Optimization of Apodized Pupil Lyot Coronagraph for ELTs

We study the optimization of the Apodized Pupil Lyot Coronagraph (APLC) in the context of exoplanet imaging with ground-based telescopes. The APLC combines an apodization in the pupil plane with a small Lyot mask in the focal plane of the instrument. It has been intensively studied in the literature from a theoretical point of view, and prototypes are currently being manufactured for several projects. This analysis is focused on the case of Extremely Large Telescopes, but is also relevant for other telescope designs. We define a criterion to optimize the APLC with respect to telescope characteristics like central obscuration, pupil shape, low order segment aberrations and reflectivity as function of the APLC apodizer function and mask diameter. Specifically, the method was applied to two possible designs of the future European-Extremely Large Telescope (E-ELT). Optimum configurations of the APLC were derived for different telescope characteristics. We show that the optimum configuration is a stronger function of central obscuration size than of other telescope parameters. We also show that APLC performance is quite insensitive to the central obscuration ratio when the APLC is operated in its optimum configuration, and demonstrate that APLC optimization based on throughput alone is not appropriate.Comment: 9 pages, 17 figures, accepted for publication in Astronomy & Astrophysic

Formation, Simulation and Restoration of Hypertelescopes Images

This book is a collection of 19 articles which reflect the courses given at the Collège de France/Summer school “Reconstruction d'images − Applications astrophysiques“ held in Nice and Fréjus, France, from June 18 to 22, 2012. The articles presented in this volume address emerging concepts and methods that are useful in the complex process of improving our knowledge of the celestial objects, including Earth

The Fresnel Diffraction: A Story of Light and Darkness

This book is a collection of 19 articles which reflect the courses given at the Collège de France/Summer school “Reconstruction d'images − Applications astrophysiques“ held in Nice and Fréjus, France, from June 18 to 22, 2012. The articles presented in this volume address emerging concepts and methods that are useful in the complex process of improving our knowledge of the celestial objects, including Earth

Adaptive optics imaging of P Cygni in Halpha

We obtained Halpha diffraction limited data of the LBV star P Cyg using the ONERA Adaptive Optics (AO) facility BOA at the OHP 1.52m telescope on October 1997. Taking P Cyg and the reference star 59 Cyg AO long exposures we find that P Cyg clearly exhibits a large and diffuse intensity distribution compared to the 59 Cyg's point-like source. A deconvolution of P Cyg using 59 Cyg as the Point Spread Function was performed by means of the Richardson-Lucy algorithm. P Cyg clearly appears as an unresolved star surrounded by a clumped envelope. The reconstructed image of P Cyg is compared to similar spatial resolution maps obtained from radio aperture synthesis imaging. We put independent constraints on the physics of P Cyg which agree well with radio results. We discuss future possibilities to constrain the wind structure of P Cyg by using multi-resolution imaging, coronagraphy and long baseline interferometry to trace back its evolutionary status.Comment: 10 pages, 19 Encapsulated Postscript figure

A Comparison of Drill and Broadcast Planting Methods forBiomass Production of Two Legume Cover Crops

The effects of drill and broadcast planting methods on cover crop biomass production depend on various environmental and operational factors. We investigated whether drilling and broadcasting result in different amounts of biomass production by crimson clover (Trifolium incarnatum L.) and hairy vetch (Vicia villosa Roth) in the upstate of South Carolina, and results vary when seeding rates are increased by 50% from the standard value (22.4 kg ha−1). Field trials were conducted during the fall–winter of 2019–2020 (season one) and 2020–2021 (season two) at the Piedmont Research and Education Center in Pendleton, SC, USA. Cover crop (hairy vetch, crimson clover), planting method (broadcast, drill), and seeding rate (standard, high) treatments were arranged as a 2 × 2 × 2 factorial in both years. Aboveground biomass was measured after 22.5 weeks from planting. At standard seeding rates, crimson clover produced a higher biomass when drilled, rather than broadcasted, whereas biomass production did not vary for hairy vetch. Even with 50% higher seeding rates, broadcasting did not always produce the same biomass as that of drilling for crimson clover. Our results suggest that the advantage of drilling over broadcasting depends upon the cover crop species, as crimson clover responds well to drilling, whereas hairy vetch does not

Speckle Statistics in Adaptively Corrected Images

(abridged) Imaging observations are generally affected by a fluctuating background of speckles, a particular problem when detecting faint stellar companions at small angular separations. Knowing the distribution of the speckle intensities at a given location in the image plane is important for understanding the noise limits of companion detection. The speckle noise limit in a long-exposure image is characterized by the intensity variance and the speckle lifetime. In this paper we address the former quantity through the distribution function of speckle intensity. Previous theoretical work has predicted a form for this distribution function at a single location in the image plane. We developed a fast readout mode to take short exposures of stellar images corrected by adaptive optics at the ground-based UCO/Lick Observatory, with integration times of 5 ms and a time between successive frames of 14.5 ms ($\lambda=2.2$ $\mu$m). These observations temporally oversample and spatially Nyquist sample the observed speckle patterns. We show, for various locations in the image plane, the observed distribution of speckle intensities is consistent with the predicted form. Additionally, we demonstrate a method by which $I_c$ and $I_s$ can be mapped over the image plane. As the quantity $I_c$ is proportional to the PSF of the telescope free of random atmospheric aberrations, this method can be used for PSF calibration and reconstruction.Comment: 7 pages, 4 figures, ApJ accepte

Ringing effects reduction by improved deconvolution algorithm Application to A370 CFHT image of gravitational arcs

We develop a self-consistent automatic procedure to restore informations from astronomical observations. It relies on both a new deconvolution algorithm called LBCA (Lower Bound Constraint Algorithm) and the use of the Wiener filter. In order to explore its scientific potential for strong and weak gravitational lensing, we process a CFHT image of the galaxies cluster Abell 370 which exhibits spectacular strong gravitational lensing effects. A high quality restoration is here of particular interest to map the dark matter within the cluster. We show that the LBCA turns out specially efficient to reduce ringing effects introduced by classical deconvolution algorithms in images with a high background. The method allows us to make a blind detection of the radial arc and to recover morphological properties similar to thoseobserved from HST data. We also show that the Wiener filter is suitable to stop the iterative process before noise amplification, using only the unrestored data.Comment: A&A in press 9 pages 9 figure

Eight-Coordinate, Stable Fe(II) Complex as a Dual 19F and CEST Contrast Agent for Ratiometric pH Imaging

Accurate mapping of small changes in pH is essential to the diagnosis of diseases such as cancer. The difficulty in mapping pH accurately in vivo resides in the need for the probe to have a ratiometric response so as to be able to independently determine the concentration of the probe in the body independently from its response to pH. The complex FeII-DOTAm-F12 behaves as an MRI contrast agent with dual 19F and CEST modality. The magnitude of its CEST response is dependent both on the concentration of the complex and on the pH, with a significant increase in saturation transfer between pH 6.9 and 7.4, a pH range that is relevant to cancer diagnosis. The signal-to-noise ratio of the 19F signal of the probe, on the other hand, depends only on the concentration of the contrast agent and is independent of pH. As a result, the complex can ratiometrically map pH and accurately distinguish between pH 6.9 and 7.4. Moreover, the iron(II) complex is stable in air at room temperature and adopts a rare 8-coordinate g..