scholarly journals A High-Contrast Search for Variability in HR 8799bc with VLT-SPHERE

2021 ◽  
Author(s):  
B A Biller ◽  
D Apai ◽  
M Bonnefoy ◽  
S Desidera ◽  
R Gratton ◽  
...  
Keyword(s):  
Position Angle ◽  
High Contrast ◽  
Rule Out

Abstract The planets HR8799bc display nearly identical colours and spectra as variable young exoplanet analogues such as VHS 1256-1257ABb and PSO J318.5-22, and are likely to be similarly variable. Here we present results from a 5-epoch SPHERE IRDIS broadband-H search for variability in these two planets. HR 8799b aperture photometry and HR 8799bc negative simulated planet photometry share similar trends within uncertainties. Satellite spot lightcurves share the same trends as the planet lightcurves in the August 2018 epochs, but diverge in the October 2017 epochs. We consider Δ(mag)b − Δ(mag)c to trace non-shared variations between the two planets, and rule out non-shared variability in Δ(mag)b − Δ(mag)c to the 10-20% level over 4-5 hours. To quantify our sensitivity to variability, we simulate variable lightcurves by inserting and retrieving a suite of simulated planets at similar radii from the star as HR 8799bc, but offset in position angle. For HR 8799b, for periods <10 hours, we are sensitive to variability with amplitude $>5\%$. For HR 8799c, our sensitivity is limited to variability $>25\%$ for similar periods.

scholarly journals NaCo polarimetric observations of Sz 91 transitional disc: a remarkable case of dust filtering

2019 ◽  
Vol 492 (2) ◽  
pp. 1531-1542 ◽  
Author(s):  
Karina Maucó ◽  
Johan Olofsson ◽  
Hector Canovas ◽  
Matthias R Schreiber ◽  
Valentin Christiaens ◽  
...  
Keyword(s):  
Polarized Light ◽  
Position Angle ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Remarkable Case ◽  
The North ◽  
Near Ir ◽  
Hot Start ◽  
Low Mass ◽  
Rule Out

ABSTRACT We present polarized light observations of the transitional disc around Sz 91 acquired with VLT/NaCo at H (1.7μm) and Ks (2.2μm) bands. We resolve the disc and detect polarized emission up to ∼0.5 arcsec (∼80 au) along with a central cavity at both bands. We computed a radiative transfer model that accounts for the main characteristics of the polarized observations. We found that the emission is best explained by small, porous grains distributed in a disc with a ∼45 au cavity. Previous ALMA observations have revealed a large sub-mm cavity (∼83 au) and extended gas emission from the innermost (<16 au) regions up to almost 400 au from the star. Dynamical clearing by multiple low-mass planets arises as the most probable mechanism for the origin of Sz 91’s peculiar structure. Using new L′-band ADI observations, we can rule out companions more massive than Mp ≥ 8 MJup beyond 45 au assuming hot-start models. The disc is clearly asymmetric in polarized light along the minor axis, with the north side brighter than the south side. Differences in position angle between the disc observed at sub-mm wavelengths with ALMA and our NaCo observations were found. This suggests that the disc around Sz 91 could be highly structured. Higher signal-to-noise near-IR and sub-mm observations are needed to confirm the existence of such structures and to improve the current understanding of the origin of transitional discs.

scholarly journals Investigating the presence of two belts in the HD 15115 system

2019 ◽  
Vol 622 ◽  
pp. A192 ◽  
Author(s):  
N. Engler ◽  
A. Boccaletti ◽  
H. M. Schmid ◽  
J. Milli ◽  
J.-C. Augereau ◽  
...  
Keyword(s):  
Imaging Techniques ◽  
Polarized Light ◽  
Position Angle ◽  
Structural Features ◽  
High Contrast ◽  
Photometric Analysis ◽  
Near Ir ◽  
Average Grain Size ◽  
Gravitational Influence ◽  
Differential Imaging

Context. High-contrast instruments like SPHERE (Spectro- Polarimetric High-contrast Exoplanet REsearch) enable spatial resolution of young planetary systems and allow us to study the connection between planets and the dust contained in debris discs by the gravitational influence a planet can have on its environment. Aims. We present new observations of the edge-on debris disc around HD 15115 (F star at 48.2 pc) obtained in the near-IR. We search for observational evidence for a second inner planetesimal ring in the system. Methods. We obtained total intensity and polarimetric data in the broad bands J and H and processed the data with differential imaging techniques achieving an angular resolution of about 40 mas. A grid of models describing the spatial distribution of the grains in the disc is generated to constrain the geometric parameters of the disc and to explore the presence of a second belt. We perform a photometric analysis of the data and compare disc brightness in two bands in scattered and in polarized light. Results. We observe an axisymmetric planetesimal belt with a radius of ~2′′, an inclination of 85.8° ± 0.7° and position angle of 278.9° ± 0.1°. The photometric analysis shows that the west side is ~2.5 times brighter in total intensity than the east side in both bands, while for polarized light in the J band this ratio is only 1.25. We also find that the J–H colour of the disc appears to be red for the radial separations r ≲ 2′′ and is getting bluer for the larger separations. The maximum polarization fraction is 15–20% at r ~ 2.5′′. The polarized intensity image shows some structural features inside the belt which can be interpreted as an additional inner belt. Conclusions. The apparent change of disc colour from red to blue with an increasing radial separation from the star could be explained by the decreasing average grain size with distance. The presence of an inner belt slightly inclined with respect to the main planetesimal belt is suspected from the data but the analysis and modelling presented here cannot establish a firm conclusion due to the faintness of the disc and its high inclination.

Resistance Monitor and Control for Vacuum Evaporation of Metals and Carbon

1976 ◽  
Vol 34 ◽  
pp. 572-573
Author(s):  
Russell L. Steere ◽  
Eric F. Erbe ◽  
J. Michael Moseley
Keyword(s):  
Electronic Device ◽  
Point Sources ◽  
High Contrast ◽  
Variable Resistor ◽  
Quality Of Results ◽  
Low Contrast ◽  
Evaporation Source ◽  
And Control ◽  
At Will

We have designed and built an electronic device which compares the resistance of a defined area of vacuum evaporated material with a variable resistor. When the two resistances are matched, the device automatically disconnects the primary side of the substrate transformer and stops further evaporation.This approach to controlled evaporation in conjunction with the modified guns and evaporation source permits reliably reproducible multiple Pt shadow films from a single Pt wrapped carbon point source. The reproducibility from consecutive C point sources is also reliable. Furthermore, the device we have developed permits us to select a predetermined resistance so that low contrast high-resolution shadows, heavy high contrast shadows, or any grade in between can be selected at will. The reproducibility and quality of results are demonstrated in Figures 1-4 which represent evaporations at various settings of the variable resistor.

Confocal laser microscopy of impregnated central nervous system tissue

1988 ◽  
Vol 46 ◽  
pp. 94-95
Author(s):  
J.N. Turner ◽  
M. Siemens ◽  
D. Szarowski ◽  
D.N. Collins
Keyword(s):  
Electron Microscopy ◽  
Central Nervous System ◽  
Nervous System ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Confocal Laser ◽  
High Contrast ◽  
Central Nervous System Tissue ◽  
Tissue Samples ◽  
Reflected Light

A classic preparation of central nervous system tissue (CNS) is the Golgi procedure popularized by Cajal. The method is partially specific as only a few cells are impregnated with silver chromate usualy after osmium post fixation. Samples are observable by light (LM) or electron microscopy (EM). However, the impregnation is often so dense that structures are masked in EM, and the osmium background may be undesirable in LM. Gold toning is used for a subtle but high contrast EM preparation, and osmium can be omitted for LM. We are investigating these preparations as part of a study to develop correlative LM and EM (particularly HVEM) methodologies in neurobiology. Confocal light microscopy is particularly useful as the impregnated cells have extensive three-dimensional structure in tissue samples from one to several hundred micrometers thick. Boyde has observed similar preparations in the tandem scanning reflected light microscope (TSRLM).

The CM120 Biotwin: a high-contrast objective lens, optimum cryo-vacuum and improved EDX performance

1995 ◽  
Vol 53 ◽  
pp. 584-585
Author(s):  
Uwe Lücken ◽  
Michael Felsmann ◽  
Wim M. Busing ◽  
Frank de Jong
Keyword(s):  
Life Science ◽  
Focal Length ◽  
Objective Lens ◽  
High Contrast ◽  
Contrast Imaging ◽  
X Ray ◽  
Forming Mechanism ◽  
Similar Image ◽  
High Contrast Imaging ◽  
Low Concentrations

A new microscope for the study of life science specimen has been developed. Special attention has been given to the problems of unstained samples, cryo-specimens and x-ray analysis at low concentrations.A new objective lens with a Cs of 6.2 mm and a focal length of 5.9 mm for high-contrast imaging has been developed. The contrast of a TWIN lens (f = 2.8 mm, Cs = 2 mm) and the BioTWTN are compared at the level of mean and SD of slow scan CCD images. Figure 1a shows 500 +/- 150 and Fig. 1b only 500 +/- 40 counts/pixel. The contrast-forming mechanism for amplitude contrast is dependent on the wavelength, the objective aperture and the focal length. For similar image conditions (same voltage, same objective aperture) the BioTWIN shows more than double the contrast of the TWIN lens. For phasecontrast specimens (like thin frozen-hydrated films) the contrast at Scherzer focus is approximately proportional to the √ Cs.

A rapid method for the direct identification of paramyxovirus in canine CSF by ultracentrifugation and negative staining as a rule out for distemper

1990 ◽  
Vol 48 (3) ◽  
pp. 594-595
Author(s):  
W.L. Steffens ◽  
M.B. Ard ◽  
C.E. Greene ◽  
A. Jaggy
Keyword(s):  
Subacute Sclerosing Panencephalitis ◽  
Clinical Signs ◽  
Viral Disease ◽  
Etiologic Agent ◽  
Mucosal Inflammation ◽  
Worldwide Distribution ◽  
Negative Stain ◽  
Viral Particles ◽  
Systemic Manifestations ◽  
Rule Out

Canine distemper is a multisystemic contagious viral disease having a worldwide distribution, a high mortality rate, and significant central neurologic system (CNS) complications. In its systemic manifestations, it is often presumptively diagnosed on the basis of clinical signs and history. Few definitive antemortem diagnostic tests exist, and most are limited to the detection of viral antigen by immunofluorescence techniques on tissues or cytologic specimens or high immunoglobulin levels in CSF (cerebrospinal fluid). Diagnosis of CNS distemper is often unreliable due to the relatively low cell count in CSF (<50 cells/μl) and the binding of blocking immunoglobulins in CSF to cell surfaces. A more reliable and definitive test might be possible utilizing direct morphologic detection of the etiologic agent. Distemper is the canine equivalent of human measles, in that both involve a closely related member of the Paramyxoviridae, both produce mucosal inflammation, and may produce CNS complications. In humans, diagnosis of measles-induced subacute sclerosing panencephalitis is through negative stain identification of whole or incomplete viral particles in patient CSF.

Performance and applications of the holography electron microscope

1993 ◽  
Vol 51 ◽  
pp. 1078-1079
Author(s):  
Akira Tonomura
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Phase Measurement ◽  
Electron Holography ◽  
Imaging Method ◽  
High Contrast ◽  
Magnetic Lens ◽  
High Brightness ◽  
Holographic Imaging ◽  
Dynamic Observation

Electron holography is a two-step imaging method. However, the ultimate performance of holographic imaging is mainly determined by the brightness of the electron beam used in the hologram-formation process. In our 350kV holography electron microscope (see Fig. 1), the decrease in the inherently high brightness of field-emitted electrons is minimized by superposing a magnetic lens in the gun, for a resulting value of 2 × 109 A/cm2 sr. This high brightness has lead to the following distinguished features. The minimum spacing (d) of carrier fringes is d = 0.09 Å, thus allowing a reconstructed image with a resolution, at least in principle, as high as 3d=0.3 Å. The precision in phase measurement can be as high as 2π/100, since the position of fringes can be known precisely from a high-contrast hologram formed under highly collimated illumination. Dynamic observation becomes possible because the current density is high.

Compositional Analysis of III-V Interface Lattice Images

1980 ◽  
Vol 38 ◽  
pp. 318-319
Author(s):  
A. Olsen ◽  
J.C.H. Spence ◽  
P. Petroff
Keyword(s):  
Crystal Structure ◽  
Image Matching ◽  
Compositional Analysis ◽  
Depth Of Field ◽  
Limit Set ◽  
High Contrast ◽  
Resolution Limit ◽  
Fourier Image ◽  
Lattice Images ◽  
True Structure

Since the point resolution of the JEOL 200CX electron microscope is up = 2.6Å it is not possible to obtain a true structure image of any of the III-V or elemental semiconductors with this machine. Since the information resolution limit set by electronic instability (1) u0 = (2/πλΔ)½ = 1.4Å for Δ = 50Å, it is however possible to obtain, by choice of focus and thickness, clear lattice images both resembling (see figure 2(b)), and not resembling, the true crystal structure (see (2) for an example of a Fourier image which is structurally incorrect). The crucial difficulty in using the information between Up and u0 is the fractional accuracy with which Af and Cs must be determined, and these accuracies Δff/4Δf = (2λu2Δf)-1 and ΔCS/CS = (λ3u4Cs)-1 (for a π/4 phase change, Δff the Fourier image period) are strongly dependent on spatial frequency u. Note that ΔCs(up)/Cs ≈ 10%, independent of CS and λ. Note also that the number n of identical high contrast spurious Fourier images within the depth of field Δz = (αu)-1 (α beam divergence) decreases with increasing high voltage, since n = 2Δz/Δff = θ/α = λu/α (θ the scattering angle). Thus image matching becomes easier in semiconductors at higher voltage because there are fewer high contrast identical images in any focal series.

Impairment Questions and Answers

1999 ◽  
Vol 4 (4) ◽  
pp. 4-4
Keyword(s):  
Symptom Validity ◽  
Validity Testing ◽  
Symptom Validity Testing ◽  
Negative Results ◽  
Tunnel Vision ◽  
Questions And Answers ◽  
Blurry Vision ◽  
Fatigue Evaluation ◽  
Choice Testing ◽  
Rule Out

Abstract Symptom validity testing, also known as forced-choice testing, is a way to assess the validity of sensory and memory deficits, including tactile anesthesias, paresthesias, blindness, color blindness, tunnel vision, blurry vision, and deafness—the common feature of which is a claimed inability to perceive or remember a sensory signal. Symptom validity testing comprises two elements: A specific ability is assessed by presenting a large number of items in a multiple-choice format, and then the examinee's performance is compared with the statistical likelihood of success based on chance alone. Scoring below a norm can be explained in many different ways (eg, fatigue, evaluation anxiety, limited intelligence, and so on), but scoring below the probabilities of chance alone most likely indicates deliberate deception. The positive predictive value of the symptom validity technique likely is quite high because there is no alternative explanation to deliberate distortion when performance is below the probability of chance. The sensitivity of this technique is not likely to be good because, as with a thermometer, positive findings indicate that a problem is present, but negative results do not rule out a problem. Although a compelling conclusion is that the examinee who scores below probabilities is deliberately motivated to perform poorly, malingering must be concluded from the total clinical context.

Case Exercise: Toxic Exposure-Related Illness: Causation, Diagnosis, and Permanent Impairment

2007 ◽  
Vol 12 (2) ◽  
pp. 4-8
Author(s):  
Frederick Fung
Keyword(s):  
Concentration Level ◽  
Treatment Plan ◽  
Toxic Exposure ◽  
Dose Response Relationship ◽  
Specialty Board ◽  
History Of ◽  
Subjective Complaints ◽  
Based Medicine ◽  
Illness Causation ◽  
Rule Out

Abstract A diagnosis of toxic-related injury/illness requires a consideration of the illness related to the toxic exposure, including diagnosis, causation, and permanent impairment; these are best performed by a physician who is certified by a specialty board certified by the American Board of Preventive Medicine. The patient must have a history of symptoms consistent with the exposure and disease at issue. In order to diagnose the presence of a specific disease, the examiner must find subjective complaints that are consistent with the objective findings, and both the subjective complaints and objective findings must be consistent with the disease that is postulated. Exposure to a specific potentially causative agent at a defined concentration level must be documented and must be sufficient to induce a particular pathology in order to establish a diagnosis. Differential diagnoses must be entertained in order to rule out other potential causes, including psychological etiology. Furthermore, the identified exposure at the defined concentration level must be capable of causing the diagnosis being postulated before the examiner can conclude that there has been a cause-and-effect relationship between the exposure and the disease (dose-response relationship). The evaluator's opinion should make biological and epidemiological sense. The treatment plan and prognosis should be consistent with evidence-based medicine, and the rating of impairment must be based on objective findings in involved systems.

Sign in / Sign up

Export Citation Format

Share Document