CANDLE: Calibration using an Artificial star with NIST-traceable Distribution of Luminous Energy

We describe the preliminary design of a precision artificial star, CANDLE, that provides calibrated light covering the spectral range 350 nm to 2500 nm to match that of surveys for dark energy studies with the Roman Space Telescope and Rubin Observatory. The absolute and spectral relative flux calibration uncertainty of CANDLE light projected to the observatory is estimated to be < 0.5 %. To enable cross-checks and mitigate systematic effects, the CANDLE consists of three complementary modes: (1) single mode fiber lasers providing calibrated flux at four laser wavelengths; (2) reflected sunlight from a convex mirror, providing a well-calibrated solar spectral energy distribution across the entire spectral range; (3) programmable spectrum (PS) mode that mimics celestial source spectral energy distributions. In the PS mode, the CANDLE can produce monochromatic spectra that can be tuned across the spectral range to measure the spectral response of observatory instruments. Alternatively, the CANDLE PS mode can mimic a calibration star or supernova spectrum, for example, to act as an independently calibrated comparison target for simultaneous observations made of real sources in the same field to check for systematic errors.

CANDLE is being designed to fit into a volume <24U (1U=1000 cm³) for a future spaceflight mission. By calibrating the output beam profiles, rigorously demonstrating the flux uncertainty budget, and establishing performance parameters for different orbits, we aim to establish the path toward a flight-ready payload that enhances the science from future astrophysics missions.