Opaque Disk Research Articles

ASpitzerStudy of Dusty Disks in the Scorpius‐Centaurus OB Association

We have obtained Spitzer Space Telescope MIPS observations of 40 F- and G-type common proper motion members of the Scorpius-Centaurus OB association with ages between 5 and 20 Myr at 24 and 70 ?m. We report the detection of 14 objects that possess 24 ?m fluxes ?30% larger than their predicted photospheres, tentatively corresponding to a disk fraction of ?35%, including seven objects that also possess 70 ?m excesses ?100 times larger than their predicted photospheres. The 24 ?m plus 70 ?m excess sources possess high fractional infrared luminosities, LIR/L* = 7 ? 10-4 to 3 ? 10-3; either they possess optically thin, dusty ? Pictoris-like disks or compact, opaque HD 98800-like disks.

Hubble Space TelescopeImaging of HD 44179, The Red Rectangle

We present Hubble Space Telescope (HST) Wide Field Planetary Camera 2 and deep ground-based images of the Red Rectangle (RR), a bipolar proto–planetary nebula associated with the post-AGB binary system HD 44179. The high-resolution HST images reveal complex new structures, many of them unique to this object. The RR nebula is dominated by a discontinuous whose bright, sharp linear edges give the nebula an overall X-shaped appearance. The edges of the bicone are connected by a remarkable series of linear features elongated perpendicular to the radius vector, giving the object a ladder-like structure. The rungs of the ladder structure show a quasi-periodic spacing, suggesting that they have arisen from discrete episodes of mass loss from the central star, separated by a few hundred years. The total timescale over which mass has been shed into the visible nebula is of order 14,000 yr. Outside the X-shaped bicone, parabolas curl inward, resembling wineglasses, which terminate on the bicone edges in large, limb-brightened vortices. The central object is bisected by a dark band, indicating that the star is not seen directly but is instead obscured by a surrounding opaque dust disk.

Perceived transparency of neutral density filters across dissimilar backgrounds.

We examine how the luminance distributions of overlaid surfaces affect the perception of transparency of neutral density filters. Pairs of neutral density filters were generated overlying variegated backgrounds of varying luminance distributions, and observers adjusted a single parameter of one filter until the pair appeared equally transparent. Physically identical filters appeared equally transparent on similar backgrounds, but did not appear equally transparent when backgrounds differed in luminance or contrast. Reducing luminance or contrast of the background decreased perceived transparency of the overlaying filter by a multiplicative factor. Observers matched perceived transparency of physically dissimilar filters by applying a linear trade-off between reflectivity and inner transmittance. In a second experiment, filters had their spatial structure altered in order to abolish the perception of transparency and appeared as patterned opaque disks, and observers equated perceived contrast of the two overlaid areas. Match settings gave results similar to the previous experiment, indicating that, in general, perceived transparency corresponds closely to the perceived contrast of the overlaid region.

Companion Detection Limits with Adaptive Optics Coronagraphy

We present a study of the Palomar Adaptive Optics System and the PHARO near infrared camera in coronagraphic mode. The camera provides two different focal plane occulting masks–opaque circular disks 0.43 and 0.97″ across. Three different pupil plane apodizing masks (Lyot masks) are also provided. The six different combinations of Lyot mask and focal plane mask suppress differently the point spread function of a bright star centered on the focal plane mask. We obtained images of the bright nearby star Gliese 614 with all six different configurations in the K filter. We measured the dynamic range achievable with these configurations. Within 2.5″, the dynamic range is at least 8 magnitudes at the 5σ level and as high as 12 in a 1 s exposure. This represents a substantial gain over similar techniques without adaptive optics.

Axial irradiance distribution throughout the whole space behind an annular aperture

In many photonics and fiber-optics applications, the irradiance distribution in the very near field (z/D < 0.25) behind a circular or annular aperture is of interest. We present the results of detailed calculations of the irradiance distribution throughout the entire space behind an annular aperture. Included as a special case of the annular aperture is the circular aperture and the opaque circular disk. A log-log plot over many orders of magnitude in axial distance provides particular insight. The behavior throughout the Fresnel and Fraunhofer region is well known; however, we pay particular attention to the behavior in the near field. A variety of subtle effects in the near field are presented and discussed.

The ever challenging emission-line binaryβ Lyrae

A brief history of investigations of Lyr, an emission-line binary and one of the first ever discovered Be stars is presented. A rather fast progress in the understanding of this enigmatic object during the past fifteen years is then discussed in some detail. The current picture of β Lyr is that it is an eclipsing binary in a stage of mass transfer between the components. The mass-losing star is a B6-8II object, with a mass of about 3 M⊙, which is filling the Roche lobe and sending material towards its more massive companion at a rate of about 2 × 10—5 M⊙ yr—1. This leads to the observed rapid increase of the orbital period at a rate of 19 s per year. The mass-gaining star is as early B star with a mass of about 13 M⊙. It is completely hidden inside an opaque accretion disk, jet-like structures, perpendicular to the orbital plane and a light-scattering halo above the poles of the star. The observed radiation of the disk corresponds to an effective temperature which is much lower than what would correspond to an early B star. The disk shields the radiation of the central star in the directions along the orbital plane and redistributes it in the directions perpendicular to it. That is why the mass-losing star appears brighter of the two in the optical region of the spectrum. At present, rather reliable estimates of all basic properties of the binary and its components are available. However, in spite of great progress in understanding the system in recent years, some disagreement between the existing models and observed phase variations still remains, both for continuum and line spectrum, which deserves further effort.

Optoelectronic Simulation of the PMS 260X Optical Array Probe and Application to Drizzle in a Marine Stratocumulus

Abstract Measurement of drizzle drop sizes and concentrations are often made using optical probes with linear arrays. Their accuracy is affected by both diffraction of light and response times of the electronics connected to the sensor photodiodes. In this study the behavior of the Particle Measuring Systems, Inc. (PMS), 260X probe (a 62-photodiode system) is studied by calculating the two-dimensional Fresnel diffraction patterns for opaque disks and averaging this optical signal onto areas corresponding to the sizes of the photodiodes. The two-dimensional optical field is then transformed to a one-dimensional optical time-varying field; this simulates the passage of a drop past the photodiode array when the probe is mounted outside an aircraft. The optical field is convolved with an electronic response function to simulate the variation of the electronic signal as a drop passes through the diode array. For aircraft speeds less than 120 m s−1, one component of the probe sample volume, the depth of field, ...

Effect of Partial Waxy Wheat on Processing and Quality of Wheat Flour Tortillas

ABSTRACTThe processing and quality of wheat flour tortillas prepared with partial waxy and normal flour were evaluated. Control procedures and formula were utilized with water absorption varied to obtain machineable doughs. Amylose content was lower in most partial waxy compared with normal wheats. The type of wheat starch did not affect most dough properties or tortilla diameter. Tortilla height and opacity were adversely affected by the decreased amount of amylose in partial waxy wheats. Sufficient leavening reactions occurred early in baking (after 10 sec) to yield an opaque disk, but some baked tortillas lost opacity and become partially transparent after baking. Starch gelatinizes, disperses, and retrogrades concurrently with the leavening reaction during the short (&lt;30 sec) baking time. Amylose functionality during baking and cooling appears to be involved in the retention of air bubbles in tortillas.

Applications of Dispersion Staining Technique in Image Analysis of Colorless Particles

particles and their surrounding immersion liquid medium into a color in the When analyzing particle size distribution of colorless, translucent or transparent particles by image analysis, a major challenge is to obtain images of particles that ensure proper object detection, especially if the particles are amorphous or non-crystalline. Conventional imaging techniques, such as brightfield, darkfield, cross-polarized light, etc., might not applicable for these types of materials.Dispersion staining (DS) is a technique that coverts the refractive index (RI) difference between visible range and renders particles optically stained with that particular color. There are two modes of dispersion staining techniques: central stop (CS) and annular Stop (AS). For image analysis, CS is preferred.In the CS mode, the matching wavelength λm, i.e., the wavelength at which the RI of a particle equals that of liquid, is not refracted at the particle/liquid interface and therefore blocked by a 3-4 mm opaque round disk located at the center of the back focal plane of objective lens.

Principles of Hartmann-Shack aberrometry.

RAY OPTICS DESCRIPTION Nearly 400 years ago, the celebrated Jesuit philosopher-astronomer, Christopher Scheiner, professor at the University of Ingolstadt, demonstrated the focusing ability of the human eye using a simple device known as the Scheiner Disk.1 Scheiner's experiments showed that if an optically imperfect eye views through an opaque disk perforated with two pinholes, a single distant point of light such as a star will form two retinal images as illustrated in Figure 1. If the eye's optical imperfection is a simple case of defocus, then the double retinal images can be brought into register by viewing through a spectacle lens of the appropriate power. For optical aberrations other than defocus, however, a simple lens won't bring the two retinal images into coincidence. In such cases a more general method is needed for quantifying the refractive imperfections of the eye at each pupil location. This is achieved by using a fixed light source for the central, reference pinhole and a moveable light source for the outer pinhole as illustrated in Figure 2. By adjusting the moveable source horizontally and vertically, the isolated ray of light is redirected until it intersects the fixed ray at the retina and the patient now reports seeing a single point of light. Having made this adjustment, the displacement distances x and y are measures of the ray aberration of the eye at the given pupil point. This subjective aberrometer was first described by Smirnov2 and has been used extensively in visual optics research the past 40 years. To convert the Scheiner-Smirnov subjective technique into an objective aberrometer, we reverse the direction of light propagation by placing a spot of light on the retina. This spot then becomes a point source which radiates light back out of the eye as illustrated in Figure 3. Additional holes are drilled in Scheiner's disk, which astronomers and optical designers call a Hartmann screen.3 Each aperture in the Hartmann screen isolates a narrow pencil of rays emerging from the eye through a different part of the pupil. These emerging rays intersect a video Principles of Hartmann-Shack Aberrometry

The Flared Disc Project: RXTE and ASCA observations of X 1822--371

We present archival Rossi X-ray Timing Explorer (RXTE) and simultaneous Advanced Satellite for Cosmology and Astrophysics (ASCA) data of the eclipsing low mass X-ray binary (LMXB) X 1822-371. Our spectral analysis shows that a variety of simple models can fit the spectra relatively well. Of these models, we explore two in detail through phase-resolved fits. These two models represent the case of a very optically thick and a very optically thin corona. While systematic residuals remain at high energies, the overall spectral shape is well approximated. The same two basic models are fitted to the X-ray light curve, which shows sinusoidal modulations interpreted as absorption by an opaque disc rim of varying height. The geometry we infer from these fits is consistent with previous studies: the disc rim reaches out to the tidal truncation radius, while the radius of the corona (approximated as spherical) is very close to the circularization radius. Timing analysis of the RXTE data shows a time-lag from hard to soft consistent with the coronal size inferred from the fits. Neither the spectra nor the light curve fits allow us to rule out either model, leaving a key ingredient of the X 1822-371 puzzle unsolved. Furthermore, while previous studies were consistent with the central object being a 1.4 M⊙ neutron star, which has been adopted as the best guess scenario for this system, our light curve fits show that a white dwarf or black hole primary can work just as well. Based on previously published estimates of the orbital evolution of X 1822-371, however, we suggest that this system contains either a neutron star or a low mass (≲2.5 M⊙) black hole and is in a transitional state of duration shortward of 107 yr.

Enhancement of transverse trapping efficiency for a metallic particle using an obstructed laser beam

We report that the transverse trapping efficiency for a metallic particle can be enhanced by use of a laser beam obstructed by a circular opaque disk. In the case of gold particles, the enhancement factor for a p- or s-polarized trapping beam is at least 1.7 or 2.5, respectively. The dependence of the transverse trapping efficiency for gold particles (diameter=2 μm) on the size of the obstruction is measured and agrees with the theoretical prediction based on the ray-optics model.

The Quiescent Accretion Disk in IP Pegasi at Near‐Infrared Wavelengths

We present near-infrared, H-band (1.45-1.85 μm) observations of an eclipsing dwarf nova, IP Peg, in quiescence. The light curves are composed of ellipsoidal variations from the late-type secondary star and emission from the accretion disk and the bright spot. The light curves have two eclipses: a primary eclipse of the accretion disk and the bright spot by the companion star, and a secondary eclipse of the companion star by the disk. The ellipsoidal variations of the secondary star were modeled and subtracted from the data. The resulting light curve shows a pronounced double-hump variation. The double-hump profile resembles those seen in the light curves of WZ Sge and AL Com and likely originates in the accretion disk. The primary eclipse was modeled using maximum entropy disk mapping techniques. The accretion disk has a flat intensity distribution and a cool brightness temperature (Tbr 3000 K) in the near-infrared. Superimposed on the face of the disk is the bright spot (Tbr 10,000 K); the position of the bright spot is different from the observed range of visible bright spot positions. The near-infrared accretion disk flux is dominated by optically thin emission. The secondary eclipse indicates the presence of some occulting medium in the disk, but the eclipse depth is too shallow to be caused by a fully opaque accretion disk.

Ultrasensitive detection of hydrogen peroxide-mediated DNA damage after alkaline single cell gel electrophoresis using occultation microscopy and TUNEL labeling

DNA damage at the level of individual cells can be detected using the single cell gel electrophoresis (SCGE) or `comet' assay. In the present study, we report novel variations on the conventional comet assay that can be used to enhance the microscopic detection of DNA damage. Hydrogen peroxide-treated peripheral blood leukocytes were used as a DNA damage model system. Cells were embedded in agarose, treated, and electrophoresed according to the procedure of Singh et al. [N.P. Singh, M.T. McCoy, R.R. Tice, E.L. Schneider, A simple technique for quantitation of low levels of DNA damage in individual cells, Exp. Cell Res. 175 (1988), p. 184–191]. However, sites of strand breaks were directly labeled with the TUNEL (TdT-mediated fluorescein-dUTP nick end labeling) method. This labeling protocol revealed clumps and/or a series of stripes in the comet tail perpendicular to the direction of electrophoresis; these sites may account for the substructure seen in conventional comet assays. In a second comet variation, we passed an opaque disk into a field-conjugated plane of the microscope near the lamp, thus occluding the nucleus' image. Nuclear occultation allows the intensified charge-coupled device (ICCD) camera gain to increase to a single photon detection level thus revealing low levels of DNA damage in the tail. These methods offer a substantial improvement in sensitivity.

Early Membrane Rupture Events During Neutrophil-Mediated Antibody-Dependent Tumor Cell Cytolysis

Although cell-mediated cytolysis is a fundamental immune effector response, its mechanism remains poorly understood at the cellular level. In this report, we image for the first time transient ruptures, as inferred by cytoplasmic marker release, in tumor cell membranes during Ab-dependent cellular cytolysis. The cytosol of IgG-opsonized YAC tumor cells was labeled with tetra-methylrhodamine diacetate followed by the formation of tumor cell-neutrophil conjugates. We hypothesized that tumor cell cytolysis proceeds via a series of discrete membrane rupture/resealing events that contribute to marker release. To test this hypothesis, we occluded the fluorescence image of the labeled tumor cells by passing an opaque disk into a field-conjugated plane between the light source and the sample. Multiple small bursts of fluorescent label release from tumor cells could be detected using a photomultiplier tube. Similarly, multiple fluorescent plumes were observed at various sites around the perimeter of a target. These findings support a multihit model of target cytolysis and suggest that cytolytic release is not focused at specific sites. Cytolytic bursts were generally observed at 20-s intervals, which match the previously described reduced nicotinamide-adenine dinucleotide phosphate and superoxide release oscillation periods for neutrophils; we speculate that metabolic oscillations of the effector cell drive the membrane damage of the target.

Gas and Dust in Ultraluminous Galactic Nuclei

Millimeter-wave interferometry has clearly shown the existence of enormous masses (109 – 1010M⊙) of molecular gas concentrated in the nuclear regions (R &lt; 500 pc) of many luminous and ultraluminous infrared galaxies. In these systems, molecular gas is an obvious source of fuel for nuclear starbursts and active galactic nuclei (AGN). In several ultraluminous systems (e.g., Arp 220 and Mrk 231), there now exists CO (2-1) interferometry at ≤ 1″ resolution which reveals for the first time extremely dense, gaseous accretion disks on the scale 50-300 pc. Based on the low velocity dispersion of the molecular gas in the nuclear disks, we believe them to be extremely thin (10-50 pc). In addition, high brightness temperatures in the CO lines (10-20 K) imply that these disks are nearly uniformly filled with a continuous gas distribution, rather than being relatively isolated, self-gravitating GMCs. Although the gas is ‘uniformly’ distributed, the gas densities must be high, &gt; 104 cm−3. When viewed near the plane of the disk, the central AGNs, if they exist, will be totally obscured at optical and near infrared wavelengths. In Mrk 231, our line of sight is probably within 60° of the disk axis, but in Arp 220 the disk is closer to edge-on. In fact, recent near infrared imaging of Arp 220 with the NICMOS camera on the HST reveals totally opaque dust disks embedded within the central star clusters of both nuclei.

Evaluation of the Accuracy of PMS Optical Array Probes

This paper considers the theory of diffraction image formation of spherical particles and peculiarities of particle sizing by discrete imaging probes. The diffraction images of spherical water droplets are approximated by Fresnel diffraction by an opaque disc. The approach developed in the paper is applicable to all types of array and matrix imaging probes. The analysis measurement accuracy is performed for the PMS Optical Array Prove (OAP)-2D-C and OAP-2Dgray probes. It is shown that a 25-μm resolution PMS OAP-2D-C probe can both oversize and undersize droplets smaller than approximately 100 μm in diameter, and oversize droplets larger than approximately 100 μm. The errors in droplet sizing increase with decreasing size. The discrete manner of particle image registration also leads to losses of particles with sizes smaller than 100 μm. For the ideal case with zero photodiode response time, these losses reach 70% for 25-μm droplets. A nonzero response time will increase these losses. These findings help explain discrepancies observed in the overlap region of the PMS FSSP and OAP droplet spectra. A variety of calculated digital images for PMS OAP-2D-C and OAP-2Dgray probes is presented. Different methods of particle image sizing are discussed. Several methods of size correction of individual droplets and droplet ensembles are suggested. Correction algorithms for these effects are derived, and distortion and correction retrieval matrices are calculated. Several examples of actual and measured size distributions are presented.

NICMOS Imaging of the Nuclei of Arp 220

We report high-resolution imaging of the ultraluminous infrared galaxy Arp 220 at 1.1, 1.6, and 2.22 μm with the Near-Infrared Camera and Multiobject Spectrometer on the Hubble Space Telescope. The diffraction-limited images at 01-02 resolution clearly resolve both nuclei of the merging galaxy system and reveal for the first time a number of luminous star clusters in the circumnuclear envelope. The morphologies of both nuclei are strongly affected by dust obscuration, even at 2.2 μm: the primary nucleus (west) presents a crescent shape, concave to the south, and the secondary (eastern) nucleus is bifurcated by a dust lane with the southern component being very reddened. In the western nucleus, the morphology of the 2.2 μm emission is most likely the result of obscuration by an opaque disk embedded in the nuclear star cluster. The morphology of the central starburst cluster in the western nucleus is consistent with either a circumnuclear ring of star formation or a spherical cluster with the bottom half obscured by the embedded dust disk. Comparison of centimeter-wave radio continuum maps with the near-infrared images suggests that the radio nuclei lie in the dust disk on the west and near the highly reddened southern component of the eastern complex. The radio nuclei are separated by 098 (corresponding to 364 pc at 77 Mpc), and the half-widths of the infrared nuclei are ~02-05. At least eight unresolved infrared sources—probably globular clusters—are also seen in the circumnuclear envelope at radii of 2''-7''. Their near-infrared colors do not significantly constrain their ages.

Computerized scatter correction in diagnostic radiology

The field of diagnostic radiology continues to generate interesting lines of physics research even though it is over a century since X-rays were first used for medical imaging. One of these concerns scatter processes which are well known to be a major influence on the quality of X-ray images. The components, effects, reduction and measurement of scatter and the potential of computerized scatter correction schemes are reviewed in this paper. The effect of scatter on indices of image quality is considered using analytical models and published experimental results. Scatter measurement based on the widely applied opaque disc technique and a novel aperture technique are discussed in detail. In addition, computerized scatter correction based on convolution filtering schemes and interpolated local sampling schemes are critically reviewed. The treatment focuses on fluoroscopy- fluorography, although extensive reference is also made to other radiographic imaging techniques.

Direct Imaging of Circumstellar Disks in the Orion Nebula

AbstractWe present observations of the Orion Nebula made with the Hubble Space Telescope in which a number of stars are seen surrounded by dark silhouettes seen projected against the bright background HII region. We find a variety of morphologies, all consistent with thin circumstellar disks spanning a range of diameters (50 to 1000 AU) and inclination angles (0 to &gt; 80 degrees). The silhouette intensity profiles cannot be fit by standard disk models in which the surface density follows a radial power law with an exponent in the range −0.75 to −1.5. Rather, the data are best fit by opaque inner disks with exponential edges, and we discuss possible physical origins of this apparent truncation. Masses in the range 6 × l026−4 × 1030 g (i.e., up to 0.002 M⊙) are determined for the disks by assuming that the faint light measured from them is background light transmitted through the disk. However, these are strict lower limits on the true disk masses, as most of this light can be accounted for by PSF blurring and scattering in the HST optical train; the present observations are in fact consistent with completely opaque disks. Central stars are seen directly in five of the silhouettes, while the presence of a star is inferred in the sixth, where small reflection nebulae are seen above and below the plane of the near edge-on disk. Optical and near-infrared stellar photometry is consistent with young (~ 1 Myr) low-mass (0.3−1.5 M⊙) stars, with several showing evidence for excess near-infrared emission from the disk inner edge. These direct imaging observations are discussed in the wider context of circumstellar disks in the Orion Nebula and Trapezium Cluster, additionally revealed as compact ionized nebulae (so-called “proplyds”) in the vicinity of the central OB stars, and via infrared (&gt;2µm) excesses in stellar photometry. Overall, disks are found to be common in the cluster (&gt;50% of all stars), implying that they can survive the rigours of life near massive stars.