The measurement of type Ia supernovae magnitudes provides cosmological distances, which can be used to constrain dark energy parameters. Large photometric surveys require a substantial improvement in the calibration precision of their photometry to reduce systematic uncertainties in cosmological constraints. The StarDICE experiment is designed to establish accurate broadband flux references for these surveys, aiming for sub-percent precision in magnitude measurements. This requires a precise measurement of the filter bandpasses of both the StarDICE and survey instruments with sub-nanometer accuracy. To that end, we have developed the Collimated Beam Projector (CBP), an optical device capable of calibrating the throughput of an astronomical telescope and of its filters. The CBP is built from a tunable laser source and a reversed telescope to emit a parallel monochromatic light beam that is continuously monitored in flux and wavelength. The CBP output light flux is measured using a large area photodiode, previously calibrated relative to a NIST photodiode. We derive the StarDICE telescope throughput and filter transmissions from the CBP measurements, anchoring it to the absolute calibration provided by the NIST. After analyzing the systematic uncertainties, we achieved sub-nanometer accuracy in determining filter central wavelengths, measured each filter transmission with a precision of 0.5% per 1nm bin, and detected out-of-band leakages at 0.01%. Furthermore, we have synthesized the equivalent transmission for full pupil illumination from four sample positions in the StarDICE telescope mirror, with an accuracy of approximately 0.2nm for central wavelengths and 7mmag for broadband fluxes. We demonstrated our ability to characterize a telescope throughput down to the mmag, and paved the way for future developments, such as a portable CBP version for in-situ transmission monitoring.

Context. The Hubble diagram of type-Ia supernovae (SNe-Ia) provides cosmological constraints on the nature of dark energy with an accuracy limited by the flux calibration of currently available spectrophotometric standards. This motivates new developments to improve the link between existing astrophysical flux standards and laboratory standards.Aims. The StarDICE experiment aims to establish a five-stage metrology chain from NIST photodiodes to stars, with a targeted accuracy of 1 mmag in griz colors. We present the first two stages, resulting in the calibration transfer from NIST photodiodes to a demonstration 150 mpixel CMOS sensor (Sony IMX411ALR as implemented in the QHY411M camera by QHYCCD). As a side-product, we provide full characterization of this camera, which we believe to be of potential interest in astronomical imaging and photometry and specifically discuss its use in the context of gravitational wave optical follow-up.Methods. A fully automated spectrophotometric bench was built to perform the calibration transfer. The sensor readout electronics was studied using thousands of flat-field images from which we derived stability, high-resolution photon transfer curves (PTC), and estimates of the individual pixel gain. The sensor quantum efficiency (QE) was then measured relatively to a NIST-calibrated photodiode, in a well-defined monochromatic light beam from 375 to 1078 nm. Last, flat-field scans at 16 different wavelengths were used to build maps of the sensor response, fully characterizing the sensor for absolute photometric measurements.Results. We demonstrated statistical uncertainty on QE below 0.001 e(-)/gamma between 387 nm and 950 nm, the range being limited by the sensitivity decline of the tested sensor in the infrared. Systematic uncertainties in the bench optics are controlled at the level of 1 x 10(-3) e(-)/gamma. Linearity issues are detected at the level of 5 x 10(-3) e(-)/gamma for the tested camera and require further developments to fully correct. Uncertainty in the overall normalization of the QE curve (without relevance for the cosmology, but relevant to evaluate the performance of the camera itself) is 1%. Regarding the camera we demonstrate stability in steady state conditions at the level of 32.5 ppm. Homogeneity in the response is below 1% RMS across the entire sensor area. Quantum efficiency stays above 50% in most of the visible range, peaking well above 80% between 440 nm and 570 nm. Differential nonlinearities at the level of 1% are detected. A simple two-parameter model is proposed to mitigate the effect and found to adequately correct the shape of the PTC on half the numerical scale. No significant deviations from integral linearity were detected in our limited test. Static and dynamical correlations between pixels are low, making the device likely suitable for galaxy shape measurements.

Cosmic explosions have emerged as a major field of astrophysics over the last years with our increasing capability to monitor large parts of the sky in different wavelengths and with different messengers (photons, neutrinos, and gravitational waves). In this context, gamma-ray bursts (GRBs) play a very specific role, as they are the most energetic explosions in the Universe. The forthcoming Sino-French SVOM mission will make a major contribution to this scientific domain by improving our understanding of the GRB phenomenon and by allowing their use to understand the infancy of the Universe. In order to fulfill all of its scientific objectives, SVOM will be complemented by a fast robotic 1.3 m telescope, COLIBRI, with multiband photometric capabilities (from visible to infrared). This telescope is being jointly developed by France and Mexico. The telescope and one of its instruments are currently being extensively tested at OHP in France and will be installed in Mexico in spring 2023.

The DESI Legacy Imaging Surveys are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing-Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image approximately 14,000 deg^2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12 and 22 micorons) observed by the Wide-field Infrared Survey Explorer (WISE) satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project.

DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. The DESI instrument is a robotically-actuated, fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm spectrographs with resolution R= λ/Δλ between 2000 and 5500, depending on wavelength. The DESI instrument will be used to conduct a five-year survey designed to cover 14,000 deg^2. This powerful instrument will be installed at prime focus on the 4-m Mayall telescope in Kitt Peak, Arizona, along with a new optical corrector, which will provide a three-degree diameter field of view. The DESI collaboration will also deliver a spectroscopic pipeline and data management system to reduce and archive all data for eventual public use.

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. To trace the underlying dark matter distribution, spectroscopic targets will be selected in four classes from imaging data. We will measure luminous red galaxies up to $z=1.0$. To probe the Universe out to even higher redshift, DESI will target bright [O II] emission line galaxies up to $z=1.7$. Quasars will be targeted both as direct tracers of the underlying dark matter distribution and, at higher redshifts ($ 2.1 < z < 3.5$), for the Ly-$\alpha$ forest absorption features in their spectra, which will be used to trace the distribution of neutral hydrogen. When moonlight prevents efficient observations of the faint targets of the baseline survey, DESI will conduct a magnitude-limited Bright Galaxy Survey comprising approximately 10 million galaxies with a median $z\approx 0.2$. In total, more than 30 million galaxy and quasar redshifts will be obtained to measure the BAO feature and determine the matter power spectrum, including redshift space distortions.

The Concordia Base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3- month long night during the Antarctic winter, favorable weather conditions, and low scintillation. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project which seeks to identify transiting planets and understand the limits of visible photometry from this site. ASTEP 400 is an optical 40cm telescope with a field of view of 1° x 1°. The expected photometric sensitivity is 1E-3, per hour for at least 1,000 stars. The optical design guarantees high homogeneity of the PSF sizes in the field of view. The use of carbon fibers in the telescope structure guarantees high stability. The focal optics and the detectors are enclosed in a thermally regulated box which withstands extremely low temperatures. The telescope designed to run at -80°C (-110°F) was set up at Dome C during the southern summer 2009- 2010. It began its nightly observations in March 2010.

We report the status of ELP-OA (Etoile Laser polychromatique pour l'Optique Adaptative), the full demonstrator which we are building at OHP 1.52m telescope. The goal is to open adaptive optics to the domain of visible wavelengths at large telescopes, which is almost not feasible today because of the tiny isoplanatic patch. ELP-OA relies on the 2-photon excitation of sodium in the mesosphere, through 589 and 569 nm transitions. We use 2 pulsed dye lasers (on loan from CEA) pumped with NdYAGs. The average power at the mesosphere will be 2 x 22W. The twin laser beams are projected to the mesosphere by a 3-aperture interferometer. The backscattered spots in NaI lines at 330, 569 and 589nm are oberved through an adaptive optics at the telescope coude focus, derived from the ONERA's BOA device. The differential tilt measurement channel is equipped with an EMCCD. We use a correlation algorithm to extract it. From our end to end model we expect tilt Strehl ratios of 35% at 550nm (see Meilard et al in this conference). First lasers launches are planned early 2010, with the full experiment running 2011.

We report the status of ELP-OA (Etoile Laser polychromatique pour l'Optique Adaptative), the full demonstrator which we are building at OHP 1.52m telescope. The goal is to open adaptive optics to the domain of visible wavelengths at large telescopes, which is almost not feasible today because of the tiny isoplanatic patch. ELP-OA relies on the 2-photon excitation of sodium in the mesosphere, through 589 and 569 nm transitions. We use 2 pulsed dye lasers (on loan from CEA) pumped with NdYAGs. The average power at the mesosphere will be 2 x 22W. The twin laser beams are projected to the mesosphere by a 3-aperture interferometer. The backscattered spots in NaI lines at 330, 569 and 589nm are oberved through an adaptive optics at the telescope coude focus, derived from the ONERA's BOA device. The differential tilt measurement channel is equipped with an EMCCD. We use a correlation algorithm to extract it. From our end to end model we expect tilt Strehl ratios of 35% at 550nm (see Meilard et al in this conference). First lasers launches are planned early 2010, with the full experiment running 2011.

The Polychromatic Laser Guide Star aims at providing for the tilt measurement from a LGS without any natural guide star. Thus it allows adaptive optics to provide us with a full sky coverage. This is critical in particular to extend adaptive optics to the visible range, where isoplanatism is so small that the probability is negligible to find a natural star to measure the tilt. We report new results obtained within the framework of the Polychromatic LGS programme ELP-OA. Natural stars have been used to mimic the PLGS, in order to check the feasibility of using the difference in the tilt at two wavelengths to derive the tilt itself. We report results from the ATTILA experiment obtained at the 1.52 m telescope at Observatoire de Haute-Provence. Tilts derived from the differential tilts are compared with direct tilt measurements. The accuracy of the measurements is currently ≈ 1.5 Airy disk rms at 550 nm. These results prove the feasibility of the Polychromatic Laser Guide Star programme ELP-OA. New algorithms based on inverse problems under development within our programme would lead to smaller error bars by 1 magnitude, as soon as they will run fast enough. We describe the ELP-OA demonstrator which we are setting up at the same telescope, with a special emphasis on the optimization of the excitation process, which definitely has to rely on the two-photon excitation of sodium atoms in the mesosphere. We will describe the implementation at the telescope, including the projector device, the focal instrumentation and the NdYAG pumped dye lasers.

Resume. The correction of the tilt for adaptive optics devices from the only laser guide star can be done with the polychromatic laser guide star. We report the progress of the first demonstrator of the implementation of this concept, at Observatoire de Haute-Provence. We review the last steps of the feasibility studies, the optimization of the laser parameters, and the studies of the implementation at the OHP 1.52m telescope, including the beam propagation to the lasers room to the mesosphere and the algorithms for tip-tilt measurements.