arXiv subjects

Thibault Guillemin

Publications and source records attributed to Thibault Guillemin.

3 recordsLinked to original sources

arXiv2026

The On-Sky Performance of the LSST Camera CCD Array

The focal plane of the LSST Camera contains 189 individual science CCDs, arranged into 21 raft tower modules, along with 4 wavefront and 8 guider CCDs located in 4 additional corner RTMs. Altogether, the LSST Camera CCDs compose the largest focal plane ever constructed. The LSST Camera is the primary instrument of Rubin Observatory, which will begin the Legacy Survey of Space and Time in 2026. In this paper, we describe the on-sky performance of the LSST Camera CCDs, from receipt at NSF/DOE Vera C. Rubin Observatory in May 2024 to on-sky observations during the first year of operations. We discuss the process to establish functionality of several CCDs which were affected by an electrical short and faulty analog-digital converter, optimizations of readout timing in response to changes in the survey strategy, and implementation of enhanced focal plane safety measures through an active clearing mechanism on the CCDs. Finally, we discuss sensor features observed on-sky, and global performance during the first year of operations. The operations to date of the LSST Camera CCDs have demonstrated the capability of performing a wide, fast, and deep optical imaging survey of the entire southern sky at the Rubin Observatory.

astro-ph.IM↗

arXiv2026

Early Telescope Throughput Results from the Collimated Beam Projector at the Vera C. Rubin Observatory

The Vera C. Rubin Observatory LSST requires precise photometric calibration to meet its science goals, particularly for cosmological analyses based on Type Ia supernovae. The Collimated Beam Projector (CBP) has been developed to support this effort by projecting monochromatic point sources of known wavelength and flux directly into the telescope aperture, enabling direct in situ measurements of the full system throughput. We present initial results demonstrating the CBP capability to characterize the instrumental response of the Rubin Telescope and to measure the transmission profiles of LSSTCam broadband filters. In particular, the CBP enables spatially resolved mapping of filter bandpass edge shifts across the focal plane, which can vary by several nanometers as a function of the ray angle of incidence. These early results establish the CBP as a powerful photometric calibration tool and lay the groundwork for continuous throughput monitoring throughout LSST operations.

astro-ph.IM↗

arXiv2025

Weak lensing mass-richness relation of redMaPPer clusters in the LSST DESC DC2 simulations

Cluster scaling relations are key ingredients in cluster abundance-based cosmological studies. In optical cluster cosmology, where clusters are detected through their richness, cluster-weak gravitational lensing has proven to be a powerful tool to constrain the cluster mass-richness relation. This work is conducted as part of the Dark Energy Science Collaboration (DESC), which aims to analyze the Legacy Survey of Space and Time (LSST) of the Vera C. Rubin Observatory, starting in 2026. Weak lensing-inferred cluster properties, such as mass, suffer from several sources of bias. We constrain the mass-richness relation of 3,600 clusters detected by the redMaPPer algorithm in the cosmoDC2 extra-galactic mock catalog of the LSST DESC DC2 simulation, covering 440 square degrees, using number count measurements and either stacked weak lensing profiles or mean cluster masses in intervals of richness ($20 < λ< 200$) and redshift ($0.2 < z < 1$). We find that, for an LSST-like source galaxy density, our constraints are robust to changes in the concentration-mass relation and dark matter density profile modeling choices, when source redshifts and shapes are perfectly known. We find that photometric redshift uncertainties can introduce bias at the 1$σ$ level, which can be mitigated by an overall correction factor, fitted jointly with the scaling parameters. We find that including positive shear-richness covariance in the fit shifts the results by up to 0.5$σ$. Our constraints also compare fairly to a fiducial mass-richness relation, obtained from matching cosmoDC2 halo masses to redMaPPer-detected cluster richnesses.

astro-ph.CO↗