Secondary Disk Research Articles

JWST-TST High Contrast: Asymmetries, Dust Populations, and Hints of a Collision in the β Pictoris Disk with NIRCam and MIRI

We present the first JWST Mid-Infrared Instrument (MIRI) and Near Infrared Camera (NIRCam) observations of the prominent debris disk around β Pictoris. Coronagraphic observations in eight filters spanning from 1.8 to 23 μm provide an unprecedentedly clear view of the disk at these wavelengths. The objectives of the observing program were to investigate the dust composition and distribution and to investigate the presence of planets in the system. In this paper, we focus on the disk components, providing surface brightness measurements for all images and a detailed investigation of the asymmetries observed. A companion paper by Kammerer et al. will focus on the planets in this system using the same data. We report for the first time the presence of an extended secondary disk in thermal emission, with a curved extension bent away from the plane of the disk. This feature, which we refer to as the “cat’s tail,” seems to be connected with the previously reported CO clump, mid-infrared asymmetry detected on the southwest side of the disk, and the warp observed in scattered light. We present a model of this secondary disk sporadically producing dust that broadly reproduces the morphology, flux, and color of the cat’s tail, as well as other features observed in the disk, and which suggests the secondary disk is composed largely of porous, organic refractory dust grains.

On the Formation and Interaction of Multiple Supermassive Stars in Cosmological Flows

Supermassive primordial stars with masses exceeding ∼105 M ⊙ that form in atomically cooled halos are the leading candidates for the origin of high-redshift quasars at z > 6. Recent numerical simulations, however, find that multiple accretion disks can form within a halo, each of which can potentially host a supermassive star. We investigate the formation and evolution of secondary supermassive stars in atomically cooled halos, including strong variations in their accretion histories driven by gravitational interactions between their disks and those surrounding the primary supermassive stars in each halo. We find that all secondary disks produce long-lived supermassive stars under sustained rapid accretion. We also find, however, that the majority of secondary supermassive stars do undergo at least one protracted quiescent accretion phase, during which time they thermally relax and may become powerful sources of ionizing feedback. In many halos, the two satellite disks collide, suggesting that the two stars can come into close proximity. This may induce additional mass exchange between them, leading to a great diversity of possible outcomes. These range from coevolution as main-sequence stars to main sequence—black hole pairs and black hole—black hole mergers. We discuss the likely outcome for these binary interactions based on the evolutionary state of both supermassive stars at the end of our simulations, as well as prospects for their future detection by current and next-generation facilities.

Modeling disk fragmentation and multiplicity in massive star formation

Context. There is growing evidence that massive stars grow by disk accretion in a similar way to their low-mass counterparts. Early in evolution, these disks can achieve masses that are comparable to the current stellar mass, and therefore the forming disks are highly susceptible to gravitational fragmentation. Aims. We investigate the formation and early evolution of an accretion disk around a forming massive protostar, focussing on its fragmentation physics. To this end, we follow the collapse of a molecular cloud of gas and dust, the formation of a massive protostar, the formation of its circumstellar disk, and the formation and evolution of the disk fragments. Methods. We used a grid-based, self-gravity radiation hydrodynamics code including a sub-grid module for stellar evolution and dust evolution. We purposely do not use a sub-grid module for fragmentation such as sink particles to allow for all paths of fragment formation and destruction, but instead we keep the spatial grid resolution high enough to properly resolve the physical length scales of the problem, namely the pressure scale height and Jeans length of the disk. Simulations are performed on a grid in spherical coordinates with a logarithmic spacing of the grid cells in the radial direction and a cosine distribution of the grid cells in the polar direction, focusing the spatial resolution on the disk midplane. As a consequence, roughly 25% of the total number of grid cells, corresponding to ~26 million grid cells, are used to model the disk physics. These constitute the highest resolution simulations performed up to now on disk fragmentation around a forming massive star with the physics considered here. For a better understanding of the effects of spatial resolution and to compare our high-resolution results with previous lower resolution studies in the literature, we perform the same simulation at five different resolutions, each run differing in resolution from its predecessor by a factor of two. Results. The cloud collapses and a massive (proto)star is formed in its center surrounded by a fragmenting Keplerian-like accretion disk with spiral arms. The fragments have masses of ~1 M⊙, and their continuous interactions with the disk, spiral arms, and other fragments result in eccentric orbits. Fragments form hydrostatic cores surrounded by secondary disks with spiral arms that also produce new fragments. We identified several mechanisms of fragment formation, interaction, and destruction. Central temperatures of the fragments can reach the hydrogen dissociation limit, form second Larson cores, and evolve into companion stars. Based on this, we study the multiplicity predicted by the simulations and find approximately six companions at different distances from the primary: from possible spectroscopic multiples, to companions at distances between 1000 and 2000 au.

Evidence for the formation of the young counter-rotating stellar disk from gas acquired by IC 719

Aims. The formation scenario of extended counter-rotating stellar disks in galaxies is still debated. In this paper, we study the S0 galaxy IC 719 known to host two large-scale counter-rotating stellar disks in order to investigate their formation mechanism. Methods. We exploit the large field of view and wavelength coverage of the Multi Unit Spectroscopic Explorer (MUSE) spectrograph to derive two-dimensional (2D) maps of the various properties of the counter-rotating stellar disks, such as age, metallicity, kinematics, spatial distribution, the kinematical and chemical properties of the ionized gas, and the dust map. Results. Due to the large wavelength range, and in particular to the presence of the Calcium Triplet λλ8498, 8542, 8662 Å (CaT hereafter), the spectroscopic analysis allows us to separate the two stellar components in great detail. This permits precise measurement of both the velocity and velocity dispersion of the two components as well as their spatial distribution. We derived a 2D map of the age and metallicity of the two stellar components, as well as the star formation rate and gas-phase metallicity from the ionized gas emission maps. Conclusions. The main stellar disk of the galaxy is kinematically hotter, older, thicker and with larger scale-length than the secondary disk. There is no doubt that the latter is strongly linked to the ionized gas component: they have the same kinematics and similar vertical and radial spatial distribution. This result is in favor of a gas accretion scenario over a binary merger scenario to explain the origin of counter-rotation in IC 719. One source of gas that may have contributed to the accretion process is the cloud that surrounds IC 719.

Numerical simulation of multipactor phenomenon on the surface of cylinder window disk

A particle model that is based on Monte Carlo particle simulation arithmetic is built up to investigate the multipactor behavior on the surface of cylinder window disk in pill-box window. The regime of multipactor in the inhomogeneous electric field is obtained. The simulation results prove that the interaction between secondary electrons and window disk is sustained by magnetic field force on the upstream side. The multipactor phenomenon acts intensively in the area with a great electric field. The ponderomotive force does not devote any effort to multipactor on the upstream side. On the downstream side, the multipactor cannot be excited without strong enough surface electrostatic field because of the positive magnetic field force. With the increase of transmitting power, secondary electrons can obtain more energies. Due to the effect of ponderomotive force, the multipactor region transfers from the area with powerful electric field to the weak one on the downstream side. Besides, the resistance effect of electrostatic isolation on multipactor is also confirmed in the input port of cylinder waveguide.

Spectral observations of ɛ aurigae during the 2009–2011 eclipse

The results of the spectral observations of a unique eclipsing system {\epsilon} Aurigae obtained during the recent eclipse are presented. We traced the spectral lines variations at different eclipse phases. The part of these changes is the result of the absorption of stellar radiation by the gas component of circumstellar (CS) disk around the secondary. The other part arises due to the obscuration of the stellar photosphere and the closest circumstellar area by the dusty CS disk. Comparison of our results with the previous one, obtained by Lambert & Sawyer during the 1982-1984 eclipse, indicates the good agreement, and argues in favor of stability of the secondary disk structure. On the base of the new observational data we provide a new mass estimation of the system components.

Experimental Study on Vertical Base-Isolated System with Disk Spring

A new vertical isolator designed by disk spring, called combined disk spring bearing (DSB), is introduced in this paper. DSB is composed of one main disk spring bearing and eight secondary disk spring bearings. Performance tests show that DSB had good property of variable vertical stiffness and high vertical damping. Then, the effectiveness of DSB vertical base-isolated devices in reducing structural responses caused by earthquakes through a series of 1/2 scale shaking table tests. are conducted to study the seismic responses of the and the DSB vertical-isolated system. Compared with the fixed-base system, experimental results show that the DSB vertical-isolated system can isolate vertical earthquake energy remarkably. Large displacement of the DSB vertical-isolated system occurred on the isolation layer, and the inter-story deformation of the superstructure changed slightly. The acceleration responses of DSB vertical-isolated system decreased more than 50% and the displacement responses decreased more than 40% at 0.4g PGA, which confirmed that DSB could decrease the seismic responses effectively.

GAS ACCRETION FROM A CIRCUMBINARY DISK

A new computational scheme is developed to study gas accretion from a circumbinary disk. The scheme decomposes the gas velocity into two components one of which denotes the Keplerian rotation and the other of which does the deviation from it. This scheme enables us to solve the centrifugal balance of a gas disk against gravity with better accuracy, since the former inertia force cancels the gravity. It is applied to circumbinary disk rotating around binary of which primary and secondary has mass ratio, 1.4:0.95. The gravity is reduced artificially softened only in small circular regions around the primary and secondary. The radii are 7% of the binary separation and much smaller than those in the previous grid based simulations. 7 Models are constructed to study dependence on the gas temperature and the initial inner radius of the disk. The gas accretion shows both fast and slow time variations while the binary is assumed to have a circular orbit. The time variation is due to oscillation of spiral arms in the circumbinary disk. The masses of primary and secondary disks increase while oscillating appreciably. The mass accretion rate tends to be higher for the primary disk although the secondary disk has a higher accretion rate in certain periods. The primary disk is perturbed intensely by the impact of gas flow so that the outer part is removed. The secondary disk is quiet in most of time on the contrary. Both the primary and secondary disks have traveling spiral waves which transfer angular momentum within them.

DUST DISTRIBUTION IN THE β PICTORIS CIRCUMSTELLAR DISKS

We present 3-D models of dust distribution around beta Pictoris that produce the best fits to the Hubble Space Telescope Advanced Camera for Surveys' (HST/ACS) images obtained by Golimowski and co-workers. We allow for the presence of either one or two separate axisymmetric dust disks. The density models are analytical, radial two-power-laws joined smoothly at a cross-over radius with density exponentially decreasing away from the mid-plane of the disks. Two-disk models match the data best, yielding a reduced chi^2 of ~1.2. Our two-disk model reproduces many of the asymmetries reported in the literature and suggests that it is the secondary (tilted) disk which is largely responsible for them. Our model suggests that the secondary disk is not constrained to the inner regions of the system (extending out to at least 250 AU) and that it has a slightly larger total area of dust than the primary, as a result of slower fall-off of density with radius and height. This surprising result raises many questions about the origin and dynamics of such a pair of disks. The disks overlap, but can coexist owing to their low optical depths and therefore long mean collision times. We find that the two disks have dust replenishment times on the order of 10^4 yr at ~100 AU, hinting at the presence of planetesimals that are responsible for the production of 2nd generation dust. A plausible conjecture, which needs to be confirmed by physical modeling of the collisional dynamics of bodies in the disks, is that the two observed disks are derived from underlying planetesimal disks; such disks would be anchored by the gravitational influence of planets located at less than 70 AU from beta Pic that are themselves in slightly inclined orbits.

The Evolution of Circumstellar Disks in Ophiuchus Binaries

Four Ophiuchus binaries, two Class I systems and two Class II systems, with separations of ~450-1100 AU, were observed with the Owens Valley Radio Observatory (OVRO) millimeter interferometer. In each system, the 3 mm continuum maps show dust emission at the location of the primary star, but no emission at the position of the secondary. This result is different from observations of less evolved Class 0 binaries, in which dust emission is detected from both sources. The nondetection of secondary disks is, however, similar to the dust distribution seen in wide Class II Taurus binaries. The combined OVRO results from the Ophiuchus and Taurus binaries suggest that secondary disk masses are significantly lower than primary disk masses by the Class II stage, with initial evidence that massive secondary disks are reduced by the Class I stage. Although some of the secondaries retain hot inner disk material, the early dissipation of massive outer disks may negatively impact planet formation around secondary stars. Masses for the circumprimary disks are within the range of masses measured for disks around single T Tauri stars and, in some cases, larger than the minimum mass solar nebula. More massive primary disks are predicted by several formation models and are broadly consistent with the observations. Combining the 3 mm data with previous 1.3 mm observations, the dust opacity power-law index for each primary disk is estimated. The opacity index values are all less than the scaling for interstellar dust, possibly indicating grain growth within the circumprimary disks.

Hubble Space TelescopeACS Multiband Coronagraphic Imaging of the Debris Disk around β Pictoris

We present F435W (B), F606W (broad V), and F814W (broad I) coronagraphic images of the debris disk around β Pictoris obtained with the Hubble Space Telescope's Advanced Camera for Surveys. These images provide the most photometrically accurate and morphologically detailed views of the disk between 30 and 300 AU from the star ever recorded in scattered light. We confirm that the previously reported warp in the inner disk is a distinct secondary disk inclined by ∼5° from the main disk. The projected spine of the secondary disk coincides with the isophotal inflections, or "butterfly asymmetry," previously seen at large distances from the star. We also confirm that the opposing extensions of the main disk have different position angles, but we find that this "wing-tilt asymmetry" is centered on the star rather than offset from it, as previously reported. The main disk's northeast extension is linear from 80 to 250 AU, but the southwest extension is distinctly bowed with an amplitude of ∼1 AU over the same region. Both extensions of the secondary disk appear linear, but not collinear, from 80 to 150 AU. Within ∼120 AU of the star, the main disk is ∼50% thinner than previously reported. The surface brightness profiles along the spine of the main disk are fitted with four distinct radial power laws between 40 and 250 AU, while those of the secondary disk between 80 and 150 AU are fitted with single power laws. These discrepancies suggest that the two disks have different grain compositions or size distributions. The F606W/F435W and F814W/F435W flux ratios of the composite disk are nonuniform and asymmetric about both projected axes of the disk. The disk's northwest region appears 20%-30% redder than its southeast region, which is inconsistent with the notion that forward scattering from the nearer northwest side of the disk should diminish with increasing wavelength. Within ∼120 AU, the mF435W - mF606W and mF435W - mF814W colors along the spine of the main disk are ∼10% and ∼20% redder, respectively, than those of β Pic. These colors increasingly redden beyond ∼120 AU, becoming 25% and 40% redder, respectively, than the star at 250 AU. These measurements overrule previous determinations that the disk is composed of neutrally scattering grains. The change in color gradient at ∼120 AU nearly coincides with the prominent inflection in the surface brightness profile at ∼115 AU and the expected water-ice sublimation boundary. We compare the observed red colors within ∼120 AU with the simulated colors of nonicy grains having a radial number density ∝r-3 and different compositions, porosities, and minimum grain sizes. The observed colors are consistent with those of compact or moderately porous grains of astronomical silicate and/or graphite with sizes ≳0.15-0.20 μm, but the colors are inconsistent with the blue colors expected from grains with porosities ≳90%. The increasingly red colors beyond the ice sublimation zone may indicate the condensation of icy mantles on the refractory grains, or they may reflect an increasing minimum grain size caused by the cessation of cometary activity.

THE CLASSIC: Pyogenic Vertebral Osteomyelitis

THE CLASSIC: Pyogenic Vertebral Osteomyelitis

On the origin of isophotal shapes in elliptical galaxies

Using semi-analytical models of galaxy formation, the origin of boxy and disky elliptical galaxies is investigated. We find that the simple scenario, motivated by N-body simulations, in which the isophotal shape is only dependent on the mass ratio of the last major merger, is not able to reproduce the observation that the fraction of boxy and disky ellipticals depends on galaxy luminosity. The observations can however be reproduce with the following reasonable assumptions: (i) equal-mass mergers lead to boxy ellipticals and unequal-mass mergers produce disky ellipticals (as motivated by N-body simulations) (ii) major mergers between bulge-dominated galaxies result always in boxy ellipticals, independent of the mass ratio, (iii) merger remnants that subsequently accrete gas leading to a secondary stellar disk with more than $20 %$ the total stellar fraction are always disky. Boxy and disky ellipticals can be divided into two subclasses, depending on their formation history. Boxy ellipticals either formed by equal mass mergers of disk galaxies or by major mergers of early-type galaxies. We find that disky ellipticals are indicators of unequal-mass mergers or late gas infall. Disky ellipticals with high luminosities preferentially are 1-component systems that result from unequal mass mergers whereas low-luminosity disky ellipticals are more likely to harbor secondary disk components. In addition, the fraction of disky ellipticals with secular disk components should increase in regions with higher galaxy densities. Taking into account the conversion of cuspy cores into flat low-density cores by black hole merging we find that disky ellipticals should contain central density cusps whereas boxy ellipticals should in general be characterized by flat cores.

EMISSION AND REEMISSION PROPERTIES OF GOLD DOUBLE-DISK TARGETS HEATED BY LASER

A new kind of double-disk gold targets were irradiated by 0.35μm intense laser and-the properties of impvoved X-ray spectra were investigated at “Xingguang”laser facilities.-Collision velocities between the-primary and secondary disks' plasmas have been measured.This double-disk target's design has avoided the influence of the spraying plasma from primary disk to a certain extent, and increased the “clearance” for ablated secondary disk. Two soft X-ray spectrometers were used to measure X-ray radiation from the primary and secondary disks, respectively. An X-ray streaked camera was used to obtain time-spactial images emitted from laser-plasma of double-disks targets. Experimental results were-analyzed physically.

INDUSTRY AND PRACTICE

Response time of a database system is largely determined by the number of secondary disk accesses required to process database transactions. To minimize disk accesses, a database file should be structured in such a way as to closely match data requirements of these transactions. The way in which data are organized for efficient processing of database transactions is called database partitioning. As data are stored in the form of tables in a relational database, data partitioning can be performed either vertically (i.e, along the attributes or columns) or horizontally (i.e., along the tuples or rows).

DCD —disk caching disk

This paper presents a novel disk storage architecture called DCD, Disk Caching Disk, for the purpose of optimizing I/O performance. The main idea of the DCD is to use a small log disk, referred to as cache-disk, as a secondary disk cache to optimize write performance. While the cache-disk and the normal data disk have the same physical properties, the access speed of the former differs dramatically from the latter because of different data units and different ways in which data are accessed. Our objective is to exploit this speed difference by using the log disk as a cache to build a reliable and smooth disk hierarchy. A small RAM buffer is used to collect small write requests to form a log which is transferred onto the cache-disk whenever the cache-disk is idle. Because of the temporal locality that exists in office/engineering work-load environments, the DCD system shows write performance close to the same size RAM (i.e. solid-state disk) for the cost of a disk. Moreover, the cache-disk can also be implemented as a logical disk in which case a small portion of the normal data disk is used as the log disk. Trace-driven simulation experiments are carried out to evaluate the performance of the proposed disk architecture. Under the office/engineering work-load environment, the DCD shows superb disk performance for writes as compared to existing disk systems. Performance improvements of up to two orders of magnitude are observed in terms of average response time for write operations. Furthermore, DCD is very reliable and works at the device or device driver level. As a result, it can be applied directly to current file systems without the need of changing the operating system.

Galactic evolution. II - Disk galaxies with massive halos

Models of galactic evolution are computed in which matter shed by dying halo stars accumulates in a smaller, more rapidly rotating disk. The models are simpler and more successful than one-zone (pure disk) models in that (1) the observed absence of low-metal-abundance low-mass dwarfs is expected, not anomalous and (2) the relative birthrate function (or IMF) need not be a strongly variable function of time in agreement with recent interpretations of observed stellar populations and neutral hydrogen in our own and other galaxies. Even a simple 'Salpeter' IMF for both disk and halo will produce an acceptable model. The model with a halo 'Salpeter' IMF, roughly one-quarter of the mass in the secondary disk, and approximately half the metals produced in the halo seems most compatible with observations of the metal abundance in low-mass stars, the deuterium abundance, halo planetary nebulae, and light from Population II stars, as well as with arguments on the stability of the disk.

Effect of Particle Size on the Diffraction Image in Microscopy with Narrow-Coned, Axial Illumination

The distribution of energy density is derived for the diffraction image produced by an Airy type objective of a single, uniform, opaque or transmitting particle located in a uniform, transmitting surround and illuminated by a narrow cone of axial illumination. It is shown that for a large class of particles the diffraction image can have an irregular variation in energy density in addition to a regular variation and that these variations are in accord with experiments performed with opaque particles. The irregular variation can appear as a secondary Airy disk located well within the regular Airy disk. The development of the diffraction image with increasing radii of disk-shaped particles is described. The equations which govern this development are adapted to the determination of the radius of the particle from linear or photometric measurements upon the diffraction image. The smallest measurable radii are restricted by practical limits rather than by physical limits as in the resolution of two particles. The practical limit is about 0.6 Airy unit for the linear measurements but may fall below 0.3 Airy unit with photometric measurements.

A Study of the Reflection Effect in Eclipsing Binaries

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of the Reflection Effect in Eclipsing Binaries Pike, Eugene W. Abstract By means of approximations, the equations of Milne for re-radiation from stellar surfaces are applied to close binaries. The variation of the reflection effect with phase is computed, and a more cwcurate approximation than the one in present use is proposed. The exaggerated darkening at the limb shown by the secondary disk, as seen at second- ary minimum, is illustrated, and its possible effect on solutions of the light-curve dis- cussed. An approximate correction to the spectroscop~ically determined masses of a binary, to account for the asymmetrical lighting of the secondary as seen at quadrature, is com- puted. A large discrepancy between the computed and observed absolute magnitudes of the reflection effect is illustrated and discussed Publication: The Astrophysical Journal Pub Date: May 1931 DOI: 10.1086/143305 Bibcode: 1931ApJ....73..205P full text sources ADS |