A Spectroscopic Reconnaissance of UV-Bright Stars

We have carried out spectroscopic observations and made preliminary classifications of 62 UV-bright stars identified by Lanning on plates taken by A. Sandage. The goal was to search for "interesting" objects, such as emission-line stars, hot sub-dwarfs, and high-gravity stars. Our targets were grouped into two samples, a bright, B < 13, sample of 35 stars observed with the Kitt Peak 2.1m telescope and a faint, 13< B < 16, sample of 27 stars observed with the Hobby-Eberly Telescope. We find 39% fairly normal O-mid B stars, 15% late ~B-late A stars and 32% F-G stars, with 13% of the stars being high gravity objects, composite, or otherwise peculiar. Included are four emission-line stars, three composite systems. Thus one out of every ten Lanning stars is "interesting" and may deserve individual study. Stars in the bright sample are often found to be late F or early G stars, although this sample does include interesting stars as well. No such large contamination occurs among the fainter stars, however, owing to "deselection" of these stars by interstellar reddening in the low-latitude fields of the survey.Comment: 9 pages in total, to appear in February 2002 issue of P.A.S.

Three-sided pyramid wavefront sensor. II. Preliminary demonstration on the new CACTI testbed

The next generation of giant ground and space telescopes will have the light-collecting power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of Giant Segmented Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are optimized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance, and as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the new Comprehensive Adaptive Optics and Coronagraph Test Instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We detail the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the Raw Intensity and Slopes Map signal processing methods. This experiment was repeated for a modulation radius of 1.6 lambda/D and 3.25 lambda/D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.Comment: 28 Pages, 15 Figures, and 4 Table

Development and Verification of the non-linear Curvature Wavefront Sensor

Adaptive optics (AO) systems have become an essential part of ground-based telescopes and enable diffraction-limited imaging at near-IR and mid-IR wavelengths. For several key science applications the required wavefront quality is higher than what current systems can deliver. For instance obtaining high quality diffraction-limited images at visible wavelengths requires residual wavefront errors to be well below 100 nm RMS. High contrast imaging of exoplanets and disks around nearby stars requires high accuracy control of low-order modes that dominate atmospheric turbulence and scatter light at small angles where exoplanets are likely to be found. Imaging planets using a high contrast corona graphic camera, as is the case for the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) on the Very Large Telescope (VLT), and the Gemini Planet Imager (GPI), requires even greater wavefront control accuracy. My dissertation develops a highly sensitive non-linear Curvature Wavefront Sensor (nlCWFS) that can deliver diffraction-limited (λ/D) images, in the visible, by approaching the theoretical sensitivity limit imposed by fundamental physics. The nlCWFS is derived from the successful curvature wavefront sensing concept but uses a non-linear reconstructor in order to maintain sensitivity to low spatial frequencies. The nlCWFS sensitivity makes it optimal for extreme AO and visible AO systems because it utilizes the full spatial coherence of the pupil plane as opposed to conventional sensors such as the Shack-Hartmann Wavefront Sensor (SHWFS) which operate at the atmospheric seeing limit (λ/r₀). The difference is equivalent to a gain of (D/r₀)² in sensitivity, for the lowest order mode, which translates to the nlCWFS requiring that many fewer photons. When background limited the nlCWFS sensitivity scales as D⁴, a combination of D² gain due to the diffraction limit and D² gain due to telescope's collecting power. Whereas conventional wavefront sensors only benefit from the D² gain due to the telescope's collecting power. For a 6.5 m telescope, at 0.5 μm, and seeing of 0.5", the nlCWFS can deliver for low order modes the same wavefront measurement accuracy as the SHWFS with 1000 times fewer photons. This is especially significant for upcoming extremely large telescopes such as the Giant Magellan Telescope (GMT) which has a 25.4 m aperture, the Thirty Meter Telescope (TMT) and the European Extremely Large Telescope (E-ELT) which has a 39 m aperture

Three-sided pyramid wavefront sensor, part 1: simulations and analysis for astronomical adaptive optics

International audienceThe Giant Segmented Mirror Telescopes (GSMTs) including the Giant Magellan Telescope (GMT), the Thirty Meter Telescope (TMT), and the European Extremely Large Telescope (E-ELT), all have extreme adaptive optics (ExAO) instruments planned that will use pyramid wavefront sensors (PWFS). The ExAO instruments all have common features: a high-actuator-count deformable mirror running at extreme speeds (>1  kHz); a high-performance wavefront sensor (WFS); and a high-contrast coronagraph. ExAO WFS performance is currently limited by the need for high spatial sampling of the wavefront which requires large detectors. For ExAO instruments for the next generation of telescopes, alternative architectures of WFS are under consideration because there is a trade-off between detector size, speed, and noise that reduces the performance of GSMT-ExAO wavefront control. One option under consideration for a GSMT-ExAO wavefront sensor is a three-sided PWFS (3PWFS). The 3PWFS creates three copies of the telescope pupil for wavefront sensing, compared to the conventional four-sided PWFS (4PWFS), which uses four pupils. The 3PWFS uses fewer detector pixels than the 4PWFS and should therefore be less sensitive to read noise. Here we develop a mathematical formalism based on the diffraction theory description of the Foucault knife-edge test that predicts the intensity pattern after the PWFS. Our formalism allows us to calculate the intensity in the pupil images formed by the PWFS in the presence of phase errors corresponding to arbitrary Fourier modes. We use these results to motivate how we process signals from a 3PWFS. We compare the raw intensity (RI) method, and derive the Slopes Maps (SM) calculation for the 3PWFS, which combines the three pupil images of the 3PWFS to obtain the X and Y slopes of the wavefront. We then use the Object Oriented MATLAB Adaptive Optics toolbox (OOMAO) to simulate an end-to-end model of an AO system using a PWFS with modulation and compare the performance of the 3PWFS to the 4PWFS. In the case of a low read noise detector, the Strehl ratios of the 3PWFS and 4PWFS are within 0.01. When we included higher read noise in the simulation, we found a Strehl ratio gain of 0.036 for the 3PWFS using RI over the 4PWFS using SM at a stellar magnitude of 10. At the same magnitude, the 4PWFS RI also outperformed the 4PWFS SM, but the gain was only 0.012 Strehl. This is significant because 4PWFS using SM is how the PWFS is conventionally used for AO wavefront sensing. We have found that the 3PWFS is a viable WFS that can fully reconstruct a wavefront and produce a stable closed-loop with correction comparable to that of a 4PWFS, with modestly better performance for high read-noise detectors

Analyse pyramide à trois faces, partie II: démonstration préliminaire sur le banc de test OA et Haut Contraste

The next generation of giant ground and space telescopes will have the light-collect-ing power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of the Giant Segment Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are opti-mized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance and, as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the innovative comprehensive adaptive optics and coronagraph test instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We describe the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. We detail the error budget of the CACTI system, review its operation and calibration procedures, and discuss its current status. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. This experiment was repeated for a modulation radius of 1.6 and 3.25 λ∕D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.La prochaine génération de télescopes terrestres et spatiaux géants aura la capacité de collecter la lumière pour détecter et caractériser des exoplanètes terrestres potentiellement habitables en utilisant pour la première fois une imagerie à contraste élevée. Cela ne sera réalisable que si les performances des systèmes d'optique adaptative extrême (ExAO) des télescopes à miroir à segmentés géants (GSMT) sont optimisées à leur plein potentiel. Un composant clé d'un système ExAO est le senseur de front d'onde (WFS), qui mesure les aberrations de la turbulence atmosphérique. Un choix courant dans les instruments actuels et de prochaine génération est le senseur de front d'onde pyramidal (PWFS). Les systèmes ExAO nécessitent un échantillonnage spatial et temporel élevé des fronts d'onde pour optimiser les performances et en conséquence nécessitent des détecteurs de grande taille pour le WFS. Nous présentons une démonstration de banc d'essai en boucle fermée d'un capteur de front d'onde pyramidal à trois côtés (3PWFS) comme alternative au capteur conventionnel de front d'onde pyramidal à quatre côtés (4PWFS) pour les applications GSMT-ExAO sur l'optique adaptative complète innovante et l'instrument de test coronographe ( CACTUS). Le 3PWFS est moins sensible au bruit de lecture que le 4PWFS car il utilise moins de pixels détecteurs. Le 3PWFS a un avantages supplémentaire : une optique pyramidale à trois côtés de haute qualité est plus facile à fabriquer qu'une pyramide à quatre côtés. Nous décrivons la conception des deux composants du système CACTI, le simulateur d'optique adaptative et le banc d'essai PWFS qui comprend à la fois un 3PWFS et un 4PWFS. Nous détaillons le budget d'erreur du système CACTI, passons en revue ses procédures de fonctionnement et d'étalonnage, et discutons de son état actuel. Une expérience préliminaire a été réalisée sur CACTI pour étudier les performances de la 3PWFS à la 4PWFS dans différentes forces de turbulence en utilisant à la fois l'intensité brute et les méthodes de traitement du signal de la carte des pentes. Cette expérience a été répétée pour un rayon de modulation de 1,6 et 3,25 λ∕D. Nous avons constaté que les performances des deux capteurs de front d'onde sont comparables si les gains de boucle modale sont réglés

Three-sided pyramid wavefront sensor, part II: preliminary demonstration on the new comprehensive adaptive optics and coronagraph test instrument testbed

The next generation of giant ground and space telescopes will have the light-collecting power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of the Giant Segment Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are optimized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance and, as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the innovative comprehensive adaptive optics and coronagraph test instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We describe the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. We detail the error budget of the CACTI system, review its operation and calibration procedures, and discuss its current status. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. This experiment was repeated for a modulation radius of 1.6 and 3.25 lambda / D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.(c) 2022 Society of Photo-Optical Instrumentation Engineers (SPIE

Characteristics of Susac syndrome: a review of all reported cases

In Susac syndrome, occlusions of microvessels-presumed to be mediated by an autoimmune response to an as yet unknown antigen--lead to a characteristic clinical triad of CNS dysfunction, branch retinal artery occlusions, and sensorineural hearing impairment. Susac syndrome is considered a rare but important differential diagnosis in numerous neurological, psychiatric, ophthalmological, and ear, nose and throat disorders. Improved understanding of this disorder is crucial, therefore, to ensure that patients receive appropriate treatment and care. Current knowledge on Susac syndrome is largely based on reports of single patients, small case series, and nonsystematic reviews. The aim of this Review is to extend these previous, primarily anecdotal findings by compiling data from all 304 cases of Susac syndrome that have been published worldwide, which were identified following a literature search with predefined search, inclusion and exclusion criteria. From this data, we present an overview of demographic, clinical and diagnostic data on Susac syndrome, providing a reliable basis for our current understanding of this rare disease. Where possible, we make recommendations for clinical diagnosis, differential diagnosis, and management of patients with suspected Susac syndrome