583 research outputs found
Feasibility of transit photometry of nearby debris discs
Dust in debris discs is constantly replenished by collisions between larger
objects. In this paper, we investigate a method to detect these collisions. We
generate models based on recent results on the Fomalhaut debris disc, where we
simulate a background star transiting behind the disc, due to the proper motion
of Fomalhaut. By simulating the expanding dust clouds caused by the collisions
in the debris disc, we investigate whether it is possible to observe changes in
the brightness of the background star. We conclude that in the case of the
Fomalhaut debris disc, changes in the optical depth can be observed, with
values of the optical depth ranging from for the densest dust
clouds to for the most diffuse clouds with respect to the background
optical depth of .Comment: 19 pages, 15 figures, accepted for publication in MNRA
Reentrant stability of BEC standing wave patterns
We describe standing wave patterns induced by an attractive finite-ranged
external potential inside a large Bose-Einstein Condensate (BEC). As the
potential depth increases, the time independent Gross-Pitaevskii equation
develops pairs of solutions that have nodes in their wavefunction. We elucidate
the nature of these states and study their dynamical stability. Although we
study the problem in a two-dimensional BEC subject to a cylindrically symmetric
square-well potential of a radius that is comparable to the coherence length of
the BEC, our analysis reveals general trends, valid in two and three
dimensions, independent of the symmetry of the localized potential well, and
suggestive of the behavior in general, short- and large-range potentials. One
set of nodal BEC wavefunctions resembles the single particle n node bound state
wavefunction of the potential well, the other wavefunctions resemble the n-1
node bound-state wavefunction with a kink state pinned by the potential. The
second state, though corresponding to the lower free energy value of the pair
of n node BEC states, is always unstable, whereas the first can be dynamically
stable in intervals of the potential well depth, implying that the standing
wave BEC can evolve from a dynamically unstable to stable, and back to unstable
status as the potential well is adiabatically deepened, a phenomenon that we
refer to as "reentrant dynamical stability".Comment: 13 pages, 9 figures; revised discussion in Sec.
Modeling Self-Subtraction in Angular Differential Imaging: Application to the HD 32297 Debris Disk
We present a new technique for forward-modeling self-subtraction of spatially
extended emission in observations processed with angular differential imaging
(ADI) algorithms. High-contrast direct imaging of circumstellar disks is
limited by quasi-static speckle noise and ADI is commonly used to suppress
those speckles. However, the application of ADI can result in self-subtraction
of the disk signal due to the disk's finite spatial extent. This signal
attenuation varies with radial separation and biases measurements of the disk's
surface brightness, thereby compromising inferences regarding the physical
processes responsible for the dust distribution. To compensate for this
attenuation, we forward-model the disk structure and compute the form of the
self-subtraction function at each separation. As a proof of concept, we apply
our method to 1.6 and 2.2 micron Keck AO NIRC2 scattered-light observations of
the HD 32297 debris disk reduced using a variant of the "locally optimized
combination of images" (LOCI) algorithm. We are able to recover disk surface
brightness that was otherwise lost to self-subtraction and produce simplified
models of the brightness distribution as it appears with and without
self-subtraction. From the latter models, we extract radial profiles for the
disk's brightness, width, midplane position, and color that are unbiased by
self-subtraction. Our analysis of these measurements indicates a break in the
brightness profile power law at r~110 AU and a disk width that increases with
separation from the star. We also verify disk curvature that displaces the
midplane by up to 30 AU towards the northwest relative to a straight fiducial
midplane.Comment: Accepted for publication in ApJ, 20 pages, 10 figures, 1 tabl
Proteoglycan neofunctions: regulation of inflammation and autophagy in cancer biology.
Inflammation and autophagy have emerged as prominent issues in the context of proteoglycan signaling. In particular, two small, leucine-rich proteoglycans, biglycan and decorin, play pivotal roles in the regulation of these vital cellular pathways and, as such, are intrinsically involved in cancer initiation and progression. In this minireview, we will address novel functions of biglycan and decorin in inflammation and autophagy, and analyze new emerging signaling events triggered by these proteoglycans, which directly or indirectly modulate these processes. We will critically discuss the dual role of proteoglycan-driven inflammation and autophagy in tumor biology, and delineate the potential mechanisms through which soluble extracellular matrix constituents affect the microenvironment associated with inflammatory and neoplastic diseases
Asymmetric Heating of the HR 4796A Dust Ring Due to Pericenter Glow
We have obtained new resolved images of the well-studied HR 4796A dust ring
at 18 and 25 microns with the 8-meter Gemini telescopes. These images confirm
the previously observed spatial extent seen in mid-IR, near-IR, and optical
images of the source. We detect brightness and temperature asymmetries such
that dust on the NE side is both brighter and warmer than dust in the SW. We
show that models of so-called pericenter glow account for these asymmetries,
thus both confirming and extending our previous analyses. In this scenario, the
center of the dust ring is offset from the star due to gravitational
perturbations of a body with an eccentric orbit that has induced a forced
eccentricity on the dust particle orbits. Models with 2-micron silicate dust
particles and a forced eccentricity of 0.06 simultaneously fit the observations
at both wavelengths. We also show that parameters used to characterize the
thermal-emission properties of the disk can also account for the disk asymmetry
observed in shorter-wavelength scattered-light images.Comment: accepted for publication in A&A; 7 pages, 4 figure
First optical images of circumstellar dust surrounding the debris disk candidate HD 32297
Near-infrared imaging with the Hubble Space Telescope recently revealed a
circumstellar dust disk around the A star HD 32297. Dust scattered light is
detected as far as 400 AU radius and the linear morphology is consistent with a
disk ~10 degrees away from an edge-on orientation. Here we present the first
optical images that show the dust scattered light morphology from 560 to 1680
AU radius. The position angle of the putative disk midplane diverges by 31
degrees and the color of dust scattering is most likely blue. We associate HD
32297 with a wall of interstellar gas and the enigmatic region south of the
Taurus molecular cloud. We propose that the extreme asymmetries and blue disk
color originate from a collision with a clump of interstellar material as HD
32297 moves southward, and discuss evidence consistent with an age of 30 Myr or
younger.Comment: 5 pages; Accepted for publication in ApJ Letter
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