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Photonic technologies offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile that combines the light-gathering power of four 8 m telescopes through a complex photonic interferometer. Fully integrated astrophotonic devices stand to offer critical advantages for instrument development, including extreme miniaturization when operating at the diffraction-limit, as well as integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering significant cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including for example the development of photonic lanterns to convert from multimode inputs to single mode outputs, complex aperiodic fiber Bragg gratings to filter OH emission from the atmosphere, complex beam combiners to enable long baseline interferometry with for example, ESO Gravity, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of (1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient integration of photonics with detectors, to name a few. In this roadmap, we identify 24 key areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional integrated instruments will be realized leading to novel observing capabilities for both ground and space based platforms, enabling new scientific studies and discoveries.

So far, only two interstellar objects have been observed within our Solar System. While the first one, 1I/‘Oumuamua, had asteroidal characteristics, the second one, 2I/Borisov, showed clear evidence of cometary activity. We performed polarimetric observations of comet 2I/Borisov using the European Southern Observatory Very Large Telescope to derive the physical characteristics of its coma dust particles. Here we show that the polarization of 2I/Borisov is higher than what is typically measured for Solar System comets. This feature distinguishes 2I/Borisov from dynamically evolved objects such as Jupiter-family and all short- and long-period comets in our Solar System. The only object with similar polarimetric properties as 2I/Borisov is comet C/1995 O1 (Hale-Bopp), an object that is believed to have approached the Sun only once before its apparition in 1997. Unlike Hale-Bopp and many other comets, though, comet 2I/Borisov shows a polarimetrically homogeneous coma, suggesting that it is an even more pristine object. Polarimetry provides information about physical characteristics of cometary dust. Here, the authors show that the polarization of interstellar comet 2I/Borisov exceeds the typical values for comets, and this together with its polarimetrically homogenous coma suggests a more pristine nature of the object.

The effects of a proposed green-energy facility in Chile could be devastating for some of the most powerful instruments available to astronomers. The effects of a proposed green-energy facility in Chile could be devastating for some of the most powerful instruments available to astronomers.

The Cherenkov Telescope Array Observatory (CTAO) is a next-generation facility comprised of ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs). The observatory, currently under construction, will include more than 70 telescopes at two locations: in the northern hemisphere, CTAO-North at the Observatorio del Roque de Los Muchachos (ORM), La Palma, Canary Islands, Spain, and in the southern hemisphere, CTAO-South at a site belonging to the European Southern Observatory (ESO), Cerro Paranal, Chile. IACTs indirectly detect high-energy cosmic photons in an energy range from tens of GeV to several hundreds of TeV by measuring Cherenkov light emitted by atmospheric showers of secondary particles, produced through interactions between incident photons and nuclei of atmospheric gasses in the upper layers. The size of the CTAO will improve the detection sensitivity in the designed energy range by about an order of magnitude with respect to present experiments and aim at improved energy and angular resolution, as well as greatly reduced systematic uncertainties. The key to achieving improvements in accuracy on the absolute energy and flux scales is the precise monitoring of the atmospheric properties for the Cherenkov light, which can be obtained with a specifically designed LIDAR. The Barcelona Raman LIDAR (BRL) prototype is the official CTAO-North Pathfinder and was deployed at ORM for extensive tests between February 2021 and May 2022. We report the BRL’s prospects for the CTAO-North, emphasizing the technical implementation and the preliminary data taken during its deployment period.

The Extremely Large Telescope of the European Southern Observatory (ESO) is currently under construction and is expected to become the world’s largest optical/near-infrared terrestrial astronomical observatory. Its optical design incorporates five mirrors of varying shapes, sizes, and materials. The primary mirror, with a diameter of 39 m, is perhaps the most remarkable. The fifth mirror (M5), made of SiC, ranks among the largest tip-tilt mirrors globally. Various structural joining techniques, such as bonding and brazing, are applied to these optical components to enable nanometric relative positioning between the assembled parts. This study reviews advanced real-time ultrasonic imaging based on Total Focusing Methods (TFM) for their inspection. For the M1 mirror, TFM is utilized in a tandem configuration for regular industrial use and is also applied once with Rayleigh waves to inspect the surface and subsurface of the M5 mirror. Highlights Real-time non-destructive imaging of structural bonding and brazing is conducted. The Total Focusing Method is employed in tandem configuration. A Total Focusing Method with a surface wave is applied. A method validated for industrial applications is also implemented.

EARTH-LIKE PLANET SPOTTED ORBITING SUN'S CLOSEST STAR Astronomers have discovered a third planet orbiting Proxima Centauri, the star closest to the Sun. The team used a state-of-the art instrument called the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations at the Very Large Telescope, a system of four 8.2-metre telescopes at the European Southern Observatory in Cerro Paranal, Chile. The reduction - a drop of close to 50% compared with the 27 cases reported in 2020 - is the result of a near 40-year effort by international organizations and national governments to rid the world of Guinea worm, says Weiss.

The Atacama desert stands as the most arid, non-polar, region on Earth and has accommodated a considerable portion of the world’s ground-based astronomical observatories for an extended period. The comprehension of factors important for observational conditions in this region, and the potential alterations induced by the escalating impact of climate change, are, therefore, of the utmost significance. In this study, we conduct an analysis of the surface-level air temperature, water vapour density, and astronomical seeing at the European Southern Observatory (commonly known by its acronym, ESO) telescope sites in northern Chile. Our findings reveal a discernible rise in temperature across all sites during the last decade. Moreover, we establish a correlation between the air temperature and water vapour density with the El Niño Southern Oscillation (ENSO) phases, wherein, the warm anomaly known as El Niño (EN) corresponds to drier observing conditions, coupled with higher maximum daily temperatures favouring more challenging near-infrared observations. The outcomes of this investigation have potential implications for the enhancement of the long-term scheduling of observations at telescope sites in northern Chile, thereby aiding in better planning and allocation of resources for the astronomy community.

The wide-field spectrographs 4MOST and MOONS are expected to enter operations in late 2024 at the ESO Paranal Observatory. These upcoming survey facilities will play an important role in various fields over the next decade. In particular, both will host surveys aimed at observing Local Group (LG) galaxies. We describe how their scientific performances complement Gaia and other spectroscopic surveys in the field of nearby galaxy kinematics, and provide an overview of the planned surveys that focus on LG galaxy kinematics. We outline the policies for community access to data and observing time, which is different for the two instruments. The contribution concludes with a summary of the main scientific goals of MOONS and 4MOST survey science regarding the LG galaxy masses and dynamics.

Satellite constellation interference occurs across astronomical disciplines. We touch on the challenges for existing regulatory frameworks in radio astronomy, and present examples of interference from radio and γ -ray astronomy to optical and spectroscopic interference in ground-based and space-borne facilities. In particular, we discuss the impact of artificial satellites on the Hubble Space Telescope (HST), the High Energy Stereoscopic System (H.E.S.S.), an Imaging Atmospheric Cherenkov Telescope array, as well as possible mitigation strategies for the European Southern Observatory 4-metre Multi-Object Spectrograph Telescope (ESO 4MOST). Furthermore, we shed light on how ground-based optical telescopes such as the Oukaimeden Observatory contribute to IAU Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS) efforts that quantify satellite brightness.