scholarly journals Expelled grains from an unseen parent body around AU Microscopii

2017 ◽  
Vol 607 ◽  
pp. A65 ◽  
Author(s):  
É. Sezestre ◽  
J.-C. Augereau ◽  
A. Boccaletti ◽  
P. Thébault
Keyword(s):  
Point Source ◽  
Stellar Wind ◽  
Local Density ◽  
Dust Emission ◽  
Parent Body ◽  
Static Case ◽  
Dust Grains ◽  
Periodic Process ◽  
The Common ◽  
Debris Disk

Context. Recent observations of the edge-on debris disk of AU Mic have revealed asymmetric, fast outward-moving arch-like structures above the disk midplane. Although asymmetries are frequent in debris disks, no model can readily explain the characteristics of these features. Aims. We present a model aiming to reproduce the dynamics of these structures, more specifically their high projected speeds and their apparent position. We test the hypothesis of dust emitted by a point source and then expelled from the system by the strong stellar wind of this young M-type star. In this model we make the assumption that the dust grains follow the same dynamics as the structures, i.e., they are not local density enhancements. Methods. We perform numerical simulations of test particle trajectories to explore the available parameter space, in particular the radial location R0 of the dust producing parent body and the size of the dust grains as parameterized by the value of β (ratio of stellar wind and radiation pressure forces over gravitation). We consider the cases of a static and of an orbiting parent body. Results. We find that for all considered scenarios (static or moving parent body), there is always a set of (R0,β) parameters able to fit the observed features. The common characteristics of these solutions is that they all require a high value of β, of around 6. This means that the star is probably very active, and the grains composing the structures are submicronic in order for observable grains to reach such high β values. We find that the location of the hypothetical parent body is closer in than the planetesimal belt, around 8 ± 2 au (orbiting case) or 28 ± 7 au (static case). A nearly periodic process of dust emission appears, of 2 yr in the orbiting scenarios and 7 yr in the static case. Conclusions. We show that the scenario of sequential dust releases by an unseen point-source parent body is able to explain the radial behavior of the observed structures. We predict the evolution of the structures to help future observations discriminate between the different parent body configurations that have been considered. In the orbiting parent body scenario, we expect new structures to appear on the northwest side of the disk in the coming years.

scholarly journals The W75 — Cygnus - X IRAS loop:- OB - ‘Bubble’ or SNR?

1991 ◽  
Vol 147 ◽  
pp. 511-512
Author(s):  
D. Ward-Thompson ◽  
E. I. Robson
Keyword(s):  
Spherical Shell ◽  
Shock Front ◽  
Stellar Wind ◽  
Supernova Remnant ◽  
Dust Emission ◽  
Ob Stars ◽  
Wind Action

IRAS Calibrated Raw Detector Data (CRDD) are presented of a part of the Cygnus-X region, incorporating W75, DR21 and W75N, and a previously unknown loop of dust emission is observed. This loop is interpreted as a spherical shell-like shock front, and two alternative explanations for its origin are explored — a wind-blown bubble around an OB association, and an old supernova remnant. The arguments for each are outlined, and it is deduced that there are insufficient OB stars old enough to have formed the loop by combined stellar wind action, although a SNR appears consistent with the data.

WSRT 21-cm continuum field in Cygnus OB2: in search of more Wolf-Rayet stars

1999 ◽  
Vol 193 ◽  
pp. 103-104
Author(s):  
Diah Y.A. Setia Gunawan ◽  
Karel A. van der Hucht ◽  
A. Ger de Bruyn ◽  
Peredur M. Williams
Keyword(s):  
Point Source ◽  
Stellar Wind ◽  
Noise Level ◽  
Angular Resolution ◽  
Ob Stars ◽  
Near Ir ◽  
Continuum Field

We present a deep look into the Cygnus OB2 region using the WSRT. A 2° x 2° map of the optically highly-obscured region was obtained at 1400 MHz, with a noise level down to 0.2 mJy and an angular resolution of 1″. We will compare the resulting radio point source list with optical and near-IR catalogues, in order to identify stellar wind sources like WR and OB stars.

scholarly journals Possible depletion of metals into dust grains in the core of the Centaurus cluster of galaxies

2019 ◽  
Vol 623 ◽  
pp. A17 ◽  
Author(s):  
K. Lakhchaura ◽  
F. Mernier ◽  
N. Werner
Keyword(s):  
Dust Emission ◽  
Temperature Structure ◽  
Central Metal ◽  
Dust Grains ◽  
Cluster Of Galaxies ◽  
Systematic Uncertainties ◽  
Central Regions ◽  
Metal Abundance ◽  
Reactive Metals ◽  
The Continuum

We present azimuthally averaged metal abundance profiles from a full, comprehensive, and conservative re-analysis of the deep (∼800 ks total net exposure) Chandra/ACIS-S observation of the Centaurus cluster core (NGC 4696). After carefully checking various sources of systematic uncertainties, including the choice of the spectral deprojection method, assumptions about the temperature structure of the gas, and uncertainties in the continuum modeling, we confirm the existence of a central drop in the abundances of the “reactive” elements Fe, Si, S, Mg, and Ca, within r≲10 kpc. The same drops are also found when analyzing the XMM-Newton/EPIC data (∼150 ks). Adopting our most conservative approach, we find that, unlike the central drops seen for Fe, Si, S, Mg and Ca, the abundance of the “nonreactive” element Ar is fully consistent with showing no central drop. This is further confirmed by the significant (> 3σ) central radial increase of the Ar/Fe ratio. Our results corroborate the previously proposed “dust depletion scenario”, in which central metal abundance drops are explained by the deposition of a significant fraction of centrally cooled reactive metals into dust grains present in the central regions of the Centaurus cluster. This is also supported by the previous findings that the extent of the metal abundance drops in NGC 4696 broadly coincides with the infrared dust emission.

Statistical analysis of dust grain tracks in Rosetta/OSIRIS images

2020 ◽  
Author(s):  
Pablo Lemos
Keyword(s):  
Radiation Pressure ◽  
Gas Flow ◽  
Dust Emission ◽  
Three Dimensional ◽  
Large Set ◽  
Dust Grains ◽  
Transform Method ◽  
Nucleus Surface ◽  
Dust Grain ◽  
Grain Properties

<p>In some of the images taken by OSIRIS, pieces of debris can be seen as bright tracks instead of points sources as result of the combination of movements of both particles and spacecraft. The properties of those tracks, such as orientation, length and total brightness, depend on various comets parameters, including the activity on the nucleus surface, capable of lifting and accelerating the particles, and the characteristics of dust grains, as grain sizes, spatial distribution, velocity, density and sensitivity to radiation pressure. Previous works have focused on retrieving some of these grain properties from the mentioned images, but since the images show the 2D projection of the 3D dust motion, they rely on different methods to obtain the distance between the camera and the debris.</p> <p>In this work, a new method to bypass this distance determination requirement is proposed. The main steps involved are <em>(i)</em> analyze a large set of images containing tracks generated by moving dust grains, and obtain distribution for selected track parameters (orientation, length, total brightness, etc.) using an algorithm based on the Hough transform method; <em>(ii)</em> compare these results with the ones obtained from artificial images, generated by modeling the three dimensional motion of the debris in the gas flow field of the comet, under the influence of gravity, radiation pressure and gaseous drag; <em>(iii)</em> iterate this process in order to refine the parameters characterizing the physical properties of the dust emission used by the model.</p>

Two Different Grain Distributions within the Protoplanetary Disk around HD 142527

2018 ◽  
Vol 14 (A30) ◽  
pp. 136-136
Author(s):  
Satoshi Ohashi ◽  
Akimasa Kataoka ◽  
Hiroshi Nagai
Keyword(s):  
Grain Size ◽  
Magnetic Fields ◽  
Dust Emission ◽  
Northern Region ◽  
Southern Region ◽  
Continuum Emission ◽  
Dust Grains ◽  
Size Segregation ◽  
Grain Alignment ◽  
Polarized Emission

AbstractThe origin of polarized emission from protoplanetary disks is uncertain. Three mechanisms have been proposed for such polarized emission so far, (1) grain alignment with magnetic fields, (2) grain alignment with radiation gradients, and (3) self-scattering of thermal dust emission. Aiming to observationally identify the polarization mechanisms, we present ALMA polarization observations of the 0.87 mm dust continuum emission toward the circumstellar disk around HD 142527 with a spatial resolution of ∼0.2 arcsec as shown in Ohashi et al. (2018). We confirm that the polarization vectors in the northern region are consistent with self-scattering because of a flip of the polarization vectors. Furthermore, we show that the polarization vectors in the southern region are consistent with grain alignment by magnetic fields, although self-scattering cannot be ruled out. To understand these differences between the polarization mechanisms, we propose a simple grain size segregation model: small dust grains ( $\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $ 100 microns) are dominant and aligned with magnetic fields in the southern region, and middle-sized (∼100 microns) grains in the upper layer emit self-scattered polarized emission in the northern region. The grain size near the middle plane in the northern region cannot be measured because the emission at 0.87 mm is optically thick. However, it can be speculated that larger dust grains ( $\mathbin{\lower.3ex\hbox{$\buildrel>\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $ cm) may accumulate near this plane. These results are consistent with those of a previous analysis of the disk, in which large grain accumulation and optically thick emission from the northern region were found. This model is also consistent with theories where smaller dust grains are aligned with magnetic fields. We find that the magnetic fields are toroidal, at least in the southern region.

An ultrastructural study of reproduction in the parthenogenetic metacercariae of Cercaria margaritensis Ching, 1982 (Digenea: Gymnophallidae)

Parasitology ◽  
2003 ◽  
Vol 126 (3) ◽  
pp. 261-271 ◽  
Author(s):  
S. W. B. IRWIN ◽  
K. V. GALAKTIONOV ◽  
I. I. MALKOVA ◽  
D. H. SAVILLE ◽  
S. M. FITZPATRICK
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Embryo Development ◽  
Ultrastructural Study ◽  
Definitive Host ◽  
Parent Body ◽  
Common Eider ◽  
Somateria Mollissima ◽  
Transmission Electron ◽  
The Common

The parthenogenetic metacercarial stages of the gymnophallid trematode Cercaria margaritensis are found in the extrapallial cavity of the subtidal prosobranch mollusc Margarites helicinus. The primary metacercariae (M1) produce second-generation metacercariae (M2) which become independent and give rise to M3 metacercariae which are infective to the definitive host, the common eider (Somateria mollissima). This study used transmission electron microscopy to follow the development of M2 inside M1 organisms and M3 inside M2 organisms. The process is similar in both cases with embryos developing from individual cells from the parent body walls. In each case the brood sac was divided into brood chambers by multilaminated cells and both M2 and M3 embryos developed inside embryonic membranes that originated from specialized blastomeres. The tegument of M2 and M3 embryos developed in a similar manner underneath the embryonic membrane. Both the multilaminated cells and the embryonic membranes possessed features that indicated that they are involved in transport of nutrients. It is suggested that the continuous nature of M2 and M3 embryo development may well be similar to that postulated for ancestral digeneans.

scholarly journals A Resolved Millimeter Emission Belt in the AU Mic Debris Disk

2013 ◽  
Vol 8 (S299) ◽  
pp. 313-317
Author(s):  
Meredith MacGregor
Keyword(s):  
Angular Resolution ◽  
Scattered Light ◽  
Dust Emission ◽  
Emission Peak ◽  
Parametric Models ◽  
Central Component ◽  
Millimeter Wavelengths ◽  
Stellar Photosphere ◽  
Debris Disk ◽  
Centroid Position

AbstractImaging debris disks at millimeter wavelengths is important, because emission at these long wavelengths is dominated by large grains with dynamics similar to the population of dust-producing planetesimals. We have used the SMA and ALMA to make 1.3 millimeter observations of the debris disk surrounding the nearby (9.9 pc), ~10 Myr-old, M-type flare star AU Microscopii. We characterize the disk by implementing Markov Chain Monte Carlo methods to fit parametric models to the visibilities. The millimeter observations reveal a belt of dust emission that peaks at a radius of 40 AU. This outer size scale agrees with predictions for a reservoir of planetesimals (a “birth ring”) based on the shape of the midplane scattered light profile. We do not find any significant asymmetries in the structure or the centroid position of the emission belt. The ALMA observations with a resolution of 0.6 arcsec (6 AU) also reveal a previously unknown central emission peak, ~6 times brighter than the stellar photosphere at these wavelengths. This central component remains unresolved and could be explained by stellar activity or an inner planetesimal belt located ≲3 AU from the star and containing roughly 1% the mass of the outer belt. Future observations with higher angular resolution will be able to distinguish between these possibilities.

scholarly journals Dust traps and the formation of cavities in transition discs: a millimetre to sub-millimetre comparison survey

2021 ◽  
Vol 502 (4) ◽  
pp. 5779-5796
Author(s):  
Brodie J Norfolk ◽  
Sarah T Maddison ◽  
Christophe Pinte ◽  
Nienke van der Marel ◽  
Richard A Booth ◽  
...  
Keyword(s):  
Dust Emission ◽  
Dust Grains ◽  
Cavity Size ◽  
Dust Trap ◽  
Compact Array ◽  
Clearing Mechanism

ABSTRACT The origin of the inner dust cavities observed in transition discs remains unknown. The segregation of dust and size of the cavity is expected to vary depending on which clearing mechanism dominates grain evolution. We present the results from the Discs Down Under program, an 8.8-mm continuum Australia Telescope Compact Array (ATCA) survey targeting 15 transition discs with large (≳20 au) cavities and compare the resulting dust emission to Atacama Large millimetre/sub-millimetre Array (ALMA) observations. Our ATCA observations resolve the inner cavity for 8 of the 14 detected discs. We fit the visibilities and reconstruct 1D radial brightness models for 10 sources with a S/N &gt; 5σ. We find that, for sources with a resolved cavity in both wavebands, the 8.8 mm and sub-mm brightness distributions peak at the same radius from the star. We suggest that a similar cavity size for 8.8 mm and sub-mm dust grains is due to a dust trap induced by the presence of a companion.

scholarly journals Multiple Rings of Millimeter Dust Emission in the HD 15115 Debris Disk

2019 ◽  
Vol 877 (2) ◽  
pp. L32 ◽  
Author(s):  
Meredith A. MacGregor ◽  
Alycia J. Weinberger ◽  
Erika R. Nesvold ◽  
A. Meredith Hughes ◽  
D. J. Wilner ◽  
...  
Keyword(s):  
Dust Emission ◽  
Debris Disk ◽  
Multiple Rings

scholarly journals Numerical models for the dust in RCW 120

2019 ◽  
Vol 631 ◽  
pp. A170 ◽  
Author(s):  
A. Rodríguez-González ◽  
Z. Meliani ◽  
M. Sánchez-Cruces ◽  
P. R. Rivera-Ortiz ◽  
A. Castellanos-Ramírez
Keyword(s):  
Stellar Wind ◽  
Numerical Models ◽  
Dust Emission ◽  
Bow Shock ◽  
Ionising Radiation ◽  
Hii Region ◽  
Infrared Observations ◽  
Hydrodynamic Simulations ◽  
Drag Forces ◽  
Stellar Motion

Context. The interstellar bubble RCW 120 seen around a type O runaway star is driven by the stellar wind and the ionising radiation emitted by the star. The boundary between the stellar wind and interstellar medium (ISM) is associated with the arc-shaped mid-infrared dust emission around the star within the HII region. Aims. We aim to investigate the arc-shaped bow shock in RCW 120 by means of numerical simulations, including the radiation, dust, HII region, and wind bubble. Methods. We performed 3D radiation-hydrodynamic simulations including dust using the GUACHO code. Our model includes a detailed treatment of dust grains in the ISM and takes into account the drag forces between dust and gas and the effect of radiation pressure on the gas and dust. The dust is treated as a pressureless gas component. The simulation uses typical properties of RCW 120. We analyse five simulations to deduce the effect of the ionising radiation and dust on both the emission intensity and the shape of the shock. Results. The interaction of the wind and the ionising radiation from a runaway star with the ISM forms an arc-shaped bow shock where the dust from the ISM accumulates in front of the moving star. Moreover, the dust forms a second small arc-shaped structure within the rarefied region at the back of the star inside the bubble. In order to obtain the decoupling between the gas and the dust, it is necessary to include the radiation-hydrodynamic equations together with the dust and the stellar motion. In this work all these elements are considered together, and we show that the decoupling between gas and dust obtained in the simulation is in agreement with the morphology of the infrared observations of RCW 120.

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