei and quasars is useful for understanding the physics of the accretion disk and is gradually being attributed to stochastic fluctuations over the accretion disk. Quasars generally appear bluer when they brighten in the UV–optical bands; the nature of this phenomenon remains controversial. Recently, Sun et al. discovered that the color variation of quasars is timescale-dependent, in the way that faster variations are even bluer than longer term ones. While this discovery can directly rule out models that simply attribute the color variation to contamination from the host galaxies, or to changes in the global accretion rates, it favors the stochastic disk fluctuation model as fluctuations in the inner-most hotter disk could dominate the short-term variations. In this work, we show that a revised inhomogeneous disk model, where the characteristic timescales of thermal fluctuations in the disk are radius-dependent (i.e., τ ˜ r; based on that originally proposed by Dexter & Agol), can reproduce well a timescale-dependent color variation pattern, similar to the observed one and unaffected by the uneven sampling and photometric error. This demonstrates that one may statistically use variation emission at different timescales to spatially resolve the accretion disk in quasars, thus opening a new window with which to probe and test the accretion disk physics in the era of time domain astronomy. Caveats of the current model, which ought to be addressed in future simulations, are discussed.

  12. Computer Model Shows a Disk Galaxy's Life History

    NASA Video Gallery

    This cosmological simulation follows the development of a single disk galaxy over about 13.5 billion years, from shortly after the Big Bang to the present time. Colors indicate old stars (red), you...

  13. Model scattering envelopes of young stellar objects. I - Method and application to circumstellar disks

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara A.; Hartmann, Lee

    1992-01-01

    We describe a Monte Carlo code that accurately treats multiple scattering, absorption, and polarization by dust, and use this code to calculate images of dusty disks around young stellar objects. We present some approximate analytic results that describe the behavior of the Monte Carlo calculations. A geometrically thin disk illuminated by a central T Tauri star scatters very little light at distances of many AU from the star. Viewed at any inclination, the flux scattered by such a disk at the distance to the nearest star-forming region will be overwhelmed by the stellar image. An optically thick disk that has a flaring surface may be observable, especially if viewed nearly edge-on so that the stellar source becomes occulted. An optically thin disk with a finite opening angle, similar to the one surrounding beta Pictoris, is about as observable as the typical flared optically thick disk at a similar distance from the earth. The polarization position angle is perpendicular to the disk plane in all of the models, in contrast to observations of many young stellar objects which have the position angle oriented parallel to the presumed disk plane. We suggest that the scattered light structures observed around many premain-sequence objects are dusty envelopes rather than disks.

  14. Stability of general-relativistic accretion disks

    NASA Astrophysics Data System (ADS)

    Korobkin, Oleg; Abdikamalov, Ernazar B.; Schnetter, Erik; Stergioulas, Nikolaos; Zink, Burkhard

    2011-02-01

    Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios such as binary neutron star and black hole-neutron star coalescences, as well as the core collapse of massive stars. We explore the stability of such disks against runaway and nonaxisymmetric instabilities using three-dimensional hydrodynamics simulations in full general relativity using the Thor code. We model the disk matter using the ideal fluid approximation with a Γ-law equation of state with Γ=4/3. We explore three disk models around nonrotating black holes with disk-to-black hole mass ratios of 0.24, 0.17, and 0.11. Because of metric blending in our initial data, all of our initial models contain an initial axisymmetric perturbation which induces radial disk oscillations. Despite these oscillations, our models do not develop the runaway instability during the first several orbital periods. Instead, all of the models develop unstable nonaxisymmetric modes on a dynamical time scale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the nonaxisymmetric mode with azimuthal number m=1 is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the m=1 mode in some cases. Overall, our simulations show that the properties of the unstable nonaxisymmetric modes in our disk models are qualitatively similar to those in the Newtonian theory.

  15. Stability of general-relativistic accretion disks

    SciTech Connect

    Korobkin, Oleg; Abdikamalov, Ernazar B.; Schnetter, Erik; Stergioulas, Nikolaos; Zink, Burkhard

    2011-02-15

    Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios such as binary neutron star and black hole-neutron star coalescences, as well as the core collapse of massive stars. We explore the stability of such disks against runaway and nonaxisymmetric instabilities using three-dimensional hydrodynamics simulations in full general relativity using the Thor code. We model the disk matter using the ideal fluid approximation with a {Gamma}-law equation of state with {Gamma}=4/3. We explore three disk models around nonrotating black holes with disk-to-black hole mass ratios of 0.24, 0.17, and 0.11. Because of metric blending in our initial data, all of our initial models contain an initial axisymmetric perturbation which induces radial disk oscillations. Despite these oscillations, our models do not develop the runaway instability during the first several orbital periods. Instead, all of the models develop unstable nonaxisymmetric modes on a dynamical time scale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the nonaxisymmetric mode with azimuthal number m=1 is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the m=1 mode in some cases. Overall, our simulations show that the properties of the unstable nonaxisymmetric modes in our disk models are qualitatively similar to those in the Newtonian theory.

  16. Promoting the Understanding of Scientific Reasoning, Mathematical Modeling and Data Analysis: A Course for Astrophysics Majors

    NASA Astrophysics Data System (ADS)

    Robbins, Dennis; Ford, S.

    2014-01-01

    The NSF-supported “AstroCom NYC” program, a collaboration of the City University of New York, American Museum of Natural History (AMNH), and Columbia University has the explicit goal of increasing the participation of underrepresented minorities in astronomy and astrophysics by providing pedagogical mentoring and research experiences to undergraduate students. To supplement AstroCom scholars' undergraduate course work, and as a gateway to summer astrophysics research opportunities, we implemented a course called “Methods of Scientific Research” (MSR). The semester-long MSR course emphasizes the study of data using computers and other digital tools in a laboratory environment that encourages collaborative and active learning. We enroll early physical science majors and deliberately seek to inculcate habits of mind needed for science research, including assigning physical meaning to variables and measurements; engaging in mathematical modeling; quantifying error; eliminating bias; proposing hypotheses; creating predictions; testing predictions. Using laptop computers interfaced with probeware, students collect and analyze data using graphing software. Students study concepts such as motion, temperature, magnetism, electricity, gas pressure, and force with open-ended investigations where large data sets can be readily collected and replicated during a course meeting. Students are guided to examine data for patterns and trends, to make meaning of descriptive statistics such as means, standard deviations, maximum and minimum values, correlation coefficients and root mean square error values, and in general to understand, judge, and describe the studied phenomena based on data. A secondary goal of the course is to familiarize students with the facilities at AMNH, where they will do summer research as part of AstroCom NYC, in an effort to build a sense of belonging and to help them begin to self-identify as a scientist. We will discuss some our activities and

  17. Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim

    NASA Astrophysics Data System (ADS)

    Shafter, A. W.; Misselt, K. A.

    2006-06-01

    Multicolor (BVRI) light curves of the eclipsing classical nova V Per are presented, and a total of 12 new eclipse timings are measured for the system. When combined with previous eclipse timings from the literature, these timings yield a revised ephemeris for the times of mideclipse given by HJD=2,447,442.8260(1)+0.107123474(3)E. The eclipse profiles are analyzed with a parameter-fitting model that assumes four sources of luminosity: a white dwarf primary star, a main-sequence secondary star, a flared accretion disk with a rim, and a bright spot at the intersection of the mass transfer stream and the disk periphery. Model parameters include the temperatures of the white dwarf (T1) and the secondary star (T2), the radius (Rd) and temperature (Td), of the disk periphery, the inner disk radius (Rin), the disk power-law temperature exponent (α) and thickness (hr), and a bright spot temperature enhancement factor (χs). A matrix of model solutions are computed, covering an extensive range of plausible parameter values. The solution matrix is then explored to determine the optimum values for the fitting parameters and their associated errors. For models that treat the accretion disk as a flat structure without a rim, optimum fits require that the disk have a flat temperature profile. Although models with a truncated inner disk (Rin>>R1) result in a steeper temperature profile, steady state models with a temperature profile characterized by T(r)~r-3/4 are found only for models with a significant disk rim. A comparison of the observed brightness and color at mideclipse with the photometric properties of the best-fitting model suggests that V Per lies at a distance of ~1 kpc.

  18. Modeling self-subtraction in angular differential imaging: Application to the HD 32297 debris disk

    SciTech Connect

    Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.; Kalas, Paul

    2014-01-01

    We present a new technique for forward-modeling self-subtraction of spatially extended emission in observations processed with angular differential imaging (ADI) algorithms. High-contrast direct imaging of circumstellar disks is limited by quasi-static speckle noise, and ADI is commonly used to suppress those speckles. However, the application of ADI can result in self-subtraction of the disk signal due to the disk's finite spatial extent. This signal attenuation varies with radial separation and biases measurements of the disk's surface brightness, thereby compromising inferences regarding the physical processes responsible for the dust distribution. To compensate for this attenuation, we forward model the disk structure and compute the form of the self-subtraction function at each separation. As a proof of concept, we apply our method to 1.6 and 2.2 μm Keck adaptive optics NIRC2 scattered-light observations of the HD 32297 debris disk reduced using a variant of the 'locally optimized combination of images' algorithm. We are able to recover disk surface brightness that was otherwise lost to self-subtraction and produce simplified models of the brightness distribution as it appears with and without self-subtraction. From the latter models, we extract radial profiles for the disk's brightness, width, midplane position, and color that are unbiased by self-subtraction. Our analysis of these measurements indicates a break in the brightness profile power law at r ≈ 110 AU and a disk width that increases with separation from the star. We also verify disk curvature that displaces the midplane by up to 30 AU toward the northwest relative to a straight fiducial midplane.

  19. Modeling Self-subtraction in Angular Differential Imaging: Application to the HD 32297 Debris Disk

    NASA Astrophysics Data System (ADS)

    Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.; Kalas, Paul

    2014-01-01

    We present a new technique for forward-modeling self-subtraction of spatially extended emission in observations processed with angular differential imaging (ADI) algorithms. High-contrast direct imaging of circumstellar disks is limited by quasi-static speckle noise, and ADI is commonly used to suppress those speckles. However, the application of ADI can result in self-subtraction of the disk signal due to the disk's finite spatial extent. This signal attenuation varies with radial separation and biases measurements of the disk's surface brightness, thereby compromising inferences regarding the physical processes responsible for the dust distribution. To compensate for this attenuation, we forward model the disk structure and compute the form of the self-subtraction function at each separation. As a proof of concept, we apply our method to 1.6 and 2.2 μm Keck adaptive optics NIRC2 scattered-light observations of the HD 32297 debris disk reduced using a variant of the "locally optimized combination of images" algorithm. We are able to recover disk surface brightness that was otherwise lost to self-subtraction and produce simplified models of the brightness distribution as it appears with and without self-subtraction. From the latter models, we extract radial profiles for the disk's brightness, width, midplane position, and color that are unbiased by self-subtraction. Our analysis of these measurements indicates a break in the brightness profile power law at r ≈ 110 AU and a disk width that increases with separation from the star. We also verify disk curvature that displaces the midplane by up to 30 AU toward the northwest relative to a straight fiducial midplane.

  20. Constraints on black hole spins with a general relativistic accretion disk corona model

    NASA Astrophysics Data System (ADS)

    You, Bei; Cao, Xin-Wu; Yuan, Ye-Fei

    2016-04-01

    The peaks in the spectra of the accretion disks surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disk corona model, soft photons from the disk are Comptonized to high energy in the hot corona, and the hard X-ray spectra (luminosity and spectral shape) contain information on the incident spectra from the disk. The values of black hole spin parameter a* are inferred from the spectral fitting, which are spread over a large range, ∼ ‑0.94 to 0.998. We find that the inclination angles and mass accretion rates are well determined by the spectral fitting, but the results are sensitive to the accuracy of black hole mass estimates. No tight constraints on the black hole spins are achieved, if the uncertainties in black hole mass measurements are a factor of four, which are typical for the single-epoch reverberation mapping method. Recently, the accuracy of black hole mass measurement has been significantly improved to 0.2 – 0.4 dex with the velocity resolved reverberation mapping method. The black hole spin can be well constrained if the mass measurement accuracy is ≲ 50%. In the accretion disk corona scenario, a fraction of power dissipated in the disk is transported into the corona, and therefore the accretion disk is thinner than a bare disk for the same mass accretion rate, because the radiation pressure in the disk is reduced. We find that the thin disk approximation, H/R ≲ 0.1, is still valid if 0.3 < ṁ < 0.5, provided half of the dissipated power is radiated in the corona above the disk.

  1. Computational Astrophysics

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Astsatryan, H. V.

    2015-07-01

    Present astronomical archives that contain billions of objects, both Galactic and extragalactic, and the vast amount of data on them allow new studies and discoveries. Astrophysical Virtual Observatories (VO) use available databases and current observing material as a collection of interoperating data archives and software tools to form a research environment in which complex research programs can be conducted. Most of the modern databases give at present VO access to the stored information, which makes possible also a fast analysis and managing of these data. Cross-correlations result in revealing new objects and new samples. Very often dozens of thousands of sources hide a few very interesting ones that are needed to be discovered by comparison of various physical characteristics. VO is a prototype of Grid technologies that allows distributed data computation, analysis and imaging. Particularly important are data reduction and analysis systems: spectral analysis, SED building and fitting, modelling, variability studies, cross correlations, etc. Computational astrophysics has become an indissoluble part of astronomy and most of modern research is being done by means of it.

  2. Models that Teach about the Computer: AppleWorks and ProDOS, the Computer's Memory and Disk Storage.

    ERIC Educational Resources Information Center

    Niess, Margaret L.

    1989-01-01

    This final article in a series on creating models for teaching about computer memory and disk storage and retrieval focuses on AppleWorks software and the Professional Disk Operating System (ProDOS). Instructions for creating a paper model of the AppleWorks menu system and the ProDOS disk file are given. (LRW)

  3. A SMACK Model of Colliding Planetesimals in the β Pictoris Debris Disk

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika R.; Kuchner, Marc J.

    2015-12-01

    We present a new model of the β Pictoris disk-and-planet system that simulates both the planetesimal collisions and the dynamics of the resulting dust grains, allowing us to model features and asymmetries in both thermal and scattered light images of the disk. Our two-part model first simulates the collisional and dynamical evolution of the planetesimals with the Superparticle-Method Algorithm for Collisions in Kuiper belts and then simulates the dynamical evolution of the resulting dust grains with a standard Bulirsch-Stoer N-body integrator. Given the observed inclination and eccentricity of the β Pictoris b planet, the model neatly ties together several features of the disk: the central hole in the submillimeter images, the two-disk “x”-pattern seen in scattered light, and possibly even the clumpy gas seen by ALMA. We also find that most of the dust in the β Pictoris system is likely produced outside the ring at 60-100 AU. Instead of a birth ring, this disk has a “stirring ring” at 60-100 AU where the high-velocity collisions produced by the secular wave launched by the planet are concentrated. The two-disk x-pattern arises because collisions occur more frequently at the peaks and troughs of the secular wave. The perturbations of the disk in this region create an azimuthally and vertically asymmetric spatial distribution of collisions, which could yield an azimuthal clump of gas without invoking resonances or an additional planet.

  4. Accretion disk dynamics. α-viscosity in self-similar self-gravitating models

    NASA Astrophysics Data System (ADS)

    Kubsch, Marcus; Illenseer, Tobias F.; Duschl, Wolfgang J.

    2016-04-01

    Aims: We investigate the suitability of α-viscosity in self-similar models for self-gravitating disks with a focus on active galactic nuclei (AGN) disks. Methods: We use a self-similar approach to simplify the partial differential equations arising from the evolution equation, which are then solved using numerical standard procedures. Results: We find a self-similar solution for the dynamical evolution of self-gravitating α-disks and derive the significant quantities. In the Keplerian part of the disk our model is consistent with standard stationary α-disk theory, and self-consistent throughout the self-gravitating regime. Positive accretion rates throughout the disk demand a high degree of self-gravitation. Combined with the temporal decline of the accretion rate and its low amount, the model prohibits the growth of large central masses. Conclusions: α-viscosity cannot account for the evolution of the whole mass spectrum of super-massive black holes (SMBH) in AGN. However, considering the involved scales it seems suitable for modelling protoplanetary disks.

  5. Finite element simulation of an artificial intervertebral disk using fiber reinforced laminated composite model.

    PubMed

    Shahmohammadi, Mehrdad; Asgharzadeh Shirazi, Hadi; Karimi, Alireza; Navidbakhsh, Mahdi

    2014-10-01

    Degeneration of intervertebral disk (IVD) has been increased in recent years. The lumbar herniation can be cured using conservative and surgical procedures. Surgery is considered after failure of conservative treatment. Partial discectomy, fusion, and total disk replacement (TDR) are also common surgical treatments for degenerative disk disease. However, due to limitations and disadvantages of the current treatments, many studies have been carried out to approach the best design of mimicking natural disk. Recently, a new method of TDRs has been introduced using nature deformation of IVD by reinforced fibers of annulus fibrosis. Nonetheless, owing to limitations of experimental works on the human body, numerical studies of IVD may help to understand load transfer and biomechanical properties within the disks with reinforced fibers. In this study, a three-dimensional (3D) finite element model of the L2-L3 disk vertebrae unit with 12 vertical fibers embedded into annulus fibrosis was constructed. The IVD was subjected to compressive force, bending moment, and axial torsion. The most important parameters of disk failures were compared to that of experimental data. The results showed that the addition of reinforced fibers into the disk invokes a significant decrease of stress in the nucleus and annulus. The findings of this study may have implications not only for developing IVDs with reinforced fibers but also for the application of fiber reinforced IVD in orthopedics surgeries as a suitable implant. PMID:24981720

  6. Modeling dust growth in protoplanetary disks: The breakthrough case

    NASA Astrophysics Data System (ADS)

    Drążkowska, J.; Windmark, F.; Dullemond, C. P.

    2014-07-01

    Context. Dust coagulation in protoplanetary disks is one of the initial steps toward planet formation. Simple toy models are often not sufficient to cover the complexity of the coagulation process, and a number of numerical approaches are therefore used, among which integration of the Smoluchowski equation and various versions of the Monte Carlo algorithm are the most popular. Aims: Recent progress in understanding the processes involved in dust coagulation have caused a need for benchmarking and comparison of various physical aspects of the coagulation process. In this paper, we directly compare the Smoluchowski and Monte Carlo approaches to show their advantages and disadvantages. Methods: We focus on the mechanism of planetesimal formation via sweep-up growth, which is a new and important aspect of the current planet formation theory. We use realistic test cases that implement a distribution in dust collision velocities. This allows a single collision between two grains to have a wide range of possible outcomes but also requires a very high numerical accuracy. Results: For most coagulation problems, we find a general agreement between the two approaches. However, for the sweep-up growth driven by the "lucky" breakthrough mechanism, the methods exhibit very different resolution dependencies. With too few mass bins, the Smoluchowski algorithm tends to overestimate the growth rate and the probability of breakthrough. The Monte Carlo method is less dependent on the number of particles in the growth timescale aspect but tends to underestimate the breakthrough chance due to its limited dynamic mass range. Conclusions: We find that the Smoluchowski approach, which is generally better for the breakthrough studies, is sensitive to low mass resolutions in the high-mass, low-number tail that is important in this scenario. To study the low number density features, a new modulation function has to be introduced to the interaction probabilities. As the minimum resolution

  7. Modeling Circumstellar Disks of B-Type Stars with Observations from the Palomar Testbed Interferometer

    NASA Technical Reports Server (NTRS)

    Grzenia, B. J.; Tycner, C.; Jones, C. E.; Rinehart, S. A.; vanBelle, G. T.; Sigut, T. A. A.

    2013-01-01

    Geometrical (uniform disk) and numerical models were calculated for a set of B-emission (Be) stars observed with the Palomar Testbed Interferometer (PTI). Physical extents have been estimated for the disks of a total of15 stars via uniform disk models. Our numerical non-LTE models used parameters for the B0, B2, B5, and B8spectral classes and following the framework laid by previous studies, we have compared them to infrared K-band interferometric observations taken at PTI. This is the first time such an extensive set of Be stars observed with long-baseline interferometry has been analyzed with self-consistent non-LTE numerical disk models.

  8. MODELING CIRCUMSTELLAR DISKS OF B-TYPE STARS WITH OBSERVATIONS FROM THE PALOMAR TESTBED INTERFEROMETER

    SciTech Connect

    Grzenia, B. J.; Tycner, C.; Jones, C. E.; Sigut, T. A. A.; Rinehart, S. A.; Van Belle, G. T.

    2013-05-15

    Geometrical (uniform disk) and numerical models were calculated for a set of B-emission (Be) stars observed with the Palomar Testbed Interferometer (PTI). Physical extents have been estimated for the disks of a total of 15 stars via uniform disk models. Our numerical non-LTE models used parameters for the B0, B2, B5, and B8 spectral classes and following the framework laid by previous studies, we have compared them to infrared K-band interferometric observations taken at PTI. This is the first time such an extensive set of Be stars observed with long-baseline interferometry has been analyzed with self-consistent non-LTE numerical disk models.

  9. Comparison of central axis and jet ring coolant supply for turbine disk cooling on a SSME-HPOTP model

    NASA Technical Reports Server (NTRS)

    Kim, Y. W.; Metzger, D. E.

    1992-01-01

    The test facility, test methods and results are presented for an experimental study modeling the cooling of turbine disks in the blade attachment regions with multiple impinging jets, in a configuration simulating the disk cooling method employed on the Space Shuttle Main Engine oxygen turbopump. The study's objective was to provide a comparison of detailed local convection heat transfer rates obtained for a single center-supply of disk coolant with those obtained with the present flight configuration where disk coolant is supplied through an array of 19 jets located near the disk outer radius. Specially constructed disk models were used in a program designed to evaluate possible benefits and identify any possible detrimental effects involved in employing an alternate disk cooling scheme. The study involved the design, construction and testing of two full scale rotating model disks, one plane and smooth for baseline testing and the second contoured to the present flight configuration, together with the corresponding plane and contoured stator disks. Local heat transfer rates are determined from the color display of encapsulated liquid crystals coated on the disk in conjunction with use of a computer vision system. The test program was composed of a wide variety of disk speeds, flowrates, and geometrical configurations, including testing for the effects of disk boltheads and gas ingestion from the gas path region radially outboard of the disk-cavity.

  10. Scour around a perforated disk modeling a marine hydrokinetic device

    NASA Astrophysics Data System (ADS)

    Beninati, M. L.; Soliani, G.; Zhou, C. C.; Krane, M.; Fontaine, A.

    2013-12-01

    A study was conducted to investigate the behavior of scour hole dimensions and scour rates around a bottom-mounted cylindrical support structure of a perforated disk. The experiments focus on collecting temporal variations of scour depth around the support structure of the perforated disk for two scour regimes: transitional (ReD = 8500 and 9400) and live-bed (ReD = 10200). A perforated disk is used to approximate the drag of a submerged, horizontal axis, marine hydrokinetic (MHK) turbine. The goal is to compare the scour behavior around a perforated disk to that of a marine hydrokinetic (MHK) device. This study is motivated by the need to predict the environmental effect of MHK devices on an erodible bed. Testing is conducted in the small-scale hydraulic flume facility (1.2 m wide, 0.38 m deep, and 9.75 m long) at Bucknell University. The base of the support structure is marked incrementally to allow for time based observations of changes in scour depth. Bed form topologies are then acquired after a three hour time interval using a 2D sediment bed profiler. Experimental results show that scour rate is dependent on flow speed. Additionally, an increase in scour hole size occurs as the scour conditions are varied from transitional to live-bed.

  11. Magnetocentrifugally driven flows from young stars and disks. 1: A generalized model

    NASA Astrophysics Data System (ADS)

    Shu, Frank; Najita, Joan; Ostriker, Eve; Wilkin, Frank; Ruden, Steven; Lizano, Susana

    1994-07-01

    We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin of winds, jets, and bipolar outflows from young stellar objects. We consider the steady state dynamics of accretion of matter from a viscous and imperfectly conducting disk onto a young star with a strong magnetic field. For an aligned stellar magnetosphere, shielding currents in the surface layers of the disk prevent stellar field lines from penetrating the disk everywhere except for a range of radii about pi = Rx, where the Keplerian angular speed of rotation Omegax equals the angular speed of the star Omega*. For the low disk accretion rates and high magnetic fields associated with typical T Tauri stars, Rx exceeds the radius of the star R* by a factor of a few, and the inner disk is effectively truncated at a radius Rt somewhat smaller than Rx. Where the closed field lines between Rt and Rx bow sufficiently inward, the accreting gas attaches itself to the field and is funneled dynamically down the effective potential (gravitational plus centrifugal) onto the star. Contrary to common belief, the accompanying magnetic torques associated with this accreting gas may transfer angular momentum mostly to the disk rather than to the star. Thus, the star can spin slowly as long as Rx remains significantly greater than R*. Exterior to Rx field lines threading the disk bow outward, which makes the gas off the mid-plane rotate at super-Keplerian velocities. This combination drives a magnetocentrifugal wind with a mass-loss rate Mw equal to a definite fraction f of the disk accretion rate MD. For high disk accretion rates, Rx is forced down to the stellar surface, the star is spun to breakup, and the wind is generated in a manner identical to that proposed by Shu, Lizano, Ruden, & Najita in a previous communication to this journal. In two companion papers (II and III), we develop a detailed but idealized theory of the magnetocentrifugal acceleration process.

  12. An alternative model for the origin of gaps in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Regaly, Zsolt; Guedel, Manuel; Lin, Doug N. C.

    2016-03-01

    Aims: Motivated by recent observational and numerical studies suggesting that collapsing protostellar cores may be replenished from the local environment, we explore the evolution of protostellar cores submerged in the external counter-rotating environment. These models predict the formation of counter-rotating disks with a deep gap in the gas surface density separating the inner disk (corotating with the star) and the outer counter-rotating disk. The properties of these gaps are compared to those of planet-bearing gaps that form in disks hosting giant planets. Methods: We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment and numerical hydrodynamics simulations of isolated disks hosting giant planets to derive the properties of the gaps that form in both cases. Results: Our numerical simulations demonstrate that counter-rotating disks can form for a wide range of mass and angular momentum available in the local environment. The gap that separates both disks has a substantial depletion factor, can be located at a distance from ten to over a hundred AU from the star, and can propagate inward with velocity ranging from 1 AU Myr-1 to >100 AU Myr-1. Unlike our previous conclusion, the gap can therefore be a long-lived phenomenon that is, in some case, comparable to the lifetime of the disk itself. For a proper choice of the planetary mass, the viscous α-parameter and disk mass, the planet-bearing gaps and gaps in counter-rotating disks may show a remarkable similarity in the gas density profile and depletion factor, which may complicate their observational differentiation.

  13. Models of Be Star Disks Constrained by Long-baseline Interferometry

    NASA Astrophysics Data System (ADS)

    Tycner, Christopher; Jones, C. E.; Sigut, T. A.; Thomson, L.; Molak, A.

    2006-12-01

    We demonstrate how theoretical models of the circumstellar disks surrounding Be stars are constrained by interferometric observations that spatially resolve the circumstellar regions. The disk models are constructed using a non-LTE radiative transfer code developed by Sigut & Jones, which incorporates a number of improvements over previous treatments of the thermal structure, including a realistic chemical composition. We show that the disk models of three Be stars, κ Dra, υ Cyg, and β Psc agree with the interferometric observations only for particular ranges of the disk parameters, which results in specific density structure and temperature distribution constraints. C.T. acknowledges that this work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson Fellowship Program. JPL is managed for NASA by the California Institute of Technology. C. E. J. and T. A. A. S. acknowledge financial support from NSERC.

  14. Using FU Orionis outbursts to constrain self-regulated protostellar disk models

    NASA Technical Reports Server (NTRS)

    Bell, K. R.; Lin, D. N. C.

    1994-01-01

    One-dimensional, convective, vertical structure models and one dimensional time-dependent, radial diffusion models are combined to create a self-consistent picture in which FU Orionis outbursts occur in young stellar objects (YSOs) as the result of a large-scale, self-regulated, thermal ionization instability in the surrounding protostellar accretion disk. Although active accretion disks have long been postulated to be ubiqitous among low-mass YSOs, few constraints have until now been imposed on physical conditions in these disks. By fitting the results of time-dependent disk models to observed timescales of FU Orionis events, we estimate the magnitude of the effective viscous stress in the inner disk (r approximately less than 1 AU) to be, in accordance with an ad hoc 'alpha' prescription, the product of the local sound speed, pressure scale height, and an efficiency factor alpha of 10(exp -4) where hydrogen is neutral and 10(exp 3) where hydrogen is ionized. We hypothesize that all YSOs receive infall onto their outer disks which is steady (or slowly declining with time) and that FU Orionis outbursts are self-regulated, disk outbursts which occur only in systems which transport matter inward at a rate sufficiently high to cause hydrogen to be ionized in the inner disk. We estimate a critical mass flux of dm(sub crit)/dt = 5 x 10(exp 7) solar mass/yr independent of the magnitude of alpha for systems with one solar mass, three solar radius central objects. Infall accretion rates in the range of dm(sub in)/dt = 1-10) x 10(exp -6) solar mass/yr produce observed FU Orionis timescales consistent with estimates of spherical molecular cloud core collapse rates. Modeled ionization fronts are typically initiated near the inner edge of the disk and propogate out to a distance of several tens of stellar radii. Beyond this region, the disk transports mass steadily inward at the supplied constant infall rate. Mass flowing through the innermost disk annulus is equal to dm

  15. High Energy Astrophysics Tests of Lorentz Invariance and Quantum Gravity Models

    NASA Technical Reports Server (NTRS)

    Stecker, Floyd W.

    2011-01-01

    High-energy astrophysics observations provide the best possibilities to detect a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of approximately 10-35 m. I will discuss here the possible signatures of Lorentz invariance violation (LIV) from observations of the spectra, polarization, and timing of gamma-rays from active galactic nuclei and gamma-ray bursts. Other sensitive tests are provided by observations ofthe spectra of ultrahigh energy cosmic rays and neutrinos. Using the latest data from the Pierre Auger Observatory one can already derive an upper limit of 4.5 x 10(exp -23) to the amount of LIV at a proton Lorentz factor of -2 x 10(exp 11). This result has fundamental implications for quantum gravity models. I will also discuss the possibilities of using more sensitive space based detection techniques to improve searches for LIV in the future.

  16. The power of structural modeling of sub-grid scales - application to astrophysical plasmas

    NASA Astrophysics Data System (ADS)

    Georgiev Vlaykov, Dimitar; Grete, Philipp

    2015-08-01

    In numerous astrophysical phenomena the dynamical range can span 10s of orders of magnitude. This implies more than billions of degrees-of-freedom and precludes direct numerical simulations from ever being a realistic possibility. A physical model is necessary to capture the unresolved physics occurring at the sub-grid scales (SGS).Structural modeling is a powerful concept which renders itself applicable to various physical systems. It stems from the idea of capturing the structure of the SGS terms in the evolution equations based on the scale-separation mechanism and independently of the underlying physics. It originates in the hydrodynamics field of large-eddy simulations. We apply it to the study of astrophysical MHD.Here, we present a non-linear SGS model for compressible MHD turbulence. The model is validated a priori at the tensorial, vectorial and scalar levels against of set of high-resolution simulations of stochastically forced homogeneous isotropic turbulence in a periodic box. The parameter space spans 2 decades in sonic Mach numbers (0.2 - 20) and approximately one decade in magnetic Mach number ~(1-8). This covers the super-Alfvenic sub-, trans-, and hyper-sonic regimes, with a range of plasma beta from 0.05 to 25. The Reynolds number is of the order of 103.At the tensor level, the model components correlate well with the turbulence ones, at the level of 0.8 and above. Vectorially, the alignment with the true SGS terms is encouraging with more than 50% of the model within 30° of the data. At the scalar level we look at the dynamics of the SGS energy and cross-helicity. The corresponding SGS flux terms have median correlations of ~0.8. Physically, the model represents well the two directions of the energy cascade.In comparison, traditional functional models exhibit poor local correlations with the data already at the scalar level. Vectorially, they are indifferent to the anisotropy of the SGS terms. They often struggle to represent the energy

  17. Astrophysical site(s) of r-process elements in galactic chemodynamical evolution model

    NASA Astrophysics Data System (ADS)

    Hirai, Yutaka; Ishimaru, Yuhri; Saitoh, Takayuki R.; Fujii, Michiko S.; Hidaka, Jun; Kajino, Toshitaka

    2016-02-01

    Astrophysical site(s) of rapid neutron-capture process (r-process) is (are) not identified yet. Although core-collapse supernovae have been regarded as one of the possible candidates of the astrophysical site of r-process, nucleosynthesis studies suggest that serious difficulties in core-collapse supernovae to produce heavy elements with mass number of ≳110. Recent studies show that neutron star mergers (NSMs) can synthesize these elements due to their neutron rich environment. Some chemical evolution studies of the Milky Way halo, however, hardly reproduce the observed star-to-star scatters of the abundance ratios of r-process elements (e.g., Eu) in extremely metal-poor stars. This is because of their low rate (˜ 10-4 yr-1 for a Milky Way size galaxy) and long merger time (≳ 100 Myr). This problem might be solved if the stars in the Galactic halo are consisted of the stars formed in dwarf galaxies where the star formation efficiencies were very low. In this study, we carry out numerical simulations of galactic chemo-dynamical evolution using an N-body/smoothed particle hydrodynamics code. We construct detailed chemo-dynamical evolution model for the Local Group dwarf spheroidal galaxies (dSphs) assuming that the NSMs are the major source of r-process elements. Our models successfully reproduce the observed dispersion in [Eu/Fe] as a function of [Fe/H] if we set merger time of NSMs, ≲ 300 Myr with the Galactic NSM rate of ˜ 10-4 yr-1. In addition, our results are consistent with the observed metallicity distribution of dSphs. In the early phase (≲1 Gyr) of galaxy evolution is constant due to low star formation efficiency of dSphs. This study supports the idea that NSMs are the major site of r-process nucleosynthesis.

  18. Spectral Modeling in Astrophysics - The Physics of Non-equilibrium Clouds

    NASA Astrophysics Data System (ADS)

    Ferland, Gary; Williams, Robin

    2016-02-01

    Collisional-radiative spectral modeling plays a central role in astrophysics, probing phenomena ranging from the chemical evolution of the Universe to the energy production near supermassive black holes in distant quasars. The observed emission lines form in non-equilibrium clouds that have very low densities by laboratory standards, and are powered by energy sources which themselves are not in equilibrium. The spectrum is the result of a large number of microphysical processes, thermal statistics often do not apply, and analytical theory cannot be used. Numerical simulations are used to understand the physical state and the resulting spectrum. The greatest distinction between astrophysical modeling and conventional plasma simulations lies in the range of phenomena that must be considered. A single astronomical object will often have gas with kinetic temperatures of T˜10^6 K, 10^4 K, and T≤ 10^3 K, with the physical state ranging from molecular to fully ionized, and emitting over all wavelengths between the radio and x-ray. Besides atomic, plasma, and chemical physics, condensed matter physics is important because of the presence of small solid `grains' which affect the gas through catalytic reactions and the infrared emission they produce. The ionization, level populations, chemistry, and grain properties must be determined self-consistently, along with the radiation transport, to predict the observed spectrum. Although the challenge is great, so are the rewards. Numerical spectral simulations allow us to read the message contained in the spectrum emitted by objects far from the Earth that existed long ago.

  19. MODELING THE RESOLVED DISK AROUND THE CLASS 0 PROTOSTAR L1527

    SciTech Connect

    Tobin, John J.; Hartmann, Lee; Calvet, Nuria; Chiang, Hsin-Fang; Looney, Leslie W.; Wilner, David J.; Loinard, Laurent; D'Alessio, Paola

    2013-07-01

    We present high-resolution sub/millimeter interferometric imaging of the Class 0 protostar L1527 IRS (IRAS 04368+2557) at {lambda} = 870 {mu}m and 3.4 mm from the Submillimeter Array and Combined Array for Research in Millimeter Astronomy. We detect the signature of an edge-on disk surrounding the protostar with an observed diameter of 180 AU in the sub/millimeter images. The mass of the disk is estimated to be 0.007 M{sub Sun }, assuming optically thin, isothermal dust emission. The millimeter spectral index is observed to be quite shallow at all the spatial scales probed: {alpha} {approx} 2, implying a dust opacity spectral index {beta} {approx} 0. We model the emission from the disk and surrounding envelope using Monte Carlo radiative transfer codes, simultaneously fitting the sub/millimeter visibility amplitudes, sub/millimeter images, resolved L' image, spectral energy distribution, and mid-infrared spectrum. The best-fitting model has a disk radius of R = 125 AU, is highly flared (H{proportional_to}R {sup 1.3}), has a radial density profile {rho}{proportional_to}R {sup -2.5}, and has a mass of 0.0075 M{sub Sun }. The scale height at 100 AU is 48 AU, about a factor of two greater than vertical hydrostatic equilibrium. The resolved millimeter observations indicate that disks may grow rapidly throughout the Class 0 phase. The mass and radius of the young disk around L1527 are comparable to disks around pre-main-sequence stars; however, the disk is considerably more vertically extended, possibly due to a combination of lower protostellar mass, infall onto the disk upper layers, and little settling of {approx}1 {mu}m-sized dust grains.

  20. 1/f Fluctuation and a Many-Body Disk Model of Slip Phenomena

    NASA Astrophysics Data System (ADS)

    Hirata, Takayuki

    1999-10-01

    A many-body disk system was investigated as a model of slip phenomena. A two-dimensional many-body disk system was used as a model of the boundary layer between slip surfaces. Frustrated states occurred in this system depending on the disk configuration. Experiments with this were carried out using a random packing configuration (packing fraction: 0.74 ˜0.76). Acrylic resin disks were packed between a co-axial outer rotating cylinder and an inner fixed cylinder. The outer cylinder was rotated by a motor and the torque at the fixed inner cylinder was measured in a time series. Stick-slip and 1/f fluctuation were observed in the time series.

  1. Hydrodynamic Models of Line-Driven Accretion Disk Winds III: Local Ionization Equilibrium

    NASA Technical Reports Server (NTRS)

    Pereyra, Nicolas Antonio; Kallman, Timothy R.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We present time-dependent numerical hydrodynamic models of line-driven accretion disk winds in cataclysmic variable systems and calculate wind mass-loss rates and terminal velocities. The models are 2.5-dimensional, include an energy balance condition with radiative heating and cooling processes, and includes local ionization equilibrium introducing time dependence and spatial dependence on the line radiation force parameters. The radiation field is assumed to originate in an optically thick accretion disk. Wind ion populations are calculated under the assumption that local ionization equilibrium is determined by photoionization and radiative recombination, similar to a photoionized nebula. We find a steady wind flowing from the accretion disk. Radiative heating tends to maintain the temperature in the higher density wind regions near the disk surface, rather than cooling adiabatically. For a disk luminosity L (sub disk) = solar luminosity, white dwarf mass M(sub wd) = 0.6 solar mass, and white dwarf radii R(sub wd) = 0.01 solar radius, we obtain a wind mass-loss rate of M(sub wind) = 4 x 10(exp -12) solar mass yr(exp -1) and a terminal velocity of approximately 3000 km per second. These results confirm the general velocity and density structures found in our earlier constant ionization equilibrium adiabatic CV wind models. Further we establish here 2.5D numerical models that can be extended to QSO/AGN winds where the local ionization equilibrium will play a crucial role in the overall dynamics.

  2. Observations and models of deuterated H3+ in proto-planetary disks.

    PubMed

    Ceccarelli, Cecilia; Dominik, Carsten

    2006-11-15

    Young, gas-rich proto-planetary disks orbiting around solar-type young stars represent a crucial phase in disk evolution and planetary formation. Of particular relevance is to observationally track the evolution of the gas, which governs the overall evolution of the disk and is eventually dispersed. However, the bulk of the mass resides in the plane, which is so cold and dense that virtually all heavy-element-bearing molecules freeze out onto the dust grains and disappear from the gas phase. In this paper, we show that the ground-state ortho-H2D+ transition is the best, if not the only, tracer of the disk-plane gas. We report the theoretical models of the chemical structure of the plane of the disk, where the deuterated forms of H3+, including H2D+, play a major role. We also compare the theoretical predictions with the observations obtained towards the disk of the young star DM Tau and show that the ionization rate is probably enhanced there, perhaps owing to the penetration of X-rays from the central object through the disk plane. We conclude by remarking that the ground-state ortho-H2D+ transition is such a powerful diagnostic that it may also reveal the matter in the dark halos of external galaxies, if it is hidden in cold, dense and small clouds, as several theories predict. PMID:17015395

  3. Nonlinear dynamics of accretion disks with stochastic viscosity

    SciTech Connect

    Cowperthwaite, Philip S.; Reynolds, Christopher S.

    2014-08-20

    We present a nonlinear numerical model for a geometrically thin accretion disk with the addition of stochastic nonlinear fluctuations in the viscous parameter. These numerical realizations attempt to study the stochastic effects on the disk angular momentum transport. We show that this simple model is capable of reproducing several observed phenomenologies of accretion-driven systems. The most notable of these is the observed linear rms-flux relationship in the disk luminosity. This feature is not formally captured by the linearized disk equations used in previous work. A Fourier analysis of the dissipation and mass accretion rates across disk radii show coherence for frequencies below the local viscous frequency. This is consistent with the coherence behavior observed in astrophysical sources such as Cygnus X-1.

  4. MODELING THE HD 32297 DEBRIS DISK WITH FAR-INFRARED HERSCHEL DATA

    SciTech Connect

    Donaldson, J. K.; Lebreton, J.; Augereau, J.-C.; Krivov, A. V.

    2013-07-20

    HD 32297 is a young A-star ({approx}30 Myr) 112 pc away with a bright edge-on debris disk that has been resolved in scattered light. We observed the HD 32297 debris disk in the far-infrared and sub-millimeter with the Herschel Space Observatory PACS and SPIRE instruments, populating the spectral energy distribution (SED) from 63 to 500 {mu}m. We aimed to determine the composition of dust grains in the HD 32297 disk through SED modeling, using geometrical constraints from the resolved imaging to break the degeneracies inherent in SED modeling. We found the best fitting SED model has two components: an outer ring centered around 110 AU, seen in the scattered light images, and an inner disk near the habitable zone of the star. The outer disk appears to be composed of grains >2 {mu}m consisting of silicates, carbonaceous material, and water ice with an abundance ratio of 1:2:3 respectively and 90% porosity. These grains appear consistent with cometary grains, implying the underlying planetesimal population is dominated by comet-like bodies. We also discuss the 3.7{sigma} detection of [C II] emission at 158 {mu}m with the Herschel PACS instrument, making HD 32297 one of only a handful of debris disks with circumstellar gas detected.

  5. Modeling the HD 32297 Debris Disk With Far-Infrared Herschel Data

    NASA Technical Reports Server (NTRS)

    Donaldson, J.K.; Lebreton, J.; Roberge, A.; Augereau, J.-C.; Krivov, A. V.

    2013-01-01

    HD 32297 is a young A-star (approx. 30 Myr) 112 pc away with a bright edge-on debris disk that has been resolved in scattered light. We observed the HD 32297 debris disk in the far-infrared and sub-millimeter with the Herschel Space Observatory PACS and SPIRE instruments, populating the spectral energy distribution (SED) from 63 to 500 micron..We aimed to determine the composition of dust grains in the HD 32297 disk through SED modeling, using geometrical constraints from the resolved imaging to break the degeneracies inherent in SED modeling. We found the best fitting SED model has two components: an outer ring centered around 110 AU, seen in the scattered light images, and an inner disk near the habitable zone of the star. The outer disk appears to be composed of grains>2 micron consisting of silicates, carbonaceous material, and water ice with an abundance ratio of 1:2:3 respectively and 90% porosity. These grains appear consistent with cometary grains, implying the underlying planetesimal population is dominated by comet-like bodies. We also discuss the 3.7 sigma detection of [C ii] emission at 158 micron with the Herschel PACS instrument, making HD 32297 one of only a handful of debris disks with circumstellar gas detected

  6. HERSCHEL PACS OBSERVATIONS AND MODELING OF DEBRIS DISKS IN THE TUCANA-HOROLOGIUM ASSOCIATION

    SciTech Connect

    Donaldson, J. K.; Roberge, A.; Chen, C. H.; Augereau, J.-C.; Menard, F.; Eiroa, C.; Meeus, G.; Krivov, A. V.; Mathews, G. S.; Riviere-Marichalar, P.; Sandell, G.

    2012-07-10

    We present Herschel PACS photometry of 17 B- to M-type stars in the 30 Myr old Tucana-Horologium Association. This work is part of the Herschel Open Time Key Programme 'Gas in Protoplanetary Systems'. 6 of the 17 targets were found to have infrared excesses significantly greater than the expected stellar IR fluxes, including a previously unknown disk around HD30051. These six debris disks were fitted with single-temperature blackbody models to estimate the temperatures and abundances of the dust in the systems. For the five stars that show excess emission in the Herschel PACS photometry and also have Spitzer IRS spectra, we fit the data with models of optically thin debris disks with realistic grain properties in order to better estimate the disk parameters. The model is determined by a set of six parameters: surface density index, grain size distribution index, minimum and maximum grain sizes, and the inner and outer radii of the disk. The best-fitting parameters give us constraints on the geometry of the dust in these systems, as well as lower limits to the total dust masses. The HD105 disk was further constrained by fitting marginally resolved PACS 70 {mu}m imaging.

  7. Important plasma problems in astrophysics

    SciTech Connect

    Kulsrud, R.M.

    1995-01-01

    In astrophysics, plasmas occur under very extreme conditions. For example there are ultra strong magnetic fields in neutron stars) relativistic plasmas around black holes and in jets, extremely energetic particles such as cosmic rays in the interstellar medium, extremely dense plasmas in accretion disks, and extremely large magnetic Reynold`s numbers in the interstellar medium. These extreme limits for astrophysical plasmas make plasma phenomena much simpler to analyze in astrophysics than in the laboratory. An understanding of such phenomena often results in an interesting way, by simply taking the extreme limiting case of a known plasma theory. I will describe one of the more exciting examples. I will attempt to convey the excitement I felt when I was first exposed to it. However, not all plasma astrophysical phenomena are so simple. There are certain important plasma phenomena in astrophysics, which have not been so easily resolved. In fact a resolution of them is blocking significant progress in astrophysical research. They have not yet yielded to attacks by theoretical astrophysicists nor to extensive numerical simulation. I will attempt to describe one of the more important of these plasma-astrophysical problems, and discuss why its resolution is so important to astrophysics. This significant example is fast, magnetic reconnection. Another significant example is the large-magnetic-Reynold`s-number MHD dynamos.

  8. Modeling of end-pumped Yb:YAG thin-disk lasers with nonuniform temperature distribution.

    PubMed

    Zhu, Guangzhi; Zhu, Xiao; Zhu, Changhong; Shang, Jianli; Wan, Hailin; Guo, Fei; Qi, Lijun

    2012-05-10

    A plane wave model with nonuniform temperature distribution in the thin-disk crystal is developed to describe the dynamic behavior of an end-pumped Yb:YAG thin-disk laser. A set of couple-rate equations and 2D stationary heat-conduction equations are derived. The stable temperature distribution in the disk crystal is calculated using a numerical iterative method. The analytic expression is capable of dealing with more practical laser systems than previous works on this subject as it allows for nonuniform temperature distribution in the disk crystal. Based on these results, we examined laser output intensity as a function of pump intensity, dopant concentration, resonator coupler reflectivity, crystal thickness and temperature of cooling liquid. PMID:22614469

  9. THE STRUCTURE OF PRE-TRANSITIONAL PROTOPLANETARY DISKS. I. RADIATIVE TRANSFER MODELING OF THE DISK+CAVITY IN THE PDS 70 SYSTEM

    SciTech Connect

    Dong Ruobing; Rafikov, Roman; Zhu Zhaohuan; Brandt, Timothy; Hashimoto, Jun; Whitney, Barbara; Kudo, Tomoyuki; Egner, S.; Guyon, O.; Hayano, Y.; Muto, Takayuki; McClure, Melissa K.; Wisniewski, John; Abe, L.; Brandner, W.; Feldt, M.; Goto, M.; Carson, J.; Grady, C.; Hayashi, M.; and others

    2012-12-01

    Through detailed radiative transfer modeling, we present a disk+cavity model to simultaneously explain both the spectral energy distribution (SED) and Subaru H-band polarized light imaging for the pre-transitional protoplanetary disk PDS 70. In particular, we are able to match not only the radial dependence but also the absolute scale of the surface brightness of the scattered light. Our disk model has a cavity 65 AU in radius, which is heavily depleted of sub-micron-sized dust grains, and a small residual inner disk that produces a weak but still optically thick near-IR excess in the SED. To explain the contrast of the cavity's edge in the Subaru image, a factor of {approx}1000 depletion for the sub-micron-sized dust inside the cavity is required. The total dust mass of the disk may be on the order of 10{sup -4} M {sub Sun }, only weakly constrained due to the lack of long-wavelength observations and the uncertainties in the dust model. The scale height of the sub-micron-sized dust is {approx}6 AU at the cavity edge, and the cavity wall is optically thick in the vertical direction at H-band. PDS 70 is not a member of the class of (pre-)transitional disks identified by Dong et al., whose members only show evidence of the cavity in the millimeter-size dust but not the sub-micron-sized dust in resolved images. The two classes of (pre-)transitional disks may form through different mechanisms, or they may simply be at different evolution stages in the disk-clearing process.

  10. A model of an X-ray-illuminated accretion disk and corona

    NASA Technical Reports Server (NTRS)

    Raymond, John C.

    1993-01-01

    The X-ray-illuminated surface of the accretion disk in a low-mass X-ray Binary (LMXRB) and the X-ray-heated corona above the disk produce optical, UV, and soft X-ray emission lines. This paper presents 1D models of the emission line spectra and the vertical temperature and density structures at different radii. The models include a detailed treatment of the important atomic processes and an escape probability treatment of radiative transfer. Soker and Raymond (1993) use the density structure predicted by these models for a 2D Monte Carlo simulation of the photon scattering in the accretion disk corona (ADC) to examine the effects of the ADC on the angular distribution of X-rays and the flux of X-rays incident on the outer disk. This paper concentrates on the emission line fluxes for various elemental abundances and disk parameters. The UV lines of the classic LMXRBs are consistent with the model predictions. Some CNO processing is necessary to account for the nitrogen and helium abundances in Sco X-1 and other LMXRBs. Comparison of the models with observed spectra also points to a soft X-ray component with luminosity comparable to the hard X-rays. The models predict a substantial luminosity in the group of highly ionized iron lines near 100 A.

  11. The Disk Wind Model and the Effect on the Virial Black Hole Mass Estimation

    NASA Astrophysics Data System (ADS)

    Yong, Suk Yee

    2015-09-01

    The current 'standard quasar model' consists of a central engine, accretion disk, and jet. However, these components cannot entirely explain some quasar spectral features, specifically, the presence of broad emission lines (BELs), which are assumed to originate from high velocity gas in the broad line region (BLR). The addition of a wind to the standard model provides a mechanism to drive the outflowing gas emanated from the accretion disk. The shape of the emission line profiles in the BLR, in particular, the velocity offsets and skewness for different viewing angles, are explored. The impact on the virial black hole mass calculation due to the quasar's orientation to the observer is also tested. The geometry of the BLR is modelled by implementing the wind component or the disk wind model. While the models are dependent on the specified parameters, they are able to qualitatively reproduce the predicted features of the emission lines.

  12. Monte Carlo models and analysis of galactic disk gamma-ray burst distributions

    NASA Technical Reports Server (NTRS)

    Hakkila, Jon

    1989-01-01

    Gamma-ray bursts are transient astronomical phenomena which have no quiescent counterparts in any region of the electromagnetic spectrum. Although temporal and spectral properties indicate that these events are likely energetic, their unknown spatial distribution complicates astrophysical interpretation. Monte Carlo samples of gamma-ray burst sources are created which belong to Galactic disk populations. Spatial analysis techniques are used to compare these samples to the observed distribution. From this, both quantitative and qualitative conclusions are drawn concerning allowed luminosity and spatial distributions of the actual sample. Although the Burst and Transient Source Experiment (BATSE) experiment on Gamma Ray Observatory (GRO) will significantly improve knowledge of the gamma-ray burst source spatial characteristics within only a few months of launch, the analysis techniques described herein will not be superceded. Rather, they may be used with BATSE results to obtain detailed information about both the luminosity and spatial distributions of the sources.

  13. Astrophysical Magnetic Fields and Topics in Galaxy Formation

    NASA Technical Reports Server (NTRS)

    Field, George B.

    1997-01-01

    The grant was used to support theoretical research on a variety of astro-physical topics falling broadly into those described by the proposal: galaxy formation, astrophysical magnetic fields, magnetized accretion disks in AGN, new physics, and other astrophysical problems. Work accomplished; references are to work authored by project personel.

  14. Three-dimensional radiative transfer calculations on an SIMD machine applied to accretion disks

    NASA Astrophysics Data System (ADS)

    Vath, H.

    We have developed a tool to solve the radiative transfer equation for a three-dimensional astrophysical object on the SIMD computer MasPar MP-1. With this tool we can rapidly calculate the image of such an object as seen from an arbitrary direction and at an arbitrary wavelength. Such images and spectra can then be used to directly compare observations with the model. This tool can be applied to many different areas in astrophysics, e.g., HI disks of galaxies and polarized radiative transfer of accretion columns onto white dwarfs. Here we use this tool to calculate the image and spectrum of a simple model of an accretion disk.

  15. SMACK: A New Algorithm for Modeling Collisions and Dynamics of Planetesimals in Debris Disks

    NASA Technical Reports Server (NTRS)

    Nesvold, Erika Rose; Kuchner, Marc J.; Rein, Hanno; Pan, Margaret

    2013-01-01

    We present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. We show that SMACK is stable to numerical viscosity and numerical heating over 10(exp 7) yr, and that it can reproduce analytic models of disk evolution. We use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit. Differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring.

  16. An interferometric study of the Fomalhaut inner debris disk. III. Detailed models of the exozodiacal disk and its origin

    NASA Astrophysics Data System (ADS)

    Lebreton, J.; van Lieshout, R.; Augereau, J.-C.; Absil, O.; Mennesson, B.; Kama, M.; Dominik, C.; Bonsor, A.; Vandeportal, J.; Beust, H.; Defrère, D.; Ertel, S.; Faramaz, V.; Hinz, P.; Kral, Q.; Lagrange, A.-M.; Liu, W.; Thébault, P.

    2013-07-01

    Context. Debris disks are thought to be extrasolar analogs to the solar system planetesimal belts. The star Fomalhaut harbors a cold debris belt at 140 AU comparable to the Edgeworth-Kuiper belt, as well as evidence of a warm dust component, unresolved by single-dish telescopes, which is suspected of being a bright analog to the solar system's zodiacal dust. Aims: Interferometric observations obtained with the VLTI/VINCI instrument and the Keck Interferometer Nuller have identified near- and mid-infrared excesses attributed respectively to hot and warm exozodiacal dust residing in the inner few AU of the Fomalhaut environment. We aim to characterize the properties of this double inner dust belt and to unveil its origin. Methods: We performed parametric modeling of the exozodiacal disk ("exozodi") using the GRaTeR radiative transfer code to reproduce the interferometric data, complemented by mid- to far-infrared photometric measurements from Spitzer and Herschel. A detailed treatment of sublimation temperatures was introduced to explore the hot population at the size-dependent sublimation rim. We then used an analytical approach to successively testing several source mechanisms for the dust and suspected parent bodies. Results: A good fit to the multiwavelength data is found by two distinct dust populations: (1) a population of very small (0.01 to 0.5 μm), hence unbound, hot dust grains confined in a narrow region (~0.1-0.3 AU) at the sublimation rim of carbonaceous material; (2) a population of bound grains at ~2 AU that is protected from sublimation and has a higher mass despite its fainter flux level. We propose that the hot dust is produced by the release of small carbon grains following the disruption of dust aggregates that originate in the warm component. A mechanism, such as gas braking, is required to further confine the small grains for a long enough time. In situ dust production could hardly be ensured for the age of the star, so we conclude that the

  17. Nuclear astrophysics

    SciTech Connect

    Haxton, W.C.

    1992-12-31

    The problem of core-collapse supernovae is used to illustrate the many connections between nuclear astrophysics and the problems nuclear physicists study in terrestrial laboratories. Efforts to better understand the collapse and mantle ejection are also motivated by a variety of interdisciplinary issues in nuclear, particle, and astrophysics, including galactic chemical evolution, neutrino masses and mixing, and stellar cooling by the emission of new particles. The current status of theory and observations is summarized.

  18. Nuclear astrophysics

    SciTech Connect

    Haxton, W.C.

    1992-01-01

    The problem of core-collapse supernovae is used to illustrate the many connections between nuclear astrophysics and the problems nuclear physicists study in terrestrial laboratories. Efforts to better understand the collapse and mantle ejection are also motivated by a variety of interdisciplinary issues in nuclear, particle, and astrophysics, including galactic chemical evolution, neutrino masses and mixing, and stellar cooling by the emission of new particles. The current status of theory and observations is summarized.

  19. Quasi-static model of collimated jets and radio lobes. I. Accretion disk and jets

    SciTech Connect

    Colgate, Stirling A.; Li, Hui; Fowler, T. Kenneth; Pino, Jesse

    2014-07-10

    This is the first of a series of papers showing that when an efficient dynamo can be maintained by accretion disks around supermassive black holes in active galactic nuclei, it can lead to the formation of a powerful, magnetic helix that could explain both the observed radio jet/lobe structures on very large scales and ultimately the enormous power inferred from the observed ultra-high-energy cosmic rays. In this work, we solve a set of one-dimensional equations similar to the steady-state standard accretion disk model, but now including the large-scale magnetic fields giving rises to jets. We find that the frequently made assumption that large-scale fields are frozen into the disk is fundamentally incorrect, due to the necessity for current and the accreting mass to flow perpendicular to magnetic flux surfaces. A correct treatment greatly simplifies the calculations, yielding fields that leave the disk nearly vertically with magnetic profiles uniquely determined by disk angular momentum conservation. Representative solutions of the magnetic fields in different radial regions of the disk surface are given, and they determine the overall key features in the jet structure and its dissipation, which will be the subjects of later papers.

  20. Shell model study on the astrophysical neutron capture of 8Li

    NASA Astrophysics Data System (ADS)

    Ma, Hai-Liang; Dong, Bao-Guo; Yan, Yu-Liang; Zhang, Xi-Zhen

    2012-09-01

    The astrophysical important neutron capture of 8Li is investigated by combining the shell model and potential model. Three effective interactions, SFO, PSDMK2 and PSDWBP are used to calculate the spectroscopic factors and reaction widths. For the resonant capture from 8Li to the first continuum state of 9Li , the three effective interactions give similar neutron partial widths, and they are well compared with the experimental results. However, the calculated photon widths are over 5 times less than the previous estimate. This will make the substantial difference that, at high temperature, the direct capture mechanism still dominates. The calculated capture rates generally agree well with the experimental data. The uncertainty of calculated cross-sections and capture rates mainly results from the different prediction of spectroscopic factors for the three effective interactions. The total neutron capture rates in our calculations are less than 4300 cm3 mole-1 s-1 for T 9 < 5 which confirms that the main reaction flow will proceed through the reaction 8Li ( α, n) 11B in the stellar environments.

  1. Period Analysis, Photometry, and Astrophysical Modelling of the Contact Eclipsing Binary BC Gruis

    NASA Astrophysics Data System (ADS)

    Moriarty, D. J. W.

    2016-06-01

    BC Gruis is a W UMa type contact binary system of the W-subtype with the primary minimum 0.1 magnitudes fainter than the secondary minimum. The period is currently 0.3073060 ± 0.0000001 days; it was 4 seconds longer prior to 2000. There were small modulations of 0.001 - 0.003 days in the Observed-Calculated diagram due to asymmetry in the light curves, most likely caused by star spots. An astrophysical model of the system was developed with the mass ratio of 1.16 determined from published spectral data. The best fit to light curves in B, V and I pass bands in 2014-9-30 was given by including 2 large cool star spots on the more massive, cooler component and 1 cool spot on the hotter star. In 2015-9-8, the asymmetry in the light curves was different and was modelled best with a hot spot on the more massive component at the neck joining the stars and 1 cool spot on the other component.

  2. Circumnuclear Keplerian Disks in Galaxies

    NASA Astrophysics Data System (ADS)

    Bertola, Francesco; Cappellari, Michele; Funes, S. J., José G.; Corsini, Enrico M.; Pizzella, Alessandro; Beltrán, Juan C. Vega

    1998-12-01

    In this Letter, we demonstrate the possibility of inferring the presence of Keplerian gaseous disks using properly equipped optical ground-based telescopes. We have modeled the peculiar bidimensional shape of the emission lines in a sample of five early-type disk galaxies as due to the motion of a gaseous disk rotating in the combined potential of a central pointlike mass and of an extended stellar disk. The value of the central mass concentration estimated for four galaxies of the sample (NGC 2179, NGC 4343, NGC 4435, and NGC 4459) is ~109 Msolar. This value, according to the assumptions made in our model, is overestimated. However, we have calculated that the effect is well within the errors. For the remaining galaxy, NGC 5064, an upper limit of 5×107 Msolar is estimated. Based on observations carried out at ESO, La Silla, (Chile) (ESO N. 58, A-0564) and at the Mount Graham International Observatory (AZ) with the VATT: the Alice P. Lennon Telescope and the Thomas J. Bannan Astrophysics Facility.

  3. Improved reflection models of black hole accretion disks: Treating the angular distribution of X-rays

    SciTech Connect

    García, J.; Steiner, J. F.; McClintock, J. E.; Brenneman, L. E-mail: jsteiner@head.cfa.harvard.edu E-mail: lbrenneman@cfa.harvard.edu; and others

    2014-02-20

    X-ray reflection models are used to constrain the properties of the accretion disk, such as the degree of ionization of the gas and the elemental abundances. In combination with general relativistic ray tracing codes, additional parameters like the spin of the black hole and the inclination to the system can be determined. However, current reflection models used for such studies only provide angle-averaged solutions for the flux reflected at the surface of the disk. Moreover, the emission angle of the photons changes over the disk due to relativistic light bending. To overcome this simplification, we have constructed an angle-dependent reflection model with the XILLVER code and self-consistently connected it with the relativistic blurring code RELLINE. The new model, relxill, calculates the proper emission angle of the radiation at each point on the accretion disk and then takes the corresponding reflection spectrum into account. We show that the reflected spectra from illuminated disks follow a limb-brightening law highly dependent on the ionization of disk and yet different from the commonly assumed form I∝ln (1 + 1/μ). A detailed comparison with the angle-averaged model is carried out in order to determine the bias in the parameters obtained by fitting a typical relativistic reflection spectrum. These simulations reveal that although the spin and inclination are mildly affected, the Fe abundance can be overestimated by up to a factor of two when derived from angle-averaged models. The fit of the new model to the Suzaku observation of the Seyfert galaxy Ark 120 clearly shows a significant improvement in the constraint of the physical parameters, in particular by enhancing the accuracy in the inclination angle and the spin determinations.

  4. SMACK: A NEW ALGORITHM FOR MODELING COLLISIONS AND DYNAMICS OF PLANETESIMALS IN DEBRIS DISKS

    SciTech Connect

    Nesvold, Erika R.; Kuchner, Marc J.; Pan, Margaret; Rein, Hanno E-mail: Marc.Kuchner@nasa.gov E-mail: rein@ias.edu

    2013-11-10

    We present the Superparticle-Method/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in three dimensions, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. We show that SMACK is stable to numerical viscosity and numerical heating over 10{sup 7} yr and that it can reproduce analytic models of disk evolution. We use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit. Differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring.

  5. An Efficient Monte Carlo Method for Modeling Radiative Transfer in Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Kim, Stacy

    2011-01-01

    Monte Carlo methods have been shown to be effective and versatile in modeling radiative transfer processes to calculate model temperature profiles for protoplanetary disks. Temperatures profiles are important for connecting physical structure to observation and for understanding the conditions for planet formation and migration. However, certain areas of the disk such as the optically thick disk interior are under-sampled, or are of particular interest such as the snow line (where water vapor condenses into ice) and the area surrounding a protoplanet. To improve the sampling, photon packets can be preferentially scattered and reemitted toward the preferred locations at the cost of weighting packet energies to conserve the average energy flux. Here I report on the weighting schemes developed, how they can be applied to various models, and how they affect simulation mechanics and results. We find that improvements in sampling do not always imply similar improvements in temperature accuracies and calculation speeds.

  6. Molecular Astrophysics

    NASA Astrophysics Data System (ADS)

    Hartquist, T. W.

    2005-07-01

    Part I. Molecular Clouds and the Distribution of Molecules in the Milky Way and Other Galaxies: 1. Molecular clouds in the Milky Way P. Friberg and A. Hjalmarson; 2. Molecules in galaxies L. Blitz; Part II. Diffuse Molecular Clouds: 3. Diffuse cloud chemistry E. F. Van Dishoeck; 4. Observations of velocity and density structure in diffuse clouds W. D. Langer; 5. Shock chemistry in diffuse clouds T. W. Hartquist, D. R. Flower and G. Pineau des Forets; Part III. Quiescent Dense Clouds: 6. Chemical modelling of quiescent dense interstellar clouds T. J. Millar; 7. Interstellar grain chemistry V. Buch; 8. Large molecules and small grains in astrophysics S. H. Lepp; Part IV. Studies of Molecular Processes: 9. Molecular photoabsorption processes K. P. Kirby; 10. Interstellar ion chemistry: laboratory studies D. Smith, N. G. Adams and E. E. Ferguson; 11. Theoretical considerations on some collisional processes D. R. Bates; 12. Collisional excitation processes E. Roueff; 13. Neutral reactions at Low and High Temperatures M. M. Graff; Part V. Atomic Species in Dense Clouds: 14. Observations of atomic species in dense clouds G. J. Melnick; 15. Ultraviolet radiation in molecular clouds W. G. Roberge; 16. Cosmic ray induced photodissociation and photoionization of interstellar molecules R. Gredel; 17. Chemistry in the molecular cloud Barnard 5 S. B. Charnley and D. A. Williams; 18. Molecular cloud structure, motions, and evolution P. C. Myers; Part VI. H in Regions of Massive Star Formation: 19. Infrared observations of line emission from molecular hydrogen T. R. Geballe; 20. Shocks in dense molecular clouds D. F. Chernoff and C. F. McKee; 21. Dissociative shocks D. A. Neufeld; 22. Infrared molecular hydrogen emission from interstellar photodissociation regions A. Sternberg; Part VII. Molecules Near Stars and in Stellar Ejecta: 23. Masers J. M. Moran; 24. Chemistry in the circumstellar envelopes around mass-losing red giants M. Jura; 25. Atoms and molecules in supernova 1987a R

  7. High Energy Astrophysics Tests of Lorentz Invariance and Quantum Gravity Models

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.

    2011-01-01

    High energy astrophysics observations provide the best possibilities to detect a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of approximately 10(exp -35)m. I will discuss the possible signatures of Lorentz invariance violation (LIV) that can be manifested by observing of the spectra, polarization, and timing of gamma-rays from active galactic nuclei and y-ray bursts. Other sensitive tests are provided by observations of the spectra of ultrahigh energy cosmic rays and neutrinos. Using the latest data from the Pierre Auger Observatory one can already derive an upper limit of 4.5 x 10(exp -23) on the fraction of LIV at a Lorentz factor of approximately 2 x 10(exp 11). This result has fundamental implications for quantum gravity models. I will also discuss the possibilities of using more sensitive space-based detection techniques to improve searches for LIV in the future.

  8. High Energy Astrophysics Tests of Lorentz Invariance and Quantum Gravity Models

    NASA Technical Reports Server (NTRS)

    Stecker, Floyd W.

    2012-01-01

    High energy astrophysics observations provide the best possibilities to detect a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of approx.10(exp -35) m. I will discuss the possible signatures of Lorentz invariance violation (LIV) that can be manifested by observing of the spectra, polarization, and timing of gamma-rays from active galactic nuclei and gamma-ray bursts. Other sensitive tests are provided by observations of the spectra of ultrahigh energy cosmic rays and neutrinos. Using the latest data from the Pierre Auger Observatory one can already derive an upper limit of 4.5 x 10(exp -23) on the fraction of LIV at a Lorentz factor of approx. 2 x 10(exp 11). This result has fundamental implications for quantum gravity models. I will also discuss the possibilities of using more sensitive space-based detection techniques to improve searches for LIV in the future. I will also discuss how the LIV formalism casts doubt on the OPERA superluminal neutrino claim.

  9. Multi-scale/multi-physical modeling in head/disk interface of magnetic data storage

    NASA Astrophysics Data System (ADS)

    Chung, Pil Seung; Smith, Robert; Vemuri, Sesha Hari; Jhon, Young In; Tak, Kyungjae; Moon, Il; Biegler, Lorenz T.; Jhon, Myung S.

    2012-04-01

    The model integration of the head-disk interface (HDI) in the hard disk drive system, which includes the hierarchy of highly interactive layers (magnetic layer, carbon overcoat (COC), lubricant, and air bearing system (ABS)), has recently been focused upon to resolve technical barriers and enhance reliability. Heat-assisted magnetic recording especially demands that the model simultaneously incorporates thermal and mechanical phenomena by considering the enormous combinatorial cases of materials and multi-scale/multi-physical phenomena. In this paper, we explore multi-scale/multi-physical simulation methods for HDI, which will holistically integrate magnetic layers, COC, lubricants, and ABS in non-isothermal conditions.

  10. RADIATIVE TRANSFER MODELS OF A POSSIBLE PLANET IN THE AB AURIGAE DISK

    SciTech Connect

    Jang-Condell, Hannah; Kuchner, Marc J.

    2010-05-01

    Recent coronagraphic imaging of the AB Aurigae disk has revealed a region of low polarized scattered light suggestive of perturbations from a planet at a radius of {approx}100 AU. We model this darkened region using our fully non-plane-parallel radiative-transfer code combined with a simple hydrostatic equilibrium approximation to self-consistently solve for the structure of the disk surface as seen in scattered light. By comparing the observations to our models, we find that the observations are consistent with the absence of a planet, with an upper limit of 1 M {sub J}.

  11. Active Microwave Remote Sensing of a Natural, Tallgrass Prairie and a Projected Disk Component Model to Explain the Behavior of a Modified Dielectric Disk Model.

    NASA Astrophysics Data System (ADS)

    Martin, Robert David, Jr.

    C-band scatterometer measurements were made of a tallgrass prairie in an attempt to determine the degree of correlation between (1) the backscattering coefficient (sigma_sp{rm tr}{ circ}) and different expressions of soil moisture and (2) the backscattering coefficient and various canopy parameters. The findings of this study support those made in previous studies in terms of the optimum polarization and view angle selection for soil moisture work (i.e., near-nadir view angles and HH and VV polarizations). In contrast to previous studies, view angles of 30 ^circ and 45^circ also produced strong correlations with soil moisture. A moderately strong correlation and partial correlation was found between sigma_sp{rm tr}{circ} and leaf water potential, indicating some capability of C-band measurements to detect extremes in the water status of prairie vegetation under shallow soil conditions. Also, site differences due to burn treatments appeared to cause significant differences in the sensitivity of sigma_sp{ rm tr}{circ} to soil moisture. In a second study, the disk model developed by Drs. Eom and Fung was tested against a set of field measurements of sigma_sp{rm tr} {circ} from a crop of sunflowers. The model overestimated sigma_sp{ rm tr}{circ} at early growth stages, but decreased the overestimate as the crop matured. The author modified the model to accommodate canopies with non-uniform, continuous leaf angle distributions. The modification altered the shape of the response curve for predicted sigma_sp{rm tr }{circ} versus view angle, but failed to reduce the overestimate in the early growth states. Additional modifications (e.g., incorporating row structure information) may be necessary. A new model, called the Projected Disk Component Model (PDCM), was developed to help explain the behavior of the modified disk model (MDM). By reducing several types of theoretical disk canopies to a simple, quantitative measure of their constituent horizontal and vertical

  12. A semi-analytical model for exploring Galilean satellites formation from a massive disk

    NASA Astrophysics Data System (ADS)

    Miguel, Yamila; Ida, Shigeru

    2016-03-01

    A better knowledge of jovian satellites' origins will bring light on the environment that surrounded Jupiter during its formation and can help us to understand the characteristics of this unique satellite system. We developed a semi-analytical model to investigate Jupiter's regular satellite formation and present the results of our population synthesis calculations. We performed simulations adopting a massive, static, low-viscosity circumplanetary disk model, in agreement with a current study of magnetorotational instability in a circum-planetary disk. We find that the high gas density leads to very rapid migration of satellitesimals due to gas drag and type II migration of satellites in a faster disk-dominated mode. A large concentration of solids, large building blocks and longer type II migration time-scales favor formation and survival of large satellites. However, bodies as massive as Ganymede and those located far away from Jupiter, such as Callisto, are difficult to form with this scenario.

  13. High-Contrast Near-Infrared Imaging and Modeling of Planets and Debris Disks

    NASA Astrophysics Data System (ADS)

    Rodigas, Timothy; Hinz, P.; Weinberger, A. J.; Close, L. M.; Debes, J. H.

    2014-01-01

    wavelength range. These images reveal the disk at unprecedented detail, allowing detailed compositional and morphological modeling of the dust.

  14. Magnetocentrifugally driven flows from young stars and disks. 1: A generalized model

    NASA Technical Reports Server (NTRS)

    Shu, Frank; Najita, Joan; Ostriker, Eve; Wilkin, Frank; Ruden, Steven; Lizano, Susana

    1994-01-01

    We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin of winds, jets, and bipolar outflows from young stellar objects. We consider the steady state dynamics of accretion of matter from a viscous and imperfectly conducting disk onto a young star with a strong magnetic field. For an aligned stellar magnetosphere, shielding currents in the surface layers of the disk prevent stellar field lines from penetrating the disk everywhere except for a range of radii about pi = R(sub x), where the Keplerian angular speed of rotation Omega(sub x) equals the angular speed of the star Omega(sub *). For the low disk accretion rates and high magnetic fields associated with typical T Tauri stars, R(sub x) exceeds the radius of the star R(sub *) by a factor of a few, and the inner disk is effectively truncated at a radius R(sub t) somewhat smaller than R(sub x). Where the closed field lines between R(sub t) and R(sub x) bow sufficiently inward, the accreting gas attaches itself to the field and is funneled dynamically down the effective potential (gravitational plus centrifugal) onto the star. Contrary to common belief, the accompanying magnetic torques associated with this accreting gas may transfer angular momentum mostly to the disk rather than to the star. Thus, the star can spin slowly as long as R(sub x) remains significantly greater than R(sub *). Exterior to R(sub x) field lines threading the disk bow outward, which makes the gas off the mid-plane rotate at super-Keplerian velocities. This combination drives a magnetocentrifugal wind with a mass-loss rate M(sub w) equal to a definite fraction f of the disk accretion rate M(sub D). For high disk accretion rates, R(sub x) is forced down to the stellar surface, the star is spun to breakup, and the wind is generated in a manner identical to that proposed by Shu, Lizano, Ruden, & Najita in a previous communication to this journal. In two companion papers (II and III), we develop a

  15. Herniated disk

    MedlinePlus

    ... the disk. This may place pressure on nearby nerves or the spinal cord. ... Lumbar radiculopathy; Cervical radiculopathy; Herniated intervertebral disk; Prolapsed intervertebral disk; Slipped disk; Ruptured disk; Herniated nucleus pulposus

  16. MHD of accretion-disk flows

    NASA Astrophysics Data System (ADS)

    Yankova, Krasimira

    2015-01-01

    Accretion is one of the most important problems of astrophysics concerning the transfer of matter and the transformation of energy into space. Process represents a falling of the substance on a cosmic object from the surrounding area and is a powerful gravitational mechanism for the production of radiation. Accretion disc effectively converts the mass of the substance by viscous friction and released potential energy transformed into radiation by particle collisions. Accretion onto compact object shows high energy efficiency and temporal variability in a broad class of observational data in all ranges. In the disks of these objects are developed a series instabilities and structures that govern the distribution of the energy. They are expressed in many variety non-stationary phenomena that we observe. That is why we propose generalized model of magnetized accretion disk with advection, which preserves the nonlinearity of the problem. We study interaction of the plasmas flow with the magnetic field, and how this affects the self-organizing disk. The aim of the work is to describe the accretion flow in detail, in his quality of the open astrophysical system, to investigate the evolution and to reveal the mechanisms of the structuring the disk-corona system for to interpret correctly the high energy behavior of such sources.

  17. Accretion disk models for QSOs and active galactic nuclei - The role of magnetic viscosity

    NASA Technical Reports Server (NTRS)

    Sakimoto, P. J.; Coroniti, F. V.

    1981-01-01

    The inner regions of standard accretion disk models are known to be thermally unstable, and when scaled to quasar black hole masses, optically thin. Alternative accretion disk models are constructed under the assumption of a purely magnetic viscosity in the limiting cases of equipartition of gas and magnetic pressures and global flux conservation. The inner regions of these models are considerably denser than the standard model and therefore remain optically thick in all regions. The equipartition model is thermally stable throughout, while flux conservation leads to a localized thermal instability at the gas pressure/radiation pressure boundary and marginal stability as the radial distance approaches zero. The outer regions of quasar scaled accretion disks are strongly self-gravitating, leading to a vertical scale height which is smaller than that found in the inner region. Most of the outer region is gravitationally unstable, implying that the outer parts of galactic nuclei accretion disks are populated by dense self-gravitating gas clouds or possibly by stars.

  18. An Accretion Disk-outflow Model for Hysteretic State Transition in X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Cao, Xinwu

    2016-01-01

    We suggest a model of the advection-dominated accretion flow (ADAF) with magnetically driven outflows to explain the hysteretic state transition observed in X-ray binaries (XRBs). The transition from a thin disk to an ADAF occurs when the mass accretion rate is below a critical value. The critical mass accretion rate for the ADAF can be estimated by equating the equilibration timescale to the accretion timescale of the ADAF, which is sensitive to its radial velocity. The radial velocity of thin disks is very small, which leads to the advection of the external field in thin disks becoming very inefficient. ADAFs are present in the low/hard states of XRBs, and their radial velocity is large compared with the thin disk. The external field can be dragged inward efficiently by the ADAF, so a strong large-scale magnetic field threading the ADAF can be formed, which may accelerate a fraction of gas in the ADAF into the outflows. Such outflows may carry away a large amount of angular momentum from the ADAF, which significantly increases the radial velocity of the ADAF. This leads to a high critical mass accretion rate, below which an ADAF with magnetic outflows can survive. Our calculations show that the critical luminosity of the ADAF with magnetic outflows can be one order of magnitude higher than that for a conventional ADAF, if the ratio of gas to magnetic pressure β ∼ 4 in the disk. This can naturally explain the hysteretic state transition observed in XRBs.

  19. Spectropolarimetric test of the relativistic disk model for the broad emission lines of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Chen, Kaiyou; Halpern, Jules P.

    1990-01-01

    Previously, it was claimed that the broad emission lines of the radio galaxy Arp 102B can be fitted by the line profile from a simple relativistic Keplerian thin disk. It was argued that the lines originating from the relativistic accretion disk could be polarized due to electron scattering, which is likely to be the dominant opacity in the line-emitting region of Arp 102B. In the present work, the expected polarization properties of these broad emission lines are calculated. The percentage of polarization depends strongly on the inclination angle. For some angles, the red peak of the polarized, double-peaked line profile can be higher than the blue peak. This is in contrast to the total line profile, in which the blue peak is always higher than the red one. Spectropolarimetric observations could, therefore, provide an independent test of the relativistic disk model for the broad emission lines of Arp 102B and other active galactic nuclei.

  20. Ceramic Inclusions In Powder Metallurgy Disk Alloys: Characterization and Modeling

    NASA Technical Reports Server (NTRS)

    Bonacuse, Pete; Kantzos, Pete; Telesman, Jack

    2002-01-01

    Powder metallurgy alloys are increasingly used in gas turbine engines, especially as the material chosen for turbine disks. Although powder metallurgy materials have many advantages over conventionally cast and wrought alloys (higher strength, higher temperature capability, etc.), they suffer from the rare occurrence of ceramic defects (inclusions) that arise from the powder atomization process. These inclusions can have potentially large detrimental effect on the durability of individual components. An inclusion in a high stress location can act as a site for premature crack initiation and thereby considerably reduce the fatigue life. Because these inclusions are exceedingly rare, they usually don't reveal themselves in the process of characterizing the material for a particular application (the cumulative volume of the test bars in a fatigue life characterization is typically on the order of a single actual component). Ceramic inclusions have, however, been found to be the root cause of a number of catastrophic engine failures. To investigate the effect of these inclusions in detail, we have undertaken a study where a known population of ceramic particles, whose composition and morphology are designed to mimic the 'natural' inclusions, are added to the precursor powder. Surface connected inclusions have been found to have a particularly large detrimental effect on fatigue life, therefore the volume of ceramic 'seeds' added is calculated to ensure that a minimum number will occur on the surface of the fatigue test bars. Because the ceramic inclusions are irregularly shaped and have a tendency to break up in the process of extrusion and forging, a method of calculating the probability of occurrence and expected intercepted surface and embedded cross-sectional areas were needed. We have developed a Monte Carlo simulation to determine the distributions of these parameters and have verified the simulated results with observations of ceramic inclusions found in macro

  1. Multi-Color Model for the Protoplanetary Disks HL Tau and HD142527

    NASA Astrophysics Data System (ADS)

    Hanawa, Tomoyuki; Mochida, Kazuki

    2016-05-01

    Protoplanetary disks are circumstellar disks of gas and dust, from which planets may eventually form or be in the process of forming. Recent direct imaging of them has enabled us to derive the density and temperature distributions. Interestingly they often show quite different features depending on the wavelength observed. The near-infrared emission is dominated by scattering of stellar light while the mm- and submm- wave emissions are dominated by thermal dust emission. Thus, the near-infrared emission traces a low density surface layer where stellar light is scattered toward us. The mm- and submm- wave emission trace the high density part of the disk near the mid plane. In order to explain the wavelength- dependent images, we have constructed a passive disk model for HL Tau and HD142527. The former shows concentric rings in the ALMA image while the latter shows a highly asymmetric arc. Our models are based on the multi-color radiation transfer calculation. It takes account of radiation ranging from 100 nm to 3.16 mm. We used the M1 model to solve the radiative equilibrium. Our model gives some constraints on the optical properties of the dust.

  2. Self-Gravitating Eccentric Disk Models for the Double Nucleus of M31

    NASA Astrophysics Data System (ADS)

    Salow, Robert M.; Statler, Thomas S.

    2004-08-01

    We present new dynamical models of weakly self-gravitating, finite dispersion eccentric stellar disks around central black holes for the double nucleus of M31. The disk is fixed in a frame rotating at constant precession speed and is populated by stars on quasi-periodic orbits whose parents are numerically integrated periodic orbits in the total potential. A distribution of quasi-periodic orbits about a given parent is approximated by a distribution of Kepler orbits dispersed in eccentricity and orientation, using an approximate phase-space distribution function written in terms of the integrals of motion in the Kepler problem. We use these models, along with an optimization routine, to fit available published kinematics and photometry in the inner 2" of the nucleus. A grid of 24 best-fit models is computed to accurately constrain the mass of the central black hole and nuclear disk parameters. We find that the supermassive black hole in M31 has mass MBH=5.62+/-0.66×107 Msolar, which is consistent with the observed correlation between the central black hole mass and the velocity dispersion of its host spheroid. Our models precess rapidly, at Ω=36.5+/-4.2 km s-1 pc-1, and possess a characteristic radial eccentricity distribution, which gives rise to multimodal line-of-sight velocity distributions along lines of sight near the black hole. These features can be used as sensitive discriminants of disk structure.

  3. Model Selection and Parameter Estimation in Neutrino Cosmology and High Energy Astrophysics Around the Galactic Center

    NASA Astrophysics Data System (ADS)

    Canac, Nicolas

    Understanding the particle nature of dark matter and determining the properties of neutrinos remain two of the most important questions within the physics community. Both problems lie within the intersection between astrophysics and particle physics, a fact which gives rise to a rich set of independent and complementary approaches to making progress on both fronts. This thesis presents three works that attempt to construct models and constrain the properties of these particles using empirical data from a large host of astronomical observations. The first work uses observations from the Fermi Gamma-ray Space Telescope's Large Area Telescope (Fermi LAT) to construct empirical models of the diffuse gamma-ray background in the Galactic Center (GC). A new template associated with cosmic rays interacting with molecular gas is detected with high significance. Using this new template along with other known sources of gamma-ray emission in the GC, I find that the previously detected extended gamma-ray excess is still detected for all permutations of the background model, although its properties vary significantly within the observed range of models. The second work presents a detection of a new source of gamma-ray emission in the GC that traces the morphology of infrared starlight, again using observations from the Fermi LAT. I argue that this emission is likely due to the same source of cosmic rays responsible for producing the emission associated with the molecular gas template in the previous work, and further make the case that this population of cosmic rays could be produced by the same source responsible for the GC excess. The last work explores how derived neutrino parameter constraints depend on the assumed form of the primordial power spectrum, using constraints derived from a host of cosmological data sets, including cosmic microwave background, baryon acoustic oscillation, power spectrum, cluster counts, and hubble constant measurements. I find that for a model

  4. Model-independent determination of the astrophysical S factor in laser-induced fusion plasmas

    DOE PAGESBeta

    Lattuada, D.; Barbarino, M.; Bonasera, A.; Bang, W.; Quevedo, H. J.; Warren, M.; Consoli, F.; De Angelis, R.; Andreoli, P.; Kimura, S.; et al

    2016-04-19

    In this paper, we present a new and general method for measuring the astrophysical S factor of nuclear reactions in laser-induced plasmas and we apply it to 2H(d,n)3He. The experiment was performed with the Texas Petawatt Laser, which delivered 150–270 fs pulses of energy ranging from 90 to 180 J to D2 or CD4 molecular clusters (where D denotes 2H). After removing the background noise, we used the measured time-of-flight data of energetic deuterium ions to obtain their energy distribution. We derive the S factor using the measured energy distribution of the ions, the measured volume of the fusion plasma,more » and the measured fusion yields. This method is model independent in the sense that no assumption on the state of the system is required, but it requires an accurate measurement of the ion energy distribution, especially at high energies, and of the relevant fusion yields. In the 2H(d,n)3He and 3He(d,p)4He cases discussed here, it is very important to apply the background subtraction for the energetic ions and to measure the fusion yields with high precision. While the available data on both ion distribution and fusion yields allow us to determine with good precision the S factor in the d+d case (lower Gamow energies), for the d+3He case the data are not precise enough to obtain the S factor using this method. Our results agree with other experiments within the experimental error, even though smaller values of the S factor were obtained. This might be due to the plasma environment differing from the beam target conditions in a conventional accelerator experiment.« less

  5. Model-independent determination of the astrophysical S factor in laser-induced fusion plasmas

    NASA Astrophysics Data System (ADS)

    Lattuada, D.; Barbarino, M.; Bonasera, A.; Bang, W.; Quevedo, H. J.; Warren, M.; Consoli, F.; De Angelis, R.; Andreoli, P.; Kimura, S.; Dyer, G.; Bernstein, A. C.; Hagel, K.; Barbui, M.; Schmidt, K.; Gaul, E.; Donovan, M. E.; Natowitz, J. B.; Ditmire, T.

    2016-04-01

    In this work, we present a new and general method for measuring the astrophysical S factor of nuclear reactions in laser-induced plasmas and we apply it to :mmultiscripts>(d ,n )3He . The experiment was performed with the Texas Petawatt Laser, which delivered 150-270 fs pulses of energy ranging from 90 to 180 J to D2 or CD4 molecular clusters (where D denotes 2H ) . After removing the background noise, we used the measured time-of-flight data of energetic deuterium ions to obtain their energy distribution. We derive the S factor using the measured energy distribution of the ions, the measured volume of the fusion plasma, and the measured fusion yields. This method is model independent in the sense that no assumption on the state of the system is required, but it requires an accurate measurement of the ion energy distribution, especially at high energies, and of the relevant fusion yields. In the :mmultiscripts>(d ,n )3He and 3He(d ,p )4He cases discussed here, it is very important to apply the background subtraction for the energetic ions and to measure the fusion yields with high precision. While the available data on both ion distribution and fusion yields allow us to determine with good precision the S factor in the d +d case (lower Gamow energies), for the d +3He case the data are not precise enough to obtain the S factor using this method. Our results agree with other experiments within the experimental error, even though smaller values of the S factor were obtained. This might be due to the plasma environment differing from the beam target conditions in a conventional accelerator experiment.

  6. The Gaia-ESO Survey: Separating disk chemical substructures with cluster models. Evidence of a separate evolution in the metal-poor thin disk

    NASA Astrophysics Data System (ADS)

    Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.

    2016-02-01

    Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims: The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods: We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at RGC< 10 kpc) from the Gaia-ESO survey (GES) internal data release 2 (iDR2). We aim at decomposing it into data groups highlighting number density and/or slope variations in the abundance-metallicity plane. An independent sample of disk red clump stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) was used to cross-check the identified features. Results: We find that the sample is separated into five groups associated with major Galactic components; the metal-rich end of the halo, the thick disk, and three subgroups for the thin disk sequence. This is confirmed with the sample of red clump stars from APOGEE. The three thin disk groups served to explore this sequence in more detail. The two metal-intermediate and metal-rich groups of the thin disk decomposition ([Fe/H] > -0.25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] < -0.25 dex) is shifted to larger distances than those of the more metal-rich parts. Moreover, the metal-poor part of the thin disk presents indications of a scale height

  7. Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo

    SciTech Connect

    Stepanovs, Deniss; Fendt, Christian; Sheikhnezami, Somayeh E-mail: fendt@mpia.de

    2014-11-20

    We present MHD simulations exploring the launching, acceleration, and collimation of jets and disk winds. The evolution of the disk structure is consistently taken into account. Extending our earlier studies, we now consider the self-generation of the magnetic field by an α{sup 2}Ω mean-field dynamo. The disk magnetization remains on a rather low level, which helps to evolve the simulations for T > 10, 000 dynamical time steps on a domain extending 1500 inner disk radii. We find the magnetic field of the inner disk to be similar to the commonly found open field structure, favoring magneto-centrifugal launching. The outer disk field is highly inclined and predominantly radial. Here, differential rotation induces a strong toroidal component, which plays a key role in outflow launching. These outflows from the outer disk are slower, denser, and less collimated. If the dynamo action is not quenched, magnetic flux is continuously generated, diffuses outward through the disk, and fills the entire disk. We have invented a toy model triggering a time-dependent mean-field dynamo. The duty cycles of this dynamo lead to episodic ejections on similar timescales. When the dynamo is suppressed as the magnetization falls below a critical value, the generation of the outflows and also accretion is inhibited. The general result is that we can steer episodic ejection and large-scale jet knots by a disk-intrinsic dynamo that is time-dependent and regenerates the jet-launching magnetic field.

  8. Astrophysical S-factor for 6Li(ρ, γ)7Be in the coupled-channel Gamow shell model

    NASA Astrophysics Data System (ADS)

    Dong, G. X.; Fossez, K.; Michel, N.; Płoszajczak, M.

    2016-02-01

    We have applied the Gamow shell model (GSM) in the coupled-channel representation to study the astrophysical S-factor for the proton radiative capture reaction of 6Li. Reaction channels are built by coupling the proton wave function expanded in different partial waves with the GSM wave functions of the ground state (1+) and the excited states (31+, 01+ and 21+) of 6Li. All relevant E1, M1, and E2 transitions from the initial continuum states in 7Be to the final bound states (3/21- and 1/21-) are included. It is found that the calculated total astrophysical S factor for this reaction agrees well with the experimental data.

  9. Slotted-wall research with disk and parachute models in a low-speed wind tunnel

    SciTech Connect

    Macha, J.M.; Buffington, R.J.; Henfling, J.L. ); Every, D. Van; Harris, J.L. )

    1990-01-01

    An experimental investigation of slotted-wall blockage interference has been conducted using disk and parachute models in a low speed wind tunnel. Test section open area ratio, model geometric blockage ratio, and model location along the length of the test section were systematically varied. Resulting drag coefficients were compared to each other and to interference-free measurements obtained in a much larger wind tunnel where the geometric blockage ratio was less than 0.0025. 9 refs., 10 figs.

  10. Thermal modeling of head disk interface system in heat assisted magnetic recording

    SciTech Connect

    Vemuri, Sesha Hari; Seung Chung, Pil; Jhon, Myung S.; Min Kim, Hyung

    2014-05-07

    A thorough understanding of the temperature profiles introduced by the heat assisted magnetic recording is required to maintain the hotspot at the desired location on the disk with minimal heat damage to other components. Here, we implement a transient mesoscale modeling methodology termed lattice Boltzmann method (LBM) for phonons (which are primary carriers of energy) in the thermal modeling of the head disk interface (HDI) components, namely, carbon overcoat (COC). The LBM can provide more accurate results compared to conventional Fourier methodology by capturing the nanoscale phenomena due to ballistic heat transfer. We examine the in-plane and out-of-plane heat transfer in the COC via analyzing the temperature profiles with a continuously focused and pulsed laser beam on a moving disk. Larger in-plane hotspot widening is observed in continuously focused laser beam compared to a pulsed laser. A pulsed laser surface develops steeper temperature gradients compared to continuous hotspot. Furthermore, out-of-plane heat transfer from the COC to the media is enhanced with a continuous laser beam then a pulsed laser, while the temperature takes around 140 fs to reach the bottom surface of the COC. Our study can lead to a realistic thermal model describing novel HDI material design criteria for the next generation of hard disk drives with ultra high recording densities.

  11. Evolution of spiral galaxies. 3: Application of the multiphase model to the galactic disk

    NASA Astrophysics Data System (ADS)

    Ferrini, Federico; Molla, Mercedes; Pardi, Maria Chiara; Diaz, Angeles I.

    1994-06-01

    We present an application of the multiphase model of Ferrini and coworkers, developed for the solar neighborhood, to other regions of the disk of the Galaxy in order to reproduce the observed element abundance gradients. The model describes the Galaxy as a two-zone system (halo and disk) sliced into nine cylindrical concentric regions and studies the time evolution of the five populations which inhabit the Milky Way: diffuse gas, molecular clouds, low-mass (m less than 4 M solar masses) and high-mass stars, and stellar remnants. Our final aim is to reproduce the metallicity gradients that are observed in the Milky Way and in other external galaxies. We analyze the evolution of these gradients in time in order to relate their behavior to other galactic quantities such as the star formation rate and the infall rate. The model describes the Galaxy by fitting a large number of observational constraints: abundance gradients, age-metallicity relations for disk and halo, both gas and mass distributions (including radial differences in the characteristic shapes of atomic and molecular gas), and radial distribution and history of star formation rate. The time evolution of abundance gradients is computed, revealing a flattening of gradients with time. In particular, the oxygen abundance was steeper at early times as a consequence of a larger infall. Since the disk is evolving and the gas is consumed, a saturation level is reached in every ring and the gradient will decrease to a minimum value.

  12. Ceramic Inclusions in Powder Metallurgy Disk Alloys: Characterization and Modeling

    NASA Technical Reports Server (NTRS)

    Bonacuse, Peter J.

    2001-01-01

    Powder metallurgy alloys are increasingly used in gas turbine engines, especially in turbine disk applications. Although powder metallurgy materials have many advantages over conventionally cast and wrought alloys (higher strength, higher temperature capability, etc.), they suffer from the rare occurrence of ceramic defects (inclusions) that are inherent to the powder atomization process. These inclusions can have a potentially large detrimental effect on the durability of individual components. An inclusion in a high stress location can act as a site for premature crack initiation and thereby considerably reduce the fatigue life. Because these inclusions are exceedingly rare, they typically do not reveal themselves in the process of characterizing the material for a particular application (the cumulative volume of the test bars in a fatigue life characterization is typically on the order of a single actual component). Ceramic inclusions have, however, been found to be the root cause of a number of catastrophic engine failures. To investigate the effect of these inclusions in detail, we have undertaken a study where known populations of ceramic particles, whose composition and morphology are designed to mimic the "natural" inclusions, are added to the precursor powder. Surface-connected inclusions have been found to have a particularly large detrimental effect on fatigue life; therefore, the quantity of ceramic "seeds" added is calculated to ensure that a minimum number will intersect the surface of the fatigue test bars. Because the ceramic inclusions are irregularly shaped and have a tendency to break up in the process of extrusion and forging, a method of calculating the probability of occurrence and expected intercepted surface area was needed. We have developed a Monte Carlo simulation to determine the distributions of these parameters and have verified the simulated results with observations of ceramic inclusions found in macroscopic slices from extrusions

  13. Multitechnique testing of the viscous decretion disk model. I. The stable and tenuous disk of the late-type Be star β CMi

    NASA Astrophysics Data System (ADS)

    Klement, R.; Carciofi, A. C.; Rivinius, Th.; Panoglou, D.; Vieira, R. G.; Bjorkman, J. E.; Štefl, S.; Tycner, C.; Faes, D. M.; Korčáková, D.; Müller, A.; Zavala, R. T.; Curé, M.

    2015-12-01

    Context. The viscous decretion disk (VDD) model is able to explain most of the currently observable properties of the circumstellar disks of Be stars. However, more stringent tests, focusing on reproducing multitechnique observations of individual targets via physical modeling, are needed to study the predictions of the VDD model under specific circumstances. In the case of nearby, bright Be star β CMi, these circumstances are a very stable low-density disk and a late-type (B8Ve) central star. Aims: The aim is to test the VDD model thoroughly, exploiting the full diagnostic potential of individual types of observations, in particular, to constrain the poorly known structure of the outer disk if possible, and to test truncation effects caused by a possible binary companion using radio observations. Methods: We use the Monte Carlo radiative transfer code HDUST to produce model observables, which we compare with a very large set of multitechnique and multiwavelength observations that include ultraviolet and optical spectra, photometry covering the interval between optical and radio wavelengths, optical polarimetry, and optical and near-IR (spectro)interferometry. Results: A parametric VDD model with radial density exponent of n = 3.5, which is the canonical value for isothermal flaring disks, is found to explain observables typically formed in the inner disk, while observables originating in the more extended parts favor a shallower, n = 3.0, density falloff. Theoretical consequences of this finding are discussed and the outcomes are compared with the predictions of a fully self-consistent VDD model. Modeling of radio observations allowed for the first determination of the physical extent of a Be disk (35+10-5 stellar radii), which might be caused by a binary companion. Finally, polarization data allowed for an indirect measurement of the rotation rate of the star, which was found to be W ≳ 0.98, i.e., very close to critical. Based partly on observations from Ond

  14. Non-LTE spectral models for the gaseous debris-disk component of Ton 345

    NASA Astrophysics Data System (ADS)

    Hartmann, S.; Nagel, T.; Rauch, T.; Werner, K.

    2014-11-01

    Context. For a fraction of single white dwarfs with debris disks, an additional gaseous disk was discovered. Both dust and gas are thought to be created by the disruption of planetary bodies. Aims: The composition of the extrasolar planetary material can directly be analyzed in the gaseous disk component, and the disk dynamics might be accessible by investigating the temporal behavior of the Ca ii infrared emission triplet, hallmark of the gas disk. Methods: We obtained new optical spectra for the first helium-dominated white dwarf for which a gas disk was discovered (Ton 345) and modeled the non-LTE spectra of viscous gas disks composed of carbon, oxygen, magnesium, silicon, sulfur, and calcium with chemical abundances typical for solar system asteroids. Iron and its possible line-blanketing effects on the model structure and spectral energy distribution was still neglected. A set of models with different radii, effective temperatures, and surface densities as well as chondritic and bulk-Earth abundances was computed and compared with the observed line profiles of the Ca ii infrared triplet. Results: Our models suggest that the Ca ii emission stems from a rather narrow gas ring with a radial extent of R = 0.44-0.94 R⊙, a uniform surface density Σ = 0.3 g cm-2, and an effective temperature of Teff ≈ 6000 K. The often assumed chemical mixtures derived from photospheric abundances in polluted white dwarfs - similar to a chondritic or bulk-Earth composition - produce unobserved emission lines in the model and therefore have to be altered. We do not detect any line-profile variability on timescales of hours, but we confirm the long-term trend over the past decade for the red-blue asymmetry of the double-peaked lines. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

  15. A Statistical Study of Accretion Disk Model Spectra for Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

    Puebla, Raúl E.; Diaz, Marcos P.; Hubeny, Ivan

    2007-11-01

    We have performed a statistical test of the currently used accretion disk models for cataclysmic variables (CVs) using a set of 33 CVs with steady disks (10 old novae and 23 nova-like systems). The mass transfer rate () for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain the values. It was verified that these accretion disk models fail to fit both color and flux simultaneously, as previously noted when composite stellar atmosphere models were fitted to the UV spectra of CVs by Wade. By applying such models to a sample of novae and nova-like CVs, we confirm that the limb-darkening effect must be taken into account when estimating mass transfer rates, especially for high-inclination systems. Important fitting degeneracies of the basic disk parameters are analyzed. Our simulations suggest that to reproduce the observations a revision of the temperature profile, at least in the innermost parts of the disk, seems to be required, and possibly the vertical distribution of the viscosity should be revised. In addition, an optically thin layer or an extended disk component should be considered. This component may be physically represented by a disk wind and/or a chromosphere. A physical description of the emission-line profiles may help to break the degeneracies that appear when only the continuum is analyzed. The average value of found for nova-like systems is ~9.3 × 10-9 Modot yr-1, while ~1.3 × 10-8 Modot yr-1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation between and the orbital period. Such correlation analysis was performed for high accretion rate systems (15 nova-like systems and 10 old novae), but we were not able to find a well-defined correlation as found by Patterson. By measuring the equivalent width of the emission lines (C IV λ1550 and He II λ1640) we found a lack of systems with low and

  16. Modeling the Formation and Evolution of Wind-Capture Disks In Binary Systems

    NASA Astrophysics Data System (ADS)

    Huarte-Espinosa, M.; Carroll-Nellenback, J.; Nordhaus, J.; Frank, A.; Blackman, E.

    2014-04-01

    In this talk I will present results of recent models of the formation, evolution and physical properties of accretion disks formed via wind capture in binary systems. Using the AMR code AstroBEAR, we have carried out high resolution 3D simulations that follow a stellar mass secondary in the co-rotating frame as it orbits a wind producing AGB primary. A resolution criteria, based on considerations of Bondi-Hoyle flows, must be met in order to properly resolve the formation of accretion disks around the secondary. We then compare simulations of binaries with three different orbital radii (10, 15, 20 AU). Disks are formed in all three cases, however the size of the disk and, most importantly, its accretion rate decreases with orbital radii. In addition, the shape of the orbital motions of material within the disk becomes increasingly elliptical with increasing binary separation. The flow is mildly unsteady with "fluttering" around the bow shock observed. The disks are generally well aligned with the orbital plane after a few binary orbits. We do not observe the presence of any large scale, violent instabilities (such as the flip-flop mode). For the first time it is observed that the wind component that is accreted towards the secondary has a vortex tube-like structure. In the context of AGB binary systems that might be precursors to Pre-Planetary and Planetary Nebula, we find that the wind accretion rates at the chosen orbital separations are generally too small to produce the most powerful outflows observed in these systems if the companions are main sequence stars but marginally capable if the companions are white dwarfs. It is likely that many of the more powerful PPN and PN involve closer binaries than the ones considered here.

  17. Large eddy simulation of unsteady wind farm behavior using advanced actuator disk models

    NASA Astrophysics Data System (ADS)

    Moens, Maud; Duponcheel, Matthieu; Winckelmans, Gregoire; Chatelain, Philippe

    2014-11-01

    The present project aims at improving the level of fidelity of unsteady wind farm scale simulations through an effort on the representation and the modeling of the rotors. The chosen tool for the simulations is a Fourth Order Finite Difference code, developed at Universite catholique de Louvain; this solver implements Large Eddy Simulation (LES) approaches. The wind turbines are modeled as advanced actuator disks: these disks are coupled with the Blade Element Momentum method (BEM method) and also take into account the turbine dynamics and controller. A special effort is made here to reproduce the specific wake behaviors. Wake decay and expansion are indeed initially governed by vortex instabilities. This is an information that cannot be obtained from the BEM calculations. We thus aim at achieving this by matching the large scales of the actuator disk flow to high fidelity wake simulations produced using a Vortex Particle-Mesh method. It is obtained by adding a controlled excitation at the disk. We apply this tool to the investigation of atmospheric turbulence effects on the power production and on the wake behavior at a wind farm level. A turbulent velocity field is then used as inflow boundary condition for the simulations. We gratefully acknowledge the support of GDF Suez for the fellowship of Mrs Maud Moens.

  18. THE STABILITY OF LOW SURFACE BRIGHTNESS DISKS BASED ON MULTI-WAVELENGTH MODELING

    SciTech Connect

    MacLachlan, J. M.; Wood, K.; Matthews, L. D.; Gallagher, J. S.

    2011-11-01

    To investigate the structure and composition of the dusty interstellar medium (ISM) of low surface brightness (LSB) disk galaxies, we have used multi-wavelength photometry to construct spectral energy distributions for three low-mass, edge-on LSB galaxies (V{sub rot} = 88-105 km s{sup -1}). We use Monte Carlo radiation transfer codes that include the effects of transiently heated small grains and polycyclic aromatic hydrocarbon molecules to model and interpret the data. We find that, unlike the high surface brightness galaxies previously modeled, the dust disks appear to have scale heights equal to or exceeding their stellar scale heights. This result supports the findings of previous studies that low-mass disk galaxies have dust scale heights comparable to their stellar scale heights and suggests that the cold ISM of low-mass, LSB disk galaxies may be stable against fragmentation and gravitational collapse. This may help to explain the lack of observed dust lanes in edge-on LSB galaxies and their low current star formation rates. Dust masses are found in the range (1.16-2.38) x 10{sup 6} M{sub sun}, corresponding to face-on (edge-on), V-band, optical depths 0.034 {approx}< {tau}{sub face} {approx}< 0.106 (0.69 {approx}< {tau}{sub eq} {approx}< 1.99).

  19. Contact graphs of disk packings as a model of spatial planar networks

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongzhi; Guan, Jihong; Ding, Bailu; Chen, Lichao; Zhou, Shuigeng

    2009-08-01

    Spatially constrained planar networks are frequently encountered in real-life systems. In this paper, based on a space-filling disk packing we propose a minimal model for spatial maximal planar networks, which is similar to but different from the model for Apollonian networks (Andrade et al 2005 Phys. Rev. Lett. 94 018702). We present an exhaustive analysis of various properties of our model, and obtain the analytic solutions for most of the features, including degree distribution, clustering coefficient, average path length and degree correlations. The model recovers some striking generic characteristics observed in most real networks. To address the robustness of the relevant network properties, we compare the structural features between the investigated network and the Apollonian networks. We show that topological properties of the two networks are encoded in the way of disk packing. We argue that spatial constraints of nodes are relevant to the structure of the networks.

  20. Anisotropic Multishell Analytical Modeling of an Intervertebral Disk Subjected to Axial Compression.

    PubMed

    Demers, Sébastien; Nadeau, Sylvie; Bouzid, Abdel-Hakim

    2016-04-01

    Studies on intervertebral disk (IVD) response to various loads and postures are essential to understand disk's mechanical functions and to suggest preventive and corrective actions in the workplace. The experimental and finite-element (FE) approaches are well-suited for these studies, but validating their findings is difficult, partly due to the lack of alternative methods. Analytical modeling could allow methodological triangulation and help validation of FE models. This paper presents an analytical method based on thin-shell, beam-on-elastic-foundation and composite materials theories to evaluate the stresses in the anulus fibrosus (AF) of an axisymmetric disk composed of multiple thin lamellae. Large deformations of the soft tissues are accounted for using an iterative method and the anisotropic material properties are derived from a published biaxial experiment. The results are compared to those obtained by FE modeling. The results demonstrate the capability of the analytical model to evaluate the stresses at any location of the simplified AF. It also demonstrates that anisotropy reduces stresses in the lamellae. This novel model is a preliminary step in developing valuable analytical models of IVDs, and represents a distinctive groundwork that is able to sustain future refinements. This paper suggests important features that may be included to improve model realism. PMID:26833355

  1. FROM DUST TO PLANETESIMALS: AN IMPROVED MODEL FOR COLLISIONAL GROWTH IN PROTOPLANETARY DISKS

    SciTech Connect

    Garaud, Pascale; Meru, Farzana; Galvagni, Marina; Olczak, Christoph

    2013-02-20

    Planet formation occurs within the gas- and dust-rich environments of protoplanetary disks. Observations of these objects show that the growth of primordial submicron-sized particles into larger aggregates occurs at the earliest evolutionary stages of the disks. However, theoretical models of particle growth that use the Smoluchowski equation to describe collisional coagulation and fragmentation have so far failed to produce large particles while maintaining a significant population of small grains. This has generally been attributed to the existence of two barriers impeding growth due to bouncing and fragmentation of colliding particles. In this paper, we demonstrate that the importance of these barriers has been artificially inflated through the use of simplified models that do not take into account the stochastic nature of the particle motions within the gas disk. We present a new approach in which the relative velocities between two particles are described by a probability distribution function that models both deterministic motion (from the vertical settling, radial drift, and azimuthal drift) and stochastic motion (from Brownian motion and turbulence). Taking both into account can give quite different results to what has been considered recently in other studies. We demonstrate the vital effect of two 'ingredients' for particle growth: the proper implementation of a velocity distribution function that overcomes the bouncing barrier and, in combination with mass transfer in high-mass-ratio collisions, boosts the growth of larger particles beyond the fragmentation barrier. A robust result of our simulations is the emergence of two particle populations (small and large), potentially explaining simultaneously a number of longstanding problems in protoplanetary disks, including planetesimal formation close to the central star, the presence of millimeter- to centimeter-sized particles far out in the disk, and the persistence of {mu}m-sized grains for millions of

  2. Astrophysical symmetries

    PubMed Central

    Trimble, Virginia

    1996-01-01

    Astrophysical objects, ranging from meteorites to the entire universe, can be classified into about a dozen characteristic morphologies, at least as seen by a blurry eye. Some patterns exist over an enormously wide range of distance scales, apparently as a result of similar underlying physics. Bipolar ejection from protostars, binary systems, and active galaxies is perhaps the clearest example. The oral presentation included about 130 astronomical images which cannot be reproduced here. PMID:11607715

  3. Modelling Dusty Circumbinary Disk around B[e] Supergiant RY Sct

    NASA Astrophysics Data System (ADS)

    Men'shchikov, Alexander; Miroshnichenko, Anatoly

    2005-08-01

    The supergiant RY Sct is an eclipsing binary system with a fairly large infrared (IR) excess caused by the presence of circumbinary dust. Many strong forbidden lines ([O i], [N ii], [S iii], [Fe ii]), in combination with the near-IR excess, put it in the list of peculiar Be or B[e] stars. Although RY Sct is one of the best-studied systems, even its basic physical parameters remain unreliable. Recent IR images of the system, obtained with a 0.3 arcsec resolution at the 10-m Keck telescope, showed the dusty disk at the wavelengths 3-20 μm and stimulated us to perform its detailed modelling using our 2-D radiative transfer code. Our model reproduces all available observations of RY Sct obtained during the last few decades. The modelling demonstrated that the observations cannot be described by a single model at one moment in time, implying rapid changes in the dusty disk during the last 20 years. Assuming that a temperature of 27,000 K describes both components of the binary and that its distance is 1.8 kpc, its total luminosity is 4.2 - 105 solar luminosity. The model disk has the optical depth of 0.04 and the opening angle of 26° (between the boundaries). Dust in the disk exists between 60 AU and 105 AU, where it blends into the interstellar medium. We observe the disk almost edge-on, at an angle of 14° to its midplane. The total mass of the disk is 0.017 solar mass. There is a strong density enhancement at 1800 AU from the binary, which emits most of the IR radiation and is prominent in the Keck telescope images. Presumably, the dense ring has been created by a fast wind that swept out and compressed the previously lost material in the older and slower stellar wind. Our model predicts that presently there is a large amount of small, hot dust grains in the dust formation zone, whose emission changed the shape of the SED of RY Sct in the near IR. The dust density must now be significantly greater in the dust formation zone, suggesting a much higher massloss rate

  4. Simple wideband models for disks and wires in the eddy current approximation

    NASA Astrophysics Data System (ADS)

    Scott, Waymond R.; McFadden, Michael

    2013-05-01

    Wideband electromagnetic induction systems have shown improved false alarm rates when compared with traditional metal detectors. Calibration of these sensors and the development of algorithms for target discrimination could be assisted by a set of models for common targets. In this paper, simple wideband models of the eddy current response for a wire and disk are provided. These are provided in the form of a singularity expansion of the polarizability dyadic. In an effort to make this form more concrete, a major focus of the paper is on relating the terms of the expansion to graphs of the currents present on the disk. The models provided in the paper are based on limiting forms of a cylinder as computed using the body-of-revolutions finite element method. Measured polarizability dyadics are also shown to fit the forms provided reasonably well.

  5. A Resonantly Excited Disk-Oscillation Model of High-Frequency QPOs of Microquasars

    NASA Astrophysics Data System (ADS)

    Kato, Shoji

    2012-12-01

    A possible model of twin high-frequency QPOs (HF QPOs) of microquasars is examined. The disk is assumed to have global magnetic fields and to be deformed with a two-armed pattern. In this deformed disk, a set of a two-armed (m = 2) vertical p-mode oscillation and an axisymmetric (m = 0) g-mode oscillation is considered. They resonantly interact through the disk deformation when their frequencies are the same. This resonant interaction amplifies the set of the above oscillations in the case where these two oscillations have wave energies of opposite signs. These oscillations are assumed to be excited most efficiently in the case where the radial group velocities of these two waves vanish at the same place. The above set of oscillations is not unique, depending on the node number n, of oscillations in the vertical direction. We consider that the basic two sets of oscillations correspond to the twin QPOs. The frequencies of these oscillations depend on the disk parameters, such as the strength of the magnetic fields. For observational mass ranges of GRS 1915+ 105, GRO J1655-40, XTE J1550-564, and HEAO H1743-322, the spins of these sources are estimated. High spins of these sources can be described if the disks have weak poloidal magnetic fields as well as toroidal magnetic fields of moderate strength. In this model the 3:2 frequency ratio of high-frequency QPOs is not related to their excitation, but occurs by chance.

  6. The structure and appearance of winds from supercritical accretion disks. I - Numerical models

    NASA Technical Reports Server (NTRS)

    Meier, D. L.

    1979-01-01

    Equations for the structure and appearance of supercritical accretion disks and the radiation-driven winds which emanate from them are derived and solved by a steady-state hydrodynamic computer code with a relaxation technique used in stellar structure problems. The present model takes into account the mass of the accreting star, the total accretion rate, a generalization of the disk alpha parameter which accounts for heating by processes in addition to viscosity, and the ratio of the total luminosity to the Eddington luminosity. Solutions indicate that for accretion onto a hard-surfaced star, steady, optically thick winds result for even slightly supercritical accretion, and the object will appear as a supergiant star with a high mass loss rate and a nonblackbody spectrum. Winds from black hole accretion disks are expected to depend on the form of the accretion interior to the critical radius, possibly consisting of no ejection at all, a wind similar to that of a hard-surfaced star, or a column of material ejected from a hole in the accretion disk.

  7. A model for the magnetic field in the molecular disk at the Galactic center

    SciTech Connect

    Wardle, M.; Konigl, A. )

    1990-10-01

    A model for the magnetic field configuration in the Galactic center disk is presented. The field has an open geometry and represents the poloidal field detected at larger distances from the Galactic center, stretched and twisted by the effects of advection and shear in a magnetized accretion disk. It is concluded that the 100 micron polarization measurements of Hildebrand et al. (1990) imply that the radial and azimuthal components of the magnetic field in the disk are comparable and have opposite signs, consistent with the generation of B(phi) from B(r) by differential rotation. The polarization measurements indicate that the z-component of the field is smaller than both /B(phi)/ and /B(r)/; thus, they do not by themselves require that the field lines thread the disk. The field strengths of order 1 mG inferred from the Zeeman measurements and the fact that /B(phi)/ and /B(r)/ exceed B(z) imply that the field could remove the excess angular momentum of the accreted matter in the form of a centrifugally driven outflow. 31 refs.

  8. Development of an advanced actuator disk model for Large-Eddy Simulation of wind farms

    NASA Astrophysics Data System (ADS)

    Moens, Maud; Duponcheel, Matthieu; Winckelmans, Gregoire; Chatelain, Philippe

    2015-11-01

    This work aims at improving the fidelity of the wind turbine modelling for Large-Eddy Simulation (LES) of wind farms, in order to accurately predict the loads, the production, and the wake dynamics. In those simulations, the wind turbines are accounted for through actuator disks. i.e. a body-force term acting over the regularised disk swept by the rotor. These forces are computed using the Blade Element theory to estimate the normal and tangential components (based on the local simulated flow and the blade characteristics). The local velocities are modified using the Glauert tip-loss factor in order to account for the finite number of blades; the computation of this correction is here improved thanks to a local estimation of the effective upstream velocity at every point of the disk. These advanced actuator disks are implemented in a 4th order finite difference LES solver and are compared to a classical Blade Element Momentum method and to high fidelity wake simulations performed using a Vortex Particle-Mesh method in uniform and turbulent flows.

  9. THE DISK EVAPORATION MODEL FOR THE SPECTRAL FEATURES OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Qiao, Erlin; Liu, B. F.; Panessa, Francesca; Liu, J. Y.

    2013-11-10

    Observations show that the accretion flows in low-luminosity active galactic nuclei probably have a two-component structure with an inner, hot, optically thin, advection-dominated accretion flow (ADAF) and an outer, truncated, cool, optically thick accretion disk. As shown by Taam et al., the truncation radius as a function of mass accretion rate is strongly affected by including the magnetic field within the framework of disk evaporation model, i.e., an increase in the magnetic field results in a smaller truncation radius of the accretion disk. In this work, we calculate the emergent spectrum of an inner ADAF + an outer truncated accretion disk around a supermassive black hole based on the prediction by Taam et al.. It is found that an increase in the magnetic field from β = 0.8 to β = 0.5 (with magnetic pressure p{sub m} = B {sup 2}/8π = (1 – β)p{sub tot}, p{sub tot} = p{sub gas} + p{sub m}) results in a factor of ∼8.7 increase in the luminosity from the truncated accretion disk. Meanwhile, results of the peak emission of the truncated accretion disk shift toward a a factor of ∼5 higher frequency. We found that the equipartition of gas pressure to magnetic pressure, i.e., β = 0.5, failed to explain the observed anti-correlation between L{sub 2-10{sub keV}}/L{sub Edd} and the bolometric correction κ{sub 2-10{sub keV}} (with κ{sub 2-10{sub keV}} = L{sub bol}/L{sub 2-10{sub keV}}). The emergent spectra for larger values of β = 0.8 or β = 0.95 can explain the observed L{sub 2-10{sub keV}}/L{sub Edd}-κ{sub 2-10{sub keV}} correlation. We argue that in the disk evaporation model, the electrons in the corona are assumed to be heated only by a transfer of energy from the ions to electrons via Coulomb collisions, which is reasonable for accretion with a lower mass accretion rate. Coulomb heating is the dominated heating mechanism for the electrons only if the magnetic field is strongly sub-equipartition, which is roughly consistent with observations.

  10. A GENERAL RELATIVISTIC MODEL OF ACCRETION DISKS WITH CORONAE SURROUNDING KERR BLACK HOLES

    SciTech Connect

    You Bei; Cao Xinwu; Yuan Yefei E-mail: cxw@shao.ac.cn

    2012-12-20

    We calculate the structure of a standard accretion disk with a corona surrounding a massive Kerr black hole in the general relativistic frame, in which the corona is assumed to be heated by the reconnection of the strongly buoyant magnetic fields generated in the cold accretion disk. The emergent spectra of accretion disk-corona systems are calculated by using the relativistic ray-tracing method. We propose a new method to calculate the emergent Comptonized spectra from the coronae. The spectra of disk-corona systems with a modified {alpha}-magnetic stress show that both the hard X-ray spectral index and the hard X-ray bolometric correction factor L{sub bol}/L{sub X,2-10keV} increase with the dimensionless mass accretion rate, which is qualitatively consistent with the observations of active galactic nuclei. The fraction of the power dissipated in the corona decreases with increasing black hole spin parameter a, which leads to lower electron temperatures of the coronae for rapidly spinning black holes. The X-ray emission from the coronae surrounding rapidly spinning black holes becomes weak and soft. The ratio of the X-ray luminosity to the optical/UV luminosity increases with the viewing angle, while the spectral shape in the X-ray band is insensitive to the viewing angle. We find that the spectral index in the infrared waveband depends on the mass accretion rate and the black hole spin a, which deviates from the f{sub {nu}}{proportional_to}{nu}{sup 1/3} relation expected by the standard thin disk model.

  11. Gamma-ray astrophysics

    NASA Technical Reports Server (NTRS)

    Stecker, F. W. (Editor); Trombka, J. I. (Editor)

    1973-01-01

    Conference papers on gamma ray astrophysics are summarized. Data cover the energy region from about 0.3 MeV to a few hundred GeV and theoretical models of production mechanisms that give rise to both galactic and extragalactic gamma rays.

  12. X-RAY REFLECTED SPECTRA FROM ACCRETION DISK MODELS. I. CONSTANT DENSITY ATMOSPHERES

    SciTech Connect

    Garcia, J.; Kallman, T. R. E-mail: timothy.r.kallman@nasa.go

    2010-08-01

    We present new models for illuminated accretion disks, their structure, and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by simultaneously solving the equations of radiative transfer, energy balance, and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell processes of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent K{alpha} line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.

  13. Numerical Modeling of Dusty Disk System Morphologies With Deep Impact Derived Opacities

    NASA Astrophysics Data System (ADS)

    Fraine, Jonathan; Lisse, C. M.; Kuchner, M.; Stark, C.

    2008-09-01

    We have taken existing dust morphology modeling software, ZODIPIC (Kuchner et al. 2007) and modified the opacity data to reflect the species detected in comets from the Deep Impact mission, the Spitzer survey of comets, STARDUST, and bright exo-planetary dust spectra. Opacities from multiple chemical species were adapted to the ZODIPIC code and now contain spectra that can match the existing spectra from the debris disk systems. User supplied coefficients can now modify pre-programmed spectral species to match morphological outputs with desired empirical expectations. This tool can aid in generating expectations for direct or indirect observations of exoplanetary debris disks. We show example morphological models of silicate rich (e.g., HD69830, Beichman et al. 2005) and carbon-rich (Beta Pic like, Roberge et al. 2007) systems.

  14. X-ray Reflected Spectra from Accretion Disk Models. I. Constant Density Atmospheres

    NASA Technical Reports Server (NTRS)

    Garcia, Javier; Kallman, Timothy R.

    2009-01-01

    We present new models for illuminated accretion disks, their structure and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by solving simultaneously the equations of radiative transfer, energy balance and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent Ka line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.

  15. Computational Relativistic Astrophysics Using the Flowfield-Dependent Variation Theory

    NASA Technical Reports Server (NTRS)

    Richardson, G. A.; Chung, T. J.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Theoretical models, observations and measurements have preoccupied astrophysicists for many centuries. Only in recent years, has the theory of relativity as applied to astrophysical flows met the challenges of how the governing equations can be solved numerically with accuracy and efficiency. Even without the effects of relativity, the physics of magnetohydrodynamic flow instability, turbulence, radiation, and enhanced transport in accretion disks has not been completely resolved. Relativistic effects become pronounced in such cases as jet formation from black hole magnetized accretion disks and also in the study of Gamma-Ray bursts (GRB). Thus, our concern in this paper is to reexamine existing numerical simulation tools as to the accuracy and efficiency of computations and introduce a new approach known as the flowfield-dependent variation (FDV) method. The main feature of the FDV method consists of accommodating discontinuities of shock waves and high gradients of flow variables such as occur in turbulence and unstable motions. In this paper, the physics involved in the solution of relativistic hydrodynamics and solution strategies of the FDV theory are elaborated. The general relativistic astrophysical flow and shock solver (GRAFSS) is introduced, and some simple example problems for Computational Relativistic Astrophysics (CRA) are demonstrated.

  16. Microstructure Modeling of 3rd Generation Disk Alloys

    NASA Technical Reports Server (NTRS)

    Jou, Herng-Jeng

    2010-01-01

    The objective of this program is to model, validate, and predict the precipitation microstructure evolution, using PrecipiCalc (QuesTek Innovations LLC) software, for 3rd generation Ni-based gas turbine disc superalloys during processing and service, with a set of logical and consistent experiments and characterizations. Furthermore, within this program, the originally research-oriented microstructure simulation tool will be further improved and implemented to be a useful and user-friendly engineering tool. In this report, the key accomplishment achieved during the second year (2008) of the program is summarized. The activities of this year include final selection of multicomponent thermodynamics and mobility databases, precipitate surface energy determination from nucleation experiment, multiscale comparison of predicted versus measured intragrain precipitation microstructure in quench samples showing good agreement, isothermal coarsening experiment and interaction of grain boundary and intergrain precipitates, primary microstructure of subsolvus treatment, and finally the software implementation plan for the third year of the project. In the following year, the calibrated models and simulation tools will be validated against an independently developed experimental data set, with actual disc heat treatment process conditions. Furthermore, software integration and implementation will be developed to provide material engineers valuable information in order to optimize the processing of the 3rd generation gas turbine disc alloys.

  17. Lower Bound on the Mean Square Displacement of Particles in the Hard Disk Model

    NASA Astrophysics Data System (ADS)

    Richthammer, Thomas

    2016-08-01

    The hard disk model is a 2D Gibbsian process of particles interacting via pure hard core repulsion. At high particle density the model is believed to show orientational order, however, it is known not to exhibit positional order. Here we investigate to what extent particle positions may fluctuate. We consider a finite volume version of the model in a box of dimensions 2 n × 2 n with arbitrary boundary configuration, and we show that the mean square displacement of particles near the center of the box is bounded from below by c log n. The result generalizes to a large class of models with fairly arbitrary interaction.

  18. A METHOD FOR THE STUDY OF ACCRETION DISK EMISSION IN CATACLYSMIC VARIABLES. I. THE MODEL

    SciTech Connect

    Puebla, Raul E.; Diaz, Marcos P.; John Hillier, D.; Hubeny, Ivan E-mail: marcos@astro.iag.usp.br E-mail: hubeny@as.arizona.edu

    2011-07-20

    We have developed a spectrum synthesis method for modeling the ultraviolet (UV) emission from the accretion disk from cataclysmic variables (CVs). The disk is separated into concentric rings, with an internal structure from the Wade and Hubeny disk-atmosphere models. For each ring, a wind atmosphere is calculated in the comoving frame with a vertical velocity structure obtained from a solution of the Euler equation. Using simple assumptions, regarding rotation and the wind streamlines, these one-dimensional models are combined into a single 2.5-dimensional model for which we compute synthetic spectra. We find that the resulting line and continuum behavior as a function of the orbital inclination is consistent with the observations, and verify that the accretion rate affects the wind temperature, leading to corresponding trends in the intensity of UV lines. In general, we also find that the primary mass has a strong effect on the P Cygni absorption profiles, the synthetic emission line profiles are strongly sensitive to the wind temperature structure, and an increase in the mass-loss rate enhances the resonance line intensities. Synthetic spectra were compared with UV data for two high orbital inclination nova-like CVs-RW Tri and V347 Pup. We needed to include disk regions with arbitrary enhanced mass loss to reproduce reasonably well widths and line profiles. This fact and a lack of flux in some high ionization lines may be the signature of the presence of density-enhanced regions in the wind, or alternatively, may result from inadequacies in some of our simplifying assumptions.

  19. Astrophysics with MILAGRO

    SciTech Connect

    Not Available

    1993-01-01

    This paper describes how data from a new type of air shower detector, MILAGRO can shed light on a variety of interesting problems in astrophysics. MILAGRO has the capability to make observations of VHE/UHE emission from the recently discovered TeV gamma-ray source Markarian 421, an Active Galactic Nucleus (AGN). An observation of the attenuation of this signal in the range of 1--20 TeV can be used to make the first measurement of the intergalactic infrared radiation. We will also describe how MILAGRO can improve the existing limits on the density of Primordial Black Holes (PBH) by three orders of magnitude. Finally, we will discuss how this instrument can be used to measure the diffuse galactic emission of gamma-rays which must come from the disk.

  20. Astrophysics with MILAGRO

    SciTech Connect

    The MILAGRO Collaboration

    1993-05-01

    This paper describes how data from a new type of air shower detector, MILAGRO can shed light on a variety of interesting problems in astrophysics. MILAGRO has the capability to make observations of VHE/UHE emission from the recently discovered TeV gamma-ray source Markarian 421, an Active Galactic Nucleus (AGN). An observation of the attenuation of this signal in the range of 1--20 TeV can be used to make the first measurement of the intergalactic infrared radiation. We will also describe how MILAGRO can improve the existing limits on the density of Primordial Black Holes (PBH) by three orders of magnitude. Finally, we will discuss how this instrument can be used to measure the diffuse galactic emission of gamma-rays which must come from the disk.

  1. Astrophysics. A primer

    NASA Astrophysics Data System (ADS)

    Kundt, Wolfgang

    For a quantitative understanding of the physics of the universe - from the solar system through the Milky Way to clusters of galaxies all the way to cosmology - these edited lecture notes are perhaps among the most concise and also among the most critical ones: Astrophysics has not yet stood the redundancy test of laboratory physics, hence should be aware of early interpretations. Special chapters are devoted to magnetic and radiation processes, supernovae, disks, black-hole candidacy, bipolar flows, cosmic rays, gamma-ray bursts, image distortions, and special sources. At the same time, planet earth is viewed as the arena for life, with plants and animals having evolved to homo sapiens during cosmic time. This text is unique in covering the basic qualitative and quantitative tools, formulae as well as numbers, needed for the precise interpretation of frontline phenomena. The author compares mainstream interpretations with new and even controversial ones he wishes to emphasize.

  2. Astrophysical cosmology

    SciTech Connect

    Bardeen, J.M.

    1986-01-01

    The last several years have seen a tremendous ferment of activity in astrophysical cosmology. Much of the theoretical impetus has come from particle physics theories of the early universe and candidates for dark matter, but what promise to be even more significant are improved direct observations of high z galaxies and intergalactic matter, deeper and more comprehensive redshift surveys, and the increasing power of computer simulations of the dynamical evolution of large scale structure. Upper limits on the anisotropy of the microwave background radiation are gradually getting tighter and constraining more severely theoretical scenarios for the evolution of the universe. 47 refs.

  3. METALLICITY GRADIENTS THROUGH DISK INSTABILITY: A SIMPLE MODEL FOR THE MILKY WAY'S BOXY BULGE

    SciTech Connect

    Martinez-Valpuesta, Inma; Gerhard, Ortwin E-mail: gerhard@mpe.mpg.de

    2013-03-20

    Observations show a clear vertical metallicity gradient in the Galactic bulge, which is often taken as a signature of dissipative processes in the formation of a classical bulge. Various evidence shows, however, that the Milky Way is a barred galaxy with a boxy bulge representing the inner three-dimensional part of the bar. Here we show with a secular evolution N-body model that a boxy bulge formed through bar and buckling instabilities can show vertical metallicity gradients similar to the observed gradient if the initial axisymmetric disk had a comparable radial metallicity gradient. In this framework, the range of metallicities in bulge fields constrains the chemical structure of the Galactic disk at early times before bar formation. Our secular evolution model was previously shown to reproduce inner Galaxy star counts and we show here that it also has cylindrical rotation. We use it to predict a full mean metallicity map across the Galactic bulge from a simple metallicity model for the initial disk. This map shows a general outward gradient on the sky as well as longitudinal perspective asymmetries. We also briefly comment on interpreting metallicity gradient observations in external boxy bulges.

  4. Modeling X-ray Absorbers in AGNs with MHD-Driven Accretion-Disk Winds

    NASA Astrophysics Data System (ADS)

    Fukumura, Keigo; Kazanas, D.; Shrader, C. R.; Tombesi, F.; Contopoulos, J.; Behar, E.

    2013-04-01

    We have proposed a systematic view of the observed X-ray absorbers, namely warm absorbers (WAs) in soft X-ray and highly-ionized ultra-fast outflows (UFOs), in the context of magnetically-driven accretion-disk wind models. While potentially complicated by variability and thermal instability in these energetic outflows, in this simplistic model we have calculated 2D kinematic field as well as density and ionization structure of the wind with density profile of 1/r corresponding to a constant column distribution per decade of ionization parameter. In particular we show semi-analytically that the inner layer of the disk-wind manifests itself as the strongly-ionized fast outflows while the outer layer is identified as the moderately-ionized absorbers. The computed characteristics of these two apparently distinct absorbers are consistent with X-ray data (i.e. a factor of ~100 difference in column and ionization parameters as well as low wind velocity vs. near-relativistic flow). With the predicted contour curves for these wind parameters one can constrain allowed regions for the presence of WAs and UFOs.The model further implies that the UFO's gas pressure is comparable to that of the observed radio jet in 3C111 suggesting that the magnetized disk-wind with density profile of 1/r is a viable agent to help sustain such a self-collimated jet at small radii.

  5. An interferometric view of hot star disks

    NASA Astrophysics Data System (ADS)

    Faes, Daniel Moser

    2015-08-01

    Optical long baseline interferometry was recently established as a technique capable of resolving stars and their circumstellar environments at the milliarcsecond (mas) resolution level. This high-resolution opens an entire new window to the study of astrophysical systems, providing information inaccessible by other techniques. Astrophysical disks are observed in a wide variety of systems, from galaxies up to planetary rings, commonly sharing similar physical processes. Two particular disk like systems are studied in the thesis: (i) B He-rich stars that exhibits magnetic fields in order of kG and that trap their winds in structures called magnetospheres; and (ii) Be stars, fast rotating stars that create circumstellar viscous disks. This study uses the interferometric technique to investigate both the photosphere proper and the circumstellar environment of these stars. The objective is to combine interferometry with other observational techniques (such as spectroscopy and polarimetry) to perform a complete and well-constrained physical description of these systems. This description is accompanied by radiative transfer models performed by the HDUST code.

  6. AdS Black Disk Model for Small-x Deep Inelastic Scattering

    SciTech Connect

    Cornalba, Lorenzo; Costa, Miguel S.; Penedones, Joao

    2010-08-13

    Using the approximate conformal invariance of QCD at high energies we consider a simple anti-de Sitter black disk model to describe saturation in deep inelastic scattering. Deep inside saturation the structure functions have the same power law scaling, F{sub T}{approx}F{sub L}{approx}x{sup -{omega}}, where {omega} is related to the expansion rate of the black disk with energy. Furthermore, the ratio F{sub L}/F{sub T} is given by the universal value (1+{omega}/3+{omega}), independently of the target. For {gamma}*-{gamma}* scattering at high energies we obtain explicit expressions and ratios for the total cross sections of transverse and longitudinal photons in terms of the single parameter {omega}.

  7. The Kozai–Lidov Mechanism in Hydrodynamical Disks. II. Effects of Binary and Disk Parameters

    NASA Astrophysics Data System (ADS)

    Fu, Wen; Lubow, Stephen H.; Martin, Rebecca G.

    2015-07-01

    Martin et al. showed that a substantially misaligned accretion disk around one component of a binary system can undergo global damped Kozai–Lidov (KL) oscillations. During these oscillations, the inclination and eccentricity of the disk are periodically exchanged. However, the robustness of this mechanism and its dependence on the system parameters were unexplored. In this paper, we use three-dimensional hydrodynamical simulations to analyze how various binary and disk parameters affect the KL mechanism in hydrodynamical disks. The simulations include the effect of gas pressure and viscosity, but ignore the effects of disk self-gravity. We describe results for different numerical resolutions, binary mass ratios and orbital eccentricities, initial disk sizes, initial disk surface density profiles, disk sound speeds, and disk viscosities. We show that the KL mechanism can operate for a wide range of binary-disk parameters. We discuss the applications of our results to astrophysical disks in various accreting systems.

  8. The Kozai-Lidov mechanism in hydrodynamical disks. II. Effects of binary and disk parameters

    SciTech Connect

    Fu, Wen; Lubow, Stephen H.; Martin, Rebecca G.

    2015-07-01

    Martin et al. (2014b) showed that a substantially misaligned accretion disk around one component of a binary system can undergo global damped Kozai–Lidov (KL) oscillations. During these oscillations, the inclination and eccentricity of the disk are periodically exchanged. However, the robustness of this mechanism and its dependence on the system parameters were unexplored. In this paper, we use three-dimensional hydrodynamical simulations to analyze how various binary and disk parameters affect the KL mechanism in hydrodynamical disks. The simulations include the effect of gas pressure and viscosity, but ignore the effects of disk self-gravity. We describe results for different numerical resolutions, binary mass ratios and orbital eccentricities, initial disk sizes, initial disk surface density profiles, disk sound speeds, and disk viscosities. We show that the KL mechanism can operate for a wide range of binary-disk parameters. We discuss the applications of our results to astrophysical disks in various accreting systems.

  9. A Disk-Corona Model for Optical-to-Hard X-ray spectrum of AGN

    NASA Astrophysics Data System (ADS)

    Kawaguchi, T.; Shimura, T.; Mineshige, S.

    We construct a disk-corona model to account for the optical-to-X-ray spectral energy distributions of Seyfert nuclei and QSOs. We study the emission spectrum emerging from a vertical disk-corona structure composed of two-temperature plasma by solving hydrostatic equilibrium and radiative transfer self-consistently. A fraction f of viscous heating is assumed to be dissipated in a corona where advective cooling is also included, and the remaining fraction, 1-f, within the main body of the disk. The model exhibits different photon indices in X-ray (Γ ~ 2.5 below 2 keV and ~ 1.5 above, where Fν ∝ ν(1 - Γ)) as the result of different emission mechanisms and different sites; the former slope is due to unsaturated Comptonization from the innermost zone and the latter is due to a combination of Comptonization and bremsstrahlung from the entire corona (<= 300 RSch). Because of the shorter dynamical time-scale at inner region than that at outer region, the emission from the inner radii is likely to be more variable than radiation from the outer parts. Then, the X-ray spectrum is expected to be softer in brighter phase, as observed in many Broad-Line Seyfert 1 nuclei.

  10. Titius-Bode laws in the solar system. 2: Build your own law from disk models

    NASA Astrophysics Data System (ADS)

    Dubrulle, B.; Graner, F.

    1994-02-01

    Simply respecting both scale and rotational invariance, it is easy to construct an endless collection of theoretical models predicting a Titius-Bode law, irrespective to their physical content. Due to the numerous ways to get the law and its intrinsic arbitrariness, it is not a useful constraint on theories of solar system formation. To illustrate the simple elegance of scale-invariant methods, we explicitly cook up one of the simplest examples, an infinitely thin cold gaseous disk rotating around a central object. In that academic case, the Titius-Bode law holds during the linear stage of the gravitational instability. The time scale of the instability is of the order of a self-gravitating time scale, (G rhod)-1/2, where rhod is the disk density. This model links the separation between different density maxima with the ratio MD/MC of the masses of the disk and the central object; for instance, MD/MC of the order of 0.18 roughly leads to the observed separation between the planets. We discuss the boundary conditions and the limit of the Wentzel-Kramer-Brillouin (WKB) approximation.

  11. Two-dimensional modeling of an aircraft engine structural bladed disk-casing modal interaction

    NASA Astrophysics Data System (ADS)

    Legrand, Mathias; Pierre, Christophe; Cartraud, Patrice; Lombard, Jean-Pierre

    2009-01-01

    In modern turbo machines such as aircraft jet engines, structural contacts between the casing and bladed disk may occur through a variety of mechanisms: coincidence of vibration modes, thermal deformation of the casing, rotor imbalance due to design uncertainties to name a few. These nonlinear interactions may result in severe damage to both structures and it is important to understand the physical circumstances under which they occur. In this study, we focus on a modal coincidence during which the vibrations of each structure take the form of a k-nodal diameter traveling wave characteristic of axi-symmetric geometries. A realistic two-dimensional model of the casing and bladed disk is introduced in order to predict the occurrence of this very specific interaction phenomenon versus the rotation speed of the engine. The equations of motion are solved using an explicit time integration scheme in conjunction with the Lagrange multiplier method where friction is accounted for. This model is validated from the comparison with an analytical solution. The numerical results show that the structures may experience different kinds of behaviors (namely damped, sustained and divergent motions) mainly depending on the rotational velocity of the bladed disk.

  12. Magnetic fields in astrophysics /Helen B. Warner Prize Lecture/

    NASA Astrophysics Data System (ADS)

    Blandford, R. D.

    1983-03-01

    Magnetic fields play many important roles in interpretative models of astronomical phenomena. They can provide diagnostics of the physical conditions within active objects. They may mediate and collimate the energy release from a deep gravitational potential well. On a microscopic level, they may control the transport properties of astrophysical plasmas with large-scale thermal and dynamical consequences. Some of these facets of the behavior of magnetic fields are illustrated with examples drawn mainly from contemporary high-energy astrophysics. In particular, attention is given to the case that most double radio sources are powered by the electromagnetic or hydromagnetic extraction of energy from a spinning massive black hole and accretion disk and subsequently collimated by the pinching action of toroidal field wrapped around the jet. The origin of neutron star magnetic field is also discussed and it is argued that the magnetization can be generated thermoelectrically by the heat flux escaping from the interior of the star.

  13. Astrophysical Probes of Dark Matter Interactions

    NASA Astrophysics Data System (ADS)

    Reece, Matthew

    The majority of matter in the universe is dark matter, made up of some particle beyond those in the Standard Model of particle physics. So far we have very little information about what dark matter is and how it interacts, except through gravity. Constraints from halo shapes and the Bullet Cluster give upper bounds on the self-interaction strength of dark matter, but these bounds are very weak: roughly the same size as nuclear physics cross sections, which are very large by the standards of particle physics. Given how little we know about dark matter, it is important to search for it in as broad a context as possible. Existing direct and indirect detection analyses are typically motivated by simple particle physics models like WIMP dark matter. This research will aim to widen the scope of searches for dark matter by considering a more complete range of particle physics models, working out their implications for astrophysical data, and interpreting existing data in terms of these new models. New models of dark matter can affect searches in a variety of ways. Signals may show up in conventional indirect detection searches, e.g. in gamma rays detected by Fermi-LAT or in antiprotons detected by AMS-02. The new particle physics content of the models could be reflected in surprising spectral shapes or other features of such signals, or in gamma rays with a different profile on the sky than expected in typical models. The PI has worked, for example, on a model in which signals may arise from a dark disk, which is just one of many possibilities. Signals of new dark matter models might also arise in more subtle ways. Structure in the dark sector could influence the development of structure in the visible sector, indirectly. For instance, a dark matter disk or other dark structures could alter the orbits of stars in the galaxy and may be detectable through detailed studies of the kinematics of stellar populations. Dark accretion disks could exist around astrophysical objects

  14. Chemistry in disks. IX. Observations and modelling of HCO+ and DCO+ in DM Tauri

    NASA Astrophysics Data System (ADS)

    Teague, R.; Semenov, D.; Guilloteau, S.; Henning, Th.; Dutrey, A.; Wakelam, V.; Chapillon, E.; Pietu, V.

    2015-02-01

    Aims: We study the deuteration and ionization structure of the DM Tau disk via interferometric observations and modelling of the key molecular ions, HCO+ and DCO+. Methods: The Plateau de Bure Array is used to observe DM Tau in lines of HCO+ (1-0), (3-2) and DCO+ (3-2) with a ~ 1.5'' angular and ~0.2 km s-1 spectral resolution. Using a power-law fitting approach the observed column densities profiles are derived and thus the isotopic ratio RD = DCO+/HCO+. Chemical modelling allowed an exploration of the sensitivity of HCO+ and DCO+ abundances to physical parameters out with temperature. A steady state approximation was employed to observationally constrain the ionization fraction x(e-). Results: Fitting of radiative transfer models suggests that there is a chemical hole in HCO+ and DCO+, extending up to 50 AU from the star. More work is required to discern the cause of this. The observed column densities of HCO+ and DCO+ at 100 AU were (9.8+0.3-0.7) × 1012 and (1.2 ± 0.7) × 1012 cm-2 respectively. Where both HCO+ and DCO+ were present, RD was found to increase radially from 0.1 at 50 AU to 0.2 at 450 AU. This behaviour was well reproduced by the chemical model. The X-ray luminosity of the central star, the interstellar UV and CO depletion were found to be the most important physical parameters controlling the abundances of HCO+ and DCO+. Differences in the vertical extent of HCO+ and DCO+ molecular layers resulted in different responses to changing physical parameters, manifesting as radial gradients in RD. The ionization fraction was found to be x(e-) ~ 10-7 in the molecular layer, comparable to the disk averaged value. Modelling shows that while HCO+ is the most dominant charged molecular ion in our disk model, atomic ions, such as C+, S+, H+, Na+ and Mg+, dominate the charge in both the molecular layer and disk atmosphere. Conclusions: A high value of RD is indicative of continued deuterium fractionation in a protoplanetary disk after pre/protostellar phases

  15. The Gaseous Disks of Young Stellar Objects

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.

    2006-01-01

    Disks represent a crucial stage in the formation of stars and planets. They are novel astrophysical systems with attributes intermediate between the interstellar medium and stars. Their physical properties are inhomogeneous and are affected by hard stellar radiation and by dynamical evolution. Observing disk structure is difficult because of the small sizes, ranging from as little as 0.05 AU at the inner edge to 100-1000 AU at large radial distances. Nonetheless, substantial progress has been made by observing the radiation emitted by the dust from near infrared to mm wavelengths, i.e., the spectral energy distribution of an unresolved disk. Many fewer results are available for the gas, which is the main mass component of disks over much of their lifetime. The inner disk gas of young stellar objects (henceforth YSOs) have been studied using the near infrared rovibrational transitions of CO and a few other molecules, while the outer regions have been explored with the mm and sub-mm lines of CO and other species. Further progress can be expected in understanding the physical properties of disks from observations with sub-mm arrays like SMA, CARMA and ALMA, with mid infrared measurements using Spitzer, and near infrared spectroscopy with large ground-based telescopes. Intense efforts are also being made to model the observations using complex thermal-chemical models. After a brief review of the existing observations and modeling results, some of the weaknesses of the models will be discussed, including the absence of good laboratory and theoretical calculations for essential microscopic processes.

  16. Particle astrophysics

    NASA Astrophysics Data System (ADS)

    Sadoulet, Bernard; Cronin, James; Aprile, Elena; Barish, Barry C.; Beier, Eugene W.; Brandenberger, Robert; Cabrera, Blas; Caldwell, David; Cassiday, George; Cline, David B.

    The following scientific areas are reviewed: (1) cosmology and particle physics (particle physics and the early universe, dark matter, and other relics); (2) stellar physics and particles (solar neutrinos, supernovae, and unconventional particle physics); (3) high energy gamma ray and neutrino astronomy; (4) cosmic rays (space and ground observations). Highest scientific priorities for the next decade include implementation of the current program, new initiatives, and longer-term programs. Essential technological developments, such as cryogenic detectors of particles, new solar neutrino techniques, and new extensive air shower detectors, are discussed. Also a certain number of institutional issues (the funding of particle astrophysics, recommended funding mechanisms, recommended facilities, international collaborations, and education and technology) which will become critical in the coming decade are presented.

  17. Molecular astrophysics

    NASA Astrophysics Data System (ADS)

    Herzberg, G.

    1989-01-01

    A brief history of Molecular Astrophysics is presented. The first molecules in space were identified in the 1920s in comets followed soon after by those in planetary atmospheres. The recent identification by MCKELLAR of the dimer of H 2, that is, (H 2) 2 in the atmosphere of Jupiter as well as the discovery, by DROSSART, MAILLARD, WATSON and others, of the H 3+ ion in the auroral zone of Jupiter are described. In this laboratory there is a continuing interest in interstellar molecules. Several molecules and molecular ions were observed by collaboration of laboratory spectroscopists and astronomers. Only the most recent ones are discussed. Also a few of the molecules not yet observed but likely to be observed are mentioned.

  18. Particle astrophysics

    NASA Technical Reports Server (NTRS)

    Sadoulet, Bernard; Cronin, James; Aprile, Elena; Barish, Barry C.; Beier, Eugene W.; Brandenberger, Robert; Cabrera, Blas; Caldwell, David; Cassiday, George; Cline, David B.

    1991-01-01

    The following scientific areas are reviewed: (1) cosmology and particle physics (particle physics and the early universe, dark matter, and other relics); (2) stellar physics and particles (solar neutrinos, supernovae, and unconventional particle physics); (3) high energy gamma ray and neutrino astronomy; (4) cosmic rays (space and ground observations). Highest scientific priorities for the next decade include implementation of the current program, new initiatives, and longer-term programs. Essential technological developments, such as cryogenic detectors of particles, new solar neutrino techniques, and new extensive air shower detectors, are discussed. Also a certain number of institutional issues (the funding of particle astrophysics, recommended funding mechanisms, recommended facilities, international collaborations, and education and technology) which will become critical in the coming decade are presented.

  19. As the Disk Turns... Monitoring the Azimuthal Thermal Gradient of the Irradiated Dust Disk in Epsilon Aurigae

    NASA Astrophysics Data System (ADS)

    Hoard, Donald; Howell, Steve; Stencel, Robert

    2013-10-01

    Epsilon Aurigae is the eclipsing binary star with the longest known orbital period, showing a single long (~2 yr) eclipse every 27.1 yr. For the last ~200 years, the nature of the eclipsing object defied explanation. We recently showed that epsilon Aur most likely consists of a high luminosity F0 post-AGB star, and a B5 V star surrounded by a solar system size (~8 AU diameter) disk of dusty material. We propose to continue our IRAC monitoring of epsilon Aur, to characterize the disk's azimuthal thermal variation as its irradiated, warm (1150 K) portion increasingly comes into view. We request 0.2 hr to obtain 2 IRAC observations. If Cycle 10 is extended through Jan 2015, we request another 6 visits (0.6 hr) in Dec 2014, coinciding with the predicted start of coherent pulsations of the F star, which occur every ~3000 days. The most recent eclipse was in Aug 2009-Jul 2011; we are now in the post-eclipse phase, when the heated side of the disk begins rotating into view. During the majority of our past IRAC observations (starting a few months prior to the eclipse ingress), only the cool (550 K) side of the disk was visible. In 2014-2015, as we move toward quadrature, the effect of heating due to the F star will increase the IRAC ch1/ch2 flux ratio. The eclipse of epsilon Aur is a rare event and a unique astrophysical opportunity, since backlighting of the disk by the luminous eclipsed star reveals details that cannot be detected in similar disks around single stars. This is one of the very few astrophysical disks where azimuthal thermal gradients can be mapped and interpreted. Observations of the warm side of the disk are crucial to test and constrain new models of disk structure. As part of our overall monitoring campaign with Spitzer, Hubble, Herschel, and numerous ground-based facilities, the proposed observations will make an important contribution to the understanding of binary stars, including mass transfer and evolution, along with new insights into

  20. Numerical modelling of Mars supersonic disk-gap-band parachute inflation

    NASA Astrophysics Data System (ADS)

    Gao, Xinglong; Zhang, Qingbin; Tang, Qiangang

    2016-06-01

    The transient dynamic behaviour of supersonic disk-gap-band parachutes in a Mars entry environment involving fluid structure interactions is studied. Based on the multi-material Arbitrary Lagrange-Euler method, the coupling dynamic model between a viscous compressible fluid and a flexible large deformation structure of the parachute is solved. The inflation performance of a parachute with a fixed forebody under different flow conditions is analysed. The decelerating parameters of the parachute, including drag area, opening loads, and coefficients, are obtained from the supersonic wind tunnel test data from NASA. Meanwhile, the evolution of the three-dimensional shape of the disk-gap-band parachute during supersonic inflation is presented, and the structural dynamic behaviour of the parachute is predicted. Then, the influence of the presence of the capsule on the flow field of the parachute is investigated, and the wake of unsteady fluid and the distribution of shock wave around the supersonic parachute are presented. Finally, the structural dynamic response of the canopy fabric under high-pressure conditions is comparatively analysed. The results show that the disk-gap-band parachute is well inflated without serious collapse. As the Mach numbers increase from 2.0 to 2.5, the drag coefficients gradually decrease, along with a small decrease in inflation time, which corresponds with test results, and proves the validity of the method proposed in this paper.

  1. Numerical Investigations of Photoevaporative Disks: Processes relevant to planet and regular satellite formation

    NASA Astrophysics Data System (ADS)

    Mitchell, Tyler Robert

    Traditional models of disks around young planets and stars make a number of simplifying assumptions. These include the use of ad hoc radial temperature profiles, or isothermal disks. Another common assumption is in regard to the treatment of the outer boundary, which is allowed to expand to infinity, or neglected completely. There has also been a lack of time-dependent viscous models that include the affects of photoevaporation and/or ongoing accretion. We alleviate many of these issues by adapting numerical methods for solving propagating phase change problems to astrophysical disks in a completely novel way. These models are all viscous, time-dependent models that include a self-consistent treatment of mass loss via photoevaporation at the disk outer edge. In the case of circumplanetary disks, they also include continued accretion from the solar nebula. I present investigations of disks around young planets and stars, made using a variety of numerical models. The investigations are primarily focused on how disk structure and evolution affect the growth and migration of growing satellite and planetary embryos. Another focus is to assess what, if any, processes are responsible for angular momentum transport in circumplanetary disks. I present detailed descriptions of these models as well as the results of applying these models to both the solar nebula and to disks around giant planets, in which regular satellites formed. Photoevaporation can substantially truncate disks and has a similar level of affect on disk evolution and morphology as variations in the viscosity parameter, alpha All of the solar nebula models were truncated, yet none of them match the steep radial surface density profile inferred from the compact configuration of the giant planets in the Nice model. Furthermore, photoevaporation has the ability to remove gas and dissipate disks on very short timescales. Despite their evolving nature, we find that giant planets and satellites can form in the

  2. Chemistry in the Molecular Disks of Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Harada, Nanase; Herbst, Eric

    2010-06-01

    Active galactic nuclei (AGNs) are the centers of galaxies with supermassive blackholes whose accretion of mass causes very high luminosities of L˜1044-46erg s-1. An accretion disk has a molecular component that extends to hundreds of pc from the central AGN core. The question of how much central illumination affects the disk and how much star formation is present near the core have been astrophysical interests. Rotational lines from these disks at a sub-kpc scale have been observed for molecules such as CO, HCO+, HCN, and HNC. When ALMA becomes fully operational, it will be able to resolve these disks at much higher resolution than currently. Molecular observations at higher resolution may give some hints on the physics in the molecular disk. We modeled the chemical composition of a molecular disk in an AGN on a scale of tens of pc. To do this, we extended our standard gas-phase OSU network to include important processes at much higher temperatures, approaching 1000 K. We used the density model of Thompson et al., and determined the temperature by the blackbody approximation from the luminosity of the AGN core. The ionization by X-rays from the AGN core, by cosmic-rays from the AGN core, supernovae and stellar winds, and by UV-photons from OB stars are considered. We will briefly mention the effects from other factors that may change the molecular abundances such as shock waves and inhomogeneity of the density of the disk. T. Thompson, E. Quataert, and N. Murray, Astrophysical J. 630, 167 (2005)

  3. MODELING COLLISIONAL CASCADES IN DEBRIS DISKS: STEEP DUST-SIZE DISTRIBUTIONS

    SciTech Connect

    Gaspar, Andras; Psaltis, Dimitrios; Rieke, George H.; Oezel, Feryal E-mail: dpsaltis@as.arizona.edu E-mail: fozel@as.arizona.edu

    2012-07-20

    We explore the evolution of the mass distribution of dust in collision-dominated debris disks, using the collisional code introduced in our previous paper. We analyze the equilibrium distribution and its dependence on model parameters by evolving over 100 models to 10 Gyr. With our numerical models, we confirm that systems reach collisional equilibrium with a mass distribution that is steeper than the traditional solution by Dohnanyi. Our model yields a quasi-steady-state slope of n(m) {approx} m{sup -1.88} [n(a) {approx} a{sup -3.65}] as a robust solution for a wide range of possible model parameters. We also show that a simple power-law function can be an appropriate approximation for the mass distribution of particles in certain regimes. The steeper solution has observable effects in the submillimeter and millimeter wavelength regimes of the electromagnetic spectrum. We assemble data for nine debris disks that have been observed at these wavelengths and, using a simplified absorption efficiency model, show that the predicted slope of the particle-mass distribution generates spectral energy distributions that are in agreement with the observed ones.

  4. Exploring Stability of General Relativistic Accretion Disks

    NASA Astrophysics Data System (ADS)

    Korobkin, Oleg; Abdikamalov, Ernazar; Schnetter, Erik; Stergioulas, Nikolaos; Zink, Burkhard

    2011-04-01

    Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios, involving core collapse of massive stars and mergers of compact ob jects. I will present results on our recent study of the stability of such disks against runaway and non-axisymmetric instabilities, which we explore using three-dimensional hydrodynamics simulations in full general relativity. All of our models develop unstable non-axisymmetric modes on a dynamical timescale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the non-axisymmetric mode with azimuthal number m=1 is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the m=1 mode in some cases. We will discuss the types, growth rates and pattern speeds of the unstable modes, as well as the detectability of the gravitational waves from such objects.

  5. Extreme Scale Computational Astrophysics

    NASA Astrophysics Data System (ADS)

    Shoemaker, Deirdre

    2009-11-01

    We live in extraordinary times. With increasingly sophisticated observatories opening up new vistas on the universe, astrophysics is becoming more complex and data-driven. The success in understanding astrophysical systems that are inherently multi-physical, nonlinear systems demands realism in our models of the phenomena. We cannot hope to advance the realism of these models to match the expected sophistication of future observations without extreme-scale computation. Just one example is the advent of gravitational wave astronomy. Detectors like LIGO are about to make the first ever detection of gravitational waves. The gravitational waves are produced during violent events such as the merger of two black holes. The detection of these waves or ripples in the fabric of spacetime is a formidable undertaking, requiring innovative engineering, powerful data analysis tools and careful theoretical modeling. I will discuss the computational and theoretical challenges ahead in our new understanding of physics and astronomy where gravity exhibits its strongest grip on our spacetime.

  6. Elastic, charge transfer, and related transport cross sections for proton impact of atomic hydrogen for astrophysical and laboratory plasma modeling

    NASA Astrophysics Data System (ADS)

    Schultz, D. R.; Ovchinnikov, S. Yu; Stancil, P. C.; Zaman, T.

    2016-04-01

    Updating and extending previous work (Krstić and Schultz 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3458 and other references) comprehensive calculations were performed for elastic scattering and charge transfer in proton—atomic hydrogen collisions. The results, obtained for 1301 collision energies in the center-of-mass energy range of 10‑4–104 eV, are provided for integral and differential cross sections relevant to transport modeling in astrophysical and other plasma environments, and are made available through a website. Use of the data is demonstrated through a Monte Carlo transport simulation of solar wind proton propagation through atomic hydrogen gas representing a simple model of the solar wind interaction with heliospheric neutrals.

  7. ZAPP: The Z Astrophysical Plasma Properties collaboration

    SciTech Connect

    Rochau, G. A.; Bailey, J. E.; Falcon, R. E.; Loisel, G. P.; Nagayama, T.; Mancini, R. C.; Hall, I.; Winget, D. E.; Montgomery, M. H.; Liedahl, D. A.

    2014-05-15

    The Z Facility at Sandia National Laboratories [Matzen et al., Phys. Plasmas 12, 055503 (2005)] provides MJ-class x-ray sources that can emit powers >0.3 PW. This capability enables benchmark experiments of fundamental material properties in radiation-heated matter at conditions previously unattainable in the laboratory. Experiments on Z can produce uniform, long-lived, and large plasmas with volumes up to 20 cc, temperatures from 1–200 eV, and electron densities from 10{sup 17–23} cc{sup −1}. These unique characteristics and the ability to radiatively heat multiple experiments in a single shot have led to a new effort called the Z Astrophysical Plasma Properties (ZAPP) collaboration. The focus of the ZAPP collaboration is to reproduce the radiation and material characteristics of astrophysical plasmas as closely as possible in the laboratory and use detailed spectral measurements to strengthen models for atoms in plasmas. Specific issues under investigation include the LTE opacity of iron at stellar-interior conditions, photoionization around active galactic nuclei, the efficiency of resonant Auger destruction in black-hole accretion disks, and H-Balmer line shapes in white dwarf photospheres.

  8. V3885 Sagittarius: A Comparison With a Range of Standard Model Accretion Disks

    NASA Technical Reports Server (NTRS)

    Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion, Edward M; Szkody, Paula; Barrett, Paul E.

    2009-01-01

    A chi-squared analysis of standard model accretion disk synthetic spectrum fits to combined Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph spectra of V3885 Sagittarius, on an absolute flux basis, selects a model that accurately represents the observed spectral energy distribution. Calculation of the synthetic spectrum requires the following system parameters. The cataclysmic variable secondary star period-mass relation calibrated by Knigge in 2006 and 2007 sets the secondary component mass. A mean white dwarf (WD) mass from the same study, which is consistent with an observationally determined mass ratio, sets the adopted WD mass of 0.7M(solar mass), and the WD radius follows from standard theoretical models. The adopted inclination, i = 65 deg, is a literature consensus, and is subsequently supported by chi-squared analysis. The mass transfer rate is the remaining parameter to set the accretion disk T(sub eff) profile, and the Hipparcos parallax constrains that parameter to mas transfer = (5.0 +/- 2.0) x 10(exp -9) M(solar mass)/yr by a comparison with observed spectra. The fit to the observed spectra adopts the contribution of a 57,000 +/- 5000 K WD. The model thus provides realistic constraints on mass transfer and T(sub eff) for a large mass transfer system above the period gap.

  9. A Comprehensive Opacities/Atomic Database for the Analysis of Astrophysical Spectra and Modeling

    NASA Technical Reports Server (NTRS)

    Pradhan, Anil K. (Principal Investigator)

    1997-01-01

    The main goals of this ADP award have been accomplished. The electronic database TOPBASE, consisting of the large volume of atomic data from the Opacity Project, has been installed and is operative at a NASA site at the Laboratory for High Energy Astrophysics Science Research Center (HEASRC) at the Goddard Space Flight Center. The database will be continually maintained and updated by the PI and collaborators. TOPBASE is publicly accessible from IP: topbase.gsfc.nasa.gov. During the last six months (since the previous progress report), considerable work has been carried out to: (1) put in the new data for low ionization stages of iron: Fe I - V, beginning with Fe II, (2) high-energy photoionization cross sections computed by Dr. Hong Lin Zhang (consultant on the Project) were 'merged' with the current Opacity Project data and input into TOPbase; (3) plans laid out for a further extension of TOPbase to include TIPbase, the database for collisional data to complement the radiative data in TOPbase.

  10. Molecular Abundances in the Disk of AN Active Galactic Nucleus

    NASA Astrophysics Data System (ADS)

    Harada, N.; Thompson, T. A.; Herbst, E.

    2011-06-01

    There are galactic nuclei that emit high luminosities L˜1044-46 erg S-1 including luminosity produced by X-rays from high mass accretion onto the central black holes. These nuclei are called active galactic nuclei (AGNs), and they are accompanied by molecular disks. Observations show high abundances of CN and HCN in the disks; the molecules are proposed to be probes of X-ray dominated regions (XDRs) created by the X-rays from AGNs. We have constructed a spatially-dependent chemical-abundance model of the molecular disk in NGC 1068, a typical AGN-dominated galaxy. Recently, new observations of CN and HCN have been made at much higher spatial resolution, and there are also detections of polyatomic molecules such as HC3N, c-C3H2, and C2H. We discuss how these observations and our simulations can help us to better understand the physical conditions, the disk structure, and conditions for star formation within molecular disks, which are still uncertain. We also include a comparison with other types of galaxies such as (ultra-) luminous infrared galaxies. Usero et al.Astronomy and Astrophysics. 419 (897), 2004. Initial results were presented at the International Symposium on Molecular Spectroscopy 2010, RF05 Garcia-Burillo et al. Astronomy and Astrophysics. 519 (2), 2010. Garcia-Burillo et al. Journal of Physics Conference Series, 131 (12031), 2008. Costagliola et al. ArXiv e-print arXiv:1101.2122, 2011. Nakajima et al. Astrophysical Journal Letters 728 (L38), 2008.

  11. Models of the η Corvi Debris Disk from the Keck Interferometer, Spitzer, and Herschel

    NASA Astrophysics Data System (ADS)

    Lebreton, J.; Beichman, C.; Bryden, G.; Defrère, D.; Mennesson, B.; Millan-Gabet, R.; Boccaletti, A.

    2016-02-01

    Debris disks are signposts of analogs to small-body populations of the solar system, often, however, with much higher masses and dust production rates. The disk associated with the nearby star η Crv is especially striking, as it shows strong mid- and far-infrared excesses despite an age of ∼1.4 Gyr. We undertake constructing a consistent model of the system that can explain a diverse collection of spatial and spectral data. We analyze Keck Interferometer Nuller measurements and revisit Spitzer and additional spectrophotometric data, as well as resolved Herschel images, to determine the dust spatial distribution in the inner exozodi and in the outer belt. We model in detail the two-component disk and the dust properties from the sub-AU scale to the outermost regions by fitting simultaneously all measurements against a large parameter space. The properties of the cold belt are consistent with a collisional cascade in a reservoir of ice-free planetesimals at 133 AU. It shows marginal evidence for asymmetries along the major axis. KIN enables us to establish that the warm dust consists of a ring that peaks between 0.2 and 0.8 AU. To reconcile this location with the ∼400 K dust temperature, very high albedo dust must be invoked, and a distribution of forsterite grains starting from micron sizes satisfies this criterion, while providing an excellent fit to the spectrum. We discuss additional constraints from the LBTI and near-infrared spectra, and we present predictions of what James Webb Space Telescope can unveil about this unusual object and whether it can detect unseen planets.

  12. Rheological properties of the soft-disk model of two-dimensional foams.

    PubMed

    Langlois, Vincent J; Hutzler, Stefan; Weaire, Denis

    2008-08-01

    The soft-disk model previously developed and applied by Durian [D. J. Durian, Phys. Rev. Lett. 75, 4780 (1995)] is brought to bear on problems of foam rheology of longstanding and current interest, using two-dimensional systems. The questions at issue include the origin of the Herschel-Bulkley relation, normal stress effects (dilatancy), and localization in the presence of wall drag. We show that even a model that incorporates only linear viscous effects at the local level gives rise to nonlinear (power-law) dependence of the limit stress on strain rate. With wall drag, shear localization is found. Its nonexponential form and the variation of localization length with boundary velocity are well described by a continuum model in the spirit of Janiaud etal [Phys. Rev. Lett. 97, 038302 (2006)]. Other results satisfactorily link localization to model parameters, and hence tie together continuum and local descriptions. PMID:18850830

  13. Modeling the X-ray Irradiation of the LkCa 15 Protoplanetary Disk Using XMM-Newton Archival Data

    NASA Astrophysics Data System (ADS)

    Skinner, Stephen

    A giant protoplanet has been detected orbiting the nearby T Tauri star LkCa 15 using IR masked aperture techniques. The protoplanet (LkCa 15b) orbits within the dust-depleted inner region of a circumstellar disk at a projected separation of ~16 AU from the central star. The star itself is quite young (age ~2 Myr) making this system an excellent laboratory for studying the earliest stages of exoplanet formation. We detected LkCa 15 as a bright X-ray source in a short 9.8 ks Chandra observation during 2009. More recently, we obtained a deeper follow-up X-ray observation of LkCa 15 in 2014 with XMM-Newton providing a higher quality spectrum. We propose here to analyze the XMM-Newton data and use the derived spectral parameters along with known disk properties to model the X-ray heating and ionization of the LkCa 15 disk and to determine the gas-to-dust ratio (G/D) along the line-of-sight through the disk. X-ray heating and ionization affect the thermal and chemical structure in the disk and, along with the G/D ratio, are crucial parameters needed to determine physical conditions in the inner disk and construct realistic planet formation models. We are requesting ADAP funding to support the analysis and publication of this valuable XMM-Newton data set, which is now in the public archive.

  14. Modelling circumbinary protoplanetary disks. I. Fluid simulations of the Kepler-16 and 34 systems

    NASA Astrophysics Data System (ADS)

    Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.

    2015-10-01

    Context. The Kepler mission's discovery of a number of circumbinary planets orbiting close (ap< 1.1 au) to the stellar binary raises questions as to how these planets could have formed given the intense gravitational perturbations the dual stars impart on the disk. The gas component of circumbinary protoplanetary disks is perturbed in a similar manner to the solid, planetesimal dominated counterpart, although the mechanism by which disk eccentricity originates differs. Aims: This is the first work of a series that aims to investigate the conditions for planet formation in circumbinary protoplanetary disks. Methods: We present a number of hydrodynamical simulations that explore the response of gas disks around two observed binary systems: Kepler-16 and Kepler-34. We probe the importance of disk viscosity, aspect-ratio, inner boundary condition, initial surface density gradient, and self-gravity on the dynamical evolution of the disk, as well as its quasi-steady-state profile. Results: We find there is a strong influence of binary type on the mean disk eccentricity, e̅d, leading to e̅d = 0.02 - 0.08 for Kepler-16 and e̅d = 0.10 - 0.15 in Kepler-34. The value of α-viscosity has little influence on the disk, but we find a strong increase in mean disk eccentricity with increasing aspect-ratio due to wave propagation effects. The choice of inner boundary condition only has a small effect on the surface density and eccentricity of the disk. Our primary finding is that including disk self-gravity has little impact on the evolution or final state of the disk for disks with masses less than 12.5 times that of the minimum-mass solar nebula. This finding contrasts with the results of self-gravity relevance in circumprimary disks, where its inclusion is found to be an important factor in describing the disk evolution.

  15. THE MASS-DEPENDENT STAR FORMATION HISTORIES OF DISK GALAXIES: INFALL MODEL VERSUS OBSERVATIONS

    SciTech Connect

    Chang, R. X.; Hou, J. L.; Shen, S. Y.; Shu, C. G.

    2010-10-10

    We introduce a simple model to explore the star formation histories of disk galaxies. We assume that the disk originate and grows by continuous gas infall. The gas infall rate is parameterized by the Gaussian formula with one free parameter: the infall-peak time t{sub p} . The Kennicutt star formation law is adopted to describe how much cold gas turns into stars. The gas outflow process is also considered in our model. We find that, at a given galactic stellar mass M{sub *}, the model adopting a late infall-peak time t{sub p} results in blue colors, low-metallicity, high specific star formation rate (SFR), and high gas fraction, while the gas outflow rate mainly influences the gas-phase metallicity and star formation efficiency mainly influences the gas fraction. Motivated by the local observed scaling relations, we 'construct' a mass-dependent model by assuming that the low-mass galaxy has a later infall-peak time t{sub p} and a larger gas outflow rate than massive systems. It is shown that this model can be in agreement with not only the local observations, but also with the observed correlations between specific SFR and galactic stellar mass SFR/M{sub *} {approx} M{sub *} at intermediate redshifts z < 1. Comparison between the Gaussian-infall model and the exponential-infall model is also presented. It shows that the exponential-infall model predicts a higher SFR at early stage and a lower SFR later than that of Gaussian infall. Our results suggest that the Gaussian infall rate may be more reasonable in describing the gas cooling process than the exponential infall rate, especially for low-mass systems.

  16. SUSTAINING STAR FORMATION RATES IN SPIRAL GALAXIES: SUPERNOVA-DRIVEN TURBULENT ACCRETION DISK MODELS APPLIED TO THINGS GALAXIES

    SciTech Connect

    Vollmer, Bernd; Leroy, Adam K.

    2011-01-15

    Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M{sub sun}) {approx}< 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.

  17. Trends in nuclear astrophysics

    NASA Astrophysics Data System (ADS)

    Schatz, Hendrik

    2016-06-01

    Nuclear astrophysics is a vibrant field at the intersection of nuclear physics and astrophysics that encompasses research in nuclear physics, astrophysics, astronomy, and computational science. This paper is not a review. It is intended to provide an incomplete personal perspective on current trends in nuclear astrophysics and the specific role of nuclear physics in this field.

  18. A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS

    SciTech Connect

    Bans, Alissa; Koenigl, Arieh E-mail: akonigl@uchicago.edu

    2012-10-20

    Protostellar systems, ranging from low-luminosity classical T Tauri and Herbig Ae stars to high-luminosity Herbig Be stars, exhibit a near-infrared (NIR) excess in their spectra that is dominated by a bump in the monochromatic luminosity with a peak near 3 {mu}m. The bump can be approximated by a thermal emission component of temperature {approx}1500 K that is of the order of the sublimation temperature of interstellar dust grains. In the currently popular 'puffed-up rim' scenario, the bump represents stellar radiation that propagates through the optically thin inner region of the surrounding accretion disk and is absorbed and reemitted by the dust that resides just beyond the dust sublimation radius r {sub sub}. However, this model cannot account for the strongest bumps measured in these sources, and it predicts a pronounced secondary bounce in the interferometric visibility curve that is not observed. In this paper we present an alternative interpretation, which attributes the bump to reemission of stellar radiation by dust that is uplifted from the disk by a centrifugally driven wind. Winds of this type are a leading candidate for the origin of the strong outflows associated with protostars, and there is observational evidence for disk winds originating on scales {approx}r {sub sub}. Using a newly constructed Monte Carlo radiative transfer code and focusing on low-luminosity sources, we show that this model can account for the NIR excess emission even in bright Herbig Ae stars such as AB Auriga and MWC 275, and that it successfully reproduces the basic features of the visibilities measured in these protostars. We argue that a robust dusty outflow in these sources could be self-limiting-through shielding of the stellar FUV photons-to a relatively narrow launching region between r {sub sub} and {approx}2 r {sub sub}. We also suggest that the NIR and scattered-light variability exhibited by a source like MWC 275 can be attributed in this picture to the uplifting of

  19. Numerical Simulation and Wake Modeling of Wind Turbine Rotor as AN Actuator Disk

    NASA Astrophysics Data System (ADS)

    Shen, Xiang; Wang, Tongguang; Zhong, Wei

    Numerical simulations of flow fields around the wind turbine rotor simplified as an actuator disk (AD) with zero thickness have been made to investigate the flow structure and wake development in different operation states. A N-S solver has been used and the energy extracted by the rotor is represented by a discontinuous pressure jump through the actuator disk. Axial pressure and velocity development from far upstream to far downstream is fully described by the simulations, which could never be obtained by the momentum theory. It is showed that there are significant differences in wake development between inviscid and viscous conditions. In inviscid simulations, the axial velocity keeps decreasing along the oncoming flow direction, which is consistent with the momentum theory. In viscous simulations, however, the axial velocity first decreases but then gradually recovers approaching to the undisturbed velocity, due to momentum transport from outer flow to wake flow by viscous shear effect. Based on the numerical analysis, the work of this paper is also focused on wake modeling. A new two-dimensional models based on nonlinear wake development has been developed, which is capable to describe the far wake more accurately.

  20. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    NASA Astrophysics Data System (ADS)

    Tombesi, F.

    2016-05-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this ``quasar mode'' feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. However, fundamental improvements on these studies will come only from the unprecedented energy resolution and sensitivity of the upcoming X-ray observatories, namely ASTRO-H (launch date early 2016) and Athena (2028).

  1. Workshop on the origin of the heavy elements: Astrophysical models and experimental challenges, Santa Fe, New Mexico, September 3-4, 1999

    SciTech Connect

    Robert C. Haight; John L. Ullmann; Daniel D. Strottman; Paul E. Koehler; Franz Kaeppeler

    2000-01-01

    This Workshop was held on September 3--4, 1999, following the 10th International Symposium on Capture Gamma-Ray Spectroscopy. Presentations were made by 14 speakers, 6 from the US and 8 from other countries on topics relevant to s-, r- and rp-process nucleosynthesis. Laboratory experiments, both present and planned, and astrophysical observations were represented as were astrophysical models. Approximately 50 scientists participated in this Workshop. These Proceedings consist of copies of vu-graphs presented at the Workshop. For further information, the interested readers are referred to the authors.

  2. A NEW RAYTRACER FOR MODELING AU-SCALE IMAGING OF LINES FROM PROTOPLANETARY DISKS

    SciTech Connect

    Pontoppidan, Klaus M.; Meijerink, Rowin; Blake, Geoffrey A.; Dullemond, Cornelis P.

    2009-10-20

    The material that formed the present-day solar system originated in feeding zones in the inner solar nebula located at distances within approx20 AU from the Sun, known as the planet-forming zone. Meteoritic and cometary material contain abundant evidence for the presence of a rich and active chemistry in the planet-forming zone during the gas-rich phase of solar system formation. It is a natural conjecture that analogs can be found among the zoo of protoplanetary disks around nearby young stars. The study of the chemistry and dynamics of planet formation requires: (1) tracers of dense gas at 100-1000 K and (2) imaging capabilities of such tracers with 5-100 mas (0.5-20 AU) resolution, corresponding to the planet-forming zone at the distance of the closest star-forming regions. Recognizing that the rich infrared (2-200 mum) molecular spectrum recently discovered to be common in protoplanetary disks represents such a tracer, we present a new general ray-tracing code, RADLite, that is optimized for producing infrared line spectra and images from axisymmetric structures. RADLite can consistently deal with a wide range of velocity gradients, such as those typical for the inner regions of protoplanetary disks. The code is intended as a back-end for chemical and excitation codes, and can rapidly produce spectra of thousands of lines for grids of models for comparison with observations. Such radiative transfer tools will be crucial for constraining both the structure and chemistry of planet-forming regions, including data from current infrared imaging spectrometers and extending to the Atacama Large Millimeter Array and the next generation of Extremely Large Telescopes, the James Webb Space Telescope and beyond.

  3. An Eccentric-Disk Model for the Nucleus of M31

    NASA Astrophysics Data System (ADS)

    Tremaine, Scott

    1995-08-01

    The nucleus of M31 may be a thick eccentric disk, composed of stars traveling on nearly Keplerian orbits around a black hole or other dark compact object. This hypothesis reproduces most of the features seen in HST photometry of the center of M31; in particular the bright off-center source P1 is the apoapsis region of the disk. An eccentric disk can also explain the rotation curve and asymmetric dispersion profile revealed by ground-based observations. The central object must be smaller than ~1 pc so that the potential felt by the disk is nearly Keplerian. The disk eccentricity may be excited by dynamical friction from the bulge.

  4. Confronting Standard Models of Proto-planetary Disks with New Mid-infrared Sizes from the Keck Interferometer

    NASA Astrophysics Data System (ADS)

    Millan-Gabet, Rafael; Che, Xiao; Monnier, John D.; Sitko, Michael L.; Russell, Ray W.; Grady, Carol A.; Day, Amanda N.; Perry, R. B.; Harries, Tim J.; Aarnio, Alicia N.; Colavita, Mark M.; Wizinowich, Peter L.; Ragland, Sam; Woillez, Julien

    2016-08-01

    We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inner rim and MIR disk emission. We find a high degree of correlation between the stellar luminosity and the MIR disk sizes after using near-infrared data to remove the contribution from the inner rim. We then use a semi-analytical physical model to also find that the very widely used “star + inner dust rim + flared disk” class of models strongly fails to reproduce the spectral energy distribution (SED) and spatially resolved MIR data simultaneously; specifically a more compact source of MIR emission is required than results from the standard flared disk model. We explore the viability of a modification to the model whereby a second dust rim containing smaller dust grains is added, and find that the 2-rim model leads to significantly improved fits in most cases. This complexity is largely missed when carrying out SED modeling alone, although detailed silicate feature fitting by McClure et al. recently came to a similar conclusion. As has been suggested recently by Menu et al., the difficulty in predicting MIR sizes from the SED alone might hint at “transition disk”-like gaps in the inner au; however, the relatively high correlation found in our MIR disk size versus stellar luminosity relation favors layered disk morphologies and points to missing disk model ingredients instead.

  5. A guide to the use of the pressure disk rotor model as implemented in INS3D-UP

    NASA Technical Reports Server (NTRS)

    Chaffin, Mark S.

    1995-01-01

    This is a guide for the use of the pressure disk rotor model that has been placed in the incompressible Navier-Stokes code INS3D-UP. The pressure disk rotor model approximates a helicopter rotor or propeller in a time averaged manner and is intended to simulate the effect of a rotor in forward flight on the fuselage or the effect of a propeller on other aerodynamic components. The model uses a modified actuator disk that allows the pressure jump across the disk to vary with radius and azimuth. The cyclic and collective blade pitch angles needed to achieve a specified thrust coefficient and zero moment about the hub are predicted. The method has been validated with experimentally measured mean induced inflow velocities as well as surface pressures on a generic fuselage. Overset grids, sometimes referred to as Chimera grids, are used to simplify the grid generation process. The pressure disk model is applied to a cylindrical grid which is embedded in the grid or grids used for the rest of the configuration. This document will outline the development of the method, and present input and results for a sample case.

  6. Modeling Self-Subtraction of Extended Emission in Angular Differential Imaging: Application to the HD 32297 Debris Disk

    NASA Astrophysics Data System (ADS)

    Esposito, Thomas; Fitzgerald, M. P.; Kalas, P.; Graham, J. R.

    2012-01-01

    We have spatially resolved the debris disk around the A star HD 32297 in scattered light using Keck NIRC2 coronagraphic imaging with adaptive optics in the H and K bands. We used angular differential imaging and the LOCI algorithm to suppress the stellar PSF and reveal the nearly edge-on disk. Although LOCI is effective in subtracting quasistatic speckles in the stellar PSF, its application can result in self-subtraction of the disk signal due to its finite spatial extent. The degree of self-subtraction varies with radius, which would preclude accurate measurement of the surface brightness profile and compromise our inferences regarding the physical processes responsible for the dust distribution. We have developed a new technique to model the effects of self-subtraction on spatially extended emission introduced by the LOCI-processed angular differential imaging. Our method accounts for both the self-subtraction kernel's dependence on LOCI parameters and spatial location. We forward model the structure of the disk and compute the form of the self-subtraction at each radius, and then use this to jointly extract the disk surface brightness, scale height, and midplane location as functions of radius. Our investigation into the inner structure of the disk recovers a previously reported brightness asymmetry. This may be indicative of a perturbed density distribution or a change in average grain properties due to a recent stochastic event. A comparison of the surface brightness and morphology of the disk between two wavelengths can provide insight into the size and distribution of dust grains as well as the grains’ interaction with the surrounding environment. In addition, we can apply our self-subtraction modeling technique to future high-contrast imaging of this system and others like it. This work was supported in part by University of California Lab Research Program 09-LR-01-118057-GRAJ and NSF grant AST-0909188.

  7. Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects. II; Application to Cygnus X-1

    NASA Technical Reports Server (NTRS)

    Dove, James B.; Wilms, Joern; Maisack, Michael; Begelman, Mitchell C.

    1997-01-01

    We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broadband X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper, models in which the Comptonizing medium is a slab surrounding the cold accretion disk cannot have a temperature higher than about 140 keV for optical depths greater than 0.2, resulting in spectra that are much softer than the observed 10-30 keV spectrum of Cyg X-1. In addition, the slab-geometry models predict a substantial "soft excess" at low energies, a feature not observed for Cyg X-1, and Fe K-alpha fluorescence lines that are stronger than observed. Previous Comptonization models in the literature have invoked a slab geometry with optical depth tau(sub T) approx. greater than 0.3 and coronal temperature T(sub c) approx. 150 keV, but they are not self-consistent. Therefore, ADC models with a slab geometry are not appropriate for explaining the X-ray spectrum of Cyg X-1. Models with a spherical corona and an exterior disk, however, predict much higher self-consistent coronal temperatures than the slab-geometry models. The higher coronal temperatures are due to the lower amount of reprocessing of coronal radiation in the accretion disk, giving rise to a lower Compton cooling rate. Therefore, for the sphere-plus-disk geometry, the predicted spectrum can be hard enough to describe the observed X-ray continuum of Cyg X-1 while predicting Fe fluorescence lines having an equivalent width of approx. 40 eV. Our best-fit parameter values for the sphere-plus-disk geometry are tau(sub T) approx. equal to 1.5 and T(sub c) approx. equal to 90 keV.

  8. Theoretical study of the α +d →6Li +γ astrophysical capture process in a three-body model

    NASA Astrophysics Data System (ADS)

    Tursunov, E. M.; Kadyrov, A. S.; Turakulov, S. A.; Bray, I.

    2016-07-01

    The astrophysical capture process α +d →6Li is studied in a three-body model. The initial state is factorized into the deuteron bound state and the (α +d )-scattering state. The final nucleus 6Li (1+) is described as a three-body bound state α +n +p in the hyperspherical Lagrange-mesh method. The contribution of the E 1 -transition operator from the initial isosinglet states to the isotriplet components of the final state is estimated to be negligible. An estimation of the forbidden E 1 transition to the isosinglet components of the final state is comparable with the corresponding results of the two-body model. However, the contribution of the E 2 -transition operator is found to be much smaller than the corresponding estimations of the two-body model. The three-body model perfectly matches the new experimental data of the LUNA Collaboration with the spectroscopic factor of 2.586 estimated from the bound-state wave functions of 6Li and a deuteron.

  9. The evolution of dust in extreme astrophysical environments

    NASA Astrophysics Data System (ADS)

    Dwek, E.; Galliano, F.; Jones, A. P.

    Dust is present in almost every astrophysical environment, ranging from circumstellar shells and disks to spiral, elliptical, starburst, and active galaxies, and to pre-galactic objects such as QSO absorption-line and damped Lyα systems. Dust leaves its imprint on interstellar extinction curves, IR spectra, and the elemental depletion patterns in the ISM of galaxies. Understanding the origin and the complex evolutionary cycle of dust is therefore an important goal in astrophysics. In this contribution, we present models to describe the evolutionary history of interstellar dust in a diverse set of astrophysical environments, ranging from normal star-forming galaxies like the Milky Way to high-redshift galaxies undergoing extreme rates of star formation. In particular, we show how the chemical evolution models can explain the correlations of dust abundances with galactic metallicities, and the presence of large amounts of dust in young dusty hyperluminous infrared galaxies in which supernovae are the only source of newly-condensed dust.

  10. Evaluation of the polyurethane foam (PUF) disk passive air sampler: Computational modeling and experimental measurements

    NASA Astrophysics Data System (ADS)

    May, Andrew A.; Ashman, Paul; Huang, Jiaoyan; Dhaniyala, Suresh; Holsen, Thomas M.

    2011-08-01

    Computational fluid dynamics (CFD) simulations coupled with wind tunnel-experiments were used to determine the sampling rate (SR) of the widely used polyurethane foam (PUF) disk passive sampler. In the wind-tunnel experiments, water evaporation rates from a water saturated PUF disk installed in the sampler housing were determined by measuring weight loss over time. In addition, a modified passive sampler designed to collect elemental mercury (Hg 0) with gold-coated filters was used. Experiments were carried out at different wind speeds and various sampler angles. The SRs obtained from wind-tunnel experiments were compared to those obtained from the field by scaling the values by the ratios of air diffusivities. Three-dimensional (3D) CFD simulations were also used to generate SRs for both polychlorinated biphenyls (PCBs) and Hg 0. Overall, the modeled and measured SRs agree well and are consistent with the values obtained from field studies. As previously observed, the SRs increased linearly with increasing wind speed. In addition, it was determined that the SR was strongly dependent on the angle of the ambient wind. The SRs increased when the base was tilted up pointing into the wind and when the base was tilted down (i.e., such that the top of the sampler was facing the wind) the SR decreased initially and then increased. The results suggest that there may be significant uncertainty in concentrations obtained from passive sampler measurements without knowledge of wind speed and wind angle relative to the sampler.

  11. How does the mass transport in disk galaxy models influence the character of orbits?

    NASA Astrophysics Data System (ADS)

    Zotos, Euaggelos E.

    We explore the regular or chaotic nature of orbits of stars moving in the meridional (R,z) plane of an axially symmetric time-dependent disk galaxy model with a central, spherically symmetric nucleus. In particular, mass is linearly transported from the disk to the galactic nucleus, in order to mimic, in a way, the case of self-consistent interactions of an actual N-body simulation. We thus try to unveil the influence of this mass transportation on the different families of orbits of stars by monitoring how the percentage of chaotic orbits, as well as the percentages of orbits of the main regular resonant families, evolve as the galaxy develops a dense and massive nucleus in its core. The SALI method is applied to samples of orbits in order to distinguish safely between ordered and chaotic motion. In addition, a method based on the concept of spectral dynamics is used for identifying the various families of regular orbits and also for recognizing the secondary resonances that bifurcate from them. Our computations strongly suggest that the amount of the observed chaos is substantially increased as the nucleus becomes more massive. Furthermore, extensive numerical calculations indicate that there are orbits which change their nature from regular to chaotic and vice versa and also orbits which maintain their orbital character during the galactic evolution. The present outcomes are compared to earlier related work.

  12. Astrophysical fluid dynamics

    NASA Astrophysics Data System (ADS)

    Ogilvie, Gordon I.

    2016-06-01

    These lecture notes and example problems are based on a course given at the University of Cambridge in Part III of the Mathematical Tripos. Fluid dynamics is involved in a very wide range of astrophysical phenomena, such as the formation and internal dynamics of stars and giant planets, the workings of jets and accretion discs around stars and black holes and the dynamics of the expanding Universe. Effects that can be important in astrophysical fluids include compressibility, self-gravitation and the dynamical influence of the magnetic field that is `frozen in' to a highly conducting plasma. The basic models introduced and applied in this course are Newtonian gas dynamics and magnetohydrodynamics (MHD) for an ideal compressible fluid. The mathematical structure of the governing equations and the associated conservation laws are explored in some detail because of their importance for both analytical and numerical methods of solution, as well as for physical interpretation. Linear and nonlinear waves, including shocks and other discontinuities, are discussed. The spherical blast wave resulting from a supernova, and involving a strong shock, is a classic problem that can be solved analytically. Steady solutions with spherical or axial symmetry reveal the physics of winds and jets from stars and discs. The linearized equations determine the oscillation modes of astrophysical bodies, as well as their stability and their response to tidal forcing.

  13. Astrophysical fluid dynamics

    NASA Astrophysics Data System (ADS)

    Ogilvie, Gordon I.

    2016-06-01

    > These lecture notes and example problems are based on a course given at the University of Cambridge in Part III of the Mathematical Tripos. Fluid dynamics is involved in a very wide range of astrophysical phenomena, such as the formation and internal dynamics of stars and giant planets, the workings of jets and accretion discs around stars and black holes and the dynamics of the expanding Universe. Effects that can be important in astrophysical fluids include compressibility, self-gravitation and the dynamical influence of the magnetic field that is `frozen in' to a highly conducting plasma. The basic models introduced and applied in this course are Newtonian gas dynamics and magnetohydrodynamics (MHD) for an ideal compressible fluid. The mathematical structure of the governing equations and the associated conservation laws are explored in some detail because of their importance for both analytical and numerical methods of solution, as well as for physical interpretation. Linear and nonlinear waves, including shocks and other discontinuities, are discussed. The spherical blast wave resulting from a supernova, and involving a strong shock, is a classic problem that can be solved analytically. Steady solutions with spherical or axial symmetry reveal the physics of winds and jets from stars and discs. The linearized equations determine the oscillation modes of astrophysical bodies, as well as their stability and their response to tidal forcing.

  14. Chondrites and the Protoplanetary Disk, Part 1

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The papers discussed the following: The Formation Process of Adhering and Consorting Compound Chondrules Inferred Their Petrology and Major-Element Composition. The Prospect of High-Precision Pb Isotopic Dating of Meteorites. Evolution of UV-Irradiated Protoplanetary Disks. A Model for the Formation of E Chondrites. Oxygen Isotopic Diffusion and Exchange Experiments on Olivine and Chondrule Melts: Preliminary Results. Shock Heating: Origin of Shock Waves in the Protoplanetary Disk. Thermal Structures of Protoplanetary Disks. Meteoritical Astrophysics: A New Subdiscipline. Origin and Thermal History of FeNi-Metal in Primitive Chondrites. The Collisions of Chondrules Behind Shock Waves. Primary Signatures of the Nebular Dust Preserved in Accretionary Rims and Matrices of CV Chondrites. History of Thermally Processed Solids in the Protoplanetary Disk: Reconciling Theoretical Models and Meteoritical. Evidence Evaporation and Condensation During CAI and Chondrule Formation. Shock Heating: Effects on Chondritic Material. Rhounite-bearing Inclusions E201 and E202 from Efremovka: Constraints from Trace. Element Measurements Element Mapping in Anhydrous IDPs: Identification of the Host Phases of Major/Minor Elements as a Test of Nebula Condensation Models. Theoretical Studies of Disk Evolution Around Solar Mass Stars. Chemical Effects of High-Temperature Processing of Silicates. I-Xe and the Chronology of the Early Solar System. The Effects of X-Rays on the Gas and Dust in Young Stellar Objects. Origin of Short-lived Radionuclides in the Early Solar System. On Early Solar System Chronology: Implications of an Initially Heterogeneous Distribution of Short-lived Radionuclides. The Origin of Short-lived Radionuclides and Early Solar System Irradiation. Disequilibrium Melting and Oxygen Isotope Exchange of CAIs and Chondrules in the Solar Nebula. Mineralogy and Chemistry of Fine-grained Matrices, Rims, and Dark Inclusions in the CR Carbonaceous Chondrites Acfer/El Djouf 001 and

  15. Chemistry in disks. IV. Benchmarking gas-grain chemical models with surface reactions

    NASA Astrophysics Data System (ADS)

    Semenov, D.; Hersant, F.; Wakelam, V.; Dutrey, A.; Chapillon, E.; Guilloteau, St.; Henning, Th.; Launhardt, R.; Piétu, V.; Schreyer, K.

    2010-11-01

    Context. We describe and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. Aims: The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. Methods: We considered three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking was performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. The chemical evolution is modeled within 109 years using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form. Results: The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result, however, required a lot of effort to make all necessary details consistent through the model runs, e.g., definition of the gas particle density, density of grain surface sites, or the strength and shape of the UV radiation field. Conclusions: The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available on the internet. This will facilitate and ease the development of other astrochemical models and provide nonspecialists with a detailed description of the model ingredients and requirements to analyze the cosmic

  16. Modeling Far-UV Fluorescent Emission Features of Warm Molecular Hydrogen in the Inner Regions of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Hoadley, Keri; France, Kevin

    2015-01-01

    Probing the surviving molecular gas within the inner regions of protoplanetary disks (PPDs) around T Tauri stars (1 - 10 Myr) provides insight into the conditions in which planet formation and migration occurs while the gas disk is still present. We model observed far ultraviolet (FUV) molecular hydrogen (H₂) fluorescent emission lines that originate within the inner regions (< 10 AU) of 9 well-studied Classic T Tauri stars, using the Hubble Space Telescope Cosmic Origins Spectrograph (COS), to explore the physical structure of the molecular disk at different PPD dust evolutionary stages. We created a 2D radiative transfer model that estimates the density and temperature distributions of warm, inner radial H₂ (T > 1500 K) with a set of 6 free parameters and produces a data cube of expected emission line profiles that describe the physical structure of the inner molecular disk atmosphere. By comparing the modeled emission lines with COS H₂ fluorescence emission features, we estimate the physical structure of the molecular disk atmosphere for each target with the set of free parameters that best replicate the observed lines. First results suggest that, for all dust evolutionary stages of disks considered, ground-state H₂ populations are described by a roughly constant temperature T(H₂) = 2500 +/- 1000 K. Possible evolution of the density structure of the H₂ atmosphere between intact and depleting dust disks may be distinguishable, but large errors in the inferred best-fit parameter sets prevent us from making this conclusion. Further improvements to the modeling framework and statistical comparison in determining the best-fit model-to-data parameter sets are ongoing, beginning with improvements to the radiative transfer model and use of up-to-date HI Lyman α absorption optical depths (see McJunkin in posters) to better estimate disk structural parameters. Once improvements are implemented, we will investigate the possible presence of a molecular wind

  17. Analytical model of thermal effect and optical path difference in end-pumped Yb:YAG thin disk laser.

    PubMed

    Zhu, Guangzhi; Zhu, Xiao; Wang, Mu; Feng, Yufan; Zhu, Changhong

    2014-10-10

    An analytical model of the thermal effect and optical path difference (OPD) of a thin disk laser is developed with the combination of the analytical method and commercial finite element analysis software. The distributions of temperature, stress, strain, and OPD caused by temperature gradient, axial thermal strain (bulging), thermal strain-induced birefringence, and deformation are obtained. Based on the analytical model, the production mechanisms, features, and influence of OPD in an end-pumped thin disk laser are discussed, which make the causes of spherical and aspherical parts of the OPD more obvious. Furthermore, the OPD including the spherical and aspherical parts of the thin disk crystal is discussed for various pumping intensities. PMID:25322379

  18. Herniated Disk

    MedlinePlus

    Your backbone, or spine, is made up of 26 bones called vertebrae. In between them are soft disks filled with a jelly-like substance. These disks cushion the vertebrae and keep them in place. As you age, ...

  19. Physical Properties of Tidal Features of Interacting Disk Galaxies: Three-dimensional Self-consistent Models

    NASA Astrophysics Data System (ADS)

    Oh, Sang Hoon; Kim, Woong-Tae; Lee, Hyung Mok

    2015-07-01

    Using self-consistent three-dimensional (3D) N-body simulations, we investigate the physical properties of nonaxisymmetric features in a disk galaxy created by a tidal interaction with its companion. The primary galaxy consists of a stellar disk, a bulge, and a live halo, corresponding to Milky-Way-type galaxies, while the companion is represented by a halo alone. We vary the companion mass and the pericenter distance to explore situations with differing tidal strength parameterized by either the relative tidal force P or the relative imparted momentum S. We find that the formation of a tidal tail in the outer parts requires P≳ 0.05 or S≳ 0.07. A stronger interaction results in a stronger, less wound tail that forms earlier. Similarly, a stronger tidal forcing produces stronger, more loosely wound spiral arms in the inner parts. The arms are approximately logarithmic in shape, with both amplitude and pitch angle decaying with time. The derived pattern speed decreases with radius and is close to the {{Ω }}-κ /2 curve at late time, with Ω and κ denoting the angular and epicycle frequencies, respectively. This suggests that the tidally induced spiral arms are most likely kinematic density waves weakly modified by self-gravity. Compared to the razor-thin counterparts, arms in the 3D models are weaker, have a smaller pitch angle, and wind and decay more rapidly. The 3D density structure of the arms is well described by the concentrated and sinusoidal models when the arms are in the nonlinear and linear regimes, respectively. We demonstrate that dynamical friction between interacting galaxies transfers the orbital angular momentum of one galaxy to the spin angular momentum of the companion halo.

  20. GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS: Viscoelastic BISQ Model for Low-Permeability Sandstone with Clay

    NASA Astrophysics Data System (ADS)

    Nie, Jian-Xin; Yang, Ding-Hui

    2008-08-01

    A modified BISQ (Biot/Squirt) model for wave propagation in low-permeability sandstone is developed by introducing the viscoelastic mechanism of a porous skeleton into Dvorkin's model. The linear viscoelasticity of the Kelvin Voigt constitutive law is employed to describe the stress-strain relation of a solid frame with clay while the ultrasonic waves propagate through the fluid-saturated sandstone. The phase velocity and attenuation of two p-waves are given based on the present BISQ model. The comparisons between numerical results and experimental data indicate that our viscoelastic model is more realistic and feasible for wave propagation in the low-permeability sandstone, especially with clay, than traditional BISQ models.

  1. Does the Debris Disk around HD 32297 Contain Cometary Grains?

    NASA Astrophysics Data System (ADS)

    Rodigas, Timothy J.; Debes, John H.; Hinz, Philip M.; Mamajek, Eric E.; Pecaut, Mark J.; Currie, Thayne; Bailey, Vanessa; Defrere, Denis; De Rosa, Robert J.; Hill, John M.; Leisenring, Jarron; Schneider, Glenn; Skemer, Andrew J.; Skrutskie, Michael; Vaitheeswaran, Vidhya; Ward-Duong, Kimberly

    2014-03-01

    We present an adaptive optics imaging detection of the HD 32297 debris disk at L' (3.8 μm) obtained with the LBTI/LMIRcam infrared instrument at the Large Binocular Telescope. The disk is detected at signal-to-noise ratio per resolution element ~3-7.5 from ~0.''3 to 1.''1 (30-120 AU). The disk at L' is bowed, as was seen at shorter wavelengths. This likely indicates that the disk is not perfectly edge-on and contains highly forward-scattering grains. Interior to ~50 AU, the surface brightness at L' rises sharply on both sides of the disk, which was also previously seen at Ks band. This evidence together points to the disk containing a second inner component located at lsim50 AU. Comparing the color of the outer (50 disk at L' with archival Hubble Space Telescope/NICMOS images of the disk at 1-2 μm allows us to test the recently proposed cometary grains model of Donaldson et al. We find that the model fails to match this disk's surface brightness and spectrum simultaneously (reduced chi-square = 17.9). When we modify the density distribution of the model disk, we obtain a better overall fit (reduced chi-square = 2.87). The best fit to all of the data is a pure water ice model (reduced chi-square = 1.06), but additional resolved imaging at 3.1 μm is necessary to constrain how much (if any) water ice exists in the disk, which can then help refine the originally proposed cometary grains model. Based on observations made at the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: the University of Arizona on behalf of the Arizona University system; Istituto Nazionale di Astrosica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; the Ohio State University, and the Research Corporation, on behalf of the University of Notre Dame

  2. Baryon isocurvature scenario in inflationary cosmology - A particle physics model and its astrophysical implications

    NASA Technical Reports Server (NTRS)

    Yokoyama, Jun'ichi; Suto, Yasushi

    1991-01-01

    A phenomenological model to produce isocurvature baryon-number fluctuations is proposed in the framework of inflationary cosmology. The resulting spectrum of density fluctuation is very different from the conventional Harrison-Zel'dovich shape. The model, with the parameters satisfying several requirements from particle physics and cosmology, provides an appropriate initial condition for the minimal baryon isocurvature scenario of galaxy formation discussed by Peebles.

  3. Analytical model of optical field distribution of thin disk laser with thermal-optical aberration gain medium

    NASA Astrophysics Data System (ADS)

    Zhu, Guangzhi; Qiu, Yuli; Wang, Zexiong; Zhu, Xiao; Zhu, Changhong

    2016-08-01

    An analytical model is developed to analyze the optical field distribution of thin disk laser with a thermal-optical aberration gain medium. The fundamental mode field distribution is calculated by using the eigenvector method of the resonator transit matrix for different pumping parameters. The analytical results show that the uniformity of the pumping spot is an important factor that impacts the beam quality of thin disk laser. The uniform pumping spot is beneficial to decrease thermal aberration and Optical Path Difference (OPD) of thin disk crystal, and to improve the beam quality. However, the beam quality still decreases slightly with the increasing of pumping intensity under the uniform pumping condition. The main reason for degradation of beam quality is the aspherical part of OPD which leads to diffraction losses of the resonator and wavefront deformation.

  4. Theoretical Modeling of Formic Acid (HCOOH), Formate (HCOO(-)), and Ammonia (NH(4)) Vibrational Spectra in Astrophysical Ices

    NASA Technical Reports Server (NTRS)

    Park, Jin-Young; Woon, David E.

    2006-01-01

    Ions embedded in icy grain mantles are thought to account for various observed infrared spectroscopic features, particularly in certain young stellar objects. The dissociation of formic acid (HCOOH) in astrophysical ices to form the formate ion (HCOO(-)) was modeled with density functional theory cluster calculations. Like isocyanic acid (HOCN), HCOOH was found to spontaneously deprotonate when sufficient water is present to stabilize charge transfer complexes. Both ammonia and water can serve as proton acceptors, yielding ammonium (NH4(+)) and hydronium (H3O(+)) counterions. Computed frequencies of weak infrared features produced by stretching and bending modes in both HCOO(-) and HCOOH were compared with experimental and astronomical data. Our results confirm laboratory assignments that a band at 1381 cm(exp -1) can be attributed to the CH bend in either HCOO(-) or HCOOH, but a band at 1349 cm(exp -1) corresponds to CO stretching in HCOO(-). Another feature at 1710 cm(exp -1) (5.85 m) can possibly be assigned to a CO stretching mode in HCOOH, as suggested by experiment, but the agreement is less satisfactory. In addition, we examine and analyze spectroscopic features associated with NH+4, both as a counterion to HCOO(-) or OCN(-) and in isolation, in order to compare with experimental and astronomical data in the 7 m region.

  5. Inert doublet model in light of LHC Run I and astrophysical data

    NASA Astrophysics Data System (ADS)

    Ilnicka, Agnieszka; Krawczyk, Maria; Robens, Tania

    2016-03-01

    We discuss the parameter space of the inert doublet model, a two Higgs doublet model with a dark matter candidate. An extensive set of theoretical and experimental constraints on this model is considered, where both collider as well as astroparticle data limits, the latter in the form of dark matter relic density as well as direct detection, are taken into account. We discuss the effects of these constraints on the parameter space of the model. In particular, we do not require the inert doublet model to provide the full dark matter content of the Universe, which opens up additional regions in the parameter space accessible at collider experiments. The combination of all constraints leads to a relatively strong mass degeneracy in the dark scalar sector for masses ≳200 GeV , and to a minimal scale ˜45 GeV for the dark scalar masses. We also observe a stringent mass hierarchy MH±>MA. We propose benchmark points and benchmark planes for dark scalar pair production for the current LHC run being in compliance with all theoretical as well as experimental bounds.

  6. GIANT PLANET FORMATION BY DISK INSTABILITY IN LOW MASS DISKS?

    SciTech Connect

    Boss, Alan P.

    2010-12-20

    Forming giant planets by disk instability requires a gaseous disk that is massive enough to become gravitationally unstable and able to cool fast enough for self-gravitating clumps to form and survive. Models with simplified disk cooling have shown the critical importance of the ratio of the cooling to the orbital timescales. Uncertainties about the proper value of this ratio can be sidestepped by including radiative transfer. Three-dimensional radiative hydrodynamics models of a disk with a mass of 0.043 M{sub sun} from 4 to 20 AU in orbit around a 1 M{sub sun} protostar show that disk instabilities are considerably less successful in producing self-gravitating clumps than in a disk with twice this mass. The results are sensitive to the assumed initial outer disk (T{sub o}) temperatures. Models with T{sub o} = 20 K are able to form a single self-gravitating clump, whereas models with T{sub o} = 25 K form clumps that are not quite self-gravitating. These models imply that disk instability requires a disk with a mass of at least {approx}0.043 M{sub sun} inside 20 AU in order to form giant planets around solar-mass protostars with realistic disk cooling rates and outer-disk temperatures. Lower mass disks around solar-mass protostars must rely upon core accretion to form inner giant planets.

  7. Marriage of Electromagnetism and Gravity in an Extended Space Model and Astrophysical Phenomena

    NASA Astrophysics Data System (ADS)

    Andreev, V. A.; Tsipenyuk, D. Yu.

    2013-09-01

    The generalization of Einstein's special theory of relativity (SRT) is proposed. In this model the possibility of unification of scalar gravity and electromagnetism into a single unified field is considered. Formally, the generalization of the SRT is that instead of (1+3)-dimensional Minkowski space the (1+4)-dimensional extension G is considered. As a fifth additional coordinate the interval S is used. This value is saved under the usual Lorentz transformations in Minkowski space M, but it changes when the transformations in the extended space G are used. We call this model the extended space model (ESM). From a physical point of view our expansion means that processes in which the rest mass of the particles changes are acceptable now. If the rest mass of a particle does not change and the physical quantities do not depend on an additional variable S, then the electromagnetic and gravitational fields exist independently of each other. But if the rest mass is variable and there is a dependence on S, then these two fields are combined into a single unified field. In the extended space model a photon can have a nonzero mass and this mass can be either positive or negative. The gravitational effects such as the speed of escape, gravitational red shift and detection of light can be analyzed in the frame of the extended space model. In this model all these gravitational effects can be found algebraically by the rotations in the (1+4) dimensional space. Now it becomes possible to predict some future results of visible size of supermassive objects in our Universe due to new stage of experimental astronomy development in the RadioAstron Project and analyze phenomena is an explosion of the star V838 Mon.

  8. ASTROPHYSICS. Exclusion of leptophilic dark matter models using XENON100 electronic recoil data.

    PubMed

    2015-08-21

    Laboratory experiments searching for galactic dark matter particles scattering off nuclei have so far not been able to establish a discovery. We use data from the XENON100 experiment to search for dark matter interacting with electrons. With no evidence for a signal above the low background of our experiment, we exclude a variety of representative dark matter models that would induce electronic recoils. For axial-vector couplings to electrons, we exclude cross sections above 6 × 10(-35) cm(2) for particle masses of m(χ) = 2 GeV/c(2). Independent of the dark matter halo, we exclude leptophilic models as an explanation for the long-standing DAMA/LIBRA signal, such as couplings to electrons through axial-vector interactions at a 4.4σ confidence level, mirror dark matter at 3.6σ, and luminous dark matter at 4.6σ. PMID:26293959

  9. Unveiling Accretion Disks - Physical Parameter Eclipse Mapping of Accretion Disks in Dwarf Novae

    NASA Astrophysics Data System (ADS)

    Vrielmann, S.

    1997-06-01

    This work presents a new tomography algorithm, the Physical Parameter Eclipse Mapping method. It has been designed to reconstruct the structure of accretion disks in cataclysmic variables in terms of the basic physical parameters. Cataclysmic variables are close interacting binaries, in which mass transfer from one of the stars, typically a main sequence star, to the other star, a white dwarf, proceeds via an accretion disk around the white dwarf. Accretion disks are of general importance in astrophysics, since they occur in a number of objects with mass accretion, like active galactic nuclei and young stellar objects. The eclipsing cataclysmic variables are ideal systems to study such accretion process, since with the varying orbital phase different parts of the accretion disk can be viewed. The tomography method is based on the classical Eclipse Mapping algorithm which yields intensity distributions in the accretion disk by fitting the observed eclipse light curve. In order to avoid ambiguities this back-projection is using a maximum entropy algorithm, with selects the smoothest solution still compatible with the data. In my new method the intensity distributions are replaced by distributions of physical parameters, using a specific theoretical model spectrum to fit a set of eclipse light curves at various wavelengths. The spectrum is chosen according to the type of cataclysmic variable under investigation and its state at the time of observation. This work shows through application to synthetic data that with such an approach given distributions in physical parameters can be reproduced, as long as the parameters assume values in the parameter space outside of regions where ambiguities arise. Versions with two simple models are tested, but in principle this method can cope with any given model spectrum. The Physical Parameter Eclipse Mapping method is applied to two sets of real data of the dwarf nova IP Pegasi on decline from outburst and HT Cassiopeiae in

  10. A Comprehensive Dust Model Applied to the Resolved Beta Pictoris Debris Disk from Optical to Radio Wavelengths

    NASA Astrophysics Data System (ADS)

    Ballering, Nicholas P.; Su, Kate Y. L.; Rieke, George H.; Gáspár, András

    2016-06-01

    We investigate whether varying the dust composition (described by the optical constants) can solve a persistent problem in debris disk modeling—the inability to fit the thermal emission without overpredicting the scattered light. We model five images of the β Pictoris disk: two in scattered light from the Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph at 0.58 μm and HST/Wide Field Camera 3 (WFC 3) at 1.16 μm, and three in thermal emission from Spitzer/Multiband Imaging Photometer for Spitzer (MIPS) at 24 μm, Herschel/PACS at 70 μm, and Atacama Large Millimeter/submillimeter Array at 870 μm. The WFC3 and MIPS data are published here for the first time. We focus our modeling on the outer part of this disk, consisting of a parent body ring and a halo of small grains. First, we confirm that a model using astronomical silicates cannot simultaneously fit the thermal and scattered light data. Next, we use a simple generic function for the optical constants to show that varying the dust composition can improve the fit substantially. Finally, we model the dust as a mixture of the most plausible debris constituents: astronomical silicates, water ice, organic refractory material, and vacuum. We achieve a good fit to all data sets with grains composed predominantly of silicates and organics, while ice and vacuum are, at most, present in small amounts. This composition is similar to one derived from previous work on the HR 4796A disk. Our model also fits the thermal spectral energy distribution, scattered light colors, and high-resolution mid-IR data from T-ReCS for this disk. Additionally, we show that sub-blowout grains are a necessary component of the halo.

  11. Effect of Degeneration on Fluid–Solid Interaction within Intervertebral Disk Under Cyclic Loading – A Meta-Model Analysis of Finite Element Simulations

    PubMed Central

    Nikkhoo, Mohammad; Khalaf, Kinda; Kuo, Ya-Wen; Hsu, Yu-Chun; Haghpanahi, Mohammad; Parnianpour, Mohamad; Wang, Jaw-Lin

    2015-01-01

    The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid–fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid–solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid–fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk. PMID:25674562

  12. A Modification of the Levich Model to Flux at a Rotating Disk in the presence of Planktonic Bacteria

    NASA Astrophysics Data System (ADS)

    Jones, Akhenaton-Andrew; Buie, Cullen

    2015-11-01

    The Levich model of flow at a rotating disk describes convective mass transport to a disk when edge effects and wall effects can be neglected. It is used to interpret electrochemical reaction kinetics and electrochemical impedance of flow systems. The solution has been shown to be invalid for high densities (~ 1 % v/v) of inert, non-motile nano-sized particles (<0.1 μm) and macro-particles (>1.5 μm), yet little work has been done for motile bacteria and bacterial sized particles. The influence of planktonic bacteria on rotating disk experiments is crucial for the evaluation of electrochemically active biofilms. In this work, we show that the presence of bacteria creates significant deviation from the ideal Levich model not shared by inert particles. We also study the impact of dead (fixed) bacteria on deviation form the Levich model. This work has implications for studies of microbial induced corrosion, microbial adhesion, and antibiotic transport to adhered biofilms preformed in rotating disk systems.

  13. Structure of Disk-dominated Galaxies. II. Color Gradients and Stellar Population Models

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren A.; Courteau, Stéphane; Bell, Eric; Holtzman, Jon A.

    2004-06-01

    We investigate optical and near-IR color gradients in a sample of 172 low-inclination galaxies spanning Hubble types S0-Irr. The colors are compared with stellar population synthesis models from which luminosity-weighted average ages and metallicities are determined. We explore the effects of different underlying star formation histories and additional bursts of star formation. Our results are robust in a relative sense under the assumption that our galaxies shared a similar underlying star formation history and that no bursts involving more than ~10% of the galaxy mass have occurred in the past 1-2 Gyr. Because the observed gradients show radial structure, we measure ``inner'' and ``outer'' disk age and metallicity gradients. Trends in age and metallicity and their gradients are explored as a function of Hubble type, rotational velocity, total near-IR galaxy magnitude, central surface brightness, and scale length. We find strong correlations in age and metallicity with Hubble type, rotational velocity, total magnitude, and central surface brightness in the sense that earlier-type, faster rotating, more luminous, and higher surface brightness galaxies are older and more metal-rich, suggesting an early and more rapid star formation history for these galaxies. The increasing trends with rotational velocity and total magnitude level off for Vrot>~120kms-1 and MK<~-23 mag, respectively. This effect is stronger for metallicity (than age), which could reflect a threshold potential above which all metals are retained and thus metallicity saturates at the yield. Outer disk gradients are found to be weaker than the inner gradients as expected for a slower variation of the potential and surface brightness in the outer parts. We find that stronger age gradients are associated with weaker metallicity gradients. Trends in gradients with galaxy parameters are compared with model predictions: these trends do not agree with predictions of semianalytic models of hierarchical galaxy

  14. A numerical model for the formation and long-term evolution of protostars and protostellar disks

    NASA Astrophysics Data System (ADS)

    Fateeva, A. M.; Zhilkin, A. G.; Pavlyuchenkov, Ya. N.; Vorobyov, E. I.

    2016-02-01

    We present a physical and numerical model for studying the formation and evolution of protostellar objects with solar and sub-solar masses. The model covers several evolutionary phases of these objects starting from the gravitational collapse of an initially unstable pre-stellar cloud, proceeding through the formation and collapse of the first hydrostatic core, and ending with the complete dissipation of the initial cloud and formation of a protostar and protostellar disk. The model is described by a system of MHD equations that includes Ohmic dissipation and ambipolar diffusion, and also a scheme for calculating the thermal and ionization structure of the cloud. We employ the multicomponent approach for computing the thermal structure of collapsing protostellar cloud, in which the dust and gas temperatures are treated separately, allowing us to accurately describe the initial stages of the cloud's gravitational contraction and collapse. We present the first results showing the structure of an initially quasi-equilibrium protostellar cloud during the first stages of gravitational collapse and subsequent evolution.

  15. Testing astrophysical models for the PAMELA positron excess with cosmic ray nuclei.

    PubMed

    Mertsch, Philipp; Sarkar, Subir

    2009-08-21

    The excess in the positron fraction measured by PAMELA has been interpreted as due to annihilation or decay of dark matter in the Galaxy. More prosaically it has been ascribed to direct production of positrons by nearby pulsars or due to pion production during diffusive shock acceleration of hadronic cosmic rays in nearby sources. We point out that measurements of secondary cosmic ray nuclei can discriminate between these possibilities. New data on the titanium-to-iron ratio support the hadronic source model above and enable a prediction for the boron-to-carbon ratio at energies above 100 GeV. PMID:19792709

  16. Physical and Chemical Structure of Planet-Forming Disks Probed by Millimeter Observations and Modeling

    NASA Astrophysics Data System (ADS)

    Dutrey, A.; Semenov, D.; Chapillon, E.; Gorti, U.; Guilloteau, S.; Hersant, F.; Hogerheijde, M.; Hughes, M.; Meeus, G.; Nomura, H.; Piétu, V.; Qi, C.; Wakelam, V.

    Protoplanetary disks composed of dust and gas are ubiquitous around young stars and are commonly recognized as nurseries of planetary systems. Their lifetime, appearance, and structure are determined by an interplay between stellar radiation, gravity, thermal pressure, magnetic field, gas viscosity, turbulence, and rotation. Molecules and dust serve as major heating and cooling agents in disks. Dust grains dominate the disk opacities, reprocess most of the stellar radiation, and shield molecules from ionizing ultraviolet (UV)/X-ray photons. Disks also dynamically evolve by building up planetary systems, which drastically change their gas and dust density structures. Over the past decade, significant progress has been achieved in our understanding of disk chemical composition thanks to the upgrade or advent of new millimeter/infrared (IR) facilities [Submillimeter Array (SMA), Plateau de Bure Interferometer (PdBI), Combined Array for Research in Millimeter-wave Astronomy (CARMA), Herschel, Expanded Very Large Array (e-VLA), Atacama Large Millimeter/submillimeter Array (ALMA)]. Some major breakthroughs in our comprehension of the disk physics and chemistry have been done since Protostars and Planets V (Reipurth et al., 2007). This review will present and discuss the impact of such improvements on our understanding of the disk physical structure and chemical composition.

  17. New Directions in Black Hole Astrophysics

    NASA Astrophysics Data System (ADS)

    Reynolds, C. S.

    2002-12-01

    The astrophysics of accreting black holes has been a scientific focus of most major future X-ray missions. In this presentation, I will describe how our science goals and expectations have been effected by new data from Chandra and XMM-Newton as well as new theoretical work. I will argue on the basis of XMM-Newton data that black hole spin does not manifest itself through subtle effects but may have dramatic astrophysical consequences. If this is correct, the exotic astrophysics of black hole spin, including astrophysical realizations of the Penrose and Blandford-Znajek processes, will be a principal focus of Constellation-X, XEUS and MAXIM. On the other hand, data from the late stages of the RXTE/ASCA missions as well as XMM-Newton suggest that the simple technique of relativistic X-ray iron line reverberation mapping, which was originally touted as a good method for studying the inner accretion disk, may be hard to realize. Finally, I will discuss recent theoretical/simulation work on the appearance of a MHD turbulent accretion disk around a black hole. Such simulations may be a good framework to understand future timing observations of Galactic Black Hole Candidates and their quasi-periodic oscillations. They also suggest a quantitative way of measuring the space-time geometry around supermassive black holes in AGN.

  18. Density fluctuations in the interstellar medium: Evidence for anisotropic magnetogasdynamic turbulence. I - Model and astrophysical sites

    NASA Astrophysics Data System (ADS)

    Higdon, J. C.

    1984-10-01

    A model of anisotropic magnetogasdynamic turbulence is developed in order to investigate quantitatively a turbulent fluid origin for the small spatial scale density fluctuations observed in 1981 by Armstrong, Cordes, and Rickett in the interstellar medium. The anisotropy at these small spatial scales results from the presence of a large-scale approximately uniform magnetic field that is a sum of the steady-state galactic magnetic field and the large-scale turbulent magnetic field fluctuations. The observed density fluctuations are interpreted to be two-dimensional isobaric entropy variations with oppositely directed gradients in temperature and density projected transverse to the local approximately uniform magnetic field. Three possible sites - cloud shell H II regions, diffuse H II regions produced by O stars, and the tenuous intercloud medium - are investigated as possible locations for turbulent flows.

  19. Photometric models of disk-integrated observations of the OSIRIS-REx target Asteroid (101955) Bennu

    NASA Astrophysics Data System (ADS)

    Takir, Driss; Clark, Beth Ellen; Drouet d'Aubigny, Christian; Hergenrother, Carl W.; Li, Jian-Yang; Lauretta, Dante S.; Binzel, Richard P.

    2015-05-01

    We used ground-based photometric phase curve data of the OSIRIS-REx target Asteroid (101955) Bennu and low phase angle data from Asteroid (253) Mathilde as a proxy to fit Bennu data with Minnaert, Lommel-Seeliger, (RObotic Lunar Orbiter) ROLO, Hapke, and McEwen photometric models, which capture the global light scattering properties of the surface and subsequently allow us to calculate the geometric albedo, phase integral, spherical Bond albedo, and the average surface normal albedo for Bennu. We find that Bennu has low reflectance and geometric albedo values, such that multiple scattering is expected to be insignificant. Our photometric models relate the reflectance from Bennu's surface to viewing geometry as functions of the incidence, emission, and phase angles. Radiance Factor functions (RADFs) are used to model the disk-resolved brightness of Bennu. The Minnaert, Lommel-Seeliger, ROLO, and Hapke photometric models work equally well in fitting the best ground-based photometric phase curve data of Bennu. The McEwen model works reasonably well at phase angles from 20° to 70°. Our calculated geometric albedo values of 0.047-0.014+0.012,0.047-0.014+0.005 , and 0.048-0.022+0.012 for the Minnaert, the Lommel-Seeliger, and the ROLO models respectively are consistent with the geometric albedo of 0.045 ± 0.015 computed by Emery et al. (Emery, J.P. et al. [2014]. Icarus 234, 17-35) and Hergenrother et al. (Hergenrother, C.W. et al. [2014].

  20. How The Inner Disk Communicates to the Outer Disk

    NASA Astrophysics Data System (ADS)

    Goto, Miwa

    2009-08-01

    We investigated how evolution in the outer disk has an influence on the inner disk of a protoplanetary disk system. Thanks to two-layer models that give the theoretical platform of disk geometry, we now have a good handle on how dust evolves in outer protoplanetary disks (>10 AU). It has long been thought that the outer and inner disks dissipate on roughly the same time scale as sub-mm observations of nearby T Tauri systems has suggested. However, new high spatial resolution observations point toward the dissipation of an inner disk as not being a simple extension of the outer disk. We performed preliminary tests of the differential disk evolution in gas and dust in the inner disks of Herbig Ae/Be stars using the CO vibrational band as the gas probe. The line luminosity of CO v = 1-0 P(30) has a reasonable correlation with the near-infrared excess over the stellar photosphere. It guarantees that the CO vibration band is a secure probe of the inner disk, as is expected from its high critical density, high excitation temperature, and kinematics. On the other hand, the line luminosity of P(30) does not show a clear trend either with far-infrared color, near-infrared/far-infrared-color, or the type of the spectral energy distribution (SED) (I/II). The inner disks (<1 AU) of Herbig Ae/Be stars of our sample are influenced little by the geometry of the outer disks.

  1. Dynamics of flux tubes in accretion disks

    NASA Technical Reports Server (NTRS)

    Vishniac, E. T.; Duncan, R. C.

    1994-01-01

    The study of magnetized plasmas in astrophysics is complicated by a number of factors, not the least of which is that in considering magnetic fields in stars or accretion disks, we are considering plasmas with densities well above those we can study in the laboratory. In particular, whereas laboratory plasmas are dominated by the confining magnetic field pressure, stars, and probably accretion disks, have magnetic fields whose beta (ratio of gas pressure to magnetic field pressure) is much greater than 1. Observations of the Sun suggest that under such circumstances the magnetic field breaks apart into discrete flux tubes with a small filling factor. On the other hand, theoretical treatments of MHD turbulence in high-beta plasmas tend to assume that the field is more or less homogeneously distributed throughout the plasma. Here we consider a simple model for the distribution of magnetic flux tubes in a turbulent medium. We discuss the mechanism by which small inhomogeneities evolve into discrete flux tubes and the size and distribution of such flux tubes. We then apply the model to accretion disks. We find that the fibrilation of the magnetic field does not enhance magnetic buoyancy. We also note that the evolution of an initially diffuse field in a turbulent medium, e.g., any uniform field in a shearing flow, will initially show exponential growth as the flux tubes form. This growth saturates when the flux tube formation is complete and cannot be used as the basis for a self-sustaining dynamo effect. Since the typical state of the magnetic field is a collection of intense flux tubes, this effect is of limited interest. However, it may be important early in the evolution of the galactic magnetic field, and it will play a large role in numerical simulations. Finally, we note that the formation of flux tubes is an essential ingredient in any successful dynamo model for stars or accretion disks.

  2. Thin-disk models in an integrable Weyl-Dirac theory

    NASA Astrophysics Data System (ADS)

    Vieira, Ronaldo S. S.; Letelier, Patricio S.

    2014-01-01

    We construct a class of static, axially symmetric solutions representing razor-thin disks of matter in the Integrable Weyl-Dirac theory proposed in Israelit (Found Phys 29:1303, 1999). The main differences between these solutions and the corresponding general relativistic one are analyzed, focusing on the behavior of physical observables (rotation curves of test particles, density and pressure profiles). We consider the case in which test particles move along Weyl geodesics. The same rotation curve can be obtained from many different solutions of the Weyl-Dirac theory, although some of these solutions present strong qualitative differences with respect to the usual general relativistic model (such as the appearance of a ring-like density profile). In particular, for typical galactic parameters all rotation curves of the Weyl-Dirac model present Keplerian fall-off. As a consequence, we conclude that a more thorough analysis of the problem requires the determination of the gauge function on galactic scales, as well as restrictions on the test-particle behavior under the action of the additional geometrical fields introduced by this theory.

  3. Flexible, Mastery-Oriented Astrophysics Sequence.

    ERIC Educational Resources Information Center

    Zeilik, Michael, II

    1981-01-01

    Describes the implementation and impact of a two-semester mastery-oriented astrophysics sequence for upper-level physics/astrophysics majors designed to handle flexibly a wide range of student backgrounds. A Personalized System of Instruction (PSI) format was used fostering frequent student-instructor interaction and role-modeling behavior in…

  4. Experimental High Energy Neutrino Astrophysics

    SciTech Connect

    Distefano, Carla

    2005-10-12

    Neutrinos are considered promising probes for high energy astrophysics. More than four decades after deep water Cerenkov technique was proposed to detect high energy neutrinos. Two detectors of this type are successfully taking data: BAIKAL and AMANDA. They have demonstrated the feasibility of the high energy neutrino detection and have set first constraints on TeV neutrino production astrophysical models. The quest for the construction of km3 size detectors have already started: in the South Pole, the IceCube neutrino telescope is under construction; the ANTARES, NEMO and NESTOR Collaborations are working towards the installation of a neutrino telescope in the Mediterranean Sea.

  5. IP Pegasi: Investigation of the accretion disk structure. Searching evidences for spiral shocks in the quiescent accretion disk

    NASA Astrophysics Data System (ADS)

    Neustroev, V. V.; Borisov, N. V.; Barwig, H.; Bobinger, A.; Mantel, K. H.; Šimić, D.; Wolf, S.

    2002-10-01

    We present the results of spectral investigations of the cataclysmic variable IP Peg in quiescence. Optical spectra obtained on the 6-m telescope at the Special Astrophysical Observatory (Russia), and on the 3.5-m telescope at the German-Spanish Astronomical Center (Calar Alto, Spain), have been analysed by means of Doppler tomography and Phase Modelling Technique. From this analysis we conclude that the quiescent accretion disk of IP Peg has a complex structure. There are also explicit indications of spiral shocks. The Doppler maps and the variations of the peak separation of the emission lines confirm this interpretation. We have detected that all the emission lines show a rather considerable asymmetry of their wings varying with time. The wing asymmetry shows quasi-periodic modulations with a period much shorter than the orbital one. This indicates the presence of an emission source in the binary rotating asynchronously with the binary system. We also have found that the brightness of the bright spot changes considerably during one orbital period. The spot becomes brightest at an inferior conjunction, whereas it is almost invisible when it is located on the distant half of the accretion disk. Probably, this phenomenon is due to an anisotropic radiation of the bright spot and an eclipse of the bright spot by the outer edge of the accretion disk. Based on observations made at the Special Astrophysical Observatory, Nizhnij Arkhyz, Russia, and at the German-Spanish Astronomical Center, Calar Alto, Spain.

  6. On the Relative Relevance of Subject-Specific Geometries and Degeneration-Specific Mechanical Properties for the Study of Cell Death in Human Intervertebral Disk Models

    PubMed Central

    Malandrino, Andrea; Pozo, José M.; Castro-Mateos, Isaac; Frangi, Alejandro F.; van Rijsbergen, Marc M.; Ito, Keita; Wilke, Hans-Joachim; Dao, Tien Tuan; Ho Ba Tho, Marie-Christine; Noailly, Jérôme

    2015-01-01

    Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration. PMID:25717471

  7. On the relative relevance of subject-specific geometries and degeneration-specific mechanical properties for the study of cell death in human intervertebral disk models.

    PubMed

    Malandrino, Andrea; Pozo, José M; Castro-Mateos, Isaac; Frangi, Alejandro F; van Rijsbergen, Marc M; Ito, Keita; Wilke, Hans-Joachim; Dao, Tien Tuan; Ho Ba Tho, Marie-Christine; Noailly, Jérôme

    2015-01-01

    Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration. PMID:25717471

  8. 3He (α , γ)7Be and 3H (α , γ)7Li astrophysical S factors from the no-core shell model with continuum

    NASA Astrophysics Data System (ADS)

    Dohet-Eraly, Jérémy; Navrátil, Petr; Quaglioni, Sofia; Horiuchi, Wataru; Hupin, Guillaume; Raimondi, Francesco

    2016-06-01

    The 3He(α , γ)7Be and 3H(α , γ)7Li astrophysical S factors are calculated within the no-core shell model with continuum using a renormalized chiral nucleon-nucleon interaction. The 3He(α , γ)7Be astrophysical S factors agree reasonably well with the experimental data while the 3H(α , γ)7Li ones are overestimated. The seven-nucleon bound and resonance states and the α + 3He/3H elastic scattering are also studied and compared with experiment. The low-lying resonance properties are rather well reproduced by our approach. At low energies, the s-wave phase shift, which is non-resonant, is overestimated.

  9. The Milky Way disk

    NASA Astrophysics Data System (ADS)

    Carraro, G.

    2015-08-01

    This review summarises the invited presentation I gave on the Milky Way disc. The idea underneath was to touch those topics that can be considered hot nowadays in the Galactic disk research: the reality of the thick disk, the spiral structure of the Milky Way, and the properties of the outer Galactic disk. A lot of work has been done in recent years on these topics, but a coherent and clear picture is still missing. Detailed studies with high quality spectroscopic data seem to support a dual Galactic disk, with a clear separation into a thin and a thick component. Much confusion and very discrepant ideas still exist concerning the spiral structure of the Milky Way. Our location in the disk makes it impossible to observe it, and we can only infer it. This process of inference is still far from being mature, and depends a lot on the selected tracers, the adopted models and their limitations, which in many cases are neither properly accounted for, nor pondered enough. Finally, there are very different opinions on the size (scale length, truncation radius) of the Galactic disk, and on the interpretation of the observed outer disk stellar populations in terms either of external entities (Monoceros, Triangulus-Andromeda, Canis Major), or as manifestations of genuine disk properties (e.g., warp and flare).

  10. Towards Bayesian Machine Learning for Estimating Parameters of Accretion Disk Models for SPH Simulations

    NASA Astrophysics Data System (ADS)

    Goel, Amit; Montgomery, Michele; Wiegand, Paul

    2016-01-01

    Accretion disks are ubiquitous in Active Galactic Nuclei, in protostellar systems forming protoplanets, and in close binary star systems such as X-ray binaries, Cataclysmic Variables, and Algols, for example. Observations such as disk tilt are found in all of these different accreting system types, suggesting a common physics must be present. To understand the common connections between these different system types, which can help us understand their unique evolutions, we need to better understand the physics of accretion. For example, viscosity is typically a constant value in the disk of a system that is in a specific state such as a quiescent state. However, viscosity can't be constant throughout the disk, especially at the boundaries. To learn more about viscosity and other common parameters in these disk, we use Bayesian Inference and Markov Chain Monte Carlo techniques to make predictions of events to come in the numerical simulations of these accreting disks. In this work, we present our techniques and initial findings.

  11. Design, testing and two-dimensional flow modeling of a multiple-disk fan

    SciTech Connect

    Engin, Tahsin; Oezdemir, Mustafa; Cesmeci, Sevki

    2009-11-15

    A multiple-disk Tesla type fan has been designed, tested and analyzed two-dimensionally using the conservation of angular momentum principle. Experimental results showed that such multiple-disk fans exhibited exceptionally low performance characteristics, which could be attributed to the low viscosity, tangential nature of the flow, and large mechanical energy losses at both suction and discharge sections that are comparable to the total input power. By means of theoretical analysis, local and overall shearing stresses on the disk surfaces have been determined based on tangential and radial velocity distributions of the air flow of different volume flow rates at prescribed disk spaces and rotational speeds. Then the total power transmitted by rotating disks to air flow, and the power acquired by the air flow in the gap due to transfer of angular momentum have been obtained by numerically integrating shearing stresses over the disk surfaces. Using the measured shaft and hydraulic powers, these quantities were utilized to evaluate mechanical energy losses associated with the suction and discharge sections of the fan. (author)

  12. Astronomy & Astrophysics: an international journal

    NASA Astrophysics Data System (ADS)

    Bertout, C.

    2011-07-01

    After a brief historical introduction, we review the scope, editorial process, and production organization of A&A, one of the leading journals worldwide dedicated to publishing the results of astrophysical research. We then briefly discuss the economic model of the Journal and some current issues in scientific publishing.

  13. A Pulsar and a Disk

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-07-01

    Recent, unusual X-ray observations from our galactic neighbor, the Small Magellanic Cloud, have led to an interesting model for SXP 214, a pulsar in a binary star system.Artists illustration of the magnetic field lines of a pulsar, a highly magnetized, rotating neutron star. [NASA]An Intriguing BinaryAn X-ray pulsar is a magnetized, rotating neutron star in a binary system with a stellar companion. Material is fed from the companion onto the neutron star, channeled by the objects magnetic fields onto a hotspot thats millions of degrees. This hotspot rotating past our line of sight is what produces the pulsations that we observe from X-ray pulsars.Located in the Small Magellanic Cloud, SXP 214 is a transient X-ray pulsar in a binary with a Be-type star. This star is spinning so quickly that material is thrown off of it to form a circumstellar disk.Recently, a team of authors led by JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) have presented new Chandra X-ray observations of SXP 214, tracking it for 50 ks (~14 hours) in January 2013. These observations reveal some very unexpected behavior for this pulsar.X-ray PuzzleThe energy distribution of the X-ray emission from SXP 214 over time. Dark shades or blue colors indicate high counts, and light shades or yellow colors indicate low counts. Lower-energy X-ray emission appeared only later, after about 20 ks. [Hong et al. 2016]Three interesting pieces of information came from the Chandra observations:SXP 214s rotation period was measured to be 211.5 s an increase in the spin rate since the discovery measurement of a 214-second period. Pulsars usually spin down as they lose angular momentum over time so what caused this one to spin up?Its overall X-ray luminosity steadily increased over the 50 ks of observations.Its spectrum became gradually softer (lower energy) over time; in the first 20 ks, the spectrum only consisted of hard X-ray photons above 3 keV, but after 20 ks, softer X-ray photons below 2 ke

  14. Towards a comprehensive model of Earth's disk-integrated Stokes vector

    NASA Astrophysics Data System (ADS)

    García Muñoz, A.

    2015-07-01

    at three wavelengths (0.48, 0.56 and 0.63 μm) during a flyby in 2005. The light curves show distinct structure associated with the varying aspect of the Earth's visible disk (phases of 98-107°) as the planet undergoes a full 24 h rotation; the structure is reasonably well reproduced with model simulations.

  15. Constraining the Physics of AM Canum Venaticorum Systems with the Accretion Disk Instability Model

    NASA Astrophysics Data System (ADS)

    Cannizzo, John K.; Nelemans, Gijs

    2015-04-01

    Recent work by Levitan et al. has expanded the long-term photometric database for AM CVn stars. In particular, their outburst properties are well correlated with orbital period and allow constraints to be placed on the secular mass transfer rate between secondary and primary if one adopts the disk instability model for the outbursts. We use the observed range of outbursting behavior for AM CVn systems as a function of orbital period to place a constraint on mass transfer rate versus orbital period. We infer a rate ˜5× {{10}-9}{{M}⊙ } y{{r}-1}{{({{P}orb}/1000 s)}-5.2}. We show that the functional form so obtained is consistent with the recurrence time-orbital period relation found by Levitan et al. using a simple theory for the recurrence time. Also, we predict that their steep dependence of outburst duration on orbital period will flatten considerably once the longer orbital period systems have more complete observations.

  16. A Hydrodynamical Mechanism for Generating Astrophysical Jets

    NASA Astrophysics Data System (ADS)

    Hernández, X.; Rendón, P. L.; Rodríguez-Mota, R. G.; Capella, A.

    2014-04-01

    Whenever in a classical accretion disk the thin disk approximation fails interior to a certain radius, a transition from Keplerian to radial infalling trajectories should occur. We show that this transition is actually expected to occur interior to a certain critical radius, provided surface density profiles are steeper than Sigma(R) ~ R(-1/2) , and further, that it probably corresponds to the observationally inferred phenomena of thick hot walls internally limiting the extent of many stellar accretion disks. Infalling trajectories will lead to the convergent focusing and concentration of matter towards the very central regions, most of which will simply be swallowed by the central object. We show through a perturbative hydrodynamical analysis, that this will naturally develop a well collimated pair of polar jets. A first analytic treatment of the problem described is given, proving the feasibility of purely hydrodynamical mechanisms for astrophysical jet generation.

  17. Future Experiments in Astrophysics

    NASA Technical Reports Server (NTRS)

    Krizmanic, John F.

    2002-01-01

    The measurement methodologies of astrophysics experiments reflect the enormous variation of the astrophysical radiation itself. The diverse nature of the astrophysical radiation, e.g. cosmic rays, electromagnetic radiation, and neutrinos, is further complicated by the enormous span in energy, from the 1.95 Kappa relic neutrino background to cosmic rays with energy greater than 10(exp 20)eV. The measurement of gravity waves and search for dark matter constituents are also of astrophysical interest. Thus, the experimental techniques employed to determine the energy of the incident particles are strongly dependent upon the specific particles and energy range to be measured. This paper summarizes some of the calorimetric methodologies and measurements planned by future astrophysics experiments. A focus will be placed on the measurement of higher energy astrophysical radiation. Specifically, future cosmic ray, gamma ray, and neutrino experiments will be discussed.

  18. Models of Chemistry, Thermal Balance, and Infrared Spectra from Intermediate-Aged Disks around G and K Stars

    NASA Astrophysics Data System (ADS)

    Gorti, U.; Hollenbach, D.

    2004-09-01

    We model gas and dust emission from regions 0.3-20 AU from a central low-mass star in intermediate-aged (~107 yr) disks whose dust is fairly optically thin to stellar radiation. The models treat thermal balance and chemistry self-consistently and calculate the vertical density and temperature structure of the gas in a disk. The gas and dust temperatures are calculated separately. The models cover gas masses 10-3 to 1 MJ and dust masses 10-7 to 10-4 MJ and treat solar-type (G and K) stars. We focus on mid-infrared and far-infrared emission lines from various gas species such as the rotational lines of H2, OH, H2O, and CO molecules and the fine-structure lines of carbon, oxygen, sulfur, iron, and silicon atoms and ions. These lines and the dust continuum are observable by the Spitzer Space Telescope and future missions including SOFIA and the Herschel Space Observatory. We find that the [S I] 25.23 μm line is the strongest emission line for a wide range of disk and stellar parameters, followed by emission from [Si II] 34.8 μm, [Fe II] 26 μm, and [O I] 63 μm. [Fe I] 24 μm and rotational lines of OH and H2O are strong when gas masses are high (>~0.1 MJ). Emission from the rotational lines of H2 is more difficult to detect unless disk gas masses are substantial (>~0.1 MJ). For emission from H2 lines to be observable and yet for the dust to be optically thin in stellar light, the ratio of gas to small submillimeter-sized dust particle mass in the disk needs to be >~1000, or at least an order of magnitude higher than that in the interstellar medium. This may be possible at intermediate stages in disk evolution, such as in the gas-gathering stage of the core accretion scenario for giant planet formation, in which most of the dust has coagulated into larger objects (>>1 mm) but the gas has not yet fully dispersed. Whereas the absolute fluxes observed in some lines such as [Fe I] 24 μm and H2 S(0) 28 μm primarily measure the gas mass in the disks, various line ratios

  19. Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC 2264

    NASA Astrophysics Data System (ADS)

    Landin, N. R.; Mendes, L. T. S.; Vaz, L. P. R.; Alencar, S. H. P.

    2016-02-01

    Context. Rotational evolution in young stars is described by pre-main sequence evolutionary tracks including non-gray boundary conditions, rotation, conservation of angular momentum, and simulations of disk-locking. Aims: By assuming that disk-locking is the regulation mechanism for the stellar angular velocity during the early stages of pre-main sequence evolution, we use our rotating models and observational data to constrain disk lifetimes (Tdisk) of a representative sample of low-mass stars in two young clusters, the Orion Nebula cluster (ONC) and NGC 2264, and to better understand their rotational evolution. Methods: The period distributions of the ONC and NGC 2264 are known to be bimodal and to depend on the stellar mass. To follow the rotational evolution of these two clusters' stars, we generated sets of evolutionary tracks from a fully convective configuration with low central temperatures (before D- and Li-burning). We assumed that the evolution of fast rotators can be represented by models considering conservation of angular momentum during all stages and of moderate rotators by models considering conservation of angular velocity during the first stages of evolution. With these models we estimate a mass and an age for all stars. Results: The resulting mass distribution for the bulk of the cluster population is in the ranges of 0.2-0.4 M⊙ and 0.1-0.6 M⊙ for the ONC and NGC 2264, respectively. For the ONC, we assume that the secondary peak in the period distribution is due to high-mass objects still locked in their disks, with a locking period (Plock) of ~8 days. For NGC 2264 we make two hypotheses: (1) the stars in the secondary peak are still locked with Plock = 5 days, and (2) NGC 2264 is in a later stage in the rotational evolution. Hypothesis 2 implies in a disk-locking scenario with Plock = 8 days, a disk lifetime of 1 Myr and, after that, constant angular momentum evolution. We then simulated the period distribution of NGC 2264 when the mean age

  20. Theory and laboratory astrophysics

    NASA Technical Reports Server (NTRS)

    Schramm, David N.; Mckee, Christopher F.; Alcock, Charles; Allamandola, Lou; Chevalier, Roger A.; Cline, David B.; Dalgarno, Alexander; Elmegreen, Bruce G.; Fall, S. Michael; Ferland, Gary J.

    1991-01-01

    Science opportunities in the 1990's are discussed. Topics covered include the large scale structure of the universe, galaxies, stars, star formation and the interstellar medium, high energy astrophysics, and the solar system. Laboratory astrophysics in the 1990's is briefly surveyed, covering such topics as molecular, atomic, optical, nuclear and optical physics. Funding recommendations are given for the National Science Foundation, NASA, and the Department of Energy. Recommendations for laboratory astrophysics research are given.

  1. Modelling circumbinary protoplanetary disks. II. Gas disk feedback on planetesimal dynamical and collisional evolution in the circumbinary systems Kepler-16 and 34

    NASA Astrophysics Data System (ADS)

    Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.

    2016-05-01

    Aims: We investigate the feasibility of planetesimal growth in circumbinary protoplanetary disks around the observed systems Kepler-16 and Kepler-34 under the gravitational influence of a precessing eccentric gas disk. Methods: We embed the results of our previous hydrodynamical simulations of protoplanetary disks around binaries into an N-body code to perform 3D, high-resolution, inter-particle gravity-enabled simulations of planetesimal growth and dynamics that include the gravitational force imparted by the gas. Results: Including the full, precessing asymmetric gas disk generates high eccentricity orbits for planetesimals orbiting at the edge of the circumbinary cavity, where the gas surface density and eccentricity have their largest values. The gas disk is able to efficiently align planetesimal pericenters in some regions leading to phased, non-interacting orbits. Outside of these areas eccentric planetesimal orbits become misaligned and overlap leading to crossing orbits and high relative velocities during planetesimal collisions. This can lead to an increase in the number of erosive collisions that far outweighs the number of collisions that result in growth. Gravitational focusing from the static axisymmetric gas disk is weak and does not significantly alter collision outcomes from the gas free case. Conclusions: Due to asymmetries in the gas disk, planetesimals are strongly perturbed onto highly eccentric orbits. Where planetesimals orbits are not well aligned, orbit crossings lead to an increase in the number of erosive collisions. This makes it difficult for sustained planetesimal accretion to occur at the location of Kepler-16b and Kepler-34b and we therefore rule out in situ growth. This adds further support to our initial suggestions that most circumbinary planets should form further out in the disk and migrate inwards.

  2. Instability of counter-rotating stellar disks

    NASA Astrophysics Data System (ADS)

    Hohlfeld, R. G.; Lovelace, R. V. E.

    2015-09-01

    We use an N-body simulation, constructed using GADGET-2, to investigate an accretion flow onto an astrophysical disk that is in the opposite sense to the disk's rotation. In order to separate dynamics intrinsic to the counter-rotating flow from the impact of the flow onto the disk, we consider an initial condition in which the counter-rotating flow is in an annular region immediately exterior the main portion of the astrophysical disk. Such counter-rotating flows are seen in systems such as NGC 4826 (known as the "Evil Eye Galaxy"). Interaction between the rotating and counter-rotating components is due to two-stream instability in the boundary region. A multi-armed spiral density wave is excited in the astrophysical disk and a density distribution with high azimuthal mode number is excited in the counter-rotating flow. Density fluctuations in the counter-rotating flow aggregate into larger clumps and some of the material in the counter-rotating flow is scattered to large radii. Accretion flow processes such as this are increasingly seen to be of importance in the evolution of multi-component galactic disks.

  3. Astrophysics and Space Science

    NASA Astrophysics Data System (ADS)

    Mould, Jeremy; Brinks, Elias; Khanna, Ramon

    2015-08-01

    Astrophysics and Space Science publishes original contributions and invited reviews covering the entire range of astronomy, astrophysics, astrophysical cosmology, planetary and space science, and the astrophysical aspects of astrobiology. This includes both observational and theoretical research, the techniques of astronomical instrumentation and data analysis, and astronomical space instrumentation. We particularly welcome papers in the general fields of high-energy astrophysics, astrophysical and astrochemical studies of the interstellar medium including star formation, planetary astrophysics, the formation and evolution of galaxies and the evolution of large scale structure in the Universe. Papers in mathematical physics or in general relativity which do not establish clear astrophysical applications will not longer be considered.The journal also publishes topical collections consisting of invited reviews and original research papers selected special issues in research fields of particular scientific interest. These consist of both invited reviews and original research papers.Conference proceedings will not be considered. All papers published in the journal are subject to thorough and strict peer-reviewing.Astrophysics and Space Science has an Impact Factor of 2.4 and features short editorial turnaround times as well as short publication times after acceptance, and colour printing free of charge. Published by Springer the journal has a very wide online dissemination and can be accessed by researchers at a very large number of institutes worldwide.

  4. High Energy Astrophysics Program

    NASA Technical Reports Server (NTRS)

    1996-01-01

    This report reviews activities performed by members of the USRA (Universities Space Research Association) contract team during the six months during the reporting period (10/95 - 3/96) and projected activities during the coming six months. Activities take place at the Goddard Space Flight Center, within the Laboratory for High Energy Astrophysics. Developments concern instrumentation, observation, data analysis, and theoretical work in Astrophysics. Missions supported include: Advanced Satellite for Cosmology and Astrophysics (ASCA), X-ray Timing Experiment (XTE), X-ray Spectrometer (XRS), Astro-E, High Energy Astrophysics Science, Archive Research Center (HEASARC), and others.

  5. High Energy Astrophysics Program

    NASA Technical Reports Server (NTRS)

    1996-01-01

    This report reviews activities performed-by members of the USRA contract team during the six months of the reporting period and projected activities during the coming six months. Activities take place at the Goddard Space Flight Center, visiting the Laboratory for High Energy Astrophysics. Developments concern instrumentation, observation, data analysis, and theoretical work in Astrophysics. Missions supported include: Advanced Satellite for Cosmology and Astrophysics (ASCA); X-ray Timing Experiment (XTE); X-ray Spectrometer (XRS); Astro-E; High Energy Astrophysics Science Archive Research Center (HEASARC), and others.

  6. Optical Disks.

    ERIC Educational Resources Information Center

    Gale, John C.; And Others

    1985-01-01

    This four-article section focuses on information storage capacity of the optical disk covering the information workstation (uses microcomputer, optical disk, compact disc to provide reference information, information content, work product support); use of laser videodisc technology for dissemination of agricultural information; encoding databases…

  7. From Collapsing Cloud Core to Protoplanetary Disk - A radiation transfer model for L1489 IRS

    NASA Astrophysics Data System (ADS)

    Brinch, Christian; Hogerheijde, Michiel R.; Jørgensen, Jes K.

    We present a new molecular line radiation transfer model of the low-mass Young Stellar Object L1489 IRS (d ~ 140 pc) which may represent a short-lived transitional stage from collapsing cloud core to a star with a protoplanetary disk in Keplarian rotation (Hogerheijde 2001). The model includes a detailed description of the velocity field, the abundance of several molecular species and the shape and orientation of the object. L1489 IRS is seen to be surrounded by a flattened structure, in which both Keplarian rotation and inward motion are detected over size scales ranging from an outer radius of 2000 AU to within 0.1 AU from the central star (Boogert et al. 2002). With the observed inward motions, it would only take a few times 104 years for material at 2000 AU to spiral into the star, suggesting that this object may be very short lived. We use a flattened density distribution in our model to accommodate the non-spherical structure of L1489 IRS. In this study we aim to provide a better description of the physical and chemical characteristics of L1489 IRS through comparison between a detailed model and existing observations. Our model is described by a flattened Plummer-like density distribution (Stamatellos et al. 2004) given by, n(r, θ) = n0 ( 1 + [r/r0]2 )p/2 sinf ( θ ), where the parameter f determines the flatness. We adopt the value p = -1.8 for the radial density slope, based on the fit to the SCUBA submillimeter emission by Jørgensen et al. (2002). Integrating this profile results in a total disk mass of 0.03 M*. We use a radial temperature distribution given by a power-law with an index of -0.35 and T0 = 19.4 K at r0 = 1000 AU. The velocity field is parameterised by the mass of the central star M* and the angle α between the resulting velocity vector and the azimuthal direction. A value of α = 0 thus correspond to pure Keplarian rotation around a star of mass M*. Our free parameters are: M*, α, f, Xmol, and the inclination angle, i. The molecular

  8. MODELING HIGH-VELOCITY QSO ABSORBERS WITH PHOTOIONIZED MAGNETOHYDRODYNAMIC DISK WINDS

    SciTech Connect

    Fukumura, Keigo; Kazanas, Demosthenes; Behar, Ehud

    2010-11-10

    We extend our modeling of the ionization structure of magnetohydrodynamic (MHD) accretion-disk winds, previously applied to Seyfert galaxies, to a population of quasi-stellar objects (QSOs) of much lower X-ray-to-UV flux ratios, i.e., smaller {alpha}{sub ox} index, motivated by UV/X-ray ionized absorbers with extremely high outflow velocities in UV-luminous QSOs. We demonstrate that magnetically driven winds ionized by a spectrum with {alpha}{sub ox} {approx_equal} -2 can produce the charge states responsible for C IV and Fe XXV/Fe XXVI absorption in wind regions with corresponding maximum velocities of v(C IV) {approx_lt}0.1c and v(Fe XXV) {approx_lt} 0.6c (where c is the speed of light) and column densities N {sub H} {approx} 10{sup 23}-10{sup 24} cm{sup -2}, in general agreement with observations. In contrast to the conventional radiation-driven wind models, high-velocity flows are always present in our MHD-driven winds but manifest in the absorption spectra only for {alpha}{sub ox} {approx_lt} -2, as larger {alpha}{sub ox} values ionize the wind completely out to radii too large to demonstrate the presence of these high velocities. We thus predict increasing velocities of these ionized absorbers with decreasing (steeper) {alpha}{sub ox}, a quantity that emerges as the defining parameter in the kinematics of the active galactic nucleus UV/X-ray absorbers.

  9. History of Thermally Processed Solids in the Protoplanetary Disk: Reconciling Theoretical Models and Meteoritical Evidence

    NASA Technical Reports Server (NTRS)

    Cuzzi, J. N.; Petaev, M.; Scott, E. R. D.; Weidenschilling, S.; Ciesla, F. J.

    2004-01-01

    In this talk we assess theoretical models of the radial, temporal, and thermal evolution of nebula solids, and their ultimate accretion into planetesimals such as we see today, using meteorite evidence as a guide. Each class of chondrites contains a characteristic suite of chondrules and CAIs that may have formed over a period of several Myr during which planetesimals were accreting in the disk. Details of the various models for transient melting of chondrules and igneous CAIs will be left to others. However, high-temperature processes of different kinds evaporation, alteration, etc did affect these constituents and their environment over this time span. Here we describe evolutionary scenarios consistent with a large time gap between CAI and chondrule formation and the presence of distinctive suites of chondrules and CAIs in each chondrite class. Particle-gas dynamical processes transport particles of all relevant sizes (microns to many meters) within the nebula and affect their evolution in a variety of important ways. Turbulent radial diffusion spreads particles radially down their concentration gradients - as one example, it can prevent CAIs from being lost into the sun on several Myr timescales [1]. Vertical diffusion spreads the dense midplane particle layer, determining its volume density, which in turn affects the particle growth rate and even the dominant growth process [2-4]. Turbulent concentration selects aerodynamically sorted particles for orders-of-magnitude density enhancement, and is applicable to porous, fluffy particles of appropriate size as well as to solid chondrules [5]. Inward radial drift under gas drag brings a surprisingly large amount of material to regions where it evaporates; these evaporation fronts cause significant chemical modification of the nebula gas over a wide range of radii [6]. Radial transport by stellar winds can be important for small particles [7].

  10. Observations of Circumstellar Disks with Infrared Interferometry

    NASA Technical Reports Server (NTRS)

    Akeson, Rachel

    2008-01-01

    Star formation is arguably the area of astrophysics in which infrared interferometry has had the biggest impact. The optically thick portion of T Tauri and Herbig Ae/Be disks DO NOT extend to a few stellar radii of the stellar surface. Emission is coming from near the dust sublimation radius, but not all from a single radius. The Herbig Ae stars can be either flared or self-shadowed but very massive (early Be) stars are geometrically thin. The Herbig Ae stars can be either flared or self-shadowed but very massive (early Be) stars are geometrically thin. Observational prospects are rapidly improving: a) Higher spectral resolution will allow observations of the gas: jets, winds, accretion. b) Closure phase and imaging will help eliminate model uncertainties/dependencies.

  11. ROSSBY WAVE INSTABILITY AT DEAD ZONE BOUNDARIES IN THREE-DIMENSIONAL RESISTIVE MAGNETOHYDRODYNAMICAL GLOBAL MODELS OF PROTOPLANETARY DISKS

    SciTech Connect

    Lyra, Wladimir; Mac Low, Mordecai-Mark E-mail: mordecai@amnh.org

    2012-09-01

    It has been suggested that the transition between magnetorotationally active and dead zones in protoplanetary disks should be prone to the excitation of vortices via Rossby wave instability (RWI). However, the only numerical evidence for this has come from alpha disk models, where the magnetic field evolution is not followed, and the effect of turbulence is parameterized by Laplacian viscosity. We aim to establish the phenomenology of the flow in the transition in three-dimensional resistive-magnetohydrodynamical models. We model the transition by a sharp jump in resistivity, as expected in the inner dead zone boundary, using the PENCIL CODE to simulate the flow. We find that vortices are readily excited in the dead side of the transition. We measure the mass accretion rate finding similar levels of Reynolds stress at the dead and active zones, at the {alpha} Almost-Equal-To 10{sup -2} level. The vortex sits in a pressure maximum and does not migrate, surviving until the end of the simulation. A pressure maximum in the active zone also triggers the RWI. The magnetized vortex that results should be disrupted by parasitical magneto-elliptic instabilities, yet it subsists in high resolution. This suggests that either the parasitic modes are still numerically damped or that the RWI supplies vorticity faster than they can destroy it. We conclude that the resistive transition between the active and dead zones in the inner regions of protoplanetary disks, if sharp enough, can indeed excite vortices via RWI. Our results lend credence to previous works that relied on the alpha-disk approximation, and caution against the use of overly reduced azimuthal coverage on modeling this transition.

  12. Simulations of Ice Nucleation by Model AgI Disks and Plates.

    PubMed

    Zielke, Stephen A; Bertram, Allan K; Patey, G N

    2016-03-10

    Silver iodide is one of the most effective ice nuclei known. We use molecular dynamics simulations to investigate ice nucleation by AgI disks and plates with radii ranging from 1.15 to 2.99 nm. It is shown that disks and plates in this size range are effective ice nuclei, nucleating bulk ice at temperatures as warm as 14 K below the equilibrium freezing temperature, on simulation time scales (up to a few hundred nanoseconds). Ice nucleated on the Ag exposed surface of AgI disks and plates. Shortly after supercooling an ice cluster forms on the AgI surface. The AgI-stabilized ice cluster fluctuates in size as time progresses, but, once formed, it is constantly present. Eventually, depending on the disk or plate size and the degree of supercooling, a cluster fluctuation achieves critical size, and ice nucleates and rapidly grows to fill the simulation cell. Larger AgI disks and plates support larger ice clusters and hence can nucleate ice at warmer temperatures. This work may be useful for understanding the mechanism of ice nucleation on nanoparticles and active sites of larger atmospheric particles. PMID:26878341

  13. SPIN (Version 3.83): A FORTRAN program for modeling one-dimensional rotating-disk/stagnation-flow chemical vapor deposition reactors

    NASA Astrophysics Data System (ADS)

    Coltrin, M. E.; Kee, R. J.; Evans, G. H.; Meeks, E.; Rupley, F. M.; Grcar, J. F.

    1991-08-01

    In a rotating-disk reactor, a heated substrate spins (at typical speeds of 1000 rpm or more) in an enclosure through which the reactants flow. The rotating disk geometry has the important property that in certain operating regimes the species and temperature gradients normal to the disk are equal everywhere on the disk. Thus, such a configuration has great potential for highly uniform chemical vapor deposition (CVD), and indeed commercial rotating-disk CVD reactors are now available. In certain operating regimes, the equations describing the complex three-dimensional spiral fluid motion can be solved by a separation-of-variables transformation that reduces the equations to a system of ordinary differential equations. Strictly speaking, the transformation is only valid for an unconfined infinite-radius disk and buoyancy-free flow. Furthermore, only some boundary conditions are consistent with the transformation (e.g., temperature, gas-phase composition, and approach velocity all specified to be independent of radius at some distances above the disk). Fortunately, however, the transformed equations will provide a very good practical approximation to the flow in a finite-radius reactor over a large fraction of the disk (up to approximately 90 percent of the disk radius) when the reactor operating parameters are properly chosen, i.e., high rotation rates. In the limit of zero rotation rate, the rotating disk flow reduces to a stagnation-point flow, for which a similar separation-of-variables transformation is also available. Such flow configurations ('pedestal reactors') also find use in CVD reactors. In this report we describe a model formulation and mathematical analysis of rotating-disk and stagnation-point CVD reactors. Then we apply the analysis to a compute code called SPIN and describe its implementation and use.

  14. SPIN (Version 3. 83): A Fortran program for modeling one-dimensional rotating-disk/stagnation-flow chemical vapor deposition reactors

    SciTech Connect

    Coltrin, M.E. ); Kee, R.J.; Evans, G.H.; Meeks, E.; Rupley, F.M.; Grcar, J.F. )

    1991-08-01

    In rotating-disk reactor a heated substrate spins (at typical speeds of 1000 rpm or more) in an enclosure through which the reactants flow. The rotating disk geometry has the important property that in certain operating regimes{sup 1} the species and temperature gradients normal to the disk are equal everywhere on the disk. Thus, such a configuration has great potential for highly uniform chemical vapor deposition (CVD),{sup 2--5} and indeed commercial rotating-disk CVD reactors are now available. In certain operating regimes, the equations describing the complex three-dimensional spiral fluid motion can be solved by a separation-of-variables transformation{sup 5,6} that reduces the equations to a system of ordinary differential equations. Strictly speaking, the transformation is only valid for an unconfined infinite-radius disk and buoyancy-free flow. Furthermore, only some boundary conditions are consistent with the transformation (e.g., temperature, gas-phase composition, and approach velocity all specified to be independent of radius at some distances above the disk). Fortunately, however, the transformed equations will provide a very good practical approximation to the flow in a finite-radius reactor over a large fraction of the disk (up to {approximately}90% of the disk radius) when the reactor operating parameters are properly chosen, i.e, high rotation rates. In the limit of zero rotation rate, the rotating disk flow reduces to a stagnation-point flow, for which a similar separation-of-variables transformation is also available. Such flow configurations ( pedestal reactors'') also find use in CVD reactors. In this report we describe a model formulation and mathematical analysis of rotating-disk and stagnation-point CVD reactors. Then we apply the analysis to a compute code called SPIN and describe its implementation and use. 31 refs., 4 figs.

  15. Magnetized and collimated millimeter scale plasma jets with astrophysical relevance

    SciTech Connect

    Brady, Parrish C.; Quevedo, Hernan J.; Valanju, Prashant M.; Bengtson, Roger D.; Ditmire, Todd

    2012-01-15

    Magnetized collimated plasma jets are created in the laboratory to extend our understanding of plasma jet acceleration and collimation mechanisms with particular connection to astrophysical jets. In this study, plasma collimated jets are formed from supersonic unmagnetized flows, mimicking a stellar wind, subject to currents and magnetohydrodynamic forces. It is found that an external poloidal magnetic field, like the ones found anchored to accretion disks, is essential to stabilize the jets against current-driven instabilities. The maximum jet length before instabilities develop is proportional to the field strength and the length threshold agrees well with Kruskal-Shafranov theory. The plasma evolution is modeled qualitatively using MHD theory of current-carrying flux tubes showing that jet acceleration and collimation arise as a result of electromagnetic forces.

  16. Theoretical Particle Astrophysics

    SciTech Connect

    Kamionkowski, Marc

    2013-08-07

    Abstract: Theoretical Particle Astrophysics The research carried out under this grant encompassed work on the early Universe, dark matter, and dark energy. We developed CMB probes for primordial baryon inhomogeneities, primordial non-Gaussianity, cosmic birefringence, gravitational lensing by density perturbations and gravitational waves, and departures from statistical isotropy. We studied the detectability of wiggles in the inflation potential in string-inspired inflation models. We studied novel dark-matter candidates and their phenomenology. This work helped advance the DoE's Cosmic Frontier (and also Energy and Intensity Frontiers) by finding synergies between a variety of different experimental efforts, by developing new searches, science targets, and analyses for existing/forthcoming experiments, and by generating ideas for new next-generation experiments.

  17. Studies of Circumstellar Disk Evolution

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2005-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  18. Theoretical Astrophysics at Fermilab

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The Theoretical Astrophysics Group works on a broad range of topics ranging from string theory to data analysis in the Sloan Digital Sky Survey. The group is motivated by the belief that a deep understanding of fundamental physics is necessary to explain a wide variety of phenomena in the universe. During the three years 2001-2003 of our previous NASA grant, over 120 papers were written; ten of our postdocs went on to faculty positions; and we hosted or organized many workshops and conferences. Kolb and collaborators focused on the early universe, in particular and models and ramifications of the theory of inflation. They also studied models with extra dimensions, new types of dark matter, and the second order effects of super-horizon perturbations. S tebbins, Frieman, Hui, and Dodelson worked on phenomenological cosmology, extracting cosmological constraints from surveys such as the Sloan Digital Sky Survey. They also worked on theoretical topics such as weak lensing, reionization, and dark energy. This work has proved important to a number of experimental groups [including those at Fermilab] planning future observations. In general, the work of the Theoretical Astrophysics Group has served as a catalyst for experimental projects at Fennilab. An example of this is the Joint Dark Energy Mission. Fennilab is now a member of SNAP, and much of the work done here is by people formerly working on the accelerator. We have created an environment where many of these people made transition from physics to astronomy. We also worked on many other topics related to NASA s focus: cosmic rays, dark matter, the Sunyaev-Zel dovich effect, the galaxy distribution in the universe, and the Lyman alpha forest. The group organized and hosted a number of conferences and workshop over the years covered by the grant. Among them were:

  19. THE GAS/DUST RATIO OF CIRCUMSTELLAR DISKS: TESTING MODELS OF PLANETESIMAL FORMATION

    SciTech Connect

    Horne, David; Gibb, Erika; Rettig, Terrence W.; Tilley, David; Balsara, Dinshaw; Brittain, Sean

    2012-07-20

    We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. {sup 12}CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.

  20. The Gas/Dust Ratio of Circumstellar Disks: Testing Models of Planetesimal Formation

    NASA Astrophysics Data System (ADS)

    Horne, David; Gibb, Erika; Rettig, Terrence W.; Brittain, Sean; Tilley, David; Balsara, Dinshaw

    2012-07-01

    We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. 12CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.

  1. Numerical relativity simulations of thick accretion disks around tilted Kerr black holes

    NASA Astrophysics Data System (ADS)

    Mewes, Vassilios; Font, José A.; Galeazzi, Filippo; Montero, Pedro J.; Stergioulas, Nikolaos

    2016-03-01

    In this paper we present 3D numerical relativity simulations of thick accretion disks around tilted Kerr black holes. We investigate the evolution of three different initial disk models with a range of initial black hole spin magnitudes and tilt angles. For all the disk-to-black hole mass ratios considered (0.044-0.16) we observe significant black hole precession and nutation during the evolution. This indicates that for such mass ratios, neglecting the self-gravity of the disks by evolving them in a fixed background black hole spacetime is not justified. We find that the two more massive models are unstable against the Papaloizou-Pringle (PP) instability and that those PP-unstable models remain unstable for all initial spins and tilt angles considered, showing that the development of the instability is a very robust feature of such PP-unstable disks. Our lightest model, which is the most astrophysically favorable outcome of mergers of binary compact objects, is stable. The tilt between the black hole spin and the disk is strongly modulated during the growth of the PP instability, causing a partial global realignment of black hole spin and disk angular momentum in the most massive model with constant specific angular momentum l . For the model with nonconstant l -profile we observe a long-lived m =1 nonaxisymmetric structure which shows strong oscillations of the tilt angle in the inner regions of the disk. This effect might be connected to the development of Kozai-Lidov oscillations. Our simulations also confirm earlier findings that the development of the PP instability causes the long-term emission of large amplitude gravitational waves, predominantly for the l =m =2 multipole mode. The imprint of the black hole (BH) precession on the gravitational waves from tilted BH-torus systems remains an interesting open issue that would require significantly longer simulations than those presented in this paper.

  2. REGULATION OF STAR FORMATION RATES IN MULTIPHASE GALACTIC DISKS: A THERMAL/DYNAMICAL EQUILIBRIUM MODEL

    SciTech Connect

    Ostriker, Eve C.; McKee, Christopher F.; Leroy, Adam K. E-mail: cmckee@astro.berkeley.ed

    2010-10-01

    We develop a model for the regulation of galactic star formation rates {Sigma}{sub SFR} in disk galaxies, in which interstellar medium (ISM) heating by stellar UV plays a key role. By requiring that thermal and (vertical) dynamical equilibrium are simultaneously satisfied within the diffuse gas, and that stars form at a rate proportional to the mass of the self-gravitating component, we obtain a prediction for {Sigma}{sub SFR} as a function of the total gaseous surface density {Sigma} and the midplane density of stars+dark matter {rho}{sub sd}. The physical basis of this relationship is that the thermal pressure in the diffuse ISM, which is proportional to the UV heating rate and therefore to {Sigma}{sub SFR}, must adjust until it matches the midplane pressure value set by the vertical gravitational field. Our model applies to regions where {Sigma} {approx}< 100 M{sub sun} pc{sup -2}. In low-{Sigma}{sub SFR} (outer-galaxy) regions where diffuse gas dominates, the theory predicts that {Sigma}{sub SFR{proportional_to}{Sigma}{radical}}({rho}{sub sd}). The decrease of thermal equilibrium pressure when {Sigma}{sub SFR} is low implies, consistent with observations, that star formation can extend (with declining efficiency) to large radii in galaxies, rather than having a sharp cutoff at a fixed value of {Sigma}. The main parameters entering our model are the ratio of thermal pressure to total pressure in the diffuse ISM, the fraction of diffuse gas that is in the warm phase, and the star formation timescale in self-gravitating clouds; all of these are (at least in principle) direct observables. At low surface density, our model depends on the ratio of the mean midplane FUV intensity (or thermal pressure in the diffuse gas) to the star formation rate, which we set based on solar-neighborhood values. We compare our results to recent observations, showing good agreement overall for azimuthally averaged data in a set of spiral galaxies. For the large flocculent spiral

  3. Outward Migration of Jupiter and Saturn in 3:2 or 2:1 Resonance in Radiative Disks: Implications for the Grand Tack and Nice models

    NASA Astrophysics Data System (ADS)

    Pierens, Arnaud; Raymond, Sean N.; Nesvorny, David; Morbidelli, Alessandro

    2014-11-01

    Embedded in the gaseous protoplanetary disk, Jupiter and Saturn naturally become trapped in 3:2 resonance and migrate outward. This serves as the basis of the Grand Tack model. However, previous hydrodynamical simulations were restricted to isothermal disks, with moderate aspect ratio and viscosity. Here we simulate the orbital evolution of the gas giants in disks with viscous heating and radiative cooling. We find that Jupiter and Saturn migrate outward in 3:2 resonance in modest-mass (M disk ≈ M MMSN, where MMSN is the "minimum-mass solar nebula") disks with viscous stress parameter α between 10-3 and 10-2. In disks with relatively low-mass (M disk <~ M MMSN), Jupiter and Saturn get captured in 2:1 resonance and can even migrate outward in low-viscosity disks (α <= 10-4). Such disks have a very small aspect ratio (h ~ 0.02-0.03) that favors outward migration after capture in 2:1 resonance, as confirmed by isothermal runs which resulted in a similar outcome for h ~ 0.02 and α <= 10-4. We also performed N-body runs of the outer solar system starting from the results of our hydrodynamical simulations and including 2-3 ice giants. After dispersal of the gaseous disk, a Nice model instability starting with Jupiter and Saturn in 2:1 resonance results in good solar systems analogs. We conclude that in a cold solar nebula, the 2:1 resonance between Jupiter and Saturn can lead to outward migration of the system, and this may represent an alternative scenario for the evolution of the solar system.

  4. OUTWARD MIGRATION OF JUPITER AND SATURN IN 3:2 OR 2:1 RESONANCE IN RADIATIVE DISKS: IMPLICATIONS FOR THE GRAND TACK AND NICE MODELS

    SciTech Connect

    Pierens, Arnaud; Raymond, Sean N.; Nesvorny, David; Morbidelli, Alessandro

    2014-11-01

    Embedded in the gaseous protoplanetary disk, Jupiter and Saturn naturally become trapped in 3:2 resonance and migrate outward. This serves as the basis of the Grand Tack model. However, previous hydrodynamical simulations were restricted to isothermal disks, with moderate aspect ratio and viscosity. Here we simulate the orbital evolution of the gas giants in disks with viscous heating and radiative cooling. We find that Jupiter and Saturn migrate outward in 3:2 resonance in modest-mass (M {sub disk} ≈ M {sub MMSN}, where MMSN is the {sup m}inimum-mass solar nebula{sup )} disks with viscous stress parameter α between 10{sup –3} and 10{sup –2}. In disks with relatively low-mass (M {sub disk} ≲ M {sub MMSN}), Jupiter and Saturn get captured in 2:1 resonance and can even migrate outward in low-viscosity disks (α ≤ 10{sup –4}). Such disks have a very small aspect ratio (h ∼ 0.02-0.03) that favors outward migration after capture in 2:1 resonance, as confirmed by isothermal runs which resulted in a similar outcome for h ∼ 0.02 and α ≤ 10{sup –4}. We also performed N-body runs of the outer solar system starting from the results of our hydrodynamical simulations and including 2-3 ice giants. After dispersal of the gaseous disk, a Nice model instability starting with Jupiter and Saturn in 2:1 resonance results in good solar systems analogs. We conclude that in a cold solar nebula, the 2:1 resonance between Jupiter and Saturn can lead to outward migration of the system, and this may represent an alternative scenario for the evolution of the solar system.

  5. Astrophysical Institute, Potsdam

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    Built upon a tradition of almost 300 years, the Astrophysical Institute Potsdam (AIP) is in an historical sense the successor of one of the oldest astronomical observatories in Germany. It is the first institute in the world which incorporated the term `astrophysical' in its name, and is connected with distinguished scientists such as Karl Schwarzschild and Albert Einstein. The AIP constitutes on...

  6. Accretion disk radiation dynamics and the cosmic battery

    SciTech Connect

    Koutsantoniou, Leela E.; Contopoulos, Ioannis E-mail: icontop@academyofathens.gr

    2014-10-10

    We investigate the dynamics of radiation in the surface layers of an optically thick astrophysical accretion disk around a Kerr black hole. The source of the radiation is the surface of the accretion disk itself, and not a central object as in previous studies of the Poynting-Robertson effect. We generate numerical sky maps from photon trajectories that originate on the surface of the disk as seen from the inner edge of the disk at the position of the innermost stable circular orbit. We investigate several accretion disk morphologies with a Shakura-Sunyaev surface temperature distribution. Finally, we calculate the electromotive source of the Cosmic Battery mechanism around the inner edge of the accretion disk and obtain characteristic timescales for the generation of astrophysical magnetic fields.

  7. DIAGNOSING CIRCUMSTELLAR DEBRIS DISKS

    SciTech Connect

    Hahn, Joseph M.

    2010-08-20

    A numerical model of a circumstellar debris disk is developed and applied to observations of the circumstellar dust orbiting {beta} Pictoris. The model accounts for the rates at which dust is produced by collisions among unseen planetesimals, and the rate at which dust grains are destroyed due to collisions. The model also accounts for the effects of radiation pressure, which is the dominant perturbation on the disk's smaller but abundant dust grains. Solving the resulting system of rate equations then provides the dust abundances versus grain size and dust abundances over time. Those solutions also provide the dust grains' collisional lifetime versus grain size, and the debris disk's optical depth and surface brightness versus distance from the star. Comparison to observations then yields estimates of the unseen planetesimal disk's radius, and the rate at which the disk sheds mass due to planetesimal grinding. The model can also be used to measure or else constrain the dust grain's physical and optical properties, such as the dust grains' strength, their light-scattering asymmetry parameter, and the grains' efficiency of light scattering Q{sub s}. The model is then applied to optical observations of the edge-on dust disk orbiting {beta} Pictoris, and good agreement is achieved when the unseen planetesimal disk is broad, with 75 {approx}< r {approx}< 150 AU. If it is assumed that the dust grains are bright like Saturn's icy rings (Q{sub s} = 0.7), then the cross section of dust in the disk is A{sub d} {approx_equal} 2 x 10{sup 20} km{sup 2} and its mass is M{sub d} {approx_equal} 11 lunar masses. In this case, the planetesimal disk's dust-production rate is quite heavy, M-dot {sub d{approx}}9 M {sub +} Myr{sup -1}, implying that there is or was a substantial amount of planetesimal mass there, at least 110 Earth masses. If the dust grains are darker than assumed, then the planetesimal disk's mass-loss rate and its total mass are heavier. In fact, the apparent dearth

  8. Magnetic disk

    NASA Technical Reports Server (NTRS)

    Mallinson, John C.

    1991-01-01

    Magnetic disk recording was invented in 1953 and has undergone intensive development ever since. As a result of this 38 years of development, the cost per byte and the areal density has halved and doubled, respectively every 2 to 2 1/2 years. Today, the cost per byte is lower than 10(exp -6) dollars per byte and area densities exceed 100 x 10(exp 6) bits per square inch. The recent achievements in magnetic disk recording will first be surveyed briefly. Then the principal areas of current technical development will be outlined. Finally, some comments will be made about the future of magnetic disk recording.

  9. The Evolution of Inner Disk Gas in Transition Disks

    NASA Astrophysics Data System (ADS)

    Hoadley, K.; France, K.; Alexander, R. D.; McJunkin, M.; Schneider, P. C.

    2015-10-01

    Investigating the molecular gas in the inner regions of protoplanetary disks (PPDs) provides insight into how the molecular disk environment changes during the transition from primordial to debris disk systems. We conduct a small survey of molecular hydrogen (H2) fluorescent emission, using 14 well-studied Classical T Tauri stars at two distinct dust disk evolutionary stages, to explore how the structure of the inner molecular disk changes as the optically thick warm dust dissipates. We simulate the observed Hi-Lyman α-pumped H2 disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H2 emission in the disk atmosphere and compare these to observations from the Hubble Space Telescope. We find the radial distributions that best describe the observed H2 FUV emission arising in primordial disk targets (full dust disk) are demonstrably different than those of transition disks (little-to-no warm dust observed). For each best-fit model, we estimate inner and outer disk emission boundaries (rin and rout), describing where the bulk of the observed H2 emission arises in each disk, and we examine correlations between these and several observational disk evolution indicators, such as n13-31, rin, CO, and the mass accretion rate. We find strong, positive correlations between the H2 radial distributions and the slope of the dust spectral energy distribution, implying the behavior of the molecular disk atmosphere changes as the inner dust clears in evolving PPDs. Overall, we find that H2 inner radii are ˜4 times larger in transition systems, while the bulk of the H2 emission originates inside the dust gap radius for all transitional sources.

  10. Radiative properties of astrophysical matter : a quest to reproduce astrophysical conditions on earth.

    SciTech Connect

    Bailey, James E.

    2010-10-01

    . Z dynamic hohlraums provide such a megajoule-class source. Initial Z experiments measured transmission through iron samples ionized to the same charge states that exist at the solar convection zone base. The resulting data made it possible to test challenging aspects of the opacity calculations such as the ionization balance and the completeness and accuracy of the atomic energy level description. However, the density was too low to provide a definitive test of the physics at the solar convection zone base. Recent experiments have reached higher densities, and opacity model tests for stellar interiors now appear within reach. Accretion powered objects, including active galactic nuclei, x-ray binaries, and black hole accretion disks, are the most luminous objects in the universe. Astrophysical models for these objects rely largely on comparing spectroscopic predictions with observations. A dilemma arises because the spectra originate from plasmas that are bathed in the enormous photon flux from the accretion disk and photoionization dominates the atomic ionization and energy level populations. Thus, constraining astrophysical models depends on accurate atomic models for photoionized plasmas. Unfortunately, to date the ionization in almost all laboratory experiments is collision-dominated and very few tests of photoionized plasma atomic kinetics exist. Megajoule class high-energy-density facilities can help because they generate higher x-ray fluence over larger spatial scales and longer times. Expanded iron foils and pre-filled neon gas cells have been used in experiments at Z to study photoionized atomic kinetics in two elements commonly observed in astrophysical objects. In these experiments, low density samples are exposed to a measured intense x-ray spectrum, emergent emission or absorption spectra are recorded, and the results are compared to predictions made with spectral synthesis codes used by astrophysicists. Initial experiments focused on testing models used

  11. Condensation Processes in Astrophysical Environments

    NASA Technical Reports Server (NTRS)

    Nuth, Joseph A., III; Rietmeijer, Frans J. M.; Hill, Hugh G. M.

    2002-01-01

    Astrophysical systems present an intriguing set of challenges for laboratory chemists. Chemistry occurs in regions considered an excellent vacuum by laboratory standards and at temperatures that would vaporize laboratory equipment. Outflows around Asymptotic Giant Branch (AGB) stars have timescales ranging from seconds to weeks depending on the distance of the region of interest from the star and, on the way significant changes in the state variables are defined. The atmospheres in normal stars may only change significantly on several billion-year timescales. Most laboratory experiments carried out to understand astrophysical processes are not done at conditions that perfectly match the natural suite of state variables or timescales appropriate for natural conditions. Experimenters must make use of simple analog experiments that place limits on the behavior of natural systems, often extrapolating to lower-pressure and/or higher-temperature environments. Nevertheless, we argue that well-conceived experiments will often provide insights into astrophysical processes that are impossible to obtain through models or observations. This is especially true for complex chemical phenomena such as the formation and metamorphism of refractory grains under a range of astrophysical conditions. Data obtained in our laboratory has been surprising in numerous ways, ranging from the composition of the condensates to the thermal evolution of their spectral properties. None of this information could have been predicted from first principals and would not have been credible even if it had.

  12. X-ray Reflected Spectra from Accretion Disk Models. III. A Complete Grid of Ionized Reflection Calculations

    NASA Technical Reports Server (NTRS)

    Garcia, J.; Dauser, T.; Reynolds, C. S.; Kallman, T. R.; McClintock, J. E.; Wilms, J.; Ekmann, W.

    2013-01-01

    We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk. The spectra were computed using an updated version of our code xillver that incorporates new routines and a richer atomic data base. We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters. Each individual model is characterized by the photon index Gamma of the illuminating radiation, the ionization parameter zeta at the surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and the iron abundance A(sub Fe) relative to the solar value. The ranges of the parameters covered are: 1.2 <= Gamma <= 3.4, 1 <= zeta <= 104, and 0.5 <= A(sub Fe) <= 10. These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state. This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux. The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin. A total of 720 reflection spectra are provided in a single FITS file suitable for the analysis of X-ray observations via the atable model in xspec. Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of xillver.

  13. X-RAY REFLECTED SPECTRA FROM ACCRETION DISK MODELS. III. A COMPLETE GRID OF IONIZED REFLECTION CALCULATIONS

    SciTech Connect

    Garcia, J.; McClintock, J. E.; Dauser, T.; Wilms, J.; Eikmann, W.; Reynolds, C. S.; Kallman, T. R. E-mail: jem@cfa.harvard.edu E-mail: thomas.dauser@sternwarte.uni-erlangen.de E-mail: wiebke.eikmann@sternwarte.uni-erlangen.de

    2013-05-10

    We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk. The spectra were computed using an updated version of our code XILLVER that incorporates new routines and a richer atomic database. We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters. Each individual model is characterized by the photon index {Gamma} of the illuminating radiation, the ionization parameter {xi} at the surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and the iron abundance A{sub Fe} relative to the solar value. The ranges of the parameters covered are 1.2 {<=} {Gamma} {<=} 3.4, 1 {<=} {xi} {<=} 10{sup 4}, and 0.5 {<=} A{sub Fe} {<=} 10. These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state. This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux. The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin. A total of 720 reflection spectra are provided in a single FITS file (http://hea-www.cfa.harvard.edu/{approx}javier/xillver/) suitable for the analysis of X-ray observations via the atable model in XSPEC. Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of XILLVER.

  14. Theoretical Astrophysics - Volume 1, Astrophysical Processes

    NASA Astrophysics Data System (ADS)

    Padmanabhan, T.

    2000-12-01

    Preface; 1. Order-of-magnitude astrophysics; 2. Dynamics; 3. Special relativity, electrodynamics and optics; 4. Basics of electromagnetic radiation; 5. Statistical mechanics; 6. Radiative processes; 7. Spectra; 8. Neutral fluids; 9. Plasma physics; 10. Gravitational dynamics; 11. General theory of relativity; 12. Basics of nuclear physics; Notes and References; Index.

  15. A formula for the Shakura-Sunyaev turbulent viscosity parameter. [for modeling of accretion disks

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Goldman, I.; Hubickyj, O.

    1984-01-01

    A formula for the Shakura-Suniaev alpha parameter is proposed in terms of the growth rate of the unstable modes of the physical mechanisms that generates turbulence. Turbulent convection is discussed as a particular example. The effect of rotation on turbulent viscosity is considered, and some remarks are made on convective fluxes, disk stability, and other types of instabilities.

  16. IMPROVED MODELING OF THE MASS DISTRIBUTION OF DISK GALAXIES BY THE EINASTO HALO MODEL

    SciTech Connect

    Chemin, Laurent; De Blok, W. J. G.; Mamon, Gary A. E-mail: edeblok@ast.uct.ac.za

    2011-10-15

    Analysis of the rotation curves (RCs) of spiral galaxies provides an efficient diagnostic for studying the properties of dark matter halos and their relations with baryonic material. Since the cored pseudo-isothermal (Iso) model usually provides a better description of observed RCs than does the cuspy Navarro-Frenk-White (NFW) model, there have been concerns that the {Lambda}CDM primordial density fluctuation spectrum may not be the correct one. We have modeled the RCs of galaxies from The H I Nearby Galaxy Survey (THINGS) with the Einasto halo model, which has emerged as the best-fitting model of the halos arising in dissipationless cosmological N-body simulations. We find that the RCs are significantly better fit with the Einasto halo than with either Iso or NFW halo models. In our best-fit Einasto models, the radius of density slope -2 and the density at this radius are highly correlated. The Einasto index, which controls the overall shape of the density profile, is near unity on average for intermediate and low mass halos. This is not in agreement with the predictions from {Lambda}CDM simulations. The indices of the most massive halos are in rough agreement with those cosmological simulations and appear correlated with the halo virial mass. We find that a typical Einasto density profile declines more strongly in its outermost parts than any of the Iso or NFW models whereas it is relatively shallow in its innermost regions. The core nature of those regions of halos thus extends the cusp-core controversy found for the NFW model with low surface density galaxies to the Einasto halo with more massive galaxies like those of THINGS. The Einasto concentrations decrease as a function of halo mass, in agreement with trends seen in numerical simulations. However, they are generally smaller than values expected for simulated Einasto halos. We thus find that, so far, the Einasto halo model provides the best match to the observed RCs and can therefore be considered as a new

  17. GROWTH OF GRAINS IN BROWN DWARF DISKS

    SciTech Connect

    Meru, Farzana; Galvagni, Marina; Olczak, Christoph

    2013-09-01

    We perform coagulation and fragmentation simulations using the new physically motivated model by Garaud et al. to determine growth locally in brown dwarf disks. We show that large grains can grow and that if brown dwarf disks are scaled-down versions of T Tauri disks (in terms of stellar mass, disk mass, and disk radius) growth at an equivalent location with respect to the disk truncation radius can occur to the same size in both disks. We show that similar growth occurs because the collisional timescales in the two disks are comparable. Our model may therefore potentially explain the recent observations of grain growth to millimeter sizes in brown dwarf disks, as seen in T Tauri disks.

  18. Theoretical study of the electronically excited radical cations of naphthalene and anthracene as archetypal models for astrophysical observations. Part II. Dynamics consequences.

    PubMed

    Ghanta, S; Reddy, V Sivaranjana; Mahapatra, S

    2011-08-28

    Nuclear dynamics is investigated theoretically from first principles by employing the ab initio vibronic models of the prototypical naphthalene and anthracene radical cations developed in Part I. This Part is primarily aimed at corroborating a large amount of available experimental data with a specific final goal to establish an unambiguous link with the current observations in astrophysics and astronomy. The detailed analyses presented here perhaps establish that these two prototypical polycyclic aromatic hydrocarbon radical cations are indeed potential carriers of the observed diffuse interstellar bands. PMID:21750791

  19. The Hall Instability of Weakly Ionized, Radially Stratified, Rotating Disks

    NASA Astrophysics Data System (ADS)

    Liverts, Edward; Mond, Michael; Chernin, Arthur D.

    2007-09-01

    Cool weakly ionized gaseous rotating disks are considered by many models to be the origin of the evolution of protoplanetary clouds. Instabilities against perturbations in such disks play an important role in the theory of the formation of stars and planets. Thus, a hierarchy of successive fragmentations into smaller and smaller pieces as a part of the Kant-Laplace theory of formation of the planetary system remains valid also for contemporary cosmogony. Traditionally, axisymmetric magnetohydrodynamic (MHD) and, recently, Hall-MHD instabilities have been thoroughly studied as providers of an efficient mechanism for radial transfer of angular momentum and of radial density stratification. In the current work, the Hall instability against nonaxisymmetric perturbations in compressible rotating fluid in external magnetic field is proposed as a viable mechanism for the azimuthal fragmentation of the protoplanetary disk and, thus, perhaps initiates the road to planet formation. The Hall instability is excited due to the combined effect of the radial stratification of the disk and the Hall electric field, and its growth rate is of the order of the rotation period. This family of instabilities is introduced here for the first time in an astrophysical context.

  20. Brown dwarf disks with ALMA

    SciTech Connect

    Ricci, L.; Isella, A.; Testi, L.; De Gregorio-Monsalvo, I.; Natta, A.; Scholz, A.

    2014-08-10

    We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

  1. ACCRETION OUTBURSTS IN CIRCUMPLANETARY DISKS

    SciTech Connect

    Lubow, S. H.; Martin, R. G.

    2012-04-20

    We describe a model for the long-term evolution of a circumplanetary disk that is fed mass from a circumstellar disk and contains regions of low turbulence (dead zones). We show that such disks can be subject to accretion-driven outbursts, analogous to outbursts previously modeled in the context of circumstellar disks to explain FU Ori phenomena. Circumplanetary disks around a proto-Jupiter can undergo outbursts for infall accretion rates onto the disks in the range M-dot{sub infall} approx. 10{sup -9} to 10{sup -7} M{sub Sun} yr{sup -1}, typical of accretion rates in the T Tauri phase. During outbursts, the accretion rate and disk luminosity increases by several orders of magnitude. Most of the planet mass growth during planetary gas accretion may occur via disk outbursts involving gas that is considerably hotter than predicted by steady state models. For low infall accretion rates M-dot{sub infall} {approx}< 10{sup -10} M{sub sun} yr{sup -1} that occur in late stages of disk accretion, disk outbursts are unlikely to occur, even if dead zones are present. Such conditions are favorable for the formation of icy satellites.

  2. Interferometry of ɛ Aurigae: Characterization of the Asymmetric Eclipsing Disk

    NASA Astrophysics Data System (ADS)

    Kloppenborg, B. K.; Stencel, R. E.; Monnier, J. D.; Schaefer, G. H.; Baron, F.; Tycner, C.; Zavala, R. T.; Hutter, D.; Zhao, M.; Che, X.; ten Brummelaar, T. A.; Farrington, C. D.; Parks, R.; McAlister, H. A.; Sturmann, J.; Sturmann, L.; Sallave-Goldfinger, P. J.; Turner, N.; Pedretti, E.; Thureau, N.

    2015-09-01

    We report on a total of 106 nights of optical interferometric observations of the ɛ Aurigae system taken during the last 14 years by four beam combiners at three different interferometric facilities. This long sequence of data provides an ideal assessment of the system prior to, during, and after the recent 2009-2011 eclipse. We have reconstructed model-independent images from the 10 in-eclipse epochs which show that a disk-like object is indeed responsible for the eclipse. Using new three-dimensional, time-dependent modeling software, we derive the properties of the F-star (diameter, limb darkening), determine previously unknown orbital elements (Ω, i), and access the global structures of the optically thick portion of the eclipsing disk using both geometric models and approximations of astrophysically relevant density distributions. These models may be useful in future hydrodynamical modeling of the system. Finally, we address several outstanding research questions including mid-eclipse brightening, possible shrinking of the F-type primary, and any warps or sub-features within the disk.

  3. Nonazimuthal linear polarization in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Canovas, H.; Ménard, F.; de Boer, J.; Pinte, C.; Avenhaus, H.; Schreiber, M. R.

    2015-10-01

    Several studies discussing imaging polarimetry observations of protoplanetary disks use the so-called radial Stokes parameters Qφ and Uφ to discuss the results. This approach has the advantage of providing a direct measure of the noise in the polarized images under the assumption that the polarization is only azimuthal, i.e., perpendicular to the direction toward the illuminating source. However, a detailed study of the validity of this assumption is currently missing. We aim to test whether departures from azimuthal polarization can naturally be produced by scattering processes in optically thick protoplanetary disks at near infrared wavelengths. We use the radiative transfer code MCFOST to create a generic model of a transition disk using different grain size distributions and dust masses. From these models we generate synthetic polarized images at 2.2 μm. We find that even for moderate inclinations (e.g., i = 40°), multiple scattering alone can produce significant (up to ~ 4.5% of the Qφ image, peak-to-peak) nonazimuthal polarization reflected in the Uφ images. We also find that different grain populations can naturally produce radial polarization (i.e., negative values in the Qφ images). Despite the simplifications of the models, our results suggest that caution is recommended when interpreting polarized images by only analyzing the Qφ and Uφ images. We find that there can be astrophysical signal in the Uφ images and negative values in the Qφ images, which indicate departures from azimuthal polarization. If significant signal is detected in the Uφ images, we recommend checking the standard Q and U images to look for departures from azimuthal polarization. On the positive side, signal in the Uφ images once all instrumental and data-reduction artifacts have been corrected for means that there is more information to be extracted regarding the dust population and particle density.

  4. Modeling the effect of head drag reduction for a cylinder with a protruding disk at high mach numbers

    NASA Astrophysics Data System (ADS)

    Isaev, S. A.; Baranov, P. A.; Mikhalev, A. N.; Sudakov, A. G.

    2014-11-01

    Various approaches to modeling super- and hypersonic turbulent airflow past cylindrical bodies with a nontraditional nose in the form of a protruding rod-supported disk have been compared. Aeroballistic experiments on a light-gas propulsion setup were combined with wind tunnel tests and numerical simulations using VP2/3 program package based on multiblock computational techniques and a model of shear stress transport with flow-line curvature corrections. The phenomenon of the head and wave drag reduction for the stepped body is analyzed at high Mach numbers (up to 10) and variation of the supporting rod length under conditions of existence of the frontal flow separation zone.

  5. Atomic data generation and collisional radiative modeling of argon II, argon III, and neon I for laboratory and astrophysical plasmas

    NASA Astrophysics Data System (ADS)

    Munoz Burgos, Jorge Manuel

    Accurate knowledge of atomic processes plays a key role in modeling the emission in laboratory as well as in astrophysical plasmas. These processes are included in a collisional-radiative model and the results are compared with experimental measurements for Ar and Ne ions from the ASTRAL (Auburn Steady sTate Research fAciLity) experiment. The accuracy of our model depends upon the quality of the atomic data we use. Atomic data for near neutral systems present a challenge due to the low accuracy of perturbative methods for these systems. In order to improve our model we rely on non-perturbative methods such as R - Matrix and RMPS ( R -Matrix with Pseudo-States) to include correlation in the collision cross-sections. In the case of Ar + we compared R -Matrix electron-impact excitation data against the results from a new RMPS calculation. The aim was to assess the effects of continuum-coupling effects on the atomic data and the resulting spectrum. We do our spectral modeling using the ADAS suite of codes. Our collisional-radiative formalism assumes that the excited levels are in quasi- static equilibrium with the ground and metastable populations. In our model we allow for N e and T e variation along the line of sight by fitting our densities and temperature profiles with those measured within the experiment. The best results so far have been obtained by the fitting of the experimental temperature and density profiles with Gaussian and polynomial distribution functions. The line of sight effects were found to have a significant effect on the emission modeling. The relative emission rates were measured in the ASTRAL helicon plasma source. A spectrometer which features a 0.33 m Criss-Cross Scanning monochromator and a CCD camera is used for this study. ASTRAL produces bright intense Ar and Ne plasmas with n e = 10 11 to 10 13 cm -3 and T e = 2 to 10 eV. A series of 7 large coils produce an axial magnetic field up to 1.3 kGauss. A fractional helix antenna is used to

  6. Modeling Spitzer Observations of VV Ser. II. An Extended Quantum-heated Nebula and a Disk Shadow

    NASA Astrophysics Data System (ADS)

    Pontoppidan, Klaus M.; Dullemond, Cornelis P.; Blake, Geoffrey A.; Evans, Neal J., II; Geers, Vincent C.; Harvey, Paul M.; Spiesman, William

    2007-02-01

    We present mid-infrared Spitzer IRAC and MIPS images of the UX Orionis star VV Ser and the surrounding cloud. The 5.6-70 μm images show bright, localized, and nebulous emission extended over 4' centered on VV Ser. This nebulosity is due to transiently heated grains excited by UV photons emitted by VV Ser. Imprinted on the nebulosity is a wedge-shaped dark band, centered on the star. We interpret this as the shadow cast by the inner regions of a near-edge-on disk, allowing the PAHs to be excited only outside of this shadow. We extend an axisymmetric radiative transfer model of the VV Ser disk described in a companion paper to include quantum-heated PAH molecules and very small grains (VSGs) in the thermal cooling approximation. The presence of a disk shadow strongly constrains the inclination as well as the position angle of the disk. The nebulosity at 5.6-8.0 μm and the 2175 Å absorption feature seen in an archival spectrum from the IUE can be fit using only PAHs, consistent with the main carrier of the 2175 Å feature being due to the graphite-like structure of the PAHs. The PAH component is found to be relatively smoothly distributed in the cloud, while the population of VSGs emitting at 20-70 μm is strongly concentrated ~50'' to the southeast of VV Ser. Depending on the adopted PAH opacity, the abundance of PAHs in the surrounding cloud is constrained to 5%+/-2% of the total dust mass. Although relatively rare, quantum-heated nebulosities surrounding single, well-defined stars are well-suited for gaining unique insights into the physics of very small particles in molecular clouds.

  7. Computational Infrastructure for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Smith, M. S.; Lingerfelt, E. J.; Scott, J. P.; Nesaraja, C. D.; Hix, W. R.; Bardayan, D. W.; Blackmon, J. C.; Chae, K.; Guidry, M. W.; Hard, C. C.; Sharp, J. E.; Kozub, R. L.; Meyer, R. A.

    2004-12-01

    The Computational Infrastructure for Nuclear Astrophysics is a platform-independent, online suite of computer codes developed by the ORNL Nuclear Data Project that makes a rapid connection between laboratory nuclear physics results and astrophysical models. It enables users to evaluate cross sections, process them into thermonuclear reaction rates, and parameterize (with a few percent accuracy) these rates that vary by up to 30 orders of magnitude over the temperatures of interest. Users can then properly format these rates for input into astrophysical computer simulations, create and manipulate libraries of rates, as well as run and visualize sample post-processing nucleosynthesis calculations. For example, we have developed animated nuclide charts that show how predicted abundances (represented by a user-defined color scale) change in time. With this unique suite, users can within a very short time quantify the astrophysical impact of a newly measured or calculated cross section, or a newly created customized reaction rate library, and then document and share their results with the scientific community. The suite has a straightforward interface with a "Windows Wizard" motif whereby users progress through complicated calculations in a step-by-step fashion. Users can upload their own files for processing and save their work on our server, as well as work with files that other users wish to share. These tools are currently being used to investigate novae and X-ray bursts. The suite is available through nucastrodata.org, a website that also hyperlinks available nuclear data sets relevant for nuclear astrophysics research. New features are continually being added to this software, which is funded by the U.S. Department of Energy Low Energy Nuclear Physics and Nuclear Data Programs. ORNL is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725.

  8. Atomic data generation and collisional radiative modeling of argon II, argon III, and neon I for laboratory and astrophysical plasmas

    NASA Astrophysics Data System (ADS)

    Munoz Burgos, Jorge Manuel

    Accurate knowledge of atomic processes plays a key role in modeling the emission in laboratory as well as in astrophysical plasmas. These processes are included in a collisional-radiative model and the results are compared with experimental measurements for Ar and Ne ions from the ASTRAL (Auburn Steady sTate Research fAciLity) experiment. The accuracy of our model depends upon the quality of the atomic data we use. Atomic data for near neutral systems present a challenge due to the low accuracy of perturbative methods for these systems. In order to improve our model we rely on non-perturbative methods such as R - Matrix and RMPS ( R -Matrix with Pseudo-States) to include correlation in the collision cross-sections. In the case of Ar + we compared R -Matrix electron-impact excitation data against the results from a new RMPS calculation. The aim was to assess the effects of continuum-coupling effects on the atomic data and the resulting spectrum. We do our spectral modeling using the ADAS suite of codes. Our collisional-radiative formalism assumes that the excited levels are in quasi- static equilibrium with the ground and metastable populations. In our model we allow for N e and T e variation along the line of sight by fitting our densities and temperature profiles with those measured within the experiment. The best results so far have been obtained by the fitting of the experimental temperature and density profiles with Gaussian and polynomial distribution functions. The line of sight effects were found to have a significant effect on the emission modeling. The relative emission rates were measured in the ASTRAL helicon plasma source. A spectrometer which features a 0.33 m Criss-Cross Scanning monochromator and a CCD camera is used for this study. ASTRAL produces bright intense Ar and Ne plasmas with n e = 10 11 to 10 13 cm -3 and T e = 2 to 10 eV. A series of 7 large coils produce an axial magnetic field up to 1.3 kGauss. A fractional helix antenna is used to

  9. HERschel Observations of Edge-on Spirals (HEROES). II. Tilted-ring modelling of the atomic gas disks

    NASA Astrophysics Data System (ADS)

    Allaert, F.; Gentile, G.; Baes, M.; De Geyter, G.; Hughes, T. M.; Lewis, F.; Bianchi, S.; De Looze, I.; Fritz, J.; Holwerda, B. W.; Verstappen, J.; Viaene, S.

    2015-10-01

    Context. Edge-on galaxies can offer important insight into galaxy evolution because they are the only systems where the distribution of the different components can be studied both radially and vertically. The HEROES project was designed to investigate the interplay between the gas, dust, stars, and dark matter (DM) in a sample of 7 massive edge-on spiral galaxies. Aims: In this second HEROES paper, we present an analysis of the atomic gas content of 6 out of 7 galaxies in our sample. The remaining galaxy was recently analysed according to the same strategy. The primary aim of this work is to constrain the surface density distribution, the rotation curve, and the geometry of the gas disks in a homogeneous way. In addition we identify peculiar features and signs of recent interactions. Methods: We have constructed detailed tilted-ring models of the atomic gas disks based on new GMRT 21-cm observations of NGC 973 and UGC 4277 and re-reduced archival H i data of NGC 5907, NGC 5529, IC 2531, and NGC 4217. Potential degeneracies between different models were resolved by requiring good agreement with the data in various representations of the data cubes. Results: From our modelling we find that all but one galaxy are warped along the major axis. In addition, we identify warps along the line of sight in three galaxies. A flaring gas layer is required to reproduce the data for only one galaxy, but (moderate) flares cannot be ruled out for the other galaxies either. A coplanar ring-like structure is detected outside the main disk of NGC 4217, which we suggest could be the remnant of a recent minor merger event. We also find evidence of a radial inflow of 15 ± 5 km s-1 in the disk of NGC 5529, which might be related to the ongoing interaction with two nearby companions. For NGC 5907, the extended, asymmetric, and strongly warped outer regions of the H i disk also suggest a recent interaction. In contrast, the inner disks of these three galaxies (NGC 4217, NGC 5529, and NGC

  10. Hydrodynamic Stability and Magnetic Reconnection in Disks and Stars

    NASA Technical Reports Server (NTRS)

    Goodman, Jeremy; Kulsrud, Russell

    1999-01-01

    The purpose of this grant is to study parametric instability. The simplest example of parametric instability is a harmonic oscillator with a periodic modulation of the spring constant. If the modulation frequency is close to twice the natural frequency of the oscillator, the amplitude of oscillation tends to grow exponentially. The growth rate is proportional to the strength of the modulation, but it also depends upon the closeness to resonance of the two frequencies, and upon natural damping rate or "Q" of the oscillator. Parametric instabilities are very common in physics. A familiar example is a jogger's ponytail--normally a very strongly damped pendulum, it can be destabilized by the variation in effective gravity during the jogger's stride. Observation confirms that the period of the pendulum is half that of the jogger's vertical motion. In astrophysics, parametric instability may occur by external tidal forcing, or by interaction among eigenmodes. In the latter case, an energetic eigenmode may destabilize modes of half its frequency, provided some weak nonlinearity exists to couple them. Under a previous Astrophysical Theory grant (NAGW-2419), the PI discovered a parametric instability of tidally forced disks such as the accretion disks in cataclysmic variables and X ray binaries [2]. The destabilized modes are tightly-wound, incompressible, three-dimensional waves analogous to g-modes and r-modes in stars. Later work has confirmed our analysis [4]. It was hoped that these modes might provide a source of turbulence and angular momentum transport in accretion disks. However, a follow-up investigation of this instability by local numerical simulations, although confirming the analytically estimated growth rates, found negligible angular momentum flux [3]. Other work, partly supported by the ATP, now strongly indicates that the transport mechanism in such disks is magnetohydrodynamic turbulence [6]. Nevertheless, the parametric mechanism may truncate the outer

  11. The Kozai-Lidov mechanism in hydrodynamical disks. II. Effects of binary and disk parameters

    DOE PAGESBeta

    Fu, Wen; Lubow, Stephen H.; Martin, Rebecca G.

    2015-07-01

    Martin et al. (2014b) showed that a substantially misaligned accretion disk around one component of a binary system can undergo global damped Kozai–Lidov (KL) oscillations. During these oscillations, the inclination and eccentricity of the disk are periodically exchanged. However, the robustness of this mechanism and its dependence on the system parameters were unexplored. In this paper, we use three-dimensional hydrodynamical simulations to analyze how various binary and disk parameters affect the KL mechanism in hydrodynamical disks. The simulations include the effect of gas pressure and viscosity, but ignore the effects of disk self-gravity. We describe results for different numerical resolutions,more » binary mass ratios and orbital eccentricities, initial disk sizes, initial disk surface density profiles, disk sound speeds, and disk viscosities. We show that the KL mechanism can operate for a wide range of binary-disk parameters. We discuss the applications of our results to astrophysical disks in various accreting systems.« less

  12. Driving of Accretion Disk Variability by the Disk Dynamo

    NASA Astrophysics Data System (ADS)

    Hogg, J. Drew; Reynolds, Christopher S.

    2016-01-01

    Variability is a univeral feature of emission from accreting objects, but many questions remain as to how the variability is driven and how it relates to the underlying accretion physics. We use a long, semi-global MHD simulation of a thin accretion disk around a black hole to perform a detailed study of the fluctuations in the internal disk stress and the affect these fluctuations have on the accretion flow. In this poster, we show that low frequency fluctuations in the effective α-parameter in the disk are due to oscillations of the disk dynamo. Additionally, we show that fluctuations in the effective α-parameter drive "propagating fluctuations" in mass accretion rate through the disk that qualitatively resemble the variability from astrophysical black hole systems. In particular, we show that several of the ubiquitous phenomenological properties of black hole variability, including log-normal flux distributions, RMS-flux relationships, and radial coherence are present in the mass accretion rate fluctuations of our simulation.

  13. Modeling and optimization of thin disk structure for high power sub-joule laser

    NASA Astrophysics Data System (ADS)

    Severová, Patricie; Smrz, Martin; Chyla, Michal; Miura, Taisuke; Endo, Akira; Mocek, Tomáš

    2013-05-01

    We analyzed the transient response characteristics of Yb:YAG thin disk in to clarify the experimentally obtained advantages of pulsed pumping in 1-kHz repetition rate reported in ref. 2. We applied commercial 2D FEA software which can calculate transient response of thermal effects. The temperature distributions of thin disk in both the CW power of 125-W and the average power of pulsed 125-W have been calculated. Even the net heat power were same in both CW and pulsed pumping, the temperature distribution was lower in pulsed pumping which can provide higher O-O efficiency and smaller beam distortion. The time evolution of OPD in the pulsed pumping has been analyzed, too.

  14. Dust in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Rodmann, Jens

    2006-02-01

    This thesis presents observational and theoretical studies of the size and spatial distribution of dust particles in circumstellar disks. Using millimetre interferometric observations of optically thick disks around T Tauri stars, I provide conclusive evidence for the presence of millimetre- to centimetre-sized dust aggregates. These findings demonstrate that dust grain growth to pebble-sized dust particles is completed within less than 1 Myr in the outer disks around low-mass pre-main-sequence stars. The modelling of the infrared spectral energy distributions of several solar-type main-sequence stars and their associated circumstellar debris disks reveals the ubiquity of inner gaps devoid of substantial amounts of dust among Vega-type infrared excess sources. It is argued that the absence of circumstellar material in the inner disks is most likely the result of the gravitational influence of a large planet and/or a lack of dust-producing minor bodies in the dust-free region. Finally, I describe a numerical model to simulate the dynamical evolution of dust particles in debris disks, taking into account the gravitational perturbations by planets, photon radiation pressure, and dissipative drag forces due to the Poynting-Robertson effect and stellar wind. The validity of the code it established by several tests and comparison to semi-analytic approximations. The debris disk model is applied to simulate the main structural features of a ring of circumstellar material around the main-sequence star HD 181327. The best agreement between model and observation is achieved for dust grains a few tens of microns in size locked in the 1:1 resonance with a Jupiter-mass planet (or above) on a circular orbit.

  15. Testing the Propagating Fluctuations Model with a Long, Global Accretion Disk Simulation

    NASA Astrophysics Data System (ADS)

    Hogg, J. Drew; Reynolds, Christopher S.

    2016-07-01

    The broadband variability of many accreting systems displays characteristic structures; log-normal flux distributions, root-mean square (rms)-flux relations, and long inter-band lags. These characteristics are usually interpreted as inward propagating fluctuations of the mass accretion rate in an accretion disk driven by stochasticity of the angular momentum transport mechanism. We present the first analysis of propagating fluctuations in a long-duration, high-resolution, global three-dimensional magnetohydrodynamic (MHD) simulation of a geometrically thin (h/r ≈ 0.1) accretion disk around a black hole. While the dynamical-timescale turbulent fluctuations in the Maxwell stresses are too rapid to drive radially coherent fluctuations in the accretion rate, we find that the low-frequency quasi-periodic dynamo action introduces low-frequency fluctuations in the Maxwell stresses, which then drive the propagating fluctuations. Examining both the mass accretion rate and emission proxies, we recover log-normality, linear rms-flux relations, and radial coherence that would produce inter-band lags. Hence, we successfully relate and connect the phenomenology of propagating fluctuations to modern MHD accretion disk theory.

  16. Compressible Astrophysics Simulation Code

    Energy Science and Technology Software Center (ESTSC)

    2007-07-18

    This is an astrophysics simulation code involving a radiation diffusion module developed at LLNL coupled to compressible hydrodynamics and adaptive mesh infrastructure developed at LBNL. One intended application is to neutrino diffusion in core collapse supernovae.

  17. Observations and modelling of CO and [C i] in protoplanetary disks. First detections of [C i] and constraints on the carbon abundance

    NASA Astrophysics Data System (ADS)

    Kama, M.; Bruderer, S.; Carney, M.; Hogerheijde, M.; van Dishoeck, E. F.; Fedele, D.; Baryshev, A.; Boland, W.; Güsten, R.; Aikutalp, A.; Choi, Y.; Endo, A.; Frieswijk, W.; Karska, A.; Klaassen, P.; Koumpia, E.; Kristensen, L.; Leurini, S.; Nagy, Z.; Perez Beaupuits, J.-P.; Risacher, C.; van der Marel, N.; van Kempen, T. A.; van Weeren, R. J.; Wyrowski, F.; Yıldız, U. A.

    2016-04-01

    Context. The gas-solid budget of carbon in protoplanetary disks is related to the composition of the cores and atmospheres of the planets forming in them. The principal gas-phase carbon carriers CO, C0, and C+ can now be observed regularly in disks. Aims: The gas-phase carbon abundance in disks has thus far not been well characterized observationally. We obtain new constraints on the [C]/[H] ratio in a large sample of disks, and compile an overview of the strength of [C i] and warm CO emission. Methods: We carried out a survey of the CO 6-5 line and the [C i] 1-0 and 2-1 lines towards 37 disks with the APEX telescope, and supplemented it with [C ii] data from the literature. The data are interpreted using a grid of models produced with the DALI disk code. We also investigate how well the gas-phase carbon abundance can be determined in light of parameter uncertainties. Results: The CO 6-5 line is detected in 13 out of 33 sources, [C i] 1-0 in 6 out of 12, and [C i] 2-1 in 1 out of 33. With separate deep integrations, the first unambiguous detections of the [C i] 1-0 line in disks are obtained, in TW Hya and HD 100546. Conclusions: Gas-phase carbon abundance reductions of a factor of 5-10 or more can be identified robustly based on CO and [C i] detections, assuming reasonable constraints on other parameters. The atomic carbon detection towards TW Hya confirms a factor of 100 reduction of [C]/[H]gas in that disk, while the data are consistent with an ISM-like carbon abundance for HD 100546. In addition, BP Tau, T Cha, HD 139614, HD 141569, and HD 100453 are either carbon-depleted or gas-poor disks. The low [C i] 2-1 detection rates in the survey mostly reflect insufficient sensitivity for T Tauri disks. The Herbig Ae/Be disks with CO and [C ii] upper limits below the models are debris-disk-like systems. An increase in sensitivity of roughly order of magnitude compared to our survey is required to obtain useful constraints on the gas-phase [C]/[H] ratio in most of the

  18. Astrophysics and cosmic physics

    NASA Astrophysics Data System (ADS)

    Siuniaev, R. A.

    Recent astrophysical studies undertaken in the Soviet Union are surveyed. Papers are presented on the role of observations of galactic clusters in cosmological studies; photometric observations of active nuclei; investigations of the fine structure of radio sources; and interstellar molecules. Also considered are Type I supernovae, gamma-ray bursts, the motion of the sun in the interstellar medium, and astrophysical observations on Mt. Maidanak in Central Asia.

  19. SPAN: Astronomy and astrophysics

    NASA Technical Reports Server (NTRS)

    Thomas, Valerie L.; Green, James L.; Warren, Wayne H., Jr.; Lopez-Swafford, Brian

    1987-01-01

    The Space Physics Analysis Network (SPAN) is a multi-mission, correlative data comparison network which links science research and data analysis computers in the U.S., Canada, and Europe. The purpose of this document is to provide Astronomy and Astrophysics scientists, currently reachable on SPAN, with basic information and contacts for access to correlative data bases, star catalogs, and other astrophysic facilities accessible over SPAN.

  20. Arcetri Astrophysical Observatory

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    The Arcetri Astrophysical Observatory, a government research institute founded in 1972, is located close to the villa where Galileo spent the last 11 years of his life. Under the directorship of Giorgio Abetti (1921-53) it became the growth point of Italian astrophysics with emphasis on solar physics; a tradition continued by his successor Guglielmo Righini (1953-78). Since 1978 the activities ha...

  1. THICK-DISK EVOLUTION INDUCED BY THE GROWTH OF AN EMBEDDED THIN DISK

    SciTech Connect

    Villalobos, Alvaro; Helmi, Amina; Kazantzidis, Stelios E-mail: ahelmi@astro.rug.n E-mail: villalobos@oats.inaf.i

    2010-07-20

    We perform collisionless N-body simulations to investigate the evolution of the structural and kinematical properties of simulated thick disks induced by the growth of an embedded thin disk. The thick disks used in the present study originate from cosmologically common 5:1 encounters between initially thin primary disk galaxies and infalling satellites. The growing thin disks are modeled as static gravitational potentials and we explore a variety of growing-disk parameters that are likely to influence the response of thick disks. We find that the final thick-disk properties depend strongly on the total mass and radial scale length of the growing thin disk, and much less sensitively on its growth timescale and vertical scale height as well as the initial sense of thick-disk rotation. Overall, the growth of an embedded thin disk can cause a substantial contraction in both the radial and vertical direction, resulting in a significant decrease in the scale lengths and scale heights of thick disks. Kinematically, a growing thin disk can induce a notable increase in the mean rotation and velocity dispersions of thick-disk stars. We conclude that the reformation of a thin disk via gas accretion may play a significant role in setting the structure and kinematics of thick disks, and thus it is an important ingredient in models of thick-disk formation.

  2. Encounters with Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Heller, Clayton H.

    1992-12-01

    A numerical study of encounters between stars with circumstellar disks has bee completed. Cross sections and rates for disk tilt, disk disruption, and binary formation are estimated using a large data base of encounter simulations. The consequences of these results for star-forming regions and our solar system are discussed. A numerical code is developed which is capable of evolving a mixture of stars and gas in three dimensions. The algorithm is based on the method of smoothed-particle hydrodynamics combined with the heirarchical tree method of computing gravitational forces. The code is tested by simulating the collision between two sheets of gas and the radial pulsations of a polytropic gas sphere. A protostellar-disk model is developed based on simple assumptions. Test encounters are performed to determine the sensitivity of measured quantities on algorithm parameters, such as the gravitational tolerance and viscosity. It is shown that the solar system could have had an encounter shortly after its formation of sufficient strength to generate the observed obliquity yet retain enough mass and radial extent to form the planetary system. For the Orion B clusters as a whole, it is estimated that during a one-million-year period of time a few percent of the stars will experience an enoucnter that results in a disk tilt of 7 degrees or greater. For the central regions of NGC 2024 and the Trapezium cluster values of 24% and 39% are obtained, respectively. Encounters between equal-mass stars with periastra of 0.5, 1.0, 1.5, and 2.0 disk radii will retain on average about 15%, 40%, 55%, and 75% of the disk mass, respectively. For encounters that do not penetrate the disk a minimum of 15% of the mass is retained. Even in dense environments the characteristic lifetime of a disk due to disruptive encounters can be many millions of years. On average, an encounter that penetrates the disk will dissipate an amount of orbital energy equal to approximately 50% of the initial

  3. Laboratory Astrophysics White Paper

    NASA Technical Reports Server (NTRS)

    Brickhouse, Nancy; Federman, Steve; Kwong, Victor; Salama, Farid; Savin, Daniel; Stancil, Phillip; Weingartner, Joe; Ziurys, Lucy

    2006-01-01

    Laboratory astrophysics and complementary theoretical calculations are the foundations of astronomical and planetary research and will remain so for many generations to come. From the level of scientific conception to that of the scientific return, it is our understanding of the underlying processes that allows us to address fundamental questions regarding the origins and evolution of galaxies, stars, planetary systems, and life in the cosmos. In this regard, laboratory astrophysics is much like detector and instrument development at NASA and NSF; these efforts are necessary for the astronomical research being funded by the agencies. The NASA Laboratory Astrophysics Workshop met at the University of Nevada, Las Vegas (UNLV) from 14-16 February, 2006 to identify the current laboratory data needed to support existing and future NASA missions and programs in the Astrophysics Division of the Science Mission Directorate (SMD). Here we refer to both laboratory and theoretical work as laboratory astrophysics unless a distinction is necessary. The format for the Workshop involved invited talks by users of laboratory data, shorter contributed talks and poster presentations by both users and providers that highlighted exciting developments in laboratory astrophysics, and breakout sessions where users and providers discussed each others' needs and limitations. We also note that the members of the Scientific Organizing Committee are users as well as providers of laboratory data. As in previous workshops, the focus was on atomic, molecular, and solid state physics.

  4. A two-dimensional numerical model of gas mixing and deposition in a rotating disk CVD reactor

    SciTech Connect

    Winters, W.S.; Evans, G.H.; Greif, R.

    1996-04-01

    Gas phase transport with mixing and surface chemistry is studied in an axisymmetric, isothermal rotating disk chemical vapor deposition reactor. A simple one-step surface reaction is used to model deposition of gallium on the rotating surface. Partitioning of the inlet flow into separate gas streams of different species can lead to nonuniform deposition on the growth surface. The nonuniformity is caused by incomplete radial diffusion of gas species; depending on reactor temperature and pressure it can be worsened by large buoyant flow instabilities. The nonuniformity is relatively insensitive to the magnitude of the specified sticking coefficient.

  5. A Gas-poor Planetesimal Feeding Model for the Formation of Giant Planet Satellite Systems: Disk Size and Formation Timescale

    NASA Astrophysics Data System (ADS)

    Estrada, P. R.; Mosqueira, I.

    2003-05-01

    Mosqueira and Estrada (2003a) argue that following giant planet accretion a largely quiescent circumplanetary disk may form with most of the mass inside a radius located outside, but perhaps close to, the centrifugal radius rc = RH/48, where the specific angular momentum of the collapsing giant planet gaseous envelope achieves centrifugal balance, and extending as far as the irregular satellites at RH/5 due to the high specific angular momentum of parcels of gas accreted from distances several times RH during the final stages of planetary growth (Lubow et al. 1999). Provided that allowances are made for the capture of Triton from heliocentric orbit, this picture fits well with the primordial satellite systems of all four giant planets. Because strong gas turbulence would smooth out the gas surface density of the disk, this description can only apply if the turbulence subsides as planetary accretion ceases. Although the viability of a hydrodynamic shear instability in Keplerian disks that can sustain significant post-accretion turbulence and drive evolution of the gas disk is in serious doubt (see Mosqueira et al. this conference), the possibility has not yet been totally ruled out. This leads us to consider gas-poor scenarios that might produce a close-in regular satellite system. To this end, we re-examine the ideas of Safronov et al. (1986) to see whether a gas-free (or nearly gas-free) model can be made consistent with the extent of the regular satellites of the giant planets. In this model, planetesimals containing most of the mass of solids (Mizuno et al. 1978; Weidenschilling 1997) that are de-coupled from the gas and whose dynamics must be followed independently are collisionally captured and form a swarm of circumplanetary objects lasting for perhaps ˜ 106 years. While such a swarm might occupy a significant fraction of the Hill radius of the planet, the small net angular momentum of the swarm might lead to the formation of close-in prograde satellites as

  6. EMPIRE: A code for nuclear astrophysics

    NASA Astrophysics Data System (ADS)

    Palumbo, A.

    2016-01-01

    The nuclear reaction code EMPIRE is presented as a useful tool for nuclear astrophysics. EMPIRE combines a variety of the reaction models with a comprehensive library of input parameters providing a diversity of options for the user. With exclusion of the direct- semidirect capture all reaction mechanisms relevant to the nuclear astrophysics energy range of interest are implemented in the code. Comparison to experimental data show consistent agreement for all relevant channels.

  7. The Evolutionary State of Anemic Circumstellar Disks in IC 348: Transitions Disks, The Earliest Debris Disks, and Terrestrial Planet Formation

    NASA Astrophysics Data System (ADS)

    Currie, Thayne M.

    2008-05-01

    I investigate the evolution of 3 Myr-old MIPS-detected circumstellar disks in IC 348 that may be in an intermediate stage between primordial, optically-thick disks of gas/dust and debris disks characteristic of the final stages of planet formation. I demonstrate that these anemic disks are not a homogenous class of objects corresponding to a unique evolutionary state. Analysis of their mid-IR colors, accretion signatures (or lack thereof), and SED modeling suggest that such disks around early spectral type stars are most likely warm debris disks indicative of terrestrial planet formation: perhaps the youngest yet known. MIPS-detected anemic disks around later (M) stars are likely evolved primordial disks such as transition disks. Anemic disks surrounding G and K stars contain both populations. IC 348 also contains a small number of non-accreting sources with weak 24 micron emission characteristic of cold debris disks. The difference in evolutionary states between anemic disks surrounding early type vs. late-type stars is consistent with a mass-dependent evolution of circumstellar disks from the primordial disk phase through the debris disk phase similar to that found for 5 Myr-old Upper Scorpius.

  8. Astrophysical Applications of Fractional Calculus

    NASA Astrophysics Data System (ADS)

    Stanislavsky, Aleksander A.

    The paradigm of fractional calculus occupies an important place for the macroscopic description of subdiffusion. Its advance in theoretical astrophysics is expected to be very attractive too. In this report we discuss a recent development of the idea to some astrophysical problems. One of them is connected with a random migration of bright points associated with magnetic fields at the solar photosphere. The transport of the bright points has subdiffusive features that require the fractional generalization of the Leighton's model. Another problem is related to the angular distribution of radio beams, being propagated through a medium with random inhomogeneities. The peculiarity of this medium is that radio beams are trapped because of random wave localization. This idea can be useful for the diagnostics of interplanetary and interstellar turbulent media.

  9. Astrophysical processes on the Sun

    PubMed Central

    Parnell, Clare E.

    2012-01-01

    Over the past two decades, there have been a series of major solar space missions, namely Yohkoh, SOHO, TRACE, and in the past 5 years, STEREO, Hinode and SDO, studying various aspects of the Sun and providing images and spectroscopic data with amazing temporal, spatial and spectral resolution. Over the same period, the type and nature of numerical models in solar physics have been completely revolutionized as a result of widespread accessibility to parallel computers. These unprecedented advances on both observational and theoretical fronts have led to significant improvements in our understanding of many aspects of the Sun's behaviour and furthered our knowledge of plasma physics processes that govern solar and other astrophysical phenomena. In this Theme Issue, the current perspectives on the main astrophysical processes that shape our Sun are reviewed. In this Introduction, they are discussed briefly to help set the scene. PMID:22665891

  10. Timescales for planetary accretion and the structure of the protoplanetary disk

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.

    1987-01-01

    Models of planetary accretion which assume the mass of condensable matter in the protoplanetary disk was equal to that present in the planets today predict accretion timescales for the outer planets approximately or less than 10 to the 8th years. Such timescales are inconsistent with observations of star forming regions, which suggest that most of the gas in disks around one solar mass is removed in a few x 10 to the 6th years. A unified scenario was outlined for solar system formation consistent with astrophysical constraints. Jupiter's core could have grown by runaway accretion of planetesimals to a mass sufficient to initiate rapid accretion of gas in times of order of 500,000 to 5,000,000 years, provided the surface density of solids in its accretion zone was at least 5 to 10 times greater than that required by minimum mass models of the protoplanetary disk. The inner planets and the asteroids can be accounted for in this picture if the surface density of the solar nebula was relatively uniform out to Jupiter's orbit. The formation of such a protoplanetary disk requires significant transport of mass and angular momentum, and is consistent with viscous accretion disk models of the solar nebula.

  11. Gravitational Radiation of a Vibrating Physical String as a Model for the Gravitational Emission of an Astrophysical Plasma

    NASA Astrophysics Data System (ADS)

    Lewis, Ray A.; Modanese, Giovanni

    Vibrating media offer an important testing ground for reconciling conflicts between General Relativity, Quantum Mechanics and other branches of physics. For sources like a Weber bar, the standard covariant formalism for elastic bodies can be applied. The vibrating string, however, is a source of gravitational waves which requires novel computational techniques, based on the explicit construction of a conserved and renormalized energy-momentum tensor. Renormalization (in a classical sense) is necessary to take into account the effect of external constraints, which affect the emission considerably. Our computation also relaxes usual simplifying assumptions like far-field approximation, spherical or plane wave symmetry, TT gauge and absence of internal interference. In a further step towards unification, the method is then adapted to give the radiation field of a transversal Alfven wave in a rarefied astrophysical plasma, where the tension is produced by an external static magnetic field.

  12. Emission of gravitational waves by precession of slim accretion disks dynamically driven by the Bardeen-Petterson effect

    NASA Astrophysics Data System (ADS)

    Alfonso, W. D.; Sánchez, L. A.; Mosquera, H. J.

    2015-11-01

    The electromagnetic radiation emitted from some astrophysical objects such as active galactic nuclei (AGN), micro-quasars (M-QSRs), and central engines of gamma-ray burst (GRBs), seems to have a similar physical origin: a powerful jet of plasma ejected from a localized system, presumably composed of an accretion disk encircling a compact object. This radiation is generally beamed in the polar directions and in some cases, it appears to have a spiral-like structure that could be explained if the central system itself precesses. In this work, we use the slim disk accretion model, presented by Popham et al. (1999), to studying the gravitational waves (GWs) emitted by the precession of the accretion disk around a solar-mass Kerr black hole (KBH). For practical purposes, this model describes the central engine of a class of GRBs when some astrophysical constrains are fulfilled. The induced precession considered here is driven by the Bardeen-Petterson effect, which results from the combination of viscous effects in such disks and the relativistic frame-dragging effect. We evaluate the feasibility of direct detection of the GWs computed for such a model and show that the precession of this kind of systems could be detected by gravitational wave observatories like DECIGO, ultimate-DECIGO, and BBO, with higher probability if such a class of sources are placed at distances less than 1 Mpc.

  13. Radiative Transfer Models of Mid-Infrared H2O Lines in the Planet-Forming Region of Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Meijerink, R.; Pontoppidan, K. M.; Blake, G. A.; Poelman, D. R.; Dullemond, C. P.

    2009-10-01

    The study of warm molecular gas in the inner regions of protoplanetary disks is of key importance for the study of planet formation and especially for the transport of H2O and organic molecules to the surfaces of rocky planets/satellites. Recent Spitzer observations have shown that the mid-infrared spectra of protoplanetary disks are covered in emission lines due to water and other molecules. Here, we present a non-local thermodynamic equilibrium (LTE) two-dimensional radiative transfer model of water lines in the 10-36 μm range that can be used to constrain the abundance structure of water vapor, given an observed spectrum, and show that an assumption of LTE does not accurately estimate the physical conditions of the water vapor emission zones, including temperatures and abundance structures. By applying the model to published Spitzer spectra we find that: (1) most water lines are subthermally excited, (2) the gas-to-dust ratio must be as much as 1-2 orders of magnitude higher than the canonical interstellar medium ratio of 100-200, (3) the gas temperature must be significantly higher than the dust temperature, in agreement with detailed heating/cooling models, and (4) the water vapor abundance in the disk surface must be significantly truncated beyond ~1 AU. A low efficiency of water formation below T ~ 300 K may naturally result in a lower water abundance beyond a certain radius. However, we find that chemistry, although not necessarily ruled out, may not be sufficient to produce a sharp abundance drop of many orders of magnitude and speculate that the depletion may also be caused by vertical turbulent diffusion of water vapor from the superheated surface to regions below the snow line, where the water can freeze out and be transported to the midplane as part of the general dust settling. Such a vertical cold finger effect is likely to be efficient due to the lack of a replenishment mechanism of large, water-ice coated dust grains to the disk surface.

  14. Slotted-wall research with disk and parachute models in the DSMA low-speed wind tunnel

    SciTech Connect

    Van Every, D.; Harris, J.L. )

    1990-06-01

    A test program investigated the effects of wall open area ratio (OAR) and model axial position on the measured drag of disk and parachute models in a low-speed wind tunnel. The data and discussion presented in this report provide new insight into the nature of slotted-wall interference for bluff bodies in steady flow and give the first quantitative information on nonsteady wall interference and airflow response during the inflation of a parachute. The report concludes that a fixed OAR of between 5% and 15% should eliminate wall interference during inflation and greatly reduce steady-flow interference for geometric blockages up to 15%. Preliminary arguments suggest that an optimum OAR may be found that alleviates wall interference for large models at low speeds while providing for acceptable testing of smaller models in the transonic speed range. 10 refs., 36 figs., 14 tabs.

  15. Theoretical analysis of the astrophysical S-factor for the capture reaction α + d → {sup 6}Li + γ in the two-body model

    SciTech Connect

    Tursunov, E. M. Turakulov, S. A.; Descouvemont, P.

    2015-03-15

    Theoretical estimates for the astrophysical S-factor and the rate of the reaction d(α, γ){sup 6}Li were obtained on the basis of the two-body model involving an α−d potential that has a simple Gaussian form and which describes correctly S-, P-, and D-wave phase shifts, the binding energy, and the asymptotic normalization coefficient for the S-wave bound state. The wave functions for the bound and continuum channels were calculated with the aid of the highly precise Numerov algorithm. The results for the contributions of the E1 and E2 transition components reveal a good convergence as the upper limit in the effective integrals increases up to 40 fm. The results obtained for the astrophysical S-factor and the rate of the reaction d(α, γ){sup 6}Li in the temperature range of 10{sup 6}K ≤ T ≤ 10{sup 10} K agree well with the results of the calculations performed by A.M. Mukhamedzhanov and his coauthors [Phys. Rev. C 83, 055805 (2011)] by using the known asymptotic form of the wave function at low energies and a complicated two-body potential at higher energies.

  16. Astrophysical implications of periodicity

    NASA Technical Reports Server (NTRS)

    Muller, Richard A.

    1988-01-01

    Two remarkable discoveries of the last decade have profound implications for astrophysics and for geophysics. These are the discovery by Alvarez et al., that certain mass extinctions are caused by the impact on the earth of a large asteroid or comet, and the discovery by Raup and Sepkoski that such extinctions are periodic, with a cycle time of 26 to 30 million years. The validity of both of these discoveries is assumed and the implications are examined. Most of the phenomena described depend not on periodicity, but just on the weaker assumption that the impacts on the earth take place primarily in showers. Proposed explanations for the periodicity include galactic oscillations, the Planet X model, and the possibility of Nemesis, a solar companion star. These hypotheses are critically examined. Results of the search for the solar companion are reported. The Deccan flood basalts of India have been proposed as the impact site for the Cretaceous impact, but this hypotheisis is in contradiction with the conclusion of Courtillot et al., that the magma flow began during a period of normal magnetic field. A possible resolution of this contradiction is proposed.

  17. Numerical Relativity and Astrophysics

    NASA Astrophysics Data System (ADS)

    Lehner, Luis; Pretorius, Frans

    2014-08-01

    Throughout the Universe many powerful events are driven by strong gravitational effects that require general relativity to fully describe them. These include compact binary mergers, black hole accretion, and stellar collapse, where velocities can approach the speed of light and extreme gravitational fields (ΦNewt/c2≃1) mediate the interactions. Many of these processes trigger emission across a broad range of the electromagnetic spectrum. Compact binaries further source strong gravitational wave emission that could directly be detected in the near future. This feat will open up a gravitational wave window into our Universe and revolutionize our understanding of it. Describing these phenomena requires general relativity, and—where dynamical effects strongly modify gravitational fields—the full Einstein equations coupled to matter sources. Numerical relativity is a field within general relativity concerned with studying such scenarios that cannot be accurately modeled via perturbative or analytical calculations. In this review, we examine results obtained within this discipline, with a focus on its impact in astrophysics.

  18. Neutron reactions in astrophysics

    NASA Astrophysics Data System (ADS)

    Reifarth, R.; Lederer, C.; Käppeler, F.

    2014-05-01

    The quest for the origin of matter in the Universe had been the subject of philosophical and theological debates over the history of mankind, but quantitative answers could be found only by the scientific achievements of the last century. A first important step on this way was the development of spectral analysis by Kirchhoff and Bunsen in the middle of the 19th century, which provided first insight in the chemical composition of the sun and the stars. The energy source of the stars and the related processes of nucleosynthesis, however, could be revealed only with the discoveries of nuclear physics. A final break-through came eventually with the compilation of elemental and isotopic abundances in the solar system, which reflect the various nucleosynthetic processes in detail. This review focuses on the mass region above iron, where the formation of the elements is dominated by neutron capture, mainly in the slow (s) and rapid (r) processes. Following a brief historic account and a sketch of the relevant astrophysical models, emphasis is put on the nuclear physics input, where status and perspectives of experimental approaches are presented in some detail, complemented by the indispensable role of theory.

  19. Magneto-rotational instability in the protolunar disk

    NASA Astrophysics Data System (ADS)

    Carballido, Augusto; Desch, Steven J.; Taylor, G. Jeffrey

    2016-04-01

    We perform the first study of magnetohydrodynamic processes in the protolunar disk (PLD). With the use of published data on the chemical composition of the PLD, along with existing analytical models of the disk structure, we show that the high temperatures that were prevalent in the disk would have led to ionization of Na, K, SiO, Zn and, to a lesser extent, O2. For simplicity, we assume that the disk has a vapor structure. The resulting ionization fractions, together with a relatively weak magnetic field, possibly of planetary origin, would have been sufficient to trigger the magneto-rotational instability, or MRI, as demonstrated by the fact that the Elsasser criterion was met in the PLD: a magnetic field embedded in the flow would have diffused more slowly than the growth rate of the linear perturbations. We calculate the intensity of the resulting magnetohydrodynamic turbulence, as parameterized by the dimensionless ratio α of turbulent stresses to gas pressure, and obtain maximum values α ∼10-2 along most of the vertical extent of the disk, and at different orbital radii. This indicates that, under these conditions, turbulent mixing within the PLD due to the MRI was likely capable of transporting isotopic and chemical species efficiently. To test these results in a conservative manner, we carry out a numerical magnetohydrodynamic simulation of a small, rectangular patch of the PLD, located at 4 Earth radii (rE) from the center of the Earth, and assuming once again that the disk is completely gaseous. We use a polytrope-like equation of state. The rectangular patch is threaded initially by a vertical magnetic field with zero net magnetic flux. This field configuration is known to produce relatively weak MRI turbulence in studies of astrophysical accretion disks. We accordingly obtain turbulence with an average intensity α ∼ 7 ×10-6 over the course of 280 orbital periods (133 days at 4rE). Despite this relatively low value of α , the effective turbulent

  20. Velocity shear induced phenomena in solar and astrophysical flows

    NASA Astrophysics Data System (ADS)

    Tevzadze, A. G.

    2006-04-01

    with weak or moderate magnetic fields. The magneto-mechanical mode may generate more waves in strongly magnetized plasma for stronger velocity shear. In Chapter 5 we have studied compressible convection in shear flows. In particular we have focused on linear small-scale perturbations in unstably stratified flows with constant shear of velocity. We have found that the mode conversion originates from the velocity shear of the flow. Exponentially growing perturbations of convection are able to excite acoustic waves. At particular wave-numbers g-mode perturbations (perturbations of buoyancy) feed the acoustic radiation of the turbulent convection. The generated oscillations are spatially correlated with the source flow. This process may be important for convection in astrophysical objects. We discussed the solar convective envelope as an example. Generating waves in high shear regions of a stratified turbulent flow, this non-resonant phenomenon can contribute to the production of sound in the solar convection zone. In Chapter 6 we have investigated non-axisymmetric perturbations in differentially rotating hydrodynamic flows in a gravitational field. The aim here was twofold: Firstly, shear flows commonly occur in many astrophysical situations and they are thought to be the key to the explanation of accretion disk phenomena. Secondly, it gives us an opportunity to study vortex-wave mode conversion in a medium, where two intrinsically different wave modes are present: sound waves as well as internal gravity-spiral waves. We found that vortices are able to generate gravity-spiral waves in flows with Keplerian shear. Higher shear rates are necessary to trigger the double excitation of density spiral and acoustic waves. We have analyzed the dynamics of accretion disks and based on our results promote the hydrodynamic model of the turbulence. Firstly, we describe the general balances in the rotating disk flows in 2D and show that the stabilizing effect of the Coriolis force can

  1. PLANETESIMAL DISK MICROLENSING

    SciTech Connect

    Heng, Kevin; Keeton, Charles R. E-mail: keeton@physics.rutgers.ed

    2009-12-10

    Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

  2. Generalized Wind Turbine Actuator Disk Parameterization in the Weather Research and Forecasting (WRF) Model for Real-World Simulations

    NASA Astrophysics Data System (ADS)

    Marjanovic, N.; Mirocha, J. D.; Chow, F. K.

    2013-12-01

    In this work, we examine the performance of a generalized actuator disk (GAD) model embedded within the Weather Research and Forecasting (WRF) atmospheric model to study wake effects on successive rows of turbines at a North American wind farm. These wake effects are of interest as they can drastically reduce down-wind energy extraction and increase turbulence intensity. The GAD, which is designed for turbulence-resolving simulations, is used within downscaled large-eddy simulations (LES) forced with mesoscale simulations and WRF's grid nesting capability. The GAD represents the effects of thrust and torque created by a wind turbine on the atmosphere within a disk representing the rotor swept area. The lift and drag forces acting on the turbine blades are parameterized using blade-element theory and the aerodynamic properties of the blades. Our implementation permits simulation of turbine wake effects and turbine/airflow interactions within a realistic atmospheric boundary layer flow field, including resolved turbulence, time-evolving mesoscale forcing, and real topography. The GAD includes real-time yaw and pitch control to respond realistically to changing flow conditions. Simulation results are compared to SODAR data from operating wind turbines and an already existing WRF mesoscale turbine drag parameterization to validate the GAD parameterization.

  3. Modelling the Accretion History of the Galactic Disk (and the Gravitational Lensing of a High-z Galaxy)

    NASA Astrophysics Data System (ADS)

    Meyers, Adrian

    2015-01-01

    Over its long history, the Milky Way is expected to have accreted many dwarf galaxies. The debris from the destruction of most of these dwarf galaxies will by now be fully phase-mixed throughout the Galaxy and hence undetectable as local over-densities in position-space. However, the debris from these systems could have distinct kinematic signatures that may help distinguish these stars from, for example, the Galactic disk. We aim to construct a reliable method of determining the contributions to the Milky Way disk from accreted structures that could be applied to current kinematic data sets, such as SDSS's APOGEE survey. In an effort to mimic the kinematic traits of an accreted satellite, we construct single-orbit models to compare to a cosmologically motivated simulation of satellite accretion. We find that these orbit models adhere to the kinematic signatures of certain types of accreted galaxies better than others, giving us insight on which parameters to trust when searching for accreted populations. As a bonus, we describe a separate project in which we attempt to deduce the intrinsic properties of the 8 o'clock arc, a gravitationally lensed Lyman break galaxy at redshift 2.73. Using the lensmodel code and its pixel-based source reconstruction extension pixsrc, we derive a de-lensed image of the galaxy in the source plane.

  4. Computational Astrophysics reaches its Third Age: From Star Formation to the Death of the Sun.

    NASA Astrophysics Data System (ADS)

    Frank, Adam

    2006-12-01

    The use of simulations in astrophysics has progressed to the point where computational datasets can be as rich as those obtained from observations. In this sense the field has reached maturity or its “third age”. In this talk I will review progress in the use of simulations as a tool for astronomical research. The talk will include the basic elements of numerical simulations as well as advances in algorithms which have led to recent dramatic progress. The scientific focus will be hydrodynamic and magneto-hydrodynamic simulations of star formation and the death of solar-type stars. We will explore the most recent models of collimated outflows (jets) from young stars and their interaction with natal environments. The source of these outflows are magnetized disks surrounding the stars. Models of this process have also reached new levels of realism. At the other end of a star’s lifetime we also find outflows to be ubiquitous phenomena. Here magnetic fields are again a principle actor creating collimated jets though in this case binary companions may be critical. In all cases the physics involved is too non-linear to investigate solely with analytic methods. Direct simulation must be used to fill out the story. Finally we introduce the field of High Energy Density Laboratory Astrophysics where fusion devices are used to create astrophysically relevant laboratory experiments. Simulations play a key role in the design and analysis of these studies as well.

  5. On circumstellar disks: Spitzer identifies two possible evolutionary paths

    NASA Astrophysics Data System (ADS)

    Teixeira, Paula S.; Lada, Charles J.; Marengo, Massimo; Lada, Elizabeth

    Multi-wavelength surveys have vastly improved our understanding of many astrophysical objects, in particular, circumstellar disks. We present our results for the disk population of the young cluster NGC 2264. Our study was based on data obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer on board the Spitzer Space Telescope combined with previously published optical data. We divide the disk population into 3 classes based on their spectral energy distribution shapes: optically thick disks, homologously depleted anemic disks, and radially depleted transition disks. We find that there are two distinct evolutionary paths for disks: a homologous one, where the disk emission decreases uniformly in NIR and mid-infrared wavelengths (anemic disks) and throughout which most sources pass, and a radially differential one where the emission from the inner region of the disk decreases more rapidly than from the outer region (transition disks). Whether a disk evolves in a homologously or radially depleted fashion is still unknown and may depend on the nature of planet formation in the disk.

  6. Musculoskeletal Modeling of the Lumbar Spine to Explore Functional Interactions between Back Muscle Loads and Intervertebral Disk Multiphysics

    PubMed Central

    Toumanidou, Themis; Noailly, Jérôme

    2015-01-01

    During daily activities, complex biomechanical interactions influence the biophysical regulation of intervertebral disks (IVDs), and transfers of mechanical loads are largely controlled by the stabilizing action of spine muscles. Muscle and other internal forces cannot be easily measured directly in the lumbar spine. Hence, biomechanical models are important tools for the evaluation of the loads in those tissues involved in low-back disorders. Muscle force estimations in most musculoskeletal models mainly rely, however, on inverse calculations and static optimizations that limit the predictive power of the numerical calculations. In order to contribute to the development of predictive systems, we coupled a predictive muscle model with the passive resistance of the spine tissues, in a L3–S1 musculoskeletal finite element model with osmo-poromechanical IVD descriptions. The model included 46 fascicles of the major back muscles that act on the lower spine. The muscle model interacted with activity-related loads imposed to the osteoligamentous structure, as standing position and night rest were simulated through distributed upper body mass and free IVD swelling, respectively. Calculations led to intradiscal pressure values within ranges of values measured in vivo. Disk swelling led to muscle activation and muscle force distributions that seemed particularly appropriate to counterbalance the anterior body mass effect in standing. Our simulations pointed out a likely existence of a functional balance between stretch-induced muscle activation and IVD multiphysics toward improved mechanical stability of the lumbar spine understanding. This balance suggests that proper night rest contributes to mechanically strengthen the spine during day activity. PMID:26301218

  7. Role of the UV external radiation field on the presence of astrophysical ices in protostellars environments

    NASA Astrophysics Data System (ADS)

    Robson Monteiro Rocha, Will; Pilling, Sergio

    2016-07-01

    The astrophysical ices survival is directly related with the temperature and ionizing radiation field in protostellars environments such as disks and envelopes. Computational models has shown that pure volatile molecules like CO and CH _{4} should survive only inside densest regions of molecular clouds or protoplanetary disks On the other hand, solid molecules such as H _{2}O and CH _{3}OH can be placed around 5 - 10 AU from the central protostar. Unlike of the previous models, we investigate the role of the UV external radiation field on the presence of ices in disks and envelopes. Once that a star-forming region is composed by the formation of many protostars, the external radiation field should be an important component to understand the real localization of the ices along the sight line. To address this topic it was employed the radiative transfer code RADMC-3D based on the Monte Carlo method. The code was used to model the spectrum and the near-infrared image of Elias 29. The initial parameters of the disk and envelope was taken from our previous paper (Rocha & Pilling (2015), ApJ 803:18). The opacities of the ices were calculated from the complex refractive index obtained at laboratory experiments perfomed at Grand Accélerateur National d'Íons Lourds (GANIL), by using the NKABS code from Rocha & Pilling (2014), SAA 123:436. The partial conclusions that we have obtained shows that pure CO volatile molecule cannot be placed at disk or envelope of Elias 29, unlike shown in our paper about Elias 29. Once it was observed in Elias 29 spectrum obtained with Infrared Space Observatory (ISO) between 2.5 - 190 μm, this molecule should be placed in foreground molecular clouds or trapped in the water ice matrix. The next calculations will be able to show where are placed the ices such as CH _{3}OH and CH _{3}CHO observed in Elias 29 spectrum.

  8. NASA Announces 2009 Astronomy and Astrophysics Fellows

    NASA Astrophysics Data System (ADS)

    2009-02-01

    searching for transits among hot Neptunes and super-Earths, microlensing planets through modeling algorithms, conducting high-contrast imaging surveys to detect planetary-mass companions, interferometrically imaging of the inner regions of protoplanetary disks, and modeling of super-Earth planetary atmospheres. The 10 fellows in the Einstein program conduct research broadly related to the mission of NASA's Physics of the Cosmos Program. Its science goals include understanding the origin and destiny of the universe, the nature of gravity, phenomena near black holes, and extreme states of matter. The Chandra X-ray Center in Cambridge, Mass., administers the Einstein Fellowships for NASA. The 17 awardees of the Hubble Fellowship pursue research associated with NASA's Cosmic Origins Program. The missions in this program examine the origins of galaxies, stars, and planetary systems, and the evolution of these structures with cosmic time. The Space Telescope Science Institute in Baltimore, Md., administers the Hubble Fellowships for NASA. The Sagan Fellowship, created in September 2008, supports five scientists whose research is aligned with NASA's Exoplanet Exploration Program. The primary goal of this program is to discover and characterize planetary systems and Earth-like planets around other stars. The NASA Exoplanet Science Institute, which is operated at the California Institute of Technology in coordination with NASA's Jet Propulsion Laboratory in Pasadena, Calif., administers the Sagan Fellowship Program

  9. Astrophysics Source Code Library

    NASA Astrophysics Data System (ADS)

    Allen, A.; DuPrie, K.; Berriman, B.; Hanisch, R. J.; Mink, J.; Teuben, P. J.

    2013-10-01

    The Astrophysics Source Code Library (ASCL), founded in 1999, is a free on-line registry for source codes of interest to astronomers and astrophysicists. The library is housed on the discussion forum for Astronomy Picture of the Day (APOD) and can be accessed at http://ascl.net. The ASCL has a comprehensive listing that covers a significant number of the astrophysics source codes used to generate results published in or submitted to refereed journals and continues to grow. The ASCL currently has entries for over 500 codes; its records are citable and are indexed by ADS. The editors of the ASCL and members of its Advisory Committee were on hand at a demonstration table in the ADASS poster room to present the ASCL, accept code submissions, show how the ASCL is starting to be used by the astrophysics community, and take questions on and suggestions for improving the resource.

  10. New Scattered Disk Object and Centaur Colors

    NASA Astrophysics Data System (ADS)

    Brucker, Melissa; Wilcox, P.; Stansberry, J.

    2013-10-01

    We report B, V, and R magnitudes for scattered disk objects and centaurs from observations taken in December 2011 and August 2013 using the Lowell Observatory Perkins Telescope with PRISM and observations taken in March 2012 at the Vatican Advanced Technology Telescope (VATT) on Mt. Graham, Arizona. Targeted scattered disk objects include 2002 CY224, 2003 UY117, 2006 QJ181, 2008 CT190, 2009 YG19, 2010 FD49, 2010 VZ98. Targeted centaurs include 2002 QX47, 2005 UJ438, 2006 UX184, and 2007 RH283. We will determine if the resultant centaur colors follow the bimodal distribution (B-R either red or gray) previously detected. We will also compare the resultant scattered disk object colors to those published for other scattered disk objects. This work is based on observations with the Perkins Telescope at Lowell Observatory, and with the VATT: The Alice P. Lennon Telescope and the Thomas J. Bannan Astrophysics Facility.

  11. Astrophysical Boundary Layers: A New Picture

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail; Rafikov, Roman R.; Mclellan Stone, James

    2016-04-01

    Accretion is a ubiquitous process in astrophysics. In cases when the magnetic field is not too strong and a disk is formed, accretion can proceed through the mid plane all the way to the surface of the central compact object. Unless that compact object is a black hole, a boundary layer will be formed where the accretion disk touches its surfaces. The boundary layer is both dynamically and observationally significant as up to half of the accretion energy is dissipated there.Using a combination of analytical theory and computer simulations we show that angular momentum transport and accretion in the boundary layer is mediated by waves. This breaks with the standard astrophysical paradigm of an anomalous turbulent viscosity that drives accretion. However, wave-mediated angular momentum transport is a natural consequence of "sonic instability." The sonic instability, which we describe analytically and observe in our simulations, is a close cousin of the Papaloizou-Pringle instability. However, it is very vigorous in the boundary layer due to the immense radial velocity shear present at the equator.Our results are applicable to accreting neutron stars, white dwarfs, protostars, and protoplanets.

  12. Comparison of Multi Disk Exponential Gas Distribution vs. Single Disk

    NASA Astrophysics Data System (ADS)

    Rao, Erica; O'Brien, James

    2013-04-01

    In fitting galactic rotation curves to data, most standard theories make use of a single exponential disk approximation of the gas distribution to account for the HI synthesis data observed at various radio telescope facilities. We take a sample of surface brightness profiles from The HI Nearby Galaxy Survey (THINGS), and apply both single disk exponentials and Multi-Disk exponentials, and use these various models to see how the modelling procedure changes the Newtonian prediction of the mass of the galaxy. Since the missing mass problem has not been fully explained in large spiral galaxies, different modelling procedures could account for some of the missing matter.

  13. Packings of soft disks

    NASA Astrophysics Data System (ADS)

    Ziherl, Primoz; Vidmar, Marija

    2011-03-01

    We explore the stability of 2D ordered structures formed by soft disks treated as isotropic solid bodies. Using a variational model, we compute the equilibrium shapes and the elastic energy of disks in regular columnar, honeycomb, square, and hexagonal lattice. The results reproduce the Hertzian interaction in the regime of small deformations. The phase diagram of elastic disks is characterized by broad regions of phase coexistence; its main feature is that the coordination number of the stable phases decreases with density. These results may provide an insight into structure of the non-close-packed lattices observed in certain nanocolloidal systems. This work was supported by Slovenian Research Agency (grant No. P1-0055) and by EU through ITN COMPLOIDS (grant FP7-People-ITN-2008 No. 234810).

  14. Disk filter

    DOEpatents

    Bergman, Werner

    1986-01-01

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  15. Disk filter

    DOEpatents

    Bergman, W.

    1985-01-09

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  16. Addressing Thermal Model Run Time Concerns of the Wide Field Infrared Survey Telescope using Astrophysics Focused Telescope Assets (WFIRST-AFTA)

    NASA Technical Reports Server (NTRS)

    Peabody, Hume; Guerrero, Sergio; Hawk, John; Rodriguez, Juan; McDonald, Carson; Jackson, Cliff

    2016-01-01

    The Wide Field Infrared Survey Telescope using Astrophysics Focused Telescope Assets (WFIRST-AFTA) utilizes an existing 2.4 m diameter Hubble sized telescope donated from elsewhere in the federal government for near-infrared sky surveys and Exoplanet searches to answer crucial questions about the universe and dark energy. The WFIRST design continues to increase in maturity, detail, and complexity with each design cycle leading to a Mission Concept Review and entrance to the Mission Formulation Phase. Each cycle has required a Structural-Thermal-Optical-Performance (STOP) analysis to ensure the design can meet the stringent pointing and stability requirements. As such, the models have also grown in size and complexity leading to increased model run time. This paper addresses efforts to reduce the run time while still maintaining sufficient accuracy for STOP analyses. A technique was developed to identify slews between observing orientations that were sufficiently different to warrant recalculation of the environmental fluxes to reduce the total number of radiation calculation points. The inclusion of a cryocooler fluid loop in the model also forced smaller time-steps than desired, which greatly increases the overall run time. The analysis of this fluid model required mitigation to drive the run time down by solving portions of the model at different time scales. Lastly, investigations were made into the impact of the removal of small radiation couplings on run time and accuracy. Use of these techniques allowed the models to produce meaningful results within reasonable run times to meet project schedule deadlines.

  17. A Spitzer Survey of Mid-infrared Molecular Emission from Protoplanetary Disks. II. Correlations and Local Thermal Equilibrium Models

    NASA Astrophysics Data System (ADS)

    Salyk, C.; Pontoppidan, K. M.; Blake, G. A.; Najita, J. R.; Carr, J. S.

    2011-04-01

    We present an analysis of Spitzer Infrared Spectrograph observations of H2O, OH, HCN, C2H2, and CO2 emission, and Keck-NIRSPEC observations of CO emission, from a diverse sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections and strengths of most mid-IR molecular emission features are correlated with each other, suggesting a common origin and similar excitation conditions for this mid-infrared line forest. Aside from the remarkable differences in molecular line strengths between T Tauri, Herbig Ae/Be, and transitional disks discussed in Pontoppidan et al., we note that the line detection efficiency is anti-correlated with the 13/30 μm spectral slope, which is a measure of the degree of grain settling in the disk atmosphere. We also note a correlation between detection efficiency and Hα equivalent width, and tentatively with accretion rate, suggesting that accretional heating contributes to line excitation. If detected, H2O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L sstarf. However, significant sample variation, especially in molecular line ratios, remains, and its origin has yet to be explained. Local thermal equilibrium (LTE) models of the H2O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H2O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near ~1018 cm-2 and 450 K for all sources, suggesting a high abundance of H2O in many planet-forming regions. Other molecules have a range of excitation temperatures from ~500to1500 K, also consistent with an origin in planet-forming regions. We find molecular ratios relative to water of ~10-3 for all molecules, with the exception of CO, for which n(CO)/n(H2O) ~ 1. However, LTE fitting caveats and differences in the way thermo-chemical modeling results are reported make comparisons with

  18. A SPITZER SURVEY OF MID-INFRARED MOLECULAR EMISSION FROM PROTOPLANETARY DISKS. II. CORRELATIONS AND LOCAL THERMAL EQUILIBRIUM MODELS

    SciTech Connect

    Salyk, C.; Pontoppidan, K. M.; Blake, G. A.; Najita, J. R.; Carr, J. S.

    2011-04-20

    We present an analysis of Spitzer Infrared Spectrograph observations of H{sub 2}O, OH, HCN, C{sub 2}H{sub 2}, and CO{sub 2} emission, and Keck-NIRSPEC observations of CO emission, from a diverse sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections and strengths of most mid-IR molecular emission features are correlated with each other, suggesting a common origin and similar excitation conditions for this mid-infrared line forest. Aside from the remarkable differences in molecular line strengths between T Tauri, Herbig Ae/Be, and transitional disks discussed in Pontoppidan et al., we note that the line detection efficiency is anti-correlated with the 13/30 {mu}m spectral slope, which is a measure of the degree of grain settling in the disk atmosphere. We also note a correlation between detection efficiency and H{alpha} equivalent width, and tentatively with accretion rate, suggesting that accretional heating contributes to line excitation. If detected, H{sub 2}O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L{sub *}. However, significant sample variation, especially in molecular line ratios, remains, and its origin has yet to be explained. Local thermal equilibrium (LTE) models of the H{sub 2}O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H{sub 2}O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near {approx}10{sup 18} cm{sup -2} and 450 K for all sources, suggesting a high abundance of H{sub 2}O in many planet-forming regions. Other molecules have a range of excitation temperatures from {approx}500to1500 K, also consistent with an origin in planet-forming regions. We find molecular ratios relative to water of {approx}10{sup -3} for all molecules, with the exception of CO, for which n(CO)/n(H{sub 2}O) {approx} 1. However, LTE

  19. Super-spinning compact objects generated by thick accretion disks

    SciTech Connect

    Li, Zilong; Bambi, Cosimo E-mail: bambi@fudan.edu.cn

    2013-03-01

    If astrophysical black hole candidates are the Kerr black holes predicted by General Relativity, the value of their spin parameter must be subject to the theoretical bound |a{sub *}| ≤ 1. In this work, we consider the possibility that these objects are either non-Kerr black holes in an alternative theory of gravity or exotic compact objects in General Relativity. We study the accretion process when their accretion disk is geometrically thick with a simple version of the Polish doughnut model. The picture of the accretion process may be qualitatively different from the one around a Kerr black hole. The inner edge of the disk may not have the typical cusp on the equatorial plane any more, but there may be two cusps, respectively above and below the equatorial plane. We extend previous work on the evolution of the spin parameter and we estimate the maximum value of a{sub *} for the super-massive black hole candidates in galactic nuclei. Since measurements of the mean radiative efficiency of AGNs require η > 0.15, we infer the ''observational'' bound |a{sub *}|∼<1.3, which seems to be quite independent of the exact nature of these objects. Such a bound is only slightly weaker than |a{sub *}|∼<1.2 found in previous work for thin disks.

  20. Augmented Reality in astrophysics

    NASA Astrophysics Data System (ADS)

    Vogt, Frédéric P. A.; Shingles, Luke J.

    2013-09-01

    Augmented Reality consists of merging live images with virtual layers of information. The rapid growth in the popularity of smartphones and tablets over recent years has provided a large base of potential users of Augmented Reality technology, and virtual layers of information can now be attached to a wide variety of physical objects. In this article, we explore the potential of Augmented Reality for astrophysical research with two distinct experiments: (1) Augmented Posters and (2) Augmented Articles. We demonstrate that the emerging technology of Augmented Reality can already be used and implemented without expert knowledge using currently available apps. Our experiments highlight the potential of Augmented Reality to improve the communication of scientific results in the field of astrophysics. We also present feedback gathered from the Australian astrophysics community that reveals evidence of some interest in this technology by astronomers who experimented with Augmented Posters. In addition, we discuss possible future trends for Augmented Reality applications in astrophysics, and explore the current limitations associated with the technology. This Augmented Article, the first of its kind, is designed to allow the reader to directly experiment with this technology.

  1. Astrophysics: An Integrative Course

    ERIC Educational Resources Information Center

    Gutsche, Graham D.

    1975-01-01

    Describes a one semester course in introductory stellar astrophysics at the advanced undergraduate level. The course aims to integrate all previously learned physics by applying it to the study of stars. After a brief introductory section on basic astronomical measurements, the main topics covered are stellar atmospheres, stellar structure, and…

  2. The NASA Astrophysics Program

    NASA Technical Reports Server (NTRS)

    Zebulum, Ricardo S.

    2011-01-01

    NASA's scientists are enjoying unprecedented access to astronomy data from space, both from missions launched and operated only by NASA, as well as missions led by other space agencies to which NASA contributed instruments or technology. This paper describes the NASA astrophysics program for the next decade, including NASA's response to the ASTRO2010 Decadal Survey.

  3. Surprises in astrophysical gasdynamics.

    PubMed

    Balbus, Steven A; Potter, William J

    2016-06-01

    Much of astrophysics consists of the study of ionized gas under the influence of gravitational and magnetic fields. Thus, it is not possible to understand the astrophysical universe without a detailed knowledge of the dynamics of magnetized fluids. Fluid dynamics is, however, a notoriously tricky subject, in which it is all too easy for one's a priori intuition to go astray. In this review, we seek to guide the reader through a series of illuminating yet deceptive problems, all with an enlightening twist. We cover a broad range of topics including the instabilities acting in accretion discs, the hydrodynamics governing the convective zone of the Sun, the magnetic shielding of a cooling galaxy cluster, and the behaviour of thermal instabilities and evaporating clouds. The aim of this review is to surprise and intrigue even veteran astrophysical theorists with an idiosyncratic choice of problems and counterintuitive results. At the same time, we endeavour to bring forth the fundamental ideas, to set out important assumptions, and to describe carefully whatever novel techniques may be appropriate to the problem at hand. By beginning at the beginning, and analysing a wide variety of astrophysical settings, we seek not only to make this review suitable for fluid dynamic veterans, but to engage novice recruits as well with what we hope will be an unusual and instructive introduction to the subject. PMID:27116247

  4. Surprises in astrophysical gasdynamics

    NASA Astrophysics Data System (ADS)

    Balbus, Steven A.; Potter, William J.

    2016-06-01

    Much of astrophysics consists of the study of ionized gas under the influence of gravitational and magnetic fields. Thus, it is not possible to understand the astrophysical universe without a detailed knowledge of the dynamics of magnetized fluids. Fluid dynamics is, however, a notoriously tricky subject, in which it is all too easy for one’s a priori intuition to go astray. In this review, we seek to guide the reader through a series of illuminating yet deceptive problems, all with an enlightening twist. We cover a broad range of topics including the instabilities acting in accretion discs, the hydrodynamics governing the convective zone of the Sun, the magnetic shielding of a cooling galaxy cluster, and the behaviour of thermal instabilities and evaporating clouds. The aim of this review is to surprise and intrigue even veteran astrophysical theorists with an idiosyncratic choice of problems and counterintuitive results. At the same time, we endeavour to bring forth the fundamental ideas, to set out important assumptions, and to describe carefully whatever novel techniques may be appropriate to the problem at hand. By beginning at the beginning, and analysing a wide variety of astrophysical settings, we seek not only to make this review suitable for fluid dynamic veterans, but to engage novice recruits as well with what we hope will be an unusual and instructive introduction to the subject.

  5. Disk Dispersal Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2004-01-01

    We first review the evidence pertaining to the lifetimes of planet-forming disks of gas and dust around young stars and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) photoevaporation caused by the heating of the disk surface by ultraviolet radiation. Photoevaporation is likely the most important dispersal mechanism for the outer regions of disks, and this talk focuses on the evaporation caused by the presence of a nearby, luminous star rather than the central star itself. We also focus on disks around low-mass stars like the Sun rather than high-mass stars, which we have treated previously. Stars often form in clusters and the ultraviolet flux from the most luminous star in the cluster can have a dramatic effect on the disk orbiting a nearby low-mass star. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We find a possible explanation for the differences between Neptune and Jupiter, and make a prediction concerning recent searches for giant planets in large clusters. We discuss recent models of the infrared spectra from gaseous disks around young stars.

  6. Ringed Accretion Disks: Equilibrium Configurations

    NASA Astrophysics Data System (ADS)

    Pugliese, D.; Stuchlík, Z.

    2015-12-01

    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  7. Analytical model of optical path difference in an end-pumped Yb:YAG thin-disk laser with nonuniform pumping light.

    PubMed

    Zhu, Guangzhi; Zhu, Xiao; Dai, Zhongxiong; Wang, Zexiong; Zhu, Changhong

    2015-04-01

    An analytical model of the thermal effect and optical path difference (OPD) of a thin-disk laser is developed by an arbitrary form pumping spot. Based on the analytical model, the distribution of temperature, stress, and strain can be derived using a super-Gaussian form pumping spot. The total OPD caused by temperature gradient, axial thermal strain, thermal strain-induced birefringence, and deformation of the thin-disk crystal is discussed for different super-Gaussian factors and is separated into spherical and aspherical parts. The analytical results show that the aspherical part of the OPD is the main reason leading to the decrease of the laser beam quality and it is closely related to super-Gaussian factors, which are very useful for thin-disk laser design and evaluation. PMID:25967218

  8. Supersized Disk (Artist's Concept)

    NASA Technical Reports Server (NTRS)

    2006-01-01

    called R 66. The disk contains complex organic molecules called polycyclic aromatic hydrocarbons as well as silicate dust grains. Polycyclic aromatic hydrocarbons can be found on Earth, in dirty barbeques and automobile exhaust pipes, among other places. They are thought to be necessary for primitive life to evolve. Silicates are essentially sand, and, in this case, were found in both their crystalline and non-crystalline, or amorphous, forms.

    The data were taken by Spitzer's infrared spectrometer, an instrument that spreads light apart into its basic parts like a prism turning sunlight into a rainbow. In this graph, or spectrum, light from the dust surrounding hypergiant R 66 is plotted according to its component wavelengths (white line). Astronomers determined the contents of this dust by creating a model (gray line) that best fits the observations. The model is the sum total of contributions from various types of dust grains (colored lines).

    In addition to R 66, Spitzer made similar observations of a huge disk around the hypergiant star R 126, only this star's disk did not possess crystalline silicate grains. Both disks might represent either an early or late evolutionary phase of the planet-building process. In either scenario, the possible solar systems would be supersized, with host stars that are 30 and 70 times the mass of our sun, respectively.

  9. Review of Astrophysics Experiments on Intense Lasers

    SciTech Connect

    Remington, B A; Drake, R P; Takabe, H; Arnett, D

    2000-01-19

    Astrophysics has traditionally been pursued at astronomical observatories and on theorists' computers. Observations record images from space, and theoretical models are developed to explain the observations. A component often missing has been the ability to test theories and models in an experimental setting where the initial and final states are well characterized. Intense lasers are now being used to recreate aspects of astrophysical phenomena in the laboratory, allowing the creation of experimental testbeds where theory and modeling can be quantitatively tested against data. We describe here several areas of astrophysics--supernovae, supernova remnants, gamma-ray bursts, and giant planets--where laser experiments are under development to test our understanding of these phenomena.

  10. Einstein Toolkit for Relativistic Astrophysics

    NASA Astrophysics Data System (ADS)

    Collaborative Effort

    2011-02-01

    The Einstein Toolkit is a collection of software components and tools for simulating and analyzing general relativistic astrophysical systems. Such systems include gravitational wave space-times, collisions of compact objects such as black holes or neutron stars, accretion onto compact objects, core collapse supernovae and Gamma-Ray Bursts. The Einstein Toolkit builds on numerous software efforts in the numerical relativity community including CactusEinstein, Whisky, and Carpet. The Einstein Toolkit currently uses the Cactus Framework as the underlying computational infrastructure that provides large-scale parallelization, general computational components, and a model for collaborative, portable code development.

  11. Constraining the structure of the transition disk HD 135344B (SAO 206462) by simultaneous modeling of multiwavelength gas and dust observations

    NASA Astrophysics Data System (ADS)

    Carmona, A.; Pinte, C.; Thi, W. F.; Benisty, M.; Ménard, F.; Grady, C.; Kamp, I.; Woitke, P.; Olofsson, J.; Roberge, A.; Brittain, S.; Duchêne, G.; Meeus, G.; Martin-Zaïdi, C.; Dent, B.; Le Bouquin, J. B.; Berger, J. P.

    2014-07-01

    Context. Constraining the gas and dust disk structure of transition disks, particularly in the inner dust cavity, is a crucial step toward understanding the link between them and planet formation. HD 135344B is an accreting (pre-)transition disk that displays the CO 4.7 μm emission extending tens of AU inside its 30 AU dust cavity. Aims: We constrain HD 135344B's disk structure from multi-instrument gas and dust observations. Methods: We used the dust radiative transfer code MCFOST and the thermochemical code ProDiMo to derive the disk structure from the simultaneous modeling of the spectral energy distribution (SED), VLT/CRIRES CO P(10) 4.75 μm, Herschel/PACS [O i] 63 μm, Spitzer/IRS, and JCMT 12CO J = 3-2 spectra, VLTI/PIONIER H-band visibilities, and constraints from (sub-)mm continuum interferometry and near-IR imaging. Results: We found a disk model able to describe the current gas and dust observations simultaneously. This disk has the following structure. (1) To simultaneously reproduce the SED, the near-IR interferometry data, and the CO ro-vibrational emission, refractory grains (we suggest carbon) are present inside the silicate sublimation radius (0.08 100 to account for the 870 μm continuum upper limit and the CO P(10) line flux. (5) The gas-to-dust ratio in the outer disk (30 disk, most of the gas and dust mass should be located in the midplane, and a significant fraction of the dust should be in large grains. Conclusions: Simultaneous modeling of the gas and

  12. Constraining the Structure of the Transition Disk HD 135344B (SAO 206462) by Simultaneous Modeling of Multiwavelength Gas and Dust Observations

    NASA Technical Reports Server (NTRS)

    Carmona, A.; Pinte, C.; Thi, W. F.; Benisty, M.; Menard, F.; Grady, C.; Kamp, I.; Woitke, P.; Olofsson, J.; Roberge, A.; Brittain, S.; Duchene, G.; Meeus, G.; Martin-Zaidi, C.; Dent, B.; Le Bouquin, J. E.; Berger, J. P.

    2014-01-01

    Context: Constraining the gas and dust disk structure of transition disks, particularly in the inner dust cavity, is a crucial step toward understanding the link between them and planet formation. HD 135344B is an accreting (pre-)transition disk that displays the CO 4.7 micrometer emission extending tens of AU inside its 30 AU dust cavity. Aims: We constrain HD 135344B's disk structure from multi-instrument gas and dust observations. Methods: We used the dust radiative transfer code MCFOST and the thermochemical code ProDiMo to derive the disk structure from the simultaneous modeling of the spectral energy distribution (SED), VLT/CRIRES CO P(10) 4.75 Micrometers, Herschel/PACS [O(sub I)] 63 Micrometers, Spitzer/IRS, and JCMT CO-12 J = 3-2 spectra, VLTI/PIONIER H-band visibilities, and constraints from (sub-)mm continuum interferometry and near-IR imaging. Results: We found a disk model able to describe the current gas and dust observations simultaneously. This disk has the following structure. (1) To simultaneously reproduce the SED, the near-IR interferometry data, and the CO ro-vibrational emission, refractory grains (we suggest carbon) are present inside the silicate sublimation radius (0.08 is less than R less than 0.2 AU). (2) The dust cavity (R is less than 30 AU) is filled with gas, the surface density of the gas inside the cavity must increase with radius to fit the CO ro-vibrational line profile, a small gap of a few AU in the gas distribution is compatible with current data, and a large gap of tens of AU in the gas does not appear likely. (4) The gas-to-dust ratio inside the cavity is >100 to account for the 870 Micrometers continuum upper limit and the CO P(10) line flux. (5) The gas-to-dust ratio in the outer disk (30 is less than R less than 200 AU) is less than 10 to simultaneously describe the [O(sub I)] 63 Micrometers line flux and the CO P(10) line profile. (6) In the outer disk, most of the gas and dust mass should be located in the midplane, and

  13. DISK MASSES AT THE END OF THE MAIN ACCRETION PHASE: CARMA OBSERVATIONS AND MULTI-WAVELENGTH MODELING OF CLASS I PROTOSTARS

    SciTech Connect

    Eisner, J. A.

    2012-08-10

    We present imaging observations at the 1.3 mm wavelength of Class I protostars in the Taurus star-forming region, obtained with the CARMA interferometer. Of an initial sample of 10 objects, we detected and imaged millimeter wavelength emission from 9. One of the nine is resolved into two sources and detailed analysis of this binary protostellar system is deferred to a future paper. For the remaining eight objects, we use the CARMA data to determine the basic morphology of the millimeter emission. Combining the millimeter data with 0.9 {mu}m images of scattered light, Spitzer Infrared Spectrograph spectra, and broadband spectral energy distributions (all from the literature), we attempt to determine the structure of the circumstellar material. We consider models including both circumstellar disks and envelopes, and constrain the masses (and other structural parameters) of each of these components. We show that the disk masses in our sample span a range from {approx}< 0.01 to {approx}> 0.1 M{sub Sun }. The disk masses for our sample are significantly higher than for samples of more evolved Class II objects. Thus, Class I disk masses probably provide a more accurate estimate of the initial mass budget for star and planet formation. However, the disk masses determined here are lower than required by theories of giant planet formation. The masses also appear too low for gravitational instability, which could lead to high mass accretion rates. Even in these Class I disks, substantial particle growth may have hidden much of the disk mass in hard-to-see larger bodies.

  14. Debris Disks and Hidden Planets

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc

    2008-01-01

    When a planet orbits inside a debris disk like the disk around Vega or Beta Pictoris, the planet may be invisible, but the patterns it creates in the disk may give it away. Observing and decoding these patterns may be the only way we can detect exo-Neptunes orbiting more than 20 AU from their stars, and the only way we can spot planets in systems undergoing the late stages of planet formation. Fortunately, every few months, a new image of a debris disk appears with curious structures begging for explanation. I'll describe some new ideas in the theory of these planet-disk interactions and provide a buyers guide to the latest models (and the planets they predict).

  15. Accretion disk coronae

    NASA Technical Reports Server (NTRS)

    White, N. E.; Holt, S. S.

    1981-01-01

    Recent observations of partial X-ray eclipses from 4U1822-37 have shown that the central X-ray source in this system is diffused by a large Compton-thick accretion disk corona (ADC). Another binary, 4U2129-47, also displays a partial eclipse and contains an ADC. The possible origin of an ADC is discussed and a simple hydrostatic evaporated ADC model is developed which, when applied to 4U1822-37, 4U2129+47 and Cyg X-3, can explain their temporal and spectral properties. The quasi-sinusoidal modulation of all three sources can be reconciled with the partial occultation of the ADC by a bulge at the edge of the accretion disk which is caused by the inflowing material. The height of this bulge is an order of magnitude larger than the hydrostatic disk height and is the result of turbulence in the outer region of the disk. The spectral properties of all three sources can be understood in terms of Compton scattering of the original source spectrum by the ADC. Spectral variations with epoch in Cyg X-3 are probably caused by changes in the optical depth of the corona. A consequence of our model is that any accreting neutron star X-ray source in a semi-detached binary system which is close to its Eddington limit most likely contains an optically thick ADC.

  16. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2003-05-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  17. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2008-02-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  18. Selected Papers on Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Bell, K. R.; Cassen, P. M.; Wasson, J. T.; Woolum, D. S.; Klahr, H. H.; Henning, Th.

    2004-01-01

    Three papers present studies of thermal balances, dynamics, and electromagnetic spectra of protoplanetary disks, which comprise gas and dust orbiting young stars. One paper addresses the reprocessing, in a disk, of photons that originate in the disk itself in addition to photons that originate in the stellar object at the center. The shape of the disk is found to strongly affect the redistribution of energy. Another of the three papers reviews an increase in the optical luminosity of the young star FU Orionis. The increase began in the year 1936 and similar increases have since been observed in other stars. The paper summarizes astronomical, meteoric, and theoretical evidence that these increases are caused by increases in mass fluxes through the inner portions of the protoplanetary disks of these stars. The remaining paper presents a mathematical-modeling study of the structures of protostellar accretion disks, with emphasis on limits on disk flaring. Among the conclusions reached in the study are that (1) the radius at which a disk becomes shadowed from its central stellar object depends on radial mass flow and (2) most planet formation has occurred in environments unheated by stellar radiation.

  19. Recognizing Patterns in Debris Disks

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc

    2009-01-01

    An extrasolar planet sculpts the famous debris dish around Fomalhaut; probably many other debris disks contain planets that we could locate if only we could better recognize their signatures in the dust that surrounds them. I will describe the latest 3-D models of debris dish dynamics / models that include planets, grain-grain collisions and even ISM-disk interactions. I will show why all these ingredients are needed to explain disk images--and what the images are telling us about planet formation.

  20. Tracing characteristic perturbations resulting from Planet-Disk and Binary-Disk interaction in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Ruge, Jan Philipp; Wolf, Sebastian; Uribe, Ana; Demidova, Tatiana; Klahr, Hubert; Grinin, Vladimir

    2013-07-01

    The perturbation by an additional, gravitating component (planet, binary star) within a protoplanetary disk induces characteristic large-scale structures in the disk density profile. We investigate the observability of these perturbations. On the basis of a large number of (M)HD and SPH simulations, we calculate synthetic scattered and polarized light images as well as thermal re-emission maps of these models and predict the observational results for different instruments from the optical to the (sub)mm wavelength range with a special focus on ALMA. In the first study (A) (Ruge et al., 2013a,c) we investigate the observability of the planet-disk interaction for different star-disk-planet configurations. We predict that ALMA is able to observe planet-induced gaps around stars of various types and for a large range of disk masses. Besides this, we find that ALMA can trace small, local perturbations indicating zonal flows in the disk. The detectability of gaps in scattered light is limited to a range of total disk masses between 1e-4 M_sun and 1e-6 M_sun. Gap detections in both wavelength ranges are feasible for M_disk ~ 1e-4 M_sun. In our second study (B) (Ruge et al. 2013b) we investigate the observability of perturbations in young circumbinary disks for several orbital elements of the binary system. We find that ALMA will allow one to trace characteristic AU-sized spiral arm features in disks in face-on orientation and also to detect binary-induced perturbations in the edge-on brightness profiles. We find that the technique of differential polarimetry offers the potential for significantly clearer detections of these disk structures than imaging in scattered light alone.

  1. Astrophysical hints of axion-like particles

    NASA Astrophysics Data System (ADS)

    Roncadelli, M.; Galanti, G.; Tavecchio, F.; Bonnoli, G.

    2015-01-01

    After reviewing three astrophysical hints of the existence of axion-like particles (ALPs), we describe in more detail a new similar hint involving flat spectrum radio quasars (FSRQs). Detection of FSRQs above about 20GeV pose a challenge to very-high-energy (VHE) astrophysics, because at those energies the ultraviolet emission from their broad line region should prevent photons produced by the central engine to leave the source. Although a few astrophysical explanations have been put forward, they are totally ad hoc. We show that a natural explanation instead arises within the conventional models of FSRQs provided that photon-ALP oscillations occur inside the source. Our analysis takes the FSRQ PKR 1222+206 as an example, and it looks tantalizing that basically the same choice of the free model parameters adopted in this case is consistent with those that provide the other three hints of the existence of ALPs.

  2. Photoionized Plasmas in the Z Facility and in Astrophysics

    NASA Astrophysics Data System (ADS)

    Mancini, Roberto

    2013-06-01

    Many astrophysical environments such as x-ray binaries, active galactic nuclei, and accretion disks of compact objects have photoionized plasmas. Detailed x-ray spectral observations performed with the Chandra and XMM-Newton orbiting telescopes provide critical information on the state of photoionized plasmas. However, the complexity of the astrophysical environment makes the spectral analysis challenging, and thus laboratory experiments are important for data interpretation and testing of modeling codes. The Z facility at Sandia National Laboratories is a powerful source of x-rays to produce and study in the laboratory photoionized plasmas relevant for astrophysics under well characterized conditions. We discuss an experimental and theory/modeling effort in which the intense x-ray flux emitted at the collapse of a z-pinch implosion conducted at the Z pulsed-power machine is employed to produce a neon photoionized plasma. The broadband x-ray radiation flux from the z-pinch is used to both create the photoionized plasma and provide a source of backlighting photons to study the atomic kinetics through K-shell line absorption spectroscopy. The plasma is contained in a cm-scale gas cell that can be located at different distances from the z-pinch, thus effectively controlling the x-ray flux producing the plasma. Time-integrated and gated transmission spectra are recorded with a spectrometer equipped with two elliptically-bent KAP crystals and a set of slits to record up to six spatially-resolved spectra per crystal in the same shot. The transmission data shows a rich line absorption spectrum that spans over several ionization stages of neon including Be-, Li-, He- and H-like ions. Modeling calculations are used to interpret the transmission spectra recorded in the Z experiments with the goal of extracting the charge- state distribution, electron temperature and the radiation flux driving the plasma, as well as to determine the ionization parameter of the plasma. This

  3. Experimental astrophysics with high power lasers and Z pinches

    SciTech Connect

    Remington, B A; Drake, R P; Ryutov, D D

    2004-12-10

    With the advent of high energy density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, mm-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors; equations of state relevant to planetary interiors; strong shock driven nonlinear hydrodynamics and radiative dynamics, relevant to supernova explosions and subsequent evolution; protostellar jets and high Mach-number flows; radiatively driven molecular clouds and nonlinear photoevaporation front dynamics; and photoionized plasmas relevant to accretion disks around compact objects, such as black holes and neutron stars.

  4. LUNA: Nuclear astrophysics underground

    SciTech Connect

    Best, A.

    2015-02-24

    Underground nuclear astrophysics with LUNA at the Laboratori Nazionali del Gran Sasso spans a history of 20 years. By using the rock overburden of the Gran Sasso mountain chain as a natural cosmic-ray shield very low signal rates compared to an experiment on the surface can be tolerated. The cross sectons of important astrophysical reactions directly in the stellar energy range have been successfully measured. In this proceeding we give an overview over the key accomplishments of the experiment and an outlook on its future with the expected addition of an additional accelerator to the underground facilities, enabling the coverage of a wider energy range and the measurement of previously inaccessible reactions.

  5. Astrophysical terms in Armenian

    NASA Astrophysics Data System (ADS)

    Yeghikian, A. G.

    2015-07-01

    There are quite a few astrophysical textbooks (to say nothing about monographs) in Armenian, which are, however out of date and miss all the modern terms concerning space sciences. Many terms have been earlier adopted from English and, especially, from Russian. On the other hand, teachers and lecturers in Armenia need scientific terms in Armenian adequately reproducing either their means when translating from other languages or (why not) creating new ones. In short, a permanently updated astrophysical glossary is needed to serve as explanation of such terms. I am not going here to present the ready-made glossary (which should be a task for a joint efforts of many professionals) but instead just would like to describe some ambiguous examples with comments where possible coming from my long-year teaching, lecturing and professional experience. A probable connection between "iron" in Armenian as concerned to its origin is also discussed.

  6. Nuclear Astrophysics with LUNA

    NASA Astrophysics Data System (ADS)

    Broggini, Carlo

    2016-04-01

    One of the main ingredients of nuclear astrophysics is the knowledge of the thermonuclear reactions which power the stars and synthesize the chemical elements. Deep underground in the Gran Sasso Laboratory the cross section of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The main results obtained during the 'solar' phase of LUNA are reviewed and their influence on our understanding of the properties of the neutrino and of the Sun is discussed. We then describe the current LUNA program mainly devoted to the study of the nucleosynthesis of the light elements in AGB stars and Classical Novae. Finally, the future of LUNA towards the study of helium and carbon burning with a new 3.5 MV accelerator is outlined.

  7. Nuclear astrophysics at DRAGON

    SciTech Connect

    Hager, U.

    2014-05-02

    The DRAGON recoil separator is located at the ISAC facility at TRIUMF, Vancouver. It is designed to measure radiative alpha and proton capture reactions of astrophysical importance. Over the last years, the DRAGON collaboration has measured several reactions using both radioactive and high-intensity stable beams. For example, the 160(a, g) cross section was recently measured. The reaction plays a role in steady-state helium burning in massive stars, where it follows the 12C(a, g) reaction. At astrophysically relevant energies, the reaction proceeds exclusively via direct capture, resulting in a low rate. In this measurement, the unique capabilities of DRAGON enabled determination not only of the total reaction rates, but also of decay branching ratios. In addition, results from other recent measurements will be presented.

  8. CASPAR - Nuclear Astrophysics Underground

    NASA Astrophysics Data System (ADS)

    Strieder, Frank; Robertson, Daniel; Couder, Manoel; Greife, Uwe; Wells, Doug; Wiescher, Michael

    2015-10-01

    The work of the LUNA Collaboration at the Laboratori Nationali del Gran Sasso demonstrated the research potential of an underground accelerator for the field of nuclear astrophysics. Several key reactions could be studied at LUNA, some directly at the Gamow peak for solar hydrogen burning. The CASPAR (Compact Accelerator System for Performing Astrophysical Research) Collaboration will implement a high intensity 1 MV accelerator at the Sanford Underground Research Facility (SURF) and overcome the current limitation at LUNA. The installation of the accelerator in the recently rehabilitated underground cavity at SURF started in Summer 2015 and first beam should be delivered by the end of the year. This project will primarily focus on the neutron sources for the s-process, e.g. 13C(α , n) 16O and 22Ne(α , n) 25Mg , and lead to unprecedented measurements compared to previous studies. A detailed overview of the science goals of CASPAR will be presented.

  9. Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects. I: Properties of the Corona and the Spectrum of Escaping Radiation

    NASA Technical Reports Server (NTRS)

    Dove, James B.; Wilms, Jorn; Begelman, Mitchell C.

    1997-01-01

    We present the properties of accretion disk corona (ADC) models in which the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a nonlinear Monte Carlo code to perform the calculations. As an example, we discuss models in which the corona is situated above and below a cold accretion disk with a plane-parallel (slab) geometry, similar to the model of Haardt & Maraschi. By Comptonizing the soft radiation emitted by the accretion disk, the corona is responsible for producing the high-energy component of the escaping radiation. Our models include the reprocessing of radiation in the accretion disk. Here the photons either are Compton-reflected or photoabsorbed, giving rise to fluorescent line emission and thermal emission. The self- consistent coronal temperature is determined by balancing heating (due to viscous energy dissipation) with Compton cooling, determined using the fully relativistic, angle-dependent cross sections. The total opacity is found by balancing pair productions with annihilations. We find that, for a disk temperature kT(sub BB) approx. less than 200 eV, these coronae are unable to have a self-consistent temperature higher than approx. 140 keV if the total optical depth is approx. less than 0.2, regardless of the compactness parameter of the corona and the seed opacity. This limitation corresponds to the angle-averaged spectrum of escaping radiation having a photon index approx. greater than 1.8 within the 5-30 keV band. Finally, all models that have reprocessing features also predict a large thermal excess at lower energies. These constraints make explaining the X-ray spectra of persistent black hole candidates with ADC models very problematic.

  10. Libstatmech and applications to astrophysics

    NASA Astrophysics Data System (ADS)

    Yu, Tianhong

    In this work an introduction to Libstatmech is presented and applications especially to astrophysics are discussed. Libstatmech is a C toolkit for computing the statistical mechanics of fermions and bosons, written on top of libxml and gsl (GNU Scientific Library). Calculations of Thomas-Fermi Screening model and Bose-Einstein Condensate based on libstatmech demonstrate the expected results. For astrophysics application, a simple Type Ia Supernovae model is established to run the network calculation with weak reactions, in which libstatmech contributes to compute the electron chemical potential and allows the weak reverse rates to be calculated from detailed balance. Starting with pure 12C and T9=1.8, we find that at high initial density (rho~ 9x 109 g/cm3) there are relatively large abundances of neutron-rich iron-group isotopes (e.g. 66Ni, 50Ti, 48Ca) produced during the explosion, and Y e can drop to ~0.4, which indicates that the rare, high density Type Ia supernovae may help to explain the 48Ca and 50Ti effect in FUN CAIs.

  11. Analytic studies in nuclear astrophysics

    NASA Astrophysics Data System (ADS)

    Pizzochero, Pierre

    Five studies are presented in nuclear astrophysics, which deal with different stages of stellar evolution and which use analytic techniques as opposed to numerical ones. Two problems are described in neutrino astrophysics: the solar-neutrino puzzle is analyzed in the framework of the MSW mechanism for the enhancement of neutrino oscillations in matter; and the cooling of neutron stars is studied by calculating the neutrino emissivity from strangeness condensation. Radiative transfer is then examined as applied to SN1987A: its early spectrum and bolometric corrections are calculated by developing an analytic model which can describe both the extended nature of the envelope and the non-LTE state of the radiation field in the scattering-dominated early atmosphere; and a model-independent relation is derived between mass and kinetic energy for the hydrogen envelope of SN1987A, using only direct observations of its luminosity and photospheric velocity. Finally, an analytic approach is presented to relate the softness of the EOS of dense nuclear matter in the core of a supernova, the hydrostatic structure of such core and the initial strength of the shock wave.

  12. Birth of Neutrino Astrophysics

    ScienceCinema

    None

    2011-10-06

    Based mainly on the results of two experiments, KamiokaNDE and Super-KamiokaNDE, the birth of neutrino astrophysics will be described. At the end, the result of the third generation Kamioka experiment, KamLAND, will be discussed together with the future possibilities.Organiser(s): Daniel Treille / EP DivisionNote: * Tea & coffee will be served at 16:00 hrs. Please note unusual day.

  13. Birth of Neutrino Astrophysics

    SciTech Connect

    2010-05-07

    Based mainly on the results of two experiments, KamiokaNDE and Super-KamiokaNDE, the birth of neutrino astrophysics will be described. At the end, the result of the third generation Kamioka experiment, KamLAND, will be discussed together with the future possibilities.Organiser(s): Daniel Treille / EP DivisionNote: * Tea & coffee will be served at 16:00 hrs. Please note unusual day.

  14. Herschel evidence for disk flattening or gas depletion in transitional disks

    SciTech Connect

    Keane, J. T.; Pascucci, I.; Espaillat, C.; Woitke, P.; Andrews, S.; Kamp, I.; Thi, W.-F.; Meeus, G.; Dent, W. R. F.

    2014-06-01

    Transitional disks are protoplanetary disks characterized by reduced near- and mid-infrared emission, with respect to full disks. This characteristic spectral energy distribution indicates the presence of an optically thin inner cavity within the dust disk believed to mark the disappearance of the primordial massive disk. We present new Herschel Space Observatory PACS spectra of [O I] 63.18 μm for 21 transitional disks. Our survey complements the larger Herschel GASPS program ({sup G}as in Protoplanetary Systems{sup )} by quadrupling the number of transitional disks observed with PACS in this wavelength. [O I] 63.18 μm traces material in the outer regions of the disk, beyond the inner cavity of most transitional disks. We find that transitional disks have [O I] 63.18 μm line luminosities ∼2 times fainter than their full disk counterparts. We self-consistently determine various stellar properties (e.g., bolometric luminosity, FUV excess, etc.) and disk properties (e.g., disk dust mass, etc.) that could influence the [O I] 63.18 μm line luminosity, and we find no correlations that can explain the lower [O I] 63.18 μm line luminosities in transitional disks. Using a grid of thermo-chemical protoplanetary disk models, we conclude that either transitional disks are less flared than full disks or they possess lower gas-to-dust ratios due to a depletion of gas mass. This result suggests that transitional disks are more evolved than their full disk counterparts, possibly even at large radii.

  15. Chaotic dynamics around astrophysical objects with nonisotropic stresses

    SciTech Connect

    Dubeibe, F. L.; Pachon, Leonardo A.; Sanabria-Gomez, Jose D.

    2007-01-15

    The existence of chaotic behavior for the geodesics of the test particles orbiting compact objects is a subject of much current research. Some years ago, Gueron and Letelier [Phys. Rev. E 66, 046611 (2002)] reported the existence of chaotic behavior for the geodesics of the test particles orbiting compact objects like black holes induced by specific values of the quadrupolar deformation of the source using as models the Erez--Rosen solution and the Kerr black hole deformed by an internal multipole term. In this work, we are interested in the study of the dynamic behavior of geodesics around astrophysical objects with intrinsic quadrupolar deformation or nonisotropic stresses, which induces nonvanishing quadrupolar deformation for the nonrotating limit. For our purpose, we use the Tomimatsu-Sato spacetime [Phys. Rev. Lett. 29 1344 (1972)] and its arbitrary deformed generalization obtained as the particular vacuum case of the five parametric solution of Manko et al. [Phys. Rev. D 62, 044048 (2000)] characterizing the geodesic dynamics throughout the Poincare sections method. We found only regular motion for the geodesics in the Tomimatsu-Sato {delta}=2 solution. Additionally, using the deformed generalization of Tomimatsu-Sato {delta}=2 solution given by Manko et al. we found chaotic motion for oblate deformation instead of prolate deformation, which is in contrast to the results by Gueron and Letelier. It opens the possibility that the particles forming the accretion disk around a large variety of different astrophysical bodies (nonprolate, e.g., neutron stars) could exhibit chaotic dynamics. We also conjecture that the existence of an arbitrary deformation parameter is necessary for the existence of chaotic dynamics.

  16. Direct Statistical Simulation of Astrophysical and Geophysical Flows

    NASA Astrophysics Data System (ADS)

    Marston, B.; Tobias, S.

    2011-12-01

    Astrophysical and geophysical flows are amenable to direct statistical simulation (DSS), the calculation of statistical properties that does not rely upon accumulation by direct numerical simulation (DNS) (Tobias and Marston, 2011). Anisotropic and inhomogeneous flows, such as those found in the atmospheres of planets, in rotating stars, and in disks, provide the starting point for an expansion in fluctuations about the mean flow, leading to a hierarchy of equations of motion for the equal-time cumulants. The method is described for a general set of evolution equations, and then illustrated for two specific cases: (i) A barotropic jet on a rotating sphere (Marston, Conover, and Schneider, 2008); and (ii) A model of a stellar tachocline driven by relaxation to an underlying flow with shear (Cally 2001) for which a joint instability arises from the combination of shearing forces and magnetic stress. The reliability of DSS is assessed by comparing statistics so obtained against those accumulated from DNS, the traditional approach. The simplest non-trivial closure, CE2, sets the third and higher cumulants to zero yet yields qualitatively accurate low-order statistics for both systems. Physically CE2 retains only the eddy-mean flow interaction, and drops the eddy-eddy interaction. Quantitatively accurate zonal means are found for barotropic jet for long and short (but not intermediate) relaxation times, and for Cally problem in the case of strong shearing and large magnetic fields. Deficiencies in CE2 can be repaired at the CE3 level, that is by retaining the third cumulant (Marston 2011). We conclude by discussing possible extensions of the method both in terms of computational methods and the range of astrophysical and geophysical problems that are of interest.

  17. Laboratory Astrophysics Using the Electron Beam Ion Trap

    NASA Astrophysics Data System (ADS)

    Brown, Gregory V.

    2014-06-01

    X-ray astronomy has seen profound growth in discovery space for over a decade resulting almost entirely from the successful operation of three X-ray observatories: Chandra, XMM-Newton, and Suzaku. The high sensitivity, high resolution instrumentation on these satellites have provided the X-ray astrophysicists with relatively straightforward access to powerful line diagnostics that tightly constrain the physical parameters of celestial sources. For example, accurate measurements of transition energies, line shapes, and intensities provide quantitative measures of a velocity fields, electron densities and temperatures. X-ray measurements probe sources unattainable by any other wavelength bands, such as the regions of accretion disks near black holes, and the hot intracluster medium in clusters of galaxies. Thus, X-ray astronomy in the age of Chandra, XMM-Newton, and Suzaku provides important pieces of the puzzles necessary to understand the formation and evolution of galaxies, stars, the phenomena near black holes, and the evolution of the universe as a whole. Unfortunately, accurate unambiguous interpretation of high quality spectra is often limited by the accuracy and completeness of atomic data rather than the uncertainties related to counting statistics or instrumentation. Starting over twenty years ago, the electron beam ion trap facility at Lawrence Livermore National Laboratory has been used to benchmark spectral models used to interpret celestial data, and to address specific problems facing the astrophysics community. More recently, the portable FLASH-EBIT, built and maintained at the Max Planck Institute for Nuclear Physics, Heidelberg and coupled to third and fourth generation light sources has opened new measurement regimes relavant to the high energy astrophysics community. Selected results will be presented. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

  18. The Nuclear Astrophysics Explorer

    NASA Technical Reports Server (NTRS)

    Matteson, J. L.; Teegarden, B. J.; Gehrels, N.; Mahoney, W. A.

    1989-01-01

    The Nuclear Astrophysics Explorer was proposed in 1986 for NASA's Explorer Concept Study Program by an international collaboration of 25 scientists from nine institutions. The one-year feasibility study began in June 1988. The Nuclear Astrophysics Explorer would obtain high resolution observations of gamma-ray lines, E/Delta E about 1000, at a sensitivity of about 0.000003 ph/sq cm s, in order to study fundamental problems in astrophysics such as nucleosynthesis, supernovae, neutron star and black-hole physics, and particle acceleration and interactions. The instrument would operate from 15 keV to 10 Mev and use a heavily shielded array of nine cooled Ge spectrometers in a very low background configuration. Its 10 deg FWHM field of view would contain a versatile coded mask system which would provide two-dimensional imaging with 4 deg resolution, one-dimensional imaging with 2 deg resolution, and efficiendt measurements of diffuse emission. An unshielded Ge spectrometer would obtain wide-field measurements of transient gamma-ray sources. The earliest possible mission would begin in 1995.

  19. The golden age of multifrequency astrophysics

    NASA Astrophysics Data System (ADS)

    Giovannelli, Franco; Sabau-Graziati, Lola

    In occasion of the Silver Jubilee of the Frascati Workshop about Multifrequency Behaviour of High Energy Cosmic Sources we want to discuss some aspects of the Multifrequency Astrophysics. Multifrequency Astrophysics can be considered as a `new field' of astrophysics born just around the end of 1970-ies - beginning of 1980-ies to which we strongly contributed not only with our own measurements and studies of physical processes spread along the whole electromagnetic spectrum, but mostly with the organization of the Frascati Workshop Series. In this paper we discuss the methodology used in astrophysics for collecting data coming from multifrequency observations of cosmic sources - obtained in different ways - and the relative models developed through theoretical study of physical processes governing their behaviour. Several examples about X-ray binaries, cataclysmic variables, T Tauri stars, relativistic jets from different classes of sources, gamma-ray bursts, and few words about Standard Big Bang Cosmology and experimental proofs fitting the theory will be discussed. We will briefly discuss also the prospects of the multifrequency astrophysics which is now in its golden age without any pretension of completness.

  20. Photoevaporating Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2004-01-01

    Ultraviolet radiation from the central star or from a nearby massive star heats the surfaces of protoplanetary disks and causes the outer, less gravitationally bound part of the disks, to photoevaporate into interstellar space. Photoevaporation is likely the most important dispersal mechanism for the outer regions of disks. We focus in this talk on disks around low-mass stars like the Sun rather than high-mass stars, which we have treated previously. Stars often form in clusters and the ultraviolet flux from the most luminous star in the cluster can have a dramatic effect on the disk orbiting a nearby low-mass star. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We discuss recent models of the effects of the radiation from the central low mass star including both the predicted infrared spectra from the heated disks as well as preliminary results on the photoevaporation rates.

  1. Heating and Cooling Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Turner, Neal

    Many of the disks of gas and dust orbiting young Sun-like stars produce mid-infrared emission from water and other oxygen- and carbon-bearing molecules, as discovered in the last few years using the Spitzer Space Telescope. The emission reveals the temperatures, columns and chemical composition of the gas in the disk atmosphere within 2 AU of the star, directly overlying the region where the planets form. Better understanding of the processes governing the line emission is vital for converting this new class of measurements into information about the planets' raw ingredients. We propose to combine MHD models of the turbulence driving the disk accretion flows, with a thermal-chemical model of the disk atmospheres, to predict emergent spectra that will capture the dynamics, heating, and chemical composition. By comparing the predicted and observed spectra we can determine the strength of the turbulence that heats and mixes the gas, and test ideas about the conditions in the disk interior. We will investigate the coupling of the turbulence to the thermal and chemical evolution, seek to locate the line emission's power source, gauge the rate at which the atmosphere and interior exchange material, and obtain new independent measures of the disk mass accretion rates. These efforts will help infrared spectroscopy of protostellar disks reach its full potential as a diagnostic of the environments in which planets form.

  2. Modelling the spectral energy distribution of galaxies. V. The dust and PAH emission SEDs of disk galaxies

    NASA Astrophysics Data System (ADS)

    Popescu, C. C.; Tuffs, R. J.; Dopita, M. A.; Fischera, J.; Kylafis, N. D.; Madore, B. F.

    2011-03-01

    We present a self-consistent model of the spectral energy distributions (SEDs) of spiral galaxies from the ultraviolet (UV) to the mid-infrared (MIR)/far-infrared (FIR)/submillimeter (submm) based on a full radiative transfer calculation of the propagation of starlight in galaxy disks. This model predicts not only the total integrated energy absorbed in the UV/optical and re-emitted in the infrared/submm, but also the colours of the dust emission based on an explicit calculation of the strength and colour of the UV/optical radiation fields heating the dust, and incorporating a full calculation of the stochastic heating of small dust grains and PAH molecules. The geometry of the translucent components of the model is empirically constrained using the results from the radiation transfer analysis of Xilouris et al. on spirals in the middle range of the Hubble sequence, while the geometry of the optically thick components is constrained from physical considerations with a posteriori checks of the model predictions with observational data. Following the observational constraints, the model has both a distribution of diffuse dust associated with the old and young disk stellar populations as well as a clumpy component arising from dust in the parent molecular clouds in star forming regions. In accordance with the fragmented nature of dense molecular gas in typical star-forming regions, UV light from massive stars is allowed to either freely stream away into the diffuse medium in some fraction of directions or be geometrically blocked and locally absorbed in clumps. These geometrical constraints enable the dust emission to be predicted in terms of a minimum set of free parameters: the central face-on dust opacity in the B-band τ^f_B, a clumpiness factor F for the star-forming regions, the star-formation rate SFR, the normalised luminosity of the old stellar population old and the bulge-to-disk ratio B/D. We show that these parameters are almost orthogonal in their

  3. Relativistic plasma astrophysics with intense lasers

    NASA Astrophysics Data System (ADS)

    Kuramitsu, Yasuhiro; Chu, Hsu-Hsin; Hau, Lin-Ni; Chen, Shih-Hung; Liu, Yao-Li; Hsieh, Chia-Ying; Sakawa, Youichi; Hideaki, Takabe; Wang, Jyhpyng

    2015-12-01

    Recent progresses of laser technologies enable us to investigate space and astrophysical phenomena in laboratories. In space plasmas the local observations by spacecrafts provide us the microscopic information of the plasma and electric/magnetic fields, however, it is difficult to obtain the global structures of the phenomena. In astrophysical plasmas, in contrast, global images provide us the macroscopic information, although there is no local observation and thus no microscopic information. Laboratory experiments on space and astrophysical phenomena provide us the local and global information simultaneously. We have investigated so far mostly non-relativistic phenomena in the universe with long laser pulses. Now we extend our research from non-relativistic to relativistic regime with an ultra intense laser, the 100 TW laser facility at National Central University. We introduce our facility and model relativistic phenomena in laboratory, focusing on the magnetic field generation and the magnetic reconnection in the universe.

  4. Gravitational asymmetries in gaseous disks.

    NASA Astrophysics Data System (ADS)

    Junqueira, S.; Combes, F.

    1997-12-01

    The authors report preliminary results of self-gravitating simulations of spiral galaxies modeled by two components, stellar and gaseous disks. One of the objectives of this work is to study asymmetries in the distribution of the gas, features observed for a number of spiral galaxies. The gas disk is simulated by the Beam-Scheme method, where the gas is considered as a fluid. The results suggest that very concentrated galactic disks can be unstable to the one-armed (m = 1) spiral perturbation, which may explain the asymmetric patterns observed in isolated galaxies.

  5. Properties of accretion disk coronae

    NASA Technical Reports Server (NTRS)

    Wilms, J.; Dove, J.; Staubert, R.; Begelman, M. C.

    1997-01-01

    The properties of accretion disk corona in a parameter regime suitable for Galactic black hole candidates are considered and the results of an analysis of these properties using a self-consistent Monte Carlo code are presented. Examples of the coronal temperature structure, the shape and angular dependency of the spectrum and the maximum temperature allowed for each optical depth of the corona are presented. It is shown that the observed spectrum of the Galactic black hole candidate Cygnus X-1 cannot be explained by accreting disk corona models with a slab geometry, where the accretion disk is sandwiched by the comptonizing medium.

  6. 2.5D global-disk oscillation models of the Be shell star ζ Tauri. I. Spectroscopic and polarimetric analysis

    NASA Astrophysics Data System (ADS)

    Escolano, C.; Carciofi, A. C.; Okazaki, A. T.; Rivinius, T.; Baade, D.; Štefl, S.

    2015-04-01

    Context. A large number of Be stars exhibit intensity variations of their violet and red emission peaks in their H i lines observed in emission. This is the so-called V/R phenomenon, usually explained by the precession of a one-armed spiral density perturbation in the circumstellar disk. That global-disk oscillation scenario was confirmed, both observationally and theoretically, in the previous series of two papers analyzing the Be shell star ζ Tauri. The vertically averaged (2D) global-disk oscillation model used at the time was able to reproduce the V/R variations observed in Hα, as well as the spatially resolved interferometric data from AMBER/VLTI. Unfortunately, that model failed to reproduce the V/R phase of Br15 and the amplitude of the polarization variation, suggesting that the inner disk structure predicted by the model was incorrect. Aims: The first aim of the present paper is to quantify the temporal variations of the shell-line characteristics of ζ Tauri. The second aim is to better understand the physics underlying the V/R phenomenon by modeling the shell-line variations together with the V/R and polarimetric variations. The third aim is to test a new 2.5D disk oscillation model, which solves the set of equations that describe the 3D perturbed disk structure but keeps only the equatorial (i.e., 2D) component of the solution. This approximation was adopted to allow comparisons with the previous 2D model, and as a first step toward a future 3D model. Methods: We carried out an extensive analysis of ζ Tauri's spectroscopic variations by measuring various quantities characterizing its Balmer line profiles: red and violet emission peak intensities (for Hα, Hβ, and Br15), depth and asymmetry of the shell absorption (for Hβ, Hγ, and Hδ), and the respective position (i.e., radial velocity) of each component. We attempted to model the observed variations by implementing in the radiative transfer code HDUST the perturbed disk structure computed with a

  7. Understanding of Dynamics and Alignment of Astrophysical Dust

    NASA Astrophysics Data System (ADS)

    Lazarian, Alex

    2009-01-01

    For a long time the dynamics of dust particles was approximated by that of absolutely rigid spheroids with no internal structure; the driving was accounted by gas bombarding the surface of the spheroids. The real dust dynamics is very different. First of all, irregular grains have non-zero helicity, which results in strong torques that emerge when grains interact with radiation and/or gaseous flows. This results in grain alignment, which is far more efficient than the competing processes described in textbooks. Second, the processes of alignment can be different for grains which inertia is approximated by spheroids and ellipsoids of inertia. Third, interactions of grains with ions are frequently more important than with the neutral atoms. Our research shows that, in spite of all these complexities, grain dynamics and grain alignment can be understood with sufficiently simple models. In particular, I shall present an analytical model that describes well the alignment of helical grains, present the calculations of the rate of rotation and degree of alignment for grains in different astrophysical environments. In particular, I shall discuss the dynamics of very large grains, which are present in accretion disks and the dynamics of very small grains or PAHs, which are responsible for the anomalous foreground emission.

  8. Accretion disks in interacting binary stars

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.

    1991-01-01

    Accretion disks have most often been analyzed in cataclysmic variables (CVs); the structure and evolution of accretion