1,737 research outputs found
Speckle noise and dynamic range in coronagraphic images
This paper is concerned with the theoretical properties of high contrast
coronagraphic images in the context of exoplanet searches. We derive and
analyze the statistical properties of the residual starlight in coronagraphic
images, and describe the effect of a coronagraph on the speckle and photon
noise. Current observations with coronagraphic instruments have shown that the
main limitations to high contrast imaging are due to residual quasi-static
speckles. We tackle this problem in this paper, and propose a generalization of
our statistical model to include the description of static, quasi-static and
fast residual atmospheric speckles. The results provide insight into the
effects on the dynamic range of wavefront control, coronagraphy, active speckle
reduction, and differential speckle calibration. The study is focused on
ground-based imaging with extreme adaptive optics, but the approach is general
enough to be applicable to space, with different parameters.Comment: 31 pages, 18 figure
Design, analysis and test of a microdots apodizer for the Apodized Pupil Lyot Coronagraph
Coronagraphic techniques are required to detect exoplanets with future
Extremely Large Telescopes. One concept, the Apodized Pupil Lyot Coronagraph
(APLC), is combining an apodizer in the entrance aperture and a Lyot opaque
mask in the focal plane. This paper presents the manufacturing and tests of a
microdots apodizer optimized for the near IR.
The intent of this work is to demonstrate the feasibility and performance of
binary apodizers for the APLC. This study is also relevant for any coronagraph
using amplitude pupil apodization.
A binary apodizer has been designed using a halftone dot process, where the
binary array of pixels with either 0% or 100% transmission is calculated to fit
the required continuous transmission, i.e. local transmission control is
obtained by varying the relative density of the opaque and transparent pixels.
An error diffusion algorithm was used to optimize the distribution of pixels
that best approximates the required field transmission. The prototype was
tested with a coronagraphic setup in the near IR.
The transmission profile of the prototype agrees with the theoretical shape
within 3% and is achromatic. The observed apodized and coronagraphic images are
consistent with theory. However, binary apodizers introduce high frequency
noise that is a function of the pixel size. Numerical simulations were used to
specify pixel size in order to minimize this effect, and validated by
experiment.
This paper demonstrates that binary apodizers are well suited for being used
in high contrast imaging coronagraphs. The correct choice of pixel size is
important and must be adressed considering the scientific field of view.Comment: A&A accepted, 8 page
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Context-dependent expression of a conditionally-inducible form of active Akt
Akt kinases are key signaling components in proliferation-competent and post-mitotic cells. Here, we sought to create a conditionally-inducible form of active Akt for both in vitro and in vivo applications. We fused a ligand-responsive Destabilizing Domain (DD) derived from E. coli dihydrofolate reductase to a constitutively active mutant form of Akt1, Akt(E40K). Prior work indicated that such fusion proteins may be stabilized and induced by a ligand, the antibiotic Trimethoprim (TMP). We observed dose-dependent, reversible induction of both total and phosphorylated/active DD-Akt(E40K) by TMP across several cellular backgrounds in culture, including neurons. Phosphorylation of FoxO4, an Akt substrate, was significantly elevated after DD-Akt(E40K) induction, indicating the induced protein was functionally active. The induced Akt(E40K) protected cells from apoptosis evoked by serum deprivation and was neuroprotective in two cellular models of Parkinson's disease (6-OHDA and MPP+ exposure). There was no significant protection without induction. We also evaluated Akt(E40K) induction by TMP in mouse substantia nigra and striatum after neuronal delivery via an AAV1 adeno-associated viral vector. While there was significant induction in striatum, there was no apparent induction in substantia nigra. To explore the possible basis for this difference, we examined DD-Akt(E40K) induction in cultured ventral midbrain neurons. Both dopaminergic and non-dopaminergic neurons in the cultures showed DD-Akt(E40K) induction after TMP treatment. However, basal DD-Akt(E40K) expression was 3-fold higher for dopaminergic neurons, resulting in a significantly lower induction by TMP in this population. Such findings suggest that dopaminergic neurons may be relatively inefficient in protein degradation, a property that could relate to their lack of apparent DD-Akt(E40K) induction in vivo and to their selective vulnerability in Parkinson's disease. In summary, we generated an inducible, biologically active form of Akt. The degree of inducibility appears to reflect cellular context that will inform the most appropriate applications for this and related reagents
Analyse statistique de la détection de planÚtes par imagerie directe
- Cette communication est consacrée à la détection de planÚtes par imagerie directe. L'accent est mis sur les deux facteurs dégradants : les résidus de turbulence atmosphérique et la présence du coronographe. Une modélisation statistique des mesures permet de proposer et d'étudier un détecteur utilisant des images à court temps de pose. Une simulation numérique met en évidence le gain de cette technique par rapport à une image long temps de pose ou au traitement courte pose habituel
Improved SOT (Hinode mission) high resolution solar imaging observations
We consider the best today available observations of the Sun free of
turbulent Earth atmospheric effects, taken with the Solar Optical Telescope
(SOT) onboard the Hinode spacecraft. Both the instrumental smearing and the
observed stray light are analyzed in order to improve the resolution. The Point
Spread Function (PSF) corresponding to the blue continuum Broadband Filter
Imager (BFI) near 450 nm is deduced by analyzing i/ the limb of the Sun and ii/
images taken during the transit of the planet Venus in 2012. A combination of
Gaussian and Lorentzian functions is selected to construct a PSF in order to
remove both smearing due to the instrumental diffraction effects (PSF core) and
the large-angle stray light due to the spiders and central obscuration (wings
of the PSF) that are responsible for the parasitic stray light. A
Max-likelihood deconvolution procedure based on an optimum number of iterations
is discussed. It is applied to several solar field images, including the
granulation near the limb. The normal non-magnetic granulation is compared to
the abnormal granulation which we call magnetic. A new feature appearing for
the first time at the extreme- limb of the disk (the last 100 km) is discussed
in the context of the definition of the solar edge and of the solar diameter. A
single sunspot is considered in order to illustrate how effectively the
restoration works on the sunspot core. A set of 125 consecutive deconvolved
images is assembled in a 45 min long movie illustrating the complexity of the
dynamical behavior inside and around the sunspot.Comment: 15 pages, 22 figures, 1 movi
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