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 The Dust in the Hydrogen-Poor Ejecta of Abell 30

1993 ◽  
Vol 155 ◽  
pp. 386-386
Author(s):  
J.P. Harrington ◽  
K.J. Borkowski ◽  
W.P. Blair ◽  
J. Bregman
Keyword(s):  
High Resolution ◽  
Amorphous Carbon ◽  
Ir Spectrum ◽  
Stellar Wind ◽  
Thermal Emission ◽  
Central Star ◽  
Near Ir ◽  
High Resolution Images ◽  
Small Grains ◽  
Ir Emission

High-resolution images in [O III] λ5007 of the hydrogen-poor knots of Abell 30 reveal comet-like structures which may be indicative of interaction with the stellar wind. In the near IR, new, higher-resolution, K-band images show an equatorial ring of hot dust that corresponds closely to optical knots 2 and 4 of Jacoby and Ford, while their polar knots 1 and 3 show no comparable IR emission. Both the thermal IR emission and the heavy internal extinction of the central star demands an extremely dusty ejecta. Greenstein showed that the UV extinction curve is fit by amorphous carbon. Our comprehensive dust models consider both the UV extinction and the IR emission from a population of carbon grains. The thermal emission from larger grains produces the far IR emission, while the stochastic heating of very small grains to high temperatures is essential to explain the near IR flux. We are able to reproduce the shape of the near IR spectrum with an a−3.0 distribution of grain radii which extends down to a minimum grain radius of 8 Å.

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.

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 Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array

2019 ◽  
Vol 36 ◽  
Author(s):  
Cathryn M. Trott ◽  
Catherine A. Watkinson ◽  
Christopher H. Jordan ◽  
Shintaro Yoshiura ◽  
Suman Majumdar ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Point Source ◽  
Noise Level ◽  
Future Prospects ◽  
Careful Choice ◽  
Murchison Widefield Array ◽  
Using Data ◽  
Redundant Arrays ◽  
High Band ◽  
Compact Array

AbstractWe apply two methods to estimate the 21-cm bispectrum from data taken within the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA). Using data acquired with the Phase II compact array allows a direct bispectrum estimate to be undertaken on the multiple redundantly spaced triangles of antenna tiles, as well as an estimate based on data gridded to the uv-plane. The direct and gridded bispectrum estimators are applied to 21 h of high-band (167–197 MHz; z = 6.2–7.5) data from the 2016 and 2017 observing seasons. Analytic predictions for the bispectrum bias and variance for point-source foregrounds are derived. We compare the output of these approaches, the foreground contribution to the signal, and future prospects for measuring the bispectra with redundant and non-redundant arrays. We find that some triangle configurations yield bispectrum estimates that are consistent with the expected noise level after 10 h, while equilateral configurations are strongly foreground-dominated. Careful choice of triangle configurations may be made to reduce foreground bias that hinders power spectrum estimators, and the 21-cm bispectrum may be accessible in less time than the 21-cm power spectrum for some wave modes, with detections in hundreds of hours.

scholarly journals Gas-Čerenkov Detector for 10 to 100 MeV Gamma Rays

1971 ◽  
Vol 41 ◽  
pp. 77-78 ◽  
Author(s):  
H. Helmken ◽  
J. Hoffman
Keyword(s):  
Gamma Radiation ◽  
Point Source ◽  
Gamma Rays ◽  
Angular Resolution ◽  
Galactic Plane ◽  
Plastic Scintillator ◽  
Spectral Information ◽  
Cerenkov Detector ◽  
Half Angle ◽  
Cerenkov Light

A gas-Čerenkov detector sensitive to gamma radiation above 10 MeV is currently undergoing final testing. The detector relies on the conversion and Compton scattering of gamma rays in a plastic scintillator and detecting the resulting electrons via the Čerenkov light they emit in a 2-m propane-gas column. Spectral information can be attained by varying gas pressure during the flight. The present detector is approximately 34″ in diameter, 91″ in length and weight 450 lb. At 20 MeV, an angular resolution of 6° half angle is expected. With an efficiency of 1 to 2%, a 10 hr balloon-borne system should achieve a point-source sensitivity of approximately 5× 10−5 photon cm−2 s−1 above 20 MeV. A satellite version of the detector is expected to have a sensitivity of approximately 1.3 × 10−5 photon cm−2 s−1 above 10 MeV for a 1-month galactic-plane scan mode. (Helmken and Hoffman, 1970.)

scholarly journals High-resolution near-IR imaging of the WCD(+OB) environments: pinwheels

2003 ◽  
Vol 212 ◽  
pp. 121-129 ◽  
Author(s):  
Peter G. Tuthill ◽  
John D. Monnier ◽  
William C. Danchi ◽  
Nils H. Turner
Keyword(s):  
High Resolution ◽  
Angular Resolution ◽  
High Angular Resolution ◽  
Dust Formation ◽  
Near Ir ◽  
Ir Imaging ◽  
Fundamental Information

A small number of Wolf-Rayet colliding-wind binaries studied at extremely high angular resolution show elegant dust plumes with an intuitive geometry: that of an Archimedian spiral. A great deal of fundamental information on the binary and the winds is encoded, ultimately teaching us about dust formation and wind-wind collision zones in these fascinating systems. New results are presented summarizing a concerted campaign encompassing a number of systems studied with various techniques over the last five years.

scholarly journals NuSTAR observations of rotation-powered pulsars and magnetars

2012 ◽  
Vol 8 (S291) ◽  
pp. 331-336
Author(s):  
V. M. Kaspi ◽  
H. An ◽  
M. Bachetti ◽  
E. Bellm ◽  
A. M. Beloborodov ◽  
...  
Keyword(s):  
Point Source ◽  
Angular Resolution ◽  
Focal Length ◽  
Effective Area ◽  
X Ray ◽  
Large Effective Area ◽  
Better Than

AbstractNASA's NuSTAR observatory is the first focusing hard X-ray telescope. Launched in June 2012, NuSTAR is sensitive in the 3–79 keV range with unprecedented ~17″ FWHM angular resolution above 12 keV, a result of its multilayer-coated optics and 10-m focal length. With its large effective area (900 cm2 at 10 keV), NuSTAR has point-source sensitivity ~100 times better than previous hard X-ray telescopes. Here we describe NuSTAR and its planned work on rotation-powered pulsars and magnetars during its nominal 2-yr baseline mission that has just commenced.

Angle-sensitive X-ray topographs obtained with Kossel lines

1991 ◽  
Vol 24 (6) ◽  
pp. 999-1004 ◽  
Author(s):  
D. B. Wittry ◽  
S. Sun ◽  
W. Z. Chang
Keyword(s):  
Point Source ◽  
Angular Resolution ◽  
Theoretical Calculations ◽  
Simple Method ◽  
X Ray ◽  
Fluorescence Radiation ◽  
Initial Results

A simple method and simple camera of small size for obtaining X-ray topographs with a microfocus X-ray source are described and initial results and their interpretation are given for an LiF crystal. The method is based on scanning a Kossel line across the recording film by simultaneously translating the crystal and film relative to the source and to a stationary mask that blocks most of the scattered and fluorescence radiation. The mask, which is located between the specimen and the film, is made by using the Kossel line recorded on a film in the mask plane as a pattern; this provides self-alignment of the system. Theoretical calculations are given that indicate the potential angular resolution of the method when applied to nearly perfect crystals. The advantages of this method over similar methods using the X-ray continuum diverging from a point source are discussed.

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