scholarly journals Polarization reversal of scattered thermal dust emission in protoplanetary disks at submillimetre wavelengths

2019 ◽  
Vol 627 ◽  
pp. L10 ◽  
Author(s):  
R. Brunngräber ◽  
S. Wolf
Keyword(s):  
Dust Emission ◽  
Polarized Light ◽  
Protoplanetary Disks ◽  
Polarization Vector ◽  
Polarization Reversal ◽  
Polarization Pattern ◽  
Polarization Mechanism ◽  
Net Flux ◽  
Vector Orientation ◽  
Dust Grain

Investigation of the polarized light of protoplanetary disks is key for constraining dust properties, disk morphology, and embedded magnetic fields. However, different polarization mechanisms and the diversity of dust grain shapes and compositions lead to ambiguities in the polarization pattern. The so-called “self-scattering” of thermal, re-emitted radiation in the infrared and millimetre and submillimetre wavelengths is discussed as a major polarization mechanism. If the net flux of the radiation field is in the radial direction, it is commonly assumed that the polarization pattern produced by scattering in a protoplanetary disk shows concentric rings for disks seen in face-on orientation. We show that a change of 90° of the polarization vector orientation may occur and mimic the typical pattern of dichroic emission of dust grains aligned by a toroidal magnetic field in disks seen close to face-on. Furthermore, this effect of polarization reversal is a fast-changing function of wavelength and grain size, and is thus a powerful tool to constrain grain composition and size distribution present in protoplanetary disks. In addition, the effect may also provide unique constraints for the disk inclination, especially if the disk is seen close to face-on.

scholarly journals Resolved spectral variations of the centimetre-wavelength continuum from the ρ Oph W photo-dissociation-region

2021 ◽  
Author(s):  
Simon Casassus ◽  
Matías Vidal ◽  
Carla Arce-Tord ◽  
Clive Dickinson ◽  
Glenn J White ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Dust Emission ◽  
Image Synthesis ◽  
Microwave Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Parametric Image ◽  
Physical Conditions ◽  
Morphological Differences ◽  
Dust Grain

Abstract Cm-wavelength radio continuum emission in excess of free-free, synchrotron and Rayleigh-Jeans dust emission (excess microwave emission, EME), and often called ‘anomalous microwave emission’, is bright in molecular cloud regions exposed to UV radiation, i.e. in photo-dissociation regions (PDRs). The EME correlates with IR dust emission on degree angular scales. Resolved observations of well-studied PDRs are needed to compare the spectral variations of the cm-continuum with tracers of physical conditions and of the dust grain population. The EME is particularly bright in the regions of the ρ Ophiuchi molecular cloud (ρ Oph) that surround the earliest type star in the complex, HD 147889, where the peak signal stems from the filament known as the ρ Oph-W PDR. Here we report on ATCA observations of ρ Oph-W that resolve the width of the filament. We recover extended emission using a variant of non-parametric image synthesis performed in the sky plane. The multi-frequency 17 GHz to 39 GHz mosaics reveal spectral variations in the cm-wavelength continuum. At ∼30 arcsec resolutions, the 17-20 GHz intensities follow tightly the mid-IR, Icm∝I(8 μm), despite the breakdown of this correlation on larger scales. However, while the 33-39 GHz filament is parallel to IRAC 8 μm, it is offset by 15–20 arcsec towards the UV source. Such morphological differences in frequency reflect spectral variations, which we quantify spectroscopically as a sharp and steepening high-frequency cutoff, interpreted in terms of the spinning dust emission mechanism as a minimum grain size acutoff ∼ 6 ± 1 Å that increases deeper into the PDR.

Optical activity and enantiomorphism

2004 ◽  
Author(s):  
Robert E. Newnham
Keyword(s):  
Optical Activity ◽  
Polarized Light ◽  
Polarization Vector ◽  
Optically Active ◽  
Crystal Thickness ◽  
Helical Structures ◽  
Active Materials ◽  
Circularly Polarized ◽  
Space Groups ◽  
Polarized Waves

When plane-polarized light enters a crystal it divides into right- and lefthanded circularly polarized waves. If the crystal possesses handedness, the two waves travel with different speeds, and are soon out of phase. On leaving the crystal, the circularly polarized waves recombine to form a plane polarized wave, but with the plane of polarization rotated through an angle αt. The crystal thickness t is in mm, and α is the optical activity coefficient expressed in degrees/mm. The polarization vector of the combined wave can be visualized as a helix, turning α ◦/mm path length in the optically-active medium. Because of the low symmetry of a helix, optical activity is not observed in many high symmetry crystals. Point groups possessing a center of symmetry are inactive. In relating α to crystal chemistry it is convenient to divide optically-active materials into two categories: Those which retain optical activity in liquid form, and those which do not. It has long been known that optically-active solutions crystallize to give optically-active solids. This follows from the fact that molecules lacking mirror or inversion symmetry can never crystallize in a pattern containing such symmetry elements. Thus one way of obtaining optically-active materials is to begin with optically-active molecules, as in Rochelle salt, tartaric acid and cane sugar. Few of these crystals are very stable, however, and the optical activity coefficients are usually small, typically 2◦/mm. The same is true of many inorganic solids, though they are seldom optically active in the liquid state. For NaClO3 and MgSO4·7H2O, α is about 3◦/mm. Quartz and selenium, however, have coefficients an order of magnitude larger, showing the importance of helical structures to optical activity. Both compounds crystallize as right- and left-handed forms in space groups P312 and P322, with helices spiraling around the trigonal screw axes. Quartz contains nearly regular SiO4 tetrahedra with Si–O distances of 1.61 Å. Levorotatory quartz belongs to space group P312 and contains right-handed helices; enantiomorphic dextrorotatory quartz crystallizes in P322. Trigonal selenium also contains helical chains.

scholarly journals Adaptation of Orientation Vectors of Otolith-Related Central Vestibular Neurons to Gravity

2008 ◽  
Vol 100 (3) ◽  
pp. 1686-1690 ◽  
Author(s):  
Julia N. Eron ◽  
Bernard Cohen ◽  
Theodore Raphan ◽  
Sergei B. Yakushin
Keyword(s):  
Polarization Vector ◽  
Vestibular Nuclei ◽  
Perceptual Information ◽  
Behavioral Experiments ◽  
Adaptive Capabilities ◽  
Before And After ◽  
Vector Orientation ◽  
First Time ◽  
Specific Orientation ◽  
Response Vector

Behavioral experiments indicate that central pathways that process otolith-ocular and perceptual information have adaptive capabilities. Because polarization vectors of otolith afferents are directly related to the electro-mechanical properties of the hair cell bundle, it is unlikely that they change their direction of excitation. This indicates that the adaptation must take place in central pathways. Here we demonstrate for the first time that otolith polarization vectors of canal-otolith convergent neurons in the vestibular nuclei have adaptive capability. A total of 10 vestibular-only and vestibular-plus-saccade neurons were recorded extracellularly in two monkeys before and after they were in side-down positions for 2 h. The spatial characteristics of the otolith input were determined from the response vector orientation (RVO), which is the projection of the otolith polarization vector, onto the head horizontal plane. The RVOs had no specific orientation before animals were in side-down positions but moved toward the gravitational axis after the animals were tilted for extended periods. Vector reorientations varied from 0 to 109° and were linearly related to the original deviation of the RVOs from gravity in the position of adaptation. Such reorientation of central polarization vectors could provide the basis for changes in perception and eye movements related to prolonged head tilts relative to gravity or in microgravity.

scholarly journals Shadows and cavities in protoplanetary disks: HD 163296, HD 141569A, and HD 150193A in polarized light

2014 ◽  
Vol 568 ◽  
pp. A40 ◽  
Author(s):  
A. Garufi ◽  
S. P. Quanz ◽  
H. M. Schmid ◽  
H. Avenhaus ◽  
E. Buenzli ◽  
...  
Keyword(s):  
Polarized Light ◽  
Protoplanetary Disks

scholarly journals Heading choices of flying Drosophila under changing angles of polarized light

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Thomas F. Mathejczyk ◽  
Mathias F. Wernet
Keyword(s):  
Incident Angle ◽  
Polarized Light ◽  
Green Light ◽  
Behavioral Responses ◽  
Open Loop ◽  
Slow Rotation ◽  
Visually Guided ◽  
Polarization Pattern ◽  
Linearly Polarized ◽  
3D Printed

AbstractMany navigating insects include the celestial polarization pattern as an additional visual cue to orient their travels. Spontaneous orientation responses of both walking and flying fruit flies (Drosophila melanogaster) to linearly polarized light have previously been demonstrated. Using newly designed modular flight arenas consisting entirely of off-the-shelf parts and 3D-printed components we present individual flying flies with a slow and continuous rotational change in the incident angle of linear polarization. Under such open-loop conditions, single flies choose arbitrary headings with respect to the angle of polarized light and show a clear tendency to maintain those chosen headings for several minutes, thereby adjusting their course to the slow rotation of the incident stimulus. Importantly, flies show the tendency to maintain a chosen heading even when two individual test periods under a linearly polarized stimulus are interrupted by an epoch of unpolarized light lasting several minutes. Finally, we show that these behavioral responses are wavelength-specific, existing under polarized UV stimulus while being absent under polarized green light. Taken together, these findings provide further evidence supporting Drosophila’s abilities to use celestial cues for visually guided navigation and course correction.

scholarly journals Polarized light use in the nocturnal bull ant, Myrmecia midas

2017 ◽  
Vol 4 (8) ◽  
pp. 170598 ◽  
Author(s):  
Cody A. Freas ◽  
Ajay Narendra ◽  
Corentin Lemesle ◽  
Ken Cheng
Keyword(s):  
Visual Cues ◽  
Polarized Light ◽  
Food Sources ◽  
Light Change ◽  
Polarization Pattern ◽  
Returning Home

Solitary foraging ants have a navigational toolkit, which includes the use of both terrestrial and celestial visual cues, allowing individuals to successfully pilot between food sources and their nest. One such celestial cue is the polarization pattern in the overhead sky. Here, we explore the use of polarized light during outbound and inbound journeys and with different home vectors in the nocturnal bull ant, Myrmecia midas . We tested foragers on both portions of the foraging trip by rotating the overhead polarization pattern by ±45°. Both outbound and inbound foragers responded to the polarized light change, but the extent to which they responded to the rotation varied. Outbound ants, both close to and further from the nest, compensated for the change in the overhead e-vector by about half of the manipulation, suggesting that outbound ants choose a compromise heading between the celestial and terrestrial compass cues. However, ants returning home compensated for the change in the e-vector by about half of the manipulation when the remaining home vector was short (1−2 m) and by more than half of the manipulation when the remaining vector was long (more than 4 m). We report these findings and discuss why weighting on polarization cues change in different contexts.

scholarly journals Investigating the Relative Gas and Small Dust Grain Surface Heights in Protoplanetary Disks

2021 ◽  
Vol 913 (2) ◽  
pp. 138
Author(s):  
Evan A. Rich ◽  
Richard Teague ◽  
John D. Monnier ◽  
Claire L. Davies ◽  
Arthur Bosman ◽  
...  
Keyword(s):  
Protoplanetary Disks ◽  
Dust Grain ◽  
Grain Surface ◽  
Small Dust

scholarly journals Modelling the spinning dust emission from LDN 1780

2020 ◽  
Vol 495 (1) ◽  
pp. 1122-1135 ◽  
Author(s):  
Matias Vidal ◽  
Clive Dickinson ◽  
S E Harper ◽  
Simon Casassus ◽  
A N Witt
Keyword(s):  
Angular Resolution ◽  
Spectral Energy Distribution ◽  
Dust Emission ◽  
Microwave Emission ◽  
Spectral Energy ◽  
Frequency Range ◽  
Polycyclic Aromatic ◽  
The Difference ◽  
Dust Grain ◽  
Sd Model

ABSTRACT We study the anomalous microwave emission (AME) in the Lynds Dark Nebula (LDN) 1780 on two angular scales. With publicly available data at an angular resolution of 1°, we studied the spectral energy distribution of the cloud in the 0.408–2997 GHz frequency range. The cloud presents a significant (>20σ) amount of AME, making it one of the clearest examples of AME on 1 ° scales, and its spectrum can be well fitted with a spinning dust (SD) model. We also find at these angular scales that the location of the peak of the emission at lower frequencies (23–70 GHz) differs from the location at the higher frequencies (90–3000 GHz) maps. In addition to the analysis on 1° angular scales, we present data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at 31 GHz with an angular resolution of 2 arcmin, in order to study the origin of the AME in LDN 1780. We studied morphological correlations between the CARMA map and different infrared tracers of dust emission. We found that the best correlation is with the 70- μm template, which traces warm dust (T ∼ 50 K). Finally, we study the difference in radio emissivity between two locations within the cloud. We measured a factor of ≈6 difference in 31-GHz emissivity. We show that this variation can be explained, using the SD model, by a variation on the dust grain size distribution across the cloud, particularly changing the fraction of polycyclic aromatic hydrocarbon for a fixed total amount of carbon.

scholarly journals First Results from ATCA at Millimetre Wavelengths

2004 ◽  
Vol 221 ◽  
pp. 275-282
Author(s):  
Vincent Minier
Keyword(s):  
Star Formation ◽  
Angular Resolution ◽  
Galactic Plane ◽  
Dust Emission ◽  
Protoplanetary Disks ◽  
High Angular Resolution ◽  
Star Forming ◽  
Star Forming Regions ◽  
First Results ◽  
Excellent Tool

The newly upgraded Australia Telescope Compact Array (ATCA) at millimetre wavelengths is the first millimetre interferometer to be built in the Southern Hemisphere. The full array will be operational in 2004-2005 and will provide arcsec angular resolution at 3 mm and 12 mm. This will be a unique instrument to study at high angular resolution the interstellar chemistry and more generally the star formation process, especially in the bulk of the galactic plane and in the Magellanic Clouds. The upgraded ATCA will also be an excellent tool to detect dust emission from nearby protoplanetary disks. In this paper I will present the first results from the upgraded ATCA at 3 mm and 12 mm. The result review will cover the topics of massive star formation and hot molecular cores dust emission from star-forming regions and detection of protoplanetary disks.

scholarly journals Polarized emission by aligned grains in the Mie regime: Application to protoplanetary disks observed by ALMA

2020 ◽  
Vol 634 ◽  
pp. L15 ◽  
Author(s):  
V. Guillet ◽  
J. M. Girart ◽  
A. J. Maury ◽  
F. O. Alves
Keyword(s):  
Magnetic Field ◽  
Grain Size ◽  
Thermal Emission ◽  
Protoplanetary Disks ◽  
Polarization Vector ◽  
Size Distributions ◽  
Negative Polarization ◽  
Polarized Emission ◽  
Grain Size Distributions ◽  
The Magnetic Field

Context. The azimuthal polarization patterns observed in some protoplanetary disks by the Atacama Large Millimetre Array (ALMA) at millimeter wavelengths have raised doubts about whether they are truly produced by dust grains that are aligned with the magnetic field lines. These conclusions were based on the calculations of dust polarized emission in the Rayleigh regime, that is, for grain sizes that are much smaller than the wavelength. However, the grain size in such disks is typically estimated to be in the range of 0.1−1 mm from independent observations. Aims. We study the dust polarization properties of aligned grains in emission in the Mie regime, that is, when the mean grain size approaches the wavelength. Methods. By using the T-MATRIX and DustEM codes, we computed the spectral dependence of the polarization fraction in emission for grains in perfect spinning alignment for various grain size distributions. We restricted our study to weakly-elongated oblate and prolate grains of astrosilicate composition that have a mean size ranging from 10 μm to 1 mm. Results. In the submillimeter and millimeter wavelength range, the polarization by B-field aligned grains becomes negative for grains larger than ∼250 μm, meaning that the polarization vector becomes parallel to the B-field. The transition from the positive to the negative polarization occurs at a wavelength of λ ∼ 1 mm. The regime of negative polarization does not exist for grains that are smaller than ∼100 μm. Conclusions. When using realistic grain size distributions for disks with grains up to the submillimeter sizes, the polarization direction of thermal emission by aligned grains is shown to be parallel to the direction of the magnetic field over a significant fraction of the wavelengths typically used to observe young protoplanetary disks. This property may explain the peculiar azimuthal orientation of the polarization vectors in some of the disks observed with ALMA and attest to the conserved ability of dust polarized emission to trace the magnetic field in disks.

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