Direct imaging of irregular satellite discs in scattered light

ABSTRACT Direct imaging surveys have found that long-period super-Jupiters are rare. By contrast, recent modelling of the widespread gaps in protoplanetary discs revealed by Atacama Large Millimetre Array suggests an abundant population of smaller Neptune to Jupiter-mass planets at large separations. The thermal emission from such lower-mass planets is negligible at optical and near-infrared wavelengths, leaving only their weak signals in reflected light. Planets do not scatter enough light at these large orbital distances, but there is a natural way to enhance their reflecting area. Each of the four giant planets in our Solar system hosts swarms of dozens of irregular satellites, gravitationally captured planetesimals that fill their host planets’ spheres of gravitational influence. What we see of them today are the leftovers of an intense collisional evolution. At early times, they would have generated bright circumplanetary debris discs. We investigate the properties and detectability of such irregular satellite discs (ISDs) following models for their collisional evolution from Kennedy & Wyatt (2011). We find that the scattered light signals from such ISDs would peak in the 10–100 au semimajor axis range implied by ALMA, and can render planets detectable over a wide range of parameters with upcoming high-contrast instrumentation. We argue that future instruments with wide fields of view could simultaneously characterize the atmospheres of known close-in planets, and reveal the population of long-period Neptune–Jupiter mass exoplanets inaccessible to other detection methods. This provides a complementary and compelling science case that would elucidate the early lives of planetary systems.

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Evaluation of Unsupervised Change Detection Methods Applied to Landslide Inventory Mapping Using ASTER Imagery

Remote Sensing ◽

10.3390/rs10121987 ◽

2018 ◽

Vol 10 (12) ◽

pp. 1987 ◽

Cited By ~ 5

Author(s):

Rocío Ramos-Bernal ◽

René Vázquez-Jiménez ◽

Raúl Romero-Calcerrada ◽

Patricia Arrogante-Funes ◽

Carlos Novillo

Keyword(s):

Change Detection ◽

Vegetation Index ◽

Thermal Emission ◽

Principal Component ◽

Detection Methods ◽

Detection Accuracy ◽

Data Types ◽

Statistical Parameters ◽

Wide Range ◽

The World

Natural hazards include a wide range of high-impact phenomena that affect socioeconomic and natural systems. Landslides are a natural hazard whose destructive power has caused a significant number of victims and substantial damage around the world. Remote sensing provides many data types and techniques that can be applied to monitor their effects through landslides inventory maps. Three unsupervised change detection methods were applied to the Advanced Spaceborne Thermal Emission and Reflection Radiometer (Aster)-derived images from an area prone to landslides in the south of Mexico. Linear Regression (LR), Chi-Square Transformation, and Change Vector Analysis were applied to the principal component and the Normalized Difference Vegetation Index (NDVI) data to obtain the difference image of change. The thresholding was performed on the change histogram using two approaches: the statistical parameters and the secant method. According to previous works, a slope mask was used to classify the pixels as landslide/No-landslide; a cloud mask was used to eliminate false positives; and finally, those landslides less than 450 m2 (two Aster pixels) were discriminated. To assess the landslide detection accuracy, 617 polygons (35,017 pixels) were sampled, classified as real landslide/No-landslide, and defined as ground-truth according to the interpretation of color aerial photo slides to obtain omission/commission errors and Kappa coefficient of agreement. The results showed that the LR using NDVI data performs the best results in landslide detection. Change detection is a suitable technique that can be applied for the landslides mapping and we think that it can be replicated in other parts of the world with results similar to those obtained in the present work.

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Proximal Methods for Plant Stress Detection Using Optical Sensors and Machine Learning

Biosensors ◽

10.3390/bios10120193 ◽

2020 ◽

Vol 10 (12) ◽

pp. 193

Author(s):

Alanna V. Zubler ◽

Jeong-Yeol Yoon

Keyword(s):

Machine Learning ◽

Optical Sensors ◽

Near Infrared ◽

Plant Stress ◽

Machine Learning Algorithms ◽

Machine Learning Techniques ◽

Detection Methods ◽

Stress Detection ◽

Recent Advances ◽

Wide Range

Plant stresses have been monitored using the imaging or spectrometry of plant leaves in the visible (red-green-blue or RGB), near-infrared (NIR), infrared (IR), and ultraviolet (UV) wavebands, often augmented by fluorescence imaging or fluorescence spectrometry. Imaging at multiple specific wavelengths (multi-spectral imaging) or across a wide range of wavelengths (hyperspectral imaging) can provide exceptional information on plant stress and subsequent diseases. Digital cameras, thermal cameras, and optical filters have become available at a low cost in recent years, while hyperspectral cameras have become increasingly more compact and portable. Furthermore, smartphone cameras have dramatically improved in quality, making them a viable option for rapid, on-site stress detection. Due to these developments in imaging technology, plant stresses can be monitored more easily using handheld and field-deployable methods. Recent advances in machine learning algorithms have allowed for images and spectra to be analyzed and classified in a fully automated and reproducible manner, without the need for complicated image or spectrum analysis methods. This review will highlight recent advances in portable (including smartphone-based) detection methods for biotic and abiotic stresses, discuss data processing and machine learning techniques that can produce results for stress identification and classification, and suggest future directions towards the successful translation of these methods into practical use.

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Polarimetry of relativistic tidal disruption event Swift J2058+0516

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3106 ◽

2019 ◽

Vol 491 (2) ◽

pp. 1771-1776 ◽

Cited By ~ 2

Author(s):

K Wiersema ◽

A B Higgins ◽

A J Levan ◽

R A J Eyles ◽

R L C Starling ◽

...

Keyword(s):

Linear Polarization ◽

Near Infrared ◽

Thermal Emission ◽

Large Telescope ◽

Relativistic Jets ◽

Tidal Disruption ◽

Very Large Telescope ◽

Wide Range ◽

Independent Test ◽

Show Evidence

ABSTRACT A small fraction of candidate tidal disruption events (TDEs) show evidence of powerful relativistic jets, which are particularly pronounced at radio wavelengths, and likely contribute non-thermal emission at a wide range of wavelengths. A non-thermal emission component can be diagnosed using linear polarimetry, even when the total received light is dominated by emission from an accretion disc or disc outflow. In this paper, we present Very Large Telescope (VLT) measurements of the linear polarization of the optical light of jetted TDE Swift J2058+0516. This is the second jetted TDE studied in this manner, after Swift J1644+57. We find evidence of non-zero optical linear polarization, $P_{V}\sim 8{{\, \rm per\, cent}}$, a level very similar to the near-infrared polarimetry of Swift J1644+57. These detections provide an independent test of the emission mechanisms of the multiwavelength emission of jetted TDEs.

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Spatial segregation of dust grains in transition disks

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834800 ◽

2019 ◽

Vol 624 ◽

pp. A7 ◽

Cited By ~ 11

Author(s):

M. Villenave ◽

M. Benisty ◽

W. R. F. Dent ◽

F. Ménard ◽

A. Garufi ◽

...

Keyword(s):

Radiative Transfer ◽

Near Infrared ◽

Scattered Light ◽

Radiative Transfer Model ◽

Occurrence Rate ◽

Transfer Model ◽

Star Forming ◽

Spatially Resolved ◽

Wide Range ◽

Transition Disks

Context. The mechanisms governing the opening of cavities in transition disks are not fully understood. Several processes have been proposed, but their occurrence rate is still unknown. Aims. We present spatially resolved observations of two transition disks, and aim at constraining their vertical and radial structure using multiwavelength observations that probe different regions of the disks and can help understanding the origin of the cavities. Methods. We have obtained near-infrared scattered light observations with VLT/SPHERE of the transition disks 2MASS J16083070-3828268 (J1608) and RXJ1852.3-3700 (J1852), located in the Lupus and Corona Australis star-forming regions respectively. We complement our datasets with archival ALMA observations, and with unresolved photometric observations covering a wide range of wavelengths. We performed radiative transfer modeling to analyze the morphology of the disks, and then compare the results with a sample of 20 other transition disks observed with both SPHERE and ALMA. Results. We detect scattered light in J1608 and J1852 up to a radius of 0.54′′ and 0.4′′ respectively. The image of J1608 reveals a very inclined disk (i ~ 74°), with two bright lobes and a large cavity. We also marginally detect the scattering surface from the rear-facing side of the disk. J1852 shows an inner ring extending beyond the coronagraphic radius up to 15 au, a gap and a second ring at 42 au. Our radiative transfer model of J1608 indicates that the millimeter-sized grains are less extended vertically and radially than the micron-sized grains, indicating advanced settling and radial drift. We find good agreement with the observations of J1852 with a similar model, but due to the low inclination of the system, the model remains partly degenerate. The analysis of 22 transition disks shows that, in general, the cavities observed in scattered light are smaller than the ones detected at millimeter wavelengths. Conclusions. The analysis of a sample of transition disks indicates that the small grains, well coupled to the gas, can flow inward of the region where millimeter grains are trapped. While 15 out of the 22 cavities in our sample could be explained by a planet of less than 13 Jupiter masses, the others either require the presence of a more massive companion or of several low-mass planets.

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On the origin of the Kreutz family of sungrazing comets

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2562 ◽

2021 ◽

Vol 508 (1) ◽

pp. 789-802

Author(s):

Julio A Fernández ◽

Pablo Lemos ◽

Tabaré Gallardo

Keyword(s):

Semimajor Axis ◽

Oort Cloud ◽

Type Model ◽

Natural Consequence ◽

Mechanism Model ◽

Long Period ◽

Tidal Forces ◽

Short Period ◽

Wide Range ◽

Sungrazing Comets

ABSTRACT We evaluate numerically three different models for the parent comet of the Kreutz family of sungrazers: (i) A Centaur on a highly inclined or retrograde orbit that diffuse to the inner planetary region where it became a sungrazer (Model 1). (ii) A parent comet injected from the Oort cloud straight into a near-parabolic, sungrazing orbit. Near perihelion the comet was disrupted by tidal forces from the Sun giving rise to a myriad of fragments that created the Kreutz family (Model 2). (iii) A two-step process by which an Oort cloud comet is first injected in a non-sungrazing, Earth-crossing orbit where its semimajor axis decreases from typical Oort cloud values (a ∼ 104 au) to around 102 au, and then it evolves to a sungrazing orbit by the Lidov–Kozai mechanism (Model 3). Model 1 fails to produce sungrazers of the Kreutz type. Model 2 produces some Kreutz sungrazers and has the appeal of being the most straightforward. Yet the impulses received by the fragments originated in the catastrophic disruption of the parent comet will tend to acquire a wide range of orbital energies or periods (from short-period to long-period orbits) that is in contradiction with the observations. Model 3 seems to be the most promising one since it leads to the generation of some sungrazers of the Kreutz type and, particularly, it reproduces the clustering of the argument of perihelion ω of the observed Kreutz family members around 60°–90°, as a natural consequence of the action of the Lidov–Kozai mechanism.

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Direct Imaging Of Long Period Radial Velocity Targets With NICI

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313007904 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 66-67

Author(s):

Graeme S. Salter ◽

Chris G. Tinney ◽

Robert A. Wittenmyer ◽

James S. Jenkins ◽

Hugh R.A. Jones ◽

...

Keyword(s):

Radial Velocity ◽

Near Infrared ◽

Minimum Mass ◽

Post Processing ◽

Velocity Measurements ◽

Brown Dwarf ◽

Direct Imaging ◽

Parameter Spaces ◽

Long Period ◽

Imaging Parameter

AbstractWe are finally entering an era where radial velocity and direct imaging parameter spaces are starting to overlap. Radial velocity measurements provide us with a minimum mass for an orbiting companion (the mass as a function of the inclination of the system). By following up these long period radial velocity detections with direct imaging we can determine whether a trend seen is due to an orbiting planet at low inclination or an orbiting brown dwarf at high inclination. In the event of a non-detection we are still able to put a limit on the maximum mass of the orbiting body. The Anglo-Australian Planet Search is one of the longest baseline radial velocity planet searches in existence, amongst its targets are many that show long period trends in the data. Here we present our direct imaging survey of these objects with our results to date. ADI Observations have been made using NICI (Near Infrared Coronagraphic Imager) on Gemini South and analysed using an in house, LOCI-like, post processing.

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Galactic Latitude Dependence of Near-infrared Diffuse Galactic Light: Thermal Emission or Scattered Light?

The Astrophysical Journal ◽

10.3847/1538-4357/aa906c ◽

2017 ◽

Vol 849 (1) ◽

pp. 31 ◽

Cited By ~ 2

Author(s):

K. Sano ◽

S. Matsuura

Keyword(s):

Near Infrared ◽

Thermal Emission ◽

Scattered Light ◽

Galactic Latitude ◽

Latitude Dependence

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Spectral study of scattered light by interstellar dust grains

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319002990 ◽

2019 ◽

Vol 15 (S341) ◽

pp. 302-303

Author(s):

Kei Sano

Keyword(s):

Interstellar Dust ◽

Near Infrared ◽

Thermal Emission ◽

Imaging System ◽

Hubble Space Telescope ◽

Scattered Light ◽

Light Spectrum ◽

Space Instruments ◽

Infrared Background ◽

Diffuse Cloud

AbstractInterstellar dust is traced by not only thermal emission but also scattered light. The scattered light spectrum observed from ultraviolet (UV) to near-infrared (IR) is useful to constrain some dust properties, such as size distribution, albedo, and composition. Milky Way Galaxy is a unique environment to observe the diffuse scattered light because we can extract it by removing the contribution of starlight. We have observed the UV to near-IR scattered light with space instruments, including Diffuse Infrared Background Experiment (DIRBE), Hubble Space Telescope (HST), and Multi-purpose Infra-Red Imaging System (MIRIS). The scattered light spectrum is marginally consistent with prediction from a recent dust model including carbonaceous and silicate grains with polycyclic aromatic hydrocarbon (PAH). Based on the MIRIS observation of a diffuse cloud, we compare the scattered light color with the dust model with or without grains larger than 1 micrometer. The result shows that the color is consistent with the model without the large grains, which is consistent with recent simulations of dust growth in low-density regions. However, some observations have shown the spectral excess at ∼ 0.6 micrometer wavelength, suggesting the presence of extended red emission (ERE) which cannot be explained by the conventional dust model.

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Dust modeling of the combined ALMA and SPHERE datasets of HD 163296

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732299 ◽

2018 ◽

Vol 614 ◽

pp. A24 ◽

Cited By ~ 19

Author(s):

G. A. Muro-Arena ◽

C. Dominik ◽

L. B. F. M. Waters ◽

M. Min ◽

L. Klarmann ◽

...

Keyword(s):

Near Infrared ◽

Thermal Emission ◽

Scattered Light ◽

Spectral Energy Distribution ◽

Spectral Energy ◽

Dust Grains ◽

Outer Disk ◽

Group I ◽

Dust Evolution ◽

Small Dust

Context. Multiwavelength observations are indispensable in studying disk geometry and dust evolution processes in protoplanetary disks. Aims. We aim to construct a three-dimensional model of HD 163296 that is capable of reproducing simultaneously new observations of the disk surface in scattered light with the SPHERE instrument and thermal emission continuum observations of the disk midplane with ALMA. We want to determine why the spectral energy distribution of HD 163296 is intermediary between the otherwise well-separated group I and group II Herbig stars. Methods. The disk was modeled using the Monte Carlo radiative transfer code MCMax3D. The radial dust surface density profile was modeled after the ALMA observations, while the polarized scattered light observations were used to constrain the inclination of the inner disk component and turbulence and grain growth in the outer disk. Results. While three rings are observed in the disk midplane in millimeter thermal emission at ~80, 124, and 200 AU, only the innermost of these is observed in polarized scattered light, indicating a lack of small dust grains on the surface of the outer disk. We provide two models that are capable of explaining this difference. The first model uses increased settling in the outer disk as a mechanism to bring the small dust grains on the surface of the disk closer to the midplane and into the shadow cast by the first ring. The second model uses depletion of the smallest dust grains in the outer disk as a mechanism for decreasing the optical depth at optical and near-infrared wavelengths. In the region outside the fragmentation-dominated regime, such depletion is expected from state-of-the-art dust evolution models. We studied the effect of creating an artificial inner cavity in our models, and conclude that HD 163296 might be a precursor to typical group I sources.

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