In the last decades, all the main existing telescopes have been equipped with Adaptive Optics (AO) facilities, and AO is considered an enabling technology for future giant telescopes. A significant limitation to the scientific exploitation of AO data is represented by uncertainties in the knowledge of the Point Spread Function, strongly linked to the need for optimised software tools for AO image analysis. We aim to develop a software package designed and optimised to analyse AO images with complex and spatially variable PSF to maximise the exploitation of high-precision quantitative science from past, present and future AO observations. The new software will address two problems: 1) extracting and modelling the AO PSF across the field of view directly from the AO imaging and spectro-imaging data and 2) extracting quantitative information from data featuring blended sources. The new methods will be validated on simulated images and available data from existing and upcoming AO facilities. The new FAIR software, written in Python™, will be based on a version of the Starfinder software optimised to handle large-format images with variable and structured PSF.
The Simonyi Survey Telescope (SST) at the Rubin Observatory, is nearing completion. Ensuring precise image quality is essential for fulfilling the observatory’s ambitious scientific goals. To this end, the Active Optics System (AOS) will correct various factors, including gravity-induced aberrations, temperature gradients, and hysteresis. During the commissioning phase, achieving precise alignment of the telescope is critical, particularly given the wide field of view. Small errors can lead to unacceptable off-axis aberrations, especially towards the field’s edge. This paper presents an analysis tool of the impact of these aberrations on the in focus PSF moments as detected in the science field. We introduce a simplified model of the optical system under generic misalignments, designed to quickly calculate the distribution of aberrated PSF across the field. By comparing the results obtained from this model with reference data simulated using accurate ray tracing software, we can assess its accuracy and employ it to infer the state of the optical system. This work will provide an additional aid for the Rubin team during the commissioning activities.
The Extremely Large Telescopes (ELTs), thanks to their large apertures and cutting-edge Multi-Conjugate Adaptive Optics (MCAO) systems, promise to deliver sharper and deeper data even than the JWST. SHARP is a concept study for a near-IR (0.95-2.45 μm) spectrograph conceived to fully exploit the collecting area and the angular resolution of the upcoming generation of ELTs. In particular, SHARP is designed for the 2nd port of MORFEO@ELT. Composed of a Multi-Object Spectrograph, NEXUS, and a multi-Integral Field Unit, VESPER, MORFEO-SHARP will deliver high angular (∼30 mas) and spectral (R≃300, 2000, 6000, 17000) resolution, outperforming NIRSpec@JWST (100 mas). SHARP will enable studies of the nearby Universe and the early Universe in unprecedented detail. NEXUS is fed by a configurable slit system deploying up to 30 slits with ∼2.4” length and adjustable width, over a field of about 1.2’×1.2’ (35 mas/pix). Each slit is fed by an inversion prism able to rotate by an arbitrary angle the field that can be seen by the slit. VESPER is composed of 12 probes of 1.7”×1.5” each (spaxel 31 mas) probing a field 24”×70”. SHARP is conceived to exploit the ELT aperture reaching the faintest flux and the sharpest angular resolution by joining the sensitivity of NEXUS and the high spatial sampling of VESPER to MORFEO capabilities. This article provides an overview of the scientific design drivers, their solutions, and the resulting optical design of the instrument achieving the required optical performance.
An accurate alignment of the optical surfaces of a telescope is essential to guarantee an optimal image quality since even small displacements introduce aberrations increasing towards the edges of the field. This effect is especially detrimental in wide-field imagers. This work proposes the derivation of a fully analytical model of the wavefront error as a function of the most likely system misalignments. An accurate response of the telescope under a predefined set of misaligned conditions is obtained through simulations in Zemax OpticStudio. The resulting data is combined through an integrated modeling approach, obtaining a map of the aberrations as a function of a vector of perturbations applied to the optical system. The analytical wavefront error allows for a quick and accurate assessment of the theoretical PSF across the entire image field. As a case study, the example of the Rubin Observatory is adopted, featuring an 8.4m primary mirror and a large field of view.
The Starfinder code has been one of the first attempts to face with the typical adaptive optics structured Point Spread Function (PSF) in dense star fields to accomplish astrometric and photometric analysis. The last release of the software can also handle a variation of the PSF across the Field of View (FoV). The PSF can be either extracted numerically from the brightest stars in the science field or computed externally and provided as an input in the form of a single image or a cube of images. This feature makes this software suitable to work with PSF models obtained by PSF reconstruction techniques. Starfinder also accepts as an input a user-defined parametric model and a variable pointing the PSF auxiliary data required by the parametric-model. This variable might containing also information about the spatial variation across the FoV. In this paper we describe the next release of Starfinder reporting also some examples and we give the recipe to use the tool for variable PSF.
KEYWORDS: Point spread functions, Adaptive optics, 3D modeling, Data storage, Astronomy, Data processing, Galactic astronomy, Kinematics, Deconvolution, Calibration
Determining the PSF remains a key challenge for post adaptive-optics (AO) observations regarding the spatial, temporal and spectral variabilities of the AO PSF, as well as itx complex structure. This paper aims to provide a non-exhaustive but classified list of techniques and references that address this issue of PSF determination, with a particular scope on PSF reconstruction, or more generally pupil-plane-based approaches. We have compiled a large amount of references to synthesize the main messages and kept them at a top level. We also present applications of PSF reconstruction/models to post-processing, more especially PSF-fitting and deconvolution for which there is a fast progress in the community.
"We present initial results from the Multi-conjugate Adaptive-optics Visible Imager-Spectrograph Image Simulator (MAVISIM) to explore the astrometric capabilities of the next generation instrument MAVIS. A core scientific and operational requirement of MAVIS will be to achieve highly accurate differential astrometry, with accuracies on the order that of the extremely large telescopes. To better understand the impact of known and anticipated astrometric error terms, we have created an initial astrometric budget which we present here to motivate the creation of MAVISIM. In this first version of MAVISIM we include three major astrometric error sources; point spread function (PSF) field variability due to high order aberrations, PSF degradation and field variability due to tip-tilt residual error, and field distortions due to non-common path aberrations in the AO module. An overview of MAVISIM is provided along with initial results from a study using MAVISIM to simulate an image of a Milky Way-like globular cluster. Astrometric accuracies are extracted using PSF-fitting photometry with encouraging results that suggest MAVIS will deliver accuracies of 150µas down to faint magnitudes."
Precise stellar photometry and astrometry require the best possible modelling of the point spread function (PSF). To date, the best performances have been obtained when building the PSF a posteriori, meaning directly from the image of dense stellar fields, by exploiting the fact that each star represents a different realisation of the same PSF. The recent advent of the Adaptive Optics technique makes this method more challenging, because of the strong PSF variations across the field of view. One alternative is to use a priori PSF-modelling techniques such as PSF-reconstruction (PSF-R), that rely on Adaptive Optics control loop data to determine the shape of the PSF at any spatial location. Despite being theoretically well established, so far a-priori methods have never surpassed the performance obtained by standard methods when applied to real astronomical imaging. Here we report on the successful use of PRIME, a new technique that combines both PSF-R and image fitting, to perform precise photometry and astrometry on real data of the Galactic globular cluster NGC6121, observed with SPHERE/ZIMPOL. Compared to the results obtained using standard techniques, PRIME achieves improvement in precision by up to a factor of four, and ensures a photometric accuracy within ∼ 0.1 mag. A similar performance is also achieved when using the analytical PSF method described by F´etick et al. 2019, which is specifically designed to model AO-assisted data. These results thus pave the way for the exploitation of innovative techniques to investigate resolved stellar population science cases with the new generation of Adaptive Optics-assisted instrumentation at the ESO’s Very Large Telescope, Keck or the Extremely Large Telescopes.
MAORY is one of the approved instruments for the European Extremely Large Telescope. It is an adaptive optics module, enabling high-angular resolution observations in the near infrared by real-time compensation of the wavefront distortions due to atmospheric turbulence and other disturbances such as wind action on the telescope. An overview of the instrument design is given in this paper.
MAORY is one of the four instruments for the E-ELT approved for construction. It is an adaptive optics module offering two compensation modes: multi-conjugate and single-conjugate adaptive optics. The project has recently entered its phase B. A system-level overview of the current status of the project is given in this paper.
GeMS is the multi-conjugate adaptive optics instrument at the Gemini South telescope in Chile, the first facility-class MCAO system and the first to use laser guide stars. During its science verification period we have observed the Galactic globular cluster NGC 1851 and here we discuss the optimization of the analysis techniques that we adopt to extract science-ready photometric measurements. We use the large number of stars in the field of view to determine with high accuracy the PSF model for the profile fitting photometry. Understanding the correct techniques not only has proven useful with GeMS data but will be valuable on the next generation of Extremely Large Telescopes, where MCAO will be a central technology.
We overview the current status of photometric analyses of images collected with Multi Conjugate Adaptive Optics (MCAO) at 8–10m class telescopes that operated, or are operating, on sky. Particular attention will be payed to resolved stellar population studies. Stars in crowded stellar systems, such as globular clusters or in nearby galaxies, are ideal test-particles to test AO performance. We will focus the discussion on photometric precision and accuracy reached nowadays. We briefly describe our project on stellar photometry and astrometry of Galactic globular clusters using images taken with GeMS at the Gemini South telescope. We also present the photometry performed with DAOPHOT suite of programs into the crowded regions of these globulars reaching very faint limiting magnitudes Ks ∼21.5 mag on moderately large fields of view (∼1.5 arcmin squared). We highlight the need for new algorithms to improve the modeling of the complex variation of the Point Spread Function (PSF) across the field of view. Finally, we outline the role that large samples of stellar standards plays in providing a detailed description of the MCAO performance and in precise and accurate colour-magnitude diagrams.
With the aim of paving the road for future accurate astrometry with MICADO at the European-ELT, we performed an astrometric study using two different but complementary approaches to investigate two critical components that contribute to the total astrometric accuracy. First, we tested the predicted improvement in the astrometric measurements with the use of an atmospheric dispersion corrector (ADC) by simulating realistic images of a crowded Galactic globular cluster. We found that the positional measurement accuracy should be improved by up to ∼ 2 mas with the ADC, making this component fundamental for high-precision astrometry. Second, we analysed observations of a globular cluster taken with the only currently available Multi-Conjugate Adaptive Optics assisted camera, GeMS/GSAOI at Gemini South. Making use of previously measured proper motions of stars in the field of view, we were able to model the distortions affecting the stellar positions. We found that they can be as large as ∼ 200 mas, and that our best model corrects them to an accuracy of ∼ 1 mas. We conclude that future astrometric studies with MICADO requires both an ADC and an accurate modelling of distortions to the field of view, either through an a-priori calibration or an a-posteriori correction.
Multi-conjugate adaptive optics can achieve diffraction limited images over a field of arcminutes and is a central technology for the future ELTs: Gemini/GeMS is the first facility-class LGS MCAO system to operate. With it we have taken images in J and Ks bands of the globular cluster NGC 1851 for which we also have HST/ACS observations in the visible. In this paper we present the deepest to date near-infrared photometry of NGC 1851 providing a wide colour baseline CMD that reaches the lower main sequence to have a new insight into the stellar populations of this globular cluster. The use of the GGCs' lower main sequence knee to determine its age is one of the science drivers for the observation of GGCs with MCAO given its visibility in the infrared and because it requires high Strehl ratios to measure the faint stars' photometry. In addition to the stellar population analysis, these data allow to examine the photometric performance of the instrument using a large number of point sources distributed across the field.
We analyze the photometric performance of the instrument and the field dependence of the PSF, a central part on the prediction and improvement of the performance of future LGS MCAO systems like NFIRAOS for the Thirty Meter Telescope.
We present data collected using the camera PISCES coupled with the Firt Light Adaptive Optics (FLAO) mounted at the Large Binocular Telescope (LBT). The images were collected for two different pointings by using two natural guide stars with an apparent magnitude of R ~< 13 mag. During these observations the seeing was on average ~0.9 arcsec. The AO performed very well, in fact the images display a mean FWHM of 0.05 arcsec and of 0.06 arcsec in the J– and in the Ks–band, respectively. The Strehl ratio on the quoted images reaches 13–30% (J) and 50–65% (Ks), in the off and in the central pointings respectively. On the basis of this sample we have reached a J–band limiting magnitude of ~22.5 mag and the deepest Ks–band limiting magnitude ever obtained in a crowded stellar field: Ks ~23 mag. J–band images display a complex change in the shape of the PSF when moving at larger radial distances from the natural guide star. In particular, the stellar images become more elongated in approaching the corners of the J-band images whereas the Ks–band images are more uniform. We discuss in detail the strategy used to perform accurate and deep photometry in these very challenging images. In particular we will focus our attention on the use of an updated version of ROMAFOT based on asymmetric and analytical Point Spread Functions. The quality of the photometry allowed us to properly identify a feature that clearly shows up in NIR bands: the main sequence knee (MSK). The MSK is independent of the evolutionary age, therefore the difference in magnitude with the canonical clock to constrain the cluster age, the main sequence turn off (MSTO), provides an estimate of the absolute age of the cluster. The key advantage of this new approach is that the error decreases by a factor of two when compared with the classical one. Combining ground–based Ks with space F606W photometry, we estimate the absolute age of M15 to be 13.70± 0.80 Gyr.
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