WorldWideScience

Sample records for surrounding protostellar disks

  1. Nonaxisymmetric evolution in protostellar disks

    Science.gov (United States)

    Laughlin, Gregory; Bodenheimer, Peter

    1994-01-01

    We present a two-dimensional, multigridded hydrodynamical simulation of the collapse of an axisymmetric, rotating, 1 solar mass protostellar cloud, which forms a resolved, hydrotastic disk. The code includes the effects of physical viscosity, radiative transfer and radiative acceleration but not magnetic fields. We examine how the disk is affected by the inclusion of turbulent viscosity by comparing a viscous simulation with an inviscid model evolved from the same initial conditions, and we derive a disk evolutionary timescale on the order of 300,000 years if alpha = 0.01. Effects arising from non-axisymmetric gravitational instabilities in the protostellar disk are followed with a three-dimensional SPH code, starting from the two-dimensional structure. We find that the disk is prone to a series of spiral instabilities with primary azimulthal mode number m = 1 and m = 2. The torques induced by these nonaxisymmetric structures elicit material transport of angular momentum and mass through the disk, readjusting the surface density profile toward more stable configurations. We present a series of analyses which characterize both the development and the likely source of the instabilities. We speculate that an evolving disk which maintains a minimum Toomre Q-value approximately 1.4 will have a total evolutionary span of several times 10(exp 5) years, comparable to, but somewhat shorter than the evolutionary timescale resulting from viscous turbulence alone. We compare the evolution resulting from nonaxisymmetric instabilities with solutions of a one-dimensional viscous diffusion equation applied to the initial surface density and temperature profile. We find that an effective alpha-value of 0.03 is a good fit to the results of the simulation. However, the effective alpha will depend on the minimum Q in the disk at the time the instability is activated. We argue that the major fraction of the transport characterized by the value of alpha is due to the action of

  2. Global Models for Embedded, Accreting Protostellar Disks

    CERN Document Server

    Kratter, Kaitlin M; Krumholz, Mark R

    2007-01-01

    Most analytic work to date on protostellar disks has focused on disks in isolation from their environments. However, observations are now beginning to probe the earliest, most embedded phases of star formation, during which disks are rapidly accreting from their parent cores and cannot be modeled in isolation. We present a simple, one-zone model of protostellar accretion disks with high mass infall rates. Our model combines a self-consistent calculation of disk temperatures with an approximate treatment of angular momentum transport via several mechanisms. We use this model to survey the properties of protostellar disks across a wide range of stellar masses and evolutionary times, and make predictions for disks' masses, sizes, spiral structure, and fragmentation that will be directly testable by future large-scale surveys of deeply embedded disks. We define a dimensionless accretion-rotation parameter which, in conjunction with the disk's temperature, controls the disk evolution. We track the dominant mode of...

  3. Heating of protostellar accretion disks

    Science.gov (United States)

    de Campos, R. R.; Jatenco-Pereira, V.

    2017-07-01

    The magneto-rotational instability (MRI) is believed to be the mechanism responsible for a magneto-hydrodynamic turbulence that could lead to the accretion observed in protoplanetary disks. The need of a minimum amount of ionization in protostellar accretion disks is necessary for the MRI to take place. There are in the literature several studies that include the damping of Alfvén waves as an additional heating source besides the viscous heating mechanism in a geometrically thin and optically thick disk. The damping of the waves transfers energy to the disk increasing the temperature and consequently its ionization fraction, making possible the presence of the MRI in a large part of the disk. We analyzed the contribution of non-ideal effects such as Ohmic and ambipolar diffusion for the disk heating and compare these heating rates with those obtained by damping of Alfvén waves. In order to study these non-ideal effects, we have estimated the radiation emission of each effect through the energy conservation equation, and associated each emission with a black body radiation, which enabled us to assign a temperature contribution of each effect. Using the ATHENA code we were able to simulate the disk at different radial distances, and estimate the electric current density needed to calculate the radiation emission associated with each effect. Once we have those data, we were able to compare the results with other heating sources, like viscosity and Alfvén waves damping, and we concluded that the Ohmic and ambipolar diffusions do not heat the disk in any significant way.

  4. Heating and Cooling Protostellar Disks

    CERN Document Server

    Hirose, S

    2011-01-01

    We examine heating and cooling in protostellar disks using 3-D radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation diffusion approximations. The disk atmosphere is ionized by stellar X-rays, well-coupled to magnetic fields, and sustains a turbulent accretion flow driven by magneto-rotational instability, while the interior is resistive and magnetically dead. The turbulent layers heat by absorbing the light from the central star and by dissipating the magnetic fields. They are optically-thin to their own radiation and cool inefficiently. The optically-thick interior in contrast is heated only weakly, by re-emission from the atmosphere. The interior is colder than a classical viscous model, and isothermal. The magnetic fields support an extended atmosphere that absorbs the starlight 1.5 times higher than the hydrostatic viscous model. The disk thickness thus measures not the internal temperature, but the magnetic field strength. Fluctuations i...

  5. Early dust evolution in protostellar accretion disks

    OpenAIRE

    2000-01-01

    We investigate dust dynamics and evolution during the formation of a protostellar accretion disk around intermediate mass stars via 2D numerical simulations. Using three different detailed dust models, compact spherical particles, fractal BPCA grains, and BCCA grains, we find that even during the early collapse and the first 10,000 yr of dynamical disk evolution, the initial dust size distribution is strongly modified. Close to the disk's midplane coagulation produces dust particles of sizes ...

  6. Magnetic fields in early protostellar disk formation

    CERN Document Server

    González-Casanova, Diego F; Lazarian, Alexander

    2016-01-01

    We consider formation of accretion disks from a realistically turbulent molecular gas using 3D MHD simulations. In particular, we analyze the effect of the fast turbulent reconnection described by the Lazarian & Vishniac (1999) model for the removal of magnetic flux from a disk. With our numerical simulations we demonstrate how the fast reconnection enables protostellar disk formation resolving the so-called "magnetic braking catastrophe". In particular, we provide a detailed study of the dynamics of a 0.5 M$_\\odot$ protostar and the formation of its disk for up to several thousands years. We measure the evolution of the mass, angular momentum, magnetic field, and turbulence around the star. We consider effects of two processes that strongly affect the magnetic transfer of angular momentum, both of which are based on turbulent reconnection: the first, "reconnection diffusion", removes the magnetic flux from the disk, the other involves the change of the magnetic field's topology, but does not change the a...

  7. The early evolution of protostellar disks

    Science.gov (United States)

    Stahler, Steven W.; Korycansky, D. G.; Brothers, Maxwell J.; Touma, Jihad

    1994-01-01

    We consider the origin and intital growth of the disks that form around protostars during the collapse of rotating molecular cloud cores. These disks are assumed to be inviscid and pressure free, and to have masses small compared to those of their central stars. We find that there exist three distinct components-an outer disk, in which shocked gas moves with comparable azimuthal and radical velocities; and inner disk, where material follows nearly circular orbits, but spirals slowly toward the star because of the drag exerted by adjacent onfalling matter, and a turbulent ring adjoining the first two regions. Early in the evolution, i.e., soon after infalling matter begins to miss the star, only the outer disk is present, and the total mass acceration rate onto the protostar is undiminished. Once the outer disk boundary grows to more than 2.9 times the stellar radius, first the ring, and then the inner disk appear. Thereafter, the radii of all three components expand as t(exp 3). The mass of the ring increase with time and is always 13% of the total mass that has fallen from the cloud. Concurrently with the buildup of the inner disk and ring, the accretion rate onto the star falls off. However, the protostellar mass continue to rise, asymptotically as t(exp 1/4). We calculated the radiated flux from the inner and outer disk components due to the release of gravitational potential energy. The flux from the inner disk is dominant and rises steeply toward the stellar surface. We also determine the surface temperature of the inner disk as a function of radius. The total disk luminosity decreases slowly with time, while the contributions from the ring and inner disk both fall as t(exp -2).

  8. MAGNETIC FIELDS IN EARLY PROTOSTELLAR DISK FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    González-Casanova, Diego F.; Lazarian, Alexander [Astronomy Department, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706-1582 (United States); Santos-Lima, Reinaldo, E-mail: casanova@astro.wisc.edu [Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, R. do Matão, 1226, São Paulo, SP 05508-090 (Brazil)

    2016-03-10

    We consider formation of accretion disks from a realistically turbulent molecular gas using 3D MHD simulations. In particular, we analyze the effect of the fast turbulent reconnection described by the Lazarian and Vishniac model for the removal of magnetic flux from a disk. With our numerical simulations we demonstrate how the fast reconnection enables protostellar disk formation resolving the so-called “magnetic braking catastrophe.” In particular, we provide a detailed study of the dynamics of a 0.5 M{sub ⊙} protostar and the formation of its disk for up to several thousands years. We measure the evolution of the mass, angular momentum, magnetic field, and turbulence around the star. We consider effects of two processes that strongly affect the magnetic transfer of angular momentum, both of which are based on turbulent reconnection: the first, “reconnection diffusion,” removes the magnetic flux from the disk; the other involves the change of the magnetic field's topology, but does not change the absolute value of the magnetic flux through the disk. We demonstrate that for the first mechanism, turbulence causes a magnetic flux transport outward from the inner disk to the ambient medium, thus decreasing the coupling of the disk to the ambient material. A similar effect is achieved through the change of the magnetic field's topology from a split monopole configuration to a dipole configuration. We explore how both mechanisms prevent the catastrophic loss of disk angular momentum and compare both above turbulent reconnection mechanisms with alternative mechanisms from the literature.

  9. On the tilting of protostellar disks by resonant tidal effects

    CERN Document Server

    Lubow, S H

    2000-01-01

    We consider the dynamics of a protostellar disk surrounding a star in acircular-orbit binary system. Our aim is to determine whether, if the disk isinitially tilted with respect to the plane of the binary orbit, the inclinationof the system will increase or decrease with time. The problem is formulated inthe binary frame in which the tidal potential of the companion star is static.We consider a steady, flat disk that is aligned with the binary plane andinvestigate its linear stability with respect to tilting or warpingperturbations. The dynamics is controlled by the competing effects of the m=0and m=2 azimuthal Fourier components of the tidal potential. In the presence ofdissipation, the m=0 component causes alignment of the system, while the m=2component has the opposite tendency. We find that disks that are sufficientlylarge, in particular those that extend to their tidal truncation radii, aregenerally stable and will therefore tend to alignment with the binary plane ona time-scale comparable to that found ...

  10. Three Dimensional Hydrodynamic Instabilities in Protostellar Disks with Cooling

    Science.gov (United States)

    Pickett, B. K.; Cassen, P.; Durisen, R. H.; Link, R.

    1997-05-01

    We present a series of extended three dimensional hydrodynamics calculations of protostellar cores in order to investigate the role of thermal energetics. One set of protostellar core models, denoted Hot Models, are isentropic equilibrium states formed by the axisymmetric collapse of uniformly rotating singular isothermal spheres. These objects are continuous star/disk systems, in which the star, the disk, and the star/disk boundary can be resolved in 3D in our hydrodynamics code. Since the disks of these equilibria are forced to have the same entropy as the stars, they are hotter than is typically considered appropriate for protostellar disks. Thus, the second set of models, denoted Cooled Models, are generated by first cooling the Hot Models in axisymmetry, and then calculating their subsequent nonaxisymmetric evolution. We compare evolutions of the Hot and Cooled models in which the disk is treated both adiabatically and isothermally, representing two extremes in cooling. The Hot models are marginally unstable to spiral disturbances that do not alter the protostellar core over many rotation periods. The Cooled models are highly unstable to multiple spirals, particularly two-armed spirals, which transport significant angular momentum and mass in a few dynamical times. In the isothermal evolution, the instability leads to the disruption of the disk and concentration of material into several dense, thin arcs. We compare these calculations with previous results and discuss the implications for star and solar system formation. This research is supported by grants NAGW-3399 DURISEN and RTOP 344-30-5101 CASSEN.

  11. Ejection of gaseous clumps from gravitationally unstable protostellar disks

    CERN Document Server

    Vorobyov, Eduard I

    2016-01-01

    We investigate the dynamics of gaseous clumps formed via gravitational fragmentation in young protostellar disks, focusing on the fragments that are ejected from the disk via many-body gravitational interaction. Numerical hydrodynamics simulations were employed to study the evolution of young protostellar disks formed from the collapse of rotating pre-stellar cores with mass in the 1.1-1.6 M_sun range. Protostellar disks formed in our models undergo gravitational fragmentation driven by continuing mass loading from parental collapsing cores. A few fragments can be ejected from the disk during the early evolution, but the low-mass fragments (< 15~M_Jup) disperse creating spectacular bow-type structures while passing through the disk and collapsing core. The least massive fragment that survived the ejection (21 M_Jup) straddles the planetary-mass limit, while the most massive ejected fragments (145 M_Jup) can break up into several pieces, leading to the ejection of wide separation binary clumps in the brown-...

  12. Signatures of Gravitational Instability in Resolved Images of Protostellar Disks

    CERN Document Server

    Dong, Ruobing; Pavlyuchenkov, Yaroslav; Chiang, Eugene; Liu, Hauyu Baobab

    2016-01-01

    Protostellar (class 0/I) disks, having masses comparable to those of their nascent host stars, and fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and mm-wave interferometry, we explore the observational signatures of GI in disks, using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and mm dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of AUs, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane, arms therefore scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. By contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes, such fragment...

  13. Turbulence and its effect on protostellar disk formation

    CERN Document Server

    Seifried, D; Klessen, R S

    2015-01-01

    We analyse simulations of turbulent, magnetised molecular cloud cores focussing on the formation of Class 0 stage protostellar discs and the physical conditions in their surroundings. We show that for a wide range of initial conditions Keplerian discs are formed in the Class 0 stage already. Furthermore, we show that the accretion of mass and angular momentum in the surroundings of protostellar discs occurs in a highly anisotropic manner, by means of a few narrow accretion channels. The magnetic field structure in the vicinity of the discs is highly disordered, revealing field reversals up to distances of 1000 AU. These findings demonstrate that as soon as even mild turbulent motions are included, the classical disc formation scenario of a coherently rotating environment and a well-ordered magnetic field breaks down.

  14. Magnetized Accretion and Dead Zones in Protostellar Disks

    CERN Document Server

    Dzyurkevich, Natalia; Henning, Thomas; Kley, Wilhelm

    2013-01-01

    The edges of magnetically-dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically-active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically-active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 $M_\\odot$, with corresponding adjustments in the disk mass and temperature. The dead zone's size and shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by S. Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, inclu...

  15. Wind-driven Accretion in Transitional Protostellar Disks

    CERN Document Server

    Wang, Lile

    2016-01-01

    Transitional protostellar disks have inner cavities heavily depleted in dust and gas, yet most show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities imply that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside such cavities are estimated for plausible X-ray and FUV radiation fields. The gas is molecular and predominantly neutral, with a dimensionless ambipolar parameter in the right general range for wind solutions of the type developed by K\\"onigl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but not so good that the magnetic flux need be dragged inward by the accreting neutrals.

  16. Are passive protostellar disks stable to self-shadowing?

    CERN Document Server

    Dullemond, C P

    2000-01-01

    The uniqueness and stability of irradiated flaring passive protostellar disks is investigated in the context of a simplified set of equations for the vertical height H as a function of radius R. It is found that the well-known flaring disk solution with H ~ R^{9/7} is not unique. Diverging solutions and asymptotically conical (H ~ R) solutions are also found. Moreover, using time-dependent linear perturbation analysis, it is found that the flaring disk solution may become unstable to self-shadowing. A local enhancement in the vertical height alters the functional form of irradiation grazing angle, and causes the 'sunny side' of the enhancement to grow and the 'shadow side' to collapse in a run-away fashion. This instability operates in regions of the disk in which the cooling time is much shorter than the vertical sound crossing time, which may occur in the outer regions of the passive irradiated disk if dust and gas are sufficiently strongly thermally coupled. Processes that may stabilize the disk, which inc...

  17. Turbulent Mixing and the Dead Zone in Protostellar Disks

    CERN Document Server

    Turner, N J; Dziourkevitch, N

    2006-01-01

    We investigate the conditions for the presence of a magnetically inactive dead zone in protostellar disks, using 3-D shearing-box MHD calculations including vertical stratification, Ohmic resistivity and time-dependent ionization chemistry. Activity driven by the magnetorotational instability fills the whole thickness of the disk at 5 AU, provided cosmic ray ionization is present, small grains are absent and the gas-phase metal abundance is sufficiently high. At 1 AU the larger column density of 1700 g/cm^2 means the midplane is shielded from ionizing particles and remains magnetorotationally stable even under the most favorable conditions considered. Nevertheless the dead zone is effectively eliminated. Turbulence mixes free charges into the interior as they recombine, leading to a slight coupling of the midplane gas to the magnetic fields. Weak, large-scale radial fields diffuse to the midplane where they are sheared out to produce stronger azimuthal fields. The resulting midplane accretion stresses are jus...

  18. The physical and chemical evolution of protostellar disks. The growth of protostellar disks: Progress to date

    Science.gov (United States)

    Stahler, Steven W.

    1993-01-01

    This study constitutes one part of our multi-disciplinary approach to the evolution of planet-forming disks. The goal is to establish the disks' thermal and mechanical properties as they grow by the infall of their parent interstellar clouds. Thus far, significant advances toward establishing the evolving surface density of such disks was made.

  19. Rapid Mid-Infrared Variability in Protostellar Disks

    CERN Document Server

    Ke, Te T; Lin, Douglas N C

    2011-01-01

    Spectral energy distribution (SED) in protostellar disks is determined by the disks'internal dissipation and reprocessing of irradiation from their host stars. Around T Tauri stars, most mid-infrared (MIR) radiation (in a few to a few ten {\\mu}m wavelength range) emerge from regions around a fraction to a few AU's. This region is interesting because it contains both the habitable zone and the snow line. Recent observations reveal that SED variations, in the MIR wavelength range. These variations are puzzling because they occur on time scale (a few days) which is much shorter than the dynamical (months to years) time scale at 1AU to a few AU's. They are probably caused by shadows casted by inner onto outer disk regions. Interaction between disks and their misaligned magnetized host stars can lead to warped structure and periodic SED modulations. Rapid aperiodic SED variations may also be induced by observed X-ray flares from T Tauri stars. These flares can significantly modulate the ionization fraction of the ...

  20. Wind-driven Accretion in Transitional Protostellar Disks

    Science.gov (United States)

    Wang, Lile; Goodman, Jeremy J.

    2017-01-01

    Transitional protostellar disks have inner cavities that are heavily depleted in dust and gas, yet most of them show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities suggest that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside these cavities are estimated for plausible X-ray and FUV radiation fields. The gas near the midplane is molecular and predominantly neutral, with a dimensionless ambipolar parameter in the right general range for wind solutions of the type developed by Königl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but it is not so good that the magnetic flux needs to be dragged inward by the accreting neutrals.

  1. Dust Transport in Protostellar Disks Through Turbulence and Settling

    CERN Document Server

    Turner, N J; Sano, T

    2009-01-01

    We apply ionization balance and MHD calculations to investigate whether magnetic activity moderated by recombination on dust can account for the mass accretion rates and the mid-infrared spectra and variability of protostellar disks. The MHD calculations use the stratified shearing-box approach and include grain settling and the feedback from the changing dust abundance on the resistivity of the gas. The two-decade spread in accretion rates among T Tauri stars is too large to result solely from variety in the grain size and stellar X-ray luminosity, but can be produced by varying these together with the disk magnetic flux. The diversity in the silicate bands can come from the coupling of grain settling to the distribution of the magneto-rotational turbulence, through three effects: (1) Recombination on grains yields a magnetically inactive dead zone extending above two scale heights, while turbulence in the magnetically active disk atmosphere overshoots the dead zone boundary by only about one scale height. (...

  2. Molecular Line Emission from Massive Protostellar Disks: Predictions for ALMA and the EVLA

    Energy Technology Data Exchange (ETDEWEB)

    Krumholz, M R; Klein, R I; McKee, C F

    2007-05-07

    We compute the molecular line emission of massive protostellar disks by solving the equation of radiative transfer through the cores and disks produced by the recent radiation-hydrodynamic simulations of Krumholz, Klein, & McKee. We find that in several representative lines the disks show brightness temperatures of hundreds of Kelvin over velocity channels {approx} 10 km s{sup -1} wide, extending over regions hundreds of AU in size. We process the computed intensities to model the performance of next-generation radio and submillimeter telescopes. Our calculations show that observations using facilities such as the EVLA and ALMA should be able to detect massive protostellar disks and measure their rotation curves, at least in the nearest massive star-forming regions. They should also detect significant sub-structure and non-axisymmetry in the disks, and in some cases may be able to detect star-disk velocity offsets of a few km s{sup -1}, both of which are the result of strong gravitational instability in massive disks. We use our simulations to explore the strengths and weaknesses of different observational techniques, and we also discuss how observations of massive protostellar disks may be used to distinguish between alternative models of massive star formation.

  3. THE ROLE OF TURBULENT MAGNETIC RECONNECTION IN THE FORMATION OF ROTATIONALLY SUPPORTED PROTOSTELLAR DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Santos-Lima, R.; De Gouveia Dal Pino, E. M. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, R. do Matao, 1226, Sao Paulo, SP 05508-090 (Brazil); Lazarian, A. [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)

    2012-03-01

    The formation of protostellar disks out of molecular cloud cores is still not fully understood. Under ideal MHD conditions, the removal of angular momentum from the disk progenitor by the typically embedded magnetic field may prevent the formation of a rotationally supported disk during the main protostellar accretion phase of low-mass stars. This has been known as the magnetic braking problem and the most investigated mechanism to alleviate this problem and help remove the excess of magnetic flux during the star formation process, the so-called ambipolar diffusion (AD), has been shown to be not sufficient to weaken the magnetic braking at least at this stage of the disk formation. In this work, motivated by recent progress in the understanding of magnetic reconnection in turbulent environments, we appeal to the diffusion of magnetic field mediated by magnetic reconnection as an alternative mechanism for removing magnetic flux. We investigate numerically this mechanism during the later phases of the protostellar disk formation and show its high efficiency. By means of fully three-dimensional MHD simulations, we show that the diffusivity arising from turbulent magnetic reconnection is able to transport magnetic flux to the outskirts of the disk progenitor at timescales compatible with the collapse, allowing the formation of a rotationally supported disk around the protostar of dimensions {approx}100 AU, with a nearly Keplerian profile in the early accretion phase. Since MHD turbulence is expected to be present in protostellar disks, this is a natural mechanism for removing magnetic flux excess and allowing the formation of these disks. This mechanism dismisses the necessity of postulating a hypothetical increase of the ohmic resistivity as discussed in the literature. Together with our earlier work which showed that magnetic flux removal from molecular cloud cores is very efficient, this work calls for reconsidering the relative role of AD in the processes of star

  4. IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk

    CERN Document Server

    Remijan, A J; Remijan, Anthony J.

    2006-01-01

    We report high spatial resolution VLA observations of the low-mass star-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH$_3$CH$_2$CN), methyl formate (CH$_3$OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emiss ion has a spatial scale of $\\sim20''$ and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of $\\sim6''$and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2$''$ that map $\\sim2''$ northeast of the A and B symmetry axis. The redshifted SiO is $\\sim2''$ northwest of blueshifted SiO along a position angle of $\\sim135^o$ which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive $\\sim$1.4 M$_{\\odot}$ interior to the SiO emission....

  5. Occurrence of instability through the protostellar accretion disks by landing of low-mass condensations

    CERN Document Server

    Elyasi, Mahjubeh

    2016-01-01

    Low-mass condensations (LMCs) are observed inside the envelope of the collapsing molecular cloud cores. In this research, we investigate the effects of landing LMCs for occurrence of instability through the protostellar accretion disks. We consider some regions of the disk where duration of infalling and landing of the LMCs are shorter than the orbital period. In this way, we can consider the landing LMCs as density bumps and grooves in the azimuthal direction of an initial thin axisymmetric steady state self-gravitating protostellar accretion disk (nearly Keplerian). Using the linear effects of the bump quantities, we obtain a characteristic equation for growth/decay rate of bumps; we numerically solve it to find occurrence of instability. We also evaluate the minimum-growth-time-scale (MGTS) and the enhanced mass accretion rate. The results show that infalling and landing of the LMCs in the inner regions of the protostellar accretion disks can cause faster unstable modes and less enhanced accretion rates re...

  6. Embedded protostellar disks around (sub-)solar stars. II. Disk masses, sizes, densities, temperatures and the planet formation perspective

    CERN Document Server

    Vorobyov, Eduard I

    2011-01-01

    We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 Msun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M_{d,C0}^{mean}=0.12 Msun, M_{d,C0}^{mdn}=0.09 Msun and M_{d,CI}^{mean}=0.18 Msun, M_{d,CI}^{mdn}=0.15 Msun, respectively) are greater than those inferred from observations by (at least) a factor of 2--3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M_st=0.05-0.1 Msun. Concurrently, disk r...

  7. The Location of the Snow Line in Protostellar Disks

    CERN Document Server

    Podolak, Morris

    2009-01-01

    The snow line in a gas disk is defined as the distance from the star beyond which the water ice is stable against evaporation. Since oxygen is the most abundant element after hydrogen and helium, the presence of ice grains can have important consequences for disk evolution. However, determining the position of the snow line is not simple. I discuss some of the important processes that affect the position of the snow line.

  8. Testing protostellar disk formation models with ALMA observations

    CERN Document Server

    Harsono, Daniel; Bruderer, Simon; Li, Zhi-Yun; Jorgensen, Jes

    2015-01-01

    Abridged: Recent simulations have explored different ways to form accretion disks around low-mass stars. We aim to present observables to differentiate a rotationally supported disk from an infalling rotating envelope toward deeply embedded young stellar objects and infer their masses and sizes. Two 3D magnetohydrodynamics (MHD) formation simulations and 2D semi-analytical model are studied. The dust temperature structure is determined through continuum radiative transfer RADMC3D modelling. A simple temperature dependent CO abundance structure is adopted and synthetic spectrally resolved submm rotational molecular lines up to $J_{\\rm u} = 10$ are simulated. All models predict similar compact components in continuum if observed at the spatial resolutions of 0.5-1$"$ (70-140 AU) typical of the observations to date. A spatial resolution of $\\sim$14 AU and high dynamic range ($> 1000$) are required to differentiate between RSD and pseudo-disk in the continuum. The peak-position velocity diagrams indicate that the...

  9. Three Dimensional Hydrodynamics of Protostars and Protostellar Disks

    Science.gov (United States)

    Pickett, Brian Keith

    1995-01-01

    Stars form when a rotating cloud of gas and dust collapses under the influence of its own gravity. Modern studies of the collapse and fragmentation of rotating protostellar clouds suggest a wide variety of outcomes, depending on the assumed initial conditions. The post-collapse objects are subject to dynamic instabilities which may produce significant mass and angular momentum transport or, if violent enough, could lead to the breakup of the original object. I have considered the isentropic equilibrium states that might form from the collapse of uniformly rotating spherical clouds. By varying the central concentration of the assumed initial cloud, I obtain equilibrium states distinguished primarily by their different specific angular momentum distributions. Using a new code to generate the axisymmetric equilibrium states and an improved adiabatic 3D hydrodynamics code to evolve them, I have investigated the onset and nature of global dynamic instabilities in these objects. The objects corresponding to uniform initial conditions are unstable to barlike distortions at high rotation rates. These instabilities are vigorous and lead to violent ejection of mass and angular momentum. In contrast, the rapidly rotating equilibrium objects that correspond to highly centrally condensed initial clouds are subject to low-order spiral instabilities. In extremely flattened models, one -armed spirals dominate all other disturbances but do not lead to fragmentation. Significant amounts of angular momentum can be transported on very short time scales; in the most extreme case, 30% of the total angular momentum is moved from the central regions outward in about half a year. Even when the instabilities do not lead to transport or ejection of material, the original object can be significantly restructured, leading to flaring and surface distortions at large radii. The central concentration of the assumed initial cloud appears to be a good predictor of the dynamic instabilities which

  10. Signatures of Young Planets in the Continuum Emission From Protostellar Disks

    CERN Document Server

    Isella, Andrea

    2016-01-01

    (Abridged) Many protostellar disks show central cavities, rings, or spiral arms that could be caused by low-mass stellar or planetary companions. Few of these features are yet conclusively tied to objects embedded in the disks, perhaps because of shortcomings in our understanding of what a disk interacting with a planet looks like at the wavelengths we observe. We approach these issues noting that even small features on the disk's surface cast shadows, because the starlight grazes the surface at low angles. We therefore focus on accurately computing the disk's thickness, and thus its temperature. The embedded planet has 20, 100, or 1000~M$_\\oplus$, ranging from barely enough to perturb the disk gas surface density significantly, to able to clear a deep tidal gap. We compare models that are in hydrostatic equilibrium in the vertical direction to models where the disk pressure scale height varies as a power of the orbital radius. The hydrostatic balance makes a large difference to the disk's temperature and app...

  11. Protostellar Disk Formation Enabled by Removal of Small Dust Grains

    CERN Document Server

    Zhao, Bo; Li, Zhi-Yun; Krasnopolsky, Ruben; Shang, Hsien; Nakamura, Fumitaka

    2016-01-01

    It has been shown that a realistic level of magnetization of dense molecular cloud cores can suppress the formation of a rotationally supported disk (RSD) through catastrophic magnetic braking in the axisymmetric ideal MHD limit. In this study, we present conditions for the formation of RSDs through non-ideal MHD effects computed self-consistently from an equilibrium chemical network. We find that removing from the standard MRN distribution the large population of very small grains (VSGs) of ~10 $\\AA$ to few 100 $\\AA$ that dominate the coupling of the bulk neutral matter to the magnetic field increases the ambipolar diffusivity by ~1--2 orders of magnitude at densities below 10$^{10}$ cm$^{-3}$. The enhanced ambipolar diffusion (AD) in the envelope reduces the amount of magnetic flux dragged by the collapse into the circumstellar disk-forming region. Therefore, magnetic braking is weakened and more angular momentum can be retained. With continuous high angular momentum inflow, RSDs of tens of AU are able to f...

  12. Resistive double-diffusive instability in the dead-zones of protostellar disks

    CERN Document Server

    Latter, Henrik N; Balbus, Steven A

    2010-01-01

    We outline a novel linear instability that may arise in the dead-zones of protostellar disks, and possibly the fluid interiors of planets and protoplanets. In essence it is an axisymmetric buoyancy instability, but one that would not be present in a purely hydrodynamical gas. The necessary ingredients for growth include a negative radial entropy gradient (of any magnitude), weak magnetic fields, and efficient resistive diffusion (in comparison with thermal diffusion). The character of the instability is local, axisymmetric, and double-diffusive, and it attacks lengths much shorter than the resistive scale. Like the axisymmetric convective instability, it draws its energy from the negative radial entropy gradient; but by utilising the diffusing magnetic field, it can negate the stabilising influence of rotation. Its nonlinear saturated state, while not transporting appreciable angular momentum, could drive radial and vertical mixing, which may influence the temperature structure of the disk, dust dynamics and,...

  13. The instability of viscous self-gravitating protostellar disk affected by density bump

    Science.gov (United States)

    Elyasi, Mahjubeh; Nejad-Asghar, Mohsen

    2017-09-01

    In this work, we study the instability of viscous self-gravitating protostellar disk affected by infalling Low-mass condensations (LMCs) from the envelope of collapsing molecular cloud cores. The infalling low-mass-condensations (LMCs) are considered as density bumps through the nearly Keplerian viscous accretion disk, and their evolutions are analyzed by using the linear perturbation approximation. We investigate occurrence of instability in the evolution of these density bumps. We find the unstable regions of the bumped accretion disk and evaluate the growth time scale (GTS) of the instability. We also study the radial accretion and azimuthal rotation in these unstable regions. The results show that the GTS will be minimum at a special radius so that the unstable regions can be divided in two parts (inner and outer regions). The perturbed radial and azimuthal velocities in the inner unstable regions are strengthened, while in the outer unstable regions are weakened. Decreasing the radial and azimuthal velocities in the outer unstable regions may lead to coagulation of matters. This effect can help the fragmentation of the disk and formation of the self-gravitating bound objects.

  14. Protostellar Disk Evolution Over Million-Year Timescales with a Prescription for Magnetized Turbulence

    CERN Document Server

    Landry, Russell; Turner, Neal J; Abram, Greg

    2013-01-01

    Magnetorotational instability (MRI) is the most promising mechanism behind accretion in low-mass protostellar disks. Here we present the first analysis of the global structure and evolution of non-ideal MRI-driven T-Tauri disks on million-year timescales. We accomplish this in a 1+1D simulation by calculating magnetic diffusivities and utilizing turbulence activity criteria to determine thermal structure and accretion rate without resorting to a 3-D magnetohydrodynamical (MHD) simulation. Our major findings are as follows. First, even for modest surface densities of just a few times the minimum-mass solar nebula, the dead zone encompasses the giant planet-forming region, preserving any compositional gradients. Second, the surface density of the active layer is nearly constant in time at roughly 10 g/cm2, which we use to derive a simple prescription for viscous heating in MRI-active disks for those who wish to avoid detailed MHD computations. Furthermore, unlike a standard disk with constant-alpha viscosity, t...

  15. Evolution of CO lines in time-dependent models of protostellar disk formation

    CERN Document Server

    Harsono, Daniel; Bruderer, Simon; van Dishoeck, Ewine F; Kristensen, Lars E

    2013-01-01

    (Abridged) Star and planet formation theories predict an evolution in the density, temperature, and velocity structure as the envelope collapses and forms an accretion disk. The aim of this work is to model the evolution of the molecular excitation, line profiles, and related observables during low-mass star formation. Specifically, the signatures of disks during the deeply embedded stage are investigated. Semi-analytic 2D axisymmetric models have been used to describe the evolution of the density, stellar mass, and luminosity from the pre-stellar to the T-Tauri phase. A full radiative transfer calculation is carried out to accurately determine the time-dependent dust temperatures and CO abundance structure. We present non-LTE near-IR, FIR, and submm lines of CO have been simulated at a number of time steps. In contrast to the dust temperature, the CO excitation temperature derived from submm/FIR lines does not vary during the protostellar evolution, consistent with C18O observations obtained with Herschel an...

  16. Revolutionizing our View of Protostellar Multiplicity and Disks: The VLA Nascent Disk and Multiplicity (VANDAM) Survey of the Perseus Molecular Cloud

    CERN Document Server

    Tobin, John J; Li, Zhi-Yun; Chandler, Claire J; Dunham, Michael M; Segura-Cox, Dominique; Cox, Erin G; Harris, Robert J; Melis, Carl; Sadavoy, Sarah I; Pérez, Laura; Kratter, Kaitlin

    2016-01-01

    There is substantial evidence for disk formation taking place during the early stages of star formation and for most stars being born in multiple systems; however, protostellar multiplicity and disk searches have been hampered by low resolution, sample bias, and variable sensitivity. We have conducted an unbiased, high-sensitivity Karl G. Jansky Very Large Array (VLA) survey toward all known protostars (n = 94) in the Perseus molecular cloud (d~230 pc), with a resolution of ~15 AU (0.06") at 8 mm. We have detected candidate protostellar disks toward 17 sources (with 12 of those in the Class 0 stage) and we have found substructure on < 50AU scales for three Class 0 disk candidates, possibly evidence for disk fragmentation. We have discovered 16 new multiple systems (or new components) in this survey; the new systems have separations < 500 AU and 3 by < 30 AU. We also found a bi-modal distribution of separations, with peaks at ~75 AU and ~3000 AU, suggestive of formation through two distinct mechanisms...

  17. Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE

    CERN Document Server

    Takakuwa, Shigehisa; Saigo, Kazuya; Matsumoto, Tomoaki; Lim, Jeremy; Hanawa, Tomoyuki; Ho, Paul T P

    2014-01-01

    We report the ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6 times higher resolution and a ~6 times higher sensitivity than those of our previous SMA observations, which revealed a r ~300 AU-scale circumbinary disk in Keplerian rotation. The 0.9-mm continuum shows two opposing U-shaped brightenings in the circumbinary disk, and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly-observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust featur...

  18. ALMA observations of the Th 28 protostellar disk - A new exemple of counter-rotation between disk and optical jet

    CERN Document Server

    Louvet, F; Cabrit, S; Hales, A; Pinte, C; Menard, F; Bacciotti, F; Coffey, D; Mardones, D; Bronfman, L; Gueth, F

    2016-01-01

    Differences in Doppler shifts across the base of four close classical T-Tauri star jets have been detected with the HST in optical and NUV emission lines, and interpreted as rotation signatures under the assumption of steady state flow. To support this interpretation, it is necessary that the underlying disks rotate in the same sense. Agreement between disk rotation and jet rotation determined from optical lines has been verified in two cases and rejected in one. We propose here to perform this test on the fourth system, Th 28. We present ALMA high angular resolution Band 7 continuum, 12CO(2-1) and 13CO(2-1) observations of the circumstellar disk around the T-Tauri star Th 28. The sub-arcsecond angular resolution (0.46"x0.37") and high-sensitivity reached enable us to detect in CO and continuum clear signatures of a disk in Keplerian rotation around Th28. The 12CO emission allows us to derive estimates of disk position angle and inclination. The large velocity separation of the peaks in 12CO combined with the...

  19. Chemistry of protostellar envelopes and disks: computational testing of 2D abundances

    Science.gov (United States)

    Flores Rivera, Lizxandra; Willacy, Karen; Terebey, Susan

    2017-01-01

    Molecule formation is dynamic during the protostar collapse phase, driven by changes in temperature, density, and UV radiation as gas and dust flows from the envelope onto the forming protoplanetary disk. In this work, we use a chemistry model to generate fractional abundances of water and carbon monoxide using primarily as input parameters the temperature and density profile produced by the dust radiative transfer model HOCHUNK3D (Whitney et al. 2013). Contour maps are presented showing the meridional temperature, density, and fractional abundance at different outer radii. High concentrations of gas phase molecules are found within 5 AU of the star along with high temperatures in the same spatial region. Shielding by the disk leads to colder temperatures outside 10 AU near the disk mid-plane. In this region, CO freezes out onto grains and shows a much reduced abundance. Water remains solid almost everywhere during the infall and evaporates within ~10 AU.

  20. Protostellar disk formation and transport of angular momentum during magnetized core collapse

    CERN Document Server

    Joos, Marc; Ciardi, Andrea

    2012-01-01

    Theoretical studies of collapsing clouds found that the presence of a relatively strong magnetic field may prevent the formation of disks and their fragmentation. However most previous studies have been limited to cases where the magnetic field and the rotation axis of the cloud are aligned. We study the transport of angular momentum, and the effects on disk formation, for non-aligned initial configurations, and for a range magnetic intensities. We perform three-dimensional, adaptive mesh, numerical simulations of magnetically supercritical collapsing dense cores using the magneto-hydrodynamic code Ramses. At variance to earlier analysis, we show that the transport of angular momentum acts less efficiently in collapsing cores with non-aligned rotation and magnetic field. Analytically this result can be understood by taking into account the bending of field lines occurring during the gravitational collapse. We find that massive disks, containing at least 10% of the intial core mass, can form during the earlies...

  1. Coupling protoplanetary disk formation with early protostellar evolution: influence on planet traps

    Science.gov (United States)

    Baillie, Kevin; Piau, Laurent

    2016-10-01

    Protoplanetary disk structures are known to be shaped by various thermal and compositional effects such as (though not limited to) shadowed regions, sublimation lines, density bumps... The resulting irregularities in the surface mass density and temperature profiles are key elements to determine the location where planetary embryos can be trapped. These traps provide hints of which planets are most likely to survive, at what distance from the star, and potentially with what composition (Baillié, Charnoz, Pantin, 2015, A&A 577, A65; Baillié, Charnoz, Pantin, 2016, A&A 590, A60). These structures are determined by the viscous spreading of the disk, that is initially formed by the collapse of the molecular cloud.Starting from the numerical hydrodynamical model detailed in Baillié & Charnoz., 2014, ApJ 786, 35 which couples the disk thermodynamics, its photosphere geometry, its dynamics and its dust composition in order to follow its long-term evolution, we now consider the early stages of the central star. We model the joint formation of the disk and the star: their mass are directly derived from the collapse of the molecular cloud while the star temperature, radius and brightness are interpolated over pre-calculated stellar evolutions. Therefore, our simulations no longer depend on the initial profile of the "Minimum Mass Solar Nebula", and allow us to model the influence of the forming star on the protoplanetary disk. In particular, we will present the resulting distribution of the sublimation lines of the main dust species, as well as the locations of the planet traps at various disk ages. In the longer term, we intend to investigate the influence of the star properties on the selection of the surviving planets.

  2. ALMA observations of the Th 28 protostellar disk. A new example of counter-rotation between disk and optical jet

    Science.gov (United States)

    Louvet, F.; Dougados, C.; Cabrit, S.; Hales, A.; Pinte, C.; Ménard, F.; Bacciotti, F.; Coffey, D.; Mardones, D.; Bronfman, L.; Gueth, F.

    2016-12-01

    Aims: Recently, differences in Doppler shifts across the base of four close classical T Tauri star jets have been detected with the HST in optical and near-ultraviolet (NUV) emission lines, and these Doppler shifts were interpreted as rotation signatures under the assumption of steady state flow. To support this interpretation, it is necessary that the underlying disks rotate in the same sense. Agreement between disk rotation and jet rotation determined from optical lines has been verified in two cases and rejected in one case. Meanwhile, the near-ultraviolet lines, which may trace faster and more collimated inner spines of the jet than optical lines, either agree or show no clear indication. We propose to perform this test on the fourth system, Th 28. Methods: We present ALMA high angular resolution Band 7 continuum, 12CO(3-2) and 13CO(2-1) observations of the circumstellar disk around the T Tauri star Th 28. Results: The sub-arcsecond angular resolution (0.46''× 0.37'') and high sensitivity reached enable us to detect, in CO and continuum, clear signatures of a disk in Keplerian rotation around Th 28. The 12CO emission is clearly resolved, allowing us to derive estimates of disk position angle and inclination. The large velocity separation of the peaks in 12CO, combined with the resolved extent of the emission, indicate a central stellar mass in the range 1-2 M⊙. The rotation sense of the disk is well detected in both 13CO and 12CO emission lines, and this direction is opposite to that implied by the transverse Doppler shifts measured in the optical lines of the jet. Conclusions: The Th 28 system is now the second system, among the four investigated so far, where counter-rotation between the disk and the optical jet is detected. These findings imply either that optical transverse velocity gradients detected with HST do not trace jet rotation or that modeling the flow with the steady assumption is not valid. In both cases jet rotation studies that rely solely

  3. Molecule survival in magnetized protostellar disk winds. I. Chemical model and first results

    CERN Document Server

    Panoglou, D; Forets, G Pineau des; Garcia, P J V; Ferreira, J; Casse, F

    2011-01-01

    Molecular counterparts to atomic jets have been detected within 1000 AU of young stars. Reproducing them is a challenge for proposed ejection models. We explore whether molecules may survive in an MHD disk wind invoked to reproduce the kinematics and tentative rotation signatures of atomic jets in T Tauri stars. The coupled ionization, chemical and thermal evolution along dusty flow streamlines is computed for a prescribed MHD disk wind solution, using a method developed for magnetized shocks in the interstellar medium. Irradiation by wind-attenuated coronal X-rays and FUV photons from accretion hot spots is included, with self-shielding of H2 and CO. Disk accretion rates of 5e-6, 1e-6 and 1e-7 solar masses per year are considered, representative of low-mass young protostars (Class 0), evolved protostars (Class I) and very active T Tauri stars (Class II). The disk wind has an onion-like thermo-chemical structure, with streamlines launched from larger radii having lower temperature and ionisation, and higher H...

  4. Dead, Undead and Zombie Zones in Protostellar Disks as a Function of Stellar Mass

    CERN Document Server

    Mohanty, Subhanjoy; Turner, Neal J

    2012-01-01

    We investigate the viability of the magnetorotational instability (MRI) in accretion disks around both solar-type stars and very low mass stars. In particular, we determine the disk regions where the MRI can be shut off either by Ohmic resistivity (the so-called Dead and Undead Zones) or by ampipolar diffusion (a region we term the Zombie Zone). We consider 2 stellar masses: Mstar = 0.7 and 0.1 Msun. In each case, we assume that: the disk surface density profile is that of a scaled Minimum Mass Solar Nebula, with Mdisk/Mstar ~ 0.01 as currently estimated; disk ionisation is driven primarily by stellar X-rays, complemented by cosmic rays and radionuclides; and the stellar X-ray luminosity scales with bolometric luminosity as Lx/Lstar ~ 10^-3.5, as observed. Ionization rates are calculated with the MOCCASIN code, and ionisation balance determined using a simplified chemical network, including well-mixed 0.1 um grains at various levels of depletion. We find that (1) ambipolar diffusion is the primary factor cont...

  5. Do siblings always form and evolve simultaneously? Testing the coevality of multiple protostellar systems through SEDs

    CERN Document Server

    Murillo, Nadia M; Tobin, John J; Fedele, Davide

    2016-01-01

    Multiplicity is common in field stars and among protostellar systems. Models suggest two paths of formation: turbulent fragmentation and protostellar disk fragmentation. We attempt to find whether or not the coevality frequency of multiple protostellar systems can help to better understand their formation mechanism. The coevality frequency is determined by constraining the relative evolutionary stages of the components in a multiple system. SEDs for known multiple protostars in Perseus were constructed from literature data. Herschel PACS photometric maps were used to sample the peak of the SED for systems with separations >7", a crucial aspect in determining the evolutionary stage of a protostellar system. Inclination effects and the surrounding envelope and outflows were considered to decouple source geometry from evolution. This together with the shape and derived properties from the SED was used to determine each system's coevality as accurately as possible. SED models were used to examine the frequency of...

  6. ENVIRONMENT AND PROTOSTELLAR EVOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yichen [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Tan, Jonathan C., E-mail: yczhang.astro@gmail.com [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)

    2015-04-01

    Even today in our Galaxy, stars form from gas cores in a variety of environments, which may affect the properties of the resulting star and planetary systems. Here, we study the role of pressure, parameterized via ambient clump mass surface density, on protostellar evolution and appearance, focusing on low-mass Sun-like stars and considering a range of conditions from relatively low pressure filaments in Taurus, to intermediate pressures of cluster-forming clumps like the Orion Nebula Cluster, to very high pressures that may be found in the densest infrared dark clouds or in the Galactic center. We present unified analytic and numerical models for the collapse of prestellar cores, accretion disks, protostellar evolution, and bipolar outflows, coupled with radiative transfer calculations and a simple astrochemical model to predict CO gas-phase abundances. Prestellar cores in high-pressure environments are smaller and denser and thus collapse with higher accretion rates and efficiencies, resulting in higher luminosity protostars with more powerful outflows. The protostellar envelope is heated to warmer temperatures, affecting infrared morphologies (and thus classification) and astrochemical processes like CO depletion onto dust grain ice mantles (and thus CO morphologies). These results have general implications for star and planet formation, especially via their effect on astrochemical and dust grain evolution during infall to and through protostellar accretion disks.

  7. Protostellar Outflows

    Science.gov (United States)

    Bally, John

    2016-09-01

    Outflows from accreting, rotating, and magnetized systems are ubiquitous. Protostellar outflows can be observed from radio to X-ray wavelengths in the continuum and a multitude of spectral lines that probe a wide range of physical conditions, chemical phases, radial velocities, and proper motions. Wide-field visual and near-IR data, mid-IR observations from space, and aperture synthesis with centimeter- and millimeterwave interferometers are revolutionizing outflow studies. Many outflows originate in multiple systems and clusters. Although most flows are bipolar and some contain highly collimated jets, others are wide-angle winds, and a few are nearly isotropic and exhibit explosive behavior. Morphologies and velocity fields indicate variations in ejection velocity, mass-loss rate, and in some cases, flow orientation and degree of collimation. These trends indicate that stellar accretion is episodic and often occurs in a complex dynamical environment. Outflow power increases with source luminosity but decreases with evolutionary stage. The youngest outflows are small and best traced by molecules such as CO, SiO, H2O, and H2. Older outflows can grow to parsec scales and are best traced by shock-excited atoms and ions such as hydrogen-recombination lines, [Sii], and [Oii]. Outflows inject momentum and energy into their surroundings and provide an important mechanism in the self-regulation of star formation. However, momentum injection rates remain uncertain with estimates providing lower bounds.

  8. Environment and Protostellar Evolution

    CERN Document Server

    Zhang, Yichen

    2014-01-01

    Even today in our Galaxy, stars form from gas cores in a variety of environments, which may affect the properties of resulting star and planetary systems. Here we study the role of pressure, parameterized via ambient clump mass surface density, on protostellar evolution and appearance, focussing on low-mass, Sun-like stars and considering a range of conditions from relatively low pressure filaments in Taurus, to intermediate pressures of cluster-forming clumps like the Orion Nebula Cluster (ONC), to very high pressures that may be found in the densest Infrared Dark Clouds (IRDCs) or in the Galactic Center (GC). We present unified analytic and numerical models for collapse of prestellar cores, accretion disks, protostellar evolution and bipolar outflows, coupled to radiative transfer (RT) calculations and a simple astrochemical model to predict CO gas phase abundances. Prestellar cores in high pressure environments are smaller and denser and thus collapse with higher accretion rates and efficiencies, resulting...

  9. Molecule survival in magnetized protostellar disk winds. II. Predicted H2O line profiles versus Herschel/HIFI observations

    CERN Document Server

    Yvart, W; Forets, G Pineau des; Ferreira, J

    2016-01-01

    We investigate whether the broad wings of H2O emission identified with Herschel towards low-mass Class 0 and Class 1 protostars may be consistent with an origin in a dusty MHD disk wind, and the constraints it would set on the underlying disk properties. We present synthetic H2O line profiles predictions for a typical MHD disk wind solution with various values of disk accretion rate, stellar mass, extension of the launching area, and view angle. We compare them in terms of line shapes and intensities with the HIFI profiles observed by the WISH Key Program. We find that a dusty MHD disk wind launched from 0.2--0.6 AU AU to 3--25 AU can reproduce to a remarkable degree the observed shapes and intensities of the broad H2O component, both in the fundamental 557 GHz line and in more excited lines. Such a model also readily reproduces the observed correlation of 557 GHz line luminosity with envelope density, if the infall rate at 1000 AU is 1--3 times the disk accretion rate in the wind ejection region. It is also ...

  10. A Sub-arcsecond Survey Toward Class 0 Protostars in Perseus: Searching for Signatures of Protostellar Disks

    CERN Document Server

    Tobin, John J; Wilner, David J; Kwon, Woojin; Chandler, Claire J; Bourke, Tyler L; Loinard, Laurent; Chiang, Hsin-Fang; Schnee, Scott; Chen, Xuepeng

    2015-01-01

    We present a CARMA 1.3 mm continuum survey toward 9 Class 0 protostars in the Perseus molecular cloud at $\\sim$0.3$^{\\prime\\prime}$ (70 AU) resolution. This study approximately doubles the number of Class 0 protostars observed with spatial resolutions $$ 100 AU around 2 sources (L1448 IRS2 and Per-emb-14) and these sources may be strong disk candidates. Marginally-resolved structures with position angles within 30$^{\\circ}$ of perpendicular to the outflow are found toward 3 protostars (L1448 IRS3C, IRAS 03282+3035, and L1448C) and are considered disk candidates. Two others (L1448 IRS3B and IRAS 03292+3039) have resolved structure, possibly indicative of massive inner envelopes or disks; L1448 IRS3B also has a companion separated by 0.9$^{\\prime\\prime}$ ($\\sim$210 AU). IC348-MMS does not have well-resolved structure and the candidate first hydrostatic core L1451-MMS is marginally resolved on 1$^{\\prime\\prime}$ scales. The strong disk candidate sources were followed-up with C$^{18}$O ($J=2\\rightarrow1$) observa...

  11. Gravitoturbulence in magnetised protostellar discs

    CERN Document Server

    Riols, A

    2016-01-01

    Gravitational instability (GI) features in several aspects of protostellar disk evolution, most notably in angular momentum transport, fragmentation, and the outbursts exemplified by FU Ori and EX Lupi systems. The outer regions of protostellar discs may also be coupled to magnetic fields, which could then modify the development of GI. To understand the basic elements of their interaction, we perform local 2D ideal and resistive MHD simulations with an imposed toroidal field. In the regime of moderate plasma beta, we find that the system supports a hot gravito-turbulent state, characterised by considerable magnetic energy and stress and a surprisingly large Toomre parameter $Q~10$. This result has potential implications for disk structure, vertical thickness, ionisation, etc. Our simulations also reveal the existence of long-lived and dense `magnetic islands' or plasmoids. Lastly, we find that the presence of a magnetic field has little impact on the fragmentation criterion of the disk. Though our focus is on...

  12. Herbig stars' near-infrared excess: An origin in the protostellar disk's magnetically supported atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Turner, N. J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Benisty, M.; Dullemond, C. P. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Hirose, S., E-mail: neal.turner@jpl.nasa.gov [Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showamachi, Kanazawa-ku, Yokohama, Kanagawa 236-0001 (Japan)

    2014-01-01

    Young stars with masses 2-8 times solar, the Herbig Ae and Be stars, often show a near-infrared excess too large to explain with a hydrostatically supported circumstellar disk of gas and dust. At the same time, the accretion flow carrying the circumstellar gas to the star is thought to be driven by magnetorotational turbulence, which, according to numerical MHD modeling, yields an extended low-density atmosphere supported by the magnetic fields. We demonstrate that the base of the atmosphere can be optically thick to the starlight and that the parts lying near 1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generate synthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities for submicron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructed recently by Mulders and Dominik and, in particular, match the large near-infrared flux, provided the grains have a mass fraction close to interstellar near the disk's inner rim.

  13. High spatial resolution IR observations of young stellar objects - A possible disk surrounding HL Tauri

    Science.gov (United States)

    Grasdalen, G. L.; Strom, S. E.; Strom, K. M.; Capps, R. W.; Thompson, D.; Castelaz, M.

    1984-01-01

    High spatial resolution images of the T Tauri star HL Tau were obtained at 1.6 microns and 2.2 microns. The original images as well as maximum entropy image reconstructions reveal a circumstellar envelope structure, similar at both wavelenghts, and extended along P.A. = 112 deg; the 10 percent width of the structure is 1.9 sec (300 AU at 160 pc). The extended structure is interpreted as light scattered toward earth by dust in a disk surrounding this young stellar object. Polarization measurements made at 2.2 microns support this hypothesis. The total solid particle mass is, at minimum, 5 x 10 to the -7th solar mass.

  14. A Substantial Dust Disk Surrounding an Actively Accreting First-Ascent Giant Star

    CERN Document Server

    Melis, C; Song, I; Rhee, J H; Metchev, S

    2009-01-01

    We report identification of the first unambiguous example of what appears to be a new class of first-ascent giant stars that are actively accreting gas and dust and that are surrounded by substantial dusty disks. These old stars, who are nearing the end of their lives, are experiencing a rebirth into characteristics typically associated with newborn stars. The F2-type first-ascent giant star TYC 4144 329 2 is in a wide separation binary system with an otherwise normal G8 IV star, TYC 4144 329 1. From Keck near-infrared imaging and high-resolution spectroscopy we are able to determine that these two stars are $\\sim$1 Gyr old and reside at a distance of $\\sim$550 pc. One possible explanation for the origin of the accreting material is common-envelope interaction with a low-mass stellar or sub-stellar companion. The gaseous and dusty material around TYC 4144 329 2, as it is similar to the primordial disks observed around young classical T Tauri stars, could potentially give rise to a new generation of planets an...

  15. Variable protostellar accretion with episodic bursts

    CERN Document Server

    Vorobyov, Eduard I

    2015-01-01

    We present the latest development of the disk gravitational instability and fragmentation model, originally introduced by us to explain episodic accretion bursts in the early stages of star formation. Using our numerical hydrodynamics model with improved disk thermal balance and star-disk interaction, we computed the evolution of protostellar disks formed from the gravitational collapse of prestellar cores. In agreement with our previous studies, we find that cores of higher initial mass and angular momentum produce disks that are more favorable to gravitational instability and fragmentation, while a higher background irradiation and magnetic fields moderate the disk tendency to fragment. The protostellar accretion in our models is time-variable, thanks to the nonlinear interaction between different spiral modes in the gravitationally unstable disk, and can undergo episodic bursts when fragments migrate onto the star owing to the gravitational interaction with other fragments or spiral arms. Most bursts occur...

  16. MISALIGNMENT OF MAGNETIC FIELDS AND OUTFLOWS IN PROTOSTELLAR CORES

    Energy Technology Data Exchange (ETDEWEB)

    Hull, Charles L. H.; Plambeck, Richard L.; Bower, Geoffrey C.; Heiles, Carl; Meredith Hughes, A. [Astronomy Department and Radio Astronomy Laboratory, University of California, Berkeley, CA 94720-3411 (United States); Bolatto, Alberto D.; Jameson, Katherine; Mundy, Lee; Pound, Marc W. [Astronomy Department and Laboratory for Millimeter-wave Astronomy, University of Maryland, College Park, MD 20742 (United States); Carpenter, John M.; Lamb, James W.; Pillai, Thushara [Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125 (United States); Crutcher, Richard M.; Hakobian, Nicholas S.; Kwon, Woojin; Looney, Leslie W. [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W Green Street, Urbana, IL 61801 (United States); Fiege, Jason D.; Franzmann, Erica [Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2 (Canada); Houde, Martin [Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7 (Canada); Matthews, Brenda C., E-mail: chat@astro.berkeley.edu [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd., Victoria, BC V8P 5C2 (Canada); and others

    2013-05-10

    We present results of {lambda}1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with {approx}2.''5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of {approx}1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they formed.

  17. Morphologically complex protostellar envelopes : structure and kinematics

    Science.gov (United States)

    Tobin, John J.

    I present an in-depth study of protostars and their surrounding envelopes of dense gas and dust, using a multitude of observational methods to reveal new details of the star formation process. I use mid-infrared imaging from the Spitzer Space Telescope, combined with photometry spanning the near-infrared to millimeter wavelengths, to construct a model of the L1527 protostellar system. I modeled both the spectral energy distribution and resolved scattered light images to determine physical properties of the protostellar system. The nature of the apparent central point source in the Spitzer images was uncertain until high-resolution L-band imaging from the Gemini observatory resolved the point source into a disk in scattered light, having a radius of 200 AU. Protostellar envelopes are also often found to cast shadows against the 8 micron Galactic background in Spitzer imaging, enabling direct probes of envelope structure. The shadow images show that the dense envelopes around twenty-two Class 0 protostars are generally morphologically complex from 0.1 pc scales down to ˜1000 AU; they are often filamentary, and frequently non-axisymmetric. The observed envelope structure indicates a likely origin in turbulent cloud structure rather than a quasi-static/equilibrium formation. The complex envelope structure also may indicate an increased likelihood of fragmentation during collapse, forming close binaries. To further characterize these envelopes, I have observed them in the dense molecular gas tracers nthp and nht, both of which closely follow the 8 micron extinction morphology. The magnitude of the velocity gradients and envelope complexity on ˜10000 AU scales indicates that the velocity structure may reflect large-scale infall in addition to the often assumed rotation. Comparisons with three-dimensional filamentary and symmetric rotating collapse models reinforce the interpretation of velocities reflecting large-scale infall, showing that the structure of the envelope

  18. Morphologies of protostellar outflows: An ALMA view

    CERN Document Server

    Peters, Thomas; Seifried, Daniel; Banerjee, Robi; Klessen, Ralf S

    2014-01-01

    The formation of stars is usually accompanied by the launching of protostellar outflows. Observations with the Atacama Large Millimetre/sub-millimetre Array (ALMA) will soon revolutionalise our understanding of the morphologies and kinematics of these objects. In this paper, we present synthetic ALMA observations of protostellar outflows based on numerical magnetohydrodynamic collapse simulations. We find significant velocity gradients in our outflow models and a very prominent helical structure within the outflows. We speculate that the disk wind found in the ALMA Science Verification Data of HD 163296 presents a first instance of such an observation.

  19. An oxygen-rich dust disk surrounding an evolved star in the Red Rectangle

    NARCIS (Netherlands)

    Waters, LBFM; Waelkens, C; van Winckel, H; Molster, FJ; Tielens, AGGM; van Loon, JT; Morris, PW; Cami, J; Bouwman, J; de Koter, A; de Jong, T; de Graauw, T

    1998-01-01

    The Red Rectangle(1) is the prototype of a class of carbon-rich reflection nebulae surrounding low-mass stars in the final stages of evolution. The central star of this nebula has ejected most of its layers (during the red-giant phase), which now form the surrounding cloud, and is rapidly evolving t

  20. Do siblings always form and evolve simultaneously? Testing the coevality of multiple protostellar systems through SEDs

    Science.gov (United States)

    Murillo, N. M.; van Dishoeck, E. F.; Tobin, J. J.; Fedele, D.

    2016-07-01

    Context. Multiplicity is common in field stars and among protostellar systems. Models suggest two paths of formation: turbulent fragmentation and protostellar disk fragmentation. Aims: We attempt to find whether or not the coevality frequency of multiple protostellar systems can help to better understand their formation mechanism. The coevality frequency is determined by constraining the relative evolutionary stages of the components in a multiple system. Methods: Spectral energy distributions (SEDs) for known multiple protostars in Perseus were constructed from literature data. Herschel PACS photometric maps were used to sample the peak of the SED for systems with separations ≥7″, a crucial aspect in determining the evolutionary stage of a protostellar system. Inclination effects and the surrounding envelope and outflows were considered to decouple source geometry from evolution. This together with the shape and derived properties from the SED was used to determine each system's coevality as accurately as possible. SED models were used to examine the frequency of non-coevality that is due to geometry. Results: We find a non-coevality frequency of 33 ± 10% from the comparison of SED shapes of resolved multiple systems. Other source parameters suggest a somewhat lower frequency of non-coevality. The frequency of apparent non-coevality that is due to random inclination angle pairings of model SEDs is 17 ± 0.5%. Observations of the outflow of resolved multiple systems do not suggest significant misalignments within multiple systems. Effects of unresolved multiples on the SED shape are also investigated. Conclusions: We find that one-third of the multiple protostellar systems sampled here are non-coeval, which is more than expected from random geometric orientations. The other two-thirds are found to be coeval. Higher order multiples show a tendency to be non-coeval. The frequency of non-coevality found here is most likely due to formation and enhanced by

  1. Dynamo magnetic field-induced angular momentum transport in protostellar nebulae - The 'minimum mass' protosolar nebula

    Science.gov (United States)

    Stepinski, T. F.; Levy, E. H.

    1990-01-01

    Magnetic torques can produce angular momentum redistribution in protostellar nebulas. Dynamo magnetic fields can be generated in differentially rotating and turbulent nebulas and can be the source of magnetic torques that transfer angular momentum from a protostar to a disk, as well as redistribute angular momentum within a disk. A magnetic field strength of 100-1000 G is needed to transport the major part of a protostar's angular momentum into a surrounding disk in a time characteristic of star formation, thus allowing formation of a solar-system size protoplanetary nebula in the usual 'minimum-mass' model of the protosolar nebula. This paper examines the possibility that a dynamo magnetic field could have induced the needed angular momentum transport from the proto-Sun to the protoplanetary nebula.

  2. Dynamo magnetic field-induced angular momentum transport in protostellar nebulae - The minimum mass protosolar nebula

    Energy Technology Data Exchange (ETDEWEB)

    Stepinski, T.F.; Levy, E.H. (Arizona Univ., Tucson (USA))

    1990-02-01

    Magnetic torques can produce angular momentum redistribution in protostellar nebulas. Dynamo magnetic fields can be generated in differentially rotating and turbulent nebulas and can be the source of magnetic torques that transfer angular momentum from a protostar to a disk, as well as redistribute angular momentum within a disk. A magnetic field strength of 100-1000 G is needed to transport the major part of a protostar's angular momentum into a surrounding disk in a time characteristic of star formation, thus allowing formation of a solar-system size protoplanetary nebula in the usual minimum-mass model of the protosolar nebula. This paper examines the possibility that a dynamo magnetic field could have induced the needed angular momentum transport from the proto-Sun to the protoplanetary nebula. 32 refs.

  3. Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5

    CERN Document Server

    Lim, Jeremy; Hanawa, Tomoyuki; Takakuwa, Shigehisa; Matsumoto, Tomoaki; Saigo, Kazuya

    2016-01-01

    Either bulk rotation or local turbulence is widely invoked to drive fragmentation in collapsing cores so as to produce multiple star systems. Even when the two mechanisms predict different manners in which the stellar spins and orbits are aligned, subsequent internal or external interactions can drive multiple systems towards or away from alignment thus masking their formation process. Here, we demonstrate that the geometrical and dynamical relationship between the binary system and its surrounding bulk envelope provide the crucial distinction between fragmentation models. We find that the circumstellar disks of the binary protostellar system L1551 IRS 5 are closely parallel not just with each other but also with their surrounding flattened envelope. Measurements of the relative proper motion of the binary components spanning nearly 30 yr indicate an orbital motion in the same sense as the envelope rotation. Eliminating orbital solutions whereby the circumstellar disks would be tidally truncated to sizes smal...

  4. The ALMA Protostellar Interferometric Line Survey (PILS): First results from an unbiased submillimeter wavelength line survey of the Class 0 protostellar binary IRAS 16293-2422 with ALMA

    CERN Document Server

    Jørgensen, J K; Coutens, A; Lykke, J M; Müller, H S P; van Dishoeck, E F; Calcutt, H; Bjerkeli, P; Bourke, T L; Drozdovskaya, M N; Favre, C; Fayolle, E C; Garrod, R T; Jacobsen, S K; Öberg, K I; Persson, M V; Wampfler, S F

    2016-01-01

    The inner regions of the envelopes surrounding young protostars are characterised by a complex chemistry, with prebiotic molecules present on the scales where protoplanetary disks eventually may form. This paper introduces a systematic survey, "Protostellar Interferometric Line Survey (PILS)" of the Class 0 protostellar binary IRAS 16293-2422 using the Atacama Large Millimeter/submillimeter Array (ALMA). The survey covers the full frequency range from 329 to 363 GHz (0.8 mm) with additional targeted observations at 3.0 and 1.3 mm. More than 10,000 features are detected toward one component in the protostellar binary. Glycolaldehyde, its isomers, methyl formate and acetic acid, and its reduced alcohol, ethylene glycol, are clearly detected. For ethylene glycol both lowest state conformers, aGg' and gGg', are detected, the latter for the first time in the ISM. The abundance of glycolaldehyde is comparable to or slightly larger than that of ethylene glycol. In comparison to the Galactic Center, these two species...

  5. Statistics of Stellar Populations of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud

    CERN Document Server

    Santos, J F C; Claria, J J; Bica, E; Geisler, D; Dottori, H

    1999-01-01

    A comparative analysis of Washington color-magnitude diagrams (CMDs) for 14 star clusters and respective surrounding fields in the Large Magellanic Cloud (LMC) outer disk is presented. Each CCD frame including field and respective cluster covers an area of 185 arcmin^2. The stellar population sampled is of intermediate age and metallicity. CMD radial analysis involving star count ratios, morphology and integrated light properties are carried out. Luminosity functions (LFs) are also presented. Two main results are: (i) Within the range 4

  6. Misalignment of Magnetic Fields and Outflows in Protostellar Cores

    CERN Document Server

    Hull, Charles L H; Bolatto, Alberto D; Bower, Geoffrey C; Carpenter, John M; Crutcher, Richard M; Fiege, Jason D; Franzmann, Erica; Hakobian, Nicholas S; Heiles, Carl; Houde, Martin; Hughes, A Meredith; Jameson, Katherine; Kwon, Woojin; Lamb, James W; Looney, Leslie W; Matthews, Brenda C; Mundy, Lee; Pillai, Thushara; Pound, Marc W; Stephens, Ian W; Tobin, John J; Vaillancourt, John E; Volgenau, N H; Wright, Melvyn C H

    2012-01-01

    Theoretical models of star formation generally assume that bipolar outflows are parallel to the mean magnetic-field direction in protostellar cores. Here we present results of \\lambda1.3 mm dust polarization observations toward 16 nearby, low-mass protostars, mapped with ~2.5" resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of ~1000 AU are not tightly aligned with outflows from the protostars. If one assumes that outflows emerge along the rotation axes of circumstellar disks, then our results imply that these disks are not aligned with the fields in the cores from which they formed.

  7. The Protostellar Luminosity Function

    CERN Document Server

    Offner, Stella

    2011-01-01

    The protostellar luminosity function (PLF) is the present-day luminosity function of the protostars in a region of star formation. It is determined using the protostellar mass function (PMF) in combination with a stellar evolutionary model that provides the luminosity as a function of instantaneous and final stellar mass. As in McKee & Offner (2010), we consider three main accretion models: the Isothermal Sphere model, the Turbulent Core model, and an approximation of the Competitive Accretion model. We also consider the effect of an accretion rate that tapers off linearly in time and an accelerating star formation rate. For each model, we characterize the luminosity distribution using the mean, median, maximum, ratio of the median to the mean, standard deviation of the logarithm of the luminosity, and the fraction of very low luminosity objects. We compare the models with bolometric luminosities observed in local star forming regions and find that models with an approximately constant accretion time, suc...

  8. The abundance and thermal history of water ice in the disk surrounding HD 142527 from the DIGIT Herschel Key Program

    Science.gov (United States)

    Min, M.; Bouwman, J.; Dominik, C.; Waters, L. B. F. M.; Pontoppidan, K. M.; Hony, S.; Mulders, G. D.; Henning, Th.; van Dishoeck, E. F.; Woitke, P.; Evans, Neal J., II; Digit Team

    2016-08-01

    Context. The presence or absence of ice in protoplanetary disks is of great importance to the formation of planets. By enhancing solid surface density and increasing sticking efficiency, ice catalyzes the rapid formation of planetesimals and decreases the timescale of giant planet core accretion. Aims: In this paper, we analyze the composition of the outer disk around the Herbig star HD 142527. We focus on the composition of water ice, but also analyze the abundances of previously proposed minerals. Methods: We present new Herschel far-infrared spectra and a re-reduction of archival data from the Infrared Space Observatory (ISO). We modeled the disk using full 3D radiative transfer to obtain the disk structure. Also, we used an optically thin analysis of the outer disk spectrum to obtain firm constraints on the composition of the dust component. Results: The water ice in the disk around HD 142527 contains a large reservoir of crystalline water ice. We determine the local abundance of water ice in the outer disk (i.e., beyond 130 AU). The re-reduced ISO spectrum differs significantly from that previously published, but matches the new Herschel spectrum at their common wavelength range. In particular, we do not detect any significant contribution from carbonates or hydrous silicates, in contrast to earlier claims. Conclusions: The amount of water ice detected in the outer disk requires ~80% of oxygen atoms. This is comparable to the water ice abundance in the outer solar system, comets, and dense interstellar clouds. The water ice is highly crystalline while the temperatures where we detect it are too low to crystallize the water on relevant timescales. We discuss the implications of this finding.

  9. The abundance and thermal history of water ice in the disk surrounding HD142527 from the DIGIT Herschel Key Program

    CERN Document Server

    Min, M; Dominik, C; Waters, L B F M; Pontoppidan, K M; Hony, S; Mulders, G D; Henning, Th; van Dishoeck, E F; Woitke, P; Evans, Neal J

    2016-01-01

    The presence or absence of ice in protoplanetary disks is of great importance for the formation of planets. By enhancing the solid surface density and increasing the sticking efficiency, ice catalyzes the rapid formation of planetesimals and decreases the time scale for giant planet core accretion. Aims: In this paper we analyse the composition of the outer disk around the Herbig star HD~142527. We focus on the composition of the water ice, but also analyse the abundances of previously proposed minerals. Methods: We present new Herschel far infrared spectra and a re-reduction of archival data from the Infrared Space Observatory (ISO). We model the disk using full 3D radiative transfer to obtain the disk structure. Also, we use an optically thin analysis of the outer disk spectrum to obtain firm constraints on the composition of the dust component. Results: The water ice in the disk around HD~142527 contains a large reservoir of crystalline water ice. We determine the local abundance of water ice in the outer ...

  10. The Herschel Orion Protostar Survey: Constraining Protostellar Models with Mid-Infrared Spectroscopy

    Science.gov (United States)

    Furlan, Elise; HOPS Team

    2013-01-01

    During the protostellar stage of star formation, a young star is surrounded by a large infalling envelope of dust and gas; the material falls onto a circumstellar disk and is eventually accreted by the central star. The dust in the disk and envelope emits prominently at mid- to far-infrared wavelengths; at 10 micron, absorption by small silicate grains causes a broad absorption feature. By modeling the near- to far-IR spectral energy distributions (SEDs) of protostars, properties of their disks and envelopes can be derived; in particular, mid-IR spectroscopy reveals the detailed emission around the silicate absorption feature and thus provides additional constraints for the models. Here we present results from modeling a sample of protostars in the Orion star-forming region that were observed as part of the Herschel Orion Protostar Survey (HOPS). These protostars represent a subsample of HOPS; they have Spitzer/IRS spectra, which cover the mid-IR SED from 5 to 35 micron, and photometry in the near-IR (2MASS), mid-IR (Spitzer/IRAC and MIPS), and far-IR (Herschel/PACS). We show the importance of adding Spitzer/IRS spectra with appropriate weights in determining the best fit to the SED from a large grid of protostellar models. The 10 micron silicate absorption feature and the mid- to far-IR SED slope provide key constraints for the inclination angle of the object and its envelope density, with a deep absorption feature and steep SED slope for the most embedded and highly inclined objects. We show a few examples that illustrate our SED fitting method and present preliminary results from our fits.

  11. The Herschel Orion Protostar Survey: Constraining Protostellar Models with Near- to Far-Infrared Observations

    Science.gov (United States)

    Furlan, Elise; Ali, Babar; Fischer, Will; Tobin, John; Stutz, Amy; Megeath, Tom; Allen, Lori; HOPS Team

    2013-07-01

    During the protostellar stage of star formation, a young star is surrounded by a large infalling envelope of dust and gas; the material falls onto a circumstellar disk and is eventually accreted by the central star. The dust in the disk and envelope emits prominently at mid- to far-infrared wavelengths; at 10 micron, absorption by small silicate grains typically causes a broad absorption feature. By modeling the near- to far-IR spectral energy distributions (SEDs) of protostars, properties of their disks and envelopes can be derived. As part of the Herschel Orion Protostar Survey (HOPS; PI: S. T. Megeath), we have observed a large sample of protostars in the Orion star-forming complex at 70 and 160 micron with the PACS instrument on the Herschel Space Observatory. For most objects, we also have photometry in the near-IR (2MASS), mid-IR (Spitzer/ IRAC and MIPS), at 100 micron (PACS data from the Gould Belt Survey), sub-mm (APEX/SABOCA and LABOCA), and mid-infrared spectra (Spitzer/IRS). For the interpretation of the SEDs, we have constructed a large grid of protostellar models using a Monte Carlo radiative transfer code. Here we present our SED fitting techniques to determine the best-fit model for each object. We show the importance of including IRS spectra with appropriate weights, in addition to the constraints provided by the PACS measurements, which probe the peak of the SED. The 10 micron silicate absorption feature and the mid- to far-IR SED slope provide key constraints for the inclination angle of the object and its envelope density, with a deep absorption feature and steep SED slope for the most embedded and highly inclined objects. We show a few examples that illustrate our SED fitting method and present some preliminary results from our fits.

  12. CID: Chemistry in disks VI.sulfur-bearing molecules in the protoplanetary disks surrounding LkCa15, MWC480, DM Tau, and GO Tau

    CERN Document Server

    Dutrey, Anne; Boehler, Yann; Guilloteau, Stéphane; Hersant, Franck; Semenov, Dmitry; Chapillon, Edwige; Henning, Thomas; Piétu, Vincent; Launhardt, Ralf; Gueth, Frederic; Schreyer, Katharina

    2011-01-01

    We study the content in S-bearing molecules of protoplanetary disks around low-mass stars. We used the new IRAM 30-m receiver EMIR to perform simultaneous observations of the $1_{10}-1_{01}$ line of H$_2$S at 168.8 GHz and $2_{23}-1_{12}$ line of SO at 99.3 GHz. We compared the observational results with predictions coming from the astrochemical code NAUTILUS, which has been adapted to protoplanetary disks. The data were analyzed together with existing CS J=3-2 observations. We fail to detect the SO and H$_2$S lines, although CS is detected in LkCa15, DM\\,Tau, and GO\\,Tau but not in MWC\\,480. However, our new upper limits are significantly better than previous ones and allow us to put some interesting constraints on the sulfur chemistry. Our best modeling of disks is obtained for a C/O ratio of 1.2, starting from initial cloud conditions of H density of $2\\times 10^5$ cm$^{-3}$ and age of $10^6$ yr. The results agree with the CS data and are compatible with the SO upper limits, but fail to reproduce the H$_2$...

  13. The structure of the protoplanetary disk surrounding three young intermediate mass stars. II. Spatially resolved dust and gas distribution

    CERN Document Server

    Fedele, D; Acke, B; van der Plas, G; Van Boekel, R; Wittkowski, M; Henning, T; Bouwman, J; Meeus, G; Rafanelli, P

    2008-01-01

    [Abridged] We present the first direct comparison of the distribution of the gas, as traced by the [OI] 6300 AA emission, and the dust, as traced by the 10 micron emission, in the protoplanetary disk around three intermediate-mass stars: HD 101412, HD 135344 B and HD 179218. N-band visibilities were obtained with VLTI/MIDI. Simple geometrical models are used to compare the dust emission to high-resolution optical spectra in the 6300 AA [OI] line of the same targets. The disks around HD 101412 and HD 135344 B appear strongly flared in the gas, but self-shadowed in the dust beyond ~ 2 AU. In both systems, the 10 micron emission is rather compact (< 2 AU) while the [OI] brightness profile shows a double peaked structure. The inner peak is strongest and is consistent with the location of the dust, the outer peak is fainter and is located at 5-10 AU. Spatially extended PAH emission is found in both disks. The disk around HD 179218 is flared in the dust. The 10 micron emission emerges from a double ring-like str...

  14. revealing H{sub 2}D{sup +} depletion and compact structure in starless and protostellar cores with ALMA

    Energy Technology Data Exchange (ETDEWEB)

    Friesen, R. K. [Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St George Street, Toronto, ON M5S 3H4 (Canada); Di Francesco, J. [National Research Council Canada, Radio Astronomy Program, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Bourke, T. L. [Radio and Geoastronomy Division, Harvard Smithsonian Center for Astrophysics, MS-42, Cambridge, MA 02138 (United States); Caselli, P. [Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching (Germany); Jørgensen, J. K. [Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø. (Denmark); Pineda, J. E. [Institute for Astronomy, ETH Zürich, Wolfgang-Pauli-Strasse 27, CH-8093 Zürich (Switzerland); Wong, M., E-mail: friesen@dunlap.utoronto.ca [University of British Columbia, Vancouver, BC V6T 1Z4 (Canada)

    2014-12-10

    We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the submillimeter dust continuum and H{sub 2}D{sup +} 1{sub 10}-1{sub 11} emission toward two evolved, potentially protostellar cores within the Ophiuchus molecular cloud, Oph A SM1 and SM1N. The data reveal small-scale condensations within both cores, with mass upper limits of M ≲ 0.02 M {sub ☉} (∼20 M {sub Jup}). The SM1 condensation is consistent with a nearly symmetric Gaussian source with a width of only 37 AU. The SM1N condensation is elongated and extends 500 AU along its major axis. No evidence for substructure is seen in either source. A Jeans analysis indicates that these sources are unlikely to fragment, suggesting that both will form single stars. H{sub 2}D{sup +} is only detected toward SM1N, offset from the continuum peak by ∼150-200 AU. This offset may be due to either heating from an undetected, young, low-luminosity protostellar source or first hydrostatic core, or HD (and consequently H{sub 2}D{sup +}) depletion in the cold center of the condensation. We propose that SM1 is protostellar and that the condensation detected by ALMA is a warm (T ∼ 30-50 K) accretion disk. The less concentrated emission of the SM1N condensation suggests that it is still starless, but we cannot rule out the presence of a low-luminosity source, perhaps surrounded by a pseudodisk. These data observationally reveal the earliest stages of the formation of circumstellar accretion regions and agree with theoretical predictions that disk formation can occur very early in the star formation process, coeval with or just after the formation of a first hydrostatic core or protostar.

  15. A Spitzer IRS Study of Debris Disks Around Planet-Host Stars

    CERN Document Server

    Dodson-Robinson, Sarah E; Carpenter, John M; Bryden, Geoffrey

    2010-01-01

    Since giant planets scatter planetesimals within a few tidal radii of their orbits, the locations of existing planetesimal belts indicate regions where giant planet formation failed in bygone protostellar disks. Infrared observations of circumstellar dust produced by colliding planetesimals are therefore powerful probes of the formation histories of known planets. Here we present new Spitzer IRS spectrophotometry of 111 Solar-type stars, including 105 planet hosts. Our observations reveal 11 debris disks, including two previously undetected debris disks orbiting HD 108874 and HD 130322. Combining our 32 micron spectrophotometry with previously published MIPS photometry, we find that the majority of debris disks around planet hosts have temperatures in the range 60 < T < 100 K. Assuming a dust temperature T = 70 K, which is representative of the nine debris disks detected by both IRS and MIPS, we find that debris rings surrounding Sunlike stars orbit between 15 and 240 AU, depending on the mean particle ...

  16. DISPERSING ENVELOPE AROUND THE KEPLERIAN CIRCUMBINARY DISK IN L1551 NE AND ITS IMPLICATIONS FOR BINARY GROWTH

    Energy Technology Data Exchange (ETDEWEB)

    Takakuwa, Shigehisa [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Kiyokane, Kazuhiro [Department of Astronomy, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033 (Japan); Saigo, Kazuya [Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); Saito, Masao, E-mail: takakuwa@asiaa.sinica.edu.tw [Nobeyama Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano 384-1805 (Japan)

    2015-12-01

    We performed mapping observations of the Class I protostellar binary system L1551 NE in the C{sup 18}O (J = 3–2), {sup 13}CO (J = 3–2), CS (J = 7–6), and SO (J{sub N} = 7{sub 8}–6{sub 7}) lines with the Atacama Submillimeter Telescope Experiment (ASTE). The ASTE C{sup 18}O data were combined with our previous SMA C{sup 18}O data, which show a r ∼ 300 AU scale Keplerian disk around the protostellar binary system. The C{sup 18}O maps show a ∼20,000 AU scale protostellar envelope surrounding the central Keplerian circumbinary disk. The envelope exhibits a northeast (blue) to southwest (red) velocity gradient along the minor axis, which can be interpreted as a dispersing gas motion with an outward velocity of 0.3 km s{sup −1}, while no rotational motion in the envelope is seen. In addition to the envelope, two ≲4000 AU scale, high-velocity (≳1.3 km s{sup −1}) redshifted {sup 13}CO and CS emission components are found ∼40″ southwest and ∼20″ west of the protostellar binary. These redshifted components are most likely outflow components driven from the neighboring protostellar source L1551 IRS 5, and are colliding with the envelope in L1551 NE. The net momentum, kinetic, and internal energies of the L1551 IRS 5 outflow components are comparable to those of the L1551 NE envelope, and the interactions between the outflows and the envelope are likely to cause the dissipation of the envelope and thus suppression of further growth of the mass and mass ratio of the central protostellar binary in L1551 NE.

  17. Laying the Groundwork for Future Alma Direct Magnetic Field Detection in Protostellar Environments

    Science.gov (United States)

    Cox, Erin Guilfoil; Harris, Robert J.; Looney, Leslie; Segura-Cox, Dominique M.; Crutcher, Richard; Li, Zhi-Yun; Tobin, John; Stephens, Ian; Novak, Giles; Fernandez-Lopez, Manuel

    2017-06-01

    Magnetic fields are a crucial element of the star formation process on many scales, from controlling jet and outflow formation on large scales, determining the structure of any protostellar disk, to modulating the accretion rate onto the central protostar. Both the three-dimensional structure and the field strength are important in determining the outcome of star formation. Unfortunately, the method most commonly used to infer magnetic field structure - linearly polarized dust continuum emission - is limited to the plane-of-sky field structure, and gives no reliable information on field strength. Alternatively, observations of the Zeeman effect in transitions of paramagnetic molecules, especially CN, are one of the best prospects for making such measurements due to the molecules' high Zeeman coefficients. In particular, these observations have been used in determining field strengths on cloud-size scales. However, CN and other paramagnetic molecules have, to our knowledge, never been observed in the envelopes/disks of Class 0 protostars at ˜arcsecond resolution, due both to sensitivity and resolution limits of previous generations of millimeter-wave interferometers. Because field strengths near the protostar are so important to understand the star formation process, we have conducted a snapshot ALMA Band 3 (3 mm / 113 GHz) survey of the 10 brightest Class 0 protostars in the Perseus, Taurus, and ρ Ophiuchus molecular clouds in the regions surrounding five transitions of four paramagnetic species, including CN, SO, C_2S, and C_4H. We present this survey - the principle goal of which was to assess the brightness of the lines within ˜ 1000 AU of the protostar - and assess the likelihood of using ALMA observations of the Zeeman effect to determine protostellar magnetic field strength.

  18. Impact of Protostellar Outflow on Star Formation: Effects of Initial Cloud Mass

    CERN Document Server

    Machida, Masahiro N

    2011-01-01

    Star formation efficiency controlled by the protostellar outflow in a single cloud core is investigated by three-dimensional resistive MHD simulations. Starting from the prestellar cloud core, the star formation process is calculated until the end of the main accretion phase. In the calculations, the mass of the prestellar cloud is parameterized. During the star formation, the protostellar outflow is driven by the circumstellar disk. The outflow extends also in the transverse direction until its width becomes comparable to the initial cloud scale, and thus, the outflow has a wide opening angle of >40 degrees. As a result, the protostellar outflow sweeps up a large fraction of the infalling material and ejects it into the interstellar space. The outflow can eject at most over half of the host cloud mass, significantly decreasing star formation efficiency. The outflow power is stronger in clouds with a greater initial mass. Thus, the protostellar outflow effectively suppresses star formation efficiency in a mas...

  19. Distributions of molecules in the circumnuclear disk and surrounding starburst ring in the Seyfert galaxy NGC 1068 observed with ALMA

    CERN Document Server

    Takano, Shuro; Kohno, Kotaro; Harada, Nanase; Herbst, Eric; Tamura, Yoichi; Izumi, Takuma; Taniguchi, Akio; Tosaki, Tomoka

    2014-01-01

    Sensitive observations with ALMA allow astronomers to observe the detailed distributions of molecules with relatively weak intensity in nearby galaxies. In particular, we report distributions of several molecular transitions including shock and dust related species ($^{13}$CO $J$ = 1--0, C$^{18}$O $J$ = 1--0, $^{13}$CN $N$ = 1--0, CS $J$ = 2--1, SO $J_N$ = 3$_2$--2$_1$, HNCO $J_{Ka,Kc}$ = 5$_{0,5}$--4$_{0,4}$, HC$_3$N $J$ = 11--10, 12--11, CH$_3$OH $J_K$ = 2$_K$--1$_K$, and CH$_3$CN $J_K$ = 6$_K$--5$_K$) in the nearby Seyfert 2 galaxy NGC 1068 observed with the ALMA early science program. The central $\\sim$1 arcmin ($\\sim$4.3 kpc) of this galaxy was observed in the 100 GHz region covering $\\sim$96--100 GHz and $\\sim$108--111 GHz with an angular resolution of $\\sim4"\\times2"$ (290 pc$\\times$140 pc) to study the effects of an active galactic nucleus and its surrounding starburst ring on molecular abundances. Here, we present images and report a classification of molecular distributions into three main categorie...

  20. An Extreme Analogue of ɛ Aurigae: An M-giant Eclipsed Every 69 Years by a Large Opaque Disk Surrounding a Small Hot Source

    Science.gov (United States)

    Rodriguez, Joseph E.; Stassun, Keivan G.; Lund, Michael B.; Siverd, Robert J.; Pepper, Joshua; Tang, Sumin; Kafka, Stella; Gaudi, B. Scott; Conroy, Kyle E.; Beatty, Thomas G.; Stevens, Daniel J.; Shappee, Benjamin J.; Kochanek, Christopher S.

    2016-05-01

    We present TYC 2505-672-1 as a newly discovered and remarkable eclipsing system comprising an M-type red giant that undergoes a ˜3.45 year long, near-total eclipse (depth of ˜4.5 mag) with a very long period of ˜69.1 years. TYC 2505-672-1 is now the longest-period eclipsing binary system yet discovered, more than twice as long as that of the currently longest-period system, ɛ Aurigae. We show from analysis of the light curve including both our own data and historical data spanning more than 120 years and from modeling of the spectral energy distribution, both before and during eclipse, that the red giant primary is orbited by a moderately hot source (Teff ≈ 8000 K) that is itself surrounded by an extended, opaque circumstellar disk. From the measured ratio of luminosities, the radius of the hot companion must be in the range of 0.1-0.5 R⊙ (depending on the assumed radius of the red giant primary), which is an order of magnitude smaller than that for a main sequence A star and 1-2 orders of magnitude larger than that for a white dwarf. The companion is therefore most likely a “stripped red giant” subdwarf-B type star destined to become a He white dwarf. It is, however, somewhat cooler than most sdB stars, implying a very low mass for this “pre-He-WD” star. The opaque disk surrounding this hot source may be a remnant of the stripping of its former hydrogen envelope. However, it is puzzling how this object became stripped, given that it is at present so distant (orbital semimajor axis of ˜24 au) from the current red giant primary star. Extrapolating from our calculated ephemeris, the next eclipse should begin in early UT 2080 April and end in mid UT 2083 September (eclipse center UT 2081 December 24). In the meantime, radial velocity observations would establish the masses of the components, and high-cadence UV observations could potentially reveal oscillations of the hot companion that would further constrain its evolutionary status. In any case

  1. An Extreme Analogue of $\\epsilon$ Aurigae: An M-giant Eclipsed Every 69 Years by a Large Opaque Disk Surrounding a Small Hot Source

    CERN Document Server

    Rodriguez, Joseph E; Lund, Michael B; Siverd, Robert J; Pepper, Joshua; Tang, Sumin; Kafka, Stella; Gaudi, Scott; Conroy, Kyle E; Beatty, Thomas G; Stevens, Daniel J

    2016-01-01

    We present TYC 2505-672-1 as a newly discovered, remarkable eclipsing system comprising an M-type red giant that undergoes a ~3.45 year long, near-total eclipse (depth of ~4.5 mag) with a very long period of ~69.1 yr. This therefore becomes the longest-period eclipsing binary system yet discovered, more than twice as long as that of the currently longest-period system, $\\epsilon$ Aurigae. We show from analysis of the light curve including both our own data and historical data spanning more than 120 yr and from modeling of the spectral energy distribution, both before and during eclipse, that the red giant primary is orbited by a moderately hot source (T$_{eff}$~8000 K) that is itself surrounded by an extended, opaque circumstellar disk. From the measured ratio of luminosities, the radius of the hot companion must be in the range 0.1-0.5 Rsun (depending on the assumed radius of the red giant primary), which is an order of magnitude smaller than that for a main sequence A star and 1-2 orders of magnitude larger...

  2. Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz: A kpc-scale star forming disk surrounding nuclei with shocked outflows

    CERN Document Server

    Varenius, E; Martí-Vidal, I; Aalto, S; Barcos-Muñoz, L; König, S; Pérez-Torres, M A; Deller, A T; Moldón, J; Gallagher, J S; Yoast-Hull, T M; Horellou, C; Morabito, L K; Alberdi, A; Jackson, N; Beswick, R; Carozzi, T D; Wucknitz, O; Ramírez-Olivencia, N

    2016-01-01

    We analyse new observations with the International Low Frequency Array (LOFAR) telescope, and archival data from the Multi-Element Radio Linked Interferometer Network (MERLIN) and the Karl G. Jansky Very Large Array (VLA). We model the spatially resolved radio spectrum of Arp 220 from 150 MHz to 33 GHz. We present an image of Arp 220 at 150 MHz with resolution $0.65''\\times0.35''$, sensitivity 0.15 mJy beam$^{-1}$, and integrated flux density $394\\pm59$ mJy. More than 80% of the detected flux comes from extended ($6''\\approx$2.2 kpc) steep spectrum ($\\alpha=-0.7$) emission, likely from star formation in the molecular disk surrounding the two nuclei. We find elongated features extending $0.3''$ (110 pc) and $0.9''$ (330 pc) from the eastern and western nucleus respectively, which we interpret as evidence for outflows. The extent of radio emission requires acceleration of cosmic rays far outside the nuclei. We find that a simple three component model can explain most of the observed radio spectrum of the galaxy...

  3. Molecular Outflows: Explosive versus Protostellar

    Science.gov (United States)

    Zapata, Luis A.; Schmid-Burgk, Johannes; Rodríguez, Luis F.; Palau, Aina; Loinard, Laurent

    2017-02-01

    With the recent recognition of a second, distinctive class of molecular outflows, namely the explosive ones not directly connected to the accretion–ejection process in star formation, a juxtaposition of the morphological and kinematic properties of both classes is warranted. By applying the same method used in Zapata et al., and using 12CO(J = 2-1) archival data from the Submillimeter Array, we contrast two well-known explosive objects, Orion KL and DR21, to HH 211 and DG Tau B, two flows representative of classical low-mass protostellar outflows. At the moment, there are only two well-established cases of explosive outflows, but with the full availability of ALMA we expect that more examples will be found in the near future. The main results are the largely different spatial distributions of the explosive flows, consisting of numerous narrow straight filament-like ejections with different orientations and in almost an isotropic configuration, the redshifted with respect to the blueshifted components of the flows (maximally separated in protostellar, largely overlapping in explosive outflows), the very-well-defined Hubble flow-like increase of velocity with distance from the origin in the explosive filaments versus the mostly non-organized CO velocity field in protostellar objects, and huge inequalities in mass, momentum, and energy of the two classes, at least for the case of low-mass flows. Finally, all the molecular filaments in the explosive outflows point back to approximately a central position (i.e., the place where its “exciting source” was located), contrary to the bulk of the molecular material within the protostellar outflows.

  4. The ALMA Protostellar Interferometric Line Survey (PILS). First results from an unbiased submillimeter wavelength line survey of the Class 0 protostellar binary IRAS 16293-2422 with ALMA

    Science.gov (United States)

    Jørgensen, J. K.; van der Wiel, M. H. D.; Coutens, A.; Lykke, J. M.; Müller, H. S. P.; van Dishoeck, E. F.; Calcutt, H.; Bjerkeli, P.; Bourke, T. L.; Drozdovskaya, M. N.; Favre, C.; Fayolle, E. C.; Garrod, R. T.; Jacobsen, S. K.; Öberg, K. I.; Persson, M. V.; Wampfler, S. F.

    2016-11-01

    Context. The inner regions of the envelopes surrounding young protostars are characterized by a complex chemistry, with prebiotic molecules present on the scales where protoplanetary disks eventually may form. The Atacama Large Millimeter/submillimeter Array (ALMA) provides an unprecedented view of these regions zooming in on solar system scales of nearby protostars and mapping the emission from rare species. Aims: The goal is to introduce a systematic survey, the Protostellar Interferometric Line Survey (PILS), of the chemical complexity of one of the nearby astrochemical templates, the Class 0 protostellar binary IRAS 16293-2422, using ALMA in order to understand the origin of the complex molecules formed in its vicinity. In addition to presenting the overall survey, the analysis in this paper focuses on new results for the prebiotic molecule glycolaldehyde, its isomers, and rarer isotopologues and other related molecules. Methods: An unbiased spectral survey of IRAS 16293-2422 covering the full frequency range from 329 to 363 GHz (0.8 mm) has been obtained with ALMA, in addition to a few targeted observations at 3.0 and 1.3 mm. The data consist of full maps of the protostellar binary system with an angular resolution of 0.5'' (60 AU diameter), a spectral resolution of 0.2 km s-1, and a sensitivity of 4-5 mJy beam-1 km s-1, which is approximately two orders of magnitude better than any previous studies. Results: More than 10 000 features are detected toward one component in the protostellar binary, corresponding to an average line density of approximately one line per 3 km s-1. Glycolaldehyde; its isomers, methyl formate and acetic acid; and its reduced alcohol, ethylene glycol, are clearly detected and their emission well-modeled with an excitation temperature of 300 K. For ethylene glycol both lowest state conformers, aGg' and gGg', are detected, the latter for the first time in the interstellar medium (ISM). The abundance of glycolaldehyde is comparable to or

  5. Protostellar Feedback in Turbulent Fragmentation: Consequences for Stellar Clustering and Multiplicity

    CERN Document Server

    Guszejnov, David; Krumholz, Mark R

    2016-01-01

    Stars are strongly clustered on both large (~pc) and small (~binary) scales, but there are few analytic or even semi-analytic theories for the correlation function and multiplicity of stars. In this paper we present such a theory, based on our recently-developed semi-analytic model of gravito-turbulent fragmentation, including the suppression of fragmentation by protostellar radiation feedback. We compare the results including feedback to a control model in which it is omitted. We show that both classes of models robustly reproduce the stellar correlation function at >0.01 pc scales, which is well approximated by a power-law that follows generally from scale-free physics (turbulence plus gravity) on large scales. On smaller scales protostellar disk fragmentation becomes dominant over common core fragmentation, leading to a steepening of the correlation function. Multiplicity is more sensitive to feedback, with the protostellar heating model reproducing the observed multiplicity fractions and mass ratio distri...

  6. Gravitational Instabilities in Circumstellar Disks

    CERN Document Server

    Kratter, Kaitlin M

    2016-01-01

    [Abridged] Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability, and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability, supplemented with a survey of numerical simulations that aim to capture the non-linear evolution. We emphasize the role of thermodynamics and large scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analyt...

  7. Workshop on Physics of Accretion Disks Around Compact and Young Stars

    Science.gov (United States)

    Liang, E (Editor); Stepinski, T. F. (Editor)

    1995-01-01

    The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster presentations, and a list of workshop participants. Accretion disks are believed to surround many stars. Some of these disks form around compact stars, such as white dwarfs, neutron stars, or black holes that are members of binary systems and reveal themselves as a power source, especially in the x-ray and gamma regions of the spectrum. On the other hand, protostellar disks are believed to be accretion disks associated with young, pre-main-sequence stars and manifest themselves mostly in infrared and radio observations. These disks are considered to be a natural outcome of the star formation process. The focus of this workshop included theory and observations relevant to accretion disks around compact objects and newly forming stars, with the primary purpose of bringing the two communities together for intellectual cross-fertilization. The nature of the workshop was exploratory, to see how much interaction is possible between distinct communities and to better realize the local potential in this subject. A critical workshop activity was identification and documentation of key issues that are of mutual interest to both communities.

  8. Protostellar accretion traced with chemistry

    DEFF Research Database (Denmark)

    Frimann, Søren; Jørgensen, Jes Kristian; Dunham, Michael M.

    2017-01-01

    . Our aim is to characterise protostellar accretion histories towards individual sources by utilising sublimation and freeze-out chemistry of CO. Methods. A sample of 24 embedded protostars are observed with the Submillimeter Array (SMA) in context of the large program "Mass Assembly of Stellar Systems...... and their Evolution with the SMA" (MASSES). The size of the C18O-emitting region, where CO has sublimated into the gas-phase, is measured towards each source and compared to the expected size of the region given the current luminosity. The SMA observations also include 1.3 mm continuum data, which are used...

  9. Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz. A kpc-scale star forming disk surrounding nuclei with shocked outflows

    Science.gov (United States)

    Varenius, E.; Conway, J. E.; Martí-Vidal, I.; Aalto, S.; Barcos-Muñoz, L.; König, S.; Pérez-Torres, M. A.; Deller, A. T.; Moldón, J.; Gallagher, J. S.; Yoast-Hull, T. M.; Horellou, C.; Morabito, L. K.; Alberdi, A.; Jackson, N.; Beswick, R.; Carozzi, T. D.; Wucknitz, O.; Ramírez-Olivencia, N.

    2016-09-01

    Context. Arp 220 is the prototypical ultra luminous infrared galaxy (ULIRG). Despite extensive studies, the structure at MHz-frequencies has remained unknown because of limits in spatial resolution. Aims: This work aims to constrain the flux and shape of radio emission from Arp 220 at MHz frequencies. Methods: We analyse new observations with the International Low Frequency Array (LOFAR) telescope, and archival data from the Multi-Element Radio Linked Interferometer Network (MERLIN) and the Karl G. Jansky Very Large Array (VLA). We model the spatially resolved radio spectrum of Arp 220 from 150 MHz to 33 GHz. Results: We present an image of Arp 220 at 150 MHz with resolution 0.̋65 × 0.̋35, sensitivity 0.15 mJy beam-1, and integrated flux density 394 ± 59 mJy. More than 80% of the detected flux comes from extended (6''≈ 2.2 kpc) steep spectrum (α = -0.7) emission, likely from star formation in the molecular disk surrounding the two nuclei. We find elongated features extending 0.3'' (110 pc) and 0.9'' (330 pc) from the eastern and western nucleus respectively, which we interpret as evidence for outflows. The extent of radio emission requires acceleration of cosmic rays far outside the nuclei. We find that a simple three component model can explain most of the observed radio spectrum of the galaxy. When accounting for absorption at 1.4 GHz, Arp 220 follows the FIR/radio correlation with q = 2.36, and we estimate a star formation rate of 220 M⊙ yr-1. We derive thermal fractions at 1 GHz of less than 1% for the nuclei, which indicates that a major part of the UV-photons are absorbed by dust. Conclusions: International LOFAR observations shows great promise to detect steep spectrum outflows and probe regions of thermal absorption. However, in LIRGs the emission detected at 150 MHz does not necessarily come from the main regions of star formation. This implies that high spatial resolution is crucial for accurate estimates of star formation rates for such galaxies

  10. Theory of Disk Accretion onto Magnetic Stars

    Directory of Open Access Journals (Sweden)

    Lai Dong

    2014-01-01

    Full Text Available Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields, white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron star and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

  11. Theory of Disk Accretion onto Magnetic Stars

    CERN Document Server

    Lai, Dong

    2014-01-01

    Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields), white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron stars and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

  12. On the reliability of protostellar disc mass measurements and the existence of fragmenting discs

    CERN Document Server

    Dunham, Michael M; Arce, Héctor G

    2014-01-01

    We couple non-magnetic, hydrodynamical simulations of collapsing protostellar cores with radiative transfer evolutionary models to generate synthetic observations. We then use these synthetic observations to investigate the extent to which a simple method for measuring protostellar disc masses used in the literature recovers the intrinsic masses of the discs formed in the simulations. We evaluate the effects of contamination from the surrounding core, partially resolving out the disc, optical depth, fixed assumed dust temperatures, inclination, and the dust opacity law. We show that the combination of these effects can lead to disc mass underestimates by up to factors of 2-3 at millimeter wavelengths and up to an order of magnitude or larger at submillimeter wavelengths. The optically thin portions of protostellar discs are generally cooler in the Class I stage than the Class 0 stage since Class I discs are typically larger and more optically thick, and thus more shielded. The observed disc mass distribution ...

  13. The Birth of Disks Around Protostars

    Science.gov (United States)

    Kohler, Susanna

    2017-03-01

    The dusty disks around young stars make the news regularly due to their appeal as the birthplace of early exoplanets. But how do disks like these first form and evolve around their newly born protostars? New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) are helping us to better understand this process.Formation from CollapseStars are born from the gravitational collapse of a dense cloud of molecular gas. Long before they start fusing hydrogen at their centers when they are still just hot overdensities in the process of contracting we call them protostars. These low-mass cores are hidden at the hearts of the clouds of molecular gas from which they are born.Aerial image of the Atacama Large Millimeter/submillimeter Array. [EFE/Ariel Marinkovic]During this contraction phase, before a protostar transitions to a pre-main-sequence star (which it does by blowing away its outer gas envelope, halting the stars growth), much of the collapsing material will spin into a centrifugally supported Keplerian disk that surrounds the young protostar. Later, these circumstellar disks will become the birthplace for young planets something for which weve seen observational evidence in recent years.But how do these Keplerian disks which eventually have scales of hundreds of AU first form and grow around protostars? We need observations of these disks in their early stages of formation to understand their birth and evolution a challenging prospect, given the obscuring molecular gas that hides them at these stages. ALMA, however, is up to the task: it can peer through to the center of the gas clouds to see the emission from protostellar cores and their surroundings.ALMA observations of the protostar Lupus 3 MMS. The molecular outflows from the protostar are shown in panel a. Panel b shows the continuum emission, which has a compact component that likely traces a disk surrounding the protostar. [Adapted from Yen et al. 2017]New Disks Revealed?In a recent

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

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, John J. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Hartmann, Lee; Calvet, Nuria [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Chiang, Hsin-Fang; Looney, Leslie W. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Wilner, David J. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Loinard, Laurent; D' Alessio, Paola, E-mail: jtobin@nrao.edu [Centro de Radioastronomia y Astrofisica, UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacan (Mexico)

    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.

  15. Revealing H2D+ depletion and compact structure in starless and protostellar cores with ALMA

    DEFF Research Database (Denmark)

    Friesen, R. K.; Di Francesco, J.; Bourke, T. L.;

    2014-01-01

    We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the submillimeter dust continuum and H2D+ 110-111 emission toward two evolved, potentially protostellar cores within the Ophiuchus molecular cloud, Oph A SM1 and SM1N. The data reveal small-scale condensations within...... hydrostatic core, or HD (and consequently H2D+) depletion in the cold center of the condensation. We propose that SM1 is protostellar and that the condensation detected by ALMA is a warm (T ~ 30-50 K) accretion disk. The less concentrated emission of the SM1N condensation suggests that it is still starless...

  16. Protostellar Outflows in L1340

    CERN Document Server

    Walawender, Josh; Smutko, Michael; O'Linger-Luscusk, JoAnn; Moriarty-Schieven, Gerald

    2016-01-01

    We have searched the L1340 A, B, and C clouds for shocks from protostellar outflows using the H$_2$ 2.122 $\\mu$m near-IR line as a shock tracer. Substantial outflow activity has been found in each of the three regions of the cloud (L1340 A, L1340 B, & L1340 C). We find 42 distinct shock complexes (16 in L1340 A, 11 in L1340 B, and 15 in L1340 C). We were able to link 17 of those shock complexes in to 12 distinct outflows and identify candidate source stars for each. We examine the properties (A$_{V}$, T$_{bol}$, and L$_{bol}$) of the source protostars and compare that to the properties of the general population of Class 0/I and flat SED protostars and find that there is an indication, albeit at low statistical significance, that the outflow driving protostars are drawn from a population with lower A$_{V}$, higher L$_{bol}$, and lower T$_{bol}$ than the general population of protostars.

  17. Self-regulated gravitational accretion in protostellar discs

    CERN Document Server

    Vorobyov, E I

    2007-01-01

    We present a numerical model for the evolution of a protostellar disc that has formed self-consistently from the collapse of a molecular cloud core. The global evolution of the disc is followed for several million years after its formation. The capture of a wide range of spatial and temporal scales is made possible by use of the thin-disc approximation. We focus on the role of gravitational torques in transporting mass inward and angular momentum outward during different evolutionary phases of a protostellar disc with disc-to-star mass ratio of order 0.1. In the early phase, when the infall of matter from the surrounding envelope is substantial, mass is transported inward by the gravitational torques from spiral arms that are a manifestation of the envelope-induced gravitational instability in the disc. In the late phase, when the gas reservoir of the envelope is depleted, the distinct spiral structure is replaced by ongoing irregular nonaxisymmetric density perturbations. The amplitude of these density pertu...

  18. Accretion and magnetic field morphology around Class 0 stage protostellar discs

    CERN Document Server

    Seifried, D; Pudritz, R E; Klessen, R S

    2014-01-01

    We analyse the results of existing and newly performed and simulations of turbulent, collapsing molecular cloud cores focussing on the formation of Class 0 stage protostellar discs and the physical conditions in their surroundings. We show that for a wide range of initial conditions rotationally supported discs are formed in the Class 0 stage already. In particular, we show that even mild, i.e. subsonic turbulent motions, reduce the magnetic braking efficiency sufficiently in order to allow Keplerian discs to form. Based on this result we suggest that already during the Class 0 stage the fraction of Keplerian discs is significantly higher than 50%. This is consistent with recent observational trends but significantly higher than predictions based on simulations with misaligned magnetic fields and disc angular momentum vectors, demonstrating the importance of turbulent motions for the formation of Keplerian discs. We show that the accretion of mass and angular momentum in the surroundings of protostellar discs...

  19. [Kelvin-Helmholtz instability in protostellar jets

    Science.gov (United States)

    Stone, James; Hardee, Philip

    1996-01-01

    NASA grant NAG 5 2866, funded by the Astrophysics Theory Program, enabled the study the Kelvin-Helmholtz instability in protostellar jets. In collaboration with co-investigator Philip Hardee, the PI derived the analytic dispersion relation for the instability in including a cooling term in the energy equation which was modeled as one of two different power laws. Numerical solutions to this dispersion relation over a wide range of perturbation frequencies, and for a variety of parameter values characterizing the jet (such as Mach number, and density ratio) were found It was found that the growth rates and wavelengths associated with unstable roots of the dispersion relation in cooling jets are significantly different than those associated with adiabatic jets, which have been studied previously. In collaboration with graduate student Jianjun Xu (funded as a research associate under this grant), hydrodynamical simulations were used to follow the growth of the instability into the nonlinear regime. It was found that asymmetric surface waves lead to large amplitude, sinusoidal distortions of the jet, and ultimately to disruption Asymmetric body waves, on the other hand, result in the formation of shocks in the jet beam in the nonlinear regime. In cooling jets, these shocks lead to the formation of dense knots and filaments of gas within the jet. For sufficiently high perturbation frequencies, however, the jet cannot respond and it remains symmetric. Applying these results to observed systems, such as the Herbig-Haro jets HH34, HH111 and HH47 which have been observed with the Hubble Space Telescope, we predicted that some of the asymmetric structures observed in these systems could be attributed to the K-H modes, but that perturbations on timescales associated with the inner disk (about 1 year) would be too rapid to cause disruption. Moreover, it was discovered that weak shock 'spurs' in the ambient gas produced by ripples in the jet surface due to nonlinear, modes of

  20. Infall-Driven Protostellar Accretion and the Solution to the Luminosity Problem

    CERN Document Server

    Padoan, Paolo; Nordlund, Åke

    2014-01-01

    We investigate the role of mass infall in the formation and evolution of protostars. To avoid ad hoc initial and boundary conditions, we consider the infall resulting self-consistently from modeling the formation of stellar clusters in turbulent molecular clouds. We show that protostellar infall rates in turbulent clouds are always comparable to or larger than observed accretion rates, and thus cannot be neglected in modeling the luminosity of protostars and the evolution of disks, even after the embedded phase of protostars. We find large variations of infall rates from protostar to protostar, and large fluctuations during the evolution of individuals protostars. In most cases, the accretion rate is initially of order 10$^{-5}$ M$_{\\odot}$ yr$^{-1}$, and may either decay rapidly in the formation of low-mass stars, or remain relatively large when more massive stars are formed. The simulation reproduces well the observed characteristic values and scatter of protostellar luminosities and matches the observed pr...

  1. ALMA detection of the rotating molecular disk wind drom the young star HD 163296

    CERN Document Server

    Klaassen, P D; Mathews, G S; De Gregorio-Monsalvo, J C Mottram I; van Dishoeck, E F; Takahashi, S; Akiyama, E; Chapillon, E; Espada, D; Hales, A; Hogerheijde, M R; Rawlings, M; Schmalzl, M; Testi, L

    2013-01-01

    Disk winds have been postulated as a mechanism for angular momentum release in protostellar systems for decades. HD 163296 is a Herbig Ae star surrounded by a disk and has been shown to host a series of HH knots (HH 409) with bow shocks associated with the farthest knots. Here we present ALMA Science Verification data of CO J=2-1 and J=3-2 emission which are spatially coincident with the blue shifted jet of HH knots, and offset from the disk by -18.6 km/s. The emission has a double corkscrew morphology and extends more than 10" from the disk with embedded emission clumps coincident with jet knots. We interpret this double corkscrew as emission from material in a molecular disk wind, and that the compact emission near the jet knots is being heated by the jet which is moving at much higher velocities. We show that the J=3-2 emission is likely heavily filtered by the interferometer, but the J=2-1 emission suffers less due to the larger beam and measurable angular scales. Excitation analysis suggests temperatures...

  2. Long-term Evolution of Photoevaporating Protoplanetary Disks

    CERN Document Server

    Bae, Jaehan; Zhu, Zhaohuan; Gammie, Clarles

    2013-01-01

    We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically-thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting of $\\lesssim20 %$ of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly-rotating c...

  3. ALMA Observations of Infalling Flows toward the Keplerian Disk around the Class I Protostar L1489 IRS

    CERN Document Server

    Yen, Hsi-Wei; Ohashi, Nagayoshi; Aikawa, Yuri; Aso, Yusuke; Koyamatsu, Shin; Machida, Masahiro N; Saigo, Kazuya; Saito, Masao; Tomida, Kengo; Tomisaka, Kohji

    2014-01-01

    We have conducted ALMA observations in the 1.3 mm continuum and 12CO (2-1), C18O (2-1) and SO (5_6-4_5) lines toward L1489 IRS, a Class I protostar surrounded by a Keplerian disk and an infalling envelope. The Keplerian disk is clearly identified in the 12CO and C18O emission, and its outer radius (~700 AU) and mass (~0.005 Msun) are comparable to those of disks around T Tauri stars. The protostellar mass is estimated to be 1.6 Msun with the inclination angle of 66 deg. In addition to the Keplerian disk, there are blueshifted and redshifted off-axis protrusions seen in the C18O emission pointing toward the north and the south, respectively, adjunct to the middle part of the Keplerian disk. The shape and kinematics of these protrusions can be interpreted as streams of infalling flows with a conserved angular momentum following parabolic trajectories toward the Keplerian disk, and the mass infalling rate is estimated to be ~5E-7 Msun/yr. The specific angular momentum of the infalling flows (~2.5E-3 km/s*pc) is ...

  4. Consistent SPH Simulations of Protostellar Collapse and Fragmentation

    Science.gov (United States)

    Gabbasov, Ruslan; Sigalotti, Leonardo Di G.; Cruz, Fidel; Klapp, Jaime; Ramírez-Velasquez, José M.

    2017-02-01

    We study the consistency and convergence of smoothed particle hydrodynamics (SPH) as a function of the interpolation parameters, namely the number of particles N, the number of neighbors n, and the smoothing length h, using simulations of the collapse and fragmentation of protostellar rotating cores. The calculations are made using a modified version of the GADGET-2 code that employs an improved scheme for the artificial viscosity and power-law dependences of n and h on N, as was recently proposed by Zhu et al., which comply with the combined limit N\\to ∞ , h\\to 0, and n\\to ∞ with n/N\\to 0 for full SPH consistency as the domain resolution is increased. We apply this realization to the “standard isothermal test case” in the variant calculated by Burkert & Bodenheimer and the Gaussian cloud model of Boss to investigate the response of the method to adaptive smoothing lengths in the presence of large density and pressure gradients. The degree of consistency is measured by tracking how well the estimates of the consistency integral relations reproduce their continuous counterparts. In particular, C 0 and C 1 particle consistency is demonstrated, meaning that the calculations are close to second-order accuracy. As long as n is increased with N, mass resolution also improves as the minimum resolvable mass {M}\\min ∼ {n}-1. This aspect allows proper calculation of small-scale structures in the flow associated with the formation and instability of protostellar disks around the growing fragments, which are seen to develop a spiral structure and fragment into close binary/multiple systems as supported by recent observations.

  5. Secular Evolution in Disk Galaxies

    CERN Document Server

    Kormendy, John

    2013-01-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via available evolution processes. The inner parts shrink and the outer parts expand, provided that some physical process transports energy or angular momentum outward. The evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks, and galaxy disks are all fundamentally similar. These processes for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. Part 1 discusses formation, growth, and death of bars. Part 2 details the slow ("secular") rearrangement of angular momentum that results from interactions between stars or gas and nonaxisymmetries such as bars. We have a heuristic understanding of how this forms outer rings, inner rings, and stuff dumped into the center. Observations show that barred galaxies have central concentrations of gas and star formation. Timescales imply that they grow central "pseudobulges" that get mistaken for ellip...

  6. The role of angular momentum transport in establishing the accretion rate-protostellar mass correlation

    Science.gov (United States)

    DeSouza, Alexander L.; Basu, Shantanu

    2017-02-01

    We model the mass accretion rate M˙ to stellar mass M* correlation that has been inferred from observations of intermediate to upper mass T Tauri stars-that is M˙ ∝ M*1.3±0.3. We explain this correlation within the framework of quiescent disk evolution, in which accretion is driven largely by gravitational torques acting in the bulk of the mass and volume of the disk. Stresses within the disk arise from the action of gravitationally driven torques parameterized in our 1D model in terms of Toomre's Q criterion. We do not model the hot inner sub-AU scale region of the disk that is likely stable according to this criterion, and appeal to other mechanisms to remove or redistribute angular momentum and allow accretion onto the star. Our model has the advantage of agreeing with large-scale angle-averaged values from more complex nonaxisymmetric calculations. The model disk transitions from an early phase (dominated by initial conditions inherited from the burst mode of accretion) into a later self-similar mode characterized by a steeper temporal decline in M˙. The models effectively reproduce the spread in mass accretion rates that have been observed for protostellar objects of 0.2 M⊙ ≤ M* ≤ 3.0 M⊙, such as those found in the ρ Ophiuchus and Taurus star forming regions. We then compare realistically sampled populations of young stellar objects produced by our model to their observational counterparts. We find these populations to be statistically coincident, which we argue is evidence for the role of gravitational torques in the late time evolution of quiescent protostellar disks.

  7. Formation and recondensation of complex organic molecules during protostellar luminosity outbursts

    CERN Document Server

    Taquet, Vianney; Charnley, Steven B

    2016-01-01

    During the formation of stars, the accretion of the surrounding material toward the central object is thought to undergo strong luminosity outbursts, followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas phase formation and the recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas phase chemical network forming complex organic molecules in which ammonia plays a key role. The model calculations presented here demonstrate that ion-molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores, without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas phase reaction bra...

  8. Gravitational Instabilities in Circumstellar Disks

    Science.gov (United States)

    Kratter, Kaitlin; Lodato, Giuseppe

    2016-09-01

    Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review, we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small-scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability supplemented with a survey of numerical simulations that aim to capture the nonlinear evolution. We emphasize the role of thermodynamics and large-scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared with their host star, Md/M*≥0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. Although instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to the development of a turbulent cascade in thin disks and the role of mode-mode coupling in setting the maximum angular

  9. Vibrationally excited CS: A new probe of conditions in young protostellar systems

    Science.gov (United States)

    Walker, Christopher K.; Maloney, Philip R.; Serabyn, E.

    1994-01-01

    We present the first detection of vibrationally excited C(32)S J = 10-9 and J = 7-6 emission toward a young stellar object (YSO). Toward IRAS 16293-2422, the vibrationally excited C(32)S emission is redshifted approximately 3.9 km/s from the systemic velocity of the core. The emission must arise in warm (T greater than or approximately equal 1000 K), dense (n greater than or approximately equal to 10(exp 11)-10(exp 12) per cc) gas. The most plausible origin for the emission appears to be self-gravitating instabilities in a protostellar accretion disk, which produce waves and shocks.

  10. Radiation-Hydrodynamic Simulations of Massive Star Formation with Protostellar Outflows

    Energy Technology Data Exchange (ETDEWEB)

    Cunningham, A J; Klein, R I; Krumholz, M R; McKee, C F

    2011-03-02

    We report the results of a series of AMR radiation-hydrodynamic simulations of the collapse of massive star forming clouds using the ORION code. These simulations are the first to include the feedback effects protostellar outflows, as well as protostellar radiative heating and radiation pressure exerted on the infalling, dusty gas. We find that that outflows evacuate polar cavities of reduced optical depth through the ambient core. These enhance the radiative flux in the poleward direction so that it is 1.7 to 15 times larger than that in the midplane. As a result the radiative heating and outward radiation force exerted on the protostellar disk and infalling cloud gas in the equatorial direction are greatly diminished. The simultaneously reduces the Eddington radiation pressure barrier to high-mass star formation and increases the minimum threshold surface density for radiative heating to suppress fragmentation compared to models that do not include outflows. The strength of both these effects depends on the initial core surface density. Lower surface density cores have longer free-fall times and thus massive stars formed within them undergo more Kelvin contraction as the core collapses, leading to more powerful outflows. Furthermore, in lower surface density clouds the ratio of the time required for the outflow to break out of the core to the core free-fall time is smaller, so that these clouds are consequently influenced by outflows at earlier stages of collapse. As a result, outflow effects are strongest in low surface density cores and weakest in high surface density one. We also find that radiation focusing in the direction of outflow cavities is sufficient to prevent the formation of radiation pressure-supported circumstellar gas bubbles, in contrast to models which neglect protostellar outflow feedback.

  11. Protostellar outflows with Smoothed Particle Magnetohydrodynamics (SPMHD)

    CERN Document Server

    Bürzle, Florian; Stasyszyn, Federico; Dolag, Klaus; Klessen, Ralf S

    2011-01-01

    The protostellar collapse of a molecular cloud core is usually accompanied by outflow phenomena. The latter are thought to be driven by magnetorotational processes from the central parts of the protostellar disc. While several 3D AMR/nested grid studies of outflow phenomena in collapsing magnetically supercritical dense cores have been reported in the literature, so far no such simulation has been performed using the Smoothed Particle Hydrodynamics (SPH) method. This is mainly due to intrinsic numerical difficulties in handling magnetohydrodynamics within SPH, which only recently were partly resolved. In this work, we use an approach where we evolve the magnetic field via the induction equation, augmented with stability correction and divergence cleaning schemes. We consider the collapse of a rotating core of one solar mass, threaded by a weak magnetic field initially parallel to the rotation axis so that the core is magnetically supercritical. We show, that Smoothed Particle Magnetohydrodynamics (SPMHD) is a...

  12. Radio polarization study in protostellar jet

    CERN Document Server

    Cécere, Mariana; Araudo, Anabella T; De Colle, Fabio; Esquivel, Alejandro; Carrasco-González, Carlos; Rodríguez, Luis F

    2015-01-01

    Synchrotron radiation is commonly observed associated with shocks of different velocities, ranging from relativistic shocks associated with, e.g., active galactic nuclei, gamma-ray bursts or microquasars to weakly- or non-relativistic flows as those observed e.g. in supernovae and supernova remnants. Recent observations of polarization in protostellar jets are important not only because they extend the range over which the acceleration process works, but also because they allow to measure directly the jet and interstellar magnetic field structure and intensity, thus giving insights on the jet ejection mechanism itself. In this paper, we compute for the first time polarized (synchrotron) and non polarized (thermal-X-ray) synthetic emission maps from axisymmetrical simulations of magnetized protostellar jets. We consider models with different jet velocities and variability, as well as models with toroidal or helical magnetic field. Our simulations show that variable, low-density jets with velocities ~ 1000km/s ...

  13. A multiple system of high-mass YSOs surrounded by disks in NGC 7538 IRS1 . Gas dynamics on scales of 10-700 AU from CH3OH maser and NH3 thermal lines

    Science.gov (United States)

    Moscadelli, L.; Goddi, C.

    2014-06-01

    Context. It has been claimed that NGC 7538 IRS1 is a high-mass young stellar object (YSO) with 30 M⊙, surrounded by a rotating Keplerian disk, probed by a linear distribution of methanol masers. The YSO is also powering a strong compact Hii region or ionized wind, and is driving at least one molecular outflow. The axis orientations of the different structures (ionized gas, outflow, and disk) are, however, misaligned, which has led to the different competing models proposed to explain individual structures. Aims: We investigate the 3D kinematics and dynamics of circumstellar gas with very high linear resolution, from tens to 1500 AU, with the ultimate goal of building a comprehensive dynamical model for what is considered the best high-mass accretion disk candidate around an O-type young star in the northern hemisphere. Methods: We used high-angular resolution observations of 6.7 GHz CH3OH masers with the EVN, NH3 inversion lines with the JVLA B-Array, and radio continuum with the VLA A-Array. In particular, we employed four different observing epochs of EVN data at 6.7 GHz, spanning almost eight years, which enabled us to measure line-of-sight (l.o.s.) accelerations and proper motions of CH3OH masers, besides l.o.s. velocities and positions (as done in previous works). In addition, we imaged highly excited NH3 inversion lines, from (6,6) to (13,13), which enabled us to probe the hottest molecular gas very close to the exciting source(s). Results: We confirm previous results that five 6.7 GHz maser clusters (labeled from "A" to "E") are distributed over a region extended N-S across ≈1500 AU, and are associated with three components of the radio continuum emission. We propose that these maser clusters identify three individual high-mass YSOs in NGC 7538 IRS1, named IRS1a (associated with clusters "B" and "C"), IRS1b (associated with cluster "A"), and IRS1c (associated with cluster "E"). We find that the 6.7 GHz masers distribute along a line, with a regular

  14. The formation of molecules in protostellar winds

    Energy Technology Data Exchange (ETDEWEB)

    Glassgold, A.E.; Mamon, G.A.; Huggins, P.J. (New York University, NY (USA))

    1991-05-01

    The production and destruction processes for molecules in very fast protostellar winds are analyzed and modeled with a one-dimensional chemical kinetics code. Radial density and temperature distributions suggested by protostellar theory are explored as are a range of mass-loss rates. The efficiency of in situ formation of heavy molecules is found to be high if the wind temperature falls sufficiently rapidly, as indicated by theory. The degree of molecular conversion is a strong function of the mass-loss rate and of density gradients associated with the acceleration and collimation of the wind. Even in cases where essentially all of the heavy atoms are processed into molecules, a significant fraction of atomic hydrogen remains so that hghly molecular, protostellar winds are able to emit the 21-cm line. Although CO has a substantial abundance in most models relevant to very young protostars, high abundances of other molecules such as SiO and H2O signify more complete association characteristic of winds containing regions of very high density. Although the models apply only to regions close to the protostar, they are in qualitative accord with recent observations at much larger distances of both atomic and molecular emission from extremely high-velocity flow. 57 refs.

  15. The formation of molecules in protostellar winds

    Science.gov (United States)

    Glassgold, A. E.; Mamon, G. A.; Huggins, P. J.

    1991-05-01

    The production and destruction processes for molecules in very fast protostellar winds are analyzed and modeled with a one-dimensional chemical kinetics code. Radial density and temperature distributions suggested by protostellar theory are explored as are a range of mass-loss rates. The efficiency of in situ formation of heavy molecules is found to be high if the wind temperature falls sufficiently rapidly, as indicated by theory. The degree of molecular conversion is a strong function of the mass-loss rate and of density gradients associated with the acceleration and collimation of the wind. Even in cases where essentially all of the heavy atoms are processed into molecules, a significant fraction of atomic hydrogen remains so that highly molecular, protostellar winds are able to emit the 21-cm line. Although CO has a substantial abundance in most models relevant to very young protostars, high abundances of other molecules such as SiO and H2O signify more complete association characteristic of winds containing regions of very high density. Although the models apply only to regions close to the protostar, they are in qualitative accord with recent observations at much larger distances of both atomic and molecular emission from extremely high-velocity flow.

  16. The formation of molecules in protostellar winds

    Science.gov (United States)

    Glassgold, A. E.; Mamon, G. A.; Huggins, P. J.

    1991-01-01

    The production and destruction processes for molecules in very fast protostellar winds are analyzed and modeled with a one-dimensional chemical kinetics code. Radial density and temperature distributions suggested by protostellar theory are explored as are a range of mass-loss rates. The efficiency of in situ formation of heavy molecules is found to be high if the wind temperature falls sufficiently rapidly, as indicated by theory. The degree of molecular conversion is a strong function of the mass-loss rate and of density gradients associated with the acceleration and collimation of the wind. Even in cases where essentially all of the heavy atoms are processed into molecules, a significant fraction of atomic hydrogen remains so that hghly molecular, protostellar winds are able to emit the 21-cm line. Although CO has a substantial abundance in most models relevant to very young protostars, high abundances of other molecules such as SiO and H2O signify more complete association characteristic of winds containing regions of very high density. Although the models apply only to regions close to the protostar, they are in qualitative accord with recent observations at much larger distances of both atomic and molecular emission from extremely high-velocity flow.

  17. Protostellar Outflows and Radiative Feedback from Massive Stars. II. Feedback, Star Formation Efficiency, and Outflow Broadening

    CERN Document Server

    Kuiper, Rolf; Yorke, Harold W

    2016-01-01

    We perform two-dimensional axially symmetric radiation-hydrodynamic simulations to assess the impact of outflows and radiative force feedback from massive protostars by varying when the protostellar outflow starts, the ratio of ejection to accretion rates, and the strength of the wide angle disk wind component. The star formation efficiency, i.e. the ratio of final stellar mass to initial core mass, is dominated by radiative forces and the ratio of outflow to accretion rates. Increasing this ratio has three effects: First, the protostar grows slower with a lower luminosity at any given time, lowering radiative feedback. Second, bipolar cavities cleared by the outflow are larger, further diminishing radiative feedback on disk and core scales. Third, the higher momentum outflow sweeps up more material from the collapsing envelope, decreasing the protostar's potential mass reservoir via entrainment. The star formation efficiency varies with the ratio of ejection to accretion rates from 50% in the case of very we...

  18. Gravitational Instabilities in Disks with Radiative Cooling

    CERN Document Server

    Mejia, A C; Pickett, M K; Mej\\'ia, Annie C.; Durisen, Richard H.; Pickett, Megan K.

    2003-01-01

    Previous simulations of self-gravitating protostellar disks have shown that, once developed, gravitational instabilities are enhanced by cooling the disk constantly during its evolution (Pickett et al. 2002). These earlier calculations included a very simple form of volumetric cooling, with a constant cooling time throughout the disk, which acted against the stabilizing effects of shock heating. The present work incorporates more realistic treatments of energy transport. The initial disk model extends from 2.3 to 40 AU, has a mass of 0.07 Msun and orbits a 0.5 Msun star. The models evolve for a period of over 2500 years, during which extensive spiral arms form. The disks structure is profoundly altered, transient clumps form in one case, but no permanent bound companion objects develop.

  19. Protostellar Outflow Evolution in Turbulent Environments

    Energy Technology Data Exchange (ETDEWEB)

    Cunningham, A; Frank, A; Carroll, J; Blackman, E; Quillen, A

    2008-04-11

    The link between turbulence in star formatting environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers-type turbulence and produces a driving scale-length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star forming environments. In the last section we contrast our work and its conclusions with previous studies which claim that jets can not be the source of turbulence.

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

    CERN Document Server

    Vorobyov, Eduard I; Guedel, Manuel; Lin, D N C

    2016-01-01

    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. We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment, as well as numerical hydrodynamic simulations of isolated disks hosting giant planets, to derive the properties of the gaps that form in both cases. 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 b...

  1. Generation of a dynamo magnetic field in a protoplanetary accretion disk

    Science.gov (United States)

    Stepinski, T.; Levy, E. H.

    1987-01-01

    A new computational technique is developed that allows realistic calculations of dynamo magnetic field generation in disk geometries corresponding to protoplanetary and protostellar accretion disks. The approach is of sufficient generality to allow, in the future, a wide class of accretion disk problems to be solved. Here, basic modes of a disk dynamo are calculated. Spatially localized oscillatory states are found to occur in Keplerain disks. A physical interpretation is given that argues that spatially localized fields of the type found in these calculations constitute the basic modes of a Keplerian disk dynamo.

  2. ALMA Observations of Infalling Flows toward the Keplerian Disk around the Class I Protostar L1489 IRS

    Science.gov (United States)

    Yen, Hsi-Wei; Takakuwa, Shigehisa; Ohashi, Nagayoshi; Aikawa, Yuri; Aso, Yusuke; Koyamatsu, Shin; Machida, Masahiro N.; Saigo, Kazuya; Saito, Masao; Tomida, Kengo; Tomisaka, Kohji

    2014-09-01

    We have conducted ALMA observations in the 1.3 mm continuum and 12CO (2-1), C18O (2-1), and SO (56-45) lines toward L1489 IRS, a Class I protostar surrounded by a Keplerian disk and an infalling envelope. The Keplerian disk is clearly identified in the 12CO and C18O emission, and its outer radius (~700 AU) and mass (~0.005 M ⊙) are comparable to those of disks around T Tauri stars. The protostellar mass is estimated to be 1.6 M ⊙ with the inclination angle of 66°. In addition to the Keplerian disk, there are blueshifted and redshifted off-axis protrusions seen in the C18O emission pointing toward the north and the south, respectively, adjunct to the middle part of the Keplerian disk. The shape and kinematics of these protrusions can be interpreted as streams of infalling flows with a conserved angular momentum following parabolic trajectories toward the Keplerian disk, and the mass infalling rate is estimated to be ~5 × 10-7 M ⊙ yr-1. The specific angular momentum of the infalling flows (~2.5 × 10-3 km s-1 pc) is comparable to that at the outer radius of the Keplerian disk (~4.8 × 10-3 km s-1 pc). The SO emission is elongated along the disk major axis and exhibits a linear velocity gradient along the axis, which is interpreted to mean that the SO emission primarily traces a ring region in the flared Keplerian disk at radii of ~250-390 AU. The local enhancement of the SO abundance in the ring region can be due to the accretion shocks at the centrifugal radius where the infalling flows fall onto the disk. Our ALMA observations unveiled both the Keplerian disk and the infalling gas onto the disk, and the disk can further grow by accreting material and angular momenta from the infalling gas.

  3. Imaging the water-snow line during a protostellar outburst

    CERN Document Server

    Cieza, Lucas A; Tobin, John; Bos, Steven P; Williams, Jonathan P; Perez, Sebastian; Zhu, Zhaohuan; Caceres, Claudio; Canovas, Hector; Dunham, Michael M; Hales, Antonio; Prieto, Jose L; Principe, David A; Schreiber, Matthias R; Ruiz-Rodriguez, Dary; Zurlo, Alice

    2016-01-01

    A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296, at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. Here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing ...

  4. Exploring Disks Around Planets

    Science.gov (United States)

    Kohler, Susanna

    2017-07-01

    Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. Weve never detected one of these circumplanetary disks before but thanks to new simulations, we now have a better idea of what to look for.Image from previous work simulating a Jupiter-mass planet forming inside a circumstellar disk. The planet has its own circumplanetary disk of accreted material. [Frdric Masset]Elusive DisksIn the formation of giant planets, we think the final phase consists of accretion onto the planet from a disk that surrounds it. This circumplanetary disk is important to understand, since it both regulates the late gas accretion and forms the birthplace of future satellites of the planet.Weve yet to detect a circumplanetary disk thus far, because the resolution needed to spot one has been out of reach. Now, however, were entering an era where the disk and its kinematics may be observable with high-powered telescopes (like the Atacama Large Millimeter Array).To prepare for such observations, we need models that predict the basic characteristics of these disks like the mass, temperature, and kinematic properties. Now a researcher at the ETH Zrich Institute for Astronomy in Switzerland, Judit Szulgyi, has worked toward this goal.Simulating CoolingSzulgyi performs a series of 3D global radiative hydrodynamic simulations of 1, 3, 5, and 10 Jupiter-mass (MJ) giant planets and their surrounding circumplanetary disks, embedded within the larger circumstellar disk around the central star.Density (left column), temperature (center), and normalized angular momentum (right) for a 1 MJ planet over temperatures cooling from 10,000 K (top) to 1,000 K (bottom). At high temperatures, a spherical circumplanetary envelope surrounds the planet, but as the planet cools, the envelope transitions around 64,000 K to a flattened disk. [Szulgyi 2017]This work explores the effects of different planet temperatures and

  5. Structure and Stability of Steady Protostellar Accretion Flows - Part Two - Linear Stability Analysis

    Science.gov (United States)

    Balluch, M.

    1991-03-01

    Recent developments concerning spherically symmetric (1D-) numerical models of protostellar evolution show that steady protostellar accretion flows (resp. their shockfronts) may be unstable at least in the very early (Tscharnuter 1987a) and late stages (Balluch 1988) of accretion. A global, linear stability analysis of the structure of steady protostellar accretion flows with a shock discontinuity (Balluch 1990) is therefore presented to investigate such flows by different methods. Thereby three characteristic wave types, the radiation-, radiation diffusion- and acoustic modes were found. In the `ideal case' of a perfect gas law and constant opacity, the shockfront appears to be oscillatory unstable due to critical cooling as long as the mass flux rate is larger than a critical one of Mṡcrit = 10-6 Msun yr-1. In the `real case' with more realistic constitutive relations, an additional vibrational instability occurs due to the κ-mechanism in the outer layers of the core. This is shown to be the case in the whole range of core masses between 0.01 and 1 Msun, mass flow rates between 10-3 and 10-7 Msun yr-1 and different outer boundary conditions (corresponding to different states of the surrounding interstellar cloud). Analysing the first, outer protostellar cores before they get dynamically unstable due to H2-dissociation in their interiors, similar instabilities as mentioned above were found. Now the unstable κ-behaviour is due to dust instead of the deep ionisation zone as in the case of second, inner cores. According to the linear analysis, the instabilities should first appear in the velocity and the radiation flux in the settling zone. In the case of first, outer cores, these variations should be accompanied by an oscillation of the radiation flux in the region upstream from the shock up to r = 1014 cm. Sooner or later, the shockfront should oscillate in both cases too. These results are finally compared with the characteristics of the accretion shock

  6. Magnetic Field Amplification via Protostellar Disc Dynamos

    CERN Document Server

    Dyda, Sergei; Ustyugova, Galina V; Koldoba, Alexander V; Wasserman, Ira

    2015-01-01

    We model the generation of a magnetic field in a protostellar disc using an \\alpha-dynamo and perform axisymmetric magnetohydrodynamics (MHD) simulations of a T Tauri star. We find that for small values of the dimensionless dynamo parameter $\\alpha_d$ the poloidal field grows exponentially at a rate ${\\sigma} \\propto {\\Omega}_K \\sqrt{\\alpha_d}$ , before saturating to a value $\\propto \\sqrt{\\alpha_d}$ . The dynamo excites dipole and octupole modes, but quadrupole modes are suppressed, because of the symmetries of the seed field. Initial seed fields too weak to launch MHD outflows are found to grow sufficiently to launch winds with observationally relevant mass fluxes of order $10^{-9} M_{\\odot}/\\rm{yr}$ for T Tauri stars. For large values of $\\alpha_d$ magnetic loops are generated over the entire disc. These quickly come to dominate the disc dynamics and cause the disc to break up due to the magnetic pressure.

  7. Angular momentum transport in protostellar discs

    CERN Document Server

    Salmeron, Roberto Aureliano; Wardle, M; Salmeron, Raquel; Konigl, Arieh; Wardle, Mark

    2006-01-01

    Angular momentum transport in protostellar discs can take place either radially, through turbulence induced by the magnetorotational instability (MRI), or vertically, through the torque exerted by a large-scale magnetic field that threads the disc. Using semi-analytic and numerical results, we construct a model of steady-state discs that includes vertical transport by a centrifugally driven wind as well as MRI-induced turbulence. We present approximate criteria for the occurrence of either one of these mechanisms in an ambipolar diffusion-dominated disc. We derive ``strong field'' solutions in which the angular momentum transport is purely vertical and ``weak field'' solutions that are the stratified-disc analogues of the previously studied MRI channel modes; the latter are transformed into accretion solutions with predominantly radial angular-momentum transport when we implement a turbulent-stress prescription based on published results of numerical simulations. We also analyze ``intermediate field strength'...

  8. Protostellar Outflows and Radiative Feedback from Massive Stars. II. Feedback, Star-formation Efficiency, and Outflow Broadening

    Science.gov (United States)

    Kuiper, Rolf; Turner, Neal J.; Yorke, Harold W.

    2016-11-01

    We perform two-dimensional axially symmetric radiation hydrodynamic simulations to assess the impact of outflows and radiative force feedback from massive protostars by varying when the protostellar outflow starts, and to determine the ratio of ejection to accretion rates and the strength of the wide-angle disk wind component. The star-formation efficiency, i.e., the ratio of final stellar mass to initial core mass, is dominated by radiative forces and the ratio of outflow to accretion rates. Increasing this ratio has three effects. First, the protostar grows slower with a lower luminosity at any given time, lowering radiative feedback. Second, bipolar cavities cleared by the outflow become larger, further diminishing radiative feedback on disk and core scales. Third, the higher momentum outflow sweeps up more material from the collapsing envelope, decreasing the protostar's potential mass reservoir via entrainment. The star-formation efficiency varies with the ratio of ejection to accretion rates from 50% in the case of very weak outflows to as low as 20% for very strong outflows. At latitudes between the low-density bipolar cavity and the high-density accretion disk, wide-angle disk winds remove some of the gas, which otherwise would be part of the accretion flow onto the disk; varying the strength of these wide-angle disk winds, however, alters the final star-formation efficiency by only ±6%. For all cases, the opening angle of the bipolar outflow cavity remains below 20° during early protostellar accretion phases, increasing rapidly up to 65° at the onset of radiation pressure feedback.

  9. The Herschel Orion Protostar Survey: Spectral Energy Distributions and Fits Using a Grid of Protostellar Models

    CERN Document Server

    Furlan, E; Ali, B; Stutz, A M; Stanke, T; Tobin, J J; Megeath, S T; Osorio, M; Hartmann, L; Calvet, N; Poteet, C A; Booker, J; Manoj, P; Watson, D M; Allen, L

    2016-01-01

    We present key results from the Herschel Orion Protostar Survey (HOPS): spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion molecular clouds. This is the largest sample of protostars studied in a single, nearby star-formation complex. With near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and sub-millimeter photometry from APEX, our SEDs cover 1.2-870 $\\mu$m and sample the peak of the protostellar envelope emission at ~100 $\\mu$m. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II pre-main-sequence stars. We implement a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30400 model SEDs and use it to determine the best-fit model parameters for each protostar. We argue that far-IR data are essential for accurate cons...

  10. PROSAC: A Submillimeter Array survey of low-mass protostars. II. The mass evolution of envelopes, disks, and stars from the Class 0 through I stages

    CERN Document Server

    Jorgensen, Jes K; Visser, Ruud; Bourke, Tyler L; Wilner, David J; Lommen, Dave; Hogerheijde, Michiel R; Myers, Philip C

    2009-01-01

    The key question about early protostellar evolution is how matter is accreted from the large-scale molecular cloud, through the circumstellar disk onto the central star. A sample of 20 Class 0 and I protostars has been observed in continuum at (sub)millimeter wavelengths at high angular resolution with the Submillimeter Array. Using detailed dust radiative transfer models, we have developed a framework for disentangling the continuum emission from the envelopes and disks, and from that estimated their masses. For the Class I sources in the sample, HCO+ 3-2 line emission has furthermore been observed with the Submillimeter Array. Four of these sources show signs of Keplerian rotation, constraining the masses of the central stars. Both Class 0 and I protostars are surrounded by disks with typical masses of about 0.05 M_sun. No evidence is found for a correlation between the disk mass and evolutionary stage of the young stellar objects. This contrasts the envelope mass, which decreases sharply from 1 M_sun in th...

  11. FORMATION AND RECONDENSATION OF COMPLEX ORGANIC MOLECULES DURING PROTOSTELLAR LUMINOSITY OUTBURSTS

    Energy Technology Data Exchange (ETDEWEB)

    Taquet, Vianney [Leiden Observatory, Leiden University, P.O. Box 9513, 2300-RA Leiden (Netherlands); Wirström, Eva S. [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden); Charnley, Steven B. [Astrochemistry Laboratory and The Goddard Center for Astrobiology, Mailstop 691, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20770 (United States)

    2016-04-10

    During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion–molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.

  12. POLARIZATION OF FIR EMISSION FROM T-TAURI DISKS

    Directory of Open Access Journals (Sweden)

    J. Cho

    2009-01-01

    Full Text Available Recent observations of 850 gm sub-mm polarization from T-Tauri disks open up the possibility of studying the magnetic eld structure within protostellar disks. The degree of polarization is around 3% and the direction of polarization is perpendicular to the disk. Since thermal emission from dust grains dominates the spectral energy distribution at sub-mm/far-infrared (FIR wavelengths, dust grains are thought to be the cause of the polarization. We discuss grain alignment by radiation and we explore the efficiency of dust alignment in T-Tauri disks. The calculations show that dust grains located far away from the central proto-star are more efficiently aligned. In the presence of a regular magnetic eld, the aligned grains produce polarized emission in sub-mm/FIR wavelengths. The direction of polarization is perpendicular to the local magnetic eld direction. When we use a recent T-Tauri disk model and take a Mathis-Rumpl-Nordsieck-type distribution with maximum grain size of 500{1000 -m, the degree of polarization is around 2{3% level at wavelengths larger than - 100 gm. Our work indicates that multifrequency infrared polarimetric studies of protostellar disks can provide good insights into the details of their magnetic structure. We also provide predictions for polarize emission for disks viewed at di erent wavelengths and viewing angles.

  13. Investigations of Protostellar Outflow Launching and Gas Entrainment: Hydrodynamic Simulations and Molecular Emission

    CERN Document Server

    Offner, S S R

    2013-01-01

    We investigate protostellar outflow evolution, gas entrainment, and star formation efficiency using radiation-hydrodynamic simulations of isolated, turbulent low-mass cores. We adopt an X-wind launching model, in which the outflow rate is coupled to the instantaneous protostellar accretion rate and evolution. We vary the outflow collimation angle from $\\theta$=0.01-0.1 and find that even well collimated outflows effectively sweep up and entrain significant core mass. The Stage 0 lifetime ranges from 0.14-0.19 Myr, which is similar to the observed Class 0 lifetime. The star formation efficiency of the cores spans 0.41-0.51. In all cases, the outflows drive strong turbulence in the surrounding material. Although the initial core turbulence is purely solenoidal by construction, the simulations converge to approximate equipartition between solenoidal and compressive motions due to a combination of outflow driving and collapse. When compared to a simulation of a cluster of protostars, which is not gravitationally ...

  14. INVESTIGATING PARTICLE ACCELERATION IN PROTOSTELLAR JETS: THE TRIPLE RADIO CONTINUUM SOURCE IN SERPENS

    Energy Technology Data Exchange (ETDEWEB)

    Rodríguez-Kamenetzky, Adriana; Valotto, Carlos [Instituto de Astronomía Teórica y Experimental, (IATE-UNC), X5000BGR Córdoba (Argentina); Carrasco-González, Carlos; Rodríguez, Luis F. [Instituto de Radioastronomía y Astrofísica (IRyA-UNAM), 58089 Morelia, México (Mexico); Araudo, Anabella [University of Oxford, Astrophysics, Keble Road, Oxford OX1 3RH (United Kingdom); Torrelles, José M. [Institut de Ciències de l’Espai (CSIC-IEEC) and Institut de Ciències del Cosmos (UB-IEEC), Martí i Franquès 1, E-08028 Barcelona (Spain); Anglada, Guillem [Instituto de Astrofísica de Andalucía, CSIC, Camino Bajo de Huétor 50, E-18008 Granada (Spain); Martí, Josep [Dept. de Física, EPS de Jaén, Universidad de Jaén, Campus Las Lagunillas s/n, A3-402, E-23071 Jaén (Spain)

    2016-02-10

    While most protostellar jets present free–free emission at radio wavelengths, synchrotron emission has also been proposed to be present in a handful of these objects. The presence of nonthermal emission has been inferred by negative spectral indices at centimeter wavelengths. In one case (the HH 80-81 jet arising from a massive protostar), its synchrotron nature was confirmed by the detection of linearly polarized radio emission. One of the main consequences of these results is that synchrotron emission implies the presence of relativistic particles among the nonrelativistic material of these jets. Therefore, an acceleration mechanism should be taking place. The most probable scenario is that particles are accelerated when the jets strongly impact against the dense envelope surrounding the protostar. Here we present an analysis of radio observations obtained with the Very Large Array of the triple radio source in the Serpens star-forming region. This object is known to be a radio jet arising from an intermediate-mass protostar. It is also one of the first protostellar jets where the presence of nonthermal emission was proposed. We analyze the dynamics of the jet and the nature of the emission and discuss these issues in the context of the physical parameters of the jet and the particle acceleration phenomenon.

  15. Role of the UV external radiation field on the presence of astrophysical ices in protostellars environments

    Science.gov (United States)

    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.

  16. Earth, Moon, Sun, and CV Accretion Disks

    CERN Document Server

    Montgomery, M M

    2009-01-01

    Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting Cataclysmic Variable (CV) Dwarf Novae systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar and black hole systems. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our a...

  17. Numerical Simulations of Disk-Planet Interactions

    Science.gov (United States)

    D'Angelo, Gennaro

    2003-06-01

    The aim of this thesis is the study the dynamical interactions occurring between a forming planet and its surrounding protostellar environment. This task is accomplished by means of both 2D and 3D numerical simulations. The first part of this work concerned global simulations in 3D. These were intended to investigate large-scale effects caused by a Jupiter-size body still in the process of accreting matter from its surroundings. Simulations show that, despite a density gap forms along the orbital path, Jupiter-mass protoplanets still accrete at a rate on the order of 0.01 Earth's masses per year when they are embedded in a minimum-mass Solar nebula. In the same conditions, the migration time scale due to gravitational torques by the disk is around 100000 years. The second part of the work was dedicated to perform 2D calculations, by employing a nested-grid technique. This method allows to carry out global simulations of planets orbiting in disks and, at the same time, to resolve in great detail the dynamics of the flow inside the Roche lobe of both massive and low-mass planets. Regardless of the planet mass, the high resolution supplied by the nested-grid technique permits an evaluation of the torques, resulting from short and very short range gravitational interactions, more reliable than the one previously estimated with the aid of numerical methods. Likewise, the mass flow onto the planet is computed in a more accurate fashion. Resulting migration time scales are in the range from 20000 years, for intermediate-mass planets, to 1000000 years, for very low-mass as well as high-mass planets. Circumplanetary disks form inside of the Roche lobe of Jupiter-size secondaries. In order to evaluate the consequences of the flat geometry on the local flow structure around planets, 3D nested-grid simulations were carried out to investigate a range of planetary masses spanning from 1.5 Earth's masses to one Jupiter's mass. Outcomes show that migration rates are relatively

  18. Improving the thin-disk models of circumstellar disk evolution. The 2+1-dimensional model

    Science.gov (United States)

    Vorobyov, Eduard I.; Pavlyuchenkov, Yaroslav N.

    2017-09-01

    Context. Circumstellar disks of gas and dust are naturally formed from contracting pre-stellar molecular cores during the star formation process. To study various dynamical and chemical processes that take place in circumstellar disks prior to their dissipation and transition to debris disks, the appropriate numerical models capable of studying the long-term disk chemodynamical evolution are required. Aims: We improve the frequently used 2D hydrodynamical model for disk evolution in the thin-disk limit by employing a better calculation of the disk thermal balance and adding a reconstruction of the disk vertical structure. Together with the hydrodynamical processes, the thermal evolution is of great importance since it influences the strength of gravitational instability and the chemical evolution of the disk. Methods: We present a new 2+1-dimensional numerical hydrodynamics model of circumstellar disk evolution, where the thin-disk model is complemented with the procedure for calculating the vertical distributions of gas volume density and temperature in the disk. The reconstruction of the disk vertical structure is performed at every time step via the solution of the time-dependent radiative transfer equations coupled to the equation of the vertical hydrostatic equilibrium. Results: We perform a detailed comparison between circumstellar disks produced with our previous 2D model and with the improved 2+1D approach. The structure and evolution of resulting disks, including the differences in temperatures, densities, disk masses, and protostellar accretion rates, are discussed in detail. Conclusions: The new 2+1D model yields systematically colder disks, while the in-falling parental clouds are warmer. Both effects act to increase the strength of disk gravitational instability and, as a result, the number of gravitationally bound fragments that form in the disk via gravitational fragmentation as compared to the purely 2D thin-disk simulations with a simplified

  19. Misalignment of magnetic fields and outflows in protostellar cores

    NARCIS (Netherlands)

    Hull, Charles L. H.; Plambeck, Richard L.; Bolatto, Alberto D.; Bower, Geoffrey C.; Carpenter, John M.; Crutcher, Richard M.; Fiege, Jason D.; Franzmann, Erica; Hakobian, Nicholas S.; Heiles, Carl; Houde, Martin; Hughes, A. Meredith; Jameson, Katherine; Kwon, Woojin; Lamb, James W.; Looney, Leslie W.; Matthews, Brenda C.; Mundy, Lee; Pillai, Thushara; Pound, Marc W.; Stephens, Ian W.; Tobin, John J.; Vaillancourt, John E.; Volgenau, N. H.; Wright, Melvyn C. H.

    2013-01-01

    We present results of lambda 1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with similar to 2 ''.5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of similar to 1000 AU are not tightly aligned with outflows from the prot

  20. VLTI/MIDI Observations of the Massive Protostellar Candidate NGC 3603 IRS 9A

    CERN Document Server

    Vehoff, Stefan; Hummel, Christian A; Duschl, Wolfgang J

    2007-01-01

    We used MIDI, the mid-infrared interferometric instrument of the VLTI, to observe the massive protostellar candidate IRS 9A, located at a distance of about 7 kpc at the periphery of the NGC 3603 star cluster. Our ongoing analysis shows that MIDI almost fully resolves the object on all observed baselines, yet below 9 $\\mu$m we detect a steep rise of the visibility. This feature is modelled as a combination of a compact hot component and a resolved warm envelope which lowers the correlated flux at longer wavelengths. The extended envelope can already be seen in both MIDI's acquisition images and in complementary data from aperture masking observations at the Gemini South telescope. Its shape is asymmetric, which could indicate a circumstellar disk inclined against the line of sight. The compact component is possibly related to the inner edge of this (accretion) disk. The uncorrelated mid-infrared spectrum appears featureless and could be caused by optically thick emission without a significant contribution from...

  1. Galaxy Disks

    NARCIS (Netherlands)

    van der Kruit, P. C.; Freeman, K. C.

    The disks of disk galaxies contain a substantial fraction of their baryonic matter and angular momentum, and much of the evolutionary activity in these galaxies, such as the formation of stars, spiral arms, bars and rings, and the various forms of secular evolution, takes place in their disks. The

  2. The Evolutionary State of Anemic Circumstellar Disks and the Primordial-to-Debris Disk Transition

    CERN Document Server

    Currie, Thayne

    2008-01-01

    We investigate the evolution of $\\sim$ 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. We demonstrate that these \\textit{anemic} disks are not a homogenous class of objects corresponding to a unique evolutionary state. Rather, such disks around early (B/A) spectral type stars are most likely warm, terrestrial zone debris disks; MIPS-detected anemic disks around later (M) stars are likely \\textit{evolved primordial disks} such as transition disks in their mid-IR colors, accretion signatures, and disk luminosities. Anemic disks surrounding G and K stars contain both populations. 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. Specifically, disks characteristicall...

  3. `Tail-end' Bondi-Hoyle accretion in young star clusters: Implications for disks, planets, and stars

    CERN Document Server

    Throop, Henry B

    2008-01-01

    Young stars orbiting in the gravitational potential well of forming star clusters pass through the cluster's dense molecular gas and can experience Bondi-Hoyle accretion from reservoirs outside their individual protostellar cloud cores. Accretion can occur for several million years after the stars form, but before the cluster disperses. This accretion is predominantly onto the disk and not the star. N-body simulations of stars orbiting in three young model clusters containing 30, 300, and 3000 stars are presented. The simulations include the gravitational potential of the molecular gas which smoothly disperses over time. The clusters have a star formation efficiency of 33% and a radius of 0.22 pc. We find that the disks surrounding solar-mass stars in the N=30 cluster accretes ~0.01 M_sol (~1 minimum-mass solar nebula, MMSN) per Myr. The accretion rate scales as M^2.1 for stars of mass M. The accretion rate is ~5 times lower for N=3000 cluster, due to its higher stellar velocities and higher temperature. The ...

  4. Dust Stratification in Young Circumstellar Disks

    CERN Document Server

    Rettig, T; Simon, T; Gibb, E; Balsara, D S; Tilley, D A; Kulesa, C; Simon, Theodore

    2006-01-01

    We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S, RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO, and C18O as well as broad emission lines of gas phase12CO. The narrow absorption lines of CO are shown to originate from the colder circumstellar gas. We find that the line of sight gas column densities resulting from the CO absorption lines are much higher than expected for the measured extinction for each source and suggest the gas to dust ratio is measuring the dust settling and/or grain coagulation in these extended disks. We provide a model of turbulence, dust settling and grain growth to explain the results. The techniques presented here allow us to provide some observationally-motivated bounds on accretion disk alpha in protostellar systems.

  5. Chemistry in Protoplanetary Disks

    CERN Document Server

    Semenov, Dmitry

    2010-01-01

    Protoplanetary disks (PPDs) surrounding young stars are short-lived (~0.3-10 Myr), compact (~10-1000 AU) rotating reservoirs of gas and dust. PPDs are believed to be birthplaces of planetary systems, where tiny grains are assembled into pebbles, then rocks, planetesimals, and eventually planets, asteroids, and comets. Strong variations of physical conditions (temperature, density, ionization rate, UV/X-rays intensities) make a variety of chemical processes active in disks, producing simple molecules in the gas phase and complex polyatomic (organic) species on the surfaces of dust particles. In this entry, we summarize the major modern observational methods and theoretical paradigms used to investigate disk chemical composition and evolution, and present the most important results. Future research directions that will become possible with the advent of the Atacama Large Millimeter Array (ALMA) and other forthcoming observational facilities are also discussed.

  6. Modeling of Protostellar Clouds and their Observational Properties

    CERN Document Server

    Zhilkin, A G; Zamozdra, S N

    2009-01-01

    A physical model and two-dimensional numerical method for computing the evolution and spectra of protostellar clouds are described. The physical model is based on a system of magneto-gasdynamical equations, including ohmic and ambipolar diffusion, and a scheme for calculating the thermal and ionization structure of a cloud. The dust and gas temperatures are determined during the calculations of the thermal structure of the cloud. The results of computing the dynamical and thermal structure of the cloud are used to model the radiative transfer in continuum and in molecular lines. We presented the results for clouds in hydrostatic and thermal equilibrium. The evolution of a rotating magnetic protostellar cloud starting from a quasi-static state is also considered. Spectral maps for optically thick lines of linear molecules are analyzed. We have shown that the influence of the magnetic field and rotation can lead to a redistribution of angular momentum in the cloud and the formation of a characteristic rotationa...

  7. Smoothed Particle Magnetohydrodynamics Simulations of Protostellar Jets and Turbulent Dynamos

    CERN Document Server

    Tricco, Terrence S; Federrath, Christoph; Bate, Matthew R

    2013-01-01

    We presents results from Smoothed Particle Magnetohydrodynamics simulations of collapsing molecular cloud cores, and dynamo amplification of the magnetic field in the presence of Mach 10 magnetised turbulence. Our star formation simulations have produced, for the first time ever, highly collimated magnetised protostellar jets from the first hydrostatic core phase. Up to 40% of the initial core mass may be ejected through this outflow. The primary difficulty in performing these simulations is maintaining the divergence free constraint of the magnetic field, and to address this issue, we have developed a new divergence cleaning method which has allowed us to stably follow the evolution of these protostellar jets for long periods. The simulations performed of supersonic MHD turbulence are able to exponentially amplify magnetic energy by up to 10 orders of magnitude via turbulent dynamo. To reduce numerical dissipation, a new shock detection algorithm is utilised which is able to track magnetic shocks throughout ...

  8. THE VLA NASCENT DISK AND MULTIPLICITY SURVEY: FIRST LOOK AT RESOLVED CANDIDATE DISKS AROUND CLASS 0 AND I PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Segura-Cox, Dominique M.; Harris, Robert J.; Looney, Leslie W. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Tobin, John J. [Leiden Observatory, Leiden University, P.O. Box 9513, 2000-RA Leiden (Netherlands); Li, Zhi-Yun [Department of Astronomy, University of Virginia, Charlottesville, VA 22903 (United States); Chandler, Claire; Perez, Laura [National Radio Astronomy Observatory, Socorro, NM 87801 (United States); Kratter, Kaitlin [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Dunham, Michael M. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Sadavoy, Sarah [Max-Planck-Institut für Astronomie, D-69117 Heidelberg (Germany); Melis, Carl, E-mail: segurac2@illinois.edu [Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093 (United States)

    2016-02-01

    We present the first dust emission results toward a sample of seven protostellar disk candidates around Class 0 and I sources in the Perseus molecular cloud from the VLA Nascent Disk and Multiplicity (VANDAM) survey with ∼0.″05 or 12 AU resolution. To examine the surface brightness profiles of these sources, we fit the Ka-band 8 mm dust-continuum data in the u, v-plane to a simple, parametrized model based on the Shakura–Sunyaev disk model. The candidate disks are well-fit by a model with a disk-shaped profile and have masses consistent with known Class 0 and I disks. The inner-disk surface densities of the VANDAM candidate disks have shallower density profiles compared to disks around more evolved Class II systems. The best-fit model radii of the seven early-result candidate disks are R{sub c} > 10 AU; at 8 mm, the radii reflect lower limits on the disk size since dust continuum emission is tied to grain size and large grains radially drift inwards. These relatively large disks, if confirmed kinematically, are inconsistent with theoretical models where the disk size is limited by strong magnetic braking to <10 AU at early times.

  9. Misalignment of Magnetic Fields and Outflows in Protostellar Cores

    OpenAIRE

    Hull, Charles L. H.; Plambeck, Richard L.; Bolatto, Alberto D.; Bower, Geoffrey C.; Carpenter, John M.; Crutcher, Richard M.; Fiege, Jason D.; Franzmann, Erica; Hakobian, Nicholas S.; Heiles, Carl; Houde, Martin; Hughes, A. Meredith; Jameson, Katherine; Kwon, Woojin; Lamb, James W.

    2012-01-01

    We present results of λ1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with ~2."5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of ~1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotati...

  10. Analysis on Issues with Related to the Terms of Service Regarding Web Disk under Cloud Storage Surroundings%云存储环境下网络存储服务条款问题分析

    Institute of Scientific and Technical Information of China (English)

    韩元牧; 吴莉娟

    2013-01-01

    网络技术以及SaaS 行业的发展给网络存储模式注入了新的力量,网盘公司雨后春笋般地发展速度表明云存储大大促进了网盘服务的发展。不过,在行业发展的同时,法律服务也应当与时俱进,成为行业发展的有力保障,否则,混乱的市场竞争环境下,一方面是抢夺客户的需求,一方面是用户无奈地抉择,这将严重阻碍行业的进步。无论对服务提供者而言,还是普通用户而言,合法、清洁、安全、稳定的环境是行业能够稳定发展的基础,法律服务的保障也应当成为行业发展的开路先锋。本文通过对国内外多家网盘服务公司服务条款的汇总、分析、整理,针对“用户上传内容的归属问题以及服务商使用内容的约定”、“关于著作权条款的约定的设置”、“网盘服是否务应当负有高于避风港原则的注意义务”、“云存储下的信息安全问题”的探讨,试图为云存储的服务条款设置提供一定的总结和建议,希望能够为云存储行业积极健康的发展提供一些法律方面的帮助。%The development of internet technology and the industry of Saas have brought new energy to the mode of web storage .The rapid development of va-rious web disk companies has demonstrated that the web disk service has been greatly promoted by the cloud storage .However , it is well worth noting that while the industry is developing greatly , the relevant law issues should also be taken in to account , providing legal guarantee to the industry .Otherwise , under a chaotic market competition environment , both the requirement of struggling for users and the choice without alternation will at last severely hinder the progress of the indus -try.A legitimate, clean, safe and stable environment is the preliminary base for the sustainable development of the industry both from the aspect of the service pro -viders and the aspect of the common

  11. A STUDY OF RADIO POLARIZATION IN PROTOSTELLAR JETS

    Energy Technology Data Exchange (ETDEWEB)

    Cécere, Mariana [Instituto de Astronomía Teórica y Experimental, Universidad Nacional de Córdoba, X5000BGR, Córdoba (Argentina); Velázquez, Pablo F.; De Colle, Fabio; Esquivel, Alejandro [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apdo. Postal 70-543, CP: 04510, D.F., México (Mexico); Araudo, Anabella T. [University of Oxford, Astrophysics, Keble Road, Oxford OX1 3RH (United Kingdom); Carrasco-González, Carlos; Rodríguez, Luis F. [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, 58090, Morelia, Michoacán, México (Mexico)

    2016-01-10

    Synchrotron radiation is commonly observed in connection with shocks of different velocities, ranging from relativistic shocks associated with active galactic nuclei, gamma-ray bursts, or microquasars, to weakly or non-relativistic flows such as those observed in supernova remnants. Recent observations of synchrotron emission in protostellar jets are important not only because they extend the range over which the acceleration process works, but also because they allow us to determine the jet and/or interstellar magnetic field structure, thus giving insights into the jet ejection and collimation mechanisms. In this paper, we compute for the first time polarized (synchrotron) and non-polarized (thermal X-ray) synthetic emission maps from axisymmetrical simulations of magnetized protostellar jets. We consider models with different jet velocities and variability, as well as a toroidal or helical magnetic field. Our simulations show that variable, low-density jets with velocities of ∼1000 km s{sup −1} and ∼10 times lighter than the environment can produce internal knots with significant synchrotron emission and thermal X-rays in the shocked region of the leading bow shock moving in a dense medium. While models with a purely toroidal magnetic field show a very large degree of polarization, models with a helical magnetic field show lower values and a decrease of the degree of polarization, in agreement with observations of protostellar jets.

  12. A Disk Wind Model for the Near-Infrared Excess Emission in Protostars

    CERN Document Server

    Bans, Alissa

    2012-01-01

    Protostellar systems, ranging from low-luminosity 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 microns. The bump can be approximated by a thermal emission component of temperature 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, Rsub. However, this model cannot account for the strongest bumps measured in these sources, and it predicts a large 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 u...

  13. The Formation of Galactic Disks

    CERN Document Server

    Mo, H J; White, S D M; Mao, Shude; White, Simon D.M.

    1997-01-01

    We study the population of galactic disks expected in current hierarchical clustering models for structure formation. A rotationally supported disk with exponential surface density profile is assumed to form with a mass and angular momentum which are fixed fractions of those of its surrounding dark halo. We assume that haloes respond adiabatically to disk formation, and that only stable disks can correspond to real systems. With these assumptions the predicted population can match both present-day disks and the damped Lyman alpha absorbers in QSO spectra. Good agreement is found provided: (i) the masses of disks are a few percent of those of their haloes; (ii) the specific angular momenta of disks are similar to those of their haloes; (iii) present-day disks were assembled recently (at z3kpc/h and about 10% at r>10kpc/h. The cross-section for absorption is strongly weighted towards disks with large angular momentum and so large size for their mass. The galaxy population associated with damped absorbers should...

  14. Simulating the Formation of Massive Protostars: I. Radiative Feedback and Accretion Disks

    CERN Document Server

    Klassen, Mikhail; Kuiper, Rolf; Peters, Thomas; Banerjee, Robi

    2016-01-01

    We present radiation hydrodynamic simulations of collapsing protostellar cores with initial masses of 30, 100, and 200 M$_{\\odot}$. We follow their gravitational collapse and the formation of a massive protostar and protostellar accretion disk. We employ a new hybrid radiative feedback method blending raytracing techniques with flux-limited diffusion for a more accurate treatment of the temperature and radiative force. In each case, the disk that forms becomes Toomre-unstable and develops spiral arms. This occurs between 0.35 and 0.55 freefall times and is accompanied by an increase in the accretion rate by a factor of 2-10. Although the disk becomes unstable, no other stars are formed. In the case of our 100 and 200 M$_{\\odot}$ simulation, the star becomes highly super-Eddington and begins to drive bipolar outflow cavities that expand outwards. These radiatively-driven bubbles appear stable, and appear to be channeling gas back onto the protostellar accretion disk. Accretion proceeds strongly through the dis...

  15. A Spitzer-IRS Detection of Crystalline Silicates in a Protostellar Envelope

    CERN Document Server

    Poteet, Charles A; Watson, Dan M; Calvet, Nuria; Remming, Ian S; McClure, Melissa K; Sargent, Benjamin A; Fischer, William J; Furlan, Elise; Allen, Lori E; Bjorkman, Jon E; Hartmann, Lee; Muzerolle, James; Tobin, John J; Ali, Babar

    2011-01-01

    We present the Spitzer Space Telescope Infrared Spectrograph spectrum of the Orion A protostar HOPS-68. The mid-infrared spectrum reveals crystalline substructure at 11.1, 16.1, 18.8, 23.6, 27.9, and 33.6 microns superimposed on the broad 9.7 and 18 micron amorphous silicate features; the substructure is well matched by the presence of the olivine end-member forsterite. Crystalline silicates are often observed as infrared emission features around the circumstellar disks of Herbig Ae/Be stars and T Tauri stars. However, this is the first unambiguous detection of crystalline silicate absorption in a cold, infalling, protostellar envelope. We estimate the crystalline mass fraction along the line-of-sight by first assuming that the crystalline silicates are located in a cold absorbing screen and secondly by utilizing radiative transfer models. The resulting crystalline mass fractions of 0.14 and 0.17, respectively, are significantly greater than the upper limit found in the interstellar medium (< 0.02-0.05). W...

  16. Signs of Early-stage Disk Growth Revealed with ALMA

    Science.gov (United States)

    Yen, Hsi-Wei; Koch, Patrick M.; Takakuwa, Shigehisa; Krasnopolsky, Ruben; Ohashi, Nagayoshi; Aso, Yusuke

    2017-01-01

    We present ALMA 1.3 mm continuum, 12CO, C18O, and SO data for the Class 0 protostars Lupus 3 MMS, IRAS 15398‑3559, and IRAS 16253‑2429 at resolutions of ∼100 au. By measuring a rotational profile in C18O, a 100 au Keplerian disk around a 0.3 M⊙ protostar is observed in Lupus 3 MMS. No 100 au Keplerian disks are observed in IRAS 15398‑3559 and IRAS 16253‑2429. Nevertheless, embedded compact (<30 au) continuum components are detected. The C18O emission in IRAS 15398‑3559 shows signatures of infall with a constant angular momentum. IRAS 16253‑2429 exhibits signatures of infall and rotation, but its rotational profile is unresolved. By fitting the C18O data with our kinematic models, the protostellar masses and the disk radii are inferred to be 0.01 M⊙ and 20 au in IRAS 15398‑3559, and 0.03 M⊙ and 6 au in IRAS 16253‑2429. By comparing the specific angular momentum profiles from 10,000 au to 100 au in eight Class 0 and I protostars, we find that the evolution of envelope rotation can be described with conventional inside-out collapse models. In comparison with a sample of 18 protostars with known disk radii, our results reveal signs of disk growth, with the disk radius increasing as {{M}* }0.8+/- 0.14 or {t}1.09+/- 0.37 in the Class 0 stage, where M* is the protostellar mass and t is the age. The disk growth rate slows down in the Class I stage. In addition, we find a hint that the mass accretion rate declines as {t}-0.26+/- 0.04 from the Class 0 to the Class I stages.

  17. Galaxy Disks

    CERN Document Server

    van der Kruit, P C

    2011-01-01

    The formation and evolution of galactic disks is particularly important for understanding how galaxies form and evolve, and the cause of the variety in which they appear to us. Ongoing large surveys, made possible by new instrumentation at wavelengths from the ultraviolet (GALEX), via optical (HST and large groundbased telescopes) and infrared (Spitzer) to the radio are providing much new information about disk galaxies over a wide range of redshift. Although progress has been made, the dynamics and structure of stellar disks, including their truncations, are still not well understood. We do now have plausible estimates of disk mass-to-light ratios, and estimates of Toomre's $Q$ parameter show that they are just locally stable. Disks are mostly very flat and sometimes very thin, and have a range in surface brightness from canonical disks with a central surface brightness of about 21.5 $B$-mag arcsec$^{-2}$ down to very low surface brightnesses. It appears that galaxy disks are not maximal, except possibly in ...

  18. Investigating FP Tau’s protoplanetary disk structure through modeling

    Science.gov (United States)

    Brinjikji, Marah; Espaillat, Catherine

    2017-01-01

    This project presents a study aiming to understand the structure of the protoplanetary disk around FP Tau, a very young, very low mass star in the Taurus star-forming region. We have gathered existing optical, Spitzer, Herschel and submillimeter observations to construct the spectral energy distribution (SED) of FP Tau. We have used the D’Alessio et al (2006) physically self-consistent irradiated accretion disk model including dust settling to model the disk of FP Tau. Using this method, the best fit for the SED of FP Tau is a model that includes a gap located 10-20 AU away from the star. This gap is filled with optically thin dust that separates the optically thick dust in the outer disk from the optically thick dust in the inner disk. These characteristics indicate that FP Tau’s protostellar system is best classified as a pre-transitional disk. Near-infrared interferometry in the K-Band from Willson et al 2016 indicates that FP Tau has a small gap located 10-20 AU from the star, which is consistent with the model we produced, lending further support to the pre-transitional disk interpretation. The most likely explanation for the existence of a gap in the disk is a forming planet.

  19. Protostellar and cometary detections of organohalogens

    Science.gov (United States)

    Fayolle, Edith C.; Öberg, Karin I.; Jørgensen, Jes K.; Altwegg, Kathrin; Calcutt, Hannah; Müller, Holger S. P.; Rubin, Martin; van der Wiel, Matthijs H. D.; Bjerkeli, Per; Bourke, Tyler L.; Coutens, Audrey; van Dishoeck, Ewine F.; Drozdovskaya, Maria N.; Garrod, Robin T.; Ligterink, Niels F. W.; Persson, Magnus V.; Wampfler, Susanne F.; Rosina Team

    2017-10-01

    Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes1. Consequently, they have been proposed as biomarkers in the search for life on exoplanets2. Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain3,4. Here we report the interstellar detection of two isotopologues of the organohalogen CH3Cl and put some constraints on CH3F in the gas surrounding the low-mass protostar IRAS 16293-2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH3Cl in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets.

  20. INTERMEDIATE-MASS HOT CORES AT {approx}500 AU: DISKS OR OUTFLOWS?

    Energy Technology Data Exchange (ETDEWEB)

    Palau, Aina; Girart, Josep M. [Institut de Ciencies de l' Espai (CSIC-IEEC), Campus UAB-Facultat de Ciencies, Torre C5-parell 2, 08193 Bellaterra, Catalunya (Spain); Fuente, Asuncion; Alonso-Albi, Tomas [Observatorio Astronomico Nacional, P.O. Box 112, 28803 Alcala de Henares, Madrid (Spain); Fontani, Francesco; Sanchez-Monge, Alvaro [Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Firenze (Italy); Boissier, Jeremie [Istituto di Radioastronomia, INAF, Via Gobetti 101, Bologna (Italy); Pietu, Vincent; Neri, Roberto [IRAM, 300 Rue de la piscine, 38406 Saint Martin d' Heres (France); Busquet, Gemma [Istituto di Fisica dello Spazio Interplanetario, INAF, Area di Recerca di Tor Vergata, Via Fosso Cavaliere 100, 00133 Roma (Italy); Estalella, Robert [Departament d' Astronomia i Meteorologia (IEEC-UB), Institut Ciencies Cosmos, Universitat Barcelona, Marti Franques 1, 08028 Barcelona (Spain); Zapata, Luis A. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, P.O. Box 3-72, 58090 Morelia, Michoacan (Mexico); Zhang, Qizhou; Ho, Paul T. P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Audard, Marc, E-mail: palau@ieec.uab.es [Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Versoix (Switzerland)

    2011-12-20

    Observations with the Plateau de Bure Interferometer in the most extended configuration toward two intermediate-mass star-forming regions, IRAS 22198+6336 and AFGL 5142, reveal the presence of several complex organic molecules at {approx}500 AU scales, confirming the presence of hot cores in both regions. The hot cores are not rich in CN-bearing molecules, as often seen in massive hot cores, and are mainly traced by CH{sub 3}CH{sub 2}OH, (CH{sub 2}OH){sub 2}, CH{sub 3}COCH{sub 3}, and CH{sub 3}OH, with, additionally, CH{sub 3}CHO, CH{sub 3}OD, and HCOOD for IRAS 22198+6336, and C{sub 6}H and O{sup 13}CS for AFGL 5142. The emission of complex molecules is resolved down to sizes of {approx}300 and {approx}600 AU, for IRAS 22198+6336 and AFGL 5142, respectively, and most likely is tracing protostellar disks rather than flattened envelopes or toroids as is usually found. This is especially clear for the case of IRAS 22198+6336, where we detect a velocity gradient for all the mapped molecules perpendicular to the most chemically rich outflow of the region, yielding a dynamic mass {approx}> 4 M{sub Sun }. As for AFGL 5142, the hot core emission is resolved into two elongated cores separated {approx}1800 AU. A detailed comparison of the complex molecule peaks to the new CO (2-1) data and H{sub 2}O maser data from the literature suggests also that for AFGL 5142 the complex molecules are mainly associated with disks, except for a faint and extended molecular emission found to the west, which is possibly produced in the interface between one of the outflows and the dense surrounding gas.

  1. Do protostellar fountains shape the regional core mass function?

    Institute of Scientific and Technical Information of China (English)

    Jin-Zeng Li; Claudio Carlos Mallamaci; Ricardo César Podestá; Eloy Actis Vicente; Ya-Fang Huang; Ana Maria Pacheco

    2013-01-01

    The emerging massive binary system associated with AFGL 961 signifies the latest generation of massive star and cluster formation in the Rosette Molecular Complex.We present the detection of a compact cluster of dusty cores toward the AFGL 961 region based on continuum imaging at 1.3 mm by the Submillimeter Array.The binary components of AFGL 961 are associated with the most intensive millimeter emission cores or envelopes,confirming that they are indeed in an early stage of evolution.The other massive cores,however,are found to congregate in the close vicinity of the central high-mass protostellar binary.They have no apparent infrared counterparts and are,in particular,well aligned transverse to the bipolar molecular outflows originating from AFGL 961.This provides evidence for a likely triggered origin of the massive cores.All 40 individual cores with masses ranging between 0.6 and 15 M⊙ were detected above a 3 σ level of 3.6 mJy beam-1 (or 0.4 M⊙),based on which we derive a total core mass of 107 M⊙ in the AFGL 961 region.As compared to the stellar initial mass function,a shallow slope of 1.8 is,however,derived from the best fit to the mass spectrum of the millimeter cores with a prestellar and/or protostellar origin.The flatter core mass distribution in the AFGL 961 region is attributed here to dynamic perturbations from the massive molecular outflows that originated from the massive protostellar binary,which may have altered the otherwise more quiescent conditions of core or star formation,enhanced the formation of more massive cores and,as a result,influenced the core mass distribution in its close vicinity.

  2. The prestellar and protostellar population of R Coronae Australis

    CERN Document Server

    Nutter, D J; André, P; Nutter, David J.

    2004-01-01

    We present 450 and 850 um maps of R Coronae Australis. We compare the maps to previous surveys of the region, and shed new light on the previously unknown nature of the protostellar sources at the centre of the cloud. We clarify the nature of two millimetre sources previously discovered in lower resolution data. We identify one new Class 0 protostar that we label SMM 1B, and we measure the envelope masses of a number of more evolved protostars. We identify two new prestellar cores that we call SMM 1A and SMM 6.

  3. Connecting the shadows: probing inner disk geometries using shadows in transitional disks

    Science.gov (United States)

    Min, M.; Stolker, T.; Dominik, C.; Benisty, M.

    2017-08-01

    Aims: Shadows in transitional disks are generally interpreted as signs of a misaligned inner disk. This disk is usually beyond the reach of current day high contrast imaging facilities. However, the location and morphology of the shadow features allow us to reconstruct the inner disk geometry. Methods: We derive analytic equations of the locations of the shadow features as a function of the orientation of the inner and outer disk and the height of the outer disk wall. In contrast to previous claims in the literature, we show that the position angle of the line connecting the shadows cannot be directly related to the position angle of the inner disk. Results: We show how the analytic framework derived here can be applied to transitional disks with shadow features. We use estimates of the outer disk height to put constraints on the inner disk orientation. In contrast with the results from Long et al. (2017, ApJ, 838, 62), we derive that for the disk surrounding HD 100453 the analytic estimates and interferometric observations result in a consistent picture of the orientation of the inner disk. Conclusions: The elegant consistency in our analytic framework between observation and theory strongly support both the interpretation of the shadow features as coming from a misaligned inner disk as well as the diagnostic value of near infrared interferometry for inner disk geometry.

  4. 3-D MHD disk wind simulations of jets and outflows from high-mass protostars

    Science.gov (United States)

    Staff, Jan E.; Tanaka, Kei; Tan, Jonathan C.; Zhang, Yichen; Liu, Mengyao

    2017-01-01

    We present the results of a series of nested, large scale, three-dimensional magnetohydrodynamics simulations of disk winds with a Blandford-Payne like magnetic field configuration, resolving scales from the stellar surface to beyond the core. The goal is to understand the structure of massive protostellar cores at various stages of their formation as the protostellar mass grows from a massive core. At each stage of a given protostellar mass, first, we study how jets and winds develop from the inner accretion disk to ~100 AU scales. We use the results from these simulations to dictate the inner boundary condition of a set of simulation extending to the core boundary at ~10,000 AU of an initially 60 solar mass core. We run separate simulations where the protostellar mass is 1, 2, 4, 8, 12, 16, and 24 Msun, and we are working on making a small grid of models in the context of the Turbulent Core Model with three different core masses and three different core surface densities. The wind is blown into the simulation box with properties derived from the previous jet simulations. We examine the opening angle of the outflow cavity and thus the star formation efficiency from the core due to outflow feedback. We find that the opening angle increases as the protostellar mass grows, but it is always less than 10 degrees, which is surprisingly small compared with previous analytic models. This is caused by the core which confines the outflow. Finally, we use our simulation results as input to a radiative transfer calculation, to compare with observations made by the SOMA survey.

  5. Ice Chemistry in Interstellar Dense Molecular Clouds, Protostellar Disks, and Comets

    Science.gov (United States)

    Sandford, Scott A.

    2015-01-01

    Despite the low temperatures (T less than 20K), low pressures, and low molecular densities found in much of the cosmos, considerable chemistry is expected to occur in many astronomical environments. Much of this chemistry happens in icy grain mantles on dust grains and is driven by ionizing radiation. This ionizing radiation breaks chemical bonds of molecules in the ices and creates a host of ions and radicals that can react at the ambient temperature or when the parent ice is subsequently warmed. Experiments that similar these conditions have demonstrated a rich chemistry associated with these environments that leads to a wide variety of organic products. Many of these products are of considerable interest to astrobiology. For example, the irradiation of simple ices has been shown to abiotically produce amino acids, nucleobases, quinones, and amphiphiles, all compounds that play key roles in modern biochemistry. This suggests extraterrestrial chemistry could have played a role in the origin of life on Earth and, by extension, do so on planets in other stellar systems.

  6. Depletion of chlorine into HCl ice in a protostellar core

    CERN Document Server

    Kama, M; Lopez-Sepulcre, A; Wakelam, V; Dominik, C; Ceccarelli, C; Lanza, M; Lique, F; Ochsendorf, B B; Lis, D C; Caballero, R N; Tielens, A G G M

    2014-01-01

    The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances $<10^{-5}$ has not yet been well studied. Our aim here is to study the depletion of chlorine in the protostellar core, OMC-2 FIR 4. We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H$_{2}$ hyperfine collisional excitation rate coefficients. A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9e-11, a factor of only 0.001 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous fo...

  7. Prestellar and protostellar cores in Ori B9

    CERN Document Server

    Miettinen, O; Haikala, L K; Kainulainen, J; Johansson, L E B

    2009-01-01

    The aims of this study are to determine the properties and spatial distribution of dense cores in Ori B9, and to estimate their ages and dynamical timescales. The cloud was mapped in the 870 micron continuum with APEX/LABOCA, and selected positions were observed in the lines of N2H+ and N2D+ using IRAM-30m. These were used together with our previous H2D+ observations. Moreover, archival FIR Spitzer/MIPS maps were combined with the LABOCA map to distinguish between pre- and protostellar cores, and to estimate the evolutionary stages of protostars. Twelve dense cores were detected at 870 micron in the Ori B9 cloud. The submm cores constitute ~4% of the total mass of the Ori B9 region. There is an equal number of pre- and protostellar cores. Two of the submm sources, which we call SMM 3 and SMM 4, are previously unknown Class 0 candidates. We found a moderate degree of deuteration in N2H+ (0.03-0.04). There is, furthermore, evidence for N2H+ depletion in the core SMM 4. We derive a relatively high degree of ioni...

  8. Spectroscopic diagnostics of organic chemistry in the protostellar environment

    Science.gov (United States)

    Charnley, S. B.; Ehrenfreund, P.; Kuan, Y. J.

    2001-01-01

    A combination of astronomical observations, laboratory studies, and theoretical modelling is necessary to determine the organic chemistry of dense molecular clouds. We present spectroscopic evidence for the composition and evolution of organic molecules in protostellar environments. The principal reaction pathways to complex molecule formation by catalysis on dust grains and by reactions in the interstellar gas are described. Protostellar cores, where warming of dust has induced evaporation of icy grain mantles, are excellent sites in which to study the interaction between gas phase and grain-surface chemistries. We investigate the link between organics that are observed as direct products of grain surface reactions and those which are formed by secondary gas phase reactions of evaporated surface products. Theory predicts observable correlations between specific interstellar molecules, and also which new organics are viable for detection. We discuss recent infrared observations obtained with the Infrared Space Observatory, laboratory studies of organic molecules, theories of molecule formation, and summarise recent radioastronomical searches for various complex molecules such as ethers, azaheterocyclic compounds, and amino acids.

  9. Proper motions of embedded protostellar jets in Serpens

    CERN Document Server

    Djupvik, Anlaug Amanda; Zinnecker, Hans; Barzdis, Arturs; Rastorgueva-Foi, Elizaveta; Petersen, Linus R

    2016-01-01

    Context. To investigate the dynamical properties of protostellar jets. Aims. Determine the proper motion of protostellar jets around Class 0 and Class I sources in an active star forming region in Serpens. Methods. Multi-epoch deep images in the 2.122 $\\mu$m line of molecular hydrogen, v=1-0 S(1), obtained with the near-infrared instrument NOTCam over a time-scale of 10 years, are used to determine proper motion of knots and jets. K-band spectroscopy of the brighter knots is used to supply radial velocities, estimate extinction, excitation temperature, and H$_2$ column densities towards these knots. Results. We measure the proper motion of 31 knots over different time scales (2, 4, 6, and 10 years). The typical tangential velocity is around 50 km/s for the 10 year base-line, but for shorter time-scales a maximum tangential velocity up to 300 km/s is found for a few knots. Based on morphology, velocity information and the locations of known protostars, we argue for the existence of at least three partly overla...

  10. PROTOSTELLAR OUTFLOW HEATING IN A GROWING MASSIVE PROTOCLUSTER

    Energy Technology Data Exchange (ETDEWEB)

    Wang Ke; Wu Yuefang; Zhang Huawei [Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China); Zhang Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Li Huabai, E-mail: kwang@cfa.harvard.edu [Max-Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)

    2012-02-15

    The dense molecular clump P1 in the infrared dark cloud complex G28.34+0.06 harbors a massive protostellar cluster at its extreme youth. Our previous Submillimeter Array observations revealed several jet-like CO outflows emanating from the protostars, indicative of intense accretion and potential interaction with ambient natal materials. Here, we present the Expanded Very Large Array spectral line observations toward P1 in the NH{sub 3} (J,K) = (1,1), (2,2), (3,3) lines, as well as H{sub 2}O and class I CH{sub 3}OH masers. Multiple NH{sub 3} transitions reveal the heated gas widely spread in the 1 pc clump. The temperature distribution is highly structured; the heated gas is offset from the protostars, and morphologically matches the outflows very well. Hot spots of spatially compact, spectrally broad NH{sub 3} (3,3) emission features are also found coincident with the outflows. A weak NH{sub 3} (3,3) maser is discovered at the interface between an outflow jet and the ambient gas. These findings suggest that protostellar heating may not be effective in suppressing fragmentation during the formation of massive cores.

  11. Protostellar Outflow Heating in a Growing Massive Protocluster

    CERN Document Server

    Wang, Ke; Wu, Yuefang; Li, Hua-bai; Zhang, Huawei

    2011-01-01

    The dense molecular clump P1 in the infrared dark cloud (IRDC) complex G28.34+0.06 harbors a massive protostellar cluster at its extreme youth. Our previous Submillimeter Array (SMA) observations revealed several jet-like CO outflows emanating from the protostars, indicative of intense accretion and potential interaction with ambient natal materials. Here we present the Expanded Very Large Array (EVLA) spectral line observations toward P1 in the NH3 (J,K) = (1,1), (2,2), (3,3) lines, as well as H2O and class I CH3OH masers. Multiple NH3 transitions reveal the heated gas widely spread in the 1 pc clump. The temperature distribution is highly structured; the heated gas is offset from the protostars, and morphologically matches the outflows very well. Hot spots of spatially compact, spectrally broad NH3 (3,3) emission are also found coincident with the outflows. A weak NH3 (3,3) maser is discovered at the interface between an outflow jet and the ambient gas. These findings suggest that protostellar heating may n...

  12. Millimeter continuum observations of a massive protostellar core in Sagittarius B2

    Energy Technology Data Exchange (ETDEWEB)

    Carlstrom, J.E.; Vogel, S.N.

    1989-02-01

    The Hat Creek interferometer has been used to map 3.4 mm continuum emission from Sgr B2 with 4.5 x 2 arcsec resolution. The fluxes of two of the detected sources are substantially higher at 3.4 mm than at 1.3 cm; both sources are coincident with centroids of water maser clusters to less than 1 arcsec. In one, the flux can be attributed to free emission with a turnover frequency greater than 23 GHz; in the other, 3.4 mm emission comes mainly from hot dust grains in a dense protostellar core containing two embedded ultracompact H II regions. The amount of molecular material within 0.1 pc of the embedded protostars is at least one order of magnitude greater than within 0.1 pc of any of the other dozen ultracompact H II regions in Sgr B2. The observations indicate that ultracompact H II regions are much more common than the dense cores from which they presumably form, and that they survive long after most of the surrounding gas has been dispersed by outflow. 21 references.

  13. Mass accretion rates in self-regulated disks of T Tauri stars

    CERN Document Server

    Vorobyov, E I

    2008-01-01

    We have studied numerically the evolution of protostellar disks around intermediate and upper mass T Tauri stars (0.25 M_sun < M_st < 3.0 M_sun) that have formed self-consistently from the collapse of molecular cloud cores. In the T Tauri phase, disks settle into a self-regulated state, with low-amplitude nonaxisymmetric density perturbations persisting for at least several million years. Our main finding is that the global effect of gravitational torques due to these perturbations is to produce disk accretion rates that are of the correct magnitude to explain observed accretion onto T Tauri stars. Our models yield a correlation between accretion rate M_dot and stellar mass M_st that has a best fit M_dot \\propto M_st^{1.7}, in good agreement with recent observations. We also predict a near-linear correlation between the disk accretion rate and the disk mass.

  14. Counterrotating Stars in Simulated Galaxy Disks

    CERN Document Server

    Algorry, David G; Abadi, Mario G; Sales, Laura V; Steinmetz, Matthias; Piontek, Franziska

    2013-01-01

    Counterrotating stars in disk galaxies are a puzzling dynamical feature whose origin has been ascribed to either satellite accretion events or to disk instabilities triggered by deviations from axisymmetry. We use a cosmological simulation of the formation of a disk galaxy to show that counterrotating stellar disk components may arise naturally in hierarchically-clustering scenarios even in the absence of merging. The simulated disk galaxy consists of two coplanar, overlapping stellar components with opposite spins: an inner counterrotating bar-like structure made up mostly of old stars surrounded by an extended, rotationally-supported disk of younger stars. The opposite-spin components originate from material accreted from two distinct filamentary structures which at turn around, when their net spin is acquired, intersect delineating a "V"-like structure. Each filament torques the other in opposite directions; the filament that first drains into the galaxy forms the inner counterrotating bar, while material ...

  15. Volatile snowlines in embedded disks around low-mass protostars

    CERN Document Server

    Harsono, Daniel; van Dishoeck, Ewine

    2015-01-01

    (Abridged*) Models of the young solar nebula assume a hot initial disk with most volatiles are in the gas phase. The question remains whether an actively accreting disk is warm enough to have gas-phase water up to 50 AU radius. No detailed studies have yet been performed on the extent of snowlines in an embedded accreting disk (Stage 0). Quantify the location of gas-phase volatiles in embedded actively accreting disk system. Two-dimensional physical and radiative transfer models have been used to calculate the temperature structure of embedded protostellar systems. Gas and ice abundances of H$_2$O, CO$_2$, and CO are calculated using the density-dependent thermal desorption formulation. The midplane water snowline increases from 3 to 55 AU for accretion rates through the disk onto the star between $10^{-9}$-$10^{-4} \\ M_{\\odot} \\ {\\rm yr^{-1}}$. CO$_2$ can remain in the solid phase within the disk for $\\dot{M} \\leq 10^{-5} \\ M_{\\odot} \\ {\\rm yr^{-1}}$ down to $\\sim 20$ AU. Most of the CO is in the gas phase w...

  16. Observations of Protostellar Outflow Feedback in Clustered Star Formation

    CERN Document Server

    Nakamura, Fumitaka

    2015-01-01

    We discuss the role of protostellar outflow feedback in clustered star formation using the observational data of recent molecular outflow surveys toward nearby cluster-forming clumps. We found that for almost all clumps, the outflow momentum injection rate is significantly larger than the turbulence dissipation rate. Therefore, the outflow feedback is likely to maintain supersonic turbulence in the clumps. For less massive clumps such as B59, L1551, and L1641N, the outflow kinetic energy is comparable to the clump gravitational energy. In such clumps, the outflow feedback probably affects significantly the clump dynamics. On the other hand, for clumps with masses larger than about 200 M$_\\odot$, the outflow kinetic energy is significantly smaller than the clump gravitational energy. Since the majority of stars form in such clumps, we conclude that outflow feedback cannot destroy the whole parent clump. These characteristics of the outflow feedback support the scenario of slow star formation.

  17. Revealing the Jets in the BHR 71 Protostellar System

    Science.gov (United States)

    Bourke, Tyler L.; Tobin, John J.; Gusdorf, Antoine; Arce, Hector G.; Tafalla, Mario

    2017-01-01

    The BHR 71 low-mass protostellar binary system powers two highly collimated outflows, with the outflow from the primary (IRS1) producing shock-induced chemical activity only seen in a handful of other outflows (notably L1157, but also L1448 and IRAS04166). This may represent a very short phase in the outflow process that we don’t yet understand. The shocks are likely caused by jets with velocities > 50 km/s impacting on the ambient material, but unlike in the other outflows mentioned above, no such jet has yet been identified in BHR 71, although hints are found in low-resolution Herschel water observations. We report on ALMA observations of SiO toward both protostars within BHR 71, with surprising results.

  18. Transverse velocity shifts in protostellar jets: rotation or velocity asymmetries?

    CERN Document Server

    De Colle, Fabio; Riera, Angels

    2016-01-01

    Observations of several protostellar jets show systematic differences in radial velocity transverse to the jet propagation direction, which have been interpreted as evidence of rotation in the jets. In this paper we discuss the origin of these velocity shifts, and show that they could be originated by rotation in the flow, or by side to side asymmetries in the shock velocity, which could be due to asymmetries in the jet ejection velocity/density or in the ambient medium. For typical poloidal jet velocities (~ 100-200 km/s), an asymmetry >~ 10% can produce velocity shifts comparable to those observed. We also present three dimensional numerical simulations of rotating, precessing and asymmetric jets, and show that, even though for a given jet there is a clear degeneracy between these effects, a statistical analysis of jets with different inclination angles can help to distinguish between the alternative origins of transverse velocity shifts. Our analysis indicate that side to side velocities asymmetries could ...

  19. Diverse protostellar evolutionary states in the young cluster AFGL961

    CERN Document Server

    Williams, Jonathan P; Beaumont, Christopher N; Swift, Jonathan J; Adams, Joseph D; Hora, Joe; Kassis, Marc; Lada, Elizabeth A; Roman-Zuniga, Carlos G

    2009-01-01

    We present arcsecond resolution mid-infrared and millimeter observations of the center of the young stellar cluster AFGL961 in the Rosette molecular cloud. Within 0.2 pc of each other, we find an early B star embedded in a dense core, a neighboring star of similar luminosity with no millimeter counterpart, a protostar that has cleared out a cavity in the circumcluster envelope, and two massive, dense cores with no infrared counterparts. An outflow emanates from one of these cores, indicating a deeply embedded protostar, but the other is starless, bound, and appears to be collapsing. The diversity of states implies either that protostellar evolution is faster in clusters than in isolation or that clusters form via quasi-static rather than dynamic collapse. The existence of a pre-stellar core at the cluster center shows that that some star formation continues after and in close proximity to massive, ionizing stars.

  20. Disks around young stellar objects

    Indian Academy of Sciences (India)

    H C Bhatt

    2011-07-01

    By 1939, when Chandrasekhar’s classic monograph on the theory of Stellar Structure was published, although the need for recent star formation was fully acknowledged, no one had yet recognized an object that could be called a star in the process of being born. Young stellar objects (YSOs), as pre-main-sequence stars, were discovered in the 1940s and 1950s. Infrared excess emission and intrinsic polarization observed in these objects in the 1960s and 1970s indicated that they are surrounded by flattened disks. The YSO disks were seen in direct imaging only in the 1980s. Since then, high-resolution optical imaging with HST, near-infrared adaptive optics on large groundbased telescopes, mm and radiowave interferometry have been used to image disks around a large number of YSOs revealing disk structure with ever-increasing detail and variety. The disks around YSOs are believed to be the sites of planet formation and a few such associations have now been confirmed. The observed properties of the disk structure and their evolution, that have very important consequences for the theory of star and planet formation, are discussed.

  1. On radial oscillations in viscous accretion discs surrounding neutron stars

    Science.gov (United States)

    Chen, Xingming; Taam, Ronald E.

    1992-01-01

    Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding neutron stars in X-ray binary systems have been investigated. Within the framework of the alpha-viscosity model a series of hydrodynamic calculations demonstrates that the oscillations are global for alpha of about 1. On the other hand, for alpha of 0.4 or less, the oscillations are local and confined to the disk boundaries. If viscous stresses acting in the radial direction are included, however, it is found that the disk can be stabilized. The application of such instabilities in accretion disks, without reference to the boundary layer region between the neutron star (or magnetosphere) and the inner edge of the disk, to the phenomenology of quasi-periodic oscillations is brought into question.

  2. Practices Surrounding Event Photos

    NARCIS (Netherlands)

    Vyas, Dhaval; Nijholt, Antinus; van der Veer, Gerrit C.; Kotzé, P.; Marsden, G.; Lindgaard, G.; Wesson, J.; Winckler, M.

    Sharing photos through mobile devices has a great potential for creating shared experiences of social events between co-located as well as remote participants. In order to design novel event sharing tools, we need to develop indepth understanding of current practices surrounding these so called

  3. Migration and Growth of Protoplanetary Embryos I: Convergence of Embryos in Protoplanetary Disks

    CERN Document Server

    Zhang, Xiaojia; Lin, Douglas N C; Li, Hui

    2014-01-01

    According to the core-accretion scenario, planets form in protostellar disks through the condensation of dust, coagulation of planetesimals, and emergence of protoplanetary embryos. At a few AU in a minimum mass nebula, embryos' growth is quenched by dynamical isolation due to the depletion of planetesimals in their feeding zone. However, embryos with masses ($M_p$) in the range of a few Earth masses ($M_\\oplus$) migrate toward a transition radius between the inner viscously heated and outer irradiated regions of their natal disk. Their limiting isolation mass increases with the planetesimals surface density. When $M_p > 10 M_\\oplus$, embryos efficiently accrete gas and evolve into cores of gas giants. We use numerical simulation to show that, despite streamline interference, convergent embryos essentially retain the strength of non-interacting embryos' Lindblad and corotation torque by their natal disks. In disks with modest surface density (or equivalently accretion rates), embryos capture each other in the...

  4. Variational thermodynamics of relativistic thin disks

    Science.gov (United States)

    Gutiérrez-Piñeres, Antonio C.; Lopez-Monsalvo, Cesar S.; Quevedo, Hernando

    2015-12-01

    We present a relativistic model describing a thin disk system composed of two fluids. The system is surrounded by a halo in the presence of a non-trivial electromagnetic field. We show that the model is compatible with the variational multifluid thermodynamics formalism, allowing us to determine all the thermodynamic variables associated with the matter content of the disk. The asymptotic behavior of these quantities indicates that the single fluid interpretation should be abandoned in favor of a two-fluid model.

  5. Secure Disk Mixed System

    Directory of Open Access Journals (Sweden)

    Myongchol Ri

    2013-01-01

    Full Text Available We propose a disk encryption method, called Secure Disk Mixed System (SDMS in this paper, for data protection of disk storages such as USB flash memory, USB hard disk and CD/DVD. It is aimed to solve temporal and spatial limitations of existing disk encryption methods and to control security performance flexibly according to the security requirement of system.

  6. Accretion Outbursts in Self-gravitating Protoplanetary Disks

    CERN Document Server

    Bae, Jaehan; Zhu, Zhaohuan; Nelson, Richard P

    2014-01-01

    We improve on our previous treatments of long-term evolution of protostellar disks by explicitly solving disk self-gravity in two dimensions. The current model is an extension of the one-dimensional layered accretion disk model of Bae et al. We find that gravitational instability (GI)-induced spiral density waves heat disks via compressional heating (i.e. $P\\rm{d}V$ work), and can trigger accretion outbursts by activating the magnetorotational instability (MRI) in the magnetically inert disk dead-zone. The GI-induced spiral waves propagate well inside of gravitationally unstable region before they trigger outbursts at $R \\lesssim 1$ AU where GI cannot be sustained. This long-range propagation of waves cannot be reproduced with the previously used local $\\alpha$ treatments for GI. In our standard model where zero dead-zone residual viscosity ($\\alpha_{\\rm rd}$) is assumed, the GI-induced stress measured at the onset of outbursts is locally as large as $0.01$ in terms of the generic $\\alpha$ parameter. However,...

  7. Disk fragmentation and the formation of population III stars

    CERN Document Server

    Latif, M A

    2014-01-01

    Our understanding of population III star formation at the end of the cosmic dark ages is still in its infancy. Recent high resolution cosmological simulations show that a protostellar disk is formed as a consequence of gravitational collapse, which fragments into multiple clumps. However, it is not entirely clear if these clumps will be able to survive to form multiple stars. In this study, we employ a simple analytical model to derive the properties of marginally stable steady-state disks. Our results show that the stability of the disk depends on the critical value of the viscous parameter $\\alpha$. For $\\alpha_{crit} = 1$, the disk is stable for an accretion rate of $\\rm \\leq 10^{-3}~M_{\\odot}/yr$ and becomes unstable at radii about $\\rm \\geq 100~AU$ in the presence of an accretion rate of $\\rm 10^{-2}~M_{\\odot}/yr$. The fragmentation scale is consistent with numerical simulations and it occurs in the line cooling dominated regime. For $0.06 < \\alpha_{crit} < 1$, the disk can be unstable for both acc...

  8. Effects of inclined star-disk encounter on protoplanetary disk size

    CERN Document Server

    Bhandare, Asmita; Pfalzner, Susanne

    2016-01-01

    Most, if not all, young stars are initially surrounded by protoplanetary disks. Owing to the preferential formation of stars in stellar clusters, the protoplanetary disks around these stars may potentially be affected by the cluster environment. Various works have investigated the influence of stellar fly-bys on disks, although many of them consider only the effects due to parabolic, coplanar encounters often for equal-mass stars, which is only a very special case. We perform numerical simulations to study the fate of protoplanetary disks after the impact of parabolic star-disk encounter for the less investigated case of inclined up to coplanar, retrograde encounters, which is a much more common case. Here, we concentrate on the disk size after such encounters because this limits the size of the potentially forming planetary systems. In addition, with the possibilities that ALMA offers, now a direct comparison to observations is possible. Covering a wide range of periastron distances and mass ratios between t...

  9. Reading the Signatures of Extrasolar Planets in Debris Disks

    Science.gov (United States)

    Kuchner, Marc J.

    2009-01-01

    An extrasolar planet sculpts the famous debris dish around Fomalhaut; probably ma ny 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 simultanemus]y. I will describe new 3-D models of debris disk dynamics that incorporate both collisions and resonant trapping of dust for the first time, allowing us to decode debris disk images and read the signatures of the planets they contain.

  10. Measuring Magnetic Fields from Water Masers in the Synchrotron Protostellar Jet in W3(H$_2$O)

    CERN Document Server

    Goddi, C; Moscadelli, L; Imai, H; Vlemmings, W H T; van Langevelde, H J; Sanna, A

    2016-01-01

    We report full polarimetric VLBA observations of water masers towards the Turner-Welch Object in the W3(OH) high-mass star forming complex. This object drives a synchrotron jet, which is quite exceptional for a high-mass protostar, and is associated with a strongly polarized water maser source, W3(H$_2$O), making it an optimal target to investigate the role of magnetic fields on the innermost scales of protostellar disk-jet systems. The linearly polarized emission from water masers provides clues on the orientation of the local magnetic field, while the measurement of the Zeeman splitting from circular polarization provides its strength. The water masers trace a bipolar, biconical outflow at the center of the synchrotron jet. Although on scales of a few thousand AU the magnetic field inferred from the masers is on average orientated along the flow axis, on smaller scales (10s to 100s of AU), we have revealed a misalignment between the magnetic field and the velocity vectors, which arises from the compression ...

  11. Accretion Disks around Young Low Mass Stars

    Directory of Open Access Journals (Sweden)

    Paola D´Alessio

    2001-01-01

    Full Text Available In the past decade, it has become clear that almost half of the low mass pre-main sequence stars are surrounded by disks, which are responsible for the observed infrared and optical-UV excess emission. The characterization of the structure of circumstellar disks is a crucial step towards understanding the early stellar evolution and planet formation. The thesis summarized here presents physical models of the detailed structure of accretion disks surrounding T Tauri stars. The disks are assumed to be in steady state, in vertical hydrostatic equilibrium, and with a turbulent viscosity described by the alpha-prescription. We consider different heating mechanisms: viscous dissipation, heating by cosmic rays and radioactive decay, irradiation by the central star or irradiation by an infalling envelope. The energy is transported in the vertical direction by radiation, convection and the turbulent flux. Give n the disk structure, we calculate its emission by integrating the radiative transfer equation for an arbitrary orientation of the disk relative to the line of sight. Spectral energy distributions (SEDs and images are compared with observations, and disk properties can be inferred or constrained.

  12. First detection of Hydrogen Chloride towards protostellar shocks

    CERN Document Server

    Codella, C; Bottinelli, S; Salez, M; Viti, S; Lefloch, B; Cabrit, S; Caux, E; Faure, A; Vasta, M; Wiesenfeld, L

    2011-01-01

    We present the first detection of hydrogen chlorine in a protostellar shock, by observing the fundamental transition at 626 GHz with the Herschel HIFI spectrometer. We detected two of the three hyperfine lines, from which we derived a line opacity 15 K and density > 3 x 10(5) cm-3}. Combining with the Herschel HIFI CO(5-4) observations allows to further constrain the gas density and temperature, 10(5)-10(6) cm-3 and 120-250 K, as well as the HCl column density, 2 x 10(13) cm-2, and, finally, abundance: 3-6 x 10(-9). The estimated HCl abundance is consistent with that previously observed in low- and high- mass protostars. This puzzling result in the L1157-B1 shock, where species from volatile and refractory grains components are enhanced, suggests either that HCl is not the main reservoir of chlorine in the gas phase, against previous chemical models predictions, or that the elemental chlorine abundance is low in L1157-B1. Astrochemical modelling suggests that HCl is in fact formed in the gas phase, at low te...

  13. On the dynamics of dust during protostellar collapse

    Science.gov (United States)

    Bate, Matthew R.; Lorén-Aguilar, Pablo

    2017-02-01

    The dynamics of dust and gas can be quite different from each other when the dust is poorly coupled to the gas. In protoplanetary discs, it is well known that this decoupling of the dust and gas can lead to diverse spatial structures and dust-to-gas ratios. In this paper, we study the dynamics of dust and gas during the earlier phase of protostellar collapse, before a protoplanetary disc is formed. We find that for dust grains with sizes ≲ 10 μm, the dust is well coupled during the collapse of a rotating, pre-stellar core and there is little variation of the dust-to-gas ratio during the collapse. However, if larger grains are present, they may have trajectories that are very different from the gas during the collapse, leading to mid-plane settling and/or oscillations of the dust grains through the mid-plane. This may produce variations in the dust-to-gas ratio and very different distributions of large and small dust grains at the very earliest stages of star formation, if large grains are present in pre-stellar cores.

  14. On the dynamics of dust during protostellar collapse

    CERN Document Server

    Bate, Matthew R

    2016-01-01

    The dynamics of dust and gas can be quite different from each other when the dust is poorly coupled to the gas. In protoplanetary discs, it is well known that this decoupling of the dust and gas can lead to diverse spatial structures and dust-to-gas ratios. In this paper, we study the dynamics of dust and gas during the earlier phase of protostellar collapse, before a protoplanetary disc is formed. We find that for dust grains with sizes < 10 micron, the dust is well coupled during the collapse of a rotating, pre-stellar core and there is little variation of the dust-to-gas ratio during the collapse. However, if larger grains are present, they may have trajectories that are very different from the gas during the collapse, leading to mid-plane settling and/or oscillations of the dust grains through the mid-plane. This may produce variations in the dust-to-gas ratio and very different distributions of large and small dust grains at the very earliest stages of star formation, if large grains are present in pr...

  15. Young Stars and Protostellar Cores near NGC 2023

    CERN Document Server

    Mookerjea, B; Jarrett, T H; McMullin, J P

    2009-01-01

    We investigate the young (proto)stellar population in NGC 2023 and the L 1630 molecular cloud bordering the HII region IC 434, using Spitzer IRAC and MIPS archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA observations of one of the Class 0 protostars, NGC 2023 MM1. We have performed photometry of all IRAC and MIPS images, and used color-color diagrams to identify and classify all young stars seen within a 22'x26' field along the boundary between IC 434 and L 1630. For some stars, which have sufficient optical, IR, and/or sub-millimeter data we have also used the online SED fitting tool for a large 2D archive of axisymmetric radiative transfer models to perform more detailed modeling of the observed SEDs. We identify 5 sub-millimeter cores in our 850 and 450 micron SCUBA images, two of which have embedded class 0 or I protostars. Observations with BIMA are used to refine the position and characteristics of the Class 0 source NGC 2023 MM 1. These observations show that it is embedded in...

  16. A Protostellar Jet Emanating from a Hypercompact HII Region

    CERN Document Server

    Guzmán, Andrés E; Rodríguez, Luis F; Contreras, Yanett; Dougados, Catherine; Cabrit, Sylvie

    2016-01-01

    We present radio continuum observations of the high-mass young stellar object (HMYSO) G345.4938+01.4677 made using the Australia Telescope Compact Array (ATCA) at 5, 9, 17, and 19 GHz. These observations provide definite evidence that the outer and inner pairs of radio lobes consist of shock ionized material being excited by an underlying collimated and fast protostellar jet emanating from a hypercompact HII region. By comparing with images taken 6 yr earlier at 5 and 9 GHz using the same telescope, we assess the proper motions of the radio sources. The outer West and East lobes exhibit proper motions of $64\\pm12$ and $48\\pm13$ milliarcsec yr$^{-1}$, indicating velocities projected in the plane of the sky and receding from G345.4938+01.4677 of $520$ and $390$ km s$^{-1}$, respectively. The internal radio lobes also display proper motion signals consistently receding from the HMYSO, with magnitudes of $17\\pm11$ and $35\\pm10$ milliarcsec yr$^{-1}$ for the inner West and East lobes, respectively. The morphology ...

  17. The Turbulent Shock Origin of Proto--Stellar Cores

    CERN Document Server

    Padoan, P; Goodman, A A; Nordlund, A A; Padoan, Paolo; Juvela, Mika; Goodman, Alyssa A.; Nordlund, AAke

    2001-01-01

    The fragmentation of molecular clouds (MC) into protostellar cores is a central aspect of the process of star formation. Because of the turbulent nature of super-sonic motions in MCs, it has been suggested that dense structures such as filaments and clumps are formed by shocks in a turbulent flow. In this work we present strong evidence in favor of the turbulent origin of the fragmentation of MCs. The most generic result of turbulent fragmentation is that dense post shock gas traces a gas component with a smaller velocity dispersion than lower density gas, since shocks correspond to regions of converging flows, where the kinetic energy of the turbulent motion is dissipated. Using synthetic maps of spectra of molecular transitions, computed from the results of numerical simulations of super--sonic turbulence, we show that the dependence of velocity dispersion on gas density generates an observable relation between the rms velocity centroid and the integrated intensity (column density), Sigma(V_0)-I, which is i...

  18. Protostellar fragmentation in a power-law density distribution

    CERN Document Server

    Burkert, A; Bodenheimer, P

    1997-01-01

    Hydrodynamical calculations in three space dimensions of the collapse of an isothermal, rotating 1 M\\sol protostellar cloud are presented. The initial density stratification is a power law with density $\\rho \\propto r^{-p}$, with $p=1$. The case of the singular isothermal sphere ($p=2$) is not considered; however $p=1$ has been shown observationally to be a good representation of the density distribution in molecular cloud cores just before the beginning of collapse. The collapse is studied with two independent numerical methods, an SPH code with 200,000 particles, and a finite-difference code with nested grids which give high spatial resolution in the inner regions. Although previous numerical studies have indicated that such a power-law distribution would not result in fragmentation into a binary system, both codes show, in contrast, that multiple fragmentation does occur in the central regions of the protostar. Thus the process of binary formation by fragmentation is shown to be consistent with the fact th...

  19. Molecular ions in the protostellar shock L1157-B1

    CERN Document Server

    Podio, L; Ceccarelli, C; Codella, C; Bachiller, R

    2014-01-01

    We perform a complete census of molecular ions with an abundance larger than 1e-10 in the protostellar shock L1157-B1 by means of an unbiased high-sensitivity survey obtained with the IRAM-30m and Herschel/HIFI. By means of an LVG radiative transfer code the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem. We detect emission from HCO+, H13CO+, N2H+, HCS+, and, for the first time in a shock, from HOCO+, and SO+. The bulk of the emission peaks at blueshifted velocity, ~ 0.5-3 km/s with respect to systemic, has a width of ~ 4-8 km/s, and is associated with the outflow cavities (T_kin ~ 20-70 K, n(H2) ~ 1e5 cm-3). Observed HCO+ and N2H+ abundances are in agreement with steady-state abundances in the cloud and with their evolution in the compressed and heated gas in the shock for cosmic rays ionization rate Z = 3e-16 s-1. HOCO+...

  20. Protostellar Cosmic Rays and Extinct Radioactivities in Meteorites

    Energy Technology Data Exchange (ETDEWEB)

    Lee, T. [Institute of Earth Science, Academia Sinica, Taipei 115 (Taiwan); Shu, F.H.; Shang, H. [Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720-3411 (United States); Glassgold, A.E. [Department of Physics, New York University, New York, NY 10003 (United States); Rehm, K.E. [Argonne National Laboratory, Argonne, IL 60439-4832 (United States)

    1998-10-01

    Calcium-aluminum{endash}rich inclusions (CAIs) and chondrules of chondritic meteorites may originate with the melting of dustballs launched by a magnetically driven bipolar outflow from the inner edge of the primitive solar nebula. Bombardment by protostellar cosmic rays may make the rock precursors of CAIs and chondrules radioactive, producing radionuclides found in meteorites that are difficult to obtain with other mechanisms. Reasonable scalings from the observed hard X-rays for the cosmic-ray protons released by flares in young stellar objects yield the correct amounts of {sup 41}Ca, {sup 53}Mn, and {sup 138}La inferred for meteorites, but proton- and {alpha}-induced transformations underproduce {sup 26}Al by a factor of about 20. The missing {sup 26}Al may be synthesized by {sup 3}He nuclei accelerated in impulsive flares reacting primarily with {sup 24}Mg, an abundant isotope in the target precursor rocks. The mechanism allows a simple explanation for the very different ratios of {sup 26}Al/{sup 27}Al inferred for normal CAIs, CAIs with fractionated and unidentified nuclear (FUN) anomalies, and chondrules. The overproduction of {sup 41}Ca by analogous {sup 3}He reactions and the case of {sup 60}Fe inferred for eucritic meteorites require special interpretations in this picture. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}

  1. HERSCHEL FINDS EVIDENCE FOR STELLAR WIND PARTICLES IN A PROTOSTELLAR ENVELOPE: IS THIS WHAT HAPPENED TO THE YOUNG SUN?

    Energy Technology Data Exchange (ETDEWEB)

    Ceccarelli, C.; López-Sepulcre, A. [Université Grenoble Alpes, IPAG, F-38000 Grenoble (France); Dominik, C.; Kama, M. [Astronomical Institute Anton Pannekoek, University of Amsterdam, Postbus 94249, 1090-GE Amsterdam (Netherlands); Padovani, M. [Laboratoire Univers et Particules de Montpellier, UMR 5299 du CNRS, Université de Montpellier II, cc072, F-34095 Montpellier (France); Caux, E. [Université de Toulouse, UPS-OMP, IRAP, F-31062 Toulouse (France); Caselli, P., E-mail: Cecilia.Ceccarelli@obs.ujf-grenoble.fr [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2014-07-20

    There is evidence that the young Sun emitted a high flux of energetic (≥10 MeV) particles. The collisions of these particles with the material at the inner edge of the Protosolar Nebula disk induced spallation reactions that formed short-lived radionuclei, like {sup 10}Be, whose trace is now visible in some meteorites. However, it is poorly known exactly when this happened, and whether and how it affected the solar system. Here, we present indirect evidence for an ejection of energetic particles in the young protostar, OMC-2 FIR 4, similar to that experienced by the young solar system. In this case, the energetic particles collide with the material in the protostellar envelope, enhancing the abundance of two molecular ions, HCO{sup +} and N{sub 2}H{sup +}, whose presence is detected via Herschel observations. The flux of energetic particles at a distance of 1 AU from the emitting source, estimated from the measured abundance ratio of HCO{sup +} and N{sub 2}H{sup +}, can easily account for the irradiation required by meteoritic observations. These new observations demonstrate that the ejection of ≥10 MeV particles is a phenomenon occurring very early in the life of a protostar, before the disappearance of the envelope from which the future star accretes. The whole envelope is affected by the event, which sets constraints on the magnetic field geometry in the source and opens up the possibility that the spallation reactions are not limited to the inner edge of the Protosolar Nebula disk.

  2. MAGNETIC BRAKING AND FIELD DISSIPATION IN THE PROTOSTELLAR ACCRETION PHASE

    Directory of Open Access Journals (Sweden)

    D. Galli

    2009-01-01

    Full Text Available We summarize recent theoretical work addressing the role of magnetic elds in the process of star formation. First, we concentrate on the efficiency of magnetic braking during cloud collapse and its consequences on the formation of centrifugally supported disks around young stars. Then, we relate this issue to the well-known magnetic ux problem of star formation, and we show that the introduction of non-ideal MHD e ects is a necessary step toward the development of self-consistent models for the collapse of molecular clouds and the formation and evolution of accretion disks around young stars.

  3. Infall-driven protostellar accretion and the solution to the luminosity problem

    DEFF Research Database (Denmark)

    Padoan, Paolo; Haugbølle, Troels; Nordlund, Åke

    2014-01-01

    We investigate the role of mass infall in the formation and evolution of protostars. To avoid ad hoc initial and boundary conditions, we consider the infall resulting self-consistently from modeling the formation of stellar clusters in turbulent molecular clouds. We show that infall rates....... The simulation reproduces well the observed characteristic values and scatter of protostellar luminosities and matches the observed protostellar luminosity function. The luminosity problem is therefore solved once realistic protostellar infall histories are accounted for, with no need for extreme accretion...... episodes. These results are based on a simulation of randomly driven magnetohydrodynamic turbulence on a scale of 4 pc, including self-gravity, adaptive-mesh refinement to a resolution of 50 AU, and accreting sink particles. The simulation yields a low star formation rate, consistent with the observations...

  4. Direct detection of a magnetic field in the innermost regions of an accretion disk.

    Science.gov (United States)

    Donati, Jean-François; Paletou, Fréderic; Bouvier, Jérome; Ferreira, Jonathan

    2005-11-24

    Models predict that magnetic fields play a crucial role in the physics of astrophysical accretion disks and their associated winds and jets. For example, the rotation of the disk twists around the rotation axis the initially vertical magnetic field, which responds by slowing down the plasma in the disk and by causing it to fall towards the central star. The magnetic energy flux produced in this process points away from the disk, pushing the surface plasma outwards, leading to a wind from the disk and sometimes a collimated jet. But these predictions have hitherto not been supported by observations. Here we report the direct detection of the magnetic field in the core of the protostellar accretion disk FU Orionis. The surface field reaches strengths of about 1 kG close to the centre of the disk, and it includes a significant azimuthal component, in good agreement with recent models. But we find that the field is very filamentary and slows down the disk plasma much more than models predict, which may explain why FU Ori fails to collimate its wind into a jet.

  5. ALMA observations of a misaligned binary protoplanetary disk system in Orion

    Energy Technology Data Exchange (ETDEWEB)

    Williams, Jonathan P. [Institute for Astronomy, University of Hawaii, Honolulu, HI 96816 (United States); Mann, Rita K.; Francesco, James Di; Johnstone, Doug; Matthews, Brenda [NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Andrews, Sean M.; Ricci, Luca [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hughes, A. Meredith [Van Vleck Observatory, Astronomy Department, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States); Bally, John, E-mail: jpw@ifa.hawaii.edu [CASA, University of Colorado, CB 389, Boulder, CO 80309 (United States)

    2014-12-01

    We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a wide binary system in Orion, with projected separation 440 AU, in which we detect submillimeter emission from the protoplanetary disks around each star. Both disks appear moderately massive and have strong line emission in CO 3-2, HCO{sup +} 4-3, and HCN 3-2. In addition, CS 7-6 is detected in one disk. The line-to-continuum ratios are similar for the two disks in each of the lines. From the resolved velocity gradients across each disk, we constrain the masses of the central stars, and show consistency with optical-infrared spectroscopy, both indicative of a high mass ratio ∼9. The small difference between the systemic velocities indicates that the binary orbital plane is close to face-on. The angle between the projected disk rotation axes is very high, ∼72°, showing that the system did not form from a single massive disk or a rigidly rotating cloud core. This finding, which adds to related evidence from disk geometries in other systems, protostellar outflows, stellar rotation, and similar recent ALMA results, demonstrates that turbulence or dynamical interactions act on small scales well below that of molecular cores during the early stages of star formation.

  6. Simulating planet migration in globally evolving disks

    CERN Document Server

    Crida, A; Masset, F

    2006-01-01

    Numerical simulations of planet-disk interactions are usually performed with hydro-codes that -- because they consider only an annulus of the disk, over a 2D grid -- can not take into account the global evolution of the disk. However, the latter governs planetary migration of type II, so that the accuracy of the planetary evolution can be questioned. To develop an algorithm that models the local planet-disk interactions together with the global viscous evolution of the disk, we surround the usual 2D grid with a 1D grid ranging over the real extension of the disk. The 1D and 2D grids are coupled at their common boundaries via ghost rings, paying particular attention to the fluxes at the interface, especially the flux of angular momentum carried by waves. The computation is done in the frame centered on the center of mass to ensure angular momentum conservation. The global evolution of the disk and the local planet-disk interactions are both well described and the feedback of one on the other can be studied wit...

  7. Snow Line Localization in Classical Protoplanetary Disks

    Science.gov (United States)

    Blevins, S.

    2014-04-01

    Protoplanetary disks are volatile-rich environments capable of producing the essential conditions that make planet formation viable. Establishing a molecular inventory of dominant volatile species, such as water, in the planet-forming zones surrounding young, solar-type stars elevates our understanding of the chemistry involved with planet formation, composition and disk evolution. For this study we measure the water vapor content and determine the location of the condensation front, or snow line, for four classical disks selected for the strong water emission present in their mid-infrared spectra. To accomplish this we combine deep Herschel PACS observations with high resolution Spitzer IRS spectra to create molecular maps comprised of water lines with excitation temperatures that trace the disks' surfaces from 1-100 AU. We use two-dimensional, axisymmetric radiative transfer modeling to retrieve the disks' dust structures and the RADLite raytracer to render model spectra for each disk. A simple step function is used to define the abundance structure and the model spectra are fit to the observed water lines. Preliminary results will be discussed, including the inner disk chemical content, snow line radius and fractional water vapor abundances for the classical disk RNO 90.

  8. DVD - digital versatile disks

    Energy Technology Data Exchange (ETDEWEB)

    Gaunt, R.

    1997-05-01

    An international standard has emerged for the first true multimedia format. Digital Versatile Disk (by its official name), you may know it as Digital Video Disks. DVD has applications in movies, music, games, information CD-ROMS, and many other areas where massive amounts of digital information is needed. Did I say massive amounts of data? Would you believe over 17 gigabytes on a single piece of plastic the size of an audio-CD? That`s the promise, at least, by the group of nine electronics manufacturers who have agreed to the format specification, and who hope to make this goal a reality by 1998. In this major agreement, which didn`t come easily, the manufacturers will combine Sony and Phillip`s one side double-layer NMCD format with Toshiba and Matsushita`s double sided Super-Density disk. By Spring of this year, they plan to market the first 4.7 gigabyte units. The question is: Will DVD take off? Some believe that read-only disks recorded with movies will be about as popular as video laser disks. They say that until the eraseable/writable DVD arrives, the consumer will most likely not buy it. Also, DVD has a good market for replacement of CD- Roms. Back in the early 80`s, the international committee deciding the format of the audio compact disk decided its length would be 73 minutes. This, they declared, would allow Beethoven`s 9th Symphony to be contained entirely on a single CD. Similarly, today it was agreed that playback length of a single sided, single layer DVD would be 133 minutes, long enough to hold 94% of all feature-length movies. Further, audio can be in Dolby`s AC-3 stereo or 5.1 tracks of surround sound, better than CD-quality audio (16-bits at 48kHz). In addition, there are three to five language tracks, copy protection and parental ``locks`` for R rated movies. DVD will be backwards compatible with current CD-ROM and audio CD formats. Added versatility comes by way of multiple aspect rations: 4:3 pan-scan, 4:3 letterbox, and 16:9 widescreen. MPEG

  9. Dust in protoplanetary disks: observations*

    Directory of Open Access Journals (Sweden)

    Waters L.B.F.M.

    2015-01-01

    Full Text Available Solid particles, usually referred to as dust, are a crucial component of interstellar matter and of planet forming disks surrounding young stars. Despite the relatively small mass fraction of ≈1% (in the solar neighborhood of our galaxy; this number may differ substantially in other galaxies that interstellar grains represent of the total mass budget of interstellar matter, dust grains play an important role in the physics and chemistry of interstellar matter. This is because of the opacity dust grains at short (optical, UV wavelengths, and the surface they provide for chemical reactions. In addition, dust grains play a pivotal role in the planet formation process: in the core accretion model of planet formation, the growth of dust grains from the microscopic size range to large, cm-sized or larger grains is the first step in planet formation. Not only the grain size distribution is affected by planet formation. Chemical and physical processes alter the structure and chemical composition of dust grains as they enter the protoplanetary disk and move closer to the forming star. Therefore, a lot can be learned about the way stars and planets are formed by observations of dust in protoplanetary disks. Ideally, one would like to measure the dust mass, the grain size distribution, grain structure (porosity, fluffiness, the chemical composition, and all of these as a function of position in the disk. Fortunately, several observational diagnostics are available to derive constrains on these quantities. In combination with rapidly increasing quality of the data (spatial and spectral resolution, a lot of progress has been made in our understanding of dust evolution in protoplanetary disks. An excellent review of dust evolution in protoplanetary disks can be found in Testi et al. (2014.

  10. Galaxy Disks are Submaximal

    NARCIS (Netherlands)

    Bershady, Matthew A.; Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.

    2011-01-01

    We measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on intermediate-to-late-type spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars (sigma(disk)(z,R=0)) is related to the maximum rotation speed (V-max) as sigm

  11. Cooling of young stars growing by disk accretion

    CERN Document Server

    Rafikov, Roman

    2007-01-01

    In the initial formation stages young stars must acquire a significant fraction of their mass by accretion from a circumstellar disk that forms in the center of a collapsing protostellar cloud. Throughout this period mass accretion rates through the disk can reach 10^{-6}-10^{-5} M_Sun/yr leading to substantial energy release in the vicinity of stellar surface. We study the impact of irradiation of the stellar surface produced by the hot inner disk on properties of accreting fully convective low-mass stars, and also look at objects such as young brown dwarfs and giant planets. At high accretion rates irradiation raises the surface temperature of the equatorial region above the photospheric temperature T_0 that a star would have in the absence of accretion. The high-latitude (polar) parts of the stellar surface, where disk irradiation is weak, preserve their temperature at the level of T_0. In strongly irradiated regions an almost isothermal outer radiative zone forms on top of the fully convective interior, l...

  12. Vortex migration in protoplanetary disks

    CERN Document Server

    Paardekooper, S -J; Papaloizou, J C B

    2010-01-01

    We consider the radial migration of vortices in two-dimensional isothermal gaseous disks. We find that a vortex core, orbiting at the local gas velocity, induces velocity perturbations that propagate away from the vortex as density waves. The resulting spiral wave pattern is reminiscent of an embedded planet. There are two main causes for asymmetries in these wakes: geometrical effects tend to favor the outer wave, while a radial vortensity gradient leads to an asymmetric vortex core, which favors the wave at the side that has the lowest density. In the case of asymmetric waves, which we always find except for a disk of constant pressure, there is a net exchange of angular momentum between the vortex and the surrounding disk, which leads to orbital migration of the vortex. Numerical hydrodynamical simulations show that this migration can be very rapid, on a time scale of a few thousand orbits, for vortices with a size comparable to the scale height of the disk. We discuss the possible effects of vortex migrat...

  13. Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry

    CERN Document Server

    Furuya, Kenji

    2014-01-01

    We study the influence of the turbulent transport on ice chemistry in protoplanetary disks, focusing on carbon and nitrogen bearing molecules. Chemical rate equations are solved with the diffusion term, mimicking the turbulent mixing in the vertical direction. Turbulence can bring ice-coated dust grains from the midplane to the warm irradiated disk surface, and the ice mantles are reprocessed by photoreactions, thermal desorption, and surface reactions. The upward transport decreases the abundance of methanol and ammonia ices at r < 30 AU, because warm dust temperature prohibits their reformation on grain surfaces. This reprocessing could explain the smaller abundances of carbon and nitrogen bearing molecules in cometary coma than those in low-mass protostellar envelopes. We also show the effect of mixing on the synthesis of complex organic molecules (COMs) are two ways: (1) transport of ices from the midplane to the disk surface and (2) transport of atomic hydrogen from the surface to the midplane. The fo...

  14. Secular Evolution in Disk Galaxies

    Science.gov (United States)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  15. Can Massive Dark Haloes Destroy the Disks of Dwarf Galaxies?

    CERN Document Server

    Fuchs, B

    2007-01-01

    Recent high-resolution simulations together with theoretical studies of the dynamical evolution of galactic disks have shown that contrary to wide-held beliefs a `live', dynamically responsive, dark halo surrounding a disk does not stabilize the disk against dynamical instabilities. We generalize Toomre's Q stability parameter for a disk-halo system and show that if a disk, which would be otherwise stable, is embedded in a halo, which is too massive and cold, the combined disk-halo system can become locally Jeans unstable. The good news is, on the other hand, that this will not happen in real dark haloes, which are in radial hydrostatic equilibrium. Even very low-mass disks are not prone to such dynamical instabilities.

  16. A Triple Protostar System Formed via Fragmentation of a Gravitationally Unstable Disk

    CERN Document Server

    Tobin, John; Persson, Magnus; Looney, Leslie; Dunham, Michael; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire; Sadavoy, Sarah; Harris, Robert; Melis, Carl; Perez, Laura

    2016-01-01

    Binary and multiple star systems are a frequent outcome of the star formation process, and as a result, almost half of all sun-like stars have at least one companion star. Theoretical studies indicate that there are two main pathways that can operate concurrently to form binary/multiple star systems: large scale fragmentation of turbulent gas cores and filaments or smaller scale fragmentation of a massive protostellar disk due to gravitational instability. Observational evidence for turbulent fragmentation on scales of $>$1000~AU has recently emerged. Previous evidence for disk fragmentation was limited to inferences based on the separations of more-evolved pre-main sequence and protostellar multiple systems. The triple protostar system L1448 IRS3B is an ideal candidate to search for evidence of disk fragmentation. L1448 IRS3B is in an early phase of the star formation process, likely less than 150,000 years in age, and all protostars in the system are separated by $<$200~AU. Here we report observations of...

  17. Supersonic turbulence, filamentary accretion,and the rapid assembly of massive stars and disks

    CERN Document Server

    Banerjee, R; Anderson, D W; Banerjee, Robi; Pudritz, Ralph E.; Anderson, Dave W.

    2006-01-01

    We present a detailed computational study of the assembly of protostellar disks and massive stars in molecular clouds with supersonic turbulence. We follow the evolution of large scale filamentary structures in a cluster-forming clump down to protostellar length scales by means of very highly resolved, 3D adaptive mesh refined (AMR) simulations, and show how accretion disks and massive stars form in such environments. We find that an initially elongated cloud core which has a slight spin from oblique shocks collapses first to a filament and later develops a turbulent disk close to the center of the filament. The continued large scale flow that shocks with the filament maintains the high density and pressure within it. Material within the cooling filament undergoes gravitational collapse and an outside-in assembly of a massive protostar. Our simulations show that very high mass accretion rates of up to 10^-2 Msol/yr and high, supersonic, infall velocities result from such filamentary accretion. Accretion at th...

  18. Stochastic oscillations of general relativistic disks

    CERN Document Server

    Harko, Tiberiu

    2012-01-01

    We analyze the general relativistic oscillations of thin accretion disks around compact astrophysical objects interacting with the surrounding medium through non-gravitational forces. The interaction with the external medium (a thermal bath) is modeled via a friction force, and a random force, respectively. The general equations describing the stochastically perturbed disks are derived by considering the perturbations of trajectories of the test particles in equatorial orbits, assumed to move along the geodesic lines. By taking into account the presence of a viscous dissipation and of a stochastic force we show that the dynamics of the stochastically perturbed disks can be formulated in terms of a general relativistic Langevin equation. The stochastic energy transport equation is also obtained. The vertical oscillations of the disks in the Schwarzschild and Kerr geometries are considered in detail, and they are analyzed by numerically integrating the corresponding Langevin equations. The vertical displacement...

  19. Exact Relativistic Magnetized Haloes around Rotating Disks

    Directory of Open Access Journals (Sweden)

    Antonio C. Gutiérrez-Piñeres

    2015-01-01

    Full Text Available The study of the dynamics of magnetic fields in galaxies is one of important problems in formation and evolution of galaxies. In this paper, we present the exact relativistic treatment of a rotating disk surrounded by a magnetized material halo. The features of the halo and disk are described by the distributional energy-momentum tensor of a general fluid in canonical form. All the relevant quantities and the metric and electromagnetic potentials are exactly determined by an arbitrary harmonic function only. For instance, the generalized Kuzmin-disk potential is used. The particular class of solutions obtained is asymptotically flat and satisfies all the energy conditions. Moreover, the motion of a charged particle on the halo is described. As far as we know, this is the first relativistic model describing analytically the magnetized halo of a rotating disk.

  20. THE CONNECTION BETWEEN EKMAN AND STEWARTSON LAYERS FOR A ROTATING-DISK

    NARCIS (Netherlands)

    When a disk of finite radius and the surrounding medium rotate coaxially with slightly different angular velocities, a so-called Stewartson layer exists at the edge of the disk. The properties of this layer outside the boundary layer of the disk have been given in a previous publication. In the

  1. A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A

    CERN Document Server

    Murillo, Nadia M; Bruderer, Simon; Harsono, Daniel; van Dishoeck, Ewine F

    2013-01-01

    Context: Rotationally supported disks are critical in the star formation process. The questions of when do they form and what factors influence or hinder their formation have been studied but are largely unanswered. Observations of early stage YSOs are needed to probe disk formation. Aims: VLA1623 is a triple non-coeval protostellar system, with a weak magnetic field perpendicular to the outflow, whose Class 0 component, VLA1623A, shows a disk-like structure in continuum with signatures of rotation in line emission. We aim to determine whether this structure is in part or in whole a rotationally supported disk, i.e. a Keplerian disk, and what are its characteristics. Methods: ALMA Cycle 0 Early Science 1.3 mm continuum and C$^{18}$O (2-1) observations in the extended configuration are presented here and used to perform an analysis of the disk-like structure using PV diagrams and thin disk modelling with the addition of foreground absorption. Results: The PV diagrams of the C$^{18}$O line emission suggest the ...

  2. Ammonia Imaging of the Disks in the NGC 1333 IRAS 4A Protobinary System

    CERN Document Server

    Choi, Minho; Park, Geumsook; Kang, Miju

    2007-01-01

    The NGC 1333 IRAS 4A protobinary was observed in the ammonia (2, 2) and (3, 3) lines and in the 1.3 cm continuum with a high resolution (about 1.0 arcsec). The ammonia maps show two compact sources, one for each protostar, and they are probably protostellar accretion disks. The disk associated with IRAS 4A2 is seen nearly edge-on and shows an indication of rotation. The A2 disk is brighter in the ammonia lines but dimmer in the dust continuum than its sibling disk, with the ammonia-to-dust flux ratios different by about an order of magnitude. This difference suggests that the twin disks have surprisingly dissimilar characters, one gas-rich and the other dusty. The A2 disk may be unusually active or hot, as indicated by its association with water vapor masers. The existence of two very dissimilar disks in a binary system suggests that the formation process of multiple systems has a controlling agent lacking in the isolated star formation process and that stars belonging to a multiple system do not necessarily ...

  3. Nature of shocks revealed by SOFIA OI observations in the Cepheus e protostellar outflow

    DEFF Research Database (Denmark)

    Gusdorf, A.; Anderl, S.; Lefloch, B.

    2017-01-01

    Context. Protostellar jets and outflows are key features of the star-formation process, and primary processes of the feedback of young stars on the interstellar medium. Understanding the underlying shocks is necessary to explain how jet and outflow systems are launched, and to quantify their chem...

  4. Protostellar feedback in turbulent fragmentation: consequences for stellar clustering and multiplicity

    Science.gov (United States)

    Guszejnov, Dávid; Hopkins, Philip F.; Krumholz, Mark R.

    2017-07-01

    Stars are strongly clustered on both large (˜pc) and small (˜binary) scales, but there are few analytic or even semi-analytic theories for the correlation function and multiplicity of stars. In this paper, we present such a theory, based on our recently developed semi-analytic framework called MISFIT (Minimalistic Star Formation Including Turbulence), which models gravito-turbulent fragmentation, including the suppression of fragmentation by protostellar radiation feedback. We compare the results including feedback to a control model in which it is omitted. We show that both classes of models robustly reproduce the stellar correlation function at >0.01 pc scales, which is well approximated by a power law that follows generally from scale-free physics (turbulence plus gravity) on large scales. On smaller scales, protostellar disc fragmentation becomes dominant over common core fragmentation, leading to a steepening of the correlation function. Multiplicity is more sensitive to feedback: we found that a model with the protostellar heating reproduces the observed multiplicity fractions and mass ratio distributions for both Solar and sub-Solar mass stars (in particular, the brown dwarf desert), while a model without feedback fails to do so. The model with feedback also produces an at-formation period distribution consistent with the one inferred from observations. However, it is unable to produce short-range binaries below the length-scale of protostellar discs. We suggest that such close binaries are produced primarily by disc fragmentation and further decrease their separation through orbital decay.

  5. Impact of Protostellar Outflows on Turbulence and Star Formation Efficiency in Magnetized Dense Cores

    Science.gov (United States)

    Offner, Stella S. R.; Chaban, Jonah

    2017-10-01

    The star-forming efficiency of dense gas is thought to be set within cores by outflow and radiative feedback. We use magnetohydrodynamic simulations to investigate the relation between protostellar outflow evolution, turbulence, and star formation efficiency. We model the collapse and evolution of isolated dense cores for ≳0.5 Myr including the effects of turbulence, radiation transfer, and both radiation and outflow feedback from forming protostars. We show that outflows drive and maintain turbulence in the core environment even with strong initial fields. The star formation efficiency decreases with increasing field strength, and the final efficiencies are 15%–40%. The Stage 0 lifetime, during which the protostellar mass is lower than that of the dense envelope, increases proportionally with the initial magnetic field strength and ranges from ∼ 0.1 {to} 0.4 {Myr}. The average accretion rate is well represented by a tapered turbulent core model, which is a function of the final protostellar mass and is independent of the magnetic field strength. By tagging material launched in the outflow, we demonstrate that the outflow entrains about three times the actual launched gas mass, a ratio that remains roughly constant in time regardless of the initial magnetic field strength. However, turbulent driving increases for stronger fields since momentum is more efficiently imparted to non-outflow material. The protostellar outflow momentum is highest during the first 0.1 Myr and declines thereafter by a factor of ≳ 10 as the accretion rate diminishes.

  6. Oscillations of disks

    CERN Document Server

    Kato, Shoji

    2016-01-01

    This book presents the current state of research on disk oscillation theory, focusing on relativistic disks and tidally deformed disks. Since the launch of the Rossi X-ray Timing Explorer (RXTE) in 1996, many high-frequency quasiperiodic oscillations (HFQPOs) have been observed in X-ray binaries. Subsequently, similar quasi-periodic oscillations have been found in such relativistic objects as microquasars, ultra-luminous X-ray sources, and galactic nuclei. One of the most promising explanations of their origin is based on oscillations in relativistic disks, and a new field called discoseismology is currently developing. After reviewing observational aspects, the book presents the basic characteristics of disk oscillations, especially focusing on those in relativistic disks. Relativistic disks are essentially different from Newtonian disks in terms of several basic characteristics of their disk oscillations, including the radial distributions of epicyclic frequencies. In order to understand the basic processes...

  7. HiRes deconvolved Spitzer images of 89 protostellar jets and outflows: New data on the evolution of the outflow morphology

    Energy Technology Data Exchange (ETDEWEB)

    Velusamy, T.; Langer, W. D. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Thompson, T., E-mail: velusamy@jpl.nasa.gov, E-mail: William.D.Langer@jpl.nasa.gov, E-mail: timthompson3@verizon.net [1947C East Huntington Drive, Duarte, CA 91010 (United States)

    2014-03-01

    To study the role of protosellar jets and outflows in the time evolution of the parent cores and the protostars, the astronomical community needs a large enough database of infrared images of protostars at the highest spatial resolution possible to reveal the details of their morphology. Spitzer provides unprecedented sensitivity in the infrared to study both the jet and outflow features, however, its spatial resolution is limited by its 0.85 m mirror. Here, we use a high-resolution deconvolution algorithm, 'HiRes,' to improve the visualization of spatial morphology by enhancing resolution (to subarcsecond levels in the IRAC bands) and removing the contaminating side lobes from bright sources in a sample of 89 protostellar objects. These reprocessed images are useful for detecting (1) wide-angle outflows seen in scattered light, (2) morphological details of H{sub 2} emission in jets and bow shocks, and (3) compact features in MIPS 24 μm images as protostar/disk and atomic/ionic line emission associated with the jets. The HiRes FITS image data of such a large homogeneous sample presented here will be useful to the community in studying these protostellar objects. To illustrate the utility of this HiRes sample, we show how the opening angle of the wide-angle outflows in 31 sources, all observed in the HiRes-processed Spitzer images, correlates with age. Our data suggest a power-law fit to opening angle versus age with an exponent of ∼0.32 and 0.02, respectively, for ages ≤8000 yr and ≥8000 yr.

  8. HST and UKIRT Observations of the Center of the Trifid Nebula: Evidence for the Photoevaporation of a Proplyd and a Protostellar Condensation

    CERN Document Server

    Yusef-Zadeh, F; Geballe, T R

    2005-01-01

    The Trifid nebula (M20) is a well-known prominent optical HII region trisected by bands of obscuring dust lanes and excited by an O7.5 star HD 164492A. Previous near-IR, mid-IR and radio continuum observations of the cluster of stars at the center of the Trifid nebula indicated circumstellar disks associated with hot stars with envelopes that are photoionized externally by the UV radiation from the hot central star, HD 164492A. Using WFPC2 of the HST, we present evidence of a resolved proplyd in H$\\alpha$ and [SII] line emission from a stellar source emitting cool dust emission. Using UKIRT, an infrared observation of the stellar source with a proplyd indicates a late F -- mid G spectral type. We also note a remarkable complex of filamentary and sheet-like structures which appear to arise from the edge of a protostellar condensation. These observations are consistent with a picture in which the bright massive star HD 164492A is responsible for the photoevaporation of protoplanetary disks of other less-massive...

  9. Warped Circumbinary Disks in Active Galactic Nuclei

    CERN Document Server

    Hayasaki, Kimitake; Okazaki, Atsuo T; Jung, Taehyun; Zhao, Guangyao; Naito, Tsuguya

    2014-01-01

    We study a warping instability of a geometrically thin, non-self-gravitating disk surrounding binary supermassive black holes on a circular orbit. Such a circumbinary disk is subject to not only tidal torques due to the binary gravitational potential but also radiative torques due to radiation emitted from an accretion disk around each black hole. We find that a circumbinary disk initially aligned with the binary orbital plane is unstable to radiation-driven warping beyond the marginally stable warping radius, which is sensitive to both the ratio of vertical to horizontal shear viscosities and the mass-to-energy conversion efficiency. As expected, the tidal torques give no contribution to the growth of warping modes but tend to align the circumbinary disk with the orbital plane. Since the tidal torques can suppress the warping modes in the inner part of circumbinary disk, the circumbinary disk starts to be warped at radii larger than the marginally stable warping radius. If the warping radius is of the order ...

  10. SOl-based radial-contour-mode micromechanical disk resonator

    Institute of Scientific and Technical Information of China (English)

    Jia Yingqian; Zhao Zhengping; Yang Yongjun; Hu Xiaodong; Li Qian

    2011-01-01

    This paper reports a radial-contour-mode micromechanical disk resonator for radio frequency applications.This disk resonator with a gold plated layer as the electrodes,was prepared on a silicon-on-insulator wafer,which is supported by an anchor on another silicon wafer through Au-Au thermo-compression bonding.The gap between the disk and the surrounding gold electrodes is 100 nm.The radius of the disk is 20 μm and the thickness is 4.5μm.In results,the resonator shows a resonant frequency of 143 MHz and a quality factor of 5600 in vacuum.

  11. Magnetic fields in primordial accretion disks

    Science.gov (United States)

    Latif, M. A.; Schleicher, D. R. G.

    2016-01-01

    Magnetic fields are considered a vital ingredient of contemporary star formation and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations and are subsequently amplified by the small-scale dynamo, leading to a strong, tangled magnetic field. We explore how the magnetic field provided by the small-scale dynamo is further amplified via the α-Ω dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop. III star with 10M⊙ and an accretion rate of 10-3M⊙ yr-1, and a supermassive star with 105M⊙ and an accretion rate of 10-1M⊙ yr-1. For the 10M⊙ Pop. III star, we find that coherent magnetic fields can be produced on scales of at least 100 AU, which are sufficient to drive a jet with a luminosity of 100L⊙ and a mass outflow rate of 10-3.7M⊙ yr-1. For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least 1000 AU. The jet luminosity corresponds to ~106.0L⊙ and a mass outflow rate of 10-2.1M⊙ yr-1. We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.

  12. Magnetic fields in primordial accretion disks

    CERN Document Server

    Latif, Muhammad A

    2016-01-01

    Magnetic fields are considered as a vital ingredient of contemporary star formation, and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations, and are subsequently amplified by the small-scale dynamo, leading to a strong tangled magnetic field. Here we explore how the magnetic field provided by the small-scale dynamo is further amplified via the $\\alpha-\\Omega$ dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop.~III star with $10$~M$_\\odot$ and an accretion rate of $10^{-3}$~M$_\\odot$~yr$^{-1}$, and a supermassive star with $10^5$~M$_\\odot$ and an accretion rate of $10^{-1}$~M$_\\odot$~yr$^{-1}$. For the $10$~M$_\\odot$ Pop.~III star, we find that coherent magnetic fields can be produced on scales of at least $100$~AU, which are sufficient to drive a jet with a luminosity of $100$~L$_\\odot$ and a mass outflow ra...

  13. Disk Storage Server

    CERN Multimedia

    This model was a disk storage server used in the Data Centre up until 2012. Each tray contains a hard disk drive (see the 5TB hard disk drive on the main disk display section - this actually fits into one of the trays). There are 16 trays in all per server. There are hundreds of these servers mounted on racks in the Data Centre, as can be seen.

  14. Galactic Disk Warps

    NARCIS (Netherlands)

    Kuijken, K.; García, I.

    2000-01-01

    Abstract: This review addresses recent developments in the field of disk galaxy warps. Both results from a new HI survey of edgeon disk galaxies, and of simulations of the interaction between a disk+halo and an orbiting satelite, will be discussed.

  15. Galactic Disk Warps

    CERN Document Server

    Kuijken, K; Kuijken, Konrad; Garcia, Inigo

    2000-01-01

    This review addresses recent developments in the field of disk galaxy warps. Both results from a new HI survey of edgeon disk galaxies, and of simulations of the interaction between a disk+halo and an orbiting satelite, will be discussed.

  16. Chemistry in Protoplanetary Disks

    CERN Document Server

    Henning, Thomas

    2013-01-01

    This comprehensive review summarizes our current understanding of the evolution of gas, solids and molecular ices in protoplanetary disks. Key findings related to disk physics and chemistry, both observationally and theoretically, are highlighted. We discuss which molecular probes are used to derive gas temperature, density, ionization state, kinematics, deuterium fractionation, and study organic matter in protoplanetary disks.

  17. Optical Disk Technology.

    Science.gov (United States)

    Abbott, George L.; And Others

    1987-01-01

    This special feature focuses on recent developments in optical disk technology. Nine articles discuss current trends, large scale image processing, data structures for optical disks, the use of computer simulators to create optical disks, videodisk use in training, interactive audio video systems, impacts on federal information policy, and…

  18. Signs of Early-Stage Disk Growth Revealed with ALMA

    CERN Document Server

    Yen, Hsi-Wei; Takakuwa, Shigehisa; Krasnopolsky, Ruben; Ohashi, Nagayoshi; Aso, Yusuke

    2016-01-01

    We present ALMA 1.3 mm continuum, 12CO, C18O, and SO data for the Class 0 protostars, Lupus 3 MMS, IRAS 15398-3559, and IRAS 16253-2429 at resolutions of ~100 AU. By measuring a rotational profile in C18O, a 100 AU Keplerian disk around a 0.3 Msun protostar is observed in Lupus 3 MMS. No 100 AU Keplerian disks are observed in IRAS 15398-3559 and IRAS 16253-2429. Nevertheless, embedded compact (<30 AU) continuum components are detected. The C18O emission in IRAS 15398-3559 shows signatures of infall with a constant angular momentum. IRAS 16253-2429 exhibits signatures of infall and rotation, but its rotational profile is unresolved. By fitting the C18O data with our kinematic models, the protostellar masses and the disk radii are inferred to be 0.01 Msun and 20 AU in IRAS 15398-3559, and 0.03 Msun and 6 AU in IRAS 16253-2429. By comparing the specific angular momentum profiles from 10,000 to 100 AU in 8 Class 0 and I protostars, we find that the evolution of envelope rotation can be described with conventio...

  19. The structure of protostellar envelopes derived from submillimeter continuum images

    CERN Document Server

    Chandler, C J; Chandler, Claire J.; Richer, John S.

    1999-01-01

    High dynamic range imaging of submillimeter dust emission from the envelopes of eight young protostars in the Taurus and Perseus star-forming regions has been carried out using the SCUBA submillimeter camera on the James Clerk Maxwell Telescope. Good correspondence between the spectral classifications of the protostars and the spatial distributions of their dust emission is observed, in the sense that those with cooler spectral energy distributions also have a larger fraction of the submillimeter flux originating in an extended envelope compared with a disk. This results from the cool sources having more massive envelopes rather than warm sources having larger disks. Azimuthally-averaged radial profiles of the dust emission are used to derive the power-law index of the envelope density distributions, p (defined by rho proportional to r^-p), and most of the sources are found to have values of p consistent with those predicted by models of cloud collapse. However, the youngest protostars in our sample, L1527 an...

  20. Variational thermodynamics of relativistic thin disks

    CERN Document Server

    Gutiérrez-Piñeres, A C; Quevedo, H

    2013-01-01

    We present a relativistic model describing a thin disk system composed of two fluids. The system is surrounded by a halo in the presence of a non-trivial electromagnetic field. We show that the model is compatible with the variational multi-fluid thermodynamics formalism, allowing us to determine all the thermodynamic variables associated with the matter content of the disk. The asymptotic behaviour of these quantities indicates that the single fluid interpretation should be abandoned in favour of a two-fluid model.

  1. How bright are the gaps in circumbinary disk systems?

    CERN Document Server

    Shi, Ji-Ming

    2016-01-01

    When a circumbinary disk surrounds a binary whose secondary's mass is at least $\\sim 10^{-2}\\times$ the primary's mass, a nearly empty cavity with radius a few times the binary separation is carved out of the disk. Narrow streams of material pass from the inner edge of the circumbinary disk into the domain of the binary itself, where they eventually join onto the small disks orbiting the members of the binary. Using data from 3-d MHD simulations of this process, we determine the luminosity of these streams; it is mostly due to weak laminar shocks, and is in general only a few percent of the luminosity of adjacent regions of either the circumbinary disk or the "mini-disks". This luminosity therefore hardly affects the deficit in the thermal continuum predicted on the basis of a perfectly dark gap region.

  2. Spiral Density Waves in a Young Protoplanetary Disk

    CERN Document Server

    Pérez, Laura M; Andrews, Sean M; Ricci, Luca; Isella, Andrea; Linz, Hendrik; Sargent, Anneila I; Wilner, David J; Henning, Thomas; Deller, Adam T; Chandler, Claire J; Dullemond, Cornelis P; Lazio, Joseph; Menten, Karl M; Corder, Stuartt A; Storm, Shaye; Testi, Leonardo; Tazzari, Marco; Kwon, Woojin; Calvet, Nuria; Greaves, Jane S; Harris, Robert J; Mundy, Lee G

    2016-01-01

    Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks of gas and dust orbiting young stars. However, previous observations that showed spiral structure were not able to probe disk midplanes, where most of the mass is concentrated and where planet formation takes place. Using the Atacama Large Millimeter/submillimeter Array we detected a pair of trailing symmetric spiral arms in the protoplanetary disk surrounding the young star Elias 2-27. The arms extend to the disk outer regions and can be traced down to the midplane. These millimeter-wave observations also reveal an emission gap closer to the star than the spiral arms. We argue that the observed spirals trace shocks of spiral density waves in the midplane of this young disk.

  3. Nonaxisymmetric Instabilities in Self-Gravitating Disks. II Linear and Quasi-Linear Analyses

    CERN Document Server

    Hadley, Kathryn Z; Imamura, James N; Keever, Erik; Tumblin, Rebecka; Dumas, William

    2014-01-01

    We studied global nonaxisymmetric hydrodynamic instabilities in an extensive collection of hot, self-gravitating polytropic disk systems, systems that covered a wide expanse of the parameter space relevant to protostellar and protoplanetary systems. We examined equilibrium disk models varying three parameters: the ratio of the inner to outer equatorial radii, the ratio of star mass to disk mass, and the rotation law exponent $q$. We took the polytropic index $n$ = 1.5 and examined the exponents $q =$ 1.5 and 2, and the transitional one $q$ = 1.75. For each of these sets of parameters, we examined models with inner to outer radius ratios from 0.1 to 0.75, and star mass to disk mass ratios from 0 to 10$^3$. We numerically calculated the growth rates and oscillation frequencies of low-order nonaxisymmetric disk modes, modes with azimuthal dependence $\\propto$ e$^{im\\phi}$. Low-$m$ modes are found to dominate with the character and strength of instability strongly dependent on disk self-gravity. Representatives o...

  4. An insight in the surroundings of HR4796

    CERN Document Server

    Lagrange, A -M; Boccaletti, A; Lacour, S; Thebault, P; Chauvin, G; Mouillet, D; Augereau, J C; Bonnefoy, M; Ehrenreich, D; Kral, Q

    2012-01-01

    HR4796 is a young, early A-type star harbouring a well structured debris disk, shaped as a ring with sharp inner edges. It forms with the M-type star HR4796B a binary system, with a proj. sep. ~560 AU. Our aim is to explore the surroundings of HR4796A and B, both in terms of extended or point-like structures. Adaptive optics images at L'-band were obtained with NaCo in Angular Differential Mode and with Sparse Aperture Masking (SAM). We analyse the data as well as the artefacts that can be produced by ADI reduction on an extended structure with a shape similar to that of HR4796A dust ring. We determine constraints on the presence of companions using SAM and ADI on HR4796A, and ADI on HR4796B. We also performed dynamical simulations of a disk of planetesimals and dust produced by collisions, perturbed by a planet located close to the disk outer edge. The disk ring around HR4796A is well resolved. We highlight the potential effects of ADI reduction of the observed disk shape and surface brightness distribution,...

  5. Clinical Application of Surrounding Puncture

    Institute of Scientific and Technical Information of China (English)

    GUO Yao-jie; HAN Chou-ping

    2003-01-01

    Surrounding puncture can stop pathogenic qi from spreading, consolidate the connection between local meridians and enrich local qi and blood, which can eventually supplement anti-pathogenic qi and remove pathogenic qi, and consequently remedy diseases. The author of this article summrized and analyzed the clinical application of surrounding puncture for the purpose of studying this technique and improving the therapeutic effect.

  6. Placing Limits on the Mass of the DH Tau b Circumplanetary Disk

    Science.gov (United States)

    Wolff, Schuyler G.; Menard, Francois; Caceres, Claudio; Lefevre, Charlene

    2017-01-01

    We present a circumplanetary disk mass limit for the DH Tau b planetary mass companion. NOEMA observations in the millimeter allow us to place constraints on the disk mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We find a conservative disk mass upper limit of 0.31 $M_{\\oplus}$ for DH Tau b, assuming that the disk temperature is dominated by irradiation from the central star. However, given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. The circumstellar disk of DH Tau A is unresolved in our observations, with an estimated disk mass of $\\sim 40 \\, M_{\\oplus}$.

  7. Disks around CQ Tau and MWC 758: dense PDR or gas dispersal?

    CERN Document Server

    Chapillon, Edwige; Dutrey, Anne; Piétu, Vincent

    2008-01-01

    The overall properties of disks surrounding intermediate PMS stars (HAe) are not yet well constrained by current observations. The disk inclination, which significantly affect SED modeling, is often unknown. We attempted to resolve the disks around CQ Tau and MWC 758, to provide accurate constraints on the disk parameters, in particular the temperature and surface density distribution. We report arcsecond resolution observations of dust and CO line emissions with the IRAM array. The disk properties are derived using a standard disk model. We use the Meudon PDR code to study the chemistry. The two disks share some common properties. The mean CO abundance is low despite disk temperatures above the CO condensation temperature. Furthermore, the CO surface density and dust opacity have different radial dependence. The CQ Tau disk appears warmer, and perhaps less dense than that of MWC 758. Modeling the chemistry, we find that photodissociation of CO is a viable mechanism to explain the low abundance. The photosphe...

  8. Formation of X-ray emitting stationary shocks in magnetized protostellar jets

    CERN Document Server

    Ustamujic, S; Bonito, R; Miceli, M; de Castro, A I Gómez; López-Santiago, J

    2016-01-01

    X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. We aim at investigating the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets, the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks, and the physical properties of the shocked plasma. We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations modelling supersonic jets ramming into a magnetized medium and explored different configurations of the magnetic field. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. We compared the model results with observations, via the emission measure and the X-ray luminosity synthesized from the simulations. Our model explains the formation of X-ray emitting stat...

  9. Protostellar Interferometric Line Survey (PILS): Constraining the formation of complex organic molecules with ALMA

    Science.gov (United States)

    Jorgensen, Jes K.; Coutens, Audrey; Bourke, Tyler L.; Favre, Cecile; Garrod, Robin; Lykke, Julie; Mueller, Holger; Oberg, Karin I.; Schmalzl, Markus; van der Wiel, Matthijs; van Dishoeck, Ewine; Wampfler, Susanne F.

    2015-08-01

    Understanding how, when and where complex organic and potentially prebiotic molecules are formed is a fundamental goal of astrochemistry and an integral part of origins of life studies. Already now ALMA is showing its capabilities for studies of the chemistry of solar-type stars with its high sensitivity for faint lines, high spectral resolution which limits line confusion, and high angular resolution making it possible to study the structure of young protostars on solar-system scales. We here present the first results from a large unbiased survey “Protostellar Interferometric Line Survey (PILS)” targeting one of the astrochemical template sources, the low-mass protostellar binary IRAS 16293-2422. The survey is more than an order of magnitude more sensitive than previous surveys of the source and provide imaging down to 25 AU scales (radius) around each of the two components of the binary. An example of one of the early highlights from the survey is unambiguous detections of the (related) prebiotic species glycolaldehyde, ethylene glycol (two lowest energy conformers), methyl formate and acetic acid. The glycolaldehyde-ethylene glycol abundance ratio is high in comparison to comets and other protostars - but agrees with previous measurements, e.g., in the Galactic Centre clouds possibly reflecting different environments and/or evolutionary histories. Complete mapping of this and other chemical networks in comparison with detailed chemical models and laboratory experiments will reveal the origin of complex organic molecules in a young protostellar system and investigate the link between these protostellar stages and the early Solar System.

  10. Self-Gravitational Force Calculation of Second Order Accuracy for Infinitesimally Thin Gaseous Disks in Polar Coordinates

    CERN Document Server

    Wang, Hsiang-Hsu; Taam, Ronald E

    2015-01-01

    Investigating the evolution of disk galaxies and the dynamics of proto-stellar disks can involve the use of both a hydrodynamical and a Poisson solver. These systems are usually approximated as infinitesimally thin disks using two- dimensional Cartesian or polar coordinates. In Cartesian coordinates, the calcu- lations of the hydrodynamics and self-gravitational forces are relatively straight- forward for attaining second order accuracy. However, in polar coordinates, a second order calculation of self-gravitational forces is required for matching the second order accuracy of hydrodynamical schemes. We present a direct algorithm for calculating self-gravitational forces with second order accuracy without artifi- cial boundary conditions. The Poisson integral in polar coordinates is expressed in a convolution form and the corresponding numerical complexity is nearly lin- ear using a fast Fourier transform. Examples with analytic solutions are used to verify that the truncated error of this algorithm is of seco...

  11. The segregation of starless and protostellar clumps in the Hi-GAL l=224deg region

    CERN Document Server

    Olmi, L; Elia, D; Jones, P

    2016-01-01

    Stars form in dense, dusty structures, which are embedded in larger clumps of molecular clouds often showing a clear filamentary structure on large scales (> 1pc). One of the best-studied regions in the Hi-GAL survey can be observed toward the l=224deg field. Here, a filamentary region has been studied and it has been found that protostellar clumps are mostly located along the main filament, whereas starless clumps are detected off this filament and are instead found on secondary, less prominent filaments. We want to investigate this segregation effect and how it may affect the clumps properties. We mapped the 12CO(1-0) line and its main three isotopologues toward the two most prominent filaments observed toward the l=224deg field using the Mopra radio telescope, in order to set observational constraints on the dynamics of these structures and the associated starless and protostellar clumps. Compared to the starless clumps, the protostellar clumps are more luminous, more turbulent and lie in regions where the...

  12. Principal Component Analysis of computed emission lines from proto-stellar jets

    CERN Document Server

    Cerqueira, A H; De Colle, F; Vasconcelos, M J

    2015-01-01

    A very important issue concerning protostellar jets is the mechanism behind their formation. Obtaining information on the region at the base of a jet can shed light into the subject and some years ago this has been done through a search for a rotational signature at the jet line spectrum. The existence of such signatures, however, remains controversial. In order to contribute to the clarification of this issue, in this paper we show that the Principal Component Analysis (PCA) can potentially help to distinguish between rotation and precession effects in protostellar jet images. We apply the PCA to synthetic spectro-imaging datacubes generated as an output of numerical simulations of protostellar jets. In this way we generate a benchmark to which a PCA diagnostics of real observations can be confronted. Using the computed emission line profiles for [O I]6300A and [S II]6716A, we recover and analyze the effects of rotation and precession in tomograms generated by PCA. We show that different combinations of the ...

  13. A Hot and Massive Accretion Disk around the High-mass Protostar IRAS 20126+4104

    Science.gov (United States)

    Chen, Huei-Ru Vivien; Keto, Eric; Zhang, Qizhou; Sridharan, T. K.; Liu, Sheng-Yuan; Su, Yu-Nung

    2016-06-01

    We present new spectral line observations of the CH3CN molecule in the accretion disk around the massive protostar IRAS 20126+4104 with the Submillimeter Array, which, for the first time, measure the disk density, temperature, and rotational velocity with sufficient resolution (0.″37, equivalent to ˜600 au) to assess the gravitational stability of the disk through the Toomre-Q parameter. Our observations resolve the central 2000 au region that shows steeper velocity gradients with increasing upper state energy, indicating an increase in the rotational velocity of the hotter gas nearer the star. Such spin-up motions are characteristics of an accretion flow in a rotationally supported disk. We compare the observed data with synthetic image cubes produced by three-dimensional radiative transfer models describing a thin flared disk in Keplerian motion enveloped within the centrifugal radius of an angular-momentum-conserving accretion flow. Given a luminosity of 1.3 × 104 L ⊙, the optimized model gives a disk mass of 1.5 M ⊙ and a radius of 858 au rotating about a 12.0 M ⊙ protostar with a disk mass accretion rate of 3.9 × 10-5 M ⊙ yr-1. Our study finds that, in contrast to some theoretical expectations, the disk is hot and stable to fragmentation with Q > 2.8 at all radii which permits a smooth accretion flow. These results put forward the first constraints on gravitational instabilities in massive protostellar disks, which are closely connected to the formation of companion stars and planetary systems by fragmentation.

  14. Visual surround suppression in schizophrenia

    Directory of Open Access Journals (Sweden)

    Marc Samuel Tibber

    2013-02-01

    Full Text Available Compared to unaffected observers patients with schizophrenia show characteristic differences in visual perception, including a reduced susceptibility to the influence of context on judgements of contrast - a manifestation of weaker surround suppression. To examine the generality of this phenomenon we measured the ability of 24 individuals with schizophrenia to judge the luminance, contrast, orientation and size of targets embedded in contextual surrounds that would typically influence the target’s appearance. Individuals with schizophrenia demonstrated weaker surround suppression compared to matched controls for stimuli defined by contrast or size, but not for those defined by luminance or orientation. As perceived luminance is thought to be regulated at the earliest stages of visual processing our findings are consistent with a suppression deficit that is predominantly cortical in origin. In addition, we propose that preserved orientation surround suppression in schizophrenia may reflect the sparing of broadly tuned mechanisms of suppression. We attempt to reconcile these data with findings from previous studies.

  15. Educational Success and Surrounding Culture

    Science.gov (United States)

    Walters, Garrison

    2016-01-01

    The curriculum, instruction, and services we provide in schools, colleges, and universities matter a lot, but if we continue to ignore our students' "surrounding culture," progress toward a more educated nation will continue to be disappointing.

  16. Educational Success and Surrounding Culture

    Science.gov (United States)

    Walters, Garrison

    2016-01-01

    The curriculum, instruction, and services we provide in schools, colleges, and universities matter a lot, but if we continue to ignore our students' "surrounding culture," progress toward a more educated nation will continue to be disappointing.

  17. REMARKS ON JOHN DISKS

    Institute of Scientific and Technical Information of China (English)

    Chu Yuming; Cheng Jinfa; Wang Gendi

    2009-01-01

    Let D R2 be a Jordan domain, D* = -R2 \\ -D, the exterior of D. In this article, the authors obtained the following results: (1) If D is a John disk, then D is an outer linearly locally connected domain; (2) If D* is a John disk, then D is an inner linearly locally connected domain; (3) A homeomorphism f: R2→R2 is a quasiconformal mapping if and only if f(D) is a John disk for any John disk D(∈)R2; and (4) If D is a bounded quasidisk, then D is a John disk, and there exists an unbounded quasidisk which is not a John disk.

  18. Multichannel spatial surround sound system

    Institute of Scientific and Technical Information of China (English)

    RAO Dan; XIE Bosun

    2004-01-01

    Based on the consideration of being compatible with 5.1 channel horizontal surround sound system, a spatial surround sound system is proposed. Theoretical and experimental results show that the system has a wide listening area. It can not only recreate stable image in the front and rear direction, but also eliminate the defect of poor lateral image of 5.1 channel system. The system can be used to reproduce special 3D sound effect and the spaciousness of hall.

  19. Measuring magnetic fields from water masers in the synchrotron protostellar jet in W3(H2O)

    Science.gov (United States)

    Goddi, C.; Surcis, G.; Moscadelli, L.; Imai, H.; Vlemmings, W. H. T.; van Langevelde, H. J.; Sanna, A.

    2017-01-01

    Context. Magnetic fields are invoked to launch, drive, and shape jets in both low- and high-mass protostars, but observational data on the spatial scales required to assess their role in the protostellar mass-loss process is still scarce. Aims: The Turner-Welch (TW) object in the W3(OH) high-mass star-forming complex drives a synchrotron jet, which is quite exceptional for a high-mass protostar, and is associated with a strongly polarized H2O maser source, W3(H2O), making it an optimal target to investigate the role of magnetic fields on the innermost scales of protostellar disk-jet systems. Methods: We report full polarimetric VLBA observations of H2O masers towards W3(H2O). Their linearly polarized emission provides clues on the orientation of the local magnetic field (on the plane of the sky), while the measurement of the Zeeman splitting provides its strength (along the line-of-sight). The linear scales probed by H2O masers are tens to hundreds of AU (at the W3(H2O) distance, 2 kpc), inaccessible to other star-formation tracers. Results: We identified a total of 148 individual maser features and we measured their physical properties. Out of 148, we measured linear polarization in 34 features, with a fractional percentage varying in the range 0.9-42%, making W3(H2O) the highest-polarized H2O maser source observed with VLBI known in the Galaxy. The H2O masers trace a bipolar, biconical outflow at the center of the synchrotron jet. Although on scales of a few thousand AU the magnetic field inferred from the masers is on average orientated along the flow axis, on smaller scales (10s to 100s of AU), we have revealed a misalignment between the magnetic field and the velocity vectors, which arises from the compression of the field component along the shock front. We also detected circularly polarized emission toward ten maser features, with a fractional percentage varying in the range 0.2-1.6%. In the gas shocked by the synchrotron jet, we estimate a total field

  20. Complex organic molecules in protostellar environments in the SKA era

    CERN Document Server

    Codella, C; Fontani, F; Jiménez-Serra, I; Caselli, P; Ceccarelli, C; Palumbo, M E; López-Sepulcre, A; Beltrán, M T; Lefloch, B; Brucato, J R; Viti, S; Testi, L

    2014-01-01

    Molecular complexity builds up at each step of the Sun-like star formation process, starting from simple molecules and ending up in large polyatomic species. Complex organic molecules (COMs; such as methyl formate, HCOOCH$_3$, dymethyl ether, CH$_3$OCH$_3$, formamide, NH$_2$CHO, or glycoaldehyde, HCOCH$_2$OH) are formed in all the components of the star formation recipe (e.g. pre-stellar cores, hot-corinos, circumstellar disks, shocks induced by fast jets), due to ice grain mantle sublimation or sputtering as well as gas-phase reactions. Understanding in great detail the involved processes is likely the only way to predict the ultimate molecular complexity reached in the ISM, as the detection of large molecules is increasingly more difficult with the increase of the number of atoms constituting them. Thanks to the recent spectacular progress of astronomical observations, due to the Herschel (sub-mm and IR), IRAM and SMA (mm and sub-mm), and NRAO (cm) telescopes, an enormous activity is being developed in the ...

  1. Isolated unilateral disk edema

    OpenAIRE

    Varner P

    2011-01-01

    Paul VarnerJohn J Pershing VAMC, Poplar Bluff, MO, USAAbstract: Isolated unilateral disk edema is a familiar clinical presentation with myriad associations. Related, non-consensus terminology is a barrier to understanding a common pathogenesis. Mechanisms for the development of disk edema are reviewed, and a new framework for clinical differentiation of medical associations is presented.Keywords: disk edema, axoplasmic flow, clinical multiplier, optic neuritis, ischemic optic neuropathy, papi...

  2. Isolated unilateral disk edema

    Directory of Open Access Journals (Sweden)

    Varner P

    2011-07-01

    Full Text Available Paul VarnerJohn J Pershing VAMC, Poplar Bluff, MO, USAAbstract: Isolated unilateral disk edema is a familiar clinical presentation with myriad associations. Related, non-consensus terminology is a barrier to understanding a common pathogenesis. Mechanisms for the development of disk edema are reviewed, and a new framework for clinical differentiation of medical associations is presented.Keywords: disk edema, axoplasmic flow, clinical multiplier, optic neuritis, ischemic optic neuropathy, papilledema

  3. A valve disk

    Energy Technology Data Exchange (ETDEWEB)

    Khayrullin, N.A.; Isayev, B.N.; Kruglov, S.A.; Molokanov, Yu.K.; Shchelkunov, V.A.; Shegay, V.R.; Vizhgorodskiy, B.N.

    1982-01-01

    A valve disk is proposed which includes a horizontal bed, on which there are laminar valves arranged in staggered order. To ensure the stable and effective operation of the disk in a broad range of loads by compensating for the direct flow and the partial sectioning of the disk bed, it is equipped with compensating elements installed in openings in the bed and hinged with it. They are made in the form of straight, triangular prisms with ports in the bases. The prisms are installed with the capability of movement relative to the disk bed. The valves are positioned on the upper lateral facets of the compensating elements.

  4. The chemical structure of the Class 0 protostellar envelope NGC 1333 IRAS 4A⋆⋆

    Science.gov (United States)

    Koumpia, E.; Semenov, D. A.; van der Tak, F. F. S.; Boogert, A. C. A.; Caux, E.

    2017-07-01

    Context. It is not well known what drives the chemistry of a protostellar envelope, in particular the role of the stellar mass and the protostellar outflows on the chemical enrichment of such environments. Aims: We study the chemical structure of the Class 0 protostellar envelope NGC 1333 IRAS 4A in order to (i) investigate the influence of the outflows on the chemistry; (ii) constrain the age of our studied object; (iii) compare it with a typical high-mass protostellar envelope. Methods: In our analysis we use JCMT line mapping (360-373 GHz) and HIFI pointed spectra (626.01-721.48 GHz). To study the influence of the outflow on the degree of deuteration, we compare JCMT maps of HCO+ and DCO+ with non-LTE (RADEX) models in a region that spatially covers the outflow activity of IRAS 4A. To study the envelope chemistry, we derive empirical molecular abundance profiles for the observed species using the Monte Carlo radiative transfer code (RATRAN) and adopting a 1D dust density/temperature profile from the literature. We use a combination of constant abundance profiles and abundance profiles that include jumps at two radii (T 100 K or T 30 K) to fit our observations. We compare our best-fit observed abundance profiles with the predictions from the time dependent gas grain chemical code (ALCHEMIC). Results: We detect CO, 13CO, C18O, CS, HCN, HCO+, N2H+, H2CO, CH3OH, H2O, H2S, DCO+, HDCO, D2CO, SO, SO2, SiO, HNC, CN, C2H and OCS. We divide the detected lines in three groups based on their line profiles: a) broad emission (FWHM = 4-11 km s-1), b) narrow emission (FWHMmodel for the outer envelope, with the exceptions of HCN, HNC, CN. These species along with the CO abundance require an enhanced UV field which points towards an outflow cavity. The abundances with respect to H2 are 1 to 2 orders of magnitude lower than those observed in the high mass protostellar envelope (AFGL 2591), while they are found to be similar within factors of a few when they are estimated with

  5. Simulating protostellar evolution and radiative feedback in the cluster environment

    CERN Document Server

    Klassen, Mikhail; Peters, Thomas

    2011-01-01

    Radiative feedback is among the most important consequences of clustered star formation inside molecular clouds. At the onset of star formation, radiation from massive stars heats the surrounding gas, which suppresses the formation of many low-mass stars. When simulating pre-main-sequence stars, their stellar properties must be defined by a prestellar model. Different approaches to prestellar modeling may yield quantitatively different results. In this paper, we compare two existing prestellar models under identical initial conditions to gauge whether the choice of model has any significant effects on the final population of stars. The first model treats stellar radii and luminosities with a ZAMS model, while separately estimating the accretion luminosity by interpolating to published prestellar tracks. The second, more accurate prestellar model self-consistently evolves the radius and luminosity of each star under highly variable accretion conditions. Each is coupled to a raytracing-based radiative feedback ...

  6. Anatomy of the internal bow shocks in the IRAS 04166+2706 protostellar jet

    Science.gov (United States)

    Tafalla, M.; Su, Y.-N.; Shang, H.; Johnstone, D.; Zhang, Q.; Santiago-García, J.; Lee, C.-F.; Hirano, N.; Wang, L.-Y.

    2017-01-01

    Context. Highly collimated jets and wide-angle outflows are two related components of the mass-ejection activity associated with stellar birth. Despite decades of research, the relation between these two components remains poorly understood. Aims: We study the relation between the jet and the outflow in the IRAS 04166+2706 protostar. This Taurus protostar drives a molecular jet that contains multiple emission peaks symmetrically located from the central source. The protostar also drives a wide-angle outflow consisting of two conical shells. Methods: We have used the Atacama Large Millimeter/submillimeter Array (ALMA) interferometer to observe two fields along the IRAS 04166+2706 jet. The fields were centered on a pair of emission peaks that correspond to the same ejection event. The observations were carried out in CO(2-1), SiO(5-4), and SO(JN = 65-54). Results: Both ALMA fields present spatial distributions that are approximately elliptical and have their minor axes aligned with the jet direction. As the velocity increases, the emission in each field moves gradually across the elliptical region. This systematic pattern indicates that the emitting gas in each field lies in a disk-like structure that is perpendicular to the jet axis and whose gas is expanding away from the jet. A small degree of curvature in the first-moment maps indicates that the disks are slightly curved in the manner expected for bow shocks moving away from the IRAS source. A simple geometrical model confirms that this scenario fits the main emission features. Conclusions: The emission peaks in the IRAS 04166+2706 jet likely represent internal bow shocks where material is being ejected laterally away from the jet axis. While the linear momentum of the ejected gas is dominated by the component in the jet direction, the sideways component is not negligible, and can potentially affect the distribution of gas in the surrounding outflow and core.

  7. Debris disks as seen by Herschel: statistics and modeling

    Science.gov (United States)

    Lebreton, J.; Marshall, J. P.; Augereau, J. C.; Eiroa, C.

    2011-10-01

    As leftovers of planet formation, debris disks represent an essential component of planetary systems. We first introduce the latest statistics obtained by the DUNES consortium, who are taking a census of extrasolar analogues to the Edgeworth-Kuiper Belt using the Herschel Space Observatory. Then we present a detailed study of the much younger debris disk surrounding the F5.5 star HD 181327. We derive strong constraints on the properties of its dust and we discuss its possible gaseous counterpart.

  8. Low-Mass Star Formation: From Molecular Cloud Cores to Protostars and Protoplanetary Disks

    Science.gov (United States)

    Inutsuka, S.-I.; Machida, M.; Matsumoto, T.; Tsukamoto, Y.; Iwasaki, K.

    2015-05-01

    This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (˜103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.

  9. On the Ionisation Fraction in Protoplanetary Disks I: Comparing Different Reaction Networks

    CERN Document Server

    Ilgner, M; Ilgner, Martin; Richard P. Nelson

    2005-01-01

    We calculate the ionisation fraction in protostellar disk models using a number of different chemical reaction networks, including gas-phase and gas-grain reaction schemes. The disk models we consider are conventional alpha-disks, which include viscous heating and radiative cooling. The primary source of ionisation is assumed to be X-ray irradiation from the central star. We consider a number of gas-phase chemical networks. In general we find that the simple models predict higher fractional ionisation levels and more extensive active zones than the more complex models. When heavy metal atoms are included the simple models predict that the disk is magnetically active throughout. The complex models predict that extensive regions of the disk remain magnetically uncoupled even with a fractional abundance of magnesium of 10(-8). The addition of submicron sized grains with a concentration of 10(-12) causes the size of the dead zone to increase dramatically for all kinetic models considered. We find that the simple ...

  10. From Cores to Envelopes to Disks: A Multi-scale View of Magnetized Star Formation

    Science.gov (United States)

    Hull, Charles L. H.

    2014-12-01

    protostellar envelope may be a turning point: at larger scales B-fields may still retain the memory of the global B-field drawn in from the ambient medium; but at smaller scales the B-fields may be affected by the dynamics of both envelope and disk rotation. This sets the stage for ALMA (the Atacama Large Millimeter/submillimeter Array), which will soon reveal the morphology of B-fields in circumstellar disks themselves.

  11. Protoplanetary Disks, Jets, and the Birth of the Stars

    Science.gov (United States)

    Anglada, G.

    2017-03-01

    Young stars are surrounded by rotating disks of gas and dust. These disks play an essential role in regulating the mass accretion onto the star and are the precursors of exoplanetary systems. Accretion disks also play an important role in driving the bipolar collimated ejections (jets) that remove the excess of angular momentum and allow the star to reach its final mass. Jets are partially ionized and their continuum free-free emission at centimeter wavelengths is a powerful tool to study at small scale (10-100 au) the region where they originate. Observations of the dust thermal emission at centimeter wavelengths are also well suited to study the distribution of dust grains that have evolved up to centimeter sizes and trace the signatures of planet formation in protoplanetary disks. I will present some recent results from VLA and ALMA observations of disks and jets in young stellar objects, and I will discuss future prospects with the SKA in this field.

  12. Deceleration Effect of Magnetic Field on Black Hole Accretion Disks

    Institute of Scientific and Technical Information of China (English)

    WANG Ding-Xiong

    2000-01-01

    The deceleration effect of magnetic field near the horizon of a spinning black hole (BH) of accretion disk is investigated in the Blandford-Znajek (BZ) process. It is shown that rates of change with respect to time for both the angular velocities of BH horizon and accreting particles at the inner edge of an accretion disk are reduced in the BZ process, behaving with non-monotonous evolution characteristics. This result implies that the magnetic field near the BH horizon has & deceleration effect not only on the spinning BH but also on the surrounding accretion disk.

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

    Science.gov (United States)

    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.

  14. Generation of dynamo magnetic fields in protoplanetary and other astrophysical accretion disks

    Science.gov (United States)

    Stepinski, T. F.; Levy, E. H.

    1988-01-01

    A computational method for treating the generation of dynamo magnetic fields in astrophysical disks is presented. The numerical difficulty of handling the boundary condition at infinity in the cylindrical disk geometry is overcome by embedding the disk in a spherical computational space and matching the solutions to analytically tractable spherical functions in the surrounding space. The lowest lying dynamo normal modes for a 'thick' astrophysical disk are calculated. The generated modes found are all oscillatory and spatially localized. Tha potential implications of the results for the properties of dynamo magnetic fields in real astrophysical disks are discussed.

  15. Generation of dynamo magnetic fields in protoplanetary and other astrophysical accretion disks

    Energy Technology Data Exchange (ETDEWEB)

    Stepinski, T.F.; Levy, E.H.

    1988-08-01

    A computational method for treating the generation of dynamo magnetic fields in astrophysical disks is presented. The numerical difficulty of handling the boundary condition at infinity in the cylindrical disk geometry is overcome by embedding the disk in a spherical computational space and matching the solutions to analytically tractable spherical functions in the surrounding space. The lowest lying dynamo normal modes for a thick astrophysical disk are calculated. The generated modes found are all oscillatory and spatially localized. Tha potential implications of the results for the properties of dynamo magnetic fields in real astrophysical disks are discussed. 30 references.

  16. Planetesimals in Debris Disks

    CERN Document Server

    Youdin, Andrew N

    2015-01-01

    Planetesimals form in gas-rich protoplanetary disks around young stars. However, protoplanetary disks fade in about 10 Myr. The planetesimals (and also many of the planets) left behind are too dim to study directly. Fortunately, collisions between planetesimals produce dusty debris disks. These debris disks trace the processes of terrestrial planet formation for 100 Myr and of exoplanetary system evolution out to 10 Gyr. This chapter begins with a summary of planetesimal formation as a prelude to the epoch of planetesimal destruction. Our review of debris disks covers the key issues, including dust production and dynamics, needed to understand the observations. Our discussion of extrasolar debris keeps an eye on similarities to and differences from Solar System dust.

  17. CID: Chemistry In Disks VII. First detection of HC3N in protoplanetary disks

    CERN Document Server

    Chapillon, E; Guilloteau, S; Pietu, V; Wakelam, V; Hersant, F; Gueth, F; Henning, T; Launhardt, R; Schreyer, K; Semenov, D

    2012-01-01

    Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30m telescope by using the new broad band correlator (FTS) to search for so far undetected molecules in the protoplanetary disks surrounding the TTauri stars DM Tau, GO Tau, LkCa 15 and the Herbig Ae star MWC 480. We report the first detection of HC3N at 5 sigma in the GO Tau and MWC 480 disks with the IRAM 30-m, and in the LkCa 15 disk (5 sigma), using the IRAM array, with derived column densities of the order of 10^{12}cm^{-2}. We also obtain stringent upper limits on CCS (N < 1.5 x 10^{12} cm^{-3}). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen and sulfur-bearing molecule observations. The observed column densiti...

  18. SMA Continuum Survey of Circumstellar Disks in Serpens

    Science.gov (United States)

    Law, Charles; Ricci, Luca; Andrews, Sean M.; Wilner, David J.; Qi, Chunhua

    2017-06-01

    The lifetime of disks surrounding pre-main-sequence stars is closely linked to planet formation and provides information on disk dispersal mechanisms and dissipation timescales. The potential for these optically thick, gas-rich disks to form planets is critically dependent on how much dust is available to be converted into terrestrial planets and rocky cores of giant planets. For this reason, an understanding of how dust mass varies with key properties such as stellar mass, age, and environment is critical for understanding planet formation. Millimeter wavelength observations, in which the dust emission is optically thin, are required to study the colder dust residing in the disk’s outer regions and to measure disk dust masses. Hence, we have obtained SMA 1.3 mm continuum observations of 62 Class II sources with suspected circumstellar disks in the Serpens star-forming region (SFR). Relative to the well-studied Taurus SFR, Serpens allows us to probe the distribution of dust masses for disks in a much denser and more clustered environment. Only 13 disks were detected in the continuum with the SMA. We calculate the total dust masses of these disks and compare their masses to those of disks in Taurus, Lupus, and Upper Scorpius. We do not find evidence of diminished dust masses in Serpens disks relative to those in Taurus despite the fact that disks in denser clusters may be expected to contain less dust mass due to stronger and more frequent tidal interactions that can disrupt the outer regions of disks. However, considering the low detection fraction, we likely detected only bright continuum sources and a more sensitive survey of Serpens would help clarify these results.

  19. Evolution of binary seeds in collapsing protostellar gas clouds

    CERN Document Server

    Satsuka, Tatsuya; Tanaka, Suguru; Nagamine, Kentaro

    2016-01-01

    We perform three dimensional smoothed particle hydrodynamics (SPH) simulations of gas accretion onto the seeds of binary stars to investigate their short-term evolution. Our simulation setup is more realistic compared to the previous works by taking into account of dynamically evolving envelope with non-uniform distribution of gas density and angular momentum of accreting flow. Our initial condition includes a seed binary and a surrounding gas envelope, modelling the phase of core collapse of gas cloud when the fragmentation has already occurred. We assume that the seed binary has no eccentricity and no growth by gas accretion. The envelope is assumed to be an isothermal gas with no self-gravity. We run multiple simulations with different values of initial mass ratio $q_0$ (the ratio of secondary over primary mass) and gas temperature, and find a critical value of $q_{\\rm c} = 0.25$ which distinguishes the later evolution of mass ratio $q$ as a function of time. If $q_0 \\ga q_{\\rm c}$, the secondary seed grow...

  20. Evolution of binary seeds in collapsing protostellar gas clouds

    Science.gov (United States)

    Satsuka, Tatsuya; Tsuribe, Toru; Tanaka, Suguru; Nagamine, Kentaro

    2017-02-01

    We perform 3D smoothed particle hydrodynamics (SPH) simulations of gas accretion on to the seeds of binary stars to investigate their short-term evolution. Taking into account the dynamically evolving envelope with non-uniform distribution of gas density and angular momentum of accreting flow, our initial condition includes a seed binary and a surrounding gas envelope, modelling the phase of core collapse of gas cloud when the fragmentation has already occurred. We run multiple simulations with different values of initial mass ratio q0 (the ratio of secondary over primary mass) and gas temperature. For our simulation setup, we find a critical value of qc = 0.25 which distinguishes the later evolution of mass ratio q as a function of time. If q0 ≳ qc, the secondary seed grows faster and q increases monotonically towards unity. If q0 ≲ qc, on the other hand, the primary seed grows faster and q is lower than q0 at the end of the simulation. Based on our numerical results, we analytically calculate the long-term evolution of the seed binary including the growth of binary by gas accretion. We find that the seed binary with q0 ≳ qc evolves towards an equal-mass binary star and that with q0 ≲ qc evolves to a binary with an extreme value of q. Binary separation is a monotonically increasing function of time for any q0, suggesting that the binary growth by accretion does not lead to the formation of close binaries.

  1. Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores

    Energy Technology Data Exchange (ETDEWEB)

    Taquet, Vianney; Charnley, Steven B. [Astrochemistry Laboratory and The Goddard Center for Astrobiology, Mailstop 691, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20770 (United States); Sipilä, Olli [Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki (Finland)

    2014-08-10

    Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H{sub 2} and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

  2. The segregation of starless and protostellar clumps in the Hi-GAL ℓ = 224° region

    Science.gov (United States)

    Olmi, L.; Cunningham, M.; Elia, D.; Jones, P.

    2016-10-01

    Context. Stars form in dense, dusty structures, which are embedded in larger clumps of molecular clouds often showing a clear filamentary structure on large scales (≳1 pc). The origin (e.g., turbulence or gravitational instabilities) and evolution of these filaments, as well as their relation to clump and core formation, are not yet fully understood. A large sample of both starless and protostellar clumps can now be found in the Herschel Infrared GALactic Plane Survey (Hi-GAL) key project, which also provides striking images of the filamentary structure of the parent molecular clouds. Recent results indicate that populations of clumps on and off filaments may differ. Aims: One of the best-studied regions in the Hi-GAL survey can be observed toward the ℓ = 224° field. Here, a filamentary region has been studied and it has been found that protostellar clumps are mostly located along the main filament, whereas starless clumps are detected off this filament and are instead found on secondary, less prominent filaments. We want to investigate this segregation effect and how it may affect the clumps properties. Methods: We mapped the 12CO (1-0) line and its main three isotopologues toward the two most prominent filaments observed toward the ℓ = 224° field using the Mopra radio telescope, in order to set observational constraints on the dynamics of these structures and the associated starless and protostellar clumps. Results: Compared to the starless clumps, the protostellar clumps are more luminous, more turbulent and lie in regions where the filamentary ambient gas shows larger linewidths. We see evidence of gas flowing along the main filament, but we do not find any signs of accretion flow from the filament onto the Hi-GAL clumps. We analyze the radial column density profile of the filaments and their gravitational stability. Conclusions: The more massive and highly fragmented main filament appears to be thermally supercritical and gravitationally bound

  3. Hydrodynamic Stability and Magnetic Reconnection in Disks and Stars

    Science.gov (United States)

    Goodman, Jeremy; Kulsrud, Russell

    1999-01-01

    edges of disks in close binaries [2], and it may be important in disks of very low ionization such as protostellar disks, or even cataclysmic-variable disks in quiescence where the MHD mechanism may be ineffective [5]. All analyses up to 1996 were done in a local approximation where the orbital frequency, shear rate, and tidal field were treated as constants. The locally computed growth rate turns out to depend strongly on radius, and it was unclear how to average these local rates to obtain the correct global rate. This is a critical issue for accretion disks in close binaries, because the local growth rate is comparable to the orbital frequency towards the outer edge of the disk but decreases rapidly inwards. Paper #1 examined this issue in a simplified global model where the destabilizing terms vary with position. We found that the global growth rate is essentially equal to the maximum local rate, provided that the latter is smoothed over a radial range equal to the distance that the destabilized wave propagates at its group speed in one growth time. Thus, in an accretion disk, waves would grow rapidly in the outer parts but would propagate both inwards and outwards at a maximum group speed of order the disk thickness divided by the orbital period.

  4. Visual Surround Suppression in Schizophrenia

    Science.gov (United States)

    Tibber, Marc S.; Anderson, Elaine J.; Bobin, Tracy; Antonova, Elena; Seabright, Alice; Wright, Bernice; Carlin, Patricia; Shergill, Sukhwinder S.; Dakin, Steven C.

    2013-01-01

    Compared to unaffected observers patients with schizophrenia (SZ) show characteristic differences in visual perception, including a reduced susceptibility to the influence of context on judgments of contrast – a manifestation of weaker surround suppression (SS). To examine the generality of this phenomenon we measured the ability of 24 individuals with SZ to judge the luminance, contrast, orientation, and size of targets embedded in contextual surrounds that would typically influence the target’s appearance. Individuals with SZ demonstrated weaker SS compared to matched controls for stimuli defined by contrast or size, but not for those defined by luminance or orientation. As perceived luminance is thought to be regulated at the earliest stages of visual processing our findings are consistent with a suppression deficit that is predominantly cortical in origin. In addition, we propose that preserved orientation SS in SZ may reflect the sparing of broadly tuned mechanisms of suppression. We attempt to reconcile these data with findings from previous studies. PMID:23450069

  5. Disk Defect Data

    Data.gov (United States)

    National Aeronautics and Space Administration — How Data Was Acquired: The data presented is from a physical simulator that simulated engine disks. Sample Rates and Parameter Description: All parameters are...

  6. THE STEWARTSON LAYER OF A ROTATING-DISK OF FINITE RADIUS

    NARCIS (Netherlands)

    1992-01-01

    It is shown that if a disk of finite radius and the surrounding medium rotate coaxially with slightly different angular velocities, an axial layer in the form of a cylindrical shell exists at the edge of the disk. This shell of thickness O(E1/3) has length O(E-1) in axial direction, where E is the E

  7. Anatomy of a flaring proto-planetary disk around a young intermediate-mass star

    NARCIS (Netherlands)

    Lagage, Pierre-Olivier; Doucet, Coralie; Pantin, Eric; Habart, Emilie; Duchene, Gaspard; Menard, Francois; Pinte, Christophe; Charnoz, Sebastien; Pel, Jan-Willem

    2006-01-01

    Although planets are being discovered around stars more massive than the Sun, information about the proto-planetary disks where such planets have built up is sparse. We have imaged mid-infrared emission from polycyclic aromatic hydrocarbons at the surface of the disk surrounding the young

  8. H2O in Protoplanetary Disks: the Snow Line and the Planets' Nest

    NARCIS (Netherlands)

    Antonellini, Stefano; Kamp, Inga; Woitke, Peter; Thi, Wing-Fai

    2013-01-01

    Protoplanetary disks represent the stage between the pre-stellar collapse of the molecolar cloud and the formation of a planetary system surrounding a main sequence star. The goal of the DIANA FP7 project (P.I.: P.Woitke) is to investigate the disks in multiwavelengths, considering available data of

  9. H2O in Protoplanetary Disks : The Snow Line and the Planets' Nest

    NARCIS (Netherlands)

    Antonellini, Stefano; Kamp, Inga; Woitke, Peter; Thi, Wing-Fai

    2013-01-01

    Protoplanetary disks represent the stage between the pre-stellar collapse of the molecolar cloud and the formation of a planetary system surrounding a main sequence star. The goal of the DIANA FP7 project (P.I.: P.Woitke) is to investigate the disks in multiwavelengths, considering available data of

  10. Verbatim Floppy Disk

    CERN Multimedia

    1976-01-01

    Introduced under the name "Verbatim", Latin for "literally", these disks that sized more than 5¼ inches have become almost universal on dedicated word processing systems and personal computers. This format was replaced more slowly by the 3½-inch format, introduced for the first time in 1982. Compared to today, these large format disks stored very little data. In reality, they could only contain a few pages of text.

  11. Direct Detection of a (Proto)Binary-Disk System in IRAS 20126+4104

    CERN Document Server

    Sridharan, T K; Fuller, G A

    2005-01-01

    We report the direct detection of a binary/disk system towards the high-mass (proto)stellar object IRAS20126+4104 at infrared wavengths. The presence of a multiple system had been indicated by the precession of the outflow and the double jet system detected earlier at cm-wavelengths. Our new K, L' & M' band infrared images obtained with the UKIRT under exceptional seeing conditions on Mauna Kea are able to resolve the central source for the first time, and we identify two objects separated by ~ 0.5'' (850 AU). The K and L' images also uncover features characteristic of a nearly edge-on disk, similar to many low mass protostars with disks: two emission regions oriented along an outflow axis and separated by a dark lane. The peaks of the L' & M' band and mm-wavelength emission are on the dark lane, presumably locating the primary young star. The thickness of the disk is measured to be ~ 850 AU for radii < 1000 AU. Approximate limits on the NIR magnitudes of the two young stars indicate a high-mass sy...

  12. 2TB hard disk drive

    CERN Multimedia

    This particular object was used up until 2012 in the Data Centre. It slots into one of the Disk Server trays. Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes (link is external). They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product). They later became known as "hard disks" to distinguish them from "floppy disks (link is external)." Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

  13. MHD of accretion-disk flows

    Science.gov (United States)

    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.

  14. Asymmetric transition disks: Vorticity or eccentricity?

    CERN Document Server

    Zsom, A; Ghanbari, J

    2013-01-01

    Context. Transition disks typically appear in resolved millimeter observations as giant dust rings surrounding their young host stars. More accurate observations with ALMA have shown several of these rings to be in fact asymmetric: they have lopsided shapes. It has been speculated that these rings act as dust traps, which would make them important laboratories for studying planet formation. It has been shown that an elongated giant vortex produced in a disk with a strong viscosity jump strikingly resembles the observed asymmetric rings. Aims. We aim to study a similar behavior for a disk in which a giant planet is embedded. However, a giant planet can induce two kinds of asymmetries: (1) a giant vortex, and (2) an eccentric disk. We studied under which conditions each of these can appear, and how one can observationally distinguish between them. This is important because only a vortex can trap particles both radially and azimuthally, while the eccentric ring can only trap particles in radial direction. Method...

  15. Protostellar collapse of magneto-turbulent cloud cores: shape during collapse and outflow formation

    CERN Document Server

    Matsumoto, Tomoaki

    2010-01-01

    We investigate protostellar collapse of molecular cloud cores by numerical simulations, taking into account turbulence and magnetic fields. By using the adaptive mesh refinement technique, the collapse is followed over a wide dynamic range from the scale of a turbulent cloud core to that of the first core. The cloud core is lumpy in the low density region owing to the turbulence, while it has a smooth density distribution in the dense region produced by the collapse. The shape of the dense region depends mainly on the mass of the cloud core; a massive cloud core tends to be prolate while a less massive cloud core tends to be oblate. In both cases, anisotropy of the dense region increases during the isothermal collapse. The minor axis of the dense region is always oriented parallel to the local magnetic field. All the models eventually yield spherical first cores supported mainly by the thermal pressure. Most of turbulent cloud cores exhibit protostellar outflows around the first cores. These outflows are clas...

  16. Searching for Class I multiple protostellar systems in the MIR in OMC-2 and OMC-3

    Science.gov (United States)

    Weber, Cornelia; Teixeira, Paula; Petr-Gotzens, Monika; Takahashi, Satoko

    2013-07-01

    The Orion molecular cloud is a rich and well known star forming region where all the different evolutionary stages of the star formation process can be found. It is thus an ideal region to study physical characteristics of protostellar binaries (protobinaries). Observational studies of protobinaries are important tools to get better constraints on star formation models. Yet there are few such studies. We present preliminary results of a protobinary survey in the Orion Molecular Cloud-2 (OMC-2) and OMC-3. Our data consists of mid-infrared images obtained using the Europen Southern Observatory VLT/VISIR, and our sample has 24 Class I protostars, previously identified via Spitzer 24 micron observations. We present at first the frequencies of protostellar multiple systems in these molecular clouds. The survey will show how many protobinary or multiple systems form in these clouds, and if these frequencies are comparable to that of other similarly observed star forming regions. Another aim of the survey is to measure the separations of the protostars in these binary or multiple systems. We also derive the mass ratios of the protostars. Comparison of these results to other similar surveys might reveal some major initial conditions necessary for the formation of binary systems. The observed parameters will help constrain star formation models, and they will shed some light on how the stellar initial mass function may be assembled from a molecular cloud core mass function.

  17. X-ray emission from protostellar jet HH 154: the first evidence of a diamond shock?

    CERN Document Server

    Bonito, R; Miceli, M; Peres, G; Micela, G; Favata, F

    2011-01-01

    X-ray emission from about ten protostellar jets has been discovered and it appears as a feature common to the most energetic jets. Although X-ray emission seems to originate from shocks internal to jets, the mechanism forming these shocks remains controversial. One of the best studied X-ray jet is HH 154 that has been observed by Chandra over a time base of about 10 years. We analyze the Chandra observations of HH 154 by investigating the evolution of its X-ray source. We show that the X-ray emission consists of a bright stationary component and a faint elongated component. We interpret the observations by developing a hydrodynamic model describing a protostellar jet originating from a nozzle and compare the X-ray emission synthesized from the model with the X-ray observations. The model takes into account the thermal conduction and radiative losses and shows that the jet/nozzle leads to the formation of a diamond shock at the nozzle exit. The shock is stationary over the period covered by our simulations and...

  18. Kinematics of the Envelope and Two Bipolar Jets in the Class 0 Protostellar System L1157

    CERN Document Server

    Kwon, Woojin; Stephens, Ian W; Looney, Leslie W

    2015-01-01

    A massive envelope and a strong bipolar outflow are the two main structures characterizing the youngest protostellar systems. In order to understand the physical properties of a bipolar outflow and the relationship with those of the envelope, we obtained a mosaic map covering the whole bipolar outflow of the youngest protostellar system L1157 with about $5"$ angular resolution in CO J=2-1 using the Combined Array for Research in Millimeter-wave Astronomy. By utilizing these observations of the whole bipolar outflow, we estimate its physical properties and show that they are consistent with multiple jets. We also constrain a preferred precession direction. In addition, we observed the central envelope structure with $2"$ resolution in the $\\lambda=1.3$ and 3 mm continua and various molecular lines: C$^{17}$O, C$^{18}$O, $^{13}$CO, CS, CN, N$_2$H$^+$, CH$_3$OH, H$_2$O, SO, and SO$_2$. All the CO isotopes and CS, CN, and N$_2$H$^+$ have been detected and imaged. We marginally detected the features that can be in...

  19. Revealing H2D+ depletion and compact structure in starless and protostellar cores with ALMA

    CERN Document Server

    Friesen, R K; Bourke, T L; Caselli, P; Jørgensen, J K; Pineda, J E; Wong, M

    2014-01-01

    We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the submillimeter dust continuum and H2D+ 1_{10}-1_{11} emission toward two evolved, potentially protostellar cores within the Ophiuchus molecular cloud, Oph A SM1 and SM1N. The data reveal small-scale condensations within both cores, with mass upper limits of M <~ 0.02M_Sun (~ 20 M_Jup). The SM1 condensation is consistent with a nearly-symmetric Gaussian source with a width of only 37 AU. The SM1N condensation is elongated, and extends 500 AU along its major axis. No evidence for substructure is seen in either source. A Jeans analysis indicates these sources are unlikely to fragment, suggesting that both will form single stars. H2D+ is only detected toward SM1N, offset from the continuum peak by ~150-200 AU. This offset may be due to either heating from an undetected, young, low luminosity protostellar source or first hydrostatic core, or HD (and consequently H2D+) depletion in the cold centre of the condensation. We propose th...

  20. Millimeter-sized grains in the protostellar envelopes: Where do they come from?

    Science.gov (United States)

    Wong, Yi Hang Valerie; Hirashita, Hiroyuki; Li, Zhi-Yun

    2016-08-01

    Grain growth during star formation affects the physical and chemical processes in the evolution of star-forming clouds. We investigate the origin of the millimeter (mm)-sized grains recently observed in Class I protostellar envelopes. We use the coagulation model developed in our previous paper and find that a hydrogen number density of as high as 1010 cm-3, instead of the typical density 105 cm-3, is necessary for the formation of mm-sized grains. Thus, we test a hypothesis that such large grains are transported to the envelope from the inner, denser parts, finding that gas drag by outflow efficiently "launches" the large grains as long as the central object has not grown to ≳0.1 M⊙. By investigating the shattering effect on the mm-sized grains, we ensure that the large grains are not significantly fragmented after being injected in the envelope. We conclude that the mm-sized grains observed in the protostellar envelopes are not formed in the envelopes but formed in the inner parts of the star-forming regions and transported to the envelopes before a significant mass growth of the central object, and that they survive in the envelopes.

  1. Millimeter-sized grains in the protostellar envelopes: where do they come from?

    CERN Document Server

    Wong, Yi Hang Valerie; Li, Zhi-Yun

    2016-01-01

    Grain growth during star formation affects the physical and chemical processes in the evolution of star-forming clouds. We investigate the origin of the millimeter (mm)-sized grains recently observed in Class I protostellar envelopes. We use the coagulation model developed in our previous paper and find that a hydrogen number density of as high as $10^{10}~{\\rm cm^{-3}}$, instead of the typical density $10^5~{\\rm cm^{-3}}$, is necessary for the formation of mm-sized grains. Thus, we test a hypothesis that such large grains are transported to the envelope from the inner, denser parts, finding that gas drag by outflow efficiently "launches" the large grains as long as the central object has not grown to $\\gtrsim 0.1$ M$_{\\odot}$. By investigating the shattering effect on the mm-sized grains, we ensure that the large grains are not significantly fragmented after being injected in the envelope. We conclude that the mm-sized grains observed in the protostellar envelopes are not formed in the envelopes but formed i...

  2. Chemistry in Disks. II. -- Poor molecular content of the AB Aur disk

    CERN Document Server

    Schreyer, Katharina; Semenov, Dmitry; Bacmann, Aurore; Chapillon, Edwige; Dutrey, Anne; Gueth, Frederic; Henning, Thomas; Hersant, Frank; Launhardt, Ralf; Pety, Jerome; Pietu, Vincent

    2008-01-01

    We study the molecular content and chemistry of a circumstellar disk surrounding the Herbig Ae star AB Aur at (sub-)millimeter wavelengths. Our aim is to reconstruct the chemical history and composition of the AB Aur disk and to compare it with disks around low-mass, cooler T Tauri stars. We observe the AB Aur disk with the IRAM Plateau de Bure Interferometer in the C- and D- configurations in rotational lines of CS, HCN, C2H, CH3OH, HCO+, and CO isotopes. Using an iterative minimization technique, observed columns densities and abundances are derived. These values are further compared with results of an advanced chemical model that is based on a steady-state flared disk structure with a vertical temperature gradient, and gas-grain chemical network with surface reactions. We firmly detect HCO+ in the 1--0 transition, tentatively detect HCN, and do not detect CS, C2H, and CH3OH. The observed HCO+ and 13CO column densities as well as the upper limits to the column densities of HCN, CS, C2H, and CH3OH are in goo...

  3. Molecular content of the circumstellar disk in AB Aur: First detection of SO in a circumstellar disk

    CERN Document Server

    Fuente, A; Agundez, M; Berne, O; Goicoechea, J R; Alonso-Albi, T; Marcelino, N

    2010-01-01

    Very few molecular species have been detected in circumstellar disks surrounding young stellar objects. We are carrying out an observational study of the chemistry of circumstellar disks surrounding T Tauri and Herbig Ae stars. First results of this study are presented in this note. We used the EMIR receivers recently installed at the IRAM 30m telescope to carry a sensitive search for molecular lines in the disks surrounding AB Aur, DM Tau, and LkCa 15. We detected lines of the molecules HCO+, CN, H2CO, SO, CS, and HCN toward AB Aur. In addition, we tentatively detected DCO+ and H2S lines. The line profiles suggest that the CN, HCN, H2CO, CS and SO lines arise in the disk. This makes it the first detection of SO in a circumstellar disk. We have unsuccessfully searched for SO toward DM Tau and LkCa 15, and for c-C3H2 toward AB Aur, DM Tau, and LkCa 15. Our upper limits show that contrary to all the molecular species observed so far, SO is not as abundant in DM Tau as it is in AB Aur. Our results demonstrate th...

  4. Circumstellar disks of the most vigorously accreting young stars.

    Science.gov (United States)

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer L; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-02-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood.

  5. Spectral Energy Distributions of T Tauri Stars With Passive Circumstellar Disks

    CERN Document Server

    Chiang, E I

    1997-01-01

    We derive hydrostatic, radiative equilibrium models for passive disks surrounding T Tauri stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer re-emits directly to space about half the stellar energy it absorbs. The other half is emitted inward and regulates the interior temperature of the disk. The heated disk flares. As a consequence, it absorbs more stellar radiation, especially at large radii, than a flat disk would. The portion of the spectral energy distribution contributed by the disk is fairly flat throughout the thermal infrared. At fixed frequency, the contribution from the surface layer exceeds that from the interior by about a factor 3 and is emitted at more than an order of magnitude greater radius. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on.

  6. Depletion of chlorine into HCl ice in a protostellar core: The CHESS spectral survey of OMC-2 FIR 4

    NARCIS (Netherlands)

    Kama, M.; Caux, E.; López-Sepulcre, A.; Wakelam, V.; Dominik, C.; Ceccarelli, C.; Lanza, M.; Lique, F.; Ochsendorf, B.B.; Lis, D.C.; Caballero, R.N.; Tielens, A.G.G.M.

    2015-01-01

    Context. The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances <10-5 has not

  7. Reducing position error signal (PES) due to disk vibration using an air shroud

    Science.gov (United States)

    He, Zhimin; Du, Chunling; Mou, Jianqiang; Ong, Eng Hong

    2008-04-01

    The advances in magnetic recording technology demand higher magnetic head positioning accuracy and faster disk rotation speed. However, the higher rotational speed of disk generates the greater flow-induced vibration known as disk flutter, which causes the increase of the track misregistration (TMR). To overcome the issue, an air shroud is presented to reduce disk vibration and position error signal (PES) for magnetic recording. Computational fluid mechanics simulations are performed to study the flow pattern surrounding a disk with an air shroud for different openings. The air-bearing stiffness and damping effects of the disk spindle assembly with an air shroud are evaluated. Based on the computational fluid dynamics (CFD) simulation, the air shroud is prototyped and the disk vibrations with and without the air shroud at different disk rotation speeds are experimentally investigated using a laser Doppler vibrometer (LDV). Significant disk vibration reductions are attained while a shroud is installed onto a disk at certain disk rotation speeds. PESs are also measured for the cases with and without an air shroud during servo implementation. Reductions of PESs are observed when an air shroud is installed at some disk rotation speeds.

  8. Faint disks around classical T Tauri stars: small but dense enough to form planets?

    CERN Document Server

    Piétu, V; di Folco, E; Dutrey, A; Boehler, Y

    2014-01-01

    (abridged) Most Class II sources (of nearby star forming regions) are surrounded by disks with weak millimeter continuum emission. These "faint" disks may hold clues to the disk dissipation mechanism. We attempt to determine the characteristics of such faint disks around classical T Tauri stars, and to explore the link between disk faintness and the proposed disk dispersal mechanisms (accretion, viscous spreading, photo-evaporation, planetary system formation). We performed high-angular resolution (0.3") imaging of a small sample of disks (9 sources) with low 1.3mm continuum flux (mostly <30 mJy) with the IRAM Plateau de Bure interferometer and simultaneously searched for 13CO (or CO) J=2-1 line emission. Using a simple parametric disk model, we determine characteristic sizes of the disks, in dust and gas, and we constrain surface densities in the central 50 AU. All disks are much smaller than the bright disks imaged so far, both in continuum and 13CO lines (5 detections). In continuum, half of the disks a...

  9. Generation of dynamo magnetic fields in thin Keplerian disks

    Science.gov (United States)

    Stepinski, T. F.; Levy, E. H.

    1990-01-01

    The combined action of nonuniform rotation and helical convection in protoplanetary disks, in the Galaxy, or in accretion disks surrounding black holes and other compact objects, enables an alpha-omega dynamo to generate a large-scale magnetic field. In this paper, the properties of such magnetic fields are investigated using a two-dimensional, partially numerical method. The structures of the lowest-order steady state and oscillatory modes are calculated for two kinds of external boundary conditions. A quadruple, steady state, highly localized mode is the most easily excited for low values of the dynamo number. The results indicate that, except under special conditions, disk dynamo modes tend to consist of relatively localized rings structures. For large values of the dynamo number, the magnetic field consists of a number of quasi-independent, spatially localized modes generated in various concentric rings filling the disk inward of a dynamo generation 'front'.

  10. Generation of dynamo magnetic fields in thin Keplerian disks

    Energy Technology Data Exchange (ETDEWEB)

    Stepinski, T.F.; Levy, E.H. (Arizona Univ., Tucson (USA))

    1990-10-01

    The combined action of nonuniform rotation and helical convection in protoplanetary disks, in the Galaxy, or in accretion disks surrounding black holes and other compact objects, enables an alpha-omega dynamo to generate a large-scale magnetic field. In this paper, the properties of such magnetic fields are investigated using a two-dimensional, partially numerical method. The structures of the lowest-order steady state and oscillatory modes are calculated for two kinds of external boundary conditions. A quadruple, steady state, highly localized mode is the most easily excited for low values of the dynamo number. The results indicate that, except under special conditions, disk dynamo modes tend to consist of relatively localized rings structures. For large values of the dynamo number, the magnetic field consists of a number of quasi-independent, spatially localized modes generated in various concentric rings filling the disk inward of a dynamo generation front. 36 refs.

  11. A model for neutrino emission from nuclear accretion disks

    Science.gov (United States)

    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).

  12. New strategy for planets serach in debris disks

    Science.gov (United States)

    Zakhozhay, O.

    2014-09-01

    Based on the modern theory of planet formation, planetary systems are formed in protoplanetary disks that could surround young stellar and substellar objects. Giant planets formation process starts at first 100 thousand years as a consequence of disk gravitational instability. Rocky planets form later, through the coagulation of planetesimals. Common feature in both types planets formation scenarios is that once planet reaches stable orbit (especially if orbit is circular), planet clears a gap in the disk along the planet's orbit. By the debris disk stage the gap opened by planet becomes optically thin. There are two observational methods to study the structure of debris disks: with an image and via an excess in stellar spectral energy distribution (SED) at the infrared. The image of such disk is the best way to detect the gap opened by planet and even the planet itself. It is almost impossible to detect the planet around the star by studying SED, due to the big difference of their luminosities. But it is possible to suspect planet based on the param- eters of the gap cleaned by planet, that could be derived based on the analysis of SED profile. The aim of present work is to investigate a possibility to detect planet in debris disk via SED profile analyze and to determine planets physical parameters that can be derived with this method. I will present the results of numerical calculations for systems with low-mass stellar and substellar objects at 1 Gyr. Debris disk particles radii vary from 0.1 microns to 1 meter; disk masses vary from 10**-16 to 0.05 masses of the star (that initially doesn't account extinction due to the gap opened by the planet). Width of the gap opened by the planet is determined as a diameter of Hill sphere. Planet masses are varied from 10 Earth to 10 Jupiter masses. Distance from the planet to the central star is within all possible positions along the disk radius.

  13. Dispersion in unit disks

    CERN Document Server

    Dumitrescu, Adrian

    2009-01-01

    We present two new approximation algorithms with (improved) constant ratios for selecting $n$ points in $n$ unit disks such that the minimum pairwise distance among the points is maximized. (I) A very simple $O(n \\log{n})$-time algorithm with ratio 0.5110 for disjoint unit disks. In combination with an algorithm of Cabello \\cite{Ca07}, it yields a $O(n^2)$-time algorithm with ratio of 0.4487 for dispersion in $n$ not necessarily disjoint unit disks. (II) A more sophisticated LP-based algorithm with ratio 0.6495 for disjoint unit disks that uses a linear number of variables and constraints, and runs in polynomial time. The algorithm introduces a novel technique which combines linear programming and projections for approximating distances. The previous best approximation ratio for disjoint unit disks was 1/2. Our results give a partial answer to an open question raised by Cabello \\cite{Ca07}, who asked whether 1/2 could be improved.

  14. Binary-disk interaction: Gap-Opening criteria

    CERN Document Server

    del Valle, Luciano

    2012-01-01

    We study the interaction of an equal mass binary with an isothermal circumbinary disk motivated by the theoretical and observational evidence of the formation of massive black holes binaries surrounded by gas, after a major merger of gas-rich galaxies. We focus on the torques that the binary produces on the disk and how the exchange of angular momentum can drive the formation of a gap on it. We propose that the angular momentum exchange between the binary and the disk is through the gravitational interaction of the binary and a (tidally formed) global non-axisymmetric perturbation in the disk. Using this gravitational interaction we derive an analytic criterion for the formation of a gap in the disk that can be expressed on the structural parameters h/a and M(< r)/M_{bin}. Using SPH simulations we show that the simulations where the binary opens a gap in the disk and the simulations where the disk does not have a gap are distributed in two well separate regions. Our analytic gap-opening criterion predicts ...

  15. Silica in Protoplanetary Disks

    CERN Document Server

    Sargent, B A; Tayrien, C; McClure, M K; Li, A; Basu, A R; Manoj, P; Watson, D M; Bohac, C J; Furlan, E; Kim, K H; Green, J D; Sloan, G C

    2008-01-01

    Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope show prominent narrow emission features indicating silica (crystalline silicon dioxide). Silica is not a major constituent of the interstellar medium; therefore, any silica present in the circumstellar protoplanetary disks of TTS must be largely the result of processing of primitive dust material in the disks surrouding these stars. We model the silica emission features in our spectra using the opacities of various polymorphs of silica and their amorphous versions computed from earth-based laboratory measurements. This modeling indicates that the two polymorphs of silica, tridymite and cristobalite, which form at successively higher temperatures and low pressures, are the dominant forms of silica in the TTS of our sample. These high temperature, low pressure polymorphs of silica present in protoplanetary disks are consistent with a grain composed mostly of tridymite named Ada found...

  16. From Disks to Planets

    Science.gov (United States)

    Youdin, Andrew N.; Kenyon, Scott J.

    This pedagogical chapter covers the theory of planet formation, with an emphasis on the physical processes relevant to current research. After summarizing empirical constraints from astronomical and geophysical data, we describe the structure and evolution of protoplanetary disks. We consider the growth of planetesimals and of larger solid protoplanets, followed by the accretion of planetary atmospheres, including the core accretion instability. We also examine the possibility that gas disks fragment directly into giant planets and/or brown dwarfs. We defer a detailed description of planet migration and dynamical evolution to other work, such as the complementary chapter in this series by Morbidelli.

  17. Lupus Alma Disk Survey

    Science.gov (United States)

    Ansdell, Megan

    2016-07-01

    We present the first unbiased ALMA survey of both dust and gas in a large sample of protoplanetary disks. We surveyed 100 sources in the nearby (150-200 pc), young (1-2 Myr) Lupus region to constrain M_dust to 2 M_Mars and M_gas to 1 M_Jup. Most disks have masses < MMSN and gas-to-dust ratios < ISM. Such rapid gas depletion may explain the prevalence of super-Earths in the exoplanet population.

  18. From Protoplanetary Disks to Extrasolar Planets: Understanding the Life Cycle of Circumstellar Gas with Ultraviolet Spectroscopy

    CERN Document Server

    France, Kevin; Ardila, David R; Bergin, Edwin A; Brown, Alexander; Burgh, Eric B; Calvet, Nuria; Chiang, Eugene; Cook, Timothy A; Désert, Jean-Michel; Ebbets, Dennis; Froning, Cynthia S; Green, James C; Hillenbrand, Lynne A; Johns-Krull, Christopher M; Koskinen, Tommi T; Linsky, Jeffrey L; Redfield, Seth; Roberge, Aki; Schindhelm, Eric R; Scowen, Paul A; Stapelfeldt, Karl R; Tumlinson, Jason

    2012-01-01

    Few scientific discoveries have captured the public imagination like the explosion of exoplanetary science during the past two decades. This work has fundamentally changed our picture of Earth's place in the Universe and led NASA to make significant investments towards understanding the demographics of exoplanetary systems and the conditions that lead to their formation. The story of the formation and evolution of exoplanetary systems is essentially the story of the circumstellar gas and dust that are initially present in the protostellar environment; in order to understand the variety of planetary systems observed, we need to understand the life cycle of circumstellar gas from its initial conditions in protoplanetary disks to its endpoint as planets and their atmospheres. In this white paper response to NASA's Request for Information "Science Objectives and Requirements for the Next NASA UV/Visible Astrophysics Mission Concepts (NNH12ZDA008L)", we describe scientific programs that would use the unique capabi...

  19. The kinematic relationship between disk and jet in the DG Tauri system

    CERN Document Server

    Testi, L; Sargent, A I; Ray, T P; Eislöffel, J

    2002-01-01

    We present high angular resolution millimeter wavelength continuum and 13CO(2-1) observations of the circumstellar disk surrounding the TTauri star DG Tauri. We show that the velocity pattern in the inner regions of the disk is consistent with Keplerian rotation about a central 0.67 Msun star. The disk rotation is also consistent with the toroidal velocity pattern in the initial channel of the optical jet, as inferred from HST spectra of the first de-projected 100 AU from the source. Our observations support the tight relationship between disk and jet kinematics postulated by the popular magneto-centrifugal models for jet formation and collimation.

  20. Unified Models of Molecular Emission from Class 0 Protostellar Outflow Sources

    CERN Document Server

    Rawlings, J M C; Carolan, P B

    2013-01-01

    Low mass star-forming regions are more complex than the simple spherically symmetric approximation that is often assumed. We apply a more realistic infall/outflow physical model to molecular/continuum observations of three late Class 0 protostellar sources with the aims of (a) proving the applicability of a single physical model for all three sources, and (b) deriving physical parameters for the molecular gas component in each of the sources. We have observed several molecular species in multiple rotational transitions. The observed line profiles were modelled in the context of a dynamical model which incorporates infall and bipolar outflows, using a three dimensional radiative transfer code. This results in constraints on the physical parameters and chemical abundances in each source. Self-consistent fits to each source are obtained. We constrain the characteristics of the molecular gas in the envelopes as well as in the molecular outflows. We find that the molecular gas abundances in the infalling envelope ...

  1. Effect of Ambipolar Diffusion on Ion Abundances in Contracting Protostellar Cores

    Science.gov (United States)

    Ciolek, Glenn E.; Mouschovias, Telemachos Ch.

    1998-09-01

    Numerical simulations and analytical solutions have established that ambipolar diffusion can reduce the dust-to-gas ratio in magnetically and thermally supercritical cores during the epoch of core formation. We study the effect that this has on the ion chemistry in contracting protostellar cores and present a simplified analytical method that allows one to calculate the ion power-law exponent k (≡d ln ni/d ln nn, where ni and nn are the ion and neutral densities, respectively) as a function of core density. We find that, as in earlier numerical simulations, no single value of k can adequately describe the ion abundance for nn 1/2 during the core formation epoch (densities principle, to determine whether ambipolar diffusion is responsible for core formation in interstellar molecular clouds. For densities >>105 cm-3, k is generally <<1/2.

  2. Simulations of protostellar collapse using multigroup radiation hydrodynamics. I. The first collapse

    CERN Document Server

    Vaytet, Neil; Chabrier, Gilles; Commercon, Benoit; Masson, Jacques

    2012-01-01

    Radiative transfer plays a major role in the process of star formation. Many simulations of gravitational collapse of a cold gas cloud followed by the formation of a protostellar core use a grey treatment of radiative transfer coupled to the hydrodynamics. However, dust opacities which dominate extinction show large variations as a function of frequency. In this paper, we used frequency-dependent radiative transfer to investigate the influence of the opacity variations on the properties of Larson's first core. We used a multigroup M1 moment model in a 1D radiation hydrodynamics code to simulate the spherically symmetric collapse of a 1 solar mass cloud core. Monochromatic dust opacities for five different temperature ranges were used to compute Planck and Rosseland means inside each frequency group. The results are very consistent with previous studies and only small differences were observed between the grey and multigroup simulations. For a same central density, the multigroup simulations tend to produce fi...

  3. The Nature of Angular Momentum Transport in Radiative Self-Gravitating Protostellar Discs

    CERN Document Server

    Forgan, Duncan; Cossins, Peter; Lodato, Giuseppe

    2010-01-01

    Semi-analytic models of self-gravitating discs often approximate the angular momentum transport generated by the gravitational instability using the phenomenology of viscosity. This allows the employment of the standard viscous evolution equations, and gives promising results. It is, however, still not clear when such an approximation is appropriate. This paper tests this approximation using high resolution 3D smoothed particle hydrodynamics (SPH) simulations of self-gravitating protostellar discs with radiative transfer. The nature of angular momentum transport associated with the gravitational instability is characterised as a function of both the stellar mass and the disc-to-star mass ratio. The effective viscosity is calculated from the Reynolds and gravitational stresses in the disc. This is then compared to what would be expected if the effective viscosity were determined by assuming local thermodynamic equilibrium or, equivalently, that the local dissipation rate matches the local cooling rate. In gene...

  4. A theoretical perspective on the formation and fragmentation of protostellar discs

    CERN Document Server

    Whitworth, A P

    2016-01-01

    We discuss the factors influencing the formation and gravitational fragmentation of protostellar discs. We start with a review of how observations of prestellar cores can be analysed statistically to yield plausible initial conditions for simulations of their subsequent collapse. Simulations based on these initial conditions show that, despite the low levels of turbulence in prestellar cores, they deliver primary protostars and associated discs which are routinely subject to stochastic impulsive perturbations; consequently misalignment of the spins and orbits of protostars are common. Also, the simulations produce protostars that collectively have a mass function and binary statistics matching those observed in nearby star formation regions, but only if a significant fraction of the turbulent energy in the core is solenoidal, and accretion onto the primary protostar is episodic with a duty cycle > 3000 yr. Under this circumstance a core typically spawns between 4 and 5 protostars, with high efficiency, and th...

  5. Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores

    CERN Document Server

    Taquet, Vianney; Sipilä, Olli

    2014-01-01

    Extremely large deuteration of several molecules has been observed towards prestellar cores and low-mass protostars for a decade. New observations performed towards low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimension model of collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H$_2$ and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation towards the surface. The differentiation...

  6. Centrifugally driven winds from protostellar accretion discs - I. Formulation and initial results

    Science.gov (United States)

    Nolan, C. A.; Salmeron, R.; Federrath, C.; Bicknell, G. V.; Sutherland, R. S.

    2017-10-01

    Protostellar discs play an important role in star formation, acting as the primary mass reservoir for accretion on to young stars and regulating the extent to which angular momentum and gas is released back into stellar nurseries through the launching of powerful disc winds. In this study, we explore how disc structure relates to the properties of the wind-launching region, mapping out the regions of protostellar discs where wind launching could be viable. We combine a series of 1.5D semi-analytic, steady-state, vertical disc-wind solutions into a radially extended 1+1.5D model, incorporating all three diffusion mechanisms (Ohm, Hall and ambipolar). We observe that the majority of mass outflow via disc winds occurs over a radial width of a fraction of an astronomical unit, with outflow rates attenuating rapidly on either side. We also find that the mass accretion rate, magnetic field strength and surface density profile each have significant effects on both the location of the wind-launching region and the ejection/accretion ratio \\dot{M}_out/\\dot{M}_in. Increasing either the accretion rate or the magnetic field strength corresponds to a shift of the wind-launching region to smaller radii and a decrease in \\dot{M}_out/\\dot{M}_in, while increasing the surface density corresponds to launching regions at larger radii with increased \\dot{M}_out/\\dot{M}_in. Finally, we discover a class of disc winds containing an ineffective launching configuration at intermediate radii, leading to two radially separated regions of wind launching and diminished \\dot{M}_out/\\dot{M}_in. We find that the wind locations and ejection/accretion ratio are consistent with current observational and theoretical estimates.

  7. Polarimetric microlensing of circumstellar disks

    CERN Document Server

    Sajadian, Sedighe

    2015-01-01

    We study the benefits of polarimetry observations of microlensing events to detect and characterize circumstellar disks around the microlensed stars located at the Galactic bulge. These disks which are unresolvable from their host stars make a net polarization effect due to their projected elliptical shapes. Gravitational microlensing can magnify these signals and make them be resolved. The main aim of this work is to determine what extra information about these disks can be extracted from polarimetry observations of microlensing events in addition to those given by photometry ones. Hot disks which are closer to their host stars are more likely to be detected by microlensing, owing to more contributions in the total flux. By considering this kind of disks, we show that although the polarimetric efficiency for detecting disks is similar to the photometric observation, but polarimetry observations can help to constraint the disk geometrical parameters e.g. the disk inner radius and the lens trajectory with resp...

  8. Warm gas in protoplanetary disks

    Science.gov (United States)

    van der Plas, Gerrit

    2010-12-01

    This thesis presents a study of warm CO, [OI] and H2 gas coming from the disks around Herbig Ae/Be stars. These various gas tracers are each a proxy for a different radial and vertical region of the PP disk surface. Our sample consists of disks whose shape (based on modeling of the the disk dust emission) can be divided into flaring and self-shadowed (flat). We find [1] evidence for the vertical decoupling of gas and dust in one disks (Chapter 2); [2] That disk geometry has a large influence on the spatial distribution and excitation mechanism of the CO emission (chapters 3,4); [3] Near-IR H 2 emission around 2 (out of 14) HAEBE stars, probably originating from large (±50AU) radii of the disk (chapter 5). In chapter 6 we investigate the trends between CO emission and disk geometry as noted in Chapter 3 and 4.

  9. Galactic Thin Disk

    NARCIS (Netherlands)

    van der Kruit, P.; Murdin, P.; Murdin, Paul

    2000-01-01

    Of the components of our MILKY WAY GALAXY, the thin disk is the most prominent part to our eyes. It manifests itself as the band of faint light that we see encircling the whole sky. Except for the bulge in the direction of the center of our Galaxy, the stars that make up the Milky Way as we see it

  10. More approximation on disks

    NARCIS (Netherlands)

    de Paepe, P.J.I.M.; Wiegerinck, J.J.O.O.

    2007-01-01

    Abstract: In this article we study the function algebra generated by z2 and g2 on a small closed disk centred at the origin of the complex plane. We prove, using a biholomorphic change of coordinates and already developed techniques in this area, that for a large class of functions g this algebra co

  11. Herniated disk repair (image)

    Science.gov (United States)

    ... is one of the most common causes of lower back pain. The mainstay of treatment for herniated disks is an initial period of rest with pain and anti-inflammatory medications followed by physical therapy. If pain and symptoms persist, surgery to remove ...

  12. Binaural Rendering in MPEG Surround

    Directory of Open Access Journals (Sweden)

    Kristofer Kjörling

    2008-04-01

    Full Text Available This paper describes novel methods for evoking a multichannel audio experience over stereo headphones. In contrast to the conventional convolution-based approach where, for example, five input channels are filtered using ten head-related transfer functions, the current approach is based on a parametric representation of the multichannel signal, along with either a parametric representation of the head-related transfer functions or a reduced set of head-related transfer functions. An audio scene with multiple virtual sound sources is represented by a mono or a stereo downmix signal of all sound source signals, accompanied by certain statistical (spatial properties. These statistical properties of the sound sources are either combined with statistical properties of head-related transfer functions to estimate “binaural parameters” that represent the perceptually relevant aspects of the auditory scene or used to create a limited set of combined head-related transfer functions that can be applied directly on the downmix signal. Subsequently, a binaural rendering stage reinstates the statistical properties of the sound sources by applying the estimated binaural parameters or the reduced set of combined head-related transfer functions directly on the downmix. If combined with parametric multichannel audio coders such as MPEG Surround, the proposed methods are advantageous over conventional methods in terms of perceived quality and computational complexity.

  13. Reduced surround inhibition in musicians.

    Science.gov (United States)

    Shin, Hae-Won; Kang, Suk Y; Hallett, Mark; Sohn, Young H

    2012-06-01

    To investigate whether surround inhibition (SI) in the motor system is altered in professional musicians, we performed a transcranial magnetic stimulation (TMS) study in 10 professional musicians and 15 age-matched healthy non-musicians. TMS was set to be triggered by self-initiated flexion of the index finger at different intervals ranging from 3 to 1,000 ms. Average motor evoked potential (MEP) amplitudes obtained from self-triggered TMS were normalized to average MEPs of the control TMS at rest and expressed as a percentage. Normalized MEP amplitudes of the abductor digiti minimi (ADM) muscles were compared between the musicians and non-musicians with the primary analysis being the intervals between 3 and 80 ms (during the movement). A mixed-design ANOVA revealed a significant difference in normalized ADM MEPs during the index finger flexion between groups, with less SI in the musicians. This study demonstrated that the functional operation of SI is less strong in musicians than non-musicians, perhaps due to practice of movement synergies involving both muscles. Reduced SI, however, could lead susceptible musicians to be prone to develop task-specific dystonia.

  14. Binaural Rendering in MPEG Surround

    Science.gov (United States)

    Breebaart, Jeroen; Villemoes, Lars; Kjörling, Kristofer

    2008-12-01

    This paper describes novel methods for evoking a multichannel audio experience over stereo headphones. In contrast to the conventional convolution-based approach where, for example, five input channels are filtered using ten head-related transfer functions, the current approach is based on a parametric representation of the multichannel signal, along with either a parametric representation of the head-related transfer functions or a reduced set of head-related transfer functions. An audio scene with multiple virtual sound sources is represented by a mono or a stereo downmix signal of all sound source signals, accompanied by certain statistical (spatial) properties. These statistical properties of the sound sources are either combined with statistical properties of head-related transfer functions to estimate "binaural parameters" that represent the perceptually relevant aspects of the auditory scene or used to create a limited set of combined head-related transfer functions that can be applied directly on the downmix signal. Subsequently, a binaural rendering stage reinstates the statistical properties of the sound sources by applying the estimated binaural parameters or the reduced set of combined head-related transfer functions directly on the downmix. If combined with parametric multichannel audio coders such as MPEG Surround, the proposed methods are advantageous over conventional methods in terms of perceived quality and computational complexity.

  15. Bridging the gap: disk formation in the Class 0 phase with ambipolar diffusion and Ohmic dissipation

    CERN Document Server

    Dapp, Wolf B; Kunz, Matthew W

    2011-01-01

    Context: Ideal MHD simulations have revealed catastrophic magnetic braking (MB) in the protostellar phase, which prevents the formation of a centrifugal disk around a nascent protostar. Aims: We determine if non-ideal MHD, including the effects of ambipolar diffusion and Ohmic dissipation determined from a detailed chemical network model, allows for disk formation at the earliest stages of star formation (SF). Methods: We employ the axisymmetric thin-disk approximation in order to resolve a dynamic range of 9 orders of magnitude in length and 16 in density, while also calculating partial ionization using up to 19 species in a detailed chemical equilibrium model. MB is applied using a steady-state approximation, and a barotropic relation is used to capture the thermal evolution. Results: We resolve the formation of the first and second cores, with expansion waves at the periphery of each, a magnetic diffusion shock, and prestellar infall profiles at larger radii. Power-law profiles in each region can be unders...

  16. On The Orbital Evolution of Jupiter Mass Protoplanet Embedded in A Self-Gravity Disk

    CERN Document Server

    Zhang, Hui; Lin, D N C; Yen, D C C

    2007-01-01

    We performed a series of hydro-dynamic simulations to investigate the orbital migration of a Jovian planet embedded in a proto-stellar disk. In order to take into account of the effect of the disk's self gravity, we developed and adopted an \\textbf{Antares} code which is based on a 2-D Godunov scheme to obtain the exact Reimann solution for isothermal or polytropic gas, with non-reflecting boundary conditions. Our simulations indicate that in the study of the runaway (type III) migration, it is important to carry out a fully self consistent treatment of the gravitational interaction between the disk and the embedded planet. Through a series of convergence tests, we show that adequate numerical resolution, especially within the planet's Roche lobe, critically determines the outcome of the simulations. We consider a variety of initial conditions and show that isolated, non eccentric protoplanet planets do not undergo type III migration. We attribute the difference between our and previous simulations to the con...

  17. Radiation thermo-chemical models of protoplanetary disks I. Hydrostatic disk structure and inner rim

    CERN Document Server

    Woitke, Peter; Thi, Wing-Fai

    2009-01-01

    This paper introduces a new disk code, called ProDiMo, to calculate the thermo-chemical structure of protoplanetary disks and to interpret gas emission lines from UV to sub-mm. We combine frequency-dependent 2D dust continuum radiative transfer, kinetic gas-phase and UV photo-chemistry, ice formation, and detailed non-LTE heating & cooling balance with the consistent calculation of the hydrostatic disk structure. We include FeII and CO ro-vibrational line heating/cooling relevant for the high-density gas close to the star, and apply a modified escape probability treatment. The models are characterized by a high degree of consistency between the various physical, chemical and radiative processes, where the mutual feedbacks are solved iteratively. In application to a T Tauri disk extending from 0.5AU to 500AU, the models are featured by a puffed-up inner rim and show that the dense, shielded and cold midplane (z/r<0.1, Tg~Td) is surrounded by a layer of hot (5000K) and thin (10^7 to 10^8 cm^-3) atomic ga...

  18. The Tilt between Acretion Disk and Stellar Disk

    Indian Academy of Sciences (India)

    Shiyin Shen; Zhengyi Shao; Minfeng Gu

    2011-03-01

    The orientations of the accretion disk of active galactic nuclei (AGN) and the stellar disk of its host galaxy are both determined by the angular momentum of their forming gas, but on very different physical environments and spatial scales. Here we show the evidence that the orientation of the stellar disk is correlated with the accretion disk by comparing the inclinations of the stellar disks of a large sample of Type 2 AGNs selected from Sloan Digital Sky Survey (SDSS, York et al. 2000) to a control galaxy sample. Given that the Type 2 AGN fraction is in the range of 70–90 percent for low luminosity AGNs as a priori, we find that the mean tilt between the accretion disk and stellar disk is ∼ 30 degrees (Shen et al. 2010).

  19. VLT imaging of the {\\beta} Pictoris gas disk

    CERN Document Server

    Nilsson, R; Olofsson, G; Fathi, K; Thébault, Ph; Liseau, R

    2012-01-01

    Circumstellar debris disks older than a few Myr should be largely devoid of primordial gas remaining from the protoplanetary disk phase. Tracing the origin of observed atomic gas in Keplerian rotation in the edge-on debris disk surrounding the ~12 Myr old star {\\beta} Pictoris requires more detailed information about its spatial distribution than has previously been acquired by limited slit spectroscopy. Especially indications of asymmetries and presence of Ca II gas at high disk latitudes call for additional investigation. We set out to recover a complete image of the Fe I and Ca II gas emission around {\\beta} Pic by spatially resolved, high-resolution spectroscopic observations to better understand the morphology and origin of the gaseous disk component. The multiple fiber facility FLAMES/GIRAFFE at the VLT, with the large IFU ARGUS, was used to obtain spatially resolved optical spectra in four regions covering the northeast and southwest side of the disk. Emission lines from Fe I and Ca II were mapped and ...

  20. An ALMA Survey of Planet Forming Disks in Rho Ophiuchus

    Science.gov (United States)

    Guilfoil Cox, Erin; Looney, Leslie; Harris, Robert J.; Dong, Jiayin; Segura-Cox, Dominique; Tobin, John J.; Sadavoy, Sarah; Li, Zhi-Yun; Dunham, Michael; Perez, Laura M.; Chandler, Claire J.; Kratter, Kaitlin M.; Melis, Carl; Chiang, Hsin-Fang

    2017-01-01

    Relatively evolved (~ 1 Myr old) protostars with little residual natal envelope, but massive disks, are commonly assumed to be the sites of ongoing planet formation. Critical to our study of these objects is information about the available mass reservior and dust structure, as they directly tie in to how much mass is available for planets as well as the modes of planet formation that occur (i.e., core-accretion vs. gravitational instability). Millimeter-wave observations provide this critical information as continuum emission is relatively optically thin, allowing for mass estimates, and the availability of high-resolution interferometry, allowing structure constraints. We present high-resolution observations of the population of Class II protostars in the Rho-Ophiuchus cloud (d ~ 130 pc). Our survey observed ~50 of these older protostars at 870µm, using the Atacama Large Millimeter/submillimeter Array (ALMA). Out of these sources, there are ~10 transition disks, where we see a ring of dust emission surrounding the central protostar -- indicative of ongoing planet formation -- as well as many binary systems. Both of these stages have implications for star and planet formation. We present results from both 1-D and 2-D disk modeling, where we try to understand disk substructure that might indicate on-going planet formation, in particular, transition disk cavities, disk gaps, and asymmetries in the dust emission.

  1. Vibration of imperfect rotating disk

    Directory of Open Access Journals (Sweden)

    Půst L.

    2011-12-01

    Full Text Available This study is concerned with the theoretical and numerical calculations of the flexural vibrations of a bladed disk. The main focus of this study is to elaborate the basic background for diagnostic and identification methods for ascertaining the main properties of the real structure or an experimental model of turbine disks. The reduction of undesirable vibrations of blades is proposed by using damping heads, which on the experimental model of turbine disk are applied only on a limited number of blades. This partial setting of damping heads introduces imperfection in mass, stiffness and damping distribution on the periphery and leads to more complicated dynamic properties than those of a perfect disk. Calculation of FEM model and analytic—numerical solution of disk behaviour in the limited (two modes frequency range shows the splitting of resonance with an increasing speed of disk rotation. The spectrum of resonance is twice denser than that of a perfect disk.

  2. Chemical segregation in the young protostars Barnard 1b-N and S. Evidence of pseudo-disk rotation in Barnard 1b-S

    Science.gov (United States)

    Fuente, A.; Gerin, M.; Pety, J.; Commerçon, B.; Agúndez, M.; Cernicharo, J.; Marcelino, N.; Roueff, E.; Lis, D. C.; Wootten, H. A.

    2017-10-01

    The extremely young Class 0 object B1b-S and the first hydrostatic core (FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical changes produced in the elusive transition from the prestellar core to the protostellar phase. We present 40″ × 70″ images of Barnard 1b in the 13CO 1 → 0, C18O 1 → 0, NH2D 11,1a→ 10,1s, and SO 32→ 21 lines obtained with the NOEMA interferometer. The observed chemical segregation allows us to unveil the physical structure of this young protostellar system down to scales of 500 au. The two protostellar objects are embedded in an elongated condensation, with a velocity gradient of 0.2-0.4 m s-1 au-1 in the east-west direction, reminiscent of an axial collapse. The NH2D data reveal cold and dense pseudo-disks (R 500 - 1000 au) around each protostar. Moreover, we observe evidence of pseudo-disk rotation around B1b-S. We do not see any signature of the bipolar outflows associated with B1b-N and B1b-S, which were previously detected in H2CO and CH3OH, in any of the imaged species. The non-detection of SO constrains the SO/CH3OH abundance ratio in the high-velocity gas. Based on observations carried out with the IRAM Northern Extended Millimeter Array (NOEMA). IRAM is supported by INSU/ CNRS (France), MPG (Germany), and IGN (Spain).The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/L3

  3. Volatiles in protoplanetary disks

    CERN Document Server

    Pontoppidan, Klaus M; Bergin, Edwin A; Brittain, Sean; Marty, Bernard; Mousis, Olvier; Oberg, Karin L

    2014-01-01

    Volatiles are compounds with low sublimation temperatures, and they make up most of the condensible mass in typical planet-forming environments. They consist of relatively small, often hydrogenated, molecules based on the abundant elements carbon, nitrogen and oxygen. Volatiles are central to the process of planet formation, forming the backbone of a rich chemistry that sets the initial conditions for the formation of planetary atmospheres, and act as a solid mass reservoir catalyzing the formation of planets and planetesimals. This growth has been driven by rapid advances in observations and models of protoplanetary disks, and by a deepening understanding of the cosmochemistry of the solar system. Indeed, it is only in the past few years that representative samples of molecules have been discovered in great abundance throughout protoplanetary disks - enough to begin building a complete budget for the most abundant elements after hydrogen and helium. The spatial distributions of key volatiles are being mapped...

  4. Depletion of chlorine into HCl ice in a protostellar core. The CHESS spectral survey of OMC-2 FIR 4

    Science.gov (United States)

    Kama, M.; Caux, E.; López-Sepulcre, A.; Wakelam, V.; Dominik, C.; Ceccarelli, C.; Lanza, M.; Lique, F.; Ochsendorf, B. B.; Lis, D. C.; Caballero, R. N.; Tielens, A. G. G. M.

    2015-02-01

    Context. The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances OMC-2 FIR 4. Methods: We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H2 hyperfine collisional excitation rate coefficients. Results: A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9 × 10-11, a factor of only 10-3 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous foreground cloud, where we find no depletion of volatile chlorine. Conclusions: Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with an abundance of ≲10-10 in most of the protostellar core. We find the [35Cl]/[37Cl] ratio in OMC-2 FIR 4 to be 3.2 ± 0.1, consistent with the solar system value. Appendices are available in electronic form at http://www.aanda.org

  5. The Evolution of Inner Disk Gas in Transition Disks

    CERN Document Server

    Hoadley, Keri; Alexander, Richard D; McJunkin, Matthew; Schneider, Christian

    2015-01-01

    Investigating the molecular gas in the inner regions of protoplanetary disks 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 (H$_2$) 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 $\\alpha$-pumped H$_2$ disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H$_{2}$ 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 H$_2$ 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 a...

  6. A 500 Parsec Halo Surrounding the Galactic Globular NGC 1851

    CERN Document Server

    Olszewski, Edward W; Knezek, Patricia; Subramaniam, Annapurni; de Boer, Thomas; Seitzer, Patrick

    2009-01-01

    Using imaging that shows four magnitudes of main sequence stars, we have discovered that the Galactic globular cluster NGC 1851 is surrounded by a halo that is visible from the tidal radius of 700 arcsec (41 pc) to more than 4500 arcsec (>250 pc). This halo is symmetric and falls in density as a power law of $r^{-1.24}$. It contains approximately 0.1% of the dynamical mass of NGC 1851. There is no evidence for tidal tails. Current models of globular cluster evolution do not explain this feature, although simulations of tidal influences on dwarf spheroidal galaxies qualitatively mimic these results. Given the state of published models it is not possible to decide between creation of this halo from isolated cluster evaporation, or from tidal or disk shocking, or from destruction of a dwarf galaxy in which this object may have once been embedded.

  7. Discovery of the Youngest Molecular Outflow associated with an Intermediate-mass protostellar Core, MMS-6/OMC-3

    CERN Document Server

    Takahashi, Satoko

    2011-01-01

    We present sub-arcsecond resolution HCN (4-3) and CO (3-2) observations made with the Submillimeter Array (SMA), toward an extremely young intermediate-mass protostellar core, MMS 6-main, located in the Orion Molecular Cloud 3 region (OMC-3). We have successfully imaged a compact molecular outflow lobe (~1500 AU) associated with MMS6-main, which is also the smallest molecular outflow ever found in the intermediate-mass protostellar cores. The dynamical time scale of this outflow is estimated to be <100 yr. The line width dramatically increases downstream at the end of the molecular outflow ({\\Delta}v~25 km s^{-1}), and clearly shows the bow-shock type velocity structure. The estimated outflow mass (~10^{-4} M_{sun}) and outflow size are approximately 2-4 orders and 1-3 orders of magnitude smaller, while the outflow force (~10^{-4} M_{sun} km s^{-1} yr^{-1}) is similar, as compared to the other molecular outflows studied in OMC-2/3. These results show that MMS 6-main is a protostellar core at the earliest e...

  8. On the Ionisation Fraction in Protoplanetary Disks II: The Effect of Turbulent Mixing on Gas--phase Chemistry

    CERN Document Server

    Ilgner, M; Ilgner, Martin; Richard P. Nelson

    2005-01-01

    We calculate the ionisation fraction in protostellar disk models using two different gas-phase chemical networks, and examine the effect of turbulent mixing by modelling the diffusion of chemical species vertically through the disk. The aim is to determine in which regions of the disk gas can couple to a magnetic field and sustain MHD turbulence. We find that the effect of diffusion depends crucially on the elemental abundance of heavy metals (magnesium) included in the chemical model. In the absence of heavy metals, diffusion has essentially no effect on the ionisation structure of the disks, as the recombination time scale is much shorter than the turbulent diffusion time scale. When metals are included with an elemental abundance above a threshold value, the diffusion can dramatically reduce the size of the magnetically decoupled region, or even remove it altogther. For a complex chemistry the elemental abundance of magnesium required to remove the dead zone is 10(-10) - 10(-8). We also find that diffusion...

  9. Warping and tearing of misaligned circumbinary disks around eccentric SMBH binaries

    CERN Document Server

    Hayasaki, Kimitake; Okazaki, Atsuo T; Jung, Taehyun; Zhao, Guangyao; Naito, Tsuguya

    2015-01-01

    We study the warping and tearing of a geometrically thin, non-self-gravitating disk surrounding binary supermassive black holes on an eccentric orbit. The circumbinary disk is significantly misaligned with the binary orbital plane, and is subject to the time-dependent tidal torques. In principle, such a disk is warped and precesses, and is torn into mutually misaligned rings in the region, where the tidal precession torques are stronger than the local viscous torques. We derive the tidal-warp and tearing radii of the misaligned circumbinary disks around eccentric SMBH binaries. We find that in disks with the viscosity parameter, alpha, larger than a critical value depending on the disk aspect ratio, the disk warping appears outside the tearing radius. This condition is expressed as alpha > sqrt{H/3r} for H/r ~<0.1, where H is the disk scale height. If alpha < sqrt{H/3r}, only the disk tearing occurs because the tidal warp radius is inside the tearing radius, where most of disk material is likely to rapi...

  10. High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

    Science.gov (United States)

    Tanii, Ryoko; Itoh, Yoichi; Kudo, Tomoyuki; Hioki, Tomonori; Oasa, Yumiko; Gupta, Ranjan; Sen, Asoke K.; Wisniewski, John P.; Muto, Takayuki; Grady, Carol A.; Hashimoto, Jun; Fukagawa, Misato; Mayama, Satoshi; Hornbeck, Jeremy; Sitko, Michael L.; Russell, Ray W.; Werren, Chelsea; Curé, Michel; Currie, Thayne; Ohashi, Nagayoshi; Okamoto, Yoshiko; Momose, Munetake; Honda, Mitsuhiko; Inutsuka, Shu-ichi; Takeuchi, Taku; Dong, Ruobing; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph; Egner, Sebastian E.; Feldt, Markus; Fukue, Tsubasa; Goto, Miwa; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kusakabe, Nobuhiko; Kuzuhara, Masayuki; Matsuo, Taro; McElwain, Michael W.; Miyama, Shoken; Morino, Jun-ichi; Moro-Martín, Amaya; Nishimura, Tetsuro; Pyo, Tae-Soo; Serabyn, Eugene; Suto, Hiroshi; Suzuki, Ryuji; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2012-12-01

    We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.''15 (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A, which extends to 120 AU, at a spatial resolution of 0.''1 (14 AU). It is inclined by 46° ± 2°, since the west side is nearest. Although SED modeling and sub-millimeter imagery have suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25-30 AU, we detect no evidence of a gap at the limit of our inner working angle (23 AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66%) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh-scattering nor Mie-scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with radii of 30μm is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations, and have grown in the circumstellar disk of UX Tau A.

  11. Molecular line emission from a protoplanetary disk irradiated externally by a nearby massive star

    CERN Document Server

    Walsh, Catherine; Nomura, Hideko; 10.1088/2041-8205/766/2/L23

    2013-01-01

    Star formation often occurs within or nearby stellar clusters. Irradiation by nearby massive stars can photoevaporate protoplanetary disks around young stars (so-called proplyds) which raises questions regarding the ability of planet formation to take place in these environments. We investigate the two-dimensional physical and chemical structure of a protoplanetary disk surrounding a low-mass (T Tauri) star which is irradiated by a nearby massive O-type star to determine the survivability and observability of molecules in proplyds. Compared with an isolated star-disk system, the gas temperature ranges from a factor of a few (in the disk midplane) to around two orders of magnitude (in the disk surface) higher in the irradiated disk. Although the UV flux in the outer disk, in particular, is several orders of magnitude higher, the surface density of the disk is sufficient for effective shielding of the disk midplane so that the disk remains predominantly molecular in nature. We also find that non-volatile molecu...

  12. High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

    Science.gov (United States)

    Serabyn, G.; Grady, C. A.; Currie, T.

    2012-01-01

    We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0.15" (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a spatial resolution of 0.1" (14 AU). It is inclined by 46 degrees plus or minus 2 degrees as the west side is nearest. Although SED modeling and sub-millimeter imagery suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at the limit of our inner working angle (23AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66 %) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh scattering nor Mie scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with the radii of 30 micrometers is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations and have grown in the circumstellar disk of UX Tau A.

  13. Using Disk Eclipsing Systems to Understand Planet Formation and Evolution

    Science.gov (United States)

    Rodriguez, Joseph E.; Osborn, Hugh P.; Shappee, Benjamin John; KELT Collaboration

    2017-01-01

    The circumstellar environments of young stellar objects (YSOs) involve complex dynamical interactions between dust and gas that directly influence the formation of planets. However, our understanding of the evolution from the material in the circumstellar disk to the thousands of planetary systems discovered to date, is limited. One means to better constrain the size, mass, and composition of this planet-forming material is to observe a YSO being eclipsed by its circumstellar disk. Unfortunately, such events are rare but have already led to such insights as dense planet-forming structures within the tidally disrupted disk of a young binary star system, Saturn-like rings and gaps in the disk surrounding a young planet, stratified dust coagulation within a young protoplanetary disk, and an evolved binary star system with remnant planet-building material. Fortunately, the advent of wide-field time domain surveys provides a ideal tool to search for rare eclipse events. Using time-series photometry from the KELT project we are conducting the Disk Eclipse Search with KELT (DESK) survey to look for disk eclipsing events, specifically in young stellar associations. In addition, we are collaborating with the SuperWASP and ASAS-SN surveys which have already led to additional discoveries. This survey has already doubled the number of “disk eclipsing” systems known and will provide a framework for discovering such systems in future surveys such as LSST. I will describe a few of our recent discoveries and their impact on our understanding of circumstellar evolution.KELT is a joint collaboration between the Ohio State University, Vanderbilt University, and Lehigh University. This work was partially supported by NSF CAREER grant AST-1056524. J.E.R. is supported by a Harvard Future Faculty Leaders Postdoctoral Fellowship.

  14. Understanding Gas-Phase Ammonia Chemistry in Protoplanetary Disks

    Science.gov (United States)

    Chambers, Lauren; Oberg, Karin I.; Cleeves, Lauren Ilsedore

    2017-01-01

    Protoplanetary disks are dynamic regions of gas and dust around young stars, the remnants of star formation, that evolve and coagulate over millions of years in order to ultimately form planets. The chemical composition of protoplanetary disks is affected by both the chemical and physical conditions in which they develop, including the initial molecular abundances in the birth cloud, the spectrum and intensity of radiation from the host star and nearby systems, and mixing and turbulence within the disk. A more complete understanding of the chemical evolution of disks enables a more complete understanding of the chemical composition of planets that may form within them, and of their capability to support life. One element known to be essential for life on Earth is nitrogen, which often is present in the form of ammonia (NH3). Recent observations by Salinas et al. (2016) reveal a theoretical discrepancy in the gas-phase and ice-phase ammonia abundances in protoplanetary disks; while observations of comets and protostars estimate the ice-phase NH3/H2O ratio in disks to be 5%, Salinas reports a gas-phase NH3/H2O ratio of ~7-84% in the disk surrounding TW Hydra, a young nearby star. Through computational chemical modeling of the TW Hydra disk using a reaction network of over 5000 chemical reactions, I am investigating the possible sources of excess gas-phase NH3 by determining the primary reaction pathways of NH3 production; the downstream chemical effects of ionization by ultraviolet photons, X-rays, and cosmic rays; and the effects of altering the initial abundances of key molecules such as N and N2. Beyond providing a theoretical explanation for the NH3 ice/gas discrepancy, this new model may lead to fuller understanding of the gas-phase formation processes of all nitrogen hydrides (NHx), and thus fuller understanding of the nitrogen-bearing molecules that are fundamental for life as we know it.

  15. Incidence and survival of remnant disks around main-sequence stars

    CERN Document Server

    Habing, H J; De Muizon, M J; Laureijs, R J; Kessler, M F; Leech, K J; Metcalfe, L; Salama, A; Siebenmorgen, R; Trams, N R; Bouchet, P

    2000-01-01

    We present photometric ISO 60 and 170um measurements, complemented by some IRAS data at 60um, of a sample of 84 nearby main-sequence stars of spectral class A, F, G and K in order to determine the incidence of dust disks around such main-sequence stars. Of the stars younger than 400 Myr one in two has a disk; for the older stars this is true for only one in ten. We conclude that most stars arrive on the main sequence surrounded by a disk; this disk then decays in about 400 Myr. Because (i) the dust particles disappear and must be replenished on a much shorter time scale and (ii) the collision of planetesimals is a good source of new dust, we suggest that the rapid decay of the disks is caused by the destruction and escape of planetesimals. We suggest that the dissipation of the disk is related to the heavy bombardment phase in our Solar System. Whether all stars arrive on the main sequence surrounded by a disk cannot be established: some very young stars do not have a disk. And not all stars destroy their dis...

  16. Misaligned disks in the binary protostar IRS 43

    DEFF Research Database (Denmark)

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

    2016-01-01

    Recent high angular resolution (∼ 0\\buildrel{\\prime\\prime}\\over{.} 2) ALMA observations of the 1.1 mm continuum and of HCO+ J = 3–2 and HCN J = 3–2 gas toward the binary protostar IRS 43 reveal multiple Keplerian disks that are significantly misaligned (\\gt 60^\\circ ), both in inclination...... and position angle and also with respect to the binary orbital plane. Each stellar component has an associated circumstellar disk while the binary is surrounded by a circumbinary disk. Together with archival VLA measurements of the stellar positions over 25 years, and assuming a circular orbit, we use our...... continuum measurements to determine the binary separation, a=74+/- 4 {au}, and its inclination, i\\lt 30^\\circ . The misalignment in this system suggests that turbulence has likely played a major role in the formation of IRS 43....

  17. Probing the Density Structure of 48 Librae's Circumstellar Disk

    Science.gov (United States)

    Silaj, J.; Jones, C. E.; Carciofi, A. C.; Escolano, C.; Tycner, C.

    2016-11-01

    48 Librae is a well-known Be shell star that exhibits spectacular cyclic V/R asymmetries in its Balmer emission lines. In this work, we use the HDUST code to investigate the disk density structure required to produce this signature. By modelling one representative Hα profile, we obtain the two initial densities required to match each peak, and from this we infer the average initial disk density. Furthermore, we investigate the parameters of the central star by modelling the SED, and we constrain the inclination angle of the system with polarization measurements. We find 48 Lib is best represented by a B3V central star surrounded by a very dense disk with an average initial density of 1.1×10-10 g cm-3, and that the system is oriented at 85°.

  18. Comprehensive Census and Complete Characterization of Nearby Debris Disk Stars

    CERN Document Server

    Cotten, Tara

    2015-01-01

    Debris disks are intimately linked to planetary system evolution since the rocky material surrounding the host stars is due to secondary generation from the collisions of planetesimals. With the conclusion and lack of future large scale infrared excess survey missions, it is time to summarize the history of using excess emission in the infrared as a tracer of debris. We have compiled a catalog of infrared excess stars from peer reviewed articles and performed an extensive search for new debris disks by cross correlating the Tycho 2 and AllWISE catalogs. This study will examine each debris disk stars parameters obtained through high resolution spectroscopy at various facilities. We will maintain a webpage devoted to these infrared excess sources and provide various resources related to our catalog creation, SED fitting, and data reduction.

  19. Imaging Protoplanetary Disks with a Square Kilometer Array

    CERN Document Server

    Wilner, D J

    2004-01-01

    The recent detections of extrasolar giant planets has revealed a surprising diversity of planetary system architectures, with many very unlike our Solar System. Understanding the origin of this diversity requires multi-wavelength studies of the structure and evolution of the protoplanetary disks that surround young stars. Radio astronomy and the Square Kilometer Array will play a unique role in these studies by imaging thermal dust emission in a representative sample of protoplanetary disks at unprecedented sub-AU scales in the innermost regions, including the ``habitable zone'' that lies within a few AU of the central stars. Radio observations will probe the evolution of dust grains up to centimeter-sized ``pebbles'', the critical first step in assembling giant planet cores and terrestrial planets, through the wavelength dependence of dust emissivity, which provides a diagnostic of particle size. High resolution images of dust emission will show directly mass concentrations and features in disk surface densi...

  20. Misaligned Disks in the Binary Protostar IRS 43

    CERN Document Server

    Brinch, Christian; Hogerheijde, Michiel R; Nelson, Richard P; Gressel, Oliver

    2016-01-01

    Recent high angular resolution ($\\sim$0.2") ALMA observations of the 1.1 mm continuum and of HCO+ J=3-2 and HCN J=3-2 gas towards the binary protostar IRS 43 reveal multiple Keplerian disks which are significantly misaligned ($\\gt$ 60$^\\circ$), both in inclination and position angle and also with respect to the binary orbital plane. Each stellar component has an associated circumstellar disk while the binary is surrounded by a circumbinary disk. Together with archival VLA measurements of the stellar positions over 25 years, and assuming a circular orbit, we use our continuum measurements to determine the binary separation, a = 74 $\\pm$ 4 AU, and its inclination, i $\\lt$ 30$^\\circ$. The misalignment in this system suggests that turbulence has likely played a major role in the formation of IRS 43.

  1. DISKS SURROUNDING MASSIVE STARS: WHEN COMPUTATIONAL MODELS ARE CONFRONTED BY OBSERVATIONS

    Directory of Open Access Journals (Sweden)

    C. E. Jones

    2010-01-01

    Full Text Available Las estrellas masivas se encuentran insertas en materia gaseosa circunstelar; a veces tambi en se encuentra polvo y mol culas. Aunque los discos son a veces demasiado peque os para ser detectados directamente, este material puede ser detectado en el espectro de la radiaci n que observamos de la estrella. A menudo, el material circunestelar posee una distribuci n tipo disco, pero el proceso f sico que forma y mantiene estos discos no es bien entendido. Las estrellas Be son un ejemplo de rotadores r pidos, estrellas calientes, cuyo esp ctro enlongitudes de onda ptica muestra ambas l neas de hidr geno en emisi n y frecuentemente, l neas de emisi n de metales una vez ionizados, debido a la presencia del disco. Hemos calculado modelos te ricos computacionales de discos circunestelares de estrellas Be, usando unc digo que incorpora un n mero de mejoras sobre tratamientos previos de la estructura t rmica del disco, incluyendo una composici n qu mica realista. Estos modelos pueden predecir los per les de l nea espectrales y anchos equivalentes, la distribuci n espectral de energ a y la polarizaci n del continuo. Los modelos con estructura t rmica precisa y campos de radiaci n son esenciales para interpretar correctamente las observaciones. Estos modelos pueden tambi n predecir im genes en el plano del cielo en importantes longitudes de onda y por lo tanto est n idealmente adecuados para compararlos con observaciones interferom etricas. Demuestro que nuestros modelos pueden ser restringidos por comparaci n directa con observaciones interferom tricas pticas para la regi n que emite H y por per les de l nea H contempor neos. Las comparaciones detalladas de nuestras predicciones con interferometr a y espectroscop a de H entregan ajustadas restricciones a los par metros libres del modelo para estos sistemas estrella-disco.

  2. Disks Surrounding Massive Stars: When Computational Models are Confronted by Observations

    Science.gov (United States)

    2010-01-01

    circunestelar posee una distribución tipo disco, pero el proceso f́ısico que forma y mantiene estos discos no es bien entendido. Las estrellas Be son un...models that correspond to the best fit from both interferometry and Hα mod- eling. Please see Jones et al. (2008) for a discussion of the errors . We find

  3. Circumstellar Disks of the Most Vigorously Accreting Young Stars

    CERN Document Server

    Liu, Hauyu Baobab; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-01-01

    Young stellar objects (YSOs) may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. We report our high angular resolution, coronagraphic near-infrared polarization imaging observations using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) of the Subaru 8.2 m Telescope, towards four YSOs which are undergoing luminous accretion outbursts. The obtained infrared images have verified the presence of several hundred AUs scale arms and arcs surrounding these YSOs. In addition, our hydrodynamics simulations and radiative transfer models further demonstrate that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation p...

  4. Audit: Automated Disk Investigation Toolkit

    Directory of Open Access Journals (Sweden)

    Umit Karabiyik

    2014-09-01

    Full Text Available Software tools designed for disk analysis play a critical role today in forensics investigations. However, these digital forensics tools are often difficult to use, usually task specific, and generally require professionally trained users with IT backgrounds. The relevant tools are also often open source requiring additional technical knowledge and proper configuration. This makes it difficult for investigators without some computer science background to easily conduct the needed disk analysis. In this paper, we present AUDIT, a novel automated disk investigation toolkit that supports investigations conducted by non-expert (in IT and disk technology and expert investigators. Our proof of concept design and implementation of AUDIT intelligently integrates open source tools and guides non-IT professionals while requiring minimal technical knowledge about the disk structures and file systems of the target disk image.

  5. Ringed accretion disks: equilibrium configurations

    CERN Document Server

    Pugliese, D

    2015-01-01

    We investigate a model of 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 be then 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 pr...

  6. IBM 3390 Hard Disk Platter

    CERN Multimedia

    1991-01-01

    The 3390 disks rotated faster than those in the previous model 3380. Faster disk rotation reduced rotational delay (ie. the time required for the correct area of the disk surface to move to the point where data could be read or written). In the 3390's initial models, the average rotational delay was reduced to 7.1 milliseconds from 8.3 milliseconds for the 3380 family.

  7. Disks and Outflows

    Science.gov (United States)

    Rodriguez, L. F.

    2002-05-01

    The presence of disks and outflows characterizes the earliest stages of stellar evolution. I will review recent results that exemplify how the radio observations have become powerful tools in the study of these extremely young objects. Binarity and multiplicity seem to be factors that we are only starting to understand. Outflows are now seen as laboratories for the chemistry of shocked regions. Finally, the efforts to extend the paradigm for low-mass stellar formation to more massive protostars can be tested critically in the radio wavelengths. I acknowledge the support from CONACyT, Mexico.

  8. VLT imaging of the β Pictoris gas disk

    Science.gov (United States)

    Nilsson, R.; Brandeker, A.; Olofsson, G.; Fathi, K.; Thébault, Ph.; Liseau, R.

    2012-08-01

    Context. Circumstellar debris disks older than a few Myr should be largely devoid of primordial gas remaining from the protoplanetary disk phase. Tracing the origin of observed atomic gas in Keplerian rotation in the edge-on debris disk surrounding the ~12 Myr old star β Pictoris requires more detailed information about its spatial distribution than has previously been acquired by limited slit spectroscopy. Especially indications of asymmetries and presence of Ca ii gas at high disk latitudes call for additional investigation to exclude or confirm its connection to observed dust structures or suggested cometary bodies on inclined eccentric orbits. Aims: We set out to recover a complete image of the Fe i and Ca ii gas emission around β Pic by spatially resolved, high-resolution spectroscopic observations to better understand the morphology and origin of the gaseous disk component. Methods: The multiple fiber facility FLAMES/GIRAFFE at the Very Large Telescope (VLT), with the large integral-field-unit ARGUS, was used to obtain spatially resolved optical spectra (from 385.9 to 404.8 nm) in four regions covering the northeast and southwest side of the disk. Emission lines from Fe i (at 386.0 nm) and Ca ii (at 393.4 and 396.8 nm) were mapped and could be used to fit a parametric function for the disk gas distribution, using a gas-ionisation code for gas-poor debris disks. Results: Both Fe i and Ca ii emission are clearly detected, with the former dominating along the disk midplane, and the latter revealing vertically more extended gas. The surface intensity of the Fe i emission is lower but more extended in the northeast (reaching the 210 AU limit of our observations) than in the southwest, while Ca ii shows the opposite asymmetry. The modelled Fe gas disk profile shows a linear increase in scale height with radius, and a vertical profile that suggests dynamical interaction with the dust. We also qualitatively demonstrate that the Ca ii emission profile can be

  9. Acceleration and Collimation of Relativistic Magnetohydrodynamic Disk Winds

    Science.gov (United States)

    Porth, Oliver; Fendt, Christian

    2010-02-01

    We perform axisymmetric relativistic magnetohydrodynamic simulations to investigate the acceleration and collimation of jets and outflows from disks around compact objects. Newtonian gravity is added to the relativistic treatment in order to establish the physical boundary condition of an underlying accretion disk in centrifugal and pressure equilibrium. The fiducial disk surface (respectively a slow disk wind) is prescribed as boundary condition for the outflow. We apply this technique for the first time in the context of relativistic jets. The strength of this approach is that it allows us to run a parameter study in order to investigate how the accretion disk conditions govern the outflow formation. Substantial effort has been made to implement a current-free, numerical outflow boundary condition in order to avoid artificial collimation present in the standard outflow conditions. Our simulations using the PLUTO code run for 500 inner disk rotations and on a physical grid size of 100 × 200 inner disk radii. The simulations evolve from an initial state in hydrostatic equilibrium and an initially force-free magnetic field configuration. Two options for the initial field geometries are applied—an hourglass-shaped potential magnetic field and a split monopole field. Most of our parameter runs evolve into a steady state solution which can be further analyzed concerning the physical mechanism at work. In general, we obtain collimated beams of mildly relativistic speed with Lorentz factors up to 6 and mass-weighted half-opening angles of 3-7 deg. The split-monopole initial setup usually results in less collimated outflows. The light surface of the outflow magnetosphere tends to align vertically—implying three relativistically distinct regimes in the flow—an inner subrelativistic domain close to the jet axis, a (rather narrow) relativistic jet and a surrounding subrelativistic outflow launched from the outer disk surface—similar to the spine-sheath structure

  10. ALMA SiO (5-4) Observations: Protostellar Outflows near Sgr A*

    Science.gov (United States)

    Yusef-Zadeh, Farhad; Royster, M.; Wardle, M.; Arendt, R.; Bushouse, H. A.; Lis, D. C.; Pound, M. W.; Roberts, D. A.; Whitney, B.; Wootten, A.

    2013-06-01

    ALMA observations of the Galactic center resulted in the detection of a number of SiO (5-4) clumps of molecular gas in the 2-pc molecular ring orbiting Sgr A*. Eleven clumps of SiO (5-4) are also found within 0.6pc (15'') of Sgr A*. The three SiO (5-4) clumps closest to Sgr A* show the largest central velocities of ~150 km/s and broadest asymmetric linewidths with full width zero intensity (FWZI) 110-147 km/s. Other clumps beyond the inner 15'' show narrow linewidths (FWZI ~18-56 km/s. Using CARMA SiO (2-1) data, LVG modeling of the broad velocity clumps, constrain the H2 gas density (3-9)x10^5 cm^-3 for an assumed kinetic temperature 100-200K. The SiO clumps combined with evidence of YSO candidates are interpreted as highly embedded protostellar outflows, signifying an early stage of massive star formation near Sgr A* in the last 10^4-10^5 years. Star formation near Sgr A* is forbidden, unless the gas density is large enough for self-gravity to overcome the strong tidal shear of the back hole. We discuss different mechanisms that increase the gas density so that star formation can take place in this tidally stressed environment.

  11. Energetic radiation and the sulfur chemistry of protostellar envelopes: Submillimeter interferometry of AFGL 2591

    CERN Document Server

    Benz, A O; Bourke, T L; vanderTak, F F S; Van Dishoeck, E F; Jørgensen, J K

    2007-01-01

    CONTEXT: The chemistry in the inner few thousand AU of accreting envelopes around young stellar objects is predicted to vary greatly with far-UV and X-ray irradiation by the central star. Aim We search for molecular tracers of high-energy irradiation by the protostar in the hot inner envelope. METHODS: The Submillimeter Array (SMA) has observed the high-mass star forming region AFGL 2591 in lines of CS, SO, HCN, HCN(v2=1), and HC15N with 0.6" resolution at 350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc. The SMA observations are compared with the predictions of a chemical model fitted to previous single-dish observations. RESULTS: The CS and SO main peaks are extended in space at the FWHM level, as predicted in the model assuming protostellar X-rays. However, the main peak sizes are found smaller than modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and HC15N, but not SO and HCN(v2=1), show pedestal emissions at radii of about 3500 AU that are not predict...

  12. The Herschel-HIFI view of mid-IR quiet massive protostellar objects

    CERN Document Server

    Herpin, F; Jacq, T; Braine, J; van der Tak, F; Wyrowski, F; van Dishoeck, E F; Baudry, A; Bontemps, S; Kristensen, L; Schmalzl, M; Mata, J

    2016-01-01

    We present Herschel/HIFI observations (WISH KP) of 14 water lines in a small sample of galactic massive protostellar objects: NGC6334I(N), DR21(OH), IRAS16272-4837, and IRAS05358+3543. We analyze the gas dynamics from the line profiles. Through modeling of the observations using RATRAN, we estimate outflow, infall, turbulent velocities, molecular abundances, and investigate any correlation with the evolutionary status of each source. The molecular line profiles exhibit a broad component coming from the shocks along the cavity walls associated with the protostars, and an infalling (or expansion for IRAS05358+3543) and passively heated envelope component, with highly supersonic turbulence likely increasing with the distance from the center. Accretion rates between 6.3 10^{-5} and 5.6 10^{-4} \\msun yr^{-1} are derived from the infall observed in three of our sources. The outer water abundance is estimated to be at the typical value of a few 10^{-8} while the inner abundance varies from 1.7 10^{-6} to 1.4 10^{-4}...

  13. Turbulent mixing layers in supersonic protostellar outflows, with application to DG Tauri

    CERN Document Server

    White, Marc C; Sutherland, Ralph S; Salmeron, Raquel; McGregor, Peter J

    2015-01-01

    Turbulent entrainment processes may play an important role in the outflows from young stellar objects at all stages of their evolution. In particular, lateral entrainment of ambient material by high-velocity, well-collimated protostellar jets may be the cause of the multiple emission-line velocity components observed in the microjet-scale outflows driven by classical T Tauri stars. Intermediate-velocity outflow components may be emitted by a turbulent, shock- excited mixing layer along the boundaries of the jet. We present a formalism for describing such a mixing layer based on Reynolds decomposition of quantities measuring fundamental properties of the gas. In this model, the molecular wind from large disc radii provides a continual supply of material for entrainment. We calculate the total stress profile in the mixing layer, which allows us to estimate the dissipation of turbulent energy, and hence the luminosity of the layer. We utilize MAPPINGS IV shock models to determine the fraction of total emission t...

  14. From Prestellar to Protostellar Cores II. Time Dependence and Deuterium Fractionation

    CERN Document Server

    Aikawa, Yuri; Hersant, Franck; Garrod, Robin T; Herbst, Eric

    2012-01-01

    We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from a dense-cloud core to a protostellar core, by solving a gas-grain reaction network applied to a 1-D radiative hydrodynamic model with infalling fluid parcels. Spatial distributions of gas and ice-mantle species are calculated at the first-core stage, and at times after the birth of a protostar. Gas-phase methanol and methane are more abundant than CO at radii $r\\lesssim 100$ AU in the first-core stage, but gradually decrease with time, while abundances of larger organic species increase. The warm-up phase, when complex organic molecules are efficiently formed, is longer-lived for those fluid parcels in-falling at later stages. The formation of unsaturated carbon chains (warm carbon-chain chemistry) is also more effective in later stages; C$^+$, which reacts with CH$_4$ to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are stro...

  15. Molecules with a peptide link in protostellar shocks: a comprehensive study of L1157

    CERN Document Server

    Mendoza, E; López-Sepulcre, A; Ceccarelli, C; Codella, C; Boechat-Roberty, H M; Bachiller, R

    2014-01-01

    Interstellar molecules with a peptide link -NH-C(=O)-, like formamide (NH$_2$CHO), acetamide (NH$_2$COCH$_3$) and isocyanic acid (HNCO) are particularly interesting for their potential role in pre-biotic chemistry. We have studied their emission in the protostellar shock regions L1157-B1 and L1157-B2, with the IRAM 30m telescope, as part of the ASAI Large Program. Analysis of the line profiles shows that the emission arises from the outflow cavities associated with B1 and B2. Molecular abundance of $\\approx~(0.4-1.1)\\times 10^{-8}$ and $(3.3-8.8)\\times 10^{-8}$ are derived for formamide and isocyanic acid, respectively, from a simple rotational diagram analysis. Conversely, NH$_2$COCH$_3$ was not detected down to a relative abundance of a few $\\leq 10^{-10}$. B1 and B2 appear to be among the richest Galactic sources of HNCO and NH$_2$CHO molecules. A tight linear correlation between their abundances is observed, suggesting that the two species are chemically related. Comparison with astrochemical models favou...

  16. On the Origin of C4H and CH3OH in Protostellar Envelopes

    Science.gov (United States)

    Lindberg, Johan E.; Charnley, Steven B.; Cordiner, Martin A.

    2016-12-01

    The formation pathways of different types of organic molecules in protostellar envelopes and other regions of star formation are subjects of intense current interest. We present here observations of C4H and CH3OH, tracing two distinct groups of interstellar organic molecules, toward 16 protostars in the Ophiuchus and Corona Australis molecular clouds. Together with observations in the literature, we present C4H and CH3OH data from single-dish observations of 40 embedded protostars. We find no correlation between the C4H and CH3OH column densities in this large sample. Based on this lack of correlation, a difference in line profiles between C4H and CH3OH, and previous interferometric observations of similar sources, we propose that the emission from these two molecules is spatially separated, with the CH3OH tracing gas that has been transiently heated to high (˜70-100 K) temperatures and the C4H tracing the cooler large-scale envelope where CH4 molecules have been liberated from ices. These results provide insight in the differentiation between hot corino and warm carbon-chain chemistry in embedded protostars. Based on observations with the Kitt Peak 12 m telescope telescope and the Atacama Pathfinder EXperiment (APEX) telescope. The Kitt Peak 12 m telescope is operated by the Arizona Radio Observatory (ARO), Steward Observatory, University of Arizona. APEX is a collaboration between the Max Planck Institute for Radio Astronomy, the European Southern Observatory, and the Onsala Space Observatory.

  17. Identifying and analysing protostellar disc fragments in smoothed particle hydrodynamics simulations

    Science.gov (United States)

    Hall, Cassandra; Forgan, Duncan; Rice, Ken

    2017-09-01

    We present a new method of identifying protostellar disc fragments in a simulation based on density derivatives, and analyse our data using this and the existing CLUMPFIND method, which is based on an ordered search over all particles in gravitational potential energy. Using smoothed particle hydrodynamics, we carry out nine simulations of a 0.25 M⊙ disc around a 1 M⊙ star, all of which fragment to form at least two bound objects. We find that when using all particles ordered in gravitational potential space, only fragments that survive the duration of the simulation are detected. When we use the density derivative method, all fragments are detected, so the two methods are complementary, as using the two methods together allows us to identify all fragments, and to then determine those that are likely to be destroyed. We find a tentative empirical relationship between the dominant azimuthal wavenumber in the disc m and the maximum semimajor axis a fragment may achieve in a simulation, such that amax∝1/m. We find the fragment destruction rate to be around half that predicted from population synthesis models. This is due to fragment-fragment interactions in the early gas phase of the disc, which can cause scattering and eccentricity pumping on short time-scales, and affects the fragment's internal structure. We therefore caution that measurements of eccentricity as a function of semimajor axis may not necessarily constrain the formation mechanism of giant planets and brown dwarfs.

  18. Simulations of protostellar collapse using multigroup radiation hydrodynamics. II. The second collapse

    CERN Document Server

    Vaytet, N; Audit, E; Commercon, B; Masson, J; Ferguson, J; Delahaye, F

    2013-01-01

    Star formation begins with the gravitational collapse of a dense core inside a molecular cloud. As the collapse progresses, the centre of the core begins to heat up as it becomes optically thick. The temperature and density in the centre eventually reach high enough values where fusion reactions can ignite; the protostar is born. This sequence of events entail many physical processes, of which radiative transfer is of paramount importance. Many simulations of protostellar collapse make use of a grey treatment of radiative transfer coupled to the hydrodynamics. However, interstellar gas and dust opacities present large variations as a function of frequency. In this paper, we follow-up on a previous paper on the collapse and formation of Larson's first core using multigroup radiation hydrodynamics (Paper I) by extending the calculations to the second phase of the collapse and the formation of Larson's second core. We have made the use of a non-ideal gas equation of state as well as an extensive set of spectral ...

  19. A Self-Perpetuating Catalyst for the Production of Complex Organic Molecules in Protostellar Nebulae

    Science.gov (United States)

    Nuth, Joseph A.; Johnson, N. M.

    2010-01-01

    The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. Many mechanisms may contribute to the total organic content in protostellar nebulae, ranging from organics formed via ion-molecule and atom-molecule reactions in the cold dark clouds from which such nebulae collapse, to similar ion-molecule and atom-molecule reactions in the dark regions of the nebula far from the proto star, to gas phase reactions in sub-nebulae around growing giant planets and in the nebulae themselves. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. The Haber-Bosch catalytic reduction of N2 by hydrogen was thought to produce the reduced nitrogen found in meteorites. However, the clean iron metal surfaces that catalyze these reactions are easily poisoned via reaction with any number of molecules, including the very same complex organics that they produce and both reactions work more efficiently in the hot regions of the nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Although none work as well as pure iron grains, and all produce a wide range of organic products rather than just pure methane, these materials are not truly catalysts.

  20. The end of star formation in Chamaeleon I ? A LABOCA census of starless and protostellar cores

    CERN Document Server

    Belloche, A; Parise, B; André, Ph; Hatchell, J; Jørgensen, J K; Bontemps, S; Weiß, A; Menten, K M; Muders, D; 10.1051/0004-6361/201015733

    2011-01-01

    Chamaeleon I is the most active region in terms of star formation in the Chamaeleon molecular cloud complex. Its population of prestellar and protostellar cores is not known and a controversy exists concerning its history of star formation. Our goal is to characterize the earliest stages of star formation in this cloud. We used the bolometer array LABOCA at APEX to map the cloud in dust continuum emission at 870 micron. The detected sources are analysed by carefully taking into account the spatial filtering inherent in the data reduction process. A search for associations with YSOs is performed using Spitzer data and the SIMBAD database. Most of the detected 870 micron emission is distributed in 5 filaments. We identify 59 starless cores, one candidate first hydrostatic core, and 21 sources associated with more evolved YSOs. The starless cores are only found above a visual extinction threshold of 5 mag. They are less dense than those detected in other nearby molecular clouds by a factor of a few on average. T...

  1. Supermassive star formation via episodic accretion: protostellar disc instability and radiative feedback efficiency

    CERN Document Server

    Sakurai, Yuya; Hosokawa, Takashi; Yoshida, Naoki; Omukai, Kazuyuki; Yorke, Harold W

    2015-01-01

    The formation of SMSs is a potential pathway to seed SMBHs in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper we study the evolution of an accreting SMS and its UV emissivity under conditions of realistic variable accretion from a self-gravitating circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the long-term protostellar accretion until the stellar mass exceeds $10^4~M_\\odot$. The disc fragments due to gravitational instability, creating a number of small clumps that rapidly migrate inward to fall onto the star. The resulting accretion history is thus highly time-dependent: short episodic accretion bursts are followed by longer, relative quiescent phases. We show that the circumstellar disc for the so-called direct collapse model is more unstable and generates greater variability over shorter timescales than normal Pop III cases. We conduct a post-process stellar evolution calculati...

  2. On the origin of C$_4$H and CH$_3$OH in protostellar envelopes

    CERN Document Server

    Lindberg, Johan E; Cordiner, Martin A

    2016-01-01

    The formation pathways of different types of organic molecules in protostellar envelopes and other regions of star formation are subjects of intense current interest. We here present observations of C$_4$H and CH$_3$OH, tracing two distinct groups of interstellar organic molecules, toward 16 protostars in the Ophiuchus and Corona Australis molecular clouds. Together with observations in the literature, we present C$_4$H and CH$_3$OH data from single-dish observations of 40 embedded protostars. We find no correlation between the C$_4$H and CH$_3$OH column densities in this large sample. Based on this lack of correlation, a difference in line profiles between C$_4$H and CH$_3$OH, and previous interferometric observations of similar sources, we propose that the emission from these two molecules is spatially separated, with the CH$_3$OH tracing gas that has been transiently heated to high ($\\sim$70-100 K) temperatures, and the C$_4$H tracing the cooler large-scale envelope where CH$_4$ molecules have been liberat...

  3. On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

    CERN Document Server

    Yellin-Bergovoy, Ron; Umurhan, Orkan M

    2015-01-01

    The dynamical response of edge waves under the influence of self-gravity is examined in an idealized two-dimensional model of a proto-stellar disc, characterized in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius r0. The fluid in basic state is prescribed to rotate with a Keplerian profile $\\Omega_k(r)\\sim r^{-3/2}$ modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabilizer irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of...

  4. The role of cosmic rays on magnetic field diffusion and the formation of protostellar discs

    CERN Document Server

    Padovani, Marco; Hennebelle, Patrick; Commerçon, Benoît; Joos, Marc

    2014-01-01

    The formation of protostellar discs is severely hampered by magnetic braking, as long as magnetic fields remain frozen in the gas. The latter condition depends on the levels of ionisation that characterise the innermost regions of a collapsing cloud. The chemistry of dense cloud cores and, in particular, the ionisation fraction is largely controlled by cosmic rays. The aim of this paper is to evaluate whether the attenuation of the flux of cosmic rays expected in the regions around a forming protostar is sufficient to decouple the field from the gas, thereby influencing the formation of centrifugally supported disc. We adopted the method developed in a former study to compute the attenuation of the cosmic-ray flux as a function of the column density and the field strength in clouds threaded by poloidal and toroidal magnetic fields. We applied this formalism to models of low- and high-mass star formation extracted from numerical simulations of gravitational collapse that include rotation and turbulence. For ea...

  5. Cosmic-ray propagation at small scale: a support for protostellar disc formation

    CERN Document Server

    Padovani, Marco; Hennebelle, Patrick; Commercon, Benoît; Joos, Marc

    2015-01-01

    As long as magnetic fields remain frozen into the gas, the magnetic braking prevents the formation of protostellar discs. This condition is subordinate to the ionisation fraction characterising the inmost parts of a collapsing cloud. The ionisation level is established by the number and the energy of the cosmic rays able to reach these regions. Adopting the method developed in our previous studies, we computed how cosmic rays are attenuated as a function of column density and magnetic field strength. We applied our formalism to low- and high-mass star formation models obtained by numerical simulations of gravitational collapse that include rotation and turbulence. In general, we found that the decoupling between gas and magnetic fields, condition allowing the collapse to go ahead, occurs only when the cosmic-ray attenuation is taken into account with respect to a calculation in which the cosmic-ray ionisation rate is kept constant. We also found that the extent of the decoupling zone also depends on the dust ...

  6. Deeply Embedded Protostellar Population in the 20 km s-1 Cloud of the Central Molecular Zone

    CERN Document Server

    Lu, Xing; Kauffmann, Jens; Pillai, Thushara; Longmore, Steven N; Kruijssen, J M Diederik; Battersby, Cara; Gu, Qiusheng

    2015-01-01

    We report the discovery of a population of deeply embedded protostellar candidates in the 20 km s$^{-1}$ cloud, one of the massive molecular clouds in the Central Molecular Zone (CMZ) of the Milky Way, using interferometric submillimeter continuum and H$_2$O maser observations. The submillimeter continuum emission shows five 1-pc scale clumps, each of which further fragments into several 0.1-pc scale cores. We identify 17 dense cores, among which 12 are gravitationally bound. Among the 18 H$_2$O masers detected, 13 coincide with the cores and probably trace outflows emanating from the protostars. There are also 5 gravitationally bound dense cores without H$_2$O maser detection. In total the 13 masers and 5 cores may represent 18 protostars with spectral types later than B1 or potential growing more massive stars at earlier evolutionary stage, given the non-detection in the centimeter radio continuum. In combination with previous studies of CH$_3$OH masers, we conclude that the star formation in this cloud is ...

  7. The HIFI spectral survey of AFGL 2591 (CHESS). III. Chemical structure of the protostellar envelope

    CERN Document Server

    Kazmierczak-Barthel, Maja; van der Tak, Floris; Chavarría, Luis; van der Wiel, Matthijs

    2014-01-01

    We aim to understand the rich chemical composition of AFGL 2591, a prototypical isolated high-mass star-forming region. Based on HIFI and JCMT data, the molecular abundances of species found in the protostellar envelope of AFGL 2591 were derived with the Monte Carlo radiative transfer code RATRAN, assuming either constant values or 1D stepwise radial profiles as abundance distributions. The reconstructed 1D abundances were compared with the results of time-dependent gas-grain chemical modeling, considering ages of 10,000 to 50,000 years, cosmic-ray ionization rates of 0.5 to 50 times 10^-16 s^-1, uniformly-sized 0.1-1 micron dust grains, a dust/gas ratio of 1%, and several sets of initial molecular abundances with C/O 1. Constant abundance models give good fits to the data for CO, CN, CS, HCO+, H2CO, N2H+, C2H, NO, OCS, OH, H2CS, O, C, C+, and CH. Models with an abundance jump at 100 K give good fits to the data for NH3, SO, SO2, H2S, H2O, HCl, and CH3OH. For HCN and HNC, the best models have an abundance jum...

  8. Complex Scattered Radiation Fields and Multiple Magnetic Fields in the Protostellar Cluster in NGC 2264

    CERN Document Server

    Kwon, Jungmi; Kandori, Ryo; Kusakabe, Nobuhiko; Hashimoto, Jun; Nakajima, Yasushi; Nakamura, Fumitaka; Nagayama, Takahiro; Nagata, Tetsuya; Hough, James H; Werner, Michael W; Teixeira, Paula S

    2011-01-01

    Near-infrared (IR) imaging polarimetry in the J, H, and Ks bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebulae clusters (IRNCs) associated with NGC 2264 IRS 2 and IRAS 12 S1 core were detected as well as local infrared reflection nebulae (IRNe). The illuminating sources of the IRNe were identified with known or new near- and mid-IR sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main sequence stars were selected to trace the magnetic field (MF) structure of the molecular cloud. The mean polarization position angle of the point-like sources is 81 \\pm 29 degree in the cluster core, and 58 \\pm 24 degree in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the MF in the observed region of the cloud. The Chandrasekhar-Fermi ...

  9. Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A

    CERN Document Server

    Goncalves, Jose; Girart, Josep M

    2008-01-01

    Magnetic fields are believed to play a crucial role in the process of star formation. We compare high-angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a low-mass protostar, with models of the collapse of magnetized molecular cloud cores. Assuming a uniform dust alignment efficiency, we computed the Stokes parameters and synthetic polarization maps from the model density and magnetic field distribution by integrations along the line-of-sight and convolution with the interferometric response. The synthetic maps are in good agreement with the data. The best-fitting models were obtained for a protostellar mass of 0.8 solar masses, of age 9e4 yr, formed in a cloud with an initial mass-to-flux ratio ~2 times the critical value. The magnetic field morphology in NGC 1333 IRAS 4A is consistent with the standard theoretical scenario for the formation of solar-type stars, where well-ordered, large-scale, rather than turbulent, magnetic fields ...

  10. Mapping water in protostellar outflows with Herschel: PACS and HIFI observations of L1448-C

    CERN Document Server

    Nisini, B; Antoniucci, S; Benedettini, M; Codella, C; Giannini, T; Lorenzani, A; Liseau, R; Tafalla, M; Bjerkeli, P; Cabrit, S; Caselli, P; Kristensen, L; Neufeld, D; Melnick, G; van Dishoeck, E F

    2012-01-01

    We investigate on the spatial and velocity distribution of H2O along the L1448 outflow, its relationship with other tracers, and its abundance variations, using maps of the o-H2O 1_{10}-1_{01} and 2_{12}-1_{01} transitions taken with the Herschel-HIFI and PACS instruments, respectively. Water emission appears clumpy, with individual peaks corresponding to shock spots along the outflow. The bulk of the 557 GHz line is confined to radial velocities in the range \\pm 10-50 km/s but extended emission associated with the L1448-C extreme high velocity (EHV) jet is also detected. The H2O 1_{10}-1_{01}/CO(3-2) ratio shows strong variations as a function of velocity that likely reflect different and changing physical conditions in the gas responsible for the emissions from the two species. In the EHV jet, a low H2O/SiO abundance ratio is inferred, that could indicate molecular formation from dust free gas directly ejected from the proto-stellar wind. We derive averaged Tkin and n(H2) values of about 300-500 K and 5 10^...

  11. A candidate protostellar object in the L 1457/MBM 12 cloud

    Science.gov (United States)

    Heithausen, A.; Böttner, C.

    2010-10-01

    Aims: The association of young T Tauri stars, MBM 12A, indicates that L 1457 was forming stars not too long ago. With our study we want to find out whether there are still signs of ongoing star formation in that cloud. Methods: Using the Max-Planck-Millimeter-Bolometer MAMBO at the IRAM 30 m telescope, we obtained a map of about 8'×8' centered on L 1457 in the dust continuum emission at 230 GHz. Towards the most intense regions in our bolometer map, we obtained spectra at high angular resolution in the CS (2 → 1) and the N2H+ (1 → 0) lines using the IRAM 30 m telescope. Results: We find that the cold dust in L 1457 is concentrated in several small cores with high H2 column densities and solar masses. The density profiles of the cores are inconsistent with a sphere with constant density. These cores are closer to virial equilibrium than is the cloud as a whole. Data from the VLA and Spitzer archives reveal two point sources in the direction of one dust core. One of the sources is probably a distant quasar, whereas the other source is projected right on a local maximum of our dust map and shows characteristics of a protostellar object.

  12. The Role of Angular Momentum Transport in Establishing the Accretion Rate--Protostellar Mass Correlation

    CERN Document Server

    DeSouza, Alexander L

    2016-01-01

    We model the mass accretion rate $\\dot{M}$ to stellar mass $M_*$ correlation that has been inferred from observations of intermediate to upper mass T Tauri stars---that is $\\dot{M} \\propto M_*^{1.3 \\pm 0.3}$. We explain this correlation within the framework of quiescent disk evolution, in which accretion is driven largely by gravitational torques acting in the bulk of the mass and volume of the disk. Stresses within the disk arise from the action of gravitationally driven torques parameterized in our 1D model in terms of Toomre's $Q$ criterion. We do not model the hot inner sub-AU scale region of the disk that is likely stable according to this criterion, and appeal to other mechanisms to remove or redistribute angular momentum and allow accretion onto the star. Our model has the advantage of agreeing with large-scale angle-averaged values from more complex nonaxisymmetric calculations. The model disk transitions from an early phase (dominated by initial conditions inherited from the burst mode of accretion) ...

  13. Disk storage at CERN

    CERN Document Server

    Mascetti, L; Chan, B; Espinal, X; Fiorot, A; Labrador, H Gonz; Iven, J; Lamanna, M; Presti, G Lo; Mościcki, JT; Peters, AJ; Ponce, S; Rousseau, H; van der Ster, D

    2015-01-01

    CERN IT DSS operates the main storage resources for data taking and physics analysis mainly via three system: AFS, CASTOR and EOS. The total usable space available on disk for users is about 100 PB (with relative ratios 1:20:120). EOS actively uses the two CERN Tier0 centres (Meyrin and Wigner) with 50:50 ratio. IT DSS also provide sizeable on-demand resources for IT services most notably OpenStack and NFS-based clients: this is provided by a Ceph infrastructure (3 PB) and few proprietary servers (NetApp). We will describe our operational experience and recent changes to these systems with special emphasis to the present usages for LHC data taking, the convergence to commodity hardware (nodes with 200-TB each with optional SSD) shared across all services. We also describe our experience in coupling commodity and home-grown solution (e.g. CERNBox integration in EOS, Ceph disk pools for AFS, CASTOR and NFS) and finally the future evolution of these systems for WLCG and beyond.

  14. Disk storage at CERN

    Science.gov (United States)

    Mascetti, L.; Cano, E.; Chan, B.; Espinal, X.; Fiorot, A.; González Labrador, H.; Iven, J.; Lamanna, M.; Lo Presti, G.; Mościcki, JT; Peters, AJ; Ponce, S.; Rousseau, H.; van der Ster, D.

    2015-12-01

    CERN IT DSS operates the main storage resources for data taking and physics analysis mainly via three system: AFS, CASTOR and EOS. The total usable space available on disk for users is about 100 PB (with relative ratios 1:20:120). EOS actively uses the two CERN Tier0 centres (Meyrin and Wigner) with 50:50 ratio. IT DSS also provide sizeable on-demand resources for IT services most notably OpenStack and NFS-based clients: this is provided by a Ceph infrastructure (3 PB) and few proprietary servers (NetApp). We will describe our operational experience and recent changes to these systems with special emphasis to the present usages for LHC data taking, the convergence to commodity hardware (nodes with 200-TB each with optional SSD) shared across all services. We also describe our experience in coupling commodity and home-grown solution (e.g. CERNBox integration in EOS, Ceph disk pools for AFS, CASTOR and NFS) and finally the future evolution of these systems for WLCG and beyond.

  15. Contour detection by surround suppression of texture

    NARCIS (Netherlands)

    Petkov, Nicolai; Tavares, JMRS; Jorge, RMN

    2007-01-01

    Based on a keynote lecture at Complmage 2006, Coimbra, Oct. 20-21, 2006, an overview is given of our activities in modelling and using surround inhibition for contour detection. The effect of suppression of a line or edge stimulus by similar surrounding stimuli is known from visual perception studie

  16. Herschel Observations and Updated Spectral Energy Distributions of Five Sunlike Stars with Debris Disks

    Science.gov (United States)

    Dodson-Robinson, Sarah E.; Su, Kate Y. L.; Bryden, Geoff; Harvey, Paul; Green, Joel D.

    2016-12-01

    Observations from the Herschel Space Observatory have more than doubled the number of wide debris disks orbiting Sunlike stars to include over 30 systems with R > 100 AU. Here, we present new Herschel PACS and reanalyzed Spitzer MIPS photometry of five Sunlike stars with wide debris disks, from Kuiper Belt size to R > 150 AU. The disk surrounding HD 105211 is well resolved, with an angular extent of >14″ along the major axis, and the disks of HD 33636, HD 50554, and HD 52265 are extended beyond the PACS point-spread function size (50% of energy enclosed within radius 4.″23). HD 105211 also has a 24 μm infrared excess, which was previously overlooked, because of a poorly constrained photospheric model. Archival Spitzer IRS observations indicate that the disks have small grains of minimum radius a min ˜ 3 μm, although a min is larger than the radiation-pressure blowout size in all systems. If modeled as single-temperature blackbodies, the disk temperatures would all be <60 K. Our radiative transfer models predict actual disk radii approximately twice the radius of a model blackbody disk. We find that the Herschel photometry traces dust near the source population of planetesimals. The disk luminosities are in the range 2 × 10-5 ⩽ L/L ⊙ ⩽ 2 × 10-4, consistent with collisions in icy planetesimal belts stirred by Pluto-size dwarf planets.

  17. Large dust grains in the inner region of circumstellar disks

    CERN Document Server

    Isella, A; Testi, L; Isella, Andrea; Testi, Leonardo

    2006-01-01

    CONTEXT: Simple geometrical ring models account well for near-infrared interferometric observations of dusty disks surrounding pre-main sequence stars of intermediate mass. Such models demonstrate that the dust distribution in these disks has an inner hole and puffed-up inner edge consistent with theoretical expectations. AIMS: In this paper, we reanalyze the available interferometric observations of six intermediate mass pre-main sequence stars (CQ Tau, VV Ser, MWC 480, MWC 758, V1295 Aql and AB Aur) in the framework of a more detailed physical model of the inner region of the dusty disk. Our aim is to verify whether the model will allow us to constrain the disk and dust properties. METHODS: Observed visibilities from the literature are compared with theoretical visibilities from our model. With the assumption that silicates are the most refractory dust species, our model computes self-consistently the shape and emission of the inner edge of the dusty disk (and hence its visibilities for given interferometer...

  18. Evolution and instabilities of disks harboring super massive black holes

    CERN Document Server

    Curir, Anna; Murante, Giuseppe

    2010-01-01

    The bar formation is still an open problem in modern astrophysics. In this paper we present numerical simulation performed with the aim of analyzing the growth of the bar instability inside stellar-gaseous disks, where the star formation is triggered, and a central black hole is present. The aim of this paper is to point out the impact of such a central massive black hole on the growth of the bar. We use N-body-SPH simulations of the same isolated disk-to-halo mass systems harboring black holes with different initial masses and different energy feedback on the surrounding gas. We compare the results of these simulations with the one of the same disk without black hole in its center. We make the same comparison (disk with and without black hole) for a stellar disk in a fully cosmological scenario. A stellar bar, lasting 10 Gyrs, is present in all our simulations. The central black hole mass has in general a mild effect on the ellipticity of the bar but it is never able to destroy it. The black holes grow in di...

  19. Dust disks around old Pre Main-Sequence stars HST\\/NICMOS2 scattered light images and modeling

    CERN Document Server

    Augereau, J C; Mouillet, D; Ménard, F

    2000-01-01

    We present recent near-infrared detections of circumstellar disks around the two old PMS Herbig stars HD 141569 and HD 100546 obtained with the HST/NICMOS2 camera. They reveal extended structures larger than 350-400 AU in radius. While the HD 100546 disk appears as a continuous disk down to 40 AU, the HD 141569 environment seems more complex, splitted at least into two dust populations. As a convincing example, the full modeling of the disk surrounding HR 4796, another old PMS star, is detailed and confronted with more recent observations.

  20. Jet magnetically accelerated from disk-corona around a rotating black hole

    CERN Document Server

    Gong, Xiaolong

    2012-01-01

    A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole is proposed. In the disk-corona scenario, we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations. The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere. It is shown that jet power increases with the increasing black hole (BH) spin, and concentrates in the inner region of the disk-corona. In addition, we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism, and show that our jet formation mechanism can simulate almost all sources with high power jet, that fail to be explained by the Blandford-Znajek (BZ) process.

  1. Using High Speed Rotating Gas to Study Angular Momentum in Accretion Disks

    Science.gov (United States)

    Berrios, William; Greess, Samuel; Merino, Enrique; Ji, Hantao

    2013-10-01

    Accretion disks are a sheet of gas and dust which surrounds black holes and quasars. The angular momentum in accretion disks is one of the biggest mysteries in astrophysics. A machine was recently built to create accretion disks in a closed chamber. In order to study this, there are several important instruments that are used: a fog machine to see the accretion disks form within the chamber, a high speed camera to observe and record the formation of the accretion disks, and Particle Image Velocimetry (PIV) to analyze velocity profile of the rotating gas and better understand this phenomenon. By collecting relevant data and subsequent computational analysis, results from a previous experiment are reproduced, expanded and the new properties observed with this experiment are characterized. A discussion of any modifications done to the machine, technical challenges and preliminary results will be presented.

  2. Can X-rays clear a circumstellar disk in 2 years?

    Science.gov (United States)

    Guenther, Hans

    2013-09-01

    Young stars are born surrounded by primordial disks. Eventually, these proto-planetary disks vanish. Some systems later form a debris disk with small dust grains. Up until May 2008 our target TYC 8241 2652 1 showed strong IR emission from such a disk. Between 2008 and 2010 the IR emission dropped by two orders of magnitude, which means that the dust mass in the inner disk decreased by 90-99%. The cause is unknown, but several hypotheses require high X-ray activity. We propose to observe this target for 10 ks with ACIS-S. This pointing will verify the association of a close-by ROSAT and XMM-Newton slew survey source with TYC 8241 2652 1, confirm the X-ray flux and look for signatures of high X-ray activity such as high plasma temperatures and Ne/Fe abundance ratios.

  3. The effect of gaseous accretion disk on dynamics of the stellar cluster in AGN

    CERN Document Server

    Shukirgaliyev, Bekdaulet

    2016-01-01

    There is a supermassive black hole, a gaseous accretion disk and compact star cluster in the center of active galactic nuclei, as known today. So the activity of AGN can be represented as the result of interaction of these three subsystems. In this work we investigate the dynamical interaction of a central star cluster surrounding a supermassive black hole and a central accretion disk. The dissipative force acting on stars in the disk leads to an asymmetry in the phase space distribution of the central star cluster due to the rotating accretion disk. In our work we present some results of Stardisk model, where we see some changes in density and phase space of central star cluster due to influence of rotating gaseous accretion disk.

  4. CAN BLACK HOLE NEUTRINO-COOLED DISKS POWER SHORT GAMMA-RAY BURSTS?

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Tong; Gu, Wei-Min [Department of Astronomy and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen, Fujian 361005 (China); Lin, Yi-Qing [School of Opto-electronic and Communication Engineering, Xiamen University of Technology, Xiamen, Fujian 361024 (China); Hou, Shu-Jin, E-mail: tongliu@xmu.edu.cn [Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming, Yunnan 650011 (China)

    2015-06-10

    Stellar-mass black holes (BHs) surrounded by neutrino-dominated accretion flows (NDAFs) are plausible sources of power for gamma-ray bursts (GRBs) via neutrino emission and their annihilation. The progenitors of short-duration GRBs (SGRBs) are generally considered to be compact binary mergers. According to the simulation results, the disk mass of the NDAF is limited after merger events. We can estimate such disk masses using the current SGRB observational data and fireball model. The results show that the disk mass of a certain SGRB mainly depends on its output energy, jet opening angle, and central BH characteristics. Even for the extreme BH parameters, some SGRBs require massive disks, which approach or exceed the limits in simulations. We suggest that there may exist alternative MHD processes or mechanisms that increase the neutrino emission to produce SGRBs with reasonable BH parameters and disk masses.

  5. Can black-hole neutrino-cooled disks power short gamma-ray bursts?

    CERN Document Server

    Liu, Tong; Hou, Shu-Jin; Gu, Wei-Min

    2015-01-01

    Stellar-mass black holes (BHs) surrounded by neutrino-dominated accretion flows (NDAFs) are the plausible candidates to power gamma-ray bursts (GRBs) via neutrinos emission and their annihilation. The progenitors of short-duration GRBs (SGRBs) are generally considered to be compact binaries mergers. According to the simulation results, the disk mass of the NDAF has been limited after merger events. We can estimate such disk mass by using the current SGRB observational data and fireball model. The results show that the disk mass of a certain SGRB mainly depends on its output energy, jet opening angle, and central BH characteristics. Even for the extreme BH parameters, some SGRBs require massive disks, which approach or exceed the limits in simulations. We suggest that there may exist alternative magnetohydrodynamic processes or some mechanisms increasing the neutrino emission to produce SGRBs with the reasonable BH parameters and disk mass.

  6. On how the optical depth tunes the effects of ISM neutral atom flow on debris disks

    CERN Document Server

    Marzari, Francesco

    2011-01-01

    The flux of ISM neutral atoms surrounding stars and their environment affects the motion of dust particles in debris disks, causing a significant dynamical evolution. Large values of eccentricity and inclination can be excited and strong correlations settle in among the orbital angles. This dynamical behaviour, in particular for bound dust grains, can potentially cause significant asymmetries in dusty disks around solar type stars which might be detected by observations. However, the amount of orbital changes due to this non--gravitational perturbation is strongly limited by the collisional lifetime of dust particles. We show that for large values of the disk's optical depth the influence of ISM flow on the disk shape is almost negligible because the grains are collisionally destroyed before they can accumulate enough orbital changes due to the ISM perturbations. On the other hand, for values smaller than $10^{-3}$, peculiar asymmetric patterns appear in the density profile of the disk when we consider 1-10 m...

  7. 2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary Sequence

    OpenAIRE

    Whitney, Barbara A.; Wood, Kenneth; Bjorkman, J. E.; Cohen, Martin

    2003-01-01

    We present model spectral energy distributions, colors, polarization, and images for an evolutionary sequence of a low-mass protostar from the early collapse stage (Class 0) to the remnant disk stage (Class III). We find a substantial overlap in colors and SEDs between protostars embedded in envelopes (Class 0-I) and T Tauri disks (Class II), especially at mid-IR wavelengths. Edge-on Class I-II sources show double-peaked spectral energy distributions, with a short-wavelength hump due to scatt...

  8. Chemistry in evolving protoplanetary disks

    NARCIS (Netherlands)

    Jonkheid, Bastiaan Johan

    2006-01-01

    Planets form in disks of gas and dust around young stars. Since the gas makes up 99 % of the disk mass, it is critical for our understanding of planet formation to gain direct information from the gas, independently of what can be learned from dust emission. In this thesis, calculations are presente

  9. RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

    2015-12-15

    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.

  10. Friction characteristics of floppy disks

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This note presents the principle and structure of a tribological measure for floppy disks.The precision of the force measuring system is 1 mN in loading and 3×10-6 N in friction.The resolution of the film thickness between head and floppy disk is 0.5 nm in the vertical and 1.5 nm in the horizontal direction.In order to investigate the tribological characteristics of floppy disks,six types of floppy disks have been tested and the floating properties of these disks are also studied with film measuring system.The experimental results of the surface morphology and friction coefficient of these floppy disks using the atomic force microscope/friction force mcroscope (AFM/FFM) are in accordance with the conclusion made by our own measuring system.The experimental results show that the air film thickness between head and disk is of the same order as the surface roughness of floppy disks.

  11. Melting of polydisperse hard disks

    NARCIS (Netherlands)

    Pronk, S.; Frenkel, D.

    2004-01-01

    The melting of a polydisperse hard-disk system is investigated by Monte Carlo simulations in the semigrand canonical ensemble. This is done in the context of possible continuous melting by a dislocation-unbinding mechanism, as an extension of the two-dimensional hard-disk melting problem. We find

  12. Melting of polydisperse hard disks

    NARCIS (Netherlands)

    Pronk, S.; Frenkel, D.

    2004-01-01

    The melting of a polydisperse hard-disk system is investigated by Monte Carlo simulations in the semigrand canonical ensemble. This is done in the context of possible continuous melting by a dislocation-unbinding mechanism, as an extension of the two-dimensional hard-disk melting problem. We find th

  13. The composition of the protosolar disk and the formation conditions for comets

    CERN Document Server

    Willacy, K; Ali-Dib, M; Ceccarelli, C; Charnley, S B; Doronin, M; Ellinger, Y; Gast, P; Gibb, E; Milam, S N; Mousis, O; Pauzat, E; Tornow, C; Wirstrom, E S; Zicler, E

    2015-01-01

    Conditions in the protosolar nebula have left their mark in the composition of cometary volatiles, thought to be some of the most pristine material in the solar system. Cometary compositions represent the end point of processing that began in the parent molecular cloud core and continued through the collapse of that core to form the protosun and the solar nebula, and finally during the evolution of the solar nebula itself as the cometary bodies were accreting. Disentangling the effects of the various epochs on the final composition of a comet is complicated. But comets are not the only source of information about the solar nebula. Protostellar disks around young stars similar to the protosun provide a way of investigating the evolution of disks similar to the solar nebula while they are in the process of evolving to form their own solar systems. In this way we can learn about the physical and chemical conditions under which comets formed, and about the types of dynamical processing that shaped the solar syste...

  14. Herschel-PACS observation of the 10 Myr old T Tauri disk TW Hya: Constraining the disk gas mass

    CERN Document Server

    Thi, W F; Ménard, F; Woitke, P; Meeus, G; Riviere-Marichalar, P; Pinte, C; Howard, C D; Roberge, A; Sandell, G; Pascucci, I; Riaz, B; Grady, C A; Dent, W R F; Kamp, I; Duchêne, G; Augereau, J C; Pantin, E; Vandenbussche, B; Tilling, I; Williams, J P; Eiroa, C; Barrado, D; Alacid, J M; Andrews, S; Ardila, D R; Aresu, G; Brittain, S; Ciardi, D R; Danchi, W; Fedele, D; de Gregorio-Monsalvo, I; Heras, A; Huelamo, N; Krivov, A; Lebreton, J; Liseau, R; Martin-Zaidi, C; Mendigutía, I; Montesinos, B; Mora, A; Morales-Calderon, M; Nomura, H; Phillips, N; Podio, L; Poelman, D R; Ramsay, S; Rice, K; Solano, E; Walker, H; White, G J; Wright, G

    2010-01-01

    Planets are formed in disks around young stars. With an age of ~10 Myr, TW Hya is one of the nearest T Tauri stars that is still surrounded by a relatively massive disk. In addition a large number of molecules has been found in the TW Hya disk, making TW Hya the perfect test case in a large survey of disks with Herschel-PACS to directly study their gaseous component. We aim to constrain the gas and dust mass of the circumstellar disk around TW Hya. We observed the fine-structure lines of [OI] and [CII] as part of the Open-time large program GASPS. We complement this with continuum data and ground-based 12CO 3-2 and 13CO 3-2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code MCFOST and the thermo-chemical code ProDiMo to derive the gas and dust masses. We detect the [OI] line at 63 micron. The other lines that were observed, [OI] at 145 micron and [CII] at 157 micron, are not detected. No extended emission has been found. Preliminary modeling of the photometric...

  15. Physical processes in protoplanetary disks

    CERN Document Server

    Armitage, Philip J

    2015-01-01

    This review introduces physical processes in protoplanetary disks relevant to accretion and the initial stages of planet formation. After reprising the elementary theory of disk structure and evolution, I discuss the gas-phase physics of angular momentum transport through turbulence and disk winds, and how this may be related to episodic accretion observed in Young Stellar Objects. Turning to solids, I review the evolution of single particles under aerodynamic forces, and describe the conditions necessary for the development of collective gas-particle instabilities. Observations show that disks are not always radially smooth axisymmetric structures, and I discuss how gas and particle processes can interact to form observable large-scale structure (at ice lines, vortices and in zonal flows). I conclude with disk dispersal.

  16. Detection of precessing circumpulsar disks

    CERN Document Server

    Grimani, C

    2014-01-01

    Experimental evidences indicate that formations of disks and planetary systems around pulsars are allowed. Unfortunately, direct detections through electromagnetic observations appear to be quite rare. In the case of PSR 1931+24, the hypothesis of a rigid precessing disk penetrating the pulsar light cylinder is found consistent with radio transient observations from this star. Disk self-occultation and precession may limit electromagnetic observations. Conversely, we show here that gravitational waves generated by disk precessing near the light cylinder of young and middle aged pulsars would be detected by future space interferometers with sensitivities like those expected for DECIGO (DECI-hertz Interferometer Gravitational Wave Observatory) and BBO (Big Bang Observer). The characteristics of circumpulsar detectable precessing disks are estimated as a function of distance from the Solar System. Speculations on upper limits to detection rates are presented.

  17. A Disk Scheduling Algorithm: SPFF

    Institute of Scientific and Technical Information of China (English)

    HU Ming

    2005-01-01

    We put forward an optimal disk schedule with n disk requests and prove its optimality mathematically. Generalizing the idea of an optimal disk schedule, we remove the limit of n requests and, at the same time, consider the dynamically arrival model of disk requests to obtain an algorithm, shortest path first-fit first (SPFF). This algorithm is based on the shortest path of disk head motion constructed by all the pendent requests. From view of the head-moving distance, it has the stronger globality than SSTF. From view of the head-moving direction, it has the better flexibility than SCAN. Therefore, SPFF keeps the advantage of SCAN and, at the same time, absorbs the strength of SSTF. The algorithm SPFF not only shows the more superiority than other scheduling polices, but also have higher adjustability to meet the computer system's different demands.

  18. A DEBRIS Disk Around The Planet Hosting M-star GJ581 Spatially Resolved with Herschel

    CERN Document Server

    Lestrade, J -F; Sibthorpe, B; Kennedy, G M; Wyatt, M C; Bryden, G; Greaves, J S; Thilliez, E; Moro-Martin, Amaya; Booth, M; Dent, W R F; Duchene, G; Harvey, P M; Horner, J; Kalas, P; Kavelaars, J J; Phillips, N M; Rodriguez, D R; Su, K Y L; Wilner, D J

    2012-01-01

    Debris disks have been found primarily around intermediate and solar mass stars (spectral types A-K) but rarely around low mass M-type stars. We have spatially resolved a debris disk around the remarkable M3-type star GJ581 hosting multiple planets using deep PACS images at 70, 100 and 160 microns as part of the DEBRIS Program on the Herschel Space Observatory. This is the second spatially resolved debris disk found around an M-type star, after the one surrounding the young star AU Mic (12 Myr). However, GJ 581 is much older (2-8 Gyr), and is X-ray quiet in the ROSAT data. We fit an axisymmetric model of the disk to the three PACS images and found that the best fit model is for a disk extending radially from 25+/-12 AU to more than 60 AU. Such a cold disk is reminiscent of the Kuiper Belt but it surrounds a low mass star (0.3 M_sol) and its fractional dust luminosity L_dust/L_* of \\sim 10^-4 is much higher. The inclination limits of the disk found in our analysis make the masses of the planets small enough to...

  19. Observations of IC348: The Disk Population at 2-3 Million Years

    CERN Document Server

    Lada, C J; Luhman, K L; Allen, L; Hartmann, L; Megeath, T; Myers, P; Fazio, G; Wood, K; Muzerolle, J; Rieke, G; Siegler, N; Young, E

    2005-01-01

    We present near and mid-infrared photometry obtained with the Spitzer Space Telescope of 300 known members of the IC348 cluster. We merge this photometry with existing ground-based optical and near-infrared photometry in order to construct optical-infrared spectral energy distributions (SEDs) for all the cluster members and present a complete atlas of these SEDs. We employ these observations to both investigate the frequency and nature of the circumstellar disk population in the cluster. The observations are sufficiently sensitive to enable the first detailed measurement of the disk frequency for very low mass stars at the peak of the stellar IMF. Using measurements of infrared excess between 3.6 and 8 microns we find the total frequency of disk-bearing stars in the cluster to be 50 +/- 6%. However, only 30 +/- 4% of the member stars are surrounded by optically thick, primordial disks, while the remaining disk-bearing stars are surrounded by what appear to be optically thin,anemic disks. The disk fraction app...

  20. Probing changes of dust properties along a chain of solar-type prestellar and protostellar cores in Taurus with NIKA

    Science.gov (United States)

    Bracco, A.; Palmeirim, P.; André, Ph.; Adam, R.; Ade, P.; Bacmann, A.; Beelen, A.; Benoît, A.; Bideaud, A.; Billot, N.; Bourrion, O.; Calvo, M.; Catalano, A.; Coiffard, G.; Comis, B.; D'Addabbo, A.; Désert, F.-X.; Didelon, P.; Doyle, S.; Goupy, J.; Könyves, V.; Kramer, C.; Lagache, G.; Leclercq, S.; Macías-Pérez, J. F.; Maury, A.; Mauskopf, P.; Mayet, F.; Monfardini, A.; Motte, F.; Pajot, F.; Pascale, E.; Peretto, N.; Perotto, L.; Pisano, G.; Ponthieu, N.; Revéret, V.; Rigby, A.; Ritacco, A.; Rodriguez, L.; Romero, C.; Roy, A.; Ruppin, F.; Schuster, K.; Sievers, A.; Triqueneaux, S.; Tucker, C.; Zylka, R.

    2017-08-01

    The characterization of dust properties in the interstellar medium is key for understanding the physics and chemistry of star formation. Mass estimates are crucial to determine gravitational collapse conditions for the birth of new stellar objects in molecular clouds. However, most of these estimates rely on dust models that need further observational constraints to capture the relevant parameter variations depending on the local environment: from clouds to prestellar and protostellar cores. We present results of a new study of dust emissivity changes based on millimeter continuum data obtained with the NIKA camera at the IRAM-30 m telescope. Observing dust emission at 1.15 mm and 2 mm allows us to constrain the dust emissivity index, β, in the Rayleigh-Jeans tail of the dust spectral energy distribution far from its peak emission, where the contribution of other parameters (i.e. dust temperature) is more important. Focusing on the Taurus molecular cloud, one of the most famous low-mass star-forming regions in the Gould Belt, we analyze the emission properties of several distinct objects in the B213 filament. This subparsec-sized region is of particular interest since it is characterized by a collection ofevolutionary stages of early star formation: three prestellar cores, two Class 0/I protostellar cores and one Class II object. We are therefore able to compare dust properties among a sequence of sources that likely derive from the same parent filament. By means of the ratio of the two NIKA channel maps, we show that in the Rayleigh-Jeans approximation, βRJ varies among the objects: it decreases from prestellar cores (βRJ 2) to protostellar cores (βRJ 1) and the Class II object (βRJ 0). For one prestellar and two protostellar cores, we produce a robust study using available Herschel data to constrain the dust temperature of the sources. By using the Abel transform inversion technique we derive accurate radial temperature profiles that allow us to obtain

  1. The Stellar Structures around Disk Galaxies

    CERN Document Server

    Drozdovsky, I; Aparicio, A; Gallart, C; Monelli, M; Hidalgo, S; Bernard, E J; Galazutdinova, O

    2016-01-01

    We present a brief summary of our current results on the stellar distribution and population gradients of the resolved stars in the surroundings of ~50 nearby disk galaxies, observed with space- (Hubble & Spitzer) and ground-based telescopes (Subaru, VLT, BTA, Palomar, CFHT & INT). We examine the radial (in-plane) and vertical (extraplanar) distributions of resolved stars as a function of stellar age and metallicity by tracking changes in the color-magnitude diagram of face-on and edge-on galaxies. Our data show, that the scale length and height of a stellar population increases with age, with the oldest detected stellar populations identified at a large galactocentric radius or extraplanar height, out to typically a few kpc. In the most massive of the studied galaxies there is evidence for a break in number density and color gradients of evolved stars, which plausibly correspond to the thick disk and halo components of the galaxies. The ratio of intermediate-age to old stars in the outermost fields c...

  2. Instability patterns between counter-rotating disks

    Directory of Open Access Journals (Sweden)

    F. Moisy

    2003-01-01

    Full Text Available The instability patterns in the flow between counter-rotating disks (radius to height ratio R/h from 3.8 to 20.9 are investigated experimentally by means of visualization and Particle Image Velocimetry. We restrict ourselves to the situation where the boundary layers remain stable, focusing on the shear layer instability that occurs only in the counter-rotating regime. The associated pattern is a combination of a circular chain of vortices, as observed by Lopez et al. (2002 at low aspect ratio, surrounded by a set of spiral arms, first described by Gauthier et al. (2002 in the case of high aspect ratio. Stability curve and critical modes are measured for the whole range of aspect ratios. From the measurement of a local Reynolds number based on the shear layer thickness, evidence is given that a free shear layer instability, with only weak curvature effect, is responsible for the observed patterns. Accordingly, the number of vortices is shown to scale as the shear layer radius, which results from the competition between the centrifugal effects of each disk.

  3. Numerical Investigation of Circumplanetary Disks

    Science.gov (United States)

    Mitchell, Tyler R.; Stewart, G. R.

    2012-10-01

    The regular satellites of Jupiter and Saturn are believed to have formed in circumplanetary disks that were present during the late stages of giant planet formation. At present, there is a large amount of uncertainly in both the structure of these disks and the nature of angular momentum transport within them. In circumstellar disks, magnetorotational rotational instability (MRI) is generally invoked as a mechanism to transfer angular momentum and drive accretion. It is unclear whether circumplanetary disks are sufficiently ionized for the MRI to be active. In an effort to better understand the physical nature of circumplanetary disks, we present 1+1D numerical models of Jovian and Saturnian circumplanetary disks. Our models include viscous diffusion, infall from the solar nebula and external photoevaporation. The combination of these three processes allow for steady-state, truncated disks roughly consistent with the present state of the regular satellite systems of Jupiter and Saturn (Mitchell & Stewart, 2011). Unlike recent models of tidal truncation (Martin & Lubow, 2010), our initial models showed that photoevaporation is able to truncate circumplanetary disks to a small fraction of the Hill radius. One goal of this work is to verify our previous results and confirm that truncated disks can be formed using models with more realistic viscous processes. In order to simplify the problem, our initial models employed a viscosity that was linearly dependent on radius. Our current disk models use a viscosity that is calculated locally based on the midplane temperature that is determined from detailed vertical structure calculations. These models are used to conduct an initial investigation of the viability of an active MRI as well as baroclinic instability and other instabilities that may exist.

  4. Evolution of magnetized protoplanetary disks

    Science.gov (United States)

    Reyes-Ruiz, Mauricio; Stepinski, Tomasz F.

    1995-01-01

    We investigate the global evolution of a turbulent protoplanetary disk in its viscous stage, incorporating the effects of Maxwell stress due to a large-scale magnetic field permeating disk. We assume that the viscous stress is given by an alpha model. A magnetic field is produced contemporaneously by an alpha omega dynamo mechanism and the resultant Maxwell stress assists the viscous stress in providing the means for disk evolution. The aim of this work is to compare the evolution of magnetized and nonmagnetized disks driven by turbulent viscosity of the same magnitude and thus assess the effects of a self-generated magnetic field on the structure and dynamical evolution of protoplanetary disks. Two illustrative examples corresponding to two different initial conditions are considered: a high-mass case that starts with a disk of 0.245 solar mass and angular momentum of 5.6 x 10(exp 52)g sq cm/s, and a low-mass that case starts with a disk of 0.11 solar mass and angular momentum of 1.8 x 10(exp 52)g sq cm/s. For each of these two cases the radial development of a disk is calculated numerically assuming a fiducial value of the dimensionless viscosity parameter alpha(sub ss) = 0.01, as well as alpha(sub ss) = 2 x 10(exp -3). In all cases the central star has a mass equal to 1 solar mass. The most striking feature of magnetized disk evolution is the presence of the surface density bulge located in the region of the disk where the dynamo mechanism cannot support a magnetic field. The bulge persists for a time of the order of 10(exp 5)-10(exp 6) yr. The presence and persistence of the surface density bulge may have important implications for the process of planet formation and the overall characteristics of resultant planetary systems.

  5. Stochastic disks that roll

    Science.gov (United States)

    Holmes-Cerfon, Miranda

    2016-11-01

    We study a model of rolling particles subject to stochastic fluctuations, which may be relevant in systems of nano- or microscale particles where rolling is an approximation for strong static friction. We consider the simplest possible nontrivial system: a linear polymer of three disks constrained to remain in contact and immersed in an equilibrium heat bath so the internal angle of the polymer changes due to stochastic fluctuations. We compare two cases: one where the disks can slide relative to each other and the other where they are constrained to roll, like gears. Starting from the Langevin equations with arbitrary linear velocity constraints, we use formal homogenization theory to derive the overdamped equations that describe the process in configuration space only. The resulting dynamics have the formal structure of a Brownian motion on a Riemannian or sub-Riemannian manifold, depending on if the velocity constraints are holonomic or nonholonomic. We use this to compute the trimer's equilibrium distribution with and without the rolling constraints. Surprisingly, the two distributions are different. We suggest two possible interpretations of this result: either (i) dry friction (or other dissipative, nonequilibrium forces) changes basic thermodynamic quantities like the free energy of a system, a statement that could be tested experimentally, or (ii) as a lesson in modeling rolling or friction more generally as a velocity constraint when stochastic fluctuations are present. In the latter case, we speculate there could be a "roughness" entropy whose inclusion as an effective force could compensate the constraint and preserve classical Boltzmann statistics. Regardless of the interpretation, our calculation shows the word "rolling" must be used with care when stochastic fluctuations are present.

  6. TRANSITIONAL DISKS AROUND YOUNG LOW MASS STARS

    Directory of Open Access Journals (Sweden)

    P. D'Alessio

    2009-01-01

    have been interpreted as produced by disks with inner holes, which have been classi ed as \\Transitional Disks". These disks are considered the evolutionary link between the full disks typically found around the young T Tauri and Herbig Ae stars, and the debris disks, found around some main sequence stars. In this contribution we summarize the observed/inferred characteristics of these transitional disks and also some of the models proposed to explain their peculiar geometry.

  7. Accretion of solid materials onto circumplanetary disks from protoplanetary disks

    Energy Technology Data Exchange (ETDEWEB)

    Tanigawa, Takayuki [Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819 (Japan); Maruta, Akito; Machida, Masahiro N., E-mail: tanigawa@pop.lowtem.hokudai.ac.jp [Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581 (Japan)

    2014-04-01

    We investigate the accretion of solid materials onto circumplanetary disks from heliocentric orbits rotating in protoplanetary disks, which is a key process for the formation of regular satellite systems. In the late stage of the gas-capturing phase of giant planet formation, the accreting gas from protoplanetary disks forms circumplanetary disks. Since the accretion flow toward the circumplanetary disks affects the particle motion through gas drag force, we use hydrodynamic simulation data for the gas drag term to calculate the motion of solid materials. We consider a wide range of size for the solid particles (10{sup –2}-10{sup 6} m), and find that the accretion efficiency of the solid particles peaks around 10 m sized particles because energy dissipation of drag with circum-planetary disk gas in this size regime is most effective. The efficiency for particles larger than 10 m becomes lower because gas drag becomes less effective. For particles smaller than 10 m, the efficiency is lower because the particles are strongly coupled with the background gas flow, which prevents particles from accretion. We also find that the distance from the planet where the particles are captured by the circumplanetary disks is in a narrow range and well described as a function of the particle size.

  8. BROAD N{sub 2}H{sup +} EMISSION TOWARD THE PROTOSTELLAR SHOCK L1157-B1

    Energy Technology Data Exchange (ETDEWEB)

    Codella, C.; Fontani, F.; Gómez-Ruiz, A.; Vasta, M. [INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Viti, S. [Department of Physics and Astronomy, University College London, London (United Kingdom); Ceccarelli, C.; Lefloch, B.; Podio, L. [UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d' Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France); Benedettini, M.; Busquet, G. [INAF, Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133 Roma (Italy); Caselli, P., E-mail: codella@rcetri.astro.it [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2013-10-10

    We present the first detection of N{sub 2}H{sup +} toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ∼0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N{sub 2}H{sup +}(1-0) line originated from the dense (≥10{sup 5} cm{sup –3}) gas associated with the large (20''-25'') cavities opened by the protostellar wind. We find an N{sub 2}H{sup +} column density of a few 10{sup 12} cm{sup –2} corresponding to an abundance of (2-8) × 10{sup –9}. The N{sub 2}H{sup +} abundance can be matched by a model of quiescent gas evolved for more than 10{sup 4} yr, i.e., for more than the shock kinematical age (≅2000 yr). Modeling of C-shocks confirms that the abundance of N{sub 2}H{sup +} is not increased by the passage of the shock. In summary, N{sub 2}H{sup +} is a fossil record of the pre-shock gas, formed when the density of the gas was around 10{sup 4} cm{sup –3}, and then further compressed and accelerated by the shock.

  9. The Gas Disk: Evolution and Chemistry

    Science.gov (United States)

    Rab, Christian; Baldovin-Saavedra, Carla; Dionatos, Odysseas; Vorobyov, Eduard; Güdel, Manuel

    2016-12-01

    Protoplanetary disks are the birthplaces of planetary systems. The evolution of the star-disk system and the disk chemical composition determines the initial conditions for planet formation. Therefore a comprehensive understanding of the main physical and chemical processes in disks is crucial for our understanding of planet formation. We give an overview of the early evolution of disks, discuss the importance of the stellar high-energy radiation for disk evolution and describe the general thermal and chemical structure of disks. Finally we provide an overview of observational tracers of the gas component and disk winds.

  10. The gas disk: Evolution and chemistry

    CERN Document Server

    Rab, Ch; Dionatos, O; Vorobyov, E; Güdel, Manuel

    2016-01-01

    Protoplanetary disks are the birthplaces of planetary systems. The evolution of the star-disk system and the disk chemical composition determines the initial conditions for planet formation. Therefore a comprehensive understanding of the main physical and chemical processes in disks is crucial for our understanding of planet formation. We give an overview of the early evolution of disks, discuss the importance of the stellar high-energy radiation for disk evolution and describe the general thermal and chemical structure of disks. Finally we provide an overview of observational tracers of the gas component and disk winds.

  11. Protecting geothermal operations with rupture disks

    Energy Technology Data Exchange (ETDEWEB)

    Porter, D.W.

    1983-02-01

    Potential rupture disk applications in geothermal operations are reviewed. Several wells manifolded together, to form the geothermal feed, cause erratic pressure. Rupture disks are used for relief. Flash tanks are equipped with rupture disks. Brine separators, heat exchanger shells, and turbine casings are protected by rupture disks. An analysis of geothermal steam will determine the rupture disk metal. Reverse Buckling disks are recommended over tension loaded disks for dealing with geothermal pressure cycling. Erratic temperature suggests that metals which retain tensile strength with temperature be used (Inconel is mentioned). In summary, geothermal projects represent an excellent rupture disk market.

  12. Supermassive star formation via episodic accretion: protostellar disc instability and radiative feedback efficiency

    Science.gov (United States)

    Sakurai, Y.; Vorobyov, E. I.; Hosokawa, T.; Yoshida, N.; Omukai, K.; Yorke, H. W.

    2016-06-01

    The formation of supermassive stars (SMSs) is a potential pathway to seed supermassive black holes in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper, we study the evolution of an accreting SMS and its UV emissivity with realistic variable accretion from a circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the protostellar accretion until the stellar mass exceeds 104 M⊙. The disc fragments by gravitational instability, creating many clumps that migrate inward to fall on to the star. The resulting accretion history is highly time-dependent: short episodic accretion bursts are followed by longer quiescent phases. We show that the disc for the direct collapse model is more unstable and generates greater variability than normal Pop III cases. Next, we conduct a stellar evolution calculation using the obtained accretion history. Our results show that, regardless of the variable accretion, the stellar radius monotonically increases with almost constant effective temperature at Teff ≃ 5000 K as the stellar mass increases. The resulting UV feedback is too weak to hinder accretion due to the low flux of stellar UV photons. The insensitivity of stellar evolution to variable accretion is attributed to the fact that time-scales of variability, ≲103 yr, are too short to affect the stellar structure. We argue that this evolution will continue until the SMS collapses to produce a black hole by the general relativistic instability after the mass reaches ≳105 M⊙.

  13. The nature of angular momentum transport in radiative self-gravitating protostellar discs

    Science.gov (United States)

    Forgan, Duncan; Rice, Ken; Cossins, Peter; Lodato, Giuseppe

    2011-01-01

    Semi-analytic models of self-gravitating discs often approximate the angular momentum transport generated by the gravitational instability using the phenomenology of viscosity. This allows the employment of the standard viscous evolution equations, and gives promising results. It is, however, still not clear when such an approximation is appropriate. This paper tests this approximation using high-resolution 3D smoothed particle hydrodynamics (SPH) simulations of self-gravitating protostellar discs with radiative transfer. The nature of angular momentum transport associated with the gravitational instability is characterized as a function of both the stellar mass and the disc-to-star mass ratio. The effective viscosity is calculated from the Reynolds and gravitational stresses in the disc. This is then compared to what would be expected if the effective viscosity were determined by assuming local thermodynamic equilibrium or, equivalently, that the local dissipation rate matches the local cooling rate. In general, all the discs considered here settle into a self-regulated state where the heating generated by the gravitational instability is modulated by the local radiative cooling. It is found that low-mass discs can indeed be represented by a local α-parametrization, provided that the disc aspect ratio is small (H/r≤ 0.1) which is generally the case when the disc-to-star mass ratio q≲ 0.5. However, this result does not extend to discs with masses approaching that of the central object. These are subject to transient burst events and global wave transport, and the effective viscosity is not well modelled by assuming local thermodynamic equilibrium. In spite of these effects, it is shown that massive (compact) discs can remain stable and not fragment, evolving rapidly to reduce their disc-to-star mass ratios through stellar accretion and radial spreading.

  14. Complex Scattered Radiation Fields And Multiple Magnetic Fields In The Protostellar Cluster In NGC 2264

    Science.gov (United States)

    KWON, Jungmi; Tamura, M.; Kandori, R.; Kusakabe, N.; Hashimoto, J.; Nakajima, Y.; Nakamura, F.; Nagayama, T.; Nagata, T.; Hough, J. H.; Werner, M. W.; Teixeira, P. S.

    2012-05-01

    Near-infrared imaging polarimetry in the J, H, and Ks bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebula clusters (IRNCs) associated with NGC 2264 IRS 2 and the IRAS 12 S1 core, as well as local infrared reflection nebulae (IRNe), were detected. The illuminating sources of the IRNe were identified with known or new near- and mid-infrared sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main-sequence stars were selected to trace the magnetic field structure of the molecular cloud. The mean polarization position angle of the point-like sources is 80 degrees in the cluster core, and 60 degrees in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the magnetic field in the observed region of the cloud. The Chandrasekhar-Fermi method gives a rough estimate of the magnetic field strength to be about 100 micro-Gauss. A comparison with recent numerical simulations of the cluster formation implies that the cloud dynamics is controlled by the relatively strong magnetic field. The local magnetic field direction is well associated with that of CO outflow for IRAS 12 S1 and consistent with that inferred from submillimeter polarimetry. In contrast, the local magnetic field direction runs roughly perpendicular to the Galactic magnetic field direction.

  15. On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

    Science.gov (United States)

    Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

    2016-05-01

    The dynamical response of edge waves under the influence of self-gravity is examined in an idealized two-dimensional model of a proto-stellar disc, characterized in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius r0. The fluid in basic state is prescribed to rotate with a Keplerian profile $\\Omega_k(r)\\sim r^{-3/2}$ modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabilizer irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non- Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density, in addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect . Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

  16. Hot methanol from the inner region of the HH 212 protostellar system

    Science.gov (United States)

    Leurini, S.; Codella, C.; Cabrit, S.; Gueth, F.; Giannetti, A.; Bacciotti, F.; Bachiller, R.; Ceccarelli, C.; Gusdorf, A.; Lefloch, B.; Podio, L.; Tafalla, M.

    2016-10-01

    The mechanisms leading to the formation of disks around young stellar objects (YSOs) and to the launching of the associated jets are crucial to the understanding of the earliest stages of star and planet formation. HH 212 is a privileged laboratory to study a pristine jet-disk system. Therefore we investigate the innermost region (uv plane of various velocity channels of the strongest high-excitation lines. The blue- and red-shifted velocity centroids are shifted roughly symmetrically on either side of the jet axis, indicating that the line-of-sight velocity beyond 0.7 km s-1 from systemic is dominated by rotational motions. The velocity increases moving away from the protostar further indicating that the emission of methanol is not associated with a Keplerian disk or rotating-infalling cavity, and it is more likely associated with outflowing gas. We speculate that CH3OH traces a disk wind gas accelerated at the base. The launching region would be at a radius of a few astronomical units from the YSO.

  17. Self-gravitational Force Calculation of Second-order Accuracy for Infinitesimally Thin Gaseous Disks in Polar Coordinates

    Science.gov (United States)

    Wang, Hsiang-Hsu; Yen, David C. C.; Taam, Ronald E.

    2015-11-01

    Investigating the evolution of disk galaxies and the dynamics of proto-stellar disks can involve the use of both a hydrodynamical and a Poisson solver. These systems are usually approximated as infinitesimally thin disks using two-dimensional Cartesian or polar coordinates. In Cartesian coordinates, the calculations of the hydrodynamics and self-gravitational forces are relatively straightforward for attaining second-order accuracy. However, in polar coordinates, a second-order calculation of self-gravitational forces is required for matching the second-order accuracy of hydrodynamical schemes. We present a direct algorithm for calculating self-gravitational forces with second-order accuracy without artificial boundary conditions. The Poisson integral in polar coordinates is expressed in a convolution form and the corresponding numerical complexity is nearly linear using a fast Fourier transform. Examples with analytic solutions are used to verify that the truncated error of this algorithm is of second order. The kernel integral around the singularity is applied to modify the particle method. The use of a softening length is avoided and the accuracy of the particle method is significantly improved.

  18. Agroforestry practice in villages surrounding Nyamure former ...

    African Journals Online (AJOL)

    cntaganda

    Key words: Agroforestry, fuel wood, tree products, woodlot, forest plantation. INTRODUCTION ... The study area included three administrative cells in the surroundings of Nyamure ..... Table 6: Distance and time spent on firewood collection.

  19. Explaining preferences for home surroundings and locations

    Directory of Open Access Journals (Sweden)

    Hans Skifter Andersen

    2011-01-01

    Full Text Available This article is based on a survey carried out in Denmark that asked a random sample of the population about their preferences for home surroundings and locations. It shows that the characteristics of social surroundings are very important and can be divided into three independent dimensions: avoiding social nuisances, preferring social homogeneity and living close to one’s social network and place of origin. The study shows that most people have many detailed preferences, whereas some have very few. This confirms an earlier theory that some people are very connected to certain places with given characteristics and thus do not have priorities regarding home surroundings and locations. For others, mostly young people and singles, home is just a place to sleep and relax, whereas life is lived elsewhere. For this group, there are only preferences for location and there are few specific preferences for surroundings.

  20. Surround-Masking Affects Visual Estimation Ability

    Science.gov (United States)

    Jastrzebski, Nicola R.; Hugrass, Laila E.; Crewther, Sheila G.; Crewther, David P.

    2017-01-01

    Visual estimation of numerosity involves the discrimination of magnitude between two distributions or perceptual sets that vary in number of elements. How performance on such estimation depends on peripheral sensory stimulation is unclear, even in typically developing adults. Here, we varied the central and surround contrast of stimuli that comprised a visual estimation task in order to determine whether mechanisms involved with the removal of unessential visual input functionally contributes toward number acuity. The visual estimation judgments of typically developed adults were significantly impaired for high but not low contrast surround stimulus conditions. The center and surround contrasts of the stimuli also differentially affected the accuracy of numerosity estimation depending on whether fewer or more dots were presented. Remarkably, observers demonstrated the highest mean percentage accuracy across stimulus conditions in the discrimination of more elements when the surround contrast was low and the background luminance of the central region containing the elements was dark (black center). Conversely, accuracy was severely impaired during the discrimination of fewer elements when the surround contrast was high and the background luminance of the central region was mid level (gray center). These findings suggest that estimation ability is functionally related to the quality of low-order filtration of unessential visual information. These surround masking results may help understanding of the poor visual estimation ability commonly observed in developmental dyscalculia.

  1. Radiation thermo-chemical models of protoplanetary disks. I. Hydrostatic disk structure and inner rim

    Science.gov (United States)

    Woitke, P.; Kamp, I.; Thi, W.-F.

    2009-07-01

    Context: Emission lines from protoplanetary disks originate mainly in the irradiated surface layers, where the gas is generally warmer than the dust. Therefore, interpreting emission lines requires detailed thermo-chemical models, which are essential to converting line observations into understanding disk physics. Aims: We aim at hydrostatic disk models that are valid from 0.1 AU to 1000 AU to interpret gas emission lines from UV to sub-mm. In particular, our interest lies in interpreting far IR gas emission lines, such as will be observed by the Herschel observatory, related to the Gasps open time key program. This paper introduces a new disk code called ProDiMo. Methods: We combine frequency-dependent 2D dust continuum radiative transfer, kinetic gas-phase and UV photo-chemistry, ice formation, and detailed non-LTE heating & cooling with the consistent calculation of the hydrostatic disk structure. We include Fe ii and CO ro-vibrational line heating/cooling relevant to the high-density gas close to the star, and apply a modified escape-probability treatment. The models are characterised by a high degree of consistency between the various physical, chemical, and radiative processes, where the mutual feedbacks are solved iteratively. Results: In application to a T Tauri disk extending from 0.5 AU to 500 AU, the models show that the dense, shielded and cold midplane (z/r ⪉ 0.1, T g≈ T d) is surrounded by a layer of hot (T g≈ 5000 K) and thin (n ≈10 7 to 10 8 cm-3) atomic gas that extends radially to about 10 AU and vertically up to z/r≈0.5. This layer is predominantly heated by the stellar UV (e.g. PAH-heating) and cools via Fe ii semi-forbidden and Oi 630 nm optical line emission. The dust grains in this “halo” scatter the starlight back onto the disk, which affects the photochemistry. The more distant regions are characterised by a cooler flaring structure. Beyond r ⪆ 100 AU, T g decouples from T d even in the midplane and reaches values of about T

  2. 8-inch IBM floppy disk

    CERN Multimedia

    1971-01-01

    The 8-inch floppy disk was a magnetic storage disk for the data introduced commercially by IBM in 1971. It was designed by an IBM team as an inexpensive way to load data into the IBM System / 370. Plus it was a read-only bare disk containing 80 KB of data. The first read-write version was introduced in 1972 by Memorex and could contain 175 KB on 50 tracks (with 8 sectors per track). Other improvements have led to various coatings and increased capacities. Finally, it was surpassed by the mini diskette of 5.25 inches introduced in 1976.

  3. VLA and CARMA observations of protostars in the Cepheus clouds: Sub-arcsecond proto-binaries formed via disk fragmentation

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, John J.; Looney, Leslie W. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Chandler, Claire J. [National Radio Astronomy Observatory, Socorro, NM (United States); Wilner, David J.; Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Loinard, Laurent; D' Alessio, Paola [Centro de Radioastronomía y Astrofísica, UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán (Mexico); Chiang, Hsin-Fang [Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii at Manoa, Hilo, HI 96720 (United States); Hartmann, Lee; Calvet, Nuria [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Kwon, Woojin, E-mail: jtobin@nrao.edu [SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen (Netherlands)

    2013-12-20

    We present observations of three Class 0/I protostars (L1157-mm, CB230 IRS1, and L1165-SMM1) using the Karl G. Jansky Very Large Array (VLA) and observations of two (L1165-SMM1 and CB230 IRS1) with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The VLA observations were taken at wavelengths of λ = 7.3 mm, 1.4 cm, 3.3 cm, 4.0 cm, and 6.5 cm with a best resolution of ∼0.''06 (18 AU) at 7.3 mm. The L1165-SMM1 CARMA observations were taken at λ = 1.3 mm with a best resolution of ∼0.''3 (100 AU) and the CB230 IRS1 observations were taken at λ = 3.4 mm with a best resolution of ∼3'' (900 AU). We find that L1165-SMM1 and CB230 IRS1 have probable binary companions at separations of ∼0.''3 (100 AU) from detections of secondary peaks at multiple wavelengths. The position angles of these companions are nearly orthogonal to the direction of the observed bipolar outflows, consistent with the expected protostellar disk orientations. We suggest that these companions may have formed from disk fragmentation; turbulent fragmentation would not preferentially arrange the binary companions to be orthogonal to the outflow direction. For L1165-SMM1, both the 7.3 mm and 1.3 mm emission show evidence of a large (R > 100 AU) disk. For the L1165-SMM1 primary protostar and the CB230 IRS1 secondary protostar, the 7.3 mm emission is resolved into structures consistent with ∼20 AU radius disks. For the other protostars, including L1157-mm, the emission is unresolved, suggesting disks with radii <20 AU.

  4. Magneto-thermal Disk Wind from Protoplanetary Disks

    CERN Document Server

    Bai, Xue-Ning; Goodman, Jeremy; Yuan, Feng

    2015-01-01

    Global evolution and dispersal of protoplanetary disks (PPDs) is governed by disk angular momentum transport and mass-loss processes. Recent numerical studies suggest that angular momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a 1D model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on 1) the magnetic field strength at the wind base, characterized by the poloidal Alfv\\'en speed $v_{Ap}$, 2) the sound speed $c_s$ near the wind base, and 3) how rapidly poloidal field lines diverge (achieve $R^{-2}$ scaling). When $v_{Ap}\\gg c_s$, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accel...

  5. Chondrule Transport in Protoplanetary Disks

    CERN Document Server

    Goldberg, Aaron Z; Jacquet, Emmanuel

    2015-01-01

    Chondrule formation remains one of the most elusive early Solar System events. Here, we take the novel approach of employing numerical simulations to investigate chondrule origin beyond purely cosmochemical methods. We model the transport of generically-produced chondrules and dust in a 1D viscous protoplanetary disk model, in order to constrain the chondrule formation events. For a single formation event we are able to match analytical predictions of the memory chondrule and dust populations retain of each other (complementarity), finding that a large mass accretion rate ($\\gtrsim 10^{-7}$~M$_\\odot$~yr$^{-1}$) allows for delays on the order of the disk's viscous timescale between chondrule formation and chondrite accretion. Further, we find older disks to be severely diminished of chondrules, with accretion rates $\\lesssim 10^{-9}$~M$_\\odot$~yr$^{-1}$ for nominal parameters. We then characterize the distribution of chondrule origins in both space and time, as functions of disk parameters and chondrule format...

  6. Poynting Jets from Accretion Disks

    CERN Document Server

    Lovelace, R V E; Ustyugova, G V; Romanova, M M; Colgate, S A

    2002-01-01

    The powerful narrow jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, {\\it hydromagnetic outflows}, which have a significant mass flux and have energy and angular momentum carried by both the matter and the electromagnetic field and, Poynting outflows, where the mass flux is negligible and energy and angular momentum are carried predominantly by the electromagnetic field. Here we consider a Keplerian disk initially threaded by a dipole-like magnetic field and we present solutions of the force-free Grad-Shafranov equation for the coronal plasma. We find solutions with Poynting jets where there is a continuous outflow of energy and toroidal magnetic flux from the disk into the external space. This behavior contradicts the commonly accepted ``theorem'' of Solar plasma physics that the motio...

  7. Accretion Disks around Young Stars: An Observational Perspective

    Science.gov (United States)

    Ménard, F.; Bertout, C.

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve this long standing mystery: how did our Solar System form? This chapter focuses on observational studies of the circumstellar environment, and in particular of circumstellar disks, associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of the typical star forming regions ( e.g. 140 pc for Taurus), a planetary system like ours (with diameter simeq50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historical perpective, the road that led to the idea that most solar-like stars are surrounded by an accretion disk at one point in their early life and how, nowadays, their structural and physical parameters can be estimated from direct observations. We will follow by a short discussion of a few of the constraints available regarding the evolution and dissipation of these disks. This last topic is particularly relevant today

  8. Collisional Grooming of Debris Disks

    CERN Document Server

    Kuchner, Marc J

    2009-01-01

    Debris disk images show clumps, rings, warps, and other structures, many of which have been interpreted as perturbations from hidden planets. But so far, no models of these structures have properly accounted for collisions between dust grains. We have developed new steady-state 3D models of debris disks that self-consistently incorporate grain-grain collisions. We summarize our algorithm and use it to illustrate how collisions interact with resonant trapping in the presence of a planet.

  9. Resolved observations of transition disks

    CERN Document Server

    Casassus, Simon

    2016-01-01

    Resolved observations are bringing new constraints on the origin of radial gaps in protoplanetary disks. The kinematics, sampled in detail in one case-study, are indicative of non-Keplerian flows, corresponding to warped structures and accretion which may both play a role in the development of cavities. Disk asymmetries seen in the radio continuum are being interpreted in the context of dust segregation via aerodynamic trapping. We summarise recent observational progress, and also describe prospects for improvements in the near term.

  10. Two-dimensional vortices and accretion disks

    NARCIS (Netherlands)

    Nauta, Michiel Doede

    2001-01-01

    Observations show that there are disks around certain stars that slowly rain down on the central (compact) object: accretion disks. The rate of depletion of the disk might be slow but is still larger than was expected on theoretical grounds. That is why it has been suggested that the disks are tu

  11. Herschel evidence for disk flattening or gas depletion in transitional disks

    CERN Document Server

    Keane, J T; Espaillat, C; Woitke, P; Andrews, S; Kamp, I; Thi, W -F; Meeus, G; Dent, W R F

    2014-01-01

    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 [OI] 63 micron for 21 transitional disks. Our survey complements the larger Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by quadrupling the number of transitional disks observed with PACS at this wavelength. [OI] 63 micron traces material in the outer regions of the disk, beyond the inner cavity of most transitional disks. We find that transitional disks have [OI] 63 micron line luminosities two 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 in...

  12. 3D Radiation Nonideal Magnetohydrodynamical Simulations of the Inner Rim in Protoplanetary Disks

    Science.gov (United States)

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

    2017-02-01

    Many planets orbit within 1 au of their stars, raising questions about their origins. Particularly puzzling are the planets found near the silicate sublimation front. We investigate conditions near the front in the protostellar disk around a young intermediate-mass star, using the first global 3D radiation nonideal MHD simulations in this context. We treat the starlight heating; the silicate grains’ sublimation and deposition at the local, time-varying temperature and density; temperature-dependent ohmic dissipation; and various initial magnetic fields. The results show magnetorotational turbulence around the sublimation front at 0.5 au. The disk interior to 0.8 au is turbulent, with velocities exceeding 10% of the sound speed. Beyond 0.8 au is the dead zone, cooler than 1000 K and with turbulence orders of magnitude weaker. A local pressure maximum just inside the dead zone concentrates solid particles, favoring their growth. Over many orbits, a vortex develops at the dead zone’s inner edge, increasing the disk’s thickness locally by around 10%. We synthetically observe the results using Monte Carlo transfer calculations, finding that the sublimation front is near-infrared bright. The models with net vertical magnetic fields develop extended, magnetically supported atmospheres that reprocess extra starlight, raising the near-infrared flux 20%. The vortex throws a nonaxisymmetric shadow on the outer disk. At wavelengths > 2 μ {{m}}, the flux varies several percent on monthly timescales. The variations are more regular when the vortex is present. The vortex is directly visible as an arc at ultraviolet through near-infrared wavelengths, given sub-au spatial resolution.

  13. Fragmentation of Kozai–Lidov Disks

    Science.gov (United States)

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

    2017-02-01

    We analyze the gravitational instability (GI) of a locally isothermal inclined disk around one component of a binary system. Such a disk can undergo global Kozai–Lidov (KL) cycles if the initial disk tilt is above the critical KL angle (of about 40◦). During these cycles, an initially circular disk exchanges its inclination for eccentricity, and vice versa. Self-gravity may suppress the cycles under some circumstances. However, with hydrodynamic simulations that include self-gravity, we show that for a sufficiently high initial disk tilts and for certain disk masses, disks can undergo KL oscillations and fragment due to GI, even when the Toomre Q value for an equivalent undisturbed disk is well within the stable regime (Q> 2). We suggest that KL triggered disk fragmentation provides a mechanism for the efficient formation of giant planets in binary systems and may enhance the fragmentation of disks in massive black hole binaries.

  14. Magneto-thermal Disk Winds from Protoplanetary Disks

    Science.gov (United States)

    Bai, Xue-Ning; Ye, Jiani; Goodman, Jeremy; Yuan, Feng

    2016-02-01

    The global evolution and dispersal of protoplanetary disks (PPDs) are governed by disk angular-momentum transport and mass-loss processes. Recent numerical studies suggest that angular-momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a one-dimensional model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on (1) the magnetic field strength at the wind base, characterized by the poloidal Alfvén speed vAp, (2) the sound speed cs near the wind base, and (3) how rapidly poloidal field lines diverge (achieve {R}-2 scaling). When {v}{Ap}\\gg {c}{{s}}, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accelerated mainly by the pressure of the toroidal magnetic field. In both cases, the dominant role played by magnetic forces likely yields wind outflow rates that exceed purely hydrodynamical mechanisms. For typical PPD accretion-rate and wind-launching conditions, we expect vAp to be comparable to cs at the wind base. The resulting wind is heavily loaded, with a total wind mass-loss rate likely reaching a considerable fraction of the wind-driven accretion rate. Implications for modeling global disk evolution and planet formation are also discussed.

  15. ALMA Observations of HD141569's Circumstellar Disk

    CERN Document Server

    White, J A; Hughes, A M; Flaherty, K M; Ford, E; Wilner, D; Corder, S; Payne, M

    2016-01-01

    We present ALMA band 7 (345 GHz) continuum and $^{12}$CO(J = 3-2) observations of the circumstellar disk surrounding HD141569. At an age of about 5 Myr, the disk has a complex morphology that may be best interpreted as a nascent debris system with gas. Our $870\\rm~\\mu m$ ALMA continuum observations resolve a dust disk out to approximately $ 56 ~\\rm au$ from the star (assuming a distance of 116 pc) with $0."38$ resolution and $0.07 ~ \\rm mJy~beam^{-1}$ sensitivity. We measure a continuum flux density for this inner material of $3.8 \\pm 0.4 ~ \\rm mJy$ (including calibration uncertainties). The $^{12}$CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated $^{12}$CO(3-2) line flux density is $15.7 \\pm 1.6~\\rm Jy~km~s^{-1}$. We estimate the mass of the millimeter debris and $^{12}$CO(3-2) gas to be $\\gtrsim0.04~\\rm M_{\\oplus}$ and $\\sim2\\times 10^{-3}~\\rm M_{\\oplus}$, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk ($&...

  16. The Disk Atmospheres of Three Herbig Ae/Be Stars

    CERN Document Server

    Harker, D E; Wooden, D H; Temi, P; Harker, David E.; Woodward, Charles E.; Wooden, Diane H.; Temi, Pasquale

    2004-01-01

    We present infrared (IR) spectrophotometry ($R \\simeq 180$) of three Herbig Ae/Be stars surrounded by possible protoplanetary disks: HD 150193, HD100546 and HD 179218. We construct a mid-IR spectral energy distributions (SED) for each object by using $7.6 - 13.2$ \\micron HIFOGS spectra, 2.4 -- 45 \\micron\\ spectrophotometry from the {\\it ISO} SWS, the 12, 25, 60, and 100 \\micron\\ photometric points from IRAS, and for HD 179218, photometric bolometric data points from the Mt. Lemmon Observing Facility. The SEDs are modeled by using an expanded version of the \\citet{chigol97} two-layer, radiative and hydrostatic equilibrium, passive disk. This expanded version includes the emission from Mg-pure crystalline olivine (forsterite) grains in the disk surface layer. HD 150193 contains no crystals while HD 100546 and HD 179218 respectively show evidence of having crystalline silicates in the surface layers of their disks. We find that the inner region of HD100546 has a 37% higher crystalline-to-amorphous silicate ratio...

  17. Searching for circumplanetary disks around LkCa 15

    CERN Document Server

    Isella, Andrea; Carpenter, John M; Pe'rez, Laura M; Ricci, Luca

    2014-01-01

    We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring, and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa~15~b is a massive planet (>5 M_J) accreting at a rate greater than 1.e-6 M_J yr^{-1}, then its circumplanetary disk is less massive than 0.1 M_J, or smaller than 0.4 Hill r...

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

    CERN Document Server

    Picogna, Giovanni

    2014-01-01

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

  19. Feasibility of Using PZT Actuators to Study the Dynamic Behavior of a Rotating Disk due to Rotor-Stator Interaction

    Directory of Open Access Journals (Sweden)

    Alexandre Presas

    2014-07-01

    Full Text Available In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids—air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction.

  20. Feasibility of using PZT actuators to study the dynamic behavior of a rotating disk due to rotor-stator interaction.

    Science.gov (United States)

    Presas, Alexandre; Egusquiza, Eduard; Valero, Carme; Valentin, David; Seidel, Ulrich

    2014-07-07

    In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids-air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm) connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction.

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

    Science.gov (United States)

    Picogna, G.; Marzari, F.

    2014-04-01

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

  2. Dense Ionized and Neutral Gas Surrounding Sgr A*

    CERN Document Server

    Shukla, Hemant; Scoville, N Z

    2004-01-01

    We present high resolution H41a hydrogen recombination line observations of the 1.2' (3 pc) region surrounding Sgr A* at 92 GHz using the OVRO Millimeter Array with an angular resolution of 7" x 3" and velocity resolution of 13 km/s. New observations of H31a, H35a, H41a, and H44a lines were obtained using the NRAO 12-m telescope, and their relative line strengths are interpreted in terms of various emission mechanisms. These are the most extensive and most sensitive observations of recombination line to date. Observations of HCO+ (1 - 0) transition at 89 GHz are also obtained simultaneously with a 40% improved angular resolution and 4-15 times improved sensitivity over previous observations, and the distribution and kinematics of the dense molecular gas in the circumnuclear disk (CND) are mapped and compared with those of the ionized gas. The line brightness ratios of the hydrogen recombination lines are consistent with purely spontaneous emission from 7000 K gas with n_e = 20,000 cm$^{-3}$ near LTE condition...

  3. Covering and piercing disks with two centers

    KAUST Repository

    Ahn, Heekap

    2013-04-01

    We give exact and approximation algorithms for two-center problems when the input is a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in D intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. © 2012 Elsevier B.V.

  4. Covering and piercing disks with two centers

    KAUST Repository

    Ahn, Heekap

    2011-01-01

    We consider new versions of the two-center problem where the input consists of a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. We give exact and approximation algorithms for these versions. © 2011 Springer-Verlag.

  5. Timescales of Disk Evolution and Planet Formation

    CERN Document Server

    Jayawarhana, R

    2000-01-01

    It has been suggested that circumstellar disks evolve from dense, actively accreting structures to low-mass, replenished remnants. During this transition, grains may assemble into planetesimals, or the disk may be cleared by newborn planets. Recently identified nearby groups of young stars provide valuable laboratories for probing disk evolution. I discuss the properties of dust disks in the TW Hydrae Association and the MBM 12 cloud, and compare the results to other studies of disk evolution and planet formation timescales.

  6. Reflected Light from Sand Grains in the Terrestrial Zone of a Protoplanetary Disk

    CERN Document Server

    Herbst, William; LeDuc, Katherine; Winn, Joshua N; Johns-Krull, Christopher M; Mundt, Reinhard; Ibrahimov, Mansur

    2008-01-01

    We show that grains have grown to ~mm size (sand sized) or larger in the terrestrial zone (within ~3 AU) of the protoplanetary disk surrounding the 3 Myr old binary star KH 15D. We also argue that the reflected light in the system reaches us by back scattering off the far side of the same ring whose near side causes the obscuration.

  7. What Shaped Elias 2-27's Disk?

    Science.gov (United States)

    Kohler, Susanna

    2017-04-01

    The young star Elias 2-27 is surrounded by a massive disk with spectacular spiral arms. A team of scientists from University of Cambridges Institute of Astronomy has now examined what might cause this disks appearance.Top: ALMA 1.3-mm observations of Elias 2-27s spiral arms, processed with an unsharp masking filter. Two symmetric spiral arms, a bright inner ellipse, and two dark crescents are clearly visible. Bottom: a deprojection of the top image (i.e., what the system would look like face-on). [Meru et al. 2017]ALMA-Imaged Spiral ArmsWith the dawn of new telescopes such as the Atacama Large Millimeter/submillimeter Array, were now able to study the birth of young stars and their newly forming planetary systems in more detail than ever before. But these new images require new models and interpretations!Case in point: Elias 2-27 is a low-mass star thats only a million years old and is surrounded by an unusually massive disk of gas and dust. Recent spatially-resolved ALMA observations of Elias 2-27 have revealed the stunning structure of the stars disk: it contains two enormous, symmetric spiral arms, as well as additional features interior to the spirals.What caused the disk to develop this structure? Led by Farzana Meru, a group of Institute of Astronomy researchers has run a series of simulations that explore different ways that Elias 2-27s disk might have evolved into the shape we see today.Modeling a DiskMeru and collaborators performed a total of 72 three-dimensional smoothed particle hydrodynamics simulations tracking 250,000 gas particles in a model disk around a star like Elias 2-27. They then modeled the transfer of energy through these simulated disks and produced synthetic ALMA observations based on the outcomes.Left: Synthetic ALMA observations of disks shaped by an internal companion (top), an external companion (middle), and gravitational instability within the disk (bottom). Right: Deprojections of the images on the left. Scales are the same as in

  8. Evolution of dynamo-generated magnetic fields in accretion disks around compact and young stars

    Science.gov (United States)

    Stepinski, Tomasz F.

    1994-01-01

    Geometrically thin, optically thick, turbulent accretion disks are believed to surround many stars. Some of them are the compact components of close binaries, while the others are throught to be T Tauri stars. These accretion disks must be magnetized objects because the accreted matter, whether it comes from the companion star (binaries) or from a collapsing molecular cloud core (single young stars), carries an embedded magnetic field. In addition, most accretion disks are hot and turbulent, thus meeting the condition for the MHD turbulent dynamo to maintain and amplify any seed field magnetic field. In fact, for a disk's magnetic field to persist long enough in comparison with the disk viscous time it must be contemporaneously regenerated because the characteristic diffusion time of a magnetic field is typically much shorter than a disk's viscous time. This is true for most thin accretion disks. Consequently, studying magentic fields in thin disks is usually synonymous with studying magnetic dynamos, a fact that is not commonly recognized in the literature. Progress in studying the structure of many accretion disks was achieved mainly because most disks can be regarded as two-dimensional flows in which vertical and radial structures are largely decoupled. By analogy, in a thin disk, one may expect that vertical and radial structures of the magnetic field are decoupled because the magnetic field diffuses more rapidly to the vertical boundary of the disk than along the radius. Thus, an asymptotic method, called an adiabatic approximation, can be applied to accretion disk dynamo. We can represent the solution to the dynamo equation in the form B = Q(r)b(r,z), where Q(r) describes the field distribution along the radius, while the field distribution across the disk is included in the vector function b, which parametrically depends on r and is normalized by the condition max (b(z)) = 1. The field distribution across the disk is established rapidly, while the radial

  9. Braking the Gas in the beta Pictoris Disk

    CERN Document Server

    Fern'andez, R; Wu, Y; Brandeker, Alexis; Fern\\'andez, Rodrigo

    2006-01-01

    (Abridged) The main sequence star beta Pictoris hosts the best studied circumstellar disk to date. Nonetheless, a long-standing puzzle has been around since the detection of metallic gas in the disk: radiation pressure from the star should blow the gas away, yet the observed motion is consistent with Keplerian rotation. In this work we search for braking mechanisms that can resolve this discrepancy. We find that all species affected by radiation force are heavily ionized and dynamically coupled into a single fluid by Coulomb collisions, reducing the radiation force on species feeling the strongest acceleration. For a gas of solar composition, the resulting total radiation force still exceeds gravity, while a gas of enhanced carbon abundance could be self-braking. We also explore two other braking agents: collisions with dust grains and neutral gas. Grains surrounding beta Pic are photoelectrically charged to a positive electrostatic potential. If a significant fraction of the grains are carbonaceous (10% in t...

  10. Smart Chips for Smart Surroundings - 4S

    NARCIS (Netherlands)

    Schuler, Eberhard; König, Ralf; Becker, Jürgen; Rauwerda, Gerard; Burgwal, van de Marcel; Smit, Gerard J.M.; Cardoso, João M.P.; Hübner, Michael

    2011-01-01

    The overall mission of the 4S project (Smart Chips for Smart Surroundings) was to define and develop efficient flexible, reconfigurable core building blocks, including the supporting tools, for future Ambient System Devices. Reconfigurability offers the needed flexibility and adaptability, it provid

  11. Three Dimensional MHD Simulation of Circumbinary Accretion Disks -2. Net Accretion Rate

    CERN Document Server

    Shi, Ji-Ming

    2015-01-01

    When an accretion disk surrounds a binary rotating in the same sense, the binary exerts strong torques on the gas. Analytic work in the 1D approximation indicated that these torques sharply diminish or even eliminate accretion from the disk onto the binary. However, recent 2D and 3D simulational work has shown at most modest diminution. We present new MHD simulations demonstrating that for binaries with mass ratios of 1 and 0.1 there is essentially no difference between the accretion rate at large radius in the disk and the accretion rate onto the binary. To resolve the discrepancy with earlier analytic estimates, we identify the small subset of gas trajectories traveling from the inner edge of the disk to the binary and show how the full accretion rate is concentrated onto them.

  12. Unveiling the structure and kinematics of B[e] stars' disks from FEROS and CRIRES spectra

    CERN Document Server

    Muratore, M F; Kraus, M; Aret, A; Cidale, L S; Fernandes, M Borges; Oudmaijer, R D; Wheelwright, H E

    2012-01-01

    We are investigating the circumstellar material for a sample of B[e] stars using high spectral resolution data taken in the optical and near-infrared regions with ESO/FEROS and ESO/CRIRES spectrographs, respectively. B[e] stars are surrounded by dense disks of still unknown origin. While optical emission lines from [O I] and [Ca II] reflect the disk conditions close to the star (few stellar radii), the near-infrared data, especially the CO band emission, mirror the characteristics in the molecular part of the disk farther away from the star (several AU). Based on our high resolution spectroscopic data, we seek to derive the density and temperature structure of the disks, as well as their kinematics. This will allow us to obtain a better understanding of their structure, formation history and evolution. Here we present our preliminary results.

  13. Vertical stability of circular orbits in relativistic razor-thin disks

    CERN Document Server

    Vieira, Ronaldo S S; Saa, Alberto

    2016-01-01

    During the last few decades, there has been a growing interest in exact solutions of Einstein equations describing razor-thin disks. Despite the progress in the area, the analytical study of geodesic motion crossing the disk plane in these systems is not yet so developed. In the present work, we propose a definite vertical stability criterion for circular equatorial timelike geodesics in static, axially symmetric thin disks, possibly surrounded by other structures preserving axial symmetry. It turns out that the strong energy condition for the disk stress-energy content is sufficient for vertical stability of these orbits. Moreover, adiabatic invariance of the vertical action variable gives us an approximate third integral of motion for oblique orbits which deviate slightly from the equatorial plane. Such new approximate third integral certainly points to a better understanding of the analytical properties of these orbits. The results presented here, derived for static spacetimes, may be a starting point to s...

  14. Jet magnetically accelerated from disk-corona around a rotating black hole

    Institute of Scientific and Technical Information of China (English)

    GONG XiaoLong; LI LiXin

    2012-01-01

    A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole (BH) is proposed.In the diskcorona scenario,we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations.The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere.It is shown that jet power increases with the increasing BH spin,and concentrates in the inner region of the disk-corona.In addition,we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism,and show that our jet formation mechanism can simulate almost all sources with high power jet,which fails to be explained by the Blandford-Znajek (BZ) process.

  15. Ultrafast disk lasers and amplifiers

    Science.gov (United States)

    Sutter, Dirk H.; Kleinbauer, Jochen; Bauer, Dominik; Wolf, Martin; Tan, Chuong; Gebs, Raphael; Budnicki, Aleksander; Wagenblast, Philipp; Weiler, Sascha

    2012-03-01

    Disk lasers with multi-kW continuous wave (CW) output power are widely used in manufacturing, primarily for cutting and welding applications, notably in the automotive industry. The ytterbium disk technology combines high power (average and/or peak power), excellent beam quality, high efficiency, and high reliability with low investment and operating costs. Fundamental mode picosecond disk lasers are well established in micro machining at high throughput and perfect precision. Following the world's first market introduction of industrial grade 50 W picosecond lasers (TruMicro 5050) at the Photonics West 2008, the second generation of the TruMicro series 5000 now provides twice the average power (100 W at 1030 nm, or 60 W frequency doubled, green output) at a significantly reduced footprint. Mode-locked disk oscillators achieve by far the highest average power of any unamplified lasers, significantly exceeding the 100 W level in laboratory set-ups. With robust long resonators their multi-microjoule pulse energies begin to compete with typical ultrafast amplifiers. In addition, significant interest in disk technology has recently come from the extreme light laser community, aiming for ultra-high peak powers of petawatts and beyond.

  16. Disk Instabilities and Cooling Fronts

    CERN Document Server

    Vishniac, E T

    1998-01-01

    Accretion disk outbursts, and their subsequent decline, offer a unique opportunity to constrain the physics of angular momentum transport in hot accretion disks. Recent work has centered on the claim by Cannizzo et al. that the exponential decay of luminosity following an outburst in black hole accretion disk systems is only consistent with a particular form for the dimensionless viscosity, $\\alpha=35(c_s/r\\Omega)^{3/2}$. This result can be understood in terms of a simple model of the evolution of cooling fronts in accretion disks. In particular, the cooling front speed during decline is $\\sim cooling front, and the exact value of $n$ depends on the hot state opacity, (although generally $n\\approx 1/2$). Setting this speed proportional to $r$ constrains the functional form of $\\alpha$ in the hot phase of the disk, which sets it apart from previous arguments based on the relative durations of outburst and quiescence. However, it remains uncertain how well we know the exponent $n$. In addition, more work is nee...

  17. Simultaneity on the Rotating Disk

    Science.gov (United States)

    Koks, Don

    2017-04-01

    The disk that rotates in an inertial frame in special relativity has long been analysed by assuming a Lorentz contraction of its peripheral elements in that frame, which has produced widely varying views in the literature. We show that this assumption is unnecessary for a disk that corresponds to the simplest form of rotation in special relativity. After constructing such a disk and showing that observers at rest on it do not constitute a true rotating frame, we choose a "master" observer and calculate a set of disk coordinates and spacetime metric pertinent to that observer. We use this formalism to resolve the "circular twin paradox", then calculate the speed of light sent around the periphery as measured by the master observer, to show that this speed is a function of sent-direction and disk angle traversed. This result is consistent with the Sagnac Effect, but constitutes a finer analysis of that effect, which is normally expressed using an average speed for a full trip of the periphery. We also use the formalism to give a resolution of "Selleri's paradox".

  18. The Interstellar Cloud Surrounding the Solar System

    Science.gov (United States)

    Frisch, P. C.

    Ultraviolet spectral data of nearby stars indicate that the cloud surrounding the solar system has an average neutral density n(HI)~0.1 cm-3, temperature ~6800 K, and turbulence ~1.7 km/s. Comparisons between the anomalous cosmic ray data and ultraviolet data suggest that the electron density is in the range n(e-)~0.22 to 0.44 cm-3. This cloud is flowing past the Sun from a position centered in the Norma-Lupis region. The cloud properties are consistent with interstellar gas which originated as material evaporated from the surfaces of embedded clouds in the Scorpius-Centaurus Association, and which was then displaced towards the Sun by a supernova event about 4 Myrs ago. The Sun and surrounding cloud velocities are nearly perpendicular in space, and this cloud is sweeping past the Sun. The morphology of this cloud can be reconstructed by assuming that the cloud moves in a direction parallel to the surface normal. With this assumption, the Sun entered the surrounding cloud 2000 to 8000 years ago, and is now about 0.05 to 0.16 pc from the cloud surface. Prior to its recent entry into the surrounding cloud complex, the Sun was embedded in a region of space with average density lower than 0.0002 cm-3. If a denser cloud velocity component seen towards alpha Cen A,B is real, it will encounter the solar system within 50,000 yr. The nearby magnetic field seen upwind has a spatial orientation that is parallel to the cloud surface. The nearby star Sirius is viewed through the wake of the solar system, but this direction also samples the hypothetical cloud interface. Comparisons of anomalous cosmic ray and interstellar absorption line data suggest that trace elements in the surrounding cloud are in ionization equilibrium. Data towards nearby white dwarfs indicate partial helium ionization, N(N(HI)(/N(HeI)>~13.7, which is consistent with pickup ion data within the solar system if less than 40% hydrogen ionization occurs in the heliopause region. However, the white dwarfs may

  19. Large-Scale Asymmetries in the Transitional Disks of SAO 206462 and SR 21

    CERN Document Server

    Pérez, Laura M; Carpenter, John M; Chandler, Claire J

    2014-01-01

    We present Atacama Large Millimeter/submillimeter Array (ALMA) observations in the dust continuum (690 GHz, 0.45 mm) and 12CO J=6-5 spectral line emission, of the transitional disks surrounding the stars SAO 206462 and SR 21. These ALMA observations resolve the dust-depleted disk cavities and extended gaseous disks, revealing large-scale asymmetries in the dust emission of both disks. We modeled these disks structures with a ring and an azimuthal gaussian, where the azimuthal gaussian is motivated by the steady-state vortex solution from Lyra & Lin (2013). Compared to recent observations of HD 142527, Oph IRS 48, and LkHa 330, these are low-contrast (< 2) asymmetries. Nevertheless, a ring alone is not a good fit, and the addition of a vortex prescription describes these data much better. The asymmetric component encompasses 15% and 28% of the total disk emission in SAO 206462 and SR 21 respectively, which corresponds to a lower limit of 2 MJup of material within the asymmetry for both disks. Although t...

  20. Unveiling the gas and dust disk structure in HD 163296 using ALMA observations

    CERN Document Server

    de Gregorio-Monsalvo, I; Dent, W; Pinte, C; López, C; Klaassen, P; Hales, A; Cortés, P; Rawlings, M G; Tachihara, K; Testi, L; Takahashi, S; Chapillon, E; Mathews, G; Juhasz, A; Akiyama, E; Higuchi, A E; Saito, M; Nyman, L - Å; Phillips, N; Rodń, J; Corder, S; Van Kempen, T

    2013-01-01

    Aims: The aim of this work is to study the structure of the protoplanetary disk surrounding the Herbig Ae star HD 163296. Methods: We have used high-resolution and high-sensitivity ALMA observations of the CO(3-2) emission line and the continuum at 850 microns, as well as the 3- dimensional radiative transfer code MCFOST to model the data presented in this work. Results: The CO(3-2) emission unveils for the first time at sub-millimeter frequencies the vertical structure details of a gaseous disk in Keplerian rotation, showing the back- and the front-side of a flared disk. Continuum emission at 850 microns reveals a compact dust disk with a 240 AU outer radius and a surface brightness profile that shows a very steep decline at radius larger than 125 AU. The gaseous disk is more than two times larger than the dust disk, with a similar critical radius but with a shallower radial profile. Radiative transfer models of the continuum data confirms the need for a sharp outer edge to the dust disk. The models for the ...

  1. The Milky Way's Stellar Disk

    CERN Document Server

    Rix, Hans-Walter

    2013-01-01

    A suite of vast stellar surveys mapping the Milky Way, culminating in the Gaia mission, is revolutionizing the empirical information about the distribution and properties of stars in the Galactic stellar disk. We review and lay out what analysis and modeling machinery needs to be in place to test mechanisms of disk galaxy evolution and to stringently constrain the Galactic gravitational potential, using such Galactic star-by-star measurements. We stress the crucial role of stellar survey selection functions in any such modeling; and we advocate the utility of viewing the Galactic stellar disk as made up from `mono-abundance populations' (MAPs), both for dynamical modeling and for constraining the Milky Way's evolutionary processes. We review recent work on the spatial and kinematical distribution of MAPs, and lay out how further study of MAPs in the Gaia era should lead to a decisively clearer picture of the Milky Way's dark matter distribution and formation history.

  2. Conformastatic disk-haloes in Einstein-Maxwell gravity

    CERN Document Server

    Gutiérrez-Piñeres, Antonio C; Quevedo, Hernando

    2012-01-01

    We present a relativistic model describing a thin disk surrounded by a halo in presence of an electromagnetic field. The model is obtained by solving the Einstein-Maxwell equations on a particular conformastatic spacetime background and by using the distributional approach for the energy-momentum tensor. A class of solutions is obtained in which the gravitational and electromagnetic potentials are completely determined by a harmonic function only. A particular solution is given that is asymptotically flat and singularity-free, and satisfies all the energy conditions.

  3. Dust Evolution in Protoplanetary Disks

    Science.gov (United States)

    Testi, L.; Birnstiel, T.; Ricci, L.; Andrews, S.; Blum, J.; Carpenter, J.; Dominik, C.; Isella, A.; Natta, A.; Williams, J. P.; Wilner, D. J.

    In the core-accretion scenario for the formation of planetary rocky cores, the first step toward planet formation is the growth of dust grains into larger and larger aggregates and eventually planetesimals. Although dust grains are thought to grow up to micrometer-sized particles in the dense regions of molecular clouds, the growth to pebbles and kilometer-sized bodies must occur at the high densities within protoplanetary disks. This critical step is the last stage of solids evolution that can be observed directly in extrasolar systems before the appearance of large planetary-sized bodies. In this chapter we review the constraints on the physics of grain-grain collisions as they have emerged from laboratory experiments and numerical computations. We then review the current theoretical understanding of the global processes governing the evolution of solids in protoplanetary disks, including dust settling, growth, and radial transport. The predicted observational signatures of these processes are summarized. We briefly discuss grain growth in molecular cloud cores and in collapsing envelopes of protostars, as these likely provide the initial conditions for the dust in protoplanetary disks. We then review the observational constraints on grain growth in disks from millimeter surveys, as well as the very recent evidence for radial variations of the dust properties in disks. We also include a brief discussion on the small end of the grain size distribution and dust settling as derived from optical, near-, and mid-infrared observations. Results are discussed in the context of global dust-evolution models; in particular, we focus on the emerging evidence for a very efficient early growth of grains and the radial distribution of maximum grain sizes as the result of growth barriers. We also highlight the limits of the current models of dust evolution in disks, including the need to slow the radial drift of grains to overcome the migration/fragmentation barrier.

  4. Formation of isothermal disks around protoplanets. I. Introductory three-dimensional global simulations for sub-Neptune-mass protoplanets

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hsiang-Hsu; Shang, Hsien; Gu, Pin-Gao [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); Bu, Defu, E-mail: hhwang@asiaa.sinica.edu.tw [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatories, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China)

    2014-07-20

    The regular satellites found around Neptune (≈17 M{sub ⊕}) and Uranus (≈14.5 M{sub ⊕}) suggest that past gaseous circumplanetary disks may have co-existed with solids around sub-Neptune-mass protoplanets (<17 M{sub ⊕}). These disks have been shown to be cool, optically thin, and quiescent, with low surface densities and low viscosities. Numerical studies of the formation are difficult and technically challenging. As an introductory attempt, three-dimensional global simulations are performed to explore the formation of circumplanetary disks around sub-Neptune-mass protoplanets embedded within an isothermal protoplanetary disk at the inviscid limit of the fluid in the absence of self-gravity. Under such conditions, a sub-Neptune-mass protoplanet can reasonably have a rotationally supported circumplanetary disk. The size of the circumplanetary disk is found to be roughly one-tenth of the corresponding Hill radius, which is consistent with the orbital radii of irregular satellites found for Uranus. The protoplanetary gas accretes onto the circumplanetary disk vertically from high altitude and returns to the protoplanetary disk again near the midplane. This implies an open system in which the circumplanetary disk constantly exchanges angular momentum and material with its surrounding prenatal protoplanetary gas.

  5. Persistent Confusion and Controversy Surrounding Gene Patents

    Science.gov (United States)

    Guerrini, Christi J.; Majumder, Mary A.; McGuire, Amy L.

    2016-01-01

    There is persistent confusion and controversy surrounding basic issues of patent law relevant to the genomics industry. Uncertainty and conflict can lead to the adoption of inefficient practices and exposure to liability. The development of patent-specific educational resources for industry members, as well as the prompt resolution of patentability rules unsettled by recent U.S. Supreme Court decisions, are therefore urgently needed. PMID:26849516

  6. Hot methanol from the inner region of the HH 212 protostellar system

    CERN Document Server

    Leurini, S; Cabrit, S; Gueth, F; Giannetti, A; Bacciotti, F; Bachiller, R; Ceccarelli, C; Gusdorf, A; Lefloch, B; Podio, L; Tafalla, M

    2016-01-01

    The mechanisms leading to the formation of disks around young stellar objects (YSOs) and to the launching of the associated jets are crucial to the understanding of the earliest stages of star and planet formation. HH 212 is a privileged laboratory to study a pristine jet-disk system. Therefore we investigate the innermost region ($<100$ AU) around the HH 212-MM1 protostar through ALMA band\\,7 observations of methanol. The 8 GHz bandwidth spectrum towards the peak of the continuum emission of the HH 212 system reveals at least 19 transitions of methanol. Several of these lines (among which several vibrationally excited lines in the v$_{\\rm t}=1,2$ states) have upper energies above 500 K. They originate from a compact ($<135$ AU in diameter), hot ($\\sim 295$ K) region elongated along the direction of the SiO jet. We performed a fit in the $uv$ plane of various velocity channels of the strongest high-excitation lines. The blue- and red-shifted velocity centroids are shifted roughly symmetrically on either...

  7. The Herschel Cold Debris Disks

    CERN Document Server

    Gaspar, Andras

    2013-01-01

    The Herschel "DUst around NEarby Stars (DUNES)" survey has found a number of debris disk candidates that are apparently very cold, with temperatures near 22K. It has proven difficult to fit their spectral energy distributions with conventional models for debris disks. Given this issue we carefully examine the alternative explanation, that the detections arise from confusion with IR cirrus and/or background galaxies that are not physically associated with the foreground star. We find that such an explanation is consistent with all of these detections.

  8. Positive binding energy of a biexciton confined in a localization center formed in a single InxGa1-xN/GaN quantum disk

    OpenAIRE

    Bardoux, R.; Kaneta, A.; Funato, M.; Kawakami, Y.; Kikuchi, A; Kishino, K.

    2009-01-01

    We report microphotoluminescence spectroscopy performed on individual and ensemble InGaN/GaN quantum disks (Q-disks). The typical spectrum of a single Q-disk exhibited the contribution of localization centers (LCs) formed in the InGaN active layer of the Q-disks, characterized by sharp lines appearing on the low energy side of the spectra. In addition, a broader emission peak identified as the luminescence of the quasi-two-dimensional (2D) InGaN active layer surrounding the LCs appears system...

  9. Modified viscosity in accretion disks. Application to Galactic black hole binaries, intermediate mass black holes and AGN

    CERN Document Server

    Grzędzielski, Mikołaj; Czerny, Bożena; Wu, Qingwen

    2016-01-01

    Black holes surrounded by accretion disks are present in the Universe in different scales of masses, from microquasars up to the Active Galactic Nuclei. The current picture of the accretion disk theory remains still ad hoc, due the complexity of the magnetic field action. In addition, the accretion disks at high Eddington rates can be radiation-pressure dominated and, according to some of the heating prescriptions, thermally unstable. The observational verification of their resulting variability patterns may shed the light on both the role of radiation pressure and magnetic field in the accretion process. We compute the structure and time evolution of an accretion disk. We supplement this model with a modified viscosity prescription, which can to some extent describe the magnetization of the disk. We study the results for a large grid of models and derive conclusions separately for different scales of black hole masses. We show the dependences between the flare, or outburst, duration, its amplitude and period...

  10. Herschel-PACS observation of the 10 Myr old T Tauri disk TW Hya. Constraining the disk gas mass

    Science.gov (United States)

    Thi, W.-F.; Mathews, G.; Ménard, F.; Woitke, P.; Meeus, G.; Riviere-Marichalar, P.; Pinte, C.; Howard, C. D.; Roberge, A.; Sandell, G.; Pascucci, I.; Riaz, B.; Grady, C. A.; Dent, W. R. F.; Kamp, I.; Duchêne, G.; Augereau, J.-C.; Pantin, E.; Vandenbussche, B.; Tilling, I.; Williams, J. P.; Eiroa, C.; Barrado, D.; Alacid, J. M.; Andrews, S.; Ardila, D. R.; Aresu, G.; Brittain, S.; Ciardi, D. R.; Danchi, W.; Fedele, D.; de Gregorio-Monsalvo, I.; Heras, A.; Huelamo, N.; Krivov, A.; Lebreton, J.; Liseau, R.; Martin-Zaidi, C.; Mendigutía, I.; Montesinos, B.; Mora, A.; Morales-Calderon, M.; Nomura, H.; Phillips, N.; Podio, L.; Poelman, D. R.; Ramsay, S.; Rice, K.; Solano, E.; Walker, H.; White, G. J.; Wright, G.

    2010-07-01

    Planets are formed in disks around young stars. With an age of ~10 Myr, TW Hya is one of the nearest T Tauri stars that is still surrounded by a relatively massive disk. In addition a large number of molecules has been found in the TW Hya disk, making TW Hya the perfect test case in a large survey of disks with Herschel-PACS to directly study their gaseous component. We aim to constrain the gas and dust mass of the circumstellar disk around TW Hya. We observed the fine-structure lines of [O i] and [C ii] as part of the open-time large program GASPS. We complement this with continuum data and ground-based 12 CO 3-2 and 13CO 3-2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code MCFOST and the thermo-chemical code ProDiMo to derive the gas and dust masses. We detect the [O i] line at 63 μm. The other lines that were observed, [O i] at 145 μm and [C ii] at 157 μm, are not detected. No extended emission has been found. Preliminary modeling of the photometric and line data assuming [ 12CO] /[ 13CO] = 69 suggests a dust mass for grains with radius <1 mm of ~1.9 × 10-4 M⊙ (total solid mass of 3 × 10-3 M⊙) and a gas mass of (0.5-5) × 10-3 M⊙. The gas-to-dust mass may be lower than the standard interstellar value of 100. Herschel is an ESA space observatory with science instruments provided by Principal Investigator consortia. It is open for proposals for observing time from the worldwide astronomical community.Appendix is only available in electronic form at http://www.aanda.org

  11. On the Orbital Evolution of a Giant Planet Pair Embedded in a Gaseous Disk. I. Jupiter-Saturn Configuration

    Science.gov (United States)

    Zhang, Hui; Zhou, Ji-Lin

    2010-05-01

    We carry out a series of high-resolution (1024 × 1024) hydrodynamical simulations to investigate the orbital evolution of Jupiter and Saturn embedded in a gaseous protostellar disk. Our work extends the results in the classical papers of Masset & Snellgrove and Morbidelli & Crida by exploring various surface density profiles (σ), where σ vprop r -α. The stability of the mean motion resonances (MMRs) caused by the convergent migration of the two planets is studied as well. Our results show that (1) the gap formation process of Saturn is greatly delayed by the tidal perturbation of Jupiter. These perturbations cause inward or outward runaway migration of Saturn, depending on the density profiles on the disk. (2) The convergent migration rate increases as α increases and the type of MMRs depends on α as well. When 0 4/3, Saturn passes through the 2:1 MMR with Jupiter and is captured into the 3:2 MMR. (3) The 3:2 MMR turns out to be unstable when the eccentricity of Saturn (es ) increases too high. The critical value above which instability will set in is es ~ 0.15. We also observe that the two planets are trapped into 2:1 MMR after the break of 3:2 MMR. This process may provide useful information for the formation of orbital configuration between Jupiter and Saturn in the solar system.

  12. Identification of -SiC surrounded by relatable surrounding diamond medium using weak Raman surface phonons

    Indian Academy of Sciences (India)

    Mohan Kumar Kuntumalla; Harish Ojha; Vadali Venkata Satya Siva Srikanth

    2013-11-01

    It is difficult to detect -SiC using micro-Raman scattering, if it is surrounded by carbon medium. Here, -SiC is identified in the presence of a relatable surrounding diamond medium using subtle, but discernible Raman surface phonons. In this study, diamond/-SiC nanocomposite thin film system is considered in which nanosized -SiC crystallites are surrounded by a relatable nanodiamond medium that leads to the appearance of a weak Raman surface phonon band at about 855 cm-1. Change in the nature of the surrounding material structure and its volume content when relatable, will affect the resultant Raman response of -SiC phase as seen in the present case of diamond/-SiC nanocomposite thin films.

  13. Herniated Disk in the Lower Back

    Science.gov (United States)

    ... two components: Healthy intervertebral disk (cross- section view). • Annulus fibrosus. This is the tough, flexible outer ring ... the Lower Back cont. Surgical Treatment Only a small percentage of patients with lumbar disk herniations require ...

  14. Intermediate-mass hot cores at 500 AU: disks or outflows?

    CERN Document Server

    Palau, Aina; Girart, Josep M; Fontani, Francesco; Boissier, Jeremie; Pietu, Vincent; Sanchez-Monge, Alvaro; Busquet, Gemma; Estalella, Robert; Zapata, Luis A; Zhang, Qizhou; Neri, Roberto; Ho, Paul T P; Alonso-Albi, Tomas; Audard, Marc

    2011-01-01

    Observations with the Plateau de Bure Interferometer in the most extended configuration toward two intermediate-mass star-forming regions, IRAS22198+6336 and AFGL5142, reveal the presence of several complex organic molecules at ~500 AU scales, confirming the presence of hot cores in both regions. The hot cores are not rich in CN-bearing molecules, as often seen in massive hot cores, and are mainly traced by CH3CH2OH, (CH2OH)2, CH3COCH3, and CH3OH, with additionally CH3CHO, CH3OD and HCOOD for IRAS22198+6336, and C6H, and O13CS for AFGL5142. The emission of complex molecules is resolved down to sizes of ~300 and ~600 AU, for IRAS22198+6336 and AFGL5142, respectively, and most likely is tracing protostellar disks rather than flattened envelopes or toroids as usually found. This is specially clear for the case of IRAS22198+6336, where we detect a velocity gradient for all the mapped molecules perpendicular to the most chemically rich outflow of the region, yielding a dynamic mass >4 Msun. As for AFGL5142, the ho...

  15. The Structure of Brown Dwarf Circumstellar Disks

    OpenAIRE

    Walker, Christina; Wood, Kenneth; Lada, C. J.; Robitaille, Thomas; Bjorkman, J. E.; Whitney, Barbara

    2004-01-01

    We present synthetic spectra for circumstellar disks that are heated by radiation from a central brown dwarf. Under the assumption of vertical hydrostatic equilibrium, our models yield scaleheights for brown dwarf disks in excess of three times those derived for classical T Tauri (CTTS) disks. If the near-IR excess emission observed from brown dwarfs is indeed due to circumstellar disks, then the large scaleheights we find could have a significant impact on the optical and near-IR detectabili...

  16. Optimization of the Processing of Mo Disks

    Energy Technology Data Exchange (ETDEWEB)

    Tkac, Peter [Argonne National Lab. (ANL), Argonne, IL (United States); Rotsch, David A. [Argonne National Lab. (ANL), Argonne, IL (United States); Stepinski, Dominique [Argonne National Lab. (ANL), Argonne, IL (United States); Makarashvili, Vakhtang [Argonne National Lab. (ANL), Argonne, IL (United States); Harvey, James [NorthStar Medical Technologies, LLC, Madison, WI (United States); Vandegrift, George F. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2016-01-01

    The objective of this work is to decrease the processing time for irradiated disks of enriched Mo for the production of 99Mo. Results are given for the dissolution of nonirradiated Mo disks, optimization of the process for large-scale dissolution of sintered disks, optimization of the removal of the main side products (Zr and Nb) from dissolved targets, and dissolution of irradiated Mo disks.

  17. Fabrication of Large YBCO Superconducting Disks

    Science.gov (United States)

    Koczor, Ronald J.; Noever, David A.; Robertson, Glen A.

    1999-01-01

    We have undertaken fabrication of large bulk items to develop a repeatable process and to provide test articles in laboratory experiments investigating reported coupling of electromagnetic fields with the local gravity field in the presence of rotating superconducting disks. A successful process was developed which resulted in fabrication of 30 cm diameter annular disks. The disks were fabricated of the superconductor YBa2Cu3O(7-x). Various material parameters of the disks were measured.

  18. CONSTRAINTS ON THE RADIAL VARIATION OF GRAIN GROWTH IN THE AS 209 CIRCUMSTELLAR DISK

    Energy Technology Data Exchange (ETDEWEB)

    Perez, Laura M.; Carpenter, John M.; Isella, Andrea; Ricci, Luca; Sargent, Anneila I. [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Chandler, Claire J. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Andrews, Sean M.; Harris, Robert J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Calvet, Nuria [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Corder, Stuartt A. [Joint ALMA Observatory, Av. Alonso de Cordova 3107, Vitacura, Santiago (Chile); Deller, Adam T. [The Netherlands Institute for Radio Astronomy (ASTRON), 7990-AA Dwingeloo (Netherlands); Dullemond, Cornelis P.; Linz, Hendrik [Center for Astronomy, Heidelberg University, Albert Ueberle Str. 2, D-69120 Heidelberg (Germany); Greaves, Jane S. [School of Physics and Astronomy, University of St. Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Henning, Thomas [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Kwon, Woojin [Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801 (United States); Lazio, Joseph [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91106 (United States); Mundy, Lee G.; Storm, Shaye [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Testi, Leonardo [European Southern Observatory, Karl Schwarzschild Str. 2, D-85748 Garching (Germany); and others

    2012-11-20

    We present dust continuum observations of the protoplanetary disk surrounding the pre-main-sequence star AS 209, spanning more than an order of magnitude in wavelength from 0.88 to 9.8 mm. The disk was observed with subarcsecond angular resolution (0.''2-0.''5) to investigate radial variations in its dust properties. At longer wavelengths, the disk emission structure is notably more compact, providing model-independent evidence for changes in the grain properties across the disk. We find that physical models which reproduce the disk emission require a radial dependence of the dust opacity {kappa}{sub {nu}}. Assuming that the observed wavelength-dependent structure can be attributed to radial variations in the dust opacity spectral index ({beta}), we find that {beta}(R) increases from {beta} < 0.5 at {approx}20 AU to {beta} > 1.5 for R {approx}> 80 AU, inconsistent with a constant value of {beta} across the disk (at the 10{sigma} level). Furthermore, if radial variations of {kappa}{sub {nu}} are caused by particle growth, we find that the maximum size of the particle-size distribution (a{sub max}) increases from submillimeter-sized grains in the outer disk (R {approx}> 70 AU) to millimeter- and centimeter-sized grains in the inner disk regions (R {approx}< 70 AU). We compare our observational constraint on a{sub max}(R) with predictions from physical models of dust evolution in protoplanetary disks. For the dust composition and particle-size distribution investigated here, our observational constraints on a{sub max}(R) are consistent with models where the maximum grain size is limited by radial drift.

  19. PSOCT studies of intervertebral disk

    Science.gov (United States)

    Matcher, Stephen J.; Winlove, Peter C.; Gangnus, Sergey V.

    2004-07-01

    Polarization-sensitive optical coherence tomography (PSOCT) is an emerging optical imaging technique that is sensitive to the birefringence properties of tissues. It thus has applications in studying the large-scale ordering of collagen fibers within connective tissues. This ordering not only provides useful insights into the relationship between structure and function for various anatomical structures but also is an indicator of pathology. Intervertebral disk is an elastic tissue of the spine and possesses a 3-D collagen structure well suited to study using PSOCT. Since the outer layer of the disk has a lamellar structure with collagen fibers oriented in a trellis-like arrangement between lamellae, the birefringence fast-axis shows pronounced variations with depth, on a spatial scale of about 100 μm. The lamellar thickness varies with age and possibly with disease. We have used a polarisation-sensitive optical coherence tomography system to measure the birefringence properties of freshly excised, hydrated bovine caudal intervertebral disk and compared this with equine flexor tendon. Our results clearly demonstrate the ability of PSOCT to detect the outer three lamellae, down to a depth of at least 700 μm, via discontinuities in the depth-resolved retardance. We have applied a simple semi-empirical model based on Jones calculus to quantify the variation in the fast-axis orientation with depth. Our data and modeling is in broad agreement with previous studies using x-ray diffraction and polarization microscopy applied to histological sections of dehydrated disk. Our results imply that PSOCT may prove a useful tool to study collagen organisation within intervertebral disk in vitro and possibly in vivo and its variation with age and disease.

  20. GIANT Hα NEBULA SURROUNDING THE STARBURST MERGER NGC 6240

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Michitoshi [Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Yagi, Masafumi; Komiyama, Yutaka; Kashikawa, Nobunari [Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Ohyama, Youichi [Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No.1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, R.O.C. (China); Tanaka, Hisashi [Department of Physical Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Okamura, Sadanori, E-mail: yoshidam@hiroshima-u.ac.jp [Department of Advanced Sciences, Faculty of Science and Engineering, Hosei University, Koganei, Tokyo 184-8584 (Japan)

    2016-03-20

    We revealed the detailed structure of a vastly extended Hα-emitting nebula (“Hα nebula”) surrounding the starburst/merging galaxy NGC 6240 by deep narrow-band imaging observations with the Subaru Suprime-Cam. The extent of the nebula is ∼90 kpc in diameter and the total Hα luminosity amounts to L{sub Hα} ≈ 1.6 × 10{sup 42} erg s{sup −1}. The volume filling factor and the mass of the warm ionized gas are ∼10{sup −4}–10{sup −5} and ∼5 × 10{sup 8} M{sub ⊙}, respectively. The nebula has a complicated structure, which includes numerous filaments, loops, bubbles, and knots. We found that there is a tight spatial correlation between the Hα nebula and the extended soft-X-ray-emitting gas, both in large and small scales. The overall morphology of the nebula is dominated by filamentary structures radially extending from the center of the galaxy. A large-scale bipolar bubble extends along the minor axis of the main stellar disk. The morphology strongly suggests that the nebula was formed by intense outflows—superwinds—driven by starbursts. We also found three bright knots embedded in a looped filament of ionized gas that show head-tail morphologies in both emission-line and continuum, suggesting close interactions between the outflows and star-forming regions. Based on the morphology and surface brightness distribution of the Hα nebula, we propose the scenario that three major episodes of starburst/superwind activities, which were initiated ∼10{sup 2} Myr ago, formed the extended ionized gas nebula of NGC 6240.