Search

We have carried out some investigation to optimize the broadband performance of the high-contrast imaging testbed (HCIT) at JPL through optical modeling and simulations. The analytical tool is an optical simulation algorithm developed by combining the HCIT's optical model with a speckle-nulling algorithm that operates directly on coronagraphic images, an algorithm very similar to the one that has been used on the HCIT. We have experimented in our simulations with different designs for the occulting mask and the Lyot Stop, and also tried several different speckle-nulling approaches. Some results predicted by our simulations agree well with the results measured on the HCIT. In this paper we describe the details of our simulations and present our results.

The Exo-Planets Imaging Camera and Spectrograph (EPICS), is the Planet Finder Instrument concept for the European Extremely Large Telescope (ELT). The study made in the frame of the OWL 100-m telescope concept is being up-dated in direct relation with the re-baselining activities of the European Extremely Large Telescope.

The performance of high contrast imaging systems is very often limited by the presence of static speckles in the point-spread function of the central source. Several techniques have already been proposed to discriminate a faint companion from these residual speckles. These techniques used different criteria to separate a speckle from a companion: polarization, spectral information or coherence. Here, we propose a new imaging device, the Self-Coherent Camera (SCC), that is based on the lack of coherence between the stellar light and the planet that is searched for. This SCC is a simple instrument that allows us to reach the fundamental limitation of the photon noise by calibrating the speckles in the recorded images. After the description of the general problem of discriminating speckles from planets, we will explain the principle of the SCC. Then, we will analyze the different limitations of this technique as well as the performance that can be reached with current telescopes.

We present the results of analysis of random errors and simulate the effects of systematic errors using specific mask designs.

On the Antarctic plateau, a joint project of French and Italian polar programmes is nearing completion: the Concordia station will be open for winter-over operation in 2005. The high altitude and high latitude of this site, the exceptionally cold, clear and stable atmosphere, its incredible astronomical seeing, the almost indefinitely flat snow surface and the not-so-difficult access make this site the most promising on Earth for future ground-based astronomical projects in various fields, including long term photometry, infrared high sensitivity imaging and high angular resolution and high contrast imaging.

Here we present the installation and successful commissioning of an L'-band Annular Groove Phase Mask (AGPM) coronagraph on VLT/NACO. The AGPM is a vector vortex coronagraph made from diamond subwavelength gratings tuned to the L' band. The vector vortex coronagraph enables high contrast imaging at very small inner working angle (here 0″.09, the diffraction limit of the VLT at L'), potentially being the key to a new parameter space. During technical and science verification runs, we discovered a late-type companion at two beamwidths from an F0V star (Mawet et al. 2013), and imaged the inner regions of β Pictoris down to the previously unexplored projected radius of 1.75 AU. The circumstellar disk was also resolved from ≃ 1″ to 5″ (see J. Milli et al., these proceedings). These results showcase the potential of the NACO L-band AGPM over a wide range of spatial scales.

We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (≈1.5–2.5 M⊙) conducted to date and includes the planet hosts β Pic and Fomalhaut. Despite detecting two new brown dwarfs, our observations did not detect new planets around our target stars, and we present upper limits on the fraction of high-mass stars that can host giant planets that are consistent with our null result.

We describe the multiple-stage Lyot coronagraph first proposed by Aime, Soummer and Ferrari (A&A 2002, 389,334344) for the detection of exoplanets. This coronagraph uses several stages. The first stage is a Prolate Apodized Lyot Coronagraph (PALC). It produces a residual wavefront on the aperture that is proportional to the entrance prolate spheroidal apodized wavefront. This permits the use of a second stage of coronagraphy, needing only a Lyot mask, identical to the first one, without any further aperture apodization. The resulting extinction factor is the square of the initial PALC. Using several stages permits to obtain considerable rejection factors for small-size coronagraphic masks and good overall throughput.

High contrast imaging opportunties abound in astronomy, and some carry such intrinsic interest that they justify considerable effort to master the technical challenges. The field has a rich history dating back to the beginnings of electromagnetic theory, and ten years ago one might have been forgiven for thinking that the topic was passe. But just within the last decade the study has fluorished with major advances on multiple fronts - scientific as well as technical. The analytical and conceptual generalization of classical coronagraphy to include complex masks and apodizations has opened a fertile field of study. Nulling in interferometry and direct imaging has developed in several promising directions, with empirical and theoretical understanding sometimes passing via different routes to arrive at firm conclusions. Critical supporting technology is developing apace, often for reasons having little to do with high contrast imaging. Thus very large telescopes, space telescopes, adaptive optics, and ultra-precision optics are all steadily advancing, and thus building a priceless technological foundation for future high contrast imaging experiments and facilities. This chapter offers a brief, simple overview, intended primarily to give a context for the many detailed technical papers in this volume.

International audience; On the Antarctica plateau, a joint project of french and italian polar programmes in just near completion: the Concordia station will be open for winterover operation in 2005. The high altitude and high latitude of this site, the exceptionally cold, clear and stable atmosphere, the almost indefinitely flat snow surface and the not so difficult access make this site the most promising on Earth for future ground based astronomical projects in various fields, including High Angular Resolution and High Contrast Imaging.

Rethinking the efficient use of 4m-class telescopes in the dawning era of larger facilities is a timely but challenging debate. The extensive use of PUEO for imaging (and now spectroscopy) has kept CFHT at the forefront of scientific research with adaptive optics since its commissioning in 1996. Even though larger facilities are now starting to think about ways to implement high order AO systems, we believe the medium size of the CFHT and the excellent quality of the site on Mauna Kea is a perfect combination to reach the highest performances with a high order AO system. The fields of application of high order adaptive optics are exciting: They include extremely high contrast imaging and coronography in the near-infrared and diffraction-limited imaging in the optical, with the corresponding gain in angular resolution. In this paper we present a quick description of a few specific astrophysical problems that would benefit from an upgraded AO system at the Canada-France-Hawaii Telescope. More technical details about the upgrade of PUEO are presented by Lai et al. and Cuillandre et al. in these proceedings, see papers 4839-78 and 4839-31.

We report experimental results from the Phase Knife Coronagaph which validate our previous theoretical and numerical simulations, prove the physical principle of it and set realistic limitations to the nulling properties of the coronagraph. The optical set-up, phase knives manufacturing technique and different aspects of the instrumental limitations are given. The first results attain easily a 3000 nulling effect obtained both on single and double simulated stars. Optical and mechanical stabilities are discussed and future steps to be carried out are outlined.

Adaptive Optics (AO) has become an integral part of almost all present and future large telescope initiatives, and will be essential in exploiting the full potential of the large optical interferometers currently under construction. This contribution focuses on the limitations of AO with respect to dynamic range, and on the potential of high-contrast imaging techniques.

We present four new epochs of Ks-band images of the young pre-transitional disk around LkCa 15, and perform extensive forward modeling to derive the physical parameters of the disk. We find indications of strongly anisotropic scattering (Henyey-Greenstein g = 0.67 [-0.11,+0.18]) and a significantly tapered gap edge ('round wall'), but see no evidence that the inner disk, whose existence is predicted by the spectral energy distribution, shadows the outer regions of the disk visible in our images. We marginally confirm the existence of an offset between the disk center and the star along the line of nodes; however, the magnitude of this offset (x = 27 [-20,+19] mas) is notably lower than that found in our earlier H-band images (Thalmann et al. 2010). Intriguingly, we also find, at high significance, an offset of y = 69 [-25, +49] mas perpendicular to the line of nodes. If confirmed by future observations, this would imply a highly elliptical -- or otherwise asymmetric -- disk gap with an effective eccentricity of e = ~0.3. Such asymmetry would most likely be the result of dynamical sculpting by one or more unseen planets in the system. Finally, we find that the bright arc of scattered light we see in direct imaging observations originates from the near side of the disk, and appears brighter than the far side because of strong forward scattering., 24 pages, 25 figures, accepted for publication in A&A

The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV) acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV trend), hinting at the existence of a distant orbiting companion. We have obtained high-contrast adaptive optics images of the star using NIRC2 at Keck Observatory and report the direct detection of the body that causes the acceleration. The companion, HD 19467 B, is dK=12.57+/-0.09 mag fainter than its parent star (contrast ratio of 9.4e-6), has blue colors J-K_s=-0.36+/-0.14 (J-H=-0.29+/-0.15), and is separated by 1.653+/-0.004" (51.1+/-1.0 AU). Follow-up astrometric measurements obtained over an 1.1 year time baseline demonstrate physical association through common parallactic and proper motion. We calculate a firm lower-limit of m>51.9^{+3.6}_{-4.3}Mjup for the companion mass from orbital dynamics using a combination of Doppler observations and imaging. We estimate a model-dependent mass of m=56.7^{+4.6}_{-7.2}Mjup from a gyrochronological age of 4.3^{+1.0}_{-1.2} Gyr. Isochronal analysis suggests a much older age of $9\pm1$ Gyr, which corresponds to a mass of m=67.4^{+0.9}_{-1.5}Mjup. HD 19467 B's measured colors and absolute magnitude are consistent with a late T-dwarf [~T5-T7]. We may infer a low metallicity of [Fe/H]=-0.15+/-0.04 for the companion from its G3V parent star. HD 19467 B is the first directly imaged benchmark T-dwarf found orbiting a Sun-like star with a measured RV acceleration., Updated to reflect ApJ version

We describe Algorithms for Calibration, Optimized Registration, and Nulling the Star in Angular Differential Imaging (ACORNS-ADI), a new, parallelized software package to reduce high-contrast imaging data, and its application to data from the SEEDS survey. We implement several new algorithms, including a method to register saturated images, a trimmed mean for combining an image sequence that reduces noise by up to ~20%, and a robust and computationally fast method to compute the sensitivity of a high-contrast observation everywhere on the field-of-view without introducing artificial sources. We also include a description of image processing steps to remove electronic artifacts specific to Hawaii2-RG detectors like the one used for SEEDS, and a detailed analysis of the Locally Optimized Combination of Images (LOCI) algorithm commonly used to reduce high-contrast imaging data. ACORNS-ADI is written in python. It is efficient and open-source, and includes several optional features which may improve performance on data from other instruments. ACORNS-ADI requires minimal modification to reduce data from instruments other than HiCIAO. It is freely available for download at www.github.com/t-brandt/acorns-adi under a BSD license., Comment: 15 pages, 9 figures, accepted to ApJ. Replaced with accepted version; mostly minor changes. Software updated

As a newly developed coherent diffraction-imaging (CDI) imaging method, the ptychographical iterative engine not only can bypass the difficulty of having high-quality optics in x-ray microscopy by a numerical reconstruction algorithm, but also has obvious advantages on traditional CDI methods in both converging speeds and view fields. However, like in the other CDI methods, the reconstruction of the image from the intensity data of a weakly diffracting specimen is still difficult because of the low signal to noise ratio. To improve this situation, a modification to the currently used algorithms is suggested to double the presence of high spatial frequencies in the diffraction pattern and accordingly to enhance the contrast and fine details of the reconstructions. The simulation and experimental results are presented, and the results can be extended to other CDI methods also.

Coronagraphy has recently been an extremely active field of research, with several high performance concepts proposed, and several new coronagraphs tested in laboratories and telescopes. Coronagraph concepts can be grouped in a few broad categories: Lyot-type coronagraphs, pupil apodization and nulling interferometers. Among existing coronagraph concepts, several approach the fundamental performance limit imposed by the physical nature of light. To achieve their full potential, coronagraphs require exquisite wavefront control and calibration. This has been, and still is, the main bottleneck for the scientifically productive use of coronagraphs on ground-based telescopes. New and promising wavefront sensing techniques suitable for high contrast imaging have however been developed in the last few years and are started to be realized in laboratories. I will review some of these enabling technologies, and show that coronagraphs are now ready for “prime time” on existing and future telescopes.

Organic monolayers of dotriacontane and tetracosanoic acid physisorbed on graphite have been studied by scanning tunneling microscopy at the liquid-solid interface. A high degree of two-dimensional ordering appeared for both the organic compounds observed : the molecules were arranged on graphite in stripelike lamellae of various shape and length. Experimental conditions for high contrast imaging are discussed.

ispartof: OPTICAL AND INFRARED INTERFEROMETRY AND IMAGING VIII vol:12183 ispartof: Conference on Optical and Infrared Interferometry and Imaging VIII Part of SPIE Astronomical Telescopes and Instrumentation Conference location:CANADA, Montreal date:17 Jul - 22 Jul 2022 status: published

We outline the concept and laboratory results of our coronagraphic testbed which has been shipped on automn 2005 to Dome C in Antarctica. We also describe the principle of our coronagraph achromatization and the laboratory first data like the coronographic nulling results which attain more than 10 3 at least. The future development of our experiment for a much larger telescope is also outlined. We finally present CORONA's on-sky first results.

We report results of a re-analysis of archival Spitzer IRAC direct imaging surveys encompassing a variety of nearby stars. Our sample is generated from the combined observations of 73 young stars (median age, distance, spectral type = 85 Myr, 23.3 pc, G5) and 48 known exoplanet host stars with unconstrained ages (median distance, spectral type = 22.6 pc, G5). While the small size of Spitzer provides a lower resolution than 8m-class AO-assisted ground based telescopes, which have been used for constraining the frequency of 0.5 - 13 $M_J$ planets at separations of $10 - 10^2$ AU, its exquisite infrared sensitivity provides the ability to place unmatched constraints on the planetary populations at wider separations. Here we apply sophisticated high-contrast techniques to our sample in order to remove the stellar PSF and open up sensitivity to planetary mass companions down to 5\arcsec\ separations. This enables sensitivity to 0.5 - 13 $M_J$ planets at physical separations on the order of $10^2 - 10^3$ AU , allowing us to probe a parameter space which has not previously been systematically explored to any similar degree of sensitivity. Based on a colour and proper motion analysis we do not record any planetary detections. Exploiting this enhanced survey sensitivity, employing Monte Carlo simulations with a Bayesian approach, and assuming a mass distribution of $dn/dm \propto m^{-1.31}$, we constrain (at 95% confidence) a population of 0.5 - 13 $M_J$ planets at separations of 100 - 1000 AU with an upper frequency limit of 9%., Comment: 21 pages, 9 figures, 3 tables, accepted for publication in ApJ

This erratum corrects the omission of authors and references from the paper as it was originally published.

Context. The direct imaging of rocky exoplanets is one of the major science goals of upcoming large telescopes. The contrast requirement for imaging such planets is challenging. However, the mid-IR (infrared) regime provides the optimum contrast to directly detect the thermal signatures of exoplanets in our solar neighbourhood. Aims. We aim to exploit novel fast-chopping techniques newly developed for astronomy with the aid of adaptive optics to look for thermal signatures of exoplanets around bright stars in the solar neighbourhood. Methods. We used the upgraded Very Large Telescope Imager and Spectrometer for the mid-InfraRed (VISIR) instrument with high-contrast imaging capability optimised for observations at 10 μm to look for exoplanets around five nearby (d < 4 pc) stars. The instrument provides an improved signal-to-noise ratio (S/N) by a factor of ~4 in the N-band compared to standard VISIR for a given S/N and time. Results. In this work, we achieve a detection sensitivity of sub-mJy, which is sufficient to detect a few Jupiter mass planets in nearby systems. Although no detections are made, we achieve most sensitive limits within ϵ Indi A and ϵ Eri, we achieve detection limits very close to the giant planets discovered by RV, with the limits on ϵ Indi A being the most sensitive to date. Our non-detection therefore supports an older age for ϵ Indi A. The results presented here are promising for high-contrast imaging and exoplanet detections in the mid-IR regime.