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Building on Canadian expertise in studies of massive star clusters, we outline outstanding prospects in this field to which we can make fundamental contributions in the next decade and beyond. These include: understanding cluster formation in the early Universe and interpreting future observations of globular cluster progenitors at high redshifts, settling the question of the presence of intermediate-mass black holes in the cores of globular clusters, mapping the kinematics and abundances in the outer parts of Galactic globular clusters to understand their formation and the interplay with Galactic tides, solving the puzzle of multiple stellar populations in globular clusters, unveiling and characterizing compact objects in dense clusters and their implications of gravitational-wave astrophysics, and bringing studies of cluster populations as fossil records of the formation and evolution of external galaxies to the next level with large statistical samples. We highlight synergies between these science goals and upcoming and proposed ground- and space-based facilities. Following up on globular cluster progenitor candidates at high redshift (identified by JWST) with a 30-m class ground-based telescope and adaptive optics will be crucial to characterize these systems and will provide important clues on the relative timing of GC formation in the context of galaxy assembly as well as the possible role of GCs in cosmic reionization. In the meantime, we have reached a stage where our computational methods can model GC formation, and these models will be important to interpret observations. The hydro+dynamics simulations needed are however very expensive, and will require Compute Canada to have capacity for such intensive simulations for our community to take full advantage of its expertise in the field of (massive) cluster formation and evolution. Extreme Multi-Conjugate Adaptive Optics (MCAO) on a 30-m class telescope also promises important breakthroughs in this field. It is the most promising option for reaching a definitive answer on the presence of IMBHs in globular clusters and their importance in the growth of supermassive black holes. It would provide order-of-magnitude improvements in angular resolution and in the precision of proper motion measurements needed for dynamical analyses. Imaging and spectroscopy with 30-m class telescopes would also enable careful studies of the companions of compact objects in clusters, especially accreting BHs, allowing to study of the link between black holes in globular clusters and gravitational sources. Important questions in the field can be tackled with deep, space-based, wide-field imaging at HST-like resolution, preferably in the blue optical/UV region. CASTOR represents a unique opportunity to fill this niche. The statistical samples of proper motion measurements over large regions that this would enable would be ideal to map the plane-of-the-sky kinematics of nearby clusters over their entire extent, for example to measure velocity anisotropy and its impact on the inferred mass/presence of IMBHs, or map the kinematics of clusters near the tidal boundary and disentangle scenarios about their formation and interaction with the Galactic tidal field. Moreover, CASTOR imaging would offer opportunities to probe the host environments of neutron star mergers and constrain their dynamical formation in GCs. At larger distances, CASTOR’s UV and blue-optical coverage would complete the SED coverage of other missions over the critical UVOIR region, allowing complete photometric characterization of potentially many tens of thousands of galaxies and their cluster systems in the local volume. MSE with its large field of view, would also be ideally suited for mapping the kinematics (line-of-sight velocities) in the outskirts of globular clusters, out to the tidal radius. But crucially, it would yield detailed chemical composition for large samples of stars in globular clusters, significantly improving upon current surveys. As such, it would be the most important next-generation facility to address the origin of multiple (chemical) populations in these systems, a great unsolved problems in the study of stellar populations. MSE would also make it possible to build large spectroscopic databases of star cluster populations in external galaxies. Finally, upcoming radio facilities like ngVLA and SKA will provide a significant step forward towards a better determination of BH populations in GCs, with substantial improvement in sensitivity that would allow the identification of typical weakly-accreting black hole candidates in clusters, as well as thoroughly test the presence of weakly-accreting intermediate-mass black holes. Significant improvements in the study of compact objects in clusters will also be possible with future advanced X-ray telescopes with higher spectral resolution and sensitivity, such as ESA’s Athena and NASA’s Lynx missions., White paper identifier W024

The Gemini Infrared Multi-Object Spectrograph (GIRMOS) is a powerful new instrument being built to facility-class standards for the Gemini telescope. It takes advantage of the latest developments in adaptive optics and integral field spectrographs. GIRMOS will carry out simultaneous high-angular-resolution, spatially-resolved infrared ($1-2.4$ $\mu$m) spectroscopy of four objects within a two-arcminute field-of-regard by taking advantage of multi-object adaptive optics. This capability does not currently exist anywhere in the world and therefore offers significant scientific gains over a very broad range of topics in astronomical research. For example, current programs for high redshift galaxies are pushing the limits of what is possible with infrared spectroscopy at $8-10$-meter class facilities by requiring up to several nights of observing time per target. Therefore, the observation of multiple objects simultaneously with adaptive optics is absolutely necessary to make effective use of telescope time and obtain statistically significant samples for high redshift science. With an expected commissioning date of 2023, GIRMOS's capabilities will also make it a key followup instrument for the James Webb Space Telescope when it is launched in 2021, as well as a true scientific and technical pathfinder for future Thirty Meter Telescope (TMT) multi-object spectroscopic instrumentation. In this paper, we will present an overview of this instrument's capabilities and overall architecture. We also highlight how this instrument lays the ground work for a future TMT early-light instrument., Comment: Corrected typos

International audience; We propose and apply two methods for estimating phase discontinuities for two realistic scenarios on VLT and Keck. The methods use both phase diversity and a form of image sharpening. For the case of VLT, we simulate the `low wind effect' (LWE) which is responsible for focal plane errors in low wind and good seeing conditions. We successfully estimate the LWE using both methods, and show that using both methods both independently and together yields promising results. We also show the use of single image phase diversity in the LWE estimation, and show that it too yields promising results. Finally, we simulate segmented piston effects on Keck/NIRC2 images and successfully recover the induced phase errors using single image phase diversity. We also show that on Keck we can estimate both the segmented piston errors and any Zernike modes affiliated with the non-common path.

International audience; SPHERE is the VLT second generation planet hunter instrument. Installed since May 2014 on UT3, the system has been commissioned and verified for more than one year now and routinely delivers unprecedented images of star surroundings, exoplanets and dust disks. The exceptional performance required for this kind of observation makes the appointment: a repeatable Strehl Ratio of 90% in H band, a rough contrast level of 10-5@0.5 arcsec, and reaches 10-6 at the same separation after differential imaging (SDI, ADI). The instrument also presents high contrast levels in the visible and an unprecedented 17mas diffraction-limited resolution at 0.65 microns wavelength. SAXO is the SPHERE XAO system, allowing the system to reach its final detectivity. Its high performance and therefore highly sensitive capacities turns a new eye on telescope environment. Even if XAO performance are reached as expected, some unexpected limitations are here described and a first work around is proposed and discussed. Spatial limitation: wave-front aberrations have been identified, deviating from kolmogorov statistics, and therefore not easily seen and compensated for by the XAO system. The impact of this limitations results in a degraded performance in some particular low wind conditions. Solutions are developed and tested on sky to propose a new operation procedure reducing this limitation. Temporal limitation: high amplitude vibrations on the low order modes have been issued, due to telescope environment and XAO behaviour. Again, a solution is developed and an assessment of its performance is dressed. The potential application of these solutions to E-ELT is proposed.

Contemporary AO systems, such as the Multi-Object Adaptive Optics system (MOAO) RAVEN currently associated with the Subaru Telescope, can suer from signicant Non-Common Path Aberrations (NCPA). These errors ultimately aect image quality and arise from optical path dierences between the wavefront sensor (WFS) path and the science path. A typical correction of NCPA involves estimating the aberration phase and correcting the system with an oset on the deformable mirror (DM). We summarize two methods used to correct for NCPA on an experimental bench. We also successfully calibrate the NCPA on RAVEN using one of these methods. Finally, we report on some rst science results with RAVEN, obtained after NCPA correction.