9,937 research outputs found
The Dust Properties of Eight Debris Disk Candidates as Determined by Submillimeter Photometry
The nature of far-infrared dust emission toward main sequence stars, whether
interstellar or circumstellar, can be deduced from submillimeter photometry. We
present JCMT/SCUBA flux measurements at 850 microns toward 8 stars with large
photospheric excesses at 60-100 microns. 5 sources were detected at 3-sigma or
greater significance and one was marginally detected at 2.5-sigma. The inferred
dust masses and temperatures range from 0.033 to 0.24 Earth masses and 43-65 K
respectively. The frequency behavior of the opacity, tau_nu ~ nu^beta, is
relatively shallow, beta < 1. These dust properties are characteristic of
circumstellar material, most likely the debris from planetesimal collisions.
The 2 non-detections have lower temperatures, 35-38 K and steeper opacity
indices, beta > 1.5, that are more typical of interstellar cirrus. The
confirmed disks all have inferred diameters > 2'', most lie near the upper
envelope of the debris disk mass distribution, and 4 are bright enough to be
feasible for high resolution imaging.Comment: accepted by Ap
З історії запровадження метричних книг на українських землях
In article features of introduction of metric books on the Ukrainian earths in XVII-XVIII cent are considered and analyzed
Spatial interference of coherent atomic waves by manipulation of the internal quantum state
A trapped 87Rb Bose-Einstein condensate is initially put into a superposition
of two internal states. Under the effect of gravity and by means of a second
transition, we prepare two vertically displaced condensates in the same
internal state. These constitute two coherent sources of matter waves with
adjustable spatial separation. Fringe patterns, observed after free expansion,
are associated with the interplay between internal and external degrees of
freedom and substantially agree with those for a double slit experiment
Resolving The Moth at Millimeter Wavelengths
HD 61005, also known as "The Moth," is one of only a handful of debris disks
that exhibit swept-back "wings" thought to be caused by interaction with the
ambient interstellar medium (ISM). We present 1.3 mm Submillimeter Array (SMA)
observations of the debris disk around HD 61005 at a spatial resolution of 1.9
arcsec that resolve the emission from large grains for the first time. The disk
exhibits a double-peaked morphology at millimeter wavelengths, consistent with
an optically thin ring viewed close to edge-on. To investigate the disk
structure and the properties of the dust grains we simultaneously model the
spatially resolved 1.3 mm visibilities and the unresolved spectral energy
distribution. The temperatures indicated by the SED are consistent with
expected temperatures for grains close to the blowout size located at radii
commensurate with the millimeter and scattered light data. We also perform a
visibility-domain analysis of the spatial distribution of millimeter-wavelength
flux, incorporating constraints on the disk geometry from scattered light
imaging, and find suggestive evidence of wavelength-dependent structure. The
millimeter-wavelength emission apparently originates predominantly from the
thin ring component rather than tracing the "wings" observed in scattered
light. The implied segregation of large dust grains in the ring is consistent
with an ISM-driven origin for the scattered light wings.Comment: 10 pages, 6 figure
Optical vortex generation from molecular chromophore arrays
The generation of light endowed with orbital angular momentum, frequently termed optical vortex light, is commonly achieved by passing a conventional beam through suitably constructed optical elements. This Letter shows that the necessary phase structure for vortex propagation can be directly produced through the creation of twisted light from the vacuum. The mechanism is based on optical emission from a family of chromophore nanoarrays that satisfy specific geometric and symmetry constraints. Each such array can support pairs of electronically delocalized doubly degenerate excitons whose azimuthal phase progression is responsible for the helical wave front of the emitted radiation. The exciton symmetry dictates the maximum magnitude of topological charge; detailed analysis secures the conditions necessary to deliver optical vortices of arbitrary order
Direct generation of optical vortices
A detailed scheme is established for the direct generation of optical vortices, signifying light endowed with orbital angular momentum. In contrast to common techniques based on the tailored conversion of the wave front in a conventional beam, this method provides for the direct spontaneous emission of photons with the requisite field structure. This form of optical emission results directly from the electronic relaxation of a delocalized exciton state that is supported by a ringlike array of three or more nanoscale chromophores. An analysis of the conditions leads to a general formulation revealing a requirement for the array structure to adhere to one of a restricted set of permissible symmetry groups. It is shown that the coupling between chromophores within each array leads to an energy level splitting of the exciton structure, thus providing for a specific linking of exciton phase and emission wavelength. For emission, arrays conforming to one of the given point-group families’ doubly degenerate excitons exhibit the specific phase characteristics necessary to support vortex emission. The highest order of exciton symmetry, corresponding to the maximum magnitude of electronic orbital angular momentum supported by the ring, provides for the most favored emission. The phase properties of the emission produced by the relaxation of such excitons are exhibited on plots which reveal the azimuthal phase progression around the ring, consistent with vortex emission. It is proven that emission of this kind produces electromagnetic fields that map with complete fidelity onto the phase structure of a Laguerre-Gaussian optical mode with the corresponding topological charge. The prospect of direct generation paves the way for practicable devices that need no longer rely on the modification of a conventional laser beam by a secondary optical element. Moreover, these principles hold promise for the development of a vortex laser, also based on nanoscale exciton decay, enabling the production of coherent radiation with a tailor-made helical wave front
Protoplanetary Disk Masses in the Young NGC 2024 Cluster
We present the results from a Submillimeter Array survey of the 887 micron
continuum emission from the protoplanetary disks around 95 young stars in the
young cluster NGC 2024. Emission was detected from 22 infrared sources, with
flux densities from ~5 to 330 mJy; upper limits (at 3sigma) for the other 73
sources range from 3 to 24 mJy. For standard assumptions, the corresponding
disk masses range from ~0.003 to 0.2Msolar, with upper limits at
0.002--0.01Msolar. The NGC 2024 sample has a slightly more populated tail at
the high end of its disk mass distribution compared to other clusters, but
without more information on the nature of the sample hosts it remains unclear
if this difference is statistically significant or a superficial selection
effect. Unlike in the Orion Trapezium, there is no evidence for a disk mass
dependence on the (projected) separation from the massive star IRS2b in the NGC
2024 cluster. We suggest that this is due to either the cluster youth or a
comparatively weaker photoionizing radiation field.Comment: ApJ, in pres
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