Context. The young disk around AB Aur features a complex assembly of spiral arms, several compact structures, and a protoplanet candidate, AB Aur b, suggesting ongoing planet formation in this young system. Because of its brightness and spatial extent, AB Aur represents a perfect laboratory for investigating the conditions under which planets start to form around intermediate-mass stars. Aims. In this paper, we present near-IR polarized images of the AB Aur disk at three epochs spanning 3.85 years with SPHERE/IRDIS, as well as Hα images obtained with SPHERE/ZIMPOL at a single epoch. The purpose of this study is to analyze the dynamics of the entire disk and of the various structures in near-IR polarimetry, and to identify sources of Hα emission to derive constraints on their mass accretion rate. Methods. We developed a method to measure the rotation of the disk as a function of the radius, covering physical separations from as close as ~25 au up to 400 au. We applied this method to the global structure of the disk as well as to specific features of interest, including both extended or compact sources. For the compact sources, we performed orbital analyses. We also studied the variability of shadows seen as thin radial streaks. For the Hα data, we extracted photometric measurements of several features and derived estimations of the accretion luminosities and mass accretion rates, assuming three different accretion models. Results. The dynamical study in the near-IR shows that the disk globally follows Keplerian rotation, but we observe a departure from this behavior at radii smaller than ~60 au. At the smallest radius of ~25 au, we measure a deviation from Keplerian rotation as large as ~12° over 3.85 years, demonstrating sub-Keplerian rotation. The two bright spirals within the millimeter cavity have different dynamic trends, and we discuss their possible link with the identified planet candidates. We also discuss the implications of the non-Keplerian behavior, and we posit that it could be related to interactions with multiple protoplanets orbiting out of the disk plane on elliptical orbits. Furthermore, the orbital analysis of the compact sources (labeled f1, f2, and f3) suggests that their orbital planes are significantly inclined with respect to the disk plane by several tens of degrees. The variability of the shadows suggests that they are produced by optically thick regions located within ~60 au. For the photometric analysis in Hα, we derive a flux of about 8.22 × 10−15 erg/s/cm2 for the entire feature f1, but only 6.46 × 10−16 erg/s/cm2 at the location of AB Aur b, consistent with non-detection. If f1 were a point source and the accretion remained constant for 1 Myr, it would correspond to ~5-20 Jupiter masses according to the magnetospheric accretion model or ~6-10 Jupiter masses according to the boundary layer accretion model. We further discuss the non-detection of Hα emission on AB Aur b. Finally, we discuss the binarity of the host star, in particular using Gaia measurements. Conclusions. AB Aur is a rare system in which the morphology and dynamics can be studied at a very high level of detail, contrasting with the generic picture of a young planet-forming disk. The excellent image quality of SPHERE, both in the near-IR and in the visible, allows us to track the disk rotation with unprecedented precision thanks to the stability of the instrument across several years and to study localized Hα emissions in the disk. Overall, these observations strongly argue for an active and complex phase of planet formation in this system.

Estimations of stellar angular diameters can be determined based on the surface brightness-colour relation (SBCR) and photometry. In the context of the PLATO space mission, the SBCR is considered to be an independent empirical alternative for estimating the stellar radii of FGK stars. We implemented a homogeneous approach, not only for calibrating the SBCR for FGK-IV/V stars, but also for determining their fundamental parameters. This made it possible to reliably place the stars on the Hertzsprung-Russell (HR) diagram and to study their impact on the SBC relations. We performed interferometric observations of 18 quiescent FGK-IV/V stars in the Gaia magnitude range of . For the first time, we used three different interferometric instruments operating in the , , and bands to measure the polychromatic limb-darkened angular diameters. In parallel, by using public domain spectra, we were able to estimate the stellar parameters (T_ . 3.088 łeq G łeq 5.498 R H K łog g, and Z) by using the open Python tool iSpec We achieved an average accuracy of 2.3% for the limb-darkened angular diameters based on polychromatic observations. However, we observed that our SBCR relation does not follow the calibration of the SBC relations in Gaia found in the literature. Furthermore, we found that the łog g and Z parameters have no impact on this relationship. Given the characteristics of our sample of quiescent stars, it constitutes an ideal set of targets for conducting a new SBCR calibration within the framework of the PLATO space mission. In this context, we report a SBCR calibration with σ_ RMS = 0.012, 0.009, and 0.009 in the G, G_ BP , and G_RP Gaia bands, respectively. This work is part of a series of papers reporting the first results obtained using a polychromatic approach to measure angular diameters, employing a fully homogeneous methodology for determining the fundamental parameters of stars and measuring the limb-darkened angular diameters

The estimation of stellar angular diameters can be performed from the surface brightness - color relation (SBCR) and photometry. The SBCR have been considered by the PLATO space mission as an independent empirical alternative for estimating stellar radii of FGK stars. In this context, we have implemented an homogeneous approach not only for calibrating the SBCR for FGK-IV/V stars but, also for determining their fundamental parameters in order to place the stars reliably on the HR diagram and to study their impact on the SBCR. We have performed interferometric observations of 18 quiescent FGK-IV/V stars in the Gaia color range of 3.088 ≤ G ≤ 5.498. For the first time, we used 3 different interferometers operating in the R, H , and K bands to measure polychromatic limb-darkened angular diameters (LDAD). In parallel, by using public domain spectra we have estimated the stellar parameters (T_eff, log g and Z) by using the open python tool iSpec. We achieved an average accuracy of 2.3

Long baseline optical and infrared interferometric arrays achieve high angular resolution and enable detailed astrophysical measurements. Interferometers have enabled observations of stars at various stages of evolution, as well as studies of binary stars, circumstellar disks, and active galactic nuclei. The Center for High Angular Resolution Astronomy (CHARA) Array is a long-baseline interferometric array at the Mount Wilson Observatory, United States. At the core of CHARA operations are the delay lines, which equalize the optical path length for all telescopes as the Earth rotates and compensate for optical path variations induced by atmospheric turbulence. We report recent upgrades and performance of the CHARA Array optical delay lines for high-precision interferometric observations. The legacy system had been operational for over two decades, and it was increasingly difficult to acquire replacement parts. Beginning in mid-2021, the control system underwent a major upgrade, replacing the aging Versa Module Eurocard-based architecture with a modern hybrid field-programmable gate array and Linux-based system; this modernization continued through the end of 2024. We describe hardware/software changes, the servo architecture, and lab/on-sky performance. The upgraded system achieves residual delay line cart tracking errors of similar to 12 nm, the same level as the legacy system, and a control bandwidth of 100 to 130 Hz, allowing fringe tracking across the R-, H-, and K-bands. Initial commissioning revealed key issues such as metrology time-tick jitter and vibration-induced visibility loss, which were diagnosed and resolved. We note ongoing and future efforts to extend baselines up to 1 km and support advanced observing modes such as dual-field interferometry and nulling. This is a reference for current and future use of the CHARA Array and for next-generation instrument design.

ANDES,the high resolution spectrograph for the ELT, will work both in seeing limited mode and with Adaptive Optics (AO) correction. ANDES-SCAO is a single conjugated AO system working with natural guide stars, feeding the IFU coupled to the YJH spectrograph. The main science goal of the ANDES AO mode is the characterization of the exo-planet atmosphere in reflected light. Hence, the driving technical requirement for the AO system is the PSF contrast. The level of achieved contrast determines the number of exo-planets on which the instrument will be able to detect bio-signatures. The key challenge for the achievement of high contrast is the control of M4 petalling. Here, we present the current status of the ANDES-SCAO design, approaching the ANDES preliminary design review scheduled in fall 2024.

To leverage the angular resolution of interferometry at high contrast, one must employ specialized beam-combiners called interferometric nullers. Nullers discard part of the astrophysical information to optimize the recording of light present in the dark fringe of the central source. Asgard/NOTT will deploy a beam-combination scheme offering good instrumental noise rejection when phased appropriately, but for which information is degenerate on the outputs, prompting a dedicated tuning strategy using the science detector. The dispersive effect of water vapor can be corrected with prisms forming a variable thickness of glass. But observations in the L band suffer from an additional and important chromatic effect due to longitudinal atmospheric dispersion coming from a resonance of CO2 at 4.3 micron. To compensate for this effect efficiently, a novel type of compensation device will be deployed leveraging a gas cell of variable length at ambient pressure. After reviewing the impact of water vapor and CO2, we present the design of this atmospheric dispersion compensation device and describe a strategy to maintain this tuning on-sky.

Performances of an adaptive optics (AO) system are directly linked with the quality of its alignment. During the instrument calibration, having open loop fast tools with a large capture range are necessary to quickly assess the system misalignment and to drive it towards a state allowing to close the AO loop. During operation, complex systems are prone to misalignments (mechanical flexions, rotation of optical elements, etc.) that potentially degrade the AO performances, creating a need for a monitoring tool to tackle their driftage. In this work, we first present an improved perturbative method to quickly assess large lateral errors in open loop. It uses the spatial correlation of the measured interaction matrix of a limited number of 2D spatial modes with a synthetic model. Then, we introduce a novel solution to finely measure and correct these lateral errors via the closed loop telemetry. Non-perturbative, this method consequently does not impact the science output of the instrument. It is based on the temporal correlation of 2D spatial frequencies in the deformable mirror commands. It is model-free (no need of an interaction matrix model) and sparse in the Fourier space, making it fast and easily scalable to complex systems such as future extremely large telescopes. Finally, we present some results obtained on the development bench of the GRAVITY+ extreme AO system (Cartesian grid, 1432 actuators). In addition, we show with on-sky results gathered with CHARA and GRAVITY/CIAO that the method is adaptable to non-conventional AO geometries (hexagonal grids, 60 actuators).

We present in this proceeding the results of the test phase of the GRAVITY+ adaptive optics. This extreme AO will enable both high-dynamic range observations of faint companions (including exoplanets) thanks to a 40x40 sub-apertures wavefront control, and sensitive observations (including AGNs) thanks to the addition of a laser guide star to each UT of the VLT. This leap forward is made thanks to a mostly automated setup of the AO, including calibration of the NCPAs, that we tested in Europe on the UT+atmosphere simulator we built in Nice. We managed to reproduce in laboratory the expected performances of all the modes of the AO, including under non-optimal atmospheric or telescope alignment conditions, giving us the green light to proceed with the Assembly, Integration and Verification phase in Paranal.

SPICA (Stellar Parameters and Images with a Cophased Array) is a 6-telescope (6T) visible instrument for the CHARA Array (Center for High Angular Resolution in Astronomy) at Mount Wilson Observatory. It uses single mode fibers for feeding the interferometric spectrograph, which offers three different spectral resolutions: R=140, R=4000, and R=14000. CHARA/SPICA has been mainly designed for large programs (surveys) in the domain of stellar fundamental parameters but also permits fast imaging thanks to the 15 baselines and the large number of spectral channels (60 in low resolution mode). SPICA is made of the visible instrument SPICA-VIS and of a new H-band, 6T, ABCD combiner performing group delay and phase delay tracking. In this paper, we present the first light results of SPICA.

The Very Large Telescope Interferometer (VLTI) is a wonderful infrastructure for long-baseline interferometry. MATISSE, the Multi AperTure mid-Infrared SpectroScopic Experiment, installed at the VLTI focus, accesses high resolution imaging over a wide spectral domain of the mid-infrared. The instrument is a spectro-interferometric imager operating in the L, M, and N transmission windows and combining four optical beams from the VLTI's unit or auxiliary telescopes. We propose at the SPIE conference to advertise the use of the MATISSE instrument. We will illustrate the instrument capabilities through astrophysical results recently achieved (the focus on the astrophysical results is not reported in the article). We also show what are the expected future infrastructure optimizations and instrument adaptations (off-axis tracking, frame of GRAVITY+) that will permit to push the sensitivities and accuracies for the astrophysical programs in the context of the JWST.

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.

The Very Large Telescope Interferometer (VLTI) has been providing breakthrough images of the dust in the central parsecs of Active Galactic Nuclei (AGN), a key component of the AGN unification scheme and AGN host galaxy interaction. In single IR bands, the images can have multiple interpretations some of which could challenge the unification scheme. This is the case for the archetypal type 2 AGN of NGC1068. The ambiguity is reduced by multi-band temperature maps which are hindered by uncertainty in intra-band alignment. We create a chromatic model capable of simultaneously explaining the VLTI GRAVITY+MATISSE 2μm-13μm observations of the AGN in NGC1068. We use a simple disk and wind geometry populated with spherical black body emitters and dust obscuration to create a versatile multi-wavelength model for IR interferometric data of dusty objects. This simple geometry is capable of reproducing the K-N-band VLTI data, explains the complex single band images, and solves the alignment between bands. We find that the resulting geometry is consistent with previous studies. Compared to molecular gas emission, our model wind position angle (PA) of 22^3_2 is close to the mas scale outflowing CO(6-5) PA of  33 seen with the ALMA. The equivalent 90 offset model disk PA is also consistent with the CO(6-5) disk axis of 112 as well as the mas scale disk axis from CO(2-1), CO(3-2), and HCO^+(4-3) of 115±5. Furthermore, the resulting model visually resembles the equivalent achromatic image reconstructions. We conclude that the IR emitting structure surrounding the AGN can indeed be explained by the clumpy disk+wind iteration of the AGN unification scheme. Within the scheme, we find it is best explained as a type 2 and the obscuring dust chemistry is consistent with a mix of olivine silicates and 16±1

With a possible angular resolution down to 0.1-0.2 millisecond of arc using the 330 m baselines and the access to the 600-900 nm spectral domain, the CHARA Array is ideally configured for focusing on precise and accurate fundamental parameters of stars. CHARA/SPICA (Stellar Parameters and Images with a Cophased Array) aims at performing a large survey of stars all over the Hertzsprung-Russell diagram. This survey will also study the effects of the different kinds of variability and surface structure on the reliability of the extracted fundamental parameters. New surface-brightness-colour relations will be extracted from this survey, for general purposes on distance determination and the characterization of faint stars. SPICA is made of a visible 6T fibered instrument and of a near-infrared fringe sensor. In this paper, we detail the science program and the main characteristics of SPICA-VIS. We present finally the initial performance obtained during the commissioning.

We present the testbench aimed at integrating the GRAVITY+ adaptive optics GPAO. It consists of two independent elements, one reproducing the Coudé focus of the telescope, including the telescope deformable mirror mount (with its surface facing down), and one reproducing the Coudé room opto-mechanical environment, including a downwards-propagating beam, and the telescope mechanical interfaces in order to fit in the new GPAO wavefront sensor. We discuss in this paper the design of this bench and the solutions we adopted to keep the cost low, keep the design compact (allowing it to be fully contained in a 20 sqm clean room), and align the bench independently from the adaptive optics. We also discuss the features we have set in this bench.

In the widely accepted ‘unified model’ 1 solution of the classification puzzle of active galactic nuclei, the orientation of a dusty accretion torus around the central black hole dominates their appearance. In ‘type-1’ systems, the bright nucleus is visible at the centre of a face-on torus. In ‘type-2’ systems the thick, nearly edge-on torus hides the central engine. Later studies suggested evolutionary effects 2 and added dusty clumps and polar winds 3 but left the basic picture intact. However, recent high-resolution images 4 of the archetypal type-2 galaxy NGC 1068 5 , 6 , suggested a more radical revision. The images displayed a ring-like emission feature that was proposed to be hot dust surrounding the black hole at the radius where the radiation from the central engine evaporates the dust. That ring is too thin and too far tilted from edge-on to hide the central engine, and ad hoc foreground extinction is needed to explain the type-2 classification. These images quickly generated reinterpretations of the dichotomy between types 1 and 2 7 , 8 . Here we present new multi-band mid-infrared images of NGC 1068 that detail the dust temperature distribution and reaffirm the original model. Combined with radio data (J.F.G. and C.M.V.I., manuscript in preparation), our maps locate the central engine that is below the previously reported ring and obscured by a thick, nearly edge-on disk, as predicted by the unified model. We also identify emission from polar flows and absorbing dust that is mineralogically distinct from that towards the Milky Way centre.

The Very Large Telescope Interferometer (VLTI) is currently the best infrastructure for long-baseline interferometry in particular in terms of sensitivity and accessibility to the general user. MATISSE, installed at the VLTI focus since end of 2017, belongs to the second generation instruments. MATISSE, the Multi AperTure mid-Infrared SpectroScopic Experiment, for the first time accesses high resolution imaging over a wide spectral domain of the mid-infrared. The instrument is a spectro-interferometric imager in the atmospheric transmission windows called L, M, and N, from 2.8 to 13.0 microns, and combines four optical beams from the VLTI’s unit or auxiliary telescopes. The instrument utilises a multi-axial beam combination that delivers spectrally dispersed fringes. The signal provides the following quantities at several spectral resolutions: photometric flux, coherent flux, visibility, closure phase, wavelength differential visibility and phase, and aperture-synthesis imaging. MATISSE can operate as a stand alone instrument or with the GRA4MAT set-up employing the GRAVITY fringe tracking capabilities. The updated MATISSE performance are presented at the conference together with a selection of two front-line science topics explored since the start of the science operations in 2019. Finally we present the perspective and benefit of two technical improvements foreseen in the coming years: the MATISSE-Wide off-axis fringe tracking capability and new adaptive optics for the UTs in the context of the GRAVITY+ project.