Lucky imaging is a high-resolution astronomical image recovery technique with two classic implementation algorithms, i.e. image selecting, shifting and adding in image space and data selecting and image synthesizing in Fourier space. This paper proposes a novel lucky imaging algorithm where with space-domain and frequency-domain selection rates as a link, the two classic algorithms are combined successfully, making each algorithm a proper subset of the novel hybrid algorithm. Experimental results show that with the same experiment dataset and platform, the high-resolution image obtained by the proposed algorithm is superior to that obtained by the two classic algorithms. This paper also proposes a new lucky image selection and storage scheme, which can greatly save computer memory and enable lucky imaging algorithm to be implemented in a common desktop or laptop with small memory and to process astronomical images with more frames and larger size. Besides, through simulation analysis, this paper discusses the binary star detection limits of the novel lucky imaging algorithm and traditional ones under different atmospheric conditions.
Lucky imaging is a technique for high resolution astronomical imaging at visible wavelengths, utilising medium sized ground based telescopes in the 2--4m class. The technique uses high speed, low noise cameras to record short exposures which may then be processed to minimise the deleterious effects of atmospheric turbulence upon image quality. The key statement of this thesis is as follows; that lucky imaging is a technique which now benefits from sufficiently developed hardware and analytical techniques that it may be effectively used for a wide range of astronomical imaging purposes at mediu…
Presented here is list of 50 pairs quasi-evenly spaced over the northern sky, and that have Separations and Position Angles accurate at the milli-arcsec, and milli-degree level. These pairs are suggested as calibration pairs for lucky imaging observations. This paper is a follow-up to our previous paper regarding southern sky calibration pairs.
The new technique of Speckle Stabilization has great potential to provide optical imaging data at the highest angular resolutions from the ground. While Speckle Stabilization was initially conceived for integral field spectroscopic analyses, the technique shares many similarities with speckle imaging (specifically shift-and-add and Lucky Imaging). Therefore, it is worth comparing the two for imaging applications. We have modeled observations on a 2.5-meter class telescope to assess the strengths and weaknesses of the two techniques. While the differences are relatively minor, we find that Spec…
Both lucky imaging techniques and adaptive optics require natural guide stars, limiting sky coverage, even when laser guide stars are used. Lucky imaging techniques become less successful on larger telescopes unless adaptive optics is used, as the fraction of images obtained with well behaved turbulence across the whole telescope pupil becomes vanishingly small. Here, we introduce a technique combining lucky imaging techniques with tomographic laser guide star adaptive optics systems on large telescopes. This technique does not require any natural guide star for the adaptive optics, and hence …
Accurate measures of double stars require accurate calibration of the instrument. Here we present a list of 50 pairs, that are quasi-evenly spaced over the southern sky, and that have Separations and Position Angles accurate at the milli-arcsec, and milli-degree level. These wide angle pairs are suggested as calibration pairs for lucky imaging observations.
Lucky Imaging is now an established observing procedure that delivers near diffraction-limited images in the visible on ground-based telescopes up to ~2.5 m in diameter. Combined with low order adaptive optics it can deliver resolution several times better than that of the Hubble Space Telescope. Many images are taken at high speed as atmospheric turbulent effects appear static on these short timescales. The sharpest images are selected, shifted and added to give a much higher resolution than is normally possible in ground-based long exposure time observations. The method is relatively ineffic…
As a consequence of the evolution in the design and of the modularity of its components, AOLI for the William Herschel Telescope (WHT 4.2m) is much smaller and more efficient than its previous designs. This success has leaded us to plan to condense it even more to get a portable and easy to integrate system, ALIOLI (Adaptive and Lucky Imaging Optics Lightweight Instrument). It consists of a DM+WFS module with a lucky imaging science camera attached. ALIOLI is an AO instrument for the 1-2m class telescopes which will also be used as on-sky testbench for AO developments. Here we describe the set…
The highest resolution images ever taken in the visible were obtained by combining Lucky Imaging and low order adaptive optics. This paper describes a new instrument to be deployed on the WHT 4.2m and GTC 10.4 m telescopes on La Palma, with particular emphasis on the optical design and the expected system performance. A new design of low order wavefront sensor using photon counting CCD detectors and multi-plane curvature wavefront sensor will allow dramatically fainter reference stars to be used, allowing virtually full sky coverage with a natural guide star. This paper also describes a signif…
In this work, we study the advantages of using a Lucky Imaging camera for the observations of potential planetary microlensing events. Our aim is to reduce the blending effect and enhance exoplanet signals in binary lensing systems composed of an exoplanet and the corresponding parent star. We simulate planetary microlensing light curves based on present microlensing surveys and follow-up telescopes where one of them is equipped with a Lucky imaging camera. This camera is used at the Danish $1.54$-m follow-up telescope. Using a specific observational strategy, For an Earth-mass planet in the r…
We present an empirical analysis of the effectiveness of frame selection (also known as Lucky Imaging) techniques for high resolution imaging. A high-speed image recording system has been used to observe a number of bright stars. The observations were made over a wide range of values of D/r0 and exposure time. The improvement in Strehl ratio of the stellar images due to aligning frames and selecting the best frames was evaluated as a function of these parameters. We find that improvement in Strehl ratio by factors of 4 to 6 can be achieved over a range of D/r0 from 3 to 12, with a slight peak …
A prototype of a low cost Adaptive Optics (AO) system has been developed at the Instituto de Astrofisica de Andalucia (CSIC) and tested at the 2.2m telescope of the Calar Alto observatory. We present here the status of the project, which includes the image stabilization system and compensation of high order wavefront aberrations with a membrane deformable mirror. The image stabilization system consists of magnet driven tip-tilt mirror. The higher order compensation system comprises of a Shack-Hartmann sensor, a membrane deformable mirror with 39 actuators and the control computer that allows o…
Here we present the Adaptive Optics Lucky Imager (AOLI), a state-of-the-art instrument which makes use of two well proved techniques, Lucky Imaging (LI) and Adaptive Optics (AO), to deliver diffraction limited imaging at visible wavelengths, 20 mas, from ground-based telescopes. Thanks to its revolutionary TP3-WFS, AOLI shall have the capability of using faint reference stars. In the extremely-big telescopes era, the combination of techniques and the development of new WFS systems seems the clue key for success. We give details of the integration and verification phases explaining the defiance…
In traditional lucky imaging (TLI), many consecutive images of the same scene are taken with a high frame-rate camera, and all but the sharpest images are discarded before constructing the final shift-and-add image. Here we present an alternative image analysis pipeline -- The Thresher -- for these kinds of data, based on online multi-frame blind deconvolution. It makes use of all available data to obtain a best estimate of the astronomical scene in the context of reasonable computational limits; it does not require prior estimates of the point-spread functions in the images, or knowledge of p…
CONTEXT: Many massive stars have nearby companions whose presence hamper their characterization through spectroscopy. AIMS: We want to obtain spatially resolved spectroscopy of close massive visual binaries to derive their spectral types. METHODS: We obtain a large number of short long-slit spectroscopic exposures of five close binaries under good seeing conditions, select those with the best characteristics, extract the spectra using multiple-profile fitting, and combine the results to derive spatially separated spectra. RESULTS: We demonstrate the usefulness of Lucky Spectroscopy by presenti…
The potential of combining Adaptive Optics (AO) and Lucky Imaging (LI) to achieve high precision astrometry and differential photometry in the optical is investigated by conducting observations of the close 0\farcs1 brown dwarf binary GJ569Bab. We took 50000 $I$-band images with our LI instrument FastCam attached to NAOMI, the 4.2-m William Herschel Telescope (WHT) AO facility. In order to extract the most of the astrometry and photometry of the GJ569Bab system we have resorted to a PSF fitting technique using the primary star GJ569A as a suitable PSF reference which exhibits an $I$-band magni…
The EMCCD is a type of CCD that delivers fast readout times and negligible readout noise, making it an ideal detector for high frame rate applications which improve resolution, like lucky imaging or shift-and-add. This improvement in resolution can potentially improve the photometry of faint stars in extremely crowded fields significantly by alleviating crowding. Alleviating crowding is a prerequisite for observing gravitational microlensing in main sequence stars towards the galactic bulge. However, the photometric stability of this device has not been assessed. The EMCCD has sources of noise…
The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential formation pathway. Additionally, contaminating light from both binary companions and unassociated stars can significantly bias the results of planet characterisation studies, but can be corrected for if the properties of the contaminating star are known. We search for binary companions to known transiting exoplanet host stars, in order to determine the multiplicity properties of hot Jupiter host stars. We also characterise unassociated stars along the line o…
We present some results of testing of commercial color CMOS cameras for astronomical applications. CMOS sensors allow to perform photometry in three filters simultaneously that gives a great advantage compared with monochrome CCD detectors. The Bayer BGR colour system realized in CMOS sensors is close to the Johnson BVR system. We demonstrate transformation from the Bayer color system to the Johnson one. Our photometric measurements with color CMOS cameras coupled to small telescopes (11 - 30 inch) reveal that in video mode stars up to V $\sim$ 9 can be shot at 24 frames per second. Using a hi…
The observations of solar photosphere from the ground encounter significant problems due to the presence of Earth's turbulent atmosphere. Prior to applying image reconstruction techniques, the frames obtained in most favorable atmospheric conditions (so-called lucky frames) have to be carefully selected. However, the estimation of the quality of images containing complex photospheric structures is not a trivial task and the standard routines applied in night-time Lucky Imaging observations are not applicable. In this paper we evaluate 36 methods dedicated for the assessment of image quality wh…
Bright single and binary stars were observed at the 4.1-m telescope with a fast electron-multiplication camera in the regime of partial turbulence correction by the visible-light adaptive optics system. We compare the angular resolution achieved by simple averaging of AO-corrected images (long-exposure), selection and re-centering (shift-and-add or "lucky" imaging) and speckle interferometry. The effect of partial AO correction, vibrations, and image post-processing on the attained resolution is shown. Potential usefulness of these techniques is evaluated for reaching the diffraction limit in …
Near-diffraction limited imaging and spectroscopy in the visible on large (8-10 meter) class telescopes has proved to be beyond the capabilities of current adaptive optics technologies, even when using laser guide stars. The need for high resolution visible imaging in any part of the sky suggests that a rather different approach is needed. This paper describes the results of simulations, experiments and astronomical observations that show that a combination of low order adaptive optic correction using a 4-field curvature sensor and fast Lucky Imaging strategies with a photon counting CCD camer…
Lucky Imaging combined with a low order adaptive optics system has given the highest resolution images ever taken in the visible or near infrared of faint astronomical objects. This paper describes a new instrument that has already been deployed on the WHT 4.2m telescope on La Palma, with particular emphasis on the optical design and the predicted system performance. A new design of low order wavefront sensor using photon counting CCD detectors and multi-plane curvature wavefront sensor will allow virtually full sky coverage with faint natural guide stars. With a 2 x 2 array of 1024 x 1024 pho…
We report high spatial resolution i' band imaging of the multiple T Tauri system LkH$α$ 262/LkH$α$ 263 obtained during the first commissioning period of the Adaptive Optics Lucky Imager (AOLI) at the 4.2 m William Herschel Telescope, using its Lucky Imaging mode. AOLI images have provided photometry for each of the two components LkH$α$ 263 A and B (0.41 arcsec separation) and marginal evidence for an unresolved binary or a disc in LkH$α$ 262. The AOLI data combined with previously available and newly obtained optical and infrared imaging show that the three components of LkH$α$ 263 are co-mov…
We recently proposed a new lucky imaging technique, the Power Spectrum Extended (PSE), adapted for image reconstruction of short-exposure astronomical images in case of weak turbulence or partial adaptive optics correction. In this communication we show applications of this technique to observations of about 30 binary stars in H band with the 1m telescope of the Calern C2PU observatory. We show some images reconstructed at the diffraction limit of the telescope and provide measurements of relative astrometry and photometry of observed couples.
We present a method for speckle holography that is optimised for crowded fields. Its two key features are an iterativ improvement of the instantaneous Point Spread Functions (PSFs) extracted from each speckle frame and the (optional) simultaneous use of multiple reference stars. In this way, high signal-to-noise and accuracy can be achieved on the PSF for each short exposure, which results in sensitive, high-Strehl re- constructed images. We have tested our method with different instruments, on a range of targets, and from the N- to the I-band. In terms of PSF cosmetics, stability and Strehl r…
A key challenge of high contrast imaging (HCI) is to differentiate a speckle from an exoplanet signal. The sources of speckles are a combination of atmospheric residuals and aberrations in the non-common path. Those non-common path aberrations (NCPA) are particularly challenging to compensate for as they are not directly measured, and because they include static, quasi-static and dynamic components. The proposed method directly addresses the challenge of compensating the NCPA. The algorithm DrWHO - Direct Reinforcement Wavefront Heuristic Optimisation - is a quasi-real-time compensation of sta…
In this paper, we present an original observational approach, which combines, for the first time, traditional speckle imaging with image post-processing to obtain in the optical domain diffraction-limited images with high contrast (1e-5) within 0.5 to 2 arcseconds around a bright star. The post-processing step is based on wavelet filtering an has analogy with edge enhancement and high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope (NOT) and the lucky imaging instrument FASTCAM show that we are able to detect L-type brown dwarf companions around a solar-type star with…
Radio interferometry is the current method of choice for deep space astronomy, but in the past few decades optical techniques have become increasingly common. This research seeks to characterize the performance of aperture masking interferometry in the near-infrared at small scales. A mask containing six pairs of apertures at varying diameters and separations was constructed for use with a 24-inch telescope at the MIT Wallace Astrophysical Observatory. Test images of Spica and Jupiter were captured for 28 different telescope configurations, varying aperture separation, aperture diameter, colle…
We present a detailed discussion of the implementation strategies for a recently developed $w$-stacking $w$-projection hybrid algorithm used to reconstruct wide-field interferometric images. In particular, we discuss the methodology used to deploy the algorithm efficiently on a supercomputer via use of a Message Passing Interface (MPI) $k$-means clustering technique to achieve efficient construction and application of non co-planar effects. Additionally, we show that the use of conjugate symmetry increases the algorithms performance by imaging an interferometric observation of Fornax A from th…
Variations of the antenna primary beam (PB) pattern as a function of time, frequency and polarization form one of the dominant direction-dependent effects at most radio frequency bands. These gains may also vary from antenna to antenna. The A-Projection algorithm, published earlier, accounts for the effects of the narrow-band antenna PB in full polarization. In this paper we present the Wide-Band A-Projection algorithm (WB A-Projection) to include the effects of wide bandwidth in the A-term itself and show that the resulting algorithm simultaneously corrects for the time, frequency and polariz…
We present high-resolution I-band imaging of the core of the globular cluster M15 obtained at the 2.5 m Nordic Optical Telescope with FastCam, a low readout noise L3CCD based instrument. Short exposure times (30 ms) were used to record 200000 images (512 x 512 pixels each) over a period of 2 hours 43 min. The lucky imaging technique was then applied to generate a final image of the cluster centre with FWHM ~ 0".1 and 13" x 13" FoV. We obtained a catalogue of objects in this region with a limiting magnitude of I=19.5. I-band photometry and astrometry are reported for 1181 stars. This is the dee…
We are building a next-generation laser adaptive optics system, Robo-AO-2, for the UH 2.2-m telescope that will deliver robotic, diffraction-limited observations at visible and near-infrared wavelengths in unprecedented numbers. The superior Maunakea observing site, expanded spectral range and rapid response to high-priority events represent a significant advance over the prototype. Robo-AO-2 will include a new reconfigurable natural guide star sensor for exquisite wavefront correction on bright targets and the demonstration of potentially transformative hybrid AO techniques that promise to ex…
The standard wide-field imaging technique, the $w$-projection, allows correction for wide-fields of view for non-coplanar radio interferometric arrays. However, calculating exact corrections for each measurement has not been possible due to the amount of computation required at high resolution and with the large number of visibilities from current interferometers. The required accuracy and computational cost of these corrections is one of the largest unsolved challenges facing next generation radio interferometers such as the Square Kilometre Array. We show that the same calculation can be per…
One key advantage of single-mode photonic technologies for interferometric use is their ability to easily scale to an ever increasing number of inputs without a major increase in the overall device size, compared to traditional bulk optics. This is particularly important for the upcoming ELT generation of telescopes currently under construction. We demonstrate the fabrication and characterization of a novel hybridized photonic interferometer, with 8 simultaneous inputs, forming 28 baselines, the largest amount to-date. Utilizing different photonic fabrication technologies, we combine a 3D pupi…
CONTEXT. Massive stars have high-multiplicity fractions, and many of them have still undetected components, thus hampering the study of their properties. AIMS. I study a sample of massive stars with high angular resolution to better characterize their multiplicity. METHODS. I observed 138 fields that include at least one massive star with AstraLux, a lucky imaging camera at the 2.2 m Calar Alto telescope. I also used observations of 3 of those fields with ACS/HRC on HST to obtain complementary information and to calibrate the AstraLux data. The results were compared with existing information f…
This work is a methodical study on hybrid reconstruction techniques for hybrid imaging/timing Cherenkov observations. This type of hybrid array is to be realized at the gamma-observatory TAIGA intended for very high energy gamma-ray astronomy (>30 TeV). It aims at combining the cost-effective timing-array technique with imaging telescopes. Hybrid operation of both of these techniques can lead to a relatively cheap way of development of a large area array. The joint approach of gamma event selection was investigated on both types of simulated data: the image parameters from the telescopes, and …
Electron tracking based Compton imaging is a key technique to improve the sensitivity of Compton cameras by measuring the initial direction of recoiled electrons. To realize this technique in semiconductor Compton cameras, we propose a new detector concept, Si-CMOS hybrid detector. It is a Si detector bump-bonded to a CMOS readout integrated circuit to obtain electron trajectory images. To acquire the energy and the event timing, signals from N-side are also read out in this concept. By using an ASIC for the N-side readout, the timing resolution of few us is achieved. In this paper, we present…
High contrast imaging at optical wavelengths is limited by the modest correction of conventional near-IR optimized AO systems.We take advantage of new fast and low-readout-noise detectors to explore the potential of fast imaging coupled to post-processing techniques to detect faint companions to stars at small separations. We have focused on I-band direct imaging of the previously detected brown dwarf binary HD130948BC,attempting to spatially resolve the L2+L2 benchmark system. We used the Lucky-Imaging instrument FastCam at the 2.5-m Nordic Telescope to obtain quasi diffraction-limited images…
Generating images from very long baseline interferometric observations poses a difficult, and generally not unique, inversion problem. This problem is simplified by the introduction of constraints, some generic (e.g., positivity of the intensity) and others motivated by physical considerations (e.g., smoothness, instrument resolution). It is further complicated by the need to simultaneously address instrumental systematic uncertainties and sparse coverage in the u-v plane. We report a new Bayesian image reconstruction technique in the parameter estimation framework Themis that has been develop…
