StarDICE: Calibration at the per mil level of a new generation of telescopes for dark energy measurement

First, this thesis introduces modern cosmology, from the Einstein equation to the first measurements of the acceleration of the Universe's expansion. This acceleration, attributed to 'dark energy', can be measured using various probes. This section presents the different cosmological probes, including type Ia supernovae (SNe Ia), the Cosmic Microwave Background (CMB), and Baryon Acoustic Oscillations (BAO), and discusses methods for constraining dark energy equation of state parameters. In the second section, I detail the mechanisms behind SNe Ia and their properties. The light curves of SNe Ia, which represent their luminosity flux over time, can be standardized using various observational parameters. By measuring their distance against redshift, SNe Ia serve as standard candles, enabling the measurement of the history of the Universe's expansion. The third section covers the observational tools used to measure SNe Ia properties, explaining the functioning of telescopes and CCD cameras that collect photons. I review past, present, and future SNe Ia surveys, highlighting the improvements over time. The fourth section addresses the challenges of photometric calibration of SNe Ia surveys and its impact on cosmological measurements. I emphasize the importance of achieving photometric calibration below the per mil level, which is crucial for attaining a new level of precision in cosmology. I then introduce the StarDICE experiment, which aims to refine the CALSPEC calibration to the per mil level by creating an artificial star with flux calibrated in the laboratory using a NIST photodiode. The StarDICE optical instrument is a Newtonian telescope with a 40 cm primary mirror, a focal length of 1.60 m, and a 1 MPixel CCD camera. We calibrated its throughput and filter transmissions using a Collimated Beam Projector (CBP). The CBP is equipped with a monochromatic light source and an optical device designed to measure telescope throughputs. Sections five and six focus on the StarDICE instrumental calibration, demonstrating how we can achieve sub-percent calibration with accurate wavelength resolution of a few Angstroms.The StarDICE telescope, currently operating at l'Observatoire de Haute-Provence in France, is collecting images with its 'ugrizy' filters and its diffraction grating for acquiring slitless spectrophotometric data. The Spectractor python library is used to extract spectra dispersed on the focal plane and perform spectrophotometry. We track the target throughout the night to perform an air mass regression, distinguishing the atmospheric transmission contribution from the star flux. The survey is also coupled with an infrared camera that monitors gray extinction due to clouds. The survey spans several tens of nights, with approximately 10,000 observations each night. Sections seven and eight present the photometric analysis conducted on the 'ugrizy' images and the spectrophotometric analysis on the grating images. The spectrophotometric is aiming at measuring the atmosphere contribution in our data analysis, while the photometric analysis aim at refining the CALSPEC calibration. To summarize, these measurements allow us to simulate the expected flux for a star based on the CALSPEC spectrum, atmospheric transmission, and the telescope's throughput at a given filter, calibrated with the CBP and the artificial star. By comparing the observed data to the theoretical CALSPEC spectrum, we can measure the deviations, and refine the calibration. The millimagnitude-level calibration of each step in the experiment enables us to achieve sub-percent photometric calibration of the CALSPEC spectra, which is crucial for reaching new levels of precision in cosmology. (author)