Multi-conjugate Adaptive Optics System Research Articles

Pushing the limits of near-infrared photometry with the Gemini Multi-Conjugate Adaptive Optics System: study of crowded fields in the globular cluster M5

ABSTRACT We present the deepest J −Ks near-infrared photometry of the globular cluster M5 (NGC 5904) from observations taken with the Gemini South Adaptive Optics Imager in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1-m Gemini South telescope. Point spread function (PSF) photometry was carried out using a spatially variable PSF, zero-point calibrations based on correlations to a standard photometric catalogue, colour corrections, and crowding corrections. The latter corrections provided a new challenge given the field variations of the adaptive optics corrections in the central crowded regions of this cluster. The final photometric precision in our J− Ks colour–magnitude diagram exposes a dispersion among the lower main-sequence stars of M5 for the first time. This dispersion occurs below a main-sequence knee due to variations in the helium and CNO (carbon, nitrogen, and oxygen) abundances from multiple stellar populations, consistent with results from the bright evolved stars in this cluster from ultraviolet to near-infrared Hubble Space Telescope photometry and ground-based spectroscopy. This paper completes our original GeMS quality analysis programme, providing insights into adaptive optics analyses in crowded fields.

Performance analysis and optimization of solar multiconjugate adaptive optics systems

ABSTRACT Multiconjugate adaptive optics (MCAO) stands as an essential technology for the development of future large-aperture solar telescopes. Its primary objective is to empower telescopes to achieve nearly diffraction-limited performance while substantially extending the correction field of view (FoV). Conventional solar MCAO relies on the combination of adaptive optics and high-altitude correction (AO + HAC) modules for multiconjugate correction. However, this architectural approach excels in correction performance primarily at the central position, with performance deteriorating as one moves farther from the centre. Consequently, it results in poor consistency of FoV correction performance. To address these limitations, a new architectural approach was introduced, which combines ground layer AO with HAC (GLAO + HAC). Preliminary results have shown that, compared to AO + HAC, this approach significantly enhances FoV correction uniformity. Building upon these initial findings, this paper undertakes a more extensive research of the GLAO + HAC system. Its objective is to compare various solar MCAO system architectures, including AO + HAC, GLAO + HAC, and general MCAO, to finally propose optimization tailored to GLAO + HAC. Through this analysis, the paper conducts the performance comparison between GLAO + HAC and general MCAO. It underscores that, under equivalent configuration parameters, the differences between these two systems are marginal. However, due to the advantage of the independent control of dual correction modules in GLAO + HAC, it can introduce an optimization strategy by increasing the number of subapertures at the cost of reducing the GLAO guide star sensing FoV. Finally, the results of this strategy demonstrate an obvious enhancement in performance and FoV correction consistency within the GLAO + HAC system.

Enhanced-resolution Shack-Hartmann wavefront sensing for extended objects.

Adaptive optics systems for large-aperture solar telescopes, especially multiconjugate adaptive optics systems, suffer from a fundamental trade-off between wavefront sampling rate and sub-aperture resolution. We introduce an enhanced-resolution Shack-Hartmann wavefront sensing method that decouples sub-aperture resolution from the desired wavefront sampling rate. We experimentally verified the validity of this method. Results show that by synthesizing multiple low-spatial samplings, this method is capable to sense higher-frequency aberrations beyond any low-spatial sampling involved in the synthesis, and it allows higher sub-aperture resolution and higher operating bandwidths, which can better fulfill the needs of solar adaptive optics.

First Implementation of Pulsed Sodium Guidestars Constellation for Large-aperture Multi-conjugate Adaptive Optics Telescopes

Multiple synthetic beacons are required for atmospheric-turbulence compensation in an extended-field-of-view multi-conjugate adaptive optics (MCAO) telescope. In this paper, we report on the first successful implementation of a microsecond-pulse sodium guidestars constellation laser system, based on a small angle precise polarized combining and splitting technology. At Lijiang Observatory of China, four-ways ∼20 W yellow laser beam with kHz repetition-rate and hundred-μs pulse width were projected into the sky through one small-aperture launching telescope, and generated a distinctive four-point grouping on a field of view of 40″ with variable configurations of linear, parallelogram, rhomboid and square. The sodium return signal could easily avoid Rayleigh light interference by the pulse synchro controlling technology delivering a higher spatial resolution. Moreover, the increase in return photons for alternated circularly and alternated linearly polarized light has been investigated. We believe that the above results could serve as a future reference for the MCAO system on large-aperture telescopes worldwide.

Optimal Differential Astrometry for Multiconjugate Adaptive Optics. I. Astrometric Distortion Mapping using On-sky GeMS Observations of NGC 6723

Abstract The Extremely Large Telescope and the Thirty Meter Telescope will use state of the art multiconjugate adaptive optics (MCAO) systems to obtain the full D 4 advantage that their apertures can provide. However, to reach the full astrometric potential of these facilities for on-sky science requires understanding any residual astrometric distortions from these systems and find ways to measure and eliminate them. In this work, we use Gemini multiconjugate adaptive optic system (GeMS) observations of the core of NGC 6723 to better understand the on-sky astrometric performance of MCAO. We develop new methods to measure the astrometric distortion fields of the observing system, which probe the distortion at the highest possible spatial resolution. We also describe methods for examining the time-variable and static components of the astrometric distortion. When applied to the GeMS Gemini South Adaptive Optics Imager (GSAOI) data, we are able to see the effect of the field rotator at the subpixel level, and we are able to empirically derive the distortion due to the optical design of GeMS/GSAOI. We argue that the resulting distortion maps are a valuable tool to measure and monitor the on-sky astrometric performance of future instrumentation. Our overall astrometry pipeline produces high-quality proper motions with an uncertainty floor of ∼45 μas yr−1. We measure the proper motion dispersion profile of NGC 6723 from a radius of ∼10″ out to ∼1′ based on ∼12,000 stars. We also produce a high-quality optical–near infrared color–magnitude diagram, which clearly shows the extreme horizontal branch and main-sequence knee of this cluster.

High-resolution images of two wiggling stellar jets, MHO 1502 and MHO 2147, obtained with GSAOI+GeMS

Aims. We investigated the possible cause–effect relation between the wiggling shape of two stellar jets, MHO 1502 and MHO 2147, and the potential binarity of the respective driving stars. Methods. We present high-angular-resolution H2 (2.122 μm) and K-band images obtained with the Gemini South Adaptive Optics Imager (GSAOI) and the Gemini Multi-conjugate Adaptive Optics System (GeMS). The profiles of the jets are depicted in detail by the H2 images. We used K-band data to search for potential close companions to the previously suggested exciting sources, and used archive data to investigate these sources and the environments in which the jets are located. We also applied a model to reproduce the wiggling profiles of the jets. Results. MHO 1502 is composed of a chain of knots delineating the wiggling jet, suggesting that the driving source emitted them in an intermittent manner. Our K-band image of the previously proposed exciting star, IRAC 18064, shows two sources separated by ~240 AU, hinting at its binarity. However, as IRAC 18064 is located off the jet axis at ~2064 AU, it is questionable as to whether this source is the true exciting star. Moreover, the orbital model centred on IRAC 18064 suggests a binary companion at a much greater distance (~2200 AU) than the nearby star (at ~240 AU). On the other hand, the orbital model centred on the axis provides the best fits. Nevertheless, the precession model centred on the axis cannot be discarded, despite having larger residuals and χ2. MHO 2147 displays an S-shaped gentle continuous emission in H2. We identify two other jets in the field of MHO 2147: a previously reported quasi-perpendicular jet, MHO 2148, and a third jet adjacent to MHO 2147. The model that best fits the morphology of the MHO 2147 jet and that of its adjacent jet is precession. The exciting source of MHO 2147 may be a triple system.

Two-telescope-based solar seeing profile measurement simulation

Measurements of the daytime seeing profile of the atmospheric turbulence are crucial for evaluating a solar astronomical site so that research on the profile of the atmospheric turbulence as a function of altitude becomes more and more critical for performance estimation and optimization of future adaptive optics (AO) including the multi-conjugate adaptive optics (MCAO) systems. Recently, the S-DIMM+ method has been successfully used to measure daytime turbulence profiles above the New Solar Telescope (NST) on Big Bear Lake. However, such techniques are limited by the requirement of using a large solar telescope which is not realistic for a new potential astronomical site. Meanwhile, the A-MASP (advanced multiple-aperture seeing profiler) method is more portable and has been proved that can reliably retrieve the seeing profile up to 16 km with the Dunn Solar Telescope (DST) on the National Solar Observatory (Townson, Kellerer et al.). But the turbulence of the ground layer is calculated by combining A-MASP and S-DIMM+ (Solar Differential Image Motion Monitor+) due to the limitation of the two-individual-telescopes structure. To solve these problems, we introduce the two-telescope seeing profiler (TTSP) which consists of two portable individual telescopes. Numerical simulations have been conducted to evaluate the performance of TTSP. We find our TTSP can effectively retrieve seeing profiles of four turbulence layers with a relative error of less than 4% and is dependable for actual seeing measurement.

Performance and limitations of using ELT and MCAO for 50 μas astrometry

Multi-conjugated adaptive optics (MCAO) is essential for performing astrometry with the Extremely Large Telescope (ELT). Unlike most of the 8-m class telescopes, the ELT will be a fully adaptive telescope, and a significant portion of the adaptive optics (AO) dynamic range will be depleted by the correction and stabilization of the telescope aberrations and instabilities. MCAO systems are of particular interest for ground-based astrometry since they stabilize the low-order field distortions and transient plate scale instabilities, which originate from the telescope and in the instrument. All instruments have several optical elements relatively far away from the pupil that can potentially challenge the astrometric precision of the observations with their residual mid-spatial frequencies errors. Using a combined simulation of ray tracing and AO numerical codes, we assess the impact of these systematic errors at different field-of-view (FoV) scales and fitting scenarios. The distortions have been assessed at different sky position angles (PA) and indicate that over large FoVs only small PA ranges (±1 deg to 3 deg) are accessible with astrometric residuals ≤50 μas. A full compliance with the astrometric requirement, at any PA, is achievable for 2 arc sec2 FoV patches already with a third-order polynomial. The natural partition of the optical system into three segments, i.e., the ELT, the MAORY MCAO module, and the MICADO instrument, resembles a splitting of the astrometric problem into the three subsystems that are characterized by different distortion amplitudes and calibration strategies. The result is a family portrait of the different optical segments with their specifications, dynamic motions, conjugation height, and AO correctability, leading to tracing their role in the bigger puzzle of the 50-μas as astrometric endeavor.

High-resolution Extinction Map in the Direction of the Strongly Obscured Bulge Fossil Fragment Liller 1*

Abstract We used optical images acquired with the Wide Field Camera of the Advanced Camera for Surveys on board the Hubble Space Telescope and near-infrared data from Gemini Multi-conjugate Adaptive Optics System (GeMS)/Gemini South Adaptive Optics Imager (GSAOI) to construct a high-resolution extinction map in the direction of the bulge stellar system Liller 1. In spite of its appearance of a globular cluster, Liller 1 has been recently found to harbor two stellar populations with remarkably different ages, and it is the second complex stellar system with similar properties (after Terzan 5) discovered in the bulge, thus defining a new class of objects: the Bulge Fossil Fragments. Because of its location in the inner bulge of the Milky Way, very close to the Galactic plane, Liller 1 is strongly affected by large and variable extinction. The simultaneous study of both the optical and the near-infrared color–magnitude diagrams revealed that the extinction coefficient R V in the direction of Liller 1 has a much smaller value than commonly assumed for diffuse interstellar medium (R V = 2.5, instead of 3.1), in agreement with previous findings along different light paths to the Galactic bulge. The derived differential reddening map has a spatial resolution ranging from 1″ to 3″ over a field of view of about 90″ × 90″. We found that the absorption clouds show patchy substructures with extinction variations as large as δE(B − V) ∼ 0.9 mag.

Towards realistic modelling of the astrometric capabilities of MCAO systems: detecting an intermediate-mass black hole with MAVIS

ABSTRACT Accurate astrometry is a key deliverable for the next generation of multiconjugate adaptive optics (MCAO) systems. The MCAO-Assisted Visible Imager and Spectrograph (MAVIS) is being designed for the Very Large Telescope Adaptive Optics Facility and must achieve 150 $\mu$as astrometric precision (50 $\mu$as goal). To test this before going on-sky, we have created MAVIS Image Simulator (mavisim), a tool to simulate MAVIS images. mavisim accounts for three major sources of astrometric error: high- and low-order point spread function (PSF) spatial variability, tip–tilt residual error, and static field distortion. When exploring the impact of these three error terms alone, we recover an astrometric accuracy of 50 $\mu$as for all stars brighter than m = 19 in a 30 s integration using PSF-fitting photometry. We also assess the feasibility of MAVIS detecting an intermediate-mass black hole (IMBH) in a Milky Way globular cluster. We use an N-body simulation of an NGC 3201-like cluster with a central 1500 M⊙ IMBH as input to mavisim and recover the velocity dispersion profile from proper motion measurements. Under favourable astrometric conditions, the dynamical signature of the IMBH is detected with a precision of ∼0.20 km s−1 in the inner ∼4 arcsec of the cluster where Hubble Space Telescope (HST) is confusion limited. This precision is comparable to measurements made by Gaia, HST, and Multi Unit Spectroscopic Explorer (MUSE) in the outer ∼60 arcsec of the cluster. This study is the first step towards building a science-driven astrometric error budget for an MCAO system and a prediction of what MAVIS could do once on sky.

High-repetition-rate 100 W level sodium beacon laser for a multi-conjugate adaptive optics system.

A 100 W level kilohertz repetition-rate microsecond (µs)-pulse all-solid-state sodium beacon laser at 589 nm is demonstrated for the first time, to the best of our knowledge, via combining two independent µs-pulsed lasers. Each beamlet is generated by the sum-frequency mixing of pulsed 1064 and 1319 nm lasers in a lithium triborate (LBO) crystal, which operate at 500 Hz pulse repetition frequency with 61 W $p$p-polarized and 53 W $s$s-polarized output, respectively. An incoherent sequence combining technology of polarized laser beams is employed to add the two beamlets. The average power of the combined beam is up to 107.5 W with a combining efficiency of 94.3%. The combined beam has a 1 kHz repetition rate with ${\sim}{120}\;\unicode{x00B5} {\rm s}$∼120µs pulse duration and beam quality ${M^2} = {1.41}$M2=1.41. The central wavelength with a linewidth of ${\sim}{0.3}\;{\rm GHz}$∼0.3GHz is locked to a sodium ${{\rm D}_{2a}}$D2a absorption line. To the best of our knowledge, this is a record-high power operating at kilohertz for µs-pulsed solid-state sodium beacon lasers.

Operation of a layer-oriented multiconjugate adaptive optics system in the partial illumination regime

Multiconjugate adaptive optics (MCAO) promises uniform wide-field atmospheric correction. However, partial illumination of the layers at which the deformable mirrors are conjugated results in incomplete information about the full turbulence field. We report on a working solution to this difficulty for layer-oriented MCAO, including laboratory and on-sky demonstration with the LINC-NIRVANA instrument at the Large Binocular Telescope. This approach has proven to be simple and stable.

GeMS/GSAOI near-infrared imaging of z ∼ 0.3 BL Lacs

AbstractBright quasars at low z have generally been found in massive, evolved host galaxies, consistent with formation at early epochs. However, deep, high resolution, multicolor imaging of some quasar hosts have found morphological evidence of tidal tails and colors indicative of active star formation. These results are consistent with theories of galaxy formation and evolution in which merger processes trigger the activation of the quasar phase, and energetic feedback is essential. Understanding the role the black hole population plays in the galaxy formation process is important, but imaging the host galaxies around bright quasars is difficult because of the contribution of the bright nuclei. Very high resolution, deep imaging is necessary to successfully remove the nuclear component. We made high-resolution near-infrared images of several bright z ˜ 0.3 BL Lacs with the Gemini Multi-Conjugate Adaptive Optics System (GeMS)/GSAOI in order to study their host galaxies. We will present the results of this imaging with the 1 arcmin AO-corrected field provided by GeMS/GSAOI and compare with available HST imaging available in the archive.

The impact of geometric distortions in multiconjugate adaptive optics astrometric observations with future extremely large telescopes

Astrometry is one of the main science case which drives the requirements of the next multiconjugate adaptive optics (MCAO) systems for future extremely large telescopes. The small diffraction limited point-spread function (PSF) and the high Signal-to-Noise Ratio (SNR) of these instruments, promise astrometric precision at the level of micro-arcseconds. However, optical distortions have to be as low as possible to achieve the high demanding astrometry requirements. In addition to static distortions, the opto-mechanical instabilities cause astrometric errors that can be major contributors to the astrometry error budget. The present article describes the analysis, at design level, of the effects of opto-mechanical instabilities when coupled with optical surface irregularities due to the manufacturing process. We analyse the notable example of the Multi-conjugate Adaptive Optics RelaY (MAORY) for the extremely large telescope (ELT). Ray-tracing simulations combined with a Monte Carlo approach are used to estimate the geometrical structure and magnitude of field distortion resulting from the optical design. We consider the effects of distortion on the MCAO correction showing that it is possible achieve the micro-arcseconds astrometric precision once corresponding accuracy is obtained by both optical design and manufacturing. We predict that for single-epoch observations, an astrometric error below 50$\mu$as can be achieved for exposure times up to 2 min, provided about 100 stars are available to remove fifth-order distortions. Such performance could be reproducible for multi-epoch observations despite the time-variable distortion induced by instrument instabilities.

Multi-aperture seeing profiler with multiple guide stars

The daytime atmospheric turbulence profile is crucial for the design of both optical systems and the control algorithm of a solar Multi-Conjugate Adaptive Optics (MCAO) system. The Multi-Aperture Seeing Profiler (MASP) is a portable instrument which can measure the daytime turbulence profile up to ∼ 30 km. It consists of two portable small telescopes that can deliver performance similar to a Solar-Differential Image Motion Monitor + (S-DIMM+) on a 1.0 m solar telescope. In the original design of MASP, only two guide stars are used to retrieve the turbulence profile. In this paper, we studied the usage of multiple guide stars in MASP using numerical simulation, and found that there are three main advantages. Firstly, the precision of the turbulence profile can be increased, especially at a height of about 15 km, which is important for characterizing turbulence at the tropopause. Secondly, the equivalent diameter of MASP can be increased up to 30%, which will reduce the cost and weight of the instruments. Thirdly, the vertical resolution of the turbulence profile near the ground increases with the help of multiple guide stars.

Unveiling the nature of Gemini multiconjugate adaptive optics system distortions

Astrometry was not a science case of the Gemini Multiconjugate adaptive optics System (GeMS) at its design stage. However, since GeMS has been in regular science operation with the Gemini South Adaptive Optics Imager (GSAOI), their astrometric performances have been deeply analysed. The non-linear component of the distortion map model shows a characteristic pattern which is similarly repeated in each detector of GSAOI. The nature of this pattern was unknown and subjected to different hypotheses. This paper describes the origin of the GeMS distortion pattern as well as its multi-epoch variation. At the end, it is showed a comparison with the current design of the Multiconjugate Adaptive Optics RelaY (MAORY) of the Extremely Large Telescope (ELT).

The GeMS/GSAOI Galactic Globular Cluster Survey (G4CS). I. A Pilot Study of the Stellar Populations in NGC 2298 and NGC 3201

Abstract We present the first results from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) of the Milky Way globular clusters NGC 3201 and NGC 2298. Using the Gemini South Adaptive Optics Imager (GSAOI), in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1 m Gemini-South telescope, we collected deep near-IR observations of both clusters, resolving their constituent stellar populations down to K s ≃ 21 Vega mag. Point-spread function (PSF) photometry was performed on the data using spatially variable PSFs to generate JHK s photometric catalogs for both clusters. These catalogs were combined with Hubble Space Telescope (HST) data to augment the photometric wavelength coverage, yielding catalogs that span the near-UV to near-IR. We then applied 0.14 mas yr−1 accurate proper-motion cleaning and differential-reddening corrections and chose to anchor our isochrones using the lower main-sequence knee and the main-sequence turnoff prior to age determination. As a result of the data quality, we found that the K s versus F606W − K s and F336W versus F336W − K s color–magnitude diagrams were the most diagnostically powerful. We used these two color combinations to derive the stellar population ages, distances, and reddening values for both clusters. Following isochrone fitting using three different isochrone sets, we derived best-fit absolute ages of 12.2 ± 0.5 Gyr and 13.2 ± 0.4 Gyr for NGC 3201 and NGC 2298, respectively. This was done using a weighted average over the two aforementioned color combinations, following a pseudo-χ 2 determination of the best-fit isochrone set. Our derived parameters are in good agreement with recent age determinations of the two clusters, with our constraints on the ages being or ranking among the most statistically robust.

Multiconjugate adaptive optics simulator for the Thirty Meter Telescope: design, implementation, and results

We present a multiconjugate adaptive optics (MCAO) system simulator bench, Herzberg NFIRAOS Optical Simulator (HeNOS). HeNOS is developed to validate the performance of the MCAO system for the Thirty Meter Telescope, as well as to demonstrate techniques critical for future AO developments. We focus on describing the derivations of parameters that scale the 30-m telescope AO system down to a bench experiment and explain how these parameters are practically implemented on an optical bench. While referring to other papers for details of AO technique developments using HeNOS, we introduce the functionality of HeNOS, in particular, three different single-conjugate AO modes that HeNOS currently offers: a laser guide star AO with a Shack–Hartmann wavefront sensor, a natural guide star AO with a pyramid wavefront sensor, and a laser guide star AO with a sodium spot elongation on the Shack–Hartmann corrected by a truth wavefront sensing on a natural guide star. Laser tomography AO and ultimate MCAO are being prepared to be implemented in the near future.

Multiconjugate Adaptive Optics for Astronomy

Since the year 2000, adaptive optics (AO) has seen the emergence of a variety of new concepts addressing particular science needs; multiconjugate adaptive optics (MCAO) is one of them. By correcting the atmospheric turbulence in 3D using several wavefront sensors and a tomographic phase reconstruction approach, MCAO aims to provide uniform diffraction limited images in the near-infrared over fields of view larger than 1 arcmin2, i.e., 10 to 20 times larger in area than classical single conjugated AO. In this review, we give a brief reminder of the AO principles and limitations, and then focus on aspects particular to MCAO, such as tomography and specific MCAO error sources. We present examples and results from past or current systems: MAD (Multiconjugate Adaptive Optics Demonstrator) and GeMS (Gemini MCAO System) for nighttime astronomy and the AO system, at Big Bear for solar astronomy. We examine MCAO performance (Strehl ratio up to 40% in H band and full width at half maximum down to 52 mas in the case of MCAO), with a particular focus on photometric and astrometric accuracy, and conclude with considerations on the future of MCAO in the Extremely Large Telescope and post–HST era.

A Subarcsecond Near-infrared View of Massive Galaxies at z > 1 with Gemini Multi-conjugate Adaptive Optics

We present images taken using the Gemini South Adaptive Optics Imager (GSAOI) with the Gemini Multiconjugate Adaptive Optics System (GeMS) in three 2 arcmin$^2$ fields in the Spitzer Extragalactic Representative Volume Survey. These GeMS/GSAOI observations are among the first $\approx 0.1^{''}$ resolution data in the near-infrared spanning extragalactic fields exceeding $1.5^{\prime}$ in size. We use these data to estimate galaxy sizes, obtaining results similar to those from studies with the Hubble Space Telescope, though we find a higher fraction of compact star forming galaxies at $z>2$. To disentangle the star-forming galaxies from active galactic nuclei (AGN), we use multiwavelength data from surveys in the optical and infrared, including far-infrared data from Herschel, as well as new radio continuum data from the Australia Telescope Compact Array and Very Large Array. We identify ultraluminous infrared galaxies (ULIRGs) at $z \sim 1-3$, which consist of a combination of pure starburst galaxies and Active Galactic Nuclei (AGN)/starburst composites. The ULIRGs show signs of recent merger activity, such as highly disturbed morphologies and include a rare candidate triple AGN. We find that AGN tend to reside in hosts with smaller scale sizes than purely star-forming galaxies of similar infrared luminosity. Our observations demonstrate the potential for MCAO to complement the deeper galaxy surveys to be made with the James Webb Space Telescope.