Bright Star Subtraction Pipeline for LSST: Phase one report

TL;DR

This report details the development of a Bright Star Subtraction pipeline for LSST, which models and subtracts bright stars from astronomical images, addressing detector position effects and optimizing PSF modeling for improved data quality.

Contribution

The paper introduces a novel pipeline for modeling and subtracting bright stars in LSST data, including an algorithm to correct for detector position effects and guidance on optimal normalization annulus selection.

Findings

Correlation between PSF shape and detector position.

Pipeline successfully subtracts 100-700 bright stars per exposure.

Optimal annulus size is critical for accurate PSF modeling.

Abstract

We present the phase one report of the Bright Star Subtraction (BSS) pipeline for the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). This pipeline is designed to create an extended PSF model by utilizing observed stars, followed by subtracting this model from the bright stars present in LSST data. Running the pipeline on Hyper Suprime-Cam (HSC) data shows a correlation between the shape of the extended PSF model and the position of the detector within the camera's focal plane. Specifically, detectors positioned closer to the focal plane's edge exhibit reduced circular symmetry in the extended PSF model. To mitigate this effect, we present an algorithm that enables users to account for the location dependency of the model. Our analysis also indicates that the choice of normalization annulus is crucial for modeling the extended PSF. Smaller annuli can exclude stars due to overlap with saturated regions, while larger annuli may compromise data quality because of lower signal-to-noise ratios. This makes finding the optimal annulus size a challenging but essential task for the BSS pipeline. Applying the BSS pipeline to HSC exposures allows for the subtraction of, on average, 100 to 700 stars brighter than 12th magnitude measured in g-band across a full exposure, with a full HSC exposure comprising ~100 detectors.